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 (Na_<i>x</i>TMO₂) 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.