Gel polymer electrolyte composition with shortened crosslinking time, secondary battery containing the same, and method for manufacturing the secondary battery

Abstract

The present invention relates to a gel polymer electrolyte composition, a secondary battery including the same, and a method for manufacturing the secondary battery, and has the advantage of improving process efficiency by shortening the curing time of the gel polymer electrolyte while preventing electrolyte leakage.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0038945, filed March 29, 2022, and Korean Patent Application No. 10-2022-0183228, filed December 23, 2022, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a gel polymer electrolyte composition with a shortened crosslinking time, a secondary battery containing the same, and a method for manufacturing the secondary battery. [Background technology]

[0003] In recent years, rechargeable secondary batteries have been widely used as energy sources for wireless mobile devices. Secondary batteries are also attracting attention as energy sources for electric vehicles and hybrid electric vehicles, which are being proposed as a solution to address air pollution caused by existing gasoline and diesel vehicles that use fossil fuels. Therefore, the types of applications using secondary batteries are becoming increasingly diverse due to the advantages of secondary batteries, and secondary batteries are expected to be applied to more fields and products in the future.

[0004] A secondary battery has a structure in which an electrode assembly is housed in a battery case together with an electrolyte, and the electrode assembly is sufficiently impregnated and wetted with the electrolyte to exhibit electrical performance. However, electrolyte leakage can occur during charging and discharging, which can cause battery cell failure and even fire.

[0005] Gel polymer electrolytes have been studied as a way to prevent electrolyte leakage. However, gel polymer electrolytes require a cross-linking process after the electrolyte is injected into the battery. This takes a long time to cross-link the electrolyte, which reduces process efficiency and increases manufacturing costs.

[0006] Therefore, there is a need for a technology that can reduce the curing time due to the cross-linking reaction within the electrolyte while incorporating a gel polymer electrolyte to prevent electrolyte leakage. Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been devised to solve the above problems, and an object of the present invention is to provide a gel polymer electrolyte composition that can significantly reduce the curing time compared to existing compositions, and a secondary battery including the same. [Means for solving the problem]

[0008] The present invention provides a composition for a gel polymer electrolyte. In one embodiment, the composition for a gel polymer electrolyte according to the present invention includes an oligomer represented by the following Chemical Formula 1, a reaction additive including a phosphate-based compound, a polymerization initiator, a non-aqueous solvent, and a lithium salt.

[0009] [ka]

[0010] In the above chemical formula 1, R is hydrogen or alkylene having 1 to 5 carbon atoms substituted with an alkyl group having 1 to 5 carbon atoms, and m is an integer of 1 to 50.

[0011] In one embodiment, the gel polymer electrolyte composition has a curing time in the range of 10 to 50 minutes under heat treatment conditions of 55 to 80°C.

[0012] In a specific embodiment, the content of the oligomer is in the range of 0.1 to 30 parts by weight relative to 100 parts by weight of the entire composition for gel polymer electrolyte.

[0013] In another embodiment, the reaction additive is represented by the following chemical formula 2:

[0014] [ka]

[0015] In the above Chemical Formula 2, R1, R2, and R3 are each independently hydrogen or alkylene having 1 to 3 carbon atoms. When at least one of R1, R2, and R3 is alkylene having 1 to 3 carbon atoms, R4, R5, and R6 are each independently a unit containing an acrylate group, a methacrylate group, or a vinyl group.

[0016] In a specific embodiment, the reaction additive is represented by any one or more of the following chemical formulae a to d:

[0017] [ka]

[0018] [ka]

[0019] [ka]

[0020] [ka]

[0021] In one embodiment, the content of the reaction additive is in the range of 0.01 to 10 parts by weight relative to 100 parts by weight of the entire composition for gel polymer electrolyte.

[0022] The present invention also provides a method for manufacturing a lithium secondary battery by applying the above-mentioned gel polymer electrolyte composition. In one embodiment, the method for manufacturing a lithium secondary battery according to the present invention includes the step of injecting the gel polymer electrolyte composition according to claim 1 into a battery case in a state where an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode is housed in the battery case.

