Kinetics of Acid Blue 1 Adsorption from Aqueous Solution by Carbonaceous Substrate Produced from Biotic Precursor

Adsorption of acid blue 1 from aqueous solution onto carbonaceous substrate produced from the wood of Paulownia tomentosa was investigated. The samples characterized by FTIR, SEM, EDS and XRD techniques, indicated that the surface functional groups like carboxyl, lactones or phenols and ethers have disappeared at high activation temperature （800 ℃） and as a result porous structure was developed that has a positive effect on the adsorption capacity. Bangham and parabolic diffusion models were applied to the kinetic adsorption data, which show that the adsorption of acid blue 1 was a diffusion controlled process. The reaction rate increased with the increase in temperatures of both the adsorption and activation. Thermodynamic parameters like △E^≠, △H^≠, △S^≠ and △G^≠ were calculated from the kinetic data. The negative values of △S^≠ reflected the decrease in the disorder of the system at the solid-solution interface during adsorption. Gibbs free energy （△G^≠）, representing the driving force for the affinity of dye for the carbon surface, increased with the increase in sample activation and the adsorption temperatures.     

Synthesis of carbon-coated Li4Ti5O12 and its electrochemical performance as anode material for lithium-ion battery

Carbon-coated Li_4Ti_5O_(12) sample was synthesized by a sol-gel method. The Li_4Ti_5O_(12) powders were obtained by calcinations of the gels at 750, 800, 850,900 ℃ at N_2 atmosphere. The structure, morphology and electrochemical properties of the materials were characterized by SEM, XRD and charge and discharge. The final product sintered at 850 ℃ demonstrates excellent performance with a specific capacity of 163.5 mAh/g after 100 cycles at 1C. Furthermore, the discharge specific capacity of the sample can retain 80 mAh/g at 10C.     

Surfactant assisted solvothermal synthesis of LiFePO_4 nanorods for lithium-ion batteries

Well-shaped and uniformly dispersed LiFePO_4 nanorods with a length of 400–500 nm and a diameter of about 100 nm, are obtained with participation of a proper amount of anion surfactant sodium dodecyl sulfonate(SDS) without any further heating as a post-treatment. The surfactant acts as a self-assembling supermolecular template, which stimulated the crystallization of LiFePO_4 and directed the nanoparticles growing into nanorods between bilayers of surfactant(BOS). LiFePO_4 nanorods with the reducing crystal size along the b axis shorten the diffusion distance of Li~+ extraction/insertion, and thus improve the electrochemical properties of LiFePO_4 nanorods. Such prepared LiFePO_4 nanorods exhibited excellent specific capacity and high rate capability with discharge capacity of 151 mAh/g, 122 mAh/g and 95 mAh/g at 0.1C, 1 C and 5 C, respectively. Such excellent performance of LiFePO_4 nanorods is supposed to be ascribed to the fast Li~+ diffusion velocity from reduced crystal size along the b axis and the well electrochemical conductivity. The structure, morphology and electrochemical performance of the samples were characterized by XRD, FE-SEM, HRTEM, charge/discharge tests, and EIS(electrochemical impedance spectra).     

Lithiated Nafion-garnet ceramic composite electrolyte membrane for solid-state lithium metal battery

