The role of oxygen vacancies in metal oxides for rechargeable ion batteries

Rechargeable ion batteries are one of the most reliable energy storage technologies for the applications ranging from small portable devices and electric vehicles to renewable energy integration and large-scale stationary energy storage. In the roadmap of developing and understanding new electrode materials for rechargeable ion batteries, oxygen vacancies, known as defects in metal oxides, have shown a high impact on the final electrochemical performance of the oxides. The present review aims to summarise the synthesis methods and characterisation techniques of oxygen vacancies as well as some of the most recent and exciting progress made to understand the role of oxygen vacancies in the electrochemical performance of Li-, Na-, K- and Zn-ion batteries. This review discusses not only the role of oxygen vacancies directly in electrode materials and indirectly in the coating layers on electrode materials, but also the synergistic role of oxygen vacancies interplaying with other contributors such as carbonaceous materials, doping, amorphisation, structural transformation, nanostructuring and functional coating. Finally, perspectives are given to stimulate new ideas and open questions to facilitate the further development of oxygen deficient electrode materials in energy research landscape.