Radial Thermal Conductivity Measurements of Cylindrical Lithium-Ion Batteries—An Uncertainty Study of the Pipe Method

Abstract

A typical method for measuring the radial thermal conductivity of cylindrical objects is the pipe method. This method introduces a heating wire in combination with standard thermocouples and optical Fiber Bragg grating temperature sensors into the core of a cell. This experimental method can lead to high uncertainties due to the slightly varying setup for each measurement and the non-homogenous structure of the cell. Due to the lack of equipment on the market, researchers have to resort to such experimental methods. To verify the measurement uncertainties and to show the possible range of results, an additional method is introduced. In this second method the cell is disassembled, and the thermal conductivity of each cell component is calculated based on measurements with the laser flash method and differential scanning calorimetry. Those results are used to numerically calculate thermal conductivity and to parameterize a finite element model. With this model, the uncertainties and problems inherent in the pipe method for cylindrical cells were shown. The surprising result was that uncertainties of up to 25% arise, just from incorrect assumption about the sensor position. Furthermore, the change in radial thermal conductivity at different states of charge (SOC) was measured with fully functional cells using the pipe method.

Effect of Ambient Temperature and Discharge Current on Thermo-Electrochemical Behaviour of Lithium-Ion Cells Using Surrogate Modelling and Analysis

“…24 The core and surface temperature of a lithium-ion cell is not the same due to the different thermal conductivities of individual cell components. The thermal resistance of each lithium-ion cell component is very high, leading to a high-temperature gradient between the core and surface of these cells, 25,26 with the temperature gradient changing with a change in the operating conditions. The current rate and ambient temperature have been regarded to be the two major factors that have the most effect on the thermo-electrochemical performance of these cells.…”

Effective Thermal Conductivity of Lithium‐Ion Battery Electrodes in Dependence on the Degree of Calendering

“…A lot of research was done on the determination of the thermal conductivity of the single components of battery cells from graphite anodes over separators to cathodes with different active materials. [8][9][10][11][12] A comprehensive overview was given by Steinhardt et al [13] Realistic values of density, specific heat capacity, and thermal conductivity are needed for the parameterization of thermal battery models, which are used to simulate the temperature distribution within battery cells. As the measurement of the temperature within the cells still poses a great challenge and the effects of inline measurement devices on the electrical cell behavior are not yet fully understood, [14,15] modeling is crucial to estimate the core temperature of the cells.…”

“…A lot of research was done on the determination of the thermal conductivity of the single components of battery cells from graphite anodes over separators to cathodes with different active materials. [ 8–12 ] A comprehensive overview was given by Steinhardt et al [ 13 ]…”