Bipolar electrode and power storage device

Abstract

To provide a bipolar electrode and a power storage device, in which increase in resistance is suppressed.SOLUTION: There is provided a bipolar electrode in which a cathode active material layer, an electrode current collector, and an anode active material layer are provided in this order. The cathode active material layer includes a first cathode active material and a second cathode active material having a layered crystal structure, the first cathode active material has a number-based first particle size distribution, the second cathode active material has a number-based second particle size distribution, and the first cathode active material and the second cathode active material satisfy the relationship of the following expression (1). 1.5<(D150 / D250)≤15 (1) In the expression (1), D150 indicates a particle size having an integrated value of 50% in the first particle size distribution, and D150 has a unit of μm. In the expression (1), D250 indicates a particle size having an integrated value of 50% in the second particle size distribution, and D250 has a unit of μm.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a bipolar electrode and an energy storage device.

Background Art

[0002] Japanese Unexamined Patent Application Publication No. 2023-91568 (Patent Document 1) discloses using two types of positive electrode active materials having different average particle diameters for the purpose of increasing the volume capacity density of the positive electrode of a non-aqueous electrolyte secondary battery.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In Patent Document 1, although the volume capacity density of the positive electrode of the non-aqueous electrolyte secondary battery is improved, there is room for improvement from the viewpoint of resistance.

[0005] Here, a bipolar electrode (bipolar battery) having a positive electrode active material layer on one surface of a current collector and a negative electrode active material layer on the other surface is known. The bipolar battery has attracted attention from the viewpoint of improving the energy density as compared with a conventional non-aqueous electrolyte secondary battery.

[0006] However, since the positive electrode and the negative electrode are pressed simultaneously in the bipolar electrode, the positive electrode is not sufficiently pressed, and the contact of the positive electrode active material deteriorates. Further, in the bipolar battery, current flows in the thickness direction of the electrode, but if the contact between the positive electrode active materials or between the positive electrode active material and the conductive material is insufficient, the current flow path becomes complicated or interrupted, etc., resulting in problems such as an increase in resistance and deterioration of durability.

[0007] An object of the present disclosure is to provide a bipolar electrode and an energy storage device in which an increase in resistance is suppressed.

Means for Solving the Problems

[0008] [1] A bipolar electrode including a positive electrode active material layer, an electrode current collector, and a negative electrode active material layer in this order, The positive electrode active material layer includes a first positive electrode active material and a second positive electrode active material having a layered crystal structure, The first positive electrode active material has a first particle size distribution based on the number, The second positive electrode active material has a second particle size distribution based on the number, The first positive electrode active material and the second positive electrode active material satisfy the following formula (1), a bipolar electrode. 1.5 < (D150 / D250) ≤ 15 (1) In the above formula (1), D150 indicates the particle diameter at which the integrated value becomes 50% in the first particle size distribution, and D150 has a unit of μm, In the above formula (1), D250 indicates the particle diameter at which the integrated value becomes 50% in the second particle size distribution, and D250 has a unit of μm.

[0009] The positive electrode active material of the present technology includes a first positive electrode active material and a second positive electrode active material. As shown in the above formula (1), the first positive electrode active material has a larger D50 than the second positive electrode active material. When the second positive electrode active material enters the gaps between the first positive electrode active materials, a conductive path is formed, and as a result, suppression of an increase in resistance is expected.

[0010] In addition, “D150 / D250” shown in the above formula (1) is also referred to as, for example, “particle diameter ratio”. It is considered that when the particle diameter ratio is in a specific range, the second positive electrode active material is more likely to enter the gaps between the first positive electrode active materials.

