Bipolar electrode and secondary battery

Abstract

The method for manufacturing a secondary battery according to the present invention comprises the steps of: forming a negative electrode film by coating and drying a negative electrode slurry on one surface of a current collector; attaching a positive electrode film formed by a dry process to the other surface of the current collector; and forming a bipolar electrode by simultaneously rolling the positive electrode film and the negative electrode film.

Description

Technology Field

[0001] The present invention relates to a secondary battery and a method for manufacturing the same, and more specifically, to a secondary battery comprising a bipolar electrode and a method for manufacturing the same. Background Technology

[0002] 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.

[0003] The electrodes used in such secondary batteries can be classified into monopolar electrodes, in which an active material with the same polarity is coated on both sides of a current collector, and bipolar electrodes, in which an active material with different polarities is coated on both sides of a current collector.

[0004] Monopolar secondary batteries utilizing monopolar electrodes may experience increased resistance in terms of current flow paths due to the parallel connection of unit cells. Consequently, this can lead to reduced output, increased heat generation, and compromised cell stability. Furthermore, space efficiency is low because components for heat dissipation structures, thermal monitoring systems, and associated wiring occupy space for heat management.

[0005] In bipolar secondary batteries utilizing bipolar electrodes, unit cells are connected in series and stacked, so the current path travels only along the thickness direction of the cell, except for the outermost electrode. Consequently, output performance is excellent, and because the structure and components are simplified and space efficiency is high, energy density and output density per unit volume can be improved compared to monopolar secondary batteries.

[0006] Meanwhile, since bipolar electrodes have a cathode and an anode having different materials coated on both sides of a single current collector, the rolling process is difficult during electrode rolling. Specifically, if the anode is coated and rolled on the current collector first, and then the cathode is coated and rolled, there is a risk that moisture will enter the anode due to the water-based solvent contained in the cathode slurry. In addition, there is a risk that the edges of the cathode will crack due to the difference in surface area between the cathode and the anode during cathode rolling.

[0007] Conversely, if the cathode is coated and rolled on the current collector first, followed by the anode, there is a problem where the cathode is continuously pressed during the rolling of the anode because the anode has a relatively high density, and the anode is not sufficiently rolled and the cathode breaks. Therefore, when rolling bipolar electrodes, it is important to roll the anode and cathode with an appropriate porosity.

[0008] In addition, since there is a difference in area between the negative and positive electrodes coated on both sides of the current collector, there is a risk that cracks may occur in the inactive region of the negative electrode during the battery activation stage. This will be explained in detail with reference to FIGS. 1 and 2.

[0009] Figure 1 illustrates a conventional bipolar electrode.

[0010] Referring to FIG. 1, a conventional bipolar electrode (1C) comprises a current collector (10C) and a negative electrode (20C) and an anode (30C) coated on both sides of the current collector (10C). In a planar view, the area of ​​the negative electrode (20C) may be larger than that of the anode (30C). In FIG. 1, the negative electrode (20C) and the anode (30C) are rolled individually, so that the entire area of ​​each electrode is rolled.

[0011] Figure 2 shows the electrode of Figure 1 activated.

[0012] When the electrode (1C) of Fig. 1 is activated by charging and discharging, only a portion of the negative electrode (20C) that overlaps with the positive electrode (30C) is activated and swollen (40). Since the edge portion of the negative electrode (20C) that does not overlap with the positive electrode (30C) does not swell, a crack may occur in the negative electrode (20C) at the boundary of the swollen portion (40). Additionally, during the activation process of the electrode (1C), some lithium ions may enter the edge of the negative electrode (20C) that does not overlap with the positive electrode (30C). However, if a crack occurs at the edge of the negative electrode (20C) and an abnormality develops, Li plating may occur, in which lithium is deposited on the surface of the negative electrode (20C) in a lithium metal state rather than being charged in an ionic state, which can cause deterioration.

[0013] Therefore, it is necessary to develop a manufacturing method for a bipolar secondary battery that can solve the aforementioned problems and achieve appropriate porosity for the bipolar cathode and anode. The problem to be solved

[0014] The present invention provides a method for manufacturing a secondary battery capable of achieving a target porosity in a bipolar electrode.

