Prominent enhancement of stability under high current density of LiFePO4-based multidimensional nanocarbon composite as cathode for lithium-ion batteries.

A facile method for synthesizing carbon-coated lithium iron phosphate (LiFePO4, LFP) and an LFP-based multidimensional nanocarbon composite to enhance the electrochemical performance of lithium-ion batteries is presented herein. Three types of cathode materials are prepared: carbon-coated LFP (LC), carbon-coated LFP with carbon nanotubes (LC@C), and carbon-coated LFP with carbon nanotubes/graphene quantum dots (LC@CG). The electrochemical performances of the LC-nanocarbon composites are compared, and both LC@C and LC@CG show improved electrochemical performance than LC. Compared with both the LC and LC@C electrodes, the LC@CG electrode exhibits the highest specific capacity of 107.1 mA h g-1 under 20C of current density, as well as higher capacities and greater stability over all measured current densities. Moreover, after 300 charge-discharge cycles, the LC@CG electrode exhibits the best stability than the LC and LC@C electrodes. This is attributable to the graphene quantum dots, which enhance the morphological stability of the LC@CG electrode during electrochemical measurements. Our findings suggest that LFP-nanocarbon composites are promising as cathode materials and highlight the potential of graphene quantum dots for improving the stability of cathodes.

Liquid-phase exfoliation of expanded graphites into graphene nanoplatelets using amphiphilic organic molecules.

Graphenes with a two-dimensional lattice of carbons have been widely employed in diverse applications owing to their excellent electrical, thermal, mechanical, and gas-barrier properties. However, the frequently-used reduced graphene oxide (rGO), which is synthesized from natural graphites by strong oxidation and subsequent reduction via highly toxic components, exhibits imperfect characteristics because of remaining defect sites on its basal planes. Therefore, in this work, we present a convenient way to prepare graphene nanoplatelets (GNPs) with minimized defect sites on their basal planes employing liquid-phase exfoliation of edge-functionalized expanded graphites (EGs) with amphiphilic organic molecules. Exfoliated GNPs revealed approximately sub-7-nm-thickness and showed stable dispersibility in an organic media during 9 months. Furthermore, spray-coated GNP films presented homogeneously stacked morphologies without noticeable agglomerations.

Electrically conductive epoxy nanocomposites with expanded graphite/carbon nanotube hybrid fillers prepared by direct hybridization.

Carbon nanotubes (CNTs) are generally used to promote the electrical conductivity of the polymer nanocomposites. However, in spite of their superior properties, CNT's high cost has limited their commercial application, so far. Thus, the development of hybrid carbon nanomaterials (CNMs) composed of CNTs and cheaper CNMs such as carbon fibers (CFs), expanded graphites (EGs), and graphene nanoplatelets (GNPs) is important in terms of reducing the cost of CNT-based fillers. In this study, we prepared EG/CNT hybrid fillers via direct CNT synthesis on the EG support using modified combustion method and thermal chemical vapor deposition (CVD) method, and investigated the electrical conductivity of the expoxy nanocomposite with EG/CNT hybrid fillers. The epoxy nanocomposites with EG/CNT hybrid fillers at 20 wt% filler loading showed 260% and 170% electrical conductivity enhancement in comparison with the EG and the simply mixed EG and CNT fillers, respectively. Our approach provides various applications including electromagnetic interference (EMI) shielding materials, thermal interface materials (TIMs), and reinforced nanocomposites.

Carbon hybrid fillers composed of carbon nanotubes directly grown on graphene nanoplatelets for effective thermal conductivity in epoxy composites.

Carbon nanomaterials are generally used to promote the thermal conductivity of polymer composites. However, individual graphene nanoplatelets (GNPs) or carbon nanotubes (CNTs) limit the realization of the desirable thermal conductivity of the composite in both through- and in-plane directions. In this work, we present the thermal conductivity enhancement of the epoxy composite with carbon hybrid fillers composed of CNTs directly grown on the GNP support. The composite with 20 wt% hybrid filler loading showed 300% and 50% through-plane thermal conductivity improvements in comparison with the individual CNTs and GNPs, respectively. Moreover, it showed an enhanced thermal conductivity of up to 12% higher than that of the simply mixed GNP and CNT fillers. In more detail, hybrid fillers, whose CNTs were synthesized on the GNP support (Support C, Fe/Mo-MgO:GNP=1:0.456) for 60 min via chemical vapor deposition process, presented the highest through-plane thermal conductivity of 2.41 W m-1 K-1 in an epoxy composite.