Method for synthesizing lithium iron phosphate by using battery factory corner tab waste

Abstract

This invention relates to the field of resource recycling technology, specifically to a method for synthesizing lithium iron phosphate from scrap electrode sheets from battery factories. The method includes the following steps: crushing and pulverizing the scrap lithium battery electrode sheets to prepare electrode powder; mixing the electrode powder, reducing agent, complexing agent, and a first alkaline solution to form a slurry, followed by washing, a first filtration, and collecting the filtrate to prepare a first solution; mixing the first solution, sulfuric acid, and hydrogen peroxide, controlling the pH to 1.5–2, followed by a second filtration to prepare a second solution and a first solid. The method of this invention enables the complete recovery of phosphorus, iron, and lithium components, and features a short process, high production efficiency, and environmental friendliness.

Description

Technical Field

[0001] This invention relates to the field of resource recycling technology, and in particular to a method for synthesizing lithium iron phosphate from waste electrode sheets from battery factories. Background Technology

[0002] Lithium-ion batteries, as a highly efficient and clean energy storage medium, possess characteristics such as high operating voltage, small size, light weight, long service life, wide operating temperature range, and low self-discharge rate, and are currently widely used in various fields. In recent years, with continuous innovation in lithium battery technology, the deepening of the global energy revolution, and the popularization of portable products such as mobile phones, laptops, and digital products, global lithium battery production has experienced explosive growth, especially in electric vehicles using lithium iron phosphate (LFP) batteries and in energy storage using LFP batteries. Consequently, the amount of scrapped batteries has increased exponentially. The average lifespan of a lithium-ion battery is 3-5 years. After thousands of charge-discharge cycles, the internal structure of a lithium battery undergoes irreversible changes, eventually leading to deactivation and disposal. Because waste batteries contain heavy metals, organic solvents, electrolytes, and other substances, improper disposal without effective treatment can cause serious and lasting pollution to the surrounding environment, such as soil and groundwater, posing significant potential hazards to the ecosystem and human health. The recycling and resource utilization of used batteries is not only necessary for environmental protection and expanding the international battery market, but also can alleviate the shortage of lithium metal resources in my country and comprehensively optimize the application of my country's phosphorus resources. How to reduce the environmental pollution and resource waste that may be caused by the massive amount of retired batteries, and achieve the recycling and reuse of used lithium batteries, has become a major challenge for the sustainable development of the new energy industry and a hot issue affecting the world's energy strategic landscape.

[0003] Traditional lithium-ion battery recycling technologies involve crushing, sorting, leaching, impurity removal, and lithium extraction. While this yields battery-grade lithium carbonate, the process only extracts lithium, resulting in a significant waste of phosphorus and iron resources. In particular, some manufacturers fail to treat iron phosphate slag environmentally, causing severe environmental damage upon disposal. Furthermore, the drying and pulverizing processes for battery-grade lithium carbonate require substantial amounts of electricity and heat, leading to significant waste.

[0004] Traditional technologies also involve recycling phosphorus, iron, and lithium from lithium iron phosphate batteries, but the process is lengthy and requires the addition of appropriate iron, lithium, or phosphorus sources to synthesize lithium iron phosphate, which increases transportation costs and reduces production efficiency.

[0005] In addition, traditional lithium iron phosphate battery recycling processes involve adding ammonia and sodium hydroxide solution to precipitate iron as ferric hydroxide, which is then used to synthesize ferric phosphate. This process generates a large amount of waste and saline wastewater, causing adverse environmental impacts. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a method for synthesizing lithium iron phosphate using waste electrode sheets from battery factories. This method enables the complete recovery of phosphorus, iron, and lithium components, and features a short process, high production efficiency, and environmental friendliness.

[0007] A method for synthesizing lithium iron phosphate using waste electrode sheets from battery factories includes the following steps:

[0008] The waste electrode material from the edge of lithium battery is crushed, pulverized, and prepared into electrode powder.

[0009] The electrode powder, reducing agent, complexing agent and first alkaline solution are mixed, slurry is prepared, then washed, filtered for the first time, and the filtrate is collected to prepare the first solution;

[0010] The first solution, sulfuric acid, and hydrogen peroxide are mixed, and the pH is controlled at 1.5-2. Then, the mixture is filtered a second time to prepare the second solution and the first solid.

