A lithium battery non-destructive recovery system and method based on multi-frequency ultrasonic cavitation

Abstract

A kind of lithium battery non-destructive recovery system based on multi-frequency ultrasonic cavitation, variable-frequency pulse ultrasonic transducer array is arranged in main stripping reaction tank, transducer array is arranged at the bottom and side wall of main stripping reaction tank, and is connected to multi-frequency signal generator;Micro-bubble injection unit is arranged at the bottom of main stripping reaction tank, including microporous aeration device or dissolved gas release nozzle, and pole piece transmission mechanism penetrates through multiple-stage processing tank, for conveying waste lithium battery pole piece in tension or suspended state to pass through swelling tank, main stripping reaction tank and rinsing tank in sequence.The spatial arrangement of variable-frequency pulse ultrasonic transducer array in main stripping reaction tank is adopted in the present application, staggered cross arrangement is adopted, sound field is diffused and superimposed in transverse and longitudinal direction, standing wave blind area is effectively eliminated, and cavitation coverage of "deep and shallow consideration, strong and weak complementation" is realized in macroscopic, to ensure the complete stripping of dense ternary material coating.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery recycling technology, specifically a non-destructive recycling system and method for lithium batteries based on multi-frequency ultrasonic cavitation. Background Technology

[0002] With the rapid development of the new energy vehicle industry, the number of retired power batteries is growing exponentially. How to efficiently, greenly, and with high value recycle waste lithium batteries has become a global issue for resource recycling and environmental protection. Among existing recycling technologies, physical methods (such as mechanical crushing and screening) are simple in process, but they generally suffer from serious damage to the current collector (aluminum foil / copper foil), crushing of active material particles, and cross-contamination of components, making it difficult to directly reuse the recycled products in battery manufacturing. While hydrometallurgy can achieve high-purity extraction of metal elements, it relies on strong acids and strong oxidants, generating a large amount of wastewater containing heavy metals and completely destroying the crystal structure of the cathode material, making it impossible to achieve "material-level" regeneration.

[0003] First, while low-frequency ultrasound (e.g., 20-30kHz) can generate high-intensity cavitation impacts, suitable for peeling dense ternary material (NCM / NCA) coatings, its concentrated energy and intense action can easily cause perforation, microcracks, or plastic deformation on aluminum foil, which is usually less than 20μm thick. On the other hand, while high-frequency ultrasound (e.g., >80kHz) has a gentler effect, its weak cavitation intensity and poor penetration make it almost ineffective for ternary materials with high compaction density or aged adhesive layers. Existing equipment mostly adopts a unidirectional bottom transducer layout, where sound waves are repeatedly reflected in the tank to form standing waves, resulting in a periodic alternation of "hot spots and blind spots" in the sound field distribution. Some areas are over-treated, while other areas are completely uncovered, causing uneven electrode peeling and a local residual rate of more than 10%, which seriously affects the consistency of recycling.

[0004] Secondly, in order to compensate for insufficient cavitation, operators are forced to increase the ultrasonic power density (often exceeding 2.0 W / cm²), but this not only aggravates foil damage, but also causes energy waste due to the strong absorption of acoustic energy by the liquid medium. It cannot effectively participate in the acoustic cavitation process, and instead causes the electrode to shake due to violent disturbance, further deteriorating the peeling uniformity.

[0005] Third, most experimental devices use free fall or simple roller conveying to transport electrodes. Electrodes are prone to bending, wrinkling or floating in liquids, which causes their relative position to the sound field to change randomly. This results in significant differences in the cavitation dose received by different areas of the same electrode. Some areas are damaged due to prolonged exposure to strong sound fields, while other areas are not completely peeled off due to deviation from the main sound beam. Summary of the Invention

[0006] In order to overcome the shortcomings of the prior art, the present invention provides a non-destructive recycling system and method for lithium batteries based on multi-frequency ultrasonic cavitation, so as to at least partially solve the above-mentioned technical problems.

[0007] The technical solution adopted in this invention is as follows: This invention proposes a non-destructive lithium battery recycling system based on multi-frequency ultrasonic cavitation, comprising: The multi-stage processing tank consists of a swelling tank, a main stripping reaction tank, and a rinsing tank arranged sequentially along the electrode conveying direction. The main stripping reaction tank is equipped with a variable frequency pulse ultrasonic transducer array. The transducer array is arranged at the bottom and side wall of the main stripping reaction tank and connected to a multi-frequency signal generator. It is configured to perform frequency sweep or dual-frequency alternating transmission between two frequency ranges of 20-30kHz and 40-80kHz. The microbubble injection unit, located at the bottom of the main stripping reaction tank, includes a microporous aeration device or dissolved gas release nozzle, used to inject microbubbles with an average particle size of 10μm-50μm into the liquid medium in the main stripping reaction tank. An electrode transport mechanism runs through the multi-stage processing tank and is used to transport waste lithium battery electrodes in a tensioned or suspended state through the swelling tank, the main stripping reaction tank, and the rinsing tank in sequence.

