1,721,149 research outputs found
Nitrides or carbides coated on hard carbon for sodium ion batteries
No full textSodium ion batteries (SIBs) are a promising substitute for lithium ion batteries (LIBs) because of the natural abundance and lower price of sodium. Hard carbon (HC), known as “non-graphitizable” carbon, is the most popular negative electrode material in SIBs. In this thesis, we investigate the development of composite materials in which the hard carbon is combined with a sodium conversion material with the aim of improving the capacity and cycling stability. Hard carbon obtained from cotton wool at 1400 °C shows a best reversible capacity of 319 mA h g-1 at current of 20 mA g-1 . The sodium storage analysis is consistent with the traditional insertion/absorption mechanism in the hard carbon. The slope region is more related with interlayer distance and degree of graphitization while the plateau part is more related to the micropores size and volume. An effective route to synthesis composites of metal nitrides and carbides with carbon was reported. Titanium tetrachloride is reacted with hydroxide groups on cellulose (cotton wool) before firing to convert the cellulose to hard carbon. Hard carbon-nanocrystalline titanium nitride composites with a good distribution of the titanium across the fibrous hard carbon structure were obtained by firing the treated cellulose under nitrogen. Hard carbon-nanocrystalline titanium carbide composites were obtained by carbonized under argon. Both composites show similar first cycle capacities to hard carbon, but the titanium nitride composite delivers a better capacity retention (85.2%) after 50 cycles than that of hard carbon (74.3 %). Ex situ grazing incidence XRD patterns of the HC-TiN composites suggest the reactions occurring only on the surface region of TiN. VN-HC composites have been synthesised using the same pyrolysis process after reacting VOCl3 with cellulose. The introduction of VN produces an increased capacity: with addition of 8.6 wt% VN, the hard carbon-based electrode achieves a first cycle reversible (oxidation, de-sodiation) capacity of 354 mA h g-1 at 50 mA g-1 , while with pure hard carbon it is 302 mA h g-1 . The additional specific capacity achieved upon addition of VN, compared with the pure hard carbon, is 605 mA h g-1 when referred to the mass of VN only, which is the highest capacity of VN materials in sodium-ion batteries reported to date. In addition, VN also improves the capacity retention with cycling: after 50 cycles the reversible capacity of hard carbon electrodes with 8.6 wt% VN is 294 mA h g-1 , while with pure hard carbon it is 239 mA h g-1 . Insights into the reaction mechanism are obtained by ex situ characterization of the discharged and charged electrodes. Amorphous silicon nitride and silicon oxycarbides were obtained at 1200 °C. The as-prepared silicon nitride coated on hard carbon shows a reversible capacity of 351 mA h g-1 at 50 mA g-1 , better than that of 284 mA h g-1 from pure hard carbon. Furthermore, hard carbon coated with silicon nitride delivers a capacity retention of 85.4% in 50 cycles. The surface evolution of electrode before and after reduction cycling has been investigated by XPS measurement
Dataset for: Enhancing the performance of hard carbon for sodium-ion batteries by coating with silicon nitride/oxycarbide nanoparticles
No full textRaw data in support of published paper:
Hang Cheng, Nuria Garcia-Araez and Andrew L. Hector (2021) Enhancing the performance of hard carbon for sodium-ion batteries by coating with silicon nitride/oxycarbide nanoparticles, Materials Advances, https://doi.org/10.1039/D1MA00613D
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Dataset for: Synthesis of vanadium nitride-hard carbon composites from cellulose and their performance for sodium ion batteries
No full textRaw data for the figures in the paper:
Cheng, H., Garcia-Araez, N., & Hector, A. L. (2020). Synthesis of vanadium nitride-hard carbon composites from cellulose and their performance for sodium ion batteries. ACS Applied Energy Materials. DOI:10.1021/acsaem.0c00003</span
Advanced aircraft seat design : the webbing concept
