Niobium oxide nanoparticle core–amorphous carbon shell structure for fast reversible lithium storage

Carbon coating on metal oxide materials for electrochemical energy storage

During the past decades, nano-structured metal oxide electrode materials have received growing attention due to their low development cost and high theoretical specific capacity, accordingly, quite a lot of metal oxide electrode materials are being used in electrochemical energy storage devices. However, the further development was limited by the relatively low electrical conductivity and the volume expansion during electrochemical reactions. Thus, many approaches have been proposed to obtain high-efficiency metal oxide electrode materials, such as designing nanomaterials with ideal morphology and high specific surface area, optimizing with carbon-based materials (such as graphene and glucose) to prepare nanocomposites, combining with conductive substrates to enhance the conductivity of electrodes, etc. Owning to the advantages of low cost and high chemical stability of carbon materials, core-shell structure formed by carbon-coated metal oxides is considered to be a promising solution to solve these problems. Therefore, this review mainly focuses on recent research advances in the field of carbon-coated metal oxides for energy storage, summarizing the advantages and disadvantages of common metal oxides and different types of carbon sources, and proposing methods to optimize the material properties in terms of structure and morphology, carbon layer thickness, coating method, specific surface area and pore size distribution, as well as improving electrical conductivity. In addition, the double or multi-layer coating strategy is also a reflection of the continuous development of carbon coating method. Hopefully, this rereview may provide a new direction for the renewal and development of future energy storage electrode materials.

Spherical Sb Core/Nb2O5-C Double-Shell Structured Composite as an Anode Material for Li Secondary Batteries

Antimony (Sb)-based materials are considered to be attractive for use in Li secondary battery anodes because of their high capacity. However, their huge volume change during Li insertion-extraction cycling limits their cycle performance. The Sb-active material can be combined with intercalation-based active materials to address these issues. In this study, spherical Sb core/Nb2O5 shell structured composite materials were synthesized through a simple solvothermal process and a carbon coating was simultaneously added during heat treatment using a naphthalene precursor. The resulting double-shelled materials were characterized with X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and electron microscopy. The electrochemical test results showed that a reversible capacity of more than 450 mAh g−1 was retained after 100 cycles. This improved performance is ascribed to the double-shelled structure. The large volume change of the nano-sized Sb core material was alleviated by the double-shelled structure, which consisted of crystalline orthorhombic Nb2O5 and amorphous carbon. The shell materials also aided rapid charge transport.

Efficient synthesis of niobium pentoxide nanowires and application in ethanolysis of furfuryl alcohol

Nb2O5 nanowires with high specific surface area and crystallinity were prepared by using ammonium oxalate and an acetic acid solvent system. The nanomaterial was applied in ethanolysis of furfuryl alcohol (FA), and the yield of the product, 2-(ethoxymethyl)furan (FEE), achieved was up to 79.6%. Compared to mesoporous Nb2O5 materials and other porous materials, the residence time of FEE on the surface of the catalyst is shorter, and the yield of ethyl levulinate (EL) is lower. Furthermore, a high temperature calcination treatment can change the acid sites and acidity type distribution on the nanowire surface. By XRD, NH3-TPD, IR, and TG-DTA determination methods, it was found that the weak and medium-strong acid sites on the surface of Nb2O5 nanowires were reduced after a 300 °C treatment, and the amount of strong acid was relatively higher. According to the catalytic performance test data and acidity determination, it was concluded that more weak acid and medium-strong acid sites improve the conversion of furfuryl alcohol to FEE, and the strong acid sites promote further conversion of FEE to EL.

Niobium-Based Oxides Toward Advanced Electrochemical Energy Storage: Recent Advances and Challenges

Niobium-based oxides including Nb₂ O₅ , TiNb_x O_2+2.5x compounds, M-Nb-O (M = Cr, Ga, Fe, Zr, Mg, etc.) family, etc., as the unique structural merit (e.g., quasi-2D network for Li-ion incorporation, open and stable Wadsley- Roth shear crystal structure), are of great interest for applications in energy storage systems such as Li/Na-ion batteries and hybrid supercapacitors. Most of these Nb-based oxides show high operating voltage (>1.0 V vs Li⁺ /Li) that can suppress the formation of solid electrolyte interface film and lithium dendrites, ensuring the safety of working batteries. Outstanding rate capability is impressive, which can be derived from their fast intercalation pseudocapacitive kinetics. However, the intrinsic poor electrical conductivity hinders their energy storage applications. Various strategies including structure optimization, surface engineering, and carbon modification are effectively used to overcome the issues. This review provides a comprehensive summary on the latest progress of Nb-based oxides for advanced electrochemical energy storage applications. Major impactful work is outlined, promising research directions, and various performance-optimizing strategies, as well as the energy storage mechanisms investigated by combining theoretical calculations and various electrochemical characterization techniques. In addition, challenges and perspectives for future research and commercial applications are also presented.

Quantum chemical calculations on NbO and its reaction with methane: ground and excited electronic states

Our high-level calculations show that high-spin NbO electronic states facilitate the methane to methanol transformation via a very efficient radical mechanism, as opposed to the [2+2] mechanism observed for the rest of the low-lying states.

Binder-Free Hybrid Titanium-Niobium Oxide/Carbon Nanofiber Mats for Lithium-Ion Battery Electrodes

Free-standing, binder-free, titanium-niobium oxide/carbon hybrid nanofibers are prepared for Li-ion battery applications. A one-pot synthesis offers a significant reduction of processing steps and avoids the use of environmentally unfriendly binder materials, making the approach highly sustainable. Tetragonal Nb₂ O₅ /C and monoclinic Ti₂ Nb₁₀ O₂₉ /C hybrid nanofibers synthesized at 1000 °C displayed the highest electrochemical performance, with capacity values of 243 and 267 mAh g^-1 , respectively, normalized to the electrode mass. At 5 A g^-1 , the Nb₂ O₅ /C and Ti₂ Nb₁₀ O₂₉ /C hybrid fibers maintained 78 % and 53 % of the initial capacity, respectively. The higher rate performance and stability of tetragonal Nb₂ O₅ compared to that of monoclinic Ti₂ Nb₁₀ O₂₉ is related to the low energy barriers for Li⁺ transport in its crystal structure, with no phase transformation. The improved rate performance resulted from the excellent charge propagation in the continuous nanofiber network.