Breaking the Thermal Conductivity-Latent Heat Trade-Off: Hierarchical Core-Shell Phase-Change Graphene Fiber Frameworks for Advanced Thermal Management.

The rapid miniaturization of electronic devices has exponentially increased power densities, making heat accumulation and transient thermal shocks primary bottlenecks. Phase-change thermal interface materials (PC-TIMs) offer a promising solution, but their application is hindered by low intrinsic thermal conductivity and liquid leakage. Furthermore, traditional outside-in impregnation strategies suffer from a severe trade-off between thermal conductivity enhancement and latent heat preservation. In this work, a hierarchical inside-out structural engineering strategy is proposed to fabricate a core-sheath phase-change graphene fiber framework (GFF@PEG). Coaxial wet-spinning densely encapsulates a polyethylene glycol (PEG) core within a graphene oxide shell. Subsequent vacuum impregnation and chemical reduction create a "thermal soldering" effect, bridging discrete fibers to convert resistive point-to-point contacts into surface-to-surface interconnections, establishing an unbroken 3D phonon transport highway. Thus, the GFF@PEG composite achieves an exceptional thermal conductivity of 77.67 W m-1 K-1 while preserving a latent heat capacity of ∼90 J g-1. Meanwhile, the robust graphene shell ensures near-zero leakage over 600 thermal cycles. In a simulated chip cooling system (20 W cm-2), it delivered a dramatic 60.7 °C temperature reduction. Ultimately, this fully enveloped paradigm circumvents traditional interfacial thermal barriers, providing a highly robust dual-mode thermal management solution for high-power electronics.