Electrolytic Iron Sulfide Products in Lithium Batteries

A technology for electrolytic production of iron sulfide compounds applicable in thin-layer lithium batteries is developed. Physicochemical and structural properties and the surface morphology of compounds are studied by x-ray diffraction and thermal analyses, absorption IR spectroscopy, and atomic force microscopy. Specific discharge characteristics of compounds in thin-layer compact nonballast and paste electrodes of model lithium power sources are determined. The discharge capacity of compounds in thin layers weighing 1.0–7.5 mg cm^–2 galvanostatically cycled in electrolyte PC, DME, 1 M LiClO₄ at room temperature stays at 200–320 mA h g^–1 for 40–50 cycles.     

Use of lithium perchlorate media in the study of protolytic equilibria

A study of the H⁺/F^– system by fluoride ion-selective electrode potentiometry over a range of ionic strengths in LiClO ₄ gives protolysis constants which differ markedly from those obtained in other media such as NaClO ₄ . This is shown to be consistent with the competitive complexation of the fluoride ion by the lithium ion. An examination of literature data indicates that lithium ion complexation is a general phenomenon and supports the conclusion that LiClO ₄ is not preferable to NaClO ₄ as a swamping electrolyte for the study of protolytic equilibria as has previously been thought.     

Solid polymer electrolytes. VI. Microstructure of organic–inorganic hybrid networks composed of 3‐glycidoxypropyltrimethoxysilane and LiClO4 and affected by different synthetic routes

Hybrid organic–inorganic materials derived from 3‐glycidoxypropyltrimethoxylsilane were prepared via two different synthetic routes: (1) the HCl‐catalyzed sol–gel approach of silane followed by the lithium perchlorate (LiClO₄)/HCl‐catalyzed opening of epoxide and (2) the simultaneous gelation of tin/LiClO₄‐catalyzed silane/epoxide groups. LiClO₄ catalyzed the epoxide polymerization, and its effects on the structures of these hybrid materials were studied by NMR. The structure of the inorganic side was probed by solid‐state ²⁹Si NMR spectroscopy, and the characterizations of the organic side and the chemical processes involved in the different synthetic routes were performed with solid‐state cross‐polarity/magic‐angle‐spinning ¹³C NMR. The different synthetic routes significantly affected the polymerization behaviors of the organic and inorganic sides in the presence of LiClO₄. A larger amount of LiClO₄ promoted the opening of epoxide and led to the formation of longer poly(ethylene oxide) chains via the HCl‐catalyzed sol–gel approach, whereas in the case of the tin‐catalyzed approach, the faster polymerization of the inorganic side hindered the growth of the organic network. The addition of LiClO₄ was proven to be without crystalline salt present in the hybrid networks by wide‐angle X‐ray powder diffraction. Also, the interactions between the ions and hybrid host, examined with Fourier transform infrared and ⁷Li proton‐decoupled magic‐angle‐spinning NMR, further demonstrated that extensive ion aggregation existed in these hybrid materials. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 151–161, 2004     

Enhanced electrochemical properties of polyethylene oxide-based composite solid polymer electrolytes with porous inorganic–organic hybrid polyphosphazene nanotubes as fillers

Solid composite polymer electrolytes consisting of polyethylene oxide (PEO), LiClO₄, and porous inorganic–organic hybrid poly (cyclotriphosphazene-co-4, 4′-sulfonyldiphenol) (PZS) nanotubes were prepared using the solvent casting method. Differential scanning calorimetry and scanning electron microscopy were used to determine the characteristics of the composite polymer electrolytes. The ionic conductivity, lithium ion transference number, and electrochemical stability window can be enhanced after the addition of PZS nanotubes. The electrochemical impedance showed that the conductivity was improved significantly. Maximum ionic conductivity values of 1.5 × 10⁻⁵ S cm⁻¹ at ambient temperature and 7.8 × 10⁻⁴ S cm⁻¹ at 80 °C were obtained with 10 wt.% content of PZS nanotubes, and the lithium ion transference number was 0.35. The good electrochemical properties of the solid-state composite polymer electrolytes suggested that the porous inorganic–organic hybrid polyphosphazene nanotubes had a promising use as fillers in SPEs and the PEO₁₀–LiClO₄–PZS nanotube solid composite polymer electrolyte might be used as a candidate material for lithium polymer batteries.     

