Method for recovering graphite from waste lithium ion battery

Abstract

The invention discloses a method for recovering graphite from a waste lithium ion battery, which comprises the following steps: uniformly mixing and stirring a waste lithium ion battery raw material and an alkali solution, carrying out heat treatment at 400-600 DEG C for 2-10 hours, and cooling to room temperature to obtain a heat treatment product; and performing acid leaching reaction, high-temperature annealing, carbon coating and secondary heat treatment, and cooling to room temperature to obtain regenerated graphite. According to the method disclosed by the invention, the graphite is recovered from the waste lithium ion battery, so that the purity of the regenerated graphite can be effectively improved, the electrochemical performance is improved, and the level of battery-grade graphite is obtained. And the purity of the optimally recycled graphite can reach 99.82%, the first specific discharge capacity reaches 383.2 mAh / g or above, and the first coulombic efficiency reaches 91.9%.

Description

Technical Field

[0001] The invention belongs to the technical field of graphite recovery, and in particular relates to a method for recovering graphite from waste lithium-ion batteries. Background Art

[0002] In recent years, lithium-ion batteries have been widely used in consumer electronics, electric vehicles, energy storage and other fields due to their high energy density and long cycle life. The life of lithium-ion batteries is generally 5 to 8 years. With the development of the times, lithium-ion batteries are about to usher in a wave of retirement. Lithium-ion batteries contain a variety of precious metals. If waste lithium-ion batteries are not properly disposed of, they may cause environmental pollution. Therefore, recycling waste lithium-ion batteries can achieve the recycling of resources and reduce their damage to the environment.

[0003] At present, the recycling of waste lithium-ion batteries in the industry is mainly focused on precious metals such as lithium, nickel, cobalt, and manganese. There is little research on the recycling of graphite in batteries, and most of the recycled graphite is of low purity and difficult to be used again in the field of lithium-ion batteries. A large amount of discarded graphite slag can easily cause serious pollution to the environment, and it is also a great waste of graphite resources.

[0004] Based on this, a method for recovering high-performance graphite from waste lithium-ion batteries is now studied. The recovered graphite has high purity and can be used as a negative electrode material for lithium-ion batteries, and has excellent electrochemical properties. Summary of the invention

[0005] Purpose of the invention: The technical problem to be solved by the present invention is to provide a method for recovering high-performance graphite from waste lithium-ion batteries, and the graphite recovered by this method has high purity.

[0006] Technical solution: The method for recovering graphite from waste lithium-ion batteries of the present invention comprises the following steps:

[0007] (1) Heat treatment: After mixing and stirring the waste lithium-ion battery raw materials with the alkaline solution, heat treatment is performed at 400-600° C. for 2-10 hours, and then cooled to room temperature to obtain a heat-treated product;

[0008] (2) Acid leaching reaction: After washing and drying the heat-treated product, acid leaching reaction is performed for 0.5-6 hours;

[0009] (3) High temperature annealing: the mixture after the acid leaching reaction is filtered, washed, and dried, and then kept at 2000-3000°C for 2-18 hours, and then cooled to room temperature to obtain an annealed product;

[0010] (4) Carbon coating: The annealed product is mixed with a carbon source and ball-milled, and the mixture is reacted at 800-1200°C in an inert atmosphere for 2-10 hours. The regenerated graphite is then obtained by cooling to room temperature.

[0011] The present invention, before recycling graphite, first mixes the waste lithium ion battery raw material with an alkaline solution and combines it with a heat treatment process at the same time, that is, before the acid leaching reaction, first performs a heat treatment and introduces an alkaline solution during the heat treatment process, on the one hand, the alkaline solution itself can widen the interlayer spacing of graphite at high temperature, on the other hand, the alkaline solution can react chemically with the metal impurity ions between the graphite layers to generate hydroxides such as LiOH, Fe(OH)3, Cu(OH)2, Al(OH)3, etc., which is not only conducive to the subsequent removal of impurities by acid leaching, but also generates volume expansion when hydroxides are generated, further increasing the interlayer spacing of graphite, widening the interlayer spacing of graphite, and under the combination of the two, it is more convenient for the subsequent acid leaching stage to effectively remove the difficult-to-remove impurity atoms such as Li, Fe, Cu, Al, Ni, Co, Mn and other metal ions left between the graphite layers. In addition, the alkaline solution and the heat treatment combined process can further remove organic matter, conductive carbon and silicon elements that are difficult to handle, etc., from the waste lithium ion battery raw material, and obtain high-purity graphite.

[0012] Subsequently, the graphite is graphitized again through high-temperature annealing to restore the graphite interlayer structure; finally, the graphite is carbon-coated by mixing with a carbon source and heat-treating it to prevent the co-embedding of lithium ions and electrolyte during the electrical cycle and improve the coulombic efficiency of the material.

