Method for separating and recycling lithium and cobalt in lithium cobalt oxide positive plate and application

Abstract

The invention provides a method for separating and recycling lithium and cobalt in a lithium cobalt oxide positive plate and application. The method for separating and recycling lithium and cobalt in the lithium cobalt oxide series positive plate comprises the following steps: disassembling a waste battery to obtain a lithium cobalt oxide positive plate and a graphite negative plate, carrying out first pretreatment on the lithium cobalt oxide positive plate to obtain lithium cobalt oxide powder, and carrying out second pretreatment on the graphite negative plate to obtain graphite powder; mixing the lithium cobalt oxide powder and the graphite powder according to a certain mass to obtain a mixed material, and pressing the mixed material to obtain a material block; putting the material block into a reaction chamber, introducing protective gas, and carrying out intermittent laser scanning on the material block by adopting a laser so as to recover the elemental cobalt agglomerated into balls and gaseous lithium carbonate. The separation and recovery method has the advantages of solid reduction and smelting reduction in traditional pyrogenic process recovery, does not need a further leaching process, has high efficiency in the aspects of material recovery and time, and has the characteristics of cost effectiveness and low energy consumption.

Description

Technical Field

[0001] The present invention relates to the technical field of recycling and utilization of lithium-ion batteries, particularly to the recycling and utilization of cathode materials, and more particularly to a method for separating and recovering lithium and cobalt in a lithium cobalt oxide-based cathode sheet and its application. Background Art

[0002] Lithium cobalt oxide is the earliest commercially applied cathode material for lithium-ion batteries, which has the characteristics of high energy density and good safety, and is widely used in mobile electronic devices such as mobile phones, laptops, cameras, etc. Waste lithium cobalt oxide secondary batteries have become the main type of waste lithium-ion batteries, which contain a large amount of cobalt resources. Therefore, waste lithium cobalt oxide secondary batteries have been studied earlier, and their recycling methods are also applicable to the recycling of waste ternary, lithium manganate and other types of lithium batteries.

[0003] At present, the research on the recycling of waste lithium cobalt oxide secondary batteries mainly focuses on the recovery of valuable metals such as cobalt and lithium with high recovery value and large content. The main recycling methods are wet process and pyrometallurgical process.

[0004] The wet process is to separate metal ions by using a liquid medium. The process conditions are mild and the energy consumption is small. It mainly includes pretreatment, leaching, recovery and other links. The purpose of leaching is to transfer the valuable metals in the cathode material into the leaching solution, which is beneficial to the subsequent precipitation and purification processes. The wet leaching of the cathode material of waste lithium-ion batteries is mainly an acid leaching scheme. At the same time, since trivalent cobalt compounds are not easily dissolved and leached, inorganic acid (sulfuric acid, hydrochloric acid or nitric acid) + hydrogen peroxide is used as the most common leaching system. The combination of inorganic acid + hydrogen peroxide can leach the cathode material better, but the inorganic acid has strong corrosiveness, high requirements for equipment, and is easy to generate harmful gases.

[0005] The pyrometallurgical process generally burns the electrode sheet at high temperature to burn off the carbon and organic matter in the broken electrode sheet, and the remaining ash that cannot be burned is finally screened to obtain a fine powder material containing metals and metal oxides. The traditional pyrometallurgical process mainly includes two types: solid-state reduction and smelting reduction. Among them, solid-state reduction reduces the cathode to metal alloy powder in the form of carbothermal reduction, but subsequent leaching processes are still required for separation. Smelting reduction directly reduces the cathode to liquid metal at high temperature, but there are limitations such as high energy consumption and difficulty in separating the obtained liquid alloy from the slag. Summary of the Invention

[0006] Based on the above problems, the purpose of the present invention is to provide a method for separating and recovering lithium and cobalt in a lithium cobalt oxide-based cathode sheet and its application. This separation and recovery method can combine the advantages of solid-state reduction and smelting reduction in traditional pyrometallurgical recycling, and does not require further leaching processes. It has high efficiency in terms of material recovery and time, and at the same time has the characteristics of cost-effectiveness and low energy consumption.

