Separation method and separation apparatus

Abstract

To separate a current collector and an electrode mixture from each other efficiently and stably with high accuracy.SOLUTION: A separation method includes a separation step of immersing an electrode to be treated that comprises a current collector and an electrode mixture formed on the current collector in treated water that is an acid solution, and then, performing ultrasonic treatment while sweeping the frequency of an ultrasonic wave to separate the current collector and the electrode mixture from each other.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] This disclosure relates to a separation method and a separation apparatus. [Background technology]

[0002] Conventionally, a recycling method for lithium-ion batteries has been proposed in which, for example, the lithium-ion battery is crushed, the resulting crushed material is sieved, and the metal powder remaining on the sieve is separated using a liquid to obtain the metal powder and the separated liquid (see, for example, Patent Document 1). This processing method is said to enable more effective utilization of resources. Another recycling method has been proposed that includes an extraction step in which at least a portion of the first resin current collector is removed from the lithium-ion battery, which is the first resin current collector, and the first electrode active material is extracted (see, for example, Patent Document 2). This processing method is said to be able to obtain electrode active material from lithium-ion batteries in a simple process without requiring high-temperature heating. Another proposed recycling method involves immersing the positive electrode in an alkaline aqueous solution to peel off the positive electrode active material layer from the positive electrode current collector, adding an organic solvent to the peeled material to extract the binder, and separating the supernatant portion containing the conductive material from the precipitate portion containing the positive electrode active material (see, for example, Patent Document 3). This processing method allows for the recovery and reuse of positive electrode active material from lithium batteries. Yet another proposed recycling method involves discharging a lithium-ion battery, shredding it into small pieces to obtain a mixture of current collectors coated with a cathode layer and current collectors coated with an anode layer, immersing these pieces in a polar solvent to form a mixture of different components, stirring this mixture with a mixer to dissolve the binder material, sieving the processed mixture of different components to separate the current collector from the cathode and anode materials, adding a polar solvent to form a suspension of electrode materials, and then isolating the electrode materials in the suspension from the polar solvent (see, for example, Patent Document 4). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Unexamined Patent Publication No. 2018-170223 [Patent Document 2] Japanese Unexamined Patent Publication No. 2021-44180 [Patent Document 3] Japanese Unexamined Patent Publication No. 2010-62105 [Patent Document 4] Japanese Unexamined Patent Publication No. 2021-73375 [Summary of the Invention] [Problem to be Solved by the Invention]

[0004] However, in the above-mentioned recycling method, even if the electrode mixture can be separated from the current collector, the current collector may be damaged; or even if damage to the current collector is suppressed, the electrode mixture may remain on the current collector. Additionally, in the above-mentioned recycling method, treatment efficiency may be low, such as requiring long-time treatment or requiring pretreatment such as crushing.

[0005] The present disclosure has been made to solve such problems, and a main object thereof is to provide a separation method and a separation apparatus that can efficiently, stably and highly accurately separate a current collector and an electrode mixture. [Means for Solving the Problem]

[0006] In order to achieve the above-mentioned object, the present inventors have found that when an electrode is subjected to ultrasonic treatment in an acid aqueous solution while sweeping the frequency of ultrasonic waves, the current collector and the electrode mixture can be separated efficiently, stably and with high accuracy, and have completed the present disclosure.

[0007] That is, the separation method of the present disclosure is comprises a separation step of: immersing a treatment target electrode including a current collector and an electrode mixture formed on the current collector in treatment water that is an acid solution, performing ultrasonic treatment while sweeping the frequency of ultrasonic waves, and separating the current collector and the electrode mixture.

[0008] Furthermore, the separation apparatus of this disclosure is A separation unit separates the current collector and the electrode mixture by immersing the electrode to be treated, which comprises a current collector and an electrode mixture formed on the current collector, in a treatment water which is an acidic solution and performing ultrasonic treatment, A control unit controls the separation unit to perform ultrasonic processing while sweeping the ultrasonic frequency, It is something that is provided. [Effects of the Invention]

[0009] The separation method and apparatus of this disclosure can efficiently, stably, and accurately separate the current collector and the electrode mixture. The reasons for achieving such effects are presumed to be as follows: This separation method and apparatus utilize a physical action using the cavitation effect of ultrasound, rather than the chemical action of organic solvents or aqueous solutions, so that the current collector and the electrode mixture can be separated using water without using organic solvents. Furthermore, water has a high surface tension and generates a cavitation effect more easily than organic solvents, so the current collector and the electrode mixture can be separated efficiently. In addition, since the ultrasonic treatment is performed in water while sweeping the ultrasonic frequency, the energy distribution becomes favorable, damage to the current collector and residual electrode mixture are suppressed, and the current collector and the electrode mixture can be separated with high precision. Furthermore, while immersing electrodes in treated water can cause ions to leach from the electrodes, potentially leading to an excessive increase in the pH of the treated water or alteration of the electrode components, the use of an acidic solution maintains the pH of the treated water within a suitable range. This allows for separation even with longer waiting times, for example, when the electrodes remain immersed in the treated water. Therefore, even in large separation facilities where there is a predetermined waiting time between electrode immersion and the start of ultrasonic treatment, the current collector and electrode composite can be separated stably and with high precision. [Brief explanation of the drawing]

[0010] [Figure 1] Diagram illustrating sweep and sweep cycle. [Figure 2] Diagram illustrating the sweep width. [Figure 3]An explanatory diagram showing the schematic configuration of the separation device 10 before ultrasonic treatment. [Figure 4] An explanatory diagram showing the general configuration of the separation device 10 after ultrasonic treatment. [Figure 5] External view of the electrode (current collector foil) after ultrasonic treatment. [Figure 6] External view of the electrode (current collector foil) after ultrasonic treatment. [Figure 7] A flowchart illustrating an example of a separation method. [Figure 8] A graph showing the relationship between immersion waiting time and asphalt removal rate for reference examples 20-28. [Figure 9] External view photographs of the electrodes (current collector foils) after ultrasonic treatment in Experimental Examples 1-9. [Figure 10] A graph showing the relationship between acid concentration and pH after sonication. [Figure 11] A graph showing the relationship between acid concentration and the removal rate of asphalt mixture. [Figure 12] A graph showing the relationship between acid concentration and the amount of Al dissolved per unit mass of current collector. [Figure 13] A graph showing the relationship between acid concentration and the amount of Al in the asphalt mixture powder. [Modes for carrying out the invention]

[0011] [Separation method] The separation method of this disclosure includes a separation step of immersing the electrode to be treated in treated water, which is an acidic solution, and performing ultrasonic treatment to separate the current collector and the electrode composite material.

[0012] (Electrode to be processed) The electrode to be processed comprises a current collector and an electrode mixture formed on the current collector. The electrode to be processed is an electrode of an ion secondary battery such as a lithium ion secondary battery, or an electricity storage device such as an electric double layer capacitor, a hybrid capacitor, or a pseudo electric double layer capacitor, and may be taken out from a used electricity storage device or a deteriorated electricity storage device. The electrode to be processed may be a positive electrode, may be a negative electrode, or may be a bipolar electrode in which a positive electrode mixture is formed on one surface and a negative electrode mixture is formed on the other surface. Among these, from the viewpoint of elution of carrier ions, the electrode to be processed is preferably a positive electrode. The electrode to be processed may remain unshredded as taken out from the electricity storage device, for example, having an area of 10 cm 2 or more, or may be 30 cm 2 or more.

[0013] Examples of the material of the current collector include aluminum, copper, titanium, stainless steel, nickel, iron, calcined carbon, conductive polymers, and conductive glass. Among these, when the electrode to be processed is a positive electrode, the current collector preferably contains aluminum. Examples of the shape of the current collector include foil, film, sheet, net, punched or expanded shapes, lath bodies, porous bodies, foamed bodies, and formed bodies of fiber groups. The thickness of the current collector is, for example, 1 to 500 μm.

