Bipolar secondary battery and method for manufacturing same

Abstract

The present invention relates to: a bipolar secondary battery in which volatilization and leakage of an electrolyte are suppressed, and which exhibits excellent conductivity, capacity, and cycle characteristics; and a method for manufacturing same. In the bipolar secondary battery, a plurality of bipolar electrodes each having a negative electrode active material layer and a positive electrode active material layer respectively formed on both surfaces of a metal current collector are stacked, the positive electrode active material layers and the negative electrode active material layers of adjacent bipolar electrodes face each other with a gel electrolyte layer disposed therebetween, and the gel electrolyte layer contains: a matrix including a cross-linked polymer of a polyfunctional (meth)acrylate-based compound; and a non-volatile electrolyte of a predetermined composition impregnated on the matrix.

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. 10-2024-0184441 filed December 12, 2024 and Korean Patent Application No. 10-2025-0149885 filed October 16, 2025, and all contents disclosed in the documents of said Korean patent applications are incorporated herein as part of this specification.

[0003] The present invention relates to a bipolar secondary battery in which the volatilization and leakage of the electrolyte are suppressed and which exhibits excellent conductivity, capacity, and cycle characteristics, and a method for manufacturing the same.

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

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

[0006] Accordingly, interest in and research on bipolar secondary batteries have recently increased significantly. 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 or electrolyte layer is interposed between adjacent bipolar electrodes.

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

[0008] However, the above-mentioned bipolar secondary battery generally has a disadvantage in that the electrolyte is injected or impregnated between the unit cells or outside the bipolar secondary battery, making it prone to causing a short circuit. Accordingly, in conventional bipolar secondary batteries, there was a disadvantage in that complex sealing and packaging structures were inevitably introduced to suppress electrolyte leakage between the unit cells and outside the battery.

[0009] The introduction of such complex sealing and packaging structures not only complicated the processes and structures of bipolar secondary batteries, but also frequently failed to completely prevent electrolyte leakage despite the introduction of such sealing structures. This acted as one of the major technical drawbacks that made the actual application of bipolar secondary batteries difficult.

[0010] To overcome these disadvantages, attempts are being made to apply a unit cell in the form of an all-solid-state battery including a solid electrolyte layer to the above-mentioned bipolar secondary battery, or to apply a gel electrolyte layer instead of the above-mentioned liquid electrolyte.

[0011] However, the unit cell of the above-mentioned all-solid-state battery type has the disadvantage of being difficult to practically implement due to technical limitations such as poor interface characteristics between the electrode and the solid electrolyte layer and low ionic conductivity.

[0012] In addition, when applying a gel electrolyte layer to a bipolar secondary battery, there were disadvantages such as organic solvents contained in the gel electrolyte layer volatilizing during the manufacturing process and battery usage, or insufficient ion conductivity at the interface between the gel electrolyte layer and the electrode. Accordingly, in the case of bipolar secondary batteries using a conventional gel electrolyte layer, there were limitations in suppressing the volatilization and leakage of the liquid electrolyte contained in the polymer matrix, such as organic solvents, and it was difficult to maintain excellent electrochemical properties such as conductivity and capacity characteristics.

[0013] Accordingly, the present invention provides a bipolar secondary battery and a method for manufacturing the same, in which volatilization and leakage of the liquid electrolyte contained in the gel electrolyte layer are effectively suppressed and excellent conductivity, capacity, and cycle characteristics are exhibited.

[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 gel electrolyte layer.

[0015] The gel electrolyte layer comprises a matrix containing a cross-linked polymer of a polyfunctional (meth)acrylate-based compound and a non-volatile electrolyte impregnated on the matrix, and

[0016] A bipolar secondary battery is provided comprising the above-mentioned nonvolatile electrolyte, a lithium salt; and a non-aqueous organic solvent including a nonvolatile carbonate-based solvent having a boiling point of 150°C or higher and a nonvolatile lactone-based solvent having a boiling point of 150°C or higher.

[0017] In a bipolar secondary battery of such an embodiment, the gel electrolyte layer may be formed to contact the surface of the positive active material layer or the negative active material layer facing each other. In a specific example, at least a portion of the gel electrolyte layer may be uniformly impregnated and cured over the entire surface of the positive active material layer or the negative active material layer facing each other, so as to be formed to overlap over at least a portion of the thickness of the positive active material layer or the negative active material layer. In a more specific example, the gel electrolyte layer may overlap the positive active material layer and / or the negative active material layer at a thickness corresponding to 60% or more, 80% or more, or 90 to 100% of the total thickness of the positive active material layer or the negative active material layer.

[0018] In addition, according to another embodiment of the invention, the method comprises the steps of: manufacturing a bipolar electrode by forming a negative active material layer and a positive active material layer on each side of a metal current collector; applying a composition for forming a gel electrolyte, comprising a polyfunctional (meth)acrylate-based compound and a non-volatile electrolyte, onto the negative active material layer or the positive active material layer; curing the polyfunctional (meth)acrylate-based compound by irradiating the composition for forming the gel electrolyte with heat or ultraviolet light; and stacking the bipolar electrodes in a plurality such that the positive active material layer and the negative active material layer of adjacent bipolar electrodes face each other.

