Evolution of Redox Density of States in Sulfurized Polyacrylonitrile Cathodes

Sulfurized polyacrylonitrile (SPAN) shows intriguing electrochemical properties as a Li-S cathode, but its structure and electrochemical mechanisms remain unclear. Previously, we hypothesized that the presence of nitrogen in SPAN is critical for enhancing its quantum capacitance by increasing the density of states (DOS), based on our analysis of sulfurized carbon derived from polymers with and without nitrogen atoms. In this work, we synthesized SPAN with controlled sulfur content (ranging from 0-35 wt.%) to experimentally investigate the evolution of its redox DOS. Using a combination of in-situ Raman spectroscopy and x-ray photoemission, we studied the structural changes in SPAN as a function of sulfur content. Rate-dependent cyclic voltammetry measurements indicate varying contributions from surface and redox-dependent reactions based on the sulfur content. We will present experimental redox DOS data for SPAN with different sulfur contents obtained through electrochemical capacitive spectroscopy. Notably, we observed a clear absence of redox DOS peaks at energies corresponding to polysulfide formation, offering new insights into the electrochemical stability of SPAN.