Session: 11-07-01 Measurements of Thermophysical Properties

Paper Number: 71488

Start Time: Tuesday, 04:30 PM

71488 - Using a Modified Frequency Domain Method Coupled to a Physics Based Model With Non-Uniform Heat Generation to Evaluate the Entropy of Reaction in a Li[NixCoyMnz]O2/Graphite Lithium Ion Battery 

Thermal modeling of Lithium-ion cells necessitates a full range of entropy of reaction values at different states of charge to predict the reversible entropic heat generation within the cell. Traditional methods of evaluating entropy of reaction require a physical measurement, where in, the cell is required to reach thermal steady state in order to take a measurement, which demands a massive investment of time. We have previously developed a fast paced frequency domain method that uses a physics-based model, to identify the entropy of reaction of each electrode in a pouch cell, which was proven to function as an effective alternative to slower traditional methods. In this method, a cell is subjected to a sinusoidal current with angular frequency and the resulting reversible entropic heat and irreversible Joule heat produce temperature signals of  and 2, respectively. However, this previous model did not take into account any changes in heat generation across the thickness dimension of the cell. For pouch cells, this would indicate that the entropic heat generation is uniform in each electrode. But there was no theoretical support that the heat generation would be uniform across the cell. To that end, a novel frequency domain model was created where in, the entropic heat generation across the cell is determined by spatially integrating the product of local enthalpy potential and local current, given an assumption of uniform cell temperature. This model was drafted both to improve the accuracy of the previous model and to test whether the assumption of uniform heat generation was viable or not. The model was used to determine the enthalpy of reaction of a custom made Li[Ni_xCo_yMn_z]O₂/Graphite pouch cell at various states of charge. The cell was designed in such a way that the Biot number of the cell was far below unity in each geometric dimension, in order to validate the assumption of uniform cell temperature. The model was then validated by comparing the results of the new non-uniform model to the previously utilized uniform model. Additionally, coin cells of the same chemistry as the pouch cell were made for both the anode and cathode of the cell and tested using a traditional potentiometric method of entropy measurement at several states of charge to validate that the model could accurately identify entropy of reaction local to each electrode. Initial results of the project indicate that the model can accurately identify the entropy of reaction of a Lithium-ion cell and that there is a slight change in model’s predicted outcomes when non-uniform heat generation is taken into account.

Presenting Author: Jonathan Hammond Washington State University

Authors:

Jonathan Hammond Washington State University
Chase McCreary Washington State University
Armin Abbasalinejad Washington State University
Sun Ung Kim Washington State University