Method for producing electrode and electrode produced thereby

Abstract

A method for manufacturing an electrode according to an embodiment of the present invention may comprise the steps of: applying a first coating layer comprising an active material on at least one surface of a current collector comprising a metal material; applying a plurality of second coating layers including the active material on at least one surface of the first coating layer; and rolling the current collector, the first coating and the second coating through a rolling device.

Description

TECHNICAL FIELD

[0001] Cross Reference to Related Applications

[0002] This application claims the benefit of priority of Korean Patent Application No. 10-2023-0179051, filed on December 11, 2023, the entire contents of which are incorporated herein by reference.

[0003]

[0004] The present application relates to a method for manufacturing an electrode and an electrode manufactured by the method. BACKGROUND

[0005] In order to solve the environmental pollution problem caused by the use of oil resources and solve the energy shortage problem due to the depletion of oil resources, research and development of power generation based on eco-friendly energy are being conducted. In particular, research on secondary batteries that can be repeatedly charged / discharged and thus have higher availability is being actively conducted, and various aspects such as materials, structures, processes, and stability of secondary batteries are being researched.

[0006] In general, secondary batteries include nickel-cadmium batteries, nickel-hydrogen batteries, lithium-ion batteries, and lithium-ion polymer batteries. Such secondary batteries are being applied and used in small products such as digital cameras, P-DVDs, MP3Ps, mobile phones, PDAs, portable game devices, power tools, electric bicycles, etc.; and large products requiring high power such as electric vehicles and hybrid vehicles, power storage devices for storing surplus power or renewable energy, and backup power storage devices.

[0007] In general, in order to manufacture a lithium secondary battery, first, an electrode active material slurry is coated on a positive electrode current collector and a negative electrode current collector to manufacture a positive electrode and a negative electrode. Then, the electrodes are stacked on both sides of a separator to form an electrode assembly. In addition, the electrode assembly can be accommodated in a battery case, electrolyte is injected, and then sealing is performed.

[0008] The secondary battery manufactured as described above can be used in various industrial applications, and research is being actively conducted in order to increase the capacity of the secondary battery, thereby further improving the performance of the secondary battery. A representative method for increasing the capacity of the secondary battery is to increase the density of the electrode by roll-pressing the electrode at a high pressure when the electrode assembly is manufactured by roll-pressing the electrode.

[0009] However, there is a problem in that electrolyte impregnability is reduced in an electrode that is highly roll-pressed. If the electrolyte impregnability is low, the electrolyte can not reach the electrode active material particles rapidly, and thus lithium ions can not move smoothly, thereby degrading the performance of the secondary battery. In addition, if the electrolyte impregnability is low, the impregnation speed is slow, leading to a problem in that the productivity of the secondary battery is degraded because a long time is required to manufacture the secondary battery.

[0010] Therefore, there is a need for a technology for manufacturing a secondary battery having high capacity and excellent electrolyte impregnability. SUMMARY

[0011] TECHNICAL PROBLEM

[0012] An object of the present application for solving the above problem is to provide a method of manufacturing an electrode by coating a plurality of second coating layers on a first coating layer such that regions having different active material densities and electrolyte impregnabilities are formed, and an electrode manufactured thereby.

[0013] TECHNICAL SOLUTION

[0014] The method for manufacturing an electrode according to an embodiment of the present application can include the steps of coating a first coating layer including an active material on at least one surface of a current collector including a metal material; coating a plurality of second coating layers including the active material on at least one surface of the first coating layer; and roll-pressing the current collector, the first coating layer, and the second coating layers by a roll-pressing device.

[0015] In the step of coating the second coating layers, the plurality of second coating layers can be coated at predetermined intervals from each other.

[0016] In the step of roll-pressing by the roll-pressing device, a first active material layer in which the first coating layer and the second coating layers are roll-pressed together, and a second active material layer in which the first coating layer is individually roll-pressed can be formed.

[0017] In the step of roll-pressing by the roll-pressing device, the density of the active material of the first active material layer can be higher than the density of the active material of the second active material layer.

[0018] In the step of roll-pressing by the roll-pressing device, the electrolyte impregnability of the second active material layer can be higher than the electrolyte impregnability of the first active material layer.

