High-energy and high-power lithium ion-batteries are essential for future development in large scale energy storage systems to meet all the requirements of modern society. Unfortunately, at present, high-power applications are limited mainly by the diffusion of lithium ions in the solids. This work aims at the improvement of lithium ion diffusivity in one of the most promising cathode material: lithium-manganese spinel (LMO). Herein we are presenting synergetic effect of potassium and sulphur doping of LMO structure. We prove that introduction of small amount of K in the Li sites can enhance effective lithium ion diffusion coefficient and allows material to retain high capacity during very fast charging/discharging processes.