Single-ion conducting solid polymer electrolytes are expected to play a vital role in the realization of solid-state Li metal batteries.In this work,a lithiated Nafion(Li-Nafion)-garnet ceramic Li6.25La3 Zr2 Al0.25O12(LLZAO)composite solid electrolyte(CSE)membrane with 30μm thickness was prepared for the first time.By employing X-ray photoelectron spectroscopy and transmission electron microscope,the interaction between LLZAO and Li-Nafion was investigated.It is found that the LLZAO interacts with the Li-Nafion to form a space charge layer at the interface between LLZAO and Li-Nafion.The space charge layer reduces the migration barrier of Li-ions and improves the ionic conductivity of the CSE membrane.The CSE membrane containing 10 wt%LLZAO exhibits the highest ionic conductivity of2.26×10-4 S cm-1 at 30℃among the pristine Li-Nafion membrane,the membrane containing 5 wt%,20 wt%,and 30 wt%LLZAO,respectively.It also exhibits a high Li-ion transference number of 0.92,and a broader electrochemical window of 0-+4.8 V vs.Li+/Li than that of 0-+4.0 V vs.Li+/Li for the pristine Li-Nafion membrane.It is observed that the CSE membrane not only inhibits the growth of Li dendrites but also keeps excellent electrochemical stability with the Li electrode.Benefitting from the above merits,the solid-state LiFePO4/Li cell fabricated with the CSE membrane was practically charged and discharged at 30℃.The cell exhibits an initial reversible discharge specific capacity of 160 mAh g-1 with 97%capacity retention after 100 cycles at 0.2 C,and maintains discharge specific capacity of 126 mAh g-1 after500 cycles at 1 C.The CSE membrane prepared with Li-Nafion and LLZAO is proved to be a promising solid electrolyte for advanced solid-state Li metal batteries.     

Reaction mechanism and additional lithium storage of mesoporous MnO_2 anode in Li batteries

Nanostructured transition metal oxides,employed as anode materials for lithium-ion batteries,exhibit a higher capacity than the theoretical capacity based on the conversion reaction.To date,the reasons behind this phenomenon are unclear.For the one-step evolution of anode material for lithium-ion batteries,it is essential to understand the lithium storage reaction mechanism of the anode material.Herein,we provide a detailed report on the lithium storage and release mechanism of MnO2,using synchrotron-based X-ray techniques.X-ray diffraction and X-ray absorption spectroscopy results indicate that during the first discharge,MnO2 is reduced in the order of MnO2→LixMnO2(1相似文献   

Synthesis of carbon nanofibers@MnO2 3D structures over copper foil as binder free anodes for lithiumion batteries

A 3D structured composite of carbon nanofibers@MnO2 on copper foil is reported here as a binder free anode of lithium ion batteries, with high capacity, fast charge/discharge rate and good stability. Carbon nanofiber yarns were synthesized directly over copper foil through a floating catalyst method. The growth of carbon nanofiber yarns was significantly enhanced by mechanical polishing of the copper foils, which can be attributed to the increased surface roughness and surface area of the copper foils. MnO2 was then grown over carbon nanofibers through spontaneous reduction of potassium permanganate by the carbon nanofibers. The obtained composites of carbon nanofibers@MnO2 over copper foil were tested as an anode in lithium ion batteries and they show superior electrochemical performance. The initial reversible capacity of carbon nanofibers@MnO2 reaches up to around 998 mAh g-1 at a rate of 60 mmA g-1 based on the mass of carbon nanofibers and MnO2 . The carbon nanofibers@MnO2 electrodes could deliver a capacity of 630 mAh g-1 at the beginning and maintain a capacity of 440 mmAh g-1 after 105 cycles at a rate of 600 mA g-1 . The high initial capacity can be attributed to the presence of porous carbon nanofiber yarns which have good electrical conductivity and the MnO2 thin film which makes the entire materials electrochemically active. The high cyclic stability of carbon nanofibers@MnO2 can be ascribed to the MnO2 thin film which can accommodate the volume expansion and shrinking during charge and discharge and the good contact of carbon nanofibers with MnO2 and copper foil.     

Synthesis of Monoclinic Li_(0.33)MnO_2 and Its Electrochemical Properties in Different Potential Windows

Li0.33MnO2 cathode material was synthesized by solid state reaction. The material showed a small coherent domain size about 10 nm determined by X-ray diffraction and transmission electron microscopy. The electrochemical properties of the material were studied in different potential windows of 3.5―2.0 V and 4.3―2.0 V. An irreversible transformation to spinel phase was observed in the initial several cycles, which was more prominent on cycling at 4.3―2.0 V. Electrochemical impedance spectroscopy showed that the Li+ diffusion coefficient of the material was about 2×10–9 cm2/s. Li0.33MnO2 showed a reversible discharge capacity of 140 and 200 mA·h/g in the potential windows of 3.5―2.0 V and 4.3―2.0 V, respectively. But the capacity retention at 4.3―2.0 V was poor due to the thicker spinel layer formed on the material surface.     

