Manufacturing method for regenerated positive electrode

Abstract

To recover capacity loss caused by lithium depletion in a positive electrode.SOLUTION: A manufacturing method for a regenerated 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, includes washing the laminate extracted from the lithium-ion secondary battery with an organic solvent, extracting the positive electrode from the laminate washed with the organic solvent, and performing a regeneration treatment on the extracted positive 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 secondary battery, including 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, in the technology for recycling secondary batteries such as that disclosed in Patent Document 1, although it is possible to remove deteriorated surface materials of the positive electrode active material of the positive electrode, it is insufficient to recover the increased resistance, and it is also unable to recover the capacity loss due to the loss of lithium in the positive electrode. Patent Document 2 does not disclose a method for recycling the positive electrode.

[0006] The present invention aims to solve the above-mentioned problems by recovering the capacity loss caused by the loss of 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 producing a recycled positive electrode in 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: washing the laminate removed from the lithium ion secondary battery with an organic solvent; removing the positive electrode from the laminate washed with the organic solvent; and subjecting the removed positive electrode to a regeneration process.

[0008] According to the above-described embodiment, by washing the positive electrode with an organic solvent, it is possible to recover the resistance increase due to the lithium-containing thin film formed on the positive electrode. Furthermore, by washing the laminate, the washing with an organic solvent can be performed using small-scale equipment, and the amount of organic solvent used or the amount of waste liquid can be reduced, making it possible to perform the washing more efficiently and economically.

[0009] [2] A method for producing a recycled positive electrode in a used lithium ion secondary battery having a laminate including a positive electrode, one of a separator and a solid electrolyte layer, and a negative electrode, comprising: washing the positive electrode removed from the lithium ion secondary battery with an organic solvent; and subjecting the positive electrode washed with the organic solvent to a regeneration treatment.

[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 regenerated positive electrode according to [1] or [2], wherein the organic solvent is an aprotic polar solvent.

[0012] According to the above embodiment, the effect of recovering the increased resistance due to the lithium-containing thin film formed on the positive electrode is further enhanced.

[0013] [4] The method for producing a regenerated positive electrode according to any one of [1] to [3], wherein the organic solvent is at least one organic solvent selected from the group consisting of ketones and carbonates.

[0014] According to the above embodiment, the effect of recovering the increased resistance due to the lithium-containing thin film formed on the positive electrode is further enhanced.

[0015] [5] The method for producing a regenerated positive electrode according to any one of [1] to [4], wherein the organic solvent is at least one organic solvent selected from the group consisting of acetone and dimethyl carbonate.

[0016] According to the above embodiment, the effect of recovering the increased resistance due to the lithium-containing thin film formed on the positive electrode is further enhanced.

[0017] [6] The method for producing a recycled positive electrode according to any one of [1] to [5], wherein the recycling treatment includes pressing the positive electrode.

[0018] According to the above embodiment, by pressing the positive electrode, it is possible to recover from the increase in resistance caused by the decrease in adhesion of particles of the positive electrode active material and the like.

[0019] [7] The method for producing a recycled positive electrode according to [6], wherein the regeneration treatment further includes doping the pressed positive electrode with lithium ions, and the doping of the lithium ions is carried out by discharging in an electrolyte using a lithium electrode as a counter electrode.

[0020] According to the above-described embodiment, by doping the pressed positive electrode with lithium ions, it is possible to recover the capacity loss due to the lithium loss in the positive electrode. Furthermore, by performing the pressing of the positive electrode and the doping of lithium ions in this order, the doping of the lithium ions becomes uniform. Furthermore, by performing the pressing of the positive electrode and the doping of lithium ions in this order, it is possible to more efficiently produce a recycled positive electrode.

[0021] [8] The method for producing a regenerated positive electrode according to any one of [1] to [7], wherein the laminate is wound.

[0022] According to the above aspect, the recovery effect in the other aspects can be maximized.

[0023] [9] A method for producing a recycled positive electrode according to any one of [2] to [8], comprising subjecting the positive electrode before washing with an organic solvent to a recycling treatment.

