Electrochemically-assisted method for rapidly stripping aluminum current collector from positive electrode active material

Abstract

The invention relates to the technical field of lithium battery recovery, and discloses an electrochemically-assisted method for rapidly stripping an aluminum current collector from a positive active material, and the preparation method comprises the following steps: under a certain potential condition, metal aluminum is in a corrosion region and exists in the form of Al < 3 + >-under an acidic condition, and the metal aluminum is in a corrosion region; the surface layer aluminum connected with the positive electrode active material is dissolved, so that a tight interface between the positive electrode active material and the aluminum current collector is damaged, and then H2 is generated on the surface of the aluminum foil under the hydrogen evolution potential to blow the positive electrode active material, so that the positive electrode active material is quickly and effectively separated from the aluminum foil. The method provided by the invention is environment-friendly, simple to operate, low in energy consumption, high in efficiency and free of harmful chemical residues, and provides a new thought for stripping the active material in the field of lithium battery recovery.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium battery recycling, and in particular relates to a method for electrochemically assisted rapid stripping of an aluminum current collector from a positive electrode active material. Background Art

[0002] Due to the advantages of high energy density, high open circuit voltage, high output power, and no memory effect, lithium-ion batteries are widely used in portable electronic devices, new energy vehicles and other fields. This year, the rapid development of the electric vehicle industry has led to a significant increase in the production of lithium-ion batteries, and the number of waste batteries has also increased sharply. The positive electrode materials of waste batteries contain a large amount of metal elements such as Li, Ni, Co, and Mn. Among them, Co is a strategic metal used in military and industrial fields, and its economic benefits cannot be underestimated. In addition, the leakage of a large amount of toxic substances such as precious metal elements, organic and inorganic compounds in lithium-ion batteries will also pollute the environment. Among them, Ni and Co are carcinogenic, mutagenic and reproductive toxic, causing irreparable damage to the human body. Therefore, the recycling of lithium-ion batteries can alleviate the problem of metal resource shortage in my country and effectively protect the ecological environment, which has great economic and social value.

[0003] In the process of recycling waste lithium batteries, the separation of positive electrode materials and aluminum foil current collectors has always been a concern. Positive electrode materials are generally Li-containing compounds, which are mixed with conductive agents and adhesives to form a slurry and then coated on aluminum foil fluid to prepare positive electrode sheets. The adhesive generally uses polyvinylidene fluoride (PVDF), which has played an irreplaceable role in the development of lithium-ion batteries due to its high stability and strong binding effect. However, it also causes the dilemma of extremely difficult separation of positive electrode materials and aluminum foil in the recycling process of lithium-ion batteries. At present, the most commonly used methods are high-temperature calcination, alkaline solution treatment and organic solvent dissolution. Among them, the high-temperature calcination method is the most commonly used and most effective method known because of its advantages such as simplicity, convenience and batch scale. However, it has high requirements for equipment investment and high energy consumption costs, and hydrogen fluoride gas is produced during the decomposition process, which leads to air pollution and equipment corrosion. The alkaline solution treatment method is to place the positive electrode material containing aluminum foil in an alkaline solution, and the alkaline solution reacts with the aluminum foil to peel off the aluminum foil and the positive electrode material. The use of alkaline solution and subsequent treatment increase production costs and environmental costs, and the reaction of alkaline solution with aluminum foil results in a large loss of aluminum, which increases the cost and difficulty of subsequent aluminum recovery and recovery of positive electrode materials. The organic solvent dissolution method is used to peel off the aluminum foil and the positive electrode material, and the PVDF therein can be dissolved to separate the two, but it faces the problems of high chemical reagent prices and environmental unfriendliness, which is even more unacceptable for the lithium battery recycling industry, where the recycling profit is already very meager.

[0004] Therefore, the prior art still needs to be improved and developed. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a method for electrochemically assisted rapid stripping of positive electrode active materials from aluminum current collectors, aiming to solve the problems of high energy consumption, long process and toxicity encountered in the existing lithium battery recycling.

