Bipolar secondary battery and method for manufacturing same
Patent Information
- Application Number
- PCT/KR2026/003036
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2025-03-27
- Filing Date
- 2026-02-24
- Publication Date
- 2026-10-01
Smart Images
Figure KR2026003036_01102026_PF_FP_ABST
Abstract
Description
Bipolar secondary battery and method for manufacturing the same
[0001] Cross-citation with related application(s)
[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2025-0039572 dated March 27, 2025, and all contents disclosed in the document of said Korean patent application are incorporated herein as part of this specification.
[0003] The present invention relates to a bipolar secondary battery exhibiting excellent capacity characteristics and reduced resistance even under large areas, and a method for manufacturing the same.
[0004] Recently, as the application areas of lithium-ion batteries have expanded beyond power supply for electronic devices such as electrical, electronic, telecommunications, and computers to include power storage for large-area devices such as automobiles and power storage systems, there is a growing demand for secondary batteries that possess high capacity, high output, and high stability.
[0005] Conventional lithium-ion batteries generally adopt a structure in which multiple unit cells are connected in parallel. Each unit cell comprises a monopolar positive and negative electrode, each coated with an active material of the same polarity on a current collector, and a separator or electrolyte interposed between them. This conventional battery structure exhibits disadvantages such as increased resistance in the current path, reduced power density, high heat generation, and low safety.
[0006] Accordingly, interest in and research on bipolar secondary batteries have been increasing recently. The above-mentioned bipolar secondary battery may have a structure in which multiple bipolar electrodes, each coated with an active material of different polarities on both sides of a current collector, are stacked, and a separator and / or electrolyte is interposed between adjacent bipolar electrodes.
[0007] The above-described bipolar secondary battery has a structure in which unit cells, defined by a positive electrode and a negative electrode facing each other and a separator between them, are connected in series. Accordingly, the current path of the bipolar secondary battery is shortened, thereby reducing resistance and increasing power density, and the components and structures controlling each unit cell within a module or pack including the bipolar secondary battery can be simplified.
[0008] However, the above-mentioned bipolar secondary battery generally has a disadvantage in that the electrolyte is injected by methods such as liquid injection while a plurality of unit cells are stacked, and the electrolyte is prone to leaking between the unit cells or outside the bipolar secondary battery, thereby easily causing a short circuit.
[0009] To overcome these drawbacks, attempts are being made to apply a gel electrolyte instead of a liquid electrolyte to the above-mentioned bipolar secondary battery. To form such a gel electrolyte, it is necessary to inject or apply a composition for a gel electrolyte in a liquid state onto each bipolar electrode or separator and then cure it.
[0010] However, conventional electrolyte injection methods, such as the liquid injection method, have the disadvantage of making it difficult to uniformly form a gel electrolyte composition on multiple stacked bipolar electrodes or separators. In particular, this disadvantage becomes even more pronounced during the manufacturing process of large-area bipolar secondary batteries.
[0011] Moreover, in such bipolar secondary batteries, there is a disadvantage in that cell resistance increases and lifespan and rate characteristics deteriorate due to limitations such as the interface characteristics between the gel electrolyte and each electrode and / or porous separator. This disadvantage, such as increased resistance, is also a more significant problem in large-area bipolar secondary batteries applied to large devices.
[0012] Accordingly, the present invention provides a bipolar secondary battery that exhibits excellent capacity characteristics and reduced resistance even under large area conditions.
[0013] The present invention also provides a method for manufacturing a bipolar secondary battery that enables the formation of a uniform gel electrolyte on a bipolar electrode and a porous separator even under a large area.
[0014] According to one embodiment of the invention, a plurality of bipolar electrodes are stacked such that a negative active material layer and a positive active material layer are formed on each side of a metal current collector, and the positive active material layer and the negative active material layer of adjacent bipolar electrodes face each other through a porous separator.
[0015] A bipolar secondary battery is provided in which a gel electrolyte is formed on the negative electrode active material layer and the porous separator, and the gel electrolyte comprises a continuous phase covering at least a portion of the boundary between the negative electrode active material layer and the porous separator.
[0016] In a bipolar secondary battery of this embodiment, the gel electrolyte may comprise a matrix comprising a cross-linked polymer of a polyfunctional organic compound and an electrolyte dispersed on the matrix comprising a lithium salt and a non-aqueous organic solvent.
[0017] In such a bipolar secondary battery, the gel electrolyte having the continuous phase may have a form chemically bonded by cross-linking, etc., at the boundary between the negative electrode active material layer and the porous separator. In a more specific example, the gel electrolyte of the continuous phase may include a single matrix integrated by cross-linking across the negative electrode active material layer and the porous separator.
[0018] Such a bipolar secondary battery can be a large-area bipolar secondary battery in which one side of the negative active material layer of the bipolar electrode is 200 cm or more, and can exhibit low cell resistance even under such a large area.
[0019] Meanwhile, according to another embodiment of the invention, a method for manufacturing a bipolar secondary battery of the above-mentioned embodiment is provided. This manufacturing method may include the steps of: forming a bipolar electrode in which a positive active material layer and a negative active material layer are respectively formed on both sides of a metal current collector; applying a gel electrolyte composition comprising a polyfunctional organic compound, a lithium salt, and a non-aqueous organic solvent onto the negative active material layer; and curing the gel electrolyte composition while a porous separator is laminated on the coated surface of the gel electrolyte composition.
[0020] In addition, in this manufacturing method, after the curing step for forming the gel electrolyte, a step of stacking the plurality of bipolar electrodes may be further included. In this stacking step, the plurality of bipolar electrodes may be stacked such that the porous separator stacked on the negative electrode active material layer contacts or faces the positive electrode active material layer of another bipolar electrode.
