Method for recovering graphite from waste lithium battery negative plate

Abstract

The invention specifically discloses a method for recovering graphite from a waste lithium battery negative electrode piece, and the method comprises the following steps: obtaining a negative electrode piece, carrying out steam heat treatment, extracting lithium from black powder, carrying out air calcination, carrying out high-temperature chlorination and carrying out replacement washing. The method has the advantages that the method is simple in operation, environmental pollution hidden dangers caused by the existence of organic solvents and loss of lithium elements in the negative plates are avoided, meanwhile, the method has a good impurity separation effect, and high-purity, high-efficiency, wastewater-free and good copper and fluorine removal effects are achieved on the premise of low cost.

Description

Technical Field

[0001] This application belongs to the technical field of waste lithium battery recycling, and particularly relates to a method for recovering graphite from the negative electrode sheets of waste lithium batteries. Background Art

[0002] Lithium-ion batteries have the advantages of high working voltage, long cycle life, large specific capacity, etc., and are widely used in fields such as new energy vehicles. However, with the rapid development of lithium-ion batteries, a large number of waste batteries will inevitably be generated. If not properly treated, it will cause serious environmental pollution and waste of resources. Generally, the negative electrode of a lithium-ion battery is composed of copper foil, graphite, conductive agent, thickening agent, and binder, which can account for about 20% of the mass and about 15% of the total cost of the lithium battery.

[0003] Among them, graphite, as an important strategic resource indispensable for the development of modern industry, is not only used in traditional industrial fields such as refractory materials, electrode brushes, pencils, casting, sealing, and lubrication, but also a key resource in strategic emerging industries such as high-end equipment manufacturing, new energy, new materials, and the nuclear power field. Therefore, its recycling and utilization is of great significance.

[0004] At present, the recovery of negative electrode graphite mainly includes pyrometallurgical and hydrometallurgical processes. The pyrometallurgical process removes impurities through high-temperature graphitization; while the hydrometallurgical process removes impurities through pickling first and then carbonization. The pyrometallurgical process requires high-temperature calcination at 3000 °C, with too high energy consumption and too long production cycle, and is also prone to emitting harmful gases; the hydrometallurgical process includes a pickling step, generating a large amount of waste liquid, corroding the equipment, polluting the environment, and it is difficult to achieve complete separation of copper foil and graphite. In short, the existing methods for recovering graphite from the negative electrode sheets of waste lithium batteries are complex, time-consuming, and costly, and are difficult to apply to actual industrial production. Therefore, it is necessary to propose a simple, feasible, high economic benefit, and low environmental hazard method for recovering lithium negative electrode graphite materials, which plays a key role in the recycling industry of lithium batteries and the sustainable development of resources. Summary of the Invention

