Method for manufacturing secondary battery electrode

Abstract

The present invention relates to a method for manufacturing a secondary battery electrode, comprising: drying an electrode paste formed on the surface of a current collector; after drying the electrode paste, firing the electrode paste at a higher temperature than during the drying; and after firing the electrode paste, bending the current collector around a roller surface such that the surface of the current collector on which the electrode paste is formed is disposed on the outside.

Description

Technical Field

[0001] This disclosure relates to a method for manufacturing a secondary battery electrode. 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 coating the respective pastes onto negative electrode current collector foils and positive electrode current collector foils. Japanese Patent Application Publication (JP-A) No. 2010-257653 describes a method for manufacturing a paste by mixing an active material and a dispersant together to produce a powder mixture, and then kneading the powder mixture (coarse kneading step, thick paste step) while adding water as a dispersion medium.

[0003] JP-A No. 2006-294512 discloses a method for creating a non-fracture electrode by bending an electrode formed by forming a composite material layer on a metal foil to create multiple cracks. The technology in JP-A No. 2006-294512 enables the metal foil to be prevented from breaking when the electrode is wound onto a shaft, provided that the electrode is pre-cracked.

[0004] Furthermore, JP-A No. H5-41209 discloses a nickel-metal hydride secondary battery in which a nickel plate is wound and housed within a battery can, wherein the surface of the nickel plate is coated with a composite material comprising hydrogen storage alloy powder. In the technology of JP-A No. H5-41209, cracks extending in a direction orthogonal to the winding direction are formed at specific intervals along the winding direction for the composite material layer containing the hydrogen storage alloy powder. This is therefore advantageous for winding the nickel plate to which the composite material layer is formed.

[0005] Furthermore, JP-A No. 2023-178250 discloses an electrode containing multiple cracks and a method for manufacturing the same. In JP-A No. 2023-178250, multiple cracks are formed in the electrode by adding an additive to an electrode slurry and evaporating the additive during a drying process. JP-A No. 2012-248477 also discloses an electrode plate containing cracks generated through drying. The technology in JP-A No. 2012-248477 enables crack formation by controlling the drying rate of the electrode slurry coated on the current collector. Summary of the Invention

[0006] However, it is difficult to form suitable cracks in the electrode using the techniques available to date, and a method for forming the desired cracks is required. In view of the above, the object of this disclosure is to provide a method for manufacturing a secondary battery electrode capable of forming suitable cracks in the electrode.

[0007] This disclosure achieves the above objectives and includes the following.

[0008] <1> A method for manufacturing a secondary battery electrode includes: drying an electrode paste formed on the surface of a current collector; firing the electrode paste at a higher temperature than during the drying process after drying; and bending the current collector around a roller surface after firing the electrode paste, such that the surface of the current collector on which the electrode paste is formed is positioned on the outside.

[0009] <2> According to the method for manufacturing a secondary battery electrode as described in item 1, when firing the electrode paste, the firing temperature and firing time satisfy the following formula:

[0010] Y≥-8X+1220

[0011] 100≤X≤150

[0012] In the formula, X is the firing temperature in degrees Celsius, and Y is the firing time in minutes.

[0013] <3> According to the method for manufacturing a secondary battery electrode as described in item 1, a roller with a diameter of 40 mm or more is used in the bending process.

[0014] <4> According to the method for manufacturing a secondary battery electrode as described in claim 1, the thickness of the electrode paste formed on the current collector is from 150 μm to 500 μm.

[0015] <5> According to the method for manufacturing a secondary battery electrode as described in claim 1, a crack is introduced during the bending process, the depth of which is more than 10% relative to the thickness of the electrode paste formed on the current collector, and the depth does not reach the current collector.

[0016] The method for manufacturing the secondary battery electrode disclosed herein enables the formation of appropriate cracks in the electrode. Attached Figure Description

[0017] Exemplary embodiments of this disclosure will be described in detail with reference to the following figures, wherein:

[0018] Figure 1 Characteristic graphs illustrating the relationship between firing temperature and firing time during the firing steps performed in the examples and comparative examples. Detailed Implementation

[0019] The following describes exemplary embodiments of the present disclosure. This description merely illustrates examples of exemplary embodiments and does not limit the scope of the present disclosure.

[0020] In this specification, a numerical range expressed using "to" represents a range that includes the numerical values before and after "to" as its minimum and maximum values, respectively.

