Bifunctional Effects of Cation Additive on Na-O2 Batteries

Aprotic Na-O-2 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-2(-)) 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-2 batteries with TBA(+) show increased Coulombic efficiency as well as good rate capability. These are rewarded by the fast desolvation kinetics of O-2(-) and suppression of the disproportionation reaction of O-2(-) 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-2 batteries.

Automated summary

A novel bifunctional cation additive TBA(+) is introduced in this study to enhance the cycling stability and Coulombic efficiency of aprotic Na-O-2 batteries. Experimental results show that the addition of TBA(+) improves the rate capability of the batteries.