Processing and properties of Al–Si microcapsules with a biomimetic-corrugated structure and corundum-mullite composite shell

The encapsulation of metal-based phase change materials using ceramics can realize safe and effective storage of high-temperature thermal energy. However, the use of a low toughness ceramic shell around the microcapsules cannot ensure the provision of a high latent heat and thermal cyclic stability. Here, we provide a new and effective design strategy for preparing biomimetic Al–Si microcapsules that are based on a sea-shell corrugated structure and a nano-scale corundum-mullite composite shell. The latent heat of the microcapsules was over 400 J/g, much greater than other metal-based microcapsules reported to date. The unique biomimetic-corrugated structure microcapsules obtained by a heat treatment at 1000 °C exhibited excellent thermal stability, achieving near zero heat loss after 5000 thermal cycles, whose latent heat of absorption and release reached up to 448.3 J/g and 451.8 J/g respectively. Furthermore, the microcapsules possessed a giant heat storage density of 945.8 J/g within 300–700 °C, and the performance figure of merit was 6384.2 × 106 J2·K–1·s–1·m–4, approximately 15 times higher than that of commercial solar salt. This new approach provides a pathway the practical application of Al–Si alloys as thermal storage materials for renewable energy applications.