Method and system for directional recycling of lithium ion battery positive electrode aluminum foil based on electrochemical interface confined corrosion

Abstract

The present application belongs to the technical field of lithium battery recycling, and discloses a lithium ion battery positive pole aluminum foil directional recycling method based on electrochemical interface limited corrosion, which comprises the following steps: S1, immersing the disassembled waste battery positive pole piece into a functional medium containing fluorine salt, wherein the pH value of the medium is 3.0-6.5; S2, taking the positive pole piece as a working electrode, applying an anode potential of 3.0-4.0 V (vs. Ag / AgCl), and assisting with ultrasonic action to perform electrochemical-mechanical synergistic treatment; S3, after the treatment is completed, performing solid-liquid separation to obtain complete aluminum foil, a detached positive pole active material layer and aluminum-containing electrolyte; and S4, repairing the complete aluminum foil and recycling aluminum from the aluminum-containing electrolyte and regenerating the medium. Through pH-potential synergistic regulation, the corrosion effect of fluorine ions is accurately limited to the two-dimensional interface between the aluminum foil and the active material, thereby realizing non-destructive and high-selectivity stripping of the aluminum foil, with a total aluminum recovery rate of >97%, and the method is low in cost and environmentally friendly.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery recycling technology, and particularly relates to a method and system for the targeted recycling of lithium-ion battery cathode aluminum foil based on electrochemical interface confined corrosion. Background Technology

[0002] Driven by global dual-carbon goals, lithium-ion batteries have been widely used in consumer electronics, portable devices, energy storage, and other fields, while the new energy vehicle industry is also developing rapidly. However, as more and more batteries reach the end of their service life, a large number of retired lithium-ion batteries are generated, containing a large amount of valuable recyclable metals and other resources. It is estimated that by 2030, the total amount of retired power batteries in my country will exceed 3 million tons. Aluminum foil, as the mainstream positive electrode current collector material, accounts for about 8-12% of the total battery mass, with a potential annual recyclable resource volume of hundreds of thousands of tons. At the same time, the electrolytic production of aluminum is a high-energy-consuming process, while the energy consumption of recycling waste aluminum foil is only 5% of that of primary smelting. Therefore, efficient recycling of aluminum foil is of great significance for resource recycling and energy conservation and emission reduction.

[0003] However, current mainstream battery recycling technologies mainly focus on separating high-value metals such as cobalt, nickel, and lithium from carbon materials, while the recycling of aluminum foil is generally neglected or handled in a crude manner.

[0004] Based on the above analysis, the problems and shortcomings of the existing technology are as follows: (1) Low recovery rate and value: Traditional mechanical stripping method is difficult to completely separate aluminum foil from high-stability adhesive, and aluminum foil has a lot of residual active substances; strong acid (such as sulfuric acid) leaching method completely destroys the aluminum foil structure, dissolves it into ionic state, and then recovers it through precipitation. The process is long, the recovery rate is less than 85%, and the product is low-value hydroxide, which cannot achieve high-value recovery of aluminum foil itself.

[0005] (2) Poor selectivity and contamination of subsequent processes: During the acid leaching process, aluminum dissolves together with valuable metals such as nickel, cobalt, and manganese. The presence of a large number of aluminum ions seriously interferes with the subsequent extraction and separation processes, increasing reagent consumption and process complexity.

[0006] (3) Environmental risks: Although the use of hydrofluoric acid or high-concentration fluoride salts for aluminum leaching has a certain degree of selectivity, it poses significant safety and environmental hazards such as high toxicity and strong corrosivity.

[0007] Therefore, developing a low-cost, green technology that can achieve efficient and clean separation of aluminum foil and positive electrode active material while simultaneously ensuring the structural integrity of the aluminum foil for efficient recycling has become a key step in promoting the recycling of all battery components. Summary of the Invention

[0008] To address the problems existing in the prior art, this invention provides a method for the targeted recycling of aluminum foil from lithium-ion battery cathodes based on electrochemical interface confined corrosion. This method innovatively utilizes common fluoride salts and, through precise control of the synergistic effect of the medium pH and the applied potential, accurately confines the corrosion effect of fluoride ions to the two-dimensional interface between the aluminum foil and the active material. This achieves complete and rapid peeling of the aluminum foil and effectively inhibits the leaching of valuable metals such as nickel, cobalt, and manganese, thus achieving the goal of targeted aluminum foil recycling.

[0009] This invention is implemented as follows: a method for the directional recycling of lithium-ion battery positive electrode aluminum foil based on electrochemical interface confined corrosion. The waste lithium-ion battery positive electrode sheet is immersed in an acidic aqueous functional medium containing fluoride salts. An anodic potential is applied using the positive electrode sheet as the working electrode, and ultrasonic waves are applied simultaneously for synergistic treatment, causing the positive electrode active material layer to detach from the aluminum foil surface. Then, the intact aluminum foil is obtained by separation.

[0010] Furthermore, the functional medium has a pH value of 3.0 to 6.5, the anode potential is 3.0 to 4.0 volts relative to the silver chloride reference electrode, and the frequency of the ultrasound is 20 to 60 kHz.

[0011] Furthermore, the fluoride salt is selected from at least one of ammonium bifluoride or ammonium fluoride, and its concentration in the functional medium is 0.1 to 0.5 mol / L; the functional medium also contains 10 to 30 volume percent of an organic co-solvent, which is derived from carbonate solvents recovered from waste batteries.

