Wet regeneration method of waste lithium battery cathode graphite

Abstract

The invention belongs to the field of lithium battery regeneration treatment, and discloses a regeneration treatment method for a graphite-containing waste pole piece in a waste lithium battery. According to the method, the separation and regeneration of the graphite in the waste lithium battery sheets are realized through the steps of mechanical separation, freezing powder removal, water washing powder removal, oxidation pickling, reverse water washing, drying demagnetization and the like. Clean and complete graphite and copper foil separation is achieved through the cold brittleness difference of different substances at the low temperature, the recovery efficiency is high, and graphite and copper foil are completely stored. The positive ions in the acid liquor are treated by an ion exchange method, so that the replacement efficiency of a wet regeneration link is higher, the reuse rate of the acid liquor is improved, the cost is saved, and the pollutant emission is reduced.

Description

Technical Field

[0001] The invention belongs to the field of lithium battery recycling and processing, and relates to a resource technology for waste lithium battery negative electrode graphite materials, in particular to a recycling method for waste negative electrode sheets containing graphite in waste lithium batteries and negative electrode sheet waste and scraps containing graphite in battery production. Background Art

[0002] With the rapid development of the lithium battery field, the number of lithium batteries produced has exploded. As the service life of lithium batteries is consumed, more and more waste lithium batteries need to be processed. Among the related wastes generated by waste lithium batteries, the negative electrode graphite material is difficult to restore to the level of artificial graphite, the raw material of lithium batteries, after being regenerated by existing technologies, and cannot be used for the manufacture of new batteries of the same quality. The main reasons include that the existing mainstream lithium battery graphite regeneration methods are physical method, high temperature method and wet method. Among them, the physical method of graphite regeneration cannot effectively remove impurities mixed in it, including Al, Ni, Co, Mn, Fe, Li, Cu and other elements. Although high temperature treatment can remove impurities, the production cost is too high and cannot be used on a large scale. Wet treatment technology is used on a large scale in the regeneration of positive electrode materials, with a high degree of technical acceptance, which can solve the problem of high impurity content in the recycled materials to a certain extent, but there are problems such as low resource utilization rate of recycled elements, high acid consumption and serious pollution.

[0003] In view of the above problems, it is urgent to develop a new wet regeneration treatment method to solve the problems of low resource utilization rate and high acid consumption, improve product performance, reduce regeneration costs, and achieve higher value resource utilization of waste. Summary of the invention

[0004] In view of the above problems, the purpose of the present invention is to overcome the shortcomings of the prior art, provide a method for wet regeneration of negative electrode graphite of waste lithium batteries, improve the quality of recycled resources, and meet the needs of high-value resource utilization of waste materials.

[0005] The invention discloses a method for wet regeneration of graphite from negative electrodes of waste lithium batteries, which is used for regenerating waste negative electrode sheets containing graphite in waste lithium batteries and negative electrode sheet waste and scraps containing graphite in battery production, and comprises the following steps:

[0006] (1) Open the waste lithium battery cell, volatilize the electrolyte by low-temperature heat treatment, and remove the negative electrode sheet from the cell;

[0007] (2) The negative electrode sheet is sent to a freezing de-powdering machine for de-powdering treatment. Liquid nitrogen is used to cool the material in the equipment. Then, the graphite powder and copper foil in the electrode sheet are separated by mechanical separation. Primary graphite powder is obtained by screening.

[0008] (3) The primary graphite powder is sent to an oxidative pickling device for treatment, an oxidizing acid solution is formed by mixing an oxidant and an acid solution in a certain ratio, and the graphite powder is soaked and stirred. After a certain period of time, the suspension is filtered to obtain the pickled graphite powder. The filtered liquid is passed through an acid treatment system to remove cationic solutes and suspended matter in the acid, and then returned to the pickling device for reuse;

[0009] (4) The acid-washed graphite powder is subjected to multi-stage reverse water washing to remove residual acid until the pH value of the washing liquid is restored to 6.5-7.0, and then filtered, dried, and demagnetized to form the final product graphite powder.

[0010] Furthermore, step (1) of the method may be composed of the following steps:

[0011] (a) Open the waste lithium battery cells by mechanical cutting under an inert atmosphere so that the gas in the cells can be discharged, and the size of the incision is sufficient to remove the electrode;

[0012] (b) heat treating the opened battery cell at 100-200° C. in an inert atmosphere to volatilize the electrolyte in the battery cell, and sending the generated waste gas to a combustion chamber for treatment. After the exhaust gas meets the emission standards, the battery cell is sent to the next step of treatment;

[0013] (c) Take out the electrodes from the battery cell and separate the positive electrode, negative electrode and separator.

