Structural Changes and Microstrain Generated on LiNi_0.80Co_0.15Al_0.05O₂during Cycling: Effects on the Electrochemical Performance

Crystal structure changes in LiNi_0.80Co_0.15Al_0.05O₂ (NCA) during electrochemical (de)intercalation of Li⁺ ions, charged to different upper cut off potentials, were investigated by means of ex situ X-ray powder diffraction.We have found that the presence of vacancies in the MO₂ slabs and subsequent Li/Ni interlayer mixing at high state of charge lead to an increased microstrain in the system. Careful examination of the crystal structures reveal the anisotropic nature of the microstrain which does not completely recover to the pristine material value after full discharge (lithiation). The microstrain created during charge and subsequent cycles has a strong impact on the cycling performance of the NCA material, and thus on the cell cycle-life.