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The LiNi0.5− x Mn0.5− x Co2 x O2 (0 < x ≤ 0.1) series was first prepared at 800 °C by the spray dry method. The structural and electrochemical characteristics of these compounds were also studied. The Co substitution seems to promote the formation of LiNi0.5− x Mn0.5− x Co2 x O2. In addition, the Co introduction in LiNi0.5Mn0.5O2 can not only reduce the cell polarization, but increase the reversible capacity. The LiNi0.5− x Mn0.5− x Co2 x O2 series shows an excellent cyclability and rate ability. After 50 cycles, LiNi0.425Mn0.425Co0.15O2 shows a reversible capacity of about 110mAh g−1 at the rate of 1mA cm−2 (100mA g−1) in 3–4.6V at room temperature and more than 140mAh g−1 at the rate of 2mA cm−2 (200mA g−1) at 55 °C.
Layered oxides, ruthenium-substituted Li2MnO3, were synthesized at 800°C and 1200°C. Their phase relation and electrical and electrochemical properties were investigated. Li2Mn1−x Ru x O3 synthesized at 800°C clearly separated into two phases, manganese-rich and ruthenium-rich phases, except for the narrow composition range of 0≤ x ≤0.05, while Li2Mn1−x Ru x O3 synthesized at 1200°C formed two solid solutions in the whole composition range across a structural transition between x =0.6 and 0.8. The electrical resistivity of Li2Mn1−x Ru x O3 decreased with increasing ruthenium content. Li2Mn0.2Ru0.8O3 (x =0.8) synthesized at 1200°C showed the lowest resistivity of 5.7×102 Ωcm at room temperature. The discharge capacity and cycling performance were improved by the ruthenium substitution. Li2Mn0.4Ru0.6O3 (x =0.6) exhibited a discharge capacity of 192mAhg−1 in the initial cycle and 169mAhg−1 in the tenth cycle with high and almost constant charge–discharge efficiencies of 99% from the second to tenth cycle at a current rate of 1/10C. The ruthenium substitution to Li2MnO3 is quite effective to improve electrical conductivity and charge–discharge performance.
Non-flammable high-performance electrolytes are in high demand for rechargeable batteries. Here the authors design cyclic phosphate-based electrolytes to enable stable operations of graphite anodes and high-voltage cathodes for lithium-ion batteries.
The alloying reaction between 14th group elements and alkali can be detrimental for Li, Na or K-ion batteries due to the large associated volume expansion that leads to a rapid capacity fading. In order to overcome this issue, their associated 2D phases are promising anodes that enable alkali intercalation without alloying reaction and volume expansion. In this study, the lamellar siloxene obtained from topotactic deintercalation of Ca from CaSi2 delivered reversible capacities of 2300, 311 and 203 mAh/g for Li, Na and K, respectively, with good capacity retention and coulombic efficiency for Li and Na. The intercalation mechanism taking place upon cycling is highlighted on the basis of ex situ Raman characterization combined with IR spectroscopy, SEM and TEM. To the best of our knowledge, it is the first time that a lamellar Silicon based material shows such high stable capacity without volume expansion, representing a real breakthrough for the batteries field and particularly for NIB.
In this study, commercial Li(Ni1/3Co1/3Mn1/3)O2/graphite (NCM/C) lithium-ion batteries were cycled at −10 °C under different current rates ranging from 0.2 C to 1C. Electrochemical measurements and post-mortem analysis were performed to identify the root causes of the degradation in the electrochemical performance of the cells. The results reveal that apart from the increase of lithium plating on the anode, there is a considerable and abnormal capacity loss on the NCM cathode with the increase in current rate. The different degradation mechanisms including the loss of lithium inventory (LLI) and the specific capacity loss of NCM material (LAM) during cycling at −10 °C were analyzed quantitatively. It is shown that the evolution trend of LLI with the increase in current rate (8.6%, 35.0%, 55.8% for 0.2 C, 0.5 C and 1 C respectively) corresponds closely to that of the capacity loss of the full-cells (8.6%, 45.5%, 63.6% for 0.2 C, 0.5 C and 1 C, respectively), which is different to the trend of LAM (7.2%, 8.8%, 22.3% for 0.2 C, 0.5 C and 1 C, respectively). Further analysis by XRD and HR-TEM clearly indicates that the crystallinity of the hexagonal layered structure of NCM was greatly impaired after low-temperature cycling at −10 °C, and spinel phase can be observed among the layered structure.
