A method for recovering graphite from waste lithium battery negative electrode sheets

Abstract

The present application specifically discloses a method for recovering graphite from waste lithium battery negative electrode sheets, the method comprising the following steps: obtaining negative electrode sheets, steam heat treatment, black powder lithium extraction, air calcination, high-temperature chlorination and displacement water washing. The method can achieve graphite recovery in the negative electrode sheets without the use of organic solvents, thus avoiding the environmental pollution risks caused by the presence of organic solvents and the loss of lithium elements in the negative electrode sheets. At the same time, the method has a good impurity separation effect, and achieves high purity and high efficiency, no wastewater generation and good copper and fluorine removal effects at a low cost.

Description

Technical Field

[0001] The present application belongs to the technical field of waste lithium battery recycling, and in particular relates to a method for recycling graphite from waste lithium battery negative electrode sheets. Background Art

[0002] Lithium-ion batteries, with their advantages of high operating voltage, long cycle life, and high specific capacity, are widely used in new energy vehicles and other fields. However, the rapid development of lithium-ion batteries has inevitably generated a large amount of waste batteries. If not properly handled, this will cause serious environmental pollution and waste of resources. Typically, the negative electrode of a lithium-ion battery is composed of copper foil, graphite, a conductive agent, a thickener, and a binder, and accounts for approximately 20% of the battery's mass and around 15% of its total cost.

[0003] Among them, graphite, as an important strategic resource indispensable to 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 is also a key resource in strategic emerging industries such as high-end equipment manufacturing, new energy, new materials, and nuclear power. Therefore, its recycling and utilization is of great significance.

[0004] Currently, negative electrode graphite recovery primarily involves pyrometallurgical and wet recycling processes. The pyrometallurgical process removes impurities through high-temperature graphitization, while the wet process removes impurities through acid washing followed by carbonization. The pyrometallurgical process requires calcination at temperatures of 3000°C, resulting in high energy consumption, a long production cycle, and the emission of harmful gases. The wet process, which includes an acid washing step, generates large amounts of waste liquid, corrodes equipment, pollutes the environment, and makes it difficult to completely separate the copper foil from the graphite. In short, existing methods for recycling graphite from spent lithium battery negative electrodes are complex, time-consuming, and costly, making them difficult to apply to actual industrial production. Therefore, it is necessary to develop a simple, feasible, cost-effective, and environmentally friendly method for recycling lithium-ion negative electrode graphite materials, which plays a key role in the sustainable development of the lithium battery recycling industry and resources. Summary of the Invention

[0005] In order to solve the above technical problems, the present application provides a method for recovering graphite from waste lithium battery negative electrode sheets, the method comprising the following steps:

[0006] Obtaining negative electrode sheets by disassembling waste lithium batteries to obtain negative electrode sheets without a separator, wherein the waste lithium batteries include lithium iron phosphate batteries and ternary lithium batteries;

[0007] Steam heat treatment uses water vapor to crack the negative electrode sheet at a first preset temperature of 600-800°C, automatically separating the copper foil and black powder in the negative electrode sheet. Since the thickener CMCC and the binder styrene-butadiene rubber in the negative electrode sheet both dissolve or swell with water, the presence of water vapor can effectively reduce the reaction temperature and promote the separation of the thickener, binder and copper foil.

[0008] Black powder is used to extract lithium. Black powder is soaked in dilute acid at room temperature and stirred to convert the lithium in the black powder into lithium salt. The black powder is then filtered to obtain a lithium-free filter residue and a lithium salt solution. After soaking in dilute acid, the lithium elements in the SEI film of the negative electrode sheet and the lithium ions in the graphite intercalation layer that are not fully discharged are transferred and dissolved into the aqueous solution. After filtration, a lithium-free filter residue is obtained.

