An Unavoidable Challenge for Ni-Rich Positive ElectrodeMaterials for Lithium-Ion Batteries

LiNi1-x-yCoxAlyO2 (NCA) and Li-Ni1-x-yMnxCoyO2 (NMC) materials are widely used in electric vehicle and energy storage applications. Derived from LiNiO2, NCA and NMC materials with various chemistries were developed by replacing Ni with different 0.9 cations. Many studies of the failure mechanisms of NCA and NMC materials have attributed the cell degradation to the anisotropic volume change of particles. In this work, it is shown that for Ni-rich layered transition metal oxide materials, regardless of composition, the unit cell volumes change in an almost identical manner during delithiation. Half-cell cycling data collected from 26 sets of Ni-rich materials with different compositions allow a relationship between` capacity retention and accessible capacity to be observed. This relationship can be correlated to the change in unit cell volume during the lithiation-delithiation process. This work suggests a universal failure mechanism for Ni-rich positive electrode materials that must be overcome.