Bipolar electrode and method for manufacturing the same

Abstract

A method for manufacturing a bipolar electrode is provided that allows the porosity of the positive electrode layer and the porosity of the negative electrode layer to be adjusted to desired ranges. [Solution] A method for manufacturing a bipolar electrode includes the steps of: shear-mixing a mixture containing a positive electrode active material or a negative electrode active material and a binder resin with a fiberizable compound to prepare a positive electrode powder and a negative electrode powder, respectively; rolling the positive electrode powder and the negative electrode powder to form a positive electrode layer and a negative electrode layer, respectively; and compressing the positive electrode layer and the negative electrode layer by applying different pressures to each layer, thereby adjusting the porosity of the positive electrode layer and the negative electrode layer, respectively.

Description

[Technical Field]

[0001] The present disclosure relates to bipolar electrodes and methods of manufacturing bipolar electrodes. [Background technology]

[0002] In recent years, bipolar batteries have attracted attention from the viewpoint of improving volumetric energy density. A bipolar battery is obtained by stacking multiple bipolar electrodes with separators interposed therebetween.

[0003] Patent Document 1 discloses a bipolar battery having a bipolar electrode having a bipolar current collector, a positive electrode composite layer, and a negative electrode composite layer, and a unit cell having a positive electrode having a positive electrode current collector and a positive electrode composite layer, and a negative electrode having a negative electrode current collector and a negative electrode composite layer, wherein the positive electrode has a positive electrode laminate portion and a positive electrode terminal portion, and the negative electrode has a negative electrode laminate portion and a negative electrode terminal portion, a first solid electrolyte layer is disposed between the bipolar electrode and the positive electrode in the lamination direction of the bipolar battery, a second solid electrolyte layer is disposed between the bipolar electrode and the negative electrode in the lamination direction of the bipolar battery, and the first solid electrolyte layer and the second solid electrolyte layer are larger than the positive electrode and the negative electrode in the in-plane direction of the bipolar battery. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2017-195076 Summary of the Invention [Problem to be solved by the invention]

[0005] A bipolar electrode has a positive electrode mixture layer on one side of a current collector and a negative electrode mixture layer on the other side. When an electrode mixture layer is formed on one side of a current collector and pressed, the electrode is subjected to stress due to elongation of the electrode mixture layer, causing warping of the electrode. Therefore, when manufacturing a bipolar electrode, it is desirable to form electrode mixture layers on both sides of the current collector and then press them simultaneously.

[0006] However, to improve input / output performance, the positive electrode layer of the bipolar electrode is required to have a high density, while the negative electrode layer is required to have a low density. In the above-mentioned method, the positive electrode layer and the negative electrode layer have different compression characteristics with respect to the pressing pressure, which can lead to problems such as the electrode density being too low in the positive electrode layer and too high in the negative electrode layer.

[0007] An object of one embodiment of the present disclosure is to provide a bipolar electrode in which the porosity of the positive electrode layer and the porosity of the negative electrode layer are each adjusted to a desired range, and a method for manufacturing the same. [Means for solving the problem]

[0008] The means for solving the above problems include the following aspects. <1> A method for manufacturing a bipolar electrode, comprising: a step of shear-mixing a mixture containing a positive electrode active material or a negative electrode active material and a resin with a compound selected from a fibrous compound and a fiberizable compound to prepare a positive electrode powder and a negative electrode powder, respectively; a step of rolling the positive electrode powder and the negative electrode powder to form a positive electrode layer and a negative electrode layer, respectively; and a step of compressing the positive electrode layer and the negative electrode layer by applying different pressures to each of them, thereby adjusting the porosity of the positive electrode layer and the porosity of the negative electrode layer, respectively. <2> The fiberizable compound is polytetrafluoroethylene (PTFE); <1> A method for producing the bipolar electrode according to claim 1. <3> A bipolar electrode comprising a positive electrode layer, a current collecting foil, and a negative electrode layer, wherein the porosity of the positive electrode layer is lower than the porosity of the negative electrode layer, and the difference between the porosities of the positive electrode layer and the negative electrode layer is 8% or more. <4> the porosity of the positive electrode layer is 20% to 26%, and the porosity of the negative electrode layer is 36% to 42%; <3> 2. The bipolar electrode according to claim 1 . [Effects of the Invention]