[0023] In one embodiment, the method for producing a lithium secondary battery further includes a step of performing thermal crosslinking for 10 to 50 minutes after the step of injecting the gel polymer electrolyte composition into the battery case.

[0024] In a specific embodiment, the thermal crosslinking step is performed at a temperature in the range of 55°C to 80°C.

[0025] In another embodiment, the method of the present invention further includes a wetting step of waiting for 1 minute to 30 hours between the step of injecting the gel polymer electrolyte composition into the battery case and the step of thermal crosslinking.

[0026] In another embodiment, the manufacturing method according to the present invention further comprises, after the thermal crosslinking step, any one or more of an activation step and a degassing step.

[0027] The present invention also provides a secondary battery manufactured by the above-described method. In one embodiment, the lithium secondary battery according to the present invention includes an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, a battery case that houses and seals the electrode assembly, and a gel polymer electrolyte composition injected into the battery case housing the electrode assembly. The gel polymer electrolyte composition is as described above.

[0028] In a specific embodiment, the lithium secondary battery is a pouch-type battery. [Effects of the Invention]

[0029] The present invention can increase the efficiency of the manufacturing process for secondary batteries using a thermally crosslinked gel polymer electrolyte, and improve the quality of the manufactured products. [Brief explanation of the drawings]

[0030] [Figure 1] 1 is a schematic diagram illustrating a leakage evaluation process for a pouch-type secondary battery according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0031] The present invention will be described in detail below. Before that, the terms and words used in the specification and claims should not be interpreted as being limited to their general or dictionary meanings, but should be interpreted as meanings and concepts that are consistent with the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concepts of the terms in order to best describe his / her invention.

[0032] The present invention provides a composition for a gel polymer electrolyte. In one embodiment, the composition for a gel polymer electrolyte according to the present invention includes an oligomer, a reaction additive including a phosphate-based compound, a polymerization initiator, a non-aqueous solvent, and a lithium salt.

[0033] The present invention significantly increases the gelation rate of the electrolyte by adding a reactive additive that accelerates the crosslinking reaction of the oligomer.

[0034] As an example, the oligomer may be a PPC (Polypropylene carbonate) oligomer. In one embodiment, the oligomer is represented by the following Chemical Formula 1:

[0035] [ka]

[0036] In the above chemical formula 1, R is hydrogen or alkylene having 1 to 5 carbon atoms substituted with an alkyl group having 1 to 5 carbon atoms, and m is an integer of 1 to 50.

[0037] Specifically, the R is an alkylene having 1 to 3 carbon atoms, and more specifically, an alkylene having 2 carbon atoms substituted with a methyl group. The m is an integer of 1 to 10, an integer of 2 to 5, an integer of 2 to 3, or 2.

[0038] In one embodiment, the content of the oligomer in the present invention is in the range of 0.1 to 30 parts by weight, relative to 100 parts by weight of the total gel polymer electrolyte composition. More specifically, the content of the oligomer is in the range of 1 to 10 parts by weight, 2 to 8 parts by weight, or 3 to 5 parts by weight. The content of the oligomer is in a range that prevents electrolyte leakage when applied to a secondary battery, while not degrading the performance of the secondary battery.

[0039] The curing temperature of the gel polymer electrolyte composition may vary depending on the type of polymerization initiator. In one embodiment, the crosslinking reaction of the gel polymer electrolyte composition proceeds under heat treatment conditions of 55°C to 80°C, 60°C to 75°C, or 68°C to 75°C. In this case, the curing time is in the range of 10 to 50 minutes, 10 to 40 minutes, or 20 to 40 minutes. The use of the reaction additive in the gel polymer electrolyte composition reduces the curing time by 25% or more compared to conventional compositions.

[0040] In one embodiment, the reaction additive is represented by the following formula 2:

[0041] [ka]

[0042] In the above Chemical Formula 2, R1, R2, and R3 are each independently hydrogen or alkylene having 1 to 3 carbon atoms, and when at least one of R1, R2, and R3 is alkylene having 1 to 3 carbon atoms, R4, R5, and R6 are each independently a unit containing an acrylate group, a methacrylate group, or a vinyl group.

