Electrode, secondary battery, battery pack and vehicle

1. An electrode comprising:

a current collector; and

an active material-containing layer which is formed on a surface of the current collector and comprises a plurality of niobium titanium composite oxide particles,

wherein a X-ray diffraction pattern using a Cu-Kα ray source with respect to a surface of the active material-containing layer comprises a peak A with a highest intensity in a range of 2θ=26°±0.2° and a peak B with a highest intensity in a range of 2θ=23.9°±0.2°,

wherein an intensity ratio (Ia/Ib) between an intensity Ia of the peak A and an intensity Ib of the peak B is in a range of 1.80 or more to 2.60 or less, and

wherein the plurality of the niobium titanium composite oxide particles have a major axis oriented towards an in-plane direction of the current collector.

2. The electrode according to claim 1 , wherein

when a cross section of the active material-containing layer along a stacking direction of the current collector and the active material-containing layer is observed by a scanning electron microscope, an average value of ratios (W/H) of bounding rectangles with respect to 200 niobium titanium composite oxide particles is in a range of 0.80 to 1.5,

the 200 niobium titanium composite oxide particles are selected at random from among niobium titanium composite oxide particles each having an area of 0.1 μm 2 to 5 μm 2 the cross section, and

with respect to each of the 200 niobium titanium composite oxide particles, the ratio (W/H) of the bounding rectangle of the niobium titanium composite oxide particle is determined, the bounding rectangle being defined by a maximum height (H) of the niobium titanium composite oxide particle along the stacking direction and a maximum width (W) of the niobium titanium composite oxide particle along an in-plane direction orthogonal to the stacking direction.

3. The electrode according to claim 1 , wherein a tap density of the plurality of the niobium titanium composite oxide particles is in a range of 1.0 g/cm 3 to 1.9 g/cm 3 .

4. The electrode according to claim 1 , wherein an electrode density is in a range of 2.2 g/cm 3 to 3.0 g/cm 3 .

5. The electrode according to claim 1 , wherein the active material-containing layer comprises a carbon material, and

a bulk density of the carbon material is in a range of 0.08 g/cm 3 to 0.15 g/cm 3 .

6. The electrode according to claim 1 , wherein

the niobium titanium composite oxide is a monoclinic niobium titanium composite oxide,

the monoclinic niobium titanium composite oxide is at least one selected from the group consisting of a composite oxide expressed by a general formula, Li x Ti 1−y M1 y Nb 2−z M2 z O 7|δ , and a composite oxide expressed by a general formula, Li x Ti 1−y M3 y+z Nb 2−z O 7−δ ,

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.

7. A secondary battery comprising:

a positive electrode;

a negative electrode; and

an electrolyte,

the negative electrode being the electrode according to claim 1 .

8. A battery pack comprising the secondary battery according to claim 7 .

9. The battery pack according to claim 8 , further comprising:

an external power distribution terminal; and

a protective circuit.

10. The battery pack according to claim 8 , wherein

the battery pack comprises a plurality of the secondary battery, and

the secondary batteries are electrically connected in series, or in parallel, or in series and in parallel in a combined manner.

11. A vehicle comprising the battery pack according to claim 8 .

12. The vehicle according to claim 11 , further comprising a mechanism configured to convert kinetic energy of the vehicle to regenerative energy.

13. The electrode according to claim 1 , wherein the plurality of niobium titanium composite oxide particles has flat shapes.

14. The electrode according to claim 1 , wherein an electrode density is in a range of 2.2 g/cm 3 to 2.9 g/cm 3 .

15. The electrode according to claim 1 , wherein the plurality of niobium titanium composite oxide particles comprise primary particles which contain niobium titanium composite oxide,

wherein an aspect ratio of the primary particles is in a range of 1 or more to less than 4, and

wherein the aspect ratio is represented by L/S where L is an arithmetic mean value of lengths of major axes of the primary particles and S is an arithmetic mean value of lengths of minor axes of the primary particles, each of the minor axes being direction of the niobium titanium composite oxide, each of the major axes being direction of the niobium titanium composite oxide and/or direction of the niobium titanium composite oxide.

16. The electrode according to claim 15 , wherein the aspect ratio of the primary particles is in a range of 1.95 or more to 3 or less.

17. The electrode according to claim 15 , wherein the aspect ratio of the primary particles is in a range of 1.95 or more to 2.07 or less.

18. The electrode according to claim 1 , wherein the intensity ratio (la/lb) is in a range of from 1.80 to 2.2.

19. The electrode according to claim 1 , wherein the intensity ratio (Ia/Ib) is in a range of from 1.91 to 2.55.

20. The electrode according to claim 1 , wherein the intensity ratio (Ia/Ib) is in a range of from 1.91 to 2.23.