Carbon addition and carbon coating to LiCoO2 has been attempted to improve the rate performance of all-solid-state battery using oxysulfide glass. The discharge capacity decreased with the current density (0.064 and 0.32 mAcm(-2)) for the given acetylene black content (0, 0.25, 2.5, and 5 wt %); the mere addition of acetylene black contributed to lower the rate capability. On the other hand. for the carbon-coated LiCoO2 by Spark-Plasma-Sintering method, the higher discharge capacity of above 100 mAhg(-1) was exhibited even at the higher current density (0.32 mAcm(-2)). Carbon coating to active material, rather than the merely mixing or addition, is effective for improving rate performance in all-solid-state batteries. (C) 2004 The Electrochemical Society.