[0021] The inventors continued to research methods for forming a gel electrolyte more uniformly in a large-area bipolar secondary battery, and furthermore, methods for lowering the cell resistance of a large-area bipolar secondary battery. Through continuous experiments by the inventors, it was confirmed that in a bipolar secondary battery containing a gel electrolyte, the factor having the greatest influence on cell resistance is the interface characteristics between the negative electrode active material layer and the porous separator mediated by the gel electrolyte. In addition, it was confirmed that a uniform gel electrolyte can be formed on each active material layer by independently applying a composition for the gel electrolyte onto the positive electrode active material layer or the negative electrode active material layer, impregnating and curing it by applying pressure, and by stacking bipolar electrodes having such gel electrolytes formed thereon.
[0022] Accordingly, a bipolar secondary battery of one embodiment is formed by applying and impregnating a gel electrolyte onto a negative electrode active material layer and curing it while a porous separator is laminated, and the gel electrolyte is formed as a continuous phase substantially integrated across the boundary between the negative electrode active material layer and the separator.
[0023] These bipolar secondary batteries have significantly improved interface characteristics between the negative electrode active material layer, the gel electrolyte, and the separator, so they can exhibit low cell resistance, improved long-term lifespan characteristics, and rate characteristics even under large areas. In addition, according to the manufacturing method of coating, impregnation, and curing described above, a uniform gel electrolyte can be formed in a large-area bipolar secondary battery.
[0024] FIG. 1 is a schematic cross-sectional view of a bipolar secondary battery according to one embodiment of the invention.
[0025] FIG. 2a is a schematic diagram showing a method of curing (Comparative Examples 1 and 2) in which a porous separator is laminated and cured on the surface coated with a gel electrolyte composition on an anode active material layer, unlike the manufacturing method of another embodiment of the invention.
[0026] FIG. 2b is a schematic diagram illustrating a method of curing (Examples 1 to 3) in which a porous separator is laminated and cured on a surface coated with a gel electrolyte composition on a cathode active material layer, according to a manufacturing method of another embodiment of the invention.
[0027] FIG. 2c is a schematic diagram showing a method (Comparative Examples 3 and 4) in which, unlike the manufacturing method of another embodiment of the invention, a composition for a gel electrolyte is applied to a positive electrode active material layer, a negative electrode active material layer, and a porous separator, respectively, and cured independently.
[0028] FIG. 3 shows the results of a comparative evaluation of the capacities exhibited by conducting initial charge and discharge tests on the bipolar secondary batteries of Example 1, Comparative Examples 1 and 2.
[0029] Figure 4 shows the results of a comparative evaluation of resistance according to state of charge (SOC) for the bipolar secondary batteries of Example 1, Comparative Examples 1 and 2.
[0030] Hereinafter, terms and words used in this specification and claims shall not be interpreted as being limited to their ordinary or dictionary meanings, but shall be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.
[0031] Unless otherwise defined, all terms used in this specification (including technical and scientific terms) may be used in a meaning that is commonly understood by those skilled in the art to which the present invention pertains. Additionally, terms defined in commonly used dictionaries are not to be interpreted ideally or excessively unless explicitly and specifically defined otherwise.
[0032] The terms used herein are for describing the embodiments and are not intended to limit the invention. In this specification, the singular form includes the plural form unless specifically stated otherwise in the text. As used herein, "comprises" and / or "comprising" do not exclude the presence or addition of one or more other components in addition to the components mentioned.
[0033] In this specification, when a part is described as including a certain component, it means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.
[0034]
[0035] Hereinafter, embodiments of the invention are described in detail with reference to the attached drawings so that those skilled in the art can easily implement the invention. In this specification and drawings, the same reference numerals indicate the same components. FIG. 1 is a schematic cross-sectional view of a bipolar secondary battery according to one embodiment of the invention.
[0036] Referring to FIG. 1, a bipolar secondary battery according to one embodiment of the invention has a plurality of bipolar electrodes stacked such that a negative active material layer (20) and a positive active material layer (30) are formed on each side of a metal current collector (10), and the positive active material layer (30) and the negative active material layer (20) of the bipolar electrodes adjacent to each other may have a structure in which they face each other through a porous separator (70).
[0037] In a bipolar secondary battery of this embodiment, a positive active material layer (30) and a negative active material layer (20) facing each other with a porous separator (70) in between can be defined as a single unit cell (100) (the dotted line portion of FIG. 1). The bipolar secondary battery may have a structure in which these unit cells are stacked and connected in series.
[0038] In addition, the bipolar secondary battery of the above embodiment includes a gel electrolyte (not shown) as an electrolyte. This gel electrolyte is formed on at least the negative electrode active material layer (20) and the porous separator (70), and is formed to fill at least some or all of the pores present within them. In particular, in the bipolar secondary battery of the above embodiment, the gel electrolyte is formed across the boundary between the negative electrode active material layer (20) and the porous separator (70). More specifically, the gel electrolyte is formed in the form of a continuous phase that covers part or all of the boundary between the negative electrode active material layer (20) and the porous separator (70).
[0039] The term "formed as a continuous phase" may refer to the gel electrolyte formed on the negative electrode active material layer (20) and the porous separator (70), respectively, being integrated by chemical bonding, for example, cross-linking, to form a single gel electrolyte membrane comprising substantially a single matrix at the boundary between the negative electrode active material layer (20) and the porous separator (70). As described in the manufacturing method described later and illustrated in FIG. 2B, this continuous phase gel electrolyte can be formed by proceeding with a curing process of the composition while covering the coated surface of the gel electrolyte composition of the negative electrode active material layer (20) with the porous separator (70).
