Electrode body for secondary battery

Abstract

An object of the present disclosure is to provide a novel electrode body for a secondary battery capable of suppressing a decrease in binding force between an active material layer and a current collector, ensuring flexibility, and suppressing an increase in ion resistance of the active material layer.SOLUTION: An electrode assembly 100 includes a current collector layer 110 and an active material layer 120 stacked on the current collector layer 110, wherein the active material layer 120 includes a first layer 121 on the current collector layer 110 and a second layer 122 on the first layer 121, a first binder 132 contained in the first layer 121 includes particles having a surface contact shape, and a second binder 141 contained in the second layer 122 includes particles having a point contact shape.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an electrode assembly for a secondary battery. [Background technology]

[0002] To improve the production efficiency of secondary battery electrode bodies, a method is available for shortening the drying time by high-temperature drying in the drying process after coating the composite slurry on the current collector layer. However, when high-temperature drying is performed, the binder contained in the composite slurry migrates from the adhesive surface to the surface, a phenomenon known as binder migration. When binder migration occurs, the current collector and active material layer tend to peel off, which can lead to a decrease in battery performance.

[0003] Various methods for suppressing binder migration have been disclosed. Patent Document 1 discloses a method for suppressing binder migration in which the specific surface area S1 based on the BET method is 3 to 20 m 2 a slurry for forming a lower layer obtained by kneading a high BET negative electrode active material of 2 to 6 m / g and a binder in a solvent; 2 / g of a low-BET negative electrode active material and a binder are kneaded in a solvent, where S1 and S2 are determined so that the ratio of S2 to S1 (S2 / S1) is 0.1 to 0.9; and coating the lower layer forming slurry on a negative electrode current collector, coating the upper layer forming slurry on the lower layer forming slurry, and simultaneously drying the lower layer forming slurry and the lower layer forming slurry at 100 to 150°C to form a negative electrode active material layer consisting of a lower layer and an upper layer, where the coating of the lower layer forming slurry and the upper layer forming slurry is performed so that the ratio (T2 / TA) of the thickness T2 of the lower layer to the overall thickness TA of the negative electrode active material layer is 0.02 to 0.3. It is said that this disclosure can provide a negative electrode in which the negative electrode active material layer is less likely to peel or collapse, even when drying is carried out at a high temperature of 100°C or higher.

[0004] Patent Document 2 also discloses a method for manufacturing an electrode body having an active material layer formed of two layers with different binder compositions. Patent Document 2 discloses a battery manufacturing method including a first layer-forming step of forming a first layer on the surface of a current collector using a first paste containing a first positive electrode active material, a hydrophilic binder, and a first solvent, and a second layer-forming step of forming a second layer on the first layer using a second paste containing a second positive electrode active material, a hydrophobic binder, and a second solvent, in which the first solvent and the second solvent are selected so that the affinity of the first solvent for water is greater than the affinity of the second solvent for water. This disclosure is said to enable the establishment of a technology for manufacturing highly safe batteries by sufficiently adhering a lower layer to the surface of the current collector, thereby improving durability and suppressing current flow between the lower layer and the upper layer in the event of overcharge. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-146272 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-015156 Summary of the Invention [Problem to be solved by the invention]

[0006] To solve the problem of binder migration causing the current collector and active material layer to easily peel off, a two-layer active material layer is generally known in which the amount of binder in the lower layer is increased and the amount of binder in the upper layer is reduced to suppress the increase in ionic resistance due to the increased amount of binder. However, in this case, the small amount of binder in the upper layer causes the problem of low flexibility.

[0007] Therefore, the present disclosure aims to provide a novel electrode body for a secondary battery that can suppress a decrease in the bonding strength between the active material layer and the current collector, ensure flexibility, and suppress an increase in the ionic resistance of the active material layer. [Means for solving the problem]

[0008] The present disclosure achieves the above object by the following means.

