Positive electrode active material and preparation method thereof, positive electrode plate, lithium-ion secondary battery, and apparatus containing such lithium-ion secondary battery
This application discloses a positive electrode active material, including bulk particles and a coating layer applied on an exterior surface of each of the bulk particles, where the bulk particle includes a lithium composite oxide that contains element nickel and a doping element M 1 , and the coating layer includes an oxide of element M 2 . When the positive electrode active material is in a 11% delithiated state, average valences of element M 1 and M 2 are α 1 and β 1 , respectively; when the positive electrode active material is in a 78% delithiated state, average valences of element M 1 and M 2 are α 2 and β 2 , respectively; and α 2 >α 1 , β 1 =β 2 . Element M 1 includes one or more of Si, Ti, Cr, Mo, V, Se, Nb, Ru, Rh, Pd, Sb, Te, Ce, and W, and element M 2 is selected from one or more of Mg, Al, Ca, Zr, Zn, Y, and B.
1. A positive electrode active material, comprising bulk particles and a coating layer applied on an exterior surface of each of the bulk particles, wherein the bulk particles comprises a lithium composite oxide that contains element nickel and a doping element M 1 , and the coating layer comprises an oxide of element M 2 ;
when the positive electrode active material is in an 11% delithiated state, an average valence of element M 1 is α 1 , and an average valence of element M 2 is β 1 ;
when the positive electrode active material is in a 78% delithiated state, an average valence of element M 1 is α 2 , and an average valence of element M 2 is β 2 ;
α 1 and α 2 satisfy α 2 >α 1 , and β 1 and β 2 satisfy β 1 =β 2 ; and
element M 1 comprises one or more of Si, Ti, Cr, Mo, V, Se, Nb, Ru, Rh, Pd, Sb, Te, Ce, and W, and element M 2 is selected from one or more of Mg, Al, Ca, Zr, Zn, Y, and B;
wherein a thickness T of the coating layer ranges from 0.001 μm to 0.5 μm, and
the thickness T of the coating layer and an average particle size D of the positive electrode active material satisfy: 0.003≤T/ D ≤0.025.
2. The positive electrode active material according to claim 1 , wherein α 1 and α 2 satisfy α 2 >α 1 ≥+3.
3. The positive electrode active material according to claim 1 , wherein α 1 is one or more of valences +3, +4, +5, and +6.
4. The positive electrode active material according to claim 1 , wherein element M 1 comprises one or more of Ti, Mo, V, Nb, Ru, Sb, and W; or
element M 2 comprises one or more of Al, Zr, Zn, Y, and B.
5. The positive electrode active material according to claim 1 , wherein element M 1 is doped into the bulk particle and a relative deviation of local mass concentration of element M 1 in the bulk particle is less than 32%.
6. The positive electrode active material according to claim 1 , wherein in the positive electrode active material, a molar ratio of element M 1 to element M 2 ranges from 0.09:1 to 4:1.
7. The positive electrode active material according to claim 1 , wherein
a true doping concentration of element M 1 in the positive electrode active material ranges from 2000 μg/cm 3 to 55000 μg/cm 3 ; or
a concentration of element M 2 in the positive electrode active material ranges from 300 ppm to 6500 ppm.
8. The positive electrode active material according to claim 1 , wherein a volume-based median particle size D v 50 of the positive electrode active material ranges from 8 μm to 20 μm.
9. The positive electrode active material according to claim 1 , wherein a thickness T of the coating layer ranges from 0.001 μm to 0.5 μm.
10. The positive electrode active material according to claim 1 , wherein the lithium composite oxide is a compound represented by chemical formula 1:
Li 1+a [Ni x Co y Mn z M 1 b ]O 2-p X p chemical formula 1
wherein in the chemical formula 1, X is selected from one or more of F, N, P, and S, 0.5≤x<1, 0≤y<0.3, 0≤z<0.3, −0.2<a<0.2, 0<b<0.2, 0≤p<0.2, and x+y+z+b=1.
