Recent advances in nanostructured Nb-based oxides for electrochemical energy storage

"Zero-Strain" NiNb2O6 Fibers for All-Climate Lithium Storage

Niobates are promising all-climate Li+-storage anode material due to their fast charge transport, large specific capacities, and resistance to electrolyte reaction. However, their moderate unit-cell-volume expansion (generally 5%-10%) during Li+ storage causes unsatisfactory long-term cyclability. Here, "zero-strain" NiNb2O6 fibers are explored as a new anode material with comprehensively good electrochemical properties. During Li+ storage, the expansion of electrochemical inactive NiO6 octahedra almost fully offsets the shrinkage of active NbO6 octahedra through reversible O movement. Such superior volume-accommodation capability of the NiO6 layers guarantees the "zero-strain" behavior of NiNb2O6 in a broad temperature range (0.53%//0.51%//0.74% at 25// - 10//60 °C), leading to the excellent cyclability of the NiNb2O6 fibers (92.8%//99.2% // 91.1% capacity retention after 1000//2000//1000 cycles at 10C and 25// - 10//60 °C). This NiNb2O6 material further exhibits a large reversible capacity (300//184//318 mAh g-1 at 0.1C and 25// - 10//60 °C) and outstanding rate performance (10 to 0.5C capacity percentage of 64.3%//50.0%//65.4% at 25// - 10//60 °C). Therefore, the NiNb2O6 fibers are especially suitable for large-capacity, fast-charging, long-life, and all-climate lithium-ion batteries.

Effect of solvothermal synthesis parameters on the crystallite size and atomic structure of cobalt iron oxide nanoparticles

We here investigate how the synthesis method affects the crystallite size and atomic structure of cobalt iron oxide nanoparticles. By using a simple solvothermal method, we first synthesized cobalt ferrite nanoparticles of ca. 2 and 7 nm, characterized by Transmission Electron Microscopy (TEM), Small Angle X-ray scattering (SAXS), X-ray and neutron total scattering. The smallest particle size corresponds to only a few spinel unit cells. Nevertheless, Pair Distribution Function (PDF) analysis of X-ray and neutron total scattering data shows that the atomic structure, even in the smallest nanoparticles, is well described by the spinel structure, although with significant disorder and a contraction of the unit cell parameter. These effects can be explained by the surface oxidation of the small nanoparticles, which is confirmed by X-ray near edge absorption spectroscopy (XANES). Neutron total scattering data and PDF analysis reveal a higher degree of inversion in the spinel structure of the smallest nanoparticles. Neutron total scattering data also allow magnetic PDF (mPDF) analysis, which shows that the ferrimagnetic domains correspond to ca. 80% of the crystallite size in the larger particles. A similar but less well-defined magnetic ordering was observed for the smallest nanoparticles. Finally, we used a co-precipitation synthesis method at room temperature to synthesize ferrite nanoparticles similar in size to the smallest crystallites synthesized by the solvothermal method. Structural analysis with PDF demonstrates that the ferrite nanoparticles synthesized via this method exhibit a significantly more defective structure compared to those synthesized via a solvothermal method.

Morphology and Crystallinity Effects of Nanochanneled Niobium Oxide Electrodes for Na-Ion Batteries

Niobium pentoxide (Nb2O5) is a promising negative electrode for sodium ion batteries (SIBs). By engineering the morphology and crystallinity of nanochanneled niobium oxides (NCNOs), the kinetic behavior and charge storage mechanism of Nb2O5 electrodes were investigated. Amorphous and crystalline NCNO samples were made by modulating anodization conditions (20-40 V and 140-180 °C) to synthesize nanostructures of varying pore sizes and wall thicknesses with identical chemical composition. The electrochemical energy storage properties of the NCNOs were studied, with the amorphous samples showing better overall rate performance than the crystalline samples. The enhanced rate performance of the amorphous samples is attributed to the higher capacitive contributions and Na-ion diffusivity analyzed from cyclic voltammetry (CV) and the galvanostatic intermittent titration technique (GITT). It was found that the amorphous samples with smaller wall thicknesses facilitated improved kinetics. Among samples with similar pore size and wall thickness, the difference in their power performance stems from the crystallinity effect, which plays a more significant role in the resulting kinetics of the materials for Na-ion batteries.

