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Recently, many researchers focus on Na-ion batteries as an alternative to Li-ion batteries, owing to their low cost and high natural abundance. However, they suffer from low electrochemical performance and large volume expansion, which makes difficult to industrial application. Therefore, various strategies have been proposed to address the current issues, such as particle-size control, surface-coating, and application of electrode material with various crystal structures. Herein, we briefly introduce and discuss the recent research with development trend of cathode material for Na-ion batteries.

An amorphorized Cu(PO3)2/C composite (A-CPO/C) achieves outstanding electrochemical performances compared to a low-crystalline Cu(PO3)2 (LC-CPO/C) composite.

Although anionic-redox-based layered oxide materials have attracted great attention as promising cathodes for Na-ion batteries because of their high practical capacities, they suffer from undesirable structural degradation, resulting in the poor electrochemical behavior. Moreover, the occurrence of stable anionic-redox reaction without the use of expensive elements such as Li, Co, and Ni is considered one of the most important issues for high-energy and low-cost Na-ion batteries. Herein, using first-principles calculation and various experimental techniques, we investigate the combination of vacancy (□) and Ti4+ cations in the transition-metal sites to enable outstanding anionic-redox-based electrochemical performance in the Na-ion battery system. The presence of vacancies in the P2-type Na0.56[Ti0.1Mn0.76□0.14]O2 structure suppresses the large structural change such as the P2–OP4 phase transition, and Ti4+ cations in the structure result in selectively oxidized oxygen ions with structural stabilization during Na+ deintercalation in the high-voltage region. The high structural stability of P2-type Na0.56[Ti0.1Mn0.76□0.14]O2 enables not only the high specific capacity of 224.92 mAh g−1 at 13 mA g−1 (1C = 264.1 mA g−1) with an average potential of ∼2.62 V (vs Na+/Na) but also excellent cycle performance with a capacity retention of ∼80.38% after 200 cycles at 52 mA g−1 with high coulombic efficiencies above 99%. Although there are some issues such as low Na contents in the as-prepared state, these findings suggest potential strategies to stabilize the anionic-redox reaction and structure in layered-oxide cathodes for high-energy and low-cost Na-ion batteries.