In-Situ Measurement of Current Distribution in a Li-Ion Cell

This paper reports in-situ measurements of current distribution in a Li-ion battery using a newly developed pouch cell with a segmented electrode. It is shown that current distribution is non-uniform from the beginning of discharge and evolves dramatically as discharge proceeds. Initially, segments closer to the negative tab generate higher local currents, which is attributed to the ohmic potential drop along the negative current collector. However, toward the end of discharge the current distribution reverses in pattern due to local SOC non-uniformity developed by uneven current production in early stages. Current distribution is more uniform at lower C rates and lower temperatures. In cells operated close to the equilibrium (e.g. at low C-rates or higher temperatures), current distribution tends to be wavy as it is dominated by the SOC non-uniformity effect and reflective of multiple plateaus in the open-circuit voltage vs. SOC curve. In contrast, current distribution exhibits a monotonic variation in cells operated at highly non-equilibrium as the ohmic potential drop along the current collector becomes more controlling. Local SOC distribution is calculated based on measured local currents. The SOC distribution is found not uniform, even at cutoff during high C rate discharge, suggesting strongly under-utilization of active materials.