A novel polyphosphonate flame-retardant additive towards safety-reinforced all-solid-state polymer electrolyte

Poly(ethylene oxide) (PEO) is by far the most popular solid polymer electrolyte material in the solid-state battery field. However, PEO polymer itself is readily flammable and detrimental to battery safety issue. Herein, a novel alkylpolyphosphonate flame retardant of poly(bis(4-phenoxyl)propane methylphosphonate) (PBMP) has been designed. Its structure was characterized by FTIR, 1H NMR, and 31P NMR. The flame-retardant performance of the PEO/PBMP was investigated by limited oxygen index (LOI), vertical burning test (UL 94) and microcombustion calorimeter (MCC). The PBMP exhibits excellent flame retardant effects in PEO. The PEO/PBMP blend with 3 wt% of phosphorus reaches UL94 V-0 rating and possesses a LOI value of 25.6%. The MCC results revealed that the total heat release (THR) of the PEO/PBMP blend decreased by 15.4% compared with the pure PEO. In addition, PEO/PBMP blend exhibits good electrochemical stability window at 4.0 V vs. Li/Li+ and enhanced ionic conductivity of 1.25 × 10−5 S cm−1 at ambient temperature. The stable charge/discharging behavior and cycling capability verify that the polyphosphonate additive has no discernible side effects on battery performance. Therefore, the polyphosphonate PBMP is an intriguing polymeric flame retardant within solid polymer electrolyte towards safety-reinforced battery.