Modeling the Effects of Thermal Gradients Induced by Tab and Surface Cooling on Lithium Ion Cell Performance

Abstract

Lithium ion batteries are increasingly important in large scale applications where thermal management is critical for safety and lifetime. Yet, the effect of different thermal boundary conditions on the performance and lifetime is still not fully understood. In this work, a two-dimensional electro-thermal model is developed to simulate cell performance and internal states under complex thermal boundary conditions. Attention was paid to model, not only the electrode stack but also the non-core components (e.g. tab weld points) and thermal boundaries, but also the experiments required to parameterize the thermal model, and the reversible heat generation. The model is comprehensively validated and the performance of tab and surface cooling strategies was evaluated across a wide range of operating conditions. Surface cooling was shown to keep the cell at a lower average temperature, but with a large thermal gradient for high C rates. Tab cooling provided much smaller thermal gradients but higher average temperatures caused by lower heat removing ability. The thermal resistance between the current collectors and tabs was found to be the most significant heat transfer bottleneck and efforts to improve this could have significant positive impacts on the performance of li-ion batteries considering the other advantages of tab cooling.

How to Cool Lithium Ion Batteries: Optimising Cell Design using a Thermally Coupled Model

“…These conclusions agree with the findings of Kim et al and Rieger et al 25,26 However, these studies only considered forced air convective thermal boundary conditions that are not representative of the more prevalent liquid-cooling thermal boundary conditions for EV battery packs. As shown in our previous work, 19,21 the inhomogeneity caused by the external thermal boundary conditions (e.g. TMS choice) can be much more dominant under aggressive usage.…”

“…The modelling framework used in this work is based on the twodimensional electro-thermal model developed in our previous work. 21 The model was developed in MATLAB R2017a using Simulink (v8.8) and Simscape toolbox (v4.1).…”

“…The modelling framework is developed based on the work of Newman, Tiedemann, Gu and Kwon (NTGK) et al [32][33][34] Figure 1 shows a schematic of the modelling framework. The detailed model description can be found in Zhao et al 21 The model simulates the length (L) and thickness (T) plane. The dimension across the width (W) is not included as it is assumed the thermal gradient is minimum.…”

“…Subsequent modelling work by Zhao et al showed that surface cooling induced a significant thermal gradient across the cell thickness leading to current and State-of-Charge (SoC) inhomogeneity. 21 As a result, colder electrode layers were at significantly different SoCs than the hotter layers, so the true capacity of the cell could not be fully utilised. It was hypothesised that the significant temperature inhomogeneity would lead to localised degradation in the hotter cell layers due to the positive feedback of higher temperature, lower impedance and larger current.…”

Localized Swelling Inhomogeneity Detection in Lithium Ion Cells Using Multi-Dimensional Laser Scanning

“…In our previous work, Zhao et al showed that the maximum temperature gradient within a cell of the same type is approximately 2.5 • C at the end of a 2C discharge under quiet aggressive thermal boundary conditions realized via metallic heat sinks. 37 In this work, all cell surfaces (electrode stack and electrical terminals) were exposed to ambient air, which should result in a much smaller thermal gradient than 2.5 • C. Hence an alternative hypothesis must be considered. Based on the above, it is hypothesized that the swelling point may have a higher thermal expansion coefficient than the 'normal' parts of the cell.…”