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.