Recycling method and application of waste lithium iron phosphate battery positive electrode materials

Abstract

The present invention discloses a method for recycling and regenerating waste lithium iron phosphate battery positive electrode materials and an application thereof, relating to the technical field of lithium battery positive electrode materials. The present invention recycles waste lithium iron phosphate batteries, thereby avoiding waste of resources and pollution to the environment and avoiding the use of strong acids and strong bases during the recycling process, thereby reducing the pollution of generated wastewater and achieving environmental protection. The method also realizes efficient recovery of lithium, iron and phosphorus elements. The lithium iron phosphate positive electrode material prepared by the present invention has excellent charge and discharge rate performance and is suitable for use as a high-power battery.

Description

Technical field:

[0001] The present invention relates to the technical field of lithium battery positive electrode materials, and in particular to a method for recycling and regenerating waste lithium iron phosphate battery positive electrode materials and applications thereof. Background technology:

[0002] Lithium iron phosphate (LiFePO4) is a lithium-ion battery electrode material with the chemical formula LiFePO4, primarily used in various lithium-ion batteries. Due to its robust PO bond, LiFePO4 is difficult to decompose. Its structure resists collapse even at high temperatures or under overcharge conditions, resulting in excellent cycling performance and safety, leading to broad application prospects.

[0003] The preparation of lithium iron phosphate is mainly divided into two methods: solid-phase method and liquid-phase method. Solid-phase method includes high-temperature solid-phase reaction method, carbothermal reduction method, microwave synthesis method, and mechanical alloying method. Liquid-phase method includes liquid-phase co-precipitation method, sol-gel method, hydrothermal synthesis method, etc. The solid-phase method is the most commonly used method for preparing electrode materials due to its simple process and ease of industrialization. Carbothermal reduction method is the most common solid-phase method. Carbothermal reduction method uses inexpensive trivalent iron to reduce it to divalent iron, and at the same time, the pyrolyzed carbon is coated on the lithium iron phosphate to enhance the conductivity, which can be said to kill two birds with one stone. The most significant feature of the liquid-phase preparation method is the addition of a solvent. Taking the hydrothermal method as an example, water is used as the solvent in a sealed pressure vessel. The raw materials undergo a chemical reaction under high temperature and high pressure conditions. After filtration, washing, and drying, a nano-precursor is obtained. Finally, lithium iron phosphate is obtained after high-temperature calcination.

[0004] From the perspective of the process flow alone, the solid-phase method is simple and suitable for large-scale production, but the materials are not mixed evenly and the particle size distribution range is wide, resulting in poor product consistency; the advantage of the liquid-phase method is uniform mixing and good product consistency, but the process is complex, the reaction conditions are demanding, and mass production is more difficult. Summary of the invention:

[0005] The technical problem to be solved by the present invention is to provide a process for preparing lithium battery positive electrode materials by recycling waste lithium iron phosphate batteries, preparing lithium iron phosphate positive electrode materials by recycling and regenerating waste lithium iron phosphate, and ensuring the charge and discharge performance of the prepared lithium iron phosphate positive electrode materials.

[0006] The technical problem to be solved by the present invention is achieved by adopting the following technical solutions:

[0007] The process for preparing lithium battery positive electrode materials by recycling waste lithium iron phosphate batteries comprises the following steps:

[0008] (1) crushing, disassembling and sorting the waste lithium iron phosphate batteries after discharge treatment to obtain lithium iron phosphate powder;

[0009] (2) adding a hydrogen peroxide solution to the lithium iron phosphate powder and introducing CO2 gas, controlling the pH value of the mixed solution to be between 3 and 5, and completing the reaction to obtain a mixed solution I;

[0010] (3) determining the ratio of lithium, iron, and phosphorus in the mixed solution I, adding a lithium source, an iron source, or a phosphorus source, and adding yttrium vanadate so that the molar ratio of lithium, iron, phosphorus, vanadium, and yttrium atoms is (1.05-1.1):1:1:(0.01-0.05):(0.01-0.05), and then adding concentrated sulfuric acid to adjust the pH value of the solution to 2-4 to obtain a mixed solution;

[0011] (4) adding a carbon source to the mixed solution under stirring, and evaporating the mixture by autothermal heating to obtain a precursor;

[0012] (5) Under the protection of inert gas, the precursor is sintered at high temperature to obtain lithium iron phosphate positive electrode material.

