Waste lithium iron phosphate positive electrode material regenerated by low-temperature normal-pressure liquid phase method and preparation method of waste lithium iron phosphate positive electrode material

Abstract

The invention discloses a waste lithium iron phosphate positive electrode material regenerated by a low-temperature normal-pressure liquid phase method and a preparation method, repair of waste lithium iron phosphate is realized through a low-temperature liquid phase, compared with a traditional hydrothermal method, the requirement for equipment in the repair process can be effectively reduced, the structure of regenerated lithium iron phosphate is stabilized through an annealing process, and the recovery rate of lithium iron phosphate is improved. Meanwhile, the added organic carbon source can repair a damaged carbon layer of the waste lithium iron phosphate, and the electrochemical performance of the regenerated lithium iron phosphate is improved. The invention aims to provide the regeneration method of the waste lithium iron phosphate positive electrode material, which is green, efficient and low in energy consumption and has an industrial application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of recycling waste lithium-ion batteries and recycling electrode materials, and specifically relates to a low-temperature, normal-pressure liquid phase method for regenerating waste lithium iron phosphate positive electrode materials and a preparation method thereof. Background Art

[0002] The rapid development of new energy vehicles has led to an explosive growth in the production of lithium-ion batteries. Among them, LiFePO4 (LFP) batteries have a higher market share due to their low cost, good thermal stability, and excellent cycle performance. The service life of LFP batteries is only 5 to 8 years, so a large number of waste LFP batteries will be produced in the future. If waste LFP batteries are discarded at will or recycled unreasonably, it will lead to a large amount of resource waste and serious environmental pollution. In industry, waste lithium-ion batteries are generally recycled by pyrometallurgy or hydrometallurgy. Among them, pyrometallurgy has high energy consumption and is difficult to recycle high-value lithium resources. Therefore, it is not suitable for recycling LFP positive electrode materials that do not contain precious metals; hydrometallurgy has a high recovery rate, but it has the disadvantages of long process, low efficiency, high cost, and high environmental pressure during the recycling process. However, LFP materials have the characteristics of stable crystal structure. After multiple cycles of lithium insertion and extraction, only Li is missing, and the crystal structure of the material is not destroyed. Therefore, direct lithium supplementation and repair regeneration of waste LFP positive electrode materials can effectively solve the main problems of pyrometallurgy and hydrometallurgy.

[0003] At present, the main methods for repairing waste lithium iron phosphate positive electrode materials are high-temperature solid-phase method and hydrothermal method. The high-temperature solid-phase method requires the detection of the element content of the waste materials, accurately determines the amount of lithium salt to be added, and then needs to be calcined for a long time at high temperature under an inert atmosphere to regenerate the waste lithium iron phosphate. The high-temperature solid-phase method has a simple process, but high energy consumption, low repair efficiency, and the solid-phase reaction cannot achieve uniform contact between the lithium salt and the waste lithium iron phosphate material, so a pre-ball milling process is required, and the regeneration effect is poor. The hydrothermal method is to disperse the waste powder in deionized water, add a reducing agent and lithium salt, mix the liquid phase evenly, and then regenerate the waste lithium iron phosphate in a reactor. The hydrothermal method does not require precise lithium content and can achieve uniform contact between lithium ions and waste lithium iron phosphate. The hydrothermal method has low energy consumption, high efficiency, and good repair effect. Compared with the solid-phase method, it is more likely to achieve large-scale industrial application. However, the current hydrothermal method for repairing waste lithium iron phosphate still requires a reaction under high temperature and high pressure to achieve sufficient lithium replenishment of waste lithium iron phosphate. This results in high equipment costs for industrial-scale production of hydrothermal repair, which hinders its large-scale promotion. In addition, the waste positive electrode materials obtained by separating the pole pieces through traditional pretreatment methods will contain more impurities, especially the current collector aluminum foil. These impurities will seriously affect the effect of direct regeneration of waste positive electrode materials, making it difficult to achieve industrial application of direct regeneration technology.

[0004] The Chinese patent with publication number CN111547697A in the prior art discloses a method for repairing waste lithium iron phosphate materials, which includes mixing the failed powder with a solution containing lithium salt and a reducing agent, placing it in a high-pressure reactor, and performing a hydrothermal reaction at 100-200°C to repair the waste lithium iron phosphate. This method has a short process and the performance of the repaired material is good, but it is difficult to achieve the performance of commercial lithium iron phosphate and has poor consistency. This is because the waste lithium iron phosphate powder is crushed and sorted, contains a large amount of impurities, and the impurity content in the raw materials is different each time. In addition, the carbon layer on the surface of the waste lithium iron phosphate positive electrode material will also affect the performance of the recycled material. The carbon layer on the surface will generally be destroyed or even fall off at high temperatures. However, the traditional hydrothermal method cannot repair the carbon layer of waste lithium iron phosphate, so the performance of the regenerated lithium iron phosphate obtained is still different from that of commercial products.

