Bengt-Erik Mellander

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.

Ionic conductivity of plasticized(PEO)-LiCF3SO3 electrolytes

Many polymer electrolytes used in practical applications contain a low molecular wcight plasticizer. Plasticizers can be used to change the mechanical and electrical properties of polymer electrolytes by reducing the degree of crystallinity and lowering the glass transition temperature T g . In this study the ionic conductivity has been determined for a (PEO) 9 LiCF 3 SO 3 polymer electrolyte with added plasticizers. The samples were in the form of thin films with the thickness 0.1- 0.5 mm and ethylene carbonate (EC), propylene carbonate (PC) or a mixture of ethylene carbonate and propylene carbonate (EC:PC) were used as plasticizers. The ionic conductivity increases with increasing amount of plasticizer but the amount of plasticizer which can be added is limited since the films become too soft for use in practical applications. Without any plasticizer, the complex (PEO) 9 LiCF 3 SO 3 only has a conductivity of 2.5 x 10 -5 S cm -1 at 332 K. Adding 50% of the plasticizers by mol. weight of PEO to the (PEO) 9 LiCF 3 SO 3 complex yielded mechanically stable films with an ionic conductivity of 9.0 x 10 -4 S cm -1 with EC and 5.2 x 10 -5 S cm -1 with PC at the same temperature

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.

Phase diagram and electrical conductivity of the Li2SO4-Li2CO3 system

Abstract The Li 2 SO 4 -Li 2 CO 3 binary system has been studied using DSC, X-ray diffraction and electrical conductivity measurements. The phase diagram shows that the solubility of Li 2 CO 3 in α-Li 2 SO 4 extends to about 10 mole% Li 2 CO 3 . At temperatures below 550°C a two-phase region exists. The electrical conductivity in this region shows a maximum for the eutectic composition, e.g. 1.46 × 10 −3 (Ω cm ) −1 at 510° C . This has been suggested to be due to a high conductivity in the interface region between the finely dispersed crystallites in the eutectic mixture. A narrow band between 549 and 573°C having a conductivity of about 1 (Ω cm) −1 extends from about 15 to 100 mole% Li 2 CO 2 COIn the high temperature solid electrolyte phase a drop in conductivity of about 3.5% has been observed when 2.5 mole% Li 2 CO 3 is added to fcc-Li 2 SO 4 .

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.

Proton conductivity in fuel cells with solid sulphate electrolytes

Abstract Fuel cell and concentration cell experiments have been carried out with various solid sulphates as the solid electrolyte. Platinum, nickel sponge and some perovskites are found to be good alternatives as electrode materials. It is evident that proton conductivity is dominating in the studied cells, while it still is an open question whether there also can be a certain contribution from oxygen ion conductivity. Although the electrodes are blocking for Li + , Na + , etc., there are correlations between the fuel cell currents and the electrical conductivity of the salt. The observed phenomena are not limited to sulphates but occur also for other salts, such as phosphates.

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.

Intermediate temperature fuel cells with electrolytes based on oxyacid salts

Abstract Electrolyte materials based on oxyacid salts are a new type of solid ionic conducting system where both cations and protons are mobile. These materials have a face-centred cubic structure. Two different proton coordination states and conduction mechanisms have been recognized in this system. The proton conduction has been used for intermediate temperature fuel cells (ITFC). ITFCs using materials based on nitrate salts as electrolytes are successful, the best fuel cell performance is a current density of 300 mA cm 2 at 0.75 V. There are still some technical problems to be solved, such as the coexistence of electrode and electrolyte materials, etc., in these fuel cells, and an improvement of the electrode materials is needed for a better performance of the practical fuel cells.

On the high-temperature phase transitions of CsH2PO4: A polymorphic transition? A transition to a superprotonic conducting phase?

X-ray diffraction, thermogravimetric (TGA), differential scanning calorimetric (DSC), and impedance analysis were used to study the reported high-temperature phase transitions at 107, 149, 230, and 256 °C in crystals of cesium dihydrogen phosphate, CsH2PO4 (CDP). Our results show strong evidence that at all these temperatures, the observed DSC or differential thermal analysis (DTA) endothermic effects appear only as a consequence of a dehydration process starting on the surface of the crystal. Our results thus show that the reported transition at 230 °C is not a polymorphic transition. This means that the monoclinic symmetry, stable at room temperature, with space group P21/m–C2k2, is maintained up to the final decomposition. Moreover, since we have not found any evidence for the existence of a superprotonic high-temperature phase above 230 °C, the high conductivity above 230 °C is thus only a consequence of the dehydration of the crystal surface.