High power nano-Nb2O5 negative electrodes for lithium-ion 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.

New insights into the electrochemical performance of precursor derived Si(Nb)OC composites as anode materials for batteries

This work represents a first attempt to synthesize Si(Nb)OC ceramic composites through the polymer pyrolysis or the precursor-derived ceramics (PDC) route for use as a hybrid anode material for lithium-ion batteries (LIB). Electron microscopy, X-ray diffraction, and various spectroscopy techniques were used to examine the micro/nano structural features and phase evolution during cross-linking, pyrolysis, and annealing stages. During the polymer-to-ceramic transformation process, in situ formation of carbon (so-called "free carbon"), and crystallization of t-NbO2, NbC phases in the amorphous Si(Nb)OC ceramic matrix are identified. The first-cycle reversible capacities of 431 mA h g-1 and 256 mA h g-1 for the as-pyrolyzed and annealed Si(Nb)OC electrodes, respectively, exceeded the theoretical Li capacity of niobium pentaoxide or m-Nb2O5 (at approximately 220 mA h g-1). With an average reversible capacity of 200 mA h g-1 and close to 100% cycling efficiency, as-pyrolyzed Si(Nb)OC demonstrates good rate capability. X-ray amorphous SiOC with uniformly distributed nanosized Nb2O5 and graphitic carbon structure likely provides stability during repeated Li+ cycling and the formation of a stable secondary electrolyte interphase (SEI) layer, leading to high efficiency.

Li iontronics in single-crystalline T-Nb2O5 thin films with vertical ionic transport channels

The niobium oxide polymorph T-Nb2O5 has been extensively investigated in its bulk form especially for applications in fast-charging batteries and electrochemical (pseudo)capacitors. Its crystal structure, which has two-dimensional (2D) layers with very low steric hindrance, allows for fast Li-ion migration. However, since its discovery in 1941, the growth of single-crystalline thin films and its electronic applications have not yet been realized, probably due to its large orthorhombic unit cell along with the existence of many polymorphs. Here we demonstrate the epitaxial growth of single-crystalline T-Nb2O5 thin films, critically with the ionic transport channels oriented perpendicular to the film's surface. These vertical 2D channels enable fast Li-ion migration, which we show gives rise to a colossal insulator-metal transition, where the resistivity drops by 11 orders of magnitude due to the population of the initially empty Nb 4d0 states by electrons. Moreover, we reveal multiple unexplored phase transitions with distinct crystal and electronic structures over a wide range of Li-ion concentrations by comprehensive in situ experiments and theoretical calculations, which allow for the reversible and repeatable manipulation of these phases and their distinct electronic properties. This work paves the way for the exploration of novel thin films with ionic channels and their potential applications.

Graphite-Based Composite Anodes with C-O-Nb Heterointerfaces Enable Fast Lithium Storage

To better satisfy the increasing demands for electric vehicles, it is crucial to develop fast-charging lithium-ion batteries (LIBs). However, the fast-charging capability of commercial graphite anodes is limited by the sluggish Li⁺ insertion kinetics. Herein, we report a synergistic engineering of uniform nano-sized T-Nb₂ O₅ particles on graphite (Gr@Nb₂ O₅ ) with C-O-Nb heterointerfaces, which prevents the growth and aggregation of T-Nb₂ O₅ nanoparticles. Through detailed theoretical calculations and pair distribution function analysis, the stable existence of the heterointerfaces is proved, which can accelerate the electron/ion transport. These heterointerfaces endow Gr@Nb₂ O₅ anodes with high ionic conductivity and excellent structural stability. Consequently, Gr@10-Nb₂ O₅ anode, where the mass ratio of T-Nb₂ O₅ /graphite=10/100, exhibits excellent cyclic stability and incredible rate capabilities, with 100.5 mAh g^-1 after 10000 stable cycles at an ultrahigh rate of 20 C. In addition, the synergistic Li⁺ storage mechanism is revealed by systematic electrochemical characterizations and in situ X-ray diffraction. This work offers new insights to the reasonable design of fast-charging graphite-based anodes for the next generation of LIBs.

Pseudohexagonal Nb2O5 Anodes for Fast-Charging Potassium-Ion Batteries

High-rate batteries will play a vital role in future energy storage systems, yet while good progress is being made in the development of high-rate lithium-ion batteries, there is less progress with post-lithium-ion chemistry. In this study, we demonstrate that pseudohexagonal Nb₂O₅(TT-Nb₂O₅) can offer a high specific capacity (179 mAh g^-1 ∼ 0.3C), good lifetime, and an excellent rate performance (72 mAh g^-1 at ∼15C) in potassium-ion batteries (KIBs), when it is composited with a highly conductive carbon framework; this is the first reported investigation of TT-Nb₂O₅ for KIBs. Specifically, multiwalled carbon nanotubes are strongly tethered to Nb₂O₅ via glucose-derived carbon (Nb₂O₅@CNT) by a one-step hydrothermal method, which results in highly conductive and porous needle-like structures. This work therefore offers a route for the scalable production of a viable KIB anode material and hence improves the feasibility of fast-charging KIBs for future applications.