[0021] For a numerical range expressed in a stepped manner in this specification, the upper limit value or the lower limit value of a numerical range can be replaced with the upper limit value or the lower limit value of another stepped numerical range. In addition, in the numerical ranges listed in this specification, the upper limit value or the lower limit value of the numerical range can be replaced with the value specified in the examples.

[0022] In this specification, the term "process" includes not only an independent process, but also cases where another process cannot be clearly distinguished from it, as long as the process achieves the intended purpose.

[0023] In this specification, when describing exemplary embodiments with reference to the drawings, the configuration of the exemplary embodiments is not limited to the configuration shown in the drawings. In addition, the dimensions of the components in the drawings are only schematic, and the relative relationships between the dimensions of the components are not limited thereto.

[0024] In this specification, each component can include various applicable materials. When referring to the amount of each component in the composition in this exemplary embodiment, when there are multiple eligible materials in each component of the composition, unless otherwise clearly stated, this refers to the total amount of the multiple materials present in the composition.

[0025] The method for manufacturing a secondary battery electrode according to the present disclosure (hereinafter simply referred to as the manufacturing method) includes: drying the electrode paste formed on the surface of the current collector (hereinafter referred to as the drying step); after drying the electrode paste, firing the electrode paste at a temperature higher than that during the drying period (hereinafter referred to as the firing step); and after firing the electrode paste, bending the current collector around the surface of the roller in such a manner that the surface of the current collector formed with the electrode paste is disposed on the outside (hereinafter referred to as the crack imparting step). The manufacturing method of the present disclosure can form appropriate cracks in the active material layer by bending the current collector around the surface of the roller while making the surface formed with the electrode paste on the outside after the firing step. The manufactured electrode has appropriate cracks formed in the active material layer, so that the electrolyte can sufficiently penetrate into the active material layer. This means that 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 having a thicker active material layer. It should be noted that the manufacturing method of the present disclosure is applicable to both the positive electrode and the negative electrode of the secondary battery.

[0026] In the manufacturing method of this disclosure, prior to the drying step, a negative electrode paste containing a negative electrode active material and a negative electrode current collector, as well as a positive electrode paste containing a positive electrode active material and a positive electrode current collector, are prepared. The negative electrode paste and the positive electrode paste are then coated onto the negative electrode current collector and the positive electrode current collector, respectively. It should be noted 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 pastes." There are no particular limitations on the method of coating the electrode pastes onto the current collectors; examples include roller coating, metal mask printing, electrostatic coating, mold coating, spraying, doctor blade coating, gravure coating, and screen printing.

[0027] Negative electrode active materials

[0028] There are no particular limitations on the negative electrode active material; any material known to date can be appropriately applied. Examples of negative electrode active materials include carbon materials. Examples of carbon materials include: coke, such as petroleum coke, pitch coke, and coal coke; carbon black, such as organic compound carbides, carbon fibers, or acetylene black; and graphite, such as artificial graphite or natural graphite. In addition, conductive polymers, lithium titanates, silicon, silicon compounds, etc., can also be used as negative electrode active materials. The above materials can be used alone as negative electrode active materials, or multiple of the above materials can be used in combination as negative electrode active materials.

[0029] The average particle size of the negative electrode active material is not particularly limited, for example, it can be 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, and 10 μm to 20 μm. It should be noted that the average particle size is a value determined using a laser refractive particle size analyzer by conventional methods.

[0030] Negative electrode paste

[0031] Anode paste is a slurry-like material containing anode active material. In addition to containing the anode active material, the anode paste also contains binders, solvents, and other components.

[0032] There are no particular restrictions on the adhesive; any adhesive used to date in the manufacture of negative electrode pastes may be used. Examples of such adhesives include butadiene rubber (BR), butyl rubber (IIR), acrylate-butadiene rubber (ABR), styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVdF), and poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) copolymers.

[0033] There are no particular restrictions on the solvent; solvents used to date in the manufacture of anode pastes can be used. Examples of solvents include, for instance, 1,2,3,4-tetrahydronaphthalene, butyl acetate, butyl butyrate, mesitylene, tetrahydronaphthalene, heptane, N-methyl-2-pyrrolidone (NMP), etc.

[0034] Examples of the other components include thickeners and conductivity enhancers. Examples of thickeners include carboxymethyl cellulose and sodium carboxymethyl cellulose. Examples of conductivity enhancers include carbon black (acetylene black, thermal cracking carbon black, furnace black, etc.), conductive oxides, and conductive nitrides.

[0035] The negative electrode paste can be prepared, for example, by mixing and kneading the above-mentioned negative electrode active material and other components using a mixer, ball mill, super mill, pressure kneader, etc., and adjusting the viscosity as needed.

