Lithium-ion secondary battery and method for manufacturing a lithium-ion secondary battery

Abstract

The present disclosure aims to provide a lithium-ion secondary battery having an electrode active material layer with high binding force to the current collector layer, particularly an electrode active material layer with high binding force to the current collector layer even when the electrode active material layer is manufactured by rapidly drying the electrode composite slurry at high temperature. [Solution] A lithium-ion secondary battery having an electrode active material layer 110, wherein the electrode active material layer 110 comprises an electrode active material 130 and a binder, the average pore diameter of the electrode active material layer 110 is 1.00 μm or less, and the porosity of the electrode active material layer 110 is 8.8% or less.

Description

[Technical Field]

[0001] This disclosure relates to lithium-ion secondary batteries and methods for manufacturing lithium-ion secondary batteries. [Background technology]

[0002] A generally known method for laminating electrode active material layers in lithium-ion secondary batteries involves generating an electrode mixture slurry by incorporating a solvent into the components of the electrode active material layer, and then laminating the electrode mixture slurry by coating and drying it.

[0003] However, when the binder contained in the electrode composite slurry is heated and dried, so-called binder migration occurs, where the binder moves from the adhesive surface to the surface. When binder migration occurs, the electrode active material layer becomes more prone to peeling, which is a factor in the deterioration of battery performance. In response to this, various disclosures have been made to suppress the decrease in peel strength.

[0004] For example, Patent Document 1 discloses a lithium-ion secondary battery comprising a wound electrode group formed by winding a positive electrode, a negative electrode, and a separator sandwiched between them, wherein the positive electrode and the negative electrode each include a current collector and an electrode mixture layer provided on the surface of the current collector, and the electrode mixture layer included in at least one of the positive electrode and the negative electrode includes a binder resin and an active material, and this active material is composed of a group of active material particles having multiple peaks in the particle size distribution, and the group of active material particles is composed of a single compound. The lithium-ion secondary battery disclosed is said to be highly reliable and have high output. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2012-134023 [Overview of the project]

Problems to be Solved by the Invention

[0006] In the process of forming an electrode active material layer, it is required to shorten the drying time of an electrode mixture slurry coated on a current collector layer. However, when the electrode mixture slurry is dried at a high temperature at high speed, the amount of binder migration increases, and the adhesion between the electrode active material layer and the current collector layer decreases.

[0007] Therefore, an object of the present disclosure is to provide a lithium ion secondary battery having an electrode active material layer with high adhesion to a current collector layer, particularly an electrode active material layer with high adhesion to a current collector layer even when the electrode active material layer is manufactured by drying an electrode mixture slurry at a high temperature at high speed.

Means for Solving the Problems

[0008] The present disclosure achieves the above object by the following means. <Aspect 1> A lithium ion secondary battery having an electrode active material layer, where the electrode active material layer has an electrode active material and a binder, the average pore diameter of the electrode active material layer is 1.00 μm or less, and the porosity of the electrode active material layer is 8.8% or less, lithium ion secondary battery. <Aspect 2> the electrode active material layer contains two or more kinds of the electrode active materials having different average particle diameters, and the average particle diameter of the electrode active material having the largest average particle diameter is 5 times or more the average particle diameter of the electrode active material having the smallest average particle diameter, the lithium ion secondary battery according to Aspect 1. <Aspect 3> the average pore diameter of the electrode active material layer is 0.30 μm or more, and / or the porosity of the electrode active material layer is 0.5% or more, the lithium ion secondary battery according to Aspect 1 or 2. <Aspect 4> A method for manufacturing a lithium-ion secondary battery having an electrode active material layer, comprising: mixing two or more electrode active materials having different average particle diameters and a binder having an average particle diameter of 0.30 μm or more to produce an electrode composite material; and forming the electrode composite material to manufacture the electrode active material layer, and the average particle diameter of the electrode active material having the largest average particle diameter is 5 times or more the average particle diameter of the electrode active material having the smallest average particle diameter, A method for manufacturing a lithium-ion secondary battery. <Aspect 5> The method according to aspect 4, further comprising drying the electrode composite material at a temperature of 100 °C or higher.

