LiFePO_4 has attracted attention as promising cathode materials for lithium ion battery, because it consists of abundant elements. However, the battery capability of this material is limited by its low electronic conductivity. To overcome the low electronic conductivity, two major approaches has been taken. One is the miniaturization of the size of LiFePO_4 particles and the other is the deposition of a conductive carbon on the surface of LiFePO_4 particles (LiFePO_4/C). We have been studied about synthesis of cathode materials as fine particle using ultrasound irradiation. In this study, we focus on Au nanoparticles synthesized by ultrasound irradiation. We expect Au nanoparticles to improve electronic conductivity of LiFePO_4/C. We synthesized Au attached LiFePO_4/C by two conditions, (1) addition of LiFePO_4/C in the solution before ultrasound irradiation, (2) addition of LiFePO_4/C to the solution after Au nanoparticles generation. 0.1mM [AuCl_4]^- aqueous solution was irradiated by 200kHz-ultrasound for 20 minutes in Ar atmosphere. 2-propanol was added into the solution before ultrasound irradiation. 2-propanol worked as a reductant under ultrasound irradiation. As a result, the size of the Au nanoparticles on the surface of LiFePO_4/C was 10 nm (from TEM). The figure of Au nanoparticles was spherical shape. Especially, the sample of condition (1) showed a lot of Au nanoparticles existed in the carbon layer. Therefore, Au-LiFePO_4 composite cathode material was effectively synthesized by ultrasound reduction of Au(III) in LiFePO_4/C suspension.