Porous core–shell CoMn_2O_4 microspheres as anode of lithium ion battery with excellent performances and their conversion reaction mechanism investigated by XAFS

Porous core–shell CoMn_2O_4 microspheres of ca. 3–5 μm in diameter were synthesized and served as anode of lithium ion battery. Results demonstrate that the as-synthesized CoMn_2O_4 materials exhibit excellent electrochemical properties. The CoMn_2O_4 anode can deliver a large capacity of 1070 mAh g~(–1) in the first discharge, a reversible capacity of 500 mAh g~(–1) after 100 cycles with a coulombic efficiency of 98.5%at a charge–discharge current density of 200 mA g~(–1), and a specific capacity of 385 mAh g~(–1) at a much higher charge-discharge current density of 1600 mA g~(–1). Synchrotron X–ray absorption fine structure(XAFS) techniques were applied to investigate the conversion reaction mechanism of the CoMn_2O_4 anode.The X–ray absorption near edge structure(XANES) spectra revealed that, in the first discharge–charge cycle, Co and Mn in CoMn_2O_4 were reduced to metallic Co and Mn when the electrode was discharged to 0.01 V, while they were oxidized respectively to CoO and MnO when the electrode was charged to 3.0 V.Experiments of both XANES and extended X–ray absorption fine structure(EXAFS) revealed that neither valence evolution nor phase transition of the porous core–shell CoMn_2O_4 microspheres could happen in the discharge plateau from 0.8 to 0.6 V, which demonstrates the formation of solid electrolyte interface(SEI) on the anode.     

Photorechargeable Properties of Metal Hydride-SrTiO3 Electrode

A photosensitive metal hydride electrode was prepared by modification with perovskite-type SrTiO3 photocatalyst. The photorechargeable properties of the prepared electrodes were investigated by using electrochemical cyclic voltammetry and EIS measurements. The results showed that the modified electrode exhibited the obvious photorechargeable properties. The reduction current increased remarkably under the xeon light irradiation compared with the unmodified electrode. During the photocharging process, the potential of the modified electrode shifted quickly to negative direction and a potential plateau of about -0.90V (vs. Hg/HgO) occurred at the end of light irradiation. The corresponding discharge capacity of the electrode was about 5.4 mAh/g.     

In situ NMR diffusion coefficients assessment of lithium ion conductor using electrochemical priors and Arrhenius constraint——A computational study

In situ NMR measurements of the diffusion coefficients,including an estimate of signal strength,of lithium ion conductor using diffusion-weighting pulse sequence are performed in this study.A cascade bilinear model is proposed to estimate the diffusion sensitivity factors of pulsed-field gradient using prior information of the electrochemical performance and Arrhenius constraint.The model postulates that the active lithium nuclei participating electrochemical reaction are relevant to the NMR signal intensity,when discharge rate or temperature condition is varying.The electrochemical data and the NMR signal strength show a highly fit with the proposed model according our simulation and experiments.Furthermore,the diffusion time is constrained by temperature based on Arrhenius equation of reaction rates dependence.An experimental calculation of Li_4Ti_5O_(12)(LTO)/carbon nanotubes(CNTs) with the electrolyte evaluating at 20 ℃ is presented,which the b factor is estimated by the discharge rate.     

