Method for recycling and repairing waste graphite

Abstract

The application provides a recycling, repairing and regenerating method of waste graphite, which comprises the following steps: recycling, classifying and roughly breaking the waste lithium ion battery, then sequentially performing supercritical CO2 electrolyte impurity removal, microwave stripping and impurity removal, ultrasonic crushing, liquid phase coating, spray drying, heat treatment and screening on the waste graphite powder to obtain the repaired graphite material. The application can deeply remove the metal impurities and organic impurities in the waste graphite, repair the defects on the surface of the waste graphite caused by aging by liquid phase coating alcohol substances, improve the high-temperature performance and cycle performance of the recycled graphite, and can achieve or even exceed the electrochemical performance effect of the conventional graphite.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of batteries, and relates to recovery of waste graphite, in particular to a recovery, repair and regeneration method of waste graphite. BACKGROUND

[0002] The lithium ion battery industry has entered a stage of rapid development, and the number of lithium batteries discarded every day is countless, so recycling and reuse have become an inevitable trend. However, due to the scarcity and high value of precious metal resources, the recovery benefit is large, so the current recovery hotspot mainly focuses on precious metals in lithium batteries, such as lithium, cobalt, nickel, etc. As an important component of lithium batteries, graphite accounts for about 70%-80% of the battery, but the overall graphite resources are not abundant in China, and high-grade graphite ore is even scarce. Therefore, recycling and reusing graphite materials not only can avoid the waste of graphite resources, but also can alleviate the situation of insufficient supply of graphite materials in the market to a certain extent.

[0003] Waste graphite has undergone various aging mechanisms, resulting in changes in the functional groups on the surface of the graphite and the structure of the graphite, especially the surface SEI film and the embedded solvent molecules, which change the properties of the graphite. Therefore, the current mainstream method for repairing the surface defects of graphite is to use heat treatment and wet coating, but the energy consumption is high, the recovery efficiency is low, and the purity of the graphite is low. Therefore, it is necessary to develop a new way to recycle and reuse the failed lithium ion battery negative graphite material to realize the recycling of graphite resources. SUMMARY

[0004] In view of the insufficient recovery of existing waste graphite, the purpose of the present application is to provide a recovery, repair and regeneration method of waste graphite of lithium ion batteries. The recovery, repair and regeneration method of the present application is simple to operate, and the prepared negative electrode material has excellent electrochemical performance, aiming to solve the problems of poor cycle performance and low capacity of the recovered graphite after the existing method. The method described in the present application can effectively repair the interface of the original waste graphite, and provide a migration path for lithium ions and solvent molecules of electrolyte. The capacity of the repaired graphite prepared by the recovery, repair and regeneration method of the waste graphite of the present application can be improved to (345-355) mAh / g, and has good high-temperature cycle performance.

[0005] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0006] The present application provides a recovery, repair and regeneration method of waste graphite, and the steps of the recovery, repair and regeneration method comprise:

[0007] 1) Recovery, classification and rough breaking to obtain negative electrode sheets;

[0008] 2) Breaking and screening: after washing and drying the negative electrode sheets obtained in step 1), the copper foil and graphite powder are mechanically broken and separated;

[0009] 3) Extracting electrolyte impurities, performing supercritical CO2 extraction on the graphite powder obtained in step 2) to obtain crude graphite;

[0010] 4) Microwave stripping and impurity removal: stirring the crude graphite obtained in step 3) with a solvent under ice bath, performing microwave stripping and impurity removal to obtain graphite;

[0011] 5) Ultrasonic crushing and liquid phase coating: adding the graphite obtained in step 4) into a solvent and adding a coating agent, performing ultrasonic crushing to obtain a suspension;

[0012] 6) Spray drying: performing spray drying on the suspension obtained in step 5) to obtain pure graphite;

[0013] 7) Heat treatment: performing heat treatment on the pure graphite obtained in step 6);

[0014] 8) Screening to obtain repaired graphite material.

[0015] As a preferred scheme of the present application, in step 1), the recovered and classified crude is subjected to complete discharge, and is soaked in brine for 1 h, and the positive electrode, negative electrode, separator and outer packaging are obtained by disassembling the battery.

[0016] As a preferred scheme of the present application, in step 2), the temperature of drying is 80℃, and the obtained graphite powder is removed from large particles through two layers of 150-200 mesh sieves.

[0017] As a preferred scheme of the present application, in step 3), the temperature of supercritical CO2 extraction is 10-25℃, and the pressure is 40Mpa.

[0018] As a preferred scheme of the present application, in step 4), the solid-liquid ratio of the crude graphite and the solvent is 1-5g:100mL, and the power of microwave stripping is 500w, and the time is 0.5h.

[0019] As a preferred scheme of the present application, in step 5), the solid-liquid ratio of the graphite and the solvent is 1g:5-10mL, and the added amount of the coating agent is 1-3% of the mass of the graphite, and the coating agent is a mixture of polyacrylonitrile and polyacrylic acid with a mass ratio of 1:1.