[0015] The present invention aims to provide a secondary battery with improved battery performance and stability. means of solving the problem

[0016] The method for manufacturing a secondary battery according to the present invention comprises the steps of: forming a negative electrode film by coating and drying a negative electrode slurry on one surface of a current collector; attaching a positive electrode film formed by a dry process to the other surface of the current collector; and forming a bipolar electrode by simultaneously rolling the positive electrode film and the negative electrode film.

[0017] In one embodiment, the anode film may be formed into a film shape by dry mixing and fiberizing the anode composite composition comprising an anode active material, a binder, and a conductive material.

[0018] In one embodiment, the method may further include the step of coating a primer layer on one or the other side of the current collector facing the cathode film or the anode film.

[0019] In one embodiment, the primer layer may include a conductive material and a polymer material.

[0020] In one embodiment, the primer layer may include a conductive material and a polymer material.

[0021] According to one embodiment, the cathode film may have a larger area than the anode film on a flat surface.

[0022] In one embodiment, the cathode film includes a first portion that overlaps with the anode film with the current collector in between, and a second portion that surrounds the first portion, and the anode film and the first portion may be rolled simultaneously in the bipolar electrode forming step. At this time, the second portion may not be rolled.

[0023] In one embodiment, after the bipolar electrode forming step, the first portion may have a first thickness, and the second portion may have a second thickness greater than the first thickness.

[0024] In one embodiment, after the bipolar electrode formation step, the method further includes a step of activating the bipolar electrode by charging and discharging it, and in the activation step, only the first portion of the cathode film may be swollen. At this time, the second portion may not be swollen and there may be substantially no change in thickness.

[0025] In one embodiment, the current collector may comprise at least one of stainless steel and copper-plated aluminum clad.

[0026] In one embodiment, the cathode slurry may include a cathode active material, a binder, and a conductive material dispersed in a solvent.

[0027] Meanwhile, the bipolar electrode of the present invention comprises a current collector; a negative electrode layer disposed on one side of the current collector; and a positive electrode layer disposed on the other side of the current collector.

[0028] The above cathode layer includes a first portion that overlaps with the anode layer with the current collector in between, and a second portion that surrounds the first portion, the thickness of the second portion is greater than the thickness of the first portion, and the anode layer may include a fibrous binder, an anode active material, and a conductive material.

[0029] In such a bipolar electrode, the current collector may comprise at least one of stainless steel and copper-plated aluminum clad, and the cathode layer may comprise a cathode active material, a microfibrous binder, and a conductive material. Additionally, the anode layer may have a film form, and the cathode layer may have a dried coating layer form.

[0030] Also, the cathode layer may have a larger area than the anode layer on a flat surface, and there may be a step difference between the first part and the second part.

[0031] In addition, in one embodiment, a primer layer formed on one or the other surface of the current collector facing the cathode layer or the anode layer may be further included. In this case, the primer layer may include a conductive material and a polymer material.

[0032] In addition, the present invention can provide a secondary battery comprising the above-mentioned bipolar electrode. Effects of the invention

[0033] The method for manufacturing a secondary battery according to the present invention can provide a method for manufacturing a bipolar electrode with a simplified manufacturing process.

[0034] The secondary battery of the present invention can have improved cell performance. Brief explanation of the drawing

[0035] Figure 1 illustrates a conventional electrode. Figure 2 shows the electrode of Figure 1 activated. Figure 3 illustrates a flowchart of a method for manufacturing a secondary battery according to one embodiment. FIG. 4 illustrates one step of a method for manufacturing a secondary battery of one embodiment. FIG. 5 illustrates one step of a method for manufacturing a secondary battery of one embodiment. FIG. 6 illustrates one step of a method for manufacturing a secondary battery of one embodiment. FIG. 7 illustrates one step of a method for manufacturing a secondary battery of one embodiment. FIG. 8 illustrates one step of a method for manufacturing a secondary battery of one embodiment. FIG. 9 illustrates a secondary battery of one embodiment. FIG. 10 illustrates a secondary battery of one embodiment being activated. Specific details for implementing the invention

[0036] Hereinafter, various embodiments of the present invention will be described in detail with reference to the attached drawings so that those skilled in the art can easily implement the present invention. The present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0037] In this specification, parts unrelated to the description have been omitted to clearly explain the invention, and the same reference numerals have been used throughout the specification for identical or similar components.

