Unraveling inhomogeneous rocksalt growth in Ni-rich cathode materials for Li-ion batteries

Abstract

Ni-rich cathode materials suffer from structural instability when cycled to high cutoff voltages. A transformation from the layered crystal structure to other phases, such as rocksalt, deteriorates the particle surface at low states of lithiation. Inhomogeneous potential and concentration fields as they occur in electrodes can have a significant impact on the degradation. In this work, we demonstrate rocksalt growth on a realistic high-energy NMC811 electrode using 3D microstructure-resolved simulations. We unravel inhomogeneities through transport in the electrode with a stronger active material degradation near the separator. To study individual particles in the electrode, we apply a watershed algorithm to segment the structure into distinct particles. A high correlation between both particle size as well as particle position and rocksalt thickness is observed in our half-cell simulations. We further shed light on inhomogeneities that can arise on single-particle level due to inhomogeneous lithiation.