Method for preparing lithium iron phosphate by recycling waste lithium iron phosphate batteries and application

Abstract

The invention provides an aza-conjugated co-dissolving agent for preparing lithium iron phosphate by recycling waste lithium iron phosphate batteries, which is characterized in that based on Michael addition, pyridine ring beta-position carbon atoms of 1, 10-phenanthroline are attacked through amino groups of diallylamine, C-N bonds are formed, a conjugated system is expanded, 2-amino-1, 3, 5-triazine reacts with an intermediate through amino groups, and the aza-conjugated co-dissolving agent is prepared. A pi electron system is further extended, p-toluenesulfonic acid is introduced into a sulfonate ion pair, the dissolving capacity is improved through coordination and electrostatic effect synergistically, and the metal leaching efficiency of valuable metal in the leaching process is improved; the invention further provides a method for recycling and preparing lithium iron phosphate from the waste lithium iron phosphate battery and application, the leaching rate of lithium and iron is remarkably increased in the process of recycling and preparing the lithium iron phosphate, and the battery prepared after recycling has high discharge capacity and good cycling stability; the recycling value and the application range of the waste lithium iron phosphate positive electrode material are effectively improved.

Description

Technical Field

[0001] The present invention belongs to the field of lithium iron phosphate materials, and particularly relates to a method and application of preparing lithium iron phosphate by recycling waste lithium iron phosphate batteries. Background Art

[0002] With the widespread use of lithium-ion batteries in new energy vehicles, consumer electronics, and other fields, a large amount of waste lithium-ion batteries has been generated. As a typical lithium-ion battery cathode material, lithium iron phosphate (LiFePO4) boasts structural stability, long cycle life, and low cost, making it widely used in electric vehicles and energy storage systems. Waste LiFePO4 cathode material contains valuable metals such as lithium, iron, and phosphorus. Recycling and reusing waste LiFePO4 cathode material not only achieves resource recycling, but also reduces dependence on primary mineral resources and reduces environmental pollution.

[0003] Currently, there are two main methods for recycling lithium iron phosphate power batteries: one is repair and regeneration, and the other is to recover valuable elements using hydrometallurgical methods.

[0004] For example, the invention patent application with publication number CN119650931A discloses a method for repairing and regenerating waste lithium iron phosphate positive electrode materials. The method includes the following steps: battery disassembly: disassembling the lithium-ion battery to obtain the positive electrode sheet, negative electrode sheet, and separator; the positive electrode sheet includes a positive electrode active material, which is lithium iron phosphate; positive electrode sheet treatment: separating and removing the positive electrode current collector to obtain a positive electrode active material coating; negative electrode sheet and separator treatment: soaking the negative electrode sheet and separator in a citric acid solution and heating and impregnating to obtain an impregnation solution; positive electrode active material regeneration: mixing the positive electrode active material coating and the impregnation solution, heating and ultrasonically treating the mixture, and then freeze-grinding and thawing. After 5-10 cycles of freeze-grinding and thawing, the mixture is dried to remove moisture, and then calcined at high temperature to complete the repair and regeneration of the waste lithium iron phosphate positive electrode material. However, the performance of lithium battery positive electrode materials after high-temperature repair is generally not ideal.

[0005] For example, the invention patent application with publication number CN119092868A discloses a low-temperature, normal-pressure liquid-phase method for regenerating waste lithium iron phosphate positive electrode materials and a preparation method, comprising the following steps: S1, placing waste lithium iron phosphate positive electrode sheets in an eluent for elution to obtain active material; S2, reducing and lithium-replenishing the active material to obtain lithium-replenished lithium iron phosphate powder; S3, subjecting the lithium-replenished lithium iron phosphate powder to a carbon layer repair treatment; and uniformly mixing the lithium-replenished lithium iron phosphate powder with an organic carbon source, annealing the mixture, and then cooling it to room temperature to obtain a regenerated lithium iron phosphate positive electrode material. However, in the wet recovery of lithium iron phosphate batteries, typical products include high-priced products such as lithium carbonate and iron phosphate. Furthermore, with the continued decline in lithium prices over the past two years, the economic efficiency of existing recovery methods has deteriorated.

[0006] In summary, the existing recycling technology for waste lithium iron phosphate cathode materials suffers from complex processes, low metal leaching efficiency, and unstable performance of the recycled materials. Traditional recycling methods struggle to effectively separate the cathode active material from the current collector, and during the leaching process, the leaching rate of valuable metals is low, resulting in poor performance of the subsequently regenerated cathode materials, limiting the development of the waste lithium iron phosphate cathode material recycling industry. Therefore, there is an urgent need to develop an efficient, environmentally friendly method for preparing high-performance recycled cathode materials. Summary of the Invention

[0007] In order to solve the above technical problems existing in the prior art, the present invention provides a method and application of preparing lithium iron phosphate by recycling waste lithium iron phosphate batteries.

