Material recovery method of bipolar storage battery

Abstract

Provided is a method for easily separating a collector foil of a bipolar electrode by sufficiently removing an adhesive layer included in the bipolar electrode. A material recovery method for a bipolar storage battery comprising a lithium ion battery having a bipolar electrode having a positive electrode mixture provided on one surface of a current collector foil and a negative electrode mixture provided on the other surface of the current collector foil, a method for recovering a material for a bipolar storage battery in which a positive electrode foil and a negative electrode foil are bonded to a current collector foil via an adhesive layer containing an epoxy resin having a polyolefin as a basic skeleton, the method comprising: a separation step for separating the positive electrode foil and the negative electrode foil by removing the adhesive layer of the current collector foil, the current collector foil is heated to a temperature higher than the thermal decomposition temperature of the epoxy resin in an inert atmosphere.

Description

Technical Field

[0001] This invention relates to a method for recycling materials from a bipolar storage battery. Background Technology

[0002] Patent Document 1 discloses a bipolar battery in which the bipolar electrode comprises a resin substrate, a resin adhesive, a positive current collector bonded to one side of the substrate via the adhesive, and a negative current collector bonded to the other side of the substrate via the adhesive. In the structure described in Patent Document 1, in the method of recovering materials from the bipolar battery, when removing the adhesive contained in the bipolar electrode, the bipolar electrode is heated to above the thermal decomposition temperature of the adhesive.

[0003] Patent Document 1: Japanese Patent Application Publication No. 2022-147471 Summary of the Invention

[0004] In the structure described in Patent Document 1, the epoxy resin constituting the adhesive is at least one of bisphenol A type epoxy resin and bisphenol F type epoxy resin. Both bisphenol A type epoxy resin and bisphenol F type epoxy resin contain benzene rings in their molecular structures.

[0005] However, epoxy resins containing benzene rings still leave residues even after thermal decomposition at high temperatures. Regarding the thermal decomposition of epoxy resins, those containing benzene rings experience a sharp weight loss around 500°C, but retain several percent of residues above 600°C. These residues are primarily carbon, but depending on the temperature, they may remain in a tar-like form.

[0006] In the structure described in Patent Document 1, since the adhesive is composed of an epoxy resin containing benzene rings, even if the bipolar electrode is heated to above the thermal decomposition temperature of the adhesive when removing the adhesive, a portion of the adhesive will remain as residues, making it difficult to separate the positive current collector and the negative current collector.

[0007] The present invention was made in view of the above circumstances, and its object is to provide a material recycling method for a bipolar battery in which the current collector foil of the bipolar electrode can be easily separated by fully removing the adhesive layer contained in the bipolar electrode.

[0008] The present invention discloses a material recycling method for a bipolar battery, wherein the bipolar battery is composed of a lithium-ion battery having bipolar electrodes. The bipolar electrodes have a positive electrode material disposed on one side of a current collector foil and a negative electrode material disposed on the other side of the current collector foil. The material recycling method for the bipolar battery is characterized in that the current collector foil is bonded to the positive electrode foil and the negative electrode foil via an adhesive layer comprising an epoxy resin with a polyolefin basic skeleton. The material recycling method for the bipolar battery includes a separation step, wherein the positive electrode foil and the negative electrode foil are separated by removing the adhesive layer of the current collector foil. In the separation step, the current collector foil is heated to a temperature higher than the thermal decomposition temperature of the epoxy resin under an inactive atmosphere.

[0009] Invention Effects

[0010] In this invention, the current collector foil of the bipolar electrode can be easily separated by fully removing the adhesive layer contained in the bipolar electrode. Attached Figure Description

[0011] Figure 1 This is a schematic cross-sectional view of the bipolar electrode in the embodiment.

[0012] Figure 2 This is a flowchart illustrating a material recycling method for bipolar batteries.

[0013] Figure 3 This diagram illustrates the separation of aluminum foil and copper foil through heating a bipolar electrode.

[0014] Figure 4 This diagram illustrates the case where the current collector foil, after the electrode composite has been removed, is used as the separation object in the separation process.