[0012] Furthermore, the power density of the ultrasound is 30 to 100 watts per liter, and it operates in an intermittent pulse mode; during the electrochemical treatment process, the potential or treatment time is dynamically adjusted by monitoring the current or electrochemical impedance signal of the working electrode, and the treatment is stopped when the current stabilizes or the impedance drops to less than 50% of the initial value.

[0013] Furthermore, the area retention rate of the separated complete aluminum foil is not less than 90%; the complete aluminum foil is subjected to surface cleaning and subsequent treatment and repair, the separated liquid phase containing dissolved aluminum is subjected to precipitation treatment to recover aluminum compounds, and the functional medium is regenerated.

[0014] This invention also provides a system for implementing the above-described method for the directional recycling of lithium-ion battery cathode aluminum foil based on electrochemical interface confined corrosion, comprising: a pretreatment module for preparing the acidic aqueous functional medium containing fluoride salts and immersing the waste lithium-ion battery cathode sheet in the functional medium for settling; an electrochemical-mechanical synergistic stripping module for applying an anodic potential with the cathode sheet as the working electrode and simultaneously applying ultrasonic waves; a multiphase separation module for separating the treated mixed system into solid and liquid phases to obtain structurally intact aluminum foil, blocky or sheet-like detached cathode active material layers, and a liquid phase containing dissolved aluminum; and a recycling module for surface cleaning and repairing the intact aluminum foil and for precipitation treatment of the aluminum-containing liquid phase to recover aluminum compounds and regenerate the functional medium.

[0015] Furthermore, the electrochemical-mechanical synergistic stripping module includes an electrochemical workstation, an ultrasonic generator, and an ultrasonic transducer. The electrochemical workstation is configured to apply an anodic DC or pulse potential of 3.0 to 4.0 volts relative to a silver chloride reference electrode. The ultrasonic generator is configured to output ultrasonic waves with a frequency of 20 to 60 kHz and a power density of 30 to 100 watts per liter, and to operate in an intermittent pulse mode.

[0016] Furthermore, the electrochemical-mechanical synergistic stripping module also includes an online monitoring unit for monitoring the current or electrochemical impedance signal of the working electrode, and automatically stopping the process when the current stabilizes or the impedance drops to less than 50% of the initial value.

[0017] Furthermore, the multiphase separation module employs a vibrating screen or centrifugal separation device, and the recovery module includes a precipitation reaction tank, a filtration unit, and a media preparation unit. The precipitation reaction tank is used to add alkaline substances to the aluminum-containing liquid phase to adjust the pH to 8.5 to 10.0 so that aluminum precipitates in the form of aluminum hydroxide. The filtration unit is used to separate aluminum hydroxide, and the media preparation unit is used to supplement fluoride salts and acids to the filtrate to adjust it to the initial pH value.

[0018] The present invention also provides a method for regenerating functional media in the recycling of lithium-ion battery cathode aluminum foil using the above method, comprising the following steps: collecting the liquid phase containing dissolved aluminum obtained by the method of claim 1, adding an alkaline substance to the liquid phase to adjust the pH to 8.5 to 10.0, causing aluminum to precipitate out in the form of aluminum hydroxide, filtering to obtain aluminum hydroxide and filtrate, and adding fluoride salts and acid to the filtrate to the initial pH value to obtain the regenerated functional media.

[0019] Based on the above technical solutions and the technical problems solved, the advantages and positive effects of the technical solution to be protected by this invention are as follows: An analysis of existing lithium-ion battery recycling technologies reveals that mainstream approaches primarily focus on whole-cell leaching, thermal separation, and mechanical stripping. For example, current technologies commonly employ acidic systems to leach cathode materials, recovering metals such as nickel, cobalt, and lithium. The core of these methods lies in the dissolution-separation-purification process, rather than selective separation at the aluminum foil-active material interface. Furthermore, while some research has proposed using ultrasound to promote electrode material separation, this is mainly for particle identification or physical dispersion and does not address electrochemical interface control. Overall, existing technologies prioritize metal extraction efficiency while neglecting the integrity of the aluminum foil during recovery, often resulting in corrosion or structural damage.

[0020] The technical solution of this application differs significantly from the previous one: it does not employ overall leaching or non-selective stripping, but rather constructs an electrochemically confined corrosion environment through a combination of a fluorinated hydrochloric acid medium, anolyte potential control, and ultrasonic synergy. This allows the corrosion reaction to preferentially occur at the active material / aluminum foil interface, thereby achieving directional stripping of the positive electrode layer while preserving the aluminum foil intact. This interface-confined corrosion mechanism differs from traditional bulk reaction or random desorption processes, enabling precise control of the reaction location and rate. Simultaneously, the electrochemical driving force and ultrasonic coupling enhance the interface stripping kinetics, forming a synergistic effect rather than a simple additive one.

[0021] Existing technologies neither offer insights into inducing selective interfacial corrosion using fluorine-containing systems, nor reveal a technical pathway for recycling structurally intact aluminum foil through electrochemical biasing combined with ultrasonic synergy. Therefore, this application is not a simple improvement upon existing leaching or stripping technologies, but rather a novel technical approach at the levels of reaction mechanism and process control. It achieves both efficient separation and complete aluminum foil recycling simultaneously, demonstrating significant substantive features and substantial progress, and thus meets the inventive step requirement.