[0008] The present invention provides a method for preparing an azo-conjugated dissolution aid for preparing lithium iron phosphate by recycling waste lithium iron phosphate batteries, comprising the following steps: (1) 18-36 parts of 1,10-phenanthroline, 7-14 parts of diallylamine and 0.5-2 parts of 2-amino-1,3,5-triazine are uniformly dispersed in a solvent, and the pH value is adjusted to 6-7 to obtain a precursor; (2) Add 1-3 parts of p-toluenesulfonic acid to the precursor and mix evenly to generate a synergistic solubilizing agent containing a nitrogen-containing conjugated structure; (3) After the reaction is completed, the solvent is removed to obtain an nitrogen-conjugated solubilizing agent.

[0009] Under acidic conditions, the amino group of diallylamine nucleophilically attacks the β-carbon atom of the pyridine ring of 1,10-phenanthroline, forming a CN bond through Michael addition and expanding the conjugated system. 22-amino-1,3,5-triazine reacts with the intermediate through the amino group, further extending the π electron system. Furthermore, p-toluenesulfonic acid introduces a sulfonate ion pair, and the product has both multi-nitrogen coordination groups (complexed with metal ions) and ionic solubility, synergistically improving the solubility through coordination and electrostatic effects.

[0010] Preferably, the solvent in step (1) is anhydrous ethanol, with a mass fraction of 200-360 parts; during dispersion, the mixture is stirred at a temperature of 60-70° C. for 2-3 h to be uniformly dispersed.

[0011] Preferably, the mixing in step (2) is carried out at a temperature of 80-90° C. for 2-6 h to achieve uniform mixing.

[0012] Optionally, after the reaction is completed, the solvent is removed to precipitate white crystals, which are filtered and washed with ethanol, then vacuum-dried at 80-90° C. for 3-4 h, and ground to obtain an aza-conjugated dissolution aid.

[0013] The present invention provides an aza-conjugated dissolution aid prepared by the preparation method.

[0014] The present invention provides a method for preparing lithium iron phosphate by recycling waste lithium iron phosphate batteries, using the nitrogen-conjugated dissolution aid, comprising the following steps: (1) Soaking the disassembled waste lithium iron phosphate positive electrode sheet in water to obtain waste lithium iron phosphate positive electrode material; (2) placing 5-10 parts of waste lithium iron phosphate positive electrode material in a mixed solution of 70-90 parts of phosphoric acid leaching agent, 5-10 parts of ascorbic acid reducing agent and 0.1-0.5 parts of nitrogen-conjugated dissolving agent to obtain a leachate; (3) Under an inert atmosphere, the pH of the leachate is adjusted to 6 to obtain an iron phosphate precipitate; (4) 5-8 parts of lithium phosphate, 40-50 parts of iron phosphate precipitate, 0.1-0.3 parts of lithium hydroxide and 3-6 parts of glucose are mixed and sintered to obtain a lithium iron phosphate positive electrode material.

[0015] At room temperature, argon was continuously introduced into the leaching solution to prevent Fe 2+ Oxidation facilitates the subsequent precipitation of iron phosphate precipitates.

[0016] (2) placing 5-10 parts of waste lithium iron phosphate positive electrode material in a mixed solution comprising 70-90 parts of phosphoric acid leaching agent, 5-10 parts of ascorbic acid reducing agent and 0.1-0.5 parts of nitrogen-conjugated dissolution aid, leaching by heating, stirring and filtering to obtain a leachate; (3) Under argon atmosphere at room temperature, slowly add ammonia water to the leachate to adjust the pH to 6 to precipitate, and then filter and vacuum dry to obtain iron phosphate precipitate; (4) 5-8 parts of lithium phosphate, 40-50 parts of iron phosphate precipitate, 0.1-0.3 parts of lithium hydroxide and 3-6 parts of glucose are mixed, ground and dried to obtain a lithium iron phosphate precursor, which is then sintered to obtain a lithium iron phosphate positive electrode material.

[0017] Preferably, step (1) specifically comprises: soaking the waste lithium iron phosphate positive electrode sheet that has been discharged and disassembled in water at 70-80°C for 20-30 min to peel off the positive electrode active material; and drying the peeled positive electrode active material at 70-80°C for 7-12 h to obtain the waste lithium iron phosphate positive electrode material.

[0018] Preferably, in step (2), the mass proportion of phosphoric acid in the phosphoric acid leaching agent is 10%-20%.

[0019] Preferably, in step (2), the mass proportion of ascorbic acid in the ascorbic acid reducing agent is 10%-20%.