[0009] <Aspect 1> An electrode assembly having a current collector layer and an active material layer laminated on the current collector layer, the active material layer has a first layer on the current collector layer and a second layer on the first layer, The first binder contained in the first layer is composed of particles having a surface contact shape, and The second binder contained in the second layer is composed of particles having a point contact shape. Electrode body. <Aspect 2> 2. The electrode assembly of embodiment 1, wherein the peel strength between the current collector and the first layer is 0.06 N / cm or greater. <Aspect 3> 3. The electrode assembly according to aspect 1 or 2, wherein the second layer has a degree of bending of 0.083 or less. <Aspect 4> A secondary battery comprising the electrode assembly according to any one of aspects 1 to 3. <Aspect 5> A method for manufacturing an electrode assembly having a current collector and an active material layer laminated on the current collector layer, comprising: depositing a first layer on a current collector; and laminating a second layer on the first layer; Including, The first binder contained in the first layer is composed of particles having a surface contact shape, and The second binder contained in the second layer is composed of particles having a point contact shape. A method for manufacturing an electrode body. [Effects of the Invention]

[0010] According to the electrode body of the present disclosure, it is possible to provide a novel electrode body for a secondary battery that can suppress a decrease in the bonding strength between the active material layer and the current collector, ensure flexibility, and suppress an increase in the ionic resistance of the active material layer. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a side cross-sectional view of one embodiment of an electrode assembly of the present disclosure. [Figure 2] Fig. 2(a) is a schematic diagram showing the state in which an active material layer having a binder composed of particles with a plane-to-plane contact shape and a current collector layer are bonded together, and Fig. 2(b) is a schematic diagram showing the state in which an active material layer having a binder composed of particles with a point-to-point contact shape and a current collector layer are bonded together. DETAILED DESCRIPTION OF THE INVENTION

[0012] 《Electrode body》 The electrode body of the present disclosure is An electrode assembly having a current collector layer and an active material layer laminated on the current collector layer, the active material layer has a first layer on the current collector layer and a second layer on the first layer, The first binder contained in the first layer is composed of particles having a surface contact shape, and The second binder contained in the second layer is composed of particles in a point contact shape.

[0013] An active material layer containing a binder (first binder) composed of particles with a surface-to-surface contact shape has excellent binding strength to the current collector layer. Without wishing to be bound by theory, this is thought to be because the first binder is composed of particles with a surface-to-surface contact shape, which increases the contact area with the current collector layer and makes binder migration less likely to occur when the composite slurry is dried at high temperatures.

[0014] An active material layer containing a binder (second binder) composed of particles in a point-contact shape can have a relatively low ionic resistance while maintaining flexibility. Without wishing to be bound by theory, this is thought to be because, since the second binder is composed of particles in a point-contact shape, the ion conduction path is less likely to be obstructed by the binder in the active material layer containing the second binder, even when a sufficient amount of binder is contained to maintain flexibility.

[0015] 1, an electrode body 100 of the present disclosure has a current collector layer 110 and an active material layer 120. The active material layer 120 is composed of a first layer 121 and a second layer 122.

[0016] 2(a), when the first layer 121 having the first binder 132 and the active material 131 is bound to the current collector layer 110, the first binder 132 is composed of particles with a surface-to-surface contact shape, so that the contact area between the first binder 132 and the current collector layer 110 is large and binder migration is unlikely to occur when the composite slurry is dried at high temperature. Therefore, the first layer 121 can have a strong binding force to the current collector layer 110.

[0017] On the other hand, as shown in FIG. 2(b), when the second layer 122 having the second binder 141 and the active material 131 is bonded to the first layer 121, the second binder 141 is composed of particles having a point contact shape, and therefore, in the second layer 122 containing the second binder 141, even when a sufficient amount of binder is contained to maintain flexibility, the binder is unlikely to obstruct the ion conduction path.

[0018] In the present disclosure, a "composite" refers to a composition that can form an active material layer either as is or by incorporating other components, and a "composite slurry" refers to a slurry that contains a "composite" and a dispersion medium and that can be applied and dried to form an active material layer.

[0019] Each component of the present disclosure will be described below.

[0020] The electrode assembly of the present disclosure has a current collector layer and an active material layer laminated on the current collector layer.

[0021] <Active material layer> The active material layer has a first layer on the current collector layer and a second layer on the first layer.

[0022] The peel strength between the current collector layer and the first layer may be 0.06 N / cm or more, 0.07 N / cm or more, or 0.08 N / cm or more, and may be 0.5 N / cm or less, 0.4 N / cm or less, 0.3 N / cm or less, or 0.2 N / cm or less.

[0023] The peel strength between the current collector layer and the first layer was calculated in accordance with JIS-K-6854-1 by fixing a test material of the current collector layer having the first layer laminated thereon to a hard base member with double-sided tape or an adhesive, peeling off one end of the film, fixing the end to a 90° peel tester, peeling off the film while pulling it in a direction forming an angle of 90° with respect to the unpeeled portion of the test material, and measuring the tensile strength with a load cell or the like.

