Unveiling the Stable Nature of Lipon-Associated Electrode/Electrolyte Interphases via Cryogenic Electron Microscopy

Abstract

The solid electrolyte interphase (SEI) is regarded as the most complex but the least understood constituent in secondary batteries using liquid and solid electrolytes. The dearth of such knowledge in all-solid-state battery (ASSB) has hindered a complete understanding of how certain solid-state electrolytes, such as LiPON, manifest exemplary stability against Li metal. By employing cryogenic electron microscopy (cryo-EM), the interphase between Li metal and LiPON is successfully preserved and probed, revealing a multilayer mosaic SEI structure with concentration gradients of nitrogen and phosphorous, materializing as crystallites within an amorphous matrix. This unique SEI nanostructure is less than 80 nm and is stable and free of any organic lithium containing species or lithium fluoride components, in contrast to SEIs often found in state-of-the-art organic liquid electrolytes. Our findings reveal insights on the nanostructure and chemistry of such SEIs as a key component in lithium metal batteries to stabilize Li metal anode. On the other hand, the results obtained via a combination of neutron depth profiling (NDP) and cryo-EM to elucidate the interfacial chemistry and structure between LiNi0.5Mn1.5O4 cathode and LiPON will also be covered, which sheds light on LiPON’s remarkable stability against high voltage cathode.