[0020] Preferably, in step (2), the mixed solution is leached at a leaching temperature of 60-70° C. and a leaching time of 2-3 h to obtain a leachate.

[0021] Further optionally, in step (2), the leachate is obtained by filtration using a circulating water vacuum pump.

[0022] Optionally, the inert atmosphere in step (3) is argon.

[0023] Preferably, in step (4), the sintering is performed by placing the mixed lithium iron phosphate precursor under an argon atmosphere in a vacuum tube furnace; Further preferably, the sintering temperature in step (4) is 600-700°C and the sintering time is 5-8 h.

[0024] On the other hand, the present invention also provides an application of lithium iron phosphate prepared by recycling waste lithium iron phosphate batteries in the recycling of waste lithium iron phosphate batteries.

[0025] Compared with the prior art, the present invention has the following beneficial effects: (1) Efficient dissolution and selective separation: Multi-nitrogen conjugated groups strongly complex transition metals and Li + , destroying the metal-oxygen bond to accelerate dissolution, and the step-by-step precipitation of lithium and transition metals can be achieved by adjusting the pH, effectively improving the separation efficiency.

[0026] (2) Green and low-cost advantages: It can replace strong acid / cyanide, reduce corrosion and toxicity, and the prepared nitrogen-conjugated dissolution aid can be recycled, which can lower the reaction temperature and reduce energy consumption, meeting the requirements of green chemistry and economy.

[0027] (3) The present invention can significantly improve the leaching rate of lithium and iron. The battery prepared after recycling has a high discharge capacity and good cycle stability, which effectively improves the recycling value of waste lithium iron phosphate positive electrode materials. DETAILED DESCRIPTION

[0028] In order to further illustrate the technical means and effects adopted by the present invention to achieve the predetermined invention object, the following is a detailed description in conjunction with examples and comparative examples: Example 1 (1) A method for preparing an aza-conjugated dissolution aid, comprising the following steps: H1: 18 g of 1,10-phenanthroline and 200 g of anhydrous ethanol were added with 7 g of diallylamine and 0.5 g of 2-amino-1,3,5-triazine to obtain a mixed solution. The pH of the mixed solution was adjusted to 6, and the mixture was stirred at 60°C for 2 h to obtain a precursor. H2: 1 g of p-toluenesulfonic acid was added to the precursor as a catalyst, and the temperature was raised to 80°C and the reaction was continued for 2 h to generate a synergistic solubilizing agent containing a nitrogen-containing conjugated structure through Michael addition; H3: After the reaction is completed, the nitrogen-conjugated co-solvent is cooled to precipitate white crystals, which are filtered, washed three times with ethanol, vacuum-dried at 80°C for 3 h, and ground into fine powder to obtain a nitrogen-conjugated co-solvent.

[0029] (2) This embodiment provides a method for preparing lithium iron phosphate by recycling waste lithium iron phosphate batteries, which specifically includes the following steps: S1 Treatment of Waste Positive Electrode Sheets: Soak the disassembled waste lithium iron phosphate positive electrode sheets in 70°C hot water for 20 minutes to separate the positive electrode active material from the current collector; dry the stripped positive electrode active material at 70°C for 7 hours, and then grind it to obtain waste lithium iron phosphate positive electrode materials; S2 leaching: 5 g of waste lithium iron phosphate cathode material was placed in a mixed solution of 70 g of 10% phosphoric acid leaching agent, 5 g of 10% ascorbic acid reducing agent and 0.1 g of nitrogen-conjugated dissolution aid, and the mixture was heated and stirred for leaching at 60 ° C for 2 h. After leaching, a circulating water vacuum pump was used for filtration to obtain a leachate. S3 Synthetic Iron Phosphate Precipitation: Add the leachate to the reactor and continue to introduce argon at room temperature to prevent Fe 2+ Oxidation, slowly adding ammonia water to adjust the pH value to 6 for precipitation; after filtering, the filter cake is vacuum dried to obtain iron phosphate precipitate; S4: preparing a lithium iron phosphate precursor: mixing 5 g of lithium phosphate, 40 g of iron phosphate precipitate, 0.1 g of lithium hydroxide, and 3 g of glucose, grinding them, and drying them to obtain a lithium iron phosphate precursor; S5 sintering to prepare lithium iron phosphate positive electrode material: the lithium iron phosphate precursor is sintered in a vacuum tube furnace under Ar atmosphere at a sintering temperature of 600°C for 5 h to obtain the lithium iron phosphate positive electrode material.

