Fast-charging lithium-ion batteries are highly required, especially in reducing the mileage anxiety of the widespread electric vehicles. One of the biggest bottlenecks lies in the sluggish kinetics of the Li+ intercalation into the graphite anode; slow intercalation will lead to lithium metal plating, severe side reactions, and safety concerns. The premise to solve these problems is to fully understand the reaction pathways and rate-determining steps of graphite during fast Li+ intercalation. Herein, we compare the Li+ diffusion through the graphite particle, interface, and electrode, uncover the structure of the lithiated graphite at high current densities, and correlate them with the reaction kinetics and electrochemical performances. It is found that the rate-determining steps are highly dependent on the particle size, interphase property, and electrode configuration. Insufficient Li+ diffusion leads to high polarization, incomplete intercalation, and the coexistence of several staging structures. Interfacial Li+ diffusion and electrode transportation are the main rate-determining steps if the particle size is less than 10 μm. The former is highly dependent on the electrolyte chemistry and can be enhanced by constructing a fluorinated interphase. Our findings enrich the understanding of the graphite structural evolution during rapid Li+ intercalation, decipher the bottleneck for the sluggish reaction kinetics, and provide strategic guidelines to boost the fast-charging performance of graphite anode.
Keywords: Cryogenic transmission electron microscopy (cryo-TEM); Fast-charging; Graphite anode; High-rate kinetics.
© 2023. Shanghai Jiao Tong University.