Method for recycling phosphorus iron slag

Abstract

The present disclosure provides a recycling method of phosphorus iron slag, which comprises the following steps: (1) mixing the phosphorus iron slag, a conductive agent and a binder, pressing into a sheet and then compounding with a current collector to obtain a cathode electrode, mixing the waste lithium ion battery positive electrode powder, a conductive agent and a binder, pressing into a sheet and then compounding with a current collector to obtain an anode electrode; (2) injecting electrolyte into the cathode chamber and the anode chamber of an electrolytic device, setting an anion exchange membrane between the cathode chamber and the anode chamber, applying voltage to the cathode electrode and the anode electrode, and performing electrolysis reaction; (3) adjusting the pH of the cathode chamber, adding an oxidizing agent to perform oxidation reaction, and sintering the obtained precipitate to obtain battery-grade iron phosphate.

Description

TECHNICAL FIELD

[0001] The present disclosure belongs to the technical field of resource recycling and relates to a recycling method of phosphorus iron slag. BACKGROUND

[0002] With the development of science and technology, lithium batteries have been widely promoted due to their environmental protection and safety characteristics, but a large number of retired lithium batteries have also been generated. Lithium iron phosphate batteries have a continuously increasing market share in the power battery market due to their low cost, high reliability, and non-toxicity.

[0003] In waste lithium iron phosphate batteries, the mass fraction of lithium iron phosphate is about 35%, so it is particularly important to recycle the waste lithium iron phosphate positive material. At present, the recycling of waste lithium iron phosphate power batteries is mainly through a wet recycling process. After lithium ions in the waste lithium iron phosphate positive material are leached out by acid immersion, carbonates are added to form lithium carbonate for recycling. This process generates a large amount of phosphorus iron slag, and the treatment of phosphorus iron slag is a big problem. The traditional treatment method is to prepare phosphorus iron slag into phosphate fertilizer, iron red, etc. Although there are reports on the preparation of iron phosphate from phosphorus iron slag, the purity of the iron phosphate is low, and iron and aluminum are difficult to separate.

[0004] CN112551498A discloses a recycling method for phosphorus iron slag after lithium extraction from lithium iron phosphate. By adding an alkali solution, the phosphate and iron ions are separated, and the pH is adjusted by adding a phosphoric acid solution, followed by adding phosphoric acid to generate battery-grade iron phosphate.

[0005] CN115448279A discloses a method for recycling and preparing battery-grade iron phosphate material from phosphorus iron slag after lithium extraction. The method includes adding concentrated sulfuric acid to the phosphorus iron slag after lithium extraction after slurry preparation, then adding iron powder for reduction, adding a complexing agent to the acid leaching solution, adjusting the pH to remove impurities to obtain a ferrous sulfate solution, adding hydrogen peroxide to the filtered ferrous sulfate solution, diluting with water, and precipitating iron phosphate dihydrate at high temperature, and then adding a phosphoric acid solution to convert the entrained iron hydroxide into iron phosphate dihydrate.

[0006] The above-mentioned scheme still contains a large amount of aluminum ions in the generated iron phosphate, and the acid and alkali consumption is large, resulting in high cost. SUMMARY

[0007] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of protection of the claims.

[0008] The purpose of the present disclosure is to provide a recycling method of phosphorus iron slag. The present disclosure uses the phosphorus iron slag as the cathode of an electrolytic cell after briquetting, so that the trivalent iron in the phosphorus iron slag is reduced to divalent iron and leached out, and the aluminum ions remain in the phosphorus iron slag briquette, achieving the separation of iron and aluminum.

[0009] To achieve this purpose, the present disclosure adopts the following technical solutions:

[0010] In a first aspect, the present disclosure provides a method for recycling phosphorus iron slag, comprising the following steps:

[0011] (1) mixing the phosphorus iron slag, the conductive agent and the binder, pressing into a sheet, and then compounding with a current collector to obtain a cathode electrode, mixing the waste lithium ion battery positive electrode powder, the conductive agent and the binder, pressing into a sheet, and then compounding with a current collector to obtain an anode electrode;

[0012] (2) injecting electrolyte into the cathode chamber and the anode chamber of an electrolytic device, placing the cathode electrode in the cathode chamber and the anode electrode in the anode chamber, and setting an anion exchange membrane between the cathode chamber and the anode chamber, and applying voltage to the cathode electrode and the anode electrode to perform electrolysis reaction;

[0013] (3) adjusting the pH of the cathode chamber, adding an oxidizing agent to perform oxidation reaction, and sintering the obtained precipitate to obtain battery-grade iron phosphate.

