Thermal Conductivity, Heat Sources and Temperature Profiles of Li-Ion Batteries

Abstract

In this paper we report the thermal conductivity of several commercial and noncommercial Li-ion secondary battery electrode materials with and without electrolyte solvents. We also measure the Tafel potential, the ohmic resistance, reaction entropy and external temperature of a commercial pouch cell secondary Li-ion battery. Finally we combined all the experimentally obtained data in a thermal model and discuss the corresponding internal temperature effects.The thermal conductivity of dry electrode material was found to range from 0.07 to 0.41 W K −1 m −1 while the electrode material soaked in electrolyte solvent ranged from 0.36 to 1.10 W K −1 m −1 . For all the different materials it was found that adding the electrolyte solvent increased the thermal conductivity by at least a factor of three. For one of the anode materials it was found that heat treatment at 3000 K increased the thermal conductivity by a factor of almost five.Measuring the electric heat sources of an air cooled commercial pouch cell battery at up to ± 2C and the thermal conductivity of the electrode components made it possible to estimate internal temperature profiles. Combining the heat sources with tabulated convective heat transfer coefficients of air allowed us to calculate the ambient temperature profiles. At 12C charging rate (corresponding to 5 minutes complete charging) the internal temperature differences was estimated to be in the range of 4-20K, depending on the electrode thermal conductivity. The external temperature drop in air flowing at the battery surface was estimated to nearly 40K. Evaluating thermal * Corresponding author; odnesb@hist.no management of batteries in the light of our measurement led to the conclusion that external cooling is more challenging than internal, though neither should be neglected.

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

“…We used an entropy change of −9 J mol·K [35] for the NMC | graphite cell. According to Burheim et al [18], we assumed an ohmic resistance of 2mΩ · m 2 and an overpotential of η = −0.042 + 0.067 · log(j). A stack of 34 cells was modelled.…”

“…If we imagine a thin electrode, we differentiate between the direction perpendicular (cross-plane) and parallel to the plane (in-plane). There are reports on thermal conductivities of Li-ion secondary battery materials [18], but they are not thoroughly investigated [5]. In particular, there is not that many reports on thermal conductivity of separators.…”

“…We found one paper from Vishwakarma and Jain [23], in which a transient DC heating method was used to obtain an in-plane thermal conductivity of a separator of 0.5 ± 0.03 WK −1 m −1 . Since the heat production is predominant in the separator-electrolyte region and to some extend within the solid electrolyte interface region at high currents [18], knowledge of the thermal conductivity of the electrolyte soaked separator is critical. In addition, temperature profiles of batteries will vary during operation, in terms of ageing, SOC and C-rate.…”

“…Using photothermal deflection In this paper we report the thermal conductivity for a wide range of pristine materials at different compaction pressures, dry, and soaked in electrolyte solvent. Thereafter, we use an already developed simple 1-dimensional thermal model [18] to compare these values and put them into a thermal context.…”

Influence of Temperature on Supercapacitor Components

“…[139]. In some cases, the thermal conductivities of electrodes with/without electrolyte may vary by a factor between three and four [140]. Electrodes saturated with paraffin lead to high thermal conductivity of 10-15 W m −1 K −1 [141].…”