A grafted flame-retardant gel polymer electrolyte stabilizing lithium metal for high-safety lithium metal batteries†

The inflammability and irregular metallic lithium electrodeposits of conventional liquid electrolytes limit their application in next-generation Li metal batteries (LMBs). Therefore, gel polymer electrolytes (GPEs) that offer flame retardancy, good ion transport performance, and stable Li deposition ability to inhibit the growth of lithium dendrites are ideal for LMBs with high safety. In this study, a novel grafted flame-retardant gel polymer electrolyte (C-GPE) is developed by grafting polyethylene glycol (PEG) and 3-aminopropylphosphonic acid (3-APPA). The host polymer is poly(methyl vinyl ether-alt-maleic anhydride), and 1 M LiTFSI in EC/DEC served as the Li salt and plasticizer. The C-GPE considerably enhances LMB performance in two key aspects. First, it exhibited excellent flame-retardant properties. The decomposition of grafted 3-APPA generated PO· free radicals, which effectively captures highly reactive radicals, rendering C-GPE nonflammable and enhancing the safety of LMBs. Second, the highly stable SEI layer containing Li₃PO₄ and Li_xPO_yF_z in C-GPE-15|Li can inhibit lithium dendrite growth, promote uniform Li metal deposition and improve the long-term cycling stability of LMBs.