Visualization of polysulfide dissolution in lithium-sulfur batteries using in-situ NMR microimaging

Abstract

Lithium-sulfur batteries offer the highest theoretical energy density among enclosed rechargeable batteries. However, there are various issues that need to be addressed before their practical adoption, such as the dissolution of intermediate lithium polysulfides (Li2Sn) into the electrolyte solution, which causes rapid degradation of the battery. Herein, we used nuclear magnetic resonance (NMR) and in-situ magnetic resonance imaging (MRI) to visualize the dissolution of the intermediate species formed during the discharge–charge process in Li-S batteries. A strong enhancement in the MRI signal was observed when the cell was first discharged, which is associated with the dissolution of intermediate polysulfides. To determine the origin of this signal enhancement, 1H NMR spectra, T1 relaxation time, and electron spin resonance (ESR) measurements were performed on electrolyte containing polysulfides. The origin of the strong enhancement of the MRI signal by the dissoluted polysulfides is mainly attributed to the paramagnetic interaction due to the formation of S3*- and S4*- radicals in the dissoluted polysulfides. The results demonstrate that 1H MRI is an indirect and effective way to study and visualize the intermediate species formed during Li-S battery operation.

Keywords

• Lithium-sulfur battery
• Degradation
• 1H NMR
• Polysulfide dissolution
• NMR imaging
• MRI