Method for manufacturing electrode for secondary battery

Abstract

To form a suitable crack in an electrode.SOLUTION: A method includes a step of drying the electrode paste formed on the surface of a current collector, a step of firing the current collector at a temperature higher than that used for drying after the drying step, and a crack-providing step of bending the current collector along a roller surface with the surface on which the electrode paste is formed facing outward after the firing step.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] In the manufacturing process of secondary batteries such as lithium-ion secondary batteries, a negative electrode paste containing a negative electrode active material and a positive electrode paste containing a positive electrode active material are prepared, and the negative electrode and positive electrode are manufactured by applying the pastes to a negative electrode current collector foil and a positive electrode current collector foil, etc. Patent Document 1 describes a method of manufacturing a paste by mixing an active material and a dispersant to prepare a powder mixture, adding water as a dispersion medium to the powder mixture, and kneading the mixture (coarse kneading step, hard kneading step).

[0003] Patent Document 2 discloses that in order to manufacture an electrode that does not break, a large number of cracks are formed by bending an electrode in which a composite layer is formed on a metal foil. According to Patent Document 2, if the electrode has cracks formed in advance, it is possible to prevent the metal foil from breaking when the electrode is wound around a shaft.

[0004] Furthermore, Patent Document 3 discloses a nickel-metal hydride secondary battery in which a composite material containing hydrogen storage alloy powder is applied to the surface of a nickel plate, which is then rolled up and housed in a battery can. In Patent Document 3, cracks extending in a direction perpendicular to the rolling direction are formed at predetermined intervals along the rolling direction in the composite material layer containing the hydrogen storage alloy powder. This is said to make it easy to roll the nickel plate on which the composite material layer is formed.

[0005] Furthermore, Patent Document 4 discloses an electrode having a plurality of cracks and a method for manufacturing the same. In Patent Document 4, an additive is added to an electrode slurry, and the additive evaporates in a drying process, thereby forming a plurality of cracks in the electrode. Furthermore, Patent Document 5 discloses an electrode plate having cracks caused by drying. Patent Document 5 states that the cracks can be formed by controlling the drying rate of the electrode slurry applied to the current collector. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-257653 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-294512 [Patent Document 3] Japanese Patent Application Publication No. 5-41209 [Patent Document 4] Japanese Patent Application Publication No. 2023-178250 [Patent Document 5] Japanese Patent Application Laid-Open No. 2012-248477 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the conventional techniques, it is difficult to form appropriate cracks in the electrodes, and a method for forming the desired cracks has been sought. In view of the above-mentioned circumstances, the present disclosure aims to provide a method for manufacturing a secondary battery electrode that can form appropriate cracks in the electrode. [Means for solving the problem]

[0008] The present disclosure, which achieves the above-mentioned objectives, includes the following. <1> a step of drying the electrode paste formed on the surface of the current collector; After the drying step, a step of firing at a temperature higher than that during drying; a step of bending the current collector along a roller surface with the surface on which the electrode paste is formed facing outward after the firing step; A method for manufacturing an electrode for a secondary battery, comprising: <2> In the baking step, the baking temperature and baking time are set to satisfy the following relational expression when the baking temperature is X (°C) and the baking time is Y (minutes): <1> A method for manufacturing an electrode for the secondary battery according to claim 1. [Formula]Y≧-8X+1220 100≦X≦150 <3> In the bending step, a roller with a roll diameter of 40 mm or more is used. <1> or <2> A method for manufacturing an electrode for the secondary battery according to claim 1. <4> The thickness of the electrode paste formed on the current collector is 150 μm or more and 500 μm or less. <1> ~ <3> 10. A method for manufacturing an electrode for a secondary battery according to claim 9. <5> In the bending step, cracks are formed to a depth of 10% or more of the thickness of the electrode paste formed on the current collector, but not to a depth that reaches the current collector. <1> ~ <4> 10. A method for manufacturing an electrode for a secondary battery according to claim 9. [Effects of the Invention]

[0009] According to the method for manufacturing an electrode for a secondary battery of the present disclosure, it is possible to form appropriate cracks in the electrode. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 10 is a characteristic diagram showing the relationship between the baking temperature and the baking time in the baking steps performed in Examples and Comparative Examples. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present disclosure will be described. The description is for illustrating the embodiments and is not intended to limit the scope of the present disclosure.

[0012] In this specification, a numerical range indicated using "to" indicates a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the present specification, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range. In addition, in the present specification, the upper or lower limit of a numerical range may be replaced with a value shown in the examples.

[0013] In this specification, the term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved.

