The work, published in Nature Nanotechnology, focuses on iron-rich sodium layered oxides, a family of positive-electrode materials in which sodium ions move in and out of stacked oxide layers during battery operation. These compounds can exploit the Fe(III)/Fe(IV) redox couple, allowing iron ions to participate in the reversible transfer of electrons that stores electrical energy. Iron is especially attractive because it is inexpensive, widely available and less vulnerable to supply constraints than metals such as nickel or cobalt. However, the researchers found that increasing the iron concentration beyond roughly 33 atomic percent of the transition-metal sites creates a severe trade-off: capacity rises, but structural damage accumulates quickly during cycling.

The central discovery is that the degradation is not simply a consequence of large-scale phase changes visible across an entire electrode particle. Instead, it begins with the instability of iron’s octahedral coordination environment at the nanoscale. In the layered oxide structure, each iron ion is normally surrounded by six oxygen ions arranged approximately at the corners of an octahedron. This local geometry helps maintain the framework that supports sodium-ion transport. When the coordination environment becomes unstable during electrochemical cycling, iron ions can migrate away from their preferred sites and, in some cases, dissolve from the active material into the battery electrolyte.

That migration and dissolution trigger a chain reaction inside individual cathode particles. Regions affected by iron movement no longer expand and contract in exactly the same way as their surroundings. The resulting mismatch in local strain produces uneven mechanical stress, while defects such as dislocations accumulate within the particles. Eventually, the stress becomes concentrated along vulnerable internal regions, generating intragranular microcracks. These cracks are particularly damaging because they divide an initially coherent active particle into mechanically disconnected domains and create new surfaces that can react with the electrolyte.

The study further shows that the damage does not stop when the first cracks form. Driven by the non-uniform strain field, microcracks spread through the particles and interact with crystallographic defects. The researchers observed planar gliding, a process in which sections of the crystal shift along defined planes. Repeated gliding can reshape the external surface of the material, producing a distinctive stepped morphology. Such steps and cracks can interfere with the movement of sodium ions, expose fresh reactive surfaces and intensify chemical degradation, creating a feedback loop in which structural damage accelerates electrochemical capacity loss.

This nanoscale-to-microscale connection helps explain why iron-rich materials can fail even when their overall crystal structure appears to remain largely intact. Conventional structural measurements may average over millions of atoms and miss local coordination changes or the earliest stages of defect formation. By examining the electrode at much smaller length scales, the researchers linked iron instability directly to mechanical failure. Their findings suggest that the crucial design target is not merely the average composition of the cathode, but the ability of the local iron–oxygen environment to remain stable as sodium ions are repeatedly extracted and reinserted.

To reinforce that environment, the team introduced three dopant elements at the nanoscale: 1 atomic percent aluminium, 1 atomic percent yttrium and 3 atomic percent cobalt. The combined addition is designed to alter the local chemical and structural landscape without replacing the iron-rich character of the cathode. Aluminium and yttrium are expected to help stabilize the oxide framework, while cobalt can influence transition-metal–oxygen interactions and the electronic structure of the material. More broadly, the multi-element approach distributes the stabilizing effect across several chemical components rather than relying on a single dopant.

The modified material showed reduced iron migration and dissolution, which in turn suppressed the formation of internal cracks and limited planar gliding. This is significant because it addresses the proposed failure mechanism at its origin rather than attempting to repair damage after it has formed. By preserving the local octahedral coordination around iron, the doped oxide can better accommodate the repeated strain associated with sodium-ion removal and reinsertion. The result is a more mechanically coherent positive electrode with improved resistance to the chain of events that normally causes rapid capacity decay in iron-rich compositions.

The researchers then moved beyond half-cell experiments and assembled full sodium-ion pouch cells using the multi-element-doped positive electrode and a hard-carbon negative electrode. The cells reached a capacity of 2.7 ampere-hours, demonstrating that the approach can operate at a scale relevant to practical battery development rather than only in small laboratory test cells. Based on the total mass of the cell, the initial specific energy reached 121 watt-hours per kilogram at a current of 26 milliamperes per gram. When cycled at 130 milliamperes per gram and 25 degrees Celsius, the cells retained 83.4 percent of their discharge capacity after 2,000 cycles.

