Separation, purification and regeneration method of waste lithium iron phosphate electrode material

Abstract

The invention discloses a method for separating, purifying and regenerating a waste lithium iron phosphate electrode material, and belongs to the technical field of recycling of waste lithium ion batteries. Graphite as a negative electrode material is separated and removed through selective water dissolution of a negative electrode binder, and meanwhile, lithium ions in the graphite negative electrode material are leached and used as a lithium supplement agent; the waste lithium iron phosphate positive electrode material is subjected to surface modification and activation by adopting a high-purity oxygen low-temperature plasma ashing technology, so that the carbon content on the surface of the waste lithium iron phosphate positive electrode material is effectively controlled while organic matters are removed and lithium iron phosphate particles are dissociated, and the purpose of deep purification and carbon removal is achieved; in addition, the crystal structure in the electrode material can be activated, a migration channel of lithium ions is activated, and the subsequent lithium supplementing efficiency is greatly improved; the waste lithium iron phosphate electrode material is subjected to in-situ repair by a liquid-phase lithium supplement-curing roasting combined repair method, and the lithium iron phosphate electrode material with excellent electrochemical performance is obtained.

Description

Technical Field

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

[0002] In recent years, with the rapid development of the electric vehicle industry, the amount of waste lithium-ion batteries commonly used in electric vehicle power batteries has also increased sharply. If waste lithium-ion batteries are not handled properly, they may cause a large amount of solid waste landfill, heavy metal pollution, dust pollution, water pollution and other environmental pollution problems, and also cause waste of resources. Therefore, the resource recycling of waste lithium-ion batteries can not only avoid environmental problems caused by solid waste stacking, but also provide raw materials for the manufacture of new batteries and improve resource utilization.

[0003] For the recycling of lithium iron phosphate electrode materials, the most economically valuable recycling method is to use in-situ repair and regeneration technology to convert waste electrode materials into circulating electrode materials that are highly consistent with a series of indicators such as the electrochemical properties of industrial-grade lithium iron phosphate electrode materials. However, the in-situ repair technology has extremely high requirements for the purity of electrode materials, especially the carbon impurity content. Therefore, separation and purification of lithium iron phosphate electrode materials, and deep removal of carbon impurities and surface activation on this basis are important links in the repair and regeneration of waste lithium iron phosphate.

[0004] Waste lithium iron phosphate electrode materials can be deeply purified and decarbonized after high-temperature aerobic roasting, but there is a large energy consumption problem in the high-temperature roasting process. Secondly, aerobic roasting will cause the electrode material to oxidize, causing its internal lattice to change, and leading to increased energy consumption in the subsequent in-situ repair process. In recent years, anaerobic pyrolysis is a technical means to achieve efficient removal of organic matter in electrode materials, but the large amount of pyrolysis carbon residue produced after anaerobic pyrolysis of organic matter blocks the migration channel of lithium ions, making it difficult to replenish and repair lithium iron phosphate. Summary of the invention

[0005] The present invention provides a method for separating, purifying and regenerating waste lithium iron phosphate electrode materials, which effectively solves a series of technical problems such as the difficulty in separating positive and negative electrode materials, high energy consumption of aerobic roasting and oxidation of electrode materials leading to changes in internal lattices, and low lithium replenishment efficiency caused by a large amount of residual carbon produced by anaerobic pyrolysis. At the same time, a new method for deep purification, impurity removal and surface activation of waste lithium iron phosphate with low energy consumption and high impurity removal efficiency is provided, which realizes purification, impurity removal and repair and regeneration of waste lithium iron phosphate electrode materials under the premise of ensuring that the internal crystal structure of the electrode material is stable and unchanged.

[0006] The first object of the present invention is to provide a method for separating, purifying and regenerating waste lithium iron phosphate electrode materials, comprising the following steps:

[0007] The waste lithium iron phosphate batteries are shredded and pre-treated and sorted to obtain mixed positive and negative electrode sheets, which are then immersed in deionized water to dissolve the water-soluble organic binder in the negative electrode and extract the lithium element in the negative electrode material. Ultrasound is used to make the negative electrode material fall off the copper foil to achieve efficient dissociation between the negative electrode material and the copper foil and between the graphite electrode material particles, and the negative electrode material, copper foil and positive electrode sheets are obtained by screening.

[0008] The negative electrode material is filtered and dried to obtain negative electrode graphite.

[0009] The positive electrode sheet and the copper foil are crushed and sieved to separate the positive electrode material from the current collector to obtain the waste lithium iron phosphate positive electrode material.

