Showing papers by "Bing Ding published in 2015"

Absorption mechanism of carbon-nanotube paper-titanium dioxide as a multifunctional barrier material for lithium-sulfur batteries

Abstract: Lithium-sulfur batteries attract much interest as energy storage devices for their low cost, high specific capacity, and energy density. However, the insulating properties of sulfur and high solubility of lithium polysulfides decrease the utilization of active materials by the battery resulting in poor cycling performance. Herein, we design a multifunctional carbon-nanotube paper/titanium-dioxide barrier which effectively reduces active material loss and suppresses the diffusion of lithium polysulfides to the anode, thereby improving the cycling stability of lithium-sulfur batteries. Using this barrier, an activated carbon/sulfur cathode with 70% sulfur content delivers stable cycling performance and high Coulombic efficiency (∼99%) over 250 cycles at a current rate of 0.5 C. The improved electrochemical performance is attributed to the synergistic effects of the carbon nanotube paper and titanium dioxide, involving the physical barrier, chemical adsorption from the binding formation of Ti-S and S-O, and other interactions unique to the titanium dioxide and sulfur species.

Porous nitrogen and phosphorus co-doped carbon nanofiber networks for high performance electrical double layer capacitors

Abstract: In this work, phytic acid is used as the protonic acid dopant and soft template to synthesize 3D polyaniline (PANI) nanofiber networks. Then, the PANI nanofiber networks are transformed to porous nitrogen and phosphorus co-doped carbon nanofibers (P-NP-CNFs) by the carbonization and chemical activation process. P-NP-CNFs have a high specific surface area of 2586 m2 g−1 and a large pore volume of 1.43 cm3 g−1, which are favorable for enhancing the electrochemical performance of electrical double layer capacitors. Moreover, nitrogen and phosphorus doping in the carbon materials can increase the specific capacitance by a pseudocapacitive redox process. At a current density of 1 A g−1, P-NP-CNFs show a large specific capacitance of 280 F g−1 and a high specific capacitance retention of 94% after 10 000 cycles. In particular, phosphorus doping can broaden the electrochemical window to increase the energy density. Therefore, the energy density of symmetric capacitors based on P-NP-CNFs is up to 22.9 W h kg−1 at a power density of 325 W kg−1, demonstrating that P-NP-CNFs are superior electrode materials for electrical double layer capacitors.

Crumpled Nitrogen-Doped Graphene for Supercapacitors with High Gravimetric and Volumetric Performances

Abstract: Graphene is considered a promising electrochemical capacitors electrode material due to its high surface area and high electrical conductivity. However, restacking interactions between graphene nanosheets significantly decrease the ion-accessible surface area and impede electronic and ionic transfer. This would, in turn, severely hinder the realization of high energy density. Herein, we report a strategy for preparation of few-layer graphene material with abundant crumples and high-level nitrogen doping. The two-dimensional graphene nanosheets (CNG) feature high ion-available surface area, excellent electronic and ion transfer properties, and high packing density, permitting the CNG electrode to exhibit excellent electrochemical performance. In ionic liquid electrolyte, the CNG electrode exhibits gravimetric and volumetric capacitances of 128 F g–1 and 98 F cm–3, respectively, achieving gravimetric and volumetric energy densities of 56 Wh kg–1 and 43 Wh L–1. The preparation strategy described here provide...

Enhanced electrochemical performance of sulfur cathodes with a water-soluble binder

Abstract: To improve the electrochemical performance of lithium–sulfur batteries, LA132, a kind of polyacrylonitrile is used as a water-soluble binder for sulfur cathodes. The optimal content of LA132 binder is investigated by electrochemical tests and morphology characteristics. Galvanostatic charge–discharge tests show that sulfur cathodes with 5 wt% LA132 (relative to the mass of whole cathode materials) exhibit a significant improvement in discharge capacity and cycle performance compared with the ones using 10 wt% polyvinylidene fluoride (PVDF) and LA132. Cyclic voltammetry and electrochemical impedance spectroscopy confirm that the LA132 sulfur cathodes show lower resistance and better kinetic characteristics. The effect of LA132 binder is further investigated via visual pictures and scanning electron microscopy (SEM). The visual picture shows the decreased bond strength of PVDF caused by its swelling, leading to a loss of active materials from the current collector. The morphologies of sulfur cathodes before and after 100 cycles indicate that the non-swellable LA132 could stabilize porous structures of cathodes during cycling and enhance the electrochemical performance of sulfur cathodes.

Nanospace-confinement copolymerization strategy for encapsulating polymeric sulfur into porous carbon for lithium-sulfur batteries.

Abstract: Given their high theoretical energy density, lithium–sulfur (Li–S) batteries have recently attracted ever-increasing research interest. However, the dissolution of polysulfides and uncontrolled deposition of insoluble discharge product significantly hinder the cycling stability. Herein, a nanospace-confinement copolymerization strategy for encapsulating polymeric sulfur into porous carbon matrix is presented. The morphologies and sulfur contents of carbon/polymeric sulfur (C/PS) composites could be readily tailored by controlling the copolymerization time. Confining polymeric sulfur in the porous carbon with abundant interparticle pores facilitates rapid electronic/ionic transport and mitigates dissolution of polysulfides intermediates. More importantly, the organic sulfur units dispersed in the insoluble/insulating Li2S2/Li2S phase could prevent its irreversible deposition. Such nanostructure with tailored chemistry property permits the C/PS electrodes to exhibit enhanced cycling stability and high rate ...

General Strategy to Fabricate Ternary Metal Nitride/Carbon Nanofibers for Supercapacitors

Abstract: In this work, ternary metal nitrides are proposed as novel electrode materials for supercapacitors. We selectively fabricate ternary vanadium titanium nitride/carbon (VTiN/C) nanofibers through a facile electrospinning strategy and investigate their electrochemical performance for the first time. The obtained well-interconnected VTiN/C nanofibers with VTiN nanoparticles embedded into carbon ensure rapid electron/ion transfer and offer a highly ion-accessible surface. Appealingly, the VTiN-4/C nanofibers exhibit a greatly improved performance, with a high specific capacitance (430.7 F g−1, 0.5 A g−1) and a good rate capability. Furthermore, the performance of the VTiN/C nanofibers is found to be controllable by adjusting the V/Ti atomic ratio. The encouraging electrochemical performance suggests that ternary VTiN could be a promising electrode material for supercapacitors.