[0040] A continuous phase gel electrolyte formed across the boundary between the negative active material layer (20) and the porous separator (70) can improve the interfacial characteristics between the negative active material layer (20) and the porous separator (70), which determine the cell resistance of the bipolar secondary battery, and the gel electrolyte. Accordingly, a bipolar secondary battery containing the continuous phase gel electrolyte can exhibit low cell resistance, improved lifespan characteristics, and rate characteristics, even under a large area where, for example, one side of the negative active material layer (20) is 200 cm or more, or 200 cm to 500 cm.
[0041] Below, these bipolar secondary batteries are explained in more detail by component.
[0042] In the bipolar secondary battery of the above embodiment, the bipolar electrode may include a metal current collector (10). For reference, due to the structural characteristics of the bipolar secondary battery in which unit cells (100) are connected in series, the metal current collector (10) needs to exhibit electrochemical stability over a wider voltage range. In the bipolar secondary battery of the above embodiment, considering these requirements and the good adhesion of the positive and negative active material layers (20, 30) to the metal current collector (10), a stainless steel metal current collector may be used as the metal current collector (10), or a stacked current collector of aluminum and copper may be used, for example, a stacked current collector comprising an aluminum layer and a copper layer, wherein the aluminum layer faces the positive active material layer (30) and the copper layer faces the negative active material layer (20).
[0043] A positive active material layer (30) is formed on one side of the metal current collector (10). This positive active material layer (30) may include a polymer binder, a conductive material, and a positive active material, and may be formed by applying and drying a slurry composition in which the polymer binder, conductive material, and positive active material are dispersed in an organic solvent on one side of the metal current collector (10). In another example of the invention, the positive active material layer (30) may be formed by dry mixing the polymer binder, conductive material, and positive active material, forming the polymer binder into a fibrous powder form under the application of shear force, and then undergoing calendering processing to form a film. However, since the wet or dry manufacturing method of the positive active material layer (30) and the resulting form of the positive active material layer (30) are obvious to those skilled in the art, further explanation regarding this is omitted.
[0044] Meanwhile, the positive active material included in the positive active material layer (30) can be any lithium transition metal oxide, lithium metal phosphate, metal oxide, etc., without any particular limitation. Specific examples of such positive active materials include layered compounds such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), or compounds substituted with one or more transition metals; chemical formula Li 1+x Mn 2-x Lithium manganese oxides such as O4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, LiMn2O3, LiMnO2, etc.; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiFe3O4, V2O5, Cu2V2O7, etc.; chemical formula LiNi 1-x M x Ni-site type lithium nickel oxide represented by O2 (where M = Co, Mn, Al, Cu, Fe, Mg, Ca, Zr, Ti, B, P, W, Si, Na, K, Mo, V, Nb, Ru, or Ga, and x = 0.01 ~ 0.3); chemical formula LiMn 2-x M x Lithium manganese complex oxides represented by O2 (where M = Co, Ni, Fe, Cr, Zn or Ta and x = 0.01 to 0.1) or Li2Mn3MO8 (where M = Fe, Co, Ni, Cu or Zn); LiMn2O4 in which part of the Li in the chemical formula is substituted with alkaline earth metal ions; lithium metal phosphate LiMPO4 (where M is M = Fe, CO, Ni, or Mn), disulfide compounds; Fe2(MoO4)3, etc., are examples, but are not limited to these.
[0045] Among these, considering the operating voltage, unit cost, and physical and electrochemical characteristics of the bipolar secondary battery, the lithium metal phosphate LiMPO4 (where M is M = Fe, CO, Ni, or Mn), more specifically lithium iron phosphate, can be preferably used as the positive electrode active material.
[0046] These positive active materials may be included in an amount of, for example, 80 to 99 weight% or 85 to 98 weight% with respect to the total weight of the positive active material layer (30).
[0047] Additionally, any polymer binder known to be usable in the electrode active material layer of a lithium secondary battery can be used as the polymer binder of the positive active material layer (30) without any particular limitations. Specific examples of such polymer binders include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polyethylene, polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluororubber, or various copolymers thereof.
[0048] Typically, the polymer binder may be included in an amount of 0.5 to 15 weight% or 0.7 to 10 weight% based on the total weight of the positive active material layer (30).
[0049] In addition, the conductive material included in the positive active material layer (30) is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, graphite such as natural graphite or artificial graphite; graphene; activated carbon; activated carbon fiber; carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, or thermal black; conductive fiber such as carbon fiber or metal fiber; metal powder such as fluorinated carbon, aluminum, or nickel powder; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxide such as titanium oxide; conductive material such as polyphenylene derivative, etc., may be used, but more specifically, in order to ensure uniform mixing of the conductive material and improve conductivity, it may include one or more selected from the group consisting of activated carbon, graphite, carbon black, graphene, and single-walled or multi-walled carbon nanotubes, and more specifically, it may include carbon black or activated carbon.
[0050] The conductive material may be included in an amount of 0.1 to 15 weight% or 0.5 to 10 weight% based on the total weight of the negative electrode active material layer (20).
[0051] In some cases, the positive active material layer (30) may further include a filler that suppresses the expansion of the electrode. The filler is not particularly limited as long as it is a fibrous material that does not cause chemical changes in the battery, and may be, for example, an olivine-based polymer such as polyethylene or polypropylene; or a fibrous material such as glass fiber or carbon fiber.
[0052] Additionally, if it is necessary to further improve the adhesion between the metal current collector (10) and the positive active material layer (30), a primer layer may be further formed between them. This primer layer may include, for example, a conductive material and a binder, and may further improve the adhesion of the positive active material layer (30) to the metal current collector (10).
[0053] Here, the conductive material may be a component equivalent to the conductive material included in the positive active material layer (30). Also, as the binder, for example, polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butylene rubber, or fluororubber may be used.
