Regeneration method of waste lithium iron phosphate battery positive electrode material

Abstract

The invention provides a method for regenerating anode materials of waste lithium iron phosphate batteries, comprising the steps of: cutting the cathode plates of waste lithium iron phosphate batteries into pieces, soaking and stirring with alkali solution to obtain lithium iron phosphate cathode materials and aluminum foil; ball milling the cathode materials, acid leaching and adding an oxidant to obtain lithium iron phosphate cathode materials and aluminum foil; + , Fe 3+ After the filtrate A is obtained, an alkali solution is added and stirred until the pH of the filtrate A is 6.5-8, and the residue B and the filtrate B are obtained by filtering; a phosphoric acid solution is added to the residue B, stirred, heated and aged, and the pH is adjusted to 1.5-2. After heat preservation, the obtained iron phosphate precursor is filtered to remove impurities, and the sodium ions in the iron phosphate solid are removed and then dried to obtain battery-grade iron phosphate; a saturated sodium carbonate solution is added to the filtrate B to precipitate lithium carbonate; the iron phosphate and lithium carbonate are stirred, and then a carbon source is added to the mixed ball mill, and then calcined at a high temperature to obtain a regenerated lithium iron phosphate battery raw material. The process flow of the present invention is short, and the low-cost recycling and regeneration of waste lithium iron phosphate battery positive electrode materials is realized.

Description

Technical Field

[0001] The invention belongs to the technical field of waste lithium battery recycling, and specifically relates to a method for recycling positive electrode materials of waste lithium iron phosphate batteries. Background Art

[0002] Lithium iron phosphate batteries are widely used in new energy vehicles and energy storage due to their abundant raw material sources, excellent power performance and low cost, and are considered to be a new generation of lithium-ion batteries. However, the service life of lithium-ion batteries is only 5-8 years, and a large number of retired batteries will pose a potential threat to the environment, especially the heavy metals, electrolytes, solvents and various organic plastics in power batteries. If they are discarded without proper disposal, they will cause great harm to the soil, water, etc. Therefore, the recycling of waste lithium batteries is imperative.

[0003] Waste lithium iron phosphate battery positive electrode materials contain abundant metals such as lithium and iron, among which the element with the best recycling value is lithium, and iron also has a certain recycling value. At present, the recycling methods can be divided into two types: pyrometallurgy and hydrometallurgy. The pyrometallurgy process is short and requires less equipment, but its energy consumption is relatively high, and the recovered products need to be processed separately. The hydrometallurgy process is simple, and the cost of the raw materials used is low, easy to obtain, and the product recovery process is easy to control, but the elements are easy to lose during the process. Chinese invention patent application CN202211156125 discloses a method for green recovery of lithium iron phosphate positive electrode materials, which uses organic acid to leach waste lithium iron phosphate powder, then adds an oxidant to the leachate and then drips alkali solution to adjust the pH value to obtain iron phosphate precipitation, and finally adjusts the pH value of the filtrate to boil and then adds carbonate to obtain lithium carbonate precipitation. The iron phosphate obtained directly from the leaching solution contains some other impurity ions that will enter the regenerated lithium iron phosphate positive electrode material, reducing the purity of the raw materials. It is also difficult to control the phosphorus-iron ratio and particle size of the recovered product, thereby affecting the electrochemical properties of the positive electrode material and resulting in poor performance of the lithium battery.

[0004] Therefore, it is necessary to solve the above problems. Summary of the invention

[0005] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a method for regenerating the positive electrode material of waste lithium iron phosphate batteries.

