TiNb2O7 Research Articles

Superimposed Effect of La Doping and Structural Engineering to Achieve Oxygen-Deficient TiNb2O7 for Ultrafast Li-Ion Storage.

TiNb2O7 (TNO) is a competitive candidate of a fast-charging anode due to its high specific capacity. However, the insulator nature seriously hinders its rate performance. Herein, the La3+-doped mesoporous TiNb2O7 materials (La-M-TNO) were first synthesized via a facile one-step solvothermal method with the assistance of polyvinyl pyrrolidone (PVP). The synergic effect of La3+ doping and the mesoporous structure enables a dual improvement on the electronic conductivity and ionic diffusion coefficient, which delivers an impressive specific capacity of 213 mAh g-1 at 30 C. The capacity retention (@30C/@1C) increases from 33 to 53 and 74% for TNO, M-TNO, and La-M-TNO (0.03), respectively, demonstrating a step-by-step improvement of rate performance by making porous structures and intrinsic conductivity enhancement. DFT calculations verify that the enhancement in electronic conductivity due to La3+ doping and oxygen vacancy, which induce localized energy levels via slight hybridization of O 2p, Ti 3d, and Nb 4d orbits. Meanwhile, the GITT result indicates that PVP-induced self-assembly of TNO accelerates the lithium ion diffusion rate by shortening the Li+ diffusion path. This work verifies the effectiveness of the porous structure and highlights the significance of electronic conductivity to rate performance, especially at >30C. It provides a general approach to low-conductivity electrode materials for fast Li-ion storage.

Engineering a TiNb2O7-Based Electrocatalyst on a Flexible Self-Supporting Sulfur Cathode for Promoting Li-S Battery Performance.

Lithium-sulfur (Li-S) batteries are considered a prospective energy storage system because of their high theoretical specific capacity and high energy density, whereas Li-S batteries still face many serious challenges on the road to commercialization, including the shuttle effect of lithium polysulfides (LiPSs), their insulating nature, the volume change of the active materials during the charge-discharge process, and the tardy sulfur redox kinetics. In this work, double transition metal oxide TiNb2O7 (TNO) nanometer particles are tactfully deposited on the surface of an activated carbon cloth (ACC), activating the surface through a hydrothermal reaction and high-temperature calcination and finally forming the flexible self-supporting architecture as an effective catalyst for sulfur conversion reaction. It has been found that ACC@TNO possesses many catalytic activity sites, which can inhibit the shuttle effect of LiPSs and increase the Coulombic efficiency by boosting the redox reaction kinetics of LiPS transformation reaction. As a consequence, the ACC@TNO/S cathode exhibits an impressive electrochemical performance, including a high initial discharge capacity of 885 mAh g-1 at a high rate of 1 C, a high discharge specific capacity of 825 mAh g-1 after 200 cycles with a prominent capacity retention rate of 93%, and a small decay rate of 0.034% per cycle. Although TNO is extensively used in the fields of lithium ion batteries and other rechargeable batteries, it is first introduced as sulfur host materials to boost the redox reaction kinetics of the LiPS transformation reaction and increase the electrochemical performance of Li-S batteries. Therefore, studies of the synergistic effect on the chemical absorption and catalytic conversion effect of TNO for LiPSs of Li-S batteries provide a good strategy for boosting further the comprehensive electrochemical performances of Li-S batteries.

Synchronous Manipulation of Ion and Electron Transfer in Wadsley-Roth Phase Ti-Nb Oxides for Fast-Charging Lithium-Ion Batteries.

Implementing fast‐charging lithium‐ion batteries (LIBs) is severely hindered by the issues of Li plating and poor rate capability for conventional graphite anode. Wadsley–Roth phase TiNb2O7 is regarded as a promising anode candidate to satisfy the requirements of fast‐charging LIBs. However, the unsatisfactory electrochemical kinetics resulting from sluggish ion and electron transfer still limit its wide applications. Herein, an effective strategy is proposed to synchronously improve the ion and electron transfer of TiNb2O7 by incorporation of oxygen vacancy and N‐doped graphene matrix (TNO− x @N‐G), which is designed by combination of solution‐combustion and electrostatic self‐assembly approach. Theoretical calculations demonstrate that Li+ intercalation gives rise to the semi‐metallic characteristics of lithiated phases (Li y TNO− x ), leading to the self‐accelerated electron transport. Moreover, in situ X‐ray diffraction and Raman measurements reveal the highly reversible structural evolution of the TNO− x @N‐G during cycling. Consequently, the TNO− x @N‐G delivers a higher reversible capacity of 199.0 mAh g−1 and a higher capacity retention of 86.5% than those of pristine TNO (155.8 mAh g−1, 59.4%) at 10 C after 2000 cycles. Importantly, various electrochemical devices including lithium‐ion full battery and hybrid lithium‐ion capacitor by using the TNO− x @N‐G anode exhibit excellent rate capability and cycling stability, verifying its potential in practical applications.

