Method for selectively recycling and reusing positive electrode material of waste lithium iron phosphate battery

Abstract

The invention discloses a method for selectively recycling and reusing a positive electrode material of a waste lithium iron phosphate battery, and relates to the technical field of waste lithium ion battery recycling. Comprising the following steps: discharging and disassembling the waste lithium iron phosphate battery, preparing a first reaction solution, preparing a second reaction solution, recycling iron phosphate, recycling lithium carbonate and recycling a lithium iron phosphate positive electrode material. According to the method, the organic weak acid with the selective chelation effect on the lithium element is matched with the mild oxidizing agent to serve as a leaching system, the photocatalytic material is introduced, the catalysis effect is activated through illumination, the iron element in the lithium iron phosphate is oxidized into trivalent from divalent, meanwhile, high-selectivity lithium leaching can be achieved, other elements such as Fe and P are almost not leached, and the leaching efficiency is greatly improved. According to the method, the lithium leaching solution can be directly obtained, lithium carbonate can be directly obtained through the precipitator, the leaching residue iron phosphate can be combined with the lithium carbonate to regenerate the lithium iron phosphate positive electrode material, the method has excellent electrochemical performance, and the whole technological process is simple, convenient, high in operability and environmentally friendly.

Description

Technical Field

[0001] The present invention relates to the technical field of recycling of waste lithium - ion batteries, and particularly to a method for selective recovery and reuse of the cathode material of waste lithium iron phosphate batteries. Background Art

[0002] The lithium iron phosphate battery is a lithium - ion battery that uses lithium iron phosphate (LiFePO4) as the cathode material and carbon as the anode material. The rated voltage of a single cell of this battery is 3.2V, and the charging cut - off voltage is 3.6 - 3.65V. During the charging process, some lithium ions in the lithium iron phosphate escape, are transferred through the electrolyte to the anode, and are embedded in the anode carbon material. At the same time, electrons are released from the cathode, reach the anode through the external circuit, and maintain the balance of the chemical reaction. During the discharging process, lithium ions escape from the anode, reach the cathode through the electrolyte, and at the same time, the anode releases electrons, which reach the cathode through the external circuit to provide energy for the outside world.

[0003] With the rapid development of new energy vehicles and energy storage systems, lithium iron phosphate batteries have been widely used due to their high safety, long cycle life, and low cost. In order to reduce environmental pollution and achieve the recycling of resources, after the end - of - life of lithium iron phosphate batteries, corresponding recycling treatments are required to recover useful materials such as metal elements like lithium, iron, phosphorus, and other components such as graphite and electrolyte. With the wide application of lithium iron phosphate batteries, the generation of a large number of waste lithium iron phosphate batteries has brought pressure on environmental protection and resource recycling.

[0004] Traditional methods for recycling waste lithium iron phosphate batteries mainly include pyrometallurgy and hydrometallurgy. During the recycling process, a large amount of strong acids and strong bases are used, harmful gases are emitted, and there is also a problem of high energy consumption, which easily leads to environmental pollution and resource waste, thus posing technical challenges to the efficient and environmentally friendly recycling of lithium iron phosphate batteries. Therefore, the present invention proposes a method for selective recovery and reuse of the cathode material of waste lithium iron phosphate batteries to solve the problems existing in the prior art. Summary of the Invention

[0005] In view of the above problems, the purpose of the present invention is to propose a method for selective recovery and reuse of the cathode material of waste lithium iron phosphate batteries, which solves the problems that traditional methods for recycling waste lithium iron phosphate batteries require a large amount of strong acids and strong bases, emit harmful gases, and have high energy consumption, and are prone to environmental pollution and resource waste.

[0006] To achieve the purpose of the present invention, the present invention is realized through the following technical solutions: A method for selective recovery and reuse of the cathode material of waste lithium iron phosphate batteries, comprising the following steps:

[0007] Step 1: Use the solution discharge method to discharge the waste lithium iron phosphate battery to be recycled. After discharging, disassemble the lithium iron phosphate positive electrode sheet and grind it to make an electrode material powder containing lithium iron phosphate.

[0008] Step 2: First, put the catalyst and the electrode material powder into the water circulation device and mix them according to the mass ratio of 1-2:50. Add deionized water according to the solid-liquid ratio of 10-20 g / L, then add an acidic leaching agent to adjust the pH value to 3-6. Subsequently, turn on the stirrer to stir evenly and introduce an oxidant. The delivery rate of the oxidant is 0.2-2 L / min to obtain the first reaction solution.

[0009] Step 3: Turn on the photocatalytic instrument and irradiate the first reaction solution under stirring to carry out the photocatalytic reaction to obtain the second reaction solution.

