Fumaronitrile-fixed in-situ gel polymer electrolyte balancing high safety and superior electrochemical performance for Li metal batteries

Safety issues (e.g., burn and aerogenesis) triggered by flammable liquid electrolyte (LE) have impeded the large-scale applications of lithium metal batteries (LMBs). It is of great importance to introduce flame-retardant constituent into LMBs system to alleviate above problems. Succinonitrile (SN) is ideally suited for application as a flame-retardant additive due to the merits of excellent thermal stability and high dielectric constant. However, the severe parasitic reactions with Li anode restrict the extensive application of SN. Herein, an in-situ polymerized gel electrolyte consisting of fumaronitrile (FN), methyl methacrylate (MMA) and ethoxylated trimethylolpropane triacrylate (ETPTA) is prepared. FN segment is fixed in polymer chains and shows the similar molecular structure with SN after polymerization, therefore the flame retardant effect is achieved and the parasitic reaction with Li anode is suppressed. Furthermore, the cross-linked structure contributed by ETPTA plays an important role in strengthening electrochemical performance of fumaronitrile based gel polymer electrolyte (FGPE) by inhibiting the growth of lithium dendrites and promoting the transfer of Li ions. Li/FGPE/Li symmetrical cell exhibits a great performance with the maximum voltage of about 11 mV after 7850 h, while a high reversible capacity of 147.6 mAh g⁻¹ is maintained after 1000 cycles for LiFePO₄/FGPE/Li battery.