Method for efficiently recycling waste lithium iron phosphate and synchronously preparing precursor through ore pulp electrolysis

Abstract

The invention provides a method for efficiently recycling waste lithium iron phosphate and synchronously preparing a precursor through ore pulp electrolysis, and belongs to the technical field of waste battery recycling. According to the method, a mixed environment-friendly organic acid electrolysis system is utilized, and leaching of lithium, iron and phosphorus elements and electrodeposition of iron-containing compounds are achieved at the same time. The method comprises the following steps: pretreating the positive electrode material of the waste lithium iron phosphate battery; compounding of an electrolyte; collecting a cathode product, removing impurities from the electrolytic bath liquid, and adding phosphate to precipitate lithium phosphate; and a cathode product and a lithium-containing solid are digested, so that efficient recovery of lithium, iron and phosphorus is realized. According to the method, lithium and iron elements in the waste lithium iron phosphate can be efficiently and selectively separated, the solid positive electrode material precursor is generated in situ, multi-step chemical treatment is omitted, the preparation efficiency is improved, the selected redox medium is low in price and environment-friendly, acidic or alkaline wastewater is not generated, and the method is suitable for industrial production. The method can be used for large-scale industrial production of waste lithium ion batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of waste battery recycling, and particularly relates to a method for efficiently recycling waste lithium iron phosphate by slurry electrolysis and simultaneously preparing a precursor. Background Art

[0002] Lithium iron phosphate batteries (LFP) are known for their high safety, long life, environmental friendliness, cost-effectiveness, and good low-temperature performance. They have high thermal stability and fast charge and discharge capabilities, making them suitable for applications with frequent charge and discharge. In addition, lithium iron phosphate batteries have a low self-discharge rate and a stable structure, making them suitable for use in cold environments. They do not contain harmful heavy metals and have little impact on the environment. These characteristics have made them widely used in electric vehicles, energy storage systems, and portable electronic devices.

[0003] Currently, the recycling and reuse of waste lithium iron phosphate batteries mainly use methods such as hydrometallurgy, pyrometallurgy, direct high-temperature solid-phase regeneration technology, and biological leaching technology. Among them, the precipitation method in hydrometallurgy is a commonly used technology. It involves leaching waste battery materials with inorganic strong acids, and then generating FePO 4 precipitate by adding a large amount of oxidant, converting retired LiFePO 4 into FePO 4 as the precursor for regenerating LiFePO 4 However, this method not only consumes a large amount of chemical reagents, but also may generate a large amount of waste gas and wastewater, posing a risk of secondary pollution to the environment.

[0004] Therefore, developing a method for efficiently recycling waste lithium iron phosphate by slurry electrolysis and simultaneously preparing a precursor, which can not only efficiently separate lithium and iron, but also recover phosphorus, in-situ generate the precursor of the cathode material, and the medium in the filtrate can be recycled, to solve the environmental pollution and low economic benefits caused by the use of a large amount of strong acids and high-cost oxidants in the existing recycling technologies, is an urgent task at present. This method is expected to reduce the use of chemical reagents, lower the recycling cost, and at the same time reduce the impact on the environment. Summary of the Invention

[0005] The present invention is to solve the above technical problems, and thus provides a method for efficiently recycling waste lithium iron phosphate by slurry electrolysis and simultaneously preparing a precursor. The method of the present invention does not require the addition of strong acids and oxidants, and no diaphragm or other materials need to be added to separate the electrode chambers during the electrolysis process. In one electrolytic cell, lithium and iron in waste lithium iron phosphate can be separated, and the precursor of the cathode material can be prepared in-situ, realizing the efficient recovery of lithium, iron, and phosphorus.

[0006] In order to achieve the above technical objectives, the technical solution adopted by the present invention is as follows:

[0007] The present invention provides a method for efficiently recovering waste lithium iron phosphate and simultaneously preparing a precursor by slurry electrolysis. Using a mixed environmentally friendly organic acid and a low-cost electrolyte system as the electrolyte, the slurry electrolysis method includes the following steps:

[0008] (1) After high-temperature calcination of the waste lithium iron phosphate cathode material, it is used as a reaction raw material;

[0009] (2) Mix the mixed organic acid and the electrolyte and use it as the electrolyte, and place it in an electrolytic cell. The mixed organic acid is a mixture of oxalic acid and ascorbic acid;

[0010] (3) Add the reaction raw material obtained in step (1) to the electrolytic cell added with the electrolyte in step (2);

[0011] (4) Place the electrode plates into the electrolytic cell to prepare an electrode for electrolysis, stir at 25 - 80 °C for 100 - 600 min, collect the cathode product, and dry it to obtain the iron-containing cathode material precursor;

[0012] (5) Adjust the pH of the remaining liquid in the electrolytic cell to 7 - 10, perform impurity removal and filtration, and add 50 - 150 wt% of sodium phosphate to the filtered remaining liquid to recover lithium.

