Measuring the reversible heat of lithium-ion cells via current pulses for modeling of temperature dynamics

Abstract

This article introduces a novel calorimetric measurement method, namely the ‘Double Pulse Method’, to measure reversible heat in lithium-ion battery cells. In Li-ion cells, reversible heat has a material-dependent characteristic as it is closely related to both entropy change and the temperature dependence of the open circuit voltage. The proposed method measures reversible heat as a highly resolved function of the cell’s state of charge. The determination of reversible heat is based on the evaluation of the temperature difference generated by two current pulses of opposite polarity. Unlike established potentiometric methods, the Double Pulse Method is simple to set up, fast, and cost-effective. The accuracy of the Double Pulse Method is demonstrated for an automotive lithium iron phosphate (LFP) cell, and the entropy changes are compared with measurements of the same cell using the established potentiometric method. Simulation results indicate that the cell temperature is more accurate when determined by the reversible heat measurement obtained by the Double Pulse Method than from the potentiometric method.