[0024] The degree of tortuosity of the second layer may be 0.083 or less, 0.080 or less, 0.070 or less, or 0.050 or less, and may be 0 or more, 0.010 or more, or 0.020 or less.

[0025] The degree of tortuosity is an index representing the conductivity of ions in the active material and is calculated using the following formula: The smaller the value of the degree of tortuosity, the better the ionic conductivity and the smaller the ionic resistance.

number

[0026] The effective conductivity can be calculated by the following formula.

number

[0027] The vacancy rate (ε) can be calculated by the following formula. Porosity (ε) = 1 - [apparent density of the second layer (g / cm 3 )] / [Second layer true density (g / cm 3 ) Here, the apparent density of the second layer can be calculated using the volume determined from the actually measured dimensions and the actually measured weight.

[0028] The electrode body resistance can be calculated according to the AC impedance method by preparing two electrode bodies of the same configuration, each having only the second layer as the active material layer, and arranging them opposite each other to form a symmetrical cell, and measuring the impedance of only the electrode body.

[0029] The flexibility of the second layer is preferably such that no visible cracks appear in the active material layer when the electrode assembly is wrapped around a cylinder with a diameter of 25.0 mm, which may have a diameter of 24.5 mm, 24.0 mm, 23.5 mm, or 23.0 mm or less.

[0030] The thickness of the active material layer is not particularly limited and may be, for example, 100 μm or more, 200 μm or more, 300 μm or more, 350 μm or more, 370 μm or more, 390 μm or more, or 400 μm or more, and may be 700 μm or less, 600 μm or less, 550 μm or less, 500 μm or less, 480 μm or less, 460 μm or less, or 450 μm or less.

[0031] The thickness of the first layer is preferably at least 0.4 times, at least 0.5 times, at least 0.6 times, at least 0.8 times, or at least 1.0 times the thickness of the second layer from the viewpoint of adhesion to the current collector layer, and is preferably at most 2.4 times, at most 2.3 times, at most 2.2 times, at most 2.0 times, or at most 1.8 times the thickness of the second layer from the viewpoint of conductivity.

[0032] The active material layer may contain, in addition to the active material and binder, a conductive aid, a dispersant, and various other additives. (binder) The first binder contained in the first layer is made up of particles in a plane contact shape, and the second binder contained in the second layer is made up of particles in a point contact shape.

[0033] Particles with a surface contact shape refer to particles in which the average length (contact ratio) of the particle that is in contact with other particles such as active material, current collector, and binder, relative to the particle periphery when observed from above, is 50% or more.

[0034] As the particles having a surface contact shape, for example, styrene-butadiene copolymer (SBR), polyacrylic acid (PAA), etc. can be used.

[0035] Particles with a point contact shape refer to particles in which, when observed from above, the proportion of the length of the particle that is in contact with other particles such as active material, current collector, or binder (contact ratio) is on average less than 50% of the particle's outer periphery.

[0036] As particles having a point contact shape, for example, styrene-acrylic acid ester copolymer (SAR), polyvinylidene fluoride (PVDF), etc. can be used.

[0037] The particle diameter of the point contact particles is not particularly limited and may be, for example, 0.05 μm or more, 0.1 μm or more, 0.2 μm or more, 0.5 μm or more, or 1.0 μm or more, and may be 5.0 μm or less, 4.0 μm or less, 3.0 μm or less, or 2.0 μm or less.

[0038] In the present disclosure, the term "particle size" refers to the average diameter of a circle equivalent to the projected area determined from a scanning electron microscope (SEM) image or a transmission electron microscope (TEM) image.

[0039] The mass of the binder is not particularly limited, and may be, for example, 0.1 parts by mass or more, 0.2 parts by mass or more, 0.5 parts by mass or more, 1.0 parts by mass or more, or 2.0 parts by mass or more, and may be 5.0 parts by mass or less, 4.5 parts by mass or less, 4.0 parts by mass or less, 3.5 parts by mass or less, or 3.0 parts by mass or less, per 100 parts by mass of the first layer or the second layer.

[0040] (active material) The active material may be a positive electrode active material or a negative electrode active material.

