Crosslinked polymer-in-salt solid electrolyte with multiple ion transport paths for solid-state lithium metal batteries

Low ionic conductivity and unsatisfactory mechanical properties of the solid polymer electrolytes hinder their applications of in solid-state lithium metal batteries. Herein, we design a polymer-in-salt solid electrolyte (PISSE) with multiple Li+ transport paths and crosslinked polymer chain networks, endowing the PISSE with both high mechanical strength and high ionic conductivity. The optimized PISSE can therefore reach ionic conductivity of 3.03×10−4 S cm−1 (25 °C) and the mechanical strength of 0.811 MPa. The percolation model explains that the salt-rich clusters account for the extra fast ion transfer paths; whereas, the crosslinking structure compensates the loss of mechanical strength at high salt concentration. Finally, the in situ polymerization of PISSE promotes the electrode-electrolyte interface compatibility, resulting in the Li//PISSE60%@LiFePO4 cells with 71% (initial capacity: 111.8 mAh g−1) of capacity retention after 800 cycles at 0.5 C. Moreover, the PISSE also exhibits compatibility with high voltage cathode LiFe0.2Mn0.8PO4 cells up to 4.3 V. Therefore, this work provides a practical strategy to fabricate stable solid electrolytes for next-generation lithium metal batteries.