Method for recovering materials from bipolar batteries

Abstract

To easily separate the current collector foil of a bipolar electrode by thoroughly removing the adhesive layer contained in the bipolar electrode. [Solution] A method for recovering materials from a bipolar storage battery comprising a lithium-ion battery having bipolar electrodes in which a positive electrode composite material is provided on one side of the current collector foil and a negative electrode composite material is provided on the other side of the current collector foil, wherein the positive electrode foil and the negative electrode foil are bonded to the current collector foil via an adhesive layer containing an epoxy resin with a polyolefin as the basic framework, and the method includes a separation step of separating the positive electrode foil and the negative electrode foil by removing the adhesive layer of the current collector foil, wherein in the separation step 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] The present invention relates to a method for recovering materials from bipolar batteries.

Background Art

[0002] Patent Document 1 discloses that a bipolar electrode of a bipolar battery has a resin substrate, a resin adhesive, a positive current collector adhered to one surface of the substrate via the adhesive, and a negative current collector adhered to the other surface of the substrate via the adhesive. In the configuration described in Patent Document 1, in a method for recovering materials from a bipolar battery, when removing the adhesive contained in the bipolar electrode, the bipolar electrode is heated to a temperature equal to or higher than the thermal decomposition temperature of the adhesive.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the configuration 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 a benzene ring in their molecular structures.

[0005] However, for an epoxy resin containing a benzene ring, residues remain even after thermal decomposition at high temperature. Regarding the thermal decomposition of the epoxy resin, although an epoxy resin containing a benzene ring rapidly loses weight around 500°C, several percent of residues remain even at 600°C or higher. This residue is mainly carbon, but there is a risk that it may remain in a tarry state depending on the temperature.

[0006] In the configuration described in Patent Document 1, since the adhesive is made of epoxy resin containing a benzene ring, even if the bipolar electrode is heated above the thermal decomposition temperature of the adhesive when removing the adhesive, some of the adhesive remains as residue, making it difficult to separate the positive electrode current collector and the negative electrode current collector.

[0007] The present invention has been made in view of the above circumstances, and aims to provide a method for recovering materials from a bipolar battery that allows for easy separation of the current collector foil of a bipolar electrode by sufficiently removing the adhesive layer contained in the bipolar electrode. [Means for solving the problem]

[0008] The present invention relates to a method for recovering materials from a bipolar storage battery comprising a lithium-ion battery having bipolar electrodes in which a positive electrode composite material is provided on one side of the current collector foil and a negative electrode composite material is provided on the other side of the current collector foil, wherein the positive electrode foil and the negative electrode foil are bonded to the current collector foil via an adhesive layer containing an epoxy resin with a polyolefin as the basic framework, and the method includes a separation step of separating the positive electrode foil and the negative electrode foil by removing the adhesive layer of the current collector foil, wherein in the separation step the current collector foil is heated to a temperature higher than the thermal decomposition temperature of the epoxy resin in an inert atmosphere. [Effects of the Invention]

[0009] In this invention, the current collector foil of the bipolar electrode can be easily separated by sufficiently removing the adhesive layer contained in the bipolar electrode. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic cross-sectional view showing a bipolar electrode in an embodiment. [Figure 2] This is a flowchart illustrating a method for recovering materials from bipolar batteries. [Figure 3] This figure shows that the aluminum foil and copper foil are separated by heating the bipolar electrode. [Figure 4]This diagram shows the case where the current collector foil, with the electrode composite removed, is the target of separation in the separation process. [Figure 5] This diagram shows that the aluminum foil and copper foil are separated by heat treatment of the current collector foil. [Modes for carrying out the invention]

[0011] The following describes in detail the method for recovering materials from a bipolar battery in an embodiment of the present invention. However, the present invention is not limited to the embodiments described below.