[0013] The concentration of the hydrogen peroxide solution is 5-30%, and the amount of the hydrogen peroxide solution used is 5-20 mL per gram of lithium iron phosphate powder.

[0014] The lithium source is one or more of lithium carbonate, lithium oxide, lithium hydroxide, lithium acetate, lithium nitrate, lithium phosphate, and lithium oxalate.

[0015] The iron source is one or more of ferric sulfate, ferrous oxalate, ferrous nitrate, ferric chloride, ferric hydroxide, ferric nitrate, and ferric citrate.

[0016] The phosphorus source is one or more of phosphoric acid, ammonium dihydrogen phosphate, and ammonium phosphate.

[0017] The carbon source is one or more of glucose, sucrose, starch, and beta-cyclodextrin.

[0018] The concentration of the concentrated sulfuric acid is 98 wt %.

[0019] The amount of the carbon source added is such that the carbon content in the final lithium iron phosphate product reaches 0.5-3%.

[0020] The inert gas is one of nitrogen, argon and helium.

[0021] The heating rate of the high-temperature sintering is 5-15°C / min, and the sintering temperature is 500-800°C.

[0022] Reaction equation for recycling waste lithium iron phosphate:

[0023] 2LiFePO4+H2O2+2CO2=2Li + +2FePO4↓+2HCO3 -

[0024] Principle 1: Lithium iron phosphate is leached in hydrogen peroxide to release Li + OH is produced in the process - , so that the pH value of the solution increases. In order to prevent the generated iron phosphate from converting into iron hydroxide, CO2 is introduced into the solution at the same time.

[0025] Principle 2: Under strong acidic and strong oxidizing conditions, lithium source, iron source and phosphorus source will spontaneously generate heat after adding carbon source. The heat generated evaporates the water in the system to obtain lithium iron phosphate precursor.

[0026] Principle 3: By adding yttrium vanadate to the raw materials, vanadium and yttrium doped lithium iron phosphate positive electrode materials are obtained, which effectively inhibits grain growth and shortens Li + diffusion path, improving Li + The migration rate of the ions can be increased, thereby improving the charge and discharge rate performance.

[0027] The present invention also provides a method for preparing a carbon source, which replaces glucose, sucrose, starch, and β-cyclodextrin as a carbon source, thereby achieving the technical effect of further optimizing the charge and discharge rate performance of the prepared lithium iron phosphate positive electrode material.

[0028] The carbon source is methyl pivalate-O-sucrose, and its preparation method is as follows: dissolving sucrose in ethyl acetate, then adding chloromethyl pivalate and triethylamine, keeping the temperature under reflux for reaction, stopping the reaction after all the chloromethyl pivalate reacts, concentrating under reduced pressure to recover the ethyl acetate, washing the obtained concentrate with ethanol, filtering, and drying.

[0029] The molar ratio of the sucrose, chloromethyl pivalate and triethylamine is 1:1:1.

[0030] By controlling the molar ratio to allow one hydroxyl group in sucrose to participate in the reaction, modified sucrose was produced and used as a carbon source. Research has found that the carbon particles produced by thermal decomposition of this carbon source in an inert atmosphere can be evenly distributed between lithium iron phosphate grains and coated on the surface of the grains, inhibiting the growth of lithium iron phosphate grains and controlling the morphology of lithium iron phosphate grains, resulting in lithium iron phosphate with better charge and discharge rate performance.

