Difficulties, strategies, and recent research and development of layered sodium transition metal oxide cathode materials for high-energy sodium-ion batteries

Energy-storage systems and their production have attracted significant interest for practical applications. Batteries are the foundation of sustainable energy sources for electric vehicles (EVs), portable electronic devices (PEDs), etc. In recent decades, Lithium-ion batteries (LIBs) have been extensively utilized in large-scale energy storage devices owing to their long cycle life and high energy density. However, the high cost and limited availability of Li are the two main obstacles for LIBs. In this regard, sodium-ion batteries (SIBs) are attractive alternatives to LIBs for large-scale energy storage systems because of the abundance and low cost of sodium materials. Cathode is one of the most important components in the battery, which limits cost and performance of a battery. Among the classified cathode structures, layered structure materials have attracted attention because of their high ionic conductivity, fast diffusion rate, and high specific capacity. Here, we present a comprehensive review of the classification of layered structures and the preparation of layered materials. Furthermore, the review article discusses extensively about the issues of the layered materials, namely (1) electrochemical degradation, (2) irreversible structural changes, and (3) structural instability, and also it provides strategies to overcome the issues such as elemental phase composition, a small amount of elemental doping, structural design, and surface alteration for emerging SIBs. In addition, the article discusses about the recent research development on layered unary, binary, ternary, quaternary, quinary, and senary-based O3- and P2-type cathode materials for high-energy SIBs. This review article provides useful information for the development of high-energy layered sodium transition metal oxide P2 and O3-cathode materials for practical SIBs.