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The possibility of producing a biodegradable polymer electrolyte based on poly-ɛ-caprolactone (PCL) with different concentrations of LiClO4 has been investigated. The maximum ionic conductivity obtained at room temperature was 1.2×10−6 Scm−1 for PCL complexed with 10wt.% LiClO4. In this mixture, complete biodegradation occurred after 110 days and was attributed to the presence of ester groups in the polymer matrix. The large electrochemical stability window of approximately 5V showed that the PCL/LiClO4 electrolyte had important electrochemical properties that would make it useful in the production of rechargeable batteries with a lower environmental impact.
A series of new poly(1-vinyl-3-alkylimidazolium) iodide polymers with different alkyl derivatives such as methyl, propyl and perflurodecyl have been synthesized. The alkyl substituent influenced some properties such as solubility, thermal stability, glass transition and crystallinity of the polymers. For instance, polymer having the propyl substituent was soluble in solvents of intermediate polarity such as acetonitrile, chloroform and THF, the one with the methyl substituent was only soluble in very polar solvents such as water and methanol and the fluorinated polymer was only soluble in DMF. The alkyl substituent also influenced the thermal stability in the order methyl>propyl>perflurodecyl and all the polymers thermally decomposed between 250 and 400°C in nitrogen. The poly(1-vinyl-3-alkyl-imidazolium) iodide polymers having propyl and methyl substituents were amorphous polymers showing a glass transition temperature of 43 and 21°C, respectively; and perflurodecyl polymers were semi-crystalline with a Tm at 153°C and a Tg at 20°C, as indicated by differential scanning calorimetry. Polymer electrolytes were formulated as mixtures of the ionic liquid 1-methyl-3-propylimidazolium iodide and the poly(1-vinyl-3-alkylimidazolium) iodide polymers. These polymer electrolytes showed ionic conductivities in the range of 10−3 to 10−7 S/cm at room temperature which strongly depended on the ionic liquid content. Finally, poly(1-vinyl-3-propyl-imidazolium) iodide was used to obtain gel electrolytes by adding it to a typical acetonitrile electrolyte used in dye sensitized solar cells (DSSCs). Solar cells with 1cm2 area prepared using the polymer gel electrolyte yielded a maximum light-to-electricity conversion efficiency of 3.73%.
Working memory (WM) is the set of mental processes holding limited information in a temporarily accessible state in service of cognition. We provide a theoretical framework to understand the relation between WM and aptitude measures. The WM measures that have yielded high correlations with aptitudes include separate storage-and-processing task components, on the assumption that WM involves both storage and processing. We argue that the critical aspect of successful WM measures is that rehearsal and grouping processes are prevented, allowing a clearer estimate of how many separate chunks of information the focus of attention circumscribes at once. Storage-and-processing tasks correlate with aptitudes, according to this view, largely because the processing task prevents rehearsal and grouping of items to be recalled. In a developmental study, we document that several scope-of-attention measures that do not include a separate processing component, but nevertheless prevent efficient rehearsal or grouping, also correlate well with aptitudes and with storage-and-processing measures. So does digit span in children too young to rehearse.
Novel ionic liquids (ILs), which were functionalized with ether oxygens to suppress crystallization and with bis(fluorosulfonyl)imide (FSI) anions to improve ionic conductivity, were synthesized and compared. Electrolyte mixtures were prepared by adding LiFSI to N-ethoxyethyl-N-methylpiperidinium FSI ([P1,2O2][FSI]) and N-ethoxyethyl-N-methylmorpholinium FSI ([M1,2O2][FSI]) in ratio of 1:9 (mol/mol). The electrolyte mixtures were found to exhibit a glass transition temperature between −71 and −93 °C and a decomposition temperature higher than 266 °C. Between these temperatures, the electrolytes were ion conductive and thermally stable liquids. [P1,2O2][FSI]-LiFSI exhibited a wider electrochemical stability window and possessed an ability to form solid electrolyte interfaces having a lower resistance compared to [M1,2O2][FSI]-LiFSI. Based on these results, the Li | LiFePO4 cells containing [P1,2O2][FSI]-LiFSI as electrolytes were assembled and found to possess a high capacity, reaching to the nominal capacity 150 mAh g−1 at C/10. Moreover, the cell retained flat potential profiles throughout 50 cycles.