[0014] Furthermore, the following steps may be added between step (2) and step (3) of the method:

[0015] (a) sending the copper foil after freeze de-powdering to a water-washing de-powdering machine for secondary de-powdering treatment, soaking the copper foil in pure water, using stirring and ultrasonic cleaning to make the residual graphite powder fall off the copper foil, filtering the suspension to separate the washed primary graphite powder, and carrying out subsequent treatment steps together with the primary graphite powder formed by freeze de-powdering;

[0016] (b) The liquid after water washing and de-powdering is filtered and then goes through a circulating water treatment process to remove solutes and suspended solids in the water, and the clear liquid is returned to the water washing and de-powdering machine for reuse;

[0017] Furthermore, the acid solution treatment system in step (3) of the method comprises the following steps:

[0018] (a) using a strong acid cation exchange resin to absorb dissolved cations in the acid solution after filtering out the graphite powder, and then replenishing the acid solution and the oxidant to the initial level according to the pH value of the treated liquid;

[0019] (b) The cation exchange resin after absorption is regenerated, and the metal ions are released into the regeneration liquid for further resource treatment, and the regenerated cation exchange resin is recycled.

[0020] Furthermore, the rapid freezing and de-powdering machine includes a pre-cooling chamber and a mechanical separation chamber. Liquid nitrogen can be introduced into the pre-cooling chamber at a controlled flow rate, and the flow rate is adjusted according to the temperature monitoring value to control the cooling rate. After the temperature is kept constant at -60 to -150°C for a period of time, it is transported to the mechanical separation chamber for de-powdering operation. The mechanical separation methods include one or more of vibration, friction, and striking.

[0021] Furthermore, the multi-stage reverse water washing described in step (4) includes at least one stage, each stage includes a container with four interfaces of feed, discharge, water inlet and water outlet. The material to be washed is mixed and maintained in the container for a certain period of time. The initial material to be processed is fed into the feed port of the first-stage container, the discharge of each stage enters the feed port of the next stage, the last stage discharges the processed material, the water inlet of the last stage is supplemented with deionized water, the drainage of each stage enters the water inlet of the previous stage, and the drainage of the first stage is used as supplementary water for the pickling system.

[0022] Furthermore, the waste lithium battery is a ternary or quaternary lithium battery, a lithium iron phosphate battery, a lithium cobalt oxide battery; or a square lithium battery, a soft-pack lithium battery or a cylindrical lithium battery; or a battery cell after the shell is cut.

[0023] The advantages and positive effects achieved by the present invention are:

[0024] 1. This method provides a combined process for the regeneration of negative electrode materials of waste lithium batteries, which has higher product purity and less pollutant emissions compared to existing technologies.

[0025] 2. This method adopts the method of freezing de-powdering, which solves the problem of copper foil and graphite powder being difficult to separate after being crushed in the existing de-powdering method, reduces the introduction of impurities, improves the recovery purity of graphite powder, reduces impurities for subsequent treatment, and enables low-concentration treatment methods to be applied in this field. Frozen de-powdering also has the advantages of low mechanical equipment failure rate and no pollution;

[0026] 3. This method adopts a combined process of physical de-powdering and ion exchange wet regeneration, which reduces the concentration of metal ions entering the wet regeneration process, makes the replacement efficiency of the wet regeneration process higher, improves the acid reuse rate, saves costs, and reduces pollutant emissions; BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The present invention is a flowchart of the present invention.

[0028] Figure 2 This is a flowchart of a reverse water washing process as described in claim 6 of the present invention. DETAILED DESCRIPTION

[0029] The present invention will be further described below in conjunction with the embodiments. The following embodiments are descriptive rather than restrictive, and the protection scope of the present invention cannot be limited by the following embodiments.

[0030] The various commonly used technical means involved in the specific embodiments are all conventional technologies in the field. For the parts not specially annotated in this document, ordinary technicians in this field can implement them by referring to various commonly used reference books, scientific and technological literature or related instructions, manuals, etc. before the filing date of this invention.

