Novel forsterite/chloride salts composite materials with high energy storage density for high temperature thermal energy storage

Composite phase change materials are particularly valuable for high temperature thermal energy storage and waste heat recovery, but the poor energy storage density and thermal conductivity limit their practical applications. Herein, this study proposed a concurrent enhancement of composite materials by utilizing SiO₂ nanoparticles-decorated KCl-NaCl as phase change materials and forsterite with high specific heat as matrix materials. The results showed that forsterite and chloride salts exhibited excellent chemical compatibility, and the appropriate content of chloride salts and suitable molding pressure were beneficial to enhancing the densification of composite materials while increasing their thermal and mechanical properties. Specifically, the composite materials with chloride salts content of 60 wt% and molding pressure of 40 MPa demonstrated the best performance, with an energy storage density of 901.7 J/g (100–800 °C), a latent heat of 180.5 J/g, thermal conductivity of 0.78–1.47 W/(m·K) at 100–500 °C, and a compressive strength of 41.5 MPa. Notably, the addition of 1.0 wt% SiO₂ nanoparticles resulted in the formation of needle-like nanostructures, which enhanced the thermal conductivity and energy storage density of composite materials. The composite materials exhibited good chemical stability after 500 thermal cycles, accompanied by an enhancement in thermal conductivity due to the formation of middle layer between forsterite and chloride salts. This suggests a promising potential for composite materials in thermal energy storage applications.