Carbon/High-Entropy Alloy Nanocomposites: Synergistic Innovations and Breakthrough Challenges for Electrochemical Energy Storage

Abstract

Against the backdrop of accelerating global energy transition, developing high-performance energy-storage systems is crucial for achieving carbon neutrality. Traditional electrode materials are limited by a single densification storage mechanism and low conductivity, struggling to meet demands for high energy/power density and a long cycle life. Carbon/high-entropy alloy nanocomposites provide an innovative solution through multi-component synergistic effects and cross-scale structural design: the “cocktail effect” of high-entropy alloys confers excellent redox activity and structural stability, while the three-dimensional conductive network of the carbon skeleton enhances charge transfer efficiency. Together, they achieve synergistic enhancement via interfacial electron coupling, stress buffering, and dual storage mechanisms. This review systematically analyzes the charge storage/attenuation mechanisms and performance advantages of this composite material in diverse energy-storage devices (lithium-ion batteries, lithium-sulfur batteries, etc.), evaluates the characteristics and limitations of preparation techniques such as mechanical alloying and chemical vapor deposition, identifies five major challenges (including complex and costly synthesis, ambiguous interfacial interaction mechanisms, lagging theoretical research, performance-cost trade-offs, and slow industrialization processes), and prospectively proposes eight research directions (including multi-scale structural regulation and sustainable preparation technologies, etc.). Through interdisciplinary perspectives, this review aims to provide a theoretical foundation for deepening the understanding of carbon/high-entropy alloy composite energy-storage mechanisms and guiding industrial applications, thereby advancing breakthroughs in electrochemical energy-storage technology under the energy transition.

1. Introduction

Since the 21st century, the global energy structure has been undergoing a profound transformation from fossil fuels to renewable energy sources (such as solar and wind power) [1]. Against this backdrop, electrochemical energy storage (EES) systems, by virtue of their high energy conversion efficiency, flexible deployment characteristics, and rapid response capabilities, have emerged as a core enabling technology for building new power systems [2,3]. Energy-storage devices such as lithium-ion batteries (LIBs), sodium-ion batteries (SIBs), supercapacitors (SCs), and sodium/potassium-ion batteries (SIBs/PIBs) play indispensable roles in fields including electric vehicles, smart grids, and portable electronics [4,5,6,7,8,9]. However, existing energy-storage technologies still face critical bottlenecks, such as relatively low energy density (LIBs typically below 300 Wh/kg), insufficient cycle life (SIBs < 2000 cycles), and safety hazards (e.g., lithium dendrite growth). These limitations hinder their ability to meet the demands of emerging fields like 5G communications and aerospace for energy storage devices operating under extreme conditions [10,11,12]. Consequently, developing electrode materials with high capacity, long cycle stability, and fast kinetics has become a major research focus in the EES field.

Electrode materials play a decisive, core role in the performance of energy-storage devices. Taking LIBs as an example, their commercialization began in 1991 when Sony Corporation adopted a system with graphite anodes and lithium cobalt oxide cathodes. After over 30 years of development, conventional materials are gradually approaching their theoretical limits: the specific capacity of graphite anodes is only 372 mAh/g, while lithium cobalt oxide faces challenges due to the scarcity of cobalt resources (global reserves ~7.1 million tons) and structural instability (layered structure prone to collapse under high voltage), making it difficult to meet the demands for next-generation high energy density [13,14,15]. Similarly, Prussian blue analogue cathodes for SIBs are limited by side reactions caused by crystalline water, and the energy density enhancement of activated carbon electrodes in SCs is constrained by low specific surface area utilization (<30%) [16,17]. More critically, electrode materials suffer from issues like volume expansion during charge/discharge (silicon anodes exhibit up to 300% expansion), active material dissolution (e.g., polysulfide shuttling in lithium–sulfur batteries), and interfacial side reactions. These lead to accelerated capacity decay and an increased risk of thermal runaway [18,19,20]. Although some researchers have achieved effective improvements in battery performance by designing intermediate layers that can prevent polysulfide dissolution and accelerate redox reaction kinetics, the root causes of these defects lie in the single-component nature, rigid electronic structure, and uncontrollable microstructure of traditional material systems, which struggle to simultaneously meet the multiple requirements of high conductivity, strong mechanical stability, and efficient ion transport [21,22].

The concept of a high-entropy alloy (HEA) was first proposed by Yeh et al. in 2004 [23,24]. They are defined as single-phase solid solutions formed by five or more principal elements (each with a molar fraction between 5% and 35%) [25,26]. The composition selection of the HEA should follow three principles: prioritizing thermodynamic stability, ensuring kinetic and structural compatibility, and implementing function-oriented collaborative design [21]. Firstly, the high-entropy effect (with at least five principal elements and a mixing entropy > 1.5 R) must be satisfied to suppress intermetallic compounds and promote the formation of solid solutions [22,27,28]. Meanwhile, the mixing enthalpy (ΔHmix < 15 kJ/mol) needs to be controlled to avoid segregation or precipitation of ordered phases; the competitive relationship between ΔHmix and ΔSmix determines phase stability. Secondly, the difference in atomic radii among elements (δ < 6.5%) is required to alleviate lattice distortion. Refractory metals with similar diffusion behaviors should be selected to slow down segregation [23,29,30]. Finally, 3D transition metals should be optimally chosen in line with application requirements to regulate catalytic performance, while refractory elements should be prioritized to enhance high-temperature oxidation resistance [31,32]. This design paradigm breaks from the traditional alloy approach dominated by 1–2 elements, leveraging the high configurational entropy effect (ΔSconfig ≥ 1.5 R) of multiple components to suppress element segregation and phase transformations, thereby endowing the materials with four unique advantages:

• Structural Stability: The high-entropy effect lowers the Gibbs free energy, enabling the alloy to maintain a single-phase structure under high-temperature, corrosive, or irradiation environments [32,33]. For instance, refractory HEA like Nb₂₅Mo₂₅Ta₂₅W₂₅ and V₂₀Nb₂₀Mo₂₀Ta₂₀W₂₀ remain stable and disordered, retaining a single-phase body-centered cubic structure without superlattice reflections even after exposure to 1400 °C [34].
• Tunable Mechanical Properties: By adjusting element types and ratios, the synergistic optimization of hardness and ductility can be achieved, surpassing traditional stainless steels and nickel-based alloys [34,35].
• Enhanced Catalytic Activity: Multi-element synergy tunes the d-band center position, optimizing the adsorption free energy of reaction intermediates. For example, the design of PtFeCoNiCu high-entropy alloys adheres to three core principles: atomic size compatibility (radius 1.24–1.39 Å), high mixing entropy (1.576 R), and electronic synergistic effects [36,37]. The comparable atomic sizes facilitate the formation of face-centered cubic (fcc) solid solutions, while the high mixing entropy suppresses elemental segregation through positive dissolution energies confirmed based on DFT calculations, thereby enhancing structural stability. The electronic effects manifest as follows: electronegativity differences induce electron transfer, resulting in a negative shift of 0.3 eV in Pt 4f binding energy and a downward shift of 0.36 eV in the d-band center, which optimizes the -OOH adsorption energy (ΔG = 0.369–0.428 eV). Specifically, Fe/Co/Ni synergistically activates the O-O bond with low activation barriers (0.291–0.326 eV), while Cu modulates electron density to prevent overoxidation. This multi-active-site synergistic mechanism endows the material with exceptional ORR performance, achieving a mass activity of 1.738 A/mg Pt (surpassing commercial Pt/C by 15.8 times) and unprecedented stability with only 3 mV decay after 10,000 cycles.
• Improved Ion Storage Capacity: Some HEAs possess open crystal structures, exhibiting lithium-ion diffusion coefficients significantly superior to graphite [38].

These properties have propelled HEAs to prominence in fields like electrocatalysis, battery anodes, and electromagnetic shielding [39]. However, HEA nanoparticles are prone to agglomeration due to high surface energy (especially under volume changes during cycling), and their intrinsic conductivity remains lower than carbon-based materials, limiting their application under high-current conditions [40].

Carbon materials, owing to their rich allotropes (graphite, diamond, graphene, etc.) and tunable microstructures, consistently occupy a central position in EES research [41]. Taking graphene as an example, its theoretical specific surface area is as high as 2630 m²/g, electron mobility exceeds 200,000 cm²/(V·s), and chemical modification can introduce functional groups (-OH, -COOH, etc.) to enhance interfacial reactivity [42]. The core functionalities of carbon materials can be summarized into four aspects:

• Conductive Network Construction: Three-dimensional conductive frameworks formed by carbon nanotubes (CNTs) or reduced graphene oxide can reduce overall electrode resistance below 10 Ω/sq [43].
• Mechanical Stress Buffering: Carbon coatings (e.g., amorphous carbon) absorb volume changes of active materials through elastic deformation, enabling silicon anodes to achieve double the capacity after 800 cycles [44].
• Multi-scale Mass Transport Optimization: Hierarchically porous carbon (micro-meso-macro pores) provides rapid ion transport channels, allowing SCs to achieve power densities exceeding 512 kW/kg [45].
• Interfacial Chemistry Regulation: Heteroatom doping (N, S, P) alters the electron distribution of the carbon skeleton, enhancing the chemical anchoring of polysulfides (capacity decay rate < 0.032% per cycle over 500 cycles in Li-S batteries) [46].

However, the energy storage capacity of single-component carbon materials is constrained by the electric double-layer mechanism or lithium intercalation chemistry (graphite), making it difficult to surpass theoretical ceilings [17]. Therefore, compositing carbon materials with high-capacity active materials has become an essential strategy for balancing energy density and cycle stability.

The integration of carbon materials (graphene, CNTs, porous carbon) with HEA to form composites demonstrates core advantages in the EES field, primarily through the synergistic enhancement of conductivity and structural stability [47]. Carbon materials (especially graphene and CNTs) provide exceptional intrinsic conductivity and mechanical flexibility, while porous carbon contributes a high specific surface area and ion transport channels, collectively establishing an efficient 3D electron conduction network and skeleton [48,49]. Although HEAs possess relatively weaker conductivity, their unique solid–solution structure grants them excellent structural stability and resistance to pulverization, particularly during the volume changes inherent to repeated charge/discharge cycles [50,51]. The composite achieves crucial complementarity: the carbon network significantly improves the electron transport efficiency of HEAs and buffers volume change stresses, inhibiting particle fragmentation and agglomeration to maintain electrode integrity; simultaneously, the stability of the HEA protects the carbon structure, enhancing its long-term cycling durability [52].

Furthermore, this composite significantly enhances the utilization efficiency of active materials and reaction kinetics. The high specific surface area and pore structure of carbon materials provide an ideal dispersion matrix for HEA nanoparticles, effectively preventing agglomeration and fully exposing HEA active sites [53]. HEA, leveraging their multi-principal element nature which induces the “cocktail effect” and severe lattice distortion, potentially generate more highly active catalytic sites (crucial for reactions like sulfur conversion in Li-S batteries), optimize the adsorption energy for reaction intermediates (e.g., polysulfides), and provide richer redox reactions (pseudocapacitive behavior) [54]. The synergistic interplay ensures that the carbon carrier maximizes the exposure of HEA active sites and enables rapid ion/electron contact; meanwhile, the unique electronic structure and catalytic activity of HEA significantly accelerate interfacial reaction rates (e.g., ion insertion/extraction, polysulfide conversion, Faradaic reactions), thereby enhancing rate capability and reversible capacity [55].

Moreover, the composite offers targeted solutions and enables multifunctional integration:

• In Li-S batteries, carbon materials (especially porous carbon) provide physical confinement and some chemical adsorption to capture polysulfides, while HEAs exert strong chemical adsorption and efficient catalytic action to accelerate polysulfide conversion. This synergy forms a “physical confinement + chemical adsorption + efficient catalysis” triple mechanism, effectively suppressing the shuttle effect [56].
• In SIBs, the composite leverages the sodium-storage capacity and buffering effect of carbon (e.g., hard carbon) combined with the potentially suitable open structure of HEAs for Na⁺ storage, jointly improving rate performance and cycle stability [57].

Additionally, the diversity of carbon material dimensions, the flexibility to tune HEA components for precise performance control, and the controllability of composite structures (e.g., core-shell, porous networks) provide a vast scope for optimizing the performance of various energy storage devices.

This review systematically summarizes the recent progress in carbon/HEA nanocomposites for EES in Figure 1. Firstly, the intrinsic properties of HEAs and carbon materials, along with their synergistic mechanisms, are thoroughly analyzed. Secondly, material preparation strategies and structure control methods are summarized. Thirdly, their performance breakthroughs in LIBs, SIBs, SCs, and SIBs/PIBs are critically reviewed. Finally, technical bottlenecks for scalable application and future research directions are explored. Through an interdisciplinary perspective (encompassing materials science, electrochemistry, computational science, etc.), this review aims to provide theoretical guidance and a technical roadmap for developing next-generation high-performance energy storage devices.