[0019] In the step of roll-pressing by the roll-pressing device, the electrode, the first coating layer, and the second coating layers can be roll-pressed such that an outer surface of the first active material layer and an outer surface of the second active material layer are disposed on the same surface.

[0020] In the step of applying the second coating, the second coating may be applied along the width direction of the current collector.

[0021] An electrode according to another embodiment of the present invention may include: a current collector comprising a metallic material; and an active material layer coated on at least one surface of the current collector, wherein the active material layer may include: a first active material layer; and a second active material layer, the second active material layer being alternately disposed with the first active material layer and having an active material density lower than that of the first active material layer.

[0022] The electrolyte impregnation property of the second active material layer can be higher than that of the first active material layer.

[0023] The first active material layer and the second active material layer can be formed along the width direction of the current collector.

[0024] Beneficial effects

[0025] According to a preferred embodiment of the present invention, a plurality of second coatings may be applied on the first coating to form regions with different active material densities and electrolyte impregnation properties, thereby manufacturing a high-capacity electrode and also an electrode with excellent electrolyte impregnation properties.

[0026] Furthermore, the configuration according to a preferred embodiment of the present invention may include effects that can be easily predicted by those skilled in the art. Attached Figure Description

[0027] The following accompanying drawings illustrate preferred embodiments of this disclosure and are used to further understand the technical spirit of this disclosure in conjunction with its detailed description. This disclosure should not be construed as being limited to the drawings.

[0028] Figure 1 This is a flowchart illustrating a method for manufacturing an electrode according to an embodiment of the present invention.

[0029] Figure 2 This is a perspective view illustrating a method for manufacturing an electrode according to an embodiment of the present invention, wherein a second coating is applied to the outer surface of a first coating.

[0030] Figure 3 This is a cross-sectional view showing the configuration of rolling a first coating, a second coating, and a current collector in a method for manufacturing an electrode according to an embodiment of the present invention.

[0031] Figure 4 This is a perspective view of an electrode according to another embodiment of the present invention.

[0032] Figure 5This is a perspective view of an electrode according to another embodiment of the present invention. Detailed Implementation

[0033] Preferred embodiments of the invention will be described in detail below with reference to the accompanying drawings, enabling those skilled in the art to readily implement the invention. However, the invention can be implemented in many different forms and is not limited to or construed as follows.

[0034] To clearly explain the invention, detailed descriptions of relevant well-known technologies that are irrelevant to the description or may unnecessarily obscure the spirit of the invention have been omitted, and reference numerals have been added to components in each drawing throughout this specification. In this case, the same or similar reference numerals are assigned to the same or similar elements throughout the specification.

[0035] Furthermore, the terms or words used in this specification and claims should not be construed as having a general meaning or a dictionary-based meaning, but should be interpreted in accordance with the principle that the inventor can appropriately define the concepts of the terms to best describe and interpret his or her invention, in a meaning and concept that is consistent with the scope of the invention.

[0036] Figure 1 This is a flowchart illustrating a method for manufacturing an electrode according to an embodiment of the present invention.

[0037] Reference Figure 1 Electrode 1 can be manufactured using a method for manufacturing electrodes according to an embodiment of the present invention. For example, according to the method for manufacturing electrodes, a coating comprising an active material can be coated on at least one surface of the current collector 10. With the coating coated on at least one surface of the current collector 10, the current collector 10 and the coating can be rolled using a rolling device to manufacture electrode 1 according to another embodiment of the present invention as described below.

[0038] Specifically, a first coating 11a and a second coating 11b can be sequentially coated on at least one surface of the current collector 10, and then the current collector 10, the first coating 11a and the second coating 11b can be rolled by a rolling device.

[0039] The current collector 10 can refer to a thin film used to form an electrode assembly, which includes a structure in which plate-like materials are wound into a roll or cut to stack. The current collector 10 can be used to transfer electrons from the outside to the active material or release electrons from the active material to the outside during the charging and discharging process of a secondary battery, thereby enabling an electrochemical reaction to occur.

