The last decade has seen the early commercialization of electric and hybrid-electric vehicles by most of the world's major auto manufacturers in response to both environmental and political concerns. While, at present, nickel-metal hydride batteries are predominantly used for this purpose, future cars are expected to use lithium-ion batteries, owing to their superior performance. Due to its low cost, the natural-graphite/iron-phosphate lithium-ion cell has been identified as one of the leading candidates for these applications. However, in order for this battery to reach the marketplace, it will need to be designed so that its performance is improved, especially during high-power operation. We address this issue by developing mathematical models for the system and using them as a design tool to achieve this goal. This talk will detail the development of the model, which uses a mechanistic approach to understand, and mathematically describe, the various processes in the battery. Subsequently, the model is compared to experimental data in order to gain insight into its behavior and to identify performance-limiting factors. This comparison allows us to suggest possible design changes that could assist in alleviating these limitations. Finally, we use the model to optimize the porosity and thickness of the battery electrodes in order to maximize the specific energy for a wide range of applications. These optimized designs are expected to be a starting point for battery manufacturers and to help decrease the time to commercialization.