[0010] The waste lithium iron phosphate positive electrode material is subjected to plasma ashing treatment in an oxygen atmosphere at 140° C. to 150° C. to remove organic binder, fluorine and carbon impurities in the positive electrode material and to achieve surface activation, thereby obtaining a deeply impurity-removed and purified lithium iron phosphate electrode material.

[0011] In a reducing atmosphere, the deeply impurity-removed and purified lithium iron phosphate electrode material is supplemented with lithium to fill the lithium ions missing in the internal crystal structure to obtain a lithium-supplemented electrode material. The lithium-supplemented electrode material is calcined at 550° C. to 800° C. in an inert atmosphere to achieve material solidification and crystal structure repair to obtain a regenerated lithium iron phosphate electrode material.

[0012] As a preferred implementation manner, the solid-liquid ratio of the positive and negative electrode mixed electrode sheets to deionized water is 100-150 g:1 L, and the soaking time is 45 min to 75 min.

[0013] As a preferred implementation, the ultrasound frequency is 35KHz to 45KHz, and the ultrasound time is 1min to 3min.

[0014] As a preferred embodiment, during screening, the aperture of the screen used is >2 mm and smaller than the size of the positive electrode sheet.

[0015] As a preferred embodiment, when screening, the aperture of the screen used is 0.075 mm.

[0016] As a preferred embodiment, the plasma ashing treatment is specifically: plasma ashing treatment is performed for 5min to 25min in a low-temperature plasma ashing instrument at 140°C to 150°C, a purity of 99.999%, an oxygen atmosphere with a flow rate of 0.15L / min to 0.2L / min, a power of 70W to 110W, and a vacuum degree of 3mbar.

[0017] As a preferred embodiment, after filtering the negative electrode material, a lithium-containing solution is obtained, and the lithium-containing solution is used as a lithium supplement, lithium carbonate or lithium sulfate is used as an external lithium source, and citric acid and ascorbic acid are used as lithium supplement media to obtain a liquid lithium supplement solution.

[0018] As a preferred embodiment, the lithium replenishment is specifically: mixing the deeply impurity-removed and purified lithium iron phosphate electrode material with a liquid lithium replenisher solution at a solid-liquid ratio of 80g to 120g:1L, and reacting at 70°C to 90°C and normal pressure for 5h to 7h.

[0019] As a preferred embodiment, the concentration of lithium ions in the liquid lithium supplement is 0.15 mol / L to 0.2 mol / L, and the mass ratio of the lithium deficiency of the deeply impurity-removed and purified lithium iron phosphate electrode material to the lithium content of the liquid lithium supplement is 1:1.05 to 1.2.

[0020] As a preferred implementation, the calcination time is 2h to 3h.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The present invention provides a method for separation, purification and regeneration of waste lithium iron phosphate electrode materials, which performs water immersion-ultrasound-screening on the positive and negative mixed electrode sheets of waste lithium iron phosphate batteries to achieve selective separation and removal of negative electrode graphite, and at the same time achieves leaching of lithium ions in graphite; uses low-temperature plasma ashing technology to complete the decomposition and removal of organic matter in the positive electrode material lithium iron phosphate, as well as deep impurity removal and surface modification; and sequentially passes lithium supplementation and curing and roasting on the electrode materials after deep decarbonization and purification to achieve in-situ repair and regeneration of the electrode materials. The present invention realizes the coordination of graphite separation and removal and selective extraction of lithium elements in graphite through the method of selective dissolution of organic binders; the method of low-temperature plasma ashing can achieve efficient removal of organic matter in a short time, and can also achieve removal of carbon impurities, avoid residual carbon blocking the lithium ion migration channel, and at the same time achieve the purpose of surface activation, making the lithium supplementation process simpler; through the technical means of combining liquid phase lithium supplementation with curing and roasting, the in-situ repair and regeneration of waste lithium iron phosphate electrode materials is achieved, thereby obtaining lithium iron phosphate electrode materials with better electrochemical performance.

[0023] During the later stage of liquid phase lithium replenishment and solidification roasting, the present invention adopts a lithium-containing solution obtained after filtering the negative electrode material in the lithium replenishment process for liquid phase lithium replenishment. Since the lithium-containing solution contains a dissolved organic binder, it realizes carbon coating on the electrode material during the later stage of solidification roasting, thereby further repairing the waste lithium iron phosphate electrode material and obtaining a lithium iron phosphate electrode material with better electrochemical performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1The present invention is a process flow chart of the method for separating, purifying and regenerating waste lithium iron phosphate electrode materials.

