Energy storage device and method for manufacturing a regenerated negative electrode current collector
A two-layer negative electrode structure with a thermoplastic resin layer facilitates easy separation of the active material from the current collector, improving recyclability and purity in energy storage devices.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- PRIME PLANET ENERGY & SOLUTIONS INC
- Filing Date
- 2023-09-25
- Publication Date
- 2026-07-03
Smart Images
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Abstract
Description
Technical Field
[0001] The present disclosure relates to a power storage device and a method for manufacturing a regenerated negative electrode current collector.
Background Art
[0002] Japanese Unexamined Patent Application Publication No. 2017-98155 discloses a method for manufacturing a non-aqueous electrolyte secondary battery. This manufacturing method includes a step 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; a step of adding a negative electrode active material and a binder to the aqueous solution and kneading to obtain a negative electrode paste; and a step of applying the negative electrode paste onto a negative electrode current collector and drying to obtain a negative electrode. The publication describes that with such a configuration, a non-aqueous electrolyte secondary battery having good initial resistance and suppressing an increase in battery resistance when repeatedly charged and discharged at a high rate can be manufactured.
[0003] Japanese Unexamined Patent Application Publication No. 9-45328 discloses a lithium secondary battery including a spiral electrode body formed by spirally winding a negative electrode and a positive electrode with a separator interposed therebetween, and a non-aqueous electrolyte. The negative electrode has an active material layer containing a powder composed of carbon particles and a binder formed 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 film on their surfaces. The publication describes that the polyethylene oxide film present on the surfaces of the carbon particles prevents contact between the hydrohalic acid generated in the battery can and the carbon particles in a charged state, so self-discharge is unlikely to occur even when stored for a long time.
[0004] Japanese Patent Publication No. 2014-127417 discloses a method for reusing the 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 reattached to the current collector. The publication states that because 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. The publication also states that after drying the peeled negative electrode active material layer, a viscosity-adjusting solvent is added and it is stirred with a homogenizer to form a slurry which can then be applied to the negative electrode current collector, allowing it to be reused as a negative electrode.
[0005] Japanese Patent Publication No. 2006-228509 discloses a method for reusing negative electrode active material for non-aqueous electrolyte secondary batteries. 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 negative electrode active material and a binder, and a current collector substrate; and mixing the negative electrode mixture with a solvent capable of dissolving or dispersing the binder to produce a negative electrode paste, which is then applied onto the negative electrode current collector. The publication states that by this method, used negative electrode active material can be reused as negative electrode active material for non-aqueous electrolyte secondary batteries. [Prior art documents] [Patent Documents]
[0006] [Patent Document 1] Japanese Patent Publication No. 2017-98155 [Patent Document 2] Japanese Patent Application Publication No. 9-45328 [Patent Document 3] Japanese Patent Publication No. 2014-127417 [Patent Document 4] Japanese Patent Publication No. 2006-228509 [Overview of the Initiative] [Problems that the invention aims to solve]
[0007] In recent years, with the widespread adoption of energy storage devices, interest in reusing them has increased, and there is a growing demand for advancements in energy storage device reuse technology. Therefore, the inventors decided to investigate the configuration of an energy storage device that would be easier to reuse after use. The 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 energy storage device disclosed herein comprises 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. 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, wherein 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 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. With this configuration, the negative electrode active material layer can be more easily separated from the negative electrode current collector. [Brief explanation of the drawing]
[0009] [Figure 1] Figure 1 is a schematic cross-sectional view of the energy storage device 100. [Figure 2] Figure 2 is a schematic diagram of the electrode body 20. [Figure 3] Figure 3 is a schematic cross-sectional view of the negative electrode 60. [Figure 4] Figure 4 is a schematic cross-sectional view of the first negative electrode active material layer 641. [Figure 5] Figure 5 shows the SEM observation image of Example 1. [Figure 6] Figure 6 shows the binarized image of Example 1. [Figure 7] Figure 7 shows the SEM image of Example 2. [Figure 8] Figure 8 is the binary image of Example 2. [Figure 9] Figure 9 is the SEM observation image of Comparative Example 1. [Figure 10] Figure 10 is the binary image of Comparative Example 1.
