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Here we report for the first time of synthesizing ultrathin hematite nanoflakes (NFs) through an electrochemically induced morphological transformation from hematite nanorods (NRs). The NR–NF structural transformation was induced electrochemically at a negative potential (−1.2V vs. Ag/AgCl). The synthesized NFs have an average thickness of 10nm and an average diameter of 100nm. In comparison to NR, NF exhibits enhanced surface area and reduced charge transfer resistance, which are highly desirable for electrode materials of electrochemical devices. In this work, we investigated the mechanism of structural transformation and tested the performance of NR and NF electrodes for electrochemical capacitors and photoelectrochemical cells. Significantly, the NF electrode achieved an order of magnitude larger capacitance than NR electrode. The NF electrode also exhibited approximately three times higher photocurrent than NR electrode. This work opens up a new strategy to fabricate hematite electrodes with enhanced performance for electrochemical capacitors and photoelectrochemical cells, and can be potentially extended to other applications such as fuel cells and lithium-ion batteries.
Poly(ethylene carbonate) (PEC) is known as an alternating copolymer derived from carbon dioxide (CO2) and an epoxide as monomers. Here, we describe a new quaternary PEC-based composite electrolyte containing lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) salt, N-n-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl) imide (Pyr14TFSI) ionic liquid, and an electrospun silica (SiO2) fiber (SiF) with a submicron diameter in view of its possible applications in solid-state Li polymer batteries. A free-standing electrolyte membrane is prepared by a solvent casting method. The Pyr14TFSI ionic liquid enhances the ionic conductivity of the electrolyte as a result of its plasticizing effect. The electrochemical properties, such as ionic conductivity and Li transference number (t Li+), as well as mechanical strength of the electrolyte, are further improved by the SiF. We show that the quaternary electrolyte has a conductivity of the order of 10−7 Scm−1 at ambient temperature and a high t Li+ value of 0.36 with an excellent flexibility. A prototype Li polymer cell using LiFePO4 as a cathode material is assembled and tested. We demonstrate that this battery delivers a reversible charge-discharge capacity close to 100mAh g−1 at 75°C and C/15 rate. We believe that this work may pave the road to utilize CO2 as a carbon source for highly-demanded, functional battery materials in future.
Resumen Objetivos valorar la capacidad funcional de las personas mayores de 70 años según la escala Short Physical Performance Battery (sppb), para detectar incapacidad funcional precoz/prefragilidad y analizar la relación entre la puntuación del cuestionario y los niveles de calcio, albúmina y vitamina D. Métodos estudio descriptivo transversal que incluyó a 77 pacientes mayores de 70 años que acudieron a consulta con su médico familiar por diversos motivos. Se les aplicó la escala sppb y se midieron valores de calcio, albúmina y vitamina D. Se consideró prefragilidad cuando la puntuación obtenida del spbb fue menor a 10. Resultados la puntuación global del cuestionario fue de 7.75 ±2.72 puntos, lo cual colocó a 67.5% de los pacientes en prefragilidad. Se determinó una correlación entre la puntuación global y la puntuación por secciones; la velocidad al andar cuatro metros fue la sección con el mayor coeficiente de correlación con la puntuación total. Los niveles de vitamina D, calcio o albúmina no se correlacionaron con la puntuación del cuestionario sppb. Conclusiones el porcentaje de pacientes prefrágiles por encima de 70 años fue muy alto. Se propone la utilización de la velocidad de la marcha (1.9±0.5min) para aquellos médicos que tengan saturación de pacientes, ya que presentó la relación lineal directa más fuerte con la realización completa del cuestionario sppb.
