Power storage device, and method for manufacturing recycled negative electrode current collector

Abstract

To easily separate a negative electrode active substance from a negative electrode current collector.SOLUTION: A power storage device 100 includes a negative electrode 60 having a sheet-like negative electrode current collector 62, and a negative electrode active substance layer 64 provided on the negative electrode current collector 62. The negative electrode active substance layer 64 includes a first negative electrode active substance layer 641 and a second negative electrode active substance layer 642. The first negative electrode active substance layer 641 contains a negative electrode active substance, a binder composed of a resin A, and a resin B. The second negative electrode active substance layer 642 contains a negative electrode active substance, and a binder, and a content of the resin B is smaller than a content of the resin B in the first negative active substance layer 641. Here, the resin B is a resin having water solubility and thermoplasticity. The first negative electrode active substance layer 641 is provided between the second negative electrode active substance layer 642 and the negative electrode current collector 62.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to an electricity storage device and a method for producing a recycled negative electrode current collector. [Background technology]

[0002] JP 2017-98155 A discloses a method for manufacturing a non-aqueous electrolyte secondary battery. This manufacturing method includes the steps of mixing polyethylene oxide (PEO) having a number average molecular weight of 2 million or more, carboxymethyl cellulose (CMC), and water to prepare an aqueous solution of PEO and CMC, adding a negative electrode active material and a binder to the aqueous solution and kneading the mixture to obtain a negative electrode paste, and applying the negative electrode paste onto a negative electrode current collector and drying the negative electrode to obtain a negative electrode. The publication states that this configuration makes it possible to manufacture a non-aqueous electrolyte secondary battery that has good initial resistance and suppresses an increase in battery resistance when repeatedly charged and discharged at a high rate.

[0003] Japanese Patent Laid-Open Publication No. 9-45328 discloses a lithium secondary battery including a spirally wound electrode body formed by winding a negative electrode and a positive electrode with a separator therebetween, and a non-aqueous electrolyte. The negative electrode is formed by forming an active material layer containing a powder of carbon particles and a binder on a metal foil or film. The non-aqueous electrolyte contains a halogen-containing lithium salt as a solute. The carbon particles have a polyethylene oxide coating on the surface. The publication describes that the polyethylene oxide coating on the surface of the carbon particles prevents contact between the hydrohalic acid generated in the battery can and the carbon particles in a charged state, so that self-discharge is unlikely to occur even when the battery is stored for a long period of time.

[0004] JP 2014-127417 A discloses a method for reusing a negative electrode active material layer of a lithium ion battery. This method includes steps (1) to (3). In step (1), a negative electrode having a negative electrode active material layer containing a non-aqueous binder and a current collector is immersed in an aqueous solution at a temperature higher than 50° C. In step (2), the peeled negative electrode active material layer is recovered. In step (3), the recovered negative electrode active material layer is attached to the current collector again. This publication describes that since the negative electrode active material layer and the current collector can be peeled off using an aqueous solution, the negative electrode active material layer can be recovered with almost no change in composition. This publication also describes that the peeled negative electrode active material layer can be dried, and then a viscosity adjusting solvent is added and stirred with a homogenizer to form a slurry, which can be applied to the negative electrode current collector, and therefore the layer can be reused as a negative electrode.

[0005] JP 2006-228509 A discloses a method for recycling a negative electrode active material for a non-aqueous electrolyte secondary battery. This method includes the steps of removing a negative electrode plate from a non-aqueous electrolyte secondary battery, washing the negative electrode plate with a liquid containing water, separating the washed negative electrode plate into a negative electrode mixture containing a negative electrode active material and a binder and a current collecting substrate, and mixing the negative electrode mixture with a solvent capable of dissolving or dispersing the binder to prepare a negative electrode paste, which is then applied to a negative electrode current collector. The publication states that this method makes it possible to reuse used negative electrode active materials as negative electrode active materials for non-aqueous electrolyte secondary batteries. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2017-98155 A [Patent Document 2] Japanese Patent Application Publication No. 9-45328 [Patent Document 3] JP 2014-127417 A [Patent Document 4] JP 2006-228509 A Summary of the Invention [Problem to be solved by the invention]

[0007] In recent years, as electricity storage devices have become more widespread, interest in reusing electricity storage devices has increased, and there is an increasing demand for the development of recycling technologies for electricity storage devices. Therefore, the present inventors decided to study the configuration of electricity storage devices that can be easily reused after use. The present inventors wanted to make it easier to separate the negative electrode active material layer from the negative electrode current collector. [Means for solving the problem]

