Modelling Thermodynamic Properties of Intercalation Compounds for Lithium Ion Batteries

DFT calculations were employed to model thermodynamic properties on intercalation compounds for lithium ion batteries. Two compounds were investigated: the commercially available Li$_{x}$CoO$_{2}$ and the silicon based Li$_{x}$Mg$_{2}$Si. The LiCoO$_{2}$ compound was modelled under two aspects. Firstly, total energy calculations were carried out on the two-phase region between the delithiated, metallic phase and the lithiated, semiconducting phase in the attempt to model the two-phase equilibrium. It was possible to observe that the metallic state is energetically more stable at low lithium contents agreeing with experimental evidence. It was, however, not possible to map the two-phase region properly, most likely due to deficiencies in the applied approach usinga single Hubbard U parameter on the cobalt d-orbitals. The computed average intercalation voltage was derived for a series of compositional segments between LiCoO$_{2}$ and Li$_{0.5}$CoO$_{2}$ and demonstrate a good agreement to prior DFT calculations. Secondly, isobaric heat capacities were calculated within the quasi-harmonic approximation for three stoichiometries of Li$_{x}$CoO$_{2}$ ranging from LiCoO$_{2}$ to Li$_{0.5}$CoO$_{2}$. The results indicate a good agreement withavailable experimental data when accounting for the phase impurities of the sample. Calculations on a boron doped compound LiCo$_{11/12}$B$_{1/12}$O$_{2}$ were also done and yielded results which fall into the expected range [...