[0014] The electrode mixture may contain an electrode active material, a binder, and optionally a conductive material and the like. For example, the electrode mixture may be formed by mixing an electrode active material, a conductive material and a binder, adding an appropriate solvent to obtain a paste, applying the paste onto the surface of the current collector, drying the paste, and compressing the paste to increase the electrode density as needed. The electrode mixture may be formed on one side or both sides of the current collector.

[0015] Examples of the electrode active material contained in the electrode mixture include transition metal sulfides such as TiS2, TiS3, MoS3, and FeS2, and those having a basic composition formula of Li (1-x) MnO2 (where 0<x<1, the same applies hereinafter) and Li (1-x)Lithium manganese composite oxide such as Mn₂O₄, whose basic composition formula is Li (1-x) Lithium cobalt composite oxide such as CoO₂, whose basic composition formula is Li (1-x) Lithium nickel composite oxide such as NiO₂, whose basic composition formula is Li (1-x) Ni a Co b Mn c O₂ (a+b+c=1) lithium nickel cobalt manganese composite oxide, lithium vanadium composite oxide such as LiV₂O₅ whose basic composition formula is, transition metal oxide such as V₂O₅ whose basic composition formula is, lithium iron phosphate, and other active materials used for positive electrodes of lithium ion secondary batteries can be mentioned. The term "basic composition formula" means that the material may contain other elements such as Al and Mg. Examples of electrode active materials also include active materials used for positive electrodes and / or negative electrodes of capacitors and lithium ion capacitors, such as activated carbons, cokes, glassy carbons, graphites, non-graphitizable carbons, pyrolytic carbons, carbon fibers, carbon nanotubes, and polyacenes. Further, examples of electrode active materials also include active materials used for negative electrodes of lithium ion secondary batteries, such as inorganic compounds including lithium alloys and tin compounds, carbonaceous materials capable of occluding and releasing lithium ions, composite oxides containing a plurality of elements, and conductive polymers. Examples of the carbonaceous material include cokes, glassy carbons, graphites, non-graphitizable carbons, pyrolytic carbons, and carbon fibers. Examples of the composite oxide include lithium titanium composite oxides and lithium vanadium composite oxides. Examples of the conductive material contained in the electrode mixture include graphites such as natural graphite (flaky graphite, scaly graphite) and artificial graphite, acetylene black, carbon black, Ketjen black, carbon whiskers, needle coke, carbon fibers, and metals (copper, nickel, aluminum, silver, gold, etc.).

[0016] The binder contained in the electrode mixture plays the role of binding the active material particles and conductive material particles together. It may be an organic binder dissolved in an organic solvent, an aqueous binder dissolved in an aqueous solvent, or a mixture thereof. Examples of organic binders include fluororesins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and fluororubber, or thermoplastic resins such as polypropylene and polyethylene, ethylene propylene diene monomer (EPDM) rubber, sulfonated EPDM rubber, and natural butyl rubber (NBR). Examples of aqueous binders include polyvinyl alcohol (PVA), styrene-butadiene copolymer (SBR), and polyethylene oxide (PEO), and may also contain carboxymethylcellulose (CMC). Examples of organic solvents include N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethylenetriamine, N,N-dimethylaminopropylamine, ethylene oxide, and tetrahydrofuran. Examples of aqueous solvents include water and various aqueous solutions. The conductive material included in the electrode mixture can be, for example, a mixture of one or more of the following: graphite such as natural graphite (scaly graphite, flake graphite) or artificial graphite, acetylene black, carbon black, Ketjenblack, carbon whiskers, needle coke, carbon fiber, or metals (copper, nickel, aluminum, silver, gold, etc.). Among these, carbon black and acetylene black are preferred as conductive materials from the viewpoint of electronic conductivity and coating properties.

[0017] (separation process) In the separation process, the electrode to be treated is immersed in a treatment water solution (an acidic solution), and ultrasonic treatment is performed while sweeping the ultrasonic frequency to separate the current collector and the electrode composite material. Sweeping the frequency means periodically changing the frequency, for example, as shown in Figures 1 and 2.

[0018] In the separation process, the ultrasonic frequency may be periodically changed so as to oscillate between the maximum frequency Fmax and the minimum frequency Fmin, centered around the fundamental frequency F0 (see Figures 1 and 2). The fundamental frequency F0 is preferably 40 kHz or more and 240 kHz or less, and more preferably 80 kHz or more and 200 kHz or less. In ultrasonic processing, when the range of frequency fluctuation centered on the fundamental frequency F0 is defined as the sweep width (see Figure 2), the sweep width may be within ±5 kHz. That is, Fmax - F0 ≤ +5 kHz and Fmin - F0 ≥ -5 kHz. The sweep width may be within ±3 kHz or within ±1 kHz. In ultrasonic processing, when one sweep cycle is defined as the period from the rising edge of the wave at the minimum frequency Fmin to the falling edge of the wave at the maximum frequency Fmax (see Figure 1), and the number of sweep cycles per second is defined as the sweep rate, the sweep rate may be 500 sweep cycles / second or more. The sweep rate may be 700 sweep cycles / second or more, or 1000 sweep cycles / second or more. Alternatively, the sweep rate may be 2000 sweep cycles / second or less. One sweep cycle may be defined as half the time from the rising edge of the wave with the minimum frequency Fmin to the rising edge of the next wave with the minimum frequency Fmin.

[0019] In the separation step, ultrasonic treatment is preferably performed for a period of 30 minutes or less, more preferably for a period of 10 minutes or less, even more preferably for a period of 300 seconds or less, and even more preferably for a period of 180 seconds or less. In the separation step, ultrasonic treatment may be performed for 1 second or more, 5 seconds or more, or 15 seconds or more.

[0020] In the separation process, the contact area between the current collector and the electrode composite material is A [cm²]. 2 When the ultrasonic output (oscillator output) is B[W], the power density (power density) expressed as B / A is 30 W / cm². 2 It is preferable to perform ultrasonic treatment as follows: The output density B / A is 10 W / cm². 2 The following is preferable: 5 W / cm 2The following is also acceptable: Power density B / A is 0.1 W / cm². 2 The above is also acceptable, 0.5 W / cm 2 You may leave it at that.

[0021] In the separation process, ultrasonic treatment is preferably performed in a non-heating environment. In the separation process, ultrasonic treatment may be performed in a temperature range of 0°C to 30°C, or in a temperature range of 15°C to 25°C.

[0022] In this separation process, an acidic solution is used as the treatment water in which the electrode to be treated is immersed. The acidic solution is acidic. Using an acidic solution helps to suppress excessive pH increases due to components leached from the electrode and maintain the pH within a suitable range, thereby ensuring the separation of the current collector and the electrode composite layer. Furthermore, separation can be achieved even if the waiting time from immersion of the electrode to be treated to the start of ultrasonic treatment is longer. The waiting time is not required, but it may be, for example, 5 minutes or more, 10 minutes or more, or 30 minutes or more. Also, from the viewpoint of ensuring more reliable separation of the current collector and the electrode composite layer, a shorter waiting time is preferable, for example, 60 minutes or less, 30 minutes or less, or 10 minutes or less.

[0023] In the separation process, it is preferable to use treated water that is an acidic solution with a pH of 3 or higher. Using an acidic solution with a pH of 3 or higher allows the pH to be maintained within a relatively suitable range (for example, pH 3 to pH 8) even after sonication, thereby further suppressing the elution of current collector components. The treated water is preferably pH 5 or lower, preferably pH 4.4 or lower, and more preferably pH 4.2 or lower. The treated water may also have a pH of 2.5 or higher or pH 2.8 or higher. In this specification, unless otherwise specified, the pH of the treated water refers to the pH of the treated water before electrode immersion.