[0019] A method for manufacturing a bipolar secondary battery is provided, wherein the above-mentioned nonvolatile electrolyte comprises a lithium salt; and a non-aqueous organic solvent comprising a nonvolatile carbonate-based solvent having a boiling point of 150°C or higher and a nonvolatile lactone-based solvent having a boiling point of 150°C or higher.

[0020] In the manufacturing method of this other embodiment, between the application step and the curing step of the gel electrolyte forming composition, the step of impregnating the applied gel electrolyte forming composition into the negative electrode active material layer or the positive electrode active material layer may be further included. In a more specific example, this impregnation step may include a step of rolling the surface of the negative electrode active material layer or the positive electrode active material layer to which the gel electrolyte forming composition is applied.

[0021] The bipolar secondary battery according to the above embodiment applies a gel electrolyte layer formed between adjacent bipolar electrodes instead of a conventional liquid electrolyte, thereby effectively suppressing leakage of the electrolyte and enabling the application of a simplified sealing structure.

[0022] In addition, the bipolar secondary battery can suppress the volatilization of the liquid electrolyte by optimizing the composition of the liquid electrolyte included in the matrix of the gel electrolyte layer, and can further improve the conductivity of the gel electrolyte layer and the battery.

[0023] Furthermore, the gel electrolyte layer included in the secondary battery of the above embodiment can be formed by coating and curing on a bipolar electrode, and can be formed in a state of being uniformly impregnated and cured on the electrode due to excellent wettability. As a result, the interfacial characteristics between the electrode and the gel electrolyte layer can be improved, and the overall electrochemical characteristics of the bipolar secondary battery can be excellently expressed.

[0024] FIG. 1 is a schematic cross-sectional view of a bipolar secondary battery according to one embodiment of the invention.

[0025] FIG. 2 is a graph showing the relationship between the time until the negative active material layer is wetted and the porosity of the negative active material layer formed with the gel electrolyte layer of Examples 1 to 3.

[0026] Figures 3a and 3b show photographs of the surface of the negative active material layer after the gel electrolyte layer has been formed in Examples 1 and 2.

[0027] Figure 4a shows the relationship between capacity and voltage obtained as a result of conducting a charge and discharge test using the bipolar secondary battery of Comparative Example 1, and Figure 4b shows the relationship between capacity and voltage obtained as a result of conducting a charge and discharge test using the bipolar secondary battery of Example 2.

[0028] Figure 5 shows the results of evaluating the pattern of capacity change per cycle by conducting charge and discharge tests on the bipolar secondary batteries of Example 2 and Comparative Example 1.

[0029] Figure 6 shows the results of evaluating the capacity retention rate per cycle by conducting charge and discharge tests on the bipolar secondary batteries of Examples 1, 4 to 6.

[0030] Figure 7 shows the results of evaluating the capacity retention rate per cycle by conducting charge and discharge tests on the bipolar secondary batteries of Examples 1, 7 to 9.

[0031] FIG. 8 shows the results of evaluating the capacity retention rate per cycle by conducting charge and discharge tests on the bipolar secondary batteries of Examples 1, 10 to 13.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036]

[0037] Hereinafter, embodiments of the invention are described in detail with reference to the attached drawings so that those skilled in the art can easily practice the invention. In this specification and drawings, like reference numerals indicate like components.

[0038] 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 gel electrolyte layer (70).

[0039] 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 gel electrolyte layer (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.

[0040] In addition, in the bipolar secondary battery of the above embodiment, the gel electrolyte layer (70) comprises a matrix including a cross-linked polymer of a polyfunctional (meth)acrylate-based compound and a non-volatile electrolyte impregnated on the matrix, and the non-volatile electrolyte may comprise a lithium salt; and a non-aqueous organic solvent including a non-volatile carbonate-based solvent having a boiling point of 150°C or higher and a non-volatile lactone-based solvent having a boiling point of 150°C or higher.

[0041] The bipolar secondary battery of the above embodiment includes a gel electrolyte layer comprising a liquid electrolyte impregnated in a polymer matrix, thereby reducing the risk of liquid electrolyte leakage.

[0042] Additionally, the gel electrolyte layer (70) has a non-volatile electrolyte having a predetermined composition impregnated within a matrix of a cross-linked polymer in which a polyfunctional (meth)acrylate-based compound is cured. More specifically, the non-volatile electrolyte comprises a non-aqueous organic solvent including a non-volatile carbonate-based solvent having a boiling point of 150°C or higher, 170 to 270°C, or 200 to 250°C, and a non-volatile lactone-based solvent having a boiling point of 150°C or higher, 170 to 270°C, or 200 to 250°C, together with a lithium salt.

[0043] By using a nonvolatile electrolyte composed of the above-mentioned nonvolatile solvents, the volatilization of the electrolyte from the gel electrolyte layer (70) during the manufacture and use of the battery of one embodiment can be effectively suppressed. In addition, it has been confirmed that by combining the above-mentioned carbonate-based solvent and lactone-based solvent, the ion conductivity of the gel electrolyte layer (70) and the bipolar secondary battery containing it can be improved, and as a result, the electrochemical characteristics such as the capacity and cycle characteristics of the battery can be maintained and expressed excellently.