[0010] Step 4: Filter and separate the second reaction solution obtained after the photocatalytic reaction to obtain a filtrate and a filter residue respectively. Then, selectively recycle the obtained filtrate and filter residue to obtain iron phosphate and lithium carbonate respectively.

[0011] Step 5: Mix the iron phosphate and lithium carbonate recovered in Step 4 according to the molar ratio of 2:1-1.05, then add a carbon source accounting for 8%-35% of the mass of the iron phosphate and make a mixed slurry by ball milling. Then, dry the mixed slurry and grind it again. Move the ground product to a tubular furnace for calcination. After the calcination is completed, a regenerated lithium iron phosphate positive electrode material is obtained.

[0012] Further improvement lies in: In Step 1, the specific steps of using the solution discharge method for discharging are as follows: First, place the waste lithium iron phosphate battery in a 20 wt% concentration of NaCl solution and soak it until the waste lithium iron phosphate battery is completely discharged. After discharging, put it into a vacuum oven and dry it at a temperature of 70 °C for 24 h. Use a voltmeter to measure the battery voltage as 0 V, indicating that the waste lithium iron phosphate battery has been completely discharged.

[0013] Further improvement lies in: In Step 1, the specific steps of making the positive electrode sheet into an electrode material powder containing lithium iron phosphate are as follows: Disassemble the discharged waste lithium iron phosphate battery in a ventilated place, select the lithium iron phosphate positive electrode sheet, then place the disassembled lithium iron phosphate positive electrode sheet in a calcination furnace and calcine it at a temperature of 480-550 °C for 3-4 h to remove PVDF and conductive carbon black. Then, ultrasonically peel the lithium iron phosphate from the aluminum foil, and grind the peeled material to obtain a powder, which is the electrode material powder containing lithium iron phosphate.

[0014] A further improvement lies in that: in the second step, the catalyst is selected from one or two composite catalysts of MOF-based materials, phosphomolybdic acid or nano-WO3, the oxidant is selected from one or two composite oxidants of oxygen, ozone, air, and the leaching agent is selected from one or two composite leaching agents of glacial acetic acid, citric acid, oxalic acid, formic acid.

[0015] A further improvement lies in that: in the second step, the stirring mode of the stirrer is magnetic stirring, the stirring speed is set to 500 - 800 r / min, and the table temperature is set to 25 - 50 °C.

[0016] A further improvement lies in that: in the third step, the light reaction intensity of the photocatalytic instrument is set to 10 - 80 mW / cm 2 , the light wavelength is 654 - 750 nm, and the photocatalytic reaction time is 0.5 - 12 h.

[0017] A further improvement lies in that: in the fourth step, the specific steps for recycling the filter residue are: first, wash the filter residue separated by filtration 3 times with deionized water, then place the washed filter residue in a vacuum oven and dry it at a temperature of 70 °C for 12 h to obtain iron phosphate powder after drying.

[0018] A further improvement lies in that: in the fourth step, the specific steps for recycling the filtrate are: add a precipitant to the filtrate according to the volume ratio of the filtrate to the precipitant of 1:2, mix evenly, heat to 95 °C and keep warm. Utilize the characteristic that the solubility of lithium carbonate in water decreases with the increase of temperature to generate white lithium carbonate precipitate. Then filter with a vacuum filtration device and take out the precipitate. Next, wash it 3 times with deionized water at 95 °C and place it in a vacuum oven to dry to constant weight at a temperature of 70 - 80 °C to obtain pure lithium carbonate material. The precipitant is selected from one of saturated sodium carbonate solution and saturated potassium carbonate solution.

[0019] A further improvement lies in that: in the fifth step, the carbon source is selected from one of glucose, sucrose, starch or graphite. The specific steps of ball milling are: first, put the mixture of iron phosphate, lithium carbonate and carbon source into a ball milling tank, use zirconium balls as the ball milling medium, add alcohol as a dispersant, set the ball milling time to 10 h, the rotation speed to 500 - 700 r / min. After ball milling, place it in a blast drying oven and dry it at a temperature of 60 - 80 °C for 10 h. After drying, place it in a mortar and grind and mix evenly to obtain a ground product.

[0020] A further improvement lies in: First, place the grinding product in a porcelain boat and put it into a tube furnace. Before heating up, pass nitrogen for 1 - 2 hours. Set the tube furnace program to heat up to 350 °C at a rate of 5 °C / min for pretreatment for 5 hours, then heat up to 600 - 700 °C at a rate of 5 °C / min, and then keep the temperature for 10 hours, and naturally cool down to room temperature. After calcination, the regenerated lithium iron phosphate cathode material is obtained.