[0008] In one embodiment of the present invention, the multiple transducers in the frequency-converting pulse ultrasonic transducer array are arranged in a staggered and cross-shaped manner, that is, the adjacent rows of transducers are staggered by half a transducer spacing in the horizontal direction to avoid forming a standing wave blind zone in the sound field.

[0009] In one embodiment of the invention, the microporous aeration device or dissolved gas release nozzle of the microbubble injection unit is located at the bottom of the main stripping reaction tank and below the ultrasonic transducer array, so that the generated microbubbles pass through the acoustic field region excited by the ultrasonic transducer from bottom to top.

[0010] In one embodiment of the present invention, the bottom of the main stripping reaction tank is provided with a slurry outlet, which is connected to a solid-liquid separation device through a pipe for exporting the stripped active material slurry and performing solid-liquid separation.

[0011] In one embodiment of the present invention, the multi-stage processing tank is equipped with a temperature control system for maintaining the temperature of the liquid medium in the main stripping reaction tank within the range of 40°C to 60°C.

[0012] In one embodiment of the present invention, a method for a lithium battery non-destructive recycling system based on multi-frequency ultrasonic cavitation includes the following steps: S1: Send the waste lithium battery electrode sheets into the swelling tank and soak them in an aqueous solution containing less than 5% organic solvent by volume for 1-3 minutes to cause the adhesive layer to swell. S2: The electrode sheet treated by S1 is sent into the main stripping reaction tank, and the microbubble injection unit is started to make the concentration of microbubbles in the liquid medium reach a gas-liquid mixing ratio of 3%-8%; S3: Synchronously start the variable frequency pulse ultrasonic transducer array, so that it sweeps and oscillates in two frequency ranges of 20-30kHz and 40-80kHz with a period of 50-100Hz, continuously acting on the electrode surface. S4: The stripped aluminum foil is sent to the rinsing tank for cleaning, and the slurry formed in the main stripping reaction tank is discharged to the solid-liquid separation device to recover the aluminum foil and active material powder respectively.

[0013] In one embodiment of the present invention, in step S3, the power density of the ultrasonic action is controlled at 0.5-1.5 W / cm², and the sweep bandwidth is ±2 kHz.

[0014] In one embodiment of the present invention, the organic solvent is N-methylpyrrolidone or dimethyl sulfoxide, and the liquid medium further contains a nonionic surfactant with a volume fraction of less than 1%.

[0015] In one embodiment of the present invention, in step S2, the average particle size of the injected microbubbles is 20±10μm.

[0016] In one embodiment of the present invention, the method is applicable to waste lithium battery electrodes of lithium iron phosphate or ternary material system, and the coating peeling rate is not less than 99.5% after passing through the main stripping reaction tank once.

[0017] The beneficial effects of the technical solution of this invention are as follows: This invention utilizes the spatial arrangement of the frequency-converted pulse ultrasonic transducer array within the main stripping reaction tank, employing a staggered cross arrangement (adjacent rows are horizontally offset by half a spacing), to diffuse and superimpose the sound field in both the lateral and longitudinal directions, effectively eliminating standing wave blind zones. Combined with dual-band frequency sweeping or alternating transmission of 20-30kHz (strong penetration, high impact) and 40-80kHz (high density, low damage), it can macroscopically achieve cavitation coverage that is both deep and shallow, strong and weak complementary. This ensures complete stripping of the dense ternary material coating while avoiding perforation or plastic deformation of thin aluminum foil (typically <20μm).

[0018] This invention utilizes a microporous aeration device or dissolved gas release nozzle to generate 10-50μm microbubbles that pass upwards through a three-dimensional composite sound field jointly excited by bottom and sidewall transducers. During the ascent, the microbubbles are repeatedly excited, resonate, and even implode by the sound pressure, forming a large number of directional microjets. The microjets vertically impact the bottom surface of the electrode, forming orthogonal stress coupling with the ultrasonic shear force, improving the interface debonding efficiency. This allows the system to trigger efficient cavitation at a relatively low power density (0.5-1.5W / cm²), saving energy and reducing cumulative fatigue damage to the foil.

[0019] This invention utilizes an electrode transport mechanism to maintain a tensioned or suspended state throughout the entire process, ensuring that the electrode remains flat, wrinkle-free, and moves at a uniform speed through each processing zone in the liquid medium. This transport method not only prevents uneven local stress caused by electrode vibration but also ensures that the entire coating surface receives a consistent cavitation dose, achieving uniform peeling. Simultaneously, the tensioned state helps maintain a stable relative position between the electrode and the sound field and microbubble flow, making the physical interactions repeatable and predictable.

