METHOD FOR RECYCLING LITHIUM IRON PHOSPHATE WASTE BATTER

Abstract

The disclosure discloses a method for recycling a lithium iron phosphate waste battery, and belongs to the technical field of battery recycling. In the method for recycling the lithium iron phosphate waste battery according to the disclosure, it takes a cathode material of the waste lithium iron phosphate battery as a main body, uses a lithium source, a ferric source and a phosphorus source to supplement lithium to the cathode material for repairing, and meanwhile, rebuilds a new lithium iron phosphate coating layer containing a carbon layer cross-linked structure on a surface of the cathode material to realize regeneration of the lithium iron phosphate The disclosure also provides a regenerated lithium iron phosphate/C cathode material prepared by the recycling method.

Claims

1. A method for recycling lithium iron phosphate waste batteries, comprising the following steps of: (1) preprocessing a cathode material: subjecting a cathode plate of the lithium iron phosphate waste batteries to washing, removal of impurity by heating, and sieving to obtain a lithium iron phosphate powder A; (2) preprocessing an anode material: after washing and drying an anode graphite plate of the lithium iron phosphate waste batteries, adding an obtained graphite powder into a mixed acid solution, stirring and reacting for 5 hours to 10 hours to obtain a mixed solution B; wherein, the mixed acid solution is a mixed solution of hydrochloric acid and nitric acid, and a ratio of a mass of the graphite powder to a volume of the mixed acid solution is (100 to 300) g:1 L, and in the mixed solution, a concentration of the hydrochloric acid is 6 mol/L, to 8 mol/L, and a concentration of the nitric acid is 1 mol/L to 2 mol/L; and then, adding an oxidant into the mixed solution B, and heating until the reaction is complete, then adding a reductant for a reduction reaction, and obtaining a modified graphite powder C after heating and heat preservation; wherein, the oxidant is at least one selected from the group consisting of sodium hypochlorite and potassium hypochlorite, the reductant is hydrogen peroxide, and the heating and heat preservation is heating to a temperature of 450? C. to 600? C. in an inert atmosphere and keeping the temperature for 1 hour to 3 hours; (3) preparing a precursor: dispersing the lithium iron phosphate powder A and the modified graphite powder C in deionized water, introducing a soluble ferric salt, PEG, a soluble phosphate and gelatin, uniformly mixing, then adding a lithium salt, and drying to obtain a precursor gel D; wherein a mass ratio of the lithium iron phosphate powder A, the modified graphite powder C and the gelatin is 1:(0.1 to 0.5):(0.01 to 0.5); and (4) preparing a regenerated lithium iron phosphate/C cathode material: calcining the precursor gel D at 600? C. to 800? C. in an inert atmosphere for 5 hours to 10 hours, washing and drying to obtain the regenerated lithium iron phosphate/C cathode material.

2. The method for recycling the lithium iron phosphate waste batteries according to claim 1, wherein in the step (1), the cathode plate is washed with an organic solvent, wherein the organic solvent is at least one selected from the group consisting of ethanol, methanol and NMP.

3. The method for recycling the lithium iron phosphate waste batteries according to claim 1, wherein in the step (1), the removal of impurity by heating involves heating the cathode plate after being washed to a temperature of 100? C. to 200? C. in an inert atmosphere and keeping the temperature for 1 hour to 2 hours.

4-6. (canceled)

7. The method for recycling the lithium iron phosphate waste batteries according to claim 1, wherein in the step (3), the soluble ferric salt comprises at least one selected from the group consisting of ferric sulfate, ferric nitrate and ferric chloride; the soluble phosphate is ammonium dihydrogen phosphate; and the lithium salt is at least one selected from the group consisting of lithium carbonate, lithium oxalate, lithium acetate and lithium bromide.

8. The method for recycling the lithium iron phosphate waste batteries according to claim 7, wherein a molar ratio of Fe.sup.3+ in the soluble ferric salt, PO4.sup.3? in the soluble phosphate and Li.sup.+ in the lithium salt is (0.8 to 1):(0.8 to 1):(1 to 1.2).

9. The method for recycling the lithium iron phosphate waste batteries according to claim 8, wherein a molar ratio of Lit in the lithium salt to the lithium iron phosphate powder A is (0.05 to 0.1):1.

