The influence of Li sources on physical and electrochemical properties of LiNi _0.5Mn _1.5O ₄ cathode materials for lithium-ion batteries

LiNi _0.5Mn _1.5O ₄ cathode materials were successfully prepared by sol-gel method with two different Li sources. The effect of both lithium acetate and lithium hydroxide on physical and electrochemical performances of LiNi _0.5Mn _1.5O ₄ was investigated by scanning electron microscopy, Fourier transform infrared, X-ray diffraction, and electrochemical method. The structure of both samples is confirmed as typical cubic spinel with Fd3m space group, whichever lithium salt is adopted. The grain size of LiNi _0.5Mn _1.5O ₄ powder and its electrochemical behaviors are strongly affected by Li sources. For the samples prepared with lithium acetate, more spinel nucleation should form during the precalcination process, which was stimulated by the heat released from the combustion of extra organic acetate group. Therefore, the particle size of the obtained powder presents smaller average and wider distribution, which facilitates the initial discharge capacity and deteriorates the cycling performance. More seriously, there exists cation replacement of Li sites by transition metal elements, which causes channel block for Li ion transference and deteriorates the rate capability. The compound obtained with lithium hydroxide exhibits better electrochemical responses in terms of both cycling and rate properties due to higher crystallinity, moderate particle size, narrow size distribution and lower transition cation substitute content.