Zhi Zhang

Prussian blue analogues (PBAs) are promising cathode materials for sodium‐ion batteries (SIBs) because of their open frameworks, tunable redox sites, and low‐cost synthesis. However, they face the critical challenge of balancing specific capacity and cycling stability. This Review examines how their crystal structures, phase transition behaviors, and sodium‐ion migration pathways affect Na ⁺ storage in single‐ and double‐electron‐transfer configurations within a specified voltage window. Complementary in situ and operando techniques connect these processes with the structural and chemical changes accompanying capacity loss. The discussion links these changes to cyanide coordination electronic structure, vacancy–water interactions, and multiscale optimization strategies for activating redox sites and retaining their activity during cycling. Challenges and future prospects center on reproducible synthesis, mechanistic validation, and sustained capacity. This review provides guidance for developing high‐performance PBA cathode materials for SIBs.

The low intrinsic electronic conductivity of polyanionic cathodes, caused by electronic localization of isolated anionic groups, restricts the fast‐charging performance of sodium‐ion batteries. To address this challenge, we strategically introduce low‐valence Cs ⁺ into Na ₄ Fe ₃ (PO ₄ ) ₂ (P ₂ O ₇ ) (NFPP) to enhance small polaron hopping and electronic conductivity. The Cs ⁺ triggers a charge‐compensation effect that pre‐stabilizes Fe ³⁺ species and establishes an Fe ³⁺ reservoir in NFPP. This configuration creates a built‐in electric field that introduces electron‐relaying states above the valence‐band maximum, significantly lowering the small‐polaron hopping barrier between Fe ²⁺ /Fe ³⁺ couples. Crucially, Hall‐effect measurements directly validate this mechanism, revealing enhanced carrier mobility and concentration that overcompensate for conventional doping strategies with reduced carrier mobility trade‐off due to carrier scattering from doped foreign ions. Consequently, the optimized NFPP‐Cs cathode overcomes carrier transport bottlenecks and hence enhances charge storage kinetics, achieving an 80% state‐of‐charge in just 7.9 min at 5 C and achieving full charge in 58 s at 50 C with a high specific capacity of 81.0 mAh g ⁻¹ . Distribution of relaxation times analysis further substantiates that this charge‐compensation‐driven small polaron hopping constitutes the core mechanism for the enhanced electrochemical reaction kinetics. This work provides a compelling paradigm for designing polyanionic frameworks with enhanced reaction kinetics.

Aqueous sodium‐ion batteries (ASIBs) are attractive for large‐scale storage due to intrinsic safety and low cost. However, their practical applications are often limited by sluggish kinetics and the dependence on purified electrolytes. Here, we report a layered organic–MXene heterostructured anode by direct thermal polymerization of a conjugated naphthalene‐based polyimide (NPI) in the presence of multilayer Ti ₃ C ₂ T _x MXene, forming a tightly coupled 2D architecture (NPI@MXene). NPI provides reversible imide‐carbonyl redox sites, while MXene facilitates electron transport and interfacial ion‐transfer kinetics, thereby reducing polarization and accelerating Na ⁺ storage. Benefiting from the reversible carbonyl conversion, enhanced pseudocapacitive behavior, and improved Na ⁺ diffusion kinetics, the optimized NPI@MXene anode delivers a specific capacity of 124.5 mAh g ^{− 1} at 1.00 A g ^{− 1} and shows excellent durability with 100.0% retention over 65 000 cycles at 15.0 A g ^{− 1} . For practical operation, seawater is used to prepare a 1.00 M sodium acetate electrolyte with the most favorable interfacial kinetics among the tested seawater‐based electrolytes. The assembled NPI@MXene//Cu‐PBA full cell operated stably over the 0–1.60 V range and maintained its performance for 15 000 cycles.

Proton storage in transition-metal oxides is often linked to fast proton transport, but how crystal phase governs structural evolution, electronic response, and kinetics remains insufficiently understood. Here, α-MoO3 and h-MoO3 are compared as model polymorphs to reveal phase-dependent proton-storage behavior. In situ XRD and state-resolved XPS show that α-MoO3 undergoes an initial irreversible structural reconstruction and then enters a reversible regime with lattice breathing and multivalent Mo redox, exhibiting battery-type behavior and favorable rate capability. In contrast, h-MoO3 rapidly loses long-range order after deep protonation, with poor structural recovery, limited Mo-valence evolution, and predominantly pseudocapacitive charge storage. Electrochemical impedance spectroscopy coupled with distribution of relaxation times analysis and first-principles calculations further indicate that α-MoO3 preserves electronic delocalization and stronger electron–proton coupling, whereas h-MoO3 shows weakened electronic coherence and kinetically dispersed charge compensation. These findings identify structural/electronic coherence as a key criterion for high-performance proton storage.