[0043] In the above description of Chemical Formula 2, when any one of R1, R2 and R3 is hydrogen, it is understood that there is no substituent connected thereto.

[0044] In Formula 2, if any one or more of R1, R2, and R3 has 4 or more carbon atoms, side reactions may become more severe, resulting in poor performance when applied to a secondary battery.

[0045] In a specific embodiment, in the above Chemical Formula 2, R1, R2, and R3 are each independently hydrogen or alkylene having 1 to 2 carbon atoms, and when any one or more of R1, R2, and R3 are alkylene having 1 to 2 carbon atoms, R4, R5, and R6 are each independently an acrylate group or a methacrylate group.

[0046] In a more specific embodiment, in the above Chemical Formula 2, R1, R2, and R3 are each independently an alkylene having 1 to 2 carbon atoms, and R4, R5, and R6 are each independently an acrylate group or a methacrylate group.

[0047] In a more specific embodiment, in the above Chemical Formula 2, R1 and R2 are alkylene having 1 to 2 carbon atoms, R3 is hydrogen, and R4 and R5 are each independently an acrylate group or a methacrylate group.

[0048] For example, the reaction additive is represented by one or more of the following chemical formulae a to d.

[0049] [ka]

[0050] [ka]

[0051] [ka]

[0052] [ka]

[0053] In the present invention, the content of the reactive additive is in the range of 0.01 to 10 parts by weight relative to 100 parts by weight of the total gel polymer electrolyte composition. Specifically, the content of the reactive additive is in the range of 0.1 to 10 parts by weight, 0.01 to 5 parts by weight, 0.2 to 5 parts by weight, or 0.5 to 2 parts by weight. The content of such reactive additive is within a range that can sufficiently reduce the curing rate while minimizing the amount of additive added.

[0054] The present invention also provides a method for manufacturing a lithium secondary battery using the above-described gel polymer electrolyte. In one embodiment, the method for manufacturing a lithium secondary battery according to the present invention includes the steps of: injecting a gel polymer electrolyte composition into a battery case in a state where an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode is housed in the battery case.

[0055] In the present invention, a secondary battery is manufactured by injecting the above-described gel polymer electrolyte composition into a battery case containing an electrode assembly. Then, a process of gelling the gel polymer electrolyte composition by heat treatment is performed. Specifically, the present invention includes a step of performing thermal crosslinking for 10 to 50 minutes after the step of injecting the gel polymer electrolyte composition into the battery case. This thermal crosslinking step is a process of inducing a crosslinking reaction of the injected gel polymer electrolyte to harden it. The hardening time is in the range of 10 to 50 minutes, 10 to 40 minutes, or 20 to 40 minutes. The present invention has the effect of reducing the hardening time by 25% or more compared to conventional methods.

[0056] In addition, the temperature of the thermal crosslinking step may vary depending on the type of polymerization initiator added. In the present invention, for example, a reaction additive represented by the above-mentioned Chemical Formula 2 may be used. In this case, the thermal crosslinking step may be performed at a temperature range of 55°C to 80°C, 60°C to 75°C, or 68°C to 75°C.

[0057] In another embodiment, the present invention includes a wetting step of waiting for 1 minute to 30 hours between the step of injecting the gel polymer electrolyte composition into the battery case and the step of thermal crosslinking.

[0058] In another embodiment, the present invention includes one or more of an activation step and a degassing step after the thermal crosslinking step.

[0059] The present invention also provides a secondary battery manufactured by the above-described manufacturing method. In one embodiment, the secondary battery according to the present invention includes an electrode assembly including a positive electrode, one negative electrode, and a separator disposed between the positive electrode and the negative electrode, a battery case that houses and seals the electrode assembly, and a gel polymer electrolyte composition injected into the battery case housing the electrode assembly. The gel polymer electrolyte composition is as described above.

