Tuning Rate‐Limiting Factors for Graphite Anodes in Fast‐Charging Li‐Ion Batteries

Localized high‐concentration electrolyte (LHCE) is considered to be a promising substitution for the conventional carbonate electrolytes in fast‐charging Li‐ion batteries. However, the rate‐determining steps (RDS) for fast‐charging electrodes (i.e., graphite anode) in LHCE remain unclear. Herein, a typical localized high‐concentration electrolyte consisting of lithium bis(fluorosulfonyl)imide in dimethoxyethane with 1,1,2,2‐tetrafluoroethyl‐2,2,3,3‐tetrafluoropropyl ether as a diluent is selected to investigate the RDS of lithiation process in graphite anode, including the diffusion of solvated Li+ in the electrolyte, the desolvation behavior of solvated Li+, the Li+ transfer in solid electrolyte interphase (SEI) on the graphite surface, and the Li+ diffusion in bulk graphite. The results indicated that the rate performance of graphite anode in LHCE lies in the balance between Li+ desolvation process and Li+ migration in SEI. Through the regulation of solvated Li+ structure and SEI component, excellent fast‐charging performance can be obtained in the LHCE. The present studies not only offer fresh insights in the mechanistic understanding of fast‐charging batteries, but also provide new clues to the performance improvement of graphite anodes. Localized high‐concentration electrolytes (LHCEs) with varying concentrations are designed to investigate the rate‐determining steps (RDSs) in the lithiation process of graphite anodes. It is revealed that the desolvation of solvated Li+ and the Li+ transfer in solid electrolyte interphase (SEI) are the RDSs for fast‐charging of graphite. This study provides new insights into electrolyte design for the fast‐charging lithium‐ion batteries.