Bipolar secondary battery and manufacturing method therefor
Patent Information
- Application Number
- PCT/KR2026/001513
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2025-09-22
- Filing Date
- 2026-01-26
- Publication Date
- 2026-09-03
Smart Images
Figure KR2026001513_03092026_PF_FP_ABST
Abstract
Description
Bipolar secondary battery and method for manufacturing the same
[0001] Cross-citation with related application(s)
[0002] The present application claims the benefit of priority based on Korean Patent Application No. 10-2025-0025906 filed February 27, 2025 and Korean Patent Application No. 10-2025-0136349 filed September 22, 2025, and all contents disclosed in the documents of said Korean patent applications are incorporated herein as part of the specification.
[0003] The present invention relates to a bipolar secondary battery comprising a gel electrolyte that suppresses leakage of the electrolyte while exhibiting excellent lifespan characteristics and low resistance, 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, resistance increases in terms of the current flow path, power density decreases, and problems such as high heat generation and low safety can occur.
[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 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 for 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 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 drawbacks, 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 instead of a liquid electrolyte. However, the unit cell in the form of an all-solid-state battery 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.
[0011] In addition, bipolar secondary batteries with gel electrolytes also had the disadvantage that it was difficult to achieve excellent ionic conductivity and low resistance because the interface characteristics between the gel electrolyte and each electrode were insufficient, and as the electrolyte contained in the gel electrolyte volatilized or was consumed during the use of the battery, the electrochemical characteristics of the bipolar secondary battery deteriorated and the lifespan characteristics of the bipolar secondary battery were insufficient.
[0012] Accordingly, the present invention provides a bipolar secondary battery that includes a gel electrolyte and exhibits excellent lifespan characteristics, ion conductivity, and low resistance while suppressing electrolyte leakage, and a method for manufacturing the same.
[0013] 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 with a separator interposed therebetween, and a gel electrolyte is impregnated in one or more of the separator, the positive active material layer, and the negative active material layer.
[0014] A bipolar secondary battery is provided in which the above gel electrolyte is formed with a volume corresponding to 103% to 200% based on the total pore volume of the separator, positive active material layer, and negative active material layer in a state not impregnated with the above gel electrolyte.
[0015] In a bipolar secondary battery of this embodiment, the gel electrolyte may comprise a first gel electrolyte impregnated within one or more of the separator, the positive active material layer, and the negative active material layer, and a second gel electrolyte additionally formed between the separator and the positive active material layer or the negative active material layer facing each other. These first and second gel electrolytes may, for example, be formed with the same composition and may be formed continuously in a mutually bonded state.
[0016] In a more specific example, the total thickness of the second gel electrolyte additionally formed between the separator and the positive active material layer or the negative active material layer can be 0.1 to 20 μm.
[0017] In a more specific embodiment, the first gel electrolyte may be impregnated into the separator, the positive active material layer, and the negative active material layer.
[0018] In addition, the second gel electrolyte can be formed between the separator and the positive active material layer, and between the separator and the negative active material layer, respectively.
[0019] At this time, the second gel electrolyte may be additionally formed between the separator and the positive active material layer and / or between the separator and the negative active material layer, respectively, in a volume corresponding to 2% to 60% of the total pore volume of the separator, the positive active material layer, and the negative active material layer in a state not impregnated with the gel electrolyte.
[0020] In this way, the second gel electrolyte additionally formed between the separator and the positive active material layer and / or between the separator and the negative active material layer may each have a thickness of 0.05 to 20 μm.
[0021] Meanwhile, according to another embodiment of the invention, a method for manufacturing a bipolar secondary battery of the first embodiment is provided. The manufacturing method of this other embodiment comprises: a first 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 second step of applying and curing a composition for forming a gel electrolyte, comprising a curable polyfunctional compound and an electrolyte, on the negative active material layer or the positive active material layer; a third step of applying and curing the composition for forming a gel electrolyte on at least one surface of a separator; and a fourth step of stacking the bipolar electrodes in a plurality such that the positive active material layer and the negative active material layer of the bipolar electrodes adjacent to each other face each other through the interposed separator, wherein the composition for forming a gel electrolyte may be applied in a volume greater than the total pore volume of the separator, the positive active material layer, and the negative active material layer.
