Carnallite granules: Unlocking the future of low-cost, high-performance thermochemical storage

Efficient, durable, and cost-effective thermochemical heat storage is essential for advancing renewable energy utilization and waste heat recovery. This study introduces millimeter-sized, semi-spherical granules of potassium carnallite ( ), an abundant and low-cost double salt of magnesium chloride (MgCl 2 ), as a promising material for long-term thermal energy storage in large-scale fixed-bed systems. Unlike MgCl 2 , which suffers from hydrolysis, material degradation, and over-hydration at moderate humidity levels, carnallite demonstrates remarkable stability, resisting liquefaction and hydrolysis under operational conditions. Comprehensive analysis confirms that the granules maintain good structural integrity during cycling, although measurable inter-particle agglomeration is observed, with no phase segregation or loss of chemical homogeneity. In cyclic tests conducted under controlled charging and discharging conditions, carnallite achieves a gravimetric energy density exceeding 470 kJ kg −1 and a volumetric power density of 95 kW m −3 . Notably, the material retains over 90 % of its initial capacity after fifteen consecutive cycles, significantly outperforming MgCl 2 , which exhibits substantial degradation under similar conditions. These findings highlight carnallite’s exceptional potential as a stable, high-performance candidate for scalable thermochemical heat storage systems. Further research into enhancing particle durability will unlock its full potential for large-scale energy storage applications.