[0031] The beneficial effects of the present invention are:

[0032] (1) The present invention recycles waste lithium iron phosphate batteries, which not only avoids the waste of resources and pollution to the environment, but also avoids the use of strong acids and strong bases in the recycling process, reduces the pollution of the generated wastewater, is green and environmentally friendly, and at the same time achieves efficient recovery of lithium, iron and phosphorus elements.

[0033] (2) The present invention adopts self-heating evaporation liquid phase to synthesize lithium iron phosphate, which does not require external heat, reduces the preparation cost, and has simple process, uniform material mixing, good product consistency, and is suitable for large-scale production.

[0034] (3) The lithium iron phosphate cathode material prepared by the present invention has excellent charge and discharge rate performance and is suitable for use as a high-power battery. Specific implementation method:

[0035] In order to make the technical means, creative features, objectives and effects achieved by the present invention easier to understand, the present invention is further described below in conjunction with specific embodiments.

[0036] Sucrose was purchased from Nanjing Chemical Reagent Co., Ltd.

[0037] Glucose was purchased from Nanjing Chemical Reagent Co., Ltd.

[0038] β-Cyclodextrin was purchased from Zhengzhou Kangyuan Chemical Products Co., Ltd.

[0039] Example 1

[0040] (1) After the waste lithium iron phosphate batteries are discharged, they are crushed, disassembled and sorted in sequence to obtain lithium iron phosphate powder.

[0041] (2) 1000 mL of a 20% hydrogen peroxide solution was added to 100 g of lithium iron phosphate powder, and CO2 gas was introduced. The pH value of the mixed solution was controlled at 5. The reaction was completed to obtain a mixed solution I.

[0042] (3) Determine the ratio of lithium, iron, and phosphorus elements in the mixed solution I, add lithium carbonate, ferric chloride or phosphoric acid, and add yttrium vanadate so that the molar ratio of lithium, iron, phosphorus, vanadium, and yttrium atoms is 1.05:1:1:0.05:0.02, then add 98wt% concentrated sulfuric acid and adjust the pH value of the solution to 3 to obtain a mixed solution.

[0043] (4) Glucose is added to the mixed solution under stirring. The amount of glucose added is such that the carbon content in the final lithium iron phosphate product reaches 2%, and the mixture is evaporated by autothermal heating to obtain a precursor.

[0044] (5) Under nitrogen protection, the precursor is subjected to high-temperature sintering, the temperature is increased to 500°C at a heating rate of 5°C / min and the temperature is kept at this temperature for 2 hours, and the temperature is further increased to 700°C and the temperature is kept at this temperature for 5 hours to obtain a lithium iron phosphate positive electrode material.

[0045] Example 2

[0046] (1) After the waste lithium iron phosphate batteries are discharged, they are crushed, disassembled and sorted in sequence to obtain lithium iron phosphate powder.

[0047] (2) Add 2000 mL of 25% hydrogen peroxide solution to 100 g of lithium iron phosphate powder, introduce CO2 gas, control the pH value of the mixed solution to 5, and terminate the reaction to obtain mixed solution I.

[0048] (3) Determine the ratio of lithium, iron, and phosphorus elements in the mixed solution I, add lithium acetate, ferric nitrate, or ammonium dihydrogen phosphate, and add yttrium vanadate so that the molar ratio of lithium, iron, phosphorus, vanadium, and yttrium atoms is 1.05:1:1:0.04:0.02, then add 98 wt% concentrated sulfuric acid and adjust the pH value of the solution to 4 to obtain a mixed solution.

[0049] (4) Add sucrose to the mixed solution under stirring. The amount of sucrose added is such that the carbon content in the final lithium iron phosphate product reaches 1.5%, and evaporate it by autothermal heating to obtain a precursor.

[0050] (5) Under nitrogen protection, the precursor is subjected to high-temperature sintering, the temperature is increased to 550°C at a heating rate of 10°C / min and the temperature is kept at 550°C for 3 hours, and the temperature is further increased to 750°C and the temperature is kept at 750°C for 3 hours to obtain a lithium iron phosphate positive electrode material.