2. Synergistic Mechanisms of Carbon/HEA Nanocomposites

Carbon/HEA nanocomposites significantly enhance the performance of EES devices through multiple synergistic mechanisms. The core mechanisms include the following: interfacial electronic structure reconstruction (enhancing conductivity and catalytic activity), nano-confinement and steric hindrance effects (suppressing particle growth/agglomeration, anchoring active materials, improving structural stability), bicontinuous network and biomimetic channel design (promoting uniform ion/electron transport), and strain-adaptive characteristics (alleviating cycling stress) [58]. These mechanisms work synergistically to optimize reaction kinetics, interfacial stability, and electrode structural integrity, thereby achieving high specific capacity, excellent rate capability, a long cycle life, and high Coulombic efficiency.

2.1. Interfacial Electronic Reconstruction and Band Structure Modulation Mechanism

Carbon/HEA nanocomposites enable interfacial charge reconstruction and band structure modulation through electronic structure coupling [59]. At the interface between the carbon matrix (e.g., graphene, CNTs) and HEA nanoparticles within the composite, unique electronic structure coupling occurs. This coupling primarily functions via the following mechanisms: the high conductivity and electron-rich nature of carbon materials combine with the multi-element synergistic effects of HEAs, leading to charge transfer and redistribution (charge reconstruction) at the interface, thereby optimizing the electronic density of states at active sites. Simultaneously, band alignment between the two components modulates the overall band structure of the composite, for instance, by forming metal-semiconductor heterojunctions or adjusting the Fermi level position, thus enhancing carrier separation efficiency or catalytic activity. This electronic-level synergy provides new insights for designing high-performance electrocatalysts, photocatalysts, and energy-storage materials. The interfacial electronic coupling between carbon materials and HEA extends beyond simple charge transfer; it achieves the synergistic optimization of catalytic activity and ion transport through atomic-level hybrid orbital reconstruction [38,58]. The locally distorted lattice induced by the high-entropy effect on the HEA surface can form hybrid sp²-d orbitals with the π-electron cloud of graphene, significantly increasing the density of states near the Fermi level [38,60].

For example, HEA nucleates at defect sites of activated carbonized wood (ACW) while catalyzing the deposition of adjacent carbon atoms to form a few-layer graphitic carbon shell. This physical encapsulation effectively isolates the HEAs from electrolyte corrosion and mitigates the nanoparticle detachment caused by bubble impact. PtNiCoFeCu@ACW exhibits a high electronic density of states near the Fermi level, enabling superior electron transport capability. The d-orbitals of Ni, Co, and Fe dominate intermediate adsorption near the Femi level, while Pt and Cu provide an electron-rich environment, synergistically accelerating charge transfer. The self-encapsulated structure, high-entropy synergy, and interfacial stability collectively enable highly efficient and durable HER performance (no degradation observed during a 500 h stability test) [61]. HEA nanoparticles are uniformly embedded onto the rGO surface, forming tight interfacial bonding with stable M-C bonds via defect sites. The multi-metallic synergy within the HEAs potentially optimizes the electronic structure of the M-C bonds, enhancing interfacial stability. Consequently, the HEA/rGO interface exhibits high reversibility during charge/discharge, suppressing side reactions and structural degradation. The strong chemical adsorption and catalytic conversion of lithium polysulfides (LiPSs) by HEA nanoparticles effectively inhibit the LiPS shuttle effect. An HEA/rGO@PP battery maintains a Coulombic efficiency close to 100% after 200 cycles, with the shuttle effect significantly suppressed [56].

2.2. Nano-Confinement and Steric Hindrance Stabilization Mechanism

The nanoscale confinement effect in carbon/high-entropy alloy (HEA) nanocomposites refers to the physical spatial constraints imposed by the carbon matrix (e.g., graphene or carbon nanotubes) on HEA components at the nanoscale [58]. This effect enhances material performance through two mechanisms: first, kinetic stability enhancement—the nanoscale spatial confinement mediated by the carbon matrix significantly suppresses the atomic diffusion and lattice migration of HEA components. Under high temperatures or stress conditions, this effectively delays phase separation and grain coarsening, maintaining structural integrity under thermodynamic metastability over extended periods. Second, electronic structure modulation—the confined environment of the carbon matrix tunes the electronic states of HEA components (e.g., curvature-induced electron density redistribution in carbon nanotubes), optimizing the intrinsic reactivity of catalytic active sites. The steric hindrance effect originates from the geometric arrangement of surface atoms/groups of HEA components, functioning through two mechanisms: first, selective exposure of active sites—the steric hindrance from specific HEA surface configurations (e.g., step edges, kink sites) precisely controls reactant molecule access to active sites, suppressing side reactions. Second, volume expansion suppression—during charge–discharge cycles, the rigid structure of HEA components resists lattice distortion via atomic-scale steric hindrance, mitigating powdering caused by volumetric changes. The synergistic interaction between nanoscale confinement and steric hindrance effects collectively enhances the catalytic activity and energy-storage stability of the composite material [62].

This enhancement of kinetic stability and optimization of steric hindrance through nano-confinement provides an important theoretical basis and technical pathway for developing novel multifunctional composites with both high stability and high activity, showing broad application prospects in frontier fields like energy storage and catalytic conversion. For example, a multi-layer graphene shell (~3–5 layers) suppresses HEA nanoparticle growth (average size < 5 nm) and enhances kinetic stability via the confinement effect, enabling the material to maintain structural stability even at 800 °C. A 3D porous laser-induced graphene (LIG) substrate restricts nanoparticle migration through steric hindrance, achieving uniform HEA NP distribution (density > 10⁵ particles/μm²). The HEA NPs/LIG electrode exhibits low overpotential (268 mV@10 mA/cm²) and high stability (>100 h), attributed to the graphene shell preventing active component detachment (only a 0.8 nm particle size increase after cycling) and the porous structure facilitating mass transport (porosity > 80%) [63]. HEA nanocrystallites (40–60 nm) uniformly embedded in a nitrogen-doped carbon (NC) matrix form nano-confined spaces that suppress grain aggregation and provide abundant active sites. The 3D porous structure of the NC matrix (specific surface area 198.1 m²/g) anchors polysulfides through dual mechanisms: physical confinement and chemical adsorption (via nitrogen-doped defect sites). HEAs and NC synergistically construct steric hindrance, limiting polysulfide diffusion paths. The highly conductive NC matrix accelerates electron transport, while HEA catalyzes polysulfide conversion, achieving a sulfur utilization of 89.4% (1079.5 mAh/g) at 0.1 C. The 3D porous structure promotes Li⁺ diffusion (validated by GITT showing increased diffusion coefficient), delivering 440.5 mAh/g even at 5 C. The confinement effect and chemical adsorption synergistically suppress the shuttle effect, resulting in a 99.0% capacity retention after 100 cycles. Thus, nano-confinement optimizes the reaction kinetics, steric hindrance inhibits side reactions, and nitrogen doping enhances interfacial stability, ultimately achieving a high specific capacity, long cycle life, and excellent rate performance [64].

2.3. Multiscale Structure Synergy and Strain-Adaptive Mechanism

Carbon/HEA nanocomposites exhibit multiscale structure synergy through bicontinuous networks and biomimetic transport channels. Within these composites, the bicontinuous network structure manifests as a 3D interpenetrating framework of the carbon matrix (e.g., 3D porous carbon or graphene aerogel) and HEA nanoparticles. This structure constructs efficient mass/charge transport channels via biomimetic design (e.g., hierarchical channels resembling plant vascular bundles) [65]. The continuous conductive skeleton of the carbon network ensures rapid electron conduction, while the continuous active interface of the HEA network promotes ion/molecule transport. In electrochemical systems, pore structures across different scales play critical and complementary roles: micropores (<2 nm), with sizes comparable to electrolyte ion diameters, provide high-density charge storage sites. However, single-phase microporous systems inherently increase ion transport resistance due to narrow channels, limiting rate performance. At this stage, mesopores (2–50 nm) act as “ion highways” to accelerate ion diffusion toward microporous regions, shortening transport pathways. Experimental evidence confirms that materials with a high mesopore content maintain superior capacitance retention at high current densities. Moreover, mesopore wall structures reduce ion migration energy barriers, synergistically enhancing kinetics alongside micropores. Macropores (>50 nm) function as macroscopic buffers and guiding channels. As “ion reservoirs,” they shorten diffusion distances to active regions (mesopores/micropores), particularly preventing local concentration polarization in thick electrodes. In reactions involving gaseous products, graded macroporous structures (e.g., 200–300 nm) facilitate directional bubble release, avoiding active site blockage. Ultimately, macropores, mesopores, and micropores form an efficient three-tier synergistic mechanism: macropores buffer ions → mesopores enable rapid transport → micropores store charges [66]. This structural synergy endows the material with both high activity and high kinetic performance in applications like electrocatalysis and battery electrodes.

For example, CuInNiSnCd HEA nanoparticles (HEA-NPs) are uniformly loaded onto a 3D carbon fiber (CF) framework, forming a bicontinuous network structure. This structure combines a high specific surface area with low local current density, promoting uniform lithium deposition. The lithiophilic nature of HEA-NPs reduces the Li nucleation barrier, and biomimetic transport channels accelerate ion transport. This multiscale synergy significantly enhances battery performance, enabling stable cycling for over 3000 h at 10 mA cm⁻²/10 mAh cm⁻². A full cell exhibits 93.3% capacity retention after 160 cycles at 1 C, with Coulombic efficiency reaching 99.2% [67]. Combining strain-adaptive characteristics and a potential auxetic-like (negative Poisson’s ratio) effect, HEAs/graphite composites (HEAs/C) significantly optimize lithium-ion battery electrode performance. The strain-adaptive property allows the material to self-adjust stress during charge/discharge, maintaining structural stability; the auxetic effect promotes isotropic expansion, suppressing volumetric deformation. After 1000 cycles, the electrode thickness of HEAs/C increased from 14.78 μm to 20.25 μm, yet it still delivered a discharge specific capacity of 1196.5 mAh g⁻¹ at 0.5 A g⁻¹ with nearly 100% Coulombic efficiency. Compared to pure HEA electrodes, HEAs/C exhibit significantly enhanced cycling stability and drastically reduced capacity decay. The synergistic effect of dispersed HEA multi-components and the graphite buffer alleviates volume expansion and promotes electron transport, reducing the electrode volume change rate by 84% (37% vs. 235%) and extending the cycle life [68].

3. Preparation Methods

In recent years, the nanoscale composite technology integrating carbon materials (graphene, CNTs, porous carbon, etc.) with HEAs has advanced rapidly, focusing on interface regulation and multiscale structural design. Preparation techniques have expanded from traditional mechanical alloying and chemical vapor deposition (CVD) to sol-gel methods, electrospinning, 3D printing, and other additive manufacturing technologies, and has different advantages and disadvantages in

Table 1. Comparative Analysis of Preparation Technologies.

Technology	Advantages	Disadvantages	Application Scenarios
Mechanical Alloying	Low cost, easy to scale up	Easy to introduce impurities, uneven particle size	Bulk materials, energy storage electrodes
CVD	Strong interface bonding, controllable structure	Expensive equipment, high energy consumption at a high temperature	Thin films, catalytic materials
Sol-Gel	Porous structure, high specific surface area	Calcination shrinkage, low mechanical strength	Porous electrodes, catalyst carriers
Electrospinning	Flexible fibers, high specific surface area	Low fiber strength, difficult mass production	Flexible devices, sensors
3D Printing	Customized complex structures, high precision	Limited material selection, complex post-processing	Bionic structures, functional devices

. Concurrently, Atomic Layer Deposition (ALD) is emerging due to its advantages in atomic-level precision and biomimetic structures. Current research hotspots include low-temperature/green processes (e.g., plasma-assisted CVD, bio-templated low-temperature synthesis), heterointerface optimization (enhancing interfacial bonding strength via ALD or gradient ball milling), and function-oriented design (e.g., 3D printed customized porous electrodes, electrospun flexible devices).