"Fast-Charging" Anode Materials for Lithium-Ion Batteries from Perspective of Ion Diffusion in Crystal Structure

"Fast-charging" lithium-ion batteries have gained a multitude of attention in recent years since they could be applied to energy storage areas like electric vehicles, grids, and subsea operations. Unfortunately, the excellent energy density could fail to sustain optimally while lithium-ion batteries are exposed to fast-charging conditions. In actuality, the crystal structure of electrode materials represents the critical factor for influencing the electrode performance. Accordingly, employing anode materials with low diffusion barrier could improve the "fast-charging" performance of the lithium-ion battery. In this Review, first, the "fast-charging" principle of lithium-ion battery and ion diffusion path in the crystal are briefly outlined. Next, the application prospects of "fast-charging" anode materials with various crystal structures are evaluated to search "fast-charging" anode materials with stable, safe, and long lifespan, solving the remaining challenges associated with high power and high safety. Finally, summarizing recent research advances for typical "fast-charging" anode materials, including preparation methods for advanced morphologies and the latest techniques for ameliorating performance. Furthermore, an outlook is given on the ongoing breakthroughs for "fast-charging" anode materials of lithium-ion batteries. Intercalated materials (niobium-based, carbon-based, titanium-based, vanadium-based) with favorable cycling stability are predominantly limited by undesired electronic conductivity and theoretical specific capacity. Accordingly, addressing the electrical conductivity of these materials constitutes an effective trend for realizing fast-charging. The conversion-type transition metal oxide and phosphorus-based materials with high theoretical specific capacity typically undergoes significant volume variation during charging and discharging. Consequently, alleviating the volume expansion could significantly fulfill the application of these materials in fast-charging batteries.

Polymorphs of Nb2O5 Compound and Their Electrical Energy Storage Applications

Niobium pentoxide (Nb2O5), as an important dielectric and semiconductor material, has numerous crystal polymorphs, higher chemical stability than water and oxygen, and a higher melt point than most metal oxides. Nb2O5 materials have been extensively studied in electrochemistry, lithium batteries, catalysts, ionic liquid gating, and microelectronics. Nb2O5 polymorphs provide a model system for studying structure-property relationships. For example, the T-Nb2O5 polymorph has two-dimensional layers with very low steric hindrance, allowing for rapid Li-ion migration. With the ever-increasing energy crisis, the excellent electrical properties of Nb2O5 polymorphs have made them a research hotspot for potential applications in lithium-ion batteries (LIBs) and supercapacitors (SCs). The basic properties, crystal structures, synthesis methods, and applications of Nb2O5 polymorphs are reviewed in this article. Future research directions related to this material are also briefly discussed.

Niobium: The Focus on Catalytic Application in the Conversion of Biomass and Biomass Derivatives

The world scenario regarding consumption and demand for products based on fossil fuels has demonstrated the imperative need to develop new technologies capable of using renewable resources. In this context, the use of biomass to obtain chemical intermediates and fuels has emerged as an important area of research in recent years, since it is a renewable source of carbon in great abundance. It has the benefit of not contributing to the additional emission of greenhouse gases since the CO2 released during the energy conversion process is consumed by it through photosynthesis. In the presented review, the authors provide an update of the literature in the field of biomass transformation with the use of niobium-containing catalysts, emphasizing the versatility of niobium compounds for the conversion of different types of biomass.

Electrochemically induced amorphous-to-rock-salt phase transformation in niobium oxide electrode for Li-ion batteries

Intercalation-type metal oxides are promising negative electrode materials for safe rechargeable lithium-ion batteries due to the reduced risk of Li plating at low voltages. Nevertheless, their lower energy and power density along with cycling instability remain bottlenecks for their implementation, especially for fast-charging applications. Here, we report a nanostructured rock-salt Nb₂O₅ electrode formed through an amorphous-to-crystalline transformation during repeated electrochemical cycling with Li⁺. This electrode can reversibly cycle three lithiums per Nb₂O₅, corresponding to a capacity of 269 mAh g^-1 at 20 mA g^-1, and retains a capacity of 191 mAh g^-1 at a high rate of 1 A g^-1. It exhibits superb cycling stability with a capacity of 225 mAh g^-1 at 200 mA g^-1 for 400 cycles, and a Coulombic efficiency of 99.93%. We attribute the enhanced performance to the cubic rock-salt framework, which promotes low-energy migration paths. Our work suggests that inducing crystallization of amorphous nanomaterials through electrochemical cycling is a promising avenue for creating unconventional high-performance metal oxide electrode materials.

