Novel cross-linked copolymer gel electrolyte supported by hydrophilic polytetrafluoroethylene for rechargeable lithium batteries

A novel hydrophilic polytetrafluoroethylene (PTFE)-supported gel polymer electrolyte (GPE) membrane based on the cross-linked poly(ethylene glycol) and poly(glycidyl methacrylate) block copolymer (PEG–b–PGMA) is successfully prepared by cationic ring-opening polymerization and followed by in situ cross-linking process. The poly(ethylene glycol) side chains of PEG–b–PGMA interact with the liquid electrolyte and hold it inside the membrane, while the hydrophilic and highly-porous PTFE membrane offers mechanical support for the cross-linked GPE. The ionic conductivity of the optimized GPE-3 reaches 1.30×10−3 S cm−1 at 25 °C and is high enough to be applied in lithium secondary batteries. The GPE is electrochemically stable up to 4.5 V versus Li/Li+. Moreover, the optimized GPE membrane demonstrates non-flammability and good dimensional stability at elevated temperature, which can improve the safety of the cell. The Li/LiFePO4 cell using the GPE-3 exhibits stable cycling behavior and superior rate performance comparable to the cell based on conventional liquid electrolyte. Therefore, the reported GPE is very promising for the use in rechargeable lithium batteries.