[0013] Furthermore, in step (1) of the recovery method of the present invention, the alkaline solution is a sodium hydroxide or potassium hydroxide solution with a molar concentration of 1 to 12 mol / L.

[0014] Furthermore, in step (1) of the recovery method of the present invention, the solid-to-liquid ratio of the waste lithium-ion battery raw material to the alkaline solution is 1 g: (0.5-2) mL.

[0015] Furthermore, in step (2) of the recovery method of the present invention, the acid leaching is to mix the dried product with deionized water in a mass ratio of 1:(2-6), and add acid solution dropwise until the pH value is 0.5-1.5.

[0016] Furthermore, in step (2) of the recovery method of the present invention, the acid solution used for acid leaching is sulfuric acid, hydrochloric acid, oxalic acid or citric acid.

[0017] Furthermore, in step (4) of the recovery method of the present invention, the carbon source may be asphalt, phenolic resin or epoxy resin, and the mass ratio of the annealed product to the carbon source is 100:(1-5). Preferably, the asphalt may include at least one of coal tar asphalt, petroleum asphalt or natural asphalt.

[0018] Furthermore, in step (4) of the recovery method of the present invention, the inert atmosphere is nitrogen, argon or a hydrogen-argon mixed gas.

[0019] Furthermore, in step (4) of the recovery method of the present invention, the rotation speed of the mixed ball milling of the annealing product and the carbon source is 800-2000 rpm.

[0020] Beneficial effects: Compared with the prior art, the significant advantages of the present invention are: the method is based on the recovery of graphite from waste lithium-ion batteries, which can effectively improve the purity of the regenerated graphite, thereby improving the electrochemical performance and obtaining the level of battery-grade graphite. The best purity of the recovered graphite can reach 99.82%, the first discharge specific capacity reaches more than 383.2 mAh / g, and the first coulombic efficiency reaches 91.9%. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a flow chart of the recovery method of Example 1 of the present invention. DETAILED DESCRIPTION

[0022] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0023] It should be noted that the raw materials to be recycled in the present invention are derived from waste lithium-ion batteries, which can be black powder or negative electrode powder of waste lithium-ion batteries, and have stronger applicability.

[0024] Example 1

[0025] The method for recovering graphite from waste lithium-ion batteries in Example 1 is as follows: Figure 1 As shown, the following steps are included:

[0026] (1) black powder and 6.0 mol / L sodium hydroxide aqueous solution were mixed in a crucible at a solid-liquid ratio of 1 g:1 mL and stirred evenly, heat treated at 500° C. for 6 h, and cooled to room temperature;

[0027] (2) The heat-treated product obtained in step (1) is washed with deionized water until neutral and then dried in an oven at 110° C.;

[0028] (3) adding the washed product obtained in step (2) into deionized water, controlling the mass ratio to be 1:4 and stirring evenly, slowly adding sulfuric acid dropwise to adjust the pH of the solution to 1.0, and reacting for 3 hours;

[0029] (4) filtering the mixture after the reaction in step (3), washing with deionized water until neutral, and then drying in an oven at 110° C.;

[0030] (5) transferring the material obtained in step (4) into a crucible, then transferring the crucible into a high temperature treatment device, introducing argon gas, keeping the temperature at 2600° C. for 10 h, and cooling to room temperature;

[0031] (6) mixing the annealed product obtained in step (5) with coal tar pitch in a mass ratio of 100:3, and high-energy ball milling at a rotation speed of 2000 rpm for 1 h;

[0032] (7) The ball-milled product obtained in step (6) is transferred to a crucible, and the crucible is transferred to a high-temperature treatment device, nitrogen is introduced, and the crucible is kept at 1000° C. for 6 hours. After cooling to room temperature, regenerated graphite is obtained.

[0033] Example 2

[0034] The basic steps are the same as those in Example 1, except that the raw material used in step (1) is negative electrode powder of waste lithium-ion batteries.

[0035] Example 3

[0036] The basic steps are the same as those in Example 1, except that the alkaline solution used in step (1) is potassium hydroxide solution.

[0037] Example 4

[0038] The basic steps are the same as those in Example 1, except that the concentration of the alkaline solution used in step (1) is 1.0 mol / L.

[0039] Example 5

[0040] The basic steps are the same as those in Example 1, except that the concentration of the alkaline solution used in step (1) is 12.0 mol / L.

[0041] Example 6

[0042] The basic steps are the same as those in Example 1, except that in step (1), the solid-to-liquid ratio of black powder to sodium hydroxide aqueous solution is 1 g:0.5 mL.

[0043] Example 7

[0044] The basic steps are the same as those in Example 1, except that in step (1), the solid-to-liquid ratio of black powder to sodium hydroxide aqueous solution is 1 g:2 mL.

