A method for recycling positive electrodes of waste lithium-ion batteries

Abstract

The invention provides a method for recycling positive electrodes of waste lithium ion batteries, and relates to the technical field of recycling positive electrodes of waste lithium ion batteries. The method utilizes the characteristic that positive electrode waste of lithium cobalt oxide batteries contains both lithium cobalt oxide and a high-purity aluminum foil current collector, combines recycling of lithium cobalt oxide positive electrodes with aluminothermic reduction reaction, thereby smelting valuable metals such as cobalt and aluminum through aluminothermic reduction reaction, with low smelting cost, and controls and delays aluminothermic reaction rate and improves safety by utilizing carbonization of a binder in the positive electrode of the waste lithium ion battery into amorphous carbon, and avoids waste of resources and energy consumption caused by direct combustion and removal of PVDF. The method for recycling positive electrodes of waste lithium ion batteries has low cost, is environmentally friendly, and has high valuable metal recovery efficiency.

Description

Technical Field

[0001] The invention relates to the technical field of recycling positive electrodes of waste lithium-ion batteries, and in particular to a method for recycling positive electrodes of waste lithium-ion batteries. Background Art

[0002] In recent years, the global electric vehicle and new energy storage market has exploded, driving the rapid increase in demand for lithium batteries. As a result, the demand for resources such as lithium, cobalt, and nickel has also gradually increased. However, due to the relatively low reserves of the above elements in the earth's crust (such as cobalt), and the current large number of lithium-ion batteries are facing major sustainable development issues such as retirement and subsequent harmless treatment and resource utilization. Among them, the content of valuable metal components in lithium-ion batteries is relatively certain (the most economically valuable metal elements are Li and Co), which far exceeds the content of natural ores. Therefore, the research on the resource recycling of waste lithium batteries is a very necessary and urgent task.

[0003] Commonly used waste lithium battery recycling technologies mainly include pyrometallurgy and hydrometallurgy. The advantages of pyrometallurgy are that it can process a wide range of raw materials, large processing capacity, simple process, and no need for battery pretreatment, but the process usually requires a high smelting temperature (above 1400°C), high energy cost, and cannot directly recover Li. Metal recovery in the alloy requires further refining. A large amount of harmful gases will also be emitted during the smelting process, and strict safety precautions and pollution treatment facilities need to be taken; hydrometallurgy has the advantages of high metal recovery rate and product purity, strong product flexibility, low energy consumption, high energy utilization rate, and no waste gas emissions, but its process usually requires the use of corrosive solvents such as hydrochloric acid, sulfuric acid and nitric acid, and has the disadvantages of large reagent consumption and a large amount of salt-containing wastewater that needs to be treated.

[0004] The prior art with Chinese patent number CN110541077A discloses a method for recovering valuable components from waste lithium cobalt oxide battery positive electrode sheets, which uses a pyrolysis method to remove residual electrolyte and organic binder in the positive electrode sheet, and simultaneously achieves thermal reduction of the lithium cobalt oxide in the positive electrode sheet; through hydraulic stirring and water bath heating, the positive electrode sheet material particles and aluminum foil are efficiently dissociated, and the water-soluble lithium-containing compounds are ionized simultaneously to achieve the purpose of separating lithium and cobalt elements; a screening method is used to separate and purify the electrode material and the aluminum foil; and the cobalt element is purified by acid leaching with an acid without a reducing agent.

[0005] Due to the high cost of aluminum smelting, thermite reaction is generally used in welding rails, aerospace ignition and other fields, and is rarely used to smelt other metals. Therefore, there is an urgent need for a low-cost, environmentally friendly and efficient recycling method for the positive electrode of waste lithium-ion batteries. Summary of the invention

[0006] The purpose of the present invention is to provide a method for recycling positive electrodes of waste lithium ion batteries in view of the shortcomings of the prior art. The method utilizes the characteristics that waste positive electrodes of lithium cobalt oxide batteries contain both lithium cobalt oxide and a high-purity aluminum foil current collector, combines the recycling of lithium cobalt oxide positive electrodes with aluminothermic reduction reaction, thereby smelting valuable metals such as cobalt and aluminum through aluminothermic reduction reaction, with low smelting cost, and controls and delays the aluminothermic reaction rate and improves safety by utilizing the carbonization of a binder in the positive electrodes of waste lithium ion batteries into amorphous carbon, thereby avoiding the waste of resources and energy consumption caused by direct combustion and removal of PVDF. The method for recycling positive electrodes of waste lithium ion batteries has low cost, is environmentally friendly and has high efficiency in recovering valuable metals.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] A method for recycling positive electrodes of waste lithium-ion batteries comprises the following steps:

[0009] S1. Discharge the retired ternary or lithium cobalt oxide batteries, disassemble them and dry them in a negative pressure environment to remove the volatile solvent in the electrolyte and obtain the positive electrode sheet;

[0010] S2, rolling the positive electrode sheet obtained in step S1 into a strip, transferring it to an atmosphere furnace, heating it for the first time under a nitrogen atmosphere, then controlling the nitrogen flow rate for purging, and heating it for the second time to carbonize the binder into amorphous carbon, and the tail gas of the nitrogen atmosphere is absorbed by an alkaline solution and then discharged;

[0011] S3, transferring the strips cooled in step S2 to an explosion-proof furnace, wherein the explosion-proof furnace contains a high-temperature resistant reaction plate with grooves, one end of the high-temperature resistant reaction plate is raised to form a high end and a low end, the strips are laid on the grooves of the high-temperature resistant reaction plate, and an aluminothermic igniter is used at the high end to initiate the aluminothermic reaction of the strips and blocks of positive electrode material;

[0012] S4, after the reaction of step S3 is completed, the metallic lithium is collected on the cooling plate at the gas outlet at the upper end of the explosion-proof furnace, and an alloy crucible is set at the lower end of the high-temperature resistant reaction plate to collect the molten cobalt-aluminum alloy;

[0013] S5. The high-temperature exhaust gas in step S4 is used as a heat source for drying the positive electrode after the battery is disassembled in step S1. The oxide slag remaining from the reaction is reduced in the subsequent repeated step S3 to generate new residue.

[0014] Preferably, in step S2, the positive electrode sheets are rolled into strips at 20-80 MPa after being agglomerated.

[0015] Preferably, in step S2, the atmosphere furnace is heated for the first time from room temperature to 280°C at a rate of 10°C / min.

[0016] Preferably, in step S2, the nitrogen purge flow rate is greater than 0.5 L / min.

[0017] Preferably, in step S2, the atmosphere furnace is heated for the second time at a rate of 2°C / min to 360°C and then maintained for 0.5-1.0h.

[0018] Preferably, in step S2, the alkaline solution is a sodium hydroxide solution.

[0019] Preferably, in step S3, the high temperature resistant reaction plate is elevated at an angle of 10 to 30 degrees.

[0020] Preferably, in step S3, the explosion-proof furnace is filled with nitrogen or argon atmosphere.

[0021] Preferably, in step S4, the molten cobalt-aluminum alloy is separated by utilizing density difference.

[0022] In step S3, the explosion-proof furnace includes: a furnace body, a gas outlet is opened on the top of the furnace body, and a cooling plate is arranged in the gas outlet; a reaction plate, the reaction plate is obliquely installed in the furnace body to form a high end and a low end, and the reaction plate has a groove; and an alloy crucible, the alloy crucible is arranged at the low end of the reaction plate.

[0023] The beneficial effects of the present invention are:

[0024] 1. This method combines the recovery of lithium cobalt oxide positive electrode with aluminothermic reduction reaction by utilizing the characteristics that the positive electrode waste of lithium cobalt oxide battery contains both lithium cobalt oxide and high-purity aluminum foil current collector, thereby smelting cobalt and aluminum valuable metals through aluminothermic reduction reaction, with low smelting cost, and controlling and delaying the aluminothermic reaction rate and improving safety by utilizing the binder in the positive electrode of waste lithium ion batteries to be carbonized into amorphous carbon;

[0025] 2. Since conventional heating cannot be achieved (temperature above 2000°C) and the energy consumption cost is high, carbon reduction is not used in industry but electrolysis is used to reduce alumina. The present invention utilizes the high temperature (above 3000°C) generated by the aluminothermic reaction itself to achieve a coordinated carbon reduction reaction of alumina to recover aluminum, thus overcoming the high energy consumption and difficulty of carbon reduction of alumina.

[0026] 3. The present invention adopts low-temperature pre-carbonization to convert the PVDF binder into a carbon source for subsequent thermite reaction to cooperate with carbon to reduce alumina, which can appropriately delay the intensity of thermite reaction and avoid the waste of resources and energy caused by direct combustion and removal of PVDF at 500-600°C in the current actual recycling of waste lithium batteries.