[0031] Example 1

[0032] Step 1: Under an inert atmosphere, use a cutting device to cut off the top cover of the waste ternary square battery shell, so that the electrolyte and the electrode inside the battery are connected to the external environment;

[0033] Step 2: Heat treat the opened battery cell at 100-200℃ in an inert atmosphere to volatilize the electrolyte in the battery cell. Force convection of the airflow inside the heat treatment device to maintain ventilation and exhaust. The insulation time is determined according to the discharge of volatile gases until the concentration of volatile gases detected is lower than the set value. The pyrolysis treatment is completed, and the exhaust gas discharged from the device is sent to the secondary combustion chamber for combustion treatment. The exhaust gas meets the emission standards, and the battery cell is sent to the next step of treatment;

[0034] Step 3: Take out the inner core of the battery cell and separate the positive electrode sheet, negative electrode sheet and separator;

[0035] Step 4: Send the negative electrode sheet to a rapid freezing de-powdering machine for de-powdering treatment, place the electrode sheet in a pre-cooling chamber, introduce liquid nitrogen according to a ratio of liquid nitrogen mass to electrode mass of 1-3, control the liquid nitrogen flow rate according to temperature detection feedback, and keep it at a constant temperature of -120°C for 5-15 minutes according to the quality of the electrode sheet, and transport it to a mechanical separation chamber for de-powdering operation. After passing through a vibrating screen, the graphite powder and copper foil in the electrode sheet are separated, and frozen primary graphite powder is obtained by screening;

[0036] Step 5: Place the copper foil after freezing and de-powdering in a water-washing de-powdering machine for secondary de-powdering. Soak the copper foil in pure water for 1-2 hours. The container is a round tank with a top-entry agitator. Insert ultrasonic vibrators at intervals of 50 cm in the container and input ultrasonic waves at a frequency of 20kHz. Ultrasonic de-powdering takes 10-20 minutes to make the graphite powder adhering to the copper foil fall off into the solution, and then filter to obtain washed primary graphite powder. The liquid after water-washing and de-powdering is treated with circulating water to remove solutes and suspended matter in the water. The clear liquid is returned to the water-washing de-powdering machine for reuse. Suspended matter is removed by forced precipitation and filtration, and lithium ions in the solution are extracted using existing technology.

[0037] Step 6: The two primary graphite powders are sent to an oxidative pickling device for treatment, and hydrogen peroxide is used as an oxidant and sulfuric acid is used as an acid solution in a ratio of 1:10 as an oxidizing acid solution. The graphite powder is immersed and stirred, and stirring is maintained in the reaction equipment to prevent the graphite powder from precipitating. The reaction time is greater than 30 minutes, and the suspension is discharged and filtered to obtain the pickled graphite powder;

[0038] Step 7: After filtering and removing the graphite powder, the acid solution is subjected to absorption of dissolved cations in the acid solution by a strong acid cation exchange resin, and the acid solution is passed into a strong acid cation exchange resin reactor. Two reactors are provided, one for operation and one for standby. Sulfuric acid and an oxidant are added to the acid solution after the ion exchange until the pH value is less than 2;

[0039] Step 8: Regenerate the absorbed cation exchange resin using 3-4% sulfuric acid. The metal ions are released into the regeneration liquid for further resource recovery and regeneration. The regenerated cation exchange resin is reused. The filtered liquid passes through the acid treatment system to remove solutes and suspended solids in the acid, and then returns to the pickling equipment for reuse.

[0040] Step 9: The acid-washed graphite powder is subjected to three-stage reverse water washing to remove residual acid until the pH value of the washing liquid is restored to above 6.6. After filtering, drying and demagnetization treatment, the final product graphite powder is formed.

[0041] The analysis results of graphite powder obtained by the above method are as follows:

[0042] Graphite powder recovery rate: 99.1%.

[0043] The impurity contents of the recovered graphite powder are as follows:

[0044]

[0045] Example 2

[0046] Step 1: Under an inert atmosphere, use a cutting device to cut off the top cover of the waste liquid-filled battery cell shell so that the electrolyte and the electrode inside the battery cell are connected to the external environment;

[0047] Step 2: Heat treat the opened battery cell at 100-200℃ in an inert atmosphere to volatilize the electrolyte in the battery cell. Force convection of the airflow inside the heat treatment device to maintain ventilation and exhaust. The insulation time is determined according to the discharge of volatile gases until the concentration of volatile gases detected is lower than the set value. The pyrolysis treatment is completed, and the exhaust gas discharged from the device is sent to the secondary combustion chamber for combustion treatment. The exhaust gas meets the emission standards, and the battery cell is sent to the next step of treatment;

[0048] Step 3: Take out the inner core of the battery cell and separate the positive electrode sheet, negative electrode sheet and separator;

[0049] Step 4: Send the negative electrode sheet to the rapid freezing powder removal machine for powder removal treatment, place the electrode sheet in the pre-cooling chamber, introduce liquid nitrogen according to the ratio of liquid nitrogen mass to electrode mass of 1-3, control the liquid nitrogen flow rate according to the temperature detection feedback, keep the temperature at -120℃ for 5-15 minutes, and transport it to the mechanical separation chamber for powder removal operation. After passing through the vibrating screen, the graphite powder and copper foil in the electrode sheet are separated, and the primary graphite powder is obtained by screening;

[0050] Step 5: Send the primary graphite powder to the water washing equipment for treatment, soak the primary graphite powder in pure water for 1-2 hours, keep stirring during the process, and remove the solutes and suspended matter in the water through the circulating water treatment link. The clear liquid is returned to the water washing and de-powdering machine for reuse, and the suspended matter is removed by precipitation and filtration. The lithium ions in the solution are extracted using existing technology.

