Fluorinated polycarbonate-based solid electrolyte plasticized using succinonitrile for 4.5 V lithium metal batteries

Solid polymer electrolytes (SPEs) are a great promising choice for energy storage owing to their enhanced safety compared to liquid electrolytes. However, challenges such as the decomposition under the high voltage, low room-temperature ionic conductivity and poor room-temperature cycling performance have hindered the practical application of SPEs. In this study, SNSPE-40, a novel fluorinated polycarbonate-based electrolyte was prepared by the in-situ polymerization of 2,2,2-trifluoroethyl acrylate and 4-vinyl-1,3-dioxolan-2-one; succinonitrile was added to the electrolyte as a plasticizer. Notably, SNSPE-40 exhibits a high ionic conductivity of 1.33 mS cm⁻¹ and wide electrochemical window of 5.4 V (vs. Li/Li⁺) at 25°C. Due to the LiF-rich solid electrolyte interphase (SEI), the Li∣SNSPE-40∣Li symmetric cell remained stable for 2000 h at 0.1 mA cm⁻². Finally, the Li∣SNSPE-40∣LiNi_0.9Co_0.05Mn_0.05O₂ cell, with a cut-off voltage of 4.5 V, displayed good cycling stability at 0.5 C (1 C = 220 mA g⁻¹) and 26°C (57.4% capacity retention after 300 cycles). The Li∣SNSPE-40∣LiCoO₂ cell displayed a long-cycling ability with a capacity retention of 54.9% for 250 cycles at 1 C (1 C = 200 mA g⁻¹) under the same voltage and temperature conditions. This new solid polymer electrolyte shows great potential for the application in high-voltage solid-state lithium metal batteries.