[0020] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0021] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein: Figure 1 This is a system module framework diagram of the lithium battery non-destructive recycling system based on multi-frequency ultrasonic cavitation proposed in an embodiment of the present invention; Figure 2 This is a functional framework diagram of the system modules of the lithium battery non-destructive recycling system based on multi-frequency ultrasonic cavitation proposed in an embodiment of the present invention. Figure 3 This is a flowchart illustrating the method of the lithium battery non-destructive recycling system based on multi-frequency ultrasonic cavitation proposed in an embodiment of the present invention. Figure 4 This is a flowchart illustrating the functional framework of a lithium battery non-destructive recycling system based on multi-frequency ultrasonic cavitation proposed in an embodiment of the present invention. Detailed Implementation

[0022] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0023] The following describes a lithium battery non-destructive recycling system and method based on multi-frequency ultrasonic cavitation according to an embodiment of the present invention, with reference to the accompanying drawings.

[0024] like Figures 1 to 4 As shown, this embodiment of the invention provides a lithium battery non-destructive recycling system based on multi-frequency ultrasonic cavitation, including: a multi-stage processing tank, wherein a swelling tank, a main stripping reaction tank and a rinsing tank are arranged sequentially along the electrode conveying direction; The main stripping reaction tank is equipped with a frequency conversion pulse ultrasonic transducer array. The transducer array is arranged at the bottom and side wall of the main stripping reaction tank and connected to a multi-frequency signal generator. It is configured to perform frequency sweep or dual-frequency alternating transmission between two frequency ranges of 20-30kHz and 40-80kHz. The microbubble injection unit, located at the bottom of the main stripping reaction tank, includes a microporous aeration device or dissolved gas release nozzle, used to inject microbubbles with an average particle size of 10μm-50μm into the liquid medium in the main stripping reaction tank. The electrode conveying mechanism runs through multiple processing tanks and is used to transport waste lithium battery electrodes in a tensioned or suspended state through the swelling tank, the main stripping reaction tank, and the rinsing tank in sequence.

[0025] In specific applications of this invention, after the electrode enters the system from the feed end, it first enters the swelling tank. The tank contains an aqueous solution containing trace amounts of organic solvents (such as NMP or DMSO) and a small amount of nonionic surfactants. Through selective penetration, the binder (such as PVDF) undergoes controlled swelling, thereby weakening the interfacial bonding force between it and the current collector (aluminum foil or copper foil) and the active material particles. Excessive swelling should not lead to foil deformation or active layer collapse, nor should insufficient swelling affect the subsequent peeling efficiency. The swelling time is usually controlled at 1-3 minutes to ensure that the binder network structure is relaxed but the overall coating still maintains its integrity, providing an ideal mechanical response basis for subsequent ultrasonic cavitation.

[0026] Subsequently, the swollen electrode sheets are smoothly fed into the main peeling reaction tank by the electrode sheet transport mechanism. The tank integrates a frequency-converting pulse ultrasonic transducer array and a microbubble injection unit, which are highly matched in spatial layout and temporal coordination. Specifically, the ultrasonic transducers are not only arranged at the bottom of the tank, but also staggered and cross-arranged along the side walls to form a three-dimensional stereo sound field coverage, effectively eliminating the sound shadow zone or standing wave blind zone that is easily generated by traditional unidirectional ultrasonic devices. The transducers are connected to a multi-frequency signal generator, which can periodically sweep frequencies or alternately transmit frequencies between two frequency bands: 20-30kHz and 40-80kHz. The low-frequency band (20-30kHz) is conducive to generating high-intensity cavitation bubbles, and the local shock waves released when they collapse can exert strong shear forces on the adhesive-current collector interface; while the high-frequency band (40-80kHz) generates denser and more uniform microcavitation nuclei, increasing the spatial distribution density of cavitation events and suppressing the mechanical damage of large-scale cavitation bubbles to the foil surface.

[0027] Simultaneously, the microbubble injection unit located at the bottom of the main peeling reaction tank works in sync, continuously injecting microbubbles with an average particle size in the range of 10-50μm into the liquid medium through a microporous aeration device or dissolved gas release nozzle. The microbubbles act as "pre-set seeds" for cavitation nuclei, reducing the cavitation threshold and enabling ultrasonic energy to be converted into local cavitation effects more efficiently. In particular, when the microbubbles rise and pass through the composite sound field region excited by the bottom and side wall transducers, they resonate, oscillate, and even implode under the action of sound pressure, forming a large number of secondary microjets and local high temperature and high pressure micro-regions. The micro-regions act on the already swollen adhesive interface, further amplifying the interface peeling force. At the same time, because the size of the microbubbles is controllable and the distribution is uniform, the violent disturbance and foil shaking caused by the rupture of large bubbles in the traditional bubbling method are avoided.

