Electric storage device and method for manufacturing regenerative negative collector

Abstract

The invention relates to an electricity storage device and a method for manufacturing a regenerative negative electrode current collector. A negative electrode active material is easily separated from a negative electrode current collector. An electricity storage device (100) is provided with 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) contains a negative electrode active material, a binder comprising a resin A, and a resin B. The second negative electrode active material layer (642) contains a negative electrode active material and a binder, and the content of the resin B is lower than the content of the resin B in the first negative electrode active material layer (641). Wherein the resin B is resin with water solubility and thermoplasticity. 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).

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing an electricity storage device and a regenerated negative electrode current collector. Background Art

[0002] Japanese Patent Publication No. 2017-98155 discloses a method for manufacturing a non-aqueous electrolyte secondary battery. The manufacturing method includes: a process of mixing polyethylene oxide (PEO) with a number average molecular weight of more than 2 million, carboxymethyl cellulose (CMC) and water to prepare an aqueous solution of PEO and CMC; a process of adding a negative electrode active material and a binder to the aqueous solution and kneading to obtain a negative electrode paste; and a process of applying the negative electrode paste to a negative electrode collector and drying to obtain a negative electrode. The bulletin records that by using this structure, a non-aqueous electrolyte secondary battery with good initial resistance and suppressed increase in battery resistance during repeated charge and discharge at a high rate can be manufactured.

[0003] Japanese Patent Publication No. 9-45328 discloses a lithium secondary battery, which includes a spiral electrode body formed by winding a diaphragm (separator) between a negative electrode and a positive electrode into a spiral shape, and a non-aqueous electrolyte. The negative electrode is formed by forming an active material layer containing a powder composed 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 bulletin records that the polyethylene oxide coating present on the surface of the carbon particles prevents the contact between the hydrohalic acid generated in the battery can and the carbon particles in a charged state, so that self-discharge is difficult to occur even in the case of long-term storage.

[0004] Japanese Patent Publication No. 2014-127417 discloses a method for recycling the negative electrode active material layer of a lithium ion battery. The 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 stripped negative electrode active material layer is recovered. In step (3), the recovered negative electrode active material layer is again attached to the current collector. The publication states that the negative electrode active material layer and the current collector can be stripped using an aqueous solution, so there is almost no change in the composition and the negative electrode active material layer can be recovered. The publication states that by drying the stripped negative electrode active material layer, adding a viscosity adjusting solvent, and stirring with a homogenizer, the slurry can be formed and applied to the negative electrode collector, so that it can be reused as a negative electrode.

[0005] Japanese Patent Publication No. 2006-228509 discloses a method for recycling negative electrode active materials for non-aqueous electrolyte secondary batteries. The method includes: a process of removing the negative electrode plate from the non-aqueous electrolyte secondary battery; a process of washing the negative electrode plate with a liquid containing water; a process of separating the washed negative electrode plate into a current collector substrate and a negative electrode composite material containing a negative electrode active material and a binder; a process of mixing the negative electrode composite material in a solvent that can dissolve or disperse the binder, preparing a negative electrode paste, and then applying it on the negative electrode collector. The publication records that by using this method, the used negative electrode active material can be reused as a negative electrode active material for non-aqueous electrolyte secondary batteries.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Publication No. 2017-98155

[0009] Patent Document 2: Japanese Patent Application Laid-Open No. 9-45328

[0010] Patent Document 3: Japanese Patent Application Publication No. 2014-127417

[0011] Patent Document 4: Japanese Patent Application Publication No. 2006-228509 Summary of the invention

[0012] Problems to be solved by the invention

[0013] In recent years, with the popularization of power storage devices, the concern about the recycling of power storage devices has been increasing, and the development of recycling technology for power storage devices has been increasingly needed. Therefore, the present inventors have studied the structure of power storage devices that are easy to reuse after use. The present inventors have tried to more easily separate the negative electrode active material layer from the negative electrode collector.

[0014] Means for solving problems

[0015] The power storage device disclosed herein includes a negative electrode having a sheet-shaped negative electrode collector and a negative electrode active material layer arranged on the negative electrode 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 contains a negative electrode active material, a binder composed of resin A, and resin B. The second negative electrode active material layer contains a negative electrode active material and a binder, and the content of resin B in the second negative electrode active material layer is less than the content of resin B in the first negative electrode active material layer. Among them, resin B is a water-soluble and thermoplastic resin. The first negative electrode active material layer is arranged between the second negative electrode active material layer and the negative electrode collector. According to this structure, the negative electrode active material layer can be more easily separated from the negative electrode collector. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a schematic cross-sectional view of the power storage device 100 .

