Non-coordinating flame retardants with varied vapor pressures enabling biphasic fire-extinguishing electrolyte for high safety lithium-ion batteries

Safety issues of LIBs are closely related to flammable carbonate electrolytes. Traditional strategies for nonflammable electrolytes involve soluble and coordinative flame retardants with limited choices, which interact with lithium ions and lead to deteriorated electrochemical performance. Meanwhile, single dosage of flame retardants fails to suppress ignition of both gas and liquid phases during thermal runaway (TR) of LIBs, thus generating multi-stage fire. Here, we introduce two flame retardants with high and low vapor pressure into carbonate electrolyte through a bridge co-solvent to obtain a non-flammable electrolyte with biphasic fire extinguishing capability. The designed electrolyte not only affords excellent electrochemical performance, but also simultaneously suppresses the combustion of flammable gases and liquid electrolytes. The Li[Ni0.78Co0.10Mn0.12]O2 | graphite pouch cell (2.90 Ah) empowered with such electrolyte exhibits outstanding cycling stability (87.5 % retention after 1000 cycles at 0.5 C) and shows only smoke under the severe nail penetration test as well as maximum temperature of TR reduced by 300 °C. What's more, the onset time of TR is delayed by 86 s under thermal abuse test. Furthermore, the pouch cell after 1000 cycles remains flameless under the nail penetration test. This work provides a promising path for expanding the selectivity of flame retardants and offers new strategy for designing advanced non-flammable electrolytes for safe LIBs.