Manufacturing method of recycled positive electrode

Abstract

To provide a manufacturing method for a regenerated positive electrode capable of recovering resistance increase due to reduced adhesion of positive electrode active material particles, etc., and recovering capacity reduction due to lithium depletion in a positive electrode.SOLUTION: A manufacturing method for a regenerated positive electrode in a used lithium-ion secondary battery including a laminate having a positive electrode, either a separator or a solid electrolyte layer, and a negative electrode, includes extracting the positive electrode from the laminate, pressing the extracted positive electrode, and doping lithium ions into the pressed positive electrode. The doping of lithium ions is performed by discharging in an electrolyte solution using a lithium electrode as a counter electrode.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method for producing a recycled positive electrode. [Background technology]

[0002] In recent years, research and development has been conducted into the reuse of lithium-ion secondary batteries, which contribute to energy efficiency, in order to ensure that more people have access to affordable, reliable, sustainable and advanced energy.

[0003] For example, Patent Document 1 discloses a method for regenerating electrodes of a lithium ion battery, which includes the steps of treating at least one of the positive and negative electrodes of a used lithium ion secondary battery with a polar solvent, drying the solvent-treated electrode, and re-injecting the liquid into a battery having the dried electrode. For example, Patent Document 2 discloses a method for recycling a negative electrode plate for a non-aqueous electrolyte secondary battery, which comprises removing the negative electrode plate from a non-aqueous electrolyte secondary battery using a carbon material as the negative electrode active material, washing the plate with a liquid containing water, drying the plate, and then recycling the plate. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-022969 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-228510 Summary of the Invention [Problem to be solved by the invention]

[0005] However, while the technology for recycling secondary batteries such as that disclosed in Patent Document 1 can remove deteriorated surface materials of the positive electrode active material of the positive electrode, it cannot recover the increased resistance caused by the decrease in adhesion of particles of the positive electrode active material, or the reduced capacity caused by the reduction in lithium in the positive electrode. Patent Document 2 does not disclose a method for recycling the positive electrode.

[0006] In order to solve the above problems, the present application aims to recover the increase in resistance caused by a decrease in the adhesion of particles of a positive electrode active material, or to recover the decrease in capacity caused by a decrease in lithium in the positive electrode. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention has the following aspects. [1] A method for manufacturing a recycled positive electrode for a used lithium-ion secondary battery comprising a laminate having a positive electrode, either a separator or a solid electrolyte layer, and a negative electrode, the method comprising: removing the positive electrode from the laminate; pressing the removed positive electrode; and doping the pressed positive electrode with lithium ions, wherein the doping of the lithium ions is performed by discharging in an electrolyte solution using a lithium electrode as a counter electrode.

[0008] According to the above-described embodiment, pressing the positive electrode makes it possible to recover the increased resistance due to the decrease in adhesion of the positive electrode active material particles, and doping the pressed positive electrode with lithium ions makes it possible to recover the capacity loss due to the decrease in lithium in the positive electrode. Furthermore, by performing the pressing of the positive electrode and the doping with lithium ions in this order, the doping of the lithium ions becomes uniform. Furthermore, the recycled positive electrode can be produced more efficiently.

[0009] [2] The method for producing a recycled positive electrode according to [1], which includes washing the positive electrode with an organic solvent before pressing it.

[0010] According to the above aspect, by washing the positive electrode with an organic solvent, it is possible to recover from the increase in resistance caused by the lithium-containing thin film formed on the positive electrode.

[0011] [3] The method for producing a recycled positive electrode according to [1] or [2], wherein the laminate removed from the lithium ion secondary battery is washed with an organic solvent, and the positive electrode is removed from the laminate washed with the organic solvent.

[0012] According to the above-described embodiment, cleaning with an organic solvent can be carried out using small-sized equipment, and the amount of organic solvent used or the amount of waste liquid can be reduced, making it possible to carry out the cleaning more efficiently and economically.

[0013] [4] The method for producing a recycled positive electrode according to any one of [1] to [3], wherein the positive electrode is pressed so that the thickness of the positive electrode after pressing is 85 to 100% of the thickness of the positive electrode before use.