Practical high-capacity Li-ion cells containing Li1.2Ni0.15Mn0.55Co0.1O2-based positive and graphite-based negative electrodes show substantial capacity loss and impedance rise when repeatedly cycled to, or held for extended periods, at voltages exceeding 4.5 V. Their performance can be effectively improved by modifying the positive electrode. The positive composite electrodes are modified here in two different ways: by (i) alumina coatings of up to ∼4 nm applied via atomic layer deposition (ALD), and (ii) addition of nanoscale alumina powder. Thicknesses of the ALD coatings are estimated via X-ray photoelectron spectroscopy (XPS). Electrochemical cycling reveals that capacity retention is better, and impedance rise is smaller for cells containing ALD-coated electrodes. Cells with alumina-powder modified electrodes show also improved capacity retention, but without improvements in impedance. Improved capacity retention is primarily due to reduced Li trapping on the negative electrode. Lower impedance growth, in ALD modified cells, is attributed to improved electro-mechanical integrity and altered surface films inside the positive electrode. The alumina coating inhibits, but does not prevent, transition metal dissolution. The coating also reduces electrolyte oxidation. Significant accumulation of Al on the negative electrode indicates electrochemical crosstalk between the electrodes and chemical instability of the ALD coatings during extended cycling.
Carbon nanotubes (CNTs) were chemically modified by a series of binuclear hexamino-metallo (M2Pc2) which were produced by reducing the corresponding binuclear hexanitro-metallophthalocyanines (M2HnPc2) (M=Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II)). The compounds were characterized with different techniques: IR, UV–vis, XRD, SEM, XPS. The electrocatalytic performances of the CNTs bonding with M2Pc2 (M2Pc2-CNTs) to Li/SOCl2 battery was tested by adding these compounds into the electrolyte. The capacities of the battery were improved, with increases by 59.1–128.5%. In addition, sequence of the electrochemical catalytic performance of M2Pc2-CNTs is as follow: Fe>Co>Cu>Zn>Ni>Mn. The CNTs bonding with M2Pc2 can greatly promote the electronic transmission, which significantly improve the performance and the initial voltage of Li/SOCl2 battery. Cyclic voltammetry measurements are applied to verify the M2Pc2-CNTs possessing catalytic performances and a reasonable mechanism is proposed.
X-ray absorption spectra of the spinel LiCu0.5Mn1.5O4 were recorded at the Cu K and L3, Mn K and L3, and O K edge. The spectra are aligned on a common energy scale with the aim to establish an experimental picture of the conduction band structure. The fine structures observed a few electron volts around the absorption thresholds are discussed in terms of hybridisation of cation and anion orbitals. Emphasis is put on the identification of spectral features correlated with the presence of lithium on the tetrahedral sites of the spinel structure. The consequences of lithium insertion/extraction on the intensities of these spectral structures are discussed. Previous studies by X-ray absorption spectroscopy of lithium insertion/extraction in various spinels are found to agree with our expectations.
The (La4MgNi17.5Mn1.5) alloys at different melt-spun speeds were prepared by using a vacuum melt-spun furnace, and the phase structure and electrochemical properties of alloys were studied. X-ray diffraction analysis results show that melt-spun La4MgNi17.5Mn1.5 alloys are composed of CeCu5-type, Pr5Co19-type and CeNi2-type phase. As the melt-spun speed increased, the phase abundance of CeCu5-type increased, but that of Pr5Co19-type decreased. Scanning electron microscopy–energy-dispersive spectroscopy analysis results show that melt-spun treatment can refine grain and make the alloys homogenization. Electrochemical tests show that all alloys have good activation performance within four cycles. With the increase in melt-spun speed, the cycle stability (S) of the alloys was improved obviously. After 100 cycles, the retention rate (S100) of the alloy increased from 54.82% (as-cast) to 82.29% (25 m/s). Nevertheless, the maximum discharge capacity (Cmax) and high-rate dischargeability gradually decreased.
We have successfully fabricated 3D carbon nanotube foams macrostructure by direct conversing CO2. Taking these carbon nanotube foams as substrates, large scale mace-like carbon nanotube foams/Co(OH)2 ordered arrays have been fabricated by a simple hydrothermal method. Electrochemical analysis indicates that the carbon nanotube foams hybrid architectures exhibit good energy-storage performance with high specific capacity of 614.3Cg−1 at 0.5Ag−1 and 444.5Cg−1 at 10Ag−1 calculated based on active materials with a voltage window of 0.45V. Besides, the electrodes also illustrate excellent long cycle life along with 96.8% specific capacity retained after 3000 cycle tests. An asymmetric supercapacitor was also assembled using carbon nanotube foams/Co(OH)2 as positive electrode and bare carbon nanotube foams as negative electrode. The highest power density and energy density of the asymmetric cell is 7.2kWkg−1 and 13.0Whkg−1, respectively. Moreover, this environmental friendly template-directed CVD technique is adaptable and multitalented, and can be a general strategy for preparing a kind of three-dimensional macroscopic structures with excellent properties and novel applications.