[0008] The power storage device disclosed herein includes a negative electrode having a sheet-shaped negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector. The negative electrode active material layer includes a first negative electrode active material layer and a second negative electrode active material layer. The first negative electrode active material layer includes a negative electrode active material, a binder made of resin A, and resin B. The second negative electrode active material layer includes a negative electrode active material and a binder, and the content of resin B is smaller than the content of resin B in the first negative electrode active material layer. Here, resin B is a resin that is water-soluble and thermoplastic. The first negative electrode active material layer is provided between the second negative electrode active material layer and the negative electrode current collector. This configuration makes it easier to separate the negative electrode active material layer from the negative electrode current collector. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic cross-sectional view of an electricity storage device 100. As shown in FIG. [Diagram 2] FIG. 2 is a schematic diagram of the electrode body 20. [Diagram 3] FIG. 3 is a schematic cross-sectional view of the negative electrode 60. [Figure 4] FIG. 4 is a schematic cross-sectional view of the first negative electrode active material layer 641. [Diagram 5] FIG. 5 is an SEM image of Example 1. [Figure 6] FIG. 6 is a binarized image of the first embodiment. [Figure 7] FIG. 7 is an SEM image of Example 2. [Figure 8] FIG. 8 is a binarized image of the second embodiment. [Figure 9] FIG. 9 is an SEM image of Comparative Example 1. [Figure 10] FIG. 10 is a binarized image of Comparative Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] An embodiment of the technology disclosed herein will be described below. The embodiment described herein is not intended to limit the technology disclosed herein. The technology disclosed herein is not limited to the embodiment described herein unless otherwise specified. The drawings are drawn typically and do not necessarily reflect the actual product. In addition, the same reference numerals are appropriately used for members and parts that perform the same function, and duplicated explanations are omitted. In addition, the notation "A to B" indicating a numerical range means "A or more and B or less" unless otherwise specified, and also includes the meaning of "greater than A and less than B."

[0011] In this specification, the term "electricity storage device" refers to a device in which charging and discharging occurs by the movement of charge carriers between a pair of electrodes (positive and negative electrodes) via an electrolyte. Such electricity storage devices include secondary batteries such as lithium ion secondary batteries, nickel-metal hydride batteries, and nickel-cadmium batteries; and capacitors such as lithium ion capacitors and electric double layer capacitors. In the following, an embodiment in which a lithium ion secondary battery is used as an example of the above-mentioned electricity storage device will be described.

[0012] Fig. 1 is a schematic cross-sectional view of an electricity storage device 100. Fig. 1 is a schematic cross-sectional view along a first side surface 31b of the electricity storage device 100. As shown in Fig. 1, the electricity storage device 100 includes an electrode body 20, a case 30, and a non-aqueous electrolyte solution 80.

[0013] Fig. 2 is a schematic diagram of the electrode assembly 20. As shown in Fig. 1 and Fig. 2, the electrode assembly 20 is a wound electrode assembly in which a long sheet-like positive electrode 50 and a long sheet-like negative electrode 60 are stacked with a long sheet-like separator 70 interposed therebetween and wound in the sheet longitudinal direction (hereinafter also simply referred to as the "longitudinal direction"). In the electrode assembly 20, an exposed region 52a in the positive electrode 50 and an exposed region 62a in the negative electrode 60 protrude outward from both ends in the lateral direction perpendicular to the longitudinal direction.

[0014] As shown in FIG. 1 and FIG. 2, the positive electrode 50 includes a long sheet-like positive electrode collector 52 and a positive electrode active material layer 54. The positive electrode collector 52 is, for example, an aluminum foil. In this embodiment, the positive electrode collector 52 has a region where the positive electrode active material layer 54 is provided and an exposed region 52a where the positive electrode active material layer 54 is not provided and the surface of the positive electrode collector 52 is exposed. The positive electrode active material layer 54 is provided, for example, in a strip shape along the longitudinal direction on one side or both sides (both sides here) of the positive electrode collector 52. The positive electrode active material layer 54 is not provided at the end in the short side direction (the end on the left side in the figure). Here, the exposed region 52a is a strip-shaped region at the end in the short side direction (the end on the left side in the figure). As shown in FIG. 1, the current collector 42a is attached to the exposed region 52a.

[0015] The positive electrode active material layer 54 contains, for example, a positive electrode active material. The positive electrode active material is, for example, a lithium nickel cobalt manganese composite oxide (NCM) (for example, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2), LiNiO2, LiCoO2, LiFeO2, LiMn2O4, LiNi 0.5 Mn 1.5Examples of the positive electrode active material layer 54 include lithium transition metal oxides such as LiFePO4, and lithium transition metal phosphate compounds such as LiFePO4. The positive electrode active material layer 54 may contain a conductive material, a binder, and the like in addition to the positive electrode active material. Examples of the conductive material include carbon black such as acetylene black (AB), and other carbon materials such as graphite. Examples of the binder include polyvinylidene fluoride (PVDF).

