Highly flexible gel polymer electrolytes (GPEs) is a prospective substitute of traditional solvent-based electrolytes to design the next-generation lithium-ion batteries (LIB). However, the practical application of GPEs is still challenged due to their low ionic conductivity, limited mechanical property and poor interfacial compatibility with electrodes. Herein, a novel GPE with 3D cross-linked network was prepared by thermally initiate bulk free radical co-polymerization of methyl methacrylate (MMA) and a functional flame-retardant monomer (BPOD-HEMA), during which polyhedral oligomeric silsesquioxane (POSS) was added as the crosslinking agent and 1-ethyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI) ionic liquid was applied as the solvent. The introduction of BPOD-HEMA significantly enhances the thermal stability and flame-retardant properties of GPEs, while the affinity between polymer chain and Li+ was also enhanced. When POSS was added, a crosslinked network was constructed in the PMMA based GPE, which inhibited the crystallization of PMMA segments and prevented the migration of bulky anions. As a result, fast Li+ transport channels were established in the GPE to improve the ionic conductivity and facilitate the uniformly Li+ stripping/plating process. The developed GPE exhibits high ionic conductivity (2.0 mS cm-1), enhanced Li+ transference number (0.41), and wide electrochemical stability window (5.5 V vs. Li+/Li). The LiFePO4|Li cell assembled with the prepared GPE was then fabricated, achieving a high initial discharge capacity of 163.2 mAh g-1 with a capacity retention of 87.7% at 0.2 C after 200th. Thus, a general method is developed herein to design GPEs with improved flame retardancy and electrochemical properties.

3D cross-linked network gel polymer electrolyte with improved flame retardancy and fast Li+ ion transport for high safety lithium ion batteries

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