[0011] The first solid was washed, pulped, and subjected to a crystal reforming reaction. After the reaction was completed, it was aged, filtered for the third time, and the filter cake was collected to prepare the second solid. The second solid was dried and calcined for the first time to prepare the third solid.

[0012] The second solution is mixed with the second alkaline solution to prepare the third solution; the third solution is passed through a filter column packed with calcium and magnesium characteristic adsorption resin to prepare the fourth solution; the fourth solution is concentrated to prepare the fifth solution; the fifth solution, lithium carbonate seed crystals and sodium carbonate are mixed to carry out a lithium carbonate synthesis reaction; after the reaction is completed, the mixture is washed, filtered, and the filter cake is taken to prepare the fourth solid.

[0013] The third solid, the fourth solid, sugars, and water are mixed, slurryed, dried, and then calcined a second time in a protective atmosphere.

[0014] In one embodiment, after washing the first solid, the conductivity of the washing water is 50 μS / M to 200 μS / M.

[0015] In one embodiment, the conditions for the crystal reforming reaction include: a temperature of 85°C to 95°C and a rotation speed of 80 r / min to 120 r / min.

[0016] In one embodiment, the conditions for mixing the second solution with the second alkaline solution include: a temperature of 60°C to 80°C and a pH of 8 to 11.

[0017] In one embodiment, the conditions for the lithium carbonate synthesis reaction include: a temperature of 85°C to 95°C and a rotation speed of 80 r / min to 120 r / min.

[0018] In one embodiment, the molar ratio of sodium carbonate to the fifth solution is (1.1 to 1.2):1.

[0019] In one embodiment, the first alkaline solution and the second alkaline solution are each independently selected from one or more of an aqueous sodium hydroxide solution and an aqueous potassium hydroxide solution.

[0020] In one embodiment, the conditions for the first calcination include: a temperature of 500°C to 600°C and a time of 4 to 6 hours; and / or

[0021] The conditions for the second calcination include: 700℃~850℃, and a time of 18h~24h.

[0022] In one embodiment, the sugar is selected from one or more of glucose, sucrose, and reduced starch.

[0023] In one embodiment, the mass ratio of the third solid, water, sugars, and the dry base of the fourth solid is 1:2:(0.15-0.2):(0.25-0.35).

[0024] The beneficial effects of this invention are reflected in its ability to achieve full-component recovery of phosphorus, iron, and lithium, avoiding the waste of phosphorus and iron resources and improving recovery efficiency and economic value. Simultaneously, the required process flow is shorter, eliminating the need to integrate anhydrous iron phosphate resources from other manufacturers, avoiding transportation, and significantly improving production efficiency. Furthermore, the preparation of the third solid does not generate large amounts of waste or saline wastewater as in traditional iron phosphate production processes, avoiding environmental impact from the production process. Further, the fifth solution obtained after the second alkaline solution, calcium-magnesium characteristic adsorption resin-filled filter column, and concentration treatment has high lithium purity. The lithium carbonate synthesized using the fifth solution as a reactant can reach battery-grade lithium carbonate levels, enabling direct on-site recycling and avoiding the significant waste of electricity and heat caused by drying and pulverizing. Attached Figure Description

[0025] Figure 1 The flowchart provided by this invention describes the synthesis of lithium iron phosphate from waste electrode sheets from battery factories. Detailed Implementation

[0026] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0027] This invention provides a method for synthesizing lithium iron phosphate using waste electrode material from battery factories, comprising the following steps:

[0028] The waste electrode material from the edge of lithium battery is crushed, pulverized, and prepared into electrode powder.

[0029] The electrode powder, reducing agent, complexing agent and first alkaline solution are mixed, slurry is prepared, then washed, filtered for the first time, and the filtrate is collected to prepare the first solution;

[0030] The first solution, sulfuric acid, and hydrogen peroxide are mixed, and the pH is controlled at 1.5-2. Then, the mixture is filtered a second time to prepare the second solution and the first solid.