[0017] Figure 2 is a schematic diagram of the electrode body 20 .

[0018] Figure 3 Schematic cross-sectional view of the negative electrode 60 .

[0019] Figure 4 FIG. 6 is a schematic cross-sectional view of the first negative electrode active material layer 641 .

[0020] Figure 5 This is the SEM observation image of Example 1.

[0021] Figure 6 This is the binarized image of Example 1.

[0022] Figure 7 This is the SEM observation image of Example 2.

[0023] Figure 8 This is the binarized image of Example 2.

[0024] Fig. 9 This is a SEM observation image of Comparative Example 1.

[0025] Fig.10 This is the binarized image of Comparative Example 1.

[0026] Description of Reference Numerals

[0027] 20 Electrode body

[0028] 30 Shell

[0029] 50 Positive

[0030] 60 Negative electrode

[0031] 62 negative electrode collector

[0032] 64 Negative electrode active material layer

[0033] 641 First negative electrode active material layer

[0034] 642 Second negative electrode active material layer

[0035] 100 Energy Storage Devices DETAILED DESCRIPTION

[0036] An embodiment of the technology disclosed herein is described below. The embodiment described herein is not intended to specifically limit the technology disclosed herein. The technology disclosed herein is not limited to the embodiment described herein unless otherwise mentioned. The drawings are schematically depicted and may not reflect the actual objects. In addition, the same figure marks are appropriately marked on components and parts that play the same role, and repeated descriptions are omitted. In addition, the notation "A to B" indicating a numerical range means "above A and below B" unless otherwise mentioned, and also includes the meaning of "greater than A and less than B".

[0037] In this specification, "electrical storage device" refers to a device that is charged and discharged by the movement of charge carriers between a pair of electrodes (positive electrode and negative electrode) via an electrolyte. The electrical storage device includes 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. As an example of the above-mentioned electrical storage device, the following describes an implementation method when a lithium-ion secondary battery is used as the object.

[0038] Figure 1 is a schematic cross-sectional view of the power storage device 100 . Figure 1 31b is a cross-sectional view along the first side surface 31b of the power storage device 100. Figure 1 As shown, the electricity storage device 100 includes an electrode body 20 , a case 30 , and a non-aqueous electrolyte 80 .

[0039] Figure 2 Schematic diagram of the electrode body 20. Figure 1 and Figure 2 As shown, the electrode body 20 is a wound electrode body in which a long sheet-shaped positive electrode 50 and a long sheet-shaped negative electrode 60 are overlapped via a long sheet-shaped separator 70 and wound in the longitudinal direction of the sheet (hereinafter also referred to as "longitudinal direction"). In the electrode body 20, the exposed area 52a in the positive electrode 50 and the exposed area 62a in the negative electrode 60 protrude outward from both ends in the transverse direction orthogonal to the longitudinal direction.

[0040] like Figure 1 and Figure 2 As shown, the positive electrode 50 includes a long sheet-shaped positive electrode collector 52 and a positive electrode active material layer 54. The positive electrode collector 52 is, for example, aluminum foil. In this embodiment, the positive electrode collector 52 has an area where the positive electrode active material layer 54 is provided, and an exposed area 52a where the positive electrode active material layer 54 is not provided so that the surface of the positive electrode collector 52 is exposed. The positive electrode active material layer 54 is, for example, provided in a strip shape along the longitudinal direction on one side or both sides (here, both sides) of the positive electrode collector 52. The positive electrode active material layer 54 is not provided at the lateral end (the left end in the figure). The exposed area 52a is here a strip-shaped area at the lateral end (the left end in the figure). As Figure 1 As shown, the current collector plate 42a is installed in the exposed area 52a.

[0041] The positive electrode active material layer 54 includes, for example, a positive electrode active material. Examples of the positive electrode active material include lithium nickel cobalt manganese composite oxide (NCM) (eg, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2), LiNiO2, LiCoO2, LiFeO2, LiMn2O4, LiNi 0.5 Mn 1.5 Lithium transition metal oxides such as O4; lithium transition metal phosphates such as LiFePO4, etc. The positive electrode active material layer 54 may include a conductive material, a binder, etc. 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), etc.

