Impact of phosphorus structural position on the electrochemical enhancement of phosphorus doped LiMn₂O₄

Nanostructures of phosphorus doped and undoped LiMn₂O₄ have been obtained through the thermal decomposition of different citrate precursors. The oxides have been characterized by XRD, XPS, ⁷Li-NMR-MAS, STEM and electrochemical tests in aqueous electrolyte. XPS showed that no pyrophosphate species were formed during the doping process. The position of the phosphorus in the LiMn₂O₄ nanostructure were elucidated on both samples through analyses of STEM images and structural refinement using the Rietveld method. These analyses allowed to set the P in a 48f position with coordinates (1/8, 1/8, 0.338) at the crystalline structure of the LiMn₂O₄ spinel. Electrochemical tests corroborated the improvement of electrochemical properties of the oxide when phosphorus is used as dopant. XRD measurements on cycled electrodes showed the inhibition of segregated collateral phases during the cycling process. That allows to propose an explanation of the achieved advantages of doping the lithium manganese oxide spinel structure on the ground of the phosphorous position in the LiMn₂O₄ crystalline cell.