A smart amphiphilic quasi-solid polymer electrolyte with hierarchical safeguards for advanced lithium metal batteries

Combining lithium (Li) metal anode with nickel-rich (LiNi x Co y Mn 1− x −y O 2 , NCM) cathode promises high energy density batteries. Nevertheless, lithium metal batteries (LMBs) still face critical challenges in overall safety and electrode-electrolyte interfacial stability. Herein, we design and synthesize a quasi-solid polymer electrolyte (QSPE) integrating essential isocyanate ( N = C = O ) and fluorinated (C-F) groups, with dual interfacial compatibility and multi-tiered protection strategy. The polymer chain units of smart amphiphilic QSPE (HIET) exhibits lower values for both the Lowest Unoccupied Molecular Orbital (LUMO) and Highest Occupied Molecular Orbital (HOMO) than TEGDME, resulting in an excellent Li passivation layer and high oxidation resistance. QSPE's safety performance is enhanced by the synergistic action of residual C = C bonds, crosslinked N = C = O groups, and flame-retardant CF 3 groups, providing protection across difference temperature ranges and overall safety against thermal runaway and other hazards. A Li/HIET/Li cell can be stably cycled for 2200 h with the decomposition voltage of HIET extending to 5 V. Additionally, the retention rate of NCM622/HIET/Li is as high as 95% after 200 cycles at 1C. Such hierarchical design principles provide actionable insights for advancing next generation QSPE materials toward practical LMB applications.