In this report, cycling induced capacity fade of a LiFePO4 battery was studied and cycle-life models were established. Cell life data for establishing the model were collected using a large cycle-test matrix. The test matrix included three parameters, temperature (−30 to 60°C), depth of discharge (DOD) (90–10%), and discharge rate (C-rate, ranging from C/2 to 10C, with the 1C rate corresponding to 2A). At the low C-rates, experimental results indicated that the capacity loss was strongly affected by time and temperature, while the DOD effect was less important. At the high C-rates, the charge/discharge rate effects became significant. To establish a life model, we adopt a power law equation in which the capacity loss followed a power law relation with time or charge throughput while an Arrhenius correlation accounted for the temperature effect. This model, when parameters were allowed to change with C-rates, was found to represent a large array of life cycle data. Finally, we discuss our attempts in establishing a generalized battery life model that accounts for Ah throughput (time), C-rate, and temperature.
The electrochemical performance of a composite of nano-Si powder and a pyrolytic carbon of polyvinyl chloride (PVC) with carbon nanofiber (CNF) was examined as an anode for lithium-ion batteries. CNF was incorporated into the composite by two methods; direct mixing of CNF with the nano-Si powder coated with carbon produced by pyrolysis of PVC (referred to as Si/C/CNF-1) and mixing of CNF, nano-Si powder, and PVC with subsequent firing (referred to as Si/C/CNF-2). The external Brunauer–Emmett–Teller (BET) surface area of Si/C/CNF-1 was comparable to that of Si/C/CNF-2. The micropore BET surface area of Si/C/CNF-2 (73.86m2 g−1) was extremely higher than that of Si/C/CNF-1 (0.74m2 g−1). The composites prepared by both methods exhibited high capacity and excellent cycling stability for lithium insertion and extraction. A capacity of more than 900mAhg−1 was maintained after 30 cycles. The coulombic efficiency of the first cycle for Si/C/CNF-1 was as low as 53%, compared with 73% for Si/C/CNF-2. Impedance analysis of cells containing these anode materials suggested that the charge transfer resistance for Si/C/CNF-1 was not changed by cycling, but that Si/C/CNF-2 had high charge transfer resistance after cycling. A composite electrode prepared by mixing Si/C/CNF-2 and CNF exhibited a high reversible capacity at high rate, excellent cycling performance, and a high coulombic efficiency during the first lithium insertion and extraction cycles.
A new ternary composite of polyaniline/manganese dioxide/nitrogen, phosphorus co-doped carbon nanofiber (PANI/MnO2/NPCNF) has been synthesized by electrospinning technology and chemical oxidative reactions. The results show that MnO2 and PANI layers are uniformly coated on the surface of N, P co-doped CNF. The optimal ternary nanocomposite shows excellent electrochemical performance (587.3Fg−1 at 0.5Ag−1, ~63% capacitance retention from 0.5Ag−1 to 20Ag−1 and capacitance retention is ~84% after 1000cycles at 10Ag−1). That could be attributed to the synergistic effects contributed from individual components. The N, P co-doped CNF acts as carbon scaffold to facilitate the electron transform and improves the poor electrical conductivity of MnO2. The outer PANI layer could achieve high pseudo-capacitance, protect the MnO2 layer from reductive-dissolving and further heighten its electrochemical utilization.
Here we report a synthesis of nickel cobalt oxysulfide nanocage trifunctional electrocatalysts by sulfurizing zeolitic imidazolate framework-67. Benefiting from the synergistic coupling of nickel cobalt oxysulfide and N-doped carbon polyhedron in a hollow dodecahedral structure, the nickel cobalt oxysulfide nanocages exhibit superior trifunctional electrocatalytic activity and durability towards oxygen reduction and evolution, and hydrogen evolution reactions in alkaline conditions. Moreover, the nickel cobalt oxysulfide nanocage trifunctional electrocatalysts are used in an air cathode for a rechargeable zinc-air battery and in both anode and cathode for overall water splitting, where the water splitting is directly powered by the assembled zinc-air battery. Such integrative power-to-hydrogen device can operate stably over 17 h without visible energy efficiency losses for hydrogen gas production.
