Ni-Doped Layered Manganese Oxide as a Stable Cathode for Potassium-Ion Batteries

Potassium-ion batteries (PIBs) are one of the promising alternatives to lithium-ion batteries (LIBs). Layered potassium manganese oxides are more attractive as cathodes for PIBs due to their high capacity, low cost, and simple synthesis method but suffer from the Jahn-Teller effect of Mn³⁺ in material synthesis. Here, a layered P3-type K_0.67Mn_0.83Ni_0.17O₂ material with a suppressed Jahn-Teller effect was successfully synthesized. K_0.67Mn_0.83Ni_0.17O₂ delivers a specific capacity of 122 mAh g^-1 at 20 mA g^-1 in the first discharge, superior rate performance, and good cycling stability (75% capacity retention cycled at a high rate of 500 mA g^-1 after 200 cycles). Besides, the K ion diffusion coefficient of the K_0.67Mn_0.83Ni_0.17O₂ electrode can reach 10^-11 cm² s^-1, which are larger than the Ni-free electrode. The X-ray diffraction and electron diffraction analyses demonstrate that appropriate nickel could suppress the Jahn-Teller effect and reduce the structural deterioration, resulting in more migration pathways for K ions, thus enhancing the rate capability and cycling performance. These results provide a strategy to develop high-performance cathode materials for PIBs and deepen the understanding of structural deterioration in layered manganese-based oxides.