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US-12626920-B2 - Niobium-titanium oxide, active material, electrode, secondary battery, battery pack, and vehicle

US12626920B2US 12626920 B2US12626920 B2US 12626920B2US-12626920-B2

Abstract

In general, according to one embodiment, a niobium-titanium oxide is provided. The niobium-titanium oxide satisfies Formulae (1) to (3) below in an L*a*b* color space according to Japanese Industrial Standard JIS Z 8722:2009: 95.0≤ L *≤100  (1) −1.0≤ a *≤1.0  (2) −1.0≤ b *≤6.0  (3).

Inventors

  • Yoshiaki Murata
  • Kakuya UEDA
  • Yasuhiro Harada
  • Kazuki Ise
  • Norio Takami

Assignees

  • KABUSHIKI KAISHA TOSHIBA

Dates

Publication Date
20260512
Application Date
20230216
Priority Date
20220908

Claims (19)

  1. 1 . A niobium-titanium oxide satisfying Formulae (1) to (3) below in an L*a*b* color space according to Japanese Industrial Standard JIS Z 8722:2009; 95.0≤ L*≤ 100.0 (1) −1.0≤ a*≤ 1.0 (2) −1.0≤ b*≤ 6.0 (3).
  2. 2 . The niobium-titanium oxide according to claim 1 , wherein the niobium-titanium oxide is a primary particle containing the niobium-titanium oxide form, the primary particle contains, as an element A, at least one selected from the group consisting of Fe, Cr, W, and Mo, the primary particle includes a surface layer defined as a region having a depth of 20 nm from a surface of the primary particle and a center-of-gravity portion present on an inside of the surface layer, and the primary particle has a gradient in which an amount of the element A increases from the center-of-gravity portion toward the surface layer.
  3. 3 . The niobium-titanium oxide according to claim 2 , wherein in the surface layer, a ratio AA/AM between a content AA of the element A and a total amount AM of niobium atoms and titanium atoms satisfies 0.02≤AA/AM≤0.10, and in the center-of-gravity portion, the ratio AA/AM between the content AA of the element A and the total amount AM of niobium atoms and titanium atoms satisfies 0.001≤AA/AM≤0.01.
  4. 4 . The niobium-titanium oxide according to claim 1 , wherein in thermogravimetric analysis in air, a weight increase of the niobium-titanium oxide in a range of 200° C. to 500° C. is in a range of 100 ppm to 10000 ppm.
  5. 5 . The niobium-titanium oxide according to claim 1 , wherein the niobium-titanium oxide is a primary particle form, the primary particle contains nitrogen atoms, the primary particle includes a surface layer defined as a region having a depth of 20 nm from a surface of the primary particle and a center-of-gravity portion present on an inside of the surface layer, and the primary particle has a gradient in which an amount of nitrogen atoms increases from the center-of-gravity portion toward the surface layer.
  6. 6 . The niobium-titanium oxide according to claim 5 , wherein in the surface layer, a ratio AN/AM between a content AN of nitrogen atoms and a total amount AM of niobium atoms and titanium atoms satisfies 0.01≤AN/AM≤0.3, and in the center-of-gravity portion, the ratio AN/AM between the content AN of nitrogen atoms and the total amount AM of niobium atoms and titanium atoms satisfies 0.0001≤AN/AM≤0.001.
  7. 7 . The niobium-titanium oxide according to claim 1 , comprising a Nb 2 TiO 7 phase as a main phase.
  8. 8 . The niobium-titanium oxide according to claim 2 , wherein, on a surface of the primary particle, an amorphous phase containing niobium and titanium is present with a thickness in a range of 2 nm or less.
  9. 9 . The niobium-titanium oxide according to claim 1 , comprising a monoclinic Nb 2 TiO 7 phase, wherein the monoclinic Nb 2 TiO 7 phase is at least one selected from the group consisting of a composite oxide represented by a general formula Li x Ti 1−y M1 y Nb 2−z M2 z O 7+δ , and a composite oxide represented by a general formula Li x Ti 1−y M 3 y+z Nb 2−z O 7−δ , where the M1 is at least one selected from the group consisting of Zr, Si, and Sn, the M2 is at least one selected from the group consisting of V, Ta, and Bi, and the M3 is at least one selected from the group consisting of Mg, Fe, Ni, Co, W, Ta, and Mo, and the x satisfies 0≤x≤5, the y satisfies 0≤y<1, the z satisfies 0≤z<2, and the δ satisfies −0.3≤δ≤0.3.
  10. 10 . The niobium-titanium oxide according to claim 1 , wherein an amount of adsorbed moisture according to a Karl Fischer method is 800 ppm or less.
  11. 11 . An active material comprising the niobium-titanium oxide according to claim 1 .
  12. 12 . An electrode comprising an active material-containing layer, wherein the active material-containing layer contains the active material according to claim 11 .
  13. 13 . A secondary battery comprising: a positive electrode; a negative electrode; and an electrolyte, wherein the negative electrode is the electrode according to claim 12 .
  14. 14 . A battery pack comprising the secondary battery according to claim 13 .
  15. 15 . The battery pack according to claim 14 , further comprising: an external power distribution terminal; and a protective circuit.
  16. 16 . The battery pack according to claim 14 , comprising a plurality of the secondary battery, wherein the secondary batteries are electrically connected in series, in parallel, or in combination of series and parallel.
  17. 17 . A vehicle comprising the battery pack according to claim 14 .
  18. 18 . The vehicle according to claim 17 , comprising a mechanism configured to convert kinetic energy of the vehicle into regenerative energy.
  19. 19 . The niobium-titanium oxide according to claim 2 , wherein there is no amorphous phase containing niobium and titanium on a surface of the primary particle.