Full text linkThesis (M.Eng.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1999.Includes bibliographical references (leaf 95).Air travel is so common in this day and age that any significant improvement in seat comfort on board a commercial passenger jet is likely to affect almost everybody. A proposed design concept in this project is the use of webbing as the substitute for current foam cushioning in the seat back. The result is a webbing-foam hybrid cushioning design that utilizes the benefits of both cushioning types to maximum effect. Experimental tests suggest that this design would also provide better overall comfort for the passenger. As a result, both consumer and industry would profit immensely from the implementation of such a design.by Cheng Hang Teo.M.Eng
Nocardioides vastitatis sp. nov., isolated from Taklamakan desert soil
No full textLiu, Shao-Wei, Xue, Chun-Mei, Li, Fei-Na, Sun, Cheng-Hang (2020): Nocardioides vastitatis sp. nov., isolated from Taklamakan desert soil. International Journal of Systematic and Evolutionary Microbiology 70 (1): 77-82, DOI: 10.1099/ijsem.0.003718, URL: http://dx.doi.org/10.1099/ijsem.0.00371
Synthesis of vanadium nitride-hard carbon composites from cellulose and their performance for sodium ion batteries
No full textA promising material for sodium-ion battery anodes has been developed through the controlled formation of a thin, uniformly dispersed layer of vanadium nitride (VN) nanoparticles onto a high-performance hard carbon. Hard carbon is the standard (pre)commercial material for sodium-ion negative electrodes, and our hard carbon electrodes exhibit an electrochemical performance comparable to the state-of-the-art. The introduction of VN produces an increased capacity: with addition of 8.6 wt% VN, the hard carbon-based electrode achieves a first cycle reversible (oxidation, de-sodiation) capacity of 354 mA h g-1 at 50 mA g-1, while with pure hard carbon it is 302 mA h g 1. The additional specific capacity achieved upon addition of VN, compared with the pure hard carbon, is 605 mA h g-1 when referred to the mass of VN only, which is the highest capacity of VN materials in sodium-ion batteries reported to date. In addition, VN also improves the capacity retention with cycling: after 50 cycles the reversible capacity of hard carbon electrodes with 8.6 wt% VN is 294 mA h g-1, while with pure hard carbon it is 239 mA h g-1. This promising new material is obtained via a new and easily scalable synthesis method in which cotton wool is reacted with a vanadium source (VOCl3), followed by a single firing step in N2. Insights into the reaction mechanism are obtained by ex situ characterization of the discharged and charged electrodes
Dataset for: Synthesis of Hard Carbon-TiN/TiC Composites by Reacting Cellulose with TiCl4 Followed by Carbothermal Nitridation/Reduction
No full textDataset supports: Cheng, H., Garcia-Araez, N., Hector, A. L., & Soule, S. (2019). Synthesis of hard carbon-TiN/TiC composites by reacting cellulose with TiCl4 followed by carbothermal nitridation/reduction. Inorganic Chemistry. https://doi.org/10.1021/acs.inorgchem.9b00116</span
Enhancing the performance of hard carbon for sodium-ion batteries by coating with silicon nitride/oxycarbide nanoparticles
No full textA simple synthesis method to produce hard carbon decorated with silicon nitride or silicon oxycarbide nanoparticles was developed. Silicon tetrachloride is reacted with the hydroxide groups on cellulose (cotton wool) before carbonisation to form hard carbon. Use of a nitrogen or argon carbonisation atmosphere enables production of silicon nitride or oxycarbide coatings by carbothermal nitridation or reduction. This is the first time that a silicon nitride has been used in sodium-ion batteries, and it has a very high capacity. The incorporation of 7.9 wt% of silicon nitride produces an increase in the reversible (desodiation) capacity from 284 mA h g-1 for pure hard carbon to 351 mA h g-1 for the silicon nitride-hard carbon composite, at 50 mA g-1 in sodium half-cells. The associated silicon nitride capacity is estimated as 848 mA h g-1 when normalised by the mass of silicon nitride, ascribed to the good dispersion of silicon nitride nanoparticles on the hard carbon, and facile electrochemical reactions in the amorphous and non-stoichiometric silicon nitride. X-ray photoelectron spectroscopy (XPS) of the electrodes before and after cycling is used to elucidate the mechanism of sodium storage, involving formation of amorphous silicon, which then reacts with the electrolyte forming SiOx surface species.</p
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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