Bipolar battery and method for manufacturing the same

Abstract

According to one embodiment of the present invention, a bipolar battery is provided, comprising a laminate including a bipolar electrode and a separation membrane, a bipolar assembly including a gel electrolyte impregnated throughout the laminate, and a battery case, wherein there is no interfacial gap at the interface between the bipolar electrode and the separation membrane, and the voids in the gel electrolyte inside the laminate are 5% or less of the total volume in which the gel electrolyte can be impregnated, and a method for manufacturing the same.

Description

[Technical Field]

[0001] [Cross-reference of related applications] This application claims priority rights under Korean Patent Application No. 10-2024-0092124 dated July 12, 2024, and Korean Patent Application No. 10-2025-0093154 dated July 10, 2025, and all content disclosed in the documents of said Korean patent applications is incorporated herein by reference.

[0002] This invention relates to a bipolar battery and a method for manufacturing the same. [Background technology]

[0003] Recently, as the application areas of lithium-ion batteries have rapidly expanded from power supply for electronic devices such as electrical, electronic, communications, and computers to power storage and supply for large-area devices such as automobiles and energy storage devices, there is a growing demand for high-capacity, high-output, and highly stable secondary batteries.

[0004] The electrodes used in such secondary batteries can be divided into monopolar electrodes, in which an active material with the same polarity is coated on both sides of the current collector, and bipolar electrodes, in which an active material with different polarities is coated on both sides of the current collector.

[0005] Secondary batteries using monopolar electrodes have connections between the electrodes, which can lead to a decrease in output due to the electrical resistance of the connections. Furthermore, the temperature rise due to Joule heating can pose various safety concerns for the cells. Additionally, the heat dissipation structure, thermal monitoring, and wiring components occupy a significant portion of the battery pack, resulting in poor space efficiency. In contrast, secondary batteries using bipolar electrodes stack the electrodes without connections, minimizing electrode connection resistance and resulting in significantly improved output performance. The simplified structure and components also contribute to better space efficiency, leading to a substantial improvement in energy density and power density per unit volume compared to conventional lithium-ion batteries.

[0006] Despite these advantages, preventing leakage of the electrolyte impregnated in bipolar batteries is extremely important, and non-flowable all-solid electrolytes have been applied.

[0007] However, current technology has not yet developed an all-solid electrolyte that is industrially usable, and it is still necessary to manufacture them using liquid or gel electrolytes.

[0008] Conventional manufacturing methods for bipolar batteries using such liquid or gel electrolytes include direct injection, electrode coating / impregnation, and electrode slurry mixing.

[0009] The aforementioned direct electrolyte injection method involves manufacturing the bipolar capacitors in unit cell units and sealing them to prevent electrolyte leakage; in other words, it is a method of manufacturing them in a sealed structure and then injecting the electrolyte. However, achieving such a sealed structure is complex, and since this process is carried out for each unit cell before manufacturing the assembly, there are difficulties in the process and it is time-consuming.

[0010] Furthermore, the electrode coating / impregnation method involves coating an electrode sheet or separation membrane with an electrolyte, impregnating it with the electrolyte, and then, after a curing process, cutting and stacking the electrode and separation membrane to manufacture the product. The slurry mixing method involves manufacturing a mixed electrode by combining the electrode slurry and electrolyte, and then, after a curing process, cutting and stacking the electrodes to manufacture the product.

[0011] However, in both of the above methods, the electrodes impregnated with the electrolyte, or electrodes mixed with the electrolyte, are exposed to the outside during the manufacturing process. This not only causes significant volatilization of the electrolyte, but also leads to safety problems because the presence of oxygen during the electrolyte curing process severely reduces the curability.

[0012] Furthermore, when manufacturing bipolar batteries using such conventional manufacturing methods, as shown in Figure 1 below, the electrolyte 20 generated on the surface of the electrode 11 is depleted due to evaporation. This creates a volatile space for the gel electrolyte between the interface of the electrode 11 and the separation membrane 12, i.e., a gel electrolyte interface void 13, which acts as resistance in the battery, resulting in a decrease in battery performance.

[0013] Therefore, the current situation necessitates the development of a bipolar battery with a simplified structure that simultaneously solves the above problems. [Overview of the Initiative] [Problems that the invention aims to solve]

[0014] The present invention aims to provide a bipolar battery and a method for manufacturing the same, in which the gel electrolyte is cured after the laminate is manufactured, resulting in virtually no voids in the gel electrolyte within the laminate and thus improved battery performance.

[0015] The present invention also has the effect of simplifying the structure without requiring a separate sealed structure, even while applying a gel electrolyte.

[0016] Furthermore, the objective is to provide a method for manufacturing a bipolar assembly that not only ensures uniform electrolyte impregnation of the components within the bipolar assembly but also saves electrolyte impregnation time.

[0017] The present invention goes a step further to provide a bipolar battery and a method for manufacturing the same that can minimize the volatilization of the gel electrolyte during the manufacturing of the bipolar battery and can be used with a wide variety of electrolytes without being limited by the electrolyte material. [Means for solving the problem]

[0018] According to one embodiment of the present invention, A bipolar assembly comprising a laminate containing bipolar electrodes and a separation membrane, and a gel electrolyte impregnated throughout the laminate, and a battery case, A bipolar battery is provided in which the voids in the gel electrolyte within the laminate are 5% or less of the total volume in which the gel electrolyte can be impregnated.

[0019] In this case, the bipolar electrode may include an integrated electrode in which a positive electrode active material layer and a negative electrode active material layer are coated on both sides of a single current collector, a positive electrode in which a positive electrode active material layer is formed on one surface of a positive electrode current collector, or a negative electrode in which a negative electrode active material layer is formed on one surface of a negative electrode current collector.

[0020] The laminate may be a structure in which one or more selected from the group consisting of a unit cell having a structure in which the positive electrode active material layer of the integrated electrode and the separation membrane face each other, a unit cell having a structure in which the positive electrode and the negative electrode are separately included and the separation membrane is interposed between the positive electrode and the negative electrode, a unit cell having a structure in which a single-sided electrode and a separation membrane are laminated, and a single-sided electrode are laminated.

[0021] Furthermore, in the laminate, single-sided electrodes with different polarities can be positioned on the outermost sides of both sides in the stacking direction.

[0022] Such a laminate does not need to include a sealing member.

[0023] On the other hand, the gel electrolyte may contain an electrolyte composition with a flash point of less than 90°C, and specifically, the electrolyte composition with a flash point of less than 90°C may be present in an amount of 10% or more of the total volume of the electrolyte composition contained in the gel electrolyte.

[0024] Such an electrolyte composition having a flash point of less than 90°C may be one or more selected from the group consisting of methyl formate, ethyl formate, 1,2-dimethoxyethane, methyl acetate, 1,3-dioxolane, ethyl acetate, methyl propionate, propyl acetate, methyl butyrate, tris(trimethylsilyl) phosphate, dimethyl carbonate, propyl propionate, ethyl methyl carbonate, diethyl carbonate, ethyl propionate, ethyl butyrate, butyronitrile, ethyl methyl sulfone, propyl butyrate, diethylene glycol dimethyl ether, vinylene carbonate, and glycol sulfite.

[0025] Taking it a step further, according to the present invention, all of the bipolar electrodes and all of the separation membranes contained in the laminate may be collectively bonded by the gel electrolyte in the laminated state.

[0026] Furthermore, positive and negative electrode terminals may be attached to the outermost electrodes on both sides of the bipolar assembly in the stacking direction, respectively.

[0027] On the other hand, according to another embodiment of the present invention, a method for manufacturing the bipolar battery, (a) Prepare a unit cell by stacking bipolar electrodes and a separation membrane. (b) Two or more of the unit cells are stacked together to manufacture a laminate such that a single-sided electrode is placed on the outermost side. (c) A method for manufacturing a bipolar battery is provided, in which the laminate is placed in a storage member containing a gel electrolyte composition and impregnated, and the gel electrolyte composition is cured under pressure to form a gel electrolyte.

[0028] In this case, the unit cell may be manufactured by cutting the bipolar electrode and the separation membrane to a unit size and then bonding them together.

[0029] Each of these unit cells may have a structure that does not include a sealing member.

[0030] The gel electrolyte composition may contain 10% or more of an electrolyte composition with a flash point of less than 90°C, based on the total solvent volume.

[0031] On the other hand, when impregnating the laminate with such a gel electrolyte composition, the storage member in which the laminate is housed may be, for example, an open-type electrolyte box with an open top, or a battery case for housing the laminate.

[0032] Therefore, if the storage member is an electrolyte box, the process may further include storing the laminate in a battery case after the formation of the gel electrolyte.

[0033] On the other hand, the impregnation of the gel electrolyte composition may be carried out under vacuum.

[0034] The application of the vacuum may involve repeating the vacuum application and release process four or more times.

[0035] The aforementioned vacuum application can be maintained in the range of -100kPa to -90kPa for 3 to 10 minutes at a time.

[0036] Thereafter, the curing process, which is carried out in conjunction with pressurization, may be performed by applying heat in a vacuum at a temperature of 50°C to 80°C for 2 to 10 hours.

[0037] Taking it a step further, the method for manufacturing a bipolar battery according to the present invention may further include a step of releasing the pressurized state after the gel electrolyte composition has cured.