[0014] According to the above embodiment, the effect of recovering the resistance increase caused by the decrease in adhesion of the particles of the positive electrode active material is further enhanced.

[0015] [5] The method for producing a regenerated positive electrode according to any one of [1] to [4], wherein the laminate is wound.

[0016] According to the above aspect, the recovery effect in the other aspects can be maximized. [Effects of the Invention]

[0017] According to the above-described aspects of the present invention, it is possible to recover from an increase in resistance due to a decrease in adhesion of particles of a positive electrode active material, or to recover from a decrease in capacity due to a decrease in lithium in the positive electrode.Furthermore, it is possible to reuse secondary batteries more efficiently. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a schematic cross-sectional view showing an example of a layer structure of a laminate in a lithium ion secondary battery according to one embodiment of the present invention. [Figure 2] FIG. 4 is a schematic cross-sectional view showing an example of a layer structure of a laminate in a lithium ion secondary battery according to another embodiment of the present invention. [Figure 3] 1 is a flowchart of a method for manufacturing a regenerative positive electrode according to a first embodiment of the present invention. [Figure 4] 10 is a flowchart of a method for producing a regenerated positive electrode according to another first embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] The following describes in detail the embodiments of the present invention. However, the following description is an example of an embodiment of the present invention, and the present invention is not limited to these contents and can be modified and implemented within the scope of its gist.

[0020] The method for manufacturing a recycled positive electrode of this embodiment is a method for manufacturing a recycled positive electrode in a lithium ion secondary battery including a laminate having a positive electrode, either a separator or a solid electrolyte layer, and a negative electrode. That is, the lithium ion secondary battery of this embodiment includes a lithium ion secondary battery with a liquid electrolyte (hereinafter also referred to as a "liquid electrolyte lithium ion secondary battery") and a lithium ion secondary battery with a solid electrolyte (hereinafter also referred to as an "all-solid-state lithium ion secondary battery").

[0021] The method for producing a recycled positive electrode includes removing the positive electrode from the laminate, pressing the removed positive electrode (hereinafter also referred to as "pressing treatment"), and doping the pressed positive electrode with lithium ions (hereinafter also referred to as "lithium ion doping treatment"). The doping of lithium ions is performed by discharging in an electrolyte using a lithium electrode as a counter electrode.

[0022] <Lithium-ion secondary battery> FIG. 1 is a schematic cross-sectional view showing an example of the layer structure of a laminate in a lithium ion secondary battery (liquid electrolyte lithium ion secondary battery) according to one embodiment.

[0023] A lithium-ion battery 10 (LIB) includes a positive electrode 13, a separator 17, and a negative electrode 16 stacked in this order. The positive electrode 13 includes a positive electrode current collector 11 and a positive electrode active material layer 12 provided on the surface of the positive electrode current collector 11. While the positive electrode active material layer 12 is shown on only one side of the positive electrode current collector 11 in FIG. 1, it may be provided on both sides. The negative electrode 13 includes a negative electrode current collector 14 and a negative electrode active material layer 15 provided on the surface of the negative electrode current collector 14. Although the negative electrode active material layer 15 is shown on only one side of the negative electrode current collector 14 in FIG. 1, it may be provided on both sides. Although only one positive electrode 13 and one negative electrode 16 are included in FIG. 1, an electrode group in which multiple positive electrodes 13 and multiple negative electrodes 16 are alternately stacked may also be used. In this case, a separator 17 is provided between the positive electrode 13 and the negative electrode 16.

[0024] FIG. 2 is a schematic cross-sectional view showing an example of the layer structure of a laminate in a lithium ion secondary battery (all-solid-state lithium ion secondary battery) according to another embodiment.

