Highly conductive solid-solid phase change composites and devices enhanced by aligned graphite networks for solar/electro-thermal energy storage

Abstract

Phase change materials (PCMs) are widely considered as promising energy storage materials for solar/electro-thermal energy storage. Nevertheless, the inherent low thermal/electrical conductivities of most PCMs limit their energy conversion efficiencies, hindering their practical applications. Herein, we fabricate a highly thermally/electrically conductive solid-solid phase change composite (PCC) enabled by forming aligned graphite networks through pressing the mixture of the trimethylolethane and porous expanded graphite (EG). Experiments indicate that both the thermal and electrical conductivities of the PCC increase with increasing mass proportion of the EG because the aligned graphite networks establish highly conductive pathways. Meanwhile, the PCC4 sample with the EG proportion of 20 ​wt% can achieve a high thermal conductivity of 12.82 ​± ​0.38 ​W·m⁻¹·K⁻¹ and a high electrical conductivity of 4.11 ​± ​0.02 ​S·cm⁻¹ in the lengthwise direction. Furthermore, a solar-thermal energy storage device incorporating the PCC4, a solar selective absorber, and a highly transparent glass is developed, which reaches a high solar-thermal efficiency of 77.30 ​± ​2.71% under 3.0 suns. Moreover, the PCC4 can also reach a high electro-thermal efficiency of 91.62 ​± ​3.52% at a low voltage of 3.6 ​V, demonstrating its superior electro-thermal storage performance. Finally, stability experiments indicate that PCCs exhibit stabilized performance in prolonged TES operations. Overall, this work offers highly conductive and cost-effective PCCs, which are suitable for large-scale and efficient solar/electro-thermal energy storage.