Non-precious Fe/N/S-composited hierarchically porous carbon materials (Fe(x)/N/S-PAD, PAD: poly(acrylamide-co-diallyldimethyl ammonium chlor), x: the weight ratio of FeSO4 7H2O/PAD) are synthesized using a facile silica colloid template approach with FeSO4 7H2O as Fe and S sources, and PAD as N source, respectively. A simultaneous creation of porous structures and surface functionalities (Fe, N and S) of such catalysts is realized just by simply tuning the weight ratio of FeSO4 7H2O and PAD in the synthetic precursors. As a result, a series of catalyst samples with high oxygen reduction reaction (ORR) activity/stability are obtained, demonstrating the promotion role of FeSO4/PAD ratio in synthesizing high-performing catalysts. Particularly, a catalyst (Fe(1.5)/N/S-PAD) with a trace Fe content down to 1.0wt.% is tested to be superior to a commercial Pt/C catalyst in alkaline media and exhibits impressive ORR performance in acidic media. Combined with characterization results such as TEM, Raman spectra, BET and XPS analysis, it is found that the well-defined micro- and meso-porous structure play the key role in enhancing catalytic ORR performance rather than the final total N contents in the carbon. Regarding the stability of such a catalyst, test using cyclic voltammetry for 5000 cycles in O2-saturated solution shows a negligible degradation rate when compared with Pt/C one, suggesting that this catalyst could be used for catalyzing the high-performing cathode ORR in proton-exchange membrane fuel cells, alkaline fuel cells and metal–air batteries.
As robot swarms move from the laboratory to real-world applications, a routine checklist of questions could help ensure their safe operation.
The fundamental determinant of death in donation after circulatory determination of death is the cessation of brain circulation and function. We therefore propose the term donation after brain circulation determination of death [DBCDD].
A time dependence of three-dimensional simulation including water phase change and heat transfer of a PEMFC model has been studied. The overshoot behavior has been observed during a change in the electrical load during operation with fixed flow rates of hydrogen and air. The simulation of 25-cm2 active area with a serpentine flow path shows the interactions of the anode and cathode flow streams, the flow through the gas diffusion media, and the movement of water through the MEA by electroosmotic and back diffusion forces. The simulation used a commercial computational fluid dynamics (CFD) solver, STAR-CD with and add-on PEMFC module, es-pemfc. The operating conditions corresponded to 101kPa, 70°C cell temperature, anode and cathode dew points and stoichiometries of 78°C and 72°C and 1.2 and 2.0 at an initial operating voltage of 0.7V and current density of 0.57Acm−2.
Lithium–manganese spinel is prepared by a hydrothermal process that uses ethanol as the co-solvent. The crystallinity, particle morphology and electrochemical performance of the spinel are examined and compared with those obtained without the co-solvent. The amount of co-solvent and reaction time are adjusted to control the properties. The addition of ethanol leads to uniform particle size and shape, as well as higher crystallinity, than for spinel prepared in pure water. The co-solvent also reduces the time required for synthesis. A prolonged reaction time is effective in obtaining high-purity Li–Mn spinel in pure water but more impurities form after a long reaction time in an ethanol-added solvent. A mechanism for this process is suggested. A report is given of the electrochemical performance of Li–Mn spinel, including the capacity, rate capability and cyclability, as well as the effects of the co-solvent on these properties.