[0005] Therefore, at present, people are more concerned about lowering the liquid phase repair regeneration temperature, such as lowering the repair temperature to below 100°C. For example, the prior art publication number CN113629244A discloses a method for low-temperature liquid phase repair of waste lithium iron phosphate positive electrode materials, and liquid phase repair is performed at a temperature below 100°C. This method does not require a high-pressure reactor, reduces safety hazards in production, and is conducive to promotion and application. However, the damaged carbon layer of the waste lithium iron phosphate is not repaired or impurities are removed. Due to the poor efficiency of low-temperature lithium replenishment, the electrochemical performance of the regenerated material is poor, far from meeting the performance requirements of commercial lithium iron phosphate materials. Summary of the invention

[0006] The purpose of the present invention is to solve the shortcomings of the existing liquid phase repair and regeneration methods. Specifically, in response to the main problems of the hydrothermal method, the present application provides a green, efficient, low-energy consumption method for regenerating waste lithium iron phosphate positive electrode materials with industrial application prospects. The traditional methods for separating the current collector and the waste positive electrode materials mainly include high-temperature pyrolysis of the binder, organic solvent dissolution of the binder, alkali solution immersion and dissolution of aluminum foil, etc. The pyrolysis method has high energy consumption, produces harmful gases, and the aluminum foil is easily broken and remains in the waste positive electrode material after heat treatment. The solubility of organic solvents in binders is limited, so a large amount of organic solvents is required, and the separation effect is not good, and external mechanical force is required to assist, resulting in the aluminum foil breaking and remaining in the waste positive electrode material. Alkaline solution immersion and dissolution of aluminum foil will produce a large amount of hydrogen, which is dangerous, and the positive electrode material will also dissolve in an alkaline environment. Therefore, the waste positive electrode material obtained by the traditional separation method has a high impurity content, is difficult to regenerate, and has a poor regeneration effect. In this application, a homemade eluent is used to treat the waste electrode sheet, and the eluent will react quickly with the surface of the current collector aluminum foil to generate Al 3+Ions and bubbles cause the waste positive electrode material layer to lose contact with the aluminum foil, thereby separating the waste positive electrode material from the current collector. After the eluent contacts the aluminum foil, an ultra-thin and dense passivation layer will be immediately formed in situ on the surface, which can effectively inhibit the continuous corrosion of the aluminum foil, so the complete aluminum foil can be recovered. In addition, the reaction-passivation mechanism can inhibit the dissolution of the positive electrode and separate the waste positive electrode material with high crystal structure integrity. The eluent can successfully obtain waste positive electrode materials with low impurity content and intact structure. Therefore, there is no need to repair waste lithium iron phosphate under high temperature and high pressure like the traditional hydrothermal method. It only needs to be repaired and regenerated at a temperature of 60 to 80 ° C, and the damaged carbon layer of the waste lithium iron phosphate can be repaired by adding an organic carbon source during the short annealing process, thereby obtaining a high-performance lithium iron phosphate positive electrode material.

[0007] In addition, this method also solves the problems of high energy consumption of the solid-phase method, the inability to achieve uniform contact between lithium ions and waste lithium iron phosphate, and the need for precise element ratios resulting in low repair efficiency. It also solves the problem that the hydrothermal method requires a high-pressure environment for lithium replenishment and cannot repair the carbon layer on the surface of waste lithium iron phosphate. It not only achieves the purpose of energy saving and high efficiency, but also provides the possibility of industrial application for the recovery of waste lithium iron phosphate positive electrode materials through repair and regeneration.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions to achieve it.

[0009] A preparation method for regenerating waste lithium iron phosphate positive electrode material by low-temperature and normal-pressure liquid phase method, comprising the following steps:

[0010] S1. Place the waste lithium iron phosphate positive electrode sheet in an eluent for elution to obtain an active material;

[0011] S2, the active material is reduced and lithium-supplemented to obtain lithium-supplemented lithium iron phosphate powder,

[0012] S3, performing carbon layer repair treatment on the lithium-replenished lithium iron phosphate powder; uniformly mixing the lithium-replenished lithium iron phosphate powder with an organic carbon source, annealing the mixture, and then cooling the mixture to room temperature to obtain a regenerated lithium iron phosphate positive electrode material.

[0013] Preferably, the step S1 further includes the following steps:

[0014] The waste lithium iron phosphate positive electrode pieces are cut and transferred to an eluent for elution to separate the active material and the electrode pieces to obtain the active material.

[0015] Preferably, the heating temperature for elution is 60° C. to 80° C., and the soaking time for elution is 2 min to 5 min.