[0044] Furthermore, by dispersing the above-mentioned non-volatile electrolyte in a matrix containing the above-mentioned (meth)acrylate-based crosslinked polymer, the interface characteristics between the gel electrolyte layer (70) and the electrode can be maintained well, the ion conductivity of the battery of the above-mentioned embodiment can be further increased, and the resistance, etc. can be further lowered. In contrast, when the above-mentioned non-volatile electrolyte is dispersed or supported in another matrix, an inorganic material such as silica, or an inorganic solid electrolyte such as an oxide-based solid electrolyte, the interface characteristics between the electrolyte layer and the electrode are insufficient, so the ion conductivity may decrease or the resistance may increase.

[0045] Meanwhile, 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).

[0046] 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.

[0047] 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 LiMn2-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.

[0048] 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.

[0049] 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).

[0050] 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.

[0051] 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).

[0052] 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.

[0053] 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).

[0054] 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.

[0055] 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).

[0056] 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.

[0057] 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.

[0058] 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).

[0059] 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.

[0060] 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).

[0061] 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.

[0062] The above-described bipolar electrode, comprising a negative active material layer (20) and a positive active material layer (30) formed on each side of the metal current collector (10), is stacked in multiple layers. At this time, in order for unit cells (100), defined by a negative active material layer (20) and a positive active material layer (30) facing each other and a gel electrolyte layer (70) between them, to be connected in series, in the bipolar electrodes adjacent to each other, the negative active material layer (20) of one bipolar electrode and the positive active material layer (30) of another bipolar electrode face each other with the gel electrolyte layer (70) interposed.

[0063] As will be explained in more detail below, the gel electrolyte layer (70) can be manufactured by undergoing the processes of coating, impregnation, and curing on the negative active material layer (20) or positive active material layer (30) facing each other. Specifically, a composition for forming a gel electrolyte can be applied to the surface of the negative active material layer (20) or positive active material layer (30) facing each other, and the composition can be impregnated into the active material layer by a method such as rolling, and then the polyfunctional (meth)acrylate-based compound included in the composition can be cured and crosslinked to form the gel electrolyte layer (70).

[0064] As a result, the gel electrolyte layer (70) may be formed to contact the surface of the positive active material layer (30) or the negative active material layer (20) facing each other, and furthermore, at least a portion of the gel electrolyte layer (70) may be formed to overlap in the thickness direction of the positive active material layer (30) or the negative active material layer (20) facing each other.

[0065] In a more specific example, the gel electrolyte layer (70) may overlap the positive active material layer (30) 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) or the negative active material layer (20). In this overlapping area, the gel electrolyte layer (70) may fill some or all of the voids within the positive active material layer (30) or the negative active material layer (20).

[0066] Thus, the interface characteristics between the gel electrolyte layer (70) and the positive or negative active material layer (30, 20) 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.

[0067] Meanwhile, in the gel electrolyte layer (70), the matrix thereof may comprise a cross-linked polymer in which a polyfunctional (meth)acrylate-based compound having two or more functional (meth)acrylate groups, or two to six functional (meth)acrylate groups, is cured. Such a matrix enables the stable formation of the gel electrolyte layer (70) and enables the uniform and stable retention of the non-volatile electrolyte impregnated in the matrix.

[0068] Examples of polyfunctional (meth)acrylate compounds that can be used to form such a matrix are not particularly limited, and, for example, 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 may be included.

[0069] In the gel electrolyte layer (70) above, a non-volatile electrolyte is uniformly impregnated within the matrix, and the non-volatile electrolyte includes a lithium salt.

[0070] 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.

[0071] Specifically, the lithium salt is LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10 It 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 and lifespan characteristics.

[0072] In a more specific example, the lithium salt may contain LiPF6 alone or a mixed salt of LiPF6 and LiFSI (Lithium bis(fluorosulfonyl)imide), and when using such a mixed salt, the LiPF6:LiFSI may be included in a molar ratio of 9:1 to 7:3 or 9:1 to 8:2.

[0073] 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 non-volatile electrolyte at a concentration of 0.5 M to 3 M, specifically, 1 M to 2.5 M, and 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 of the secondary battery is sufficient, and the viscosity of the electrolyte is appropriate, so the impregnation of the non-volatile electrolyte can be improved.

[0074] Meanwhile, the above-mentioned non-volatile electrolyte comprises a non-aqueous organic solvent together with the lithium salt, and such non-aqueous organic solvent comprises a non-volatile carbonate-based solvent having a boiling point of 150°C or higher, 170 to 270°C, or 200 to 250°C, and a non-volatile lactone-based solvent having a boiling point of 150°C or higher, 170 to 270°C, or 200 to 250°C.

[0075] By using the combination of the above non-volatile solvents, the volatilization of the electrolyte from the gel electrolyte layer (70) during the manufacture and use of the battery of one embodiment can be effectively suppressed. In addition, by combining the carbonate-based solvent and the lactone-based solvent, the ion conductivity of the gel electrolyte layer (70) and the bipolar secondary battery containing it can be improved.

