Topic “Electrochemical Energy Storage Materials”—An Overview

The quest for efficient and reliable electrochemical energy storage (EES) systems is at the forefront of modern energy research, as these systems play a pivotal role in addressing the intermittent nature of renewable energy sources and the growing demands of portable electronics and electric vehicles. The performance, reliability, and efficiency of EES systems are intrinsically linked to the materials used in their construction, making material innovation a critical driver for advancements in this field. This Topic, “Electrochemical Energy Storage Materials”, in collaboration with the esteemed journals Energies, Nanomaterials, Materials, Electrochem, and Batteries, presents a curated collection of cutting-edge research articles and comprehensive reviews that highlight the latest advancements across a broad spectrum of topics, including, but not limited to, lithium-ion batteries, solid-state batteries, sodium-ion batteries, potassium-ion batteries, and zinc-ion batteries.

Son et al. [Contribution 1] investigated the performance of graphite-blended electrodes with micron-sized SiO_x anode material, a widely utilized Si-based anode material in lithium-ion batteries, aiming to generate a commercially viable and practical solution. Their results show that SiO_x blending electrodes have better cycling performance than silicon micron particle blending electrodes. Using post-mortem techniques, the degrading mechanisms were clarified, providing insights into their electrochemical behavior and helping to meet both industrial and academic demands for improved anode materials.

Zhang et al. [Contribution 2] reported the synthesis of orthorhombic V₂O₅·nH₂O nanorods as cathodes for aqueous zinc batteries. This material exhibited superior zinc storage performance with high reversible capacity and long-term cycle stability, due to enhanced material stability, reduced electrolyte breakdown, and improved charge transfer kinetics. Additionally, a full cell design using microsized zinc powder as the anode demonstrated high capacity and stable cycling, confirming the practical applicability of these materials.

Cai et al. [Contribution 3] demonstrated the fabrication of highly loaded and binder-free α-MoO₃ on carbon fiber cloth (α-MoO₃@CFC) up to 15 mg/cm² via multi-arc ion plating and subsequent oxidative heating treatment. The α-MoO₃@CFC cathode material possessed significantly improved electrochemical performance compared to commercial MoO₃ using conventional slurry-based electrode fabrication processes. This study offers a simple way to make high-loading, binder-free cathodes for aqueous zinc-ion batteries (ZIBs), suggesting potential for use in future flexible devices.

Shanov et al. [Contribution 4] provided a comprehensive review on the basics and latest advancements in CNT-fiber-based supercapacitors. They overviewed supercapacitor types based on charge storage mechanisms and electrode design and discussed various fiber-making methods with an emphasis on improving electrochemical performance, stretchability, and multifunctionality. Lastly, they prospected the current performance and scalability challenges of CNT-based supercapacitors, highlighting their future potential in wearable electronic devices.

Nazhipkyzy et al. [Contribution 5] demonstrated a new approach to using the sawdust of karagash and pine trees to produce activated carbon material for EDLC application. At a relatively high scan rate of 160 mV/s, a decent specific capacitance of 147 F/g and 114 F/g was obtained, leading to high energy densities of 26.0 and 22.1 Wh/kg based on average electrode mass. This study showed that the use of electrode composites consisting of activated carbon derived from an available biomass precursor leads to the improved performance of electrochemical capacitors.

Cai et al. [Contribution 6] created a MnWO₄ cathode electrolyte interphase (CEI) layer on a δ-MnO₂ cathode using cyclic voltammetry. This layer effectively prevents Mn dissolution and enhances reaction kinetics. Consequently, the δ-MnO₂ cathode with the CEI layer shows improved cycling performance, retaining 98.2% of its capacity after 2000 cycles at 10 A/g. This shows that the simple electrochemical method used to build the MnWO₄ CEI layer significantly advances the development of MnO₂ cathodes for aqueous zinc ion batteries.

Li et al. [Contribution 7] prepared a series of 3D hierarchical porous carbon materials (PCs) by a low-cost and template-free method using calcium lignosulfonate (CL) as the precursor. The effects of enzymatic hydrolysis and different KOH feeding ratios on the structure and electrochemical properties of enzymatic hydrolysis CL (EHCL)-derived PCs were evaluated. The optimal PCs with a honeycomb-like microscopic morphology possessed a high capacitance (147 F/g at 0.25 A/g), significant rate capability (capacitance retention of 78% at 10 A/g), and good long-term cycling stability (95.3% capacitance retention after 15,000 cycles), demonstrating a promising route to apply renewable lignin derivatives in high-performance supercapacitors.