Reading comprehension difficulties in children with ADHD are well established; however, limited information exists concerning the cognitive mechanisms that contribute to these difficulties and the extent to which they interact with one another. The current study examines two broad cognitive processes known to be involved in children’s reading comprehension abilities—(a) working memory (i.e., central executive processes [CE], phonological short-term memory [PH STM], and visuospatial short-term memory [VS STM]) and (b) orthographic conversion (i.e., conversion of visually presented text to a phonological code)—to elucidate their unique and interactive contribution to ADHD-related reading comprehension differences. Thirty-one boys with ADHD-combined type and 30 typically developing (TD) boys aged 8 to 12 years (M = 9.64, SD = 1.22) were administered multiple counterbalanced tasks assessing WM and orthographic conversion processes. Relative to TD boys, boys with ADHD exhibited significant deficits in PH STM (d = −0.70), VS STM (d = −0.92), CE (d = −1.58), and orthographic conversion (d = −0.93). Bias-corrected, bootstrapped mediation analyses revealed that CE and orthographic conversion processes modeled separately mediated ADHD-related reading comprehension differences partially, whereas PH STM and VS STM did not. CE and orthographic conversion modeled jointly mediated ADHD-related reading comprehension differences fully wherein orthographic conversion’s large magnitude influence on reading comprehension occurred indirectly through CE’s impact on the orthographic system. The findings suggest that adaptive cognitive interventions designed to improve reading-related outcomes in children with ADHD may benefit by including modules that train CE and orthographic conversion processes independently and interactively.
There is increasing interest in vanadium redox flow batteries (VRFBs) for large scale-energy storage systems. Vanadium electrolytes which function as both the electrolyte and active material are highly important in terms of cost and performance. Although vanadium electrolyte technologies have notably evolved during the last few decades, they should be improved further towards higher vanadium solubility, stability and electrochemical performance for the design of energy-dense, reliable and cost-effective VRFBs. This timely review summarizes the vanadium electrolyte technologies including their synthesis, electrochemical performances, thermal stabilities, and spectroscopic characterizations and highlights the current issues in VRFB electrolyte development. The challenges that must be confronted to further develop vanadium electrolytes may stimulate more researchers to push them forward.
PEO16–LiClO4–ZnAl2O4 nanocomposite polymer electrolyte (NCPE) films prepared by hot-pressing method have been investigated. In order to compare with the hot-pressed NCPEs, the NCPE films have also been prepared using the conventional solution-casting method. Field emission scanning electron microscopy (FESEM), differential scanning calorimetry (DSC), conductivity (σ) and interface property studies have been carried out on above two kinds of films. The results show that the NCPE film prepared by hot-pressing method has smoother surface, higher interface stability, lower crystallization and melting temperature values than that prepared by solution-casting method. An all-solid-state lithium polymer battery using the hot-pressed NCPE film as electrolyte, lithium metal and LiFePO4 as anode and cathode respectively, shows high discharge specific capacity, good rate capacity, high coulombic efficiency, and excellent cycling stability as revealed by galvanostatical charge/discharge cycling tests.
Li2MnSiO4/C composites have been prepared by a facile molten salt method followed by a carbon coating process. Submicron Li2MnSiO4 particles are obtained in KCl–NaCl molten phase with a short reaction time of 3h. The orthorhombic structure and sphere-like morphology are confirmed by X-ray diffraction and scanning electron microscope. Ex-situ XRD study confirms amorphous transition of Li2MnSiO4 during the first charge process. Galvanostatic charge-discharge tests display high initial charge and discharge capacities of 265 and 194 mAh g−1, respectively, at 0.05C rate for the Li2MnSiO4/C composite prepared at 700°C. At 0.1C rate, it maintains a discharge capacity of 165 mAh g−1 and its capacity retention at the 50th cycle is up to 78%, showing superior cycling stability.
In this study, a simple cobalt oxide modification approach for graphite felt is investigated as the positive electrode for the all-vanadium redox flow battery. A thin coating layer of cobalt oxide on the surface of graphite felt is applied via impregnation in conjunction with ultrasonication and calcination. Cyclic voltammetry and electrochemical impedance spectroscopy reveal that the modified graphite felt exhibits excellent electro-catalytic activity and reversibility toward the VO2+/VO2 + redox reaction and stability after repetitive 50-cycle testing. Full cell performance is assessed via charge-discharge and polarization curve analysis. The coulombic efficiency, voltage efficiency, energy efficiency and discharge capacity of the cell employing the modified electrode (without flow field) are 89.5%, 77.6%, 69.4% and 373.9 mAh at 150 mA cm−2, respectively, 12.7% higher in energy efficiency and 101.7% higher in discharge capacity than a cell employing pristine graphite felt. The polarization curve analysis exhibits a much higher limiting current density and maximum power density at a state of charge of 95% due to the inhibition of ohmic polarization. Overall, the results demonstrate an enhanced and stable catalytic effect of the facile cobalt modification for promoting the electrochemical performance of graphite felt in the vanadium redox flow battery.
