Separation method and separation device

Abstract

To separate a collector and an electrode mixture from each other efficiently and stably with high accuracy.SOLUTION: A separation method includes a separation step of impregnating a processing target electrode including a collector and an electrode mixture formed on the collector in processing water being a buffer solution not including a halogen compound, performing ultrasonic treatment while sweeping the frequency of ultrasonic waves, and separating the collector and the electrode mixture from each other. In the separation step, as the pH of the processing water is closer to a neutral range, the collector and the electrode mixture can be separated from each other even with a longer standby time for standby while impregnating the processing target electrode before the ultrasonic treatment in the processing water.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to a separation method and a separation device. [Background technology]

[0002] Conventionally, a proposed method for recycling lithium-ion batteries involves crushing lithium-ion batteries, sieving the resulting crushed material, and using a liquid to peel and separate the metal powder from the remaining material on the sieve, thereby obtaining the metal powder and a separated liquid (see, for example, Patent Document 1). This processing method is said to enable more efficient use of resources. Another proposed recycling method 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 enable electrode active material to be obtained from the lithium-ion battery in a simple process without requiring high-temperature heating. Another proposed recycling method involves immersing a positive electrode in an alkaline aqueous solution to peel the positive electrode active material layer from the positive electrode current collector, adding an organic solvent to the peeled material to extract the binder from the peeled material, and separating the supernatant containing the conductive material from the precipitate containing the positive electrode active material (see, for example, Patent Document 3). This processing method is said to enable the recovery and reuse of the positive electrode active material from lithium batteries. Another proposed recycling method involves discharging a lithium-ion battery, shredding it into small pieces to obtain a mixture of a current collector coated with a cathode layer and a current collector coated with an anode layer, immersing these small pieces in a polar solvent to form a heterogeneous mixture, stirring the mixture in a mixer to dissolve the binder material, sieving the treated heterogeneous mixture to separate the current collector from the cathode and anode materials, adding a polar solvent to form a suspension of electrode materials, and 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 Patent Application Publication No. 2018-170223 [Patent Document 2] Patent Publication No. 2021-44180 [Patent Document 3] Japanese Patent Application Laid-Open No. 2010-62105 [Patent Document 4] Patent Publication No. 2021-73375 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the above-mentioned recycling methods, 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. Furthermore, the above-mentioned recycling methods have low processing efficiency, such as requiring long processing times or preprocessing such as crushing.

[0005] The present disclosure has been made to solve such problems, and its main object is to provide a separation method and separation device 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 inventors discovered that when an electrode is subjected to ultrasonic treatment in a buffered aqueous solution while sweeping the frequency of the ultrasonic waves, the current collector and the electrode composite can be separated efficiently, stably, and with high precision, and have completed the present disclosure.

[0007] That is, the separation method of the present disclosure includes: a separation step of immersing a treatment target electrode, which includes a current collector and an electrode composite formed on the current collector, in treatment water that is a buffer solution, and performing ultrasonic treatment while sweeping the frequency of ultrasonic waves to separate the current collector from the electrode composite; In the separation process, the closer the pH of the treated water is to the neutral range, the longer the waiting time for immersing the electrode to be treated in the treated water before the ultrasonic treatment can be for separation.

[0008] The separation device of the present disclosure also includes: a separation unit that immerses a target electrode, which includes a current collector and an electrode composite formed on the current collector, in treatment water that is a buffer solution and performs ultrasonic treatment to separate the current collector from the electrode composite; a control unit that controls the separation unit so that the closer the pH of the treatment water is to a neutral range, the longer the waiting time during which the electrode to be treated is immersed in the treatment water before the ultrasonic treatment is performed, and starts the ultrasonic treatment within the waiting time and performs the ultrasonic treatment while sweeping the frequency of the ultrasonic waves; It is equipped with the following. [Effects of the Invention]

[0009] The separation method and separation device disclosed herein enable efficient, stable, and highly accurate separation of the current collector and electrode composite. The reasons for this effect are believed to be as follows: This separation method and separation device utilize the physical action of ultrasonic cavitation, rather than the chemical action of an organic solvent or aqueous solution, thereby enabling separation of the current collector and electrode composite using water without the use of organic solvents. Furthermore, water has a high surface tension and is more susceptible to cavitation than organic solvents, enabling efficient separation of the current collector and electrode composite. Furthermore, ultrasonic treatment is performed in water while sweeping the ultrasonic frequency, resulting in a favorable energy distribution, suppressing damage to the current collector and residual electrode composite, and enabling highly accurate separation of the current collector and electrode composite. Furthermore, immersing an electrode in treated water can cause ions to elute from the electrode, potentially changing the pH of the treated water or altering electrode components. However, the use of a buffer solution suppresses pH changes in the treated water, enabling separation even when the electrode is left immersed in the treated water for a longer waiting time. Therefore, even in the case of a large separation facility, for example, where there is a predetermined waiting time between the immersion of the electrodes and the start of the ultrasonic treatment, the current collector and the electrode mixture can be separated stably and with high precision. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 2 is an explanatory diagram of a sweep and a sweep cycle. [Figure 2] An explanatory diagram of sweep width. [Figure 3] FIG. 2 is an explanatory diagram showing the outline of the configuration of the separation device 10 before ultrasonic treatment. [Figure 4] FIG. 2 is an explanatory diagram showing the outline of the configuration of the separation device 10 after ultrasonic treatment. [Figure 5] Photograph of the appearance of the electrode (collecting foil) after ultrasonic treatment. [Figure 6] Photograph of the appearance of the electrode (collecting foil) after ultrasonic treatment. [Figure 7] 10 is a flowchart showing an example of a separation method. [Figure 8] Photograph of the appearance of an electrode that was immersed in a buffer solution for 30 minutes and then ultrasonically treated. [Figure 9]Photograph of the electrode after immersion in a buffer solution for 60 minutes and then ultrasonic treatment. [Figure 10] A graph showing the relationship between the waiting time after immersion in carbonate / bicarbonate and the appearance of the electrode after ultrasonic treatment. [Figure 11] Graph showing the relationship between the pH of the buffer solution during preparation and the composite removal rate. [Figure 12] This is a graph showing the relationship between the pH of the buffer solution when the positive electrode is immersed and the mixture removal rate. [Figure 13] Graph showing the relationship between the pH of the buffer solution after ultrasonic treatment and the composite removal rate. [Figure 14] A graph showing the relationship between the waiting time when the electrodes are immersed in carbonated / bicarbonate water and the mixture removal rate. DETAILED DESCRIPTION OF THE INVENTION

[0011] [Separation method] The separation method of the present disclosure includes a separation step in which the electrode to be treated is immersed in treatment water, which is a buffer solution, and subjected to ultrasonic treatment to separate the current collector and the electrode mixture.

