ABSTRACT
Graphene-based thermally conductive composites have been proposed as effective thermal management materials for cooling high-power electronic devices. However, when flexible graphene nanosheets are assembled into macroscopic thermally conductive composites, capillary forces induce shrinkage of graphene nanosheets to form wrinkles during solution-based spontaneous drying, which greatly reduces the thermal conductivity of the composites. Herein, graphene nanosheets/aramid nanofiber (GNS/ANF) composite films with high thermal conductivity were prepared by in-plane stretching of GNS/ANF composite hydrogel networks with hydrogen bonds and π-π interactions. The in-plane mechanical stretching eliminates graphene nanosheets wrinkles by suppressing inward shrinkage due to capillary forces during drying and achieves a high in-plane orientation of graphene nanosheets, thereby creating a fast in-plane heat transfer channel. The composite films (GNS/ANF-60 wt%) with eliminated graphene nanosheets wrinkles showed a significant increase in thermal conductivity (146 W m-1 K-1) and tensile strength (207 MPa). The combination of these excellent properties enables the GNS/ANF composite films to be effectively used for cooling flexible LED chips and smartphones, showing promising applications in the thermal management of high-power electronic devices.
ABSTRACT
We propose an efficient strategy based on the electrospinning technique combined with multi-dimensional fillers to fabricate composites with well-established thermal pathways. A bridge-type structure is constructed in the composite fibers by integrating 1D boron nitride nanofibers and 2D boron nitride nanosheets, which can accelerate the formation of a valid thermal network, thereby the BNNS/BNNF/polyacrylonitrile (bsf) composites perform better than the BNNS/polyacrylonitrile (bs) composites. This strategy can be extended to the preparation of other electrospun 1D/2D nanofiller/polymer composite fiber films.
ABSTRACT
Exploring porous nano-structured materials has great significance for energy storage equipment. The metal-organic frameworks (MOFs) can be used as the outstanding sacrificial templates for electrode material of high performance supercapacitors due to their superior features that high specific surface area and tunable pore size distribution. However, the poor conductivity of MOFs is one of the biggest barriers to achieve high rate capacity and stable cycling performance. Herein, MOFs derived NiCo-layered double-hydroxide (NiCo-LDH) and nitrogen-doped carbon nanosheets (NC) on the flexible carbon nanotubes (CNTs) film are rationally designed, both of which as the binder-free electrodes can greatly improve the specific surface area and reaction sites. An asymmetric supercapacitor based on porous NiCo-LDH nanosheets on CNTs (CNT@NiCo-LDH) as the positive electrode and the NC nanosheets on carbon nanotubes film (CNT@NC) as the negative electrode exhibits the maximum energy density of 37.4â¯Wâ¯h/kg at the power density of 750â¯W/kg, as well as a long-term cycling stability (94.5% capacity retention after 5000 cycles). Rationally design such combination is a meaningful process for energy storage equipment with excellent electrochemical performance.
