Method for comprehensively utilizing PVDF (Polyvinylidene Fluoride) binder waste

Abstract

The invention provides a method for comprehensively utilizing PVDF binder waste, and belongs to the technical field of chemical engineering, the method for comprehensively utilizing the PVDF binder waste comprises the following steps: performing solvothermal reaction on a PVDF binder, an organic solvent and hydroxide, separating to obtain an organic phase and slurry, and filtering, washing and drying the slurry to obtain fluoride; and removing the organic solvent in the organic phase, and calcining the residual residue to obtain the hard carbon negative electrode material. According to the method, fluorine in the PVDF binder waste is converted into inorganic fluoride, carbon is converted into a hard carbon negative electrode material, efficient utilization of resources is achieved, the method has the advantages that the process is in closed cycle, secondary pollution is avoided and the like, and the green and clean production requirement is met.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical engineering, and in particular relates to a method for comprehensive utilization of PVDF binder waste. Background Art

[0002] PVDF (polyvinylidene fluoride) is a high-performance polymer material with excellent chemical resistance, heat resistance and mechanical properties, and is often used as a binder for new energy batteries. At present, the number of retired power batteries in my country is on the eve of explosive growth. Data released at the 2024 New Energy Battery Recycling Conference showed that the cumulative retirement volume of power and reserve batteries in my country will exceed 3 million tons in 2030, and the recycling industry of used batteries will face huge challenges.

[0003] However, the existing technology for recycling lithium batteries is mostly for the recycling of valuable metals, aluminum foil, negative electrodes and other materials, while PVDF binders are mostly decomposed by high-temperature calcination, producing a large amount of fluorine-containing gas, causing secondary pollution to the environment, and also seriously wasting fluorine and carbon resources. Although a variety of methods have been published to extract and recycle PVDF binders from waste batteries, there are no reasonable measures to fully reuse PVDF binders. Therefore, it is urgent to develop green and high-value recycling processes to maximize the utilization of PVDF binder resources and achieve clean production. Summary of the invention

[0004] The purpose of the present invention is to provide a method for comprehensive utilization of PVDF binder waste, so as to solve the problem that green and high-value utilization of PVDF binder cannot be achieved in the prior art.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is: A method for comprehensive utilization of PVDF binder waste, comprising: S1. Solvothermally reacting a PVDF binder with an organic solvent and an alkali metal or alkaline earth metal hydroxide solution to separate an organic phase and a slurry, filtering, washing and drying the slurry to obtain a fluoride; S2. The organic solvent in the organic phase is removed, and the remaining residue is calcined to obtain a hard carbon negative electrode material.

[0006] The present invention is a pioneering invention, which converts fluorine in the PVDF binder into inorganic fluoride and carbon into hard carbon negative electrode material, thereby achieving efficient resource utilization, having the advantages of closed-loop process and no secondary pollution, and meeting the requirements of green and clean production.

[0007] Preferably, the filtrate washed in step S1 is recovered and used to prepare the hydroxide solution, the organic solvent removed in step S2 is recovered and recycled, and the tail gas from the calcination is absorbed by alkaline solution and then discharged, so as to achieve efficient utilization of resources and meet the requirements of green and clean production.

[0008] Preferably, the hydroxide solution includes one or more of a sodium hydroxide solution, a lithium hydroxide solution, and a barium hydroxide solution, which can accelerate the efficient separation of fluorocarbon resources in PVDF under strong alkaline conditions.

[0009] Further preferably, the mass of the hydroxide in the hydroxide solution is 2-5 times the mass of the PVDF binder, and the concentration of the hydroxide solution is 20-40%.

[0010] Preferably, the organic solvent is one or more of benzene, toluene, xylene, cyclohexanol and carbon tetrachloride.

[0011] Further preferably, the mass of the organic solvent is 1-3 times the mass of the PVDF binder.

[0012] Preferably, the reaction temperature of the solvent thermal reaction is 100-300° C., and the reaction time is 2-5 h. Under high temperature conditions, the efficient separation of fluorocarbon resources in PVDF can be accelerated.

[0013] Preferably, the calcination is carried out under an inert gas, the calcination temperature is 1200-1500° C., the treatment time is 2-6 hours, and the hard carbon negative electrode material is prepared, and the heating rate is preferably 5-10° C. / min.

