Intrinsically Safe Gel Polymer Electrolyte Comprising Flame-Retarding Polymer Matrix for Lithium Ion Battery Application.

State-of-the-art (SOTA) liquid electrolyte/polyolefin separator setups used in lithium ion batteries (LIBs) suffer from the hazard of leakage and high flammability. To address these issues, phosphonate, a flame-retarding moiety, is chemically bonded to a polymer matrix to fabricate a nonflammable gel polymer electrolyte (GPE). The obtained phosphonate-based polymer matrix as well as its corresponding GPE (gelled with flammable SOTA nonaqueous liquid electrolyte) shows remarkable flame resistivity. Unlike poly(vinylidene fluoride- co-hexafluoropropylene)-based GPEs, the phosphonate-based GPE does not react with lithiated graphite at high temperatures. Both features indicate that the phosphonate-based GPE is superior to SOTA GPEs in the aspect of safety performance. As the flame-retarding moiety is chemically bonding to the polymer, the parasitic reactions between the flame-retarding moiety and the electrodes are avoided. Consequently, LIB cells comprising phosphonate-based GPE show good capacity retention comparable to cells comprising SOTA GPEs. Compared with SOTA GPEs, phosphonate-based polymer-based GPEs show improved intrinsic safety performance and comparable cycle life. Therefore, phosphonate-based polymers exhibit high potential to be used as a new class of polymer matrix for GPE used in LIBs.