[0014] The phosphorus iron slag according to the present disclosure is the residue after selective lithium extraction of waste lithium iron phosphate positive electrode material (for example, acid leaching method), and the main components are iron phosphate, aluminum phosphate, etc. The waste lithium ion battery can be one or more of waste lithium iron phosphate battery, waste lithium manganese iron phosphate battery, waste nickel cobalt manganese lithium battery, and waste lithium cobalt oxide battery.

[0015] The present disclosure prepares an electrode sheet by reducing the phosphorus iron slag in the cathode, enriches lithium ions in the anode chamber by electrolysis, and dissolves ferrous phosphate in the cathode chamber. The present disclosure converts insoluble iron phosphate into ferrous phosphate with higher solubility through reduction electrolysis, and can not use strong acid and strong base reagents in the process of separating iron and aluminum, which is more environmentally friendly compared with the traditional phosphorus iron slag recovery method. And it can also reduce the entrainment of aluminum ions in the impurity removal process, and the separation of iron and aluminum is more thorough.

[0016] The reaction ion equations of the cathode and the anode are as follows:

[0017] Anode oxidation, the reaction is as follows:

[0018] LiFePO4-e - →Li + +FePO4

[0019] Al-3e - →Al 3+

[0020] Cathode reduction, the reaction is as follows:

[0021] Fe 3+ +e - →Fe 2+ .

[0022] In one embodiment, the mass ratio of the phosphorus iron slag, the conductive agent and the binder in step (1) is (80-95):(1-10):(1-10), for example: 80:10:10, 85:7:8, 88:8:4, 90:5:5 or 92:2:3.

[0023] In one embodiment, the mass ratio of the waste lithium ion battery positive electrode powder, the conductive agent and the binder is (80-95):(1-10):(1-10), for example: 80:10:10, 85:7:8, 88:8:4, 90:5:5 or 92:2:3.

[0024] In one embodiment, the conductive agent includes any one or a combination of at least two of carbon powder, carbon nanotubes, acetylene black or ketjen black.

[0025] In one embodiment, the binder includes polyvinyl butyral and / or polyvinylidene fluoride.

[0026] In one embodiment, the current collector includes aluminum foil and / or foamed nickel.

[0027] In one embodiment, the pressure of the pressing in step (1) is 12-20 MPa, for example: 12 MPa, 15 MPa, 16 MPa, 18 MPa or 20 MPa, etc.

[0028] In one embodiment, the thickness of the sheet is 50-200 μm, for example: 50 μm, 80 μm, 100 μm, 150 μm or 200 μm, etc.

[0029] In one embodiment, the compounding method in step (1) includes compounding the sheet and the current collector into a sandwich structure, the outermost layer of the sandwich structure being the current collector, and the inner layer being composed of the current collector and the sheet alternately.

[0030] In one embodiment, the electrolyte in the electrolyte solution in step (2) includes a strong acid weak base salt.

[0031] The electrolyte used in the present disclosure is weakly acidic, and the trivalent iron phosphate in the cathode is reduced to ferrous phosphate, the solubility is increased, and it is dissolved in weakly acidic phosphate, and the aluminum ions in the phosphorus iron slag are difficult to reduce, so that iron and aluminum are separated.

[0032] In one embodiment, the electrolyte in the electrolyte solution includes an ammonium phosphate salt.

[0033] In one embodiment, the concentration of the electrolyte in the electrolyte solution is 0.5-2 mol / L, for example: 0.5 mol / L, 0.8 mol / L, 1 mol / L, 1.5 mol / L or 2 mol / L, etc.