[0022] In the bipolar secondary battery according to the above embodiment, by applying a gel electrolyte formed on adjacent bipolar electrodes and a separator instead of a liquid electrolyte, leakage of the electrolyte can be effectively suppressed, and a simplified sealing structure can be applied.
[0023] In addition, the above-described bipolar secondary battery includes the gel electrolyte in a state where it is impregnated in the electrode active material layer and / or separator, while additionally including it in a certain excess volume between the electrode active material layer and the separator.
[0024] In this way, the excess gel electrolyte formed between the electrode active material layer and the separator forms a continuous state with the gel electrolyte impregnated in the electrode active material layer and / or the separator, thereby further improving the interfacial characteristics between each electrode and the gel electrolyte, improving the ion conductivity of the bipolar secondary battery, and reducing resistance.
[0025] In addition, the excess gel electrolyte can serve as a reservoir for excess electrolyte. Accordingly, even if the electrolyte contained in the gel electrolyte is consumed or volatilized during the use of the bipolar secondary battery, the excellent electrochemical characteristics of the bipolar secondary battery can be maintained for a long period, and its lifespan characteristics can be further improved.
[0026] FIG. 1 is a schematic cross-sectional view of a bipolar secondary battery according to one embodiment of the invention.
[0027] Figure 2 is a graph showing the resistance evaluation results for the bipolar secondary batteries of Examples 1 and 2 and Comparative Example 1.
[0028] Figure 3 is a graph showing the results of evaluating the capacity retention rate per cycle by conducting charge and discharge tests on the bipolar secondary batteries of Examples 1 and 2 and Comparative Example 1.
[0029] 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.
[0030] 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.
[0031] 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.
[0032] In this specification, when a part is described as including a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.
[0033]
[0034] 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.
[0035] 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, for example, a porous separator (70).
[0036] 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 separator (70) in between can be defined as a single unit cell (100). The bipolar secondary battery may have a structure in which these unit cells are stacked and connected in series.
[0037] In addition, in the bipolar secondary battery of the above embodiment, one or more of the porous separator (70), positive active material layer (30), or negative active material layer (20), or all of them, are contained in a state in which a hardened gel electrolyte is impregnated.
[0038] In a more specific example, the gel electrolyte may be included in a state of being impregnated and cured within the porous separator (70), the positive active material layer (30), and / or the negative active material layer (20) at a thickness corresponding to 60% or more, 70% or more, 80% or more, or 90% to 100% from the surface, based on the total thickness of the porous separator (70), the positive active material layer (30), and / or the negative active material layer (20).
[0039] Thus, the gel electrolyte can fill some or all of the pores present in the separator (70), the positive active material layer (30), and / or the negative active material layer (20), and more specifically, can fill 60% or more, 70% or more, 80% or more, or 90% to 100% of the pores with respect to the total volume of the pores.
[0040] Furthermore, in the bipolar secondary battery of the above embodiment, in addition to the first gel electrolyte (not shown) impregnated in the separator (70), the positive active material layer (30), and / or the negative active material layer (20), a second gel electrolyte (80) with excess volume or thickness is additionally formed between the separator (70) and the positive active material layer (30) and / or between the separator (70) and the negative active material layer (20) facing each other. This second gel electrolyte (80) with excess volume can be cured together with the first gel electrolyte impregnated in the separator (70), the positive active material layer (30), and / or the negative active material layer (20) to have a continuous state.
[0041] By the continuous formation of these first and second gel electrolytes, the interface characteristics between the first and second gel electrolytes and the positive and / or negative active material layers (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.
