Direct measurement of gaussian distributed radial crystallographic orientations of polycrystalline, layered-oxide secondary particles and their impact on materials utilization in battery cathodes
The sub-microstructure of polycrystalline lithium nickel manganese cobalt oxide (, abbr. NMC) secondary particles is determined by the arrangement, morphology and crystallographic orientation of the primary particles and strongly impacts their capacity, rate capability and aging. Although most electrochemical models do not resolve the sub-microstructure, understanding the relationship between a secondary particle's sub-microstructure and its electrochemical behavior is essential for the rational design of advanced secondary particles. In this paper we investigate the sub-microstructure of polycrystalline NMC secondary particles both experimentally and computationally. Experimentally, electron backscatter diffraction (EBSD) measurements characterize the crystallography of the primary particles and a radial orientation of the a-b diffusion planes of the individual atomically layered (NMC622, Ni-rich) primary particles, revealing a Gaussian distribution. Computationally, three-dimensional electrochemical simulations of polycrystalline secondary particles model the impact of the crystallographic orientation of the primary particles on the secondary particle's capacity. These simulations predict that the investigated NMC secondary particles have a capacity at a discharge rate of that is up to 8% higher than that of a randomly oriented material. This shows that the crystallographic orientations of polycrystalline secondary particles have a severe impact on the utilization of NMC particles.