Method for manufacturing electrodes for energy storage devices and composite materials for active material layers.

Abstract

To provide an electrode for a power storage device capable of suppressing occurrence of a defect caused by an edge of an active material layer, and a method for manufacturing a composite material for the active material layer.SOLUTION: An active material layer 12 of an electrode 10 contains an active material, carbon nanotubes, and CMC derived from carboxymethyl cellulose ammonium (NH4-CMC). Content of the CMC derived from NH4 CMC in the active material layer 12 is 0.3% by weight or more and 0.6% by weight or less. A content of the carbon nanotubes in the active material layer 12 is 0.005 mass% or more and 0.08 mass% or less. The active material layer 12 includes a body portion 12a and an edge portion 12b surrounding the body portion 12a. A maximum value of thickness of the edge portion 12b is 104% of that of the body portion 12a. In a plan view in which the electrode 10 is viewed in a thickness direction of the active material layer 12, a maximum size of the edge portion 12b from a boundary between the main body portion 12a and the edge portion 12b to a tip of the edge portion 12b is 5 mm.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing electrodes for energy storage devices and composite materials for active material layers. [Background technology]

[0002] Patent Document 1 discloses a bipolar energy storage device constructed by stacking multiple individually manufactured energy storage cells in series. The energy storage cell comprises a positive electrode and a negative electrode as electrodes, and a separator placed between the positive electrode and the negative electrode. The positive electrode has a positive electrode active material layer as an active material layer in the center of one side of a positive electrode current collector as a current collector. The positive electrode has an uncoated portion other than the center of one side of the positive electrode current collector. The uncoated portion is frame-shaped and surrounds the positive electrode active material layer. The negative electrode has a negative electrode active material layer as an active material layer in the center of one side of a negative electrode current collector as a current collector. The negative electrode has an uncoated portion other than the center of one side of the negative electrode current collector. The uncoated portion is frame-shaped and surrounds the negative electrode active material layer. The positive electrode active material layer and the negative electrode active material layer face each other with the separator in between.

[0003] The energy storage cell includes a sealing section positioned between the positive and negative electrodes. The sealing section is frame-shaped. The sealing section is positioned between the unpainted portion of the positive electrode current collector and the unpainted portion of the negative electrode current collector. The sealing section surrounds the outer periphery of the positive electrode active material layer and the negative electrode active material layer. The sealing section maintains the distance between the positive electrode current collector and the negative electrode current collector to prevent short circuits between the current collectors, and also provides a liquid-tight seal between the positive electrode current collector and the negative electrode current collector. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2017-16825 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] The edges of the positive electrode active material layer may be thicker than the rest of the layer. In this case, the amount of active material at the edges of the positive electrode active material layer in the energy storage device will exceed the preset amount. Similarly, the edges of the negative electrode active material layer may be thicker than the rest of the layer. In this case, when the negative electrode active material layer is compressed for negative electrode manufacturing, there is a risk that the edges of the negative electrode active material layer may be damaged.

[0006] Furthermore, the edges of the positive electrode active material layer may become distorted. In this case, the planar size of the positive electrode active material layer becomes larger than the preset size. Because the entire surface of the positive electrode active material layer faces the negative electrode active material layer, the planar size of the negative electrode active material layer also becomes larger. Furthermore, the edges of the negative electrode active material layer may become distorted. In this case, the planar size of the negative electrode active material layer becomes larger than the preset size. Therefore, it is necessary to suppress the occurrence of defects caused by the shape of the edges of the positive electrode active material layer and the negative electrode active material layer. [Means for solving the problem]

[0007] An electrode for a power storage device to solve the above problems comprises an active material layer provided on the surface of a current collector, and an uncoated portion provided on the surface of the current collector other than the portion on which the active material layer is provided, and surrounding the active material layer, wherein the active material layer comprises a main body portion and an edge portion that surrounds the main body portion and is located between the main body portion and the uncoated portion, and the thickness of the main body portion is 100 μm or more and 400 μm or less, wherein the active material layer comprises an active material capable of intercalating and releasing charge carriers, carbon nanotubes, and carboxymethylcellulose ammonium (NH4- The material contains CMC derived from carboxymethylcellulose ammonium (NH4-CMC), the content of CMC derived from carboxymethylcellulose ammonium (NH4-CMC) in the active material layer is 0.3% by mass or more and 0.6% by mass or less, the content of carbon nanotubes in the active material layer is 0.005% by mass or more and 0.08% by mass or less, the maximum thickness of the edge is 104% of the thickness of the main body, and in a plan view of the electrode as seen in the thickness direction of the active material layer, the maximum dimension of the edge from the boundary between the main body and the edge to the tip of the edge is 5 mm.

[0008] According to this, by including CMC derived from carboxymethylcellulose ammonium (NH4-CMC) in the active material layer, the occurrence of edge height is suppressed. The maximum thickness of the edge is 104% of the thickness of the main body. Therefore, in the energy storage device, it is suppressed that the amount of active material at the edge of the active material layer exceeds a preset amount. Furthermore, even if the active material layer is compressed during electrode manufacturing, damage to the edge of the active material layer can be suppressed. In addition, by including carbon nanotubes in the active material layer, the occurrence of sagging at the edge is suppressed. The maximum dimension of the edge is 5 mm. Therefore, it is possible to suppress the size of the planar shape of the active material layer from exceeding a preset size. As a result, the occurrence of defects caused by the shape of the edge of the active material layer can be suppressed.

[0009] Regarding electrodes for energy storage devices, the surface of the current collector may be provided with a carbon coating layer containing carbon particles and a binder, and the active material layer may be formed on top of the carbon coating layer. In this case, the carbon coating layer improves the peel strength of the active material layer from the current collector.

[0010] Regarding electrodes for energy storage devices, the carbon nanotubes may be single-walled carbon nanotubes. In this case, since single-walled carbon nanotubes have a longer fiber length compared to multi-walled carbon nanotubes, the amount of carbon nanotubes required to suppress sagging at the edges can be reduced.

[0011] A method for manufacturing an active material mixture for an electrode for an energy storage device, comprising: a first step of preparing a primary material by mixing powder of an active material capable of adsorbing and releasing charge carriers with powder of carboxymethylcellulose ammonium (NH4-CMC); a second step of preparing a secondary material by mixing a solvent containing water and carbon nanotubes with the primary material; and a third step of preparing an active material mixture by mixing and kneading the secondary material with a water-based binder, wherein the maximum viscosity of the secondary material is defined as the initial viscosity, and in the third step, the active material mixture is kneaded until its viscosity is 1 / 3 or less of the initial viscosity.

[0012] According to this, the composite material contains ammonium carboxymethyl cellulose (NH4-CMC). Therefore, when the active material layer is manufactured from the composite material, the active material layer contains CMC derived from ammonium carboxymethyl cellulose (NH4-CMC). Therefore, in the active material layer manufactured using the composite material, the generation of the end height at the edge is suppressed. Further, since the composite material contains carbon nanotubes, even when the composite material is kneaded in the third step, the viscosity of the composite material is adjusted to 1 / 3 or less of the initial viscosity. Therefore, it is possible to suppress the occurrence of sagging at the edge of the coating layer of the composite material formed when the composite material is applied to the current collector material. As a result, in the active material layer manufactured using the composite material, the occurrence of sagging at the edge is suppressed. Therefore, according to the manufacturing method of the composite material, it is possible to suppress the occurrence of defects caused by the shape of the edge of the active material layer.