[0016] Preferably, the active material obtained in S1 is dried and ground to obtain lithium iron phosphate powder;

[0017] In S2, the lithium iron phosphate powder is reduced and supplemented with lithium to obtain lithium-supplemented lithium iron phosphate powder.

[0018] Preferably, in S2, the obtained lithium iron phosphate powder is dispersed in deionized water containing a lithium salt and a reducing agent to obtain a repair suspension stock solution;

[0019] The obtained repair suspension stock solution is placed in a stirring state and heated to react, so as to carry out liquid phase repair of waste lithium iron phosphate.

[0020] The lithium-supplemented lithium iron phosphate powder is obtained.

[0021] Preferably, the lithium salt is one or two of lithium sulfate, lithium hydroxide and lithium acetate.

[0022] Preferably, the reducing agent is one or more of ascorbic acid, citric acid, tartaric acid and malic acid.

[0023] Preferably, the eluent is prepared by diluting one or two of phytic acid, phytic acid iron, and ferric acetate in deionized water to a pH between 6 and 7.

[0024] Preferably, the organic carbon source is one or more of glucose, sucrose and starch.

[0025] A low-temperature, normal-pressure liquid phase method for regenerating waste lithium iron phosphate positive electrode materials using the preparation method described above, wherein the preparation raw materials used include waste lithium iron phosphate positive electrode materials; the waste lithium iron phosphate positive electrode materials have active lithium loss during the charge and discharge process, the material contains Fe(PO)4 impurities, and the carbon coating layer on the surface of the waste lithium iron phosphate positive electrode material particles is destroyed, and the chemical formula is Li x Fe y PO4, where 0<x<y<1.

[0026] The prepared regenerated lithium iron phosphate positive electrode material has good process repair performance, and also has excellent cycle stability and excellent rate performance.

[0027] Compared with the prior art, the present invention has the following advantages after adopting the above method:

[0028] 1) Compared with direct regeneration by solid phase method, it can reduce the energy consumption of repair, achieve uniform contact between lithium ions and waste lithium iron phosphate, and repair materials without precise element ratio.

[0029] 2) Compared with the traditional hydrothermal liquid phase direct regeneration, the reaction conditions are milder, do not require a high-pressure environment, and can repair the carbon coating on the surface of the waste LFP positive electrode material, improve the electrochemical performance of the regenerated LFP material, and have greater prospects for industrial application.

[0030] 3) The waste lithium iron phosphate positive electrode material obtained by separation with an eluent has a low impurity content. Therefore, it does not need to be repaired under high temperature and high pressure like the traditional hydrothermal method. The waste lithium iron phosphate can be repaired and regenerated at a temperature of 60 to 80°C, and the damaged carbon layer of the waste lithium iron phosphate is repaired by adding an organic carbon source during a short annealing process, thereby obtaining a high-performance lithium iron phosphate positive electrode material. The prepared regenerated lithium iron phosphate positive electrode material has good process repair performance, and also has excellent cycle stability and excellent rate performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a diagram of the current collector aluminum foil and flaky active powder obtained by separating the pole pieces through soaking in an eluent in Example 1 of the present invention.

[0032] Figure 2 This is an XRD comparison chart of the regenerated lithium iron phosphate, waste lithium iron phosphate and standard lithium iron phosphate in Example 1 of the present invention.

[0033] Figure 3 This is a SEM image of the regenerated lithium iron phosphate according to Example 1 of the present invention.

[0034] Figure 4 This is a charge and discharge curve diagram of the first cycle of a lithium-ion battery made of lithium iron phosphate active material regenerated in Example 1 at a rate of 0.1C.

[0035] Figure 5 This is a rate performance diagram of a lithium-ion battery made from the lithium iron phosphate active material regenerated in Example 1.

[0036] Figure 6 This is an XRD comparison chart of the regenerated lithium iron phosphate, waste lithium iron phosphate and standard lithium iron phosphate in Example 2 of the present invention.

[0037] Figure 7 This is a SEM image of the regenerated lithium iron phosphate in Example 2 of the present invention.

[0038] Figure 8 This is a charge and discharge curve of the first cycle of a lithium-ion battery made of lithium iron phosphate active material regenerated in Example 2 at a rate of 0.1C.

[0039] Fig. 9 This is a cycle performance diagram of a lithium-ion battery made of lithium iron phosphate active material regenerated in Example 2 of the present invention, which is activated for 3 cycles at a rate of 0.1C and then cycled for 100 cycles at a rate of 5C.

[0040] Fig.10 This is an XRD comparison chart of the regenerated lithium iron phosphate, waste lithium iron phosphate and standard lithium iron phosphate in comparative example 1 of the present invention.

