Thermophysical properties of a commercial 18650 LiCoO2 lithium-ion battery were determined using several different techniques, including analytical, numerical and experimental methods. A reasonable level of consistency was observed in values for heat capacity, which were found to be 972 ± 92 J/kg-K from the analytical method, 814 ± 19 J/kg-K from the numerical technique, and 896 ± 31 J/kg-K from calorimetry. The value for radial thermal conductivity with the best correlation to reported literature values obtained in this study (0.219 ± 0.020 W/m-K) was found via the numerical technique, and the axial thermal conductivity was found to be 22.3 ± 1.3 W/m-K. Values for heat capacity and thermal conductivity were also determined for aluminum and Teflon as controls, and all thermophysical properties in this work were found to be within, or very close to, reported literature values. These properties will aid in the development of ongoing and future lithium-ion battery simulation models and battery management systems.

Spinner, Neil S.; Hinnant, Katherine M.; Mazurick, Ryan; Brandon, Andrew; Rose-Pehrsson, Susan L.; and Tuttle, Steven G., "Novel 18650 lithium-ion battery surrogate cell design with anisotropic thermophysical properties for studying failure events" (2016 b s t r a c tCylindrical 18650-type surrogate cells were designed and fabricated to mimic the thermophysical properties and behavior of active lithium-ion batteries. An internal jelly roll geometry consisting of alternating stainless steel and mica layers was created, and numerous techniques were used to estimate thermophysical properties. Surrogate cell density was measured to be 1593 ± 30 kg/m 3 , and heat capacity was found to be 727 ± 18 J/kg-K. Axial thermal conductivity was determined to be 5.1 ± 0.6 W/m-K, which was over an order of magnitude higher than radial thermal conductivity due to jelly roll anisotropy. Radial heating experiments were combined with numerical and analytical solutions to the time-dependent, radial heat conduction equation, and from the numerical method an additional estimate for heat capacity of 805 ± 23 J/kg-K was found. Using both heat capacities and analysis techniques, values for radial thermal conductivity were between 0.120 and 0.197 W/m-K. Under normal operating conditions, relatively low radial temperature distributions were observed; however, during extreme battery failure with a hexagonal cell package, instantaneous radial temperature distributions as high as 43e71 C were seen. For a vertical cell package, even during adjacent cell failure, similar homogeneity in internal temperatures were observed, demonstrating thermal anisotropy.Published by Elsevier B.V.

In this presentation, we will investigate the thermophysical properties of LiCoO2 18650 battery cells. Due to their versatility and high energy density, lithium-ion batteries have become a major power source in a number of consumer and industrial products over the last decade. As their popularity and number of applications increase, so do instances of catastrophic battery failure. Excessive external heating, which in turn leads to thermal runaway, is a principle cause of cell failure and failure events continue to occur despite the installation of safety features, such as vents and thermal fuses, within the cells. Models of cell failure do exist and they have been used to improve upon battery safety features; however, failure models require prior knowledge of the cell’s thermophysical properties.     For many common, commercial lithium-ion batteries, LiCoO2 18650 cells included, knowledge of their thermophysical properties is often either incomplete or absent entirely. To determine the radial thermal conductivity and specific heat of a LiCoO2 18650 cell, we conducted external heating experiments and created a numerical heat transfer model.  In our experiments, a thermocouple and a heat flux sensor were mounted to the battery surface and, without damaging the cell, external heat was provided using NiCr wire, wrapped helically around the cell’s exterior. Using the time-dependent heat flux data measured at the battery’s surface, our computational model solved the heat conduction equation for the cell’s radial temperature profile. The radial thermal conductivity and specific heat of the LiCoO2 18650 cell were then found by minimizing the difference between the experimental surface temperature data and the model’s predicted surface temperature over time. Matching the model’s results with the experimental data was achieved with a parametric exploration of specific heat values and the Secant Method, which iterated over the radial thermal conductivity. Over the course of our presentation, the experimental setup, the numerical model, and the results we obtained will be explored in detail. We will also discuss how this method can be used to study the radial thermal conductivity and specific heat of any cylindrical cell.