[0021] The beneficial effects of the present invention are as follows: The present invention uses an organic weak acid with a selective chelating effect on lithium element and a mild oxidant as the leaching system; introduces a photocatalytic material, and the light activation catalysis oxidizes the iron element in lithium iron phosphate from divalent to trivalent, and at the same time can achieve high-selectivity lithium leaching, with the lithium leaching rate reaching 99%, while other elements such as Fe and P are hardly leached, and the lithium leaching solution can be directly obtained. Lithium carbonate can be directly obtained through a precipitant, and the leaching residue iron phosphate can be combined with lithium carbonate to regenerate the lithium iron phosphate cathode material, which has excellent electrochemical performance. The entire process flow is simple and highly operable, does not require the addition of excessive strong acid and strong base leaching agents, can avoid toxic gases and excessive acid waste liquid in the photochemical precipitation process, and has high efficiency in selectively leaching lithium and is green and environmentally friendly compared with the traditional acid leaching process. Brief Description of the Drawings

[0022] Figure 1 is the X-ray diffraction pattern (XRD) of iron phosphate in Example 1 of the present invention;

[0023] Figure 2 is the X-ray diffraction pattern (XRD) of lithium carbonate in Example 1 of the present invention;

[0024] Figure 3 is the electrochemical performance diagram of the regenerated lithium iron phosphate cathode material in Example 1 of the present invention;

[0025] Figure 4 is the schematic flow chart of the method for selective recovery and reuse of the cathode material of waste lithium iron phosphate batteries of the present invention. Detailed Embodiments

[0026] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0027] As a green and efficient oxidation process, photocatalysis technology has shown great potential in environmental governance and the energy field in recent years. Photocatalytic MOF nanocomposites exhibit excellent performance in photocatalytic reactions due to their high specific surface area and adjustable catalytic active sites;

[0028] The present invention aims to utilize photocatalysis technology to solve the problems of selective leaching and regeneration of lithium elements in the cathode materials of waste lithium iron phosphate batteries. An organic weak acid with a selective chelating effect on lithium elements is used, combined with a mild oxidant and a photocatalytic catalyst as the leaching system, and the efficient recovery of lithium and iron elements is achieved by precisely controlling experimental conditions such as pH, temperature, oxidant, and catalyst.

[0029] Example 1

[0030] See Figure 1 、 Figure 2 、 Figure 3 This example provides a method for the selective recovery and reuse of the cathode materials of waste lithium iron phosphate batteries, including the following steps:

[0031] S1. Discharge and disassemble the waste lithium iron phosphate battery

[0032] First, place the waste lithium iron phosphate battery in a 20wt% NaCl solution for 4.4 h to fully discharge the battery. After discharging, put it into a vacuum oven and dry it at 70 °C for 24 h. After drying, disassemble the dried waste lithium iron phosphate battery in a ventilated place, separate the lithium iron phosphate cathode sheet, and after drying the obtained lithium iron phosphate cathode sheet, calcine it at 480 °C for 3 h. After calcination, ultrasonically peel the lithium iron phosphate from the aluminum foil, and grind the peeled material into a powder of electrode material containing lithium iron phosphate;

[0033] S2. Prepare the first reaction solution

[0034] Put 0.5 g of the electrode material powder containing lithium iron phosphate and 10 mg of the MOF-based material UIO-66 into a water circulation device and mix them. According to a solid-liquid ratio of 10 g / L, add 51 mL of deionized water and mix evenly by magnetic stirring. Then add glacial acetic acid to adjust the pH value of the solution to 3, set the stirring speed to 700 r / min, set the table temperature to 25 °C, and then introduce oxygen into it at a gas flow rate of 0.6 L / min to obtain the first reaction solution;

[0035] S3. Prepare the second reaction solution

[0036] Irradiate the first reaction solution under stirring at a rotation speed of 700 rpm through a photocatalytic instrument, set the light intensity of the photoreaction to 10 mW / cm 2 , the light wavelength is 654 nm, and the photocatalytic reaction time is 1 h. The second reaction solution is obtained through the photocatalytic reaction;

[0037] S4. Recovery of iron phosphate

[0038] Filter and separate the second reaction solution into a filtrate and a filter residue. Wash the filter residue after filtration and separation with deionized water three times, and then place the washed filter residue in a vacuum oven and dry it at 70 °C for 12 h. After drying, iron phosphate is obtained, as Figure 1 shown.