[0013] The above method provided by the present invention can effectively improve the recovery rate of each component. Using the method of the present invention to recycle the cathode material of waste lithium iron phosphate batteries can significantly improve the recovery rate of each component. At the same time, it is a green and efficient technology with low operating costs, a simple recovery process, no secondary pollution, high economic value, and is suitable for industrial promotion and use.

[0014] Further, in step (1), the calcination is carried out in an atmosphere of air, argon, oxygen or nitrogen, and the calcination temperature is 200 - 800 °C.

[0015] Further, in step (2), the volume ratio of oxalic acid to ascorbic acid in the mixed organic acid is 1:1.

[0016] Further, in step (2), the electrolyte is any one of sodium sulfate, sodium chloride, sodium thiosulfate, potassium chloride, ammonium chloride, copper chloride, potassium dihydrogen phosphate; the weight ratio of the mixed organic acid to the electrolyte in the electrolyte is 1:1 - 1:10.

[0017] Further, the pH value range of the electrolyte in step (2) is 0.1 - 7.

[0018] Further, the liquid-solid ratio of the reaction raw material to the electrolyte in step (3) is 50 - 175 mL / g.

[0019] Furthermore, in step (4), the electrode is an inert electrode, and the electrode plate material is any one of ruthenium-coated titanium mesh, graphite plate, stainless steel, carbon fiber cloth or graphite paper.

[0020] Furthermore, in step (4), the voltage for electrolysis is 1 - 50 V, and the reaction time is 100 - 600 min.

[0021] Furthermore, in step (5), the addition amount of sodium phosphate accounts for 50 - 150 wt% of the weight of the remaining liquid.

[0022] The present invention also provides a cathode material precursor recovered by the method as described above.

[0023] The beneficial effects of the present invention are as follows:

[0024] (1) The present invention uses a mixed organic acid and electrolyte as the electrolyte, adopts the method of slurry electrolysis, and simultaneously leaches lithium, iron, and phosphorus and electro-deposits an iron-containing compound precursor. It can recover lithium, iron, and copper from the cathode material of waste lithium iron phosphate batteries and obtain an iron-containing compound precursor as the raw material for lithium iron phosphate batteries. This electrolyte needs to contain H+ to promote the reaction, and an appropriate amount of Cl - , SO 4 2- or Na + is added to accelerate the leaching of lithium, iron, and phosphorus in the reaction zone, and can also act as a conductive ion to accelerate the ion migration rate in the solution and reduce the resistance.

[0025] (2) The method of the present invention can simultaneously leach and recover lithium, iron, and phosphorus in waste lithium iron phosphate batteries in the same device, greatly shortening the reaction time, reducing energy consumption, and obtaining an iron-containing compound precursor product. It is a green and efficient technology with low operating costs, a simple recovery process, no secondary pollution, and high economic value.

[0026] (3) Under normal temperature and low voltage, the present invention can obtain high recovery rates of lithium, iron, and phosphorus, and even more than 90% can be achieved simultaneously.

[0027] (4) The present invention has high selectivity for metals, mainly using electron redox reactions. Impurity metals such as aluminum are insoluble or slightly soluble in this system and form precipitates. The lithium source and iron source obtained from the reaction can be used as precursors to prepare lithium iron phosphate battery materials. Brief Description of the Drawings

[0028] Figure 1 is the process flow chart of the present invention.

[0029] Figure 2 is the schematic diagram of the electrolysis device of the present invention. Detailed Embodiments

[0030] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be specifically described below in conjunction with embodiments. It is necessary to point out that the following embodiments are only used to explain and illustrate the present invention, and are not used to limit the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above invention content still fall within the protection scope of the present invention.

