Salt-in-polymer electrolytes for lithium ion batteries based on organo-functionalized polyphosphazenes and polysiloxanes

An overview is given on polymer electrolytes based on organo-functionalized polyphosphazenes and polysiloxanes. Chemical and electrochemical properties are discussed with respect to the synthesis, the choice of side groups and the goal of obtaining membranes and thin films that combine high ionic conductivity and mechanical stability. Electrochemical stability, concentration polarization and the role of transference numbers are discussed with respect to possible applications in lithium batteries. It is shown that the ionic conductivities of salt-in-polymer membranes without additives and plasticizers are limited to maximum conductivities around 10-4 S/cm. Nevertheless, a straightforward strategy based on additives can increase the conductivities to at least 10-3 S/cm and maybe further. In this context, the future role of polymers for safe, alternative electrolytes in lithium batteries will benefit from concepts based on polymeric gels, composites and hybrid materials. Presently developed polymer electrolytes with oligoether sidechains are electrochemically stable in the potential range 0-4.5V (vs. Li/Li+ reference). © by Oldenbourg Wissenschaftsverlag, München.Deutsche Forschungsgemeinschaft --This work was part of the research program A2 within the collaborative research center “SFB 458”, funded by the Deutsche Forschungsgemeinschaft. We thank K. Funke, R. Banhatti, H. Eckert, C. Cramer-Kellers, M. Schönhoff, A. Heuer, R. Pöttgen, B. Krebs, T. Nilges, N. Stolwijk, L. van Wüllen and D. Wilmer for helpful discussions, thanks also to all colleagues in the SFB 458 for the excellent collaboration. Finally, we would like to acknowledge the collaboration with D. Richter, R. Zorn, and W. Pyckhout-Hintzen on SANS experiments in Jülich, the collaboration with S. Passerini and M. Winter regarding the electrochemical analysis of polymer electrolytes in lithium ion cells, and we thank H. Gores (University Regensburg) and G. Röschenthaler (Jacobs University Bremen) for preparing and making available a number of novel lithium salts. -

Highly Conducting and Flexible Few-Walled Carbon Nanotube Thin Film

We report an effective route to prepare highly conducting and flexible few walled carbon nanotube (FWNT) thin films. The free-standing thin films were fabricated by functionalizing FWNTs with 4-ethoxybenzoic acid (EBA) via a direct Friedel-Crafts acylation reaction in a nondestructive polyphosphoric acid/Phosphorus pentoxide medium. The resulting ethoxybenzoyl-functionalized FWNT (EBA-f-FWNT) was readily dispersible in water. EBA-f-FWNT thin films were formed by a simple suction filtration of the dispersed solution. Electron microscopic studies were employed to characterize the morphologies of the resulting thin films. The obtained results indicate that the structure of FWNTs was not perturbed by the incorporation of EBA moieties, which were uniformly grafted onto FWNTs forming the FWNT networks. Room temperature electrical conductivity of the thin films was obtained using standard four-probe measurements, which revealed a value as high as 29 400 S m(-1), While the tensile strength and modulus of the film were found to be about 80 MPa and 15 GPa, respectively. Cyclic voltammograms revealed a rectangular shape, with superior capacitive behaviors nearing 133 F/g for the thin films, which is very attractive for capacitor applications.close222