Fast Charge and Discharge Characterization and Modeling of Heat Generation at the Cell Level

Abstract

Fast charging in lithium ion batteries is a critical process in the automotive industry that will drive the adoption of electrified products. The process of fast charging and discharging raises significant engineering challenges at the vehicle level related to thermal management. One key understanding that drives solutions to these thermal management challenges is the heat generation of the battery under high rate operation.Characterization of heat generation rates in a battery requires a highly accurate and dynamic calorimeter coupled with mathematical modeling at multiple scales. Here we present a multifunctional calorimeter for lithium-ion batteries that incorporates thermoelectric assemblies which enables the measurement of the heat generation at the cell level as a function of fast charging and discharging rates, states of charge, and temperatures. Due to the dynamic nature of the calorimeter and the ability to rapidly respond to heat generation changes at the cell level, it is possible to decouple the temperature fluctuations during charging and discharging to determine the entropy coefficient of the cell.For this work, large format battery cells were utilized that are typically seen in the automotive industry which contain a LMO/NMC cathode and a graphite anode. The lumped heat generation rate of the cell is measured, and the heat source terms are characterized and split into reversible and irreversible sources. A model is presented that predicts heat generation and the outputs are compared to measured heat generation from the dynamic calorimeter.