  We report first-principles density-functional theory studies of native point
defects and defect complexes in olivine-type LiFePO4, a promising candidate for
rechargeable Li-ion battery electrodes. The defects are characterized by their
formation energies which are calculated within the GGA+U framework. We find
that native point defects are charged, and each defect is stable in one charge
state only. Removing electrons from the stable defects always generates defect
complexes containing small hole polarons. Defect formation energies, hence
concentrations, and defect energy landscapes are all sensitive to the choice of
atomic chemical potentials which represent experimental conditions. One can,
therefore, suppress or enhance certain native defects in LiFePO4 via tuning the
synthesis conditions. Based on our results, we provide insights on how to
obtain samples in experiments with tailored defect concentrations for targeted
applications. We also discuss the mechanisms for ionic and electronic
conduction in LiFePO4 and suggest strategies for enhancing the electrical
conductivity.