[0009] According to one embodiment of the present disclosure, there is provided a bipolar electrode in which the porosity of the positive electrode layer and the porosity of the negative electrode layer are each adjusted to a desired range, and a method for manufacturing the same. DETAILED DESCRIPTION OF THE INVENTION

[0010] A method for manufacturing a bipolar electrode according to the present disclosure will be described below, and details of the bipolar electrode according to the present disclosure will also be described throughout the description.

[0011] The method for manufacturing a bipolar electrode of the present disclosure includes a step of shear-mixing a mixture containing a positive electrode active material or a negative electrode active material and a resin with a compound selected from a fibrous compound and a fiberizable compound to prepare a positive electrode powder and a negative electrode powder, respectively (hereinafter also referred to as a "powder preparation step"); a step of rolling the positive electrode powder and the negative electrode powder to form a positive electrode layer and a negative electrode layer, respectively (hereinafter also referred to as a "rolling step"); and a step of compressing the positive electrode layer and the negative electrode layer by applying different pressures to each layer to adjust the porosity of the positive electrode layer and the porosity of the negative electrode layer, respectively (hereinafter also referred to as a "compression step"). The method for producing a bipolar electrode according to the present disclosure includes the above steps, and thus the porosity of the positive electrode layer and the porosity of the negative electrode layer can be adjusted to each within a desired range.

[0012] Each of these will be explained in detail below.

[0013] -Powder preparation process- In the powder preparation step, a mixture containing a positive electrode active material or a negative electrode active material and a resin is shear-mixed with a fiberizable compound to prepare a positive electrode powder and a negative electrode powder, respectively.

[0014] The positive electrode powder contains a positive electrode active material and a resin. As the positive electrode active material, for example, lithium cobalt oxide (LiCoO2, LCO); lithium nickel oxide (LiNiO2, LNO); lithium manganate (LiMn2O4, LMO); nickel cobalt manganese lithium oxide such as NCM-111, NCM-523, NCM-622, NCM-811 (Li(Ni , ,

[0018] Mn y Co z )O2 (x + y + z = 1, 0 < x < 1, 0 < y < 1, 0 < z < 1), NCM); lithium nickel cobalt aluminum oxide (NCA); lithium iron phosphate (LiFePO4, LFP), etc. can be mentioned. The positive electrode active material can be appropriately selected from these according to the desired battery performance and the like.

[0015] The negative electrode powder contains a negative electrode active material and a resin. As the negative electrode active material, for example, carbon-based negative electrode active materials such as natural graphite, artificial graphite, and graphite; Li-based negative electrode active materials such as lithium titanate (for example, Li4Ti5O 12 ) etc.; and Si-based negative electrode active materials such as Si single body etc. can be mentioned. The negative electrode active material can be appropriately selected from these. <00000�8> Examples of the resin used for the positive electrode powder or the negative electrode powder include polyvinylidene fluoride (PVdF), polyvinylidene fluoride - hexafluoropropylene copolymer (PVdF - HFP), styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyacrylic acid (PAA), etc. Among them, polyvinylidene fluoride (PVdF) is particularly preferable from the viewpoints of excellent electrochemical stability and obtaining a self - supporting film of the positive electrode layer or the negative electrode layer. By using PVdF, the adhesiveness between components such as the active material in the powder can be enhanced.

[0017] The content of the resin is, for example, 5 parts by mass to 10 parts by mass with respect to 100 parts by mass of the positive electrode active material or the negative electrode active material.

