RESUMO
The use of dipolar aprotic solvents to swell lithiated Nafion ionomer membranes simultaneously serving as electrolyte and separator is of great interest for lithium battery applications. This work attempts to gain an insight into the physicochemical nature of a Li-Nafion ionomer material whose phase-separated nanostructure has been enhanced with a binary plasticiser comprising non-volatile high-boiling ethylene carbonate (EC) and sulfolane (SL). Gravimetric studies evaluating the influence both of mixing temperature (25 to 80 °C) and plasticiser composition (EC/SL ratio) on the solvent uptake of Li-Nafion revealed a hysteresis between heating and cooling modes. Differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) revealed that the saturation of a Nafion membrane with such a plasticiser led to a re-organisation of its amorphous structure, with crystalline regions remaining practically unchanged. Regardless of mixing temperature, the preservation of crystallites upon swelling is critical due to ionomer crosslinking provided by crystalline regions, which ensures membrane integrity even at very high solvent uptake (≈200% at a mixing temperature of 80 °C). The physicochemical properties of a swollen membrane have much in common with those of a chemically crosslinked polymer gel. The conductivity of ≈10-4 S cm-1 demonstrated by Li-Nafion membranes saturated with EC/SL at room temperature is promising for various practical applications.
RESUMO
Anion solvation in acetonitrile solutions was comparatively studied using FTIR spectroscopy and quantum chemical calculations at the RTF + MP2/6-311G** level of theory with solvation model density (SMD) corrections. Infrared spectra for all stable anionic complexes X-(CH3CN)n (where X- = Br- (monatomic halide), ClO4- (polyatomic tetrahedral), AsF6- (polyatomic octahedral), CF3SO3- (polyatomic ethane-like) and n = 1-8) were calculated and subsequently used in the analysis of the FTIR spectra of (Bu4N)X and LiX acetonitrile solutions across a wide range of concentrations. Spectroscopic manifestations of solvation were established for all X- examined. The results for all four anions under investigation were generalized to reveal the regularities of anion solvation by acetonitrile.
RESUMO
The glass-ceramic composite electrolytes based on tetragonal Li7La3Zr2O12 (t-LLZ) and cubic Al-doped Li7La3Zr2O12 (c-LLZ) with the LiPO3 glass additive have been prepared. The electrical conductivity and microstructure of the t-LLZ/LiPO3 and c-LLZ/LiPO3 composites have been investigated. The phase evolution of electrolytes has been studied using XRD, SEM, and Raman spectroscopy. It was indicated that the impurities formation depends on the composition of the composite. The phase composition of the solid electrolytes determines their thermal properties, which have been studied by the DSC method. The relative density of the obtained composite electrolytes was established to be higher than one of the sintered t-LLZ and c-LLZ. The Li+ conductivity of the t-LLZ-based composites gradually increased from 4.6 × 10-7 S cm-1 (undoped t-LLZ) to 2.5 × 10-6 S cm-1 (t-LLZ/5 wt % LiPO3 composite) at 25 °C. The highest total conductivity of the c-LLZ/LiPO3 composites has been achieved by introducing 1 wt % additive (0.11 mS cm-1 at room temperature), whereas further doping resulted in the impurities formation.
RESUMO
The heat capacities of molten salts are very important for their practical use. Experimental investigation of this property is challenging because of the high temperatures involved and the corrosive nature of these materials. It is preferable to combine experimental investigations with empirical relationships, which allows for the evaluation of the heat capacity of molten salt mixtures. The isobaric molar heat capacities of all molten alkali and alkaline-earth halides were found to be constant for each group of salts. The value depends on the number of atoms in the salt, and the molar heat capacity per atom is constant for all molten halide salts with the exception of the lithium halides. The molar heat capacities of molten halides do not change when the anions are changed.
RESUMO
The solubility mechanism of silica in a fluoride-chloride melt has been determined in situ using Raman spectroscopy. The spectroscopy data revealed that the silica solubility process involved Si-O bond breakage and Si-F bond formation. The process results in the formation of silicate complexes, fluorine-bearing silicate complexes, and silicon tetrafluoride in the melt. Mass spectrometry of the vapor phase over the KF-KCl-K2SiF6 and KF-KCl-K2SiF6-SiO2 melts and differential scanning calorimetry coupled with thermal gravimetric analysis of these melts were performed to verify the silica solubility mechanism.
