Visualization of Li Profile in an All-Solid-State Li-Ion Battery By In Situ Electron Holography and Spatially-Resolved Eels

All-solid-state Li-ion batteries (LIBs) have been expected to be next generation energy-storage-devices. However, a large interfacial resistance of Li-ion transfer at the electrode/solid-electrolyte interfaces prevents from the practical use. We have so far developed technique to operate the LIB in a TEM and observed the electric potential change around the interfaces by in situ electron holography (EH) [1]. However, it is still unclear how the Li-ions are distributed and what kind of relation the Li and the potential profiles have in nanometer scale. In this report, we used spatially-resolved electron energy loss spectroscopy (SR-EELS) to directly detect the Li distribution around the interface, and compared with the potential profile observed by EH.

Figure 1(a) shows a schematic of our battery model sample. The Li₂O-Al₂O₃-TiO₂-P₂O₅-based glass-ceramics sheet (LATP) was used as the solid electrolyte, and the LiCoO₂ positive electrode was deposited on one side. The negative electrode was prepared in situ by Li insertion reaction to the negative side LATP [2].

After 50 CV cycles, the negative side region was lifted out by a focused ion beam method and the TEM sample was prepared. The TEM image (Fig. 1(b)) shows a slightly different contrast around the interface. Fig. 1(c) shows the Li spectrum image detected by SR-EELS, the horizontal and vertical axes correspond to the electron energy loss and the sample position of the Fig. 1(b) in the vertical direction, respectively. The Li profile (Fig. 1(d)) was similar to the potential profile (Fig. 1(e)). Therefore, the EH detects the nanometer scale potential change due to the Li insertion reaction. The electronic structure changes of the other important elements (Ti and O) due to the Li insertion will be discussed in this presentation.

This work was supported by the RISING project of the New Energy and Industrial Technology Development Organization (NEDO) in Japan.

[1] K. Yamamoto et al., Angew. Chem. Int. Ed. 49 (2010) 4414 - 4417.

[2] Y. Iriyama et al., Electrochem. Commun. 8 (2006) 1287-1291.