[0042] Figure 3 Schematic diagram of the cross section of the negative electrode 60. Figure 3 In FIG. 1 , the schematic cross-sectional structure of the negative electrode current collector 62 and the negative electrode active material layer 64 in the negative electrode 60 is partially enlarged and shown. Figure 1 to Figure 3 As shown, the negative electrode 60 includes a long sheet-shaped negative electrode collector 62 and a negative electrode active material layer 64. The negative electrode collector 62 is, for example, copper foil. In this embodiment, the negative electrode collector 62 has: an area where the negative electrode active material layer 64 is provided, and an exposed area 62a where the negative electrode active material layer 64 is not provided so that the surface of the negative electrode active material layer 64 is exposed. The negative electrode active material layer 64 is, for example, provided in a strip shape along the longitudinal direction on one side or both sides (here, both sides) of the negative electrode collector 62. The negative electrode active material layer 64 is not provided at the end in the lateral direction orthogonal to the longitudinal direction (the end on the right side in the figure). The exposed area 62a is a strip-shaped area at the lateral end (the end on the right side in the figure) here. As shown Figure 1 As shown, the current collector plate 44a is mounted on the exposed area 62a.

[0043] like Figure 3 As shown, 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 is provided between the negative electrode collector 62 and the second negative electrode active material layer 642. Figure 4 FIG. 6 is a schematic cross-sectional view of the first negative electrode active material layer 641. Figure 4 6 is a schematic cross-sectional structure of a portion near the negative electrode current collector 62 in the first negative electrode active material layer 641, which is partially enlarged. Figure 4 As shown, the first negative electrode active material layer 641 includes a negative electrode active material 681 , a binder 682 , and a resin B 683 .

[0044] The negative electrode active material 681 may be, for example, a carbon material such as graphite, hard carbon, soft carbon, or silicon (Si). The binder 682 is composed of resin A. Resin A may be a resin that is used as a binder in the negative electrode active material layer of the storage device for this purpose. Resin A may be, for example, a water-soluble binder, such as styrene butadiene rubber (SBR). By using SBR as the binder 682 (resin A), the bonding between the negative electrode collector 62 and the first negative electrode active material layer 641 can be made into a preferred state, and the current collection efficiency in the negative electrode 60 can be made into an appropriate current collection efficiency. SBR can form an emulsion solution with water. Therefore, for example, water can be used when processing the negative electrode 60, and the environmental load can be reduced.

[0045] Resin B683 is, for example, a resin different from resin A682. Resin B683 is a water-soluble and thermoplastic resin. In this specification, the so-called "thermoplastic resin" refers to a resin that has the property of being able to reversibly soften or melt and plastically deform at a temperature above the glass transition temperature, and reversibly solidify at a temperature below the glass transition temperature. By including a water-soluble and thermoplastic resin B683 in the first negative electrode active material layer 641, for example, when the negative electrode 60 is treated with water at a specified temperature, the resin B683 softens or melts, and the adhesion between the first negative electrode active material layer 641 and the negative electrode collector 62 is reduced. As a result, the first negative electrode active material layer 641 is easily separated from the negative electrode collector 62.

[0046] As the resin B683, for example, a resin having a softening point corresponding to the temperature of water when the negative electrode 60 is processed can be preferably used. The softening point of the resin B683 is about 120°C or less, for example, 100°C or less, preferably 90°C or less, more preferably 85°C or less, further 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 collector 62 and the negative electrode active material layer 64 can be separated with less energy, which can also contribute to the reduction of 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 processed at a temperature preferred for separating the negative electrode collector 62 and the negative electrode active material layer 64, and the separation efficiency of the negative electrode collector 62 and the negative electrode active material layer 64 can be improved.

[0047] It should be noted that in this specification, the so-called "softening point" of a resin refers to the temperature at which the resin begins to deform as the temperature of the resin rises. As the softening point of a resin, for example, a value obtained using a differential scanning calorimeter (DSC) can be used. Alternatively, a nominal value of a manufacturer or the like can be used.

[0048] The weight average molecular weight of resin B683 can be determined, for example, in consideration of the bonding strength of the first negative electrode active material layer 641 to the negative electrode collector 62. The weight average molecular weight of resin B683 is about 30,000 or more, for example, 50,000 or more, preferably 100,000 or more, more preferably 500,000 or more, further preferably 1 million or more, and particularly preferably 3 million or more. The larger the weight average molecular weight of resin B683, the more it can improve the bonding strength between the negative electrode collector 62 and the first negative electrode active material layer 641, and the more it can stably maintain the negative electrode active material layer 64 on the negative electrode collector 62. Therefore, the current collection efficiency in the negative electrode 60 can be improved. The weight average molecular weight of resin B683 is about 30 million or less, for example, 25 million or less, preferably 20 million or less, more preferably 15 million or less, and further preferably 10 million or less. The smaller the weight average molecular weight of the resin B683, the more the separation efficiency of the first negative electrode active material layer 641 from the negative electrode collector 62 can be improved, and the negative electrode collector 62 with higher purity can be recovered. In addition, 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 of a manufacturer or the like can be used.

