Method for recycling a negative electrode sheet

Abstract

This invention belongs to the field of battery recycling technology. It provides a method for recycling negative electrode sheets. This method uses a mixed solution comprising nitric acid, phosphoric acid, and a water-soluble alcohol solvent as a specific treatment liquid to soak the negative electrode sheets. This allows the negative electrode active material to detach directly from the negative electrode current collector. For any parts that do not detach directly, shaking and / or swishing are sufficient to remove them, thus allowing the separated negative electrode active material and negative electrode current collector to be collected separately. Using this specific treatment liquid achieves rapid and efficient separation and recycling while preventing the copper foil from oxidizing during the recycling process and reducing secondary pollution. The overall operation of this recycling method is simple, cost-effective, and suitable for large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of battery recycling technology and relates to a method for recycling negative electrode sheets. Background Technology

[0002] The rapid proliferation of electric vehicles and new energy storage systems has led to a significant increase in the production and use of lithium-ion batteries. As these batteries reach the end of their lifespan, the proper disposal and scrapping of them has become a significant environmental and economic issue.

[0003] Among all structural components of lithium-ion batteries, copper and aluminum foil, used as current collectors, are valuable materials that can be recycled and reused. Foil recycling not only solves the problem of lithium-ion battery waste but also has significant implications for protecting natural resources. However, recovering copper and aluminum foil from spent lithium-ion batteries currently faces serious technical challenges, primarily due to the complex internal structure of the battery and the strong adhesion between the foil and the active material, making separation of the material from the electrode sheet quite difficult.

[0004] Traditional separation methods generally include three types: physical, chemical, and electrochemical. Compared to chemical methods such as acid / alkali leaching, which are prone to environmental pollution risks, and electrochemical methods such as pulsed discharge, which are costly, physical methods, such as mechanical stirring and ultrasonication, and ultrasonic-assisted water immersion, produce less pollution, are less expensive, and are suitable for large-scale processing. However, these physical methods usually require a large amount of water as a medium. While ultrasonic stripping is highly efficient in water, it easily causes the active material to react or dissolve with the water, and has a strong oxidizing effect on copper foil, which seriously affects the quality, recovery value, and economic benefits of the separated and recovered products. Summary of the Invention

[0005] To address the problems existing in the prior art, the present invention aims to provide a method for recycling negative electrode sheets. This recycling method uses a mixed solution comprising nitric acid, phosphoric acid, and a water-soluble alcohol solvent as a specific treatment liquid to immerse the negative electrode sheet. This allows the negative electrode active material to detach directly from the negative electrode current collector. For any parts that do not detach directly, they can be detached simply by shaking and / or swishing, thereby allowing the separated negative electrode active material and negative electrode current collector to be collected separately. Using this specific treatment liquid achieves rapid and efficient separation and recycling while preventing the copper foil from being oxidized during the recycling process and reducing secondary pollution. The recycling method is simple to operate, has low cost, and is suitable for large-scale production.

[0006] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, in one or more embodiments of the present invention, a method for recycling negative electrode sheets is provided, comprising: A negative electrode sheet to be processed is provided, the negative electrode sheet comprising a negative electrode current collector and a negative electrode active material disposed on the negative electrode current collector; The negative electrode sheet is immersed in the treatment solution to allow at least a portion of the negative electrode active material to detach from the negative electrode current collector; or, after immersing the negative electrode sheet in the treatment solution, if at least a portion of the negative electrode active material remains attached to the negative electrode current collector, the negative electrode sheet is removed from the treatment solution and shaken and / or tossed to allow the negative electrode active material to detach from the negative electrode current collector; the separated negative electrode active material and the negative electrode current collector are collected separately. The treatment solution comprises a mixed solution of nitric acid, phosphoric acid, and a water-soluble alcohol solvent.

[0007] The recycling method provided by this invention achieves efficient separation of the negative electrode active material (such as graphite) and the negative electrode current collector (such as copper foil) by immersing the negative electrode sheet in a mixed solution of nitric acid, phosphoric acid, and a water-soluble alcohol solvent. This process of separating the active material and the current collector involves a multi-mechanism synergistic effect, including: nitric acid can effectively destroy the binding sites between the active material and the binder, achieving peeling, but it also easily oxidizes the current collector; therefore, adding a certain amount of phosphoric acid allows it to adsorb onto the surface of the current collector, forming a corrosion-inhibiting layer that hinders direct contact between nitric acid and the current collector, effectively preventing nitric acid from corroding the current collector; thus, the synergistic use of nitric acid and phosphoric acid balances peeling effectiveness and protection. Meanwhile, water-soluble alcohol solvents possess excellent solubility and permeability, allowing them to penetrate the binder between the current collector and the active material. This increases the inter-chain spacing of the binder (such as PVDF), further weakening its adhesion and effectively reducing the bond strength between the active material and the current collector. Furthermore, water-soluble alcohol solvents can inhibit excessive oxidative corrosion of the current collector by nitric acid, thus further protecting it in conjunction with the corrosion-inhibiting layer formed by phosphoric acid. The synergistic use of nitric acid and ethanol, through wetting and swelling, loosens the network structure of the binder, thereby better promoting the separation of the current collector from the negative electrode material. Simultaneously, in the nitric acid-phosphoric acid-water-soluble alcohol solvent system, phosphoric acid helps prevent nitric acid corrosion of the current collector. In contrast, other strong acids such as sulfuric acid and hydrochloric acid tend to corrode the negative electrode active material or the current collector, resulting in weaker separation and protection effects compared to the nitric acid-phosphoric acid-water-soluble alcohol solvent mixture.

