Electrode, secondary battery, battery pack, and vehicle

1. An electrode comprising an active material-containing layer which comprises an active material, wherein

the active material comprises a plurality of primary particles comprising a niobium-titanium composite oxide,

an average crystallite diameter of the plurality of primary particles is 90 nm or more,

an average particle size (D50) of the plurality of primary particles is in a range of 0.1 μm to 5 μm, which is based on a particle size distribution chart according to a laser diffraction scattering method,

an average value (FU ave ) of a roughness shape coefficient (FU) according to Formula (1) below is less than 0.70 in 100 primary particles among the plurality of primary particles, and

each of the 100 primary particles has a particle size of 0.2 times to 4 times the average particle size (D50),

[

Formula

⁢

⁢

1

]

FU

=

f

f

c

=

4

⁢

π

⁢

⁢

a

ℓ

⁢

2

(

1

)

where l represents an outer circumference length of a projected cross-section of each of the 100 primary particles, and a represents a cross-sectional area in the projected cross-section of each of the 100 primary particles.

2. The electrode according to claim 1 , wherein the average particle size (D50) is in a range of 0.5 μm to 3.0 μm.

3. The electrode according to claim 1 , wherein a content of the niobium-titanium composite oxide comprised in the active material is in a range of 75% by weight to 100% by weight.

4. The electrode according to claim 1 , wherein an electrode density is in a range of 2.20 g/cm 3 to 2.70 g/cm 3 .

5. The electrode according to claim 1 , wherein the niobium-titanium composite oxide is a compound represented by a first general formula or a second general formula,

the first general formula is Li x Ti 1-y M1 y Nb 2-z M2 z O 7+δ , where M1 is at least one selected from the group consisting of Zr, Si, and Sn, M2 is at least one selected from the group consisting of V, Ta, Bi, K, Ca, B, Co, Fe, Mn, Ni, Si, P, and Mo,

the second general formula is Ti 1-y M3 y+z Nb 2-z O 7−δ , where M3 is at least one selected from Mg, Fe, Ni, Co, W, Ta, and Mo,

where x satisfies 0≤x≤5, y satisfies 0≤y<1, z satisfies 0≤z<2, and δ satisfies −0.3≤δ≤0.3.

6. The electrode according to claim 1 , wherein the niobium-titanium composite oxide comprises at least one selected from the group consisting of Nb 2 TiO 7 , Nb 2 Ti 2 O 9 , Nb 10 Ti 2 O 29 , N 14 TiO 37 , and Nb 24 TiO 62 .

7. The electrode according to claim 1 , wherein the average value (FU ave ) is in a range of 0.40 to 0.69.

8. The electrode according to claim 1 , wherein the average value (FU ave ) is in a range of 0.50 to 0.65.

9. A negative electrode, which is the electrode according to claim 1 .

10. A secondary battery comprising:

a positive electrode;

a negative electrode; and

an electrolyte, wherein

the negative electrode is the electrode according to claim 1 .

11. A battery pack comprising the secondary battery according to claim 10 .

12. The battery pack according to claim 11 , further comprising:

an external power distribution terminal; and

a protective circuit.

13. The battery pack according to claim 11 , comprising plural of the secondary battery, wherein the secondary batteries are electrically connected in series, in parallel, or in a combination of in series and in parallel.

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

15. The vehicle according to claim 14 , which comprises a mechanism configured to convert kinetic energy of the vehicle into regenerative energy.