Hexagonal boron nitride reinforced thermal conductivity improved composite material design applications in electric vehicles

Abstract

Electric vehicles are essential for ensuring the sustainability of transportation and have the advantage of not emitting environmentally detrimental gases due to their lack of reliance on fossil fuels, such as internal combustion engines. Consequently, they provide a significant contribution to the reduction of air pollution. Multiple studies have been conducted to promote the utilization of electric vehicles in order to capitalize on this characteristic. Nevertheless, battery performance remains a significant barrier to wider use. The functioning of batteries leads to an increase in temperature due to the Joule effect, which in turn negatively impacts the efficiency of the battery. Consequently, ongoing research is being conducted on the thermal regulation of batteries, with a focus on the development of materials that can efficiently disperse heat throughout the battery. The objective of the project is to create a polymer-based hybrid composite material that enhances thermal conductivity and impact strength. This material will be used to manufacture battery module casing for electric vehicles. Polyamide 6 (PA6) was chosen as the matrix material because of its extensive usage and ease of fabrication. Hexagonal boron nitride (h-BN) was used to enhance thermal conductivity. Furthermore, a Styrene-ethylene-butylene-styrene (SEBS) elastomer supplement has been included to enhance protection against probable ground impact damage. Furthermore, graphene nanoplate (GnP) was employed to enhance the mechanical and thermal characteristics, so achieving a synergistic effect with the h-BN reinforcing material. Following the production of the compounds through extrusion and injection molding, samples underwent physical, mechanical and thermal characterization.The addition of 30wt.% h-BN increased 38.7% the elastic modulus. The results demonstrate that the thermal conductivity had a significant rise of 194.3% when 30wt.% h-BN. The addition of 2.5wt.% GnPs led to an 8.9% enhancement in the elastic modulus and a 4.97% improvement in the tensile strength value. The addition of 5 wt.% SEBS led to a significant 45% enhancement in the impact strength. Subsequently, a scanning electron microscope (SEM) was employed to examine the cracked surfaces for the purpose of analyzing the mechanisms that cause the damage to the material. Afterwards, the thermal conductivity and elastic constants of the compositions were determined utilizing analytical methods. The Maxwell-Eucken and Cheng-Vachon models were employed for the analysis of thermal conductivity, while the Halpin Tsai (HT) model was utilized to determine the elastic constants. Furthermore, the mechanical and thermal characteristics of these compositions were assessed by creating a representative volume element (RVE) using Digimat FE. To verify the accuracy of these models, they were compared to experimental data. In the end, the compositions were evaluated based on several qualities which are tensile strength, elastic modulus, impact strength, thermal conductivity, and price to determine the most effective composite that could be used as battery module casing material. The optimization study utilized the response surface method (RSM) in combination with a Python-based optimization tool. Once the most suitable composite material was chosen, it was utilized for the ground impact investigation during the last phase of the study. The investigation was conducted with the simulation software Abaqus CAE. A simulation model was developed to replicate the ground impact, and an analysis was conducted using two distinct situations. In the first situation, an aluminum battery module casing was utilized, while in the second scenario, a battery module casing with a honeycomb structure incorporating PHS30 was employed. By utilizing the honeycomb form of PHS30 battery module casing, a significant weight reduction of 26.9% was attained, while ensuring the integrity of the battery cells in the design.