[0038] Furthermore, the size and thickness of each component shown in the drawings are depicted arbitrarily for convenience of explanation, and thus the present invention is not necessarily limited to what is illustrated. Thicknesses have been enlarged in the drawings to clearly represent various layers and regions. Additionally, for convenience of explanation, the thickness of some layers and regions has been exaggerated in the drawings.

[0039] Furthermore, when a part such as a layer, membrane, region, or plate is said to be "on" or "on" another part, this includes not only cases where it is "immediately above" another part, but also cases where there is another part in between. When a part is said to be "immediately above" another part, it means that there is no other part in between. Also, saying that a part is "on" or "on" a reference part means that it is located above or below the reference part, and does not necessarily mean that it is located "on" or "on" facing the opposite direction of gravity.

[0040] Furthermore, throughout the specification, when a part is described as “comprising” a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0042] The method for manufacturing a secondary battery according to the present invention comprises the steps of: forming a negative electrode film by coating and drying a negative electrode slurry on one surface of a current collector; attaching a positive electrode film formed by a dry process to the other surface of the current collector; and forming a bipolar electrode by simultaneously rolling the positive electrode film and the negative electrode film.

[0044] Figure 3 illustrates a flowchart of a method for manufacturing a secondary battery according to one embodiment.

[0045] Referring to FIG. 3, a method for manufacturing a secondary battery according to one embodiment includes the steps of providing a current collector (S100), forming a negative electrode film on one side of the current collector (S200), forming a positive electrode film by a dry process (S300), attaching the positive electrode film to the other side of the current collector (S400), and forming a bipolar electrode (S500).

[0046] A method for manufacturing a secondary battery according to one embodiment relates to a method for manufacturing a secondary battery including a bipolar electrode, and the secondary battery described below refers to a secondary battery to which a bipolar electrode is applied.

[0048] The step of providing a current collector (S100) is a step of providing a current collector for a bipolar electrode. The current collector comprises a material having conductivity without causing chemical changes in the battery. Furthermore, it is preferable that the current collector of the present invention has low elongation due to rolling and possesses a predetermined strength so that there is no problem of the active material of the electrode being embedded in the current collector when the electrode is rolled.

[0049] Generally, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or a material with a surface treatment such as copper, carbon, nickel, titanium, silver, etc., may be used as the current collector. For example, in the present invention, stainless steel (SUS) may be used as the current collector, or copper-coated aluminum clad may be used.

[0050] In addition, the current collector may have a thickness of 3 μm to 500 μm, and may form fine irregularities on the surface to increase adhesion to the active material described later. For example, it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics, and specifically, stainless steel foil can be used.

[0052] The step of forming a negative film on one side of the current collector (S200) is a step of forming a negative film by coating and drying a negative slurry on one side of the current collector.

[0053] In the present invention, the cathode film is manufactured wet using a cathode slurry.

[0054] Figure 4 illustrates a flowchart of a method for manufacturing a secondary battery according to one embodiment.

[0055] Referring to FIG. 4, a cathode film (20) is formed by coating and drying a cathode slurry on one surface of a current collector (10).

[0056] A cathode slurry can be prepared by mixing a cathode active material, a binder, and a conductive material in a solvent. In such a cathode slurry, the cathode active material, the binder, and the conductive material may be included in a dispersed form in the solvent.

[0057] The cathode active material is one or more carbon-based materials selected from the group consisting of graphite, amorphous hard carbon, low-crystalline soft carbon, carbon black, acetylene black, Ketjen black, Super P, graphene, and fibrous carbon, Si-based materials, 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; Al, Cu, Ge, Si, Sn 등의 금속; 리튬 합금; 규소계 합금; 주석계 합금; SiO, SiO2, SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5등의 금속 산화물; 폴리아세틸렌 등의 도전성 고분자; Li-Co-Ni 계 재료; 티타늄 산화물; 리튬 티타늄 산화물 등을 포함할 수 있지만, 당업계에 알려진 것이라면 이들만으로 한정되는 것은 아니다.

