Improvement of initial coulombic efficiency of Co3O4 by ballmilling using Ni as an additive

Graphite has been widely used as the anode material of commercial Li-ion secondary batteries. With the growing demands of high-capacity secondary batteries, the low capacity of graphite has been looked upon as the limiting factor in wide applications and new anode materials with high capacity have been sought. Among many materials, Co3O4 showed the best anode performance. It has high capacity of about 700 mAh/g and good cycle life (93.4% of initial capacity is maintained after 100 cycles). However, because its irreversible capacity comes to about 30% of initial capacity, the initial coulombic efficiency needs improvement in order to commercialize Co3O4 as the anode material of Li secondary batteries. Because it was reported that Co3O4 is cycled through the formation and decomposition of Li2O, a poor decomposition of Li2O at the first charge can be regarded as the cause of high initial irreversible capacity. Therefore, at first, addition of Ni to Co3O4 was selected as a method to decrease the initial irreversible capacity, but it didn't have any effect. The ballmilling method was known to be very effective, connecting original material with additive material. As a result of ballmilling with Ni, Co3O4 on which Ni is well dispersed was obtained, and as expected, its irreversible capacity was decreased from 30 to 20%. (C) 2003 The Electrochemical Society.