Efficient two-stage encapsulation of metallic phase change materials achieving excellent thermal storage performance

The growing global demand for sustainable energy highlights the urgent need for efficient and durable thermal energy storage technologies. Metal-based phase change materials (PCMs) offer high latent heat and excellent thermal conductivity but face challenges such as leakage and corrosion during melting. Traditional ceramic encapsulation suffers from poor thermal conductivity, large mass ratio and lacks latent heat capacity, limiting energy storage performance. This study proposes a two-stage encapsulation strategy: Al-Si alloy is first cold-pressed with ceramic for pre-encapsulation, followed by outer encapsulation using Al-Si microencapsulated PCMs (MEPCM) with thermal expansion voids. Unlike conventional inert ceramic shells, this microcapsule-based encapsulation layer itself actively participates in latent heat storage, thereby further increasing the overall energy storage density of the system. In addition, the internal voids within the microcapsules accommodate volume expansion during phase transition, effectively mitigating thermal stress. During long-term thermal cycling, the secondary encapsulation layer also acts as a protective barrier, isolating the pre-encapsulated composite from oxygen diffusion and significantly suppressing molten metal leakage. During sintering, leaked molten Al-Si infiltrates MEPCM/ceramic pores and solidifies at the interface, forming a strong and permanent metallic bond. The resulting composite exhibits a high latent heat of 392.2 J/g, encapsulation efficiency of 78.5%, and thermal conductivity of 4.52 W/(mF09EK), which is 401% higher than conventional ceramic encapsulation. After 300 thermal cycles, latent heat retention remains at 96.85%. Overall, this two-stage encapsulation strategy offers a scalable route for integrating high-temperature thermal energy storage into renewable and sustainable energy systems, thereby supporting low-carbon energy transitions.