In situ microscopy techniques for understanding Li plating and stripping in solid-state batteries

Solid-state batteries have potential to realize a rechargeable Li-metal anode. However, several challenges persist in the charging and discharging processes of the Li-metal anode, which require a fundamental understanding of Li plating and stripping across the interface of solid-state electrolytes (SEs) to address. This review overviews studies on Li-metal anodes in solid-state batteries using in situ observation techniques with an emphasis on Li electrodeposition and dissolution using scanning electron microscopy and SEs such as lithium phosphorus oxynitride and garnet-type compounds such as Li₇La₃Zr₂O₁₂. The previous research is categorized into three topics: (i) Li nucleation, growth and dissolution at the anode-free interface, (ii) electrochemical reduction of SE and (iii) short-circuit phenomena in SE. The current trends of each topic are summarized.