[0058] A binder is a component that assists in the bonding between a conductive material, an active material, and a current collector. Examples of such binders include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polyethylene, polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof.

[0059] A conductive material is a component for further enhancing the conductivity of an active material, and such a conductive material is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, carbon powder such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powder such as natural graphite, artificial graphite, or graphite; conductive fibers such as carbon fibers or metal fibers; fluorinated carbon powder; conductive powder such as aluminum powder or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; polyphenylene derivatives; conductive materials such as carbon nanotubes, etc. may be used.

[0060] Generally, organic solvents or aqueous solvents can be used as the solvent, and aqueous solvents can be used as the solvent for the cathode slurry, for example, water can be used.

[0061] The method of manufacturing the cathode film (20) follows a general wet electrode manufacturing process. For example, the cathode film (20) is formed by mixing the aforementioned cathode active material, binder, conductive material, etc. in a solvent to prepare a cathode slurry, and then coating the cathode slurry onto a current collector and drying it. At this stage, the cathode film (20) is in an unrolled state.

[0063] Subsequently, the step of forming an anode film (S300) is carried out.

[0064] The step of forming an anode film (S300) is a step of forming a free-standing anode film by a dry process using an anode composite composition. Specifically, the step of forming an anode film (S300) may involve dry mixing and fiberizing an anode composite composition containing an anode active material, a fiberizable binder, and a conductive material without a separate liquid medium, and forming it into a film. That is, the anode film of the present invention is manufactured dry.

[0065] The anode composite composition does not contain a solvent and comprises an anode active material, a fiberizable binder, and a conductive material.

[0066] The cathode active material is a compound capable of reversible intercalation and deintercalation of lithium, and various combinations are possible, for example, lithium-manganese oxides (e.g., LiMnO2, LiMn2O4, etc.), lithium-cobalt oxides (e.g., LiCoO2, etc.), lithium-nickel oxides (e.g., LiNiO2, etc.), and lithium-nickel-manganese oxides (e.g., LiNi 1-Y Mn Y O2(here, 0 <Y<1), LiMn 2-Z Ni Z O4 (where 0 < Z < 2), etc.), lithium-nickel-cobalt oxides (e.g., LiNi 1-Y1 Co Y1 O2(here, 0 <Y1<1) 등), 리튬-망간-코발트계 산화물(예를 들면, LiCo 1-Y2 Mn Y2 O2(here, 0 <Y2<1), LiMn 2-Z1 Co Z1 O4 (where 0 < Z1 < 2), etc.), lithium-nickel-manganese-cobalt oxides (e.g., Li(Ni p Co q Mn r )O2(where, 0<p<1, 0<q<1, 0<r<1, p+q+r=1) or Li(Ni p1 Co q1 Mnr1 )O4 (where 0<p1<2, 0<q1<2, 0<r1<2, p1+q1+r1=2), etc.), or lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r2 M s2 )O2(wherein M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r2, and s2 are the atomic fractions of independent elements, respectively, 0 < p2 < 1, 0 < q2 < 1, 0 < r2 < 1, 0 < s2 < 1, p2 + q2 + r2 + s2 = 1), etc.), lithium iron phosphate (e.g., Li 1+a1 Fe 1-x1 M x1 (PO 4-b1 )X b1 (Here, M is one or more selected from Al, Mg and Ti, and X is one or more selected from F, S and N, and -0.5≤a1≤0.5, 0≤x1≤0.5, 0≤b1≤0.1) etc., and any one or more of these compounds may be included.

[0067] The binder may be applied in the same way as described above in the cathode slurry, but the binder used in the cathode slurry and the binder used in the anode composite composition may be different from each other. For example, the binder used in the anode composite composition may be a fiberizable polymer binder that enables the formation of an anode film by a dry process, such as polytetrafluoroethylene (PTFE).

[0068] The conductive material can be applied in the same way as described above in the cathode slurry.

[0069] An anode composite composition containing the aforementioned components can become an anode powder through a mixing process, a kneading process, and a grinding process, and an anode film can be formed by calendering the anode powder.

