2,030 research outputs found

    Optimized synthesis of ultrahigh-surface-area and oxygen-doped carbon nanobelts for high cycle-stability lithium-sulfur batteries

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    Hierarchical clews of carbon nanobelts (CsCNBs) with ultrahigh specific surface area (2300 m2 g−1) and large pore volume (up to 1.29 cm3 g−1) has been successfully fabricated through carbonization and KOH activation of phenolic resin based nanobelts. The product possesses hierarchically porous structure, three-dimensional conductive network framework, and polar oxygen-rich groups, which are very befitting to load sulfur leading to excellent cycling stability of lithium-sulfur batteries. The composites of CsCNBs/sulfur exhibit an ultrahigh initial discharge capacity of 1245 mA h g−1 and ultralow capacity decay rate as low as 0.162% per cycle after 200 cycles at 0.1 C. Even at high current rate of 4 C, the cells still display a high initial discharge capacity (621 mA h g−1) and ultralow capacity decay rate (only 0.039% per cycle) after 1000 cycles. These encouraging results indicate that polar oxygen-containing functional groups are important for improving the electrochemical performance of carbons. The oxygen-doped carbon nanobelts have excellent energy storage potential in the field of energy storage

    Nitrogen-doped micropores binder-free carbon-sulphur composites as the cathode for long-life lithium-sulphur batteries

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    Nitrogen-doped micropores-contained carbon nanofibres (NMCNFs) were prepared by carbonizing ZIF-8 grown in liquid-phase along with electrospinning. When NMCNFs act as sulphur host materials in lithium–sulphur batteries, NMCNFs can retard the shuttle effect and dissolution of polysulfides through the synergic action of effective physical confinement to micropores and nitrogen surface chemical absorption. NMCNFs show a capacity up to 636 mAh g−1 after 500 cycles against Li anode

    High-performance supercapacitors based on hierarchically porous carbons with a three-dimensional conductive network structure

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    Clews of polymer nanobelts (CsPNBs) have the advantages of inexpensive raw materials, simple synthesis and large output. Novel clews of carbon nanobelts (CsCNBs) have been successfully prepared by carbonizing CsPNBs and by KOH activation subsequently. From the optimized process, CsCNBs*4, with a specific surface area of 2291 m2 g−1 and a pore volume of up to 1.29 cm3 g−1, has been obtained. Fundamentally, the CsCNBs possess a three-dimensional conductive network structure, a hierarchically porous framework, and excellent hydrophilicity, which enable fast ion diffusion through channels and a large enough ion adsorption/desorption surface to improve electrochemical performance of supercapacitors. The product exhibits a high specific capacitance of 327.5 F g−1 at a current density of 0.5 A g−1 in a three-electrode system. The results also reveal a high-rate capacitance (72.2% capacitance retention at 500 mV s−1) and stable cycling lifetime (95% of initial capacitance after 15 000 cycles). Moreover, CsCNBs*4 provides a high energy density of 29.8 W h kg−1 at a power density of 345.4 W kg−1 in 1 M tetraethylammonium tetrafluoroborate/acetonitrile (TEABF4/AN) electrolyte. These inspiring results imply that this carbon material with a three-dimensional conductive network structure possesses excellent potential for energy storage

    A universal strategy to prepare sulfur-containing polymer composites with desired morphologies for lithium−sulfur batteries

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    Lithium–sulfur (Li–S) batteries are probably the most promising candidates for the next-generation batteries owing to their high energy density. However, Li–S batteries face severe technical problems where the dissolution of intermediate polysulfides is the biggest problem because it leads to the degradation of the cathode and the lithium anode, and finally the fast capacity decay. Compared with the composites of elemental sulfur and other matrices, sulfur-containing polymers (SCPs) have strong chemical bonds to sulfur and therefore show low dissolution of polysulfides. Unfortunately, most SCPs have very low electron conductivity and their morphologies can hardly be controlled, which undoubtedly depress the battery performances of SCPs. To overcome these two weaknesses of SCPs, a new strategy was developed for preparing SCP composites with enhanced conductivity and desired morphologies. With this strategy, macroporous SCP composites were successfully prepared from hierarchical porous carbon. The composites displayed discharge/charge capacities up to 1218/1139, 949/922, and 796/785 mA h g–1 at the current rates of 5, 10, and 15 C, respectively. Considering the universality of this strategy and the numerous morphologies of carbon materials, this strategy opens many opportunities for making carbon/SCP composites with novel morphologies

    Microwave-assisted rapid preparation of hollow carbon nanospheres@TiN nanoparticles for lithium-sulfur batteries