[0008] It should be noted that the shaking and / or swaying described in this invention are two physical-assisted desorption methods used to detach the loosened negative electrode active material from the current collector after special treatment. The specific method used—shaking, swaying, or a combination of both—should be chosen rationally based on the actual situation. Generally, shaking refers to high-frequency, small-amplitude periodic vibration (such as reciprocating motion) that repeatedly impacts the interfacial micro-gap through alternating stress, using micro-vibration friction and inertia to sieve-like detachment of particles. This disperses stress, making it less likely to deform the current collector, facilitating subsequent recycling, and making dust control easier. However, it may take longer to process. Therefore, shaking is preferably suitable for situations where the adhesion has been significantly weakened. Swaying refers to low-frequency, large-amplitude oscillation or rotational motion, usually dominated by inertial / centrifugal force. This is beneficial for directly overcoming residual adhesion and is suitable for blocky or locally stubborn adhesions. However, localized stress concentration at high speeds can easily lead to wrinkles, tears, or fatigue damage in the current collector and other parts. Therefore, swaying is more suitable for situations requiring rapid peeling and large processing volumes. Furthermore, shaking can be performed first, followed by swaying, to enhance the peeling effect.

[0009] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical objectives and beneficial effects of the present invention can be better achieved and realized through the following technical solutions.

[0010] In some specific embodiments, the negative electrode current collector includes copper foil, and the negative electrode active material includes graphite.

[0011] In some specific embodiments, the negative electrode sheet is obtained by disassembling the waste battery cell after discharge.

[0012] In some specific embodiments, the negative electrode sheet includes the negative electrode current collector and a negative electrode active layer disposed on one or both sides of the negative electrode current collector, the negative electrode active material is disposed in the negative electrode active layer, and the negative electrode active layer further includes a negative electrode binder.

[0013] In some specific embodiments, based on the mass of the negative electrode active layer as 100%, the mass percentage of the negative electrode binder is ≤3%, for example, it can be 3%, 2.5%, 2%, 1.5%, 1%, or 0.5%, preferably 2%~3%; and in the negative electrode sheet, the peel force between the negative electrode active layer and the negative electrode current collector is ≤30N / m, for example, it can be 30N / m, 25N / m, 20N / m, 15N / m, 10N / m, or 5N / m. Therefore, the negative electrode sheet can achieve better separation and recovery results using the separation and recovery method of the present invention.

[0014] In some specific embodiments, with the mass of the negative electrode active layer as 100%, the mass of the negative electrode active material accounts for 95% to 96.5%, for example, it can be 96%, 96.1%, 96.2%, 96.3%, 96.4%, or 96.5%, etc.

[0015] In some specific embodiments, the negative electrode active layer further includes a negative electrode conductive agent, and the negative electrode conductive agent accounts for 1.5% to 2% of the mass of the negative electrode active layer, for example, 1.5%, 1.6%, 1.7%, 1.8%, 1.9% or 2%.

[0016] In some specific embodiments, based on the mass of the mixed solution as 100%, the mass of the nitric acid is 0.1% to 0.3%, for example, it can be 0.1%, 0.15%, 0.2%, 0.25%, or 0.3%; the mass of the phosphoric acid is 0.01% to 0.03%, for example, it can be 0.01%, 0.015%, 0.02%, 0.025%, or 0.03%; the mass percentage of the water-soluble alcohol solvent is ≥97.5%, for example, it can be 97.5%, 97.8%, 97.9%, 98%, 98.3%, 98.5%, 98.8%, 99%, 99.3%, 99.67%, 99.7%, 99.75%, 99.8%, 99.85%, or 99.89%, preferably >97.9%.

[0017] In this invention, when the nitric acid content in the mixed solution used as the treatment liquid is low, there is insufficient oxidant to break down the tight interface between the copper foil and the active material, making it difficult to achieve the target separation effect. When the nitric acid content is high, the copper foil and active material are easily oxidized. When the phosphoric acid content is too low, the corrosion inhibition layer formed by the phosphoric acid is insufficient, and the strong acidity and strong oxidizing properties of nitric acid cannot be effectively suppressed, easily oxidizing and corroding the copper foil and damaging the structure of the active material. When the phosphoric acid content is too high, the excess phosphoric acid will form an excessively thick and dense corrosion inhibition layer on the surface of the copper foil, which will instead prevent the separation of the copper foil and the active layer. When the ethanol content is too low, the concentration of water and acid is high, and the overall reactivity of the solution is stronger, which may lead to corrosion and oxidation of the copper foil and the active material. When the ethanol content is too high, the nitric acid and phosphoric acid are over-diluted, and their effective concentration in the solution is too low, which is not conducive to the separation of the copper foil and the active material. At the same time, under appropriate content and ratio, the treatment solution will not oxidize or dissolve the current collector, thus maintaining the integrity of the copper foil. This is because the concentration of nitric acid is relatively low and does not meet the conditions for large-scale dissolution, thereby avoiding other secondary pollution.

[0018] In some specific embodiments, the water-soluble alcohol solvent includes ethanol and / or isopropanol. Preferably, a pure water-soluble alcohol solvent is used, and more preferably, anhydrous ethanol. Thus, after immersing the electrode in the treatment solution to remove it, any residual or adsorbed solvent on the surface easily evaporates, leaving almost no impurities, thus better balancing low cost and environmental friendliness.

[0019] In some specific embodiments, the mixed solution also contains water. The water in the mixed solution may come from a raw material for nitric acid, such as dilute nitric acid (aqueous solution of nitric acid); or from a raw material for phosphoric acid, such as dilute phosphoric acid (aqueous solution of phosphoric acid).