Na0.74(Li1/3Mn2/3)xCo1-xO2 (x=0, 1/6, 1/3, 1/2) as sodium-ion battery cathode materials are prepared by using sol-gel method. The XRD tests demonstrate that Na0.74CoO2 and its Li1/3Mn2/3-substituted samples possess typical P2 structure. The charging/discharging tests exhibit that the Na0.74CoO2 electrode has a reversible capacity of 131mAhg−1 with good cycling performance. When Co is partially substituted by Li1/3Mn2/3, the Li1/3Mn2/3-substituted samples exhibit decreasing reversible capacity of 122, 115, 83mAhg−1 for x=1/6, 1/3, 1/2, respectively. However, the rate capability of the Li1/3Mn2/3-substituted samples is greatly improved due to the suppression of the complicated phase conversion in intercalation process. Moreover, the structure stability for Li1/3Mn2/3-substituted samples is apparently observed when cycled between 4.5 and 2.0V. Therefore, the substitution of Li1/3Mn2/3 can suppress the complex phase changes of the Na-based oxides and improve their electrochemical performance, which can provide a promising choose for high-performance Na-ion storage cathode material.
Publisher Summary The chapter presents the author's personal insights into life as a research assistant. The chapter describes how the author stumbled into accounting academia as a failed practising accountant and informs how he got into this job profile, what were his aims and plans, and how he dealt with everything that came his way during the process. It provides additional background to research projects, the research teams, and the work undertaken. It outlines the issues faced by the author during his tenure as a research assistant and presents reflections on how he dealt with these issues, which included traveling; heavy and complicated work schedules; tensions between multiple duties; supervision; and management of research teams. The chapter presents the positive side of being a research assistant, and how the experience influences one's entire academic career and not just the years spent servicing the project.
Seawater desalination is a leading method for tackling the challenge of global freshwater shortage. However, existing desalination technologies like capacitive deionization (CDI) have their own limits, including high energy consumption or low ion removal capacity, which is not sufficient for desalting high-concentration saline water with low cost. Herein, we present a concept of flow dual-ions electrochemical deionization technology, which consists of BiOCl for chloride ion Faradaic electrode on the negative side, sodium manganese oxide (Na0.44MnO2) as sodium ion Faradaic electrode on the positive side, and a flow salt feed as electrolyte. It utilizes a redox reaction to individually capture chloride ions and sodium ions concurrently. Under positive electric current operations, the two ions are released for NaCl water electrolyte to flow. On switching to negative electric current, the chloride ions are extracted into the negative electrode, and thus prevented from flowing into the NaCl solution while sodium ions are electrochemically captured into the positive electrode. The novel dual-ions in Faradaic deionization deliver a stable and reversible salt removal/release capacity of 68.5 mg g−1 when operated at a current density 100 mA g−1, which indicates an amount over twice the salt absorption amount of the previously reported best performance (31.2 mg g−1) obtained by a hybrid capacitive deionization system. The electric charge efficiency is up to 0.977 during salt desorption process and 0.958 during absorption process. Owing to the salt removal, energy will be released during discharge process; therefore, the current system is called “desalination generator”. Our research will supply a new method for desalination flow-through system.
Sulfonated SiO2 particles containing poly(lithium 4-styrenesulfonte) in their shell are synthesized and used as coating materials for the preparation of ceramic-coated separators for lithium-ion cells. The ceramic-coated separators exhibit good thermal stability and wettability for liquid electrolyte due to the presence of a heat-resistant silica with hydrophilic poly(lithium 4-styrenesulfonte). By using these ceramic-coated separators, lithium-ion cells composed of a carbon negative electrode and a LiNi1/3Co1/3Mn1/3O2 positive electrode are assembled and their cycling performances are evaluated. The cells assembled with the ceramic-coated separators demonstrate superior cycling performance compared to cell prepared with a polyethylene separator.
Based on the voltammetric behaviour of a series of halogen-substituted dimethoxybenzene in 1M LiPF6/EC:DEC electrolyte, 2,5-difluoro-1,4-dimethoxybenzene (F2DMB) was selected and tested as an electrolyte additive for overcharge protection of Li/Li4Ti5O12 cell. From the galvanostatic study of the cells at different overcharge current (C/20, C/50, C/100 and C/200) in the presence of F2DMB, it was found that the shuttle additive can be adsorbed at the cathode surface and form a dense layer which prevents the intercalation of Li+ ion in the positive electrode. At low overcharge current (C/200 rate) the voltage of the cell levelled off at the oxidation potential of the shuttle molecule for more than 50 cycles, but at higher charge rates (C/50 and C/100), the voltage of the cell was levelled off for only 16 cycles. The reason is that the F2DMB molecules remaining in solution after the formation of the layer at the cathode cannot carry the current even at charge rates as low as C/100.