[0007] To achieve the above object, on the one hand, the present invention provides a method for separating and recovering lithium and cobalt in a lithium cobalt oxide-based positive electrode sheet, including: (1) Preparation of materials Dismantle waste batteries to obtain lithium cobalt oxide positive electrode sheets and graphite negative electrode sheets. Perform a first pretreatment on the lithium cobalt oxide positive electrode sheets to obtain lithium cobalt oxide powder, and perform a second pretreatment on the graphite negative electrode sheets to obtain graphite powder. (2) Sample preparation Mix the lithium cobalt oxide powder and the graphite powder in a certain mass to obtain a mixed material, and press the mixed material to obtain a material block. (3) Laser sintering Place the material block in a reaction chamber and introduce a protective gas. Use a laser to perform intermittent laser scanning on the material block to recover elemental cobalt condensed into spheres and lithium carbonate in gaseous form.

[0008] Compared with the traditional pyrometallurgical process, the present invention adopts the laser sintering method, the reaction speed is greatly accelerated, the reduction reaction is completed faster, and there is no need for subsequent leaching process, and Li and Co in the lithium cobalt oxide material can be conveniently separated and recovered. At the same time, laser sintering recovery is an in-situ recovery process, and no other chemical reagents need to be added throughout the process. The specific process of laser sintering recovery of the present invention is as follows.

[0009] The present invention makes a material block from lithium cobalt oxide powder and graphite powder for intermittent laser sintering. During the sintering process, when the surface of the material block is heated by a laser beam, its temperature can instantaneously rise above 1500 °C. LiCoO that does not contact graphite 2 undergoes a thermal decomposition reaction to generate lithium oxide and cobalt oxide, while LiCoO that contacts graphite 2 and graphite undergo a thermal reduction reaction. Due to the temperature difference inside the material block, the temperature in the area close to the laser port is high, and the product of the thermal reduction reaction is molten (liquid) elemental Co. Due to intermittent laser sintering, the surface of the material block is in a heating-cooling cycle, so the molten elemental Co can condense into cobalt balls for cobalt recovery. At the same time, after the elemental Co condenses, the underlying material block is exposed, and the elemental Co in it continues to condense and be recovered. The cobalt oxide generated by the thermal decomposition reaction and the thermal reduction reaction will react with the slowly exposed graphite to generate elemental cobalt, which continues to participate in the above reaction and is condensed, so that the cobalt oxide is converted into elemental cobalt and recovered. The lithium carbonate generated by the thermal reduction reaction and the lithium carbonate generated by the reaction of lithium oxide and carbon dioxide will be presented in gaseous form due to its boiling point being lower than the temperature reached by laser sintering and can be trapped, so as to separate and recover Li and Co.

[0010] As a technical solution of the present invention, the lithium cobalt oxide-based positive electrode sheet includes a positive electrode active material, a binder, and a conductive agent, and the chemical formula of the positive electrode active material is Li aCo b M (1-b) O 2 wherein, M is at least one of Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V, and Ti, 0.95 ≤ a ≤ 1.05, 0.95 ≤ b ≤ 1.00, the binder includes PVDF, and the conductive agent includes at least one of conductive carbon black, conductive graphite, carbon fiber, carbon nanotube, and graphene.

[0011] As a technical solution of the present invention, the first pretreatment includes sintering the lithium cobalt oxide positive electrode sheet at 400 - 600 °C for 2 - 4 h and crushing it to obtain the lithium cobalt oxide powder.

[0012] As a technical solution of the present invention, the second pretreatment includes crushing and screening the graphite negative electrode sheet to obtain the graphite powder.

[0013] As a technical solution of the present invention, the mass ratio of the lithium cobalt oxide powder to the graphite powder is 3 - 4:1.

[0014] As a technical solution of the present invention, the pressing is performed by a cold press at 70 - 90 MPa for 1 - 2 min.

[0015] As a technical solution of the present invention, the protective gas includes at least one of nitrogen, argon, helium, neon, and xenon.