[0020] In some specific embodiments, the soaking time is 0.5h to 1.5h, for example, it can be 0.5h, 0.6h, 0.7h, 0.8h, 0.9h, 1h, 1.2h, or 1.5h, preferably 0.9h to 1.1h. The soaking time required using the treatment solution described in this invention is relatively short. For negative electrode sheets with a typical active layer thickness of 30μm to 150μm, a soaking time of about 1 hour is sufficient to achieve the detachment of the active layer, or the active material can be completely separated from the current collector by gently applying external force to shake / flick it.

[0021] In some specific embodiments, the soaking is carried out at 15°C to 35°C, that is, at room temperature without additional heating, such as 15°C, 20°C, 25°C, 30°C or 35°C.

[0022] In some specific embodiments, the recycling method further includes: if the negative electrode sheet needs to be cleaned or dried, the negative electrode sheet is removed from the treatment solution and then cleaned and / or dried. Cleaning and drying facilitate the removal of adsorbed or residual nitric acid, phosphoric acid, and water-soluble alcohol solvents. If volatile water-soluble alcohol solvents are used during cleaning, it helps ensure that the recovered current collector and active material remain free of impurities.

[0023] In some specific embodiments, the cleaning agent used for cleaning includes the water-soluble alcohol solvent. In this invention, the water-soluble alcohol solvent used in the cleaning agent is preferably consistent with the water-soluble alcohol solvent in the mixed solution used as the treatment liquid, in order to balance cleaning effectiveness and avoid introducing excess substances and contamination.

[0024] In some specific embodiments, the drying time is 10 min to 20 min, for example, it can be 10 min, 12 min, 14 min, 16 min, 18 min or 20 min.

[0025] In some specific embodiments, the method for preparing the mixed solution includes adding an aqueous solution of nitric acid and an aqueous solution of phosphoric acid to a water-soluble alcohol solvent to obtain a mixed solution. Further, the preparation of the nitric acid-phosphoric acid-water-soluble alcohol solvent mixed solution can be carried out in a fume hood, and the prepared mixed solution is preferably stored in a dark glass bottle to avoid light and the risk of explosion.

[0026] It should be noted that there is a potential safety risk in mixing nitric acid with alcohol solvents. The present invention preferably ensures the process safety of preparing the treatment solution by at least one of the following measures: (1) controlling the concentration of nitric acid in the raw nitric acid aqueous solution to be below 75%, i.e., avoiding the direct use of concentrated nitric acid; (2) adopting the method of adding alcohol first and then adding nitric acid dropwise to avoid large-scale premixing of the two in a short time; (3) controlling the reaction temperature not to exceed 40°C during mixing.

[0027] In some specific embodiments, the mass percentage concentration of nitric acid in the nitric acid aqueous solution is 25% to 35%, for example, it can be 25%, 28%, 30%, 33%, or 35%. The nitric acid aqueous solution can be prepared by mixing concentrated nitric acid with water, wherein the mass percentage concentration of the concentrated nitric acid is 65% to 75%, for example, it can be 65%, 68%, 70%, 72%, or 75%. In the method for preparing the mixed solution of the present invention, the concentrated nitric acid is diluted to a nitric acid aqueous solution before use to prevent the concentrated nitric acid from reacting violently with water-soluble alcohol solvents such as ethanol, which could cause boiling or explosion.

[0028] In some specific embodiments, the mass percentage concentration of phosphoric acid in the phosphoric acid aqueous solution is 1% to 5%, for example, it can be 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%. The phosphoric acid aqueous solution can be prepared by mixing concentrated phosphoric acid with water, and the mass percentage concentration of the concentrated phosphoric acid is 75% to 85%, for example, it can be 75%, 78%, 80%, 82%, or 85%.

[0029] In some specific implementations, after separating and collecting the negative electrode active material and the negative electrode current collector respectively, the recovery rate of the negative electrode active material is 90% to 95%, for example, it can be 90%, 91%, 92%, 93%, 94% or 95%, etc.

[0030] In some specific embodiments, after separating and collecting the negative electrode active material and the negative electrode current collector separately, the area of ​​oxidation in the negative electrode current collector is ≤1%, taking the total area of ​​the negative electrode current collector as 100%. For example, it can be 1%, 0.8%, 0.5%, 0.3%, 0.1%, or 0% (i.e., no oxidation area). In this invention, the oxidized area in the recovered negative electrode current collector can be determined by observing the color. For example, after copper foil is oxidized, the surface will show irregular dark red marks. Then, the proportion of the total area of ​​the dark red marks to the area of ​​that side of the negative electrode current collector can be measured and estimated.

[0031] In some specific embodiments, the recycling process includes the following steps: S1. Prepare a mixed solution of nitric acid, phosphoric acid, and water-soluble alcohol solvent as the treatment solution: First, take concentrated nitric acid with a mass percentage concentration of 65%~75% and add it to water to prepare a nitric acid aqueous solution with a mass percentage concentration of 25%~35%; take concentrated phosphoric acid with a mass percentage concentration of 75%~85% and add it to water to prepare a phosphoric acid aqueous solution with a mass percentage concentration of 1%~5%. Subsequently, aqueous solutions of nitric acid and phosphoric acid were added to ethanol to obtain a mixed solution; based on the mass of the mixed solution as 100%, the mass of nitric acid was controlled to be 0.1%~0.3%, the mass of phosphoric acid to be 0.01%~0.03%, the mass of water-soluble alcohol solvent to be ≥97.5%, and the balance being water; the water-soluble alcohol solvent included ethanol; S2. Cell Disassembly: Discharge the waste lithium-ion battery and then disassemble the cell, removing the negative electrode sheet for later use; the negative electrode sheet includes a negative current collector copper foil and a negative active layer disposed on the negative current collector; the negative active layer contains ≤3% by mass of binder, 1.5%~2% of negative conductive agent and 95%~96.5% of negative active material graphite; and the peel force between the negative active layer and the negative current collector is ≤30N / m; S3. Electrode Immersion: Immerse the negative electrode in a mixed solution of nitric acid, phosphoric acid, and water-soluble alcohol at room temperature (15℃~35℃) to ensure that the mixed solution can completely submerge the electrode. The immersion time is 0.5h~1.5h. After immersion, remove the negative electrode, wash it with ethanol, and let it air dry for 10min~20min. After drying, gently apply external force to the negative electrode and shake and / or swing it to completely separate the remaining negative electrode active layer from the copper foil. S4. Recycling: Finally, the separated active materials and copper foil are collected separately, and the collected copper foil can be recycled.