[0006] The technical solution of the present invention is as follows:

[0007] A method for electrochemically assisted rapid stripping of positive electrode active materials from aluminum current collectors, comprising the steps of:

[0008] Discharging and disassembling the waste lithium-ion battery in a salt solution to obtain a positive electrode sheet, wherein the positive electrode sheet includes an aluminum foil and a positive electrode active material adhered to the aluminum foil;

[0009] The positive electrode sheet is used as a working electrode, combined with a counter electrode, a reference electrode and an electrolyte to construct a three-electrode system;

[0010] Based on the three-electrode system, the active dissolution potential and hydrogen evolution potential of the aluminum foil in the positive electrode sheet in the electrolyte were screened by the potentiodynamic polarization curve method.

[0011] Based on the three-electrode system, the positive electrode sheet is subjected to constant potential polarization using an electrochemical workstation under the active dissolution potential condition, so that the aluminum foil surface in the positive electrode sheet undergoes active dissolution to generate Al 3+ , thereby destroying the interface connecting it with the positive electrode active material, and then polarizing the positive electrode sheet for a predetermined time at a hydrogen evolution potential, and further peeling the positive electrode active material from the surface of the aluminum foil through the bubbles generated on the surface of the aluminum foil.

[0012] The electrochemically assisted method for rapid stripping of positive electrode active materials from an aluminum current collector, wherein the positive electrode active material on the aluminum foil is one or more of lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, and lithium iron phosphate.

[0013] The electrochemically assisted method for rapid stripping of positive electrode active materials from aluminum current collectors comprises the following steps: the electrolyte is an acidic solution having a pH value less than 4, and the acidic solution is one or more of sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid and citric acid.

[0014] The electrochemically assisted method for rapid stripping of positive electrode active materials from an aluminum current collector comprises the following steps: the counter electrode is one of a platinum electrode, a titanium electrode, a silver electrode and a graphite electrode; and the reference electrode is a saturated calomel electrode or a silver / silver chloride electrode.

[0015] The electrochemically assisted method for rapid stripping of the positive electrode active material from the aluminum current collector comprises the following steps: the voltage of the constant potential polarization for the positive electrode sheet is 0.5V to 2V vs. the open circuit potential, and the time is 1 to 30 minutes.

[0016] The electrochemically assisted method for rapid stripping of the positive electrode active material from the aluminum current collector comprises the following steps: in the step of polarizing the positive electrode sheet for a predetermined time at a hydrogen evolution potential, the polarization voltage is -1V to -2V vs. the open circuit potential, and the predetermined time is 1-10 minutes.

[0017] Beneficial effect: The present invention provides a method for electrochemically assisted rapid stripping of the positive electrode active material from the aluminum current collector, using the fact that under certain potential conditions, the metal aluminum is in the corrosion zone and will be converted to Al under acidic conditions. 3+ The surface aluminum connected to the positive electrode active material will corrode and dissolve, thereby destroying the tight interface between the positive electrode active material and the aluminum current collector. Then, H2 is generated on the surface of the aluminum foil under the hydrogen evolution potential to blow the positive electrode active material, thereby realizing the rapid and effective separation of the positive electrode active material from the aluminum foil. The peeled high-purity positive electrode active material can be further processed to restore its activity and can continue to be used as a raw material for lithium battery production. The aluminum foil can be directly recycled. The method proposed by the present invention is environmentally friendly, simple to operate, low in energy consumption, high in efficiency, and free of harmful chemical residues, providing a new idea for the stripping of active materials in the field of lithium battery recycling. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A flow chart of a method for electrochemically assisted rapid stripping of positive electrode active materials from an aluminum current collector according to the present invention is shown.

[0019] Figure 2 In the figure, a is a three-electrode system subjected to electrochemical stripping in Example 1, and a picture of the positive electrode material and the aluminum foil current collector being separated during the stripping process; in the figure, b is a picture of the positive electrode active material and the aluminum foil current collector being completely separated after being rinsed with distilled water after stripping.

[0020] Figure 3 This is a SEM characterization image of the morphology of the aluminum foil after electrochemical stripping in Example 1.

