Yunlong Xu

Synthesis and characterization of F-doped nanocrystalline Li4Ti5O12/C compounds for lithium-ion batteries

The F-doped and carbon coated Li4Ti5O12−xFx/C (LTOF/C) composite anode materials are synthesized via a conventional solid-state reaction with lithium citric acid as the conductive carbon source, and LiF as the fluorine source. The structure and electrochemical properties of the LTOF/C materials are investigated and the effects of carbon coating and F ion doping on the performance of as-prepared materials are discussed. Under a potential range from 0.01 to 2.5 V, LTOF/C exhibits better reversibility and higher cyclic stability compared with LTO and LTO/C, especially at high current rates. The initial specific discharge capacity is 325.6 mA h g−1 at a current density of 170 mA g−1, and remains about 165 mA h g−1 over 1000 cycles when the current density increases to 850 mA g−1. The main factors influencing the excellent performances should be attributed to the cooperation of the F-doping and carbon-coating, which can increase the amount of mixed Ti3+/Ti4+, leading to improved ionic conductivity and electron conductivity in LTO at the same time.

Comprehensive Understanding of High Polar Polyacrylonitrile as an Effective Binder for Li-Ion Battery Nano-Si Anodes

Well-defined polyacrylonitriles (PANs) with different molecular weights were synthesized through an activator regenerated by electron-transfer atom-transfer radical polymerization method and employed as binders in silicon negative electrode for lithium-ion batteries. Compared with poly(vinylidene fluoride) and carboxyl methyl cellulose as binders, the electrode performance of PANs is well-improved. Specifically, at 100 mA g(-1) from 0.01 to 1.5 V, the initial discharge capacity of PAN100-based electrode is 4147.8 mA h g(-1) and still remains about 1639.6 mA h g(-1) over 50 cycles. A comprehensive understanding on the improvement mechanism is preliminarily discussed. The results indicate that the superior performance largely depends on the higher lithium ion diffusion efficiency in PAN which results from the weak interaction between lithium ions and PAN polymer chain, and the hydrogen bonds among the nitrile group (C≡N) of PAN, Si nanoparticles, and the current collector, which will lead to an efficient coating of PAN with the Si particles and well-improved adhesion strength, synergistically depressing the structural deterioration of silicon electrodes.

Novel nanostructured LiMn2O4 microspheres for high power Li-ion batteries

A novel type of nanostructured LiMn2O4 microsphere was successfully synthesized by wet ball milling combined with high-temperature calcinations. The prepared materials were characterized by XRD, SEM, BET surface area measurement, electrochemical galvanostatic cycling tests, EIS, and XRF. The results show that the well-shaped microspheres with a diameter of approximately 0.5–2 μm are composed of reorganized nanoparticles. The LiMn2O4 microspheres have a high tap density of 2.8 g cm−3, and as electrodes, these micro/nanostructured spheres show excellent rate capability and cycle stability, resulting in a high volumetric energy density, even at elevated temperature. These materials are promising for power battery applications.

Enabling a High Performance of Mesoporous α-Fe2O3 Anodes by Building a Conformal Coating of Cyclized-PAN Network

The mesoporous α-Fe2O3/cyclized-polyacrylonitrile (C-PAN) composite was synthesized by a rapid and facile two-step method. The electrode was fabricated without conductive carbon addictive and employed as anode for lithium-ion batteries. Results demonstrate that building a conformal coating of a C-PAN network can provide a strong adhesion with active materials and contribute excellent electronic conductivity to the electrode, which can relieve the huge volume changes during a lithiation/delithiation process and accelerate the charge transfer rate. The material exhibited high reversible capacity of ca. 996 mAh g(-1) after 100 cycles at 0.2C, 773 mAh g(-1) at 1C and 655 mAh g(-1) at 2C, respectively, showing well-enhanced cycling performance and superior rate capacity, and also exhibiting significantly improved power density and energy density compared to the traditional graphite materials. Our results provide a facile and efficient way to enhance the performance of α-Fe2O3 anode material, which also can be applied for other oxide anode materials.

PEG-assisted hydrothermal synthesis and electrochemical performance of ZnO/Ketjenblack nanocomposite for lithium ion batteries

ZnO/Ketjenblack(KB) composite was fabricated by means of a facile PEG-assisted hydrothermal synthesis process, characterized by X-ray powder diffraction, scanning electron microscopy, field emission transmission electron microscopy, thermogravimetric analysis, nitrogen sorption, energy dispersion spectroscopy, galvanostastic charge/discharge test, cyclic voltammogram and electrochemical impedance spectroscopies. The results show that the composite forms a special porous structure with ZnO particles embedded in the mesopores of Ketjenblack, which favors the improvement of electrochemical performance. Compared with unmodified ZnO, ZnO/KB composite exhibits superior electrochemical performances. ZnO/KB composite delivers a discharge capacity of 418.9 mA h g−1 at the discharge density current of 800 mA g−1, whereas the ZnO only gives 116.1 mA h g−1. Moreover, the sample retains a discharge capacity of 538.4 mA h g−1 after 100 cycles at a current density of 100 mA g−1. The improved electrochemical performance can be ascribed to the combined Ketjenblack, which serves as conducting buffering matrix during lithiation/delithiation process.

