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In this paper, we report the chemical compositional variations and target surface history of lithium nickel vanadate material during RF-magnetron sputtering. Amorphous films were characterized by nuclear methods [Rutherford backscattering spectroscopy (RBS) and nuclear reaction analysis (NRA)], Auger electron spectroscopy (AES), X-ray diffraction (XRD), scanning electron microscope (SEM), atomic force microscope (AFM), and high resolution transmission electron microscopy (HTEM) techniques. Various nanostructured/porous LiNiVO4 thin film materials were obtained, depending on the composition of films, total pressure, annealing temperatures, thickness and heating time. Optimum film composition was obtained with the sputtering parameters; oxygen partial pressure (Po 2)=10mPa, total pressure of (P Ar)=1Pa, Rf-power=30W. Cathodic and anodic electrochemical properties of LiNiVO4 films were evaluated by galvanostatic cycling at constant current and cyclic voltammetry electroanalytical techniques. Electrochemical performance of the LiNiVO4 film deliver a capacity of ∼780mAhg−1 (10th cycle), potential range, 0.02–3.0V (anodic), at a current rate, 75μAcm−2. In the potential range 1.2–4.5V, deliver a capacity of 280mAhg−1, and in the potential window, 3.0–4.8V (cathodic), 0.6 Li are removed from the host LiNiVO4 lattice.
The sentiment detection of texts has been witnessed a booming interest in recent years, due to the increased availability of online reviews in digital form and the ensuing need to organize them. Till to now, there are mainly four different problems predominating in this research community, namely, subjectivity classification, word sentiment classification, document sentiment classification and opinion extraction. In fact, there are inherent relations between them. Subjectivity classification can prevent the sentiment classifier from considering irrelevant or even potentially misleading text. Document sentiment classification and opinion extraction have often involved word sentiment classification techniques. This survey discusses related issues and main approaches to these problems.
The effects of temperature on the dissolution of solid electrolyte interface (SEI) films in the propylene carbonate (PC)-based electrolyte are investigated. The SEI films on the mesocarbon microbeads (MCMB) electrode of the Li|1.0M LiPF6-PC/DEC (= 7/3, v/v)|MCMB cell are characterized by cyclic voltammetry, scanning electron microscopy (SEM), AC impedance, X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The SEM and electrochemical results show that the MCMB electrode cannot undergo the lithiation and delithiation process at 30°C due to the co-intercalation of PC and the exfoliation of MCMB. By contrast, the Li∥MCMB cell can be successfully discharged and charged at 0°C because a PC-based SEI film forms on MCMB. The energy capacity of the MCMB electrode is 281.3 mAh g−1 at 0.2C. However, the SEI film dissolves in the PC-based electrolyte as the temperature is increased to 30°C. The results of Raman spectroscopy and XPS also confirm that the composition of the PC-based SEI formed at 0°C consists of LiF, LixPFy, LixPOyFz, ROLi, and ROCO2Li.
A survey of the electrochemical stability of electrostatic spray deposited thin film of LiMn2O4 was performed in LiClO4–EC–PC, LiBF4–EC–PC, and LiPF6–EC–PC solutions at 55°C. The solution resistance, the surface film resistance, and the charge-transfer resistance were all found to depend on the electrolyte composition. Among the LiX-salts studied, the lowest charge transfer-resistance, and surface layer resistance were obtained in LiBF4–EC–PC solution. There is no major influence of the electrolyte solution compositions upon lithium ion transport in the LiMn2O4 bulk at 55°C. The diffusion coefficient of lithium in the solid phase varied within 10−10–10−8 cm2 s−1 in the three solutions. In general, it seems that in LiBF4 solutions, the surface chemistry is the most stable in the three solutions examined, and hence the electrode impedance in LiBF4 solutions was the lowest. In LiPF6 solutions, HF seems to play an important role, and thus, the electrode impedance is relatively high due to the precipitation of surface LiF.
