A novel PEO-based composite solid-state electrolyte modified by ion conducting Cr₃C₂ for lithium metal batteries

PEO-based polymer solid-state electrolytes have attracted significant traction in solid-state lithium metal batteries owing to their flexibility and preeminent lithium ions transfer capability. However, their progress has been constrained by limited ion conductivity, poor mechanical properties, and unstable interfaces. In this study, we incorporated the inorganic filler Cr₃C₂ into PEO and blended it with the plasticizer succinonitrile (SN), thereby developing PEO-based composite solid-state electrolytes (CSSEs) that exhibit superior electrochemical performance. The synergistic effect of Cr₃C₂ and PEO restricts the movement of lithium salt anions through chemical bonds, thereby creating more active space for efficient lithium-ion transport and improving the lithium transference number (t_Li+). The PCN5 CSSEs exhibits excellent room temperature lithium-ion migration of 0.96 and superior ionic conductivity over an extensive temperature range (25 °C–80 °C). Moreover, the LFP|PCN5|Li cell delivers discharge capacity of 165.3 mAh g⁻¹ and retains 70.6 % of its original capacity after 500 cycles when tested at 60 °C. Furthermore, the Li|PCN5|Li cell operates stably over 5000 h at a current density of 0.1 mA cm⁻² owing to the improved mechanical properties from hydrogen bonding between Cr₃C₂ and PEO along with lithium dendrites suppressing effect of SN, which ensures long-term cycling performance. These results may position the PCN5 CSSEs as a viable option for next-generation solid-state lithium metal batteries.