Full-resource cyclic regeneration method of waste lithium iron phosphate positive electrode material

Abstract

The invention discloses a waste lithium iron phosphate positive electrode material full-resource cyclic regeneration method, and belongs to the technical field of lithium ion batteries, the regeneration method comprises the following steps: S1, adding an oxalic acid solution to carry out acid leaching treatment on a waste lithium iron phosphate positive electrode material; s2, solid and liquid in the mixture obtained through acid leaching treatment are separated, and first filtrate and first filter residues are obtained; s3, adding an impurity removal agent into the first filtrate, and precipitating and removing copper ions, aluminum ions and fluorine ions in the first filtrate to obtain second filtrate; s4, mixing the first filter residue, sodium hydroxide and hydrogen peroxide, and reacting; carrying out solid-liquid separation on the reacted mixed solution to obtain second filter residues; and S5, mixing the second filtrate with the second filter residue to prepare the lithium iron phosphate positive electrode material. The regeneration method provided by the invention has the advantages of short process and few byproducts; only impurities in the waste lithium phosphate are removed, the obtained second filtrate and second filter residue are directly used for preparing the lithium iron phosphate positive electrode material, and phosphorus and iron elements are recycled and regenerated.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and in particular to a method for recycling waste lithium iron phosphate positive electrode materials. Background Art

[0002] As the positive electrode material of lithium-ion batteries, lithium iron phosphate has the advantages of good thermal stability, relatively cheap raw materials, and mature preparation technology. The prepared lithium-ion batteries have a long cycle life and are widely used in electric vehicles, energy storage systems, power tools and other fields. With the increase in the application of lithium-ion batteries, the amount of scrapped lithium iron phosphate batteries has also gradually increased.

[0003] As the demand for electric vehicles and energy storage systems continues to increase, lithium resources are becoming increasingly scarce. In addition to lithium, lithium iron phosphate cathode materials also contain valuable elements such as iron and phosphorus. The recycling of these elements can provide raw materials for industry, reduce the demand for mining of primary resources, and reduce dependence on new mineral resources. Recycling materials from waste batteries is usually cheaper than extracting new materials from ores. Recycling lithium iron phosphate cathode materials in lithium batteries is not only a need for resource conservation and environmental protection, but also a requirement for economic benefits and social responsibility. Through effective recycling and reuse, not only can dependence on natural resources be reduced, but environmental pollution can also be reduced.

[0004] There are three main types of recycling processes currently in use: The first type is to use inorganic acid + hydrogen peroxide to extract lithium first, and then to recover phosphorus and iron. The main products are battery-grade lithium carbonate or battery-grade lithium hydroxide, and battery-grade iron phosphate; the second type is to use inorganic acid leaching, first recover phosphorus and iron, and then extract lithium. Its main products are also battery-grade lithium carbonate or battery-grade lithium hydroxide, and battery-grade iron phosphate; the third type is to add lithium, additives, etc. to the waste lithium iron phosphate positive electrode material, and then granulate and calcine again. Both the first and second types of processes have the disadvantages of long process steps, high loss of precious metal lithium, many by-products, and large amounts of wastewater and waste residue. The electrical properties and processing properties of the positive electrode material obtained by the third type of process are greatly affected by the raw materials. Summary of the invention

[0005] The object of the present invention is to provide a method for the full resource recycling of waste lithium iron phosphate positive electrode materials with short process steps and few by-products.

[0006] The present invention discloses a method for recycling waste lithium iron phosphate cathode materials, comprising the following steps:

[0007] S1: adding oxalic acid solution to acid-leach the waste lithium iron phosphate positive electrode material;

[0008] S2: separating the solid and the liquid in the mixture obtained by the acid leaching treatment to obtain a first filtrate and a first filter residue;

[0009] S3: adding an impurity remover to the first filtrate to precipitate and remove copper ions, aluminum ions, and fluoride ions in the first filtrate to obtain a second filtrate;

[0010] S4: mixing the first filter residue, sodium hydroxide and hydrogen peroxide and reacting them; performing solid-liquid separation on the mixed liquid after the reaction to obtain a second filter residue;

[0011] S5: Mix the second filtrate with the second filter residue to prepare a lithium iron phosphate positive electrode material.

[0012] Lithium iron phosphate reacts with oxalic acid to generate ferrous oxalate and lithium dihydrogen phosphate. Ferrous oxalate has extremely low solubility in aqueous solution and exists in the form of precipitation; lithium dihydrogen phosphate has good solubility in aqueous solution, so it exists in the form of solution.