[0014] Preferably, the method for removing the organic solvent comprises vacuum distillation, the vacuum distillation temperature is 60-140° C., the distillation pressure is -0.08 to -0.09 MPa, and the organic solvent discharged during the vacuum distillation is recovered and recycled. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a process flow chart of an embodiment of the present invention; Figure 2 This is a SEM photo of the hard carbon material obtained in Example 1 of the present invention; Figure 3 This is the first charge and discharge curve of the hard carbon material obtained in Example 1 of the present invention; Figure 4 This is the first charge and discharge curve of the hard carbon material obtained in Example 2 of the present invention; Figure 5 This is the first charge and discharge curve of the hard carbon material obtained in Example 3 of the present invention; Figure 6 This is the first charge and discharge curve of the hard carbon material obtained in Example 4 of the present invention; Figure 7 This is the first charge and discharge curve of the hard carbon material obtained in Example 5 of the present invention. DETAILED DESCRIPTION

[0016] The present invention mainly aims at the problem that the PVDF binder is usually directly calcined and decomposed at high temperature in the prior art, which not only pollutes the environment, but also cannot be recycled to obtain valuable products. The technical route of the present invention is as follows: Figure 1 As shown, by converting the fluorine in the PVDF binder into fluoride, the carbon is converted into a hard carbon negative electrode material, and the intermediate product can be effectively recovered and re-enter the process cycle, and the tail gas is discharged after being absorbed by alkaline solution. This method has the advantages of efficient resource utilization and green and clean production.

[0017] The technical solution of the present invention is further described below in conjunction with specific embodiments. The following % means mass % unless otherwise specified.

[0018] The method for obtaining PVDF binder waste is as follows: the battery is disassembled to obtain the electric chip, which is cut into small pieces. The pieces are then added into an organic solvent and stirred to dissolve. The positive electrode material and the filtrate are filtered to obtain the positive electrode material and the filtrate. Water is added to the filtrate, and the PVDF waste is obtained by precipitation, filtration and drying. The fluorine content in the PVDF waste is 59.35%, and the carbon content is 37.42%.

[0019] 1. Specific embodiments of the present invention Example 1 A method for comprehensive utilization of PVDF binder waste, the method specifically comprising the following steps: 1) Weigh 10 g of PVDF binder waste and add it into a high-pressure reactor, add 30 g of cyclohexanol and 100 g of 20% sodium hydroxide solution, control the temperature at 200°C, continue the solvent thermal reaction for 2 hours, and the reaction filling degree is 70%. Then cool it to room temperature, separate the organic phase, filter, wash and dry the obtained slurry to obtain 12 g of sodium fluoride with a purity of 98.65%. The fluorine recovery rate is 90.2% (the mass of fluorine element in sodium fluoride / the mass of fluorine element in PVDF waste × 100%), and return the filtrate to prepare the sodium hydroxide solution.

[0020] 2) The organic phase was subjected to reduced pressure distillation, the distillation temperature was controlled at 138°C, the distillation pressure was -0.08MPa, the discharged cyclohexanol was recovered and recycled, the residue was placed in a tubular furnace, the temperature was raised to 1500°C at a heating rate of 10°C / min, and calcined for 2h under nitrogen atmosphere to obtain 1.73g of hard carbon negative electrode material, the carbon recovery rate was 46.3% (mass of hard carbon negative electrode material / mass of carbon element in PVDF waste × 100%), and the calcination tail gas was discharged after absorption by alkali solution.

[0021] The SEM photo of the prepared hard carbon negative electrode material is shown in Figure 2 As shown, from Figure 2 It can be seen that the obtained hard carbon material particles have a smooth surface, fewer pores, irregular morphology, uniform overall distribution of particles, and a particle size of about 5~10μm, which can provide good compaction density and sodium storage sites.