[0038] A bipolar battery is provided in which a positive electrode terminal and a negative electrode terminal are attached to the outermost electrodes on both sides of the bipolar assembly in the stacking direction, respectively. [Brief explanation of the drawing]

[0039] [Figure 1]This is a schematic cross-sectional view of a bipolar unit cell manufactured using a conventional manufacturing method.

[0040] [Figure 2] This is a schematic cross-sectional view of a bipolar assembly according to one embodiment of the present invention.

[0041] [Figure 3] This is a schematic cross-sectional view of a bipolar unit cell according to one embodiment of the present invention.

[0042] [Figure 4] This is a schematic cross-sectional view of a bipolar unit cell according to another embodiment of the present invention.

[0043] [Figure 5] This is a schematic cross-sectional view of a bipolar battery according to one embodiment of the present invention.

[0044] [Figure 6] This is a schematic diagram of a method for manufacturing a bipolar battery according to one embodiment of the present invention.

[0045] [Figure 7] This is a comparative graph showing the amount of electrolyte evaporation due to structural differences, as shown in Experimental Example 1.

[0046] [Figure 8] This is a voltage-capacitance graph corresponding to the cycle of Comparative Example 1, based on Experimental Example 2.

[0047] [Figure 9] This is a voltage-capacitance graph corresponding to the cycle of the example in Experimental Example 2. [Modes for carrying out the invention]

[0048] Hereafter, terms and words used in this specification and in the claims should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather in a manner and concept consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may appropriately define the concepts of terms in order to best describe their invention.

[0049] Unless otherwise defined, all terms used herein (including technical and scientific terms) should be used in a sense that is commonly understood by a person of ordinary skill in the art to which the present invention pertains. Furthermore, terms defined in commonly used dictionaries should not be interpreted ideally or excessively unless explicitly defined otherwise.

[0050] The terms used herein are for illustrative purposes only and are not intended to limit the invention. In this specification, the singular form includes the plural form unless otherwise specified. The terms “comprises” and / or “comprising” as used in this specification do not exclude the presence or addition of one or more other components in addition to those mentioned.

[0051] In this specification, when a part is said to include a component, this means that, unless otherwise stated, it may further include other components rather than excluding them.

[0052] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings so that those with ordinary skill in the art to which the present invention pertains can easily implement it. However, the present invention can be realized in various different forms and is not limited to the embodiments described below. In this specification and drawings, the same reference numerals indicate the same components.

[0053] Furthermore, the drawings of the present invention include parts with a diagonal structure and parts without a diagonal structure. The parts with a diagonal structure represent a state in which the gel electrolyte is impregnated, while the parts without a diagonal structure represent a state in which the gel electrolyte is not impregnated.

[0054] Therefore, Figure 2, which will be described later, uses a diagonal structure to show the state in which each component is impregnated with the gel electrolyte. In contrast, the unit cells in Figures 3 and 4 are not shown with a diagonal structure because, according to the present invention, the gel electrolyte is impregnated after the manufacturing of the laminate, and therefore the gel electrolyte has not yet been impregnated.

[0055] According to one embodiment of the present invention, a bipolar assembly comprising a laminate including a bipolar electrode and a separation membrane, and a gel electrolyte impregnated throughout the laminate, and a battery case, A bipolar battery is provided in which the voids in the gel electrolyte within the laminate are 5% or less of the total volume in which the gel electrolyte can be impregnated.

[0056] Bipolar assembly The bipolar assembly comprises a laminate containing bipolar electrodes and a separation membrane, and a gel electrolyte impregnated in the laminate, wherein the voids of the gel electrolyte in the laminate are 5% or less of the total volume in which the gel electrolyte can be impregnated.

[0057] Figure 2 schematically shows a cross-sectional view to more clearly explain the structure of the bipolar assembly 1000, Figure 3 schematically shows a cross-sectional view of a unit cell making up the bipolar assembly 1000 as one example, and Figure 4 schematically shows a cross-sectional view of a unit cell making up the bipolar assembly 1000 as another example.

[0058] Referring to Figure 2, the bipolar assembly 1000 includes a laminate 1100, and the laminate 1100 has a structure in which a gel electrolyte is impregnated.

[0059] In this case, according to the present invention, the voids of the gel electrolyte inside the laminate 1100 do not need to be present at all, and can be 5% or less.

[0060] Here, the voids in the gel electrolyte are those where the gel electrolyte has evaporated during the manufacturing of the laminate and is absent, with only the material forming the electrode (typically 121) or separation membrane (typically 122) present. It is not necessary for the voids in the gel electrolyte to be uniformly present throughout the entire structure.

[0061] At this time, the voids in the gel electrolyte refer to the total volume that the gel electrolyte can impregnate, in other words, the volume that is not impregnated by the gel electrolyte, based on the total volume of the voids in the electrode (121, for example) and the voids in the separation membrane (122, for example).

[0062] Therefore, the void volume of the gel electrolyte can be calculated by determining the void volume of the electrode and the separation membrane, using the thickness and weight of each component. In addition, the weight of the impregnated electrolyte can be calculated from the difference in weight before and after the electrolyte impregnated inside the laminate is completely evaporated at high temperature, and the impregnation volume of the electrolyte can be calculated based on the density of the electrolyte. Subsequently, by subtracting the impregnation volume of the electrolyte from the total void volume, the void volume of the gel electrolyte can be obtained, and the ratio of the void volume of the gel electrolyte to the total void can be calculated.

[0063] In other words, the bipolar assembly 1000 according to the present invention has low volatilization of the gel electrolyte and almost no voids where the gel electrolyte is not present, and may contain 5% or less, more specifically 3% or less, even more specifically 0.1% to 2%, and most specifically 0.1% to 1%.

[0064] On the other hand, the laminate 1100 may have a structure in which unit cells 110, 120, 130, 140, 150, and 160 are stacked, but each of the unit cells 120, 130, 140, 150, and 160 can basically include a bipolar electrode (typically 121) and a separation membrane (typically 122), and the unit cell 110 may consist of a bipolar electrode 111 so that a single-sided electrode can be located on the outermost side in the overall structure.

[0065] Such a laminate 1100 may have a structure in which single-sided electrodes 111 and 161 with different polarities are located on the outermost sides of both sides in the stacking direction.

[0066] In this case, the bipolar electrode 121 may include an integrated electrode in which a positive electrode active material layer and a negative electrode active material layer are coated on both sides of a single current collector, a positive electrode in which a positive electrode active material layer is formed on one surface of a positive electrode current collector, or a negative electrode in which a negative electrode active material layer is formed on one surface of a negative electrode current collector.

[0067] Therefore, the laminate 1100 may be a structure in which one or more selected from the group consisting of a unit cell having a structure in which the positive electrode active material layer and the separation membrane of the integrated electrode face each other, a unit cell having a structure in which the positive electrode and the negative electrode are separately included and the separation membrane is interposed between the positive electrode and the negative electrode, a unit cell having a structure in which a single-sided electrode and a separation membrane are laminated, and a single-sided electrode are laminated.

[0068] Here, the single-sided electrode may be either a positive electrode on one side or a negative electrode on the other.

[0069] The laminate 1100 may be made of one type of material, a mixture of two types, or a mixture of three types, as long as it has a structure in which positive and negative electrodes are arranged alternately.

[0070] As shown in Figure 2, the unit cell 110 consists of a single-sided electrode 111, and the unit cell 160 has a structure in which a single-sided electrode 161 and a separation membrane are stacked. Therefore, this structure will not be explained in detail.

[0071] On the other hand, Figures 3 and 4 show unit cells 210 and 210' with two types of structures, excluding the unit cell with a single-sided electrode and the unit cell with a single-sided electrode and a separation membrane stacked on top of each other.

[0072] Referring to Figures 3 and 4, Figure 3 shows a unit cell 210 including an integrated electrode, and Figure 4 shows a unit cell 210' having both a positive and negative electrode as separate electrodes.

[0073] First, referring to Figure 3, the unit cell 210 includes an integrated electrode structure in which a positive electrode active material layer 212 is formed on one surface of a current collector 211, and a negative electrode active material layer 213 is formed on the other surface.

[0074] The separation membrane 214 may be formed on one or both sides of the positive electrode active material layer 212 and the negative electrode active material layer 213, and its position is not limited, but more specifically, it may be formed on one side facing the positive electrode active material layer 212.

[0075] Therefore, when unit cells 210 having such a structure are sequentially stacked to form a laminate, a separation membrane is located on the outermost side of one side. As such, a single-sided electrode can be further included on the outermost side where the separation membrane is located, and by positioning the unit cells consisting of the separation membrane and the single-sided electrode so that there is no active material layer on the outermost side of the other side, a laminate with the structure shown in Figure 2 can be completed.

[0076] Next, referring to Figure 4, the unit cell 210' has a structure in which a positive electrode includes a positive electrode active material layer 212' on one side of a positive electrode current collector 211', a negative electrode includes a negative electrode active material layer 214' on one side of a negative electrode current collector 213', and a separation membrane 215' is interposed between the positive electrode and the negative electrode.

[0077] When such unit cells 210' are stacked sequentially to form a laminate, single-sided electrodes of the other polarity are located on the outermost sides on both sides, so there is no need to include a separate single-sided electrode or a unit cell with a structure in which a single-sided electrode and a separation membrane are stacked.

[0078] However, in a laminate of such a structure, the current collectors of the unit cells face each other, so a conductive adhesive may be applied between the current collectors for stronger bonding.

