Adriane V. Rosario

Characterisation of PEO–Al2O3 composite polymer electrolytes

Abstract The behaviour of PEO 8 LiClO 4 with different quantities of α-Al 2 O 3 or γ-Al 2 O 3 was investigated using DSC, AC conductivity and 7 Li NMR experiments. DSC results showed that the presence of the filler does not change the glass transition temperature of the electrolyte but, on the other hand, modifies the quantity of its crystalline phase. From the AC impedance measurements, it was observed that the sample with the highest conductivity at room temperature is PEO 8 LiClO 4 5.3 wt.% α-Al 2 O 3 . The change in the quantity of crystalline phase cannot alone explain the conductivity data, and it is suggested that the space charge contribution in the interphase of the filler particles and the polymeric chains influences the behaviour of the samples. The 7 Li NMR results showed that line width narrowing begins at temperatures close to T g . From the hydrogen decoupling experiments it was possible to estimate the LiH average distances as 2.7 A. The LiLi distance was calculated as being between 2.6 and 3.5 A depending on the number of near neighbours lithium nuclei used in the model.

Nuclear magnetic resonance study of PEO-based composite polymer electrolytes

Abstract The effect of carbon black and ceramic (a-Al 2 O 3 and g-Al 2 O 3 ) particles on the cationic and polymer chain mobilityhave been investigated in poly(ethylene oxide)–lithium salt (LiClO 4 and LiBF 4 ) solid composite polymer electrolytesby using nuclear magnetic resonance (NMR) techniques. Proton ( 1 H) and lithium ( 7 Li) lineshapes and spin–latticerelaxation times were measured as a function of temperature. The 7 Li data indicates that the lineshape and relaxationis affected by the coupling of its quadrupolar moment to the surrounding electric field gradients. Activation energiesextracted from the 7 Li relaxation data are in the range 0.20–0.25 eV. Results show that the addition of a-Al 2 O 3 influenced both, the relative cation mobility and the polymer chain motion. Calculation shows that this result is inquantitative agreement with the conductivity data.

NMR and conductivity study of PEO-based composite polymer electrolytes

The influence of the space charge created by the presence of TiO2 nanoparticles on the lithium and polymer chain mobility have been investigated in solid composite polymer electrolytes (CPE), poly(ethylene oxide) (PEO) LiClO4, by using complex impedance spectroscopy and nuclear magnetic resonance (NMR). Special care was taken with the synthesis and the characterization of the TiO2 particles and with the composite preparation. The conductivity and NMR measurements were undertaken in composite samples nanoparticles having constant total surface area. Proton (1H) and lithium (7Li) lineshapes and spin-lattice relaxation times were measured as a function of temperature. Activation energies extracted from the 7Li relaxation data are in the range 0.20–0.22 eV. The NMR decoupling experiment suggests that the Li–Li interactions are stronger in the composites when compared with those of the ceramic free electrolytes.

Comparison of the electrochemical behavior of CeO2–SnO2 and CeO2–TiO2 electrodes produced by the Pechini method

CeO2–SnO2 and CeO2–TiO2 thin films were prepared by the Pechini method and their characteristics were compared, using a fractional factorial design to quantify the effect of five preparation variables. It was observed that CeO2–SnO2 electrodes show a greater electrochemical response than the CeO2–TiO2 films. The best intercalation charge densities were 18.11 and 9.91 mC/cm2 for CeO2–SnO2 and CeO2–TiO2, respectively. Both films were optically inactive with transparencies, in most cases, higher than 90%.

Lithium insertion in TiO2 doped Nb2O5 electrochromic thin films

TiO2 doped Nb2O5 thin films of concentration 0.1–10 mol% were prepared by the Pechini method and their electrochemical and electrochromic properties were characterized by cyclic voltammetry, chronoamperometry, ‘in situ’ UV–Vis spectrophotometry and scanning electron microscopy. The films obtained have a thickness between 440 and 550 nm. The cyclic voltammograms showed an increase in the cathodic current densities for the doped films. The highest values of the insertion charge density were observed for films containing TiO2 between 0.05 and 0.5 mol%. The undoped Nb2O5 films showed a transmittance variation (ΔT at 620 nm) of 56.8% and a coloration efficiency (CE) of 14.9 cm2 C-−1. An increase in ΔT and CE was observed with the increase of the TiO2 concentration up to 1.0 mol%, which presented ΔT=84% and CE=26.9 cm2 C−1. Above this concentration, the ΔT and CE values decreased. These results are discussed considering the electronic and morphological properties of the samples.

NMR Study of the Polymer Electrolyte Formed by Ethylene Glycol, Citric Acid and LiClO 4

In this work we report a proton ( 1 H) and lithium ( 7 Li) NMR lineshape and spin-lattice relaxation time investigation of this polymer electrolyte obtained from the polymerization of ethylene glycol and citric acid with lithium salt. The 7 Li data indicates that the lineshape and spin-lattice relaxation is affected by the coupling of its quadrupolar moment to the surrounding electric field gradients. The activation energy for the lithium motion extracted from the 7 Li relaxation data is 0.23 eV. The dynamics parameters obtained from the NMR data indicate that the lithium mobility in the EG:CA:LiClO 4 is comparable to those found in polymer gel electrolytes and in plasticized polymer electrolytes.

A Solid Electrochromic Device Based on Poly(o­methoxyaniline) and Tungsten Oxide Electrochemically Synthetized

In this work a complementary organic-inorganic electrochromic device (DE) using solid polymeric electrolyte (EP) based on Poly(o-methoxyaniline) (POMA) and tungsten oxide (WO3) was assembled. The electrochromic materials were deposited by electrochemical method on ITO (indium tin oxide) coated glass and characterized in separate and under the device form. Characterization by cyclic voltammetry, spectrochronoamperometry, scan electronic microscopy, X-ray diffraction and perfilometry were carried out. The electrochromic behavior of the materials was studied in 650 nm, applying 1000 double potential steps. POMA films maintained 33% of the initial optical contrast. WO3 films presentedà a à i easeà ofà theà t a s itta eà a iatio à ΔTmax à ithà theà sta ilizatio à te de à i à 53%. The DE was produced according to the configuration ITO/POMA/(EP)/WO3/ITO, which presented sta leàΔTmax à àa ou dà %.àTheàelectrochromic films (POMA and WO3) and the DE presented in 650 ,à olo atio àeffi ie àη àa ou dà ,à 8àa dà à 2 C, respectively, and reduced response time