Phosphorus-Fixed Stable Interfacial Nonflammable Gel Polymer Electrolyte for Safe Flexible Lithium-Ion Batteries

A high content of flame retardant in non-combustible electrolytes leads to deterioration of the electrochemical performance of lithium-ion batteries (LIBs). Besides, fire hazard of most non-flammable electrolytes is studied in coin cell, for which it is impossible to reveal real performance. Thus, the stable interfacial, phosphorus-fixed nonflammable gel polymer electrolyte (GPE) with low content of flame retardant (7.5 wt.%) has been designed by in situ polymerization of tri(acryloyloxyethyl) phosphate and triethylene glycol dimethacrylate in electrolyte. After being heated by fire for >10 s, the GPE is still not ignited. The average capacity attenuation rate of graphite//GPE//Li (0.008%) is much lower than that of the liquid electrolyte (0.039%). Besides, the nonflammable GPE based pouch cell with good flexibility and excellent fire safety is prepared. No fire, no thermal runaway and no electrolyte leakage occur for 1 Ah flexible pouch cell with 100% SOC. The mechanism for high safety of pouch cell has also been revealed. First the amount of combustible pyrolysis products from thermal degradation of GPE is reduced through forming P and F containing char. Second, the combustion of GPE is extinguished through OH free radical quenching effect of flame retardant molecular. This work provides a guideline for designing high-safety LIBs.

Automated summary

A stable and non-flammable gel polymer electrolyte (GPE) with low content of flame retardant was designed, which exhibited excellent fire resistance and stable electrochemical performance. A non-flammable pouch cell based on GPE was also prepared, showing good flexibility and outstanding fire safety.