• Paepe, Michel De
• Nonneman, Jasper
• Tjollyn, Ilya
• Beyne, Wim

Abstract

Thermal management of Li-ion batteries is critical for its performance and lifetime. Furthermore, when batteries are submitted to excessive temperatures by a bad thermal management system, thermal runaway can occur which can destroy the afflicted cell and the adjacent cells in a battery pack. Batteries are subject to cyclic behavior, charging and discharging, which is accompanied by a non-steady-state heat dissipation. Through thermal buffering, heat can be stored temporarily, which allows the heat transfer to the environment to be more evenly and thus reducing the maximal cooling load. Phase change materials or PCMs for thermal buffering are studied in this paper. By melting and solidifying, these substances take up and release a large amount of heat in a small volume and mass. To be able to design a thermal buffering system with PCMs, a one-dimensional transient model is developed to identify which influence design parameters have on the battery temperature. Simulations are performed for pure PCMs and for PCMs enhanced with three types of thermally conducting structures: metal foam, expanded graphite and carbon fibers. The results show that the effectiveness of thermal buffering is highly dependent on the cycle duration. For long cycles in the order of one day or more, thermal buffering can reduce peak temperature by around 4°C. For medium duration cycles in the order of several hours, peak temperatures can be reduced by around 13°C. For shorter cycles, heat buffering in the simulated cases was only slightly beneficial for the battery temperature. Furthermore, the simulations show that thermal buffering for battery packs requires a relatively small amount of PCM which results in short heat paths through the PCM. Enhancing the thermal conductivity by using thermally conductive structures slightly improves the thermal buffering performance, but might not be advisable due to the added complexity and cost.

Topics

• impedance spectroscopy
• Carbon
• phase
• simulation
• thermal conductivity
• one-dimensional
• metal foam