[0041] The mass of the active material is not particularly limited, and may be, for example, 60 parts by mass or more, 70 parts by mass or more, 80 parts by mass or more, 90 parts by mass or more, 91 parts by mass or more, 92 parts by mass or more, 93 parts by mass or more, or 94 parts by mass or more, relative to 100 parts by mass of the first layer or the second layer, or 100 parts by mass or less, 99 parts by mass or less, 98 parts by mass or less, 97 parts by mass or less, or 96 parts by mass or less.

[0042] The material of the positive electrode active material is not particularly limited, and examples thereof include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMn2O4), and nickel-cobalt-manganese lithium oxide (NCM:LiCO 1 / 3 Ni 1 / 3 Mn 1 / 3 O2), lithium nickel-cobalt-aluminate (LiNi 0.8 (CoAl) 0.2 O2), Li 1+x Mn 2-x-y M y It may be a different element-substituted Li-Mn spinel having a composition represented by O4 (M is one or more metal elements selected from Al, Mg, Co, Fe, Ni, and Zn), or the like.

[0043] The positive electrode active material is not particularly limited, and may have a coating layer. The coating layer is a layer containing a substance that has conductivity, low reactivity with the positive electrode active material and the solid electrolyte, and can maintain the shape of the coating layer without flowing even when in contact with the active material and the solid electrolyte. Specific examples of materials constituting the coating layer include LiNbO3 and Li4Ti5O 12 , Li3PO4, etc., but are not limited to these.

[0044] The shape of the positive electrode active material is not particularly limited as long as it is a general shape for a positive electrode active material in a battery. The positive electrode active material may be, for example, in a particulate form. The particle diameter is not particularly limited and may be 5 μm or more, 6 μm or more, 8 μm or more, 10 μm or more, or 12 μm or more, and may be 30 μm or less, 25 μm or less, 20 μm or less, or 15 μm or less.

[0045] The material of the negative electrode active material is not particularly limited, and may be metallic lithium or a material capable of absorbing and releasing metal ions such as lithium ions. Examples of materials capable of absorbing and releasing metal ions such as lithium ions include alloy-based negative electrode active materials, carbon materials, and lithium titanate (Li4Ti5O 12 ) and the like can be mentioned, but are not limited to these.

[0046] The alloy-based negative electrode active material is not particularly limited, and examples thereof include Si alloy-based negative electrode active materials and Sn alloy-based negative electrode active materials. Examples of Si alloy-based negative electrode active materials include silicon, silicon oxide, silicon carbide, silicon nitride, and solid solutions thereof. The Si alloy-based negative electrode active material may contain metal elements other than silicon, such as Fe, Co, Sb, Bi, Pb, Ni, Cu, Zn, Ge, In, Sn, and Ti. Examples of Sn alloy-based negative electrode active materials include tin, tin oxide, tin nitride, and solid solutions thereof. The Sn alloy-based negative electrode active material may contain metal elements other than tin, such as Fe, Co, Sb, Bi, Pb, Ni, Cu, Zn, Ge, In, Ti, and Si.

[0047] The carbon material is not particularly limited, and examples thereof include hard carbon, soft carbon, graphite, and the like.

[0048] The shape of the negative electrode active material is not particularly limited, and may be any shape commonly used for negative electrode active materials in batteries. The negative electrode active material may be, for example, particulate. The particle size is not particularly limited, and may be 5 μm or more, 6 μm or more, 8 μm or more, 10 μm or more, or 12 μm or more, and may be 30 μm or less, 25 μm or less, 20 μm or less, or 15 μm or less.

[0049] (dispersant) The dispersant is not particularly limited, and may be, for example, carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyvinylpyrrolidone (PVP), polyacrylate, polymethacrylate, polyoxyethylene alkyl ether, polyalkylene polyamine, benzimidazole, or the like.

[0050] The mass of the dispersant is not particularly limited, and may be, for example, 0.1 parts by mass or more, 0.3 parts by mass or more, 0.5 parts by mass or more, 1.0 parts by mass or more, or 2.0 parts by mass or more, and may be 5.0 parts by mass or less, 4.5 parts by mass or less, 4.0 parts by mass or less, 3.5 parts by mass or less, or 3.0 parts by mass or less, relative to 100 parts by mass of the first layer or the second layer.

[0051] (Conductive additive) The conductive additive is not particularly limited. The conductive additive may be, for example, vapor grown carbon fiber (VGCF), acetylene black (AB), ketjen black (KB), carbon nanotube (CNT), carbon nanofiber (CNF), etc., but is not limited thereto. The conductive additive may be, for example, particulate or fibrous, and its size is not particularly limited. The conductive additive is not particularly limited, and one type may be used alone, or two or more types may be used in combination.