Aqueous energy storage systems (AESS) offer advantages such as safety and environmental friendliness. Among them, the rapid charge-discharge capabilities of ammonium-ion batteries (AIBs) and the high energy density of zinc-ion batteries (ZIBs) complement each other. Although V2O5 holds promise as a key electrode material in both AIBs and ZIBs, it is limited by its slow kinetics and structural instability. Herein, V2O5·0.47H2O (HEVOH) with extended interlayer spacing and an optimized electronic structure is successfully constructed via a high-entropy doping strategy, effectively solving the issues of slow kinetics and structural instability of V2O5, and demonstrating outstanding performance in both AIBs and ZIBs. When used in AIBs, it delivers a capacity of 137.6 mAh g–1 at 0.20 A g–1, with a capacity retention of 92.7% at 1.00 A g–1 after 3000 cycles. When used in ZIBs, it achieves a capacity of 543.6 mAh g–1 at 0.10 A g–1, maintaining 76.6% capacity at 10.00 A g–1 after 7000 cycles. The NH4+ storage mechanism involves interlayer intercalation, hydrogen bond reconstruction, and oxygen vacancy generation. The Zn2+ storage mechanism is interlayer intercalation and reversible deposition of Zn4SO4(OH)6·4H2O to construct a dynamic interface protective layer. This work provides a direction for the universal design of high-performance AESS.

Fast‐charging operation in lithium‐ion batteries is influenced by internal mechanical heterogeneity, while its spatiotemporal evolution under high‐rate conditions remains poorly resolved. Existing diagnostic approaches provide only surface‐level information, leaving internal mechanical heterogeneity during fast charging inaccessible. Here, we employ operando distributed optical fiber sensing to reconstruct the strain evolution within LiFePO ₄ pouch cells at millimeter‐scale resolution. The reconstructed strain evolution exhibits a clear transition in deformation behavior with increasing C‐rate. Under low‐rate cycling, the electrode stack undergoes largely synchronous deformation during lithiation and delithiation. As the charging rate increases, this uniform response breaks down, and the deformation becomes kinetically desynchronized. At 1.5 C, pronounced spatial heterogeneity emerges, characterized by strain inversion and amplification of strain gradients near constrained regions. In these regions, the deformation response reflects coupled electrochemical expansion and local thermal loading, with the effective strain–temperature sensitivity increasing from ∼0.71 to ∼2.13 µε °C ⁻¹ . The strain‐concentrated regions exhibit mechanical irreversibility, quantified by a strain asymmetry factor (η) reaching 0.588, and are spatially associated with post‐cycling microstructural evolution, as reflected by an apparent ∼6.8% residual electrode‐thickness difference. Together, these insights provide a mechanistic basis for optimizing cell‐level architectures in next‐generation fast‐charging batteries.

P-orbital hybridization engineering for multistep electron excitation via intermediate states in wide-bandgap polyanion cathodes.

A proton battery is considered as a promising energy storage solution with the merits of fast kinetics, high safety, low cost, and environmental benignity. The realization of these merits depends on the exploration of the appropriate and high-performance electrode materials. Although many anode materials of proton batteries have been reported, a dedicated summary of the progress, challenges, and prospects of anode materials for proton batteries has not been reported. Through discussions on the proton storage mechanisms, advantages and limitations of various anode materials, optimization strategies to boost their proton storage capability, and their potential applications, this review seeks to provide a comprehensive theoretical foundation and practical guidance for future research and development of proton battery technology. First, the preparation methods and proton storage mechanism of anode materials have been discussed. Then, the limitations and optimization strategies have been summarized. After that, the next section elaborately focuses on the proton storage performance of different types of anode materials. Finally, the challenges and prospects of anode materials for proton batteries have been proposed. This review aims to provide insight into the efficient design and optimization of anode materials for practical applications of proton batteries.

Antimony oxide (Sb₂O₃) exhibits a high theoretical capacity for sodium storage but suffers from poor reaction kinetics and significant volume expansion. Exposing specific crystal facets of an electrode material is considered to be an effective strategy to reduce the expansion ratio and ion diffusion barrier. Here, in situ TEM investigations and theoretical calculations indicate that the exposure of (010) facets in Sb₂O₃ ameliorates the expansion ratio and reduces the Na⁺ diffusion barrier to enhance reversible Na⁺ storage. Theoretical calculations also reveal that polyvinylpyrrolidone facilitates the exposure of (010) facets. A facet-engineered Sb₂O₃ nanobelt with exposed (010) facets (Sb₂O₃-(010)) demonstrates superior performance, including higher capacity, excellent rate performance, and enhanced cycling stability compared to conventional Sb₂O₃. Notably, at 60 °C, Sb₂O₃-(010) shows excellent sodium storage properties and even maintains an 80.6% capacity retention ratio after 200 cycles at 5.00 A g^-1. This work underscores the potential of crystalline facet engineering to improve sodium-ion battery performance.

Sodium‐ion batteries (SIBs) are highly anticipated as an efficient energy storage solution in addressing contemporary energy challenges. The pursuit of high‐performance cathode materials is critical for the commercialization of SIBs. Among the contenders, Na₄Fe₃(PO₄)₂(P₂O₇) (NFPP) is one of the most promising commercial cathode materials due to its stable structure framework and excellent sodium storage capability. Although the research on NFPP has achieved great progress, especially in the last 10 years, the timely and dedicated summary of the research progress and prospect of this rising star of cathode materials for SIBs has not been reported. This review provides a comprehensive overview of the advancement and prospect of NFPP as commercial cathode material in SIBs. In this review, the crystal structure and sodium storage mechanism of NFPP are examined first. Then, different proposed preparation methods of NFPP have been elaborated in the following section. After that, the optimization strategies are discussed to enhance the sodium storage performance of NFPP cathode material in detail. At last, the gap between current research and the practical application of NFPP is highlighted, and possible future research directions for the commercialization of NFPP cathode material in SIBs are proposed.