[0042] In order to form such a surplus second gel electrolyte (80), the volumes of the first and second gel electrolytes may be larger than the total pore volume of the separator, positive active material layer, and negative active material layer in the state without gel electrolyte impregnation. In a more specific example, the total volumes of the first and second gel electrolytes may be 103% to 200%, or 105% to 160%, or 107% to 150%, or 108% to 130% based on the total pore volume of the separator, positive active material layer, and negative active material layer in the state without gel electrolyte impregnation.
[0043] At this time, the ratio of the total volumes of the first and second gel electrolytes can be measured and calculated by the following method. First, the total pore volume of the separator, the positive active material layer, and the negative active material layer can be measured using the BET (Brunauer-Emmett-Teller) method. At this time, the gel electrolyte or other organic material contained within the pores of the separator, the positive active material layer, and the negative active material layer can be dissolved and removed by treating with an organic solvent capable of dissolving the gel electrolyte, for example, an organic solvent such as dimethyl carbonate, and then the total pore volume of these can be measured.
[0044] In addition, by using an analysis device equipped with an electron microscope, the ratio of the first gel electrolyte impregnated and embedded within the separator, the positive active material layer, and the negative active material layer can be calculated, and the volume of the first gel electrolyte can be measured and calculated therefrom. In addition, by using the analysis device, the thickness of the second gel electrolyte additionally formed between the separator, the positive active material layer, and / or the negative active material layer can be measured, and the volume of the second gel electrolyte can be measured and calculated therefrom.
[0045] From the total pore volume of the separator, positive active material layer, and negative active material layer measured and calculated as above, and the total volume of the first and second gel electrolytes, the ratio of the total volume of the first and second gel electrolytes can be calculated.
[0046] In a more specific example, the second gel electrolyte (80) additionally formed between the separator (70) and the positive and / or negative active material layer (30, 20) may have a thickness of, for example, 0.1 to 20 μm, or 0.5 to 18 μm, or 1 to 15 μm based on the total thickness sum on the positive and / or negative active material layer (30, 20).
[0047] The second gel electrolyte (80) additionally formed with the above volume or thickness can act as a reservoir for a type of excess electrolyte. Therefore, even if the electrolyte contained in the first gel electrolyte is consumed or volatilized due to continuous use of the bipolar secondary battery, the excellent electrochemical characteristics of the bipolar secondary battery can be maintained for a long period and its lifespan characteristics can be improved. However, if the volume or thickness of the second gel electrolyte (80) becomes excessively large, the manufacturing of the bipolar secondary battery itself may be difficult or its energy density may decrease.
[0048] In a more specific example, the second gel electrolyte (80) may be additionally formed between the separator (70) and the positive active material layer (30), and between the separator (70) and the negative active material layer (20), respectively. At this time, the second gel electrolyte (80) additionally formed between the separator (70) and the positive active material layer (30) and / or between the separator (70) and the negative active material layer (20) may have a uniform volume and thickness.
[0049] For example, each of these second gel electrolytes (80) may be formed with an excess volume corresponding to 2% to 60%, or 2.5% to 50%, or 3% to 30%, or 3.5% to 20%, based on the total pore volume of the separator (70), positive active material layer (30), and negative active material layer (20) in a state where the gel electrolyte is not impregnated. In addition, each of these second gel electrolytes (80) may have a thickness of 0.05 to 20 μm, or 0.1 to 15 μm, or 0.5 to 8 μm.
[0050] In this way, as an excess second gel electrolyte (80) is formed with a uniform volume or thickness between the separator (70) and the positive active material layer (30) and between the separator (70) and the negative active material layer (20), the battery of one embodiment can maintain improved conductivity and electrochemical properties for a long period of time.
[0051] Meanwhile, in the bipolar secondary battery of the above-described 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).
[0052] 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.
[0053] 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.
[0054] Among these, considering the operating voltage, unit cost, and physical and electrochemical characteristics of the bipolar secondary battery, the lithium transition 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.
[0055] 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).
[0056] 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.
[0057] 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).
[0058] 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.
[0059] 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 positive active material layer (30).
[0060] 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.
[0061] 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).
[0062] 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.
[0063] 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.
