In situ generated composite gel polymer electrolyte with crosslinking structure for dendrite-free and high-performance sodium metal batteries

Sodium metal batteries (SMBs) with potentially high theoretical capacity are considered as one of the most promising candidates for high energy density batteries. However, the safety problems caused by sodium dendrite seriously hinder the practical application of SMBs. Composite gel polymer electrolytes (CGPE) composed of inorganic ionic conductors and organic polymers can suppress the growth of sodium dendrites and improve the safety of SMBs. Nevertheless, the presence of incompatible interfaces between organic and inorganic components leads to low ionic conductivity and ineffective Na+ transport for CGPE. Herein we demonstrate a CGPE composed of silane-modified beta-Al2O3 powders and PVDF-HFP matrix with crosslinking structure to eliminate the incompatibility of the inorganic-organic interfaces, thereby enhancing electrochemical performance of the synthesized composite electrolyte. Experimental results show that the obtained composite electrolyte possesses a high ionic conductivity of 1.37 x 10-3 S cm-1 at 20 degrees C and a sodium-ion transference number up to 0.424. Moreover, the assembled sodium symmetric cell based on the obtained composite electrolyte shows an excellent cycling performance for 800 h with no obvious voltage polarization at 0.5 mA cm-2, demonstrating an effective protection for the sodium anode. Furthermore, when used as a separator in the Na3V2(PO4)3-cathode based full cell, it could deliver an excellent electrochemical performance with a high-capacity retention of 92.2% even after 1000 cycles under an average columbic efficiency up to 99.9% at 3 C. The impressive performance enhancement of the full cell implies that such a composite electrolyte design could provide an effective strategy for the construction of highly stable SMBs.