[0032] It should be noted that, due to space limitations and to avoid redundancy, this invention does not exhaustively list all point values ​​within the above numerical range, but it is not limited to the listed values ​​either; other unlisted values ​​within the above numerical range are also applicable.

[0033] Compared with existing technical solutions, the present invention has at least the following beneficial effects: The present invention provides a method for recycling negative electrode sheets by immersing the negative electrode sheets in a mixed solution of nitric acid, phosphoric acid, and a water-soluble alcohol solvent. The synergistic use of nitric acid, phosphoric acid, and the water-soluble alcohol solvent achieves efficient separation of the negative electrode active material (such as graphite) and the negative electrode current collector (such as copper foil). This method results in a short processing time and a significant peeling effect. After immersion, the active material can be directly detached, and any remaining material can be easily removed by gentle shaking or agitation. No additional post-processing steps are required, thus avoiding contamination and reducing costs. Simultaneously, the synergistic use of nitric acid, phosphoric acid, and the water-soluble alcohol solvent protects both the active material and the current collector, effectively preventing significant damage and high recovery losses due to excessive reactions, corrosion, or oxidation. This further helps to avoid contamination and improves recovery value and economic benefits. Attached Figure Description

[0034] Figure 1 This is a schematic diagram illustrating the recovery effect of the negative electrode current collector and the negative electrode active material in Example 1.

[0035] Figure 2 This is a schematic diagram illustrating the recovery effect of the negative electrode current collector and the negative electrode active material in Example 9.

[0036] Figure 3 This is a schematic diagram illustrating the recovery effect of the negative electrode current collector and the negative electrode active material in Comparative Example 1. Detailed Implementation

[0037] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0038] The scope of this invention can be defined by lower and upper limits. The selected lower and upper limits define the boundaries of a specific range. The range defined in this way can be defined by the inclusion or exclusion of endpoints. Any endpoint can be independently selected for inclusion or exclusion, and all lower and upper limits can be arbitrarily combined to form new ranges. That is, any lower limit can be combined with any upper limit to form an effective range. For example, if the ranges of 60~120 and 80~110 are listed for specific parameters, it should be understood that the ranges of 60~110 and 80~120 also fall within the scope of this invention. In addition, if the minimum range values ​​1 and 2 are listed, and the maximum range values ​​3, 4 and 5 are also listed, then all ranges of 1~3, 1~4, 1~5, 2~3, 2~4 and 2~5 fall within the scope of this invention. In this invention, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0~5" means that all real numbers between 0 and 5 have been fully listed in this document, and "0~5" is only a shortened representation of this set of numerical combinations. When a parameter is expressed as an integer ≥2, it is equivalent to listing positive integers that meet the requirements, such as 2, 3, 4, 5, 6, 7, 8, 9, 10, etc. When a parameter is expressed as an integer selected from "2~10", it is equivalent to listing any integer among 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0039] In this invention, "a combination of at least two" refers to a quantity greater than or equal to 2 unless otherwise specified. For example, "any one or a combination of at least two" means that any one of the listed items can be selected, or a combination of at least two of the listed items formed in a manner that does not conflict and enables the implementation of this invention. In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" cover any one of two or more related listed items, as well as any and all combinations of the related listed items. The arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" means a set consisting of A, B, and combinations of A and B, where "containing A and / or B" can be understood, depending on the context of the statement, as containing A, containing B, or simultaneously containing both A and B. In this invention, "optional" means that the corresponding feature, component, step or solution is not necessary, that is, it is selected from either "with" or "without". If there are multiple "optional" limitations in a technical solution, unless otherwise specified and there is no technical conflict or mutual constraint, each "optional" limitation is independent and does not affect the others.

[0040] In this invention, technical features or solutions described using open-ended terms such as "comprising" or "including" do not exclude additional non-conflicting elements beyond the listed elements unless otherwise specified. They are considered to disclose both closed-ended features or solutions consisting solely of the listed elements and open-ended features or solutions that may include additional non-conflicting elements beyond the listed elements. For example, if A includes a1, a2, and a3, unless otherwise specified, this means that A can consist only of a1, a2, and a3, or it can include other non-conflicting elements based on a1, a2, and a3. This corresponds to the disclosure of technical solutions such as "A consists of a1, a2, and a3," "A is selected from a1, a2, and a3," and "A not only includes a1, a2, and a3, but may also include other non-conflicting elements." All embodiments and optional embodiments of this invention, unless otherwise specified and without technical conflict, can be combined to form new technical solutions, and such combinations fall within the scope of this invention. The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of the invention. The appearance of this phrase in various locations throughout the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will understand, explicitly and implicitly, that the embodiments described in this invention can be combined with other embodiments that do not conflict with the technology. The ordinal numbers "first," "second," "third," and "fourth," etc., used in the expressions "first aspect," "second aspect," "third aspect," and "fourth aspect" in this invention are for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly specifying the importance or quantity of the indicated technical features. They serve only as a non-exhaustive enumeration and do not constitute a closed limitation on quantity.