Improved electrochemical hydrogen storage properties of Mg-Y thin films as a function of substrate temperature

Pd-capped Mg_(78)Y_(22) thin films have been prepared by direct current magnetron co-sputtering system at different substrate temperatures and their electrochemical hydrogen storage properties have been investigated.It is found that rising substrate temperature to 60 ℃ can coarsen the surface of thin film,thus facilitating the diffusion of hydrogen atoms and then enhancing its discharge capacity to ~1725 mAh·g~(-1).Simultaneously,the cyclic stability is effectively improved due to the increased adhesion force between film and substrate as a function of temperature.In addition,the specimen exhibits a very long and flat discharge plateau at about —0.67 V,at which nearly 60%of capacity is maintained.The property is favorable for the application in metal hydride/nickel secondary batteries.The results indicate that rising optimal substrate temperature has a beneficial effect on the electrochemical hydrogen storage of Mg-Y thin films.     

Preparation of nano-PANI@MnO_2 by surface initiated polymerization method using as a nano-tubular electrode material:The amount effect of aniline on the microstructure and electrochemical performance

In this study,nano-polyanline and manganese oxide nanometer tubular composites(nano-PANI@MnO2)were prepared by a surface initiated polymerization method and used as electrochemical capacitor electrode materials; and the effect of aniline amount on the microstructure and electrochemical performance was investigated. The microstructures and surface morphologies of nano-PANI@MnO2 were characterized by X-ray diffraction,scanning electron microscopy and fourier transformation infrared spectroscope. The electrochemical performance of these composite materials was performed with cyclic voltammetry,charge–discharge test and electrochemical impedance spectroscopy,respectively. The results demonstrate that the feed ratio of aniline to MnO2 played a very important role in constructing the hierarchically nano-structure,which would,hence,determine the electrochemical performance of the materials. Using the templateassisted strategy and controlling the feed ratio of aniline to MnO2,the nanometer tubular structure of nanoPANI@MnO2 was obtained. A maximum specific capacitance of 386 F/g was achieved in aqueous 1 mol/L Na NO3 electrolyte with the potential range from 0 to 0.6 V(vs. SCE).     

LiFePO4 doped with magnesium prepared by hydrothermal reaction in glucose solution

Lithium iron phosphate （LiFePO4） doped with magnesium was hydrothermally synthesized from commercial LiOH, FeSO4, H3PO4 and MgSO4 with glucose as carbon precursor in aqueous solution. The samples were characterized by X-ray powder diffraction, scanning electron microscopy and constant charge-discharge cycling. The results show that the synthesized powders have been in situ coated with carbon precursor produced from caramel reaction of glucose. At ambient temperature （28±2℃）, the electrochemical performances of LiFePO4 prepared exhibit the high discharge capacity of 135 mAh g^-1 at 5C and good capacity retention of 98% over 90 cycles. The excellent electrochemical performances should be correlated with the intimate contact between carbon and LiFePO4 primary and secondary particles, resulting from the in situ formation of carbon precursor/carbon, leading to the increase in conductivity of LiFePO4.     

超声波处理对球形β-Ni(OH)2结构及电化学性能的影响

A method of ultrasonic treatment （UST） was first used to modify the structure and electrochemical performance of nickel hydroxide for the active material of nickel series alkaline batteries. The experimental results showed that UST was an effective method to improve the electrochemical performance of β-Ni（OH）2 such as specific discharge capacity, discharge potential, electrochemical reversibility and oxygen evolution over-potential. The results of electrochemical impedance spectroscopy, powder X-ray diffraction and particle size distribution indicated that the improvement of the performance of β-Ni（OH）2 through UST was attributed to the reduction of the charge-transfer resistance （Rt） and the diffusion impedance （Zw）, which resulted from the decrease of the crystallite and particle size and the increase of interlayer spacing. Diffusion coefficient of proton DH of ultrasonic treated β-Ni（OH）2 gained by CV tests was 1.13 × 10^-11 cm^2/s, and the average discharge specific capacity of ultrasonic treated β-Ni（OH）2 electrode was 301 mAh/g.     

