In recent years, tremendous effort has been invested into researching energy storage chemistries that will replace lithium ion.  New strategies with higher capacities must be considered, such as a chemical conversion cathode. The lithium sulfur chemistry is a promising candidate as it uses earth abundant, inexpensive, high capacity sulfur as its cathode.  Conversion cathodes like sulfur are much more challenging as a secondary battery, and behave differently than intercalation cathodes.  Because of this, different design criteria must be applied to conversion cathodes to maximize power and capacity.  The interplay of conductive network, insulating active cathode, and binder all give rise to differences in performance for the dissolution and precipitation of the cathode material.  This work attempts to identify key design criteria for sulfur cathodes by systemically varying the basic components of cathode chemistry and structure.  A matrix of ~110 different cathode formulations were fabricated by varying conducting carbon, % active material, binder system, and sulfur loading.  Performance of these cathodes was evaluated by means of 2032 coin cell tests under constant current and pulsed loads.   First discharge capacity, capacity retention, coulombic efficiency, impedance, cathode surface area, and cathode porosity are utilized to gauge the effectiveness of the cathode and explain trends observed in cycling tests.  The effects of cathode rheology on porosity surface area and overall cathode utilization was also investigated.  Observed differences in performance between different electronically conductive elements and different cathode support elements were observed, with nuanced changes in morphology resulting in significant performance changes.

Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.