Improved Electrode Reversibility of Nanosized Li_1.15Nb_0.15Mn_0.7O₂ through Li₃PO₄ Integration

抄録

A lithium-excess cation-disordered rocksalt oxide, Li_1.15Nb_0.15Mn_0.7O₂, is synthesized and tested as positive electrode materials for battery applications. Although nanosized Li_1.15Nb_0.15Mn_0.7O₂ delivers a large reversible capacity using cationic/anionic redox reaction, the inferior capacity retention hinders its use for practical applications. Such degradation of electrode reversibility, including electrochemical and structural reversibility, is anticipated to originate from the gradual oxygen loss for the electrode materials with anionic redox. Herein, Li₃PO₄ is integrated into Li_1.15Nb_0.15Mn_0.7O₂ by high-energy mechanical milling, and 7 mol% Li₃PO₄ integrated Li_1.15Nb_0.15Mn_0.7O₂, Li_1.2P_0.06Nb_0.13Mn_0.61O₂, shows much improved cyclability when compared with the sample without Li₃PO₄. Approximately 80 % of reversible capacity is retained after 100-cycle test at a rate of 200 mA g⁻¹. Moreover, electrode kinetics are significantly improved by Li₃PO₄ integration, and Li_1.2P_0.06Nb_0.13Mn_0.61O₂ delivers a discharge capacity of 200 mA h g⁻¹ at a rate of 640 mA g⁻¹. Li_1.2P_0.06Nb_0.13Mn_0.61O₂ also shows improved thermal stability at elevated temperatures. From these results, the effectiveness of Li₃PO₄ integration into nanosized disordered rocksalt oxides with anionic redox is discussed, and this finding leads to the development of metastable high-capacity positive electrode materials for advanced Li-ion batteries.