Bipolar electrode, manufacturing method therefor, and bipolar secondary battery comprising same

Abstract

The present invention relates to a bipolar electrode, a manufacturing method therefor, and a bipolar secondary battery comprising same, the bipolar electrode incurring reduced damage to an anode mixture layer during a rolling process and including an anode and a cathode that have uniform porosity and are formed on each of two sides of a metal current collector.

Description

Bipolar electrode, method for manufacturing the same, and bipolar secondary battery including the same

[0001] Cross-citation with related application(s)

[0002] The present application claims the benefit of priority based on Korean Patent Application No. 10-2024-0123554 filed September 10, 2024, Korean Patent Application No. 10-2024-0173645 filed November 28, 2024, and Korean Patent Application No. 10-2025-0127214 filed September 8, 2025, and all contents disclosed in the documents of said Korean patent applications are incorporated herein as part of the specification.

[0003] The present invention relates to a bipolar electrode in which damage to the cathode composite layer is reduced during the rolling process and a cathode and an anode having mutually uniform porosity are formed on both sides of a metal current collector, a method for manufacturing the same, and a bipolar secondary battery including the same.

[0004] Recently, as the application areas of lithium-ion batteries have rapidly expanded to include not only power supply for electronic devices such as electrical, electronic, telecommunications, and computers, but also power storage for large-area devices such as automobiles and power storage systems, there is a growing demand for high-capacity, high-output, and high-stability secondary batteries.

[0005] Conventional lithium-ion batteries generally adopt a structure in which multiple unit cells are connected in parallel. Each unit cell comprises a monopolar positive and negative electrode, each coated with an active material of the same polarity on a current collector, and a separator or electrolyte layer interposed between them. In this conventional battery structure, problems such as increased resistance, reduced power density, high heat generation, and low safety can occur in terms of the current flow path.

[0006] Accordingly, interest in and research on bipolar secondary batteries including bipolar electrodes have recently increased significantly. The bipolar electrode has a structure in which active materials of different polarities are coated on each side of a current collector, and the bipolar secondary battery has a structure in which multiple such bipolar electrodes are stacked with a separator or an electrolyte layer interposed therebetween.

[0007] In such bipolar secondary batteries, unit cells defined by mutually facing positive and negative electrodes and a separator or electrolyte layer between them are connected in series. Accordingly, the current path of the bipolar secondary battery is shortened, thereby reducing resistance and increasing power density, and the components and structures for controlling each unit cell within a module or pack containing the bipolar secondary battery can be simplified.

[0008] However, the above-described bipolar electrode has a disadvantage in that the electrode formation process, particularly the rolling process, becomes difficult to proceed with as active materials and composite layers having different characteristics are formed on both sides of the current collector. As a typical example, a lithium transition metal oxide can be used as the positive electrode active material and a graphite-based active material can be used as the negative electrode active material in the above-described bipolar electrode. However, since the graphite-based active material has lower strength and ductility compared to the lithium transition metal oxide, if rolling is performed on both sides of the bipolar electrode under the same conditions, it is difficult to achieve a desired level of porosity or rolling density for the positive electrode composite layer (when rolling is performed based on the negative electrode composite layer), or damage may occur to the negative electrode composite layer, particularly at the ends of the negative electrode composite layer (when rolling is performed based on the positive electrode composite layer).

[0009] To solve this, a method may be considered in which a positive electrode composite layer is formed and dried first, a first rolling is performed on the positive electrode composite layer before forming and drying the negative electrode composite layer, and a second rolling is performed on both sides after forming and drying the negative electrode composite layer. However, according to this configuration, the manufacturing process of the overall bipolar electrode becomes excessively complex, and disadvantages such as difficulty in controlling the loading amount of the negative electrode composite layer may occur.

[0010] Accordingly, the present invention provides a bipolar electrode and a method for manufacturing the same, which can simplify the manufacturing process of the bipolar electrode, particularly the rolling process, while reducing damage to the cathode composite layer during the rolling process and enabling the formation of a cathode and an anode having mutually uniform porosity.

[0011] The present invention also provides a bipolar electrode assembly and a bipolar secondary battery that include the bipolar electrode and exhibit excellent physical and electrochemical properties.

[0012] According to one embodiment of the invention, a bipolar electrode is provided, comprising: a metal current collector; a negative electrode composite layer coated on one surface of the metal current collector and comprising a polymer binder, a conductive material, and a negative electrode active material; and a positive electrode composite film attached to the other surface of the metal current collector and comprising a fibrous polymer binder, the fibrous polymer binder, a conductive material, and a positive electrode active material.

[0013] In the bipolar electrode of this embodiment, the positive electrode composite film is a dry film prepared in the absence of a solvent, and the negative electrode composite layer may be a wet composite layer prepared by applying and drying a slurry composition in which the polymer binder, conductive material, and negative active material are dispersed in an organic solvent on one surface of the metal current collector.

[0014] In addition, according to another embodiment of the invention, a method for manufacturing a bipolar electrode of the first embodiment is provided. This manufacturing method may include the steps of: applying and drying a slurry composition comprising a polymer binder, a conductive material, a negative electrode active material, and an organic solvent on one surface of a metal current collector to form a negative electrode composite layer; dry mixing and calendering a fiberizable polymer binder, a conductive material, and a positive electrode active material to form a positive electrode composite film; attaching the positive electrode composite film to the other surface of the metal current collector; and applying pressure to the negative electrode composite layer and the positive electrode composite film to roll.

[0015] According to an additional embodiment of the invention, a bipolar electrode assembly is provided in which the bipolar electrodes of the first embodiment are alternately stacked via a separator, an electrolyte layer, or a stack thereof, and the negative electrode composite layer and the positive electrode composite film of adjacent bipolar cells face each other with the separator, the electrolyte layer, or the stack thereof in between.

[0016] According to another embodiment of the invention, a bipolar secondary battery is provided, comprising: a bipolar electrode assembly; an electrode terminal electrically connected to the outermost electrode of the bipolar electrode assembly; and a case housing the bipolar electrode assembly.

[0017] The bipolar electrode according to the above embodiment includes an anode composite film formed by a dry process without a separate solvent, replacing the anode composite layer formed by a conventional wet process.

[0018] Such anode composite film is manufactured in the form of a free-standing film through calendering processing, etc., after each component, such as an anode active material, is dry-mixed, for example, and can be pressed alone before being attached to the metal current collector of the bipolar electrode.