[0009] Air calcination: The obtained lithium-free filter residue is calcined in air at a calcination temperature of 400-550°C, so that the cracked products in the lithium-free filter residue are oxidized and volatilized, and the metal elements are oxidized to form metal oxides. By calcining the lithium-free filter residue, the residual organic matter and elemental metal 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 the metallic copper is quickly oxidized to copper oxide. The reaction formula is as follows:

[0010] 2C+O2=2CO

[0011] 2Cu+O2=2CuO

[0012] CMCC (carboxymethyl cellulose) + O2 → H2O + CO2

[0013] SBR (styrene-butadiene rubber) + O2 → H2O + CO2

[0014] High-temperature chlorination converts metals and metal oxides into chlorides under a second preset temperature and high-purity chlorine atmosphere, wherein the second preset temperature is 700-900°C. Specifically, an inert gas is first filled to evacuate the air, and then high-purity chlorine is introduced to create a chlorine atmosphere in the reaction vessel. Under the second preset temperature, the high-purity chlorine converts the metal and the metal oxides calcined with air into the corresponding chlorides. The reaction formula is as follows:

[0015] Cu + Cl2 = CuCl2

[0016] 2CuO + 2Cl2 = 2CuCl2 +O2

[0017] Replace water washing, introduce inert gas to replace chlorine, and then wash and filter with brine to obtain battery-grade graphite. In this step, first introduce inert gas to replace the chlorine in the reaction vessel to replace the chlorine adsorbed by the graphite, and then use brine washing to remove any cuprous chloride that may be present. The reaction formula is as follows:

[0018] CuCl+NaCl=Na[CuCl2].

[0019] In some embodiments, the steam heat treatment lasts for 15-60 minutes.

[0020] In some embodiments, the reaction time of the high-temperature chlorination is 30-120 min, and the ratio of high-purity chlorine gas to air after calcination is 10-30 L:100 g.

[0021] In some embodiments, the inert gas is one or more of nitrogen, argon, or helium.

[0022] Compared with the prior art, the method for recovering graphite from waste lithium battery negative electrode sheets provided in this application has the following beneficial technical effects:

[0023] In the present application, since the thickener and adhesive in the negative electrode sheet both dissolve or swell with water, at a relatively low temperature, the negative electrode sheet can be cracked by water vapor so that the copper foil and black powder in the negative electrode sheet are automatically separated; then, the black powder is soaked in dilute acid so that the lithium element in the black powder is converted into lithium salt, and a lithium-free filter residue can be obtained after filtration; the filter residue is then air-calcined to convert the organic matter and elemental metal in the filter residue into corresponding oxides; at the same time, in a chlorine atmosphere, the metal oxide is converted into 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 negative electrode sheets provided in the present application can realize graphite recovery in the negative electrode sheet without using organic solvents, avoids the environmental pollution risks caused by the presence of organic solvents and the loss of lithium elements in the negative electrode sheet, and at the same time, the method also has a good impurity separation effect, and achieves high purity and high efficiency, no wastewater generation and good copper and fluorine removal effects at a low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0025] Figure 1 A flow chart of a method for recovering graphite from waste lithium battery negative electrode sheets in some embodiments of the present application is shown. DETAILED DESCRIPTION

[0026] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0027] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0028] refer to Figure 1 As shown, the embodiment of the present application provides a method for recovering graphite from waste lithium battery negative electrode sheets, the method comprising the following steps:

[0029] Obtaining negative electrode sheets by disassembling waste lithium batteries to obtain negative electrode sheets without a separator, wherein the waste lithium batteries include lithium iron phosphate batteries and ternary lithium batteries;

[0030] Steam heat treatment, using water vapor and a first preset temperature condition to crack the negative electrode sheet, 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 steam heat treatment time is 15-60 minutes;

[0031] In this step, since the thickener CMCC and the binder styrene-butadiene rubber in the negative electrode sheet both dissolve or swell with water, water vapor can effectively lower the reaction temperature and promote the separation of the thickener, binder and copper foil; the first preset temperature is any temperature between 600-800°C. For example, 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 between 15-60 minutes. For example, 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.

[0032] Black powder is used to extract lithium. Black powder is soaked in dilute acid at room temperature and stirred to convert the lithium in the black powder into lithium salt. The black powder is then filtered to obtain a lithium-free filter residue and a lithium salt solution. After soaking in dilute acid, the lithium elements in the SEI film of the negative electrode sheet and the lithium ions in the graphite intercalation layer that are not fully discharged are transferred and dissolved into the aqueous solution. After filtration, a lithium-free filter residue is obtained.

