Effect of carbon additive on electrochemical performance of LiCoO 2 composite cathodes

Abstract

LiCoO 2 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 LiCoO 2 particles. The LiCoO 2 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 LiCoO 2 active material. Better mixing in the slurry preparation step that is due to a similarity in the grain size of Lonza KS6 and LiCoO 2 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 LiCoO 2-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 LiCoO 2 grains. As a result, both the electrode conductivity and active surface-area of the LiCoO 2|carbon interface are enlarged. This leads to a decrease in the electrode polarization and a better utilization of the active material.