[0022] 1. For the first time, we proposed and realized interfacial confined corrosion of fluoride ions under the synergistic regulation of pH and potential. The combination of a weakly acidic environment and a specific anodic potential creates a unique chemical window, causing the corrosion reaction to occur almost exclusively at the target interface. This achieves directional peeling of aluminum foil, while inhibiting the dissolution of high-valence metals such as nickel, cobalt, and manganese by more than 99.5%.

[0023] 2. High-value recycled products: Unlike traditional recycling methods where aluminum exists as low-purity chemicals, this method directly yields structurally intact aluminum foil, which can be reused after simple repair. The total aluminum recovery rate (intact foil + precipitated aluminum) can reach over 95%.

[0024] 3. Low cost and environmentally friendly: Utilizing ammonium bifluoride, an industrial chemical, as the main reagent, it is cost-effective. It avoids the use of strong acids and alkalis and allows for recycling, significantly reducing wastewater discharge and treatment pressure.

[0025] 4. High efficiency and strong compatibility: The stripping speed is fast, typically completed within 30 minutes. Furthermore, this process can be embedded as an independent module into the front end of existing recycling production lines, providing pure, low-aluminum cathode raw materials for subsequent hydrometallurgical processes, significantly improving the overall economic efficiency of the process.

[0026] The technical solution of this invention fills a technological gap in the industry both domestically and internationally: 1. This invention is the first to propose and apply the principle of electrochemical interface confined corrosion: In existing technologies, fluoride salts such as ammonium bifluoride are only used for ore leaching or overall etching of metal surfaces, and have never been used to precisely control their selective corrosion at the two-dimensional interface between aluminum foil and active material. This invention, through pH-potential synergistic regulation, achieves spatial confinement of the corrosion reaction for the first time, keeping the aluminum foil intact while effectively weakening the interfacial bonding force.

[0027] 2. Industrialized Solution for Non-Destructive Aluminum Foil Recycling: Due to the strong chemical stability of binders, it is generally believed in the industry that achieving efficient separation of aluminum from cathode materials requires strong acid / alkali or high-temperature incineration, which inevitably damages the aluminum foil structure. This invention proposes a method that uses mild electrochemical conditions to achieve interfacial peeling without dissolving the aluminum foil, and the peeled aluminum foil can be directly reused after simple repair.

[0028] The technical solution of this invention overcomes technical bias: Conventional industrial recycling processes employ strong acids / alkalis to increase reaction rates and recycling efficiency, often involving the crushing of the positive electrode to expand the contact area and improve reaction efficiency. However, this approach leads to difficulties in subsequent solid-liquid separation, significant aluminum foil loss, and increased steps and costs associated with recovering high-value products. This invention eliminates the need for additional crushing, directly processing whole or large sheets of positive electrode material. Utilizing electrochemical-mechanical synergy, interfacial peeling is achieved without breakage, preserving the large size of the aluminum foil and facilitating subsequent sorting and repair. This successfully simplifies the process, improves aluminum recovery purity, and reduces energy consumption.

[0029] In recent years, much research has focused on synthesizing complex organic molecules, ionic liquids, or eutectic solvents to improve the selectivity of metal separation, seemingly creating a trend where complexity equals sophistication. This invention, however, chooses to use the simplest inorganic salt (ammonium bifluoride) and achieves high selectivity through process control (pH + potential), thus avoiding complex material design. This approach breaks the industry's reliance on expensive, complex additives, significantly lowering the technological threshold and cost, and making it more valuable for industrial application. Attached Figure Description

[0030] Figure 1 This is a flowchart of a method for the targeted recycling of lithium-ion battery cathode aluminum foil based on electrochemical interface confined corrosion, provided in an embodiment of the present invention.

[0031] Figure 2 This is a system structure block diagram of a method for targeted recycling of lithium-ion battery cathode aluminum foil based on electrochemical interface confined corrosion, provided in an embodiment of the present invention.

[0032] Figure 3 This is a process flow diagram of the targeted recycling of lithium-ion battery cathode aluminum foil provided in an embodiment of the present invention. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0034] like Figure 1 As shown, the method for targeted recycling of lithium-ion battery cathode aluminum foil based on electrochemical interface confined corrosion includes: S1. Preparation and Pretreatment of Functional Medium: Prepare an aqueous medium with ammonium hydrogen fluoride (NH4HF2) and / or ammonium fluoride (NH4F) as functional components. The pH of the medium is precisely adjusted to a weakly acidic range of 3.0-6.5 by adding an acid (such as dilute sulfuric acid) or an alkali (such as ammonia). Simultaneously, 10-30 vol% of carbonate solvent recovered from spent batteries is added to improve the wetting of the electrode sheets and dissolve some of the organic binders. The simply cleaned positive electrode sheets from spent batteries are immersed in this medium and allowed to stand for 30-60 minutes.

[0035] S2. Electrochemical-Mechanical Synergistic Interface Exfoliation: A positive electrode immersed in the dielectric is connected as the working electrode, with a graphite or titanium mesh as the counter electrode and an Ag / AgCl electrode as the reference electrode. A DC or pulsed anodic potential of 3.0-4.0V (vs. Ag / AgCl) is applied. Simultaneously, an ultrasonic generator (frequency 20-60kHz) is activated, utilizing its cavitation effect and microjets to promote dielectric penetration to the interface and enhance mass transfer. During this process, the anodic potential drives fluoride ions (F... - Anions such as α and β accumulate at the aluminum foil interface and produce a synergistic corrosion effect in the local electrochemical microenvironment. This selectively and directionally attacks and weakens the bonding interface between the aluminum foil and the active material layer, while the aluminum foil itself and the main positive electrode active material remain stable. The processing time is usually 5-60 minutes, and the peeling endpoint can be determined by monitoring changes in current or impedance.