Embodiments for Carrying Out the Invention
[0010] Hereinafter, one embodiment of the technology disclosed herein will be described. The embodiments described here are not intended to particularly limit the technology disclosed here. The technology disclosed here is not limited to the embodiments described here unless otherwise specified. The drawings are schematically drawn and do not necessarily reflect the actual objects. Also, members and parts having the same function are appropriately assigned the same reference numerals, and duplicate descriptions are omitted. Also, the notation "A~B" indicating a numerical range means "A or more and B or less" and also includes the meaning of "exceeding A and less than B" unless otherwise specified.
[0011] In this specification, the "power storage device" refers to a device in which charge carriers move between a pair of electrodes (a positive electrode and a negative electrode) through an electrolyte to cause charge and discharge. Such power storage devices include secondary batteries such as lithium-ion secondary batteries, nickel-metal hydride batteries, and nickel-cadmium batteries; capacitors such as lithium-ion capacitors and electric double-layer capacitors. Hereinafter, as an example of the above-described power storage device, an embodiment in the case of targeting a lithium-ion secondary battery will be described.
[0012] Figure 1 is a schematic cross-sectional view of the power storage device 100. Figure 1 is a schematic cross-sectional view along the first side surface 31b in the power storage device 100. As shown in Figure 1, the power storage device 100 includes an electrode body 20, a case 30, and a non-aqueous electrolyte 80.
[0013] Figure 2 is a schematic diagram of the electrode body 20. As shown in FIGS. 1 and 2, 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 with a long sheet-shaped separator 70 interposed therebetween and wound in the sheet longitudinal direction (hereinafter, also simply referred to as the "longitudinal direction"). In the electrode body 20, the exposed region 52a of the positive electrode 50 and the exposed region 62a of the negative electrode 60 protrude outward from both ends in the short direction orthogonal to the longitudinal direction, respectively.
[0014] As shown in FIGS. 1 and 2, the positive electrode 50 includes a long sheet-shaped positive electrode current collector 52 and a positive electrode active material layer 54. The positive electrode current collector 52 is, for example, an aluminum foil. In this embodiment, the positive electrode current collector 52 has a region where the positive electrode active material layer 54 is provided and an exposed region 52a where the surface of the positive electrode current collector 52 is exposed without the positive electrode active material layer 54. 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 (here, both sides) of the positive electrode current collector 52. The positive electrode active material layer 54 is not provided at the end in the short direction (the left end in the figure). The exposed region 52a is a strip-shaped region at the end in the short direction (the left end in the figure). As shown in FIG. 1, a current collecting plate 42a is attached to the exposed region 52a.
[0015] The positive electrode active material layer 54 contains, for example, a positive electrode active material. Examples of the positive electrode active material include lithium nickel cobalt manganese composite oxide (NCM) (for example, LiNi 1.5 , 1 / 3 , 0.5 Co 1 / 3 Mn 1 / 3 O2), LiNiO2, LiCoO2, LiFeO2, LiMn2O4, LiNi 0.5 Mn 1.5Examples include lithium transition metal oxides such as O4; lithium transition metal phosphate compounds such as LiFePO4; and so on. The positive electrode active material layer 54 may contain conductive materials, binders, etc., in addition to the positive electrode active material. Examples of conductive materials include carbon black such as acetylene black (AB); and other carbon materials such as graphite. Examples of binders include polyvinylidene fluoride (PVDF).
[0016] Figure 3 is a schematic cross-sectional view of the negative electrode 60. Figure 3 shows a partially enlarged schematic cross-sectional structure of the negative electrode current collector 62 and the negative electrode active material layer 64 in the negative electrode 60. As shown in Figures 1 to 3, the negative electrode 60 comprises a long, sheet-like negative electrode current collector 62 and a negative electrode active material layer 64. The negative electrode current collector 62 is, for example, copper foil. In this embodiment, the negative electrode current 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, for example, provided in a strip shape along the longitudinal direction on one or both sides (here, both sides) of the negative electrode current collector 62. The negative electrode active material layer 64 is not provided at the ends in the short direction perpendicular to the longitudinal direction (the right end in the figure). The exposed region 62a is, in this case, a band-shaped region at the short-side end (the right-hand end in the figure). As shown in Figure 1, a current collector plate 44a is attached to the exposed region 62a.
