Electrochemical and Structural Properties of a 4.7 V-Class LiNi[sub 0.5]Mn[sub 1.5]O[sub 4] Positive Electrode Material Prepared with a Self-Reaction Method

LiNi(0.5)Mn(1.5)O(4) as 4.7 V-class cathode materials were prepared with our self-reaction method at 650, 700, and 750DGC calcination temperatures respectively, and their electrochemical properties and crystal structures were studied. The sample at 700DGC was assigned to the space group P4(3)32 in the X-ray diffraction analysis. On the contrary, the space group of the sample calcined at 650 or 750DGC fell into Fd3m because diffraction peaks from P4(3)32 were missing. The sample at 700DGC showed a one-step profile in the charge/discharge curve and this contrasted with the other samples showing two-step ones. In spite of their different structures, these three samples had the same initial capacities of about 123 mAh/g. They gave similarly good cycle performance as well, but the sample at 650 or 750DGC maintained a little higher capacity after 50 cycles of charge/discharge than the sample at 700DGC. From the analysis of transformation of the crystal structure of LiNi(0.5)Mn(1.5)O(4)&&& during charging, it was found that LiNi(0.5)Mn(1.5)O(4) underwent the electrochemical reactions at three stages unlike LiMn(2)O(4) with two stages.