[0040] The current collector 10 may include a metallic material. Specifically, the material of the current collector 10 may vary according to the type of electrode plates divided into the negative electrode and the positive electrode. For the current collector 10 of the negative electrode, copper foil that is electrochemically stable within the operating range of the carbon electrode 1 and has excellent electrical conductivity may be mainly used. On the other hand, for the current collector 10 of the positive electrode, aluminum foil that is stable even in the electrochemical reaction at a high potential and has excellent electrical conductivity may be used.

[0041] The method for manufacturing the current collector 10 may vary according to the type of electrode plates. Aluminum foil may be manufactured by thinly spreading an aluminum sheet through a rolling process. On the other hand, copper foil may be manufactured by melting a copper wire through an electrolytic electroplating process.

[0042] Each of the first coating 11a and the second coating 11b may include an active material paste. The active material paste may refer to a material that is coated on the outer surface of the current collector 10 to generate electrical energy through a chemical reaction. In addition, the active material paste may include an active material, a conductive material, and an adhesive. That is, each of the first coating 11a and the second coating 11b may include an active material.

[0043] The active material may chemically react to generate electrical energy. The active material may include a positive electrode active material or a negative electrode active material.

[0044] The positive electrode active material may include: layered compounds such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or compounds substituted with one or more transition metals; lithium manganese oxides such as LiMnO3, LiMn2O3, LiMnO2, etc.; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiFe3O4, V2O5, Cu2V2O7, etc.; nickel-site type lithium nickel oxides represented by the chemical formula LiNi 1-x M x O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B, or Ga, x = 0.01 to 0.3); lithium manganese composite oxides represented by the chemical formula LiMn 2-x M x O2 (where M = Co, Ni, Fe, Cr, Zn, or Ta, x = 0.01 to 0.1) or Li2Mn3MO8 (where M = Fe, Co, Ni, Cu, or Zn); lithium manganese composite oxides with a spinel structure represented by the chemical formula LiNi x Mn 2-x O4; lithium transition metal phosphate oxides represented by the chemical formula Li x CoPO4 (0.5 < x < 1.3); LiMn2O4 in which part of Li is substituted with an alkaline earth metal ion; disulfide compounds; Fe2(MoO4)3, etc., but not limited thereto.

[0045] The negative electrode active material may include: carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, amorphous carbon, etc.; metal compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys or Al alloys; metal oxides capable of plating and de-plating lithium such as SiO x (0 < x < 2), SnO2, vanadium oxides and lithium vanadium oxides; composites including metal compounds and carbonaceous materials such as lithium titanium oxides, metal composite oxides including two or more metals, or Si-C composites or Sn-C composites, etc. In addition, any one of these materials or a mixture of two or more of them may be used. In addition, a thin film of metallic lithium may be used as the negative electrode active material. In addition, low-crystalline carbon and high-crystalline carbon may be used. Representative examples of low-crystalline carbon may include soft carbon and hard carbon, and representative examples of high-crystalline carbon may include amorphous, plate-like, flaky, spherical or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature sintered carbons such as petroleum or coal tar pitch derived cokes.

[0046] The conductive material can facilitate the movement of electrons between the positive electrode active material and the negative electrode active material. For example, the conductive material may include a small amount of fine carbon powder to improve the conductivity between the active material particles or the current collector 10 and prevent the binder from acting as an insulator.

[0047] Although not particularly limited, exemplary examples of the conductive material may include: carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black and carbon fiber; graphite such as natural graphite or artificial graphite; metal powders or metal fibers such as copper, nickel, aluminum or silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these materials or a mixture of two or more of them may be used alone. The conductive material may be included in an amount of 1 wt% to 30 wt%, specifically 1 wt% to 10 wt%, more specifically 1 wt% to 5 wt% based on the total weight of the solid content in the active material slurry.

[0048] Adhesives can bond active materials to conductive materials. For example, adhesives can facilitate the mixing of active and conductive materials. Therefore, adhesives can ensure that the active and conductive materials are uniformly coated on the current collector 10. With repeated charging and discharging of the secondary battery, the bond between the active and conductive materials may weaken, and the volume of the current collector 10 may change, thus degrading the battery's lifespan and function. However, adhesives can mitigate this problem by increasing the bond strength between the active and conductive materials.

