A Comprehensive Review on the Rapid Development of Silicon/MXene Nanocomposites for Lithium-Ion Battery Applications

Abstract

Silicon (Si) has attracted extensive attention as a promising anode material for next-generation lithium-ion batteries (LIBs) due to its ultra-high theoretical capacity, low lithiation potential, and economic advantages. However, drastic volume expansion during cycling and slow reaction kinetics severely compromise its structural stability and practical application. Recently, two-dimensional (2D) MXenes have been explored as effective functional components in Si-based electrodes because of their excellent electrical conductivity, high specific surface area, adjustable surface terminations, and mechanical robustness. When integrated with Si, MXenes serve as conductive matrices that alleviate volumetric stress, enhance charge transport, and accelerate electron/ion diffusion. Consequently, Si/MXene nanocomposites (NCs) exhibit significantly improved lithium (Li) storage performance. This review outlines recent advances in Si/MXene NCs, covering fabrication strategies, structural engineering, and various configurations, including particulate materials, three-dimensional (3D) architectures, films, and fibrous systems, and establishes the relationship between structural design and electrochemical behavior. Remaining challenges and prospective research directions are also discussed to guide the development of high-energy-density LIB anodes.

1. Introduction

Heavy dependence on traditional fossil fuels has led to severe environmental degradation and escalating energy shortages, prompting rapid expansion of sustainable renewable resources such as solar, wind, and tidal energy [1,2,3,4,5,6,7]. However, the fluctuating and intermittent nature of these energy sources necessitates efficient energy storage (ES) technologies capable of supplying reliable and regulated power for applications including electric vehicles, portable electronics, and grid-scale storage systems [8,9,10,11,12,13,14]. Among existing ES technologies, lithium-ion batteries (LIBs) are particularly attractive because of their high energy and power densities, extended cycling stability, and absence of memory effect [15,16,17,18]. Nevertheless, increasing demands for higher energy density and longer operational lifespan have exposed the intrinsic limitations of graphite anodes, whose theoretical capacity of 372 mAh/g is insufficient for next-generation requirements.

Among potential anode materials for LIBs, silicon (Si) stands out as a leading candidate for next-generation high-energy storage. Its advantages include: (i) an ultrahigh theoretical capacity of ~4200 mAh/g via full lithiation to Li₂₂Si₄, exceeding that of graphite by more than an order of magnitude; (ii) a relatively low lithiation plateau (~0.3 V vs. Li/Li⁺), which allows a broad operating voltage window and suppresses Li dendrite growth [19,20,21]; and (iii) high natural abundance, low toxicity, and environmental compatibility, supporting scalable and cost-efficient deployment [22,23,24]. Despite these merits, severe volume expansion (~360%) during alloying with Li induces particle pulverization, unstable solid electrolyte interphase (SEI) formation, and mechanical degradation, ultimately leading to rapid capacity fading and poor cycling durability (Figure 1). Furthermore, the intrinsically low electrical conductivity of Si (~10⁻³ S/cm) restricts charge-transfer kinetics [22,25,26]. To mitigate these issues, Si suboxides (SiO_x, 0 < x ≤ 2) have been investigated as alternative anodes, offering high theoretical capacities (2200–3850 mAh/g) with reduced volume variation (~200%) [27,28]. Nevertheless, SiO_x still struggles to achieve stable and fast Li storage performance.

Conductive carbon (C) materials, including graphite [29], graphene [30] and C nanotubes (CNTs) [31], have long been integrated into Si anodes to mitigate volume expansion and improve electrical conductivity. However, their contribution is primarily confined to forming passive conductive frameworks and mechanical reinforcement. In comparison, MXenes possess several intrinsic characteristics that differentiate them from traditional C allotropes. They exhibit metallic-level conductivity without the need for high-temperature graphitization and contain abundant surface terminations (-O, -OH, -F, -Cl) that promote strong interfacial interactions, including possible covalent bonding (e.g., Ti-O-Si and Ti-Si linkages), thereby enhancing structural stability during cycling [32,33,34]. Furthermore, the hydrophilic nature and excellent aqueous dispersibility of MXenes enable homogeneous integration with Si particles without complicated surface treatments. Their flexible layered structure allows them to serve multiple roles simultaneously, such as conductive frameworks, mechanical buffers, binders, and even lightweight current collectors. Additionally, adjustable interlayer spacing and surface chemistry facilitate Li-ion transport and help regulate SEI formation by minimizing direct contact between Si and the electrolyte. These combined advantages position MXenes as multifunctional components rather than simple conductive additives, highlighting the significance of Si/MXene NCs beyond conventional Si/C systems [35].

MXenes are typically produced through selective removal of the A-layer elements (primarily group IIIA and IVA elements) from their parent MAX phases, resulting in two-dimensional (2D) compounds with the general formula M_n+1X_nT_x. In this structure, M represents an early transition metal (such as Ti, V, Mo, or Nb), X refers to carbon and/or nitrogen, n ranges from 1 to 4, and T_x denotes surface terminations (e.g., -O, -Cl, -S) (Figure 2a,b) [32,33,34]. Various synthesis routes have been developed for MXene preparation. Conventional approaches include fluorine (F)-containing etchants such as HF [35], LiF/HCl [36], NH₄HF₂ [37] and SF₆ [38], as well as F-free methods like Lewis acidic molten-salt etching [39]. For example, treatment of Ti₃AlC₂ in molten ZnCl₂ at elevated temperatures (~550 °C) selectively removes Al layers, followed by vacuum distillation to eliminate Zn by-products, yielding Cl-terminated Ti₃C₂Cl_x [40]. Similar molten-salt strategies have been extended to other MAX precursors, including Nb₂AlC, Nb₂AlN, and Nb₄AlC₃. More recently, chemical vapor deposition (CVD) techniques employing CH₄ and titanium chlorides (TiCl₄ [41] or TiCl₃ [42]) have enabled direct synthesis of Cl-terminated Ti₂C MXene, offering potential for scalable production. To date, more than 50 MXene compositions have been reported, with projections exceeding 100 when accounting for solid-solution systems and varied surface terminations [43]. Owing to their layered morphology, MXenes exhibit adjustable electrical conductivity, abundant functional groups, high mechanical strength, and structural flexibility, making them promising materials for energy storage [44], catalysis [45], sensing [46], and electromagnetic interference shielding [47].

In addition to improving electrical conductivity, MXenes significantly alleviate the extreme volume variation in Si anodes during repeated lithiation and delithiation. Their mechanically robust and flexible 2D architecture enables MXene sheets to function as conductive frameworks that physically restrain Si nanoparticles (NPs) while accommodating their expansion and contraction [40]. The rich surface terminations (-O, -OH, -F, -Cl) further promote strong interfacial coupling or even covalent bonding (e.g., Ti-O-Si and Ti-Si), which enhances structural cohesion and preserves electrical connectivity during cycling [24,44]. Meanwhile, MXene layers can partially isolate Si from direct electrolyte exposure, facilitating the formation of a uniform and stable SEI and suppressing parasitic side reactions. Through these combined effects, MXene-based composites effectively relieve mechanical stress, maintain electrode integrity, and improve long-term cycling performance [21]. The increasing volume of related publications highlights the growing attention toward MXenes as emerging 2D materials (Figure 2c). In energy storage systems, they serve as versatile conductive matrices for hybridization with Si and other active phases such as metal oxides and sulfides. Since the initial demonstration of Si@Ti₃C₂ prepared via ultrasonic assembly [48], diverse Si/MXene configurations, including spherical [49], fibrous [50], film-like [51] and powder forms [52], have been developed for Li storage applications.

While numerous review papers have addressed Si-based anodes, MXene materials for energy storage, and Si/C composite systems (Figure 2d), a comprehensive review specifically centered on Si/MXene NCs remains absent. Most existing literature discusses MXenes and Si separately or briefly mentions Si/MXene hybrids within broader material classifications, without systematically linking synthesis methods, interfacial interactions, structural design, and electrochemical behavior. Furthermore, insufficient attention has been devoted to understanding how different fabrication strategies influence the multifunctional roles of MXenes, such as conductive frameworks, mechanical buffers, binders, and even current collectors in Si electrodes. To address this research gap, this review presents a systematic and critical overview of Si/MXene NCs, categorized according to their synthesis routes and structural forms, including powders, thin films, 3D porous frameworks, and fibrous structures (Figure 3). By establishing clear relationships among fabrication strategies, interfacial interactions, microstructural evolution, and Li-storage performance, this work aims to clarify the fundamental design principles for high-efficiency Si/MXene anodes. In addition, the strengths, drawbacks, and scalability of various preparation methods are comparatively evaluated from both scientific and practical viewpoints. The review concludes by identifying key challenges and proposing future research directions to advance next-generation Si/MXene electrodes for high-energy LIBs.