[0076] As the above non-volatile 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 non-volatile 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. Among these, as the above non-volatile carbonate-based solvent, for example, ethylene carbonate may be used alone or a mixed solvent of ethylene carbonate and propylene carbonate may be used, and when such a mixed solvent is used, propylene carbonate may be used in an amount of 35 to 45 weight% of the total non-volatile carbonate-based solvent. In addition, as the above non-volatile lactone-based solvent, for example, gamma-butyrolactone may be appropriately used, and the lifespan characteristics of the battery can be further improved by a combination of these solvents.

[0077] Meanwhile, the above-mentioned non-aqueous organic solvent may further include a non-volatile 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 non-volatile sulfone-based solvents, one or more selected from the group consisting of dimethyl sulfone, ethylmethyl sulfone, and diethyl sulfone may be used. Such non-volatile sulfone-based solvents may be used in an amount that replaces one or more of the above-mentioned non-volatile carbonate-based solvents or non-volatile lactone-based solvents, for example, 5% by weight or more, 10% by weight or more, or 15 to 30% by weight.

[0078] In addition, considering the ionic conductivity of the secondary battery of one embodiment and the low volatility and appropriate viscosity of the non-volatile electrolyte, the above-mentioned non-aqueous organic solvent may contain the above-mentioned non-volatile carbonate-based solvent : above-mentioned non-volatile 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.

[0079] 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 a difluoroalkyl ether compound based on 100 parts by weight of the total of the above-mentioned non-volatile carbonate-based solvent and the above-mentioned non-volatile 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.

[0080] The above difluoroalkyl ether-based compound can be included in the above nonvolatile electrolyte to lower its surface tension and contact angle, thereby improving the wettability of the above nonvolatile electrolyte. As a result, when such a difluoroalkyl ether-based compound is further used, the nonvolatile electrolyte and the composition for forming the gel electrolyte containing it can be impregnated more uniformly on the positive active material layer (30) or the negative active material layer (20) during the process of forming the gel electrolyte layer (70), which enables more uniform and easier formation of the gel electrolyte layer (70). Accordingly, a secondary battery of one embodiment including the above gel electrolyte layer (70) can exhibit excellent physical and electrochemical properties.

[0081] In a specific example, the non-volatile electrolyte further comprising the difluoroalkyl ether compound may exhibit a surface tension of 30 to 60 mN / m, or 35 to 55 mN / m, or 35 to 45 mN / m, and a contact angle of 30° to 60°, or 35° to 55°, or 35° to 52°, thereby exhibiting excellent wettability with respect to the positive active material layer (30) or the negative active material layer (20).

[0082] Meanwhile, the above-described non-volatile 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 10 parts by weight based on 100 parts by weight of the total of the non-volatile carbonate-based solvent and the non-volatile lactone-based solvent.

[0083] In a more specific example, vinylene carbonate and / or ethylene sulfate may be used as the additive. Specifically, the non-volatile electrolyte may include 1 to 5 parts by weight of vinylene carbonate and 0.1 to 2 parts by weight of ethylene sulfate as additives, based on 100 parts by weight of the total of the non-volatile carbonate-based solvent and the non-volatile lactone-based solvent.

[0084] Meanwhile, in the bipolar secondary battery of the above embodiment, a porous separator supporting the gel electrolyte layer (70) may be further included between the positive active material layer (30) and the negative active material layer (20) of the bipolar electrodes adjacent to each other.

[0085] Such porous separators may be porous polymer films comprising polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, for example, or laminated structures of two or more layers thereof.

[0086] In addition, the above-mentioned separator 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 thereof of which is obvious to those skilled in the art.

[0087] 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.

[0088] 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: manufacturing a bipolar electrode by forming a negative electrode active material layer (20) and a positive electrode active material layer (30) on each side of a metal current collector (10); applying a composition for forming a gel electrolyte, comprising a multifunctional (meth)acrylate-based compound and a non-volatile electrolyte, onto the negative electrode active material layer (20) or the positive electrode active material layer (30); curing the multifunctional (meth)acrylate-based compound by irradiating the composition for forming the gel electrolyte with heat or ultraviolet rays; and stacking the bipolar electrodes in a plurality such that the positive electrode active material layer (30) and the negative electrode active material layer (20) of adjacent bipolar electrodes face each other, and the composition of the non-volatile electrolyte is as described above.

[0089] In this manufacturing method, a bipolar electrode is first manufactured by forming a negative active material layer (20) and a positive active material layer (30) on each side of a metal current collector (10). 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.

[0090] 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.

[0091] 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.

[0092] Meanwhile, after forming the above bipolar electrode, a composition for forming a gel electrolyte comprising a polyfunctional (meth)acrylate-based compound and a non-volatile electrolyte may be applied on the negative electrode active material layer (20) or the positive electrode active material layer (30). At this time, regarding the composition of the non-volatile electrolyte, it is as described above for a secondary battery of one embodiment.