[0060] Depending on the method of stacking the electrode assemblies, they can be classified into a jelly roll type, which is a rolled-up type, and a stack type, which is sequentially stacked. Furthermore, depending on the shape of the battery case, secondary batteries can be classified into cylindrical batteries and prismatic batteries, in which the electrode assembly is housed in a cylindrical or prismatic metal can, and pouch batteries, in which the electrode assembly is housed in a pouch-shaped case made of an aluminum laminate sheet. The secondary battery of the present invention can be a cylindrical, prismatic, or pouch-type secondary battery, and preferably a pouch-type secondary battery.

[0061] The case may be made of a laminate sheet including a metal layer and a resin layer. Specifically, the laminate sheet may be an aluminum laminate sheet. The laminate sheet battery case may include a lower case having a recessed receiving portion and an outer shell extending from the receiving portion, and an upper case joined to the lower case by thermal fusion.

[0062] The components of the secondary battery of the present invention will be described below.

[0063] A positive electrode, which is one of the components of a secondary battery, has a structure in which a positive electrode active material layer is laminated on one or both sides of a positive electrode current collector. In one example, the positive electrode active material layer includes a positive electrode active material, a conductive material, a binder polymer, etc., and may further include a positive electrode additive commonly used in the art, as needed.

[0064] The positive electrode active materials may be the same or different lithium-containing oxides, and the lithium-containing oxides may be lithium-containing transition metal oxides.

[0065] For example, lithium-containing transition metal oxides include Li x CoO2(0.5 <x<1.3)、Li x NiO2(0.5 <x<1.3)、Li x MnO2(0.5 <x<1.3)、Li x Mn2O4(0.5 <x<1.3)、Li x (Ni a Co b Mnc )O2(0.5 < x < 1.3, 0 < a < 1, 0 < b < 1, 0 < c < 1, a + b + c = 1), Li x Ni 1-y Co y )O2(0.5 < x < 1.3, 0 < y < 1), Li x Co 1-y Mn y )O2(0.5 < x < 1.3, 0 ≤ y < 1), Li x Ni 1-y Mn y )O2(0.5 < x < 1.3, 0 ≤ y < 1), Li x (Ni a ​​​​​​​​​​​​​​​​​​​​​​​​​​​​The current collector used in the positive electrode may be any metal that has high conductivity, is easily adhered to the positive electrode active material slurry, and is non-reactive within the voltage range of the electrochemical device. Specific examples of the positive electrode current collector include foils made of aluminum, nickel, or a combination thereof. The positive electrode active material layer further includes a conductive material.

[0068] The conductive material is often a carbon-based conductive material, and includes spherical or needle-type carbon-based conductive materials. The spherical carbon-based conductive material, when mixed with a binder, fills the pores between active material particles, improving physical contact between the active materials, reducing interfacial resistance, and improving adhesion between the lower positive electrode active material and the current collector.

[0069] The conductive material may be contained in the positive electrode active material layer in a range of 0.5% by weight to 5% by weight. When the content of the conductive material satisfies the above range, sufficient conductivity of the positive electrode is imparted, and the interfacial resistance between the electrode current collector and the active material is reduced.

[0070] The binder polymer may be any binder commonly used in the art without limitation. For example, the binder may be a water-insoluble polymer that is soluble in organic solvents but insoluble in water, or a water-soluble polymer that is insoluble in organic solvents but soluble in water. The water-insoluble polymer may be one or more selected from the group consisting of polyvinylidene fluoride (PVDF), polyvinylidene chloride (PVDC), polyacrylonitrile (PAN), polypropylene oxide (PPO), polyethylene oxide-propylene oxide copolymer (PEO-PPO), polytetrafluoroethylene (PTFE), polyimide (PI), polyetherimide (PEI), styrene-butadiene rubber (SBR), polyacrylate, and derivatives thereof.

[0071] The water-soluble polymer may be one or more selected from the group including various cellulose derivatives such as carboxymethyl cellulose (CMC), methyl cellulose (MC), cellulose acetate phthalate (CAP), hydroxypropyl methyl cellulose (HPMC), and hydroxypropyl methyl cellulose phthalate (HPMCP).

[0072] The content of the binder polymer is proportional to the content of the conductive material contained in the upper and lower positive electrode active material layers. This is because the binder polymer provides adhesive strength to the conductive material, which has a relatively small particle size compared to the active material, and therefore, as the content of the conductive material increases, more binder polymer is required, while as the content of the conductive material decreases, less binder polymer can be used.