With the approaching commercialization of PEM fuel cell technology, developing active, inexpensive non-precious metal ORR catalyst materials to replace currently used Pt-based catalysts is a necessary and essential requirement in order to reduce the overall system cost. This review paper highlights the progress made over the past 40 years with a detailed discussion of recent works in the area of non-precious metal electrocatalysts for oxygen reduction reaction, a necessary reaction at the PEM fuel cell cathode. Several important kinds of unsupported or carbon supported non-precious metal electrocatalysts for ORR are reviewed, including non-pyrolyzed and pyrolyzed transition metal nitrogen-containing complexes, conductive polymer-based catalysts, transition metal chalcogenides, metal oxides/carbides/nitrides/oxynitrides/carbonitrides, and enzymatic compounds. Among these candidates, pyrolyzed transition metal nitrogen-containing complexes supported on carbon materials (M–Nx/C) are considered the most promising ORR catalysts because they have demonstrated some ORR activity and stability close to that of commercially available Pt/C catalysts. Although great progress has been achieved in this area of research and development, there are still some challenges in both their ORR activity and stability. Regarding the ORR activity, the actual volumetric activity of the most active non-precious metal catalyst is still well below the DOE 2015 target. Regarding the ORR stability, stability tests are generally run at low current densities or low power levels, and the lifetime is far shorter than targets set by DOE. Therefore, improving both the ORR activity and stability are the major short and long term focuses of non-precious metal catalyst research and development. Based on the results achieved in this area, several future research directions are also proposed and discussed in this paper.
Severe capacity fading and poor high rate performance of lithium sulfur (Li–S) battery caused by “shuttle effect” and low conductivity of sulfur hampers its further developments and applications. Li4Ti5O12 (LTO) possesses high lithium ion conductivity, and it is also can be used as an active adsorbent for polysulfide. Herein, fine LTO particle coated carbon nanofibers (CNF) were prepared and a conductive network both for electron and lithium ion was built, which can greatly promote the electrochemical conversion of polysulfide and improve the rate performance of Li–S batteries. Meanwhile, a quantity of adsorption sites is constructed by defects of the surface of LTO-CNF membrane to effectively immobilize polysulfide. The multifunctional LTO-CNF interlayer could impede the shuttle effect and enhance comprehensive electrochemical performance of Li–S batteries, especially high rate performance. With such LTO-CNF interlayer, the Li–S battery presents a specific capacity of 641.9 mAh/g at 5 C rate. After 400 cycles at 1 C, a capacity of 618.0 mAh/g is retained. This work provides a feasible strategy to achieve high performance of Li–S battery for practical utilization.
Given the considerable amount of energy dissipated in the salinity gradient at the point where a river flows into the sea, we investigate the technology of capacitive mixing (CapMix), an attractive technology for generating electrical power from this gradient. We determine the performances of multiple wire-shaped electrode pairs connected either in series or in parallel in a CapMix system. The bundles of pairs were immersed in synthetic river and seawater. Pairs connected in parallel and placed next to each other allowed for 18% more energy extraction than the total energy extracted by the same number of pairs individually. An even higher additional energy gain is possible if contact resistances are further minimized. The improvement is due to the additional flow paths for ions between electrode pairs in parallel connection, reducing the total internal resistance. The highest power density achieved (in terms of the mass of activated carbon material used) was 2.7mW/g, which was higher than the power densities that have been achieved previously using a flat plate CapMix cell (1.26mW/g) and a wire electrode cell (0.34mW/g). The lower ohmic resistance in the parallel system was identified using a current distribution model and experimental measurements.
The recent progress of investigation in this laboratory on some interesting electrolytes for lithium ion batteries is summarized. Nano-Al2O3 filler was found to act as a solid solvent in the LiClO4/polyacrylonitrile electrolyte system. Novel room temperature molten salt was prepared and showed a series of interesting electrochemical properties. Addition of vinyl ethylene carbonate (VEC) into propylene carbonate based electrolyte helped to form a compact solid electrolyte interphase layer on graphite anode during the first discharge process.