[0041] In this invention, the order in which the steps are written in the methods described in the various embodiments does not imply a strict execution order. The actual execution order of each step should be determined based on its function and possible internal logic. Unless otherwise specified, all steps of this invention can be executed in the order they are written, or in any order without technical conflict. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) executed sequentially, or it may include steps (b) and (a) executed sequentially. If the method also includes step (c), then step (c) can be added to the method in any conflict-free order, including but not limited to the execution order of steps (a), (b), and (c), steps (a), (c), and (b), steps (c), (a), and (b), etc.

[0042] Example 1 This embodiment provides a method for recycling negative electrode sheets, including the following steps: S1. Prepare a mixed solution of nitric acid, phosphoric acid, and ethanol as the treatment solution: First, 68% concentrated nitric acid was added to water to obtain a 28% nitric acid aqueous solution (density 1.17 g / cm³). 3 Simultaneously, 75% concentrated phosphoric acid was added to water to obtain a 3% phosphoric acid aqueous solution (density 1.01 g / cm³). 3 Then, 1.11 mL of nitric acid aqueous solution and 1.20 mL of phosphoric acid were added dropwise to 150 mL of ethanol (density 0.789 g / cm³). 3 In a mixture of nitric acid, phosphoric acid, and ethanol, a mixed solution of nitric acid, phosphoric acid, and ethanol is obtained; based on the mass of the mixed solution as 100%, the mass of nitric acid is 0.30%, the mass of phosphoric acid is 0.03%, the mass of ethanol is 97.92%, and the balance is water. S2. Battery cell disassembly: The discarded lithium-ion batteries are discharged until they are completely depleted, and then the cells are disassembled to remove the negative electrode sheets for later use. The negative electrode sheet includes a copper foil negative current collector and a negative active layer disposed on the negative current collector. The negative active layer contains 2% by mass of binder, 1.5% by mass of negative conductive agent, and 96.5% by mass of negative active material graphite. The peel force between the negative active layer and the negative current collector is ≤30N / m. S3, Electrode soaking: The negative electrode sheet was immersed in a mixed solution of nitric acid, phosphoric acid, and ethanol at room temperature (25°C), ensuring complete submersion for 1 hour. After immersion, active material was observed detaching from the edges of the electrode sheet. The negative electrode sheet was then removed, cleaned with ethanol, and allowed to air dry for 10 minutes. After drying, a gentle shake was applied to completely separate the active material from the copper foil, achieving the desired separation. Figure 1 As shown; S4. Recycling: Finally, the separated active material and copper foil are collected separately. The collected copper foil can be recycled and reused, which can solve the pollution disposal problem of waste lithium-ion batteries.

[0043] Example 2 This embodiment provides a method for recycling negative electrode sheets, including the following steps: S1. Prepare a mixed solution of nitric acid, phosphoric acid, and ethanol as the treatment solution: First, 68% concentrated nitric acid was added to water to obtain a 35% nitric acid aqueous solution (density 1.21 g / cm³). 3Simultaneously, 75% concentrated phosphoric acid was added to water to obtain a 5% phosphoric acid aqueous solution (density 1.02 g / cm³). 3 Then, 1.21 mL of nitric acid aqueous solution and 0.5 mL of phosphoric acid were added to 150 mL of ethanol (density 0.789 g / cm³). 3 In a mixture of nitric acid, phosphoric acid, and ethanol, a mixed solution of nitric acid, phosphoric acid, and ethanol is obtained; based on the mass of the mixed solution as 100%, the mass of nitric acid is 0.23%, the mass of phosphoric acid is 0.02%, the mass of ethanol is 98.92%, and the remainder is water. S2. Battery cell disassembly: The discarded lithium-ion batteries are discharged until they are completely depleted, and then the cells are disassembled to remove the negative electrode sheets for later use. The negative electrode sheet includes a copper foil negative current collector and a negative active layer disposed on the negative current collector. The negative active layer contains 1% by mass of binder, 2% by mass of negative conductive agent, and 97% by mass of negative active material graphite. The peel force between the negative active layer and the negative current collector is ≤30N / m. S3, Electrode soaking: The negative electrode sheet was immersed in a mixed solution of nitric acid, phosphoric acid, and ethanol at room temperature (35°C), ensuring that the solution completely submerged the electrode sheet. The immersion time was 0.5 hours. After immersion, it was observed that most of the active material on the electrode sheet detached directly. The negative electrode sheet was then removed, cleaned with ethanol, and allowed to air dry for 10 minutes. After the electrode sheet was dried, it was gently shaken by hand to completely separate the active material from the copper foil, thus achieving the desired separation of the active material from the copper foil. S4. Recycling: Finally, the separated active material and copper foil are collected separately. The collected copper foil can be recycled and reused, which can solve the pollution disposal problem of waste lithium-ion batteries.

