A breakthrough utilizing an anionic redox reaction (O²⁻/Oⁿ⁻) for charge compensation has led to the development of high‐energy cathode materials in sodium‐ion batteries. However, its reaction results in a large voltage hysteresis due to the structural degradation arising from an oxygen loss. Herein, an interesting P2‐type Mn‐based compound exhibits a distinct two‐phase behavior preserving a high‐potential anionic redox (≈4.2 V vs Na⁺/Na) even during the subsequent cycling. Through a systematic series of experimental characterizations and theoretical calculations, the anionic redox reaction originating from O 2p‐electron and the reversible unmixing of Na‐rich and Na‐poor phases are confirmed in detail. In light of the combined study, a critical role of the anion‐redox‐induced two‐phase reaction in the positive‐negative point of view is demonstrated, suggesting a rational design principle considering the phase separation and lattice mismatch. Furthermore, these results provide an exciting approach for utilizing the high‐voltage feature in Mn‐based layered cathode materials that are charge‐compensated by an anionic redox reaction.

中文翻译：

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阴离子氧化还原过程中锰基钠层氧化物的结构和热力学理解。

利用阴离子氧化还原反应（O ^2- / O ^n-）进行电荷补偿的突破导致了钠离子电池中高能阴极材料的开发。然而，由于氧损失引起的结构劣化，其反应导致大的电压滞后。在此，一种有趣的P2型Mn基化合物表现出独特的两相行为，保留了高电势的阴离子氧化还原（≈4.2 V vs Na ⁺/ Na），即使在随后的循环中也是如此。通过一系列系统的实验表征和理论计算，详细证实了源自O 2p电子的阴离子氧化还原反应以及富钠相和贫钠相的可逆分解。根据结合的研究，证实了阴离子-氧化还原诱导的两相反应在正负观点中的关键作用，提出了考虑相分离和晶格失配的合理设计原则。此外，这些结果为在锰基层状阴极材料中利用高压功能提供了令人兴奋的方法，该材料通过阴离子氧化还原反应进行了电荷补偿。