[0024] In the separation process, the acid dissociation constant pK a It is preferable to use treated water that is an acid solution containing an acid of 4 or higher. Acid dissociation constant pK aIn acid solutions containing an acid of 4 or higher, a pH of 3 or higher can be achieved even at relatively high acid concentrations, such as an acid concentration of 0.005 mol / L or higher. a Examples of acids with a pK of 4 or higher include carbonic acid (pK a 6.35), propionic acid (pK a 4.88), acetic acid (pK a 4.76), benzoic acid (pK a Examples include 4.00). The acid concentrations at which a pH of 3 or higher can be achieved with these acids are 2.2 mol / L or less for carbonic acid, 0.07 mol / L or less for propionic acid, 0.05 mol / L or less for acetic acid, and 0.01 mol / L or less for benzoic acid. Acid dissociation constant pK a The acid dissociation constant pK is preferably 8 or less, and may be 7 or less. a If the solution contains an acid (such as carbonic acid) with a pH of 5.5 or higher, the treated water may have a pH of 3.5 to 5, a pH of 3.8 to 4.3, or a pH of 3.9 to 4.2. Also, the acid dissociation constant pK... a If the treated water contains an acid with a pH of less than 5.5 (such as acetic acid, propionic acid, or benzoic acid), the treated water may have a pH of 3 to 4, a pH of 3 to 3.5, or a pH of 3 to 3.2.

[0025] In the separation process, treated water containing an inorganic acid or treated water containing an organic acid may be used. Suitable inorganic acids include, for example, oxoacids such as carbonic acid. Suitable organic acids include, for example, carboxylic acids such as acetic acid, propionic acid, and benzoic acid. The treated water may be an acid solution containing one or more acids selected from the group consisting of carbonic acid, acetic acid, propionic acid, and benzoic acid. It is more preferable that the treated water be carbonated water. Using treated water in which a gaseous acid is dissolved in water, such as carbonated water, is preferable because the acid can be removed from the treated water relatively easily by gas bubbling or other methods. It is preferable that the acid contained in the treated water is not a halogenated acid such as hydrochloric acid.

[0026] In the separation step, treated water with an acid concentration of 0.0001 mol / L or higher may be used. This acid concentration is preferably 0.005 mol / L or higher, more preferably 0.008 mol / L or higher, and even more preferably 0.01 mol / L or higher. The higher the acid concentration, the more reliable the separation of the current collector and the electrode composite layer tends to be, for example, by keeping the pH of the treated solution after sonication relatively low (e.g., pH 8 or lower). The acid concentration may be, for example, 2 mol / L or lower, 1 mol / L or lower, or 0.5 mol / L or lower.

[0027] In the separation process, it is preferable to use treated water with a low alkali metal ion concentration from the viewpoint of suppressing the inclusion of impurities. The alkali metal ion concentration of the treated water may be, for example, 0.01 mol / L or less, or 0.001 mol / L or less. Furthermore, in the separation process, it is preferable to use treated water with a low halogen ion concentration from the viewpoint of suppressing pitting corrosion of the aluminum current collector by halogen ions. The halogen ion concentration of the treated water may be, for example, 0.01 mol / L or less, or 0.001 mol / L or less.

[0028] In the separation process, the amount per gram of active material contained in the electrode to be processed, or per 100 cm of current collector foil, is calculated. 2 The amount of treated water used may be in the range of 5g to 200g, or in the range of 50g to 150g. In addition, in the separation process, the surface area of ​​the current collector is 100cm². 2 The amount of treated water used may be between 2.5g and 100g, or between 25g and 75g. If the current collector is a current collector foil, the surface area of ​​the foil can be calculated using the formula: area of ​​the foil × 2 (the same applies hereafter).

[0029] In the separation process, the amount per gram of active material contained in the electrode to be processed, or per 100 cm of current collector foil, is calculated. 2The amount of acid contained in the treated water may be set to 0.00001 mol or more, 0.0005 mol or more, or even more than 0.001 mol. Per 1 g of active material contained in the electrode to be treated, or per 100 cm of current collector foil. 2 The amount of acid contained in the treated water may be 0.1 mol or less, or 0.01 mol or less. Also, in the separation process, the surface area of ​​the current collector is 100 cm². 2 The amount of acid contained in the treated water may be set to 0.00001 mol or more, or to 0.0001 mol or more, or to exceed 0.0005 mol. Surface area of ​​the current collector: 100 cm² 2 The amount of acid contained in the treated water may be 0.1 mol or less, or 0.01 mol or less.

[0030] The separation process may be carried out under conditions where the treated water after ultrasonic treatment has a pH of 3 or higher and a pH of 10.5 or lower. Maintaining the treated water at a pH of 3 or higher and a pH of 10.5 or lower after ultrasonic treatment further suppresses the elution of current collector components. The conditions can be determined empirically; for example, the pH of the treated water after ultrasonic treatment can be adjusted by adjusting the composition of the treated water, the immersion waiting time, and the ultrasonic treatment conditions. The treated water after ultrasonic treatment may have a pH of 3.5 or higher, or a pH of 4 or higher. Preferably, the treated water after ultrasonic treatment has a pH of 10 or lower, more preferably 8 or lower, and even more preferably 7 or lower. Note that the acid dissociation constant pK a If the acid contains a pH of 5.5 or higher, the treated water after ultrasonic treatment may have a pH of 5 to 10.5, a pH of 5.5 to 9, or a pH of 6 to 6.5. Also, the acid dissociation constant pK a If the acid has a pH of less than 5.5, the treated water after ultrasonic treatment may have a pH of 3 to 6, a pH of 3.5 to 5.5, or a pH of 4 to 4.5.

[0031] After performing the separation process described above, the electrode mixture is removed from the current collector, and the removed electrode mixture dissolves and / or disperses in water or precipitates. Thus, after ultrasonic treatment, the current collector and the electrode mixture are separated, and the current collector and the mixture-containing water are obtained. Furthermore, because an acid solution is used, to ensure electrode separation, the waiting time during which the electrode to be treated is immersed in the treated water can be extended to ensure separation.

[0032] The proportion of current collector components (current collector components) in the electrode mixture separated in the separation step is preferably less than 0.18%, preferably less than 0.15%, and more preferably less than 0.1%. Furthermore, the proportion of electrode mixture components (electrode mixture components) in the current collector separated in the separation step is preferably less than 0.36%, preferably less than 0.3%, and more preferably less than 0.2%. The "proportion of current collector components in the electrode mixture" may be a value obtained, for example, as follows: First, water is removed from the mixture-containing water obtained in the separation step to obtain the electrode mixture. The mass of the current collector components in the obtained electrode mixture is analyzed by inductively coupled plasma atomic emission spectroscopy (ICP-OES). Then, the mass ratio of the current collector components to the mass of the electrode mixture analyzed is determined, and this mass ratio is taken as the proportion of current collector components in the electrode mixture. The "proportion of electrode mixture components in the current collector" may be a value obtained, for example, as follows: First, the electrode (current collector) after ultrasonic treatment is removed and rinsed and dried. For electrodes that have been rinsed and dried, the mass of the electrode composite components is analyzed by ICP-OES, and the mass ratio of the electrode composite components to the mass of the electrode being analyzed is determined. This mass ratio is then defined as the proportion of the electrode composite components contained in the current collector. Alternatively, for electrodes that have been rinsed and dried, the mass ratio of the electrode composite components is determined by the fundamental parameter method (FP method) of X-ray fluorescence analysis (XRF), and this mass ratio is then defined as the proportion of the electrode composite components contained in the current collector. The proportion of the electrode composite components contained in the current collector may be the proportion of the active material components contained in the current collector, or, if the active material contains transition metals, the proportion of the transition metals contained in the current collector (however, the transition metals contained in the active material) may be used. Since transition metals may alloy with current collector components when the current collector (such as Al) is remelted, it is desirable that the amount of transition metal remaining in the current collector be small.