[0034] In one embodiment, the voltage in step (2) is 0.8-1.2 V, for example, 0.8 V, 0.9 V, 1 V, 1.1 V or 1.2 V, etc.

[0035] The present disclosure can reduce ferric iron to ferrous iron without generating hydrogen by controlling the voltage to be 0.8-1.2 V.

[0036] In one embodiment, a non-oxidizing gas is introduced during the process of applying the voltage.

[0037] In one embodiment, the non-oxidizing gas includes any one or a combination of at least two of hydrogen, nitrogen or argon.

[0038] In one embodiment, the flow rate of the non-oxidizing gas is 5-10 mL / min, for example, 5 mL / min, 6 mL / min, 8 mL / min, 9 mL / min or 10 mL / min, etc.

[0039] In one embodiment, the pH in step (3) is 2-3, for example, 2, 2.2, 2.5, 2.8 or 3, etc.

[0040] In one embodiment, the method of adjusting the pH in the cathode chamber includes adding phosphoric acid.

[0041] In one embodiment, the oxidizing agent in step (3) includes hydrogen peroxide.

[0042] In one embodiment, the molar ratio of the oxidizing agent to ferrous ions in the cathode chamber is 1-2:1, for example, 1:1, 1.2:1, 1.5:1, 1.8:1 or 2:1, etc.

[0043] In one embodiment, the temperature of the oxidation reaction is 60-100℃, for example, 60℃, 70℃, 80℃, 90℃ or 100℃, etc.

[0044] In one embodiment, the temperature of the sintering treatment in step (3) is 400-600℃, for example, 400℃, 450℃, 500℃, 550℃ or 600℃, etc.

[0045] In one embodiment, the time of the sintering treatment is 3-7 h, for example, 3 h, 4 h, 5 h, 6 h or 7 h, etc.

[0046] As an optional solution of the present disclosure, the preparation method includes the following steps:

[0047] (1)mixing phosphorus iron slag, conductive agent and binder according to the mass ratio of (80-95):(1-10):(1-10), pressing into a sheet with a thickness of 50-200 μm under 12-20 MPa, and then compounding with a current collector to obtain a cathode electrode; mixing waste lithium ion battery positive electrode powder, conductive agent and binder according to the mass ratio of (80-95):(1-10):(1-10), pressing into a sheet with a thickness of 50-200 μm under 12-20 MPa, and then compounding with a current collector to obtain an anode electrode;

[0048] (2)injecting a strong acid weak base salt electrolyte with a concentration of 0.5-2 mol / L into the cathode chamber and the anode chamber of an electrolysis device, placing the cathode electrode in the cathode chamber and the anode electrode in the anode chamber, arranging an anion exchange membrane between the cathode chamber and the anode chamber, applying a voltage of 0.8-1.2 V to the cathode electrode and the anode electrode, and introducing a non-oxidizing gas to perform an electrolysis reaction;

[0049] (3)adjusting the pH of the cathode chamber to 2-3 by adding phosphoric acid, performing an oxidation reaction at 60-100 ℃ by adding an oxidizing agent, and sintering the obtained precipitate at 400-600 ℃ for 3-7 h to obtain battery-grade iron phosphate.

[0050] Compared with the prior art, the present disclosure has the following beneficial effects:

[0051] (1) The present disclosure prepares an electrode sheet by reducing phosphorus iron slag in the cathode, and converts insoluble iron phosphate into ferrous phosphate with higher solubility through reduction electrolysis, so that strong acid and strong base reagents are not used in the process of separating iron and aluminum, which is more environmentally friendly than the traditional phosphorus iron slag recovery method. And it can also reduce the entrainment of aluminum ions in the impurity removal process, and the separation of iron and aluminum is more thorough.

[0052] (2) In the recycling method of the present disclosure, the aluminum content in the prepared iron phosphate can reach 0.002% or less, which is much lower than the aluminum content in the iron phosphate recovered from the prior art phosphorus iron slag, and the separation of aluminum and iron is achieved.

[0053] Other aspects can be apparent after reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF DRAWINGS

[0054] The accompanying drawings are used to provide a further understanding of the technical solutions of the present disclosure, and constitute a part of the specification, and are used together with embodiments of the present application to explain the technical solutions of the present disclosure, and do not constitute a limitation on the technical solutions of the present disclosure.