Novel composite polymer electrolytes based on poly(ether-urethane) network polymer and modified montmorillonite

Novel composite solid polymer electrolytes (CSPEs) and composite gel polymer electrolytes (CGPEs) have been prepared. CSPE consists of poly(ether-urethane) network polymer, which is superior to poly(ethylene oxide) in mechanical stability due to its cross-linked structure, modified montmorillonite (MMMT) and LiClO₄, and CGPE with good mechanical strength comprises of the CSPE and LiClO₄–PC (propylene carbonate) solution. The ionic conductivity can be enhanced after the addition of MMMT, and CGPE exhibits ionic conductivity in the order of 10⁻³ S/cm at room temperature. The temperature dependence of the ionic conductivity of the CSPE follows the Vogel–Tamman–Fulcher (VTF) equation. The effects of MMMT on the interactions in these systems and the possible conduction mechanisms are also discussed.     

Influence of molar ratios of precursor,catalyst, solvent and water on monolithicity and physical properties of TMOS silica aerogels

In continuation to our earlier work on aerogels, the experimental results on the monolithicity and physical properties of silica aerogels as a function of the molar ratios of tetramethoxysilane (TMOS) precursor, catalyst (NH₄OH), methanol (MeOH) solvent and water, are reported. The molar ratios of NH₄OH/TMOS, MeOH/TMOS and H₂O/TMOS were varied from 7.1 × 10^–6 to 9.6 × 10^–1, 1 to 90 and 1 to 18 respectively. It has been found that larger molar ratios of NH₄OH/TMOS (10^–2), MeOH/TMOS (13 to 60) and H₂O/TMOS (>10) resulted in transparent but cracked aerogels, and very low molar ratios of these combinations gave monolithic but less transparent or opaque aerogels. The best quality silica aerogels, in terms of monolithicity, transparency and low density, have been obtained with TMOS:MeOH:H₂O:NH₄OH in the molar ratio of 1:12:4:3.7 × 10^–3 respectively. The aerogels have been characterized by density, optical transmission, surface area and porosity measurements. The results have been discussed by taking into account the hydrolysis and condensation reactions, and syneresis effects.     

Conductivity and interfacial behaviour of bis-1,4-dioxapentyl sulfate (IV) and 1,4,7-trioxaoctyl sulfate (IV) based electrolyte for lithium batteries

The electrolytic conductivity and viscosity of lithium perchlorate in bis-1,4-dioxapentyl sulfate (IV) [OS22] and 1,4,7-trioxaoctyl sulfate (IV) [OS32] were determined as a function of salt concentration (0.00005–2 M) and temperature (286–318 K). At 298 K, the highest conductivity (=2.77×10^{–3 –1} cm^–1) was achieved for OS22 based solutions containing 1–2 M LiClO₄. Formation of electrically neutral ion pairs appeared to be the main reason for a continuous decline in the molar conductivity () observed in dilute solutions with increasing salt concentration. Additionally, an increase in the dynamic viscosity () accounted for a decrease in the mobility of charge carriers with increasing length of the oxaalkyl chain in the podand molecules. The temperature dependence of the conductivity and viscosity was found to be of the Arrhenius type for both systems investigated, while the activation energies, E ^# and E ^#, varied in parallel with the degree of interionic aggregation. CVs obtained on a polycrystalline Pt electrode indicated the electrochemical stability of OS22 in the potential range between –0.8 V and 4.7 V versus Li⁺/Li. A linear current density–potential dependence, with the same slope for the anodic and cathodic branches proved the reversibility of lithium electrodeposition and re-dissolution at the Pt/1 M LiClO₄+OS22 interface.     