[0052] The mass of the conductive additive is not particularly limited, and may be, for example, 0.005 parts by mass or more, 0.01 parts by mass or more, 0.02 parts by mass or more, 0.03 parts by mass or more, or 0.05 parts by mass or more, and may be 0.10 parts by mass or less, 0.09 parts by mass or less, 0.08 parts by mass or less, 0.07 parts by mass or less, or 0.06 parts by mass or less, per 100 parts by mass of the first layer or the second layer.

[0053] <Current collector layer> The material of the current collector layer that can be used for the positive electrode is not particularly limited, and any material commonly used for a battery positive electrode current collector can be appropriately used. Examples of materials that can be used for the positive electrode current collector layer include, but are not limited to, Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, and stainless steel. The positive electrode current collector layer may also have a coating layer on its surface for purposes such as adjusting resistance. The positive electrode current collector layer may also be a metal foil or a substrate on which the above metals are plated or vapor-deposited.

[0054] The shape of the positive electrode current collector layer is not particularly limited, and may be, for example, a foil, a plate, a mesh, or the like.

[0055] The thickness of the positive electrode current collector layer is not particularly limited, and may be 0.1 μm or more, or 1 μm or more, and may be 1 mm or less, or 100 μm or less.

[0056] The material of the current collector layer that can be used for the negative electrode is not particularly limited, and any material commonly used for negative electrode current collectors in batteries can be appropriately used. Materials that can be used for the negative electrode current collector layer include, but are not limited to, Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, stainless steel, and carbon sheet. The negative electrode current collector layer may have a coating layer on its surface for purposes such as adjusting resistance.

[0057] The shape of the negative electrode current collector layer is not particularly limited, and examples thereof include a foil shape, a plate shape, and a mesh shape.

[0058] The thickness of the negative electrode current collector layer is not particularly limited, and may be 0.1 μm or more, or 1 μm or more, and may be 1 mm or less, or 100 μm or less.

[0059] 《Secondary battery》 The secondary battery of the present disclosure includes the electrode assembly described above. The electrode assembly may be a positive electrode or a negative electrode.

[0060] <Electrolyte> The electrolyte contained in the secondary battery of the present disclosure may be a solid electrolyte or a liquid electrolyte held in a separator.

[0061] The material of the solid electrolyte is not particularly limited, and may be, for example, a sulfide solid electrolyte, an oxide solid electrolyte, or a polymer electrolyte.

[0062] Examples of sulfide solid electrolytes include, but are not limited to, sulfide-based amorphous solid electrolytes, sulfide-based crystalline solid electrolytes, and argyrodite-type solid electrolytes. Specific examples of sulfide solid electrolytes include Li2S-P2S5-based (Li7P3S 11 , Li3PS4, Li8P2S9, etc.), Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-LiBr-Li2S-P2S5, Li2S-P2S5-GeS2(Li 13 GeP3S 16 , Li 10 GeP2S 12 ), LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, Li 7-x PS 6-x Cl x etc.; or combinations thereof, but are not limited to these.

[0063] An example of an oxide solid electrolyte is Li7La3Zr2O 12 , Li 7-x La3Zr 1-x Nb x O 12 , Li 7-3x La3Zr2Al x O 12 , Li 3x La 2 / 3-x TiO3, Li 1+x Al x Ti 2-x (PO4)3, Li 1+x Al x Ge 2-x (PO4)3, Li3PO4, or Li 3+x PO 4-x N x (LiPON), etc.; or combinations thereof.

[0064] The sulfide solid electrolyte and the oxide solid electrolyte may be glass or crystallized glass (glass ceramics).

[0065] Examples of polymer electrolytes include, but are not limited to, polyethylene oxide (PEO), polypropylene oxide (PPO), and copolymers thereof.

[0066] The liquid electrolyte is not particularly limited, but preferably contains a supporting salt and a solvent.

[0067] The supporting salt (lithium salt) of the liquid electrolyte having lithium ion conductivity is not particularly limited, and examples thereof include inorganic lithium salts and organic lithium salts. Examples of inorganic lithium salts include, but are not limited to, LiPF, LiBF, LiClO, and LiAsF. Examples of organic lithium salts include, but are not limited to, LiCF, SO, LiN(CF, SO), LiN(CF, SO), LiN(FSO), LiC(CF, SO), and LiC.