[0011] [2] The first positive electrode active material satisfies the following formula (2), The second positive electrode active material satisfies the following formula (3), the bipolar electrode according to [1]. 9 ≤ D150 ≤ 20 (2) 2 ≤ D250 ≤ 5 (3)

[0012] [3] The first positive electrode active material satisfies the relationship of the following formula (4), The second positive electrode active material satisfies the relationship of the following formula (5), the bipolar electrode according to [1] or [2]. (D190 - D110) / D150 ≤ 2.1 (4) (D290 - D210) / D250 ≤ 2.5 (5) In the above formula (4), D110 and D190 respectively represent the particle diameter at which the integrated value becomes 10% and the particle diameter at which the integrated value becomes 90% in the first particle size distribution, and D110 and D190 each have a unit of μm, In the above formula (5), D210 and D290 respectively represent the particle diameter at which the integrated value becomes 10% and the particle diameter at which the integrated value becomes 90% in the second particle size distribution, and D210 and D290 each have a unit of μm.

[0013] "(D90 - D10) / D50" shown in the above (4) and (5) is also referred to as, for example, "span value", etc. The span value is an index of the spread of the particle size distribution. The smaller the span value, the sharper the particle size distribution is considered to be. When the relationships of the above (4) and (5) are satisfied, the amount of fine particles and coarse particles is reduced, so in addition to suppressing the increase in resistance, an improvement in thermal stability is expected.

[0014] [4] A power storage device including the bipolar electrode according to any one of [1] to [3].[[]END]]

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Mode for Carrying Out the Invention

[0016] Hereinafter, embodiments of the present disclosure (hereinafter may be abbreviated as "the present embodiment"), and examples of the present disclosure (hereinafter may be abbreviated as "the present example") will be described. However, the present embodiment and the present example do not limit the technical scope of the present disclosure.

[0017] In this specification, when a compound is represented by a stoichiometric composition formula such as "LiCoO2", the stoichiometric composition formula is merely a representative example. For example, when lithium cobaltate is represented as "LiCoO2", unless otherwise specified, lithium cobaltate is not limited to a composition ratio of "Li / Co / O = 1 / 1 / 2", and may contain Li, Co, and O at any composition ratio. The composition ratio may be non-stoichiometric.

[0018] In this specification, "at least one of the first positive electrode active material and the second positive electrode active material" may be collectively referred to as "the positive electrode active material". "The ratio of the D50 of the second positive electrode active material to the D50 of the first positive electrode active material" is also referred to as "the particle size ratio".

[0019] Regarding the "particle size distribution" in this specification, "D10", "D50", and "D90" are defined as follows. D10 indicates the particle size (unit: μm) at which the cumulative frequency (integrated value) from the smaller particle size becomes 10% in the particle size distribution based on the number. D50 indicates the particle size at which the cumulative frequency from the smaller particle size becomes 50% in the particle size distribution based on the number. D90 indicates the particle size at which the cumulative frequency from the smaller particle size becomes 90% in the particle size distribution based on the number.

[0020] In this specification, the volume-based particle size distribution is converted into the number-based particle size distribution. The volume-based particle size distribution can be measured by a laser diffraction particle size distribution measuring device. The measurement procedure can be as follows. A measurement target (positive electrode active material) is prepared. A measurement sample (particle dispersion liquid) is prepared by mixing the measurement target, a dispersant, and a dispersion medium. The volume-based particle size distribution is measured by introducing the measurement sample into a laser diffraction particle size distribution measuring device.

[0021] <Bipolar electrode> The bipolar electrode of this embodiment is used as an electrode of an energy storage device. The energy storage device is a non-aqueous electrolyte secondary battery such as a lithium-ion secondary battery, for example. In this embodiment, the bipolar electrode used in a lithium-ion secondary battery will be described.

[0022] FIG. 1 is a schematic diagram showing an example of the bipolar electrode of this embodiment. The bipolar electrode 20 includes a positive electrode active material layer 21, an electrode current collector 10, and a negative electrode active material layer 22 in this order. That is, the positive electrode active material layer 21 is adhered to one main surface of the electrode current collector 10, and the negative electrode active material layer 22 is adhered to the other main surface, respectively.