In recent years, several review articles have addressed related topics from different perspectives. Reviews on Si-based anodes mainly focus on strategies to mitigate volume expansion through nanostructuring, alloying, and composite design, but typically emphasize general performance improvements without systematically comparing practical metrics such as initial Coulombic efficiency (ICE), mass loading, or areal capacity [23,26]. Reviews on MXenes for energy storage primarily discuss synthesis methods, surface chemistry, and their applications in various electrochemical systems, while the role of MXenes in stabilizing high-capacity alloy-type anodes is often only briefly mentioned [32,34]. In addition, numerous reviews on Si/C composites summarize conductive buffering strategies but rarely consider the unique interfacial chemistry introduced by MXene surface terminations [54,55]. A few recent reports have mentioned Si/MXene hybrid systems [51,56]; however, these discussions are generally descriptive and lack consistent evaluation criteria, particularly regarding cycling duration, electrode mass loading, and cell configuration (half-cell vs. full-cell), which are critical for assessing practical relevance. Therefore, a comprehensive and critical analysis specifically focused on Si/MXene NCs remains necessary. In this review, we aim to fill this gap by systematically comparing reported Si/MXene systems using practical performance indicators (ICE, capacity retention, mass loading, areal capacity, and testing duration), while emphasizing structure–interface–performance relationships and identifying design principles for balancing capacity, stability, and scalability.

2. Preparation of Si/MXene NCs

2.1. Electrostatic Self-Assembly

Electrostatic self-assembly is an ex situ fabrication technique that constructs hybrid structures by attracting oppositely charged species at their interface. In aqueous environments, MXene sheets carry negative surface charges due to their high aspect ratio and abundant oxygen (O)-containing functional groups, making them well-suited for this method. Beyond structural integration, MXenes function as conductive backbones, facilitating efficient electron transfer across the heterointerfaces of the assembled NCs [57].

To achieve electrostatic interaction with negatively charged MXene sheets, Si NPs must first acquire a positive surface charge through appropriate functionalization. This is commonly accomplished using cationic surfactants, which introduce positively charged groups onto the Si surface. For example, poly(diallyldimethylammonium chloride) (PDDA) can be deposited onto Si NPs via a simple solution-mixing process, resulting in a pronounced positive zeta potential of +66.9 mV (Figure 4a,b) [58]. This surface modification enhances both the positive charge density and aqueous dispersibility of Si particles. Upon mixing PDDA-treated Si with MXene dispersions, electrostatic attraction drives the attachment of Si@PDDA onto negatively charged MXene sheets, partially neutralizing their surface charge. The interaction leads to the formation of large aggregates that settle with a transparent supernatant (Figure 4c). The assembled Si@PDDA@MXene composite exhibits an intermediate zeta potential of +33.8 mV, confirming successful electrostatic coupling. Besides PDDA, other cationic agents, including cetyltrimethylammonium bromide (CTAB) [59], (3-aminopropyl) triethoxylsilane (APTES) [60] and iodine-acetone systems [61] have also been employed to endow Si with positive surface charges.

The C coating has been applied either before or after electrostatic self-assembly to enhance the mechanical integrity of Si/MXene NCs. For instance, ZIF-8 can be grown on amino-modified Si/Ti₃C₂T_x assembled through electrostatic interactions; subsequent pyrolysis generates an in situ C layer that encapsulates the Si/Ti₃C₂T_x structures, forming a 3D sandwiched Si/Ti₃C₂T_x@C composite (Figure 4d,e) [60]. In this architecture, Ti-O-Si bonds are established between the MXene substrate and Si NPs, while the outer C shell forms Si-C bonds, jointly improving structural durability and electrochemical stability during repeated lithiation/delithiation (Figure 4f,g). Alternatively, Si spheres can be C-coated prior to PDDA functionalization [62]. This C layer supplies additional adsorption sites for surfactants, thereby promoting electrostatic assembly with MXene and yielding a MXene-Si@C hybrid with a continuous conductive network and internal void space capable of accommodating volume expansion.

Polymethyl methacrylate (PMMA) carries plentiful positive surface charges due to the incorporation of cationic surfactants as stabilizers and comonomers during dispersion polymerization. This characteristic allows PMMA to serve as an alternative interfacial mediator that promotes self-assembly between MXene nanosheets (NSs) and Si NPs. For instance, Xia et al. [49] coated porous Si nanospheres (Si p-NS) with a PMMA layer, enabling subsequent electrostatic assembly with Ti₃C₂T_x NSs. After pyrolysis, the PMMA decomposed, resulting in a Si/Ti₃C₂T_x core–shell structure with improved interfacial coupling. Electrostatic assembly can also be combined with additional synthetic methods. In one example, CTAB-modified Si NPs were electrostatically anchored onto MXene NSs to form MXene-encapsulated Si hybrids (SiNP@MX1) [63]. These hybrids were then incorporated into a 3D MXene scaffold through hydrothermal processing and freeze-drying, producing a hierarchical porous electrode with dual MXene protection (Figure 4h,i). In another study, Liu’s group [64] prepared a Si@Ti₃C₂T_x@graphene monolith via a multistep process involving electrostatic self-assembly, solvothermal treatment, air drying, and annealing. Initially, Si@Ti₃C₂T_x hybrids formed through electrostatic attraction and were subsequently embedded into a graphene hydrogel under solvothermal conditions. During drying and annealing, the hydrogel shrank into a dense monolith, yielding a composite with a density of 1.5 g/cm³ and an electrical conductivity of 151 S/cm.

Electrostatic self-assembly is a simple and efficient strategy for fabricating Si/MXene NCs with strong interfacial interactions between their constituents. However, this method generally necessitates surface functionalization of Si to enable electrostatic attraction. The incorporation of surfactant molecules introduces bulky organic groups that may hinder electron transport and consequently lower the electrical conductivity of the composites. To address this limitation and improve electrochemical performance, a post-synthesis thermal treatment is commonly applied to remove residual surfactants.

2.2. Ball-Milling

Ball-milling is a commonly used ex situ technique for integrating MXene with Si-based materials. In a typical process, Si NPs are mixed with MXene in a sealed vial and subjected to high-speed milling. The strong shear forces generated by the rapid motion of the milling balls provide sufficient energy to induce robust interfacial bonding between the two components, thereby forming stable NCs [65,66]. Nevertheless, the high-energy environment may also trigger oxidation and structural degradation of MXene owing to its intrinsic instability. To alleviate this problem, ball-milling is usually performed under an inert atmosphere, and the incorporation of a third component can further reduce shear stress while acting as an interfacial bridge between MXene and Si. For example, ternary Ti₃C₂T_x-Si-CNT NCs were produced by milling MXene and Si in the presence of 2 wt % CNTs, which enhanced structural robustness (Figure 5a–c) [65]. During the milling process, reactive Si NPs form Ti-Si bonds with MXene and C-Si bonds with CNTs (Figure 5d), both of which are essential for stabilizing the composite framework for energy-storage applications. The milling speed critically influences the structural integrity of the Ti₃C₂T_x-Si-CNT NCs composites. At a low speed of 100 rpm, the obtained materials show poor structural homogeneity, whereas increasing the speed to 300 rpm leads to the formation of an electrochemically inactive TiSi₂ phase (Figure 5e,f), as revealed by XRD analysis. The presence of this phase hinders lithiation/delithiation processes and consequently deteriorates the electrochemical performance.

Ball-milling can be employed to fabricate Si-P nanohybrids with a core–shell architecture, offering a high theoretical Li-storage capacity of approximately 2900 mAh/g. Building on this strategy, Tang et al. [67] integrated the Si-P nanohybrid with Ti₃C₂T_x, yielding a Si-P/Ti₃C₂T_x composite in which Ti₃C₂T_x served as an outer coating layer. In this configuration, the red phosphorus (red-P) shell functioned as an intermediate layer that enabled the formation of stable Si-P-Ti bonds, thereby maintaining close interfacial contact and structural coherence among Si, red-P, and Ti₃C₂T_x. In a related study, SiO_x was combined with multilayer Ti₃C₂T_x via ball-milling [68]. Melamine was introduced as a third component because of its low adsorption energy on Ti₃C₂T_x surfaces, arising from its amino and triazine groups. These interactions promoted melamine intercalation into MXene interlayers, and under strong shear forces, facilitated exfoliation of MXene into crumpled flakes that attached to SiO_x through strong Ti-O-Si bonds. After annealing, melamine was removed, while residual N-atoms remained doped within the MXene matrix, improving its electrochemical performance.

Due to its operational simplicity and high efficiency, ball-milling presents significant promise for the scalable production of Si/MXene NCs for energy-storage applications. However, the structural characteristics and electrochemical performance of the resulting composites are highly sensitive to several key parameters, such as the particle size and content of Si, the type of added guest species, and the milling speed and time. Therefore, systematic optimization of these variables is crucial for promoting the practical deployment of ball-milled Si/MXene NCs.

