Method for recycling waste lithium iron phosphate by selective oxidation-reduction, recycled lithium iron phosphate, and lithium ion battery

1. A method for recycling waste lithium iron phosphate by selective oxidation-reduction, comprising steps of:

performing primary sintering on the waste lithium iron phosphate under a condition where a mild oxidizing gas is introduced;

separating a lithium iron phosphate powder material from a material obtained by the primary sintering; and

supplementing lithium and supplementing carbon to the lithium iron phosphate powder material and regulating a composition of the lithium iron phosphate powder material using a lithium source and a carbon source by secondary sintering, to obtain recycled lithium iron phosphate,

wherein the mild oxidizing gas is a mixed gas of water vapor and CO 2 gas.

2. The method according to claim 1 , having at least one of following situations (1) to (3):

(1) the mild oxidizing gas is a mixed gas of water vapor and CO 2 gas, and a flow rate ratio of the water vapor and the CO 2 gas is from 1:9 to 9:1;

(2) the water vapor is derived from at least one of deionized water and ultrapure water, and the water vapor has a resistance ≥18 MΩ; and

(3) the CO 2 gas has a purity ≥99.0%.

3. The method according to claim 1 , having at least one of following situations (1) to (2):

(1) the waste lithium iron phosphate is derived from at least one of waste lithium iron phosphate battery electrode sheets and a waste lithium iron phosphate slurry; and

(2) the waste lithium iron phosphate battery electrode sheets comprise: waste LFP electrode sheets obtained by dismantling spent and decommissioned waste LFP batteries, waste LFP electrode sheets obtained by dismantling defective batteries scrapped from battery factories, and defective LFP electrode sheets scrapped from battery factories.

4. The method according to claim 1 , having at least one of following situations (1) to (3):

(1) a mass ratio of the waste lithium iron phosphate to the mild oxidizing gas is from 1:0.1 to 1:10.0, and the mild oxidizing gas is introduced at a constant flow rate;

(2) a heating device used in a process of the primary sintering comprises one of a tube furnace, a box furnace, a roller kiln, and a rotary kiln; and

(3) in the primary sintering, a temperature is maintained at 300° C. to 700° C. for 0.5 hours to 15 hours.

5. The method according to claim 1 , wherein the separating a lithium iron phosphate powder material from a material obtained by the primary sintering comprises: pulverizing and then separating the material obtained by the primary sintering.

6. The method according to claim 1 , having at least one of following situations (1) to (2):

(1) the lithium source used for the supplementing lithium comprises any one of Li 2 CO 3 , LiOH·H 2 O, Li 3 PO 4 , or LiNO 3 , or a combination of at least two therefrom; and

(2) the lithium source has a purity of an industrial grade or a battery grade.

7. The method according to claim 6 , having at least one of following situations (1) to (3):

(1) a method for the supplementing lithium comprises wet supplementation of lithium and dry supplementation of lithium;

(2) Li 2 CO 3 is used as the lithium source for the dry supplementation of lithium, and the Li 2 CO 3 has a median particle diameter ranging from 0.2 μm to 10 μm; and

(3) the lithium source is added in an amount calculated according to a molar ratio of Li:Fe, and an excess amount of Li ranges from 0.1% to 10.0%.

8. The method according to claim 1 , wherein the carbon source comprises any one of glucose, sucrose, citric acid, acetylene black, polypropylene, or polyethylene glycol, or a combination of at least two therefrom.

9. The method according to claim 8 , having at least one of following situations (1) to (3):

(1) a method for the supplementing carbon comprises wet supplementation of carbon and dry supplementation of carbon;

(2) the carbon source is added in an amount calculated such that resulting recycled lithium iron phosphate has a carbon content of 1.0 wt % to 6.0 wt %; and

(3) a mixed carbon source of glucose and polyethylene glycol is used for the dry supplementation of carbon, and the mixed carbon source has a median particle diameter ranging from 0.2 μm to 10.0 μm; and in the mixed carbon source, glucose and polyethylene glycol are blended in a mass ratio ranging from 1:9 to 9:1.