[0017] As shown in Figure 3, the negative electrode active material layer 64 comprises 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 here between the negative electrode current collector 62 and the second negative electrode active material layer 642. Figure 4 is a schematic cross-sectional view of the first negative electrode active material layer 641. Figure 4 shows a partially enlarged schematic cross-sectional structure of the portion of the first negative electrode active material layer 641 near the negative electrode current collector 62. As shown in Figure 4, the first negative electrode active material layer 641 includes a negative electrode active material 681, a binder 682, and a resin B683.
[0018] The negative electrode active material 681 may be a carbon material such as graphite, hard carbon, or soft carbon, but it may also be silicon (Si). The binder 682 here consists of resin A. Resin A may be a resin that constitutes a binder used in the negative electrode active material layer of an energy storage device for this type of application. Resin A may be a water-soluble binder, for example, 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 favorable, and consequently, the current collection efficiency at 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 processing the negative electrode 60, and consequently, the environmental burden can be reduced.
[0019] Resin B683 is, for example, a different resin from resin A681. Here, resin B683 is a resin that is both water-soluble and thermoplastic. In this specification, "thermoplastic resin" means a resin that has the property of reversibly softening or melting at temperatures above its glass transition point, allowing for plastic deformation, and reversibly hardening at temperatures below its glass transition point. By including 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 predetermined temperature, resin B683 softens or melts, reducing the adhesion between the first negative electrode active material layer 641 and the negative electrode current collector 62. This makes it easier for the first negative electrode active material layer 641 to separate from the negative electrode current collector 62.
[0020] As resin B683, for example, a resin having a softening point corresponding to the water temperature when processing the negative electrode 60 can be preferably used. The softening point of resin B683 is generally 120°C or lower, for example 100°C or lower, preferably 90°C or lower, more preferably 85°C or lower, even more preferably 80°C or lower, and particularly preferably 75°C or lower. By using a resin with a lower softening point as resin B683, the negative electrode current collector 62 and the negative electrode active material layer 64 can be separated with less energy, which can also contribute to reducing the environmental burden. The softening point of resin B683 is, for example 50°C or higher, preferably 55°C or higher, and more preferably 60°C or higher. By using a resin with a higher softening point as resin B683, the negative electrode 60 can be processed at a temperature favorable for separating the negative electrode current collector 62 and the negative electrode active material layer 64, which can increase the separation efficiency between the negative electrode current collector 62 and the negative electrode active material layer 64.
[0021] In this specification, the term "softening point" for a resin refers to the temperature at which the resin begins to deform when its temperature is increased. The softening point of a resin may be, for example, a value obtained using a differential scanning calorimetry (DSC). Alternatively, a nominal value from the manufacturer or other relevant authority may be used.
[0022] The weight-average molecular weight of resin B683 is preferably determined considering, for example, 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 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 1,000,000 or more, and particularly preferably 3,000,000 or more. The larger the weight-average molecular weight of resin B683, the stronger 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. As a result, the current collection efficiency at the negative electrode 60 can be increased. The weight-average molecular weight of resin B683 is generally 30,000,000 or less, for example 25,000,000 or less, preferably 20,000,000 or less, more preferably 15,000,000 or less, and even more preferably 10,000,000 or less. The smaller the weight-average molecular weight of resin B683, the higher the separation efficiency of the first negative electrode active material layer 641 from the negative electrode current collector 62, and consequently, the higher purity negative electrode current collector 62 can be recovered. The weight-average molecular weight of resin B683 can be, for example, a value obtained using gel permeation chromatography (GPC). Alternatively, a nominal value from the manufacturer may be used.
[0023] The type of resin B683 is not particularly limited, as long as it is water-soluble and thermoplastic 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 resins (e.g., sodium polyacrylate). Among these, 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 realizing the effects of the technology disclosed herein, the proportion of resin B683 in the first negative electrode active material layer 641 is generally 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 a similar viewpoint, the proportion of resin B683 in the first negative electrode active material layer 641 is generally 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.
[0025] The ratio (mass ratio) (resin A:resin B) of resin A682 to resin B683 in the first negative electrode active material layer 641 is preferably 1:3 to 3:1, more preferably 1:2 to 2:1, and even more preferably set to about 1:1, from the viewpoint of appropriately realizing the effects of the technology disclosed herein.
[0026] The second negative electrode active material layer 642 here contains a negative electrode active material and a binder, and is a layer in which the content of resin B is smaller than the content of resin B683 in the first negative electrode active material layer 641. The negative electrode active material 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 it is preferable that it be the same resin as resin A682 contained in the first negative electrode active material layer 641.
