Transition metal oxides for aqueous sodium-ion electrochemical energy storage

The electrochemical storage of sodium ions from aqueous electrolytes in transition metal oxides is of interest for energy and sustainability applications. These include low-cost and safe energy storage and energy-efficient water desalination. The strong interactions between water and transition metal oxide surfaces, as well as those between water and sodium ions, dictate the stability and electrochemical energy storage mechanisms in these materials. This review summarizes the implications of water as an electrolyte solvent for transition metal oxide electrodes, and sodium ion intercalation from neutral pH electrolytes into a diverse set of transition metal oxides. Increased control of the aqueous electrolyte/transition metal oxide interface is likely to lead to improvements in stability and capacity, which are critical breakthroughs for the implementation of transition metal oxides in aqueous sodium ion energy storage technologies.