[0025] The lithium-ion battery 20 (LIB) includes a positive electrode 23, an electrolyte layer 27, and a negative electrode 26 stacked in this order. The positive electrode 23 includes a positive electrode current collector 21 and a positive electrode active material layer 22 provided on the surface of the positive electrode current collector 21. While the positive electrode active material layer 22 is provided on only one surface of the positive electrode current collector 21 in FIG. 2, it may be provided on both surfaces. The negative electrode 26 includes a negative electrode current collector 24 and a negative electrode active material layer 25 provided on the surface of the negative electrode current collector 24. Although the negative electrode active material layer 25 is provided on only one surface of the negative electrode current collector 24 in FIG. 1, it may be provided on both surfaces. Although only one positive electrode 23 and one negative electrode 26 are included in FIG. 2, it may be an electrode group in which multiple positive electrodes 23 and multiple negative electrodes 26 are alternately stacked. In this case, an electrolyte layer 27 is also provided between the positive electrode and the negative electrode.

[0026] (Cathode active material layer) The positive electrode active material layer 12 (22) contains a positive electrode active material, a conductive additive, and a binder. Note that, if the positive electrode active material has conductivity, the positive electrode active material layer does not need to contain the conductive additive.

[0027] The positive electrode active material is not particularly limited as long as it can absorb and release lithium ions. Examples of the positive electrode active material include lithium nickel oxide (e.g., LiNiO2), lithium cobalt oxide (e.g., LiCoO2), lithium nickel cobalt oxide, lithium nickel cobalt manganese oxide, LiFePO4, LiMn 1-x Fe x PO4, LiMnPO4, LiCoPO4, LiNiPO4, etc. The positive electrode active material preferably contains one or more elements selected from the group consisting of manganese, nickel, and cobalt.

[0028] The conductive additive assists in forming a conductive path between the positive electrode active material and the positive electrode current collector 11 (21). The conductive additive is not particularly limited as long as it has conductivity, and examples thereof include carbon black such as acetylene black, carbon nanotubes, and graphite such as artificial graphite.

[0029] The binder binds the positive electrode active material, the conductive additive, and the positive electrode current collector 11 (21), respectively. Examples of binders include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyamide (PA), polyimide (PI), polyacrylic acid and its copolymers, polyamideimide (PAI), polybenzimidazole, polyethersulfone (PES), maleic anhydride-modified polypropylene, and mixtures thereof. The binder preferably contains a crystalline polymer having a melting point. The binder is preferably a polymer containing fluorine. Examples of fluorine-containing polymers include PVDF and PTFE.

[0030] (Positive electrode current collector) The positive electrode current collector 11 (21) may be, for example, a metal foil such as an aluminum foil, a stainless steel foil, or a nickel foil. A carbon coating layer may be formed on the positive electrode current collector 21. The positive electrode current collector 11 (21) may also be processed into a mesh shape.

[0031] (Negative electrode active material layer) The negative electrode active material layer 15 (25) contains a negative electrode active material, a conductive additive, and a binder. Note that, when the negative electrode active material has conductivity, the negative electrode active material layer does not necessarily contain the conductive additive.

[0032] The negative electrode active material is not particularly limited as long as it can absorb and release lithium ions. Examples of the negative electrode active material include graphite (artificial graphite, natural graphite), amorphous carbon (hard carbon), mesocarbon microbeads, carbon fiber, and Si materials (silicon, Si alloys, Si oxides).

[0033] The conductive additive assists in forming a conductive path between the negative electrode active material and the negative electrode current collector 14 (24). The conductive additive is not particularly limited as long as it has conductivity, and examples thereof include carbon black such as acetylene black, carbon nanotubes, and graphite such as artificial graphite.

[0034] The binder binds the negative electrode active material, the conductive additive, and the negative electrode current collector 14 (24), respectively. Examples of binders include carboxymethyl cellulose, polyvinylidene fluoride, polytetrafluoroethylene, polyacrylic acid, fluororubber, and diene rubber such as styrene-butadiene rubber. The binder preferably contains a crystalline polymer having a melting point. The binder is preferably a polymer containing fluorine. Examples of fluorine-containing polymers include PVDF, PTFE, and fluororubber.

[0035] The negative electrode current collector 14 (24) may be, for example, a metal foil such as copper foil, stainless steel foil, or nickel foil. A carbon coating layer may be formed on the negative electrode current collector 14 (24). The negative electrode current collector 14 (24) may also be processed into a mesh shape.

