Constructing Highly Conductive and Thermomechanical Stable Quasi‐Solid Electrolytes by Self‐Polymerization of Liquid Electrolytes within Porous Polyimide Nanofiber Films

Abstract Solid electrolytes are being considered as an effective solution to replace liquid ones for building safer batteries, but they suffer either low ionic conductivity or large contact ohmic impedance. Here, a highly conductive and thermomechanically stable quasi‐solid electrolytes (QSE) by self‐polymerization of a commercially available liquid electrolytes (1,3‐dioxolane (DOL), 1,2‐dimethoxyethane (DME), lithium trifluoromethane sulfonimide (LiTFSI) and LiPF 6 ) at room temperature in a porous polyimide nanofiber film are reported. LiPF 6 initiates the ring‐opening reaction of DOL and LiTFSI promotes the self‐polymerization to form poly‐DOL (PDOL), while the plasticizer of DME solidifies the PDOL. On the other hand, polyimide has a great affinity with PDOL that facilitates to form stable QSE network. As a result, the QSE film shows a high room‐temperature ionic conductivity of 2.9 × 10 −3 S cm −1 , a high mechanical strength of 31 MPa, and high heat resistance to 160 °C. The LiFePO 4 ||QSE||Li batteries with a high cathode loading of ≈18.7 mg cm −2 show great cycling performance and stable electrode/electrolyte interfaces at a high current rate of 0.5 C with a capacity retention of 91.8% over 200 cycles at room temperature.