Role of the carbon nanocoating on the electronic conductivity of LiFePO4 based electrodes for lithium ion batteries

J.C. Badot, K.A. Seid, O. Dubrunfaut, S. Levasseur, B. Lestriez, D. Guyomard

Keywords: nanocoating, dielectric spectroscopy, electronic transport, lithium batteries


Recently, we used the broadband dielectric spectroscopy (BDS), from low (a few Hz) to microwave (a few GHz) frequencies. This technique is very sensitive to the different scales of the electrode architecture involved in the electronic transport, from interatomic distances to macroscopic sizes, as well as to the morphology at these scales, coarse or fine distribution of the constituents. In this work, BDS is used to study LiFePO4 wrapped in a carbon nanocoating. Model samples prepared from different LiFePO4 varying in particle size (from 50nm to 400nm) and carbon nanocoating content (from 2 to 4 nm) are studied. The decomposition of the dielectric spectra evidenced different relaxations attributed to: (a) space-charge polarization (low-frequency range) due to the interface sample/current collector; (b) polarization of C-LiFePO4 clusters (micronic and/or submicronic scale) due to the existence of resistive junctions between them; and (c) electron hopping between sp2 domains within the carbon coating (higher frequency range). The complex resistivity plots allow determining the conductivity at the different scales of the material, i.e. macroscopic, cluster, coating and sp2 domains. This work opens up new prospects for a more fundamental understanding of the electronic transport in nanostructured coatings.