[0023] 《Positive electrode active material layer》 FIG. 2 is a schematic diagram showing an example of the positive electrode active material layer of this embodiment. The positive electrode active material layer 21 contains a positive electrode active material. The positive electrode active material contains a first positive electrode active material 1 and a second positive electrode active material 2. The first positive electrode active material 1 and the second positive electrode active material 2 have a layered crystal structure. The crystal structure of the positive electrode active material can be identified by, for example, Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) or the like.

[0024] (Positive electrode active material) The positive electrode active material of this embodiment can reversibly occlude and release lithium ions. The positive electrode active material is a positive electrode active material containing a lithium metal-containing composite oxide. The positive electrode active material of this embodiment may be a positive electrode active material composed of a lithium metal-containing composite oxide. As the lithium metal-containing composite oxide, for example, at least one selected from the group consisting of LiCoO2, LiNiO2, LiMnO2, Li(NiCoMn)O2, and Li(NiCoAl)O2 may be used. Among them, Li(NiCoMn)O2 is preferable because of its particularly excellent resistance characteristics. Such a lithium metal-containing composite oxide preferably has a composition represented by the following formula (i). Note that the first positive electrode active material 1 and the second positive electrode active material 2 may have the same composition or different compositions. Also, the chemical composition of the positive electrode active material can be measured by, for example, ICP-AES or the like. Li z Ni 1-x-y Co x Mn y O2(i) In the above formula (i), x, y, and z satisfy the relationships of 0.1 ≦ x ≦ 0.4, 0.1 ≦ y ≦ 0.5, and 0.95 ≦ z ≦ 1.2.

[0025] (The first positive electrode active material) The first positive electrode active material 1 is, so to speak, large particles. The first positive electrode active material 1 has a relatively larger particle diameter compared to the second positive electrode active material 2. The first positive electrode active material 1 can contribute to the improvement of energy density, input / output characteristics, storage characteristics, etc. The first positive electrode active material 1 has a first particle size distribution based on the number. D150 is D50 in the first particle size distribution. D150 may be, for example, 9 μm or more and 20 μm or less.

[0026] (The second positive electrode active material) The second positive electrode active material 2 is, so to speak, small particles. The second positive electrode active material 2 has a relatively small particle diameter compared to the first positive electrode active material 1. The second positive electrode active material 2 can form a conductive path between large particles. The second positive electrode active material 2 can contribute to the improvement of cycle durability. The second positive electrode active material 2 has a second particle size distribution based on the number. D250 is the D50 in the second particle size distribution. D250 may be, for example, 2 μm or more and 5 μm or less.

[0027] (Particle size ratio) The "particle size ratio (D150 / D250)" in the present embodiment is obtained by dividing D150 of the first positive electrode active material 1 by D250 of the second positive electrode active material 2. The particle size ratio is more than 1.5 and 15 or less. When the particle size ratio is within the above range, suppression of an increase in resistance is expected. This is presumably because the small particle second positive electrode active material 2 easily enters the gaps between the large particle first positive electrode active materials 1. The particle size ratio may be, for example, 1.8 or more, or may be 3.0 or more. The particle size ratio may be, for example, 10 or less, or may be 9.0 or less.

[0028] (Span value) The first particle size distribution may be a sharper distribution than the second particle size distribution. That is, the first particle size distribution may have a smaller span value than the second particle size distribution. Thereby, since the amounts of fine particles and coarse particles are reduced, in addition to suppression of an increase in resistance, an improvement in thermal stability is expected.

[0029] D110 is the D10 in the first particle size distribution. D190 is the D90 in the first particle size distribution. The span value [(D190 - D110) / D150] of the first particle size distribution is 2.1 or less.

[0030] D210 is the D10 in the second particle size distribution. D290 is the D90 in the second particle size distribution. The span value [(D290 - D210) / D250] of the second particle size distribution is 2.5 or less.

