The Nature of Oxidized Oxygen in Oxygen Redox Cathodes

Oxygen redox cathodes (ORCs) are expected to surpass the capacity limits of conventional batteries. However, the commercialization of ORCs has suffered from severe voltage decay due to irreversible structural reconstructions, which are related to the evolution of oxidized oxygen upon charging. Several models have been proposed to elucidate the relationship between oxygen redox and cathode failures. However, the oxidized oxygen states in batteries are under debate, which limits the solution and hinders further ORC application. In this perspective, a critical overview of research progress on oxidized oxygen states in ORCs is provided. The controversies regarding the chemical states of oxidized oxygen are also presented. Finally, this work ends with a prospect on how to scientifically identify oxidized oxygen and design stable ORC batteries. With this article, the aim is to promote the clarification of anionic redox chemistry and the development of more efficient and long-lasting batteries.