[0030] (3) Preparation of positive electrode sheets and assembly of batteries: 70 g of lithium iron phosphate positive electrode material regenerated in S5, 5 g of acetylene black and 5 g of polyvinylidene fluoride were added to 20 g of N-methylpyrrolidone, mixed and ground evenly, then coated on aluminum foil and dried at 100°C for 3 h; then the electrode sheet was punched into a positive electrode sheet using a punching machine; in a vacuum glove box, the positive electrode sheet, metal lithium negative electrode, electrolyte, and glass fiber separator were assembled into a button-type battery, where the electrolyte was 1 mol / L LiPF6 / EC+DEC+DMC, and the volume ratio was 1:1:1.

[0031] Example 2 (1) A method for preparing an aza-conjugated dissolution aid, comprising the following steps: H1: 24 g of 1,10-phenanthroline and 260 g of anhydrous ethanol were added with 9 g of diallylamine and 1 g of 2-amino-1,3,5-triazine to obtain a mixed solution. The pH of the mixed solution was adjusted to 6, and the mixture was stirred at 65°C for 2.5 h to obtain a precursor. H2: Add 2 g of p-toluenesulfonic acid as a catalyst to the precursor, raise the temperature to 85°C and continue the reaction for 3 h to generate a nitrogen-containing conjugated structure synergistic solubilizer through Michael addition; H3: After the reaction is completed, the nitrogen-conjugated co-solvent is cooled to precipitate white crystals, which are filtered, washed three times with ethanol, dried in vacuum at 85°C for 3.5 h, and ground into fine powder to obtain a nitrogen-conjugated co-solvent.

[0032] (2) This embodiment provides a method for preparing lithium iron phosphate by recycling waste lithium iron phosphate batteries, which specifically includes the following steps: S1 Treatment of Waste Positive Electrode Sheets: Soak the disassembled waste lithium iron phosphate positive electrode sheets in 75°C hot water for 25 minutes to separate the positive electrode active material from the current collector; dry the stripped positive electrode active material at 75°C for 8 hours, and then grind it to obtain waste lithium iron phosphate positive electrode materials; S2 leaching: 6 g of waste lithium iron phosphate cathode material was placed in a mixed solution of 75 g of a 15% phosphoric acid leaching agent, 6 g of a 15% ascorbic acid reducing agent, and 0.2 g of an azo-conjugated dissolution aid, and the mixture was heated and stirred for leaching at a temperature of 65°C for 2.5 h. After leaching, a circulating water vacuum pump was used for filtration to obtain a leachate. S3 Synthetic Iron Phosphate Precipitation: Add the leachate to the reactor and continue to introduce argon at room temperature to prevent Fe 2+ Oxidation, slowly adding ammonia water to adjust the pH value to 6 for precipitation; after filtering, the filter cake is vacuum dried to obtain iron phosphate precipitate; S4: preparing a lithium iron phosphate precursor: mixing 6 g of lithium phosphate, 43 g of iron phosphate precipitate, 0.2 g of lithium hydroxide, and 4 g of glucose, grinding, and drying to obtain a lithium iron phosphate precursor; S5 sintering to prepare lithium iron phosphate cathode material: the lithium iron phosphate precursor is sintered in a vacuum tube furnace under Ar atmosphere at a sintering temperature of 640°C for 6 h to obtain the lithium iron phosphate cathode material; (3) Preparation of positive electrode sheets and assembly of batteries: 73 g of lithium iron phosphate positive electrode material regenerated in S5, 6 g of acetylene black, and 6 g of polyvinylidene fluoride were added to 25 g of N-methylpyrrolidone, mixed and ground evenly, then coated on aluminum foil and dried at 105°C for 3.5 h; then the electrode sheet was punched into a positive electrode sheet using a punching machine; in a vacuum glove box, the positive electrode sheet, metal lithium negative electrode, electrolyte, and glass fiber separator were assembled into a button-type battery, where the electrolyte was 1 mol / L LiPF6 / EC+DEC+DMC, and the volume ratio was 1:1:1.

[0033] Example 3 (1) A method for preparing an aza-conjugated dissolution aid, comprising the following steps: H1: 33 g of 1,10-phenanthroline and 330 g of anhydrous ethanol were added with 12 g of diallylamine and 1.5 g of 2-amino-1,3,5-triazine to obtain a mixed solution. The pH of the mixed solution was adjusted to 7, and the mixture was stirred at 65°C for 2.5 h to obtain a precursor. H2: Add 2 g of p-toluenesulfonic acid as a catalyst to the precursor, raise the temperature to 85°C and continue the reaction for 5 h to generate a nitrogen-containing conjugated structure synergistic solubilizer through Michael addition; H3: After the reaction is completed, the nitrogen-conjugated co-solvent is cooled to precipitate white crystals, which are filtered, washed three times with ethanol, dried in vacuum at 85°C for 3.5 h, and ground into fine powder to obtain a nitrogen-conjugated co-solvent.