[0039] S5. Recovery of lithium carbonate

[0040] Analysis of the filtrate by ICP (Inductively Coupled Plasma Spectrometer) shows that the leaching rate of lithium element is 99.6%. According to the volume ratio of the filtrate to the saturated sodium carbonate solution of 1:2, ensure that the precipitant is in excess. Add the saturated sodium carbonate solution to the filtrate obtained by filtration and separation and mix evenly. Heat to 95 °C and react for 2.5 h to produce a white precipitate. Filter and collect the precipitate while it is hot using a vacuum filtration device, and then wash the precipitate three times with deionized water at 95 °C. Dry it to constant weight in a vacuum oven at 80 °C to obtain lithium carbonate (Li2CO3), as Figure 2 shown;

[0041] S6. Recovery of lithium iron phosphate cathode material

[0042] Mix the iron phosphate and lithium carbonate recovered in S4 and S5 according to a molar ratio of 2:1. Then add 10% of the mass of iron phosphate of glucose into the ball mill tank. Use zirconium balls as the ball milling medium and add alcohol as the dispersant. Set the ball milling time to 10 h and the rotation speed to 500 r / min. After ball milling, place it in a blast drying oven and dry it at 80 °C for 10 h. After drying, place it in a mortar and grind it to mix evenly to obtain a ground product. Place the ground product in a porcelain boat and put it into a tube furnace. Before heating up, pass nitrogen for 1 h. Set the tube furnace program to heat up to 350 °C at a rate of 5 °C / min and pre-treat for 5 h, then heat up to 700 °C at a rate of 5 °C / min, and then keep it warm for 10 h. Naturally cool to room temperature. After calcination, a regenerated lithium iron phosphate cathode material is obtained, which has good electrochemical performance. As Figure 3 shown.

[0043] Example 2

[0044] This example provides a method for selective recovery and reuse of the cathode material of waste lithium iron phosphate batteries, including the following steps:

[0045] S1. Discharge and disassembly treatment of waste lithium iron phosphate batteries

[0046] First, place the used lithium iron phosphate battery in a 20wt% NaCl solution for 4.4 h to fully discharge the used lithium iron phosphate battery. After discharging, put it into a vacuum oven and dry it at a temperature of 70 °C for 24 h. After drying, disassemble the dried used lithium iron phosphate battery in a ventilated place, and separate the lithium iron phosphate positive electrode sheet. After drying the obtained lithium iron phosphate positive electrode sheet, calcine it at a temperature of 500 °C for 3 h. After calcination, ultrasonically peel the lithium iron phosphate from the aluminum foil, and grind the peeled material into an electrode material powder containing lithium iron phosphate;

[0047] S2. Prepare the first reaction solution

[0048] Put 0.5 g of the electrode material powder containing lithium iron phosphate and 10 mg of the MOF-based material UIO-66 into a water circulation device and mix them. According to a solid-liquid ratio of 20 g / L, add 100 mL of deionized water and mix evenly by magnetic stirring. Then add formic acid to adjust the pH value of the solution to 4, set the stirring speed to 800 r / min, set the table temperature to 25 °C, and then pass oxygen into it at a gas flow rate of 0.6 L / min to obtain the first reaction solution;

[0049] S3. Prepare the second reaction solution

[0050] Irradiate the first reaction solution under stirring at a rotation speed of 800 rpm through a photocatalytic instrument, set the light irradiation reaction intensity to 20 mW / cm 2 , the light wavelength to 750 nm, and the photocatalytic reaction time to 2 h to obtain the second reaction solution through the photocatalytic reaction;

[0051] S4. Recover iron phosphate

[0052] Filter and separate the second reaction solution into a filtrate and a filter residue. Wash the filter residue after filtration and separation 3 times with deionized water, and then place the washed filter residue in a vacuum oven and dry it at a temperature of 70 °C for 12 h to obtain iron phosphate after drying;

[0053] S5. Recover lithium carbonate

[0054] Analysis of the filtrate by ICP (inductively coupled plasma spectrometer) shows that the leaching rate of lithium element is 98.7%. According to the volume ratio of the filtrate to the saturated sodium carbonate solution of 1:2, ensure that the precipitant is in excess. Add the saturated sodium carbonate solution to the filtrate obtained by filtration and separation and mix evenly. Heat it to 95 °C and react for 2.5 h to produce a white precipitate. Filter and collect the precipitate while it is hot with a vacuum filtration device, and then wash the precipitate 3 times with deionized water at 95 °C. Dry it to constant weight in a vacuum oven at 80 °C to obtain lithium carbonate (Li2CO3).

