Sphere-in-Contact Model/Theorem for the Development of New Graphite-based Intercalated Battery Materials

In this study we show that on the basis of simple crystallographic rules applied to the sphere-in-contact model/theorem that we can predict that under ambient conditions of pressure and temperature that the most dense and stable form of lithium in GICs is LiC6 and that two distinct form of LiC8 are possible. We find that other empirical formulas such as MC2, MC3 and M3C8 are possible based on crystallography, but not stable based on intercalate repulsions. The results are based on the unit cell description of GICs with the sphere-in-contact model/theorem that is used to model the intercalation of an arbitrary atom within the AαAα stacking1 of two graphene layers in GICs. We calculate the density and the packing fraction of these materials. This approach offers a simple description of the structure of GICs in which the unit cell can be defined and the diffusion of ions can be estimated on the basis of the void space in these materials. We anticipate that this simple description of GIC will be useful for the rational design of new graphite-based materials that can find use in various energy storage applications such as ion-based batteries but also as an educational tool in which university level education in materials and surface chemistry is directly connected to basic laws in chemistry, physics and mathematics.