Investigation of different locations for reference electrodes inside lithium-ion pouch cells

Three-electrode lithium-ion battery cells enable information about internal cell processes and properties. In this paper, the impact of the reference electrode location inside pouch cells with negative electrodes that have a geometrical overhang are analyzed. Reference electrode measurements of commercially available three-electrode coin cells are used as the benchmark for the self made three-electrode pouch cells with a Li4Ti5O12 (LTO) reference electrode. Different designs of three-electrode pouch cells lead to overestimations or underestimations of the electrodes' overpotentials compared to the benchmark. These results lead to a theory about the requirements of an ideal reference electrode position in pouch cells. Based on that, the reference electrode is placed next to the outer edge of the positive electrode, opposite to the negative electrode's overhang area. By means of experiments and 2D simulations it is shown that the insulation of the negative electrode's overhang area is necessary for appropriate measurement fidelity of the electrode potentials. Moreover, the measured electrode potentials are verified by the correlation of lithium-plating with measured negative electrode potentials below 0 V vs. Li/Li+.