In Situ Orthorhombic to Amorphous Phase Transition of Nb2O5 and Its Temperature Effect on Pseudocapacitive Behavior

Niobium pentoxide (Nb₂O₅) represents an exquisite class of negative electrode materials with unique pseudocapacitive kinetics that engender superior power and energy densities for advanced electrical energy storage devices. Practical energy devices are expected to maintain stable performance under real-world conditions such as temperature fluctuations. However, the intercalation pseudocapacitive behavior of Nb₂O₅ at elevated temperatures remains unexplored because of the scarcity of suitable electrolytes. Thus, in this study, we investigate the effect of temperature on the pseudocapacitive behavior of submicron-sized Nb₂O₅ in a wide potential window of 0.01-2.3 V. Furthermore, ex situ X-ray diffraction and X-ray photoelectron spectroscopy reveal the amorphization of Nb₂O₅ accompanied by the formation of NbO via a conversion reaction during the initial cycle. Subsequent cycles yield enhanced performance attributed to a series of reversible Nb^V, IV/Nb^III redox reactions in the amorphous Li_xNb₂O₅ phase. Through cyclic voltammetry and symmetric cell electrochemical impedance spectroscopy, temperature elevation is noted to increase the pseudocapacitive contribution of the Nb₂O₅ electrode, resulting in a high rate capability of 131 mAh g^-1 at 20,000 mA g^-1 at 90 °C. The electrode further exhibits long-term cycling over 2000 cycles and high Coulombic efficiency ascribed to the formation of a robust, [FSA]^--originated solid-electrolyte interphase during cycling.

Layered Niobium Oxide Hydrate Anode with Excellent Performance for Lithium-Ion Batteries

Benefiting from the advantages of cost-effectiveness and sustainability, lithium-ion batteries (LIBs) are recognized as a next-generation energy technology with great development potential. Herein, niobium oxide hydrate (H₃ONb₃O₈) synthesized by a facile and inexpensive solvothermal method is proposed as the anode of LIBs. It is a layered two-dimensional material composed of negatively charged two-dimensional lamellae and positively charged interlayer hydronium ions. The former consist of NbO₆ octahedral units connected by bridging oxygen. Because of the mutual effect of hydronium ions and niobium oxide quantum dots, niobium oxide hydrate exhibits excellent electrochemical activity when used as an anode material. This compound is first applied to lithium-ion batteries, obtaining a high specific capacity (1232 mAh g^-1) at 100 mA g^-1 and maintaining an outstanding performance after 200 cycles. Therefore, this work not only proposes a simple preparation method of niobium oxide hydrate but also expands the variety of high-performance anode materials.

Polyaniline–niobium oxide nanohybrids with photocatalytic activity under visible light irradiation

In this study, we reported the production of polyaniline and niobium oxide hybrids synthesized by the direct reaction between a niobium peroxyoxalate complex and anilinium salt in an aqueous medium.

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.

Ultrafast and Stable Li-(De)intercalation in a Large Single Crystal H-Nb2 O5 Anode via Optimizing the Homogeneity of Electron and Ion Transport

Exploring anode materials with fast, safe, and stable Li-(de)intercalation is of great significance for developing next-generation lithium-ion batteries. Monoclinic H-type niobium pentoxide possesses outstanding intrinsic fast Li-(de)intercalation kinetics, high specific capacity, and safety; however, its practical rate capability and cycling stability are still limited, ascribed to the asynchronism of phase change throughout the crystals. Herein this problem is addressed by homogenizing the electron and Li-ion conductivity surrounding the crystals. An amorphous N-doped carbon layer is introduced on the micrometer single-crystal H-Nb₂ O₅ particle to optimize the homogeneity of electron and Li-ion transport. As a result, the as-prepared H-Nb₂ O₅ exhibits high reversible capacity (>250 mAh g^-1 at 50 mA g^-1 ), unprecedented high-rate performance (≈120 mAh g^-1 at 16.0 A g^-1 ) and excellent cycling stability (≈170 mAh g^-1 at 2.0 A g^-1 after 1000 cycles), which is by far the highest performance among the H-Nb₂ O₅ materials. The inherent principle is further confirmed via operando transmission electron microscopy and X-ray diffraction. A novel insight into the further development of electrode materials forlithium-ion batteries is thus provided.

