Oxygen redox pathway reconstruction via ZrO polarized layer and transition metal vacancies: a dynamic confinement strategy for high-performance sodium-ion battery.

Substitution is a vital strategy for developing high-performance sodium layered oxides (SLOs), which demonstrates great potential for making sodium-ion batteries a viable alternative to lithium-ion batteries. Numerous studies have been conducted on substituted SLOs; however, each substitute exhibits varied effects on the structure and electrochemical performance of the SLOs, and no clear design principles have been established. Clarifying the relationship among substitution, structure and performance is therefore important to enable a rational design strategy for high-performance SLOs. In this Review, the up-to-date substitution guidelines and the current understanding of how substitution affects the structure and electrochemistry in SLOs are discussed, and the site preference and characteristic redox features of different types of substitutes are outlined. The inherent challenges and opportunities for the innovation of better-performing SLOs are summarized, paving the way for accelerating the commercialization of SLO-based sodium-ion batteries and the realization of their applications ranging from electric vehicles to grid energy storage systems.

Prussian blue analogues (PBAs) have emerged as promising cathode materials for next-generation potassium-ion (PIBs)and sodium-ion batteries (SIBs) owing to their simple synthesis, low cost, structural robustness, and well-balanced electrochemical properties. Despite these advantages, several intrinsic challenges continue to limit their practical implementation. This review provides a concise roadmap connecting material-level fundamentals with key lab-scale optimization strategies, and highlights the factors that most critically influence the real-world viability of PBAs. Beyond targeting high performance, we evaluate the practicality of different approaches, with particular attention to particle size, crystal water, and safety considerations. The discussion aims to guide researchers in advancing PBAs toward scalable non-aqueous energy-storage systems and in supporting the broader development of sustainable battery technologies.

Impurities remain the key challenge for Na4-xFe3-x(PO4)2-xP2O7 (NFPP, 0 ≤ x ≤ 1) cathode materials in sodium-ion batteries (SIBs), addressed by modulating the Na2FeP2O7: Na4Fe3(PO4)2P2O7 ratio in this study. The optimal Na3.5Fe2.5(PO4)1.5P2O7 (Na3.5Fe2.5PP) material at a 1:3 ratio with the least impurities is scalably synthesized via a dual-iron-source system. Crucially, this study reveals the illusion of seemingly high discharge capacities caused by the "voltage tailing" phenomenon in some cathode materials, defining the "effective voltage range" as 2.4-3.7V in full-cells (N/P ratio = 1.1) through the triple-electrode measurements. Within this window, Na3.5Fe2.5PP delivers: (1) the highest initial charge/discharge capacities (116.05/ 102.33mAhg-1 at 0.1 C); (2) excellent rate capability (74.23 mAh g-1 at 30 C), and (3) superior cycling performance (75.4% capacity retention ratio after 10000 cycles at 20C). Finally, combined with hard carbon (HC) anode, Na3.5Fe2.5PP//HC pouch cells exhibit excellent safety, low-temperature performance (88.8% capacity retention ratio at -30°C), rate capability (84.1% capacity retention ratio at 30 C), and cycling stability (83.25% capacity retention ratio after 2300 cycles), enabling practical energy storage applications. This work refines NFPP purity enhancement strategies and reveals the capacity mismatch between half-cell and full-cell-a finding broadly applicable to SIBs using HC anodes, thereby facilitating practical SIBs applications in energy storage.

Sodium-ion batteries (SIB) have attracted significant attention as promising alternatives to lithium-ion batteries, due to the abundance, low cost, and environmental compatibility of sodium resources. Among various SIB cathode materials, NASICON-type Na3V2(PO4)3 (NVP) stands out for its stable 3D framework and fast Na+ diffusion kinetics. However, its inherently low electronic conductivity has posed challenges for practical implementation. Promising in this context, the NASICON-structure NVP nanomaterial was successfully synthesized using a modified Pechini method. Owing to the reduced particle size and carbon coating, the cathode exhibits exceptional performance, demonstrating a capacity of 74.13 mAh g−1 at 0.2 C even at −20 °C, which is 76.26% of its room-temperature capacity. Furthermore, the electrode retained 74.99% of its room-temperature capacity at −25 °C, demonstrating outstanding low-temperature resilience. These results confirm that the modified Pechini-derived NVP/C composite is a highly promising cathode material for high-performance sodium-ion batteries operating under subzero conditions.