Here two chemical reduction pathways to synthesize the vinylene carbonate (VC) and poly(VC) reduction products are investigated, with the precise aim of further deciphering the lithium-ion battery solid electrolyte interphase (SEI) layer composition and the associated reduction mechanisms. The liquid synthesis pathway offers the opportunity of varying the concentration of Li-4,4′-Di-tert-butylbiphenyl reducing agent, whereas the dry synthesis pathway by ball milling allows to solve issues related to solvent-induced side reactions and washing procedure. As a result, the two syntheses do not unveil the same reduction mechanisms, favouring either carboxylate or carbonate salts as the major end product. The latter pathway is very efficient in terms of providing SEI-layers products resulting in well-defined IR spectra and comparisons with simulated spectra enable us to obtain IR fingerprints of the Li di-vinylene di-carbonate (LDVD) compound. Taken together the synthesis procedures provide information on conditions favouring radical polymerization and further poly(VC) reduction into Li2CO3 and polyacetylene. Overall, this chemical simulation of SEI-layers formation assists in a proper characterization of the SEI-layers created on graphite surfaces by their IR spectra showing that Li2CO3, LDVD and poly(VC) are all present in different proportions dependent on the VC content in the electrolyte.
The growing demand for electrical power and the limited capital invested to provide this power is forcing countries like Brazil to search for new alternatives for electrical power generation. The purpose of this paper is to present a technical and economic study on a 15kW solar plant installed in an isolated community, highlighting the importance of the need for financial subsidy from the government. It evaluates the importance of parameters such as the annual interest rate, specific investment, the marginal cost of expanding the electrical power supply and the government subsidy on amortization time of capital invested.
Stoichiometric and non-stoichiometric Mg-doped lithium iron phosphates were synthesised via spray-pyrolysis, followed by sintering at high temperature for crystallization. The spray pyrolysis process allows the homogeneous mixing of the ingredient reactants at atomic level. The electronic conductivities of the Mg-doped lithium iron phosphates have been drastically improved by 4 orders of magnitude, comparing to the undoped LiFePO4. The electrochemical properties of as-prepared lithium iron phosphates were systematically measured by cyclic voltammetry and constant current charge/discharge cycling tests.
Cost-efficient generation of second-generation biofuels requires plant biomass that can easily be degraded into sugars and further fermented into fuels. However, lignocellulosic biomass is inherently recalcitrant toward deconstruction technologies due to the abundant lignin and cross-linked hemicelluloses. Furthermore, lignocellulosic biomass has a high content of pentoses, which are more difficult to ferment into fuels than hexoses. Engineered plants with decreased amounts of xylan in their secondary walls have the potential to render plant biomass a more desirable feedstock for biofuel production.
Operations of lithium-ion batteries have long been limited to a narrow temperature range close to room temperature. At elevated temperatures, cycling degradation speeds up due to enhanced side reactions, especially when high-reactivity lithium metal is used as the anode. Here, we demonstrate enhanced performance in lithium metal batteries operated at elevated temperatures. In an ether-based electrolyte at 60 °C, an average Coulombic efficiency of 99.3% is obtained and more than 300 stable cycles are realized, but, at 20 °C, the Coulombic efficiency drops dramatically within 75 cycles, corresponding to an average Coulombic efficiency of 90.2%. Cryo-electron microscopy reveals a drastically different solid electrolyte interface nanostructure emerging at 60 °C, which maintains mechanical stability, inhibits continuous side reactions and guarantees good cycling stability and low electrochemical impedance. Furthermore, larger lithium particles grown at the elevated temperature reduce the electrolyte/electrode interfacial area, which decreases the per-cycle lithium loss and enables higher Coulombic efficiencies.
A novel conductive sulfur-containing nanocomposite cathode material was synthesized by heating the mixture of sublimed sulfur and multi-walled carbon nanotubes (MWNTs) in certain conditions. The cathode with MWNTs–sulfur nanocomposite (MSN) material shows the improvement of not only the charge–discharge capacity but also cycle durability. From the results, it is confirmed that the MWNTs shows a vital role on adsorbing sublimed sulfur and the polysulfides within the cathode and is an excellent electric conductor for the lithium–sulfur rechargeable system. It can effectively prevent the shuttle behavior of the lithium–sulfur battery.