To evaluate the accuracy of a Functional Activity Monitor (FAM) in 1) detecting daily activities including postures (sitting, standing, lying), transfers between postures and walking, and 2) measuring activity duration and step frequency. A cross-sectional study comparing the outcomes of the FAM to 1) video recordings (HS100P/PC, Panasonic Inc. and VIXIA HG21, Canon Inc.) for activity identification, and 2) 3D motion analysis system recordings (Optotrak 3020 NDI) for measuring step frequencies. The FAM includes one triaxial accelerometer, and one triaxial gyroscope, powered by 3.7V lithium ion battery (sample frequency of 50 Hz; Sparkfun Inc, Boulder CO, USA). One FAM was positioned on the sternum and two on each thigh. Wireless transmission of data to a PDA (Motorola Inc.) was established by means of Bluetooth. Trials included postures, transfers between postures and walking at preferred, slow and fast speeds. Statistical analysis included the determination of percentage of agreement and an ANOVA with repeated measures. Clinical Movement Sciences Laboratory, Boston University. Ten young adults (range 20-26 years of age) including 5 males and 5 females. Not applicable. Frequency of occurrence of activities, activity duration and step frequencies. The agreement between tools for identification of postures ranged from 96.2% to 100%, and for the identification of transfers and walking from 98.6% to1:00%. There was no significant difference between tools in terms of activity duration and step frequencies at different walking speeds. The FAM is an accurate device to monitor daily functional activities, activity durations and step frequencies of healthy young adults in research lab settings. Future research will focus on the validation of the FAM in the evaluation of daily activities of elderly in their home and community environment.
External sediment supply is an important control on wetland morphology and vulnerability to storms, sea-level rise, and land use change. Constraining sediment supply and net budgets is difficult due to multiple timescales of variability in hydrodynamic forcing and suspended sediment concentrations, as well as the fundamental limitations of measurement and modeling technologies. We used two independent observational campaigns and one hydrodynamic modeling effort to estimate the sediment supply to Jamaica Bay, New York, USA, an urbanized embayment with a history of extensive wetland loss. We found that all three estimates indicate a net import to the system, ranging from 36 to 74 kt/year, with a mean estimate of 55 kt/year ± 31 kt/year, which is consistent with a prior estimate derived from radionuclide tracers. Net sediment import is controlled by flood-ebb asymmetry in bed shear stress, which results in higher suspended sediment concentrations on flood tide relative to ebb. This indicates a seaward source of sediment that is resuspended by waves in the coastal ocean, likely offshore marine deposits or potentially from the adjacent Hudson River estuary. Despite the net sediment import, a simple sediment budget suggests that the rate of supply is not sufficient to maintain the present geomorphic planform of the system relative to sea-level rise. The convergent estimates from independent methods provide reasonable guidance as context for sediment-based restoration efforts.
Starting from the pro-environmental potential of virtual reality (VR), the aim was to understand how different statistical information formats can enhance VR persuasive potential for plastic consumption, recycling and waste. Naturalistic, immersive virtual reality environments (VREs) were designed ad hoc to display three kinds of statistical evidence formats, featured as three different formats (i.e., numerical, concrete and mixed). Participants were exposed only to one of the three formats in VR, and their affect, emotions, sense of presence, general attitudes toward the environment, specific attitudes and behavioral intentions toward plastic, use, waste, recycle, as well as their social desirability proneness were measured. Numerical format was the least effective across all dimensions. Concrete and mixed formats were similar. Social desirability only partially affected participants’ attitudes and behavioral intentions. Numerical format did not increase the persuasive efficacy of statistical evidence displayed in VR, with respect to visual alone. Implications and future directions for designing effective VRE promoting pro-environmental behaviors were discussed.
