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

A Nonstoichiometric Niobium Oxide/Graphite Composite for Fast-Charge Lithium-Ion Batteries

Electrification of transportation has spurred the development of fast-charge energy storage devices. High-power lithium-ion batteries require electrode materials that can store lithium quickly and reversibly. Herein, the design and construction of a Nb₂ O_5-δ /graphite composite electrode that demonstrates remarkable rate capability and durability are reported. The presence of graphite enables the formation of a dominant Nb₁₂ O₂₉ phase and a minor T-Nb₂ O₅ phase. The high rate capability is attributed to the enhanced electronic conductivity and lower energy barriers for fast lithium diffusion in both Nb₁₂ O₂₉ and T-Nb₂ O₅ , as unraveled by density functional theory calculations. The excellent durability or long cycling life is originated from the coherent redox behavior of Nb ions and high reversibility of lithium intercalation/deintercalation, as revealed by operando X-ray absorption spectroscopy analysis. When tested in a half-cell at high cycling rates, the composite electrode delivers a specific capability of 120 mAh g^-1 at 80 C and retains over 150 mAh g^-1 after 2000 cycles at 30 C, implying that it is a highly promising anode material for fast-charging lithium-ion batteries.

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.

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.

Carboxyl functionalized carbon incorporation of stacked ultrathin NiO nanosheets: topological construction and superior lithium storage

Two-dimensional (2D) nanostructure engineering and surface modification with functional groups are of great importance to anode materials for rechargeable lithium-ion batteries. Herein, stacked NiO nanosheets@carbon (denoted as NiO@C) and 3 nm-ultrathin NiO nanosheets@functionalized carbon with surface functional groups NO3-, CO32-, OH-, and COOH- (denoted as NiO@FC) were prepared via a facile one-pot reaction and topotactic conversion. Specifically, NiO@FC exhibits excellent lithium storage performance: the capacity of NiO@FC is 489.2 mA h g-1, higher than that of NiO@C (1018.7 mA h g-1 at 0.2 A g-1), and maintains a capacity of 1133 mA h g-1 after 800 cycles, which exceed that of all previously reported NiO anodes. The enhanced lithium storage performance is attributed to the sufficient void space, which offers buffer space for volume change and speeds up the diffusion of Li+ ions. In addition, the surface functional groups were proved to not only hinder the agglomeration of nanosheets but also further donate active sites and improve storage capacity. These advantageous features achieved by designing such a stacked structure with functionalized carbon modification provide a promising strategy for the preparation of high-performance anode materials and other 2D functional materials.

A free-standing, flexible PEDOT:PSS film and its nanocomposites with graphene nanoplatelets as electrodes for quasi-solid-state supercapacitors

Research and development on all-solid-state, flexible supercapacitors is the prime concern of the scientific community these days due to their various advantages including their easy transportability, miniaturization, and compactness in different appliances. We report the novel configuration of all-solid symmetrical supercapacitors employing free-standing, flexible films of poly(3,4-ethylenedioxythiophene) poly(styrene sulfonate) (PEDOT:PSS) and its nanocomposite electrodes with graphene nanoplatelets (GNPs), separated by ionic liquid (IL) (1-ethyl 3-methylimidazolium trifluoromethanesulfonate (EMITf))-based gel polymer electrolyte (GPE) films. The free-standing and flexible form of PEDOT:PSS/GNP nanocomposite films have been prepared via simple mixing of the two counterparts. Scanning electron microscopy, x-ray diffraction, Raman analysis, and thermal and mechanical characterizations have been performed to ascertain the suitability of pristine and nanocomposite PEDOT:PSS films as potential supercapacitor electrodes. The GPE film, comprising of a solution of NH₄CF₃SO₃ (NH₄-triflate or NH₄Tf) in IL, entrapped in poly(vinylidine fluoride-co-hexafluoropropylene) (PVdF-HFP), is a promising electrolyte due to its high ionic conductivity and sufficient electrochemical stability window. The supercapacitor with a PEDOT:PSS nanocomposite containing ∼3.8 wt.% of GNP has been found to give an optimum specific capacitance of ∼106 F g^-1 (evaluated from electrochemical impedance spectroscopy), and specific energy and power of ∼6.95 Wh kg^-1 and 2.58 kW kg^-1, respectively (evaluated from galvanostatic charge-discharge). More importantly, the capacitors demonstrate stable performance for more than 2000 charge-discharge cycles, with only ∼10% initial fading in capacitance. Interestingly, the PEDOT:PSS/GNP nanocomposite-based solid-state supercapacitors with the IL-incorporated GPE have shown comparable (even better) performance than other reported PEDOT:PSS-based supercapacitors.