Sodium-ion batteries are attractive for large-scale energy storage due to the abundance of sodium, but the deficient capacity achieved by cathode materials prevents their further applications. Chemical substitution of Na in transition metal layers is a promising solution to utilize both the cationic and anionic redox activities for boosting energy storage. Unfortunately, different from the classic Li-rich Li₂MnO₃, a pure prototype with anionic redox activity has not been found among the typical Na-rich cathodes. Herein, we originally design a Na-rich layered oxide prototype, namely Na₃RuO₄ (Ru⁵⁺), which delivers a partial reversible capacity solely via the participation of oxygen anions. More importantly, the anionic redox activity is validated by the in situ Raman observation of reversible peroxo-based O–O (de)bonding upon cycling. Our findings not only highlight the multiple electron-transfer strategy for capacity extension, but also broaden the horizon in designing Na-rich electrode materials for high-energy sodium-ion batteries.

中文翻译：

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Na ₃ RuO ₄阴极中可逆的阴离子氧化还原活性：富钠原型层状氧化物†

钠离子丰富，因此钠离子电池对于大规模储能具有吸引力，但是阴极材料的容量不足会阻止其进一步应用。在过渡金属层中化学取代Na是一种有前途的解决方案，可以利用阳离子和阴离子氧化还原活性来增强能量存储。不幸的是，不同于经典的富含Li的Li ₂ MnO ₃，在典型的富含Na的阴极中尚未发现具有阴离子氧化还原活性的纯原型。在此，我们最初设计了一种富含Na的分层氧化物原型，即Na ₃ RuO ₄（Ru ⁵⁺），该原型仅通过以下方式即可提供部分可逆容量：氧阴离子的参与。更重要的是，阴离子的氧化还原活性通过原位拉曼观察到的可循环的过氧基O-O（脱键）结合得到了验证。我们的发现不仅突显了用于扩展容量的多种电子转移策略，而且为设计用于高能钠离子电池的富钠电极材料开阔了眼界。