[0013] Furthermore, in step S1, the oxalic acid solution is an aqueous solution of oxalic acid, wherein the mass ratio of waste lithium iron phosphate to oxalic acid is 1:1.7-1.8; and the acid leaching process is carried out at 75-85° C. and stirred for 3.5-5 hours.

[0014] Controlling the acid leaching process temperature within this range can significantly increase the reaction rate and leaching efficiency, while reducing energy consumption and operational complexity. In addition, this temperature can also reduce the risk of side reactions and equipment corrosion, and improve the recovery rate and purity of metals.

[0015] Furthermore, after the acid leaching treatment, ferric hydroxide is added to adjust the pH of the mixed reaction solution to 3.9-4.2.

[0016] Ferrous oxalate has a high solubility in an acidic environment. Adding ferric hydroxide to adjust the pH of the mixed reaction solution to 3.9-4.2 can greatly reduce the solubility of ferrous oxalate and greatly reduce the amount of ferrous oxalate remaining in the solution. Adding ferric hydroxide reacts with excess oxalic acid to form ferrous oxalate without introducing additional impurities.

[0017] Furthermore, in step S3, the impurity remover is selected from one or more of sodium fluoride, sodium sulfide, lithium hydroxide, lithium carbonate, and hydrogen peroxide.

[0018] Sodium fluoride can remove aluminum ions and fluoride ions in lithium dihydrogen phosphate; sodium sulfide, lithium hydroxide, lithium carbonate, and hydrogen peroxide can remove copper ions and iron ions.

[0019] Furthermore, in step S4, the mass ratio of sodium hydroxide to hydrogen peroxide is 14:3.5-4; the first filter residue, sodium hydroxide and hydrogen peroxide are mixed and reacted at a temperature of 35-45° C. for 0.8-2 h; and then the temperature is raised to 85-95° C. and the reaction is continued for 1-2 h.

[0020] Hydrogen peroxide oxidizes the divalent iron in ferrous oxalate into trivalent iron, and then reacts with sodium hydroxide to form ferric hydroxide precipitate; hydrogen peroxide will decompose significantly above 80°C, and the mixed solution after the reaction is heated to 85-95°C to remove the unreacted excess hydrogen peroxide.

[0021] Furthermore, in step S4, sodium carbonate is added to the filtrate obtained after solid-liquid separation; impurities are then removed by ion exchange resin to obtain a sodium oxalate solution.

[0022] The main component of the filtrate after solid-liquid separation is sodium oxalate. Sodium carbonate is added to remove the aluminum ions in the sodium oxalate solution in the form of basic aluminum carbonate; other impurity ions are then removed through resin ion exchange to obtain a refined sodium oxalate solution.

[0023] Furthermore, in step S4, the obtained sodium oxalate solution is treated by a bipolar membrane system to obtain an oxalic acid aqueous solution and a sodium hydroxide aqueous solution.

[0024] The bipolar membrane system is a special electrodialysis technology that combines the functions of cation exchange membrane and anion exchange membrane to decompose water molecules into hydrogen ions (H + ) and hydroxide ions (OH - ). This technology is widely used in many industrial processes, especially in the production and recovery of acids and alkalis, wastewater treatment, and certain chemical synthesis reactions. The bipolar membrane consists of three layers: a cation exchange layer that allows cations to pass through; an intermediate hydrolysis layer, which is usually a hydrophilic polymer layer that allows water molecules to decompose in this layer; and an anion exchange layer that allows anions to pass through. Under the action of the electric field, water molecules in the intermediate hydrolysis layer decompose into H + and OH - The generated H + Migrate to one side through the cation exchange layer to form an acidic solution; the generated OH - Migrate through the anion exchange layer to the other side to form an alkaline solution.

[0025] Sodium oxalate is converted into sodium hydroxide solution and oxalic acid solution through a bipolar membrane system, which are recycled and applied to step S1 and step S4 without generating any extra by-products. The problem of a large amount of by-products, waste water and waste residues in the process of recycling waste lithium iron phosphate can be solved. The auxiliary materials oxalic acid and sodium hydroxide used in the present invention are recycled through a bipolar membrane system, so the process has the advantages of being green, environmentally friendly and energy-saving.

[0026] Furthermore, in step S5, the ratio of Li / Fe / P in the second filtrate and the second filter residue is adjusted by lithium carbonate and lithium phosphate.

