Hierarchical porous carbon microtubes derived from willow catkins exhibited excellent electrochemical performances in both aqueous and organic electrolytes.

The intercalation pseudocapacitance which leads to the extraordinary charge storage properties has been confirmed as an intrinsic capactive property of orthorhombic Nb2O5 (T-Nb2O5) nanocrystals. However, the poor electronic conductivity of T-Nb2O5 nanocrystals may limit its electrochemical utilization and high-rate performance especially for thick electrodes with high mass loadings. To address this issue, we herein reported a hydrothermal-heat treatment method to anchor T-Nb2O5 nanocrystals on conductive graphene sheets, which forms a layer-by-layer integrated electrode with much shortened ion transport paths and results in excellent electrochemical capacitive properties, including high capacitance (626 C g -1 ), excellent rate handling and cyclic stability. Furthermore, asymmetric supercapacitors were constructed by using the high-rate response T-Nb2O5/graphene nanocomposite and mesoporous carbon as the negative and positive electrode, respectively. The asymmetric supercapacitor could deliver a high energy density of 16 Wh kg -1 at an unprecedented power density of 45 kW kg -1 (discharge time of 1.2 s). The outstanding power properties of the supercapacitors are mainly attributed to the improved high-rate Li-insertion/extraction capability of the T-Nb2O5/graphene electrode and appropriate pairing of mesoporous carbon electrode. Fig. 1 (a) Schematic diagram of the fabrication of the T-Nb2O5/graphene nanocomposites; (b) XRD patterns and (c) Raman spectra of GO, Nb2O5/rGO and T-Nb2O5/graphene.We report a simple hydrothermal and heat-treatment process to fabricate T-Nb2O5/graphene nanocomposite as a high-performance pseudocapactive materials. With the unique pairing of T-Nb2O5/graphene pseudocapactive material with mesoporous carbon electrodes, the asymmetrical supercapacitors show high energy and power densities, and excellent cycling performance.

Nitrogen-enriched mesoporous carbons (NMCs) were decorated with ultrafine La 2 O 3 nanoparticles via a simple wet impregnation method. The resulting composites with well developed mesoporous structures, high nitrogen content and uniform dispersions of La 2 O 3 nanoparticles served as scaffolds to house sulfur for high rate lithium-sulfur batteries. Apart from their on-site trapping of polysulfides, the La 2 O 3 nanoparticles decorated on the mesoporous carbon framework were also found to have a strong catalytic effect on sulfur reduction, offering high discharge voltages and fast electrochemical reaction kinetics. Combining the multiple effects of the well developed mesopores, nitrogen doping and La 2 O 3 nanoparticles, the resulting ternary NMC/La 2 O 3 /S nanocomposites can deliver an initial capacity of 1043 mA h g À1 at 1 C, which remains at 799 mA h g À1 after 100 cycles. Moreover, they still maintain ultrahigh rate capacities of 579 and 475 mA h g À1 at 3 C and 5 C, respectively, after 100 cycles. These encouraging results suggest that other metal oxides with suitable adsorption and catalytic abilities can be widely applied to decorate carbon frameworks for use in high rate lithium-sulfur systems.

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Using graphene oxide and a cobalt salt as precursor, a three-dimensional graphene aerogel with embedded Co3 O4 nanoparticles (3D Co3 O4 -RGO aerogel) is prepared by means of a solvothermal approach and subsequent freeze-drying and thermal reduction. The obtained 3D Co3 O4 -RGO aerogel has a high specific capacitance of 660 F g(-1) at 0.5 A g(-1) and a high rate capability of 65.1 % retention at 50 A g(-1) in a three-electrode system. Furthermore, the material is used as cathode to fabricate an asymmetric supercapacitor utilizing a hierarchical porous carbon (HPC) as anode and 6 M KOH aqueous solution as electrolyte. In a voltage range of 0.0 to 1.5 V, the device exhibits a high energy density of 40.65 Wh kg(-1) and a power density of 340 W kg(-1) and shows a high cycling stability (92.92 % capacitance retention after 2000 cycles). After charging for only 30 s, three CR2032 coin-type asymmetric supercapacitors in series can drive a light-emitting-diode (LED) bulb brightly for 30 min, which remains effective even after 1 h.

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