[0020] In the present application, the solvent for dissolving the graphite powder can be ethanol, ethylene glycol, dimethylformamide, sodium dodecyl sulfonate, ethylene glycol diacetate. The coating agent can be one or several of asphalt, polyacrylic acid and polyacrylonitrile.

[0021] Preferably, the present application uses ethanol as the solvent, and uses a mixture of polyacrylonitrile and polyacrylic acid with a mass ratio of 1:1 as the coating agent.

[0022] As a preferred scheme of the present application, in the step 6), the inlet temperature of the spray drying is 300 DEG C, the outlet temperature is 150 DEG C, and the feeding rate is 500 mL / h.

[0023] As a preferred scheme of the present application, in the step 7), the heat treatment is carried out in a nitrogen atmosphere, at 800 DEG C for 6 h, and after cooling, the temperature is increased to 1200 DEG C and maintained for 1 h.

[0024] As a preferred scheme of the present application, in the step 8), the screening is carried out by sequentially passing the heat-treated pure graphite through 2 layers of 200-mesh sieve and 1 layer of 325-mesh sieve.

[0025] Compared with the prior art, the present application has the following beneficial effects:

[0026] 1) The waste graphite recycling and repairing regeneration method provided by the present application completely removes impurities, is simple in process, and improves the utilization value of the recycled graphite. The regenerated graphite prepared by the method has good performance and is basically comparable to artificial graphite.

[0027] 2) The present application can deeply remove metal impurities and organic impurities in waste graphite, and the liquid phase coating of alcohol substances repairs the defects on the surface of waste graphite due to aging, improves the high-temperature performance and cycle performance of the recycled graphite, and can achieve or even exceed the electrochemical performance effect of conventional graphite. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is a flow chart of the present application.

[0029] Figure 2 is a cycle curve diagram of the present application. DETAILED DESCRIPTION

[0030] In order to make the technical means, creative features, purposes and effects of the present application easy to understand, the present application is further described below in combination with specific embodiments, but the following embodiments are only preferred embodiments of the present application, not all. Based on the embodiments in the embodiments, other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application. In the following examples, the experimental methods are conventional methods, and the materials, reagents, etc. used in the following examples are commercially available unless otherwise specified.

[0031] Reference is made to Figure 1The application provides a recycling, repairing and regenerating method of waste graphite, which comprises the following steps of recycling, classifying and roughly breaking the waste lithium ion battery, and then sequentially performing supercritical CO2 electrolyte impurity removal, microwave stripping and impurity removal, ultrasonic crushing, liquid phase coating, spray drying, heat treatment and screening on the waste graphite powder to prepare the repaired graphite material.

[0032] Example 1

[0033] The application provides a recycling, repairing and regenerating method of waste graphite, which comprises the following steps of recycling, classifying and roughly breaking the waste lithium ion battery, and then sequentially performing supercritical CO2 electrolyte impurity removal, microwave stripping and impurity removal, ultrasonic crushing, liquid phase coating, spray drying, heat treatment and screening on the waste graphite powder to prepare the repaired graphite material.

[0034] Step 1: recycling, classifying and roughly breaking

[0035] The recycled waste lithium ion battery is completely discharged and soaked in salt water for 1 h. After the battery is disassembled, it is divided into positive and negative electrodes, a diaphragm and an outer package.

[0036] Step 2: crushing and screening

[0037] The negative electrode sheet obtained in step 1 is washed with deionized water for multiple times, dried at 80 DEG C, mechanically crushed to separate copper foil and graphite powder, and the powder is removed through two layers of 150-200 mesh screen to remove large particles.

[0038] Step 3: extracting electrolyte impurities

[0039] The powder obtained in step 2 is transferred to a supercritical CO2 extraction device, a suitable temperature (10-25) DEG C is set, CO2 is added to change the pressure in the instrument to 40 Mpa, electrolyte impurities in the powder are extracted, and coarse graphite is obtained.

[0040] Step 4: microwave stripping and impurity removal

[0041] (1-5) g of the coarse graphite obtained in step 3 is added to 100 mL of a solvent for dissolving graphite powder, the solvent used is ethanol, and the mixture is stirred in an ice bath at-10 DEG C for 1 h. The mixture is placed in a 500 W microwave oven for 0.5 h, and cooled to room temperature.

[0042] Step 5: ultrasonic crushing and liquid phase coating

[0043] The graphite obtained in step 4 is placed in a beaker, a solvent is added according to a ratio of 1: (5-10), and (1-3) % of a coating agent is added, the coating agent used is a mixture of polyacrylonitrile and polyacrylic acid with a mass ratio of 1:1, and the mixture is placed in an ultrasonic crusher for 2 h to form a suspension.

[0044] Step 6: spray drying

[0045] The suspension obtained in step 5 was charged into a dryer, and the inlet / outlet temperature was set to 300 °C / 150 °C, and the feeding rate was 500 mL / h. After spraying, the pure graphite was obtained by drying.

[0046] Step 7: heat treatment

[0047] The pure graphite obtained in step 6 was put into a tube furnace, filled with N2, and heated at 800 °C for 6 h. After cooling, the temperature was continued to rise to 1200 °C for 1 h.