Optimized Lithography-Free Fabrication of Sub-100 nm Nb2O5 Nanotube Films as Negative Supercapacitor Electrodes: Tuned Oxygen Vacancies and Cationic Intercalation

The direct growth of sub-100 nm thin-film metal oxides has witnessed a sustained interest as a superlative approach for the fabrication of smart energy storage platforms. Herein, sub-100 nm Zr-doped orthorhombic Nb₂O₅ nanotube films are synthesized directly on the Nb-Zr substrate and tested as negative supercapacitor electrode materials. To boost the pseudocapacitive performance of the fabricated films, supplement Nb⁴⁺ active sites (defects) are subtly induced into the metal oxide lattice, resulting in 13% improvement in the diffusion current at 100 m V/s over that of the defect-free counterpart. The defective sub-100 nm film (H-NbZr) exhibits areal and volumetric capacitances of 6.8 mF/cm² and 758.3 F/cm³, respectively. The presence of oxygen-deficient states enhances the intrinsic conductivity of the thin film, resulting in a reduction in the band gap energy from 3.25 to 2.5 eV. The assembled supercapacitor device made of nitrogen-doped activated carbon (N-AC) and H-NbZr (N-AC//H-NbZr) is able to retain 93, 83, 78, and 66% of its first cycle capacitance after 1000, 2000, 3000, and 4500 successive charge/discharge cycles, respectively. An eminent energy record of approximately 0.77 μW h/cm² at a power of 0.9 mW/cm² is achieved at 1 mA/cm² with superb capability.

Multidefect N-Nb2 O5- x @CNTs Incorporated into Capillary Transport Framework for Li+ /Na+ Storage

As an ion-embedded material with small strain and low transport energy barrier, the limited ion transport rate and conductivity of niobium pentaoxide (Nb₂ O₅ ) are the main factors limiting its application in lithium/sodium storage systems. In this work, the microsphere composites (N-Nb₂ O_{5- x} @CNTs) are prepared by combining Nb₂ O₅ , rich in nitrogen doping and vacancy defects, with carbon nanotubes (CNTs) penetrating the bulk phase. With the capillary effect, CNTs can enable the rapid electrolyte infiltration into the microspheres, thus shorting the Li⁺ /Na⁺ transport path. In addition, CNTs also hinder the direct contact between the electrolyte and Nb₂ O₅ , and inhibit the irreversible reaction. Meanwhile, nitrogen doping and oxygen vacancy defects reduce the energy barrier of Li⁺ /Na⁺ transport, and improve their transport rate, proved by density functional theory. Highly conductive CNTs and unpaired electrons from defects also ameliorate the insulation property of Nb₂ O₅ . Therefore, N-Nb₂ O_{5- x} @CNTs display good electrochemical performance in both Li/Na half-cell and Li/Na hybrid capacitors. Interestingly, kilogram-scale microsphere composites can be produced in laboratory conditions by using industrial grade raw materials, implying its potential for practical application.

Facile synthesis of SnNb2O6@C composite with ultrathin carbon layer as anode materials for high-performance sodium-ion batteries

Niobium-based oxides have attracted a lot of attention as anode materials for sodium-ion batteries (SIBs) due to their high theoretical specific capacity, excellent rate capability and exceptional safety. However, their poor intrinsic electronic conductivity and sluggish sodium ions diffusion kinetics severely hinder their practical applicability. Here, SnNb 2 O 6 @C was successfully prepared by a simple solid-state reaction technique coupled with carbon coating. HRTEM images show that the SnNb 2 O 6 @C particles are covered by a uniformly ultrathin amorphous carbon layer of about 1.8 nm, thus improving the electronic conductivity and diffusion coefficient of sodium ions. As anode for SIBs, the as-obtained SnNb 2 O 6 @C material exhibits excellent specific capacity (369 mAh g -1 at a current density of 50 mA g -1 ) and remarkable rate performance (177 mAh g -1 at 1000 mA g -1 ), which indicates its good prospect in practical application.