[0041] Fig.11 The first cycle charge and discharge curve of the lithium ion battery made of lithium iron phosphate active material regenerated from Example 1 and Comparative Example 1 at a rate of 0.1C.

[0042] Fig.12 This is an XRD comparison chart of the regenerated lithium iron phosphate, waste lithium iron phosphate and standard lithium iron phosphate in comparative example 2 of the present invention.

[0043] Fig.13 The first cycle charge and discharge curve of the lithium-ion battery made of the lithium iron phosphate active material regenerated from Example 2 and Comparative Example 2 at a rate of 0.1C.

[0044] Fig.14 This is a cycle performance diagram of a lithium-ion battery made of lithium iron phosphate active materials regenerated from Example 2 and Comparative Example 2, which was activated for 3 cycles at a rate of 0.1C and then cycled for 100 cycles at a rate of 5C.

[0045] Fig.15 It is a schematic diagram of the process flow of the present invention. DETAILED DESCRIPTION

[0046] Unless otherwise defined, all the professional terms used below have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0047] Unless otherwise specified, various reagents and raw materials used in the present invention can be purchased from the market or can be prepared by known methods.

[0048] A preparation method for regenerating waste lithium iron phosphate positive electrode material by a low-temperature and normal-pressure liquid phase method in one embodiment of the present invention comprises the following steps:

[0049] S1. Place the waste lithium iron phosphate positive electrode sheet in an eluent for elution to obtain an active material;

[0050] S2, the active material is reduced and lithium-supplemented to obtain lithium-supplemented lithium iron phosphate powder;

[0051] S3, performing a carbon layer repair treatment on the lithium-replenished lithium iron phosphate powder; uniformly mixing the lithium-replenished lithium iron phosphate powder with an organic carbon source, annealing the mixture, and then cooling the mixture to room temperature to obtain a regenerated lithium iron phosphate positive electrode material;

[0052] The organic carbon source is one or more of glucose, sucrose and starch.

[0053] In one embodiment, the step S1 further includes the following steps:

[0054] The waste lithium iron phosphate positive electrode pieces are cut and transferred to an eluent for elution to separate the active material and the electrode pieces to obtain the active material.

[0055] The active material is in sheet form; the waste lithium iron phosphate positive electrode plate comprises waste lithium iron phosphate positive electrode material and a plate; the plate is a current collector aluminum foil;

[0056] In one of the embodiments, the heating temperature for elution is 60° C. to 80° C., and the soaking time for elution is 2 min to 5 min.

[0057] In one embodiment, after the S1 elution is completed, the product obtained by solid-liquid separation is dried and ground to obtain lithium iron phosphate powder, i.e., active material;

[0058] In S2, the lithium iron phosphate powder is reduced and supplemented with lithium to obtain lithium-supplemented lithium iron phosphate powder.

[0059] In one embodiment, in S2, the obtained lithium iron phosphate powder is dispersed in deionized water containing a lithium salt and a reducing agent to obtain a repair suspension stock solution;

[0060] The obtained repair suspension stock solution is placed in a stirring state and heated to react, so as to carry out liquid phase repair of waste lithium iron phosphate.

[0061] The lithium-supplemented lithium iron phosphate powder is obtained.

[0062] In one embodiment, the lithium salt is one or two of lithium sulfate, lithium hydroxide, and lithium acetate.

[0063] In one of the embodiments, during the heating reaction, the stirring speed is 200rpm~1000rpm, the heating temperature is 60℃~80℃, and the heating time is 4h~6h; after the liquid phase repair is completed, the solution is cooled to room temperature, the solution is filtered, the slurry obtained by rinsing the filtration is washed with deionized water, and the lithium iron phosphate powder is obtained after the slurry is dried.

[0064] In one embodiment, the rinsed slurry is dried at a temperature of 80° C. to 120° C. for a drying time of 4 h to 12 h.

[0065] In one embodiment, the solid-liquid ratio of the waste lithium iron phosphate positive electrode sheet to the eluent in S1 is 50g / L-100g / L.

[0066] In one embodiment, the drying in S1 is carried out at 80°C-120°C.

[0067] In one embodiment, the lithium salt is one or two of lithium sulfate, lithium hydroxide, and lithium acetate, and the concentration of the lithium salt in the solution is 0.1 mol / L-0.6 mol / L.

[0068] In one embodiment, the reducing agent is one or more of ascorbic acid, citric acid, tartaric acid, and malic acid, and the reducing agent concentration in the solution is 0.1 mol / L-0.5 mol / L.

[0069] In one embodiment, the solid-to-liquid ratio of the repair suspension solution is 30 g / L to 150 g / L.

[0070] In one embodiment, the reducing agent is one or more of ascorbic acid, citric acid, tartaric acid, and malic acid.

