Synthesis and characterization of the metal-doped high-voltage spinel LiNi0.5Mn1.5O4 by mechanochemical process

The electrochemical performance of the high-voltage spinel LiNi0.5Mn1.5O4 was improved by doping the original material with the transition metal ion such as trivalent chromium, Cr3+, which had larger bonding strength with oxygen and no Jahn-Teller effect. These high-voltage spinel compounds were prepared by the mechanochemical process, and the synthetic condition was optimized for the best electrochemical performance. It is believed that the high homogeneity of the mixture prepared by mechanical activation helps the synthesis of the phase-pure LiNi0.5-xMn1.5-yMx+yO4 compound. The doping with the transition metal can enhance the electrochemical properties of LiNi0.5Mn1.5O4 because the large bonding energy between the transition metal and the oxygen prevents the doped spinel from being oxygen-deficient during the high temperature synthesis process, leading to the structural and chemical stability in LiNi0.5Mn1.5O4. The XRD patterns for the doped materials exhibited no impurity phase such as LizNi1-zO commonly found in original LiNi0.5Mn1.5O4 probably due to this structural stability of the doped materials. In addition, it is inferred that the improved cyclic performance is mainly attributed to the reduction of the Jahn-Teller distortion by substituting some portion of the high spin Mn3+ ions with other transition metal and less Mn dissolution of the doped spinel into the electrolyte, which effectively reduces the increase of impedance during the electrochemical cycling.