Bifunctional trimethylsilyl-modified fluorinated ester additive for LiF-rich solid electrolyte interphase in lithium metal batteries

Abstract

Lithium metal batteries are regarded as one of the most promising candidates for next-generation energy storage systems due to their high energy density. However, challenges such as lithium dendrite growth and poor cycling stability limit their practical application. Recent efforts focus on electrolyte additives to stabilize interphases and improve battery performance. In this study, we investigate the effect of a bifunctional additive, trimethylsilyl 2,2-difluoro-2-(fluorosulfonyl)acetate (TDFA), on lithium metal batteries, with a focus on its role in promoting uniform lithium deposition and enhancing interfacial stability. Surface analysis shows that the additive forms a LiF-rich solid-electrolyte interphase (SEI) layer, which is chemically stable and mechanically robust. Li/Li symmetric cells demonstrate that TDFA significantly reduces nucleation overpotential, suppresses dendrite formation, and extends cycling life over 500 h at 1 mA cm^-2 for 1 mAh cm^-2. In Li/LFP cells, TDFA improves capacity retention to 89.4 % after 300 cycles, with reduced polarization and enhanced rate performance. Additionally, XPS depth profiling confirms an F-rich cathode-electrolyte interphase (CEI) layer that mitigates crack formation on cathode and enhances cell durability. These findings suggest TDFA could play a critical role in advancing lithium metal batteries, offering enhanced electrochemical performance and long-term stability through improved SEI and CEI layer formation.