Large Charge Capacity Research Articles

NiO nanosheets grown on graphene nanosheets as superior anode materials for Li-ion batteries

This paper reports a hydrothermal preparation of NiO-graphene sheet-on-sheet and nanoparticle-on-sheet nanostructures. The sheet-on-sheet nanocomposite showed highly reversible large capacities at a common current of 0.1 C and good rate capabilities. A large initial charge capacity of 1056 mAh/g was observed for the sheet-on-sheet composite at 0.1 C, which decreased by only 2.4% to 1031 mAh/g after 40 cycles of discharge and charge. This cycling performance is better than that of NiO nanosheets, graphene nanosheets, NiO-graphene nanoparticle-on-sheet, and previous carbon/carbon nanotube supported NiO composites. It is believed that the mechanical stability and electrical conductivity of NiO nanosheets are increased by graphene nanosheets (GNS), the aggregation or restacking of which to graphite platelets are, on the other hand, effectively prevented by NiO nanosheets.

Micellar poly(styrene-b-4-vinylpyridine)-nanoparticle hybrid system for non-volatile organic transistor memory

We present organic field-effect transistor (OFET) memories where in-situ synthesized gold (Au) nanoparticles in self-assembled polystyrene-block-poly-4-vinylpyridine (PS-b-P4VP) block copolymer nanodomains successfully functioned as charge storage elements. Both p-type (pentacene) and n-type (perfluorinated copper phthalocyanine) OFET based memories are reported, which have stable large charge capacity and programmable-erasable properties due to charge confinement in the embedded Au nanoparticles. Optical excitation has been utilized to demonstrate photogenerated minority carrier trapping in the Au nanoparticles for efficient erasing operations. The memory devices can hence be written and read electrically and erased optically, resulting in large memory windows (∼9–11 V), high on/off ratio between memory states (103–105) and long retention times (>1000 s). The results clearly indicate the utility of the block copolymer-nanoparticle approach for OFET based memories.

Electrochromic properties of polyaniline thin film nanostructures derived from solutions of ionic liquid/polyethylene glycol

Abstract By exploiting the templating ability, wetting properties and the capability of the ionic liquid, 1-ethyl,3-methylimidazolium bromide to furnish the anionic dopant, nanostructured thin films of polyaniline (PANI) have been fabricated from an aqueous solution of the monomer encompassing this organic moiety by electropolymerization. These films have been compared to films synthesized from a medium based on a conventional polymeric surfactant, polyethylene glycol 400 (PEG). The template/dopant controls pore structure and assembly patterns as an interconnected network of nanofibrils of 50–500 nm in length and 10–40 nm in diameter constitutes the PANI films derived from the ionic liquid-based solution whereas the dominant microstructural attribute of the PANI films obtained from the PEG-containing formulation are abutting nanoparticles with elongated shapes. The effect of the different thin film nanostructures on their electrochromic properties is evident from the higher coloration efficiency, transmission modulation (in the NIR region), larger charge capacity, enhanced cycling stablity and faster color-bleach rates observed for the PANI films obtained from the ionic liquid medium as compared to that shown by the PANI films fabricated from the PEG solution. The outstanding optical and electrochemical behavior of the films, in particular, for the film derived from the ionic liquid-based solutions indicate that such recyclable and environmentally benign reaction media are most useful especially for transposing PANI films to large area substrates for electrochromic window applications.

