Effect of carbon on the electronic conductivity and discharge capacity LiCoPO4

The effect of added carbon (3, 5 and 10 wt.%) on the electronic conductivity and discharge capacity of LiCoPO4 was investigated. It was found after heat-treatment that the samples consisted of a LiCoPO4 majority phase and Co2P second phase. The added carbon was consumed reducing the LiCoPO4 surface layers to Co2P. The electronic conductivity increased as the amount of the Co2P phase increased. It was observed that the discharge capacity increased with increased Co2P content to ∼4–5 wt.%, after which the capacity rapidly decreased with increasing Co2P content. The increase in discharge capacity is likely a result of the increase in electronic conductivity. At higher Co2P volume fractions the presence of the electrochemically inert Co2P phase causes decreased capacity by: (1) reducing the amount of LiCoPO4 present and (2) preventing Li+-ions from entering/leaving LiCoPO4, even though the highest values of electronic conductivity were exhibited.