[0031] (Content ratio) The content ratio of the first positive electrode active material 1 and the second positive electrode active material 2 is not particularly limited. Their mass ratio (first positive electrode active material 1: second positive electrode active material 2) may be, for example, 30:70 to 70:30, or may be 40:60 to 60:40.

[0032] (Content ratio) The content of the positive electrode active material in the positive electrode active material layer 21, that is, the total content of the first positive electrode active material 1 and the second positive electrode active material 2 with respect to the total mass of the positive electrode active material layer 21 may be, for example, 50% by mass or more, or may be 70% by mass or more, or may be 80% by mass or more, or may be 90% by mass or more, or may be 95% by mass or more, or may be substantially 100% by mass.

[0033] (Other components) The positive electrode active material layer 21 may further contain, for example, a conductive material, a binder, etc. The conductive material may contain, for example, acetylene black (AB), etc. The binder may contain, for example, PVDF, etc. The conductive material and the binder may be, for example, 0.1% by mass or more and 10% by mass or less with respect to the positive electrode active material layer 21.

[0034] (Preparation of positive electrode active material) The preparation of the positive electrode active material is carried out, for example, according to the following procedure. Sulfates such as Ni are prepared. An acidic aqueous solution is formed by dissolving the sulfate in water. For example, an acidic aqueous solution can be formed by dissolving nickel sulfate, cobalt sulfate, and manganese sulfate in water.

[0035] A reaction vessel is prepared. An ammonium ion donor such as aqueous ammonia is added to the reaction vessel and stirred. While stirring, a pH adjuster such as sodium hydroxide is added to the reaction vessel to prepare an alkaline aqueous solution. While controlling the pH of the reaction solution to be constant, the acidic aqueous solution is dropped into the alkaline aqueous solution. Thereby, a precipitate can be formed. The precipitate is considered to contain a composite hydroxide (precursor). The precipitate is washed, filtered, and dried to form a dried product.

[0036] A mixture is formed by mixing a dried product and a lithium compound. The lithium compound may contain, for example, lithium carbonate, lithium hydroxide, etc. The mixture is heat-treated (fired) to synthesize a lithium metal-containing composite oxide powder. The synthesized lithium metal-containing composite oxide powder is crushed to prepare a positive electrode active material.

[0037] In this embodiment, by appropriately adjusting the stirring speed in the reaction vessel, the pH of the reaction solution, the mixing ratio of the ammonium ion donor and the acidic solution, the dropping speed and dropping time of the acidic solution, the firing temperature, the firing time, etc., a positive electrode active material having desired D10, D50, and D90 can be prepared.

[0038] 《Electrode current collector》 The electrode current collector 10 may contain at least one selected from the group consisting of, for example, aluminum (Al), stainless steel, nickel (Ni), chromium (Cr), platinum (Pt), niobium (Nb), iron (Fe), titanium (Ti), copper (Cu), and zinc (Zn). Further, the electrode current collector 10 may be obtained by plating the surface of a metal foil.

[0039] 《Negative electrode active material layer》 The negative electrode active material layer 22 contains a negative electrode active material. The negative electrode active material may contain at least one selected from the group consisting of, for example, graphite, soft carbon, and hard carbon. The negative electrode active material layer may further contain, for example, a binder, a thickener, etc. Examples of the binder include styrene butadiene rubber (SBR), etc. Examples of the thickener include carboxymethyl cellulose (CMC), etc.

[0040] <Electric energy storage device> FIG. 3 is a schematic diagram showing an example of the electric energy storage device of this embodiment. In this embodiment, the case where the electric energy storage device 100 is a lithium-ion secondary battery (hereinafter may be abbreviated as "battery") will be described.

[0041] The battery 100 may include an exterior body (not shown). The exterior body may contain the power generation element 50 and an electrolytic solution (not shown). The exterior body may have any form. The exterior body may be, for example, a metal case, or a pouch made of a metal foil laminate film or the like. The exterior body may contain, for example, Al or the like.