[0054] At this time, the content of the conductive material may be 5 to 50 weight%, or 5 to 30 weight%, or 10 to 30 weight% based on the total weight of the primer layer. If the content of the conductive material is too low, the resistance of the bipolar electrode may increase, and if it is too high, the adhesion between the positive active material layer (30) and the metal current collector (10) may decrease. In addition, the binder may be included as the remainder of the primer layer excluding the conductive material. The primer layer may be formed with a thickness of, for example, 0.1 to 10 μm.
[0055] Meanwhile, in the above-described bipolar secondary battery, a negative active material layer (20) is formed on the other side of the metal current collector (10). This negative active material layer (20) may include a polymer binder, a conductive material, and a negative active material, and may be formed by applying and drying a slurry composition in which the polymer binder, the conductive material, and the negative active material are dispersed in an organic solvent on one side of the metal current collector (10).
[0056] In this negative electrode active material layer (20), the negative electrode active material is a graphite-based active material such as non-graphitizable carbon, graphite-based carbon, etc.; Li x Fe2O3(0≤x≤1), Li x WO2(0≤x≤1), Sn x Me 1-x Me y O z(Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, Group 1, 2, and 3 elements of the periodic table, halogens; 0 <x≤1; 1≤y≤3; 1≤z≤8) 등의 금속 복합 산화물; 리튬 금속; 리튬 합금; 규소계 합금; 주석계 합금; SiO, SiO / C, SiO x (1 <x<2), SiO2등의 실리콘계 산화물; SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, 및 Bi2O5등의 금속 산화물; 폴리아세틸렌 등의 도전성 고분자; Li-Co-Ni 계 재료 등을 사용할 수 있다. 이 중에서도, 상기 금속 집전체(10)에 대한 음극 활물질층(20)의 양호한 형성, 상기 바이폴라 이차전지의 구동 전압 및 단가 등을 고려하여, 상기 음극 활물질로는 흑연계 활물질을 적절히 사용할 수 있다.
[0057] These negative electrode active materials may be included in an amount of, for example, 80 to 99 weight% or 85 to 98 weight% with respect to the total weight of the negative electrode active material layer (20).
[0058] Meanwhile, since the types and amounts of polymer binders, conductive materials, and additives that may be included in the above-mentioned negative electrode active material layer (20) are substantially the same as those described for the above-mentioned positive electrode active material layer (30), further explanation regarding this is omitted.
[0059] In addition, in the bipolar secondary battery of the above embodiment, a porous separator (70) is formed between the positive active material layer (30) and the negative active material layer (20) of the bipolar electrodes adjacent to each other.
[0060] This porous separator (70) may be a porous polymer film comprising a polyolefin-based polymer such as, for example, an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof.
[0061] Additionally, the porous separator (70) may be an uncoated separator comprising only a porous polymer film, but may also be a coated separator in which a coating layer comprising a binder and inorganic particles is formed on one or both sides of a substrate comprising the porous polymer film. An example of such a coated separator may be a Safety Reinforced Separator (SRS) separator, the composition of which is obvious to those skilled in the art.
[0062] Meanwhile, in the bipolar secondary battery of the above embodiment, the gel electrolyte is formed on the negative electrode active material layer (20) and the porous separator (70), and more specifically, is formed as a continuous phase covering at least a portion of the boundary between the negative electrode active material layer (20) and the porous separator (70).
[0063] Such gel electrolytes are formed in a form that includes, for example, a matrix comprising a cross-linked polymer of a polyfunctional organic compound and an electrolyte dispersed on the matrix, comprising a lithium salt and a non-aqueous organic solvent.
[0064] In a more specific example, the gel electrolyte is integrated by chemical bonding, e.g., cross-linking, and is formed in the form of a single membrane across the cathode active material layer (20) and the porous separator (70). This form can be defined as the gel electrolyte formed on the cathode active material layer (20) and the porous separator (70) being integrated by cross-linking so that the matrix has the form of a single membrane.
[0065] In this way, as the gel electrolyte is formed to have a continuous phase form and a single matrix across the boundary between the negative electrode active material layer (20) and the porous separator (70), the bipolar secondary battery of one embodiment can exhibit low cell resistance, improved lifespan characteristics, and rate characteristics even under a large area where, for example, one side of the negative electrode active material layer (20) is 200 cm or more, or 200 cm to 500 cm.
[0066] Meanwhile, the gel electrolyte may also be formed on the positive active material layer (30). The gel electrolyte on the positive active material layer (30) may be formed in a continuous phase form that covers at least a portion of the boundary with the porous separator (70), similar to the gel electrolyte on the negative active material layer (20); however, in other examples, the gel electrolyte on the positive active material layer (30) may be formed in mutually independent forms that do not cover the boundary with the porous separator (70). Due to these independent forms, the gel electrolyte on the positive active material layer (30) and the gel electrolyte on the porous separator (70) may not be chemically bonded to each other by cross-linking or the like, and may be formed as separate membranes separated from each other. This can be seen as being due to the fact that the interface characteristics between the positive active material layer (30) and the porous separator (70) have a relatively small influence on cell resistance, and in order to form a gel electrolyte on the positive active material layer (30) and the porous separator (70) in a continuous phase, the manufacturing process of the bipolar secondary battery becomes complex overall.
[0067] Accordingly, the gel electrolyte on the positive active material layer (30) can be formed by proceeding with curing after coating and impregnating the gel electrolyte composition, with the coated surface of the gel electrolyte composition exposed and not covered by the porous separator (70).
[0068] The gel electrolyte (70) described above can be manufactured by undergoing the processes of coating, impregnation, and curing on the negative active material layer (20) and / or the positive active material layer (30). As already described above, on the negative active material layer (20), the curing can proceed while the coating surface of the gel electrolyte composition is covered with the porous separator (70). In the process of forming the gel electrolyte, the gel electrolyte forming composition can be applied to the surface of the negative active material layer (20) or the positive active material layer (30), and then impregnated into the active material layer by a method such as rolling, and the gel electrolyte can be formed by curing and crosslinking the polyfunctional organic compound included in the composition.
