Solid state lithium metal batteries – Issues and challenges at the lithium-solid electrolyte interface

Solid-state Li-ion batteries employing a metallic lithium anode in conjunction with an inorganic solid electrolyte (ISE) are expected to offer superior energy density and cycle life. The realization of these metrics critically hinges on the simultaneous optimization of the ISE and the two electrode/electrolyte interfaces. In this Opinion article, we provide an overview of the materials and interfacial challenges that limit the performance of solid-state lithium metal batteries (SSLMBs). Owing to the importance of the Li/ISE interface, we dedicate a large section of this article to discuss the mechanistic aspects of lithium deposition at the Li/ISE interface. We further discuss a few recently proposed mechanisms that rationalize the growth of lithium through ISEs. We conclude our review with a brief discussion on the anode-free approach for fabricating SSLMBs where metallic lithium is generated in-situ from pre-lithiated cathodes.