Method for producing recycled material

Abstract

To provide a manufacturing method of a recycled material capable of easily obtaining a copper foil from a lithium ion secondary battery as the recycled material.SOLUTION: A method for producing a recycled material of the present disclosure includes a step of preparing a lithium ion secondary battery including a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode includes a copper foil and a negative electrode active material layer containing graphite as a negative electrode active material, and a stage structure of the graphite is at least one stage selected from the group consisting of stage 1, stage 2, and stage 3, a step of taking out the negative electrode from the lithium ion secondary battery, and a step of bringing the negative electrode into contact with water to peel off the negative electrode active material layer from the copper foil.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a method for producing recycled materials, and more particularly to a method for producing materials recycled from lithium-ion secondary batteries. [Background technology]

[0002] Lithium-ion secondary batteries are widely used in various fields. In particular, in light of the Sustainable Development Goals (SDGs), there has been an increasing demand in recent years for electric vehicles (BEVs) that use lithium-ion secondary batteries as their driving power source.

[0003] On the other hand, in recent years, from the perspective of SDGs, there has been a demand for promoting the recycling of used lithium-ion secondary batteries. To this end, various technologies have been developed to obtain reusable materials (in other words, recycled materials) from used lithium-ion secondary batteries (see, for example, Patent Documents 1 to 5). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-26566 [Patent Document 2] Special Publication No. 2023-525095 [Patent Document 3] Patent No. 7220340 [Patent Document 4] Patent Publication No. 2021-72157 [Patent Document 5] Japanese Patent Application Laid-Open No. 2013-101830 Summary of the Invention [Problem to be solved by the invention]

[0005] However, there is concern that copper will be depleted if BEVs become widespread. Therefore, there is a need for a technology that can easily recover copper foil, in particular, from used lithium-ion secondary batteries as a recycled material. However, the above-mentioned conventional technology is insufficient to meet this need.

[0006] Therefore, an object of the present disclosure is to provide a method for producing recycled materials that can easily obtain copper foil as a recycled material from lithium ion secondary batteries. [Means for solving the problem]

[0007] The method for producing recycled materials disclosed herein includes the steps of: preparing a lithium-ion secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode comprises copper foil and a negative electrode active material layer containing graphite as a negative electrode active material, and the stage structure of the graphite is at least one stage selected from the group consisting of stage 1, stage 2, and stage 3; removing the negative electrode from the lithium-ion secondary battery; and contacting the negative electrode with water to peel off the negative electrode active material layer from the copper foil.

[0008] According to this configuration, it is possible to provide a method for producing recycled materials that can easily obtain copper foil as a recycled material from lithium ion secondary batteries. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a flowchart showing the steps of a method for producing recycled materials according to one embodiment. [Figure 2] FIG. 2 is a vertical cross-sectional view schematically showing the internal structure of an example of a lithium ion secondary battery used in a method for producing a recycled material according to an embodiment. [Figure 3] FIG. 3 is a schematic exploded view showing the configuration of the electrode body of the lithium ion secondary battery shown in FIG. [Figure 4] FIG. 4 is a schematic cross-sectional view of the negative electrode of the lithium ion secondary battery shown in FIG. [Figure 5] FIG. 5 is a conceptual diagram of the graphite stage structure. [Figure 6] FIG. 6 is a schematic view illustrating an example of a method for carrying out the active material layer peeling step. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Matters not mentioned in this specification but necessary for implementing the present disclosure can be understood as design matters for a person skilled in the art based on the prior art in the relevant field. The present disclosure can be implemented based on the contents disclosed in this specification and the common general technical knowledge in the relevant field. In the following drawings, components and parts that perform the same function are denoted by the same reference numerals. Dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect actual dimensional relationships. In this specification, a numerical range expressed as "A to B" includes A and B.

[0011] In this specification, the term "secondary battery" refers to an electricity storage device that can be repeatedly charged and discharged. In addition, in this specification, the term "lithium ion secondary battery" refers to a secondary battery that uses lithium ions as charge carriers and achieves charging and discharging by the transfer of charge associated with the lithium ions between the positive and negative electrodes.