[0069] The gel electrolyte (70) is formed on the surface of the positive active material layer (30), the porous separator (70), or the negative active material layer (20), while at least a portion of the gel electrolyte may be formed to overlap in the thickness direction of the positive active material layer (30), the porous separator (70), or the negative active material layer (20).
[0070] In a more specific example, the gel electrolyte may overlap the positive active material layer (30), the porous separator (70), or the negative active material layer (20) at a thickness corresponding to 60% or more, 80% or more, or 90 to 100% from the surface, based on the total thickness of the positive active material layer (30), the porous separator (70), or the negative active material layer (20). In this overlapping area, the gel electrolyte may fill some or all of the voids within the positive active material layer (30), the porous separator (70), or the negative active material layer (20).
[0071] Thus, the interfacial characteristics between each electrode, separator, and gel electrolyte within the unit cell can be further improved, and the conductivity of the bipolar secondary battery of one embodiment can be further improved and the resistance can be lowered.
[0072] Meanwhile, in the gel electrolyte, the matrix may comprise a cross-linked polymer in which a polyfunctional organic compound having two or more functional groups, or 2 to 6 functional groups capable of curing or cross-linking, such as (meth)acrylate groups, is cured. Such a matrix enables the stable formation of the gel electrolyte and enables the uniform and stable maintenance of the electrolyte impregnated in the matrix.
[0073] Examples of polyfunctional organic compounds that can be used to form such a matrix are not particularly limited, and in one example, polyfunctional (meth)acrylate-based compounds, etc., may be used. More specifically, specific examples of the polyfunctional organic compounds include one or more selected from the group consisting of trimethylolpropane ethoxylate triacrylate (ETPTA), trimethylolpropane ethoxy triacrylate, dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate, and tris(2-hydroxyethyl)isocyanurate triacrylate.
[0074] In the above gel electrolyte, the electrolyte is included in the matrix in a state where it is uniformly dispersed and impregnated, and the electrolyte includes a lithium salt.
[0075] The above lithium salt is used as a medium for transferring ions within a secondary battery. The above lithium salt is, for example, Li as a cation + It includes, and as anion, 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 - It may include selected from a group consisting of.
[0076] Specifically, the lithium salt is LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10It may be a single substance or a mixture of two or more 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), and LiPF6, LiFSI, or a mixture thereof may be appropriately used in terms of excellent stability, etc.
[0077] The above lithium salt can be appropriately modified within a range that is typically usable, and considering the output characteristics and stability of the secondary battery of one embodiment, it may be included in the electrolyte at a concentration of 0.5 M to 3 M, specifically at a concentration of 1 M to 2.5 M, and more specifically at a concentration of 1 M to 2 M. When the concentration of the lithium salt satisfies the above range, the effect of improving the cycle characteristics of the secondary battery is sufficient, and the viscosity of the electrolyte is appropriate, so the impregnation properties can be improved.
[0078] Meanwhile, the above electrolyte includes a non-aqueous organic solvent together with the lithium salt, and such non-aqueous organic solvent may include one or more selected from the group consisting of, for example, carbonate-based solvents, lactone-based solvents, ether-based solvents and sulfone-based solvents.
[0079] As the above carbonate-based solvent, for example, one or more selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate may be used, and as the above lactone-based solvent, for example, one or more selected from the group consisting of gamma-butyrolactone, acetolactone, beta-propiolactone, and delta-beletolactone may be used.
[0080] Meanwhile, the above-mentioned non-aqueous organic solvent may further include a sulfone-based solvent having a boiling point of 150°C or higher, 170 to 270°C, or 200 to 250°C, taking into account the solubility of the lithium salt and the non-volatility of the electrolyte. As such a sulfone-based solvent, one or more selected from the group consisting of dimethyl sulfone, ethylmethyl sulfone, and diethyl sulfone may be used. Such a sulfone-based solvent may be used in an amount that replaces the content of one or more of the above-mentioned carbonate-based solvent or lactone-based solvent, for example, 5% by weight or more, 10% by weight or more, or 15 to 30% by weight.
[0081] In addition, considering the ion conductivity of the secondary battery of one embodiment and the low volatility and appropriate viscosity of the electrolyte, the above-mentioned non-aqueous organic solvent may contain the above-mentioned carbonate-based solvent : above-mentioned lactone-based solvent in a weight ratio of 50 : 50 to 10 : 90, or 60 : 40 to 15 : 90, or 70 : 30 to 20 : 80.
[0082] Meanwhile, the above-mentioned non-aqueous organic solvent may further include 1 to 10 parts by weight, or 2 to 8 parts by weight, of an ether-based additive or solvent, for example, a difluoroalkyl ether-based compound, based on 100 parts by weight of the total of the carbonate-based solvent and the lactone-based solvent. In a more specific example, the difluoroalkyl ether compound may include one or more selected from the group consisting of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), bis(2,2,2-trifluoroethyl) ether (BTFE), 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (TFTFE), 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether (OTE), 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane (TFEE), and bis(2,2,2-trifluoroethoxy)ethane.
[0083] Meanwhile, the above-described electrolyte may further include one or more additives selected from the group consisting of vinylene carbonate, fluoroethylene carbonate, and ethylene sulfate, taking into consideration ion conductivity, safety, or stability, and such additives may be included in an amount of 1 to 5 parts by weight based on 100 parts by weight of the total non-aqueous organic solvent.
[0084] The above-described bipolar secondary battery can be a battery having a large area in which one side of the negative active material layer of the bipolar electrode is 200 cm or more, and can exhibit low cell resistance even under such a large area.