[0071] In one embodiment, the eluent is prepared by diluting one or two of phytic acid, phytic acid iron, and ferric acetate in deionized water to a pH between 6 and 7.

[0072] In one embodiment, the organic carbon source is one or more of glucose, sucrose, and starch, and the added amount is 2wt.% to 10wt.% of the total amount of the organic carbon source mixed with the lithium iron phosphate powder.

[0073] In one embodiment, the atmosphere condition of the annealing treatment is one of argon, nitrogen, or argon-hydrogen mixed gas.

[0074] In one of the embodiments, the annealing treatment temperature is 500° C. to 700° C., the holding time is 2 h to 4 h, and the heating rate is 5° C. / min to 10° C. / min.

[0075] In one embodiment, the grinding degree is until the active material can pass through a 200-mesh sieve, thereby obtaining lithium iron phosphate powder.

[0076] The technical solution also provides a method for regenerating waste lithium iron phosphate positive electrode materials by a low-temperature, normal-pressure liquid phase method using the preparation method described above, wherein the preparation raw materials used include waste lithium iron phosphate positive electrode materials; the waste lithium iron phosphate positive electrode materials have active lithium loss during the charge and discharge process, the material contains Fe(PO)4 impurities, and the carbon coating layer on the surface of the waste lithium iron phosphate positive electrode material particles is destroyed, and the chemical formula is Li x Fe y PO4, where 0<x<y<1.

[0077] Compared with the prior art, the present invention has the following advantages after adopting the above method:

[0078] 1) Compared with direct regeneration by solid phase method, it can reduce the energy consumption of repair, achieve uniform contact between lithium ions and waste lithium iron phosphate, and repair materials without precise element ratio.

[0079] 2) Compared with the traditional hydrothermal liquid phase direct regeneration, the reaction conditions are milder, do not require a high-pressure environment, and can repair the carbon coating on the surface of the waste LFP positive electrode material, improve the electrochemical performance of the regenerated LFP material, and have greater prospects for industrial application.

[0080] 3) The waste lithium iron phosphate positive electrode material obtained by separation with an eluent has a low impurity content. Therefore, it does not need to be repaired under high temperature and high pressure like the traditional hydrothermal method. The waste lithium iron phosphate can be repaired and regenerated at a temperature of 60 to 80°C, and the damaged carbon layer of the waste lithium iron phosphate is repaired by adding an organic carbon source during a short annealing process, thereby obtaining a high-performance lithium iron phosphate positive electrode material. The prepared regenerated lithium iron phosphate positive electrode material has good process repair performance, and also has excellent cycle stability and excellent rate performance.

[0081] The present invention realizes the repair of waste lithium iron phosphate through low-temperature liquid phase, which can effectively reduce the requirements for equipment in the repair process compared with the traditional hydrothermal method, and stabilizes the structure of regenerated lithium iron phosphate through the annealing process. At the same time, the added organic carbon source can repair the damaged carbon layer of waste lithium iron phosphate and improve the electrochemical performance of regenerated lithium iron phosphate. The present invention aims to provide a green, efficient, low-energy consumption, and industrial application prospective regeneration method for waste lithium iron phosphate positive electrode materials.

[0082] The embodiments of the present invention will be described in detail below with reference to specific examples.

[0083] Embodiment 1

[0084] The eluent used in Example 1 is phytic acid, the lithium salt is lithium hydroxide, the reducing agent is ascorbic acid, and the organic carbon source is glucose. It can be found from the results in Table 1 that the waste lithium iron phosphate obtained by the eluent has a small content of impurity elements and does not need to be repaired in a high-temperature and high-pressure liquid phase environment. Therefore, the repair and regeneration of waste lithium iron phosphate can be achieved in a mild environment. The specific steps are as follows:

[0085] (1) Prepare the eluent, take an appropriate amount of phytic acid in a beaker, add deionized water until the solution pH is 6.2, then cut the waste lithium iron phosphate positive electrode sheet, place it in a beaker and add the eluent, the solid-liquid ratio is 100g / L, place the beaker in an oil bath, heat to 80°C and keep warm for 2 minutes, the active material and the electrode are completely separated, and the sheet active material is obtained.

[0086] (2) placing the sheet active material in a forced air drying oven at 80° C. and drying for 12 h, and then grinding the sheet active material into powder until it can pass through a 200-mesh sieve to obtain black waste lithium iron phosphate powder;

[0087] (3) 2 g of waste lithium iron phosphate powder was taken with a solid-liquid ratio of 50 g / L and dispersed in a solution containing 0.4 mol / L lithium hydroxide and 0.3 mol / L ascorbic acid to obtain a repair suspension stock solution;

[0088] (4) placing the beaker containing the repair suspension stock solution in an oil bath, stirring at a speed of 400 rpm, heating to 80°C, and keeping warm for 5 hours. After the reaction is completed, the solution is filtered, and the black slurry obtained by filtration is rinsed with deionized water three times, placed in an 80°C forced air drying oven and dried for 10 hours to obtain lithium iron phosphate powder;

[0089] (5) The dried lithium iron phosphate powder was mixed evenly with 3 wt.% of glucose, and the mixed powder was heated to 650°C at 5°C / min in an argon atmosphere for low-temperature annealing. After keeping the temperature for 2 hours, the powder was cooled to room temperature in the furnace to obtain a regenerated lithium iron phosphate positive electrode material.