[0031] The first solid was washed, pulped, and subjected to a crystal reforming reaction. After the reaction was completed, it was aged, filtered for the third time, and the filter cake was collected to prepare the second solid. The second solid was dried and calcined for the first time to prepare the third solid.

[0032] The second solution is mixed with the second alkaline solution to prepare the third solution; the third solution is passed through a filter column packed with calcium and magnesium characteristic adsorption resin to prepare the fourth solution; the fourth solution is concentrated to prepare the fifth solution; the fifth solution, lithium carbonate seed crystals and sodium carbonate are mixed to carry out the lithium carbonate synthesis reaction; after the reaction is completed, the mixture is washed, filtered, and the filter cake is taken to prepare the fourth solid.

[0033] The third solid, the fourth solid, sugars, and water are mixed, slurryed, dried, and then calcined a second time in a protective atmosphere.

[0034] The method for synthesizing lithium iron phosphate using waste electrode material from battery factories, as claimed in this invention, has a shorter process flow. At the same time, the materials required for lithium iron phosphate synthesis are complete, eliminating the need to integrate anhydrous iron phosphate resources from other manufacturers, avoiding transportation, and greatly improving production efficiency.

[0035] Understandably, in this invention, the lithium battery is a lithium iron phosphate lithium-ion battery.

[0036] In a specific example, the first solid comprises a mixture of ferric phosphate and carbon black.

[0037] In one specific example, the second solid comprises a mixture of ferric phosphate and carbon black with a moisture content of 30% to 40%.

[0038] In a specific example, the third solid comprises a mixture of anhydrous ferric phosphate and carbon black.

[0039] In a specific example, the fourth solid includes lithium carbonate.

[0040] In a specific example, the first solution contains lithium iron phosphate.

[0041] In one specific example, the second solution contains lithium.

[0042] In a specific example, the third solution contains lithium stock. More specifically, the lithium content in the third solution is 7-12 g / L.

[0043] In a specific example, the fourth solution contains Ca 2+ ≤10PPM, Mg 2+ Lithium stock solution ≤10 PPM. More specifically, the lithium content in the fourth solution is 7-12 g / L.

[0044] In a specific example, the fifth solution contains lithium stock. More specifically, the lithium content in the fifth solution is 20-25 g / L.

[0045] In a specific example, the reducing agent is selected from one or more of ascorbic acid, sodium thiosulfate, sodium metabisulfite, and sodium sulfide.

[0046] In a specific example, the complexing agent is selected from one or more of EDTA, sodium potassium tartrate, hexamethylenetetramine, and triethanolamine.

[0047] In a specific example, the preparation of electrode powder pulp includes the following steps:

[0048] Add the electrode powder to a solution containing 0.1%–5% reducing agent, 0.1%–10% complexing agent, and 1%–10% sodium hydroxide by mass percentage, and slurry at a solid-liquid ratio of 1:(5–15). Control the temperature at 25℃–60℃ and react for 30–90 minutes until the aluminum content in the slurry is found to be 10 PPM–100 PPM, which is considered acceptable.

[0049] In a specific example, the amounts of sulfuric acid and hydrogen peroxide added satisfy one or more of the following conditions:

[0050] (1) Based on the lithium content in the first solution, calculate the theoretical amount of sulfuric acid according to the molar ratio of lithium:sulfuric acid = 2:1. The amount used is 1.1 to 1.5 times the calculated amount.

[0051] (2) Based on the iron content in the first solution, calculate the theoretical amount of hydrogen peroxide according to the molar ratio of iron:hydrogen peroxide = 2:1. The amount used is 1.2-1.5 times the calculated amount.

[0052] In a specific example, sulfuric acid and hydrogen peroxide are added in three alternating, uniform portions.

[0053] Understandably, in this invention, the pH value of the first solution, sulfuric acid and hydrogen peroxide after mixing includes, but is not limited to, 1.5, 1.6, 1.7, 1.8, 1.9 and 2.

[0054] In a specific example, the process may include dehydrating or pressing the first solid before washing it.

[0055] In a specific example, after washing the first solid, the conductivity of the wash water is 50 μS / M to 200 μS / M.

