Densification of high-temperature solid-state phase change materials by cold sintering route

The eutectoid composition 79Li 2 SO 4 –21Na 2 SO 4 is investigated as a solid-state phase change material (PCM) for high-temperature thermal energy storage (TES) applications (450–500 °C). This work explores for the first time the application of the cold sintering process to enhance the densification as well as the thermophysical and mechanical performance of this eutectoid mixture. The influence of key cold sintering parameters, such as transient solvent content, applied pressure, temperature, and holding time, on microstructure, densification, thermal behaviour, and mechanical strength was systematically studied. Compared to conventional dry pressing at room temperature, cold sintering samples showed a significantly improvement in bulk density, leading to increased volumetric thermal storage density and mechanical robustness. Notably, Young's modulus increased by nearly one order of magnitude for the cold sintered samples, without compromising phase stability or thermal properties. These findings demonstrate that cold sintering is a viable, energy-efficient route to produce shape-stable, high-performant TES materials based on sulphate salts, paving the way for scalable solid-state latent heat storage systems with improved durability and energy density.