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

Abstract

LiNi0.5Mn1.5O4LiNi0.5Mn1.5O4 as 4.7 V-class cathode materials were prepared with our self-reaction method at 650, 700, and 750°C calcination temperatures respectively, and their electrochemical properties and crystal structures were studied. The sample at 700°C was assigned to the space group P4332P4332 in the X-ray diffraction analysis. On the contrary, the space group of the sample calcined at 650 or 750°C fell into Fd3mFd3m because diffraction peaks from P4332P4332 were missing. The sample at 700°C 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 750°C maintained a little higher capacity after 50 cycles of charge/discharge than the sample at 700°C. From the analysis of transformation of the crystal structure of LiNi0.5Mn1.5O4LiNi0.5Mn1.5O4 during charging, it was found that LiNi0.5Mn1.5O4LiNi0.5Mn1.5O4 underwent the electrochemical reactions at three stages unlike LiMn2O4LiMn2O4 with two stages. © 2003 The Electrochemical Society. All rights reserved.