Single fluorosilane ester additive for F/Si-enriched inorganic interphases enabling durable high-voltage graphite/LiCoO2 pouch cells

Abstract

An unstable interphase at the electrode/electrolyte interface poses a critical challenge for conventional carbonate-based electrolytes in achieving both enhanced energy density and long cycle life in lithium-ion batteries (LIBs). This study introduces ethyl 2, 2-difluoro-2-trimethylsilylacetate (DFAE) as a novel electrolyte additive designed to concurrently regulate the interphases of both the LiCoO₂ (LCO) cathode and graphite (Gra) anode. Incorporating 1 % DFAE into the electrolyte significantly improves the capacity retention across different cell configurations: from 36 % to 84 % in LCO/Li half-cell, from 57 % to 96 % in Gra/Li half-cell, and from 50 % to 80 % in LCO/Gra full-cell. Theoretical calculations and spectroscopic analyses demonstrate that DFAE preferentially undergoes redox reactions, leading to the formation of stable F/Si-enriched cathode electrolyte interphase (CEI) on LCO and solid electrolyte interphase (SEI) on graphite. This F/Si-rich nature enhances the structural robustness of the CEI/SEI, suppresses high-voltage-induced electrolyte degradation, and promotes efficient Li⁺ (de)intercalation dynamics. Furthermore, DFAE exhibits strong affinity for detrimental F⁻ ions, effectively scavenging acidic species and preserving the surface integrity of the LCO cathode. In-situ XRD analysis reveals that the CEI/SEI generated by DFAE significantly enhances the cycling reversibility of the LCO/Gra full-cell, facilitating more uniform Li⁺ (de)intercalation and maintaining the overall integrity of both electrodes. The dual interphase modulation enabled by a single DFAE additive provides valuable insights into screening electrolyte additive for high-energy-density LIBs with superior performance.