[0093] In addition, the polyfunctional (meth)acrylate-based 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 non-volatile electrolyte. By doing so, it is possible to form a good matrix and a gel electrolyte layer (70) in which the non-volatile electrolyte is uniformly impregnated, and to secure excellent conductivity of the gel electrolyte layer (70).

[0094] 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 layer (70) 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.

[0095] Meanwhile, after the impregnation step, heat or ultraviolet light may be irradiated onto the applied gel electrolyte forming composition to heat-cur or photo-cur the polyfunctional (meth)acrylate-based compound. By doing so, a gel electrolyte layer (70) comprising a matrix containing a cross-linked polymer of the polyfunctional (meth)acrylate-based compound and a non-volatile electrolyte impregnated on the matrix can be formed well.

[0096] 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 (meth)acrylate-based compound. However, 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 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.

[0097] Meanwhile, after forming a bipolar electrode including a gel electrolyte layer (70) through the curing process described above, the bipolar electrodes can be stacked in multiple layers such that the positive active material layer (30) and the negative active material layer (20) of adjacent bipolar electrodes face each other through the gel electrolyte layer (70), thereby manufacturing a bipolar secondary battery of one embodiment.

[0098]

[0099] The embodiments described above will be explained in more detail below through specific examples.

[0100] Example 1: Preparation of a bipolar secondary battery

[0101] 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.

[0102] The obtained mixture aggregate was fed into a blender, ground at 10,000 rpm for 40 seconds, and classified using a sieve with 1 mm pores to obtain electrode powder. Subsequently, the prepared electrode powder was fed several times into a lab calender (roll diameter: 88 mm, roll temperature: 100℃) to achieve an electrode layer loading of 600 mg / 25 cm 2 A 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).

[0103] 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.

[0104] 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. A non-volatile 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 non-volatile electrolyte.

[0105] At this time, the viscosity of the above non-volatile electrolyte at room temperature (25℃) was measured to be 5.12 cP, the surface tension was 46.6 mN / m, and the contact angle was approximately 55°.

[0106] Next, 0.2g of the gel electrolyte forming composition was dropped and applied onto the cathode active material layer, and the applied surface was rolled to impregnate the gel electrolyte forming composition into the cathode active material layer. Subsequently, 600W / cm² was applied to the applied surface for 5 seconds. 2 A gel electrolyte layer was formed by irradiating with UV light at an intensity.

[0107] A bipolar secondary battery of Example 1 was manufactured by stacking a plurality of bipolar electrodes, each having a gel electrolyte layer formed on the above negative electrode active material layer.

[0108]

[0109] Example 2: Preparation of a bipolar electrode

[0110] The above positive active material layer and negative active material layer were prepared in the same manner as in Example 1.

[0111] Meanwhile, 5 parts by weight of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), 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. A non-volatile 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 non-volatile electrolyte.

[0112] At this time, the viscosity of the non-volatile electrolyte at room temperature (25°C) was measured to be 5.32 cP, the surface tension to be 39.8 mN / m, and the contact angle to be approximately 49°. In addition, the viscosity of the gel electrolyte forming composition at room temperature (25°C) was measured to be 6.57 cP, the surface tension to be 39.6 mN / m, and the contact angle to be approximately 52°.

[0113] Next, the gel electrolyte layer of Example 2 and the bipolar secondary battery were prepared in the same manner as in Example 1, except that the above-mentioned composition for forming the gel electrolyte was used.

[0114]

[0115] Example 3: Preparation of a bipolar electrode

[0116] The above positive active material layer and negative active material layer were prepared in the same manner as in Example 1.

[0117] Meanwhile, 5 parts by weight of 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether (OTE), 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. A non-volatile 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 non-volatile electrolyte.

[0118] At this time, the viscosity of the non-volatile electrolyte at room temperature (25°C) was measured to be 5.32 cP, the surface tension to be 39.8 mN / m, and the contact angle to be approximately 49°. In addition, the viscosity of the gel electrolyte forming composition at room temperature (25°C) was measured to be 6.57 cP, the surface tension to be 39.6 mN / m, and the contact angle to be approximately 52°.

[0119] Next, the gel electrolyte layer of Example 3 and the bipolar secondary battery were prepared in the same manner as in Example 1, except that the above-mentioned composition for forming the gel electrolyte was used.

[0120]

[0121] Examples 4 to 6: Preparation of Bipolar Electrodes - Modification of Lithium Salt Composition in Electrolyte

[0122] The above positive active material layer and negative active material layer were prepared in the same manner as in Example 1.

[0123] 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: about 238°C) and gamma-butyrolactone (boiling point: about 204°C) were mixed in a weight ratio of 2:8. A non-volatile electrolyte was prepared by adding a mixed salt of 0.8 M LiPF6 and 0.2 M LiFSI (Lithium bis(fluorosulfonyl)imide) (Example 4), a mixed salt of 0.7 M LiPF6 and 0.3 M LiFSI (Example 5), or a mixed salt of 0.6 M LiPF6 and 0.4 M LiFSI (Example 6) to a non-aqueous organic solvent, respectively, 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 the non-volatile electrolyte.

