Mechanistic study on moisture exposure of Ti-based layered oxides for sodium storage applications

Abstract

The air stability and moisture sensitivity of titanium-based layered negative electrode materials for sodium storage play a critical role in their practical applications for advanced energy storage systems. However, the impact of moisture exposure on the electrochemical performance of these materials, as well as the potential for recovery through post-calcination treatment, remains unexplored. In this study, the impact of reactions with water molecules through exposure to moisture with high relative humidity and water soaking treatment on crystal structures and electrochemical performance in Na cells of titanium-based layered oxides is explored. The exposure to water molecules results in proton insertion associated with ion-exchange of sodium ions and the formation of sodium hydroxide, which further absorbs carbon dioxide. The removal of protons by post-calcination treatment requires relatively higher temperature, but the metastable layered oxides with oxygen vacancies, which show superior sodium storage reversibility, are newly obtained. The possibility of improvement of air stability and its practical reality for sodium battery applications are also discussed through a mechanistic study on moisture exposure of titanium-based electrode materials.