[0025] Figure 2 This is a comparison chart of the carbon content of the positive electrode material after different ashing times. DETAILED DESCRIPTION

[0026] In order to enable those skilled in the art to better understand the technical solution of the present invention and implement it, the present invention is further described below in conjunction with specific embodiments and drawings, but the embodiments are not intended to limit the present invention. The following test methods and detection methods, unless otherwise specified, are conventional methods; the reagents and raw materials, unless otherwise specified, are commercially available.

[0027] In view of the above mentioned in the background technology of the present invention: first, it is difficult to separate the positive and negative electrode materials of waste lithium iron phosphate batteries; second, although the organic matter of waste lithium iron phosphate electrode materials can be removed after high-temperature aerobic roasting and anaerobic pyrolysis, there will be a large energy consumption problem during the high-temperature roasting process; third, aerobic roasting will oxidize the electrode material and change its internal lattice, and the residual carbon from anaerobic pyrolysis will block the lithium replenishment channel, resulting in low efficiency and increased energy consumption in the subsequent in-situ repair process. The present invention provides a method for separating, purifying and regenerating waste lithium iron phosphate electrode materials.

[0028] The technical solution of the present invention is described in detail below.

[0029] The present invention provides a method for separating, purifying and regenerating waste lithium iron phosphate electrode materials, comprising the following steps:

[0030] The waste lithium iron phosphate batteries are shredded and separated by magnetic-electric-wind synergistic sorting to obtain mixed positive and negative electrode sheets, which are then immersed in deionized water to dissolve the water-soluble organic binder in the negative electrode material and extract the lithium element from the negative electrode graphite. Ultrasonic vibration is used to make the negative electrode material fall off the copper foil to achieve efficient dissociation between the graphite negative electrode material and the copper foil current collector and between the graphite electrode material particles. A large-aperture screen is then used to separate the negative electrode graphite from the copper foil and the positive electrode sheet.

[0031] The separated negative electrode material is filtered and dried to obtain negative electrode graphite and a lithium-containing solution, and the lithium-containing solution is used for subsequent lithium replenishment and repair of the positive electrode material.

[0032] The positive electrode sheet and the copper foil are crushed together, and after crushing, they are passed through a 0.075 mm aperture sieve to separate the positive electrode material from the current collector, thereby obtaining waste lithium iron phosphate positive electrode material.

[0033] The waste lithium iron phosphate positive electrode material is subjected to plasma ashing treatment in an oxygen atmosphere at 140° C. to 150° C. to remove organic binder, fluorine and carbon impurities in the positive electrode material and to achieve surface activation, thereby obtaining a deeply impurity-removed and purified lithium iron phosphate electrode material.

[0034] In a reducing atmosphere, the deeply impurity-removed and purified lithium iron phosphate electrode material is subjected to liquid phase lithium replenishment to fill the lithium ions missing in the internal crystal structure, followed by solid-liquid separation and multiple rinses of the positive electrode material to obtain the lithium replenished electrode material, and then the lithium replenished electrode material is calcined at 550°C to 800°C in an inert atmosphere to achieve material solidification and crystal structure repair to obtain the regenerated lithium iron phosphate electrode material.

[0035] In the above technical scheme, the separation and removal of graphite and the selective extraction of lithium from graphite are coordinated by the method of selective dissolution of organic binder; the low-temperature plasma ashing method can achieve efficient removal of organic matter in a short time and removal of carbon impurities, avoiding residual carbon blocking the lithium ion migration channel, and at the same time achieve the purpose of surface activation, making the lithium replenishment process simpler; the in-situ repair and regeneration of waste lithium iron phosphate electrode materials is achieved by the technical means of combining liquid phase lithium replenishment with solidification and roasting, thereby obtaining lithium iron phosphate electrode materials with better electrochemical properties.

[0036] In order to effectively improve the dissolution efficiency of the organic binder in the negative electrode material, the solid-liquid ratio of the positive and negative electrode mixed electrode sheets to deionized water is 100-150g:1L, and the immersion time is 45min-75min, to avoid insufficient dissolution of the negative electrode material binder due to too short a time, resulting in low graphite removal efficiency, and to avoid too long an immersion time, resulting in lithium ion loss in the positive electrode material lithium iron phosphate.

[0037] In order to improve the efficient stripping of negative electrode material graphite from the copper foil current collector, ultrasonic vibration is used to enhance the stripping efficiency and promote the dissociation between graphite particles. The ultrasonic frequency is 35-45KHz and the ultrasonic time is 1-3min. Ultrasonic treatment uses screening to achieve the removal of enriched material graphite. In order to improve the screening efficiency, the aperture used is greater than 2mm but smaller than the size of the positive electrode sheet.

