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Enhancement of Electrochemical Activity of LiFePO₄ (olivine) by Amphiphilic Ru-bipyridine Complex Anchored to a Carbon Nanotube

Ladislav Kavan*

J. Heyrovsk Institute of Physical Chemistry, v.v.i., Academy of Sciences of the Czech Republic, Dolejkova 3, CZ-18223 Prague 8, Czech Republic

Ivan Exnar

High Power Lithium, SA, PSE-B, Ecublens, CH-1015 Lausanne, Switzerland

Jiri Cech^†

Max Planck Institute for Solid State Research, Heisenbergstr. 1, 70569, Stuttgart, Germany

Michael Graetzel

Laboratory of Photonics and Interfaces, EPFL, Ecublens, CH-1015 Lausanne, Switzerland

Chem. Mater., 2007, 19 (19), pp 4716–4721

DOI: 10.1021/cm071107p

Publication Date (Web): August 23, 2007

Corresponding author. E-mail: kavan@jh-inst.cas.cz.

†

Present address: Lehigh University, Department of Materials Science and Engineering, 5 East Packer Avenue, Bethlehem, PA 18015.

Abstract

Single walled carbon nanotubes (SWNTs) were dissolved in an acetonitrile + tert-butanol mixture, using the amphiphilic Ru-bipyridine complex NaRu(4-carboxylic acid-4‘-carboxylate)(4,4‘-dinonyl-2,2‘bipyridine)(NCS)₂ as a surfactant. The assembly of the SWNT/Ru-bipyridine complex was adsorbed on the surface of LiFePO₄ (olivine), providing a material with approximately monolayer coverage by the Ru-bipyridine complex and ca. 0.04 wt % of SWNT. Electrodes fabricated from the surface-derivatized LiFePO₄ exhibited greatly enhanced activity for electrochemical Li⁺ extraction/insertion compared to electrodes 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 closely match each other. The nanotube-mediated redox wiring of virtually insulating electrode materials such as LiFePO₄ presents a novel strategy for application in high-energy lithium-ion batteries.

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