The polymerization capability of alkenyl phosphates and application as gel copolymer electrolytes for lithium ion batteries with high flame-retardancy

The nonflammable gel polymer electrolytes have become one of the most desirable alternatives among various electrolytes for the fabrication of stable advanced LIBs. Acryloyloxyethyl dialkyl phosphates which combine the good polymerization capability of acrylate and flame retardant properties of phosphates are designed and synthesized. The polymerization capability including the copolymerization ability of these compounds is compared with allyl phosphonate/phosphates and shows better polymerization capability than the allyl phosphonate/phosphates due to the separation of ethylenedioxy between the double bond and the phosphoryl group. The corresponding cross-linking gel polymer electrolytes with good mechanical property are prepared by in-situ radical thermal polymerization. The gel copolymer electrolytes have good thermal stability with the onset decomposition temperature above 220 °C, efficient flame retardant with low content of 5 wt%, good electrochemical stability of up to 4.5 V (vs. Li+/Li) and high ionic conductivity over 7 mS cm−1. The LiFePO4/GPE/Li cell shows good cycling performance and high coulombic efficiency. The coordination interaction is existed between acryloyloxyethyl dialkyl phosphate and lithium ion, which is testified by FT-IR, 31P NMR and HRMS.