[0033] Before the separation process, an extraction process may be performed to remove electrodes from the energy storage device. The electrodes removed in the extraction process can be used as is, without being shredded, or in a 10cm² area. 2 The above, or an area of ​​30cm² 2 The material may be cut into pieces as described above and used as the electrode to be processed.

[0034] After the separation step, a current collector processing step may be performed to wash and dry the current collectors separated in the separation step. The current collectors may be washed while running a washing solution over them, or by immersion in the washing solution. Water is preferred as the washing solution. The current collectors may be dried by forced air drying, heat drying, vacuum drying, barrel drying, spin drying, suction drying, infrared drying, or a combination thereof. After the separation step, an asphalt mixture processing step may be performed to filter and dry the electrode mixture from the asphalt mixture-containing water obtained in the separation step. In the asphalt mixture processing step, the electrode mixture may be washed during or after filtering. Water is preferred as the washing solution. The electrode mixture may be dried by forced air drying, heat drying, vacuum drying, barrel drying, spin drying, suction drying, infrared drying, or a combination thereof. In addition, in the asphalt mixture processing step, instead of filtering the electrode mixture, the electrode mixture may be separated from the asphalt mixture-containing water by solid-liquid separation methods such as centrifugal separation or evaporation to dryness.

[0035] The separation process, current collector processing process, and electrode mixture processing process may be carried out in batches or continuously. When the separation process and current collector processing process are carried out continuously, a roll-to-roll method may be used. When the separation process is carried out using a roll-to-roll method, the electrodes removed in the extraction process may be sequentially wound into rolls and used as the electrodes to be processed. Since current collectors and electrode mixtures are obtained by this separation method, this separation method is both a method for manufacturing current collectors and a method for manufacturing electrode mixtures.

[0036] [Separation device] The separation apparatus of this disclosure comprises a separation unit that separates the current collector and the electrode mixture by immersing the electrode to be processed in treated water, which is an acidic solution, and performing ultrasonic treatment, and a control unit that controls the separation unit. This separation apparatus may perform the separation method described above, or it may apply the configuration and conditions described in the separation method described above.

[0037] The following describes a separation device 10 as an example. Figures 3 and 4 show schematic diagrams illustrating the configuration of the separation device 10. Figure 3 is a schematic diagram illustrating the configuration of the separation device 10 before ultrasonic treatment. Figure 4 is a schematic diagram illustrating the configuration of the separation device 10 after ultrasonic treatment. The separation device 10 comprises a separation unit 20 and a control unit 15. In this separation device 10, ultrasonic treatment is performed on a treatment target electrode 50, which is equipped with a current collector 52 and an electrode mixture 54, to separate the current collector 52 and the electrode mixture 54. The treatment target electrode 50, the current collector 52, and the electrode mixture 54 may be the same as the treatment target electrode, current collector, and electrode mixture described in the separation method.

[0038] The separation unit 20 performs ultrasonic treatment on the electrode 50 to be treated in treated water 32, which is an acidic solution. The separation unit 20 comprises a treatment container 22, a transducer 28, an oscillator 30, and a pH detection unit 29. The treatment container 22 contains the electrode 50 to be treated and the treated water 32. The treatment container 22 comprises an inner tank 24 in which the electrode 50 to be treated is housed, a mounting base 25 on which the inner tank 24 is placed, and an outer tank 26 in which the inner tank 24 and the mounting base 25 are housed. The inner tank 24 contains the treated water 32, and the outer tank 26 contains the ultrasonic propagation medium 36. An acidic solution is used as the treated water 32. The treated water 32 may include tap water, distilled water, or ion-exchanged water. The ultrasonic propagation medium 36 is, for example, water, and plays a role in propagating ultrasound together with the treated water 32. The treatment container 22 is equipped with piping and valves (not shown), which allow for adjustment of whether or not treated water 32 is supplied to the treatment container 22 and the amount supplied.

[0039] The transducer 28 is positioned to be in contact with the processing container 22. The oscillator 30 supplies power to the transducer 28, causing it to oscillate. The oscillator 30 has a sweep function. The sweep function is a function that periodically changes the frequency, for example, as shown in Figures 1 and 2. The separation unit 20 is configured to sweep (periodically change) the frequency of the ultrasonic waves generated from the transducer 28 by using the sweep function of the oscillator 30. The pH detection unit 29 is a pH meter that measures the pH of the treated water 32. The pH detection unit 29 outputs the measured pH of the treated water 32 to the control unit 15.

[0040] The control unit 15 is configured as a microprocessor centered on a CPU, and in addition to the CPU, it includes a memory device and input / output ports (not shown). The control unit 15 is electrically connected to the oscillator 30 and the pH detection unit 29, and outputs a signal to one of them and receives a signal from one of them. The control unit 15 is configured to control the oscillator 30 to perform ultrasonic processing while sweeping the ultrasonic frequency. The conditions for ultrasonic processing may be the same as those for the separation method described above.

[0041] An example of the operation of the separation device 10 will be described. First, the treatment container 22 is filled with treatment water 32, which is an acid solution, and the electrode to be treated 50 is immersed in the treatment water 32. The acid solution can be any of those described in the separation method above. After the electrode to be treated 50 is immersed in the treatment water 32, the control unit 15 controls the oscillator 30 to supply power to the transducer 28 and cause the transducer 28 to oscillate before a predetermined waiting time has elapsed. As a result, ultrasonic treatment is performed on the electrode to be treated 50 in the treatment water 32. For ultrasonic treatment, the control unit 15 uses the sweep function of the oscillator 30 and controls the oscillator 30 to sweep the frequency under conditions such as a fundamental frequency F0 of 40 kHz or more and 240 kHz or less, a sweep width of ±5 kHz or less, and a sweep rate of 500 sweep cycles / second or more. The control unit 15 also controls the output density B / A to 30 W / cm², for example. 2The oscillator 30 is controlled to output the following power. The control unit 15 also controls the oscillator 30 to perform ultrasonic processing for a predetermined time, for example, between 1 second and 30 minutes. Through this ultrasonic processing, the current collector 52 and the electrode mixture 54 of the electrode 50 to be processed are separated, and processed water 33 containing the mixture, which includes the current collector 52 and the electrode mixture 54, is obtained.

[0042] The separation method and apparatus described above can efficiently, stably, and accurately separate the current collector and the electrode mixture. The reasons for achieving these effects can be inferred, for example, as follows: The separation method and apparatus described above utilize the physical action of ultrasonic cavitation to separate the current collector and the electrode mixture, thus enabling separation of the current collector and the electrode mixture with water. Furthermore, water has a high surface tension and generates cavitation more easily than organic solvents, thus enabling efficient separation of the current collector and the electrode mixture. In addition, since ultrasonic treatment is performed in water while sweeping the ultrasonic frequency, the energy distribution becomes favorable, suppressing damage to the current collector and residual electrode mixture, and enabling high-precision separation of the current collector and the electrode mixture. Moreover, because the separation method and apparatus described above utilize the physical action of ultrasonic cavitation, it also has the effect of being able to separate the current collector and the electrode mixture with water regardless of whether the binder contained in the electrode mixture is water-based or organic. Furthermore, because treated water is used, the treatment solution is relatively inexpensive, the treatment solution can be easily removed from the separated current collector and electrode mixture, and the wastewater can be easily treated, resulting in a low environmental impact. Moreover, because the current collector and electrode mixture can be efficiently separated, it is possible to separate the current collector and electrode mixture with high precision even at high frequencies (low energy) such as 40-240 kHz (preferably 80-200 kHz), even when the electrodes to be treated are relatively large, and even in a non-heated environment.

