Abstract: Temperature strongly influences the electrical and aging behavior of lithium-ion battery cells. Therefore, modeling of the thermal behavior of these cells is needed to depict the behavior adequately. Thermal models require the knowledge of the thermal material properties of the cell. Here, we present the thermal material properties of the components of a commercial NMC111-LMO / graphite lithium-ion battery cell. A gas pycnometer is used to measure the density and a differential scanning calorimeter to measure the heat capacity of the coatings. With knowledge of the properties of the double sided coated current collector and its thermal diffusivity measured with a laser flash apparatus, the thermal conductivity of the coatings can be calculated. The standard deviation with error propagation amounts to maximum of ≈ 8.5 %.
TechnicalRemarks: A commercial 20 Ah pouch cell (SPB58253172P2, Enertech International, Inc.), which consists of a NMC111-LMO cathode blend and a graphite anode[1] is characterized thermally. The cell opening is performed at a State of Charge (SoC) of 0 % in an inert environment in a glove box. After disassembly, the anode and cathode sheets were triple washed with DMC and left to dry. For the density and heat capacity measurements, the coatings of both anode and cathode sheets were scraped off. For the thermal diffusivity measurements 18 mm double coated coins were punched from the sheets. All probes were exposed to air only very shortly before inserting them into the measurement devices.
The experimental analysis is performed according to Oehler et al.[2]. The density measurement is done with a Micro Ultrapyc 1200e Gas (Quantachrome Instruments) pycnometer in nitrogen gas. The heat capacity is measured in a Q2000 (TA Instruments) differential scanning calorimeter in a temperature range from -40 °C to 60 °C. The thermal diffusivity measurement of the double coated coins is performed in helium atmosphere in a LFA 467 Hyperflash (NETZSCH-Gerätebau GmbH) in a temperature range from -20 °C to 60 °C. To calculate the thermal conductivity of the coatings via a serial connection[3], additional knowledge of the layer thicknesses, porosities of the coatings and the thermal material properties of the current collectors are needed. The thicknesses of the coatings and current collectors are measured with a Micromar 40 EWR (Mahr GmbH). A Balance XPE206DR precision scale (Mettler Toledo) was used to measure the mass of the coating probes. The porosity of the coating was then determined gravimetrically. All measurements were conducted at least three times. Error propagation of the standard deviation was performed for the calculated values. The measurement of the density and heat capacities of the current collectors as well as pouch foil and separator were performed as previously described. The current collector materials are assumed to be copper and aluminum and the thermal conductivities at 0 °C are taken from literature[4].
[1] L. Cloos, J. Langer, M. Schiffler, A. Weber, Th. Wetzel, J. Electrochem. Soc. 2024, 171, 040538.
[2] D. Oehler, P. Seegert, T. Wetzel, Energy Technol. 2021, 9, 2000574.
[3] A. Loges, S. Herberger, D. Werner, T. Wetzel, Journal of Power Sources 2016, 325, 104–115.
[4] P. Stephan, S. Kabelac, M. Kind, D. Mewes, K. Schaber, T. Wetzel, Eds. , VDI-Wärmeatlas: Fachlicher Träger VDI-Gesellschaft Verfahrenstechnik und Chemieingenieurwesen, Springer Berlin Heidelberg, Berlin, Heidelberg, 2019.
