Al–Si–Fe alloy-based phase change material for high-temperature thermal energy storage

Carnot batteries, a type of power-to-heat-to-power energy storage, are in high demand as they can provide a stable supply of renewable energy. Latent heat storage (LHS) using alloy-based phase change materials (PCMs), which have high heat storage density and thermal conductivity, is a promising method. However, LHS requires the development of a PCM with a melting point suitable for its application. For the Carnot battery, the reuse of a conventional ultra-supercritical coal-fired power plant with a maximum operating temperature of approximately 650°C is considered. Therefore, developing a 600°C-class alloy-based PCM is crucial for realizing a highly efficient and environmentally friendly Carnot battery. Using thermodynamic calculation software (FactSage), we found that Al-5.9 mass% Si-1.6 mass% Fe undergoes a phase transformation at 576–619°C, a potential 600°C-class PCM. In this study, we investigated the practicality of an Al–Si–Fe PCM as an LHS material based on its heat storage and release properties and form stability. The examined Al–Si–Fe PCM melted until approximately 620°C with a latent heat capacity of 375–394 J·g−1. Furthermore, the PCM was found to have a thermal conductivity of approximately 160 W·m−1·K−1 in the temperature range of 100–500°C, which is significantly better than that of conventional sensible heat storage materials in terms of heat storage capacity and thermal conductivity