[0068] The solvent used in the liquid electrolyte is not particularly limited, and examples thereof include cyclic carbonates, chain carbonates, etc. Examples of cyclic carbonates include, but are not limited to, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. Examples of chain carbonates include, but are not limited to, dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). The liquid electrolyte is not particularly limited, and one type may be used alone, or two or more types may be used in combination.

[0069] The separator is not particularly limited, and any separator commonly used for batteries can be appropriately used, such as a polyolefin-based, polyamide-based, or polyimide-based nonwoven fabric. <<Method for manufacturing electrode body>> The method for manufacturing an electrode assembly according to the present disclosure includes: A method for manufacturing an electrode assembly having a current collector and an active material layer laminated on the current collector layer, comprising: depositing a first layer on a current collector; and laminating a second layer on the first layer; Including, The first binder contained in the first layer is composed of particles having a surface contact shape, and The second binder contained in the second layer is composed of particles having a point contact shape. This includes:

[0070] According to the manufacturing method of the electrode body of the present disclosure, it is possible to provide a novel electrode body for a secondary battery that can suppress a decrease in the bonding strength between the active material layer and the current collector, ensure flexibility, and suppress an increase in the ionic resistance of the active material layer, even when the composite slurry is dried at high temperatures.

[0071] Each component of the present disclosure will be described below.

[0072] <First layer stacking> The manufacturing method of the electrode assembly of the present disclosure includes laminating a first layer on a current collector. The first layer contains a first binder composed of particles having a surface-to-surface contact shape. For the current collector, the first layer, and the first binder, please refer to the description of the electrode assembly above.

[0073] The lamination of the first layer may include coating and drying a first composite slurry. The first composite slurry refers to a slurry containing an active material and a first binder. For the active material, see the description of the electrode assembly above.

[0074] The viscosity of the first composite slurry is not particularly limited, and may be, for example, 0.1 s -1 The pressure may be 90 Pa·s or more, 100 Pa·s or more, 150 Pa·s or more, or 200 Pa or more, and may be 500 Pa·s or less, 400 Pa·s or less, 300 Pa·s or less, or 250 Pa·s or less.

[0075] The coating step is a step of coating the first composite slurry onto the current collector layer.

[0076] The coating method is not particularly limited, and may be, for example, a doctor blade method, a die coating method, a gravure coating method, a spray coating method, an electrostatic coating method, a bar coating method, or the like.

[0077] The drying step is a step of drying the applied first composite slurry.

[0078] The drying method is not particularly limited, and may be, for example, warm air drying, hot air drying, infrared drying, reduced pressure drying, dielectric heating drying, or the like.

[0079] The drying temperature is not particularly limited and may be 50°C or higher, 70°C or higher, 90°C or higher, 100°C or higher, 110°C or higher, or 120°C or higher, and may be 200°C or lower, 180°C or lower, 160°C or lower, 150°C or lower, or 140°C or lower.

[0080] <Second layer stacking> The manufacturing method of the electrode assembly of the present disclosure includes laminating a second layer on the first layer. The second layer contains a second binder composed of particles in a point-contact shape. For the second layer and the second binder, please refer to the description of the electrode assembly above.

[0081] The lamination of the second layer may include coating and drying a second composite slurry. The second composite slurry refers to a slurry containing an active material and a second binder. For the active material, see the description of the electrode assembly above.

[0082] The viscosity of the second composite slurry is not particularly limited, and may be, for example, 0.1 s -1 The pressure may be 90 Pa·s or more, 100 Pa·s or more, 150 Pa·s or more, or 200 Pa or more, and may be 500 Pa·s or less, 400 Pa·s or less, 300 Pa·s or less, or 250 Pa·s or less.

[0083] The coating step is a step of coating the second composite slurry onto the first layer. For the coating method, the above description regarding the lamination of the first layer can be referred to.

[0084] The drying step is a step of drying the second composite slurry to form a second layer. The drying step may be performed on each layer after coating the first composite slurry and the second composite slurry, or may be performed on both layers together. For the coating method, please refer to the description of the lamination of the first layer above. [Example]

[0085] The present disclosure will be specifically explained with reference to examples and comparative examples, but the present disclosure is not limited to these.