[0015] Figure 5 This diagram illustrates the separation of aluminum foil and copper foil through heat treatment of the current collector foil. Detailed Implementation

[0016] The following describes in detail the material recycling method for a bipolar storage battery according to embodiments of the present invention. However, the present invention is not limited to the embodiments described below.

[0017] Figure 1 This is a schematic cross-sectional view of the bipolar electrode in the embodiment. The bipolar electrode 1 includes a current-collecting foil 2, a positive electrode composite 3, and a negative electrode composite 4. The bipolar electrode 1 is a component constituting a bipolar battery. A bipolar battery is a battery pack having multiple battery modules. A battery module is a battery pack having multiple battery cells. The battery module has multiple bipolar electrodes 1. The bipolar battery with bipolar electrodes 1 is installed in an electric vehicle. The electric vehicle is a battery electric vehicle (BEV) or a plug-in hybrid electric vehicle (PHEV).

[0018] The current collector foil 2 comprises an aluminum foil 5, a copper foil 6, an adhesive layer 7, and carbon coatings 8 and 9. The positive electrode 10 of the bipolar electrode 1 is a positive electrode on which a positive electrode composite 3 is disposed via the carbon coating 8 on the aluminum foil 5, which serves as the positive electrode substrate. The negative electrode 20 of the bipolar electrode 1 is a negative electrode on which a negative electrode composite 4 is disposed via the carbon coating 9 on the copper foil 6, which serves as the negative electrode substrate. In the bipolar electrode 1, the aluminum foil 5 is the positive electrode foil, and the copper foil 6 is the negative electrode foil. The bipolar battery having this bipolar electrode 1 is a bipolar lithium-ion battery.

[0019] The current collector foil 2 is a current collector, formed by bonding aluminum foil 5 and copper foil 6 together via adhesive layer 7. Aluminum foil 5 is the positive current collector. Copper foil 6 is the negative current collector. Adhesive layer 7 bonds aluminum foil 5 and copper foil 6. One side of aluminum foil 5 and one side of copper foil 6 are bonded together via adhesive layer 7. In bipolar electrode 1, positive electrode 10 and negative electrode 20 are bonded together via adhesive layer 7.

[0020] Adhesive layer 7 is composed of epoxy resin with a polyolefin as its basic backbone. Adhesive layer 7 is composed of epoxy resin that does not contain benzene rings and has a low thermal decomposition temperature. Adhesive layer 7 does not contain bisphenol A type epoxy resin or bisphenol F type epoxy resin. The epoxy resin used in adhesive layer 7 is an epoxy resin with a polyolefin as its basic backbone that is easily thermally decomposed. The thermal decomposition temperature of the epoxy resin contained in adhesive layer 7 is 250–350°C.

[0021] The other sides of aluminum foil 5 and copper foil 6 are covered with carbon coatings 8 and 9, respectively. Carbon coating 8 forms one side of current collector foil 2. Carbon coating 9 forms the other side of current collector foil 2.

[0022] A positive electrode material 3 is disposed on an aluminum foil 5 via a carbon coating 8. The positive electrode material 3 is disposed on the surface of the carbon coating 8. A negative electrode material 4 is disposed on a copper foil 6 via a carbon coating 9. The negative electrode material 4 is disposed on the surface of the carbon coating 9.

[0023] The positive electrode composite 3 contains a positive electrode active material. The positive electrode active material contains NCM (ternary cathode material) or LFP (lithium iron phosphate). The positive electrode composite 3 is coated on the surface of the carbon coating 8 on the positive electrode 10 side. The positive electrode composite 3 forms a positive electrode composite layer on one side of the current collector foil 2. The positive electrode composite layer is formed as a porous structure.

[0024] The negative electrode composite 4 contains a negative electrode active material. The negative electrode active material includes carbon, silicon dioxide, etc. The negative electrode composite 4 is coated on the surface of the carbon coating 9 on the negative electrode 20 side. The negative electrode composite 4 forms a negative electrode composite layer on the other side of the current collector foil 2. The negative electrode composite layer is formed as a porous structure.