Effect of the Invention

[0013] According to the present invention, it is possible to suppress the occurrence of defects caused by the edge of the active material layer.

Brief Description of the Drawings

[0014] [Figure 1] It is a cross-sectional view showing the electrode of the embodiment. [Figure 2] It is a cross-sectional view showing an enlarged edge of the active material layer. [Figure 3] It is a plan view showing the electrode of the embodiment. [Figure 4] It is a cross-sectional view showing the power storage device. [Figure 5] It is a diagram schematically showing a coating device. [Figure 6] It is a diagram for explaining thixotropy.

Mode for Carrying Out the Invention

[0015] Hereinafter, an embodiment in which the manufacturing method of the electrode for the power storage device and the composite material for the active material layer is embodied will be described according to FIGS. 1 to 6. <Electrode> The electrode is used as the positive or negative electrode of an energy storage device. The energy storage device is, for example, a secondary battery such as a nickel-hydrogen secondary battery or a lithium-ion secondary battery. Further, the energy storage device may be an electric double layer capacitor. Hereinafter, the case where it is an electrode of a lithium-ion secondary battery will be described.

[0016] As shown in FIGS. 1 and 2, the electrode 10 includes a current collector 11, an active material layer 12 provided on the first surface 11a of the current collector 11, and an uncoated portion 11c provided on the current collector 11 other than the portion where the active material layer 12 is provided on the first surface 11a. In the following description, simply looking at the electrode 10 in the thickness direction of the active material layer 12 is referred to as a plan view.

[0017] <Current collector> The current collector 11 is a chemically inert electrical conductor for continuously passing an electric current through the active material layer 12 during discharge or charging of the lithium-ion secondary battery. The current collector 11 is, for example, in the form of a foil. The current collector 11 is rectangular in shape in plan view. The thickness of the foil-like current collector 11 is, for example, 1 μm or more and 1 hundred μm or less. The thickness of the current collector 11 is preferably 10 μm or more and 60 μm or less. As the material constituting the current collector 11, for example, a metal material, a conductive resin material, a conductive inorganic material, etc. can be used. The current collector 11 is formed by cutting a long strip-shaped current collector material 111 shown in FIG. 5 at regular intervals in the longitudinal direction of the current collector 11.

[0018] Examples of the above-mentioned metal materials include copper, aluminum, nickel, titanium, and stainless steel. Examples of the above-mentioned conductive resin materials include resins obtained by adding conductive fillers to conductive polymer materials or non-conductive polymer materials as required.

[0019] When the electrode 10 is applied as the positive electrode of an energy storage device, the current collector 11 is preferably an aluminum current collector made of aluminum. The aluminum current collector may be made of pure aluminum or an aluminum alloy. Examples of aluminum alloys include Al-Mn alloy, Al-Mg alloy, and Al-Mg-Si alloy.

[0020] A carbon coating layer C is provided over the entire surface of the first surface 11a of the current collector 11. The thickness of the carbon coating layer C is, for example, 0.1 μm to 5 μm. The carbon coating layer C is not particularly limited, and known carbon coating layers used for current collectors of electrodes can be applied. The carbon coating layer C can be formed, for example, by applying a carbon paste containing carbon particles and a binder to the first surface 11a of the current collector 11, and then solidifying the applied carbon paste film. The carbon coating layer C enhances the hydrophilicity compared to the first surface 11a of the current collector 11 itself. Therefore, the first surface 11a of the current collector 11 is provided with a carbon coating layer C containing carbon particles and a binder.

[0021] <Active material layer> The active material layer 12 is formed by drying and solidifying the composite material applied to the current collector material 111. The composite material will be described in detail later.

[0022] As shown in Figures 2 and 3, the active material layer 12 is formed on the carbon coating layer C on the first surface 11a of the current collector 11. In plan view, the active material layer 12 has a rectangular shape. Now, the current collector 11 will be described. The current collector 11 has an uncoated portion 11c surrounding the active material layer 12. The uncoated portion 11c is provided on the first surface 11a of the current collector 11, excluding the portion where the active material layer 12 is provided. In plan view, the uncoated portion 11c has a rectangular frame shape. The uncoated portion 11c has a portion that sandwiches the active material layer 12 from both sides in the longitudinal direction and a portion that sandwiches the active material layer 12 from both sides in the short direction.

[0023] The active material layer 12 comprises a rectangular main body 12a and an edge portion 12b. The edge portion 12b surrounds the main body 12a and is located between the main body 12a and the uncoated portion 11c. The thickness t of the main body 12a is approximately constant at all locations along the first surface 11a. The thickness t of the main body 12a can also be said to be the thickness of the active material layer 12.

[0024] The edge portion 12b is the portion located between the boundary M between the main body portion 12a and the edge portion 12b, and the boundary N between the first surface 11a and the edge portion 12b. The boundary N is located at the tip of the edge portion 12b. The edge portion 12b may have a shape that slopes downward from boundary M towards boundary N, or it may have a shape that is slightly thicker than the main body portion 12a before sloping downward towards boundary N. When the edge portion 12b is slightly thicker than the main body portion 12a, the maximum value of the thickness ta at the edge portion 12b is 104% of the thickness t of the main body portion 12a. Therefore, in the active material layer 12, the occurrence of edge height, where the thickness ta of the edge portion 12b exceeds a predetermined value, is suppressed. The predetermined value is 104% of the maximum value of the thickness t of the main body portion 12a. In addition, in a plan view, the maximum value of the dimension L from boundary M to boundary N is 5 mm. Therefore, in the active material layer 12, the occurrence of sagging, where the dimension L of the edge portion 12b exceeds a specified value, is suppressed. The specified value is 5 mm.

[0025] The active material layer 12 contains an active material capable of intercalating and releasing charge carriers such as lithium ions, an aqueous binder, carboxymethylcellulose derived from ammonium carboxymethylcellulose, and carbon nanotubes. Hereinafter, ammonium carboxymethylcellulose will be referred to as "NH4-CMC". Carboxymethylcellulose derived from NH4-CMC will be referred to as "NH4-CMC-derived CMC". Carbon nanotubes will be referred to as "CNT".

[0026] When the electrode 10 is applied as the positive electrode of an energy storage device, the active material contained in the active material layer 12 is the positive electrode active material. The positive electrode active material can be any material usable as a positive electrode active material for lithium-ion secondary batteries, such as lithium composite metal oxides with a layered rock salt structure, metal oxides with a spinel structure, or polyanionic compounds. Furthermore, two or more positive electrode active materials may be used in combination. A specific example of a positive electrode active material is olivine-type lithium iron phosphate (LiFePO4), which is a polyanionic compound.

