Increasing the energy density of rechargeable batteries is of paramount importance toward achieving a sustainable society. The present limitation of the energy density is owing to the small capacity of cathode materials, in which the (de)intercalation of ions is charge‐compensated by transition‐metal redox reactions. Although additional oxygen‐redox reactions of oxide cathodes have been recognized as an effective way to overcome this capacity limit, irreversible structural changes that occur during charge/discharge cause voltage drops and cycle degradation. Here, a highly reversible oxygen‐redox capacity of Na₂Mn₃O₇ that possesses inherent Mn vacancies in a layered structure is found. The cross validation of theoretical predictions and experimental observations demonstrates that the nonbonding 2p orbitals of oxygens neighboring the Mn vacancies contribute to the oxygen‐redox capacity without making the Mn−O bond labile, highlighting the critical role of transition‐metal vacancies for the design of reversible oxygen‐redox cathodes.

中文翻译：

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Na4 / 7-x [□1 / 7Mn6 / 7] O2（□：锰空位）中4.1 V时高度可逆的氧氧化还原化学

提高可充电电池的能量密度对于实现可持续发展社会至关重要。当前能量密度的限制归因于阴极材料的小容量，其中离子的（去）插层通过过渡金属氧化还原反应进行电荷补偿。尽管已经认识到氧化物阴极的其他氧-氧化还原反应是克服此容量极限的有效方法，但在充电/放电过程中发生的不可逆的结构变化会导致电压下降和循环退化。在这里，Na ₂ Mn ₃ O ₇的高度可逆的氧-氧化还原能力发现在层状结构中具有固有的Mn空位。对理论预测和实验观察结果的交叉验证表明，与Mn空位相邻的氧的非键合2p轨道有助于氧-氧化还原能力，而不会使Mn-O键不稳定，突出了过渡金属空位在金属氧空位设计中的关键作用。可逆氧-氧化还原阴极。