Gel polymer electrolyte composition achieving shortened crosslinking time, secondary battery including the same, and method of manufacturing secondary battery

Abstract

The present disclosure relates to a gel polymer electrolyte composition, a secondary battery including the same, and a manufacturing method of a secondary battery, and has an advantage of increasing processing efficiency by reducing a curing time of a gel polymer electrolyte while preventing electrolyte leakage.

Description

Technical Field

[0001] This application claims priority based on Korean Patent Application No. 10-2022-0040568, filed on March 31, 2022, and the entire contents disclosed in that Korean Patent Application are incorporated herein by reference.

[0002] This invention relates to a gel polymer electrolyte composition having reduced crosslinking time, a secondary battery including the same, and a method for manufacturing the secondary battery. Background Technology

[0003] Recently, rechargeable and discharging secondary batteries have been widely used as an energy source for wireless mobile devices. In addition, secondary batteries are gaining attention as an energy source for electric vehicles, hybrid electric vehicles, and other applications proposed as solutions to air pollution from existing fossil fuel-powered gasoline and diesel vehicles. Therefore, the types of applications using secondary batteries are becoming increasingly diverse due to their advantages, and it is expected that in the future, secondary batteries will be used in even more fields and products than they are now.

[0004] Secondary batteries have a structure in which electrode assemblies are embedded together with the electrolyte in a battery casing, and the electrode assemblies are fully impregnated and wetted by the electrolyte to exhibit electrical properties. However, electrolyte leakage can occur during charging and discharging, leading to defects in the battery cell and potentially causing a fire.

[0005] Gel polymer electrolytes are being investigated as a method to prevent electrolyte leakage. However, gel polymer electrolytes undergo a cross-linking process after being injected into the battery. This cross-linking process is time-consuming, leading to decreased processing efficiency and increased manufacturing costs.

[0006] Therefore, there is a need for a technology that can reduce curing time based on the cross-linking reaction in the electrolyte while introducing a gel polymer electrolyte to prevent electrolyte leakage. Summary of the Invention

[0007] Technical issues

[0008] The present invention is designed to solve the above problems and relates to providing a gel polymer electrolyte composition that can significantly reduce curing time compared to conventional ones, and a secondary battery including the thereof.

[0009] Technical solution

[0010] This invention provides a gel polymer electrolyte composition. In an exemplary embodiment, the gel polymer electrolyte composition according to the invention comprises: an oligomer represented by Formula 1; a curing accelerator as a monocyclic or polycyclic amine compound; a polymerization initiator; a non-aqueous solvent; and a lithium salt.

[0011] [Formula 1]

[0012]

[0013] In Equation 1,

[0014] R is an alkyl group having 1 to 5 carbons substituted with an alkyl group, and

[0015] m is an integer from 1 to 50.

[0016] In an exemplary embodiment, the gel polymer electrolyte composition has a curing time in the range of 10 to 50 minutes under heat treatment conditions of 55°C to 80°C.

[0017] In an exemplary embodiment, the content of the oligomer is in the range of 0.1 parts by weight to 30 parts by weight based on 100 parts by weight of the gel polymer electrolyte composition.

[0018] In another exemplary embodiment, the curing accelerator includes one or more of pyrimidine, imidazole, purine, thiadiazole, and pyrrole curing accelerators.

[0019] In a specific exemplary embodiment, the pyrimidine-based curing accelerator is one or more of the following formulas 1-a to 1-g:

[0020] [Equation 1-a]

[0021]

[0022] [Equation 1-b]

[0023]

[0024] [Equation 1-c]

[0025]

[0026] [Equation 1-d]

[0027]

[0028] [Equation 1-e]

[0029]

[0030] [Equation 1-f]

[0031]

[0032] [Formula 1-g]

[0033]

[0034] In a specific exemplary embodiment, the imidazole curing accelerator is one or more of the following formulas 2-a to 2-i:

[0035] [Equation 2-a]

[0036]

[0037] [Equation 2-b]

[0038]

[0039] [Equation 2-c]

[0040]

[0041] [Equation 2-d]

[0042]

[0043] [Equation 2-e]

[0044]

[0045] [Equation 2-f]

[0046]

[0047] [Equation 2-g]

[0048]

[0049] [Equation 2-h]

[0050]

[0051] [Formula 2-i]

[0052]

[0053] In a specific exemplary embodiment, the curing accelerator is represented by the following formula 3-a:

[0054] [Equation 3-a]

[0055]

[0056] In a specific exemplary embodiment, the thiadiazole curing accelerator is one or more of the following formulas 4-a to 4-b:

[0057] [Equation 4-a]

[0058]

[0059] [Equation 4-b]

[0060]

[0061] In a specific exemplary embodiment, the pyrrole-based curing accelerator is one or more of the following formulas 5-a to 5-c:

[0062] [Equation 5-a]

[0063]

[0064] [Equation 5-b]

[0065]

[0066] [Equation 5-c]

[0067]

[0068] In an exemplary embodiment, the content of the curing accelerator is in the range of 0.01 parts by weight to 10 parts by weight based on a total of 100 parts by weight of the gel polymer electrolyte composition.

