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Oxygen plasma treatment was applied on commercially available graphite felt electrodes based on rayon (GFA) and polyacrylonitrile (GFD). The formation of functional groups on the surface of the felt was confirmed by X-ray photoelectron spectroscopy measurements. The BET studies of the plasma treated electrodes showed no significant increase in surface area for both the rayon as well as the PAN based felts. Both plasma treated electrodes showed significantly enhanced V3+/V2+ redox activity compared to the pristine electrodes. Since an increase of the surface area has been ruled out for plasma treated electrode the enhanced activity could be attributed to surface functional groups. Interestingly, plasma treated GFD felts showed less electrochemical activity towards V5+/V4+ compared to the pristine electrode. Nevertheless, an overall increase of the single cell performance was still observed as the negative electrode is known to be the performance limiting electrode. Thus, to a great extent the present work helps to preferentially understand the importance of functional groups on the electrochemical activity of negative and positive redox reaction. The study emphasizes the need of highly active electrodes especially at the negative electrode side as inactive electrodes can still facilitate hydrogen evolution and degrade the electrolyte in VRFBs.
The solvation of anions with organic solvent and its electrochemical intercalation into graphite is a significant research orientation in the electrochemical energy storage. Butylene carbonate (BC), a common solvent with higher oxidation resistance compared with ethylene carbonate (EC) and propylene carbonate (PC), is profitable in studying anion-graphite intercalation compounds (AGICs). In this paper, the electrochemical intercalation behaviors of three representative anions (BF4 −, ClO4 − and PF6 −) in BC solution were studied and the solvation states of these anions were characterized by electrochemical in situ and ex situ techniques. The interpretation of results illuminated that all three anions were able to intercalate into graphite with the similar reversibility but different solvation state, and the conclusive role that solvent played in the intercalation process was also discovered.
Herein, we report a simple one pot all hydrothermal synthesis route to grow nano structure of zinc-cobalt (Zn-Co) @ nickel-cobalt (Ni-Co) layered double hydroxides through oriented attachment growth with ultrathin nanosheets on 3D graphene foam using no additives or oxidants. The pseudocapacitor electrode based on Zn-Co@Ni-Co layered double hydroxides display an enhanced areal capacitance (7485 mFcm−2, at 5 mVs−1) and energy density (1202 mWhcm−2, at 15 mAcm−2) compared to pristine Zn-Co layered double hydroxides, with a greater cycling stability of 108% after 5000 charging-discharging cycles. We fabricate an all solid state symmetrical supercapacitor device with G-Zn-Co@Ni-Co//G-Zn-Co@Ni-Co layered double hydroxides that exhibits an areal capacitance of 1278 mFcm−2, at 10 mVs−1 and energy density of 171 mWhcm−2, at 2.5 mAcm−2. The credit of superior performance of these pseudocapacitor electrodes is to the easy access of electrolyte to the nanosheets, the conductivity enhancement by 3D graphene foam scaffold and the synergistic effect due to the composite structure of the Zn-Co@Ni-Co layered double hydroxides.
A new strategy is proposed for the preparation of Fe3O4 encapsulated in N-doped carbon (denoted as Fe3O4@NC) through a self-assembly of the colloidal FeOOH with polyaniline (PANI) and then a subsequent pyrolysis. Benefiting from the well-designed heterostructure, the resultant Fe3O4@NC shows an ultra-high gravimetric capacitance of 313 F g−1 at 1 A g−1 and still delivers 193 F g−1 at a high current density of 15 A g−1, demonstrating an excellent rate performance. In addition, it has an outstanding volumetric capacitance of 20.25 F cm−3 at 1 A g−1. The asymmetric supercapacitors (ASCs) are constructed by using Fe3O4@NC as anode and layered double hydroxides (LDHs) as cathode, respectively. Due to the enlarged voltage window and matched capacity and kinetics, the obtained CoMn-LDH//Fe3O4@NC ASC device shows a remarkable electrochemical performance with a large energy density up to 35 Wh·kg−1 at a power density of 900 W kg−1 and a high energy density of 24 Wh·kg−1 at a power density of 13.5 kW kg−1 as well as an excellent rate capability and a good cycling stability. The present work may provide an insight into the design of novel anode materials for high-performance ASCs.