[0012] Figure 1 is a schematic cross-sectional view showing a bipolar electrode in an embodiment. The bipolar electrode 1 comprises a current collector foil 2, a positive electrode composite material 3, and a negative electrode composite material 4. The bipolar electrode 1 is a component of a bipolar type storage battery. A bipolar type storage battery is a battery pack comprising multiple battery modules. A battery module is a battery pack having multiple battery cells. A battery module comprises multiple bipolar electrodes 1. A bipolar type storage battery having bipolar electrodes 1 is installed in an electric vehicle. Electric vehicles include electric vehicles (BEVs) and plug-in hybrid vehicles (PHEVs).

[0013] The current collector foil 2 comprises aluminum foil 5, copper foil 6, an adhesive layer 7, and carbon coating layers 8 and 9. The positive electrode 10 of the bipolar electrode 1 is formed by providing a positive electrode composite material 3 on the aluminum foil 5, which is the positive electrode base material, via a carbon coating layer 8. The negative electrode 20 of the bipolar electrode 1 is formed by providing a negative electrode composite material 4 on the copper foil 6, which is the negative electrode base material, via a carbon coating layer 9. In the bipolar electrode 1, the aluminum foil 5 is the positive electrode foil, and the copper foil 6 is the negative electrode foil. A bipolar battery having this bipolar electrode 1 is a bipolar lithium-ion battery.

[0014] The current collector foil 2 is a current collector, and is a laminated foil in which aluminum foil 5 and copper foil 6 are bonded together via an adhesive layer 7. The aluminum foil 5 is the positive electrode current collector. The copper foil 6 is the negative electrode current collector. The adhesive layer 7 bonds the aluminum foil 5 and the copper foil 6. One side of the aluminum foil 5 and one side of the copper foil 6 are bonded together by the adhesive layer 7. In the bipolar electrode 1, the positive electrode 10 and the negative electrode 20 are bonded together via the adhesive layer 7.

[0015] The adhesive layer 7 is composed of an epoxy resin with a polyolefin as its basic structure. The adhesive layer 7 is composed of an epoxy resin that does not contain benzene rings and has a low thermal decomposition temperature. The adhesive layer 7 does not contain bisphenol A type epoxy resin or bisphenol F type epoxy resin. The epoxy resin used in the adhesive layer 7 is an epoxy resin with a polyolefin as its basic structure that is easily thermally decomposed. The thermal decomposition temperature of the epoxy resin contained in the adhesive layer 7 is 250 to 350°C.

[0016] The aluminum foil 5 and copper foil 6 each have their other surfaces covered by carbon coating layers 8 and 9. Carbon coating layer 8 forms one surface of the current collector foil 2. Carbon coating layer 9 forms the other surface of the current collector foil 2.

[0017] The aluminum foil 5 is provided with a positive electrode mixture 3 via a carbon coating layer 8. The positive electrode mixture 3 is provided on the surface of the carbon coating layer 8. The copper foil 6 is provided with a negative electrode mixture 4 via a carbon coating layer 9. The negative electrode mixture 4 is provided on the surface of the carbon coating layer 9.

[0018] The positive electrode composite material 3 contains a positive electrode active material. The positive electrode active material contains NCM (ternary positive electrode material) or LFP (lithium iron phosphate). The positive electrode composite material 3 is applied to the surface of the carbon coating layer 8 on the positive electrode 10 side. The positive electrode composite material 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 material.

[0019] The negative electrode composite material 4 contains a negative electrode active material. The negative electrode active material includes carbon, silica, etc. The negative electrode composite material 4 is applied to the surface of the carbon coating layer 9 on the negative electrode 20 side. The negative electrode composite material 4 forms a negative electrode composite material layer on the other surface of the current collector foil 2. The negative electrode composite material layer is formed as a porous body.

[0020] In the bipolar battery having the bipolar electrode 1 in which the aluminum foil 5 and the copper foil 6 are laminated as thus configured, it is desirable to recover black mass from the bipolar electrode 1 during recycling and to recover the current collector from the laminated foil as a valuable material. Black mass is a general term for a mixed substance containing a positive electrode active material, a negative electrode active material, and a composite carbon component. The composite carbon component includes a conductive assistant, a binder, an electrolyte component, etc.

