T he role of in situ generated nano-sized metal particles on the coulombic efficiency of MGeO{sub}3 (M = Cu, Fe, and Co) electrodes

摘要

To improve the coulombic efficiency of GeO{sub}2 electrode, a Cu-containing ternary metal oxide (CuGeO{sub}3) was prepared and the electrochemical behavior of Cu component was studied. The GeO{sub}2 electrode shows a low coulombic efficiency in the first cycle (43%), which is mainly caused by a poor Ge oxidation kinetics (Ge + 2Li{sub}2O → GeO{sub}2 + 2Li{sup}+ + 2e{sup}-). The X-ray absorption spectroscopy (XAS) data illustrate that the Cu component in CuGeO{sub}3 is converted to nano-sized metallic Cu in the earlier stage of lithiation but idles thereafter. In contrast, the Ge component in CuGeO{sub}3 behaves like the GeO{sub}2 electrode. It is converted to nano-sized Ge by a conversion reaction and further lithiated by alloying reaction. The de-lithiation proceeds in the reverse order. The CuGeO{sub}3 electrode shows a much improved coulombic efficiency (74%) in the first cycle, which is indebted to a facilitated Ge oxidation with a much reduced electrode polarization. This feature has been explained by the favorable roles provided by the in situ generated nano-sized metallic Cu particles that make such an intimate contact with the nano-sized Ge and Li{sub}2O that they can catalyze Li{sub}2O decomposition and provide an electronic conductive network for Ge oxidation. A similar favorable effect was observed with the other ternary oxides (FeGeO{sub}3 and CoGeGO{sub}3), wherein the formation of nano-sized metallic Fe and Co can be assumed.