Long-Lasting Nb2O5-Based Nanocomposite Materials for Li-Ion Storage

Triple Conductive Wiring by Electron Doping, Chelation Coating and Electrochemical Conversion in Fluffy Nb2 O5 Anodes for Fast-Charging Li-Ion Batteries

High-rate anode material is the kernel of developing fast-charging lithium ion batteries (LIBs). T-Nb₂ O₅ , well-known for its "room and pillar" structure and bulk pseudocapacitive effect, is expected to enable the fast lithium (de)intercalation. But this property is still limited by the low electronic conductivity or insufficient wiring manner. Herein, a strategy of triple conductive wiring through electron doping, chelation coating, and electrochemical conversion inside the microsized porous spheres consisting of dendrite-like T-Nb₂ O₅ primary particles is proposed to achieve the fast-charging and durable anodes for LIBs. The penetrative implanting of conformal carbon coating (derivative from polydopamine chelate) and NbO domains (induced by excess discharging) reinforces the global supply of electronically conductive wires, apart from those from Co/Mn heteroatom or O vacancy doping. The polydopamine etching on T-Nb₂ O₅ spheres promotes their evolution into fluffy morphology with better electrolyte infiltration. The synergic electron and ion wiring at different scales endow the modified T-Nb₂ O₅ anode with ultralong cycling life (143 mAh g^-1 at 1 A g^-1 after 8500 cycles) and high-rate performance (144.1 mAh g^-1 at 10.0 A g^-1 ). The permeation of multiple electron wires also enables a high mass loading of T-Nb₂ O₅ (4.5 mg cm^-2 ) with a high areal capacity of 0.668 mAh cm^-2 even after 150 cycles.

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.

All alginate-derived high-performance T-Nb2O5/C//seaweed carbon Li-ion capacitors

Benefitting from the well-matched kinetics and capacity between the counter electrodes and the ion transportability of sodium alginate, the all alginate-derived T-Nb2O5/C//seaweed carbon Li-ion capacitor has excellent electrochemical performance.

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.

Electrospun Nb2O5 nanorods/microporous multichannel carbon nanofiber film anode for Na+ ion capacitors with good performance

For the disadvantages of both the slow reaction kinetics and the poor conductivity for Nb₂O₅ electrode materials as sodium-ion capacitors (SICs), Nb₂O₅ NRs/NMMCNF film electrode with good flexibility and high electrochemical property has been fabricated by electrospinning PAN/PMMA/H₂Nb₂O₆·H₂O homogeneous viscous suspension and followed by an annealing treatment, in which the precursor H₂Nb₂O₆·H₂O nanorods are obtained by grinding H₂Nb₂O₆·H₂O nanowires, and Nb₂O₅ nanorods are uniformly embedded in nitrogen doped microporous multichannel carbon nanofiber. Benefiting from the multichannel network structure, Nb₂O₅ NRs/NMMCNF film electrode delivers the fast kinetics of Na⁺-storage and the superior Na-ion storage performance, it delivers outstanding rate capability (101 mAh g^-1 at 4 A g^-1) and ultralong lifespan (91% capacity retention after 10,000 cycles at 2 A g^-1). A Nb₂O₅ NRs/NMMCNF//AC SIC based on the Nb₂O₅ NRs@NMMCNF fiber film anode and the AC cathode is assembled. The energy density of the as-assembled device is as high as 91 Wh kg^-1 and its maximum power density is 7499 W kg^-1. This work offers a new structure design strategy toward intercalation-type metal oxide electrodes for application in SICs.

Orthorhombic Nb2O5-x for Durable High-Rate Anode of Li-Ion Batteries

Li₄Ti₅O₁₂ anode can operate at extraordinarily high rates and for a very long time, but it suffers from a relatively low capacity. This has motivated much research on Nb₂O₅ as an alternative. In this work, we present a scalable chemical processing strategy that maintains the size and morphology of nano-crystal precursor but systematically reconstitutes the unit cell composition, to build defect-rich porous orthorhombic Nb₂O_5-x with a high-rate capacity many times those of commercial anodes. The procedure includes etching, proton ion exchange, calcination, and reduction, and the resulting Nb₂O_5-x has a capacity of 253 mA h g^-1 at 0.5C, 187 mA h g^-1 at 25C, and 130 mA h g^-1 at 100C, with 93.3% of the 25C capacity remaining after cycling for 4,000 times. These values are much higher than those reported for Nb₂O₅ and Li₄Ti₅O₁₂, thanks to more available surface/sub-surface reaction sites and significantly improved fast ion and electron 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.