[0038] In order to deeply purify and remove organic matter and carbon impurities in waste lithium iron phosphate electrode materials, the low-temperature plasma ashing treatment is carried out using a low-temperature plasma ashing instrument. The plasma ashing treatment is specifically: at 140°C to 150°C, a purity of 99.999%, an oxygen atmosphere with a flow rate of 0.15L / min to 0.2L / min, a power of 70W to 110W, and a vacuum degree of 3mbar, the low-temperature plasma ashing instrument performs plasma ashing for 5min to 25min.

[0039] In order to separate the lithium iron phosphate electrode material from the current collector, the sample after the ashing treatment was screened using a screening mesh with an aperture of 0.075 mm.

[0040] In order to carry out liquid-phase lithium replenishment for the deeply impurity-removed and purified lithium iron phosphate electrode material, a lithium-containing solution is obtained after filtering the negative electrode material. The lithium-containing solution is used as a lithium replenisher, lithium carbonate or lithium sulfate is used as an external lithium source, and citric acid and ascorbic acid are used as lithium replenishment media to obtain a liquid lithium replenisher solution.

[0041] In order to effectively fill the lithium ions missing in the crystal structure of the purified electrode material, the lithium replenishment is specifically as follows: the deeply impurity-removed and purified lithium iron phosphate electrode material is mixed with a liquid lithium replenisher solution at a solid-liquid ratio of 80g to 120g:1L, and reacted at 70°C to 90°C and normal pressure for 5 to 7 hours.

[0042] In order to improve the reduction efficiency of iron elements in waste lithium iron phosphate and thus promote lithium replenishment, the concentration of lithium ions in the liquid lithium replenisher is 0.15 mol / L to 0.2 mol / L, and the mass ratio of the lithium deficiency of the lithium iron phosphate electrode material after deep impurity removal and purification to the lithium content of the liquid lithium replenisher is 1:1.05 to 1.2.

[0043] In order to further achieve a better lithium replenishment effect, the electrode material after liquid phase lithium replenishment is calcined at 550°C to 800°C in an inert atmosphere to achieve material solidification and crystal structure repair, and obtain regenerated lithium iron phosphate electrode material. The calcination time is 2 to 3 hours, which saves energy while achieving full lithium ion embedding, avoiding insufficient solidification due to too short calcination time and serious energy waste due to too long calcination time.

[0044] The technical effects of the present invention are described in detail below through specific embodiments and comparative examples.

[0045] Example 1

[0046] A method for separating, purifying and regenerating waste lithium iron phosphate electrode materials comprises the following steps:

[0047] S1. Shred and sort the waste lithium iron phosphate batteries to obtain mixed positive and negative electrode sheets, immerse the mixed positive and negative electrode sheets in deionized water for 60 minutes at a solid-liquid ratio of 100g:1L to dissolve the water-soluble organic binder in the negative electrode material, and use ultrasonic vibration at a frequency of 40KHz for 1 minute to make the negative electrode material fall off the copper foil to achieve efficient dissociation between the graphite negative electrode material and the copper foil current collector and between the graphite electrode material particles, and then use a large-aperture screen to separate the graphite from the copper foil and the positive electrode sheet.

[0048] S2. Filter and dry the separated negative electrode material to obtain negative electrode graphite and a lithium-containing solution, and the lithium-containing solution is used for subsequent lithium replenishment and repair of the positive electrode material.

[0049] S3, crushing the separated positive electrode sheet and the copper foil together, and passing through a 0.075 mm aperture sieve after crushing to separate the positive electrode material from the current collector, so as to obtain waste lithium iron phosphate positive electrode material.

[0050] S4. The separated positive electrode material is subjected to plasma ashing treatment for 15 minutes in a low-temperature plasma ashing instrument at 145° C., a purity of 99.999%, an oxygen atmosphere with a flow rate of 0.2 L / min, a power of 100 W, and a vacuum degree of 3 mbar to remove organic binders, fluorine, and carbon impurities in the positive electrode material and achieve surface activation to obtain a deeply impurity-removed and purified lithium iron phosphate electrode material.

