Graphical Carbon, the master : Constructed with unique carbon emcoating structure through CO 2 acivation, NbO 2 benefited from an effective and highly conductive carbon network, giving rise to exceptional electrochemical performances in terms of reversible capacities, rate capability, and cyclic stability. As a promising alternative as lithium-ion anode, niobium dioxide appeals to researchers due to high theoretical capacity and good electron conductivity. However, rarely work about NbO 2 based high performance anode is reported. Here, NbO 2 nanoparticles emcoated in continuous carbon matrix is constructed through CO 2 /H 2 coupling treatment. CO 2 activation introduces unique carbon emcoating structure, which builds interconnected electron conductive network with low carbon content. Furthermore, crystallographic phase of NbO 2 is enhanced during H 2 treatment, which increases the lithium storage ability. Electrochemical performance of NbO 2 anodes is significantly improved based on the carbon emcoating structure. A high reversible capacity of 391 mAh g −1 is retained after 350 cycles at 0.2 C. Additionally, at a current density of 1 A g −1 , the reversible capacity reaches 139 mAh g −1 . Compared with conventional NbO 2 /C nanohybrids, the lithium diffusion coefficient of carbon-emcoated sample shows improvement of three orders of magnitude. Moreover, the in situ XRD investigation shows a reversible lithium insertion behaviour with a limited volume change.
Niobium dioxide (NbO 2 ) features a high theoretical capacity and an outstanding electron conductivity, which makes it a promising alternative to the commercial graphite negative electrode. However, studies on NbO 2 based lithium-ion battery negative electrodes have been rarely reported. In the present work, NbO 2 nanoparticles homogeneously embedded in a carbon matrix are synthesized through calcination using a dental resin monomer (bisphenol A glycidyl dimethacrylate, Bis-GMA) as the solvent and a carbon source and niobium ethoxide (NbETO) as the precursor. It is revealed that a low Bis-GMA/NbETO mass ratio (from 1:1 to 1:2) enables the conversion of Nb (V) to Nb (IV) due to increased porosity induced by an alcoholysis reaction between the NbETO and Bis-GMA. The as-prepared NbO 2 /carbon nanohybrid delivers a reversible capacity of 225 mAh g −1 after 500 cycles at a 1 C rate with a Coulombic efficiency of more than 99.4% in the cycles. Various experimental and theoretical approaches including solid state nuclear magnetic resonance, ex situ X-ray diffraction, differential electrochemical mass spectrometry, and density functional theory are utilized to understand the fundamental lithiation/delithiation mechanisms of the NbO 2 /carbon nanohybrid. The results suggest that the NbO 2 /carbon nanohybrid bearing high capacity, long cycle life, and low gas evolution is promising for lithium storage applications.
Niobium-based phosphates have the advantages of high stability and environmental protection and have good application prospects in sodium-ion batteries. The pure phase of Na(NbO 2 ) 2 PO 4 (NNP) powder was successfully synthesized by different methods in this work, and the materials were characterized via XRD, XPS, SEM, and electrochemical methods. At the current density of 100 mA g −1 , the discharge-specific capacity of NNP is 521.8 mAh g −1 in the first cycle and remains at 462.4 mAh g −1 after 200 cycles, indicating that it has good cycling stability. The kinetic results obtained from cyclic voltammetry (CV) show the pseudo-capacitance contribution accounts for a large percentage of the capacity. The charge transfer resistance of NNP is 260.3 Ω, which is significantly smaller than the others derived from electrochemical impedance spectroscopy (EIS). These pointed to the advantages of NNP in anode material for SIBs.
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