Measurement of heat generation rate and heat sources of pouch type Li-ion cells

Abstract

Fundamental understanding of heat generation of lithium-ion batteries during operations is crucial to the cost-effective and efficient design of a thermal management system (TMS) in electric vehicles. Accurate characterization of the heat requires a calorimeter that meets inherent dynamics of the heat with accuracy. Therefore, we have developed an isothermal calorimeter using the thermoelectric assemblies (TEAs) along with the temperature control and Kalman filter, which is used to measure the heat generation rate (HGR) of large format pouch type lithium-ion batteries as an example. The measured HGR is a function of charge and discharge rates, state-of-charge (SOC), and temperatures. Analysis has shown that both the HGR and the ratio of the total heat generation to the total energy stored or released (pheat) of the tested cells increase as the current increases or the temperature decreases. In addition, a new calorimetric method is developed which enables a simultaneous determination of the entropy coefficient and internal resistance in the reversible and irreversible heat source terms in the frequency domain. The method can reduce the testing time about 92% compared with those by the conventional potentiometric method and electrochemical impedance spectroscopy (EIS) analysis, respectively, and the determined parameters are in good accordance with the reference values. Moreover, the calculated reversible and irreversible heat sources terms are compared with the experimental measurement and matched each other.