[0021] Figure 4 Figure a is a picture of the positive electrode sheet in comparative example 1 after being immersed in a citric acid solution (the positive electrode active material cannot be peeled off from the aluminum foil surface); Figure b is a picture of the separation of the positive electrode active material and the aluminum foil current collector after electrochemical stripping in comparative example 2 (the stripping rate is less than 100%). DETAILED DESCRIPTION

[0022] The present invention provides a method for electrochemically assisted rapid stripping of positive electrode active materials from aluminum current collectors. To make the purpose, technical solution and effect of the present invention clearer and more specific, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0023] See also Figure 1 , Figure 1A flow chart of a method for electrochemically assisted rapid stripping of positive electrode active materials from aluminum current collector provided by the present invention is shown in the figure, which comprises the following steps:

[0024] S10, discharging the waste lithium-ion battery in a salt solution and disassembling the battery to obtain a positive electrode sheet, wherein the positive electrode sheet includes an aluminum foil and a positive electrode active material adhered to the aluminum foil;

[0025] S20, using the positive electrode sheet as a working electrode, combining a counter electrode, a reference electrode and an electrolyte to construct a three-electrode system;

[0026] S30. Based on the three-electrode system, the active dissolution potential and hydrogen evolution potential of the aluminum foil in the positive electrode sheet in the electrolyte are screened by using the potentiodynamic polarization curve method;

[0027] S40, based on the three-electrode system, using an electrochemical workstation to perform constant potential polarization on the positive electrode sheet under the active dissolution potential condition, so that the surface of the aluminum foil in the positive electrode sheet undergoes active dissolution to generate Al 3+ , thereby destroying the interface connecting it with the positive electrode active material, and then polarizing the positive electrode sheet for a predetermined time at a hydrogen evolution potential, and further peeling the positive electrode active material from the surface of the aluminum foil through the bubbles generated on the surface of the aluminum foil.

[0028] Specifically, the present invention proposes a two-step electrochemical assisted method, firstly dissolving part of the aluminum at the interface between the aluminum current collector and the positive electrode active material to generate Al 3+ , and then generate H2 on the surface of the aluminum current collector under the hydrogen evolution potential to blow the positive electrode active material, thereby realizing the rapid separation and recovery of the positive electrode active material and the aluminum current collector. The method provided by the present invention is simple, fast, low in energy consumption, high in separation efficiency, and high in material purity, and provides a new idea for the stripping of active materials in the field of lithium battery recycling.

[0029] In some embodiments, the positive electrode active material on the aluminum foil is one or more of lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, and lithium iron phosphate, but is not limited thereto.

[0030] In some embodiments, the electrolyte is an acidic liquid with a pH value less than 4, and the acidic liquid is one or more of sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid and citric acid, but is not limited thereto.

[0031] In some embodiments, the counter electrode is one of a platinum electrode, a titanium electrode, a silver electrode and a graphite electrode; the reference electrode is a saturated calomel electrode or a silver / silver chloride electrode, but is not limited thereto.

[0032] In some embodiments, the voltage of the positive electrode sheet subjected to constant potential polarization is 0.5V to 2V vs. open circuit potential, and the time is 1-30min, but not limited thereto. Within this voltage range, the chemical reaction of the positive electrode sheet subjected to constant potential polarization in an acidic solution is: Al→Al 3+ Under the action of potential, aluminum will undergo anodic dissolution to generate soluble Al 3+ , the interface between the aluminum current collector and the positive electrode material is destroyed.

[0033] In some embodiments, in the step of polarizing the positive electrode sheet at a hydrogen evolution potential for a predetermined time, the polarization voltage is -1V to -2V vs. open circuit potential, and the predetermined time is 1-10 min.

[0034] The present invention will be further explained below by means of specific embodiments:

[0035] Example 1

[0036] A method for electrochemically assisted rapid stripping of positive electrode active materials from an aluminum current collector comprises the following steps:

[0037] (1) Waste lithium-ion batteries (18650) were discharged for 24 hours using a 20 g / L NaCl solution and then manually disassembled to separate the steel shell, diaphragm, negative electrode sheet (negative electrode material / copper current collector), and positive electrode sheet (positive electrode active material / aluminum current collector).