[0012] (electrode to be treated) The electrode to be treated comprises a current collector and an electrode composite formed on the current collector. The electrode to be treated is an electrode of an electricity storage device such as an ion secondary battery such as a lithium ion secondary battery, an electric double layer capacitor, a hybrid capacitor, or a pseudo-electric double layer capacitor, and may be removed from a used electricity storage device or a deteriorated electricity storage device. The electrode to be treated may be a positive electrode, a negative electrode, or a bipolar electrode with a positive electrode composite formed on one side and a negative electrode composite formed on the other side. Of these, the electrode to be treated is preferably a positive electrode from the viewpoint of elution of carrier ions. The electrode to be treated may be an unshredded electrode removed from the electricity storage device, for example, an electrode having an area of ​​10 cm. 2 It can be more than 30cm 2 The above may also be used.

[0013] Examples of the material of the current collector include aluminum, copper, titanium, stainless steel, nickel, iron, fired carbon, conductive polymer, conductive glass, etc. Among these, when the electrode to be processed is a positive electrode, it is preferable that the current collector contains aluminum. Examples of the shape of the current collector include foil shape, film shape, sheet shape, net shape, punched or expanded shape, lath body, porous body, foam body, formed body of fiber group, etc. The thickness of the current collector is, for example, 1 to 500 μm.

[0014] The electrode mixture may include an electrode active material, a binder, and a conductive material or the like as necessary. 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 make it into a paste form, applying and drying it on the surface of the current collector, and compressing it as necessary to increase the electrode density. 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, FeS2, lithium manganese composite oxides having a basic composition formula of Li (1-x) MnO2 (0 < x < 1, etc., the same below), Li (1-x) Mn2O4, etc., lithium cobalt composite oxides having a basic composition formula of Li (1-x) CoO2, etc., lithium nickel composite oxides having a basic composition formula of Li (1-x) NiO2, etc., lithium nickel cobalt manganese composite oxides having a basic composition formula of Li (1-x) Ni a Co b Mn cExamples of active materials used in the positive electrodes of lithium-ion secondary batteries include lithium-nickel-cobalt-manganese composite oxides with a basic formula such as LiV2O3, transition metal oxides with a basic formula such as V2O5, and lithium iron phosphate. The term "basic formula" refers to materials that may contain other elements such as Al and Mg. Examples of electrode active materials include active materials used in the positive 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. Examples of electrode active materials include inorganic compounds such as lithium alloys and tin compounds, carbonaceous materials capable of absorbing and releasing lithium ions, composite oxides containing multiple elements, and conductive polymers. Examples of carbonaceous materials include cokes, glassy carbons, graphites, non-graphitizable carbons, pyrolytic carbons, and carbon fibers. Examples of composite oxides include lithium-titanium composite oxide and lithium-vanadium composite oxide. Examples of conductive materials contained in the electrode mixture 54 include graphite such as natural graphite (scale graphite, flake 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 serves to bind the active material particles and the 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 of these. Examples of organic binders include fluorine-containing resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and fluororubber; 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 carboxymethyl cellulose (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 contained in the electrode mixture can be, for example, one or a mixture of two or more of graphite, such as natural graphite (scale graphite, flake graphite) and artificial graphite, acetylene black, carbon black, ketjen black, carbon whisker, needle coke, carbon fiber, and metals (copper, nickel, aluminum, silver, gold, etc.). Among these, carbon black and acetylene black are preferred as the conductive material from the viewpoints of electronic conductivity and coatability.

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

[0018] In the separation process, the ultrasonic frequency may be periodically changed so as to reciprocate between a maximum frequency Fmax and a minimum frequency Fmin, centered on a fundamental frequency F0 (see FIGS. 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 treatment, when the sweep width is defined as the frequency fluctuation range centered on the fundamental frequency F0 (see FIG. 2), the sweep width may be within ±5 kHz. That is, Fmax - F0 ≦ +5 kHz, Fmin - F0 ≧ −5 kHz. The sweep width may be within ±3 kHz or ±1 kHz. In ultrasonic treatment, 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 FIG. 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. The sweep rate may also be 2000 sweep cycles / second or less. Note that one sweep cycle may be 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 carried out for 30 minutes or less, more preferably for 10 minutes or less, even more preferably for 300 seconds or less, and even more preferably for 180 seconds or less. In the separation step, ultrasonic treatment may be carried out 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 mixture is A [cm 2 ] and the ultrasonic output (oscillator output) is B [W], the output density (power density) expressed as B / A is 30W / cm 2 It is preferable to perform ultrasonic treatment so that the power density B / A is 10 W / cm 2 It is preferable that the power consumption is 5 W / cm or less. 2The power density B / A may be 0.1 W / cm or less. 2 More than 0.5W / cm 2 It may be more than that.

[0021] In the separation step, ultrasonic treatment is preferably performed in a non-heated environment, for example, 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 step, a buffer solution is used as the treatment water in which the electrode to be treated is immersed. The use of a buffer solution further suppresses pH fluctuations due to components eluted from the electrode, thereby ensuring separation of the current collector and the electrode composite layer and enabling separation even with a longer waiting time between the immersion of the electrode to be treated and the start of ultrasonic treatment. In this separation step, the closer the pH of the treatment water is to the neutral range, the longer the waiting time during which the electrode to be treated is immersed in the treatment water before ultrasonic treatment. In the separation step, it is preferable to use one or more of the treatment waters (1) to (3). Furthermore, the pH of the treatment water during preparation, during the immersion of the electrode, and after ultrasonic treatment is more preferably in the range of 3 or more and less than 9, and even more preferably in the range of 4 or more and less than 8. (1) The pH of the treated water during preparation is in the range of 2.2 to 8.6. (2) The pH of the treatment water when the electrode to be treated is immersed is in the range of 2.4 to 8.8. (3) The treated water after immersing the electrode to be treated and ultrasonic treatment is in the pH range of 2.6 to 9.0.