[0006] The method for regenerating waste lithium iron phosphate battery positive electrode materials provided by the present invention comprises the following steps:

[0007] (1) Cutting the positive electrode sheets obtained after the waste lithium iron phosphate battery is discharged and disassembled into small pieces, and then soaking and stirring them in alkaline solution to separate them, and filtering to obtain the separated lithium iron phosphate positive electrode material and aluminum foil;

[0008] (2) The positive electrode material obtained in step (1) is ball-milled and then placed in an acid solution for leaching. An oxidant is added during leaching and stirred. The residue A and filtrate A are obtained by filtration. The residue A is an insoluble carbon-containing substance, and the filtrate A is a Li-rich + , Fe 3+ Acid solution;

[0009] (3) Add an alkaline solution to the filtrate A and stir continuously until the pH of the filtrate A is 6.5-8. After standing, filter to obtain a filter residue B and a filtrate B. The filter residue B is Fe(OH) 3 and FePO 4 A mixture of, the filtrate B is an acid solution containing Li element;

[0010] (4) After washing the filter residue B, add phosphoric acid solution, stir, heat and age, so as to improve the purity of iron phosphate and adjust its particle size, and then adjust the pH to 1.5-2.0. After heat preservation, precipitate iron phosphate, filter and wash to obtain iron phosphate precursor FePO 4 ·2H 2 O;

[0011] (5) The iron phosphate precursor FePO obtained in step (4) 4 ·2H 2 O is placed in a nitric acid solution to remove impurities, then the solid-liquid mixture after impurities removal is filtered, sodium ions in the iron phosphate solid are removed with deionized water, and then dried to obtain battery-grade iron phosphate;

[0012] (6) adding a saturated sodium carbonate solution to the filtrate B obtained in step (3) to precipitate lithium carbonate;

[0013] (7) The iron phosphate obtained in step (5) and the lithium carbonate obtained in step (6) are mechanically stirred uniformly, a carbon source is added to the mixture, and high-energy ball milling is performed. The ball-milled product is then placed in a high-temperature furnace, an inert gas is introduced, and calcined at a temperature of 300 to 800° C. for 2 to 10 hours to obtain a regenerated lithium iron phosphate battery raw material.

[0014] The present invention separates the disassembled waste lithium iron phosphate battery positive electrode sheets through an alkali method to obtain positive electrode materials and aluminum foil, and the aluminum foil can be directly recycled after being washed. An oxidant is added to the positive electrode material while the positive electrode material is acid leaching and dissolving, and an oxidizing effect is played during the acid leaching process, so that divalent ferrous ions entering the system are quickly oxidized into trivalent ferrous ions. After the positive electrode material is acid dissolved, basic iron phosphate is prepared, which is further heated and aged to obtain an iron phosphate precursor, and high-purity iron phosphate is obtained after purification; the filtrate is evaporated and concentrated, and a saturated sodium carbonate process is added to realize the preparation of lithium carbonate, and finally the iron phosphate and lithium carbonate are carbon thermally reduced to prepare lithium iron phosphate positive electrode materials, which can be further used in the production of lithium iron phosphate batteries, provide a technical basis for resource recovery of waste lithium iron phosphate power batteries, improve the recovery rate of lithium and iron elements in the waste lithium iron phosphate battery positive electrode materials and resource utilization efficiency, and save production costs.

[0015] The iron phosphate and lithium carbonate products obtained by the present invention have a wide range of uses. They can be used as industrial raw materials and can also be used as precursors for synthesizing positive electrode materials for lithium iron phosphate batteries. They have very important practical significance in the field of recycling waste lithium batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a flow chart of the present invention;

[0017] Figure 2 This is the XRD pattern of lithium carbonate recovered in Example 1 of the present invention;

[0018] Figure 3 This is the XRD diagram of lithium iron phosphate recovered in Example 1 of the present invention;

[0019] Figure 4 This is the XRD pattern of lithium carbonate recovered in Example 2 of the present invention;

[0020] Figure 5 This is the XRD diagram of lithium iron phosphate recovered in Example 2 of the present invention;

[0021] Figure 6 This is the XRD pattern of lithium carbonate recovered in Example 3 of the present invention;

[0022] Figure 7 This is the XRD diagram of lithium iron phosphate recovered in Example 3 of the present invention. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0024] The method for regenerating waste lithium iron phosphate battery positive electrode materials provided by the present invention comprises the following steps:

[0025] (1) The positive electrode sheets obtained after the waste lithium iron phosphate battery is discharged and disassembled are cut into small pieces with a diagonal length of 1.5 to 2.5 inches, and separated by immersion and stirring in alkaline solution, and filtered to obtain the separated lithium iron phosphate positive electrode material and aluminum foil.