Synthesis and electrochemical properties of dual doped spinels LiNi_xAl_yMn_(2-x-y)O_4 via facile novel chelated sol–gel method as possible cathode material for lithium rechargeable batteries

LiMn_2O_4 and LiNi_xAlyMn_(2-x-y)O_4(x= 0.50;y = 0.05-0.50) powders have been synthesized via facile solgel method using Behenic acid as active cheiating agent.The synthesized samples are subjected to physical characterizations such as thermo gravimetric analysis(TG/DTA),X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FT-IR),field-emission scanning electron microscopy(FESEM),transmission electron microscopy(TEM) and electrochemical studies viz.,galvanostatic cycling properties,electrochemical impedance spectroscopy(EIS) and differential capacity curves(dQ/dE).Finger print XRD patterns of LiMn_2O_4 and LiNi_xAl_yMn_(2-x-y)O_4 fortify the high degree of crystallinity with better phase purity.FESEM images of the undoped pristine spinel illustrate uniform spherical grains surface morphology with an average particle size of 0.5 μm while Ni doped particles depict the spherical grains growth(50nm) with ice-cube surface morphology.TEM images of the spinel LiMn_2O_4 shows the uniform spherical morphology with particle size of(100 nm) while low level of Al-doping spinel(LiNio.5Alo.05Mn1.45O4) displaying cloudy particles with agglomerated particles of(50nm).The LiMn_2O_4 samples calcined at 850℃ deliver the discharge capacity of 130 mAh/g in the first cycle corresponds to 94%coiumbic efficiency with capacity fade of 1.5 mAh/g/cycle over the investigated 10 cycles.Among all four dopant compositions investigated,LiNi_(0.5)Al_(0.05)Mn_(1.45)O_4 delivers the maximum discharge capacity of 126 mAh/g during the first cycle and shows the stable cycling performance with low capacity fade of 1 mAh/g/cycle(capacity retention of 92%) over the investigated 10 cycles.Electrochemical impedance studies of spinel LiMn_2O_4 and LiNi_(0.5)Al_(0.05)Mn_(1.45)O_4 depict the high and low real polarization of 1562 and 1100 Ω.     

MOF-derived Co_9S_8 nano-flower cluster array modified separator towards superior lithium sulfur battery

Lithium sulfur batteries with high energy density are thought to be the most potential energy storage technology that can be commercialized.However,the shuttle effect of polysulfides deteriorates its electrochemical performance.Herein,a novel Co_9 S_8 nanostructure derived from metal organic framework material(MOF) was explored by simple liquid phase reaction and heat vulcanization of2-methylimidazole and Co(NO_3)_2·6 H_2 O on the surface of the original PP separator.The Co_9 S_8 nano-flower cluster array wall was vertically and closely arranged with the thickness of 200 nm,and the polysulfide can be adsorbed by its physical and chemical action to slow down the "shuttle effect".It is found that the cell with the modified separator can achieve an ideal discharge capacity of about 600 mAh/g at 1 C.The specific capacity is maintained at 500 mAh/g after 200 cycles,with only 0.11% of capacity decay per cycle.It provides a new way for the utilization of MOF material derivatives to modify the separator in order to improve the electrochemical performance of lithium-sulfur batteries.     

A novel synthetic route for LiFePO_4/C cathode materials by addition of starch for lithium-ion batteries

LiFePO4/Carbon composite cathode material was prepared using starch as carbon source by spray-pelleting and subsequent pyrolysis in N2. The samples were characterized by XRD, SEM, Raman, and their electrochemical performance was investigated in terms of cycling behavior. There has a special micro-morphology via the process, which is favorable to electrochemical properties. The discharge capacity of the LiFePO4.C composite was 170 mAh g-1, equal to the theoretical specific capacity at 0.1 C rate. At 4 C current density, the specific capacity was about 80 mAh g-1, which can satisfy for transportation applications if having a more flat discharge flat.     