[0045] Example 8

[0046] The basic steps are the same as those in Example 1, except that the heat treatment temperature in step (1) is 400°C.

[0047] Example 9

[0048] The basic steps are the same as those in Example 1, except that the heat treatment temperature in step (1) is 600°C.

[0049] Example 10

[0050] The basic steps are the same as those in Example 1, except that the heat treatment time in step (1) is 2 h.

[0051] Embodiment 11

[0052] The basic steps are the same as those in Example 1, except that the heat treatment time in step (1) is 10 h.

[0053] Example 12

[0054] The basic steps are the same as those in Example 1, except that the acid solution used in step (1) is concentrated hydrochloric acid.

[0055] Comparative Example 1

[0056] The basic steps are the same as those in Example 1, except that only a heat treatment process is used. Specifically, the steps include:

[0057] (1) heat treating the black powder at 500°C for 6 hours and cooling to room temperature;

[0058] (2) adding the heat-treated product obtained in step (1) into deionized water, controlling the mass ratio to be 1:4 and stirring evenly, slowly adding sulfuric acid dropwise, adjusting the pH of the solution to 1.0, and reacting for 3 hours;

[0059] (3) filtering the mixture after the reaction in step (2), washing with deionized water until neutral, and then drying in an oven at 110° C.;

[0060] (4) transferring the material obtained in step (3) into a crucible, then transferring the crucible into a high temperature treatment device, introducing argon gas, keeping the temperature at 2600° C. for 10 h, and cooling to room temperature;

[0061] (5) mixing the annealed product obtained in step (4) with coal tar pitch in a ratio of 100:3, and high-energy ball milling at a rotation speed of 2000 rpm for 1 h;

[0062] (6) The ball-milled product obtained in step (5) is transferred to a crucible, and the crucible is transferred to a high-temperature treatment device, nitrogen is introduced, and the crucible is kept at 1000° C. for 6 hours. After cooling to room temperature, regenerated graphite is obtained.

[0063] Comparative Example 2

[0064] The basic steps are the same as those in Example 1, except for the annealing temperature in step (5), which specifically includes the following steps:

[0065] (1) black powder and 6.0 mol / L sodium hydroxide aqueous solution were mixed in a crucible at a solid-liquid ratio of 1 g:1 mL and stirred evenly, heat treated at 500° C. for 6 h, and cooled to room temperature;

[0066] (2) The heat-treated product obtained in step (1) is washed with deionized water until neutral and then dried in an oven at 110° C.;

[0067] (3) adding the washed product obtained in step (2) into deionized water, controlling the mass ratio to be 1:4 and stirring evenly, slowly adding sulfuric acid dropwise to adjust the pH of the solution to 1.0, and reacting for 3 hours;

[0068] (4) filtering the mixture after the reaction in step (3), washing with deionized water until neutral, and then drying in an oven at 110° C.;

[0069] (5) transferring the material obtained in step (4) into a crucible, then transferring the crucible into a high temperature treatment device, introducing argon gas, keeping the temperature at 1200° C. for 10 h, and cooling to room temperature;

[0070] (6) mixing the annealed product obtained in step (5) with coal tar pitch in a mass ratio of 100:3, and high-energy ball milling at a rotation speed of 2000 rpm for 1 h;

[0071] (7) The ball-milled product obtained in step (6) is transferred to a crucible, and the crucible is transferred to a high-temperature treatment device, nitrogen is introduced, and the crucible is kept at 1000° C. for 6 hours. After cooling to room temperature, regenerated graphite is obtained.

[0072] The carbon recovered from Examples 1 to 12 and Comparative Examples 1 to 2 was tested for content, secondary discharge specific capacity and first coulombic efficiency, and the results obtained are shown in Table 1 below.

[0073] Table 1 Carbon content, first discharge specific capacity and first coulombic efficiency of regenerated graphite

[0074] Recycled graphite Fixed carbon content (%) <![CDATA[Initial discharge specific capacity (mAh g -1 )]]> First coulombic efficiency (%) Example 1 99.82 383.2 91.9 Example 2 99.79 379.4 91.7 Example 3 99.81 381.3 91.5 Example 4 99.79 378.8 90.8 Example 5 99.81 383.5 90.7 Example 6 99.82 378.7 91.8 Example 7 99.78 384.3 91.5 Example 8 99.83 383.9 90.6 Example 9 99.81 379.6 91.8 Example 10 99.78 378.1 91.2 Embodiment 11 99.80 381.5 90.9 Example 12 99.82 379.4 91.3 Comparative Example 1 92.34 335.5 90.7 Comparative Example 2 99.79 402.3 75.6