[0027] In summary, the method for recycling the positive electrode of waste lithium-ion batteries of the present invention has the advantages of low cost, low energy consumption, environmental friendliness and high efficiency of valuable metal recovery. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1The XRD spectra of Li and Co collected after the reaction in Example 1 of the present invention;

[0029] Figure 2 It is a structural schematic diagram of the explosion-proof furnace in the present invention. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined.

[0032] Embodiment 1

[0033] like Figure 1 As shown, the present invention provides a method for recycling the positive electrode of waste lithium-ion batteries, comprising the following steps:

[0034] S1. Discharge the retired ternary or lithium cobalt oxide battery, disassemble it in a negative pressure environment to obtain the positive electrode sheet and dry it to remove the volatile solvent in the electrolyte;

[0035] It should be noted that in step S1, the positive electrode sheet is prepared by slurrying the positive electrode active material (lithium cobalt oxide, etc.), the binder (PVDF), and the conductive carbon powder together, coating the slurry on the aluminum foil, and drying the slurry.

[0036] S2, rolling the positive electrode sheet obtained in step S1 into a strip at 20-80 MPa, transferring it to an atmosphere furnace, setting the atmosphere furnace to first heat up from room temperature to 280°C at a rate of 10°C / min, then controlling the nitrogen flow rate to be greater than 0.5 L / min, and continuing to heat up to 360°C at a rate of 2°C / min and then maintaining it for 0.5-1.0h to carbonize the binder into amorphous carbon; the tail gas is absorbed by the alkaline solution and then discharged;

[0037] It should be noted that in step S2, the scrapped positive electrode sheets are directly rolled into strips; the reaction equation for carbonization of the binder into amorphous carbon is as follows:

[0038] Reaction 1: (CH2CF2) n →2nHF+2nC;

[0039] Since the HF produced by the above reaction 1 will corrode the aluminum foil and generate AlF3, the HF is quickly blown out by controlling the nitrogen flow rate to be greater than 0.5 L / min, thereby reducing the contact time between the aluminum foil and the HF generated at low temperature;

[0040] In addition, the purpose of rolling in step S2 is:

[0041] (1) Since the positive electrode active materials such as lithium cobalt oxide are evenly coated on the aluminum foil through the binder, the positive electrode active materials and the binder will also be evenly wrapped in the long strip of positive electrode rolled material during rolling. Therefore, rolling is performed first and then the carbonization reaction is performed. This can avoid the problem of powder separation caused by heating and carbonization before rolling, so that the pre-carbonized carbon particles are evenly retained in the aluminum foil rolled material, thereby delaying the aluminum thermal reaction to a certain extent, controlling its reaction rate, and improving safety;

[0042] (2) Since the specific surface area of ​​the aluminum foil is greatly reduced after rolling, the contact area of ​​the aluminum foil that can be corroded by HF produced by the carbonization and decomposition of the binder is reduced. Therefore, rolling can reduce the contact area between the aluminum foil and the HF decomposition product of the binder during the low-temperature pre-carbonization process, thereby reducing the corrosion consumption of the aluminum foil.

[0043] S3, transferring the strips cooled in step S2 to an explosion-proof furnace in a nitrogen or argon atmosphere, wherein the explosion-proof furnace contains a high-temperature resistant reaction plate with a groove, one end of the high-temperature resistant reaction plate is raised by 10 to 30 degrees to form a high end and a low end, the strips are laid on the groove of the high-temperature resistant reaction plate, and an aluminothermic igniter is used at the high end to initiate the aluminothermic reaction of the strip block positive electrode material;

[0044] In step S3, thermite reaction is a conventional technical means in the field of metal smelting, and the general reaction formula is:

[0045] Reaction 2: 2yAl+3MxOy→yAl2O3+3xM (M is a metal element);

[0046] It should be noted that the amorphous carbon obtained by carbonizing the binder in step S2 participates in the aluminothermic reaction in step S3. Specifically, the reactions involved include C directly reducing LiCoO2 and generating CO2 (reaction 3), CO2 generated in reaction 3 further reacting with C and generating CO (reaction 4), CO generated in reaction 4 further reducing LiCoO2 (reaction 5), and C directly reducing Al2O3 (reaction 6). The relevant chemical reaction equations are as follows:

[0047] Reaction 3: 3C + 4LiCoO2 = 2Li2CO3 + 4Co + CO2;

[0048] Reaction 4: C + CO2 = 2CO;

[0049] Reaction 5: 3CO + 2LiCoO2 = Li2CO3 + 2Co + 2CO2;

[0050] Reaction 6: 3C + 2Al2O3 = 4Al + 3CO2 (2300°C);

[0051] In addition, lithium carbonate decomposes at high temperatures to form lithium oxide: Li2CO3=Li2O+CO2, which further participates in reaction 2 to obtain metallic lithium.