[0090] The results in Table 2 show that the lithium content of the lithium iron phosphate regenerated in Example 1 is effectively supplemented. Figure 2 This is the XRD diffraction pattern of regenerated lithium iron phosphate and waste lithium iron phosphate. As shown in the figure, the structure of the waste lithium iron phosphate has been successfully repaired and the impurity phase peak has disappeared. Figure 3 This is a SEM picture of regenerated lithium iron phosphate. As shown in the figure, the structure of the regenerated lithium iron phosphate particles is complete. Figure 4 This is the first cycle charge and discharge curve of regenerated lithium iron phosphate at 0.1C. The first cycle discharge specific capacity is 159.4mAh / g, and the first cycle coulomb efficiency is 99.1%. Figure 5 This is the rate performance diagram of the material. As shown in the figure, after the material has been cycled at a high rate of 5C and then returned to 0.5C, the discharge specific capacity of the material has not decreased. The regenerated lithium iron phosphate has excellent rate performance.

[0091] Embodiment 2

[0092] The eluent used in Example 2 is phytic acid iron, the lithium salt is lithium acetate, the reducing agent is citric acid, and the organic carbon source is sucrose. The specific steps are as follows:

[0093] (1) Prepare an eluent, take an appropriate amount of phytic acid iron in a beaker, add deionized water until the solution pH is 6.7, then cut the waste lithium iron phosphate positive electrode sheet, place it in a beaker, add the eluent, the solid-liquid ratio is 50g / L, place the beaker in an oil bath, heat to 60°C and keep warm for 5 minutes, the active material and the electrode are completely separated, and a sheet-like active material is obtained;

[0094] (2) drying the sheet active material in a 100° C. forced air drying oven for 10 h, and grinding the sheet active material into powder until it can pass through a 200-mesh sieve to obtain black waste lithium iron phosphate powder;

[0095] (3) 2 g of waste lithium iron phosphate powder was taken, with a solid-liquid ratio of 60 g / L, and dispersed in a solution containing 0.3 mol / L lithium acetate and 0.2 mol / L citric acid to obtain a repair suspension stock solution;

[0096] (4) placing the beaker containing the repair suspension stock solution in an oil bath, stirring at a speed of 500 rpm, heating to 60°C, and keeping warm for 6 hours. After the reaction is completed, the solution is filtered, and the black slurry obtained by filtration is rinsed with deionized water 5 times, placed in a 100°C forced air drying oven and dried for 10 hours to obtain lithium iron phosphate powder;

[0097] (5) The dried lithium iron phosphate powder was mixed evenly with 5 wt.% sucrose, and the mixed powder was heated to 600°C at 8°C / min in an argon atmosphere for low-temperature annealing. After keeping the temperature for 3 hours, the powder was cooled to room temperature in the furnace to obtain a regenerated lithium iron phosphate positive electrode material.

[0098] The results in Table 2 show that the lithium content of the lithium iron phosphate regenerated in Example 2 is effectively supplemented. Figure 6 This is the XRD diffraction pattern of regenerated lithium iron phosphate and waste lithium iron phosphate. As shown in the figure, the structure of the waste lithium iron phosphate has been successfully repaired and the impurity phase peak has disappeared. Figure 7 This is a SEM picture of regenerated lithium iron phosphate. As shown in the figure, the structure of the regenerated lithium iron phosphate particles is complete. Figure 8 This is the first cycle charge and discharge curve of regenerated lithium iron phosphate at 0.1C. The first cycle discharge specific capacity is 155.0mAh / g, and the first cycle coulomb efficiency is 98.7%. Fig. 9 This is the cycle performance diagram of the material. As shown in the figure, the first-cycle discharge capacity of the material at a 5C rate is 136.3mAh / g, and the capacity retention rate after 100 cycles is 96.3%. The regenerated lithium iron phosphate has excellent cycle stability.