[0033] In this step, since the SEI film of the negative electrode sheet of the waste lithium battery and the graphite intercalation layer of the incompletely discharged graphite contain lithium, the content can reach more than 0.6%. In order to maximize the purity of the recovered graphite, the lithium element needs to be removed from the black powder. In this embodiment, a dilute acid soaking method can be used to convert the lithium element in the black powder into a corresponding lithium salt solution. That is, the lithium ions on the surface of the black powder and adsorbed are transferred to the aqueous solution, and a lithium-free filter residue is obtained after filtration. It should be noted that the dilute acid can be sulfuric acid or hydrochloric acid. The resulting lithium-containing solution containing sulfate or chloride ions is convenient for the subsequent preparation of lithium carbonate.

[0034] Air calcination: The obtained lithium-free filter residue is calcined in air at a calcination temperature of 400-550°C, so that the cracked products in the lithium-free filter residue are oxidized and volatilized, and the metal elements are oxidized to form metal oxides. By calcining the lithium-free filter residue, the residual organic matter and elemental metal 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, the metallic copper is quickly oxidized into copper oxide, and the cracked inorganic carbon is amorphous carbon. After removal, a product with a relatively ideal graphitization degree can be obtained. The reaction formula is as follows:

[0035] 2C+O2=2CO

[0036] 2Cu+O2=2CuO

[0037] CMCC (carboxymethyl cellulose) + O2 → H2O + CO2

[0038] SBR (styrene-butadiene rubber) + O2 → H2O + CO2

[0039] In this step, to remove residual organic matter in the filter residue, the resulting lithium-free filter residue is air-calcined at a temperature below the graphite oxidation temperature. The remaining polymer cracking products in the filter residue are oxidized into volatile gases, including carbon monoxide, carbon dioxide, and water. At the same time, the metallic copper in the filter residue can also be rapidly oxidized to copper oxide, reducing the surface coating effect for the subsequent chlorination reaction. It is worth mentioning that the air calcination temperature is lower than the graphite oxidation temperature, which can effectively improve the final yield of graphite.

[0040] High-temperature chlorination converts metals and metal oxides into chlorides under a second preset temperature and high-purity chlorine (in this embodiment, the purity of chlorine is ≥50%) atmosphere. The second preset temperature is 700-900°C. Specifically, an inert gas is first filled to evacuate the air, and then high-purity chlorine is introduced to create a chlorine atmosphere in the reaction vessel. Under the second preset temperature, the high-purity chlorine converts the metal oxides calcined with air into the corresponding chlorides. The reaction formula is as follows:

[0041] Cu + Cl2 = CuCl2

[0042] 2CuO + 2Cl2 = 2CuCl2 +O2

[0043] In this step, the reaction vessel is first evacuated with an inert gas and heated to a second preset temperature. High-purity chlorine gas is then introduced to create a chlorine atmosphere in the reaction vessel. At this point, the metal oxides and residual metal elements react with the chlorine gas to generate corresponding chlorides.

[0044] In this embodiment, the reaction time of high-temperature chlorination can be any value between 30 and 120 min. For example, 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 calcined material ratio after calcining high-purity chlorine and air can be any value between 10 and 30 L: 100 g. For example, the calcined material ratio after calcining high-purity chlorine and air can be 10 L: 300 g, 15 L: 300 g, 20 L: 300 g, 25 L: 300 g, 30 L: 300 g, etc.

[0045] Replace water washing, introduce inert gas to replace chlorine, and then wash and filter with brine to obtain battery-grade graphite. In this step, first introduce inert gas to replace the chlorine in the reaction vessel to replace the chlorine adsorbed by the graphite, and then use brine washing to remove any small amount of cuprous chloride that may exist. The reaction formula is as follows:

[0046] CuCl+NaCl=Na[CuCl2]

[0047] In this step, an inert gas is first introduced to replace the chlorine in the reaction vessel, and then the product after high-temperature chlorination is washed with salt water to remove cuprous chloride. After drying, battery-grade graphite can be obtained.