[0043] Furthermore, while immersing electrodes in treated water can cause ions to leach from the electrodes, potentially leading to an excessive increase in the pH of the treated water or alteration of the electrode components, the use of an acidic solution maintains the pH of the treated water within a suitable range (e.g., pH 3 to 8, which suppresses the leaching of Al). This allows for separation even with longer waiting times, for example, when the electrodes remain immersed in the treated water. Therefore, even with large separation equipment, where there is a predetermined waiting time between electrode immersion and the start of ultrasonic treatment, the current collector and electrode composite can be separated stably and with high precision.

[0044] Furthermore, the inventors have confirmed that even if a buffer solution is used in the treated water instead of an acid solution, the pH change of the treated water is suppressed, and separation can be achieved even with a longer waiting time, for example. However, since alkali metal or halogen salts are often used in buffer solutions, the salt concentration of the treated water increases when the pH of the treated water is repeatedly adjusted, which may result in a higher salt concentration in the wastewater or the inclusion of salt as an impurity in the recovered electrode mixture. In contrast, in this invention, an acid solution is used in the treated water, which can suppress the increase in the salt concentration of the wastewater and the increase in impurities contained in the recovered electrode mixture. In addition, if treated water prepared using a gaseous acid (e.g., carbonic acid) is used, any unreacted acid remaining in the treated water after ultrasonic treatment can be easily removed by gas bubbling or other methods.

[0045] It goes without saying that this disclosure is not limited in any way to the embodiments described above, and can be implemented in various forms as long as they fall within the technical scope of this disclosure.

[0046] For example, in the embodiment described above, the separation device 10 performs ultrasonic processing in a batch manner, but it may also perform ultrasonic processing in a continuous manner.

[0047] This disclosure may be any of the following [1] to

[10] . [1] The treatment electrode, comprising a current collector and an electrode mixture formed on the current collector, is immersed in a treatment water which is an acidic solution, and ultrasonic treatment is performed while sweeping the frequency of the ultrasonic waves, including a separation step of separating the current collector and the electrode mixture. Separation method. [2] The separation method according to [1], wherein the treated water is an acidic solution with a pH of 3 or higher. [3] The treated water has an acid dissociation constant pK a The separation method according to [1] or [2], wherein the solution contains an acid between 4 and 8 degrees Celsius. [4] The separation method according to any one of [1] to [3], wherein the treated water is an acid solution containing one or more acids selected from the group consisting of carbonic acid, acetic acid, propionic acid, and benzoic acid. [5] The separation method according to any one of [1] to [4], wherein the treated water has an acid concentration of 0.005 mol / L or more. [6] The separation method according to any one of [1] to [5], wherein the treated water has an alkali metal ion concentration of 0.01 mol / L or less and a halogen ion concentration of 0.01 mol / L or less. [7] The separation method according to any one of [1] to [6], wherein in the separation step, the amount of treated water used is in the range of 5 g to 200 g per 1 g of active material contained in the electrode to be treated. [8] The separation step is carried out under conditions that the treated water after ultrasonic treatment has a pH of 3 or higher and a pH of 8 or lower, according to any one of [1] to [7]. [9] The separation method according to any one of [1] to [8], wherein the separation step is carried out under one or more of the conditions (1) to (8). (1) In the separation step, the sweep is performed with a fundamental frequency of 80 kHz or more and 200 kHz or less as the center. (2) In the separation step, the sweep is performed with a sweep width of ±3 kHz or less around the fundamental frequency. (3) In the separation step, the sweep is performed at a sweep rate of 500 sweep cycles / second or more. (4) In the separation step, the ultrasonic treatment is performed within a period of 10 minutes or less. (5) In the separation step, the contact area between the current collector and the electrode composite material is A [cm] 2 When the output of the ultrasound is B[W], the power density expressed as B / A is 10W / cm². 2 The ultrasonic treatment is performed as follows. (6) In the separation step, the removal rate of the electrode mixture from the current collector is 98% or more, and the proportion of the current collector component in the separated electrode mixture is less than 0.1% by mass. (7) In the separation step, the ultrasonic treatment is performed in a non-heated environment. (8) In the separation step, the ultrasonic treatment is performed in batch or continuous manner.

[10] A separation unit that separates the current collector and the electrode mixture, which comprises a current collector and an electrode mixture formed on the current collector, by immersing the electrode to be treated in a treatment water which is an acidic solution and performing ultrasonic treatment, A control unit controls the separation unit to perform ultrasonic processing while sweeping the ultrasonic frequency, A separation device equipped with this device. [Examples]

[0048] The following describes examples of implementing the separation method of this disclosure. Experimental Examples 1 to 8 correspond to the examples, and Experimental Example 9 corresponds to the comparative example.

[0049] 1.Reference examples 1~19 First, ultrasonic treatment was performed with pure water, and the optimal separation conditions were investigated in Reference Examples 1 to 19. Reference Examples 1 to 19 were carried out as follows.

[0050] [Preparation of electrodes to be processed] Positive electrodes A-C and negative electrodes A-B, as shown below, were prepared as electrodes to be processed (see Table 1).

[0051] Positive electrode A is LiNi 1 / 3 Co 1 / 3 Mn 1 / 3A positive electrode composite material containing 92% by mass of O2 (NCM, manufactured by Toda Kogyo), 5% by mass of acetylene black (manufactured by Denka Co., Ltd.), and 3% by mass of polyvinylidene fluoride (PVDF, manufactured by Kureha Corporation) was prepared as a paste using N-methylpyrrolidone (NMP) and coated onto both sides of a 20 μm thick aluminum current collector foil.

[0052] Positive electrode B is LiNi 0.8 Co 0.15 Al 0.05 A positive electrode composite material containing 92% by mass of O2 (NCA, manufactured by Toda Kogyo), 5% by mass of acetylene black (manufactured by Denka Co., Ltd.), and 3% by mass of polyvinylidene fluoride (PVDF, manufactured by Kureha Corporation) was formed into a paste using NMP and coated onto both sides of a 20 μm thick aluminum current collector foil.

[0053] The positive electrode C was prepared by forming a paste from a positive electrode mixture containing 92% by mass of LiFePO4 (company-synthesized product), 5% by mass of acetylene black (manufactured by Denka Co., Ltd.), and 3% by mass of polyvinylidene fluoride (PVDF, manufactured by Kureha Corporation) using NMP, and coating both sides of a 20 μm thick aluminum current collector foil.

[0054] Negative electrode A was prepared by mixing a negative electrode composite material containing 98% by mass of graphite (OMAC1.5s, manufactured by Osaka Gas Chemical), 1% by mass of carboxymethylcellulose (CMC, manufactured by Daicel), and 1% by mass of styrene-butadiene copolymer (SBR, manufactured by JSR) with water to form a paste, which was then coated onto both sides of a 10 μm thick copper current collector foil.

[0055] Negative electrode B was prepared by mixing a negative electrode composite material containing 98% by mass of graphite (SCMG-XR-s, manufactured by Showa Denko), 1% by mass of carboxymethylcellulose (CMC, manufactured by Daicel), and 1% by mass of styrene-butadiene copolymer (SBR, manufactured by JSR) with water to form a paste, which was then coated onto both sides of a 10 μm thick copper current collector foil.