[0085] Meanwhile, in the bipolar secondary battery of the above-described embodiment, electrode terminals electrically connected to the respective current collectors (10a, 10b) on both sides in the stacking direction of the unit cells (100) may be directly connected or indirectly connected via a separate current collector plate. Additionally, the bipolar secondary battery may be housed in a separate case, and the electrode terminals may be connected to the outside of the case.
[0086] Meanwhile, according to another embodiment of the invention, a method for manufacturing the above-described bipolar secondary battery is provided. This manufacturing method may include the steps of: forming a bipolar electrode in which a positive active material layer (30) and a negative active material layer (20) are respectively formed on both sides of a metal current collector (10); applying a gel electrolyte composition comprising a polyfunctional organic compound, a lithium salt, and a non-aqueous organic solvent onto the negative active material layer (20); and curing the gel electrolyte composition while a porous separator (70) is laminated onto the coated surface of the gel electrolyte composition.
[0087] In this manufacturing method, a gel electrolyte is formed on the positive active material layer (30) or the negative active material layer (20) through a method of coating, impregnating, and curing. In particular, when forming the gel electrolyte on the negative active material layer (20), as shown on the right side of FIG. 2B, the gel electrolyte composition is cured while a porous separator (70) is laminated on the coated surface of the gel electrolyte composition. At this time, considering ease of process, when coating, impregnating, and curing the gel electrolyte composition on the positive active material layer (30), the porous separator (70) is not laminated, and the curing is carried out with the coated surface of the gel electrolyte composition exposed.
[0088] Through the above coating, curing, and impregnation processes, it is possible to form a uniform gel electrolyte on the positive active material layer (30) or the negative active material layer (20), and in particular, a uniform gel electrolyte can be formed even under a large-area battery manufacturing process. In addition, in the manufacturing method of the other embodiment, by curing the composition for the gel electrolyte on the negative active material layer (20) while the porous separator (70) is stacked, a gel electrolyte formed continuously on the boundary between them can be obtained, and the cell resistance of the bipolar secondary battery can be further reduced.
[0089] In contrast, as shown in FIG. 2a, when the composition for the gel electrolyte is cured with the porous separator (70) laminated only on the positive active material layer (30), or as shown in FIG. 2c, when the composition for the gel electrolyte is cured independently on the positive active material layer (30), the negative active material layer (20), and the porous separator (70) to form a gel electrolyte, it was confirmed that the interfacial characteristics between the negative active material layer (20) and the porous separator (70) deteriorate, and the resistance of the large-area bipolar secondary battery increases.
[0090] Meanwhile, in the manufacturing method of the other embodiment above, a negative active material layer (20) and a positive active material layer (30) are first formed on each side of a metal current collector (10) to manufacture a bipolar electrode. At this time, the negative active material layer (20) and the positive active material layer (30) may be formed by a wet method of applying, drying, and rolling a slurry composition comprising a polymer binder, a conductive material, a negative active material or a positive active material, and an organic solvent. Since the process of forming these positive and negative active material layers (30, 20) can follow a general wet electrode process, further explanation regarding this is omitted.
[0091] In addition, in the other example above, the positive active material layer (30) may be formed into a free-standing film by a dry method of dry mixing, powder formation under shear force application, and calendering of a fiberizable polymer binder such as PTFE, a conductive material, and a positive active material. The dry manufacturing process of such a positive active material layer (30) may follow a general dry electrode film formation process known, for example, in U.S. Patent Publication No. 8815443 or U.S. Patent Publication No. 10153096.
[0092] As an example, the positive active material layer (30) can be manufactured by dry mixing positive active material particles, a fiberizable polymer binder, and conductive material particles, while applying a shear force to the dry mixture to fiberize the polymer binder and form a dry electrode powder, and then calendering the resulting product into a film shape.
[0093] Meanwhile, after forming the above bipolar electrode, a composition for forming a gel electrolyte, comprising a polyfunctional organic compound and an electrolyte, may be applied on the negative electrode active material layer (20) and / or the positive electrode active material layer (30). At this time, regarding the composition of the electrolyte, it is as described above for a secondary battery of one embodiment.
[0094] In addition, the polyfunctional organic compound may be included in the composition for forming the gel electrolyte in an amount of 3 to 20 parts by weight, 4 to 15 parts by weight, or 5 to 13 parts by weight per 100 parts by weight of the electrolyte. This enables the good formation of a matrix in which the electrolyte is uniformly dispersed and a gel electrolyte, and ensures excellent conductivity of the gel electrolyte.
[0095] After applying the gel electrolyte forming composition, a further step of uniformly pressing the surface of the negative electrode active material layer (20) or the positive electrode active material layer (30) to which the gel electrolyte forming composition is applied may be performed in order to impregnate it into the negative electrode active material layer (20) or the positive electrode active material layer (30). By doing so, the gel electrolyte forming composition can be uniformly permeated into the negative electrode or positive electrode active material layer (20, 30), thereby uniformly forming a gel electrolyte that overlaps at least a portion with the negative electrode or positive electrode active material layer (20, 30). In a more specific example, the step of impregnating the gel electrolyte forming composition may be performed by uniformly rolling the surface of the negative electrode or positive electrode active material layer (20, 30) to which the gel electrolyte forming composition is applied.
[0096] Meanwhile, after the impregnation step, a porous separator (70) is laminated on the coating surface of the negative electrode active material layer (20), and heat or ultraviolet rays are irradiated onto the composition for forming a gel electrolyte coated on the negative electrode active material layer (20) and the positive electrode active material layer (30) to heat-cur or photo-cur the polyfunctional organic compound. By doing so, a gel electrolyte comprising a matrix containing a cross-linked polymer of the polyfunctional organic compound and an electrolyte dispersed on such a matrix can be formed well, and the gel electrolyte can be formed in a continuous phase at the boundary between the negative electrode active material layer (20) and the porous separator (70).