[0016] FIG. 3 is a schematic cross-sectional view of the negative electrode 60. In FIG. 3, a schematic cross-sectional structure of the negative electrode collector 62 and the negative electrode active material layer 64 in the negative electrode 60 is partially enlarged and shown. As shown in FIGS. 1 to 3, the negative electrode 60 includes a long sheet-like negative electrode collector 62 and a negative electrode active material layer 64. The negative electrode collector 62 is, for example, a copper foil. In this embodiment, the negative electrode collector 62 has a region where the negative electrode active material layer 64 is provided and an exposed region 62a where the negative electrode active material layer 64 is not provided and the surface of the negative electrode active material layer 64 is exposed. The negative electrode active material layer 64 is provided in a strip shape along the longitudinal direction on one or both sides (both sides in this case) of the negative electrode collector 62, for example. The negative electrode active material layer 64 is not provided on the end (the right end in the figure) in the short direction perpendicular to the longitudinal direction. The exposed area 62a is a strip-shaped area at the end in the short direction (the end on the right side in the drawing). As shown in Fig. 1, the current collector plate 44a is attached to the exposed area 62a.

[0017] As shown in FIG. 3, the negative electrode active material layer 64 has a first negative electrode active material layer 641 and a second negative electrode active material layer 642. Here, the first negative electrode active material layer 641 is provided between the negative electrode current collector 62 and the second negative electrode active material layer 642. FIG. 4 is a schematic cross-sectional view of the first negative electrode active material layer 641. FIG. 4 shows a schematic cross-sectional structure of a part of the first negative electrode active material layer 641 near the negative electrode current collector 62 in an enlarged partial view. As shown in FIG. 4, the first negative electrode active material layer 641 contains a negative electrode active material 681, a binder 682, and a resin B 683.

[0018] The negative electrode active material 681 may be, for example, a carbon material such as graphite, hard carbon, or soft carbon, but may also be silicon (Si). The binder 682 is made of resin A here. The resin A may be a resin constituting a binder used in a negative electrode active material layer in an electricity storage device for this type of application. The resin A may be, for example, a water-soluble binder, and may be styrene butadiene rubber (SBR). By using SBR as the binder 682 (resin A), the bonding between the negative electrode current collector 62 and the first negative electrode active material layer 641 can be made in a favorable state, and the current collection efficiency in the negative electrode 60 can be made appropriate. SBR can form an emulsion solution with water. For this reason, for example, water can be used when treating the negative electrode 60, and the environmental load can be reduced.

[0019] The resin B683 is, for example, a resin different from the resin A681. Here, the resin B683 is a resin having water solubility and thermoplasticity. In this specification, the term "thermoplastic resin" refers to a resin that has a property of reversibly softening or melting at a temperature equal to or higher than the glass transition point to be plastically deformed, and reversibly hardening at a temperature equal to or lower than the glass transition point. By including the resin B683 that is water soluble and has thermoplasticity in the first negative electrode active material layer 641, for example, when the negative electrode 60 is treated with water at a predetermined temperature, the resin B683 softens or melts, and the adhesiveness between the first negative electrode active material layer 641 and the negative electrode current collector 62 decreases. This makes it easier for the first negative electrode active material layer 641 to separate from the negative electrode current collector 62.

[0020] As the resin B683, for example, a resin having a softening point according to the temperature of water used in treating the negative electrode 60 can be preferably used. The softening point of the resin B683 is generally 120°C or less, for example, 100°C or less, preferably 90°C or less, more preferably 85°C or less, even more preferably 80°C or less, and particularly preferably 75°C or less. By using a resin with a lower softening point as the resin B683, the negative electrode current collector 62 and the negative electrode active material layer 64 can be separated with less energy, which can contribute to reducing the environmental load. The softening point of the resin B683 is, for example, 50°C or more, preferably 55°C or more, and more preferably 60°C or more. By using a resin with a higher softening point as the resin B683, the negative electrode 60 can be treated at a temperature suitable for separating the negative electrode current collector 62 and the negative electrode active material layer 64, which can increase the efficiency of separation between the negative electrode current collector 62 and the negative electrode active material layer 64.

[0021] In this specification, the term "softening point" refers to the temperature at which the resin begins to deform when the temperature of the resin is increased. As the softening point of the resin, for example, a value obtained using a differential scanning calorimeter (DSC) may be used. Alternatively, a nominal value from a manufacturer or the like may be used.

[0022] The weight average molecular weight of the resin B683 may be determined, for example, in consideration of the bonding strength of the first negative electrode active material layer 641 to the negative electrode current collector 62. The weight average molecular weight of the resin B683 is generally 30,000 or more, for example 50,000 or more, preferably 100,000 or more, more preferably 500,000 or more, even more preferably 1 million or more, and particularly preferably 3 million or more. The larger the weight average molecular weight of the resin B683, the higher the bonding strength between the negative electrode current collector 62 and the first negative electrode active material layer 641 can be, and the negative electrode active material layer 64 can be stably held on the negative electrode current collector 62. Therefore, the current collection efficiency of the negative electrode 60 can be increased. The weight average molecular weight of the resin B683 is generally 30 million or less, for example 25 million or less, preferably 20 million or less, more preferably 15 million or less, and even more preferably 10 million or less. The smaller the weight-average molecular weight of the resin B683, the higher the efficiency of separating the first negative electrode active material layer 641 from the negative electrode current collector 62, and thus the higher the purity of the negative electrode current collector 62 that can be recovered. Note that, as the weight-average molecular weight of the resin B683, for example, a value obtained using gel permeation chromatography (GPC) can be used. Alternatively, a nominal value provided by a manufacturer or the like may be used.

