Advancing electrochemical energy storage beyond lithium-ion technologies has become increasingly critical in response to sustainable development. Rechargeable magnesium metal batteries (RMBs), recognized for their inherent advantages in resource abundance, potential for higher volumetric capacity, and enhanced safety characteristics due to the dendrite-free plating of magnesium, stand out as highly promising for next-generation energy storage. Recent breakthroughs in magnesium-compatible electrolytes have effectively overcome longstanding issues of anode passivation and low coulombic efficiency, thereby accelerating RMB research into a new stage of development. However, the practical application of RMBs continues to face significant challenges, predominantly centered on cathode materials. These challenges primarily stem from the strong polarization and high charge density of divalent Mg²⁺ ions, which lead to strong electrostatic interactions with the host cathode materials, resulting in sluggish solid-state diffusion kinetics that limit achievable energy density and cycling stability. To systematically address these hurdles and promote the development of cathode materials, this review provides a comprehensive summary of recent progress in inorganic cathode materials for RMBs, focusing on four major categories: polyanionic compounds, oxides, sulfides, and selenides. For each class, we delve into the relationships between crystal structure, electrochemical performance, and Mg²⁺ storage mechanism, discussing both significant advances and persistent issues. Each material class faces distinct limitations, from short lifespan in polyanionic compounds to kinetic barriers in oxides and shuttle effects in chalcogenides. From this survey, we summarize effective material engineering strategies to address these challenges, which include nanostructural design to shorten diffusion pathways, composite engineering to enhance conductivity, interlayer expansion to facilitate ion transport, defect modulation to create active sites, amorphization, and elemental doping to stabilize crystal structures. The rational integration of these strategies tailored to specific material limitations is crucial for breaking the current performance ceiling. Future research should emphasize advanced in situ/operando characterization, explore new cathode design paradigms, and pursue synergistic electrode-electrolyte pairings. This review aims to provide theoretical fundamentals for the rational design of high-performance cathode materials, promoting the technological advancement and practical application of RMBs.

Potassium-ion batteries (PIBs) have emerged as promising candidates for large-scale energy storage systems, owing to the abundant potassium resources and electrochemical properties similar to those of lithium-ion systems. Cathode materials play a pivotal role in determining the overall performance of PIBs. Among them, transition metal oxides (TMOs) have attracted extensive research interest due to their high theoretical capacity, suitable operating voltage, and tunable crystal structures. However, the relatively large ionic radius of K⁺ often leads to significant volume variation and anisotropic strain during (de)intercalation, which induces irreversible phase transitions, severe lattice distortion, and structural collapse. In addition, the Jahn-Teller effect associated with transition-metal ions such as Mn³⁺ further aggravates local structural distortion and triggers transition metal dissolution, severely limiting the cycling stability and energy density of TMO cathodes. These issues underscore the importance of rational material design and interface regulation to achieve stable electrochemical performance. This review systematically summarizes the recent progress in TMO cathode materials for PIBs, encompassing evaluation metrics and synthesis methods. A variety of modification strategies, including elemental doping, surface coating, and multi-scale structural design, have been developed to modulate lattice parameters and defects, suppress phase transitions, and enhance ionic conductivity, operating voltage, structural stability, and cycling endurance. Among these approaches, P2/P3 biphasic integration and high-entropy doping, for example, have been shown to effectively inhibit Jahn-Teller distortion and volume change, thereby enabling long-term cyclability. In addition, the combination of in situ characterization and theoretical calculations has significantly deepened the understanding of K⁺ storage mechanisms and structure-performance relationships. Notwithstanding the substantial progress achieved, several critical challenges persist. These include capacity enhancement and structural stability optimization, cycle life improvement and the formulation of integrated strategies, cathode-electrolyte interphase engineering, the development of composite materials and hybrid systems, ensuring manufacturing consistency and scalability, advancing theoretical modeling and computational guidance, as well as leveraging artificial intelligence (AI)-assisted material design and prediction. Future efforts should focus on developing novel structural motifs, optimizing electrode/electrolyte interfaces, advancing sustainable manufacturing processes, and integrating AI-guided material design. This review provides a comprehensive overview of mechanistic strategies and recent progress, offering valuable insights for the rational design of high-performance PIBs suitable for practical applications in large-scale energy storage and next-generation energy storage applications.