[0023] In the separation step, it is preferable to use treated water that is a buffer solution containing one or more of carboxylic acid, phosphoric acid, and carbonic acid. Examples of carboxylic acids include carboxylic acids such as acetic acid, dicarboxylic acids such as oxalic acid, and tricarboxylic acids such as citric acid. The acetate buffer solution may contain acetic acid and an acetate salt. The citrate buffer solution may contain citric acid and a citrate salt. The phosphate buffer solution may contain phosphoric acid and a phosphate salt. The carbonate buffer solution may contain carbonic acid and a carbonate salt. The treated water may also be a carbonate / bicarbonate (hydrogencarbonate) buffer solution, a citrate phosphate buffer solution, a borate buffer solution, or a tartrate buffer solution. The citrate phosphate buffer solution may contain citric acid and a hydrogen phosphate salt. The borate buffer solution may contain boric acid and a borate salt. The tartrate buffer solution may contain tartaric acid and a tartrate salt. Examples of salts contained in the buffer solution include lithium salts, sodium salts, and potassium salts, with sodium salts being preferred. The treated water is preferably a buffer solution that does not contain halogen compounds that cause pitting corrosion of aluminum. Examples of halogens include fluorine, chlorine, bromine, and iodine. Such buffer solutions are preferred because they are less likely to cause separation of the electrode mixture or elution of the current collector, even when the solution is left standing for a longer period of time. This separation step may be carried out under one or more of the conditions (4) to (7). Satisfying the following conditions is preferred because it ensures separation of the electrodes and further suppresses elution of the current collector. (4) Use a citrate buffer solution with a pH of 3 or higher as the treatment water, and the waiting time shall be 30 minutes or less for a citrate buffer solution with a pH of less than 4, and 60 minutes or less for a citrate buffer solution with a pH of 4 or higher. (5) Use an acetate buffer solution with a pH of 4 or higher as the treatment water, and limit the waiting time to 60 minutes or less. (6) Use a phosphate buffer solution with a pH of 6 or higher as the treatment water, and limit the waiting time to 60 minutes or less. (7) Use a carbonate / bicarbonate buffer solution with a pH of 9 or less as the treatment water, and for carbonate / bicarbonate buffer solutions with a pH of over 8, the waiting time shall be 10 minutes or less, and for carbonate / bicarbonate buffer solutions with a pH of 8 or less, the waiting time shall be 60 minutes or less.

[0024] By carrying out the separation process described above, the electrode composite is removed from the current collector, and the electrode composite removed from the current collector is dissolved and / or dispersed in water, or precipitates. Thus, after ultrasonic treatment, the current collector and the electrode composite are separated, and the current collector and composite-containing water containing the electrode composite are obtained. Furthermore, because a buffer solution is used, separation of the electrode can be ensured even if the waiting time for immersing the electrode to be treated in the treatment water is extended.

[0025] The proportion of the current collector components (current collector components) contained 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 the electrode mixture components (electrode mixture components) contained 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 the current collector components contained in the electrode mixture" may be a value determined, for example, as follows: First, water is removed from the mixture-containing water obtained in the separation step to obtain an electrode mixture. The mass of the current collector components in the obtained electrode mixture is analyzed by inductively coupled plasma optical 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 defined as the proportion of the current collector components contained in the electrode mixture. The "proportion of the electrode mixture components contained in the current collector" may be a value determined, for example, as follows: First, the electrode (current collector) after ultrasonic treatment is removed, rinsed, and dried. The electrode that has been rinsed and dried is analyzed for the mass of the electrode composite components using ICP-OES to determine the mass ratio of the electrode composite components to the mass of the analyzed electrode, and this mass ratio is used as the proportion of the electrode composite components contained in the current collector. Alternatively, the electrode that has been rinsed and dried is analyzed for the mass ratio of the electrode composite components using the fundamental parameter method (FP method) of X-ray fluorescence analysis (XRF), and this mass ratio is used as the proportion of the electrode composite components contained in the current collector. Note that 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 a transition metal, it may be the proportion of the transition metal contained in the current collector (provided that the transition metal is contained in the active material). Because transition metals may form alloys with the current collector components when the current collector (e.g., Al) is remelted, it is desirable for as little of them to remain on the current collector.

[0026] Before the separation step, a removal step of removing the electrodes from the electricity storage device may be performed. The electrodes removed in the removal step may be left as they are without being shredded, or may be cut into pieces with an area of ​​10 cm. 2 or more, area 30cm 2 It may be cut into the above-mentioned shapes and used as the electrode to be treated.

[0027] After the separation step, a current collector treatment step may be performed in which the current collector separated in the separation step is washed and dried. The current collector may be washed while a washing liquid is flowing through it, or by immersing it in the washing liquid. The washing liquid is preferably water. The current collector may be dried by air drying, heat drying, vacuum drying, barrel drying, spin drying, suction drying, infrared drying, or a combination thereof. After the separation step, a composite treatment step may be performed in which the electrode composite is filtered from the composite-containing water obtained in the separation step and dried. In the composite treatment step, the electrode composite may be washed during or after filtration of the electrode composite. The washing liquid is preferably water. The electrode composite may be dried by air drying, heat drying, vacuum drying, barrel drying, spin drying, suction drying, infrared drying, or a combination thereof. In the composite treatment step, instead of filtering the electrode composite, the electrode composite may be separated from the composite-containing water by a solid-liquid separation method such as centrifugation or evaporation to dryness.

[0028] The separation step, current collector treatment step, and composite treatment step may be performed in a batch system or a continuous system. When the separation step or current collector treatment step is performed continuously, a roll-to-roll system may be adopted. When the separation step is performed using the roll-to-roll system, the electrodes removed in the removal step may be sequentially wound into rolls and used as electrodes to be treated. Note that this separation method produces a current collector and an electrode composite, and therefore this separation method is also a method for producing a current collector and an electrode composite.

[0029] [Separation device] The separation device of the present disclosure includes a separation unit that immerses the electrode to be treated in treatment water that is a buffer solution and ultrasonically treats it to separate the current collector and the electrode composite, and a control unit that controls the separation unit. This separation device may perform the above-mentioned separation method, and the configurations and conditions described in the above-mentioned separation method may be applied.

[0030] Hereinafter, a separation device 10 will be described as an example of a separation device. FIGS. 3 and 4 are explanatory diagrams showing an outline of the configuration of the separation device 10. FIG. 3 is an explanatory diagram showing an outline of the configuration of the separation device 10 before ultrasonic treatment. FIG. 4 is an explanatory diagram showing an outline of the configuration of the separation device 10 after ultrasonic treatment. The separation device 10 includes a separation unit 20 and a control unit 15. The separation device 10 performs ultrasonic treatment on a treatment target electrode 50 including a current collector 52 and an electrode mixture 54, thereby separating the current collector 52 from 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, the current collector, and the electrode mixture described in the separation method, respectively.

[0031] The separation unit 20 performs ultrasonic treatment on the electrode 50 to be treated in treatment water 32, which is a buffer solution. The separation unit 20 includes a treatment container 22, a vibrator 28, a transmitter 30, and a pH detection unit 29. The treatment container 22 accommodates the electrode 50 to be treated and the treatment water 32. The treatment container 22 includes an inner tank 24 in which the electrode 50 to be treated is accommodated, a mounting stand 25 on which the inner tank 24 is placed, and an outer tank 26 in which the inner tank 24 and the mounting stand 25 are accommodated. The inner tank 24 accommodates the treatment water 32, and the outer tank 26 accommodates an ultrasonic propagation medium 36. A buffer solution is used as the treatment water 32. The treatment water 32 may include tap water, distilled water, ion-exchanged water, etc. The ultrasonic propagation medium 36 is, for example, water, and serves to propagate ultrasonic waves together with the treatment water 32. The treatment vessel 22 is provided with piping and valves (not shown), which allow the supply of the treated water 32 to the treatment vessel 22 and the amount of the water to be supplied to be adjusted.