[0075] It can be seen from the results of Table 1 that based on the recovery method of the present invention, Examples 1 to 12 all have extremely high fixed carbon content, first discharge specific capacity and first coulomb efficiency, reaching the level of battery-grade graphite. Compared with Comparative Example 1, only a heat treatment process is used before acid leaching, and the recovered carbon content is low, that is, the purity is low. This is because only a heat treatment process is used to remove impurities on the surface of graphite, and impurities between graphite layers cannot be effectively removed, which leads to its overall low purity. Compared with Comparative Example 2, after widening the graphite interlayer spacing, if the interlayer spacing is large and the active sites are reduced because the effect of restoring the graphite spacing is not achieved, more graphite surfaces are exposed to the electrolyte, forming more solid electrolyte membranes, consuming more lithium ions, resulting in a higher first discharge capacity, but a lower first coulomb efficiency and a lower reversible capacity.

[0076] Therefore, based on the present invention, the graphite interlayer spacing is first widened as much as possible to remove impurities that are difficult to remove between the graphite layers, and then sufficient heat treatment is performed to restore the graphite spacing. Only with the cooperation of the two can battery-grade high-purity graphite be recovered.

[0077] In addition to the above embodiments, it should be noted that in the method for recovering graphite from waste lithium-ion batteries of the present invention, the mass ratio of the dried product to deionized water during acid leaching can also be 1: (2-6), the acid solution used for acid leaching can also be oxalic acid or citric acid, the pH value adjusted by acid leaching can also be 0.5-1.5, and the reaction time can be 0.5-5h. The reaction temperature of high-temperature annealing after acid leaching can also be 2000-3000°C, and the reaction time can be 2-18h. The carbon source used for carbon coating can also be phenolic resin or epoxy resin, and the mass ratio of annealed product to carbon source can also be 100: (1-5). The heat treatment atmosphere after carbon coating can also be argon or hydrogen-argon mixed gas. The speed of the mixed ball milling of the annealed product and the carbon source is also 800-2000rpm. The heat treatment temperature of carbon coating can be 800-1200°C, and the reaction time is 2-10h.

[0078] That is, within the above parameter range, the technical effects claimed by the present invention can be obtained, and thus they will not be listed one by one for verification.

Claims

1. A method for recovering graphite from waste lithium-ion batteries, characterized in that: The steps include: (1) Heat treatment: After the waste lithium-ion battery raw materials are mixed with the alkaline solution and stirred evenly, heat treatment is performed at 400-600° C. for 2-10 hours, and cooling to room temperature to obtain a heat-treated product; (2) Acid leaching reaction: After washing and drying the heat-treated product, acid leaching reaction is performed for 0.5-6 hours; (3) High temperature annealing: the mixture after the acid leaching reaction is filtered, washed, and dried, and then kept at 2000-3000°C for 2-18 hours, and then cooled to room temperature to obtain an annealed product; (4) Carbon coating: The annealed product is mixed with a carbon source and ball-milled, and the mixture is reacted at 800-1200°C in an inert atmosphere for 2-10 hours. The regenerated graphite is then obtained by cooling to room temperature.

2. The method for recovering graphite from waste lithium-ion batteries according to claim 1, characterized in that: In step (1), the alkaline solution is a sodium hydroxide or potassium hydroxide solution with a molar concentration of 1 to 12 mol / L.

3. The method for recovering graphite from waste lithium-ion batteries according to claim 1 or 2, characterized in that: The solid-to-liquid ratio of the waste lithium-ion battery raw material to the alkaline solution is 1 g: (0.5-2) mL.

4. The method for recovering graphite from waste lithium-ion batteries according to claim 1, characterized in that: In step (2), the acid leaching is to mix the dried product with deionized water in a mass ratio of 1:(2-6), and then add acid solution dropwise until the pH value is 0.5-1.

5.

5. The method for recovering graphite from waste lithium-ion batteries according to claim 1 or 4, characterized in that: The acid solution used in the acid leaching is sulfuric acid, concentrated hydrochloric acid, oxalic acid or citric acid.

6. The method for recovering graphite from waste lithium-ion batteries according to claim 1 or 4, characterized in that: In step (4), the carbon source is asphalt, phenolic resin or epoxy resin, and the mass ratio of the annealing product to the carbon source is 100:(1-5).

7. The method for recovering graphite from waste lithium-ion batteries according to claim 1 or 4, characterized in that: The asphalt includes at least one of coal tar asphalt, petroleum asphalt or natural asphalt.

8. The method for recovering graphite from waste lithium-ion batteries according to claim 1 or 4, characterized in that: In step (4), the inert atmosphere is nitrogen, argon or a hydrogen-argon mixed gas.

9. The method for recovering graphite from waste lithium-ion batteries according to claim 1 or 4, characterized in that: In step (4), the rotation speed of the mixed ball milling of the annealed product and the carbon source is 800-2000 rpm.

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