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

Abstract 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 Na x MnO 2 ( x = 0.7, 0.8, 0.9) cathode materials with varying P2/O′3 ratios and further investigated their electrochemical performances. The optimized Na 0.8 MnO 2 , 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·g −1 with an initial Coulombic efficiency of 98.2% in half‐cell configuration. The Na 0.8 MnO 2 //hard carbon full cell also achieved a high specific capacity of 126.7 mAh·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.