Anti-Site Defects and Ion Migration in the LiFe_(0.5)Mn_(0.5)PO4 Mixed-Metal Cathode Material

摘要

Olivine-type phosphates have attracted considerable attention as cathode materials for rechargeable lithium batteries. Here, the defect and ion transport properties of the mixed-metal material LiFe_(0.5)Mn_(0.5)PO4 are investigated by atomistic modeling methods. The intrinsic defect type with the lowest energy is the cation antisite defect, in which Li and Fe/Mn ions exchange positions. As found in the LiFePO4 material, lithium ion diffusion in the mixed-metal system occurs down the i-axis channels following a curved path. Migration energies for Fe and Mn antisite cations on Li sites suggest that Mn defects would impede bulk Li mobility in LiFe_(0.5)Mn_(0.5)PO4 to a greater extent than Fe antisite defects in LiFePO4. Association or binding energies for various defect clusters comprised of lithium vacancies and/or antisite cations are examined.