Preparation and performance evaluation of a rock wool–based CaCl 2 composite for thermochemical heat storage applications

“Salt-in-matrix” composites are a promising class of materials for sorption-driven thermal energy storage, where the structural and chemical properties of the matrix strongly affect salt loading and heat storage performance. In this study, rock wool – a low-cost, fibrous mineral material – was employed as a macroporous matrix for calcium chloride (CaCl2) to develop a high-capacity composite adsorbent. By varying the CaCl2 solution concentration from 5% to 20%, the salt loading of the rock wool increased from 50% to 80.95%. The optimized composite (13RW–20%CaCl2) achieved a water uptake of 0.9 g g−1 under 20°C and 80% relative humidity, corresponding to a theoretical heat storage capacity of 2335.28 kJ kg−1. Fixed-bed reactor experiments demonstrated stable and repeatable hydration – dehydration behavior, with a peak discharge power of 10.26 kW m−3 and an overall energy output density of 79.61 kWh m−3 at an air flow rate of 2.5 m s−1. These results confirm that rock wool can serve as a robust and scalable host matrix for salt-based thermochemical heat storage. Unlike previous studies on rock wool composites, this work emphasizes the influence of matrix geometry and macroscopic dimensions on salt loading and sorption kinetics, providing new insights for optimizing material design and reactor configuration in large-scale thermal energy storage systems.