[0028] The electrode transport mechanism employs a tensioning wheel assembly or a suspended guide rail structure to ensure the electrode remains flat and wrinkle-free in the liquid, and passes through the acoustic field action zone at a constant speed. This transport method avoids uneven local stress or repeated processing caused by electrode shaking, and ensures that the entire coating surface receives consistent cavitation effects in time and space, guaranteeing uniform peeling. Furthermore, the temperature of the liquid medium in the main peeling reaction tank is maintained at 40-60℃ by a temperature control system, which accelerates the swelling kinetics of the binder and optimizes the growth and collapse characteristics of cavitation bubbles, further improving peeling efficiency.

[0029] After stripping, the metal foil, stripped of its active coating, continues into a rinsing tank, where it is washed with clean water or a weakly alkaline solution to remove residual slurry and chemical reagents, ultimately outputting a clean, directly reusable current collector. Simultaneously, a slurry outlet at the bottom of the main stripping reaction tank continuously discharges a mixture containing detached active material, swollen binder fragments, and microbubble residues to a downstream solid-liquid separation device (such as a centrifuge or membrane filtration system), achieving efficient recovery of the active material powder and partial recycling of the liquid medium.

[0030] In one specific implementation, multiple transducers in the frequency-conversion pulse ultrasonic transducer array are arranged in a staggered and cross-shaped manner, that is, adjacent rows of transducers are staggered by half a transducer spacing in the horizontal direction to avoid forming a standing wave blind zone in the acoustic field. The microporous aeration device or dissolved gas release nozzle of the microbubble injection unit is located at the bottom of the main stripping reaction tank and below the ultrasonic transducer array, so that the generated microbubbles pass through the acoustic field region excited by the ultrasonic transducer from bottom to top.

[0031] In specific applications, the variable frequency pulse ultrasonic transducers of this invention employ a staggered cross-arrangement. Adjacent rows of transducers are offset horizontally by half a transducer spacing, breaking the acoustic interference mode caused by the periodic array and effectively suppressing the formation of standing waves. In a conventional arrangement, the acoustic waves emitted by multiple in-phase transducers superimpose and intensify at specific locations, while canceling each other out at others, forming energy "hot spots" and "cold spots," the so-called standing wave blind zones. The cavitation intensity decreases in the cold spot areas, preventing effective peeling of the local coating on the electrode sheet and affecting overall recovery consistency. Through the staggered cross-arrangement, the spatial phase distribution of the sound source is disrupted, and the sound field energy tends to disperse and homogenize in both the horizontal and vertical dimensions, increasing the density and continuous distribution of cavitation events throughout the electrode sheet's pass-through area. Especially when the system switches between or sweeps frequencies between 20-30kHz and 40-80kHz dual-band operation, the wavelength differences corresponding to different frequencies further weaken the stability of the fixed interference pattern, dynamically "refreshing" the sound field and continuously covering potential blind zones, ensuring that every micrometer of the electrode sheet's surface undergoes sufficient cavitation.

[0032] Meanwhile, the microbubble injection unit is positioned directly below all the ultrasonic transducers, at the bottom of the main stripping reaction tank. Microporous aeration devices or dissolved gas release nozzles release a large number of microbubbles with an average particle size of 10-50 μm. Due to buoyancy, these bubbles naturally rise, passing precisely through the three-dimensional composite acoustic field region jointly excited by the bottom and sidewall transducers. Under the influence of the acoustic pressure field, the microbubbles participate in the cavitation process: as pre-set cavitation nuclei, they are rapidly stretched and expanded in the negative pressure phase of the acoustic wave, and violently implode in the positive pressure phase, generating localized microjets, shock waves, and instantaneous high-temperature, high-pressure micro-regions. Because of the small size, large number, and dense distribution of the microbubbles, their collapse process is more controllable and gentler than spontaneously nucleated cavitation bubbles, providing sufficient interfacial stripping force while avoiding mechanical damage to the metal current collector.

[0033] As the electrode passes through the main peeling reaction tank at a constant speed under tension, its lower surface is continuously exposed to the area where the microbubble flow from below and the ultrasonic waves from above / sides interact. The microbubbles are continuously activated, oscillate, and collapse during their passage through the acoustic field, generating micro-jet streams that vertically impact the bottom surface of the electrode. Meanwhile, the ultrasonic waves apply shear stress from multiple angles. This multi-directional synergistic effect allows the adhesive layer to swell and soften while simultaneously withstanding micro-impacts from the vertical direction and acoustic shearing from the horizontal direction, accelerating the interface debonding process. Furthermore, the presence of microbubbles lowers the cavitation threshold of the liquid medium, enabling the system to trigger efficient cavitation at lower ultrasonic power. This not only saves energy but also reduces potential fatigue damage to the foil caused by the collapse of high-energy cavitation bubbles.