[0051] S5. According to the solid-liquid ratio of 100g:1L, the deeply impurity-removed and purified lithium iron phosphate electrode material is placed in a reducing atmosphere, and liquid-phase lithium replenishment is carried out in a liquid lithium replenisher with a lithium ion concentration of 1.05mol / L. The liquid lithium replenisher is a lithium-containing solution obtained by filtering the negative electrode material as the lithium replenisher, lithium carbonate is used as an additional lithium source, and citric acid and ascorbic acid are mixed as lithium replenishing media. The molar ratio of the lithium deficiency amount of the deeply impurity-removed and purified lithium iron phosphate electrode material to the lithium content of the liquid lithium replenisher is 1:1.05. The reaction is carried out at 80°C and normal pressure for 6h to fill the lithium ions missing in the internal crystal structure, followed by solid-liquid separation and multiple washing of the positive electrode material, and then the electrode material after liquid-phase lithium replenishment is calcined in an inert atmosphere at 600°C for 2.0h to achieve material solidification and crystal structure repair, so as to obtain a regenerated lithium iron phosphate electrode material.

[0052] Example 2

[0053] A method for separating, purifying and regenerating waste lithium iron phosphate electrode materials comprises the following steps:

[0054] S1. Shred and sort the waste lithium iron phosphate batteries to obtain mixed positive and negative electrode sheets, soak the mixed positive and negative electrode sheets in deionized water for 45 minutes at a solid-liquid ratio of 150g:1L to dissolve the water-soluble organic binder in the negative electrode material, and use 35KHz frequency ultrasonic vibration for 2 minutes to make the negative electrode material fall off the copper foil to achieve efficient dissociation between the graphite negative electrode material and the copper foil current collector and between the graphite electrode material particles, and then use a large-aperture screen to separate the graphite from the copper foil and the positive electrode sheet.

[0055] S2. Filter and dry the separated negative electrode material to obtain negative electrode graphite and a lithium-containing solution, and the lithium-containing solution is used for subsequent lithium replenishment and repair of the positive electrode material.

[0056] S3, crushing the separated positive electrode sheet and the copper foil together, and passing through a 0.075 mm aperture sieve after crushing to separate the positive electrode material from the current collector, so as to obtain waste lithium iron phosphate positive electrode material.

[0057] S4. The separated positive electrode material is subjected to plasma ashing treatment for 5 minutes in a low-temperature plasma ashing instrument at 140° C., a purity of 99.999%, an oxygen atmosphere with a flow rate of 0.15 L / min, a power of 70 W, and a vacuum degree of 3 mbar to remove organic binders, fluorine, and carbon impurities in the positive electrode material and achieve surface activation to obtain a deeply impurity-removed and purified lithium iron phosphate electrode material.

[0058] S5. According to the solid-liquid ratio of 100g:1L, the deeply impurity-removed and purified lithium iron phosphate electrode material is placed in a reducing atmosphere, and liquid-phase lithium replenishment is carried out in a liquid lithium replenisher with a lithium ion concentration of 1.2mol / L. The liquid lithium replenisher is a lithium-containing solution obtained by filtering the negative electrode material as the lithium replenisher, lithium sulfate is used as an additional lithium source, and citric acid and ascorbic acid are mixed as lithium replenishing media. The molar ratio of the lithium deficiency amount of the deeply impurity-removed and purified lithium iron phosphate electrode material to the lithium content of the liquid lithium replenisher is 1:1.2. The reaction is carried out at 80°C and normal pressure for 6h to fill the lithium ions missing in the internal crystal structure, followed by solid-liquid separation and multiple washing of the positive electrode material, and then the electrode material after liquid-phase lithium replenishment is calcined in an inert atmosphere at 550°C for 2h to achieve material solidification and crystal structure repair, thereby obtaining a regenerated lithium iron phosphate electrode material.

[0059] Example 3

[0060] A method for separating, purifying and regenerating waste lithium iron phosphate electrode materials comprises the following steps:

[0061] S1. Shred and sort the waste lithium iron phosphate batteries to obtain mixed positive and negative electrode sheets, immerse the mixed positive and negative electrode sheets in deionized water at a solid-liquid ratio of 120g:1L for 75 minutes to dissolve the water-soluble organic binder in the negative electrode material, and use ultrasonic vibration at a frequency of 45KHz for 3 minutes to make the negative electrode material fall off the copper foil to achieve efficient dissociation between the graphite negative electrode material and the copper foil current collector and between the graphite electrode material particles, and then use a large-aperture screen to separate the graphite from the copper foil and the positive electrode sheet.

[0062] S2. Filter and dry the separated negative electrode material to obtain negative electrode graphite and a lithium-containing solution, and the lithium-containing solution is used for subsequent lithium replenishment and repair of the positive electrode material.