[0032] The vibrator 28 is arranged so as to be in contact with the treatment vessel 22. The oscillator 30 supplies power to the vibrator 28 to cause it to oscillate. The oscillator 30 has a sweep function. The sweep function is a function of periodically changing the frequency, as shown in Figures 1 and 2, for example. The separation unit 20 is configured to sweep (periodically change) the frequency of the ultrasonic waves generated from the vibrator 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 treatment water 32. The pH detection unit 29 outputs the measurement result, the pH of the treatment water 32, to the control unit 15.

[0033] The control unit 15 is configured as a microprocessor centered on a CPU, and in addition to the CPU, is equipped with a storage device, input / output ports, etc. (not shown). The control unit 15 is electrically connected to the oscillator 30 and the pH detection unit 29, and outputs signals to either of them, and receives signals from either of them. The control unit 15 is configured to control the oscillator 30 so that ultrasonic treatment is performed while sweeping the ultrasonic frequency. The ultrasonic treatment conditions may be the same as those for the separation method described above.

[0034] An example of the operation of the separation device 10 will be described. First, the treatment vessel 22 is filled with treatment water 32, which is a buffer solution, and the treatment target electrode 50 is immersed in the treatment water 32. Any of the buffer solutions described in the separation method above may be used as the buffer solution. After the treatment target electrode 50 is immersed in the treatment water 32, the control unit 15 controls the oscillator 30 to supply power to the vibrator 28 and oscillate the vibrator 28 before a predetermined waiting time has elapsed. This causes ultrasonic treatment of the treatment target electrode 50 in the treatment water 32. During ultrasonic treatment, the control unit 15 uses the sweep function of the oscillator 30 to control the oscillator 30 to sweep the frequency under the following conditions: a fundamental frequency F0 of 40 kHz or more and 240 kHz or less, a sweep width within ±5 kHz, and a sweep rate of 500 sweep cycles / second or more. The control unit 15 also controls the oscillator 30 to sweep the frequency under the following conditions: a fundamental frequency F0 of 40 kHz or more and 240 kHz or less, a sweep width within ±5 kHz, and a sweep rate of 500 sweep cycles / second or more. For example, the control unit 15 controls the oscillator 30 to sweep the frequency under the following conditions: a power density B / A of 30 W / cm 2The control unit 15 controls the oscillator 30 to output the following power. The control unit 15 also controls the oscillator 30 to perform the ultrasonic treatment for a predetermined time, for example, in the range of 1 second to 30 minutes. By this ultrasonic treatment, the current collector 52 and the electrode composite 54 of the electrode 50 to be treated are separated, and composite-containing treated water 33 containing the current collector 52 and the electrode composite 54 is obtained.

[0035] The separation method and separation device described above enable efficient, stable, and highly accurate separation of the current collector and the electrode composite. The reason for this effect is presumed to be as follows: The separation method and separation device described above utilize a physical action utilizing the cavitation effect of ultrasound to separate the current collector and the electrode composite, allowing the current collector and the electrode composite to be separated using water. Furthermore, water has a high surface tension and is more susceptible to the cavitation effect than organic solvents, allowing the current collector and the electrode composite to be separated efficiently. Furthermore, ultrasonic treatment is performed in water while sweeping the ultrasonic frequency, resulting in a favorable energy distribution, suppressing damage to the current collector and the remaining electrode composite, and allowing the current collector and the electrode composite to be separated with high accuracy. Furthermore, the separation method and separation device described above utilize a physical action utilizing the cavitation effect of ultrasound, thereby enabling the current collector and the electrode composite to be separated using water, regardless of whether the binder contained in the electrode composite is aqueous or organic. In addition, because treated water is used, the treatment liquid is relatively inexpensive, the treatment liquid is easily removed from the separated current collector and electrode composite, waste liquid treatment is easy, and the environmental impact is small. Furthermore, because the current collector and electrode composite can be separated efficiently, the current collector and electrode composite can be separated with high precision even at high frequencies (low energy) such as 40 to 240 kHz (preferably 80 to 200 kHz), even when the electrode to be treated is relatively large, and even in a non-heated environment.

[0036] Furthermore, immersing an electrode in treated water can cause ions to elute from the electrode, which can change the pH of the treated water and alter the electrode components. However, the use of a buffer solution suppresses pH changes in the treated water, allowing separation even if the electrode is left immersed in the treated water for a longer waiting time. Therefore, even in large separation equipment, where there is a predetermined waiting time between immersion of the electrode and the start of ultrasonic treatment, the current collector and electrode composite can be separated stably and with high precision.

[0037] It goes without saying that the present disclosure is not limited to the above-described embodiments, and can be embodied in various forms as long as they fall within the technical scope of the present disclosure.

[0038] For example, in the above-described embodiment, the separation device 10 performs ultrasonic treatment in a batch manner, but may also perform ultrasonic treatment in a continuous manner.

[0039] The present disclosure may be any of the following [1] to [7]. [1] A method for manufacturing a semiconductor device comprising: a separation step of immersing a target electrode having a current collector and an electrode composite formed on the current collector in treatment water that is a buffer solution; and performing ultrasonic treatment while sweeping the frequency of ultrasonic waves to separate the current collector from the electrode composite; In the separation step, the closer the pH of the treated water is to a neutral range, the longer the waiting time for immersing the electrode to be treated in the treated water before the ultrasonic treatment can be for separation. Separation method. [2] The separation method according to [1], wherein the separation step uses any one or more of the treated waters (1) to (3). (1) The treated water, which is a buffer solution during preparation, has a pH in the range of 2.2 to 8.6. (2) The treatment water, which is a buffer solution when the electrode to be treated is immersed, has a pH in the range of 2.4 to 8.8. (3) The treated water, which is a buffer solution in which the electrode to be treated is immersed and which has been subjected to the ultrasonic treatment, has a pH in the range of 2.6 to 9.0. [3] The separation method according to [1] or [2], wherein the treated water is a buffer solution containing one or more of carboxylic acid, phosphoric acid, and carbonic acid. [4] The separation method according to any one of [1] to [3], wherein the treated water is a buffer solution that does not contain halogen compounds. [5] The separation method according to any one of claims [1] to [4], wherein the separation step is carried out under one or more of the conditions (4) to (7). (4) A citrate buffer solution having a pH of 3 or higher is used as the treatment water, and the waiting time is set to 30 minutes or less for the citrate buffer solution having a pH of less than 4, and set to 60 minutes or less for the citrate buffer solution having a pH of 4 or higher. (5) An acetate buffer solution having a pH of 4 or higher is used as the treated water, and the waiting time is 60 minutes or less. (6) A phosphate buffer solution with a pH of 6 or higher is used as the treated water, and the waiting time is 60 minutes or less. (7) A carbonate / bicarbonate buffer solution having a pH of 9 or less is used as the treated water, and the waiting time is 10 minutes or less for the carbonate / bicarbonate buffer solution having a pH of over 8, and 60 minutes or less for the carbonate / bicarbonate buffer solution having a pH of 8 or less. [6] The separation method according to any one of [1] to [5], wherein the separation step is carried out under one or more of the conditions (8) to (15). (8) In the separation step, the sweep is performed centered on a fundamental frequency of 80 kHz or more and 200 kHz or less. (9) In the separation step, the sweep is performed with a sweep width within ±3 kHz centered on the fundamental frequency. (10) In the separation step, the sweep is performed at a sweep rate of 500 sweep cycles / second or more. (11) In the separation step, the ultrasonic treatment is carried out for a period of 10 minutes or less. (12) In the separation step, the contact area between the current collector and the electrode mixture is A [cm 2 ], and the output of the ultrasonic wave is B [W], the output density expressed as B / A is 10 W / cm 2 The ultrasonic treatment is carried out as follows. (13) In the separation step, the removal rate of the electrode mixture removed 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. (14) In the separation step, the ultrasonic treatment is carried out in a non-heated environment. (15) In the separation step, the ultrasonic treatment is carried out in a batch or continuous manner. [7] A separation unit that immerses a treatment target electrode having a current collector and an electrode composite formed on the current collector in treatment water that is a buffer solution, performs ultrasonic treatment, and separates the current collector from the electrode composite; a control unit that controls the separation unit so that the closer the pH of the treatment water is to a neutral range, the longer the waiting time during which the electrode to be treated is immersed in the treatment water before the ultrasonic treatment is performed, and starts the ultrasonic treatment within the waiting time and performs the ultrasonic treatment while sweeping the frequency of the ultrasonic waves; A separation device comprising: [Example]

