Carbon-coated lithium iron phosphate positive active material, method for preparing same, positive electrode plate containing same, and lithium-ion battery
A positive active material made of carbon-coated lithium iron phosphate includes a lithium iron phosphate substrate, and a carbon coating layer on a surface of the substrate. The lithium iron phosphate substrate has a general structural formula LiFe 1-a M a PO 4 , where M is at least one selected from Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, or Ti, and 0≤a≤0.01. A carbon coating factor of the carbon-coated lithium iron phosphate, η = BET 1 BET 2 , satisfies 0.81≤η≤0.95, where BET1 denotes a specific surface area of mesopore and macropore structures in the carbon-coated lithium iron phosphate, and BET2 denotes a total specific surface area of the carbon-coated lithium iron phosphate.
1. A carbon-coated lithium iron phosphate positive active material, comprising:
a lithium iron phosphate substrate and a carbon coating layer on a surface of the substrate, the lithium iron phosphate substrate having a general structural formula LiFe 1-a M a PO 4 , wherein M is at least one selected from Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, or Ti, and 0≤a≤0.01;
wherein a carbon coating factor of the carbon-coated lithium iron phosphate material is
η
=
BET
1
BET
2
,
wherein BET1 denotes a specific surface area of mesopore and macropore structures in the carbon-coated lithium iron phosphate, BET2 denotes a total specific surface area of the carbon-coated lithium iron phosphate, and η satisfies 0.81≤η≤0.95.
2. The positive active material according to claim 1 , wherein:
η satisfies 0.85≤η≤0.93.
3. The positive active material according to claim 1 , wherein:
a value range of BET1 is 5.5 to 9.5 m 2 /g, and a value range of BET2 is 6.0 to 11.5 m 2 /g.
4. The positive active material according to claim 1 , wherein:
a carbon component accounts for 0.7% to 1.3% of a total mass of the carbon-coated lithium iron phosphate.
5. The positive active material according to claim 1 , wherein:
a ratio H/D of a thickness H of the carbon coating layer to an average particle diameter D of the carbon-coated lithium iron phosphate is 0.01 to 0.04.
6. The positive active material according to claim 1 , wherein:
a volume median diameter D v50 of the carbon-coated lithium iron phosphate satisfies 840 nm≤D v50 ≤3570 nm.
7. The positive active material according to claim 1 , wherein a powder compaction density of the carbon-coated lithium iron phosphate is at least 2.4 g/cm 3 .
8. The positive active material according to claim 1 , wherein:
a graphitization degree of the carbon-coated lithium iron phosphate is 0.15 to 0.32.
9. The positive active material according to claim 1 , wherein:
a powder resistivity of the carbon-coated lithium iron phosphate is not greater than 60 Ω·m.
10. The positive active material according to claim 1 , wherein the lithium iron phosphate substrate is doped with 0.1 wt % to 0.5 wt % carbon based on a mass of the lithium iron phosphate substrate.
11. A method for manufacturing the positive active material according to claim 1 , comprising:
providing the lithium iron phosphate substrate; and
performing carbon coating on the lithium iron phosphate substrate to obtain the carbon-coated lithium iron phosphate positive active material;
wherein:
the positive active material comprises the lithium iron phosphate substrate and the carbon coating layer located on the surface of the substrate, the lithium iron phosphate substrate has a general structural formula LiFe 1-a M a PO 4 , wherein M is at least one selected from Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, or Ti, and 0≤a≤0.01; and
the carbon coating factor of the carbon-coated lithium iron phosphate material is
η
=
BET
1
BET
2
,
wherein BET1 denotes a specific surface area of mesopore and macropore structures in the carbon-coated lithium iron phosphate, and BET2 denotes a total specific surface area of the carbon-coated lithium iron phosphate, and η satisfies 0.81≤η≤0.95.
12. The method according to claim 11 , wherein the lithium iron phosphate substrate is doped with 0.1 wt % to 0.5 wt % carbon based on a mass of the lithium iron phosphate substrate.
13. A positive electrode plate of a lithium-ion battery, comprising:
a positive current collector; and
a positive active material disposed on at least one surface of the positive current collector, wherein the positive active material is the positive active material according to claim 1 .
14. The positive electrode plate according to claim 13 , wherein a saturated water content of the positive electrode plate at 25° C. and a relative humidity of 45% is not greater than 500 ppm.
15. A lithium-ion battery, comprising:
a positive electrode plate; and
a negative electrode plate;
wherein the positive electrode plate comprises a positive current collector and a positive active material disposed on at least one surface of the positive current collector, wherein the positive active material is the positive active material according to claim 1 .
16. The lithium-ion battery according to claim 15 , wherein:
an electrode compaction density of the positive electrode plate is at least 2.35 g/cm 3 ;
an electrode compaction density of the negative electrode plate is at least 1.6 g/cm 3 ; and
a negative active material of the negative electrode plate is graphite coated with amorphous carbon.
17. A battery module, comprising the lithium-ion battery according to claim 15 .
18. A battery pack, comprising the lithium-ion battery according to claim 15 .
19. An electrical device, comprising the lithium-ion battery according to claim 15 , wherein the lithium-ion battery is used as a power supply of the electrical device or an energy storage unit of the electrical device.