[0026] The alkaline solution selected in this step is one or a combination of NaOH, KOH, and ammonia water; the concentration of the alkaline solution is 1-4 mol / L, and the stirring time is 10-60 min.

[0027] In this step, the positive electrode sheets obtained after the waste lithium iron phosphate battery is discharged and disassembled are cut into small pieces, and then soaked and stirred in alkaline solution, which can not only separate the aluminum foil on the positive electrode material, but also remove the adhesive on the positive electrode material, reduce impurities in the recycled positive electrode material, and the separated aluminum foil can be directly recycled after cleaning.

[0028] (2) The positive electrode material obtained in step (1) is ball-milled and then placed in an acid solution for leaching. An oxidant is added during leaching and stirred. The residue A and filtrate A are obtained by filtration. The residue A is an insoluble carbon-containing substance that can be removed. The filtrate A is a Li-rich + , Fe 3+ of acid solution.

[0029] In this step, the positive electrode material is first ball-milled to reduce the diameter of the positive electrode material, so that it forms a granular positive electrode powder to accelerate the subsequent acid leaching rate. Preferably, the ball milling medium is at least one of spherical zirconium oxide or natural agate, the ball milling jar is made of at least one of polytetrafluoroethylene or zirconium oxide, the ball milling speed is 200-600 r / min, and the ball milling time is 20-60 min.

[0030] The acid selected in this step is one of sulfuric acid, nitric acid, citric acid or glacial acetic acid. The acid concentration is 1-5 mol / L, and the liquid-to-solid ratio between the acid solution and the separated lithium iron phosphate positive electrode material is 5-100 mL / g. Compared with the organic acid used in the prior art, the acid selected in the present invention has lower cost, is easy to obtain in industry, is conducive to large-scale industrial production, and can avoid the defect of the prior art that hydrochloric acid is used to produce a certain amount of iron hydroxide colloid and affect its electrochemical performance.

[0031] In this step, an oxidant is added and stirred during acid leaching, which can play an oxidizing role during the acid leaching process to accelerate the reaction of the system, enhance the leaching efficiency, and improve the leaching effect. At the same time, Fe (II) can be quickly converted into Fe (III) during the leaching process, so that the filtrate can obtain more Li + , Fe 3+ , and the iron ions in the filtrate A are always Fe 3+ Existence can recycle more lithium and iron elements.

[0032] The oxidant is H2 O 2 、MnO 2 、KMnO 4 The concentration of the oxidant aqueous solution is 1-10 vol%, the liquid-solid ratio of the separated lithium iron phosphate positive electrode material is 25-100 mL / g, the treatment temperature during leaching oxidation is 30-60°C, and the stirring speed is 100-800 rpm.

[0033] (3) Add alkaline solution to filtrate A and stir continuously until the pH of filtrate A is 6.5-8. After standing, filter to obtain residue B and filtrate B, where residue B is Fe(OH) 3 and FePO 4 A mixture of filtrate B and filtrate B, wherein filtrate B is an acid solution containing Li element.

[0034] The alkaline substance added in this step is one or more of hydroxide, ammonia, and carbonate. When the pH value of the filtrate A is 6.5 to 8, the Al in the system 3+ , Cu 2+ The precipitation is more complete, which is convenient for subsequent Li + of recycling.

[0035] (4) After washing the filter residue B, add phosphoric acid solution, stir, heat and age, so as to improve the purity of iron phosphate and adjust its particle size. Then adjust the pH to 1.5-2.0. After heat preservation, precipitate iron phosphate, filter and wash to obtain iron phosphate precursor FePO 4 ·2H 2 O.

[0036] In this step, the filter residue B is dissolved in 1-3 mol / L phosphoric acid at a liquid-solid ratio of 20-50 g / mL, and then the solution is heated to 60-90°C for aging for 0.5-2 hours, and the pH value of the solution is adjusted to 1.5-2.0 with sodium hydroxide, and the solution is kept warm for 2-3 hours to precipitate iron phosphate precipitate, which is filtered and washed to obtain the iron phosphate precursor FePO 4 ·2H 2 O.