Predicting the performance of Li-ion batteries over lifetime is necessary for design and optimal operation of integrated energy systems, as electric vehicles and energy grids. For prediction purposes, several models have been suggested in the literature, with different levels of complexity and predictability. In particular, electrochemical models suffer of high computational costs, while empirical models are deprived of physical meaning. In the present work, a semi-empirical model is suggested, holding the computational efficiency of empirical approaches (low number of fitting parameters, low-order algebraic equations), while providing insights on the processes occurring in the battery during operation. The proposed model is successfully validated on experimental battery cycles: specifically, in conditions of capacity fade >20%, and dynamic cycling at different temperatures. A comparable performance to up-to-date empirical models is achieved both in terms of computational time, and correlation coefficient R 2. In addition, analyzing the evolution of fitting parameters as a function of cycle number allows to identify the limiting processes in the overall battery degradation for all the protocols considered. The model suggested is thus suitable for implementation in system modelling, and it can be employed as an informative tool for improved design and operational strategies.
Morphology variations during electrochemical lithium plating–stripping reactions at the lithium phosphorus oxynitride glass electrolyte (LiPON)/copper current collector (Cu) interface are observed in-situ by scanning electron microscopy (SEM). This in-situ SEM observation shows dynamically that the plating reactions at 50 μA cm−2 distribute initial lithium growth sites sparsely at the LiPON/Cu interface, later, local lithium growth occurs from the pre-plated sites through the Cu film, and finally, most of the precipitated lithium grows to be needle-shape with the height of micron order. This local growth rate attains to be 6.8 mA cm−2, about 100 times higher value than applied one. When those precipitated lithium are stripped at 50 μA cm−2, core region of each precipitate is mostly stripped but its degree depends on the length of the precipitate. This dependency will arise from the diffusivity of Li. When this stripping current density is increased to 500 μA cm−2, the coulomb efficiency is further decreased. In-situ SEM observation shows that plated lithium around the interface becomes thin preferentially while that far away from the interface (upper side of plated lithium) remains unchanged. This will isolate most of precipitate lithium from LiPON film electrically, leading to further decreasing of the coulomb efficiency.
Surface modification as a method for enhancing the cyclability of LiCoO2 cathodes is reviewed. The performances of TiO2 and ZrO2, and their mixed oxide, ZrTiO4, as coating materials, are compared. Coating techniques such as sol–gel and mechano-thermal processes are described. Structural data and morphology of the oxide-coated LiCoO2 are correlated with electrochemical behavior. Their enhanced cyclability is attributed to the suppression of the cycle-limiting phase transitions accompanying the charge–discharge processes. The higher cyclability of the mixed oxide-coated cathodes over those coated with the corresponding individual oxides is also demonstrated. It is also shown that the nature of the core material and the sol–gel precursors for the coatings play a definitive role in the electrochemical behavior of the coated cathode materials.
DaimlerChrysler has asserted itself as an industry leader in the development of fuel cell vehicles. The company began production of a line of New Electric Car (NECAR) vehicles in 1994, and recently announced its latest prototype, the fourth in the series, in March 1999. While the NECAR 4 exhibits significant improvements in fuel cell design, obstacles still remain to the commercial viability of fuel cell vehicles. Cost remains a significant factor, and production costs need to be reduced by a factor of ten. The lack of an existing infrastructure to supply hydrogen for refueling also presents difficulties. To address these remaining concerns, DaimlerChrysler has joined the California Fuel Cell Partnership, a public/private partnership created to demonstrate the viability of fuel cell cars. The Partnership will advance automobile technology towards its goal of practicality , affordability, and environmental conscientiousness. DaimlerChyrsler continues to mature fuel cell technology through its willingness to partner, innovation, and commitment.
