Composite positive electrodes for all-solid-state In/LiCoO2 cells with Li2S-P2S5 glass–ceramic electrolytes were designed in order to improve the high rate performances of the cells. The composite electrodes consisted of the active material, the solid electrolyte and carbon conductive additive powders. The cell with vapor grown carbon fiber (VGCF) as a conductive additive was charged and discharged at current densities of over 1mAcm−2, while the cell with acetylene black (AB) did not work as a rechargeable battery. The difference in the cell performances was explained from viewpoints of the morphology of the carbon additives. VGCF formed a more continuous electron conducting path in the composite positive electrode than AB. The cells without conductive additives were charged and discharged by increasing LiCoO2 content in the composite positive electrode. Using a suitable morphology and amount of component powders for composite electrodes is a key to improve rate performances of all-solid-state secondary batteries.