[0037] In this step, the filter residue B is dissolved in phosphoric acid and then stirred, aged and heated, and then the pH of the solution is adjusted to 1.5-2.0, so that the obtained precipitate is the iron phosphate precursor FePO 4 ·2H 2 O, which can avoid the precipitation of aluminum phosphate, thereby reducing the purity of iron phosphate. The precipitate is the iron phosphate precursor FePO 4 ·2H 2O, impurities in the precipitate can be removed by subsequent processes, so that the subsequently obtained iron phosphate has a higher purity, thereby improving the quality of the synthetic positive electrode raw materials. At the same time, by controlling the amount of phosphoric acid solution and the aging time and temperature, the phosphorus-iron ratio, particle size, etc. of the iron phosphate product can be effectively controlled, and the morphology and purity of the material can be further regulated. The situation in which more impurities are contained when the iron phosphate is directly recovered from the leaching solution can be avoided, and the problem of difficulty in controlling the phosphorus-iron ratio and particle size in the recovered product is solved, thereby improving the defect of poor electrochemical performance of the positive electrode material prepared from the recovered product.

[0038] (5) The iron phosphate precursor FePO obtained in step (4) 4 ·2H 2 O is placed in a nitric acid solution to remove impurities, and then the solid-liquid mixture after impurities removal is filtered, and the sodium ions in the iron phosphate solid are removed with deionized water, and then dried to obtain battery-grade iron phosphate.

[0039] The concentration of the nitric acid solution used for impurity removal in this step is 5% to 25%. The nitric acid solution and the iron phosphate precursor FePO 4 ·2H 2 O has a liquid-to-solid ratio of 5 to 100 mL / g. During the precipitation process, the iron phosphate precursor FePO 4 ·2H 2 O is immersed in nitric acid solution for 0.5 to 3 hours to remove the iron phosphate precursor FePO 4 ·2H 2 The solid-liquid mixture is filtered, and the sodium ions in the iron phosphate solid can be washed away after rinsing with deionized water, and then dried at 70-90°C for 10-12 hours to obtain battery-grade iron phosphate.

[0040] (6) Add saturated sodium carbonate solution to the filtrate B obtained in step (3) to precipitate lithium carbonate.

[0041] In this step, the filtrate B can be concentrated at 30-100°C, and then a saturated sodium carbonate solution (n(CO 3 2- ): n(Li + )=1.1-1.5:1), so that the lithium in the filtrate B is precipitated out as lithium carbonate solid, the precipitation temperature is 25-100°C, the precipitation stirring speed is 100-1500rpm, the stirring time is 0.5-5h, and then the precipitate is filtered, separated and washed, the washing water temperature is 10-100°C, and the washing time is 0.5-10min, so as to achieve separation of solid and impurities, and obtain high-purity lithium carbonate.

[0042] (7) The iron phosphate obtained in step (5) and the lithium carbonate obtained in step (6) are mechanically stirred uniformly, a carbon source is added to the mixture, and high-energy ball milling is performed, and then the ball-milled product is calcined to obtain a raw material for a regenerated lithium iron phosphate battery.

[0043] The carbon source is at least one or more of oxalic acid, sucrose, acetylene black and glucose, the mass of the added carbon source is 1%wt-30%wt, the ball milling speed is 400-800r / min, the ball milling medium is at least one of spherical zirconia or natural agate, the ball milling jar material is at least one of polytetrafluoroethylene or zirconia, and the ball milling time is 20-100min.

[0044] The ball-milled product is placed in a high-temperature furnace, and an inert gas is introduced, wherein the inert gas is at least one of nitrogen, argon or helium, and then calcined at a temperature of 300 to 800° C. for 2 to 10 hours to obtain the raw material for re-manufacturing lithium iron phosphate batteries.