[0042] The battery 100 includes the power generation element 50. The power generation element 50 may also be referred to as an electrode body or an electrode group. The power generation element 50 includes the bipolar electrode 20 and the separator 30. The power generation element 50 may be formed by alternately laminating the bipolar electrode 20 and the separator 30.

[0043] 《Separator》 The separator 30 is porous. The separator 30 can permeate the electrolytic solution. The separator 30 separates the positive electrode active material layer 21 and the negative electrode active material layer 22. The separator 30 is electrically insulating. The separator 30 may contain, for example, polyolefin resins such as polyethylene (PE) and polypropylene (PP). The separator 30 may have, for example, a single-layer structure or a multilayer structure. The separator 30 may consist essentially of a PE layer, or may be formed by laminating a PP layer, a PE layer, and a PP layer in this order.

[0044] 《Electrolytic Solution》 The electrolytic solution contains a solvent and a Li salt. The solvent is aprotic. The solvent may contain any components. The solvent may contain, for example, at least one selected from the group consisting of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC).

[0045] The Li salt is a supporting electrolyte. The Li salt is dissolved in the solvent. The Li salt may contain, for example, at least one selected from the group consisting of LiPF6 and LiBF4. The Li salt may have, for example, a molar concentration of 0.5 mol / L or more and 2.0 mol / L or less.

[0046] The electrolyte may further contain an optional additive. For example, the electrolyte may contain an additive in an amount of 0.01% by mass or more and 5% by mass or less. The additive may contain, for example, at least one selected from the group consisting of vinylene carbonate (VC) and vinyl ethylene carbonate (VEC).

Examples

[0047] <Manufacture of the positive electrode active material> 《No.A》 An acidic aqueous solution was obtained by dissolving nickel sulfate, cobalt sulfate, and manganese sulfate in ion-exchanged water. The molar ratio of Ni, Co, and Mn in the acidic aqueous solution was 8:1:1, and the concentration of the acidic aqueous solution was 30% by mass.

[0048] Ammonia water was supplied to the reaction vessel and stirred with a stirrer. Next, an alkaline aqueous solution was prepared by supplying an aqueous sodium hydroxide solution to the reaction vessel. While the alkaline aqueous solution in the reaction vessel was stirred by the stirrer, the acidic aqueous solution was dropped into the alkaline aqueous solution. During the dropping of the acidic aqueous solution, ammonia water and the aqueous sodium hydroxide solution were appropriately added so that the ammonia concentration and pH of the reaction solution became constant. The precipitate after the reaction was washed with water and filtered to obtain a composite hydroxide. The obtained composite hydroxide was dried at 120°C for 16 hours to obtain a dried product. In the above reaction, the atmosphere of the reaction vessel, the stirring speed, the pH of the reaction solution, the mixing volume ratio of ammonia water to the acidic solution (NH3 / acidic solution), the dropping speed of the acidic solution, and the dropping time are as shown in FIG. 4.

[0049] The dried product and lithium carbonate were mixed in a mortar to obtain a mixture. The mixture was fired in a muffle furnace under an oxygen atmosphere to obtain a lithium metal-containing composite oxide powder. The lithium metal-containing composite oxide powder was pulverized using a jet mill to obtain the positive electrode active material of No.A. The mixing molar ratio of Li to Ni, Co, and Mn in the dried product (Li / Ni+Co+Mn), the firing temperature, and the firing time are as shown in FIG. 4.

[0050] 《No.B~F, No.a~e》 The positive electrode active materials of No.B~F and No.a~e were obtained by the same process as No.A, except that the manufacturing conditions were changed as shown in Fig. 4. Each positive electrode active material of No.A~F is the first positive electrode active material, and each positive electrode active material of No.a~e is the second positive electrode active material.