[0019] Accordingly, the bipolar electrode of one embodiment including the anode composite film can achieve a desired level of porosity and rolling density for the cathode composite layer and the anode composite film without risk of damage to the ends of the cathode composite layer, even when rolling is performed by applying an equal pressure (e.g., a pressure suitable for the cathode composite layer) to the cathode composite layer and the anode composite film after the film is attached to a current collector.

[0020] In addition, the bipolar electrode of the above embodiment can be manufactured with simplified formation and rolling processes for each electrode composite layer (composite film), and excellent physical and electrochemical properties, such as uniform porosity for the anode and cathode, can be achieved even with simplified processes.

[0021] Therefore, the bipolar electrode of one embodiment can significantly contribute to manufacturing a bipolar secondary battery with excellent physical properties through a simplified process.

[0022] FIG. 1 is a schematic cross-sectional view of a bipolar electrode according to one embodiment of the invention.

[0023] FIGS. 2a to 2e are schematic diagrams of each step illustrating an example of a method for manufacturing a bipolar electrode according to another embodiment of the invention.

[0024] FIG. 3 is a schematic cross-sectional view of a bipolar electrode assembly according to an additional embodiment of the invention.

[0025] Hereinafter, terms and words used in this specification and claims shall not be interpreted as being limited to their ordinary or dictionary meanings, but shall be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0026] Unless otherwise defined, all terms used in this specification (including technical and scientific terms) may be used in a meaning that is commonly understood by those skilled in the art to which the present invention pertains. Additionally, terms defined in commonly used dictionaries are not to be interpreted ideally or excessively unless explicitly and specifically defined otherwise.

[0027] The terms used herein are for describing the embodiments and are not intended to limit the invention. In this specification, the singular form includes the plural form unless specifically stated otherwise in the text. As used herein, "comprises" and / or "comprising" do not exclude the presence or addition of one or more other components in addition to the components mentioned.

[0028] In this specification, when a part is described as including a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0029] In addition, in this specification, the term “(anode) composite film” is used to define that it is manufactured by a dry process, unlike the “(anode or cathode) composite layer” manufactured by a wet process. For example, unlike the “(anode or cathode) composite layer” formed by applying and drying a slurry in which an active material, a binder, and a conductive material are dispersed in an organic solvent onto a current collector, etc., the “(anode) composite film” may refer to a film formed by mixing an active material, a binder (e.g., a fiberizable binder), and a conductive material in a dry state and calendering them under pressure. Such a “(anode) composite film” may have a form and characteristics that are distinguished from the “(anode or cathode) composite layer” in terms of, for example, residual solvent, the form of the fiberized binder, or the porosity immediately after manufacturing.

[0030]

[0031] Hereinafter, embodiments of the invention are described in detail with reference to the attached drawings so that those skilled in the art can easily practice the invention. In this specification and drawings, like reference numerals indicate like components.

[0032] As illustrated in FIG. 1, a bipolar electrode (1) according to one embodiment of the invention may include a metal current collector (10); a negative electrode composite layer (20) coated on one side of the metal current collector (1) and comprising a polymer binder, a conductive material, and a negative electrode active material; and a positive electrode composite film (30) attached to the other side of the metal current collector (10) and comprising a fibrous polymer binder, the fibrous polymer binder, a conductive material, and a positive electrode active material. In the bipolar electrode (1) of this embodiment, the positive electrode composite film (30) may be a dry film manufactured in the absence of a solvent, and the negative electrode composite layer (20) may be a wet composite layer manufactured by coating and drying a slurry composition in which the polymer binder, the conductive material, and the negative electrode active material are dispersed in an organic solvent on one side of the metal current collector (10).

[0033] In a more specific example, the type of the metal current collector (10) is not particularly limited, but in a specific example, it may be a single-layer metal current collector including stainless steel (SUS), or a current collector including a metal laminate including an aluminum layer and a copper layer. In a more specific embodiment, when using a metal current collector including the metal laminate, the aluminum layer may come into contact with the anode composite film (30), and the copper layer may come into contact with the cathode composite layer (20).

[0034] In addition, in a metal current collector including the above-mentioned metal laminate, a separate primer layer or adhesive layer may be added between the aluminum layer and the copper layer to improve their adhesion, but in terms of energy density and resistance, it is more appropriate for the aluminum layer and the copper layer to be directly attached without the addition of a separate layer. These aluminum layer and the copper layer can be attached at their contact surface by a method such as welding.

[0035] The metal current collector (10), including the stainless steel (SUS) or metal laminate described above, can exhibit electrochemical stability in all voltage ranges in which the bipolar secondary battery is operated and can exhibit appropriate adhesion to the positive composite film (30).

[0036] Additionally, the metal current collector (10) may have a thickness of, for example, 3 to 200 μm or 5 to 100 μm. In a more specific example, the metal current collector (10) including stainless steel is suitable to have a thickness of 5 to 100 μm or 7 to 40 μm, and the metal current collector (10) including the metal laminate is suitable to have a thickness of 20 to 200 μm or 30 to 100 μm. At this time, the aluminum layer may have a thickness of 10 to 100 μm or 20 to 70 μm, and the copper layer may have a thickness of 1 to 100 μm or 2 to 30 μm.

[0037] If the thickness of the metal current collector (10) is excessively small, it may not properly support the bipolar electrode, or pinholes may occur between the metal laminates. If the thickness of the metal current collector (10) is excessively large, the overall energy density of the battery may decrease.

[0038] Meanwhile, the anode composite film (30) may be a dry film manufactured by mixing, for example, a positive active material powder including a lithium transition metal oxide, a fiberizable polymer binder, and a conductive material in a dry state, and then calendering it under pressure. In the processing process, the binder may be fiberized, and the anode active material and conductive material may be uniformly dispersed on the fiberized binder to form a free-standing film. For reference, the anode composite film in the form of such a dry film and the manufacturing process thereof are known through U.S. Patent Publication No. 8815443, U.S. Patent Publication No. 10153096, etc.

[0039] A bipolar electrode (1) according to one embodiment of the invention comprises a negative electrode composite layer (20) manufactured by a conventional wet process on one side of a metal current collector (10), while comprising an anode composite film (30) manufactured by a dry process on the other side of the metal current collector (10). This anode composite film (30) may exhibit a reduced porosity by applying a certain amount of pressure during the process of calendering, etc., or it may exhibit a reduced porosity by being manufactured in the form of a free-standing film and then rolled alone.

