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 Mn in material synthesis. Here, a layered P3-type KMnNiO material with a suppressed Jahn-Teller effect was successfully synthesized. KMnNiO delivers a specific capacity of 122 mAh g at 20 mA g in the first discharge, superior rate performance, and good cycling stability (75% capacity retention cycled at a high rate of 500 mA g after 200 cycles). Besides, the K ion diffusion coefficient of the KMnNiO electrode can reach 10 cm s, 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.