Vacancy Control in TiNb₂O₇: Implications for Energy Applications

Abstract

Rapid global electrification, including for transportation, has dramatically increased demand for long-lasting and faster-charging batteries. Titanium niobium oxide (TiNb2O7) is one of the most promising anode materials for high-power lithium-ion batteries (LIBs). However, the intrinsic low electronic conductivity of TiNb2O7 is a significant drawback. Herein, an almost 10 orders of magnitude increase in conductivity is achieved via reduction of TiNb2O7 in H2 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, TiNb2O7 converts into a distorted rutile TiNb2O6 structure, which can be reoxidized back into the crystallographic shear phase. In addition, TiNb2O7 can be thermally reduced in an inert atmosphere and reoxidized by CO2 with excellent oxygen exchange capacity. Thus, the TiNb2O7 Wadsley–Roth phase demonstrates outstanding potential for solar-driven thermochemical CO2 splitting at 1400 °C. These findings manifest that controlling defect chemistry paves the way for developing advanced materials for LIBs and solar-driven thermochemical fuel production.

“Fast-Charging” Anode Materials for Lithium-Ion Batteries from Perspective of Ion Diffusion in Crystal Structure

“…In a full battery with LiNi 0.6 Mn 0.2 Co 0.2 O 2 (NMC) as the cathode and TiNb 2 O 7 @C as the anode, a high energy density of 142.8 Wh kg –1 (357 Wh L –1 ) could be obtained, and the capacity retention of more than 80% could be maintained after 500 cycles in a 10 min fast-charging protocol (Figure f) . The electronic conductivity of the material could be considerably enhanced by reducing TiNb 2 O 7 at 900 °C in an atmosphere of H 2 . TiNb 2 O 7 nanofibers with the 1D hollow structure are prepared using coelectrostatic spinning (Figure g), and the reversible capacity is maintained at 210.1 mAh g –1 after 150th at a current of 154.8 mA g –1 , while the reversible capacity reaches 158.4 mAh g –1 after the 900th cycle at a current of 3.87 A g –1 with an excellent capacity retention of 80.6% .…”

Enhanced Energy Storage Performance of Zr-Doped TiNb2O7 Nanospheres Prepared by the Hydrolytic Method

“…Oxygen vacancy is an intrinsic defect which can trigger lattice distortion and electron concentration improvement. 18 Introducing an oxygen vacancy into a lattice leads to the reduction of partial metal atoms, and the existence of Nb 4+ and Ti 3+ can not only increase the electron conductivity 19 but also enlarge the lattice spacing owing to their bigger ionic radii. 20 Therefore, introducing an oxygen vacancy is a practical solution for solving the unpleasing ion transport kinetics of TiNb 2 O 7 .…”

“…In order to relieve the issues suffered by bulk TiNb 2 O 7 , various strategies have been tried, such as introducing an oxygen vacancy, − regulating the morphology, ,− doping with alien ions, − etc. Oxygen vacancy is an intrinsic defect which can trigger lattice distortion and electron concentration improvement .…”

“…In order to relieve the issues suffered by bulk TiNb 2 O 7 , various strategies have been tried, such as introducing an oxygen vacancy, − regulating the morphology, ,− doping with alien ions, − etc. Oxygen vacancy is an intrinsic defect which can trigger lattice distortion and electron concentration improvement . Introducing an oxygen vacancy into a lattice leads to the reduction of partial metal atoms, and the existence of Nb 4+ and Ti 3+ can not only increase the electron conductivity but also enlarge the lattice spacing owing to their bigger ionic radii .…”

Engineering Oxygen Vacancies in IrOx Clusters Supported on Metal–Organic Framework Derived Porous CeO2 for Enhanced Oxygen Evolution in Acidic Media

“…To improve the catalytic performance, increasing the number of accessible active sites and enhancing the intrinsic activity of each active site are two dominant ways to construct an outstanding catalyst . On the one hand, the high surface-to-volume ratio enables metal oxide clusters to display high atomic utilization efficiency and abundantly accessible sites. , On the other hand, the incorporation of oxygen vacancies in metal oxide could regulate the electronic structure and optimize the intrinsic activity. − Meanwhile, doping heteroatoms (such as N, P, S, F, and Cl) could trigger a lack of long-range crystals and generate oxygen vacancies . Notably, oxygen vacancies in metal oxides can lower the O 2p band and Fermi level as well as modulate the binding energy between metal and oxygen bonds, leading to optimization of the free energy barrier and improvement in OER performance. ,,− Against this backdrop, tuning the oxygen vacancies in metal oxide clusters could be an effective strategy integrating these two strategies for constructing a high-performance OER electrocatalyst, but it remains challenging.…”