[0034] In one specific embodiment, the bottom of the main stripping reaction tank is provided with a slurry outlet, which is connected to a solid-liquid separation device through a pipeline to export the stripped active material slurry and perform solid-liquid separation. The multi-stage treatment tank is equipped with a temperature control system to maintain the temperature of the liquid medium in the main stripping reaction tank within the range of 40℃-60℃.

[0035] In specific applications of this invention, after waste lithium battery electrodes undergo multi-frequency ultrasonic cavitation and the synergistic effect of microbubbles in the main stripping reaction tank, the active material layer (such as lithium iron phosphate or ternary materials) and binder mixture on their surface are peeled off layer by layer, forming a fine-particle slurry suspended in a liquid medium. Due to the combined effects of ultrasonic disturbance, microbubble upflow, and liquid circulation, this slurry remains in a uniform suspension state. To prevent excessive accumulation of slurry in the tank, which could lead to increased concentration and viscosity, thereby affecting cavitation efficiency or causing pipe blockage, a dedicated slurry outlet is provided at the bottom of the main stripping reaction tank. The outlet is typically located at the lowest point of the tank and slightly off the center of the main fluid disturbance. This effectively collects coarse particles with a clear settling tendency without drawing in a large number of air bubbles that would interfere with subsequent separation due to being directly in the strong cavitation zone. The slurry is continuously discharged from this outlet through a corrosion-resistant pipe and directly transported to downstream solid-liquid separation devices such as high-speed centrifuges, filter presses, or ceramic membrane filtration systems. This ensures that the solid phase concentration in the main stripping reaction tank is always maintained at a low level (usually controlled below 5 wt%), thereby ensuring that ultrasonic energy can be efficiently transferred to the electrode surface, avoiding the scattering and absorption of sound waves by high-concentration slurry, and maintaining the stability of cavitation intensity.

[0036] Meanwhile, the system maintains the temperature of the liquid medium in the tank within the range of 40°C to 60°C by using heating / cooling coils embedded in the tank wall or outer jacket, combined with temperature sensors and PID controllers. The binder (such as PVDF) is most sensitive to the swelling response of trace organic solvents (such as NMP) at the temperature, which enhances the mobility of molecular chain segments and reduces the interfacial bonding force, providing an ideal mechanical condition for ultrasonic exfoliation. Secondly, the viscosity of the liquid medium decreases with increasing temperature. In the 40-60°C range, the viscosity of water-based solutions decreases by about 20%-30% compared to room temperature, which not only facilitates the generation and rise of microbubbles but also reduces the energy attenuation of ultrasound during propagation, further reducing the cavitation threshold. Furthermore, the collapse intensity of cavitation bubbles is closely related to the saturated vapor pressure of the liquid, and the vapor pressure increases exponentially with increasing temperature. Below 60°C, a moderate increase in vapor pressure helps to form a more violent asymmetric implosion inside the cavitation bubble, enhancing the impact force of the microjet, but without weakening the cavitation intensity due to excessive vapor "cushioning effect". Above 60°C, excess vapor will fill the cavitation bubble and suppress its collapse power.

[0037] The temperature control system and the slurry discharge mechanism are coupled here: on the one hand, a stable temperature environment ensures the consistency of the physical properties of the slurry (such as density, viscosity, and particle dispersibility), enabling the solid-liquid separation device to operate efficiently under preset parameters and avoid the increase of filter cake moisture content or the inaccuracy of centrifugal separation factor due to temperature fluctuations; on the other hand, the continuously discharged slurry also carries away some of the heat generated by ultrasonic action, preventing local overheating, while the temperature control system compensates for heat loss in real time and maintains overall thermal balance.

[0038] In one specific implementation, the method for a lithium battery non-destructive recycling system based on multi-frequency ultrasonic cavitation includes the following steps: S1: Send the waste lithium battery electrode sheets into the swelling tank and soak them in an aqueous solution containing less than 5% organic solvent by volume for 1-3 minutes to cause the adhesive layer to swell. S2: The electrode sheet treated by S1 is sent into the main stripping reaction tank, and the microbubble injection unit is started to make the concentration of microbubbles in the liquid medium reach a gas-liquid mixing ratio of 3%-8%; S3: Synchronously start the variable frequency pulse ultrasonic transducer array, so that it sweeps and oscillates in two frequency ranges of 20-30kHz and 40-80kHz with a period of 50-100Hz, continuously acting on the electrode surface. S4: The stripped aluminum foil is sent to the rinsing tank for cleaning, and the slurry formed in the main stripping reaction tank is discharged to the solid-liquid separation device to recover the aluminum foil and active material powder respectively.

