Non-flammable and stable phosphate quasi-solid electrolyte with low salt concentration for lithium metal batteries

Lithium metal batteries face serious safety challenges caused by flammable organic electrolytes and the growth of lithium dendrite. Trimethyl phosphate (TMP) is a promising alternative for flammable carbonate electrolyte solvents owing to its nonflammable nature. But the low-concentration TMP-based electrolyte is unstable with the lithium metal anode. Here, a TMP-contained quasi-solid electrolyte (PIQSE) with porous polyimide (PI) as supporting skeleton is designed. The cross-linking structure generated by UV curing in PIQSE can lock the reactive TMP solvent to reduce its contact with Li metal. Besides, the PI supporting skeleton with high-temperature resistance can significantly enhance the thermal stability of PIQSE. The combination of PI and TMP prompts the high ionic conductivity and excellent nonflammability of PIQSE. The LiFePO₄/Li cell using PIQSE shows superior electrochemical performance in a wide temperature range from −10 to 60 °C. Furthermore, the cells with high-voltage cathode of LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622) were matched with PIQSE exhibit good cyclic and rate performance. The NCM622/PIQSE/Li pouch cell was also fabricated. It exhibits a high discharge capacity of 182.9 mAh·g⁻¹, and can stably light up LEDs after folding and shearing tests, demonstrating broad prospects for highly safe energy storage applications.