[0023] The type of resin B683 is not particularly limited as long as it has water solubility and thermoplasticity and can realize the effects of the technology disclosed herein. Examples of resin B683 include polyethylene glycol (PEG), polyethylene oxide (PEO), polyvinyl alcohol (PVA), polyvinyl acetate (PVAc), and water-soluble acrylic resin (e.g., sodium polyacrylate). Among them, polyethylene oxide (PEO) can be preferably used from the viewpoint of more appropriately realizing the effects of the technology disclosed herein.

[0024] From the viewpoint of appropriately achieving the effects of the technology disclosed herein, the ratio of the resin B683 in the first negative electrode active material layer 641 is approximately 10 mass % or less, for example 5 mass % or less, preferably 3 mass % or less, and more preferably 2 mass % or less, relative to the entire first negative electrode active material layer 641. From the same viewpoint, the ratio of the resin B683 in the first negative electrode active material layer 641 is approximately 0.1 mass % or more, for example 0.3 mass % or more, preferably 0.5 mass % or more, and more preferably 0.7 mass % or more, relative to the entire first negative electrode active material layer 641.

[0025] From the viewpoint of appropriately achieving the effects of the technology disclosed herein, the ratio (mass ratio) of resin A682 to resin B683 in the first negative electrode active material layer 641 (resin A:resin B) is preferably 1:3 to 3:1, more preferably 1:2 to 2:1, and even more preferably set to about 1:1.

[0026] The second negative electrode active material layer 642 here is a layer that contains a negative electrode active material and a binder, and the content of resin B is smaller than the content of resin B 683 in the first negative electrode active material layer 641. The negative electrode active material used here is the same negative electrode active material as the negative electrode active material 681 contained in the first negative electrode active material layer 641. The binder here is resin A, and is preferably the same resin as the resin A 682 contained in the first negative electrode active material layer 641.

[0027] 3, the second negative electrode active material layer 642 is provided on the first negative electrode active material layer 641. By providing the first negative electrode active material layer 641 and the second negative electrode active material layer 642, which are layers having different configurations, in the negative electrode 60, it is possible to realize the effects of the technology disclosed herein and to appropriately charge and discharge the electricity storage device 100.

[0028] The content of resin B in the second negative electrode active material layer 642 is, for example, ½ or less, preferably ⅓ or less, more preferably ¼ or less, and even more preferably 1 / 10 or less of the content of resin B in the first negative electrode active material layer 641. The smaller the content of resin B in the second negative electrode active material layer 642, the higher the charge / discharge efficiency of the electricity storage device 100 can be. For this reason, it is preferable that the second negative electrode active material layer 642 does not contain resin B.

[0029] The proportion of the binder in the second negative electrode active material layer 642 may be, for example, 0.3 mass % to 10 mass %, and preferably 0.5 mass % to 5 mass %, in consideration of the fact that the binder is appropriately retained in the first negative electrode active material layer 641 and that charging and discharging of the electricity storage device 100 is appropriately performed.

[0030] The first negative electrode active material layer 641 and the second negative electrode active material layer 642 are configured as described above, but may contain other additives (e.g., dispersants, surfactants, thickeners, etc.) as necessary, as long as the effects of the technology disclosed herein can be realized. The other additives exclude the above-mentioned negative electrode active material, resin A, and resin B.

[0031] A method for producing (manufacturing) the negative electrode 60 includes, for example, forming a first negative electrode active material layer 641 and forming a second negative electrode active material layer 642. In forming the first negative electrode active material layer 641, for example, the first negative electrode active material layer 641 is formed on the surface of the negative electrode current collector 62. In this embodiment, the formation of the first negative electrode active material layer 641 includes a preparation step, a kneading step, a dilution step, a mixing step, a coating step, a drying step, and a pressing step.

[0032] The preparation step is, for example, a step of preparing a material for the first negative electrode active material layer 641. Here, a negative electrode active material, resin A as a binder, and resin B are prepared. The kneading step is, for example, a step of kneading the negative electrode active material and resin B. Here, a predetermined amount of the negative electrode active material and resin B are first put into a kneading machine (for example, a planetary mixer, etc.) to obtain a mixed powder. Next, water is added to the mixed powder until the mixed powder becomes clayey. Then, the mixed powder to which water has been added is kneaded. The solid content rate in the kneading step is appropriately changed depending on the type and combination of materials used, but is preferably approximately 60% or more (for example, 60% to 70%). The kneading is preferably performed, for example, until the kneaded product has no particles (so-called lumps) that have grown to a predetermined size or more and is in a uniform state. As described above, in the kneading step, the negative electrode active material and resin B are kneaded at a high solid content rate and in a clayey state. This allows resin B to be more uniformly disposed on the surface of the negative electrode active material.

