Abstract:Based on the hexagonal crystallite model of graphite, the electrochemical characteristics of carbon atoms on the edge and basal plane were proposed by analyzing graphite crystal structure and bonds of carbon atoms in different sites. A spherical close-packed model for graphite particle was developed. The fractions of surface carbon atoms (SCA) and edge carbon atoms (ECA) were derived in the expression of crystallographic parameters and particle size, and the effects of ECA on the initial irreversible capacity and the mechanisms of action were analyzed and verified. The results show that the atoms on the edge are more active for electrochemical reactions, such as electrolyte decomposition and tendency to form stable bond with other atoms and groups. For the practical graphite particle, corresponding modifying factors were introduced to revise the difference in calculating results. The revised expression is suitable for the calculation of the fractions of SCA and ECA for carbon materials such as graphite, disordered carbon and modified graphite.

Key words: Li-ion batteries; carbon anode; calculation model; electrochemical properties; mechanism of action