[0025] In a bipolar battery having a bipolar electrode 1 formed by bonding aluminum foil 5 and copper foil 6 in this configuration, it is preferable to recover black powder from the bipolar electrode 1 during recycling, and to recover the collecting element from the bonding foil as a valuable resource. Black powder is a general term for a mixture containing positive electrode active material, negative electrode active material, and composite carbon components. The composite carbon components include conductive additives, binders, electrolyte components, etc.

[0026] For example, when recycling black powder, sometimes the bipolar electrode 1 is broken apart by contacting it with a rotating body. In this case, the bonding foil can be separated from the black powder, but due to the stress of the breakage, the aluminum and copper are complexly entangled by riveting, making physical separation difficult, and thus the bonding foil is difficult to separate. Methods for recovering copper by dissolving aluminum with acids are common, but the reagents for dissolving aluminum are costly, and the dissolved aluminum cannot be recycled as metal, which is a problem. Therefore, in the bipolar electrode 1, the basic framework of the epoxy resin used for bonding is a polyolefin that is easily thermally decomposed. The material recycling method for the bipolar battery in the embodiment includes a process in the lithium-ion battery recycling method of the bipolar electrode 1, in which the aluminum foil 5 and copper foil 6 of the bonding foil are separated to separate the bipolar electrode 1 into a single electrode in a sorting pretreatment step.

[0027] Figure 2 This is a flowchart illustrating a material recycling method for a bipolar battery. The bipolar battery material recycling method includes a decontamination process (step S1), a battery pack disassembly process (step S2), a battery module disassembly process (step S3), an electrolyte recovery process (step S4), a battery cell disassembly process (step S5), and a separation process (step S6). This bipolar battery material recycling method is a method for dry-separating the electrode assembly of a lithium-ion battery, and is included in the recycling method of a lithium-ion battery having bipolar electrodes 1. In this material recycling method, the electrode assembly is not peeled off from the current collector foil 2, but rather the bonding foil is separated while the electrode assembly is still attached.

[0028] The harmless disposal process is a process of discharging the battery pack to make it safe for disposal (step S1). The harmless disposal process includes the discharge process of the battery pack. The battery pack is a bipolar rechargeable battery with bipolar electrodes 1.

[0029] The battery pack disassembly process is the process of disassembling the battery pack and separating the battery modules from the components of the battery pack (step S2).

[0030] The battery module disassembly process involves removing the resin from the four sides of the battery module to allow separation by each bipolar electrode 1 (step S3). In this disassembly process, the resin, including sealing material, is removed from the four sides of the battery module, which is formed in a quadrilateral shape. This disassembly process includes removing the sealing material from the battery module to release the sealing of each battery cell.

[0031] The electrolyte recovery process is a process of recovering the electrolyte filled between the bipolar electrodes 1 by heating, depressurization, drying, etc., before the heat treatment of the bipolar electrodes 1 (step S4). In the electrolyte recovery process, the electrolyte is recovered from the battery cell after it has been desealed.

[0032] The battery cell disassembly process is a process of disassembling the battery cell after the electrolyte has been recovered (step S5). In this disassembly process, the battery cell is separated into terminals, resin components, bipolar electrodes 1, and a separator.

[0033] The separation process involves separating the bipolar electrode 1 into a positive electrode 10 and a negative electrode 20 (step S6). In this separation process, the bipolar electrode 1 is heated to remove the adhesive layer 7, thereby separating the bonding foil into an aluminum foil 5 and a copper foil 6. Figure 3 As shown, the separation process involves heating the bipolar electrode 1 in an inactive atmosphere at a high temperature for a short time to make it unipolar.

[0034] High-temperature heating refers to a temperature higher than the thermal decomposition temperature of epoxy resin. Since the thermal decomposition temperature of the epoxy resin contained in the adhesive layer 7 is 250–350°C, the heating temperature in the separation process is higher than 350°C. Preferably, the heating temperature in the separation process is 500°C or higher. Short heating time refers to a time of 5 minutes or less. Preferably, the heating time in the separation process is 2–3 minutes or less.