[0022] Example 2 A method for comprehensive utilization of PVDF binder waste, the method specifically comprising the following steps: 1) Weigh 20 g of PVDF binder and add it into a high-pressure reactor, add 20 g of benzene and 333 g of 30% lithium hydroxide solution, control the temperature at 300°C, continue the solvent thermal reaction for 3 hours, and the reaction filling degree is 55%. Then cool to room temperature, separate the organic phase, filter, wash and dry the obtained slurry to obtain 15.3 g of lithium fluoride with a purity of 98.37% and a fluorine recovery rate of 92.6%. The filtrate is returned to prepare the lithium hydroxide solution.

[0023] 2) The organic phase was subjected to reduced pressure distillation, and the distillation temperature was controlled at 68°C and the distillation pressure was -0.085MPa. The discharged benzene was recovered and recycled. The residue was placed in a tubular furnace and heated to 1300°C at a heating rate of 5°C / min. It was calcined for 4 hours under nitrogen atmosphere to obtain 3.61g of hard carbon negative electrode material (carbon recovery rate was 48.2%). The calcination tail gas was absorbed by alkaline solution and then discharged.

[0024] Example 3 A method for comprehensive utilization of PVDF binder waste, the method specifically comprising the following steps: 1) Weigh 15 g of PVDF binder and add it into a hydrothermal autoclave, add 22.5 g of carbon tetrachloride and 150 g of 40% sodium hydroxide solution, control the temperature at 100 °C, continue the solvent thermal reaction for 5 h, and the reaction filling degree is 50%, then cool to room temperature, separate the organic phase, filter, wash and dry the obtained slurry to obtain 18.63 g of sodium fluoride with a purity of 98.56% and a fluorine recovery rate of 93.3%. The filtrate is returned to prepare the sodium hydroxide solution.

[0025] 2) The organic phase was subjected to reduced pressure distillation, the distillation temperature was controlled at 65°C, the distillation pressure was -0.09MPa, the discharged carbon tetrachloride was recovered and recycled, the residue was placed in a tubular furnace, the temperature was raised to 1200°C at a heating rate of 8°C / min, and calcined for 6 hours under nitrogen atmosphere to obtain 2.78g of hard carbon negative electrode material (carbon recovery rate was 49.6%), and the calcination tail gas was absorbed by alkali solution and then discharged.

[0026] Example 4 A method for comprehensive utilization of PVDF binder waste, the method specifically comprising the following steps: 1) Weigh 25 g of PVDF binder and add it into a hydrothermal autoclave, add 62.5 g of xylene and 191.6 g of 30% sodium hydroxide solution, control the temperature at 150°C, continue the solvent thermal reaction for 4.5 h, and the reaction filling degree is 55%. Then cool it to room temperature, separate the organic phase, filter the obtained slurry, wash and dry it to obtain 30.59 g of sodium fluoride with a purity of 98.72% and a fluorine recovery rate of 92.1%. The filtrate is returned to prepare the sodium hydroxide solution.

[0027] 2) The organic phase was subjected to reduced pressure distillation, and the distillation temperature was controlled at 126°C and the distillation pressure was -0.083MPa. The discharged xylene was recovered and recycled. The residue was placed in a tubular furnace and heated to 1400°C at a heating rate of 10°C / min. It was calcined for 5 hours under nitrogen atmosphere to obtain 4.48g of hard carbon negative electrode material (carbon recovery rate was 47.9%). The calcination tail gas was absorbed by alkali solution and then discharged.

[0028] Example 5 A method for comprehensive utilization of PVDF binder waste, the method specifically comprising the following steps: 1) Weigh 18 g of PVDF binder and add it into a hydrothermal autoclave, add 32.5 g of toluene and 242.6 g of 23% barium hydroxide solution, control the temperature at 220°C, continue the solvent thermal reaction for 3.5 h, and the reaction filling degree is 65%. Then cool it to room temperature, separate the organic phase, filter the obtained slurry, wash and dry it to obtain 46.59 g of barium fluoride with a purity of 98.59% and a fluorine recovery rate of 93.2%. The filtrate is returned to prepare the barium hydroxide solution.

[0029] 2) The organic phase was subjected to reduced pressure distillation, and the distillation temperature was controlled at 96°C and the distillation pressure was -0.09MPa. The discharged toluene was recovered and recycled. The residue was placed in a tubular furnace and heated to 1450°C at a heating rate of 7°C / min. It was calcined for 5 hours under nitrogen atmosphere to obtain 3.29g of hard carbon negative electrode material (carbon recovery rate was 48.8%). The calcination tail gas was absorbed by alkali solution and then discharged.

