Correlating Structure and Function of Battery Interphases at Atomic Resolution Using Cryoelectron Microscopy

Battery decay and failure depend strongly on the solid electrolyte interphase (SEI), a surface corrosion layer that forms on the surface of all battery electrodes. Recently, we revealed the atomic structure of these reactive and sensitive battery materials and their SEIs using cryoelectron microscopy (cryo-EM). However, the SEI nanostructure's fundamental role and effect on battery performance remain unclear. Here, we use cryo-EM to discover the function of two distinct SEI nanostructures (i.e., mosaic and multilayer) and correlate their stark effects with Li metal battery performance. We identify fluctuations in crystalline grain distribution within the SEI as the critical feature differentiating the mosaic SEI from the multilayer SEI, resulting in their distinct electrochemical stripping mechanisms. Whereas localized Li dissolution occurs quickly through regions of high crystallinity in the mosaic SEI, uniform Li stripping is observed for the more ordered multilayer SEIs, which reduces Li loss during battery cycling by a factor of three. This dramatic performance enhancement from a subtle change in SEI nanostructure highlights the importance of cryo-EM studies in revealing crucial failure modes of high-energy batteries at the nanoscale. [Display omitted] •Cryo-EM preserves and stabilizes Li metal anode for atomic-scale imaging•Two distinct nanostructures form on Li metal surface, dictating battery performance•Fundamental relationship between SEI nanostructure and performance is established•Ideal SEI nanostructure is critical in building efficient and safe batteries Batteries with high energy density are actively being pursued for applications in transportation and grid-level energy storage. Although high-energy battery chemistries exist, the fundamental mechanisms governing their failure modes are not well known at the atomic level. In particular, the solid electrolyte interphase (SEI) is a critical battery interface that forms on all lithium battery anodes whose exact mechanistic function is poorly understood at the atomic scale. It has been widely believed that the SEI chemistry is the major factor in regulating performance. In our present work using cryoelectron microscopy, we show for the first time that it is instead the SEI nanostructure that ultimately dictates battery performance. This surprising yet consistent finding provides an entirely new direction to explore for engineering the SEI nanostructure in battery materials. The solid electrolyte i