[0052] Since the above reactions are all endothermic reactions, they can absorb the heat generated by the thermite reaction, thereby slowing down the rate of the thermite reaction to a certain extent.

[0053] S4, after the reaction of step S3 is completed, the metallic lithium is collected on the cooling plate at the gas outlet at the upper end of the explosion-proof furnace, and an alloy crucible is set at the lower end of the high-temperature resistant reaction plate to collect the molten cobalt-aluminum alloy, and the molten alloy is subsequently separated by density difference;

[0054] It should be noted that in step S4, since aluminum is a relatively light metal and cobalt has a very high density, the cobalt and aluminum in the molten cobalt-aluminum alloy can be separated by using a conventional density difference separation method.

[0055] S5. The high-temperature exhaust gas in step S4 is used as a heat source for drying the positive electrode after the battery is disassembled in step S1. In addition, the oxide slag remaining from the reaction is reduced in the subsequent repeated aluminum thermal coordinated carbon thermal reduction step S3 to produce new residue.

[0056] It should be noted that in step S5, the oxide slag components remaining after the reaction include aluminum oxide, lithium oxide, cobalt oxide, etc., and the subsequent reduction reaction is carried out according to the general formula of reaction 2.

[0057] Embodiment 2

[0058] like Figure 1As shown, the components identical or corresponding to those in the first embodiment are marked with the corresponding reference numerals in the first embodiment. For the sake of simplicity, only the differences from the first embodiment are described below. The second embodiment differs from the first embodiment in that:

[0059] A method for recycling positive electrodes of waste lithium-ion batteries comprises the following steps:

[0060] S1. After discharging the retired lithium cobalt oxide battery to nearly 0V, disassemble it in a negative pressure environment, sort and screen to obtain the positive electrode sheet, and dry it to remove the excess electrolyte solvent;

[0061] S2, rolling the positive electrode sheet obtained in step S1 into a strip at 30MPa, transferring it to an atmosphere furnace, and first heating it from room temperature to 280°C at a rate of 10°C / min under a nitrogen atmosphere; then controlling the nitrogen flow rate to be greater than 0.8L / min, and continuing to heat it to 360°C at a rate of 2°C / min and then maintaining it for 1.0h, so that the binder is carbonized into amorphous carbon, and the tail gas is absorbed by a sodium hydroxide solution and then discharged;

[0062] S3, transferring the strip block cathode material after cooling in step S2 to an explosion-proof furnace in a nitrogen atmosphere, wherein the furnace body 1 of the explosion-proof furnace contains a high temperature resistant reaction plate 3 with a groove 31, wherein one end of the reaction plate 3 is raised by 30° to form a high end and a low end, wherein the strip block cathode material is laid on the groove 31 of the high temperature resistant reaction plate 3, and an aluminothermic igniter is used at the high end to initiate an aluminothermic reaction of the strip block cathode material;

[0063] S4, after the reaction in step S3 is completed, the metallic lithium is collected on the cooling plate 2 at the gas outlet 11 at the upper end of the furnace body 1, and an alloy crucible 4 is set at the lower end of the reaction plate 3 to collect the molten cobalt-aluminum alloy, and the molten cobalt-aluminum alloy is separated by density difference;

[0064] S5. The high-temperature tail gas of step S4 is used as a heat source for drying the positive electrode after disassembly. The oxide slag remaining from the reaction is reduced in the subsequent repeated step S3 to generate new residue.

[0065] Embodiment 3

[0066] like Figure 2 As shown, the components identical or corresponding to those in the second embodiment are marked with the corresponding reference numerals in the second embodiment. For the sake of simplicity, only the differences from the second embodiment are described below. The difference between the third embodiment and the second embodiment is that:

[0067] This embodiment provides the structure of the explosion-proof furnace in step S3, such as Figure 2 As shown, specifically including:

[0068] A furnace body 1, wherein an air outlet 11 is provided at the top of the furnace body 1, and a cooling plate 2 is arranged in the air outlet 11; a reaction plate 3, wherein the reaction plate 3 is obliquely installed in the furnace body 1 to form a high end and a low end, and the reaction plate 3 has a groove 31; and an alloy crucible 4, wherein the alloy crucible 4 is arranged at the low end of the reaction plate 3.

