At present, lithium-ion batteries (LIBs) rule the energy storage sector, right from small scale portable electronics to large electric vehicles. However, the rising energy demand, safety concerns, and constrained lithium supply limit the LIBs’ potential. Thus, it is necessary to develop potassium-ion batteries (KIBs) with comparable energy densities, similar chemistry, low cost, and improved safety. KIBs are suitable for economical large-scale grid applications due to their significant abundance, high ionic mobility in electrolyte (smaller stroke radius compared to Li⁺/Na⁺), wider electrochemical potential window without K-plating and lower standard redox potential than their counterparts. They are ideal for the development of stable and reversible cathodic materials. However, the chemistry of KIBs is still in its infancy. In this spirit, the potassium-based P3 type K_0.5Mn_1-xM_xO₂ has been explored involving both experimental and (first principle) computational approaches.

Mn-based systems are associated with complex phase transformations. The structural disintegrity at low K-content due to stacking faults/other defects results in rapid fading of capacity, even with lower potential operating window. Partial substitution of Mn by Ni or Co confers higher average voltage, facile ionic and electronic migration, leads to better structural integrity and smoother voltage profile. Herein, we have synthesized various mixed transition metals P3 type layered oxides using simple solid state and wet chemistry routes. Additionally, the structural ordering in the layers, electronic properties (density of states) and electrochemical performance have been examined. Overall, a novel ~3.2 V (vs. K/K⁺) cathode for KIBs was produced. Apart from ambient temperature, it can also deliver stable electrochemical activity even at higher temperatures (ca. 40-50 °C). This study enriches the oxide cathode chemistry for the development of potassium-ion batteries.