Mechanically Robust Phase‐Change Multiscale‐Architected Metastructures Integrating Asymmetric MXene/T‐CNF Aerogel for Thermal Energy Storage and Electromagnetic Interference Shielding

Abstract The rapid advancement of high‐power, miniaturized, and integrated electronic and energy storage systems necessitates multifunctional interfaces capable of simultaneously providing thermal management, electromagnetic interference (EMI) shielding, and mechanical robustness. Phase change materials (PCMs) offer substantial latent heat storage to mitigate overheating and overcooling but suffer from leakage and interfacial instability during liquid‐solid phase transitions. Conversely, MXene‐based composites exhibit high thermal conductivity and EMI shielding yet remain mechanically fragile and have limited thermal energy storage capacity. Here, a structurally engineered multiscale metastructure that integrates an octet‐truss (OT) framework is introduced, an asymmetric MXene/TEMPO‐oxidized cellulose nanofiber (T‐CNF) aerogel (MXA), and n‐eicosane (EC) as the PCM (OT‐MXA‐EC). The OT framework significantly enhances mechanical resilience, effectively stabilizing the composite during phase transitions. Meanwhile, the anisotropically aligned MXene aerogel facilitates directional heat transport, suppresses PCM leakage, and augments EMI shielding. The composite demonstrates superior active thermal regulation and thermal buffering, prolonging heat release or delaying temperature rise, thereby maintaining temperatures within a stable operating range. This multifunctional, multiscale architecture overcomes key limitations of PCM‐based composites, enabling their application in advanced electronic and energy systems, including wearable devices, autonomous technologies, and future mobility, where integrated thermal, mechanical, and electrical functionality is essential.