[0016] As a technical solution of the present invention, the power of the intermittent laser scanning is 1500 - 2000 W, the duration of each scanning is 10 - 40 s, and the interval time is 5 - 20 s.

[0017] As a technical solution of the present invention, the reaction chamber is provided with a flue gas recovery device to recover the lithium carbonate.

[0018] On the other hand, the present invention provides an application of a method for lithium - cobalt separation and recovery in a lithium cobalt oxide - based positive electrode sheet in a lithium cobalt oxide secondary battery, with the lithium recovery rate ≥ 90% and the cobalt recovery rate ≥ 95%. Detailed Embodiments

[0019] The present invention provides a method for lithium - cobalt separation and recovery in a lithium cobalt oxide - based positive electrode sheet, which can realize the separation and purification of Li and Co.

[0020] The lithium cobalt oxide - based positive electrode sheet of the present invention refers to a positive electrode sheet containing a lithium cobalt oxide - based positive electrode active material. The lithium cobalt oxide - based positive electrode sheet includes a positive electrode active material, a binder, and a conductive agent. The positive electrode active material includes a lithium cobalt oxide - based positive electrode active material, and its chemical formula is Li a Co b M (1-b) O 2, wherein, M is at least one of Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V and Ti, 0.95 ≤ a ≤ 1.05, 0.95 ≤ b ≤ 1.00. The binder includes PVDF. The conductive agent includes at least one of conductive carbon black, conductive graphite, carbon fiber, carbon nanotube and graphene. The mass ratio of the positive electrode active material, the binder and the conductive agent can be, but is not limited to, 85-98:0.5-3.0:0.5-3.0. The positive electrode active material, the binder and the conductive agent are made into a slurry with a solvent and coated on the positive electrode current collector, and then dried, roll-pressed, etc. to obtain the positive electrode sheet.

[0021] The method for separating and recovering lithium and cobalt in the lithium cobalt oxide-based positive electrode sheet of the present invention includes the following steps.

[0022] (1) Preparation of materials The waste battery is disassembled to obtain the lithium cobalt oxide positive electrode sheet and the graphite negative electrode sheet. The lithium cobalt oxide positive electrode sheet is subjected to a first pretreatment to obtain lithium cobalt oxide powder, and the graphite negative electrode sheet is subjected to a second pretreatment to obtain graphite powder.

[0023] (2) Sample preparation The lithium cobalt oxide powder and the graphite powder are mixed in a certain mass to obtain a mixed material, and the mixed material is pressed to obtain a material block.

[0024] (3) Laser sintering The material block is placed in the reaction chamber and a protective gas is introduced. The material block is subjected to intermittent laser scanning by a laser to recover the elemental cobalt condensed into spheres and the gaseous lithium carbonate.

[0025] Among them, the first pretreatment includes sintering the lithium cobalt oxide positive electrode sheet at 400-600 °C for 2-4 h and then crushing to obtain lithium cobalt oxide powder. The binder is decomposed by sintering to separate from the current collector, and then lithium cobalt oxide powder can be obtained by crushing. The lithium cobalt oxide powder includes the lithium cobalt oxide positive electrode material and the conductive agent, and the conductive agent such as CNT can act as a reducing agent during the laser sintering process. The second pretreatment includes crushing and screening the graphite negative electrode sheet to obtain graphite powder. The graphite powder includes the graphite negative electrode material and the conductive agent, and the conductive agent can also act as a reducing agent during the laser sintering process.

[0026] The mass ratio of the lithium cobalt oxide powder and the graphite powder is 3-4:1. As an example, it can be, but is not limited to, 3:1, 4:1. The pressing is carried out by a cold press at 70-90 MPa for 1-2 min. Preferably, the lithium cobalt oxide powder and the graphite powder are pressed into a cylindrical shape.

