Abstract
Li-ion intercalation materials with extremely high rate capability will blur the distinction between batteries and supercapacitors. We construct a series of nanoarchitectured intercalation materials including orthorhombic (o-) Nb2O5 hollow microspheres, o-Nb2O5@carbon core-shell microspheres and tetragonal (t-) NbO2@carbon core-shell microspheres, through a one-pot hydrothermal method with different post-treatments. These nanoarchitectured materials consist of small nanocrystals with highly exposed active surface, and all of them demonstrate good Li+ intercalation pseudocapacitive properties. In particular, o-Nb2O5 hollow microspheres can deliver the specific capacitance of 488.3 F g−1, and good rate performance of 126.7 F g−1 at 50 A g−1. The o-Nb2O5@carbon core-shell microspheres show enhanced specific capacitance of 502.2 F g−1 and much improved rate performance (213.4 F g−1 at 50 A g−1). Furthermore, we demonstrate for the first time, t-NbO2 exhibits much higher rate capability than o-Nb2O5. For discharging time as fast as 5.9 s (50 A g−1), it still exhibits a very high specific capacitance of 245.8 F g−1, which is 65.2% retention of the initial capacitance (377.0 F g−1 at 1 A g−1). The unprecedented rate capability is an intrinsic feature of t-NbO2, which may be due to the conductive lithiated compounds.
Highlights
Those of supercapacitors, which may open the door to a new energy storage concept that materials can possess battery and capacitor properties simultaneously
Zhang et al reported that the hydrothermal growth of Nb2O5 nanoparticles on carbide-derived carbons and consequent CO2 heat treatment could result in an increased gravimetric capacitance (157 C g−1) at a charge-discharge time of 3 min[28]
Our recently work demonstrated that the synergistic effects between graphene and Nb2O5 nanoparticles, including minimizing the particle size, preventing particles from agglomerating, and facilitating electron and proton conduction, could give the composites very high capacitance and excellent rate capability[29]. All these results suggest that nanostructured technology is a superior strategy to boost the electrochemical capacitive performance of the intercalation electrode
Summary
Those of supercapacitors, which may open the door to a new energy storage concept that materials can possess battery and capacitor properties simultaneously. Our recently work demonstrated that the synergistic effects between graphene and Nb2O5 nanoparticles, including minimizing the particle size, preventing particles from agglomerating, and facilitating electron and proton conduction, could give the composites very high capacitance and excellent rate capability[29] All these results suggest that nanostructured technology is a superior strategy to boost the electrochemical capacitive performance of the intercalation electrode. We successfully constructed a series of nanoarchitectured materials including o-Nb2O5 hollow microspheres, o-Nb2O5@carbon core-shell microspheres and t-NbO2@carbon core-shell microspheres, through a one-pot hydrothermal method with different post-treatments This synthetic procedure was straightforward and inexpensive, and can be readily adopted to produce larger quantities of nanostructured microspheres. The ultrafast Li+ intercalation kinetics of t-NbO2 may open up exciting possibilities of producing improved intercalation electrodes for high-power supercapacitors
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