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.

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Potassium-ion batteries are an emerging energy storage technology that could be a promising alternative to lithium-ion batteries due to the abundance and low cost of potassium. Research on potassium-ion batteries has received considerable attention in recent years. With the progress that has been made, it is important yet challenging to discover electrode materials for potassium-ion batteries. Here, we report pyrrhotite Fe1−xS microcubes as a new anode material for this exciting energy storage technology. The anode delivers a reversible capacity of 418 mAh g−1 with an initial coulombic efficiency of ~70% at 50 mA g−1 and a great rate capability of 123 mAh g−1 at 6 A g−1 as well as good cyclability. Our analysis shows the structural stability of the anode after cycling and reveals surface-dominated K storage at high rates. These merits contribute to the obtained electrochemical performance. Our work may lead to a new class of anode materials based on sulfide chemistry for potassium storage and shed light on the development of new electrochemically active materials for ion storage in a wider range of energy applications.