[0056] [Ultrasonic treatment] For the ultrasonic treatment in Reference Examples 1 to 19, an ultrasonic device (Branson GCX-M-3FQ12, output 500W, outer tank capacity 20L) was used. Specifically, as shown in Figures 3 and 4, water was placed in the outer tank 26, 40 mL of treatment water 32 was placed in a glass container (inner tank 24), the electrode to be treated 50 was immersed in it, and ultrasonic waves were applied from the transducer 28 below the outer tank 26. When using the ultrasonic frequency sweep function, the sweep speed was set to 1000 sweep cycles / second. The power density was calculated by dividing the output of the ultrasonic device (500W) by the contact area between the current collector foil and the electrode composite layer (here, electrode area × 2), and the power density was adjusted by adjusting the electrode area.

[0057] In Reference Example 1, a 40mm x 100mm positive electrode A was used as the electrode to be processed. The processing solution was water, the ultrasonic frequency (fundamental frequency F0) was 170kHz, the sweep condition (sweep width) was ±1kHz, the processing time was 60 seconds, and the power density was 6.3W / cm². 2 That's what I decided.

[0058] In Reference Example 2, a 40mm x 100mm negative electrode A was used as the electrode to be treated. The treatment solution was water, the ultrasonic frequency was 170kHz, the sweep condition was ±1kHz, the treatment time was 30 seconds, and the power density was 6.3W / cm². 2 That's what I decided.

[0059] Reference Example 3 was the same as Reference Example 1 except that the ultrasonic frequency was set to 120 kHz. Reference Example 4 was the same as Reference Example 3 except that the processing time was set to 30 seconds. In Reference Example 5, the power density was increased to 3.1 W / cm by setting the electrode size to 40 mm x 200 mm. 2 Except for the change made, the procedure was the same as in Reference Example 3. In Reference Example 6, the procedure was the same as in Reference Example 3, except that the electrode to be processed was positive electrode B. In Reference Example 7, the procedure was the same as in Reference Example 3, except that the electrode to be processed was positive electrode C.

[0060] Reference Example 8 was the same as Reference Example 2 except that the ultrasonic frequency was set to 120 kHz. Reference Example 9 was the same as Reference Example 8 except that the processing time was set to 10 seconds. In Reference Example 10, the power density was increased to 3.1 W / cm by setting the electrode size to 40 mm × 200 m.2 Except for the above, the procedure was the same as in Reference Example 8. In Reference Example 11, the processing time was set to 60 seconds and the electrode size to 40 mm x 715 mm, resulting in a power density of 0.9 W / cm². 2 Except for the change made, the procedure was the same as in Reference Example 8. In Reference Example 12, the procedure was the same as in Reference Example 8, except that the electrode to be processed was set to negative electrode B.

[0061] Reference Example 13 was the same as Reference Example 1, except that the ultrasonic frequency was set to 80 kHz. Reference Example 14 was the same as Reference Example 2, except that the ultrasonic frequency was set to 80 kHz.

[0062] Reference Example 15 was the same as Reference Example 3, except that the sweep condition was set to no sweep. Reference Example 16 was the same as Reference Example 8, except that the sweep condition was set to no sweep.

[0063] Reference Example 17 was the same as Reference Example 3, except that the processing solution was NMP. Reference Example 18 was the same as Reference Example 17, except that the ultrasonic frequency was 40 kHz and the processing time was 30 seconds.

[0064] Reference Example 19 was the same as Reference Example 1, except that the ultrasonic frequency was set to 40 kHz.

[0065] [Analysis of the proportion of current collector foil components in the asphalt mixture] For Reference Examples 1-19, the proportion of current collector foil components in the asphalt mixture was determined by inductively coupled plasma atomic emission spectroscopy (ICP-OES, Hitachi High-Tech Science PS3520UVDDII II). Specifically, first, a solution containing the asphalt mixture powder after ultrasonic treatment (asphalt mixture-containing treatment solution) was pressure filtered while washing with pure water using a membrane filter (Merckmillpore JGWP 0.45 μm), and dried at 50°C for 1 hour to obtain the asphalt mixture powder. The mass of the current collector foil components (aluminum or copper) in the asphalt mixture powder was analyzed by ICP, and the mass ratio of the current collector foil components to the total mass of the asphalt mixture powder was determined. This was defined as the proportion of current collector foil components in the asphalt mixture. Then, a ratio of less than 0.1% was evaluated as "A (Excellent)", 0.1% or more and less than 0.18% as "B (Good)", and 0.18% or more as "F (Unacceptable)".

[0066] [Analysis of the proportion of composite material components in current collector foil] For Reference Examples 1, 3-7, 13, 15, and 17-19 (positive electrodes), the proportion of composite material components in the current collector foil was determined by inductively coupled plasma atomic emission spectroscopy (ICP-OES). Specifically, the electrodes were first removed after ultrasonic treatment, rinsed with water, and then air-dried. The mass of the composite material components (transition metal components in the composite material; Ni, Co, and Mn in positive electrode A) was determined by ICP-OES, and the mass ratio of the composite material components to the total mass of the electrode was determined. This was taken as the proportion of composite material components in the current collector foil. For Reference Examples 2, 8-12, 14, and 16 (negative electrodes), the proportion of composite material components in the current collector foil was determined by the fundamental parameter method (FP method) of X-ray fluorescence analysis (XRF). Specifically, the electrodes were first removed after ultrasonic treatment, rinsed with water, and then air-dried. The amount of C (mass ratio) was determined by the FP method of XRF within a φ30 mm analysis range for these electrodes. In the XRF FP method, the quantitative value is calculated by normalizing the detected elements to 100% for the entire sample. Furthermore, the carbon content is measured on one side and the surface layer. The carbon content thus determined was used as the proportion of composite material components in the current collector foil. The results were evaluated as follows: less than 0.2% was rated "A (Excellent)", 0.2% to less than 0.36% was rated "B (Good)", and 0.36% or more was rated "F (Unacceptable)".

[0067] (Results and Discussion) Table 2 summarizes the proportion of current collector foil components in the composite material and the proportion of composite material components in the current collector foil for Reference Examples 1 to 19. Figure 5 shows photographs of the electrode (current collector foil) after ultrasonic treatment for Reference Examples 8, 16, 3, and 15. Figure 6 shows a photograph of the electrode (current collector foil) after ultrasonic treatment for Reference Example 11.

[0068] As shown in Table 2, in Reference Examples 1-14 and 19, where water was used as the processing liquid and ultrasonic treatment was performed using a sweep function, the evaluation of the ratio of current collector foil components in the asphalt mixture and the ratio of asphalt components in the current collector foil were both A or B, indicating that the asphalt mixture and current collector foil can be separated with high accuracy. Furthermore, it was found that the asphalt mixture and current collector foil can be separated with high accuracy even with short ultrasonic treatment of 60 seconds or less. Also, at 6.3 W / cm² 2It was found that the composite material and current collector foil can be accurately separated at the following low power densities. Furthermore, although the positive electrode binder (PVDF) is organic and the negative electrode binder (SBR) is water-based, it was found that the composite material and current collector foil can be accurately separated by ultrasonic treatment with water regardless of which binder is used.

[0069] In contrast, in Reference Examples 15 and 16, where water was used as the processing liquid and ultrasonic treatment was performed without using a sweep function, a large amount of composite material remained on the current collector foil.