[0005] In order to solve the above technical problems, this application provides a method for recovering graphite from the negative electrode sheets of waste lithium batteries. The method includes the following steps: Obtain the negative electrode sheet. Disassemble the waste lithium battery to obtain the negative electrode sheet without the separator. Among them, the waste lithium battery includes lithium iron phosphate batteries and ternary lithium batteries; Steam heat treatment. Use water vapor to pyrolyze the negative electrode sheet under the condition of the first preset temperature, so that the copper foil and black powder in the negative electrode sheet are automatically separated. The first preset temperature is 600 - 800 °C; since both the thickening agent CMCC and the binder styrene-butadiene rubber in the negative electrode sheet have a dissolution or swelling effect with water, in the presence of water vapor, it can effectively reduce the reaction temperature and promote the detachment effect of the thickening agent, binder and copper foil; Lithium extraction from black powder. Under normal temperature conditions, the black powder is soaked in dilute acid and stirred to convert the lithium in the black powder into lithium salts, and then filtered to obtain a lithium-free filter residue and a lithium salt solution; after soaking with dilute acid, the lithium element in the SEI film of the negative electrode sheet and the lithium ions in the incompletely discharged graphite intercalation layer are transferred and dissolved into the aqueous solution, and a lithium-free filter residue can be obtained after filtration; Air calcination. The obtained lithium-free filter residue is subjected to air calcination at a calcination temperature of 400 - 550 °C to oxidize and volatilize the pyrolyzates in the lithium-free filter residue and oxidize the metal elements to form metal oxides; by calcining the lithium-free filter residue, the residual organic matter and elemental metals in the filter residue are converted into corresponding oxides, the pure carbon and hydrogen and oxygen elements in the organic matter are converted into volatile gases, and metallic copper is rapidly oxidized to copper oxide. The reaction equations are as follows: 2C + O2 = 2CO 2Cu + O2 = 2CuO CMCC (carboxymethyl cellulose) + O2 → H2O + CO2 SBR (styrene-butadiene rubber) + O2 → H2O + CO2 High-temperature chlorination. Under the conditions of the second preset temperature and a high-purity chlorine gas atmosphere, the metal and metal oxides are converted into chlorides, and the second preset temperature is 700 - 900 °C; specifically, first, an inert gas is filled to evacuate, and then high-purity chlorine gas is introduced to make the inside of the reaction vessel an atmosphere of chlorine gas. Under the condition of the second preset temperature, the high-purity chlorine gas converts the metal and the metal oxides after air calcination into corresponding chlorides. The reaction equations are as follows: Cu + Cl2 = CuCl2 2CuO + 2Cl2 = 2CuCl2 + O2 Displacement and water washing. An inert gas is introduced to displace chlorine gas, and then washed and filtered with brine to obtain battery-grade graphite. In this step, an inert gas is first introduced to displace the chlorine gas in the reaction vessel to displace the chlorine gas adsorbed by the graphite, and then brine is used for washing to remove the possible cuprous chloride. The reaction equation is as follows: CuCl + NaCl = Na[CuCl2].

[0006] In some embodiments, the time of the steam heat treatment is 15 - 60 min.

[0007] In some embodiments, the reaction time of the high-temperature chlorination is 30 - 120 min, and the ratio of high-purity chlorine gas to the calcined material after air calcination is 10 - 30 L:100 g.

[0008] In some embodiments, the inert gas is one or more of nitrogen, argon, or helium.

[0009] Compared with the prior art, the method for recovering graphite from waste lithium battery anode sheets provided by the present application has the following beneficial technical effects: In the present application, since both the thickener and the binder in the anode sheet have a dissolution or swelling effect with water, at a relatively low temperature, the anode sheet can be cracked by using water vapor, so that the copper foil and the black powder in the anode sheet are automatically separated; then, the black powder is soaked in dilute acid to convert the lithium element in the black powder into a lithium salt, and the lithium-free filter residue can be obtained after filtration; then, the filter residue is calcined in air to convert the organic matter and elemental metal in the filter residue into corresponding oxides; at the same time, in a chlorine gas atmosphere, the metal oxide is converted into a metal chloride; finally, the metal chloride is removed by washing with brine and then dried to obtain battery-grade graphite. Therefore, the method for recovering graphite from waste lithium battery anode sheets provided by the present application can realize the recovery of graphite in the anode sheet without using organic solvents, avoiding the potential environmental pollution hazards caused by the presence of organic solvents and the loss of lithium elements in the anode sheet. At the same time, this method also has a good impurity separation effect, achieving high purity, high efficiency, no wastewater generation and good copper and fluorine removal effects on the premise of low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0011] Figure 1 Shows a flowchart of the method for recovering graphite from waste lithium battery anode sheets in some embodiments of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0012] The "range" disclosed in this application is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a particular range. The ranges defined in this way can include or exclude the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, ranges of 60-110 and 80-120 are also contemplated. In addition, if the minimum range values of 1 and 2 are listed, and if the maximum range values of 3, 4, and 5 are listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise specified, the numerical range "a-b" represents an abbreviated representation of any real number combination between a and b, where both a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been fully listed herein, and "0-5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0013] If there is no special instruction, "including" and "comprising" mentioned in this application mean open-ended or can also be closed-ended. For example, the said "including" and "comprising" can mean that other components not listed can also be included or comprised, or can only include or comprise the listed components.

