Where Does Sulfur Precipitate in Lithium Sulfur Batteries? an Operando SANS Experiment

Abstract

In-situ and operando measurements are done to gain a better understanding of the precipitation mechanisms during charge and discharge in lithium sulfur batteries. In this work we used a carbon felt networked with microfibers consisting of pores, 2 nm and smaller, as a freestanding sulfur host. First, three different infiltration methods of sulfur infiltration are explored to determine the best method. Second, in-situ electrochemical impedance spectroscopy measurements were done that showed a solid product formation occurring at the sulfur cathode, both during the high voltage plateau and at the end of discharge. In an additional 3-electrode EIS measurement, a similar solid product formation on the Li counter electrode due to its reaction with polysulfides is also observed. Operando small angle neutron scattering measurements show the solid product formation, in the carbon, both near the beginning and at the end of discharge, confirming the precipitation data via contrast changes as a function of charge and discharge. We will show in this presentation that Li2S precipitates in the pores at the beginning and the end of discharge, whereas S8 precipitates on the surface of the carbon felt.