[0055] Figure 1 is a schematic diagram of the device used in the recycling method according to an embodiment of the present disclosure, wherein 1 is a cathode electrode, 2 is an anode electrode, 3 is an anion exchange membrane, and 4 is an electrolyte. DETAILED DESCRIPTION

[0056] The technical solutions of the present disclosure are further illustrated by specific embodiments below. Those skilled in the art should understand that the embodiments are only used to help understand the present disclosure, and should not be regarded as specific limitations of the present disclosure.

[0057] Embodiment 1

[0058] The present embodiment provides a recycling method of phosphorus iron slag, and a schematic diagram of the device used in the recycling method is shown in Figure 1 , wherein 1 is a cathode electrode, 2 is an anode electrode, 3 is an anion exchange membrane, and 4 is an electrolyte. The recycling method comprises the following steps:

[0059] (1) The lithium-extracted phosphorus iron slag is mixed with carbon nanotubes and polyvinyl butyral according to a ratio of 90:3:7, and a sheet with a thickness of 100 μm is pressed under a pressure of 15 MPa. The pressed lithium-extracted slag sheet is combined with an aluminum foil into a sandwich structure, the outermost layer of the sandwich structure is a current collector, and the inner layer is assembled by alternately assembling the current collector and the phosphorus iron slag sheet to obtain a cathode electrode. The waste lithium iron phosphate positive electrode powder is mixed with carbon nanotubes and polyvinyl butyral according to a ratio of 90:3:7, and a sheet with a thickness of 100 μm is pressed under a pressure of 15 MPa. The pressed waste positive electrode powder sheet is combined with an aluminum foil into a sandwich structure, the outermost layer of the sandwich structure is a current collector, and the inner layer is assembled by alternately assembling the current collector and the phosphorus iron slag sheet to obtain an anode electrode;

[0060] (2) A 1 mol / L ammonium phosphate electrolyte is injected into the cathode chamber and the anode chamber of the electrolytic device, the cathode electrode is placed in the cathode chamber, the anode electrode is placed in the anode chamber, an anion exchange membrane is arranged between the cathode chamber and the anode chamber, a voltage of 1 V is applied to the cathode electrode and the anode electrode, and a mixed gas of hydrogen and nitrogen with a volume ratio of 1:4 is continuously introduced into the cathode chamber at a rate of 8 mL / min, so that lithium ions are enriched in the anode chamber and ferrous phosphate is dissolved in the cathode chamber;

[0061] (3) The pH of the cathode chamber is adjusted to 2.5 by adding phosphoric acid, hydrogen peroxide is added, the non-oxidizing atmosphere is removed, the temperature is controlled at 80℃, the divalent iron is oxidized to trivalent iron, and pure iron phosphate precipitate is obtained. The amount of hydrogen peroxide used is 1.3 times the molar amount of ferrous ions in the cathode chamber solution. The obtained precipitate is sintered at 500℃ for 4h to obtain battery-grade iron phosphate.

[0062] Embodiment 2

[0063] The present embodiment provides a recycling method of phosphorus iron slag, and a schematic diagram of the device used in the recycling method is shown in Figure 1 , wherein 1 is a cathode electrode, 2 is an anode electrode, 3 is an anion exchange membrane, and 4 is an electrolyte. The recycling method comprises the following steps:

[0064] (1) the lithium-extracted phosphorous iron slag is mixed with acetylene black and polyvinylidene fluoride at a ratio of 92:3:5, and a sheet with a thickness of 50 μm is pressed under a pressure of 20 MPa; the lithium-extracted phosphorous iron slag sheet is combined with an aluminum foil to form a sandwich structure, the outermost layer of the sandwich structure is a current collector, and the inner layer is assembled by alternately arranging the current collector and the phosphorous iron slag sheet to obtain a cathode electrode; the waste lithium iron phosphate positive electrode powder is mixed with acetylene black and polyvinylidene fluoride at a ratio of 92:3:5, and a sheet with a thickness of 50 μm is pressed under a pressure of 20 MPa; the waste positive electrode powder sheet is combined with an aluminum foil to form a sandwich structure, the outermost layer of the sandwich structure is a current collector, and the inner layer is assembled by alternately arranging the current collector and the phosphorous iron slag sheet to obtain an anode electrode;