Thermal behavior of Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>/TiO<Subscript>2</Subscript> mesoporous gels

Summary Titania-based photocatalytic materials were prepared by sol-gel method using Fe³⁺ and polyethyleneglycol (PEG₆₀₀) as additives. Thermogravimetry (TG), differential thermal analysis (DTA) and evolved gas analysis (EGA) with MS detection were used to elucidate processes that take place during heating of Fe³⁺ containing titania gels. The microstructure development of the Fe₂O₃/TiO₂ gel samples with and without PEG₆₀₀ admixtures was characterized by emanation thermal analysis (ETA) under in situ heating in air. A mathematical model was used for the evaluation of ETA results. Surface area and porosity measurements of the samples dried at 120&deg;C and the samples preheated for 1 h to 300 and 500&deg;C were compared. From the XRD measurements it was confirmed that the crystallization of anatase took place after thermal heating up to 600&deg;C.     

Synthesis of a novel one‐pot approach of hyperbranched polyurethanes and their properties

A new method for the synthesis of hyperbranched polymers involving the use of AB_x macromonomers containing linear units have been investigated. Two types of novel hyperbranched polyurethanes have been synthesized by a one‐pot approach. The structures of monomers and polymers were characterized by elemental analysis, ¹H NMR, ¹³C NMR, Fourier transform infrared spectroscopy, gel permeation chromatography, and thermogravimetric analysis. The hyperbranched polymers have been proven to be extremely soluble in a wide range of solvents. Polymer electrolytes were prepared with hyperbranched polymer, linear polymer as the host, and lithium perchlorate (LiClO₄) as the ion source. Analysis of the isotherm conductivity dependence of the ion concentration indicated that these hyperbranched polymers could function as a “solvent” for the lithium salt. The conductivity increased with the increasing concentration of hyperbranched polymers in the host polymer. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 344–350, 2002     

Evaluation of dissociation constants of ammonium ion in aqueous lithium perchlorate and lithium chloride-sodium chloride mixed solutions

The Pitzer approach has been applied to the evaluation of dissociation constants of ammonium ion in lithium perchlorate and lithium chloride-sodium chloride mixed solutions at 25°C. The calculated values showed good agreement with the observed values, provided all the higher-order interaction terms ('s and 's) concerned were introduced. The unknown (NH₄LiClO₄) value was determined from the isopiestic measurements of NH₄ClO₄–LiClO₄ mixed solutions. Parameters in the Pitzer formalism for ammonia-ion interactions involved in LiCl and NaCl media were determined by use of the activity coefficients of ammonia measured in LiCl–NaCl mixed solutions by a transpiration method.     

FTIR study of ion solvation and ion-pair formation in alkaline and alkaline earth metal salt solutions in acetonitrile

The IR spectra of alkaline and alkaline earth metal perchlorate and of lithium bromide solutions in acetonitrile, obtained with the help of FTIR measurements in the region of the C-N stretching mode of the solvent, reveal bands produced by acetonitrile molecules in the solvation shells and bands of ClO ₄ ^– ions in contact and solvent separated ion pairs. The shift and the attenuation of the C-N stretching band of acetonitrile at 2254 cm^–1 is used for the calculation of cation solvation numbers for Li⁺(4), Na⁺(4), Mg²⁺(6), Ca²⁺(6), and Ba²⁺(6). No solvation is assumed for the contact ion pairs of LiClO₄, LiBr, NaClO₄, Mg(ClO₄)₂, Ca(ClO₄)₂, and Ba(ClO₄)₂. The association constants of the symmetrical electrolytes are compared to those obtained from other methods.     

