Raman spectroscopic studies of LixSiy compounds

The phase diagram of the Li–Si system contains several phases with Li and Si in well defined ratios. So far, only the Raman spectrum of LiSi has been reported. In this work, we present experimental Raman scattering results for the crystalline lithium silicide phases Li₁₂Si₇, Li₇Si₃, Li₁₃Si₄, and Li₂₁Si₅/Li₂₂Si₅, which show clearly distinguishable Raman modes. The experimental results are compared with theoretical data obtained by density functional theory calculations. Copyright © 2013 John Wiley & Sons, Ltd.     

Raman spectroscopic studies of planar gettering effects

Raman scattering spectroscopy is used to study the elastic stress distribution in the epitaxial silicon operating areas in the vicinity of planar getter areas, the latter being created by previous ion implantation of the substrate. Data concerning the effect of the operating element size and the dose of implantation into the getter area are obtained. The results are compared with those of X-ray topographic analysis of the structures.     

Raman spectroscopic studies of ZnSe/GaAs interfaces

ZnSe/semi‐insulating GaAs interfaces were studied by observing photogenerated plasmon–LO (PPL) coupled modes by nonresonant micro‐Raman spectroscopy. The effect of the carriers generated by the focused laser beam was investigated for a series of different thicknesses of ZnSe epitaxial layers. The PPL mode in GaAs was observed in the micro‐Raman spectra for all samples, but with different magnitude. The plasma is believed to be an electron gas as a result of the negative nature of the interfacial region that contains predominantly hole traps. The free carrier concentration is estimated to be > 10¹⁸ cm⁻³ and their lifetime ∼0.1 ns. This relatively long lifetime suggests that the ZnSe/GaAs interface has to be of high structural quality leading to a low recombination velocity. ZnSe/GaAs heterostructures of less crystalline quality (as determined by resonant Raman measurements) shows the effect of photogenerated carriers only to lesser extent. Copyright © 2007 John Wiley & Sons, Ltd.     

A low-temperature electrolyte for lithium-ion batteries

In this paper, the electrochemical performance of a new low-temperature electrolyte, 0.9 mol L^?1 lithium oxalyldifluoroborate (LiODFB)/LiBF₄ (5.365:1, by mass) mixed salts in the ethylene carbonate (EC)/dimethyl sulfite (DMS)/ethyl methyl carbonate (EMC) mixed solvent (1:1:3, by volume, the same below), is studied to seek the promising candidate for advanced low-temperature lithium-ion batteries (LIBs). The results show that LIBs using this new electrolyte can be operable well at temperature below ?20 °C. This is useful to expand the application range of LIBs, especially at specific low-temperature environments, such as military and aerospace applications.     

High‐pressure Raman spectroscopic and other structural studies of hydrotalcites containing intercalated dicarboxylic acid anions

The results of pressure‐tuning Raman spectroscopic, X‐ray powder diffraction and solid‐state ¹³C‐NMR studies of selected dicarboxylate anions intercalated in a Mg–Al layered double hydroxide lattice are reported. The pressure dependences of the vibrational modes are linear for pressures up to 4.6 GPa, indicating that no phase transitions occur. The interlayer spacings show that the oxalate, malonate and succinate dianions are oriented perpendicular to the layers, but the glutarate and adipate are tilted. The solid‐state ¹³C‐NMR spectra of these materials show full chemical shift anisotropy and, therefore, the anions are not mobile at room temperature. Copyright © 2011 John Wiley & Sons, Ltd.     

Trimesitylborane-embedded radical scavenging separator for lithium-ion batteries

Here, we propose a new strategy that employs a functional separator composed of radical scavenging agents for removal of radical species in the cell. In detail, a radical scavenger, trimesitylborane (TRMSB), is embedded on the surface of nano-sized tungsten oxide (WO₃) by a simple one-step process and the resulting nanoparticles are coated onto conventional separators by a dip-coating process. Our screening test performed by chemical reaction of TRMSB with a radical indicator (2,2-diphenyl-1-picrylhydrazyl, DPPH) confirms that TRMSB effectively scavenges radical species via a chemical reaction, implying that the use of a WO₃-TRMSB–functionalized separator would be effective for decreasing radical concentrations during electrochemical processes. In our electrochemical tests, the cell cycled with a WO₃-TRMSB–functionalized separator exhibit showed both improved cycling retention compared to a cell cycled with a bare separator and improved physical and mechanical properties.     

