A study on correlation between volumetric salt content and hydration kinetics of vermiculite-CaCl2 composites via variable preparation methods

Thermochemical energy storage (TCES) based on salt hydrates offers high energy density and negligible standby thermal losses, but deployment is often constrained by a fundamental trade-off: increasing volumetric energy storage density can intensify vapour-transport limitations and slow hydration. This study establishes volumetric salt content as a unifying design parameter for CaCl 2 -vermiculite composites and quantifies its relationship with hydration kinetics. Atmospheric impregnation and vacuum-assisted impregnation are used deliberately to achieve volumetric salt contents of approximately 0.02 g cm −3 to 0.16 g cm −3 ; density measurements, SEM-EDX, and mercury intrusion porosimetry characterize how salt deposition and pore restructuring modify vapour transport pathways. Static sorption tests across two relative-humidity levels (33% and 53%) show that intrinsic hydration kinetics decrease systematically with increasing volumetric salt content and follow a humidity-corrected power-law relationship (coefficient of determination R 2 = 0 . 9319 ). Packed-bed experiments confirm that higher volumetric salt content yields higher and more sustained temperature rise under flowing-air conditions. In addition, at 40 wt% solution concentration, vacuum-assisted impregnation produces approximately 2.6 times higher volumetric salt content than atmospheric impregnation and delivers a larger sustained temperature rise. The proposed correlation provides a practical basis for selecting preparation conditions that balance volumetric capacity and power delivery in building applications. • Preparation route tunes pore structure and volumetric salt content. • Volumetric salt content correlates systematically with hydration kinetics. • Higher salt content yields higher and sustained temperature rise. • Preparation balances volumetric capacity and power delivery.