Non-aqueous secondary battery and method for manufacturing a non-aqueous secondary battery

Abstract

To provide a nonaqueous secondary battery and a method for manufacturing a nonaqueous secondary battery, which can reduce a resistance difference in a negative electrode mixture layer in a width direction.SOLUTION: A nonaqueous secondary battery includes an electrode body in which a positive electrode plate and a negative electrode plate 24 are laminated with a separator interposed therebetween, and a nonaqueous electrolytic solution containing a film forming agent including a lithium salt. The negative electrode plate 24 includes a negative electrode base material 25 and a negative electrode mixture layer 26 coated on the negative electrode base material 25. The negative electrode mixture layer 26 includes a negative electrode active material 26X and a negative electrode thickener including a sodium salt. The negative electrode mixture layer 26 includes an end region AE including each end in a width direction D2 and a central region AC located between the two end regions AE. The BET specific surface area of the negative electrode active material 26X in the central region AC is greater than the BET specific surface area of the negative electrode active material 26X in the end region AE.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] This invention relates to a non-aqueous secondary battery and a method for manufacturing a non-aqueous secondary battery. [Background technology]

[0002] In non-aqueous secondary batteries such as lithium-ion secondary batteries, a Solid Electrolyte Interface (SEI) film is formed on the surface of the negative electrode mixture layer. The SEI film incorporates lithium ions during its formation process. Therefore, as the SEI film thickens due to repeated charging and discharging or long-term storage of the battery, the amount of lithium ions contributing to charging and discharging decreases, resulting in a decrease in battery capacity.

[0003] A known technique for addressing this problem involves adding lithium bisoxalate borate (LiBOB, LiB(C2O4)2) to a non-aqueous electrolyte. By adding a film-forming agent to the non-aqueous electrolyte, bisoxalate borate ions (BOB ions, B(C2O4)2) are ionized from LiBOB. - A stable coating derived from ) can be formed on the particle surface of the negative electrode active material particles. This suppresses the growth of the SEI coating (see Patent Document 1). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2013-225440 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] On the other hand, BOB ions, which are anions ionized from LiBOB, react with sodium ions contained in the negative electrode mixture layer to form a NaBOB film on the surface of the negative electrode mixture layer. The sodium ions originate, for example, from carboxymethylcellulose (CMC), which is used as a dispersant and thickener in the negative electrode mixture layer.

[0006] When the non-aqueous electrolyte is injected into the battery case, it penetrates into the negative electrode mixture layer from the edges in the width direction. Sodium ions dissolved in the non-aqueous electrolyte have a faster ion diffusion rate than BOB ions. Therefore, the NaBOB film tends to form more abundantly in the center of the negative electrode plate. As a result, differences in the amount of NaBOB film in the negative electrode mixture layer create a resistance difference, where the resistance is higher in the center in the width direction compared to the edges in the width direction. In the negative electrode mixture layer where a resistance difference occurs, metallic lithium may be deposited in the high-resistance areas as charging and discharging are repeated. [Means for solving the problem]

[0007] A non-aqueous secondary battery for solving the above problems comprises an electrode body in which a positive electrode plate and a negative electrode plate are laminated with a separator in between, and a non-aqueous electrolyte containing a film-forming agent containing a lithium salt, wherein the negative electrode plate comprises a negative electrode substrate and a negative electrode mixture layer coated on the negative electrode substrate, the negative electrode mixture layer comprises a negative electrode active material and an additive containing a sodium salt, the negative electrode mixture layer comprises end regions including each end in the width direction and a central region located between the two end regions, and the BET specific surface area of ​​the negative electrode active material in the central region is larger than the BET specific surface area of ​​the negative electrode active material in the end regions.

[0008] A method for manufacturing a non-aqueous secondary battery to solve the above problems comprises an electrode body in which a positive electrode plate and a negative electrode plate are laminated with a separator in between, and a non-aqueous electrolyte containing a film-forming agent containing a lithium salt, and the method for manufacturing a non-aqueous secondary battery comprises a step of manufacturing the negative electrode plate by coating a negative electrode substrate with a negative electrode mixture layer containing a negative electrode active material and an additive containing a sodium salt, wherein the negative electrode mixture layer comprises end regions including each end in the width direction and a central region located between the two end regions, and the step of manufacturing the negative electrode plate is to form the negative electrode mixture layer such that the BET specific surface area of ​​the negative electrode active material in the central region is greater than the BET specific surface area of ​​the negative electrode active material in the end regions.

[0009] According to the above configuration or manufacturing method, the anions formed by the ionization of the lithium salt contained in the film-forming agent react with the sodium ions formed by the ionization of the sodium salt, thereby forming a sodium-containing film on the surface of the negative electrode mixture layer. In this case, the central region tends to have higher resistance because a larger amount of sodium-containing film is formed compared to the edge regions. On the other hand, the central region tends to have lower resistance because the BET specific surface area of ​​the negative electrode active material is larger compared to the edge regions. Therefore, by making the BET specific surface area of ​​the negative electrode active material in the central region larger than the BET specific surface area of ​​the negative electrode active material in the edge regions, the resistance difference between the central region and the edge regions can be reduced.

[0010] In the above-described method for manufacturing a non-aqueous secondary battery, the step of forming the negative electrode mixture layer may include forming uncoated portions at both ends of the negative electrode substrate in which the negative electrode substrate is exposed, and forming the negative electrode mixture layer such that the BET specific surface area of ​​the negative electrode active material in the third region is greater than the BET specific surface area of ​​the negative electrode active material in the first and second regions, in the portions of the negative electrode mixture layer located at both ends in the width direction and adjacent to the uncoated portions, the second region located in the center in the width direction of the negative electrode mixture layer, and the two third regions located between the first and second regions of the negative electrode mixture layer. The step of manufacturing the negative electrode plate may also include cutting the negative electrode substrate on which the negative electrode mixture layer is formed in the center in the width direction so as to divide the second region into two.

[0011] According to the above manufacturing method, the first and second regions where the negative electrode mixture layer is formed correspond to the end regions in the state after the negative electrode substrate has been cut. Furthermore, the third region where the negative electrode mixture layer is formed corresponds to the central region in the state after the negative electrode substrate has been cut. Therefore, with this manufacturing method, two negative electrode plates can be manufactured at once.

[0012] In the above-described method for manufacturing a non-aqueous secondary battery, the step of forming the negative electrode mixture layer includes the steps of coating the negative electrode substrate with a negative electrode mixture paste that serves as a precursor to the negative electrode mixture layer, and drying the negative electrode mixture paste, wherein in the step of drying the negative electrode mixture paste, the drying rate of the portion of the negative electrode mixture paste corresponding to the central region may be slower than the drying rate of the portion of the negative electrode mixture paste corresponding to the edge region.

[0013] When the negative electrode mixture paste dries, the binder contained in the negative electrode mixture paste becomes unevenly distributed on the surface of the paste due to heat-induced migration. The surface side of the negative electrode mixture layer is more prone to battery charge and discharge reactions compared to the interior (negative electrode substrate side) of the negative electrode mixture layer. Therefore, as binder migration progresses, the BET specific surface area of ​​the negative electrode active material contained in the negative electrode mixture layer decreases. Furthermore, the rate of binder migration has a positive correlation with the drying rate of the negative electrode mixture paste. Thus, by making the drying rate of the negative electrode mixture paste in the central region slower than that of the negative electrode mixture paste in the edge regions, binder migration is suppressed in the central region compared to the edge regions. As a result, the BET specific surface area of ​​the negative electrode active material in the central region can be increased compared to the edge regions.

[0014] In the above-described method for manufacturing a non-aqueous secondary battery, the step of forming the negative electrode mixture layer includes the steps of coating the negative electrode substrate with a first negative electrode mixture paste which is a precursor for the portion constituting the end region of the negative electrode mixture layer, and a second negative electrode mixture paste which is a precursor for the portion constituting the central region of the negative electrode mixture layer, and drying the first negative electrode mixture paste and the second negative electrode mixture paste, wherein a negative electrode active material with a BET specific surface area larger than the negative electrode active material used as the raw material for the first negative electrode mixture paste may be used as the raw material for the second negative electrode mixture paste.

[0015] By changing the specific surface area of ​​the anode active material used as a raw material in the edge region and the central region of the anode mixture layer, the BET specific surface area of ​​the anode active material in the central region can be increased compared to the edge region.

[0016] In the above-described method for manufacturing a non-aqueous secondary battery, the step of forming the negative electrode mixture layer includes the steps of: kneading a first negative electrode mixture paste containing the raw materials for the portion constituting the end region of the negative electrode mixture layer; diluting the kneaded first negative electrode mixture paste; kneading a second negative electrode mixture paste containing the raw materials for the portion constituting the central region of the negative electrode mixture layer; diluting the kneaded second negative electrode mixture paste; coating the first negative electrode mixture paste and the second negative electrode mixture paste onto the negative electrode substrate; and drying the first negative electrode mixture paste and the second negative electrode mixture paste, wherein the solid content of the second negative electrode mixture paste in the step of kneading the second negative electrode mixture paste may be lower than the solid content of the first negative electrode mixture paste in the step of kneading the first negative electrode mixture paste.

