Characterization of Polymerized Sulfur Cathodes upon Cycling

Rechargeable Li-S batteries offer an unprecedented opportunity for energy storage technology.  Sulfur is a very cheap material with remarkably high energy storage density when used as a cathode.  Sulfur cathodes have historically suffered from a myriad of problems, including low active material utilization due to low electronic conductivity and significant capacity fade upon cycling due to polysulfide dissolution and cracking of the cathode.  The main approach for improving active material utilization and maintaining capacity has been to sequester sulfur within various forms of electronically conductive, nanostructured carbons. 

Recently, researchers have developed a copolymer with a very high sulfur content via a process termed inverse vulcanization.¹  The sulfur-containing polymer is inexpensive to produce, and full Li-S cells utilizing this copolymer in the cathode achieve capacities of 635 mAhr/g after 500 cycles at a rate of C/10.²

This talk will focus on results of characterization studies to determine the morphology and composition of the sulfur copolymer cathode and electrolyte solution during the cycling process.  Microscopy studies show that the sulfur copolymer cathode maintains greater uniformity and shows less cracking upon cycling than an elemental sulfur cathode.  We will also report on results of in-situ Raman and XPS studies to identify the products present in the cathode and in the electrolyte at various potentials during cycling.

1. J. Pyun et. al., Nature Chemistry, 5:518-524, 2013.

2. J. Pyun, et. al., ACS Macro Letters, 3:229-232, 2014.