The morphological and chemical modifications induced by repeated cycling of conversion-type negative electrode material were studied for iron sulfide thin films in 1M-LiClO4/PC by combining AFM, XPS and ToF-SIMS analysis with electrochemical control. The topographical changes were consistent with irreversible swelling of the material caused by repeated volume expansion/contraction. A 3% capacity fading measured after 9 conversion/deconversion cycles resulted mainly from the loss of electroactive material forming pinhole defects in the thin film electrode. Repeated cycling caused increasing accumulation of non deconverted material in the bulk thin film electrode. Repeated cycling also resulted in continuous surface up-take and increasing accumulation of the SEI layer in the bulk thin film electrode, rich in Li2CO3. Formation of a duplex-like structure with organic and inorganic compounds primarily distributed in the outer and inner parts, respectively, was suggested by ToF-SIMS depth profiling of the SEI layer.
Thin polypyrrole (PPy) films (thickness = 5–10 nm) were electrochemically deposited in situ on a carbon paste (97% of graphite plus 3% of Teflon) by means of cyclic voltammetry (CV), from an acetonitrile solution of pyrrole (0.2 M) and NaClO4 (0.1 M). The obtained PPy/graphite composite electrode was investigated by CV and chronopotentiometry in 0.3 M NaClO4 aqueous electrolytic solution. The capacitance of a composite electrode, calculated by CV, was about 10 F g−1. The capacitance value of the composite electrode was approximately nine times larger than that of pure graphite. The massic charge and discharge capacity (Q) values, calculated by chronopotentiometry, were considerably higher for the composite electrode—by more than 60 times—than for the pure graphite electrode. Electrochemical impedance spectroscopy (EIS) measurements, performed under stationary conditions, led to an interfacial capacitance value intermediate between that of pure graphite and that of the composite electrode.
In this article, the chemical synthesis and characterization of Al2O3 nanoparticles dispersed into poly (P-phenylendiamine) (PpDP) was reported. The morphology, conductivity and structure of the nanocomposite was characterized by scanning electron microscopy (SEM), four probe testing and XRD experiment, respectively. Catalytic activity and stability for the oxidation of hydrazine were studied by using cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The results show that the nanocomposite significantly enhances the effective surface area and the catalytic activity of the CPE (carbon paste electrode) for oxidation of hydrazine. The results obtained confirmed that the dispersion of the Al2O3 particles is connected with catalytic response to a higher activity. The nanotubular morphology of poly (P-phenylendiamine) helps in the effective dispersion of Al2O3 particles facilitating the easier access of hydrazine to the catalytic sites. The poly (P-phenylendiamine) nanotubes modified with Al2O3 nanoparticles cause a great increase in electroactivity and the electro-catalytic properties of CPE for hydrazine oxidation.
In an effort to reduce thermal shrinkage and improve electrochemical performance of porous polypropylene (PP) separators for lithium-ion batteries, a new composite separator is developed by introducing ceramic coated layers on both sides of PP separator through a dip-coating process. The coated layers are comprised of heat-resistant and hydrophilic silica nanoparticles and polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) binders. Highly porous honeycomb structure is formed and the thickness of the layer is only about 700 nm. In comparison to the pristine PP separator, the composite separator shows significant reduction in thermal shrinkage and improvement in liquid electrolyte uptake and ionic conduction, which play an important role in improving cell performance such as discharge capacity, C-rate capability, cycle performance and coulombic efficiency.
Guidance recommendations by the Committee for Medicinal Products for Human Use (CHMP) and Pharmaceutical Research and Manufacturers of America (PhRMA) acknowledge the presence of potential toxic impurities in some pharmaceutical ingredients and have proposed setting limits on impurities with genotoxic activity as a means to protect patients in clinical trials and for marketing of the approved products. Recently, there have been suggestions that drug excipients, including existing products, should also be subjected to the same testing procedures and intake limits as proposed for active ingredients. This report is an attempt to put such recommendations into the proper perspective regarding the likelihood of protecting or improving public health.