[0033] The dilution process is, for example, a process of diluting the kneaded material obtained in the kneading process. In this embodiment, water is added to the kneaded material obtained in the kneading process (here, the kneaded material without lumps) and kneading is continued until the kneaded material becomes a paste. The mixing process is, for example, a process of mixing the kneaded material after the dilution process with a binder. In this embodiment, a binder emulsion solution (for example, an aqueous emulsion solution of resin A) prepared to a predetermined concentration is added to the kneaded material that has become a paste after the dilution process, and mixed with the paste-like kneaded material to obtain a slurry for forming a first negative electrode active material layer.

[0034] The coating step is, for example, a step of coating a first negative electrode active material layer forming slurry on a negative electrode current collector. In this embodiment, the slurry is coated on a copper foil as a negative electrode current collector. The coating method is not particularly limited, and a conventionally known method may be adopted. The drying step is, for example, a step of drying the first negative electrode active material layer forming slurry coated on the negative electrode current collector in the coating step to obtain a dry film. The drying conditions are not particularly limited, and the conditions used in producing this type of negative electrode may be appropriately adopted. The pressing step is, for example, a step of pressing the dry film obtained in the drying step to obtain a first negative electrode active material layer. The pressing conditions are not particularly limited, and the conditions used in producing this type of negative electrode may be appropriately adopted.

[0035] The formation of the second negative electrode active material layer 642 is not particularly limited, and for example, a negative electrode active material and a binder are dispersed in water to prepare a slurry for forming the second negative electrode active material layer. Next, the slurry is applied to the surface of the first negative electrode active material layer 641 and dried. Then, here, by pressing, the negative electrode 60 is produced in which the negative electrode active material layer 64 having the first negative electrode active material layer 641 and the second negative electrode active material layer 642 is provided on the surface of the negative electrode current collector 62.

[0036] The separator 70 may be, for example, a porous sheet (film) made of a resin material such as polyethylene (PE), polypropylene (PP), polyester, cellulose, or polyamide. The porous sheet may have a single-layer structure or a laminated structure of two or more layers (for example, a three-layer structure in which PP layers are laminated on both sides of a PE layer). A heat-resistant layer (HRL) may be provided on the surface of the separator 70.

[0037] The case 30 is, for example, an outer container that houses the electrode body 20 and the nonaqueous electrolyte solution 80. Here, the case 30 is a flat rectangular case. As shown in FIG. 1, the case 30 includes a main body 31 and a sealing plate 32. Here, the main body 31 houses the electrode body 20. In this embodiment, the main body 31 has a rectangular bottom surface 31a, a pair of opposing first side surfaces 31b, a pair of opposing second side surfaces 31c, and an opening 31h. In the embodiment shown in FIG. 1, the pair of opposing first side surfaces 31b are surfaces extending from a pair of opposing long sides of the bottom surface 31a. The pair of opposing second side surfaces 31c are surfaces extending from a pair of opposing short sides of the bottom surface 31a. The opening 31h is surrounded by the pair of opposing first side surfaces 31b and the pair of opposing second side surfaces 31c, and faces the bottom surface 31a.

[0038] The sealing plate 32 is, for example, a member that closes the opening 31h. The sealing plate 32 may have, for example, a shape that corresponds to the outer shape of the opening 31h. In this embodiment, the sealing plate 32 is fitted into the opening 31h and joined to the periphery of the opening 31h (the main body 31), thereby closing the opening 31h. The main body 31 and the sealing plate 32 are joined by, for example, laser welding or the like.

[0039] As shown in FIG. 1, the case 30 has a positive electrode terminal 42, a negative electrode terminal 44, a safety valve 36, and a liquid injection hole (not shown) in the sealing plate 32. The positive electrode terminal 42 is, for example, a terminal for external connection on the positive electrode side. Here, the positive electrode terminal 42 is electrically connected to the positive electrode 50 of the electrode body 20 via a current collector 42a. The negative electrode terminal 44 is, for example, a terminal for external connection on the negative electrode side. Here, the negative electrode terminal 44 is electrically connected to the negative electrode 60 of the electrode body 20 via a current collector 44a. The safety valve 36 is, for example, a thin-walled portion that is set to release the internal pressure when the internal pressure of the case 30 rises to a predetermined level or higher. The liquid injection hole is, for example, a portion for injecting a nonaqueous electrolyte 80 into the case 30.