[0040] Examples of carrying out the separation method of the present disclosure are described below. Experimental Examples 1 to 28 and 35 to 37 correspond to Examples, Experimental Examples 29 to 34 correspond to Comparative Examples, and Experimental Examples 38 and 39 correspond to Reference Examples. First, ultrasonic treatment was performed using pure water, and the optimum separation conditions were examined as Reference Examples.

[0041] [Preparing the electrode to be treated] As electrodes to be treated, the following positive electrodes A to C and negative electrodes A to B were prepared (see Table 1).

[0042] Positive electrode A is LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 A positive electrode composite containing 92 mass% O2 (NCM, manufactured by Toda Kogyo Kogyo Co., Ltd.), 5 mass% acetylene black (manufactured by Denka Co., Ltd.), and 3 mass% polyvinylidene fluoride (PVDF, manufactured by Kureha) was made into a paste using N-methylpyrrolidone (NMP), and this paste was applied to both sides of a 20 μm thick aluminum current collector foil.

[0043] Positive electrode B is LiNi 0.8 Co 0.15 Al 0.05 A positive electrode composite containing 92 mass% O2 (NCA, manufactured by Toda Kogyo Kogyo Co., Ltd.), 5 mass% acetylene black (manufactured by Denka Co., Ltd.), and 3 mass% polyvinylidene fluoride (PVDF, manufactured by Kureha) was made into a paste using NMP and coated on both sides of a 20 μm thick aluminum current collector foil.

[0044] Positive electrode C was prepared by forming a paste of a positive electrode composite containing 92 mass% LiFePO4 (a proprietary compound), 5 mass% acetylene black (manufactured by Denka Co., Ltd.), and 3 mass% polyvinylidene fluoride (PVDF, manufactured by Kureha) using NMP, and applying the paste to both sides of a 20 μm-thick aluminum current collector foil.

[0045] Negative electrode A was prepared by mixing a negative electrode composite containing 98% by mass of graphite (OMAC1.5s, manufactured by Osaka Gas Chemicals), 1% by mass of carboxymethyl cellulose (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 applied to both sides of a 10 μm-thick copper current collector foil.

[0046] Negative electrode B was prepared by mixing a negative electrode composite containing 98% by mass of graphite (SCMG-XR-s, manufactured by Showa Denko), 1% by mass of carboxymethyl cellulose (CMC, manufactured by Daicel), and 1% by mass of styrene-butadiene copolymer (SBR, manufactured by JSR) in water to form a paste, which was then applied to both sides of a 10 μm-thick copper current collector foil.

[0047] [Ultrasonic treatment] An ultrasonic device (Branson GCX-M-3FQ12, output power 500 W, outer tank capacity 20 L) was used for the ultrasonic treatments in Reference Examples 1 to 19. Specifically, as shown in Figures 3 and 4, water was placed in outer tank 26, 40 mL of treatment water 32 was placed in glass container (inner tank 24), and electrode 50 to be treated was immersed therein, and ultrasonic waves were applied from transducer 28 below 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 power (500 W) of the ultrasonic device by the contact area between the current collecting foil and the electrode composite layer (here, electrode area × 2). The power density was adjusted by adjusting the electrode area.

[0048] In Reference Example 1, a 40 mm × 100 mm positive electrode A was used as the electrode to be treated. The treatment liquid was water, the ultrasonic frequency (fundamental frequency F0) was 170 kHz, the sweep conditions (sweep width) were ±1 kHz, the treatment time was 60 seconds, and the power density was 6.3 W / cm. 2 It was decided.

[0049] In Reference Example 2, a 40 mm × 100 mm negative electrode A was used as the electrode to be treated. The treatment liquid was water, the ultrasonic frequency was 170 kHz, the sweep conditions were ±1 kHz, the treatment time was 30 seconds, and the power density was 6.3 W / cm. 2 It was decided.

[0050] Reference Example 3 was the same as Reference Example 1 except that the ultrasonic frequency was 120 kHz. Reference Example 4 was the same as Reference Example 3 except that the treatment time was 30 seconds. Reference Example 5 was the same as Reference Example 3 except that the electrode size was 40 mm × 200 mm, and the power density was 3.1 W / cm. 2 Reference Example 6 was the same as Reference Example 3 except that the electrode to be treated was positive electrode B. Reference Example 7 was the same as Reference Example 3 except that the electrode to be treated was positive electrode C.

[0051] Reference Example 8 was the same as Reference Example 2 except that the ultrasonic frequency was 120 kHz. Reference Example 9 was the same as Reference Example 8 except that the treatment time was 10 seconds. Reference Example 10 was the same as Reference Example 8 except that the electrode size was 40 mm × 200 m, and the power density was 3.1 W / cm2 In Reference Example 11, the treatment time was set to 60 seconds, and the electrode size was set to 40 mm × 715 mm, so that the power density was 0.9 W / cm 2 In Reference Example 12, the same procedures as in Reference Example 8 were carried out except that the electrode to be treated was negative electrode B.

