Soft Elastic, Thermally Conductive, Electrically Insulating h‐BN@EGaIn/Ecoflex Composites as Encapsulation and Thermal Interface Materials Applicated in Wearable Electronics

Abstract Thermal management is crucial in advanced wearable electronics, especially those with high integration and miniaturization, or incorporating self‐powered systems utilizing body heat. However, the low thermal conductivity of traditional silicone rubber encapsulation presents a major challenge to thermal management in wearable electronics. In this study, hexagonal boron nitride@Eutectic Gallium‐Indium/Ecoflex (h‐BN@EGaIn/Ecoflex) composites, a soft elastic material is developed that is thermally conductive yet electrically insulating, capable of serving as encapsulation and thermal interface materials in wearable devices. The key of successfully designing h‐BN@EGaIn/Ecoflex composites with such thermal, mechanical, and electrical properties is the anchoring of EGaIn on the h‐BN surface. Also, there exists a trade‐off in thermal‐electrical and thermal‐mechanical properties of the composites during the preparation of h‐BN@EGaIn hybrid fillers and their incorporation into the Ecoflex elastomer. In application demonstrations, through replacing the polydimethylsiloxane supporting layer with h‐BN@EGaIn/Ecoflex composites, a 20 K operation temperature decrease is observed in a wearable light‐emitting diode lamp. In addition, the output of a wearable thermoelectric generator encapsulated with h‐BN@EGaIn/Ecoflex composites increases by 100% compared to that encapsulated by Ecoflex. These results clearly show the benefits of substituting h‐BN@EGaIn/Ecoflex for silicon rubber encapsulation in wearable electronics.