Positive active material, lithium ion secondary battery, battery module, battery pack and electric device
A positive active material is provided. In some embodiments, the positive material includes: a substrate and a coating layer coating the substrate, wherein the coating layer includes a fast ion conductor layer and a carbon coating layer, the substrate includes more than one compound of formula (I): LiFe 1-a M1 a PO 4 formula (I), in formula (I), M1 is more than one selected from Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb and Ti, and 0≤a≤0.01; the fast ion conductor layer includes a fast ion conductor of a NASICON structure shown in formula (II), Li 3-b Fe 2-b M2 b (PO 4 ) 3 formula (II), in formula (II), M2 is more than one selected from Ti, Zr, Hf, Ge and Sn with valence of +4, and 0≤b≤1.
1. A positive active material, comprising:
a substrate and a coating layer, wherein the coating layer coats the substrate, and the coating layer comprises a fast ion conductor layer and a carbon coating layer,
the substrate comprises more than one compound as shown in formula (I):
LiFe 1-a M1 a PO 4 formula (I), wherein
in the formula (I), M1 is one of more selected from Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb and Ti, and 0≤a≤0.01,
the fast ion conductor layer comprises a fast ion conductor of a NASICON structure as shown in formula (II),
Li 3-b Fe 2-b M2 b (PO 4 ) 3 formula (II), wherein
in the formula (II), M2 is one or more selected from Ti, Zr, Hf, Ge and Sn with valence of +4, and 0<b≤1,
the carbon has a mass percentage content C % of 1%-1.5% in the positive active material;
the positive active material has a specific surface area S of 10 m 2 /g-15 m 2 /g; and
a ratio of the specific surface area S to the carbon content C % of the positive active material satisfies 9≤S/C≤12.
2. The positive active material according to claim 1 ,
wherein in the positive active material, a molar ratio of the LiFe 1-a M1 a PO 4 and the Li 3-b Fe 2-b M2 b (PO 4 ) 3 satisfies (1−x):x, and 0<x≤0.005.
3. The positive active material according to claim 1 ,
wherein the positive active material has pH not less than 9.
4. The positive active material according to claim 1 ,
wherein the positive active material has a volume average particle size satisfying 1 μm≤Dv50≤2 μm and 0.4 μm≤Dv10≤0.7 μm.
5. The positive active material according to claim 1 ,
wherein the positive active material has a powder compaction density ρ≥2.5 g/cm 3 .
6. The positive active material according to claim 1 ,
wherein the positive active material has a powder resistivity R≤11 Ω·cm.
7. The positive active material according to claim 1 ,
wherein a positive plate fabricated from the positive material has an electrode plate compaction density of 2.5 g/cm 3 .
8. A lithium ion secondary battery, comprising the positive active material according to claim 1 .
9. The lithium ion secondary battery according to claim 8 , comprising:
a positive plate, comprising a positive current collector and a positive film layer provided on at least one surface of the positive current collector and containing the positive active material, and when a button cell is formed by the positive plate and a lithium metal plate, in a 0.1 C charging-discharging curve of the button cell, a charging-discharging platform exists within a voltage range of 2.5-2.9 Vvs Li + .
10. A battery module, comprising the lithium ion secondary battery according to claim 8 .
11. A battery pack, comprising more than one of the lithium ion secondary battery according to claim 8 .
12. An electric device, comprising:
more than one of the lithium ion secondary battery according to claim 8 , wherein the lithium ion secondary battery is used as a power source of the electric device or an energy storage unit of the electric device.
13. A positive active material, comprising:
a substrate and a coating layer, wherein the coating layer coats the substrate, and the coating layer comprises a fast ion conductor layer and a carbon coating layer,
the substrate comprises more than one compound as shown in formula (I):
LiFe 1-a M1 a PO 4 formula (I), wherein
in the formula (I), M1 is one of more selected from Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb and Ti, and 0≤a≤0.01,
the fast ion conductor layer comprises a fast ion conductor of a NASICON structure as shown in formula (II),
Li 3-b Fe 2-b M2 b (PO 4 ) 3 formula (II), wherein
in the formula (II), M2 is one or more selected from Ti, Zr, Hf, Ge and Sn with valence of +4, and 0≤b≤1,
free lithium is present in the positive active material, and a pH of the positive active material and a mass percentage content N Li+ % of the free lithium satisfy 0.15≤pH−(36N Li+ +8)≤1.1.
14. The positive active material according to claim 1 ,
wherein the fast ion conductor of the NASICON structure is selected from the group consisting of Li 2 FeTi(PO 4 ) 3 , Li 2 FeZr(PQ 4 ) 3 , Li 2 FeSn(PO 4 ) 3 , and any combination thereof.
15. The positive active material according to claim 1 ,
wherein the positive active material is in a form of primary particles or a pseudo-single crystal.
16. The positive active material according to claim 13 ,
wherein in the positive active material, a molar ratio of the LiFe 1-a M1 a PO 4 and the Li 3-b Fe 2-b M2 b (PO 4 ) 3 satisfies (1−x):x, and 0<x≤0.005.
17. The positive active material according to claim 13 ,
wherein the positive active material has a volume average particle size satisfying 1 μm≤Dv50≤2 μm and 0.4 μm≤Dv10≤0.7 μm.
18. The positive active material according to claim 13 ,
wherein the positive active material has a powder compaction density ρ≥2.5 g/cm 3 and a powder resistivity R≤11 Ω·cm.
19. The positive active material according to claim 13 ,
wherein a positive plate fabricated from the positive material has an electrode plate compaction density of 2.5 g/cm 3 .
20. The positive active material according to claim 13 ,
wherein the fast ion conductor of the NASICON structure is selected from the group consisting of Li 2 FeZr(PQ 4 ) 3 , Li 2 FeSn(PO 4 ) 3 , and a combination thereof.