Decoding the functional roles of multimetallic constituents in high-entropy prussian blue analogues for sodium-ion batteries.

Mn-rich layered oxides are among the most promising cathode materials for large-scale sodium-ion batteries due to their high capacity, elemental abundance, and low cost. Nevertheless, the practical application of these materials is impeded by the pronounced and intractable Jahn-Teller effect associated with Mn3+ ions. This effect triggers cooperative lattice distortion, resulting in structural degradation and compromised cycling stability. In this work, we demonstrate that spatially localizing Jahn-Teller active Mn3+ ions within confined Mn-rich slabs effectively suppresses long-range distortion and stabilizes the layered framework. The engineered Mn-rich oxide, NaNi0.3Cu0.1Mn0.6O2 (NCM316), exhibits exceptional electrochemical performance, achieving 89.5% voltage retention after 200 cycles. In full-cell configurations, NCM316 delivers a high discharge voltage of 3.36 V, the highest reported for Mn-based layered cathodes, while maintaining 84% capacity retention after 500 cycles and reaching an energy density of 337 Wh kg-1, outperforming all other Mn-based layered cathodes under a high cutoff voltage of 4.4 V. Comprehensive characterization using synchrotron X-ray and neutron scattering techniques, supported by theoretical simulations, confirm the localized presence of Mn3+ and elucidate its role in maintaining structural integrity and mitigating adverse interactions with neighboring transition metals. This work offers insight into the mechanism of Jahn-Teller distortion in Mn-rich layered oxides and proposes a broadly applicable design principle for stabilizing other Jahn-Teller active systems, such as layered lithium-rich cathodes, spinel-type oxides, and manganese-based materials for aqueous batteries.

Sodium superionic conductor (NASICON)-type materials are promising cathodes for sodium-ion batteries due to their stable multi-channel frameworks and exceptional ionic conductivity. Among them, Na3V2(PO4)2F3 (NVPF) has attracted significant attention. However, the low electronic conductivity and phase impurities limit its sodium storage capability. Herein, we present a Fe and Mn dual-doped NVPF (FM-NVPF) cathode with improved phase purity, electronic conductivity, and electrochemical activities. Detailed ex-situ analyses and density functional theory calculations reveal that Fe and Mn dopants induce defect energy levels and modulate the electronic structure, resulting in a direct-to-indirect bandgap transition in NVPF, which in turn increases carrier concentration and lifetime, accelerates ionic/electronic transport, and improves structural stability. As a result, the FM-NVPF cathode delivers a high capacity of 126.6mAh g⁻1 at 0.1C (1C = 128mAh g⁻1) and outstanding high-rate capability of 67.6mAh g⁻1 at 50C, corresponding to 1.2min per charge. Furthermore, Na ion full cells assembled with the FM-NVPF cathodes and hard carbon anodes exhibit a high energy density of about 175Wh kg-1cathode+anode mass and appealing cyclic stability. This work provides an efficient strategy for developing high-purity and high-performance NVPF cathode materials for advanced sodium-ion batteries.

O3-type layered transition metal oxides are considered promising cathode materials for sodium-ion batteries (SIBs) due to their high capacity and favorable Na+ storage characteristics. However, their practical application is severely hindered by structural instability associated with multiphase transitions during electrochemical cycling. Herein, we propose a spatially selective multi-element substitution strategy that induces spatially differentiated distributions of Mg, Cu, Ti, and B, thereby enhancing structural robustness. This spatially differentiated substitution architecture synergistically improves structural stability by concurrently inhibiting interfacial degradation and strengthening the lattice framework. The optimized composition (NaNi0.4Mg0.05Cu0.05Mn0.3Ti0.2B0.05O2) enables a stabilized O3→P3 phase transition, which relieves lattice distortion and suppresses structural collapse upon cycling. Density functional theory (DFT) analysis reveals that the strong covalency of B─O bonds is crucial for anchoring the P3 framework. Hence, it delivers superior high-temperature performance in half cells and durable cycling in full cells (85% capacity retention after 300 cycles at 0.5 C within 1.9-3.9V). By elucidating the role of spatially selective substitution in structural stabilization, this work provides fundamental insights and paves the way for the design of advanced SIB cathodes.

Tuning the upper cut-off voltage for enabling Co3+/Co2+ redox in a P2/P3/spinel composite cathode material for sodium-ion batteries: An in operando study

Spin-state-mediated mitigation of Jahn-Teller distortion in Prussian blue analogs enabling high-performance sodium-ion batteries.