[0036] Negative current collector

[0037] There are no particular limitations on the negative electrode current collector; any negative electrode current collector used to date in the manufacture of negative electrodes can be used. There are no particular limitations on the material of the negative electrode current collector; examples include Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, stainless steel, etc. There are no particular limitations on the thickness of the negative electrode current collector; for example, it can be in the range of 0.1 μm to 1 mm. Furthermore, the negative electrode current collector can be used in the form of a strip, such as a foil, a perforated foil, or a mesh.

[0038] Positive electrode active material

[0039] There are no particular limitations on the positive electrode active material; any material known to date can be used appropriately. Examples of such positive electrode active materials include LiCoO2, LiNiO2, LiMnO2, LiMn2O4, Li(NiCoMn)O2, Li(NiCoAl)O2, LiFePO4, etc. It should be noted that the "(NiCoMn)" in "Li(NiCoMn)O2" indicates that the total composition ratio of the components within the parentheses is 1. The amounts of each component can be freely chosen, as long as their total is 1. Furthermore, as a positive electrode active material, Li(NiCoMn)O2 may, for example, include 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 0.1O2, etc. It should be noted that the positive electrode active material particles can be high nickel (positive electrode active materials with a high Ni ratio) and can be ternary positive electrode materials (NMC (nickel, manganese and cobalt) positive electrode active materials).

[0040] Positive electrode paste

[0041] The positive electrode paste comprises a positive electrode active material and is a slurry-like material. In addition to the positive electrode active material, the positive electrode paste may also contain binders, solvents, and other components. It should be noted that the same binders, solvents, and other components described in the negative electrode paste can be used.

[0042] Positive current collector

[0043] The positive electrode current collector is not particularly limited and can be in the form of foil, plate, mesh, perforated 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, from the viewpoint of ensuring oxidation resistance, the positive electrode current collector can be a positive electrode current collector containing Al.

[0044] Drying steps

[0045] In the manufacturing method of this disclosure, during the drying step, the electrode formed on the current collector is dried with a paste. 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 arbitrary, and can 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.

[0046] Firing steps

[0047] Next, in the preparation method of this disclosure, a firing step is performed by firing the electrode paste at a temperature higher than that in the drying step. Firing at a temperature higher than that in the drying step can create a state that is conducive to the formation of appropriate cracks in the active material layer in the crack-inducing step, which will be detailed below.

[0048] There are no particular limitations on the firing step, as long as it is carried out at a firing temperature higher than that of the drying step described above, for example, preferably in the range of 100 to 150 degrees Celsius, and more preferably in the range of 120 to 140 degrees Celsius. Furthermore, there are no particular limitations on the firing time of the firing step, and it can be any time; it can be set longer when the firing temperature is low and shorter when the firing temperature is high. For example, the firing time can be from 10 minutes to 1440 minutes, preferably from 30 minutes to 1440 minutes, more preferably from 60 minutes to 1440 minutes, even more preferably from 90 minutes to 1440 minutes, further more preferably from 100 minutes to 1440 minutes, further more preferably from 120 minutes to 1440 minutes, further more preferably from 150 minutes to 1440 minutes, further more preferably from 180 minutes to 1440 minutes, further more preferably from 200 minutes to 1440 minutes, further more preferably from 260 minutes to 1440 minutes, further more preferably from 280 minutes to 1440 minutes, and even more preferably from 420 minutes to 1440 minutes. By limiting the firing temperature and firing time in the firing step as described above, a state conducive to the formation of appropriate cracks in the active material layer in the crack-inducing step, which will be detailed below, can be formed.

[0049] In particular, in the firing step of the preparation method of this disclosure, when firing the electrode paste, the firing temperature and firing time satisfy the following formula Y≥-8X+1220, where X is the firing temperature in degrees Celsius and Y is the firing time in minutes.

[0050] It should be noted that the value of X in the above formula is 100 ≤ X ≤ 150. The value of X is preferably 110 ≤ X ≤ 150, and more preferably 120 ≤ X ≤ 150. There is no particular upper limit to the range of Y, and from a productivity point of view, it can be 1440 minutes or less, and preferably 300 minutes or less. By limiting the firing temperature and firing time in the firing step to satisfy this relationship, a state conducive to the formation of appropriate cracks in the active material layer is achieved in the crack-inducing step, which is detailed below.

