Method for manufacturing bipolar electrodes

Abstract

To provide a bipolar electrode manufacturing method capable of increasing positive electrode density while suppressing the increase in negative electrode density.SOLUTION: The bipolar electrode manufacturing method includes: a step of forming a negative electrode layer on one side of a current collector; after the negative electrode layer forming step, a first press step of roll pressing the negative electrode layer; after the first press step, a positive electrode layer forming step of forming a positive electrode layer on the other side of the current collector; after the positive electrode layer forming step, a second press step of roll pressing the negative electrode layer and the positive electrode layer at the same time. The press line pressure in the second press step is greater than the press line pressure in the first press step.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] This application relates to a method for manufacturing a bipolar electrode.

Background Art

[0002] Unlike ordinary electrodes, in a bipolar electrode, a negative electrode is disposed on one surface of a current collector and a positive electrode is disposed on the other surface. Then, by alternately laminating such bipolar electrodes and separators and filling the surroundings thereof with an electrolytic solution, a bipolar battery can be obtained. The bipolar battery is expected to have improved output compared to ordinary batteries.

[0003] Patent Document 1 discloses a method for manufacturing a bipolar electrode in which a negative electrode active material layer is formed on a first surface of a first metal foil, the negative electrode active material layer is pressed in a state where a first surface of a second metal foil faces a second surface of the first metal foil, a positive electrode active material layer is formed on a second surface of the second metal foil, and the positive electrode active material layer is pressed. Further, Patent Document 1 describes that when pressing the positive electrode active material layer, the negative electrode active material layer is also pressed simultaneously.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In a bipolar electrode, usually, the densities required for the negative electrode and the positive electrode are different. Specifically, within a range that does not impair the electrode performance, it is required to make the negative electrode density as low as possible and the positive electrode density as high as possible. By satisfying such requirements, the battery performance can be enhanced.

[0006] However, while it is common practice to manufacture bipolar electrodes by roll-pressing a laminate in which a negative electrode layer is arranged on one side of the current collector and a positive electrode layer on the other side, this manufacturing method may not satisfy the above requirements. For example, in order to lower the negative electrode density, the press pressure must be set low, but this makes it difficult to increase the positive electrode density. On the other hand, in order to increase the positive electrode density, the press pressure must be set high, but this makes it difficult to lower the negative electrode density.

[0007] Therefore, the main objective of this disclosure is to provide a method for manufacturing a bipolar electrode that can increase the positive electrode density while suppressing an increase in the negative electrode density, in light of the above circumstances. [Means for solving the problem]

[0008] This disclosure provides a method for manufacturing a bipolar electrode, comprising: a negative electrode layer forming step of forming a negative electrode layer on one side of a current collector; a first pressing step of roll-pressing the negative electrode layer after the negative electrode layer forming step; a positive electrode layer forming step of forming a positive electrode layer on the other side of the current collector after the first pressing step; and a second pressing step of roll-pressing the negative electrode layer and the positive electrode layer simultaneously after the positive electrode layer forming step, wherein the press line pressure in the second pressing step is greater than the press line pressure in the first pressing step.

[0009] In the above manufacturing method, the press line pressure in the second pressing step may be 4 kN / cm or more and 15 kN / cm or less. Alternatively, the press line pressure in the first pressing step may be 1 kN / cm or more and less than 4 kN / cm. [Effects of the Invention]

[0010] The method for manufacturing a bipolar electrode according to this disclosure makes it possible to increase the positive electrode density while suppressing an increase in the negative electrode density. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic diagram of a manufacturing method according to one embodiment. [Figure 2] This is a conceptual diagram of when laminate E is roll-pressed from both sides. [Figure 3] This shows the relationship between the thickness of the negative electrode layer and the linear pressure after the first press in the example. [Figure 4] (a) This figure shows the relationship between the density of the positive electrode layer and the linear pressure after the second pressing in the example. (b) This figure shows the relationship between the density of the negative electrode layer and the linear pressure after the second pressing in the example. [Figure 5] This figure shows the relationship between the negative electrode density and positive electrode density after the second press in the example. [Modes for carrying out the invention]

[0012] [Manufacturing method for bipolar electrodes] The method for manufacturing a bipolar electrode according to this disclosure will be described using the manufacturing method of one embodiment. Figure 1 shows a schematic diagram of the manufacturing method of one embodiment. Figures 1(a) to (e) are described in chronological order.

