Thermal Modeling of Large Format Lithium-Ion Cells

Abstract

This paper describes a thermal model that represents the heat generation behavior of a large format (10.5 Ah) Li-ion pouch cell. The thermal model is based on the calculation of the heat generation from experimental measurements of internal resistance and the entropic heat coefficient. Predictions from the thermal model are compared with experimental adiabatic calorimetry data. Higher discharge rates and larger temperature operation ranges than the ones reported in prior studies are considered. Results from the thermal model simulations have a prediction error of 21% in comparison with the experimental ones for discharge processes carried out at moderate rates. For discharge processes carried out at high discharge rates a maximum prediction error of 15% has been determined. The advantages and disadvantages of the model are further discussed, taking into account aspects such as accuracy, model development and implementation in different thermal management system designs.The rechargeable battery industry will experience significant growth in the near future given the increased need for battery systems for power electronics, renewable energy storage and power systems for transportation applications. 1 These new applications require large format lithium-ion (Li-ion) cells (2-100 Ah) that need to be integrated in large scale modules and packs and be managed by ad hoc control electronics, the so-called battery management systems (BMS). 2 New large format Li-ion batteries are rapidly becoming available from commercial cell manufacturers. 3,4 However, these cells still have many problems that need to be overcome -problems such as operating temperature behavior and cell temperature non-uniformities, 5 among others -which could result in accelerated degradation of the battery power performance and the reduction of the operating life, 6 critically affecting the safety issues of battery packs.Therefore, the kinds of applications that are powered by largescale Li-ion batteries make it necessary to design thermal management systems (TMS) that improve battery performance. A precise determination of heat generation in batteries could improve the TMS design process. Several investigations deal with the thermal modeling of single-cell batteries 7-11 and battery packs. 12-14 Some of these models predict heat generation rates based on experimental data 5,12,15-19 or electrochemical models. 8,10,13,14,[20][21][22] Pals and Newman 10,14 developed a thermal model for a Li-ion cell based on the electrochemical model presented by Doyle et al. 23 Song and Evans 13 took a similar approach and presented a 2D thermal model for a cell stack where the heat generation was estimated from a 1D electrochemical model. Such models are well-suited for designing batteries, but they are not suitable for the computational resources of the electronics used in BMSs. 24 Experimental studies show that the overpotential and entropic heat coefficients gathered from experiments can be used to predict the volumetric heat generation rate. These thermal simulat...

Review of Parameter Determination for Thermal Modeling of Lithium Ion Batteries

“…It was assumed that heat transfer with the surroundings, electrical work, mixing, phase changes, reactions, and changes in the heat capacity of the system determined the temperature changes over time. The heat source could be calculated from the simplified energy balance, which is formulated in the equation [15] .…”

“…On the other side, the entropic heat coefficient (EHC) is needed to be determined for heat generation calculation. The EHC is one of the most important factors, which affects the magnitude of the reversible heat, notwithstanding; entropic heat can be the same as irreversible heat in order of magnitude [15].…”

“…Entropic heat coefficient or temperature coefficient is the potential derivative with respect to temperature [15] EHC = dU avg /dT (3) EHC is a function of temperature and SOC levels, which can be either negative or positive. The effect of entropic heat, which can be exothermic or endothermic during charge and discharge processes, is shown in Table 2.…”

“…The cell is discharged or charged to a specific SOC level and then is allowed to relax. The relaxation is accompanied by a thermal cycle [15].…”

A Parameter Identification Method for Dynamics of Lithium Iron Phosphate Batteries Based on Step-Change Current Curves and Constant Current Curves

“…It is composed of heat generation process and heat transfer process, which are mainly determined by operating current and ambient temperature, respectively [11]. Several thermodynamic-based electrochemical models have been proposed for characterization of a battery [12][13][14] or battery pack [15][16][17]. These models highlight the general pattern of thermal process, but model parameters are obtained from typical experiments under laboratory conditions [18][19][20][21].…”