[0051] 《Composition》 The composition of the positive electrode active material of each No. was confirmed by an ICP emission spectroscopic analyzer (PS3520UVDD, manufactured by Hitachi High-Technologies Corporation). The results are shown in Fig. 4. Also, as a result of confirming the crystal structure of each No., it was confirmed that all the positive electrode active materials have a layered crystal structure.

[0052] 《Particle Size Distribution》 The volume-based particle size distribution of the positive electrode active material of each No. was measured by a laser diffraction particle size distribution measuring device. The measured volume-based particle size distribution was converted into a number-based particle size distribution. D50 of the positive electrode active material of each No. is shown in Fig. 4. Also, in the test battery for evaluation described later, the particle size ratio (D150 / D250), the span value of the first particle size distribution [(D190 - D110) / D150], and the span value of the second particle size distribution [(D290 - D210) / D250] were obtained from D10, D50, and D90 of the positive electrode active material of each No. The results are shown in Fig. 5.

[0053] <Manufacture of Lithium-Ion Secondary Battery> As materials for the positive electrode active material layer, the positive electrode active materials of No.A~F and No.a~e, AB (Denka Co., Ltd.) as a conductive material, and PVdF (Kureha Corporation) as a binder were prepared. The positive electrode active material layer was fabricated using the above materials. The mass ratio of each material in the positive electrode active material layer is First positive electrode active material: Second positive electrode active material: Conductive material: Binder = 45:45:5:5.

[0054] As materials for the negative electrode active material layer, natural graphite (Hitachi Chemical Co., Ltd.) as the negative electrode active material, SBR (JSR Corporation) as the binder, and CMC (Nippon Paper Industries Co., Ltd.) as the thickener were prepared. Using the above materials, a negative electrode active material layer was fabricated. The mass ratio of each material in the negative electrode active material layer is negative electrode active material: binder: thickener = 95:2.5:2.5.

[0055] Al foil (thickness: 15 μm) was prepared as the electrode current collector. A bipolar electrode was fabricated by laminating the positive electrode active material layer, the electrode current collector, and the negative electrode active material layer in this order.

[0056] As the separator, a porous resin (PP / PE / PP) (thickness: 24 μm) with PP layers laminated on both sides of the PE layer was prepared. The bipolar electrode, the separator, and the bipolar electrode were laminated so that the separator separated the positive electrode active material layer and the negative electrode active material layer. Thereby, an electrode body was formed.

[0057] As the exterior body, a pouch made of a laminated film was prepared. The electrode body was housed in the exterior body. As the electrolytic solution, a mixture obtained by dissolving a supporting salt (LiPF6) in a mixed solvent containing EC, DMC, and EMC at a concentration of 1 mol / L was prepared. The electrolytic solution was injected into the exterior body. After injecting the electrolytic solution, the exterior body was sealed. Thus, test cells for evaluation Nos. 1 to 13 were manufactured. The first positive electrode active material and the second positive electrode active material used in each No. are shown in FIG. 5.

[0058] <Evaluation> 《Normalized IV Resistance》 Under a temperature environment of 25°C, the SOC (State of Charge) of the test battery was adjusted to 50% by constant current-constant voltage (CC-CV) charging. The current during constant current (CC) charging was 1It. "1It" is defined as the current that discharges the rated capacity of the battery in 1 hour. At 50% SOC, the voltage of the battery was 3.7V. After the adjustment of SOC, with a 30-minute pause in between, the battery was discharged for 10 seconds at a current of 10It. The initial discharge resistance (normalized IV resistance) was obtained by the following formula (ii). The results are shown in Figure 5. The initial resistance in Figure 5 is a relative value. The initial resistance of No.1 is defined as 1.

[0059] r=(V0-V 10 ) / current (ii) In the above formula (ii), r represents the discharge resistance. V0 represents the voltage at the start of discharge. V 10 represents the voltage 10 seconds after the start of discharge.

