Papers by Keyword: Carbon Coating

Abstract: Carbon coated lithium titanate (Li₄Ti₅O₁₂/C) was obtained by a facile solid state approach in inert Ar atmosphere. The composition, morphology, residual carbon content and Ti valence of the samples were systematically investigated. The carbon content of Li₄Ti₅O₁₂/C should be optimized, since excess carbon in the composite leads to the reduction of Ti (IV) to form Ti (III), which results in large irreversible capacity of Li₄Ti₅O₁₂/C. With an optimal carbon content of 0.68wt%, the Li₄Ti₅O₁₂/C sample shows high rate capabilities and good cycling ability, delivering discharge capacities of 160.8 mAh/g at 5C. The superior high rate properties are ascribed to the specific nanostructures, which enables fast electronic and ionic transport by introducing carbon coating and decreasing the particle size of lithium titanate.

Abstract: The synthesis of LiFeSi_0.03P_0.97O₄/C (LFSP/C) composites have been done by solid state method. This study investigates the effects of carbon coating on the structure, microstructure and electrical conductivity of LFSP/C cathode materials. The carbon coating on Lithium Ferro Phosphate (LFP) plays a crucial role in determining its electrical conductivity. The variation of carbon content is 0wt.%; 6wt.%; 7wt.%; 8wt.% (LFP-0%, LFP-6%, LFP-7% and LFP-8%). The characterization was performed using X-Ray Diffraction (XRD), Scanning Electron Microscopy - Energy Dispersive X-ray (SEM-EDX), HighResolution-Transmission Electron Microscopy (HR-TEM) and LCR Meter tests. The XRD result have shown single-phase olivine (LiFePO₄) in all samples. The analysis microstructure using SEM have shown increasing carbon content can reduce agglomeration. The particles size of LFSP is 845.570 nm, and after coating carbon the particles size decreased up to 457.191 nm. The EDX results showed that the amount of atomic percentage for carbon tends to increase as the amount of carbon content increased. HR-TEM images indicates that the formation of carbon layer have formed, but not perfectly coat the LFP particle. The average carbon layer size is 78,31 nm with the size of LFSP particle is 352.82 nm. The LCR Meter result showed that LFP-7% had the largest electronic conductivity (2,275x10^-7 S/cm). The carbon coating led to significant enhancement in electronic conductivity from ~10^-9-10^-10 S/cm to ~10^-7 S/cm.

Abstract: In this study, the effect of SBR concentration (10 Phr, 20 Phr & 30 Phr ) on the thermal behavior of EPDM/SBR blends was studied. Thermogravimetric analysis (TGA) was used to check weight loss of samples as function of temperature by heating upto 600^°C. X-ray diffraction (XRD) was performed to determine quality and % crystallinity of the elastomer blends. It was seen that % crystallinity improved with an increase in the content of SBR in EPDM/SBR blends. TGA revealed that the thermal stability of EPDM/SBR blends has improved by 17% than neat EPDM. Carbon nano-coatings produced by sputtering have no beneficial influence on thermal behaviour of elastomers.

Abstract: Two different approaches to modify the structure and reaction ability of nanocrystalline MgO have been discussed. In the first case, a series of two-component x%MO_x–MgO systems (M = Fe, Co and Ni, x = 1–45 wt.%) was synthesized via sol–gel technique. Aqueous solution of inorganic salt precursor was used as a hydrolyzing agent. Samples obtained were characterized by number of physicochemical methods (differential thermal analysis, X-ray diffraction analysis, low-temperature adsorption, etc.). It was shown that presence of inorganic salt in magnesium hydroxide matrix shifts the temperature of decomposition of latter towards lower values. Structural and textural characteristics of MgO-based oxide systems were found to be strongly affected by the presence of additive and their concentration. Formation of joint phase was observed in the case of cobalt oxide only. Second way of MgO modification was represented by creating a controlled carbon coating over its surface via decomposition of C₄H₁₀ at 400 °C. The obtained x%C/MgO (x = 1–10 wt.%) samples were shown to possess the improved reaction ability in destruction sorption of CF₂Cl₂ as well as in catalytic dehydrochlorination of 1-chlorobutane in presence of water vapors.