3.1. Mechanical Alloying

Mechanical alloying combined with Spark Plasma Sintering, Hot Pressing (HP), or Hot Isostatic Pressing is a mainstream process enabling the uniform dispersion of carbon materials and strong interfacial bonding. This primarily involves the mechanical mixing of carbon materials and HEA metal powders via high-energy ball milling, achieving atomic-level compounding through repeated collisions [69,70]. Strengthening mechanisms include load transfer, grain refinement, dislocation pinning, and interfacial reactions (e.g., carbide formation) [71]. Carbon materials significantly enhance the strength, hardness, and wear resistance of HEAs, while some systems can retain good ductility [72]. Key parameters include the milling time (10–50 h), rotation speed (200–500 rpm), and atmosphere control (Ar/N₂). Liu et al. fabricated graphene nanoplatelet-reinforced layered CoCrFeNiMn HEA matrix composites (GNPs/CoCrFeNiMn HEAs) via mechanical ball milling and flake powder metallurgy, followed by vacuum hot-press sintering, forming a unique nacre-like structure in Figure 2. The microstructure comprised a FCC matrix phase and Cr₂₃C₆ and CrMn₁.₅O₄ precipitate phases, along with numerous dislocations and twins. Isothermal oxidation testing at 1000 °C for 100 h revealed that the composite’s mass increased over time, initially linearly and later exponentially, indicating superior long-term oxidation resistance. The layered structure’s anisotropy endowed the composite with excellent resistance to high-temperature steam oxidation perpendicular to the lamellae. The oxide layer consisted mainly of outer (Mn, Cr)₃O₄ and Mn₃O₄, with an inner Cr₂O₃ layer. Elemental depletion zones of Mn and Cr appeared in the matrix near the oxide scale, and the diffusion of these elements effectively enhanced the material’s oxidation resistance [72]. Singh et al. prepared a FeCoCrNiCu HEA powder via mechanical alloying (MA), with functionalized CNTs (0.1–7.0 wt.%) uniformly dispersed within the HEA matrix via ball milling. Subsequent densification was achieved via Spark Plasma Sintering at 800 °C and 50 MPa, optimizing the process to balance grain growth and CNT structural integrity. The uniform CNT dispersion and interface regulation addressed issues of microstructural inhomogeneity and insufficient corrosion performance in conventional HEAs. The synergistic combination of the HEA multi-principal element effects and CNT reinforcement optimized material performance. The optimal CNT content (2 wt.%) significantly promoted HEA microstructural homogenization, forming a single FCC phase; excessive CNT (>2 wt.%) triggered Cr₂₃C₆ carbide precipitation, leading to renewed phase separation. CNTs inhibited grain coarsening during sintering, reduced lattice strain, and increased interface density. The composite with 2 wt.% CNTs exhibited an 88.6% reduction in the corrosion rate compared to pure HEA (0.52 vs. 4.58 mil/yr/cm²) in a 3.5% NaCl solution, with a significant positive shift in corrosion potential. However, an excessive CNT content (7 wt.%) caused a sharp 58% increase in the corrosion rate, demonstrating a clear threshold effect. The corrosion performance improvement stemmed from CNTs promoting elemental diffusion uniformity and reducing galvanic corrosion risk. At a high CNT content, Cr₂₃C₆ precipitation induced intergranular corrosion, disrupting chemical homogeneity. CNTs synergistically enhanced corrosion resistance through grain refinement, increased dislocation density, and interfacial barrier effects; the bimodal phase distribution and carbide control were key factors in the performance transition [73].

3.2. Chemical Vapor Deposition (CVD)

CVD is primarily used to grow carbon materials (CNTs, graphene, etc.) on or within HEAs. Key aspects include the catalyst design, temperature control, and suppression of interfacial reactions. This involves decomposing carbon sources (e.g., CH₄) and metal precursors in a high-temperature reaction chamber to co-deposit carbon materials and HEA nanoparticles onto a substrate [75,76]. Carbon materials enhance strength and toughness through load transfer, dislocation pinning, and grain refinement. For instance, graphene/HEA heterojunctions can optimize conductivity, catalytic activity, and oxidation resistance [74]. Peng et al. demonstrated the in situ growth of CNTs on the surface of HEA particles via CVD in Figure 2. Subsequently, CNTs/HEAs-particle synergistically reinforced aluminum matrix composites were fabricated using powder metallurgy (ball milling and Spark Plasma Sintering). In situ synthesis of the CNTs@HEAs hybrid reinforcement ensured high crystallinity and structural integrity of the CNTs, resolving issues of poor dispersion and weak interfacial bonding in the aluminum matrix. The composite exhibited a bimodal grain distribution (coarse and fine grains), with CNTs uniformly dispersed in the aluminum matrix. Interfacial Al₄C₃ and Cr₇C₃ carbides enhanced the load-bearing capacity of the CNTs. Furthermore, the presence of high-density stacking faults further improved material performance. Compared to pure aluminum and HEA-only reinforced composites, the CNTs@HEAs/Al composite demonstrated significantly improved tensile strength (230 MPa) and elongation, achieving a synergy of strength and plasticity superior to similar studies. Strengthening mechanisms included load transfer, back stress strengthening, Orowan strengthening, grain refinement, and stacking fault strengthening. The bimodal grain structure and interfacial carbides jointly promoted strain hardening capability, while the strong HEAs-CNTs-Al interfacial bonding and the presence of SFs significantly enhanced ductility [74]. Hassan et al. successfully synthesized FeCoNiCuMnₓ/C nanoparticles with excellent electromagnetic wave absorption performance via an innovative core-shell structure design, composition tuning, and Metal-Organic Chemical Vapor Deposition. Encapsulating FeCoNiCuMn HEA nanoparticles with a graphitic carbon shell effectively solved the agglomeration problem of magnetic nanoparticles, reduced the material density, and improved impedance matching. The fine-tuning of electromagnetic properties was achieved by adjusting the Mn content, further optimizing the absorption performance. The nanoparticles featured a uniform core-shell structure, with a metal core diameter of ~14 nm and a carbon shell thickness of ~3 nm. The carbon shell possessed a high degree of graphitization, beneficial for conductive loss and polarization loss. The metal core exhibited an FCC structure, with slight lattice constant changes as the Mn content increased. The core-shell design and Mn content tuning effectively optimized impedance matching, reducing electromagnetic wave reflection and enhancing absorption efficiency. The heterogeneous interface between the carbon shell and metal core promoted interfacial polarization, while defects in the carbon shell enhanced defect polarization. Concurrently, magnetic loss mechanisms (natural resonance, exchange resonance, eddy current loss) in the HEA nanoparticles further strengthened the absorption capability. FeCoNiCuMn₀.₅/C nanoparticles achieved a reflection loss of −52.3 dB at a thickness of 2.35 mm, with an effective absorption bandwidth covering 5.52 GHz [77].

3.3. Sol-Gel Method

The sol-gel method is a wet-chemical process for synthesizing materials via liquid-phase reactions. It utilizes highly reactive metal salts or organic precursors as raw materials, forming a stable sol through hydrolysis and condensation polymerization, followed by gelation, drying, and thermal treatment to obtain nanostructured materials [78]. Carbon/HEA nanocomposites are fabricated by combining a carbon matrix (e.g., CNTs, graphene, or polymer-derived carbon) with multi-component HEA nanoparticles via this method, forming functional materials with combined dielectric and magnetic loss characteristics [79]. The sol stage achieves atomic/molecular-level mixing, ensuring a uniform distribution of the carbon matrix and HEA components, enabling precise control of the porosity and nanoparticle size [80]. The gel network forms nanopores, increasing the material’s specific surface area and enhancing multiple reflections and interfacial polarization effects in electromagnetic wave absorption [79]. By combining the molecular controllability of sol-gel with the multi-element synergy of HEAs, this method provides efficient and designable nanocomposite solutions for electromagnetic shielding, new energy storage, and other fields. Zhang et al. synthesized FeCoNiCuAl HEAs via the sol-gel method. Subsequently, a heterojunction between HEAs and nitrogen-doped carbon (NC) was constructed through the self-polymerization of dopamine hydrochloride and subsequent annealing in Figure 3 [81]. This approach leveraged the uniformity of the sol-gel and the flexibility of self-polymerization to successfully prepare a composite with a core-shell structure. Introducing nitrogen-doped carbon nanospheres to form a heterojunction with HEAs not only addressed the impedance mismatch issue of single-phase HEA materials in EM absorption but also enhanced dielectric loss through defects and interface effects in NC, achieving synergistic magnetic and dielectric loss for improved absorption performance. The HEAs/NC composite featured tightly bonded heterojunction interfaces, with NC exhibiting the (002) crystal plane of graphitic carbon, forming a graphitic carbon network. Nitrogen doping introduced defects and interface effects that significantly enhanced dielectric loss. The heterojunction interface promoted interfacial polarization. Furthermore, the graphitic network improved material conductivity, enhancing conductive loss. Finally, the inherent magnetic loss mechanisms of the HEAs (natural resonance, exchange resonance, eddy current loss) contributed to absorption. This synergistic effect made HEAs/NC an efficient EM absorber. The prepared HEAs/NC2 composite achieved a minimum reflection loss of −56.38 dB at a thickness of 1.80 mm, with a maximum effective absorption bandwidth of 5.69 GHz. Yu et al. prepared Pt₁₈Ni₂₆Fe₁₅Co₁₄Cu₂₇ HEA nanocrystals via a colloidal synthesis strategy, with reduced graphene oxide (rGO) synthesized simultaneously during nanocrystal formation [82]. Pt₁₈Ni₂₆Fe₁₅Co₁₄Cu₂₇ nanocrystals grew uniformly on the rGO surface, forming a Pt₁₈Ni₂₆Fe₁₅Co₁₄Cu₂₇/rGO composite. The nanocrystals were uniformly dispersed on rGO with high crystallinity. Combining HEA nanocrystals with rGO leveraged the 2D structure and superior properties of rGO to enhance the composite’s EM absorption. Monodisperse HEA nanocrystals (~3.3 nm) were successfully synthesized, providing more polarization-active sites. Multiple new polarization interfaces formed between the HEA nanocrystals and rGO; charge rearrangement at these interfaces generated strong polarization effects, enhancing absorption. Compared to pure Pt₁₈Ni₂₆Fe₁₅Co₁₄Cu₂₇ nanocrystals, the composite exhibited superior EM absorption performance in the 2–18 GHz range. At a 4 mm thickness, the minimum reflection loss reached −41.8 dB, with an effective absorption bandwidth of 2.5 GHz in the 9.4–11.9 GHz band.

3.4. Electrospinning

Electrospinning is a technique that utilizes a high-voltage electric field to induce the jetting and stretching of a polymer solution/melt to form nanofibers [83]. Carbon/HEA nanocomposites fabricated via this technology combine multi-component HEA nanoparticles with a carbon matrix (e.g., carbon nanofibers, graphene composite fibers), forming functional materials characterized by porous structures, a high specific surface area, and multi-element synergistic effects [84]. Electrospinning enables the atomic-level uniform distribution of HEA nanoparticles (<10 nm) within the carbon matrix, reducing agglomeration. By precisely controlling fiber microstructure and component distribution, this method provides a design paradigm for high-performance nanocomposites in fields like new energy and electromagnetic protection [85]. Liu et al. used a bottom-up synthesis approach combining electrospinning and calcination to prepare FeCoNiMnCu HEAs/carbon nanofiber (HEAs/CNF) composites [86]. The calcination temperature was tuned to regulate the composite’s crystallinity, graphitization degree, and electromagnetic parameters. FeCoNiMnCu HEA nanoparticles were uniformly embedded within carbon nanofibers, forming partial core-shell structures and abundant interfaces. The fiber diameter was uniform (170–230 nm), with alloy particles averaging ~20 nm in diameter. HEA particles had an FCC structure, and the carbon matrix was highly crystalline. The 1D carbon nanofiber network promoted electron migration and transition, enhancing conductive loss. Abundant interfaces between alloy particles and the carbon matrix induced multiple interfacial polarizations, increasing polarization loss. Natural resonance and eddy current loss from the HEAs contributed to magnetic loss. This design yielded a composite achieving strong absorption (−64.4 dB) and a broad bandwidth (4.1 GHz) at low filler loading (10 wt%) and thin thickness (1.9 mm). Wang et al. prepared FeCoNiMnRu-HCB composites via electrospinning, activation, and carbonization, embedding HEA catalysts within a highly mesoporous carbon material to significantly increase the specific surface area and catalytic activity in Figure 3 [87]. Benzooxazine was added to the electrospinning solution; its thermal polymerization and subsequent activation process created rich mesopores, increasing the specific surface area and catalytic sites. The prepared nanofibers had high aspect ratios and uniform diameters (50–150 nm), forming a 3D porous structure. HEA particles (FeCoNiMnRu) were uniformly dispersed in the carbon nanofiber matrix with high crystallinity (lattice spacings of 2.1 Å and 1.8 Å, corresponding to (111) and (200) planes). The abundant mesoporous structure provided more active sites, facilitating electrolyte penetration and gas product release, thereby boosting catalytic performance. The unique composition and structural features of the HEAs (high configurational entropy, lattice distortion, sluggish diffusion, synergistic “cocktail effect”) endowed the catalyst with excellent electrocatalytic activity and stability. Nitrogen from the residual PBZ resin formed metal–nitrogen bonds, stabilizing the crystal structure and enhancing catalytic efficiency. The FeCoNiMnRu-HCB_0.5 electrode exhibited outstanding electrocatalytic performance for alkaline water electrolysis: overpotentials for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) at 10 mA cm⁻² were 42 mV and 229 mV, respectively, lower than commercial noble metal catalysts. Both HER and OER current densities remained stable after 20 h of continuous electrolysis, demonstrating good long-term stability.