[0014] Referring Figure 1 As shown, the embodiment of this application provides a method for recovering graphite from the negative electrode sheet of a waste lithium battery. The method includes the following steps: Obtain the negative electrode sheet. Disassemble the waste lithium battery to obtain a negative electrode sheet without a separator. Among them, the waste lithium battery includes a lithium iron phosphate battery and a ternary lithium battery; Steam heat treatment. Use water vapor to pyrolyze the negative electrode sheet under the condition of a first preset temperature, so that the copper foil and black powder in the negative electrode sheet are automatically separated. The first preset temperature is 600-800 °C, and the time of steam heat treatment is 15-60 min; In this step, since both the thickening agent CMCC and the binder styrene-butadiene rubber in the negative electrode sheet have a dissolution or swelling effect with water, water vapor can effectively reduce the reaction temperature and promote the detachment effect of the thickening agent, binder, and copper foil; the first preset temperature is any temperature in the range of 600 - 800 °C. Exemplarily, the value of the first preset temperature can be 600 °C, 650 °C, 700 °C, 750 °C, 800 °C, etc.; the steam heat treatment time is any value in the range of 15 - 60 minutes. Exemplarily, the steam heat treatment time can be 15 minutes, 20 minutes, 25 minutes, 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes, 60 minutes, etc.

[0015] For lithium extraction from black powder, soak the black powder in dilute acid at room temperature and stir to convert the lithium in the black powder into lithium salts, and then filter to obtain a lithium-free filter residue and a lithium salt solution; after soaking with dilute acid, the lithium element in the SEI film of the negative electrode sheet and the lithium ions in the incompletely discharged graphite intercalation layer are transferred and dissolved into the aqueous solution, and a lithium-free filter residue can be obtained after filtration; In this step, since both the SEI film of the waste lithium battery negative electrode sheet and the incompletely discharged graphite intercalation layer contain lithium elements, with a content of over 0.6%, in order to improve the purity of graphite recovery as much as possible, it is necessary to remove the lithium elements from the black powder. In this embodiment, the dilute acid soaking method can be used to convert the lithium elements in the black powder into corresponding lithium salt solutions by dilute acid, that is, the lithium ions on the surface and adsorbed by the black powder are transferred into the aqueous solution, and a lithium-free filter residue can be obtained after filtration. It should be noted that the dilute acid can be sulfuric acid or hydrochloric acid, and the obtained lithium-containing solution containing sulfate or chloride ions is convenient for the subsequent preparation of lithium carbonate.

[0016] Air calcination: Calcinate the obtained lithium-free filter residue in air at a calcination temperature of 400 - 550 °C to oxidize and volatilize the pyrolysis products in the lithium-free filter residue and oxidize the metal elements to form metal oxides; by calcining the lithium-free filter residue, the residual organic matter and elemental metals in the filter residue are converted into corresponding oxides, the pure carbon and hydrogen and oxygen elements in the organic matter are converted into volatile gases, metallic copper is quickly oxidized to copper oxide, and the pyrolyzed inorganic carbon is amorphous carbon. After removal, a product with an ideal degree of graphitization can be obtained. The reaction formulas are as follows: 2C + O2 = 2CO 2Cu + O2 = 2CuO CMCC (carboxymethyl cellulose) + O2 → H2O + CO2 SBR (styrene-butadiene rubber) + O2 → H2O + CO2 In this step, in order to remove the residual organic matter in the filter residue, the lithium-free filter residue obtained is subjected to air calcination at a temperature lower than the temperature of graphite oxidation. The residual polymer pyrolysis products in the filter residue are oxidized into volatile gases, carbon monoxide, carbon dioxide and water. At the same time, the metallic copper in the filter residue can also be quickly oxidized to copper oxide, reducing the surface coating effect for the subsequent chlorination reaction. It is worth mentioning that the temperature of air calcination is lower than the graphite oxidation temperature, which can effectively improve the final yield of graphite.

