Positive electrode active material, method for preparing positive electrode active material, positive electrode plate, secondary battery, battery module, battery pack, and electric apparatus
This application provides a positive electrode active material, a method for preparing a positive electrode active material, a positive electrode plate, a secondary battery, a battery module, a battery pack, and an electric apparatus. The positive electrode active material includes a first positive electrode active material and a second positive electrode active material. The first positive electrode active material includes a compound LiNi b Co d Mn e M′ f O 2 , and the second positive electrode active material includes a core, a first coating layer enveloping the core, and a second coating layer enveloping the first coating layer, where the core includes a compound Li 1+x Mn 1−y A y P 1−z R z O 4 , the first coating layer includes pyrophosphate M a P 2 O 7 and phosphate X n PO 4 , and the second coating layer includes carbon.
1. A positive electrode active material comprising a first positive electrode active material and a second positive electrode active material, wherein
the first positive electrode active material comprises a compound LiNi b Co d Mn e M′ f O 2 , wherein b is selected from the range of 0.314 to 0.970, d is selected from the range of greater than 0 to 0.320, e is selected from the range of 0.006 to 0.390, the sum of b, d, e, and f is 1 with f greater than 0, and M′ is one or more elements selected from Mn, Al, Mg, Ca, Na, Ti, W, Zr, Sr, Cr, Zn, Ba, B, S, and Y; and
the second positive electrode active material comprises a core, a first coating layer enveloping the core, and a second coating layer enveloping the first coating layer, wherein the core comprises a compound Li 1+x Mn 1−y A y P 1−z R z O 4 , the first coating layer comprises pyrophosphate M a P 2 O 7 and phosphate X n PO 4 , and the second coating layer comprises carbon, wherein x is selected from the range of −0.100 to 0.100, y is selected from the range of 0.001 to 0.909, z is selected from the range of 0.001 to 0.100, a is greater than 0 and less than or equal to 4, n is greater than 0 and less than or equal to 2, A is one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge, and Mg, R is one or more elements selected from B, Si, N, and S, and M and X are each independently one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al.
2. The positive electrode active material according to claim 1 , wherein a mass of the first positive electrode active material is m 1 , a mass of the second positive electrode active material is m 2 , and a value of m 1 /(m 1 +m 2 ) is 2%-55%.
3. The positive electrode active material according to claim 2 , wherein a value of b×m 1 /(m 1 +m 2 ) is 0.017-0.457.
4. The positive electrode active material according to claim 1 , wherein the first positive electrode active material is a quasi-single crystal material, and a particle size D v 50 of the first positive electrode active material is less than or equal to 5.8 μm, optionally 2.3-5.8 μm.
5. The positive electrode active material according to claim 1 , wherein when the first positive electrode active material is a quasi-single crystal material,
d is selected from the range of 0.047-0.320, and/or
b is greater than 0.314 and less than 0.97.
6. The positive electrode active material according to claim 1 , wherein the first positive electrode active material further comprises lithium carbonate and/or lithium hydroxide; and
based on mass of the first positive electrode active material, a mass percentage of the lithium carbonate is less than or equal to 1.05%, a mass percentage of the lithium hydroxide is less than or equal to 1.02%.
7. The positive electrode active material according to claim 1 , wherein a ratio of y to 1−y in the core is 1:10 to 10:1.
8. The positive electrode active material according to claim 1 , wherein a ratio of z to 1−z in the core is 1:999 to 1:9.
9. The positive electrode active material according to claim 1 , wherein based on a weight of the core, an application amount of the first coating layer is greater than 0 wt % and less than or equal to 7 wt %.
10. The positive electrode active material according to claim 1 , wherein a weight ratio of the pyrophosphate to the phosphate in the first coating layer is 1:3 to 3:1.
11. The positive electrode active material according to claim 1 , wherein a crystallinity of the pyrophosphate and a crystallinity of the phosphate are each independently 10% to 100%.
12. The positive electrode active material according to claim 1 , wherein based on weight of the core, an application amount of the second coating layer is greater than 0 wt % and less than or equal to 6 wt %.
13. The positive electrode active material according to claim 1 , wherein A is at least two elements selected from Fe, Ti, V, Ni, Co, and Mg.
14. The positive electrode active material according to claim 1 , wherein
a Li/Mn antisite defect concentration of the second positive electrode active material is below 4%.
15. The positive electrode active material according to claim 1 , wherein
a lattice change rate of the second positive electrode active material before and after complete deintercalation or intercalation of lithium is below 6%.
16. The positive electrode active material according to claim 1 , wherein
a surface oxygen valence of the second positive electrode active material is below −1.88.
17. The positive electrode active material according to claim 1 , wherein
a compacted density of the second positive electrode active material under 3T is above 2.0 g/cm 3 .
18. The positive electrode active material according to claim 1 , wherein in the second positive electrode active material, the pyrophosphate in the first coating layer has an interplanar spacing of 0.293-0.326 nm and an included angle of 26.41°−32.57° in the [111] orientation; and/or
the phosphate in the first coating layer has an interplanar spacing of 0.345-0.358 nm and an included angle of 24.25°-26.45° in the [111] orientation.
19. The positive electrode active material according to claim 1 , wherein the first positive electrode active material is a polycrystalline material, and a particle size D v 50 of the first positive electrode active material is 3.0-13.5 μm,
a BET specific surface area of the first positive electrode active material is less than or equal to 1.73 m 2 /g, and/or
a compacted density of the first positive electrode active material under 3T pressure is greater than or equal to 2.90 g/cm 3 .
20. A method for preparing a positive electrode active material, comprising the following steps:
providing a first positive electrode active material and a second positive electrode active material; and
mixing the first positive electrode active material with the second positive electrode active material, wherein
the first positive electrode active material comprises a compound LiNi b Co d Mn e M′ f O 2 , and the second positive electrode active material comprises a core, a first coating layer enveloping the core, and a second coating layer enveloping the first coating layer, wherein the core comprises a compound Li 1+x Mn 1−y A y P 1−z R z O 4 , the first coating layer comprises pyrophosphate M a P 2 O 7 and phosphate X n PO 4 , and the second coating layer comprises carbon,
wherein b is selected from the range of 0.314 to 0.970, d is selected from the range of greater than 0 to 0.320, e is selected from the range of 0.006 to 0.390, the sum of b, d, e, and f is 1 with f greater than 0, and M′ is one or more elements selected from Mn, Al, Mg, Ca, Na, Ti, W, Zr, Sr, Cr, Zn, Ba, B, S, and Y;
wherein x is selected from the range of −0.100 to 0.100, y is selected from the range of 0.001 to 0.909, z is selected from the range of 0.001 to 0.100, a is greater than 0 and less than or equal to 4, n is greater than 0 and less than or equal to 2, A is one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge, and Mg, R is one or more elements selected from B, Si, N, and S, and M and X are each independently one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al.