Characterization of the Effect of Cell Design on Li−S Battery Resistance Using Electrochemical Impedance Spectroscopy
Aysegul Kilic, Damla Eroğlu
Abstract
Abstract The effect of two critical cathode design parameters, electrolyte‐to‐sulfur (E/S) and carbon‐to‐sulfur (C/S) ratios, on the kinetic and transport resistances in a Li−S cell is determined as a function of discharge depth by using electrochemical impedance spectroscopy. Electrolyte, charge transfer, and Li 2 S film resistances are identified as the major contributors to cell resistance. Both E/S and C/S ratios have a significant impact on cell resistance, predominantly at the early and final stages of discharge. The E/S ratio controls the cathode kinetics in the first plateau together with Li 2 S precipitation near the end of discharge. Consequently, the highest cell resistances are obtained for the cell with the lowest E/S ratio of 6 mL g −1 . Increasing the E/S ratio up to 19 mL g −1 decreases the resistances considerably, no notable change is achieved after this point. On the other hand, the C/S ratio reflects a tradeoff between high electrochemically active surface area vs. sufficient and homogeneous S loading in the cathode. The minimum cell resistance is attained for the cell with C/S=1; any increase or decrease in the C/S ratio leads to higher resistances. The results suggest a mechanistic interpretation of the connection between cathode design and cell performance in Li−S batteries.