Multi-Scale Simulation and Experimental Study of High Voltage High Capacity Cathode Materials for Lithium Ion Battery

Presented in this dissertation is combined research of multi-scale simulation and experimental study of high voltage high capacity cathode materials for Lithium ion batteries. The materials under study are Li-Mn-rich layered oxides and Ni-rich layered oxides, which are widely regarded as the next generation cathode materials. However, they both face different challenges towards final commercialization. Many of these challenges have not been well understood, resulting in the difficulties of rationally optimizing battery performances. Therefore, we applied the ab initio method (density functional theory) to understand the underlying mechanisms that determine various important properties of these oxides, including redox potential, structural stability, ionic conductivity, electronic conductivity, cation mixing, etc. Based on these understandings, we proposed some rationalized optimizing strategies. Some of the strategies have also been experimentally validated by chemical synthesis and electrochemical performance testing via assembling coin cell type devices. Furthermore, as a way of extending the simulation limit (time scale and space scale) of the ab initio method, we have developed a new interatomic potential method by introducing dynamic charge transfer potential into the modified embedding atomic method (CT-MEAM). The potential method has been successfully applied to Li-Mn-O, Mn-O and Li-Ni-O systems with validated high accuracy in reproducing and predicting redox potentials, Li dynamics, surface effects, phase stabilities, structural parameters, phase diagrams, etc. These works could not only stimulate the large scale simulation of cathode materials for Li ion batteries, but also other materials involving strong charge transfer effects and electrochemical reactions.