Kinetic Limits of Graphite Anode for Fast-Charging Lithium-Ion Batteries

The microstructure of graphite upon rapid Li+ intercalation is a mixture of differently staging structures in the macroscopic and microscopic scales due to the incomplete and inhomogeneous intercalation reactions hindered by the sluggish reaction kinetics.The Li+ interface diffusion dominates the reaction kinetics at high rates in thin graphite electrode, while Li+ diffusion through the electrode cannot to be neglected for thick graphite electrode. 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 & mu;m. 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.

Automated summary

The microstructure of graphite undergoes a mixture of staging structures during rapid Li+ intercalation due to incomplete and inhomogeneous reactions. The kinetics of Li+ diffusion at the electrode interface is dominant in thin graphite electrodes, while Li+ diffusion through the electrode becomes more important in thick graphite electrodes. Understanding the reaction pathways and rate-determining steps in graphite during fast Li+ intercalation is crucial for improving the performance of lithium-ion batteries. The particle size, interphase property, and electrode configuration play a significant role in determining the rate-determining steps.