[0073] The negative electrode has a structure in which a negative electrode active material layer is laminated on one or both sides of a negative electrode current collector. In one example, the negative electrode active material layer includes a negative electrode active material, a conductive material, a binder polymer, etc., and may further include a negative electrode additive commonly used in the art, as needed.

[0074] The negative electrode active material may include a carbon material, lithium metal, silicon, or tin. When a carbon material is used as the negative electrode active material, both low-crystalline carbon and high-crystalline carbon may be used. Typical low-crystalline carbons include soft carbon and hard carbon, while typical high-crystalline carbons include natural graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitches, and high-temperature-calcined carbons such as petroleum or coal tar pitch-derived cokes.

[0075] Non-limiting examples of the current collector used in the negative electrode include foils made of copper, gold, nickel, copper alloys, or combinations thereof. The current collector may also be laminated with a substrate made of any of the above materials.

[0076] The negative electrode may also contain a conductive material and a binder commonly used in the art.

[0077] The separator may be any porous substrate used in lithium secondary batteries, for example, a polyolefin-based porous membrane or nonwoven fabric, but is not limited thereto.

[0078] Examples of the polyolefin-based porous membrane include membranes formed from polyolefin-based polymers such as polyethylene (e.g., high-density polyethylene, linear low-density polyethylene, low-density polyethylene, ultra-high molecular weight polyethylene), polypropylene, polybutylene, and polypentene, either alone or in combination.

[0079] In addition to polyolefin-based nonwoven fabrics, examples of the nonwoven fabric include nonwoven fabrics made from polymers such as polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfide, and polyethylenenaphthalene, either alone or in combination. The nonwoven fabric may be a spunbonded or meltblown nonwoven fabric made of long fibers.

[0080] The thickness of the porous substrate is not particularly limited, but may be 5 μm to 50 μm. The size and porosity of the pores present in the porous substrate are also not particularly limited, but may be 0.01 μm to 50 μm and 10% to 95%, respectively.

[0081] Meanwhile, in order to improve the mechanical strength of the separator formed of the porous substrate and to prevent short circuits between the positive electrode and the negative electrode, a porous coating layer including inorganic particles and a binder polymer may be further included on at least one surface of the porous substrate.

[0082] The electrolyte may include an organic solvent and an electrolyte salt, and the electrolyte salt may be a lithium salt. The lithium salt may be any lithium salt commonly used in non-aqueous electrolytes for lithium secondary batteries. For example, a lithium salt containing Li as a cation may be used. + Contains F as an anion - , Cl - , Br - , I - , NO 3- , N(CN) 2-, B.F. 4- , ClO 4- , AlO 4- , AlCl 4- , P.F. 6- , SbF 6- , AsF 6- , BF2C2O 4- , BC4O 8- , (CF3)2PF 4- , (CF3)3PF 3- , (CF3)4PF 2- , (CF3)5PF - , (CF3)6P - , CF3SO 3- , C4F9SO 3- , CF3CF2SO 3- , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO 3- , CF3CO 2- , CH3CO 2- , SCN - , and (CF3CF2SO2)2N - It may include at least one selected from the group consisting of:

[0083] The organic solvent contained in the electrolyte may be any organic solvent commonly used in secondary battery electrolytes, and may be used alone or in combination of two or more thereof, such as ethers, esters, amides, linear carbonates, and cyclic carbonates. Among these, representative examples include carbonate compounds such as cyclic carbonates, linear carbonates, and mixtures thereof.

[0084] Specific examples of the cyclic carbonate compound include any one or mixture of two or more selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate, and halides thereof. Examples of halides thereof include, but are not limited to, fluoroethylene carbonate (FEC).

[0085] Specific examples of the linear carbonate compound include, but are not limited to, any one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate, and ethyl propyl carbonate, or a mixture of two or more of these.