10. A regenerated lithium iron phosphate/C cathode material prepared by the method for recycling the lithium iron phosphate waste batteries according to claim 1.

11. (canceled)

12. A regenerated lithium iron phosphate/C cathode material prepared by the method for recycling the lithium iron phosphate waste batteries according to claim 2.

13. A regenerated lithium iron phosphate/C cathode material prepared by the method for recycling the lithium iron phosphate waste batteries according to claim 3.

14-16. (canceled)

17. A regenerated lithium iron phosphate/C cathode material prepared by the method for recycling the lithium iron phosphate waste batteries according to claim 7.

18. A regenerated lithium iron phosphate/C cathode material prepared by the method for recycling the lithium iron phosphate waste batteries according to claim 8.

19. A regenerated lithium iron phosphate/C cathode material prepared by the method for recycling the lithium iron phosphate waste batteries according to claim 9.

Description

DETAILED DESCRIPTION

[0031] In order to better explain the objects, technical solutions and advantages of the present disclosure, the present disclosure will be further explained with reference to specific embodiments and comparative examples, with the aim of understanding the content of the present disclosure in detail, but not limiting the present disclosure. All other embodiments obtained by those having ordinary skills in the art without paying creative work belong to the protection scope of the present disclosure. Unless otherwise specified, the experimental reagents, raw materials and instruments designed in the embodiments and comparative examples of the present disclosure are all commonly used common reagents, raw materials and instruments, especially the used lithium iron phosphate waste battery. The cathode material and the anode graphite material in the battery are all conventionally purchased raw materials, and the self-made recycled raw materials are also be used.

Example 1

[0032] A method for recycling a lithium iron phosphate waste battery according to an example of the present disclosure comprised the following steps of: [0033] (1) preprocessing a cathode material: washing a cathode plate of the lithium iron phosphate waste battery by using a mixed solution of ethanol and NMP (volume ratio of 1:1), heating to 150? C. in an argon atmosphere in a sealed manner, preserving heat for 2 hours, removing impurities, and sieving to obtain a lithium iron phosphate powder A; [0034] (2) preprocessing an anode material: after washing an anode graphite plate of the lithium iron phosphate waste battery with ethanol and drying, adding the obtained graphite powder into a mixed acid solution, stirring and reacting for 8 hours to obtain a mixed solution B; wherein, the mixed acid solution was a mixed solution of hydrochloric acid (6 mol/L) and nitric acid (2 mol/L), and a ratio of a mass of the graphite powder to a volume of the mixed acid solution was 200 g:1 L; and [0035] then, adding an oxidant sodium hypochlorite into the mixed solution B, and heating until the reaction is complete, then adding a reductant hydrogen peroxide for a reduction reaction (a mass ratio of the graphite powder to the oxidant to the hydrogen peroxide was 1:0.5:1), and obtaining a modified graphite powder C after heating and heat preservation for 2 hours at 500? C. under an argon atmosphere; [0036] (3) preparing a precursor: dispersing the lithium iron phosphate powder A and the modified graphite powder C in deionized water, introducing a soluble ferric salt ferric chloride, PEG, a soluble phosphate ammonium dihydrogen phosphate and gelatin, uniformly mixing, then adding a lithium salt lithium carbonate, and drying to obtain a precursor gel D; wherein a mass ratio of the lithium iron phosphate powder A to the modified graphite powder C and the gelatin was 1:0.2:0.04; a molar ratio of Li.sup.+ in the lithium salt to the lithium iron phosphate powder A was 0.1:1; and a molar ratio of Fe.sup.3+ in the soluble ferric salt, PO4.sup.3? in the soluble phosphate and Lit in the lithium salt was 1:1.1:1.2; and [0037] (4) preparing a regenerated lithium iron phosphate/C cathode material: calcining the precursor gel D at 700? C. in an argon atmosphere for 8 hours, washing and drying to obtain the regenerated lithium iron phosphate/C cathode material.