[0040] Accordingly, after attaching the anode composite film (30) to the metal current collector (10), an equivalent pressure is applied to achieve the target porosity of the cathode composite layer (20), and even if rolling is performed on the cathode composite layer (20) and the anode composite film (30), a porosity and rolling density suitable for the anode composite film (30) can be achieved. Accordingly, the bipolar electrode (1) of one embodiment can achieve a desired level of adhesion, porosity, and rolling density for the cathode composite layer (20) and the anode composite film (30) without the risk of damage to the end of the cathode composite layer (20) due to excessive pressure during the rolling process.

[0041] Meanwhile, in the bipolar electrode (1) of the above embodiment, the negative electrode composite layer (20) may include a polymer binder, a conductive material, and a negative electrode active material, and may be a wet composite layer prepared by applying and drying a slurry composition in which the polymer binder, the conductive material, and the negative electrode active material are dispersed in an organic solvent on one surface of the metal current collector.

[0042] In this cathode composite layer (20), the cathode active material is a graphite-based active material such as non-graphitizable carbon, graphite-based carbon, etc.; Li x Fe2O3(0≤x≤1), Li x WO2(0≤x≤1), Sn x Me 1-x Me y O z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, Group 1, 2, and 3 elements of the periodic table, halogens; 0 <x≤1; 1≤y≤3; 1≤z≤8) 등의 금속 복합 산화물; 리튬 금속; 리튬 합금; 규소계 합금; 주석계 합금; SiO, SiO / C, SiO x(1 <x<2), SiO2등의 실리콘계 산화물; SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, 및 Bi2O5등의 금속 산화물; 폴리아세틸렌 등의 도전성 고분자; Li-Co-Ni 계 재료 등을 사용할 수 있다. 이 중에서도, 상기 금속 집전체(10)에 대한 음극 합제층(20)의 양호한 형성 및 접착력 등을 고려하여, 상기 음극 활물질로는 흑연계 활물질을 적절히 사용할 수 있다.

[0043] These cathode active materials may be included in an amount of, for example, 80 to 99 weight% or 85 to 98 weight% with respect to the total weight of the cathode composite layer (20).

[0044] Additionally, any polymer binder known to be usable in the negative electrode composite layer of a lithium secondary battery can be used as the polymer binder of the negative electrode composite layer (20) without any particular limitations. Specific examples of such polymer binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polyethylene, polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluororubber, or various copolymers thereof.

[0045] Typically, the polymer binder may be included in an amount of 0.5 to 15 weight% or 0.7 to 10 weight% based on the total weight of the cathode composite layer (20).

[0046] In addition, the conductive material included in the above-mentioned cathode composite layer (20) is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, graphite such as natural graphite or artificial graphite; graphene; activated carbon; activated carbon fiber; carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, or thermal black; conductive fiber such as carbon fiber or metal fiber; metal powder such as fluorinated carbon, aluminum, or nickel powder; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxide such as titanium oxide; conductive material such as polyphenylene derivative, etc. may be used, but more specifically, in order to ensure uniform mixing of the conductive material and improve conductivity, it may include one or more selected from the group consisting of activated carbon, graphite, carbon black, graphene, and single-walled or multi-walled carbon nanotubes, and more specifically, it may include carbon black or activated carbon.

[0047] The conductive material may be included in an amount of 0.1 to 15 weight% or 0.5 to 10 weight% based on the total weight of the cathode composite layer (20).

[0048] Considering the overall thickness, resistance, and other electrochemical characteristics of the bipolar electrode (1) and the bipolar secondary battery, the cathode composite layer (20) may have a thickness of, for example, 20 to 200 μm, or 20 to 150 μm, or 30 to 100 μm, and may have a porosity of 20 to 40%, or 22% to 40%, or 25% to 35%. Additionally, the cathode composite layer (20) may have a porosity of 150 to 400 mg / 25 cm per unit area of ​​the bipolar electrode (1). 2 , or 200 to 400 mg / 25 cm 2 A negative electrode active material may be included in the loading amount. By doing so, it can be combined with the positive electrode composite film (30) described later to exhibit appropriate capacity and / or output characteristics.

[0049] Meanwhile, in the bipolar electrode (1) of the above embodiment, the positive electrode composite film (30) comprises a fibrous polymer binder, a conductive material, and a positive electrode active material. In a specific example, the conductive material and the positive electrode active material may be uniformly dispersed on the fibrous polymer binder in the form of particles, for example.

[0050] Among these, the above-mentioned positive electrode active material may be any lithium transition metal oxide, lithium metal phosphate, metal oxide, etc., without any particular limitation. Specific examples of such positive electrode active materials include layered compounds such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), or compounds substituted with one or more transition metals; chemical formula Li 1+x Mn 2-x Lithium manganese oxides such as O4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, LiMn2O3, LiMnO2, etc.; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiFe3O4, V2O5, Cu2V2O7, etc.; chemical formula LiNi 1-x M x Ni-site type lithium nickel oxide represented by O2 (where M = Co, Mn, Al, Cu, Fe, Mg, Ca, Zr, Ti, B, P, W, Si, Na, K, Mo, V, Nb, Ru, or Ga, and x = 0.01 ~ 0.3); chemical formula LiMn 2-x M xLithium manganese complex oxides represented by O2 (where M = Co, Ni, Fe, Cr, Zn or Ta and x = 0.01 to 0.1) or Li2Mn3MO8 (where M = Fe, Co, Ni, Cu or Zn); LiMn2O4 in which part of the Li in the chemical formula is substituted with alkaline earth metal ions; lithium metal phosphate LiMPO4 (where M is M = Fe, CO, Ni, or Mn), disulfide compounds; Fe2(MoO4)3, etc., are examples, but are not limited to these.

[0051] Among these, considering the physical and electrochemical properties and stability of the bipolar battery (1), the lithium metal phosphate LiMPO4 (where M is M = Fe, CO, Ni, or Mn), more specifically lithium iron phosphate, can be preferably used as the positive electrode active material.

[0052] These positive active materials may be included in an amount of, for example, 80 to 99 weight% or 85 to 98 weight% with respect to the total weight of the positive composite film (30).

[0053] In addition, the anode composite film (30) may be manufactured using a fiberizable polymer binder for a dry process, and the polymer binder may be included in a fiberized form in the final manufactured state. As the fiberizable polymer binder, a polyolefin-based polymer with multiple fluorine bonds, such as polytetrafluoroethylene (PTFE), may be used in terms of adhesion to the metal current collector (10) and the formation of a good self-supporting dry film. The fiberized polymer binder may be included in an amount of at least 50 weight%, or 60 weight%, or 70 to 100 weight% of the total polymer binder of the anode composite film (30).