[0069] In addition, the present invention provides a method for manufacturing a lithium secondary battery by applying the above-described gel polymer electrolyte composition. In an exemplary embodiment, the method for manufacturing a lithium secondary battery according to the present invention includes: injecting the above-described gel polymer electrolyte composition into a battery casing while an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode is stored in a battery casing.

[0070] In an exemplary embodiment, the method of manufacturing the lithium secondary battery further includes performing thermal crosslinking in the range of 10 to 50 minutes after injecting the gel polymer electrolyte composition into the battery casing.

[0071] In a specific exemplary embodiment, thermal crosslinking is performed within a temperature range of 55°C to 80°C.

[0072] In another specific exemplary embodiment, the manufacturing method according to the invention further includes: waiting 1 minute to 30 hours for wetting between injecting the gel polymer electrolyte composition into the battery casing and performing thermal crosslinking.

[0073] In another specific exemplary embodiment, the manufacturing method according to the invention further includes either or more of activation and degassing after performing thermal crosslinking.

[0074] In addition, the present invention provides a secondary battery manufactured by the above method. In an exemplary embodiment, the lithium secondary battery according to the present invention includes: an electrode assembly comprising a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; a battery casing housing and sealing the electrode assembly; and the gel polymer electrolyte composition injected therein into the battery casing housing the electrode assembly. The gel polymer electrolyte composition is as described above.

[0075] In a specific exemplary embodiment, the lithium secondary battery is a pouch battery.

[0076] Beneficial effects

[0077] This invention can increase the efficiency of the manufacturing process of secondary batteries using thermally crosslinkable gel polymer electrolytes and improve the quality of the manufactured products. Attached Figure Description

[0078] Figure 1 This is a schematic diagram illustrating a leakage evaluation process for a pouch-type secondary battery according to an exemplary embodiment of the present invention. Detailed Implementation

[0079] The invention will be described in detail below. Prior to this, the terms or words used in this specification and claims should not be construed as limited to their common or dictionary meanings, but rather should be interpreted as meanings and concepts consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concepts of the terms in order to best interpret his / her invention.

[0080] This invention provides a gel polymer electrolyte composition. In an exemplary embodiment, the gel polymer electrolyte composition according to the invention comprises: an oligomer represented by Formula 1; a curing accelerator as a monocyclic or polycyclic amine compound; a polymerization initiator; a non-aqueous solvent; and a lithium salt.

[0081] In this invention, "single ring" includes the case in which a single ring structure is included in the structural formula. "Multi-ring" refers to the case in which two or more, specifically two to four ring structures are included in the structural formula, and the two or more ring structures include the case in which they are fused or combined with each other.

[0082] In this invention, the gelation rate of the electrolyte is significantly increased by adding a curing accelerator that promotes the crosslinking reaction of the oligomers.

[0083] As an example, the oligomer can be a polypropylene carbonate (PPC) type oligomer. In an exemplary embodiment, the oligomer is represented by the following formula 1.

[0084] [Formula 1]

[0085]

[0086] In Formula 1, R is an alkyl group having 1 to 5 carbons substituted with an alkyl group having 1 to 5 carbons, and m is an integer from 1 to 50.

[0087] Specifically, R is an alkyl group having 1 to 3 carbons, or more specifically, a methyl-substituted alkyl group having 2 carbons. m is an integer from 1 to 10, an integer from 2 to 5, an integer from 2 to 3, or 2.

[0088] In an exemplary embodiment of the invention, the oligomer content ranges from 0.1 parts by weight to 30 parts by weight based on a total of 100 parts by weight of the gel polymer electrolyte composition. More specifically, the oligomer content ranges from 1 part by weight to 10 parts by weight, 2 parts by weight to 8 parts by weight, or 3 parts by weight to 5 parts by weight. When applied to a secondary battery, the oligomer content is within a range that does not degrade the performance of the secondary battery while preventing electrolyte leakage.

