Electrode, secondary battery, battery pack, and vehicle
According to one embodiment, an electrode including active material particles is provided. The active material particles contain monoclinic niobium-titanium composite oxide particles and an amorphous carbon body. The amorphous carbon body covers at least a part of surfaces of the monoclinic niobium-titanium composite oxide particles. A ratio S2/S1 of a carbon atom concentration S2 to a niobium atom concentration S1 at a surface of the electrode, according to X-ray photoelectron spectroscopy, is from 5 to 100.
1. A secondary battery comprising an electrode comprising active material particles and an electrolyte,
wherein:
the active material particles contain monoclinic niobium-titanium composite oxide particles and an amorphous carbon body covering at least a part of surfaces of the monoclinic niobium-titanium composite oxide particles;
at least a part of a surface of the amorphous carbon body is covered with a coating film containing carbon;
the coating film has a thickness of 10 nm to 150 nm;
a ratio S2/S1 of a carbon atom concentration S2 to a niobium atom concentration S1 at a surface of the electrode, according to X-ray photoelectron spectroscopy, is from 5 to 100;
the niobium atom concentration S1 is an intensity of an area for a peak related to Nb3d; and
the carbon atom concentration S2 is a total of intensities of areas for peaks related to C1s within a range of 286 eV to 294 eV and the peaks comprising a peak assigned to a C—O bond, a peak assigned to a C═O bond, a peak assigned to a C(═O)—O bond, and a peak assigned to a CO 3 2− bond.
2. The secondary battery according to claim 1 ,
wherein:
the surface of the electrode further comprises a phosphorus atom, and
a ratio S3/S1 of a concentration S3 of the phosphorus atom to the niobium atom concentration S1 at the surface of the electrode, according to X-ray photoelectron spectroscopy, is from 0.3 to 20;
the concentration S3 of the phosphorus atom is an intensity of an area for a peak related to P2p within a range of 133 eV to 137 eV and assigned to a PF x O y bond;
x is from 0 to 1; and
y is more than 0 and 1 or less.
3. The secondary battery according to claim 1 , wherein a thickness of the amorphous carbon body is from 1 nm to 10 nm.
4. The secondary battery according to claim 1 ,
wherein:
a Raman spectrum of the active material particles according to Raman spectroscopy has a G band within a range of 1530 cm −1 to 1630 cm −1 and a D band within a range of 1280 cm −1 to 1380 cm −1 ; and
a ratio I G /I D of peak intensity I G of the G band to peak intensity I D of the D band is 1.2 or less.
5. The secondary battery according to claim 1 , comprising:
the electrode as a negative electrode; and
a positive electrode.
6. The secondary battery according to claim 1 , wherein the electrolyte contains at least one compound selected from the group consisting of vinylene carbonate (VC), fluoroethylene carbonate (FEC), and ethylene sulfite (ES).
7. A battery pack comprising the secondary battery according to claim 1 .
8. The battery pack according to claim 7 , further comprising:
an external power distribution terminal; and
a protective circuit.
9. The battery pack according to claim 7 ,
wherein:
the battery pack includes a plural secondary batteries; and
the plural secondary batteries are electrically connected in series, in parallel, or in combination of series and parallel.
10. A vehicle comprising the battery pack according to claim 7 .
11. The vehicle according to claim 10 , which comprises a mechanism configured to convert kinetic energy of the vehicle into regenerative energy.
12. The secondary battery according to claim 1 , wherein the thickness of the coating film is 15 nm to 150 nm.