[0070] Furthermore, in Reference Examples 17 and 18, where NMP was used as the processing solution and ultrasonic treatment was performed using a sweep function, a large amount of composite material remained on the current collector foil. Since organic binders dissolve with NMP, it was presumed that Reference Examples 17 and 18, which used NMP as the processing solution, would remove more composite material than Reference Examples 3 and 19, which used water as the processing solution. However, in reality, more composite material was removed when water was used as the processing solution. This was presumed to be because the cavitation effect by ultrasound is weaker when NMP is used. In addition, in Reference Examples 17 and 18, it was found that in Reference Example 18, where the ultrasonic frequency was 40 kHz, not only did the proportion of composite material components in the current collector foil increase, but the proportion of current collector foil components in the composite material also increased, resulting in greater damage to the current collector foil. In Reference Example 19, the ultrasonic frequency was also 40 kHz, but perhaps because the processing solution was water, the damage to the current collector foil was suppressed more than in Reference Example 18.

[0071] From the above, it was found that by using water as the processing liquid and performing ultrasonic treatment using a sweep function, the current collector and electrode composite material can be separated efficiently and with high precision.

[0072] [Table 1]

[0073] [Table 2]

[0074] 2.Reference examples 20~28 Prior to the ultrasonic treatment described above, it was observed that if the waiting time for immersion of the electrodes, especially the positive electrode, in water was prolonged, the current collector and the electrode composite material became difficult to separate. This point is shown in Reference Examples 20-28. In Reference Examples 20-28, pure water (pH=6) was used as the treated water. Reference Examples 20-28 were carried out as follows.

[0075] [Electrodes to be processed] The positive electrode A described above was used as the electrode to be processed. The proportion of the composite material in the positive electrode was 74% by weight.

[0076] [Ultrasonic treatment] An ultrasonic device (Branson GCX-M-3FQ12, 500W output, 20L cleaning tank capacity) was used. Water (pure water, pH 6) was placed in the cleaning tank (outer tank), 50 ml of aqueous solution was placed in the glass container of the inner tank, and a positive electrode with an area of ​​40 mm x 100 mm was placed in it and immersed for a predetermined time. After that, ultrasound was applied from the transducer at the bottom of the outer tank. The ultrasonic treatment conditions were a frequency of 120 kHz, a sweep width of ±1 kHz, a sweep speed of 1000 sweep cycles / second, and the treatment time was 60 seconds.

[0077] [analysis] The weight of the positive electrode was measured at the timings shown in Figure 7, and the asphalt removal rate was derived from the weight measurement results. The asphalt removal rate is the value expressed as a percentage by dividing the weight decrease rate of the positive electrode before and after the separation process by the weight percentage of the asphalt in the positive electrode, which is 74%. If the Al foil is damaged and its weight decreases, that amount is also included in the calculated asphalt removal rate.

[0078] (Results and Discussion) Figure 8 is a graph showing the relationship between immersion waiting time and asphalt removal rate for Reference Examples 20-28. As shown in Figure 8, in Reference Examples 20-28, which used pure water, the peelability of the electrode asphalt tended to decrease as the waiting time increased. The reason for this was inferred as follows: When pure water is used as the treatment water, immersing the positive electrode in the water causes the water to become alkaline due to the leaching of Li contained in the positive electrode active material. It was inferred that this change to alkalinity causes the aluminum of the current collector to leach into the aqueous solution, and consequently, a compound is formed between the asphalt and the aluminum, or the PVdF binder is altered by the alkali, inhibiting separation and potentially causing the asphalt to remain on the Al foil. Furthermore, if aluminum leaches out, there is a risk that aluminum may be mixed into the asphalt powder after separation, or that the recovery rate of metallic aluminum will decrease. From this perspective as well, it was inferred that it is desirable to suppress the leaching of aluminum.

[0079] 3. Experimental Examples 1-9 In a method for separating a current collector (e.g., Al) and an electrode composite material by ultrasonic treatment, experimental examples 1-9 confirmed that using an acidic solution for the treatment water further reduces the influence of eluted components, enabling stable separation regardless of the length of immersion time in the treatment water. The treatment water, cathode material, ultrasonic treatment, and analysis were performed under the following conditions.

[0080] [Treated water] <Carbonated water: Experimental examples 1-5> Carbonated water was prepared by absorbing carbon dioxide into pure water (alkali metal ion concentration less than 10 μg / L, halogen ion concentration less than 10 μg / L). The pH of the prepared carbonated water was measured, and the carbon dioxide concentration was calculated using the acid dissociation constant of carbon dioxide from the following equations (A) and (B), which are shown below. (A): H2CO3 + H2O ⇔ H3O + +HCO3 - K a1 =([H + ][HCO3 - ]) / ([H2CO3])=4.45×10 -7 pK a1 =6.35 (B): HCO3 - +H2O⇔H3O + +CO3 2- K a2 =([H + ][CO3 2- ]) / ([HCO3])=4.7×10 -11 pK a2 =10.33 Experiment Example 1: Carbonated water (1): pH 3.99, carbon dioxide concentration 0.024 mol / L Experiment Example 2: Carbonated water (2): pH 4.14, carbon dioxide concentration 0.012 mol / L Experiment Example 3: Carbonated water (3): pH 4.29, carbon dioxide concentration 0.0059 mol / L Experiment Example 4: Carbonated water (4): pH 4.49, carbon dioxide concentration 0.0024 mol / L Experiment Example 5: Carbonated water (5): pH 4.71, carbon dioxide concentration 0.00086 mol / L <Acetic acid solution: Experimental examples 6-7> Experimental Example 6: 3.0 g of 99.7% acetic acid was diluted with 1 L of pure water to prepare a 0.05 mol / L acetic acid aqueous solution. The pH at that time was 3.03. Experimental Example 7: 0.60 g of 99.7% acetic acid was diluted in 1 L of pure water to prepare a 0.01 mol / L acetic acid aqueous solution. The pH at that time was 3.08. <Benzoic acid solution: Experimental example 8> Experimental Example 8: 1.22 g of 99.5% benzoic acid was diluted in 1 L of pure water to prepare a 0.01 mol / L benzoic acid aqueous solution. The pH at that time was 3.12. <Pure water: Experimental example 9> Pure water without dissolved acid was used as the treatment solution. The pH was 5.5. The carbon dioxide concentration was calculated in the same manner as in Experimental Example 1, and it was found to be trace (Tr).

[0081] [Electrodes to be processed] A 20 μm thick aluminum foil was used for the current collector foil. LiNi was used as the positive electrode active material in the electrode composite layer. 1 / 3 Co 1 / 3 Mn 1 / 3A mixture of O2 (NCM: manufactured by Toda Kogyo), acetylene black (manufactured by Denka Co., Ltd.) as a conductive material, and polyvinylidene fluoride (PVdF: manufactured by Kureha Corporation) as a binder was used in a mass ratio of 92:5:3. The above electrode mixture layer was coated on both sides of a current collector foil and used as the positive electrode. The amount of active material in the positive electrode was 1 g / 100 cm. 2 That was the case.

[0082] [Ultrasonic treatment] Using an ultrasonic device (Branson GCX-M-3FQ12, 500W output, 20L outer tank capacity), water is placed in the washing tank (outer tank), 50mL of treated water is placed in the glass container of the inner tank, and an area of ​​5cm x 10cm (50cm) is placed inside. 2 The positive electrode was placed inside the tank and immersed for a predetermined waiting time (30 minutes in this case). After that, ultrasonic waves were applied from a transducer located below the outer tank. The ultrasonic treatment conditions were a frequency of 120 kHz, a sweep width of ±1 kHz, and a sweep speed of 1000 sweep cycles / second, with a treatment time of 60 seconds. pH measurement of the treated water, mass measurement of the positive electrode, and ICP analysis were performed at the timings shown in Figure 7. Note that the liquid ICP-OES measurement in Figure 7 was performed using the filtrate obtained by filtering the asphalt powder from the treated liquid.