Structure design and electrochemical performance regulation of Na4Fe3(PO4)2P2O7 cathode materials for sodium-ion batteries

Green and low-cost modified Na4Fe3(PO4)2(P2O7) cathode material for sodium-ion batteries with wide temperature operation

Prussian blue analogues as cathode materials for nonaqueous sodium-ion batteries: Fundamentals, mechanisms, and performance

Manganese-based Prussian blue analogues (Mn-PBA) are promising cathode materials for aqueous sodium-ion batteries (ASIBs) owing to their open framework that facilitates efficient sodium ion insertion/extraction. However, their practical deployment is hindered by structural collapse arising from high-spin Mn3+ (HS-Mn3+) dissolution during cycling, triggered by the Jahn-Teller effect, which severely limits long-term stability. Here, we design an in situ chemically regulated Mn@Fe/H-PBA electrode with a hierarchical hollow structure via co-precipitation. The hollow architecture provides a large surface area for enhanced active site utilization, while the stabilized hierarchical framework enriched with low-spin Mn3+ (LS-Mn3+) effectively suppresses structural distortion. Together, these features enable Mn@Fe/H-PBA to deliver a high discharge capacity of 121 mA h g-1 at 1 A g-1 with excellent cycling durability. In situ/ex situ characterization combined with density functional theory (DFT) calculations confirm the improved redox activity and mitigated Jahn-Teller distortion. Full cells paired with a polyimide (PI) anode achieve an energy density of 74.32 W h kg-1, while pouch cells demonstrate stable cycling over 500 cycles at 1 A g-1. This work provides a robust strategy to overcome stability challenges in Mn-PBA cathodes for next-generation ASIBs.

Covalency regulation of metal-oxygen ligand in O3-type layered cathode material for high-performance sodium-ion batteries

Accelerated and cost-effective synthesis of NaFe0.5Mn0.5O2 layered oxide cathode material and performance evaluation in sodium-ion batteries

A review on the thermal stability of sodium-ion battery cathode materials

This study introduces ME-Na3V1.4Fe0.1Mn0.2Cr0.2Zr0.1(PO4)2O2F@C (ME-NVOPF 1.01@C), a medium-entropy engineered sodium-ion battery (SIB) cathode material, addressing low conductivity of NASICON-type Na3V2(PO4)2O2F. Medium-entropy doping regulates the energy band structure and vanadium coordination, enhancing electronic conductivity and enabling a nonphase-change reaction with minimal volume change during Na+ insertion/extraction. Density functional theory calculations demonstrate that Na+ migration barriers and a narrowed bandgap were reduced, improving redox reversibility. The 3D carbon network further boosts the conductivity and sodium storage kinetics, achieving a Na+ diffusion coefficient of ∼10-11 cm2·s-1. ME-NVOPF 1.01@C delivers 97.2 mAh·g-1 at 0.1 C, with 72% capacity retention after 4500 cycles at 5 C, confirming exceptional cycling stability. This work elucidates the entropy-performance correlation and highlights the superiority of medium-entropy materials in overcoming the inherent limitations of polyanion cathodes, providing a strategic pathway for designing higher electrochemical performance sodium-ion battery materials.

O3-type layered oxides are promising cathode materials for sodium-ion batteries but suffer from structural instability, sluggish kinetics, and moisture sensitivity. This work proposes a synergistic modification of O3-NaNi1/3Fe1/3Mn1/3O2 (NFM). Among various perovskite titanates (CaTiO3, SrTiO3, BaTiO3) investigated, CaTiO3 proves to be the most effective modifier. DFT calculations reveal that Ca2+ doping uniquely strengthens the Na-O interaction, fundamentally enhancing the air stability. The conformal CaTiO3 coating serves as a robust physical barrier against humid air, significantly suppressing the formation of surface carbonates and residual alkali. Simultaneously, Ca2+ and Ti4+ are doped into Na and transition metal (TM) sites, respectively, which enlarges the Na+ layer spacing (from 3.701 to 3.812Å), strengthens the TM─O framework, and mitigates irreversible phase transitions. As a result, the modified NFM@CTO06 cathode exhibits outstanding electrochemical performance,demonstrating a high capacity retention of 85.1% after 300 cycles at 1 C. Furthermore, it demonstrates reduced voltage hysteresis, enhanced Na+ diffusion kinetics, and significantly improved air stability. This surface-to-bulk strategy offers a feasible approach toward practical high-energy-density sodium-ion batteries.