Anion Doping for Layered Oxides with a Solid-Solution Reaction for Potassium-Ion Battery Cathodes
Yan‐Song Xu, Mu‐Yao Qi, Qinghua Zhang, Fanqi Meng, Yong‐Ning Zhou, Sijie Guo, Yonggang Sun, Lin Gu, Baobao Chang, Chuntai Liu, Amin Cao, Li‐Jun Wan
Abstract
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.