[0070] Since the anode film is manufactured in a free-standing form as described above and is manufactured in a space separate from the cathode, the problem of solvent contained in the cathode slurry flowing into the anode film does not occur during the manufacture of conventional bipolar electrodes.

[0071] Meanwhile, the anode film has been sheeted through calendering but has not yet been rolled to the target porosity.

[0073] Afterwards, a step (S400) of attaching the positive film to the other side of the current collector is performed.

[0074] In one embodiment, the method may further include the step of coating a primer layer on one or the other side of the current collector facing the cathode film or the anode film. The cathode film or the anode film may be attached to the primer layer.

[0075] In other words, the anode film can be attached to the current collector through a primer layer to exhibit enhanced adhesion.

[0076] FIG. 5 illustrates one step of a method for manufacturing a secondary battery of one embodiment.

[0077] Referring to FIG. 5, a primer layer (31) is shown coated on the other side of the current collector (10). The other side of the current collector (10) is the side opposite to the one side of the current collector (10) on which the negative film (20) is coated.

[0078] The primer layer (31) serves to increase the adhesion of the anode film to the current collector (10) and may include a conductive material and a polymer material. For example, the primer layer (31) may include a conductive material such as carbon powder such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powder such as natural graphite, artificial graphite, or graphite; conductive fibers such as carbon fibers or metal fibers; fluorinated carbon powder; conductive powder such as aluminum powder or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; polyphenylene derivatives; and conductive materials such as carbon nanotubes.

[0079] For example, the primer layer (31) may be a polymer material such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polyethylene, polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof.

[0080] In one embodiment, the primer layer (31) may contain carbon black and polyvinylidene fluoride (PVDF) in a weight ratio of 3:7, but the embodiment is not limited thereto.

[0081] A method of providing a primer layer (31) to a current collector (10) may, for example, use a method of adding a conductive material and a polymer material to a predetermined volatile solvent to form a coating solution, applying it to the current collector (10), and then removing the solvent. Examples of volatile solvents include NMP, water, MIBK (methyl isobutyl ketone), isopropanol, etc., but are not limited to these.

[0083] FIG. 6 illustrates one step of a method for manufacturing a secondary battery of one embodiment.

[0084] Referring to FIGS. 5 and FIGS. 6 together, a primer layer (31) is applied to the other side of the current collector (10), and then an anode film (30) can be attached and laminated on the primer layer (31). In FIGS. 6 and the following drawings, the primer layer (31) is omitted for convenience of explanation.

[0085] FIG. 7 illustrates one step of a method for manufacturing a secondary battery of one embodiment.

[0086] Referring to FIGS. 6 and FIGS. 7 together, the area of ​​the cathode film (20) in a planar plane may be larger than the area of ​​the anode film (30). Specifically, the cathode film (20) includes a first portion (21) that overlaps with the anode film (30) with the current collector (10) in between, and a second portion (22) that surrounds the first portion (21). In a planar plane, the first portion (21) has the same size and the same area as the anode film (30). Also in a planar plane, the second portion (22) surrounds the first portion (21) and does not overlap with the anode film (30).

[0088] Afterwards, the step of forming a bipolar electrode (S500) is carried out.

[0089] Specifically, the step of forming a bipolar electrode (S500) is a step of simultaneously rolling the positive film (30) and the first part (21).

[0090] FIG. 8 illustrates one step of a method for manufacturing a secondary battery of one embodiment.

[0091] Referring to FIG. 8, an anode film (30) and a cathode film (20) are attached to both sides of a current collector (10). The step of forming a bipolar electrode (S500) is to simultaneously roll the anode film (30) and the first portion (21) of the cathode film (20) facing it, with the current collector (10) in between. At this time, the second portion (22) of the cathode film (20) is not rolled.

[0092] The first part (21) of the cathode film (20) has a first thickness (LL1) through rolling. Since the second part (22) is not rolled, it has a second thickness (LL2), which is the thickness of the cathode film (20) before rolling. The second thickness (LL2) is greater than the first thickness (LL1). When rolling the cathode film (20), the first part (21) is rolled simultaneously with the anode film (30), and since the second part (22) is not rolled, there is a difference in thickness between the first part (21) and the second part (22).

