Gel Polymer Electrolytes Based on Facile In Situ Ring‐Opening Polymerization Enabling High‐Performance Rechargeable Magnesium Batteries

Abstract Rechargeable magnesium batteries (RMBs) have emerged as one of the promising energy storage devices, and polymer electrolytes with high safety, stability, and structural flexibility are the ideal choice for RMBs. Herein, a novel in situ crosslinked gel polymer electrolyte, PDTE is reported, via facile ring‐opening polymerization in RMBs. The electrolyte exhibits a remarkable room‐temperature ionic conductivity of 2.8 × 10 −4 S cm −1 and highly reversible Mg plating/stripping behavior (98.9% Coulombic efficiency, 2000 cycles) with a low overpotential (<0.1 V). Mo 6 S 8 ||PDTE||Mg coin cells demonstrate exceptional cycling stability and rate capability at a wide temperature range (−20 to 50 °C), characterizing an average discharge capacity of 81.6 mAh g −1 at 10 C for 7500 cycles at room temperature, and 97.4 and 111.7 mAh g −1 at 0.2 C for 400 and 50 cycles at −20 and 50 °C, respectively. The pouch cell exhibits a high energy density of 204 Wh kg −1 with a high retention of 90.6% at 0.2 C for 350 cycles, along with significantly improved safety and remarkable flexibility. Additionally, good compatibility with conversion‐type cathode Cu 3 Se 2 validates the application versatility of PDTE. The development of this gel polymer electrolyte provides a feasible approach for the research on semi‐solid‐state electrolytes for RMBs.