Electron paramagnetic resonance (EPR), a sensitive probe for unpaired electron spins, has been widely used in the investigation of various electrochemical systems. Despite its success in studying electrochemical processes involving radicals or other species with narrow line widths, interpreting EPR results for systems with broad featureless signals, particularly ions in solid materials, remains challenging. In this work, we develop a quantitative operando EPR method to study redox-active ions in electrode materials. The relationship between the variation in absolute spin amounts and electron transfer amounts is established to assign the signals. Four conversion-type electrode materials, MnO, MnF₂, Mn₂O₃, and MnF₃, are used as typical representatives of Kramers and non-Kramers ions to exemplify this method. The results accurately reveal the electrode processes, including redox mechanisms, local structural variations, and transition metal dissolution. It offers a new strategy for properly interpreting the broad featureless signals from ions in electrode materials, paving the way for understanding electrochemical processes in critical systems such as cathode materials.

电子顺磁共振（EPR）是一种灵敏的探测未配对电子自旋的方法，已被广泛用于各种电化学系统的研究。尽管在研究涉及自由基或其他具有狭窄线宽物种的电化学过程方面取得了成功，但对于解释具有宽带无特征信号的系统（特别是固体材料中的离子）的结果仍然存在挑战。在这项工作中，我们开发了一种定量的操作EPR方法来研究电极材料中活性红ox离子。建立了绝对自旋量变化与电子转移量之间的关系以分配信号。使用四种转换型电极材料MnO、MnF₂、Mn₂O₃和MnF₃作为Kramers和非Kramers离子的典型代表来说明这种方法。结果准确揭示了电极过程，包括氧化还原机制、局部结构变化以及过渡金属溶解。这为正确解释电极材料中离子的宽带无特征信号提供了新的策略，并为进一步理解诸如正极材料等关键系统的电化学过程铺平道路。

@10.1021/jacs.3c06849