Graphene/thermally expandable microsphere composite films with switchable thermal conductivity for intelligent...

Smart thermal management materials possess the ability to sense the surrounding environment and generate corresponding thermal responses. Unlike traditional materials, smart thermal management systems offer advantages such as lower operational energy consumption, the potential for passive or self-regulated operation, and the capability for active thermal control. Herein, depending on the characteristic expansion of thermally expandable microspheres (TEMs) upon heating, a polyvinyl alcohol (PVA)-based graphene composite film with an aligned structure for directional heat transfer was designed to achieve intelligent thermal management. Before the thermal expansion of the microspheres, the composite film (with 50 wt% graphene content) exhibited a high thermal conductivity of 17.61 W/(m·K). After thermal expansion, the thermal conductivity decreased significantly to 0.62 W/(m·K), achieving a thermal conductivity ratio of 28.4 (before-after R). In addition, when dealing with thermal runaway of pouch batteries, the composites can quickly transition from a "high thermal conductive state" to an "thermal insulating state", avoiding the expansion of the thermal runaway. This composite can respond to abnormal temperature changes in the external environment, and demonstrate significant potential for applications such as preventing thermal runaway in electronic components and batteries.