Electrode Performances of Amorphous Molybdenum Oxides of Different Molybdenum Valence for Lithium-ion Batteries

초록

Amorphous molybdenum oxides are prepared by a reduction of Mo6+ aqueous solution with KBH4. Two molybdenum oxides that differ in the average Mo valence are obtained by changing the solution pH, and their electrode performance is compared with each other. The X-ray absorption spectroscopy and thermogravimetric analysis illustrate that the sample prepared at the higher pH (4.0) shows an Mo valence of +5.5, which is close to that for MoO3, whereas the Mo valence (+4.4) for the other sample, prepared at the lower pH (0.8), is close to that for MoO2. The latter electrode outperforms the former with respect to cycle retention. The former electrode is lithiated by a conversion reaction, which is the case for MoO3. This electrode exhibits a larger initial capacity, but poorer cycle performance, due to massive volume change and repeated metal-oxygen bond breaking/formation with cycling. The other electrode, the Mo valence, which is +4.4, is lithiated by an addition reaction, in which Li+ ions are stored in structural defects, such as vacancies and void spaces. The superior cycle performance of this electrode can be ascribed to the absence of massive volume change and bond breaking/formation.

키워드