[0034] (2) This embodiment provides a method for preparing lithium iron phosphate by recycling waste lithium iron phosphate batteries, which specifically includes the following steps: S1 Treatment of Waste Positive Electrode Sheets: Soak the disassembled waste lithium iron phosphate positive electrode sheets in 75°C hot water for 25 minutes to separate the positive electrode active material from the current collector; dry the stripped positive electrode active material at 75°C for 10 hours, and then grind it to obtain waste lithium iron phosphate positive electrode materials; S2 leaching: 8 g of waste lithium iron phosphate positive electrode material was placed in a mixed solution of 85 g of a 15% phosphoric acid leaching agent, 8 g of a 15% ascorbic acid reducing agent, and 0.4 g of an azo-conjugated dissolution aid, and the mixture was heated and stirred for leaching at a temperature of 65°C for 2.5 h. After leaching, a circulating water vacuum pump was used for filtration to obtain a leachate. S3 Synthetic Iron Phosphate Precipitation: Add the leachate to the reactor and continue to introduce argon at room temperature to prevent Fe 2+ Oxidation, slowly adding ammonia water to adjust the pH value to 6 for precipitation; after filtering, the filter cake is vacuum dried to obtain iron phosphate precipitate; S4: preparing a lithium iron phosphate precursor: mixing 7 g of lithium phosphate, 48 g of iron phosphate precipitate, 0.2 g of lithium hydroxide, and 5 g of glucose, grinding, and drying to obtain a lithium iron phosphate precursor; S5 sintering to prepare lithium iron phosphate cathode material: the lithium iron phosphate precursor is sintered in a vacuum tube furnace under Ar atmosphere at a sintering temperature of 680°C for 7 h to obtain the lithium iron phosphate cathode material; (3) Preparation of positive electrode sheets and assembly of batteries: 78 g of lithium iron phosphate positive electrode material regenerated in S5, 8 g of acetylene black, and 8 g of polyvinylidene fluoride were added to 35 g of N-methylpyrrolidone and mixed and ground evenly, then coated on aluminum foil and dried at 115°C for 3.5 h; then the electrode sheet was punched into a positive electrode sheet using a punching machine; in a vacuum glove box, the positive electrode sheet, metal lithium negative electrode, electrolyte, and glass fiber separator were assembled into a button-type battery, where the electrolyte was 1 mol / L LiPF6 / EC+DEC+DMC, and the volume ratio was 1:1:1.

[0035] Example 4 (1) A method for preparing an aza-conjugated dissolution aid, comprising the following steps: H1: 14 g of diallylamine and 2 g of 2-amino-1,3,5-triazine were added to 36 g of 1,10-phenanthroline and 360 g of anhydrous ethanol to obtain a mixed solution. The pH of the mixed solution was adjusted to 7, and the mixture was stirred at 70°C for 3 h to obtain a precursor. H2: Add 3 g of p-toluenesulfonic acid as a catalyst to the precursor, raise the temperature to 90°C and continue the reaction for 6 h to generate a synergistic solubilizer containing a nitrogen-containing conjugated structure through Michael addition; H3: After the reaction is completed, the nitrogen-conjugated co-solvent is cooled to precipitate white crystals, which are filtered, washed three times with ethanol, vacuum-dried at 90°C for 4 h, and ground into fine powder to obtain a nitrogen-conjugated co-solvent.

[0036] (2) This embodiment provides a method for preparing lithium iron phosphate by recycling waste lithium iron phosphate batteries, which specifically includes the following steps: S1 Treatment of Waste Positive Electrode Sheets: Soak the disassembled waste lithium iron phosphate positive electrode sheets in 80°C hot water for 30 minutes to separate the positive electrode active material from the current collector; dry the stripped positive electrode active material at 80°C for 12 hours, and then grind it to obtain waste lithium iron phosphate positive electrode materials; S2 leaching: 10 g of waste lithium iron phosphate positive electrode material was placed in a mixed solution of 90 g of a 20% mass concentration phosphoric acid leaching agent, 10 g of a 20% mass concentration ascorbic acid reducing agent, and 0.5 g of an azo-conjugated dissolution aid, and the mixture was heated and stirred for leaching at a temperature of 70°C for 3 h. After leaching, a circulating water vacuum pump was used for filtration to obtain a leachate. S3 Synthetic Iron Phosphate Precipitation: Add the leachate to the reactor and continue to introduce argon at room temperature to prevent Fe 2+ Oxidation, slowly adding ammonia water to adjust the pH value to 6 for precipitation; after filtering, the filter cake is vacuum dried to obtain iron phosphate precipitate; S4: preparing a lithium iron phosphate precursor: mixing 8 g of lithium phosphate, 50 g of iron phosphate precipitate, 0.3 g of lithium hydroxide, and 6 g of glucose, grinding them, and drying them to obtain a lithium iron phosphate precursor; S5 sintering to prepare lithium iron phosphate cathode material: the lithium iron phosphate precursor is sintered in a vacuum tube furnace under Ar atmosphere at a sintering temperature of 700°C for 8 h to obtain the lithium iron phosphate cathode material; (3) Preparation of positive electrode sheets and assembly of batteries: 80 g of lithium iron phosphate positive electrode material regenerated in S5, 10 g of acetylene black and 10 g of polyvinylidene fluoride were added to 40 g of N-methylpyrrolidone and mixed and ground evenly, then coated on aluminum foil and dried at 120°C for 4 h; then the electrode sheet was punched into a positive electrode sheet using a sheet puncher; in a vacuum glove box, the positive electrode sheet, metal lithium negative electrode, electrolyte, and glass fiber separator were assembled into a button-type battery, where the electrolyte was 1 mol / L LiPF6 / EC+DEC+DMC, and the volume ratio was 1:1:1.