[0056] In a specific example, washing is performed multiple times. Understandably, in this invention, after washing the first solid, the conductivity of the washing water is the final conductivity after multiple washes, including but not limited to 50 μS / M, 60 μS / M, 70 μS / M, 80 μS / M, 90 μS / M, 100 μS / M, 110 μS / M, 120 μS / M, 130 μS / M, 140 μS / M, 150 μS / M, 160 μS / M, 170 μS / M, 180 μS / M, 190 μS / M, and 200 μS / M.

[0057] In a specific example, the conditions for the crystal reforming reaction include: a temperature of 85℃~95℃ and a rotation speed of 80r / min~120r / min.

[0058] In a specific example, the crystal reforming reaction takes 2 to 3 hours.

[0059] Understandably, in this invention, the temperature of the crystal reforming reaction includes, but is not limited to, 85°C, 86°C, 87°C, 88°C, 89°C, 90°C, 91°C, 92°C, 93°C, 94°C, and 95°C.

[0060] The rotation speeds for the crystal reforming reaction include, but are not limited to, 80 r / min, 82 r / min, 84 r / min, 86 r / min, 88 r / min, 90 r / min, 92 r / min, 94 r / min, 96 r / min, 98 r / min, 100 r / min, 102 r / min, 104 r / min, 106 r / min, 108 r / min, 110 r / min, 112 r / min, 114 r / min, 116 r / min, 118 r / min, and 120 r / min;

[0061] The time for the crystal reforming reaction includes, but is not limited to, 2h, 2.1h, 2.2h, 2.3h, 2.4h, 2.5h, 2.6h, 2.7h, 2.8h, 2.9h, and 3h.

[0062] In this invention, the process of obtaining the third solid does not generate a large amount of waste or saline wastewater as in the traditional iron phosphate production process, thus avoiding the environmental impact of the production process.

[0063] In a specific example, the conditions for mixing the second solution with the second alkaline solution include: a temperature of 60°C to 80°C and a pH of 8 to 11.

[0064] Understandably, in this invention, the mixing temperature of the second solution and the second alkaline solution includes, but is not limited to, 60°C, 62°C, 64°C, 66°C, 68°C, 70°C, 72°C, 74°C, 76°C, 78°C, and 80°C.

[0065] The pH value of the mixture of the second solution and the second alkaline solution includes, but is not limited to, 8, 9, 10, and 11.

[0066] In this invention, the lithium liquid obtained by the fifth solution has high purity. The lithium carbonate synthesized by using the fifth solution as a reactant can reach the range of battery-grade lithium carbonate, which can be directly recycled and used on site, avoiding the waste of a large amount of electricity and heat caused by drying and crushing.

[0067] In a specific example, the conditions for the lithium carbonate synthesis reaction include: a temperature of 85℃ to 95℃ and a rotation speed of 80 r / min to 120 r / min.

[0068] Understandably, in this invention, the temperature of the lithium carbonate synthesis reaction includes, but is not limited to, 85°C, 86°C, 87°C, 88°C, 89°C, 90°C, 91°C, 92°C, 93°C, 94°C, and 95°C.

[0069] The rotation speeds for the lithium carbonate synthesis reaction include, but are not limited to, 80 r / min, 82 r / min, 84 r / min, 86 r / min, 88 r / min, 90 r / min, 92 r / min, 94 r / min, 96 r / min, 98 r / min, 100 r / min, 102 r / min, 104 r / min, 106 r / min, 108 r / min, 110 r / min, 112 r / min, 114 r / min, 116 r / min, 118 r / min, and 120 r / min.

[0070] In a specific example, mixing the fifth solution, lithium carbonate seed crystals, and sodium carbonate includes the following steps:

[0071] First, mix sodium carbonate with lithium carbonate seed crystals, then add the fifth solution to the mixture, controlling the addition time of the fifth solution to be 2h to 3h.

[0072] In a specific example, sodium carbonate is present in the form of an aqueous solution. More specifically, the concentration of the aqueous solution is 200 g / L to 300 g / L.

