In situ and operando microscopy studies on lithium metal anodes: a review

Abstract

Lithium metal is regarded as an ultimate anode for rechargeable batteries, ascribed to its extremely high capacity. Its implementation can remarkably boost the energy density of the resultant lithium metal batteries. However, it is very challenging to commercialize lithium metal anodes, primarily due to the intertwined nature of the formation of a solid electrolyte interphase (SEI) and the growth of lithium dendrites. To understand these issues and therefore develop technical solutions, various instrumental techniques have been employed. This review highlights the most recent advancements of in situ and operando microscopy studies that are critical for investigating and addressing the issues related to SEI and lithium dendrites, including optical, electron, and atomic force microscopies. Low magnification in situ optical microscopy techniques are used to analyze dendrite morphology behaviors, the development of capping layers after cycling, and the impact of various dendrite suppression methods. High magnification in situ scanning electron microscopy enables more detailed dendrites and interface evolution analysis, revealing complex behavior mechanisms over extended cycling. While in situ transmission electron microscopy techniques can also investigate dendrite nucleation and morphology, they are particularly valuable in characterizing the SEI layer development at unparalleled spatial resolution. Additionally, in situ atomic force microscopy contributes valuable information for identifying the SEI layer growth through surface topology and force mapping. Together, these microscopy studies help us advance a better understanding on the underlying mechanisms of the formation of the SEI and lithium dendrites. They also are valuable for us to develop solutions for commercializing lithium metal anodes for high-energy lithium metal batteries.