Thermal analysis and management of lithium titanate batteries for use in battery and hybrid electric vehicles

Abstract

Lithium-titanate batteries have become a viable option for automotive energy storage due to their long lifetime, good energy density, and ability to withstand large charge/discharge currents. Normal vehicle operation exposes the battery to significant current demands which can cause substantial heat generation. Therefore, the battery pack requires an active thermal management system in order to maintain a safe operating temperature and prevent battery degradation. The goals for this research are to analyze the temperature rise and heat generation in a battery pack of 50 Ah lithium- titanate cells, and to design and evaluate cooling systems that maintain safe operating temperatures without consuming excessive parasitic power. A liquid crystal thermography technique was devised to measure the temperature rise of the cells under various charge/discharge current cycles. Two cooling systems, one water-cooled and the other air-cooled, were designed and implemented, and their performance was evaluated. While both systems performed effectively, the air-cooled system is more efficient as it consumes less parasitic power. Finally, the experimental data were employed within a numerical model to accurately characterize the spatially-varying heat generation source term within the cells. Ultimately, it has been shown that ambient air can be used as the active fluid to adequately cool the cells through proper heat exchanger design. The results from the numerical model to characterize the heat generation term will be useful in future thermal modeling and management studies of lithium-titanate cells.