[0021] For example, when recovering black mass, crushing separation may be performed by a method of bringing the bipolar electrode 1 into contact with a rotating body. In this case, although it can be separated into the laminated foil and the black mass, separation of the laminated foil is difficult because aluminum and copper are intricately intertwined by caulking due to the stress of crushing and physical separation becomes difficult. Generally, there is a method of dissolving aluminum with an acid or the like to recover copper, but problems are that the reagent for dissolving aluminum is costly and the dissolved aluminum cannot be recycled as a metal. Therefore, in the bipolar electrode 1, the basic skeleton of the epoxy resin used for adhesion is made of a polyolefin that is easily thermally decomposed. The material recovery method of the bipolar battery in the embodiment includes a step of separating the aluminum foil 5 and the copper foil 6 of the laminated foil to separate the bipolar electrode 1 into monopolar electrodes in a pretreatment step of sorting among the recycling methods of the lithium ion battery provided with the bipolar electrode 1.

[0022] Figure 2 is a flowchart illustrating a method for recovering materials from a bipolar battery. The method for recovering materials from a bipolar battery includes a detoxification step (step S1), a battery pack dismantling step (step S2), a battery module dismantling step (step S3), an electrolyte recovery step (step S4), a battery cell dismantling step (step S5), and a separation step (step S6). This method for recovering materials from a bipolar battery is a method for dry-separating the electrode composite material of a lithium-ion battery and is included in the recycling method for lithium-ion batteries having bipolar electrodes 1. This material recovery method separates the bonded foil while the electrode composite material is still attached, rather than peeling it off the current collector foil 2.

[0023] The detoxification process is a process of discharging the battery pack to make it safe to handle (step S1). The detoxification process includes a battery pack discharge process. This battery pack is a bipolar type rechargeable battery having bipolar electrodes 1.

[0024] The battery pack dismantling process involves dismantling the battery pack and separating the battery module from the battery pack's components (step S2).

[0025] The battery module disassembly process involves disassembling the battery module and removing the resin from all four sides of the battery module so that each bipolar electrode can be separated (step S3). In this disassembly process, the resin, such as sealing material, from all four sides of the rectangularly shaped battery module is removed. This disassembly process includes removing the sealing material from the battery module to release the sealed state of each battery cell.

[0026] The electrolyte recovery step is a process of recovering the electrolyte that fills the space between the bipolar electrodes 1 by heating, vacuum drying, etc., before heat treatment of the bipolar electrodes 1 (step S4). In the electrolyte recovery step, the electrolyte is recovered from the battery cell after the sealed state has been released.

[0027] The battery cell dismantling process is the process of dismantling the battery cell after the electrolyte has been recovered (step S5). In this dismantling process, the battery cell is separated into terminals, resin components, bipolar electrodes 1, and separators.

[0028] The separation step is a process of separating the bipolar electrode 1 into a positive electrode 10 and a negative electrode 20 (step S6). In the separation step, the bipolar electrode 1 is heat-treated to remove the adhesive layer 7, thereby separating the bonded foil into aluminum foil 5 and copper foil 6. As shown in Figure 3, in the separation step, the bipolar electrode 1 is heat-treated in an inert atmosphere at a high heating temperature and for a short heating time to make it monopolar.

[0029] A high heating temperature is a temperature higher than the thermal decomposition temperature of the 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 step will be higher than 350°C. Preferably, the heating temperature in the separation step is 500°C or higher. A short heating time is a time of 5 minutes or less. Preferably, the heating time in the separation step is 2-3 minutes or less.