[0012] The flowchart in Figure 1 shows the steps of a method for producing a recycled material according to the present embodiment, which is an example of a method for producing a recycled material according to the present disclosure. As shown in Figure 1, the method for producing a recycled material according to the present embodiment includes the following essential steps: a step (battery preparation step) S101 of preparing a lithium-ion secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, the negative electrode comprising copper foil and a negative electrode active material layer containing graphite as the negative electrode active material, the graphite having a stage structure of at least one stage selected from the group consisting of stage 1, stage 2, and stage 3; a step (negative electrode removal step) S102 of removing the negative electrode from the lithium-ion secondary battery; and a step (active material layer removal step) S103 of contacting the negative electrode with water to peel the negative electrode active material layer from the copper foil. Each step is described in detail below.

[0013] 1. Battery preparation process S101 The lithium ion secondary batteries prepared in the battery preparation step S101 are preferably used lithium ion secondary batteries. However, without being limited thereto, the lithium ion secondary batteries prepared in the battery preparation step S101 may be unused lithium ion secondary batteries that were deemed defective during manufacturing and could not be shipped. This makes it possible to produce recycled materials while reducing the burden on the environment. Therefore, in the battery preparation step S101, for example, used lithium ion secondary batteries or unused lithium ion secondary batteries that were deemed defective during manufacturing and could not be shipped are collected.

[0014] Examples of the structure of a lithium ion secondary battery are shown in Figures 2 and 3. Figure 2 is a longitudinal sectional view schematically showing the internal structure of an example of a lithium ion secondary battery used in the method for producing a recycled material according to this embodiment. Figure 3 is an exploded view schematically showing an electrode body of the lithium ion secondary battery shown in Figure 2. Figure 4 is a schematic sectional view taken along the thickness direction of the negative electrode of the lithium ion secondary battery shown in Figure 2.

[0015] As shown in FIG. 2, the lithium-ion secondary battery 100 is a rectangular sealed battery constructed by accommodating a flat electrode assembly 20 and a non-aqueous electrolyte (not shown) inside a battery case 30. The battery case 30 is provided with a positive electrode terminal 42 and a negative electrode terminal 44 for external connection. The battery case 30 is also provided with a thin-walled safety valve 36 that is designed to release internal pressure when the internal pressure of the battery case 30 rises above a predetermined level. The battery case 30 is provided with an injection port (not shown) for injecting the non-aqueous electrolyte. The positive electrode terminal 42 is electrically connected to a positive electrode current collector plate 42a. The negative electrode terminal 44 is electrically connected to a negative electrode current collector plate 44a.

[0016] 2, the battery case 30 is composed of an exterior body 32 that houses the electrode assembly 20 and a lid body 34 that seals the opening of the exterior body 32. The exterior body 32 and the lid body 34 are welded and sealed by laser welding or the like. The material of the battery case 30 is, for example, a lightweight metal material with good thermal conductivity, such as aluminum.

[0017] In this embodiment, the battery case 30 is rectangular. However, the shape of the battery case 30 is not limited thereto and may be, for example, cylindrical. Alternatively, the battery case 30 may be a laminate case having a gas barrier layer such as an aluminum layer and a sealant layer containing a thermoplastic resin. The battery case 30 may also be made of resin.

[0018] 2 and 3, the electrode assembly 20 has a configuration in which a long positive electrode sheet 50 and a long negative electrode sheet 60 are overlapped with two long separator sheets 70 interposed therebetween and wound in the longitudinal direction. Thus, in this embodiment, the electrode assembly 20 is a wound electrode assembly. However, the electrode assembly 20 is not limited to this, and may be a stacked electrode assembly in which multiple positive electrodes and multiple negative electrodes are alternately stacked with separators interposed therebetween.

[0019] 3 and 4, the negative electrode sheet 60 has a configuration in which a negative electrode active material layer 64 is formed along the longitudinal direction on one or both sides (both sides in this case) of a long negative electrode current collector 62. The negative electrode active material layer 64 is supported by the negative electrode current collector 62. Thus, the negative electrode current collector 62 and the negative electrode active material layer 64 are in contact with each other. The negative electrode sheet 60 has a negative electrode active material layer-free portion 62a, which is a portion where the negative electrode active material layer 64 is not formed and the negative electrode current collector 62 is exposed.

