Improving safety while increasing the charging rates and extending the lifetime is the grand challenge for lithium-ion batteries. The key challenge is to control lithium plating, a parasitic reaction on graphite anodes that competes with lithium intercalation. Here, we determine the fundamental mechanism for the onset of lithium plating on graphite particles. We perform in situ optical microscopy coupled with electrochemical measurements to resolve the spatial dynamics of lithiation and plating on the surface of a single graphite particle. We observe that the onset of plating is strongly coupled with phase separation in graphite and occurs only on the fully lithiated edges of the particles. The competition between Li insertion and plating is further elucidated by examining the energetics and kinetics of both reactions. Based on the physical insights drawn from the experiments, we propose a phase-field model that predicts the onset of Li plating.

锂离子电池在提高安全性的同时提高充电率并延长使用寿命是巨大的挑战。关键的挑战是控制锂电镀，这是石墨阳极上与锂嵌入竞争的寄生反应。在这里，我们确定了石墨颗粒上锂电镀开始的基本机理。我们就地表演光学显微镜与电化学测量相结合，以解决单个石墨颗粒表面锂化和电镀的空间动力学问题。我们观察到，镀层的开始与石墨中的相分离紧密相关，并且仅在颗粒的完全锂化边缘上发生。通过检查两个反应的能量和动力学进一步阐明了锂插入和电镀之间的竞争。基于从实验中得出的物理见解，我们提出了一个相场模型，该模型可预测锂电镀的开始。