[0063] S3, crushing the separated positive electrode sheet and the copper foil together, and passing through a 0.075 mm aperture sieve after crushing to separate the positive electrode material from the current collector, so as to obtain waste lithium iron phosphate positive electrode material.

[0064] S4. The separated positive electrode material is subjected to plasma ashing treatment for 25 minutes in a low-temperature plasma ashing instrument at 150° C., a purity of 99.999%, an oxygen atmosphere with a flow rate of 0.2 L / min, a power of 100 W, and a vacuum degree of 3 mbar to remove organic binders, fluorine, and carbon impurities in the positive electrode material and achieve surface activation to obtain a deeply impurity-removed and purified lithium iron phosphate electrode material.

[0065] S5. According to the solid-liquid ratio of 100g:1L, the deeply impurity-removed and purified lithium iron phosphate electrode material is placed in a reducing atmosphere, and liquid-phase lithium replenishment is carried out in a liquid lithium replenisher with a lithium ion concentration of 1.1mol / L. The liquid lithium replenisher is a lithium-containing solution obtained by filtering the negative electrode material as the lithium replenisher, lithium carbonate is used as an additional lithium source, and citric acid and ascorbic acid are mixed as lithium replenishing media. The molar ratio of the lithium deficiency amount of the deeply impurity-removed and purified lithium iron phosphate electrode material to the lithium content of the liquid lithium replenisher is 1:1.1. The reaction is carried out at 80°C and normal pressure for 6h to fill the lithium ions missing in the internal crystal structure, followed by solid-liquid separation and multiple rinses of the positive electrode material, and then the electrode material after liquid-phase lithium replenishment is calcined in an inert atmosphere at 800°C for 3h to achieve material solidification and crystal structure repair, to obtain a regenerated lithium iron phosphate electrode material.

[0066] Example 4

[0067] A method for separating, purifying and regenerating waste lithium iron phosphate electrode materials comprises the following steps:

[0068] S1. Shred and sort the waste lithium iron phosphate batteries to obtain mixed positive and negative electrode sheets, immerse the mixed positive and negative electrode sheets in deionized water at a solid-liquid ratio of 130g:1L for 50 minutes to dissolve the water-soluble organic binder in the negative electrode material, and use 38KHz frequency ultrasonic vibration for 3 minutes to make the negative electrode material fall off the copper foil to achieve efficient dissociation between the graphite negative electrode material and the copper foil current collector and between the graphite electrode material particles, and then use a large-aperture screen to separate the graphite from the copper foil and the positive electrode sheet.

[0069] S2. Filter and dry the separated negative electrode material to obtain negative electrode graphite and a lithium-containing solution, and the lithium-containing solution is used for subsequent lithium replenishment and repair of the positive electrode material.

[0070] S3, crushing the separated positive electrode sheet and the copper foil together, and passing through a 0.075 mm aperture sieve after crushing to separate the positive electrode material from the current collector, so as to obtain waste lithium iron phosphate positive electrode material.

[0071] S4. The separated positive electrode material is subjected to plasma ashing treatment for 10 min in a low-temperature plasma ashing instrument at 148° C., a purity of 99.999%, an oxygen atmosphere with a flow rate of 0.18 L / min, a power of 100 W, and a vacuum degree of 3 mbar to remove organic binders, fluorine, and carbon impurities in the positive electrode material and achieve surface activation to obtain a deeply impurity-removed and purified lithium iron phosphate electrode material.

[0072] S5. According to the solid-liquid ratio of 100g:1L, the deeply impurity-removed and purified lithium iron phosphate electrode material is placed in a reducing atmosphere, and liquid-phase lithium replenishment is carried out in a liquid lithium replenisher with a lithium ion concentration of 1.05mol / L. The liquid lithium replenisher is a lithium-containing solution obtained by filtering the negative electrode material, lithium sulfate is used as an additional lithium source, and citric acid and ascorbic acid are mixed as lithium replenishing media. The molar ratio of the lithium deficiency amount of the deeply impurity-removed and purified lithium iron phosphate electrode material to the lithium content of the liquid lithium replenisher is 1:1.15. The reaction is carried out at 80°C and normal pressure for 6h to fill the lithium ions missing in the internal crystal structure, followed by solid-liquid separation and multiple washing of the positive electrode material, and then the electrode material after liquid-phase lithium replenishment is calcined in an inert atmosphere at 700°C for 2.5h to achieve material solidification and crystal structure repair, to obtain a regenerated lithium iron phosphate electrode material.