[0013] One embodiment of the manufacturing method includes a negative electrode layer forming step of forming a negative electrode layer 20 on one surface 11 of the current collector 10; a first pressing step of roll-pressing the negative electrode layer 20 after the negative electrode layer forming step; a positive electrode layer forming step of forming a positive electrode layer 30 on the other surface 12 of the current collector 10 after the first pressing step; and a second pressing step of roll-pressing the negative electrode layer 20 and the positive electrode layer 30 simultaneously after the positive electrode layer forming step. This makes it possible to manufacture a bipolar electrode 100. Each step will be described below.

[0014] <Negative electrode layer formation process> In the negative electrode layer formation process, a negative electrode layer 20 is formed on one surface 11 of the current collector 10. Figure 1(a) shows a schematic diagram of the negative electrode layer formation process.

[0015] (Current collector 10) The current collector 10 is not particularly limited as long as it is a sheet-like member that functions as a current collector for bipolar electrodes. For example, the current collector 10 may be a metal foil made of a metal such as stainless steel, copper, aluminum, titanium, nickel, etc. The metal foil may be made of an alloy containing two or more of these metals. Also, the metal foil may be subjected to surface treatment such as plating. The current collector 10 may be composed of two or more metal foils. In this case, the metal foils may be joined with an adhesive or the like, or may be joined by pressing or the like. The thickness of the current collector 10 is not particularly limited, but for example, it is 5 μm or more and 70 μm or less.

[0016] (Negative electrode layer 20) The negative electrode layer 20 contains a negative electrode active material. The negative electrode active material is not particularly limited and may be appropriately selected from known materials according to the intended battery performance. For example, carbon such as graphite, artificial graphite, highly oriented graphite, mesocarbon microbeads, hard carbon, soft carbon, metal compounds, elements or their compounds that can alloy with lithium, boron-added carbon, etc. may be mentioned. Examples of elements that can alloy with lithium include silicon and tin.

[0017] The negative electrode layer 20 may optionally contain a conductive assistant. The conductive assistant is not particularly limited and may be appropriately selected from known materials according to the intended battery performance. For example, acetylene black, carbon black, graphite, etc. may be mentioned.

[0018] The negative electrode layer 20 may optionally contain a binder. The binder is not particularly limited and may be appropriately selected from known materials according to the intended battery performance. For example, fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene, fluororubber, thermoplastic resins such as polypropylene, polyethylene, imide resins such as polyimide, polyamideimide, alkoxysilyl group-containing resins, acrylic resins such as poly(meth)acrylic acid, styrene-butadiene rubber (SBR), carboxymethyl cellulose, alginates such as sodium alginate and ammonium alginate, water-soluble cellulose ester cross-linked bodies, starch-acrylic acid graft polymers, etc. may be mentioned.

[0019] The negative electrode layer 20 may be a layered member, and its thickness is not particularly limited. For example, it is in the range of 1 μm to 1 mm. From the perspective of output improvement, the area of the negative electrode layer 20 may be larger than that of the positive electrode layer 30. The content of each material in the negative electrode layer 20 is not particularly limited and may be appropriately set according to the target battery performance. In addition, the negative electrode layer 20 may contain materials other than the above-mentioned materials.

[0020] (Method for forming the negative electrode layer 20) The method for forming the negative electrode layer 20 on one surface 11 of the current collector 10 is not particularly limited, and a known method may be appropriately adopted. For example, the materials constituting the negative electrode layer 20 can be mixed in a mortar or the like and pressed to obtain the negative electrode layer 20. Then, the obtained negative electrode layer 20 may be disposed on one surface of the current collector 10. Alternatively, after mixing the materials constituting the negative electrode layer 20 with a solvent to obtain a slurry, the slurry may be applied and dried on one surface 11 of the current collector 10.