Polyvinylpyrrolidone regulated synthesis of mesoporous titanium niobium oxide as high-performance anode for lithium-ion batteries

TiNb₂O₇ (TNO) as a promising candidate anode for lithium-ion batteries (LIBs) shows obvious advantages in terms of specific capacity and safety, but which undergoes the intrinsic poor electrical and ionic conductivity. Herein, we propose a simple synthesis strategy of mesoporous TNO via a polymeric surfactant-mediated evaporation-induced sol-gel method, using polyvinylpyrrolidone (PVP) with different molecular weights (average Mw: 10000/58000/1300000) as the regulating agent, which greatly affects the lithium storage performance of the as-prepared TNO. The optimized TNO (i.e., PVP of 58000) delivers a high reversible capacity of 303.1 mAh/g at 1 C, with a retention rate of 73.4% (222.5 mAh/g) after 300 cycles. Even at 5 C, a high reversible capacity of 185.6 mAh/g can be achieved, with a retention rate of 72.3% after 1000 cycles. The superior lithium storage behavior is attributed to the fine mesoporous framework consisting of interconnected TNO nanocrystallites with high specific surface area and high mesoporosity, which greatly increases the active sites, improves the Li⁺ diffusion kinetics and alleviates volume fluctuation induced by the repetitive Li⁺ insertion-extraction processes.

T-Nb2O5 nanoparticles confined in carbon nanotubes with fast ion diffusion rates for lithium storage

A T-Nb₂O₅/CNT nanohybrid with short transmission paths, many active sites, and favorable mechanical flexibility can achieve the fast transportation of ions/electrons. The obtained nanohybrid with continuous conductive networks exhibited better lithium storage performance than sodium storage performance, due to lower resistance to the diffusion of Li⁺ ions crossing the carbon matrix.

Atomic-resolution STEM-EDS studies of cation ordering in Ti-Nb oxide crystals

Ternary metal oxide compounds, such as Ti-Nb and Nb-W oxides, have renewed research interest in energy storage materials because these oxides contain multivalent metal ions that may be able to control the ion transport in solid lithium batteries. One of these oxides is Ti₂Nb₁₀O₂₉, which is composed of metal-oxygen octahedra connected through corner-sharing and edge-sharing to form "block structures". In the early 1970s Von Dreele and Cheetham proposed a metal-atoms ordering in this oxide crystal using Rietveld refined neutron powder diffraction method. Most recent studies on these oxides, however, have not considered cation ordering in evaluating the battery electrode materials. In this paper, by utilizing the latest scanning transmission electron microscopy combined with energy dispersive X-ray spectroscopy imaging technology, the cation chemical ordering in those oxide crystals was directly revealed at atomic resolution.

Natural Self-Confined Structure Effectively Suppressing Volume Expansion toward Advanced Lithium Storage

Volume expansion hinders conversion-type transition-metal oxides (TMOs) as potential anode candidates for high-capacity lithium-ion batteries. While nanostructuring and nanosizing have been employed to improve the cycling stability of TMOs, we show here that both high initial Coulombic efficiency (ICE) and stable cycling reversibility are achieved in the layered compound Li_0.9Nb_0.9Mo_1.1O₆ (L0.9NMO) by inherent properties of the bulk crystal structure. In this model, MoO₆ octahedra as active centers react with lithium ions and endow capacity, while a grid composed of NbO₆ octahedra effectively suppresses the volume expansion, enhances the conductivity, and supports the structural skeleton from collapse. As a result, bulk L0.9NMO not only delivers a high discharge capacity of 1128 mA h g^-1 at 100 mA g^-1 with a considerable ICE of 87% but also exhibits long cycling stability and good rate performance (339 mA h g^-1 after 500 cycles at 1 A g^-1 with an average Coulombic efficiency approaching 100%). The self-confined structure provides a competitive strategy for stable conversion-type lithium storage.

