Anion–Cation Synergetic Contribution to High Capacity, Structurally Stable Cathode Materials for Sodium‐Ion Batteries
Hang Xu, Chen Cheng, Shiyong Chu, Xueping Zhang, Jianghua Wu, Liang Zhang, Shaohua Guo, Haoshen Zhou
Abstract
Abstract 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 Na 0.67 [Li 0.21 Mn 0.59 Ti 0.2 ]O 2 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.