The current energy crisis has placed increased interest in all aspects related to electrical energy generation, conversion and storage with particular emphasis on fuel cells, batteries and supercapacitors. Clearly these are all electrochemical interfaces and thus our discipline has been put front and center in the energy landscape. Addressing these aspects represents the primary objective of this special issue which covers numerous aspects related to the above-mentioned research areas. In the general subject of fuel cells, this special issue presents contributions dealing with various aspects of electrocatalysis including transport effects (Lindstroma et al.) as well as the electrooxydation of hydrogen (Zhuang et al.) and ethylene glycol (Behm et al.). Studies of the oxidation of CO (González et al. and Herrero et al.) on Pt aggregates as well as the study of CO tolerance pathways on Pt–Ru electrodes (Ticianell et al.) provide additional insights into this most important process. In batteries, Novak et al. presents a novel approach to the determination of lithium ion mobility while Zhang et al. discuss the effects of Mg doping on the performance of Li2FeSiO4 while in supercaps, Rolison et al. discuss the effects of temperature and atmosphere on the performance of electrochemical capacitors. All of these contributions, from well-recognized leaders, constitute a volume of great currency and relevance that will be of great value and interest to the electrochemical community, in general, and to those involved in electrochemical energy generation and storage, in particular.
Lab-size rechargeable metal hydride–air (MH–air) cells with a gas management device were designed in order to minimize the loss of electrolyte. An AB5-type hydrogen storage alloy was used as anode materials of the MH–air. The thickness of the metal hydride electrodes was in the range of 3.0–3.4mm. Porous carbon-based air electrodes with Ag2O catalysts were used as bi-functional electrodes for oxygen reduction and generation. The electrodes were first examined in half-cells to evaluate their performance and then assembled into one MH–air cell. The results showed the good cycling stability of the rechargeable MH–air cell with a capacity of 1990mAh. The discharge voltage was 0.69V at 0.05–0.1C. The charge efficiency was about 90%. The specific and volumetric energy densities were about 95Whkg−1 and 140WhL−1, respectively.
This paper reviews the antimicrobial research undertaken on South African medicinal plants during the period 1997–2008. Antimicrobial methods (disc diffusion, minimum inhibitory concentration (MIC), bio-autography) are briefly discussed and an analysis of the publications reviewed indicates that the majority of papers use MIC assays for antimicrobial determination. Antimicrobial investigations on extracts are presented where the most active plants are identified from screening publications. A summary of some bioactive compounds are given with data restricted to papers reporting quantitative antimicrobial activity equivalent to or below 200μg/ml. Antimicrobial activities on the essential oils of indigenous medicinal aromatic plants are also reviewed. An overview is given on what activities (extracts, compounds and oils) should be considered noteworthy for publication. Studies focusing on geographical ethnobotany, specific pathogenesis, formulation aspects and in vivo investigations are examined. Future recommendations to consider include pathogen selection, interactive studies and dosage administrations.
The drawbacks of Li-rich layered oxides, such as large initial irreversible capacity, phase transformation and electrochemical performance degradation, are closely related to the surface states of the Li-rich layered oxide. To overcome these problems, a new surface modification method to the Li-rich layered oxide is proposed, in which the fast lithium-ion conductor (Li-La-Ti-O composite, LLTO) is coated on the surface of Li1.2Ni0.13Co0.13Mn0.54O2 (LRO) particles. SEM, EDS and HRTEM analyses reveal that an entire and homogeneous coating layer is formed. Electrochemical performances display that the LLTO coated samples, especially the LRO-LLTO5 material, exhibit better cycle stability, higher rate capabilities and less voltage decay. To investigate the origins of enhanced electrochemical performances for LLTO coated samples, the electrode processes at various cycles and the structural stability of the samples are studied by EIS and DSC. The protective effect of LLTO coating layer to the bulk crystallographic structure of cathode material is revealed by HRTEM images. Our study shows that the reduced interface impedances and definitely protective effect resulting from the complete and homogeneous LLTO coating layer are responsible for the enhanced electrochemical performances of the LLTO coated samples.
The hierarchical Cu nanosheets @ CuO nanorods nanostructures were fabricated by a facile hydrothermal approach using Cu nanosheets as self-template and nano-substrate in an aqueous solution of NaOH/H2O2. The hierarchical Cu nanosheets @ CuO nanorods electrodes show a high reversible capacity of 620mAh/g after 200 cycles, much higher than that of the pure CuO nanocrystals at a current 0.1C. The excellent electrochemical performance of the hierarchical Cu nanosheets @ CuO nanorods electrode can be attributed to the unique architecture, which not only provides appropriate spaces between nanorod arrays to accommodate the volume change during the discharge/charge process, but also enables fast charge transport owing to the reduced diffusion paths for electrons and induced the Cu nanosheet as the nano-substrates.
