Evaluation of the entropy of reaction using modified frequency-domain method and a physics-based thermoelectrochemical model of a lithium-ion battery

The entropy of reaction (ΔS) is one of the key parameters required for predicting temperature and performance in lithium-ion batteries. A frequency-domain method that reduces the ΔS measurement time by factor of 100 compared to traditional potentiometric methods was introduced by Schmidt et al. [Electrochimica Acta. 311(137), 2014]. The method applies a sinusoidal current of an angular frequency ω, and observes temperature signals with frequencies of ω and 2ω for the reversible entropic heat and irreversible Joule heat, respectively. In this work, the previous frequency-domain method was modified to implement a physics-based thermoelectrochemical model that physically couples the internal state changes of batteries to their open-circuit potentials. The modified frequency-domain method was applied to a commercial pouch battery (graphite/LiCoO2) to show its validity. The physics-based model was used to fit the entropy of reaction while operating the battery, and the obtained ΔS values correlate well with previously reported values that were measured by traditional potentiometric methods. This work shows that the modified frequency domain method can be an alternative to the time-consuming potentiometric method, with potential application in on-board vehicle battery diagnostics.