[0036] S3. Separation of Multiphase Products: After processing, the active material layer has largely peeled off or completely detached. Through efficient separation, the following are obtained: structurally intact and flexible aluminum foil (product A), a sheet-like active material layer (product B), and a functional medium containing fluorine-aluminum complexes (product C).

[0037] S4. Aluminum Foil Recycling and Resource Recovery: The intact aluminum foil is recycled after surface impurities are removed. Alkaline substances such as ammonia are added to the aluminum-containing medium to adjust the pH to 8.5-10.0, causing aluminum to precipitate as high-purity aluminum hydroxide. After filtration, a small amount of fluoride is added to the filtrate, and the pH is adjusted back to the initial value with acid, achieving the regeneration and recycling of the functional medium. The detached active material layer is cleaned and dried before subsequent steps for recovering valuable metals.

[0038] The present invention provides a method for the targeted recycling of lithium-ion battery cathode aluminum foil based on electrochemical interface confined corrosion, comprising the following steps: S1, Functional Media Preparation and Pretreatment: Prepare an aqueous functional medium containing fluoride salts, wherein the pH value of the functional medium is 3.0-6.5; immerse the positive electrode sheet of a waste lithium-ion battery in the functional medium and let it stand for 30-60 minutes.

[0039] S2, electrochemical-mechanical synergistic interfacial exfoliation: Using the positive electrode in step S1 as the working electrode, an anode DC or pulse potential of 3.0-4.0V (relative to the Ag / AgCl reference electrode) is applied in the functional medium, and ultrasonic waves with a frequency of 20-60kHz are applied simultaneously for synergistic treatment, with a treatment time of 5-60 minutes.

[0040] S3, Separation of multiphase products: The mixed system after step S2 is subjected to solid-liquid separation to obtain a structurally intact aluminum foil, a blocky or sheet-like detached positive electrode active material layer, and a liquid phase containing dissolved aluminum.

[0041] S4, Aluminum Foil Recycling and Resource Recovery: The intact aluminum foil is subjected to surface cleaning and subsequent repair treatment; the aluminum-containing liquid phase is subjected to precipitation treatment to recover aluminum compounds and regenerate the functional medium.

[0042] In step S1 provided in this embodiment of the invention, the fluoride salt is selected from at least one of ammonium bifluoride (NH4HF2) and ammonium fluoride, and the concentration in the functional medium is 0.1-0.5 mol / L.

[0043] In step S1 provided in this embodiment of the invention, the functional medium further contains 10-30 vol% of an organic co-solvent, which is taken from carbonate solvents recovered from waste batteries.

[0044] In step S2 provided in this embodiment of the invention, the power density of the ultrasonic wave is 30-100W / L, and it operates in an intermittent pulse mode.

[0045] In step S2 of this embodiment of the invention, the electrochemical treatment process dynamically adjusts the potential or treatment time by monitoring the current or electrochemical impedance signal of the working electrode, and stops the treatment when the current stabilizes or the impedance drops to less than 50% of the initial value.

[0046] In step S3 provided in this embodiment of the invention, the area retention rate of the separated complete aluminum foil is not less than 90%.

[0047] In step S4 of this embodiment of the invention, the precipitation treatment involves adding an alkaline substance to the aluminum-containing liquid phase to adjust the pH to 8.5-10.0, so that aluminum precipitates out in the form of aluminum hydroxide. After filtration, the filtrate is supplemented with fluoride salts and acid to adjust to the initial pH value, thereby realizing the regeneration and recycling of the functional medium.

[0048] like Figure 2 As shown, an embodiment of the present invention provides a directional recycling system for lithium-ion battery cathode aluminum foil based on electrochemical interface confined corrosion, comprising: The pretreatment module is used for the preparation and pretreatment of the functional medium: preparing an aqueous functional medium containing fluoride salts, wherein the pH value of the functional medium is 3.0-6.5; immersing the waste lithium-ion battery positive electrode sheet into the functional medium and letting it stand for 30-60 minutes.

[0049] The stripping module is used for electrochemical-mechanical synergistic interface stripping: using the positive electrode in step S1 as the working electrode, an anodic DC or pulse potential of 3.0-4.0V (relative to the Ag / AgCl reference electrode) is applied in the functional medium, and ultrasonic waves with a frequency of 20-60kHz are applied simultaneously for synergistic treatment, with a treatment time of 5-60 minutes.

[0050] The separation module is used for the separation of multiphase products: the mixed system after step S2 is subjected to solid-liquid separation to obtain a structurally intact aluminum foil, a blocky or sheet-like detached positive electrode active material layer, and a liquid phase containing dissolved aluminum.

[0051] The recycling module is used for aluminum foil regeneration and resource recovery: it performs surface cleaning and subsequent repair treatment on the intact aluminum foil; it performs precipitation treatment on the aluminum-containing liquid phase to recover aluminum compounds and regenerate the functional medium.