[0017] The higher the solid content when kneading the anode mixture paste, the more uniformly the raw materials can be mixed. However, the anode active material, which is a raw material, is coated with the binder, which reduces the effective specific surface area of ​​the anode active material. Therefore, by making the solid content when kneading the second anode mixture paste lower than that when kneading the first anode mixture paste, the BET specific surface area of ​​the anode active material in the central region can be increased compared to the edge region.

[0018] In the above-described method for manufacturing a non-aqueous secondary battery, the step of forming the negative electrode mixture layer includes a step of pressing the negative electrode mixture layer to adjust its thickness, and the amount of pressure applied to the central region may be greater than the amount of pressure applied to the end regions.

[0019] As the pressing amount on the negative electrode mixture layer increases, new surfaces are formed due to cracking of the negative electrode active material or the like, and the BET specific surface area of the negative electrode active material contained in the negative electrode mixture layer increases. Therefore, by making the pressing amount on the central region larger than the pressing amount on the end region, the BET specific surface area of the negative electrode active material in the central region can be made larger than that in the end region.

[0020] In the method for manufacturing the non-aqueous secondary battery, the step of forming the negative electrode mixture layer includes a step of applying a negative electrode mixture paste to the negative electrode substrate and a step of drying the negative electrode mixture paste. In the step of applying the negative electrode mixture paste to the negative electrode substrate, the basis weight of the portion corresponding to the central region in the negative electrode mixture paste may be made larger than the basis weight of the portion corresponding to the end region in the negative electrode mixture paste.

[0021] By making the basis weight of the portion corresponding to the central region in the negative electrode mixture paste larger than the basis weight of the portion corresponding to the end region in the negative electrode mixture paste, the pressing amount on the central region can be made larger than the pressing amount on the end region.

[0022] In the method for manufacturing the non-aqueous secondary battery, the step of forming the negative electrode mixture layer includes a step of kneading a first negative electrode mixture paste containing raw materials of the portion constituting the end region in the negative electrode mixture layer, a step of diluting the kneaded first negative electrode mixture paste, a step of kneading a second negative electrode mixture paste containing raw materials of the portion constituting the central region in the negative electrode mixture layer, a step of diluting the kneaded second negative electrode mixture paste, a step of applying the first negative electrode mixture paste and the second negative electrode mixture paste to the negative electrode substrate, and a step of drying the first negative electrode mixture paste and the second negative electrode mixture paste. In the step of diluting the second negative electrode mixture paste, the second negative electrode mixture paste may be diluted so that the solid content ratio of the second negative electrode mixture paste becomes higher than the solid content ratio after the first negative electrode mixture paste is diluted.

[0023] When the basis weights of the first negative electrode active material paste and the second negative electrode active material paste are the same, the central region with a higher solid content rate of the second negative electrode active material paste after dilution is more likely to have a larger thickness in the state before being pressed. Therefore, the pressing amount for the central region can be made larger than the pressing amount for the end region.

[0024] In the method for manufacturing the non-aqueous secondary battery, the step of forming the negative electrode active material layer includes a step of coating the negative electrode substrate with a first negative electrode active material paste that is a precursor of a portion constituting the end region of the negative electrode active material layer and a second negative electrode active material paste that is a precursor of a portion constituting the central region of the negative electrode active material layer, and a step of drying the first negative electrode active material paste and the second negative electrode active material paste. As the raw material of the second negative electrode active material paste, a negative electrode active material having a lower tap density than the negative electrode active material used as the raw material of the first negative electrode active material paste may be used.

[0025] When the basis weights of the first negative electrode active material paste and the second negative electrode active material paste are the same, the central region with a lower tap density of the negative electrode active material used as the raw material is more likely to have a larger thickness in the state before being pressed. Therefore, the pressing amount for the central region can be made larger than the pressing amount for the end region.

Advantages of the Invention

[0026] According to the present invention, the resistance difference in the width direction in the negative electrode active material layer can be reduced.

Brief Description of the Drawings

[0027] [Figure 1] FIG. 1 is a perspective view of a lithium ion secondary battery. [Figure 2] FIG. 2 is a perspective view showing the electrode body in a developed state. [Figure 3] FIG. 3 is a cross-sectional view taken along line III-III of FIG. 2. [Figure 4] FIG. 4 is an enlarged cross-sectional view showing the negative electrode plate. [Figure 5]Figure 5 is a graph showing the BET specific surface area of ​​the negative electrode active material against its position in the width direction within the negative electrode mixture layer. [Figure 6] Figure 6 is a graph showing the amount of NaBOB coating per unit weight of the negative electrode active material against its position in the width direction of the negative electrode mixture layer. [Figure 7] Figure 7 is a graph showing the local resistance value with respect to the amount of NaBOB coating per unit weight of the negative electrode active material in a negative electrode mixture layer having a predetermined BET specific surface area. [Figure 8] Figure 8 is a flowchart showing the manufacturing process of the negative electrode mixture paste. [Figure 9] Figure 9 is a flowchart showing the process of forming a negative electrode mixture layer on a negative electrode substrate. [Figure 10] Figure 10 is a schematic cross-sectional view showing the state in which two negative electrode plates are integrally assembled when two negative electrode plates are manufactured at the same time. [Figure 11] Figure 11 is a graph showing the change in the BET specific surface area of ​​the negative electrode plate during the manufacturing process of lithium-ion secondary batteries. [Figure 12] Figure 12 is a schematic cross-sectional view showing the configuration of a drying apparatus when drying conditions are changed between the edge region and the central region, and the state of the negative electrode active material and negative electrode binder at that time. [Figure 13] Figure 13 is a graph showing the BET specific surface area of ​​the negative electrode active material with respect to its position in the width direction within the negative electrode mixture layer, in a state where two negative electrode plates are integrally configured. [Figure 14] Figure 14 is a schematic diagram showing the configuration of a pressing roll when the pressing conditions are changed in the end region and the central region. [Figure 15] Figure 15 is a schematic diagram showing the configuration of a coating apparatus when the basis weight of the negative electrode mixture paste is varied between the edge region and the central region. [Modes for carrying out the invention]

[0028] One embodiment of the present invention will be described below with reference to Figures 1 to 15. [Lithium-ion rechargeable battery] As shown in FIG. 1, a lithium-ion secondary battery 10, which is an example of a non-aqueous secondary battery, includes a case 11 and an electrode body 20. The case 11 has a flat bottomed rectangular outer shape with an opening on the upper side. The case 11 houses the electrode body 20 and a non-aqueous electrolyte. The lid 12 closes the opening of the case 11. The case 11 forms a sealed battery case in a rectangular parallelepiped shape by attaching the lid 12.

[0029] The lid 12 is provided with a positive electrode external terminal 13A and a negative electrode external terminal 13B. The positive electrode current collector portion 20A, which is the end portion on the positive electrode side of the electrode body 20, is electrically connected to the positive electrode external terminal 13A via the positive electrode current collector member 14A. The negative electrode current collector portion 20B, which is the end portion on the negative electrode side of the electrode body 20, is electrically connected to the negative electrode external terminal 13B via the negative electrode current collector member 14B. The lid 12 is provided with an injection port 15 for injecting the non-aqueous electrolyte. Note that the shapes of the external terminals 13A and 13B are not limited to the shapes shown in FIG. 1 and may be any shape.

[0030] [Electrode body] As shown in FIG. 2, the electrode body 20 is a flat wound body formed by winding a laminate in which a long positive electrode plate 21 and a negative electrode plate 24 are laminated via a separator 27. The positive electrode plate 21, the negative electrode plate 24, and the separator 27 are laminated such that their longitudinal directions coincide with the longitudinal direction D1. The electrode body 20 has a structure in which the positive electrode plate 21 and the negative electrode plate 24 laminated with the separator 27 interposed therebetween are wound around a winding axis L1 extending along the strip-shaped width direction D2.

[0031] As shown in FIG. 3, in the state of the laminate before winding, the positive electrode plate 21, the separator 27, the negative electrode plate 24, and the separator 27 are laminated in this order in the lamination direction D3. Note that the lamination direction D3 is a direction orthogonal to the plane including the longitudinal direction D1 and the width direction D2.

[0032] [Positive electrode plate] The positive electrode plate 21 comprises a positive electrode substrate 22 and a positive electrode mixture layer 23. The positive electrode substrate 22 is a long, foil-like member. The positive electrode mixture layer 23 is provided on each of two surfaces of the positive electrode substrate 22 facing opposite directions. The positive electrode substrate 22 has a positive electrode side uncoated portion 22A at one end in the width direction D2 where the positive electrode substrate 22 is exposed and the positive electrode mixture layer 23 is not formed.

