Li ion batteries are ubiquitous in modern society and the technology will become even more important as non-petroleum based energy sources grow. The efficiency of Li ion batteries is therefore a major concern for consumers, business and government. In this talk, I will discuss how performance depends mainly on the materials that make up the three components of the battery: the anode, the cathode and the electrolyte. I will show how computational methods can be used to understand the underlying processes that govern Li ion exchange through these materials and how these same methods can be used predictively to improve battery materials. Specifically, I will discuss how ionic mobility and electronic conduction, the main necessary processes in a battery cycle, can be enhanced (or destroyed) through sometimes slight changes in materials composition or structure.