Fully Ferrocenated Hexanethiolate Monolayer-Protected Gold Clusters

The synthesis and compositional analysis of four different gold clusters with protecting monolayers comprised solely of ferrocene hexanethiolate ligands is described. The gold nanoparticles have average core diameters of 1.4, 1.6, 2.0, and 2.2 nm with estimated average atom counts of 55, 140, 225, and 314 Au atoms and average monolayer coverages of 37, 39, 43, and 58 ferrocenated ligands, respectively. The data show unequivocally that the number of ferrocene hexanethiolate ligands bound to each core size is constrained by the steric requirements of the ferrocene head group; the ligand numbers are significantly smaller than those for hexanethiolate ligands bonded to analogous-sized Au cores. Voltammetry of dilute solutions of these nanoparticles shows a large ferrocene oxidation wave and, at more negative potentials, smaller one-electron waves for the quantized double-layer charging of the Au cores. Together, the ferrocenes and core of the ferrocenated Au314 nanoparticle deliver 60 electrons at the ferrocene oxidation potential, which amounts to a very large volume charge capacity, 7x10(9) C/m3, for an undiluted nanoparticle sample.

Structures and electrochromic properties of tungsten oxide films prepared by magnetron sputtering

Tungsten oxide (WO 3) films were deposited by DC magnetron sputtering of tungsten target in O 2/Ar atmosphere. The structures of the films following the various O 2 flow rate in a fixed Ar gas supply were investigated by X-ray diffraction patterns, Raman spectra and transmission electron microscopy. The electrochromic properties were characterized by a cyclic voltammetry and UV–vis absorption spectra. The results show that nanocrystalline WO 3 film with crystallite size about 10–20 nm, deposited at 16 sccm O 2, has larger charge capacity and coloration efficiency than the other amorphous films. Post-annealing the film at 200 °C would create 30–50 nm nanocrystalline film, whose electrochromic properties are promoted further due to even larger internal volume, essential to conduct ions and electrons for electrochromic intercalation. However, the electrochromic property deteriorates apparently in the film with 60–100 nm nanocrystallites annealed at 300 °C, which may be caused by another electrochromism occurring always in the well-crystallized WO 3 films.

The Orbitrap: a new mass spectrometer

Research areas such as proteomics and metabolomics are driving the demand for mass spectrometers that have high performance but modest power requirements, size, and cost. This paper describes such an instrument, the Orbitrap, based on a new type of mass analyzer invented by Makarov. The Orbitrap operates by radially trapping ions about a central spindle electrode. An outer barrel-like electrode is coaxial with the inner spindlelike electrode and mass/charge values are measured from the frequency of harmonic ion oscillations, along the axis of the electric field, undergone by the orbitally trapped ions. This axial frequency is independent of the energy and spatial spread of the ions. Ion frequencies are measured non-destructively by acquisition of time-domain image current transients, with subsequent fast Fourier transforms (FFTs) being used to obtain the mass spectra. In addition to describing the Orbitrap mass analyzer, this paper also describes a complete Orbitrap-based mass spectrometer, equipped with an electrospray ionization source (ESI). Ions are transferred from the ESI source through three stages of differential pumping using RF guide quadrupoles. The third quadrupole, pressurized to less than 10(-3) Torr with collision gas, acts as an ion accumulator; ion/neutral collisions slow the ions and cause them to pool in an axial potential well at the end of the quadrupole. Ion bunches are injected from this pool into the Orbitrap analyzer for mass analysis. The ion injection process is described in a simplified way, including a description of electrodynamic squeezing, field compensation for the effects of the ion injection slit, and criteria for orbital stability. Features of the Orbitrap at its present stage of development include high mass resolution (up to 150,000), large space charge capacity, high mass accuracy (2-5 ppm), a mass/charge range of at least 6000, and dynamic range greater than 10(3). Applications based on electrospray ionization are described, including characterization of transition-metal complexes, oligosaccharides, peptides, and proteins. Use is also made of the high-resolution capabilities of the Orbitrap to confirm the presence of metaclusters of serine octamers in ESI mass spectra and to perform H/D exchange experiments on these ions in the storage quadrupole.