[0064] 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).
[0065] 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.
[0066] 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).
[0067] 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.
[0068] 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. As previously described, in order for unit cells (100) defined by a negative active material layer (20) and a positive active material layer (30) facing each other, a separator (70) between them, and a first and second gel electrolyte to be connected in series, 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 a porous separator (70) interposed therebetween. Furthermore, as previously described, a first gel electrolyte impregnated inside each of these active material layers and a second gel electrolyte (80) between them can be formed.
[0069] Meanwhile, the first and second gel electrolytes may have the same or identical composition. More specifically, the first and second gel electrolytes may comprise a matrix containing a crosslinked polymer and an electrolyte impregnated in the matrix. More specifically, the matrix may comprise a crosslinked polymer cured from a polyfunctional (meth)acrylate-based compound having two or more functional (meth)acrylate groups, or two to six functional (meth)acrylate groups. This matrix enables the stable formation of the first and second gel electrolytes and enables the uniform and stable retention of the electrolyte impregnated in the matrix.
[0070] 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.
[0071] In the first and second gel electrolytes above, the matrix contains an electrolyte that is uniformly impregnated, and the electrolyte contains a lithium salt.
[0072] 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.
[0073] 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, etc.
[0074] 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, 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 is appropriate, so the impregnation of the electrolyte can be improved.
[0075] Meanwhile, the above electrolyte includes a non-aqueous organic solvent together with the lithium salt, and the non-aqueous organic solvent includes 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.
[0076] By using the combination of the above non-volatile solvents, the volatilization of the electrolyte from the first and second gel electrolytes 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 ionic conductivity of the first and second gel electrolytes and the bipolar secondary battery containing them can be improved.
[0077] 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.
[0078] 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 the content of 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.
[0079] 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 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.
[0080] 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.
[0081] The above difluoroalkyl ether-based compound can be included in the electrolyte to lower its surface tension and contact angle, thereby improving the wettability of the electrolyte. As a result, when such a difluoroalkyl ether-based compound is further used, the electrolyte and the gel electrolyte forming composition containing it can be impregnated more uniformly onto the positive active material layer (30) or the negative active material layer (20) during the formation process of the first and second gel electrolytes, which enables more uniform and easier formation of the first and second gel electrolytes. Accordingly, a secondary battery of one embodiment containing the first and second gel electrolytes can exhibit excellent physical and electrochemical properties.
[0082] In a specific example, the 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).
[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 of the non-volatile carbonate-based solvent and the non-volatile lactone-based solvent.
[0084] In addition, in the bipolar secondary battery of the above embodiment, a porous separator (70) supporting the second gel electrolyte (80) is 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] 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.
[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 (10) may be directly or indirectly connected to the respective current collectors, either by means of a separate current collector plate, on the outermost current collectors (10) on both sides in the stacking direction of the unit cells (100). 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: a first 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 second step of applying and curing a composition for forming a gel electrolyte, comprising a curable polyfunctional compound and an electrolyte, on the negative active material layer or the positive active material layer; a third step of applying and curing the composition for forming a gel electrolyte on at least one surface of a separator; and a fourth step of stacking the bipolar electrodes in a plurality such that the positive active material layer and the negative active material layer of the bipolar electrodes adjacent to each other face each other through a separator.
[0089] In the manufacturing method of this other embodiment, for example, the composition for forming a gel electrolyte may be used in an excess amount or volume in the second or third step. For example, the composition for forming a gel electrolyte may be applied and cured in a volume greater than the total pore volume of the separator, the positive active material layer, and the negative active material layer. Thus, after the second or third step, an additional second gel electrolyte with an excess volume or thickness may be formed on at least one surface of the separator, or on the negative or positive active material layer.
[0090] According to a more specific example, in the third step of forming a gel electrolyte on one or both sides of the separator, an additional second gel electrolyte with the aforementioned excess volume or thickness may be formed on one or both sides of the separator by using the gel electrolyte forming composition in an excess amount or volume. In this case, in the second step, the gel electrolyte forming composition may be used to such an extent that the first gel electrolyte can be fully impregnated within the negative active material layer and / or the positive active material layer.