[0014] In this specification, when an embodiment is described with reference to drawings, the configuration of the embodiment is not limited to the configuration shown in the drawings. Furthermore, the sizes of components in each drawing are conceptual, and the relative size relationships between components are not limited to these.

[0015] In this specification, each component may contain a plurality of corresponding substances. When referring to the amount of each component in the composition in this embodiment, if a plurality of substances corresponding to each component are present in the composition, the amount refers to the total amount of the plurality of substances present in the composition unless otherwise specified.

[0016] The method for manufacturing a secondary battery electrode according to the present disclosure (hereinafter simply referred to as the manufacturing method) includes the steps of drying an electrode paste formed on a current collector surface (hereinafter referred to as the drying step), baking the current collector at a temperature higher than that used for drying (hereinafter referred to as the baking step), and bending the current collector along a roller surface with the electrode paste surface facing outward after the baking step (hereinafter referred to as the cracking step). According to the manufacturing method of the present disclosure, by bending the current collector along a roller surface with the electrode paste surface facing outward after the baking step, appropriate cracks can be formed in the active material layer. The manufactured electrode has appropriate cracks formed in the active material layer, allowing the electrolyte to sufficiently penetrate the active material layer. Therefore, the electrode obtained by the manufacturing method of the present disclosure can be used, for example, as an optimal electrode for a high-capacity secondary battery with an increased active material layer thickness. The manufacturing method of the present disclosure can be applied to both positive and negative electrodes of secondary batteries.

[0017] In the manufacturing method of the present disclosure, prior to the drying step, a negative electrode paste containing a negative electrode active material and a negative electrode current collector, and a positive electrode paste containing a positive electrode active material and a positive electrode current collector are prepared, and the negative electrode paste and positive electrode paste are applied to the negative electrode current collector and the positive electrode current collector, respectively. Note that in this disclosure, the negative electrode current collector and the positive electrode current collector are collectively referred to as "current collectors," and the negative electrode paste and the positive electrode paste are collectively referred to as "electrode paste." The method for applying the electrode paste to the current collector is not particularly limited, and examples include roll coating, metal mask printing, electrostatic coating, dip coating, spray coating, doctor blade coating, gravure coating, and screen printing.

[0018] <Negative electrode active material> The negative electrode active material is not particularly limited, and conventionally known materials can be used as appropriate. Examples of the negative electrode active material include carbon materials. Examples of carbon materials include cokes such as petroleum coke, pitch coke, and coal coke; carbon blacks such as carbides of organic compounds, carbon fiber, and acetylene black; and graphites such as artificial graphite and natural graphite. Other examples of the negative electrode active material include conductive polymers, lithium titanate, silicon, and silicon compounds. The above-mentioned materials may be used alone or in combination as the negative electrode active material.

[0019] The average particle size of the negative electrode active material is not particularly limited and can be, for example, 1 μm to 100 μm, 5 μm to 80 μm, 10 μm to 50 μm, 10 μm to 30 μm, 10 μm to 25 μm, or 10 μm to 20 μm. The average particle size is a value measured by a standard method using a laser diffraction particle size distribution analyzer.

[0020] <Negative electrode paste> The negative electrode paste is a slurry-like substance containing the negative electrode active material, and also contains a binder, a solvent, and other components in addition to the negative electrode active material.

[0021] The binder is not particularly limited, and binders conventionally used in preparing negative electrode pastes can be used. Examples of binders include butadiene rubber (BR), butylene rubber (IIR), acrylate butadiene rubber (ABR), styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVdF), and polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP).

[0022] The solvent is not particularly limited, and any solvent that has been conventionally used in preparing a negative electrode paste can be used, including, but not limited to, 1,2,3,4-tetrahydronaphthalene, butyl acetate, butyl butyrate, mesitylene, tetralin, heptane, and N-methyl-2-pyrrolidone (NMP).

[0023] Other components include thickeners and conductive aids. Examples of thickeners include carboxymethyl cellulose and sodium salt of carboxymethyl cellulose. Examples of conductive aids include carbon black (acetylene black, thermal black, furnace black, etc.), conductive oxides, and conductive nitrides.

[0024] The negative electrode paste can be prepared, for example, by stirring and kneading the components such as the above-mentioned negative electrode active material using a stirrer, ball mill, super sand mill, pressure kneader, or the like, and further adjusting the viscosity as necessary.

[0025] <Negative electrode current collector> The negative electrode current collector is not particularly limited, and any negative electrode current collector conventionally used in producing negative electrodes can be used. The material of the negative electrode current collector is not particularly limited, and examples thereof include Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, and stainless steel. The thickness of the negative electrode current collector is not particularly limited, and can be, for example, in the range of 0.1 μm to 1 mm. The negative electrode current collector can also be in the form of a strip, such as a foil, a perforated foil, or a mesh.

