High-energy P2-type Na-layered oxide cathode with sequentially occurred anionic redox and suppressed phase transition

• Published in: Applied physics reviews 2022-12, Vol.9 (4)
• Main Authors: Lee, Sangyeop, Kang, Jungmin, Cho, Min-kyung, Park, Hyunyoung, Ko, Wonseok, Lee, Yongseok, Ahn, Jinho, Lee, Seokjin, Sim, Eunji, Ihm, Kyuwook, Hong, Jihyun, Kim, Hyungsub, Kim, Jongsoon
• Format: Article
• Language: English
• ISSN: 1931-9401; 1931-9401
• DOI: 10.1063/5.0100108

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.