To improve the coulombic efficiency of GeO2 electrode, a Cu-containing ternary metal oxide (CuGeO3) was prepared and the electrochemical behavior of Cu component was studied. The GeO2 electrode shows a low coulombic efficiency in the first cycle (43%), which is mainly caused by a poor Ge oxidation kinetics (Ge + 2Li2O → GeO2 + 2Li+ + 2e-). The X-ray absorption spectroscopy (XAS) data illustrate that the Cu component in CuGeO3 is converted to nano-sized metallic Cu in the earlier stage of lithiation but idles thereafter. In contrast, the Ge component in CuGeO3 behaves like the GeO2 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 CuGeO3 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 Li2O that they can catalyze Li2O decomposition and provide an electronic conductive network for Ge oxidation. A similar favorable effect was observed with the other ternary oxides (FeGeO3 and CoGeO3), wherein the formation of nano-sized metallic Fe and Co can be assumed.
Bibliographical noteFunding Information:
This work was supported by WCU program through KOSEF funded by the Ministry of Education, Science and Technology (400-2008-0230). The authors also wish to acknowledge the Research Center for Energy Conversion and Storage for financial support, and the Pohang Light Source (PLS) for the XAS measurements.
All Science Journal Classification (ASJC) codes
- Chemical Engineering(all)