[0027] When electrode 10 is applied as the negative electrode of an energy storage device, the active material contained in the active material layer 12 is the negative electrode active material. As the negative electrode active material, any material usable as a negative electrode active material for a lithium-ion secondary battery may be used, such as Li, or carbon, metal compounds, elements or compounds thereof that can be alloyed with lithium. Examples of carbon include natural graphite, artificial graphite, or hard carbon (carbon that is difficult to graphitize) or soft carbon (carbon that is easily graphitized). Examples of artificial graphite include highly oriented graphite and mesocarbon microbeads. Examples of elements that can be alloyed with lithium include silicon and tin.

[0028] The content of the active material in the active material layer 12 is not particularly limited. The content of the active material in the active material layer 12 is, for example, 94% by mass or more, preferably 95% by mass or more. The content of the active material in the active material layer 12 is, for example, 99.5% by mass or less, preferably 98.5% by mass or less.

[0029] A water-based binder is a binder that is soluble or dispersible in an aqueous solvent. The water-based binder is a binder that is used by mixing it with the active material in a dispersed or dissolved state in an aqueous solvent. The water-based binder is not particularly limited, and conventionally known materials can be used as water-based binders contained in the active material layer of a lithium-ion secondary battery. Examples of water-based binders include fluororesins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluororubber; thermoplastic resins such as polypropylene and polyethylene; imide resins such as polyimide and polyamideimide; alkoxysilyl group-containing resins; acrylic resins such as poly(meth)acrylic acid; styrene-butadiene rubber; alginates such as sodium alginate and ammonium alginate; water-soluble cellulose ester crosslinks; and starch-acrylic acid graft polymers. The water-based binder contained in the active material layer 12 may be one type or two or more types.

[0030] The content of the aqueous binder in the active material layer 12 is not particularly limited. The content of the aqueous binder in the active material layer 12 is, for example, 0.5% by mass or more, preferably 1% by mass or more. It is preferable that the active material layer 12 contains styrene-butadiene rubber as the aqueous binder.

[0031] CMC derived from NH4-CMC is produced when a mixture containing NH4-CMC is dried, resulting in the elimination of all or part of the ammonia (NH3) from the NH4-CMC. If all of the ammonia (NH3) is eliminated from the NH4-CMC, the resulting NH4-CMC-derived CMC will be H-CMC. If only some of the ammonia (NH3) is eliminated from the NH4-CMC, the resulting NH4-CMC-derived CMC will contain a mixture of NH4-CMC and H-CMC.

[0032] The degree of etherification of the CMC derived from NH4-CMC is preferably 0.5 to 0.65. The content of CMC derived from NH4-CMC in the active material layer 12 is 0.3% by mass to 0.6% by mass, preferably 0.35% by mass to 0.5% by mass. Note that the content of CMC derived from NH4-CMC in the active material layer 12 refers to the total content of NH4-CMC and H-CMC. When the mixture is dried, if the entire amount of ammonia (NH3) in the NH4-CMC is removed, the total content of NH4-CMC and H-CMC refers to the total amount of H-CMC.

[0033] If the CMC content derived from NH4-CMC is less than 0.3% by mass, poor dispersion of the composite material forming the active material layer 12 occurs, which is undesirable. On the other hand, if the CMC content derived from NH4-CMC exceeds 0.6% by mass, the flexibility of the active material layer 12 decreases, making the electrode 10 more prone to cracking, which is also undesirable. Therefore, by setting the CMC content derived from NH4-CMC within the above range, the occurrence of edge height at the edge portion 12b of the active material layer 12 can be suppressed, and the occurrence of damage to the active material layer 12 during compression can be suppressed. Furthermore, by setting the CMC content derived from NH4-CMC within the above range, the peel strength of the active material layer 12 against the current collector 11 is improved.

[0034] The carbon nanotubes (CNTs) may be multi-walled carbon nanotubes (MWCNTs) or single-walled carbon nanotubes (SWCNTs). These CNTs can be used individually or in combination of two or more types. The fiber length and fiber diameter of the CNTs are not particularly limited. The fiber length of the CNTs is, for example, 1 μm to 50 μm, preferably 3 μm to 30 μm. The fiber diameter of the CNTs is, for example, 1 nm to 5 μm, preferably 1.1 nm to 3 μm, and more preferably 1.2 nm to 2 μm. In this embodiment, SWCNTs are used.

[0035] The CNT content in the active material layer 12 is 0.005% by mass or more and 0.08% by mass or less, preferably 0.008% by mass or more and 0.06% by mass or less, and more preferably 0.01% by mass or more and 0.05% by mass or less. By setting the CNT content within the above range, the loss of thixotropy in the composite material forming the active material layer 12 can be suppressed. "Thixotropy" refers to the property that a material initially appears solid, but when shear stress is continuously applied, such as by stirring or shaking, its viscosity decreases and it becomes liquid, while when the stress is removed, its viscosity gradually recovers and it returns to its original state. Having such properties is called having thixotropy.

[0036] The active material layer 12 may contain other components as needed, in addition to the four components described above: the active material, the aqueous binder, the CNTs, and the CMC derived from NH4-CMC. Examples of other components include conductive additives, electrolytes (polymer matrix, ion-conductive polymer, electrolyte solution, etc.), and electrolyte-supporting salts (lithium salts) to enhance ion conductivity. Examples of conductive additives include acetylene black, carbon black, and graphite. The types and contents of other components are not particularly limited, and conventionally known knowledge regarding lithium-ion secondary batteries may be referenced as appropriate.

[0037] The active material layer 12 is formed thicker than usual from the viewpoint of increasing the energy density of the energy storage device. When the energy storage device is used as a power source for a vehicle, in particular when the energy storage device is used as a power source for an electric vehicle, a high-capacity energy storage device of 50 kWh or more is required. For this reason, the thickness of the active material layer 12 is increased. The thickness t of the main body portion 12a of the active material layer 12 is between 100 μm and 400 μm.

[0038] The density of the active material layer 12 is not particularly limited. For example, the density of the active material layer 12 is 1.0 g / cm³. 3 That concludes the explanation. When the density of the active material layer 12 is high, a long-term decrease in the output of the energy storage device due to the inclusion of CNTs is more likely to occur. Also, the density of the active material layer 12 is, for example, 3.0 g / cm³. 3 The following applies:

[0039] The basis weight of the active material layer 12 is not particularly limited, and conventionally known knowledge about lithium ion secondary batteries can be appropriately referred to. However, from the viewpoint of increasing the energy density of the storage cell 20, it is preferable to increase the basis weight of the active material layer 12. The basis weight of the positive electrode active material layer 21b is, for example, 55 mg / cm 2 or more and 90 mg / cm 2 or less, preferably 60 mg / cm 2 or more, and more preferably 70 mg / cm 2 or more. The basis weight of the negative electrode active material layer 22b is, for example, 25 mg / cm 2 or more and 45 mg / cm 2 or less, and preferably 30 mg / cm 2 or more.

[0040] <Power storage device> Next, an example of a power storage device to which the electrode 10 is applied will be described. The power storage device to which the electrode 10 is applied is, for example, a power storage module used as a power source for various vehicles such as forklifts, hybrid vehicles, and electric vehicles. In the present embodiment, the case where the power storage device is a lithium ion secondary battery will be exemplified.