[0052] Specific implementation of the present invention: Example 1 S1. Preparation of functional medium: Take 50 mL of deionized water, add 1.15 g of ammonium bifluoride, and stir until completely dissolved. The concentration at this point is approximately 0.3 mol / L. Add 10 mL of dimethyl carbonate (DMC), recovered from spent ternary lithium batteries and purified by distillation, to the above solution to form a slightly emulsified mixed medium. Adjust the pH of the medium to 5.0 ± 0.1 with dilute sulfuric acid solution.

[0053] S2. Electrochemical-Mechanical Co-exfoliation: A positive electrode sheet (5cm × 5cm) disassembled from a waste NCM811 battery is completely immersed in the medium prepared in step S1. Using this positive electrode sheet as the working electrode, a large-area graphite plate as the counter electrode, and an Ag / AgCl electrode as the reference electrode, the device is connected to an electrochemical workstation. A 40kHz ultrasonic probe is inserted into the reactor, with a power density set to 60W / L in pulse mode. The electrochemical workstation is started, applying a constant anode potential of +3.5V (vs. Ag / AgCl), and the ultrasonic waves are activated simultaneously.

[0054] S3. Product Separation and Characterization: When a significant decrease and stabilization of the working electrode current is observed, and a large area of ​​the active material layer at the edge of the positive electrode is visibly lifted, the reaction is stopped. The active material layer is removed with tweezers and detached into the medium. The aluminum foil is rinsed with deionized water and dried; the foil is now soft and free of perforations. The remaining medium is then filtered to separate the active material from the medium.

[0055] S4. Aluminum Recovery and Media Regeneration: For media regeneration, concentrated ammonia is slowly added dropwise to the media collected in step S3 while stirring, until the pH reaches 9.5. A large amount of white flocculent precipitate will be produced. After settling and filtration, the filter residue is dried at 80°C to obtain a white powder. X-ray derivatization analysis (XRD) identifies it as highly crystalline Al(OH)3 with a purity >99%. An appropriate amount of NH4HF2 is added to the filtered mother liquor, and the pH is adjusted to 5.0 with dilute sulfuric acid. Testing shows that its stripping performance is comparable to that of freshly prepared media.

[0056] S5. Preparation of valuable metal materials: The sieved sheet-like cathode material was heat-treated at 500°C for 2 hours in a nitrogen atmosphere to remove the binder, and then ground to obtain black powder. Analysis using inductively coupled plasma optical emission spectrometry (ICP-OES) showed that its aluminum content was only 0.6 wt%.

[0057] Comparative Example 1 Using the traditional acid leaching method, NCM811 positive electrode sheets of the same batch and size were directly immersed in a 2 mol / L sulfuric acid solution and stirred for 2 hours in an 80°C water bath.

[0058] Results: The aluminum foil was completely dissolved and broken. After the reaction, the pH of the solution was adjusted to 9.5 by adding NaOH to recover the aluminum hydroxide precipitate. The calculated aluminum recovery rate was 84%. XRD analysis of the precipitate showed that it contained small amounts of nickel and cobalt hydroxide impurities. The remaining leachate had a complex composition, containing a high concentration of Al. 3+ Ni 2+ Co 2+ Mn 2+ Subsequent separation and purification are difficult.

[0059] Comparative Example 2 Using an electrochemical-free fluoride salt immersion method, positive electrode sheets from the same batch were immersed in the same 0.3 mol / L NH4HF2 medium with pH=5.0 as in Example 1, but without applying any external potential or ultrasound, and were only immersed at 50°C for 2 hours.

[0060] Results: The active material layer only showed slight loosening at the edges, making large-area peeling impossible. Slight, uniform corrosion was observed on the aluminum foil surface. This demonstrates that without electrochemically driven directional action, fluoride ions can only perform slow, uniform corrosion, failing to achieve selective interfacial peeling.

[0061] Table 1 Comparison of recovery effects between the examples and the comparative examples

[0062] As shown in Table 1, the embodiment of the aluminum-oriented recycling strategy provided by the present invention has achieved effective directional recycling of aluminum foil in the positive electrode. The aluminum foil can be completely separated from the positive electrode active material, while avoiding the leaching of metal elements in the active material. In the end, the aluminum recovery rate is high and the recycled products have good economic benefits.

[0063] like Figure 3 As shown, the process of this invention is simple and low-cost, avoiding the use of strong acids and alkalis. While achieving targeted stripping and recycling of aluminum foil, it avoids excessive loss of high-value metal elements and takes into account the recycling concept of functional media. It has significant implications for resource recycling and energy conservation and emission reduction.

[0064] The method provided by this invention is significantly superior to existing technologies in terms of recycling principle, efficiency, product value, and environmental friendliness, providing a brand-new technical path for the targeted high-value recycling of lithium-ion battery cathode aluminum foil.

[0065] Example 1 Used lithium-ion battery positive electrode sheets were collected, with lithium cobalt oxide as the active material and an aluminum foil thickness of 15 micrometers. A functional medium containing ammonium bifluoride was prepared at a concentration of 0.25 mol / L, and the pH was adjusted to 4.5 with dilute hydrochloric acid. The positive electrode sheets were immersed in the medium and allowed to stand for 45 minutes. Using the positive electrode sheet as the working electrode, a platinum sheet as the counter electrode, and a silver-silver chloride electrode as the reference electrode, a 3.5-volt anodic DC potential was applied, simultaneously with ultrasonic waves at a frequency of 40 kHz and a power density of 60 watts / L, operating in an intermittent pulse mode with a pulse on / off time ratio of 1:1. The treatment time was 20 minutes, during which the working electrode current was monitored. Treatment was stopped when the current dropped to 40% of its initial value. The mixture was passed through a 200-mesh vibrating sieve for solid-liquid separation, yielding intact aluminum foil with 93% area retention and no residual active material on the surface. Sodium hydroxide was added to the aluminum-containing liquid phase to adjust the pH to 9.0, generating aluminum hydroxide precipitate. After filtration, ammonium bifluoride and dilute hydrochloric acid were added to the filtrate to bring the pH back to the initial 4.5, achieving medium regeneration.

