In Situ Measurement of Radial Temperature Distributions in Cylindrical Li-Ion Cells

Abstract

Temperature is critical to the performance, durability and safety of Li-ion batteries. This paper reports in situ measurement of the radial temperature distribution inside a cylindrical Li-ion battery cell. 18650-size cylindrical cells with multiple micro thermocouples embedded are designed and manufactured. The radial temperature distribution is obtained under various operating conditions. The effects of critical parameters, such as discharge C rate, ambient temperature, and cooling condition, are investigated. It is found that higher discharge C rate and lower ambient temperature lead to higher temperature rise and larger temperature gradient within the battery cell. Stronger cooling results in smaller temperature rise but larger temperature gradient. Correlation between relative temperature gradient and cooling coefficient suggests that the assumption of uniform temperature distribution is applicable under natural-convection conditions but not applicable under strong forced convection conditions. The present results provide valuable experimental data that can be readily used to validate electrochemical-thermal coupled (ECT) battery models.Driven by the ever-increasing applications in electric vehicles and grand challenges, 1-4 the need for Li-ion batteries with enhanced performance, durability and safety is increasing. Previous studies show that temperature is critical to the performance, durability and safety of Li-ion batteries. 5-25 On one hand, the performance is reduced at lower temperatures, 6-11 and too low temperature can even cause detrimental lithium plating during charge. 12-14 On the other hand, a Li-ion battery degrades considerably faster at higher temperatures, 15-19 and excessively high temperature can lead to breakdown of the solid electrolyte interface (SEI) layer, 20-22 electrolyte decomposition, 23-25 and even to disastrous thermal runaway. 2,26,27 The surface temperatures of Li-ion cells, batteries and battery packs are commonly monitored. 28,29 However, surface temperature is expected to be different from internal temperature due to the very low thermal conductivity (∼1 W m −1 K −1 ) of electrodes and separator in the through plane direction. 5,30-32 This spatial temperature distribution inside a Li-ion battery may exacerbate the non-uniform distribution of current density 33-35 due to complex interactions among local reaction current, state of charge (SOC) and temperature. Under extreme conditions, e.g. accidental short circuit or overcharge, substantial heat is generated internally and monitoring of surface temperature could significantly underestimate the maximum temperature. Measuring internal temperature can thus provide more accurate information and is a better indicator of the health and safety of a Li-ion battery.In addition, electrochemical-thermal coupled (ECT) modeling has been widely used in the research and development of Li-ion batteries to gain insight into internal processes, to optimize battery design and operation, as well as to improve performance, durability and safety...

Thermal conductivity and internal temperature profiles of Li-ion secondary batteries

“…Moreover, improved thermal management will improve the understanding of local ageing mechanism and may lead to better battery designs and enhanced lifetimes. We find reports of several researchers using an in-situ measurement setup [13][14][15][16] to determine internal temperatures.…”

Novel 18650 lithium-ion battery surrogate cell design with anisotropic thermophysical properties for studying failure events

“…Predictably, the largest magnitude step change (Fig. 6C) displayed the highest instantaneous radial temperature distributions (7e9 C) due to a greater driving force for heat transfer, and the other step changes showed maximum radial distributions between about 4 and 6 C. During a battery failure or aggressive heating event, the radial temperature distribution would likely be significantly higher [19,26,27]; however, the moderate temperature range (0e50 C) and controlled nature of these surrogate cell tests were designed to illustrate typical behavior during normal operation of an active lithium-ion battery, where the radial temperature distribution is expected to be under 10 C [28]. Under typical operating conditions, it is therefore reasonable to assume, barring any abrupt temperature shifts or cell malfunctions, that the internal temperature of an 18650 lithium-ion battery is reasonably homogeneous.…”

Lithium-Ion Battery Failure: Effects of State of Charge and Packing Configuration

“…________________ Manuscript approved May 19, 2016. Another relevant point of emphasis with respect to cell packings concerns anisotropy of the 18650 battery's thermal conductivity; that is, due to the internal construction of a cylindrical cell, heat transfer in the axial direction is much more facile than in the radial direction [23][24][25]. This can give rise to either moderate radial temperature distributions (< 10°C) during normal cell operation [26], or more extreme discrepancies between surface and internal temperatures (as high as 40-50°C) during an adjacent failure or rapid heating event [27][28][29]. With respect to this anisotropy, a related area of study that has not been investigated is the effect of horizontal and vertical cell packings on these radial temperature distributions.…”