Technical Proceedings of the 2009 Clean Technology Conference and Trade Show

Clean Technology 2009

Chapter 5: Energy Storage, Fuel Cells and Hydrogen

L. Kavan, I. Exnar, M. Graetzel
J. Heyrovsky Institute of Physical Chemistry, CZ
163 - 166
Li-ion batteries, olivine FePO4, carbon nanotubes
The amphiphilic Ru-bipyridine complex, NaRu(4-carboxylic acid-4’-carboxylate-2, 2’bipyridine)(4,4’-dinonyl-2,2’bipyridine)(NCS)2 can be used as a surfactant for solubilization of single walled carbon nanotubes (SWNTs) in acetonitrile-t-butanol mixture. The Ru-complex represents a redox functionality of 3.5 V vs. Li/Li+, which is matching almost exactly the formal potential of LiFePO4/FePO4 couple. The supramolecular assembly of SWNT/Ru-bipyridine complex is adsorbed on the surface of LiFePO4 (olivine) via the free carboxylic groups at the bipyridine ligand. This provides a composite material with roughly monolayer coverage by the Ru-bipyridine complex. Electrodes fabricated from the Ru-complex/SWNT/LiFePO4 composite exhibited greatly enhanced activity for electrochemical Li+ extraction/insertion compared to the performance of electrodes made from commercial carbon-coated LiFePO4 or from LiFePO4 derivatized either by adsorption of sole Ru-bipyridine complex or by carbon nanotubes dispersed with the redox inactive pyrene butanoic acid. The SWNT backbone promotes the interfacial charge transfer between LiFePO4 and the Ru-complex, whose redox potentials are closely matching each other. The so called “nanotube wiring” effect is based on a synergic action of adsorbed redox-active molecule, which provides the interfacial charge transfer to the olivine surface and the SWNT, which transports charge to longer distances in the composite.
Promoting the activity of LiFePO4 (olivine) cathode of Li-ion battery by supramolecular complexes with single walled carbon nanotubes