Example 2

[0038] A method for recycling a lithium iron phosphate waste battery according to an example of the present disclosure comprised the following steps of: [0039] (1) preprocessing a cathode material: washing a cathode plate of the lithium iron phosphate waste battery by using a mixed solution of ethanol and NMP (volume ratio of 1:1), heating to 200? C. in an argon atmosphere in a sealed manner, preserving heat for 1.5 hours, removing impurities, and sieving to obtain a lithium iron phosphate powder A; [0040] (2) preprocessing an anode material: after washing an anode graphite plate of the lithium iron phosphate waste battery with ethanol and drying, adding the obtained graphite powder into a mixed acid solution, stirring and reacting for 8 hours to obtain a mixed solution B; wherein, the mixed acid solution was a mixed solution of hydrochloric acid (6 mol/L) and nitric acid (2 mol/L), and a ratio of a mass of the graphite powder to a volume of the mixed acid solution was 200 g:1 L; and [0041] then, adding an oxidant potassium hypochlorite into the mixed solution B, and heating until the reaction is complete, then adding a reductant hydrogen peroxide for a reduction reaction (a mass ratio of the graphite powder to the oxidant to the hydrogen peroxide was 1:0.5:1), and obtaining a modified graphite powder C after heating and heat preservation for 2 hours at 500? C. under an argon atmosphere; [0042] (3) preparing a precursor: dispersing the lithium iron phosphate powder A and the modified graphite powder C in deionized water, introducing a soluble ferric salt ferric nitrate, PEG, a soluble phosphate ammonium dihydrogen phosphate and gelatin, uniformly mixing, then adding a lithium salt lithium acetate, and drying to obtain a precursor gel D; wherein a mass ratio of the lithium iron phosphate powder A to the modified graphite powder C and the gelatin was 1:0.2:0.04; a molar ratio of Li.sup.+ in the lithium salt to the lithium iron phosphate powder A was 0.1:1; and a molar ratio of Fe.sup.3+ in the soluble ferric salt, PO4.sup.3? in the soluble phosphate and Li.sup.+ in the lithium salt was 1:1.1:1.2; and [0043] (4) preparing a regenerated lithium iron phosphate/C cathode material: calcining the precursor gel D at 650? C. in an argon atmosphere for 10 hours, washing and drying to obtain the regenerated lithium iron phosphate/C cathode material.

Example 3

[0044] A method for recycling a lithium iron phosphate waste battery according to an example of the present disclosure comprised the following steps of: [0045] (1) preprocessing a cathode material: washing a cathode plate of the lithium iron phosphate waste battery by using a mixed solution of ethanol and NMP (volume ratio of 1:1), heating to 150? C. in an argon atmosphere in a sealed manner, preserving heat for 2 hours, removing impurities, and sieving to obtain a lithium iron phosphate powder A; [0046] (2) preprocessing an anode material: after washing an anode graphite plate of the lithium iron phosphate waste battery with ethanol and drying, adding the obtained graphite powder into a mixed acid solution, stirring and reacting for 8 hours to obtain a mixed solution B; wherein, the mixed acid solution was a mixed solution of hydrochloric acid (8 mol/L) and nitric acid (1 mol/L), and a ratio of a mass of the graphite powder to a volume of the mixed acid solution was 300 g:1 L; and then, adding an oxidant sodium hypochlorite into the mixed solution B, and heating until the reaction is complete, then adding a reductant hydrogen peroxide for a reduction reaction (a mass ratio of the graphite powder to the oxidant to the hydrogen peroxide was 1:0.5:1), and obtaining a modified graphite powder C after heating and heat preservation for 2 hours at 500? C. under an argon atmosphere; [0047] (3) preparing a precursor: dispersing the lithium iron phosphate powder A and the modified graphite powder C in deionized water, introducing a soluble ferric salt ferric nitrate, PEG, a soluble phosphate ammonium dihydrogen phosphate and gelatin, uniformly mixing, then adding a lithium salt lithium carbonate, and drying to obtain a precursor gel D; wherein a mass ratio of the lithium iron phosphate powder A to the modified graphite powder C and the gelatin was 1:0.2:0.04; a molar ratio of Li.sup.+ in the lithium salt to the lithium iron phosphate powder A was 0.1:1; and a molar ratio of Fe.sup.3+ in the soluble ferric salt, PO4.sup.3? in the soluble phosphate and Li.sup.+ in the lithium salt was 1:1.1:1.2; and [0048] (4) preparing a regenerated lithium iron phosphate/C cathode material: calcining the precursor gel D at 750? C. in an argon atmosphere for 6 hours, washing and drying to obtain the regenerated lithium iron phosphate/C cathode material.