Facile Construction of Hierarchical TiNb2O7/rGO Nanoflower With Robust Charge Storage Properties for Li Ion Batteries via an Esterification Reaction

TiNb2O7 (TNO) compound has been pursued tremendously due to its high theoretical capacity, high potential, and excellent cycle stability. Unfortunately, an intrinsic low electronic and ionic conductivity feature has restricted its broad applications in electrochemical energy storage fields. Two-dimensional (2D) nanostructures can effectively shorten Li-ion transport path and enhance charge transfer. Here, hierarchical structure TNO was constructed by using ethanol and acetic acid as particularly important organic chemicals of basic raw materials via a simple solvothermal reaction. Ethanol was found to play a critical role in the formation of 2D sheet structure. Meantime, reduced graphene oxide nanosheets can effectively improve electronic conductivity. As-obtained TiNb2O7 were wrapped further by graphene oxide nanosheets through a flocculation process. Their unique structure is beneficial to the final electrochemical performance. This study not only provides a general approach for the design of novel 2D nanomaterials wrapped by graphene because of the advantage of esterification reaction and flocculation reaction, but also improves the electronic and ionic conductivity simultaneously.

Kinetics modulation of titanium niobium oxide via hierarchical MXene coating for high-rate and high-energy density lithium-ion half/full batteries

Titanium niobium oxide has great potential in fast charging and discharging due to the high capacity at large rate. But its poor capacity retention rate seriously restricts the further development. MXene, a two-dimensional transition metal carbide with high conductivity, was adopted to complex with TiNb2O7 (TNO) to improve the electrochemical performance. TNO coated with MXene exhibits better conductivity and limited volume expansion, which benefits the capacity and stability of TNO in the cycle process. The capacity of TNO@MXene remains 153 mAh g−1 after 2000 cycles at 10 C, and the capacity retention rate is 81.4%. The capacity of TNO@MXene can reach 145 mAh g−1 after 5000 cycles at 20 C, and the capacity retention rate is 77.1%. The full battery was assembled using commercial NCM811 as the cathode material, and its energy density was 241.7 Wh kg−1, further verifying its potential application.

Operando Analysis of Gas Evolution in TiNb2O7 (TNO)-Based Anodes for Advanced High-Energy Lithium-Ion Batteries under Fast Charging.

TiNb2O7 (TNO) is regarded as one of the promising next-generation anode materials for lithium-ion batteries (LIBs) due to its high rate capabilities, higher theoretical capacity, and higher lithiation voltage. This enables the cycling of TNO-based anodes under extreme fast charging (XFC) conditions with a minimal risk of lithium plating compared to that of graphite anodes. Here, the gas evolution in real time with TNO-based pouch cells is first reported via operando mass spectrometry. The main gases are identified to be CO2, C2H4, and O2. A solid-electrolyte interphase is detected on TNO, which continues evolving, forming, and dissolving with the lithiation and delithiation of TNO. The gas evolution can be significantly reduced when a protective coating is applied on the TNO particles, reducing the CO2 and C2H4 evolution by ∼2 and 5 times, respectively, at 0.1C in a half-cell configuration. The reduction on gas generation in full cells is even more pronounced. The surface coating also enables 20% improvement in capacity under XFC conditions.

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.

Doping with W6+ ions enhances the performance of TiNb2O7 as an anode material for lithium-ion batteries

Monoclinic TiNb2O7 (TNO) has recently been reported as a promising anode candidate for next-generation high-energy–density lithium-ion batteries (LIBs). Unfortunately, poor electronic and ionic conductivities have limited its practical application. In this study, we prepared selectively W6+-doped TNO to overcome these drawbacks. We demonstrate herein the effect of site-selective substitution on the electrochemical performance of TNO after selectively doping its Ti4+ and Nb5+ sites with W6+ ions. The W6+ ions were incorporated into the TNO lattice without dramatically altering the lattice parameters. The ionic substitution of both Ti4+ and Nb5+ ions with W6+ ions in TNO improved the electronic conductivity because of partial reduction of the Ti4+ and Nb5+ ions as a result of charge compensation. Compared with the Nb-substituted TNO (i.e., the TNO derivative in which some of the Nb5+ ions had been replaced by W6+ ions), the Ti-substituted TNO displayed superior transfer properties, presumably because of its lower effective mass. As a result, the Ti-substituted TNO had the highest energy storage performance with its reversible capacity reaching 156.2 mA h/g, even at a rate of 20 C. After 500 repetitive cycles at 6 C, 85.5% of the capacity was retained without significant capacity fading.