2.3. Vacuum Filtration

Vacuum filtration is an efficient separation method that allows rapid recovery of solids from liquid suspensions by utilizing a pressure differential across the filter membrane. Due to their 2D lamellar structure, MXene NSs are particularly suitable for assembling films via vacuum filtration of mixed dispersions containing MXene and various active materials, including graphene [69], CNTs [70], transition-metal oxides [71] and Si [72,73]. During filtration, MXene NSs tend to align parallel to the filter surface, thereby embedding the active components within flexible and free-standing nanostructured films. To ensure uniform dispersion, especially for Si in aqueous systems, ultrasonication or continuous stirring is typically employed. For example, a MXene-Si@C hybrid film can be fabricated by mixing dispersions of MXene and Si@C followed by vacuum filtration (Figure 6a) [73]. In this configuration, MXene functions simultaneously as a conductive pathway, binder, flexible scaffold, and buffering matrix for Si. SEM observations indicate that interconnected MXene flakes form a cross-linked porous network, enabling uniform distribution of Si@C within the MXene matrix (Figure 6b–d). The resulting porous framework enhances active surface exposure and establishes a well-developed mesoporous structure (Figure 6e,f), which helps alleviate Si volume expansion during lithiation while facilitating rapid electron and ion transport. Furthermore, the lamellar 2D architecture of MXene endows the film with excellent mechanical flexibility, allowing it to withstand bending, twisting, rolling, and folding. Notably, the film can be folded into intricate shapes such as a windmill (Figure 6g), demonstrating its promise for flexible and wearable electronics.

Vacuum filtration is widely considered an effective approach for fabricating MXene/Si film electrodes. However, their electrochemical performance is highly dependent on several key parameters, such as the lateral size of MXene sheets, the particle size of Si, and the overall Si content. Larger MXene flakes can enhance the mechanical strength and flexibility of the composite film, yet they tend to orient perpendicular to the electrode surface, which lengthen electron and ion diffusion pathways and thus restrict rate capability. Likewise, the size of Si particles critically affects the pore structure, specific surface area, and mechanical stability of the electrode. In addition, excessive Si loading may cause mechanical degradation and poor cycling durability due to its substantial volume expansion during lithiation, whereas too little Si results in underutilization of active sites because of compact MXene stacking. Therefore, rational structural design of MXene/Si films is necessary to balance mechanical robustness, flexibility, pore architecture, and electrochemical performance.

2.4. Blade Casting

Blade casting provides an effective approach for achieving ordered alignment of MXene NSs embedded with Si NPs. In contrast to vacuum filtration, this technique requires the formulation of a concentrated MXene slurry and is typically conducted on conductive substrates such as Cu foil commonly used in LIBs. In a representative study, Zhang et al. [74] utilized a Ti₃C₂T_x dispersion (25 mg/mL) as a conductive binder for Si-based electrodes. Nanosized Si or Si/graphene composites were milled directly in the MXene ink to form homogeneous slurries, which were then cast onto Cu foil and vacuum-dried to produce MXene-coated nSi or Gr-Si electrodes (Figure 6h,i). Electrodes encapsulated with Ti₃C₂T_x containing 30 wt % MXene exhibited high electrical conductivities of 3448 S/m for nSi and 5333 S/m for Gr-Si, while also retaining mechanical stability during repeated bending (Figure 6j,k). The electrode properties were strongly influenced by the concentration of the Ti₃C₂T_x ink; a concentration of 25 mg/mL enabled uniform coating on Cu foil and imparted favorable rheological properties, including high viscosity, storage modulus, and loss modulus, allowing the fabrication of thick films up to 650 µm for nSi and 2100 µm for Gr-Si electrodes. Moreover, the Ti₃C₂T_x-encapsulated Gr-Si electrode exhibited a critical cracking thickness of 351 µm, substantially higher than that of Gr-Si electrodes prepared with conventional binders (<100 µm), highlighting the mechanical robustness of MXene inks for practical Si electrode design.

In addition to employing highly concentrated MXene inks, MXene flakes have also been utilized as conductive additives in the fabrication of Si-based electrodes. For example, sodium alginate (SA) can be integrated with Ti₃C₂T_x to form a hybrid conductive binder. When Si particles are mixed with the SA/Ti₃C₂T_x system, blade casting of the viscous slurry onto Cu foil yields Si electrodes [75]. The abundant surface functional groups on Ti₃C₂T_x facilitate strong interactions with both Si and SA, thereby enhancing interfacial adhesion and ensuring stable long-term electrochemical performance. Using Si/graphite (Si/G) composite electrodes as a model system, Mao et al. [76] investigated the influence of Ti₃C₂ MXene additives on lithiation-induced stress through the Halpin–Tsai empirical model. The results indicated that even at low loading levels, Ti₃C₂ significantly increased the elastic modulus of the active layer, with more pronounced reinforcement observed for higher aspect ratios and thinner flakes. In bilayer Si/G electrodes, Ti₃C₂ effectively mitigated tensile stress in the current collector and compressive stress within the active layer; however, when its content exceeded 0.76%, the effect reversed due to an increased stiffness mismatch between the layers. Consequently, incorporating an optimized amount of high-aspect-ratio Ti₃C₂ is beneficial for improving both mechanical robustness and electrochemical performance of Si-based LIB electrodes.

An N-doped C (N-C) interfacial layer was incorporated between MXene and Si to enhance the durability of Si-based anodes [77]. The electrode was prepared by blade-casting a slurry composed of 50 wt % Si, 40 wt % polyacrylonitrile (PAN), and 10 wt % MXene onto copper foil, forming a precursor film. After heat treatment at 700 °C under an Ar/H₂ atmosphere, PAN was transformed into amorphous N-C, which chemically anchored to both Si and MXene through Si-N and N-MXene bonds. This interfacial bonding improved adhesion and reinforced the mechanical stability of the Si-N-MXene electrode. Beyond serving as conductive additives, vacuum-filtered MXene films, with their excellent flexibility, electrical conductivity, lightweight nature, and mechanical robustness, have also been utilized as current collectors [78]. When porous Si, poly(acrylic acid) (PAA), and Super P carbon were coated onto these MXene films, the resulting active layer exhibited stronger adhesion compared with conventional copper collectors. This improvement was attributed to the rich surface terminations of MXene, which enhanced electrical connectivity and structural stability during Li storage.

Blade casting represents a simple and economically viable approach for producing Si/MXene electrodes, offering strong potential for scalable manufacturing. However, similar to vacuum filtration methods, the layered configuration may generate electrochemically inactive (“dead”) regions within the electrode. To overcome this limitation, introducing supplementary structural agents such as CNTs, nanocellulose, or conductive C is advantageous. These components can generate internal porosity to increase accessible active sites and simultaneously bridge the Si and MXene networks, thereby alleviating volume expansion during lithiation.

2.5. Spray/Freeze Drying

Spray drying involves atomizing a homogeneous emulsion or suspension into a heated chamber, where rapid solvent evaporation transforms the droplets into solid NPs. The precursor solution generally contains both core and shell components subjected to appropriate pretreatment, and the surface tension of the shrinking droplets promotes the formation of quasi-spherical particles [79]. For instance, Si@Ti₃C₂T_x MXene microspheres were prepared by blending dispersions of Si and Ti₃C₂T_x, followed by spray drying (Figure 7a) [80,81]. During solvent removal, MXene NSs self-crosslinked via covalent Ti-O-Ti bonds, forming a continuous and mechanically stable MXene network, as confirmed by Ti 2p XPS analysis (Figure 7b). Si NPs were homogeneously confined within the crumpled MXene scaffold, yielding a pomegranate-like architecture with plentiful internal voids (Figure 7c,d). Importantly, the resulting microstructure is highly sensitive to processing variables, including droplet size, feed rate, inlet temperature, gas pressure, and drying gas flow rate, which must be carefully optimized to maximize electrochemical performance.

Unlike spray- or vacuum-drying, freeze-drying involves first solidifying the Si/MXene aqueous dispersion through freezing. During the subsequent sublimation process, the ice crystals act as sacrificial templates, leading to the formation of a highly porous Si/MXene framework. For example, rapid freezing of a Si/MXene suspension using liquid nitrogen produced a solid monolith [82]. Vacuum drying at −50 °C under 10 Pa then facilitated ice sublimation, during which MXene NSs curled and folded due to capillary forces, resulting in a lightweight and porous structure with homogeneously distributed Si NPs. In another study, adjusting the pH of a Si/Ti₃C₂T_x mixture to 10 prior to freeze-drying promoted the self-assembly of MXene NSs into scroll-like morphologies. These structures encapsulated Si NPs within internal cavities, yielding a pea-shaped composite architecture [83]. Although such porous configurations improve ion/electron transport and accommodate Si volume expansion, the absence of strong chemical bonding at the Si-MXene interface, due to simple physical mixing, may weaken structural integrity during long-term cycling.

