Integration of Micro-Encapsulated Phase Change Materials into Thin Coatings for a Passive Battery Thermal Management System

• Published in: Meeting abstracts (Electrochemical Society) Vol. MA2025-01; no. 8; p. 835
• Main Authors: Quarrell, Matthew James, Batty, Robert, Neale, Alex R., Harvey, Daniel, Shchukin, Dmitry, Hardwick, Laurence J.
• Format: Journal Article
• Language: English
• Published: The Electrochemical Society, Inc 11.07.2025
• ISSN: 2151-2043; 2151-2035
• DOI: 10.1149/MA2025-018835mtgabs

Battery thermal management systems (BTMS) are an important component of electric vehicles. BTMS provide key safety measures with the aim of maintaining operating temperatures of Li-ion cells within optimum ranges between 15 – 35 °C and a maximum 5 °C difference across the cell. 1 Current commercial BTMS use air or liquid cooling to maintain optimum temperatures of Li-ion cells, which can be bulky, reducing volumetric and gravimetric energy densities of the battery pack. Additionally, the most effective systems, active BTMS, require energy from the battery to pump the cooling fluid resulting in less energy being available from the battery pack for useful work. Without BTMS in place, cells can exceed 60 °C leading to cycle life loss or thermal runaway. 2 To overcome these issues, in recent years there has been great interest in including phase change materials (PCMs) in BTMS. PCMs make use of latent heat and can store and release up to 150 - 250 J•g -1 of energy to passively manage cell temperatures. It has been demonstrated that PCMs can keep cells below 50 °C when cells are subject to fast charging conditions in addition to being more energy efficient than active BTMS requiring no additional energy input from the cell. 3 However, effective integration of PCMs into BTMS has proven difficult due to the low thermal conductivity and tendency for leaking of the active PCM. 3 Current methodologies for integration have involved the development of composite PCMs – a porous housing for the PCM. The composite PCM allows additives such as graphene to enhance thermal conductivity and leakage prevention. 4 However, concerns remain about PCM integration into battery packs and volumetric efficiency as a remaining barrier for full commercialisation. Micro-encapsulation, i.e., the formation of a thin, non-permeable shell around a PCM core, provides an increased surface area-to-volume ratio resulting in a smaller volume requirement for heat absorption. 5 The micro-encapsulation of PCMs can also be used to mitigate leakage during operation and has previously been suggested to enable the use of PCMs in thermal management systems but there have been limited attempts demonstrating a practical use. 6 In this work, Octadecane (C 18 H 38 , melting point 27 °C) has been encapsulated using a graphene oxide (GrO) shell, producing capsules with a diameter of 2 µm. The PCM/GrO capsules were applied to LiFePO 4 |Graphite 18650 cylindrical cells (RS Pro, 1600 mAh), via an outer coating (~3 mm thick), to passively manage the thermal performance of the cell. The coating had a latent heat of melting of ~100 J g -1 and thermal imaging was used to assess temperature change of the cycling cells. Cells were tested under fast charging conditions to assess the efficacy of the coatings ( Figure 1 ). At a rate of 2C (3.2 A), the ~3 mm thick PCM/GrO coating was able to reduce the peak cell temperature by 8 °C during charging compared with an uncoated cell, requiring only a 13% increase in total mass of the cell. The PCM/GrO capsule coatings have the advantage of direct application to the exterior of the cell without the additional need of external components or cell stacking. The coating makes good contact and allows cells to be independent of each other allowing for straightforward implementation into an existing BTMS. Furthermore, coating formulations can be readily modified to select desired temperature maxima. Figure 1 Temperature profile of a coated and uncoated cell cycling by initially resting for 30 minutes and then discharging at 0.5 C (C = 1600 mAh) to 2.6 V. Cells were then charged at 2 C to 4.5 V followed by an hours rest. Thermal images were taken every 20 seconds. D. Chen, J. Jiang, G.-H. Kim, C. Yang, and A. Pesaran, Appl. Therm. Eng. , 94 , 846–854 (2016). J. Luo, D. Zou, Y. Wang, S. Wang, and L. Huang, Chem. Eng. J. l , 430 , 132741 (2022). R. Kumar and V. Goel, J. Energy Storage , 71 , 108025 (2023). Z. Li, Y. Zhang, X. Wang, F. Cao, X. Guo, S. Zhang, and B. Tang J. Power Sources , 603 , 234447 (2024). E. Shchukina, M. Graham, Z. Zheng, and D. Shchukin, Chem. Soc. Rev. , 47 , 4156–4175 (2018). J. Gu, J. Du, Y. Li, J. Li, L. Chen, Y. Chai, and Y. Li, Energies , 16 , 1498 (2023). Figure 1