[0054] In addition, the anode composite film (30) may further include additional polymer binders in addition to the fiberized polymer binder described above, for example, PEO (polyethylene oxide), PVdF (polyvinylidene fluoride), PVdF-HFP (polyvinylidene fluoride-co-hexafluoropropylene), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polyethylene, polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluororubber, or various copolymers thereof.

[0055] In addition, the polymer binder having the above-mentioned fiberized polymer binder as a main component may be included in an amount of 0.5 to 15 weight% or 0.7 to 10 weight% based on the total weight of the anode composite film (30).

[0056] Additionally, since the type and content of the conductive material that may be included in the anode composite film (30) are substantially the same as the conductive material included in the cathode composite layer (20) described above, further explanation regarding this is omitted.

[0057] Meanwhile, in some cases, the anode composite film (30) may further include a filler which is a component that suppresses the expansion of the electrode. The filler is not particularly limited as long as it is a fibrous material that does not cause chemical changes in the battery, and may be, for example, an olivine-based polymer such as polyethylene or polypropylene; or a fibrous material such as glass fiber or carbon fiber.

[0058] The anode composite film (30) described above may have a thickness of, for example, 20 to 300 μm or 30 to 200 μm, and a porosity of 20% to 40% or 22% to 38%, taking into account the overall thickness, resistance, and other electrochemical properties of the bipolar electrode (1) and the bipolar secondary battery. As already described above, since the bipolar electrode (1) in one embodiment includes a dry-manufactured anode composite film (30), the porosity required for the anode composite film (30) can be easily satisfied even if a rolling process is performed under uniform pressure on the cathode composite layer (20) and the anode composite film (30) without applying excessive pressure to the cathode composite layer (20) or damaging the cathode composite layer (20).

[0059] In a more specific example, the physical properties required of the bipolar electrode (1) may vary depending on the type and application of the bipolar secondary battery to which the bipolar electrode (1) of one embodiment is applied. For example, when the bipolar electrode (1) of one embodiment is used in a bipolar secondary battery applied as a driving source for, for example, a hybrid vehicle or a plug-in hybrid vehicle, the need for the bipolar secondary battery to have relatively high output characteristics and low resistance increases, rather than high capacity characteristics and energy density.

[0060] To this end, the bipolar electrode (1) used in the secondary battery for such hybrid vehicles or the secondary battery for plug-in hybrid vehicles needs to have a relatively large porosity, a small loading amount of electrode active material, for example, a positive active material, and a small thickness, based on one bipolar electrode (1) included in the unit cell. This is because the impregnation of the electrolyte into the positive composite film (30) is increased, and as a result, the resistance of each unit cell and bipolar electrode (1) can be reduced.

[0061] One example of such a bipolar electrode (1) is, for example, 150 to 400 mg / 25 cm² per unit area of ​​the bipolar electrode (1). 2 , or 200 to 350 mg / 25 cm 2 , or 250 to 300 mg / 25 cm 2 A positive composite film (30) containing a positive active material may be included with a small loading amount. Additionally, such a positive composite film (30) may have a thickness of, for example, 20 to 90 μm, or 20 to 70 μm, or 30 to 50 μm, and may have a relatively large porosity of 30% to 40%, or 32% to 38%. By doing so, the characteristics required for the secondary battery for a hybrid vehicle or the secondary battery for a plug-in hybrid vehicle can be appropriately satisfied.

[0062] Meanwhile, in another example of the bipolar electrode (1) of one embodiment, such bipolar electrode (1) may be used in a bipolar secondary battery applied as a driving source for, for example, an electric vehicle. In this case, the bipolar secondary battery needs to have higher capacity characteristics and energy density.

[0063] To this end, the bipolar electrode (1) included in the secondary battery for such electric vehicles needs to have a relatively small porosity, for example, a large loading amount of positive active material and a large thickness, based on one bipolar electrode (1) included in the unit cell. As a result, the bipolar secondary battery can exhibit greater capacity characteristics and energy density.

[0064] Another example of such a bipolar electrode (1) is, for example, 500 to 900 mg / 25 cm² per unit area of ​​the bipolar electrode (1). 2 , or 600 to 800 mg / 25 cm 2A positive composite film (30) containing a positive active material may be included with a large loading amount. Additionally, such a positive composite film (30) may have a thickness of, for example, 80 to 300 μm, or 90 to 200 μm, or 90 to 180 μm, or 100 to 150 μm, and may have a relatively small porosity of 20% to 30%, or 22% to 29%. By doing so, the characteristics required for the secondary battery for the electric vehicle can be adequately satisfied.

[0065] In the bipolar electrode (10) applied to each of the above-described uses, the appropriate thickness of the anode composite film (30) can be determined depending on the loading amount of the anode active material and the porosity of the anode composite film (30). In addition, the thickness range of the cathode composite layer (20) combined with the anode composite film (30) can also be determined depending on the appropriate N / P ratio, the loading amount of the cathode active material and the porosity of the cathode composite layer (20).

[0066] Meanwhile, the anode composite film (30) may be attached to the metal current collector (10) with an adhesive strength of 5gf / 20mm or more, or 5gf / 20mm to 70gf / 20mm, or 15gf / 20mm to 65gf / 20mm, or 20gf / 20mm to 60gf / 20mm. This adhesive strength may be measured, for example, by using UTS (Ultimate tensile strength) measuring equipment and conducting a peel test on an electrode sample to which the anode composite film (30) is attached to the metal current collector (10).

[0067] As the above adhesive strength is satisfied, the bipolar electrode (1) of one embodiment exhibits excellent physical and mechanical properties while maintaining excellent electrochemical properties. To satisfy the above adhesive strength, a suitable release film may be used when attaching the anode composite film (30) in the manufacturing method described below.

[0068] Additionally, depending on the case, a primer layer may be further formed between the metal current collector (10) and the positive composite film (30) and / or the negative composite layer (20). This primer layer may include, for example, a conductive material and a binder, and may further improve the adhesion of the positive composite film (30) and / or the negative composite layer (20) to the metal current collector (10). In particular, when lithium metal phosphate, for example, lithium iron phosphate, is used as the positive active material, the need to form the primer layer increases. This is because the particle strength of the lithium iron phosphate is relatively small compared to other positive active materials, for example, ternary positive active materials including nickel, cobalt, and manganese. Due to this small particle strength, the lithium metal phosphate particles are difficult to physically embed or fix onto the surface of the metal current collector, and as the positive composite film (30) containing it exhibits relatively low adhesion, the need to form the primer layer may increase.