[0086] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents with high dielectric constants, and can more effectively dissociate lithium salts in the electrolyte. When such cyclic carbonates are mixed with linear carbonates with low viscosity and low dielectric constants, such as dimethyl carbonate and diethyl carbonate, in a suitable ratio, an electrolyte with higher electrical conductivity can be produced.

[0087] Furthermore, the ether among the organic solvents may be any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, and ethyl propyl ether, or a mixture of two or more of these, but is not limited thereto.

[0088] Among the organic solvents, the ester may be any one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone, or a mixture of two or more thereof, but is not limited thereto.

[0089] The electrode assembly may be a lamination / stack type in which unit cells with a separator interposed therebetween are stacked, or a stack / folding type in which unit cells are wound with a separator sheet.

[0090] The electrode assembly is fabricated by applying electrode active materials to positive and negative electrode current collectors to form composite layers, then fabricating positive and negative electrodes with pinholes in the electrode tabs and electrode plates using a notching device, and bonding the positive and negative electrodes to a separator without pinholes. The type of separator is not limited, but can be an organic / inorganic composite porous safety-reinforcing separator (SRS) separator.

[0091] Specifically, the SRS separator is fabricated using inorganic particles and a binder polymer as active layer components on a polyolefin-based separator substrate. The separator substrate itself has a uniform pore structure formed by the interstitial volume between the inorganic particles, which are the active layer components. The use of such organic / inorganic composite porous separators has the advantage of suppressing battery thickness increase due to swelling during the formation process compared to conventional separators. Furthermore, when a polymer capable of gelling during impregnation with a liquid electrolyte is used as the binder polymer component, the separator can also be used as an electrolyte. Furthermore, the organic / inorganic composite porous separator exhibits excellent adhesive properties by adjusting the content of the inorganic particles and binder polymer, which are the active layer components, within the separator, thereby facilitating the battery assembly process.

[0092] The present invention will be described in more detail below with reference to examples. Since the present invention can be modified in various ways and can have various embodiments, specific examples will be illustrated and described in detail in the text. However, this is not intended to limit the present invention to the specific disclosed form, and it should be understood that all modifications, equivalents, and alternatives falling within the spirit and technical scope of the present invention are included.

[0093] Example 1 Lithium salt LiPF was dissolved at a concentration of 1M in a solvent prepared by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7, and additives were added in amounts based on the total weight of the gel polymer electrolyte as shown in Table 1 below to prepare gel polymer electrolyte compositions.

[0094] Specifically, the oligomer was added at a content of 4 wt %, and the structural formula of the oligomer was as shown in Chemical Formula 1, where R is an alkylene having 2 carbon atoms substituted with a methyl group, and m is an integer ranging from 2 to 3.

[0095] The reactive additive was added in an amount of 1% by weight, and the structural formula of the reactive additive was as follows:

[0096] [ka]

[0097] As a polymerization initiator, a thermal initiator, V-59 product, an azo-based initiator manufactured by FUJIFILM WAKO Co., Ltd., was used at a content of 1 wt %.

[0098] The positive electrode active material is LiNi with a particle size of 5 μm. 0.5 Mn 1.5 O4 was prepared and mixed with polyvinylidene fluoride as a carbon-based conductive agent and binder in N-methylpyrrolidone (NMP) in a weight ratio of 94:3:3 to form a slurry, which was then cast onto an aluminum sheet, dried in a vacuum oven at 120°C, and rolled to produce a positive electrode.

[0099] Separately, a negative electrode active material was prepared by mixing artificial graphite and silicon dioxide (SiO2) in a weight ratio of 9:1. 97 parts by weight of the negative electrode active material and 3 parts by weight of styrene butadiene rubber (SBR) were mixed with water to form a slurry, which was then cast onto a copper sheet, dried in a vacuum oven at 130°C, and rolled to produce a negative electrode.

[0100] The obtained positive and negative electrodes were inserted into a case with an 18 μm polypropylene separator therebetween, and the gel polymer electrolyte composition was then poured in. After that, the case was cured at 70° C. for 30 minutes to prepare a pouch-type lithium secondary battery.

[0101] <Examples 2 to 4> A gel polymer electrolyte composition was prepared in the same manner as in Example 1, except that the reactive additive was added in an amount of 1 wt % and the structural formulas of the reactive additive were the following chemical formulas b to d, respectively.

