Moderate active Fe3+ doping enables improved cationic and anionic redox reactions for wide-voltage-range sodium storage
Congcong Cai, Xinyuan Li, Hao Fan, Zhuo Chen, Ting Zhu, Jiantao Li, Ruohan Yu, Tianyi Li, Ping Hu, Liang Zhou
Abstract
Abstract Layered metal oxides are promising cathode materials for sodium-ion batteries (SIBs) due to their high theoretical specific capacity and wide Na + diffusion channels. However, the irreversible phase transitions and cationic/anionic redoxes cause fast capacity decay. Herein, P2-type Na 0.67 Mg 0.1 Mn 0.8 Fe 0.1 O 2 (NMMF-1) cathode material with moderate active Fe 3+ doping has been designed for sodium storage. Uneven Mn 3+ /Mn 4+ distribution is observed in NMMF-1 and the introduction of Fe 3+ is beneficial for reducing the Mn 3+ contents both at the surface and in the bulk to alleviate the Jahn–Teller effect. The moderate Fe 3+ /Fe 4+ redox can realize the best tradeoff between capacity and cyclability. Therefore, the NMMF-1 demonstrates a high capacity (174.7 mAh g −1 at 20 mA g −1 ) and improved cyclability (78.5% over 100 cycles) in a wide-voltage range of 1.5–4.5 V ( vs. Na + /Na). In-situ X-ray diffraction reveals a complete solid-solution reaction with a small volume change of 1.7% during charge/discharge processes and the charge compensation is disclosed in detail. This study will provide new insights into designing high-capacity and stable layered oxide cathode materials for SIBs.