Relocation of cobalt ions in electrochemically delithiated LiCoPO ₄ cathode materials

The point defects in crystal lattices including antisite cation exchange, dopants, and atomic vacancies have been the topic of extraordinary research interest in solid state physics and chemistry. The ordered olivine structure was maintained after delithiation as indicated in high-resolution TEM images and selected-area electron diffraction (SAED) patterns. The increased degree of defect suggests that the cobalt metal ions have diffused and occupied vacancies created by Li extraction during the delithiation process. The extraction of Li ions from the lattice promotes the relocation of Co ion from M2 sites to the vacancy M1 sites. The vacancies created by Co ions migration appear to be locally segregated in the channel. The relocation resulted in the large capacity loss (low coulomb efficiency) in the initial discharge process.