Thermal Characterization of Large-Format Li-Ion Pouch Cells with Transient Cooling and Lock-in Thermography

Abstract

Electrification of transport and heating is an important part to combat climate change. This leads to an increasing demand for energy storage options for power grids and electric vehicles.Recent progress in battery management systems, and energy density improvements, have favored the deployment of Li-ion batteries as the leading electrochemical energy storage technology [1]. At the same time, battery thermal management is a critical challenge due to inevitable heat generation from ohmic, reaction and entropic heating [2]. If the amount of heat generated is not sufficiently dissipated from the battery, it could substantially increase the cell temperature which leads to severe degradation and even catastrophic thermal runaway [3, 4]. Especially for large-format pouch cells, high temperature and large temperature non-uniformity are common issues and thus require careful battery thermal design. One tool to address this is by establishing an electrochemical-thermal model of performance – but this requires accurate knowledge of various battery properties. Commercial Li-ion batteries have a multi-layered unit-cell structure in jelly roll or stack, with each unit cell containing current collectors, cathode, anode and separator. The cell components with different properties, multiphase electrodes and complex electrode morphology have made it difficult to obtain battery properties without proper characterization methods.Therefore, in this study, we propose novel thermal characterization approaches to measuring the specific heat capacity and anisotropic thermal conductivity of large-format Li-ion pouch cells. The specific heat is characterized via a transient cooling method together with an analytical model, while the thermal diffusivity can be obtained by fitting a 3D thermal model to the dynamic surface temperature response measured with lock-in thermography. A nonlinear least-squares optimization algorithm is used to parameterize the battery thermal diffusivity. After that, the battery thermal conductivity can be decoupled from the measured specific heat and thermal diffusivity. Validated with aluminum reference samples, the present characterization methods have the merits of fast speed and good accuracy, which will be appealing to both scientific research and engineering practice. References G. Zubi, R. Dufo-López, M. Carvalho and G. Pasaoglu, Renewable and Sustainable Energy Reviews, 89, 292 (2018).D. Bernardi, E. Pawlikowski and J. Newman, J Electrochem Soc, 132, 5 (1985).D. P. Finegan, E. Darcy, M. Keyser, B. Tjaden, T. M. M. Heenan, R. Jervis, J. J. Bailey, R. Malik, N. T. Vo, O. V. Magdysyuk, R. Atwood, M. Drakopoulos, M. DiMichiel, A. Rack, G. Hinds, D. J. L. Brett and P. R. Shearing, Energy & Environmental Science, 10, 1377 (2017).Y. Zhu, J. Xie, A. Pei, B. Liu, Y. Wu, D. Lin, J. Li, H. Wang, H. Chen, J. Xu, A. Yang, C. L. Wu, H. Wang, W. Chen and Y. Cui, Nat Commun, 10, 2067 (2019).