Lead dioxide (PbO2) thin films were prepared on Ti/SnO2 substrates by means of electrodeposition method. Galvanostatic technique was applied in PbO2 film formation process, and the effect of deposition current on morphology and crystalline form of the PbO2 thin films was studied by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD). The energy storage capacity of the prepared PbO2 electrode was investigated by means of cyclic voltammetry (CV) and charge/discharge cycles, and a rough surface structure PbO2 film was selected as positive electrode in the construction of PbO2/AC hybrid capacitor in a 1.28gcm−3 H2SO4 solution. The electrochemical performance was determined by charge/discharge tests and electrochemical impedance spectroscopy (EIS). The results showed that the PbO2/AC hybrid capacitor exhibited high capacitance, good cycling stability and long cycle life. In the voltage range of 1.8–0.8V during discharge process, considering the weight of all components of the hybrid capacitor, including the two electrodes, current collectors, H2SO4 electrolyte and separator, the specific energy and power of the device were 11.7Whkg−1 and 22Wkg−1 at 0.75mAcm−2, and 7.8Whkg−1 and 258Wkg−1 at 10mAcm−2 discharge currents, respectively. The capacity retains 83% of its initial value after 3000 deep cycles at the 4C rate of charge/discharge.
LiCoO2 thin film cathodes have been well established in Li-ion rechargeable batteries, however, its useful capacity hardly exceeds 50% of the theoretical value. Irreversible structural changes will occur upon exchange of Li ions i.e. >0.5 per unit formula limit, during intercalation/deintercalation reactions. Reportedly, lattice doping phenomenon has noticed an improvement in cyclability of LiCoO2. In this work, the influence of Zr doping on microstructural and electrochemical properties of RF magnetron sputtered LiCoO2 thin film cathodes have been presented. A series of LiZr x Co1−x O2 thin films have been deposited on Au/Ti/SiO2/Si (100) substrates using a Zr–LiCoO2 mosaic target. All the films were deposited at optimized processing conditions. XRD and Raman spectroscopy measurements confirmed the hexagonal layered structure with R 3 ¯ m symmetry for Zr doped LiCoO2 film cathodes. The AFM reveals the estimated average grain size is around 50 nm. The cyclic voltammetry studies for these cathodes exhibit narrow potential peak separation of 24 mV and resulting highest diffusion coefficient ( D ¯ Li) of about 1.8 × 10−11 cm2 s−1, respectively. These films exhibited a highest initial discharge capacity of 64.4 μA h cm−2 μm−1 with a capacity retention of 98.5% even after 25 cycles. In non-aqueous region, the cell exhibited an initial discharge capacity of about 65 μA h cm−2 μm−1 with good cycling stability even after 80 cycles, and is observed to be the more promising cathode candidate than the pristine LiCoO2 films.
We fabricated nitrogen-decorated porous carbon exhibiting high capacitance per unit volume and unit weight via chemical activation of novolac resin containing peptide linkage. The porosity and the amount of nitrogen atoms were controlled by changing the molecular weight of novolac resin, the added amount of potassium hydroxide, or both. After chemical activation, positively charged nitrogen atoms (i.e., pyridine/pyrrole) at 400.3eV in photoemission spectra contributed to both a shift in the point of zero charge toward negative potential and the generation of pseudocapacitance. Suitably developed pores and the positively charged nitrogen atoms make nitrogen-decorated novolac resin-derived porous carbon a promising material for electrodes in high-performance supercapacitors.
Distributed generation can be defined as power generation by small scale generating units that are installed at distribution systems. The penetration of distributed generation (DG) units in electric distribution systems is continually increasing. The process of finding optimal type, location and size of DG units is called “DG allocation”. DG allocation is a hot area of research and represents a difficult problem in electrical power engineering. In this paper, the existing research works on DG allocation problem are reviewed from viewpoint of their used optimisation algorithms, objectives, decision variables, DG type, applied constraints and kind of uncertainty modelling. Based on the review of existing research works, the research gaps are identified and some helpful recommendations for future research on DG allocation will be provided. The author strongly believes that this paper can be helpful for researchers and engineers in the related field.