[0095] FIG. 9 illustrates a secondary battery of one embodiment.

[0096] When the step (S500) of forming a bipolar electrode is completed, the bipolar electrode (1) of the present invention is formed.

[0097] The bipolar electrode (1) of the present invention comprises a current collector (10), a negative electrode layer (20a) disposed on one side of the current collector (10), and a positive electrode layer (30a) disposed on the other side of the current collector (10).

[0098] In FIG. 8, when the cathode film (20) is rolled, a cathode layer (20a) is formed, and when the anode film (30) is rolled, an anode layer (30a) is formed.

[0099] The cathode layer (20a) includes a first portion (21) having a first thickness (LL1) and a second portion (22) having a second thickness (LL2). The second thickness (LL2) is greater than the first thickness (LL1), and there is a step difference between the first portion (21) and the second portion (22).

[0101] A method for manufacturing a secondary battery according to one embodiment may further include an activation step of activating the bipolar electrode by charging and discharging it after the step of forming the bipolar electrode (S500).

[0102] FIG. 10 illustrates a secondary battery of one embodiment being activated.

[0103] Referring to FIG. 10, in the activation step, the first portion (21) of the negative electrode layer (20a) swells (40) as charging and discharging are repeated. Specifically, since the first portion (21) that overlaps with the positive electrode layer (30a) is activated and the second portion (22) that does not overlap with the positive electrode layer (30a) is deactivated, the phenomenon of swelling (40) occurring only in the first portion (21) occurs in the activation step. At this time, since the thickness of the second portion (22) is formed to be relatively thick, the thickness of the second portion (22) remains unchanged even if the first portion (21) swells. Therefore, the bipolar electrode (1) of the present invention can maintain the thickness and shape of the negative electrode layer (20a) without being affected by the swelling (40) of the first portion (21) in the activation step. Accordingly, it is possible to prevent cracks from occurring in the negative electrode layer (20a) in the activation step and to provide a secondary battery with improved performance.

[0105] Experimental Example

[0106] Example 1: Preparation of a bipolar electrode

[0107] 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.

[0108] 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 achieve an electrode layer loading of 600 mg / 25 cm 2 An anode film was manufactured in the form of a freestanding film with a thickness of 100㎛.

[0109] 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 a thickener are mixed in water to prepare a slurry, the slurry is coated on one side of a stainless steel foil (8㎛), and then dried and rolled to obtain an electrode layer loading of 300mg / 25cm 2 A cathode composite layer with a thickness of 100㎛ was formed.

[0110] Next, the anode film was attached to the other side of the stainless steel foil on which the cathode composite layer was not formed.

[0111] Next, a rolling process was carried out using a roll press while simultaneously applying a pressure of 1-3 ton / cm to the cathode composite layer and the anode film to manufacture the bipolar electrode of Example 1.

[0113] Example 2: Preparation of a bipolar electrode

[0114] The bipolar electrode of Example 2 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.

[0116] Comparative Example 1: Preparation of a bipolar electrode

[0117] An anode film was formed in the same manner as in Example 1 and attached to the other side of a stainless steel foil. A rolling process was first performed on the anode film using a roll press while applying a pressure of 1-3 ton / cm to the anode film.

[0118] Next, a cathode composite layer was additionally formed on one side of a stainless steel foil in the same manner as in Example 1. After the formation of the cathode composite layer, a rolling process was additionally performed on the cathode composite layer using a roll press while applying a pressure of 1-3 ton / cm. By doing so, the bipolar electrode of Comparative Example 1 was manufactured.

[0120] Comparative Example 2: Preparation of a bipolar electrode

[0121] A cathode composite layer was formed on one side of a stainless steel foil in the same manner as in Example 1. After the formation of the cathode composite layer, a rolling process was performed on the cathode composite layer using a roll press while applying a pressure of 1-3 ton / cm.

[0122] Next, an anode film was formed in the same manner as in Example 1 and additionally attached to the other side of a stainless steel foil. A rolling process was additionally performed on the anode film using a roll press while applying a pressure of 1-3 ton / cm to the anode film. By doing so, the bipolar electrode of Comparative Example 2 was manufactured.