[0041] As shown in FIG. 4, the power storage device 100 includes a cell stack 30 in which a plurality of storage cells 20 are stacked in the stacking direction. Hereinafter, the stacking direction of the plurality of storage cells 20 will be simply referred to as the stacking direction. The storage cell 20 includes a positive electrode 21, a negative electrode 22, a separator 23, and a spacer 24. Either one or both of the positive electrode 21 and the negative electrode 22 of the storage cell 20 are the above-described electrode 10. In FIG. 4, the illustration of the carbon coat layer C and the detailed illustration of the edge portion 12b are omitted.

[0042] The positive electrode 21 includes a positive electrode current collector 21a and a positive electrode active material layer 21b provided on the first surface 21a1 of the positive electrode current collector 21a. When the positive electrode 21 is the electrode 10, the positive electrode current collector 21a is the current collector 11. Also, the positive electrode active material layer 21b is the active material layer 12.

[0043] In a plan view, the positive electrode active material layer 21b is formed in the central part of the first surface 21a1 of the positive electrode current collector 21a. In a plan view, the peripheral part of the first surface 21a1 of the positive electrode current collector 21a is the uncoated positive electrode portion 21c, where the positive electrode active material layer 21b is not provided. In a plan view, the uncoated positive electrode portion 21c is arranged to surround the positive electrode active material layer 21b.

[0044] The negative electrode 22 comprises a negative electrode current collector 22a and a negative electrode active material layer 22b provided on the first surface 22a1 of the negative electrode current collector 22a. When the negative electrode 22 is electrode 10, the negative electrode current collector 22a is the current collector 11, and the negative electrode active material layer 22b is the active material layer 12.

[0045] In a plan view, the negative electrode active material layer 22b is formed in the central part of the first surface 22a1 of the negative electrode current collector 22a. In a plan view, the peripheral part of the first surface 22a1 of the negative electrode current collector 22a is the uncoated negative electrode portion 22c where the negative electrode active material layer 22b is not provided. The uncoated negative electrode portion 22c is arranged to surround the negative electrode active material layer 22b in a plan view. The positive electrode 21 and the negative electrode 22 are arranged such that the positive electrode active material layer 21b and the negative electrode active material layer 22b face each other in the stacking direction. In other words, the opposing directions of the positive electrode 21 and the negative electrode 22 coincide with the stacking direction. The negative electrode active material layer 22b is formed to be slightly larger than the positive electrode active material layer 21b. When the negative electrode active material layer 22b is formed to be slightly larger than the positive electrode active material layer 21b, in a plan view, the entire formation region of the positive electrode active material layer 21b is located within the formation region of the negative electrode active material layer 22b.

[0046] The positive electrode current collector 21a has a second surface 21a2 which is the surface opposite to the first surface 21a1. The positive electrode 21 is a monopolar electrode in which neither the positive electrode active material layer 21b nor the negative electrode active material layer 22b is formed on the second surface 21a2 of the positive electrode current collector 21a. The negative electrode current collector 22a has a second surface 22a2 which is the surface opposite to the first surface 22a1. The negative electrode 22 is a monopolar electrode in which neither the positive electrode active material layer 21b nor the negative electrode active material layer 22b is formed on the second surface 22a2 of the negative electrode current collector 22a.

[0047] The separator 23 is positioned between the positive electrode 21 and the negative electrode 22, preventing short circuits caused by contact between the two electrodes while allowing charge carriers such as lithium ions to pass through.

[0048] The separator 23 is, for example, a porous sheet or nonwoven fabric containing a polymer that absorbs and retains electrolytes. Examples of materials constituting the separator 23 include polyolefins such as polypropylene and polyethylene, and polyester. The separator 23 may have a single-layer structure or a multilayer structure. The multilayer structure may include, for example, an adhesive layer, a ceramic layer as a heat-resistant layer, and the like.

[0049] The spacer 24 is positioned between the first surface 21a1 of the positive electrode current collector 21a of the positive electrode 21 and the first surface 22a1 of the negative electrode current collector 22a of the negative electrode 22, and on the outer circumference of the positive electrode active material layer 21b and the negative electrode active material layer 22b. The spacer 24 is bonded to both the positive electrode current collector 21a and the negative electrode current collector 22a. The spacer 24 maintains the distance between the positive electrode current collector 21a and the negative electrode current collector 22a, preventing a short circuit between them, and also provides a liquid-tight seal between the positive electrode current collector 21a and the negative electrode current collector 22a.

[0050] In a plan view, the spacer 24 extends along the periphery of the positive electrode current collector 21a and the negative electrode current collector 22a, and is formed in a frame shape that surrounds the positive electrode current collector 21a and the negative electrode current collector 22a. The spacer 24 is positioned between the uncoated positive electrode portion 21c of the first surface 21a1 of the positive electrode current collector 21a and the uncoated negative electrode portion 22c of the first surface 22a1 of the negative electrode current collector 22a.

[0051] Examples of materials that make up the spacer 24 include various resin materials such as polyethylene (PE), modified polyethylene (modified PE), polystyrene (PS), polypropylene (PP), modified polypropylene (modified PP), ABS resin, and AS resin.

[0052] Inside the energy storage cell 20, a sealed space S is formed, surrounded by a frame-shaped spacer 24, a positive electrode 21, and a negative electrode 22. The sealed space S houses a separator 23 and an electrolyte. The peripheral portion of the separator 23 is embedded in the spacer 24.

[0053] Examples of electrolytes include liquid electrolytes and polymer gel electrolytes containing electrolytes held in a polymer matrix. Examples of liquid electrolytes include liquid electrolytes containing a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Known lithium salts such as LiClO4, LiAsF6, LiPF6, LiBF4, LiCF3SO3, LiN(FSO2)2, and LiN(CF3SO2)2 can be used as the electrolyte salt. Known solvents such as cyclic carbonates, cyclic esters, linear carbonates, linear esters, and ethers can be used as the non-aqueous solvent. Two or more of these known solvent materials may be used in combination.

[0054] The spacer 24 can prevent the electrolyte contained in the sealed space S from leaking to the outside by sealing the sealed space S between the positive electrode 21 and the negative electrode 22. The spacer 24 can also prevent moisture from entering the sealed space S from outside the energy storage device 100. Furthermore, the spacer 24 can prevent gas generated from the positive electrode 21 or the negative electrode 22, for example, due to a charge-discharge reaction, from leaking to the outside of the energy storage device 100. In order to enable the spacer 24 to be placed between the positive electrode 21 and the negative electrode 22 to perform the above functions, the positive electrode 21 is provided with an uncoated positive electrode portion 21c, and the negative electrode 22 is provided with an uncoated negative electrode portion 22c.

[0055] The cell stack 30 has a structure in which multiple energy storage cells 20 are stacked on top of each other such that the second surface 21a2 of the positive electrode current collector 21a and the second surface 22a2 of the negative electrode current collector 22a are in contact. As a result, the multiple energy storage cells 20 constituting the cell stack 30 are connected in series.

