Abstract
LiNiO2 is the most attractive material with the lower cost and higher discharge capacity to replace LiCoO2 material in Li-ion battery. Nevertheless, stoichiometric LiNiO2 is difficult to synthesize, transition metals such as cobalt and manganese are added to stabilize the structure and to improve the properties. In this study, the Ni1-x-yCoyMnx(OH)2 precursor was obtained by the chemical co-precipitation method. Ni1-x-yCoyMnx(OH)2 and Li2CO3 were thoroughly mixed and then calcined at elevated temperature in the flowing oxygen atmosphere to obtain the LiNi1-x-yCoyMnxO2 cathode material. The thermal analysis showed that the hexagonal structure LiNi1-x-yCoyMnxO2 was formed at 750 oC, and the total weight loss was around 30%. On the basis of the laser scattering data and FESEM micrographs, larger agglomerates (5-15□□m) of rather small primary particles (0.3-1 □m) were revealed. For increasing calcined temperature, the particle size of primary grain increased. The XPS measurement demonstrated that Mn dopant had an effect upon the valence number of Ni. As the Mn content increased, the amount of Ni2+ increased. Compared with XRD data, it was argued that the cation mixing was attributed to the increasing of the Ni2+ ion content and the resulting initial capacity was decreased accordingly. The electrochemical behavior of LiNi1-x-yCoyMnxO2 powder was examined by using two-electrode test cells consisted of a cathode, metallic lithium anode, and an electrolyte of 1M LiPF6 in a 1:1 (volume ratio) mixture of EC/DMC. Cyclic charge/discharge testing of the coin cells, LiNi0.6Co0.25Mn0.15O2 calcined at 900oC exhibited the best electrochemical characteristics, in which the initial discharge capacities attained 178mAh/g and the capacity retention was 98.1% after 20 cycling tests. After cycled at 1C rate, LiNi0.6Co0.25Mn0.15O2 showed excellent capacity retention around 95.7% after 20 cycles. It is demonstrated that LiNixCoyMn1-x-yO2 electrode should exhibit great potential for the future application in lithium-ion battery cathode.