[0027] During laser sintering, the protective gas includes at least one of nitrogen, argon, helium, neon, and xenon. The flow rate of the protective gas is 15 - 30 L / min. As an example, the flow rate can be, but is not limited to, 15 L / min, 16 L / min, 17 L / min, 18 L / min, 19 L / min, 20 L / min, 21 L / min, 22 L / min, 23 L / min, 24 L / min, 25 L / min, 26 L / min, 27 L / min, 28 L / min, 29 L / min, 30 L / min. The power of the intermittent laser scanning is 1500 - 2000 W. As an example, the power can be, but is not limited to, 1500 W, 1600 W, 1700 W, 1800 W, 1900 W, 2000 W. At this power, when the material block is heated by the laser beam, the temperature of the surface part can instantaneously rise above 1500 °C. LiCoO that does not contact graphite 2 undergoes a thermal decomposition reaction as shown in Equation (1), while LiCoO that contacts graphite 2 and graphite undergo thermal reduction reactions as shown in Equations (2) and (3).

[0028] LiCoO 2 →Li 2 O + CoO + O 2 Equation (1) LiCoO 2 + C → Co + Li 2 CO 3 + CoO + O 2 Equation (2) LiCoO 2 + 3C → Co + Li 2 CO 3 + CO 2 Equation (3) As shown in Table 1, the melting point of LiCoO 2 is 1000 °C. When heated by the laser beam, the part that melts and contacts graphite undergoes a thermal reduction reaction, and the part that does not contact undergoes a thermal decomposition reaction. Due to the temperature difference inside the material block, the part closer to the laser port has a higher temperature, and the generated elemental cobalt has a low melting point and is in a molten state (liquid state). Due to the intermittent laser scanning, the surface of the material block is constantly in a heating - cooling cycle. Therefore, when the temperature drops below 1495 °C, the molten elemental cobalt condenses into cobalt balls and is easy to collect. After the elemental cobalt condenses, the bottom of the material block is exposed, and the above - mentioned reaction continues to repeat. In addition, the generated CoO will react with the slowly exposed graphite as shown in Equation (4), and the generated elemental cobalt condenses into cobalt balls as described above and is collected. Li 2 O and CO 2 generate lithium carbonate during the laser sintering process. Based on the melting point and boiling point conditions in Table 1, the generated Li 2 CO 3Due to its low boiling point, it presents in gaseous form and can be captured by a gas collection device. Thus, Li and Co are separated and recovered.

[0029] CoO + C → Co + CO 2 Equation Four Table 1 Melting Points and Boiling Points of Each Substance

[0030] The duration of each laser scan is 10 - 40 s. By way of example, the time can be, but is not limited to, 10 s, 15 s, 20 s, 25 s, 30 s, 35 s, 40 s. The interval time is 5 - 20 s. By way of example, it can be, but is not limited to, 5 s, 7 s, 9 s, 10 s, 12 s, 14 s, 16 s, 18 s, 20 s. The reaction chamber is equipped with a flue gas recovery device to recover lithium carbonate in gaseous form.

[0031] To better illustrate the purpose, technical solution, and beneficial effects of the present invention, the present invention will be further described below in conjunction with specific embodiments. It should be noted that the methods described in the following embodiments are further explanatory descriptions of the present invention and should not be regarded as limitations on the present invention.

[0032] Example 1 This example is a method for separating and recovering lithium and cobalt in a lithium cobalt oxide - based cathode sheet, and the steps are as follows.

[0033] (1) Preparation of materials The used lithium cobalt oxide secondary battery No. 1 is disassembled to obtain a lithium cobalt oxide cathode sheet and a graphite anode sheet. The lithium cobalt oxide cathode sheet is sintered at 500 °C for 4 h and then crushed to obtain lithium cobalt oxide powder, and the graphite anode sheet is crushed and screened to obtain graphite powder.

[0034] (2) Sample preparation The lithium cobalt oxide powder and graphite powder are mixed at a mass ratio of 3:1 to obtain a mixed material, and the mixed material is pressed by a cold press at 90 MPa for 1 min to obtain a material block.

[0035] (3) Laser sintering The material block is placed in the reaction chamber and nitrogen is introduced. The material block is subjected to intermittent laser scanning by a laser. The power of the intermittent laser scanning is 1800 W, the duration of each scan is 25 s, and the interval time is 10 s. The elemental cobalt condensed into balls at the bottom of the reaction chamber is recovered, and lithium carbonate in gaseous form is recovered through a flue gas recovery device connected to the reaction chamber. The recovery rates of lithium and cobalt are calculated to be 95% and 98% respectively, indicating that the recovery rates of lithium and cobalt prepared by the recovery method of the present invention are relatively high.