[0024] According to the above aspect, by subjecting the positive electrode to a regeneration treatment and then cleaning the regenerated positive electrode, it is possible to recover the capacity loss due to lithium loss in the positive electrode, and also to recover the resistance increase due to the lithium-containing thin film formed on the positive electrode. [Effects of the Invention]

[0025] According to the above-described aspects of the present invention, it is possible to recover the capacity loss due to the loss of lithium in the positive electrode, and it is also possible to reuse the secondary battery more efficiently, which in turn contributes to energy efficiency. [Brief explanation of the drawings]

[0026] [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. [Figure 5] FIG. 3 is a diagram showing the results of measuring the capacity of secondary batteries in Examples 1 to 3 and Comparative Examples 1 to 4. [Figure 6]FIG. 3 is a diagram showing the results of measuring the resistance of the positive electrode in Examples 1 to 3 and Comparative Examples 1 to 4. DETAILED DESCRIPTION OF THE INVENTION

[0027] 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.

[0028] 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").

[0029] The method for producing a recycled positive electrode includes washing the laminate with an organic solvent (hereinafter also referred to as "washing treatment"), removing the positive electrode from the laminate washed with the organic solvent, and performing a regeneration treatment on the removed positive electrode. In addition, a method for producing a recycled positive electrode in another embodiment includes washing the positive electrode removed from a lithium ion secondary battery with an organic solvent, and performing a recycling treatment on the positive electrode washed with the organic solvent.

[0030] <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.

[0031] A lithium-ion secondary 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 16 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.

[0032] 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.

[0033] The lithium-ion secondary battery 20 (LIB) includes a positive electrode 23, a solid 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 also be an electrode group in which multiple positive electrodes 23 and multiple negative electrodes 26 are alternately stacked. In this case, a solid electrolyte layer 27 is provided between the positive electrode and the negative electrode.

[0034] (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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] (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.

[0039] (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.

[0040] 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).

[0041] 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.

[0042] 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.

[0043] 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.

[0044] (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.

[0045] 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.

[0046] (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 achieving 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.

[0047] 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.

[0048] (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.

[0049] 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.

[0050] (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.

[0051] (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.

[0052] <Manufacturing method for recycled positive electrodes> The method for producing a recycled positive electrode includes washing a laminate removed from a lithium-ion secondary battery with an organic solvent (washing treatment), removing the positive electrode from the laminate washed with the organic solvent, and performing a regeneration treatment on the removed positive electrode. Figure 3 is a flowchart of the method for producing a recycled positive electrode according to the first embodiment of the present invention.

[0053] <Cleaning process> In the cleaning process S1, the laminate is cleaned with an organic solvent. 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.

[0054] The cleaning process S1 is performed by immersing the positive electrode in an organic solvent. It can also be performed while ultrasonic treatment is being performed. 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 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 permeated 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.

[0055] 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.

[0056] 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, the thin film is removed, thereby recovering the increased resistance of the lithium-ion secondary battery.

[0057] The cleaning process S1 is preferably carried out prior to other regeneration processes. The positive electrode is then removed from the stack after the cleaning process S1 and subjected to other regeneration processes. In the method for producing a regenerated positive electrode of this embodiment, as long as the regeneration process is carried out after the cleaning process S1, other processes may be carried out between the cleaning process S1 and the regeneration process.

[0058] <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.

[0059] <Mechanism of action> In the method for producing a recycled positive electrode of this embodiment, the cleaning process S1 is performed before other regeneration processes. 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. Furthermore, in the method for producing a recycled positive electrode of this embodiment, the laminate is washed. 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. Furthermore, while the regeneration process described below requires the positive electrode to be removed before performing the cleaning process S1, the positive electrode does not necessarily need to be removed. By performing the cleaning process S1 first, the laminate can be washed.

[0060] <Recycling process> Examples of the regeneration treatment include regeneration treatments other than washing treatments, and among these, pressing the positive electrode (hereinafter also referred to as "pressing treatment") and doping the positive electrode with lithium ions (hereinafter also referred to as "lithium ion doping treatment") are preferred. The pressing treatment and lithium ion doping treatment are preferably performed in this order. Figure 4 is a flowchart of a method for producing a regenerated positive electrode according to another first embodiment of the present invention.

[0061] <Press processing> In the pressing step S2-1, the positive electrode 13 (23) removed from the laminate after the cleaning step S1 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 as-manufactured positive electrode), and more preferably set so that the thickness of the positive electrode after pressing is 95 to 100% of the thickness of the positive electrode before use (the as-manufactured positive electrode).

[0062] In the pressing step S2-1, pressing is preferably performed while heating. By performing pressing while heating, the binder contained in the positive electrode active material layer can be softened, making it easier to restore adhesion. 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.