[0055] S6. Recover the lithium iron phosphate positive electrode material

[0056] Mix the recovered iron phosphate and lithium carbonate from S4 and S5 in a molar ratio of 2:1. Then add oxalic acid accounting for 35% of the mass of iron phosphate into the ball milling tank. Use zirconium balls as the ball milling medium and add alcohol as a dispersant. Set the ball milling time to 10 h and the rotation speed to 600 r / min. After ball milling, place it in a blast drying oven and dry at 80 °C for 10 h. After drying, place it in a mortar and grind and mix evenly to obtain a ground product. Place the ground product in a porcelain boat and put it into a tube furnace. Before heating up, pass nitrogen for 2 h. Set the tube furnace program to heat up to 350 °C at a rate of 5 °C / min and pretreat for 5 h, then heat up to 650 °C at a rate of 5 °C / min, and then keep it warm for 10 h. Naturally cool down to room temperature. After calcination, the regenerated lithium iron phosphate cathode material is obtained.

[0057] Example 3

[0058] This example provides a method for selective recovery and reuse of the cathode material of waste lithium iron phosphate batteries, including the following steps:

[0059] S1. Discharge and disassemble the waste lithium iron phosphate battery

[0060] First, place the waste lithium iron phosphate battery in a 20 wt% NaCl solution for 4.4 h to fully discharge the waste lithium iron phosphate battery. After discharging, put it into a vacuum drying oven and dry at 70 °C for 24 h. After drying, disassemble the dried waste lithium iron phosphate battery in a ventilated place, and separate out the lithium iron phosphate cathode sheet. After drying the disassembled lithium iron phosphate cathode sheet, calcine it at 550 °C for 4 h. After calcination, ultrasonically peel the lithium iron phosphate from the aluminum foil, and grind the peeled material into an electrode material powder containing lithium iron phosphate;

[0061] S2. Prepare the first reaction solution

[0062] Mix 0.5 g of the electrode material powder containing lithium iron phosphate and 20 mg of phosphomolybdic acid in a water circulation device. According to a solid-liquid ratio of 10 g / L, add 51 mL of deionized water and mix evenly by magnetic stirring. Then add oxalic acid to adjust the pH value of the solution to 3, set the stirring speed to 700 r / min, set the table temperature to 25 °C, and then pass ozone (O3) into it at an air flow rate of 1.5 L / min to obtain the first reaction solution;

[0063] S3. Prepare the second reaction solution

[0064] Irradiate the first reaction solution under stirring at a rotation speed of 700 rpm through a photocatalytic instrument. Set the light irradiation reaction intensity to 40 mW / cm 2 , the light wavelength to 654 nm, and the photocatalytic reaction time to 12 h. Obtain the second reaction solution through the photocatalytic reaction;

[0065] S4. Recovery of iron phosphate

[0066] Filter and separate the second reaction solution into a filtrate and a filter residue. Wash the filter residue after filtration and separation 3 times with deionized water, and then place the washed filter residue in a vacuum oven and dry it at 70 °C for 12 h to obtain iron phosphate after drying.

[0067] S5. Recovery of lithium carbonate

[0068] Analysis of the filtrate by ICP (Inductively Coupled Plasma Spectrometer) shows that the leaching rate of lithium element is 99.3%. According to the volume ratio of the filtrate to the saturated sodium carbonate solution of 1:2, ensure that the precipitant is in excess. Add the saturated sodium carbonate solution to the filtrate obtained by filtration and separation and mix evenly. Heat to 95 °C and react for 2.5 h to produce a white precipitate. Filter and collect the precipitate while it is hot with a vacuum filtration device, and then wash the precipitate 3 times with deionized water at 95 °C. Dry it to constant weight in a vacuum oven at 80 °C to obtain lithium carbonate (Li2CO3).

[0069] S6. Recovery of lithium iron phosphate cathode material

[0070] Mix the iron phosphate and lithium carbonate recovered in S4 and S5 according to a molar ratio of 2:1.05. Then add starch accounting for 8% of the mass of iron phosphate into the ball mill tank. Use zirconium balls as the ball milling medium, add alcohol as the dispersant, set the ball milling time to 10 h, the rotation speed to 600 r / min. After ball milling, place it in a blast drying oven and dry it at 80 °C for 10 h. After drying, place it in a mortar and grind and mix it evenly to obtain a ground product. Place the ground product in a porcelain boat and put it into a tubular furnace. Before heating up, pass nitrogen for 2 h. Set the tubular furnace program to heat up to 350 °C at a rate of 5 °C / min and pre-treat for 5 h, then heat up to 700 °C at a rate of 5 °C / min, and then keep it warm for 10 h. Naturally cool to room temperature. After calcination, obtain the regenerated lithium iron phosphate cathode material.