2.6. Electrospinning

Electrospinning is a versatile technique for producing ultrafine one-dimensional (1D) nanofibers (NFs), 2D nonwoven membranes, and even three-dimensional (3D) structures. In general, polymers can be mixed with Si NPs and MXene NSs in appropriate solvents to form a homogeneous precursor solution. Under a high electric field, the charged polymer jet is elongated into continuous fibers through the combined influence of electrostatic forces, Coulombic repulsion, viscoelastic effects, and surface tension [84,85]. For example, electrospinning a DMF-based suspension containing PAN, Si NPs, and Ti₃C₂T_x flakes yields a composite fibrous membrane [86]. Thermal stabilization at 240 °C followed by carbonization at 600 °C converts PAN into C, producing a flexible Si/MXene@C composite. Yang et al. [87] further compared the effects of various conductive additives, including MXene, graphene oxide (GO), and CNTs on Si@C NFs. The results demonstrated that each additive contributed distinct benefits: MXene enhanced cycling durability and capacity retention, CNTs improved rate performance by lowering charge-transfer resistance, and GO increased reversible Li storage capacity.

Furthermore, the composite NFs were designed with a core–shell architecture by selecting PAN as the shell precursor and Si@Ti₃C₂T_x MXene as the core component (Figure 7e) [50]. This structure was fabricated via coaxial electrospinning, in which the shell and core solutions were delivered separately through the outer and inner channels of a dual-capillary spinneret. After electrospinning, followed by stabilization and carbonization, core–shell NFs were obtained, featuring a carbonaceous shell and a Si@Ti₃C₂T_x MXene-confined core. This process resulted in carbon nanofiber (CNF)-encapsulated Si@Ti₃C₂T_x MXene structures (Figure 7f,g). Additionally, incorporating PMMA into the core precursor allowed it to decompose during carbonization, generating internal voids within the fibers that effectively accommodate the volumetric changes in Si during repeated lithiation and delithiation.

2.7. In Situ Thermal Reduction

Thermal reduction is an in situ approach for transforming silica precursors into Si nanostructures through reactions with reducing agents at elevated temperatures. Traditional carbothermal reduction typically operates at temperatures ≥2000 °C, which surpasses the melting point of Si and thus restricts its practical application. In contrast, the magnesiothermal reduction reaction (MRR) has emerged as a more feasible alternative. In this process, Mg reduces silica within a temperature range of 500–950 °C, producing Si and MgO (Reaction 1) [88]. The MgO by-product can subsequently be removed by HCl treatment, leaving behind a porous Si framework.

SiO₂ + 2 Mg → Si + 2 MgO

(1)

Zhang’s team [52] demonstrated the construction of a Ti₃C₂ MXene/Si composite through a MRR strategy (Figure 8). In their procedure, silica was initially deposited onto layered Ti₃C₂ MXene via the Stöber process using tetraethoxysilane (TEOS) as the silica precursor. The obtained SiO₂-coated Ti₃C₂ MXene was then subjected to Mg vapor reduction at 650 °C under a 4% H₂/Ar atmosphere, forming a Ti₃C₂ MXene/Si hybrid structure. To improve structural robustness, PMMA was grafted onto the hybrid surface, with urea acting as a N-source. Subsequent pyrolysis generated a C coating along with partial SiO_x formation, resulting in a 3D sandwich-like Ti₃C₂ MXene/Si@SiO_x@C superstructure (Figure 8a–d). The Si loading could be regulated by adjusting the TEOS hydrolysis time, reaching 64.8%, 72.8%, and 78.7% after 3, 4, and 5 h, respectively. Furthermore, urea-derived pyrolysis introduced pyridinic, pyrrolic, and graphitic N species into the C layer and formed N-Ti bonds within the MXene framework (Figure 8e), strengthening the heterointerface and enhancing the cycling stability of the electrode.

A comparable MRR strategy has been extended to single-layer Ti₃C₂T_x flakes. For example, a Ti₃C₂@Si/SiO_x hybrid was synthesized by reducing silica-coated Ti₃C₂T_x at 650 °C in a H₂/Ar atmosphere (Figure 8f) [89]. The SiO₂ layer was deposited through TEOS hydrolysis assisted by CTAB and NaOH, where NaOH served both as a catalyst and as a surface modifier, introducing additional -OH groups onto Ti₃C₂T_x. This surface functionalization facilitated the formation of strong Ti-O-Si bonds at the Si/SiO_x-Ti₃C₂T_x interface. Owing to the large aspect ratio of Ti₃C₂T_x NSs, the resulting Ti₃C₂@Si/SiO_x composite delivered a high specific surface area (655.8 m²/g) and a well-developed porous architecture at a Si content of 46.7%, thereby improving electrolyte penetration and charge-transfer kinetics (Figure 8g). In addition, an amorphous TiO₂ shell was introduced via a sol–gel method using tetrabutyl titanate as the Ti precursor, leading to a sandwich-structured Ti₃C₂@Si/SiO_x@TiO₂ composite composed of a Ti₃C₂T_x core, a Si/SiO_x intermediate layer, and an outer TiO₂ coating.

Although the MRR strategy allows Si to be anchored onto MXene sheets, the high processing temperature (around 650 °C) can lead to structural deterioration of MXene. To mitigate this problem, molten AlCl₃ has been introduced as a liquid-phase reaction medium for silica reduction [90]. In this system, Mg reacts synergistically with AlCl₃, producing AlOCl and MgAl₂Cl₈ as side products (Reaction 2). This cooperative pathway reduces the reaction temperature dramatically, lowering it to roughly 200 °C.

Figure 8. Preparation of Si/MXene NCs via thermal reduction strategies. (a) Schematic representation, (b) SEM, (c,d) TEM micrographs and (e) N 1s XPS spectrum of Ti₃C₂ MXene/Si@SiO_x@C NCs. Adapted from [52]. Copyright 2019, American Chemical Society. (f) Schematic diagram and (g) N₂ adsorption–desorption curves of Ti₃C₂@Si/SiO_x@TiO₂ NCs with inset showing corresponding pore-size distribution. Adapted from [89]. Copyright 2020, American Chemical Society. (h) Schematic diagram and (i) TEM micrograph of Ti₃C₂/Si NCs obtained through low-temperature MRR strategy. Adapted from [91]. Copyright 2019, Wiley-VCH.

Figure 8. Preparation of Si/MXene NCs via thermal reduction strategies. (a) Schematic representation, (b) SEM, (c,d) TEM micrographs and (e) N 1s XPS spectrum of Ti₃C₂ MXene/Si@SiO_x@C NCs. Adapted from [52]. Copyright 2019, American Chemical Society. (f) Schematic diagram and (g) N₂ adsorption–desorption curves of Ti₃C₂@Si/SiO_x@TiO₂ NCs with inset showing corresponding pore-size distribution. Adapted from [89]. Copyright 2020, American Chemical Society. (h) Schematic diagram and (i) TEM micrograph of Ti₃C₂/Si NCs obtained through low-temperature MRR strategy. Adapted from [91]. Copyright 2019, Wiley-VCH.

2 Mg + 6 AlCl₃ + SiO₂ → 2 MgAl₂Cl₈ + 2 AlOCl + Si

(2)

2 AlCl₃ + 3 SiO₂ + 4 Al → 6 AlOCl + 3 Si

(3)

For instance, SiO₂/Ti₃C₂ NCs were mixed with Mg and AlCl₃ powders and sealed in a stainless-steel autoclave under an Ar atmosphere. Performing MRR at 200 °C produced Si/Ti₃C₂ NCs (Figure 8h) [91]. The obtained materials displayed a lamellar porous structure with homogeneously dispersed Si NPs. Notably, the formation of interfacial Si-O-Ti covalent bonds between Si and Ti₃C₂ significantly reinforced structural integrity (Figure 8i). In a related strategy, Al can function as a reductant in the low-temperature aluminothermic reduction of SiO₂ (LTARR, Reaction 3). Following this approach, Wu et al. [92] synthesized Si/Ti₃C₂T_x NCs by mechanically blending Al, AlCl₃, Ti₃C₂T_x, and commercial SiO₂ powders in an Ar-filled autoclave, followed by reduction at 250 °C.

Thermal reduction represents an economical and effective route for fabricating Si/MXene NCs, producing strong interfacial interactions along with micro- and meso-porous structures. However, this approach faces several drawbacks, including limited Si yield, the requirement for post-synthesis purification to remove by-products and residual silica, and the risk of MXene structural damage at high temperatures.