Landa-Medrano et al. [Contribution 8] reported the use of a design of experiments (DoE) matrix to obtain a mathematical model that predicts the best formulation of cathodes with LiNi_0.5Mn_1.5O₄ (LNMO) as the active material. After obtaining and validating this formulation, its upscaling to a semi-industrial coating line is described. The optimization and upscaling of the LNMO electrode recipe resulted in obtaining high-energy pouch cells of 1 Ah that could be used to gain knowledge in the chemistry of this lithium-ion cathode material.

Mori [Contribution 9] summarized the recent development of functional separators for lithium–sulfur batteries. The classification and modification of the separators with their working mechanisms, as well as the resulting electrochemical performance, were described. In addition, necessary performance metrics and material characteristics for separators were prospected to further improve the electrochemical properties of lithium–sulfur batteries.

Durdel et al. [Contribution 10] introduced, for the first time, a Newman p2D model for a lithium-ion cell with a silicon-dominant anode and a nickel–cobalt–aluminum–oxide cathode. The parametrization was based on values from the electrode manufacturing process, measured values using lab cells, and data from the literature. Future work was emphasized with more in-depth studies on the material parameters for silicon to expand the data available in the literature and facilitate further simulation work.

Yu et al. [Contribution 11] designed a three-layer garnet-applied PAN-added polymer ceramic electrolyte (g-PPCE) consisting of a PVDF-HFP-based SPE-Ga-doped-LLZO with 5 wt.% of PAN by using a simple tape-casting and impregnation process. Both LFP||Li-metal and NCM||Li-metal batteries using the g-PPCE exhibited high discharge capacity and cycle stability. The preparation of a pouch cell with a g-PPCE and a cell capacity of 5 mAh demonstrated the potential for large-scale production.

Wang et al. [Contribution 12] reported a Co/Al co-substitution strategy to construct a P3-type K_0.45Mn_0.7Co_0.2Al_0.1O₂ cathode material for potassium-ion batteries. This co-substitution effectively suppressed the Jahn–Teller distortion and alleviated the severe phase transition during K⁺ intercalation/de-intercalation processes, resulting in improved potassium storage performance. The Co/Al co-substitution strategy employed in this work provided an effective approach for designing high-performance Mn-based cathode materials in potassium-ion batteries.

Zhao et al. [Contribution 13] presented shape-controllable flexible composite electrodes based on Poly(3,4-ethylenedioxythiophene) and reduced graphene oxide (PEDOT/rGO) for planar micro-supercapacitors. The high electrical conductivity of rGO facilitated rapid electron transport on the electrode surface, and its high specific surface area contributed to more active sites available for electrochemical reactions, enhancing the electrochemical performance. This presented work highlighted the potential of PEDOT/rGO electrodes in flexible supercapacitor applications.

Wiggers et al. [Contribution 14] reported, for the first time, the bottom-up approach for α phase NASICON Li_1+xY_xZr_2−x(PO₄)₃ (α-LYZP) synthesis. Phase-pure rhombohedral α-LYZP was synthesized by a spray-flame process followed by a short annealing step. The results showed that the addition of Y³⁺ as a dopant was efficient to stabilize the α phase and enhance the ionic conductivity.

Drozhzhin et al. [Contribution 15] used differential scanning calorimetry (DSC) and ex situ powder X-ray diffraction to examine the thermal stability of various sodium-ion electrolytes and electrode materials. The results revealed that liquid sodium-ion electrolytes exhibit good thermal stability, only beginning to decompose at 270–300 °C. Vanadium-based cathodes, while stable on their own, show increased decomposition energy and lower DSC peak temperatures when in contact with a specific electrolyte solution. Most significantly, the anode material’s interaction with the electrolyte had the greatest thermal effect, with the decomposition heat of the soaked, charged electrode being nearly 40% higher than the combined decomposition heat of the dry electrode and electrolyte alone.

These contributions from this Topic, entitled “Electrochemical Energy Storage Materials”, offer the latest and most innovative solutions that can overcome the current limitations of EES materials and devices, providing valuable insights into the challenges and opportunities associated with the development of next-generation EES materials, as well as strategies for overcoming current limitations and scaling up to commercial applications. Together with the co-Topic Editor, Prof. Dr. Yuan Ma, we wish to thank the authors that contributed their works to this Topic.