Boosting the lithium transport in phase-change polymer electrolytes towards stable cycling lithium metal batteries with thermal robustness†

Abstract

Phase-change electrolytes hold great promise for sustainable energy storage technologies but are constrained by limited ionic conductivity and inefficient ion transport across phase transitions. In this work, to boost the lithium transport in polycaprolactone (PCL)-based phase-change polymer electrolytes, a novel semi-vehicle lithium transport pathway, which integrates solvent-mediated and polymer-assisted migration, has been created via a co-solvent strategy. It is demonstrated that the preferential coordination of dimethyl dodecanedioate (DDCA) and propylene carbonate (PC) attenuates the interaction between the lithium ions and PCL chain, achieving continuous and rapid ion transport across phase transition. Furthermore, the synergistic effect of linear and cyclic solvents promotes the formation of a LiF-rich inorganic SEI layer, effectively stabilizing the lithium anode. The resulting electrolyte (PCL-DDCA-PC) achieves a high ionic conductivity of 3.38 × 10⁻⁴ S cm⁻¹ and Li⁺ transference number of 0.84. In cell tests, the Li‖Li symmetric cell exhibits stable cycling over 1000 hours at 0.05 mA cm⁻². The Li‖LiFePO₄ cells retain 91% capacity after 500 cycles at 0.5C, while Li‖NCM811 cells retain 80% after 200 cycles. Due to the unique endothermic phase-change effect of PCL and DDCA, the obtained electrolyte enables Li//LFP pouch cells to demonstrate enhanced thermal hysteresis, reaching 100 °C at a rate four times slower than those with liquid electrolytes.