Hybridized time-frequency method for the measurement of entropy coefficient of lithium-ion battery

Entropy coefficient (dU(OC)/dT) is the key parameter of lithium-ion battery that determines the amount of the reversible heat generated during operations. In this paper, we propose a new measurement method of the entropy coefficient that uses a newly developed thermostat system in conjunction with a two-step data processing technique that reduces the measurement time by a time-domain background voltage offset correction and a frequency-domain entropy coefficient determination. The cell used for the experiments is a large format pouch type lithium-ion battery with graphite-LMO/NMC chemistry. The measured entropy coefficient profile is compared with the results of the potentiometric and calorimetric method, which has shown that the measurement time is drastically reduced while the accuracy is comparable with that by the potentiometric method. Further investigations on effects of temperatures and aging on the entropy coefficient have facilitated the measurement of the reversible heat source term dependent upon the operating conditions such as SOC, temperature and cycle life. (C) 2020 Elsevier Ltd. All rights reserved.