[0051] In the manufacturing method of this disclosure, the thickness of the electrode paste formed on the current collector after the firing step is not particularly limited, and can be, for example, 150 μm to 500 μm, and preferably 200 μm to 500 μm, more preferably 250 μm to 500 μm, and even more preferably 300 μm to 500 μm. In the preparation method of this disclosure, by setting the thickness of the electrode paste within these ranges, suitable cracks can be formed in the active material layer during the crack induction step, which is detailed below.

[0052] Crack induction steps

[0053] In the manufacturing method of this disclosure, the crack-introducing step is a step after the firing step in which the current collector is bent around the surface of a roller in such a way that the surface of the current collector on which the electrode paste is formed is disposed on its outer side. This crack-introducing step enables the formation of appropriate cracks in the active material layer constructed by drying and firing the electrode paste formed on the current collector. Specifically, by winding the current collector onto the roller at a specific wrap angle and transporting the current collector on the surface of the roller, cracks can be sequentially formed in the active material layer formed on the current collector.

[0054] In the crack induction step, there are no restrictions on the roller surface, as long as a suitable crack can be formed in the active material layer, and for example, a roller with a diameter of 40 mm or more is preferred. When a roller with a diameter less than 40 mm is used, the radius of curvature of the current collector bending around the roller surface is too large, raising concerns that the crack may extend beyond the active material layer and reach the current collector. Using a roller with a diameter of 40 mm or more in the crack induction step allows for the formation of a suitable crack in the active material layer.

[0055] In the manufacturing method of this disclosure, a suitable crack is defined as a crack depth that is 10% or more of the thickness of the electrode paste and does not reach the current collector. Specifically, in the manufacturing method of this disclosure, the crack depth is preferably 30% or more of the thickness of the electrode paste, more preferably 50% or more, even more preferably 70% or more, and even more preferably 90% or more. The amount of crack depth ensures that it does not reach the current collector, and by falling within the above-mentioned range, sufficient penetration of the electrolyte can be achieved.

[0056] Secondary batteries

[0057] The manufacturing method of this disclosure as described above can produce electrodes that can be used in so-called secondary batteries. Such a secondary battery can be configured to include electrodes (negative and positive electrodes) manufactured as described above, and an electrolyte layer disposed between the negative and positive electrodes. The electrolyte layer in such a secondary battery can be configured to include a liquid electrolyte instead of a solid electrolyte, or it can be configured to include both a solid and a liquid electrolyte. When the electrolyte layer includes a liquid electrolyte, it preferably includes a separator that retains the liquid electrolyte while preventing contact between the positive and negative electrodes. When the electrolyte layer includes a solid electrolyte, it may also include, in addition to the solid electrolyte, an optional binder or the like.

[0058] It should be noted that there are no particular limitations on the electrolyte, and examples can include electrolytes used in non-aqueous electrolyte secondary batteries. Examples of such electrolytes include, for example, so-called organic electrolytes, in which lithium salts such as LiClO4, LiPF6, LiAsF6, LiBF4, and LiSO3CF3 are dissolved in a non-aqueous solvent constructed by using ethylene carbonate, propylene carbonate, butyl carbonate, vinyl 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, and ethyl acetate, alone or as a mixture of two or more of these components.

[0059] There are no particular limitations on the structure of a secondary battery. Typically, the positive electrode, the negative electrode, and the separator, which may be provided as needed, are wound into a flat spiral shape to form a wound electrode assembly, or stacked into a flat plate shape to form a stacked electrode assembly. These electrode assemblies are usually constructed as encapsulated within a casing. It should be noted that the secondary battery described in this disclosure is not particularly limited and can be made of paper-type batteries, button-type batteries, coin-type batteries, stacked batteries, cylindrical batteries, prismatic batteries, etc.

[0060] The manufacturing method disclosed herein can be applied to the manufacture of electrodes suitable for use in so-called bipolar secondary batteries. A bipolar secondary battery has a configuration in which a negative electrode is formed on one surface of a current collector and a positive electrode is formed on its other surface. In this case, as described above, by performing the drying step, the firing step, and the crack-introducing step, a negative electrode can be formed on one surface of the current collector, and then by performing the drying step, the firing step, and the crack-introducing step, a positive electrode can be formed on the other surface of the current collector. However, there is no particular limitation on which electrode, the negative or the positive, is formed first, and this can be freely determined by considering factors such as the coating conditions of the positive and negative electrodes.

[0061] Example

[0062] The present disclosure will be further described in detail below by way of embodiments; however, the technical scope of the present disclosure is not limited to the following embodiments.

