Microtech2010 2010

Activation of Phosphate Olivines LiMPO4 (M = Fe, Mn) by Functionalized Carbon Nanotubes: Application for Cathode Materials of Li-Ion Battery

L. Kavan
J. Heyrovsky Institute of Physical Chemistry, CZ

Keywords: olivine phospates, carbon nanoatubes

Abstract:

The nanotube-mediated redox wiring is based on a synergic action of adsorbed redox-active molecule, which provides the interfacial charge transfer to the surface and the single-walled carbon nanotube (SWNT), which transports charge to longer distances in the cathode material. A Ru-bipyridine complex Z-907Na, turned to be particularly suitable for this purpose, because of its amphiphilic character enabling solubilization of SWNT. Electrodes fabricated from optimized composite materials containing LiFePO4 (olivine) exhibit a 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 redox-mediator molecules or by pristine SWNT. Multi-walled carbon nanotubes (MWNT) functionalized by carboxylic groups, exhibit better affinity towards LiMPO4 (M – Fe, Mn) as compared to that of pristine MWNT. The surface functionalization of MWNT enhances charge storage capacity and reversibility of a composite with LiMnPO4 (olivine), but mediates also the electrolyte breakdown at potentials >4.2 V. Whereas the electrochemical activation of LiMnPO4 (olivine) by functionalized MWNT is quite modest, excellent performance was found for LiFePO4 (olivine) in composite materials containing only 2wt% of functionalized nanotubes.
 
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