Novel materials and methods of synthesis in the field of energy conversion and economy are reported. The main goal is to prepare and characterize Li(4 - x)Mn(5 - 2x)Fe3xO12 compounds. These compounds crystallize in a spinel-type structure, AB2O4, in which the cationic location in the A and B sublattices drives the potential application of these materials in two current prominent research fields: magnetic refrigeration and lithium batteries. This solid solution is revealed as a tunable system that nicely permits a specific response to be highlighted, depending on the composition and particle size: the magnetocaloric effect or active electrochemical behavior.