Recent progress on strategies to improve the high-voltage stability of layered-oxide cathode materials for sodium-ion batteries

Sodium-ion batteries offer a low-cost sustainable alternative to current lithium-ion batteries and can be made on the same manufacturing lines. The sustainability arises from the low cost, reduction in the use of critical elements and strategic materials, and potential long-life. To maximize their potential, higher energy density batteries are required, this can be achieved in part through the stabilization of higher voltage cathode materials. In this review we summarize the failure and degradation processes associated with the high capacity and higher voltage layered oxide cathode materials. Material crystal structure rearrangements, electrolyte oxidation, particle cracking and reactive surfaces form most of the degradation mechanisms. Strategies to overcome these processes are discussed in detail, and the synergistic requirements to stabilize the materials structure and the interfaces highlighted. The importance of surface engineering in future materials design is emphasized.