[0091] Meanwhile, after forming the first and second gel electrolytes in the second or third step, if the bipolar electrodes are stacked with a separator interposed therebetween, a bipolar secondary battery of one embodiment may be manufactured in which a second gel electrolyte with excess thickness or volume is additionally formed between the separator facing each other and the positive active material layer or the negative active material layer.
[0092] In this manufacturing method, the amount of the composition for forming the gel electrolyte in the second and third steps can be appropriately determined by a person skilled in the art by taking into account the total pore volume of the separator, the positive active material layer, and the negative active material layer, and the volume / thickness of the second gel electrolyte to be additionally formed between them.
[0093] Meanwhile, in this manufacturing method, a bipolar electrode is first manufactured by forming a negative active material layer and a positive active material layer on each side of a metal current collector. At this time, the negative active material layer and the positive active material layer may be formed by a wet method of coating, 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 can follow a general wet electrode process, further explanation regarding this is omitted.
[0094] In addition, in the other example above, the positive active material layer may be formed into a free-standing film by a dry method of dry mixing, powder formation under the application of shear force, 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 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.
[0095] As an example, the positive active material layer 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.
[0096] Meanwhile, after forming the above-mentioned bipolar electrode, a composition for forming a gel electrolyte comprising a polyfunctional (meth)acrylate-based compound and an electrolyte may be applied on the above-mentioned negative electrode active material layer and / or the above-mentioned positive electrode active material layer. At this time, regarding the composition of the electrolyte, it is as described above for a bipolar secondary battery of one embodiment.
[0097] 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 electrolyte. By doing so, it is possible to form a good matrix and gel electrolyte in which the electrolyte is uniformly impregnated, and to secure excellent conductivity of the gel electrolyte.
[0098] After applying the gel electrolyte forming composition, a further step of uniformly pressing the surface of the negative or positive active material layer coated with the gel electrolyte forming composition may be performed to impregnate it into the negative active material layer or the positive active material layer. By doing so, the gel electrolyte forming composition permeates uniformly into the negative or positive active material layer, thereby uniformly forming first and second gel electrolytes that overlap at least partially with the negative or positive active material layer and optionally have additional volume or thickness on the active material layer. 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 or positive active material layer coated with the gel electrolyte forming composition.
[0099] 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 first and second gel electrolyte comprising a matrix containing a cross-linked polymer of the polyfunctional (meth)acrylate-based compound and an electrolyte impregnated on the matrix can be well formed.
[0100] 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.
[0101] Meanwhile, the gel electrolyte forming composition can be applied and cured not only on the cathode or anode active material layer but also on at least one surface of the separator to form first and second gel electrolytes on the separator. At this time, as previously described, the gel electrolyte composition can be used in excess so that the second gel electrolyte has an excess volume or thickness on the separator.
[0102] The composition of the composition for forming a gel electrolyte applied on the above-mentioned separator is similar to the composition used in the second step described above, so further explanation regarding this is omitted. Also, the conditions for the rolling process for applying, curing, and impregnating the composition for forming a gel electrolyte on the above-mentioned separator are also the same as those described in the second step, so further explanation regarding this is omitted.
[0103] After forming a bipolar electrode and a separator containing first and second gel electrolytes through the process described above, the bipolar electrodes can be stacked in multiple layers such that the positive active material layer and the negative active material layer of adjacent bipolar electrodes face each other through the first and second gel electrolytes and the separator, thereby manufacturing a bipolar secondary battery of one embodiment. At this time, the first and / or second gel electrolyte forming surfaces of the active material layer and the separator can be brought into contact with each other to further improve the ion conductivity of the battery.
[0104]
[0105] The embodiments described above will be explained in more detail below through specific examples.