[0039] In specific applications of this invention, the electrode sheet is immediately introduced into a swelling tank after entering the system, where it remains briefly for 1 to 3 minutes. The liquid in the tank is a mild swelling medium composed of water as the main solvent, supplemented by an organic solvent (such as NMP or DMSO) with a volume fraction of less than 5%, and a trace amount of nonionic surfactant. The organic solvent molecules preferentially penetrate into the polymer network structure of the binder (such as PVDF), causing it to swell to a limited extent. This increases the molecular chain spacing and lowers the glass transition temperature, thereby weakening the van der Waals forces and mechanical anchoring effects between the binder and the current collector (aluminum foil) and the active material particles. Due to the limited solvent concentration and short reaction time, the binder as a whole maintains a continuous film structure and will not dissolve or cause the coating to collapse. Immediately afterwards, the swollen electrode sheet is smoothly fed into the main peeling reaction tank by a transport mechanism. At this point, microbubble injection and multi-frequency ultrasonic excitation are used. The microbubble injection unit begins to inject a large number of microbubbles with an average particle size in the range of 10-50μm into the liquid at the bottom of the tank, which quickly makes the gas-liquid mixing ratio reach 3%-8%. This provides sufficient cavitation nucleus density to reduce the cavitation threshold, and avoids hindering the propagation of sound waves or causing the electrode to float and become unstable due to excessive gas phase.

[0040] Meanwhile, the frequency-converting pulse ultrasonic transducer array is activated, sweeping oscillations between two frequency ranges of 20-30kHz and 40-80kHz with a period of 50-100Hz. The cavitation bubbles generated in the low-frequency range (20-30kHz) have larger volumes and higher collapse energy, making them suitable for applying strong shear and micro-impact to the swollen binder-current collector interface. The high-frequency range (40-80kHz) generates denser and more uniform micro-cavitation events with a wide coverage area and gentler effect, effectively supplementing the micro-areas missed by the low-frequency range and suppressing the cumulative damage of large-scale cavitation to the foil. By periodically switching, the completeness of peeling is ensured (single-pass peeling rate ≥99.5%), while maintaining the integrity and flatness of the aluminum foil surface. During this process, microbubbles actively participate in cavitation enhancement: when they pass through the composite sound field excited by the transducer, they are repeatedly compressed and expanded by the sound pressure, and finally violently implode in the negative pressure phase, generating directional micro-jet vertically impacting the bottom surface of the electrode, causing the adhesive layer to undergo brittle fracture debonding within milliseconds. The active material falls off in the form of intact particles, greatly preserving its electrochemical activity.

[0041] Throughout the stripping process, the electrode remains taut and moves at a constant speed through the main stripping reaction tank, ensuring that each area receives an effective cavitation dose. After stripping, the exposed aluminum foil continues into the rinsing tank, where it is thoroughly cleaned with deionized water or multi-stage countercurrent rinsing to remove residual slurry, solvents, and additives from the surface, ultimately outputting clean, dry, high-purity aluminum foil that can be directly reused in battery manufacturing.

[0042] Meanwhile, the active material-binder mixture slurry formed in the main stripping reaction tank is not retained, but is continuously discharged to the solid-liquid separation device through the bottom slurry outlet. Because the stripping process is carried out in a controlled temperature environment (40-60℃), the slurry viscosity is low and the particle dispersion is good, thus improving the solid-liquid separation efficiency. After centrifugation or filtration, the solid phase is a highly recoverable active material powder, while the liquid phase, after simple treatment, can be partially reused in the swelling tank or main stripping tank, achieving resource recycling.

[0043] In one specific implementation, in step S3, the power density of the ultrasonic action is controlled at 0.5-1.5 W / cm², and the sweep bandwidth is ±2 kHz; in step S2, the average particle size of the injected microbubbles is 20 ± 10 μm.

[0044] In specific applications of this invention, after the swollen electrode enters the main stripping reaction tank, the system first activates the microbubble injection unit to inject a large number of microbubbles with an average particle size of 20±10μm into the liquid medium. Bubbles with too small a particle size (e.g., <5μm) are difficult to resonate effectively in the acoustic field, and the cavitation threshold actually increases; while bubbles with too large a particle size (e.g., >60μm) are prone to rapid floating and bursting under buoyancy, generating violent but non-directional impacts, which can easily lead to local dents in the foil or coating splashing. In the ultrasonic frequency range of 20-80kHz, its resonant frequency is highly matched with the sound wave period, and it can be fully stretched in the negative phase of sound pressure and rapidly implode in the positive phase, generating highly directional microjets. At the same time, the tolerance range of ±10μm ensures that a stable cavitation nucleus density can still be maintained under actual working conditions (e.g., temperature fluctuations, slight changes in liquid composition), avoiding uneven spatiotemporal distribution of cavitation events due to excessively wide bubble size distribution.