[0027] As shown in Figure 3, the second negative electrode active material layer 642 is provided on the first negative electrode active material layer 641. By providing layers with mutually different configurations, the first negative electrode active material layer 641 and the second negative electrode active material layer 642, in the negative electrode 60, the effects of the technology disclosed herein can be realized, and charging and discharging can be performed appropriately in the energy storage device 100.
[0028] The content of resin B in the second negative electrode active material layer 642 is, for example, 1 / 2 or less of the content of resin B in the first negative electrode active material layer 641, preferably 1 / 3 or less, more preferably 1 / 4 or less, and even more preferably 1 / 10 or less. The lower the content of resin B in the second negative electrode active material layer 642, the higher the charge and discharge efficiency of the energy storage device 100 may 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 is preferably, for example, 0.3 mass% to 10 mass%, and more preferably 0.5 mass% to 5 mass%, taking into consideration that it is properly retained in the first negative electrode active material layer 641 and that the charge and discharge of the energy storage device 100 is performed properly.
[0030] The configuration of the first negative electrode active material layer 641 and the second negative electrode active material layer 642 are as described above, but other additives (e.g., dispersants, surfactants, thickeners, etc.) may be included as needed, as long as the effects of the technology disclosed herein can be achieved. The negative electrode active material, resin A, and resin B described above are excluded from the other additives.
[0031] A method for producing the negative electrode 60 (manufacturing method) 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, the step of preparing the materials for the first negative electrode active material layer 641. Here, the negative electrode active material, resin A as a binder, and resin B are prepared. The solid mixing step is, for example, the step of solid mixing the negative electrode active material and resin B. Here, first, a predetermined amount of negative electrode active material and resin B are placed in a mixer (for example, a planetary mixer, etc.) to obtain a mixed powder. Next, water is added to the mixed powder until the mixed powder becomes clay-like. Then, the mixed powder with water added is kneaded. The solid content ratio in the solid mixing step is appropriately changed depending on the type and combination of materials used, but it is generally good to have 60% or more (for example, 60% to 70%). Solid mixing should be carried out, for example, until there are no particles that have grown to a predetermined size or larger (so-called lumps) in the mixed material and it becomes a uniform state. In this way, in the solid mixing step, the negative electrode active material and resin B are kneaded in a clay-like state with a high solid content ratio. This allows for a more uniform distribution of resin B on the surface of the negative electrode active material.
[0033] The dilution step is, for example, a step of diluting the mixture obtained in the solid kneading step. In this embodiment, water is added to the mixture obtained in the solid kneading step (here, the mixture from which lumps have been removed), and the mixture is kneaded until it becomes a paste. The mixing step is, for example, a step of mixing the mixture after the dilution step with the binder. In this embodiment, an emulsion solution of the binder prepared to a predetermined concentration (for example, an aqueous emulsion of resin A) is added to the paste-like mixture after the dilution step and mixed with the paste-like mixture to obtain a slurry for forming the first negative electrode active material layer.
[0034] The coating step is, for example, a step of coating a slurry for forming the first negative electrode active material layer onto a negative electrode current collector. In this embodiment, the slurry is coated onto a copper foil serving as the negative electrode current collector. The coating method is not particularly limited, and conventionally known methods may be used. The drying step is, for example, a step of drying the slurry for forming the first negative electrode active material layer coated onto the negative electrode current collector in the coating step to obtain a dried film. The drying conditions are not particularly limited, and conditions used when manufacturing this type of negative electrode may be appropriately adopted. The pressing step is, for example, a step of pressing the dried film obtained in the drying step to obtain the first negative electrode active material layer. The pressing conditions are not particularly limited, and conditions used when manufacturing this type of negative electrode may be appropriately adopted.
