Enhancement of the Through‐Thickness Electrical Conductivity of Carbon‐Fiber‐Reinforced Plastics Using Large Graphite Particles

A carbon‐fiber‐reinforced plastic (CFRP) with enhanced through‐thickness electrical conductivity is developed by incorporating spherical graphite particles (GPs). The introduction of large spherical GPs reduces interparticle contact resistance in the low‐viscosity uncured resin required for carbon‐fiber (CF) fabric impregnation while maintaining the viscosity within a range suitable for fabric impregnation (≤19.0 Pa s at 30 vol%), thereby providing favorable processing conditions during composite fabrication. Because the particle size was intentionally selected to be larger than the interfiber spacing ( D 50 = 8 μm), the GPs remain at the interfaces between CF layers rather than penetrating into the fiber bundles. Under compressive pressure during molding, the GPs promote closer contact between CFs. Consequently, the number of CFs per unit area within the CF layer increases by a factor of 1.4 relative to that in the GP‐free system, resulting in a distinctive alternating CF/GP layered architecture through the thickness. This structural arrangement substantially increased the through‐thickness electrical conductivity from 4.5 × 10 − 3 S/cm for GP‐free CFRP to 8.1 × 10 − 1 S/cm for GP‐containing CFRP. These findings demonstrate that the deliberate use of large‐diameter GPs enables the formation of a CF/GP layered structure, thereby markedly enhancing the through‐thickness electrical conductivity of CFRP.