[0037] Comparative Example 1 (1) Comparative Example 1 provides a method for preparing lithium iron phosphate by recycling waste lithium iron phosphate batteries without using a dissolving agent, and specifically includes the following steps: S1 Treatment of Waste Positive Electrode Sheets: Soak the disassembled waste lithium iron phosphate positive electrode sheets in 70°C hot water for 20 minutes to separate the positive electrode active material from the current collector; dry the stripped positive electrode active material at 70°C for 7 hours, and then grind it to obtain waste lithium iron phosphate positive electrode materials; S2 leaching: 5 g of waste lithium iron phosphate cathode material was placed in a mixed solution of 70 g of a 10% phosphoric acid leaching agent and 5 g of a 10% ascorbic acid reducing agent, and the mixture was heated and stirred for leaching at 60°C for 2 h. After leaching, a circulating water vacuum pump was used for filtration to obtain a leachate. S3 Synthetic Iron Phosphate Precipitation: Add the leachate to the reactor and continue to introduce argon at room temperature to prevent Fe 2+Oxidation, slowly adding ammonia water to adjust the pH value to 6 for precipitation; after filtering, the filter cake is vacuum dried to obtain iron phosphate precipitate; S4: preparing a lithium iron phosphate precursor: mixing 5 g of lithium phosphate, 40 g of iron phosphate precipitate, 0.1 g of lithium hydroxide, and 3 g of glucose, grinding them, and drying them to obtain a lithium iron phosphate precursor; S5 sintering to prepare lithium iron phosphate cathode material: the lithium iron phosphate precursor is sintered in a vacuum tube furnace under Ar atmosphere at a sintering temperature of 600°C for 5 h to obtain the lithium iron phosphate cathode material; (2) Preparation of positive electrode sheets and assembly of batteries: 70 g of lithium iron phosphate positive electrode material regenerated in S5, 5 g of acetylene black and 5 g of polyvinylidene fluoride were added to 20 g of N-methylpyrrolidone, mixed and ground evenly, then coated on aluminum foil and dried at 100°C for 3 h; then the electrode sheet was punched into a positive electrode sheet using a punching machine; in a vacuum glove box, the positive electrode sheet, metal lithium negative electrode, electrolyte, and glass fiber separator were assembled into a button-type battery, where the electrolyte was 1 mol / L LiPF6 / EC+DEC+DMC, and the volume ratio was 1:1:1.

[0038] Comparative Example 2 (1) The preparation method of the dissolution aid 1 comprises the following steps: H1: 0.5 g of 2-amino-1,3,5-triazine was added to 18 g of 1,10-phenanthroline and 200 g of anhydrous ethanol to obtain a mixed solution. The pH of the mixed solution was adjusted to 6, and the mixture was stirred at 60°C for 2 h to obtain a precursor. H2: Add 1 g of p-toluenesulfonic acid as a catalyst to the precursor, raise the temperature to 80°C and continue the reaction for 2 h; H3: After the reaction is completed, the white crystals are precipitated by cooling, filtered, washed three times with ethanol, dried in vacuo at 80°C for 3 h, and ground into fine powder to obtain dissolution aid 1.