[0063] Example 1

[0064] In Example 1, the electrode paste was manufactured as follows: 90 parts by weight of active material, 1 part by weight of dispersant (carboxymethyl cellulose), 5 parts by weight of binder (styrene-butadiene rubber), and 4 parts by weight of conductive reinforcing agent (carbon nanotubes) were mixed using a planetary mixer to produce a paste with a solids content (non-volatile (NV) value) of 60%.

[0065] Next, the fabricated electrode paste was applied to the surface of a 10 μm current collector (material: Cu) to achieve a thickness of 450 μm. The electrode paste was then dried at 100 degrees Celsius for 4 minutes.

[0066] After drying under the above conditions, the electrode paste is fired at 120 degrees Celsius for 280 minutes. Then, a crack induction step is performed by bending the current collector (with a wrap angle of 70° on the roller) along the surface of a φ40mm roller, with the side containing the electrode paste facing outwards. The current collector is then transported in this state to check whether cracks have formed in the active material layer formed by drying and firing the electrode paste. It is important to note that a microscope is used to confirm the presence of cracks.

[0067] Example 2

[0068] The process up to the crack induction step was performed in the same way as in Example 1, except that the firing temperature in the firing step was 130 degrees Celsius and the firing time was 200 minutes, and it was confirmed whether cracks were generated in the active material layer.

[0069] Example 3

[0070] The process up to the crack induction step was performed in the same way as in Example 1, except that the firing temperature in the firing step was 140 degrees Celsius and the firing time was 120 minutes, and it was confirmed whether cracks were generated in the active material layer.

[0071] Comparative Example 1

[0072] The process up to the crack induction step was performed in the same way as in Example 1, except that the firing temperature in the firing step was 120 degrees Celsius and the firing time was 250 minutes, and it was confirmed whether cracks were generated in the active material layer.

[0073] Comparative Example 2

[0074] The process up to the crack induction step was performed in the same way as in Example 1, except that the firing temperature in the firing step was 130 degrees Celsius and the firing time was 120 minutes, and it was confirmed whether cracks were generated in the active material layer.

[0075] Comparative Example 3

[0076] The process up to the crack induction step was performed in the same way as in Example 1, except that the firing temperature in the firing step was 130 degrees Celsius and the firing time was 150 minutes, and it was confirmed whether cracks were generated in the active material layer.

[0077] Comparative Example 4

[0078] The process up to the crack induction step was performed in the same way as in Example 1, except that the firing temperature in the firing step was 140 degrees Celsius and the firing time was 90 minutes, and it was confirmed whether cracks were generated in the active material layer.

[0079] result

[0080] In Examples 1 to 3, crack formation was observed with a depth of 10% or more relative to the thickness of the active material layer, but not reaching the current collector. However, in Comparative Examples 1 to 4, no crack formation with a depth of 10% or more relative to the thickness of the active material layer was observed. The results are shown in... Figure 1 The figure is drawn using the firing temperature and firing time of Examples 1 to 3 and Comparative Examples 1 to 4.

[0081] from Figure 1 It is clearly shown that, under the condition that the firing temperature and firing time satisfy the following relationship, appropriate cracks can be formed in the active material layer.

[0082] Y≥-8X+1220

[0083] 100≤X≤150

[0084] Where X is the firing temperature in degrees Celsius and Y is the firing time in minutes.

[0085] It should be noted that, according to this formula, the firing time should be more than 420 minutes when the firing temperature is 100 degrees Celsius, more than 260 minutes when the firing temperature is 120 degrees Celsius, more than 180 minutes when the firing temperature is 130 degrees Celsius, and more than 100 minutes when the firing temperature is 140 degrees Celsius.

Claims

1. A method of manufacturing a secondary battery electrode, the method comprising: drying an electrode paste formed on a surface of a current collector; firing the electrode paste at a higher temperature than during the drying after the electrode paste is dried; and bending the current collector around a roll surface in a manner such that the surface of the current collector on which the electrode paste is formed is disposed on the outer side after the electrode paste is fired.

2. The method for manufacturing a secondary battery electrode according to claim 1, wherein When the electrode paste is fired, the firing temperature and the firing time satisfy the following formula: Y > -8X + 1220 100≤X≤150 where, in the formula, X is the firing temperature and the unit is degrees Celsius, and Y is the firing time and the unit is minutes.

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

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

5. The method of manufacturing a secondary battery electrode according to claim 1, wherein a crack is imparted in the bending, the depth of the crack is 10% or more relative to the thickness of the electrode paste formed on the current collector, and the depth does not reach the current collector.

Images