[0065] (2) an ammonium phosphate electrolyte with a concentration of 0.5 mol / L is injected into the cathode chamber and the anode chamber of an electrolytic device, the cathode electrode is placed in the cathode chamber, the anode electrode is placed in the anode chamber, an anion exchange membrane is arranged between the cathode chamber and the anode chamber, a voltage of 0.8 V is applied to the cathode electrode and the anode electrode, and a mixed gas of hydrogen and nitrogen with a volume ratio of 1:4 is continuously introduced into the cathode chamber at a rate of 5 mL / min, so that lithium ions are enriched in the anode chamber and ferrous phosphate is dissolved in the cathode chamber;

[0066] (3) the pH of the cathode chamber is adjusted to 2 by adding phosphoric acid, hydrogen peroxide is added, the non-oxidizing atmosphere is removed, the temperature is controlled at 60℃, the divalent iron is oxidized to trivalent iron, and a pure iron phosphate precipitate is obtained, the amount of hydrogen peroxide used is 1 times the molar amount of ferrous ions in the cathode chamber solution, and the obtained precipitate is sintered at 400℃ for 7 h to obtain battery-grade iron phosphate.

[0067] Example 3

[0068] The present embodiment provides a recycling method for phosphorous iron slag, and a device used in the recycling method is shown in Figure 1 , wherein 1 is a cathode electrode, 2 is an anode electrode, 3 is an anion exchange membrane, and 4 is an electrolyte, the recycling method comprises the following steps:

[0069] (1) the lithium-extracted phosphorous iron slag is mixed with carbon powder and polyvinylidene fluoride at a ratio of 95:2:3, and a sheet with a thickness of 200 μm is pressed under a pressure of 12 MPa; the lithium-extracted phosphorous iron slag sheet is combined with an aluminum foil to form a sandwich structure, the outermost layer of the sandwich structure is a current collector, and the inner layer is assembled by alternately arranging the current collector and the phosphorous iron slag sheet to obtain a cathode electrode; the waste lithium iron phosphate positive electrode powder is mixed with carbon powder and polyvinylidene fluoride at a ratio of 95:2:3, and a sheet with a thickness of 200 μm is pressed under a pressure of 12 MPa; the waste positive electrode powder sheet is combined with an aluminum foil to form a sandwich structure, the outermost layer of the sandwich structure is a current collector, and the inner layer is assembled by alternately arranging the current collector and the phosphorous iron slag sheet to obtain an anode electrode;

[0070] (2) Injecting the ammonium phosphate electrolyte with a concentration of 2 mol / L into the cathode chamber and the anode chamber of the electrolytic device, placing the cathode electrode in the cathode chamber and the anode electrode in the anode chamber, arranging an anion exchange membrane between the cathode chamber and the anode chamber, applying a voltage of 1.2 V to the cathode electrode and the anode electrode, and continuously introducing a mixed gas of hydrogen and nitrogen into the cathode chamber at a volume ratio of 1:4 and a gas introduction rate of 10 mL / min, so that the anode chamber is enriched with lithium ions and the cathode chamber is dissolved with ferrous phosphate;

[0071] (3) Adjusting the pH of the cathode chamber to 3 by adding phosphoric acid, adding hydrogen peroxide, removing the non-oxidizing atmosphere, and controlling the temperature to 100℃, so that the divalent iron is oxidized to trivalent iron, obtaining a pure iron phosphate precipitate, the amount of hydrogen peroxide used is 2 times the molar amount of ferrous ions in the cathode chamber solution, and the obtained precipitate is sintered at 600℃ for 3h to obtain battery-grade iron phosphate.

[0072] Example 4

[0073] The difference between this example and Example 1 is only that the voltage in step (2) is 0.5 V, and the other conditions and parameters are exactly the same as in Example 1.

[0074] Example 5

[0075] The difference between this example and Example 1 is only that the voltage in step (2) is 1.5 V, and the other conditions and parameters are exactly the same as in Example 1.

