Ionic Liquid as Plasticizer and Liquid Conductive Filler for Polypropylene‐Based Composite Bipolar Plates

ABSTRACT To develop high‐performance polypropylene (PP)‐based composite bipolar plates (BPs) with enhanced processability and electrical conductivity, this work introduces a halogen‐free ionic liquid (IL) containing long alkyl chains in cation and anion, namely trihexyl(tetradecyl)phosphonium di(2‐ethylhexyl) phosphate ([P ₆₆₆₁₄ ][DEHP]), as a multifunctional plasticizer. The composite BPs containing binary graphite (Gr) and carbon black (CB) conductive fillers and IL are fabricated by twin‐screw extrusion and compression molding. Results show that after adding 4 wt% IL to the 30PP/63Gr/7CB BP, the torque decreases from 14.3 to 7.8 N m, the storage modulus at processing temperature (210°C) lowers from 1894 to 856 MPa, and the electrical conductivity increases by 192%. The added IL enhances melt fluidity, ensuring uniform filler dispersion; at the same time, it provides additional electron pathways boosting conductivity. Moreover, IL also reduces the density and improves the hydrophobicity of the composite BP. The incorporation of the IL‐based plasticizer offers a novel approach for designing easily processable and high‐performance composite BPs.