[0033] The positive electrode base material 22 is made of a metal foil composed of aluminum or an alloy mainly composed of aluminum. In the state of the wound body, the uncoated positive electrode side portion 22A of the positive electrode base material 22 is pressed against each other by opposing portions to form the positive electrode side current collector portion 20A.

[0034] The positive electrode mixture layer 23 is a cured form of a liquid positive electrode mixture paste. The positive electrode mixture paste contains a positive electrode active material, a positive electrode solvent, a positive electrode conductive agent, and a positive electrode binder. The positive electrode mixture layer 23 is formed when the positive electrode mixture paste dries and the positive electrode solvent vaporizes. Therefore, the positive electrode mixture layer 23 contains a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder.

[0035] The positive electrode active material is a lithium-containing composite metal oxide capable of intercalating and releasing lithium ions, which are charge carriers in the lithium-ion secondary battery 10. The lithium-containing composite oxide is an oxide containing lithium and other metal elements other than lithium. The other metal elements other than lithium are, for example, at least one selected from the group consisting of nickel, cobalt, manganese, vanadium, magnesium, molybdenum, niobium, titanium, tungsten, aluminum, and iron contained as iron phosphate in the lithium-containing composite oxide.

[0036] For example, lithium-containing composite oxides include lithium cobaltate (LiCoO2), lithium nickelate (LiNiO2), and lithium manganate (LiMn2O4). For example, a lithium-containing composite oxide is a ternary lithium-containing composite oxide (NCM) containing nickel, cobalt, and manganese, specifically lithium nickel-cobalt-manganate (LiNiCoMnO2). For example, a lithium-containing composite oxide is lithium iron phosphate (LiFePO4).

[0037] The positive electrode solvent is an NMP (N-methyl-2-pyrrolidone) solution, which is an example of an organic solvent. Examples of positive electrode conductive materials include carbon black such as acetylene black (AB) and Ketjenblack, carbon fibers such as carbon nanotubes (CNTs) and carbon nanofibers, and graphite. The positive electrode binder is an example of a resin component contained in the positive electrode paste. The positive electrode binder is, for example, at least one selected from the group consisting of polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), and styrene-butadiene rubber (SBR).

[0038] The positive electrode plate 21 may also be provided with an insulating layer at the boundary between the uncoated portion 22A on the positive electrode side and the positive electrode mixture layer 23. The insulating layer comprises an inorganic component having insulating properties and a resin component that functions as a binder. The inorganic component is at least one selected from the group consisting of powdered boehmite, titania, and alumina. The resin component is at least one selected from the group consisting of PVDF, PVA, and acrylic.

[0039] [negative electrode plate] The negative electrode plate 24 is a negative electrode plate comprising a negative electrode substrate 25 and a negative electrode mixture layer 26. The negative electrode substrate 25 is a long, foil-like member. The negative electrode mixture layer 26 is provided on each of two surfaces of the negative electrode substrate 25 facing opposite directions. The negative electrode substrate 25 has a negative electrode side uncoated portion 25A at one end in the width direction D2, which is located opposite the positive electrode side uncoated portion 22A, where the negative electrode mixture layer 26 is not formed and the negative electrode substrate 25 is exposed.

[0040] The negative electrode substrate 25 is made of metal foil composed of copper or an alloy mainly composed of copper. In the state of the wound body, the uncoated portion 25A on the negative electrode side is pressed against each other by opposing portions to form the negative electrode side current collector portion 20B.

[0041] The negative electrode mixture layer 26 is a cured form of the liquid negative electrode mixture paste. That is, the negative electrode mixture paste is a precursor of the negative electrode mixture layer 26. The negative electrode mixture paste contains a negative electrode active material 26X (see Figure 4), a negative electrode solvent, a negative electrode conductive agent, a negative electrode thickener, and a negative electrode binder 26Y (see Figure 12). The negative electrode mixture layer 26 is formed when the negative electrode mixture paste is dried and the negative electrode solvent vaporizes. Therefore, the negative electrode mixture layer 26 contains the negative electrode active material 26X, the negative electrode conductive agent, the negative electrode thickener, and the negative electrode binder 26Y.

[0042] The negative electrode active material 26X is a material capable of intercalating and releasing lithium ions. Examples of negative electrode active material 26X include graphite, non-graphitizable carbon, easily graphitizable carbon, carbon nanotubes, and other carbon materials. The negative electrode active material 26X may also be composite particles in which graphite particles are coated with an amorphous carbon layer.

[0043] The negative electrode solvent is, for example, water. The negative electrode conductive agent can be, for example, the same as that used for the positive electrode conductive agent. The negative electrode thickener can be, for example, carboxymethylcellulose (CMC). The mass ratio of the negative electrode thickener is, for example, 0.1% by mass or more and 20% by mass or less relative to the mass of the negative electrode mixture layer 26. Note that CMC is an example of an additive containing a sodium salt. CMC also functions as a dispersant for dispersing the negative electrode active material in the negative electrode mixture paste. The negative electrode binder 26Y is at least one selected from the group consisting of PVDF, PVA, and SBR. The mass ratio of the negative electrode binder 26Y is, for example, 0.1% by mass or more and 20% by mass or less relative to the mass of the negative electrode mixture layer 26.

[0044] [Separator] Separator 27 prevents the positive electrode plate 21 and the negative electrode plate 24 from contacting each other, and holds the non-aqueous electrolyte between the positive electrode plate 21 and the negative electrode plate 24. When the electrode body 20 is immersed in the non-aqueous electrolyte, the non-aqueous electrolyte penetrates from the end portion of the separator 27 toward the central portion.

[0045] Separator 27 is a non-woven fabric made of polypropylene or the like. As the separator 27, for example, porous polymer films such as porous polyethylene films, porous polyolefin films, and porous polyvinyl chloride films, and ion conductive polymer electrolyte films can be used.

[0046] [Non-aqueous electrolyte] The non-aqueous electrolyte is a composition in which a supporting salt is contained in a non-aqueous solvent. The non-aqueous solvent is, for example, one or more materials selected from the group consisting of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate. The supporting salt is, for example, one or more lithium compounds (lithium salts) selected from LiPF6, LiBF4, LiClO4, LiAsF6, LiCF3SO3, LiC4F9SO3, LiN(CF3SO2)2, LiC(CF3SO2)3, LiI, etc.

[0047] In the present embodiment, ethylene carbonate is employed as the non-aqueous solvent. A film-forming agent is added to the non-aqueous electrolyte as an additive. The film-forming agent is, for example, lithium bis(oxalato)borate (LiBOB), which is an example of a lithium salt. For example, LiBOB is added to the non-aqueous electrolyte so that the concentration of LiBOB in the non-aqueous electrolyte is 0.001 or more and 0.1 or less [mol / L].

[0048] [Configuration of negative electrode mixture layer] As shown in FIG. 4, the negative electrode mixture layer 26 includes a first end E1 that is one end in the width direction D2 and a second end E2 that is the other end in the width direction D2. The first end E1 is an end portion on the side of the non-coated portion 25A on the negative electrode side in the width direction D2. The second end E2 is an end portion on the side opposite to the non-coated portion 25A on the negative electrode side in the width direction D2.

[0049] The negative electrode mixture layer 26 comprises two end regions AE and a central region AC. In the negative electrode mixture layer 26, the end regions AE and the central region AC each extend along the longitudinal direction D1. There is one end region AE at each end in the width direction D2. One of the two end regions AE includes the first end E1. The other of the two end regions AE includes the second end E2. The central region AC is located between the two end regions AE in the width direction D2. The two end regions AE and the central region AC are, for example, regions obtained by dividing the negative electrode mixture layer 26 into three equal parts in the width direction D2, but their respective widths may be equal or different.

[0050] The width of the end region AE including the first end E1 is, for example, 20 mm to 40 mm from the first end E1. The width of the end region AE including the second end E2 is, for example, 20 mm to 40 mm from the second end E2. The width of the central region AC is, for example, 20 mm to 60 mm. The width of the end region AE is, as an example, 20% to 40% of the total width of the negative electrode mixture layer 26. The width of the central region AC is, as an example, 20% to 60% of the total width of the negative electrode mixture layer 26.

[0051] In the negative electrode mixture layer 26, the BET specific surface area of ​​the negative electrode active material 26X in the central region AC is larger than that of the negative electrode active material 26X in the edge region AE. The BET specific surface area is a value measured by the BET (Brunauer, Emmett, Teller) method on a sample cut from a portion of the negative electrode mixture layer 26. Nitrogen gas is used as an adsorbent gas in the measurement of the BET specific surface area. The BET specific surface area represents the effective specific surface area per unit weight. Here, "effective specific surface area" refers to the specific surface area of ​​the reaction surface that contributes to the charge-discharge reaction in the negative electrode active material 26X. For example, the area of ​​the surface of the negative electrode active material 26X that does not contribute to the charge-discharge reaction for reasons such as the surface being covered with the negative electrode binder 26Y is not included in the BET specific surface area.