[0045] The invention separates waste lithium iron phosphate pole pieces by an alkali method to obtain lithium iron phosphate positive electrode material and aluminum foil, then leaches in an acid solution to dissolve the lithium iron phosphate, allowing valuable metals lithium and iron to enter the solution, and at the same time, adds an oxidant to play an oxidizing role during the acid leaching process, so that divalent ferrous ions are quickly oxidized into trivalent ferrous ions, and then purifies the leachate to obtain iron-containing precipitation and purified leachate; the iron-containing precipitation is dissolved in phosphoric acid to adjust the pH, filtered, washed with water, and heated for aging to obtain an iron phosphate precursor, which is purified by nitric acid to obtain high-purity iron phosphate; the filtrate is evaporated and concentrated, and a saturated sodium carbonate process is added to realize the preparation of lithium carbonate, and finally the obtained iron phosphate and lithium carbonate are used to prepare the lithium iron phosphate positive electrode material by a carbon thermal reduction method.

[0046] The present invention realizes the efficient separation of elements in waste lithium iron phosphate battery materials, and adjusts the particle size during aging to obtain battery-grade iron phosphate and lithium carbonate, so that iron and lithium are recovered to the maximum extent, and finally lithium iron phosphate positive electrode materials are obtained, thereby realizing the low-cost recycling and regeneration of waste lithium iron phosphate battery positive electrode materials.

[0047] The invention has a short process flow, low cost, is environmentally friendly, realizes the comprehensive recycling of all components of waste lithium iron phosphate battery positive electrode materials, and has high product added value.

[0048] The method for regenerating the above-mentioned waste lithium iron phosphate battery positive electrode material is further described in detail below in conjunction with specific embodiments. Example 1

[0049] The method for regenerating the positive electrode material of waste lithium iron phosphate batteries in this embodiment 1 comprises the following specific steps:

[0050] (1) The positive electrode sheets obtained after the waste lithium iron phosphate battery is discharged and disassembled are cut into small pieces with a diagonal length of 1.5 inches and stirred in a 1 mol / L NaOH solution for 20 minutes. The separated lithium iron phosphate positive electrode material and aluminum foil are obtained by solid-liquid separation. The aluminum foil is directly recycled after cleaning.

[0051] (2) The positive electrode material obtained in step (1) was placed in a polytetrafluoroethylene tank and ball-milled for 20 min. The ball-milling medium was spherical zirconium oxide beads. The ball-milling speed was 300 r / min. The positive electrode material was placed in a 1 mol / L sulfuric acid solution for leaching. H 2 O 2 (4 vol%), liquid-to-solid ratio of 20 mL / g, temperature of 30 °C, stirring speed of 300 rpm, filtering to obtain residue A and filtrate A, residue A is insoluble carbon-containing matter;

[0052] (3) Add NaOH solution to filtrate A and stir continuously until the pH of filtrate A reaches 7. Stop adding alkali solution and stirring. After standing, filter to obtain residue B and filtrate B. Residue B is Fe(OH) 3 and FePO 4 A mixture of, filtrate B is an acid solution containing Li element;

[0053] (4) After washing the filter residue B, add it into a 1 mol / L phosphoric acid solution at a liquid-to-solid ratio of 20 g / mL, heat it to 60 °C, stir and age it for 2 hours, adjust the pH of the solution to 2.0 with sodium hydroxide, keep it warm for 2 hours, precipitate iron phosphate, and filter to obtain the iron phosphate precursor (FePO 4 ·2H 2 O);

[0054] (5) placing the iron phosphate precursor obtained in step (4) in a 5% nitric acid solution at a rate of 10 mL / g for impurity removal, and soaking for 1 hour to remove calcium, aluminum, and magnesium impurities therein; then filtering the solid-liquid mixture, rinsing and filtering with deionized water to remove sodium ions in the iron phosphate solid, and drying at 80° C. for 12 hours to obtain battery-grade iron phosphate;

[0055] (6) The filtrate B obtained in step (3) was heated to 80°C and concentrated, and then a saturated sodium carbonate solution (n(CO 3 2- ): n(Li + )=1.1:1) stirred and precipitated at a stirring speed of 300 rpm. After stirring for 5 hours, it was washed with 80°C deionized water for 3 minutes to precipitate high-purity lithium carbonate (see Figure 2 );

[0056] (7) The iron phosphate obtained in step (5) and the lithium carbonate obtained in step (6) are mechanically stirred uniformly, 10 wt% oxalic acid is added and the mixture is subjected to high-energy ball milling, the ball milling speed is 600 r / min, the ball milling medium is spherical zirconia, the ball milling jar is made of zirconia, and the ball milling time is 20 min; the ball milled product is then placed in a sintering furnace, nitrogen is introduced, and calcined at 600° C. for 5 h to obtain a new lithium iron phosphate material (see Figure 3 ), used as raw material for remanufacturing lithium iron phosphate batteries. Example 2