[0035] In forming the second negative electrode active material layer 642, there are no particular limitations. For example, a slurry for forming the second negative electrode active material layer is prepared by dispersing the negative electrode active material and a binder in water. Then, the slurry is applied to the surface of the first negative electrode active material layer 641 and dried. Here, by pressing, a negative electrode 60 is produced in which a 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] Examples of separators 70 include porous sheets (films) made of resin materials such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and 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] Case 30 is, for example, an outer container for housing an electrode body 20 and a non-aqueous electrolyte 80. Case 30 is, in this case, a flat, rectangular case. As shown in Figure 1, case 30 comprises a main body 31 and a sealing plate 32. 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 sides 31b, a pair of opposing second sides 31c, and an opening 31h. In the configuration shown in Figure 1, the pair of opposing first sides 31b are surfaces extending from a pair of opposing long sides of the bottom surface 31a. The pair of opposing second sides 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 sides 31b and the pair of opposing second sides 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 a shape that corresponds to the outer shape of the opening 31h. In this embodiment, the sealing plate 32 closes the opening 31h by being fitted into the opening 31h and joined to the periphery of the opening 31h (main body 31). The main body 31 and the sealing plate 32 are joined by, for example, laser welding.
[0039] As shown in Figure 1, the case 30 has a positive electrode terminal 42, a negative electrode terminal 44, a safety valve 36, and an injection hole (not shown) in the sealing plate 32. The positive electrode terminal 42 is, for example, an external connection terminal 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 plate 42a. The negative electrode terminal 44 is, for example, an external connection terminal 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 plate 44a. The safety valve 36 is, for example, a thin-walled portion set to release internal pressure when the internal pressure of the case 30 rises above a predetermined level. The injection hole is, for example, a place for injecting non-aqueous electrolyte 80 into the case 30.
[0040] The non-aqueous electrolyte 80 contains, for example, an electrolyte salt and a non-aqueous solvent. An example of the electrolyte salt is LiPF6. The concentration of the electrolyte salt in the non-aqueous electrolyte 80 is preferably, for example, 0.7 mol / L to 1.3 mol / L. The non-aqueous solvent may be a carbonate such as ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), monofluoroethylene carbonate (MFEC), difluoroethylene carbonate (DFEC), monofluoromethyldifluoromethyl carbonate (F-DMC), or trifluorodimethyl carbonate (TFDMC). These can be used individually or in combination of two or more.
[0041] The energy storage device 100 can be used for various applications. Suitable applications include power supplies for vehicles such as battery electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs). The energy storage device 100 can be used as a battery for small-scale power storage devices, etc. Multiple energy storage devices 100 may be connected in series and / or parallel to construct a battery pack.
[0042] As described above, the energy 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 comprises 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 resin B 683 (see Figure 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, 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 making the negative electrode active material layer 64 a two-layer structure consisting of a first negative electrode active material layer 641 and a second negative electrode active material layer 642, each layer can be given a mutually different function. By including a relatively large amount of resin B863, which has water-soluble and thermoplastic properties, in the first negative electrode active material layer, the affinity between the first negative electrode active material layer 641 and water can be increased when processing the negative electrode 60. When the water used to process the negative electrode 60 is heated, the thermoplastic resin B863 deforms due to the heat, which can reduce the adhesion of the first negative electrode active material layer 641 to the negative electrode current collector 62. Therefore, by placing the first negative electrode active material layer 641 between the negative electrode current collector 62 and the second negative electrode active material layer 642, the negative electrode active material layer 64 can be separated from the negative electrode current collector 62 more easily. This makes it possible to recover a high-purity negative electrode current collector, thereby improving the recyclability of the energy storage device 100. In addition, by relatively reducing the content of resin B in the second negative electrode active material layer 642, a configuration is realized in which the energy storage device 100 is charged and discharged appropriately.
[0044] The technology disclosed herein provides a method for manufacturing a regenerated negative electrode current collector. The method for manufacturing a regenerated negative electrode current collector disclosed herein includes, for example, removing the negative electrode 60 from the energy storage device 100 described above and isolating the negative electrode current collector 62 from the negative electrode 60. As described above, in the energy storage device 100, the negative electrode active material layer 64 is easily separated from the negative electrode current collector 62. The method for manufacturing a regenerated negative electrode current collector disclosed herein allows for the production of a negative electrode current collector with high purity as a raw material, which can improve the recyclability of the energy storage device 100.
[0045] This manufacturing method includes, for example, an opening step, a first extraction step, a second extraction step, an isolation step, and a drying step. The opening step is, for example, a step of opening the energy storage device 100. In this embodiment, the energy storage device 100 is opened by separating the sealing plate 32 from the main body 31 of the case 30. For separating the sealing plate 32 from the main body 31, for example, means used when processing this type of energy storage device 100 can be used without particular limitation. Prior to the opening step, the energy storage device 100 may be discharged as needed. The first extraction step is, for example, a step of removing the electrode body 20 from the opened energy 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. For this reason, for example, the electrode body 20 may be removed from the energy storage device 100 as a combined unit with the sealing plate 32 after the opening step.