In order to prepare bundle-type silicon nanorods, a silver-assisted chemical etching technique was used to modify a 1.6μm silicon thin film, which was deposited on Cu foil by Electron Cyclotron Resonance Plasma Enhanced Chemical Vapor Deposition. The bundle-type silicon nanorods on Cu foil were employed as anodes for a lithium secondary battery, without further treatment. The electrochemical characteristics of the pristine silicon thin film anodes and the bundle-type silicon nanorod anodes are different from one another. The electrochemical performance of the bundle-type silicon nanorod anodes exceeded that of the pristine Si thin film anodes. The specific capacity of the bundle-type silicon nanorod anodes is much higher than 3000mAhg−1 at the first charge (Li insertion) cycle. The coulombic efficiency of bundle-type silicon anodes was stable at more than 97%, and the charge capacity remained at 1420mAhg−1, even after 100 cycles of charging and discharging. The results from the differential voltage analysis showed a side reaction at around 0.44–0.5V, and the specific potential of this side reaction decreased after each cycle. The apparent diffusion coefficients of the two anode types were in the range of 10−13–10−16 cm2 s−1 in the first cycle. In subsequent charge cycles, these values for the silicon thin film anodes and the silicon nanorod bundle anode were approximately 10−12–10−14 and 10−13–10−15 cm2 s−1, respectively.
The effect of carbon black and ceramic (α-Al2O3 and γ-Al2O3) particles on the cationic and polymer chain mobility have been investigated in poly(ethylene oxide)–lithium salt (LiClO4 and LiBF4) solid composite polymer electrolytes by using nuclear magnetic resonance (NMR) techniques. Proton (1H) and lithium (7Li) lineshapes and spin–lattice relaxation times were measured as a function of temperature. The 7Li data indicates that the lineshape and relaxation is affected by the coupling of its quadrupolar moment to the surrounding electric field gradients. Activation energies extracted from the 7Li relaxation data are in the range 0.20–0.25 eV. Results show that the addition of α-Al2O3 influenced both, the relative cation mobility and the polymer chain motion. Calculation shows that this result is in quantitative agreement with the conductivity data.
Pyrolysis conditions for the production of silicon/disordered carbon (Si–DC) nanocomposites using PVA as the carbon source were optimized in this work. It was found that the optimum sintering temperature for the Si–DC nanocomposites is 800°C. In order to achieve good cell performance, a high argon gas flow rate and a slow heating rate are preferred in sample preparation. The morphology of the carbon source (PVA) affects the electrochemical performance of the Si–DC nanocomposites as well. The key point to obtain Si–DC nanocomposites with good electrochemical performance is to reduce the chances of pyrolysis gases (especially CO2) to react with carbon, thereby preventing carbon burnoff during the sintering process.
The thermal stabilities of delithiated LiNi0.5Co0.2Mn0.3O2 (L523), delithiated LiMn2O4 (LMO), and delithiated LiFePO4 (LFP) for lithium ion batteries with bare electrode, solvent and different concentration of electrolyte under delithiated state have been investigated by using differential scanning calorimetry (DSC) and ex X-ray diffraction (XRD). The LFP has the best thermal stability, follows by the LMO and then the L523. The existing of solvent facilitates the decomposition of materials. The addition of Li salt in solvent can further accelerate the thermal decomposition of LMO and LFP; but hold back the decomposition of L523 at some extent that although the total reaction heat grown by 297Jg−1, the first exothermic peak (ca. 279°C) moves backwards comparing with L523 and solvent coexisting system (ca. 255.7°C). As increasing the ratio of electrode material quality to electrolyte, the total exothermic quantity of L523 and LMO becomes large, meanwhile the unit mass exothermic quantity of the L523 varies with little dropping tendency, and that of the LMO decreases obviously. However, for the LFP, the total exothermic quantity decreases and the unit mass exothermic quantity decreases more obviously. Also, the XRD patterns of the three samples at ambient temperature and after 350°C processing with existing of solvent or electrolyte suggest that the L532, LMO and LFP suffer evident structure changes since their pristine peaks become broader, weaker and splitting or disappearing at high temperature.