[0083] [analysis] The treated water after ultrasonic treatment was filtered through a 0.2 μm pore size hydrophilic Teflon membrane filter (Teflon is a registered trademark). The positive electrode mixture held in the filter was dried at 80°C. The amount of aluminum in the treated water and positive electrode mixture powder was quantified by ICP-OES to determine the amount of dissolved aluminum per unit mass of the positive electrode current collector and the proportion of Al in the positive electrode mixture powder. The measurements were performed using an inductively coupled plasma atomic emission spectrometer (ICP-OES, Hitachi High-Tech Science PS3520UVDDII II).

[0084] (Results and Discussion) Table 3 shows the type of treatment solution, pH after preparation, acid concentration after preparation, and pH after ultrasonic treatment for each of the experimental examples 1 to 9. It also shows the asphalt removal rate, amount of Al dissolved per unit mass of current collector, and amount of Al in the asphalt powder.

[0085] Figure 9 shows photographs of the appearance of each electrode (current collector foil) after ultrasonic treatment. Figure 10 is a graph showing the relationship between acid concentration and pH after treatment. Figure 11 is a graph showing the relationship between acid concentration and asphalt removal rate. Figure 12 is a graph showing the relationship between acid concentration and amount of Al dissolved per unit mass of current collector. Figure 13 is a graph showing the relationship between acid concentration and amount of Al in asphalt powder. In Experimental Examples 1 and 2, the removal rate of the asphalt layer after ultrasonic peeling test was 100% in both cases, and the pH of the solution after treatment was 6.10 for Experimental Example 1 and 6.35 for Experimental Example 2. Furthermore, the amount of dissolved aluminum current collector and the amount of aluminum in the asphalt powder were both 0.01% or less. In Experimental Example 3, the asphalt removal rate was 98%, the pH after treatment was 6.93, the amount of dissolved aluminum current collector was 0.01% or less, and the amount of aluminum in the asphalt powder was 0.03%. In Experimental Example 4, the asphalt removal rate was 92%, the pH after treatment was 9.39, the amount of dissolved aluminum current collector was 0.03%, and the amount of aluminum in the asphalt powder was 0.05%. In Experimental Example 5, the asphalt removal rate was 94%, the pH after treatment was 10.34, the amount of dissolved aluminum current collector was 0.12%, and the amount of aluminum in the asphalt powder was 0.10%. In Experimental Example 6, the asphalt removal rate was 100%, the pH after treatment was 4.14, the amount of dissolved aluminum current collector was 0.01% or less, and the amount of aluminum in the asphalt powder was 0.01%. In Experimental Example 7, the asphalt removal rate was 99%, the pH after treatment was 5.52, the amount of dissolved aluminum current collector was 0.01% or less, and the amount of aluminum in the asphalt powder was 0.04%. In Experimental Example 8, the asphalt removal rate was 99%, the pH after treatment was 5.48, the amount of dissolved aluminum current collector was 0.01% or less, and the amount of aluminum in the asphalt powder was 0.02%. In Experimental Example 9, the asphalt removal rate was 94%, the pH after treatment was 10.88, the amount of dissolved aluminum current collector was 0.29%, and the amount of aluminum in the asphalt powder was 0.10%. In Experimental Examples 1-8, the pH after treatment was lower than in Experimental Example 9, the pH increase due to treatment was suppressed, and consequently, the amount of dissolved aluminum current collector and the amount of aluminum in the asphalt powder were also lower. In particular, in Experimental Examples 1, 2, 3, 6, 7, and 8, where the pH was 8 or lower, no dissolution of aluminum current collector was observed, and the asphalt removal rate was 98% or higher, allowing for efficient separation of the current collector and the asphalt layer. The acid concentration at that time was 0.005 mol / L or higher.

[0086] In this embodiment, the amount of active material is 0.5g (positive electrode 50cm²). 2The treatment was carried out using 50 mL of treatment solution for 0.5 g of active material. When applied to an actual battery, for example, when using a treatment solution with an acid concentration of 0.005 mol / L, it was inferred that it is preferable to use 50 or more units of treatment solution for every 0.5 units of active material mass. Furthermore, when the weight of the positive electrode to be treated or the acid concentration is changed, 1 g of active material (100 cm³ of positive electrode) 2 It was inferred that it is preferable to use an acid solution prepared so that the amount of acid is 0.0005 mol or more relative to ).

[0087] [Table 3] [Industrial applicability]

[0088] This disclosure is applicable to the field of the battery industry. [Explanation of Symbols]

[0089] 10 Separation device, 15 Control unit, 20 Separation unit, 22 Processing container, 24 Inner tank, 25 Mounting platform, 26 Outer tank, 28 Transducer, 29 pH detection unit, 30 Oscillator, 32 Treated water, 33 Treated water containing mixture, 36 Ultrasonic propagation medium, 50 Electrode to be treated, 52 Current collector, 54 Electrode mixture.

Claims

1. The process includes a separation step in which an electrode to be treated, comprising a current collector and an electrode mixture formed on the current collector, is immersed in treated water which is an acid solution with an acid concentration of 0.005 mol / L or higher and a pH of 3 or higher, and ultrasonic treatment is performed while sweeping the ultrasonic frequency to separate the current collector and the electrode mixture. The separation method involves processing the separation step under one or more of the following conditions: (1) to (2). (1) In the separation step, the sweep is performed with a sweep width of ±3 kHz or less around the fundamental frequency. (2) In the separation step, the sweep is performed at a sweep rate of 500 sweep cycles / second or more.

2. The treated water has an acid dissociation constant pK a The separation method according to claim 1, wherein the solution is an acid solution containing an acid of 4 to 8.

3. The separation method according to claim 1 or 2, wherein the treated water is an acid solution containing one or more acids selected from the group consisting of carbonic acid, acetic acid, propionic acid, and benzoic acid.

4. The separation method according to claim 1 or 2, wherein the treated water has an alkali metal ion concentration of 0.01 mol / L or less and a halogen ion concentration of 0.01 mol / L or less.

5. The separation method according to claim 1 or 2, wherein in the separation step, the treated water is used in an amount of 5 g to 200 g per 1 g of active material contained in the electrode to be treated.

6. The separation method according to claim 1 or 2, wherein the separation step is performed under conditions that the treated water after ultrasonic treatment has a pH of 3 or higher and a pH of 8 or lower.

7. The separation method according to claim 1 or 2, wherein the separation step is performed under one or more of the conditions (3) to (8). (3) In the separation step, the sweep is performed with a fundamental frequency of 80 kHz to 200 kHz as the center. (4) In the separation step, the ultrasonic treatment is performed within a period of 10 minutes or less. (5) In the separation step, the contact area between the current collector and the electrode mixture is A [cm²]. 2 ]year, When the output of the ultrasound is B [W], the power density expressed as B / A is 10 W / cm². 2 The ultrasonic treatment is performed as follows. (6) In the separation step, the removal rate of the electrode mixture from the current collector is 98% or more, and the proportion of the current collector component in the separated electrode mixture is less than 0.1% by mass. (7) In the separation step, the ultrasonic treatment is performed in a non-heated environment. (8) In the separation step, the ultrasonic treatment is performed in batch or continuous manner.

8. A separation unit separates the current collector and the electrode material by immersing the electrode to be treated, which comprises a current collector and an electrode mixture formed on the current collector, in treated water that is an acid solution with an acid concentration of 0.005 mol / L or higher and a pH of 3 or higher, and performing ultrasonic treatment. The system includes a control unit that controls the separation unit to perform ultrasonic processing while sweeping the ultrasonic frequency, A separation device that processes under one or more of the following conditions: (1) or (2). (1) The control unit performs the sweep with a sweep width of ±3 kHz or less around the fundamental frequency. (2) The control unit performs the sweep at a sweep rate of 500 sweep cycles / second or more.

Images