Organic–inorganic hybrid materials. I. Characterization and degradation of poly(imide–silica) hybrids

Poly(imide–silica) hybrid materials with covalent bonds were prepared by (3-aminopropyl)methyldiethoxysilane (APrMDEOS) terminated amic acid, water, and tetramethoxysilane (TMOS) via a sol–gel technique. Infrared (IR), ²⁹Si and ¹³C CP/MAS nuclear magnetic resonance (NMR) spectroscopy, and thermogravimetric analysis (TGA) were used to study hybrids containing various proportions of TMOS and hydrolysis ratios. The microstructure and chain mobility of hybrids were investigated by proton spin–spin relaxation T₂ measurements. The apparent activation energy E_a for degradation of hybrids in air was studied by the van Krevelen method. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2275–2284, 1999     

Characterization of Hydrophobic SiO2 Powders Prepared by Surface Modification on Wet Gel

Hydrophobic porous silica has been prepared by surface modification of TEOS (tetraethylorthosilicate) wet gel with 6 and 12 vol.% of TMCS (trimethylchlorosilane). We characterized the products by using FT-IR, TGA, DTA, N₂ adsorption/desorption, contact angle and SEM. Surface silanol groups of the gel were widely replaced by–Si(CH₃)₃ to result in a hydrophobic SiO₂ powder as confirmed by contact angle measurements with H₂O, 1-butanol and ethanol. The modified dried gels had a surface area of 950–1000 m²/g (average pore size 120 Å), compared to the non-modified surface which had a surface area of 690 m²/g (average pore size 36 Å). The adsorption/desorption isotherm curves indicated they had similar pore characteristics as aerogels prepared by the supercritical drying process.     

Protective layer with oligo(ethylene glycol) borate anion receptor for lithium metal electrode stabilization

The gel polymer electrolyte based on semi-IPN (interpenetrating polymer network) structure for the protection of lithium metal electrode was successfully developed by ultraviolet (UV) radiation-curing method. A curable mixed solution consists of linear polymer (Kynar 2801), crosslinking agent (1,6-hexanediol diacrylate), liquid electrolyte (ethylene carbonate (EC)/propylene carbonate (PC)/1 M LiClO₄), oligo(ethylene glycol) borate (OEGB) anion receptor, and photoinitiator (methyl benzoylformate). The OEGB was synthesized by the dehydrocoupling reaction of hydroxyl group in di(ethylene glycol) methyl ether with hydrogen in BH₃ and characterized by ¹H NMR. The presence of OEGB anion receptor in the protection layer could lead to an enhancement in the ionic conductivity, electrochemical stability, and the interfacial properties. The deposited lithium exhibited particle-like shape resulting from the introduction of the protection layer onto the lithium electrode surface. The unit cell based on the lithium anode protected with gel polymer electrolyte containing OEGB showed higher discharge capacity than that of the unit cell without OEGB after 100 cycles at C/2 rate (1.25 mA cm⁻²).     

Kinetic study of the aquation of K2 TcBr6 in perchlorate solutions

The aquation of TcBr ₆ ^2– in perchlorate solutions at various hydrogen ion concentrations and ionic strengths has been investigated. Although the same products form in all cases the proportions of the cationic and neutral products depend on the [H⁺] and the ionic strength. Differences in LiClO₄/HClO₄ and NaClO₄/HClO₄ can be attributed to differences in the activities, although at constant ionic strength. A rate constant of 1.75·10^–5 s^–1 was found for the aquation at =1, together with an activation energy of 101.6±12.5 kJ/mol.     

Vibrational spectroscopic and density functional theory studies on ion solvation and ion association of lithium tetrafluoroborate in N,N-dimethylcarbamoyl chloride-based solvents

Solvation and association interactions in solutions of LiBF₄/DMCC (DMCC for N,N-dimethylcarbamoyl chloride) and LiBF₄/DMCC–DME (DME for 1,2-dimethoxyethane) have been studied as a function of concentration of lithium tetrafluoroborate by infrared and Raman spectroscopy. Strong interactions between Li⁺ and solvent molecules or BF₄⁻ anions are observed. The apparent solvation numbers of Li⁺ in LiBF₄/DMCC solutions were deduced. Band-fitting to the B–F stretching band of BF₄⁻ anion permits detailed assess of the ion pairing. Based on the calculations of density function theory, optimal structures of Li⁺(DMCC)_n (n = 1–3) were suggested. It is found that the lithium ion was preferentially solvated by DME in DMCC–DME binary solvents. This finding is supported by quantum chemistry calculations.     

