TPFPP@PMMA core-shell polymer modified flame retardant separator achieved by aqueous technique for high-voltage lithium metal batteries.

The safety of lithium metal batteries (LMBs) is a critical barrier to their further development towards achieving higher energy densities exceeding 400 Wh kg−1. Although the incorporation of flame-retardant additives into the liquid electrolyte can enhance the safety of LMBs, it often compromises electrochemical performance. To achieve a balance, a flame-retardant separator with thermally responsive properties has been developed by coating a core-shell flame-retardant polymer (poly(methyl methacrylate) (PMMA) as the shell and tris (pentafluorophenyl) phosphine (TPFPP) as the core) onto a polyethylene (PE) separator using an aqueous technique. Compared to the original PE separator, the TPFPP@PMMA flame-retardant separator exhibits superior mechanical strength and electrolyte wettability, along with significantly improved flame retardancy and thermal stability. Due to the excellent compatibility of PMMA polymer with lithium anode, a stable cycle life of over 500 hours for the Li||Li symmetrical coin cell has been achieved. The capacity retention of the Li||LiNi 0.8 Co 0.1 Mn 0.1 O 2 battery is higher than that of the PE separator (80.0% vs. 65.8%) after 100 cycles between 3.0 V and 4.35 V, ascribed to the formation of a stable and robust cathode electrolyte interface (CEI) film, primarily composed of rich LiF and poor Li 2 CO 3 on the cathode surface, induced by the PT/PE separator. Thus, the developed flame-retardant separator offers new prospects to the revival of high-energy-density LMBs. [Display omitted] • TPFPP flame retardant is wrapped by PMMA polymer to form the core-shell structure. • PT/PE flame-retardant separator is obtained by coating TPFPP@PMMA on PE support. • TPFPP can timely release to deter thermal runaway of battery in thermal anomalies. • PT/PE separator is compatible with both lithium anode and high-voltage cathode. • PT/PE assists in forming LiF-rich and Li 2 CO 3 -poor CEI film on the NCM811 surface. [ABSTRACT FROM AUTHOR]