[0057] The method for regenerating the positive electrode material of waste lithium iron phosphate batteries in this embodiment 2 includes the following specific steps:

[0058] (1) The positive electrode sheets obtained after the waste lithium iron phosphate battery is discharged and disassembled are cut into small pieces with a diagonal length of 2.0 inches, and then stirred in a 2 mol / L NaOH solution for 40 minutes. The separated lithium iron phosphate positive electrode material and aluminum foil are obtained by solid-liquid separation, and the aluminum foil is directly recycled after washing;

[0059] (2) The positive electrode material obtained in step (1) was placed in a polytetrafluoroethylene tank and ball-milled for 40 min. The ball-milling medium was spherical zirconium oxide beads. The ball-milling speed was 500 r / min. The positive electrode material was placed in a 2 mol / L nitric acid solution for leaching. MnO was added while heating. 2 (6 vol%), liquid-to-solid ratio of 50 mL / g, temperature of 40 °C, stirring speed of 400 rpm, filtering to obtain residue A and filtrate A, residue A is insoluble carbonaceous matter;

[0060] (3) Add ammonia water to the filtrate A and stir continuously until the pH of the filtrate A reaches 7.5. Stop adding ammonia water and stirring. After standing, filter to obtain residue B and filtrate B. The residue B is Fe(OH) 3 and FePO 4 A mixture of, filtrate B is an acid solution containing Li element;

[0061] (4) After washing the filter residue B, add it into a 2 mol / L phosphoric acid solution at a liquid-to-solid ratio of 40 g / mL, heat it to 70 °C, stir and age it for 1 h, adjust the pH to 1.5, keep it warm for 2 h, precipitate the iron phosphate precipitate, and filter to obtain the iron phosphate precursor (FePO 4 ·2H 2 O);

[0062] (5) placing the iron phosphate precursor obtained in step (4) in a 10% nitric acid solution at a rate of 50 mL / g for impurity removal, and soaking for 2 h to remove calcium, aluminum, and magnesium impurities therein; then filtering the solid-liquid mixture, rinsing the filtered mixture with deionized water to remove sodium ions in the iron phosphate solid, and drying at 90° C. for 10 h to obtain battery-grade iron phosphate;

[0063] (6) The filtrate B obtained in step (3) was heated to 90°C and concentrated, and then a saturated sodium carbonate solution (n(CO 3 2- ): n(Li + )=1.2:1) stirred and precipitated at a stirring speed of 500 rpm. After stirring for 4 hours, it was washed with 90°C deionized water for 5 minutes to precipitate high-purity lithium carbonate (see Figure 4 );

[0064] (7) The iron phosphate obtained in step (5) and the lithium carbonate obtained in step (6) are mechanically stirred uniformly, 20 wt% glucose is added to the mixture and high-energy ball milling is performed. The ball milling speed is 600 r / min, the ball milling medium is spherical zirconium oxide, the ball milling jar is made of zirconium oxide, and the ball milling time is 40 min. The ball milled product is then placed in a sintering furnace, argon gas is introduced, and calcined at 700° C. for 8 h to obtain a new lithium iron phosphate material (see Figure 5 ), used as raw material for remanufacturing lithium iron phosphate batteries. Example 3

[0065] The method for regenerating the positive electrode material of waste lithium iron phosphate batteries in this embodiment 3 includes the following specific steps:

[0066] (1) The positive electrode sheets obtained after the waste lithium iron phosphate battery is discharged and disassembled are cut into small pieces with a diagonal length of 2.5 inches, and then stirred in a 1.5 mol / L KOH solution for 60 minutes. The separated lithium iron phosphate positive electrode material and aluminum foil are obtained by solid-liquid separation, and the aluminum foil is directly recycled after washing;