[0102] [ka]

[0103] [ka]

[0104] [ka]

[0105] A lithium secondary battery was manufactured in the same manner as in Example 1 using the prepared gel polymer electrolyte composition.

[0106] <Comparative Example 1> An electrolyte composition was prepared by dissolving LiPF6 as a lithium salt at a concentration of 1M in a solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 3:7.

[0107] The positive electrode active material is LiNi with a particle size of 5 μm. 0.5 Mn 1.5 O4 was prepared and mixed with polyvinylidene fluoride as a carbon-based conductive agent and binder in N-methylpyrrolidone (NMP) in a weight ratio of 94:3:3 to form a slurry, which was then cast onto an aluminum sheet, dried in a vacuum oven at 120°C, and rolled to produce a positive electrode.

[0108] Separately, a negative electrode active material was prepared by mixing artificial graphite and silicon dioxide (SiO2) in a weight ratio of 9:1. 97 parts by weight of the negative electrode active material and 3 parts by weight of styrene butadiene rubber (SBR) were mixed with water to form a slurry, which was then cast onto a copper sheet, dried in a vacuum oven at 130°C, and rolled to produce a negative electrode.

[0109] The obtained positive and negative electrodes were interposed with a separator made of 18 μm polypropylene, and inserted into a case, and then the prepared electrolyte composition was injected to prepare a pouch-type lithium secondary battery.

[0110] <Comparative Example 2> Lithium salt LiPF was dissolved at a concentration of 1M in a solvent prepared by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7, and additives were added in amounts based on the total weight of the gel polymer electrolyte as shown in Table 1 below to prepare gel polymer electrolyte compositions.

[0111] Using the prepared gel polymer electrolyte composition, a lithium secondary battery was prepared in the same manner as in Example 1, except that the curing time was changed to 30 minutes.

[0112] <Comparative Example 3> Lithium salt LiPF was dissolved at a concentration of 1M in a solvent prepared by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7, and additives were added in amounts based on the total weight of the gel polymer electrolyte as shown in Table 1 below to prepare gel polymer electrolyte compositions.

[0113] Using the prepared gel polymer electrolyte composition, a lithium secondary battery was prepared in the same manner as in Example 1, except that the curing time was changed to 100 minutes.

[0114] <Comparative Example 4> Lithium salt LiPF was dissolved at a concentration of 1M in a solvent prepared by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7, and additives were added in amounts based on the total weight of the gel polymer electrolyte as shown in Table 1 below to prepare gel polymer electrolyte compositions.

[0115] Using the prepared gel polymer electrolyte composition, a lithium secondary battery was prepared in the same manner as in Example 1, except that the curing time was changed to 300 minutes.

[0116] <Comparative Example 5> Lithium salt LiPF was dissolved at a concentration of 1M in a solvent prepared by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7, and additives were added in amounts based on the total weight of the gel polymer electrolyte as shown in Table 1 below to prepare gel polymer electrolyte compositions.

[0117] However, the compound represented by the following chemical formula 1a was used as the oligomer component.

[0118] [ka]

[0119] Using the prepared gel polymer electrolyte composition, a lithium secondary battery was prepared in the same manner as in Example 1, except that the curing time was changed to 30 minutes.

[0120] [Table 1]

[0121] <Experimental example: Evaluation of leakage> The presence or absence of electrolyte leakage was evaluated for each of the secondary batteries manufactured in Examples 1 to 4 and Comparative Examples 1 to 3. Each secondary battery was a large cell of the 100 Ah class.

[0122] The evaluation process is illustrated in FIG. 1. Referring to FIG. 1, each pouch-type secondary battery 100 is a large-scale battery cell of the 100 Ah class. The pouch-type secondary battery 100 has a structure in which an electrode assembly is housed in a pouch-type case. The pouch-type case is used as a base, and a sealing area 120 is formed by heat-sealing four sides surrounding an electrode assembly housing area 110, with electrode terminals 130 extending out from both sides. One side of the bottom end of each pouch-type secondary battery 100 was cut open by approximately d (d = 25 cm) and tilted at an angle θ (θ = 5°) at room temperature for one week. The amount of electrolyte leakage from each pouch-type secondary battery 100 was then measured.

