Low Concentration Electrolytes for Lithium-Sulfur Batteries

Abstract

As a promising cathode material due to its high theoretical capacity (1166 mAh/g) lithium sulfide (Li2S) has been the focus of research worldwide. In addition to being based on inexpensive, widely-available, and non-toxic sulfur, Li-Li2S or Li-S batteries offer remarkably high specific energy, which is critically important for weight-sensitive applications. Previous research demonstrated that highly concentrated electrolytes (e.g., 2.5-5M) may reduce polysulfide dissolution and improve performance of cells with Li2S cathodes.1 , 2 However, salts in the organic electrolyte are fairly expensive and relatively heavy. In addition, high salt concentrations reduce Li+ mobility and may severely limit the rate performance of high loading cathodes. In contrast, low concentration electrolytes have not been explored for Li-S batteries, despite being significantly lighter, cheaper and less viscous than their high concentration counterparts. Furthermore, salts and additives that are not soluble in some solvents used in Li-S batteries at high concentrations can offer sufficient solubility at low concentrations, thus offering more options for the design of high-loading and high performance Li-Li2S or Li-S cells. In our study, we examine a broad range of low concentration electrolytes with various salt and solvent combinations and ratios. In contrast to our initial expectations, some low-concentration electrolytes demonstrated strong rate performance. We also examine lifetime performance and performance with high loading cathodes. In this talk, we will discuss the impact of electrolyte salt chemistries, their mixtures, relative concentrations and solvent compositions on electrolyte conductivity, the anode and cathode solid electrolyte interphase layers (CEI and SEI) as well as cell rate performance and stability. (1) Lee, J. T.; Zhao, Y.; Thieme, S.; Kim, H.; Oschatz, M.; Borchardt, L.; Magasinski, A.; Cho, W. Il; Kaskel, S.; Yushin, G. Adv. Mater. 2013, 25 (33), 4573–4579. (2) Suo, L.; Hu, Y. S.; Li, H.; Armand, M.; Chen, L. Nat. Commun. 2013, 4, 1–9.