Ion-Solvent Chemistry-Inspired Cation-Additive Strategy to Stabilize Electrolytes for Sodium-Metal Batteries

Building stable electrolytes is one of the key technologies for sodium (Na)-metal batteries as the reactive nature and the dendritic growth of Na-metal anodes. Herein, a paradigmatic and rational strategy of cation additive was proposed to stabilize electrolytes for Na metal batteries. Three principles, including the electrode potential of introduced cations, the lowest unoccupied molecular orbital energy level decrease of solvents after coordinating with cations, and the interaction strength between cations and solvents, were proved through first-principles calculations and molecular dynamics simulations. Li+ was predicted to be a good cation additive candidate for Na metal batteries. Finite element method simulations, in situ optical microscopic observations, and electrochemical tests further validated the resisted Na dendritic growth due to the electrostatic shield effect and enhanced electrolyte stability after introducing Li+ additives. The proven cation additive strategy affords emerging chances for rational electrolyte design for stable and safe Na metal batteries.