Abstract: Thermally conductive polymeric nanocomposite films have demonstrated great potential for battery thermal management (BTM). However, it has remained an enormous challenge to create low-cost, scalable, flexible, highly thermally conductive films capable of Joule heating performance due to a lack of rational material design strategies. Herein, an efficient approach is proposed to overcome this long-standing barrier via the strategy of welding carbon nanotubes on the graphene nanoplatelets’ surface (GNPs@CNTs) and the bionic lay-by-lay (LBL) assembly technique. The horizontally aligned continuous GNPs layers function as primary in-plane thermally conductive paths, minimizing the thermal resistance. Meanwhile, the secondary CNTs network interconnects the GNPs into an integrated and densified 3D thermally conductive framework. As results, the as-prepared nacre-inspired waterborne polyurethane (WPU) nanocomposite film presents outstanding thermally conductive performances (high in-plane thermal conductivity (λ) of 25.2 W m^-1 K^-1 and out-of-plane λ of 1.94 W m^-1 K^-1), ultralow cost (96.5 USD/kg), and excellent Joule heating performance (Joule-thermal response of 13.5 °C/s), which far outperforms previous thermal management counterparts. Also, the WPU nanocomposite film could achieve higher cooling and preheating efficiency for Li-ion battery compared to commercial counterpart products. This work provides a promising solution to create high-performance thermal management polymeric nanocomposite films, which hold great potential for BTM systems.

Key words: Thermal conductivity, Battery thermal management, Joule heating, Nacre-inspired, 3D framework