Operando calorimetry informs the origin of rapid rate performance in microwave-prepared TiNb 2 O 7 electrodes
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Baek, Sun Woong↗
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Vacancy Control in TiNb 2 O 7 : Implications for Energy Applications
Rapid global electrification, including for transportation, has dramatically increased demand for long-lasting and faster-charging batteries. Titanium niobium oxide (TiNb 2 O 7 ) is one of the most promising anode materials for high-power lithium-ion batteries (LIBs). However, the intrinsic low electronic conductivity of TiNb 2 O 7 is a significant drawback. Herein, an almost 10 orders of magnitude increase in conductivity is achieved via reduction of TiNb 2 O 7 in H 2 at 900 °C. The observed dramatic increase in electron conductivity upon reduction is unprecedented and opens new possibilities to produce niobium-based conductive materials for next-generation energy storage. Upon extended reduction, TiNb 2 O 7 converts into a distorted rutile TiNb 2 O 6 structure, which can be reoxidized back into the crystallographic shear phase. In addition, TiNb 2 O 7 can be thermally reduced in an inert atmosphere and reoxidized by CO 2 with excellent oxygen exchange capacity. Thus, the TiNb 2 O 7 Wadsley–Roth phase demonstrates outstanding potential for solar-driven thermochemical CO 2 splitting at 1400 °C. In conclusion, these findings manifest that controlling defect chemistry paves the way for developing advanced materials for LIBs and solar-driven thermochemical fuel production.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Crystallographic Insight of Reduced Lattice Volume Expansion in Mesoporous Cu 2+ -Doped TiNb 2 O 7 Microspheres during Li + Insertion
TiNb 2 O 7 represents a promising anode material for lithium-ion batteries (LIBs), but its practical applications are currently hampered by the non-negligible volumetric expansion and contraction during the charge/discharge process and the sluggish ion/electron kinetics. Here a combination technique is reported by systematically optimizing the porous and spherical morphology, crystal structure, and surface decoration of mesoporous Cu 2+ -doped TiNb 2 O 7 microspheres to enhance the electrochemical Li + storage performance and stability simultaneously. The Cu 2+ dopants preferentially replace Ti 4+ in crystal lattices, which decreases the Li + diffusion barrier and increases the electronic conductivity, as confirmed by density functional theory (DFT) calculation and demonstrated by diverse electrochemical characterizations. The successful Cu 2+ doping significantly reduces the lattice expansion coefficient from 7.26% to 4.61% after Li + insertion along the b-axis of TiNb 2 O 7 , as visualized from in situ and ex situ XRD analysis. The optimal 5% Cu 2+ -doped TiNb 2 O 7 with surface coating of N-doped carbon exhibits significantly enhanced specific capacity and rate and cyclic performances in both half- and full-cell configurations, demonstrating an excellent electrochemical behavior for fast-charging LIB applications.
36 MATERIALS SCIENCE↗
Mechanistic Insights into the Surface Instabilities of TiNb 2 O 7, a High‐Power Li‐Ion Anode
TiNb 2 O 7 (TNO) is a promising Li-ion battery anode for high-power applications, such as implantable medical devices and heavy-duty equipment. Hailed as being safe due to its elevated operating potential near 1.6 V, TNO has long been assumed to be highly stable in the carbonate-based electrolytes used in Li-ion batteries. Herein, all mechanisms occurring at the surface of both TNO and Nd-doped TNO are identified, and both materials in fact show significant gassing. CO 2 is even released at open circuit conditions, demonstrating the poor chemical stability of the material in the electrolyte even prior to battery operation. Such extreme instability is a critical safety concern. In addition, it was found that Ti dissolves from the surface of TNO particles at low voltage (below 1.4 V vs Li), and in fact deposits on the counter electrode. Ti further inside TNO particles then diffuses to the Ti-poor surface during discharge. Partial carbon-coating as a mitigating measure has also been tested and found to exacerbate these processes. The findings identify novel reactions occurring within TNO, and clearly highlight the need to stabilize the surfaces of TNO in order to prevent such aggressive deterioration at the surface of the particles.