Nanoparticle iron-phosphate anode material for Li-ion battery

Nanoparticle crystalline iron phosphates (FePO4∙2H2O and FePO4) were synthesized using a (CTAB) surfactant as an anode material for Li rechargeable batteries. The electrochemical properties of the nanoparticle iron phosphates were characterized with a voltage window of 2.4–0 V. A variscite orthorhombic FePO4∙2H2O showed a large initial charge capacity of 609mAh∕g. On the other hand, a tridymite triclinic FePO4 exhibited excellent cyclability: the capacity retention up to 30 cycles was ∼80%, from 485 to 375mAh∕g. The iron phosphate anodes exhibited the highest reported capacity, while the cathode LiFePO4 has an ideal capacity of 170mAh∕g.

Characterization of nano-structured thin films of electrodeposited Ce–Co mixed oxides for EC devices

Composite films of Ce–Co oxides were deposited on ITO-coated glass using electrochemical deposition in aqueous solutions containing cerium and cobalt nitrates with various molar ratios (Ce/Co). Films deposited in equimolar mixture gave highest transmittance and little spectral change during charging and discharging processes in 0.05 M NaOH solution. They have also large charge capacity in the potential range from −900 to 600 mV vs. Ag. The TEM observations and EDS measurements of the Ce–Co composite films revealed that they consist of CeO 2 nano-crystals in amorphous host structures. It was concluded that these Ce–Co composite films (Ce/Co=1.0) are most suitable for transparent counter electrodes in electrochromic (EC) devices.

Low temperature synthesis of γ-LixMnO2 powders in ethylene glycol

The reaction of Electrolytic Manganese Dioxide (EMD γ-MnO2) with anhydrous LiOH in ethylene glycol (EG) was studied. It was found that this reaction proceeds in three steps while the reaction temperature increases: (1) chemical insertion of lithium in γ-MnO2 structure leading to γ-LixMnO2 phase, (2) progressive dissolution of this reduced phase and (3) precipitation of a Li-free organo-metallic compound Mn(OCH2CH2O) with lamellar structure (Mn-EG). If the reaction is performed at moderate temperature (T<120°C), we can limit the dissolution reaction and completely avoid the precipitation of the organo-metallic phase. The x value in the resulting LixMnO2 phases is found to be mainly linked to the temperature of the reaction medium. Although a maximum value of x=0.35 can be obtained at 30°C, Li0.84MnO2 can be prepared at 120°C. We showed that the LixMnO2 formation mechanism consists of a direct lithium insertion in the structure of MnO2 concomitant with Mn reduction by the organic medium. By changing the medium cationic content of the medium, we were able to prepare various reduced MnO2 compositions, such as HxMnO2, (Li,H)xMnO2, (Na,H)xMnO2, (K,H)xMnO2. These LixMnO2 phases, when tested in half Li-cells, show poor cyclability but large first charge capacity (260 mAh/g for x=0.84) that takes place at significantly higher voltage than observed for electrochemically inserted EMD. This finding was related to the presence of chemically inserted protons besides lithium ions.

Lithium ion secondary battery technologies, present and future

Since the introduction of lithium ion secondary batteries (LIB) in 1991,the ceaseless and remarkable improvement has been done and the energy density has been doubled. New classes of anode and cathode active materials with possibly large charge and discharge capacity are in the course of development and further improvement in LIB performances can be expected by their adoption. The present status and future trends of LIB are discussed here including new types of LIB with polymer gel electrolytes.

Microstructure and electrochemical properties of some synthetic carbons

Four kinds of synthetic carbons were prepared by vacuum pyrolysis of black polyacene-based polymers: poly[( Z)-1-methoxy-4-phenyl-1-buten-3-yne]-750 [poly(MPB EY)-750], poly(1,4-diphenyl-1-buten-3-yne)-750 [poly(DPBEY)-750], poly[5-(2-pyridyl)-2,4-pentadiyn-1-ol]-800 [poly(PyPDO)-800], and poly(2,4-hexadiyn-1,6-diol)-800 (PHDO-800). The carbonization yields and electrochemical properties of carbons were dependent on precursor polymers. The relationship between the structure of synthetic carbons and electrochemical behavior was investigated by transmission electron microscopy (TEM), discharge/charge tests and cyclic voltammetry studies. Precursor polymers from enynes yielded synthetic carbons with many defect sites. Poly(DPBEY)-750, poly(PyPDO)-800, and PHDO-800 show smaller charge capacities than graphite (372 mA h/g), while a large charge capacity of 496 mA h/g is observed from poly(MPBEY)-750 in the first cycle. Poly(PyPDO)-800 displays very large capacity on cyclic voltammetry tests compared to other carbon samples indicating that the kinetics of lithium insertion/deinsertion in poly(PyPDO)-800 is faster than those of other carbons.