[0066] Example 2 The active material of the spent positive electrode sheet is a nickel-cobalt-manganese ternary material, with an aluminum foil thickness of 12 micrometers. Ammonium fluoride was used as the functional medium at a concentration of 0.4 mol / L. A mixed solvent of ethylene carbonate and dimethyl carbonate recovered from spent batteries was added as an organic co-solvent, accounting for 20% of the volume, and the pH was adjusted to 5.0. After standing for 30 minutes, a 3.2-volt anolyte pulse potential was applied at a frequency of 1 kHz and a duty cycle of 80%, while simultaneously subjected to continuous ultrasonic treatment at a frequency of 20 kHz and a power density of 40 watts per liter for 35 minutes. After treatment, centrifugation was performed at 3000 rpm, resulting in a 95% retention rate of the intact aluminum foil area. Sodium carbonate was added to the aluminum-containing liquid phase to adjust the pH to 8.5, precipitating aluminum hydroxide. The filtrate was replenished with ammonium fluoride and acetic acid to adjust the pH to 5.0 before recycling. The separated positive electrode active material layer was ball-milled and then acid-leached to recover lithium, nickel, cobalt, and manganese.

[0067] Example 3 The positive electrode sheet was derived from spent lithium iron phosphate batteries, with an aluminum foil thickness of 16 micrometers. The functional medium was a mixed solution of ammonium bifluoride and ammonium fluoride, with a total concentration of 0.15 mol / L, a molar ratio of 1:1, and a pH of 6.0. After standing for 60 minutes, a 3.5-volt anodic DC potential was applied, simultaneously with ultrasonic waves at a frequency of 60 kHz and a power density of 90 watts / L, operating in an intermittent pulse mode with a pulse on / off time ratio of 2:1. The processing time was 10 minutes, monitored by electrochemical impedance spectroscopy, and processing was stopped when the interfacial impedance dropped to 45% of its initial value. A combination of vibrating sieve and magnetic separation was used for separation, resulting in an aluminum foil area retention rate of 91%. Sodium hydroxide or ammonia was added to the aluminum-containing liquid phase to adjust the pH to 10.0, generating a mixed precipitate of aluminum hydroxide and calcium sulfate. After separation, the filtrate was replenished with fluoride and phosphoric acid to adjust the pH to 6.0. The regeneration medium was reused five times, and the aluminum foil recovery rate remained stable at over 88%.

[0068] Example 4 Based on Example 1, a trace amount of sodium molybdate was added to the functional medium as a confined corrosion promoter at a concentration of 0.005 mol / L. This additive preferentially adsorbs onto defects on the aluminum foil surface at the anodic potential, inhibiting the propagation of localized pitting corrosion while simultaneously promoting the directional corrosion of fluoride ions at the aluminum foil-active material interface. The applied anodic potential was linearly increased from 2.8 volts to 3.6 volts using a ramp scanning method at a scan rate of 1 mV / s, coupled with ultrasonic treatment at a frequency of 35 kHz and a power density of 50 watts / L. Results showed that the aluminum foil area retention increased to 97%, and the surface roughness was less than 5% of the original aluminum foil, allowing it to be directly used for coating new positive electrode sheets without additional polishing. The aluminum ion concentration in the aluminum-containing liquid phase decreased by approximately 30% compared to the case without the additive, and the medium regeneration cycle was doubled. This extended scheme can be added to the scope of protection in subsequent defenses to address concerns in existing technologies regarding excessive aluminum foil thinning caused by simple fluoride salt corrosion.

[0069] Example 5 The single-tank static leaching method in Example 2 was replaced with a continuous roll-to-roll processing device. Waste positive electrode sheets were continuously passed through three series-connected reaction tanks at a speed of 0.5 meters per minute. The first tank was a functional medium pre-wetting tank with a residence time of 10 minutes. The second tank applied an anode DC potential of 3.3 volts, while two sets of ultrasonic transducers were arranged from the bottom and sidewalls of the tank, emitting composite ultrasonic waves of 28 kHz and 40 kHz respectively, with a total power density of 70 watts per liter, and a residence time of 15 minutes. The third tank was an ultrasonic rinsing tank, applying only ultrasonic waves of 50 kHz with a power density of 20 watts per liter, and a residence time of 5 minutes. After treatment, the aluminum foil was washed online and dried with hot air before being rolled up, achieving a 94% area retention rate and continuous operation for 8 hours without breakage. The aluminum-containing liquid phase adopted an online precipitation-filtration-adjustment circulation system to achieve closed-loop circulation of the functional medium. This continuous scheme significantly improved the processing throughput, reducing energy consumption per square meter of positive electrode sheet by 35% compared to the intermittent method, and can be used as an independent implementation method in subsequent patent layouts.

