Synthesis of one-dimensional carbon nanostructures and their application as anode materials in lithium ion batteries

An efficient synthesis of carbon nanofibers by pyrolysis of as-prepared polypyrrole nanowires was reported. Under the subsequent KOH activation, a significant morphology variation was detected and the obtained sample took on a ribbon-like structure. The morphology and structure of the carbon nanofibers and carbon nanoribbons were characterized. When the as-prepared one-dimensional carbon nanostructures were used as anode materials in lithium ion batteries, both of them exhibited superior cyclical stability and good rate properties. After 50 cycles, the reversible capacity of carbon nanofibers electrode maintained 530 mA·h/g. Concerning carbon nanoribbons, the reversible capacity is always larger than 850 mA·h/g and the reversible capacity retention after 23 cycles is 86%.

Influence of thermomechanical treatments on localized corrosion susceptibility and propagation mechanism of AA2099 Al-Li alloy

In order to manifest the influence of specific microstructural component on the development of severe localized corrosion in an AA2099 aluminum-lithium alloy, the corrosion behavior of the alloy subjected to solution heat treatment, cold working and artificial ageing was investigated. Immersion testing and potentiodynamic polarization were employed to introduce localized corrosion; scanning electron microscopy and transmission electron microscopy were used to characterize the alloy microstructure and corrosion morphology. It was found that the susceptibility of the alloy to severe localized corrosion was sensitive to thermomechanical treatments. Additionally, the state of alloying elements influenced the mechanism of localized corrosion propagation. Specifically, the alloy in T8 conditions showed higher susceptibility to severe localized corrosion than that in other conditions. During potentiodynamic polarization, the alloy in solution heat-treated and T3 conditions displayed crystallographic corrosion morphology while the alloy in T6 and T8 conditions exhibited selective attack of grain interiors and grain boundaries in local regions.

Synthesis of γ-LiV_2O_5/VO_2 mixture by thermal lithiation of vanadium (+4,+5) oxides

γ-LiV2O5/VO2 composites were synthesized through thermal lithiation reaction of mixed valence (+4, +5) vanadium oxides by lithium bromide. The phase evolution, morphology and discharge behavior at 500 ℃ were investigated by thermal gravimeter/differential thermal analysis (TG/DTA), X-ray diffraction(XRD), scanning electron microscopy(SEM) and specific surface analysis(BET). The mixed vanadium oxides are obtained from the pyrolytic decomposition of ammonium metavanadate, with V6O13 as main phase. Results show that the lithiation reaction begins at about 258 ℃, with γ-LiV2O5 and VO2(B) as the product. VO2(B) can transit to VO2(R) in the range of 400-500 ℃, following by grain growth and crystalline development with the increase of temperature and roasting time. The ratio of γ-LiV2O5 to VO2 can be modified by the additive content of lithium bromide. A lattice shearing model about the nucleation and growth of LixV2O5 and VO2(B) inside mixed valence (+4, +5) vanadium oxides (e.g. V6O13, V3O7) is speculated, which is relative to oxygen-/vacancy-diffusion and structural evolution inspired by lithium-insertion. The open-circuit voltage of 2.6 V is observed in the single cell of Li-B/LiCl-KCl/(γ-LiV2O5/VO2) at 500 ℃, and the specific capacities of 146 and 167 mA·h/g (cut-off voltage 1.4 V) are measured for the positive material at 100 mA/cm2 and 200 mA/cm2, respectively.

Microstructure and tensile properties of Mg-Li-Al-Zn based alloys with Ce addition

Mg-5Li-3Al-2Zn-xCe（x=0-2.5;mass fraction,%） alloys were prepared by casting,and heat treatments of homogenization at 300 °C and solid solution at 370 °C were carried out.The microstructure and tensile properties of as-cast alloys and their evolutions after solid solution were investigated.The results show that with the increase of Ce content,Al2Ce/Al3Ce precipitates are formed and the alloys mainly consist of α-Mg,Al2Ce,Al3Ce and AlLi phases,and the amount of AlLi and Al-Ce intermetallics decreases after solid solution.The content and morphology of the second phases have important effects on the mechanical properties of the alloys;the alloy with 1.0%Ce content exhibits excellent tensile strength.The tensile strength and elongation of Mg-5Li-3Al-2Zn-0.5Ce alloy is remarkably improved by the solution strengthening effect because of the addition of Ce.

Age softening phenomenon and microscopic mechanism of Li−B alloy

The age softening phenomenon of the Li−B alloy was investigated by a series of tensile tests under various aging conditions.The results show that the tensile strength of the rolled Li−B alloy decreases with increasing aging time.Higher aging temperature accelerates the softening process,and leads to an early end of aging.A model was proposed to analyze the mechanism of the age softening.The vacancy annihilation is the control factor of age softening.The strength−temperature relationship was estimated by the newly proposed model and a standard heat treatment,annealing at 150℃ for 1 h,was designed to eliminate the age softening of rolled Li−B alloy.

