摘要
Lithium plating in graphite electrodes is a side reaction that prevents the fast charging of Li-ion batteries. Understanding its mechanism and onset condition is critical for effective material design, cell engineering, and battery management to realize fast charging. This work revealed the lithium plating mechanism on single graphite particles by combining in situ experiments with theory and simulation. 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. The long charging time (40 min or longer) of electric vehicles compared with the short refueling time of gasoline cars (several minutes) is one of the main barriers preventing the wide adoption of EVs. Under fast charging conditions, side reactions happen inside a lithium-ion battery, significantly compromising its performance and safety. Addressing this challenge first requires an in-depth understanding of the mechanism of these side reactions. This work focuses on lithium plating on graphite particle, the most important side reaction that governs battery's safety and cycle life. By combining in situ experiment with theory and simulation, we successfully elucidated the mechanism and onset condition of lithium plating on graphite particles, which provides fundamental insights for material design, cell engineering, and battery management to achieve fast charging.