[0099] Comparative Example 1

[0100] Corresponding to the above-mentioned embodiment 1, the lithium salt used is lithium hydroxide, the reducing agent is ascorbic acid, and the organic carbon source is glucose. The difference is that the waste lithium iron phosphate powder used is obtained from industrial production and has a high content of impurity elements. The specific steps are as follows:

[0101] (1) 2 g of waste lithium iron phosphate powder was taken, with a solid-liquid ratio of 50 g / L, and dispersed in a solution containing 0.3 mol / L LiOH and 0.3 mol / L ascorbic acid to obtain a repair suspension stock solution;

[0102] (2) placing the beaker containing the repair suspension stock solution in an oil bath, stirring at a speed of 400 rpm, heating to 80°C, and keeping warm for 5 hours. After the reaction is completed, the solution is filtered, and the black slurry obtained by filtration is rinsed with deionized water three times, and placed in an 80°C forced air drying oven for 10 hours to obtain lithium iron phosphate powder after drying;

[0103] (3) The dried lithium iron phosphate powder was mixed evenly with 3 wt.% of glucose, and the mixed powder was heated to 650°C at 5°C / min in an argon atmosphere for low-temperature annealing. After keeping the temperature for 2 hours, the powder was cooled to room temperature in the furnace to obtain a regenerated lithium iron phosphate positive electrode material.

[0104] The results in Table 2 show that since the waste lithium iron phosphate used in Comparative Example 1 contains too many impurity elements, it is impossible to supplement the active lithium therein by the low-temperature liquid phase method. Fig.10 This is the XRD diffraction pattern of the regenerated lithium iron phosphate and the waste lithium iron phosphate in Example 1. As shown in the figure, the impurity peak still exists. The repair of the waste lithium iron phosphate in Example 1 failed. This is mainly because the raw material used in Example 1 has a high content of impurity elements and the low-temperature liquid phase method cannot repair its structure. Fig.11 The first cycle charge and discharge curves of the regenerated lithium iron phosphate of Example 1 and Comparative Example 1 at 0.1C are shown in the figure. As shown in the figure, the first cycle discharge specific capacity of the comparative example is 128.6 mAh / g, and the first cycle coulomb efficiency is 95.7%. Since the active lithium is not replenished and the structure is not repaired, the electrochemical performance of the comparative example 1 is significantly different from that of the exemplary embodiment 1.

[0105] Comparative Example 2

[0106] Corresponding to Example 2, the eluent used is phytic acid iron, the lithium salt is lithium acetate, and the reducing agent is citric acid. The difference is that no organic carbon source is added during the annealing process. The specific steps are as follows:

[0107] (1) Prepare an eluent, take an appropriate amount of phytic acid iron in a beaker, add deionized water until the solution pH is 6.7, then cut the waste lithium iron phosphate positive electrode sheet, place it in a beaker, add the eluent, the solid-liquid ratio is 50g / L, place the beaker in an oil bath, heat to 60°C and keep warm for 5 minutes, the active material and the electrode are completely separated, and a sheet-like active material is obtained;

[0108] (2) drying the sheet active material in a 100° C. forced air drying oven for 10 h, and grinding the sheet active material into powder until it can pass through a 200-mesh sieve to obtain black waste lithium iron phosphate powder;

[0109] (3) 2 g of waste lithium iron phosphate powder was taken, with a solid-liquid ratio of 60 g / L, and dispersed in a solution containing 0.3 mol / L lithium acetate and 0.2 mol / L citric acid to obtain a repair suspension stock solution;

[0110] (4) placing the beaker containing the repair suspension stock solution in an oil bath, stirring at a speed of 500 rpm, heating to 60°C, and keeping warm for 6 hours. After the reaction is completed, the solution is filtered, and the black slurry obtained by filtration is rinsed with deionized water 5 times, placed in a 100°C forced air drying oven and dried for 10 hours to obtain lithium iron phosphate powder;

[0111] (5) The dried lithium-supplemented lithium iron phosphate powder was heated to 600° C. at 8° C. / min in an argon atmosphere for low-temperature annealing, kept at this temperature for 3 h, and then cooled to room temperature in the furnace to obtain a regenerated lithium iron phosphate positive electrode material.

[0112] From the performance test of Example 1 and Example 2, it can be seen that the prepared regenerated lithium iron phosphate has excellent rate performance and cycle stability. In addition, due to the high content of impurity elements in the raw materials in Comparative Example 1, the low-temperature phase method cannot repair its structure. The performance gap between Comparative Example 1 and Example 1 or Example 2 is large. The regenerated lithium iron phosphate prepared by this technical solution has good performance after repair and has more prospects for industrial application.

