Tunable solvation structures for fast charging of micron-Si anodes in energy-dense lithium-ion batteries

Abstract

Realization of electrification in transportation and other applications depends on lithium-ion battery performance. Although micron-silicon (μ-Si) anodes enable energy-dense batteries, their rapid charging capability must be enhanced for electric vehicles. Additionally, significant volume changes of μ-Si anodes during lithiation and delithiation hinder their use in transportation. Herein, we reveal the mechanism of fluoroethylene carbonate (FEC) in tuning the solvation structure and topology of the solid–electrolyte interphase (SEI) for fast charging μ-Si/NCM811 full cells with reduced volume changes. The weak solvating nature of FEC allows PF₆⁻ anions to participate in the primary solvation sheath, improving Li⁺ desolvation kinetics and facilitating anode lithiation at rapid charge rates. This interaction forms SEI nanograins that enhance mechanical integrity and provide multiple ion paths. Notably, μ-Si/NCM811 full cells, with 99.5 % Coulombic efficiency, leveraging FEC for salt dissociation retain 76.6 % of their original capacity after 100 cycles at 3C; in contrast, electrolytes utilizing FEC as a cosolvent show a significantly poor capacity-retention performance. This study offers a comprehensive understanding of solvation chemistry and SEI engineering to improve fast-charging performance in μ-Si anodes.