Ingvar Albinsson

Effect of nano-porous Al2O3 on thermal, dielectric and transport properties of the (PEO)9LiTFSI polymer electrolyte system

Thermal, electrical conductivity and dielectric relaxation measurements have been performed on (PEO)9LiTFSI+10 wt.% Al2O3 nano-porous polymer electrolyte system. It is observed that the conductivity enhances substantially due to the presence of the filler particles with different surface groups. The highest enhancement is found for the filler particles with acidic groups followed by basic, neutral, and weakly acidic. The results reveal that the filler particles do not interact directly with poly(ethelene) oxide (PEO) chains indicating that the main chain dynamics governing the ionic transport has not significantly affected due to the filler. The results are consistent with the idea that the conductivity enhancement is due to the creation of additional sites and favourable conduction pathways for ionic transport through Lewis acid–base type interactions between the filler surface groups and the ionic species. This is reflected as an increase in the mobility rather than an increase in the number of charge carriers. A qualitative model has been proposed to explain the results.

Effect of concentration and grain size of alumina filler on the ionic conductivity enhancement of the (PEO)9LiCF3SO3:Al2O3 composite polymer electrolyte

Abstract Nano-composite polymer electrolytes are receiving attention as potential candidates to be used as electrolyte membranes in lithium polymer batteries and other devices. However, a survey of literature reveals that a systematic study of the effect of concentration and surface area of ceramic fillers on the conductivity enhancement of micro- and nano-composite polymer electrolytes is lacking. In this work, we have studied the thermal and electrical properties of the composite polymer electrolyte (PEO) 9 LiCF 3 SO 3 +Al 2 O 3 incorporating alumina filler grains of four different sizes with different specific surface areas. The results show that the PEO crystallite melting temperature decreased by a few degrees in samples with fillers exhibiting a minimum for samples with high conductivity. The presence of the filler enhanced the ionic conductivity substantially above as well as below 60xa0°C, and the nano-porous alumina grains with 5.8xa0nm pore size and 150xa0m 2 /g specific area and 15xa0wt.% filler concentration exhibited the maximum enhancement. The observed conductivity enhancement has been attributed to Lewis acid–base type surface interactions of ionic species with O/OH groups on the filler surface, with an additional contribution below 60xa0°C coming from the retention of an increased fraction of the amorphous phase due to the presence of the filler. The conductivity versus filler concentration curves exhibit two conductivity maxima which has been explained in terms of the surface interactions, blocking effect and grain consolidation. The conductivity enhancement appears to saturate beyond 100xa0m 2 /g grain surface area.

Dielectric relaxation, ionic conductivity and thermal studies of the gel polymer electrolyte system PAN/EC/PC/LiTFSI

Abstract Dielectric relaxation, ionic conductivity and thermal properties have been measured for the gel polymer electrolyte system poly(acrylonitrile)/ethylene carbonate/propylene carbonate/lithium bis(trifluoromethanesulfone)imide (PAN/EC/PC/LiTFSI) and for its components in the frequency range from 1 MHz to 1.8 GHz and over a temperature range from −20 to 50 °C. DSC results suggest that EC/PC exists in two different environments within the gel network; as regions in which the EC/PC molecules subjected to pairing interactions by the CN group in PAN and also as regions consisting of “free” EC/PC molecules. Addition of PAN to the EC/PC/LiTFSI liquid electrolyte has increased the ionic conductivity. Out of the various PAN/LiTFSI composition ratios studied for the gel polymer electrolyte, the 6:1 composition ratio by weight gives the highest ionic conductivity. The room temperature (23 °C) conductivity of the gel electrolyte with this composition, PAN(15.4%)/EC(41.0%)/PC(41.0%)/LiTFSI(2.6%) (by weight) is 2.5×10−3 S cm−1. DSC results show that this composition has the most amorphous nature, above −105 °C. The e″ spectra of gel electrolytes with various compositions show the presence of a high-frequency peak in the 0.5-GHz region attributed to the α relaxation process and a peak/shoulder in the 10-MHz region attributed to the ion-pair relaxation. Li+ ion transport probably takes place in the vicinity of the PAN chains and the ion-pair relaxation frequency appears to reflect the dynamic environment in which the cations migrate. However, the coupling between the conductivity and the α relaxations, attributed to EC/PC molecules, appears to be weak. A model has been presented according to which the Li+ ions in the gel electrolyte appears to be solvated by both PAN (through CN) and EC/PC.

Ionic conductivity in poly(propylene glycol) complexed with lithium and sodium triflate

Conductivity and viscosity measurements have been made for poly(propylene glycol)‐MCF3SO3 (M=Li, Na) complexes in order to examine more closely the Vogel–Tammann–Fulcher (VTF) empirical relationship which has been found in previous reports to provide a good fit to the experimental data. Further, a dynamic bond percolation model of ion conduction in polymer electrolytes has predicted VTF behavior and an inverse relationship between molar conductivity and viscosity or Walden ‘‘rule’’ behavior. We find that deviations occur from both the VTF and Walden empirical relationships and propose a modest alteration in the form of the dynamic percolation model for ions moving in polyether systems.