Dicationic ionic liquids are promising solvents for safe high performance Li-ion battery applications. In this work, we report on the synthesis and characterization of new electrolytes based on geminal dicationic pyrrolidinium and piperidinium bis(trifluoromethane)sulfonimide ionic liquids, where the two cations are linked by variable length oxyethylene chain spacers. All 1 M LiTFSI doped synthesized electrolytes are thermally stable up to 300 °C, and they exhibited remarkable electrochemical stability window up to 6.0 V vs. Li/Li+. Electrolytes were assembled with LiMn2O4 (LMO) spinel in lithium half-cells. Electrochemical cell performance in terms of cyclic voltammetry, rate capability and galvanostatic cycling studies have been studied at 60 °C. Results obtained indicate that both the cationic structure and the length of the oxyethylene chain spacer has a significant influence on the electrochemical performance of LMO-cells. The cell based on the pyrrolidinium electrolyte with the two cationic structures linked by two oxyethylene units exhibit the faster rate capability, with a capacity retention of 45% at 5C, and the highest reversible capacity (ca. 80 mAhg-1).
We report on the formation of carbon/Co3O4 (C@Co3O4) composite nanospheres using a hydrothermal approach, followed by application of a thin coating of monosaccharide-derived carbon veneered on the surface of Co3O4 by high temperature calcination. When evaluated as the negative electrode for Li-ion batteries (LIBs), the C@Co3O4 structures exhibit attractive energy storage capacity and improved cycle life, over more than 100 repeated discharge/charge cycles. We hypothesize that the improved electrochemical performance of the composite electrodes originates from the enhanced structural stability of the active Co3O4 particles, imparted by the carbon coating. Consistent with this hypothesis, post mortem analysis performed on pristine Co3O4 and composite C@Co3O4 anodes subjected to prolonged cycling indicate that surface cracking, particle breakage, and primary particle fusion evident in the pristine Co3O4 material are substantially reduced in anodes comprised of C@Co3O4.
The present work focuses on the structural stability upon hydrogenation of three typical La–Mg–Ni-based alloys: La2MgNi9, La3MgNi14 and La4MgNi19. Structural changes during gaseous and electrochemical cycles were characterized, and the influence of the structure distortion on the hydrogen storage properties was concerned. Hydrogen-induced amorphization (HIA) and disproportionation of the three alloys have occurred during both the gaseous and electrochemical cycles. Structural stability of the phase structures in the La–Mg–Ni system is found to follow the order: LaNi5 > (La,Mg)5Ni19 > (La,Mg)2Ni7 > (La,Mg)Ni3 > (La,Mg)Ni2. HIA increases thermal stability of the metal hydrides and difficulty to dehydrogenation and leads to degradation of both the gaseous and electrochemical capacities. Interestingly, La2MgNi9 with poor stability presents elevated discharge capability even at 60 °C which can be attributed to increase in the hydrogen desorption capability and inhibition of the self-discharge induced by severe HIA at higher temperatures. In addition, HIA in the electrochemical reactions is obviously weaker than the extent during the gaseous cycles, which is mainly due to the slower hydrogenation speed. The development of HIA in the gaseous and electrochemical process is considered to follow the direct and gradual modes, respectively.
The cointercalation of sodium with the solvent organic molecule diglyme into graphite, forming a ternary graphite intercalation compound (t-GIC), can resolve the difficulty of making the stage 1 Na-GIC in order to use as a potential anode for Na-ion batteries (NIBs). To clarify the mechanism of such cointercalation, we investigate the atomistic structure, energetics, electrochemical properties, ion and electron conductance, and charge transferring upon the de/intercalation of the solvated Na-diglyme ion into graphite with ab initio calculations. It is found that the t-GICs Na(digl)2C n have the lowest negative intercalation energy at n ≈21, the Na(digl)2 complex diffuses relatively fast in the interlayer space, and the electronic conductance can be enhanced upon the cointercalation compared with graphite. The calculations reveal that the diglyme molecule as well as Na atom donates electrons to the graphene layer, indicating an ionic bond between the graphene layer and the diglyme molecule. We belive that this work will contribute to the development of graphite-based anode materials for NIBs.
This paper presents a generalized method of moments algorithm for estimating the structural parameters of a macroeconomic model subject to the restriction that the coefficients of the monetary policy rule minimize the central bank's expected loss function. The algorithm combines least-squares normal equations with moment restrictions derived from the first-order necessary conditions of the auxiliary optimization. We assess the performance of the algorithm with Monte Carlo simulations using three increasingly complex models. We find that imposing the optimizing restrictions when they are true improves estimation accuracy and that imposing those restrictions when they are false biases estimates of some of the structural parameters but not of the policy-rule coefficients.