[0035] Thus, the separation process is carried out for a short time (within 5 minutes) in an inactive atmosphere at a temperature higher than the thermal decomposition temperature of epoxy resin (250-350°C), preferably above 500°C. By performing the separation process, the epoxy resin can be volatilized and removed without causing aluminum oxidation and embrittlement, and the bipolar electrode 1 can be separated into a single electrode, a positive electrode 10 and a negative electrode 20.

[0036] For example, in the separation process, the bipolar electrode 1 is rapidly heated to over 500°C under an inactive atmosphere, causing the epoxy resin constituting the adhesive layer 7 in the bonding foil to vaporize without burning. This separates the positive electrode assembly 3 and the negative electrode assembly 4 from the current collector foil 2, separating them into the positive electrode 10 and the negative electrode 20. The inactive atmosphere used in the separation process can be a gas such as nitrogen or heating steam, or it can be a state where no new gas is supplied in a closed furnace. By using an inactive atmosphere, combustion of flammable gases originating from the adhesive layer 7, the positive electrode 10, and the negative electrode 20 does not occur during heat treatment, preventing the aluminum foil 5 from oxidizing and becoming embrittled, thus separating the bipolar electrode 1. At this time, through heating, the electrode assembly does not slip off; only the adhesive layer 7 volatilizes, allowing separation into the positive electrode 10 and the negative electrode 20. This suppresses embrittlement caused by aluminum oxidation and prevents the electrode assembly from slipping off.

[0037] The material is separated into positive electrode 10 and negative electrode 20 through a separation process, allowing for the separate recycling of each electrode composite. The unipolar material can be efficiently recycled using existing recycling processes. After the separation process, positive electrode 10 undergoes a positive electrode processing step, and negative electrode 20 undergoes a negative electrode processing step. In the positive electrode processing step, only the positive electrode composite 3 can be recovered.

[0038] The positive electrode composite 3 contains PVdF (polyvinylidene fluoride) as a binder. The negative electrode composite 4 contains SBR (styrene-butadiene rubber) as a binder. It is presumed that the PVdF or SBR binders also thermally decompose at around 350°C, but since both the positive and negative electrode composites 3 and 4 are porous and contain carbon materials that act as thermal insulation, the heating of the electrode composites is delayed during the heat treatment in the separation process. Therefore, by limiting the heating time in the separation process, the thermal decomposition of the binder can be suppressed, preventing the electrode composites from slipping off. In the separation process, a high-temperature, short-time heat treatment is performed under an inactive atmosphere, specifying that the epoxy resin is decomposed first. In summary, there exists a condition where, through high-temperature, short-time heat treatment, only the adhesive layer 7 of the bonding foil can be decomposed before the binder of the electrode composites decomposes. The short heating time in the separation process refers to the time before the thermal decomposition of the binder contained in the positive electrode composite 3 and the time before the thermal decomposition of the binder contained in the negative electrode composite 4.

[0039] Suppose that during a prolonged heating process in the separation step, such as heating for more than 10 minutes, in addition to the thermal decomposition of the adhesive layer 7, the binder in the electrode assembly also undergoes thermal decomposition. The effect of the binder's thermal decomposition becomes significant, causing the electrode assembly to slip off the current collector foil 2. As a result, the electrode assembly, aluminum foil 5, and copper foil 6 are recovered, but this electrode assembly is a mixed powder formed by mixing the positive electrode assembly 3 and the negative electrode assembly 4. Therefore, it is not possible to recover only the positive electrode assembly 3, making direct recycling difficult.

[0040] As explained above, according to the embodiment, since the epoxy resin constituting the adhesive layer 7 has a basic framework of polyolefin that is easily thermally decomposed and volatile, the adhesive layer 7 can be completely removed when treated at a temperature sufficiently higher than the thermal decomposition temperature of the resin during the separation process. Therefore, the aluminum foil 5 and copper foil 6 can be easily separated from the laminating foil. Furthermore, the heat treatment at a sufficiently high temperature can also decompose trace amounts of electrolyte components remaining in the electrode composite, achieving harmlessness simultaneously with the separation.