[0036] (electrode tab) In order to extract current to the outside of the battery, the positive electrode current collector 11 (21) and the negative electrode current collector 14 (24) may each be connected to an electrode tab (not shown). The electrode tab is electrically connected to these current collectors and is taken out, for example, to the outside of the exterior body of the lithium-ion secondary battery.

[0037] The material for the electrode tab is not particularly limited, and a known highly conductive material conventionally used for electrode tabs is preferably used. Examples of the material for the electrode tab include metal materials such as aluminum, copper, titanium, nickel, stainless steel, and alloys thereof, and more preferably aluminum and copper from the viewpoints of light weight, corrosion resistance, and high conductivity.

[0038] (exterior body) The laminate is housed in an exterior body (not shown). In the case of a liquid electrolyte lithium-ion secondary battery, the exterior body is filled with an electrolyte. As the exterior body, a known metal can case can be used, or a bag-shaped case using an aluminum-containing laminate film that can cover the power generating element can also be used. As the laminate film, for example, a three-layer laminate film formed by laminating polypropylene, aluminum, and nylon in this order can be used. From the viewpoint of high output and excellent cooling performance, and being suitable for use in batteries for large equipment such as EVs and HEVs, a laminate film is desirable as the exterior body.

[0039] Positive and negative electrode terminal leads (not shown) connected to the electrode tabs may also be used as needed. Known materials can be used for the positive and negative electrode terminal leads. The portions removed from the outer casing are preferably covered with a heat-resistant, insulating heat-shrinkable tube or the like to prevent contact with peripheral devices or wiring, resulting in electrical leakage and affecting the product (e.g., automobile parts, particularly electronic devices). In a wound-type lithium-ion secondary battery, terminals may be formed using, for example, a cylindrical can (metal can) instead of electrode tabs.

[0040] (electrolyte) The electrolytic solution contains an electrolyte and an organic solvent. The electrolyte can be selected from electrolytes known in the art, for example, LiClO4, LiPF6, LiAsF6, LiSbF6, LiBF4, LiCF3SO3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(COCF3), Li(C4F9SO3), LiC(SO2CF3)3, Li2B 10 Cl 10 Examples of lithium salts include: The electrolytes may be used alone or in combination of two or more.

[0041] The organic solvent can be selected from organic solvents known in the art, and examples thereof include carbonates such as propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 4-trifluoromethyl-1,3-dioxolan-2-one, and 1,2-di(methoxycarbonyloxy)ethane; esters such as methyl formate, methyl acetate, and γ-butyrolactone; ethers such as 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropyl methyl ether, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, tetrahydrofuran, and 2-methyltetrahydrofuran; amides such as N,N-dimethylformamide and N,N-dimethylacetamide; nitriles such as acetonitrile and butyronitrile; carbamates such as 3-methyl-2-oxazolidone; and sulfur-containing compounds such as sulfolane, dimethyl sulfoxide, and 1,3-propane sultone. The organic solvents may be used singly or in combination of two or more kinds.

[0042] (separator) Examples of separator 17 include separators made of olefin resins such as polyethylene and polypropylene, fluororesins, aromatic resins containing nitrogen atoms, etc. Examples of the form of separator 17 include porous membranes, nonwoven fabrics, and woven fabrics.

[0043] (solid electrolyte) Examples of the solid electrolyte of the solid electrolyte layer 27 include inorganic solid electrolytes and organic solid electrolytes. Any inorganic solid electrolyte or organic solid electrolyte known in the art can be used. Examples of the inorganic solid electrolyte include oxides containing oxygen atoms and having both lithium ion conductivity and electrical insulation, and oxides containing sulfur atoms and having both lithium ion conductivity and electrical insulation. Examples of the organic solid electrolyte include polymer compounds exhibiting ion conductivity. For example, polyethylene oxide, polypropylene oxide, and copolymers thereof can be used. The organic solid electrolyte may also be in the form of a gel containing the electrolytic solution.