[0106] Comparative Example 1: Manufacture of a bipolar secondary battery
[0107] 496 g of LiFePO4 as the positive active material, 0.5 g of carbon black as the conductive material, and 3.5 g of polytetrafluoroethylene (PTFE) as the binder were added to a blender and mixed dry at 10,000 rpm for 1 minute to prepare a mixture. The temperature of the kneader was stabilized to 150°C, the mixture was placed into the kneader, and then operated at a speed of 50 rpm for 5 minutes under a pressure of 1.1 atm to obtain a lump of the mixture.
[0108] The obtained mixture aggregate was fed into a blender, ground at 10,000 rpm for 40 seconds, and classified using a sieve with 1 mm pores to obtain electrode powder. Subsequently, the prepared electrode powder was fed several times into a lab calender (roll diameter: 88 mm, roll temperature: 100℃) to achieve an electrode layer loading of 600 mg / 25 cm 2 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).
[0109] Meanwhile, 96g of graphite as a negative electrode active material, 1.0g of Super C-65 as a conductive material, and 3.0g of an SBR binder and a thickener 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.
[0110] 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.
[0111] Next, 0.2g of the gel electrolyte forming composition was dropped and applied onto the anode and cathode active material layers, and the applied surface was rolled to impregnate the gel electrolyte forming composition into the anode and cathode active material layers, respectively. Subsequently, 600W / cm² was applied to the applied surface for 5 seconds. 2 A gel electrolyte was formed by irradiating with UV light at an intensity.
[0112] A bipolar secondary battery of Comparative Example 1 was manufactured by stacking multiple bipolar electrodes, each having a gel electrolyte formed on the positive and negative active material layers, with a porous polyethylene separator having a thickness of 5 μm interposed therebetween.
[0113]
[0114] Example 1: Preparation of a bipolar secondary battery
[0115] 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.
[0116] 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).
[0117] 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.
[0118] 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.
[0119] Next, 0.2g of the gel electrolyte forming composition was dropped and applied onto the anode and cathode active material layers, and the applied surface was rolled to impregnate the gel electrolyte forming composition into the anode and cathode active material layers, respectively. Subsequently, 600W / cm² was applied to the applied surface for 5 seconds. 2 A gel electrolyte was formed by irradiating with UV light at an intensity.
[0120] Meanwhile, approximately 0.08 g of the gel electrolyte forming composition was dropped and applied to one side of a 5 μm thick porous polyethylene separator, and the applied surface was rolled to impregnate the gel electrolyte forming composition into the separator. At this time, the composition that was not impregnated into the separator was left as is on one side of the separator to form an additional thickness of gel electrolyte. Subsequently, 600 W / cm² was applied to the applied surface for 5 seconds. 2 A gel electrolyte was formed by irradiating with UV light at an intensity.
[0121] A bipolar secondary battery of Example 1 was manufactured by stacking the bipolar electrodes in multiple layers with a porous polyethylene separator interposed, such that the gel electrolyte forming surfaces of each active material layer and the separator are in contact with each other.
[0122]
[0123] Example 2: Preparation of a bipolar secondary battery
[0124] 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.
[0125] 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).
[0126] 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.
[0127] 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.
[0128] Next, 0.2g of the gel electrolyte forming composition was dropped and applied onto the anode and cathode active material layers, and the applied surface was rolled to impregnate the gel electrolyte forming composition into the anode and cathode active material layers, respectively. Subsequently, 600W / cm² was applied to the applied surface for 5 seconds. 2 A gel electrolyte was formed by irradiating with UV light at an intensity.
[0129] Meanwhile, approximately 0.02 g of the gel electrolyte forming composition was dropped and applied to one side of a 5 μm thick porous polyethylene separator, and the applied surface was rolled to impregnate the gel electrolyte forming composition into the separator. At this time, the composition that was not impregnated into the separator was left as is on one side of the separator to form an additional thickness of gel electrolyte. Subsequently, 600 W / cm² was applied to the applied surface for 5 seconds. 2 A gel electrolyte was formed by irradiating with UV light at an intensity.