[0052] Graph 40 in Figure 5 shows the correspondence between the position in the width direction D2 of the negative electrode mixture layer 26, represented by the horizontal axis, and the BET specific surface area of ​​the negative electrode active material 26X, represented by the vertical axis. As shown by the solid curve 41 in Graph 40, in the width direction D2 of the negative electrode mixture layer 26, the BET specific surface area of ​​the negative electrode active material 26X increases from the first end E1 toward the central region AC. Similarly, in the width direction D2 of the negative electrode mixture layer 26, the BET specific surface area of ​​the negative electrode active material 26X increases from the second end E2 toward the central region AC. Therefore, in the width direction D2, the BET specific surface area of ​​the negative electrode active material 26X is largest in the central region AC.

[0053] For reference, the dashed line 42 in Graph 40 shows an example of the position in the width direction D2 of the negative electrode mixture layer 26 and the BET specific surface area of ​​the negative electrode active material 26X contained in the negative electrode mixture layer 26 in a conventional lithium-ion secondary battery. As shown by line 42, in a conventional lithium-ion secondary battery, the BET specific surface area of ​​the negative electrode active material 26X is almost constant at any position in the width direction D2 of the negative electrode mixture layer 26.

[0054] In the edge region AE, for example, the BET specific surface area of ​​the negative electrode active material 26X is 3.7 cm². 2 / g or more 3.9cm 2 This includes portions less than / g. The central region AC is, for example, a negative electrode active material 26X with a BET specific surface area of ​​3.9 cm². 2 / g or more 4.1cm 2 This includes portions less than or equal to / g. The difference between the maximum BET specific surface area of ​​the negative electrode active material 26X contained in the central region AC and the minimum BET specific surface area of ​​the negative electrode active material 26X contained in the edge region AE is, for example, 0.1 cm. 2 / g or more 0.3cm 2 It is less than or equal to / g. The maximum BET specific surface area of ​​the negative electrode active material 26X contained in the central region AC is, for example, 1.02 times or more and 1.12 times or less than the minimum BET specific surface area of ​​the negative electrode active material 26X in the edge region AE.

[0055] As an example of the method for measuring the BET specific surface area, a plurality of curves 41 are obtained by measuring the BET specific surface area of the negative electrode active material 26X at a plurality of positions in the longitudinal direction D1 of the negative electrode binder layer 26 at predetermined intervals along the width direction D2. The maximum value of the BET specific surface area of the negative electrode active material 26X included in the central region AC is, for example, the average value of the maximum values in each curve 41. The minimum value of the BET specific surface area of the negative electrode active material 26X included in the end region AE is, for example, the average value of the minimum values in each curve 41.

[0056] In the negative electrode binder layer 26, the portion located in the end region AE and the portion located in the central region AC may have different raw materials or different manufacturing conditions in order to make the BET specific surface area of the negative electrode active material 26X different.

[0057] [NaBOB film] In the negative electrode binder layer 26, sodium ions (Na + ) derived from the sodium salt contained in an additive such as a negative electrode thickener (e.g., CMC) and BOB ions (BOB - ) derived from LiBOB added to the non-aqueous electrolyte form a NaBOB film. The BOB ion is an example of an anion obtained by ionizing a lithium salt contained in a film-forming agent. The NaBOB film is an example of a sodium-containing film. When the non-aqueous electrolyte is injected into the case 11, the non-aqueous electrolyte penetrates from each of the first end E1 and the second end E2 in the width direction D2 toward the central region AC in the negative electrode binder layer 26. The ion diffusion rate in the non-aqueous electrolyte is faster for sodium ions than for BOB ions. As a result, the BOB ions arrive late in a state where the sodium ions have a high concentration in the central region AC in the width direction D2, and thus a large amount of the NaBOB film is likely to be formed in the central region AC.

[0058] Graph 50 in Figure 6 shows the correspondence between the position in the width direction D2 of the negative electrode mixture layer 26, represented by the horizontal axis, and the amount of NaBOB coating per unit weight of the negative electrode active material 26X in the negative electrode mixture layer 26, represented by the vertical axis. As shown by curve 51 in Graph 50, the amount of NaBOB coating per unit weight of the negative electrode active material 26X increases towards the center in the width direction D2. That is, in the central region AC, the amount of NaBOB coating per unit weight of the negative electrode active material 26X is greater than in the edge region AE. The central region AC, where the amount of NaBOB coating is relatively large, tends to have higher resistance than the edge region AE, where the amount of NaBOB coating is relatively small.

[0059] When a lithium-ion secondary battery 10 containing such a negative electrode mixture layer 26 is repeatedly charged and discharged, metallic lithium is deposited in the central region AC, which has relatively high resistance, leading to a decrease in battery performance. In particular, as shown by the dashed line 42 in Figure 5, the above phenomenon is more likely to occur when the BET specific surface area of ​​the negative electrode active material 26X contained in the negative electrode mixture layer 26 is uniform in the width direction D2.

[0060] In this regard, by making the BET specific surface area of ​​the negative electrode active material 26X in the central region AC larger than the BET specific surface area of ​​the negative electrode active material 26X contained in the end region AE, the resistance of the central region AC tends to be lower than that of the end region AE. That is, from the viewpoint of NaBOB coating amount, the resistance of the central region AC tends to be higher than that of the end region AE, and from the viewpoint of BET specific surface area, the resistance of the central region AC tends to be lower than that of the end region AE. Therefore, by making the BET specific surface area of ​​the negative electrode active material 26X in the central region AC larger than the BET specific surface area of ​​the negative electrode active material 26X contained in the end region AE, the resistance difference in the width direction D2 of the negative electrode mixture layer 26 can be reduced.

[0061] [Resistance difference in the negative electrode mixture layer] Graph 60 in Figure 7 shows the relationship between the amount of NaBOB coating per unit weight of the negative electrode active material 26X in the negative electrode mixture layer 26, represented by the horizontal axis, and the local resistance value of the negative electrode mixture layer 26, represented by the vertical axis. Line 61 in Graph 60 represents the relationship between the amount of NaBOB coating of the negative electrode mixture layer 26 and the local resistance value when the BET specific surface area of ​​the negative electrode active material 26X is the first specific surface area. Line 62 in Graph 60 represents the relationship between the amount of NaBOB coating of the negative electrode mixture layer 26 and the local resistance value when the BET specific surface area of ​​the negative electrode active material 26X is the second specific surface area, which is larger than the first specific surface area.

[0062] As shown by lines 61 and 62 respectively, when the BET specific surface area of ​​the negative electrode active material 26X is the same, the local resistance value increases as the amount of NaBOB coating in the negative electrode mixture layer 26 increases. Also, when the amount of NaBOB coating per unit weight of the negative electrode active material 26X in the negative electrode mixture layer 26 is the same, the local resistance value increases as the BET specific surface area of ​​the negative electrode active material 26X decreases.

[0063] For example, in the negative electrode mixture layer 26, the amount of NaBOB coating in the portion located in the edge region AE is defined as the first coating amount X1, and the amount of NaBOB coating in the portion located in the central region AC is defined as the second coating amount X2 (X2 > X1). If the BET specific surface area of ​​the negative electrode active material 26X in the edge region AE of the negative electrode mixture layer 26 is the first specific surface area, then the local resistance value in the edge region AE is the first resistance value R1. Note that point 63 in graph 60 is a point on the line 61 and indicates the local resistance value when the amount of NaBOB coating in the negative electrode mixture layer 26 is the first coating amount X1.

[0064] If the BET specific surface area of ​​the negative electrode active material 26X in the central region AC is the same as the first specific surface area in the edge region AE, then the local resistance value in the central region AC will be a second resistance value R2, which is greater than the first resistance value R1. Note that point 64, shown by a dashed line in graph 60, is a point on the straight line 61 and represents the local resistance value when the amount of NaBOB coating on the negative electrode mixture layer 26 is the second coating amount X2.

[0065] Here, by making the BET specific surface area of ​​the negative electrode active material 26X in the central region AC larger than the first specific surface area, the local resistance value in the central region AC can be brought closer to the local current value in the end region AE. In other words, the BET specific surface area of ​​the negative electrode active material 26X in the central region AC should be determined so that the local current value in the central region AC approaches the first resistance value R1.

[0066] Figure 6 illustrates the case where the local resistance value is the first resistance value R1 when the amount of NaBOB coating on the negative electrode mixture layer 26 is the second coating amount X2, and the BET specific surface area of ​​the negative electrode active material 26X is the second specific surface area. Point 65 shown in Graph 60 is a point on the line 62 and represents the local resistance value when the amount of NaBOB coating on the negative electrode mixture layer 26 is the second coating amount X2.

