Synthesis, characterizations, and utilization of oxygen-deficient metal oxides for lithium/sodium-ion batteries and supercapacitors

Oxygen vacancy (V_O), the most common type of defect in metal oxides, could alter intrinsic properties which are usually determined by crystal structures. Oxygen-deficient metal oxides with regulated properties have been applied in many aspects, especially lithium/sodium-ion batteries and supercapacitors, in which the V_O-induced mobility, conductivity, and structural stability could affect their performance to a great extent. By modeling certain oxygen-deficient metal oxides, the mechanisms behind such performance regulations are comprehensively described. For instance, while appropriate V_O can enhance the electrochemical properties of anode materials by providing extra active sites, built-in electric field, etc.; the influences of oxygen non-stoichiometry vary with the cathode's crystal structure and cationic composition. In addition to these, the synthesis strategies and common physical characterization techniques for V_O are also introduced. This review aims to introduce oxygen defect chemistry and propel its reasonable applications in the field of electrochemical energy storage.