[0017] High-temperature chlorination: Under the conditions of the second preset temperature and a high-purity chlorine gas (in this embodiment, the purity of chlorine gas ≥ 50%) atmosphere, the metal and metal oxides are converted into chlorides. The second preset temperature is 700 - 900 °C. Specifically, first, an inert gas is filled to evacuate, and then high-purity chlorine gas is introduced to make the inside of the reaction vessel a chlorine gas atmosphere. Under the condition of the second preset temperature, the high-purity chlorine gas converts the metal and the metal oxide after air calcination into corresponding chlorides. The reaction equations are as follows: Cu + Cl2 = CuCl2 2CuO + 2Cl2 = 2CuCl2 +O2 In this step, first, the reaction vessel is evacuated by an inert gas and heated to the second preset temperature, and then high-purity chlorine gas is introduced to make the inside of the reaction vessel a chlorine gas atmosphere. At this time, the metal oxide and the residual metal elements react with chlorine gas, and then the corresponding chlorides are formed.

[0018] In this embodiment, the reaction time of high-temperature chlorination can be any value within 30 - 120 min. Exemplarily, the reaction time of high-temperature chlorination can be 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, 120 min, etc.; the ratio of high-purity chlorine gas to the calcined material after air calcination can be any value between 10 - 30 L: 100 g. Exemplarily, the ratio of high-purity chlorine gas to the calcined material after air calcination can be 10 L: 300 g, 15 L: 300 g, 20 L: 300 g, 25 L: 300 g, 30 L: 300 g, etc.

[0019] Replacement and water washing: An inert gas is introduced to replace the chlorine gas, and then it is washed and filtered with brine to obtain battery-grade graphite. In this step, first, an inert gas is introduced to replace the chlorine gas in the reaction vessel to remove the chlorine gas adsorbed by the graphite, and then it is washed with brine to remove the possible small amount of cuprous chloride. The reaction equation is as follows: CuCl+NaCl=Na[CuCl2] In this step, first, an inert gas is introduced to replace the chlorine gas in the reaction vessel, and then the product after high-temperature chlorination is washed with brine to remove cuprous chloride. After drying, battery-grade graphite can be obtained.

[0020] In the above-described embodiment, the inert gas is one or more of nitrogen, argon, or helium. In this embodiment, nitrogen is selected as the inert gas.

[0021] In the above-described embodiment, first, the negative electrode sheet is pyrolyzed with water vapor at a first preset temperature, so that the copper foil and the black powder in the negative electrode sheet are automatically separated; then, the black powder is soaked in dilute acid to convert the lithium element in the black powder into a lithium salt, and the lithium-free filter residue can be obtained after filtration; then, the filter residue is calcined in air to convert the organic matter and elemental metals in the filter residue into corresponding oxides; at the same time, in a chlorine gas atmosphere, the residual metal elements and metal oxides are all converted into metal chlorides, and some metal chlorides escape as gases under the condition of a second preset temperature; finally, the residual metal chlorides are removed by washing with brine and then dried to obtain battery-grade graphite. Therefore, the method for recovering graphite from the negative electrode sheet of a waste lithium battery provided by the present application can realize the recovery of graphite in the negative electrode sheet without using organic solvents, avoiding the potential environmental pollution caused by the presence of organic solvents and the loss of lithium elements in the negative electrode sheet. At the same time, this method also has a good impurity separation effect, achieving high purity, high efficiency, no wastewater generation, and good copper and fluorine removal effects on the premise of low cost.

[0022] The following examples more specifically describe the content disclosed in the present application. These examples are only for illustrative purposes, because various modifications and changes within the scope of the content disclosed in the present application are obvious to those skilled in the art. Unless otherwise stated, all reagents and raw materials used in the examples are commercially available or can be synthesized according to conventional methods, and the instruments and equipment used in the examples are also commercially available.

