Revolutionizing Thermochemical Adsorption Heat Storage: An MgSO4/MgCl2/MEG Composite Prepared by the Ball Milling Method for Efficient and Stable Low-Temperature Heat Storage

Efficient and sustainable low-temperature energy storage are essential for thermochemical adsorption heat storage materials. This study introduces a novel thermochemical heat storage material prepared using the ball milling method for the first time. The optimised Mix@EG10 material, comprising MgSO4/MgCl2 and hydrophilic-modified expanded graphite, demonstrated excellent comprehensive performance. It exhibited a thermal storage density of 1142 kJ/kg, thermal conductivity of 2.53 W/(m·K), retained 84.5% of its initial heat storage capacity after 40 cycles, and the single-cycle stability drop rate was low (up to 0.3857%). The desorption temperature of Mix@EG10 prepared by ball milling was only 100.2 °C, which was 32.4 °C and 19.3 °C lower than those of the mixture of two salts without expanded graphite and the same material prepared by impregnation (132.6 °C and 119.5 °C, respectively). This decrease was attributed to the ball milling process, which modified the microstructure, enhanced active sites, and reduced the reaction activation energy to 64.8 kJ/mol—a decrease of 46.2% and 79.2% compared to pure MgSO₄ and MgCl₂, respectively. The simulation parameters used in this study were measured for each composite. Numerical simulations validate the material's practicality, demonstrating a maximum instantaneous exothermic power of 116.7 W and volumetric energy storage density of 237.2 kWh/m³. This study highlights the significant potential of ball-milled composite materials for advancing low-temperature heat storage applications, such as solar energy and industrial waste heat recovery.