Electrical conductivity of doped LiCoPO4

The effect of Cr or Cu doping on the electronic conductivity of LiCoPO4 was investigated. It was observed that neither type of doping for the samples heated under air lead to electronic conductivity values above ~10−9 S cm−1. Based on these results it is suggested that the room temperature electronic conductivity of LiCoPO4 is much lower than that for LiFePO4. For the case of the doped samples heated under argon, they all exhibited an electronic conductivity ~10−4 S cm−1. It is likely that the enhanced conductivity of the LiCoPO4 samples heated under argon versus air is a result of conductive Co2P along LiCoPO4 particle surfaces that forms as a result of carbothermal reduction during heat-treatment. The electronic conductivity of the LiCoPO4 samples heated under high-purity argon is essentially independent of dopant type and concentration. This is because it is the conductive Co2P layer that controls the electronic conductivity of the doped samples overriding any possible dopant effects.