[0020] Similarly, the positive electrode sheet 50 has a configuration in which a positive electrode active material layer 54 is formed along the longitudinal direction on one or both sides (both sides in this case) of a long positive electrode current collector 52. The positive electrode sheet 50 has a positive electrode active material layer-free portion 52a, which is a portion where the positive electrode active material layer 54 is not formed and the positive electrode current collector 52 is exposed.

[0021] The positive electrode active material layer-free portion 52a and the negative electrode active material layer-free portion 62a are formed so as to protrude outward from both ends in the winding axis direction (i.e., the sheet width direction perpendicular to the longitudinal direction) of the wound electrode body 20. A positive electrode current collector plate 42a and a negative electrode current collector plate 44a are joined to the positive electrode active material layer-free portion 52a and the negative electrode active material layer-free portion 62a, respectively.

[0022] In this embodiment, the negative electrode current collector 62 constituting the negative electrode sheet 60 is copper foil. The thickness of the copper foil is not particularly limited and is, for example, 5 μm or more and 35 μm or less, and preferably 7 μm or more and 20 μm or less.

[0023] The negative electrode active material layer 64 contains a negative electrode active material. In this embodiment, graphite is used as the negative electrode active material. The graphite may be natural graphite or artificial graphite, or may be amorphous carbon-coated graphite in which graphite is coated with an amorphous carbon material.

[0024] The median diameter (D50) of graphite is not particularly limited, but is, for example, 0.1 μm to 50 μm, preferably 1 μm to 25 μm, and more preferably 5 μm to 20 μm. The median diameter (D50) of graphite can be determined, for example, by a laser diffraction scattering method.

[0025] The negative electrode active material layer 64 may contain components other than graphite, such as a binder or a thickener. Examples of binders that may be used include styrene butadiene rubber (SBR) and polyvinylidene fluoride (PVDF). Examples of thickeners that may be used include carboxymethyl cellulose (CMC). The negative electrode active material layer 64 may further contain a negative electrode active material other than graphite, as long as the effects of the present disclosure are not impaired. The negative electrode active material is preferably composed of graphite alone.

[0026] The graphite content in the negative electrode active material layer 64 is preferably 90% by mass or more, and more preferably 95% by mass to 99% by mass. The binder content in the negative electrode active material layer 64 is preferably 0.1% by mass to 8% by mass or less, and more preferably 0.5% by mass to 3% by mass. The thickener content in the negative electrode active material layer 64 is preferably 0.3% by mass to 3% by mass or less, and more preferably 0.5% by mass to 2% by mass.

[0027] The positive electrode current collector 52 constituting the positive electrode sheet 50 may be a known positive electrode current collector used in lithium ion secondary batteries, and examples thereof include aluminum foil.

[0028] The positive electrode active material layer 54 contains a positive electrode active material. Examples of the positive electrode active material include lithium composite metal oxides (e.g., lithium manganese composite oxides, lithium nickel manganese composite oxides, lithium nickel cobalt manganese composite oxides, lithium nickel cobalt aluminum composite oxides, etc.) and lithium transition metal phosphate compounds (e.g., lithium iron phosphate, etc.). The positive electrode active material layer 54 may also contain a conductive material, a binder, etc. Suitable conductive materials include carbon black such as acetylene black (AB) and carbon nanotubes. Suitable binders include polyvinylidene fluoride (PVDF), etc.

[0029] The separator 70 may be a known separator used in lithium ion secondary batteries, and examples thereof include a porous sheet made of a resin such as polyethylene (PE) or polypropylene (PP). The porous sheet may have a single-layer structure or a multi-layer structure. A heat-resistant layer (HRL) may be provided on the surface of the separator 70.

[0030] The nonaqueous electrolyte may be a known nonaqueous electrolyte used in lithium ion secondary batteries. Typically, the nonaqueous electrolyte contains a nonaqueous solvent and a supporting salt (in other words, an electrolyte salt). Examples of the nonaqueous solvent include carbonates, esters, and ethers. Examples of the supporting salt include lithium salts such as LiPF6. The nonaqueous electrolyte may contain various additives such as a gas generating agent, a film-forming agent, a dispersant, and a thickener. Although a nonaqueous electrolyte is used as the electrolyte in this embodiment, the electrolyte may be a solid electrolyte.

[0031] The lithium ion secondary battery 100 is preferably for in-vehicle use (i.e., for use as a driving power source for vehicles such as electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs)), but is not limited thereto. The lithium ion secondary battery 100 may also be used as a power source for electronic devices, etc.

