Simulation and Measurement of Local Potentials of Modified Commercial Cylindrical Cells

This work presents a modification approach and first measurements of commercial cylindrical Li-ion cells with multiple local potential probes and an internal temperature sensor. Local potential measurements at low currents show a non-uniform potential distribution along the electrode, dominated by the open circuit voltage (OCV) of the negative electrode. For higher currents, the overpotential along the current collector becomes dominant and instead of a corrugated potential distribution, a significant current dependent voltage gradient can be detected, indicating a highly non-uniform state of charge (SOC) distribution with increasing distance to the current collecting tab. After the discharge operation, a quick potential equalization can be witnessed which results in a non-detectable potential difference between the single electrode sections after 12 min, even though the overall cell voltage relaxation has not reached an equilibrium state yet. The presented modification approach combines the advantages of high quality industrial manufactured cells showing uniform coating thicknesses and packing density with the advantages of special tailor made cells for in situ measurements. Due to the low impact of the modification and its long-term stability, highly reproducible measurements can be conducted at different locations of the electrodes.