[0124] Next, the gel electrolyte layers and bipolar secondary batteries of Examples 4 to 6 were each prepared in the same manner as in Example 1, except that the above-mentioned composition for forming the gel electrolyte was used.

[0125]

[0126] Examples 7 to 9: Preparation of Bipolar Electrodes - Change in Solvent Composition in Electrolyte

[0127] The above positive active material layer and negative active material layer were prepared in the same manner as in Example 1.

[0128] Meanwhile, 100 parts by weight of a solvent mixed in a weight ratio of 3:7 of ethylene carbonate (boiling point: approx. 238°C) and gamma-butyrolactone (boiling point: approx. 204°C) (Example 7), 100 parts by weight of a solvent mixed in a weight ratio of 3:5:2 of ethylene carbonate (boiling point: approx. 238°C), gamma-butyrolactone (boiling point: approx. 204°C), and propylene carbonate (boiling point: approx. 240°C) (Example 8), and 100 parts by weight of a solvent mixed in a weight ratio of 3:6:1 of ethylene carbonate (boiling point: approx. 238°C), gamma-butyrolactone (boiling point: approx. 204°C), and propylene carbonate (boiling point: approx. 240°C) (Example 8) were each prepared.

[0129] For 100 parts by weight of each of the above mixed solvents, 3 parts by weight of vinylene carbonate and 0.5 parts by weight of ethyl sulfate were mixed. A non-volatile 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 non-volatile electrolyte.

[0130] Next, the gel electrolyte layers and bipolar secondary batteries of Examples 7 to 9 were each prepared in the same manner as in Example 1, except that the above-mentioned composition for forming the gel electrolyte was used.

[0131]

[0132] Example 10: Preparation of a bipolar secondary battery

[0133] The above positive active material layer and negative active material layer were prepared in the same manner as in Example 1.

[0134] Meanwhile, 3 parts by weight of vinylene carbonate 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. A non-volatile 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 non-volatile electrolyte.

[0135] Next, the gel electrolyte layer of Example 10 and the bipolar secondary battery were each prepared in the same manner as in Example 1, except that the above-mentioned composition for forming the gel electrolyte was used.

[0136]

[0137] Example 11: Preparation of a bipolar secondary battery

[0138] The above positive active material layer and negative active material layer were prepared in the same manner as in Example 1.

[0139] Meanwhile, 5 parts by weight of vinylene carbonate 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. A non-volatile 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 non-volatile electrolyte.

[0140] Next, the gel electrolyte layer of Example 11 and the bipolar secondary battery were each prepared in the same manner as in Example 1, except that the above-mentioned composition for forming the gel electrolyte was used.

[0141]

[0142] Example 12: Preparation of a bipolar secondary battery

[0143] The above positive active material layer and negative active material layer were prepared in the same manner as in Example 1.

[0144] Meanwhile, 5 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. A non-volatile 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 non-volatile electrolyte.

[0145] Next, the gel electrolyte layer of Example 12 and the bipolar secondary battery were each prepared in the same manner as in Example 1, except that the above-mentioned composition for forming the gel electrolyte was used.

[0146]

[0147] Example 13: Preparation of a bipolar secondary battery

[0148] The above positive active material layer and negative active material layer were prepared in the same manner as in Example 1.

[0149] Meanwhile, 5 parts by weight of vinylene carbonate and 1 part 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. A non-volatile 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 non-volatile electrolyte.

[0150] Next, the gel electrolyte layer of Example 13 and the bipolar secondary battery were each prepared in the same manner as in Example 1, except that the above-mentioned composition for forming the gel electrolyte was used.

[0151]

[0152] Comparative Example 1: Preparation of a bipolar electrode

[0153] The above positive active material layer and negative active material layer were prepared in the same manner as in Example 1.

[0154] 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), dimethyl carbonate (boiling point: approx. 90°C), and ethyl methyl carbonate (boiling point: approx. 107°C) were mixed in a weight ratio of 3:5:2. 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.

[0155] At this time, the viscosity of the above non-volatile electrolyte at room temperature (25℃) was measured to be 2.96 cP, the surface tension was 32.5 mN / m, and the contact angle was approximately 31°.

[0156] Next, the gel electrolyte layer of Comparative Example 1 and the bipolar secondary battery were prepared in the same manner as in Example 1, except that the above-mentioned composition for forming the gel electrolyte was used.

[0157]

[0158] Experimental Example 1: Evaluation of wettability of gel electrolyte forming composition and porosity of cathode active material layer

[0159] In the process of forming the gel electrolyte layer of the example, the time until the gel electrolyte forming composition is wetted onto the negative electrode active material layer (or positive electrode composite film) was measured by the following method based on the time until the lower surface of the active material layer or composite film is completely wetted by the gel electrolyte composition.

[0160] For these measurements, an electrode active material layer (or composite film) was formed and attached on a transparent substrate in the same manner as in the above example. After taking an initial photograph or video of the bottom of the transparent substrate, 0.2 g of a gel electrolyte forming composition was applied dropwise onto the active material layer (or composite film) in the same manner as in Example 1, and the coated surface was rolled to impregnate it with the gel electrolyte forming composition. At this time, the time from the initial application point until it reached the bottom surface of the active material layer and the bottom surface became wet was measured in a photograph or video.