Electrochemical investigation of gel polymer electrolytes based on poly(methyl methacrylate) and dimethylacetamide for application in Li-ion batteries

In the present work, gel polymer electrolytes (GPEs) were prepared using poly(methyl methacrylate) (PMMA), lithium perchlorate (LiClO₄) and dimethylacetamide as a plasticizer. Solution-casting technique was used to fabricate GPEs containing different weight percentage of PMMA. The degree of crystallinity of GPE samples was studied by X-ray diffraction (XRD) analysis. Fourier transform infrared (FT-IR) spectroscopy was applied to study the level of interactions between lithium salt and PMMA in the prepared GPEs. Electrochemical properties were studied by electrochemical impedance spectroscopy, linear sweep voltammetry and DC polarization techniques. Lithium ion conductivity of GPEs was determined by calculating the bulk resistance of polymer electrolytes from Nyquist plot. Increasing PMMA content of GPEs resulted in an improvement in the electrochemical potential window from 4.2 to 4.5 V. The highest lithium transference number (0.42) and also the best electrochemical properties were obtained for GPE containing 0.75 M LiClO₄ and 10 wt% PMMA. Scanning electron microscopy images of the optimized GPE showed a porous and heterogeneous surface structure which is desirable for application in Li-ion batteries.     

Synthesis and photophysical properties of novel organic–inorganic hybrid materials covalently linked to a europium complex

A novel sol–gel derived hybrid material (classed as Eu-DBM-Si) covalently grafted with Eu(DBM-OH)₃·2H₂O (where DBM-OH = o-hydroxydibenzoylmethane) was prepared through the primary β-diketone ligand DBM-OH. All the synthesized ligands were characterized by ¹H NMR, elemental analyses and Fourier transform infrared spectra (FTIR). The resultant Eu-DBM-Si material exhibited good transparent and homogenous property. Compared to the Eu-DBM hybrid prepared by physically doped silicon dioxide with Eu(DBM-OH)₃·2H₂O, the Eu-DBM-Si hybrid presented more efficient ligand-to-Eu³⁺ energy transfer and a significant improvement in the measured emission quantum yield. Furthermore, the photophysical properties of these hybrid materials, such as the photoluminescence (PL) spectra, PL intensities, symmetry properties, lifetime decays, and Judd-Ofelt parameters were also investigated in detail.     

Energy Transfer Between Eu3+ Ions and CdS Quantum Dots in Sol-Gel Derived CdS/SiO2 : Eu3+ Gel

We have investigated the energetic correlation between rare-earth ions and semiconductor nanocrystals, using europium ion (Eu³⁺) doped silica (SiO₂) gel with adsorbed cadmium sulfide (CdS) particles. Samples were prepared by a sol-gel technique, in which several methods for the precipitation of CdS colloids were attempted. The fluorescence intensities were compared for different gels, with and without CdS particles. The intrinsic emission lines due to ⁵D₀ ⁷F_J(J = 0–4) transitions of Eu³⁺ were observed, which were enhanced for 24 h-immersed gel (dried at 50°C). From the results on the decay dynamics of fluorescence, we proposed the model that surface-trapped electrons on CdS particles nonradiatively excited 4f electrons in Eu³⁺ ions due to an energy transfer process.     

Salt effects in the mercuration of unsaturated compounds. Kinetic evidence for the formation of ion pairs and a solvated ion

The kinetics of mercuration of bornylene and cyclohexene in different solvents in the presence of NaOAc and LiClO₄ has been investigated. Addition of NaOAc sharply decreases the rate of addition reactions of mercuric acetate to bornylene and cyclohexene in alcohols; the main direction of the mercuration of bornylene is the formation of acetoxy-adducts, and the yield of solvo-adducts decreases from 76 % in the absence of NaOAc, to 19 % in the presence of the salt (4·10^–3 mol L^–1). A reaction scheme involving the participation of intermediate ion pairs and a solvated mercurinium ion is suggested and confirmed by a steady-state concentration method. The influence of NaOAc on the rate of the reaction and on product formation is realized through the common ion effect.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 819–826, May, 1994.