10. The method according to claim 1 , wherein the supplementing lithium and supplementing carbon to the lithium iron phosphate powder material and regulating a composition of the lithium iron phosphate powder material using a lithium source and a carbon source by secondary sintering, to obtain recycled lithium iron phosphate, comprises:

mixing the lithium source and the carbon source with the lithium iron phosphate powder material and secondarily sintering the resulting mixture, to obtain the recycled lithium iron phosphate.

11. The method according to claim 10 , having at least one of following situations (1) to (5):

(1) the secondary sintering is performed under an inert gas, and the inert gas comprises any one of nitrogen, argon, helium, neon, krypton and xenon, or a combination of at least two therefrom;

(2) a mass ratio of the lithium iron phosphate powder material to the inert gas is from 1:0.1 to 1:10.0;

(3) during the secondary sintering, the inert gas is introduced at a constant flow rate;

(4) in the secondary sintering, a temperature is maintained at 700° C. to 800° C. for 2 hours to 20 hours; and

(5) a heating device used in the secondary sintering comprises any one of a tube furnace, a box furnace, a roller kiln and a rotary kiln.

12. The method according to claim 1 , wherein after the recycled lithium iron phosphate is obtained, the method further comprises: sieving and demagnetizing the recycled lithium iron phosphate.

13. The method according to claim 1 , comprising steps of:

placing waste electrode sheets in a rotary kiln, into which the mixed gas of water vapor and carbon dioxide is introduced in a flow rate ratio of 4:6 to 6:4 and at a constant flow rate, increasing a temperature to 300° C. to 700° C. at a temperature increasing rate of 2° C./min to 5° C./min, maintaining the temperature for 0.5 hours to 15 hours, and cooling down the resultant along with the kiln;

wherein a mass ratio of waste lithium iron phosphate to the mixed gas is from 1:0.1 to 1:10.0, with the waste lithium iron phosphate being an active ingredient in the waste electrode sheets;

allowing electrode sheets after undergoing the primary sintering to be mechanically crushed and sieved through a screen with 10 to 400 meshes, and determining a content of Li, Fe, and C in a sieved out powder material by ICP and high-frequency infrared carbon and sulfur analysis;

using Li 2 CO 3 with a median particle diameter of 0.2 to 10 μm, and a mixed carbon source of glucose and polyethylene glycol in a mass ratio of 1:9 to 9:1, supplementing lithium to an excess amount of Li of 0.1% to 10.0% based on a molar ratio of Li:Fe, wherein an amount of the carbon source added is calculated such that resulting recycled lithium iron phosphate has a carbon content of 1.0 wt % to 6.0 wt %, mixing a mixture in a VC mixer for 0.1 to 8 hours, introducing nitrogen as a protective gas into a box furnace, secondarily sintering a mixture, and cooling down a resultant along with the furnace, to obtain the recycled lithium iron phosphate,

wherein in the secondary sintering, a temperature is increased to 700° C. to 800° C. at a temperature increasing rate of 2° C./min to 5° C./min and maintained for 2 to 20 hours.

14. A recycled lithium iron phosphate, wherein the recycled lithium iron phosphate is prepared by the method according to claim 1 .

15. The recycled lithium iron phosphate according to claim 14 , having at least one of following situations (1) to (5):

(1) a material of the recycled lithium iron phosphate has a median particle diameter of 0.1 μm to 10.0 μm;

(2) the material of the recycled lithium iron phosphate has a specific surface area of 1.0 m 2 /g to 20.0 m 2 /g;

(3) the material of the recycled lithium iron phosphate has a compacted powder density of 1.0 g/cm 3 to 2.8 g/cm 3 ;

(4) the material of the recycled lithium iron phosphate has a pH of 6.0 to 12.0; and

(5) the material of the recycled lithium iron phosphate has a carbon content of 1.0 wt % to 6.0 wt %.

16. A lithium ion battery, comprising the recycled lithium iron phosphate according to claim 14 .

17. The method according to claim 5 , wherein the material obtained by the primary sintering is mechanically pulverized and then sieved through a screen.

18. The method according to claim 5 , wherein the material is pulverized at a median particle diameter ranging from 0.2 μm to 10.0 μm.

19. The method according to claim 5 , wherein the screen has a number of meshes ranging from 10 meshes to 400 meshes.

20. The method according to claim 10 , wherein a method for the mixing comprises mixing in a VC mixer, mixing in a single-cone drying mixer, or mixing in a double-cone drying mixer.