Numerous attempts have been made over the last thirty years to estimate fluid flow rates at hydrothermal vents, either at the exit of black smoker chimneys or within diffuse flow areas. In this study, we combine two methods to accurately estimate fluid flow velocities at diffuse flow areas. While the first method uses a hot film anemometer that performs high-frequency measurements, the second allows a relatively rapid assessment of fluid flow velocity through video imagery and provides in situ data to calibrate the sensor. Measurements of flow velocities on hydrothermal diffuse flow areas were obtained on the Mid-Atlantic Ridge (MAR). They range from 1.1 to 4.9mm/s at the substratum level, in low-temperature (4.5–16.4°C) diffuse flow areas from the Tour Eiffel sulfide edifice. A strong correlation was observed between fluid flow velocities and temperature, supporting the possible use of temperature as a proxy to estimate the flow rates in diffuse flow areas where such a simple linear flow/temperature relation is shown to dominate.
Bipolar all-solid-state lithium-ion batteries (LIBs) have attracted considerable attention as a promising approach to address the ever-increasing demand for high energy and safety. However, the use of (sulfide- or oxide-based) inorganic solid electrolytes, which have been the most extensively investigated electrolytes in LIBs, causes problems with respect to mechanical flexibility and form factors in addition to their longstanding issues such as chemical/electrochemical instability, interfacial contact resistance and manufacturing processability. Here, we develop a new class of flexible/shape-versatile bipolar all-solid-state LIBs via ultraviolet (UV) curing-assisted multistage printing, which does not require the high-pressure/high-temperature sintering processes adopted for typical inorganic electrolyte-based all-solid-state LIBs. Instead of inorganic electrolytes, a flexible/nonflammable gel electrolyte consisting of a sebaconitrile-based electrolyte and a semi-interpenetrating polymer network skeleton is used as a core element in the printed electrodes and gel composite electrolytes (GCEs, acting as an ion-conducting separator membrane). Rheology tuning (toward thixotropic fluid behavior) of the electrode and GCE pastes, in conjunction with solvent-drying-free multistage printing, enables the monolithic integration of in-series/in-plane bipolar-stacked cells onto complex-shaped objects. Because of the aforementioned material and process novelties, the printed bipolar LIBs show exceptional flexibility, form factors, charge/discharge behavior and abuse tolerance (nonflammability) that far exceed those achievable with inorganic-electrolyte-based conventional bipolar cell technologies.
The operation of polymer electrolyte membrane fuel cells (PEMFCs) with dry feeds has been examined with different fuel cell flow channel designs as functions of pressure, temperature and flow rate. Auto-humidified (or self-humidifying) PEMFC operation is improved at higher pressures and low gas velocities where axial dispersion enhances “back-mixing” of the product water with the dry feed. We demonstrate auto-humidified operation of the channel-less, self-draining fuel cell, based on a stirred tank reactor; data is presented showing auto-humidified operation from 25 to 115°C at 1 and 3atm. Design and operating requirements are derived for the auto-humidified operation of the channel-less, self-draining fuel cell. The auto-humidified self-draining fuel cell outperforms a fully humidified serpentine flow channel fuel cell at high current densities. The new design offers substantial benefits for simplicity of operation and control including: the ability to self-drain reducing flooding, the ability to uniformly disperse water removing current gradients and the ability to operate on dry feeds eliminating the need for humidifiers. Additionally, the design lends itself well to a modular design concept.
The effect of operating temperature on performance and aging of Zebra cells was investigated. The cells were cycled at 260°C and 350°C using a modified charging regime to accelerate damage. The cathode and solid electrolyte of degraded cells at the end of cycling were analyzed by scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. It is hypothesized that the formation of AlF3 on the surface of the β″ alumina electrolyte contributes to the failure of cells at low temperatures. A mechanism based on the overcharge reaction is proposed for the formation of this phase. At 350°C, a significant capacity loss was observed with cycle life, which correlates to nickel particle growth as the cause of this phenomenon. The factors responsible for Ni grain growth are discussed.