Metal doping is a key modification strategy for MnO₂ cathodes in aqueous zinc-ion batteries, with parameter selection directly governing the resulting electrochemical performance. However, the intricate interplay among dopant type and concentration, synthesis conditions, and electrochemical performance renders the optimization of MnO₂ cathodes for high electrochemical properties still elusive. Traditional trial-and-error experimental screening is time-consuming and expensive, and developing a unified guideline on the design of metal-doped MnO₂ remains a long-standing challenge. To efficiently study the performance of metal-doped MnO₂, we proposed a machine learning (ML) model driven by data from the literature. A dataset was constructed from 36 articles covering 21 dopant elements, integrating elemental descriptors, synthesis parameters, and electrochemical testing conditions. After feature filtering and model evaluation, the extreme gradient boosting (XGB) model achieves a high predictive accuracy with an R² of 0.921 on the test set. Beyond prediction, model interpretability using Shapley additive explanations (SHAP) analysis identifies the dominant factors affecting capacity, revealing the influence of current density, dopant ratio, and molecular weight. Feature importance analysis further guided the design of a series of experiments that validated the accuracy and reliability of the model. Experiments on Fe- and Ni-doped MnO₂ cathodes confirmed the ability of metal doping to enhance specific capacity, and the model achieved a mean absolute error (MAE) below 12 mAh g⁻¹ for all cases. Density functional theory (DFT) calculations further verified the molecular-level mechanism of metal doping by demonstrating that dopant incorporation modulates the electronic structure of MnO₂ and narrows the bandgap, improving conductivity. The consistency between the ML results, experimental validation, and theoretical calculations highlights the robustness of the proposed framework. Having established the feasibility from multiple perspectives, we further deployed a performance prediction platform based on this model, providing a convenient tool for researchers to rapidly estimate the specific capacity of metal-doped MnO₂ under user-defined conditions. This work demonstrates a comprehensive data-driven paradigm that integrates ML, experimental validation, and theoretical calculations. We believe that this approach provides a new strategy and framework for the rational design of high-performance MnO₂ cathodes, and is broadly applicable for accelerating the discovery of other metal-doped energy storage materials.

Sulfide-based all-solid-state lithium-ion batteries (ASSLIBs) have emerged as one of the most promising candidates for next-generation energy storage systems owing to their high energy density, wide electrochemical stability window, and intrinsic safety benefits over liquid electrolyte counterparts. Nevertheless, their practical implementation faces a fundamental bottleneck: the strong dependence on high external stack pressure to maintain interfacial contact and suppress mechanical degradation during operation. This requirement not only reduces energy efficiency and packaging flexibility but also severely restricts scalability and commercialization, as maintaining uniform high pressure in large-format cells is technically challenging and economically costly. Addressing the critical challenge of achieving low-pressure or even ambient-pressure operation in sulfide-based ASSLIBs is therefore of both scientific and technological significance. In this review, we systematically analyze the origins of pressure-dependent performance, including particle fracture in Ni-rich layered cathodes, dynamic interfacial instability, and insufficient mechanical compliance of composite electrodes. Building on this mechanistic understanding, we summarize recent advances and design strategies across multiple scales. At the cathode level, particle size regulation, compositional doping, and engineered porosity, combined with conformal interfacial coatings, effectively mitigate stress concentration and suppress degradation. On the electrolyte and electrode interface, optimizing particle size distribution, tailoring interfacial chemistry, and introducing dynamic polymeric binders with balanced adhesion and elasticity significantly enhance ionic transport and maintain robust contact under low pressure. At the system level, strategies such as optimized temperature management, adjustment of the electrochemical window, and controlled isostatic pressure provide additional means to stabilize operation and complement materials-level solutions. Taken together, these advances demonstrate that the key to pressure-independent ASSLIBs lies in a synergistic design framework that integrates intrinsic materials engineering, interfacial stabilization, and system-level control. We further propose a cross-scale design roadmap toward the realization of low-pressure and flexible ASSLIBs, highlighting the need for dynamic adaptation between mechanical properties and electrochemical processes. This perspective underscores that enabling stable performance under minimized external pressure is not only essential for translating laboratory demonstrations into practical large-scale devices but also paves the way for safer, lighter, and more energy-efficient solid-state battery technologies.

