Impedance-engineered HDPE hybrid nanocomposites for electromagnetic interference shielding in high-voltage electric vehicle battery enclosures

Electromagnetic interference (EMI) shielding for high-voltage electric-vehicle (EV) battery enclosures requires lightweight, recyclable materials capable of broadband attenuation without the high filler loadings that typically compromise melt processability and ductility. Here, impedance-engineered high-density polyethylene (HDPE) hybrid nanocomposites were fabricated via solvent-free melt processing followed by compression moulding using graphene nanoplatelets (GNPs, 3 wt%) as a conductive phase and barium titanate (BaTiO₃, 7 wt%) as a high-permittivity dielectric phase. Three formulations were investigated: neat HDPE, HDPE/3 wt% GNP, and HDPE/3 wt% GNP/7 wt% BaTiO₃. EMI shielding effectiveness (ASTM D4935, 0.1–1.0 GHz) increased from ~ 12.6 dB (neat HDPE) to ~ 17.9 dB (HDPE/GNP) and ~ 20.2 dB (HDPE/GNP/BaTiO₃) at 1 GHz, with comparable reflection and absorption contributions, indicating impedance-balanced attenuation. Mechanical testing (ASTM D638) showed concurrent reinforcement, with tensile strength rising from ~ 28 MPa (neat HDPE) to ~ 34 MPa (HDPE/GNP) and ~ 36 MPa (hybrid), while Shore D hardness increased from ~ 52 to ~ 59 and ~ 61, respectively. Dielectric spectroscopy (1 kHz–1 GHz) confirmed a moderate permittivity increase (ε′ ≈ 2.8 for the hybrid) while maintaining low dielectric loss (tan δ ≤ 0.0065), consistent with interfacial polarization at conductive–dielectric boundaries. Thermogravimetric analysis revealed enhanced thermal stability through a carbon–ceramic barrier effect, increasing char yield from < 0.3% (neat HDPE) to ~ 4.75% (HDPE/GNP) and ~ 6.9% (hybrid). Although the present coupon-scale shielding (~ 20 dB, 3 mm) remains below enclosure-level automotive EMC targets, the results demonstrate a scalable pathway to recyclable thermoplastic EMI shields using conductivity–permittivity synergy rather than excessive conductive percolation.