Poly(ionic liquid)-polyethylene oxide semi-interpenetrating polymer network solid electrolyte for safe lithium metal batteries

Solid-state polymer electrolyte with high ionic conductivity and electrochemical stability is desirable for lithium metal batteries. A poly(ionic liquid)-polyethylene oxide semi-interpenetrating polymer network composite solid electrolyte for safe lithium metal batteries is designed to satisfy the demand of ionic conductivity, safety and electrochemical stability. This composite solid electrolyte is fabricated via polymerizing 1-vinyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (ionic liquid monomer) in polyethylene oxide matrix by one-step method. Differential scanning calorimetry results reveal that the crystallinity of composite solid electrolyte reduce to 15.5% comparing with polyethylene oxide solid electrolyte owing to the confinement of poly(ionic liquid) interpenetrating network. The semi-interpenetrating polymer network structure simultaneously endow the composite solid electrolyte with high ionic conductivity (6.12×10⁻⁴ S cm⁻¹ at 55 °C) and wide electrochemical window (5.44 V vs. Li/Li⁺) and thermal decomposition temperature (280 °C). In order to verify the favorable electrochemical performance of composite solid electrolyte, we assemble the cells with LiFePO₄/Li using the electrolyte. The reversible capacity of LiFePO₄ is 147 mAh g⁻¹ with high Coulombic efficiency (up to 99%) at the 0.2 C rate and 55 °C.