Autogenic Synthesis of High Rate, High Energy Carbon-Sulfur Cathodes for Rechargeable Lithium Sulfur Batteries

There is an increasing demand for longer lasting and higher performance energy storage. Today’s rechargeable lithium-ion batteries cannot satisfy the high-energy requirements for grid energy systems, longer-lasting electronics, and long range electric vehicles. In contrast, the theoretical performance values for lithium-sulfur batteries exceed the minimum requirements for these emerging technologies. However, technical challenges including low conductivity and the polysulfide shuttle – a parasitic mechanism in which the cathode decomposes into soluble chemical intermediates during cycling – inhibit battery lifetime to fewer than 10 cycles.

To address these issues, this work introduces the autogenic process to synthesize high conductivity carbon-sulfur composites. Developed in 2004 by Pol et al., the autogenic process enables high temperature reactions within a solvent-free reactor. The autogenic process allows for high sulfur loading (up to 75% by TGA) with higher specific capacity compared to mechanical mixing techniques. Specifically, the high specific capacity (ca. 1227 Ah kg^-1) at fast charging rates (up to 1C) is hypothesized to be due to sulfur distribution: as shown by energy-dispersive X-ray spectroscopy, autogenic synthesis selectively inserts sulfur into the carbon substrate with a highly isotropic distribution. The better sulfur distribution is believed to improve conductivity and the resulting electrochemical kinetics with autogenic synthesis.