[0049] As for the type of resin B683, as long as it has water solubility and thermoplasticity and can achieve the technical effect disclosed herein, it is not particularly limited. As resin B683, for example, polyethylene glycol (PEG), polyethylene oxide (PEO), polyvinyl alcohol (PVA), polyvinyl acetate (PVAc), water-soluble acrylic resin (such as sodium polyacrylate) and the like can be listed. Among them, from the viewpoint of more appropriately achieving the technical effect disclosed herein, polyethylene oxide (PEO) can be preferably used.

[0050] From the viewpoint of suitably achieving the technical effects disclosed herein, the proportion of the resin B683 in the first negative electrode active material layer 641 is about 10% by mass or less, for example, 5% by mass or less, preferably 3% by mass or less, and more preferably 2% by mass or less, relative to the entire first negative electrode active material layer 641. From the same viewpoint, the proportion of the resin B683 in the first negative electrode active material layer 641 is about 0.1% by mass or more, for example, 0.3% by mass or more, preferably 0.5% by mass or more, and more preferably 0.7% by mass or more, relative to the entire first negative electrode active material layer 641.

[0051] The ratio (mass ratio) of resin A682 to resin B683 (resin A:resin B) in the first negative electrode active material layer 641 is preferably 1:3 to 3:1, more preferably 1:2 to 2:1, and further preferably set to about 1:1, from the viewpoint of appropriately achieving the technical effects disclosed herein.

[0052] The second negative electrode active material layer 642 is a layer containing a negative electrode active material and a binder, and the content of the resin B is smaller than the content of the resin B683 in the first negative electrode active material layer 641. As for the negative electrode active material, the same negative electrode active material as the negative electrode active material 681 contained in the first negative electrode active material layer 641 is used here. The binder is resin A here, and can be the same resin as the resin A682 contained in the first negative electrode active material layer 641.

[0053] The second negative electrode active material layer 642 is Figure 3 As shown, it is disposed on the first negative electrode active material layer 641. In the negative electrode 60, by providing the first negative electrode active material layer 641 and the second negative electrode active material layer 642 having different structures from each other, the technical effects disclosed herein can be achieved, and at the same time, the power storage device 100 can be appropriately charged and discharged.

[0054] The content of the resin B in the second negative electrode active material layer 642 is, for example, 1 / 2 or less, preferably 1 / 3 or less, more preferably 1 / 4 or less, and further preferably 1 / 10 or less of the content of the resin B in the first negative electrode active material layer 641. The smaller the content of the resin B in the second negative electrode active material layer 642, the higher the charge and discharge efficiency in the power storage device 100 can be. Therefore, the second negative electrode active material layer 642 preferably does not contain the resin B.

[0055] The ratio of the binder in the second negative electrode active material layer 642 may be, for example, 0.3% by mass to 10% by mass, preferably 0.5% by mass to 5% by mass, in consideration of appropriate retention in the first negative electrode active material layer 641 and appropriate charge and discharge of the energy storage device 100 .

[0056] The first negative electrode active material layer 641 and the second negative electrode active material layer 642 are as described above, and other additives (such as dispersants, surfactants, thickeners, etc.) may be included as needed as long as the technical effects disclosed herein can be achieved. It should be noted that the other additives do not include the negative electrode active material, resin A, and resin B described above.

[0057] The manufacturing method (manufacturing method) of 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 the formation of 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 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.

[0058] The preparation process is, for example, a process for preparing the material of the first negative electrode active material layer 641. Among them, the negative electrode active material, the resin A as a binder, and the resin B are prepared. The kneading process is, for example, a process for kneading the negative electrode active material and the resin B. Among them, first, a predetermined amount of the negative electrode active material and the resin B are put into a kneading machine (such as a planetary mixer, etc.) to obtain a mixed powder. Secondly, water is added to the mixed powder until the mixed powder becomes clayey. Then, the mixed powder to which water is added is kneaded. The solid content rate in the kneading process is appropriately changed according to the type and combination of the materials used, and can be approximately 60% or more (for example, 60% to 70%). Kneading can be carried out, for example, until particles (so-called lumps) that have increased to a size larger than a predetermined size disappear from the kneaded material and become a uniform state. In this way, in the kneading process, the negative electrode active material and the resin B are kneaded at a high solid content rate and in a clayey state. As a result, the resin B can be more uniformly arranged on the surface of the negative electrode active material.