[0038] (2) Cut the dried positive electrode sheet directly into small pieces, such as Figure 2 As shown in a, it is connected to the electrode clip as the working electrode, the saturated calomel electrode as the reference electrode, the platinum electrode as the counter electrode, and a 0.1 mol / L citric acid solution as the electrolyte. Potentiodynamic polarization is performed on the electrochemical workstation to determine the active dissolution potential and hydrogen evolution potential of the aluminum foil under acidic conditions.

[0039] (3) Take another positive electrode sheet connected to the electrode clip as the working electrode, a saturated calomel electrode as the reference electrode, a platinum electrode as the counter electrode, and a 0.1 mol / L citric acid solution as the electrolyte, and perform constant potential polarization on an electrochemical workstation.

[0040] (4) The potential of the positive electrode sheet was selected to be 1.5 V vs. open circuit potential (OCP), and the working electrode was subjected to constant potential polarization at room temperature for 5 min.

[0041] (5) Then, a -1.5 V potential was applied to the positive electrode sheet after constant potential polarization to conduct a hydrogen evolution experiment for 1 min. Under the action of bubbles, the positive electrode active material was blown off the aluminum current collector.

[0042] During the implementation of this embodiment, bubbles can be seen continuously emerging from the surface of the positive electrode active material, which bulges out soon after and separates from the aluminum foil under the action of the potential. After the experiment, the aluminum foil and the positive electrode active material film can be obtained by washing with distilled water. Figure 2 a in the middle is a three-electrode system for electrochemical stripping, with a picture of the separation of the positive electrode material and the aluminum foil current collector during the stripping process; Figure 2 The photo in b is a photo of the positive electrode active material and the aluminum foil current collector being completely separated after stripping and washing with distilled water. This embodiment utilizes the aluminum anodic dissolution and H2 precipitation in the two-step electrochemical polarization process to achieve efficient separation of the positive electrode active material and the aluminum current collector. The stripping rate of the positive electrode active material and the aluminum foil in the positive electrode sheet immersed in the solution can reach 100% ( Figure 2 The unpeeled portion in (b) is the electrode clamp connection area and is not immersed in the solution).

[0043] The changes in the morphology of the aluminum foil after electrochemical stripping in this example were characterized by SEM. The results are as follows: Figure 3 As shown in the figure, the aluminum content in the solution can be measured by ICP-MS to determine the aluminum foil recovery rate. Figure 3 It can be seen that pits appear on the surface of the aluminum foil after electrochemical polarization, which reduces the contact area between the positive electrode active material and the aluminum current collector, and further realizes the efficient separation of the two under the action of H2 precipitation. At the same time, since the polarization time is very short (5min), the amount of aluminum dissolved is very low, and the aluminum foil can be recycled for resource utilization. In addition, it can be seen from the ICP-MS results that the electrochemical polarization process only causes slight damage to the aluminum current collector, the metal dissolution rate is low, and the aluminum recovery rate is greater than 90%. In addition, impurities will not be mixed into the positive electrode active material, and it can be used as a raw material for battery materials after subsequent recycling and simple treatment.

[0044] Comparative Example 1

[0045] (1) Used batteries (18650) were discharged for 24 hours using a 20 g / L NaCl solution and then manually disassembled to separate the steel shell, diaphragm, negative electrode sheet (negative electrode material / copper current collector), and positive electrode sheet (positive electrode active material / aluminum current collector).

[0046] (2) The dried positive electrode sheet is cut into small pieces and placed in a 0.1 mol / L citric acid solution for direct acid leaching.

[0047] (3) During the immersion in the citric acid solution, bubbles slowly formed on the surface, and there was no obvious change on the surface of the positive electrode after immersion for 5 minutes.

[0048] After the experiment, it was observed that the surface of the positive electrode material lost its glossiness. The scheme of comparative example 1 could not separate the positive electrode active material from the surface of the aluminum foil (such as Figure 4 (shown in a).

[0049] Comparative Example 2

[0050] A method for stripping a positive electrode active material from an aluminum current collector comprises the following steps:

[0051] (1) Used batteries (18650) were discharged for 24 hours using a 20 g / L NaCl solution and then manually disassembled to separate the steel shell, diaphragm, negative electrode sheet (negative electrode material / copper current collector), and positive electrode sheet (positive electrode active material / aluminum current collector).