[0044] <Manufacturing method for recycled positive electrodes> The method for producing a recycled positive electrode includes removing the positive electrode from the laminate included in a lithium-ion secondary battery, pressing the removed positive electrode (pressing process), and doping the pressed positive electrode with lithium ions (lithium ion doping process). The doping of lithium ions is performed by discharging in an electrolyte using a lithium electrode as a counter electrode. Figure 3 is a flowchart of the method for producing a recycled positive electrode according to a first embodiment of the present invention.

[0045] <Press processing> In the pressing step S1, the positive electrode 13 (23) is pressed in the thickness direction of the positive electrode 13 (23). Pressing can be performed by a known means such as a roll press. The pressing pressure is preferably set so that the thickness of the positive electrode after pressing is 85 to 100% of the thickness of the positive electrode before use (the positive electrode at the time of manufacture), and more preferably so that the thickness of the positive electrode after pressing is 95 to 100% of the thickness of the positive electrode before use (the positive electrode at the time of manufacture).

[0046] In the press treatment S1, it is preferable to perform the pressing while heating. By performing the pressing while heating, the binder contained in the positive electrode active material layer can be softened, making it easier to restore the adhesive strength. The heating temperature is, for example, preferably from the melting point of the binder to 200°C or less, more preferably from the melting point to 170°C or less.

[0047] It is preferable to press the cathode until it reaches the thickness of the cathode before use (the cathode at the time of manufacture). Repeated charge and discharge in a lithium-ion secondary battery reduces the adhesion between the particles of the cathode active material and the particles of the conductive additive, resulting in an increase in thickness and resistance. In the press treatment S1, pressing improves the adhesion between the particles of the cathode active material and the particles of the conductive additive, thereby reducing the resistance and restoring the functionality of the cathode.

[0048] It is preferable to measure the thickness of the positive electrode before use in advance. If information on the thickness of the positive electrode at the time of manufacturing the lithium-ion secondary battery is available, that information is used as the thickness of the positive electrode before use (positive electrode at the time of manufacture). If such information is not available, for example, the thickness of the used positive electrode excluding the void portion of the positive electrode may be used as an estimated thickness.

[0049] The pressing step S1 preferably further includes applying a conductive agent to the surface of the positive electrode 13 (23). The conductive agent is not particularly limited, but examples thereof include carbonaceous materials such as acetylene black and carbon nanotubes. Carbon fiber is preferred as the conductive agent. Applying the conductive agent can compensate for conductivity and reduce the resistance of the positive electrode active material layer.

[0050] The method for applying the conductive agent is not particularly limited. For example, a dispersion liquid in which the conductive agent is dispersed may be applied and dried. It is also preferable to apply ultrasonic waves during the application process. By applying ultrasonic waves, the conductive agent can penetrate into the voids in the positive electrode 13 (23), further reducing the resistance. This can further improve and restore the condition of the positive electrode.

[0051] The application of the conductive agent is preferably carried out before pressing the positive electrode 13 (23). That is, it is preferable to press the positive electrode 13 (23) after applying the conductive agent to the surface of the positive electrode 13 (23).

[0052] <Lithium ion doping treatment> The lithium ion doping process S2 is performed by discharging in an electrolyte using a lithium electrode as a counter electrode. The lithium electrode is not particularly limited as long as it contains lithium, and examples thereof include lithium metal, lithium alloys, and lithium metal oxides, with lithium metal being preferred. The electrode may also be fixed to a current collector. The current collector may be made of the materials described for the positive electrode current collector and the negative electrode current collector. The electrolyte may be any of the above-mentioned electrolytes.

[0053] The positive electrode 13 (23) and the lithium electrode are energized in the electrolyte. Specifically, a discharge current is passed from the lithium electrode to the positive electrode to discharge the battery. During this process, lithium ions move from the lithium electrode to the positive electrode 13 (23), and the positive electrode 13 (23) is doped with lithium ions.