[0049] Although not particularly limited, exemplary examples of adhesives may include: polyvinylidene fluoride (PVDF), PVDF-co-HFP copolymer, polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluorinated elastomers, or various copolymers thereof, which may be used alone or in mixtures of two or more thereof. The adhesive may be contained in an amount from 1% to 30% by weight, specifically from 1% to 10% by weight, and more specifically from 1% to 5% by weight, based on the total weight of solids in the active material slurry.

[0050] According to the method used to manufacture the electrode, a coating can be applied multiple times to the outer surface of the current collector, and a second coating 11b can be applied with a specific structure. Therefore, multiple regions with different active material densities and electrolyte impregnation properties can be formed in the electrode 1. That is, in the electrode 1, a region with a relatively high active material density and a relatively high electrolyte impregnation property can be formed compared to other regions.

[0051] Figure 2 This is a perspective view showing a method for manufacturing an electrode according to an embodiment of the present invention, in which a second coating 11b is coated on the outer surface of a first coating 11a.

[0052] Reference Figure 2 The method for manufacturing the electrode may include: a step of coating a first coating 11a (S10), a step of coating a second coating 11b (S20), and a step of performing rolling by a rolling device (S30).

[0053] In the step (S10) of applying the first coating 11a, the first coating 11a may be applied to at least one surface of the current collector 10, which includes a metallic material. For example, the first coating 11a may be applied to one surface or both surfaces of the current collector 10. Furthermore, the first coating 11a may be formed only on a specific portion of the current collector 10, rather than being formed on the entire current collector 10.

[0054] The first coating 11a can be applied to at least one surface of the current collector 10 along its length. For example, the first coating 11a can be applied to the outer surface of the current collector 10 so that it has a length direction parallel to the length direction of the current collector 10.

[0055] When manufacturing electrode 1, the portion of current collector 10 on which the first coating 11a is formed can be formed as a coated portion including an active material slurry. Other portions of current collector 10 on which the first coating 11a is not formed can be formed as uncoated portions excluding an active material slurry.

[0056] In the step (S20) of coating the second coating 11b, a plurality of second coatings 11b comprising an active material may be coated on at least one surface of the first coating 11a. For example, the second coating 11b may be coated on one surface of the first coating 11a, and the other surface of the first coating 11a may be coated on the current collector 10. In other words, the first coating 11a may be coated on the top surface of the current collector 10, and the second coating 11b may be coated on the top surface of the first coating 11a.

[0057] In the step (S20) of coating the second coating 11b, multiple second coatings 11b can be coated at intervals. For example, the second coatings 11b can be coated along the width direction of the current collector 10, and multiple second coatings 11b can be formed at predetermined intervals. That is, the length direction of the second coatings 11b can be parallel to the width direction of the current collector 10. In other words, multiple second coatings 11b can be coated in strips on the outer surface of the first coating 11a.

[0058] However, the direction in which the second coating 11b is applied is not limited to this; the second coating 11b can be applied perpendicular to the width direction of the current collector 10.

[0059] The second coating 11b can be formed to be spaced apart from both ends of the first coating 11a. For example, the outermost pair of second coatings 11b among a plurality of second coatings 11b can be spaced apart from both ends of the first coating 11a by a predetermined distance.

[0060] According to the structure of the second coating 11b as described above, since the second coating 11b may not be formed at each of the two ends of the first coating 11a, it is possible to prevent the active material slurry from forming too high at both ends of the first coating 11a, thereby preventing problems such as slippage of the active material slurry.

[0061] In the step (S30) of performing rolling by a rolling device, the current collector 10, the first coating 11a, and the second coating 11b can be rolled by the rolling device. For example, the rolling device may include a rolling mill.

[0062] Specifically, the current collector 10, on which a first coating 11a and a second coating 11b are coated, can move between a pair of roller presses. The first coating 11a, the second coating 11b, and the current collector 10 can be rolled by pressing with the pair of roller presses.