[0041] Furthermore, in the separation process, the heating treatment is carried out at high temperature for a short time under an inactive atmosphere, so that only the adhesive layer 7 of the current collector foil 2 can be decomposed before the binders of the positive electrode 10 and the negative electrode 20 decompose. As a result, combustion caused by oxygen does not occur in the separation process, and the bipolar electrode 1 can be separated into a unipolar electrode. As a result, direct recycling is possible.

[0042] Alternatively, carbon coatings 8 and 9 may be omitted. For example, positive electrode material 3 is formed by coating the surface of aluminum foil 5 with positive electrode paste. Similarly, negative electrode material 4 is formed by coating the surface of copper foil 6 with negative electrode paste.

[0043] Furthermore, in the separation process, to prevent repolymerization, combustion, solidification, and tarring caused by prolonged retention of decomposition gases, it is preferable to effectively vent the combustible gases from the decomposition of epoxy resin outside the system. Therefore, the heating treatment under an inactive atmosphere in the separation process is preferably carried out while the inactive gas is flowing, rather than being heated in a closed furnace.

[0044] And, as Figure 4 As shown, in the separation process, the current collector foil 2, in a state where the positive electrode material 3 and the negative electrode material 4 have been removed, can also be used as the separation object. That is, the battery cell disassembly process (step S5) may include a process of removing the positive electrode material 3 and the negative electrode material 4 coated on the current collector foil 2 from the separated bipolar electrode 1 and recovering the positive electrode material 3 and the negative electrode material 4 from the bipolar electrode 1. In this separation process (step S6), as Figure 5 As shown, the current collector foil 2, after the positive electrode composite 3 and negative electrode composite 4 have been recovered, is separated into aluminum foil 5 and copper foil 6. During the separation process, when the current collector foil 2 after the electrode composites have been removed is heated, the short-time condition is eliminated because the thermal decomposition of the adhesive is not a concern, allowing for a longer heating time. This separation process is carried out at a temperature higher than the thermal decomposition temperature of epoxy resin (250–350°C) (preferably 500°C or higher) and in an inactive atmosphere. Unlike epoxy resins with a general bisphenol A-based backbone, the adhesive layer 7 residues are not left during thermal decomposition, allowing for easy separation into aluminum foil 5 and copper foil 6.

[0045] Symbol Explanation

[0046] 1-Bipolar electrode, 2-Current collector foil, 3-Positive electrode composite, 4-Negative electrode composite, 5-Aluminum foil, 6-Copper foil, 7-Adhesive layer, 8, 9-Carbon coating.

Claims

1. A method for recycling materials from a bipolar storage battery, wherein the bipolar storage battery is composed of a lithium-ion battery having bipolar electrodes, wherein a positive electrode material is disposed on one side of a current collector foil, and a negative electrode material is disposed on the other side of the current collector foil, the method for recycling materials from the bipolar storage battery being characterized in that... The current collector foil is bonded to the positive electrode foil and the negative electrode foil via an adhesive layer comprising an epoxy resin with a polyolefin-based skeleton. The material recycling method for the bipolar battery includes: The separation process involves removing the adhesive layer of the current-collecting foil to separate the positive electrode foil and the negative electrode foil. In the separation process, the current collector foil is heated to a temperature higher than the thermal decomposition temperature of the epoxy resin under an inactive atmosphere.

2. The material recycling method for a bipolar storage battery according to claim 1, characterized in that, In the separation process, the bipolar electrode containing the positive electrode material and the negative electrode material is used as the separation object, and the bipolar electrode is heated in the inactive atmosphere at a heating temperature higher than the thermal decomposition temperature of the epoxy resin for a short heating time.

3. The material recycling method for a bipolar storage battery according to claim 2, characterized in that, The short heating time refers to the time before the binder contained in the positive electrode composite material undergoes thermal decomposition, and the time before the binder contained in the negative electrode composite material undergoes thermal decomposition.

4. The material recycling method for a bipolar storage battery according to claim 2, characterized in that, The short heating time is within 5 minutes.

5. The material recycling method for a bipolar storage battery according to claim 1, characterized in that, In the separation process, the current collector foil, which is the object of separation, is in a state in which the positive electrode composite and the negative electrode composite are removed from each side of the current collector foil.

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