Transition Metal Segregation and Phase Transformations on the Surfaces of Layered Li(Ni_1-x-yMn_xCo_y)O₂ (NMC) Cathode Materials for Li-ion Batteries

Layered Li(Ni_1-x-yMn_xCo_y)O₂ (NMC) oxides are promising cathode materials capable of addressing some of the challenges associated with next-generation energy storage devices. In particular, improved energy densities, longer cycle-life, and improved safety characteristics with respect to current technologies are needed. However, transformations taking place in the positive electrodes of battery cells decrease electrochemical performance. For instance, the segregation of transition metals from the bulk to the surface of cathode particles plays a critical role in the formation of surface reconstruction layers (SRLs). Such layers are thought to decrease the performance of batteries by, for example, impeding the diffusion of lithium during charge and discharge. A preferential segregation of Ni and Co to specific facets of as-prepared, pristine NMC materials has been found previously. This presentation will discuss recent results of a computational analysis of segregation and phase transformation processes using Density Functional Theory (DFT). A discussion on the thermodynamics that govern such processes will be given.