Realizing high initial Coulombic efficiency in manganese-based layered oxide cathodes for sodium-ion batteries via P2/O′3 biphasic structure optimization

Mn-based layered oxides are among the most promising cathode materials for sodium-ion batteries owing to the advantages of abundance, environmental friendliness, low cost and high specific capacity. P2 and O ' 3 are two representative structures of Mn-based layered oxides. However, the P2 structure containing insufficient Na generally exhibits low initial charge capacity, while O ' 3 structure with sufficient Na delivers high initial charge capacity but poor cycle stability. This study prepared a multitude of NaxMnO2 (x = 0.7, 0.8, 0.9) cathode materials with varying P2/O ' 3 ratios and further investigated their electrochemical performances. The optimized Na0.8MnO2, comprising 69.9 wt% O ' 3 and 30.1 wt% P2 phase, exhibited relatively balanced specific capacity, Coulombic efficiency and cycle stability. Specifically, it achieved a high specific capacity of 128.9 mAh<middle dot>g(-1) with an initial Coulombic efficiency of 98.2% in half-cell configuration. The Na0.8MnO2//hard carbon full cell also achieved a high specific capacity of 126.7 mAh<middle dot>g(-1) with an initial Coulombic efficiency of 98.9%. Moreover, the capacity fading mechanism was revealed by combining in-situ and ex-situ X-ray diffraction. The findings of this study provide theoretical guidance for further modification design of Mn-based layered cathodes.