[0018] The mixture containing the positive electrode active material or the negative electrode active material and the resin preferably further contains a conductive agent for improving conductivity in order to improve battery performance. Examples of the conductive agent include carbon materials such as acetylene black, ketjen black, vapor grown carbon fiber (VGCF (registered trademark)), and carbon nanotubes (CNT). The content of the conductive agent is, for example, 1 to 3 parts by mass per 100 parts by mass of the positive electrode active material or the negative electrode active material.

[0019] As described above, in the powder preparation process, a mixture containing a positive electrode active material or a negative electrode active material and a resin is shear-mixed with a compound selected from a fibrous compound and a fiberizable compound to prepare a positive electrode powder and a negative electrode powder, respectively. By shear-mixing a mixture containing a positive electrode active material or a negative electrode active material and a resin with a compound selected from a fibrous compound and a fiberizable compound, the positive electrode active material or the negative electrode active material and the resin can be entangled in the fibrous compound to form a positive electrode powder or a negative electrode powder. This makes it possible to form a free-standing positive electrode layer and a free-standing negative electrode layer after the rolling process. In this disclosure, the term "free-standing film" refers to a film that maintains its shape even without a support (current collector).

[0020] Examples of the fibrous compound include carbon nanofibers (CNF) and carbon nanotubes (CNT). Examples of compounds that can be made into fibers include polytetrafluoroethylene (PTFE) and ultra-high molecular weight polyethylene (UHMWPE). Among these, polytetrafluoroethylene (PTFE) is preferred from the viewpoints that it is easily fibrillated, functions as a binder resin, and has excellent oxidation resistance and reduction resistance.

[0021] The average particle size of the fibrous compound and the fibrous compound is preferably 200 μm to 700 μm (secondary particle size) from the viewpoint of obtaining positive electrode powder and negative electrode powder that form a positive electrode layer that is a self-supporting film and a negative electrode layer that is a self-supporting film.

[0022] By including a fibrous compound and a fiberized product of a fiberizable compound, it is easy to prepare positive electrode powder and negative electrode powder that can form a positive electrode layer and a negative electrode layer that are self-supporting films after the rolling step.

[0023] Shear mixing can be carried out using a known kneading device capable of applying shear force, such as a colloid mill, a bead mill, an attritor, a three-roll mill, a two-roll mill, a dissolver, or a kneader.

[0024] During shear mixing, the rotation speed of the stirring mechanism (e.g., rotor) of the kneading device is, for example, 5 rpm to 20 rpm, and from the viewpoint of fiberizing a fiberizable compound, it is preferably 5 rpm to 15 rpm, and more preferably 9 rpm to 11 rpm.

[0025] The shear mixing time is, for example, 1 to 60 minutes when the rotation speed of the stirring mechanism of the kneading device is 9 to 11 rpm, and from the viewpoint of fiberizing a fiberizable compound, it is preferably 1 to 10 minutes.

[0026] The shape of the stirring mechanism is not particularly limited as long as a self-supporting positive electrode layer and a self-supporting negative electrode layer are obtained after the rolling step, and can be appropriately selected depending on the kneading device.

[0027] -Rolling process- In the rolling step, the positive electrode powder or the negative electrode powder obtained in the powder preparation step is rolled to form a positive electrode layer and a negative electrode layer, respectively. By including this rolling step, it is possible to form a positive electrode layer that is a free-standing film and a negative electrode layer that is a free-standing film. This makes it possible to carry out the compression step described below.

[0028] The rolling can be carried out using a roll press.

[0029] The pressing pressure during rolling is preferably 0.1 t / cm to 1.5 t / cm, and more preferably 0.3 t / cm to 0.5 t / cm, for the positive electrode powder. When the pressing pressure during rolling is within the above range for the positive electrode powder, a positive electrode layer that is a self-supporting film is easily obtained, and the porosity of the positive electrode layer is easily adjusted to a desired range in the compression step.