Ni-rich layered cathodes have become the mainstream choice to meet the growing demand for high-energy lithium-ion batteries (LIBs), which typically involves the use of highly polar N-methyl-2-pyrrolidone (NMP) to dissolve polymeric binders and form rheologically stable slurries for strong mechanical adhesion within the electrode. However, growing health and environmental concerns over NMP have triggered increasingly stringent regulations for sustainable development of LIB industries, thereby accelerating a long-overdue paradigm shift toward greener and safer solvent systems. In this context, this review first establishes a comprehensive theoretical framework for green solvent selection and slurry evaluation, including key concepts of solvent-binder compatibility, such as solubility theory, Hansen solubility parameters, Flory-Huggins interactions, and rheological characterization. Subsequently, the review highlights recent research progress in the development of green solvent-based slurries, covering a variety of solvent systems such as lactones, sulfoxides, phosphates, amides, and bio-based alternatives. Special emphasis is placed on elucidating how the processing behavior of green slurry influences the architecture of electrodes and determines their key performance indicators. Binder solubility, dispersion stability, rheological properties, and drying dynamics are analyzed in relation to their effects on electrode morphology, mechanical cohesion, capacity retention, and cycling stability. Despite encouraging laboratory results, these green slurry systems still face several practical barriers, including incomplete binder dissolution, binder migration during drying, and limited adaptability to high-solid-content formulations and accelerated drying protocols. To address these challenges, this review also proposes corresponding mitigation strategies and design recommendations, including thermodynamic-based solvent screening, rheological optimization, and drying kinetics control tailored to Ni-rich electrode systems. Finally, by integrating the latest advances in artificial intelligence, this review outlines future directions for predictable green slurry systems enabled by techniques such as machine learning-assisted solubility prediction, data-driven rheology modeling, and numerical model-enhanced drying simulations. By combining classical theoretical insights with advanced computational strategies, this review is expected to provide new perspectives for the sustainable manufacturing of next-generation high-energy batteries.

Sodium-ion batteries (SIBs) have demonstrated enormous application potential in large-scale energy storage systems due to their abundant sodium resources, low cost, and environmental friendliness. The ion migration rate and electron transfer efficiency of cathode materials are key factors determining the rate performance, cycle life, and capacity retention rate of batteries, and synergistic improvement of both is essential to overcoming performance bottlenecks. This paper takes the three mainstream cathode materials of sodium-ion batteries as its research objects, including layered transition metal oxides (LTMOs), polyanionic compounds (PACs), and Prussian blue analogues (PBAs). It systematically reviews the structural basis of ion migration channels and electron transfer pathways in different material systems and thoroughly analyzes their synergistic regulatory mechanisms. Combining the latest research findings, this paper explains, from three dimensions of elemental optimization, structural design, and composite modification, the specific pathways and mechanisms for synergistically enhancing the efficiency of ion channels and the continuity of electronic pathways. It distills universal strategies for designing high-performance SIBs cathode materials, providing a valuable reference for further developing SIBs cathode materials that combine high capacity, exceptional rate performance, and robust stability.