[0069] Here, the conductive material may be a component equivalent to the conductive material contained in the anode composite film (30). Also, as the binder, for example, polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene ter polymer (EPDM), sulfonated EPDM, styrene-butylene rubber, or fluororubber may be used.

[0070] At this time, the content of the conductive material may be 5 to 50 weight%, or 5 to 30 weight%, or 10 to 30 weight% based on the total weight of the primer layer. If the content of the conductive material is too low, the resistance of the bipolar electrode (1) may increase, and if it is too high, the adhesion between the anode composite film (30) and the metal current collector (10) may decrease. In addition, the binder may be included as the remainder of the primer layer excluding the conductive material. The primer layer may be formed with a thickness of, for example, 0.1 to 10 μm.

[0071] Meanwhile, according to another embodiment of the invention, a method for manufacturing a bipolar electrode of the first embodiment is provided. This manufacturing method may include the steps of: applying and drying a slurry composition comprising a polymer binder, a conductive material, a negative electrode active material, and an organic solvent on one surface of a metal current collector to form a negative electrode composite layer; dry mixing and calendering a fiberizable polymer binder, a conductive material, and a positive electrode active material to form a positive electrode composite film; attaching the positive electrode composite film to the other surface of the metal current collector; and applying pressure to the negative electrode composite layer and the positive electrode composite film to roll them.

[0072] In the above manufacturing method, as shown in FIG. 2a, a slurry composition comprising a polymer binder, a conductive material, a negative electrode active material, and an organic solvent can be applied and dried on one surface of a metal current collector (10) to form a negative electrode composite layer (20). The type of the metal current collector (10) is as described above, and since the process of forming the negative electrode composite layer (20) can follow a general wet negative electrode process, further explanation regarding this is omitted.

[0073] In addition, in the manufacturing method of the other embodiment above, a fiberizable polymer binder, a conductive material, and an anode active material can be dry-mixed and calendered separately from the formation of the cathode composite layer (20) to produce an anode composite film (30) in the form of a free-standing film. The manufacturing process of such an anode composite film (30) may follow a general dry electrode film formation process known, for example, in U.S. Patent Publication No. 8815443 or U.S. Patent Publication No. 10153096.

[0074] As an example, the anode composite film (30) can be manufactured by dry mixing anode active material particles, a fiberizable polymer binder, and conductive material particles, while applying shear force to the dry mixture to fiberize the polymer binder, and then calendering the resulting product into a film shape.

[0075] In the manufacturing process of such an anode composite film (30), a certain amount of pressure is applied, so the annode composite film (30) can be manufactured to have a reduced porosity and increased density compared to an anode composite layer manufactured by a conventional wet process. For this reason, even if a rolling process is performed under relatively low pressure after attaching such an anode composite film (30) to a metal current collector (10), a porosity suitable for the annode composite film (30) can be easily achieved. Therefore, even if a rolling process is performed under uniform pressure on the cathode composite layer (20) and the annode composite film (30), a porosity suitable for the cathode composite layer (20) and the annode composite film (30) can be achieved together without damaging the cathode composite layer (20).

[0076] In some cases, before attaching the anode composite film (30) to the metal current collector (10), a step of pre-rolling the anode composite film may be further performed to make it easier to achieve the porosity through the rolling process after attachment to the metal current collector (10).

[0077] Additionally, after manufacturing the anode composite film (30), a polyester release film (31) can be attached to one side of the anode composite film (30) as shown in FIG. 2b to facilitate attachment to the metal current collector (10), and this attachment process can be carried out by laminating the anode composite film (30) and the polyester release film (31) by passing them between opposing pressure rolls (40).

[0078] Since the anode composite film (30) itself has limitations in being attached to the metal current collector (10), the anode composite film (30) is attached to the surface of the metal current collector (10) with high adhesive strength in the presence of the polyester release film (31), and subsequently, the polyester release film (31) can be removed.

[0079] At this time, the polyester release film (31) may be a film comprising a polyalkylene terephthalate polymer film modified with an acrylic functional group or a fluorine-containing functional group, in terms of ease of attachment to the anode composite film (30) and ease of subsequent removal. Among these, by using a polyalkylene terephthalate polymer film modified with an acrylic functional group, which is relatively easy to remove, as the polyester release film (31), the anode composite film (30) can be attached to the metal current collector (10) while maintaining superior adhesion. In contrast, if a different type of release film is used, the adhesion of the anode composite film (30) to the metal current collector (10) may be weakened during the process of removing the polyester release film (31), and the physical and mechanical properties of the bipolar electrode (1) may be degraded.

[0080] Meanwhile, after forming the anode composite film (30) in the form of a free-standing film to which the above polyester release film (31) is attached, it can be punched into a size corresponding to the cathode composite layer (20), as shown in FIG. 2C. For this punching, a punching device (50), such as a die cutting device, can be used.

[0081] Next, as shown in FIG. 2d, an anode composite film (30) having the polyester release film (31) attached is attached to the other side of a metal current collector (10) on which a cathode composite layer (20) is formed on one side. Due to the presence of the polyester release film (31), the anode composite film (30) can be attached to the metal current collector (10) with a higher adhesive strength.

[0082] Next, as shown in FIG. 2e, the polyester release film (31) is removed, and rolling can be performed by applying pressure to the cathode composite layer (20) and the anode composite film (30). At this time, the anode composite film (30) is in a state where it has a reduced porosity due to the application of some pressure during the previous film processing step, pre-rolling step, or release film attachment step. Accordingly, in the rolling step, the bipolar electrode can be rolled by passing it through the rolling rolls (60) under the application of a relatively low pressure to achieve the porosity of the cathode composite layer (20). In a more specific example, in the rolling step, the same pressure of, for example, 0.5 to 3.5 ton / cm or 1.0 to 3.0 ton / cm can be applied to the cathode composite layer (20) and the anode composite film (30), and an optimized porosity for the cathode and anode can be easily achieved under this single rolling process.

[0083] Meanwhile, according to an additional embodiment of the invention, a bipolar electrode assembly and a bipolar secondary battery including the bipolar electrode described above are provided. As also illustrated in FIG. 3, in the structure of the bipolar electrode assembly, a plurality of bipolar electrodes including the negative electrode composite layer (20), the metal current collector (10), and the positive electrode composite film (30) are alternately stacked through a separator, an electrolyte layer, or a stack thereof (70), and the negative electrode composite layer (20) and the positive electrode composite film (30) of adjacent bipolar electrodes face each other with the separator, the electrolyte layer, or the stack thereof (70) in between.