Advantages of the Invention

[0009] According to the present disclosure, it is possible to provide a lithium-ion secondary battery having an electrode active material layer with a high adhesion force to a current collector layer, particularly an electrode active material layer with a high adhesion force to a current collector layer even when the electrode composite material slurry is dried at a high temperature at high speed to manufacture the electrode active material layer.

Brief Description of the Drawings

[0010] [Figure 1] FIG. 1 is a schematic diagram for explaining binder migration in an electrode active material layer.

Modes for Carrying Out the Invention

[0011] 《Lithium-Ion Secondary Battery》 \The lithium-ion secondary battery of the present disclosure is a lithium-ion secondary battery having an electrode active material layer, wherein the electrode active material layer has an electrode active material and a binder, the average pore diameter of the electrode active material layer is 1.00 μm or less, and the porosity of the electrode active material layer is 8.8% or less.

[0012] According to this disclosure, it is possible to provide a lithium-ion secondary battery having an electrode active material layer with high binding force to the current collector layer, particularly an electrode active material layer with high binding force to the current collector layer even when the electrode mixture slurry is manufactured by high-speed drying at high temperature.

[0013] The Disclosers have found that when the pore size of the electrode active material layer is 1.00 μm or less and the porosity is 8.8% or less, the electrode active material layer and the current collector layer have a high bonding strength. Although not limited to theory, when the pore size and porosity are sufficiently small, the binder does not easily move from the bonding surface between the electrode active material layer and the current collector layer to the opposite side during high-temperature drying, and a large amount of binder remains on the bonding surface side, so it is thought that the electrode active material layer and the current collector layer have a high bonding strength.

[0014] Furthermore, the Disclosers have found that the above-mentioned pore size and porosity can be satisfied by using an electrode active material in the electrode active material layer that is a mixture of electrode active materials in which the particle size of the electrode active material with the largest average particle size is five times or more the particle size of the electrode active material with the smallest average particle size.

[0015] Specifically, as shown in Figure 1(a), the electrode body 100 has an electrode active material layer 110 and a current collector layer 140. The electrode active material layer 110 is formed by adding a solvent to an electrode mixture having an electrode active material 130 and a binder (not shown), forming an electrode mixture slurry, coating it onto the current collector layer 140, and then drying it. In particular, when drying at high temperatures, binder migration is likely to occur, and for example, the binder moves from the current collector layer 140 side to the surface side through the binder migration path 120. Therefore, as shown in Figure 1(b), the electrode active material 130 contains two or more types of electrode active materials with different average particle sizes, thereby reducing the pore size and porosity of the electrode active material layer 110. Here, among the two or more types of electrode active materials with different average particle sizes, the average particle size of the electrode active material 131 with the largest average particle size is five times or more the average particle size of the electrode active material 132 with the smallest average particle size. As the pore size and porosity of the electrode active material layer 110 decrease, the binder migration path 120 narrows, making binder migration less likely to occur, and increasing the bonding force between the electrode active material layer 110 and the current collector layer 140.

[0016] In relation to this disclosure, “electrode mixture” means a composition that can constitute an electrode active material layer, either as is or by further containing other components. In relation to the first disclosure, “electrode mixture slurry” means a slurry that, in addition to the “electrode mixture,” contains a dispersion medium and can be applied and dried to form an electrode active material layer.

[0017] The following describes each component of the present invention.

[0018] The lithium-ion secondary battery of this disclosure has an electrode active material layer. The lithium-ion secondary battery may also have a positive electrode current collector layer, a negative electrode current collector layer, an electrolyte layer, etc.

[0019] In this disclosure, a lithium-ion secondary battery may be a liquid-type battery containing an electrolyte as an electrolyte layer, or a solid-state battery having a solid electrolyte layer as an electrolyte layer. In this disclosure, "solid-state battery" means a battery that uses at least a solid electrolyte as an electrolyte, and therefore a solid-state battery may use a combination of a solid electrolyte and a liquid electrolyte as an electrolyte. Furthermore, in this disclosure, a solid-state battery may be an all-solid-state battery, that is, a battery that uses only a solid electrolyte as an electrolyte.