[0056] In the cell stack 30, two adjacent energy storage cells 20 in the stacking direction form a pseudo-bipolar electrode 25 in which the positive electrode current collector 21a and the negative electrode current collector 22a that are in contact with each other are considered as a single current collector. The pseudo-bipolar electrode 25 includes a current collector having a structure in which the positive electrode current collector 21a and the negative electrode current collector 22a are superimposed, a positive electrode active material layer 21b formed on one side of the current collector, and a negative electrode active material layer 22b formed on the other side.

[0057] Alternatively, the positive electrode current collector 21a and the negative electrode current collector 22a may form a bipolar current collector by joining the second surface 21a2 of the positive electrode current collector 21a and the second surface 22a2 of the negative electrode current collector 22a. In this case, the positive electrode 21 and the negative electrode 22 form a bipolar electrode 25 comprising a single bipolar current collector formed by joining the positive electrode current collector 21a and the negative electrode current collector 22a.

[0058] The energy storage device 100 includes a pair of conductive elements, consisting of a positive electrode conductive plate 40 and a negative electrode conductive plate 50, which are arranged to sandwich the cell stack 30 in the stacking direction of the cell stack 30. The positive electrode conductive plate 40 and the negative electrode conductive plate 50 are each made of a material with excellent conductivity.

[0059] The positive electrode current-carrying plate 40 is electrically connected to the second surface 21a2 of the positive electrode current collector 21a of the positive electrode 21, which is located on the outermost side at one end in the stacking direction. The negative electrode current-carrying plate 50 is electrically connected to the second surface 22a2 of the negative electrode current collector 22a of the negative electrode 22, which is located on the outermost side at the other end in the stacking direction.

[0060] The energy storage device 100 is charged and discharged through terminals provided on the positive electrode current-carrying plate 40 and the negative electrode current-carrying plate 50, respectively. For example, the same material as the material that makes up the positive electrode current-carrying plate 40 can be used. The positive electrode current-carrying plate 40 may be made of a metal plate that is thicker than the positive electrode current-carrying plate 21a used in the cell stack 30. For example, the same material as the material that makes up the negative electrode current-carrying plate 50 can be used. The negative electrode current-carrying plate 50 may be made of a metal plate that is thicker than the negative electrode current-carrying plate 22a used in the cell stack 30.

[0061] <Method for manufacturing electrodes for energy storage devices> Next, we will explain how to manufacture the electrode 10. The electrode 10 is manufactured by sequentially going through a composite material manufacturing process and an active material layer formation process.

[0062] <Mixture manufacturing process> The method for producing the composite material includes a first step of preparing a primary material by mixing a powdered active material with powdered NH4-CMC; a second step of preparing a secondary material by mixing the primary material with a solvent containing water and CNTs; and a third step of preparing a slurry-like composite material by adding styrene-butadiene rubber to the secondary material and kneading it. In the following description, styrene-butadiene rubber will be referred to as [SBR].

[0063] When the total mass of solids contained in the mixture is 100 parts by mass, the active material content is preferably 94 parts by mass or more and 95 parts by mass or less. The amount of NH4-CMC mixed in the first step is preferably 0.3 parts by mass or more and 0.6 parts by mass or less. The mixing method in the first step is not particularly limited as long as it can uniformly disperse the solids contained in the primary materials, and conventionally known mixing methods used for mixing powders can be applied. Examples of the above mixing methods include mixing by hand using a stirring rod or the like, and mixing by mechanical stirring using an ultrasonic disperser or the like.

[0064] The second step involves preparing a secondary material by mixing the primary material with a water-containing solvent and CNTs. The CNTs are pre-prepared in paste form. The secondary material is prepared by mixing the primary material with a water-containing solvent and CNTs and kneading the mixture. The initial viscosity is defined as the highest viscosity of the secondary material in a slurry or capillary state after adding the solvent. The initial viscosity may also be defined after the third step. The water-containing solvent is preferably a solvent mainly composed of water, for example, a solvent in which the mass percentage of water is 50 to 100% by mass. In this embodiment, water is used as the solvent. Water is added to the mixture, for example, so that the solid content of the mixture is 50% by mass or more and 70% by mass or less.

[0065] The third step involves adding SBR to the secondary material and kneading to prepare a slurry-like mixture. The SBR is pre-prepared into a paste. When the total mass of solids contained in the mixture is 100 parts by mass, the CNT content is preferably 0.005 parts by mass or more and 0.08 parts by mass or less. Furthermore, when the total mass of solids contained in the mixture is 100 parts by mass, the SBR content is preferably 1.0 part by mass or more and 5.0 parts by mass or less.

[0066] The specific mixing methods in the second and third steps are not particularly limited as long as they can uniformly mix each component contained in the secondary material and the composite material, and conventionally known mixing methods used in the manufacture of composite materials for secondary battery electrodes can be applied. Examples of the above mixing methods include mixing by hand using a stirring rod, and mixing by mechanical stirring using conventional mixers such as planetary mixers, homo mixers, homo dispersers, Henschel mixers, Banbury mixers, ribbon mixers, V-type mixers, and orbital mixers, as well as ultrasonic dispersers.

[0067] In the third step, the mixing of the asphalt mixture is preferably carried out until its viscosity is 1 / 3 or less of its initial viscosity, and particularly preferably until it is 1 / 4 or less. When the viscosity of the asphalt mixture is reduced to 1 / 3 or less of its initial viscosity, the decrease in viscosity due to mixing stabilizes, and it becomes suitable for coating.

[0068] <Active material layer formation process> The active material layer formation process involves applying an asphalt mixture to the first surface 111a of the current collector material 111, followed by drying the applied layer of the asphalt mixture. As described above, the current collector material 111 is in the form of a long strip. A die coating method can be used as a method for applying the asphalt mixture to the current collector material 111.

[0069] As shown in Figure 5, the application of the composite material 121 to the current collector material 111 is performed by a coating apparatus 31. The coating apparatus 31 includes a slit die 32, a backup roller 33, a supply roll 34, and a tension roller 35.

[0070] The slit die 32 includes a storage section 31a where the asphalt mixture 121 is stored, and a discharge port 31b from which the asphalt mixture 121 stored in the storage section 31a is discharged. In the slit die 32, the asphalt mixture 121 stored in the storage section 31a is pumped by a pump (not shown). The asphalt mixture 121 pumped by the pump is discharged from the discharge port 31b.

[0071] The backup roller 33 is positioned opposite the discharge port 31b of the slit die 32. The backup roller 33 is provided so as to be movable relative to the slit die 32, in a coating position where the asphalt mixture 121 can be applied to the first surface 111a of the current collector material 111 by the slit die 32, and in a retracted position where the asphalt mixture 121 cannot be applied to the current collector material 111 by the slit die 32.

[0072] The current collector material 111 is wound around the supply roll 34. The current collector material 111 fed from the supply roll 34 is supplied to the slit die 32. The tension roller 35 applies tension to the current collector material 111 fed from the supply roll 34. As the current collector material 111 is transported along the backup roller 33, which has moved to the coating position, the composite material 121 discharged from the slit die 32 is coated onto the first surface 111a of the current collector material 111. As a result, a coating layer of the composite material 121 is formed on the current collector material 111.