[0031] Example 1

[0032] Referring to Figure 1 the technological process shown, this embodiment provides a method for efficiently recycling waste lithium iron phosphate and synchronously preparing a precursor by slurry electrolysis, which includes the following steps:

[0033] S1. The waste lithium iron phosphate battery is pretreated to obtain a lithium iron phosphate waste powder with the mass ratio of Fe being about 36.42%, the mass ratio of Li being about 4.61%, and the mass ratio of P being about 19.81%.

[0034] S2. The electrolyte composition is a 1:1 mixture of oxalic acid and ascorbic acid, which is then mixed with sodium sulfate at a mass ratio of 1:1.

[0035] S3. The electrolyte obtained in step S2 is placed in an electrolytic cell, and the raw material obtained in step S1 is placed in the electrolytic reaction zone.

[0036] S4. Insert a ruthenium-coated titanium mesh inert electrode as the anode and a stainless steel plate electrode as the cathode, and set the voltage to 10V for electrolysis (see Figure 2 ), the electrolysis is carried out at room temperature, and the reaction zone is continuously stirred during the electrolysis process to make the particles in a suspended state. After 6h of electrolysis, the electrolysis is stopped, the product on the cathode plate is collected and dried to obtain an iron compound precursor. The pH of the remaining liquid in the electrolytic cell is adjusted to 7.5 for weak alkaline impurity removal and then filtered, and 50% sodium phosphate and other agents are added to recover lithium.

[0037] Through the above method, after completely digesting the cathode product and the lithium-containing solid, measuring the concentrations of lithium, iron, and phosphorus in the digestion solution, it is calculated that the lithium recovery rate in the waste lithium iron phosphate plate powder reaches 90.56%, the iron recovery rate is 92.1%, and the phosphorus recovery rate is 91.45%.

[0038] The recovery rate calculation formulas involved in the embodiment are as follows:

[0039] Lithium recovery rate (%) = (mass of lithium in the digestion solution / mass of lithium in the initial waste battery powder) × 100%

[0040] Iron recovery rate (%) = (mass of iron in the digestion solution / mass of iron in the initial waste battery powder) × 100%

[0041] Recovery rate of phosphorus (%) = ((mass of phosphorus in digestion solution - mass of added phosphorus) / mass of phosphorus in initial waste battery powder) × 100%

[0042] Example 2

[0043] Reference Figure 1 As shown, this example provides a method for efficiently recovering waste lithium iron phosphate and synchronously preparing a precursor by slurry electrolysis, including the following steps:

[0044] S1. The waste lithium iron phosphate battery is pretreated to obtain lithium iron phosphate waste powder with a mass fraction of Fe of about 36.42%, a mass fraction of Li of about 4.61%, and a mass fraction of P of about 19.81%.

[0045] S2. The electrolyte composition is a 1:1 mixture of oxalic acid and ascorbic acid, which is then mixed with sodium sulfate at a mass ratio of 1:1.5.

[0046] S3. The electrolyte obtained in step S2 is placed in an electrolytic cell, and the raw material obtained in step S1 is placed in the electrolytic reaction zone.

[0047] S4. An inert electrode coated with ruthenium titanium mesh is inserted as the anode, and a stainless steel plate electrode is used as the cathode. The voltage is set to 10 V for electrolysis. The electrolysis is carried out at room temperature, and the reaction zone is continuously stirred during the electrolysis process to keep the particles in a suspended state. After 6 h of electrolysis, the electrolysis is stopped, and the product on the cathode plate is collected and dried to obtain an iron compound precursor. The pH of the remaining liquid in the electrolytic cell is adjusted to 7.5 for weak alkaline impurity removal, followed by filtration, and 50% sodium phosphate and other reagents are added to recover lithium.

[0048] According to the above method, after completely digesting the cathode product and lithium-containing solid, the concentrations of lithium, iron, and phosphorus in the digestion solution are measured, and it is calculated that the recovery rate of lithium in the waste lithium iron phosphate plate powder reaches 92.36%, the recovery rate of iron is 93.17%, and the recovery rate of phosphorus is 92.76%.

[0049] Example 3

[0050] Reference Figure 1 As shown, this example provides a method for efficiently recovering waste lithium iron phosphate and synchronously preparing a precursor by slurry electrolysis, including the following steps:

[0051] S1. The waste lithium iron phosphate battery is pretreated to obtain lithium iron phosphate waste powder with a mass fraction of Fe of about 36.42%, a mass fraction of Li of about 4.61%, and a mass fraction of P of about 19.81%.