[0030] In this separation process, the epoxy resin is treated at a temperature higher than the thermal decomposition temperature of the epoxy resin (250-350°C), preferably 500°C or higher, for a short time (within 5 minutes) in an inert atmosphere. By performing this separation process, the epoxy resin is removed by volatilization without the aluminum becoming oxidatively embrittlementable, and the bipolar electrode 1 can be separated into a monopolar electrode consisting of a positive electrode 10 and a negative electrode 20.

[0031] For example, the separation process involves rapidly heating the bipolar electrode 1 to over 500°C in an inert atmosphere, gasifying the epoxy resin constituting the adhesive layer 7 in the laminated foil without combustion, and separating the positive electrode 10 and negative electrode 20 without peeling the positive electrode composite material 3 and negative electrode composite material 4 from the current collector foil 2. The inert atmosphere used in the separation process may be a gaseous atmosphere such as nitrogen or heated steam, or it may be a sealed furnace without a new gas supply. Because it is an inert atmosphere, combustion from flammable gases generated from the adhesive layer 7, positive electrode 10 and negative electrode 20 during the heat treatment does not occur, and the bipolar electrode 1 can be separated without oxidative embrittlement of the aluminum foil 5. At that time, the electrode composite material does not slide off during heating, and only the adhesive layer 7 volatilizes, separating the positive electrode 10 and negative electrode 20. In this way, embrittlement due to aluminum oxidation can be suppressed, and the sliding off of the electrode composite material can be prevented.

[0032] The separation process separates the positive electrode 10 and the negative electrode 20, allowing for the separate recovery of each electrode composite material. The monopolarized material can be recycled efficiently using existing recycling flows. After the separation process, the positive electrode 10 undergoes a positive electrode processing process, and the negative electrode 20 undergoes a negative electrode processing process. In the positive electrode processing process, only the positive electrode composite material 3 can be recovered.

[0033] The positive electrode mixture 3 contains PVdF (polyvinylidene fluoride) as a binder. The negative electrode mixture 4 contains SBR (styrene-butadiene rubber) as a binder. Although the binders PVdF and SBR also decompose at around 350°C, it is presumed that the porous nature of the positive electrode mixture 3 and negative electrode mixture 4, and the inclusion of carbon material, slows down the heating of the electrode mixture during the separation process. Therefore, the short heating time in the separation process suppresses the thermal decomposition of the binder, preventing the electrode mixture from sliding off. In the separation process, high-temperature, short-time heating in an inert atmosphere creates conditions under which the epoxy resin is heated and decomposed first. In short, by heating at high temperature for a short time, conditions exist that allow only the adhesive layer 7 of the bonded foil to decompose before the binder of the electrode mixture decomposes. The short heating time in the separation process is the time until the binder contained in the positive electrode mixture 3 decomposes due to thermal decomposition, and the time until the binder contained in the negative electrode mixture 4 decomposes due to thermal decomposition.

[0034] If the separation process involves prolonged heating, for example, for more than 10 minutes, the adhesive layer 7 will decompose due to thermal decomposition. In addition, the binder in the electrode mixture will also decompose, and the effects of this thermal decomposition will become significant, causing the electrode mixture to slide off the current collector foil 2. As a result, the electrode mixture, aluminum foil 5, and copper foil 6 will be recovered. However, this electrode mixture is a mixed powder of positive electrode mixture 3 and negative electrode mixture 4. Therefore, it becomes impossible to recover only the positive electrode mixture 3, making direct recycling difficult.

[0035] As explained above, according to the embodiment, since the epoxy resin constituting the adhesive layer 7 is based on a polyolefin that is easily thermally decomposed and volatile, if the separation process is performed at a temperature sufficiently higher than the thermal decomposition temperature of the resin, it is possible to remove the entire adhesive layer 7. This makes it possible to easily separate the aluminum foil 5 and the copper foil 6 in the bonded foil. In addition, heating at a sufficiently high temperature can also decompose trace amounts of electrolyte components remaining in the electrode mixture, making them harmless along with the separation.

