Battery Aging and Characterization of Nickel Metal Hydride and Lead-Acid Batteries

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The Ohio State University

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This thesis discusses the research done on battery aging characteristics for both Nickel Metal Hydride and Lead-Acid batteries. In an effort to relate real duty cycles of Hybrid Electric Vehicles and their effects on battery aging, a set of basis current profiles were created. The basis current waveforms can effectively make up any duty cycle a Hybrid Electric Vehicle encounters. These basis profiles can then be characterized for their effect on battery aging. Once their effect on aging is determined, a comprehensive aging model can be created in order to determine a battery’s age and predict its future aging. Lead-Acid batteries were studied for their two common failure modes: loss of capacity and loss of power. Developing different current profiles through which the battery will be aged is expected to provide insight into how real world activities affect the battery differently. These differences will help provide further insight into the development of a similar comprehensive aging model for Lead-Acid batteries. The effects of State of Charge (SOC) on internal battery resistance were examined and showed that as the SOC decreases, the battery resistance increases, which can be justly related to physical interactions inside the battery. EIS model fitting showed that a third order Randle Model was needed in order to fit to an open circuit battery’s frequency response spectrum. However, a Large Signal Response analysis showed that a second order model was sufficient to fit to the response. Regardless of the discrepancy, these models and parameters can be used to investigate and quantify aging. Additionally, these tests prove the battery parameters’ dependence on current level, which means that the battery is inherently a non-linear system. Engine cranking tests also showed the relationship between SOC and internal resistance, as well as the change in battery performance at different temperatures. Finally, the relationship between a Lead-Acid battery’s open circuit voltage and its SOC was investigated. The relationship proved to be nearly linear and a reasonable approximation for establishing a desired battery SOC for a given test. Advisor: Giorgio Rizzoni



Battery Aging, Battery Characterization