The influence of geometry in 2D simulation on the charge/discharge processes in Li-ion batteries

A two dimensional simulation approach is proposed for examining the influence of geometry and morphology on current and potential distribution in Li-ion batteries at a microscopic scale. The study was focused on two different geometries of graphite anodes: close packed spheres and flakes (in different aspect ratios). The simulation output, which includes charge/discharge curves, concentration and voltage gradients in the cells, and the current density at each point in the cells, allows studying the significance of the particles' geometry and the layered structure of composite electrodes. We found that at high electrolyte solutions conductivities, when the secondary aspect of current distribution is dominant, interspacing the particles in the same layer, perpendicular to the ion flow (e.g. from 0.2 μm to 0.4 μm), leads to a significant moderation of the maximum solution current density (e.g. from 190 A/m² to 97 A/m²). The results also show that when the cells are changed from an anode containing spherical particles to an anode containing flaky particles, the intercalation reaction becomes intensively nonuniform with anodes comprising flaky particles and the solution over-potential increases, so that the cell voltage decreases by up to ∼70 mV. In addition, a small vertical increase in the interspacing between the graphite flake particles leads to a significant increase in the cell voltage (i.e. decreasing the solution overvoltage), and we also show that 10% expansion of the particles active surface area, leads to an additional improvement of ∼150 mV in the cell voltage. However, there is no significance change in the solution's current density.