[0020] <Electrode active material layer> The electrode active material layer of this disclosure comprises an electrode active material and a binder. The electrode active material layer may further optionally contain a conductive additive, a solid electrolyte, etc. The electrode active material layer may also contain various other additives. The electrode active material layer may be a positive electrode active material layer or a negative electrode active material layer.

[0021] The average pore size of the electrode active material layer is 1.00 μm or less. A small average pore size reduces the likelihood of binder migration. The average pore size may also be 0.95 μm or less, 0.90 μm or less, or 0.85 μm or less. Furthermore, an average pore size of 0.30 μm or more, 0.35 μm or more, 0.40 μm or more, 0.45 μm or more, or 0.50 μm or more is preferable from the viewpoint of ensuring rapid charging performance.

[0022] The porosity of the electrode active material layer is 8.8% or less. A low porosity reduces the likelihood of binder migration. The porosity may also be 8.6% or less, 8.4% or less, 8.0% or less, or 7.5% or less. Furthermore, a porosity of 0.5% or more, 0.6% or more, 0.7% or more, 0.8% or more, or 0.9% or more is preferable from the viewpoint of ensuring rapid charging performance.

[0023] The average pore diameter was measured using the mercury intrusion method with a mercury porosimeter, in accordance with JIS-R-1655. The sample was immersed in mercury under vacuum, and uniform pressure was applied. The pressure was gradually increased, causing mercury to be injected into the pores starting with the largest diameters, increasing the cumulative volume of mercury. Finally, when all pores were filled with mercury, the cumulative volume reached the measured value. This cumulative volume was defined as the pore volume, and the median diameter (D50) at which 50% of the pore volume of mercury had been injected was defined as the average pore diameter. Porosity was calculated from the above pore volume.

[0024] Preferably, the peel strength characteristics between the electrode active material layer and the current collector layer are such that the peel strength after drying at 150°C for 2 minutes is the same as the peel strength after drying at 50°C for 20 minutes. This suppresses migration, enabling high-speed drying.

[0025] The peel strength between the electrode active material layer and the current collector layer can be measured in accordance with JIS-K-6854-1 by fixing the test material, which has a current collector layer with an electrode active material layer laminated on it, to a base member in a 90° peel tester and peeling the electrode active material layer from one end.

[0026] The respective content amounts of electrode active material, conductive additive, solid electrolyte, etc., in the electrode active material layer can be appropriately determined according to the desired battery performance. For example, with the total solid content of the electrode active material layer being 100% by mass, the content of electrode active material may be 40% by mass or more, 50% by mass or more, 60% by mass or more, 100% by mass or less, or 90% by mass or less.

[0027] The binder content is not particularly limited and may be 0.1 parts by mass or more, 0.2 parts by mass or more, 0.5 parts by mass or more, 1.0 part by mass or more, or 2.0 parts by mass or more per 100 parts by mass of electrode active material, 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.

[0028] (electrode active material) The electrode active material layer may contain two or more electrode active materials with different average particle diameters, and the average particle diameter of the electrode active material with the largest average particle diameter may be five times or more the average particle diameter of the electrode active material with the smallest average particle diameter.

[0029] The average particle diameter of the electrode active material with the largest average particle diameter is not particularly limited and may be, for example, 5 nm or more, or 10 nm or more, or it may be 500 μm or less, 100 μm or less, 50 μm or less, or 30 μm or less.

[0030] The average particle diameter of the electrode active material with the smallest average particle diameter is not particularly limited and may be, for example, 1 nm or more, 5 nm or more, or 10 nm or more, or it may be 100 μm or less, 50 μm or less, or 30 μm or less.

[0031] Here, the average particle diameter is the particle diameter (median diameter) at 50% of the cumulative value in the volume-based particle size distribution obtained by laser diffraction and scattering.

