A Flexible Thermal Interface Material as the Heat Switch for Solid‐State Cooling

Abstract The development of miniaturized, high‐integrated, and powerful electronic devices needs optimized thermal management solutions that enable active heat flow switching without moving components – a functionality that goes beyond the conventional thermal interface material (TIM). In this work, a flexible composite TIM is developed that enables magnetic field‐triggered direction change of heat flow, namely, the TIM acts effectively as a thermal switch. The material consists of liquid metal@nickel (LM@Ni) networks and diamond microparticles embedded in a polydimethylsiloxane (PDMS) matrix. The LM@Ni achieves both enhanced wettability on PDMS and magnetic responsiveness, while diamond provides the composite with high intrinsic thermal conductivity (13.92 W m ⁻¹ K ⁻¹ ). Upon applying a magnetic field, the composite undergoes a rapid deformation, creating an “on” or “off” state with a switching ratio of 22. By integrating the material with elastocaloric components, all‐solid‐state elastocaloric cooling cycles are successfully realized, which achieves cooling power of 81 W m ⁻² and heating power of 77 W m ⁻² . This work not only extends the application of TIM, but also bridges compact solid‐state cooling with efficient thermal management, establishing a new paradigm for TIM in smart thermal management applications.