[0089] The gel polymer electrolyte composition may have different curing temperatures depending on the type of polymerization initiator. In an exemplary embodiment, the gel polymer electrolyte composition undergoes a crosslinking reaction under heat treatment conditions of 55°C to 80°C, 60°C to 75°C, or 68°C to 75°C, and in this case, the curing time is in the range of 10 minutes to 50 minutes, 10 minutes to 40 minutes, or 20 minutes to 40 minutes. In the gel polymer electrolyte composition, by using a curing accelerator, the curing time is reduced by 25% or more compared to the curing time of the prior art.

[0090] In an exemplary embodiment, the curing accelerator includes one or more of pyrimidine, imidazole, purine, thiadiazole, and pyrrole curing accelerators. The invention includes cases involving mixtures of one, two, or more of these curing accelerators.

[0091] In a specific exemplary embodiment, the pyrimidine-based curing accelerator is one or more of the following formulas 1-a to 1-g:

[0092] [Equation 1-a]

[0093]

[0094] [Equation 1-b]

[0095]

[0096] [Equation 1-c]

[0097]

[0098] [Equation 1-d]

[0099]

[0100] [Equation 1-e]

[0101]

[0102] [Equation 1-f]

[0103]

[0104] [Formula 1-g]

[0105]

[0106] In a specific exemplary embodiment, the imidazole curing accelerator is one or more of the following formulas 2-a to 2-i:

[0107] [Equation 2-a]

[0108]

[0109] [Equation 2-b]

[0110]

[0111] [Equation 2-c]

[0112]

[0113] [Equation 2-d]

[0114]

[0115] [Equation 2-e]

[0116]

[0117] [Equation 2-f]

[0118]

[0119] [Equation 2-g]

[0120]

[0121] [Equation 2-h]

[0122]

[0123] [Formula 2-i]

[0124]

[0125] In a specific exemplary embodiment, the curing accelerator is represented by the following formula 3-a:

[0126] [Equation 3-a]

[0127]

[0128] In a specific exemplary embodiment, the thiadiazole curing accelerator is one or more of the following formulas 4-a to 4-b:

[0129] [Equation 4-a]

[0130]

[0131] [Equation 4-b]

[0132]

[0133] In a specific exemplary embodiment, the pyrrole-based curing accelerator is one or more of the following formulas 5-a to 5-c:

[0134] [Equation 5-a]

[0135]

[0136] [Equation 5-b]

[0137]

[0138] [Equation 5-c]

[0139]

[0140] In this invention, the content of the curing accelerator is in the range of 0.01 parts by weight to 10 parts by weight based on a total of 100 parts by weight of the gel polymer electrolyte composition. Specifically, the content of the curing accelerator is in the range of 0.1 parts by weight to 10 parts by weight, 0.01 parts by weight to 5 parts by weight, 0.2 parts by weight to 5 parts by weight, or 0.5 parts by weight to 2 parts by weight. These curing accelerator contents are within a range that can sufficiently reduce the curing rate while minimizing the input amount.

[0141] In addition, the present invention provides a method for manufacturing a lithium secondary battery using the above-described gel polymer electrolyte composition. In an exemplary embodiment, the method for manufacturing a lithium secondary battery according to the present invention includes injecting the gel polymer electrolyte composition into a battery casing while an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode is stored in a battery casing.

[0142] In this invention, a secondary battery is manufactured by injecting the aforementioned gel polymer electrolyte composition into a battery casing in which electrode components are housed. Then, gelation of the gel polymer electrolyte composition is performed by heat treatment. Specifically, this invention includes performing thermal crosslinking within a range of 10 to 50 minutes after injecting the gel polymer electrolyte composition into the battery casing. This thermal crosslinking is performed as a curing process by inducing a crosslinking reaction in the injected gel polymer electrolyte. The curing time is in the range of 10 to 50 minutes, 10 to 40 minutes, or 20 to 40 minutes. This invention has the effect of reducing the curing time by 25% or more compared to the curing time of the prior art.

[0143] In addition, the heat treatment temperature during thermal crosslinking can vary depending on the type of polymerization initiator introduced. In this invention, for example, a curing accelerator represented by Formula 2 above can be used. In this case, thermal crosslinking can be performed within a temperature range of 55°C to 80°C, 60°C to 75°C, or 68°C to 75°C.

[0144] In another exemplary embodiment, the invention includes wetting for 1 minute to 30 hours between injecting the gel polymer electrolyte composition into the battery casing and performing thermal crosslinking.

[0145] In another exemplary embodiment, the invention includes one or more of activation and degassing following thermal crosslinking.

[0146] In addition, the present invention provides a secondary battery manufactured by the above-described manufacturing method. In an exemplary embodiment, the secondary battery according to the present invention includes: an electrode assembly comprising a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; a battery casing housing and sealing the electrode assembly; and a gel polymer electrolyte composition injected into the battery casing housing the electrode assembly therein. The gel polymer electrolyte composition is as described above.