[0073] The asphalt mixture 121 is discharged from the slit die 32 away from both short edges of the current collector material 111. As a result, uncoated portions 11c of the asphalt mixture 121 are formed on both short sides of the current collector material 111.

[0074] By discharging and stopping the asphalt mixture 121 from the slit die 32 at predetermined intervals, the asphalt mixture 121 is applied intermittently to the first surface 111a of the current collector material 111. Because the application of the asphalt mixture 121 is intermittent, a coating start end and a coating end of the asphalt mixture 121 are formed in the coating layer. The coating start end of the asphalt mixture 121 is formed at the first end in the longitudinal direction of the active material layer 12, which is formed when the coating layer dries. The coating end of the asphalt mixture 121 is formed at the second end in the longitudinal direction of the active material layer 12, which is formed when the coating layer dries. The thickness, longitudinal length, and width of the coating layer of the asphalt mixture 121 are appropriately set according to the size of the lithium-ion secondary battery.

[0075] Furthermore, by stopping the discharge of the asphalt mixture 121 from the slit die 32, uncoated areas 11c are formed between adjacent coating layers in the longitudinal direction of the current collector material 111 where the asphalt mixture 121 is not applied. When discharge is stopped, a suck-back mechanism (not shown) instantly reduces the pressure inside the slit die 32, instantly stopping the discharge of the asphalt mixture 121. Therefore, coating layers of the asphalt mixture 121 and uncoated areas 11c are formed alternately in the longitudinal direction of the current collector material 111.

[0076] Methods for drying the coating layer of the composite material 121 include, for example, natural drying, low-temperature air, hot air, vacuum, infrared radiation, far-infrared radiation, electron beam, and microwave. Two or more of these drying methods may be combined. The drying temperature is 20 degrees Celsius or higher and 120 degrees Celsius or lower, preferably 40 degrees Celsius or higher and 100 degrees Celsius or lower.

[0077] As the coating layer of the asphalt mixture 121 dries, NH3 is detached from the NH4-CMC contained in the asphalt mixture 121. As a result, CMC derived from NH4-CMC is incorporated into the active material layer 12.

[0078] Furthermore, to increase the electrode density, a compression step may be performed after the drying step to compress the active material layer 12. Examples of methods for compressing the active material layer 12 include the roll press method, the die press method, and the calender press method. The press pressure is 0.1 t / cm². 2 More than 10t / cm 2 Preferably, it is 0.5 t / cm 2 More than 5.0t / cm 2 The following is more preferable:

[0079] A winding process may be performed to wind the electrode 10 into a roll during the coating process, drying process, and compression process, and at least some timing after the compression process. Alternatively, a drying process may be performed again after the compression process. By doing so, an active material layer 12 is formed on the current collector material 111.

[0080] Then, the electrode 10 is manufactured by cutting the current collector material 111, on which the active material layer 12 is formed, at the uncoated portion 11c between the active material layers 12. <Manufacturing method for energy storage devices> A method for manufacturing the energy storage device 100 will be described.

[0081] The energy storage device 100 is manufactured by sequentially going through an energy storage cell formation process and a cell stack formation process. <Energy storage cell formation process> In the energy storage cell formation process, first, the positive electrode 21 and negative electrode 22 are arranged with a separator 23 in between so that the positive electrode active material layer 21b and the negative electrode active material layer 22b face each other in the stacking direction, and spacers 24 are placed between the positive electrode 21 and the negative electrode 22, and in the uncoated portions 21c of the positive electrode and 22c of the negative electrode. At this time, the edge 12b of the positive electrode active material layer 21b faces the negative electrode active material layer 22b with the separator 23 in between. Also, the edge 12b of the negative electrode active material layer 22b faces the separator 23.

[0082] Subsequently, the positive electrode 21, the negative electrode 22, and the separator 23 are joined to the spacer 24 by welding, thereby forming an assembly in which each component is integrated. Examples of welding methods for the spacer 24 include known welding methods such as heat welding, ultrasonic welding, or infrared welding.

[0083] Next, the electrolyte is injected into the sealed space S inside the assembly through an inlet provided in a part of the spacer 24, and then the inlet is sealed. This forms the energy storage cell 20. <Cell stack formation process> The cell stack formation process first involves stacking multiple energy storage cells 20 so that the second surface 21a2 of the positive electrode current collector 21a and the second surface 22a2 of the negative electrode current collector 22a face each other. At this time, the second surface 21a2 of the positive electrode current collector 21a of one energy storage cell 20 and the second surface 22a2 of the negative electrode current collector 22a of the other energy storage cell 20 are brought into contact with each other. Subsequently, the multiple energy storage cells 20 are integrated by joining the outer peripheral portions of the spacers 24 in adjacent energy storage cells 20 in the stacking direction.

[0084] Next, the positive electrode current-carrying plate 40 is fixed to the second surface 21a2 of the positive electrode current collector 21a of the positive electrode 21, which is located on the outermost side at one end of the stacking direction, in an electrically connected state. Similarly, the negative electrode current-carrying plate 50 is fixed to the second surface 22a2 of the negative electrode current collector 22a of the negative electrode 22, which is located on the outermost side at the other end of the stacking direction, in an electrically connected state. At this time, the second surface 22a2 of the negative electrode current collector 22a and the negative electrode current-carrying plate 50 are brought into contact with each other. This completes the formation of the energy storage device 100.

[0085] <Operation of the Embodiment> Next, the operation of this embodiment will be described. The active material layer 12 contains NH4-CMC-derived CMC in an amount of 0.3% to 0.6% by mass. The composite material 121 forming the active material layer 12 also contains NH4-CMC.

[0086] The solid line in Figure 6 shows the relationship between viscosity and shear stress after kneading asphalt 121 containing 0.4 mass% NH4-CMC and 0.05 mass% SWCNT for 30 minutes. The dashed line in Figure 6 shows the relationship between viscosity and shear stress after kneading asphalt 121 without SWCNT for 30 minutes. As shown in Figure 6, the viscosity at low shear stress is maintained at a higher level compared to the case without SWCNT, indicating improved thixotropy of asphalt 121. Due to the improved thixotropy of asphalt 121, the viscosity of asphalt 121 is also higher compared to the case without NH4-CMC.

[0087] Therefore, the generation of edge height is suppressed at the start and end ends of the coating layer formed by applying the composite material 121 to the current collector material 111. As a result, in the active material layer 12 formed by drying the coating layer, the generation of edge height is suppressed at the edges 12b formed from the start and end ends of the coating layer.

[0088] When SWCNTs are included in 0.05 mass% of the asphalt mixture 121, the viscosity of the asphalt mixture 121 is increased under low shear stress conditions. The inventors discovered that when NH4-CMC is included in the asphalt mixture 121, the thixotropy is lost upon kneading of the asphalt mixture 121, as shown by the dashed line in Figure 6.