[0030] The pressing pressure during rolling is preferably 0.01 t / cm to 1.0 t / cm, and more preferably 0.03 t / cm to 0.05 t / cm, for the negative electrode powder. When the pressing pressure during rolling is within the above range for the negative electrode powder, a negative electrode layer that is a self-supporting film is easily obtained, and the porosity of the negative electrode layer is easily adjusted to a desired range in the compression step.

[0031] The roll temperature during rolling is preferably 120° C. to 200° C. for the positive electrode powder, and more preferably 140° C. to 180° C. When the roll temperature during rolling of the positive electrode powder is within the above range, a positive electrode layer that is a self-supporting film is easily obtained, and the porosity of the positive electrode layer is easily adjusted to a desired range in the compression step.

[0032] The roll temperature during rolling is preferably 120° C. to 200° C. for the negative electrode powder, and more preferably 140° C. to 180° C. When the roll temperature during rolling of the negative electrode powder is within the above range, a negative electrode layer that is a self-supporting film is easily obtained, and the porosity of the negative electrode layer is also easily adjusted to a desired range in the compression step.

[0033] -Compression process- In the subsequent compression step, different pressures are applied to the positive electrode layer and the negative electrode layer obtained in the rolling step to compress them, thereby adjusting the porosity of the positive electrode layer and the porosity of the negative electrode layer to their respective desired ranges. By including this compression step, the porosity of the positive electrode layer and the porosity of the negative electrode layer are adjusted to their respective desired ranges. This reduces or maintains the resistance of the positive electrode layer and the negative electrode layer, thereby reducing the internal resistance of the battery.

[0034] Compression can be performed using a means capable of applying pressure to the positive electrode layer and the negative electrode layer, and examples thereof include a method of pressing with a hot plate and a method of passing through a pair of heated rolls (a method of passing through a pair of heated rolls using a roll press). Of these, the method of passing through a pair of heated rolls using a roll press is particularly suitable.

[0035] The pressure applied to the positive electrode layer during compression is preferably 0.8 t / cm to 2.0 t / cm, and more preferably 1.0 t / cm to 1.8 t / cm. When the pressure applied to the positive electrode layer during compression is within the above range, the porosity of the positive electrode layer can be easily adjusted to a desired range.

[0036] The pressing pressure during compression is preferably 0.1 t / cm to 0.7 t / cm, and more preferably 0.2 t / cm to 0.5 t / cm, for the negative electrode layer. When the pressing pressure during compression is within the above range, the porosity of the negative electrode layer can be easily adjusted to a desired range.

[0037] The roll temperature during compression for the positive electrode layer is preferably 10° C. to 100° C., and more preferably 20° C. to 50° C. When the roll temperature during compression is within the above range, the porosity of the positive electrode layer can be easily adjusted to a desired range.

[0038] The roll temperature during compression for the negative electrode layer is preferably 10° C. to 100° C., and more preferably 20° C. to 50° C. When the roll temperature during compression is within the above range, the porosity of the negative electrode layer can be easily adjusted to a desired range.

[0039] After compression, the porosity of the positive electrode layer is preferably lower than that of the negative electrode layer, and the absolute value of the difference between the porosities of the positive electrode layer and the negative electrode layer is preferably 8% or more. When the porosity of the positive electrode layer is 8% or more lower than that of the negative electrode layer, the electrode density of the positive electrode layer is not too low and the electrode density of the negative electrode layer is not too high, making it easy to keep the internal resistance of the entire battery low. The electrode density is related to the porosity of the electrode layer, and in order to keep the internal resistance of the battery low, it is preferable that the porosity of the positive electrode layer and the negative electrode layer are each adjusted to the following values.

[0040] After compression, the porosity of the positive electrode layer is preferably 20% to 26%, more preferably 21% to 25%. When the porosity of the positive electrode layer is 20% to 26%, the resistance in the positive electrode layer is likely to decrease, and the internal resistance of the battery is likely to decrease. It is presumed that the decrease in resistance in the positive electrode layer is achieved by improving electronic conductivity due to an increase in the electrode density of the positive electrode layer.