Efficiency enhancement in dye sensitized solar cells using gel polymer electrolytes based on a tetrahexylammonium iodide and MgI2 binary iodide system

Quasi-solid-state dye-sensitized solar cells have drawn the attention of scientists and technologists as a potential candidate to supplement future energy needs. The conduction of iodide ions in quasi-solid-state polymer electrolytes and the performance of dye sensitized solar cells containing such electrolytes can be enhanced by incorporating iodides having appropriate cations. Gel-type electrolytes, based on PAN host polymers and mixture of salts tetrahexylammonium iodide (Hex4N(+)I(-)) and MgI2, were prepared by incorporating ethylene carbonate and propylene carbonate as plasticizers. The salt composition in the binary mixture was varied in order to optimize the performance of solar cells. The electrolyte containing 120% Hex4N(+)I(-) with respect to weight of PAN and without MgI2 showed the highest conductivity out of the compositions studied, 2.5 × 10(-3) S cm(-1) at 25 °C, and a glass transition at -102.4 °C. However, the electrolyte containing 100% Hex4N(+)I(-) and 20% MgI2 showed the best solar cell performance highlighting the influence of the cation on the performance of the cell. The predominantly ionic behaviour of the electrolytes was established from the dc polarization data and all the electrolytes exhibit iodide ion transport. Seven different solar cells were fabricated employing different electrolyte compositions. The best cell using the electrolyte with 100% Hex4N(+)I(-) and 20% MgI2 with respect to PAN weight showed 3.5% energy conversion efficiency and 8.6 mA cm(-2) short circuit current density.

Intermediate-temperature proton-conducting fuel cells — Present experience and future opportunities

In view of nearly 10 years experience of intermediate-temperature (about 300 to 700°C) fuel cells using proton-conducting salts and relevant composites as electrolytes, we discuss in this paper the present status, problems, possible solutions and future opportunities for further development.

Ion association effects and ionic conductivity in polymer electrolytes

Abstract Ion association effects are essential for the understanding of ionic transport in polymer electrolytes. Ionic conductivity measurements on polyether-salt systems such as poly (propylene glycol), poly(ethylene oxide) and polyether modified poly-di-methyl-siloxanes complexed with triflate and perclorate salts have shown that plots of the molar conductivity versus the salt concentration have a characteristic shape. An aprotic polymer electrolyte behaves very much like a solution of a salt in a low permittivity aprotic solvent in which there are dissociated (“free”) ions, contact ion pairs and triplets present. The permittivity of the polymer electrolytes has been determined in order to calculate the fraction of free ions using an extended Denison-Ramsey equation. The enhancement of the ionic conductivity has earlier been suggested to be mainly due to either redissociation or the formation of triplets. This investigation supports redissociation.

Ion association effects and phase separation in poly(propylene oxide) modified poly(dimethylsiloxane) complexed with triflate salts

Abstract Phase separation is observed in poly(propylene oxide) modified poly(dimethylsiloxane) (PPO-PDMS) with excess poly(propylene oxide) (PPO) when salts of MCF 3 SO 3 (M = Li, Na) are added. The same behaviour is inferred for KCF 3 SO 3 . The solutions above and below the boundary layer have been studied by Raman spectroscopy and in particular by examining the non-degenerate, symmetric stretch ( A 1 , SO 3 ) Raman mode of the CF 3 SO − 3 anion. The upper part is siloxane rich; salt is present on both sides of the boundary layer with a much lower concentration in the upper part. The formation of the boundary layer is attributed to an increasing difference in surface tension between the PPO/salt/PPO-PDMS complexes and the separate PPO, PPO-PDMS components. The boundary layer moves up with increase in concentration. The number of ‘free’ ions decreases and ion association increases with increase in temperature. There is evidence of contact ion pairs, triplets and aggregates. Values of conductivity are quoted for 293 K.

Ion conductivity, electrical relaxation and ion association in poly(propylene glycol) complexed with ammonium triflate

Abstract Ion conductivity and electrical relaxation have been studied in poly(propylene glycol) 4000 (PPG) complexed with NH 4 CF 3 SO 3 in a concentration range of O:M=9800 to 10. A dielectric relaxation peak at about 1 MHz at room temperature is suggested to be due to ion pairs. Results indicate that the electrical relaxation times associated with these peaks could act as a probe for the local flexibility of the polymer chains and that, in the concentration range studied, the fraction of ion pairs increases with increasing salt concentration. Other features of ion association are inferred from an analysis due to Pettit and Bruckenstein. Ion conductivity in NH 4 SF 3 SO 3 complexed with PPG is enhanced by a factor of 3 to 4 over that measured for LiCF 3 SO 3 complexed PPG. Ion conductivity in ND 4 CF 3 SO 3 complexed PPG is used to comment on proton conduction in these systems.

Ionic conductivity in poly(ethylene oxide) modified poly(dimethylsiloxane) complexed with lithium salts

Abstract Poly(ethylene oxide) modified poly(dimethylsiloxane) has been complexed with LiClO4 or LiCF3SO3. The configuration of these polymers enhances their flexibility. The ionic conductivity has been measured using complex impedance spectroscopy for different Li+ ion concentrations. The temperature dependence of the conductivity has been measured for some of the samples. The ionic conductivity increases more rapidly with the addition of LiClO4 than with LiCF3SO3 but the maximum conductivity is higher for complexes with LiCF3SO3. At room temperature the highest ionic conductivity values were of the order of 9 × 10 −5 Ω −1 cm −1 for LiCF3SO3 compounds with the polymer. Effects of viscosity and ethylene oxide chain length are discussed.