[0032] Here, when graphite is used as the negative electrode active material of a lithium ion secondary battery, lithium ions are absorbed between layers of the layered structure of graphite during charging of the lithium ion secondary battery. At this time, it is known that graphite has a stage structure in which lithium ions are regularly absorbed between specific layers. In this embodiment, in the lithium ion secondary battery prepared in the battery preparation step S101, the graphite has a specific stage structure. This will be explained using FIG. 5. FIG. 5 is a conceptual diagram of the graphite stage structure, and also shows a graph in which the horizontal axis represents the negative electrode capacity (capacity per unit weight of the negative electrode; mAh / g) and the vertical axis represents the negative electrode potential relative to lithium metal.

[0033] In Figure 5, the horizontal lines in the diagram above the graph represent each graphite layer, and the circles represent lithium ions. Graphite has four stage structures, which are divided into stages 1 to 4. In stage 1, lithium ions are absorbed into each graphite layer. In stage 2, one layer without lithium ions exists between two layers with absorbed lithium ions. In stage 3, two layers without lithium ions exist between two layers with absorbed lithium ions. In stage 4, three layers without lithium ions exist between two layers with absorbed lithium ions. As shown in Figure 5, as the negative electrode capacity of a lithium-ion secondary battery increases, i.e., as charging progresses, the stage structure of graphite progresses from an uncharged state to stage 4, then to a state where stage 4 and stage 3 coexist, then to stage 3, then to a state where stage 3 and stage 2 coexist, then to stage 2, and then to a state where stage 2 and stage 1 coexist, then to stage 1.

[0034] Here, in the lithium-ion secondary battery 100 prepared in the battery preparation step S101, the graphite stage structure is at least one stage selected from the group consisting of stage 1, stage 2, and stage 3. The graphite stage structure may be a state in which stage 3 and stage 2 coexist, or a state in which stage 2 and stage 1 coexist. A lithium-ion secondary battery having a graphite stage structure in which stage 4 and stage 3 coexist does not fall under the category of the lithium-ion secondary battery 100 prepared in the battery preparation step S101. If the graphite stage structure of the lithium-ion secondary battery 100 is known, the lithium-ion secondary battery 100 may be selected accordingly. If the graphite stage structure of the lithium-ion secondary battery 100 is not known, the graphite stage structure is confirmed. This will be described below.

[0035] In the results of the Examples and Comparative Examples described later, the negative electrode potential (based on lithium metal, the same applies below) was 220 mV (vs. Li + / Li), the graphite stage structure was stage 4, and when the negative electrode potential was 180 mV, the graphite stage structure was stage 3. When the negative electrode potential was 130 mV, 110 mV, 80 mV, and 60 mV, the graphite stage structure was stage 2, stage 2, stage 1, and stage 1, respectively.

[0036] Therefore, in the battery preparation step S101, it may be confirmed whether the potential of the negative electrode 60 of the lithium ion secondary battery 100 is 180 mV or less versus metallic lithium. If the potential of the negative electrode 60 of the lithium ion secondary battery 100 is 180 mV or less, the stage structure of the graphite is either stage 1, stage 2, or stage 3. This confirmation can be performed by a known method, and specifically, by inserting metallic lithium as a reference electrode into the lithium ion secondary battery 100 and using a known potential measuring device.

[0037] Alternatively, as shown in Fig. 5, the stage structure of graphite is related to the capacity of the negative electrode of the lithium ion secondary battery (i.e., the state of charge (SOC)). Therefore, the SOC of the lithium ion secondary battery 100 may be checked to confirm the stage structure of graphite.

[0038] Alternatively, in the battery preparation step S101, the state of charge of the lithium ion secondary battery 100 may be adjusted so that the stage structure of the graphite is at least one stage selected from the group consisting of stage 1, stage 2, and stage 3. Specifically, for example, the state of charge of the lithium ion secondary battery 100 may be adjusted to a state of charge such that the potential of the negative electrode 60 of the lithium ion secondary battery 100 is 180 mV or less versus lithium metal. The state of charge can be checked and adjusted according to a known method, for example, using a known charger / discharger.