2.8. Others

Besides conventional approaches, techniques such as ultrasonication, immersion treatment, and TEOS hydrolysis have been employed to combine Si-based materials with MXenes. In the ultrasonication-assisted route, Si NPs can be partially intercalated into the interlayer spaces of multilayer MXene sheets, forming Si/MXene NCs. Because Si NPs exhibit poor affinity toward aqueous media, ethanol is commonly used as the solvent. In this configuration, MXene sheets function as conductive scaffolds that accommodate Si NPs and facilitate charge transport. However, the lack of strong chemical bonding results in Si being physically attached to the MXene surface and interlayers, which necessitates a high MXene fraction to mitigate Si volume expansion. For example, Si/Ti₃C₂T_x and Si/V₂CT_x composites containing approximately 83.3% MXene display relatively limited Li-storage capacities compared with other Si/MXene systems [93].

In situ fabrication of Si-based materials generally proceeds through two stages: hydrolysis of TEOS to form SiO₂, followed by high-temperature reduction to produce Si. Alternatively, employing SiO₂ directly as the anode circumvents the energy-intensive reduction step, offering a simpler and more economical pathway. For example, a laminated MXene-SiO₂-MXene architecture was constructed by incorporating SiO₂ NPs into multilayered MXene sheets using the Stöber process [94]. Spray-drying subsequently converted the composites into microspherical SiO₂/MXene structures, where SiO₂ NPs were uniformly confined within MXene shells. Although MXenes are electrochemically active, severe layer restacking reduces accessible surface sites and impedes charge and ion transport. Bimb et al. [95] demonstrated that immersing Mo₂TiC₂ in a TEOS–dodecylamine solution enabled intercalation of both TEOS and amine molecules between adjacent layers. Subsequent hydrolysis in water and calcination removed the amine template and generated a SiO₂-pillared MXene framework. The resulting structure exhibited an expanded interlayer spacing and a specific surface area of 202 m²/g, far exceeding that of pristine Mo₂TiC₂ (8 m²/g), highlighting the effectiveness of SiO₂ pillaring in preventing restacking and improving electrochemical performance.

Soaking represents a practical approach for depositing MXene sheets onto diverse porous substrates, such as C foam [96], Ni foam [97], cotton textile [98] and C cloth [99]. For example, a polyvinylpyrrolidone (PVP)-functionalized Si@melamine foam was first prepared by immersing melamine foam into a Si/PVP solution, followed by thermal treatment to carbonize the melamine framework and generate Si@N-C foam [100]. Subsequent dipping of this foam into a Ti₃C₂T_x suspension allowed MXene sheets to uniformly coat the surface, forming a 3D, hollow, and conductive MXene@Si@N-C network. A comprehensive comparison of the fabrication approaches described above is provided in

Table 1. Comparison of preparation methods for Si/MXene NCs used in LIB anodes.

Preparation Method	Typical Structure	Advantages	Limitations	Scalability	Refs.
Electrostatic self-assembly	Powders, 3D frameworks, core–shell	Simple process; strong interfacial interaction; uniform Si distribution	Requires surface functionalization; surfactant residues may reduce conductivity	Moderate	[58,59,60]
Ball-milling	Powders	Scalable; strong mechanical mixing; chemical bonding possible	MXene oxidation; possible inactive phase formation at high energy	High	[65,66,67]
Vacuum filtration	Flexible films	Binder-free; high conductivity; excellent mechanical flexibility	Limited thickness; restacking of MXene sheets	Low-moderate	[73,74]
Blade casting	Coated electrodes, films	Industry-compatible; high mass loading; good mechanical robustness	Possible “dead” active regions; MXene stacking	High	[75,76,77,78]
Spray drying	Microspheres	Uniform spherical morphology; internal voids buffer volume expansion	Process parameters need precise control		[79,80,81]
Freeze drying	3D porous frameworks	High porosity; effective stress accommodation	Weak interfacial bonding if no chemical linkage	Moderate	[82,83]
Electrospinning	Fibers, membranes	Continuous conductive network; flexible and freestanding electrodes	Polymer removal required; complex setup		[50]
In situ thermal reduction	Core–shell, sandwiched	Strong chemical bonding; high structural stability	High temperature may degrade MXene; post-treatment needed		[89,90,91]

, which outlines their main characteristics, benefits, drawbacks, and scalability.

3. Li-Storage Characteristics of Si/MXene NCs

It is important to note that the electrochemical performance reported for Si/MXene NCs in the literature is strongly influenced by experimental conditions, including current density normalization, Si loading, electrode thickness, electrolyte composition, and cell configuration. Therefore, rather than directly comparing absolute capacity values, this section focuses on identifying consistent performance trends and correlating structural design with Li-storage behavior. This approach provides more meaningful insight into the design principles of effective Si/MXene electrodes.

Silicon-based materials, such as elemental Si [101], SiO_x [102] and silica [94], have attracted considerable interest as high-capacity anodes for LIBs due to their ability to alloy with Li. Nevertheless, their practical implementation is limited by intrinsically low electronic conductivity and substantial volume expansion during lithiation. To overcome these drawbacks, MXenes have been widely adopted as conductive matrices to fabricate various Si/MXene nanostructures, including powders [93], 3D architectures [60,63], films [73,103], spherical assemblies [49,80] and NFs [50]. These engineered hybrids markedly improve the Li-storage performance of Si-based systems. This section summarizes recent developments in Si/MXene NCs, focusing on electrochemical characteristics and structure–property relationships to facilitate the advancement of Si-based anodes.

3.1. Powders

Si@Ti₃C₂ NCs were prepared by ultrasonically blending Si NPs with multilayer MXene powders [48]. In the resulting structure, Si NPs were partially agglomerated and randomly dispersed on MXene surfaces and within interlayer spaces. Despite a relatively low Si content (~16.7%), the composite achieved a reversible capacity of 879 mAh/g at 0.2 A/g. However, the lack of strong interfacial bonding and limited structural confinement led to poor cycling durability, with capacity retention dropping to 21.4% (188 mAh/g) after 150 cycles. A similar ultrasonication strategy was employed for Si@V₂C composites [93]. Although the reversible capacity was lower (691 mAh/g), the cycling stability improved significantly, maintaining 62.2% of the initial capacity over 150 cycles.

High-energy ball milling generates strong shear forces that facilitate the chemical coupling of Si with MXene. During this process, Si forms interfacial Ti-Si bonds with MXene and C-Si bonds with CNTs (Figure 9a) [65]. These dual interactions effectively anchor Si NPs within the conductive matrix, resulting in a MXene-Si-CNT composite that delivers ~1000 mAh/g after 200 cycles with ~80% capacity retention (Figure 9b). The multidimensional conductive network further accelerates electron transport, enabling a rate capacity of 841 mAh/g at 2 A/g (Figure 9c). Similarly, ball milling has been employed to couple SiO with N-doped Ti₃C₂T_x NSs (NTS) through Si-O-Ti interfacial bonding [68]. The resulting SiO@NTS electrode achieves discharge capacities of 1302.7 and 596.4 mAh/g at 0.1 and 5 A/g, respectively, while maintaining 1141.3 mAh/g after 200 cycles at 0.5 A/g. Beyond mechanical activation, electrostatic self-assembly offers an alternative strategy for interfacial integration. For example, CTAB-modified SiO adheres strongly to crumpled MXene sheets due to electrostatic attraction (Figure 9d) [59]. Unlike bare SiO electrodes that undergo severe pulverization and delamination upon volume expansion (Figure 9e), the SiO@MXene composite benefits from MXene’s high conductivity, large specific surface area, structural flexibility, and low Li⁺ diffusion barrier (0.07 eV). As a result, it exhibits superior electrochemical performance (Figure 9f), delivering ~1350 mAh/g at 0.1 A/g, 85.8% retention after 100 cycles at 0.5 A/g, and 712.9 mAh/g at 2 A/g. Collectively, these results highlight the importance of chemically bonded MXene frameworks in improving Si-based anodes.

Beyond ex situ approaches, in situ Si growth on MXene supports has also been reported to enable stable Li storage. Hui’s group [91] prepared Si/Ti₃C₂ NCs using a low-temperature MRR process, in which Si NPs were strongly immobilized on MXene NSs through Ti-O-Si interfacial bonding. The Ti₃C₂ framework promoted efficient Li⁺ and electron transport while simultaneously mitigating Si volume expansion, thereby improving electrochemical performance. Consequently, the Si/Ti₃C₂ composite delivered an initial reversible capacity of 2145.1 mAh/g at 100 mA/g and retained 1475 mAh/g after 200 cycles, exhibiting minimal capacity fading beyond the tenth cycle. In a separate work, PMMA pyrolysis on MRR-derived MXene/Si composites produced a hierarchical MXene/Si@SiO_x@C architecture [52]. This heterostructure combines silicon’s high theoretical capacity with the mechanical buffering effects of MXene, SiO_x, and an N-C shell, while robust Ti-N interfacial bonding further enhances structural integrity. Cyclic voltammetry revealed reduction peaks at 0.01–0.4 V and oxidation peaks near 0.4 and 0.53 V, corresponding to Li-Si alloy formation and subsequent Li extraction from Li_xSi (Figure 9g). Compared with commercial Si/C, the composite exhibited stronger redox responses and reduced polarization, indicating faster reaction kinetics. The electrode delivered capacities of 1674 mAh/g at 0.2 C and 398 mAh/g at 10 C (Figure 9h). Even after 1000 cycles at 10 C, it maintained 76.4% capacity with only 12% electrode swelling and no observable structural failure, unlike pure Si electrodes (Figure 9i–l). When assembled with a Li[Ni_0.6Co_0.2Mn_0.2]O₂ cathode, the flexible pouch cell achieved an energy density of 485 Wh/kg and demonstrated stable operation under repeated bending.