11. The positive electrode active material according to claim 10 , wherein when the bulk particles are doped with element X, element X is doped into the bulk particle and a relative deviation of local mass concentration of the doping elements (comprising element M 1 and element X) in the bulk particle is less than 32%; or
element X shows a mass concentration gradient decreasing from the exterior surface of the bulk particle to the core of the particle; optionally, element X is doped into the exterior surface of the bulk particle.
12. The positive electrode active material according to claim 1 , wherein the positive electrode active material further satisfies one or more of the following requirements (1) to (3):
(1) a specific surface area of the positive electrode active material ranges from 0.2 m 2 /g to 1.5 m 2 /g;
(2) a true density of the positive electrode active material ranges from 4.6 g/m 3 to 5.2 g/m 3 ; or
(3) a tap density of the positive electrode active material ranges from 2.3 g/cm 3 to 2.8 g/cm 3 .
13. A lithium-ion secondary battery, comprising a positive electrode plate, wherein the positive electrode plate comprises a positive electrode current collector and a positive electrode active substance layer disposed on the positive electrode current collector, and the positive electrode active substance layer comprises the positive electrode active material according to claim 1 .
14. A method for preparing the positive electrode active material according to claim 1 , comprising the steps of:
(a) providing a mixture comprising a nickel-containing transition metal source, a lithium source, and a precursor of element M 1 , and subjecting the mixture to a sintering treatment to obtain bulk particles doped with element M 1 ; and
(b) mixing the bulk particles and a precursor of element M 2 , and subjecting a resulting mixture to a sintering treatment to form on an exterior surface of the bulk particle a coating layer that contains an oxide of element M 2 , so as to obtain the positive electrode active material; wherein
when the positive electrode active material is in an 11% delithiated state, an average valence of element M 1 is α 1 , and an average valence of element M 2 is β 1 ;
when the positive electrode active material is in a 78% delithiated state, an average valence of element M 1 is α 2 , and an average valence of element M 2 is β 2 ;
α 1 and α 2 satisfy α 2 >α 1 , and β 1 and β 2 satisfy β 1 =β 2 ; and
element M 1 comprises one or more of Si, Ti, Cr, Mo, V, Se, Nb, Ru, Rh, Pd, Sb, Te, Ce, and W, and element M 2 is selected from one or more of Mg, Al, Ca, Zr, Zn, Y, and B.
15. The preparation method according to claim 14 , wherein
the mixture further comprises a precursor of element X, the obtained bulk particles are also doped with element X, and element X is selected from one or more of F, N, P, and S; or
before mixing the bulk particles and the precursor of element M2, the preparation method further comprises:
(c) mixing the bulk particles and aprecursor of element X, and subjecting a resulting mixture to a sintering treatment to cause element X to be doped into the bulk particles, wherein element X is selected from one or more of F, N, P, and S.
16. The preparation method according to claim 15 , wherein an atmosphere for the sintering treatment in step (a) is an oxygen-containing atmosphere; optionally, a percentage of oxygen in the sintering atmosphere ranges from 70% to 100%, optionally being more than 85%; a temperature for the sintering treatment ranges from 500° C. to 1000° C., optionally from 700° C. to 900° C., and further optionally from 750° C. to 850° C.; and duration for the sintering treatment ranges from 5 hours to 25 hours, optionally from 5 hours to 15 hours.
17. The preparation method according to claim 16 , wherein an atmosphere for the sintering treatment in step (b) is an oxygen-containing atmosphere; optionally, a percentage of oxygen in the sintering atmosphere ranges from 70% to 100%, optionally being more than 85%; a temperature for the sintering treatment ranges from 100° C. to 550° C., optionally from 200° C. to 500° C.; and duration for the sintering treatment ranges from 3 hours to 25 hours, optionally from 5 hours to 10 hours.
18. The preparation method according to claim 15 , wherein an atmosphere for the sintering treatment in step (c) is an oxygen-containing atmosphere; optionally, a percentage of oxygen in the sintering atmosphere ranges from 70% to 100%, optionally from 80% to 95%; a temperature for the sintering treatment ranges from 400° C. to 1000° C., optionally from 400° C. to 850° C., and optionally from 400° C. to 750° C.; and duration for the sintering treatment ranges from 3 hours to 25 hours, optionally from 5 hours to 10 hours.