[0039] The state of charge may be adjusted for all lithium ion secondary batteries 100. Alternatively, the potential of the negative electrode 60 may be checked, and the state of charge may be adjusted only for lithium ion secondary batteries 100 whose potential of the negative electrode 60 exceeds 180 mV. Alternatively, the SOC of the lithium ion secondary batteries may be checked, and the state of charge may be adjusted only for those whose graphite stage structure is in stage 4 or which are uncharged.

[0040] Generally, when a lithium-ion secondary battery is recycled, the lithium-ion secondary battery is fully discharged from the viewpoint of safe disassembly. When a lithium-ion secondary battery is fully discharged, there are no lithium ions between the graphite layers, and therefore the graphite does not have a stage structure of stage 1, stage 2, stage 3, or stage 4. Therefore, when the stage structure of the graphite is stage 1, stage 2, or stage 3, the lithium-ion secondary battery 100 is in a somewhat charged state.

[0041] In this manner, a lithium ion secondary battery 100 in which the graphite stage structure is at least one stage selected from the group consisting of stage 1, stage 2, and stage 3 can be prepared.

[0042] 2. Negative electrode extraction process S102 The negative electrode removal step S102 can be performed according to a known method. Specifically, for example, first, the battery case 30 of the lithium-ion secondary battery 100 is opened to expose the electrode assembly 20. The battery case 30 can be opened, for example, by cutting a portion of the exterior body 32 slightly below the lid body 34 using cutting means such as a tool equipped with a cutting blade (e.g., an electric saw), an electric cutting tool (e.g., a grinder, a router), a water cutter, or a laser cutter.

[0043] Next, the exposed electrode assembly 20 is removed, and the negative electrode 60 is extracted from the electrode assembly 20. For example, first, the positive electrode active material layer-free portion 52a and the negative electrode active material layer-free portion 62a of the electrode assembly 20 are detached from the positive electrode current collector plate 42a and the negative electrode current collector plate 44a, respectively. Next, for example, if the electrode assembly 20 is a wound electrode assembly as in the illustrated example, the wound electrode assembly 20 is unwound and separated into the positive electrode 50, the negative electrode 60, and the separator 70. If the electrode assembly 20 is a stacked electrode assembly, it is separated into the positive electrode 50, the separator 70, and the negative electrode 60. In this manner, the negative electrode extraction step S102 is performed, and the negative electrode 60 can be extracted.

[0044] 3. Active material layer peeling step S103 In this step, the negative electrode 60 is brought into contact with water. In the negative electrode 60, the graphite is in a state of stage 1, stage 2, or stage 3, in which lithium ions have entered between the layers of the graphite. Here, the graphite with the lithium ions entering between the layers and water undergo a reaction represented by the following formula (I): 2C6Li+2H2O → 2C6+2LiOH+H2...(I)

[0045] As a result, lithium ions are released one after another from between the graphite layers and react with water, reducing the interlayer distance. This results in rapid volumetric contraction of the graphite. This volume change can be as much as 10%. The stress caused by this rapid volumetric contraction of the graphite causes the negative electrode active material layer 64 to peel off from the negative electrode current collector 62, i.e., the copper foil. In this way, the negative electrode active material layer 64 and the copper foil can be easily separated. Note that when the graphite is in stage 4, the amount of lithium ions is small, so this volumetric contraction is small and sufficient stress cannot be obtained.

[0046] The active material layer peeling step S103 can be performed, for example, by preparing a container, tank, or the like filled with water and immersing the negative electrode 60 in the water, which may or may not be stirred.

[0047] As another example, the active material layer peeling step S103 can be performed by spraying water onto the negative electrode 60. This will be specifically described with reference to FIG.

[0048] As shown in FIG. 6, a stand 110 and a sprayer 120 above it are prepared. The stand 110 may be a movable belt conveyor or the like, since it allows the negative electrode 60 to be continuously brought into contact with water. Water is supplied to the sprayer 120. The negative electrode 60 is placed on the stand 110, and water is sprayed onto the negative electrode 60 from the sprayer 120. Here, even if the amount of water is small, it is possible to peel the negative electrode active material layer 64 from the copper foil. Therefore, the amount of water sprayed by the sprayer 120 may be approximately 20 mm / hour to 30 mm / hour.