[0021] <The first pressing step> The first pressing step is carried out after the negative electrode layer forming step, and the negative electrode layer 20 is roll-pressed. A schematic diagram of the first pressing step is shown in Fig. 1(b). As shown in Fig. 1(b), the negative electrode layer 20 is pressed from both sides by the opposing rolls X. The pressing line pressure P1 in the first pressing step will be described later.

[0022] <Positive electrode layer forming step> The positive electrode layer forming step is carried out after the first pressing step, and the positive electrode layer 30 is formed on the other surface 12 of the current collector 10. A schematic diagram of the positive electrode layer forming step is shown in Fig. 1(c).

[0023] (Positive electrode layer 30) The positive electrode layer 30 contains a positive electrode active material. The positive electrode active material is not particularly limited and may be appropriately selected from known materials depending on the desired battery performance. Examples include composite oxides, metallic lithium, and sulfur. The composition of the composite oxide includes, for example, at least one of iron, manganese, titanium, nickel, cobalt, and aluminum, and lithium. An example of a composite oxide is olivine-type lithium iron phosphate (LiFePO4).

[0024] The positive electrode layer 30 may optionally contain a conductive additive. The conductive additive is not particularly limited and may be appropriately selected from known materials depending on the desired battery performance. For example, it may be appropriately selected from conductive additives applicable to the negative electrode layer 20.

[0025] The positive electrode layer 30 may optionally contain a binder. The binder is not particularly limited and may be appropriately selected from known materials depending on the desired battery performance. For example, it may be appropriately selected from binders applicable to the negative electrode layer 20.

[0026] The positive electrode layer 30 can be any layered material, and its thickness is not particularly limited. For example, it can be in the range of 1 μm to 1 mm. The area of ​​the positive electrode layer 30 may be smaller than that of the negative electrode layer 20. The content of each material in the positive electrode layer 30 is not particularly limited and may be set appropriately according to the desired battery performance. The positive electrode layer 30 may also contain materials other than those described above.

[0027] (Method for forming the positive electrode layer 30) The method for forming the positive electrode layer 30 on the other surface 12 of the current collector 10 is not particularly limited, and known methods may be used as appropriate. For example, the same method as for forming the negative electrode layer 20 may be used.

[0028] <Second pressing process> The second pressing process is performed after the positive electrode layer formation process, and the negative electrode layer 20 and the positive electrode layer 30 are roll-pressed simultaneously. A schematic diagram of the second pressing process is shown in Figure 1(d). As shown in Figure 1(d), the negative electrode layer 20 and the positive electrode layer 30 are pressed from both sides by opposing rolls X. The press line pressure P2 in the second pressing process will be described later.

[0029] <Bipolar electrode 100> Figure 1(e) shows the manufactured bipolar electrode 100. The type of bipolar electrode 100 that can be manufactured by one embodiment is not particularly limited. For example, it may be an electrode for chemical batteries such as nickel-metal hydride secondary batteries and lithium-ion secondary batteries, or an electrode for physical batteries such as electric double-layer capacitors. However, nickel-metal hydride secondary batteries are less affected by the density of the positive and negative electrode layers, while lithium-ion secondary batteries are more affected. Therefore, one embodiment is suitable for manufacturing bipolar electrodes for lithium-ion secondary batteries.

[0030] <Improved compression characteristics of positive electrode layer 30> In one embodiment of the manufacturing method, a two-stage roll pressing process is performed, consisting of a first pressing step in which the negative electrode layer 20 is roll-pressed, and a second pressing step in which the negative electrode layer 20 and the positive electrode layer 30 are pressed simultaneously. First, in the first pressing step, the thickness of the negative electrode layer 20 is reduced by roll pressing the negative electrode layer 20, and therefore the total thickness of the laminate in the second pressing step is also reduced. Then, in the second pressing step, the compression characteristics of the positive electrode layer 30 can be improved by roll-pressing the laminate with reduced thickness. That is, even if the laminate is roll-pressed at a low linear pressure, a positive electrode layer 30 with a high density can be obtained. Furthermore, because the compression characteristics of the positive electrode layer 30 are improved, a positive electrode layer 30 with the desired density can be obtained at a low linear pressure, thus suppressing an increase in the density of the negative electrode layer 20.