Example 4

[0049] The only difference between this comparative example and Example 1 was that a mass ratio of the lithium iron phosphate powder A to the modified graphite powder C and the gelatin in the step (3) was 1:0.5:0.05.

Example 5

[0050] The only difference between this comparative example and Example 1 was that a mass ratio of the lithium iron phosphate powder A to the modified graphite powder C and the gelatin in the step (3) was 1:0.1:0.01.

Comparative Example 1

[0051] The only difference between this comparative example and Example 1 was that the soluble ferric salt, the soluble phosphate and the lithium salt were not introduced in the step (3).

Comparative Example 2

[0052] The only difference between this comparative example and Example 1 was that the modified graphite powder C in the step (3) was replaced by commercially available graphite.

Comparative Example 3

[0053] The only difference between this comparative example and Example 1 was that the modified graphite powder C in the step (3) was replaced by self-prepared graphene by using HUMMER method.

[0054] The specific steps of HUMMER method were as follows: adding 5 g of graphite powder, 1 g of sodium nitrate and 6 g of potassium permanganate into an appropriate amount (about 200 mL) of a mixed solution of high-concentration concentrated sulfuric acid solution and phosphoric acid solution at 0? C. in an ice bath, stirring and mixing, adding 6 g of potassium permanganate again, heating to a normal temperature, reacting for 12 hours, adding an appropriate amount of hydrogen peroxide for completely reaction, drying the resulted product to be viscous, dispersing a part of the viscous product in water, adding an appropriate amount of hydrazine hydrate under an ultrasonic condition, reacting for 24 hours completely, washing the obtained product with ethanol and water, and drying to obtain the self-prepared graphene.

Comparative Example 4

[0055] The only difference between this comparative example and Example 1 was that in the step (2), the graphite powder was added into the mixed acid solution and stirred for reaction for 15 hours to obtain the mixed solution B; and a ratio of a mass of the graphite powder to a volume of the mixed acid solution was 50 g:1 L.

Comparative Example 5

[0056] The only difference between this comparative example and Example 1 was that the gelatin in the step (3) was replaced by glucose.

Comparative Example 6

[0057] The only difference between this comparative example and Example 1 was that the gelatin in the step (3) was replaced by sucrose.

Comparative Example 7

[0058] The only difference between this comparative example and Example 1 was that the PEG in the step (3) was replaced by CTAB (cetyltrimethylammonium bromide).

Comparative Example 8

[0059] The only difference between this comparative example and Example 1 was that a mass ratio of the lithium iron phosphate powder A to the modified graphite powder C and the gelatin in the step (3) was 1:0.2:0.005.

Comparative Example 9

[0060] The only difference between this comparative example and Example 1 was that a mass ratio of the lithium iron phosphate powder A to the modified graphite powder C and the gelatin in the step (3) was 1:0.1:0.1.

Effect Example 1

[0061] In order to verify the performances of the regenerated lithium iron phosphate/C cathode materials prepared by the method for recycling the lithium iron phosphate waste battery according to the present disclosure, the products of each example and comparative example were prepared into lithium ion half batteries for performance test, wherein the lithium-ion half batteries were assembled by using metal lithium plates as anode electrodes and commercial electrolyte. The test was carried out at a working voltage of 2.5 V to 4.3 V. Each group of assembled batteries was subjected to long cycle tests for 200 cycles at a multiplying factor of 0.5 C, and the results were shown in Table 1.

TABLE-US-00001 TABLE 1 Initial specific Specific discharge Tested discharge capacity capacity after 200 performance at (mAh/g) cycles (mAh/g) Example 1 152.5 142.7 Example 2 150.1 139 Example 3 155.6 140.5 Example 4 143 136.1 Example 5 158.4 137 Comparative 121.5 98.6 Example 1 Comparative 154.7 126 Example 2 Comparative 153.9 131 Example 3 Comparative 145.3 118.4 Example 4 Comparative 148 115.9 Example 5 Comparative 150.5 106 Example 6 Comparative 146.7 121.8 Example 7 Comparative 156 125.5 Example 8 Comparative 141.2 113.7 Example 9