Figure 3. Sol-gel and electrospinning method for the fabrication of carbon/HEA nanocomposites: (a) schematic diagram, (b) TEM, and (c) XRD of HEAs/NC [82], copyright 2025, Royal Society of Chemistry; (d) schematic diagram, and (e) TEM of FeCoNiMnRu-HCB [87], copyright 2025, Elsevier; (f) schematic diagram, and (g) TEM of HEAs@CNFs [88], copyright 2024, Springer.

Figure 3. Sol-gel and electrospinning method for the fabrication of carbon/HEA nanocomposites: (a) schematic diagram, (b) TEM, and (c) XRD of HEAs/NC [82], copyright 2025, Royal Society of Chemistry; (d) schematic diagram, and (e) TEM of FeCoNiMnRu-HCB [87], copyright 2025, Elsevier; (f) schematic diagram, and (g) TEM of HEAs@CNFs [88], copyright 2024, Springer.

3.5. 3D Printing

The 3D printing of carbon/HEA nanocomposites refers to the use of additive manufacturing processes (e.g., Laser Powder Bed Fusion (LPBF), Fused Deposition Modeling (FDM)) to combine multi-principal element HEAs with carbon-based materials (e.g., CNTs, graphene), forming advanced functional materials with nanoscale multiphase composite structures [89,90]. Carbon-based materials (e.g., CNTs) are uniformly dispersed within the alloy matrix through shear forces and high temperatures during printing, forming strong “alloy-carbon” interfacial bonding. Rapid cooling suppresses elemental segregation, promoting single-phase solid solution formation in the HEAs, while the nanoconfinement effect of the carbon matrix stabilizes alloy lattice distortion [90]. These materials combine the strength and toughness of HEAs with the lightweight, high thermal/electrical conductivity of carbon materials, showing potential in electromagnetic shielding, thermal management, catalysis, etc. [91]. By precisely controlling the microstructure and multiphase synergy, this method provides a new paradigm for designing and scaling high-performance composites. Yan et al. prepared HEOs@C-GR/PLA composites via high-temperature carbonization and 3D printing, achieving uniform dispersion and structural densification [92]. The composite exhibited a distinct double core-shell structure: HEO cores were uniformly coated by a carbon shell, while graphene (GR) dispersed within the PLA matrix formed a continuous conductive network. This double core-shell design (HEOs@C), with an inner high-entropy multi-metal oxide phase and an outer carbon shell, combined with the GR hierarchical conductive network. The “cocktail effect” of the high-entropy material modulated lattice distortion and oxygen vacancies, synergizing with GR’s conductivity to achieve coupled dielectric-magnetic loss enhancement, breaking the limitations of single materials. The 3D printing enabled precise shaping of complex structures. Double core-shell interfacial polarization and the GR network induced multiple relaxations. Lattice distortion, oxygen vacancies, and carbon defects formed dipole polarization centers, enhancing energy dissipation. The ferromagnetic components (Co, Fe, Ni) in HEOs converted EM energy via natural resonance and eddy current effects; the high-entropy effect optimized permeability, improving low-frequency absorption. GR modulated material conductivity, while the HEOs@C core-shell structure reduced surface reflection. Thickness-frequency synergistic matching based on λ/4 theory broadened the absorption bandwidth. The coupling of multilevel heterogeneous interfaces and the conductive network enabled multiple reflection-scattering-absorption of EM waves, significantly boosting the overall absorption efficiency. The composite achieved a minimum reflection loss of −51.36 dB and an effective absorption bandwidth of 5.20 GHz covering the C to Ku bands within 2–18 GHz. Compared to pure HEO systems, filler usage was reduced by 40%, while achieving light weight (density < 2.0 g/cm³) and high mechanical strength (tensile strength > 45 MPa). Wu et al. prepared the flexible films by mixing HEAs@CNFs or pure CNFs with PDMS resin using electrospinning, pyrolysis, and 3D printing, followed by curing to form composites with different filler contents (10 wt%, 15 wt%, 20 wt%) in Figure 3 [88]. HEAs@CNFs were nanoscale-diameter fibers embedding uniformly distributed HEA nanoparticles (~10 nm), with five metals (Fe, Co, Ni, Cu, Ru) uniformly distributed within the alloy particles (atomic ratio 5–35%). Embedding HEA nanoparticles within carbon nanofibers (CNFs) significantly reduced the electron delocalization capability, tuning carrier concentration, and effective electron mass, achieving epsilon-near-zero (ENZ) performance in the radio frequency (RF) range (21 MHz) for the first time. Combined with the flexibility and biocompatibility of PDMS, 3D printing enabled the construction of wearable electronic devices suitable for human motion detection and medical monitoring. HEA introduction reduced the delocalization ability of electrons around carbon atoms (decreased ELF value), increased the work function (3.438 eV → 4.831 eV), and reduced the carrier concentration. HEAs flattened the CNF band structure (enhanced non-parabolicity), increasing the effective electron mass and further lowering the plasma frequency. Charge accumulation at the PDMS/CNFs interface enhanced positive permittivity, while conductive network formation led to negative permittivity. Consequently, at 20 wt% HEAs@CNFs, the PDMS/HEAs@CNFs film achieved ENZ (permittivity transition from negative to positive) at 21 MHz, with plasma frequency significantly reduced to the RF range. The high filler content formed a continuous conductive network, endowing the film with high conductivity and excellent flexibility (bendable, foldable). Cell experiments (H&E staining, CCK-8) showed no cytotoxicity (cell viability >95%). This study innovatively introduced HEAs into a CNF system via electrospinning and 3D printing, achieving breakthroughs in both RF ENZ performance and biocompatibility, providing new material solutions for wearable medical electronics and flexible sensing.

4. EES Applications

4.1. Lithium-Ion Batteries (LIBs)

Nanocomposites of carbon materials (e.g., graphene, CNTs, porous carbon) and HEAs, leveraging their unique synergistic effects (high conductivity, multiple active sites, excellent mechanical stability), have demonstrated broad application prospects in LIBs in recent years. The carbon framework provides continuous electron/ion transport pathways and mitigates volume expansion, while the multi-element synergistic effect of HEA nanoparticles enhances structural stability, significantly extending the cycle life. The abundant active sites in HEAs contribute to high theoretical capacity (>500 mAh/g), and the carbon carrier accelerates reaction kinetics, supporting high-rate charging/discharging. HEA surfaces can efficiently catalyze electrode reactions (e.g., sulfur conversion or oxygen reduction), suppressing the shuttle effect and improving energy efficiency.

In terms of anode materials, carbon matrices buffer the volume expansion of HEAs, enhancing cycling stability. HEA nanoparticles composed of Ge, Sn, Sb, Si, Fe, Cu, and P elements were synthesized with carbon materials via high-energy mechanical ball milling for LIB anodes by Wei et al. in Figure 4 [38]. The rational selection of elements with complementary electrochemical properties (e.g., high-capacity Si, Ge, Sn, Sb, and P and high-conductivity Cu and Fe) enabled the construction of a novel HEA/C composite anode featuring a unique dragon-fruit-like dense structure. This composite process ensured the uniform dispersion and encapsulation of HEA nanoparticles within the carbon matrix, which functions as a multifunctional framework: (1) providing mechanical support that prevents nanoparticle agglomeration and pulverization during cycling; (2) buffering volume expansion during lithiation (reduced from 34% to 25%) to maintain electrode integrity; (3) facilitating rapid electron transport through its high conductivity (2.14 × 10¹ S/m), flexibility, and chemical stability. The multi-elemental synergy within HEA nanoparticles generated distinct electrochemical behaviors during lithiation, enhancing the lithium storage capacity and reaction activity while alleviating volume stress. This synergistic effect—combined with the carbon matrix’s defective structure (D/G band ratio ≈1:1), increasing reaction sites and uniform element distribution (e.g., Ge, Sn, Sb) and exposing active sites—was further reinforced by P-C/P-O-C bonds at the HEA–carbon interface (confirmed by XPS), stabilizing the framework and promoting electron/ion diffusion. Consequently, the anode achieved a high initial Coulombic efficiency of 91%, stable cycling exceeding 1600 h, and 63% capacity retention at 2000 mA/g, significantly outperforming conventional alloy anodes. Xiao et al. synthesized Sn-Si-Co-Cu-P high-entropy alloy/graphite (HEA/C) composite anode materials via high-energy ball milling, forming an amorphous composite structure with HEA nanoparticles uniformly dispersed at the atomic scale within the graphite matrix [68]. This architecture delivers threefold synergistic advantages: (1) the graphite matrix provides high conductivity (significantly reducing charge transfer resistance R_ct) and layered mechanical support, effectively suppressing phase separation and particle agglomeration while buffering volume expansion (experimental value 37% vs. theoretical 235%); (2) its porous structure (specific surface area: 13.93 m²/g) increases lithium-ion adsorption/diffusion sites. Elemental mapping confirms the homogeneous distribution of Sn/Si/Co/Cu/P/C without segregation, where high-capacity elements (Sn/Si/P) synergistically optimize the electronic environment of active sites with conductive copper and structurally stabilizing cobalt. The multi-component synergy enhances the lithium storage capacity and reaction activity, coupled with ion transport facilitation through graphite interlayer channels and lithium storage enhancement at HEA active sites. Consequently, the material delivers an initial discharge capacity of 1881 mAh/g, retains 1196.5 mAh/g after 1000 cycles, achieves 47.2% capacity retention at a 10 A/g high current density, and maintains structural integrity over 1000 cycles.

In terms of cathode materials, the multi-element synergy of HEAs optimizes structural stability at high voltages. Yi et al. synthesized an FeCoNiMnCuAl@C material with a hierarchical structure via carbothermal reduction using recycled metal ions from spent LIBs, serving as a cathode catalyst for rechargeable Li–CO₂ batteries in Figure 4 [93]. The hierarchical nanosheet architecture, derived from MOF-pyrolyzed carbon material, integrates high electrical conductivity with a large specific surface area (221.1483 m²/g). This unique structure ensures the uniform distribution of HEA nanoparticles across carbon nanosheets, simultaneously providing the following: (1) high porosity enhancing mass transport and CO₂ diffusion; (2) abundant ion transport channels boosting catalytic activity (discharge capacity: 27,664 mAh/g at 100 mA/g). The carbon substrate facilitates rapid electron transport while buffering volume changes, with its flexibility preventing HEA structural collapse during cycling. DFT calculations confirm that multi-element sites (e.g., Co, Mn, Al) in the HEA exhibit optimal CO₂ adsorption energy. Through high-entropy effects and carbon–HEA synergy, inert CO₂ molecules are activated to drive reversible Li₂CO₃ formation/decomposition, reducing overpotential to 1.05 V and maintaining a high discharge voltage plateau (2.77 V). These mechanisms collectively enable stable cycling over 134 cycles. Wen et al. fabricated FeCoNiCuRu high-entropy alloy/carbon nanofiber (HEA/CNF) composites as Li-CO₂ battery cathodes via electrospinning and thermal treatment, achieving tunable configurational entropy [94]. The 3D conductive CNF network (specific surface area: 295.6 m²/g) uniformly anchors sub-10 nm HEA nanoparticles, concurrently providing mechanical support to prevent agglomeration, establishing rapid electron transport pathways, and facilitating CO₂/electrolyte diffusion through its flexible framework. The HEA nanoparticles drive efficient CO₂ adsorption/activation and reversible Li₂CO₃ conversion via triple synergistic mechanisms: (1) high-entropy effects optimizing active site distribution; (2) electron transfer from low-electronegativity elements (Fe, Co) to Ru generating electron-rich sites (verified by XPS/XANES); (3) defective carbon matrix structures increasing catalytic sites. This synergy enhances CO₂ adsorption (evidenced by negative adsorption energy) and reduces Li₂CO₃ decomposition barriers to 0.70 eV, ultimately delivering a discharge capacity of 6160 mAh/g at 200 mA/g with a low charge voltage plateau (<4.0 V), enhanced rate capability, and ultralong cycling stability over 550 cycles (5500 h).

Despite the outstanding advantages of carbon materials (such as graphene, CNTs, porous carbon, etc.) and HEA nanocomposites in the field of LIBs, this material system still faces some key challenges. The precise control of HEA element ratios (e.g., equiatomic) and uniform dispersion are difficult; current methods (e.g., ball milling, sputtering) are costly, energy-intensive, and hard to scale. Insufficient carbon/HEA interfacial bonding strength can lead to particle detachment during cycling. Active metals in HEAs (e.g., Fe, Cr) may dissolve in the electrolyte, causing continuous SEI growth (>50% increase in interfacial impedance after cycling), increasing resistance, and reducing the Coulombic efficiency. Incorporating precious metals (e.g., Pt, Ir) increases the cost, and the high density of HEAs (>8 g/cm³) limits gravimetric energy density, hindering EV applications. Future research must focus on developing low-cost synthesis processes, optimizing interfacial coating techniques (e.g., ALD of Al₂O₃), and exploring precious-metal-free HEA systems to advance practicality.