The carbon fibrous mats (CFMs) formed by carbon nanofibers whose average diameter is about 150nm have been fabricated by thermally treating the electrospun polyacrylonitrile fibrous mats. The electrocatalytic activity of commercial Pt/C supported on the CFMs for methanol oxidation in a sulfuric acid solution has been investigated by cyclic voltammetry, chronoamperometry, quasi-steady state polarization, and electrochemical impedance spectroscopy (EIS) methods. The results show that the commercial Pt/C supported on the CFMs exhibits higher electrocatalytic activity, more stability, larger exchange current and smaller charge transfer resistance than that on commercial carbon papers (CPs), which reveals that the CFMs could be developed as suitably-supporting materials for Pt/C catalyst due to their special porous and continuous fibrous structures.
Autism spectrum disorder (ASD) diagnosis can be delayed due in part to the time required for administration of standard exams, such as the Autism Diagnostic Observation Schedule (ADOS). Shorter and potentially mobilized approaches would help to alleviate bottlenecks in the healthcare system. Previous work using machine learning suggested that a subset of the behaviors measured by ADOS can achieve clinically acceptable levels of accuracy. Here we expand on this initial work to build sparse models that have higher potential to generalize to the clinical population.
In this paper, nano-lead-doped active carbon (nano-Pb/AC) composite with low hydrogen evolution current for lead-acid battery was prepared by ultrasonic-absorption and chemical-precipitate method. The nano-Pb/AC composite was characterized by SEM, EDS and TEM. The electrochemical characterizations are performed by linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) in a three-electrode system. Since intermediate adsorption is the rate-determining step, the hydrogen evolution reaction (HER) is markedly inhibited as the intermediate adsorption impedance of nano-Pb/AC increased. Meanwhile, the working potential of nano-Pb/AC is widened to the whole potential region of Pb negative plate (from −1.36 V to −0.86 V vs. Hg/HgSO4) in lead-acid battery. In addition, nano-Pb can improve the interfacial compatibility between AC and Pb paste, accordingly relieve the symptoms of carbon floatation. Finally, 2.0 V single-cell flooded lead-acid batteries with 1.0 wt.% nano-Pb/AC or 1.0 wt.% AC addition in negative active materials are assembled. The cell performances test results show that the 3 h rate capacity, quick charging performance, high current discharging performance and cycling performance of nano-Pb/AC modified battery are all improved compared with regular lead-acid battery and AC modified lead-acid battery.
Fourteen kinds of ammonium salt, including nine ionic liquids, were evaluated for use as the electrolyte (as a solute) of an electric double layer capacitor (EDLC) from the viewpoint of practical performance and thermal stability. For this study, three kinds of anion species were selected for the counter anion: tetrafluoroborate (BF4), hexafluorophosphate (PF6) and bis(trifluoromethylsulfonyl)imide (TFSI) anions. A series of EDLCs with only 0.4% deviation in the capacitance of each cell, based on activated carbon and various salts in propylene carbonate (PC), were strictly prepared. The capacitance at room temperature, and the resistance value of the EDLCs at a relatively large direct current at low temperatures were measured. We also examined the durability of these systems by continuous charging at 70°C and 3.0V. We report that N-(2-methoxyethyl)-N-methylpyrrolidinium-BF4, a cyclic aliphatic quaternary ammonium with a methoxyethyl functional group, is the preferred ionic liquid for an EDLC electrolyte with respect to capacitance, power density, even at low temperatures and thermal durability.
Transition metal oxide is widely studied type of high-capacity anode material for lithium ion batteries. Herein, oxygen-defective cobalt oxide with attractive lithium storage performance is prepared via a two-step strategy. Experimental results shows that there is certain amount of oxygen vacancies in Co3O4. Reversible conversion between metallic Co and CoO during the charge-discharge process was revealed by ex-situ XRD. Reversible morphology evolution is also confirmed by the ex-situ FE-SEM. The oxygen-defective Co3O4 anode shows attractive stability and rate performance. It possesses a discharge capacity of 1006 mAh∙g−1 in the first cycle, with a high initial Coulombic efficiency of 73.9%. A reversible capacity of 896 mAh∙g−1 can be maintained after 200 cycles at 250 mA g−1. It could even stably operate at an elevated current density of 5000 mA g−1 for 500 times. Further kinetic analysis reveals that pseudo-capacitance plays a dominant role in the lithium storage of oxygen-defective Co3O4. Existence of oxygen vacancies could not only facilitate Li+ migration but also enhance electric conductivity to a certain extent, resulting in improved lithium storage performance.