[0023] Example 1 1) The negative electrode sheet without a separator is disassembled from a waste lithium iron phosphate battery, and 400 g of the negative electrode sheet is weighed and cut into a size of 50 * 50 mm; 2) The negative electrode sheet is placed in a tubular reactor and purged with nitrogen. After heating to 700 °C, water vapor is introduced for 30 min, the amount of water vapor is 1 L, and the separated copper foil and black powder are obtained after cooling; 3) Under normal temperature conditions, 320 g of black powder is soaked in 0.5 M hydrochloric acid for 1 h, and then filtered to obtain a lithium-free filter residue and a lithium salt solution. The lithium-free filter residue is washed with pure water and then dried for 4 h, and the drying temperature is 110 °C; 4) 300 g of the dried filter residue is placed in a tubular reaction furnace and calcined in air at a temperature of 450 °C for 1 h; 5) The tubular reaction furnace is closed, nitrogen is purged at a flow rate of 5 L / min for 30 min to discharge the air in the tubular reaction furnace, then the temperature is raised to 800 °C and nitrogen is turned off, and then chlorine is introduced at a flow rate of 1 L / min for 60 min; 6) Close the chlorine gas and fill nitrogen at a flow rate of 5 L / min for 30 min, then discharge the chlorine gas in the tubular reactor, cool down and unload the materials; then wash with 1 mol / L sodium chloride solution and filter, and dry to obtain the product, weighing the product to be 279 g.

[0024] Example 2 1) Remove the separator-free negative electrode sheet from the used lithium iron phosphate battery, and weigh 300 g of the negative electrode sheet and cut it into pieces with a size of 50*50 mm; 2) Put the negative electrode sheet into the tubular reactor, fill nitrogen to evacuate, heat up to 600 °C and then introduce steam for 60 min, with the steam consumption of 1.5 L, and obtain separated copper foil and black powder after cooling; 3) Under normal temperature conditions, soak 285 g of the black powder in 0.8 M hydrochloric acid for 1 h, then filter to obtain lithium-free filter residue and lithium salt solution, wash the lithium-free filter residue with pure water and then dry for 4 h, and the drying temperature is 110 °C; 4) Put 280 g of the dried filter residue into the tubular reactor and calcine in air at a temperature of 400 °C for 1 h; 5) Seal the tubular reactor, fill nitrogen at a flow rate of 5 L / min for 30 min to discharge the air in the tubular reactor, then heat up to 700 °C, close the nitrogen, and then fill chlorine at a flow rate of 0.8 L / min for 120 min; 6) Close the chlorine gas and fill nitrogen at a flow rate of 5 L / min for 30 min, then discharge the chlorine gas in the tubular reactor, cool down and unload the materials; then wash with 1 mol / L sodium chloride solution and filter, and dry to obtain the filter residue, weighing the filter residue to be 255 g.

[0025] Example 3 1) Remove the separator-free negative electrode sheet from the used lithium iron phosphate battery, and weigh 500 g of the negative electrode sheet and cut it into pieces with a size of 50*50 mm; 2) Put the negative electrode sheet into the tubular reactor, fill nitrogen to evacuate, heat up to 800 °C and then introduce steam for 15 min, with the steam consumption of 1.2 L, and obtain separated copper foil and black powder after cooling; 3) Under normal temperature conditions, soak 473 g of the black powder in 1 M hydrochloric acid for 1 h, then filter to obtain lithium-free filter residue and lithium salt solution, wash the lithium-free filter residue with pure water and then dry for 4 h, and the drying temperature is 110 °C; 4) Put 440 g of the dried filter residue into the tubular reactor and calcine in air at a temperature of 550 °C for 1 h; 5) Seal the tubular reactor, fill nitrogen at a flow rate of 5 L / min for 30 min to discharge the air in the tubular reactor, then heat up to 900 °C, close the nitrogen, and then fill chlorine at a flow rate of 0.6 L / min for 30 min; 6) Close the chlorine gas and fill nitrogen at a flow rate of 5 L / min for 30 min, then discharge the chlorine gas in the tubular reactor, cool down and unload the materials; then wash with 1 mol / L sodium chloride solution and filter, dry to obtain the filter residue, and weigh the weight of the filter residue as 406 g.

