Phosphorus flame retardant-fixed in situ gel polymer electrolyte for safety-enhanced and superior electrochemical performance lithium metal battery

Abstract

Non-flammable polymer electrolytes are attractive due to their potential to inherently eliminating the fire hazards of conventional liquid electrolytes. However, the most widespread used flame-retardant additives are facile to react with Li anode and adverse to the conduction of Li ions, restricting the improvement of electrochemical performance. Herein, a flame-retardant gel polymer electrolyte (FGPE) is prepared by in situ copolymerizing flame-retardant additive on polymer backbone. Phosphorus additive 9, 10-dihydro-9-oxa-10-phosphame-10-oxide (DOPO) presents excellent flame-retardant property, while the abundant C=O/C−O groups on polyethylene glycol methyl ether methacrylate (PEGMEMA) and polyethylene glycol diacrylate (PEGDA) promotes the rapid transfer of lithium ions. After the reaction between P−H bond in the former and the unsaturated double bond in the latter, the adverse reactions between DOPO and Li anode are suppressed and an excellent polymer electrolyte with high safety and outstanding electrochemical performances is developed. Given the feasibility of our strategy, a record of sustained firing for 190 s without ignition is presented. Moreover, a high ionic conductivity (1.13 mS cm−1 at 25°C) is achieved after specifically regulating the content of DOPO, the assembled LiFePO4/FGPE/Li battery shows excellent cycling performance after 300 cycles with the capacity of 165.7 mAh g−1 and the capacity retention of 99.7%, realizing the balance of high safety and high performance. This electrolyte design philosophy provides a promising path for high safety and high energy density lithium metal batteries.