Active material, electrode, secondary battery, battery pack, and vehicle
According to one embodiment, an active material is provided. The active material includes a primary particle containing a phosphorus-containing monoclinic niobium-titanium composite oxide. The primary particle has a concentration gradient in which a phosphorus concentration increases from the gravity point of the primary particle toward the surface of the primary particle.
1. An active material comprising
a primary particle comprising a phosphorus-containing monoclinic niobium-titanium composite oxide,
wherein the primary particle has a concentration gradient in which a phosphorus concentration increases from a gravity point of the primary particle toward a surface of the primary particle, and
the phosphorus-containing monoclinic niobium-titanium composite oxide has an average composition represented by a general formula Ti 1-x M1 x Nb 2-y-z M2 y P z O 7 ,
where
0≤x<1, 0≤y<1, 0<z≤0.5,
each of elements M1 and M2 is at least one selected from the group consisting of V, Ta, Fe, Bi, Cr, Mo, W, B, K, Na, Mg, Al, and Si, and
the element M1 and the element M2 may be the same element or different elements from each other.
2. The active material according to claim 1 , wherein a ratio (C2/C1) of a phosphorus concentration (C2) at a position corresponding to 80% of a length defined from the gravity point to the surface of the primary particle, with respect to a phosphorus concentration (C1) at a position of the gravity point of the primary particle is in a range of 1.05 to 100.
3. The active material according to claim 1 , wherein a phosphate compound is present at least a part of the surface of the primary particle.
4. The active material according to claim 3 , comprising
a secondary particle formed of a plurality of the primary particle,
wherein the phosphate compound is present between the plurality of the primary particle.
5. The active material according to claim 3 , wherein the phosphate compound comprises at least one selected from the group consisting of phosphorus oxide, iron phosphate, and potassium phosphate.
6. The active material according to claim 5 , wherein the phosphate compound comprises at least one selected from the group consisting of iron phosphate and potassium phosphate.
7. An electrode comprising the active material according to claim 1 .
8. The electrode according to claim 7 , wherein the electrode comprises an active material-containing layer comprising the active material.
9. A secondary battery comprising:
a positive electrode;
a negative electrode; and
an electrolyte,
wherein the negative electrode is the electrode according to claim 7 .
10. A battery pack comprising the secondary battery according to claim 9 .
11. The battery pack according to claim 10 , further comprising
an external power distribution terminal; and
a protective circuit.
12. The battery pack according to claim 10 , comprising a plurality of the secondary battery, wherein the plurality of the secondary battery are electrically connected in series, in parallel, or in combination of in series and in parallel.
13. A vehicle comprising the battery pack according to claim 10 .
14. The vehicle according to claim 13 , comprising a mechanism configured to convert kinetic energy of the vehicle into regenerative energy.