[0084] In such an electrode assembly, an anode composite film (30) and a cathode composite layer (20) facing each other with a separator, an electrolyte layer, or a laminate thereof (70) in between can be defined as a single unit cell (100) (dotted line portion of FIG. 3).

[0085] At this time, the electrode assembly may include only a polyolefin-based porous separator, but may also include a gel electrolyte layer separately from the separator, or a gel electrolyte-separator laminate (70) in which a gel electrolyte is impregnated on the separator. In addition, in another specific example, the electrode assembly may include only a solid electrolyte layer. Thus, the leakage of electrolyte from the bipolar secondary battery can be effectively suppressed while simplifying the sealing structure in the bipolar secondary battery.

[0086] In a more specific example, the electrolyte layer including the gel electrolyte comprises, for example, a polyurethane-based or polyacrylic-based crosslinked polymer, a lithium salt, and a non-aqueous organic solvent, and may have a form in which the lithium salt and the non-aqueous organic solvent are dispersed or encapsulated within the crosslinked polymer. However, since the types of crosslinked polymers, lithium salts, and organic solvents that may be included in the gel electrolyte are obvious to those skilled in the art, further explanation regarding this is omitted.

[0087] In addition, in another specific example, the solid electrolyte layer may include one or more selected from the group consisting of any solid electrolyte, for example, polymer-based solid electrolytes, oxide-based solid electrolytes, sulfide-based solid electrolytes, and halogenated solid electrolytes. However, since the composition of such solid electrolyte layer may follow that of a general solid electrolyte layer known previously, further explanation is omitted.

[0088] Meanwhile, in the above-described bipolar electrode assembly, electrode terminals electrically connected to the respective current collectors (10a, 10b) on both sides in the stacking direction of the unit cells (100) may be directly connected or indirectly connected via a separate current collector plate. Additionally, the above-described bipolar electrode assembly may be housed in a separate case, and the electrode terminals may be connected to the outside of the case to form a bipolar secondary battery.

[0089]

[0090] The embodiments described above will be explained in more detail below through specific examples.

[0091] Example 1: Preparation of a bipolar electrode

[0092] 496 g of LiFePO4 as the positive active material, 0.5 g of carbon black as the conductive material, and 3.5 g of polytetrafluoroethylene (PTFE) as the binder were added to a blender and mixed dry at 10,000 rpm for 1 minute to prepare a mixture. The temperature of the kneader was stabilized to 150°C, the mixture was placed into the kneader, and then operated at a speed of 50 rpm for 5 minutes under a pressure of 1.1 atm to obtain a lump of the mixture.

[0093] The obtained mixture aggregate was fed into a blender, ground at 10,000 rpm for 40 seconds, and classified using a sieve with 1 mm pores to obtain electrode powder. Subsequently, the prepared electrode powder was fed several times into a lab calender (roll diameter: 88 mm, roll temperature: 100℃) to obtain an anode active material loading of 700 mg / 25 cm² per unit area. 2 An anode composite film was manufactured in the form of a freestanding film with a thickness of 100㎛.

[0094] The above anode composite film was attached to a PET release film modified with acrylic groups (product name: acrylic release film, thickness: 25-100㎛).

[0095] Meanwhile, 96g of graphite as a negative electrode active material, 1.0g of Super C-65 as a conductive material, and 3.0g of an SBR binder and thickener are mixed in an organic solvent to prepare a slurry, the slurry is coated on one side of a stainless steel foil (8㎛), and then dried and rolled to obtain a negative electrode active material loading amount of 300mg / 25cm² per unit area. 2 A cathode composite layer with a thickness of 100㎛ was formed.

[0096] Next, the anode composite film was attached to the other side of the stainless steel foil on which the cathode composite layer was not formed, and the PET release film modified with acrylic was removed.

[0097] Next, a rolling process was performed using a roll press while applying a pressure of 1-3 ton / cm to the cathode composite layer and the anode composite film to manufacture the bipolar electrode of Example 1.

[0098]

[0099] Example 2: Preparation of a bipolar electrode

[0100] The bipolar electrode of Example 2 was prepared in the same manner as Example 1, except that the above anode composite film was attached to a fluorine-substituted PET release film (product name: fluorine-based release film, thickness: 25-150 μm).

[0101]

[0102] Example 3: Preparation of a bipolar electrode

[0103] The bipolar electrode of Example 3 was prepared in the same manner as Example 1, except that a current collector (Al thickness: 30 to 45 μm and Cu thickness: 3 to 10 μm) including an Al / Cu metal laminate was used instead of the stainless steel foil (8 μm) above.

[0104]

[0105] Comparative Example 1: Preparation of a bipolar electrode

[0106] 496 g of LiFePO4 was used as the positive active material, 0.5 g of carbon black as the conductive material, and 3.5 g of polyvinylidene fluoride (PvDF) as the binder. Among these components, the conductive material and the binder were pre-added into an organic solvent and mixed to prepare a pre-dispersed solution. Subsequently, the positive active material was divided into equal amounts and added and further mixed twice to prepare a slurry. The slurry was coated onto one side of a stainless steel foil (8 μm) and dried to obtain a positive active material loading amount of 700 mg / 25 cm² per unit area. 2 An anode composite layer with a thickness of 100㎛ was formed.

[0107] Meanwhile, 96g of graphite as a negative electrode active material, 1.0g of Super C-65 as a conductive material, and 3.0g of an SBR binder and thickener are mixed in an organic solvent to prepare a slurry, the slurry is coated onto the other side of a stainless steel foil (8㎛), and dried to obtain a negative electrode active material loading amount of 300mg / 25cm² per unit area. 2 A cathode composite layer with a thickness of 100㎛ was formed.

[0108] Next, the bipolar electrode of Comparative Example 1 was prepared by rolling the cathode composite layer and the anode composite layer under the same conditions as in Example 1.

[0109]

[0110] Comparative Example 2: Preparation of a bipolar electrode

[0111] An anode composite film attached to a PET release film modified with acrylic groups (product name: acrylic release film, thickness: 25-100 μm) was prepared in the same manner as in Example 1.