[0048] In the above embodiments, the inert gas is one or more of nitrogen, argon or helium. In this embodiment, nitrogen is selected as the inert gas.

[0049] In the above embodiment, first, steam is used to crack the negative electrode sheet at a first preset temperature, so that the copper foil and 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 lithium salt, and a lithium-free filter residue can be obtained after filtration; the filter residue is then air-calcined to convert the organic matter and elemental metal in the filter residue into corresponding oxides; at the same time, in a chlorine atmosphere, the residual metal elements and metal oxides are all converted into metal chlorides, and some metal chlorides escape as gas under the second preset temperature condition; finally, the residual metal chloride is removed by washing with salt water and then dried to obtain battery-grade graphite. Therefore, the method for recovering graphite from waste lithium battery negative electrode sheets provided by the present application can realize graphite recovery in negative electrode sheets without using organic solvents, avoiding the environmental pollution risks caused by the presence of organic solvents and the loss of lithium elements in the negative electrode sheets. At the same time, the method also has a good impurity separation effect, and achieves high purity and high efficiency, no wastewater generation and good copper and fluorine removal effects at a low cost.

[0050] The following examples further describe the present disclosure. These examples are intended for illustrative purposes only, as various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise indicated, all reagents and starting materials used in the examples are commercially available or synthesized according to conventional methods, and all instruments and equipment used in the examples are commercially available.

[0051] Example 1

[0052] 1) Disassemble the negative electrode sheet without the separator from the waste lithium iron phosphate battery, weigh 400g of the negative electrode sheet and cut it into 50*50mm size;

[0053] 2) Place the negative electrode sheet in a tubular reactor and fill it with nitrogen to evacuate. After heating to 700°C, introduce 1L of steam for 30 minutes. After cooling, separate the copper foil and black powder.

[0054] 3) At room temperature, soak 320 g of black powder in 0.5 M hydrochloric acid for 1 hour, then filter to obtain a lithium-free filter residue and a lithium salt solution. Wash the lithium-free filter residue with pure water and dry it at 110°C for 4 hours.

[0055] 4) Place 300 g of the dried filter residue in a tubular reactor and calcine in air at 450°C for 1 hour;

[0056] 5) Close the tubular reactor and inject nitrogen at a flow rate of 5 L / min for 30 minutes to expel the air inside the tubular reactor. Then, heat the reactor to 800°C, turn off the nitrogen, and inject chlorine at a flow rate of 1 L / min for 60 minutes.

[0057] 6) The chlorine gas was turned off and nitrogen was introduced at a flow rate of 5 L / min for 30 min to discharge the chlorine in the tubular reactor. The reactor was cooled and then unloaded. The product was then washed with 1 mol / L sodium chloride solution, filtered, and dried to obtain a product weighing 279 g.

[0058] Example 2

[0059] 1) Disassemble the negative electrode sheet without the separator from the waste lithium iron phosphate battery, weigh 300g of the negative electrode sheet and cut it into 50*50mm size;

[0060] 2) Place the negative electrode sheet in a tubular reactor and fill it with nitrogen to evacuate. After heating to 600°C, introduce 1.5L of steam for 60 minutes. After cooling, separate the copper foil and black powder.

[0061] 3) At room temperature, soak 285 g of black powder in 0.8 M hydrochloric acid for 1 hour, then filter to obtain a lithium-free filter residue and a lithium salt solution. Wash the lithium-free filter residue with pure water and dry it at 110°C for 4 hours.

[0062] 4) Place 280 g of the dried filter residue in a tubular reactor and calcine in air at 400°C for 1 hour;

[0063] 5) Close the tubular reactor and inject nitrogen at a flow rate of 5 L / min for 30 minutes to expel the air inside the tubular reactor. Then, heat the reactor to 700°C, turn off the nitrogen, and inject chlorine at a flow rate of 0.8 L / min for 120 minutes.

[0064] 6) Turn off the chlorine gas and introduce nitrogen at a flow rate of 5 L / min for 30 minutes to discharge the chlorine in the tubular reactor. After cooling, unload the material. Then wash with 1 mol / L sodium chloride solution and filter. After drying, the filter residue is weighed to obtain 255 g.

