Investigations of lithium-sulfur batteries using electrochemical impedance spectroscopy

Kurzfassung

The lithium-sulfur (Li-S) battery is a promising rechargeable system due to its high theoretical capacity (1675 mAh gsulfur-1), energy density (2500 Wh kg-1), low cost and the non-toxicity of sulfur. In order to optimize the performance of the cell, it is highly important to understand the electrochemical and degradation processes of the cell during cycling. In this work, the electrochemical behavior of lithium-sulfur (Li-S) batteries was investigated by means of electrochemical impedance spectroscopy (EIS). Measurements were performed in equidistant charge intervals at different depths of discharge and charge during the first cycle. Additionally, the degradation of the cells was analyzed for up to 50 cycles. An equivalent electrical circuit is proposed to simulate the electrochemical processes and to quantify the impedance contributions of Li-S batteries. EIS as a function of the cycle number shows an increased capacity for fading correlated with a decrease in the charge transfer resistance of the cathode.