[0027] During the processing, impurities in lithium dihydrogen phosphate and ferric hydroxide are removed, and then the lithium iron phosphate positive electrode material is directly synthesized. Its electrical properties and processing properties are no different from those of the newly synthesized and processed lithium iron phosphate positive electrode material.

[0028] Furthermore, in step S5, the molar ratio of Li / Fe / P in the mixture of the first filtrate and the second residue is adjusted to (1.033-1.035):1:1, and a carbon source is added after evaporation and concentration, and then spray granulation is performed and calcined to obtain a lithium iron phosphate positive electrode material, wherein the carbon source is selected from one or more of glucose, sucrose or carbon black.

[0029] Furthermore, in step S5, the concentration is carried out by evaporation; the evaporation concentration is carried out until the solid-liquid ratio in the mixed liquid is 30-40%, and then spray granulation is carried out after adding a carbon source, and the obtained solid is calcined at 700-800° C. to obtain a lithium iron phosphate positive electrode material.

[0030] The invention provides a method for recycling waste lithium iron phosphate positive electrode materials in a full resource manner. The waste lithium iron phosphate is subjected to acid leaching with an oxalic acid solution to obtain a first filtrate, a lithium dihydrogen phosphate solution, while almost no lithium element is taken away in the first filter residue, and the loss of lithium element is small; the process is short, the by-products are small, and only impurities in the waste lithium phosphate are removed; the obtained lithium dihydrogen phosphate solution and the second filter residue are directly used for the subsequent preparation of lithium iron phosphate positive electrode materials, and phosphorus and iron elements are recovered and regenerated. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a process flow chart of the full resource recycling method of waste lithium iron phosphate positive electrode materials provided by the present invention;

[0032] Figure 2 This is a test diagram of the lithium iron phosphate positive electrode material prepared in Example 1 of the present invention;

[0033] Figure 3 This is a test diagram of the lithium iron phosphate positive electrode material prepared in Example 2 of the present invention. DETAILED DESCRIPTION

[0034] In order to make the technical solution of the present invention clearer, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0035] Example 1

[0036] Waste lithium iron phosphate positive electrode powder was collected, and the test indicators (mass percentage) were: Li 4.05%, Fe 31.12%, P17.40%, Cu 0.00325%, Al 0.3162%, 0.00254%, Mg 0.0032%, Ti 0.1015%, Ni 0.0036%, Co0.0004%, Mn 0.0062%, Cr 0.0017%. Figure 1 As shown, the waste lithium iron phosphate positive electrode powder is fully recycled:

[0037] S1: Use 200g of waste lithium iron phosphate positive electrode powder and 2L of oxalic acid solution (use 170g of oxalic acid to add deionized water to make a 2L solution). Stir the reaction at a constant temperature of 80℃ for 4h. Add iron hydroxide to adjust the pH of the reaction solution to 4.2, and stir the reaction for 0.5h.

[0038] S2: The reaction mixture obtained in step S1 is vacuum filtered to obtain 1850 ml of the first filtrate and 390 g of the first filter residue.

[0039] S3: Add 10 ml of 25 wt% hydrogen peroxide and 1 g of lithium carbonate to the 1850 ml first filtrate obtained in step S2, stir and react for 1 hour, and vacuum filter to obtain 1820 ml of the second filtrate and 15 g of filter residue. The main component of the filter residue is aluminum iron slag. The second filtrate after impurity removal is reserved for later use.

[0040] S4: The first filter residue obtained in step S2 is treated with 1.4L of 10wt% NaOH and 150mL of 25wt% hydrogen peroxide, and the reaction is first carried out at 40°C for 1h, and then the temperature is raised to 90°C for further reaction for 1.5h. Vacuum filtration is performed to obtain 1.45L of filtrate and 100g of the second filter residue (containing iron hydroxide). The second filter residue is washed with a small amount of deionized water to obtain the second filter residue after impurities removal (containing a mixture of iron red and iron hydroxide). A small amount of sodium carbonate is added to the filtrate (the amount added is determined according to the aluminum content in the filtrate, generally 1-1.2 times the theoretical amount), stirred for reaction, filtered, and the aluminum ions in the filtrate are removed in the form of basic aluminum carbonate, and then the filtrate after impurities removal is passed through an ion exchange resin to remove the calcium and magnesium ions therein to obtain a refined filtrate (sodium oxalate solution); the obtained refined filtrate is introduced into a bipolar membrane system to obtain 10wt% sodium hydroxide solution and 1900ml of 1.35mol / L oxalic acid solution.