[0039] (2) Comparative Example 2 provides a method for preparing lithium iron phosphate by recycling waste lithium iron phosphate batteries using dissolution aid 1, which specifically includes the following steps: S1 Treatment of Waste Positive Electrode Sheets: Soak the disassembled waste lithium iron phosphate positive electrode sheets in 70°C hot water for 20 minutes to separate the positive electrode active material from the current collector; dry the stripped positive electrode active material at 70°C for 7 hours, and then grind it to obtain waste lithium iron phosphate positive electrode materials; S2 leaching: 5 g of waste lithium iron phosphate positive electrode material was placed in a mixed solution of 70 g of a 10% phosphoric acid leaching agent, 5 g of a 10% ascorbic acid reducing agent, and 0.1 g of a dissolving agent 1, and the mixture was heated and stirred for leaching at 60°C for 2 h. After leaching, a circulating water vacuum pump was used for filtration to obtain a leachate. S3 Synthetic Iron Phosphate Precipitation: Add the leachate to the reactor and continue to introduce argon at room temperature to prevent Fe 2+ Oxidation, slowly adding ammonia water to adjust the pH value to 6 for precipitation; after filtering, the filter cake is vacuum dried to obtain iron phosphate precipitate; S4: preparing a lithium iron phosphate precursor: mixing 5 g of lithium phosphate, 40 g of iron phosphate precipitate, 0.1 g of lithium hydroxide, and 3 g of glucose, grinding them, and drying them to obtain a lithium iron phosphate precursor; S5 sintering to prepare lithium iron phosphate cathode material: the lithium iron phosphate precursor is sintered in a vacuum tube furnace under Ar atmosphere at a sintering temperature of 600°C for 5 h to obtain the lithium iron phosphate cathode material; (3) Preparation of positive electrode sheets and assembly of batteries: 70 g of lithium iron phosphate positive electrode material regenerated in S5, 5 g of acetylene black and 5 g of polyvinylidene fluoride were added to 20 g of N-methylpyrrolidone, mixed and ground evenly, then coated on aluminum foil and dried at 100°C for 3 h; then the electrode sheet was punched into a positive electrode sheet using a punching machine; in a vacuum glove box, the positive electrode sheet, metal lithium negative electrode, electrolyte, and glass fiber separator were assembled into a button-type battery, where the electrolyte was 1 mol / L LiPF6 / EC+DEC+DMC, and the volume ratio was 1:1:1.

[0040] Comparative Example 3 (1) The preparation method of the dissolution aid 2 comprises the following steps: H1: Add 7 g of diallylamine to 18 g of 1,10-phenanthroline and 200 g of anhydrous ethanol, adjust the pH to 6, and stir at 60°C for 2 h. H2: Add 1 g of p-toluenesulfonic acid as a catalyst, raise the temperature to 80°C and continue the reaction for 2 h; H3: After the reaction is completed, the white crystals are precipitated by cooling, filtered, washed three times with ethanol, dried in vacuum at 80°C for 3 h, and ground into fine powder to obtain dissolution aid 2.

[0041] (2) Comparative Example 3 provides a method for preparing lithium iron phosphate by recycling waste lithium iron phosphate batteries using dissolution aid 2, which specifically includes the following steps: S1 Treatment of Waste Positive Electrode Sheets: Soak the disassembled waste lithium iron phosphate positive electrode sheets in 70°C hot water for 20 minutes to separate the positive electrode active material from the current collector; dry the stripped positive electrode active material at 70°C for 7 hours, and then grind it to obtain waste lithium iron phosphate positive electrode materials; S2 leaching: 5 g of waste lithium iron phosphate cathode material was placed in a mixed solution of 70 g of 10% phosphoric acid leaching agent, 5 g of 10% ascorbic acid reducing agent and 0.1 g of dissolution aid 2, and the mixture was heated and stirred for leaching at 60°C for 2 h. After leaching, a circulating water vacuum pump was used for filtration to obtain a leachate. S3 Synthetic Iron Phosphate Precipitation: Add the leachate to the reactor and continue to introduce argon at room temperature to prevent Fe 2+ Oxidation, slowly adding ammonia water to adjust the pH value to 6 for precipitation; after filtering, the filter cake is vacuum dried to obtain iron phosphate precipitate; S4: preparing a lithium iron phosphate precursor: mixing 5 g of lithium phosphate, 40 g of iron phosphate precipitate, 0.1 g of lithium hydroxide, and 3 g of glucose, grinding them, and drying them to obtain a lithium iron phosphate precursor; S5 sintering to prepare lithium iron phosphate cathode material: the lithium iron phosphate precursor is sintered in a vacuum tube furnace under Ar atmosphere at a sintering temperature of 600°C for 5 h to obtain the lithium iron phosphate cathode material; (3) Preparation of positive electrode sheets and assembly of batteries: 70 g of lithium iron phosphate positive electrode material regenerated in S5, 5 g of acetylene black and 5 g of polyvinylidene fluoride were added to 20 g of N-methylpyrrolidone, mixed and ground evenly, then coated on aluminum foil and dried at 100°C for 3 h; then the electrode sheet was punched into a positive electrode sheet using a punching machine; in a vacuum glove box, the positive electrode sheet, metal lithium negative electrode, electrolyte, and glass fiber separator were assembled into a button-type battery, where the electrolyte was 1 mol / L LiPF6 / EC+DEC+DMC, and the volume ratio was 1:1:1.