[0079] Referring again to Figures 3 and 4, the current collector 211 used in the integrated electrode having the structure of Figure 3 must have both a positive electrode active material layer 212 and a negative electrode active material layer 213 formed on both sides. It is not particularly limited as long as it is conductive without inducing a chemical change in the battery, and for example, stainless steel, nickel, titanium, calcined carbon, or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. can be used. More specifically, stainless steel, or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., can be used. Alternatively, it may be a clad foil made by rolling two or more metal foils, for example, a structure in which two or more metals made of Al, Cu, Ni, and SUS are bonded together by cold rolling, or a structure in which one metal is vapor-deposited or coated with another metal as a thin film.

[0080] In contrast, in a unit cell 210' having the structure shown in Figure 4, manufactured using a positive electrode current collector 211' and a negative electrode current collector 213' separately, the positive electrode current collector 211' is not particularly limited as long as it is conductive without inducing a chemical change in the battery. For example, the current collector can be stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. More specifically, it may be an Al current collector. Here, the Al current collector may be made of Al, and this concept includes those further containing other metallic substances to varying degrees of impurity.

[0081] Said negative electrode current collector 121 is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery. For example, copper, stainless steel, nickel, titanium, calcined carbon, copper or stainless steel whose surface is surface-treated with carbon, nickel, titanium, silver or the like, and aluminum-cadmium alloy can be used. Specifically, it may be a Cu current collector, wherein the Cu current collector may be made of Cu, and the concept includes those further containing other metallic substances in terms of impurity content.

[0082] Regardless of its type, the current collector used in the bipolar assembly 1100 may have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance adhesion to the active material layer. For example, it can be used in various forms such as films, sheets, foils, nets, porous bodies, foamed bodies, and non-woven fabrics.

[0083] The positive electrode active material layers 212, 212' may include a positive electrode active material, a binder, and further optionally a conductive material.

[0084] The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and various combinations are possible. Examples thereof include lithium-manganese based oxides (e.g., LiMnO2, LiMn2O4, etc.), lithium-cobalt based oxides (e.g., LiCoO2, etc.), lithium-nickel based oxides (e.g., LiNiO2, etc.), lithium-nickel-manganese based oxides (e.g., LiNi 1-Y Mn Y O2 (where 0<Y<1), LiMn 2-Z Ni Z O4 (where 0<Z<2), etc.), lithium-nickel-cobalt based oxides (e.g., LiNi 1-Y1 Co Y1 O2 (where 0<Y1<1), etc.), lithium-manganese-cobalt based oxides (e.g., LiCo 1-Y2 Mn Y2 O2 (where 0<Y2<1), LiMn 2-Z1 Co Z1O4 (where 0<Z1<2), etc.), lithium-nickel-manganese-cobalt-based oxides (for example, 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 Mn r1 )O4 (where 0<p1<2, 0<q1<2, 0<r1<2, p1+q1+r1=2), etc.), or lithium-nickel-cobalt-transition metal (M) oxides (for example, 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 each independent atomic fractions of the elements, and 0<p2<1, 0<q2<1, 0<r2<1, 0<s2<1, p2+q2+r2+s2=1), etc.), lithium iron phosphate oxides (for example, Li 1+a1 Fe 1-x1 M x1 (PO 4-b1 )X b1 (wherein M is one or more selected from the group consisting of Al, Mg and Ti, X is one or more selected from the group consisting of F, S and N, -0.5≦a1≦0.5, 0≦x1≦0.5, 0≦b1≦0.1), etc., and any one or two or more of these compounds may be included. Specifically, the positive electrode active material may include a lithium transition metal oxide represented by Chemical Formula 1 below. More specifically, 0.5≦x≦0.7 and 0≦b≦0.1 may be satisfied. Even more specifically, M may be Co and Mn, or may be Co, Mn, and Al.

[0085] [Chemical Formula 1] Li 1+a Ni x M 1-x O 2-b X b In the above chemical formula 1, M is one or more elements selected from the group consisting of Mn, Co, Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and X is one or more elements selected from F, S, and N, with 0 ≤ a ≤ 0.5, 0.3 ≤ x < 0.8, and 0 ≤ b ≤ 0.1.

[0086] Alternatively, more specifically, lithium iron phosphate may also be used.

[0087] The binder is a component that helps to bond the conductive material, the positive electrode active material, and the positive electrode current collector. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, polytetrafluoroethylene (PTFE), carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polyethylene, polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluororubber, and various copolymers thereof.

[0088] Typically, the binder may be present in an amount of 0.5 to 20% by weight, more specifically 0.5 to 10% by weight, or even more specifically 0.5 to 5% by weight, based on the total weight of the positive electrode active material layers 212, 212'.

[0089] The conductive material is a component for further improving the conductivity of the positive electrode active material, and such a conductive material is not particularly limited as long as it has conductivity without inducing a chemical change in the battery. For example, carbon powders such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powders such as natural graphite, artificial graphite, or graphite with a highly developed crystalline structure; conductive fibers such as carbon fibers and metal fibers; carbon nanotubes; fluorinated carbon powder; conductive powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives can be used.

[0090] The conductive material may be present in an amount of 0.01 to 20% by weight, more specifically 0.1 to 10% by weight, or more specifically 0.1 to 5% by weight, based on the total weight of the positive electrode active material layers 212 and 212'.

[0091] Furthermore, other additives may include, for example, fillers that suppress expansion. The filler is not particularly limited as long as it can suppress the expansion of the electrodes without inducing a chemical change in the battery, and for example, olefin polymers such as polyethylene and polypropylene; fibrous materials such as glass fibers and carbon fibers; etc. can be used.

[0092] The negative electrode active material layers 213 and 214' may include the negative electrode active material and the aforementioned binder, conductive material, and other additives.

[0093] The negative electrode active material is one or more carbon-based materials, Si-based materials, Si / C composites, or Li selected from the group consisting of graphite, amorphous hard carbon, low-crystalline soft carbon, carbon black, acetylene black, Ketjenblack, Super P, graphene, and fibrous carbon. 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, Group 2, Group 3 elements of the periodic table, halogen; 0<x≦1; 1≦y≦3; 1≦z≦8) and other metal composite oxides; lithium metal; metals such as Al, Cu, Ge, Si, and Sn; lithium alloys; silicon-based alloys; tin-based alloys; metal oxides such as SiO, SiO₂, SnO, SnO₂, PbO, PbO₂, Pb₂O₃, Pb₃O₄, Sb₂O₃, Sb₂O₄, Sb₂O₅, GeO, GeO₂, Bi₂O₃, Bi₂O₄, and Bi₂O₅; conductive polymers such as polyacetylene; Li-Co-Ni based materials; titanium oxides; lithium titanium oxides, etc., but the material is not limited to these as long as it is known in the art.

[0094] Such a positive electrode active material layer and a negative electrode active material layer may be produced by a wet or dry method. Specifically, both a wet method in which an electrode material including the active material, a binder, a conductive material, etc. is dispersed in a solvent and then coated, and a dry method in which an active material, a conductive material, etc. is dry-mixed with a fibrillated binder such as PTFE, and a freestanding film produced by calendering is applied, can be used.

[0095] There is no particular limitation on the separation membranes 214, 215' as long as they are normally used as separation membranes in lithium secondary batteries, and those having low resistance to ion migration of the electrolyte and excellent electrolyte wettability are particularly preferred.

[0096] For example, as the separation membranes 214, 215', a porous polymer film containing a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof can be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber or the like, may be used as the separation membrane.

[0097] Alternatively, it may be an SRS (Safety Reinforced Separator) separation membrane in which a coating layer containing a binder and inorganic particles is formed on one or both sides of the polymer substrate as described above.

[0098] The polyolefin substrate of the SRS separation membrane can be the separation membrane material described above, and the coating layer contains inorganic particles and a binder.

[0099] Here, the inorganic particles serve both the role of forming micropores by enabling the creation of empty spaces between them and the role of a kind of spacer that can maintain its physical form. Furthermore, since the inorganic particles generally have the property that their physical properties do not change even at high temperatures of 200°C or higher, the formed organic-inorganic mixed layer has excellent heat resistance.

[0100] The inorganic particles are not particularly limited as long as they are electrochemically stable. In other words, the inorganic particles that can be used in the present invention are not particularly limited as long as oxidation and / or reduction reactions do not occur within the operating voltage range of the battery to which they are applied. In particular, when using inorganic particles with ion transfer capability, it is preferable that the ionic conductivity is as high as possible, as this improves performance by increasing the ionic conductivity within the electrochemical element. Furthermore, if the inorganic particles have a high density, it is not only difficult to disperse them during manufacturing, but there is also the problem of increased weight during battery manufacturing, so it is preferable that the density is as low as possible. Moreover, in the case of inorganic materials with a high dielectric constant, it is possible to improve the ionic conductivity of the electrolyte by contributing to an increase in the degree of dissociation of electrolyte salts in the liquid electrolyte, such as lithium salts. Finally, in the case of inorganic particles with thermal conductivity, it is even more preferable because they have excellent heat endothermic capacity, which suppresses the phenomenon of heat concentrating locally to form heat-generating points and leading to thermal runaway.

[0101] For the reasons stated above, the inorganic particles are preferably one or more selected from the group consisting of (a) high dielectric constant inorganic particles having a dielectric constant of 1 or more, 5 or more, preferably 10 or more, (b) piezoelectric inorganic particles, (c) thermally conductive inorganic particles, and (d) inorganic particles having lithium ion transport capability.