3.2. Architectures

Constructing 3D porous architectures is an effective strategy to mitigate the large volume changes in Si during cycling by providing internal void space, while simultaneously enabling rapid ion and electron transport pathways that improve Li storage performance. A simple freeze-drying approach has been used to fabricate sandwich-structured Si/MXene composites, where ice crystals act as temporary templates and generate abundant pores after sublimation [82,104]. In this configuration, Si NPs are uniformly embedded within the conductive MXene network, delivering a reversible capacity of 1137.6 mAh/g after 200 cycles at 0.5 A/g with 63.6% retention, and maintaining 890 mAh/g at 2 A/g [104]. The facile synthesis process combined with favorable electrochemical properties highlights its strong potential for practical applications.

Zhou’s group [105] prepared Si@MXene NCs through electrostatic self-assembly between APS-functionalized Si NPs and Ti₃C₂T_x NSs. The electrostatic interaction between positively charged Si particles and negatively charged MXene layers triggered the restacking of the 2D sheets into a porous framework, enabling uniform encapsulation of Si within the conductive matrix. This structure effectively accommodated Si volume expansion during lithiation, while the MXene coating suppressed direct contact between Si and the electrolyte, facilitating stable SEI formation. As a result, the initial Coulombic efficiency (ICE) increased from 62.3% for pure Si to 71.3% at 0.2 A/g. After 100 cycles, the Si@MXene electrode retained approximately 981 mAh/g with about 94% capacity retention, significantly outperforming bare Si. Further coating with a C shell [60] produced a cross-linked 3D porous Si/MXene@C framework, where strong Ti-O-Si and Si-C bonds enhanced the stability of Si anchoring. This composite delivered a reversible capacity of 862.9 mAh/g and maintained 85.7% of its capacity after 150 cycles.

Beyond C coating, Si/Ti₃C₂T_x NCs (SiNP@MX1) obtained through electrostatic self-assembly can be further integrated into a 3D MXene framework via hydrothermal treatment followed by freeze-drying [63]. This strategy yields a hierarchical porous Si-based structure featuring dual MXene encapsulation (SiNP@MX1/MX2). In this configuration, the inner MXene layer anchored on Si NPs prevents particle aggregation, while the outer MXene network provides continuous pathways for ion and electron transport (Figure 9m). Moreover, the dual-shell architecture effectively buffers electrode volume variation and reduces direct exposure of Si to the electrolyte, thereby stabilizing SEI formation. Consequently, the composite exhibits a reversible capacity of 1422 mAh/g at 0.5 A/g after 200 cycles, along with excellent rate capability and long-term cycling stability (Figure 9n,o). Electrochemical impedance spectroscopy further reveals lower interfacial resistance and enhanced Li-ion diffusion compared with bare Si electrodes (Figure 9p). After extended cycling, the SiNP@MX1/MX2 electrode shows a significantly reduced R_SEI of 4.5 Ω relative to 1061 Ω for pure SiNP, indicating the formation of a thin and stable SEI layer.

3.3. Films

The Si NPs can be incorporated into layered MXene NSs through vacuum filtration to form flexible, binder-free composite films that can be directly used as LIB anodes [103]. In this architecture, the interconnected MXene network effectively restrains Si particles, mitigating volume expansion while improving electrical conductivity, providing additional active sites, and enabling rapid ion transport (Figure 10a). Consequently, the Si/MXene electrode demonstrates markedly enhanced cycling stability, delivering a capacity of 2118 mAh/g at 0.2 A/g after 100 cycles, significantly higher than that of pure Si (Figure 10b). Even at a high current density of 5 A/g, the electrode maintains 890 mAh/g (Figure 10c). Post-cycling observations further confirm that the MXene-confined composite retains structural integrity, whereas the bare Si electrode undergoes severe cracking and pulverization (Figure 10d,e). Xu et al. [73] further showed that MXene can act as a multifunctional conductive binder for Si@C electrodes. Upon stacking, MXene forms a porous and continuous framework that uniformly encapsulates Si@C NPs, simultaneously serving as a binder, conductive network, mechanical support, and buffer for volume changes. The MXene-bonded Si@C film exhibits a high electrical conductivity of 208.7 S/cm, far exceeding those of CMC- and PVDF-based electrodes. This structure achieves a reversible capacity of 1040.7 mAh/g after 150 cycles and retains 553 mAh/g even at an ultrahigh current density of 8.4 A/g (Figure 10f,g). SEM analysis reveals that the MXene-based film remains intact without cracks or delamination, unlike electrodes fabricated with conventional binders, demonstrating the advantages of MXene in constructing flexible, high-performance Si anodes (Figure 10h–j).

In addition to vacuum filtration, blade casting has emerged as an effective technique for uniformly incorporating Si NPs into layered MXene frameworks. In a representative study, Zhang’s group [74] fabricated MXene-bonded Si electrodes by mixing concentrated Ti₃C₂T_x (MX-C) or Ti₃CNT_x (MX-N) inks with either nanosized Si or graphene-Si particles, followed by blade casting. Compared with conventional polymer-bonded systems, such as nSi/PAA/CB electrodes, the MXene-based architecture demonstrated markedly higher electronic conductivity and mechanical durability, even under repeated bending. As shown in Figure 11a, the nSi/MX-C electrode containing 30 wt % MXene exhibited significantly improved rate capability, approaching its theoretical capacity. With a mass loading of approximately 0.9 mg/cm², the electrode maintained superior cycling stability relative to polymer-based counterparts, retaining 84% of its initial capacity after 50 cycles at 0.15 A/g (Figure 11b). Although performance decreased at higher loadings, substantial areal capacity was still preserved over extended cycling. Moreover, Gr-Si/MX-C electrodes displayed excellent electrochemical performance under ultrahigh mass loading conditions (13 mg/cm², Figure 11c), achieving ICEs of 81–83% and nearly linear scaling of areal capacity, with specific capacities reaching 1850 mAh/g.

In an alternative strategy, Ti₃C₂T_x was integrated with sodium alginate (SA) to form a hybrid conductive binder capable of firmly anchoring Si NPs onto the copper current collector [75]. Comparative studies indicated that Ti₃C₂T_x offered significantly stronger interfacial stabilization than C black (CB) in conventional Si-CB electrodes. Differential capacity (dQ/dV) analysis (Figure 11d–g) revealed three typical delithiation peaks for both systems, corresponding to the phase transitions a-Li_3.5Si → a-Li₂Si (D1), c-Li_3.75Si → a-Li_1.1Si (D2), and a-Li₂Si → a-LiSi (D3). The pronounced D2 peak suggested that most Si participated in reversible alloying reactions to form crystalline Li_3.75Si. However, capacity partition analysis showed severe degradation in the Si-CB electrode after 100 cycles. In contrast, the Si-MXene electrode maintained strong D1-D3 peak intensities, indicating improved electrical continuity, stable SEI formation, and reduced loss of active Si (Figure 11h,i). These findings demonstrate the promise of MXene-based binders for scalable blade-casting fabrication of high-performance Si anodes.

3.4. Spheres

Ti₃C₂T_x NSs (TNSs) were uniformly attached to porous Si nanospheres (Si p-NSs) through electrostatic interactions mediated by a PMMA interlayer. After pyrolysis removed the PMMA, core–shell Si p-NS@TNS composite spheres were obtained [49]. The conformal MXene coating enhanced electrical conductivity and provided structural reinforcement against particle pulverization. Mechanical simulations indicated that both radial and circumferential stresses decayed more rapidly from the Si/TNS interface toward the particle interior than in uncoated Si p-NSs (Figure 12a–c). Stress evaluations at different states of charge further (Figure 12d,e) confirmed reduced internal stress in the coated structure, demonstrating effective accommodation of volume expansion. As a result, the composite delivered a reversible capacity of 1154 mAh/g at 0.2 A/g, along with outstanding cycling stability, exhibiting only 0.026% capacity decay per cycle over 2000 cycles, and excellent rate capability. When assembled into a full cell with a LiFePO₄ cathode, the device achieved 138 mAh/g after 80 cycles, significantly outperforming the counterpart based on uncoated Si. The energy density reached 385 Wh/kg in the initial cycle and increased to 405 Wh/kg after prolonged cycling.

