Highly thermally conductive and flexible phase change composites enabled by polymer/graphite nanoplatelet-based dual networks for efficient thermal management

Phase change materials (PCMs) have been widely used for passive thermal management and energy storage due to the high latent heat capacity near phase transition points. However, the low thermal conductivity and leakage issue are two long-standing bottlenecks in PCM-based heat-related applications. Although the state of the art can address one or both of these issues by synthesizing phase change composites (PCCs), it remains challenging to achieve high-performance PCCs with simultaneously superior thermal and mechanical properties and phase change behaviors. In this work, a new method is reported to prepare highly thermally conductive, flexible and leakage-proof PCCs by constructing dual polymer and graphite nanoplatelet networks as the functional matrix of PCMs. In the composites, paraffin wax serves as the PCM, the macromolecular olefin block copolymer (OBC) forms a cross-linked polymer network to enclose the molten PCM and endow the composite film with flexibility, and expanded graphite (EG) with a long-chain structure forms an aligned and interconnected graphite nanoplatelet percolation network to enable the high thermal conductivity of PCCs. The radial thermal conductivities reach 4.2-32.8 W m(-1)K(-1)at EG loadings of 5-40 wt%. The resultant flexible composite film shows efficient and reliable thermal management performance by lowering the working temperature of a commercial lithium-ion battery by more than 12 degrees C at high discharge rates. Our work provides an efficient and cost-effective route to synthesizing high-performance PCCs for various heat-related applications including the thermal harvesting of renewable energy, building energy management, thermal management of electronics,etc.