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• This paper reviews history and evolution of layered oxides. • The challenges and prospects are included. • This review paper also offers some guidance for further designing layer oxides. 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. [ABSTRACT FROM AUTHOR]

• LiCrTiO 4 nanoparticles with carbon layer (LCTOC) are successfully prepared by sol–gel method. • Reversible capacity of 114.3 mAh/g is achieved at 1 A/g over 2500 cycles, indicating its ultrastable cycling stability. • Morphology and structure of LCTOC are maintained perfectly during long-term cycling. • Such a superior capacity of LCTOC is attributed to the improved conductivity and ion-diffusion rate. Hybrid magnesium-lithium ion batteries (HMLBs) merge Li+ faster kinetics with dentrite-free and low-cost Mg anode and are arousing widespread concern. It is regrettable that its development is limited by the lack of advanced electrode materials. Herein, LiCrTiO 4 nanoparticles with/without carbon layer (LCTOC/LCTON) are successfully prepared by sol–gel method and used as cathodes for HMLBs. Compared with LCTON, LCTOC not only exhibits a high reversible capacity (139.3 mAh/g at 100 mA/g after 100 cycles), but also possesses an excellent rate performance (123.1 mAh/g at 500 mA/g). Notably, a reversible capacity of 114.3 mAh/g at 1 A/g has been achieved over 2500 cycles, indicating an ultrastable cycling stability. The enhanced electrochemical performance of LCTOC is attributed to the improved conductivity and ion diffusion rate, and decreased polarization value induced by the carbon coating layer with a higher surface area. In addition, the ion storage mechanism of LCTOC is explored by ex-situ tests. The morphology and structure of LCTOC have been maintained perfectly during the long-term charge–discharge process, indicating a highly structural stability and reversibility. This study exhibits a promising application of LCTOC in the fabrication of advanced HMLBs. [ABSTRACT FROM AUTHOR]