UC San Diego

Lithium ion batteries (LIB) are regarded as one of the near-term solutions to the gloable energy shortage and have drawn increasing attentions. To be implemented in the large-scale high-power system, performance requirements are raised especially from the aspects of energy/power density, cycling life and safety issues, therefore further LIB material and system developments are necessary. Among Li-intercalation compounds, high voltage spinel compound LiM₀.₅Mn₁.₅O₄ and high capacity layered lithium-excess oxide compounds Li[NixLi₁/₃-₂x/₃Mn₂/₃-x/₃]O₂ are of great interests. On the other hand, the poor rate capability and cycling performances are preventing these materials from commercialization. In this dissertation, systematic studies are performed on these two types of candidate materials using first principles method. The dissertation can be divided into two parts. In the first part, cation charge ordering in LiMn₂O₄ and its effects on Li diffusion in LiMn₂O₄ spinel are investigated. The conclusions are used as the criteria to pre-screen the dopant M in LiM₀.₅Mn₁.₅O₄ by computation. Cu is found to be able to reduce the Li diffusion barriers and a new type of bi- doped spinel LiNixCuyMn₂-x-yO₄ (0