Quantification of Temperature Implications and Investigation of Battery Design Options for Electrified Vehicles
Battery cost, limited battery life and range anxiety are some barriers to widespread adoption of electrified vehicles. This thesis examines the implications of these issues with a particular focus of analyzing the effect of temperature by addressing several questions: How do range, emissions, and battery life vary with regional climate and driving patterns? How much does thermal management affect these outcomes? How does the cost-minimizing battery design change with chemistry? A modeling and simulation approach is followed throughout the thesis, where physics based models, as well as models based on real world and experimental data are developed to address the aforementioned questions. Battery electrical, thermal and life models are created to estimate battery degradation under various different usage scenarios, and the effect of air-cooling on improving battery life is investigated. Real world driving data and dynamometer test data are used to estimate driving behavior, and are combined with regional effects of climate and electrical grid mix to evaluate emissions benefits of vehicle electrification across different regions. A battery cost model is used as an objective function in a mixed integer nonlinear program to find the battery design that minimizes the purchase cost for different battery chemistries. Sensitivity analyses are performed to understand the effect of modeling assumptions and design decisions on the results. Results indicate that battery degradation is particularly sensitive to battery and vehicle design characteristics, such as battery size and powertrain control strategies. In addition, operational factors that change regionally, such as driving cycle and climate, can have significant implications. Aggressive driving can decrease battery life by 67% compared to average driving conditions, and battery life is about 46% shorter in Phoenix than in San Francisco. However battery life can be doubled if battery is thermally conditioned by air-cooling. Regional climate has also significant implications on battery electric vehicle range and energy consumption. Annual energy consumption of battery electric vehicles can increase by an average of 15% in the Upper Midwest or in the Southwest compared to the Pacific Coast due to temperature differences, and cold climate regions can encounter days with substantial reduction in EV range. vii Environmental benefits of electrified vehicles vary substantially by vehicle model and region: The Nissan Leaf battery electric vehicle creates lower GHG emissions than the most efficient gasoline vehicle (Toyota Prius) in most of the country except in the Midwest and the South. The Chevrolet Volt plug-in hybrid electric vehicle has higher emissions than the Prius everywhere. Regional grid mix, temperature, driving patterns, and vehicle model all have significant implications on the relative benefits of PEVs versus gasoline vehicles. Similar to degradation profile and environmental benefits, the cost minimizing design depends on battery energy requirement as well. As the energy requirement from the battery pack increases and the pack gets bigger, optimum design uses the maximum allowable cathode thickness. Among the chemistries explored, Lithium Manganese Oxide (LMO) provides the battery design with the least expensive production cost for vehicles with small size batteries; however as battery size increases it becomes comparable with other chemistries. Lithium Iron Phosphate (LFP) based batteries lead to most expensive design.