[0030] Experimental Example 1 The sodium storage performance of the hard carbon negative electrode materials prepared in Examples 1-5 of the present invention was evaluated by button cells, and the evaluation specifically included the following steps: The electrode slurry is prepared in a mass ratio of hard carbon negative electrode material: conductive agent SP: PVDF binder = 90:5:5. An appropriate amount of N-methylpyrrolidone methanol NMP is added to prepare a slurry, and the coating thickness is 200 μm. After drying and rolling, the electrode is made into a pole piece. Sodium metal is used as the counter electrode, 1 mol / L NaPF6 propylene carbonate PC / diethyl carbonate DEC / ethylene carbonate EC (mass ratio 1:1:1) solution is used as the electrolyte, and a glass fiber filter paper membrane GF / C is used as the diaphragm to assemble a 2032 button battery. The charge and discharge performance is tested at a current density of 0.1C and 20 mA / g. The first charge and discharge curves of the button battery based on the hard carbon negative electrode material of Examples 1 to 5 are as follows: Figure 3-7As shown, red is the charging curve, i.e., the sodium removal process, and blue is the discharge curve, i.e., the sodium insertion process. The first-cycle coulomb efficiency = the first-cycle charging specific capacity / the first-cycle discharge specific capacity. After calculation, the reversible specific capacities of the button cells prepared using the hard carbon negative electrode materials of Examples 1-5 are 290.32 mAh / g, 269.78 mAh / g, 277.63 mAh / g, 311.50 mAh / g, and 292.46 mAh / g, respectively; the first-cycle coulomb efficiencies are 77.63%, 76.16%, 81.25%, 81.01%, and 81.31%, respectively, indicating that the battery material can remain stable in the first cycle, and the hard carbon negative electrode material prepared by the present invention has good sodium storage performance.

Claims

1. A method for comprehensive utilization of PVDF binder waste, characterized in that: include: S1. Solvothermally reacting a PVDF binder with an organic solvent and an alkali metal or alkaline earth metal hydroxide solution to separate an organic phase and a slurry, filtering, washing, and drying the slurry to obtain a fluoride; S2. removing the organic solvent in the organic phase, and calcining the remaining residue to obtain a hard carbon negative electrode material.

2. The method for comprehensive utilization of PVDF binder waste according to claim 1, characterized in that: The filtrate washed in step S1 is recovered and used to prepare the hydroxide solution, the organic solvent removed in step S2 is recovered and recycled, and the tail gas from the calcination is absorbed by alkaline solution and then discharged.

3. The method for comprehensive utilization of PVDF binder waste according to claim 1 or 2, characterized in that: The hydroxide solution includes one or more of a sodium hydroxide solution, a lithium hydroxide solution, and a barium hydroxide solution.

4. The method for comprehensive utilization of PVDF binder waste according to claim 3, characterized in that: The mass of the hydroxide in the hydroxide solution is 2-5 times the mass of the PVDF binder, and the concentration of the hydroxide solution is 20-40%.

5. The method for comprehensive utilization of PVDF binder waste according to claim 1 or 2, characterized in that: The organic solvent is one or more of benzene, toluene, xylene, cyclohexanol and carbon tetrachloride.

6. The method for comprehensive utilization of PVDF binder waste according to claim 5, characterized in that: The mass of the organic solvent is 1-3 times the mass of the PVDF binder.

7. The method for comprehensive utilization of PVDF binder waste according to claim 1, characterized in that: The reaction temperature of the solvent thermal reaction is 100-300° C., and the reaction time is 2-5 hours.

8. The method for comprehensive utilization of PVDF binder waste according to claim 1, characterized in that: The calcination is carried out under inert gas, the calcination temperature is 1200-1500° C., and the treatment time is 2-6 hours.

9. The method for comprehensive utilization of PVDF binder waste according to claim 1, characterized in that: The method for removing the organic solvent includes vacuum distillation, wherein the vacuum distillation temperature is 60-140° C. and the distillation pressure is -0.08 to -0.09 MPa.

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