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.