[0026] Respectively take the products obtained in Examples 1 - 3 for elemental detection, and the detection results are shown in Table 1.

[0027] Table 1 Elemental detection results of the products obtained in Examples 1 - 3 Fluorine (%) Copper (%) Fixed Carbon (%) Example 1 Not detected Not detected 99.96 Example 2 Not detected Not detected 99.87 Example 3 Not detected Not detected 99.95 It can be seen from Table 1 that in the products obtained in Examples 1 - 3, the contents of fluorine and copper are not detected, and the carbon content is above 99.85%. Based on the elemental detection results of the products obtained in Examples 1 - 3, the corresponding graphitization degrees are calculated. After calculation, the graphitization degree of the product obtained in Example 1 is 95.3%, the graphitization degree of the product obtained in Example 2 is 95.1%, and the graphitization degree of the product obtained in Example 3 is 95.8%. That is, the present application can effectively recycle the graphite in waste lithium batteries. Since the method provided by the present application can achieve the recycling of graphite in the negative electrode sheet without using organic solvents, it avoids the potential environmental pollution hazards caused by the presence of organic solvents and the loss of lithium elements in the negative electrode sheet. Therefore, the present application not only has a good impurity separation effect, but also realizes high purity, high efficiency, no waste water generation and good copper and fluorine removal effects on the premise of low cost.

[0028] The above has introduced in detail a method for recycling graphite from the negative electrode sheet of waste lithium batteries provided by the present application. Specific examples are used in this article to elaborate on the principle and implementation manner of the present application. The description of the above examples is only used to help understand the core idea of the present application. It should be noted that for those of ordinary skill in the art in this technical field, without departing from the principle of the present application, several improvements and modifications can be made to the present application, and these improvements and modifications also fall within the protection scope of the claims of the present application.

Claims

1. A method for recovering graphite from the negative electrode sheets of waste lithium batteries, characterized in that, The method includes the following steps: Obtain a negative electrode sheet. Disassemble a waste lithium battery to obtain a negative electrode sheet without a separator; Steam heat treatment. Use water vapor to pyrolyze the negative electrode sheet under the condition of a first preset temperature, so that the copper foil and black powder in the negative electrode sheet are automatically separated. The first preset temperature is 600-800 °C; Lithium extraction from black powder. Soak the black powder in dilute acid at room temperature and stir it to convert the lithium in the black powder into a lithium salt, and then filter to obtain a lithium-free filter residue and a lithium salt solution; Air calcination. Calcinate the obtained lithium-free filter residue in air at a calcination temperature of 400-550 °C, so that the pyrolyzate in the lithium-free filter residue is oxidized and volatilized and the metal elements are oxidized to form metal oxides; High-temperature chlorination. Convert the metal oxides into chlorides under the conditions of a second preset temperature and a high-purity chlorine gas atmosphere. The second preset temperature is 700-900 °C; Replacement and water washing. Introduce an inert gas to replace chlorine gas, and then wash and filter with brine to obtain battery-grade graphite.

2. The method for recovering graphite from the negative electrode sheet of waste lithium batteries according to claim 1, characterized in that, The time of the steam heat treatment is 15-60 min.

3. The method for recovering graphite from the negative electrode sheet of waste lithium batteries according to claim 1, wherein The reaction time of the high-temperature chlorination is 30-120 min, and the ratio of high-purity chlorine gas to the calcined material after air calcination is 10-30 L:100 g.

4. The method for recovering graphite from the negative electrode sheet of waste lithium batteries according to claim 1, characterized in that, The inert gas is one or more of nitrogen, argon or helium.

Images