[0041] After compression, the porosity of the negative electrode layer is preferably 36% to 42%, and more preferably 36% to 40%. When the porosity of the negative electrode layer is 36% to 42%, the resistance in the negative electrode layer is easily reduced and maintained, and the internal resistance of the battery is easily reduced. It is presumed that the reduction and maintenance of the resistance in the negative electrode layer is achieved by maintaining and improving the diffusibility of lithium ions in the negative electrode layer due to the small change in porosity before and after compression.

[0042] After compression, the difference in porosity between the positive electrode layer and the negative electrode layer is preferably 8% or more, more preferably 10% or more, from the viewpoint of reducing the internal resistance of the battery, and is preferably 22% or less, more preferably 16% or less.

[0043] The porosity of the positive electrode layer can be calculated by the following formula.

[0044] Porosity of the positive electrode layer (%) = {1 - (electrode density of the positive electrode layer / true density of the positive electrode layer)} × 100

[0045] In the formula, the electrode density of the positive electrode layer is obtained by dividing the mass of the positive electrode layer by the product of the area of ​​the positive electrode layer and the thickness of the positive electrode layer, and the true density of the positive electrode layer is obtained by dividing the total mass of the positive electrode active material, resin, and conductive agent by the product of the area of ​​the positive electrode layer and the thickness of the positive electrode layer, and means the inherent density of each component constituting the positive electrode layer.

[0046] The porosity of the negative electrode layer can be calculated by the following formula.

[0047] Porosity of negative electrode layer (%) = {1 - (electrode density of negative electrode layer / true density of negative electrode layer)} × 100

[0048] In the formula, the electrode density of the negative electrode layer is obtained by dividing the mass of the negative electrode layer by the product of the area of ​​the negative electrode layer and the thickness of the negative electrode layer, and the true density of the negative electrode layer is obtained by dividing the total mass of the negative electrode active material, resin, and conductive agent by the product of the area of ​​the negative electrode layer and the thickness of the negative electrode layer, and means the inherent density of each component constituting the negative electrode layer.

[0049] In this step, a positive electrode layer and a negative electrode layer that are free-standing films that have been adjusted in advance so that the porosity can be easily adjusted in the rolling step can also be used.

[0050] According to the method described above, the porosity of the positive electrode layer and the porosity of the negative electrode can be adjusted to the desired ranges, and the internal resistance of the battery can be reduced.

[0051] In addition to the above steps, the method for manufacturing a bipolar electrode according to the present disclosure may further include a step of alternately stacking positive electrode layers and negative electrode layers with bipolar current collectors (current collector foils) interposed therebetween (hereinafter also referred to as a "stacking step").

[0052] The bipolar current collector is preferably a laminate of aluminum foil and copper foil, but the type of metal foil is not particularly limited as long as it is not decomposed and alloyed at the potentials of the positive and negative electrodes.

[0053] The metal foil of the bipolar current collector may have an adhesive layer or a carbon coating layer provided on the surface thereof in order to improve wettability and adhesion to the positive electrode layer and the negative electrode layer.

[0054] The adhesive used to bond the metal foils together is not particularly limited, and for example, a polyolefin adhesive can be used. The adhesive preferably contains a conductive agent to improve the conductivity in the stacking direction of the bipolar battery. Examples of the conductive agent include nickel-plated particles and carbon black.

[0055] The lamination process may be performed manually or by using a stacker. The laminate obtained by lamination may be further rolled to the extent that the porosity does not change, and a bipolar electrode is produced through this additional rolling process. [Example]

[0056] Hereinafter, embodiments of the present disclosure will be described in more detail using examples, but the embodiments of the present disclosure are not limited to the following examples.