Figure 4. Carbon/HEA nanocomposites for LIBs: (a) schematic diagram, (b) TEM, and (c) cycle stability of HEAs/C [38], copyright 2022, Elsevier; (d) schematic diagram, (e) TEM, and (f) discharge and charge profiles of FeCoNiMnCuAl@C [93], copyright 2024, Wiley-VCH GmbH.

Figure 4. Carbon/HEA nanocomposites for LIBs: (a) schematic diagram, (b) TEM, and (c) cycle stability of HEAs/C [38], copyright 2022, Elsevier; (d) schematic diagram, (e) TEM, and (f) discharge and charge profiles of FeCoNiMnCuAl@C [93], copyright 2024, Wiley-VCH GmbH.

4.2. Lithium Metal Batteries (LMBs)

Carbon/HEA nanocomposites significantly optimize LMB performance by synergizing carbon-based carriers (e.g., graphene, CNTs) with multi-element HEA nanoparticles. HEA nanoparticle-decorated carbon skeletons homogenize Li⁺ flux, suppress dendrite growth, and enhance cycling stability. Multi-element active sites in HEAs accelerate the reversible conversion of polysulfides/lithium peroxide, mitigating the shuttle effect and improving energy efficiency. The carbon/HEA composite interface provides high mechanical strength and 3D ion/electron channels, reducing the local current density and delaying electrode pulverization.

Wang’s group developed three types of high-entropy alloy/carbon (HEA/C) composite materials through innovative methods to enhance lithium metal battery performance, including an AgCuInCdZn HEA nanoparticle-embedded porous carbon fiber (HEA/PCF) system synthesized via a fusion method [55]. This design utilizes a rigid 3D porous PCF skeleton constructed via Ag⁺ etching (calcined at 1000 °C to form a single-phase alloy), synergistically integrated with molten-state embedded HEA nanoparticles. The composite preserves the porosity while enhancing ion/electron conduction through HEA lattice distortion. Key synergistic mechanisms include the following: (1) the PCF skeleton buffers volume expansion during lithium deposition and regulates mass transfer under high currents; (2) HEA nanoparticles uniformly distributed within pores (verified via molecular skeleton-level analysis) provide abundant lithiophilic sites, significantly reducing lithium nucleation overpotential (~5.3 mV); (3) the highly conductive network lowers the local current density, cooperatively suppressing dendrite formation and “dead lithium”. Through coordinated pore engineering and catalytic site optimization, this HEA/PCF architecture achieves homogeneous lithium deposition and volume change regulation, ultimately enabling stable symmetric cell cycling > 1200 h at 60 mA/cm² and full cells (NCM-811 cathode) maintaining > 99.5% Coulombic efficiency over 200 cycles.

Secondly, CuInNiSnCd high-entropy alloy/carbon fiber (HEA/CF) composites were synthesized via a high-temperature redox strategy with calcination at 1100 °C, forming a single-phase face-centered cubic (FCC) structure featuring uniformly distributed HEA nanoparticles on the CF surface [67]. This 3D framework delivers triple synergistic functions: (1) the CF skeleton structurally regulates lithium deposition by reducing the local current density, buffering volume expansion, and providing spatial accommodation; (2) HEA nanoparticles electrochemically optimize nucleation through abundant lithiophilic sites with ultralow overpotential (3.4 mV, surpassing pure carbon’s 14 mV and copper’s 40 mV), enabling uniform Li deposition/stripping; (3) multi-element synergy kinetically enhances stability, as confirmed via dynamic electrochemical impedance spectroscopy (DEIS) demonstrating improved Li⁺ transport kinetics and cycling reversibility. These mechanisms collectively contribute to dendrite-free symmetric cell operation exceeding 3000 h at 10 mA cm⁻², while maintaining Coulombic efficiencies > 99.2% over 160 cycles in full cells and 99.5% over 800 cycles at 2 mA cm⁻² in half-cells.

Finally, a NiCdCuInZn high-entropy alloy/carbon fiber (HEAs/C) composite was fabricated via a thermodynamically driven phase transition method (Figure 5) [95]. This material features an ultrathin (~20 nm), uniformly distributed high-entropy alloy (HEA) layer comprising nanoparticles (NPs) and nanosheets on the carbon fiber (CF). This structural design provides a high-performance solution for anode-free lithium metal batteries (LMBs): the carbon fiber skeleton ensures efficient ion/electron transport and mechanical flexibility, while the single-phase face-centered cubic (FCC) structured HEA forms a strong bond with CF at 1100 °C, enhancing interfacial stability through lattice distortion. Leveraging the “cocktail effect” of its components, the HEA generates a gradient adsorption energy (−3.18 eV to −2.03 eV; e.g., Ni/Cu sites exhibit strong adsorption), enabling selective lithium-ion adsorption and rapid diffusion. This effectively reduces nucleation overpotential and guides uniform deposition. The ultrathin HEA nanostructure (nanosheets and NPs) provides continuous Li⁺ transport pathways, abundant active sites for lithium deposition, and shortened Li⁺ diffusion paths, thereby significantly suppressing dendrite growth. The exceptional performance is demonstrated as follows: asymmetric cells maintain > 99.6% Coulombic efficiency (CE) after 2000 cycles; symmetric cells achieve > 7200 h of dendrite-free stable cycling even at a high current density of 60 mA cm⁻²; and full cells with a high-loading NCM-811 cathode deliver an average CE of 99.5% after 160 cycles at a 1C rate.

Although carbon/HEA nanocomposite-based lithium-metal batteries present excellent potential for application, they still face bottlenecks. The high catalytic activity of HEA surfaces can exacerbate electrolyte decomposition (e.g., oxidation of carbonate solvents), leading to thick, unstable CEI layers (>100 nm), increased impedance, and reduced Coulombic efficiency (<95% after cycling). The uniform dispersion of HEA NPs relies on high-energy ball milling or sputtering; composite processes (e.g., CVD growth) are complex and costly for mass production. Transition metals in HEAs (e.g., Mn, Co) may dissolve at high voltages (>4.3 V), causing active material loss and electrode passivation (>30% capacity fade after 100 cycles). The high density of HEAs hinders battery lightweighting. Future efforts need to develop in situ coating strategies (e.g., ALD of Al₂O₃ interlayers), design precious-metal-free HEA systems (e.g., TiZrNbMo), and explore solid-state electrolyte-compatible interfaces to drive practical application.

4.3. Lithium-Oxygen Batteries (Li-O₂)

Carbon/HEA nanocomposites demonstrate unique advantages in Li-O₂ batteries. These materials combine HEA nanoparticles with carbon-based carriers (e.g., porous carbon fibers, graphene) to construct electrode systems integrating high catalytic activity and conductivity. The multi-element synergistic effect of HEAs significantly enhances the catalytic activity for the ORR and OER, while the carbon matrix provides a conductive network and reaction interface, collectively optimizing the battery’s discharge capacity and cycling stability. The tunable composition of HEAs allows precise regulation of the electronic structure of catalytic sites. The porous structure of the carbon matrix facilitates oxygen/electrolyte transport. Synergistic interfacial effects within the composite suppress side reactions.

Peng Wang et al. synthesized Pt HEAs@N-C via a Joule-heating strategy using recycled metals (Ni, Co, Mn) from spent LiNi₁/₃Mn₁/₃Co₁/₃O₂ cathodes combined with Pt in Figure 5 [96]. The Pt HEAs@N-C catalyst features uniformly anchored HEA nanoparticles (~3.36 nm) on an N-doped carbon (NC) carrier, forming abundant active sites and efficient electron pathways. The NC carrier delivers three core functions: (1) a high specific surface area (261.36 m²/g) with abundant mesopores (Type IV isotherm) facilitates electrolyte infiltration, rapid Li⁺/O₂ transport, and Li₂O₂ deposition; (2) superior conductivity ensures efficient charge transfer and reduced interfacial resistance; (3) N-doping defects enhance interactions with Pt HEA, optimizing the electronic structure. Its molecular skeleton—composed of porous ultrathin nanosheets with a tortuous 2D architecture—confines HEA nanoparticles to prevent aggregation and ensures uniform dispersion, while the rigid framework stabilizes HEA loading during cycling. During synthesis, the nitrogen atoms/defects on NC electrostatically anchor Ni/Co/Mn/Pt ions, enabling the Joule heating-induced formation of single-phase solid-solution alloys. This process triggers reverse electron transfer (Pt → Ni/Co/Mn), optimizing the Pt d-band structure to enhance O-intermediate adsorption and accelerate ORR/OER kinetics. The NC/HEA interface establishes an efficient triple-phase boundary (catalyst/electrolyte/O₂), promoting LiO₂ adsorption and Li₂O₂ decomposition. Consequently, the catalyst achieves an ultra-low polarization voltage (0.27 V) at 200 mA/g, stable cycling over 240 cycles, and excellent rate performance even at 500 mA/g. A PtFeCoNiCu@rGO composite catalyst was prepared via high-temperature annealing by Wu et al. [97]. Constructed on a reduced graphene oxide (rGO) carrier, this material features a layered skeleton that retains the wrinkled texture of pristine GO, with flexible layers conformally encapsulating uniformly distributed PtFeCoNiCu high-entropy alloy (HEA) nanoparticles (~50 nm). The rGO carrier delivers three core functions: (1) an ultrahigh specific surface area (512.28 m²/g) and hierarchical porosity accelerate Li⁺/O₂ diffusion while providing ample space for Li₂O₂ storage; (2) exceptional conductivity synergizes with HEA to enhance charge transfer efficiency; (3) surface oxygen-containing functional groups strengthen interactions with the HEA, stabilizing the composite structure. The porous network formed via interlayer stacking effectively buffers volume fluctuations during Li₂O₂ deposition/decomposition. Active site analysis reveals the following: the high defect density (I_D/I_G = 1.21) cooperates with HEA metal sites to boost O₂/LiO₂ intermediate adsorption, while tight rGO-HEA interfacial contact establishes efficient electron pathways. The multi-element synergistic effect of HEA optimizes oxygen intermediate adsorption/conversion processes, significantly enhancing ORR/OER kinetics. Consequently, the catalyst achieves the following: a high initial discharge capacity (13,949 mAh/g at 100 mA/g), low overpotential (0.77 V), and stable cycling over 148 cycles (under 500 mAh/g capacity limitation), with the Li₂O₂-dominated formation pathway confirming its high selectivity and reversibility. Tian et al. designed an HEAs/C electrocatalyst featuring high-entropy alloy (HEA) nanoparticles, combining Pt/Ir with Fe/Co/Ni/Mn, uniformly dispersed within a carbon matrix [98]. This carbon matrix plays several pivotal roles in the catalyst. As a functional support, it provides high electrical conductivity for efficient charge exchange between the HEA particles and the external circuit, it maintains chemical stability in the harsh oxidizing environment, and its porous structure (e.g., carbon paper fiber networks) facilitates O₂ diffusion and reversible Li₂O₂ conversion. As a structural framework, the loose skeleton of amorphous carbon particles or fibrous structures effectively accommodates the HEA nanoparticles, preventing their agglomeration while preserving structural integrity; 3D carbon paper networks further enhance the mechanical strength of the electrode. At the material sites, defects and functional groups on the carbon surface anchor the HEA particles, enabling their in situ growth and uniform dispersion. Critically, the carbon–HEA interfacial interactions modulate the d-band center distribution of the alloy. This broad distribution, combined with the diverse local atomic environments within the HEAs, enhances catalytic flexibility and optimizes the adsorption/desorption balance strength of oxygen species (O₂/LiO₂ intermediates). Benefiting from this synergistic structural design, the catalyst achieved outstanding performance: an energy conversion efficiency exceeding 80%, stable cycling for 2000 h at a 4000 mAh/g capacity with 66.7% efficiency retention, and a discharge capacity of 39.1 Ah/g, significantly outperforming conventional catalysts.

However, key challenges remain for carbon/HEA nanocomposites in Li-O₂ batteries. HEA nanoparticles are susceptible to elemental segregation or oxidation during cycling, leading to catalytic activity decay. Carbon matrices may corrode at high potentials, impacting the long-term stability. The interfacial interaction mechanisms, particularly charge transfer and catalysis at the HEA–carbon interface, are not fully elucidated and require deeper investigation. Furthermore, current synthesis methods (e.g., high-temperature fusion, electrodeposition) are costly, hindering scalability and practical application.

4.4. Sodium/Potassium-Ion Batteries (SIBs/PIBs)

Driven by lithium resource scarcity and rising costs, SIBs/PIBs have gained significant attention as alternative energy-storage technologies. However, the larger ionic radii and sluggish diffusion kinetics of Na⁺/K⁺ ions lead to bottlenecks like low capacity and a short cycle life in traditional electrode materials. Composites of carbon materials (e.g., hard carbon, graphene) with HEAs, synergistically optimizing ion-storage sites, electron conduction, and mechanical stability, present a key solution to overcome these limitations. The composite design shows significant promise in SIBs/PIBs.