[0042] Test Example 1 Li + and Fe 2+ Leaching rate test: Inductively coupled plasma optical emission spectrometry was used to determine the content of each element.

[0043] Test Example 2 Electrochemical performance tests were performed on Examples 1-4 and Comparative Examples 1-3: using a CHI1000C electrochemical workstation, the initial discharge capacity was tested at 0.1 C in the voltage range of 2.5-4.1 V, and the capacity retention was tested after 200 cycles at 1 C.

[0044] The test results of Test Example 1 and Test Example 2 are shown in Table 1.

[0045] Table 1

[0046] Through the data analysis of the above embodiments and comparative examples, the present invention can significantly improve the leaching rate of lithium and iron. The battery prepared after recycling has a high discharge capacity and good cycle stability, which effectively improves the recycling value of waste lithium iron phosphate positive electrode materials.

[0047] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as above in terms of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art can, without departing from the scope of the technical solution of the present invention, make some changes or modifications to equivalent embodiments using the technical contents disclosed above. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for preparing an aza-conjugated dissolution aid, characterized in that: Calculated by mass, comprising the following steps: (1) 18-36 parts of 1,10-phenanthroline, 7-14 parts of diallylamine and 0.5-2 parts of 2-amino-1,3,5-triazine are uniformly dispersed in a solvent, and the pH value is adjusted to 6-7 to obtain a precursor; (2) Add 1-3 parts of p-toluenesulfonic acid to the precursor and mix evenly to generate a synergistic solubilizing agent containing a nitrogen-containing conjugated structure; (3) After the reaction is completed, the solvent is removed to obtain an nitrogen-conjugated solubilizing agent.

2. The method for preparing the nitrogen-conjugated dissolution aid according to claim 1, wherein: The solvent in step (1) is anhydrous ethanol, with a mass fraction of 200-360 parts; during dispersion, the mixture is stirred at a temperature of 60-70° C. for 2-3 h to be uniformly dispersed.

3. The method for preparing the nitrogen-conjugated dissolution aid according to claim 1, wherein: During the mixing in step (2), the mixture is reacted at a temperature of 80-90° C. for 2-6 h until uniform mixing is achieved.

4. An aza-conjugated solubilizing agent prepared according to the preparation method according to any one of claims 1 to 3.

5. A method for preparing lithium iron phosphate by recycling waste lithium iron phosphate batteries, characterized in that: The use of the nitrogen-conjugated dissolution aid according to claim 4 comprises the following steps, calculated by weight: (1) Soaking the disassembled waste lithium iron phosphate positive electrode sheet in water to obtain waste lithium iron phosphate positive electrode material; (2) placing 5-10 parts of waste lithium iron phosphate positive electrode material in a mixed solution of 70-90 parts of phosphoric acid leaching agent, 5-10 parts of ascorbic acid reducing agent and 0.1-0.5 parts of nitrogen-conjugated dissolving agent to obtain a leachate; (3) Under an inert atmosphere, the pH of the leachate is adjusted to 6 to obtain an iron phosphate precipitate; (4) 5-8 parts of lithium phosphate, 40-50 parts of iron phosphate precipitate, 0.1-0.3 parts of lithium hydroxide and 3-6 parts of glucose are mixed and sintered to obtain a lithium iron phosphate positive electrode material.

6. The method for preparing lithium iron phosphate by recycling waste lithium iron phosphate batteries according to claim 5, characterized in that: Step (1) specifically includes: soaking the discharged and disassembled waste lithium iron phosphate positive electrode sheet in water at 70-80°C for 20-30 minutes, and then stripping out the positive electrode active material; drying the stripped positive electrode active material at a temperature of 70-80°C for 7-12 hours to obtain the waste lithium iron phosphate positive electrode material.

7. The method for preparing lithium iron phosphate by recycling waste lithium iron phosphate batteries according to claim 5, characterized in that: In step (2), the mass proportion of phosphoric acid in the phosphoric acid leaching agent is 10%-20%.

8. The method for preparing lithium iron phosphate by recycling waste lithium iron phosphate batteries according to claim 5, characterized in that: In step (2), the mass proportion of ascorbic acid in the ascorbic acid reducing agent is 10%-20%.

9. The method for preparing lithium iron phosphate by recycling waste lithium iron phosphate batteries according to claim 5, characterized in that: In step (2), the mixed solution is leached at a leaching temperature of 60° C. to 70° C. and a leaching time of 2 h to 3 h to obtain a leachate.

10. The method for preparing lithium iron phosphate by recycling waste lithium iron phosphate batteries according to claim 5, characterized in that: The sintering temperature in step (4) is 600-700°C, and the sintering time is 5-8 h.

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