[0049] In the active material layer peeling step S103, it is advantageous to recover hydrogen generated by contact of the negative electrode 60 with water. The hydrogen can be used as fuel for a fuel cell, etc. Recovery of hydrogen can be performed by a known method. In the example shown in FIG. 6, a hood of a hydrogen recovery device 130 is installed above the spray device 120, and hydrogen can be recovered by the hydrogen recovery device 130.

[0050] In the active material layer peeling step S103, it is advantageous to recover lithium hydroxide (LiOH) generated by contact between the negative electrode 60 and water. Lithium hydroxide is usually dissolved in the water that has been in contact with the negative electrode 60. Therefore, for example, by recovering the water that has been in contact with the negative electrode 60 and volatilizing the water, lithium hydroxide can be obtained as a recycled material.

[0051] After contacting the negative electrode 60 with water, the negative electrode active material layer 64 and the copper foil may be dried to remove the water. The obtained copper foil may be further subjected to washing, purification, and the like.

[0052] By performing the active material layer peeling step S103, copper foil can be easily obtained as a recycled material. By performing the active material layer peeling step S103, the negative electrode active material layer 64 can be obtained at the same time. Graphite can also be obtained as a recycled material from the negative electrode active material layer 64 according to a known method. If a binder, thickener, or the like has been used, the binder, thickener, or the like can also be obtained as a recycled material from the negative electrode active material layer 64 according to a known method. Therefore, the method for producing a recycled material according to this embodiment is useful in material recycling.

[0053] Test examples relating to the present disclosure will be described in detail below, but it is not intended that the present disclosure be limited to those shown in these examples.

[0054] [Preparation of Evaluation Battery] A negative electrode slurry was prepared by mixing graphite (C), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in a mass ratio of C:SBR:CMC = 99:0.5:0.5 in ion-exchanged water. This slurry was applied in strips to both sides of a long copper foil with a thickness of 8 μm, dried, and then pressed to prepare a negative electrode sheet.

[0055] LiNi 1 / 3 Co 1 / 3 Mn 1 / 3A positive electrode slurry was prepared by mixing O2 (LNCM), acetylene black (AB), and polyvinylidene fluoride (PVdF) in a mass ratio of LNCM:AB:PVdF = 92:5:3 in N-methylpyrrolidone (NMP). This slurry was applied in strips to both sides of a 15 μm-thick long aluminum foil, dried, and pressed to prepare a positive electrode sheet.

[0056] Two separators were prepared, each consisting of a porous polyolefin sheet with a three-layer structure of PP / PE / PP and provided with an HRL. The positive electrode sheet prepared above, the negative electrode sheet prepared above, and two separator sheets prepared above were stacked and wound, and then pressed from the side to compress the stack, thereby producing a flat wound electrode assembly.

[0057] Next, the wound electrode body was connected to a positive electrode terminal and a negative electrode terminal, and housed in a rectangular battery case with an inlet. A nonaqueous electrolyte was then poured into the inlet of the battery case, and the inlet was hermetically sealed. The nonaqueous electrolyte was prepared by dissolving LiPF6 as a supporting electrolyte at a concentration of 1.1 mol / L in a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of EC:DMC:EMC = 3:3:4. An initial charging process and an aging process were then performed to obtain a lithium-ion secondary battery for evaluation.

[0058] Examples and Comparative Examples The state of charge of the evaluation lithium ion secondary battery was adjusted to the negative electrode potential (based on lithium metal) shown in Table 1. However, in Comparative Example 1, the evaluation lithium ion secondary battery was left in an uncharged state. The evaluation lithium ion secondary battery was disassembled under an argon atmosphere, and the negative electrode was removed. The removed negative electrode was dried and then weighed, and the weight of the negative electrode active material layer of the negative electrode (referred to as weight A) was calculated based on this.

[0059] Next, the negative electrode was immersed in water for 3 minutes. The negative electrode was removed, dried, and then weighed. If the negative electrode active material layer had peeled off, the copper foil was removed, dried, and then weighed. Based on this, the weight of the negative electrode active material layer attached to the copper foil (referred to as weight B) was calculated. The peeling rate was calculated using the formula: (1 - weight B / weight A) x 100. The results are shown in Table 1.