[0062] As can be seen from Table 1, the initial capacity of all the regenerated lithium iron phosphate/C cathode material prepared by the method for recycling the lithium iron phosphate waste battery according to the present disclosure is high, and the specific discharge capacity is still maintained more than 135 mAh/g after 200 cycles at a low multiplying factor of 0.5 C. After calculation, the capacity retention rates of Examples 1 to 5 are 93.57%, 92.6%, 90.29%, 95.17% and 86.48% respectively. In contrast, the long-cycle specific discharge capacities or capacity retention rates of the products of the comparative examples are difficult to reach the level of the examples, and the products of Comparative Example 1 prepared without building a new lithium iron phosphate layer and lithium supplementation of the original lithium iron phosphate layer have either low initial specific discharge capacity or capacity retention rate. However, in Comparative Examples 2 and 3, the commercial graphite or graphene which are common in the prior art are used as the graphite layers in the process, since the interlayer spacing between the commercial graphite and graphene is small, it is difficult to achieve an ideal lithium iron phosphate loading effect, and the cycle stability is not as good as that of the product of Example 1. The degree of acidification and oxidation of the graphite powder in the product of Comparative Example 4 are too high, so an interlayer structure of the graphite powder is destroyed to a certain extent. The original lithium iron phosphate particles from the waste battery are difficult to uniformly load on the surface of the graphite layer, and the newly generated lithium iron phosphate cannot be uniformly dispersed, so the cycle stability of the product is not high. An amorphous carbon source and a surfactant used in the process methods of Comparative Examples 5 to 7 are not the preferred types of the present disclosure. Compared with the gelatin, the soluble carbon source is difficult to form a good gel dispersion system in the precursor preparation process, and the product appears obvious unevenness in the subsequent sintering process. Even if the gelatin is used as the amorphous carbon source matching the graphite layer, selecting other kinds of surfactants will also lead to the difficulty in reaching the ideal degree of uniformity of each component, so the specific discharge capacity and cycle stability of the product are not high. The ratio of the graphite powder to the amorphous carbon in Comparative Examples 8 and 9 is inappropriate, and the specific discharge capacities or cycle stabilities of the products are not as good as those of Examples 1, 4 and 5.

Effect Example 2

[0063] The same method as that in Effect Example 1 was used. When testing the electrochemical performance, each product was first cycled for 20 cycles at a multiplying factor rate of 0.5 C, then cycled for 200 cycles at a multiplying factor of IC, and finally lowered to a multiplying factor of 0.5 C again. The test results were shown in Table 2.

TABLE-US-00002 TABLE 2 Specific Initial discharge capacity specific discharge Specific discharge after returning Tested capacity at 0.5 C capacity at 1 C back to 0.5 C performance (mAh/g) (mAh/g) (mAh/g) Example 1 150.6 132.5 139.5 Example 2 151.3 126.1 137 Example 3 157.2 128 135.8 Example 4 139.5 118.5 129.5 Example 5 152.6 119.6 126 Comparative 125.4 76.8 92.2 Example 1 Comparative 150 115 124 Example 2 Comparative 152.7 120.7 125.7 Example 3 Comparative 148.1 108.5 120.5 Example 4 Comparative 145.2 105.2 116.7 Example 5 Comparative 151 96.5 109 Example 6 Comparative 148.9 115.9 122.6 Example 7 Comparative 152.5 104.6 119.2 Example 8 Comparative 145.7 98.5 108 Example 9

[0064] It can be seen from Table 2 that the regenerated lithium iron phosphate/C cathode material prepared by the method for recycling the lithium iron phosphate waste battery according to the present disclosure also has an ideal rate performance, and can still maintain a specific discharge capacity more than 115 mAh/g at a multiplying factor of 1 C. At the same time, the capacity of the product returning back to multiplying factor cycle after high multiplying factor cycle is equivalent to that of low multiplying factor cycle in Table 1, indicating that the product has high structural stability and will not be destroyed by high multiplying factor cycle.

[0065] Finally, it should be noted that the embodiments above are merely used to illustrate the technical solutions of the present disclosure, but are not intended to limit the protection scope of the present disclosure. Although the present disclosure has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present disclosure can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present disclosure.