Technique to Determine the Specific Heat Capacity of Lithium-Ion Battery Cells

摘要

The poster presents a new approach for determining the specific heat capacity of any physical body in general and of lithium-ion battery cells in particular without the use of a calorimeter. The specific heat capacity is usually missing on lithium-ion battery's data sheet and cell manufacturers rarely provide a precise value upon request of small and medium sized customers, even though it is an essential thermodynamic parameter for thermal modelling and simulation of a battery cell. Therefore, this characteristic has to be measured by the battery pack designer, which is usually done using a costly calorimeter. The presented method uses less expensive equipment by applying a temperature change procedure in which the temperature of the test specimen slowly adapts to the ambient air temperature as a result of a sharp change in the ambient temperature. In addition, it can be used to determine the specific heat capacity over a wide temperature range with high temperature resolution using only one set of measurements. The poster shows the specific measurement setup that was used for the experiments and gives details on the measurement procedures. A thermal insulation of the test specimen ensures a homogeneous temperature distribution within the specimen and thus simplifies both the necessary measurement effort and the model needed to calculate the specific heat capacity significantly. Since the thermal insulation needs to both enclose the specimen completely and fit tightly, the limitations of this method are ultimately determined by the individual manufacturing capabilities. The poster explains the design of the 3D printed thermal insulation that was used for the presented measurements. The model, which uses the measurement data of the temperature change of the test specimen to calculate the specific heat capacity analytically, is based on a simplified, quasi steady state combination of the energy conservation and heat equation. This simplified model, however, needs the thermal resistance value - or thermal conductivity value respectively - of the utilized thermal insulation that has to be determined prior to the specific heat capacity measurement. The poster exhibits measurement results of the heat capacity of a 21700 cylindrical lithium-ion battery cell as well as of the thermal resistance value of its thermal insulation.