Bai et al. developed a lightweight, mechanically flexible sodium deposition substrate through a carbon-thermal encapsulation strategy (Figure 6), integrating zinc-based multi-element alloys (ranging from ternary to medium/high-entropy alloys) with carbon nanotubes (CNTs) [99]. Leveraging their lightweight nature (1.0–1.2 mg/cm²), mechanical flexibility, and high conductivity, the CNTs act as conductive substrates for sodium deposition, reducing localized current density and enabling uniform Na⁺ diffusion. Their interwoven network structure accommodates high-capacity sodium deposition (up to 10 mA h/cm²) while suppressing dendrite formation. Using carbon-thermal encapsulation, the CNTs uniformly encapsulate multi-element alloy nanoparticles (FeCoNiAlZn), forming a stable “alloy@CNT” composite framework. This design prevents nanoparticle aggregation and direct contact with the electrolyte, avoiding side reactions and preserving the structural integrity. Simultaneously, the integration embeds high-entropy alloy (HEA) nanoparticles within the CNT network, creating a conductive and sodiumophilic composite material. The synergistic architecture enhances mechanical stability, conductivity, Na⁺ adsorption/transport kinetics, and deposition/stripping efficiency: CNTs provide rapid electron transport and structural support, while HEAs enable efficient Na⁺ adsorption, uniform distribution, and reduced nucleation overpotential. In an anode-free sodium-ion battery prototype, the FeCoNiAlZn@CNT composite paired with an NaVPO₄F cathode achieved a high energy density of 351.6 Wh/kg and power density of 1335.5 W/kg, retaining 93.7% of its capacity after 200 cycles. The system demonstrated excellent rate capability and mechanical flexibility, maintaining stable performance even under flexible conditions. Zhang et al. synthesized the HEAs-NPs@NC material using a sacrificial template method, encapsulating high-entropy alloy (HEA) nanoparticles (Mn, Co, Ni, Cu, Zn) within a nitrogen-doped carbon (NC) matrix [100]. The NC matrix, derived from the pyrolysis of a metal-organic framework (Me-(CHX)-MOF), features high conductivity, a porous structure (BET specific surface area: 188.5 m² g⁻¹), and abundant surface defects (particularly N-doping sites), which collectively facilitate K⁺ transport, enhance potassium adsorption, mitigate volume expansion, and provide additional K⁺-storage sites. The chelation effect of the flexible ligand CHX ensures the uniform distribution of multiple metals, suppressing phase separation. A robust “HEA-NPs@NC” framework is formed via metal-N bonding, where the NC matrix not only acts as a conductive substrate and mechanical support but also prevents the aggregation of HEA nanoparticles while enabling rapid electron transport. The uniformly embedded HEA nanoparticles contribute high surface area and porosity, forming a multi-path K⁺ transport network through their homogeneous distribution. The HEAs’ “cocktail effect” and configurational entropy synergistically optimize electrochemical activity and K⁺-adsorption capacity, with the resulting potassium-intercalated metal solid solution further enhancing K⁺-storage efficiency and stability. Benefiting from this synergistic design, the HEAs-NPs@NC anode exhibits exceptional electrochemical performance: a high specific capacity (513 mAh/g at 0.1 A/g), excellent rate capability (retaining 202 mAh/g at 5 A/g), and ultra-long cycling stability (96.6% capacity retention after 3000 cycles). The assembled potassium-ion full battery retains 82.8% of its capacity after 500 cycles, fully validating the material’s advantages in high-capacity and long-term cycling stability.

Chang et al. fabricated an HEA-N-PCNF composite by integrating high-entropy alloy (HEA) nanoparticles (Mn, Fe, Co, Cu, Ni) with nitrogen-doped porous carbon nanofibers (N-PCNF) (Figure 6) [101]. The N-PCNF matrix, featuring a large specific surface area (122.44 m²/g) and a porous structure, reduces localized current density while providing space for potassium deposition. Its fibrous network enhances electron/ion transport efficiency and rate capability. The three-dimensional porous N-PCNF network uniformly anchors HEA nanoparticles, forming a composite “HEA-N-PCNF” framework that offers conductivity, structural stability, and enhanced surface activity. The HEA nanoparticles distributed on N-PCNF pores/surfaces further increase the surface area, providing additional K⁺-adsorption sites, improving electrolyte permeability and facilitating rapid ion/electron transport. Critically, the configurational entropy effect of HEAs and their induced local charge enhancement (notably the high electronegativity of Cu/Ni sites) significantly improve potassium metal affinity, optimizing the K⁺-adsorption capacity and deposition uniformity. Electron transfer and lattice distortion within HEAs generate strong K⁺-adsorption sites, inducing Frank–Van der Merwe-type layer-by-layer growth, effectively suppressing dendrite formation. This synergistic structural design regulates K⁺ flux and stabilizes the solid–electrolyte interphase layer. Benefiting from this design, the symmetric battery based on this material achieved an ultra-long cycling life of over 2350 h at 8 mA/cm². The assembled HEA-N-PCNF-K||PTCDA full battery delivered a high energy density of 331 Wh/kg and retained 58% of its capacity after 2000 cycles, significantly outperforming conventional potassium batteries. This highlights the composite’s efficiency in dendrite suppression and stability enhancement. Zheng et al. synthesized the HEA-CNF composite through an electrospinning technique, uniformly embedding HEA nanoparticles within CNFs [102]. The CNFs, derived from the pyrolysis of a polyacrylonitrile precursor after electrospinning, feature a three-dimensional network structure that provides high conductivity and prevents particle aggregation. Their porous nature (HEA-CNF specific surface area: 672 m²/g) enhances electrolyte wettability, facilitates Li⁺/K⁺ diffusion, and buffers volume changes during cycling. HEA nanoparticles (composition: Co₀.₂Sb₀.₂Fe₀.₂Mn₀.₂Ni₀.₂) are uniformly encapsulated within the CNFs, forming a fibrous “HEA-CNFs” composite framework: the tight connection between HEA nanoparticles and CNFs enables rapid electron/ion transport, while the CNF network offers mechanical support to accommodate volume deformation. The configurational entropy and synergistic multi-metal effects of HEAs significantly improve ion diffusion rates and structural stability, enhance Li⁺/K⁺-storage capacity via alloying reactions, and suppress aggregation and phase separation. Notably, this design ensures uniform elemental distribution—active metals (e.g., Co, Sb) participate in alloying reactions for Li⁺/K⁺ storage, while inert metals (e.g., Mn) maintain structural stability. Benefiting from this synergistic architecture, the HEA-CNF anode exhibits exceptional Li⁺/K⁺-storage performance: as a lithium-ion battery anode, it retains a capacity of 1400 mAh/g after 800 cycles at 0.5 A/g; as a potassium-ion battery anode, it delivers a reversible capacity of 280 mAh/g after 200 cycles at 0.2 A/g. Its performance surpasses that of the binary alloy counterpart (CoSb-CNFs), fully demonstrating the dual advantages of high capacity and long-term cycling stability offered by the composite structure.

Despite the promising performance of carbon/HEA nanocomposites in SIBs/PIBs, several bottlenecks persist. Active metals in HEAs (e.g., Sn, Sb) readily react with ester-based electrolytes, forming thick, inhomogeneous CEI layers, increasing impedance, and accelerating capacity fade (CE < 95% after 100 cycles). HEA nanoparticle synthesis relies on high-energy ball milling/sputtering, leading to high production energy consumption. The high density of HEAs constrains the battery gravimetric energy density. The Na⁺/K⁺-storage mechanism under multi-element synergy remains unclear. Transition metal dissolution causes active site loss, limiting the lifespan. Therefore, developing solid-state electrolyte-compatible interfaces (e.g., sulfide-coated HEAs), designing lightweight medium-entropy alloys (MEAs), and revealing multi-element dynamic evolution mechanisms via in situ characterization will be key future research focuses.

4.5. Lithium-Sulfur Batteries (Li-S)

Li-S batteries have attracted significant attention due to their high theoretical energy density (2600 Wh/kg), low cost, and environmental friendliness. However, their practical application is hindered by challenges such as the polysulfide “shuttle effect,” low conductivity of the sulfur cathode, substantial volume expansion (~80%), and lithium anode dendrite growth. HEAs/carbon composites suppress the polysulfide shuttle effect through dual mechanisms of chemical adsorption and catalytic conversion.

Han et al. synthesized PtCuFeCoNi high-entropy alloy (PCFCN-HEA) nanoparticles via a hydrothermal method followed by subsequent annealing and loaded them onto hollow carbon spheres (HCSs) hybridized with mycelium-derived carbon nanobelt (HCNB) composites, serving as a sulfur host material for lithium-sulfur battery cathodes [103]. The carbon framework (HCSs and HCNBs) provides three core functionalities: (1) the high conductivity and porous structure enable rapid electron/ion transport, addressing the insulating nature of sulfur and its discharge products (Li₂S₂/Li₂S); (2) the synergistic physical adsorption and spatial confinement suppress the polysulfide (LiPSs) shuttle effect; (3) acting as a carrier for HEA nanoparticles, ensuring their uniform dispersion and maximizing catalytic site exposure. Specifically, the HCSs’ hollow spherical structure, with a large surface area and internal voids, accommodates sulfur, while the HCNBs form an interwoven nanobelt network that enhances structural stability, mechanical strength, and electrolyte contact; this hierarchical architecture balances porosity with continuous conductive network connectivity. HEA nanoparticles (~5.6 nm) uniformly deposited on HCSs are interconnected via HCNBs. The HEA integrates five metals with distinct work functions (high: Pt/Ni; low: Fe/Co/Cu), achieving a d-band center shift upward (to −1.70 eV) through work function modulation. Electron transfer (from low- to high-work function metals) and multi-metal synergy precisely regulate the d-band center position, optimizing LiPSs adsorption and catalytic activity. Consequently, carbon sites physically anchor LiPSs, while HEA catalytic sites (synergistically enhanced by Pt/Cu/Fe) accelerate LiPS conversion, forming an integrated “adsorption-catalysis” synergy mechanism—carbon restricts LiPS diffusion, while HEA lowers reaction energy barriers—dramatically boosting sulfur reduction reaction (SRR) kinetics. Benefiting from this design, the material exhibits exceptional electrochemical performance: reversible capacity of 652 mAh/g at an ultrahigh 8 C rate; 40.9% capacity retention after 1500 cycles at 2 C (ultra-low decay rate: 0.039% per cycle); 81.5% capacity retention after 500 cycles at 6 C; and a specific activity of 2.58 mA/cm² for Li₂S₄-to-Li₂S conversion, 6.14 times higher than that of Pt catalysts. Ma et al. developed an efficient electrocatalyst composed of high-entropy alloy (HEA) nanoparticles, nitrogen-doped carbon (NC), and carbon nanotubes (CNTs) [104]. The material is based on NC derived from pyrolyzed metal–organic frameworks (MOFs), of which the porous structure is rich in nitrogen active sites (e.g., pyridinic nitrogen/pyrrolic nitrogen). These sites chemically anchor lithium polysulfides (LiPSs) through polar interactions, effectively suppressing the shuttle effect. The CNTs form an interconnected one-dimensional conductive network that permeates the NC, creating a three-dimensional framework. This not only prevents NC aggregation and enhances mechanical strength and conductivity, but also provides rapid electron/ion transport channels, reducing internal resistance. HEA nanoparticles (~13 nm) uniformly dispersed within the NC matrix are encapsulated by NC and interconnected with CNTs. This stable composite conductive framework integrates three functionalities synergistically: NC’s nitrogen sites chemically immobilize LiPSs; CNTs’ conductive sites ensure efficient electron transport; HEAs’ catalytic sites (attributed to the oxidation states of Fe/Co/Ni) accelerate the bidirectional conversion reactions of LiPSs. This integrated “adsorption-transport-catalysis” system significantly improves the composite’s conductivity, adsorption capacity, and structural stability, endowing the battery with excellent cycling stability and rate capability: a discharge capacity of 692.0 mAh/g after 300 cycles at a 1 C rate (ultra-low decay rate: 0.03% per cycle), and a retained capacity of 521.1 mAh/g even at a high 5 C rate. Wang et al. fabricated FeCoNiCuMn high-entropy alloy nanocrystals (HEA-NCs) supported on nitrogen-doped carbon (NC) using a reflux–chelation–confinement annealing strategy (Figure 7) [64]. The method employed 1,10-phenanthroline chelation, g-C₃N₄ templating, and polydopamine coating to achieve spatial confinement, effectively suppressing HEA aggregation and phase separation. The resulting HEA nanoparticles (40–60 nm) are uniformly dispersed on the NC surface, forming a single-face-centered cubic (FCC) phase. EDS mapping confirmed atomic-level mixing, while HRTEM revealed significant lattice distortion (lattice spacing of 0.28 nm > 0.20 nm for pure Ni). In this composite structure, ultrathin, highly crumpled NC sheets with abundant pores and a large surface area act as a Lewis basic matrix, chemically anchoring lithium polysulfides (LiPSs) through acid–base interactions at pyridinic nitrogen/graphitic nitrogen sites (confirmed by UV-vis) and enhancing conductivity to mitigate sulfur’s insulation. Meanwhile, HEA nanocrystals uniformly dispersed on NC synergistically leverage lattice distortion and the “cocktail effect,” particularly their catalytic sites (Fe²⁺/Co²⁺/Ni²⁺) collaborating with pyridinic nitrogen sites, to dramatically accelerate LiPS conversion (especially the solid-state Li₂S₂→Li₂S step). This lowers the energy barrier (evidenced by increased P3-phase capacity in GDC curves), boosts reaction kinetics (exchange current density of 0.18 mA cm⁻²), and induces reticular, loose Li₂S₂/Li₂S deposition (confirmed by SEM). This dual-site synergistic mechanism of NC anchoring and HEA catalysis enables exceptional practical performance under high sulfur loading and lean electrolyte conditions: a cathode capacity of 1079.5 mAh/g at 72.3% sulfur content (89.4% sulfur utilization); 807.8 mAh/g retention after 160 cycles at 4.4 mg/cm² sulfur loading and lean electrolyte (5 μL/mg) with 0.3% decay per cycle; 868.2 mAh/g (32.4 mAh/cm² area capacity) under ultra-high sulfur loading (27 mg/cm²) and extreme lean electrolyte (3 μL/mg); and 95.2% capacity retention after 970 cycles at a 1 C rate with only 0.05% decay per cycle.