Structural and electrochemical properties of disordered carbon prepared by the pyrolysis of poly( p-phenylene) below 1000°C for the anode of a lithium-ion battery

The structural and the charge–discharge characteristics of poly( p-phenylene)(PPP)-based carbon materials pyrolyzed at temperatures from 650 to 1000°C are investigated by a series of structural analyses and charge–discharge electrochemical techniques. The charge–discharge capacity is then correlated with the change in structure of the PPP-based carbon. It is found that the sizes of the crystallites only increase a little, while both the charge and the discharge capacities decrease sharply with increasing heat-treatment temperature (HTT), and the carbon material pyrolyzed at 650°C has the largest charge capacity (>600 mA h g −1). The charge capacity for each sample includes two components, one is probably related to that of lithium intercalation into graphene layers, and the other to that of lithium species doped on the surface of the porosities existing in the PPP-based carbon. The charge capacity of the first component hardly changes, while that of the second one decreases sharply with increasing HTT, which corresponds to a sharp decrease in the amount, the total specific surface areas of porosity in carbon materials. Small pores can collapse and coalesce with each other and form larger pores due to an increase in crystal size when HTT increases, resulting in an increase in the butanol displacement density.

Effect of fluoroesters on the low temperature electrochemical characteristics of graphite electrode

The electrochemical behavior of graphite electrode has been investigated in 1 M LiClO 4-ethylene carbonate (EC)/diethyl carbonate (DEC) and fluoroester-mixed (4.8 vol %) EC/DEC solutions at low temperatures to evaluate the effect of addition of fluoroesters on the electrochemical characteristics. The cyclic voltammetry study revealed that the fluoroesters used were electrochemically reduced at more positive potentials between 0.87 V and 1.41 V vs. Li/Li +, mainly at 0.99–1.10 V, than EC reduced at 0.60 V, and with decreasing reduction potentials of the fluoroesters, the larger reduction and oxidation currents reversibly flowed in the fluoroester-mixed solvents than in EC/DEC at 0 °C. The charge-discharge cycling accompanying the lithium ion deintercalation and intercalation reactions has been also studied by a constant current method at 25 °C, 0 °C and −4 °C. A low molecular weight ftuoroester, CHF 2COOCH 3-mixed EC/DEC demonstrated the much larger charge capacities than EC/DEC itself and other fluoroester-mixed solvents at 0 °C and −4 °C, though its capacity was comparable to that in EC/DEC at 25 °C. The charge capacities obtained in the solvents mixed with other fluoroesters having larger molecular weights were not largely different from that in EC/DEC at 0 °C.

Electronic properties and double layer of activated carbon

According to the ion exchange, between the electrolyte in the pores and the external electrolyte, as well as to the conductivity of the solid material, the large charge capacity of the activated carbon under investigation does not arise from redox properties of surface groups but from mobile charge carriers in the solid. The dependence of the conductivity (minimum value 1000 S m −1) and of the thermopower on the electrode potential and on the temperature shows that the mechanism of the electronic conduction resembles neither that of metals nor of semiconductors. It is characterized as “hopping” between electronically coherent domains and resembles the process in conducting polymers. According to e.s.r. measurements, the spin density is low and does not change markedly with the potential. The prevalence of paired charges is proposed as a hypothetic explanation.