Four-electrode symmetric setup for electrochemical impedance spectroscopy study of Lithium–Sulfur batteries

Electrochemical impedance spectroscopy is a powerful tool to probe into the complexity of the internal resistance, which is critical in affecting the actual energy density of lithium-sulfur battery. However, due to the limit of cell setup, both two and three-electrode cells are unable to reveal the resistances of individual cell components directly. We analyze the resistance of the cell components by using a novel four-electrode symmetric setup. The in situ impedance responses unmask the resistance of solid electrolyte interphase on the lithium foil, the electrolyte resistance, the diffusion resistance of porous in the cathode, the charge transfer resistance and its coupling ionic resistance in pores of the four-electrode cell. The solid electrolyte interphase consists of two layers which have differences in ion transport properties. The stripping/plating of lithium has a significant effect on the anode resistance. The charge transfer resistance and pores resistance are sensitive to the polysulfides species and cathode passivation. Finally, the loss of energy caused by the internal resistance indicates the cell-level energy density will reduce rapidly when the operating current is higher than 1 C.