Effects of Hybrid Solid Electrolyte on Internal Resistance of TiNb2O7/LiNi0.5Co0.3 Mn0.2O2 Cells

Lithium-ion batteries have been required to enhance power density, high and low temperature performance, energy density, and safety due to electrification of various mobilities. We have developed hybrid solid electrolytes consisting of lithium-ion conducting solid particles and a gel polymer or liquid electrolyte as candidate to respond to these demands [1]. Our previous study revealed that hybrid solid electrolytes in the cell reduce the internal resistance, particularly at low temperatures. Moreover, we proposed the mechanism of the resistance reduction, which the lithium ion transference number was increased by attracting the cyclic carbonates such as PC and PF6 - anion on the surface of Lithium-ion conducting solid particles [2]. In this study, we have investigated the effect of hybrid electrolytes on the internal resistance of TiNb2O7(TNO)-based high-power lithium ion batteries.We prepared 1Ah TNO/LiNi0.5Co0.3Mn0.2O2 (NCM) pouch cells with hybrid electrolytes consisting of lithium-ion conducting solid electrolyte wetted by PF6-based liquid electrolyte. The solid electrolyte layer was formed on cathode as shown in Fig.1. NASICON-type Li1.2Zr1.9Ca0.1(PO4)3 (LZCP) was used as a lithium-ion conducting solid electrolyte because of its wide potential window, high chemical stability, and relatively low cost of raw materials. We compared electrochemical properties of the LZCP-based hybrid electrolytes cell to that of the liquid electrolyte cell and the Al2O3 (non-ion conductivity ceramic)-based hybrid electrolytes cell. The particle size and the film thickness of layer for Al2O3 were comparable to those for LZCP.Figure 2 shows DC resistance (DCR) of the three types of cells at various state of charge (SOC) conditions for 10 sec charging at 25℃ and -20℃. The DCR of LZCP-based hybrid electrolyte cell is smaller than that of liquid electrolyte in the whole SOC range at 25℃. At low temperature, the difference of DCR of two cells becomes remarkable, and DCR of LZCP-based hybrid electrolyte cell is about 20% lower than that of liquid electrolyte cell at -20℃. On the other hand, the DCR of the Al2O3-based hybrid electrolyte cell was a little higher than that of liquid electrolyte cell in the all temperature range. Therefore, the solid electrolyte contributes to the reduction of internal resistance especially at low temperatures.Typical AC-impedance spectra of the cells with the three kinds of electrolytes at 25℃ and -20℃ are shown in Figure 3. The impedance spectra exhibit a depressed semicircle, which can be interpreted as resulting from the interface resistance such as the charge-transfer process on the electrodes. The semicircle of the hybrid electrolytes cell is significantly smaller than that of liquid electrolyte cell and Al2O3-based hybrid electrolyte cell especially at -20℃. It is considered that the concentration overpotential near the cathode mainly decreased due to the increase of lithium ion transference numbers by using solid electrolyte to promote the supply of lithium ion to the electrode surface. On the other hand, the LZCP-based hybrid electrolytes cell and the Al2O3-based hybrid electrolyte cell have a larger bulk resistance than that of the liquid electrolytes cell at 25℃. This bulk resistance is mainly ascribable to lithium ion conductive resistance in liquid electrolyte. The lithium ion conductive resistance increased because the porosity was decreased by inserting of solid electrolyte layer or Al2O3 layer between electrodes.These results reveal that LZCP particles in the hybrid solid electrolyte reduces the charge transfer resistance between the electrolyte and active materials rather than the bulk ionic resistance in the electrolyte. The charge transfer resistance rapidly increases compared to the bulk ionic resistance with decreasing temperature. Therefore, it is considered that the DCR of LZCP-based hybrid electrolyte cell decreases especially at low temperatures. In this report, the detail of this hybrid electrolytes cell performance and the mechanism of resistance decreasing will be discussed.[1] K. Yoshima, Y. Harada and N. Takami, J. Power Sources, 302,283-290(2016).[2] T. Kusama, K. Yoshima, T. Sugizaki, K. Hoshina, T. Sasakawa, Y. Harada, and N. Takami, No A02-0172, The Electrochemical Society Meeting MA2019-01, Dallas, TX, May 27 (2019) Figure 1

Operation Mechanism in Hybrid Mg-Li Batteries with TiNb2O7 Allowing Stable High-Rate Cycling.

