Linking structure to function at the solid electrolyte interphase: Insights from NMR spectroscopy

The performance of Li metal batteries is tightly coupled to the composition and properties of the solid electrolyte interphase (SEI). Even though the role of the SEI in battery function is well understood (e.g., it must be electronically insulating and ionically conductive, it must enable uniform Li+ flux to the electrode to prevent dendrite growth, it must accommodate the large volume changes of Li electrodeposition), the challenges associated with probing this delicate composite layer have hindered the development of Li metal batteries for practical applications. In this review, we detail how nuclear magnetic resonance (NMR) spectroscopy can help bridge this gap in characterization due to its unique ability to describe local structure in conjunction with ion dynamics while connecting these properties to electrochemical behavior. By leveraging NMR, we can gain molecular-level insight to aid in the design of Li surfaces that enable reactive anodes for next generation, high energy density batteries.