Simulation of Gas-Fired Triple-Effect LiBr/Water Absorption Cooling System with Exhaust Heat Recovery Generator

An exhaust heat recovery generator is proposed to be integrated with conventional gas-fired triple-effect LiBr/water absorption cooling cycles to improve system energy efficiency. As a case study, simulation of the novel cycle based on promising parallel flow with cooling capacity of 1 150 kW is carried out under various heat recovery generator vapor production ratios ranging from 0 to 3.5%. The life cycle saving economic analysis, for which the annual gas conservation is estimated with Bin method, is employed to prove the worthiness of extra expenditure. Results show that the optimum gas saving revenue is obtained at 2.8% heat recovery generator vapor production ratio with 42 kW exhaust heat recovered, and the system energy efficiency is improved from 1.78 to 1.83. The initial investment of exchanger can be paid back within 7 years and 9 000 CNY of gas saving revenue will be achieved over the 15-year life cycle of the machine. This technology can be easily implemented and present desirable economic effects, which is feasible to the development of triple-effect absorption cycles.

Hydrothermal Synthesis of Molybdenum Disulfide for Lithium Ion Battery Applications

Molybdenum disulfide nanoflakes were synthesized by a simple hydrothermal process using sodium molybdate and thiourea as reactants at a relatively low temperature. X-ray diffraction(XRD) and transmission elec-tron microscopy(TEM) indicate that the samples have the structure of 2H-MoS2 and the morphology of nanoflakes with the average thickness around 5-10 nm. The results of electrochemical properties indicate that the morphology and size of MoS2 particles have effects on their capacity when they are used as the anode for lithium ion battery. The as-prepared MoS2 samples have high reversible discharge capacity up to 994.6 mA·h·g-1 for the MoS2-1 elec-trode and 930.1 mA·h·g-1 for the MoS2-2 electrode and show excellent cycling performances. The MoS2-1 electrode has a better cycling stability than the MoS2-2 electrode due to their difference in the uniformity of the samples.

Modeling and Parametric Study of the Heat Transfer Inside a Lithium Bromide Flow Confined by Wire Screen

The present study deals with the numerical analysis of heat transfer inside a lithium bromide-water solution flowing down between finely meshed plastic wire screens. These screens confine the flow through capillary action while allowing the water vapour transfer inside an innovative absorber technology. The complex menisci shape formed on the confinement grid level, where the surface tension forces are of first importance, are reconstructed by a volume-of-fluid model. A continuum surface force model is used to account for the surface tension force. A static contact angle is used to define the wall adhesion. A new algorithm, consisting to set an unique constant temperature at the liquid/vapour interface and to determine the evolution of heat transfer characteristics over the simulation domain, has been implemented and validated by analytical solution. A parametric study has been conducted to determine the effect of the geometry, the contact angle and the shape of the wire on the heat transfer.

First Principles Study of AI-Li Intermetallic Compounds

The structural properties, heats of formation, elastic properties, and electronic structures of four compositions of binary A1-Li intermetallics, A13Li, A1Li, A12Li3, and A14Li9, are ana- lyzed in detail by using density functional theory. The calculated formation heats indicate a strong chemical interaction between A1 and Li for all the A1-Li intermetallics. In partic- ular, in the Li-rich A1-Li compounds, the thermodynamic stability of intermetallics linearly decreases with increasing concentration of.Li. According to the computational single crystal elastic constants, all the four A1-Li intermetallic compounds considered here are mechani- cally stable. The polycrystalline elastic modulus and Poisson＇s ratio have been deduced by using Voigt, Reuss, and Hill approximations, and the calculated ratios of bulk modulus to shear modulus indicate that the four compositions of binary A1-Li intermetallics are brittle materials. With the increase of Li concentration, the bulk modulus of A1-Li intermetallics decreases in a linear manner.

Thermodynamic Analysis of Double Effect Absorption System along with Boiler and Cooling Tower

Many researchers have studied single and double effect absorption cycles based on first and second lows of thermodynamics But so far the relation of different parameters inside these cycles to the second law of thermodynamics in boiler and cooling tower has not been investigated. In this paper, a system comprised of a series flow double effect water-Lithium bromide absorption chiller, a boiler and a cooling tower is studied based on the first and second laws of thermodynamics, and also exergy analysis is investigated. For this purpose, mass and energy conservation laws governing the system are written, and coefficient of performance of the system, exergy destruction （loss） of each component and exergy efficiency have been calculated.

吸收式热泵应用于锅炉烟气余热回收案例分析

选取5个供热项目的6台溴化锂吸收式热泵作为案例,对回收燃气锅炉烟气余热情况进行测试,分析热泵运行效果。6台热泵中,5台热泵性能系数均接近或超过1.6,锅炉烟气余热回收比例达到60%以上,热泵运行效果较好,另外1台热泵性能系数为1.3,锅炉烟气余热回收比例为39.56%,未能实现对烟气余热的有效回收。通过测试分析得出,热泵性能系数能有效反映热泵运行效果,烟气余热回收比例有一个较适宜范围,并不是越高越好。

Study on falling film generation heat transfer of lithium bromide solution in vertical tubes

Falling film generation process in lithium bromide absorption refrigeration generation system is researched in thispaper. To describe the coupled heat and mass transfer of laminar falling film in vertical generation tube, a mathematicalmodel is developed, in which the effect of mass transfer on heat transfer is carefully evaluated. Moreover,an equation related Re number with solution volume flow was also obtained in given conditions. We carried outthe experiments with the mass fraction of the inlet solution LiBr being 49.5% and obtained an empirical correlationof heat transfer with the film Re number and heat flux in different volume flow. Specifically, when 5kW/m2<qw<25kW/m2 and Re<500 the heat transfer correlation is given as: h=14009.87qw0.0764Re-0.5391.