[0031] The effect of improving the compression characteristics of the positive electrode layer 30 will be described using the following formula (1). First, formula (1) will be described using FIG. 2. FIG. 2 is a conceptual diagram when the laminate E (laminated in this order: positive electrode layer, current collector layer, negative electrode layer) is roll-pressed from both sides. Here, when the press surface pressure is P, the load by the roll X is F, the width of the electrode layer (positive electrode layer or negative electrode layer) arranged in the laminate E (the length in the depth direction in FIG. 2) is W (not shown), the roll radius is R, and the compression amount when the electrode layer is compressed by the roll X is Δh, the following formula (1) holds. This formula (1) also holds for a laminate in which an electrode layer is laminated on one surface of the current collector. Here, √RΔh represents the contact arc length between the roll and the electrode layer.

[0032]

Number

[0033] As described above, by the first pressing step, the total thickness of the laminate in the second pressing step is reduced. That is, the compression amount Δh becomes smaller. Then, the contact arc length √RΔh becomes smaller, and the press surface pressure P increases as a whole. Therefore, according to the manufacturing method of one embodiment, even if the laminate is roll-pressed with a low line pressure by two-stage roll pressing, a positive electrode layer 30 with a high density can be obtained.

[0034] Here, in one embodiment, the press line pressure P2 in the second pressing step is set to be larger than the press line pressure P1 in the first pressing step (P1 < P2). Thereby, while adjusting the positive electrode to the target density, it is possible to suppress the improvement in the density of the negative electrode layer 20. For example, when the press line pressure P1 in the first pressing step is set to be equal to or higher than the press line pressure P2 in the second pressing step (P1 ≧ P2), when trying to adjust the positive electrode layer 30 to the target density, P1 becomes excessive, and it may be difficult to suppress the improvement in the density of the negative electrode layer 20.

[0035] From the viewpoint of further enhancing the effect, the press line pressure P2 in the second pressing process may be set to 4 kN / cm or higher, or 9 kN / cm or higher. However, if the press line pressure P2 is too high, there is a risk that the density of the negative electrode layer 30 will become too high, so the press line pressure P2 may be set to 15 kN / cm or lower. Also, from the viewpoint of further reducing the density of the negative electrode layer 30, the press line pressure P1 in the first pressing process may be set to 8 kN / cm or lower, 6 kN / cm or lower, 4 kN / cm or lower, or less than 4 kN / cm. The lower P1 is, the more the density of the negative electrode layer 30 can be reduced. However, if P2 is too low, the effect of improving the compression characteristics of the positive electrode layer 30 will be reduced, so for example, P1 may be set to 1 kN / cm or higher, or 2 kN / cm or higher.

[0036] The method for manufacturing a bipolar electrode according to the present disclosure has been described above using one embodiment. According to the method for manufacturing a bipolar electrode according to the present disclosure, it is possible to increase the positive electrode density while suppressing an increase in the negative electrode density. In other words, according to the method for manufacturing a bipolar electrode according to the present disclosure, the requirements for negative electrode density and positive electrode density in a bipolar electrode can be met in a simple manner. [Examples]

[0037] The compression characteristics of the negative electrode layer and the positive electrode layer were investigated according to the following procedure.

[0038] First, a negative electrode layer was coated onto one side of the current collector using a die and dried. Then, the resulting laminate was roll-pressed. At this time, the press line pressure was set to one of the following: 8 kN / cm (high line pressure), 6 kN / cm (medium line pressure), or 4 kN / cm (low line pressure). Figure 3 shows the relationship between the thickness of the negative electrode layer and the line pressure at this time. Here, the result for the unpressed negative electrode layer is shown as Ref.

