Design of Novel Electrolytes to Protect Lithium Metal Anodes in Li-S Batteries

Wednesday, 31 May 2017: 17:40
Grand Salon C - Section 18 (Hilton New Orleans Riverside)
B. Adams, R. Cao (Pacific Northwest National Laboratory), J. Chen (Joint Center for Energy Storage Research (JCESR)), and J. G. Zhang (Pacific Northwest National Laboratory)
With a theoretical specific energy of 2500 W h kg-1 and energy density of 2800 W h L-1, the Li-S battery system is believed to provide the step-up in energy density necessary for lithium-based battery technologies to expand from portable electronics to transportation and grid-storage applications.1 However, the growth of dendrites during repeated Li plating/stripping and the low coulombic efficiency (CE) of these processes have limited application of rechargeable Li metal batteries.2 For example, a 300% excess amount of lithium often used in these batteries would directly result in halving the theoretical specific energy of the Li/S cells.

In this presentation, the design of new electrolyte systems which enable high CE of lithium metal plating/stripping and high stability in the sulfur environment will be discussed. Tailoring of electrolyte properties for the lithium negative electrode has proven to be a successful strategy for improving the capacity retention and cycle life of Li-S full cells. This also enables lower electrolyte/sulfur mass ratios to be used and a lower excess of lithium metal; ultimately increasing the energy density of the system.

A new class of electrolytes based on a high concentration of selected lithium salts in pure diethylene glycol dimethyl ether (diglyme) solvent provides a CE for lithium plating/stripping of greater than 99% for over 200 cycles and greater than 95% for over 500 cycles (Figure 1). In contrast, lithium metal cycles for less than 40 cycles at high CE in the standard 1 M LiTFSI + 2wt% LiNO3 in DOL:DME electrolyte.

To realize the benefits of sulfur cathodes over intercalation cathodes currently using in Li-ion cells, high loading (high capacity) cathodes need to be used. In Figure 2a, a Cu||Li cell is cycled with the new diglyme-based electrolyte to a capacity of 6 mAh/cm2 at a current density of 0.6 mA/cm2 (C/10). Even at this high capacity, lithium is cycling with >99% CE. Lithium symmetrical cells were also cycled at a current density of 0.5 mA/cm2 to 5 mAh/cm2 (Figure 2b). In this case, the increase in polarization was used a metric to determine the practical cycle life of Li metal in the different electrolytes. No polarization is observed for the diglyme-based electrolyte after 2200 hours in the Li||Li cell. 

The inexpensive sulfur cathode paired with a low excess of lithium metal and the low-cost salt/solvent system may accelerate the applications of high energy density Li-S batteries in both electrical vehicles and large-scale grid energy storage markets.


1. A. Manthiram, Y. Fu, S.-H. Chung, C. Zu, Y.-S. Su, Chem. Rev. 2014, 114, 11751-11787.

2. W. Li, H. Yao, K. Yan, G. Zheng, Z. Liang, Y.-M. Chiang, Y. Cui, Nature Comm. 2015, 6, 7436.