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- Backholm, Jonas, et al.
(författare)
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Determination of solid phase chemical diffusion coefficient and density of states by electrochemical methods : Application to iridium oxide-based thin films
- 2008
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 103:2, s. 023702-
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Tidskriftsartikel (refereegranskat)abstract
- Potentiostatic intermittent titration technique (PITT) and electrochemical impedance spectroscopy (EIS) were investigated as methods to determine solid phase chemical diffusion coefficient (D) and electronic density of states (DOS). These techniques were then applied to iridium oxide (IrOx) and iridium-tantalum oxide (IrTaOx) thin films prepared by sputter deposition. The experiments, performed in 1M propionic acid between -0.2 and 0.8 V vs Ag/AgCl, showed effects of interfacial side reactions, whose contribution to the electrochemical response could be identified and corrected for in the case of PITT as well as EIS. It was found that D is strongly underestimated when using PITT with the common Cottrell formalism, which follows from non-negligible interfacial charge transfer and Ohmic resistances. EIS indicated an anomalous diffusion mechanism, and D was determined to be in the 10(-11)-10(-10) cm(2)/s range for IrOx and IrTaOx. Both PITT and EIS showed that the intercalated charge as a function of potential exhibits a shape that resembles the theoretical DOS of crystalline iridium oxide, especially for IrTaOx.
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| 6. |
- Bayrak Pehlivan, Ilknur, et al.
(författare)
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Ion conduction of branched polyethyleneimine-lithium bis(trifluoromethylsulfonyl) imide electrolytes
- 2011
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Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 57, s. 201-206
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Tidskriftsartikel (refereegranskat)abstract
- Ionic conductivity of polymer electrolytes containing branched poly (ethylene imine) (BPEI) and lithium bis(trifluoromethyl sulfonyl)imide (LiTFSI) was measured between temperatures of 20 and 70◦C and molar ratios of 20:1 and 400:1. The electrolytes were characterized by impedance spectroscopy, differential scanning calorimetry, and viscosity measurements. At room temperature, the maximum conductivity was 2×10−6 S/cm at a molar ratio of 50:1. The molar conductivity of the electrolytes displayed first a minimum and then a maximum upon increasing salt concentration. A proportionality of molar conductivity to segmental mobility was seen from glass transition temperature and viscosity measurements. Analysis of the Walden product and isoviscosity conductivity showed that the percentage of ions bound in ion pairs increased at low concentrations below 0.1 mol/kg. The average dipole moment decreased with salt concentration. The temperature dependence of the ionic conductivity showed an Arrhenius behavior.
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| 9. |
- Bayrak Pehlivan, Ilknur, et al.
(författare)
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[PEI-SiO2]:[LiTFSI] nanocomposite polymer electrolytes : Ion conduction and optical properties
- 2012
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Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier BV. - 0927-0248 .- 1879-3398. ; 98, s. 465-471
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Tidskriftsartikel (refereegranskat)abstract
- Ion conductivity and optical properties were investigated for polymer electrolytes based on poly (ethyleneimine) and lithium bis(trifluoromethylsulfonyl)imide and also containing up to 9 wt.% of 7-nm-diameter SiO2 nanoparticles. The [N]:[Li] molar ratio was kept constant at 50:1. Impedance measurements were performed in the frequency range 10(-2)-10(7) Hz and between the temperatures 20 and 70 degrees C with an applied ac voltage of 1 V. Spectrophotometric data of total and diffuse transmittance were taken between the wavelengths 300 and 2500 nm. The bulk impedance was fitted to a conductive Havriliak-Negami circuit model. The ion conductivity increased monotonically for increasing SiO2 contents: specifically its room temperature value went from 8.5 x 10(-7) S/cm without nanoparticles to 3.8 x 10(-5) S/cm for 8 wt.% of SiO2 while the diffuse transmittance remained at similar to 1% so that optical clarity prevailed.
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| 10. |
- Brown, Shelley, et al.
(författare)
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Characterisation and modelling of a high-power density lithium-ion positive electrode for HEV application
- 2004
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Konferensbidrag (refereegranskat)abstract
- In this study, the impedance response of a porous electrode based on LiNi0.8Co0.15Al0.05O2 was investigated using an impedance model including the following features: Butler-Volmer kinetics; double layer capacitance; solid phase concentration and potential gradients; electrolyte phase concentration and potential according to the concentrated electrolyte theory; particle size distribution; and an empirical relation between equilibrium potential and state of charge. The model was evaluated by fitting it to experimental results using different electrolytes and states of charge. In addition, the characteristic parameters for the electrode were obtained from the fitting results.
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