Phase transitions of Na-ion layered oxide materials and their influence on properties

Na-ion batteries possess great potential applications in the large-scale energy storage. The Na-ion layered oxide cathode (NaxTMO2) has received increasing attention in scientific and industrial research due to its high capacity, easy manufacture, adjustable voltage, and low cost. However, the larger the Na+ radius and the stronger the Na+-Na+ electrostatic repulsion is, which will lead to various structural configurations and complex structural transitions, resulting in multiple structure-property connections. In this paper, the structural types of Na-ion layered transition metal oxide cathode materials are introduced, and their structural evolutions during Na+ de/intercalation are summarized for revealing the mechanism for structural transformation of Na-ion layered transition-metal oxide cathode material and its effect on electrochemical performance; the existing challenges are discussed; the improvement strategies are proposed finally.