Enhancing Cycle Life in Superoxide‐Based Na–O2 Batteries by Reducing Interface Reactivity

A new sodium–oxygen (Na–O₂) battery is designed with highly active vanadium phosphide (VP) nanoparticles as a catalyst, an ether/ionic liquid-based electrolyte, and an effective sodium bromide (NaBr) anode protection layer. This designed Na–O₂ cell that produces NaO₂ is able to reduce the interfacial reactivity between cell materials and the product to achieve a cycle life of 1070 cycles with a high energy efficiency of more than 83% at the first cycle.

Abstract

Sodium–oxygen (Na–O₂) batteries are considered a promising energy storage alternative to current state-of-the-art technologies owing to their high theoretical energy density, along with the natural abundance and low price of Na metal. The chemistry of these batteries depends on sodium superoxide (NaO₂) or peroxide (Na₂O₂) being formed/decomposed. Most Na–O₂ batteries form NaO₂, but reversibility is usually quite limited due to side reactions at interfaces. By using new materials, including a highly active catalyst based on vanadium phosphide (VP) nanoparticles, an ether/ionic liquid-based electrolyte, and an effective sodium bromide (NaBr) anode protection layer, the sources of interface reactivity can be reduced to achieve a Na–O₂ battery cell that is rechargeable for 1070 cycles with a high energy efficiency of more than 83%. Density functional theory calculations, along with experimental characterization confirm the three factors leading to the long cycle life, including the effectiveness of the NaBr protective layer on the anode, a tetraglyme/EMIM-BF₄ based electrolyte that prevents oxidation of the VP cathode catalyst surface, and the EMIM-BF₄ ionic liquid aiding in avoiding electrolyte decomposition on NaO₂.