[0051] Step 6: The primary graphite powder is sent to an oxidative pickling device for treatment, and hydrogen peroxide is used as an oxidant and sulfuric acid is used as an acid solution in a ratio of 1:20 as an oxidizing acid solution. The graphite powder is immersed and stirred, and stirring is maintained in the reaction equipment to prevent the graphite powder from precipitating. The reaction time is greater than 40 minutes, and the suspension is discharged and filtered to obtain the pickled graphite powder;

[0052] Step 7: After filtering and removing the graphite powder, the acid solution is subjected to absorption of dissolved cations in the acid solution by a strong acid cation exchange resin, and the acid solution is passed into a strong acid cation exchange resin reactor. Two reactors are provided, one for operation and one for standby. Sulfuric acid and an oxidant are added to the acid solution after the ion exchange until the pH value is less than 2.5;

[0053] Step 8: Regenerate the absorbed cation exchange resin using 3-4% sulfuric acid. The metal ions are released into the regeneration liquid for further resource recovery and regeneration. The regenerated cation exchange resin is reused. The filtered liquid passes through the acid treatment system to remove solutes and suspended solids in the acid, and then returns to the pickling equipment for reuse.

[0054] Step 9: The acid-washed graphite powder is subjected to three-stage reverse water washing to remove residual acid until the pH value of the washing liquid is restored to above 6.6. After filtering, drying and demagnetization treatment, the final product graphite powder is formed.

[0055] The analysis results of graphite powder obtained by the above method are as follows:

[0056] Graphite powder recovery rate: 87.4%.

[0057] The impurity contents of the recovered graphite powder are as follows:

[0058]

[0059] Example 3

[0060] Step 1: The waste negative electrode sheets and negative electrode scraps generated in the battery production are sent to the rapid freezing powder removal machine for powder removal. The electrode sheets are placed in a pre-cooling chamber, and liquid nitrogen is introduced according to the ratio of liquid nitrogen mass to electrode mass of 1-3. According to the temperature detection feedback, the liquid nitrogen flow rate is controlled, and the temperature is kept constant at -120℃ for 5-15 minutes, and then the liquid nitrogen is transported to the mechanical separation chamber for powder removal. After passing through the vibrating screen, the graphite powder and copper foil in the electrode sheets are separated, and the primary graphite powder is obtained by screening;

[0061] Step 2: The primary graphite powder is sent to an oxidative pickling device for treatment, and hydrogen peroxide is used as an oxidant and sulfuric acid is used as an acid solution in a ratio of 1:20 as an oxidizing acid solution. The graphite powder is soaked and stirred, and stirring is maintained in the reaction equipment to prevent the graphite powder from precipitating. The reaction time is greater than 20 minutes, and the suspension is discharged and filtered to obtain the pickled graphite powder;

[0062] Step 6: After filtering and removing the graphite powder, the acid solution is subjected to absorption of dissolved cations in the acid solution by a strong acid cation exchange resin, and the acid solution is passed into a strong acid cation exchange resin reactor. Two reactors are provided, one for operation and one for standby. Sulfuric acid and an oxidant are added to the acid solution after the ion exchange until the pH value is less than 2.5;

[0063] Step 7: Regenerate the absorbed cation exchange resin using 3-4% sulfuric acid. The metal ions are released into the regeneration liquid for further resource recovery and regeneration. The regenerated cation exchange resin is reused. The filtered liquid passes through the acid treatment system to remove solutes and suspended solids in the acid, and then returns to the pickling equipment for reuse.

[0064] Step 8: The acid-washed graphite powder is subjected to three-stage reverse water washing to remove residual acid until the pH value of the washing liquid is restored to above 6.6. After filtering, drying and demagnetization treatment, the final product graphite powder is formed.

[0065] The analysis results of graphite powder obtained by the above method are as follows:

[0066] Graphite powder recovery rate: 86.8%.

[0067] The impurity contents of the recovered graphite powder are as follows:

[0068]

[0069] Although the embodiments of the present invention are disclosed for illustrative purposes, those skilled in the art will appreciate that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments.