[0040] The non-aqueous electrolyte 80 contains, for example, an electrolyte salt and a non-aqueous solvent. The electrolyte salt can be, for example, LiPF6. The concentration of the electrolyte salt in the non-aqueous electrolyte 80 may be, for example, 0.7 mol / L to 1.3 mol / L. The non-aqueous solvent may be, for example, a carbonate such as ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), monofluoroethylene carbonate (MFEC), difluoroethylene carbonate (DFEC), monofluoromethyl difluoromethyl carbonate (F-DMC), or trifluorodimethyl carbonate (TFDMC). These may be used alone or in combination of two or more.

[0041] The power storage device 100 can be used for various purposes. Suitable applications include a driving power source mounted on vehicles such as electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs). The power storage device 100 can be used as a storage battery for small-sized power storage devices and the like. A plurality of power storage devices 100 may be connected in series and / or in parallel to form a battery pack.

[0042] As described above, the power storage device 100 includes a negative electrode 60 having a sheet-shaped negative electrode current collector 62 and a negative electrode active material layer 64 provided on the negative electrode current collector 62. The negative electrode active material layer 64 includes a first negative electrode active material layer 641 and a second negative electrode active material layer 642. The first negative electrode active material layer 641 includes a negative electrode active material 681, a binder 682 made of resin A, and a resin B 683 (see FIG. 4). The second negative electrode active material layer 642 includes a negative electrode active material and a binder, and the content of resin B is smaller than the content of resin B 683 in the first negative electrode active material layer 641. Here, the resin B 683 is a resin that is water-soluble and thermoplastic. The first negative electrode active material layer 641 is provided between the second negative electrode active material layer 642 and the negative electrode current collector 62.

[0043] By forming the negative electrode active material layer 64 into a two-layer structure of the first negative electrode active material layer 641 and the second negative electrode active material layer 642, it is possible to impart different functions to each layer. By making the first negative electrode active material layer contain a relatively large amount of the resin B863 having water solubility and thermoplasticity, it is possible to increase the affinity between the first negative electrode active material layer 641 and water when treating the negative electrode 60. When the water used to treat the negative electrode 60 is heated, the resin B863 having thermoplasticity is deformed by heat, so that the adhesiveness of the first negative electrode active material layer 641 to the negative electrode current collector 62 may decrease. For this reason, by providing the first negative electrode active material layer 641 between the negative electrode current collector 62 and the second negative electrode active material layer 642, it is possible to more easily separate the negative electrode active material layer 64 from the negative electrode current collector 62. As a result, it is possible to recover a high-purity negative electrode current collector, and therefore the recyclability of the electricity storage device 100 can be improved. In addition, by making the content of resin B in the second negative electrode active material layer 642 relatively small, a configuration is realized in which charging and discharging of the electricity storage device 100 is performed appropriately.

[0044] According to the technology disclosed herein, a method for manufacturing a recycled negative electrode current collector is disclosed. The method for manufacturing a recycled negative electrode current collector disclosed herein includes, for example, removing the negative electrode 60 from the above-mentioned electricity storage device 100 and isolating the negative electrode current collector 62 from the negative electrode 60. As described above, in the electricity storage device 100, the negative electrode active material layer 64 is easily separated from the negative electrode current collector 62. According to the method for manufacturing a recycled negative electrode current collector disclosed herein, a negative electrode current collector with high purity as a raw material can be manufactured, and therefore the recyclability of the electricity storage device 100 can be improved.

[0045] This manufacturing method includes, for example, an opening step, a first removal step, a second removal step, an isolation step, and a drying step. The opening step is, for example, a step of opening the electricity storage device 100. In this embodiment, the electricity storage device 100 is opened by separating the sealing plate 32 from the main body 31 of the case 30. For example, a means for processing this type of electricity storage device 100 is adopted without any particular limitation for separating the sealing plate 32 from the main body 31. Prior to the opening step, it is preferable to discharge the electricity storage device 100 as necessary. The first removal step is, for example, a step of removing the electrode body 20 from the opened electricity storage device 100. In this embodiment, the electrode body 20 is connected to a positive electrode terminal 42 and a negative electrode terminal 44 provided on the sealing plate 32. Therefore, for example, the electrode body 20 may be removed from the electricity storage device 100 as a combined body with the sealing plate 32 after the opening step.

[0046] The second removal step is, for example, a step of removing the negative electrode 60 from the electrode body 20 in the first removal step. In this first removal step, the electrode body 20 is removed as a combination of the sealing plate 32, the positive electrode terminal 42, and the negative electrode terminal 44. For example, in the second removal step, the electrode body 20 and the sealing plate 32 may be separated by first removing the current collector plate 22a and the current collector plate 24a from the electrode body 20. Next, the negative electrode 60 may be removed from the electrode body 20 separated from the sealing plate 32.

