Cyano and Fluorine-Enhanced Copolymer Electrolytes: Synergistically Boosting High-Voltage Lithium Metal Batteries

In high-voltage lithium metal batteries, designing electrolytes with low salt concentrations to achieve stable electrode interfaces presents a formidable challenge. High-concentration electrolytes stabilize the interface through an anion-derived LiF-rich interphase; however, their anion-rich solvation structures compromise the ionic conductivity. This study introduces a polymer-derived interphase that maintains interface stability at low lithium salt concentrations (∼1 M). This strategy enables copolymer electrolytes to sustain the Li|Li cell for over 2500 h at 0.1 mA/cm², even with a water content of 1000 ppm. Moreover, this research addresses the weak solvation effects in fluorinated polymer electrolytes by modulating the strongly solvating cyano groups, resulting in electrolytes with a high ionic conductivity of 4 × 10^-5 S/cm at 30 °C. A 143.8 Wh/kg Li|LiNi_0.8Co_0.1Mn_0.1O₂ pouch cell, with a lean electrolyte ratio of 5 g/Ah and a low negative/positive capacity ratio of 4, maintains a capacity retention of 90.5% after 29 cycles.