Abstract: The electrochemical properties of carbon-coated FeS₂ were investigated as a positive electrode material for lithium secondary batteries. The carbon-coated FeS₂ powders were synthesized by ball-milling using polyaniline as the carbon source. The particles in the carbon-coated FeS₂ samples were smaller than those in the pristine FeS₂ samples. The electrochemical performance, including capacity, of these batteries was improved by carbon-coating by ball-milling. However, the initial coulombic efficiency decreased because of the reduction of the oxidized products on FeS₂ surface. The reduction in particle size provides a larger contact area for the electrolyte. Larger quantities of oxidation products were formed by the reduction of FeS₂ in the presence of air and water after carbon-coating. Therefore, the poor initial coulombic efficiencies of carbon-coated FeS₂ electrodes were caused by the reduction of the oxidized products on the FeS₂ surface.

Abstract: We investigated the electrochemical properties of carbon-coated niobium dioxide (NbO₂) as a negative electrode material for lithium-ion batteries. Carbon-coated NbO₂ powders were synthesized by ball-milling using carbon nanotubes as the carbon source. The carbon-coated NbO₂ samples were of smaller particle size compared to the pristine NbO₂ samples. The carbon layers were coated non-uniformly on the NbO₂ surface. The X-ray diffraction patterns confirmed that the inter-layer distances increased after carbon coating by ball-milling. This lead to decreased charge-transfer resistance, confirmed by electrochemical impedance spectroscopy, allowing electrons and lithium-ions to quickly transfer between the active material and electrolyte. Electrochemical performance, including capacity and initial coulombic efficiency, was therefore improved by carbon coating by ball-milling.

Abstract: Ascorbic acid (VC) was used as carbon source for Li₂MnSiO₄/C composite synthesized by a sol-gel method. By comparing the electrochemical performance of the Li₂MnSiO₄/C composite and pure Li₂MnSiO₄, it was found that VC adding can improve the capacity of Li₂MnSiO₄. The Li₂MnSiO₄/C with 10% VC shows a discharge capacity of 212 mAh/g at 0.05C and Li₂MnSiO₄/C with 15% VC shows discharge capacity of 192 mAh/g at 0.1C, that were higher than the capacity of pure Li₂MnSiO₄.

Abstract: Li_0.95Na_0.05Ti₂(PO₄)₃/C nanocomposite was prepared by sol-gel method.The structure and morphology of the samples were characterized by XRD, SEM which showed the particles had typical NASICON structure and diameter range from 400~500nm. The electrochemical performance were tested by cyclic voltammetry and galvanostatic charge–discharge. Results show Li_0.95Na_0.05Ti₂(PO₄)₃/C nanocomposite exhibitsmuch better electrochemical performance than bare Li_0.95Na_0.05Ti₂(PO₄)_3.

Abstract: The changes in the growth quartz ampoule of AgGaS₂ are studied. Coating a layer of carbon film on the inner surface of growth quartz ampoule is an effective measure to prevent AgGaS₂ melt conglutinate with quartz ampoule. It can prevent the impurities of quartz ampoule diffuse into the AgGaS₂ melt. The anomalous thermal expansion phenomenon of the AgGaS₂ crystal usually makes the growth quartz ampoule broken, and crystal crack. Double-layer quartz ampoule can solve the problem. High-quality and large-size AgGaS₂ single crystal is obtained by using carbon coated and double-layer growth quartz ampoule. These methods are simple and effective.

Abstract: Carbon-coated, bismuth-doped, lithium iron phosphates, LiFe_1xBi_xPO₄ (0x0.05), have been synthesized by a solid-state reaction method. From the optimization, the carbon-coated LiFe_0.95Bi_0.05PO₄ phase showed superior performances in terms of phase purity and high discharge capacity. The structural, morphological, and electrochemical properties were studied and compared to carbon-coated, LiFePO₄. The Li/LiFe_0.95Bi_0.05PO₄ with carbon coating cell delivered an initial discharge capacity of 145 mAh/g and was 30 mAh/g higher than the Li/LiFePO₄ with carbon coating cell. Cyclic voltammetry revealed excellent reversibility of the LiFe_0.95Bi_0.05PO₄ with carbon coating material. High rate capability studies were also performed and showed a capacity retention over 93% during the cycling. It was concluded that substituted Bi ion play an important role in enhancing battery performance of the LiFePO₄ material through improving the kinetics of the lithium insertion/extraction reaction on the electrode.