Understanding the influence of conductive carbon additives surface area on the rate performance of LiFePO4 cathodes for lithium ion batteries

Conductive carbon additives with different surface area and particle size, alone or in different combinations, were tested as conductive additives for LiFePO4 cathode materials in lithium ion batteries. Their influence on the conductivity, rate capability as well as the structure of the resulting electrodes was investigated. Mercury porosimetry was carried out to define the porosity and pore size distribution of electrodes, and scanning electron microscopy was used to image their morphology. By comparing the discharge capacity, especially at higher rates, it can be concluded that the electrochemical performance of LiFePO4 cathode material is significantly affected by the surface area, particle size and morphology of the used carbon additives. The best rate performance is achieved with the electrode containing a carbon additive with a specific surface area of 180 m2 g−1. This work reveals that the choice of conductive additive influences discharge capacity of LiFePO4 Li-ion battery cells by as much as 20-30%. This is due to conductive additive's influence on both electronic conductivity and porosity (which determines ionic conductivity) of LiFePO4 electrodes. A system approach to lithium ion battery material research should always consider inactive materials, such as conductive additives and binders, in addition to active materials.