Sulfurized Polymer Cathodes for Li-S batteries: Mechanisms, Misconceptions, and Metrics*

Lithium–sulfur (Li-S) battery are a promising candidate for electrical energy storage. Beyond elemental sulfur electrodes, many researchers proposed sulfurized polymers (SP) for circumventing polysulfide formation and achieving long cycling stability and high C-rate performance. However, practical application of SP electrodes are often written off due to their low S loading (~35 wt. %). In this talk, we will show that SP electrodes function as hybrid supercapacitors with carbon backbone contributing to the total capacity using a comprehensive array of tools including in situ electrochemical Raman spectroscopy. Based on our results, we address the following fundamental questions in Li-SP electrochemistry that are critical for industrial translation: 1) Are the critical metrics for S8/C cathodes (which consider carbon to be dead weight) relevant for SP cathodes? 2) Does the superior performance of N-containing SP result from the alleviation quantum capacitance? 4) Are SP with S content >35 wt. % fundamentally unstable? 4) If stability of SP is limited to ~35 wt. %, how can practical S-loadings >5 mg/cm² be achieved? 5) In case of “active” carbon skeleton, does the practical realization still require high S content ~70 wt. % in SP cathodes?