Engineered expanded graphite/paraffin wax shape-stable phase change composite coated by copper and silver with outstanding latent heat storage capacity and thermal conductivity

Overcoming heat management bottlenecks via surface engineering rather than internal additives, this study utilizes a Cu/Ag armor to transition heat transfer from slow phonon diffusion to ultrafast free-electron conduction, achieving unmatched thermal conductivity without sacrificing phase-change encapsulation. Expanded graphite (EG) matrices, encapsulated 93% paraffin wax (PW) by weight, were coated with a thick Cu shell (electrolytic) and then a thin Ag film (electroless). Results of characterization confirmed that the EG/PW@Cu@Ag composite developed by the experiment raised the thermal conductivity of pure PW from 0.21 W/m·K to a record 43 W/m·K, which indicated that, although the conductivities increased greatly, the latent storage of heat in the system (199.6 J/g) of material was maintained overcoming the trade-off problem. Due to the Ag layer the passivation of Cu surface occurred and demonstrated that the chemical structure is not changed even in 500 melt-freeze cycles with a negligible enthalpy loss at 3.6%. Infrared thermography confirmed the ultra-fast heat dissipation of the Cu-Ag armor, accelerating early-stage heat spreading (from 42.4 °C to 51.1 °C at 60 s) while ultimately capping the peak surface temperature at 70.1 °C (120 s) to suppress localized overheating. Therefore, the composite developed in this work provides a competitive and environmentally friendly candidate for application in thermal control of electric vehicle battery pack and next-generation high-power electronic systems due to its high energy density and best heat transfer rate.