[0123] If the amount of electrolyte decreased by 3% by weight or more compared to the initial amount of electrolyte injected, it was determined that there was electrolyte leakage. The evaluation results are shown in Table 2 below.

[0124] [Table 2]

[0125] Referring to Table 2, in Examples 1 to 4, no electrolyte leakage was observed even with a curing time of 30 minutes. In contrast, in Comparative Example 1, the electrolyte did not gel, and therefore leakage was observed. Referring to Comparative Examples 2 and 3, it can be seen that when the reactive additive according to the present invention is not added, electrolyte leakage is observed with a curing time of 30 minutes or 100 minutes. Referring to Comparative Example 4, it can be seen that when the reactive additive is not added, no leakage is observed with a curing time of 300 minutes. Furthermore, in Comparative Example 5, electrolyte leakage was observed. In Comparative Example 5, a compound represented by Chemical Formula 1a was used as the oligomer component, and it was confirmed that sufficient curing did not proceed through 100 minutes of curing. [Explanation of symbols]

[0126] 100: Pouch-type secondary battery 110: Electrode assembly storage area 120: Sealing area 130: Terminal

Claims

1. An oligomer represented by the following chemical formula 1: a reactive additive containing a phosphate-based compound; a polymerization initiator, a non-aqueous solvent, and lithium salts, 【Chemical 1】 In the above Chemical Formula 1, R is hydrogen or alkylene having 1 to 5 carbon atoms substituted with an alkyl group having 1 to 5 carbon atoms; m is an integer from 1 to 50, The reaction additive is represented by the following chemical formula 2: 【Chemistry 2】 In the above Chemical Formula 2, R 1 , R 2 and R 3 are each independently an alkylene group having 1 to 2 carbon atoms, and R 4 , R 5 and R 6 are each independently an acrylate group or a methacrylate group, or A composition for a gel polymer electrolyte, wherein R 1 and R 2 are alkylene having 1 to 2 carbon atoms, R 3 is hydrogen, R 4 and R 5 are each independently an acrylate group or a methacrylate group, and R 6 is absent.

2. 2. The gel polymer electrolyte composition according to claim 1, wherein the gel polymer electrolyte composition has a curing time in the range of 10 to 50 minutes under heat treatment conditions of 55 to 80°C.

3. 2. The composition for a gel polymer electrolyte according to claim 1, wherein the content of the oligomer is in the range of 0.1 to 30 parts by weight per 100 parts by weight of the total composition for a gel polymer electrolyte.

4. The composition for a gel polymer electrolyte according to claim 1, wherein the reactive additive is represented by any one or more of the following chemical formulae a to d: 【Chemistry 3】

5. 2. The gel polymer electrolyte composition according to claim 1, wherein the content of the reactive additive is in the range of 0.01 to 10 parts by weight per 100 parts by weight of the total gel polymer electrolyte composition.

6. An electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode is housed in a battery case, A method for producing a lithium secondary battery, comprising the step of injecting the gel polymer electrolyte composition according to claim 1 into a battery case.

7. After the step of injecting the gel polymer electrolyte composition into the battery case, The method for manufacturing a lithium secondary battery according to claim 6, further comprising the step of performing thermal cross-linking for a period of 10 to 50 minutes.

8. The method of claim 7, wherein the thermal cross-linking is performed at a temperature in the range of 55°C to 80°C.

9. 10. The method for manufacturing a lithium secondary battery according to claim 7, further comprising a wetting step of waiting for 1 minute to 30 hours between the step of injecting the composition for the gel polymer electrolyte into the battery case and the step of thermal crosslinking.

10. an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; a battery case that houses and seals the electrode assembly; and A lithium secondary battery comprising a polymer of the gel polymer electrolyte composition according to any one of claims 1 to 5 injected into a battery case housing an electrode assembly.

11. The lithium secondary battery according to claim 10, wherein the lithium secondary battery is a pouch-type battery.

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