[0036] Example 2 This example is a method for separating and recovering lithium and cobalt in a lithium cobalt oxide - based cathode sheet, and the steps are as follows.

[0037] (1) Preparation of materials The waste 2# lithium cobalt oxide secondary battery is disassembled to obtain the lithium cobalt oxide positive electrode sheet and the graphite negative electrode sheet. The lithium cobalt oxide positive electrode sheet is sintered at 550 °C for 3 h and then crushed to obtain lithium cobalt oxide powder. The graphite negative electrode sheet is crushed and screened to obtain graphite powder.

[0038] (2) Sample preparation The lithium cobalt oxide powder and the graphite powder are mixed at a mass ratio of 4:1 to obtain a mixed material. The mixed material is pressed by a cold press at 80 MPa for 1 min to obtain a material block.

[0039] (3) Laser sintering The material block is placed in the reaction chamber and argon is introduced. The material block is irradiated by a laser intermittently. The power of the intermittent laser irradiation is 2000 W. The duration of each irradiation is 35 s and the interval time is 15 s. The elemental cobalt condensed into balls at the bottom of the reaction chamber is recovered, and the lithium carbonate in gaseous state is recovered through the flue gas recovery device connected to the reaction chamber. The recovery rates of lithium and cobalt are calculated to be 93% and 97% respectively, indicating that the recovery rates of lithium and cobalt prepared by the recovery method of the present invention are relatively high.

[0040] Example 3 This example is a method for separating and recovering lithium and cobalt in a lithium cobalt oxide-based positive electrode sheet, and the steps are as follows.

[0041] (1) Preparation of materials The waste 3# lithium cobalt oxide secondary battery is disassembled to obtain the lithium cobalt oxide positive electrode sheet and the graphite negative electrode sheet. The lithium cobalt oxide positive electrode sheet is sintered at 400 °C for 4 h and then crushed to obtain lithium cobalt oxide powder. The graphite negative electrode sheet is crushed and screened to obtain graphite powder.

[0042] (2) Sample preparation The lithium cobalt oxide powder and the graphite powder are mixed at a mass ratio of 4:1 to obtain a mixed material. The mixed material is pressed by a cold press at 85 MPa for 2 min to obtain a material block.

[0043] (3) Laser sintering The material block is placed in the reaction chamber and nitrogen is introduced. The material block is irradiated by a laser intermittently. The power of the intermittent laser irradiation is 2000 W. The duration of each irradiation is 40 s and the interval time is... 13 s. The elemental cobalt condensed into balls at the bottom of the reaction chamber is recovered, and the lithium carbonate in gaseous state is recovered through the flue gas recovery device connected to the reaction chamber. The recovery rates of lithium and cobalt are calculated to be 92% and 95% respectively, indicating that the recovery rates of lithium and cobalt prepared by the recovery method of the present invention are relatively high.

[0044] Comparative example 1 This comparative example is a method for separating and recovering lithium and cobalt in a lithium cobalt oxide-based positive electrode sheet, and the steps are as follows.

[0045] (1) Preparation of materials The waste lithium cobalt oxide secondary battery No. 1 was disassembled to obtain a lithium cobalt oxide positive electrode sheet and a graphite negative electrode sheet. The lithium cobalt oxide positive electrode sheet was sintered at 500 °C for 4 h and then crushed to obtain lithium cobalt oxide powder. The graphite negative electrode sheet was crushed and screened to obtain graphite powder.

[0046] (2) Sample preparation The lithium cobalt oxide powder and the graphite powder were mixed at a mass ratio of 3:1 to obtain a mixed material.

[0047] (3) Sintering The mixed material was placed into a reaction chamber and nitrogen was introduced. After heating to 1500 °C for sintering, it was washed with water to dissolve lithium carbonate and then filtered to separate the filter residue. The filter residue was leached with 4M sulfuric acid to obtain cobalt sulfate. The recovery rates of lithium and cobalt were calculated to be 81% and 85% respectively.