Those figures do not make sodium-ion batteries a universal replacement for lithium-ion cells, and the reported energy density remains dependent on the complete cell design, electrode balancing and testing conditions. Nevertheless, the results offer a compelling answer to a major obstacle facing iron-rich sodium layered oxides. The study shows that a material composed largely of abundant elements can be made more durable by controlling local coordination chemistry and the mechanical stresses that emerge from it. For sodium-ion technology, the implication is powerful: preventing a few unstable iron environments at the nanoscale may be the key to preserving performance across thousands of charge–discharge cycles and bringing cost-effective, large-format batteries closer to widespread use.

Subject of Research: Nanoscale structural degradation and multi-element doping in iron-rich sodium layered oxide cathodes for sodium-ion batteries.

Article Title: Multi-element nanoscale doping of iron-rich sodium layered oxides enables ampere-hour-level Na-ion batteries

Article References: Jin, RX., Lei, X., Su, XC. et al. Multi-element nanoscale doping of iron-rich sodium layered oxides enables ampere-hour-level Na-ion batteries. Nat. Nanotechnol. (2026). https://doi.org/10.1038/s41565-026-02257-3

Image Credits: AI Generated

DOI: https://doi.org/10.1038/s41565-026-02257-3

Keywords: sodium-ion batteries, iron-rich layered oxides, cathode materials, Fe(III)/Fe(IV) redox, nanoscale doping, aluminium, yttrium, cobalt, iron migration, microcracking, planar gliding, hard carbon, pouch cells, battery durability

Sodium-ion batteries have emerged as promising contenders to lithium-ion systems, owing to sodium’s abundance and cost advantages. However, developing cathodes that deliver high voltage, fast sodium-ion transport, and long-term stability remains a formidable challenge. Traditional investigations often examined NVPF and NVOPF separately, leaving a gap in understanding how their anion chemistries influence their properties. This study bridges that divide by systematically analyzing how partial fluorine-to-oxygen substitution reshapes their crystal structure and electrochemical behavior.

Structurally, NVPF crystallizes in the P4₂/mnm space group with vanadium coordinated to oxygen and fluorine in dioctahedral units. Its strong inductive effect from fluorine elevates the vanadium redox potential to nearly 4.1 volts, but a highly ordered sodium arrangement induces phase transitions that hamper ion mobility. Conversely, NVOPF adopts an I4/mmm structure with mixed O and F coordination, resulting in a slightly lower voltage around 3.8 V but enhanced electronic conductivity. Oxygen substitution fosters π-electron delocalization, enabling solid-solution sodium storage and suppressing intermediate phase formations, which favor fast Na⁺ diffusion.

Advanced computational modeling further reveals distinct ion transport mechanisms: NVPF’s sodium migration primarily occurs via anisotropic pathways in the (002) plane, facing a 0.43 eV activation barrier. NVOPF, in contrast, features intrinsic ab-plane “ion highways” with significantly reduced barriers between 0.15 and 0.31 eV. These findings underscore how tuning anion chemistry directly modulates bulk electronic structure, ionic diffusion channels, and interfacial kinetics.

Beyond fundamental insights, the review critically assesses synthesis and doping strategies that can optimize these cathodes for practical use. Scalable mechanochemical methods permit kilogram-scale NVOPF production at ambient temperatures, while controlled hydrothermal processes yield tailored nanostructures enhancing electrochemical activity. Surface carbon coatings and elemental doping—such as Fe, Mn, Cr, and Li—significantly improve conductivity, stabilize frameworks, and extend cycle life. Notably, Li-doped NVPF achieves remarkable capacity retention after tens of thousands of cycles by disrupting ordered sodium arrangements.