[0044] Example 3 This embodiment provides a method for recycling negative electrode sheets, including the following steps: S1. Prepare a mixed solution of nitric acid, phosphoric acid, and isopropanol as the treatment solution: First, 68% concentrated nitric acid was added to water to obtain a 25% nitric acid aqueous solution (density 1.14 g / cm³). 3 Simultaneously, 75% concentrated phosphoric acid was added to water to obtain a 1% phosphoric acid aqueous solution (density 1.00 g / cm³). 3 Then, 0.43 mL of nitric acid aqueous solution and 1.20 mL of phosphoric acid were added to 152 mL of isopropanol (density 0.785 g / cm³). 3In a mixture of nitric acid, phosphoric acid, and isopropanol, a mixed solution of nitric acid, phosphoric acid, and isopropanol is obtained; based on the mass of the mixed solution as 100%, the mass of nitric acid is 0.10%, the mass of phosphoric acid is 0.01%, the mass of isopropanol is 98.60%, and the remainder is water. S2. Battery cell disassembly: The discarded lithium-ion batteries are discharged until they are completely depleted, and then the cells are disassembled to remove the negative electrode sheets for later use. The negative electrode sheet includes a copper foil negative current collector and a negative active layer disposed on the negative current collector. The negative active layer contains 1% by mass of binder, 2% by mass of negative conductive agent, and 97% by mass of negative active material graphite. The peel force between the negative active layer and the negative current collector is ≤30N / m. S3, Electrode soaking: The negative electrode sheet is immersed in a mixed solution of nitric acid, phosphoric acid, and isopropanol at room temperature (25°C), ensuring that the solution completely submerges the electrode sheet. The immersion time is 1.5 hours. After immersion, it can be observed that active material is detached from the edge of the electrode sheet. The negative electrode sheet is then removed, cleaned with isopropanol, and allowed to air dry for 10 minutes. After the electrode sheet is dried, it can be gently shaken by hand to completely separate the active material from the copper foil, achieving the desired separation of the active material from the copper foil. S4. Recycling: Finally, the separated active material and copper foil are collected separately. The collected copper foil can be recycled and reused, which can solve the pollution disposal problem of waste lithium-ion batteries.

[0045] Example 4 The difference between this embodiment and Embodiment 1 is that, in step S1, a mixed solution of nitric acid, phosphoric acid, and ethanol is prepared as the treatment solution as follows: a 28% nitric acid aqueous solution (density 1.17 g / cm³) is prepared. 3 ) and a 3% phosphoric acid aqueous solution (density 1.01 g / cm³) 3 Then, 0.37 mL of nitric acid aqueous solution and 1.20 mL of phosphoric acid were added to 148.9 mL of ethanol (density 0.789 g / cm³). 3 A mixed solution of nitric acid, phosphoric acid, and ethanol was obtained by adding 0.868 mL of water to the solution. The mass of the mixed solution was 100%, the mass of nitric acid was 0.10%, the mass of phosphoric acid was 0.03%, the mass of ethanol was 97.91%, and the remainder was water. Thus, separation can be achieved after soaking in step S3. Except for the above, the other conditions are exactly the same as in Example 1.

[0046] Example 5 The difference between this embodiment and Embodiment 1 is that, in step S1, a mixed solution of nitric acid, phosphoric acid, and ethanol is prepared as the treatment solution as follows: a 35% nitric acid aqueous solution (density 1.21 g / cm³) is prepared. 3 ) and a 4.60% phosphoric acid aqueous solution (density 1.02 g / cm³) 3 Then, 2.24 mL of nitric acid aqueous solution and 1.20 mL of phosphoric acid were added to 234 mL of ethanol (density 0.789 g / cm³). 3 In step S3, a mixed solution of nitric acid, phosphoric acid, and ethanol is obtained. The mass of the mixed solution is 100%, with nitric acid accounting for 0.50%, phosphoric acid for 0.03%, and ethanol for 97.91%, with the remainder being water. Thus, separation can be achieved after soaking in step S3, but slight oxidation of the copper foil is observed, resulting in losses. Apart from the above, all other conditions are identical to those in Example 1.

[0047] Example 6 The difference between this embodiment and Embodiment 1 is that, in step S1, a mixed solution of nitric acid, phosphoric acid, and ethanol is prepared as the treatment solution as follows: a 28% nitric acid aqueous solution (density 1.17 g / cm³) is prepared. 3 ) and a 3.0% phosphoric acid aqueous solution (density 1.01 g / cm³) 3 Then, 1.11 mL of nitric acid aqueous solution and 0.38 mL of phosphoric acid were added to 149 mL of ethanol (density 0.789 g / cm³). 3 A mixed solution of nitric acid, phosphoric acid, and ethanol was obtained by adding 0.789 mL of water to the solution. The nitric acid comprised 0.30% of the total mass, the phosphoric acid comprised 0.01%, and the ethanol comprised 97.94%, with the remainder being water. Therefore, in step S3, after soaking, separation can be achieved without oxidation of the copper foil. Except for the above, all other conditions are exactly the same as in Example 1.

[0048] Example 7 The difference between this embodiment and Embodiment 1 is that, in step S1, a mixed solution of nitric acid, phosphoric acid, and ethanol is prepared as the treatment solution as follows: a 35% nitric acid aqueous solution (density 1.21 g / cm³) is prepared. 3 ) and a 4.60% phosphoric acid aqueous solution (density 1.02 g / cm³) 3 Then, 1.48 mL of nitric acid aqueous solution and 2.48 mL of phosphoric acid were added to 258 mL of ethanol (density 0.789 g / cm³). 3In step S3, a mixed solution of nitric acid, phosphoric acid, and ethanol is obtained. The nitric acid comprises 0.30% of the total mass, the phosphoric acid comprises 0.06%, and the ethanol comprises 97.92%, with the remainder being water. Therefore, in step S3, separation can be achieved after soaking. However, due to the relatively high amount of phosphoric acid added, slight incomplete separation occurs between the copper foil and the active material. Except for the above, all other conditions are exactly the same as in Example 1.

