Cement-diatomite composite phase change capsules for thermal energy storage

Packed-bed latent heat storage systems using phase change material (PCM) have attracted considerable attention in harnessing renewable energy for heat supply. Various high-performance composite phase change materials (CPCMs) have been prepared but face challenges in large-scale thermal applications. This work designed a new type of encapsulated compacted capsules using cement-diatomite-based composite phase change materials. The effects of component content and mixing temperature on the micro-bonding mechanism and macro-performance of spherical capsules were investigated. The results show that when the CPCMs content is set at 70 wt%, the fabricated capsule achieves an average latent heat of 58 J g⁻¹, with a corresponding latent heat storage capacity of 1.305 kJ per capsule and a density of 1083 kg m⁻³. The capsule can maintain a stable shape while significantly increasing the CPCMs content, thereby increasing the thermal storage capacity. Moreover, the capsule has a higher storage power than that of CPCM due to its higher thermal conductivity of 0.58 W m⁻¹ K⁻¹. In terms of thermal response, the encapsulated capsule with cement-based binders takes only 10 min to complete the solid-liquid phase transition in the heat charging process, which is 1.4 times faster than its unencapsulated counterparts. More importantly, the compressive strength was 2.87 MPa, which will increase by 21.53 % when the specimen is covered with an external cement shell. Overall, this capsule shows significant potential in packed bed thermal storage system application and it can provide a new pathway for the practical application of shape-stable composite PCMs.