[0059] The dilution process is, for example, a process of diluting the kneaded product obtained in the kneading process. In this embodiment, water is added to the kneaded product obtained in the kneading process (here, the kneaded product with no lumps) and kneading is performed until the kneaded product becomes a paste. The mixing process is, for example, a process of mixing the kneaded product after the dilution process with a binder. In this embodiment, an emulsion solution of a binder (for example, an emulsion aqueous solution of resin A) modulated to a predetermined concentration is added to the kneaded product that becomes a paste after the dilution process, and mixed with the paste-like kneaded product to obtain a slurry for forming the first negative electrode active material layer.

[0060] The coating process is, for example, a process of coating the slurry for forming the first negative electrode active material layer on the negative electrode collector. In this embodiment, the slurry is coated on a copper foil serving as the negative electrode collector. There is no particular limitation on the coating method, and a conventionally known method can be used. The drying process is, for example, a process of drying the slurry for forming the first negative electrode active material layer coated on the negative electrode collector in the coating process to obtain a dry film. There is no particular limitation on the drying conditions, and the conditions used to make such a negative electrode can be appropriately used. The pressing process is, for example, a process of pressing the dry film obtained in the drying process to obtain the first negative electrode active material layer. There is no particular limitation on the pressing conditions, and the conditions used to make such a negative electrode can be appropriately used.

[0061] The formation of the second negative electrode active material layer 642 is not particularly limited. For example, the negative electrode active material and the 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, by pressing, the negative electrode 60 having 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 formed on the surface of the negative electrode collector 62.

[0062] As the diaphragm (separator) 70, for example, a porous sheet (film) made of a resin material such as polyethylene (PE), polypropylene (PP), polyester, cellulose, polyamide, etc. can be cited. The porous sheet can be 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) can be provided on the surface of the diaphragm 70.

[0063] The housing 30 is, for example, an outer packaging container for accommodating the electrode body 20 and the non-aqueous electrolyte 80. The housing 30 is a flat square housing. Figure 1 As shown, the housing 30 includes a main body 31 and a sealing plate 32. The main body 31 accommodates the electrode body 20. In this embodiment, the main body 31 has a rectangular bottom surface 31a, a pair of opposite first side surfaces 31b, a pair of opposite second side surfaces 31c, and an opening 31h. Figure 1 In the embodiment shown, a pair of opposite first side surfaces 31b are surfaces extending from a pair of opposite long sides of the bottom surface 31a. A pair of opposite second side surfaces 31c are surfaces extending from a pair of opposite short sides of the bottom surface 31a. The opening 31h is surrounded by a pair of opposite first side surfaces 31b and a pair of opposite second side surfaces 31c, and is opposite to the bottom surface 31a.

[0064] The sealing plate 32 is, for example, a member for plugging the opening 31h. The sealing plate 32 may have, for example, a shape corresponding to the outer shape of the opening 31h. In this embodiment, the sealing plate 32 is embedded in the opening 31h and joined to the periphery (main body 31) of the opening 31h, thereby plugging the opening 31h. The main body 31 and the sealing plate 32 are joined, for example, by laser welding.

[0065] like Figure 1 As shown, the housing 30 has a positive terminal 42, a negative terminal 44, a safety valve 36 and an injection hole (not shown) in the sealing plate 32. The positive terminal 42 is, for example, a terminal for external connection on the positive electrode side. The positive terminal 42 is electrically connected to the positive electrode 50 of the electrode body 20 via the collector plate 42a. The negative terminal 44 is, for example, a terminal for external connection on the negative electrode side. The negative terminal 44 is electrically connected to the negative electrode 60 of the electrode body 20 via the collector plate 44a. The safety valve 36 is, for example, a thin-walled portion set in a manner that releases the internal pressure when the internal pressure of the housing 30 rises to a predetermined level or above. The injection hole is, for example, a portion where the non-aqueous electrolyte 80 is injected into the housing 30.

