Oxygen anionic redox activated high-energy cathodes: Status and prospects

The rapidly growing electric vehicle market as well as large-scale electric grid application harshly enforces the progress of high-energy Li-ion batteries (LIBs), and arouses the urgent renovation of high-capacity cathode materials. To this end, oxygen anionic redox (OAR), the electrochemical conversions between different oxygen states in oxides to compensate charges during the extraction/insertion process of alkali metal ions, has served as a new design paradigm to produce “extra” capacities for cathodes. By balancing the metal cationic redox (MCR) and OAR, a variety of high-energy cathodes, especially Li-rich layered oxides (LLOs), have been developed and extensively studied on issues such as material design, reaction mechanism, and performance enhancement, making LLOs one of the most appealing candidates for practical high-energy LIBs in the near future. On the other hand, the employment of pure OAR triggers the emerging lithia-based sealed batteries with great long-term potentials, although diverse fundamental issues require urgent elucidation. This review paper provides an overview of OAR and OAR-activated cathodes ranging from transition metal oxides to lithia-based composites, followed by a personnel perspective with a hope to promote the development of high-energy cathodes for more advanced batteries.