[0048] Step 8: sieving

[0049] The graphite obtained in step 7 was sequentially passed through 2 layers of 200 mesh sieves and 1 layer of 325 mesh sieves, and the final repaired graphite material was obtained.

[0050] Example 2

[0051] Different from example 1: the method for extracting electrolyte impurities in step 3 is subcritical CO2 extraction, and the others are the same as example 1.

[0052] Example 3

[0053] Different from example 1: step 3 is the same as example 1, step 4 is removed, and the others are the same as example 1.

[0054] Example 4

[0055] Different from example 1: step 3 is the same as example 1, step 4 is retained, the mass ratio of the coating agent in step 5 is (5-10)%, and the others are the same as example 1.

[0056] Comparative example 1

[0057] Steps 1-6 are the same as example 1.

[0058] Step 7: heat treatment

[0059] The pure graphite obtained in step 6 was put into a tube furnace, filled with air, and heated at 800 °C for 6 h. After cooling, the temperature was continued to rise to 1200 °C for 1 h.

[0060] Step 8 is the same as example 1.

[0061] Comparative example 2

[0062] Steps 1-6 are the same as example 1.

[0063] Step 7: heat treatment

[0064] The pure graphite obtained in step 6 was put into a tube furnace, filled with N2, and heated at 500 °C for 6 h. After cooling, the temperature was continued to rise to 1500 °C for 1 h.

[0065] Step 8 is the same as Example 1.

[0066] The graphites obtained in the above four examples and two comparative examples were assembled into button cells, and then subjected to capacity test and cycle test, the process route map of the graphite recovery repair of Example 1 is shown in Figure 1 , the capacity data are shown in the following table, and the cycle curve is shown in Figure 2 .

[0067]

[0068]

[0069] As can be seen from the graph, the impurity removal method and coating method used in the four examples can significantly improve the capacity and initial efficiency of the repaired waste graphite negative electrode, which means that the impurities and surface defects of the waste graphite have been greatly improved in the repair process, especially the graphite performance of Example One after multiple impurity removal has been restored according to the cycle curve.

[0070] The above is only the preferred embodiment of the present application, and is not any form and substantial limitation of the present application. It should be pointed out that for ordinary skilled persons in the art, some improvements and supplements can be made without departing from the method of the present application, and these improvements and supplements should also be regarded as the protection scope of the present application. For those skilled in the art, some minor changes, modifications and equivalent changes made by using the disclosed technical content without departing from the spirit and scope of the present application are equivalent embodiments of the present application; at the same time, any equivalent changes, modifications and evolution of the above examples according to the essential technology of the present application are still within the scope of the technical solutions of the present application.

Claims

1. A method for recycling, repairing and regenerating waste graphite, characterized by, The steps of the recycling repair regeneration method include: 1) recycling classification rough breaking, obtaining negative electrode sheets; 2) breaking and screening: after washing and drying the negative electrode sheets obtained in step 1), the copper foil and graphite powder are separated by mechanical breaking; 3) extracting electrolyte impurities: the graphite powder obtained in step 2) is subjected to supercritical CO2 extraction, obtaining crude graphite; the temperature of supercritical CO2 extraction is 10-25℃, and the pressure is 40Mpa; 4) microwave stripping and impurity removal: the crude graphite obtained in step 3) is mixed with a solvent and stirred under ice bath, and impurities are removed by microwave stripping, obtaining graphite; the solid-liquid ratio of crude graphite and solvent is 1-5g:100mL, the power of microwave stripping is 500w, and the time is 0.5h; 5) ultrasonic crushing and liquid coating: the graphite obtained in step 4) is added to a solvent and a coating agent, and ultrasonic crushing is performed, obtaining a suspension; the solid-liquid ratio of graphite and solvent is 1g:5-10mL, the amount of coating agent added is 1-3% of the mass of graphite, and the coating agent is a mixture of polyacrylonitrile and polyacrylic acid with a mass ratio of 1:1; the solvent is ethanol; 6) spray drying: the suspension obtained in step 5) is subjected to spray drying, obtaining pure graphite; the inlet temperature of spray drying is 300℃, the outlet temperature is 150℃, and the feeding rate is 500mL / h; 7) heat treatment: the pure graphite obtained in step 6) is heated and kept warm; the heat treatment is carried out in a nitrogen atmosphere, at 800℃ for 6h, and after cooling, the temperature is increased to 1200℃ and kept for 1h; 8) screening, obtaining repaired graphite material.

2. The method for recycling and repairing waste graphite according to claim 1, characterized in that, In step 1), the recycling classification rough breaking is to completely discharge the recycled waste lithium ion battery, soak in salt water for 1h, disassemble the battery to obtain the positive electrode, negative electrode, separator and outer packaging.

3. The method for recycling and repairing waste graphite according to claim 1, characterized in that, In step 2), the drying temperature is 80℃, and the obtained graphite powder is passed through two layers of 150-200 mesh screen to remove large particles.

4. The method for recycling and repairing waste graphite according to claim 1, characterized in that, In step 8), the screening is to pass the pure graphite after heat treatment through 2 layers of 200 mesh screen and 1 layer of 325 mesh screen in sequence.

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