[0066] The non-aqueous electrolyte 80 includes, for example, an electrolyte salt and a non-aqueous solvent. Examples of the electrolyte salt include 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, carbonates 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), and trifluorodimethyl carbonate (TFDMC). These may be used alone or in combination of two or more.

[0067] The power storage device 100 can be used in various applications. Preferred applications include driving power supplies installed in 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 a small power storage device or the like. A plurality of power storage devices 100 can be connected in series and / or in parallel to construct a battery pack.

[0068] As described above, the power storage device 100 includes a negative electrode 60 having a sheet-like 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 contains a negative electrode active material 681, a binder 682 composed of a resin A, and a resin B 683 (see Figure 4 ). The second negative electrode active material layer 642 contains a negative electrode active material and a binder, and the content of the resin B is smaller than the content of the resin B683 in the first negative electrode active material layer 641. Here, the resin B683 is a water-soluble and thermoplastic resin. The first negative electrode active material layer 641 is provided between the second negative electrode active material layer 642 and the negative electrode collector 62.

[0069] By making the negative electrode active material layer 64 a two-layer structure of the first negative electrode active material layer 641 and the second negative electrode active material layer 642, different functions can be given to each layer. By making the first negative electrode active material layer 641 contain a large amount of water-soluble and thermoplastic resin B683, the affinity of the first negative electrode active material layer 641 with water can be improved when the negative electrode 60 is processed. When the water used to process the negative electrode 60 is heated, the thermoplastic resin B683 is deformed due to heat, so the adhesion of the first negative electrode active material layer 641 to the negative electrode collector 62 can be reduced. Therefore, by arranging the first negative electrode active material layer 641 between the negative electrode collector 62 and the second negative electrode active material layer 642, the negative electrode active material layer 64 can be more easily separated from the negative electrode collector 62. As a result, the high-purity negative electrode collector can be recovered, so the cyclability of the storage device 100 can be improved. In addition, by reducing the content of the resin B in the second negative electrode active material layer 642 , it is possible to realize a configuration in which the charge and discharge of the electricity storage device 100 can be appropriately performed.

[0070] According to the technology disclosed herein, a method for manufacturing a regenerated negative electrode collector is disclosed. The method for manufacturing a regenerated negative electrode collector disclosed herein includes, for example, removing the negative electrode 60 from the above-mentioned power storage device 100 and separating the negative electrode collector 62 from the negative electrode 60. As described above, in the power storage device 100, the negative electrode active material layer 64 is easily separated from the negative electrode collector 62. According to the method for manufacturing a regenerated negative electrode collector disclosed herein, a high-purity negative electrode collector can be manufactured as a raw material, so the recyclability of the power storage device 100 can be improved.

[0071] The manufacturing method includes, for example, an unsealing process, a first taking-out process, a second taking-out process, a separation process, and a drying process. The unsealing process is, for example, a process of unsealing the power storage device 100. In this embodiment, the power storage device 100 is unsealed by separating the sealing plate 32 from the main body 31 of the shell 30. For example, the means for handling such a power storage device 100 are adopted without particular restrictions for separating the sealing plate 32 from the main body 31. Before the unsealing process, the power storage device 100 can be discharged in advance as needed. The first taking-out process is, for example, a process of taking out the electrode body 20 from the unsealed power storage device 100. In this embodiment, the electrode body 20 is connected to the positive terminal 42 and the negative terminal 44 provided on the sealing plate 32. Therefore, for example, after the unsealing process, the electrode body 20 can be taken out from the power storage device 100 as an integral object with the sealing plate 32.

[0072] The second removal process is, for example, a process of removing the negative electrode 60 from the electrode body 20 removed in the first removal process. In this first removal process, the electrode body 20 is taken out as an integral body with the sealing plate 32, the positive terminal 42, and the negative terminal 44. For example, in the second removal process, first, the electrode body 20 and the sealing plate 32 can be separated by removing the collector plate 22a and the collector plate 24a from the electrode body 20. Next, the negative electrode 60 can be taken out from the electrode body 20 separated from the sealing plate 32.