[0097] At this time, the conditions for proceeding with the curing step are not particularly limited, and may be carried out under appropriate curing conditions considering the type and content of the polyfunctional organic compound. In a specific example, the curing step may be carried out by irradiating ultraviolet light for 3 seconds to 5 minutes or 5 seconds to 1 minute or applying heat in the presence of a gas-impermeable film that does not allow oxygen gas or the like, which inhibits radical photocuring reactions, to pass through.
[0098] Meanwhile, after forming a bipolar electrode containing a gel electrolyte through the curing process described above, the bipolar electrodes can be stacked in multiple layers so that the positive active material layer (30) and the negative active material layer (20) of adjacent bipolar electrodes face each other through a porous separator (70), thereby manufacturing a bipolar secondary battery of one embodiment. At this time, since the porous separator (70) is already bonded to the negative active material layer (20) by the gel electrolyte, in the stacking step, the multiple bipolar electrodes can be stacked so that the porous separator (70) stacked on the negative active material layer (20) comes into contact with the positive active material layer (30) of another bipolar electrode.
[0099]
[0100] The embodiments described above will be explained in more detail below through specific examples.
[0101] Example 1: Preparation of a bipolar secondary battery
[0102] 496 g of LiFePO4 as the positive active material, 0.5 g of carbon black as the conductive material, and 3.5 g of polytetrafluoroethylene (PTFE) as the binder were added to a blender and mixed dry at 10,000 rpm for 1 minute to prepare a mixture. The temperature of the kneader was stabilized to 150°C, the mixture was placed into the kneader, and then operated at a speed of 50 rpm for 5 minutes under a pressure of 1.1 atm to obtain a lump of the mixture.
[0103] The obtained mixture aggregate was fed into a blender, ground at 10,000 rpm for 40 seconds, and classified using a sieve with 1 mm pores to obtain electrode powder. Subsequently, the prepared electrode powder was fed several times into a lab calender (roll diameter: 88 mm, roll temperature: 100℃) to achieve an electrode layer loading of 600 mg / 25 cm 2A positive active material layer was manufactured in the form of a freestanding film with a thickness of 100 μm. The positive active material layer was attached to and rolled on one side of a stainless steel foil (8 μm).
[0104] Meanwhile, 96g of graphite as a negative electrode active material, 1.0g of Super C-65 as a conductive material, and 3.0g of an SBR binder and a thickener were mixed in an organic solvent to prepare a slurry, and the slurry was coated on the other side of a stainless steel foil (8㎛), dried, and rolled to form a negative electrode active material layer.
[0105] Meanwhile, 3 parts by weight of vinylene carbonate and 0.5 parts by weight of ethyl sulfate were mixed with 100 parts by weight of a solvent in which ethylene carbonate (boiling point: approx. 238°C) and gamma-butyrolactone (boiling point: approx. 204°C) were mixed in a weight ratio of 2:8. An electrolyte was prepared by adding 1M LiPF6 to this non-aqueous organic solvent, and a composition for forming a gel electrolyte was prepared by mixing 5 parts by weight of trimethylolpropane ethoxylate triacrylate with 100 parts by weight of this electrolyte.
[0106] Next, 0.2 g of the gel electrolyte forming composition was dropped onto the negative electrode active material layer (20) and the positive electrode active material layer (30), and the coated surface was rolled to impregnate the gel electrolyte forming composition into each active material layer (20, 30). Subsequently, a polyethylene porous separator (70) was laminated onto the coated surface of the gel electrolyte composition on the negative electrode active material layer (20) (see FIG. 2b). 600 W / cm² for 5 seconds was applied to each of the coated surfaces of the gel electrolyte composition on the negative electrode active material layer (20) and the positive electrode active material layer (30). 2 A gel electrolyte was formed by irradiating with UV light at an intensity.
[0107] A bipolar secondary battery of Example 1 was manufactured by stacking multiple bipolar electrodes in which a gel electrolyte is formed in a continuous phase at the boundary between the negative active material layer (20) and the porous separator (70).
[0108]
[0109] Comparative Example 1: Manufacture of a bipolar secondary battery
[0110] A positive active material layer and a negative active material layer were formed on both sides of a stainless steel foil (8 μm) in the same manner as in Example 1.
[0111] Next, a composition for forming a gel electrolyte was prepared using the same composition and method as in Example 1.
[0112] 0.2 g of the gel electrolyte forming composition was dropped onto the negative electrode active material layer (20) and the positive electrode active material layer (30), and the coated surface was rolled to impregnate the gel electrolyte forming composition into each active material layer (20, 30). Subsequently, a polyethylene porous separator (70) was laminated onto the coated surface of the gel electrolyte composition on the positive electrode active material layer (30) (see FIG. 2a). 600 W / cm² for 5 seconds was applied to the coated surfaces of the gel electrolyte composition on the negative electrode active material layer (20) and the positive electrode active material layer (30), respectively. 2 A gel electrolyte was formed by irradiating with UV light at an intensity.
[0113] A bipolar secondary battery of Comparative Example 1 was manufactured by stacking multiple bipolar electrodes in which a gel electrolyte is formed continuously at the boundary between the positive active material layer (30) and the porous separator (70).
[0114]
[0115] Comparative Example 2: Manufacture of a bipolar secondary battery
[0116] A positive active material layer and a negative active material layer were formed on both sides of a stainless steel foil (8 μm) in the same manner as in Example 1.
[0117] Next, a composition for forming a gel electrolyte was prepared with the same composition as in Example 1.
[0118] 0.2g of the gel electrolyte forming composition was dropped onto each of the negative electrode active material layer (20), the porous separator (70), and the positive electrode active material layer (30), and the coated surface was rolled to impregnate the gel electrolyte forming composition into each active material layer (20, 30) and the porous separator (70) (see FIG. 2c). 600W / cm² for 5 seconds was applied to each of the coated surfaces of the gel electrolyte composition on the negative electrode active material layer (20), the porous separator (70), and the positive electrode active material layer (30). 2 A gel electrolyte was formed by irradiating with UV light at an intensity.