[0076] Example 6

[0077] The difference between this example and Example 1 is only that the ammonium phosphate salt is replaced by sodium chloride, and the other conditions and parameters are exactly the same as in Example 1.

[0078] Comparative Example 1

[0079] This comparative example provides a method for recycling phosphorus iron slag, which comprises the following steps:

[0080] (1) Take the phosphorus iron slag and adjust the slurry according to the solid-liquid ratio of 1:2, control the temperature to 60℃, add 30% mass fraction of sodium hydroxide solution to the slurry, the amount of sodium hydroxide used is 2 times the mass of the phosphorus iron slag, the addition time is 1h, and after filtration, the alkali leaching solution and the alkali leaching residue are obtained.

[0081] (2) Adjust the pH of the first filtrate to 9.0 by adding 85% mass fraction of phosphoric acid solution to the alkali leaching solution, filter the aluminum hydroxide impurities, and then add 35% mass fraction of phosphoric acid to the first filtrate to obtain a premix. In a water bath kettle at 90℃, add a ferric chloride solution so that the ratio of phosphorus to iron in the solution is 1:1, and the concentration of iron ions is 2.5 mol / L, the reaction time is 4h, and the obtained slurry is filtered, washed, dried and then calcined at 700℃ for 2h to obtain battery-grade iron phosphate.

[0082] Performance test:

[0083] The proportion of each metal element in the iron phosphate obtained by testing each embodiment and the comparative example is shown in Table 1:

[0084] Table 1

[0085]

[0086] As can be seen from Table 1, by Examples 1-3, in the recycling method of the phosphate iron slag according to the present disclosure, the aluminum content in the prepared iron phosphate can reach 0.002% or less, which is much lower than the aluminum content in the iron phosphate prepared from the prior art phosphate iron slag, and the separation of aluminum and iron is achieved.

[0087] As can be seen from the comparison between Example 1 and Examples 4-5, in the recycling method according to the present disclosure, the voltage of electrolysis affects the recycling effect. When the voltage of electrolysis is controlled at 0.8-1.2V, the recycling effect of the phosphate iron slag is better, and no hydrogen gas is generated. If the voltage is too low, the trivalent iron cannot be reduced to divalent iron, and if the voltage is too high, hydrogen gas will be generated during the reaction process, affecting the reduction effect of trivalent iron.

[0088] As can be seen from the comparison between Example 1 and Example 6, the electrolyte used in the present disclosure is weakly acidic, and the trivalent iron phosphate at the cathode is reduced to ferrous phosphate, which has a higher solubility and dissolves in weakly acidic phosphate, making it difficult to reduce aluminum ions in the phosphate iron slag, so that iron and aluminum are separated.

[0089] As can be seen from the comparison between Example 1 and Comparative Example 1, in the present disclosure, the phosphate iron slag is prepared into an electrode sheet by cathodic reduction, and the insoluble iron phosphate is converted into ferrous phosphate with higher solubility by reduction electrolysis. In the process of separating iron and aluminum, no strong acid or strong base reagent is used, which is more environmentally friendly compared with the traditional phosphate iron slag recycling method. And it can also reduce the entrainment of aluminum ions in the impurity removal process, and the separation of iron and aluminum is more thorough.

Claims

1. A method for recycling ferrophosphate slag, the recycling method comprising the following steps: (1) Mix phosphorus iron slag, conductive agent and binder, press into thin sheet and then combine with current collector to obtain cathode electrode; mix waste lithium-ion battery positive electrode powder, conductive agent and binder, press into thin sheet and then combine with current collector to obtain anode electrode. (2) Electrolyte is injected into the cathode chamber and anode chamber of the electrolysis device, the cathode electrode is placed in the cathode chamber and the anode electrode is placed in the anode chamber, an anion exchange membrane is set between the cathode chamber and the anode chamber, and a voltage is applied to the cathode electrode and the anode electrode to carry out the electrolysis reaction; (3) Adjust the pH of the cathode chamber, add an oxidant to carry out an oxidation reaction, and sinter the obtained precipitate to obtain battery-grade iron phosphate; The voltage in step (2) is 0.8 to 1.2V, and a non-oxidizing gas is introduced during the application of the voltage.

