Cation-disordered rocksalt (DRS) materials have shown good initial reversibility and facile Li⁺ insertion and extraction in the structure at high rates. However, all of the Li-rich oxyfluorides introduced so far suffer from short cycle lifetimes and severe capacity fading. In the current study, we combine the strategy of using high-valent cations with partial substitution of oxygen anions by fluorine ions to achieve the optimal Mn⁴⁺/Mn²⁺ double redox reaction in the composition system Li₂Mn_1–xTi_xO₂F (0 ≤ x ≤ 2/3). While Ti-rich compositions correlate to an O-oxidation plateau and a partial Mn³⁺–Mn⁴⁺ redox process at high voltages, owing to the presence of Ti³⁺ in the structure, a new composition Li₂Mn_2/3Ti_1/3O₂F with a lower amount of Ti shows better electrochemical performance with an initial high discharge capacity of 227 mAh g^–1 (1.5–4.3 V window) and a Coulombic efficiency of 82% after 200 cycles with a capacity of 136 mAh g^–1 (>462 Wh kg^–1). The structural characteristics, oxidation states, and charge-transfer mechanism have been examined as a function of composition and state of charge. The results indicate a double redox mechanism of Mn⁴⁺/Mn²⁺ in agreement with Mn–Ti structural charge compensation. The findings point to a way for designing high-capacity DRS materials with multi-electron redox reactions.

中文翻译：

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提高无序岩盐氟氧化物阴极材料中 Mn4+/Mn2+ 双氧化还原活性的稳定性和可逆性

阳离子无序岩盐（DRS）材料已显示出良好的初始可逆性和容易栗⁺以高速率在结构插入和抽出。然而，迄今为止引入的所有富锂氟氧化物都存在循环寿命短和容量衰减严重的问题。在目前的研究中，我们结合使用高价阳离子和氟离子部分取代氧阴离子的策略，在组成体系 Li ₂ Mn _{1– x} Ti _{x 中}实现最佳的 Mn ⁴⁺ /Mn ²⁺双氧化还原反应O ₂ F (0 ≤ x ≤ 2/3)。虽然富含 Ti 的成分与 O-氧化平台和部分 Mn ^{3+ 相关}–Mn ⁴⁺高电压氧化还原过程，由于结构中存在 Ti ³⁺，具有较低 Ti 量的新成分 Li ₂ Mn _2/3 Ti _1/3 O ₂ F 显示出更好的电化学性能，初始高放电容量为 227 mAh g ^–1（1.5-4.3 V 窗口），200 次循环后库仑效率为 82%，容量为 136 mAh g ^–1（>462 Wh kg ^–1）。结构特征、氧化态和电荷转移机制已作为组成和电荷状态的函数进行了检查。结果表明Mn ⁴⁺ /Mn ²⁺的双重氧化还原机制与 Mn-Ti 结构电荷补偿一致。这些发现指出了一种设计具有多电子氧化还原反应的高容量 DRS 材料的方法。