[0039] Next, a positive electrode layer was formed on the other side of the current collector using the pressed laminate, and then the laminate was pressed again. The pressing line pressure varied. The results are shown in Figures 4(a) and (b). Figure 4(a) shows the relationship between the density of the positive electrode layer and the line pressure (compression characteristics of the positive electrode layer). Figure 4(b) shows the relationship between the density of the negative electrode layer and the line pressure (compression characteristics of the negative electrode layer). Ref represents the result when a second press was performed using a laminate that had not undergone the first press. Also, in Figures 4(a) and 4(b), approximation curves are provided for each result. Furthermore, Figure 5 shows the relationship between the negative electrode density and the positive electrode density created based on Figures 4(a) and (b).

[0040] First, the compression characteristics of the positive electrode layer were examined. As shown in Figure 4(a), the positive electrode layer after the second press showed improved compression characteristics compared to the approximation curve of Ref, and maintained a high density even when roll-pressed at a low linear pressure. This confirmed that the compression characteristics of the positive electrode layer improved with a two-stage press. In particular, when the linear pressure was 9 kN / cm or higher, the improvement in compression characteristics was significant regardless of the linear pressure of the first roll press. Furthermore, it was found that the improved compression characteristics of the positive electrode layer allowed for roll-pressing at a lower linear pressure, thus suppressing the increase in density of the negative electrode layer.

[0041] On the other hand, Figure 4(b) shows that a linear pressure exceeding 15 kN / cm is undesirable because it results in excessively high density in the negative electrode layer. Therefore, it is considered acceptable to set the linear pressure for the second roll press within the range of 9 kN / cm to 15 kN / cm.

[0042] Furthermore, as shown in Figure 4(b), when the linear pressure is 15 kN / cm or less, the compression characteristics of the negative electrode layer after the second press were improved compared to the approximation curve of Ref. Therefore, it appears that the effect of suppressing the density increase of the negative electrode is reduced. However, in the range of 9 kN / cm to 15 kN / cm, the effect of improving the compression characteristics of the negative electrode is smaller than that of improving the compression characteristics of the positive electrode, so overall, it is considered that the effect of improving the compression characteristics of the positive electrode layer can be enjoyed. Accordingly, by setting the linear pressure of the second roll press to 9 kN / cm to 15 kN / cm, it is possible to increase the positive electrode density while suppressing the increase in negative electrode density. However, it has been found that depending on the configuration of the electrode layer, the effect of improving the compression characteristics of the positive electrode layer can be enjoyed even at lower linear pressures (e.g., 4 kN / cm or more) in the second roll press.

[0043] Furthermore, while the compression characteristics of the positive electrode layer were significantly improved regardless of the linear pressure of the first roll press, the compression characteristics of the negative electrode layer were suppressed as the linear pressure of the first roll press decreased. Therefore, it can be concluded that a lower linear pressure in the first roll press is preferable. [Explanation of symbols]

[0044] 10 Current collector 11, 12 sides 20 Negative electrode layer 30 Positive electrode layer 100 bipolar electrodes X Roll E Laminate

Claims

1. A negative electrode layer formation step in which a negative electrode layer is formed on one side of the current collector, After the negative electrode layer formation step, a first pressing step is performed in which the negative electrode layer is roll-pressed, After the first pressing step, a positive electrode layer forming step is performed to form a positive electrode layer on the other surface of the current collector, The process includes a second pressing step in which the negative electrode layer and the positive electrode layer are roll-pressed simultaneously after the positive electrode layer forming step, The press line pressure in the second pressing step is greater than the press line pressure in the first pressing step. The press line pressure in the second pressing process is 9 kN / cm or more and 15 kN / cm or less. A method for manufacturing bipolar electrodes.

2. The method for manufacturing a bipolar electrode according to claim 1, wherein the press line pressure in the first pressing step is 1 kN / cm or more and less than 4 kN / cm.

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