[0089] The inventors then discovered that by including CNTs in the composite material 121, the loss of thixotropy is suppressed, thereby preventing the viscosity of the composite material 121 from decreasing and becoming liquid.

[0090] In this embodiment, the active material layer 12 contains SWCNTs as CNTs in an amount of 0.005% by mass or more and 0.08% by mass or less. In other words, the composite material 121 that forms the active material layer 12 also contains SWCNTs. As a result, the occurrence of sagging at the edges of the coating layer formed by applying the composite material 121 to the current collector material 111 is suppressed. Consequently, the occurrence of sagging at the edges 12b of the active material layer 12 formed by drying the coating layer is also suppressed.

[0091] <Effects of the Embodiment> According to the above embodiment, the following effects can be obtained. (1) In the electrode 10 for the energy storage device, the content of CMC derived from NH4-CMC in the active material layer 12 is 0.3% by mass or more and 0.6% by mass or less. This suppresses the generation of edge height at the edge 12b of the active material layer 12.

[0092] In the positive electrode active material layer 21b of the positive electrode 21, the generation of edge height at the edge 12b is suppressed. Therefore, in the energy storage device 100, the amount of active material at the edge 12b of the positive electrode active material layer 21b is prevented from exceeding a preset amount, and when the positive electrode active material layer 21b is compressed, it is possible to prevent the edge 12b of the positive electrode active material layer 21b from being overcompressed by the amount of edge height. Similarly, in the negative electrode active material layer 22b of the negative electrode 22, the generation of edge height at the edge 12b is suppressed. Therefore, when the negative electrode active material layer 22b is present on both sides of the negative electrode current collector 22a, it is possible to prevent the edge 12b of the negative electrode active material layer 22b from being overcompressed by the amount of edge height when the negative electrode active material layer 22b is compressed. When the negative electrode active material layer 22b is on one side of the negative electrode current collector 22a and the positive electrode active material layer 21b is on the other side of the negative electrode current collector 22a, it is possible to suppress the bending and damage of the edge portion 12b of the negative electrode active material layer 22b when the negative electrode active material layer 22b is compressed. Furthermore, in the energy storage device 100, it is possible to suppress the edge portion 12b of the negative electrode active material layer 22b from piercing the separator 23.

[0093] The active material layer 12 contains CNTs in an amount of 0.005% by mass or more and 0.08% by mass or less. This suppresses the occurrence of sagging at the edges of the coating layer formed by applying the composite material 121 to the current collector material 111. As a result, the occurrence of sagging at the edges 12b of the active material layer 12 formed by drying the coating layer is suppressed.

[0094] Therefore, the size of the positive electrode active material layer 21b in planar shape can be suppressed from becoming larger than a preset size. Since the entire surface of the positive electrode active material layer 21b faces the negative electrode active material layer 22b, the size of the negative electrode active material layer 22b in planar shape can be suppressed from becoming larger. In addition, the occurrence of sagging at the edge 12b of the negative electrode active material layer 22b is suppressed. The size of the negative electrode active material layer 22b in planar shape can be suppressed from becoming larger than a preset size. As a result, the occurrence of defects caused by the shape of the edge 12b of the active material layer 12 can be suppressed.

[0095] (2) A carbon coating layer C is provided on the first surface 11a of the current collector 11. The active material layer 12 is formed on top of the carbon coating layer C. This carbon coating layer C improves the peel strength of the active material layer 12 from the current collector 11.

[0096] (3) The CNTs are single-walled carbon nanotubes. Single-walled carbon nanotubes have longer fiber lengths compared to multi-walled carbon nanotubes, which makes it easier to improve the thixotropy of the composite material 121. Therefore, the amount of CNTs required to impart the desired thixotropy to the composite material 121 can be reduced. As a result, the amount of CNTs required to suppress the sagging of the edges 12b of the active material layer 12 can be reduced.

[0097] This embodiment can be implemented with the following modifications. This embodiment and the following modifications can be combined with each other to the extent that they do not contradict each other technically. ○The formation range of the carbon coating layer C on the first surface 11a of the current collector 11 may be changed. For example, the carbon coating layer C may be formed only in the area where the active material layer 12 is formed on the first surface 11a, or the carbon coating layer C may be formed partially in a part of that area.

[0098] ○The electrode 10 may be a bipolar electrode. The electrode 10 includes a bipolar current collector. The bipolar current collector is a laminate in which a foil-shaped positive electrode current collector and a foil-shaped negative electrode current collector are integrally joined in the thickness direction. Examples of bipolar current collectors include a current collector made by bonding aluminum foils together, and a current collector made by bonding aluminum foil and copper foil together.

[0099] ○The specific configuration of the energy storage device 100 to which the electrode 10 is applied is not particularly limited, as long as at least one positive electrode or at least one negative electrode corresponds to the electrode 10. For example, the number of energy storage cells 20 constituting the energy storage device 100 may be 1. The energy storage device 100 may also be equipped with a restraining member that applies a restraining load to the cell stack 30 in the stacking direction. Furthermore, the energy storage device 100 may be equipped with an electrode 10 configured as a bipolar electrode. [Examples]

[0100] The following describes an embodiment that further elaborates on the above embodiment. <Examples 1-2> <Fabrication of the positive electrode sheet> Cathode composite materials were prepared containing LiFePO4, carboxymethylcellulose ammonium (NH4-CMC), single-walled carbon nanotubes (SWCNTs), and styrene-butadiene rubber (SBR) in the solid content proportions shown in Table 1.

[0101] First, as the first step, the primary material was prepared by mixing the entire amount of LiFePO4 and the entire amount of NH4-CMC. Next, as the second step, the secondary material was prepared by adding the entire amount of SWCNTs to the primary material in an amount that resulted in a solid content ratio of 83% by mass of the final composite material. As the third step, the composite material was prepared by adding the entire amount of SBR to the secondary material. Finally, as the third step, the composite material was kneaded using a planetary mixer at 20 rpm for 5 hours to obtain a cathode composite material with a viscosity of 1 / 4 or less of the initial viscosity of the secondary material.

[0102] A carbon-coated aluminum foil with a thickness of 30 μm was prepared as the positive electrode current collector 21a. A coating layer was formed by applying a positive electrode composite material in a film-like manner to the surface of the carbon coating layer C of the positive electrode current collector 21a using a die coating method. The coating layer of the positive electrode composite material was heat-treated at 50°C to dry and solidify the coating layer of the positive electrode composite material, and then compressed. Positive electrode sheets of Examples 1 and 2 were fabricated, in which a positive electrode active material layer 21b with a thickness of 400 μm was formed on the positive electrode current collector 21a.

[0103] [Table 1] <Comparative Example 1 to Comparative Example 2> As shown in Table 1, in Comparative Example 1, the blending ratio of NH4-CMC in the positive electrode active material layer was set to 0.2% by mass. In Comparative Example 2, the CMC salt was replaced with carboxymethylcellulose ammonium, and the positive electrode active material layer was formed from a positive electrode mixture containing carboxymethylcellulose sodium.