[0161] In addition, after forming the gel electrolyte layer, the porosity of the negative electrode active material layer formed with the gel electrolyte layer was measured and evaluated by the following method.

[0162] - Porosity:

[0163] In calculating the porosity of the electrode (anode or cathode) active material layer, first, the electrode density was calculated by dividing the loading amount of each electrode active material layer by its thickness. In addition, the porosity was calculated from the electrode density and the true density of the electrode active material according to the following Equation 1:

[0164] [Equation 1]

[0165] P = (1-D) / T×100

[0166] In Equation 1 above, P represents the porosity of the electrode active material layer, D represents the electrode density, and T represents the true density of the electrode active material excluding the current collector from the electrode. Here, true density refers to the intrinsic density of the electrode active material without pores.

[0167] For the gel electrolyte layers of Examples 1 to 3, a graph showing the relationship between the time until the negative active material layer is wetted and the porosity of the negative active material layer formed with the gel electrolyte layer is shown in FIG. 2. In addition, for Examples 1 and 2, photographs of the surface of the negative active material layer after the gel electrolyte layer is formed are shown for comparison in FIG. 3a and 3b.

[0168] Referring to FIG. 2 and FIG. 3a and 3b, it was confirmed that the gel electrolyte forming compositions of Examples 2 and 3, which additionally include TTE or OTE, not only have a short time until wetting of the negative electrode active material layer but are also uniformly coated on the negative electrode active material layer, thereby enabling the formation of a uniform gel electrolyte layer throughout the negative electrode active material layer. Furthermore, this can be clearly demonstrated by the fact that, despite the longer time until wetting in Example 1, the porosity of the negative electrode active material layer after gel electrolyte layer formation does not show a large variation in Examples 1 to 3.

[0169]

[0170] Experimental Example 2: Evaluation of Electrochemical Properties

[0171] Charge and discharge tests were conducted using the bipolar secondary batteries of Comparative Example 1 and Example 2 under conditions of applying a current of 0.1C and 6mA. At this time, charge and discharge tests were performed under the same conditions on four cells manufactured under the same conditions to reconfirm the uniformity of the test results. The relationship between capacity and voltage derived from these charge and discharge test results is illustrated in FIG. 4a (Comparative Example 1) and FIG. 4b (Example 2), respectively.

[0172] In addition, charge and discharge tests were conducted using the bipolar secondary batteries of Comparative Example 1 and Example 2 under conditions of applying a current of 0.33C and approximately 18mA. The pattern of capacity change per cycle according to these charge and discharge tests was evaluated and is shown in Fig. 5.

[0173] Referring to Figures 4a, 4b, and 5 above, it is confirmed that the bipolar secondary battery of Example 2 exhibits superior cycle characteristics and driving characteristics compared to Comparative Example 1. In the case of the secondary battery of Comparative Example 1, as shown in Figure 4a, abnormal driving occurred in at least one cell manufactured under the same conditions, and as shown in Figure 5, it exhibited poor cycle characteristics compared to Example 2.

[0174] Meanwhile, charge and discharge tests were conducted using the bipolar secondary batteries of Examples 1, 4 to 6 under conditions of a temperature of 45°C, 0.33°C, and a current of approximately 18 mA. The capacity retention rate per cycle according to these charge and discharge tests was evaluated and is shown in Fig. 6.

[0175] Referring to Fig. 6, Examples 1 and 4 to 6 generally exhibited excellent dose retention rates. Among these, the best dose retention rate was exhibited in Example 4, in which a mixed salt of 0.8 M LiPF6 and 0.2 M LiFSI was used.

[0176] In addition, charge and discharge tests were conducted using the bipolar secondary batteries of Examples 1, 7 to 9 under conditions of a temperature of 45°C, 0.33°C, and a current of approximately 18 mA. The capacity retention rate per cycle according to these charge and discharge tests was evaluated and is shown in Fig. 7.

[0177] Referring to FIG. 7, Examples 1 and 7 to 9 generally exhibited excellent dose retention rates. Among these, Examples 1, 7, and 8 exhibited even better dose retention rates.

[0178] Additionally, charge and discharge tests were conducted using the bipolar secondary batteries of Examples 1, 10 to 13 under conditions of a temperature of 45°C, 0.33°C, and a current of approximately 18 mA. The capacity retention rate per cycle according to these charge and discharge tests was evaluated and is shown in Fig. 8.

[0179] Referring to FIG. 8, Examples 1 and 10 to 13 showed generally excellent capacity retention rates despite some differences in the composition of the additives.

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 gel electrolyte layer interposed therebetween, and The gel electrolyte layer comprises a matrix containing a cross-linked polymer of a polyfunctional (meth)acrylate-based compound and a non-volatile electrolyte impregnated on the matrix, and The above-mentioned non-volatile electrolyte comprises a lithium salt; and a bipolar secondary battery comprising a non-aqueous organic solvent including a non-volatile carbonate-based solvent having a boiling point of 150°C or higher and a non-volatile lactone-based solvent having a boiling point of 150°C or higher.