[0067] For reference, in Graph 60, the first coating amount X1 is 0.005 mmol / g, the second coating amount X2 is 0.025 mmol / g, and the first specific surface area is 3.80 cm². 2 When set to / g, the difference between the first resistance R1 and the second resistance R2 is approximately 2.5Ω. In this case, the second specific surface area, which is the target value for reducing the difference between the first resistance R1 and the second resistance R2, is 4.26 cm². 2 It is / g.

[0068] [Manufacturing method for negative electrode plates] The method for manufacturing the negative electrode plate 24 includes steps S1-1 to S1-3 shown in Figure 8 and steps S2-1 to S2-4 shown in Figure 9. Steps S1-1 to S1-3 shown in Figure 8 are part of the process for manufacturing the negative electrode plate 24 and are steps for manufacturing the negative electrode mixture paste. Steps S2-1 to S2-4 shown in Figure 9 are part of the process for manufacturing the negative electrode plate 24 and are steps for forming a negative electrode mixture layer 26 on the negative electrode substrate 25 using the negative electrode mixture paste. The process for manufacturing the positive electrode plate 21 differs from the process for manufacturing the negative electrode plate 24 in terms of raw materials and manufacturing conditions, but the basic process flow is the same, so a detailed explanation of that process is omitted.

[0069] [Manufacturing of negative electrode mixture paste] In the process of manufacturing the negative electrode mixture paste, first, in step S1-1, the raw materials for the negative electrode mixture layer 26 are mixed. Next, in step S1-2, the negative electrode mixture paste is manufactured by kneading the raw materials together in a way that results in a solid content higher than that of the final negative electrode mixture paste. Finally, in step S1-3, the solid content of the kneaded negative electrode mixture paste is adjusted by diluting it with the negative electrode solvent. The negative electrode mixture paste is manufactured through these steps.

[0070] Furthermore, in the negative electrode mixture layer 26, the same and different negative electrode mixture paste may be used for the portion constituting the end region AE and the portion constituting the central region AC, or different negative electrode mixture pastes may be used. When different negative electrode mixture pastes are used for the end region AE and the central region AC, a first negative electrode mixture paste containing the raw materials for the portion constituting the end region AE and a second negative electrode mixture paste containing the raw materials for the portion constituting the central region AC are manufactured separately. In this case, the first negative electrode mixture paste and the second negative electrode mixture paste may be coated simultaneously or separately.

[0071] [Formation of the negative electrode mixture layer] Steps S2-1 to S2-4 shown in Figure 9 represent an example of the manufacturing process when two negative electrode plates 24 are manufactured at once. In the process of forming the negative electrode mixture layer 26 on the negative electrode substrate 25, first, in step S2-1, the negative electrode mixture paste is applied to one surface of the negative electrode substrate 25. At this time, the negative electrode substrate 25 used has a width approximately twice that of the electrode body 20 shown in Figure 2. Furthermore, the negative electrode mixture paste is applied so as to have a width approximately twice that of the negative electrode mixture layer 26 in the electrode body 20 shown in Figure 2, and so as to form one uncoated negative electrode side portion 25A at each end in the width direction D2 of the negative electrode substrate 25.

[0072] Next, in step S2-2, the negative electrode mixture paste is dried and the negative electrode solvent is vaporized, forming a negative electrode mixture layer 26 on one surface of the negative electrode substrate 25. At this time, for example, the first negative electrode mixture paste is dried so that drying air blows on the negative electrode mixture paste from the side opposite to the negative electrode substrate 25. Then, in step S2-3, the thickness of the negative electrode mixture layer 26 is adjusted by pressing the negative electrode mixture layer 26 with a press roll.

[0073] As shown in Figure 10, subsequently, on the negative electrode substrate 25, the negative electrode mixture layer 26 is formed on the surface opposite to the surface on which the negative electrode mixture layer 26 is formed, using the same procedure as in steps S2-1 to S2-3. Through this procedure, one negative electrode mixture layer 26 is formed on each of the two opposing surfaces of the negative electrode substrate 25.

[0074] In this state, two negative electrode plates 24 are integrally formed with respect to the center line CL located in the center of the width direction D2. Therefore, the first end E1 is located at each end of the width direction D2 in the negative electrode mixture layer 26. With the two negative electrode plates 24 integrally formed, the two end regions AE adjacent to the uncoated negative electrode side portion 25A in the negative electrode mixture layer 26 are the first region A1. The portion where the two end regions AE are continuous in the center of the width direction D2 is the second region A2. The two portions located between the first region A1 and the second region A2 are the third region A3. In other words, the first region A1 and the second region A2 correspond to the end regions AE. The third region A3 corresponds to the central region AC.

[0075] Finally, in step S2-4, the negative electrode substrate 25 is cut along the center line CL so as to divide the second region A2 into two in the width direction D2. The cut point at this time becomes the second end E2 of the negative electrode mixture layer 26. Through these steps, two negative electrode plates 24 are manufactured at once.

[0076] [Method for manufacturing electrodes and method for assembling lithium-ion secondary batteries] After the positive electrode plate 21 and the negative electrode plate 24 are manufactured, a process is carried out to manufacture the electrode body 20 using the positive electrode plate 21, the negative electrode plate 24, and the separator 27. In the process of manufacturing the electrode body 20, first, the positive electrode plate 21 and the negative electrode plate 24 are stacked with the separator 27 in between, then wound up, and then pressed flat. Next, the unpainted portion 22A on the positive electrode side is pressed to form the positive electrode side current collector portion 20A. Similarly, the unpainted portion 25A on the negative electrode side is pressed to form the negative electrode side current collector portion 20B. The electrode body 20 is manufactured by following these steps.

[0077] Next, the electrode body 20 is housed in the case 11. At this time, the positive electrode current collector 20A is electrically connected to the positive electrode external terminal 13A via the positive electrode current collector 14A. The negative electrode current collector 20B is electrically connected to the negative electrode external terminal 13B via the negative electrode current collector 14B. The opening at the top of the case 11 is closed with the lid 12. Then, after removing moisture from the electrode body 20 by heat treatment, a non-aqueous electrolyte is injected into the case 11. The lithium-ion secondary battery 10 is assembled by following these steps.

[0078] [Method for controlling BET specific surface area] The method for controlling the BET specific surface area of ​​the negative electrode active material 26X contained in the negative electrode mixture layer 26 will be explained below with reference to Figures 11 to 15. The BET specific surface area of ​​the negative electrode active material 26X contained in the negative electrode mixture layer 26 changes from the raw material state through the manufacturing process.

[0079] [BET specific surface area in raw material state] Point P1 in Figure 11 represents the BET specific surface area of ​​the anode active material 26X in the raw material state in step S1-1. The BET specific surface area of ​​the anode active material 26X in the raw material state has a positive correlation with the BET specific surface area of ​​the anode active material 26X contained in the anode mixture layer 26.

[0080] One example of a method for controlling the BET specific surface area is to use a first anode mixture paste as a precursor for the portion constituting the edge region AE in the anode mixture layer 26, and a second anode mixture paste as a precursor for the portion constituting the central region AC. Furthermore, as the raw material for the second anode mixture paste, a negative electrode active material 26X with a larger BET specific surface area than the negative electrode active material 26X used as the raw material for the first anode mixture paste is used. This manufacturing method also makes it possible to make the BET specific surface area of ​​the negative electrode active material 26X in the central region AC larger than the BET specific surface area of ​​the negative electrode active material 26X in the edge region AE.

[0081] [Solid content ratio when kneaded to a stiff consistency] Point P2 in Figure 11 represents the BET specific surface area of ​​the negative electrode active material 26X in the state of the negative electrode mixture paste after the raw materials have been kneaded in step S1-2. When the raw materials are kneaded together in step S1-2, the surface of the negative electrode active material 26X is covered with the negative electrode binder 26Y and the negative electrode thickener (e.g., CMC), which reduces the BET specific surface area.

[0082] In step S1-2, the higher the solid content of the negative electrode mixture paste when the raw materials are kneaded together, the stronger the friction between the raw materials, resulting in a larger amount of negative electrode binder 26Y adhering to the surface of the negative electrode active material 26X. In other words, the higher the solid content of the negative electrode mixture paste when the raw materials are kneaded together, the greater the decrease in the BET specific surface area of ​​the negative electrode active material 26X associated with kneading.

[0083] One example of a method for controlling the BET specific surface area is to use a first anode mixture paste as a precursor for the portion constituting the edge region AE in the anode mixture layer 26, and a second anode mixture paste as a precursor for the portion constituting the central region AC. Then, the solid content ratio when kneading the second anode mixture paste is made lower than the solid content ratio when kneading the first anode mixture paste. After that, the first anode mixture paste and the second anode mixture paste are each diluted.

[0084] This makes it possible to reduce the area of ​​the surface of the negative electrode active material 26X covered by the negative electrode binder 26Y in the central region AC. This manufacturing method also makes it possible to make the BET specific surface area of ​​the negative electrode active material 26X in the central region AC larger than the BET specific surface area of ​​the negative electrode active material 26X in the edge region AE.