2. The reuse method as described in claim 1, wherein, The mass ratio of the phosphorus iron slag, conductive agent and binder in step (1) is (80-95):(1-10):(1-10).

3. The reuse method as described in claim 1, wherein, The mass ratio of the waste lithium-ion battery cathode powder, conductive agent and binder is (80-95):(1-10):(1-10).

4. The reuse method as described in claim 1, wherein, The conductive agent includes any one or a combination of at least two of the following: carbon powder, carbon nanotubes, acetylene black, or Ketjen black.

5. The reuse method as described in claim 1, wherein, The adhesive comprises polyvinyl butyral and / or polyvinylidene fluoride.

6. The reuse method as described in claim 1, wherein, The current collector includes aluminum foil and / or nickel foam.

7. The reuse method as described in claim 1, wherein, The pressing pressure in step (1) is 12-20 MPa.

8. The reuse method as described in claim 1, wherein, The thickness of the sheet is 50–200 μm.

9. The reuse method as described in claim 1, wherein, The composite method described in step (1) includes combining the sheet and the current collector into a sandwich structure, wherein the outermost layer of the sandwich structure is the current collector, and the inner layer is composed of alternating current collectors and sheets.

10. The reuse method as described in claim 1, wherein, The electrolyte in the electrolyte in step (2) includes strong acid and weak base salts.

11. The reuse method as described in claim 1, wherein, The electrolyte in the electrolyte solution includes ammonium phosphate.

12. The reuse method as described in claim 1, wherein, The concentration of the electrolyte in the electrolyte solution is 0.5–2 mol / L.

13. The reuse method as described in claim 1, wherein, The non-oxidizing gas includes any one or a combination of at least two of hydrogen, nitrogen, or argon.

14. The reuse method as described in claim 1, wherein, The flow rate of the non-oxidizing gas is 5–10 mL / min.

15. The reuse method as described in claim 1, wherein, The pH value in step (3) is 2 to 3.

16. The reuse method as described in claim 1, wherein, The method of adjusting the pH of the cathode chamber includes adding phosphoric acid.

17. The reuse method as described in claim 1, wherein, The oxidant in step (3) includes hydrogen peroxide.

18. The reuse method as described in claim 1, wherein, The molar ratio of the oxidant to the ferrous ions in the cathode chamber is 1 to 2:

1.

19. The reuse method as described in claim 1, wherein, The oxidation reaction is carried out at a temperature of 60–100°C.

20. The reuse method as described in claim 1, wherein, The sintering temperature in step (3) is 400–600°C.

21. The reuse method as described in claim 1, wherein, The sintering process takes 3 to 7 hours.

22. The reuse method as described in claim 1, wherein, The reuse method includes the following steps: (1) Phosphorus iron slag, conductive agent and binder are mixed in a mass ratio of (80-95):(1-10):(1-10), and pressed into a thin sheet with a thickness of 50-200μm under 12-20MPa. The sheet is then combined with a current collector to obtain a cathode electrode. Waste lithium-ion battery positive electrode powder, conductive agent and binder are mixed in a mass ratio of (80-95):(1-10):(1-10), and pressed into a thin sheet with a thickness of 50-200μm under 12-20MPa. The sheet is then combined with a current collector to obtain an anode electrode. (2) A strong acid-weak base salt electrolyte with a concentration of 0.5-2 mol / L is injected into the cathode chamber and anode chamber of the electrolysis device. The cathode electrode is placed in the cathode chamber and the anode electrode is placed in the anode chamber. An anion exchange membrane is set between the cathode chamber and the anode chamber. A voltage of 0.8-1.2V is applied to the cathode electrode and the anode electrode, and a non-oxidizing gas is introduced to carry out the electrolysis reaction. (3) Add phosphoric acid to adjust the pH of the cathode chamber to 2-3, add oxidant and carry out oxidation reaction at 60-100℃, and sinter the obtained precipitate at 400-600℃ for 3-7h to obtain battery-grade iron phosphate.

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