[0045] Based on this, below 0.5 W / cm², even with microbubble assistance, the cavitation intensity is insufficient to overcome the residual interfacial bonding force after swelling, resulting in incomplete peeling. Above 1.5 W / cm², the cavitation bubble collapse energy is too high, not only breaking through the softened adhesive layer and causing the active particles to break, but also inducing microcracks, pitting, or even perforation on the aluminum foil surface. Within the range of 0.5-1.5 W / cm², combined with the synergistic effect of 20±10 μm microbubbles, the system can trigger high-density, highly controllable cavitation events with lower energy input. Simultaneously, the ultrasonic signal sweeps between two frequency bands, 20-30 kHz and 40-80 kHz, with a period of 50-100 Hz, and the sweep bandwidth at each frequency point is controlled within ±2 kHz. In the low-frequency band (e.g., 25 kHz ± 2 kHz), the longer wavelength and stronger penetration are suitable for exciting large-scale cavitation bubbles to shear deep layers of the interface; in the high-frequency band (e.g., 60 kHz ± 2 kHz), the shorter wavelength and significant near-field effect allow for precise processing of microstructure regions.

[0046] Throughout the process, microbubbles of 20±10μm continuously rise from the bottom of the tank, passing through a multi-frequency acoustic field driven by 0.5-1.5W / cm² power. Their implosion positions are concentrated near the lower surface of the electrode. The microjet impacts the swollen adhesive layer vertically at a speed of hundreds of meters per second, while the ultrasonic shear force acts on the interface in the horizontal direction. The multi-directional stress coupling causes the adhesive layer to fracture brittlely within milliseconds. The active material detaches as intact primary particles, and the microbubbles buffer part of the impact energy. The aluminum foil surface only undergoes elastic deformation without plastic damage.

[0047] In one specific embodiment, the organic solvent is N-methylpyrrolidone or dimethyl sulfoxide, and the liquid medium also contains a nonionic surfactant with a volume fraction of less than 1%. The method is applicable to waste lithium battery electrodes of lithium iron phosphate or ternary material systems, and the coating peeling rate is not less than 99.5% after passing through the main peeling reaction tank once.

[0048] In specific applications, this invention addresses the polyvinylidene fluoride (PVDF) binder system commonly used in LFP or ternary material electrodes. The system selects N-methylpyrrolidone (NMP) or dimethyl sulfoxide (DMSO) as the organic component in the swelling medium. Both solvents are strongly polar aprotic solvents, containing carbonyl or sulfoxide groups with high electron density in their molecular structure. These groups can form dipoles and dipole interactions with fluorine atoms in the PVDF molecular chain, effectively weakening the van der Waals forces between PVDF molecules and promoting partial untangling of the crystalline region and full swelling of the amorphous region. However, unlike traditional recycling processes that use high concentrations (>20%) or even pure NMP for complete dissolution, this method controls the volume fraction of organic solvent to below 5%, and further adds nonionic surfactants (such as Tween-80 or Triton X-100) with a volume fraction of less than 1%. The low concentration of organic solvent only induces limited swelling of PVDF, increasing the molecular chain spacing by about 15%-30% and reducing the interfacial bonding strength by more than 60%, but the overall membrane structure remains continuous, preventing the coating from falling off or curling due to excessive softening before entering the main stripping tank. On the other hand, the trace amount of nonionic surfactant reduces the surface tension of the liquid medium (down to 35-40 mN / m), enhancing its wetting and penetration ability to the microporous structure of the electrode, so that the swelling effect can penetrate evenly into the micro-interface between the active material particles and the binder, rather than just acting on the surface.

[0049] When these pretreated electrodes enter the main peeling reaction tank, they face a peeling field constructed by multi-frequency ultrasonic cavitation and microbubbles. Due to the differences in the coating structures of LFP and ternary materials—LFP particles are typically large (~1μm) and loosely packed, while ternary material particles are finer (~0.2-0.5μm) and have higher compaction density—the system achieves universal and efficient peeling through a unified process window. The PVDF bonding networks exhibit similar mechanical weakening characteristics after swelling, significantly reducing the critical peeling stress required for ultrasonic cavitation. Based on this, the cavitation field, alternately excited by dual-band frequencies of 20-30kHz and 40-80kHz, combined with the directional microjets generated by 20±10μm microbubbles, can penetrate the coating pores from bottom to top, releasing energy at the binder-aluminum foil interface. For the LFP system, the strong cavitation at lower frequencies is sufficient to overcome its weak interparticle bonding; for the dense ternary material coating, the synergistic effect of high-frequency dense cavitation events and microbubble penetration gradually "pry open" the bonding bridges between particle clusters.