[0086] <<Preparation of electrode body>> Example 1 Lithium cobalt oxide (LiCoO2) as the active material, styrene-butadiene copolymer (SBR) as a binder to form surface-contact particles, carbon nanotubes (CNT) as a conductive additive, and carboxymethyl cellulose (CMC) as a dispersant were mixed in a mass ratio of 95:3.9:0.1:1 and mixed with ion-exchanged water to form a slurry with a viscosity of 120 Pa·s (shear rate 0.1 s). -1 ) was prepared as a first composite slurry.

[0087] Lithium cobalt oxide (LiCoO2) as the active material, styrene-acrylic acid ester copolymer (SAR) as a binder that forms point-contact particles, carbon nanotubes (CNT) as a conductive additive, and carboxymethyl cellulose (CMC) as a dispersant were mixed in a mass ratio of 95:3.9:0.1:1 and mixed with ion-exchanged water to form a solution with a viscosity of 120 Pa·s (shear rate 0.1 s). -1 ) was prepared as a second composite slurry.

[0088] The first composite slurry was applied to a copper foil surface as a current collector layer to a thickness of 210 μm and dried at 100° C. for 3 minutes. The second composite slurry was applied to a copper foil surface as a current collector layer to a thickness of 210 μm and dried at 100° C. for 3 minutes to prepare an electrode body of Example 1.

[0089] Comparative Example 1 An electrode body as Comparative Example 1 was produced in the same manner as in Example 1, except that the second layer in Example 1 was not applied and the first layer was applied to a thickness of 420 μm. Comparative Example 2 An electrode body as Comparative Example 2 was produced in the same manner as in Example 1, except that the first layer in Example 1 was not coated and the second layer was coated to a thickness of 420 μm.

[0090] "evaluation" <Evaluation of the adhesive strength between the active material layer and the current collector layer> In Examples and Comparative Examples 1 and 2, the peel strength between the active material layer and the current collector layer was measured using a 90° peel tester to evaluate the bonding strength. The evaluation criteria were as follows. A: Peel strength is 0.06 N / cm or more. B: Peel strength is less than 0.06 N / cm.

[0091] <Evaluation of Electrode Flexibility> In Examples and Comparative Examples 1 and 2, the electrode assembly was wound around a cylinder with a diameter of 25 mm. Flexibility was evaluated based on whether or not cracks were visually confirmed in the active material layer. The evaluation criteria were as follows: A: Cracks were observed in the active material layer. B: No cracks were found in the active material layer.

[0092] <Evaluation of bending degree of active material layer> In Examples and Comparative Examples 1 and 2, the ionic resistance of the active material layer was evaluated by measuring the degree of bending of the active material layer. The evaluation criteria were as follows. A: The degree of bending is 0.083 or less. B: The bending degree exceeds 0.083.

[0093] The evaluation results are shown in Table 1.

[0094] [Table 1]

[0095] From Example 1 and Comparative Example 2 in Table 1, it can be seen that the first layer having a binder made up of particles in a plane-to-plane contact shape faces the current collector layer, thereby providing a high binding force.

[0096] From Example 1 and Comparative Example 1 in Table 1, it can be seen that by including a second layer having a binder composed of particles in a point contact shape, an increase in the degree of bending is suppressed while maintaining flexibility. [Explanation of symbols]

[0097] 100 electrode body 110 Current collector layer 120 Active material layer 121 1st layer 122 2nd layer 131 Active material 132 First binder 141 Secondary binder

Claims

1. An electrode assembly having a current collector layer and an active material layer laminated on the current collector layer, the active material layer has a first layer on the current collector layer and a second layer on the first layer, The first binder contained in the first layer is composed of particles having a surface contact shape, and The second binder contained in the second layer is composed of particles having a point contact shape. Electrode body.

2. The electrode body according to claim 1 , wherein the peel strength between the current collector layer and the first layer is 0.06 N / cm or more.

3. The electrode assembly according to claim 1 or 2, wherein the second layer has a degree of bending of 0.083 or less.

4. A secondary battery comprising the electrode assembly according to claim 1 or 2.

5. A method for manufacturing an electrode assembly having a current collector and an active material layer laminated on the current collector layer, comprising: depositing a first layer on a current collector; and laminating a second layer on the first layer; Including, The first binder contained in the first layer is composed of particles having a surface contact shape, and The second binder contained in the second layer is composed of particles having a point contact shape. A method for manufacturing an electrode body.

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