Precisely Tunable T-Nb2O5 Nanotubes via Atomic Layer Deposition for Fast-Charging Lithium-Ion Batteries

The demand for fast-charging of lithium-ion batteries (LIBs) in modern electric transportation and wearable electronics is rapidly growing. However, commercially available graphite anodes still suffer from slow kinetics of lithium-ion diffusion and severe safety concerns of lithium plating when achieving the fast-charging goal. Here, it is demonstrated that the Li-ion diffusion kinetics of orthorhombic Nb₂O₅ nanotubes (T-Nb₂O₅ NTs) is enhanced by atomically precise manufacturing of nanoarchitectures. The controlled fabrication of T-Nb₂O₅ NTs with wall thicknesses from 24 to 43 nm is realized via atomic layer deposition (ALD) using electrospun polyacrylonitrile nanofibers as a sacrificing template. The wall thickness of T-Nb₂O₅ NTs can be precisely tuned by adjusting the number of ALD cycles. The relationship between the wall thicknesses and electrochemical performances is investigated in detail. The electrochemical kinetic analysis suggests that the lithium storage in T-Nb₂O₅ NTs is dominated by surface and intercalation pseudocapacitance. The morphology of T-Nb₂O₅ crystallites is found to have significant effects on the Li-ion insertion/extraction kinetics and the performance of the electrodes in LIBs. The resulting T-Nb₂O₅ NTs exhibit fast charge-storage kinetics and enable highly reversible insertion/extraction of Li ions without a phase change. This work may open up a new avenue for further development of intercalation-pseudocapacitive nanostructured materials for high-rate and ultrastable energy-storage devices.

Pillared Mo2TiC2 MXene for high-power and long-life lithium and sodium-ion batteries

In this work, we apply an amine-assisted silica pillaring method to create the first example of a porous Mo₂TiC₂ MXene with nanoengineered interlayer distances. The pillared Mo₂TiC₂ has a surface area of 202 m² g^-1, which is among the highest reported for any MXene, and has a variable gallery height between 0.7 and 3 nm. The expanded interlayer distance leads to significantly enhanced cycling performance for Li-ion storage, with superior capacity, rate capably and cycling stability in comparison to the non-pillared analogue. The pillared Mo₂TiC₂ achieved a capacity over 1.7 times greater than multilayered MXene at 20 mA g^-1 (≈320 mA h g^-1) and 2.5 times higher at 1 A g^-1 (≈150 mA h g^-1). The fast-charging properties of pillared Mo₂TiC₂ are further demonstrated by outstanding stability even at 1 A g^-1 (under 8 min charge time), retaining 80% of the initial capacity after 500 cycles. Furthermore, we use a combination of spectroscopic techniques (i.e. XPS, NMR and Raman) to show unambiguously that the charge storage mechanism of this MXene occurs by a conversion reaction through the formation of Li₂O. This reaction increases by 2-fold the capacity beyond intercalation, and therefore, its understanding is crucial for further development of this family of materials. In addition, we also investigate for the first time the sodium storage properties of the pillared and non-pillared Mo₂TiC₂.

Niobium pentoxide based materials for high rate rechargeable electrochemical energy storage

The demand for high rate energy storage systems is continuously increasing driven by portable electronics, hybrid/electric vehicles and the need for balancing the smart grid. Accordingly, Nb₂O₅ based materials have gained great attention because of their fast cation intercalation faradaic charge storage that endows them with high rate energy storage performance. In this review, we describe the crystalline features of the five main phases of Nb₂O₅ and analyze their specific electrochemical characteristics with an emphasis on the intrinsic ion intercalation pseudocapacitive behavior of T-Nb₂O₅. The charge storage mechanisms, electrochemical performance and state-of-the-art characterization techniques for Nb₂O₅ anodes are summarized. Next, we review recent progress in developing various types of Nb₂O₅ based fast charging electrode materials, including Nb₂O₅ based mixed metal oxides and composites. Finally, we highlight the major challenges for Nb₂O₅ based materials in the realm of high rate rechargeable energy storage and provide perspectives for future research.

Quaternary type IV deep eutectic solvent-based tungsten oxide/niobium oxide photochromic and reverse fading composite complex

An excellent photochromic material based on a WO3/Nb2O5 complex with the fast fading property for promising application in optical glasses/lenses and color display devices.