[0047] The isolation step is, for example, a step of isolating the negative electrode current collector 62 from the negative electrode 60. The negative electrode 60 is the negative electrode 60 taken out in the second removal step. In this embodiment, in the isolation step, the negative electrode current collector 62 is isolated by immersing the negative electrode 60 in heated water. The temperature of the water can be appropriately set according to, for example, the type and content of the resin B. The lower the temperature of the water in which the negative electrode 60 is immersed, the smaller the energy required to recover the negative electrode current collector 62 can be, and the environmental load can be reduced. The temperature of the water is, for example, the boiling point or lower (100°C or lower), and from the above-mentioned viewpoint, is preferably 95°C or lower, more preferably 90°C or lower, further preferably 85°C or lower, and particularly preferably 80°C or lower. The higher the temperature of the water in which the negative electrode 60 is immersed, the easier it is to separate the first negative electrode active material layer 641 from the negative electrode current collector 62, and therefore the higher purity negative electrode current collector 62 can be recovered. From this viewpoint, the temperature of the water is, for example, 50° C. or higher, preferably 55° C. or higher, and more preferably 60° C. or higher. Although not particularly limited, from the viewpoint of more efficiently isolating the negative electrode current collector 62, the water in which the negative electrode 60 is immersed may be stirred, or a container containing the negative electrode 60 and water may be shaken.

[0048] The negative electrode current collector 62 isolated by the isolation step can be used as a raw material for a regenerated negative electrode current collector, for example, after washing, drying, etc. as necessary. Although not particularly limited, the isolated negative electrode current collector 62 can be used, for example, as a copper raw material in a refining step of electrolytic copper foil. Since the isolated negative electrode current collector 62 has a higher purity, the use of this as a copper raw material allows efficient electrolytic refining.

[0049] Test examples relating to the present invention will be described below, but it is not intended that the present invention be limited to those shown in the following test examples.

[0050] <Preparation of Test Negative Electrode> Example 1 Natural graphite particles were prepared as the negative electrode active material. Styrene butadiene rubber (SBR) was prepared as resin A. Polyethylene oxide (PEO) with a weight average molecular weight of 8 million was prepared as resin B. First, the negative electrode active material and resin B were weighed to a predetermined ratio and mixed using a planetary mixer to obtain a mixed powder. Next, water was added to the mixed powder until the mixed powder became clayey. Then, the mixed powder was kneaded using a planetary mixer. The solid content rate during the kneading was approximately 60%. The kneading was performed until particles (so-called lumps) that had grown to a predetermined size or more in the kneaded material were no longer visually observed. Then, the kneaded material was further kneaded while adding water until it became a paste. Next, an SBR emulsion solution prepared to a predetermined concentration was added and mixed with the paste-like mixture to obtain a slurry for forming a first negative electrode active material layer. The mass ratio of the negative electrode active material, resin A (binder), and resin B in the slurry (negative electrode active material:resin A:resin B) was 98:1:1.

[0051] Next, the first negative electrode active material layer forming slurry was applied to both sides of a copper foil, dried, and then compressed using a roll press to form a first negative electrode active material layer on the copper foil. This was the test negative electrode of this example. The coating amount (weight per unit area) of the negative electrode was 10 mg / cm per side. 2 The density of the first negative electrode active material layer after pressing was 1.5 g / cm 3 It was.

[0052] Example 2 Polyethylene oxide (PEO) having a weight average molecular weight of 5 million was used as the resin B. Except for this, the test negative electrode of this example was produced using the same materials and procedures as in Example 1.

[0053] Example 3 Polyethylene oxide (PEO) having a weight average molecular weight of 4 million was used as the resin B. Except for this, the test negative electrode of this example was produced using the same materials and procedures as in Example 1.

[0054] -Comparative Example- Carboxymethyl cellulose (CMC) having a weight average molecular weight of 300,000 was used in place of Resin B. Except for this, the test negative electrode of this example was produced using the same materials and procedures as in Example 1.

[0055] <Measurement of carbon residual rate> The test negative electrode of each example was stirred in warm water at 70°C for 1 hour. Then, the test negative electrode was taken out of the water and dried. Next, the surface of the test negative electrode after drying was observed using a scanning electron microscope (SEM), and five observation images were randomly obtained. The size of the observation image was set to be a surface image of the negative electrode and to include a field of view of 1.5 cm x 1.5 cm. The obtained observation images were binarized using the image analysis software "ImageJ", and the area ratio of the black part in the observation image was calculated. The arithmetic average value of the area ratio of the black part calculated in the five observation images was obtained, and it was defined as the carbon residual rate (%) in the test negative electrode. The results are shown in the corresponding column in Table 1.

[0056] 5 to 10 show SEM observation images and binarized images obtained by binarization processing. FIG. 5 is an SEM observation image of Example 1. FIG. 6 is a binarized image of Example 1. FIG. 7 is an SEM observation image of Example 2. FIG. 8 is a binarized image of Example 2. FIG. 9 is an SEM observation image of Comparative Example 1. FIG. 10 is a binarized image of Comparative Example 1. The images shown in FIGS. 5 to 10 all have an observation field of 1.5 cm long x 1.5 cm wide. The scale bar indicates 5 mm. In FIGS. 6, 8, and 10, as described above, the black parts are parts where carbon remains.

