Oriented thermal conductive composite phase-change material enabled by oriented expandable graphite skeleton for heat storage

Commonly used PCMs have low thermal conductivity and high thermal resistance, which is not conducive to heat transfer, making it difficult for materials to quickly absorb and conduct heat. This study presents the fabrication and characterization of an oriented thermal conductive composite phase-change material (OTC-CPCM) using the vacuum adsorption method and compression-induced self-assembly method. Paraffin wax (PW), oriented worm expandable graphite (WEG), and high-purity graphite sheets (GS) were incorporated to form distinct layered structures perpendicular to the pressure direction, establishing stable thermal flow channels. The influence of WEG content on microstructure, thermal conductivity, and phase change characteristics was investigated. Results show that higher WEG content enhances the layered structures and thermal conductivity of the OTC-CPCM while reducing the supercooling degree during solid-state phase transition. The OTC-CPCM enables the directional thermal conductivity to 27.09 W/mK at WEG loading below 30 wt%. Inspired by the synergetic effects of the layered structures inside OTC-CPCM with directional thermal transport, the OTC-CPCM energy storage block demonstrated excellent solar-thermal conversion efficiency (~ 90.8%) and electro-thermal conversion efficiency (~ 90.3%). Moreover, the OTC-CPCM exhibits excellent leak-proof performance, with cyclic stability increasing with higher WEG content. These findings demonstrate the potential of OTC-CPCM in solar-thermal utilization, thermal management, building energy conservation, and heat storage applications.