Role of mesopores on the electrochemical performance of LiCoO2 composite cathodes for lithium ion batteries

Mesoporous carbon (MC) was utilized to increase the mesoporosity of LiCoO2 composite cathode. Graphite powder (GP) was chosen as a standard of comparison because of its very low mesoporosity. Compared with MC, GP has similar particle size, lower specific surface area, and higher electronic conductivity. Acetylene black (AB) exists in the form of chains of nanoparticles. With all other factors held constant, the mixture of AB and MC (ABMC)-loaded LiCoO2 composite cathode (ABMC cathode) was superior to the mixture of AB and GP (ABGP)-loaded LiCoO2 composite cathode (ABGP cathode). The reason is described as follows. Both GP and MC form a conductive network with AB chains. ABGP cathode has higher electronic conductivity than ABMC cathode. But the ionic conductivity of the ABMC cathode is more easily enhanced than the ABGP cathode because the former has much greater mesoporosity. In addition, the mesopores absorb and retain electrolyte solution and then provide buffer lithium ions for quick electrochemical reactions, so shortening the lithium ion transfer path in the composite cathode.