Preparation and Characterization of NbxOy Thin Films: A Review

Niobium oxides (NbO, NbO2, Nb2O5), being a versatile material has achieved tremendous popularity to be used in a number of applications because of its outstanding electrical, mechanical, chemical, and magnetic properties. NbxOy films possess a direct band gap within the ranges of 3.2–4.0 eV, with these films having utility in different applications which include; optical systems, stainless steel, ceramics, solar cells, electrochromic devices, capacitor dielectrics, catalysts, sensors, and architectural requirements. With the purpose of fulfilling the requirements of a vast variety of the named applications, thin films having comprehensive properties span described by film composition, morphology, structural properties, and thickness are needed. The theory, alongside the research status of the different fabrication techniques of NbxOy thin films are reported in this work. The impact of fabrication procedures on the thin film characteristics which include; film thickness, surface quality, optical properties, interface properties, film growth, and crystal phase is explored with emphases on the distinct deposition process applied, are also described and discussed.

Facile formation of tetragonal-Nb2O5 microspheres for high-rate and stable lithium storage with high areal capacity

Niobium pentoxide (Nb₂O₅) has attracted great attention as an anode for lithium-ion battery, which is attributed to the high-rate and good stability performances. In this work, TT-, T-, M-, and H-Nb₂O₅ microspheres were synthesized by a facile one-step thermal oxidation method. Ion and electron transport properties of Nb₂O₅ with different phases were investigated by both electrochemical analyses and density functional theoretical calculations. Without nanostructuring and carbon modification, the tetragonal Nb₂O₅ (M-Nb₂O₅) displays preferable rate capability (121 mAh g^-1 at 5 A g^-1), enhanced reversible capacity (163 mAh g^-1 at 0.2 A g^-1) and better cycling stability (82.3% capacity retention after 1000 cycles) when compared with TT-, T-, and H-Nb₂O₅. Electrochemical analyses further reveal the diffusion-controlled Li⁺ intercalation kinetics and in-situ X-ray diffraction analysis indicates superior structural stability upon Li⁺ intercalation/deintercalation. Benefiting from the intrinsic fast ion/electron transport, a high areal capacity of 2.24 mAh cm^-2 is obtained even at an ultrahigh mass loading of 22.51 mg cm^-2. This work can promote the development of Nb₂O₅ materials for high areal capacity and stable lithium storage towards practical applications.

CVD-assisted fabrication of hierarchical microparticulate Li2TiSiO5-carbon nanospheres for ultrafast lithium storage

Particular recent interest has been given to the Li₂TiSiO₅ (LTSO) anode material owing to its low lithiation potential (0.28 V vs. Li/Li⁺) and decent theoretical capacity (308 mA h g^-1). However, its poor electronic conductivity (∼10^-7 S m^-1) fundamentally limits the utilization of this material, and current strategies fail to tackle such issues in practical ways. Herein, a hierarchical microparticulate LTSO-carbon composite (LTSO/C) is fabricated by chemical vapor deposition (CVD), where microsized LTSO/C particles assembled from nanospheres guarantee a practical tap density of ∼1.3 g mL^-1. Meanwhile, significantly elevated conductivity of LTSO/C (∼10³ S m^-1) is achieved by a thin layer (15 nm) of graphitic carbon growth on LTSO, which is theoretically catalyzed by the surface functional groups on the parent LTSO. The electrochemical characterization of LTSO/C reveals a superior graphite-like volumetric capacity of 441.1 mA h cm^-3 and Li₄Ti₅O₁₂-like rate capability (120.1 mA h cm^-3 at 4.5 A g^-1), providing inspiring guidance for designing analogous Ti or Si-based compounds for ultrafast lithium storage materials.