[0026] <Cathode active material> The positive electrode active material is not particularly limited, and conventionally known materials can be used as appropriate. Examples of the positive electrode active material include LiCoO2, LiNiO2, LiMnO2, LiMn2O4, Li(NiCoMn)O2, Li(NiCoAl)O2, and LiFePO4. Note that "(NiCoMn)" in "Li(NiCoMn)O2" indicates that the sum of the composition ratios in parentheses is 1. As long as the sum is 1, the amount of each component is arbitrary. Furthermore, as the positive electrode active material, Li(NiCoMn)O2 can be, for example, Li(Ni 1 / 3 Co 1 / 3 Mn 1 / 3 )O2, Li(Ni 0.5 Co 0.2 Mn 0.3 )O2, Li(Ni 0.8 Co 0.1 Mn 0.1 )O2, etc. The positive electrode active material particles may be Hi-Nickel (a positive electrode active material with a high Ni ratio) or a ternary positive electrode active material.

[0027] <Positive electrode paste> The positive electrode paste is a slurry-like substance containing the positive electrode active material. The positive electrode paste also contains a binder, a solvent, and other components in addition to the positive electrode active material. The binder, solvent, and other components can be the same as those described for the negative electrode paste.

[0028] <Positive electrode current collector> The positive electrode current collector is not particularly limited and may be in the form of a foil, plate, mesh, punched metal, or foam. Examples of metals constituting the positive electrode current collector include Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, and stainless steel. In particular, the positive electrode current collector may contain Al from the viewpoint of ensuring oxidation resistance.

[0029] [Drying process] In the manufacturing method of the present disclosure, the electrode paste formed on the current collector is dried in a drying step. Specifically, the temperature conditions for the drying step can be, for example, 50°C to 150°C, preferably 80°C to 120°C, and more preferably 90°C to 110°C. The drying time can be any time, but should be set longer when the drying temperature is low and shorter when the drying temperature is high. Specifically, the drying temperature and drying time can be, for example, 12 minutes at 50°C, 6 minutes at 80°C, 3 minutes at 100°C, and 1 minute at 150°C.

[0030] [Baking process] Next, in the method of the present disclosure, a baking step is performed in which the electrode paste is baked at a temperature higher than that in the drying step. By baking at a temperature higher than that in the drying step, it is possible to create a state in which appropriate cracks are likely to be formed in the active material layer in the cracking step, which will be described in detail later.

[0031] The baking temperature in the baking step is not particularly limited as long as it is higher than the treatment temperature in the drying step described above, but is preferably in the range of 100° C. to 150° C., and more preferably in the range of 120° C. to 140° C. The baking time in the baking step is not particularly limited and can be any time, but should be set longer when the baking temperature is low and shorter when the baking temperature is high. For example, the baking time can be 10 minutes to 1440 minutes, preferably 30 minutes to 1440 minutes, more preferably 60 minutes to 1440 minutes, even more preferably 90 minutes to 1440 minutes, even more preferably 100 minutes to 1440 minutes, even more preferably 120 minutes to 1440 minutes, even more preferably 150 minutes to 1440 minutes, even more preferably 180 minutes to 1440 minutes, even more preferably 200 minutes to 1440 minutes, even more preferably 260 minutes to 1440 minutes, even more preferably 280 minutes to 1440 minutes, even more preferably 420 minutes to 1440 minutes. By specifying the baking temperature and baking time in the baking step as above, a state in which appropriate cracks are easily formed in the active material layer can be created in the crack imparting step, which will be described in detail later.

[0032] In particular, in the baking step of the manufacturing method of the present disclosure, when the baking temperature is X (° C.) and the baking time is Y (minutes), it is preferable to set the baking temperature and baking time to satisfy the following relational expression: [Formula]Y≧-8X+1220 In this formula, the value of X is 100≦X≦150. The value of X is preferably 110≦X≦150, and more preferably 120≦X≦150. The upper limit of the range of Y is not particularly limited, but from the viewpoint of production efficiency, it can be set to 1440 minutes or less, and preferably 300 minutes or less. By specifying the baking temperature and baking time in the baking step to satisfy the relationship shown in [formula], appropriate cracks can be easily formed in the active material layer in the crack imparting step, which will be described in detail later.