[0054] When a lithium-ion secondary battery is used, the electrolyte reacts with lithium ions on the negative electrode, forming a thin film containing lithium on the negative electrode. Some of the lithium ions are also captured in the separator 17 and the electrolyte layer 27. This reduction in lithium ions in the positive electrode causes a decrease in the capacity of the lithium-ion secondary battery. By performing the lithium ion doping process S2, the amount of lithium ions in the positive electrode is restored, and as a result, the capacity of the lithium-ion secondary battery is also restored.

[0055] The discharge conditions are not particularly limited, but may be, for example, conditions that result in the capacity of the positive electrode before use (the positive electrode at the time of manufacture). For example, if the capacity of the positive electrode before use (the positive electrode at the time of manufacture) is x (Ah), one or both of the discharge current and the discharge time may be adjusted so that the product of the discharge current y (A) and the discharge time z (h), y × z (Ah), becomes x (Ah).

[0056] <Laminate Form> The lithium ion secondary battery according to this embodiment may be in any of the conventionally known forms and structures, such as a wound (cylindrical) battery, a laminated (flat) battery, or a flat-wound (prismatic) battery. Of these, wound (cylindrical) batteries and flat-wound (prismatic) batteries are preferred, with wound (cylindrical) batteries being even more preferred. The reasons for this are explained below.

[0057] <Mechanism of action> In the method for producing a recycled positive electrode of this embodiment, pressing the positive electrode makes it possible to recover the increased resistance caused by a decrease in the adhesion of positive electrode active material particles. Furthermore, doping the pressed positive electrode with lithium ions makes it possible to recover the capacity loss caused by the loss of lithium in the positive electrode. Furthermore, in the method for producing a recycled positive electrode of this embodiment, pressing step S1 and lithium ion doping step S2 are performed in this order. In the lithium ion doping step S2, if the positive electrode is curled (wound-type (cylindrical) battery) or if the positive electrode has creases (flat-wound (prismatic) battery), the lithium ions may not be doped uniformly. Positive electrodes that are not doped uniformly with lithium ions may have to be discarded from the perspective of performance, resulting in a low yield. While flattening the positive electrode during the lithium ion doping step S2 is conceivable, this requires the use of a jig or other tool, which is inefficient. On the other hand, in the method for producing a recycled positive electrode according to the present embodiment, the lithium ion doping process S2 is performed on the positive electrode in a state where the electrode is flattened by the pressing process S1, which facilitates uniform doping of lithium ions. Furthermore, the lithium ion doping process S2 does not require the use of a jig or the like for flattening the positive electrode, or the jig can be simplified, which is efficient.

[0058] <Other embodiments> The method for producing a recycled positive electrode according to this embodiment may include other recycling processes in addition to the pressing process S1 and the lithium ion doping process S2. Other examples of the regeneration treatment include a washing treatment S1-1 in which the positive electrode is washed with an organic solvent. Figure 4 is a flowchart of a method for producing a regenerated positive electrode according to another first embodiment of the present invention.

[0059] The organic solvent is preferably a polar organic solvent, such as a protic polar solvent or an aprotic polar solvent, with aprotic polar solvents being preferred. Examples of protic polar solvents include alcohols such as methanol, ethanol, n-propanol, isopropanol, 1-butanol, and 2-butanol; carboxylic acids such as formic acid, acetic acid, and propionic acid; and glycols such as ethylene glycol and propylene glycol. Examples of aprotic polar solvents include ethers such as dimethyl ether, diethyl ether, tetrahydrofuran, and ethylene glycol dimethyl ether; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; esters such as ethyl acetate; carbonates such as ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, and ethylene carbonate; and organic solvents containing a nitrogen atom or a sulfur atom such as pyridine, dimethyl sulfoxide, acetonitrile, 1,4-dioxane, and 1,3-dioxolane. Among these, at least one organic solvent selected from the group consisting of ketones and carbonates is preferred, and at least one organic solvent selected from the group consisting of acetone and dimethyl carbonate is more preferred. The organic solvents may be used singly or in combination of two or more kinds.

