Unveiling the adsorption tendency of film-forming additives to enable fast-charging hard carbon anodes with regulated Li plating

Abstract

Regulating lithium (Li) plating with high reversibility on hard carbon (HC) anodes is a practical approach to breaking through the bottleneck of the fast-charging lithium-ion batteries (LIBs). However, the solid electrolyte interphase (SEI) working in the complex interfacial Li intercalation/deposition processes is unstable, leading to unsafe Li plating with rapid capacity fading. Herein, we gauge the adsorption tendency of film-forming additives (ethylene carbonate (EC) and fluoroethylene carbonate (FEC)) on a carbon matrix containing defect features, thus achieving a robust SEI for HC to facilitate uniform and reproducible Li plating. The results demonstrate that the tilted conformation of FEC induced by the asymmetric electrostatic interaction leads to weaker adsorption between the CO of FEC and the defect site compared to that of EC. Therefore, the FEC encourages the SEI with more uniform and excellent space continuity irrespective of the distribution of the defect on the HC. Combined with local high-concentration electrolyte systems, the FEC-assisted SEI is excellent in regulating the Li plating morphology and maintaining self-structural stability over cycling. Under Li plating occupation greater than 16%, an average Coulombic efficiency (CE) of 99.8% for the HC anode over 250 cycles is retained by FEC, while that for the EC system is merely 97.9%. These findings are helpful in guiding the selection of film-forming additives for different anodes in achieving reversible Li plating for fast-charging LIBs.