Development of a new kaolinite/phase change material (PCM) composite for latent heat thermal energy storage in building applications

• First successful encapsulation of Glauber’s salt into kaolinite matrix. • Achieved 1.94 W/m·K thermal conductivity via in-situ ball milling . • Latent heat of 44.25 J/g with < 8 % loss over 50 cycles. • In-situ method prevents leakage and enhances durability. • Cost-effective synthesis using abundant, low-cost raw materials. Thermal energy storage (TES) systems utilizing phase change materials (PCMs) are essential for sustainable energy strategies. However, large-scale implementation of PCMs is limited by leakage during phase transitions, low thermal conductivity , and poor cycling stability. This study presents a scalable mechanochemical approach to synthesize kaolinite/Glauber’s salt (Na 2 SO 4 ·10H 2 O) composites using both in-situ and ex-situ methods, effectively addressing these challenges. The in-situ method integrates ball milling and PCM encapsulation, achieving a thermal conductivity of 1.94 W/m·K at 65 % PCM content 1.6 times higher than ex-situ samples and three times that of conventional kaolinite-based PCMs while completely preventing leakage at PCM contents ≤ 30 %. Comprehensive structural and thermal characterizations (SEM, XRD, FTIR, DSC, and LFA) confirm interlayer expansion of 7.79 Å, enabling stable PCM encapsulation. A latent heat capacity of 44.25 J/g (NCM15) surpasses commercial paraffin PCMs. Long-term cycling tests show moderate thermal stability over 50 cycles, with < 8 % loss in capacity. Suppressed supercooling (ΔT < 5 °C) further ensures reliable phase transitions.