Eco-friendly polyurethane thermally conductive composites with enhanced mechanical strength and toughness based on isocyanate index regulating for cell-to-pack battery system

New requirements for thermal interface materials to combine both mechanical properties and heat dissipation have been proposed by long cruising range and lightweight cell-to-pack (CTP) battery system. Here we report an environment-friendly thermally conductive composite based on polyurethane (PU) as the matrix and alumina (Al2O3) as the thermally conductive filler, which presented all of the thermally conductive, notable mechanical strength and toughness, and electrical insulation with a thermal conductivity of 0.84 W/(m & sdot;K), a tensile strength of 8.09 MPa, an elongation at break of 117.51 %, and a volume resistivity of 4.3 x 1014 Omega & sdot;cm. Aluminum alloy 5052 adherends were used to manufacture the single-lap joints (SLJs) of composites with different isocyanate indices, and the single-lap shear test was used to investigate the tensile lap-shear strengths and failure modes of the joints. A critical discussion was conducted regarding the relationship between the isocyanate index (R index) and the bonding mechanism. It was found that changing the isocyanate index under the premise of fixed hard segment content enhanced the lap-shear strength of joints from 4.49 MPa to 8.24 MPa. Meanwhile, the failure mode transitioned from the adhesive failure mode to the adhesive/cohesive mixed failure mode, and then to the cohesive failure mode. Hence, the present study sheds light on the rational design of thermally conductive composites to promote the multi-functionality of thermal management applications in the new energy vehicle battery domains.