[0052] Reference Example 13 was the same as Reference Example 1 except that the ultrasonic frequency was 80 kHz. Reference Example 14 was the same as Reference Example 2 except that the ultrasonic frequency was 80 kHz.

[0053] Reference Example 15 was the same as Reference Example 3 except that the sweep condition was changed to no sweep. Reference Example 16 was the same as Reference Example 8 except that the sweep condition was changed to no sweep.

[0054] Reference Example 17 was the same as Reference Example 3 except that the treatment liquid was NMP. Reference Example 18 was the same as Reference Example 17 except that the ultrasonic frequency was 40 kHz and the treatment time was 30 seconds.

[0055] Reference Example 19 was the same as Reference Example 1 except that the ultrasonic frequency was 40 kHz.

[0056] [Analysis of the ratio of current collecting foil components in the composite] For Reference Examples 1 to 19, the proportion of the current collecting foil component in the composite was determined using inductively coupled plasma optical emission spectroscopy (ICP-OES, Hitachi High-Tech Science PS3520UVDDII II). Specifically, first, the solution containing the composite powder after ultrasonic treatment (composite-containing treatment solution) was pressure filtered using a membrane filter (Merck Millpore JGWP 0.45 μm) while washing with pure water, and then dried at 50°C for 1 hour to obtain a composite powder. The mass of the current collecting foil component (aluminum or copper) in the composite powder was analyzed using ICP to determine the mass ratio of the current collecting foil component to the total mass of the composite powder. This was defined as the proportion of the current collecting foil component in the composite. A content of less than 0.1% was evaluated as "A (Excellent)," 0.1% to less than 0.18% as "B (Good)," and 0.18% or more as "F (Unacceptable)."

[0057] [Analysis of the proportion of composite components in current collecting foil] For Reference Examples 1, 3 to 7, 13, 15, and 17 to 19 (positive electrodes), the proportions of the composite components in the current collecting foil were determined by inductively coupled plasma optical emission spectroscopy (ICP-OES). Specifically, the electrodes were first removed from the ultrasonic treatment, rinsed with water, and then air-dried. For these electrodes, the masses of the composite components (transition metal components in the composite; Ni, Co, and Mn for positive electrode A) were determined by ICP-OES, and the mass ratios of the composite components to the total electrode mass were calculated. These were used as the proportions of the composite components in the current collecting foil. For Reference Examples 2, 8 to 12, 14, and 16 (negative electrodes), the proportions of the composite components in the current collecting foil were determined by the fundamental parameter method (FP method) of X-ray fluorescence analysis (XRF). Specifically, the electrodes were first removed from the ultrasonic treatment, rinsed with water, and then air-dried. For these electrodes, the carbon content (mass ratio) was calculated within a φ30 mm analysis range by the FP method of XRF. In the XRF FP method, the quantitative value is calculated by normalizing all detected elements to 100%. The amount of C on one side and in the surface layer is also calibrated. The amount of C determined in this way was used as the percentage of the composite component in the current collector foil. Less than 0.2% was then rated as "A (Excellent)," 0.2% to 0.36% as "B (Good)," and 0.36% or more as "F (Fail)."

[0058] [Results and Discussion] The proportions of the current collecting foil components in the composite and the proportions of the composite components in the current collecting foil for Reference Examples 1 to 19 are summarized in Table 2. Photographs of the appearance of the electrodes (current collecting foils) after ultrasonic treatment for Reference Examples 8, 16, 3, and 15 are shown in Fig. 5. Photographs of the appearance of the electrode (current collecting foil) after ultrasonic treatment for Reference Example 11 are shown in Fig. 6.

[0059] As shown in Table 2, in Reference Examples 1 to 14 and Reference Example 19, in which water was used as the treatment liquid and ultrasonic treatment was performed using the sweep function, the ratio of the current collecting foil components in the composite and the ratio of the composite components in the current collecting foil were both evaluated as A or B, demonstrating that the composite and the current collecting foil can be separated with high precision. Furthermore, it was found that the composite and the current collecting foil can be separated with high precision by ultrasonic treatment for a short time of 60 seconds or less. Furthermore, at 6.3 W / cm 2It was found that the composite and current collecting foil could be separated with high precision at the following low power density: Furthermore, although the binder for the positive electrode (PVDF) is organic and the binder for the negative electrode (SBR) is water-based, it was found that the composite and current collecting foil could be separated with high precision using ultrasonic treatment with water regardless of which binder was used.

[0060] In contrast to this, in Reference Examples 15 and 16 in which water was used as the treatment liquid and ultrasonic treatment was performed without using the sweep function, a large amount of the composite material remained on the current collecting foil.

[0061] Furthermore, in Reference Examples 17 and 18, in which NMP was used as the treatment solution and ultrasonic treatment was performed using the sweep function, a large amount of composite material remained on the current collecting foil. Because organic binders dissolve in NMP, it was expected that more composite material would be removed in Reference Examples 17 and 18, which used NMP as the treatment solution, than in Reference Examples 3 and 19, which used water as the treatment solution. However, in reality, more composite material was removed when the treatment solution was water. This is presumed to be due to the weak cavitation effect of ultrasound when NMP was used. Furthermore, among Reference Examples 17 and 18, Reference Example 18, in which the ultrasonic frequency was 40 kHz, not only increased the proportion of composite material components in the current collecting foil, but also increased the proportion of current collecting foil components in the composite, resulting in greater damage to the current collecting foil. In Reference Example 19, the ultrasonic frequency was also 40 kHz, but damage to the current collecting foil was suppressed compared to Reference Example 18, possibly due to the water treatment solution.

[0062] From the above, it was found that by using water as the treatment liquid and performing ultrasonic treatment using the sweep function, the current collector and the electrode mixture can be separated efficiently and with high precision.

[0063] [Table 1]

[0064] [Table 2]

[0065] Here, prior to the ultrasonic separation, the elution of components from the current collector was confirmed when the waiting time for immersing the electrode, particularly the positive electrode, in water was prolonged (see Table 4 below). This is because immersing the positive electrode in water causes the water to become alkaline due to the elution of Li contained in the positive electrode active material. It is presumed that the change to alkaline water causes the aluminum from the current collector to elute into the aqueous solution, resulting in the formation of a compound between the composite and the aluminum, or that the PVdF binder is altered by the alkali, inhibiting separation and causing the composite to remain on the Al foil. In this example, a method for separating the positive electrode current collector (Al) and the positive electrode composite by ultrasonic treatment was investigated, in which the effect of eluted components was further reduced by using a buffer solution for the treated water, enabling stable separation regardless of the waiting time for immersion in the treated water. Figure 7 is a flowchart showing an example of the separation method used in this example. The treated water, positive electrode material, ultrasonic treatment, and analysis were performed under the following conditions.