[0130] A bipolar secondary battery of Example 2 was manufactured by stacking the bipolar electrodes in multiple layers with a porous polyethylene separator so that the gel electrolyte forming surfaces of each active material layer and the separator come into contact with each other.
[0131]
[0132]
[0133] Test Example 1: Measurement of the total volume ratio of the gel electrolyte
[0134] For the bipolar secondary batteries of Examples 1 and 2 and Comparative Example 1, the ratio of the total volume of the gel electrolyte was measured and calculated by the following method.
[0135] First, the total pore volume of the separator, the positive active material layer, and the negative active material layer was measured using the BET (Brunauer-Emmett-Teller) method. Specifically, the total pore volume was measured and calculated from the nitrogen adsorption isotherm obtained under a 77K liquid nitrogen atmosphere using BELSORP-MAX (MicrotracBEL corp.).
[0136] When measuring the total pore volume, if a gel electrolyte was already formed on the separator, the positive active material layer, or the negative active material layer, the gel electrolyte or other organic materials contained within the pores of the separator, the positive active material layer, and the negative active material layer were treated with an organic solvent of dimethyl carbonate to dissolve and remove the gel electrolyte or other organic materials, and then the total pore volume was measured. The total pore volumes of the separator, the positive active material layer, and the negative active material layer measured in this way are summarized in Table 1 below.
[0137] Meanwhile, using an analysis device equipped with an electron microscope, the ratio of the gel electrolyte impregnated and embedded within the separator, the positive active material layer, and the negative active material layer was calculated, and the volume of the first gel electrolyte was measured and calculated from this. In addition, using the analysis device, the thickness of the second gel electrolyte additionally formed between the separator, the positive active material layer, and / or the negative active material layer was measured, and the formation area of the second gel electrolyte was also measured, and the volume of the second gel electrolyte was measured and calculated from this.
[0138] From the total pore volumes of the separator, positive active material layer, and negative active material layer measured and calculated as above, and the total volumes of the first and second gel electrolytes, the ratio of the total volumes of the first and second gel electrolytes was calculated and summarized in Table 2 below.
[0139] Total pore volume (μl) Anode active material layer 55 Cathode active material layer 42 Separator 16 Total 113
[0140] Volume of gel electrolyte formed on the positive and negative active material layers (μl) Volume of gel electrolyte formed on the separator (μl) Volume ratio (%) of gel electrolyte to the total pore volume (113 μl) of the active material layer and the separator Sum of thicknesses (μm) of the second gel electrolyte additionally formed between the active material layer and the separator Comparative Example 1106.7094.40.01 Example 1106.716108.66.0 Example 2106.724115.78.0
[0141] Referring to Tables 1 and 2 above, it was confirmed that in the bipolar secondary batteries of Examples 1 and 2, a gel electrolyte is formed with an excess volume of 103% to 200% or 105% to 120% based on the total pore volume of the separator, the positive active material layer, and the negative active material layer, and thereby a second gel electrolyte with additional thickness is formed between each active material layer and the separator.
[0142]
[0143] Test Example 2: Evaluation of Electrochemical Properties
[0144] Charging was performed using the bipolar secondary batteries of the examples and comparative examples under conditions of applying a current of 0.1C and approximately 6.5mA. At an SOC of 50%, the initial cell resistance was evaluated using a resistance measuring device while separately applying a current of 2.5C and 16.25mA, and the evaluation results are shown in FIG. 2.
[0145] Meanwhile, charge and discharge tests were conducted using the bipolar secondary batteries of the examples and comparative examples under conditions of applying a current of 0.33C and approximately 21.5mA. During these charge and discharge tests, the capacity retention rate per cycle was evaluated, and the results are shown in Fig. 3. When evaluating the capacity retention rate, charge and discharge tests were conducted under the same conditions on two cells manufactured under the same conditions to reconfirm the uniformity of the test results.
