In Situ Electrochemical Oxidation for High‐Energy‐Density Aqueous Batteries: Mechanisms, Materials, and Prospects

To advance the commercial utilization of aqueous electrochemical devices for grid-scale energy storage, it is crucial to address the current limitations related to energy density and cycle stability. Indeed, the lack of high-performance cathodes is still an obstructive issue, not to mention the limited capacities related to the monotonic cation intercalation/deintercalation mechanism. Fortunately, conversion chemistries with redox reactions bring a new dimension, where materials with multiple valence states facilitate multi-electron redox reactions, offering the potential for high-energy-density storage. Recently, the in situ electrochemical oxidation technique has been developed to diversify element valences and transform the structure and chemical environment of cathode materials, which is conducive to efficient conversion reaction and extended lifespan for aqueous batteries. This review systematically investigates the newly developing in situ electrochemical oxidation technique, shedding light on the mechanism investigations with different reaction pathways and facing the rapid developments for aqueous batteries. A comprehensive knowledge of the corresponding superiorities of multiplied specific capacity, broadened voltage window, and accelerated reaction kinetics associated with higher energy and power densities has been explored extensively. In the end, future research directions are outlined to advance the development of stationary energy storage systems with high energy density, fast charging capability, and long-term cycling stability.