[0104] <Examples 3 to 5> <Fabrication of the negative electrode sheet> A negative electrode composite was prepared containing graphite, carboxymethylcellulose ammonium (NH4-CMC), single-walled carbon nanotubes (SWCNT), and styrene-butadiene rubber (SBR) in the solid content ratios shown in Table 2. First, in the first step, the entire amount of graphite and the entire amount of NH4-CMC were mixed to prepare the primary material. Next, in the second step, water and the entire amount of SWCNT were added to the primary material in an amount that would result in a final composite with a solid content ratio of 60% by mass, to prepare the secondary material. In the third step, the entire amount of SBR was added to the secondary material to prepare the composite. Finally, in the third step, the composite was kneaded using a planetary mixer at 20 rpm for 5 hours to obtain a negative electrode composite with a viscosity of 1 / 4 or less of the initial viscosity of the secondary material.

[0105] A carbon-coated copper foil with a thickness of 10 μm was prepared as the negative electrode current collector 22a. The negative electrode composite material was applied in a film-like manner to the surface of the negative electrode current collector 22a where the carbon coating layer C was provided, using a die coating method to form a coating layer. The coating layer of the negative electrode composite material was heat-treated at 50°C to dry and solidify the negative electrode composite material, and then compressed. Negative electrode sheets of Examples 3 to 5 were fabricated, in which a negative electrode active material layer 22b with a thickness of 400 μm was formed on the negative electrode current collector 22a.

[0106] [Table 2] <Comparative Example 3 to Comparative Example 5> As shown in Table 2, in Comparative Example 3, the blending ratio of NH4-CMC in the negative electrode active material layer was set to 0.2% by mass. In Comparative Example 4, the CMC salt was replaced with carboxymethylcellulose ammonium, and the negative electrode active material layer was formed from a negative electrode mixture containing carboxymethylcellulose sodium. In Comparative Example 5, the negative electrode active material layer was formed from a negative electrode mixture that did not contain SWCNTs.

[0107] <Measurement of the edge> The thickness ta and dimension L of the edge 12b of each active material layer 12 were measured in Examples 1 to 5 and Comparative Examples 1 to 5. A [○] mark was used if the thickness ta of the edge 12b was 104% or less of the thickness t of the main body 12a, and a [×] mark was used if the thickness ta of the edge 12b exceeded 104% of the thickness t of the main body 12a. Furthermore, a [○] mark was used if the dimension L from boundary M to boundary N in a plan view of the active material layer 12 was 5 mm or less, and a [×] mark was used if the dimension L exceeded 5 mm. The results are shown in Tables 1 and 2. In Tables 1 and 2, the CMC salt is either NH4-CMC or Na-CMC, and CMC represents NH4-CMC.

[0108] In Comparative Examples 1 and 3, when the NH4-CMC blending ratio was 0.2% by mass, the edges 12b collapsed during compression after the coating layer of each asphalt mixture was dried and solidified. This is thought to be due to poor dispersion of the asphalt mixture. Furthermore, in Comparative Examples 1 and 3, edge height measurements were not performed because the edges 12b collapsed. On the other hand, as shown in Examples 1 to 2 and Examples 3 to 5, when the NH4-CMC blending ratio was 0.3% by mass or more and 0.6% by mass or less, the occurrence of edge height was suppressed.

[0109] Furthermore, as shown in Comparative Examples 2 and 4, edge height occurred when Na-CMC was used. On the other hand, as shown in Examples 1-2 and Examples 3-5, edge height was suppressed by using NH4-CMC.

[0110] These results show that, unlike when Na-CMC is used, by including a specified amount of NH4-CMC, the occurrence of edge height at the edges 12b of the active material layer 12 formed by drying, solidifying, and compressing the composite material was suppressed.

[0111] On the other hand, when NH4-CMC is included in the asphalt mixture, the thixotropy is lost due to the mixing of the mixture. However, it was shown that the thixotropy is not lost when SWCNT is included in the asphalt mixture. As a result, by including a specified amount of SWCNT, the occurrence of sagging at the edge 12b of the active material layer 12 was suppressed, as shown in Examples 1 to 2 and Examples 3 to 5. [Explanation of Symbols]

[0112] C...carbon coating layer, 10...electrode, 11...current collector, 11a...first surface, 11c...uncoated part, 12...active material layer, 100...energy storage device.

Claims

1. An electrode for a power storage device, comprising: an active material layer provided on the surface of a current collector; and an uncoated portion provided on the surface of the current collector other than the portion on which the active material layer is provided, and surrounding the active material layer, wherein the active material layer comprises a main body portion and an edge portion surrounding the main body portion and located between the main body portion and the uncoated portion, and the thickness of the main body portion is 100 μm or more and 400 μm or less, The active material layer comprises an active material capable of intercepting and releasing charge carriers, carbon nanotubes, and carboxymethylcellulose ammonium (NH4). ４ - Contains CMC derived from CMC, The carboxymethylcellulose ammonium (NH ４ CMC derived from -CMC is generated when the coating layer of the composite material forming the active material layer applied to the surface of the current collector is dried, and all or part of the ammonia (NH3) in the carboxymethylcellulose ammonium (NH4-CMC) contained in the composite material is desorbed. The content of carboxymethylcellulose ammonium (NH4-CMC) in the solid content contained in the aforementioned mixture is 0.3% by mass or more and 0.6% by mass or less. The carbon nanotube content in the solid content of the composite material is 0.005% by mass or more and 0.08% by mass or less. The thickness of the edge portion is 104% or less of the thickness of the main body portion. An electrode for a power storage device, characterized in that, when viewed in a plan view of the electrode in the thickness direction of the active material layer, the dimension of the edge from the boundary between the main body and the edge to the tip of the edge is 5 mm or less.

2. The electrode for an energy storage device according to claim 1, wherein the surface of the current collector is provided with a carbon coating layer containing carbon particles and a binder, and the active material layer is formed on the carbon coating layer.

3. The electrode for an energy storage device according to claim 1 or claim 2, wherein the carbon nanotube is a single-walled carbon nanotube.

4. A method for manufacturing an active material for an electrode for a power storage device, comprising: an active material layer provided on the surface of a current collector; and an uncoated portion provided on the surface of the current collector other than the portion on which the active material layer is provided, and surrounding the active material layer, wherein the active material layer comprises a main body portion and an edge portion that surrounds the main body portion and is located between the main body portion and the uncoated portion, A powder of an active material capable of adsorbing and releasing charge carriers, and carboxymethylcellulose ammonium (NH4) contained in the solid content of the composite material forming the active material layer, with a content of 0.3% by mass or more and 0.6% by mass or less. ４ - The first step is to prepare the primary material by mixing it with the powder of CMC, A second step involves preparing a secondary material by mixing the primary material with a solvent containing water and carbon nanotubes whose content in the solids of the composite material forming the active material layer is 0.005% by mass or more and 0.08% by mass or less. The process includes a third step of preparing a composite material by mixing and kneading the aforementioned secondary material with a water-based binder. A method for producing an active material for an active material layer, characterized in that, if the maximum viscosity of the secondary material is defined as the initial viscosity, the third step involves kneading the composite material until its viscosity is 1 / 3 or less of the initial viscosity.

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