Selective Laser Sintering of Phase Change Materials for Thermal Energy Storage Applications

Traditional manufacturing techniques are continuously challenged to meet the environmental and energy consumption regulations, which lead to an increasing necessity to operate more efficiently in today’s competitive market. Energy storage systems such as fuel cells, rechargeable batteries, heat exchangers, and phase change materials (PCMs) have shown a high potential to compete in the global energy market, but the methods used to manufacture such energy storage systems remain a challenge. For example, paraffin wax/expanded graphite composite has been widely investigated as a phase change composite for thermal energy storage applications. The conventional techniques for manufacturing such composites require a considerable amount of time and usually generate a massive amount of material waste. Moreover, these techniques are limited to simple geometries such as cylinders and cubes, which hinder the broader application of phase change composites. To overcome those challenges and limitations, this research aims to explore additive manufacturing techniques for the production of paraffin wax/expanded graphite phase change composite. Specifically, selective laser sintering (SLS) based additive manufacturing was investigated. Despite the efforts in laser sintering of graphite-based composites, successful selective laser sintering of paraffin wax/expanded graphite composite has not yet been reported in the literature. Expanded graphite and paraffin wax have very different thermal behaviors and mass densities. Selective laser sintering of such two very dissimilar materials to make a functional and form-stable composite is very challenging. In this research, instead of using binders, the paraffin wax is melted in such a way that the capillary forces of the molten wax allow it to be impregnated into the expanded graphite molecules and bind it together as a composite. It was found that the newly developed SLS method combines the two materials at the micro-scale, forming a phase change composite with various geometries that possesses good thermal conductivity, superior latent heat, and excellent mechanical strength. To validate the effectiveness of the proposed SLS-printed phase change composite on thermal management of lithium-ion battery cells, it was compared with other composites that were manufactured by conventional techniques. Equivalent heat generations of a cylindrical 18650 lithium-ion battery cell were imitated using a thin polyimide heater. Experimental results and finite element analysis have shown that the SLS-printed phase change composite can achieve thermal management functions comparable to those of composites manufactured by the conventional press-and-soak technique. Additionally, the effects of the proposed SLS process parameters and feedstock parameters on the printing accuracy and the printed composite thermal performance were quantified. This work provides a guideline for effective process planning to produce PCM composite with desired printing accuracy and thermal properties for thermal energy storage applications.