[0102] The aforementioned piezoelectric inorganic particles are insulators at normal pressure, but when a certain pressure is applied, they possess the property of conducting electricity due to a change in their internal structure. They not only exhibit high dielectric constant characteristics with a dielectric constant of 100 or more, but when stretched or compressed under a certain pressure, they generate electric charge, causing one side to become positively charged and the opposite side negatively charged, thereby generating a potential difference between the two sides.

[0103] Examples of piezoelectric inorganic particles include BaTiO3, Pb(Zr,Ti)O3(PZT), and Pb 1-x La x Zr 1-y Ti y O3(PLZT), PB(Mg3Nb) 2 / 3 Examples include, but are not limited to, O3-PbTiO3(PMN-PT)hafnia(HfO2), or mixtures thereof.

[0104] The inorganic particles having lithium ion transport capability refer to inorganic particles that contain the element lithium but do not store lithium and have the function of transporting lithium ions. Since these inorganic particles having lithium ion transport capability can transport and move lithium ions due to a type of defect present inside the particle structure, a decrease in lithium mobility can be prevented, and thus a decrease in battery capacity can be prevented.

[0105] Examples of inorganic particles having lithium ion transport capability include lithium phosphate (Li3PO4) and lithium titanium phosphate (Li3PO4). x Ti y(PO4)3, 0<x<2, 0<y<3), lithium aluminum titanium phosphate (Li x Al y Ti z (PO4)3, 0<x<2, 0<y<1, 0<z<3), (LiAlTiP) x O y based glass (0<x<4, 0<y<13), lithium lanthanum titanate (Li x La y TiO3, 0<x<2, 0<y<3), Li 3.25 Ge 0.25 P 0.75 S4 and the like, lithium germanium thiophosphate (Li x Ge y P z S w , 0<x<4, 0<y<1, 0<z<1, 0<w<5), lithium nitride such as Li3N (Li x N y , 0<x<4, 0<y<2), SiS2-based glass such as Li3PO4-Li2S-SiS2 (Li x Si y S z , 0<x<3, 0<y<2, 0<z<4), P2S5-based glass such as LiI-Li2S-P2S5 (Li x P y S z , 0<x<3, 0<y<3, 0<z<7), or mixtures thereof, but are not limited thereto.

[0106] Further, examples of inorganic particles having a dielectric constant of 1 or more include SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, Al2O3, TiO2, SiC, or mixtures thereof, but are not limited thereto.

[0107] The aforementioned thermally conductive inorganic particles are materials that provide low thermal resistance but do not provide electrical conductivity and instead have insulating properties, and may be, but are not limited to, one or more selected from the group consisting of aluminum nitride (AlN), boron nitride (BN), alumina (Al2O3), silicon carbide (SiC), boehmite, AlO(OH), and beryllium oxide (BeO).

[0108] When the aforementioned high dielectric constant inorganic particles, piezoelectric inorganic particles, thermally conductive inorganic particles, and inorganic particles with lithium ion transfer capability are used in combination, their synergistic effects can be doubled.

[0109] While there are no restrictions on the size of the inorganic particles, it is preferable that they be in the range of 0.001 to 10 μm to ensure an appropriate porosity between the inorganic particles. If the size is less than 0.001 μm, the dispersibility decreases, making it difficult to adjust the physical properties. If the size exceeds 10 μm, the thickness increases, reducing the mechanical properties. Furthermore, excessively large pore sizes prevent the coating layer from functioning adequately, increasing the probability of internal short circuits occurring during battery charging and discharging.

[0110] There are no particular restrictions on the content of the inorganic particles, but it is preferably in the range of 1 to 99% by weight per 100% by weight of the mixture of inorganic particles and binder, and more preferably 10 to 95% by weight. If it is less than 1% by weight, the binder content will be excessively high, which may reduce the pore size and porosity due to the decrease in the empty spaces formed between the inorganic particles, and thus reduce the mobility of lithium ions. Conversely, if it exceeds 99% by weight, the binder content will be excessively low, which will reduce the mechanical properties of the coating layer due to the weakening of the adhesive strength between the inorganic materials.

[0111] On the other hand, the binder is not limited as long as it does not undergo a side reaction with the electrolyte, but in particular, one with the lowest possible glass transition temperature (Tg) can be used, preferably in the range of -200 to 200°C. This is because it can improve the mechanical properties of the final insulating film.

[0112] Furthermore, while the binder does not necessarily need to have ion-conducting ability, it is even more preferable to use a polymer that does have ion-conducting ability.

[0113] Therefore, the binder is preferably one with the highest possible dielectric constant. In fact, the degree of salt dissociation in the electrolyte depends on the dielectric constant of the electrolyte solvent, so the higher the dielectric constant of the polymer, the better the degree of salt dissociation in the electrolyte. The dielectric constant of the polymer can be 1 or higher, more specifically in the range of 1.0 to 100 (measurement frequency = 1 kHz), and is particularly preferably 10 or higher.

[0114] In addition to the functions described above, the binder may have the characteristic of gelling upon impregnation with a liquid electrolyte, thereby exhibiting a high electrolyte impregnation rate (degree of swelling). In fact, if the binder is a polymer with excellent electrolyte impregnation rate, the electrolyte injected after the battery assembly permeates the polymer, and the polymer holding the absorbed electrolyte has the ability to conduct ions for the electrolyte. Therefore, a solubility index of 15-45 MPa is desirable. 1 / 2 A polymer is preferred, and the pressure is 15-25 MPa. 1 / 2 and 30-45 MPa 1 / 2 A range of 15 MPa is even more preferable. 1 / 2 Less than and 45 MPa 1 / 2 If the amount exceeds the limit, it becomes difficult for the material to be impregnated (swelled) by the liquid electrolyte used in normal batteries.

[0115] Examples of such binders include polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-cotrichloroethylene, polymethyl methacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinylacetate, polyimide, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, and cellulose acetate propionate. It may be one or more selected from the group consisting of propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methyl cellulose, and polyvinyl alcohol.

[0116] The total thickness of the separation membranes 214 and 215' may be 5 micrometers to 20 micrometers, more specifically 5 micrometers to 15 micrometers, or even more specifically 6 micrometers to 13 micrometers.

[0117] In a unit cell for a bipolar battery, the separation membranes 214 and 215' can have an area ranging from 100% of the area of ​​the negative electrode active material layer to 100% of the total area of ​​the negative electrode, with the negative electrode as the reference point among the bipolar electrodes.

[0118] If the separation membrane exceeds the aforementioned range and is larger than the area of ​​the negative electrode, ion short circuits may occur due to the bipolar structure. Therefore, it is preferable that the separation membrane be smaller than the area of ​​the negative electrode, and the portion of the negative electrode current collector that cannot be covered can be insulated to prevent short circuits between electrodes by applying a separate inorganic coating such as Al2O3 or an insulating treatment with a polymer film such as PP or PET.

[0119] Referring again to Figures 2 to 4, the laminate 1100, which includes electrodes (representatively 121) and separation membranes (representatively 122), contains a cured gel electrolyte, and each unit cell can have an exposed structure without sealing members. Here, an exposed structure means that no sealing members or the like are formed, and there are no physical barriers between the laminates including the bipolar electrodes (representatively 121) and separation membranes (representatively 122).

[0120] Furthermore, since the bipolar assembly 1000 according to the present invention is impregnated with a gel electrolyte composition and cured after the laminate 1100 is manufactured, all the bipolar electrodes and all the separation membranes are bonded together in a laminated state, and the assembly can have a structure in which they are joined to each other.

[0121] On the other hand, the gel electrolyte comprises a lithium salt and a non-aqueous organic solvent, and at least one polymerizable compound selected from the group consisting of polymerizable monomers, oligomers, or copolymers having polymerizable unsaturated functional groups, wherein at least a portion of the polymerizable unsaturated functional groups may be cured.

[0122] In other words, the gel electrolyte may be obtained by curing a gel electrolyte composition containing a lithium salt, a non-aqueous organic solvent, and at least one polymerizable compound selected from the group consisting of a polymerizable monomer having a polymerizable unsaturated functional group, an oligomer, and a copolymer by heat or light.

[0123] The lithium salt can generally be used in the same or similar manner as those used in conventional lithium secondary batteries. The lithium salt is used as a medium for conducting ions in a lithium battery, and includes, for example, Li as a cation + , and as anions, F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , B 10 Cl 10 - , AlCl4 - , AlO2 - , PF6 - , CF3SO3 - , CH3CO2 - , CF3CO2 - , AsF6 - , SbF6 - , CH3SO3 - , (CF3CF2SO2)2N - , (CF3SO2)2N - , (FSO2)2N - , BF2C2O4 - , BC4O8 - , PF4C2O4 - , PF2C4O8 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , C4F9SO3 - , CF3CF2SO3 - , CF3CF2(CF3)2CO - , (CF3SO2)2CH -CF3(CF2)7SO3 - and SCN - At least one of the following groups can be selected.

[0124] Specifically, the lithium salts are LiCl, LiBr, LiI, LiBF4, LiClO4, and LiB 10 Cl 10 It may contain a single substance or a mixture of two or more substances selected from the group consisting of LiAlCl4, LiAlO2, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiFSI (Lithium bis(fluorosulfonyl)imide, LiN(SO2F)2), LiBETI (lithium bis(perfluoroethanesulfonyl)imide, LiN(SO2CF2CF3)2, and LiTFSI (lithium bis(trifluoromethanesulfonyl)imide, LiN(SO2CF3)2), but it is preferable to include Li(N(SO2CF3)2) in terms of superior stability.