[0046] The second extraction step is, for example, the step of extracting the negative electrode 60 from the electrode body 20 in the first extraction step. In the first extraction step, the electrode body 20 is extracted as a combined unit of the sealing plate 32, the positive electrode terminal 42, and the negative electrode terminal 44. For example, in the second extraction step, it is preferable to first separate the electrode body 20 from the sealing plate 32 by removing the current collector plates 22a and 24a from the electrode body 20. Then, it is preferable to extract the negative electrode 60 from the electrode body 20 separated from the sealing plate 32.
[0047] The isolation step is, for example, the step of isolating the negative electrode current collector 62 from the negative electrode 60. The negative electrode 60 is the negative electrode 60 extracted in the second extraction 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, for example, depending on the type and content of resin B. The lower the temperature of the water into which the negative electrode 60 is immersed, the less energy is required to recover the negative electrode current collector 62, thereby reducing the environmental burden. The temperature of the water is, for example, below the boiling point (below 100°C), and from the above viewpoint, below 95°C is preferable, below 90°C is more preferable, below 85°C is even more preferable, and below 80°C is particularly preferable. The higher the temperature of the water into which the negative electrode 60 is immersed, the easier it is for the first negative electrode active material layer 641 to separate from the negative electrode current collector 62, so that a higher purity negative electrode current collector 62 can be recovered. From this viewpoint, the water temperature 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 the container containing the negative electrode 60 and water may be shaken.
[0048] The negative electrode current collector 62 isolated by the isolation process can be used as a raw material for regenerated negative electrode current collectors, for example, after being washed and dried as needed. While not particularly limited, the isolated negative electrode current collector 62 can also be used, for example, as a copper raw material in the refining process of electrolytic copper foil. Because the purity of the isolated negative electrode current collector 62 is higher, using it as a copper raw material allows for more efficient electrolytic refining.
[0049] The following describes test examples relating to the present invention, but it is not intended to limit the present invention to those shown in the following test examples.
[0050] <Preparation of a negative electrode for testing> -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 in a predetermined ratio and mixed using a planetary mixer to obtain a mixed powder. Next, water was added to the mixed powder until the powder became clay-like. After that, the mixed powder was kneaded using a planetary mixer. The solid content during the kneading stage was approximately 60%. The kneading was continued until no particles larger than a predetermined size (so-called clumps) were visually observed in the mixture. After that, the mixture 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 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.
[0051] Next, the slurry for forming the first negative electrode active material layer was applied to both sides of the copper foil, dried, and then compressed using a roll 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 (basis weight) on the negative electrode was 10 mg / cm² per side. 2 The density of the first negative electrode active material layer after pressing was 1.5 g / cm³. 3 That was the case.
[0052] -Example 2- Polyethylene oxide (PEO) with a weight-average molecular weight of 5 million was used as resin B. Otherwise, the same materials and procedures as in Example 1 were used to prepare the test negative electrode for this example.
[0053] -Example 3- Polyethylene oxide (PEO) with a weight-average molecular weight of 4 million was used as resin B. Otherwise, the same materials and procedures as in Example 1 were used to prepare the test negative electrode for this example.
[0054] -Comparative Example- Instead of resin B, carboxymethylcellulose (CMC) with a weight-average molecular weight of 300,000 was used. Otherwise, the same materials and procedures as in Example 1 were used to prepare the test negative electrode for this example.
[0055] <Measurement of carbon retention rate> Each test negative electrode was stirred in 70°C hot water for 1 hour. The test negative electrodes were then removed from the water and dried. Next, the surface of the dried test negative electrodes was observed using a scanning electron microscope (SEM), and five randomly selected fields of view were acquired. The size of the observation images was set to include a 1.5cm × 1.5cm field of view, representing the surface image of the negative electrode. The acquired observation images were binarized using the image analysis software "ImageJ," and the area percentage of the black portion in the observation image was calculated. The arithmetic mean of the area percentages of the black portion calculated from the five observation images was obtained and defined as the carbon retention rate (%) in the test negative electrode. The results are shown in the corresponding column of Table 1.