[0085] [Drying conditions] Point P3 in Figure 11 represents the BET specific surface area of ​​the negative electrode active material 26X after step S2-2, i.e., after the negative electrode mixture paste has dried. When the negative electrode mixture paste dries, the negative electrode binder 26Y contained in the negative electrode mixture paste becomes unevenly distributed on the surface of the negative electrode mixture paste (opposite side from the negative electrode substrate 25) due to heat-induced migration. The rate of migration of the negative electrode binder 26Y has a positive correlation with the drying rate of the negative electrode mixture paste.

[0086] The surface side of the negative electrode mixture layer 26 is a region where battery charge and discharge reactions are more likely to occur compared to the interior of the negative electrode mixture layer 26 (negative electrode substrate 25 side). Therefore, as migration of the negative electrode binder 26Y progresses, the BET specific surface area of ​​the negative electrode active material 26X contained in the negative electrode mixture layer 26 decreases.

[0087] One example of a method for controlling the BET specific surface area is to make the drying rate of the portion of the negative electrode mixture paste corresponding to the central region AC slower than the drying rate of the portion of the negative electrode mixture paste corresponding to the edge region AE. This relatively suppresses the migration of the negative electrode binder 26Y in the portion of the negative electrode mixture paste corresponding to the central region AC. As a result, the amount of decrease in the BET specific surface area of ​​the negative electrode active material 26X due to migration in the central region AC can be reduced. Even with this manufacturing method, the BET specific surface area of ​​the negative electrode active material 26X in the central region AC can be made larger than the BET specific surface area of ​​the negative electrode active material 26X in the edge region AE.

[0088] For example, the airflow rate in the portion of the negative electrode mixture paste corresponding to the central region AC may be smaller than the airflow rate in the portion of the negative electrode mixture paste corresponding to the edge region AE. An example of a method for controlling the drying rate of each part in the width direction D2 of the negative electrode mixture layer 26 by controlling the airflow rate will be described below with reference to Figure 12.

[0089] The drying apparatus 100 shown in Figure 12 comprises two first air blowers 101 and a second air blower 102. The first air blower 101 blows drying air W toward the first region A1 from an opening facing the first region A1. The second air blower 102 blows drying air W toward the second region A2 from an opening facing the second region A2.

[0090] At this time, secondary drying air W from the first air blower 101 and secondary drying air W from the second air blower 102 flow into the third region A3. However, since the drying air W to the third region A3 is secondary and weakened, the amount of drying air W hitting the third region A3 is smaller than the amount of drying air W directly hitting the first region A1 and the second region A2. As a result, the drying rate of the negative electrode mixture paste in the third region A3 is slower compared to the first region A1 and the second region A2.

[0091] In the first region A1 and the second region A2, the negative electrode binder 26Y becomes unevenly distributed on the surface of the negative electrode mixture paste due to heat-induced migration. In contrast, in the third region A3, the migration of the negative electrode binder 26Y is suppressed compared to the first region A1 and the second region A2.

[0092] Graph 70 in Figure 13 shows the correspondence between the position in the width direction D2 of the negative electrode mixture layer 26, represented by the horizontal axis, and the BET specific surface area of ​​the negative electrode active material 26X, represented by the vertical axis, when the two negative electrode plates 24 are integrally configured. As shown by curve 71 in Graph 70, with the drying method using the drying apparatus 100, the BET specific surface area of ​​the negative electrode active material 26X is larger in the third region A3 compared to the first region A1 and the second region A2, due to the difference in the degree of migration of the negative electrode binder 26Y. Therefore, even with the drying method described above, the BET specific surface area of ​​the negative electrode active material 26X in the central region AC can be made larger than the BET specific surface area of ​​the negative electrode active material 26X in the end region AE.

[0093] Furthermore, when manufacturing two negative electrode plates 24 at once, even if the BET specific surface area of ​​the negative electrode active material 26X is controlled by a method other than drying conditions, it is sufficient to increase the BET specific surface area of ​​the negative electrode active material 26X in the third region A3, similar to curve 71 in graph 70.

[0094] [Pressure conditions] Returning to Figure 11, point P4 shown in Figure 11 represents the BET specific surface area of ​​the negative electrode active material 26X after the negative electrode mixture layer 26 has been pressed in step S2-3. When the negative electrode mixture layer 26 is pressed in step S2-3, the surface of the negative electrode active material 26X cracks, forming a new surface and increasing the BET specific surface area. At this time, the greater the amount of pressure applied to the negative electrode mixture layer 26, the greater the increase in the BET specific surface area of ​​the negative electrode active material 26X.

[0095] Therefore, for example, when the negative electrode mixture layer 26 is pressed in step S2-3, the negative electrode mixture layer 26 may be pressed such that the amount of pressure applied to the central region AC is greater than the amount of pressure applied to the end region AE. This makes it possible to make the BET specific surface area of ​​the negative electrode active material 26X in the central region AC greater than the BET specific surface area of ​​the negative electrode active material 26X in the end region AE.

[0096] [Control of pressure amount by the shape of the pressing roller] The pressing roller 200 shown in Figure 14 is an example of a device configuration for pressing the negative electrode mixture layer 26 such that the amount of pressure applied to the central region AC is greater than the amount of pressure applied to the end region AE. The central axis of the pressing roller 200 extends along the width direction D2 of the negative electrode plate 24. The axial size of the pressing roller 200 is configured to be approximately twice the width of the negative electrode mixture layer 26 in the state of the electrode body 20 shown in Figure 2.

[0097] The pressing roller 200 comprises three small-diameter sections 201 and two large-diameter sections 202. One small-diameter section 201 is located at each axial end and in the center of the pressing roller 200. The large-diameter sections 202 are located between the two small-diameter sections 201. One small-diameter section 201 is located at each of the two first regions A1 and second regions A2 when the pressing surface of the pressing roller 200 faces the negative electrode mixture layer 26. One large-diameter section 202 is located at each of the two third regions A3.

[0098] The large-diameter portion 202 is the part of the pressing roller 200 that has a larger diameter than the small-diameter portion 201. For example, the pressing roller 200 may have a single curved surface formed by the small-diameter portion 201 and the large-diameter portion 202, but there may also be a step between the small-diameter portion 201 and the large-diameter portion 202.

[0099] The pressing roller 200 presses the first region A1 and the second region A2 with its small-diameter portion 201, and presses the third region A3 with its large-diameter portion 202. Therefore, the difference in diameter between the small-diameter portion 201 and the large-diameter portion 202 makes it possible to increase the amount of pressure applied to the central region AC compared to the amount of pressure applied to the end region AE.

[0100] [Control of pressure amount based on weight] As an example of a method for controlling the amount of pressure applied to the negative electrode mixture layer 26, the negative electrode mixture paste may be applied such that the basis weight of the portion of the negative electrode mixture paste corresponding to the central region AC is greater than the basis weight of the portion of the negative electrode mixture paste corresponding to the edge region AE. This allows, for example, if the required thickness of the edge region AE and the central region AC of the negative electrode mixture layer 26 are the same, the difference in basis weight between the edge region AE and the central region AC to make the pressure applied to the central region AC greater than that applied to the edge region AE.

[0101] The coating apparatus 300 shown in Figure 15 is an example of an apparatus configuration for coating a negative electrode mixture paste such that the basis weight in the portion corresponding to the central region AC is greater than the basis weight in the portion corresponding to the edge region AE. The coating apparatus 300 is equipped with a discharge port 301 for dispensing the negative electrode mixture paste toward the negative electrode substrate 25. The discharge port 301 extends along the width direction D2 with the discharge port 301 facing the negative electrode substrate 25. The longitudinal size of the discharge port 301 is configured to be approximately twice the width of the negative electrode mixture layer 26 in the state of the electrode body 20 shown in Figure 2.

[0102] The discharge port 301 comprises three narrow sections 302 and two widening sections 303. The narrow sections 302 are located one at each longitudinal end and in the center of the discharge port 301. The widening sections 303 are located between the two narrow sections 302. With the discharge port 301 facing the negative electrode substrate 25, one narrow section 302 is located at each of the two first regions A1 and second regions A2. One widening section 303 is located at each of the two third regions A3.

[0103] The widened section 303 is the part where the opening width perpendicular to the longitudinal direction of the discharge port 301 is larger than that of the narrowed section 302. That is, the amount of negative electrode mixture paste discharged from the widened section 303 per unit time is greater than the amount of negative electrode mixture paste discharged from the narrowed section 302 per unit time. Therefore, by coating the negative electrode mixture paste using such a coating apparatus 300, the negative electrode mixture paste can be coated such that the basis weight in the part corresponding to the central region AC is greater than the basis weight in the part corresponding to the end region AE.

