Showing papers by "Bing Ding published in 2016"

PAA/PEDOT:PSS as a multifunctional, water-soluble binder to improve the capacity and stability of lithium–sulfur batteries

Abstract: Lithium–sulfur (Li–S) batteries as lithium secondary batteries have drawn tremendous interest due to their high theoretical specific capacity and energy density. However, the low practical specific capacity and poor cycling life keep them from large scale usage. Herein, a novel binder based on a mixture of polyacrylic acid (PAA) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is designed to significantly improve the specific capacity and cycling stability of Li–S batteries via the synergistic effect of the different functional groups. The conductive PEDOT:PSS successfully facilitates electron transfer and prevents polysulfide dissolution. PAA improves the solvent system for sulfur cathodes and promotes lithium-ion transfer. The sulfur cathode with PAA/PEDOT:PSS binder in a ratio of 2:3 exhibits an initial specific capacity of 1121 mA h g−1 and 830 mA h g−1 after 80 cycles at 0.5C. The electrochemical performance of the sulfur cathode with the composite binder is better than either of the single-component binders.

Effect of Graphene Modified Cu Current Collector on the Performance of Li4Ti5O12 Anode for Lithium-Ion Batteries

Abstract: Interface design between current collector and electroactive materials plays a key role in the electrochemical process for lithium-ion batteries. Here, a thin graphene film has been successfully synthesized on the surface of Cu current collector by a large-scale low-pressure chemical vapor deposition (LPCVD) process. The modified Cu foil was used as a current collector to support spinel Li4Ti5O12 anode directly. Electrochemical test results demonstrated that graphene coating Cu foil could effectively improve overall Li storage performance of Li4Ti5O12 anode. Especially under high current rate (e.g., 10 C), the Li4Ti5O12 electrode using modified current collector maintained a favorable capacity, which is 32% higher than that electrode using bare current collector. In addition, cycling performance has been improved using the new type current collector. The enhanced performance can be attributed to the reduced internal resistance and improved charge transfer kinetics of graphene film by increasing electron c...

Self-Sacrificial Template-Directed Synthesis of Metal-Organic Framework-Derived Porous Carbon for Energy-Storage Devices

Abstract: Metal–organic framework (MOF)-derived carbon materials exhibit large surface areas, but dominant micropore characteristics and uncontrollable dimensions. Herein, we propose a self-sacrificial template-directed synthesis method to engineer the porous structure and dimensions of MOF-derived carbon materials. A porous zinc oxide (ZnO) nanosheet solid is selected as the self-sacrificial template and two-dimensional (2D) nanostructure-directing agent to prepare 2D ZIF-8-derived carbon nanosheets (ZCNs). The as-prepared ZCN materials exhibit a large surface area with hierarchical porosity. These intriguing features render ZCN materials advanced electrode materials for electrochemical energy-storage devices, demonstrating large ion-accessible surface area and high ion-/electron-transport rates. This self-sacrificial template-directed synthesis method offers new avenues for rational engineering of the porous structure and dimensions of MOF-derived porous carbon materials, thus exploiting their full potential for electrochemical energy-storage devices.

A two-step etching route to ultrathin carbon nanosheets for high performance electrical double layer capacitors

Abstract: Two-dimensional (2D) carbon materials have attracted intense research interest for electrical double layer capacitors (EDLCs) due to their high aspect ratio and large surface area. Herein, we propose an exfoliation-chlorination route for preparing ultrathin carbon nanosheets by using ternary layered carbide Ti3AlC2 as the precursor. Due to the large intersheet space of exfoliated layered carbide (MXene), the as-prepared carbon nanosheets exhibit a thickness of 3-4 nm and a large specific surface area of 1766 m(2) g(-1) with hierarchical porosity. These features significantly improve the ion-accessible surface area for charge storage and shorten the ion transport length in the thin dimension. As a result, the carbon nanosheets show a high specific capacitance (220 F g(-1) at 0.5 A g(-1)), remarkable high power capability (79% capacitance retention at 20 A g(-1)) when measured in a symmetrical two-electrode configuration in an aqueous electrolyte. The method described in this work provides a new route to prepare 2D electrode materials from a bulk precursor, thus exploiting their full potential for EDLCs.

