The extra capacity was discovered in many transition metal oxide anode materials. Different mechanisms without agreement for the extra capacity have been proposed. A nanosized MoO2 material is synthesized, and its structure and morphology are analyzed by X-ray powder diffraction, X-ray photoelectron spectroscopy, and Scanning and transmission electron microscopy. And its electrochemical behavior shows an outstanding increment of capacity while cycling, which is reaching 1625 mAh/g about twice as the theoretical capacity after 700 cycles at high rate. In-situ & ex- situ XRD, in-situ & ex-situ XAS and ex-situ SEM are adopted to investigate the mechanism at different cycling stage of Lithium-ion cells. The in-situ XRD and XAS results of fresh cells reveal that no conversion reaction is completed during the first discharge process. Li2O and Mo is not detected, and only Li0.98MoO2 is produced after the lithiation. According to in-situ XRD result, this lithium storage is around one fourth of the theoretical capacity. It also conflicts with the capacity of the cycling test, which at least delivers capacity about 500mAh/g. Material characterizations applied on cycled cells indicate that there may be a formation of Lithium metallic layer between the lithium-ion intercalated phase after Li0.98MoO2 formed, which contribute to the extra lithium storage. The variation of particle size probably causes the increment of capacity upon cycling.

Investigating mechanism for extra capacity of MoO2 as anode material in lithium-ion battery

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