Synthesis and electrochemical performance of Ni and F doped LiMn2O4 cathode materials

A series of Ni and F ion doped LiMn2O4 composite cathode materials are synthesized via a sol–gel method with citric acid as the chelating agent. The morphology and structure of LiNixMn2−xO4−yFy were characterized by XRD, SEM, EDS and the electrochemical performance was tested and characterized by CV and EIS. The results showed that Ni and F ions were uniformly dispersed in the lattice without changing the structure and morphology of LiMn2O4. LiNi0.03Mn1.97O3.95F0.05 exhibits an excellent electrochemical performance among all the samples, and delivers an initial discharge capacity of 120.3 mA h g−1 at 1C and with a retention of 94.5% (25 °C) and 80.4% (55 °C) after the 100th cycle respectively. The results demonstrated that the dual-doping of Ni and F ions in lithium manganate can prevent the manganate from dissolving in the electrolyte and enhance the cycling performance at elevated temperatures, exhibiting excellent performance at different discharge rates.

A Study on Direct Coal Liquefaction Behaviors in CO/H2O and H2/THN Systems

Abstract In the CO/H2O and H2/tetralin conditions, the liquefaction behaviors of two brown coals (Xiaolongtan and Shengli coal) and three bituminous coals (Huainan, Shenhua, and Yanzhou coal) were investigated. The results show that the lower rank coals have higher total conversion and oil + gas yield, lower asphaltene yield in H2/tetralin system. The total conversion of Shengli brown coal is the highest, getting to 84.4%, oil + gas yield is 72.3%, and asphaltene yield is 12.1%. The liquefaction process in CO atmosphere using water as a solvent was preliminarily probed with those coals. Shengli brown coal also shows good liquefaction property in a CO/H2O system; the total conversion is the highest among the five coals in the same condition, getting to 66.1%, oil + gas yield is 46.5%, and asphaltene yield is 19.6%. The liquefaction property decreases with the increase in coal rank. Although the total conversion and oil + gas yield in the CO/H2O system is lower than in the H2/tetralin system because of the excellent H donor ability of tetralin, the liquefaction in the CO/H2O system is still feasible and this might be a direct liquefaction process well fitting for lower rank coal, especially brown coal containing a certain amount of water. The oil from the liquefaction in the two processes was analyzed by proton nuclear magnetic resonance (1H-NMR). The results show that there is more Hali than Har in the oil from the liquefaction both in CO/H2O and H2/tetralin systems, and the Hali content of the oil from liquefaction in CO/H2O system is much higher than that in the H2/THN system. The existence of the hydroxide in the oil from the liquefaction in CO/H2O process indicates a significant difference from the H2/tetralin process.

A Study on Selective Catalytic Oxidation Desulfurization of Thiophene in Imitation Gasoline with Ti-MCM-41/H2O2·HCOOH

Abstract The selective oxidative desulfurization was conducted with a feedstock of model gasoline consisting of thiophene and n-octane in an H2O2·HCOOH oxidative system over a Ti-MCM-41 catalyst. The operations were designed by the orthogonal design method with an L9 (34) table. Experimental results show that the factors influencing the rate of desulfurization are reaction temperature, the reaction time, and the volume percent content of the hydrogen peroxide in order. Under the optimized operation conditions over Ti-MCM-41 catalyst: H2O2 volume fraction of 3% (v), reaction time of 40 min and reaction temperature of 50°C, the removal ratio of thiophene was 95.6%, and the gasoline yield was 98.7%. The activity of the catalyst has no dramatic deactivation after reusing it five times. In addition, the kinetics study indicates that this reaction is a pseudo first-order reaction with the activation energy of Ea = 40.18 kJ/mol.

The Continuous Desulfurization of FCC Gasoline through Extraction and Photocatalysis-oxidation

Abstract Removal of sulfur-containing compounds from gasoline, based on the combination of various technologies (liquid-liquid extraction and extraction- photocatalysis-oxidation desulfurization) using a biphasic system (oil/acetonitrile) has been investigated. The effect of operation conditions on desulfurization rates and the distribution coefficient in a model system for gasoline were explored. Additionally, extraction-desulfurization kinetics are studied through simulation; the kinetics equation, (−rA) = 7.1cA 0.008, was obtained. Experimental results show that the proper extraction conditions are: diluents content, 0.01–0.05; solvent/oil ratio, 1.5–2.5; and extraction temperature, 30–50°C. A successive removal of these sulfur compounds is carried out through photoirradiating in the solvent phase to form highly polarized compounds from fuel oils with a solvent. The operation conditions include a temperature of 30–50°C, atmospheric pressure, and the ratio of oxidation agent/oil of 0.01–0.005 over our home-made catalyst. Sulfur contents in the fuel oils are reduced to less than 10 μg/g. In addition, the photocatalysis kinetics were worked out to be (−rA) = 0.4221cA – 12.01. On the basis of the above results, an integrated overall refining process for sulfur removal from fluid catalyst cracking gasoline has been developed.