Ruocun Wang1 James Daubert1 Yang Liu1 Gregory Parsons1 Elizabeth Dickey1 Veronica Augustyn1

1, North Carolina State University, Raleigh, North Carolina, United States

Solid-state Li-ion batteries are next-generation energy storage devices that could offer the tantalizing possibility of high energy density coupled with high safety. Increasingly, it is recognized that the performance of solid-state batteries is limited by the structure and composition of the solid interfaces, which are difficult to study with atomic resolution during electrochemical cycling. In-situ transmission electron microscopy (TEM) of energy storage materials allows for the detailed study of structure-property relationships near solid interfaces during electrochemical charge and discharge. This work focuses on the design and characterization of an in-situ TEM platform for investigating the structure-property relationships of a model energy storage oxide, V2O5, in contact with a commercially-available solid-state Li-ion oxide electrolyte (LATP, Li1+x+3zAlx(Ti,Ge)2-xSi3zP3-zO1). The V2O5 cathode was deposited by atomic layer deposition (ALD, ~ 50 nm thick) onto the electrolyte. Ex-situ characterization of the cathode and cathode/solid state electrolyte interface structure and composition was performed using Raman mapping and electron energy loss spectroscopy (EELS). Ex-situ Raman mapping showed homogeneous lithiation of V2O5 on the LATP. Ex-situ EELS of the V2O5/LATP interface indicated that lithiation occurred throughout the 50-nm layer of V2O5 and that no significant interphase was formed on the lithiated sample. The in-situ cell was fabricated by focused ion beam (FIB) milling and lift-out of a micron-long ‘wedge’ of V2O5 on LATP. The lithium metal anode was electrochemically deposited directly onto the gold electrode of an in-situ TEM chip. Assembly of the in-situ cell was performed in a scanning electron microscope (SEM) using a micromanipulator. Bright-field TEM and EELS showed that the deposited V2O5 layer formed a well-defined interface with LATP. Overall, this work demonstrates the ex situ characterization and fabrication of an in situ platform for the TEM study of oxide electrode/solid-state electrolyte interfaces that can readily be adapted to other types of solid-state battery chemistries.