Design of Fluorinated Elastomeric Electrolyte for Solid‐State Lithium Metal Batteries Operating at Low Temperature and High Voltage

Abstract This work demonstrates the low‐temperature operation of solid‐state lithium metal batteries (LMBs) through the development of a fluorinated and plastic‐crystal‐embedded elastomeric electrolyte (F‐PCEE). The F‐PCEE is formed via polymerization‐induced phase separation between the polymer matrix and plastic crystal phase, offering a high mechanical strain (≈300%) and ionic conductivity (≈0.23 mS cm⁻¹) at −10 °C. Notably, strong phase separation between two phases leads to the selective distribution of lithium (Li) salts within the plastic crystal phase, enabling superior elasticity and high ionic conductivity at low temperatures. The F‐PCEE in a Li/LiNi_0.8Co_0.1Mn_0.1O₂ full cell maintains 74.4% and 42.5% of discharge capacity at −10 °C and −20 °C, respectively, compared to that at 25 °C. Furthermore, the full cell exhibits 85.3% capacity retention after 150 cycles at −10 °C and a high cut‐off voltage of 4.5 V, representing one of the highest cycling performances among the reported solid polymer electrolytes for low‐temperature LMBs. This work attributes the prolonged cycling lifetime of F‐PCEE at −10 °C to the great mechanical robustness to suppress the Li‐dendrite growth and ability to form superior LiF‐rich interphases. This study establishes the design strategies of elastomeric electrolytes for developing solid‐state LMBs operating at low temperatures and high voltages.