Synthesis and Electrochemical Properties Studies on Layered Li_0.7Co_xMn_(1-x)O_2 Cathode Material for Lithium-Ion Secondary Batteries

The layered Li0.7CoxMn1-xO2 cathode materials with O2-type structure were synthesized by using improved solid-state reaction and ion exchange reaction in atmosphere. The influence of sinter temperature and the content of doping cobalt of the precursor alkali bronzes was investigated, and XRD analysis, SEM analysis and electrochemical test were used to study the structure and electrochemical properties of the precursors and samples. The results show that the precursor Na0.7Co0.2Mn0.8O2 sintered at 900℃ for 16h has an obviously layered P2 structure. The electrochemical tests show that the sample Li0.7Co0.2Mn0.8O2 has the best electrochemical properties which has an initial discharge capacity of 162 mAh·g-1 cycled between 2.25-4.20V and shows only one charge-discharge plateau of 2.70-2.90V. A significant structure transformation to the spinal-type phase on cycling was not found for the material and a stabilization of the specific capacity around 153 mAh·g-1 remained after the 40 cycles for the material.