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    Highly conductive titanium nitride (TiN) has a strong anchoring ability for lithium polysulfides (LiPSs). However, the complexity and high cost of fabrication limit their practical applications. Herein, a typical structure of hollow carbon nanospheres@TiN nanoparticles (HCNs@TiN) was designed and successfully synthesized via a microwave reduction method with the advantages of economy and efficiency. With unique structural and outstanding functional behavior, HCN@TiN-S hybrid electrodes display not only a high initial discharge capacity of 1097.8 mA h g−1 at 0.1C, but also excellent rate performance and cycling stability. After 200 cycles, a reversible capacity of 812.6 mA h g−1 is still retained, corresponding to 74% capacity retention of the original capacity and 0.13% decay rate per cycle, which are much better than those of HCNs-S electrodes

    Fast Video Dehazing Using Per-Pixel Minimum Adjustment

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    To reduce the computational complexity and maintain the effect of video dehazing, a fast and accurate video dehazing method is presented. The preliminary transmission map is estimated by the minimum channel of each pixel. An adjustment parameter is designed to fix the transmission map to reduce color distortion in the sky area. We propose a new quad-tree method to estimate the atmospheric light. In video dehazing stage, we keep the atmospheric light unchanged in the same scene by a simple but efficient parameter, which describes the similarity of the interframe image content. By using this method, unexpected flickers are effectively eliminated. Experiments results show that the proposed algorithm greatly improved the efficiency of video dehazing and avoided halos and block effect

    Facile synthesis of TiN nanocrystals/graphene hybrid to chemically suppress the shuttle effect for lithium-sulfur batteries

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    Herein, we present a microwave reduction strategy for the synthesis of reduced-graphene-oxide (rGO) supported TiN nanoparticle hybrid (TiN/rGO) under N2 atmosphere. The method involves GO reduction, metal oxide reduction and nitridation reaction in one single step. Due to TiN high conductivity and good interfacial affinity between it and lithium polysulfides (LiPSs), the prepared TiN/rGO-Sulfur (TiN/rGO-S) cathodes demonstrate rapid charge transfer, lower polarization, faster surface redox reaction kinetic and enhanced stability cycling performance than rGO-Sulfur (rGO-S) and TiO2/rGO-Sulfur (TiO2/rGO-S) cathodes. The initial capacity reaches 1197.6 mA h g−1 with a reversible capacity of 888.7 mA h g−1 being retained after 150 cycles at 0.1 C

    Ultrahigh-content nitrogen-decorated nanoporous carbon derived from metal organic frameworks and its application in supercapacitors

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    Single electric double-layer capacitors cannot meet the growing demand for energy due to their insufficient energy density. Generally speaking, the supercapacitors introduced with pseudo-capacitance by doping heteroatoms (N, O) in porous carbon materials can obtain much higher capacitance than electric double-layer capacitors. In view of above merits, in this study, nanoporous carbon materials with ultrahigh N enrichment (14.23 wt%) and high specific surface area (942 m2 g−1) by in situ introduction of N-doped MOF (ZTIF-1, Organic ligands 5-methyltetrazole/C2H4N4) were produced. It was found that as supercapacitors' electrode materials, these nanoporous carbons exhibit a capacitance as high as 272 F g-1 at 0.1 A g−1, and an excellent cycle life (almost no attenuation after 10,000 cycles.). Moreover, the symmetric supercapacitors were assembled to further investigate the actual capacitive performance, and the capacitance shows up to 154 F g-1 at 0.1 A g−1. Such excellent properties may be attributed to a combination of a high specific surface area, ultrahigh nitrogen content and hierarchically porous structure. The results shown in this study fully demonstrate that the nanoporous carbon materials containing ultrahigh nitrogen content can be used as a potential electrode material in supercapacitors

    Diaqua­bis(5-carb­oxy-2-methyl-1H-imidazole-4-carboxyl­ato-κ2 N 3,O 4)manganese(II)

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    The title complex, [Mn(C6H5N2O4)2(H2O)2], was obtained by hydro­thermal synthesis. The MnII atom, which lies on an inversion centre, displays a slightly distorted octa­hedral geometry. In the crystal packing, complex mol­ecules are linked by inter­molecular O—H⋯O and N—H⋯O hydrogen bonds to form a three-dimensional supramolecular structure. The title complex is isostructural with the corresponding cadmium(II) complex [Nie, Wen, Wu, Liu & Liu (2007 ▶). Acta Cryst. E63, m753–m755]

    2D ultrathin carbon nanosheets derived from interconnected Al-MOF as excellent hosts to anchor selenium for Li-Se battery

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    Alleviating volume expansion of the electrodes and improving utilization of the active materials have become key problems restricting a successful commercialization of lithium-selenium batteries. In this paper, a 2D ultrathin carbon nanosheets derived from interconnected MOF is designed for the first time. Such carbon nanosheets are composed by parallel stacked 2D sub-units, and this unique hierarchical porous architecture is beneficial for buffering the volume expansion and for improving the utilization rate of the active materials. Therefore, the cathode displays an excellent cycling stability with a reversible capacity of 347.3 mAh g−1 at 2 C after 240 cycles
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