25 ENERGY STORAGE↗
Ionic Liquid–Directed Nanoporous TiNb 2 O 7 Anodes with Superior Performance for Fast–Rechargeable Lithium–Ion Batteries
Nanoporous TiNb 2 O 7 (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 LiNi 0.5 Mn 1.5 O 4 -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. Furthermore, 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.
25 ENERGY STORAGE↗
Operando Analysis of Gas Evolution in TiNb 2 O 7 (TNO)-Based Anodes for Advanced High-Energy Lithium-Ion Batteries under Fast Charging
TiNb 2 O 7 (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. Furthermore, 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 CO 2 , C 2 H 4 , and O 2 . 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 CO 2 and C 2 H 4 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.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Materials Data on TiNb(BiO3)3 by Materials Project
Bi3TiNbO9 crystallizes in the tetragonal I4mm space group. The structure is two-dimensional and consists of two water molecules; two Bi2O3 sheets oriented in the (0, 0, 1) direction; and two TiNbBiO5 sheets oriented in the (0, 0, 1) direction. In each Bi2O3 sheet, there are two inequivalent Bi3+ sites. In the first Bi3+ site, Bi3+ is bonded in a 4-coordinate geometry to four equivalent O2- atoms. All Bi–O bond lengths are 2.14 Å. In the second Bi3+ site, Bi3+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are four shorter (2.46 Å) and four longer (2.61 Å) Bi–O bond lengths. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded to four Bi3+ atoms to form a mixture of distorted edge and corner-sharing OBi4 tetrahedra. In the second O2- site, O2- is bonded in a distorted square co-planar geometry to four equivalent Bi3+ atoms. In each TiNbBiO5 sheet, Ti4+ is bonded to five O2- atoms to form corner-sharing TiO5 square pyramids. There is four shorter (1.84 Å) and one longer (1.93 Å) Ti–O bond length. Nb5+ is bonded in a 4-coordinate geometry to four equivalent O2- atoms. All Nb–O bond lengths are 2.05 Å. Bi3+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are four shorter (2.48 Å) and four longer (2.59 Å) Bi–O bond lengths. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent Nb5+ and two equivalent Bi3+ atoms. In the second O2- site, O2- is bonded in a linear geometry to two equivalent Ti4+ atoms. In the third O2- site, O2- is bonded in a distorted single-bond geometry to one Ti4+ and four equivalent Bi3+ atoms.
36 MATERIALS SCIENCE↗
Materials Data on TiNb(BiO3)3 by Materials Project
Bi3TiNbO9 crystallizes in the monoclinic P2_1 space group. The structure is three-dimensional. Ti4+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Ti–O bond distances ranging from 1.80–2.33 Å. Nb5+ is bonded in a distorted octahedral geometry to six O2- atoms. There are a spread of Nb–O bond distances ranging from 1.88–2.27 Å. There are three inequivalent Bi3+ sites. In the first Bi3+ site, Bi3+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Bi–O bond distances ranging from 2.26–2.61 Å. In the second Bi3+ site, Bi3+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Bi–O bond distances ranging from 2.23–2.67 Å. In the third Bi3+ site, Bi3+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Bi–O bond distances ranging from 2.22–2.67 Å. There are nine inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted single-bond geometry to one Ti4+ and two Bi3+ atoms. In the second O2- site, O2- is bonded in a distorted single-bond geometry to one Nb5+ and two Bi3+ atoms. In the third O2- site, O2- is bonded in a distorted see-saw-like geometry to one Ti4+, one Nb5+, and two equivalent Bi3+ atoms. In the fourth O2- site, O2- is bonded in a 2-coordinate geometry to one Ti4+, one Nb5+, and two equivalent Bi3+ atoms. In the fifth O2- site, O2- is bonded in a 2-coordinate geometry to one Ti4+, one Nb5+, and two equivalent Bi3+ atoms. In the sixth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Ti4+, one Nb5+, and one Bi3+ atom. In the seventh O2- site, O2- is bonded in a 2-coordinate geometry to one Ti4+, one Nb5+, and one Bi3+ atom. In the eighth O2- site, O2- is bonded to four Bi3+ atoms to form a mixture of edge and corner-sharing OBi4 tetrahedra. In the ninth O2- site, O2- is bonded to four Bi3+ atoms to form a mixture of edge and corner-sharing OBi4 tetrahedra.