Na₃V₂(PO₄)₃ (NVP) is a promising cathode material for sodium-ion batteries owing to its NASICON-type framework, which enables efficient reversible sodium insertion. However, its practical performance is limited by slow charge transfer at high cycling rates and cycling instability. Here, we report a facile impregnation method to deposit Nb₂O₅ on NVP particles, aiming to enhance high-rate capability and long-term cycling stability. Structural and spectroscopic analyses (XRD, electron microscopy, Raman, XPS, and X-ray fluorescence spectroscopy) confirm the crystallinity of NVP and the uniform presence of Nb₂O₅ on particle surfaces without compromising sodium reversibility. Electrochemical measurements reveal that Nb₂O₅-coated samples show the highest diffusion coefficients, ensuring superior high-rate performance and cycling stability. The 3% Nb₂O₅ coating delivers the highest diffusion coefficients, superior cycling stability, and sustained capacity retention at a 1C rate. Cyclic voltammetry and impedance spectroscopy indicate enhanced surface capacitance, facilitating rapid sodium storage. XPS shows the conversion of Nb₂O₅ into NbF₅, resulting from HF scavenging, which improved interfacial stability. Extended cycling tests validate the long-term durability of the coated electrode. These results demonstrate that Nb₂O₅ surface modification is an effective strategy to overcome the intrinsic limitations of NVP, offering a viable route to high-performance sodium-ion batteries.

P2-type layered transition metal oxides (P2-Na_xTMO₂) have emerged as promising cathodes for sodium-ion batteries (SIBs) owing to their superior cycling stability and excellent rate capability. However, their practical application is significantly hindered by two major challenges. Firstly, irreversible phase transitions occur during high-voltage operation, which disrupt the structural integrity and deteriorate electrochemical performance. Secondly, their inherently low theoretical specific capacity fails to meet modern energy demands. To tackle these challenges, this study proposes a novel synergistic strategy that integrates high-entropy engineering with a biphasic P2/O3 structural design. An innovative cathode material, Na_0.70Ni_0.25Mn_0.35Co_0.15Fe_0.05Ti_0.20O₂ (denoted as Na_0.70NMCFT), was successfully synthesized via a high-temperature solid-state reaction. This material design critically incorporates five distinct transition metal cations into the transition metal (TM) layer, constructing a stabilized high-entropy configuration. Careful optimization of both the five TM elements and the sodium content was essential to precisely regulate the synthesis and formation of the desired integrated P2/O3 biphasic structure within this high-entropy host. Comprehensive structural characterization unequivocally confirms the successful construction of this tailored architecture. X-ray diffraction (XRD) and transmission electron microscopy (TEM) collectively confirm the successful construction of the P2/O3 biphasic architecture. The high-entropy engineering stabilizes the P2 phase through configurational entropy, effectively suppressing irreversible phase transitions and Na⁺/vacancy ordering during cycling, as evidenced by smoother charge/discharge profiles and ex-situ XRD analysis under high potentials. Meanwhile, the introduced O3 phase compensates for capacity shortages and improves cycling stability, working in tandem with the P2 phase. Critically, the interaction between the two phases enables a highly reversible transition between P2/O3-P2/P3, further enhancing the overall performance. Under the combined action of the high-entropy and biphasic strategies, Na_0.70NMCFT exhibits optimal electrochemical performance. It delivers an initial discharge capacity of 102.08 mAh g⁻¹ at 1C, retaining 88.15% after 200 cycles, demonstrating exceptional cycling stability. Moreover, even at 10C, Na_0.70NMCFT still has an initial discharge specific capacity of 85.67 mAh g⁻¹ and a capacity retention of up to 70% after 1, 000 cycles. Kinetic analyses further reveal that Na_0.70NMCFT possesses the lowest charge transfer resistance and the highest sodium-ion diffusion coefficient among the materials studied. In conclusion, this work demonstrates that the rational design of biphasic high-entropy cathodes can synergistically achieve superior rate capability, cycling stability, and maintain high theoretical capacity. It not only overcomes the key bottlenecks of P2-type oxides but also paves the way for the development of advanced SIB cathodes, establishing a new paradigm for the engineering of high-performance cathode materials in the field of sodium-ion batteries.