[0066] [Treated water] (1) Pure water: pH=6 (2) Citrate buffer: pH = 3, 4, 5, 6 The buffer solution was prepared by weighing out predetermined amounts of anhydrous citric acid and trisodium citrate dihydrate and mixing them with pure water. (3) Acetate buffer: pH=4,5 The buffer solution was prepared by weighing predetermined amounts of acetic acid and sodium acetate trihydrate and mixing them with pure water. (4) Phosphate buffer solution: pH = 6, 7, 8 The buffer solution was prepared by weighing out predetermined amounts of disodium hydrogen phosphate dodecahydrate and sodium dihydrogen phosphate dihydrate and mixing them with purified water. (5) Carbonate / bicarbonate buffer solution: pH = 8, 9, 10 The buffer solution was prepared by weighing out predetermined amounts of sodium carbonate and sodium bicarbonate and mixing them with pure water. (6) Tris-HCl buffer: pH = 7, 8, 9 The buffer solution was prepared by weighing out predetermined amounts of tris(2-amino-2-hydroxymethyl-1,3-propanediol) and hydrochloric acid and mixing them with pure water.

[0067] [Cathode material] The current collector foil was made of 20 μm thick Al foil. The electrode mixture layer contained LiNi as the positive electrode active material. 1 / 3 Co 1 / 3 Mn 1 / 3 The positive electrode was prepared by mixing O2 (NCM: manufactured by Toda Kogyo Co., Ltd.), acetylene black (manufactured by Denka Co., Ltd.) as a conductive material, and polyvinylidene fluoride (PVdF: manufactured by Kureha) as a binder in a mass ratio of 92:5:3. The electrode mixture layer was coated on both sides of a current collector foil and used as the positive electrode. The mass ratio of the mixture in the positive electrode was 74 mass%.

[0068] [Ultrasonic treatment] Using an ultrasonic device (Branson GCX-M-3FQ12, output 500W, outer tank capacity 20L), water was placed in the cleaning tank (outer tank), 50mL of treatment water was placed in the glass container of the inner tank, and a positive electrode with an area of ​​40mm x 100mm was placed in it and immersed for a predetermined waiting time. Then, ultrasonic waves were applied from the vibrator under the outer tank. The ultrasonic treatment conditions were a frequency of 120 The treatment was performed at 1000 cycles / second, with a sweep width of ±1 kHz and a frequency of 1 kHz. The treatment time was 60 seconds. The pH of the treated water, the mass of the positive electrode, and ICP analysis were performed at the timings shown in Figure 7.

[0069] [analysis] The amount of dissolved Al per mass of the positive electrode current collector and the proportion of Al in the positive electrode composite powder were determined by inductively coupled plasma optical emission spectroscopy (ICP-OES) using an inductively coupled plasma optical emission spectroscopy analyzer (ICP-OES, Hitachi High-Tech Science PS3520UVDDII II) in the same manner as in the above Reference Example.

[0070] (Results and Discussion) Table 3 summarizes the composition of the treated water for each of Experimental Examples 1 to 28, the immersion waiting time, the pH during immersion preparation, after the electrode immersion and waiting time, and after ultrasonic treatment, as well as the composite removal rate (%), the amount of dissolved Al per current collector (mass%), and the percentage of Al in the composite powder (mass%). Similarly, Table 4 summarizes Experimental Examples 29 to 39. The composite removal rate is the percentage calculated by dividing the mass loss rate after ultrasonic treatment by the mass percentage of the composite (74%). If the Al foil is damaged and its mass decreases, this amount is also included in the composite removal rate. The composite removal rate was evaluated as follows: 99% or more: A; 97% to less than 99%: B; 90% to less than 97%: C; 80% to less than 90%: D; and less than 80%: F. Damage to the current collector was evaluated as "damaged" if holes or chips were observed visually in the foil, and "no damage" if no holes or chips were observed. In Tables 3 and 4, the "immediately after" immersion waiting time indicates that ultrasonic waves were applied immediately after the positive electrode was immersed. In this case, the pH after immersion of the positive electrode was measured by separately immersing a positive electrode of the same size as the positive electrode to be treated with ultrasonic waves.

[0071] Figure 8 shows photographs of the appearance of electrodes immersed in each buffer solution for 30 minutes and then ultrasonically treated. Figure 9 shows photographs of the appearance of electrodes immersed in each buffer solution for 60 minutes and then ultrasonically treated. Figure 10 shows the relationship between the waiting time of the positive electrode immersion in carbonate / bicarbonate and the electrode appearance after ultrasonic treatment. As shown in Table 4, when using pure water (Experimental Examples 38 and 39), the longer the waiting time, the more Al in the current collector component was eluted, and the peelability of the composite tended to decrease. In contrast, as shown in Table 3 and Figures 8 and 9, when using citrate buffer solutions with pH values ​​of 3, 4, 5, and 6 (Experimental Examples 1 to 8), acetate buffer solutions with pH values ​​of 4 and 5 (Experimental Examples 9 to 13), phosphate buffer solutions with pH values ​​of 6, 7, and 8 (Experimental Examples 14 to 19), and carbonate / bicarbonate buffer solutions with pH values ​​of 8 (Experimental Examples 20 to 28), the composite removal rate was 99% by mass or more, and the positive electrode composite was successfully peeled off for both 30 and 60 minutes. Furthermore, as shown in FIG. 10, with a carbonate / bicarbonate buffer solution of pH 9, the positive electrode mixture could be peeled off with a mixture removal rate of 99 mass % or more up to a waiting time of 10 minutes.

[0072] FIG. 11 is a graph showing the relationship between the pH of the buffer solution during preparation and the composite removal rate when the waiting time is 30 minutes and 60 minutes. FIG. 12 is a graph showing the relationship between the pH of the buffer solution during immersion of the positive electrode and the composite removal rate when the waiting time is 30 minutes and 60 minutes. FIG. 13 is a graph showing the relationship between the pH of the buffer solution after ultrasonic treatment and the composite removal rate when the waiting time is 30 minutes and 60 minutes. FIG. 14 is a graph showing the relationship between the waiting time during immersion of the electrode in carbonated / bicarbonate water and the composite removal rate. As shown in FIGS. 11 to 13, when the treated water during preparation had a pH range of 2.2 to 8.6, the treated water during positive electrode immersion had a pH range of 2.4 to 8.8, and the treated water after ultrasonic treatment had a pH range of 2.6 to 9.0, the positive electrode composite was successfully removed with a composite removal rate of 99% by mass or more. On the other hand, when ultrasonic treatment was performed with a pH 3 citrate buffer solution for a waiting time of 60 minutes, the composite removal rate was 99% or more by mass, and the positive electrode composite could be peeled off, but holes and chips were observed in the Al foil of the current collector. Therefore, when using a citrate buffer solution with a pH of 3, it is inferred that the waiting time for immersing the positive electrode in the treatment water should be less than 60 minutes, and particularly 30 minutes or less. Furthermore, as shown in Tables 3 and 4, under conditions where the composite removal rate was 99% or more by mass and peeling was possible, the amount of dissolved Al per current collector was 0.1% by mass or less, and the amount of Al in the composite powder was 0.1% by mass or less.

