Electrochemical performance and structural evolution of layered oxide cathodes materials for sodium-ion batteries: A review

The current climate-focused transition from non-renewable to renewable energies has placed strong demands on renewable and sustainable energy sources. Lithium-ion batteries have been successfully commercialized in recent years. However, because of the scarcity and high costs of lithium, sodium-ion battery technologies have emerged as pragmatic alternatives for the development of more affordable, viable energy storage and conversion devices. Since the battery performance depends strongly on the properties and efficiency of the cathode material, layered transition metal oxides with immense potential for large-scale deployment, have emerged as intriguing cathode materials for sodium-ion batteries due to their simple synthesis, environmental safety, high conductivity, and high specific capacity. However, certain challenges associated with the stability and electrochemical performance of these layered oxide cathode materials have impeded the commercialization of sodium-ion battery technologies. This review attempts a comprehensive overview of advances in the electrochemical performance, stability, and structural evolution of layered oxides. The focus is on P2 and O3-type single, binary, and ternary layered oxides, cycled at low and high voltage during charge and discharge processes. Approaches to improve cathode performance, such as doping and surface modification, are also discussed for future development. Favorable anionic redox reactions, microwave-assisted methods, and high entropy oxides are also highlighted as improvement strategies. Based on the information provided in this review, layered transition metal oxides consisting of abundant, eco-friendly, low-cost, and performant elements are most suitable as cathode materials for future sodium-ion batteries.