Development of a high latent Al–Si macrocapsule for thermal energy storage in both the core and shell

Aluminum–silicon (Al–Si) alloys, due to their excellent heat storage density and thermal conductivity, are ideal candidates for high-temperature phase change materials (PCMs). However, metal-based PCMs are prone to leakage and corrosion during melting, which affects their stability. Traditional ceramic encapsulation suffers from poor thermal conductivity, a large mass ratio, and a lack of latent heat storage capacity, limiting its ability to meet the demands of efficient energy storage. This study proposes a novel design of a macro-capsule encapsulated with microencapsulated phase change materials (MEPCMs). By introducing MEPCMs into the outer shell of the macrocapsules, the system gains latent heat storage capability, increasing the mass content of the heat storage medium within the capsule and forming a dual heat storage unit of “core + shell”. Both the macrocapsules and the microcapsules are designed with thermal expansion cavities, effectively alleviating the volume expansion during the phase change process. The resulting macrocapsules exhibit a latent heat storage density of 420.9 J g−1 with an encapsulation efficiency of 86.8%. Within the operating temperature range of 500–700 °C, the maximum total thermal storage density reaches 630.7 J g−1. In addition, the thermal conductivity of the composite shell is 4.891 W m−1 K−1, representing a 217% increase compared with conventional ceramic encapsulation. After 100 thermal cycles, the latent heat retention remains as high as 99.2%, indicating that the developed macrocapsules have good potential for high-temperature thermal applications.