[0113] The results in Table 2 show that the lithium content of the lithium iron phosphate regenerated in Comparative Example 2 is effectively supplemented. Fig.12 This is the XRD diffraction pattern of regenerated lithium iron phosphate and waste lithium iron phosphate. As shown in the figure, the structure of the waste lithium iron phosphate has been successfully repaired and the impurity phase peak has disappeared. Fig.13 The first cycle charge and discharge curves of the regenerated lithium iron phosphate of Example 2 and Comparative Example 2 at 0.1C, wherein the first cycle discharge specific capacity of the regenerated lithium iron phosphate obtained in Comparative Example 2 is 146.6mAh / g, and the first cycle coulombic efficiency is 93.3%. Since no organic carbon source is added during the annealing process, the carbon layer of the regenerated lithium iron phosphate is not repaired, so the first cycle capacity of the material obtained in Comparative Example 2 is lower than that of the material obtained in Example 2. Fig.14 It is a cycle performance diagram of regenerated lithium iron phosphate obtained from the materials of Example 2 and Comparative Example 2. As shown in the figure, the material obtained in Comparative Example 2 has a first-cycle discharge specific capacity of 129.5 mAh / g at a rate of 5C, and a capacity retention rate of 69.7% after 100 cycles, which is much lower than 96.3% of Example 2. Since no organic carbon source is added to repair the carbon layer, the cycle stability of the regenerated material is poor.

[0114] Table 1

[0115]

[0116]

[0117] Table 1 shows the ICP full spectrum results of the waste lithium iron phosphate separated by the eluent configured in Example 1 of the present invention.

[0118] Table 2

[0119]

[0120] Table 2 shows the ICP results of the Li, Fe, and P element contents of waste lithium iron phosphate, Example 1, Example 2, Comparative Example 1, and Comparative Example 2.

[0121] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0122] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

[0123] The above is a detailed description of an embodiment of a low-temperature, normal-pressure liquid phase method for regenerating waste lithium iron phosphate positive electrode materials and a preparation method provided by the present invention. Specific examples are used herein to illustrate the principles and implementation methods of the present invention, and the description of the above embodiments is only used to help understand the core idea of ​​the present invention. It should be pointed out that for ordinary technicians in this technical field, without departing from the principles of the present invention, the present invention can also be improved and modified, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing waste lithium iron phosphate positive electrode material by low temperature and normal pressure liquid phase method, characterized in that: The steps include: S1. Place the waste lithium iron phosphate positive electrode sheet in an eluent for elution to obtain an active material; S2, the active material is reduced and lithium-supplemented to obtain lithium-supplemented lithium iron phosphate powder; S3, performing carbon layer repair treatment on the lithium-replenished lithium iron phosphate powder; uniformly mixing the lithium-replenished lithium iron phosphate powder with an organic carbon source, annealing the mixture, and then cooling the mixture to room temperature to obtain a regenerated lithium iron phosphate positive electrode material.

2. The preparation method according to claim 1, characterized in that: The S1 further includes the following steps: The waste lithium iron phosphate positive electrode pieces are cut and transferred to an eluent for elution to separate the active material and the electrode pieces to obtain the active material.

3. The preparation method according to claim 2, characterized in that: The heating temperature of the elution is 60° C. to 80° C., and the soaking time of the elution is 2 min to 5 min.

4. The preparation method according to claim 1, characterized in that: After the S1 is eluted, the product obtained by solid-liquid separation is dried and ground to obtain lithium iron phosphate powder, i.e., active material; In S2, the lithium iron phosphate powder is reduced and supplemented with lithium to obtain lithium-supplemented lithium iron phosphate powder.

5. The preparation method according to claim 4, characterized in that: In S2, the obtained lithium iron phosphate powder is dispersed in deionized water containing a lithium salt and a reducing agent to obtain a repair suspension stock solution; The obtained repair suspension stock solution is placed in a stirring state and heated to react, so as to carry out liquid phase repair of waste lithium iron phosphate. The lithium-supplemented lithium iron phosphate powder is obtained.

6. The preparation method according to claim 5, characterized in that: The lithium salt is one or two of lithium sulfate, lithium hydroxide and lithium acetate.

7. The preparation method according to claim 5, characterized in that: The reducing agent is one or more of ascorbic acid, citric acid, tartaric acid and malic acid.

8. The preparation method according to claim 1, characterized in that: The eluent is prepared by diluting one or two of phytic acid, phytic acid iron and ferric acetate in deionized water until the pH value is between 6 and 7.

9. The preparation method according to claim 1, characterized in that: The organic carbon source is one or more of glucose, sucrose and starch.

10. A method for regenerating waste lithium iron phosphate positive electrode material by a low-temperature and normal-pressure liquid phase method prepared by the preparation method according to any one of claims 1 to 9, characterized in that: The raw materials used in the preparation include waste lithium iron phosphate positive electrode materials; the waste lithium iron phosphate positive electrode materials have active lithium loss during the charge and discharge process, the material contains Fe(PO)4 impurities, and the carbon coating layer on the surface of the waste lithium iron phosphate positive electrode material particles is destroyed, and its chemical formula is Li x Fe y PO4, where 0<x<y<1.

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