We studied the structural evolution and cycling behavior of TiNb2O7 (TNO) as a cathode in a nonaqueous hybrid dual-salt Mg-Li battery. A very high fraction of pseudocapacitive contribution to the overall specific capacity makes the material suitable for ultrafast operation in a hybrid battery, composed of a Mg-metal anode, and a dual-salt APC-LiCl electrolyte with Li and Mg cations. Theoretical calculations show that Li intercalation is predominant over Mg intercalation into the TNO in a dual-salt electrolyte with Mg2+ and Li+, while experimentally up to 20% Mg cointercalation was observed after battery discharge. In hybrid Mg-Li batteries, TNO shows capacities which are about 40 mA h g-1 lower than in single-ion Li batteries at current densities of up to 1.2 A g-1. This is likely due to a partial Mg cointercalation or/and location of Li cations on alternative crystallographic sites in the TNO structure in comparison to the Li-intercalation process in Li batteries. Generally, hybrid Mg-Li cells show a markedly superior applicability for a very prolonged operation (above 1000 cycles) with 100% Coulombic efficiency and a capacity retention higher than 95% in comparison to conventional Li batteries with TNO after being cycled either under a low (7.75 mA g-1) or high (1.55 A g-1) current density. The better long-term behavior of the hybrid Mg-Li batteries with TNO is especially pronounced at 60 °C. The reasons for this are an appropriate cathode electrolyte interface containing MgCl2 species and a superior performance of the Mg anode in APC-LiCl electrolytes with a dendrite-free, fast Mg deposition/stripping. This stable interface stands in contrast to the anode electrolyte interface in Li batteries with a Li anode in conventional carbonate-containing electrolytes, which is prone to dendrite formation, thus leading to a battery shortcut.

Titanium Niobium Oxide Anode-Based Lithium-Ion Batteries for 10 Minutes Fast-Charging Applications

Lithium-ion batteries (LIBs) have attracted considerable attention as environment friendly power sources for portable electronic devices. Although graphite (LiC6: 372 mAh g-1) has been used as the anode material for Li-ion batteries, the search for high rate anode materials has been actively pursued to meet the fast-growing requirements of high-power Li-ion batteries. As a promising anode candidate, TiNb2O7 (TNO) anode material with a nanoporous nature was prepared by a facile sol-gel approach. To satisfy the requirements of practical application, the hundred-gram scale synthesis of carbon coated TNO (TNO@C) have been achieved with low-cost reactants. The full cells based on high loading TNO@C anode (>13 mg/cm2) and matched LiNi0.6Mn0.2Co0.2O2 (NMC622, D50=10µm, Targray) cathode were evaluated for the 10 mins fast-charging application, delivering a high energy density of 142.8 Wh/kg (357 Wh/L) and a good energy density retention over 80% after 500 cycles.

TiNb2O7 and VNb9O25 of ReO3 Type in Hybrid Mg–Li Batteries: Electrochemical and Interfacial Insights

As one of the beyond-lithium battery concepts, hybrid metal-ion batteries have aroused growing interest. Here, TiNb2O7 (TNO) and VNb9O25 (VNO) materials were prepared using a high-temperature solid...

Interstitial and substitutional V5+-doped TiNb2O7 microspheres: A novel doping way to achieve high-performance electrodes

Dual improvement on electronic conductivity and ionic conductivity of TiNb2O7 (TNO) is of great significance for realizing high-performance lithium-ion batteries. In this work, the V5+-doped TNO microspheres (denoted as Vx-TNOMs, x = 0, 0.015, 0.030 and 0.045) were synthesized via a simple solvothermal approach. X-ray diffraction coupled with Rietveld refinements and Raman spectra analyses verified that V5+ not simply possessed substitution doping mode but also inserted into the interstices of the TNOMs lattice. The density functional theory (DFT) calculations indicated that the improved electronic conductivity could originate from the formation of impurity bands after the V5+ doping. Meanwhile, the climbing image-nudged elastic band (CI-NEB) demonstrated that a TNOMs framework with faster ion transport pathways is achieved by the V5+ doping. Served as anode material of lithium-ion batteries, the V0.030-TNOMs electrode presents an impressive discharge capacity of 163.5 mAh/g at 10 C and long cycle life up to 2000 cycles with a capacity fading of merely 0.014% per cycle. Furthermore, the full battery employing V0.030-TNOMs as an anode and commercial LiCoO2 as a cathode exhibits superior electrochemical performances with promising application prospect. Our present study sheds new light on constructing high-performance electrodes for electrochemical energy storage.

