Development of a Hydrated Salt‐Based Composite Phase Change Material With Ultrahigh Flexibility, Flame Retardancy, and Electrical Insulation

ABSTRACT Hydrated salt phase change materials have attracted significant attention in thermal energy storage due to their high energy storage density, superior thermal conductivity, non‐flammability, and cost‐effectiveness. However, inherent limitations including leakage susceptibility, rigidity, and electrical conductivity hinder their practical applications. This study proposes a dual‐encapsulation strategy combining rigid adsorbent fillers with flexible coating layers to effectively address these challenges. Specifically, expanded graphite (EG) with hierarchical porous structures is first employed to encapsulate hydrated salts through capillary adsorption, forming the primary leakage‐proof framework. Subsequently, styrene‐butadiene rubber (SBS) is uniformly integrated with the EG‐hydrated salt composite and cured to establish a secondary protective layer, achieving simultaneous flexibility enhancement and electrical insulation. At a 30 wt% SBS content, the composite simultaneously exhibited a latent heat of 125.16 J·g −1 , achieved an elongation at break exceeding 420%, and attained the UL‐94 V‐0 flammability rating. Notably, it demonstrates remarkable electrical insulation (volume resistivity > 10 5 Ω·cm). Within simulated building thermal environments, the composite effectively mediates thermal energy storage and release, thereby attenuating indoor temperature fluctuations and demonstrating its capability for passive thermal management. This material far exceeds traditional paraffin‐based phase change materials in both safety and economy, highlighting its potential as a next‐generation thermal regulation material for sustainable energy systems.