[0050] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0051] The present invention and its embodiments have been described above. This description is not restrictive, and the accompanying drawings are only one embodiment of the present invention; the actual structure is not limited thereto. In conclusion, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the invention, such designs should fall within the protection scope of the present invention.

Claims

1. A non-destructive lithium battery recycling system based on multi-frequency ultrasonic cavitation, characterized in that, include: The multi-stage processing tank consists of a swelling tank, a main stripping reaction tank, and a rinsing tank arranged sequentially along the electrode conveying direction. The main stripping reaction tank is equipped with a variable frequency pulse ultrasonic transducer array. The transducer array is arranged at the bottom and side wall of the main stripping reaction tank and connected to a multi-frequency signal generator. It is configured to perform frequency sweep or dual-frequency alternating transmission between two frequency ranges of 20-30kHz and 40-80kHz. The microbubble injection unit, located at the bottom of the main stripping reaction tank, includes a microporous aeration device or dissolved gas release nozzle, used to inject microbubbles with an average particle size of 10μm-50μm into the liquid medium in the main stripping reaction tank. An electrode transport mechanism runs through the multi-stage processing tank and is used to transport waste lithium battery electrodes in a tensioned or suspended state through the swelling tank, the main stripping reaction tank, and the rinsing tank in sequence.

2. The lithium battery non-destructive recycling system based on multi-frequency ultrasonic cavitation according to claim 1, characterized in that, The multiple transducers in the frequency-converted pulse ultrasonic transducer array are arranged in a staggered and cross manner, that is, the adjacent rows of transducers are staggered by half a transducer spacing in the horizontal direction to avoid forming a standing wave blind zone in the sound field.

3. The lithium battery non-destructive recycling system based on multi-frequency ultrasonic cavitation according to claim 1, characterized in that, The microporous aeration device or dissolved gas release nozzle of the microbubble injection unit is located at the bottom of the main stripping reaction tank and below the ultrasonic transducer array, so that the generated microbubbles pass through the sound field region excited by the ultrasonic transducer from bottom to top.

4. The lithium battery non-destructive recycling system based on multi-frequency ultrasonic cavitation according to claim 1, characterized in that, The bottom of the main stripping reaction tank is provided with a slurry outlet, which is connected to a solid-liquid separation device through a pipe to export the stripped active material slurry and perform solid-liquid separation.

5. The lithium battery non-destructive recycling system based on multi-frequency ultrasonic cavitation according to claim 1, characterized in that, The multi-stage processing tank is equipped with a temperature control system to maintain the temperature of the liquid medium in the main stripping reaction tank within the range of 40℃-60℃.

6. A method for a lithium battery non-destructive recycling system based on multi-frequency ultrasonic cavitation according to any one of claims 1 to 5, characterized in that, Includes the following steps: S1: Send the waste lithium battery electrode sheets into the swelling tank and soak them in an aqueous solution containing less than 5% organic solvent by volume for 1-3 minutes to cause the adhesive layer to swell. S2: The electrode sheet treated by S1 is sent into the main stripping reaction tank, and the microbubble injection unit is started to make the concentration of microbubbles in the liquid medium reach a gas-liquid mixing ratio of 3%-8%; S3: Synchronously start the variable frequency pulse ultrasonic transducer array, so that it sweeps and oscillates in two frequency ranges of 20-30kHz and 40-80kHz with a period of 50-100Hz, continuously acting on the electrode surface. S4: The stripped aluminum foil is sent to the rinsing tank for cleaning, and the slurry formed in the main stripping reaction tank is discharged to the solid-liquid separation device to recover the aluminum foil and active material powder respectively.

7. The method for a non-destructive lithium battery recycling system based on multi-frequency ultrasonic cavitation according to claim 6, characterized in that, In step S3, the power density of the ultrasound is controlled at 0.5-1.5 W / cm², and the sweep bandwidth is ±2 kHz.

8. The method for the non-destructive recycling system of lithium batteries based on multi-frequency ultrasonic cavitation according to claim 6, characterized in that, The organic solvent is N-methylpyrrolidone or dimethyl sulfoxide, and the liquid medium also contains a nonionic surfactant with a volume fraction of less than 1%.

9. The method for a non-destructive lithium battery recycling system based on multi-frequency ultrasonic cavitation according to claim 6, characterized in that, In step S2, the average particle size of the injected microbubbles is 20 ± 10 μm.

10. The method for a non-destructive lithium battery recycling system based on multi-frequency ultrasonic cavitation according to claim 6, characterized in that, The method is applicable to waste lithium battery electrodes of lithium iron phosphate or ternary material systems, and the coating peeling rate is not less than 99.5% after a single pass through the main stripping reaction tank.

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