Anion–Cation Synergetic Contribution to High Capacity, Structurally Stable Cathode Materials for Sodium‐Ion Batteries

• Published in: Advanced functional materials 2020-12, Vol.30 (50), p.n/a
• Main Authors: Xu, Hang, Cheng, Chen, Chu, Shiyong, Zhang, Xueping, Wu, Jianghua, Zhang, Liang, Guo, Shaohua, Zhou, Haoshen
• Format: Article
• Language: English
• Subjects: anionic redox; Cathodes; cationic redox; Cations; Crystal structure; Disproportionation; Electric potential; Electrochemical analysis; Electrode materials; Manganese; Materials science; Phase transitions; Rechargeable batteries; Redox reactions; Sodium-ion batteries; structurally stable; Transition metal oxides; Voltage
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.202005164

Layered transition metal oxides as promising cathode materials for sodium‐ion batteries have been extensively studied to obtain superior electrochemical properties. Since the cationic redox materials have almost reached the theoretical capacity limits accompanied by the migration and disproportionation of transition metals, anionic redox counterparts have been extensively explored to obtain extra capacity. In this work, P2‐type Na0.67[Li0.21Mn0.59Ti0.2]O2 is introduced, where manganese and oxygen synergistically undergo redox reaction reversibly. In situ X‐ray diffraction (XRD) experiments indicate a highly stable lattice structure with an extremely small volume strain of 0.7% during cycles with no sign of phase transitions. The stable crystal structure demonstrates the suppression of manganese disproportionation which is common in the layered Mn‐based cathode materials. Thanks to both cationic and anionic redox, this material can deliver a reversible capacity of 231 mA g−1 in the voltage range of 1.5–4.5 V and the high‐voltage plateau can be maintained during subsequent cycles with splendid cycling stability. P2‐type Na0.67[Li0.21Mn0.59Ti0.2]O2 is introduced as a promising cathode for sodium‐ion batteries where manganese and oxygen synergistically undergo redox reactions reversibly. A highly stable lattice structure is shown to have an extremely small volume strain of 0.7% and no sign of phase transitions during cycles, which demonstrates the suppression of manganese disproportionation, leading to the maintained high‐voltage plateau and splendid cycling stability.