Spherical Si/MXene NCs were fabricated through a spray-drying process driven by capillary compression forces [80]. In this structure, Si NPs were uniformly confined within wrinkled MXene microspheres, where adjacent MXene NSs were interconnected through Ti-O-Ti covalent linkages, strengthening the overall framework. As shown in Figure 12f–h, the abundant F terminations on MXene facilitated the in situ formation of a LiF-rich SEI layer via conversion reactions, producing a dense and mechanically stable interphase. This protective layer effectively suppressed parasitic reactions between Si and the electrolyte while improving structural stability during repeated cycling. Consequently, the electrode delivered a high reversible capacity of 1791.9 mAh/g at 0.2 A/g with an ICE of 74.7%. The robust architecture also supported stable long-term cycling, maintaining 1003.6 mAh/g at 0.5 A/g with 81% capacity retention after 150 cycles (Figure 12i). Post-cycling SEM observations confirmed superior structural integrity compared with bare Si, highlighting the important role of MXene F-terminations in stabilizing Si-based anodes (Figure 12j,k).

SiO₂ has also been investigated as a synergistic component with MXene to enhance Li-storage performance. By combining the Stöber method with spray-drying techniques, Mu et al. [94] synthesized microspherical SiO₂/MXene hybrid structures. This integrated architecture effectively incorporated Si NPs within a conductive MXene framework, enabling improved electron and ion transport, preventing aggregation of both Si and MXene, minimizing parasitic reactions, and providing sufficient internal space to accommodate mechanical stress during cycling. Consequently, the hybrid delivered reversible capacities of 820 mAh/g and 798 mAh/g in the first and 100th cycles at 0.2 A/g, corresponding to a high-capacity retention of 97%. Even at elevated current densities up to 3 A/g, the electrode maintained a substantial capacity of 517 mAh/g, indicating favorable reaction kinetics.

3.5. Fibers

Electrospinning is widely employed to fabricate fiber-like, self-supporting Si@C NCs. However, insufficient interfacial adhesion and limited electrical connectivity between Si NPs and the C matrix often hinder their Li-storage performance. To address these issues, Jiang’s group [50] introduced MXene NSs into a coaxial electrospinning process. In this design, MXene sheets acted as substrates for anchoring Si NPs, which were subsequently coated with a C shell, forming core–shell structured MXene/Si@C NFs. XPS results verified the presence of Ti-N and Ti-O-Si bonds among MXene, Si, and C (Figure 13a–c), indicating that MXene served as a conductive interfacial bridge that enhanced both electron transport and structural stability. The resulting MXene/Si@C NFs delivered a reversible capacity of 1080.4 mAh/g at 0.1 A/g with an ICE of 78.4%. In addition, they demonstrated enhanced electrochemical kinetics, including excellent rate performance (301.1 mAh/g at 2 A/g) and lower charge-transfer resistance compared with Si/C, CNF, and pristine Si electrodes (Figure 13d–f), highlighting their potential in flexible LIBs.

3.6. Si-Functionalized/Doped MXenes

Unlike Si/MXene NCs, where Si serves as a distinct active phase for Li storage, theoretical studies indicate that Si can also function as a surface termination or dopant in MXenes to enhance their storage capability. First-principles calculations reveal that Li can remove -F and -OH groups from Ti₂C and V₂C MXenes, whereas Si remains a stable termination, retaining metallic conductivity [106]. The Li⁺ diffusion barriers in Si-terminated MXenes are 0.29 (Ti₂CSi₂) and 0.23 eV (V₂CSi₂), comparable to Ti₂CF₂ (0.3 eV) and V₂CF₂ (0.28 eV). With this structure, theoretical capacities of 1767 (Ti₂CSi₂) and 1592 mAh/g (V₂CSi₂) are achievable. These systems also show promising Na and K storage, delivering 327/327 and 315/236 mAh/g, respectively. In another study, a (3 × 3) Ti₂C supercell was modeled, where Ti atoms bond covalently with C atoms [107]. Substitution of one or two C sites with Si preserves metallicity even after Li adsorption. The maximum Li adsorption energies were −2.02 eV (Si@Ti₂C) and −1.98 eV (2Si@Ti₂C), close to pristine Ti₂C (−2.03 eV). Theoretical capacities increased from 331.6 mAh/g (pristine) to 439.4 and 428 mAh/g for Si@Ti₂C and 2Si@Ti₂C, respectively, highlighting the beneficial role of Si doping in MXene anodes.

Powdered Si/MXene NCs are straightforward to prepare and suitable for large-scale production; however, they frequently exhibit poor structural robustness and unstable SEI formation. The 3D porous architectures can effectively buffer Si volume changes and promote ion/electron transport, thereby improving cycling durability. Nevertheless, their complicated fabrication processes and relatively low tap densities may restrict practical deployment. Film-type configurations offer high electrical conductivity, mechanical flexibility, and binder-free electrode integration. Yet, restacking of MXene layers and limited electrolyte accessibility may hinder full utilization of active materials, particularly at high mass loadings. Spherical Si/MXene composites, especially core–shell or yolk-shell designs, enable uniform stress distribution and stable SEI development, delivering a favorable balance between capacity and longevity, although precise morphological engineering is required. NFs-based systems provide interconnected conductive networks and flexibility, but the presence of polymer-derived C matrices and complex processing routes can compromise volumetric energy density. In summary, selecting an optimal Si/MXene configuration depends on balancing electrochemical performance, mechanical integrity, and scalability, with future progress likely emerging from hybrid structural strategies (

Table 2. Comparison of structural architectures for Si/MXene anodes.

Architecture	Key Advantages	Main Drawbacks	Best Application Focus
Powders	Simple, scalable	Poor mechanical stability	Fundamental studies
3D frameworks	Excellent cycling stability	Low tap density	Long-life LIBs
Films	Flexible, binder-free	Limited thickness	Flexible electronics
Spheres	Uniform stress, stable SEI	Complex synthesis	High-performance anodes
Nanofibers	Continuous conduction	Complex processing	Wearable/flexible devices

).

4. Conclusions and Future Perspectives

Thanks to their metallic conductivity, versatile surface chemistry, mechanical robustness, and flexibility, MXenes have attracted significant interest for integration with Si-based materials in advanced anodes for LIBs. This review highlights progress in Si/MXene NCs as negative electrodes. Structurally, MXenes serve as hosts to stabilize Si NPs, suppress aggregation, mitigate severe volume fluctuations during lithiation, and promote rapid electron/ion transport, thereby enhancing Li-storage performance, including long cycle life and high rate capability. Functionally, MXene coatings protect Si from direct electrolyte contact, promote the formation of stable LiF-rich SEI layers, and minimize side reactions; when arranged in stacked configurations with Si inclusions, they also provide flexibility, making them attractive for wearable energy devices. Various fabrication techniques, such as in situ thermal reduction, electrostatic self-assembly, vacuum filtration, blade casting, and ball milling, have been employed to design Si/MXene structures in diverse forms, including powders, films, fibers, 3D architectures, and spheres. Their electrochemical behaviors were systematically analyzed, with structure–performance relationships and key parameters (composition, synthesis, and capacities) summarized in

Table 3. Overview of Si/MXene NCs, highlighting synthesis approaches, structural features, Si loading, and Li-storage behavior.

