The anionic redox reaction (ARR) has become a hot topic in battery research due to its ability to provide high energy density. Nevertheless, there are still many issues in Na-based layered oxides with the ARR, such as large voltage hysteresis, lattice oxygen loss, irreversible structural changes, and cation migration in the TM layer, resulting in structural collapse and poor electrochemical performance. Herein, a series of Na_2/3[Fe_1/3Mg_xMn_2/3−x]O₂ cathodes are synthesized using a traditional solid-state reaction method. The effectiveness of Mg substitution amounts and site occupancy in regulating the reversibility of the ARR has been explored using various experimental techniques. Surprisingly, the well-designed Na/TM-site Mg substituted P2-Na_2/3[Fe_1/3Mg_1/12Mn_7/12]O₂ exhibits an extremely high initial reversible capacity of ∼253.21 mA h g⁻¹, equivalent to ∼0.94 e⁻ transfer, which is contributed by both cationic and anionic redox reactions as confirmed by hard X-ray absorption spectroscopy (hXAS) and soft X-ray absorption spectroscopy (sXAS) analyses. In addition, the improved cycling and high-rate performance of the P2-Na_2/3[Fe_1/3Mg_1/12Mn_7/12]O₂ are achieved by a well-maintained crystal structure and the highly reversible anionic redox reaction of O²⁻/Oⁿ⁻. These in-depth studies provide crucial knowledge for the development and understanding of cathode materials with a highly reversible ARR for low-cost and high-energy sodium-ion batteries.

中文翻译：

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Na/TM位Mg取代P2-Na2/3[Fe1/3Mg1/12Mn7/12]O2正极，具有极高的钠离子电池容量

阴离子氧化还原反应（ARR）由于其能够提供高能量密度而成为电池研究的热点。然而，具有ARR的钠基层状氧化物仍然存在许多问题，例如大的电压滞后、晶格氧损失、不可逆的结构变化以及TM层中的阳离子迁移，导致结构崩溃和电化学性能差。本文中，使用传统的固态反应方法合成了一系列Na _2/3 [Fe _1/3 Mg _x Mn _{2/3− x} ]O ₂阴极。已经使用各种实验技术探索了镁取代量和位点占用在调节 ARR 可逆性方面的有效性。令人惊讶的是，精心设计的Na/TM位Mg取代的P2-Na _2/3 [Fe _1/3 Mg _1/12 Mn _7/12 ]O ₂表现出极高的初始可逆容量~253.21 mA hg ^-1，相当于〜0.94 e ^-转移，这是由阳离子和阴离子氧化还原反应贡献的，经硬X射线吸收光谱（hXAS）和软X射线吸收光谱（sXAS）分析证实。此外，P2-Na _2/3 [Fe _1/3 Mg _1/12 Mn _7/12 ]O ₂的循环性能和高倍率性能得到改善，这是通过良好维持的晶体结构和高度可逆的阴离子氧化还原来实现的。 O ²⁻ /O ^{n −}的反应。这些深入的研究为开发和理解低成本高能钠离子电池具有高度可逆ARR的正极材料提供了重要的知识。