[0073] In a specific example, the molar ratio of sodium carbonate to the fifth solution is (1.1–1.2):1.

[0074] In a specific example, after the lithium carbonate synthesis reaction is completed, the mixture is kept at a constant temperature for 1 to 2 hours, filtered for the first time, and the filter cake is collected. After washing for the second time, the mixture is filtered again, and the filter cake is collected to prepare the fourth solid.

[0075] Understandably, in this invention, the second wash uses pure water to wash away sulfate, sodium, and potassium ions up to the range of battery-grade lithium carbonate.

[0076] In a specific example, the first alkaline solution and the second alkaline solution are each independently selected from one or more of an aqueous solution of sodium hydroxide and an aqueous solution of potassium hydroxide.

[0077] In a specific example, the conditions for the first calcination include: a temperature of 500℃~600℃ and a time of 4h~6h.

[0078] Understandably, in this invention, the temperature of the first calcination includes, but is not limited to, 500°C, 510°C, 520°C, 530°C, 540°C, 550°C, 560°C, 570°C, 580°C, 590°C, and 600°C.

[0079] The time for the first calcination includes, but is not limited to, 4 hours, 4.5 hours, 5 hours, 5.5 hours, and 6 hours.

[0080] In a specific example, the conditions for the second calcination include: 700℃~850℃, for 18h~24h.

[0081] Understandably, in this invention, the temperature of the second calcination includes, but is not limited to, 700°C, 720°C, 740°C, 760°C, 780°C, 800°C, 820°C, 840°C, and 850°C.

[0082] The second calcination time includes, but is not limited to, 18h, 19h, 20h, 21h, 22h, 23h, and 24h.

[0083] In a specific example, the sugar is selected from one or more of glucose, sucrose, and reduced starch.

[0084] In a specific example, the mass ratio of the dry basis of the third solid, water, sugars and the fourth solid is 1:2:(0.15-0.2):(0.25-0.35).

[0085] In a specific example, the protective atmosphere is nitrogen.

[0086] In a specific example, the second calcination process also includes the following steps: grinding, inspection, and packaging.

[0087] The following detailed description, in conjunction with specific embodiments, illustrates the method for synthesizing lithium iron phosphate from waste electrode sheets from battery factories according to the present invention. Unless otherwise specified, all raw materials used in the following embodiments are commercially available products.

[0088] Example 1

[0089] This embodiment provides a method for synthesizing lithium iron phosphate using waste electrode sheets from battery factories, combined with... Figure 1 The details are as follows:

[0090] S1. Powdering of waste electrode sheets from battery factories

[0091] The waste electrode sheets from the battery factory are pulverized using electrode crushing and pulverizing equipment to obtain lithium iron phosphate powder and aluminum particles; the lithium iron phosphate powder is then processed into the next step, while the aluminum particles are sold.

[0092] S2, Lithium iron phosphate powder for aluminum removal

[0093] The battery powder obtained from the above pretreatment is added to a solution containing 0.1-5% ascorbic acid (or sodium thiosulfate, sodium metabisulfite, sodium sulfide, etc.) as a reducing agent, 0.1-10% EDTA (or potassium sodium tartrate, hexamethylenetetramine, triethanolamine, etc.) as a complexing agent, and 1-10% sodium hydroxide. The mixture is slurried at a solid-liquid ratio of 1:5-15, utilizing the principle that aluminum dissolves in alkaline solution. The temperature is controlled at 25-60℃, and the reaction is carried out for 30-90 minutes until the aluminum content is detected to be 10-100 PPM, which is considered qualified. Then, the mixture is washed, filtered, and set aside for later use.

[0094] S3, Lithium iron phosphate oxidation leaching process

[0095] Waste from the cathode material plant is slurried and transported via pipeline to the lithium iron phosphate leaching process. Based on the lithium content in the waste lithium iron phosphate powder, the theoretical amount of sulfuric acid is calculated according to a lithium:sulfuric acid molar ratio of 2:1, and the amount used is 1.1-1.5 times the calculated amount. Based on the iron content in the lithium iron phosphate, the theoretical amount of hydrogen peroxide is calculated according to an iron:hydrogen peroxide molar ratio of 2:1, and the amount used is 1.2-1.5 times the calculated amount. Sulfuric acid and hydrogen peroxide are added evenly and alternately in three stages, ultimately controlling the pH value at 1.5-2.0. The solid and liquid are separated by pressure filtration to obtain a mixture of iron phosphate and carbon black, as well as a lithium-containing solution.

