A bilayer interface formed in high concentration electrolyte with SbF3 additive for long-cycle and high-rate sodium metal battery

The applications of sodium metal batteries are limited due to the strong reducing property of sodium, and its electrolyte design is quite challenging because of the decomposition of the solvents. In this paper, a small amount of SbF3 as an electrolyte additive is combined with high concentration electrolyte of 4 mol L−1 sodium bis(fluorosulfonyl) imide (NaFSI) in 1,2-dimethoxyethane (DME) for building a bilayer solid electrolyte interface (SEI) for long-cycle and high-rate sodium metal batteries. The SbF3 additive leads to an adamant Na-Sb alloy layer, and the 4 mol L−1 NaFSI/DME electrolyte contributes to a compact NaF-rich SEI layer on the sodium metal surface. The bilayer structure realizes the fast ion transport of sodium ions and effective suppression on the growth of sodium dendrites. The increased solvent coordination and the bilayer interface on sodium metal result in enhanced stable cycling of a Na||Na symmetric battery about 1000 h at 0.5 mA cm−2. Moreover, the Na|| Na3V2(PO4)3 battery delivers stable cycling at 2 C nearly 1400 cycles (82.6% capacity retention), and it also exhibits superior rate capability of 80 mAh g−1 at 40 C. These results demonstrate that the new electrolyte holds large potential for sodium metal battery applications.