[0069] Preferably, the reaction plate 3 is resistant to high temperatures, and one end thereof is raised by 10-30 degrees to form a high end and a low end.

[0070] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for recycling the positive electrode of waste lithium-ion batteries, characterized in that: The following steps are involved: S1. Discharge the retired ternary or lithium cobalt oxide batteries, disassemble them and dry them in a negative pressure environment to remove the volatile solvent in the electrolyte and obtain the positive electrode sheet; S2, rolling the positive electrode sheet obtained in step S1 into a strip, transferring it to an atmosphere furnace, heating it for the first time under a nitrogen atmosphere, then controlling the nitrogen flow rate for purging, and heating it for the second time to carbonize the binder into amorphous carbon, and the tail gas of the nitrogen atmosphere is absorbed by an alkaline solution and then discharged; The reaction equation for the carbonization of the binder to amorphous carbon is as follows: Reaction 1: (CH2CF2) n →2nHF+2nC; In step S2, the positive electrode sheet is rolled into a strip at 20-80 MPa after being agglomerated; In step S2, the atmosphere furnace is heated for the first time from room temperature to 280°C at a rate of 10°C / min; In step S2, the nitrogen purge flow rate is greater than 0.5 L / min; In step S2, the atmosphere furnace is heated for the second time at a rate of 2°C / min to 360°C and then maintained for 0.5-1.0h; S3, transferring the strips cooled in step S2 to an explosion-proof furnace, wherein the explosion-proof furnace contains a high-temperature resistant reaction plate with grooves, one end of the high-temperature resistant reaction plate is raised to form a high end and a low end, the strips are laid on the grooves of the high-temperature resistant reaction plate, and an aluminothermic igniter is used at the high end to initiate the aluminothermic reaction of the strips and blocks of positive electrode material; The reaction equation for amorphous carbon participating in the thermite reaction is as follows: Reaction 3: 3C + 4LiCoO2 = 2Li2CO3 + 4Co + CO2; Reaction 4: C + CO2 = 2CO; Reaction 5: 3CO + 2LiCoO2 = Li2CO3 + 2Co + 2CO2; Reaction 6: 3C + 2Al2O3 = 4Al + 3CO2 (2300°C); In addition, lithium carbonate decomposes at high temperatures to form lithium oxide: Li2CO3=Li2O+CO2, which further participates in thermite reaction to obtain metallic lithium; S4, after the reaction of step S3 is completed, the metallic lithium is collected on the cooling plate at the gas outlet at the upper end of the explosion-proof furnace, and an alloy crucible is set at the lower end of the high-temperature resistant reaction plate to collect the molten cobalt-aluminum alloy; S5. The high-temperature exhaust gas in step S4 is used as a heat source for drying the positive electrode after the battery is disassembled in step S1. The oxide slag remaining from the reaction is reduced in the subsequent repeated step S3 to generate new residue.

2. A method for recycling positive electrodes of waste lithium-ion batteries according to claim 1, characterized in that: In step S2, the alkaline solution is a sodium hydroxide solution.

3. A method for recycling positive electrodes of waste lithium-ion batteries according to claim 1, characterized in that: In step S3, the high temperature resistant reaction plate is raised at an angle of 10 to 30 degrees.

4. A method for recycling positive electrodes of waste lithium-ion batteries according to claim 1, characterized in that: In step S3, the explosion-proof furnace is filled with nitrogen or argon atmosphere.

5. The method for recycling positive electrodes of waste lithium-ion batteries according to claim 1, characterized in that: In step S4, the molten cobalt-aluminum alloy is separated by utilizing density difference.

6. A method for recycling positive electrodes of waste lithium-ion batteries according to claim 1, characterized in that: In step S3, the explosion-proof furnace comprises: A furnace body, wherein a gas outlet is provided on the top of the furnace body, and a cooling plate is provided in the gas outlet; a reaction plate, the reaction plate being obliquely mounted in the furnace body to form a high end and a low end, the reaction plate being provided with a groove; and The alloy crucible is arranged at the lower end of the reaction plate.

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