[0032] The content of the electrode active material with the smallest average particle diameter may be adjusted considering the average pore diameter and porosity of the electrode active material layer. For example, the content of the electrode active material with the smallest average particle diameter may be 20 parts by mass or more, 25 parts by mass or more, 30 parts by mass or more, 35 parts by mass or more, 40 parts by mass or more, 45 parts by mass or more, or 50 parts by mass or more, and may be 100 parts by mass or less, 90 parts by mass or less, 80 parts by mass or less, 70 parts by mass or less, or 60 parts by mass or less, per 100 parts by mass of the electrode active material with the largest average particle diameter.

[0033] The material of the positive electrode active material is not particularly limited as long as it is capable of intercalating and releasing lithium ions. Examples of positive electrode active materials include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMn2O4), and nickel-cobalt-manganese oxide (NCM:LiCO2). 1 / 3 Ni 1 / 3 Mn 1 / 3 O2), lithium nickel-cobalt aluminum oxide (LiNi 0.8 (CoAl)0.2 O2), Li 1+x Mn 2-x-y M y It may be, but is not limited to, a heteroatom-substituted Li-Mn spinel or the like having a composition represented by O4 (M is one or more metal elements selected from Al, Mg, Co, Fe, Ni, and Zn).

[0034] The positive electrode active material is not particularly limited, but may have a coating layer. The coating layer is a layer containing a substance that has lithium ion conduction performance, low reactivity with the positive electrode active material and the solid electrolyte, and can maintain the form of the coating layer that does not flow even when in contact with the active material and the solid electrolyte. Specific examples of the material constituting the coating layer include, in addition to LiNbO3, Li4Ti5O 12 , Li3PO4, etc., but are not limited thereto.

[0035] As the negative electrode active material, various substances having a potential (charge-discharge potential) for occluding and releasing lithium ions that is lower than that of the positive electrode active material can be employed. The material of the negative electrode active material is not particularly limited and may be metallic lithium or a material capable of occluding and releasing metal ions such as lithium ions. Examples of the material capable of occluding and releasing metal ions such as lithium ions include, for example, alloy-based negative electrode active materials, carbon materials, or lithium titanate (Li4Ti5O 12 ), etc., but are not limited thereto.

[0036] The alloy-based negative electrode active material is not particularly limited and examples thereof include, for example, Si alloy-based negative electrode active materials or Sn alloy-based negative electrode active materials. The Si alloy-based negative electrode active materials include silicon, silicon oxides, silicon carbides, silicon nitrides, or solid solutions thereof. Further, the Si alloy-based negative electrode active materials can contain metal elements other than silicon, for example, Fe, Co, Sb, Bi, Pb, Ni, Cu, Zn, Ge, In, Sn, Ti, etc. The Sn alloy-based negative electrode active materials include tin, tin oxides, tin nitrides, or solid solutions thereof. Further, the Sn alloy-based negative electrode active materials can contain metal elements other than tin, for example, Fe, Co, Sb, Bi, Pb, Ni, Cu, Zn, Ge, In, Ti, Si, etc.

[0037] The carbon material is not particularly limited and examples include hard carbon, soft carbon, and graphite.

[0038] (Binder) The binder is not particularly limited, but may be made of materials such as polyvinylidene fluoride (PVdF), butadiene rubber (BR), polytetrafluoroethylene (PTFE), or styrene-butadiene rubber (SBR). The binder may be used alone or in combination of two or more types.

[0039] The average particle size of the binder may be 0.30 μm or larger, 0.35 μm or larger, 0.40 μm or larger, 0.45 μm or larger, or 0.50 μm or larger. A larger average particle size of the binder makes binder migration less likely to occur. Alternatively, the average particle size of the binder may be 3.00 μm or smaller, 2.00 μm or smaller, 1.50 μm or smaller, or 1.00 μm or smaller.

[0040] Here, the average particle size refers to the average value of the projected area equivalent diameter obtained from scanning electron microscope (SEM) images of test pieces obtained by drying the binder alone.

