DOE’s energy storage hub (JCESR) is exploring “beyond lithium-ion” solutions that can attain important metrics (pack level energy density of 400 WhL^-1 and cost of $100 per kWh) relevant to transportation applications.^1,2 Lithium-ion (Li-ion) batteries have been widely applied in consumer electronics successfully for over two decades, and are being developed for other purposes such as electric vehicles, smart energy grids and renewable energies. However, further development of next-generation battery systems is an inevitable task for researchers to satisfy the demand for efficient energy storage. A propitious solution, at the outset, would be an energy storage system that exploits the Li-S redox chemistry. Elemental sulfur (S₈) is exceedingly abundant, inexpensive, and exhibits a high theoretical specific capacity of 1672 mAh g⁻¹ based on the assimilation reaction: S₈ + 16Li ↔ 8Li₂S. However, normal Li-S cells are plagued by low sulfur utilization (attributed to the highly insulating nature of initial active material, S8, and the product, Li₂S) and rapid capacity degradation with cycling (the dissolution of lithium polysulfide intermediate species Li₂S_n(2 ≤ n ≤ 8) in commonly used polar organic electrolytes triggers a parasitic redox “shuttle” phenomenon that can lead to poor coulombic efficiency, loss of active material from the positive electrode on repeated cycling).

Techno-economic modeling suggests that reduction of electrolyte volume is one of the key requirements necessary for cost-efficient Li-S transportation battery.² Under lean electrolyte conditions, the dissolved LiPSs rapidly reach saturation limits, likely leading to the deposition of insulating products on the electrode surface. The precipitates can then lead to large cell polarization and adversely affect sulfur utilization. Controlling the precipitation process in such a way that the electrode conductivity is not compromised is undoubtedly a key aspect for the success of this approach. To meet such challenges in designing lean electrolyte systems, new information on sulfur speciation is required. To this end, we have performed electrochemical and x-ray spectroscopic measurements on Li-S cells with a sparingly soluble electrolyte reported by Cuisinier et al.³The results of this study will be presented in the meeting.

Acknowledgement

This work was supported as part of the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences. The submitted abstract has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357. The U.S. Government retains for itself, and others acting on its behalf, a paid-up nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government. The use of facilities and resources at the Advanced Photon Source is gratefully acknowledged.

References

1. G. Crabtree, Physics of Sustainable Energy III: Using Energy Efficiently and Producing It Renewably, edited by R. H. Knapp et al, AIP Conference Proceedings, vol 1652 (2015), Melville, New York.

2. Eroglu et al. J. Electrochem. Soc. 162, A982 (2015).

3. M. Cuisinier et al. Energy Environ. Sci. 7, 2697 (2014).