Anion Doping for Layered Oxides with a Solid-Solution Reaction for Potassium-Ion Battery Cathodes

• Published in: ACS applied materials & interfaces Vol. 14; no. 11; pp. 13379 - 13387
• Main Authors: Xu, Yan-Song, Qi, Mu-Yao, Zhang, Qing-Hua, Meng, Fan-Qi, Zhou, Yong-Ning, Guo, Si-Jie, Sun, Yong-Gang, Gu, Lin, Chang, Bao-Bao, Liu, Chun-Tai, Cao, An-Min, Wan, Li-Jun
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 23.03.2022
• Subjects: Energy, Environmental, and Catalysis Applications; solid-solution reaction; anionic doping strategy; phase transition; layered oxides; potassium-ion battery
• ISSN: 1944-8244; 1944-8252
• DOI: 10.1021/acsami.2c00811

The development of potassium-ion batteries (PIBs) is challenged by the shortage of stable cathode materials capable of reversibly hosting the large-sized K+ (1.38 Å), which is prone to cause severe structural degradation and complex phase evolution during the potassiation/depotassiation process. Here, we identified that anionic doping of the layered oxides for PIBs is effective to combat their capacity fading at high voltage (>4.0 V). Taking P2-type K2/3Mn7/9Ni1/9Ti1/9O17/9F1/9 (KMNTOF) as an example, we showed that the partial substitution of O2– by F– enlarged the interlayer distance of the K2/3Mn7/9Ni1/9Ti1/9O2 (KMNTO), which becomes more favorable for fast K+ transition without violent structural destruction. Meanwhile, based on the experimental data and theoretical results, we identified that the introduction of F– anions effectively increased the redox-active Mn cationic concentration by lowering the average valence of the Mn element, accordingly providing more reversible capacity derived from the Mn3+/4+ redox couple, rather than oxygen redox. This anionic doping strategy enables the KMNTOF cathode to deliver a high reversible capacity of 132.5 mAh g–1 with 0.53 K+ reversible (de)­intercalation in the structure. We expect that the discovery provides new insights into structural engineering for pursuing stable cathodes to facilitate the future applications of high-performance PIBs.