Effect of carbon additive on electrochemical performance of LiCoO2 composite cathodes

LiCoO2 composite electrodes are prepared with variation in the conducting agent and their cathodic performance is analyzed. Two carbon blacks (Super P and acetylene black) and one graphite (Lonza KS6) that differ in particle size and shape are employed as the conducting agents. The carbon blacks comprise nano-sized primary particles that are fused to give an aggregate. Lonza KS6 carries a flake-like shape with an average particle size of 6 μm, which is comparable with that of LiCoO2 particles. The LiCoO2 composite cathode containing Lonza KS6 exhibits better cycle performance than that of the cathode loaded with carbon black, presumably due to a more uniform dispersion of both the conducting agent and the LiCoO2 active material. Better mixing in the slurry preparation step that is due to a similarity in the grain size of Lonza KS6 and LiCoO2 may explain this feature. In composite cathodes containing the smaller-sized carbon blacks, however, the carbon particles agglomerate by themselves to become segregated from the LiCoO2-rich region. The cathode capacity and cycle-life of a Lonza KS6 loaded electrode is improved further by adding smaller-sized carbon blacks as the conducting agents. It is expected that the smaller particles of carbon black fill the void spaces made by the larger-sized Lonza KS6 and LiCoO2 grains. As a result, both the electrode conductivity and active surface-area of the LiCoO2carbon interface are enlarged. This leads to a decrease in the electrode polarization and a better utilization of the active material.