Showing papers by "Bing Ding published in 2013"

Sulfur embedded in metal organic framework-derived hierarchically porous carbon nanoplates for high performance lithium–sulfur battery

Abstract: The wide-scale implementation of lithium–sulfur batteries is limited by their rapid capacity fading, which is induced by the pulverization of the sulfur cathode and dissolution of intermediate polysulfides. Herein, we reported the encapsulation of sulfur (S) into hierarchically porous carbon nanoplates (HPCN) derived from one-step pyrolysis of metal-organic frameworks (MOF-5). HPCN with an average thickness of ca. 50 nm exhibits a three-dimensional (3D) hierarchically porous nanostructure, high specific surface area (1645 m2 g−1) and large pore volume (1.18 cm3 g−1). When evaluated as a cathode for lithium–sulfur batteries, the HPCN–S composite demonstrates high specific capacity and excellent cycling performance. At a current rate of 0.1 C, the initial discharge capacity of HPCN–S is 1177 mA h g−1. Even at a current rate of 0.5 C, it still delivers a discharge capacity of 730 mA h g−1 after 50 cycles and the Coulombic efficiency is up to 97%. The enhanced electrochemical performance of HPCN–S is closely related to its well-defined 3D porous plate nanostructure which not only provides stable electronic and ionic transfer channels, but also plays a key role as a strong absorbent to retain polysulfides and accommodate volume variation during the charge–discharge process.

Encapsulating Sulfur into Hierarchically Ordered Porous Carbon as a High-Performance Cathode for Lithium–Sulfur Batteries

Abstract: A three-dimensional (3D) hierarchical carbon-sulfur nanocomposite that is useful as a high-performance cathode for rechargeable lithium-sulfur batteries is reported. The 3D hierarchically ordered porous carbon (HOPC) with mesoporous walls and interconnected macropores was prepared by in situ self-assembly of colloidal polymer and silica spheres with sucrose as the carbon source. The obtained porous carbon possesses a large specific surface area and pore volume with narrow mesopore size distribution, and acts as a host and conducting framework to contain highly dispersed elemental sulfur. Electrochemical tests reveal that the HOPC/S nanocomposite with well-defined nanostructure delivers a high initial specific capacity up to 1193 mAh g(-1) and a stable capacity of 884 mAh g(-1) after 50 cycles at 0.1 C. In addition, the HOPC/S nanocomposite exhibits high reversible capacity at high rates. The excellent electrochemical performance is attributed exclusively to the beneficial integration of the mesopores for the electrochemical reaction and macropores for ion transport. The mesoporous walls of the HOPC act as solvent-restricted reactors for the redox reaction of sulfur and aid in suppressing the diffusion of polysulfide species into the electrolyte. The "open" ordered interconnected macropores and windows facilitate transportation of electrolyte and solvated lithium ions during the charge/discharge process. These results show that nanostructured carbon with hierarchical pore distribution could be a promising scaffold for encapsulating sulfur to approach high specific capacity and energy density with long cycling performance.

Chemically tailoring the nanostructure of graphene nanosheets to confine sulfur for high-performance lithium-sulfur batteries

Abstract: The commercialization of lithium–sulfur (Li–S) batteries has so far been limited by their rapid capacity fading, which is induced by dissolution of intermediate polysulfides and the pulverization of the sulfur cathode due to volume expansion. Herein, we reported an efficient strategy to confine active sulfur in chemically tailored graphene nanosheets, which were prepared via modified chemical activation of hydrothermal reduced graphene oxide hydrogels. Due to its high specific surface area, large pore volume, controllable size and distribution of nanopores, the two-dimensional (2D) highly porous activated graphene nanosheets (AGNs) were proved to be a promising scaffold to uniformly confine elemental sulfur (S) in their nanopores with high loading. The resultant AGNs/S nanocomposites exhibited a reversible capacity up to 1379 mA h g−1 at 0.2 C as well as remarkable cycling stability, which may contribute to the desirable structural features. The dense nanopores of AGNs, as “micro-reactors” for the electrochemical reactions of sulfur, minimized polysulfide dissolution and shuttling in the electrolyte, and also reserved fast transport of lithium ions to the sequestered sulfur by ensuring good electrolyte penetration. Furthermore, the AGNs with good electronic conductivity allowed good transport of electrons from/to the poorly conducting sulfur for electrochemical reactions at high rates.

Porous nitrogen-doped carbon nanotubes derived from tubular polypyrrole for energy-storage applications.

Abstract: Porous nitrogen-doped carbon nanotubes (PNCNTs) with a high specific surface area (1765 m2 g−1) and a large pore volume (1.28 cm3 g−1) have been synthesized from a tubular polypyrrole (T-PPY). The inner diameter and wall thickness of the PNCNTs are about 55 nm and 22 nm, respectively. This material shows extremely promising properties for both supercapacitors and for encapsulating sulfur as a superior cathode material for high-performance lithium–sulfur (Li-S) batteries. At a current density of 0.5 A g−1, PNCNT presents a high specific capacitance of 210 F g−1, as well as excellent cycling stability at a current density of 2 A g−1. When the S/PNCNT composite was tested as the cathode material for Li-S batteries, the initial discharge capacity was 1341 mAh g−1 at a current rate of 1 C and, even after 50 cycles at the same rate, the high reversible capacity was retained at 933 mAh g−1. The promising electrochemical energy-storage performance of the PNCNTs can be attributed to their excellent conductivity, large surface area, nitrogen doping, and unique pore-size distribution.