Despite the promise of carbon/HEA composites in Li-S batteries, significant challenges remain. The dissolution and shuttle effect of LiPSs remain critical issues. The complex reaction mechanism (multi-step, multi-electron, various intermediate polysulfides) facilitates LiPS dissolution. While carbon offers some physical confinement, its adsorption capacity is limited, struggling to effectively suppress the shuttle and maintain capacity under lean electrolyte conditions. Regarding catalytic performance, simple-component catalysts lack sufficient activity for the complex 16-electron sulfur redox reactions. Some catalysts suffer from poor electrochemical stability, degrading cycling performance. Although HEAs show potential through multi-element synergy, their synthesis is complex, the precise control of element ratios/distributions is challenging, and cost is high, hindering large-scale adoption. Furthermore, under low-temperature and lean-electrolyte conditions, Li-S batteries face sluggish kinetics, electrolyte gelation, impeded ion transport, and LiPS agglomeration, severely impacting sulfur utilization and cycling stability.

4.6. Zinc–Air Batteries (ZABs)

ZABs rely on efficient ORR and OER reactions. Carbon/HEA composites are often employed as bifunctional catalysts for air electrodes. Carbon materials provide high conductivity, a porous structure for electron transport/reaction interfaces, and a 3D scaffold for dispersing HEA nanoparticles. HEAs leverage multi-element synergy to exhibit superior ORR/OER activity compared to traditional noble metal catalysts (e.g., Pt/C, IrO₂), with lower costs and better corrosion resistance. The synergy between carbon and HEAs optimizes the charge/discharge efficiency and cycling stability, showing significant potential for rechargeable ZABs.

Han et al. synthesized a PtFeCoNiMoY/CNT composite through a simple one-step vapor-phase synthesis strategy [106]. The method utilized pretreated CNTs as a support, where surface defects (functional groups/vacancies) provided uniform nucleation sites for HEA nanoparticles, effectively preventing aggregation. Pt-based hexanary HEA nanoparticles were tightly and uniformly loaded onto the CNTs, forming a single-phase solid solution (lattice spacing matching the (200) plane, with elemental homogeneity confirmed via XPS and TEM). The CNTs not only offer high conductivity, mechanical support, and a stable tubular framework but also enhance mass transport and active site utilization due to their low density, high specific surface area, and porous structure. The incorporation of Mo and Y synergistically modulated the alloy’s d-band center and electronic structure: Mo improved the continuity of spin-up states near the Fermi level, reducing the intermediate adsorption energy; Y shifted the d-band center downward, optimizing the surface adsorption strength. This synergistic electronic structure optimization significantly enhanced catalytic activity, enabling excellent bifunctional oxygen electrocatalytic performance: an OER overpotential of only 238 mV (@10 mA/cm²), an ORR half-wave potential of 0.75 V, and a bifunctional ΔE of 0.713 V. The assembled ZAB exhibited outstanding performance: an open-circuit voltage of 1.41 V, a peak power density of 128.4 mW/cm², a specific capacity of 797 mA·h/g, and stability exceeding 80 h, comprehensively outperforming the benchmark Pt/C + RuO₂ catalyst. Yao et al. developed a novel solid-state thermal reaction strategy to synthesize the HEA@N-GHCT composite [107]. This approach combines a solid-state reaction between multi-metal salts and 2-methylimidazole followed by carbonization, avoiding organic solvent use and offering eco-friendliness and scalability. The resulting material features FeCoNiMnCu high-entropy alloy (HEA) nanoparticles (<100 nm) encapsulated within nitrogen-doped graphitized hollow carbon tubes (GHCTs). Zinc volatilization during carbonization (at 908 K) effectively promotes pore formation, endowing the GHCT with a hollow, porous structure and high specific surface area (489.4 m²/g). These graphitized hollow carbon tubes (GCTs) exhibit high conductivity (from graphitic structure) and chemical stability, with their robust tubular framework preventing HEA nanoparticle aggregation during catalytic reactions (e.g., ORR) and providing efficient electron transfer pathways; their hollow/porous architecture significantly enhances mass transport and reaction kinetics. HEA nanoparticles are tightly encapsulated within the GHCT (confirmed by TEM/EDS, showing uniform distribution of Fe, Co, Ni, Mn, and Cu elements), and the GHCT protection minimizes active site loss. The material’s synergistic mechanism includes the following: graphitized layers (002 plane) and nitrogen doping (pyridinic, pyrrolic, and graphitic nitrogen) optimizing electron transfer and tuning the surface electron density to promote O₂ adsorption/activation; HEA’s synergistic effects (notably Cu’s FCC structure forming a solid solution) optimizing adsorption energies of ORR intermediates (-OH, -O), lowering reaction barriers. The assembled zinc–air battery (ZAB) demonstrates excellent performance: a peak power density of 81 mW/cm², open-circuit voltage (OCV) of 1.36 V, and over 200 h of cycling stability, outperforming the Pt/C-RuO₂ benchmark catalyst in overall performance. Cao et al. synthesized Fe₁₂Ni₂₃Cr₁₀Co₃₀Mn₂₅/CNT composites via liquid-phase reduction combined with high-temperature sintering in an H₂-Ar atmosphere, utilizing acid-treated CNTs as carriers and nucleation sites in Figure 7 [105]. The acid treatment generated surface defects (carboxyl/hydroxyl groups) and rich graphitic structures (002 plane), providing high-density, stable sites for the uniform deposition and reduction of metal ions (Fe, Ni, Cr, Co, Mn). Subsequent sintering resulted in the formation of single-phase FCC solid solution HEA nanoparticles (~30 nm) with uniform element distribution and lattice spacing characteristic of (111) and (200) planes. These HEA NPs were strongly anchored onto the CNTs via defect–particle interactions, forming a core-shell porous structure. The inherent tubular pores and high specific surface area (489.4 m²/g) of the CNTs acted as efficient gas channels and nanoreactors, accelerating mass transport (e.g., O₂/OH⁻ diffusion) for oxygen catalysis while preventing HEA nanoparticle aggregation and exposing abundant active sites. Furthermore, the CNTs’ graphitic structure and N-doping (pyridinic, pyrrolic N) facilitated electron transport. Critically, tuning the Co/Mn ratio (30:25) optimized the HEA electronic structure; the synergy between Co and Mn down-shifted the d-band center to −1.976 eV (confirmed via XPS and DFT calculations), lowering the -OOH adsorption energy (0.32 eV) to accelerate the ORR rate-determining step, while lattice distortion suppressed element dissolution. This “metal-carbon” synergy endowed the composite with superior bifunctional oxygen electrocatalysis: achieving an ORR half-wave potential (E₁/₂) of 0.81 V, an OER overpotential at 10 mA/cm² (E₁₀) of 284 mV, and a remarkably low potential gap (ΔE) of 0.7 V, outperforming the benchmark Pt/C + RuO₂ (ΔE = 0.72 V). Assembled zinc–air batteries demonstrated a peak power density of 128.6 mW/cm², a high specific capacity of 760 mA·h/g, an energy density of 865.5 Wh/kg, and exceptional stability exceeding 256 h with lower degradation than Pt/C + RuO₂.

Despite their advantages, practical applications face challenges. (1) Activity-Stability Trade-off: Selective dissolution of elements in strong alkaline electrolytes can cause activity decay; weak carbon/HEA interfacial bonding may lead to catalyst detachment during volume changes. (2) Complex Synthesis and Cost: Precise HEA composition control and nanoscale dispersion require complex processes (high-temperature sintering, sputtering), hindering scale-up; carbon surface modification to enhance bonding adds cost. (3) Operational Compatibility Issues: Electrolyte migration and Zn dendrite growth can block pores or damage the structure; repeated OER/ORR cycling may cause HEA lattice distortion, affecting durability. 4) Unclear Reaction Mechanisms: The interfacial catalysis mechanism between multi-element HEAs and carbon carriers is not fully understood, hindering theory-guided optimization for targeted performance enhancement.

4.7. Supercapacitors (SCs)

Carbon/HEA composites have demonstrated significant application potential in the field of SCs. Carbon materials, owing to their high specific surface area, excellent conductivity, and outstanding electrochemical stability, serve as ideal electrode materials for SCs. HEAs, benefiting from unique high-entropy effects, sluggish diffusion, and lattice distortion effects, exhibit superior properties in mechanics, electromagnetics, and other aspects, presenting new opportunities for enhancing supercapacitor electrode performance [51]. Research indicates that electrodes composed of HEA nanoparticles/carbon nanofibers, prepared via specific methods at certain precursor concentrations, exhibit a relatively high specific capacitance and specific energy density.

Shen et al. synthesized HEA-NP@MOL/HCPC composites through an adsorption–reductio–-carbonization strategy: Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, and Sn²⁺ metal ions were adsorbed onto a hypercrosslinked polymer, in situ reduced by NaBH₄ to form high-entropy alloy nanoparticles (HEA-NPs), and subsequently carbonized at 800 °C [108]. This process yields a ternary “metal core-oxide shell-carbon carrier” structure. The carbonized hypercrosslinked polymer-derived carbon (HCPC) retains a stable 3D porous framework with abundant micropores/mesopores (pore size ~3–4 nm) and a high specific surface area (1330 m²/g), providing ample adsorption sites for the uniform dispersion of HEA-NPs (8–135 nm) and rigid support to prevent their aggregation. Crucially, during carbonization, a nanoscale metal oxide layer (MOL, ~1–2 nm thick) spontaneously forms on the HEA-NP surface; this amorphous MOL, comprising multi-component oxides (Fe₂O₃, Co₃O₄, NiO, CuO, SnO₂), creates a “crystalline core (HEA)-amorphous shell (MOL)” interface that exposes numerous redox-active sites. The HCPC’s graphitic carbon skeleton provides efficient electron conduction paths and contributes electric double-layer capacitance (EDLC) via ion adsorption/desorption. Simultaneously, the MOL delivers significant pseudocapacitance through rapid multivalent metal ion (e.g., Fe³⁺/Fe²⁺, Co³⁺/Co²⁺) redox reactions, enhanced by d-band center tuning for improved OH⁻ adsorption. The synergy between these components—the MOL (dominant pseudocapacitance), the HCPC porous structure (facilitating ion diffusion and EDLC), and the HEA-NP metallic core (ensuring fast electron transport)—drives exceptional performance. The optimized HEA-NP@MOL/HCPC-2.0 composite (with only 4.4 wt% MOL contributing ~420 F/g enhancement over pure HCPC) achieved a high specific capacitance of 495.4 F/g at 0.5 A/g in 1 M KOH, remarkable cycling stability (94.7% capacitance retention after 15,000 cycles), and fast kinetics (88.9% capacitance contribution at 200 mV/s). Mohanty et al. synthesized Fe-Co-Ni-Cr-Mn HEA/green carbon composites (FCNCM@Green Carbon) through induction melting, ball milling, and the pyrolysis of rice husk, utilizing a 50:50 mass ratio [109]. The rice husk-derived green carbon forms a stable porous framework with the optimized mesoporous structure (BET SSA = 25 m²/g), preserving the natural biomass architecture to provide abundant loading sites and prevent HEA nanoparticle aggregation. Agglomerated FCNCM HEA nanoparticles (~520 nm) with multivalent oxide surfaces are uniformly dispersed within this carbon network, creating a synergistic “EDLC-pseudocapacitance” system. The green carbon contributes electric double-layer capacitance (EDLC) via its porous skeleton that facilitates electrolyte ion adsorption/diffusion, while the HEA nanoparticles deliver pseudocapacitance through rapid redox reactions of Fe/Co/Ni multivalent ions, with surface lattice distortion lowering the reaction overpotential. This synergy shortens ion diffusion paths, reduces electrode polarization, and enhances kinetics. Electrochemically, the composite achieved a specific capacitance of 450 F/g at 2 A/g (3 M KOH, three-electrode) with a 1.3 V voltage window. In symmetric aqueous supercapacitors, it delivered 78 F/g at 1 A/g, an energy density of 33.5 Wh/kg, a power density of 1800 W/kg (1.8 V), and 95.6% capacitance retention after 5000 cycles, significantly outperforming pure HEA or biochar electrodes. The biomass-derived carbon’s sustainable properties further amplify the composite’s functional efficacy, demonstrating green carbon’s critical role in dispersing HEA and boosting electrochemical activity. Xu et al. synthesized FeNiCoMnMg HEA-NPs/ACNFs composites via a carbothermal shock (CTS) strategy combined with self-designed aligned carbon nanofibers (ACNFs) derived from electrospun polyacrylonitrile (PAN) precursors in Figure 7 [54]. The ACNFs exhibit an oriented architecture, superior conductivity, and high specific surface area, providing ordered electron transport pathways and enhanced surface wettability to uniformly anchor ~30 nm HEA nanoparticles while preventing aggregation. Crucially, the CTS process—directing current along the fiber axis—converts metal chlorides into uniformly dispersed high-entropy solid solution NPs, with alloying-induced electron binding energy shifts ensuring tight HEA–carbon contact for efficient charge transfer. The aligned fiber structure simultaneously shortens ion diffusion paths and maintains structural integrity. Electrochemically, the composite leverages dual synergies: the ACNF skeleton delivers rapid electron conduction and stable mechanical support, while HEA-NPs provide rich redox-active sites through high-entropy effects and lattice distortion. At a 5 mM precursor concentration, the optimized FeNiCoMnMg/ACNFs achieved a specific capacitance of 203 F/g, an energy density of 21.7 Wh/kg, and 89.2% capacitance retention after 2000 cycles—significantly surpassing the performance of random CNF carriers. These gains are attributed to the oriented conductive network, homogeneous NP distribution via CTS, and enhanced interfacial kinetics, establishing ACNFs as an ideal substrate for maximizing HEA-NP activity.