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. A bipolar secondary battery according to claim 1, wherein the gel electrolyte layer is formed to contact the surface of the positive active material layer or the negative active material layer facing each other.

5. A bipolar secondary battery according to claim 1, wherein at least a portion of the gel electrolyte layer is formed to overlap the positive active material layer or the negative active material layer facing each other.

6. A bipolar secondary battery according to claim 5, wherein the gel electrolyte layer overlaps the positive active material layer or the negative active material layer at a thickness of 60% or more of the total thickness of the positive active material layer or the negative active material layer.

7. A bipolar secondary battery according to claim 1, wherein the polyfunctional (meth)acrylate compound comprises 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.

8. A bipolar secondary battery according to claim 1, wherein the lithium salt is contained in the non-volatile electrolyte at a concentration of 0.5 to 3 M.

9. A bipolar secondary battery according to claim 1, wherein the lithium salt comprises a mixed salt of LiPF6 and LiFSI (Lithium bis(fluorosulfonyl) imide).

10. A bipolar secondary battery according to claim 9, wherein the LiPF6:LiFSI is included in a molar ratio of 9:1 to 7:

3.

11. A bipolar secondary battery according to claim 1, wherein the non-volatile carbonate-based solvent comprises one or more selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate.

12. A bipolar secondary battery according to claim 1, wherein the non-volatile lactone-based solvent comprises one or more selected from the group consisting of gamma-butyrolactone, acetolactone, beta-propiolactone, and delta-beletolactone.

13. A bipolar secondary battery according to claim 1, wherein the non-volatile carbonate-based solvent and the non-volatile lactone-based solvent are included in a weight ratio of 50:50 to 10:

90.

14. A bipolar secondary battery according to claim 1, wherein the non-aqueous organic solvent further comprises a non-volatile sulfone-based solvent having a boiling point of 150°C or higher.

15. A bipolar secondary battery according to claim 14, wherein the non-volatile sulfone-based solvent comprises one or more selected from the group consisting of dimethyl sulfone, ethylmethyl sulfone, and diethyl sulfone.

16. A bipolar secondary battery according to claim 1, wherein the non-aqueous organic solvent further comprises 1 to 10 parts by weight of a difluoroalkyl ether compound based on 100 parts by weight of the total of the non-volatile carbonate-based solvent and the non-volatile lactone-based solvent.

17. In claim 16, the non-volatile electrolyte is a bipolar secondary battery having a surface tension of 30 to 60 mN / m and a contact angle of 30° to 60°.

18. A bipolar secondary battery according to claim 1, wherein the non-volatile electrolyte further comprises one or more additives selected from the group consisting of vinylene carbonate, fluoroethylene carbonate, and ethylene sulfate.

19. A bipolar secondary battery according to claim 18, wherein the non-volatile electrolyte comprises 1 to 5 parts by weight of vinylene carbonate and 0.1 to 2 parts by weight of ethylene sulfate, based on 100 parts by weight of the total of the non-volatile carbonate-based solvent and the non-volatile lactone-based solvent.

20. A bipolar secondary battery according to claim 1, wherein a porous separator supporting the gel electrolyte layer is further included between the positive active material layer and the negative active material layer of adjacent bipolar electrodes.

21. A step of manufacturing a bipolar electrode by forming a negative active material layer and a positive active material layer on each side of a metal current collector; A step of applying a gel electrolyte forming composition comprising a polyfunctional (meth)acrylate-based compound and a non-volatile electrolyte onto the above-mentioned negative electrode active material layer or the above-mentioned positive electrode active material layer; A step of curing the polyfunctional (meth)acrylate-based compound by irradiating the above gel electrolyte forming composition with heat or ultraviolet light; and The method includes the step of stacking a plurality of bipolar electrodes such that the positive active material layer and the negative active material layer of adjacent bipolar electrodes face each other. A method for manufacturing a bipolar secondary battery comprising: a lithium salt for the above-mentioned nonvolatile electrolyte; and a non-aqueous organic solvent including a nonvolatile carbonate-based solvent having a boiling point of 150°C or higher and a nonvolatile lactone-based solvent having a boiling point of 150°C or higher.

22. A method for manufacturing a bipolar secondary battery according to claim 21, wherein the polyfunctional (meth)acrylate-based compound is included in a composition for forming a gel electrolyte in an amount of 3 to 20 parts by weight per 100 parts by weight of the non-volatile electrolyte.

23. A method for manufacturing a bipolar secondary battery according to claim 21, further comprising, between the application step and the curing step of the gel electrolyte forming composition, the step of impregnating the applied gel electrolyte forming composition into the negative electrode active material layer or the positive electrode active material layer.

24. A method for manufacturing a bipolar secondary battery according to claim 23, wherein the impregnation step comprises the step of rolling the surface of the negative active material layer or the positive active material layer coated with the gel electrolyte forming composition.

25. A method for manufacturing a bipolar secondary battery according to claim 21, wherein the curing step is carried out by irradiating ultraviolet light for 3 seconds to 5 minutes in the presence of a gas impermeable film.

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