[0096] S4, Washing Process

[0097] The synthesized iron phosphate and carbon black mixture is dehydrated or filtered using a centrifuge or filter press, followed by multiple washings to control the final conductivity of the wash water to 50-200 μS / M, and to keep the sulfate, sodium, and potassium ion concentrations within the range required for battery-grade lithium iron phosphate. The synthesis filtrate then enters the lithium carbonate synthesis process.

[0098] S5, Iron Phosphate Synthesis Process

[0099] The washed ferric phosphate and carbon black mixture is slurried and transferred to a crystallization kettle. It is stirred evenly at a speed of 80-120 rpm and heated to 85-95℃ to continue the ferric phosphate crystal reforming. After reacting for 2-3 hours, it is transferred to an aging kettle for aging for 1-2 hours and then filtered.

[0100] S6, Filter press

[0101] The filter cake of the mixture of ferric phosphate and carbon black was filtered using a filter press to obtain a filter cake of the mixture of ferric phosphate and carbon black with a moisture content of 30-40%.

[0102] S7. Drying and dehydration

[0103] The qualified filter cake of the ferric phosphate and carbon black mixture is dried using a flash drying device to obtain a mixture of ferric phosphate dihydrate and carbon black. Then, the mixture of ferric phosphate dihydrate and carbon black is converted into anhydrous ferric phosphate and carbon black mixture using a rotary kiln at 500-600℃ for 4-6 hours for later use.

[0104] S8, Lithium Liquid Impurity Removal

[0105] The lithium liquid obtained from the synthesis of iron phosphate is subjected to a temperature of 60-80℃, and liquid alkali is added to control the pH value to 8-11. After the reaction is complete, iron phosphate filter cake and pure lithium stock solution are obtained. At this time, the lithium content of the lithium liquid solution is 7-12 g / L.

[0106] S9, lithium liquid deep calcium and magnesium removal

[0107] A filter column is packed with a calcium-magnesium characteristic adsorption resin (either Dusheng's CH-93 or Yunfeng's BSR(M) resin). The lithium solution undergoes deep removal of calcium and magnesium through the resin column, ultimately yielding Ca. 2+ ≤10PPM, Mg 2+ Solutions with a concentration of ≤10 PPM; solutions that pass inspection will proceed to the next step.

[0108] S10, Lithium Liquid Concentration

[0109] Use a triple-effect filter or MVR to concentrate the lithium stock solution from 7-12 g / L to 20-25 g / L, then filter it for later use.

[0110] S11, Lithium Carbonate Synthesis

[0111] The prepared sodium carbonate solution (200-300 g / L) and the finely filtered lithium solution were successively pumped into the titanium reactor at a molar ratio of 1.1-1.2:1. First, 0.5-1% of lithium carbonate seed crystals were added to the sodium carbonate solution, and then the lithium solution was added over a controlled period of 2-3 hours. The synthesis speed was 80-120 rpm, and the synthesis temperature was 85-95℃. After the synthesis was completed, the mixture was kept at the temperature for 1-2 hours and then filtered under pressure.

[0112] S12, Washing

[0113] The synthesized lithium carbonate is washed with pure water using a filter press or centrifuge to remove sulfate, sodium, and potassium ions to the range of battery-grade lithium carbonate. The filter cake is then tested for moisture content and set aside for later use.

[0114] S13, Pulping

[0115] The ingredients are prepared by mixing iron phosphate and carbon black powder, glucose (or sucrose, reduced starch, etc.), dry lithium carbonate, and water in a ratio of 1:(0.15-0.2):(0.25-0.35):2, and then pulping is carried out.

[0116] S14, Spray drying

[0117] The qualified slurry was spray-dried using a spray drying device to obtain a mixture of iron phosphate and carbon black powder, lithium carbonate and glucose.

