Balanced Solvation and Ion Transport in a Salt-Regulated Ether Electrolyte for Fast-Charging Li-Ion Batteries

Fast-charging graphite-based lithium-ion batteries (LIBs) are limited by sluggish Li+ desolvation, interfacial charge transfer, and solid-state diffusion in graphite (Gr). Herein, a salt-concentration-regulated lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in 1,3-dioxolane (DOL) and fluoroethylene carbonate (FEC) electrolyte is developed to construct an anion-involved solvation structure for fast-charging graphite-based LIBs. At an appropriate LiTFSI concentration, TFSI− is incorporated into the primary Li+ solvation sheath, forming a contact-ion-pair (CIP)-dominated solvation structure. The optimized electrolyte exhibits a Li+ transference number of 0.76 and an exchange current density of 0.28 mA cm−2, indicating accelerated Li+ transport and interfacial charge transfer. Furthermore, a more uniform interfacial Li+ flux distribution is obtained, contributing to suppressed localized Li growth. As a result, Gr||Li half cells deliver 168 mAh g−1 at 10 C (1 C = 370 mAh g−1). LFP||Gr full cells with an LiFePO4 (LFP) areal capacity of 4 mAh cm−2 deliver 115 mAh g−1 at 2 C and retain 69% capacity after 200 cycles. This work highlights moderate salt-concentration regulation in DOL/FEC electrolytes as an effective strategy for fast graphite lithiation without relying on fluorinated ether solvents or localized high-concentration formulations.