[0112] 96g of graphite as a negative electrode active material, 1.0g of Super C-65 as a conductive material, and 3.5g of polytetrafluoroethylene (PTFE) as a binder were put into a blender and mixed at 10,000 rpm for 1 minute to prepare a mixture. The temperature of the kneader was stabilized at 150℃, and the mixture was placed into the kneader and operated at a speed of 50 rpm for 5 minutes under a pressure of 1.1 atm to obtain a lump of the mixture.

[0113] The obtained mixture aggregate was fed into a blender, ground at 10,000 rpm for 40 seconds, and classified using a sieve with 1 mm pores to obtain electrode powder. Subsequently, the prepared electrode powder was fed several times into a lab calender (roll diameter: 88 mm, roll temperature: 100℃) to obtain a negative electrode active material loading of 300 mg / 25 cm² per unit area. 2 A cathode composite film was manufactured in the form of a freestanding film with a thickness of 100㎛.

[0114] After attaching the above positive electrode composite film and negative electrode composite film to the other side of a stainless steel foil (8 μm), the release film was removed, and rolling was performed under the same conditions as in Example 1 to produce the bipolar electrode of Comparative Example 2.

[0115]

[0116] Example 4: Preparation of a bipolar electrode

[0117] Anode active material loading per unit area is 300 mg / 25 cm 2 An anode composite film was prepared in the same manner as in Example 1, except that it was prepared in the form of a freestanding film with a thickness of 50 μm.

[0118] Meanwhile, the negative electrode active material loading per unit area is 250 mg / 25 cm 2 A cathode composite layer was prepared in the same manner as in Example 1, except that a cathode composite layer with a thickness of 35 μm was prepared.

[0119] After that, the bipolar electrode of Example 4 was manufactured by carrying out the same process as in Example 1.

[0120]

[0121] Comparative Example 3: Preparation of a bipolar electrode

[0122] Anode active material loading per unit area is 300 mg / 25 cm 2 An anode composite layer was prepared using the same method as Comparative Example 1, except that an anode composite layer with a thickness of 50㎛ was prepared.

[0123] Meanwhile, the negative electrode active material loading per unit area is 250 mg / 25 cm 2 A cathode composite layer was prepared using the same method as Comparative Example 1, except that a cathode composite layer with a thickness of 35 μm was prepared.

[0124] After that, the same process as Comparative Example 1 was carried out to manufacture the bipolar electrode of Comparative Example 3.

[0125]

[0126] <Experimental Example>

[0127] In the electrodes prepared in Examples 1 to 4 and Comparative Examples 1 to 3 above, the porosity and adhesion of the anode composite film (anode composite layer) and the cathode composite layer (cathode composite film) were evaluated by the following method, and the evaluation results are shown in Table 1 below.

[0128] - Electrode adhesion: After cutting the electrode to 2cm x 10cm, double-sided tape was attached to a slide glass, and the surface of the electrode to be measured was attached to the slide glass with the double-sided tape. Then, the slide glass was placed on the UTM equipment, and the electrode layer was peeled off at a speed of 2m / min at a 90-degree angle to measure.

[0129] - Porosity:

[0130] In calculating the porosity of the electrode (anode or cathode) composite layer or composite film, first, the electrode density was calculated by dividing the loading amount of each electrode composite layer or composite film by its thickness. In addition, the porosity was calculated according to the following Equation 1 from the electrode density and the true density of the electrode active material:

[0131] [Equation 1]

[0132] P = (1-D) / T×100

[0133] In the above Equation 1, P represents the porosity of the electrode composite layer (or composite film), D represents the electrode density, and T represents the true density of the electrode active material excluding the current collector from the electrode. Here, true density refers to the intrinsic density of the electrode active material without pores.

[0134] -resistance:

[0135] The resistance of each electrode was measured using a Multi-probe (MP) Tester. More specifically, each bipolar electrode, finally manufactured through rolling and drying, was measured in a 5x5 cm area. 2 After being stamped and placed on the resistance measuring equipment, the electrode resistance was measured. Each resistance was measured by applying a current of 100 μA for the anode composite film (anode composite layer) and 10 mA for the cathode composite layer, with the voltage set to 0.5 V. The measured resistance values ​​were calculated as a relative ratio with the measured value of Example 4 set to 100%, and are shown in Table 1 below.

[0136] Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Anode side adhesion (gf / 20mm) 50-60 50-60 50-60 50-60 20-30 50-60 20-30 Cathode side adhesion (gf / 20mm) 30-40 30-40 30-40 30-40 30-40 40-50 30-40 Anode side porosity (%) 25-30 25-30 25-30 30-40 25-30 25 30-40 Resistance (%) 300-350 300-350 300-350 100 250-300 350-400 110 Cathode side Porosity (%) 25-30 25-30 25-30 30-40 Cell Capacity (%) 340~350 340~350 340~350 100 Cell Output (%) 100 100 100 350 -370 90 80 330 -360

[0137] Referring to Table 1 above, it was confirmed that the bipolar electrodes of Examples 1 and 4 have the positive composite film and the negative composite layer attached to the metal current collector with excellent adhesion, and both sides exhibit good and uniform porosity.

[0138] It was confirmed that for the bipolar electrodes of Comparative Examples 1 and 3, the same rolling process was performed on the anode and cathode composite layers processed by a wet process, and the anode composite layer was not properly rolled, and the adhesion strength of the anode composite layer was relatively reduced.

[0139] In the case of the bipolar electrode of Comparative Example 2, the cathode composite film was also manufactured by a dry process, but in this case, it was confirmed that the resistance of the bipolar electrode increased compared to Examples 1 to 4.

[0140] Meanwhile, the bipolar electrodes of Examples 1 to 3 have a loading amount of positive active material per unit area of ​​600 to 800 mg / 25 cm 2 It has been confirmed that the film comprises an anode composite film with a thickness of 90 to 130 μm and has high capacity characteristics suitable for secondary batteries for electric vehicles.

[0141] Additionally, the bipolar electrode of Example 4 has a loading amount of positive active material per unit area of ​​150 to 400 mg / 25 cm² 2 It was confirmed that the film comprises an anode composite film having a thickness of 30 to 50 μm, exhibiting low resistance and high output characteristics suitable for a secondary battery for a hybrid vehicle, and having superior characteristics compared to Comparative Example 3 of the same type.

[0142]

[0143] Preparation Example: Preparation of a bipolar secondary battery

[0144] A bipolar secondary battery was manufactured using the bipolar electrode of the above example or comparative example by the following method.

