The structure of solid and liquid electrodes strongly affects the performance of Lithium batteries and of Semi-solid Redox-Flow cells. Thus understanding the formation of the structure of electrodes is an important issue. This paper proposes to study the aggregation processes that occur in electrode slurries by means of numerical simulations. For that Brownian dynamics simulations are developed and applied to a suspension composed of silicon nanoparticles and carbon black. Special attention is paid to the effects of the size of nanoparticles and of the interactions between the different components. The percolation of the carbon network and the number of contacts between the active mass and the conductive additive particles are quantified. Simulations results are found in good agreement with our previous experimental studies, showing that they can be used to improve the formulation of the slurry of electrodes. (C) 2015 The Electrochemical Society. All rights reserved.