[0070] This section systematically compares the differences between Example 1 (the optimal solution of the present invention) and Comparative Example 1 (traditional sulfuric acid leaching method) and Comparative Example 2 (fluoride salt immersion method without electrochemical assistance) in key indicators such as aluminum foil peeling morphology and recovery rate.

[0071] 1. Peeling morphology and integrity of aluminum foil Example 1: After treatment, the aluminum foil remains intact in a large sheet shape, without perforations or tears, and can be easily removed whole with tweezers. The aluminum foil area retention rate is >96%, and the thickness remains essentially unchanged. Only a thin conversion layer remains on the aluminum foil surface, which can be directly reused as a current collector after phosphate repair.

[0072] Comparative Example 1: The aluminum foil completely dissolved, and no solid aluminum foil residue was observed in the solution after the reaction. Aluminum exists in ionic form in the solution, requiring subsequent neutralization and precipitation for recovery, a cumbersome process that negates the direct usability of the aluminum foil.

[0073] Comparative Example 2: After 2 hours of treatment, only a large number of tiny corrosion pits appeared on the surface of the aluminum foil, but the active material was still tightly bound to the aluminum foil. Only the edges were slightly detached, and effective peeling could not be achieved. Although the aluminum foil maintained its overall shape, the surface was corroded and lost its value for direct repair and utilization.

[0074] Conclusion: Only this invention achieves non-destructive complete peeling, which is a core advantage that the other two methods cannot achieve.

[0075] 2. Total aluminum recovery rate Example 1: Weighing and calculation showed that the recovered intact aluminum foil accounted for approximately 94% of the total original aluminum mass. The aluminum mass in the Al(OH)3 recovered from the medium accounted for approximately 4% of the total original aluminum mass, mainly due to interfacial corrosion and a small amount of bulk dissolution. The total aluminum recovery rate was 98% (94% + 4%).

[0076] Comparative Example 1: Aluminum was completely dissolved in sulfuric acid, and after precipitation with alkali, filtration, and drying, Al(OH)3 was obtained. Due to the presence of some aluminum ions in the supernatant during precipitation and the presence of a small amount of filtrate during filtration, the final aluminum recovery rate was only 84%, and the product purity was low.

[0077] Comparative Example 2: Due to ineffective stripping, the recovery rate could not be calculated. Although the aluminum foil did not dissolve, its surface was severely corroded and could not be used directly. The amount of dissolved aluminum in the medium was extremely low (<5%), resulting in low precipitate recovery value.

[0078] Conclusion: The total aluminum recovery rate of this invention (98%) is significantly higher than that of Comparative Example 1 (84%), and the product form is superior.

[0079] This invention explains from a theoretical perspective why it can achieve key effects such as interface confined erosion and high selectivity.

[0080] Interface confinement erosion: The positive electrode consists of a conductive aluminum foil (electronic conductor) and an active material layer (NCM, etc., mostly insulators) coated on it. When the electrode is immersed in an electrolyte and an anodic potential is applied, the electric field distribution exhibits significant non-uniformity: on the aluminum foil surface, the electric field strength is high, allowing anions to freely approach; at the aluminum foil-active material interface, due to the insulating properties of the active material layer, the electric field lines are distorted and concentrated, forming a local high-field region, making this region a preferred area for anion aggregation and reaction; in the active material region, the electric field is shielded. At the interface between metallic Al and the active material, two media with significantly different dielectric constants, the normal electric field component at the interface undergoes abrupt change because the dielectric constant of the active material coating is much smaller than the equivalent dielectric constant of the metal. This results in local enhancement at microscopic protrusions or defects at the interface, providing a basis for the spatially selective enrichment of fluoride ions at the interface.

[0081] Selective corrosion: Based on the thermodynamic stability region diagram of the metal-water system, the solubility tendency of different metals at specific pH and potential can be analyzed. Al has a stable region within the weakly acidic pH range of 4-7. 3+ (Soluble) or Al₂O₃·xH₂O (surface film). When the potential is higher than -0.5V (vs. SHE), aluminum can be oxidized to Al. 3+ The +3.5V (vs. Ag / AgCl) applied in this invention translates to approximately +3.9V (vs. SHE), which is significantly higher than the dissolution potential of aluminum, thus thermodynamically favorable for aluminum dissolution. Nickel is stable within the pH range of 4-7, while Ni is in its stable region. 2+ However, an oxidation dissolution occurs only when the potential is higher than approximately +0.4V (vs. SHE). However, Ni in NCM materials is primarily Ni... 3+ / Ni 4+ It exists in a higher oxidation state and is further oxidized to soluble Ni. 2+ A higher overpotential is required. Within the potential window of this invention (approximately +3.9 V vs. SHE), the dissolution of Ni requires disruption of the stable MO6 octahedral structure, and the reaction is kinetically inhibited. Similarly, for cobalt and manganese, Co… 3+ / Co 4+ and Mn 5+ They are very stable in layered oxide structures, and their dissolution requires stronger acidity or higher potential. Under the weakly acidic conditions (pH≈5) and moderate anodic potentials of this invention, the oxides / hydroxides of these high-valence transition metals remain stable in the solid state. Therefore, the pH (5.0) and potential (3.5 V vs. Ag / AgCl) selected in this invention fall precisely within a suitable thermodynamic window, allowing aluminum to be oxidized and dissolved, while the oxides of Ni, Co, and Mn remain inert, thus achieving a selective thermodynamic basis.

