Nanoengineered Separators for a High Energy Density, Long Cycle Life Li-S Battery

Abstract

Rechargeable lithium-sulfur (Li-S) batteries are widely considered the most promising “Beyond Li-ion” candidates, notably for their high theoretical energy density. The low and moderate atomic weight of Li and S, respectively, translates to a battery chemistry pairing that is lightweight. Since each S atom can ultimately host two lithium ions (Li+), compared with 0.5–0.7 Li+ per host atom in Li-ion batteries [1], the Li-S battery chemistry offers a much higher Li storage capacity potential. Assuming a complete redox couple reaction, S8 + 16Li+ + 16e- ↔ 8Li2S, the S cathode can have a high theoretical specific capacity of 1672 mAh/g with an average discharge voltage of ~2.1V (vs. Li/Li+), which leads to a theoretical specific energy of ~2500 Wh/kg based on the active material weight of a Li-S cell [2]. Other compelling attributes of Li-S batteries include high S natural abundance, low cost of S materials and safety characteristics owing to an intrinsic tolerance to overcharge [3]. In addition, the primary constituents of Li-S batteries are non-toxic and environmentally friendly [4]. However, currently no commercial Li-S battery exists due to some significant technical challenges that have thus far prevented the realization of the tremendous energy density and performance potentials of Li-S batteries. These technical challenges include: low practical specific energy or energy density yield, significant capacity loss with cycling, high self-discharge rates, low Coulombic efficiency and safety concerns due to the use of Li metal anode [5]. We will present our efforts in the development of a high energy density and long cycle life Li-S battery technology via nanoengineered battery separators. We will show that our atomic and/or molecular level, functional material coated separators exhibit much improved physical properties including tensile strength, thermal shrinkage, and electrolyte wettability (Figure 1). When used in Li-S cells, the nanoengineered separators (coated) afforded a significant increase in specific capacity compared with the control (uncoated) separator, as illustrated in Figure 2. The enhanced Li-S cell performance suggests polysulfide blockage from the nanoscale functional material coated separators used in the resultant Li-S cells. Our study demonstrates that the nanoengineered separator approach represents a very promising strategy to develop a high energy density, long cycle life, safe and economically scalable Li-S battery technology. References Bullis, “Revisiting Lithium-Sulfur Batteries” MIT Review, May 22, 2009.Arumugam Manthiram, Yongzhu Fu, and Yu-Sheng Su, Acc. Chem. Res., 46 (5), pp 1125–1134 (2013)James R. Akridge, “Lithium Sulfur Rechargeable Battery Safety”, Battery Power Products & Technology, October 2001.Yongguang Zhang, Yan Zhao, Kyung Eun Sun and P. Chen, The Open Materials Science Journal, 5, 215-221 (2011).Monica Marinescu, Laura O’Neill, Teng Zhang, Sylwia Walus, Timothy E. Wilson, and Gregory J. Offer, J. Electrochem. Soc, 165 (1) A6107-A6118 (2018). Figure 1