[0041] (Conductive additive) The conductive additive is not particularly limited, but may include, for example, vapor-grown carbon fiber (VGCF), acetylene black (AB), Ketjenblack (KB), carbon nanotubes (CNT), carbon nanofibers (CNF), conductive carbon, etc. The conductive additive may be in particulate or fibrous form, for example, and its size is not particularly limited. The conductive additive may be used alone or in combination of two or more types.

[0042] (solid electrolyte) 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.

[0043] Examples of sulfide solid electrolytes include, but are not limited to, sulfide-based amorphous solid electrolytes, sulfide-based crystalline solid electrolytes, or argyrodite-type solid electrolytes. Specific examples of sulfide solid electrolytes include the Li2S-P2S5 system (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 not limited to these.

[0044] 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 Examples include (LiPON), etc.; or combinations thereof, but are not limited to these.

[0045] The sulfide solid electrolyte and oxide solid electrolyte may be glass or crystallized glass (glass ceramics).

[0046] Examples of polymer electrolytes include, but are not limited to, polyethylene oxide (PEO), polypropylene oxide (PPO), and copolymers thereof.

[0047] <Positive electrode current collector layer> The material used for the positive electrode current collector layer is not particularly limited, but a material commonly used for the positive electrode current collector of a battery can be appropriately adopted. 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, stainless steel, etc. The positive electrode current collector layer may also have some kind of coating layer on its surface for purposes such as adjusting resistance. Furthermore, the positive electrode current collector layer may be a metal foil or a substrate on which the above metals are plated or vapor-deposited.

[0048] The shape of the positive electrode current collector layer is not particularly limited, but examples include foil-like, plate-like, or mesh-like shapes. Among these, a foil-like shape is preferred.

[0049] The thickness of the positive electrode current collector layer is not particularly limited, but may be 0.1 μm or more, or 1 μm or more, or 1 mm or less, or 100 μm or less.

[0050] <Negative electrode current collector layer> The material used for the negative electrode current collector layer is not particularly limited, but a material commonly used for the negative electrode current collector of a battery can be appropriately adopted. Examples of materials 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, or carbon sheets. The negative electrode current collector layer may have some kind of coating layer on its surface for purposes such as adjusting resistance.

[0051] The shape of the negative electrode current collector layer is not particularly limited, but examples include foil-like, plate-like, or mesh-like shapes. Among these, a foil-like shape is preferred.

[0052] The thickness of the negative electrode current collector layer is not particularly limited, but may be 0.1 μm or more, or 1 μm or more, or 1 mm or less, or 100 μm or less.

[0053] <Electrolyte layer - solid electrolyte layer> The battery of this disclosure may be a solid-state battery, i.e., it may have a solid electrolyte layer as the electrolyte layer. The solid electrolyte layer may contain at least a solid electrolyte and may optionally contain a conductive additive, a binder, etc.

[0054] For solid electrolytes, conductive additives, and binders, refer to the above description regarding the electrode active material layer.

[0055] The thickness of the solid electrolyte layer is not particularly limited, but may be, for example, 0.1 μm or more, 1 μm or more, or 10 μm or more, or it may be 2 mm or less, 1 mm or less, or 500 μm or less.

[0056] The solid electrolyte layer can be easily formed, for example, by molding a solid electrolyte mixture containing the aforementioned solid electrolyte and binder in a dry or wet manner.

[0057] <Electrolyte layer-electrolyte> The lithium-ion secondary battery of this disclosure may be a liquid-type battery, that is, it may have an electrolyte as an electrolyte layer, particularly an electrolyte held in a separator layer.

[0058] (electrolyte) The electrolyte is not particularly limited, but it preferably contains a supporting salt and a solvent.

[0059] The supporting salt (lithium salt) for the lithium-ion conductive electrolyte is not particularly limited, but examples include inorganic lithium salts and organic lithium salts. Examples of inorganic lithium salts include, but are not limited to, LiPF6, LiBF4, LiClO4, and LiAsF6. Examples of organic lithium salts include, but are not limited to, LiCF3SO3, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiN(FSO2)2, and LiC(CF3SO2)3.

