Electrode, secondary battery, battery pack, and vehicle
According to one embodiment, an electrode is provided. The electrode includes an active material-containing layer which contains an active material. The active material includes a plurality of primary particles containing a niobium-titanium composite oxide. The average value (FU ave ) of the roughness shape coefficient (FU) according to Formula (1) below is 0.70 or more in 100 primary particles among the plurality of primary particles. [ Formula 1 ] FU = f f c = 4 π a ℓ 2 ( 1 )
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,
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,
an average value (FU ave ) of a roughness shape coefficient (FU) according to Formula (1) below is 0.70 or more 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 an average particle size (D50) determined from a particle size distribution chart of the plurality of primary particles obtained by a laser diffraction scattering method,
[
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 within a range of 0.50 μm to 5 μm.
3. The electrode according to claim 1 , wherein a content of the niobium-titanium composite oxide of the active material is within a range of 75% by weight to 100% by weight.
4. The electrode according to claim 1 , wherein an electrode density is within a range of 2.4 g/cm 3 to 3.0 g/cm 3 .
5. A secondary battery comprising:
a positive electrode;
a negative electrode; and
an electrolyte, wherein
the negative electrode is the electrode according to claim 1 .
6. A battery pack comprising the secondary battery according to claim 5 .
7. The battery pack according to claim 6 , further comprising:
an external power distribution terminal; and
a protective circuit.
8. The battery pack according to claim 6 , 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.
9. A vehicle comprising the battery pack according to claim 6 .
10. The vehicle according to claim 9 , which comprises a mechanism configured to convert kinetic energy of the vehicle into regenerative energy.
11. 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 , Nb 14 TiO 37 , and Nb 24 TiO 62 .
12. The electrode according to claim 1 , wherein a crystallite size of the active material is in a range of 50 nm to 200 nm.
13. A negative electrode that is the electrode according to claim 1 .