[0063] It is preferable to perform pressing until the thickness of the positive electrode (positive electrode at the time of manufacture) is restored before use. When a lithium-ion secondary battery is repeatedly charged and discharged, the adhesion between the particles of the positive electrode active material and the particles of the conductive additive decreases, causing the thickness to increase and the resistance to increase. In the pressing treatment S2-1, pressing is performed to improve the adhesion between the particles of the positive electrode active material and the particles of the conductive additive, thereby reducing the resistance and restoring the function of the positive electrode.

[0064] 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.

[0065] The pressing step S2-1 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.

[0066] 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.

[0067] 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).

[0068] <Lithium ion doping treatment> The lithium ion doping treatment S2-2 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.

[0069] 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.

[0070] 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 solid 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 S2-2, 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.

[0071] 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).

[0072] <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, the pressing process S2-1 and the lithium ion doping process S2-2 are performed in this order. In the lithium ion doping process S2-2, if the positive electrode is rolled (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 process S2-2 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 S2-2 is performed on the positive electrode after it has been flattened by the pressing process S2-1, which facilitates uniform doping of lithium ions. Furthermore, the lithium ion doping process S2-2 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.

[0073] <Preferred embodiment of the method for producing the recycled positive electrode of this embodiment> A first example of a preferred aspect of the method for producing a recycled positive electrode of this embodiment includes a washing treatment, a pressing treatment, and a doping treatment. In the first example, the washing treatment, the pressing treatment, and the doping treatment are performed in this order. A second example of a preferred aspect of the method for producing a recycled positive electrode of this embodiment includes a washing treatment, a doping treatment, and a pressing treatment. In the second example, the washing treatment, the doping treatment, and the pressing treatment are performed in this order. A third example of a preferred aspect of the method for producing a recycled positive electrode of this embodiment includes a doping treatment, a washing treatment, and a pressing treatment. In the third example, the doping treatment, the washing treatment, and the pressing treatment are performed in this order. A fourth example of a preferred aspect of the method for producing a regenerated positive electrode of this embodiment includes a washing treatment and a doping treatment. In the fourth example, the washing treatment and the doping treatment are performed in this order. When cleaning is carried out first, the laminate removed from the lithium ion secondary battery may be cleaned, or the positive electrode removed from the lithium ion secondary battery may be cleaned. On the other hand, the pressing and doping processes are performed on the positive electrode. [Example]

[0074] The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0075] [Example 1] The used lithium ion secondary battery was disassembled, and a laminate having a positive electrode, a separator, and a negative electrode was taken out from the lithium ion secondary battery. The positive electrode consisted of an aluminum foil current collector and a positive electrode active material layer on one side of the positive electrode current collector, which contained a positive electrode active material, a conductive additive, and a binder. The positive electrode active material was lithium nickel cobalt manganese oxide. The conductive additive was carbon black. The binder was polyvinylidene fluoride. A porous film made of polyethylene was used as the separator. A liquid electrolyte was used as the electrolyte. The negative electrode consisted of an aluminum foil current collector and a negative electrode active material layer on one side of the current collector, the layer containing a negative electrode active material, a conductive additive, and a binder. Graphite was used as the negative electrode active material. Carbon black was used as the conductive additive. Polyvinylidene fluoride was used as the binder. Next, the laminate was washed with acetone by ultrasonic treatment using an ultrasonic cleaner for 20 minutes (washing treatment). Next, the positive electrode was taken out from the washed laminate, and the positive electrode was dried in an air atmosphere at 50° C. for 20 minutes. Next, the dried positive electrode was pressed in the thickness direction of the positive electrode using a roll press (pressing treatment). Next, lithium ions were doped into the pressed positive electrode (doping treatment). Specifically, a discharge current was passed from a lithium electrode (lithium metal) serving as a counter electrode to the positive electrode in the electrolyte, and the positive electrode was discharged to dope the lithium ions into the positive electrode, thereby obtaining a regenerated positive electrode.

[0076] [Example 2] In the same manner as in Example 1, the laminate was taken out from the lithium ion secondary battery. Next, the laminate was washed in the same manner as in Example 1 (washing treatment). Next, in the same manner as in Example 1, the positive electrode was taken out of the laminate and dried. Next, in the same manner as in Example 1, lithium ions were doped into the washed positive electrode (doping treatment). Next, in the same manner as in Example 1, the doped positive electrode was pressed (pressing treatment) to obtain a recycled positive electrode.

[0077] [Example 3] In the same manner as in Example 1, the laminate was taken out from the lithium ion secondary battery, and further the positive electrode was taken out from the laminate. Next, in the same manner as in Example 1, lithium ions were doped into the positive electrode (doping treatment). Next, in the same manner as in Example 1, the doped positive electrode was washed (washing treatment). Next, in the same manner as in Example 1, the washed positive electrode was dried. Next, in the same manner as in Example 1, the dried positive electrode was pressed (pressing treatment) to obtain a regenerated positive electrode.