[0052] (2) The dried positive electrode sheet was directly cut into small pieces and connected to an electrode clip as a working electrode, a saturated calomel electrode as a reference electrode, a platinum electrode as a counter electrode, and a 0.1 mol / L citric acid solution as an electrolyte. Potentiodynamic polarization was performed on an electrochemical workstation to determine the active dissolution potential of the aluminum foil under acidic conditions.

[0053] (3) Take another positive electrode sheet connected to the electrode clip as the working electrode, a saturated calomel electrode as the reference electrode, a platinum electrode as the counter electrode, and a 0.1 mol / L citric acid solution as the electrolyte, and perform constant potential polarization on an electrochemical workstation.

[0054] (4) The potential of the positive electrode was selected to be 1.5 V vs. OCP, and the working electrode was subjected to constant potential polarization at room temperature for 5 min.

[0055] During the implementation of this embodiment, bubbles can be seen continuously emerging from the surface of the positive electrode material, and soon after, a bulge occurs, and the bulge is slowly separated from the aluminum foil under the action of the potential. After the experiment, the aluminum foil and the positive electrode material film can be obtained by washing with distilled water, but the two cannot be completely peeled off (such as Figure 4 It can be seen that the separation of the positive electrode material and the aluminum current collector can be achieved by only using the anodic dissolution of aluminum during the electrochemical polarization process, but the stripping rate cannot reach 100%. Further, the changes in the morphology of the aluminum foil after electrochemical stripping were characterized by SEM and the Al content in the solution was determined by ICP-MS. 3+ It was found that corrosion pits also appeared on the surface of the aluminum foil and dissolved in the solution in the form of ions.

[0056] It should be understood that the application of the present invention is not limited to the above examples. For ordinary technicians in this field, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A method for electrochemically assisted rapid stripping of positive electrode active materials from aluminum current collectors, characterized in that: Includes steps: Discharging and disassembling the waste lithium-ion battery in a salt solution to obtain a positive electrode sheet, wherein the positive electrode sheet includes an aluminum foil and a positive electrode active material adhered to the aluminum foil; The positive electrode sheet is used as a working electrode, combined with a counter electrode, a reference electrode and an electrolyte to construct a three-electrode system; Based on the three-electrode system, the active dissolution potential and hydrogen evolution potential of the aluminum foil in the positive electrode sheet in the electrolyte were screened by the potentiodynamic polarization curve method. Based on the three-electrode system, the positive electrode sheet is subjected to constant potential polarization using an electrochemical workstation under the active dissolution potential condition, so that the aluminum foil surface in the positive electrode sheet undergoes active dissolution to generate Al 3+ , thereby destroying the interface connecting it with the positive electrode active material, and then polarizing the positive electrode sheet for a predetermined time at a hydrogen evolution potential, and further peeling the positive electrode active material from the surface of the aluminum foil through the bubbles generated on the surface of the aluminum foil.

2. The method for electrochemically assisted rapid stripping of positive electrode active materials from aluminum current collector according to claim 1, characterized in that: The positive electrode active material on the aluminum foil is one or more of lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, and lithium iron phosphate.

3. The method for electrochemically assisted rapid stripping of positive electrode active materials from aluminum current collector according to claim 1, characterized in that: The electrolyte is an acidic liquid with a pH value less than 4, and the acidic liquid is one or more of sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid and citric acid.

4. The method for electrochemically assisted rapid stripping of positive electrode active materials from aluminum current collector according to claim 1, characterized in that: The counter electrode is one of a platinum electrode, a titanium electrode, a silver electrode and a graphite electrode; the reference electrode is a saturated calomel electrode or a silver / silver chloride electrode.

5. The method for electrochemically assisted rapid stripping of positive electrode active materials from aluminum current collector according to claim 1, characterized in that: The voltage of the positive electrode sheet subjected to constant potential polarization is 0.5V to 2V vs. open circuit potential, and the time is 1 to 30 minutes.

6. The method for electrochemically assisted rapid stripping of positive electrode active materials from aluminum current collector according to claim 1, characterized in that: In the step of polarizing the positive electrode sheet for a predetermined time at a hydrogen evolution potential, the polarization voltage is -1V to -2V vs. open circuit potential, and the predetermined time is 1 to 10 minutes.

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