Coupling Niobia Nanorods with a Multicomponent Carbon Network for High Power Lithium-Ion Batteries

High power lithium-ion batteries require highly conductive electrodes. For an active electrode material that has limited electron conductivity, it is critical to build a carbon network that is not only highly conductive itself but also highly compatible with the electroactive material for efficient interfacial charge transfer. Herein, we design a multicomponent carbon network that is optimized for electrical coupling with the electroactive Nb₂O₅ nanorods for efficient electron injection. The self-support electrode is constructed by using 0D polypyrrole-derived (Ppy) carbon nanoparticles as glue to bind the Nb₂O₅ nanorods with 1D carbon nanotubes (CNTs) and 2D graphene nanosheets (GNSs). The 0D carbon nanoparticles also cross-link 1D CNTs with 2D GNSs, which can effectively prevent the GNSs from aggregation and form the 3D CNT/GNS network that provides continuous electronic and ionic pathways. This 3D Nb₂O₅@C self-support electrode exhibits a high discharge capacity of 246.3 mA h g^-1 at 0.5 C and 100 mA h g^-1 at 20 C and excellent Coulombic efficiency of 99.98% at 20 C. Even increasing the mass loading to 7.1 mg cm^-2, the Nb₂O₅@C electrode can still reach a discharge capacity of 172.4 mA h g^-1 at 0.5 C after 100 cycles. A high power density of 1043 W kg^-1 can be achieved at an energy density of 104.3 W h kg^-1 based on the electrode weight, which is among the highest values demonstrated so far for Nb₂O₅ electrodes. The results pave the way toward practical applications of Nb₂O₅ anodes in high-power lithium-ion batteries.

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.

Simple Synthesis of K₄Nb₆O17/C Nanosheets for High-Power Lithium-Ion Batteries with Good Stability

In this work, a series of two-dimensional (2D) large-size nanosheets were prepared through one-step exfoliation of the huge K₄Nb₆O17 crystals. The K₄Nb₆O17 nanosheets with the thickness of about 2 nm was used as the templates of dopamine polymerization and was then carbonized to form C-doped K₄Nb₆O17 nanosheets. More importantly, the C-doped K₄Nb₆O17 nanosheets exhibited excellent electrochemical performance with high specific capacity (381 mA h g-1 at 0.05 A g-1, 0.5⁻3.0 V vs. Li/Li⁺) and stable cyclability at high current density (remarkably, preserved a capacity of discharge approximately 90 mA h g-1 at 5 A g-1 after 1000 cycles). The good electrochemical performances of the C-doped K₄Nb₆O17 nanosheets can be attributed to the outstanding 2D structure and large specific surface, which afforded the short transport route for ion and electron. These noteworthy results demonstrated that the new 2D nanomaterials might be potential candidates for the high-performance, environmentally friendly, and low-cost electrochemical energy storage equipment.

Neat Design for the Structure of Electrode To Optimize the Lithium-Ion Battery Performance

The appearance of mechanical cracks originated from anisotropic expansion and shrinkage of electrode particles during Li⁺ de/intercalation is a major cause of the capacity fading in Li-ion batteries. Well-designed and controlled nanostructures of electrodes have shown a prominent prospect for solving this obstacle. Here, we report a novel and convenient strategy for the preparation of graphene nanoscroll wrapping Nb₂O₅ nanoparticles (denoted as T-Nb₂O₅/G). First, high energy ball milling is conducted to acquire softly agglomerated T-Nb₂O₅ nanoparticles owing to its spontaneous reduction of surface energy among these single particles. Then freeze-drying leads to the formation of graphene nanoscroll, which easily realizes the in situ wrapping over softly agglomerated T-Nb₂O₅ nanoparticles. Extended cycling tests demonstrate that such T-Nb₂O₅/G yields a high reversible specific capacity of 222 mA h g^-1 over 700 cycles at 1C. The dominated surface capacitive insertion processes possessing favorable kinetics enable T-Nb₂O₅/G to exhibit excellent rate performance, which achieve a capacity of 110 mA h g^-1 at 10C. A combined ex situ X-ray diffraction, scanning electron microscopy, and transmission electron microscopy investigation reveal that the long-term cycling stability of T-Nb₂O₅/G is attributed to the excellent structural stability of the electrode, in which the synergistic effect between the softly agglomerated T-Nb₂O₅ nanoparticles and graphene nanoscroll prevents the formation of mechanical cracks.