[0073] In order to further illustrate the technical effect of the present invention, the present invention is also provided with a comparative example, as follows:

[0074] Comparative Example 1

[0075] Compared with Example 1, the difference is that traditional oxygen roasting is adopted.

[0076] The waste lithium iron phosphate battery positive electrode plate is baked at 450℃ for 60min under aerobic conditions, so that the organic binder in the plate reacts with oxygen and is directly converted into CO2 gas to achieve the purpose of removing the organic binder. After returning to room temperature, the electrode material is peeled off on the current collector, and then the electrode material is ball-milled and sieved, and then baked at 800℃ for 120min under aerobic conditions to ensure that impurities such as PVDF, conductive carbon and carbon coating on the surface of the electrode material are completely removed. After returning to room temperature, an electrode material free of carbon impurities can be obtained. The electrode material after carbon removal is fully mixed with the lithium supplement agent and placed in a hydrogen + argon gas atmosphere, baked at 350℃ for 5.0h, and then heated to 650℃ for 10.0h. After the baking is completed, it is returned to room temperature to obtain the repaired lithium iron phosphate electrode material.

[0077] Comparative Example 2

[0078] Compared with Example 1, the difference is that traditional anaerobic pyrolysis of organic matter is adopted.

[0079] The waste lithium iron phosphate positive electrode material was calcined at 500°C in a nitrogen atmosphere for 1.0h to decompose the organic binder in the positive electrode material, and then the positive electrode material fell off the aluminum foil. The detached positive electrode material was then ball-milled at a speed of 300r / min for 2.0h to ensure that the positive electrode material was fully dissociated. After the positive electrode material was mixed with the liquid phase lithium replenisher, it was stirred in a water bath at 80°C for 6.0h. After solid-liquid separation, the positive electrode material was fully rinsed and placed in a vacuum drying oven for 24h. Subsequently, the lithium deficiency of the positive electrode material after liquid phase lithium replenishment was determined by digestion, and lithium carbonate was added to the positive electrode material at 1.05 times the molar amount of lithium deficiency and fully ground and mixed, and then calcined at 600°C in a nitrogen atmosphere for 2.0h to complete the solid phase lithium replenishment repair.

[0080] The method for removing impurity carbon from waste lithium iron phosphate electrode materials provided in the above embodiments greatly improves the carbon removal efficiency, reduces the energy consumption for carbon removal, and has a good in-situ repair and regeneration effect. Embodiment 1 realizes the separation of positive and negative electrode materials by hydraulic immersion based on the adhesion characteristics of the positive and negative electrode materials, and realizes surface carbon removal by low-temperature plasma ashing heat treatment, which not only reduces energy consumption, but also prevents aerobic roasting from oxidizing the electrode material, and at the same time ensures the removal of the organic binder, so that the electrode material can be smoothly peeled off from the current collector; the carbon impurities in the electrode material can be effectively removed by controlling the low-temperature plasma ashing process, such as Figure 2 As shown, the carbon removal efficiency is guaranteed and the problem of high energy consumption of high-temperature aerobic roasting is avoided. At the same time, the low-temperature plasma ashing process activates the internal crystal structure of the electrode material, which has a beneficial effect on the subsequent lithium replenishment.

[0081] In the embodiment of the present invention, the separation result of the positive and negative electrode materials is that the purity of the positive electrode material is higher than 99.5%; the carbon content of the positive electrode material after crushing and screening and low-temperature plasma ashing is reduced from 5.37% before ashing to 2.79% after ashing for 15 minutes; the ratio of Li:Fe:P in the positive electrode material after lithium supplementation is increased from 0.89:1:1 before lithium supplementation to about 1:1:1, as shown in Table 1. Under the same lithium supplementation conditions, the charging capacity of the lithium iron phosphate electrode material obtained in the present invention reaches 149.51mAh / g, as shown in Table 2, and the performance is significantly better than the lithium iron phosphate electrode material obtained by the traditional technical process in the comparative example.

[0082] Table 1 Element ratios in the positive electrode material before and after lithium supplementation in Example 1 of the present invention

[0083] Li:P:Fe Before lithium supplementation 0.89：1：1 After lithium supplementation 1：1：1

[0084] Table 2 Comparison of charge and discharge specific capacity of lithium iron phosphate after repair in Example 1 of the present invention and Comparative Examples 1-2

[0085] Charge capacity Example 1 149.51mAh / g Comparative Example 1 91.93mAh / g Comparative Example 2 95.55mAh / g

[0086] To sum up, through the separation, purification and regeneration method of waste lithium iron phosphate electrode materials of the embodiment of the present invention, the free carbon in the waste lithium iron phosphate electrode materials is efficiently removed and the coated carbon is retained, the regeneration and repair effect is good, and at the same time the stability of the electrode material lattice is ensured, and the energy consumption is reduced.