A facile one-pot synthesis of solid polymer electrolytes (SPEs), composed of carbonate terminated poly(ethylene glycol) (CH3O-PEG-IC), poly(ethylene glycol)-block-polystyrene (PEG-b-PS) block copolymer nanoparticles containing a conductive PEG corona, fumed SiO2 and LiTFSI salt via polymerization-induced self-assembly is proposed. This method to prepare SPEs has the advantages of one-pot convenient synthesis, avoiding use of organic solvent and conveniently adding inorganic additives. CH3O-PEG-IC combines advantages of PEG and polycarbonate, the in situ synthesized PEG-b-PS nanoparticles containing a rigid polystyrene (PS) core and a PEG corona guarantee continuous lithium ion transport in the synthesized SPEs, and the fumed SiO2 optimizes the interfacial properties and improves the electrochemical stability, all of which afford SPEs a well considerable room temperature ionic conductivity of 1.73 × 10−4 S/cm, high lithium transference number of 0.53, and wide electrochemical stability window of 5.5 V (vs. Li+/Li). By employing these SPEs, the assembled solid state cells of LiFePO4|SPEs|Li exhibit considerable cell performance.
Pure-phase and well-crystallized spinel LiMn2O4 powders as cathode materials for lithium-ion batteries were successfully synthesized by a new simple microwave-assisted rheological phase method, which was a timesaving and efficient method. The physical properties of the as-synthesized samples compared with the pristine LiMn2O4 obtained from the rheological phase method were investigated by thermogravimetry analysis (TGA), X-ray diffraction (XRD) and scanning electronic microscope (SEM). The as-prepared powders were used as positive materials for lithium-ion battery, whose charge/discharge properties and cycle performance were examined in detail. The powders resulting from the microwave-assisted rheological phase method were pure, spinel structure LiMn2O4 particles of regular shapes with distribution uniformly, and exhibited promising electrochemical properties for battery. Furthermore, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were employed to characterize the reactions of Li-ion insertion into and extraction from LiMn2O4 electrode.
Fine-sized Li–Co–Mn–O cathode particles with various ratios of cobalt and manganese components were prepared by conventional solid-state reaction method using the nano-sized precursor particles. The nano-sized precursor particles of cobalt and manganese components were prepared by spray pyrolysis. The LiCo1−x Mn x O2 (0.1≤ x ≤0.3) particles had finer size than that of the pure LiCoO2 particles. Manganese component disturbed the growth of the LiCo1−x Mn x O2 cathode particles prepared by solid-state reaction method. The pure LiCoO2 cathode particles had high initial discharge capacity of 144mAhg−1. However, the initial discharge capacities of the LiCo1−x Mn x O2 (0.1≤ x ≤0.3) cathode particles decreased with increasing the contents of the manganese component. The discharge capacities of the LiMn2−y Co y O4 (0≤ y ≤0.2) cathode particles decreased abruptly with increasing the contents of the cobalt component. The pure LiMn2O4 cathode particles had the initial discharge capacities of 119mAhg−1.
Novel Ni-doped titanate derived from protonated layered titanate has been fabricated via a simple ion-exchange process at room temperature. The as-synthesized product was calcined at 400 °C for 3 h to obtain the Ni–TiO2 (anatase). The crystal structure of Ni–TiO2 was studied by X-ray diffraction (XRD) and the surface chemistry was studied by X-ray photoelectron spectroscopy (XPS). It was found that doped nickel ions had inhibition effects on the crystallization of TiO2 during calcination. The electrochemical properties of Ni–TiO2 and undoped TiO2 were both tested as anode materials for lithium-ion batteries at room temperature. While the undoped sample exhibited a mediocre performance, having a discharge capacity of 132 mAhg−1 after 50 cycles, the nickel-ion doped sample demonstrated noticeable improvement in both of its discharge capacity and rate capability; with a high capacity value of 226 mAhg−1 after 50 cycles. This improvement of lithium ion storage capability of Ni–TiO2 can be ascribed to the Ni-doping effect on crystallinity and the modification of electrode/electrolyte interface of the TiO2 structure.