[0104] [Control of pressure amount based on the solid content ratio of the diluted negative electrode mixture paste] One example of a method for controlling the amount of pressure applied to the negative electrode mixture layer 26 is to use a first negative electrode mixture paste as a precursor for the portion constituting the edge region AE in the negative electrode mixture layer 26, and a second negative electrode mixture paste as a precursor for the portion constituting the central region AC. In this case, the second negative electrode mixture paste may be diluted such that the solid content ratio after dilution in step S1-3 is higher for the second negative electrode mixture paste than for the first negative electrode mixture paste.

[0105] When the basis weight of the first anode mixture paste and the second anode mixture paste are the same, the central region AC, which has a higher solid content in the diluted second anode mixture paste, tends to have a larger thickness before being pressed. As a result, for example, if the required thickness is the same for the edge region AE and the central region AC in the anode mixture layer 26, the difference in thickness before pressing between the edge region AE and the central region AC allows the amount of pressure applied to the central region AC to be greater than that applied to the edge region AE.

[0106] [Control of pressing amount by tap density of raw materials] One example of a method for controlling the amount of pressure applied to the negative electrode mixture layer 26 is to use a first negative electrode mixture paste as a precursor for the portion constituting the end region AE in the negative electrode mixture layer 26, and a second negative electrode mixture paste as a precursor for the portion constituting the central region AC. In this case, a negative electrode active material 26X with a lower tap density than the negative electrode active material 26X used as the raw material for the first negative electrode mixture paste may be used as the raw material for the second negative electrode mixture paste.

[0107] When the basis weight of the first anode mixture paste and the second anode mixture paste are the same, the central region AC, which contains the anode active material 26X with a lower tap density, tends to have a greater thickness before pressing than the edge region AE. As a result, for example, if the required thickness is the same for the edge region AE and the central region AC in the anode mixture layer 26, the difference in thickness before pressing between the edge region AE and the central region AC allows the pressing amount of the central region AC to be greater than that of the edge region AE.

[0108] Furthermore, the method for controlling the BET specific surface area of ​​the negative electrode active material 26X described above may be a single method or a combination of multiple methods. Also, when the pressing amount of the central region AC is to be greater than the pressing amount of the end region AE as a method for controlling the BET specific surface area of ​​the negative electrode active material 26X, one of the pressing amount control methods described above may be a single method or a combination of multiple methods.

[0109] [Effects of the Embodiment] According to the above embodiment, the following effects can be obtained. (1) By making the BET specific surface area of ​​the negative electrode active material 26X in the central region AC larger than the BET specific surface area of ​​the negative electrode active material 26X in the edge region AE, the resistance difference due to the difference in the amount of NaBOB coating between the edge region AE and the central region AC can be reduced.

[0110] (2) In the manufacturing method of steps S2-1 to S2-4, the first region A1 and the second region A2, where the negative electrode mixture layer 26 is formed, correspond to the end region AE in the state after the negative electrode substrate 25 has been cut. Also, the third region A3, where the negative electrode mixture layer 26 is formed, corresponds to the central region AC in the state after the negative electrode substrate 25 has been cut. Therefore, by cutting in the center of the width direction D2 with a larger BET specific surface area of ​​the negative electrode active material 26X in the third region A3 compared to the first region A1 and the second region A2, two negative electrode plates 24 can be manufactured at once.

[0111] (3) By making the drying rate of the portion of the negative electrode mixture paste corresponding to the central region AC slower than the drying rate of the portion corresponding to the edge region AE, migration of the negative electrode binder 26Y is suppressed in the central region AC compared to the edge region AE. As a result, the BET specific surface area of ​​the negative electrode active material 26X in the central region AC can be made larger than the BET specific surface area of ​​the negative electrode active material 26X in the edge region AE. In this case, the same negative electrode mixture paste can be used for both the portion corresponding to the edge region AE and the portion corresponding to the central region AC, thus reducing manufacturing costs.

[0112] (4) In the negative electrode mixture layer 26, a first negative electrode mixture paste is used as a precursor for the portion constituting the edge region AE, and a second negative electrode mixture paste is used as a precursor for the portion constituting the central region AC. By using a negative electrode active material 26X, which has a larger BET specific surface area than the raw material for the first negative electrode mixture paste, as the raw material for the second negative electrode mixture paste, the BET specific surface area of ​​the negative electrode active material 26X in the central region AC can be increased compared to the edge region AE.

[0113] (5) In the anode mixture layer 26, a first anode mixture paste is used as a precursor for the portion constituting the edge region AE, and a second anode mixture paste is used as a precursor for the portion constituting the central region AC. By making the solid content ratio when the second anode mixture paste is kneaded lower than the solid content ratio when the first anode mixture paste is kneaded, the BET specific surface area of ​​the anode active material 26X in the central region AC can be increased compared to the edge region AE.

[0114] (6) By making the amount of pressure applied to the central region AC greater than the amount of pressure applied to the end region AE, the BET specific surface area of ​​the negative electrode active material 26X in the central region AC can be increased compared to the end region AE.

[0115] (7) By making the basis weight of the portion of the negative electrode mixture paste corresponding to the central region AC greater than the basis weight of the portion of the negative electrode mixture paste corresponding to the end region AE, the amount of pressure applied to the central region AC can be made greater than the amount of pressure applied to the end region AE. In this case, the same negative electrode mixture paste can be used for both the portion of the negative electrode mixture paste corresponding to the end region AE and the portion of the negative electrode mixture paste corresponding to the central region AC, thus reducing manufacturing costs.

[0116] (8) In the negative electrode mixture layer 26, a first negative electrode mixture paste is used as a precursor for the portion constituting the end region AE, and a second negative electrode mixture paste is used as a precursor for the portion constituting the central region AC. By diluting the second negative electrode mixture paste so that its solid content is higher than that of the first negative electrode mixture paste after dilution, the amount of pressure applied to the central region AC can be made greater than the amount of pressure applied to the end region AE.

[0117] (9) In the negative electrode mixture layer 26, a first negative electrode mixture paste is used as a precursor for the portion constituting the end region AE, and a second negative electrode mixture paste is used as a precursor for the portion constituting the central region AC. By using a negative electrode active material 26X with a lower tap density than the raw material for the first negative electrode mixture paste as the raw material for the second negative electrode mixture paste, the amount of pressure applied to the central region AC can be made greater than the amount of pressure applied to the end region AE.

[0118] [Example of changes] The above embodiment can be implemented with the following modifications. Furthermore, the following modifications can be combined to the extent that they do not contradict the technical standards.

[0119] The tap density of the negative electrode active material 26X used as a raw material for the second negative electrode mixture paste may be the same as, or higher than, the tap density of the negative electrode active material 26X used as a raw material for the first negative electrode mixture paste. In this case, the BET specific surface area of ​​the negative electrode active material 26X can be configured by other means to be larger in the central region AC compared to the edge region AE.

[0120] The solid content of the second anode mixture paste after dilution may be the same as or lower than the solid content of the first anode mixture paste after dilution. In this case, the BET specific surface area of ​​the anode active material 26X in the central region AC may be larger than that in the edge region AE by other means.

[0121] The basis weight of the portion of the negative electrode mixture paste corresponding to the central region AC may be the same as, or smaller than, the basis weight of the portion of the negative electrode mixture paste corresponding to the end region AE. In this case, the BET specific surface area of ​​the negative electrode active material 26X in the central region AC may be larger than that in the end region AE by other means.

[0122] The amount of pressure applied to the central region AC may be the same as or less than the amount of pressure applied to the end region AE. In this case, the BET specific surface area of ​​the negative electrode active material 26X in the central region AC may be larger than that in the end region AE by other means.

[0123] The solid content when kneading the second anode mixture paste may be higher than or the same as the solid content when kneading the first anode mixture paste. In this case, the BET specific surface area of ​​the anode active material 26X in the central region AC may be larger than that in the edge region AE by other means.

[0124] The BET specific surface area of ​​the negative electrode active material 26X used as a raw material for the second negative electrode mixture paste may be the same as, or smaller than, the BET specific surface area of ​​the negative electrode active material 26X used as a raw material for the first negative electrode mixture paste. In this case, the BET specific surface area of ​​the negative electrode active material 26X can be configured by other means to be larger in the central region AC compared to the edge region AE.

[0125] The drying rate of the portion of the negative electrode mixture paste corresponding to the central region AC may be the same as, or faster than, the drying rate of the portion corresponding to the edge region AE. In this case, the central region AC may be configured by other means to have a larger BET specific surface area of ​​the negative electrode active material 26X compared to the edge region AE.

[0126] The method for controlling the drying rate of the negative electrode mixture paste is not limited to changing the airflow rate of the drying air W. For example, the drying rate of the negative electrode mixture paste may be controlled by making the temperature of the drying air W corresponding to the central region AC of the negative electrode mixture paste lower than the temperature of the drying air W corresponding to the edge region AE of the negative electrode mixture paste.