[0057] Example 1 [Preparation] The following electrode materials were prepared: -Positive electrode powder- Positive electrode active material: Lithium nickel cobalt manganese oxide (NCM) Resin: PVdF Conductive agent: carbon nanotubes Fiberizable compound: PTFE -Anode powder- Negative electrode active material: graphite Resin: PVdF Fiberizable compound: PTFE -Bipolar current collector- Laminated current collector (aluminum foil: conductive resin layer: copper foil = 40:17:8 (μm))

[0058] [Fabrication of bipolar electrodes] A bipolar electrode was fabricated according to the following steps (1) to (7). (1) Preparation of positive electrode powder Nickel cobalt manganese oxide (NCM) as the positive electrode active material, PVdF as the resin, and carbon nanotubes as the conductive agent were mixed and kneaded in a mass ratio of positive electrode active material:resin:conductive agent=96.25:1.0:0.75. Next, PTFE as a fiberizable compound was mixed with this mixture so that the mass ratio of the positive electrode active material to the PTFE was 96.25:2.0, and the mixture was further kneaded. Next, this kneaded mixture was subjected to shearing for 3 minutes at a rotation speed of 10 rpm in a batch kneader (manufactured by Nihon Spindle Co., Ltd.) to convert the PTFE into fibers. (2) Rolling (forming a free-standing positive electrode layer film) Next, the kneaded material containing the fibrous PTFE was rolled using a roll press (manufactured by Tester Sangyo Co., Ltd.) at a press pressure of 0.4 t / cm and a roll temperature of 160°C to produce a positive electrode layer that was a self-supporting film. (3) Compression (adjusting the porosity of the positive electrode layer) Next, the positive electrode layer, which was a free-standing film, was compressed with a roll press (manufactured by Nagano Automation Co., Ltd.) at a press pressure of 1.0 t / cm and a roll temperature of 25°C, and the porosity of the positive electrode layer was adjusted to the value shown in Table 1. The porosity of the positive electrode layer can be determined by the method described above.

[0059] (4) Preparation of negative electrode powder Graphite as the negative electrode active material and PVdF as the resin were mixed and kneaded in a mass ratio of negative electrode active material:binder resin=94:5. Next, PTFE as a fiberizable compound was mixed with this mixture so that the mass ratio of negative electrode active material:PTFE was 94:1, and the mixture was kneaded. Next, this kneaded mixture was subjected to shearing for 3 minutes at a rotation speed of 10 rpm in a batch kneader (manufactured by Nihon Spindle Co., Ltd.) to convert the PTFE into fibers. (5) Rolling (forming a self-standing negative electrode layer film) Next, the kneaded material containing the fibrous PTFE was rolled using a roll press (manufactured by Nagano Automation Co., Ltd.) at a pressure of 0.04 t / cm and a roll temperature of 160°C to produce a negative electrode layer that was a self-supporting film. (6) Compression (adjusting the porosity of the negative electrode layer) Next, the anode layer, which was a free-standing film, was compressed with a roll press (manufactured by Nagano Automation Co., Ltd.) at a pressure of 0.5 t / cm and a roll temperature of 25°C, and the porosity of the anode layer was adjusted to the value shown in Table 1. The porosity of the anode layer can be determined by the method described above. (7) Fabrication of bipolar electrodes A positive electrode layer, which is a self-supporting film with an adjusted porosity, and a negative electrode layer with an adjusted porosity were laminated via a bipolar current collector, and then bonded together using a roll press to obtain a bipolar electrode.

