Investigation of rechargeable lithium-sulfur batteries by in-situ techniques

Kurzfassung

The lithium-sulfur (Li-S) battery is currently of great interest for the research community. This battery promises with its high theoretical capacity (1675 mA h-1) and energy density (2600 Wh kg-1) to be one of the energy storage systems of the future. Nevertheless, the electrochemical processes and degradation mechanisms of the cell are still not well understood. In this work, in-situ characterization methods were applied for the characterization of reaction products and changes in the electrode properties. By means of XRD, the formation of reaction products during charging and discharging were monitored in operando. The formation of dilithium sulfide and the recrystallization of sulfur have been semi-quantitatively determined. The electrochemical behavior of the cell was also investigated using electrochemical impedance spectroscopy (EIS) at different depths of discharge and charge; and up to 50 cycles. An electrical circuit is proposed to quantify the impedance contribution of the cell. Changes in the electrolyte resistance and charge transfer resistance due layer formation on the electrode are amongst others the analyzed processes in this research. Furthermore, ex-situ atomic force microscopy (AFM) measurements provide information about changes in the electrical conductivity of the cathode surface.