[0033] In the manufacturing method of the present disclosure, the thickness of the electrode paste formed on the current collector after the baking step is not particularly limited, but can be, for example, 150 μm to 500 μm, preferably 200 μm to 500 μm, more preferably 250 μm to 500 μm, and even more preferably 300 μm to 500 μm. According to the manufacturing method of the present disclosure, even if the thickness of the electrode paste is within this range, appropriate cracks can be formed in the active material layer in the crack imparting step, which will be described in detail below.

[0034] [Cracking process] In the manufacturing method of the present disclosure, the cracking step is a step of bending the current collector along the roller surface after the baking step, with the surface on which the electrode paste is formed facing outward. The cracking step allows appropriate cracks to be formed in the active material layer formed by drying the electrode paste formed on the current collector and then firing the current collector. Specifically, by wrapping the current collector around a roller at a predetermined wrap angle and transporting the current collector on the roller surface, cracks can be formed sequentially in the active material layer formed on the current collector.

[0035] In the cracking step, there are no limitations on the roller surface as long as appropriate cracks can be formed in the active material layer, but it is preferable to use a roller with a roll diameter of 40 mm or more. If a roller with a roll diameter of less than 40 mm is used, the curvature of the current collector bent along the roller surface becomes too large, and there is a risk that the cracks will extend beyond the active material layer and reach the current collector. In the cracking step, using a roller with a roll diameter of 40 mm or more allows appropriate cracks to be formed in the active material layer.

[0036] Here, in the manufacturing method of the present disclosure, appropriate cracks can be cracks that are 10% or more deep relative to the thickness of the electrode paste and do not reach the current collector. In particular, in the manufacturing method of the present disclosure, the cracks are preferably 30% or more deep relative to the thickness of the electrode paste, more preferably 50% or more deep, even more preferably 70% or more deep, and even more preferably 90% or more deep. When the crack depth is within the above range, so long as it does not reach the current collector, the electrolyte can penetrate more sufficiently.

[0037] [Secondary battery] According to the manufacturing method of the present disclosure described above, electrodes that can be used in so-called secondary batteries can be manufactured. The secondary battery can include electrodes (negative electrode and positive electrode) manufactured as described above and an electrolyte layer disposed between the positive electrode and the negative electrode. Here, the electrolyte layer of the secondary battery may contain a liquid electrolyte without a solid electrolyte, or may contain both a solid electrolyte and a liquid electrolyte. When the electrolyte layer contains a liquid electrolyte, it is preferable that the electrolyte layer has a separator for retaining the liquid electrolyte and preventing contact between the positive electrode and the negative electrode. Furthermore, when the electrolyte layer contains a solid electrolyte, the electrolyte layer may optionally contain a binder or the like in addition to the solid electrolyte.

[0038] The electrolyte is not particularly limited, and examples thereof include electrolytes used in non-aqueous electrolyte secondary batteries. For example, the electrolytic solution may be a so-called organic electrolytic solution obtained by dissolving a lithium salt such as an electrolyte LiClO4, LiPF6, LiAsF6, LiBF4, or LiSO3CF3 in a non-aqueous solvent such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, fluoroethylene carbonate, cyclopentanone, sulfolane, 3-methylsulfolane, 2,4-dimethylsulfolane, 3-methyl-1,3-oxazolidin-2-one, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, butyl methyl carbonate, ethyl propyl carbonate, butyl ethyl carbonate, dipropyl carbonate, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, methyl acetate, or ethyl acetate, either alone or as a mixture of two or more components.

[0039] The structure of the secondary battery is not particularly limited, and typically, a positive electrode, a negative electrode, and an optional separator are wound into a flat spiral to form a wound electrode assembly, or these are stacked as flat plates to form a stacked electrode assembly, and the electrode assembly is then sealed in an exterior case. The secondary battery of the present disclosure is not particularly limited, and is used as a paper-type battery, a button-type battery, a coin-type battery, a stacked battery, a cylindrical battery, a prismatic battery, etc.

[0040] The manufacturing method of the present disclosure can also be applied to the manufacture of electrodes that can be used in so-called bipolar secondary batteries. Bipolar secondary batteries have a configuration in which a negative electrode is formed on one surface of a current collector and a positive electrode is formed on the other surface. In this case, as described above, the negative electrode can be formed on one surface of the current collector by performing the drying step, baking step, and cracking step, and then the positive electrode can be formed on the other surface of the current collector by performing the drying step, baking step, and cracking step. However, whether the negative electrode or the positive electrode is formed first is not particularly limited and can be determined arbitrarily, but can also be determined taking into account the coating conditions of the negative electrode and the positive electrode, etc. [Example]