[0036] Furthermore, by performing a high-temperature, short-time heat treatment in an inert atmosphere during the separation process, it is possible to decompose only the adhesive layer 7 of the current collector foil 2 before the binders of the positive electrode 10 and negative electrode 20 decompose. As a result, the bipolar electrode 1 can be separated into a monopolar electrode without oxygen combustion occurring during the separation process. Consequently, direct recycling becomes possible.

[0037] Note that the carbon coating layers 8 and 9 are not necessarily required. For example, the positive electrode slurry is applied to the surface of the aluminum foil 5 to form the positive electrode mixture 3. Similarly, the negative electrode slurry is applied to the surface of the copper foil 6 to form the negative electrode mixture 4.

[0038] Furthermore, in the separation process, it is desirable to efficiently discharge the flammable gas produced by the decomposition of the epoxy resin from the system in order to prevent repolymerization, combustion, solidification, and tar formation due to the prolonged retention of decomposition gases. For this reason, the heat treatment in the separation process is preferable to the treatment while flowing an inert gas rather than heating in a sealed furnace.

[0039] Furthermore, as shown in Figure 4, the separation step may target the current collector foil 2 from which the positive electrode mixture 3 and negative electrode mixture 4 have been removed. That is, the battery cell dismantling step (step S5) may include a step of removing the positive electrode mixture 3 and negative electrode mixture 4 applied to the current collector foil 2 from the separated bipolar electrode 1 and recovering the positive electrode mixture 3 and negative electrode mixture 4 from the bipolar electrode 1. In this separation step (step S6), as shown in Figure 5, the aluminum foil 5 and copper foil 6 are separated from the current collector foil 2 after the positive electrode mixture 3 and negative electrode mixture 4 have been recovered. When the current collector foil 2 from which the electrode mixture has been removed is heat-treated in the separation step, it is not necessary to consider the thermal decomposition of the binder, so the condition of short duration is excluded, and the heating time may be long. This separation step is performed at a temperature higher than the thermal decomposition temperature of epoxy resin (250-350°C) (preferably 500°C or higher) and in an inert atmosphere. Unlike typical epoxy resins that use bisphenol A as their basic structure, no residues of the adhesive layer 7 remain during thermal decomposition, and the aluminum foil 5 and copper foil 6 can be easily separated. [Explanation of symbols]

[0040] 1 Bipolar electrode 2 Current collector foil 3. Positive electrode composite material 4 Negative electrode mixture 5. Aluminum foil 6 Copper foil 7 Adhesive layer 8,9 Carbon coating layer

Claims

1. A method for recovering materials from a bipolar battery comprising a lithium-ion battery having bipolar electrodes in which a positive electrode composite material is provided on one side of the current collector foil and a negative electrode composite material is provided on the other side of the current collector foil, The current collector foil is formed by bonding the positive electrode foil and the negative electrode foil via an adhesive layer containing an epoxy resin with a polyolefin as the basic framework. The separation step includes removing the adhesive layer of the current collector foil to separate the positive electrode foil and the negative electrode 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 inert atmosphere. A method for recovering materials from a bipolar battery, characterized by the following features.

2. In the separation step, the bipolar electrode containing the positive electrode mixture and the negative electrode mixture is separated, and the bipolar electrode is heated in an inert atmosphere at a heating temperature higher than the thermal decomposition temperature of the epoxy resin and for a short heating time. A method for recovering materials from a bipolar battery according to feature 1.

3. The aforementioned short heating time is the time until the binder contained in the positive electrode mixture undergoes thermal decomposition, and the time until the binder contained in the negative electrode mixture undergoes thermal decomposition. The method for recovering materials from a bipolar battery according to feature 2.

4. The aforementioned short heating time is a time of 5 minutes or less. The method for recovering materials from a bipolar battery according to feature 2.

5. The current collector foil to be separated in the separation step is in a state in which the positive electrode composite material and the negative electrode composite material have been removed from each surface of the current collector foil. A method for recovering materials from a bipolar battery according to feature 1.

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