Free-anchored Nb2O5@graphene networks for ultrafast-stable lithium storage

Orthorhombic Nb₂O₅ (T-Nb₂O₅) has structural merit but poor electrical conductivity, limiting their applications in energy storage. Although graphene is frequently adopted to effectively improve its electrochemical properties, the ordinary modified methods cannot meet the growing demands for high-performance. Here, we demonstrate that different graphene modified routes play a vital role in affecting the electrochemical performances of T-Nb₂O₅. By only manual shaking within one minute, Nb₂O₅ nano-particles can be rapidly adsorbed onto graphene, then the free-anchored T-Nb₂O₅@graphene three-dimensional networks can be successfully prepared based on hydrogel method. As for the application in lithium-ion batteries, it performs outstanding rate character (129 mA h g^-1 (25C rate), 110 mA h g^-1 (50C rate) and 90 mA h g^-1 (100C rate), correspond to 79%, 67% and 55% capacity of 0.5C rate, respectively) and excellent long-term cycling feature (∼70% capacity retention after 20000 cycles). Moreover, it still maintains similar ultrafast-stable lithium storage performances when Cu foil is substituted by Al foil as current collector. In addition, relevant kinetics mechanisms are also expounded. This work provides a versatile strategy for the preparation of graphene modified Nb₂O₅ or other types of nanoparticles.

Continuous Hydrothermal Synthesis of Inorganic Nanoparticles: Applications and Future Directions

Nanomaterials are at the leading edge of the emerging field of nanotechnology. Their unique and tunable size-dependent properties (in the range 1-100 nm) make these materials indispensable in many modern technological applications. In this Review, we summarize the state-of-art in the manufacture and applications of inorganic nanoparticles made using continuous hydrothermal flow synthesis (CHFS) processes. First, we introduce ideal requirements of any flow process for nanoceramics production, outline different approaches to CHFS, and introduce the pertinent properties of supercritical water and issues around mixing in flow, to generate nanoparticles. This Review then gives comprehensive coverage of the current application space for CHFS-made nanomaterials including optical, healthcare, electronics (including sensors, information, and communication technologies), catalysis, devices (including energy harvesting/conversion/fuels), and energy storage applications. Thereafter, topics of precursor chemistry and products, as well as materials or structures, are discussed (surface-functionalized hybrids, nanocomposites, nanograined coatings and monoliths, and metal-organic frameworks). Later, this Review focuses on some of the key apparatus innovations in the field, such as in situ flow/rapid heating systems (to investigate kinetics and mechanisms), approaches to high throughput flow syntheses (for nanomaterials discovery), as well as recent developments in scale-up of hydrothermal flow processes. Finally, this Review covers environmental considerations, future directions and capabilities, along with the conclusions and outlook.

Formation of a Surficial Bifunctional Nanolayer on Nb2 O5 for Ultrastable Electrodes for Lithium-Ion Battery

Safe and long cycle life electrode materials for lithium-ion batteries are significantly important to meet the increasing demands of rechargeable batteries. Niobium pentoxide (Nb₂ O₅ ) is one of the highly promising candidates for stable electrodes due to its safety and minimal volume expansion. Nevertheless, pulverization and low conductivity of Nb₂ O₅ have remained as inherent challenges for its practical use as viable electrodes. A highly facile method is proposed to improve the overall cycle retention of Nb₂ O₅ microparticles by ammonia (NH₃ ) gas-driven nitridation. After nitridation, an ultrathin surficial layer (2 nm) is formed on the Nb₂ O₅ , acting as a bifunctional nanolayer that allows facile lithium (Li)-ion transport (10-100 times higher Li diffusivity compared with pristine Nb₂ O₅ microparticles) and further prevents the pulverization of Nb₂ O₅ . With the subsequent decoration of silver (Ag) nanoparticles (NPs), the low electric conductivity of nitridated Nb₂ O₅ is also significantly improved. Cycle retention is greatly improved for nitridated Nb₂ O₅ (96.7%) compared with Nb₂ O₅ (64.7%) for 500 cycles. Ag-decorated, nitridated Nb₂ O₅ microparticles and nitridated Nb₂ O₅ microparticles exhibit ultrastable cycling for 3000 cycles at high current density (3000 mA g^-1 ), which highlights the importance of the surficial nanolayer in improving overall electrochemical performances, in addition to conductive NPs.

General fabrication of mesoporous Nb2O5 nanobelts for lithium ion battery anodes

Mesoporous Nb₂O₅ NBs with good crystallinity and large specific area have been synthesized by sequential annealing of solid Nb₂O₅ NBs in NH₃ and air,exhibiting an enhanced capacity and rate capability than that of solid Nb₂O₅ NBs.