A percolation micro-model is developed to predict the effective properties of the composite electrode consisting of poly-dispersed electronic and ionic-conducting particles. The analytical expressions for the percolated triple-phase-boundary (TPB) lengths, hydraulic pore radius and intra/inter-particle conductivities have been formed. The model shows that the percolated TPB lengths of a composite electrode consisting of poly-dispersed particle sizes for both materials (i.e., having a normal distribution with a non-dimensional standard deviation of 0.4) are about 32% lower than that of the composite electrode with mono-sized particles. And the higher percolated TPB lengths can be achieved by reducing the mean particle size of each material and narrowing the particle size distribution. A composite cathode may benefit from it, because of its low electrochemical activity. The model also shows that the composite electrode with large mean particle size radii ratio between the electrode- and electrolyte-materials and broad particle size distributions can not only provide higher inter-particle ion conductivity, but also reduce the percolation volume fraction threshold of the electrode-material. And this may be helpful for a composite anode to obtain a higher overall ion conductivity. (c) 2010 Elsevier B.V. All rights reserved.