[0073] The separation step is, for example, a step of separating the negative electrode collector 62 from the negative electrode 60. The negative electrode 60 is the negative electrode 60 taken out in the second taking out step. In this embodiment, in the separation step, the negative electrode collector 62 is separated by immersing the negative electrode 60 in heated water. The temperature of the water can be appropriately set according to the type and content of the resin B, for example. The lower the temperature of the water in which the negative electrode 60 is immersed, the more energy can be used to recover the negative electrode collector 62, and the environmental load can be reduced. The temperature of the water is, for example, below the boiling point (below 100°C), and from the above-mentioned viewpoint, it is preferably below 95°C, more preferably below 90°C, further preferably below 85°C, and particularly preferably below 80°C. 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 collector 62, so that a negative electrode collector 62 with a higher purity can be recovered. From this viewpoint, the temperature of the water is, for example, above 50°C, preferably above 55°C, and more preferably above 60°C. Although not particularly limited, from the viewpoint of more efficiently separating the negative electrode current collector 62 , the water in which the negative electrode 60 is immersed may be stirred, or the container in which the negative electrode 60 and the water are placed may be shaken.

[0074] The negative electrode current collector 62 separated by the separation process can be used as a raw material for a regenerated negative electrode current collector, for example, after washing and drying as needed. Although not particularly limited, the separated negative electrode current collector 62 can be used as a copper raw material in the refining process of electrolytic copper foil. Since the separated negative electrode current collector 62 has a further improved purity, it can be efficiently electrolytically refined by using it as a copper raw material.

[0075] Hereinafter, test examples related to the present invention will be described, but the present invention is not intended to be limited to the contents shown in the following test examples.

[0076] <Preparation of negative electrode for test>

[0077] -Example 1-

[0078] As the negative electrode active material, natural graphite particles were prepared. As resin A, styrene butadiene rubber (SBR) was prepared. As resin B, polyethylene oxide (PEO) with a weight average molecular weight of 8 million was prepared. First, the negative electrode active material and resin B were weighed to a specified ratio, and mixed using a planetary mixer to obtain a mixed powder. Secondly, 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 during kneading was about 60%. Kneading was carried out until no particles (so-called lumps) larger than a specified size were observed in the kneaded material by visual inspection. Then, while adding water, the kneaded material was further kneaded until it became a paste. Secondly, an SBR emulsion solution modulated to a specified concentration was added and mixed with the paste mixture to obtain a slurry for forming the 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.

[0079] Next, the first negative electrode active material layer forming slurry was applied to both sides of the copper foil, and after drying, a compression process was performed using a roller press to form the first negative electrode active material layer on the copper foil. This was used as the test negative electrode for this example. The coating amount (single-sided area mass) in the negative electrode was 10 mg / cm per single side. 2 The density of the first negative electrode active material layer after compression is 1.5 g / cm 3 .

[0080] -Example 2-

[0081] Polyethylene oxide (PEO) having a weight average molecular weight of 5,000,000 was used as the resin B. The same materials and procedures as in Example 1 were used except for the above, to prepare a test negative electrode of this example.

[0082] -Example 3-

[0083] Polyethylene oxide (PEO) having a weight average molecular weight of 4,000,000 was used as the resin B. The test negative electrode of this example was prepared by using the same materials and procedures as in Example 1 except for the above.

[0084] -Comparative Example-

[0085] Carboxymethyl cellulose (CMC) having a weight average molecular weight of 300,000 was used instead of resin B. A test negative electrode of this example was prepared using the same materials and procedures as in Example 1 except for the above.

[0086] <Determination of carbon residual rate>

[0087] The test negative electrode of each example was stirred in warm water at 70°C for 1 hour. Next, the test negative electrode was taken out of the water and dried. Next, a scanning electron microscope (SEM) was used to observe the surface of the dried test negative electrode, and observation images of 5 fields of view were randomly obtained. The size of the observation image was set so that it became a surface image of the negative electrode and included a field of view of 1.5 cm × 1.5 cm. For the obtained observation image, the image analysis software "ImageJ" was used to perform binarization processing, and the area ratio of the black part in the observation image was calculated. The arithmetic mean of the area ratio of the black part calculated using the 5 observation images was obtained and set as the carbon residual rate (%) in the test negative electrode. The results are shown in this column of Table 1.

[0088] exist Figures 5 to 10 : The SEM observation image and the binarized image obtained by binarization processing are shown in . Figure 5 This is the SEM observation image of Example 1. Figure 6 This is the binarized image of Example 1. Figure 7 This is the SEM observation image of Example 2. Figure 8 This is the binarized image of Example 2. Fig. 9 This is a SEM observation image of Comparative Example 1. Fig.10 This is the binarized image of Comparative Example 1. Figures 5 to 10 The images shown in the figure are all observation fields of 1.5 cm in length and 1.5 cm in width. The scale represents 5 mm. Figure 6 , Figure 8 and Fig.10 As described above, the black portion is the portion where carbon remains.