[0078] [Example 4] In the same manner as in Example 1, the laminate was taken out from the lithium ion secondary battery. Next, the laminate was washed in the same manner as in Example 1 (washing treatment). Next, in the same manner as in Example 1, the positive electrode was taken out of the laminate and dried. Next, in the same manner as in Example 1, lithium ions were doped into the washed positive electrode (doping treatment) to obtain a regenerated positive electrode.

[0079] [Comparative Example 1] In the same manner as in Example 1, the laminate was taken out from the lithium ion secondary battery, and further the positive electrode was taken out from the laminate. Next, in the same manner as in Example 1, lithium ions were doped into the positive electrode (doping treatment) to obtain a regenerated positive electrode.

[0080] Comparative Example 2 The used lithium ion secondary battery was disassembled, a laminate having a positive electrode, a separator, and a negative electrode was removed from the lithium ion secondary battery, and the positive electrode was further removed from the laminate.

[0081] [evaluation] (1) Battery capacity measurement A lithium ion secondary battery was fabricated, which included a laminate having a positive electrode, a separator, a liquid electrolyte, and a negative electrode. As the positive electrode, any one of the recycled positive electrodes of Examples 1 to 4, the recycled positive electrode of Comparative Example 1, and the positive electrode of Comparative Example 2 was used. The separator used was the same as that used in Example 1. The liquid electrolyte used was the same as that used in Example 1. The negative electrode used was the same as that used in Example 1. The capacity of the resulting secondary battery was measured, and the results are shown in Figure 5.

[0082] (2) Measuring the resistance of the positive electrode The resistance was measured for the recycled positive electrodes of Examples 1 to 4, the recycled positive electrode of Comparative Example 1, and the positive electrode of Comparative Example 2. The results are shown in FIG.

[0083] As shown in FIG. 5, when Comparative Example 1, in which no cleaning treatment was performed, was compared with Examples 1 to 4, in which cleaning treatment was performed, it was found that cleaning treatment was effective in restoring the capacity of the lithium ion secondary battery. Furthermore, when Comparative Example 1 and Comparative Example 2 are compared, it is found that simply doping lithium ions does not have the effect of restoring the capacity of a lithium ion secondary battery. Furthermore, when Comparative Example 1 and Example 4 are compared, it is found that the capacity recovery of the lithium ion secondary battery is large when a cleaning treatment is performed before doping with lithium ions. Furthermore, as shown in FIG. 6, when Example 4 is compared with Examples 1, 2, and 3, the effect of performing a press treatment in addition to doping with lithium ions is to reduce the resistance of the positive electrode. From the above, it is not always necessary to perform a cleaning treatment on the laminate, but performing a cleaning treatment on the laminate is more effective in restoring the capacity of the lithium ion secondary battery and reducing the resistance of the positive electrode. [Explanation of symbols]

[0084] 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... Solid 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: washing the laminate removed from the lithium ion secondary battery with an organic solvent, and removing the positive electrode from the laminate washed with the organic solvent; A method for producing a recycled positive electrode, comprising subjecting the removed positive electrode to a recycling treatment.

2. 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: washing the positive electrode removed from the lithium ion secondary battery with an organic solvent; and subjecting the positive electrode washed with the organic solvent to a regeneration treatment.

3. The method for producing a regenerated positive electrode according to claim 1 or 2, wherein the organic solvent is an aprotic polar solvent.

4. 3. The method for producing a regenerated positive electrode according to claim 1, wherein the organic solvent is at least one organic solvent selected from the group consisting of ketones and carbonates.

5. The method for producing a regenerated positive electrode according to claim 4 , wherein the organic solvent is at least one organic solvent selected from the group consisting of acetone and dimethyl carbonate.

6. The method for producing a recycled positive electrode according to claim 1 or 2, wherein the recycling treatment includes pressing the positive electrode.

7. 7. The method for producing a recycled positive electrode according to claim 6, wherein the recycling treatment further includes doping the pressed positive electrode with lithium ions, and the doping of the lithium ions is performed by discharging in an electrolyte using a lithium electrode as a counter electrode.

8. The method for producing a recycled positive electrode according to claim 1 or 2, wherein the laminate is wound.

9. The method for producing a recycled positive electrode according to claim 2 , further comprising subjecting the positive electrode to a recycling treatment before washing with an organic solvent.

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