Structural Characteristics	Materials	Preparation Approach	Si Content (%)	Li-Storage Performance			Ref.
				Initial Capacity [mAh/g]/Current Density [A/g]/Initial Coulombic Efficiency [%]	Capacity Retention (%)/Cycle Numbers	Rate Capability [mAh/g/A/g]
Powders	Si@MXene	Electrostatic self-assembly	80	1422/0.5/67.2	89.7/200	574/5	[63]
	SiO/wrinkled MXene		91	1945/0.2/69.4	85.8/100	984.8/2	[59]
	NH2-Si/Ti3C2Tx		20	1378/0.032/75.2	83.4/100	81/1.6	[108]
	Si NPs/MXene		70	3986.8/0.1/75.9	80.7/100	1701.1/1	[109]
	Sandwich-like Si/Ti3C2Tx		75	1067.6/0.3/-	60.3/100	-	[110]
	Si@V2C	Ultrasonication	16.7	691/0.2/-	62.2/150	-	[93]
	Si@Ti3C2			1195/0.2/69	21.4/150	-	[48]
	Ti3C2@Si/SiOx@TiO2	MRR	44.8	2517/0.1/66.3	-/250	355/2	[89]
	MXene/Si@SiOx@C		74.3	1674/0.84/81.3	92.4/200	398/4.2	[52]
	SiOx/N-Ti3C2Tx	Ball-milling	-	1882.1/0.1/54	-/100	596.4/5	[68]
	Si-P/Ti3C2Tx hybrid		50	3486.2/0.5/-	28.1/500	632.4/5	[67]
	MXene-Si-CNT		60	1260/0.5/-	80/200	841/2	[65]
	Si@N-C/MXene	PDA coating	-	2554/0.1/75	-/300	849/10	[111]
	Si@NC/MXene		28.2	1233.5/0.1/79.3	94/250	-	[112]
Architectures	Si/MXene@C	Electrostatic self-assembly	31.4	1530.2/0.1/65.7	85.7/150	233.3/5	[60]
	Si/MXene		60	-/0.2/71.3	94.1/100	962/2	[105]
	MXene-Si@C		-	1939.1/0.2/77.87	88.1/85	644.7/5	[62]
	Ti3C2/Si	MRR	38.3	3512.5/0.1/61.1	68.8/200	467/2	[91]
	Sandwich-like Si/Ti3C2	Freeze drying	66.7	2415.4/0.5/74.1	63.6/200	890/2	[104]
	Si/laponite/MXene/CNT	Ball-milling, blade-casting, freeze drying	60	3549.2/0.1 C/85.6	-/50	1325.6/2.1	[113]
	Si@Ti3C2Tx	Freeze drying	70	2444/1/55.6	71.6/500	577/2	[82]
	MXene@Si@NC foam	Soaking	-	3216/0.1 C/80.3	-/100	416/3 C	[100]
Flexible composite film	Porous Si/MXene	Vacuum filtration	66.7	2843.5/0.5/64	58.4/200	840.3/5	[72]
	MXene-bonded Si@C		60	2276.3/0.42/73	62.7/150	553/8.4	[73]
	MXene&Si		50	731/0.1/61	123.9/500	200/0.5	[114]
	Si/MXene		-	2930/0.2/71	72.3/100	886/5	[103]
	CNTs@MXene-Si	Ultrasonication, vacuum filtration, freeze drying	50	4093/0.1 C/77.8	-/50	1188.4/0.5 C	[115]
Composite film coated on Cu foil	Si-N-MXene	Blade-casting	72.1	2346/0.8/85.7	-/900	304/1	[77]
	Nano-Si/Ti3C2Tx		70	2240/0.15/-	-	-	[74]
	Nano-Si/Ti3CNTx			1602/1.5/-	69/70	-
	Si/MXene/SA		60	3719.1/0.1/-	67.8/100	1867.1/5	[75]
	MXene-SiOx@C		76.4	1363.3/0.1/-	98/50	604.5/6.4	[116]
Spheres	Si@Ti3C2Tx	Electrostatic self-assembly	85.6	2588/0.2/80.2	55.6/150	899/4	[49]
	Si@MXene-graphene	Spray drying	50	2943/0.1 C/89.1	47.7/200	-	[117]
	SiO2/MXene hybrid		76	1173/0.2/-	97/100	517/3	[94]
	Si@MXene capsules		70	2397.9/0.2/74.7	81/150	759/2	[80]
	Ti3C2Tx-encapsulated Si		68	1861/0.358/-	-/195	420/1.79	[88]
Fibers	Si/MXene@CNFs	Electrospinning	60.5	1348.3/0.1/75.9	48/200	648.1/5	[87]
	MXene/Si@C		18	1080.4/0.1/78.4	50/100	301.1/2	[50]
	Ti3C2Tx-Si@CNF		28	1989/0.1/86.65	79/100	289/5	[86]
Current collector	MXene supported Si	Blade casting	-	2324/0.2/83	62.5/100	1318/1.5	[78]

.

It is important to note that direct comparison of electrochemical performance across different Si/MXene systems must be treated with caution. Reported capacities and cycling stability are strongly influenced by variations in (i) current density, (ii) Si mass loading, (iii) electrode composition and binder type, (iv) electrolyte formulation and additives, (v) potential window, and (vi) cell configuration (half-cell vs. full-cell). In many reports, high specific capacities are obtained at relatively low mass loading (<1 mg cm⁻²) and moderate current densities, which may overestimate practical applicability. Comparisons are most meaningful when studies use similar testing conditions, particularly comparable current densities and mass loadings. Therefore, in the following discussion and in Table 3, performance trends are interpreted primarily within comparable experimental ranges rather than based solely on absolute capacity values.

Based on the comparative analysis of reported studies, several relatively consistent trends emerge:

Trend 1—Interfacial anchoring improves ICE and stability: Composites where Si is chemically anchored to MXene surfaces (e.g., via surface functional groups or in situ growth) generally exhibit improved ICE and reduced early-cycle capacity loss compared to simple physical mixtures. Stronger interfacial bonding suppresses unstable SEI formation.

Trend 2—Encapsulation or 3D frameworks enhance cycling stability: Architectures in which Si is confined within MXene-derived networks or sandwiched between layers show more stable long-term cycling due to mechanical buffering and maintained electrical connectivity.

Trend 3—Trade-off between high capacity and structural robustness: Systems with very high Si content often deliver higher initial capacity but suffer from faster capacity decay, indicating a compromise between energy density and mechanical integrity.

Trend 4—Mass loading critically affects performance interpretation: Many high-capacity reports are obtained at low mass loading. When tested at higher loadings, capacity retention and rate capability often decline, highlighting the importance of structural optimization for practical implementation.

Trend 5—Surface chemistry of MXenes plays a decisive role: The nature of surface terminations influences electronic conductivity, wettability, and interfacial stability, thereby affecting both ICE and long-term cycling behavior.

Some studies report that oxygen-terminated MXenes enhance interfacial stability and Li-ion transport, whereas others suggest that excessive oxidation reduces conductivity and accelerates degradation. These apparently contradictory observations likely arise from differences in oxidation degree and structural integrity. Mild surface oxidation may improve interfacial compatibility, while severe oxidation compromises electronic transport. Additionally, several reports describe capacity “activation” during initial cycles. While this is sometimes attributed to gradual electrolyte penetration and improved electrode wetting, it may also reflect progressive structural rearrangement or delayed SEI stabilization. From a practical perspective, activation behavior should be interpreted cautiously, as stable performance without prolonged activation is more desirable for real applications.

Despite recent advances, Si/MXene NCs still face challenges for practical application in energy storage. Their cycling stability generally falls short of commercial graphite and Li₄Ti₅O₁₂ anodes, even at relatively low Si loadings. Structural optimization is therefore essential to achieve both high Si content and stable cycling. Strategies such as in situ thermal reduction, electrostatic self-assembly, and ball milling can introduce interfacial bonding to reinforce structural integrity. Designing 3D porous architectures effectively buffers Si volume changes and accelerates ion/electron transport, thereby improving cycling and rate performance. However, these open structures, while delivering high capacity, often suffer from low CE due to excessive SSA and SEI accumulation in large pores, which impedes ion movement. Hence, careful control of pore morphology is required. Additionally, molecular dynamics simulations provide valuable insights into internal stress evolution, offering guidance for developing fiber-, film-, and sphere-like Si/MXene configurations.

Thanks to their layered architecture, MXene flakes can be assembled via vacuum filtration with Si NPs uniformly dispersed within, producing flexible Si/MXene NCs suitable for wearable energy-storage devices. Nevertheless, stacked MXene frameworks may lengthen electron/ion transport pathways, and the incorporation of Si NPs can reduce the mechanical integrity of the films. For high-performance wearable applications, parameters including MXene flake size, Si loading, toughness, porosity, bending conductivity, film thickness, and scalability must be carefully optimized.

Currently, Ti₃C₂T_x is the most commonly employed MXene as a conductive host for Si-based NCs. Other compositions, such as Nb₂CT_x, Ti₂NT_x and Mo₂CT_x, with distinct physicochemical properties, also warrant investigation for Si/MXene NC fabrication. Surface terminations, particularly -F groups, assist in forming stable LiF-rich SEI layers, yet they may also react with Li⁺ during cycling, causing irreversible capacity loss. Thus, the surface chemistry of MXenes has a critical impact on electrochemical behavior, highlighting the need for advanced synthesis strategies to produce MXenes with tunable terminations. In addition, MXenes are susceptible to oxidation under harsh conditions, which diminishes their conductivity and interfacial compatibility with Si, thereby impairing electrochemical performance. To address this, improvements are required across MAX-phase design, MXene etching processes, and composite fabrication to mitigate oxygen-induced degradation.

Given the high potential of Si-based candidates for next-generation LIBs, assessing Si/MXene NCs as anodes in full-cell systems is of critical importance. Although some studies have tested Si/MXene NCs with various cathodes (e.g., LiFePO₄, LiNi_0.8Co_0.1Mn_0.1O₂, and LiNi_0.5Mn_1.5O₄), further investigations are needed on parameters such as energy density, cycling stability, performance under flexible packaging, temperature tolerance, and scalability. With growing global interest in this field, Si/MXene NCs show strong promise for energy storage. This review is expected to provide a foundation for advancing their design, synthesis, and application in high-performance systems.