[0125] The lithium salt can usually be appropriately modified within a usable range, but in order to obtain an optimal film formation effect for preventing corrosion of the electrode surface, it may be included in the electrolyte at a concentration of 0.5 M to 3 M, more specifically, 1 M to 2.5 M, and even more specifically, 1 M to 2 M. When the concentration of the lithium salt satisfies the above range, the effect of improving the cycle characteristics during high-temperature storage of the battery is sufficient, the viscosity of the electrolyte is appropriate, and the electrolyte impregnation can be improved.

[0126] The aforementioned non-aqueous organic solvent is not limited as long as it can minimize decomposition due to oxidation reactions during the subsequent charging and discharging process of the bipolar battery and, together with the additive, exhibit the desired properties.

[0127] For example, carbonate-based organic solvents, ether-based organic solvents, or ester-based organic solvents can be used individually or in combination of two or more types. More specifically, carbonate-based organic solvents can be used.

[0128] The carbonate-based organic solvent among the aforementioned organic solvents may include at least one of cyclic carbonate-based organic solvents and linear carbonate-based organic solvents. Specifically, the cyclic carbonate-based organic solvent may include at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate, and fluoroethylene carbonate (FEC). Specifically, it may include a mixed solvent of ethylene carbonate having a high dielectric constant and propylene carbonate having a relatively lower melting point compared to ethylene carbonate.

[0129] Furthermore, the linear carbonate-based organic solvent is a solvent having low viscosity and low dielectric constant, and may contain at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate, and ethyl propyl carbonate, and more specifically, it may contain dimethyl carbonate.

[0130] The ether-based organic solvent may be one selected from the group consisting of ethylene glycol dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, and ethyl propyl ether, or a mixture of two or more of these, but is not limited thereto.

[0131] The ester-based organic solvent mentioned above is at least one selected from the group consisting of linear ester-based organic solvents and cyclic ester-based organic solvents.

[0132] The linear ester-based organic solvent can typically be any one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate, or a mixture of two or more of these, but is not limited to these.

[0133] The cyclic ester organic solvent may, but is not limited to, one selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone, or a mixture of two or more of these.

[0134] Among the ester solvents mentioned above, cyclic carbonate compounds are preferred because they are high-viscosity organic solvents with high dielectric constants that effectively dissociate lithium salts in electrolytes. Furthermore, by mixing such cyclic carbonate compounds with low-viscosity, low-dielectric-constant linear carbonate compounds and linear ester compounds, such as dimethyl carbonate and diethyl carbonate, in appropriate ratios, it is possible to create an electrolyte with high electrical conductivity, and this method is even more preferable.

[0135] Furthermore, the electrolyte may further contain a functional additive, which may be included to prevent the breakdown of the negative electrode from being induced in high-power environments, and to further improve low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, and swelling improvement effects during high-temperature storage.

[0136] Specifically, the functional additive may include, as a representative example, one or more functional additives selected from the group consisting of sultone compounds, sulfite compounds, sulfone compounds, sulfate compounds, halogen-substituted carbonate compounds, nitrile compounds, cyclic carbonate compounds, phosphate compounds, borate compounds, and lithium salt compounds.

[0137] The sultone compound mentioned above includes at least one compound selected from the group consisting of 1,3-propanesultone (PS), 1,4-butanesultone, ethensultone, 1,3-propensultone (PRS), 1,4-butensultone, and 1-methyl-1,3-propensultone, and may be present in an amount of 0.3% to 5% by weight, specifically 1% to 5% by weight, based on the total weight of the gel electrolyte. If the content of the sultone compound in the gel electrolyte exceeds 5% by weight, an excessively thick film may be formed on the electrode surface, leading to increased resistance and output degradation. The resistance due to the excessive additive may also increase, potentially degrading the output characteristics.

[0138] The aforementioned sulfite-based compound may be one or more compounds selected from the group consisting of ethylene sulfite, methyl ethylene sulfite, ethyl ethylene sulfite, 4,5-dimethyl ethylene sulfite, 4,5-diethyl ethylene sulfite, propylene sulfite, 4,5-dimethylpropylene sulfite, 4,5-diethylpropylene sulfite, 4,6-dimethylpropylene sulfite, 4,6-diethylpropylene sulfite, and 1,3-butylene glycol sulfite, and may be present in an amount of 3% by weight or less based on the total weight of the gel electrolyte.

[0139] The sulfone compound may be one or more compounds selected from the group consisting of divinyl sulfone, dimethyl sulfone, diethyl sulfone, methyl ethyl sulfone, and methyl vinyl sulfone, and may be present in an amount of 3% by weight or less based on the total weight of the gel electrolyte.

[0140] The sulfate compound may be ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS), and may be present in an amount of 3% by weight or less based on the total weight of the gel electrolyte.

[0141] Furthermore, the halogen-substituted carbonate compound may be fluoroethylene carbonate (FEC), and may be present in an amount of 5% by weight or less based on the total weight of the gel electrolyte. If the content of the halogen-substituted carbonate compound in the gel electrolyte exceeds 5% by weight, the cell swelling performance may deteriorate.

[0142] Furthermore, the nitrile compounds include at least one compound selected from the group consisting of succinonitrile, adiponitrile (Adn), acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonile, cyclohexanecarbonile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

[0143] The cyclic carbonate compound may be vinylene carbonate (VC) or vinylethylene carbonate, and may be present in an amount of 3% by weight or less based on the total weight of the electrolyte. If the content of the cyclic carbonate compound in the gel electrolyte exceeds 3% by weight, the cell swelling suppression performance may deteriorate.

[0144] The phosphate compound may be one or more compounds selected from the group consisting of lithium difluoro(bisoxalato) phosphate, lithium difluorophosphate, tetramethyltrimethylsilyl phosphate, trimethylsilyl phosphate, tris(2,2,2-trifluoroethyl) phosphate, and tris(trifluoroethyl) phosphate, and may be present in an amount of 3% by weight or less based on the total weight of the gel electrolyte.

[0145] The borate compound mentioned above may include lithium oxalyl difluoroborate, and may be present in an amount of 3% by weight or less based on the total weight of the gel electrolyte.

[0146] The lithium salt compound is a compound different from the lithium salt contained in the lithium non-aqueous electrolyte, and includes one or more compounds selected from the group consisting of LiPO2F2, LiODFB, LiBOB (lithium bisoxalate borate (LiB(C2O4)2) and LiBF4), and may be present in an amount of 3% by weight or less based on the total weight of the gel electrolyte.

[0147] The functional additives may be a mixture of two or more types, and may be present in an amount of 20% by weight or less, specifically 0.1% to 10% by weight, based on the total weight of the gel electrolyte. If the content of the functional additives exceeds 20% by weight, excessive side reactions may occur in the electrolyte during battery charging and discharging. In particular, they may not decompose sufficiently at high temperatures and remain unreacted or precipitated in the electrolyte at room temperature. This may cause side reactions that reduce the battery's lifespan or resistance characteristics.

[0148] On the other hand, the bipolar assembly 1000 according to the present invention can drastically reduce electrolyte volatilization during the manufacturing process by the manufacturing method according to the present invention described below. Therefore, it may contain an electrolyte composition with a volatilization temperature (flash point) of less than 90°C as the non-aqueous organic solvent or functional additive, and there is a high degree of freedom in selecting the electrolyte.

[0149] More specifically, the bipolar assembly 1000 according to the present invention may contain 10% or more of the electrolyte composition having a flash point of less than 90°C, based on the total solvent volume of the electrolyte composition contained in the gel electrolyte, more specifically 20% to 100%, more specifically 30% to 70%, and most specifically 60% to 80%.

[0150] The content of such electrolyte compositions with a flash point of less than 90°C may be determined by solvent analysis of the overall gel electrolyte. More specifically, it can be obtained by dissolving the gel electrolyte in a specific solvent, such as acetone, and then performing an electrolyte composition analysis.

[0151] Such an electrolyte composition with a flash point of less than 90°C may be, for example, a linear ester-based solvent or a linear carbonate-based solvent.

[0152] More specifically, the electrolyte compositions having a flash point of less than 90°C include methyl formate, ethyl formate, 1,2-dimethoxyethane, methyl acetate, 1,3-dioxolane, ethyl acetate, methyl propionate, propyl acetate, methyl butyrate, tris(trimethylsilyl) phosphate, dimethyl carbonate, propyl propionate, ethyl methyl carbonate, diethyl carbonate, ethyl propionate, ethyl butyrate, butyronitrile, ethyl methyl sulfone, propyl butyrate, diethylene glycol dimethyl ether, vinylene carbonate, and It may be one or more selected from the group consisting of glycol sulfites, and among these, carbonate-based and propionate-based substances can be more appropriately used as non-aqueous organic solvents and functional additives as mentioned above. For example, one or more selected from the group consisting of dimethyl carbonate, propyl propionate, ethyl methyl carbonate, diethyl carbonate, ethyl propionate, and vinylene carbonate may be included in an amount of 10% by volume or more, more specifically 20% to 100% by volume, more specifically 30% to 70% by volume, and most specifically 60% to 80%.

[0153] Electrolyte compositions with a flash point below 90°C, while highly volatile, exhibit excellent high-temperature storage characteristics and positively influence rate characteristics and lifespan, making them highly suitable for use in batteries.

[0154] In existing manufacturing methods, such substances were difficult to use due to their high volatility. However, in the present invention, electrolyte volatilization can be drastically reduced, making it possible to use such electrolyte compositions.