[0089]

Table 1

[0090] Table 1

[0091] Resin Weight average molecular weight Carbon residual rate (%) Example 1 PEO 8 million 12 Example 2 PEO 5 million 8 Example 3 PEO 4 million 7 Comparative Example CMC 300,000 35

[0092] As shown in Table 1, the carbon residual rate in Examples 1 to 3 is lower than that in the comparative example. The test negative electrodes of Examples 1 to 3 include a first negative electrode active material layer comprising a water-soluble and thermoplastic resin B (here, polyethylene oxide (PEO)). From the results of this test example, it can be seen that in the negative electrode having a negative electrode active material layer comprising a first negative electrode active material layer and a second negative electrode active material layer, and having a first negative electrode active material layer comprising a water-soluble and thermoplastic resin B between the negative electrode collector and the second negative electrode active material layer, the negative electrode active material layer is easily separated from the negative electrode collector. It can be seen that by using a storage device having this negative electrode, a regenerated negative electrode collector with higher purity can be manufactured.

[0093] As described above, specific aspects of the technology disclosed herein include aspects described in the following items.

[0094] Item 1: An energy storage device, comprising a negative electrode having a sheet-shaped negative electrode collector and a negative electrode active material layer arranged on the negative electrode collector, the negative electrode active material layer having a first negative electrode active material layer and a second negative electrode active material layer, the first negative electrode active material layer comprising a negative electrode active material, a binder composed of resin A, and resin B, the second negative electrode active material layer comprising the negative electrode active material and the binder, the content of the resin B in the second negative electrode active material layer is less than the content of the resin B in the first negative electrode active material layer, wherein the resin B is a water-soluble and thermoplastic resin, and the first negative electrode active material layer is arranged between the second negative electrode active material layer and the negative electrode collector.

[0095] Item 2: The power storage device according to Item 1, wherein a content of the resin B in the second negative electrode active material layer is 1 / 4 or less of a content of the resin B in the first negative electrode active material layer.

[0096] Item 3: The power storage device according to Item 1 or 2, wherein the resin B has a softening point of 80° C. or less.

[0097] Item 4: The power storage device according to any one of Items 1 to 3, wherein the resin B is polyethylene oxide.

[0098] Item 5: The power 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.

[0099] Item 6: The power storage device according to any one of Items 1 to 5, wherein the resin A is styrene butadiene rubber.

[0100] Item 7: A method for producing a regenerated negative electrode current collector, comprising taking out the negative electrode from the electricity storage device according to any one of Items 1 to 6, and separating the negative electrode current collector from the negative electrode.

[0101] Item 8: The production method according to Item 7, wherein the negative electrode is immersed in water at 80° C. or lower to separate the negative electrode current collector.

[0102] The above describes the implementation methods of the technology disclosed herein, but it is not intended to limit the technology disclosed herein to the above implementation methods. The technology disclosed herein can also be implemented in other implementation methods. The technology described in the patent claims includes technical solutions that have variously deformed and changed the above-mentioned exemplified implementation methods. For example, part of the above-mentioned implementation method can be replaced with other deformation methods, and other deformation methods can be added to the above-mentioned implementation method. In addition, as long as the technical features are not described as necessary features, they can be deleted as appropriate.

Claims

1. An electric storage device comprising a negative electrode having a sheet-like negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector, The negative electrode active material layer comprises a first negative electrode active material layer and a second negative electrode active material layer, wherein the first negative electrode active material layer comprises a negative electrode active material, a binder composed of a resin A, and a resin B, and the second negative electrode active material layer comprises the negative electrode active material and the binder, wherein a content of the resin B in the second negative electrode active material layer is smaller than a content of the resin B in the first negative electrode active material layer, in, The resin B is a water-soluble and thermoplastic resin. The first negative electrode active material layer is provided between the second negative electrode active material layer and the negative electrode collector.

2. The power storage device according to claim 1, wherein The content of the resin B in the second negative electrode active material layer is 1 / 4 or less of the content of the resin B in the first negative electrode active material layer.

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

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

5. The power 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 power storage device according to claim 1, wherein The resin A is styrene butadiene rubber. 7 . A method for producing a regenerated negative electrode current collector, comprising taking out the negative electrode from the electricity storage device according to claim 1 , and separating the negative electrode current collector from the negative electrode.

8. The manufacturing method according to claim 7, wherein: The negative electrode was immersed in water at 80° C. or lower to separate the negative electrode current collector.

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