Reversible anionic redox reactions represent a transformational change for creating advanced high-energy-density positive-electrode materials for lithium-ion batteries. The activation mechanism of these reactions is frequently linked to ligand-to-metal charge transfer (LMCT) processes, which have not been fully validated experimentally due to the lack of suitable model materials. Here we show that the activation of anionic redox in cation-disordered rock-salt Li_1.17Ti_0.58Ni_0.25O₂ involves a long-lived intermediate Ni^3+/4+ species, which can fully evolve to Ni²⁺ during relaxation. Combining electrochemical analysis and spectroscopic techniques, we quantitatively identified that the reduction of this Ni^3+/4+ species goes through a dynamic LMCT process (Ni^3+/4+–O²⁻ → Ni²⁺–Oⁿ⁻). Our findings provide experimental validation of previous theoretical hypotheses and help to rationalize several peculiarities associated with anionic redox, such as cationic–anionic redox inversion and voltage hysteresis. This work also provides additional guidance for designing high-capacity electrodes by screening appropriate cationic species for mediating LMCT.

可逆的阴离子氧化还原反应代表了为锂离子电池制造先进的高能量密度正极材料的变革。这些反应的激活机制通常与配体到金属电荷转移 (LMCT) 过程有关，由于缺乏合适的模型材料，这些过程尚未通过实验得到充分验证。在这里，我们表明阳离子无序岩盐 Li _1.17 Ti _0.58 Ni _0.25 O ₂中阴离子氧化还原的活化涉及长寿命中间体 Ni ^3+/4+物种，它可以完全演化为 Ni ²⁺在放松期间。结合电化学分析和光谱技术，我们定量地确定了这种 Ni ^3+/4+物种的还原经历了一个动态的 LMCT 过程（Ni ^3+/4+ –O ²⁻  → Ni ²⁺ –O ^{n −}）。我们的研究结果为先前的理论假设提供了实验验证，并有助于合理化与阴离子氧化还原相关的几个特性，例如阳离子-阴离子氧化还原反转和电压滞后。这项工作还通过筛选合适的阳离子物质来介导 LMCT，为设计高容量电极提供了额外的指导。