High-temperature composite phase change material with “concrete-like” strength even beyond the eutectic temperature

Abstract

The need for medium-to-long-term thermal energy storage has increased in tandem with the widespread adoption of variable renewable energy sources. Latent heat storage using metallic phase change materials (PCMs) presents a promising solution by combining high thermal conductivity with high heat storage density. Recent advances in microencapsulated PCMs (MEPCMs) have addressed corrosion and leakage issues commonly associated with metallic PCMs. This study develops an MEPCM composite using an Al–Cu–Si-based MEPCM as the primary component. This system exhibits a suitable structure, performance, and strength for achieving GW h-scale thermal energy storage systems. The MEPCM composite is fabricated by microencapsulating Al–Cu–Si eutectic alloy powder, which has a eutectic temperature of 520 °C, with an Al oxide shell formed via chemical conversion and heat-oxidation treatments, followed by mixing with an alumina sintering aid, forming, and sintering. The composite exhibits a heat storage density of approximately 1.0 GJ m⁻³ under a temperature difference (ΔT) of 200 °C, which is 2–3 times higher than that of conventional sensible heat storage materials. It retains both its heat storage performance and structural integrity after 1000 thermal cycles. The thermal conductivity ranges from 4.1 to 6.6 W m⁻¹ K⁻¹ between 300 and 600 °C. This study is the first to evaluate the compressive strength of composite PCMs in the liquid state, where the composite retains a compressive strength of 32 MPa at 600 °C, which is comparable to that of ordinary concrete. In the solid state, the composite exhibits 83 MPa at room temperature and 49 MPa at 500 °C. Therefore, MEPCM composites are expected to possess substantial compressive strength for applications in medium-to-high-temperature heat storage and thermal management systems, even beyond the eutectic temperature of the PCM.