[0127] Although a method for manufacturing two negative electrode plates 24 at once has been illustrated, the negative electrode plates 24 may also be manufactured one at a time. In this case as well, the configuration should be such that the BET specific surface area of ​​the negative electrode active material 26X is larger in the central region AC compared to the edge region AE.

[0128] The film-forming agent contained in the non-aqueous electrolyte may be anything other than LiBOB, as long as it contains a lithium salt, or it may contain components other than LiBOB. The electrode body 20 may not be a wound body, but rather a laminate in which a rectangular positive electrode plate 21 and a rectangular negative electrode plate 24 are stacked with a separator 27 in between, and housed in the case 11.

[0129] The lithium-ion secondary battery 10 may be any other non-aqueous secondary battery, such as a nickel-metal hydride battery. The lithium-ion secondary battery 10 may be installed in automated transport machines, special vehicles for cargo handling, electric vehicles, hybrid vehicles, etc., as well as in computers and other electronic devices, or it may constitute a system other than those mentioned above. For example, it may be installed in mobile objects such as ships and aircraft, or it may be part of a power supply system that supplies electricity from a power plant to buildings and homes where the secondary battery is installed via a substation or the like. [Explanation of Symbols]

[0130] AC…Central area AE…Edge area A1…First area A2…Second area A3…Third area D2…Width direction W... Dry air 10…Lithium-ion rechargeable battery 20...Electrode body 21…Positive plate 22…Positive electrode substrate 23…Positive electrode mixture layer 24... Negative plate 25…Negative electrode substrate 26... Negative electrode mixture layer 26X…Negative electrode active material 26Y... Negative electrode binder 27... Separator

Claims

1. The electrode body comprises a positive electrode plate and a negative electrode plate stacked with a separator in between, and a non-aqueous electrolyte containing a film-forming agent containing a lithium salt. The negative electrode plate comprises a negative electrode substrate and a negative electrode mixture layer coated on the negative electrode substrate. The negative electrode mixture layer comprises a negative electrode active material and an additive containing a sodium salt. The negative electrode mixture layer comprises end regions including each end in the width direction, and a central region located between the two end regions. The central region is adjacent to each of the two end regions, The width of the end region is 20% to 40% of the total width of the negative electrode mixture layer in the width direction. The width of the central region is 20% to 60% of the total width of the negative electrode mixture layer in the width direction. The BET specific surface area of ​​the negative electrode active material in the central region is greater than the BET specific surface area of ​​the negative electrode active material in the end region. The maximum BET specific surface area of ​​the negative electrode active material in the central region is 1.02 times or more and 1.12 times or less than the minimum BET specific surface area of ​​the negative electrode active material in the end region. Non-aqueous secondary battery.

2. A method for manufacturing a non-aqueous secondary battery comprising an electrode body in which a positive electrode plate and a negative electrode plate are stacked with a separator in between, and a non-aqueous electrolyte containing a film-forming agent containing a lithium salt, The process includes manufacturing the negative electrode plate by coating a negative electrode substrate with a negative electrode mixture layer containing a negative electrode active material and an additive containing a sodium salt, The negative electrode mixture layer comprises end regions including each end in the width direction, and a central region located between the two end regions. The central region is adjacent to each of the two end regions, The width of the end region is 20% to 40% of the total width of the negative electrode mixture layer in the width direction. The width of the central region is 20% to 60% of the total width of the negative electrode mixture layer in the width direction. In the process of manufacturing the negative electrode plate, the negative electrode mixture layer is formed such that the BET specific surface area of ​​the negative electrode active material in the central region is greater than the BET specific surface area of ​​the negative electrode active material in the end regions, and the maximum value of the BET specific surface area of ​​the negative electrode active material in the central region is 1.02 times or more and 1.12 times or less than the minimum value of the BET specific surface area of ​​the negative electrode active material in the end regions. A method for manufacturing a non-aqueous secondary battery.

3. The step of forming the negative electrode mixture layer involves forming uncoated portions at both ends of the negative electrode substrate in which the negative electrode substrate is exposed, and forming the negative electrode mixture layer in which the BET specific surface area of ​​the negative electrode active material in the third region is greater than the BET specific surface area of ​​the negative electrode active material in the first and second regions, in which the BET specific surface area of ​​the negative electrode active material in the third region is greater than the BET specific surface area of ​​the negative electrode active material in the first and second regions, in which the negative electrode mixture layer is formed in which the BET specific surface area of ​​the negative electrode active material in the third region is greater than the BET specific surface area of ​​the negative electrode active material in the first and second regions. The process for manufacturing the negative electrode plate includes a step of cutting the negative electrode substrate on which the negative electrode mixture layer is formed in the center in the width direction to divide the second region into two parts. A method for manufacturing a non-aqueous secondary battery according to claim 2.

4. The step of forming the negative electrode mixture layer includes the steps of coating the negative electrode substrate with a negative electrode mixture paste that will serve as a precursor to the negative electrode mixture layer, and drying the negative electrode mixture paste. In the process of drying the negative electrode mixture paste, the drying rate of the portion of the negative electrode mixture paste corresponding to the central region is set to be slower than the drying rate of the portion of the negative electrode mixture paste corresponding to the edge region. A method for manufacturing a non-aqueous secondary battery according to claim 2 or 3.

5. The step of forming the negative electrode mixture layer includes the steps of coating the negative electrode substrate with a first negative electrode mixture paste which is a precursor for the portion constituting the end region of the negative electrode mixture layer, and a second negative electrode mixture paste which is a precursor for the portion constituting the central region of the negative electrode mixture layer, and drying the first negative electrode mixture paste and the second negative electrode mixture paste. As a raw material for the second anode mixture paste, a negative electrode active material with a larger BET specific surface area than the negative electrode active material used as a raw material for the first anode mixture paste is used. A method for manufacturing a non-aqueous secondary battery according to claim 2 or 3.

6. The step of forming the negative electrode mixture layer is, A step of kneading a first negative electrode mixture paste containing the raw materials for the portion constituting the end region of the negative electrode mixture layer, and a step of diluting the kneaded first negative electrode mixture paste. A step of kneading a second negative electrode mixture paste containing the raw materials for the portion constituting the central region of the negative electrode mixture layer, and a step of diluting the kneaded second negative electrode mixture paste. The process includes the steps of applying the first negative electrode mixture paste and the second negative electrode mixture paste to the negative electrode substrate, and drying the first negative electrode mixture paste and the second negative electrode mixture paste, The solid content of the second negative electrode mixture paste in the process of kneading the second negative electrode mixture paste is lower than the solid content of the first negative electrode mixture paste in the process of kneading the first negative electrode mixture paste. A method for manufacturing a non-aqueous secondary battery according to claim 2 or 3.

7. The step of forming the negative electrode mixture layer includes a step of pressing the negative electrode mixture layer to adjust the thickness of the negative electrode mixture layer, The amount of pressure applied to the central region is greater than the amount of pressure applied to the end regions. A method for manufacturing a non-aqueous secondary battery according to claim 2 or 3.

8. The step of forming the negative electrode mixture layer includes the steps of coating the negative electrode mixture paste onto the negative electrode substrate and drying the negative electrode mixture paste. In the step of coating the negative electrode mixture layer onto the negative electrode substrate, the basis weight of the portion of the negative electrode mixture paste corresponding to the central region is made larger than the basis weight of the portion of the negative electrode mixture paste corresponding to the edge region. A method for manufacturing a non-aqueous secondary battery according to claim 7.

9. The step of forming the negative electrode mixture layer is, A step of kneading a first negative electrode mixture paste containing the raw materials for the portion constituting the end region of the negative electrode mixture layer, and a step of diluting the kneaded first negative electrode mixture paste. A step of kneading a second negative electrode mixture paste containing the raw materials for the portion constituting the central region of the negative electrode mixture layer, and a step of diluting the kneaded second negative electrode mixture paste. A step of applying the first negative electrode mixture paste and the second negative electrode mixture paste to the negative electrode substrate, The process includes drying the first negative electrode mixture paste and the second negative electrode mixture paste, In the step of diluting the second negative electrode mixture paste, the solid content of the second negative electrode mixture paste is made higher than the solid content of the first negative electrode mixture paste after dilution. A method for manufacturing a non-aqueous secondary battery according to claim 7.

10. The step of forming the negative electrode mixture layer is, A step of coating the negative electrode substrate with a first negative electrode mixture paste which serves as a precursor for the portion constituting the end region of the negative electrode mixture layer, and a second negative electrode mixture paste which serves as a precursor for the portion constituting the central region of the negative electrode mixture layer. The process includes drying the first negative electrode mixture paste and the second negative electrode mixture paste, As a raw material for the second anode mixture paste, a negative electrode active material with a lower tap density than the negative electrode active material used as a raw material for the first anode mixture paste is used. A method for manufacturing a non-aqueous secondary battery according to claim 7.

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