Controlled growth and ion intercalation mechanism of monocrystalline niobium pentoxide nanotubes for advanced rechargeable aluminum-ion batteries

Rechargeable aluminum-ion batteries (RAIBs) have attracted increasing attention owing to their high theoretical volumetric capacity, high resource abundance, and good safety performance. However, the existing RAIB systems usually exhibit relatively low specific capacities limited by the cathode materials. In this study, we developed a one-step chemical vapor deposition method to prepare single-crystal orthogonal Nb2O5 nanotubes for serving as high-performance electrode materials for RAIBs, showing a high reversible capability of 556 mA h g-1 at 25 mA g-1 and good thermal endurability at elevated temperatures (50 °C). A combination of a series of detailed ex situ structural characterization studies verified the reversible intercalation/deintercalation of chloroaluminate anions (AlCl4-) into/from the (001) planes of monocrystalline Nb2O5 nanotubes. It also revealed that the nanoarchitecture of Nb2O5 nanotubes with thin tube walls, hollow inner space and a short ion transport distance is conducive to the rapid kinetics of the insertion/extraction process. This work provides a promising route to design high-performance electrode materials based on transition metal compounds for RAIBs via the rational modulation of their structure and morphology.

The rational design of carbon coated Fe2(MoO4)3 nanosheets for lithium-ion storage with high initial coulombic efficiency and long cycle life

Binary metal oxides are potential anode materials for lithium-ion storage due to their high theoretical specific capacities. However, the practical applications of metal oxides are limited due to their large volume changes and sluggish reaction kinetics. Herein, carbon coated Fe₂(MoO₄)₃ nanosheets are prepared via a simple method, adopting urea as the template and carbon source. The carbon coating on the surface helps to elevate the conductivity of the active material and maintain structural integrity during the lithium storage process. Combining this with a catalytic effect from the generated Fe, leading to the reversible formation of a solid electrolyte interface layer, a high initial coulombic efficiency (>87%) can be obtained. Based on this, the carbon coated Fe₂(MoO₄)₃ nanosheets show excellent rate capability (a reversible discharge capacity of 983 mA h g^-1 at 5 A g^-1) and stable cycling performance (1376 mA h g^-1 after 250 cycles at 0.5 A g^-1 and 864 mA h g^-1 after 500 cycles at 2 A g^-1). This simple in situ carbonization and template method using urea provides a facile way to optimize electrode materials for next-generation energy storage devices.

Electrode Degradation in Lithium-Ion Batteries

Although Li-ion batteries have emerged as the battery of choice for electric vehicles and large-scale smart grids, significant research efforts are devoted to identifying materials that offer higher energy density, longer cycle life, lower cost, and/or improved safety compared to those of conventional Li-ion batteries based on intercalation electrodes. By moving beyond intercalation chemistry, gravimetric capacities that are 2-5 times higher than that of conventional intercalation materials (e.g., LiCoO₂ and graphite) can be achieved. The transition to higher-capacity electrode materials in commercial applications is complicated by several factors. This Review highlights the developments of electrode materials and characterization tools for rechargeable lithium-ion batteries, with a focus on the structural and electrochemical degradation mechanisms that plague these systems.

Copper, zinc, and manganese niobates (CuNb2O6, ZnNb2O6, and MnNb2O6): structural characteristics, Li+ storage properties, and working mechanisms

Niobium-based oxides are considered promising anode materials for Li-ion batteries due to their high capacities, good cyclability, and excellent safety.

Ti-Based Oxide Anode Materials for Advanced Electrochemical Energy Storage: Lithium/Sodium Ion Batteries and Hybrid Pseudocapacitors

Titanium-based oxides including TiO₂ and M-Ti-O compounds (M = Li, Nb, Na, etc.) family, exhibit advantageous structural dynamics (2D ion diffusion path, open and stable structure for ion accommodations) for practical applications in energy storage systems, such as lithium-ion batteries, sodium-ion batteries, and hybrid pseudocapacitors. Further, Ti-based oxides show high operating voltage relative to the deposition of alkali metal, ensuring full safety by avoiding the formation of lithium and sodium dendrites. On the other hand, high working potential prevents the decomposition of electrolyte, delivering excellent rate capability through the unique pseudocapacitive kinetics. Nevertheless, the intrinsic poor electrical conductivity and reaction dynamics limit further applications in energy storage devices. Recently, various work and in-depth understanding on the morphologies control, surface engineering, bulk-phase doping of Ti-based oxides, have been promoted to overcome these issues. Inspired by that, in this review, the authors summarize the fundamental issues, challenges and advances of Ti-based oxides in the applications of advanced electrochemical energy storage. Particularly, the authors focus on the progresses on the working mechanism and device applications from lithium-ion batteries to sodium-ion batteries, and then the hybrid pseudocapacitors. In addition, future perspectives for fundamental research and practical applications are discussed.