[0119] After forming a gel electrolyte on each of the positive active material layer (30), negative active material layer (20), and porous separator (70), a plurality of bipolar electrodes and porous separator (70) were stacked to manufacture a bipolar secondary battery of Comparative Example 2.
[0120]
[0121] Experimental Example 1: Evaluation of Electrochemical Properties
[0122] Charge and discharge tests were conducted using the bipolar secondary batteries of the examples and comparative examples under conditions of applying a current of 0.1C and about 6mA.
[0123] Figure 3 shows the results of a comparative evaluation of the capacity expressed for the bipolar secondary batteries of Example 1, Comparative Example 1 and 2 based on the results of these initial charge and discharge tests, and Figure 4 shows the results of a comparative evaluation of the cell resistance according to the state of charge (SOC) during the charge and discharge tests for the bipolar secondary batteries of Example 1, Comparative Example 1 and 2.
[0124] Referring to FIG. 3, it is confirmed that the bipolar secondary battery of the example exhibits a capacity equivalent to that of the comparative example, while exhibiting a lower cell resistance compared to the comparative example, as shown in FIG. 4.
Claims
1. A plurality of bipolar electrodes are stacked, wherein a negative active material layer and a positive active material layer are formed respectively on both sides of a metal current collector, and The positive active material layer and the negative active material layer of adjacent bipolar electrodes face each other with a porous separator in between, and A bipolar secondary battery in which a gel electrolyte is formed on the negative electrode active material layer and the porous separator, and the gel electrolyte comprises a continuous phase covering at least a portion of the boundary between the negative electrode active material layer and the porous separator.
2. A bipolar secondary battery according to claim 1, wherein the metal current collector is a current collector including stainless steel or a stacked current collector of aluminum and copper.
3. A bipolar secondary battery according to claim 1, wherein the negative electrode active material layer comprises a graphite-based negative electrode active material, and the positive electrode active material layer comprises a lithium transition metal phosphate-based positive electrode active material.
4. In claim 1, the gel electrolyte comprises a matrix including a cross-linked polymer of a polyfunctional organic compound, and A bipolar secondary battery comprising an electrolyte dispersed on the above matrix and comprising a lithium salt and a non-aqueous organic solvent.
5. A bipolar secondary battery according to claim 4, wherein the gel electrolyte formed on the negative electrode active material layer and the porous separator comprises a single matrix integrated by cross-linking.
6. A bipolar secondary battery according to claim 1, further comprising a gel electrolyte formed on the positive active material layer, wherein the gel electrolyte on the positive active material layer does not cover the boundary with the porous separator.
7. A bipolar secondary battery according to claim 6, wherein the gel electrolyte is formed to overlap with the positive active material layer, the negative active material layer, or the porous separator at a thickness of 60% or more of the total thickness of the positive active material layer, the negative active material layer, or the porous separator to fill their pores.
8. A bipolar secondary battery according to claim 4, wherein the polyfunctional organic compound comprises one or more polyfunctional (meth)acrylate compounds selected from the group consisting of trimethylolpropane ethoxylate triacrylate (ETPTA), trimethylolpropane ethoxy triacrylate, dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate, and tris(2-hydroxyethyl)isocyanurate triacrylate.
9. A bipolar secondary battery according to claim 4, wherein the lithium salt is contained in the electrolyte at a concentration of 0.5 to 3 M.
10. A bipolar secondary battery according to claim 4, wherein the non-aqueous organic solvent comprises one or more selected from the group consisting of carbonate-based solvents, lactone-based solvents, sulfone-based solvents, and fluorine-substituted ether-based solvents.
11. A bipolar secondary battery having a large area, wherein one side of the negative active material layer of the bipolar electrode is 200 cm or more, in accordance with claim 1.
12. A step of forming a bipolar electrode in which a positive active material layer and a negative active material layer are respectively formed on both sides of a metal current collector; A step of applying a gel electrolyte composition comprising a polyfunctional organic compound, a lithium salt, and a non-aqueous organic solvent onto the above-mentioned negative electrode active material layer; and A method for manufacturing a bipolar secondary battery of claim 1, comprising the step of curing the gel electrolyte composition while a porous separator is laminated on the coated surface of the gel electrolyte composition.
13. A method for manufacturing a bipolar secondary battery according to claim 12, further comprising the step of applying and curing the gel electrolyte composition on the positive electrode active material layer.
14. A method for manufacturing a bipolar secondary battery according to claim 13, wherein the step of applying and curing the gel electrolyte composition on the positive active material layer is performed with the applied surface of the gel electrolyte composition exposed.
15. A method for manufacturing a bipolar secondary battery according to claim 12 or 14, further comprising the step of impregnating the gel electrolyte composition into the negative electrode active material layer or the positive electrode active material layer by applying pressure to the coated surface of the gel electrolyte composition.
16. A method for manufacturing a bipolar secondary battery according to claim 15, wherein the impregnation step comprises the step of rolling the coated surface of the gel electrolyte forming composition.
17. A method for manufacturing a bipolar secondary battery according to claim 12, wherein in the curing step, the polyfunctional organic compound of the gel electrolyte composition is photocured or thermally cured.
18. A method for manufacturing a bipolar secondary battery according to claim 12, further comprising the step of stacking the plurality of bipolar electrodes after the curing step.
19. A method for manufacturing a bipolar secondary battery according to claim 18, wherein in the stacking step, a plurality of bipolar electrodes are stacked such that a porous separator stacked on the negative electrode active material layer contacts the positive electrode active material layer of another bipolar electrode.