[0146] Referring to FIG. 2 above, it was confirmed that the bipolar secondary batteries of Examples 1 and 2 exhibited lower cell resistance compared to Comparative Example 1. Additionally, referring to FIG. 3, it was confirmed that the bipolar secondary batteries of Examples 1 and 2 exhibited a capacity retention rate of over 90% up to about 180 cycles, whereas the battery of Comparative Example 1 showed a rapid decrease in capacity retention rate around about 70 cycles.
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 separator in between, and One or more of the separator, the positive electrode active material layer, and the negative electrode active material layer are impregnated with a gel electrolyte, and A bipolar secondary battery in which the above gel electrolyte is formed with a volume corresponding to 103% to 200% based on the total pore volume of the separator, positive active material layer, and negative active material layer in a state not impregnated with the above gel electrolyte.
2. A bipolar secondary battery according to claim 1, wherein the metal current collector is a current collector including stainless steel or a laminated 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. The gel electrolyte of claim 1, a bipolar secondary battery comprising a matrix containing a cross-linked polymer of a polyfunctional (meth)acrylate-based compound and an electrolyte impregnated on the matrix.
5. In claim 4, the 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.
6. A bipolar secondary battery according to claim 4, 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.
7. A bipolar secondary battery according to claim 5, 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.
8. A bipolar secondary battery according to claim 5, 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.
9. A bipolar secondary battery according to claim 5, 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.
10. A bipolar secondary battery according to claim 5, wherein the non-aqueous organic solvent further comprises a non-volatile sulfone-based solvent having a boiling point of 150°C or higher.
11. A bipolar secondary battery according to claim 5, 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.
12. In claim 1, the gel electrolyte comprises a first gel electrolyte impregnated inside one or more of the separator, the positive electrode active material layer, and the negative electrode active material layer, and A bipolar secondary battery comprising a separator facing each other and a second gel electrolyte additionally formed between a positive active material layer or a negative active material layer.
13. In claim 12, the first and second gel electrolytes are formed continuously in a bipolar secondary battery.
14. A bipolar secondary battery according to claim 12, wherein the total thickness of the second gel electrolyte is 0.1 to 20 μm.
15. A bipolar secondary battery according to claim 12, wherein the first gel electrolyte is impregnated in all of the separator, the positive active material layer, and the negative active material layer.
16. A bipolar secondary battery according to claim 12, wherein the second gel electrolyte is formed between the separator and the positive electrode active material layer and between the separator and the negative electrode active material layer, respectively.
17. A bipolar secondary battery according to claim 12, wherein the second gel electrolyte is additionally formed between the separator and the positive active material layer or between the separator and the negative active material layer, with a volume corresponding to 2% to 60% based on the total pore volume of the separator, the positive active material layer, and the negative active material layer in a state not impregnated with the gel electrolyte.
18. A bipolar secondary battery according to claim 17, wherein the second gel electrolyte additionally formed between the separator and the positive active material layer or between the separator and the negative active material layer has a thickness of 0.05 to 20 μm.
19. A first 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 second step of applying and curing a gel electrolyte-forming composition comprising a curable polyfunctional compound and an electrolyte on the above-mentioned negative electrode active material layer or positive electrode active material layer; A third step of applying and curing the gel electrolyte forming composition on at least one surface of the separator; and A fourth step of stacking multiple bipolar electrodes such that the positive active material layer and the negative active material layer of adjacent bipolar electrodes face each other through a separator, and A method for manufacturing a bipolar secondary battery according to claim 1, wherein the above-mentioned gel electrolyte forming composition is applied in a volume larger than the total pore volume of the separator, the positive electrode active material layer, and the negative electrode active material layer.
20. A method for manufacturing a bipolar secondary battery according to claim 19, wherein the second or third step further comprises the step of impregnating the applied gel electrolyte-forming composition into the negative electrode active material layer, the positive electrode active material layer, or the separator between the application and curing of the gel electrolyte-forming composition.
21. A method for manufacturing a bipolar secondary battery according to claim 20, wherein the impregnation step comprises the step of rolling the surface of a negative electrode active material layer, a positive electrode active material layer, or a separator coated with the gel electrolyte forming composition.