Nb2O5 Nanoparticles Anchored on an N-Doped Graphene Hybrid Anode for a Sodium-Ion Capacitor with High Energy Density

Sodium-ion capacitors (SICs) have gained great interest for mid- to large-scale energy storage applications because of their high energy and high power densities as well as long cycle life and low cost. Herein, a T-Nb₂O₅ nanoparticles/N-doped graphene hybrid anode (T-Nb₂O₅/NG) was prepared by solvothermal treating a mixed ethanol solution of graphene oxide (GO), urea, and NbCl₅ at 180 °C for 12 h, followed by calcining at 700 °C for 2 h, in which T-Nb₂O₅ nanoparticles with average size of 17 nm were uniformly anchored on the surface of the nitrogen-doped reduced GO because their growth and aggregation were hindered, and also, the electronic conductivity and the active sites of T-Nb₂O₅/NG were improved by doping nitrogen. The T-Nb₂O₅/NG anode showed superior rate capability (68 mA h g^-1 even at 2 A g^-1) and good cycling life (106 mA h g^-1 at 0.2 A g^-1 for 200 cycles and 83 mA h g^-1 at 1 A g^-1 for 1000 cycles) and also showed high-rate pseudocapacitive behavior from kinetics analysis. A novel SIC system had been constructed by using the T-Nb₂O₅/NG as anode and commercially activated carbon as the cathode; it delivered an energy density of 40.5 W h kg^-1 at a power density of 100 W kg^-1 and a long-term cycling stability (capacity retention of 63% after 5000 consecutive cycles at a current density of 1 A g^-1) and showed a promising application for highly efficient energy storage systems.

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.

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.

Pyrolytic Carbon Nanosheets for Ultrafast and Ultrastable Sodium-Ion Storage

Na-ion cointercalation in the graphite host structure in a glyme-based electrolyte represents a new possibility for using carbon-based materials (CMs) as anodes for Na-ion storage. However, local microstructures and nanoscale morphological features in CMs affect their electrochemical performances; they require intensive studies to achieve high levels of Na-ion storage performances. Here, pyrolytic carbon nanosheets (PCNs) composed of multitudinous graphitic nanocrystals are prepared from renewable bioresources by heating. In particular, PCN-2800 prepared by heating at 2800 °C has a distinctive sp² carbon bonding nature, crystalline domain size of ≈44.2 Å, and high electrical conductivity of ≈320 S cm^-1 , presenting significantly high rate capability at 600 C (60 A g^-1 ) and stable cycling behaviors over 40 000 cycles as an anode for Na-ion storage. The results of this study show the unusual graphitization behaviors of a char-type carbon precursor and exceptionally high rate and cycling performances of the resulting graphitic material, PCN-2800, even surpassing those of supercapacitors.

Hierarchically Macroporous Graphitic Nanowebs Exhibiting Ultra-fast and Stable Charge Storage Performance

The macro/microstructures of carbon-based electrode materials for supercapacitor applications play a key role in their electrochemical performance. In this study, hierarchically macroporous graphitic nanowebs (HM-GNWs) were prepared from bacterial cellulose by high-temperature heating at 2400 °C. The HM-GNWs were composed of well-developed graphitic nanobuilding blocks with a high aspect ratio, which was entangled as a nanoweb structure. The morphological and microstructural characteristics of the HM-GNWs resulted in remarkable charge storage performance. In particular, the HM-GNWs exhibited very fast charge storage behaviors at scan rates ranging from 5 to 100 V s-1, in which area capacitances ranging from ~ 8.9 to 3.8 mF cm-2 were achieved. In addition, ~ 97% capacitance retention was observed after long-term cycling for more than 1,000,000 cycles.

Designing Pseudocapacitance for Nb2O5/Carbide-Derived Carbon Electrodes and Hybrid Devices

Composite structures for electrochemical energy storage are prepared on the basis of using the high-rate lithium ion insertion properties of Nb₂O₅. The Nb₂O₅ is anchored on reduced graphene oxide (rGO) by hydrothermal synthesis to improve the charge-transfer properties, and by controlling the surface charge, the resulting Nb₂O₅-rGO particles are attached to a high-surface-area carbide-derived carbon scaffold without blocking its exfoliated layers. The electrochemical results are analyzed using a recently published multiscale physics model that provides significant insights regarding charge storage kinetics. In particular, the composite electrode exhibits surface-confined charge storage at potentials of <1.7 V (vs Li/Li⁺), where faradaic processes dominate, and electrical double layer charge storage at potentials of >2.2 V. A hybrid device composed of the composite electrode with activated carbon as the positive electrode demonstrates increased energy density at power densities comparable to an activated carbon device, provided the hybrid device operates in the faradaic potential range.