High-safety lithium metal pouch cells for extreme abuse conditions by implementing flame-retardant perfluorinated gel polymer electrolytes

Abstract

Lithium metal anodes coupled with nickel-rich cathodes promise high-energy-density batteries. Nonetheless, the overall safety of lithium metal batteries is compromised by the use of conventional thermally unstable and flammable carbonate-based electrolytes, which hinders their practical applications, especially under abuse conditions. Herein, a flame-retardant perfluorinated gel polymer electrolyte (PFGPE) is developed by in situ copolymerization of perfluorobutyl acrylate (PFBA) monomer with pentaerythritol tetraacrylate (PETEA) crosslinker. PFBA decomposes at high temperatures to generate fluorine radicals that eliminate hydrogen and hydroxyl radical chain combustion reactions in the gas phase, reducing the combustion risk of electrolytes. Additionally, the co-pyrolysis of the carbonate-based electrolytes and the copolymerization matrix produces a P- and F- containing char layer in the condensed phase, blocking the heat and oxygen required for combustion. A large-format PFGPE modified Li metal pouch cell (4.4 Ah, 381 Wh kg−1) achieves 120 cycles with 83.4% of capacity retention under a lean electrolyte of 3 g Ah−1 and a negative/positive capacity ratio of 1.82. Moreover, the modified pouch cell exhibits enhanced thermal safety characteristics and passes international standard tests (GB/T 31485–2015) for mechanical nail penetration and thermal abuse. This innovative approach represents a significant milestone towards the advancement of high-safety Li metal batteries.