Preparation and characterization of a special structural poly(acrylonitrile)-based microporous membrane for lithium-ion batteries

In this work, a special structural poly(acrylonitrile) (PAN)-based microporous membrane for lithium-ion batteries is prepared from PAN emulsion by simple casting and extracting techniques. It is found that the microporous membrane is fabricated by PAN particles with uniform size (about 580 nm), and a lot of micropores exist among the particles. The Gurley number of the microporous membrane obviously depends on the amount of additive but the porosity does not. The PAN-based microporous membrane is activated by non-aqueous liquid electrolyte to form microporous gel electrolyte (MGE), and its ionic conductivity increases with the decrease of the Gurley number. The resulting MGE shows typical thermal shut-down action because of the swelling–incorporating behaviors of PAN-based particles by the help of the solvent of liquid electrolyte at high temperature. In addition, the electrochemical stability window of the MGE can extend to 5.5 V vs. Li⁺/Li. The test cell using MGE as separator shows high initial discharge capacity (143 mAh g^-1 based on LiCoO₂) and high capacity retention ratio (around 94.8% at the 50th cycle). Generally, the special structural microporous membrane is promisingly used to prepare high-safety lithium-ion batteries.     

Observation of Raman band shifting with excitation wavelength for carbons and graphites

The Raman spectra of crystalline graphite, graphite damaged by ion-etching, and structurally disordered pyrolytic and glassy carbons were examined as a function of excitation wavelength λ over the range 488.0 to 647.1 nm. The bands located at 1360, 2720 and 2950 cm ¹ with λ = 488.0 nm undergo a progressive red-shift as λ increases, while the positions of the other major bands (1580 and 1620 cm ¹) are invariant. The significance of these observations is briefly discussed.     

Nanoscopic scale studies of LiFePO4 as cathode material in lithium-ion batteries for HEV application

We present a review of the structural properties of LiFePO₄. Depending on the mode of preparation, different impurities can poison this material. These impurities are identified and a quantitative estimate of their concentrations is deduced from the combination of X-ray diffraction analysis, Fourier transform infrared spectroscopy, Raman spectroscopy, and magnetic measurements. An optimized preparation provides samples with carbon-coated particles free of any impurity phase, insuring structural stability and electrochemical performance that justify the use of this material as a cathode element a new generation of lithium secondary batteries.     

Infrared and Raman spectroscopic studies of L‐valinium picrate

The vibrational assignments of the observed wavenumbers have been made by analyzing the infrared and Raman spectra of L ‐valinium picrate in the crystalline state at room temperature. L ‐Valinium acts as the cation of the crystal and the carbonyl CO group exists in the protonated form in it. Asymmetric deformation and symmetric deformation modes of the isopropyl group have been identified, indicating that the two CH₃ groups are in different environments. The stretching and bending modes of the various functional groups have been shifted owing to the extensive intermolecular hydrogen bonding in the crystal. The symmetry of the picrate anion has not been modified in the crystal by the hydrogen bonding with the cation. Fermi resonance is also observed. Copyright © 2006 John Wiley & Sons, Ltd.     

Phase transitions of Decylammonium chloride by Raman and infrared spectroscopic studies

Raman scattering and infrared absorption were used to study phase transition between a non intercalated structure and an intercalated one in Decylammonium chloride C₁₀H₂₁NH₃Cl, in the temperature range from 79 to 370 K and to determine the transition temperature. The melting of the chains seems to be the cause of the transition. Unusual splitting of some vibration modes help us to characterize the intercalated structure. The entering of air into the structure seems to be at the origin of the discrepancy that appears in the experimental results.     

High-pressure Raman and infrared spectroscopic studies of ZrP2O7

High-pressure Raman and mid-infrared spectroscopic studies were carried out on ZrP₂O₇ to 23.2 and 13 GPa respectively. In the pressure range 0.7–4.3 GPa the lattice mode at 248 cm^?1 disappears, new modes appear around 380 and 1111 cm^?1 and the strong symmetric stretching mode at 476 cm^?1 softens, possibly indicating a subtle phase transition. Above 8 GPa all the modes broaden, and all of the Raman modes disappear beyond 18 GPa. On decompression from the highest pressure, 23.2, to 0 GPa all of the modes reappear but with larger full width at half maximum. Lattice dynamics of the high temperature phase of ZrP₂O₇ were studied using first principles method and compared with experimental values.     

Characteristics of heat treated polyparaphenylene for lithium-ion secondary batteries

In order to clarify the mechanism of Li-ions insertion/deinsertion into/from polyparaphenylene (PPP)-based carbons, the PPP carbonization has been analyzed. The weight loss of the PPP carbonized samples increased at a faster rate in the temperature range 600–680 °C. Hydrocarbons such as benzene and biphenyl were mainly detected by gas chromotography–mass spectrometry at a temperature of 710 °C during thermo-gravimetric analysis of PPP. The microtexture and the structure of heat treated PPP samples were characterized by high resolution transmission electron microscopy and investigated by image processing. The resistivity measurements of heat treated PPP showed a drastic decrease in the 680–730 °C HTT range. We related the microtexture evolution, the hydrocarbons release and the resistivity decrease of PPP carbonized samples to Li-ion battery capacity.     

