Effect of Cr3+ doping on morphology evolution and electrochemical performance of LiNi0·5Mn1·5O4 material for Li-ion battery

Abstract

In consideration of higher bonding strength with oxygen and no Jahn-Teller effect, Cr3+ ions were substituted for equal amount of Ni2+ and Mn4+ ions to obtain series of LiNi0.5-x/2CrxMn1.5-x/2O4 (x = 0, 0.025, 0.05, 0.1, 0.2) materials, which were prepared via a combined coprecipitation-hydrothermal method followed by a two-step calcination process. The effects of different Cr3+ doping contents on the structure, morphology and electrochemical performance were systematically investigated. The results show that Cr3+ doping increases Ni/Mn disordering while reduces Mn3+ content, which can balance rate capability and cycling stability. What’s more, Cr3+ doping reduces the primary particle size and secondary agglomeration degree. More significantly, the morphology evolution of primary particles with Cr3+ doping content is very impressive. At x ≤ 0.05, the {110} and {311} planes with higher surface energies appear in turn, while at x = 0.1 and 0.2, {311} surface disappears, {100} and {110} surfaces decrease and {111} surface increases gradually. Electrochemical results show that LiNi0·475Cr0·05Mn1·475O4 material exhibits the optimal rate and cycling performances, which can be attributed to the elimination of LixNi1-xO impurity, higher Ni/Mn disordering, lower Mn3+ content, appropriate particle size with more uniform distribution, higher structural stability resulting from the introduction of Cr–O bond and no Jahn-Teller effect of Cr3+ ions, as well as lower proportion of {111} surface and higher proportion of {100}, {110} and {311} surfaces.