[0056] Figures 5 to 10 show the SEM observation images and the binarized images obtained by the binarization process. Figure 5 is the SEM observation image of Example 1. Figure 6 is the binarized image of Example 1. Figure 7 is the SEM observation image of Example 2. Figure 8 is the binarized image of Example 2. Figure 9 is the SEM observation image of Comparative Example 1. Figure 10 is the binarized image of Comparative Example 1. The images shown in Figures 5 to 10 all represent an observation field of view of 1.5 cm vertically and 1.5 cm horizontally. The scale bar indicates 5 mm. In Figures 6, 8, and 10, as described above, the black areas represent areas where carbon remains.
[0057] [Table 1]
[0058] As shown in Table 1, the carbon retention rate in Examples 1-3 was lower than that in the comparative example. The test negative electrodes in Examples 1-3 were equipped with a first negative electrode active material layer containing resin B (here, polyethylene oxide (PEO)) which is water-soluble and thermoplastic. From the results of these test examples, 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 resin B which is water-soluble and thermoplastic between the negative electrode current collector and the second negative electrode active material, the negative electrode active material layer is easily separated from the negative electrode current collector. It was found that by using an energy storage device having such a negative electrode, a regenerated negative electrode current collector with higher purity can be manufactured.
[0059] As described above, specific embodiments of the technology disclosed herein include those described in the following sections. Section 1: A power storage device comprising 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 aforementioned negative electrode active material layer is A first negative electrode active material layer comprising a negative electrode active material, a binder made of resin A, and resin B, A second negative electrode active material layer comprising the negative electrode active material and the binder, wherein the content of resin B is less than the content of resin B in the first negative electrode active material layer, It has, Here, The aforementioned 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 in an energy storage device. Section 2: The energy storage device according to item 1, wherein the content of resin B in the second negative electrode active material layer is 1 / 4 or less of the content of resin B in the first negative electrode active material layer. Section 3: The energy storage device according to item 1 or 2, wherein the softening point of the resin B is 80°C or lower. Section 4: The energy storage device according to any one of claims 1 to 3, wherein the resin B is polyethylene oxide. Section 5: The energy storage device according to any one of items 1 to 4, wherein the weight-average molecular weight of resin B is 100,000 to 10,000,000. Item 6: The energy storage device according to any one of claims 1 to 5, wherein the resin A is styrene-butadiene rubber. Section 7: A method for manufacturing a regenerated negative electrode current collector, comprising taking the negative electrode from the energy storage device described in any one of items 1 to 6 and isolating the negative electrode current collector from the negative electrode. Section 8: The method for manufacturing the negative electrode current collector according to item 7, wherein the negative electrode is isolated by immersing it in water at 80°C or below.
[0060] While embodiments of the technology disclosed herein have been described above, the technology disclosed herein is not intended to be limited to the embodiments described herein. The technology disclosed herein can also be implemented in other embodiments. The technology described in the claims includes various modifications and changes to the embodiments exemplified above. For example, it is possible to replace parts of the above embodiments with other modifications, and it is also possible to add other modifications to the above embodiments. Furthermore, if a technical feature is not described as essential, it may be deleted 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 Devices
Claims
1. A power storage device comprising 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 aforementioned negative electrode active material layer is A first negative electrode active material layer comprising a negative electrode active material, a binder made of resin A, and resin B, A second negative electrode active material layer comprising the negative electrode active material and the binder, wherein the content of the resin B is less than the content of the resin B in the first negative electrode active material layer, It has, Here, The aforementioned resin A is styrene-butadiene rubber, The aforementioned resin B is polyethylene oxide, The weight-average molecular weight of resin B is between 100,000 and 10,000,000. The first negative electrode active material layer is provided between the second negative electrode active material layer and the negative electrode current collector in an energy storage device.
2. The energy storage device according to claim 1, wherein the content of resin B in the second negative electrode active material layer is 1 / 4 or less of the content of resin B in the first negative electrode active material layer.
3. The energy storage device according to claim 1, wherein the softening point of the resin B is 80°C or lower.
4. A method for manufacturing a regenerated negative electrode current collector, comprising taking the negative electrode from the energy storage device described in any one of claims 1 to 3 and isolating the negative electrode current collector from the negative electrode.
5. The manufacturing method according to claim 4, wherein the negative electrode current collector is isolated by immersing the negative electrode in water at 80°C or lower.