Using first-principles pseudopotential calculations, an investigation was made of the formation and transport of small polarons in olivine. It was demonstrated that excess charge carriers formed small polarons in LiFePO4 and FePO4. Lower limits on the activation barrier for small polaron migration were calculated within the GGA+U framework. In addition, the interaction between Li ions and polarons was investigated, and estimates of the binding energies between Li ions and polarons were provided. The results showed that the binding energy between electron polarons and Li+ ions in FePO4 was lower than that between hole polarons and Li vacancies in LiFePO4. The electron transfer rate was predicted to be higher in FePO4 than in LiFePO4.

Ab initio Study of the Migration of Small Polarons in Olivine LixFePO4 and their Association with Lithium Ions and Vacancies. T.Maxisch, F.Zhou, G.Ceder: Physical Review B, 2006, 73[10], 104301 (6pp)