[0145] 3 parts by weight of vinylene carbonate and 0.5 parts by weight of ethyl sulfate were mixed with 100 parts by weight of a solvent in which ethylene carbonate and gamma-butyrolactone were mixed in a weight ratio of 2:8. An electrolyte was prepared by adding 1M LiPF6 to this non-aqueous organic solvent, and a composition for forming a gel electrolyte was prepared by mixing 5 parts by weight of trimethylolpropane ethoxylate triacrylate with 100 parts by weight of this electrolyte.

[0146] Next, 0.2 g of the gel electrolyte forming composition was dropped and applied onto the cathode composite layer of the bipolar electrode, and the applied surface was rolled to impregnate the gel electrolyte forming composition into the cathode composite layer. Subsequently, 600 W / cm² was applied to the applied surface for 5 seconds. 2 A gel electrolyte layer was formed by irradiating with UV light at an intensity.

[0147] A bipolar secondary battery was manufactured by stacking five stacks of bipolar electrodes, each having a gel electrolyte layer formed on the above-mentioned cathode composite layer.

[0148]

[0149] Test Example: Evaluation of Capacity and / or Output Characteristics of Bipolar Secondary Batteries

[0150] The capacity and output characteristics of the bipolar cell manufactured in the above manufacturing example were evaluated, respectively. These capacity and output characteristics were evaluated based on a voltage range of 2.5V to 3.6V per unit cell and a total voltage range of 12.5V to 18V based on the entire bipolar cell with 5 stacks stacked.

[0151] The results of these capacity characteristic evaluations were calculated as a relative ratio with respect to the measured value of Example 4 set to 100%, and the results of the output characteristic evaluations were calculated as a relative ratio with respect to the measured value of Example 1 set to 100%. These results of capacity and output characteristic evaluations are shown in Table 1 above.

Claims

1. Metal current collector; A cathode composite layer coated on one surface of the above-mentioned metal current collector and comprising a polymer binder, a conductive material, and a cathode active material; and A bipolar electrode attached to the other side of the metal current collector and comprising a fibrous polymer binder and a positive composite film including a conductive material and a positive active material.

2. The metal current collector of claim 1 comprises stainless steel (SUS) or a bipolar electrode comprising a metal laminate including an aluminum layer and a copper layer.

3. In claim 1, the anode composite film is a dry film manufactured in the absence of a solvent, and The above cathode composite layer is a bipolar electrode that is a wet composite layer prepared by applying and drying a slurry composition in which the polymer binder, conductive material, and cathode active material are dispersed in an organic solvent onto one surface of the metal current collector.

4. The bipolar electrode according to claim 1, wherein the fiberized polymer binder comprises a polyolefin-based polymer having a plurality of fluorine atoms bonded thereto.

5. A bipolar electrode according to claim 1, wherein the negative electrode active material comprises a graphite-based active material and the positive electrode active material comprises lithium iron phosphate.

6. In claim 1, the anode composite film is a bipolar electrode attached to the metal current collector with an adhesive strength of 5gf / 20mm or more.

7. In claim 1, the cathode composite layer and the anode composite film are bipolar electrodes having a porosity of 20% to 40%.

8. In claim 1, the anode composite film is 150 to 400 mg / 25 cm² per unit area of ​​the bipolar electrode. 2 A bipolar electrode containing a positive active material with a loading amount.

9. In claim 8, the anode composite film is a bipolar electrode having a porosity of 30% to 40%.

10. A bipolar electrode used in a secondary battery for a hybrid vehicle or a secondary battery for a plug-in hybrid vehicle according to claim 8.

11. In claim 1, the anode composite film has 500 to 900 mg / 25 cm per unit area of ​​the bipolar electrode. 2 A bipolar electrode containing a positive active material with a loading amount.

12. In claim 11, the anode composite film is a bipolar electrode having a porosity of 20% to 30%.

13. A bipolar electrode used in a secondary battery for an electric vehicle, according to claim 11.

14. In claim 1, formed between the metal current collector and the anode composite film or the cathode composite layer, and A bipolar electrode further comprising a primer layer including a conductive material and a binder.

15. A step of forming a cathode composite layer by applying and drying a slurry composition comprising a polymer binder, a conductive material, a cathode active material, and an organic solvent on one surface of a metal current collector; A step of forming an anode composite film by dry mixing and calendering a fiberizable polymer binder, a conductive material, and an anode active material; A step of attaching the above positive composite film to the other side of the metal current collector; and A method for manufacturing a bipolar electrode comprising the step of applying pressure to the cathode composite layer and the anode composite film and rolling.

16. A method for manufacturing a bipolar electrode according to claim 15, further comprising, prior to the attachment step, the step of punching the anode composite film into a size corresponding to the cathode composite layer.

17. A method for manufacturing a bipolar electrode according to claim 9, wherein the anode composite film is formed in the form of a free-standing film to which a polyester release film is attached.

18. A method for manufacturing a bipolar electrode according to claim 17, wherein the polyester release film comprises a polyalkylene terephthalate-based polymer film modified with a fluorine-containing functional group or an acrylic functional group.

19. A method for manufacturing a bipolar electrode according to claim 17, further comprising the step of removing the polyester release film after the step of attaching the anode composite film.

20. A method for manufacturing a bipolar electrode according to claim 15, further comprising the step of pre-rolling the anode composite film before the attachment step.

21. A method for manufacturing a bipolar electrode according to claim 15, wherein the same pressure is applied to the cathode composite layer and the anode composite film during the rolling step.

22. A method for manufacturing a bipolar electrode according to claim 21, wherein a pressure of 0.5 to 3.5 ton / cm is applied during the rolling step.

23. The bipolar electrodes of any one of claims 1 to 14 are alternately stacked via a separator, an electrolyte layer, or a stack thereof, and A bipolar electrode assembly in which a cathode composite layer and an anode composite film of adjacent bipolar electrodes face each other with the separator, electrolyte layer, or a laminate thereof in between.

24. The bipolar electrode assembly according to claim 23, wherein the electrolyte layer comprises a gel electrolyte comprising a polyurethane-based or polyacrylic-based crosslinked polymer, a lithium salt, and a non-aqueous organic solvent.

25. A bipolar electrode assembly according to claim 23, wherein the electrolyte layer comprises one or more types selected from the group consisting of polymer-based solid electrolytes, oxide-based solid electrolytes, sulfide-based solid electrolytes and halogenated solid electrolytes.

26. Bipolar electrode assembly of claim 23; An electrode terminal electrically connected to the outermost electrode of the above-mentioned bipolar electrode assembly; and A bipolar secondary battery comprising a case that accommodates the above-mentioned bipolar electrode assembly.

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