Interfacial Dynamics of Carbon Interlayers at Anode-Free Solid Electrolyte/Lithium Interfaces

Abstract

Solid electrolytes (SEs) that incorporate lithium (Li) metal anodes provide a promising pathway to improve battery energy density and safety. However, Li metal anodes still suffer from multiple challenges, including 1) uniform Li deposition and dissolution, 2) continual formation of a solid-electrolyte interphase (SEI), and 3) limited rate capability. To control the interfaces, predefined interlayers such as gold, ZnO, carbon, and other coatings have been used tune the Li metal and SE interface. However, there is a need for improved fundamental understanding of the mechanistic role of these interlayers on performance and stability. In this work, we explore the application of an amorphous carbon interlayer in an argyrodite SE system, which is used for in situ Li metal formation in an “anode-free” configuration.The incorporation of a carbon interlayer has been previously shown to act as a physical barrier between the SE and in situ formed Li metal, improve the uniform contact and current distribution across the SE/anode interface, and potentially suppress dendrite propagation [1]. However, the mechanism of this improved performance is not fully understood. Therefore, to study the influence of the carbon interlayer on interfacial performance, a detailed electrochemical analysis was performed.First, the transition in reaction pathway from carbon lithiation to Li nucleation and growth was observed to change as a function of charging rates. To probe the lithiation effects of the carbon interlayer on subsequent Li deposition, incremental electrochemical impedance spectroscopy (EIS) and current-interrupt analysis was performed to study the dynamic changes of the carbon interlayer during the charging process prior to Li nucleation. To confirm the mode of metallic Li nucleation and growth, operando video microscopy and post-mortem focused ion-beam/scanning electron microscopy (FIB-SEM) was utilized. The preferential location of Li deposition and growth at the current collector and carbon interface confirms the transport of Li-ion through the lithiated carbon interlayer. Moreover, the Li metal deposition behavior was observed to depend on the electrochemical properties of the carbon interlayer during the lithiation process. These fundamental electrochemical studies will further our understanding of the design requirements for interlayers that can enable Li metal anodes in solid-state battery systems.[1] Y.G. Lee, S. Fujiki, C. Jung, N. Suzuki, N. Yashiro, R. Omoda, D. S. Ko, T. Shiratsuchi, T. Sugimoto, S. Ryu, J. H. Ku, T. Watanabe, Y. Park, Y. Aihara, D. Im, I. T. Han, Nat. Ener. 5, 299-308 (2020)