New Separators in Lithium/Sulfur Cells with High-Capacity Cathodes. Issue 1 (1st January 2018)

• Record Type: Journal Article
• Authors: Bugga, Ratnakumar; Jones, John-Paul; Jones, Simon C.; Krause, Frederick C.; Pasalic, Jasmina; Ganapathi, Devi S.; Hendrickson, Mary; Plichta, Edward J.
• Is Part Of: Journal of the Electrochemical Society. Volume 165:Issue 1(2018)
• Page Start: A6021
• Page End: A6028
• Publication Date: 2018-01-01
• Subjects: Ceramic-coated separator -- High energy -- Lithium-sulfur; Electrochemistry -- Periodicals; 541.3705
• DOI: 10.1149/2.0051801jes
• Languages: English
• ISSNs: 0013-4651

Abstract

Abstract : Lithium-sulfur cells exhibit poor cycle life, due to the 'polysulfide shuttle' enabled by the dissolution of sulfur reduction products in organic electrolyte. Different strategies have been implemented to reduce the shuttle effects, including novel cathode designs to sequester polysulfides within the cathode, new electrolytes with reduced polysulfide solubility, and blocking layers to hinder polysulfide migration towards the anode. However, these are less successful in the case of high-energy Li/S cells with cathodes featuring substantial sulfur loadings, as proportionately greater polysulfide dissolution rapidly degrades performance. Additionally, the electrolyte/sulfur ratio is a limiting factor in high-energy cells, indicating that a minimum polysulfide solubility is required. Herein we describe the benefits of modified separators with the objective of blocking polysulfide migration. Specifically, we demonstrate improved discharge performance in laboratory Li/S cells with ceramic-coated separators, including single-sided and double-sided Al2 O3 -coated polyolefin material from commercial sources. We also developed a new AlF3 coating on a polyolefin separator that showed even greater improvements: higher initial specific capacity (∼800 mAh/gS ), coulombic efficiency (>96%), and cycle life (>100 cycles). Detailed analytical study via SEM and EDS of separators harvested from cycled cells indicated an approximately uniform sulfur distribution across the ceramic-coated separator. Finally, concentrated electrolytes, which reportedly minimize polysulfide diffusion and lithium dendrite growth, were tested and shown to yield high coulombic efficiency although with low sulfur utilization.