Kinetics of all-solid-state sulfur cathodes

All-solid-state lithium sulfur batteries (ASLSB) have many advantages over liquid electrolyte-based lithium sulfur batteries such as high sulfur utilization, low electrolyte-to-sulfur ratio and low self-discharge. However, the kinetics of all-solid-state sulfur cathodes is not well understood, which is critical to achieve their full potential. In this work, we determine the contributions of different processes to the overall kinetics of sulfur electrodes using Electrochemical Impedance Spectroscopy (EIS) and Gravimetric Intermittent Titration Technique (GITT). We show that the impedance of sulfur electrodes can be well described by the Transmission Line Model (TLM). It is found that the kinetics of the sulfur electrode is determined primarily by ionic migration at the electrode level and diffusion within the sulfur active materials. Based on this understanding, we compared kinetics of sulfur electrodes with different solid electrolytes and mixing methods. Electrodes using amorphous sulfide solid electrolyte and impregnated S/C composites display the best kinetics. ASLSB possess high capacities at moderate rates at room temperature, and can operate even at 120 degrees C. Combined with the negligible self-discharge over a year, we believe that ASLSB is a promising candidate for high-energy primary batteries.