Ionic Liquid-Directed Nanoporous TiNb2 O7 Anodes with Superior Performance for Fast-Rechargeable Lithium-Ion Batteries.

Nanoporous TiNb2 O7 (NPTNO) material is synthesized by a sol-gel method with an ionic liquid (IL) as the nanoporous structure directing template. NPTNO exhibits a high reversible capacity of 210 mAh g-1 even at the charging rate of 50 C and an excellent cyclability of half-cell capacity retention of 74% for 1000 cycles at 5 C and LiNi0.5 Mn1.5 O4 -coupled full-cell capacity retentions of 81% and 87% for 1000 cycles at 1 C and 2 C, respectively. The studies of the 1000 cycled NPTNO electrode illustrate that the IL-directed mesoporous structure can enhance the cyclability of NPTNO cells due to the alleviation of repetitive mechanical stress and volume fluctuation induced by the repetitive Li+ insertion-extraction processes. The measured Li+ diffusion coefficients from the galvanostatic intermittent titration technique suggest that the IL-templating strategy indeed ensures the fast rechargeability of NPTNO cells based on the fast Li+ diffusion kinetics. Benefitting from the nanoporous structure, NPTNO with unhindered Li+ diffusion pathways achieves a superior rate capability in the titanium-based oxide materials and the best full-cell cyclability in the TNO materials. Therefore, the templating potential of IL is demonstrated, and the superb electrochemical performance establishes the IL-directed NPTNO as a promising anode candidate for fast-rechargeable LIBs.

Systematic Material Study Reveals TiNb2 O7 as a Model Wide-Bandgap Photoanode Material for Solar Water Splitting.

This work reveals that photoanodes based on TiNb2 O7 (TNO) powder show remarkable water-oxidation properties including nearly ideal charge-transfer and charge-injection efficiencies. Furthermore, using a simplified photoanode construction and carefully surveying the structural and morphological characteristics of oriented and polycrystalline thin films and powder-based samples revealed that the water-splitting kinetics of TNO is negligibly effected by surface morphology; instead, internal grain boundaries likely play a driving role. The current powder-based TNO photoanodes exhibit ideal water-oxidation kinetics and oxidize water at minimal applied biases under illumination; consequently, TNO exhibits an early onset photocurrent voltage (0.4 V vs. RHE) that rivals that of other state-of-the-art photoanode materials.

A Long Cycle-Life High-Voltage Spinel Lithium-Ion Battery Electrode Achieved by Site-Selective Doping.

Spinel LiNi0.5 Mn1.5 O4 (LNMO) is a promising cathode candidate for the next-generation high energy-density lithium-ion batteries (LIBs). Unfortunately, the application of LNMO is hindered by its poor cycle stability. Now, site-selectively doped LNMO electrode is prepared with exceptional durability. In this work, Mg is selectively doped onto both tetrahedral (8a) and octahedral (16c) sites in the Fd m structure. This site-selective doping not only suppresses unfavorable two-phase reactions and stabilizes the LNMO structure against structural deformation, but also mitigates the dissolution of Mn during cycling. Mg-doped LNMOs exhibit extraordinarily stable electrochemical performance in both half-cells and prototype full-batteries with novel TiNb2 O7 counter-electrodes. This work pioneers an atomic-doping engineering strategy for electrode materials that could be extended to other energy materials to create high-performance devices.