36 MATERIALS SCIENCE↗
Materials Data on TiNb by Materials Project
NbTi crystallizes in the orthorhombic Cmmm space group. The structure is three-dimensional. Ti is bonded in a distorted body-centered cubic geometry to four equivalent Ti and four equivalent Nb atoms. All Ti–Ti bond lengths are 2.84 Å. All Ti–Nb bond lengths are 2.84 Å. Nb is bonded in a distorted body-centered cubic geometry to four equivalent Ti and four equivalent Nb atoms. All Nb–Nb bond lengths are 2.84 Å.
36 MATERIALS SCIENCE↗
Materials Data on TiNb(BiO3)3 by Materials Project
Bi3TiNbO9 crystallizes in the tetragonal I4mm space group. The structure is three-dimensional. Ti4+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Ti–O bond distances ranging from 1.78–2.30 Å. Nb5+ is bonded to six O2- atoms to form distorted corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles are 15°. There are a spread of Nb–O bond distances ranging from 1.92–2.25 Å. There are three inequivalent Bi3+ sites. In the first Bi3+ site, Bi3+ is bonded in a 4-coordinate geometry to eight O2- atoms. There are four shorter (2.32 Å) and four longer (2.88 Å) Bi–O bond lengths. In the second Bi3+ site, Bi3+ is bonded in a 4-coordinate geometry to eight O2- atoms. There are four shorter (2.30 Å) and four longer (2.90 Å) Bi–O bond lengths. In the third Bi3+ site, Bi3+ is bonded in a 12-coordinate geometry to twelve O2- atoms. There are a spread of Bi–O bond distances ranging from 2.49–3.03 Å. There are six inequivalent O2- sites. In the first O2- site, O2- is bonded in a single-bond geometry to one Ti4+ and four equivalent Bi3+ atoms. In the second O2- site, O2- is bonded in a single-bond geometry to one Nb5+ and four equivalent Bi3+ atoms. In the third O2- site, O2- is bonded in a distorted linear geometry to two equivalent Nb5+ and two equivalent Bi3+ atoms. In the fourth O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent Ti4+ and two equivalent Bi3+ atoms. In the fifth O2- site, O2- is bonded in a 2-coordinate geometry to one Ti4+, one Nb5+, and four equivalent Bi3+ atoms. In the sixth O2- site, O2- is bonded to four Bi3+ atoms to form a mixture of corner and edge-sharing OBi4 tetrahedra.
36 MATERIALS SCIENCE↗
Redox Mechanisms, Structural Changes, and Electrochemistry of the Wadsley–Roth Li x TiNb 2 O 7 Electrode Material
Not Available
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Ionothermally Synthesized Nanoporous Ti 0.95 W 0.05 Nb 2 O 7 : a Novel Anode Material for High-Performance Lithium-Ion Batteries
Although TiNb 2 O 7 is regarded as a fast-rechargeable lithium-ion battery (LIB) anode material, the intrinsic poor electrochemical kinetics of TiNb 2 O 7 still dramatically impedes its development. Herein, an ionothermal synthesis-assisted doping strategy is proposed for the preparation of a new W 6+ -doped TiNb 2 O 7 material (Ti 0.95 W 0.05 Nb 2 O 7 ) with nanoporous structure (denoted as NPTWNO). The improved Li + diffusion coefficient of NPTWNO suggests that the ionic-liquid-templated nanoporous architecture improves the Li+ diffusion kinetics. The density functional theory computational study reveals that the doped W 6+ successfully boosts the electronic conductivity due to the narrowed conduction-valance bandgap resulted from charge redistribution, which is reflected by the electrochemical impedance spectroscopy data. With the simultaneously enhanced Li+ diffusivity and electronic conductivity, NPTWNO achieves fast-rechargeability in LIBs. So this work indicates the potential of ionothermal synthesis-assisted doping strategy on energy storage materials and offers NPTWNO material with promising electrochemical performance.
