Printable solid-gel change composite materials with high latent heat, enhanced shape stability and combustion safety for efficient thermal management

Phase-change materials (PCM) provide large latent heat but often suffer melting-induced leakage and poor processability. Organic phase-change materials such as polyethylene glycol are attractive for energy storage, yet they lose shape and leak after melting. We introduce a solid - gel change strategy that confines molten polyethylene glycol with an ultralow-loading aramid nanofiber and MXene network. High-aspect-ratio aramid nanofibers at 1 wt% form hydrogen bonds with two-dimensional MXene at 2 wt%. The resulting crosslinked skeleton transforms the phase-change material into a shear-thinning gel above about 65 °C. This design retains high energy density with polyethylene glycol loading of 97 wt% and a latent heat of about 158.4 J g⁻¹. Liquid leakage is reduced to around 1.8 wt%. Thermal conductivity increases by nearly five times compared with pure polyethylene glycol. The composite shows high-temperature shape stability, suppressed burning-drip behavior, efficient photothermal conversion, and reversible self-healing and reprocessing. The gel state also enables direct-write printing of customized geometries. Minimal additive content preserves latent heat while adding multifunctionality. This solid - gel change approach reconciles high energy density, thermal transport, safety, and manufacturability for next-generation thermal management.