The researchers also address persistent challenges in cathode-electrolyte interfaces. Operating at high voltages above conventional electrolyte stability windows, NVPF suffers oxidative electrolyte decomposition and interphase growth, whereas NVOPF is prone to hydrofluoric acid generation and vanadium dissolution. Innovative electrolyte formulations incorporating high-concentration ethers and functional additives, along with in-situ protective interphases, emerge as promising solutions to mitigate degradation and enable long-term high-voltage operation.

This comprehensive review presents a paradigm shift—demonstrating that anion chemistry is a powerful, tunable lever to regulate structure-function relationships in sodium cathodes. These insights open new avenues to engineer fast-charging, high-energy-density, and durable sodium-ion batteries, crucial for sustainable grid-scale energy storage.

Stay tuned as this collaborative team from Zhejiang University, South China Normal University, and Zhejiang University-Quzhou continue advancing the frontier of sodium-ion battery materials science.

Subject of Research: Anion Chemistry and Electrochemical Performance of Fluorophosphate NASICON Cathodes in Sodium-Ion Batteries
Article Title: Anion Chemistry: Structure, Electrochemistry and Stability of NASICON Cathodes
News Publication Date: 2-Jun-2026
Web References: http://dx.doi.org/10.1007/s40820-026-02241-5
Image Credits: Tingting Cai, Dongxu Yu, Xueyan Zhang, Shuangshuang Zhao, Liguang Wang

Keywords

Sodium-ion batteries, NASICON cathodes, fluorophosphate, anion chemistry, Na₃V₂(PO₄)₂F₃, Na₃V₂O₂(PO₄)₂F, ionic diffusion, high-voltage cathodes, electrolyte stability, energy storage

Sodium-ion batteries have gained immense traction as a promising alternative to lithium-ion batteries, primarily due to sodium’s natural abundance, cost-effectiveness, and electrochemical properties parallel to lithium. Among various cathode materials, NASICON-type phosphates such as Na3MnTi(PO4)3 stand out for their robust three-dimensional ion diffusion pathways, exceptional structural stability, wide voltage operating window, and high theoretical capacity of 176 mAh g⁻¹. However, the electrochemical performance of Na3MnTi(PO4)3 is severely hindered by intrinsic anti-site defects—where manganese ions occupy sodium ion vacancies (Na2 sites)—leading to significant voltage hysteresis, irreversible capacity degradation, sluggish Na⁺ diffusion kinetics, and diminished cycling stability.

Conventional approaches to mitigate these defects have revolved around non-stoichiometric synthesis and doping with high-valent cations. While these techniques alleviate some issues through indirect charge compensation or reducing sodium vacancies, they have fallen short of addressing the fundamental electronic origins underlying formation of anti-site defects. Consequently, these traditional methods have not delivered optimal improvements in cycling performance and rate capability. The current study pivots from these indirect measures and presents a precise, electronic structure-based regulatory approach to inhibit Mn anti-site defect formation.

Central to this novel solution is the strategic modulation of the Mn 3d-eg orbital occupancy via Li doping, which induces the formation of a specific Li–O–Mn configuration. This configuration enhances the hybridization between manganese 3d-eg orbitals and oxygen 2p orbitals, leading to significantly strengthened Mn–O covalency. This orbital interaction elevates the formation energy barrier for Mn anti-site defects, effectively preventing Mn ions from occupying Na vacancies. By fine-tuning the local electronic structure, the researchers achieved a fundamental suppression of the defect formation altogether rather than compensating for its effects.

The optimized material, characterized as Na2.97Li0.03MnTi(PO4)3, exhibits markedly improved electrochemical robustness. During cycling, it maintains a high structural integrity with minimal volume change (~5.8%), which is crucial for long-term stability and high-rate performance under operational stress. Electrochemical tests reveal that this cathode sustains an impressive capacity retention rate of 89.6% after 3,000 cycles at a 10C rate within a broad voltage range (1.5–4.3 V versus Na⁺/Na). Unlike many battery materials that degrade rapidly or suffer from voltage hysteresis, this Li-doped NASICON cathode maintains consistent performance across a wide temperature gamut from −30 to 40 °C.

