Supported Ionic Liquid Gel Membrane Electrolytes for a Safe and Flexible Sodium Metal Battery

Concerns about the sustainability of lithium supplies has stimulated interest in alternative energy storage chemistries including in sodium metal and sodium ion batteries. Gel ionic liquid electrolytes are investigated here as an important option for secondary sodium batteries due to their leakage-free and superior safety when compared to standard flammable electrolytes. Supported ionic liquid gel membranes (SILGMs) were prepared as both electrolyte and separator for a sodium metal battery using a carbon-coated sodium vanadium phosphate material (Na₃V₂(PO₄)₃@C or NVP@C) as cathode. SILGM-based coin cells exhibit a specific capacity retention of 92% after 150 charge–discharge cycles with a Coulombic efficiency of 99.9%. We also demonstrate the operation of SILGMs in a laminated flexible sodium battery. The SILGM-based flexible battery exhibits a good flexibility and shows a remarkably stable operation even when opening the device or cutting into pieces. It is expected that SILGMs will become promising separator/electrolyte materials in practical application and thus will promote the development of nonflammable and flexible sodium batteries.