[0155] Furthermore, the gel electrolyte must contain a polymerizable monomer, oligomer, or copolymer polymer for gelation, and the polymerizable compound is a substance having a polymerizable unsaturated functional group, for example, a polymerizable unsaturated functional group selected from the group consisting of vinyl groups, epoxy groups, allyl groups, and (meth)acrylic groups, and is a compound that can be transformed into a gel by polymerization or crosslinking, and is not particularly limited as long as it is used as a polymerizable monomer, oligomer, or polymer in the production of ordinary gel electrolytes.

[0156] More specifically, the polymerizable monomers or oligomers include, as non-limiting examples, tetraethylene glycol diacrylate, polyethylene glycol diacrylate (molecular weight 50-20,000), 1,4-butanediol diacrylate, 1,6-hexandiold diacrylate, trimethylolpropane triacrylate, trimethylolpropane ethoxylate triacrylate, trimethylolpropane propoxylate triacrylate, ditrimethylolpropane tetraacrylate, pentaerythritol tetraacrylate, and pentaerythritol ethoxylate tetraacrylate. ethoxylate tetraacrylate), dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate, polyethylene glycol diglycidyl ether, 1,5-hexadiene diepoxide, glycerol propoxylate triglycidyl ether, vinylcyclohexene dioxide, 1,2,7,8-diepoxyoctane (1,2,7,Examples include, but are not limited to, 8-diepoxyoctane, 4-vinylcyclohexenedioxide, butyl glycidyl ether, diglycidyl 1,2-cyclohexanedicarboxylate, ethylene glycol diglycidyl ether, glycerol triglycidyl ether, and glycidyl methacrylate. These compounds can be used individually or in combination of two or more.

[0157] Furthermore, typical examples of the copolymer include at least one copolymer selected from the group consisting of allyl 1,1,2,2-tetrafluoroethyl ether (TFE)-(2,2,2-trifluoroethyl acrylate) polymer, TFE-vinyl acetate, TFE-(2-vinyl-1,3-dioxolane) polymer, TFE-vinyl methacrylate polymer, TFE-acrylonitrile polymer, TFE-vinyl acrylate polymer, TFE-methyl acrylate polymer, TFE-methyl methacrylate (MMA) polymer, and TFE-2,2,2-trifluoroethyl acrylate (FA) polymer.

[0158] The polymer formed by the curing of the aforementioned substance may be present in an amount of 0.01% to 20% by weight, based on the total weight of the gel electrolyte. If the polymer content exceeds 20% by weight, the amount of polymerizable substance increases during the production of the gel electrolyte, which can lead to excessively rapid gelation or excessively dense formation, resulting in a gel with high resistance. Conversely, if the content is less than 0.01% by weight, the effects of gelation are not obtained, which is undesirable.

[0159] On the other hand, the gel electrolyte of the present invention may further contain a polymerization initiator for polymerization of the polymerizable unsaturated functional group, and conventional thermal or photoinitiators known in the art can be used. For example, the initiator can be decomposed by heat to form radicals, which can then react with polymerizable monomers, oligomers, or polymers by free radical polymerization to form the gel electrolyte.

[0160] More specifically, examples of polymerization initiators include benzoyl peroxide, acetyl peroxide, dilauryl peroxide, di-tert-butyl peroxide, t-butyl peroxy-2-ethyl-hexanoate, cumyl hydroperoxide, and hydrogen peroxide. Examples include, but are not limited to, organic peroxides and hydroperoxides such as peroxide, and one or more azo compounds selected from the group consisting of 2,2'-azobis(2-cyanobutane), 2,2'-azobis(methylbutyronitrile), 2,2'-azobis(isobutyronitrile) (AIBN; 2,2'-Azobis(iso-butyronitrile)) and 2,2'-azobisdimethyl-valeronitrile (AMVN; 2,2'-Azobisdimethyl-Valeronitrile).

[0161] The polymerization initiator can be decomposed within a bipolar unit cell by heat, for example, by heat between 30°C and 100°C, or by decomposition at room temperature (5°C to 30°C) to form radicals, and the polymerizable monomer, oligomer, or polymerizable unsaturated functional groups can react by free radical polymerization to form a gel electrolyte.

[0162] The polymerization initiator may be present in an amount of 0.01 to 20 parts by weight, more specifically 0.01 to 1 part by weight, based on 100 parts by weight of the polymerizable compound.

[0163] When the polymerization initiator is in the range of 0.01 to 20 parts by weight, the gel conversion rate can be increased to ensure gel electrolyte properties, pregel reaction can be prevented, and the wetting properties of the electrolyte to the electrode can also be improved.

[0164] bipolar battery Figure 5 schematically shows a cross-sectional view of the bipolar battery 2000, including the bipolar assembly 1000.

[0165] Referring to Figure 5, the bipolar battery 2000 has a structure in which the positive electrode terminal 2100 and the negative electrode terminal 2200 are attached to the outermost single-sided electrodes located on the bipolar assembly 1000, and are housed in the battery case 2300.

[0166] In this case, the positive terminal 2100 and the negative terminal 2200 may have a structure that extends outside the battery case 2300 so that they can be electrically drawn out to the outside, and charging and discharging may be performed by electrical connection from there.

[0167] Although the drawing shows a configuration in which the positive terminal 2100 and negative terminal 2200 are attached separately, the current collector of the outermost electrode may serve the same function as the terminals, or a separate metal plate may be attached to the outside of the current collector to cover an area of ​​50% to 110% of the current collector's surface area to serve that function.

[0168] The battery case 2300 may be a conventional pouch-type battery case or a metal battery case, or is not limited to such cases. More specifically, it may be a pouch-type battery case, and other examples include polymer plastic materials such as polyolefin, specifically polypropylene.

[0169] Manufacturing method for bipolar batteries According to another embodiment of the present invention, a method for manufacturing the bipolar battery, (a) Prepare a unit cell by stacking bipolar electrodes and a separation membrane. (b) Two or more of the unit cells are stacked together to manufacture a laminate such that a single-sided electrode is placed on the outermost side. (c) A method for manufacturing a bipolar assembly is provided, in which the laminate is placed in a storage member containing a gel electrolyte composition and impregnated, and the gel electrolyte composition is cured under pressure to form a gel electrolyte.

[0170] For ease of understanding, Figure 6 schematically shows the manufacturing method of the bipolar assembly 1000 according to the present invention.

[0171] First, in order to manufacture the bipolar assembly 1000, a unit cell is manufactured by stacking the bipolar electrode 201 and the separation membrane 202 (a).

[0172] Specifically, the bipolar electrodes 201 and the separation membrane 202 are cut to unit sizes before lamination, and these are bonded together to manufacture a unit cell.

[0173] In this case, the bipolar electrode 201 and the separation membrane 202 may be bonded together using an adhesive or by laminating them.

[0174] Although the drawing shows a structure in which one bipolar electrode 201 and one separation membrane 202 are stacked, the unit cell can of course be formed with a variety of structures as described above.

[0175] In other words, according to the manufacturing method of the present invention, a unit cell is manufactured without impregnating the bipolar electrode 201 and the separation membrane 202 with a separate gel electrolyte composition. Therefore, the volatilization problem of the gel electrolyte composition does not occur during the manufacturing process of the bipolar electrode 201 and the separation membrane 202, or during the manufacturing process of the unit cell.

[0176] Furthermore, the unit cells can have an exposed structure without the formation of separate isolation membranes or sealing members. This eliminates the need to form a sealing structure for each unit cell, allowing for simpler manufacturing methods and improving the efficiency of the assembly process.

[0177] Thereafter, two or more unit cells, each containing a bipolar electrode 201 and a separation membrane 202, are stacked to manufacture a laminate 210 such that single-sided electrodes 203 are positioned on both sides of the outermost layer (b).

[0178] At this time, each unit cell and single-sided electrode is aligned and stacked so that the positive and negative electrodes are arranged alternately. However, since no additional pressure is applied at this time, the unit cells are not completely joined together, and a predetermined space can be maintained between them.

[0179] Therefore, subsequent impregnation of the gel electrolyte composition can be easily carried out in each component of the unit cell.

[0180] Furthermore, since the laminate 210 has single-sided electrodes 203 positioned on both sides of its outermost edge, a current collector is located on the outermost edge. Since such a current collector is made of a material such as metal foil, it can act as a protective film to prevent the volatilization of the gel electrolyte composition impregnated in the bipolar electrodes 201 and the separation membrane 202.

[0181] Therefore, according to the manufacturing method of the present invention, since such a laminate 210 is manufactured before the gel electrolyte composition is impregnated, even if the gel electrolyte composition is subsequently impregnated into the bipolar electrode 201 and the separation membrane 202, the possibility of the gel electrolyte composition being exposed to the surface and volatilizing can be dramatically reduced.

[0182] On the other hand, after manufacturing the laminate 210 in this manner, it is placed in a storage member 220 containing the gel electrolyte composition 221 and impregnated (c).

[0183] In other words, according to the manufacturing method of the present invention, electrolyte impregnation is possible by simply placing the laminate 210 in a storage member 220 containing the gel electrolyte composition 221. Therefore, the manufacturing process can also be simplified. In this case, the storage member 220 may be an open-type electrolyte box with an open top, or a battery case that houses the laminate 210.