Importantly, the practical potential of Na2.97Li0.03MnTi(PO4)3 was validated in a pouch-type full cell format, a key step towards real-world applications. The full cell demonstrated promising electrochemical stability and performance parameters, underscoring the industrial relevance of this strategy. These results collectively highlight that electronic structure regulation via orbital modulation is not only a powerful scientific insight but also a viable engineering pathway to producing high-performance, durable, and adaptable sodium-ion batteries.

Looking ahead, the research team plans to extend their orbital modulation framework to other polyanionic cathode materials plagued by cation disorder and anti-site defect formation. They aim to develop universal descriptors that quantitatively relate orbital occupancy, metal-oxygen covalency, and defect formation energetics. Such descriptors can accelerate the rational design and optimization of next-generation cathode materials exhibiting high voltage, enhanced capacity, and superior long-term stability, thereby expansive sodium battery technologies.

From an industrial perspective, efforts will concentrate on optimizing scalable synthesis routes to produce Li-doped NASICON cathodes with meticulously tuned electronic structures, but at lower manufacturing costs. Coupling these with advanced electrolytes and anodes opens new avenues for fabricating full cells with improved energy density, cycle life, and environmental adaptability. Such integrated advances will propel sodium-ion batteries closer to widespread commercialization, supporting large-scale energy storage applications, electric vehicles, and portable electronics.

The impact of this research is significant and multifaceted. For the first time, the intrinsic mechanism of manganese-oxygen covalent interaction in restraining anti-site defect formation is elucidated at the electronic level. This fundamentally changes the paradigm for modifying NASICON-type phosphates and offers a blueprint for addressing cation disorder in a variety of other metal oxide and polyanionic cathode materials. By innovatively linking orbital physics with defect chemistry and practical battery performance, this work accelerates the quest for low-cost, high-efficiency, and sustainable sodium-ion battery technologies critical to the global transition towards clean energy and carbon neutrality.

Published in the esteemed interdisciplinary journal Materials Futures, this research sets a new benchmark in electronic structure modulation for energy storage materials. It stands as a testament to how deep quantum-level insights can translate into macro-scale technological advancements, bridging the gap between fundamental materials science and applied battery engineering.

In summary, the orbital modulation strategy crafted by the Huazhong University team not only surmounts the detrimental effects of anti-site defects but also unlocks outstanding electrochemical performance parameters, including ultra-long cycling stability, improved rate capability, and operational versatility under extreme temperatures. As the global energy landscape increasingly demands sustainable and cost-effective storage, approaches such as these provide the scientific foundation and engineering roadmap necessary to realize sodium-ion batteries as mainstream energy solutions.

Subject of Research: Orbital modulation to suppress anti-site defects in NASICON-type cathodes for high-performance sodium-ion batteries

Article Title: Orbital Modulation to Restrain Anti-Site Defects in NASICON Cathode for High-Performance Sodium-Ion Batteries

News Publication Date: 11-Feb-2026

Web References: DOI: 10.1088/2752-5724/ae44b2

References:
Jiandong Zhang, Zhaoshi Yu, Liyuan Tian, Yanbin Zhu, Muqin Wang, Pengkun Gao, Yali Zhang, Naiqing Zhang, Deyu Wang, Yan Shen, Mingkui Wang. Orbital modulation to restrain anti-site defects in NASICON cathode for high-performance sodium-ion batteries[J]. Materials Futures. DOI: 10.1088/2752-5724/ae44b2

Image Credits: Mingkui Wang, Yan Shen, and Jiandong Zhang from Huazhong University of Science and Technology

Keywords

NASICON, Sodium-ion battery, Anti-site defects, Orbital modulation, Li doping, manganese-oxygen covalency, Defect formation energy, Long-cycle stability, Voltage hysteresis, High-rate performance, Wide-temperature adaptability, Polyanionic cathode materials