Self-Healing Flame-Retardant Core–Shell Polymer Electrolytes via 3D Coaxial Printing for High-Safety Lithium Metal Batteries

The drawbacks of flammability, low ionic conductivity and low mechanical strength limit the further development of polymer electrolytes. Here, we reported a 3D coaxial printing strategy to prepare self-healing flame-retardant core–shell polymer electrolytes for lithium metal batteries. The core–shell structure not only prevents the flame retardant from coming into direct contact with the electrolyte but also allows the flame retardant to be effectively released into the electrolyte after thermal runaway to inhibit combustion. The as-prepared polymer electrolyte exhibits an outstanding limited oxygen index (27.2%), high tensile strength and elongation at break (9.22 MPa and 67.8%), excellent cycling stability (86.53% after 250 cycles under 0.5 C), and good rate capability (126.20 mA h g–1 under 2.0 C), which exceeds previously reported flame-retardant polymer electrolytes. This work provides an effective strategy to design flame-retardant electrolytes through nanoscale dynamic cross-linking borate bonds at a molecular level for lithium metal batteries.