Interfacial-engineered 3D nano-carbon networks for synergistic enhancement of thermal–electrical transport and anisotropic heat dissipation

Despite recent advances in flexible thermal management materials, achieving simultaneous high thermal conductivity (k) and mechanical flexibility remains fundamentally challenging. A bioinspired method is demonstrated through the design of sandwich-structured cellulose nanofiber (CNF) composite films incorporating high-loading functionalized graphene nanosheets (GNS) and carbon nanospheres (CSs). CNF-GNS-MWCNT/CMC-CS/CNF-GNS-MWCNT composite (CNFGs) films are prepared by vacuum-assisted assembly followed by thermal lamination and show sandwich-like composite structure. In this composite film, a continuous three-dimensional thermal/conductive network—where vertically aligned CSs bridge horizontally organized GNS layers—is constructed, achieving superior in-plane/through-plane k (10.63/3.02 W/m·K) and efficient thermal management capabilities, effectively mitigating heat accumulation in practical applications (e.g., reducing LED chip temperatures by ∼23 °C). Furthermore, the superior Joule heating performance of CNFGs is demonstrated due to their high electrical conductivity (σ, 762 S/m in-plane; 265 S/m through-plane), with a saturated temperature of 113 °C achieved at 2.8 V, highlighting their potential for advanced thermal management and electrothermal conversion applications. Concurrently, thanks to surface-functionalized GNS/CS serving as dynamic anchoring sites for CNF chains, the composite films achieve long-range interconnectivity, retaining excellent mechanical flexibility (∼3.5 % elongation at break at 60 wt%, approaching pure CNF) while preserving over 97 % of the original k even after 1000-fold folding cycles. This work presents a simple yet effective strategy for designing high-performance flexible conductive/heat conduction polymer composites, offering new insights into interface-engineered carbon-based hybrid materials for next-generation electronics and energy devices.