[0051] Example 3

[0052] (1) After the waste lithium iron phosphate batteries are discharged, they are crushed, disassembled and sorted in sequence to obtain lithium iron phosphate powder.

[0053] (2) 1000 mL of a 30% hydrogen peroxide solution was added to 100 g of lithium iron phosphate powder, and CO2 gas was introduced. The pH value of the mixed solution was controlled at 4. The reaction was completed to obtain a mixed solution I.

[0054] (3) Determine the ratio of lithium, iron, and phosphorus elements in the mixed solution I, add lithium phosphate, iron sulfate, or ammonium phosphate, and add yttrium vanadate so that the molar ratio of lithium, iron, phosphorus, vanadium, and yttrium atoms is 1.1:1:1:0.03:0.01, then add 98 wt% concentrated sulfuric acid and adjust the pH value of the solution to 3 to obtain a mixed solution.

[0055] (4) Add β-cyclodextrin to the mixed solution under stirring. The amount of carbon source added is such that the carbon content in the final lithium iron phosphate product reaches 1.5%, and evaporate it by autothermal heating to obtain a precursor.

[0056] (5) Under nitrogen protection, the precursor is subjected to high-temperature sintering, the temperature is increased to 500°C at a heating rate of 5°C / min and the temperature is kept at this temperature for 3 hours, and the temperature is further increased to 750°C and the temperature is kept at this temperature for 4 hours to obtain a lithium iron phosphate positive electrode material.

[0057] Example 4

[0058] Preparation of methyl pivalate-O-sucrose:

[0059] Sucrose was dissolved in ethyl acetate, and then chloromethyl pivalate and triethylamine were added. The molar ratio of sucrose, chloromethyl pivalate and triethylamine was 1:1:1. The reaction was kept warm under reflux. After all the chloromethyl pivalate reacted, the reaction was stopped. The ethyl acetate was recovered by concentration under reduced pressure. The obtained concentrate was washed with ethanol, filtered and dried.

[0060] The sucrose in Example 2 was replaced with methyl pivalate-O-sucrose as the carbon source to obtain Example 4.

[0061] (1) After the waste lithium iron phosphate batteries are discharged, they are crushed, disassembled and sorted in sequence to obtain lithium iron phosphate powder.

[0062] (2) Add 2000 mL of 25% hydrogen peroxide solution to 100 g of lithium iron phosphate powder, introduce CO2 gas, control the pH value of the mixed solution to 5, and terminate the reaction to obtain mixed solution I.

[0063] (3) Determine the ratio of lithium, iron, and phosphorus elements in the mixed solution I, add lithium acetate, ferric nitrate, or ammonium dihydrogen phosphate, and add yttrium vanadate so that the molar ratio of lithium, iron, phosphorus, vanadium, and yttrium atoms is 1.05:1:1:0.04:0.02, then add 98 wt% concentrated sulfuric acid and adjust the pH value of the solution to 4 to obtain a mixed solution.

[0064] (4) adding methyl pivalate-O-sucrose to the mixed solution under stirring, wherein the amount of methyl pivalate-O-sucrose added is such that the carbon content in the final lithium iron phosphate product reaches 2%, and evaporating the mixture by autothermal heating to obtain a precursor.

[0065] (5) Under nitrogen protection, the precursor is subjected to high-temperature sintering, the temperature is increased to 550°C at a heating rate of 10°C / min and the temperature is kept at 550°C for 3 hours, and the temperature is further increased to 750°C and the temperature is kept at 750°C for 3 hours to obtain a lithium iron phosphate positive electrode material.

