Supported Ionic Liquid Gel Membranes Enhanced by Ionization Modification for Sodium Metal Batteries

Sodium batteries are attractive alternatives to the rapidly emerging large-scale intermittent renewable energy storage devices due to their low production cost and abundant sodium resources. The electrochemical performances of sodium batteries are highly dependent on the compatibility and interface resistances between electrode materials and electrolytes. Herein, we develop a simple method to modify a glass fiber (GF) separator by interfacial ionization and in situ introduction of a sodium source into the separator for a sodium metal battery. Polyionic liquid/ionic liquid gels were synthesized to incorporate into modified GF separators to prepare supported ionic liquid gel membranes (SILGMs) as dual separators and electrolytes for sodium batteries. The sodium-ion transference number of ionogel electrolytes incorporated on the support with and without modification was measured. The electrochemical performance characteristics of the battery with and without GF modification were evaluated by cyclic voltammetry, galvanostatic charge–discharge tests, and cycling stability as well as the galvanostatic intermittent titration technique (GITT). It was found that the specific capacity of the sodium metal battery increased by more than 20% after modification at a relatively high current density. Surprisingly, the specific discharge capacity of the assembled sodium metal battery can reach 112 mAh·g^–1 at 0.1 C, fairly close to the theoretical capacity of cathode materials. The specific capacity retention of the battery with the modified GF separator was up to 99% after 100 cycles at 1.0 C. This work presents a novel method for separator modification to alter the interface compatibility between electrode materials and electrolytes for sodium metal batteries and provides a new insight to improve battery performance.