[0067] (2) The positive electrode material obtained after step (1) was placed in a polytetrafluoroethylene tank and ball-milled for 60 min. The ball-milling medium was spherical zirconium oxide beads. The ball-milling speed was 600 r / min. The positive electrode material was placed in a 3 mol / L sulfuric acid solution for leaching. KMnO was added while heating. 4 (8 vol%), liquid-to-solid ratio of 100 mL / g, temperature of 60 °C, stirring speed of 300 rpm, filtering to obtain residue A and filtrate A, residue A is insoluble carbonaceous matter;

[0068] (3) Add ammonia water to the filtrate A and stir continuously until the pH of the filtrate A reaches 8. Stop adding ammonia water and stirring. After standing, filter to obtain residue B and filtrate B. The residue B is Fe(OH) 3 and FePO 4 A mixture of, filtrate B is an acid solution containing Li element;

[0069] (4) After washing the filter residue B, add it into a 3 mol / L phosphoric acid solution at a liquid-to-solid ratio of 50 g / mL, heat it to 90 °C, stir and age it for 0.5 h, adjust the pH to 2.0, keep it warm for 3 h, precipitate the iron phosphate precipitate, and filter to obtain the iron phosphate precursor (FePO 4 ·2H 2 O);

[0070] (5) placing the iron phosphate precursor obtained in step (4) in a 25% nitric acid solution at a rate of 100 mL / g for impurity removal, and soaking for 3 hours to remove calcium, aluminum, and magnesium impurities therein; then filtering the solid-liquid mixture, rinsing the filtered solid with deionized water to remove sodium ions in the iron phosphate solid, and drying at 80° C. for 12 hours to obtain battery-grade iron phosphate;

[0071] (6) The filtrate B obtained after step (3) was heated to 100°C and concentrated, and then a saturated sodium carbonate solution (n(CO 3 2- ): n(Li + )=1.4:1) stirring precipitation, stirring speed is 1000rpm, stirring for 3h, washing with 100℃ deionized water for 7min, precipitating high purity lithium carbonate (see Figure 6 );

[0072] (7) The iron phosphate obtained in step (5) and the lithium carbonate obtained in step (6) are mechanically stirred uniformly, 30 wt% sucrose is added and mixed for high-energy ball milling, the ball milling speed is 800 r / min, the ball milling medium is spherical zirconia, the ball milling jar is made of zirconia, and the ball milling time is 30 min; then the ball milled product is placed in a sintering furnace, nitrogen is introduced and calcined at 800 ° C for 10 h to obtain a new lithium iron phosphate material (see Figure 7 ), used as raw material for remanufacturing lithium iron phosphate batteries.

[0073] The element precipitation rates recovered in the above examples are shown in Table 1.

[0074] Table 1

[0075] Element precipitation rate% Example 1 Example 2 Example 3 iron 99.56 99.78 99.15 lithium 97.31 98.19 98.48

[0076] It can be seen from Table 1 that the iron recovery rate of the method of the present invention is above 99%, and the lithium recovery rate is above 97%.

[0077] The above-mentioned embodiments of the present invention are only part of the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made by those skilled in the art without departing from the essence of the present invention are within the protection scope of the present invention.

Claims

1. A method for regenerating waste lithium iron phosphate battery positive electrode materials, characterized in that: The steps include: (1) Cutting the positive electrode sheets obtained after the waste lithium iron phosphate battery is discharged and disassembled into small pieces, and then soaking and stirring them in alkaline solution to separate them, and filtering to obtain the separated lithium iron phosphate positive electrode material and aluminum foil; (2) The positive electrode material obtained in step (1) is ball-milled and then placed in an acid solution for leaching. An oxidant is added during leaching and stirred. The residue A and filtrate A are obtained by filtration. The residue A is an insoluble carbon-containing substance, and the filtrate A is a Li-rich + , Fe 3+ Acid solution; (3) adding an alkaline solution to the filtrate A and stirring continuously until the pH value of the filtrate A is 6.5 to 8, and filtering after standing to obtain a filter residue B and a filtrate B, wherein the filter residue B is a mixture of Fe(OH)3 and FePO4, and the filtrate B is an acid solution containing the Li element; (4) washing the filter residue B, adding phosphoric acid solution, stirring, heating and aging to improve the purity of the iron phosphate and adjust its particle size, then adjusting the pH to 1.5-2.0, keeping warm, precipitating the iron phosphate precipitate, filtering and washing to obtain the iron phosphate precursor FePO4·2H2O; (5) placing the iron phosphate precursor FePO4·2H2O obtained in step (4) in a nitric acid solution to remove impurities, filtering the solid-liquid mixture after impurities removal, removing sodium ions in the iron phosphate solid with deionized water, and drying to obtain battery-grade iron phosphate; (6) adding a saturated sodium carbonate solution to the filtrate B obtained in step (3) to precipitate lithium carbonate; (7) The iron phosphate obtained in step (5) and the lithium carbonate obtained in step (6) are mechanically stirred uniformly, a carbon source is added to the mixture, and high-energy ball milling is performed. The ball-milled product is then placed in a high-temperature furnace, an inert gas is introduced, and calcined at a temperature of 300 to 800° C. for 2 to 10 hours to obtain a regenerated lithium iron phosphate battery raw material.