[0118] S15, Carbon coating (protective calcination)

[0119] The dry mixture of ferric phosphate and carbon black powder and glucose powder is fed into the calcining kiln through a vacuum feeder. Under a nitrogen-protected atmosphere, it is calcined at 700-850℃ for 18-24 hours.

[0120] S16, Grinding, Packaging

[0121] The calcined lithium iron phosphate is ground and packaged after passing inspection.

[0122] In the description of embodiments of the present invention, the terms "first," "second," "third," and "fourth" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first," "second," "third," or "fourth" may explicitly or implicitly include one or more of that feature. In the description of the present invention, unless otherwise stated, "a plurality of" means two or more.

[0123] In the description of the embodiments of the present invention, it should be understood that "-" and "~" represent a range of two numerical values, and this range includes the endpoints. For example, "AB" represents a range greater than or equal to A and less than or equal to B. "A~B" represents a range greater than or equal to A and less than or equal to B.

[0124] In the description of embodiments of the present invention, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0125] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for synthesizing lithium iron phosphate using waste electrode sheets from battery factories, characterized in that, Includes the following steps: The waste electrode material from the edge of lithium battery is crushed, pulverized, and prepared into electrode powder. The electrode powder, reducing agent, complexing agent and first alkaline solution are mixed, slurry is prepared, then washed, filtered for the first time, and the filtrate is collected to prepare the first solution; wherein, the reducing agent is selected from one or more of ascorbic acid, sodium thiosulfate, sodium metabisulfite and sodium sulfide, and the complexing agent is selected from one or more of EDTA, potassium sodium tartrate, hexamethylenetetramine and triethanolamine. The first solution, sulfuric acid, and hydrogen peroxide are mixed. The sulfuric acid and hydrogen peroxide are added in three alternating batches, and the pH is controlled at 1.5-2. The mixture is then filtered a second time to prepare a second solution and a first solid. The first solid comprises a mixture of ferric phosphate and carbon black. The first solid is washed, pulped, and subjected to a crystal reforming reaction. After the reaction is complete, it is aged, filtered for the third time, and the filter cake is collected to prepare the second solid. The second solid is dried and calcined for the first time to prepare the third solid. The conditions for the crystal reforming reaction include: a temperature of 85℃~95℃ and a rotation speed of 80r / min~120r / min. The conditions for the first calcination include: a temperature of 500℃~600℃ and a time of 4h~6h. The second solution is mixed with the second alkaline solution to prepare the third solution; the third solution is passed through a filter column packed with calcium-magnesium characteristic adsorption resin to prepare the fourth solution; the fourth solution is concentrated to prepare the fifth solution; the fifth solution, lithium carbonate seed crystals, and sodium carbonate are mixed to carry out a lithium carbonate synthesis reaction; after the reaction is completed, the mixture is washed, filtered, and the filter cake is collected to prepare the fourth solid; wherein, the conditions for the lithium carbonate synthesis reaction include: temperature of 85℃~95℃, rotation speed of 80r / min~120r / min; The third solid, the fourth solid, sugars, and water are mixed, slurried, dried, and then calcined a second time in a protective atmosphere. The conditions for the second calcination include: 700℃~850℃ for 18h~24h. The sugars are selected from one or more of glucose, sucrose, and reduced starch. The mass ratio of the dry basis of the third solid, water, sugars, and fourth solid is 1:2:(0.15~0.2):(0.25~0.35).

2. The method for synthesizing lithium iron phosphate from waste electrode sheets from battery factories according to claim 1, characterized in that, After washing the first solid, the conductivity of the washing water is 50 μS / M to 200 μS / M.

3. The method for synthesizing lithium iron phosphate from waste electrode sheets from battery factories according to claim 1, characterized in that, The conditions for mixing the second solution with the second alkaline solution include: a temperature of 60℃~80℃ and a pH of 8~11.

4. The method for synthesizing lithium iron phosphate from waste electrode sheets from battery factories according to claim 1, characterized in that, The first alkaline solution and the second alkaline solution are each independently selected from one or more of sodium hydroxide aqueous solution and potassium hydroxide aqueous solution.

Images