In-situ forming flame-retardant gel polymer electrolyte through Ritter reaction: An innovative strategy for enhancing the safety of lithium metal battery

In-situ forming flame retardant gel polymer electrolyte to improve the cycle and safety performance of lithium metal batteries by promoting uniform Li deposition and suppressing the Li/Ni cation mixing. • Synthesizing a phosphonate containing cross-linkable polymer with hydroxyl and nitrile groups. • In-situ forming flame retardant gel polymer electrolyte (FR-GPE) through Ritter reaction initiated by LiPF 6 , without the need for any other initiators. • The FR-GPE showing high ionic conductivity, wide electrochemical stability window and high Li + transference number. • The FR-GPE improving the cycle performance of lithium metal batteries by stabilizing cathode structure and promoting uniform Li deposition. Lithium metal batteries (LMBs) with higher energy-density have always been urgently needed. However, the safety risk and poor cycle performance are still great challenges for the widespread application of LMBs. Here, a flame retardant gel polymer electrolyte (FR-GPE) has been developed to address these problems. Copolymer containing phosphonate (PHAP) are synthesized through free radical polymerization and used as polymer matrix for gel polymer electrolyte (GPE) containing flame retardant. The PHAP is soluble in liquid electrolyte and can be cross-linked to gel liquid electrolyte through Ritter reaction. The advantage of this strategy is that cross-linking is initiated by LiPF 6 without the need for additional initiator. The cross-linked PHAP GPE ( c -PHAP-GPE) has excellent flame retardant and self-extinguishing properties. Moreover, it has high ionic conductivity, wide electrochemical stability window (5.11 V) and high Li + transference number (0.74). The results show that the c -PHAP-GPE can improve the cycle performance of Li||NCM622 batteries by involving in the solid electrolyte interphase on both the Li anode and NCM622 cathode, promoting uniform Li deposition and suppressing the Li/Ni cation mixing. Our strategy of improving the cycle and safety performances of LMBs with in situ formed FR-GPE has paved a new way for developing advanced energy storage system.