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Description
Reactive metals are of paramount importance to the world’s industrial infrastructure and the future of energy storage. Their unique properties have led to their use in a variety of applications, but also result in challenges when handling and sustaining systems involving them. The materials in this category with the highest reactivity, such as lithium metal, react rapidly when exposed to even small concentrations of oxygen or water. This challenge adds a layer of complexity to traditional characterization tools when analyzing reactive metal surfaces. In this work, methods and designs for the characterization of reactive metal interfaces are described. These include the use of operando optical microscopy, in-situ and ex-situ Raman spectroscopy, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Using these designs, a case study was performed to examine the reaction between a lithium metal substrate and the individual components of a popular battery electrolyte: lithium hexafluorophosphate in ethylene carbonate/diethyl carbonate (LiPF6 in EC/DEC). The solid electrolyte interphase (SEI) is an aspect of lithium metal batteries that is still under much contention. Characterizing the chemical components and morphology of this layer is an important step in understanding its behavior when undergoing cycling. Due to potential impurities and oxidation on the surface of as received lithium metal, a common practice within the battery community is to scratch the sample surface before using it in an electrochemical cell. To investigate the impact this might have on the corrosion characteristics of the material and SEI formed, each test also included samples that were prepared in this manner. The chemical components and surface of the lithium metal, both before and after a reaction has occurred, were characterized with the aforementioned methods. The likely surface products were identified and the surface morphology was characterized, but the electrochemical impacts of these features are simply inferred. Future work should include electrochemical tests, which can reveal what consequences the resulting compounds might have when the reacted lithium metal is used as an anode in a battery. System improvements that could increase the capabilities and flexibility of the designs are also outlined in the conclusion.