Excellent cycling stability and superior rate capability of a graphene–amorphous FePO4 porous nanowire hybrid as a cathode material for sodium ion batteries

Abstract: A porous nanowire material consisting of graphene-amorphous FePO4 was investigated as an advanced cathode material for sodium ion batteries for large-scale applications. This hybrid cathode material showed excellent cycling performance and superior rate capability, which were attributed to the porous nanowire structure and the existence of graphene.

Nanospace-confined synthesis of oriented porous carbon nanosheets for high-performance electrical double layer capacitors

Abstract: Two-dimensional (2D) carbon nanosheets have emerged as an attractive candidate for electrical double layer capacitors (EDLCs) due to their large specific surface area, good electrical conductivity and high charge mobility. However, the easy aggregation nature of nanosheets hinders rapid transport of electrolyte ions, reducing the ion-accessible area and restricting the ion transportation. Herein, we propose a template strategy for preparing three-dimensional (3D) porous carbon nanosheets (PCNs) with an oriented and interconnected nanostructure. Zinc layered hydroxide nitrate is used as a layered template and provides a nanospace to confine the carbonization process of the organic carbon precursor (gallic acid). The unique nanostructure and large surface area of chemically activated PCNs (aPCNs) significantly shorten the ion transport length in low dimensions and improve the electrolyte wettability and ion accessible surface area for charge storage. The aPCNs exhibit excellent performance as demonstrated by their large specific capacitance (327 F g−1 at a current density of 0.5 A g−1), superior rate capability (retaining 60.2% at 20 A g−1) and stable cyclability. In particular, the assembled symmetric device based on aPCNs delivers an energy density as high as 10.2 W h kg−1 at a power density of 301 W kg−1.

Facile Synthesis of Nitrogen-Containing Mesoporous Carbon for High-Performance Energy Storage Applications.

Abstract: Porous carbon with high specific surface area (SSA), a reasonable pore size distribution, and modified surface chemistry is highly desirable for application in energy storage devices. Herein, we report the synthesis of nitrogen-containing mesoporous carbon with high SSA (1390 m(2) g(-1)), a suitable pore size distribution (1.5-8.1 nm), and a nitrogen content of 4.7 wt % through a facile one-step self-assembly process. Owing to its unique physical characteristics and nitrogen doping, this material demonstrates great promise for application in both supercapacitors and encapsulating sulfur as a superior cathode material for lithium-sulfur batteries. When deployed as a supercapacitor electrode, it exhibited a high specific capacitance of 238.4 F g(-1) at 1 A g(-1) and an excellent rate capability (180 F g(-1), 10 A g(-1)). Furthermore, when an NMC/S electrode was evaluated as the cathode material for lithium-sulfur batteries, it showed a high initial discharge capacity of 1143.6 mA h g(-1) at 837.5 mA g(-1) and an extraordinary cycling stability with 70.3% capacity retention after 100 cycles.

Interconnected core–shell pyrolyzed polyacrylonitrile@sulfur/carbon nanocomposites for rechargeable lithium–sulfur batteries

Abstract: Elemental sulfur has attracted great interest for rechargeable batteries because of its high theoretical specific capacity and low cost. However, sulfur electrodes still suffer from rapid capacity fading, which is mainly caused by the undesirable dissolution of polysulfide intermediates and the irreversible deposition of discharge products. In this work, we describe an interconnected core–shell pyrolyzed polyacrylonitrile@carbon/sulfur (pPAN@C/S) nanostructure for high-performance lithium–sulfur batteries. Sulfur was firstly confined in a conductive porous carbon host as C/S to enhance the conductivity of sulfur, constrain polysulfide intermediates and alleviate volume expansion during cycling. Then a conductive pPAN shell was formed by annealing of PAN absorbed on the surface of C/S at 300 °C to further prevent polysulfide intermediates from dissolution by an additional physical and chemical barrier. Meanwhile, the conductive pPAN shell could prevent the irreversible deposition of insoluble discharge products, leading to improved cyclic stability. The interconnected core–shell pPAN@C/S electrodes exhibit a very high initial discharge capacity of 1269 mAh g−1 at 0.5 C and show excellent cycling stability and rate performance.

