Effect of the Anion Activity on the Stability of Li Metal Anodes in Lithium-Sulfur Batteries

• Published in: Advanced functional materials Vol. 26; no. 18; pp. 3059 - 3066
• Main Authors: Cao, Ruiguo, Chen, Junzheng, Han, Kee Sung, Xu, Wu, Mei, Donghai, Bhattacharya, Priyanka, Engelhard, Mark H., Mueller, Karl T., Liu, Jun, Zhang, Ji-Guang
• Format: Journal Article
• Language: English
• Published: United States Blackwell Publishing Ltd 10.05.2016; Wiley
• Subjects: anion; Anions; Anodes; Bonding strength; concentrated electrolyte; Electrolytes; Environmental Molecular Sciences Laboratory; Li-sulfur battery; Lithium; lithium anode; lithium salt; Lithium sulfur batteries; lithium-sulfur battery; Polysulfides; Stability
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.201505074

With the significant progress made in the development of cathodes in lithium‐sulfur (Li‐S) batteries, the stability of Li metal anodes becomes a more urgent challenge in these batteries. Here the systematic investigation of the stability of the anode/electrolyte interface in Li‐S batteries with concentrated electrolytes containing various lithium salts is reported. It is found that Li‐S batteries using LiTFSI‐based electrolytes are more stable than those using LiFSI‐based electrolytes. The decreased stability is because the N–S bond in the FSI− anion is fairly weak and the scission of this bond leads to the formation of lithium sulfate (LiSOx) in the presence of polysulfide species. In contrast, in the LiTFSI‐based electrolyte, the lithium metal anode tends to react with polysulfide to form lithium sulfide (LiSx), which is more reversible than LiSOx formed in the LiFSI‐based electrolyte. This fundamental difference in the bond strength of the salt anions in the presence of polysulfide species leads to a large difference in the stability of the anode‐electrolyte interface and performance of the Li‐S batteries with electrolytes composed of these salts. Therefore, anion selection is one of the key parameters in the search for new electrolytes for stable operation of Li‐S batteries. The electrolyte selection for lithium‐sulfur batteries is critical to achieve high energy and stable cycling. The stability of concentrated electrolytes containing various lithium salts for lithium‐sulfur batteries is investigated. The anion stability of lithium salt greatly affects the anode/electrolyte interface stability and the electrochemical performance.