[0184] In other words, as shown in Figure 6, in one example, the laminate 210 is placed separately in an electrolyte box and impregnated, then the laminate 210 is removed, the gel electrolyte composition 221 remaining on the outside of the laminate 210 is removed, and a bipolar assembly 1000 impregnated with gel electrolyte is produced by curing this assembly, and a bipolar battery can be manufactured by housing this assembly in a battery case.

[0185] Alternatively, although not shown in Figure 6, the laminate 210 may be placed in the battery case from the beginning, the gel electrolyte composition may be poured in, and then the case may be sealed and cured in that state.

[0186] On the other hand, in either case, the impregnation of the gel electrolyte composition 221 may be carried out under vacuum to ensure that the gel electrolyte composition 221 is uniformly impregnated into the bipolar electrode 201 and the separation membrane 202.

[0187] Specifically, the gel electrolyte composition 221 can be impregnated by placing the laminate 210 in the storage member 220, or more specifically, with one side of the storage member 220 open, inside the vacuum chamber 230 and repeatedly applying and releasing the vacuum.

[0188] In this case, the application of vacuum may involve repeating the vacuum application and release process four or more times.

[0189] During this process, the vacuum can be maintained in the range of -100kPa to -90kPa for 3 to 10 minutes per session, or more specifically, in the range of -97kPa to -93kPa for 5 to 7 minutes per session.

[0190] The vacuum release can be maintained for 1 to 10 minutes per instance.

[0191] Such vacuum application and release may be performed four or more times, more specifically five to ten times, or more specifically seven to eight times, taking into account the impregnation and manufacturing time of the gel electrolyte composition.

[0192] Thereafter, the gel electrolyte composition can undergo a room temperature aging process to allow it to sufficiently impregnate each substance. For example, the laminate 210 can be stored at room temperature for approximately 24 hours to 5 days while housed in the storage member 220.

[0193] Once the gel electrolyte composition 221 is sufficiently impregnated into the laminate 210, the gel electrolyte composition 221 is cured under pressure to form a gel electrolyte (d).

[0194] In this case, as shown in Figure 6, the curing of the gel electrolyte composition 221 may be carried out while the laminate 210 is pressurized by an external jig 250.

[0195] Alternatively, although not shown in the drawings, if the storage member is a battery case, the process may be carried out with the storage member sealed and the laminate contained within the storage member under pressure from an external jig.

[0196] In either case, the bipolar electrode 241 and the separation membrane 242 are impregnated with the gel electrolyte composition 221 in the state of the laminate 210 and then cured. This dramatically reduces electrolyte volatilization, drastically reducing areas where the gel electrolyte is absent, i.e., the voids in the gel electrolyte. As the gel electrolyte composition 221 hardens, the electrode 241 and the separation membrane 242 become fully bonded, resulting in a structure that is firmly bonded overall. Therefore, it is possible to further improve battery performance while adjusting the thickness of the laminate 210 to the design thickness range.

[0197] Such curing may be performed in a vacuum, or by applying light or heat. Light irradiation has the advantage of curing in a short time, but it is difficult to uniformly apply light irradiation to the inside of the laminate 210 by the external jig 250, so more specifically, it can be performed by applying heat.

[0198] Specifically, the method of curing by applying heat may be carried out by placing the laminate 210, or the laminate 210 housed in a storage member, into a vacuum high-temperature chamber 260 while it is under pressure from an external jig 250, and then applying heat.

[0199] The application of heat may be carried out at a temperature of 50°C to 80°C for 2 to 10 hours, or more specifically, at a temperature of 60°C to 80°C for 4 to 8 hours, or even more specifically, at a temperature of 60°C to 70°C for 4 to 6 hours.

[0200] Furthermore, a vacuum can be created by connecting a vacuum pump that can create a vacuum inside the high-temperature chamber. When the curing process is carried out under vacuum conditions in this way, oxygen is absent, which can improve the curing properties and further enhance the battery performance of the bipolar batteries that are ultimately manufactured.

[0201] On the other hand, according to the method for manufacturing a bipolar battery of the present invention, the process may further include removing the pressure after the gel electrolyte composition 221 has been cured (e).

[0202] The aforementioned pressure is removed by separating the external jig 250. Once the pressure is removed in this way, a bipolar assembly 1000 in which the gel electrolyte is completely impregnated is produced.

[0203] Although not shown in the drawing, if the housing component is a battery case, a bipolar battery is immediately manufactured.

[0204] On the other hand, when manufacturing a bipolar assembly, an additional process can be performed to remove impurities from the outside, and bipolar batteries can be manufactured by additional processes such as packaging and electrode terminal attachment.

[0205] The following will be a description with reference to examples to demonstrate that the present invention exhibits the intended improvement effect.

[0206] <Comparative Example 1> A cathode slurry was prepared by dispersing LiFePO4 as the cathode active material, carbon nanotubes as the conductive material, and PVDF as the binder in an NMP solvent in a weight ratio of 96:1:3. This slurry was then coated onto one surface of an Al metal thin film to a thickness of 110 micrometers, dried, and rolled to produce a cathode.

[0207] Furthermore, LiPF6 was dissolved in a non-aqueous organic solvent having a composition of ethylene carbonate (EC):ethyl methyl carbonate (EMC) = 30:70 (volume ratio) to a concentration of 1.0 M. Trimethylolpropane triacrylate was added as a polymerizable compound at a concentration of 10% by weight relative to the total weight, and azobisisobutyronitrile (AIBN, V59) was added as a polymerization initiator at a concentration of 0.4 parts by weight relative to 100 parts by weight of the polymerizable compound to prepare a gel electrolyte composition.

[0208] The positive electrode was immersed in an electrolyte box containing the gel electrolyte composition, a vacuum was applied, and the box was stored for 3 days after impregnation. After removing the positive electrode, a transparent film was covered over the electrode surface to prevent the electrolyte on the surface from volatilizing, and then it was cured.

[0209] The aforementioned vacuum application method, which involves applying -95kPa for approximately 5 minutes followed by release, was repeated 8 times, and the samples were then stored at room temperature for 3 days.

[0210] The gel electrolyte composition was cured by UV light curing.

[0211] <Comparative Example 2> The positive electrode manufactured in Comparative Example 1 was used.

[0212] Furthermore, LiPF6 was dissolved in a non-aqueous organic solvent having a composition of ethylene carbonate (EC):gamabutyrolactone (GBL) = 30:70 (volume ratio) to a concentration of 1.0 M. Trimethylolpropane triacrylate was added as a polymerizable compound at a concentration of 10% by weight relative to the total weight, and azobisisobutyronitrile (AIBN, V59) was added as a polymerization initiator at a concentration of 0.4 parts by weight relative to 100 parts by weight of the polymerizable compound to prepare a gel electrolyte composition.

[0213] The positive electrode was immersed in an electrolyte box containing the gel electrolyte composition, a vacuum was applied, and the box was stored for 3 days after impregnation. After removing the positive electrode, a transparent film was covered over the electrode surface to prevent the electrolyte on the surface from volatilizing, and then it was cured.

[0214] The aforementioned vacuum application method, which involves applying -95kPa for approximately 5 minutes followed by release, was repeated 8 times, and the samples were then stored at room temperature for 3 days.

[0215] The gel electrolyte composition was cured by UV light curing.

[0216] <Examples> A negative electrode slurry was prepared by dispersing a mixture of graphite and SiO (weight ratio 95:5) as the negative electrode active material, carbon black as the conductive material, styrene-butadiene rubber (SBR) as the binder, and carboxymethylcellulose (CMC) as the filler in an aqueous solvent in a weight ratio of 96:1:2:1. This slurry was then coated onto one surface of a Cu metal thin film to a thickness of 80 micrometers, dried, and rolled to produce the negative electrode.

[0217] A unit cell was manufactured by interposing a CCS separation membrane (thickness: 13 micrometers), which had an organic-inorganic mixed layer (Al2O3:PVdF=95:5) formed on both sides of a polyolefin substrate, between the positive electrode and the negative electrode manufactured in the comparative example described above, as a separation membrane.

[0218] The unit cell was placed in an electrolyte box containing the gel electrolyte composition of the comparative example, and a vacuum of -95 kPa was applied for approximately 5 minutes, followed by the release of the vacuum. This process was repeated 8 times. After that, the unit cell was removed from the electrolyte box and stored at room temperature for 3 days.

[0219] Subsequently, the gel electrolyte composition was cured by applying heat at approximately 60°C for 5 hours.

[0220] <Experimental Example 1> To compare the degree of electrolyte volatilization between a case where the electrolyte is impregnated into the conventional electrode and separation membrane itself to manufacture a bipolar assembly, and a case where the electrolyte is impregnated after the manufacturing of the laminate according to the present invention, the following experiment was conducted.

[0221] Specifically, in order to measure the amount of electrolyte evaporation from the electrodes manufactured in Comparative Examples 1 and 2 and the unit cells manufactured in the Examples, the weight change over time was measured while the gel electrolyte compositions were left at room temperature before curing, and the amount of electrolyte evaporation was measured using the method described below. The results are shown in Table 1 and Figure 7 below.

[0222] *Total volatilization (%) = (Total weight of electrolyte before standing - Weight of electrolyte after standing) / Total weight of electrolyte after standing * 100 The weight of the electrolyte is the weight of the electrode or unit cell after impregnation minus the weight of the electrode or unit cell before impregnation.