[0060] The solvent used in the electrolyte is not particularly limited, but examples include cyclic carbonates and linear carbonates. Examples of cyclic carbonates include, but are not limited to, ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). Examples of linear carbonates include, but are not limited to, dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). The electrolyte is not particularly limited, but may be used alone or in combination of two or more types.

[0061] (Separator) The separator is not particularly limited, but any separator commonly used in batteries can be used as appropriate. For example, nonwoven fabrics such as polyolefin, polyamide, or polyimide can be used as the separator.

[0062] Manufacturing method for lithium-ion rechargeable batteries The method for manufacturing a lithium-ion secondary battery described herein is: A method for manufacturing a lithium-ion secondary battery having an electrode active material layer, Mixing two or more electrode active materials with different average particle sizes and a binder with an average particle size of 0.30 μm or more to produce an electrode composite material, and The above electrode composite material is molded to produce the above electrode active material layer. including and The average particle diameter of the electrode active material with the largest average particle diameter is more than five times the average particle diameter of the electrode active material with the smallest average particle diameter. A method for manufacturing lithium-ion rechargeable batteries.

[0063] According to the method disclosed herein, it is possible to provide a lithium-ion secondary battery having an electrode active material layer with high binding force to the current collector layer, particularly an electrode active material layer with high binding force to the current collector layer even when the electrode mixture slurry is manufactured by high-speed drying at high temperature.

[0064] The method of this disclosure includes producing an electrode composite by mixing two or more electrode active materials with different average particle sizes and a binder with a particle size of 0.30 μm or larger. The composition of the two or more electrode active materials with different average particle sizes and the binder can be referenced from the above description relating to lithium-ion secondary batteries.

[0065] The amount of electrode active material mixed is not particularly limited. For example, with the entire electrode active material layer (total solid content) being 100% by mass, it may be 40% or more by mass, 50% or more by mass, 60% or more by mass, 100% or less by mass, or 90% or less by mass.

[0066] The amount of binder mixed is not particularly limited, and may be 0.1 parts by mass or more, 0.2 parts by mass or more, 0.5 parts by mass or more, 1.0 part by mass or more, or 2.0 parts by mass or more per 100 parts by mass of electrode active material, 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.

[0067] The mixing method is not particularly limited, and may be mixed by known methods, such as using a V-type mixer. It is preferable that two or more electrode active materials with different average particle sizes are uniformly mixed.

[0068] The electrode mixture may optionally contain conductive additives, solid electrolytes, various additives, etc., in addition to the electrode active material and binder. The composition of the conductive additives and solid electrolytes can be referenced from the above description concerning lithium-ion secondary batteries.

[0069] The manufacturing method of this disclosure includes molding an electrode composite material to produce the electrode active material layer. The composition of the electrode active material layer can be referenced from the above description relating to lithium-ion secondary batteries.

[0070] The method for forming the electrode mixture is not particularly limited. For example, the electrode mixture with a solvent added may be coated onto the current collector layer, and the electrode mixture may be dried at a temperature of 100°C or higher.

[0071] The drying temperature may be 100°C or higher, 110°C or higher, 120°C or higher, 130°C or higher, 140°C or higher, or 150°C or higher, and may be 200°C or lower, 190°C or lower, 180°C or lower, 170°C or lower, or 160°C or lower. The drying method is not particularly limited and may be, for example, hot air drying, infrared drying, reduced pressure drying, dielectric heating drying, etc.

[0072] The above coating method is not particularly limited and may include, for example, the doctor blade method, die coating method, gravure coating method, spray coating method, electrostatic coating method, bar coating method, etc.

[0073] The lithium-ion secondary battery of this disclosure may have, in addition to the electrode active material layer, a positive electrode current collector layer, a negative electrode current collector layer, an electrolyte layer, etc., each of which can be manufactured by known methods. The configuration of the positive electrode current collector layer, the negative electrode current collector layer, and the electrolyte, etc., can be referenced from the above description relating to lithium-ion secondary batteries. [Examples]

[0074] The present disclosure will be specifically illustrated by examples and comparative examples, but will not be limited thereto.

