Multifunctional Flame-Retardant Gel Polymer Electrolyte for High-Voltage Lithium Metal Batteries

Developing electrolytes that can simultaneously stabilize both cathode and anode interfaces, achieve long-term cycling stability and possess intrinsic high safety, remains a critical challenges for high-voltage lithium metal batteries (LMBs). In this work, we synthesize a phosphorus-containing triacrylate monomer, tri(2-(methacryloyloxy)ethyl) phosphate, which plays a key role in promoting the dissolution of lithium nitrate (LiNO3) in ester-based electrolytes while simultaneously serving as a cross-linker in the in situ copolymerization with 2,2,6,6-Tetramethylpiperidin-4-yl methacrylate (TMPMA) and methyl methacrylate. The resultant gel polymer electrolyte (GPE) delivers a high ionic conductivity of 3.54 × 10–3 S cm–1 at room temperature, and a Li+ transference number of 0.62, as well as superior self-extinguishing behavior against ignition. The introduction of LiNO3 significantly reshapes the Li+ coordination environment, facilitates the construction of a robust solid electrolyte interphase enriched with inorganic components, and markedly improves ionic conductivity. Additionally, the piperidine ring in TMPMA effectively captures harmful hydrogen fluoride generated in the electrolyte. When applied in Li||LiNi0.6Co0.2Mn0.2O2 battery, the GPE system sustains stable cycling over 400 cycles, retaining 80.6% of the original capacity. Spectroscopic and structural analyses show that the polymer matrix in GPE suppresses interfacial degradation and the dissolution of transition metals, as well as Li/Ni cation disorder. This multifunctional GPE design shows promise for advancing high-voltage LMBs.