[0057] [Table 1]

[0058] As shown in Table 1, the carbon residual ratios in Examples 1 to 3 were lower than those in the comparative example. The test negative electrodes in Examples 1 to 3 were provided with a first negative electrode active material layer containing a resin B (here, polyethylene oxide (PEO)) having water solubility and thermoplasticity. From the results of this test example, it was found that in a negative electrode having a negative electrode active material layer containing a first negative electrode active material and a second negative electrode active material layer, and having a first negative electrode active material layer containing a resin B having water solubility and thermoplasticity between a negative electrode current collector and a second negative electrode active material, the negative electrode active material layer is easily separated from the negative electrode current collector. It was found that a recycled negative electrode current collector with higher purity can be manufactured by using an electricity storage device having such a negative electrode.

[0059] As described above, specific aspects of the technology disclosed herein include those described in the following sections. Section 1: An electricity storage device including a negative electrode having a sheet-shaped negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector, The negative electrode active material layer is a first negative electrode active material layer including a negative electrode active material, a binder made of resin A, and resin B; a second negative electrode active material layer including the negative electrode active material and the binder, the second negative electrode active material layer having a content of the resin B smaller than a content of the resin B in the first negative electrode active material layer; It has Where: The resin B is a resin having water solubility and thermoplasticity, the first negative electrode active material layer is provided between the second negative electrode active material layer and the negative electrode current collector. Section 2: Item 2. The power storage device according to item 1, wherein the content of the resin B in the second negative electrode active material layer is ¼ or less of the content of the resin B in the first negative electrode active material layer. Section 3: Item 3. The electricity storage device according to item 1 or 2, wherein the softening point of the resin B is 80° C. or lower. Section 4: 4. The electricity storage device according to any one of items 1 to 3, wherein the resin B is polyethylene oxide. Section 5: 5. The electricity storage device according to any one of items 1 to 4, wherein the resin B has a weight average molecular weight of 100,000 to 10,000,000. Item 6: 6. The electricity storage device according to any one of items 1 to 5, wherein the resin A is a styrene-butadiene rubber. Section 7: 7. A method for producing a recycled negative electrode current collector, comprising: removing the negative electrode from the electricity storage device according to any one of items 1 to 6; and isolating the negative electrode current collector from the negative electrode. Section 8: Item 8. The method according to item 7, wherein the negative electrode current collector is isolated by immersing the negative electrode in water at 80° C. or lower.

[0060] Although the embodiment of the technology disclosed herein has been described above, it is not intended that the technology disclosed herein be limited to the above embodiment. The technology disclosed herein may be implemented in other embodiments. The technology described in the claims includes various modifications and changes to the above-exemplified embodiments. For example, it is possible to replace a part of the above-described embodiment with another modified embodiment, and it is also possible to add another modified embodiment to the above-described embodiment. Furthermore, if a technical feature is not described as essential, it is also possible to delete it as appropriate. [Explanation of symbols]

[0061] 20 Electrode body 30 cases 50 positive electrode 60 negative electrode 62 Negative electrode current collector 64 Negative electrode active material layer 641 First negative electrode active material layer 642 Second negative electrode active material layer 100 Energy storage device

Claims

1. An electricity storage device including a negative electrode having a sheet-shaped negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector, The negative electrode active material layer is a first negative electrode active material layer including a negative electrode active material, a binder including a resin A, and a resin B; a second negative electrode active material layer including the negative electrode active material and the binder, the second negative electrode active material layer having a content of the resin B smaller than a content of the resin B in the first negative electrode active material layer; It has Where: The resin B is a resin having water solubility and thermoplasticity, the first negative electrode active material layer is provided between the second negative electrode active material layer and the negative electrode current collector.

2. The power storage device according to claim 1 , wherein a content of the resin B in the second negative electrode active material layer is equal to or less than ¼ of a content of the resin B in the first negative electrode active material layer.

3. The electricity storage device according to claim 1 , wherein the resin B has a softening point of 80° C. or lower.

4. The electricity storage device according to claim 1 , wherein the resin B is polyethylene oxide.

5. The electricity storage device according to claim 4, wherein the weight average molecular weight of the resin B is 100,000 to 10,000,000.

6. The electricity storage device according to claim 1 , wherein the resin A is a styrene-butadiene rubber.

7. A method for producing a recycled negative electrode current collector, comprising: removing the negative electrode from the electricity storage device according to any one of claims 1 to 6; and isolating the negative electrode current collector from the negative electrode.

8. The method according to claim 7 , wherein the negative electrode current collector is isolated by immersing the negative electrode in water at or below 80° C.

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