The storage of energy in batteries is a cause of the failure and loss of reliability in PV systems. The battery behavior has been largely described in the literature by many authors; the selected models are of Monegon and CIEMAT. This paper reviews the two general lead acid battery models and their agreement with experimental data. In order to validate these models, the behavior of different battery cycling currents has been simulated. Results obtained have been compared to real data. The CIEMAT model presents a good performance compared to Monegon’s model.
Objective People with brain tumour experience complex and distressing symptoms. Neuropsychological impairment is proposed to have a negative impact on subjective well-being; however, research is yet to examine the influence of estimated premorbid IQ on this relationship. This preliminary study investigated the moderating effect of estimated premorbid IQ on the relationship between global neuropsychological status (GNF) and depression and quality of life. Methods 73 adults (51% male) aged 21–65years with primary brain tumour (52% benign) were administered a test battery assessing estimated premorbid IQ, GNF, depression (Depression Anxiety Stress Scales) and quality of life (Functional Assessment of Cancer Therapy, FACT). Results A series of two-way analysis of covariance (ANCOVA) controlling for education found a significant interaction between estimated premorbid IQ (low average to average vs high average) and GNF (low vs high) on levels of depression (p <.05) and FACT emotional well-being (p <.05). For these outcomes, individuals with high average estimated premorbid IQ and low GNF reported better well-being than those with low-average to average estimated premorbid IQ and low GNF. Higher GNF was related to greater functional well-being (p <.01) irrespective of estimated premorbid IQ. Conclusion The finding that higher premorbid cognitive ability buffers the effect of neuropsychological impairment on emotional well-being after brain tumour advances understanding of the role of cognitive reserve in adjustment to neurological disorders.
The pulsed method of measuring impedance is described. The cell is galvanostatically stimulated by a bipolar current signal of square shape. The cell response is registered by sampling U +[i], U −[i] with selected period Δt. The impedance spectra are calculated by direct Fourier transform. The internal resistance of the lithium sulphur cell is characteristically minimum in the calculated impedance diagrams in the frequency range of 0.035–5 Hz. It is shown that the lithium sulphur cells have maximum internal resistance at the transient between high and low voltage plateaus of charge and discharge curves. The internal resistance increases significantly during the initial stages of cycling because of the formation of passivation layers at the electrodes. It was found that the internal resistance of the lithium sulphur cell in the same charge state is governed by the way in which it is achieved. This is explained by differences in molar volumes of products generated in the sulphur electrode by electrochemical reaction during charging and discharging.
Bifunctional air electrodes with tuned composition consisting of two precious metal-free oxide catalysts are manufactured for application in rechargeable zinc-air flow batteries and electrochemically tested via long-term pulse charge and discharge cycling experiments at 50mAcm−2 (mean). NiCo2O4 spinel, synthesized via direct impregnation on carbon nanofibers or nickel powder and characterized by energy dispersive X-ray spectroscopy and X-ray diffraction experiments, shows high activity toward oxygen evolution reaction with low charge potentials of < 2.0 V vs. Zn/Zn2+. La0.6Sr0.4Co0.2Fe0.8O3 perovskite exhibits bifunctional activity and outperforms the NiCo2O4 spinel in long-term stability tenfold. By combining the catalysts in one bi-catalyzed bifunctional air electrode, stable performances of more than 1000h and 450 cycles are achieved when supplied with oxygen and over 650h and 300 cycles when supplied with synthetic air. In addition, the pulse charging method, which is beneficial for compact zinc deposition, is successfully tested on air electrodes during long-term operation. The oxygen evolution potentials during pulse, i.e. at tripled charge current density of 150mAcm−2, are only 0.06–0.08V higher compared to constant charging current densities. Scanning electron microscopy confirms that mechanical degradation caused by bubble formation during oxygen evolution results in slowly decreasing discharge potentials.
