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

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.