[0049] Example 8 The difference between this embodiment and Embodiment 1 is that in step S1, the amount of ethanol is reduced to 145 mL, and the reduced mass is replenished with water, so that in the resulting mixed solution, the mass of nitric acid remains at 0.30%, the mass of phosphoric acid remains at 0.03%, the mass ratio of ethanol correspondingly becomes 94.66%, and the water ratio is adjusted accordingly. Therefore, in step S3, separation can be achieved after soaking treatment. However, due to the small amount of ethanol added, and the main function of ethanol being to inhibit excessive oxidation and corrosion of the copper foil by nitric acid, slight oxidation occurs in the separated copper foil. Except for the above, all other conditions are exactly the same as in Embodiment 1.

[0050] Example 9 The difference between this embodiment and Embodiment 1 is that in step S3, the soaking time is adjusted from 1 hour to 0.2 hours. Therefore, in step S3, after soaking, it is observed that the active material at the edge of the electrode does not detach significantly. The electrode is then removed, cleaned, and dried. After gently shaking it with external force, it is found that the active material does not completely separate from the copper foil. Figure 2 As shown, it is not possible to completely achieve the desired separation effect between the active material and the copper foil; except for the above, the other conditions are exactly the same as in Example 1.

[0051] Example 10 The difference between this embodiment and Embodiment 1 is that in step S3, the soaking time is adjusted from 1 hour to 2 hours. Consequently, after soaking in step S3, it is observed that a significant amount of active material detaches from the edge of the electrode. This detached active material deposits in the mixed solvent, requiring further separation from the solution. The electrode is removed and dried, and then gently shaken by hand to completely separate the active material from the copper foil. However, noticeable oxidation is observed at the edge of the current collector copper foil. Apart from the above, all other conditions are identical to those in Embodiment 1.

[0052] Comparative Example 1 The difference between this comparative example and Example 1 is that in step S1, an aqueous solution of phosphoric acid is not used, resulting in a mixed solution in which the mass of nitric acid is 0.3%, the mass of phosphoric acid is 0%, i.e., it does not contain phosphoric acid, the mass of ethanol is 98.92%, and the remainder is water; therefore, in step S3, after soaking, separation can be achieved, but at the same time, a slight oxidation of the copper foil portion can also be observed. Figure 3 As shown; except for the above, the other conditions are exactly the same as in Example 1.

[0053] Comparative Example 2 The difference between this comparative example and Example 1 is that, in step S1, an aqueous solution of nitric acid is not used, so that the mass of nitric acid in the resulting mixed solution is 0%, that is, it does not contain nitric acid, the mass of phosphoric acid is kept at 0.03%, the mass of ethanol is 98.99%, and the remainder is water; therefore, in step S3, after soaking treatment, the active material and the copper foil cannot be completely separated. Except for the above, the other conditions are exactly the same as in Example 1.

[0054] Comparative Example 3 The difference between this comparative example and Example 1 is that in step S1, ethanol or other water-soluble alcohol solvents are not used, but water of equal mass is used instead. In the resulting mixed solution, the mass of nitric acid remains 0.30%, the mass of phosphoric acid remains 0.03%, and the mass of water accounts for 99.67%. As a result, in step S3, after soaking treatment, the active material cannot be completely separated from the copper foil, and the copper foil shows slight oxidation. Apart from the above, the other conditions are exactly the same as in Example 1.

[0055] Comparative Example 4 The difference between this comparative example and Example 1 is that, in step S1, 1.66 mL of 20% hydrochloric acid (density 1.1 g / cm³) was used. 3 The hydrochloric acid solution is replaced with an aqueous nitric acid solution, such that the mass of the hydrochloric acid in the mixed solution is 0.30%, the mass of the phosphoric acid remains at 0.03%, and the mass of the ethanol becomes 97.50%. Thus, in step S3, after the soaking treatment, the active material cannot be completely separated from the copper foil. Except for the above, the other conditions are exactly the same as in Example 1.

[0056] Comparative Example 5 The difference between this comparative example and Example 1 is that, in step S1, 1.08 mL of 28% sulfuric acid (density 1.2 g / cm³) was used. 3The sulfuric acid solution is replaced with an aqueous nitric acid solution, such that the mass of the sulfuric acid in the mixed solution is 0.30%, the mass of the phosphoric acid remains at 0.03%, and the mass of the ethanol becomes 97.93%. Thus, in step S3, after soaking, the active material cannot be completely separated from the copper foil, and the copper foil exhibits slight oxidation. Except for the above, the other conditions are exactly the same as in Example 1.

[0057] The recovery rate of the recovered negative electrode active material in the above embodiments and comparative examples was calculated based on the area percentage that detached from the current collector; and the area percentage of the recovered current collector that was oxidized was calculated. The results are shown in Table 1.

[0058] Table 1 As can be seen from Table 1: Examples 1, 2, and 3 all efficiently separate the negative electrode active material from the negative electrode current collector, and the surface of the resulting negative electrode current collector is effectively protected. In Example 2, most of the active material can be directly separated from the copper foil. However, since some active material falls into the solution, additional filtration and other operations are required for collection. In Examples 1 and 3, most of the active material can be detached and directly collected by shaking after removing the electrode sheet, which is more convenient.

[0059] As can be seen from the comparison of Examples 1, 4 to 5 and Comparative Example 2, when the soaking time is the same, the content of phosphoric acid in the treatment solution remains unchanged, but the concentration of nitric acid increases, which leads to the problem of copper foil oxidation. Therefore, the concentration of nitric acid should be in a smaller range of 0.1% to 0.3%.

[0060] As can be seen from the comparison of Examples 1, 6 to 7 and Comparative Example 1, when the soaking time is the same, the separation of copper foil and active material is incomplete when the phosphoric acid concentration is too high. Therefore, the phosphoric acid concentration should be in a smaller range of 0.01% to 0.03%.

