Hongmei Kang

The effect of annealing on a 3D SnO2/graphene foam as an advanced lithium-ion battery anode

3D annealed SnO2/graphene sheet foams (ASGFs) are synthesized by in situ self-assembly of graphene sheets prepared by mild chemical reduction. L-ascorbyl acid is used to effectively reduce the SnO2 nanoparticles/graphene oxide colloidal solution and form the 3D conductive graphene networks. The annealing treatment contributes to the formation of the Sn-O-C bonds between the SnO2 nanoparticles and the reduced graphene sheets, which improves the electrochemical performance of the foams. The ASGF has features of typical aerogels: low density (about 19 mg cm−3), smooth surface and porous structure. The ASGF anodes exhibit good specific capacity, excellent cycling stability and superior rate capability. The first reversible specific capacity is as high as 984.2 mAh g−1 at a specific current of 200 mA g−1. Even at the high specific current of 1000 mA g−1 after 150 cycles, the reversible specific capacity of ASGF is still as high as 533.7 mAh g−1, about twice as much as that of SGF (297.6 mAh g−1) after the same test. This synthesis method can be scaled up to prepare other metal oxides particles/ graphene sheet foams for high performance lithium-ion batteries, supercapacitors, and catalysts, etc.

Ionic Conductivity and Air Stability of Al-Doped Li7La3Zr2O12 Sintered in Alumina and Pt Crucibles

Li7La3Zr2O12 (LLZO) is a promising electrolyte material for all-solid-state battery due to its high ionic conductivity and good stability with metallic lithium. In this article, we studied the effect of crucibles on the ionic conductivity and air stability by synthesizing 0.25Al doped LLZO pellets in Pt crucibles and alumina crucibles, respectively. The results show that the composition and microstructure of the pellets play important roles influencing the ionic conductivity, relative density, and air stability. Specifically, the 0.25Al-LLZO pellets sintered in Pt crucibles exhibit a high relative density (∼96%) and high ionic conductivity (4.48 × 10(-4) S cm(-1)). The ionic conductivity maintains 3.6 × 10(-4) S cm(-1) after 3-month air exposure. In contrast, the ionic conductivity of the pellets from alumina crucibles is about 1.81 × 10(-4) S cm(-1) and drops to 2.39 × 10(-5) S cm(-1) 3 months later. The large grains and the reduced grain boundaries in the pellets sintered in Pt crucibles are favorable to obtain high ionic conductivity and good air stability. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy results suggest that the formation of Li2CO3 on the pellet surface is probably another main reason, which is also closely related to the relative density and the amount of grain boundary within the pellets. This work stresses the importance of synthesis parameters, crucibles included, to obtain the LLZO electrolyte with high ionic conductivity and good air stability.

Electro-active shape memory composites enhanced by flexible carbon nanotube/graphene aerogels

In this manuscript we present a novel, shape memory aerogel/epoxy composite structure composed of a reduced carbon nanotube and graphene compound aerogel as a scaffold and epoxy resin as a matrix. The composite was prepared via a vacuum infusion method and to the best of our knowledge it represents the first instance of a shape memory effect directly driven by an electrical field observable in polymer-infused conductive carbon scaffolds. Furthermore, the composite material obtained displays a high conductivity (i.e., up to 5.2 S m−1). In the manuscript it is shown that the composites high conductivity can be attributed to the built-in 3D network of the thermally reduced graphene and carbon nanotube compound aerogel which displays high conductivity (16 S m−1) coupled with low density (6 mg mL−1). The composite material presented in this work is likely a suitable candidate for applications requiring polymer-infused conductive aerogels such as electromagnetic shielding, actuators and thermal sensors.

3D composites of layered MoS2 and graphene nanoribbons for high performance lithium-ion battery anodes

3D composites of layered MoS2 and interconnected graphene nanoribbons (GNRs) are synthesized by a facile one-pot hydrothermal method. During the synthesis process, the GNRs self-assemble into conductive bridges between the MoS2 layers to form 3D structures that exhibit large specific capacity, good cycling stability and rate capability. Specifically, the composites exhibit a specific capacity of 1009.4 mA h g−1 at 200 mA g−1 after 80 cycles of the cycling test. They also exhibit a specific capacity of 606.8 mA h g−1 at 3 A g−1 in the rate capability test. In comparison, the bare MoS2 nanoparticles exhibit a specific capacity of 139.8 mA h g−1 at 200 mA g−1 after 80 cycles of the cycling test and 37.4 mA h g−1 at 3 A g−1 in the rate capability test. The structure, morphology and chemical analysis show that the superiority of the 3D structure is due to the large surface area and abundant mesopores that render a high contact area between the electrode and electrolyte. Moreover, the synergistic effects between the 2D MoS2 layers and the 1D GNRs within the 3D structures enable fast Li ion and electron transportation, inhibit the self-aggregation of MoS2 nanosheets, and accommodate the volume expansion to gain cycling stability and rate capacity.

Slow Down Dewetting in Polymer Films by Isocyanate-treated Graphite Oxide

Isocyanate-treated graphite oxides (iGOs) were well-dispersed into the polystyrene (PS) thin films and formed a novel network structure. With control in fabrication, an iGOs-web layer was horizontally embedded near the surface of the films and thus formed a composite slightly doped by iGOs. This work demonstrated that the iGOs network can remarkably depress the dewetting process in the polymer matrix of the composite, while dewetting often leads to rupture of polymer films and is considered as a major practical limit in using polymeric materials above their glass transition temperatures (Tg). Via annealing the 50–120 nm thick composite and associated neat PS films at temperatures ranging from 35 °C to 70 °C above Tg, surface morphology evolution of the films was monitored by atomic force microscopy (AFM). The iGOs-doped PS exhibited excellent thermal stability, i.e., the number of dewetting holes was greatly reduced and the long-term hole growth was fairly restricted. In contrast, the neat PS film showed serious surface fluctuation and a final rupture induced by ordinary dewetting. The method developed in this work may pave a road to reinforce thin polymer films and enhance their thermal stability, in order to meet requirements by technological advances.