However, the practical application of these composites still faces several challenges. Precise control of the HEA nanoparticle size remains challenging; achieving uniform dispersion and strong bonding with the substrate material is difficult. For instance, in constructing HEA/carbon nanotube (CNT) composite electrodes, existing bulk preparation techniques struggle to achieve effective combination. The wettability between different metals and CNTs varies significantly, and fundamental studies on HEA-CNT wettability are lacking, making it difficult to improve compatibility and achieve strong interfacial bonding. While composites show advantages, the further enhancement of energy density is needed to meet high-performance demands. Some materials suffer from capacity fading or structural degradation during long-term cycling, impacting the supercapacitor lifespan. Introducing electrochemically active sites into the carbon skeleton increases pseudocapacitance but often leads to sluggish reaction kinetics and compromises the structural robustness of the carbon framework. This results in the rapid decay of electrode activity and insufficient cycling stability. The performance comparison of different batteries is shown in

Table 2. Comparison of different battery performances.

Type	Material	Capacity	Stability	Ref.
LIBs	HEAs/C	1462 mAh/g	1600 h	[38]
	HEA/C	1881 mAh/g	63.6% after 1000 cycles	[68]
	FeCoNiMnCuAl@C	27,664 mAh/g	134 cycles	[93]
	FeCoNiCuRu/CNFs	6160 mAh/g	550 cycles	[94]
LMBs	HEA/PCF	177.9 mAh/g	99.5% after 200 cycles	[55]
	HEA/CF	197.9 mAh/g	99.2% after 160 cycles	[67]
	HEA/C	166.3 mAh/g	99.5% after 160 cycles	[95]
Li-O2	Pt HEAs@N-C	1000 mAh/g	240 cycles	[96]
	PtFeCoNiCu@rGO	13,949 mAh/g	148 cycles	[97]
	HEAs/C	4000 mAh/g	2000 h	[98]
SIBs/PIBs	FeCoNiAlZn@CNT	10 mAh/cm2	93.7% after 200 cycles	[99]
	HEAs-NPs@NC	513 mAh/g	96.6% after 3000 cycles	[100]
	HEA-N-PCNF	120 mAh/g	2350 h	[101]
	HEA-CNFs	1164 mAh/g	1400 mAh/g after 1000 cycles	[102]
Li-S	PCFCN-HEA/HCS/HCNB	1221.6 mAh/g	82.9% after 200 cycles	[103]
	CNT/HEA-NC	622.5 mA h/g	only 0.03% per cycle after 300 cycles	[104]
	FeCoNiCuMn HEA-NC	1079.5 mAh/g	0.3% per cycle for 160 cycles	[64]
ZABs	PtFeCoNiMoY/CNT	797 mA·h/g	80 h	[106]
	FeCoNiMnCu HEA@N-GHCT	630.29 mA·h/g	>200 h	[107]
	Fe12Ni23Cr10Co30Mn25/CNT	760 mA·h/g	256 h	[105]
SCs	HEA-NP@MOL/HCPC	495.4 F/g	94.7% after 15,000 cycles	[108]
	FCNCM@Green carbon	450 F/g	94.7% after 15,000 cycles	[109]
	FeNiCoMnMg HEA-NPs/ACNFs	203 F/g	89.2% after 2000 cycles	[54]

.

5. Summary and Outlook

This review systematically summarizes the research progress on carbon material/ HEA nanocomposites in the field of EES. Carbon materials, with their high conductivity, large specific surface area, and chemical stability, provide excellent electron transport pathways and structural frameworks for energy-storage systems. HEAs, leveraging high-entropy effects, lattice distortion effects, and sluggish diffusion effects, exhibit unique catalytic activity and structural stability. The synergistic effects arising from their combination significantly enhance material performance in EES systems, including LIBs, SIBs/PIBs, Li-S, and SCs through electronic structure optimization, enhanced structural stability, and functional complementarity. This represents a crucial pathway for overcoming the performance bottlenecks of traditional energy storage materials. However, carbon/HEA composites still face the following core challenges:

(1)

Complex and Costly Synthesis: The multi-principal element nature of HEAs makes the precise control over synthesis difficult, requiring meticulous regulation of elemental ratios and reaction conditions. Traditional HEA preparation often relies on high temperatures, high pressures, and inert atmospheres, demanding stringent equipment specifications, significantly increasing energy consumption and production costs, and severely hindering large-scale production. Elemental segregation during multi-component mixing affects material homogeneity and reproducibility, leading to inconsistent product quality.

(2)

Ambiguous Interfacial Interaction Mechanisms: The interfacial bonding strength and interaction mechanisms between carbon materials and HEAs remain unclear. During electrochemical cycling, differences in thermal expansion coefficients and chemical activity can cause stress concentration and structural mismatch at the interface, reducing interfacial stability. This can lead to composite structural failure, shortening the cycle life of energy storage devices and impacting long-term operational stability.

(3)

Lagging Theoretical Research: While experiments demonstrate the excellent performance of carbon/HEA composites in EES, theoretical research providing a deep understanding of their intrinsic mechanisms at the atomic and electronic levels lags behind. The microscopic action mechanisms of high-entropy effects in complex composite systems are debated. The lack of comprehensive theoretical models hinders material design, performance optimization, and the full exploitation of material potential.

(4)

Performance-Cost Trade-off: Pursuing high performance often necessitates the use of rare or expensive elements in HEAs, increasing material costs. However, energy-storage devices are highly cost-sensitive in practical applications. Achieving a balance between high performance and low cost is a critical challenge for the large-scale adoption of these materials.

(5)

Slow Industrialization Process: Transitioning from lab-scale R&D to industrial production presents numerous obstacles for carbon/HEA composites. Existing preparation processes struggle to meet large-scale demands, lacking standardized production workflows and quality control systems. Furthermore, the incomplete industry chain and insufficient upstream–downstream collaboration further delay industrialization.

Future Research Hotspots and Priorities:

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Precise Multi-scale Structural Design and Control:

• Atomic Scale: Utilize advanced computational simulations (e.g., Density Functional Theory—DFT) to precisely control the HEA elemental composition and ratio, optimize the electronic structure, and precisely regulate active sites.
• Nanoscale: Finely tune the HEA nanoparticle size, shape, and distribution, combined with the nanostructural features of carbon materials (e.g., graphene layer number, CNT diameter/length), to achieve efficient synergy.
• Macroscale: Construct composites with three-dimensionally ordered porous structures, optimizing the pore architecture and connectivity to promote ion transport and electrolyte wetting, enhancing the overall energy-storage performance. Examples include designing gradient-structured composites for efficient ion transport/storage across scales and boosting the energy density, power density, and cycling stability.

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Cross-disciplinary Integration for New Material Systems: Integrate knowledge from materials science, chemistry, physics, and computational science to develop novel HEA systems and carbon/HEA composites.

• Materials Science: Focus on synthesis, structural characterization, and performance testing.
• Chemistry: Deepen understanding of reaction mechanisms and surface chemistry.
• Physics: Provide theoretical support from perspectives of electronic structure and energy conversion.
• Computational Science: Employ machine learning, molecular dynamics simulations, etc., to accelerate material screening and design. Use machine learning algorithms to screen HEA components with specific properties, combined with experimental validation, to develop high-performance composites for novel energy-storage/conversion devices (e.g., all-solid-state batteries, fuel cells), expanding application fields.

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Innovation and Development of Sustainable Synthesis Technologies: Develop green, low-energy-consumption synthesis technologies for sustainable material production.

• Explore bio-templating methods, utilizing specific structures of biomacromolecules or microorganisms to synthesize complex-structured composites, reducing chemical usage and energy consumption.
• Optimize existing processes (e.g., improved Joule heating for precise control and higher energy efficiency, lowering costs).
• Enhance research on recycling and reuse technologies to achieve green practices throughout the material lifecycle, laying the foundation for large-scale application.

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Deep Application of Intelligent In situ Characterization Techniques: Employ intelligent in situ characterization techniques:

• In situ XRD: Real-time monitoring of crystal structure evolution during cycling.
• In situ TEM: Observation of nanostructural and interfacial changes.
• In situ XPS: Analysis of surface element chemical states and electronic structure evolution.

These techniques provide deep insights into performance change mechanisms under operating conditions, enabling the establishment of accurate structure–property relationship models to guide material optimization design and performance enhancement, accelerating R&D of novel composites.

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Material Surface Engineering Optimization: Utilize surface modification techniques (e.g., ALD, CVD) to introduce functional coatings or active sites onto composite surfaces.

• Coatings can improve hydrophilicity/hydrophobicity, optimize electrolyte wettability, and promote fast ion transport.
• Introducing active sites can enhance electrocatalytic activity and reduce reaction overpotentials (e.g., depositing ultra-thin metal oxide coatings to boost ORR catalytic performance in ZABs, improving efficiency and stability).
• Surface engineering can also enhance corrosion resistance, preventing HEA oxidation/dissolution in electrolytes and extending device lifespan.

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Research on Novel Electrolyte Compatibility: Develop novel electrolytes highly compatible with carbon/HEA composites for different systems (e.g., LIBs, Li-S).

• Create electrolytes with high ionic conductivity, wide electrochemical windows, and good thermal stability, suppressing polysulfide shuttling in Li-Ss.
• Improve electrode–electrolyte interfacial compatibility using special additives or ionic liquid solvents, enhancing the cycle performance and Coulombic efficiency.
• Deeply study interaction mechanisms between electrolytes and composite surfaces to optimize formulations, reduce side reactions, and improve device safety and reliability.

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Research on Dynamic Response Mechanisms of Composite Structures: Utilize advanced characterization and numerical simulations to deeply investigate the dynamic response mechanisms during cycling:

• Structural evolution, stress distribution changes, and electrochemical reaction kinetics.
• Molecular dynamic simulations of HEA nanoparticle diffusion within the carbon matrix and interaction changes during cycling.Understanding these mechanisms aids in optimizing material design, improving stability and reliability under complex operating conditions, and providing a theoretical basis for high-performance devices.

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Device Integration and System Optimization: Extend research from electrode materials to the level of complete energy-storage device systems for integration and optimization.

• Study the compatibility and synergy between internal components (e.g., electrode-separator–electrolyte interfaces).
• Optimize device structure design to increase energy/power density.
• Tailor thermal management, safety management, and energy-management strategies to application scenarios (e.g., develop efficient heat dissipation structures, design safety mechanisms against overcharge/overdischarge/thermal runaway).

This will propel the practical application of composites in large-scale energy storage.

Carbon/HEA composites, through multi-element synergy and cross-scale structural design, provide revolutionary solutions for next-generation EES technologies. Future research must focus on core directions like intelligent design, dynamic interface regulation, and green manufacturing. Multi-disciplinary integration will drive their transition from the laboratory to industrialization, ultimately enabling the large-scale application of energy-storage systems characterized by high energy density, high safety, and environmental friendliness.