[0041] The present disclosure will be described in more detail below using examples, but the technical scope of the present disclosure is not limited to the following examples. [Example 1] In Example 1, an electrode paste was prepared as follows: 90 parts by mass of active material, 1 part by mass of dispersant (carboxymethyl cellulose), 5 parts by mass of binder (styrene butadiene rubber), and 4 parts by mass of conductive additive (carbon nanotubes) were kneaded in a planetary mixer to prepare a paste with a solid content (NV (Non-Volatile) value) of 60%. Next, the prepared electrode paste was applied to the surface of a 10 μm current collector (material: Cu) to a thickness of 450 μm, and then dried at 100° C. for 4 minutes. After drying under the above conditions, the electrode paste was baked at 120°C for 280 minutes. The current collector was then bent along the surface of a 40 mm diameter roller with the electrode paste facing outward (the current collector was bent at a 70° embrace angle with the roller), and a cracking step was performed. The current collector was transported in this state, and the active material layer formed by drying and firing the electrode paste was checked for cracks. The presence or absence of cracks was confirmed using a microscope.

[0042] [Example 2] The steps up to the cracking step were carried out in the same manner as in Example 1, except that the baking temperature in the baking step was 130° C. and the baking time was 200 minutes, and it was confirmed whether cracks had occurred in the active material layer.

[0043] [Example 3] The steps up to the cracking step were carried out in the same manner as in Example 1, except that the baking temperature in the baking step was 140° C. and the baking time was 120 minutes, and it was confirmed whether cracks had occurred in the active material layer.

[0044] [Comparative Example 1] The steps up to the cracking step were carried out in the same manner as in Example 1, except that the baking temperature in the baking step was 120° C. and the baking time was 250 minutes, and it was confirmed whether cracks had occurred in the active material layer.

[0045] Comparative Example 2 The steps up to the cracking step were carried out in the same manner as in Example 1, except that the baking temperature in the baking step was 130° C. and the baking time was 120 minutes, and it was confirmed whether cracks had occurred in the active material layer.

[0046] Comparative Example 3 The steps up to the cracking step were carried out in the same manner as in Example 1, except that the baking temperature in the baking step was 130° C. and the baking time was 150 minutes, and it was confirmed whether cracks had occurred in the active material layer.

[0047] Comparative Example 4 The steps up to the cracking step were carried out in the same manner as in Example 1, except that the baking temperature in the baking step was 140° C. and the baking time was 90 minutes, and it was confirmed whether cracks had occurred in the active material layer.

[0048] [result] In Examples 1 to 3, cracks were observed to have formed that were 10% or more deep relative to the thickness of the active material layer and did not reach the current collector. On the other hand, in Comparative Examples 1 to 4, cracks were not observed to have formed that were 10% or more deep relative to the thickness of the active material layer. The firing times and firing temperatures for Examples 1 to 3 and Comparative Examples 1 to 4 were plotted on a graph, and the results are shown in Figure 1.

[0049] As shown in FIG. 1, it was revealed that appropriate cracks can be formed in the active material layer when the firing temperature is X (°C) and the firing time is Y (minutes), and the firing temperature and firing time satisfy the following relationship: [Formula]Y≧-8X+1220 According to this formula, it can be understood that when the baking temperature is 100°C, the baking time should be 420 minutes or more, when the baking temperature is 120°C, the baking time should be 260 minutes or more, when the baking temperature is 130°C, the baking time should be 180 minutes or more, and when the baking temperature is 140°C, the baking time should be 100 minutes or more.

Claims

1. a step of drying the electrode paste formed on the surface of the current collector; After the drying step, a step of firing at a temperature higher than that during drying; a step of bending the current collector along a roller surface with the surface on which the electrode paste is formed facing outward after the firing step; A method for manufacturing an electrode for a secondary battery, comprising:

2. 2. The method for manufacturing a secondary battery electrode according to claim 1, wherein in the baking step, the baking temperature and the baking time satisfy the following relational expression, where X (°C) is the baking temperature and Y (minutes) is the baking time: [Formula] Y≧-8X+1220 100≦X≦150

3. The method for manufacturing a secondary battery electrode according to claim 1 , wherein a roller having a diameter of 40 mm or more is used in the bending step.

4. The method for manufacturing an electrode for a secondary battery according to claim 1 , wherein the thickness of the electrode paste formed on the current collector is 150 μm or more and 500 μm or less.

5. 2. The method for manufacturing an electrode for a secondary battery according to claim 1, wherein in the bending step, cracks are formed having a depth of 10% or more of a thickness of the electrode paste formed on the current collector and a depth that does not reach the current collector.

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