[0060] <Comparative Example 1> [Preparation] The following electrode materials were prepared: -Positive electrode powder- Positive electrode active material: Lithium nickel cobalt manganese oxide (NCM) Resin: PVdF Conductive agent: carbon nanotubes -Anode powder- Negative electrode active material: graphite Resin: SBR Conductive agent: carbon nanotubes Dispersant: Carboxymethylcellulose (CMC) -Bipolar current collector- Laminated current collector (aluminum foil: conductive resin layer: copper foil = 40:17:8 (μm), carbon coating layer formed on the aluminum foil and copper foil surfaces)

[0061] [Fabrication of bipolar electrodes] A bipolar electrode was fabricated according to the following steps (1) to (3). (1) Positive electrode coating Nickel cobalt manganese oxide (NCM) as the positive electrode active material, PVdF as the resin, and carbon nanotubes as the conductive agent were mixed in a mass ratio of positive electrode active material:binder resin:conductive agent = 97.8:1.4:0.8, and NMP was added and kneaded to prepare a positive electrode slurry. Next, the positive electrode slurry was applied to the aluminum foil side of the bipolar current collector using an applicator and dried to form a positive electrode layer. (2) Negative electrode coating Graphite as the negative electrode active material, SBR as the binder resin, carbon nanotubes as the conductive agent, and CMC as the dispersant were mixed in a mass ratio of negative electrode active material:binder resin:conductive agent:dispersant = 97.95:1.6:0.05:0.4, and water was added and the mixture was kneaded to prepare a negative electrode slurry. Next, the negative electrode slurry was applied to the copper foil side of the bipolar current collector using an applicator and dried to form a negative electrode layer. (3) Compression The bipolar electrodes with the positive and negative electrode layers formed thereon were compressed in a roll press (manufactured by Nagano Automation Co., Ltd.) at a pressure of 0.5 t / cm and a roll temperature of 25°C to produce bipolar electrodes. The porosity of the positive and negative electrode layers was determined according to the method described above. The results are shown in Table 1.

[0062] <Comparative Example 2> A bipolar electrode was fabricated in the same manner as in Comparative Example 1, except that compression was performed at a pressure of 1.0 t / cm and a roll temperature of 25° C., and the porosity of the positive electrode layer and the porosity of the negative electrode layer were determined. The results are shown in Table 1.

[0063] [Table 1]

[0064] As can be seen from the results in Table 1, the method for manufacturing a bipolar electrode according to the present disclosure allows the porosity of the positive electrode layer and the porosity of the negative electrode layer to be adjusted to the desired ranges, and this method can reduce the internal resistance of the battery.

[0065] On the other hand, in the bipolar electrode of Comparative Example 1, the porosity of the negative electrode layer was set within the target range (36% to 42%) and the positive electrode layer and negative electrode layer were pressed simultaneously, so the porosity of the negative electrode layer was within the desired range, but the porosity of the positive electrode layer was significantly higher than the desired range (20% to 26%).In the bipolar electrode of Comparative Example 2, the porosity of the positive electrode layer was set within the target range (20% to 26%) and the positive electrode layer and negative electrode layer were pressed simultaneously, as in Comparative Example 1, so the porosity of the positive electrode layer was within the desired range, but the porosity of the negative electrode layer was significantly lower than the desired range (36% to 42%).

Claims

1. a step of shear-mixing a mixture containing a positive electrode active material or a negative electrode active material and a resin with a compound selected from a fibrous compound and a compound capable of being made into a fiber to prepare a positive electrode powder and a negative electrode powder, respectively; rolling the positive electrode powder and the negative electrode powder to form a positive electrode layer and a negative electrode layer, respectively; a step of compressing the positive electrode layer and the negative electrode layer by applying different pressures to each of them, thereby adjusting the porosity of the positive electrode layer and the porosity of the negative electrode layer, respectively; A method for manufacturing a bipolar electrode, comprising:

2. The method for manufacturing a bipolar electrode according to claim 1 , wherein the fiberizable compound is polytetrafluoroethylene (PTFE).

3. a positive electrode layer, a current collecting foil, and a negative electrode layer, the porosity of the positive electrode layer is lower than the porosity of the negative electrode layer, and the difference between the porosity of the positive electrode layer and the porosity of the negative electrode layer is 8% or more; Bipolar electrodes.

4. 4. The bipolar electrode according to claim 3, wherein the porosity of the positive electrode layer is 20% to 26% and the porosity of the negative electrode layer is 36% to 42%.

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