Description

CROSS-REFERENCE TO RELATED APPLICATION This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2022-143283, filed Sep. 8, 2022, the entire contents of which are incorporated herein by reference. FIELD Embodiments described herein relate generally to a niobium-titanium oxide, an active material, an electrode, a secondary battery, a battery pack, and a vehicle. BACKGROUND These days, secondary batteries such as nonaqueous electrolyte secondary batteries such as a lithium ion secondary battery are being actively researched and developed as high energy density batteries. Secondary batteries such as nonaqueous electrolyte secondary batteries are expected as power sources for vehicles such as hybrid electric vehicles and electric vehicles, uninterruptible power supplies for mobile phone base stations, and the like. Hence, the secondary battery is required to be excellent not only in high energy density but also in other performances such as rapid charge-discharge performance and long-term reliability. For example, in a secondary battery capable of rapid charging and discharging, not only is the charging time greatly shortened, but also power performance of a vehicle such as a hybrid electric vehicle can be improved and regenerative energy of power can be efficiently recovered. To enable rapid charging and discharging, it is necessary that electrons and lithium ions be able to rapidly move between the positive electrode and the negative electrode. However, if a battery including a carbon-based negative electrode is repeatedly subjected to rapid charging and discharging, dendrite deposition of metal lithium occurs on the electrode, and there has been a concern of heat generation or ignition due to an internal short circuit. Thus, a battery using a metal composite oxide for a negative electrode instead of a carbonaceous material has been developed. Among such batteries, a battery using a titanium oxide for a negative electrode is capable of stable rapid charging and discharging, and has characteristics of a longer life than in a case where a carbon-based negative electrode is used. However, the titanium oxide has a higher potential with respect to metal lithium than the carbonaceous material, that is, the titanium oxide is nobler. In addition, the titanium oxide has a low capacity per weight. Hence, a battery using a titanium oxide for a negative electrode has a problem of low energy density. For example, the electrode potential of the titanium oxide is about 1.5 V (vs. Li/Li+) with metal lithium as a standard, which is higher (nobler) than the potential of the carbon-based negative electrode. The potential of the titanium oxide is electrochemically restricted because it is caused by an oxidation-reduction reaction between Ti3+ and Ti4+ at the time of electrochemically inserting and extracting lithium. There is also a fact that rapid charging and discharging of lithium ions can be stably performed at a high electrode potential of about 1.5 V (vs. Li/Li+). Therefore, it has so far been difficult to reduce the electrode potential in order to improve the energy density. On the other hand, regarding the capacity per unit weight, the theoretical capacity of titanium dioxide (an anatase structure) is about 165 mAh/g, and the theoretical capacity of a spinel-type lithium-titanium composite oxide such as Li4Ti5O12 is also about 180 mAh/g. On the other hand, the theoretical capacity of a common graphite-based electrode material is 385 mAh/g or more. Thus, the capacity density of the titanium oxide is much lower than that of the carbon-based negative electrode. This is because the crystal structure of the titanium oxide has few sites for inserting lithium, and lithium is easily stabilized in the structure and therefore the substantial capacity is reduced. In view of the above, a new electrode material containing Ti and Nb is being studied. Such a niobium-titanium oxide material is expected to have high charge-discharge capacity. In particular, the composite oxide represented by TiNb2O7 has a high theoretical capacity exceeding 380 mAh/g. Therefore, the niobium-titanium oxide is expected as a high-capacity material to replace Li4Ti5O12. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing a crystal structure of a niobium-titanium oxide Nb2TiO7. FIG. 2 is a schematic diagram showing a case where the crystal structure of FIG. 1 is observed from another direction. FIG. 3 is a plan view schematically showing a particle to be measured in transmission electron microscope (TEM) observation. FIG. 4 is a cross-sectional view schematically showing an example of a secondary battery according to an embodiment. FIG. 5 is an enlarged cross-sectional view of part A of the secondary battery shown in FIG. 4. FIG. 6 is a partially cutaway perspective view schematically showing another example of the secondary battery according to the embodiment. FIG. 7 is an enlarged cross-sectio