A relation between the electrochemical behaviors and morphology of Ni–Co3O4 composites prepared by the chemical reduction method or the mechanical milling

In order to improve low initial coulombic efficiency of Co3O4 (69%), Ni–Co3O4 composites were prepared by the chemical reduction method or by mechanical milling. Ni–Co3O4 composite prepared by the mechanical milling showed an improved initial coulombic efficiency (79%), whereas the initial coulombic efficiency (71%) of Ni–Co3O4 composite obtained from the chemical reduction method was almost the same as that of Co3O4. In SEM studies, when compared with Ni–Co3O4 composite prepared by the mechanical milling, only a small amount of Ni particles was found on the surface of Ni–Co3O4 composite made by the chemical reduction method. Supposing that Ni in Ni–Co3O4 composite makes the irreversible portion of Li2O decompose during the first discharge, the contact area between Ni and Co3O4 should be enlarged as much as possible. Hence, it could be suggested that the disparity between the mechanical milling and the precipitation method in the initial coulombic efficiency results from the difference in the contact area between Ni and Co3O4, which is closely related to the homogeneity of Ni dispersion on Co3O4.