[0071] Example 4

[0072] This example provides a method for selective recovery and reuse of the cathode material of waste lithium iron phosphate batteries, including the following steps:

[0073] S1. Discharge and disassembly treatment of waste lithium iron phosphate batteries

[0074] First, place the used lithium iron phosphate battery in a 20wt% NaCl solution for 4.4 h to fully discharge the used lithium iron phosphate battery. After discharging, put it into a vacuum oven and dry it at a temperature of 70 °C for 24 h. After drying, disassemble the dried used lithium iron phosphate battery in a ventilated place, and separate the lithium iron phosphate positive electrode sheet. After drying the obtained lithium iron phosphate positive electrode sheet, calcine it at a temperature of 550 °C for 4 h. After calcination, ultrasonically peel the lithium iron phosphate from the aluminum foil, and grind the peeled material into an electrode material powder containing lithium iron phosphate;

[0075] S2. Prepare the first reaction solution

[0076] Put 0.5 g of the electrode material powder containing lithium iron phosphate and 20 mg of phosphomolybdic acid into a water circulation device for mixing. According to a solid-liquid ratio of 20 g / L, add 100 mL of deionized water and mix evenly by magnetic stirring. Then add citric acid to adjust the pH value of the solution to 5, set the stirring speed to 700 r / min, set the table temperature to 25 °C, and then introduce ozone (O3) into it at a gas flow rate of 1.5 L / min to obtain the first reaction solution;

[0077] S3. Prepare the second reaction solution

[0078] Irradiate the first reaction solution under stirring at a rotation speed of 700 rpm through a photocatalytic instrument, set the light irradiation reaction intensity to 40 mW / cm 2 , the light wavelength to 654 nm, and the photocatalytic reaction time to 3 h to obtain the second reaction solution through the photocatalytic reaction;

[0079] S4. Recover iron phosphate

[0080] Filter and separate the second reaction solution into a filtrate and a filter residue. Wash the filter residue obtained after filtration and separation 3 times with deionized water, and then place the washed filter residue in a vacuum oven and dry it at a temperature of 70 °C for 12 h to obtain iron phosphate after drying;

[0081] S5. Recover lithium carbonate

[0082] Analysis of the filtrate by ICP (inductively coupled plasma spectrometer) shows that the leaching rate of lithium element is 97.6%. According to the volume ratio of the filtrate to the saturated potassium carbonate solution of 1:2 to ensure an excess of the precipitant, add the saturated potassium carbonate solution to the filtrate obtained after filtration and separation and mix evenly, heat to 95 °C and react for 3 h to produce a white precipitate. Filter and collect the precipitate while it is hot using a vacuum filtration device, and then wash the precipitate 3 times with 95 °C deionized water. Dry it to constant weight in a vacuum oven at 80 °C to obtain lithium carbonate (Li2CO3).

[0083] S6. Recover the lithium iron phosphate positive electrode material

[0084] Mix the recovered iron phosphate and lithium carbonate from S4 and S5 in a molar ratio of 2:1.05. Then add citric acid accounting for 10% of the mass of iron phosphate into the ball milling tank. Use zirconium balls as the ball milling medium, add alcohol as the dispersant, set the ball milling time to 10 h, the rotation speed to 500 r / min. After ball milling, place it in a blast drying oven and dry at 80 °C for 10 h. After drying, place it in a mortar and grind and mix evenly to obtain a ground product. Place the ground product in a porcelain boat and put it into a tube furnace. Before heating up, pass nitrogen for 2 h. Set the tube furnace program to heat up to 350 °C at a rate of 5 °C / min and pre-treat for 5 h, then heat up to 650 °C at a rate of 5 °C / min, and then keep the temperature for 10 h, and naturally cool down to room temperature. After calcination, the regenerated lithium iron phosphate cathode material is obtained.

[0085] Example 5

[0086] This example provides a method for selective recovery and reuse of the cathode material of waste lithium iron phosphate batteries, including the following steps:

[0087] S1. Discharge and disassemble the waste lithium iron phosphate battery

[0088] First, place the waste lithium iron phosphate battery in a 20 wt% NaCl solution for 4.4 h to completely discharge the waste lithium iron phosphate battery. After discharging, put it into a vacuum oven and dry at 70 °C for 24 h. After drying, disassemble the dried waste lithium iron phosphate battery in a ventilated place, separate out the lithium iron phosphate cathode sheet. After drying the obtained lithium iron phosphate cathode sheet, calcine it at 550 °C for 4 h. After calcination, ultrasonically peel the lithium iron phosphate from the aluminum foil, and grind the peeled material into an electrode material powder containing lithium iron phosphate;