[0075] Preparation of electrode mixture slurry Lithium cobalt oxide (LiCoO2) was used as the electrode active material, and the electrode active material with the largest average particle size and the electrode active material with the smallest average particle size were mixed in the mass ratio shown in Table 1. The electrode active material, styrene-butadiene copolymer (SBR) as a binder, and carboxymethylcellulose (CMC) as a dispersant were measured in a mass ratio of 95:4:1 and mixed with ion-exchanged water to obtain a viscosity of 120 Pa·s (shear rate 0.1 s). -1 The electrodes were prepared by adjusting the mixture to the specified values ​​for Examples 1 and 2 and Comparative Example 1.

[0076] Evaluation of the binding force between the electrode active material layer and the current collector layer. For each of the electrode mixture slurries from Examples 1-2 and Comparative Example 1, the first mixture slurry was coated to a thickness of 420 μm onto the surface of copper foil used as a current collector layer. Electrode bodies were then prepared by drying at 50°C for 20 minutes (low-speed drying) and at 150°C for 2 minutes (high-speed drying). In the low-speed dried electrode body, binder migration was sufficiently suppressed.

[0077] Next, the peel strength between the electrode active material layer and the current collector layer was measured for both the electrode body (slow drying) and the electrode body (high drying). The peel strength between the electrode active material layer and the current collector layer was measured in accordance with JIS-K-6854-1 using a 90° peel tester. The test material with the electrode active material layer laminated on the current collector layer was fixed to a base member, and the electrode active material layer was peeled off from one end.

[0078] Then, the degree of migration suppression was calculated by [peel strength of electrode body (high-speed drying)] / [peel strength of electrode body (low-speed drying)], and the bonding strength between the electrode active material layer and the current collector layer was evaluated. A migration suppression degree of 1.0 means that no migration occurred even during high-speed drying, and a migration suppression degree of less than 1.0 means that migration occurred. The evaluation results are shown in Table 1.

[0079] [Table 1]

[0080] From Examples 1-2 and Comparative Example 1 in Table 1, it can be seen that mixing small-particle-diameter particles into the electrode active material reduces pore size and porosity. Furthermore, it can be understood that, due to the reduction in pore size and porosity, binder migration does not occur even when high-speed drying is performed after coating the electrode mixture slurry. [Explanation of symbols]

[0081] 100 electrode body 110 Electrode active material layer 120 Binder Migration Routes 130 Electrode active material 131 Electrode active material with the largest average particle size 132 Electrode active material with the smallest average particle size 140 Current collector layer

Claims

1. A lithium-ion secondary battery having an electrode active material layer, The electrode active material layer comprises an electrode active material and a binder. The average pore size of the electrode active material layer is 1.00 μm or less, and The porosity of the electrode active material layer is 8.8% or less. Lithium-ion rechargeable battery.

2. The electrode active material layer contains two or more electrode active materials having different average particle sizes, The average particle diameter of the electrode active material with the largest average particle diameter is five times or more than the average particle diameter of the electrode active material with the smallest average particle diameter. The lithium-ion secondary battery according to claim 1.

3. The lithium-ion secondary battery according to claim 1 or 2, wherein the average pore diameter of the electrode active material layer is 0.30 μm or more, and / or the porosity of the electrode active material layer is 0.5% or more.

4. A method for manufacturing a lithium-ion secondary battery having an electrode active material layer, Mixing two or more electrode active materials with different average particle sizes and a binder with an average particle size of 0.30 μm or more to produce an electrode composite material, and The electrode composite material is molded to produce the electrode active material layer. including and The average particle diameter of the electrode active material with the largest average particle diameter is five times or more than the average particle diameter of the electrode active material with the smallest average particle diameter. A method for manufacturing lithium-ion rechargeable batteries.

5. The method according to claim 4, further comprising drying the electrode mixture at a temperature of 100°C or higher.

Images