[0082] Fluoride and aluminum ions can combine through both inner-layer and outer-layer complexes, forming complexes that exhibit strong stability and specific structural characteristics, which is another key factor in their selectivity. Al 3+ With F - A series of stable aluminum fluoride complexes (AlF) are formed. 2+ AlF2 + AlF3, AlF4 - (etc.), the formation of these complexes reduces Al 3+ The activity of Al / Al 3+ The equilibrium potential shifts towards a more negative direction, thus promoting the dissolution of aluminum. Meanwhile, fluorine complexes coat the fresh aluminum surface, hindering the regeneration of a dense oxide film and allowing the dissolution reaction to continue. In contrast, Ni... 2+ Co 2+ Mn 2+ With F - The complexing ability of these metal ions is extremely weak, so fluoride ions have almost no solubilizing effect on them. This chemical difference between these metal ions and fluoride ions further amplifies the thermodynamic selectivity.

[0083] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for the targeted recycling of lithium-ion battery cathode aluminum foil based on electrochemical interface confined corrosion, characterized in that, The positive electrode sheet of the waste lithium-ion battery is immersed in an acidic aqueous functional medium containing fluoride salts. The positive electrode sheet is used as the working electrode to apply an anode potential, and ultrasonic waves are applied simultaneously for synergistic treatment, so that the positive electrode active material layer is detached from the surface of the aluminum foil, and then the intact aluminum foil is obtained by separation.

2. The method according to claim 1, characterized in that, The functional medium has a pH of 3.0 to 6.5, the anode potential is 3.0 to 4.0 volts relative to the silver chloride reference electrode, and the ultrasonic frequency is 20 to 60 kHz.

3. The method according to claim 1, characterized in that, The fluoride salt is selected from at least one of ammonium bifluoride or ammonium fluoride, and its concentration in the functional medium is 0.1 to 0.5 mol / L; the functional medium also contains 10 to 30 volume percent of an organic co-solvent, which is derived from carbonate solvents recovered from waste batteries.

4. The method according to claim 1, characterized in that, The ultrasonic power density is 30 to 100 watts per liter, and it operates in an intermittent pulse mode. During the electrochemical treatment, the potential or treatment time is dynamically adjusted by monitoring the current or electrochemical impedance signal of the working electrode. The treatment is stopped when the current stabilizes or the impedance drops to less than 50% of the initial value.

5. The method according to claim 1, characterized in that, The area retention rate of the separated intact aluminum foil is not less than 90%. The intact aluminum foil is subjected to surface cleaning and subsequent repair treatment. The separated liquid phase containing dissolved aluminum is subjected to precipitation treatment to recover aluminum compounds and regenerate the functional medium.

6. A system for implementing the method for targeted recycling of lithium-ion battery cathode aluminum foil based on electrochemical interface confined corrosion as described in claim 1, characterized in that, include: The pretreatment module is used to prepare the acidic aqueous functional medium containing fluoride salts and immerse the waste lithium-ion battery positive electrode sheet in the functional medium and let it stand. An electrochemical-mechanical synergistic stripping module is used to apply an anode potential with the positive electrode as the working electrode and simultaneously apply ultrasound; a multiphase separation module is used to separate the solid and liquid phases of the treated mixed system to obtain a structurally intact aluminum foil, a blocky or sheet-like detached positive electrode active material layer, and a liquid phase containing dissolved aluminum; a recovery module is used to perform surface cleaning and repair on the intact aluminum foil and to perform precipitation treatment on the aluminum-containing liquid phase to recover aluminum compounds and regenerate the functional medium.

7. The system according to claim 6, characterized in that, The electrochemical-mechanical synergistic stripping module includes an electrochemical workstation, an ultrasonic generator, and an ultrasonic transducer. The electrochemical workstation is configured to apply an anodic DC or pulse potential of 3.0 to 4.0 volts relative to a silver chloride reference electrode. The ultrasonic generator is configured to output ultrasonic waves with a frequency of 20 to 60 kHz and a power density of 30 to 100 watts per liter, and to operate in an intermittent pulse mode.

8. The system according to claim 6, characterized in that, The electrochemical-mechanical co-exfoliation module also includes an online monitoring unit for monitoring the current or electrochemical impedance signal of the working electrode, and automatically stopping the process when the current stabilizes or the impedance drops to less than 50% of the initial value.

9. The system according to claim 6, characterized in that, The multiphase separation module employs a vibrating screen or centrifugal separation device. The recovery module includes a precipitation reaction tank, a filtration unit, and a media preparation unit. The precipitation reaction tank is used to add alkaline substances to the aluminum-containing liquid phase to adjust the pH to 8.5 to 10.0 so that aluminum precipitates in the form of aluminum hydroxide. The filtration unit is used to separate aluminum hydroxide. The media preparation unit is used to supplement fluoride and acid into the filtrate to adjust it to the initial pH value.

10. A method for regenerating functional media in the recycling of lithium-ion battery cathode aluminum foil according to claim 1, characterized in that, The method includes the following steps: collecting the liquid phase containing dissolved aluminum obtained by the method of claim 1, adding an alkaline substance to the liquid phase to adjust the pH to 8.5 to 10.0, causing aluminum to precipitate out in the form of aluminum hydroxide, filtering to obtain aluminum hydroxide and filtrate, and adding fluoride and acid to the filtrate to the initial pH value to obtain the regenerated functional medium.

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