Advanced Energy‐Storage Architectures Composed of Spinel Lithium Metal Oxide Nanocrystal on Carbon Textiles

Abstract: Current battery technologies are known to suffer from kinetic problems associated with the solid-state diffusion of Li+ in intercalation electrodes materials. Not only the use of nanostructure materials but also the design of electrode architectures can lead to more advanced properties. Here, advanced electrode architectures consisting of carbon textiles conformally covered by Li4Ti5O12 nanocrystal are rationally designed and synthesized for lithium ion batteries. The efficient two-step synthesis involves the growth of ultrathin TiO2 nanosheets on carbon textiles, and subsequent conversion into spinel Li4Ti5O12 through chemical lithiation. Importantly, this novel approach is simple and general, and it is used to successfully produce LiMn2O4/carbon composites textiles, one of the leading cathode materials for lithium ion batteries. The resulting 3D textile electrode, with various advantages including the direct electronic pathway to current collector, the easy access of electrolyte ions, the reduced Li+/e− diffusion length, delivers excellent rate capability and good cyclic stability over the Li-ion batteries of conventional configurations.

Enhanced cycling performance and electrochemical reversibility of a novel sulfur-impregnated mesoporous hollow TiO2 sphere cathode for advanced Li-S batteries.

Abstract: A novel, designed sulfur-impregnated mesoporous hollow TiO2 sphere cathode with a 68 wt% S loading was efficiently tailored for advanced Li–S batteries, and yielded an intriguing capacity retention (71%) and a high coulombic efficiency (93%) over 100 cycles, at a 1 C rate.

Electrochemical reduction of graphene oxide and its electrochemical capacitive performance

Abstract: A convenient method for the production of graphene is developed using the electrochemical reduction of graphite oxide (GO) in solution without assembling it onto the electrode. The samples were examined by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy. The results show that the number of oxygen functional groups can be significantly decreased. The electrochemical capacitance of the prepared graphene after 8 h of reduction is 158.5 F g−1 at 0.5 A g−1, much higher than that of GO and carbon nanotubes. The mechanism for this reaction is also proposed in this paper.

Fabrication of a sandwich structured electrode for high-performance lithium–sulfur batteries

Abstract: Lithium–sulfur (Li–S) batteries are receiving intense interest because of their high theoretical energy density. However, rapid capacity fading is a significant problem facing its practical realization. Here we present the fabrication of a sandwich structured electrode by confining elemental sulfur in a TiO2 nanocrystal (3–5 nm) decorated graphene nanosheet host (graphene/TiO2). Elemental sulfur occupies the inter-particle mesopores of the TiO2 nanocrystal layer and is in intimate contact with the graphene. The sandwich structured graphene/TiO2/S electrode exhibits enhanced cycling stability with high specific capacity and high Coulombic efficiency. The enhanced electrochemical performance is highly related to the well-defined sandwich structure and the in situ formation of a mixed ionic/electronic conductor (LixTiO2). The sandwich structure could favor rapid diffusion of the electrolyte during the charge–discharge process. Pore absorption of the graphene/TiO2 host and the on-site adsorption of the TiO2 nanocrystals could alleviate the dissolution and shuttling of the polysulfides. More importantly, the in situ formed LixTiO2 works synergistically with the highly conductive graphene layer to facilitate easier Li+/e− transport. The sandwich structure plus the unique functions of the graphene/TiO2 host conceptually provide new opportunities to achieve the long-term cycling stability of a sulfur electrode.

Preparation and electrochemical performances of porous polypyrrole film by interfacial polymerization

Abstract: In this study, porous polypyrrole (PPy) film was synthesized by facile interfacial polymerization using ionic liquid as oxidant. The morphology of PPys changed from dense microspherical/nanospherical agglomerated structure to porous structure with the increasing concentration of the oxidant. The magnetic ionic liquid, 1-butyl-3-methylimidazolium tetrachloroferrate (Bmim[FeCl4]), played a major role of oxidant when the concentration was lower than 0.075M. As the concentration increased to 0.075M, the π–π interactions between pyrrole cations and iminazole ring of Bmim[FeCl4], as evidenced by Fourier transform infrared spectrometer results, may affect the packing of PPy chains and subsequently cause the formation of porous structure of PPys. Electrochemical performances showed that PPy with porous structure displayed the highest specific capacitance of 170 F/g at a current density of 2 A/g in 1M H2SO4 solution and a good capacitive behavior, which has potential application as supercapacitor materials. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Enhancing the electrochemical performance of Li1.2Ni0.2Mn0.6O2 by surface modification with nickel–manganese composite oxide

Abstract: Li-rich layered Li1.2Ni0.2Mn0.6O2 has been surface modified by nickel–manganese composite oxide (Ni0.5Mn1.5O x ) to serve as a novel cathode material with novel layered spinel structure for lithium-ion battery. The as-prepared Li1.2Ni0.2Mn0.6O2 before and after surface modification by Ni0.5Mn1.5O x as well as simply blended Li1.2Ni0.2Mn0.6O2 with spinel LiNi0.5Mn1.5O4, have been characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electronic microscopy, and differential scanning calorimetry. Electrochemical studies indicate that the Ni0.5Mn1.5O x surface modified Li1.2Ni0.2Mn0.6O2 with peculiar layered spinel character dramatically represented increased discharge capacity, improved cycling stability as well as excellent rate capability at high-voltage even up to 5.0 V.