[0052] S2. The electrolyte composition is a 1:1 mixture of oxalic acid and ascorbic acid, which is then mixed with sodium sulfate at a mass ratio of 1:1.5.

[0053] S3. Place the electrolyte obtained in step S2 into an electrolytic cell, and place the raw material obtained in step S1 into the electrolysis reaction zone;

[0054] S4. Insert an inert electrode coated with ruthenium-titanium mesh as the anode and a stainless steel plate electrode as the cathode, and set the voltage to 10 V for electrolysis. The electrolysis is carried out at room temperature. During the electrolysis process, continuously stir the reaction zone to make the particles in a suspended state. After 10 h of electrolysis, stop the electrolysis, collect the product on the cathode plate, and dry it to obtain the iron-containing compound precursor. Adjust the pH of the remaining liquid in the electrolytic cell to 7.5 for weak alkaline impurity removal and then filter. Add agents such as 50% sodium phosphate to recover lithium.

[0055] According to the above method, after completely digesting the cathode product and the lithium-containing solid, measure the concentrations of lithium, iron, and phosphorus in the digestion solution, and calculate that the recovery rate of lithium in the waste lithium iron phosphate plate powder reaches 94.52%, the recovery rate of iron is 94.64%, and the recovery rate of phosphorus is 95.79%.

[0056] Example 4

[0057] Refer to Figure 1 As shown, this example provides a method for efficiently recovering waste lithium iron phosphate by slurry electrolysis and simultaneously preparing a precursor, including the following steps:

[0058] S1. The waste lithium iron phosphate battery undergoes pretreatment to obtain lithium iron phosphate waste powder with a mass fraction of Fe of about 36.42%, a mass fraction of Li of about 4.61%, and a mass fraction of P of about 19.81%;

[0059] S2. The electrolyte composition is a 1:1 mixture of oxalic acid and ascorbic acid, which is then mixed with sodium sulfate at a mass ratio of 1:1.5;

[0060] S3. Place the electrolyte obtained in step S2 into an electrolytic cell, and place the raw material obtained in step S1 into the electrolysis reaction zone;

[0061] S4. Insert an inert electrode coated with ruthenium-titanium mesh as the anode and a stainless steel plate electrode as the cathode, and set the voltage to 10 V for electrolysis. The electrolysis is carried out at room temperature. During the electrolysis process, continuously stir the reaction zone to make the particles in a suspended state. After 10 h of electrolysis, stop the electrolysis, collect the product on the cathode plate, and dry it to obtain the iron-containing compound precursor. Adjust the pH of the remaining liquid in the electrolytic cell to 9 for weak alkaline impurity removal and then filter. Add agents such as 50% sodium phosphate to recover lithium.

[0062] According to the above method, after completely digesting the cathode product and the lithium-containing solid, measure the concentrations of lithium, iron, and phosphorus in the digestion solution, and calculate that the recovery rate of lithium in the waste lithium iron phosphate plate powder reaches 97.87%, the recovery rate of iron is 98.94%, and the recovery rate of phosphorus is 98.4%.

[0063] Comparative Example 1

[0064] Comparative Example 1 is different from Example 1 only in that: oxalic acid is not added in Comparative Example 1, and other conditions are exactly the same.

[0065] After completely digesting the cathode product and lithium-containing solid, the concentrations of lithium, iron, and phosphorus in the digestion solution were measured, and the recovery rates of lithium, iron, and phosphorus in the waste lithium iron phosphate plate powder were calculated to be 67.47%, 58.93%, and 58.24% respectively.

[0066] Comparative Example 2

[0067] Comparative Example 2 is different from Example 2 only in that: the mixed organic acid in Comparative Example 2 is malic acid and tartaric acid, and other conditions are exactly the same.

[0068] After completely digesting the cathode product and lithium-containing solid, the concentrations of lithium, iron, and phosphorus in the digestion solution were measured, and the recovery rates of lithium, iron, and phosphorus in the waste lithium iron phosphate plate powder were calculated to be 77.82%, 68.94%, and 68.3% respectively.

[0069] Comparative Example 3

[0070] Comparative Example 3 is different from Example 3 only in that: a non-woven filter cloth is added in Comparative Example 3 as a diaphragm to divide the reaction area into an anode area and a cathode area, and the raw materials are added to the anode area, and other conditions are exactly the same.