Two-dimensional Nb2O5 holey nanosheets prepared by a graphene sacrificial template method for high performance Mg2+/Li+ hybrid ion batteries

Mg²⁺/Li⁺ hybrid ion batteries (MLIBs) are regarded as promising candidates for electrical energy devices due to their combination of a fast lithium intercalation cathode and a safe magnesium anode. Herein, two-dimensional Nb₂O₅ holey nanosheets are synthesized using a graphene oxide sacrificial template method and these are then used as the cathode of a MLIB for the first time. It exhibits a high discharge capacity (195.9 mA h g^-1 at 100 mA g^-1), excellent rate performance (72.1 mA h g^-1 at 2000 mA g^-1) and a long cycling life (exhibiting a capacity fading rate of 0.032% per cycle at 2000 mA g^-1 over 1000 cycles). The remarkable electrochemical performance can be attributed to the unique two-dimensional holey nanosheet structure, which is beneficial for improving electronic conductivity and lithium ion conductivity.

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.

H0.92K0.08TiNbO5 Nanowires Enabling High-Performance Lithium-Ion Uptake

HTiNbO₅ has been widely investigated in many fields because of its distinctive properties such as good redox activity, high photocatalytic activity, and environmental benignancy. Here, this work reports the synthesis of one-dimensional H_0.92K_0.08TiNbO₅ nanowires via simple electrospinning followed by an ion-exchange reaction. The H_0.92K_0.08TiNbO₅ nanowires consist of many small "lumps" with a uniform diameter distribution of around 150 nm. Used as an anode for lithium-ion batteries, H_0.92K_0.08TiNbO₅ nanowires exhibit high capacity, fast electrochemical kinetics, and high performance of lithium-ion uptake. A capacity of 144.1 mA h g^-1 can be carried by H_0.92K_0.08TiNbO₅ nanowires at 0.5 C in the initial charge, and even after 150 cycles, the reversible capacity can remain at 123.7 mA h g^-1 with an excellent capacity retention of 85.84%. For H_0.92K_0.08TiNbO₅ nanowires, the diffusion coefficient of lithium ions is 1.97 × 10^-11 cm² s^-1, which promotes the lithium-ion uptake effectively. The outstanding electrochemical performance is ascribed to its morphology and the formation of a stable phase during cycling. In addition, the in situ X-ray diffraction and ex situ transmission electron microscopy techniques are applied to reveal its lithium storage mechanism, which proves the structure stability and electrochemical reversibility, thus achieving high-performance lithium-ion uptake. All these advantages demonstrate that H_0.92K_0.08TiNbO₅ nanowires can be a possible alternative anode material for rechargeable batteries.

Application of metal oxide semiconductors in light-driven organic transformations

Herein, we provide an up-to-date overview of metal oxide semiconductors (MOS) as versatile and inexpensive photocatalysts to enable light-driven organic transformations.

Urchin-like hierarchical H-Nb2O5 microspheres: synthesis, formation mechanism and their applications in lithium ion batteries

Urchin-like hierarchical Nb₂O₅ microspheres are successfully synthesized through a facile solvothermal method in glycerol-isopropanol mixed media followed by thermal treatment. The sample is characterized by XRD, FESEM, TEM, HRTEM, BET, and XPS, and the results reveal that the as-formed Nb₂O₅ microspheres have a pseudohexagonal structure and are composed of nanorods with an average diameter of ca. 20 nm. It is found that glycerol not only serves as a solvent but also acts as a reactant; furthermore, isopropanol plays an important part in the morphologies of the products. When used as anodic materials for lithium ion batteries, the Nb₂O₅ microspheres deliver initial discharge capacities of 201.7, 159.7, 148.5, 123.7, and 98.5 mA h g^-1 at the current densities of 0.5, 1, 2, 5, and 10C, respectively. Additionally, the discharge capacity of Nb₂O₅ remains at 105.5 mA h g^-1 even after 500 cycles at a high rate of 5C. The good electrochemical properties of the products may be ascribed to their large surface areas and hierarchical structures.