Polymer electrolytes based on Poly(VdF-co-HFP)/ionic liquid/carbonate membranes for high-performance lithium-ion batteries

In this study, we prepared the electrolytes by mixing the poly(vinylidene fluoride-co-hexafluoropropylene) (poly(VdF-co-HFP)) with 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI), ethylene carbonate (EC) and lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) in several weight ratios. The as-prepared electrolytes reveal micropores with various morphologies depending on the added EC content. They also exhibit glass transition temperatures lower than 0 °C, decomposition temperatures higher than 200 °C and good limited oxygen index to about 34 wt%. Moreover, the addition of EC facilitates the improvement of ion transport without compromising the electrochemical stability, consequently resulting in high ionic conductivity around 2.3 × 10⁻³ S/cm at room temperature and a wide electrochemical window. In particular, the Li/LiFePO₄ cells assembled with the electrolytes deliver remarkable discharge capacities of 143 mAh g⁻¹, 120 mAh g⁻¹ and 15 mAh g⁻¹ at 0.2 C, 1 C and 5 C rates, respectively, with excellent capacity retention over 300 cycles at a rate of 0.2 C, as well as great interfacial stability after long-term cycling of charge-discharge. This study, in summary, provides a simple approach to prepare a quaternary electrolyte system and the findings indicate that the polymer electrolytes can be applied for high-performance LIBs.