Effect of carbon on the electronic conductivity and discharge capacity LiCoPO 4

Abstract

The effect of added carbon (3, 5 and 10 wt.%) on the electronic conductivity and discharge capacity of LiCoPO 4 was investigated. It was found after heat-treatment that the samples consisted of a LiCoPO 4 majority phase and Co 2P second phase. The added carbon was consumed reducing the LiCoPO 4 surface layers to Co 2P. The electronic conductivity increased as the amount of the Co 2P phase increased. It was observed that the discharge capacity increased with increased Co 2P content to ∼4–5 wt.%, after which the capacity rapidly decreased with increasing Co 2P content. The increase in discharge capacity is likely a result of the increase in electronic conductivity. At higher Co 2P volume fractions the presence of the electrochemically inert Co 2P phase causes decreased capacity by: (1) reducing the amount of LiCoPO 4 present and (2) preventing Li +-ions from entering/leaving LiCoPO 4, even though the highest values of electronic conductivity were exhibited.