Low‐temperature Raman spectroscopic studies in NaNbO3

Raman spectroscopic measurements were carried out in the temperature range 10–300 K to understand the low‐temperature antiferroelectric (AFE)–ferroelectric (FE) phase transition in NaNbO₃. Several modes in the low wavenumber range were found to disappear, while some new modes appeared across the transition. The temperature dependence of mode wavenumbers suggests that, during cooling, the AFE–FE phase transition begins to occur at 180 K, while the reverse transition starts at 260 K during heating. During cooling, the two phases were found to coexist in the temperature range of 220–160 K. Upon heating, the FE phase is retained up to 240 K and both FE and AFE phases coexist in the temperature range 240–300 K. In contrast to the earlier reports, the present results suggest a different coexistence region and the reverse transition temperature. The reported relaxor‐type FE behaviour over a broad temperature is consistent with the observed coexistence of phases during cooling and heating cycles. Copyright © 2010 John Wiley & Sons, Ltd.     

Confocal Raman spectroscopic mapping studies on a single CuO nanowire

In this study we are able, using a copper grid substrate, to successfully grow separate nanowires with a high level of crystallinity, for a length of up to 10 μm. They were synthesized under various temperatures. We compare and contrast three types of geometries (micron-, nano-scale, and tip-like single CuO nanowires), to identify their potential for monitoring the size effects of quantum confinements. The confocal Raman spectrometry results confirm the expected outcome, that reducing of the diameter of a cylindrical cross-section of a single nanowire results in Raman frequency downshifts. The results can be explained by the bond polarizability model. The applicability of investigating the size effects of the quantum confinement of the tip-like geometry of a single nanowire without any preparation for different sizes of nanoparticles is possible because the detection is relatively straightforward and the reproduced Raman signals can be observed.     

Sn-Sb and Sn-Bi alloys as anode materials for lithium-ion batteries

Sn/SnSb, Sn/Bi, and Sn/SnSb/Bi multi-phase materials were synthesised via reduction of cationic precursors with NaBH₄ and with Zn, and were tested for their suitability as anode materials for Li-ion batteries by galvanostatic cycling. The rapid reduction with NaBH₄ yielded the finer materials with the better cycling stabilities, whereas the reduction with Zn yielded the purer materials with the lower irreversible capacities in the first cycle. Reversible capacities of ∼ 600 mAh g⁻¹, ∼ 350 – 400 mAh g⁻¹, and ∼ 500 mAh g⁻¹ were obtained for Sn/SnSb, Sn/Bi, and Sn/SnSb/Bi, respectively. The cycling stability of the materials decreased in the order Sn/SnSb>Sn/SnSb/Bi>Sn/Bi, which is in part attributed to the presence / absence of intermetallic phases which undergo phase-separation during lithiation. Paper presented at the 8th EuroConference on Ionics, Carvoeiro, Algarve, Portugal, Sept. 16–22, 2001.     

Silica doped tin oxide composite anodes for lithium-ion batteries

Silica doped tin oxide composites prepared by a sol gel method have been studied as negative electrode materials for lithium-ion batteries. The composite powders fired at 500 °C were analysed by means of XRD and SEM and showed that the composite consists of a blend of crystalline and amorphous structure with different particle size distribution. The electrochemical properties of this anode material were examined by charge-discharge measurements and cyclic voltammetry. The silica doped tin oxide composite anode, which was cycled between 0.1 to 2.0 V, showed a reversible capacity of 270 mAh/g. Paper presented at the International Conference on Functional Materials and Devices 2005, Kuala Lumpur, Malaysia, June 6 – 8, 2005.     

A novel LiSnVO4 anode material for lithium-ion batteries

Ionics - In this work, a new material LiSnVO4 has been prepared via sol-gel method utilizing ammonium metavanadate, acetates of tin and lithium as starting materials, and nitric acid and oxalic...     

Mechanics of high-capacity electrodes in lithium-ion batteries

Rechargeable batteries, such as lithium-ion batteries, play an important role in the emerging sustainable energy landscape. Mechanical degradation and resulting capacity fade in high-capacity electrode materials critically hinder their use in high-performance lithium-ion batteries. This paper presents an overview of recent advances in understanding the electrochemically-induced mechanical behavior of the electrode materials in lithium-ion batteries. Particular emphasis is placed on stress generation and facture in high-capacity anode materials such as silicon. Finally, we identify several important unresolved issues for future research.     

Facile preparation of SGC composite as anode for lithium-ion batteries

The silicon/graphite/carbon (SGC) composite was successfully prepared by ball-milling combined with pyrolysis technology using nanosilicon, graphite, and phenolic resin as raw materials. The structure and morphology of the as-prepared materials are characterized by X–ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscope (TEM). Meanwhile, the electrochemical performance is tested by constant current charge–discharge technique, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) measurements. The electrodes exhibit not only high initial specific capacity at a current density of 100 mA g^?1, but also good capacity retention in the following 50 cycles. The EIS results indicate that the electrodes show low charge transfer impedance R_sf?+?R_ct. The results promote the as-prepared SGC material as a promising anode for commercial use.