[0066] Button cells were assembled using the lithium iron phosphate cathode materials prepared in Examples 1-4 as the positive active material and a lithium metal sheet as the negative electrode. The cathode sheet consisted of the positive active material, acetylene black, and PVDF in a mass ratio of 80:10:10. Celgard 2400 membrane served as the separator, and 1 mol / L LiPF6 was used as the electrolyte (the solvent was ethylene carbonate and diethyl carbonate in a volume ratio of 1:1). Constant current charge and discharge tests were conducted at room temperature using a Shenzhen Xinwei battery testing system. The charge and discharge tests ranged from 2.5 to 4.2 V. The test results are shown in Table 1.

[0067] Table 1 Charge and discharge performance of lithium iron phosphate cathode materials

[0068]

[0069]

[0070] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for recycling and regenerating waste lithium iron phosphate battery cathode materials, characterized in that: The following steps are involved: (1) crushing, disassembling and sorting the waste lithium iron phosphate batteries after discharge treatment to obtain lithium iron phosphate powder; (2) adding a hydrogen peroxide solution to the lithium iron phosphate powder and introducing CO2 gas, controlling the pH value of the mixed solution to be between 3 and 5, and completing the reaction to obtain a mixed solution I; (3) determining the ratio of lithium, iron, and phosphorus in the mixed solution I, adding a lithium source, an iron source, or a phosphorus source, and adding yttrium vanadate so that the molar ratio of lithium, iron, phosphorus, vanadium, and yttrium atoms is (1.05-1.1):1:1:(0.01-0.05):(0.01-0.05), and then adding concentrated sulfuric acid to adjust the pH value of the solution to 2-4 to obtain a mixed solution; (4) adding a carbon source to the mixed solution under stirring, and evaporating the mixture by autothermal heating to obtain a precursor; (5) Under the protection of inert gas, the precursor is sintered at a high temperature to obtain a lithium iron phosphate positive electrode material; The carbon source is methyl pivalate-O-sucrose, and its preparation method is as follows: dissolving sucrose in ethyl acetate, then adding chloromethyl pivalate and triethylamine, keeping the temperature under reflux for reaction, stopping the reaction after all the chloromethyl pivalate reacts, concentrating under reduced pressure to recover the ethyl acetate, washing the obtained concentrate with ethanol, filtering, and drying.

2. The method for recycling and regenerating waste lithium iron phosphate battery positive electrode materials according to claim 1, characterized in that: The concentration of the hydrogen peroxide solution is 5-30%, and the amount of the hydrogen peroxide solution used is 5-20 mL per gram of lithium iron phosphate powder.

3. The method for recycling and regenerating waste lithium iron phosphate battery positive electrode materials according to claim 1, characterized in that: The lithium source is one or more of lithium carbonate, lithium oxide, lithium hydroxide, lithium acetate, lithium nitrate, lithium phosphate, and lithium oxalate.

4. The method for recycling and regenerating waste lithium iron phosphate battery cathode materials according to claim 1, characterized in that: The iron source is one or more of ferric sulfate, ferrous oxalate, ferrous nitrate, ferric chloride, ferric hydroxide, ferric nitrate, and ferric citrate.

5. The method for recycling and regenerating waste lithium iron phosphate battery cathode materials according to claim 1, characterized in that: The phosphorus source is one or more of phosphoric acid, ammonium dihydrogen phosphate, and ammonium phosphate.

6. The method for recycling and regenerating waste lithium iron phosphate battery cathode materials according to claim 1, characterized in that: The concentration of the concentrated sulfuric acid is 98 wt %, and the amount of the carbon source added is such that the carbon content in the final lithium iron phosphate product reaches 0.5-3%.

7. The method for recycling and regenerating waste lithium iron phosphate battery cathode materials according to claim 1, characterized in that: The inert gas is one of nitrogen, argon and helium.

8. The method for recycling and regenerating waste lithium iron phosphate battery cathode materials according to claim 1, characterized in that: The heating rate of the high-temperature sintering is 5-15°C / min, and the sintering temperature is 500-800°C.

9. Use of the lithium iron phosphate cathode material obtained according to any one of claims 1 to 8 in a lithium iron phosphate battery.

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