[0060] The cleaning process S1-1 is performed by immersing the positive electrode in an organic solvent. It can also be performed while performing ultrasonic treatment. By performing ultrasonic treatment, it is possible to clean the inside of the positive electrode active material. In other words, the organic solvent can penetrate evenly into the inside of the positive electrode active material and clean it. The cleaning time by ultrasonic treatment is preferably 10 to 100 minutes, more preferably 20 to 60 minutes. When the cleaning time by ultrasonic treatment is equal to or greater than the lower limit, the organic solvent can be evenly penetrated into the inside of the positive electrode active material. When the cleaning time by ultrasonic treatment is equal to or less than the upper limit, deterioration of the positive electrode active material layer due to heat generated by ultrasonic waves can be suppressed.

[0061] The positive electrode after cleaning is preferably dried. Drying may be performed under vacuum, reduced pressure, or normal pressure. When drying under reduced pressure or normal pressure, the drying atmosphere may be an inert atmosphere such as nitrogen or argon, or an air atmosphere. The drying temperature is, for example, preferably 10 to 80°C, more preferably 15 to 50°C. The drying time is, for example, preferably 10 to 120 minutes, more preferably 20 to 60 minutes.

[0062] When a lithium-ion secondary battery is used, the electrolyte reacts with lithium ions on the positive electrode, forming a thin film containing lithium on the positive electrode. This thin film increases the resistance of the lithium-ion secondary battery. By performing the cleaning process S1-1, the thin film is removed, thereby recovering the increased resistance of the lithium-ion secondary battery.

[0063] The cleaning treatment S1-1 is preferably performed before the pressing treatment S1. The cleaning treatment S1-1 is preferably performed on the laminate removed from the lithium-ion secondary battery. In this case, the positive electrode is removed from the laminate after the cleaning treatment S1-1 and subjected to the pressing treatment S1.

[0064] <Mechanism of action> The method for producing a recycled positive electrode of this embodiment includes a washing process S1-1 in addition to the pressing process S1 and the lithium ion doping process S2. The washing process S1-1 is performed before the pressing process S1. Washing the positive electrode with an organic solvent makes it possible to recover the increased resistance caused by the lithium-containing thin film formed on the positive electrode. The method for producing a recycled positive electrode of this embodiment also involves washing the laminate. Because the positive electrode is sheet-shaped, washing the positive electrode removed from the laminate requires large equipment, resulting in a large amount of organic solvent used or waste liquid. On the other hand, because the laminate is smaller than the positive electrode, it can be performed with small equipment, and the amount of organic solvent used or waste liquid is reduced, making it more efficient and economical. While the pressing process S1 and the lithium ion doping process S2 require the positive electrode to be removed, the washing process S1-1 does not necessarily require the positive electrode to be removed. By first performing the washing process S1-1, the laminate can be washed. [Explanation of symbols]

[0065] 10, 20... Lithium ion secondary battery, 11, 21... Positive electrode current collector, 12, 22... Positive electrode active material layer, 13, 23... Positive electrode, 14, 24... Negative electrode current collector, 15, 25... Negative electrode active material layer, 16, 26... Negative electrode, 17... Separator, 27... Electrolyte layer

Claims

1. A method for producing a recycled positive electrode in a used lithium ion secondary battery including a laminate having a positive electrode, one of a separator and a solid electrolyte layer, and a negative electrode, comprising: removing the positive electrode from the laminate; pressing the removed positive electrode; doping the pressed positive electrode with lithium ions; The doping of lithium ions is carried out by discharging in an electrolyte using a lithium electrode as a counter electrode.

2. The method for producing a recycled positive electrode according to claim 1 , further comprising washing the positive electrode with an organic solvent before pressing the positive electrode.

3. The method for producing a recycled positive electrode according to claim 2 , wherein the laminate removed from the lithium ion secondary battery is washed with an organic solvent, and the positive electrode is removed from the laminate washed with the organic solvent.

4. The method for producing a recycled positive electrode according to claim 1, wherein the positive electrode is pressed so that the thickness of the pressed positive electrode is 85 to 100% of the thickness of the positive electrode before use.

5. The method for producing a regenerated positive electrode according to any one of claims 1 to 4, wherein the laminate is wound.

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