[0041] S5: The second filtrate obtained in step S3 and the second filter residue obtained in step S4 are mixed, and the molar ratio of Li / Fe / P is adjusted to 1:1:1 by using lithium carbonate and lithium phosphate, and concentrated by evaporation until the solid-liquid ratio is about 35%, 12 g of sucrose is added to the mixed solution, and then spray granulation is performed, and finally calcined at 780°C to obtain a lithium iron phosphate positive electrode material.

[0042] The physical and chemical properties of the lithium iron phosphate cathode material prepared in Example 1 were tested, and the test data are as follows:

[0043] Li 4.22wt%, P 19.575wt%, Fe 34.38wt%, C 1.48wt%, S 0.0084wt%, compacted density 2.45g / cm 3 , with a specific surface area of ​​13.79 m 2 / g.

[0044] Example 2

[0045] Waste lithium iron phosphate positive electrode powder was collected, and the test indicators (mass percentage) were: Li 4.01%, Fe 31.00%, P17.20%, Cu 0.00225%, Al 0.2162%, 0.00354%, Mg 0.0042%, Ti 0.1215%, Ni 0.0040%, Co0.0005%, Mn 0.0032%, Cr 0.0027%.

[0046] S1: 200g of waste lithium iron phosphate positive electrode powder and 2L of oxalic acid solution obtained in step S4 of Example 1 (supplemented with a small amount of new oxalic acid) were used. Stir and react for 4.5h at 80°C. A small amount of iron hydroxide was added to adjust the pH of the reaction solution to 3.9, and the reaction was stirred for 0.75h.

[0047] S2: The reaction mixture obtained in step S1 was vacuum filtered to obtain 1900 ml of the first filtrate and 380 g of the first filter residue.

[0048] S3: Add 10 ml of 25 wt% hydrogen peroxide and 1 g of lithium carbonate to the 1900 ml first filtrate obtained in step S2, stir and react for 1 hour, and vacuum filter to obtain 1900 ml of the second filtrate and 17 g of filter residue. The main component of the filter residue is aluminum iron slag. The second filtrate after impurity removal is reserved for later use.

[0049] S4: The first filter residue obtained in step S2, the sodium hydroxide solution obtained in step S4 of the embodiment (add a little new sodium hydroxide solid, configure to 1.6L), and 160mL of 25wt% hydrogen peroxide are reacted at 40°C for 1h, and then heated to 90°C for further reaction for 1.5h. Vacuum filtration obtains 1.5L of filtrate and 108g of the second filter residue (component is iron hydroxide). The second filter residue is washed with a small amount of deionized water to obtain the second filter residue after impurity removal (component is a mixture of iron red and iron hydroxide). A small amount of sodium carbonate is added to the filtrate, stirred for reaction, filtered, and the aluminum and lithium ions in the filtrate are removed in the form of basic aluminum carbonate, and then the filtrate after impurity removal is passed through an ion exchange resin to remove the calcium and magnesium ions therein to obtain a refined filtrate (sodium oxalate solution); the obtained refined filtrate enters the bipolar membrane system to obtain 10wt% sodium hydroxide solution and 1900ml of 1.35mol / L oxalic acid solution.

[0050] S5: The second filtrate obtained in step S3 and the second filter residue obtained in step S4 are mixed, and the molar ratio of Li / Fe / P is adjusted to 1:1:1 by using lithium carbonate and lithium phosphate, and concentrated by evaporation until the solid-liquid ratio is about 40%, 14 g of sucrose is added to the mixed solution, and then spray granulation is performed, and finally calcined at 770°C to obtain a lithium iron phosphate positive electrode material.

[0051] The physical and chemical properties of the lithium iron phosphate cathode material prepared in Example 2 were tested, and the test data are as follows:

[0052] Li 4.38wt%, Fe 34.38wt%, P 19.47wt%, C 1.49wt%, S 0.0067wt%, compacted density 2.39g / cm 3 , with a specific surface area of ​​13.54 m 2 / g.

[0053] Performance Test:

[0054] The lithium iron phosphate positive electrode materials prepared in Example 1 and Example 2 were assembled into button batteries.

[0055] The specific preparation process of button batteries is as follows: stir the positive electrode material, acetylene black, adhesive, and N-methylpyrrolidone (NMP) until the slurry is of suitable viscosity and uniform without particles, apply the slurry on the surface of aluminum foil to make an electrode sheet, dry it in a drying oven at 100°C for 0.5-1.0h to allow the NMP to fully evaporate, punch out the sheet, and make the positive electrode sheet; use the lithium sheet as the negative electrode and assemble it into a button battery.

