Non-flammable sandwich-structured TPU gel polymer electrolyte without flame retardant addition for high performance lithium ion batteries

The energy density and cycle stability of lithium-ion batteries (LIBs) are improving, but LIBs are likely to burn or even explode in case of accidents. Therefore, the safety of LIBs has attracted tremendous attention. It is a significant problem to increase battery safety while maintaining cycle stability and energy density of LIBs. We show that thermoplastic polyurethane gel polymer electrolytes (TPU GPE) with no flame retardant have noncombustible characteristics. It is found that LiPF6 can be used as a flame retardant of TPU polymer. When TPU GPE is decomposed by heating, LiPF6 is decomposed into LiF and PF5. When PF5 interacts with H2O, it produces H4P2O7 and H3PO4. TPU nanofiber's protective layer of H4P2O7 and H3PO4 may efficiently isolate oxygen and heat. It was discovered through a pouch cell thermal runaway test that an NCM811 pouch cell with GPE will not burn. The pyrolysis process of LiPF6 in the presence of H2O and O2 was simulated by Amsterdam Modeling Suite. The results reveal that an effective method to solve the fire danger of LIBs successfully is to replace the commercial separator with a TPU membrane. This discovery can effectively promote the commercialization of GPE.