High-performance binary lithium hydrated salts-biochar composites for thermochemical energy storage

Thermochemical energy storage (TCES) offers an attractive pillar for sustainable energy future. Particularly inorganic salt hydrates which features by its high energy density, low heat loss, and long-term stability. However, challenges such as salt agglomeration, poor thermal conductivity and corrosion issues hinder its practical application. To address these challenges, this study introduces a novel composite material integrating biochar; a sustainable, porous carbon derived from biomass with binary lithium hydrated salt (LiOH·H2O and LiCl·H2O). The hierarchical porosity and thermal conductivity of biochar synergize with lithium salts to enhance water vapor diffusion, mitigate agglomeration and swelling, and improve heat transfer. The developed composites with different salt contents have improved thermophysical properties. In particular, 60LiOC@BC provides a thermal conductivity of 1.69 W/m·K and a high energy storage density of 1787 kJ/kg, confirming its promising potential for high-performance thermochemical energy storage. Hydration/dehydration cycles confirm robust stability of 60LiOC@BC, with no significant degradation over repeated cycles. Furthermore, biochar's matrix significantly reduces copper corrosion by reducing direct salt-metal interactions and promoting the formation of protective passivation layers. The optimization of salt ratios and the porous framework of biochar enable scalable TCES materials that balance energy storage density, durability, and cost-effectiveness. These findings highlight biochar-based lithium hydrated salts composites as a sustainable solution for solar energy storage and renewable integration in buildings.