Advanced Grafted Epoxy Resins—Boosting Dielectric, Mechanical and Thermal Performance for Energy Storage Applications

Epoxy resins have been widely used as encapsulation and dielectric materials in energy storage systems due to their low cost, ease of handling, and good chemical resistance. However, their low dielectric breakdown strength, moderate mechanical reliability, and insufficient thermal stability, reduce the reliability of the material, threatening the operation of energy storage systems. Incorporating micro or nano-sized fillers into the epoxy resin is a common strategy to modify its properties. However, poor interface and agglomeration issues complicate the preparation process and make it hard to gain satisfactory improvement. Besides, large amounts of fillers are needed to achieve significant change, increasing the cost. Conversely, modification at the molecular level can easily solve the dispersion and agglomeration problems. Tiny amounts of additives can lead to significant improvement. Thus, this research explores the potential of introducing grafting agents into the epoxy resin to enhance its reliability. In this study, molecular modification was achieved by introducing small contents (0.5, 1.0, and 1.5 wt.%) of grafting agents into the epoxy/amine resin during the curing process. Allyl chloroacetate (AC) was selected as the grafting agent for its potential to promote crosslinking, thereby enhancing mechanical reliability and thermal stability. Moreover, its polar groups can benefit energy storage, and improve dielectric properties via charge trapping mechanisms. Fourier-transform infrared spectroscopy (FTIR) was used to identify chemical reactions and verify successful grafting. Dielectric breakdown strengths were measured and analysed using Weibull statistics to assess dielectric enhancements. Furthermore, mechanical reliability was evaluated by measuring the tensile strength and Young's modulus. Scanning electron microscopy (SEM) was utilized to reveal failure mechanisms, while energy-dispersive X-ray spectroscopy (EDX) assessed the dispersion of grafting agents. Additionally, dynamic mechanical analysis (DMA) was used to investigate the thermal stability of the modified resin system. The results indicate that the AC-modified epoxy/amine resin system exhibited remarkable improvements in various properties. The dielectric breakdown strength significantly increased to 118% of pure epoxy resin, indicating improved electrical performance. The tensile strength was notably enhanced from 70 to 78 MPa and the Young’s modulus also increased from 618 to 787 MPa, providing more reliable mechanical support. Additionally, the glass transition temperature (T_g) of the modified epoxy resin was increased by 10 °C, making it more suitable for harsh operating conditions in energy storage devices. The FTIR results confirmed the successful grafting and provided valuable insights into the mechanisms behind the property improvements. In conclusion, this grafted epoxy resin system exhibited significant improvements in dielectric ability, mechanical reliability, and thermal stability, making it a promising candidate for next-generation energy storage devices. Further optimization of grafting agent selection and incorporation could yield tailored, high-performance epoxy materials for diverse energy storage technologies.