Bifunctional Effects of Cation Additive on Na-O Batteries.

Aprotic Na-O batteries have attracted growing interest owing to their low overpotentials and high energy density. Their cycling stability and Coulombic efficiency are limited, however, by Na dendrite formation and superoxide (O ) degradation. Here, we present a bifunctional cation additive, the tetrabutylammonium cation (TBA ), to simultaneously protect the Na anode and stabilize the superoxide. The adsorption of TBA on the Na anode suppresses the dendrite formation in the Na plating and ensures stable anode cycling at high current density in both Ar and oxygen atmospheres. Aprotic Na-O batteries with TBA show increased Coulombic efficiency as well as good rate capability. These are rewarded by the fast desolvation kinetics of O and suppression of the disproportionation reaction of O with TBA , as confirmed by molecular dynamics simulation and DFT calculations. This bifunctional effect of this cation additive paves a new avenue for the development of Na-O batteries.