[0071] After completely digesting the cathode product and lithium-containing solid, the concentrations of lithium, iron, and phosphorus in the digestion solution were measured, and the recovery rates of lithium, iron, and phosphorus in the waste lithium iron phosphate plate powder were calculated to be 47.4%, 38.15%, and 48.41% respectively.

[0072] Comparative Example 4

[0073] Comparative Example 4 is different from Example 4 only in that: the raw materials in Comparative Example 4 are calcined under an inert atmosphere protection, and other conditions are exactly the same.

[0074] After completely digesting the cathode product and lithium-containing solid, the concentrations of lithium, iron, and phosphorus in the digestion solution were measured, and the recovery rates of lithium, iron, and phosphorus in the waste lithium iron phosphate plate powder were calculated to be 34.67%, 32.05%, and 42.45% respectively.

[0075] It can be seen that the method provided by the present invention can effectively improve the recovery rates of each component. Recycling the cathode material of waste lithium iron phosphate batteries by using the method of the present invention can significantly improve the recovery rates of each component, and the effect is remarkable.

Claims

1. A method for efficiently recovering waste lithium iron phosphate by slurry electrolysis and simultaneously preparing a precursor, characterized in that: The steps include: (1) calcining the waste lithium iron phosphate positive electrode material at high temperature and using it as a reaction raw material; (2) mixing a mixed organic acid with an electrolyte to form an electrolyte solution, and placing the mixed organic acid in an electrolytic cell, wherein the mixed organic acid is a mixture of oxalic acid and ascorbic acid; (3) adding the reaction raw materials obtained in step (1) into the electrolytic tank to which the electrolyte was added in step (2); (4) placing the electrode plate into an electrolytic cell to prepare an electrode for electrolysis, stirring at 25-80° C. for 100-600 min, collecting the cathode product, and drying to obtain an iron-containing positive electrode material precursor; (5) The pH of the remaining liquid in the electrolytic cell is adjusted to 7-10, and after impurity removal and filtration, 50-150 wt % of sodium phosphate is added to the remaining liquid after filtration for lithium recovery.

2. The method for efficiently recovering waste lithium iron phosphate by slurry electrolysis and simultaneously preparing a precursor according to claim 1, characterized in that: In step (1), the calcination is carried out in an atmosphere of air, argon, oxygen or nitrogen, and the calcination temperature is 200-800°C.

3. The method for efficiently recovering waste lithium iron phosphate by slurry electrolysis and simultaneously preparing a precursor according to claim 1, characterized in that: In step (2), the volume ratio of oxalic acid to ascorbic acid in the mixed organic acid is 1:

1.

4. The method for efficiently recovering waste lithium iron phosphate by slurry electrolysis and simultaneously preparing a precursor according to claim 1, characterized in that: In step (2), the electrolyte is any one of sodium sulfate, sodium chloride, sodium thiosulfate, potassium chloride, ammonium chloride, copper chloride, and potassium dihydrogen phosphate; and the weight ratio of the mixed organic acid to the electrolyte in the electrolyte is 1:1-1:

10.

5. The method for efficiently recovering waste lithium iron phosphate by electrolysis and simultaneously preparing a precursor according to claim 1, characterized in that: The pH value of the electrolyte in step (2) is in the range of 0.1-7.

6. The method for efficiently recovering waste lithium iron phosphate by electrolysis and simultaneously preparing a precursor according to claim 1, characterized in that: The liquid-to-solid ratio of the reaction raw materials to the electrolyte in step (3) is 50 to 175 mL / g.

7. The method for efficiently recovering waste lithium iron phosphate by slurry electrolysis and simultaneously preparing a precursor according to claim 1, characterized in that: In step (4), the electrode is an inert electrode, and the electrode plate material is any one of ruthenium-coated titanium mesh, graphite plate, stainless steel, carbon fiber cloth or graphite paper.

8. The method for efficiently recovering waste lithium iron phosphate by slurry electrolysis and simultaneously preparing a precursor according to claim 1, characterized in that: The voltage for electrolysis in step (4) is 1-50V, and the reaction time is 100-600min.

9. The method for efficiently recovering waste lithium iron phosphate by slurry electrolysis and simultaneously preparing a precursor according to claim 1, characterized in that: The amount of sodium phosphate added in step (5) accounts for 50-150 wt % of the weight of the remaining liquid.

10. The cathode material precursor recovered by the method according to any one of claims 1 to 9.

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