TiNb 2 O 7 microsphere anchored by polydopamine‐modified graphene oxide as a superior anode material in lithium‐ion batteries

TiNb2O7 (TNO) is considered a promising anode material for lithium-ion batteries. High contact and homogeneity of the composite fabricated by TNO powder and conductive materials with different density are significant to improve the poor electric conductivity of TNO microspheres. In this study, we introduce graphene oxide (GO) to synthesize a composite material with TNO microspheres. Moreover, a polydopamine (PDA) coating technique is applied to achieve uniform distribution and high contact between TNO and GO materials. The -OH catechol groups in the PDA have a strong adhesion ability to inorganic surfaces. After a simple sonication process, the hybrid material is well-fabricated, where TNO microspheres are attached along the surface of the PDA-coated GO (PGO). The TNO/PGO composite shows remarkably enhanced performances such as cycling stability (202.7 mAh g−1 over 300 cycles at 1C) and rate capability (136.5 mAh g−1 over 1000 cycles at 5C). The formation of a high conductive network among TNO microspheres mainly enhances those electrochemical performances, and the PDA layer is a key factor in obtaining a homogeneous GO composite through its high adhesive ability and hydrophilicity.

TiNb2O7 nano-particle decorated carbon cloth as flexible self-support anode material in lithium-ion batteries

The activated carbon cloth (ACC@TNO) with flexible self-support structure, which is decorated by TiNb2O7 (TNO) nanoparticle, is successfully obtained through hydrothermal reaction and calcination process in high temperature, and is used as the binder-free anode material of lithium ion batteries (LIBs). The morphology characteristic, pore structure properties and the phase structure of the ACC@TNO composites are detailedly studied by the scanning electron microscopy (SEM), Brunauer–Emmett–Teller adsorption/desorption measurement (BET) and X-ray diffraction (XRD). Meanwhile, the electrochemical properties of ACC@TNO composite are further tested by cyclic voltammetry and galvanostatic charge-discharge tests. As a result, the LIBs with ACC@TNO as anode material shows an initial discharge capacity of 356 mAh g−1 and an initial coulombic efficiency (ICE) of 87% at the current density of 0.5 C with the voltage window of 1.0–3.0 V. It also has been found that the reversible capacity can still keep as 290 mAh g−1 with the capacity retention of 81% after 500 cycles. Besides, when the cutoff voltage range is set to 0.01–3.0 V, the reversible capacity can reach 340 mAh g−1. Apparently, this work is of great significance for the exploration of the new anode materials with high performance and long cyclic life in next-generation LIBs.

Temperature dependent dielectric properties and AC conductivity studies on titanium niobium oxide (TiNb2O7) thin films

The dielectric properties of TiNb2O7 (TNO) thin films are studied in Metal-Insulator-Metal configuration (Au/TiNb2O7/Pt) devices. The temperature dependence of the dielectric dispersion and the AC conductivity behavior is strongly dependent on TNO thin film thickness. Low thickness (∼236 nm) films shows considerably less variation with temperatures than their thicker counterparts (∼480 nm). These behaviors are explained on physical basis – nearly constant loss (NCL) and Jonscher's Universal Dielectric Response (UDR). The TNO thin films show large dielectric constant (∼59–73) and moderate dielectric loss (∼0.07–0.11). The AC conductivity values of the thin films lie in the range of about (10−8 to 10−9) at 10 kHz. The thicker films show DC conductivity values which are thermally activated with an activation energy of about 0.44 eV. This is slightly higher (about 0.1 eV) than ωp in Jonscher's UDR response and this discrepancy is explained on the basis of mixed ionic electronic conduction in TNO thin films. The possible role of growth morphology in the dielectric response is also briefly mentioned.

Oxygen vacancy regulated TiNb2O7 compound with enhanced electrochemical performance used as anode material in Li-ion batteries

TiNb2O7 compound with extra oxygen vacancies is synthesized through unique supercritical fluid process. When fabricated as anode for lithium ion batteries, such TiNb2O7 anode exhibits high initial discharge capacity of 231 mA h g−1 at a current density of 100 mA g−1, and maintains capacity of 169 mA h g−1 even after 250 cycles in the voltage window of 1.0–3.0 V. The excellent electrochemical performance is mainly attributed to the existence of abundant oxygen vacancies in TiNb2O7 compound, which greatly increases the electronic conductivity and lithium ion diffusion coefficient. Furthermore, the contribution of pseudocapacitive effect to the superior electrochemical performance of as-prepared Ti Nb2O7 is investigated systematically. All in all, it demonstrates that the supercritical fluid is a facile and effective media to create oxygen vacancies in TiNb2O7, and the TiNb2O7 compound with introduced oxygen vacancies would be a promising candidate for anode materials in high-power lithium ion batteries. This work provides a fresh strategy and route to explore novel multicomponent oxide materials with enhanced electrochemical properties for energy storage.