Advanced layered oxide cathodes for sodium/potassium-ion batteries: Development, challenges and prospects

Rapid exploitation of renewable energy sources for replacing the conventional fossil fuels drives the development of electrical energy storage (EES) systems. Sodium-ion batteries (NIBs) and potassium-ion batteries (KIBs) are considered as the promising low-cost candidates for the application in large-scale energy storage by virtue of the abundant reserves of sodium and potassium resources. In NIBs and KIBs, cathode plays a critical role in the electrochemical performances, and hence searching for appropriate cathode materials becomes the key point. Particularly, layered oxide cathodes with superior specific capacity and appropriate operating voltage are the most fascinating electrode materials for NIBs and KIBs. In light of performances, the fundamental and recent researches of layered oxide cathodes are reviewed for NIBs and KIBs. However, several major challenges including irreversible phase transition, low energy density, poor air stability, oxygen redox chemistry and inferior cycling stability need to be overcome. All in all, a comprehensive review for the layered oxide cathodes is present accompanied with solutions for these problems, especially mentioning the different functions of different elements and ionic potential (Ф) for guiding the design of layer oxides with exceptional performances. The challenges and prospects are also included with the hope of these materials applying in the next-generation energy storage devices.