Graphite is currently an irreplaceable anode material for lithium-ion batteries due to its many advantages. Despite decades of extensive study, real-time investigation of its electrochemical processes, especially during fast charging, has been lacking. In this work, we develop a quantitative operando electron paramagnetic resonance (EPR) method and standardize data analysis for researching graphite anodes. For the first time, the density of states at the Fermi level is determined under different charge rates, revealing a consistently homogeneous electronic property across the graphite lattice. However, the lithiation shows inhomogeneity with increasing charge current, as evidenced by the EPR line width which correlates with Li-ion mobility. During fast charge, it is found that the lithiation kinetics is limited by bulk diffusion and Li deposition may commence once the surface layer reaches full lithiation at stage 1. Further analysis methods effectuate the identification of the plating onset and dead Li. Additionally, we preliminarily explore lithiation homogeneity across the electrode plane by spectral–spatial EPR imaging. At last, the competition between Li intercalation and Li deposition is elucidated by quantifying the plating current. The versatile EPR paradigm is anticipated to benefit the further development of graphite anodes and other carbon-based anodes.

中文翻译：

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石墨阳极的定量操作 EPR 方法：电子特性、锂化动力学和锂沉积

石墨由于其诸多优点，是目前锂离子电池不可替代的负极材料。尽管进行了数十年的广泛研究，但仍缺乏对其电化学过程（尤其是快速充电过程）的实时研究。在这项工作中，我们开发了一种定量操作电子顺磁共振（EPR）方法并标准化了用于研究石墨阳极的数据分析。首次确定了不同充电速率下费米能级的态密度，揭示了石墨晶格中一致均匀的电子特性。然而，随着充电电流的增加，锂化表现出不均匀性，与锂离子迁移率相关的 EPR 线宽证明了这一点。在快速充电过程中，我们发现锂化动力学受到体扩散的限制，一旦表面层在第 1 阶段达到完全锂化，锂沉积就可能开始。进一步的分析方法可以识别电镀开始和死锂。此外，我们通过光谱空间 EPR 成像初步探索了电极平面上的锂化均匀性。最后，通过量化电镀电流来阐明锂嵌入和锂沉积之间的竞争。多功能 EPR 范式预计将有利于石墨阳极和其他碳基阳极的进一步发展。