[0087] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for separating, purifying and regenerating waste lithium iron phosphate electrode materials, characterized in that: The following steps are involved: The waste lithium iron phosphate battery is shredded and pre-processed and sorted to obtain a positive and negative electrode mixed electrode sheet, the positive and negative electrode mixed electrode sheet is immersed in deionized water to dissolve the water-soluble organic binder in the negative electrode and extract the lithium element in the negative electrode material, ultrasonically remove the negative electrode material from the copper foil, and dissociate the negative electrode material from the copper foil and the graphite electrode material particles, and sieve to obtain the negative electrode material, the copper foil and the positive electrode sheet; Filtering and drying the negative electrode material to obtain negative electrode graphite; The positive electrode sheet and the copper foil are crushed and sieved to separate the positive electrode material from the current collector to obtain the waste lithium iron phosphate positive electrode material; The waste lithium iron phosphate positive electrode material is subjected to plasma ashing treatment in an oxygen atmosphere at 140° C. to 150° C. to remove organic binder, fluorine and carbon impurities in the positive electrode material and to achieve surface activation, thereby obtaining a deeply impurity-removed and purified lithium iron phosphate electrode material; In a reducing atmosphere, the deeply impurity-removed and purified lithium iron phosphate electrode material is supplemented with lithium to fill the lithium ions missing in the internal crystal structure to obtain a lithium-supplemented electrode material. The lithium-supplemented electrode material is calcined at 550° C. to 800° C. in an inert atmosphere to achieve material solidification and crystal structure repair to obtain a regenerated lithium iron phosphate electrode material.

2. The method for separation, purification and regeneration of waste lithium iron phosphate electrode materials according to claim 1, characterized in that: After filtering the negative electrode material, a lithium-containing solution is obtained. The lithium-containing solution is used as a lithium supplement, lithium carbonate or lithium sulfate is used as an external lithium source, and citric acid and ascorbic acid are used as lithium supplement media to obtain a liquid lithium supplement solution.

3. The method for separation, purification and regeneration of waste lithium iron phosphate electrode materials according to claim 2, characterized in that: The lithium replenishment is specifically as follows: the deeply impurity-removed and purified lithium iron phosphate electrode material is mixed with a liquid lithium replenisher solution at a solid-liquid ratio of 80g to 120g:1L, and reacted at 70°C to 90°C and normal pressure for 5h to 7h.

4. The method for separation, purification and regeneration of waste lithium iron phosphate electrode materials according to claim 3, characterized in that: The concentration of lithium ions in the liquid lithium supplement is 0.15 mol / L to 0.2 mol / L, and the molar ratio of the lithium deficiency of the lithium iron phosphate electrode material after deep impurity removal and purification to the lithium content of the liquid lithium supplement is 1:1.05 to 1.

2.

5. The method for separation, purification and regeneration of waste lithium iron phosphate electrode materials according to claim 1, characterized in that: The solid-liquid ratio of the positive and negative electrode mixed electrode sheet to deionized water is 100-150g:1L, and the soaking time is 45min-75min.

6. The method for separation, purification and regeneration of waste lithium iron phosphate electrode materials according to claim 1, characterized in that: The frequency of the ultrasound is 35KHz to 45KHz, and the ultrasound time is 1min to 3min.

7. The method for separation, purification and regeneration of waste lithium iron phosphate electrode materials according to claim 1, characterized in that: During screening, the aperture of the screen used is >2mm and smaller than the size of the positive electrode sheet.

8. The method for separation, purification and regeneration of waste lithium iron phosphate electrode materials according to claim 1, characterized in that: When screening, the aperture of the screen used is 0.075mm.

9. The method for separation, purification and regeneration of waste lithium iron phosphate electrode materials according to claim 1, characterized in that: The plasma ashing treatment is specifically: performing plasma ashing treatment for 5min to 25min in a low-temperature plasma ashing instrument at 140°C to 150°C, a purity of 99.999%, a flow rate of 0.15L / min to 0.2L / min, a power of 70W to 110W, and a vacuum degree of 3mbar in an oxygen atmosphere.

10. The method for removing impurities and regenerating waste lithium iron phosphate electrode materials according to claim 1, characterized in that: The calcination time is 2h to 3h.

Images