Importance of Various Thermal Effects in Battery Modeling

Abstract

Lithium-ion batteries exhibit highly temperature dependent performance and life cycle [1,2]. Safe operation of a battery is also closely related to its operating temperature [3]. Due to poor thermal transport within a Li-ion cell, specifically in the out of plane direction, temperature gradient and overheating can occur at moderate to high rates [4]. The poor thermal transport in the out of plane direction is because of the thermal resistance due to the multiple layers getting added up [5]. This leads to large total thermal resistance from the core of the cell to the surface. In addition to the layers, the interfaces between the layers also offer significant thermal interfacial resistance [6]. This makes it important to account for heat transfer within the cell in a battery model. From battery management system (BMS) standpoint, accounting for these thermal as well as electrochemical transport processes and reaction kinetics in a computationally efficient manner is critical. Various models have been proposed in the past for this purpose [7]. Among the various models, single particle model (SPM), pseudo two-dimensional (P2D) model, and pseudo three-dimensional (P3D) model are rigorously compared in their ability to predict performance of a battery under a wide variety of conditions. This includes high rates of charge and discharge, different cooling conditions at the cell surface, and a wide range of ambient/coolant temperatures. This study helps understand significance of accounting for various thermal effects in the context of accuracy of these different models. Results from this study give valuable insights into the capabilities of the different models.Additionally, using the P2D model, effect of thermal interfacial resistances at the cell stack level is studied in detail. Typically, thermal interfacial resistances are ignored in battery models which leads to temperature continuity at the interfaces [8]. However, based on the recent measurements, thermal interfacial resistance between the electrode and the separator has been found to be the rate limiting factor to heat transfer within a Li-ion cell [6]. This makes it important account for the interfacial heat transfer process by using appropriate thermal interfacial resistances between the layers, especially for a stack of cells. This has been achieved by altering the temperature continuity boundary condition at the interfaces in the P2D model. The key results from this study show that it is critical to account for this thermal effect for accurate predictions.