[0060] [Table 1]

[0061] As shown in the results in Table 1, when the stage structure of graphite is stage 1, stage 2, or stage 3, the negative electrode active material layer can be peeled off from the copper foil at a high peeling rate by contacting the negative electrode with water. Therefore, it is clear that the method for producing recycled material of the present disclosure makes it possible to easily obtain copper foil as recycled material from lithium ion secondary batteries.

[0062] Although specific examples of the present disclosure have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations of the specific examples exemplified above.

[0063] That is, the method for producing recycled materials according to the present disclosure includes the following items [1] to [8]. [1] A step of preparing a lithium ion secondary battery including a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode includes a copper foil and a negative electrode active material layer containing graphite as a negative electrode active material, and the stage structure of the graphite is at least one stage selected from the group consisting of stage 1, stage 2, and stage 3; removing the negative electrode from the lithium ion secondary battery; and a step of bringing the negative electrode into contact with water to peel off the negative electrode active material layer from the copper foil A method for producing recycled materials, comprising: [2] The manufacturing method according to item [1], wherein the recycled material is copper foil. [3] The manufacturing method according to item [1] or [2], wherein in the peeling step, the negative electrode is brought into contact with the water by spraying the water onto the negative electrode. [4] The method according to any one of items [1] to [3], wherein the peeling step includes recovering hydrogen generated by contact of the negative electrode with the water. [5] The method according to any one of items [1] to [4], wherein the peeling step includes recovering lithium hydroxide generated by contact of the negative electrode with the water. [6] The manufacturing method according to any one of items [1] to [5], wherein the step of preparing the lithium ion secondary battery includes confirming whether the potential of the negative electrode of the lithium ion secondary battery is 180 mV or less versus lithium metal. [7] The manufacturing method according to any one of items [1] to [6], wherein the step of preparing the lithium ion secondary battery includes adjusting the state of charge of the lithium ion secondary battery so that the stage structure of the graphite is at least one stage selected from the group consisting of stage 1, stage 2, and stage 3. [8] The manufacturing method according to any one of items [1] to [7], wherein the step of preparing the lithium ion secondary battery includes recovering used lithium ion secondary batteries or unused lithium ion secondary batteries that were deemed defective during manufacturing and could not be shipped. [Explanation of symbols]

[0064] 20 Electrode body 30 Battery case 32 Exterior body 34 Lid 36 Safety valve 42 Positive terminal 42a Positive current collector plate 44 Negative terminal 44a Negative current collector plate 50 positive electrode 52 Positive electrode current collector 52a Portion where positive electrode active material layer is not formed 54 Cathode active material layer 60 negative electrode 62 Negative electrode current collector 62a Part where negative electrode active material layer is not formed 64 Negative electrode active material layer 70 Separator 100 Lithium-ion secondary battery

Claims

1. preparing a lithium ion secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode comprises a copper foil and a negative electrode active material layer containing graphite as a negative electrode active material, and the stage structure of the graphite is at least one stage selected from the group consisting of stage 1, stage 2, and stage 3; removing the negative electrode from the lithium ion secondary battery; and a step of bringing the negative electrode into contact with water to peel off the negative electrode active material layer from the copper foil A method for producing recycled materials, comprising:

2. The manufacturing method of claim 1 , wherein the recycled material is copper foil.

3. The method according to claim 1 , wherein in the peeling step, the negative electrode is brought into contact with the water by spraying the water onto the negative electrode.

4. The method according to claim 1 , wherein the step of separating the negative electrode includes collecting hydrogen generated by contact of the negative electrode with the water.

5. The method according to claim 1 , wherein the step of stripping includes recovering lithium hydroxide generated by contact of the negative electrode with the water.

6. 2. The method according to claim 1, wherein the step of preparing the lithium ion secondary battery includes confirming whether the potential of the negative electrode of the lithium ion secondary battery is 180 mV or less versus lithium metal.

7. 2. The manufacturing method according to claim 1, wherein the step of preparing the lithium ion secondary battery includes adjusting a state of charge of the lithium ion secondary battery so that a stage structure of the graphite is at least one stage selected from the group consisting of stage 1, stage 2, and stage 3.

8. 2. The manufacturing method according to claim 1, wherein the step of preparing the lithium ion secondary battery includes collecting used lithium ion secondary batteries or unused lithium ion secondary batteries that were deemed defective during manufacturing and could not be shipped.

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