Electronic and Ionic Wirings Versus the Insertion Reaction Contributions to the Polarization in LiFePO4 Composite Electrodes

The different contributions to the polarization of a LiFePO4 electrode are experimentally discriminated in this work. The electrode total resistance is dominated at high rate by the contribution of the electronic and the ionic wires, the former being more important in the case of electrodes with low compaction, while the latter being more important in the case of electrodes with high compaction. A porosity in the 35%-40% range allows to minimize the electrode polarization. At low rate, the electrode resistance is dominated by the resistance to lithium insertion into the active mass and follows the predictions of M. Gaberscek and J. Jamnik [Solid State Ionics, 177, 2647 (2006)]. We show here that the resistance to lithium insertion decreases with the increase of the specific current, a feature that suggests an increase of the active particle conductivity with rate. The easy-handling methodology described in this work should enable a more rational optimization of the electrode formulation and processing conditions for better electrochemical performance. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3497353] All rights reserved.