Modifying the ORR route by the addition of lithium and potassium salts in Na-O2 batteries

Sodium-oxygen (Na-O2) batteries have been considered as promising alternatives to lithium-oxygen batteries for high energy density applications. Herein, we report the utilisation of Li+ and K+ salts to the Na+ based electrolyte in order to tailor the oxygen reduction reaction (ORR) route in Na-O2 cells. Li+ salt addition promotes a surface confined ORR due to the incapability to stabilize superoxide radical intermediate product in the electrolyte leading to a poor electrochemical performance. The discharge capacities achieved using K+ salt additive are also lower than those obtained without it due to the incapability of KO2 to precipitate on the oxygen electrode, turning the initial solution-phase ORR to a surface-confined ORR after supersaturation. In this work we show that stabilization of the intermediate products and an efficient precipitation of the final products at the oxygen electrode are key factors governing the electrochemical performance in Na O2 batteries.