SUMMARY

Energy-storing electrochemical batteries are the most critical components of high energy density storage systems for stationary and mobile applications. Lithium-ion batteries have received considerable interest for hybrid electric vehicles (HEV) because of their high specific energy, but face inherent thermal management challenges that have not been adequately addressed. In the proposed investigation, a fully coupled electrochemical and thermal model for lithium-ion batteries will be developed to investigate the impact of different thermal management strategies on battery performance. In contrast to previous battery modeling efforts, the local electrochemical reaction rates are predicted using temperature-dependent experimental data collected on a commercially available battery designed for high rates (C/LiFePO4), which significantly reduces computational effort allowing for realistic assessment under dynamic HEV loads. In addition, conventional cooling systems are external to the batteries, which have a low composite thermal conductivity (~1 W/m-K) that causes large internal temperature gradients. Thus, a novel internal cooling system that utilizes heat removal through liquid-vapor phase change will also be investigated. A cooling system performance model will be validated experimentally and integrated into the coupled electrochemical-thermal model for assessment of performance improvement relative to conventional thermal management strategies. The proposed cooling system passively removes heat almost isothermally with negligible thermal resistances between the heat source and cooling fluid. Thus, the minimization of peak temperatures and gradients within batteries will allow increased power and energy densities unencumbered by thermal limitations.