[0060] 《Thermal Stability》 Under a temperature environment of 25°C, the cell was charged up to 4.2V. By disassembling the cell in the charged state, the bipolar electrode was recovered. A sample was punched out from the bipolar electrode using a hole punch. The DSC (Differential Scanning Calorimetry) curve of the sample was obtained. The heating rate was 2°C / min, and the end temperature was 350°C. In the DSC curve, the heat generation start temperature was read. The higher the heat generation start temperature, the better the thermal stability is considered. In the item of the heat generation start temperature in Figure 5, "Ref" represents the heat generation start temperature of No.7. For example, "Ref + 8" represents a temperature 8°C higher than Ref.

[0061] <Results> As shown in Fig. 5, in Nos. 7 to 13, it can be seen that the normalized IV resistance is lower compared to Nos. 1 to 6. Also, in Nos. 5 to 13, it can be seen that the heat generation start temperature is high, that is, the thermal stability is good. From these results, it is considered that Nos. 7 to 13, in which the particle size ratio (D150 / D250), the span value of the first particle size distribution [(D190 - D110) / D150], and the span value of the second particle size distribution [(D290 - D210) / D250] are all within a predetermined range, achieve both suppression of resistance increase and good thermal stability.

[0062] This embodiment and these examples are illustrative in all respects. This embodiment and these examples are not restrictive. The technical scope of the present disclosure includes all modifications within the meaning and scope equivalent to the description of the claims. For example, any configurations are extracted from this embodiment and these examples, and their arbitrary combinations are also initially contemplated.

Description of Reference Numerals

[0063] 1 First positive electrode active material, 2 Second positive electrode active material, 10 Electrode current collector, 20 Bipolar electrode, 21 Positive electrode active material layer, 22 Negative electrode active material layer, 30 Separator, 50 Power generation element, 100 Energy storage device (lithium ion secondary battery).

Claims

1. A bipolar electrode comprising a positive electrode active material layer, an electrode current collector, and a negative electrode active material layer in this order, wherein the positive electrode active material layer contains a first positive electrode active material and a second positive electrode active material having a layered crystal structure, the first positive electrode active material has a first particle size distribution based on the number, the second positive electrode active material has a second particle size distribution based on the number, and the first positive electrode active material and the second positive electrode active material satisfy the relationship of the following formula (1): a bipolar electrode. 1.5 < (D １ 50 / D ２ 50) ≤ 15 (1) In the above formula (1), D １ 50 represents the particle diameter at which the integrated value becomes 50% in the first particle size distribution, and D １ 50 has the unit of μm, In the above formula (1), D ２ 50 represents the particle diameter at which the integrated value becomes 50% in the second particle size distribution, and D ２ 50 has the unit of µm.

2. The first positive electrode active material satisfies the relationship of the following formula (2), and the second positive electrode active material satisfies the relationship of the following formula (3): the bipolar electrode according to Claim 1. 9 ≤ D １ 50 ≤ 20 (2) 2 ≤ D ２ 50 ≤ 5(3)

3. The first positive electrode active material satisfies the relationship of the following formula (4), and the second positive electrode active material satisfies the relationship of the following formula (5): the bipolar electrode according to Claim 1. (D １ 90 - D １ 10) / D １ 50 ≤ 2.1 (4) (D ２ 90 - D ２ 10) / D ２ 50 ≤ 2.5 (5) In the above formula (4), D １ 10 and D １ 90 respectively represent the particle diameter at which the integrated value becomes 10% and the particle diameter at which the integrated value becomes 90% in the first particle size distribution, and D １ 10 and D １ 90 each have the unit of μm, In the above formula (5), D ２ 10 and D ２ 90 respectively represent the particle diameter at which the integrated value becomes 10% and the particle diameter at which the integrated value becomes 90% in the second particle size distribution, and D ２ 10 and D ２ 90 each have the unit of μm.

4. An electric storage device comprising the bipolar electrode according to any one of Claims 1 to 3.

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