[0048] It can be seen from the comparison of Examples 1 to 3 and Comparative Example 1 that the recovery method of the present invention can recover high-content cobalt and lithium. By using intermittent laser sintering and taking advantage of the temperature difference inside the material block and the different melting points and boiling points of various substances, cobalt and lithium can be recovered separately during the sintering process without subsequent leaching process. However, by using the ordinary carbothermal reduction process, the generated lithium carbonate, elemental cobalt and cobalt oxide are mixed together and difficult to separate, and a leaching process is needed to assist in the separation.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, it is not limited to only those listed in the embodiments. Those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for separating and recovering lithium and cobalt from a lithium cobalt oxide positive electrode sheet, characterized in that: include: (1) Preparation of materials Dismantling waste batteries to obtain lithium cobalt oxide positive electrode sheets and graphite negative electrode sheets, subjecting the lithium cobalt oxide positive electrode sheets to a first pretreatment to obtain lithium cobalt oxide powder, and subjecting the graphite negative electrode sheets to a second pretreatment to obtain graphite powder; (2) Sample preparation The lithium cobalt oxide powder and the graphite powder are mixed in a certain mass to obtain a mixture, and the mixture is pressed to obtain a material block; (3) Laser sintering The material block is placed in a reaction chamber and a protective gas is introduced, and a laser is used to intermittently scan the material block to recover the single cobalt condensed into balls and the gaseous lithium carbonate.

2. The method for separating and recovering lithium and cobalt from a lithium cobalt oxide positive electrode sheet according to claim 1, characterized in that: The lithium cobalt oxide positive electrode sheet comprises a positive electrode active material, a binder and a conductive agent. The chemical formula of the positive electrode active material is Li a Co b M (1-b) O2, wherein M is at least one of Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V and Ti, 0.95≤a≤1.05, 0.95≤b≤1.00, the binder includes PVDF, and the conductive agent includes at least one of conductive carbon black, conductive graphite, carbon fiber, carbon nanotube and graphene.

3. The method for separating and recovering lithium and cobalt in a lithium cobalt oxide positive electrode sheet according to claim 1, characterized in that: The first pretreatment includes sintering the lithium cobalt oxide positive electrode sheet at 400-600° C. for 2-4 hours, and crushing it to obtain the lithium cobalt oxide powder.

4. The method for separating and recovering lithium and cobalt in a lithium cobalt oxide positive electrode sheet according to claim 1, characterized in that: The second pre-treatment includes crushing and screening the graphite negative electrode sheet to obtain graphite powder.

5. The method for separating and recovering lithium and cobalt in a lithium cobalt oxide positive electrode sheet according to claim 1, characterized in that: The mass ratio of the lithium cobalt oxide powder to the graphite powder is 3-4:

1.

6. The method for separating and recovering lithium and cobalt in a lithium cobalt oxide positive electrode sheet according to claim 1, characterized in that: The pressing is performed by using a cold press to apply pressure at 70-90 MPa for 1-2 minutes.

7. The method for separating and recovering lithium and cobalt in a lithium cobalt oxide positive electrode sheet according to claim 1, characterized in that: The protective gas includes at least one of nitrogen, argon, helium, neon and xenon.

8. The method for separating and recovering lithium and cobalt in a lithium cobalt oxide positive electrode sheet according to claim 1, characterized in that: The power of the intermittent laser scanning is 1500-2000W, the duration of each scanning is 10-40s, and the interval time is 5-20s.

9. The method for separating and recovering lithium and cobalt in a lithium cobalt oxide positive electrode sheet according to claim 1, characterized in that: The reaction chamber is provided with a fume recovery device to recover the lithium carbonate.

10. Use of the method for separating and recovering lithium and cobalt in a lithium cobalt oxide positive electrode sheet according to any one of claims 1 to 9 in a lithium cobalt oxide secondary battery, characterized in that: The recovery rate of lithium is ≥90%, and the recovery rate of cobalt is ≥95%.

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