25 ENERGY STORAGE↗
Titanium Niobium Oxide: From Discovery to Application in Fast-Charging Lithium-Ion Batteries
Lithium-ion batteries are essential for portable technology and are now poised to disrupt a century of combustion-based transportation. The electrification revolution could eliminate our reliance on fossil fuels and enable a clean energy future; advanced batteries would facilitate this transition. However, owing to the demanding performance, cost, and safety requirements, it is challenging to translate new materials from laboratory prototypes to industrial-scale products. This Perspective describes that journey for a new lithium-ion battery anode material, TiNb 2 O 7 (TNO). TNO is intended as an alternative to graphite or Li 4 Ti 5 O 12 with better rate and safety characteristics than the former and higher energy density than the latter. The high capacity of TNO stems from the multielectron redox of Nb 5+ to Nb 3+ , its operating voltage window well above the Li + /Li reduction potential prevents lithium dendrite formation, and its open crystal structure leads to high-power performance. Nevertheless, the creation of a practical TNO anode was nonlinear and nontrivial. Its history is built on 30 years of fundamental science that preceded its application as a battery anode, and its battery development included a nearly 30-year gap. The insights and lessons contained in this Perspective, many of them acquired firsthand, serve two purposes: (i) to unite the disparate studies of TiNb 2 O 7 into a coherent modern understanding relevant to its application as a battery material and (ii) to highlight briefly some of the challenges faced when scaling up a new material that affect TiNb 2 O 7 as well as new electrode candidates more generally.
25 ENERGY STORAGE↗
Creep Property of Intermetallic Dispersive Steels for Nuclear Applications
To meet the materials performance demands of next-generation nuclear and high-temperature energy systems, a new class of intermetallic-dispersive steels (IDS) has been designed through integrated computational thermodynamics and alloy design strategies. The IDS alloys incorporate coherent L1₂ (γ′-Ni₃Al) nanoprecipitates within an Fe–Ni–Cr austenitic matrix, engineered to achieve both high temperature strength and thermodynamic stability while suppressing the formation of detrimental δ-Ni₃Nb and η-Ni₃Ti phases. Initial creep testing of Ti-IDS and TiTa-IDS alloys demonstrates rupture lives comparable to or exceeding those of Inconel 718 and ODS steels, despite being fabricated through conventional ingot metallurgy. Step-load creep tests identified a stress threshold near 300–350 MPa for the onset of tertiary creep, and in-situ neutron diffraction experiments on Ti-IDS revealed clear load partitioning between the matrix and γ′ precipitates: elastic strain is shared by both phases, while plastic strain localizes in the matrix. These results confirm that stable γ′–matrix interfaces play a dominant role in retarding dislocation motion and enhancing creep resistance. In FY26, the program will conduct repeat creep rupture testing of TiTa-IDS at 650 °C/400 MPa, initiate long-term rupture testing of TiNb-IDS, and perform TEM-based microstructural characterization to elucidate dislocation–precipitate interactions and microstructural stability. Collectively, these efforts will establish the mechanistic foundation for next-generation high-temperature structural materials based on the IDS concept.
22 GENERAL STUDIES OF NUCLEAR REACTORS↗