Heteroatom-Doped Porous Carbon Nanosheets: General Preparation and Enhanced Capacitive Properties.

Abstract: High-performance electrical double-layer capacitors (EDLCs) require carbon electrode materials with high specific surface area, short ion-diffusion pathways, and outstanding electrical conductivity. Herein, a general approach combing the molten-salt method and chemical activation to prepare N-doped carbon nanosheets with high surface area (654 m2 g−1) and adjustable porous structure is presented. Owing to their structural features, the N-doped carbon nanosheets exhibited superior capacitive performance, demonstrated by a maximum capacitance of 243 F g−1 (area-normalized capacitance up to 37 μF cm−2) at a current density of 0.5 A g−1 in aqueous electrolyte, high rate capability (179 F g−1 at 20 A g−1), and excellent cycle stability. This method provides a new route to prepare porous and heteroatom-doped carbon nanosheets for high-performance EDLCs, which could also be extended to other polymer precursors and even waste biomass.

Synthesis and electrochemical performances of mixed-valence vanadium oxide/ordered mesoporous carbon composites for supercapacitors

Abstract: Mixed-valence vanadium oxide (VOx)/ordered mesoporous carbon (CMK-3) composite (VOC) were synthesized through a facile liquid-phase method followed by calcination. The microstructures of the composite were characterized by X-ray diffraction (XRD), nitrogen adsorption and desorption, X-ray photoelectron spectra (XPS), scanning election microscopy (SEM) and transmission election microscopy (TEM). The relevant results showed that vanadium oxide nanoparticles with mixed valence were successfully embedded in mesoporous channels in the conductive matrix and dispersed on the CMK-3 surface to form the interwoven composite. The introduction of the CMK-3 framework not only improves electron transfer but also prevents the structure collapsing during cycling. As expected, the composite exhibits excellent electrochemical properties. It delivered a specific capacitance of 257 F g−1 at 0.5 A g−1 and maintained 77.3% at 8 A g−1 in 5 M LiNO3. After 5000 cycles, the capacitance only decreased 20%.

An in situ confinement strategy to porous poly(3,4-ethylenedioxythiophene)/sulfur composites for lithium–sulfur batteries

Abstract: Lithium–sulfur (Li–S) batteries are receiving intense interest because of their high theoretical energy density and low cost. However, the rapid capacity fading is a significant problem facing the application of Li–S batteries. Herein, we describe an in situ confinement strategy for preparing a porous poly(3,4-ethylenedioxythiophene)/sulfur (pPEDOT/S) composite for Li–S batteries. The as-prepared pPEDOT/S composite exhibits a monodispersed nanostructure with sizes in the range of 400–600 nm. The pPEDOT/S composite electrode exhibits excellent cycling stability and high specific capacity. At a current rate of 0.5C, the pPEDOT/S electrode exhibits a high specific capacity of 883 mA h g−1 and a capacity retention of 71% after 200 cycles. During the charge/discharge process, the porous nanostructure could facilitate rapid electrolyte diffusion and accommodate the volumetric expansion. The chemical interaction between the PEDOT and polysulfides and discharged products could efficiently avoid the dissolution of polysulfides and the irreversible deposition of discharged products. The unique nanostructure plus the excellent electrochemical performances of the composites described in the current study allow for new opportunities to design high-performance electrodes for Li–S batteries.