[0089] S2. Prepare the first reaction solution

[0090] Put 0.5 g of the electrode material powder containing lithium iron phosphate and 10 mg of nano-WO3 into a water circulation device and mix them. According to a solid-liquid ratio of 10 g / L, add 51 mL of deionized water and mix evenly by magnetic stirring. Then add glacial acetic acid to adjust the pH value of the solution to 3, set the stirring speed to 700 r / min, set the table temperature to 25 °C, and then pass air into it at an air flow rate of 2 L / min to obtain the first reaction solution;

[0091] S3. Prepare the second reaction solution

[0092] Irradiate the first reaction solution under stirring at a rotation speed of 700 rpm through a photocatalytic instrument, set the light irradiation reaction intensity to 10 mW / cm 2 , the light wavelength to 654 nm, and the photocatalytic reaction time to 10 h. Obtain the second reaction solution through the photocatalytic reaction;

[0093] S4. Recovery of iron phosphate

[0094] Filter and separate the second reaction solution into a filtrate and a filter residue. Wash the filter residue after filtration and separation with deionized water three times, and then place the washed filter residue in a vacuum oven and dry it at 70 °C for 12 h to obtain iron phosphate after drying.

[0095] S5. Recovery of lithium carbonate

[0096] Analysis of the filtrate by ICP (Inductively Coupled Plasma Spectrometer) shows that the leaching rate of lithium element is 99.2%. According to the volume ratio of the filtrate to the saturated potassium carbonate solution of 1:2, ensure that the precipitant is in excess. Add the saturated potassium carbonate solution to the filtrate obtained by filtration and separation and mix evenly. Heat to 95 °C and react for 3 h to produce a white precipitate. Filter and collect the precipitate while it is hot using a vacuum filtration device, and then wash the precipitate three times with deionized water at 95 °C. Dry it to constant weight in a vacuum oven at 80 °C to obtain lithium carbonate (Li2CO3).

[0097] S6. Recovery of lithium iron phosphate cathode material

[0098] Mix the iron phosphate and lithium carbonate recovered in S4 and S5 according to a molar ratio of 2:1.05. Then add 10% of the mass of iron phosphate of glucose into the ball milling tank. Use zirconium balls as the ball milling medium and add alcohol as the dispersant. Set the ball milling time to 10 h and the rotation speed to 500 r / min. After ball milling, place it in a forced air drying oven and dry it at 80 °C for 10 h. After drying, place it in a mortar and grind it to mix evenly to obtain a ground product. Place the ground product in a porcelain boat and put it into a tubular furnace. Before heating up, pass nitrogen for 2 h. Set the tubular furnace program to heat up to 350 °C at a rate of 5 °C / min and pre-treat for 5 h, then heat up to 700 °C at a rate of 5 °C / min, and then keep it warm for 10 h. Naturally cool to room temperature. After calcination, obtain the regenerated lithium iron phosphate cathode material.

[0099] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for selectively recovering and reusing waste lithium iron phosphate battery positive electrode materials, characterized in that: The following steps are involved: Step 1: Use a solution discharge method to discharge the waste lithium iron phosphate batteries to be recycled, disassemble the lithium iron phosphate positive electrode sheets after discharge, and grind and process them into electrode material powder containing lithium iron phosphate; Step 2: firstly, the catalyst and the electrode material powder are put into a water circulation device at a mass ratio of 1 to 2:50 and mixed, and deionized water is added at a solid-liquid ratio of 10 to 20 g / L, and then an acidic leaching agent is added to adjust the pH value to 3 to 6, and then the stirrer is turned on to stir evenly and the oxidant is introduced at a delivery rate of 0.2 to 2 L / min to obtain a first reaction solution; Step 3: Turn on the photocatalytic instrument, irradiate the first reaction liquid in a stirring state, perform a photocatalytic reaction, and obtain a second reaction liquid; Step 4: filtering and separating the second reaction liquid obtained after the photocatalytic reaction to obtain a filtrate and a filter residue, respectively, and then selectively recovering the obtained filtrate and filter residue to obtain iron phosphate and lithium carbonate, respectively; Step 5: Mix the iron phosphate and lithium carbonate recovered in step 4 in a molar ratio of 2:1-1.05, add 8% to 35% of the mass of the iron phosphate as a carbon source and prepare a mixed slurry by ball milling, then dry the mixed slurry and grind it, move the ground product to a tubular furnace for calcination, and obtain a regenerated lithium iron phosphate positive electrode material after calcination.

