Nikhilendra Singh1 Timothy Arthur1 James Horwath2 Eric Stach2 Marm Dixit3 Kelsey Hatzell3

1, Toyota Research Institute of North America, Ann Arbor, Michigan, United States
2, University of Pennsylvania, Philadelphia, Pennsylvania, United States
3, Vanderbilt University, Nashville, Tennessee, United States

Advances in hybrid and electric technologies combined with a demand for green initiatives have motivated recent diversification in energy storage research for automotive electrification. To meet customer expectations for hybrid and electric vehicles, furthering the capability of existing battery systems remains critical. As such, new battery systems with higher energy density, power density and cycle life than the state-of-art Lithium (Li)-ion battery are needed. Post Li-ion battery systems, especially those focused on the utilization of Li metal have recently come to the forefront of research. The ability to directly utilize Li metal anodes in rechargeable batteries presents itself as an ideal, albeit challenging, situation. Li metal anodes could provide a maximum possible theoretical specific capacity (3860 mAh/g) in comparison to commercially used anodes (e.g. graphite – 380 mAh/g). Hence, significant efforts in recent literature have targeted the development of robust systems, capable of use with Li metal.
One such system is Li-sulfur which has attracted attention due to its high theoretical capacity (1673 mAh/g) and potential low cost. However, this system is hindered by polysulfide dissolution and electrolyte decomposition at the Li metal anode. Among the various strategies which have been employed to overcome such hurdles, the use of solid-state electrolytes (inclusive of polymers, gels and conducting ceramics) stands out, as the implementation of solid-state electrolytes can also serve as a mechanical barrier towards Li dendrite formation. However, these electrolytes exhibit relatively lower ionic conductivities and display poor interfacial stability towards Li metal anodes. While advances in solid-state electrolyte materials continue to improve their ionic conductivities, little is known about the interfacial interactions between sulfide-based solid-state electrolytes and Li metal which can greatly affect their electrochemical performance. Hence, studies into understanding the relationship properties between Li metal and these solid-state electrolytes is essential towards realizing a sulfide-based all-solid-state Li battery.
Here, we present the electrochemical properties of various sulfide-based solid-state electrolytes in contact with Li metal. Further, we present tandem analytical ex-situ and in-situ studies via transmission electron microcopy and X-ray tomography to reveal the interfacial interactions between Li metal and solid-state electrolytes, the deposition and dissolution properties of Li metal from these electrolytes, and the effects of the deposition and dissolution properties on the bulk electrolyte structure. The presented studies allow for comparisons of Li deposition and dissolution properties below and above the critical current densities for each solid-state electrolyte material and stand to help clarify both interfacial and morphological evolution mechanisms during Li cycling from them.