Claims

1. A method for wet regeneration of negative electrode graphite of waste lithium batteries, which is used for the regeneration of waste negative electrode sheets containing graphite in waste lithium batteries and negative electrode sheet waste and scraps containing graphite in battery production, characterized in that: The steps include: (1) Open the waste lithium battery cell, volatilize the electrolyte by low-temperature heat treatment, and remove the negative electrode sheet from the cell; (2) The negative electrode sheet is sent to a freezing de-powdering machine for de-powdering treatment. Liquid nitrogen is used to cool the material in the equipment. Then, the graphite powder and copper foil in the electrode sheet are separated by mechanical separation. Primary graphite powder is obtained by screening. (3) The primary graphite powder is sent to an oxidative pickling device for treatment, an oxidizing acid solution is formed by mixing an oxidant and an acid solution in a certain ratio, and the graphite powder is soaked and stirred. After a certain period of time, the suspension is filtered to obtain the pickled graphite powder. The filtered liquid is passed through an acid treatment system to remove cationic solutes and suspended matter in the acid, and then returned to the pickling device for reuse; (4) The acid-washed graphite powder is subjected to multi-stage reverse water washing to remove residual acid until the pH value of the washing liquid is restored to 6.5-7.0, and then filtered, dried, and demagnetized to form the final product graphite powder.

2. The method for wet regeneration of negative electrode graphite of waste lithium batteries according to claim 1, characterized in that: Step (1) of the method comprises the following steps: (1) Open the waste lithium battery cells by mechanical cutting under an inert atmosphere so that the gas in the cells can be discharged, and the size of the incision is sufficient to remove the electrode; (2) The opened battery cell is heat treated at 100-200°C in an inert atmosphere to volatilize the electrolyte in the battery cell. The generated waste gas is sent to a combustion chamber for treatment. When the emission meets the standard, the battery cell is sent to the next step of treatment; (3) Take out the electrodes from the battery cell and separate the positive electrode, negative electrode and separator.

3. The method for wet regeneration of negative electrode graphite of waste lithium battery according to claim 1, characterized in that: The following steps may be added between step (2) and step (3) of the method: (1) sending the copper foil after freeze de-powdering to a water-washing de-powdering machine for secondary de-powdering treatment, soaking the copper foil in pure water, using stirring and ultrasonic cleaning to make the residual graphite powder fall off the copper foil, filtering the suspension to separate the washed primary graphite powder, and carrying out subsequent treatment steps together with the primary graphite powder formed by freeze de-powdering; (2) The liquid after water washing and de-powdering is filtered through a circulating water treatment process to remove solutes and suspended matter in the water, and the clear liquid is returned to the water washing and de-powdering machine for reuse.

4. The method for wet regeneration of negative electrode graphite of waste lithium battery according to claim 1, characterized in that: The acid solution treatment system in step (3) of the method comprises the following steps: (1) using a strong acid cation exchange resin to absorb dissolved cations in the acid solution after filtering out the graphite powder, and then replenishing the acid solution and the oxidant to the initial level according to the pH value of the treated liquid; (2) The absorbed cation exchange resin is regenerated, and the metal ions are released into the regeneration liquid for further resource treatment. The regenerated cation exchange resin is recycled.

5. The method for wet regeneration of negative electrode graphite of waste lithium battery according to claim 1, characterized in that: The freezing powder removal machine includes a pre-cooling chamber and a mechanical separation chamber. Liquid nitrogen can be introduced into the pre-cooling chamber. The liquid nitrogen flow rate is adjusted according to the temperature monitoring value to control the cooling speed. After the temperature is kept constant at -60 to -150℃ for a certain period of time, it is transported to the mechanical separation chamber for powder removal. The mechanical separation methods include one or more of vibration, friction, and impact.

6. The method for wet regeneration of negative electrode graphite of waste lithium batteries according to claim 1, characterized in that: The multi-stage reverse water washing described in step (4) includes at least one stage, and each stage includes a container with four interfaces: feed, discharge, water inlet and water outlet. The initial material to be processed is fed into the feed port of the first stage, the discharge of each stage enters the feed port of the next stage, the processed material is discharged from the last stage, the water inlet of the last stage is supplemented with deionized water, the water outlet of each stage enters the water inlet of the previous stage, and the water outlet of the first stage is used as supplementary water for the pickling system.

7. The method for wet regeneration of negative electrode graphite of waste lithium batteries according to claim 1, characterized in that: The waste lithium battery is a ternary or quaternary lithium battery, a lithium iron phosphate battery, a lithium cobalt oxide battery; or a square lithium battery, a soft-pack lithium battery or a cylindrical lithium battery; or a battery cell after the shell is cut.

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