Three-dimensionalization via control of laser-structuring parameters for high energy and high power lithium-ion battery under various operating conditions

Laser-structuring is an effective method to promote ion diffusion and improve the performance of lithium-ion battery(LIB)electrodes.In this work,the effects of laser structuring parameters(groove pitch and depth)on the fundamental characteristics of LIB electrode,such as interfacial area,internal resistances,material loss and electrochemical performance,are investigated,LiNi_0.5Co_0.2Mn_0.3O₂ cathodes were structured by a femtosecond laser by varying groove depth and pitch,which resulted in a material loss of 5%-14%and an increase of 140%-260%in the in terfacial area between electrode surface and electrolyte.It is shown that the importance of groove depth and pitch on the electrochemical performance(specific capacity and areal discharge capacity)of laser-structured electrode varies with current rates.Groove pitch is more im porta nt at low current rate but groove depth is at high curre nt rate.From the mapping of lithium concentration within the electrodes of varying groove depth and pitch by laser-induced breakdown spectroscopy,it is verified that the groove functions as a diffusion path for lithium ions.The ionic,electronic,and charge transfer resistances measured with symmetric and half cells showed that these internal resistances are differently affected by laser structuring parameters and the changes in porosity,ionic diffusion and electronic pathways.It is demonstrated that the laser structuring parameters for maximum electrode performance and minimum capacity loss should be determined in consideration of the main operating conditions of LIBs.     

Influence of Heat Treatment Time on Cathode Material Cr8O21 for Lithium Battery北大核心CSCD

Chromium oxide (Cr8O21) cathode material for lithium batteries was synthesized by thermal decomposition of chromium trioxide (CrO3) at high temperature. The electrochemical properties of chromium oxide depended on the time and temperature during the heat treatment. Pure phase chromium oxide was prepared, and the effects of heat treatment time on the structures and electrochemical properties of Cr8O21 were systematically studied. The first discharge mechanism of chromium oxide in lithium batteries was explored, and the results were similar to that in lithium-sulfur batteries. The crystal phases and electrochemical properties of the prepared chromium oxide were analyzed by TGA, XRD, SEM, EDS, ICP, EIS techniques and constant current discharge measurement. The results show that heat treatment time had an important impact. Extending the heat treatment time was beneficial to improve the electrochemical properties of the material. The less the amount of residual CrO3, the better the electrochemical performance. The severe oxidation reaction between CrO3 and the electrolyte caused the electrode to be corroded. The material obtained in 48 h exhibited excellent performance, complete crystallization, good morphology, and low electrochemical impedance. At a constant discharge current of 0.05 mA, the specific capacity of the material reached 383.26 mAh窑g-1 with the specific energy of 1153.83 mWh窑g-1 and the average discharge voltage of 3.01 V. This study provides an effective way to prepare pure phase chromium oxide and proves its potential application in the field of lithium batteries. © 2021 Authors. All rights reserved.     

Insight into the topology effect on the diffusion of ethene and propene in zeolites: A molecular dynamics simulation study

Selectivity control is a difficult scientific and industrial challenge in methanol-to-olefins(MTO)conversion.It has been experimentally established that the topology of zeolite catalysts influenced the distribution of products.Besides the topology effect on reaction kinetics,the topology influences the diffusion of reactants and products in catalysts as well.In this work,by using COMPASS force-field molecular dynamics method,we investigated the intracrystalline diffusion of ethene and propene in four different zeolites,CHA,MFI,BEA and FAU,at different temperatures.The self-diffusion coefficients and diffusion activation barriers were calculated.A strong restriction on the diffusion of propene in CHA was observed because the self-diffusion coefficient ratio of ethene to propene is larger than 18 and the diffusion activation barrier of propene is more than 20 kJ/mol in CHA.This ratio decreases with the increase of temperature in the four investigated zeolites.The shape selectivity on products from diffusion perspective can provide some implications on the understanding of the selectivity difference between HSAPO-34 and HZSM-5 catalysts for the MTO conversion.