Effects of conductive additives in composite positive electrodes on charge-discharge behaviors of all-solid-state lithium secondary batteries

The effects of conductive additives in composite positive electrodes on charge-discharge behaviors of all-solid-state In/LiCoO2 cells with (LiS)-S-2-P2S5 glass-ceramic electrolytes were investigated. Acetylene black (AB), vapor grown carbon fiber (VGCF), titanium nitride (TiN), and nickel metal (Ni) were used as conductive additives. Carbon materials were more effective to decrease the resistivities of composite positive electrodes compared to TiN and Ni. Under a current density of 64 mu A cm(-2), discharge capacities of about 100 mAh g(-1) were maintained over 50 cycles in the cell with VGCF, while gradual decreases in discharge capacities were observed in the cells with AB, TiN, and Ni. Furthermore, even under a current density over 1 mA cm-2, the cell with VGCF kept larger discharge capacities during 50 cycles than the cell with AB. Since VGCF is composed of submicrometer-ordered fibers, close solid-solid contacts among electrode, electrolyte, and VGCF were achieved. The design of continuous electron conducting paths from a point of view of morphology for conductive additives is important to improve cell performances of all-solid-state lithium secondary batteries. (c) 2005 The Electrochemical Society. [DOI: 10.1149/1.1939633] All rights reserved.