Magnesium ion-doped layered oxide cathodes for alkali-metal ion batteries: Recent research progress and outlook

With the widespread application of electrical energy storage technology, it is particularly essential to develop a new generation of rechargeable batteries with low cost, high capacity, and long cycle life. Alkali-metal ion batteries (AIBs) have attracted great attention in the field of secondary batteries due to their high capacity and impressive rate and cycle performance. As a typical class of AIB cathode material, transition metal (TM) layered oxides have been widely studied and applied by virtue of their unique structure and excellent tunability, but there are still some limitations such as poor capacity retention and inferior structural stability. To date, various modification strategies have been investigated to address these issues. In particular, heteroatom doping is considered to be an effective strategy to modify the lattice architecture of cathode materials. This review summarizes the effect of magnesium ion doping on the structure and performance of AIBs, including alkali metal site doping and TM site doping. Specifically, Mg doping can stabilize the structure, eliminate the order, increase conductivity, and enhance the kinetics, which are beneficial to improve the performance of AIBs. Moreover, some typical materials synthesis methods and in-situ characterization techniques for mechanistic studies are also discussed. Finally, the future development trend of electrode doping strategies for advanced AIBs is analyzed.