[0063] Due to the rolling process of this rolling device, the density of the manufactured electrode 1 can be increased, and the adhesion and bonding strength between the current collector 10 and the active material slurry can be enhanced. Furthermore, due to the rolling process, the crystal structure of the electrode 1 becomes directional, thus allowing electrical energy to be generated from the electrode 1 with a greater output. As a result, the performance of the electrode 1 manufactured through the rolling process can be enhanced.

[0064] Figure 3 This is a cross-sectional view showing a method for manufacturing an electrode according to an embodiment of the present invention, in which a first coating 11a, a second coating 11b and a current collector 10 are rolled together.

[0065] Reference Figure 3 In the rolling process (S30) performed by the rolling device, a first active material layer 110 in which the first coating 11a and the second coating 11b are rolled together, and a second active material layer 111 in which the first coating 11a is rolled separately, can be formed. For example, when multiple second coatings 11b are applied to one surface of the first coating 11a at intervals, the first coating 11a and the second coating 11b can be rolled by the rolling device to form an area where the first coating 11a and the second coating 11b overlap. That is, the first active material layer 110 can be formed only in a specific portion of the first coating 11a coated with the second coating 11b.

[0066] Multiple first active material layers 110 and multiple second active material layers 111 can be formed, and multiple first active material layers 110 and multiple second active material layers 111 can be formed along the current collector 10. For example, the first active material layers 110 and the second active material layers 111 can be formed alternately along the length direction of the current collector 10.

[0067] Furthermore, the first active material layer 110 and the second active material layer 111 can be formed along the width direction of the current collector 10. In other words, the first active material layer 110 and the second active material layer 111 can be formed in a direction parallel to the width direction of the current collector 10.

[0068] In the rolling process (S30) performed by the rolling device, the electrode 1, the first coating 11a and the second coating 11b can be rolled so that the outer surface of the first active material layer 110 and the outer surface of the second active material layer 111 are disposed on the same surface.

[0069] In the rolling process (S30) performed by the rolling device, the density of the active material in the first active material layer 110 can be higher than the density of the active material in the second active material layer 111. In other words, since the first active material layer 110 is the portion formed by rolling the first coating 11a and the second coating 11b together, unlike the second active material layer 111 which has only the first coating 11a formed, the first active material layer 110 can contain a greater amount of active material. That is, because the first active material layer 110 contains a greater amount of active material than the same volume, the density of the active material in the first active material layer 110 can be higher than the density of the active material in the second active material layer 111.

[0070] Therefore, unlike the case where only the first coating 11a is coated on the current collector 10 and then rolled, a second coating 11b can be coated on the first coating 11a and then rolled. As a result, the method for manufacturing an electrode according to an embodiment of the present invention can form an active material region with a higher density, thereby manufacturing an electrode 1 with higher capacity and higher performance.

[0071] On the other hand, in the rolling process (S30) performed by the rolling device, the electrolyte impregnation property of the second active material layer 111 can be higher than that of the first active material layer 110. In other words, since the second active material layer 111 is formed only by the first coating 11a which does not overlap with the second coating 11b, it can be further impregnated with electrolyte.

[0072] Therefore, since the second active material layer 111 has relatively high electrolyte impregnation properties, the electrolyte impregnation rate can be increased when using electrode 1 to manufacture a secondary battery, thereby improving the productivity of the secondary battery. Furthermore, since the second active material layer 111, with its high electrolyte impregnation properties, allows the electrolyte to quickly reach the electrode active material particles and enables lithium ions to move more smoothly, the performance of the secondary battery manufactured using electrode 1 can be improved.

[0073] As a result, a high-capacity electrode 1 can be manufactured by forming a first active material layer 110 and a second active material layer 111 using the method for manufacturing an electrode according to an embodiment of the present invention, thereby manufacturing an electrode 1 with excellent electrolyte impregnation properties.

[0074] In the following description, an electrode 1 according to another embodiment of the present invention will be described. The electrode 1 according to another embodiment of the present invention can be manufactured by the method for manufacturing electrodes according to the embodiment of the present invention as described above.

[0075] Figure 4 This is a perspective view of an electrode according to another embodiment of the present invention.

[0076] Reference Figure 4 The electrode 1 can be manufactured by coating an active material layer 11 onto the current collector 10. For example, the current collector 10 may include a metallic material, and the active material layer 11 may be coated on at least one surface of the current collector 10.