[0065] Example 3

[0066] 1) Disassemble the negative electrode sheet without the separator from the waste lithium iron phosphate battery, weigh 500g of the negative electrode sheet and cut it into 50*50mm size;

[0067] 2) Place the negative electrode sheet in a tubular reactor and evacuate it with nitrogen. After heating to 800°C, introduce 1.2L of steam for 15 minutes. After cooling, separate the copper foil and black powder.

[0068] 3) At room temperature, soak 473 g of black powder in 1 M hydrochloric acid for 1 hour, then filter to obtain a lithium-free filter residue and a lithium salt solution. Wash the lithium-free filter residue with pure water and dry it at 110°C for 4 hours.

[0069] 4) Place 440 g of the dried filter residue in a tubular reactor and calcine in air at 550°C for 1 hour;

[0070] 5) Close the tubular reactor and inject nitrogen at a flow rate of 5 L / min for 30 minutes to expel the air inside the tubular reactor. Then, heat the reactor to 900°C, turn off the nitrogen, and inject chlorine at a flow rate of 0.6 L / min for 30 minutes.

[0071] 6) Turn off the chlorine gas and introduce nitrogen at a flow rate of 5 L / min for 30 minutes to discharge the chlorine in the tubular reactor. After cooling, unload the material. Then, wash with 1 mol / L sodium chloride solution and filter. After drying, the filter residue weighs 406 g.

[0072] The products obtained in Examples 1-3 were respectively subjected to elemental detection, and the detection results are shown in Table 1.

[0073] Table 1 Element detection results of products obtained in Examples 1-3

[0074] 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

[0075] As can be seen from Table 1, in the products obtained in Examples 1-3, the fluorine-copper content was not detected, while the carbon content was above 99.85%. Based on the element detection results of the products obtained in Examples 1-3, the corresponding graphitization degree was calculated. After calculation, the graphitization degree of the product obtained in Example 1 was 95.3%, the graphitization degree of the product obtained in Example 2 was 95.1%, and the graphitization degree of the product obtained in Example 3 was 95.8%. That is, the present application can effectively recycle graphite in waste lithium batteries, because the method provided in the present application can achieve graphite recovery in the negative electrode sheet without using an organic solvent, thereby avoiding the environmental pollution risks 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 achieves high purity and high efficiency, no wastewater generation and good copper and fluorine removal effects at a low cost.

[0076] The above describes in detail the method for recovering graphite from waste lithium battery negative electrodes provided by this application. This document uses specific examples to illustrate the principles and implementation methods of this application. The description of the above examples is intended only to facilitate understanding of the core concepts of this application. It should be noted that those skilled in the art may make various improvements and modifications to this application without departing from the principles of this application, and such improvements and modifications are also within the scope of protection of the claims of this application.

Claims

1. A method for recovering graphite from waste lithium battery negative plates, characterized in that: The method comprises the following steps: Obtaining the negative electrode sheet, disassembling the waste lithium battery to obtain the negative electrode sheet without the separator; Steam heat treatment, using water vapor and a first preset temperature condition to crack the negative electrode sheet, so that the copper foil and black powder in the negative electrode sheet are automatically separated. The first preset temperature is 600-800°C; Extracting lithium from black powder: soaking the black powder in dilute acid and stirring at room temperature to convert the lithium in the black powder into lithium salts, which are then filtered to obtain a lithium-free filter residue and a lithium salt solution; Air calcination: calcining the obtained lithium-free filter residue in air at a calcination temperature of 400-550° C. to oxidize and volatilize the cracked products in the lithium-free filter residue and oxidize the metal elements to form metal oxides; High-temperature chlorination, converting metal oxides into chlorides at a second preset temperature of 700-900°C in a high-purity chlorine atmosphere; Replace the water and wash it, introduce inert gas to replace the chlorine, then wash and filter it with brine to obtain battery-grade graphite.

2. The method for recovering graphite from a waste lithium battery negative electrode sheet according to claim 1, wherein: The steam heat treatment time is 15-60 minutes.

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

4. The method for recovering graphite from a waste lithium battery negative electrode sheet according to claim 1, wherein: The inert gas is one or more of nitrogen, argon or helium.

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