[0061] As can be seen from the comparison of Examples 1, 8 and Comparative Example 3, when the soaking time is the same, if the ethanol content is too low, even if the purpose of separating copper foil from active substances can be achieved, the area of ​​copper foil oxidation will become larger and larger as the ethanol content decreases.

[0062] A comparison of Examples 1, 9 and 10 shows that, under suitable nitric acid, phosphoric acid concentrations and ethanol content ratios, the soaking time should be 0.5h to 1.5h. If the soaking time is too short, the active material will not separate completely from the copper foil, and if the soaking time is too long, it will easily cause excessive oxidation.

[0063] The comparison between Example 1 and Comparative Examples 4 and 5 shows that, under the same soaking time and phosphoric acid content, the separation efficiency is lower when nitric acid is replaced with hydrochloric acid and sulfuric acid, and sulfuric acid causes more severe oxidation of copper foil.

[0064] In summary, the recycling method provided by this invention uses a mixed solution of nitric acid, phosphoric acid, and water-soluble alcohol as the treatment liquid to immerse the negative electrode sheet. This efficiently separates the negative electrode active material from the negative electrode current collector copper foil. For any parts that do not detach directly, gentle shaking or jerking by hand can easily separate them without further processing. This recycling method is simple to operate, low in cost, pollution-free, and has a high separation rate for the negative electrode active material. The recovered product has minimal damage to the negative electrode active material and copper foil, and is of high quality, exhibiting significant recycling value and economic benefits. This recycling method effectively solves the pollution disposal problem of waste lithium-ion batteries while saving resources and costs.

[0065] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0066] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0067] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for recycling and processing negative electrode sheets, characterized in that, include: A negative electrode sheet to be processed is provided, the negative electrode sheet comprising a negative electrode current collector and a negative electrode active material disposed on the negative electrode current collector; The negative electrode sheet is immersed in the treatment solution to allow at least a portion of the negative electrode active material to detach from the negative electrode current collector; or, after immersing the negative electrode sheet in the treatment solution, if at least a portion of the negative electrode active material remains attached to the negative electrode current collector, the negative electrode sheet is removed from the treatment solution and shaken and / or swung to allow the negative electrode active material to detach from the negative electrode current collector; the separated negative electrode active material and the negative electrode current collector are collected separately. The treatment solution comprises a mixed solution of nitric acid, phosphoric acid, and a water-soluble alcohol solvent.

2. The method for recycling and processing the negative electrode sheet according to claim 1, characterized in that, The negative electrode current collector includes copper foil, and the negative electrode active material includes graphite; Preferably, the negative electrode sheet is obtained by disassembling a discarded battery cell after discharge.

3. The method for recycling and processing the negative electrode sheet according to claim 1, characterized in that, The negative electrode sheet includes the negative electrode current collector and a negative electrode active layer disposed on one or both sides of the negative electrode current collector. The negative electrode active material is disposed in the negative electrode active layer, and the negative electrode active layer further includes a negative electrode binder. The negative electrode sheet satisfies the following conditions A1 to A3: A1. Based on the mass of the negative electrode active layer as 100%, the mass percentage of the negative electrode binder is ≤3%, preferably 2%~3%; A2. In the negative electrode sheet, the peeling force between the negative electrode active layer and the negative electrode current collector is ≤30N / m; A3. Based on the mass of the negative electrode active layer being 100%, the mass of the negative electrode active material accounts for 95% to 96.5%.

4. The method for recycling and processing the negative electrode sheet according to claim 3, characterized in that, The negative electrode active layer further includes a negative electrode conductive agent, and the negative electrode conductive agent accounts for 1.5% to 2% of the mass of the negative electrode active layer, which is 100% of the total mass.

5. The method for recycling and processing the negative electrode sheet according to claim 1, characterized in that, Based on the mass of the mixed solution as 100%, the mass of nitric acid is 0.1% to 0.3%, the mass of phosphoric acid is 0.01% to 0.03%, and the mass of water-soluble alcohol solvent is ≥97.5%.

6. The method for recycling and processing the negative electrode sheet according to claim 1, characterized in that, The water-soluble alcohol solvents include ethanol and / or isopropanol; Preferably, the mixed solution also contains water.

7. The method for recycling and processing the negative electrode sheet according to claim 1, characterized in that, The soaking time is 0.5h to 1.5h, preferably 0.9h to 1.1h; Preferably, the soaking is carried out at 15°C to 35°C.

8. The method for recycling and processing the negative electrode sheet according to claim 1, characterized in that, The recycling method further includes: removing the negative electrode sheet from the treatment solution and then cleaning and / or drying it; Preferably, the cleaning agent used for cleaning includes the water-soluble alcohol solvent; Preferably, the drying time is 10 min to 20 min.

9. The method for recycling and processing the negative electrode sheet according to claim 1, characterized in that, The method for preparing the mixed solution includes: adding an aqueous solution of nitric acid and an aqueous solution of phosphoric acid to a water-soluble alcohol solvent to obtain a mixed solution; Preferably, the mass percentage concentration of nitric acid in the nitric acid aqueous solution is 25% to 35%; Preferably, the mass percentage concentration of phosphoric acid in the phosphoric acid aqueous solution is 1% to 5%.

10. The method for recycling and processing the negative electrode sheet according to claim 1, characterized in that, After separating and collecting the negative electrode active material and the negative electrode current collector, the recovery rate of the negative electrode active material was 90%~95%. Preferably, after separating and collecting the negative electrode active material and the negative electrode current collector separately, the area of ​​the negative electrode current collector that is oxidized is ≤1%, based on the total area of ​​the negative electrode current collector being 100%.

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