[0124] For the electrodes of Example 1, Example 2, Comparative Example 1, and Comparative Example 2 manufactured as described above, the target electrode porosity, actual electrode porosity, electrode overrolling, discharge capacity, and cycle performance were evaluated and are shown in Table 1 below.

[0125] Meanwhile, in Table 1 below, electrode overrolling refers to the rate of increase relative to the target electrode porosity. Cycle performance is capacity retention at 100 cycles.

[0126] division Target electrode porosity Actual electrode porosity Electrode overrolling 2C discharge capacity compared to 0.1C 0.33C 25℃ cycle performance (@100 cycles) Example 1 (Anode) 30%, (Cathode) 30% (Anode) 30%, (Cathode) 30% (Polygonal) -, (Cathode) - 97% 93% Example 2 (Anode) 30%, (Cathode) 30% (Anode) 30%, (Cathode) 30% (Polygonal) -, (Cathode) - 97% 94% Comparative Example 1 (Anode) 30%, (Cathode) 30% (Anode) 26%, (Cathode) 30% (Anode) 4%, (Cathode) - 94% 89% Comparative Example 2 (Anode) 30%, (Cathode) 30% (Anode) 30%, (Cathode) 25% (Positive) -, (Negative) 5% 95% 87%

[0127] Referring to Table 1 above, in the case of Examples 1 and 2, the target porosity was achieved by fabricating the anode and cathode separately and then rolling them simultaneously. As a result, excellent discharge capacity and cycle performance were exhibited. In the case of Comparative Example 1, the anode was manufactured first and then the cathode was manufactured, resulting in over-rolling of the anode. In the case of Comparative Example 2, the cathode was manufactured first and then the anode was manufactured, resulting in over-rolling of the cathode. It is expected that in Comparative Examples 1 and 2, this over-rolling increased the tortusity of the electrodes and caused problems with ion transport, leading to a decrease in discharge capacity and cycle performance. Furthermore, as the porosity of Comparative Examples 1 and 2 was lower than the target porosity, subsequent electrolyte wetting may also be disadvantageous compared to the Examples.

[0128] As described above, the method for manufacturing a secondary battery of the embodiment involves coating a negative electrode on one side of a current collector and attaching a free-standing positive electrode manufactured by a dry process to the other side of the current collector, and by simultaneously rolling the negative electrode and the positive electrode, the rolling process of the positive electrode and the negative electrode can be simplified and made easier. In addition, the secondary battery of the embodiment is manufactured according to the above method for manufacturing a secondary battery, and the stability of the electrode and the battery characteristics can be improved.

[0130] Although preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concept of the present invention as defined in the following claims are also included within the scope of the present invention. Explanation of the symbols

[0131] 1: Bipolar electrode 10: The whole house 20: Cathode film 21: Part 1 22: Part 2 30: Anode film 20a: Cathode layer 30a: Anode layer

Claims

Claim 1 A bipolar electrode comprising: a current collector; a cathode layer disposed on one side of the current collector; and an anode layer disposed on the other side of the current collector; wherein the cathode layer comprises a first portion that overlaps with the anode layer with the current collector in between, and a second portion that surrounds the first portion, the thickness of the second portion being greater than the thickness of the first portion, and the anode layer comprising a fibrous binder, an anode active material, and a conductive material. Claim 2 A bipolar electrode according to claim 1, wherein the current collector comprises at least one of stainless steel and copper-plated aluminum clad. Claim 3 In claim 1, the cathode layer is a bipolar electrode comprising a cathode active material, a microfibrous binder, and a conductive material. Claim 4 A bipolar electrode according to claim 1, wherein the anode layer has a film form and the cathode layer has a dried coating layer form. Claim 5 In claim 1, the cathode layer is a bipolar electrode having a larger area than the anode layer on a plane. Claim 6 A bipolar electrode according to claim 1, wherein a step exists between the first part and the second part. Claim 7 A bipolar electrode according to claim 1, further comprising a primer layer formed on one or the other side of the current collector facing the cathode layer or the anode layer. Claim 8 In claim 7, the primer layer comprises a bipolar electrode including a conductive material and a polymer material. Claim 9 A secondary battery comprising a bipolar electrode according to any one of claims 1 to 7.

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