We report a facile approach to fabricate a novel membrane electrode based on unique Ni@Ni(OH)2 coaxial core-sheath structures for electrochemical energy storage application in this work. The Ni nanowire membranes, prepared from vacuum filtration of Ni nanowires with unique embossments, can be used as excellent precursors for preparing Ni@Ni(OH)2 membranes by an electrochemical cyclic voltammetry method. After electrochemical treatment, a layer of amorphous Ni(OH)2 was obtained on the surface of Ni nanowires. An important property of the as-synthesized Ni@Ni(OH)2 membranes is that it can be directly utilized for electrochemical energy storage applications without the need for binders or additional conducting additives. The Ni@Ni(OH)2 electrode demonstrates a high volumetric capacity (111.1Ccm−3 at 0.12Acm−3), excellent rate capability (83.1Ccm−3 at 1.92Acm−3), and cycling stability at a high current density (78% capacity retention after 1500 cycles at 1.92Acm−3). This fabrication method is very simple and paves a new route for designing membrane electrodes based on similar structures for high-performance electrochemical energy storage electrodes.
l-Glutamic acid is used as an additive for the positive electrolyte of all-vanadium redox flow battery (VRFB), and its effect on the thermal stability and electrochemical activity is investigated. It is found that the addition of l-glutamic can significantly alleviate the precipitation of V2O5 from positive electrolyte. The conservation rate of V(V) ion can be as high as 58% after 2M V(V) solution being kept in 40°C for 89h. Besides, l-glutamic can also improve the mass transport and electrochemical performance of anolyte. A high coulombic efficiency of over 95% and energy efficiency of 74% are obtained. XPS spectra illustrate that l-glutamic can react with the surface of carbon felt electrode and introduce more oxygen-containing and nitrogen-containing groups, which should be responsible for the improvement of electrochemical performance.
Mountain AD, Kirby RL, Eskes GA, Smith C, Duncan H, MacLeod DA, Thompson K. Ability of people with stroke to learn powered wheelchair skills: a pilot study. Objectives Our primary objective was to test the hypothesis that people with stroke can learn to use powered wheelchairs safely and effectively. Our secondary objective was to explore the influence of visuospatial neglect on the ability to learn powered wheelchair skills. Design Prospective, uncontrolled pilot study using within-participant comparisons. Setting Rehabilitation center. Participants Inpatients (N=10; 6 with visuospatial neglect), all with a primary diagnosis of stroke. Interventions Participants received 5 wheelchair skills training sessions of up to 30 minutes each using the Wheelchair Skills Training Program (version 3.2). Main Outcome Measures Powered wheelchair skills were tested before and after training using the Wheelchair Skills Test, Power Mobility version 3.2 (WST-P). Results The group's total mean WST-P scores improved from 25.5% of skills passed at baseline to 71.5% posttraining (P=.002). The participants with neglect improved their WST-P scores to the same extent as the participants without neglect, although their pretraining and posttraining scores were lower. The training and testing sessions were well tolerated by the participants, and there were no serious adverse events. Conclusions Many people with stroke, with or without visuospatial neglect, can learn to use powered wheelchairs safely and effectively with appropriate training.
3d transition-metal oxides, especially Fe3O4, as anode materials for the lithium-ion batteries have been attracting intensive attentions in recent years due to their high energy capacity and low toxicity. A new Fe3O4/C composite with hollow spheres in porous three-dimensional (3D) nanostructure, which was synthesized by a facile solvothermal method using FeCl3·6H2O and porous spongy carbon as raw materials. The specific surface area and microstructures of composite were characterized by nitrogen adsorption-desorption isotherm method, FE-SEM and HR-TEM. A homogeneous distribution of hollow Fe3O4 spheres (diameter ranges from 120 nm to 150 nm) in the spongy carbon (pore size > 200 nm) conductive 3D-network significantly reduced the lithium-ion diffusion length and increased the electrochemical reaction area, and further more enhanced the lithium ion battery performance, such as discharge capacity and cycle life. As an anode material for the lithium-ion battery, the title composite exhibit excellent electrochemical properties. The Fe3O4/C composite electrode achieved a relatively high reversible specific capacity of 1450.1 mA h g−1 in the first cycle at 100 mA g−1, and excellent rate capability (69% retention at 1000 mA g−1) with good cycle stability (only 10% loss after 100 cycles).