[0056] After the test battery was left to stand for 1 hour, it was tested with an electrochemical performance tester. The discharge capacity at 0.1C, 0.5C, and 1C rates was tested in the voltage range of 2.5-3.9V. The test results are as follows: Figure 2-3 shown.

[0057] like Figure 2-3 As shown, from left to right are the charge and discharge capacity curves at 1C, 0.5C, and 0.1C rates. It can be seen from the figure that the curve of Example 1-2 is very smooth, and its capacity remains stable at a high rate, indicating that the positive electrode material prepared in Example 1-2 has good structural stability.

[0058] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for recycling waste lithium iron phosphate cathode materials, characterized in that: The following steps are involved: S1: adding oxalic acid solution to acid-leach the waste lithium iron phosphate positive electrode material; S2: separating the solid and the liquid in the mixture obtained by the acid leaching treatment to obtain a first filtrate and a first filter residue; S3: adding an impurity remover to the first filtrate to precipitate and remove copper ions, aluminum ions, and fluoride ions in the first filtrate to obtain a second filtrate; S4: mixing the first filter residue, sodium hydroxide and hydrogen peroxide and reacting them; performing solid-liquid separation on the mixed liquid after the reaction to obtain a second filter residue; S5: Mix the second filtrate with the second filter residue to prepare a lithium iron phosphate positive electrode material.

2. A method for recycling waste lithium iron phosphate cathode materials according to claim 1, characterized in that: In the step S1, the oxalic acid solution is an aqueous solution of oxalic acid, wherein the mass ratio of waste lithium iron phosphate to oxalic acid is 1:1.7-1.8; the acid leaching process is carried out at 75-85° C. and stirred for 3.5-5 hours.

3. The method for recycling waste lithium iron phosphate cathode materials according to claim 1, characterized in that: In the step S1, after the acid leaching treatment, ferric hydroxide is added to adjust the pH of the mixed reaction solution to 3.9-4.

2.

4. The method for recycling waste lithium iron phosphate cathode materials according to claim 1, characterized in that: In step S3, the impurity remover is selected from one or more of sodium fluoride, sodium sulfide, lithium hydroxide, lithium carbonate, and hydrogen peroxide.

5. The method for recycling waste lithium iron phosphate cathode materials according to claim 1, characterized in that: In the step S4, the mass ratio of sodium hydroxide to hydrogen peroxide is 14:3.5-4; the first filter residue, sodium hydroxide and hydrogen peroxide are mixed and reacted at a temperature of 35-45° C. for 0.8-2 h; and then the temperature is raised to 85-95° C. and the reaction is continued for 1-2 h.

6. The method for recycling waste lithium iron phosphate cathode materials according to claim 1, characterized in that: In the step S4, sodium carbonate is added to the filtrate obtained after solid-liquid separation; impurities are then removed by ion exchange resin to obtain a sodium oxalate solution.

7. A method for recycling waste lithium iron phosphate cathode materials according to claim 6, characterized in that: In step S4, the obtained sodium oxalate solution is subjected to a bipolar membrane system to obtain an oxalic acid solution and a sodium hydroxide solution.

8. The method for recycling waste lithium iron phosphate cathode materials according to claim 1, characterized in that: In the step S5, the molar ratio of Li / Fe / P in the mixture of the first filtrate and the second filtrate residue is adjusted to 1.033-1.035:1:1, and a carbon source is added after evaporation and concentration, and then spray granulation is performed and calcination is performed to obtain a lithium iron phosphate positive electrode material.

9. A method for recycling waste lithium iron phosphate cathode materials according to claim 8, characterized in that: In step S5, the mixture of the first filtrate and the second filtrate residue with adjusted Li / Fe / P ratio is concentrated, a carbon source is added, spray granulation is performed, and calcination is performed to obtain a lithium iron phosphate positive electrode material; wherein the carbon source is selected from one or more of glucose, sucrose or carbon black.

10. The method for recycling waste lithium iron phosphate cathode materials according to claim 8, characterized in that: In the step S5, the concentration is carried out by evaporation; the evaporation concentration is carried out until the solid-liquid ratio in the mixed liquid is 30-40%, and then the carbon source is added and spray granulation is carried out, and the obtained solid is calcined at 700-800° C. to obtain the lithium iron phosphate positive electrode material.

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