Asymmetrically Fluorinated Alkoxysilane Single-Solvent Electrolytes Enable High-Voltage and Long-Cycling Lithium...

High-voltage lithium metal batteries with nickel-rich oxide cathodes (LiNi_0.8Co_0.1Mn_0.1O₂, NCM811) represent one of the most promising approaches to achieve high energy density up to 500 Wh kg^-1. However, severe interfacial side reactions occur at both NCM811 cathode and lithium anode at ultrahigh voltages (>4.6 V). To address these issues, various electrolytes have been developed, but they still suffer from electrolyte decomposition, leading to moderate voltages and insufficient cycling. Herein, we introduce (3,3,3-trifluoropropyl)trimethoxy silane (TTMS) as an asymmetrically fluorinated single solvent, which incorporates both strongly solvating (─OCH₃) and weakly solvating (─CF₃) groups. The designed 2.1 mol L^-1 (M) LiFSI/TTMS electrolyte achieves excellent compatibility with both NCM811 cathode and Li metal anode due to its unique anion-dominating solvation structures and inorganic-rich interphase formation. Consequently, it enables stable cycling in the Li||NCM811 battery at an ultrahigh voltage of 4.8 V, with 84.5% capacity retention after 300 cycles. Even under more aggressive conditions, including high temperature (60 °C) and anode-less configuration (N/P ratio = 1.76), the Li||NCM811 battery exhibits remarkable capacity retention (>80%) over 300 cycles. This work underscores the effectiveness of electrolyte engineering for developing ultrahigh-voltage and long-cycling battery systems.