Lithium-ion attack on yttrium oxide in the presence of copper powder during Li plating in a super-concentrated electrolyte.

Li plating/stripping on Cu and Y 2 O 3 (Cu + Y 2 O 3 ) electrodes was examined in a super-concentrated electrolyte of lithium bis(fluorosulfonyl)amide and methylphenylamino-di(trifluoroethyl) phosphate. In principle, Li + ions cannot intercalate into a Y 2 O 3 crystal because its intercalation potential obtained from first-principles calculations is -1.02 V vs. Li + /Li. However, a drastic decrease in the electrode potential and a subsequent constant-potential region were observed during Li plating onto a Cu + Y 2 O 3 electrode, suggesting that Li + interacted with Y 2 O 3 . X-ray diffraction (XRD) patterns and X-ray absorption fine structure (XAFS) spectra of the Cu + Y 2 O 3 electrodes after the Li plating were recorded to verify this phenomenon. The XRD and XAFS results indicated that the crystallinity of Y 2 O 3 crystals was lowered because of attack by Li + ions or that the Y 2 O 3 crystal structure was broken while the +3 valence state of Y was maintained.