However, a V2O5 cathode exhibits the large overvoltage as well as the poor rate performances due to its low electronic conductivity. In this study, we studied the effect of substituting Mo6+ for a part of V5+ in V2O5 in order to improve the electronic conductivity of V2O5. The carrier electrons are expected to be generated by the substitution of Mo in terms of the so-called valence control expressed as V5+/V4+. We synthesized a series of Mo-substituted V2O5, i.e. V2-xMoxO5 (x=0.02, 0.06, 0.1), by solid state reaction, and evaluated their electrochemical properties in comparison with a parent V2O5.
XRD patterns of the synthesized V2-xMoxO5 (x=0.02, 0.06, 0.1) powder all exhibited main diffraction peaks similar to those of V2O5 without impurity phases, indicating the solid solution formation. In addition, XPS measurements of V2p and Mo3d orbital showed main peaks attributed to V4+ and Mo6+ by Mo substitution in V2O5. Therefore, the V sites in V2O5 were suggested to be partially substituted to Mo. Galvanostatic cycling in LIBs revealed that a V1.94Mo0.06O5 electrode showed the lowest overvoltage than that of other compositions. Therefore, we focused on V1.94Mo0.06O5 in order to evaluate electrochemical characteristics for CIBs. The V1.94Mo0.06O5 cathode evaluated in CIBs showed reversible discharge and charge profiles with less overvoltage as well as the improvement in cycle performance compared to V2O5. XRD and EDX analyses also supported the reversible insertion/extraction reaction of V1.94Mo0.06O5 with Ca2+ ions. Therefore, it is suggested that V1.94Mo0.06O5is feasible as one of cathode materials for CIBs.
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