A series of NaxLi4−xTi6O14 (0 ≤ x ≤ 4) are prepared by solid-state method and their structures, morphologies and electrochemical properties are compared by changing the Na/Li atomic ratio. It can be found that two single-phase samples of Na2Li2Ti6O14 and Na4Ti6O14 and three multi-phase samples of Li4Ti6O14 (Li4Ti5O12/TiO2), NaLi3Ti6O14 (Na2Li2Ti6O14/Li4Ti5O12/TiO2) and Na3LiTi6O14 (Na2Li2Ti6O14/Na2Ti3O7) can be formed by using a stoichiometric ratio of starting materials based on the formula of NaxLi4−xTi6O14. Besides, different Na/Li atomic ratios in NaxLi4−xTi6O14 also induce the morphology evolution shifting from round-shape to polyhedron-shape, and then to square-shape with the increase of Na content. Electrochemical tests show that Li4Ti6O14 delivers the highest charge capacities of 116 mAh g−1 at 100 mA g−1, 91.5 mAh g−1 at 200 mA g−1, 77.5 mAh g−1 at 300 mA g−1 and 66.9 mAh g−1 at 400 mA g−1 among five samples. For comparison, Na4Ti6O14 only reveals the reversible capacities of 38.6 mAh g−1 at 100 mA g−1, 30.2 mAh g−1 at 200 mA g−1, 24.8 mAh g−1 at 300 mA g−1 and 20.9 mAh g−1 at 400 mA g−1. It suggests that Li4Ti6O14 is the most potential lithium storage material among all the NaxLi4−xTi6O14 samples.
With variations in compositions in layered Li[Ni,Co,Mn]O2, we could change the several factors that might be considered to influence the electrochemical properties. The crystallographic characteristics of the samples were studied by neutron diffraction Rietveld analysis. After electrochemical operation, we measured the macroscopic crystal structure changes, the valence state of transition metals and the variations of interatomic distance for M–O (M: transition metal) through XRD and XAS. The variation in macroscopic lattice parameters was well coincident with the variation in microscopic structure changes viz. the variation of interatomic distance. We discussed the characteristics of transition metals in the structure and their effects on the electrochemical properties of the samples under electrochemical operation. We found that Li[Li1/10Ni2/10Co3/10Mn4/10]O2 with the lowest Ni/(Mn + Co) ratio among the samples showed the best capacity retention up to the 30th cycle.
As the energy demand around the world grows so does the need for devices that can be tailored to fit a specific design's parameters. Often, this can lead to a device that falls between the two traditional groups of lithium-ion battery (LIB) and lithium-ion capacitors (LIC). An emerging way to bring these devices together is using composite cathodes. Composite cathodes combine a capacitor material with battery material and have shown to be able to enhance life cycle energy and power performance compared to their non-composite counterparts. We report here on a hybrid LIC consisting of a Lithium nickel cobalt manganese oxide (NMC)/activated carbon (AC) composite cathode in combination with an ultra-thin lithium film (u-Li) pre-loaded on a hard carbon anode. Additionally, we show that by utilizing three design approaches: dry composite electrode fabrication method, cathode to anode capacity ratio design, and pre-lithiation method using u-Li, we can demonstrate an energy storage device with excellent cycle life, and that can be tailored by composite ratios within the cathode to fit different applications. Shown here is an in-depth look at various composite material ratios, pre-lithiation calculations, and hybrid lithium-ion battery-capacitor energy storage device creation based on targeting essential energy-power performance characteristics.
Recent experiments illustrate that the morphology of the electrode surface impacts the voltage - capacity curves and long term cycling performance of Li-ion batteries. The present study systematically explores the role of the electrode surface morphology and uncertainties in the reactions that occur during electrochemical cycling, by performing kinetic Monte Carlo (kMC) simulations using the lattice Boltzmann method (LBM). This allows encoding of the inherent stochasticity at discrete microscale reaction events over the deterministic mean field reaction dynamics that occur in Li-ion cells. The electrodes are taken to be dense thin films whose surfaces are patterned with conical, trapezoidal, dome-shaped, or pillar-shaped structures. It is shown that the inherent perturbations in the reactions together with the characteristics of the electrode surface configuration can significantly improve battery performance, mainly because patterned surfaces, as opposed to flat surfaces, result in a smaller voltage drop. The most efficient pattern was the trapezoidal, which is consistent with experimental evidence on Si patterned electrodes.