[0073] Furthermore, as shown in Table 4, with a pH 9 carbonate / bicarbonate buffer solution, the composite removal rate was less than 99% by mass when the waiting time was 15 to 60 minutes, meaning that peeling was possible but not complete. With a pH 10 carbonate / bicarbonate buffer solution, the composite removal rate was less than 99% by mass for both 30 and 60 minutes of waiting time, meaning that peeling was possible but not complete. With Tris-HCl buffer solutions of pH 7, 8, and 9, the composite removal rate was less than 99% by mass, meaning that peeling was possible but not complete, and furthermore, the Al foil was pitted by chloride ions. As shown in Table 4, when the composite removal rate was 90% by mass or less and peeling was not complete, the amount of Al dissolved per current collector was 0.1% by mass or more, and the Al content in the composite powder was 0.1% by mass or more.

[0074] As described above, it was found that the waiting time could be extended longer with either buffer solution than with pure water. Furthermore, it was found that the type of buffer solution used and the pH range during preparation and immersion affected the lengthening of the waiting time, and the effect on the current collector also varied. Specifically, when a citrate buffer solution with a pH of 3 or higher was used as the treatment water, it was inferred that a waiting time of 30 minutes or less was preferable for a citrate buffer solution with a pH of less than 4, and a waiting time of 60 minutes or less was preferable for a citrate buffer solution with a pH of 4 or higher. Furthermore, it was inferred that a waiting time of 60 minutes or less was preferable for an acetate buffer solution with a pH of 4 or higher. Furthermore, it was inferred that a waiting time of 60 minutes or less was preferable for a phosphate buffer solution with a pH of 6 or higher. Furthermore, when a carbonate / bicarbonate buffer solution with a pH of 9 or lower was used as the treatment water, it was inferred that a waiting time of 10 minutes or less was preferable for a carbonate / bicarbonate buffer solution with a pH of over 8, and a waiting time of 60 minutes or less was preferable for a carbonate / bicarbonate buffer solution with a pH of 8 or lower. Furthermore, it was inferred that a waiting time of 10 minutes or less was preferable for a carbonate buffer solution with a pH of 9 or lower. It was also inferred that when a Tris-HCl buffer solution with a pH of 9 or less is used as the treatment water, the waiting time should preferably be 10 minutes or less. It was also inferred that the buffer solution should preferably contain one or more of carboxylic acid, phosphoric acid, and carbonic acid, and should preferably be free of halogen compounds.

[0075] [Table 3]

[0076] [Table 4] [Industrial Applicability]

[0077] The present disclosure is applicable to the field of the battery industry. [Explanation of symbols]

[0078] 10 Separation device, 15 Control unit, 20 Separation unit, 22 Treatment container, 24 Inner tank, 25 Mounting table, 26 Outer tank, 28 Vibrator, 29 pH detection unit, 30 Oscillator, 32 Treated water, 33 Treated water containing composite, 36 Ultrasonic propagation medium, 50 Electrode to be treated, 52 Current collector, 54 Electrode composite.

Claims

1. a separation step of immersing a treatment target electrode, which includes a current collector and an electrode composite formed on the current collector, in treatment water that is a buffer solution, and performing ultrasonic treatment while sweeping the frequency of ultrasonic waves to separate the current collector from the electrode composite; In the separation step, the closer the pH of the treated water is to a neutral range, the longer the waiting time for immersing the electrode to be treated in the treated water before the ultrasonic treatment can be for separation. Separation method.

2. The separation method according to claim 1, wherein the separation step uses one or more of the treated waters (1) to (3). (1) The pH of the treated water, which is a buffer solution during preparation, is in the range of 2.2 to 8.

6. (2) The treatment water, which is a buffer solution when the electrode to be treated is immersed, has a pH in the range of 2.4 to 8.

8. (3) The treated water, which is a buffer solution in which the electrode to be treated is immersed and which has been subjected to the ultrasonic treatment, has a pH in the range of 2.6 to 9.

0.

3. 3. The separation method according to claim 1, wherein the treated water is a buffer solution containing one or more of carboxylic acid, phosphoric acid, and carbonic acid.

4. 3. The separation method according to claim 1, wherein the treated water is a buffer solution that does not contain halogen compounds.

5. The separation method according to claim 1 or 2, wherein the separation step is carried out under any one or more conditions of (4) to (7). (4) A citrate buffer solution having a pH of 3 or higher is used as the treatment water, and the waiting time is set to 30 minutes or less for the citrate buffer solution having a pH of less than 4, and set to 60 minutes or less for the citrate buffer solution having a pH of 4 or higher. (5) An acetate buffer solution having a pH of 4 or higher is used as the treatment water, and the waiting time is 60 minutes or less. (6) A phosphate buffer solution having a pH of 6 or higher is used as the treatment water, and the waiting time is 60 minutes or less. (7) A carbonate / bicarbonate buffer solution having a pH of 9 or less is used as the treatment water, and the waiting time is set to 10 minutes or less for the carbonate / bicarbonate buffer solution having a pH of over 8, and set to 60 minutes or less for the carbonate / bicarbonate buffer solution having a pH of 8 or less.

6. The separation method according to claim 1 or 2, wherein the separation step is carried out under any one or more conditions of (8) to (15). (8) In the separation step, the sweep is performed centered on a fundamental frequency of 80 kHz or more and 200 kHz or less. (9) In the separation step, the sweep is performed with a sweep width within ±3 kHz centered on the fundamental frequency. (10) In the separation step, the sweep is performed at a sweep rate of 500 sweep cycles / second or more. (11) In the separation step, the ultrasonic treatment is carried out for 10 minutes or less. (12) In the separation step, the contact area between the current collector and the electrode mixture is A [cm 2 ], and the output of the ultrasonic wave is B [W], the output density expressed by B / A is 10 W / cm 2 The ultrasonic treatment is carried out as follows. (13) 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 mass%. (14) In the separation step, the ultrasonic treatment is performed in a non-heated environment. (15) In the separation step, the ultrasonic treatment is carried out in a batch or continuous manner.

7. a separation unit that immerses a target electrode, which includes a current collector and an electrode composite formed on the current collector, in treatment water that is a buffer solution and performs ultrasonic treatment to separate the current collector from the electrode composite; a control unit that controls the separation unit so that the closer the pH of the treatment water is to a neutral range, the longer the waiting time during which the electrode to be treated is immersed in the treatment water before the ultrasonic treatment is performed, and the ultrasonic treatment is started within the waiting time, and the ultrasonic treatment is performed while sweeping the frequency of the ultrasonic waves; A separation device comprising:

Images