[0223] In this example, since the electrode consisted of two electrodes, the total volatile amount was calculated by dividing it by two. [Table 1]

[0224] Referring to Table 1 and Figure 7 below, it can be seen that when manufactured using conventional methods, the electrodes are exposed to the surface, resulting in a very large amount of electrolyte evaporation over time. Furthermore, it can be seen that even when using an electrolyte solvent with a evaporation temperature of 90°C or higher, the volatility remains high. In contrast, when the manufacturing process of the present invention is followed, the amount of electrolyte evaporation is significantly reduced. Therefore, according to the present invention, the degree of freedom in selecting the electrolyte composition can be increased.

[0225] Furthermore, it can be predicted that the bipolar battery according to this invention will experience almost no volatilization of the gel electrolyte.

[0226] <Experimental Example 2> A negative electrode slurry was prepared by dispersing a mixture of graphite and SiO (weight ratio 95:5) as the negative electrode active material, carbon black as the conductive material, styrene-butadiene rubber (SBR) as the binder, and carboxymethylcellulose (CMC) as the filler in an aqueous solvent in a weight ratio of 96:1:2:1. This slurry was then coated onto one surface of a Cu metal thin film to a thickness of 70 micrometers, dried, and rolled to produce the negative electrode.

[0227] The negative electrode was immersed in an electrolyte box containing the gel electrolyte composition, and after impregnation, it was stored for 3 days under vacuum. The negative electrode was then removed, a transparent film was covered on the electrode surface to prevent the electrolyte on the surface from volatilizing, and then it was cured. The curing method was as described in the comparative example.

[0228] Furthermore, as a separation membrane, a CCS separation membrane (thickness: 13 micrometers) with an organic-inorganic mixed layer (Al2O3:PVdF=95:5) formed on both sides of a polyolefin substrate was immersed in an electrolyte box, a vacuum was applied for impregnation, and the box was stored for 3 days. After removing the separation membrane and covering it with a transparent film to prevent the surface electrolyte from volatilizing, it was cured. Using the positive electrode, negative electrode, and separation membrane, each impregnated with gel electrolyte, a 3-stack stack was constructed to produce the bipolar battery of Comparative Example 1. During the manufacturing process, the amount of electrolyte in Comparative Example 1 decreased from 1.91 cc to 1.66 cc, a decrease of approximately 13.1 volume%.

[0229] Furthermore, a bipolar battery of the example was manufactured using the unit cell of the example. The electrolyte volume of the example decreased from 2.07cc to 2.02cc, a decrease of approximately 1.75 volume%. Therefore, it can be seen that the voids of the gel electrolyte inside the laminate are 2% or less. This is almost similar to the method defined above, where the voids of the gel electrolyte are determined by the ratio of the volume obtained by subtracting the volume of impregnated electrolyte from the total void volume, with an error range of less than 1%.

[0230] The bipolar batteries of Comparative Example 1 and the bipolar batteries of the Example, which were manufactured as described above, underwent an initial (single) charge-discharge cycle using an electrochemical charger / discharger. During this cycle, charging was performed by applying current at a current density of 0.1 C-rate up to a voltage of 4.3 V, and discharging was performed at the same current density up to 2.5 V. A total of five such charge-discharge cycles were performed.

[0231] During this charging and discharging process, the voltage and capacity of the positive and negative electrodes in each battery were measured, and the results are shown in Figures 8 and 9 below. Furthermore, the discharge capacity of each battery is shown in Table 2 below. [Table 2]

[0232] Referring to Figures 8 and 9 below and Table 2 above, it can be seen that in the case of the bipolar battery of Comparative Example 1, numerous voids are generated by the gel electrolyte evaporated between the electrodes and the separation membrane, and deposition occurs severely due to electrolyte deficiency, resulting in a very large degree of irreversibility of the battery and a rapid decrease in capacity. In contrast, the bipolar battery of the example shows improved lifespan performance.

[0233] Anyone with ordinary skill in the art to which this invention belongs will be able to make various applications and modifications within the scope of this invention based on the above. [Industrial applicability]

[0234] In the bipolar battery according to the present invention, electrolyte volatilization is minimized during the impregnation and curing process of the gel electrolyte, so the gel electrolyte impregnation into the bipolar electrode and the separation membrane is performed uniformly, and since there is almost no void in the gel electrolyte within the laminate, the performance of the bipolar battery can be improved.

[0235] The bipolar battery of the present invention also has the effect of simplifying the structure without applying a separate sealing structure, even while using a gel electrolyte.

[0236] Taking it a step further, the method for manufacturing a bipolar battery according to the present invention does not involve injecting electrolyte into individual unit cells, but rather has a structure in which the laminate itself, which is made up of multiple stacked unit cells, is placed in a housing member and impregnated all at once. As a result, the volatilization of the gel electrolyte composition during the manufacturing process can be minimized, volatile gel electrolyte materials can be used, there is a high degree of freedom in selecting the type of electrolyte, and the electrolyte impregnation time can be saved.

Claims

1. A bipolar assembly comprising a laminate containing bipolar electrodes and a separation membrane, and a gel electrolyte impregnated throughout the laminate, and a battery case, A bipolar battery in which the voids of the gel electrolyte inside the laminate are 5% or less of the total volume that can be impregnated with the gel electrolyte.

2. The bipolar battery according to claim 1, wherein the bipolar electrode includes an integrated electrode in which a positive electrode active material layer and a negative electrode active material layer are coated on both sides of a single current collector, a positive electrode in which a positive electrode active material layer is formed on one surface of a positive electrode current collector, or a negative electrode in which a negative electrode active material layer is formed on one surface of a negative electrode current collector.

3. The bipolar battery according to claim 2, wherein the laminate is a structure in which one or more selected from the group consisting of a unit cell having a structure in which the positive electrode active material layer of the integrated electrode and the separation membrane face each other, a unit cell having a structure in which the positive electrode and the negative electrode are separately included and the separation membrane is interposed between the positive electrode and the negative electrode, a unit cell having a structure in which a single-sided electrode and a separation membrane are laminated, and a single-sided electrode are laminated.

4. The bipolar battery according to claim 1, wherein the laminate has single-sided electrodes of opposite polarities located on the outermost sides in the stacking direction.

5. The bipolar battery according to claim 1, wherein the laminate does not include a sealing member.

6. The bipolar battery according to claim 1, wherein the gel electrolyte comprises an electrolyte composition having a flash point of less than 90°C.

7. The bipolar battery according to claim 6, wherein the electrolyte composition having a flash point of less than 90°C is present in an amount of 10% or more of the total volume of the electrolyte composition contained in the gel electrolyte.

8. The bipolar battery according to claim 6, wherein the electrolyte composition having a flash point of less than 90°C is one or more selected from the group consisting of methyl formate, ethyl formate, 1,2-dimethoxyethane, methyl acetate, 1,3-dioxolane, ethyl acetate, methyl propionate, propyl acetate, methyl butyrate, tris(trimethylsilyl) phosphate, dimethyl carbonate, propyl propionate, ethyl methyl carbonate, diethyl carbonate, ethyl propionate, ethyl butyrate, butyronitrile, ethyl methyl sulfone, propyl butyrate, diethylene glycol dimethyl ether, vinylene carbonate, and glycol sulfite.

9. The bipolar battery according to claim 1, wherein all the bipolar electrodes and all the separator membranes contained in the laminate are bonded together in a laminated state by the gel electrolyte.

10. The bipolar battery according to claim 1, wherein the outermost electrodes on both sides of the bipolar assembly in the stacking direction are fitted with a positive electrode terminal and a negative electrode terminal, respectively.

11. A method for manufacturing a bipolar battery, (a) Prepare a unit cell by stacking bipolar electrodes and a separation membrane. (b) Two or more of the unit cells are stacked together to manufacture a laminate such that a single-sided electrode is placed on the outermost side. (c) A method for manufacturing a bipolar battery, comprising placing the laminate in a storage member containing a gel electrolyte composition and impregnating it, and curing the gel electrolyte composition under pressure to form a gel electrolyte.

12. The method for manufacturing a bipolar battery according to claim 11, wherein the unit cell is manufactured by cutting the bipolar electrode and the separation membrane to a unit size and then bonding them together.

13. The method for manufacturing a bipolar battery according to claim 11, wherein each of the unit cells does not include a sealing member.

14. The method for producing a bipolar battery according to claim 11, wherein the gel electrolyte composition contains 10% or more of an electrolyte composition having a flash point of less than 90°C, based on the total solvent volume.

15. The method for manufacturing a bipolar battery according to claim 11, wherein the storage member is an open-type electrolyte box with an open top, or a battery case for housing the laminate.

16. The method for manufacturing a bipolar battery according to claim 15, further comprising the step of storing the laminate in a battery case after the formation of the gel electrolyte, in the case where the storage member is the electrolyte box.

17. The method for manufacturing a bipolar battery according to claim 11, wherein the impregnation of the gel electrolyte composition is carried out under an applied vacuum.

18. The method for manufacturing a bipolar battery according to claim 17, wherein the application of the vacuum is repeated four or more times by applying and releasing the vacuum.

19. The method for manufacturing a bipolar battery according to claim 18, wherein the vacuum application is maintained in the range of -100 kPa to -90 kPa for 3 to 10 minutes at a time.

20. The method for manufacturing a bipolar assembly according to claim 11, wherein the curing is performed by applying heat in a vacuum state at a temperature in the range of 50°C to 80°C for 2 to 10 hours.

21. A method for manufacturing a bipolar battery according to claim 11, further comprising the step of releasing the pressurized state after the gel electrolyte composition has hardened.

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