Improved electrochemical properties of LiNi_0.5Mn_1.5O₄ spinel material by surface modification with LiCoO₂

The attractive cathode material, LiNi_0.5Mn_1.5O₄ for lithium ion batteries was synthesized and its surface was modified by adding LiCoO₂ by a sol-gel method. This research is aimed to figure out the effects of LiCoO₂ added to pristine LiNi_0.5Mn_1.5O₄. The electrochemical performance was characterized by galvanostatic cycle tests between 3.0 and 4.9V versus Li/Li⁺ at 0.5 C-rate using the prepared coin cells consisting of a series of LiNi_0.5Mn_1.5O₄ cathode each, lithium metal anode, and 1M LiPF₆ in DMC/EC (1:1 v/v) electrolyte. In XRD results, there exist some impurity phases attributed to the added LiCoO₂ even at the high sintering temperature, but these impurities did not exert influence on the electrochemical behavior of the samples. Also, the charge/discharge results are in good agreement with the XRD data. As increasing the amount of LiCoO₂, (220) phase XRD peak which means a degree of cation mixing developed and this affected the amount of inserted/extracted Li ions. Thus, cobalt-rich samples showed the lower capacity than pristine LiNi_0.5Mn_1.5O₄. However, a little amount of LiCoO₂-added LiNi_0.5Mn_1.5O₄ showed the best electrochemical properties. The improved kinetics and electrochemical properties are discussed in detail.