Decoupled Architectures Enabling Composite Phase Change Materials With Ultra‐High Thermal Conductivity and Thermal Effusivity for Thermal Shock Protection

The rapidly increasing power density poses serious thermal shock threats for integrated electronic devices and systems, spurring the development of thermal management materials with high thermal effusivity. At present, the thermal effusivity value of metals and carbon‐based materials with ultra‐high thermal conductivity is generally below 50 J cm −3\2 (msK) −1\2 . Phase change materials (PCMs) present a compelling solution for transient thermal management due to their unique ability to absorb substantial amounts of latent heat. However, the competition between the heat conduction and energy storage constitutes significant challenges for their thermal effusivity improvement. Inspired by sponge cities, a decoupled design strategy different from prevalent integrated concepts is proposed to separate the thermal conduction architecture from the encapsulation network, thereby effectively minimizing the filler‐matrix interfacial thermal resistance. The multi‐layer composite PCMs (MLPCM), fabricated by compounding expanded graphite (EG) film with high in‐plane thermal conductivity and EG/paraffin wax composite with high energy storage density, achieve a synchronous enhancement of thermal conductivity and thermal effusivity, reaching up to 91.38 W m −1 K −1 and 108.7 J cm −3\2 (msK) −1\2 , respectively. Additionally, the state‐of‐the‐art MLPCM exhibits exceptional electromagnetic interference shielding functionality. This strategy offers a cost‐effective pathway for fabricating high‐performance composite PCMs with outstanding thermal management efficiency.