Synthesis and Properties of Cathode Materials xLi_2MnO_3·(1 - x)LiMn_(1/3)Ni_(1/3)Co_(1/3)O_2 for Li-Ion Batteries

摘要

Lithium- and manganese-rich layered electrode materials, represented by the general formula xLi_2MnO_3·(1 - x)LiMO_2 in which M is Mn, Ni, and Co, are of interest for both high-power and high-capacity lithium ion batteries. In this paper, a series of nano-sized materials based on the xLi_2MnO_3 · (1 - x)LiMn_(1/3)Ni_(1/3)Co_(1/3)O_2 (x = 0, 0.2, 0.4, 0.6) as a cathode material for lithium batteries were synthesized by the sol-gel method, citric acid as a chelating agent. Its structural and electrochemical properties were investigated using X-ray diffractometry, scanning electron microscopy, galvanostatic charge-discharge test. Differences between electrochemical and chemical activation of the Li_2MnO_3 component are discussed. The results indicated that well-ordering layered xLi_2MnO_3 · (1 - x)LiMn_(1/3)Ni_(1/3)Co_(1/3)O_2 (x = 0, 0.2,0.4,0.6) cathode materials were successfully prepared with α-NaFeO_2 typical crystal. It is found that the changes in compositional, crystal structure and electrochemical performance depend highly on the different values of x. The charge-discharge capacity and cycle number plots confirm unequivocally that the Li_2MnO_3 component serves to stabilize LiMn_(1/3)Ni_(1/3)Co_(1/3)O_2 electrodes to electrochemical cycling. The study emphasizes that, for high values of x, a relatively small LiMn_(1/3)Ni_(1/3)Co_(1/3)O_2 concentration stabilizes a layered Li_2MnO_3 electrode to reversible lithium insertion and extraction. The composition x = 0.2 leads to the best electrochemical performance cathode material with high capacity of 253 mA h/g and high-rate property.