[0077] The active material layer 11 may include a first active material layer 110 and a second active material layer 111 alternately disposed with the first active material layer 110. For example, multiple first active material layers 110 and multiple second active material layers 111 may be formed, and multiple first active material layers 110 and multiple second active material layers 111 may be formed along the current collector 10. The first active material layers 110 and the second active material layers 111 may be alternately formed along the length direction of the current collector 10.

[0078] Furthermore, the first active material layer 110 and the second active material layer 111 can be formed along the width direction of the current collector 10. In other words, the first active material layer 110 and the second active material layer 111 can be formed in a direction parallel to the width direction of the current collector 10.

[0079] The first active material layer 110 and the second active material layer 111 can be formed on the outer surface of the current collector, such that the outer surfaces of the first active material layer 110 and the second active material layer 111 are disposed on the same surface.

[0080] The density of the active material in the first active material layer 110 can be higher than that in the second active material layer 111. Furthermore, the electrolyte impregnation property of the second active material layer 111 can be higher than that of the first active material layer 110.

[0081] Figure 5 This is a perspective view of an electrode according to another embodiment of the present invention.

[0082] Reference Figure 5According to another embodiment of the present invention, the electrode 1 may include a first active material layer 110 formed along the length direction of the current collector 10. For example, according to another embodiment of the present invention, the first active material layer 110 may be formed parallel to the length direction of the current collector 10. Therefore, the second active material layer 111 may also be formed parallel to the length direction of the current collector 10. In other words, according to another embodiment of the present invention, the first active material layer 110 and the second active material layer 111 may be formed perpendicular to the width direction of the current collector.

[0083] The above disclosure is to be considered exemplary and not restrictive, and the appended claims are intended to cover all such modifications, alterations and other implementations that fall within the true spirit and scope of the invention.

[0084] Therefore, the embodiments of the present invention are to be considered exemplary rather than limiting, and the technical spirit of the present invention is not limited to the foregoing embodiments.

[0085] Therefore, the scope of the invention is not limited by the detailed description of the invention, but by the appended claims, and all differences within the scope shall be interpreted as included in the invention.

[0086] [Reference Marker Explanation]

[0087] 1: Electrode

[0088] 10: Current collector

[0089] 11: Active material layer

[0090] 110: First active material layer

[0091] 111: Second active material layer

[0092] 11a: First coating

[0093] 11b: Second coating.

Claims

1. A method for manufacturing an electrode, the method comprising the following steps: A first coating comprising an active material is applied to at least one surface of a current collector comprising a metallic material; A plurality of second coatings comprising the active material are applied to at least one surface of the first coating; as well as The current collector, the first coating, and the second coating are rolled using a rolling device.

2. The method according to claim 1, wherein, In the step of applying the second coating, the plurality of second coatings are applied at predetermined intervals.

3. The method according to claim 2, wherein, In the step of rolling by the rolling device, a first active material layer is formed in which the first coating and the second coating are rolled together, and a second active material layer in which the first coating is rolled separately.

4. The method according to claim 3, wherein, In the rolling process using the rolling device, the density of the active material in the first active material layer is higher than that in the second active material layer.

5. The method according to claim 3, wherein, In the rolling step performed by the rolling device, the electrolyte impregnation of the second active material layer is higher than that of the first active material layer.

6. The method according to claim 3, wherein, In the rolling step performed by the rolling device, the electrode, the first coating and the second coating are rolled so that the outer surfaces of the first active material layer and the second active material layer are disposed on the same surface.

7. The method according to claim 2, wherein, In the step of applying the second coating, the second coating is applied along the width direction of the current collector.

8. An electrode, comprising: Including current collectors made of metallic materials; as well as An active material layer coated on at least one surface of the current collector. The active material layer includes: First active material layer; as well as A second active material layer is alternately disposed with the first active material layer and has an active material density that is lower than that of the first active material layer.

9. The electrode according to claim 8, wherein the electrolyte impregnation property of the second active material layer is higher than that of the first active material layer.

10. The electrode according to claim 8, wherein the first active material layer and the second active material layer are formed along the width direction of the current collector.

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