2. The method for selectively recovering and reusing the positive electrode material of waste lithium iron phosphate batteries according to claim 1, characterized in that: In the step 1, the specific steps of discharging by solution discharge method are as follows: firstly, the waste lithium iron phosphate battery is placed in a 20wt% NaCl solution, and soaked until the waste lithium iron phosphate battery is completely discharged, and after discharge, the waste lithium iron phosphate battery is placed in a vacuum oven and dried at 70°C for 24 hours.

3. The method for selectively recovering and reusing the positive electrode material of waste lithium iron phosphate batteries according to claim 1, characterized in that: In the step 1, the specific steps of making the positive electrode sheet into the electrode material powder containing lithium iron phosphate are: dismantling the discharged waste lithium iron phosphate batteries in a ventilated place, sorting out the lithium iron phosphate positive electrode sheets, and then placing the disassembled lithium iron phosphate positive electrode sheets in a calcining furnace and calcining them at a temperature of 480 to 550° C. for 3 to 4 hours, then ultrasonically peeling the lithium iron phosphate and the aluminum foil, grinding the peeled material, and the obtained powder is the electrode material powder containing lithium iron phosphate.

4. The method for selectively recovering and reusing the positive electrode material of waste lithium iron phosphate batteries according to claim 1, characterized in that: In the step 2, the catalyst is selected from one or two composite catalysts of MOF-based materials, phosphomolybdic acid or nano WO3, the oxidant is selected from one or two composite oxidants of oxygen, ozone and air, and the leaching agent is selected from one or two composite leaching agents of glacial acetic acid, citric acid, oxalic acid and formic acid.

5. The method for selectively recovering and reusing the positive electrode material of waste lithium iron phosphate batteries according to claim 1, characterized in that: In the step 2, the stirring mode of the stirrer is magnetic stirring, and the stirring speed is set to 500-800 r / min, and the table temperature is set to 25-50°C.

6. The method for selectively recovering and reusing the positive electrode material of waste lithium iron phosphate batteries according to claim 1, characterized in that: In step 3, the light reaction intensity of the photocatalytic instrument is set to 10-80 mW / cm 2 , the light wavelength is 654~750nm, and the photocatalytic reaction time is 0.5~12h.

7. The method for selectively recovering and reusing the positive electrode material of waste lithium iron phosphate batteries according to claim 1, characterized in that: In the step 4, the specific steps of recovering the filter residue are: first, wash the filter residue after filtration and separation with deionized water for 3 times, and then place the washed filter residue in a vacuum oven at a temperature of 70° C. and dry it for 12 hours to obtain iron phosphate powder after drying.

8. The method for selectively recovering and reusing the positive electrode material of waste lithium iron phosphate batteries according to claim 1, characterized in that: In the step 4, the specific steps of recovering the filtrate are as follows: adding the precipitant to the filtrate in a volume ratio of 1:2 and mixing evenly, and heating to 95°C for insulation, and utilizing the property that the solubility of lithium carbonate precipitate in water decreases with increasing temperature to generate white lithium carbonate precipitate, and then filtering and removing the precipitate using a vacuum filtration device, and then washing it three times with 95°C deionized water and drying it in a vacuum oven at a temperature of 70-80°C to constant weight to obtain pure lithium carbonate material, wherein the precipitant is selected from a saturated sodium carbonate solution and a saturated potassium carbonate solution.

9. The method for selectively recovering and reusing the positive electrode material of waste lithium iron phosphate batteries according to claim 1, characterized in that: In the step 5, the carbon source is selected from one of glucose, sucrose, starch or graphite, and the specific steps of ball milling are: first, a mixture of iron phosphate, lithium carbonate and carbon source is placed in a ball mill, and zirconium balls are used as ball milling media, alcohol is added as a dispersant, the ball milling time is set to 10 hours, and the rotation speed is 500-700r / min. After the ball milling is completed, it is placed in a blast drying oven at a temperature of 60-80°C for 10 hours, and after drying, it is placed in a mortar and ground and mixed evenly to obtain a ground product.

10. The method for selectively recovering and reusing the positive electrode material of waste lithium iron phosphate batteries according to claim 1, characterized in that: In the step five, the specific steps of calcining the ground product are as follows: firstly place the ground product in a porcelain boat, put it into a tubular furnace, and before heating, pass nitrogen for 1 to 2 hours, set the tubular furnace program to heat to 350°C at a rate of 5°C / min for pretreatment for 5 hours, then heat to 600 to 700°C at a rate of 5°C / min, and then keep warm for 10 hours, and naturally cool to room temperature. After calcination, regenerated lithium iron phosphate positive electrode material is obtained.

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