2. The method for regenerating the positive electrode material of waste lithium iron phosphate batteries according to claim 1, characterized in that: The alkali solution in step (1) is one or a combination of NaOH, KOH, and ammonia water; the concentration of the alkali solution is 1 to 4 mol / L, and the stirring time is 10 to 60 min.

3. The method for regenerating the cathode material of waste lithium iron phosphate batteries according to claim 1, characterized in that: In the step (2), the ball milling speed is 200-600 r / min, the ball milling medium is at least one of spherical zirconia or natural agate, the ball milling jar material is at least one of polytetrafluoroethylene or zirconia, and the ball milling time is 20-60 min.

4. The method for regenerating the positive electrode material of waste lithium iron phosphate batteries according to claim 1, characterized in that: The acid in step (2) is one of sulfuric acid, nitric acid, citric acid or glacial acetic acid, the acid concentration is 1-5 mol / L, the liquid-solid ratio is 5-100 mL / g, the leaching temperature is 30° C.-60° C., and the stirring speed is 100-800 rpm.

5. The method for regenerating the positive electrode material of waste lithium iron phosphate batteries according to claim 1, characterized in that: The oxidant in step (2) is an aqueous solution of one or a combination of H2O2, MnO2, KMnO4, with a concentration of 1-10 vol%.

6. The method for regenerating the cathode material of waste lithium iron phosphate batteries according to claim 1, characterized in that: The alkaline substance added in step (3) is one or more of hydroxide, ammonia water and carbonate.

7. The method for regenerating the positive electrode material of waste lithium iron phosphate batteries according to claim 1, characterized in that: In the step (4), the filter residue B is dissolved in 1-3 mol / L phosphoric acid at a liquid-to-solid ratio of 20-50 g / mL, and then the solution is heated to 60-90° C. and aged for 0.5-2 hours, the pH value is adjusted to 1.5-2.0, and the solution is kept warm for 2-3 hours.

8. The method for regenerating the cathode material of waste lithium iron phosphate batteries according to claim 1, characterized in that: The concentration of the nitric acid solution for impurity removal in step (5) is 5% to 25%, the liquid-to-solid ratio is 5 to 100 mL / g, and the time for the iron phosphate precursor FePO4·2H2O to be immersed in the nitric acid solution during the precipitation process is 0.5 to 3 h.

9. The method for regenerating the cathode material of waste lithium iron phosphate batteries according to claim 1, characterized in that: In the step (6), the filtrate B is first concentrated, and then a saturated sodium carbonate solution is added to precipitate lithium carbonate, and the high-purity lithium carbonate obtained is separated and washed, wherein the concentration temperature is 30-100°C, the precipitation temperature is 25-100°C, the precipitation stirring speed is 100-1500rpm, the precipitation stirring time is 0.5-5h, the washing water temperature is 10-100°C, and the washing time is 0.5-10min.

10. The method for regenerating the cathode material of waste lithium iron phosphate batteries according to claim 1, characterized in that: The carbon source in step (7) is at least one or more of oxalic acid, sucrose, acetylene black and glucose, and the mass of the added carbon source is 1%wt to 30%wt.

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