[0147] Depending on the method of stacking the electrode assemblies, the electrode assemblies can be classified as jelly roll type, which is a roll-shaped assembly, and stack type, which involves sequentially stacking the electrode assemblies. Furthermore, depending on the shape of the battery casing, the secondary battery can be classified as a cylindrical battery or a prismatic battery in which the electrode assemblies are embedded in a cylindrical or prismatic metal can, and a pouch battery in which the electrode assemblies are embedded in a pouch-shaped casing with aluminum laminates. The secondary battery of the present invention can be a cylindrical, prismatic, or pouch-shaped secondary battery, preferably a pouch-shaped secondary battery.

[0148] Meanwhile, the housing can be made of a laminate comprising a metal layer and a resin layer. Specifically, the laminate can be an aluminum laminate. The laminated battery housing can consist of a lower housing and an upper housing, the lower housing comprising a recessed portion having a recessed structure and an exterior extending from the recessed portion, the upper housing being thermally coupled to the lower housing.

[0149] The components of the secondary battery of the present invention will be described below.

[0150] The positive electrode, as one of the components of a secondary battery, has a structure in which a layer of positive electrode mixture is stacked on one or both surfaces of the positive electrode current collector. In one example, the positive electrode active material layer includes a positive electrode active material, a conductor, a binder polymer, and the like, and may further include, if necessary, positive electrode additives commonly used in the art.

[0151] The positive electrode active material can be a lithium-containing oxide, and can be the same or different. As a lithium-containing oxide, a lithium-containing transition metal oxide can be used.

[0152] For example, lithium-containing transition metal oxides can be selected from 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 Mn c)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, O≤y<1), Li x (Ni a Co b Mn c )O4(0.5<x<1.3, 0<a<2, 0<b<2, 0<c<2, a+b+c=2), Li x Mn 2-z Ni z O4(0.5<x<1.3, 0<z<2), Li x Mn 2-z Co z O4(0.5<x<1.3, 0<z<2), Li x CoPO4 (0.5 < x < 1.3), and Li x The group consisting of FePO4 (0.5 < x < 1.3) may include one or a mixture of two or more of these compounds. In addition, lithium-containing transition metal oxides may be coated with metals or metal oxides such as aluminum (Al). Furthermore, besides lithium-containing transition metal oxides, one or more of sulfides, selenides, and halides may be used.

[0153] The positive electrode active material can be included in the positive electrode active material layer in the range of 94.0% to 98.5% by weight. When the content of the positive electrode active material meets the above range, it is advantageous for manufacturing high-capacity batteries and providing sufficient positive electrode conductivity or adhesion between electrode materials.

[0154] The current collector used in the positive electrode is a highly conductive metal that can be readily attached to the positive electrode active material, and can be any metal that is unreactive within the voltage range of the electrochemical device. Specifically, non-limiting examples of the current collector for the positive electrode include foils made of aluminum, nickel, or combinations thereof. The positive electrode active material layer further includes a conductor.

[0155] Carbon-based conductors are widely used as conductors, and they include sphere-type or needle-type carbon-based conductive materials. In a mixed state with a binder, the sphere-type carbon-based conductors fill the pores between the active material particles to improve the physical contact between the active materials, thereby reducing the interfacial resistance and improving the adhesion between the lower positive electrode active material and the current collector.

[0156] The conductor can be included in the positive electrode active material layer in an amount from 0.5% to 5% by weight. When the conductor content meets the above range, it has the effect of providing sufficient positive electrode conductivity and reducing the interfacial resistance between the electrode current collector and the active material.

[0157] As the adhesive polymer, adhesives commonly used in the art can be used without limitation. For example, the adhesive can 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 can be one or more selected from the group consisting of polyvinylidene fluoride (PVDF), polyvinylidene chloride (PVDC), polyacrylonitrile (PAN), polypropylene oxide (PPO), ethylene oxide-propylene oxide copolymer (PEO-PPO), polytetrafluoroethylene (PTFE), polyimide (PI), polyetherimide (PEI), styrene-butadiene rubber (SBR), polyacrylates, and derivatives thereof.

[0158] The water-soluble polymer may be one or more of a group of various cellulose derivatives, including carboxymethyl cellulose (CMC), methyl cellulose (MC), cellulose acetate phthalate (CAP), hydroxypropyl methyl cellulose (HPMC), and hydroxypropyl methyl cellulose phthalate (HPMCP).

[0159] The amount of binder polymer is directly proportional to the amount of conductors included in the upper and lower positive electrode active material layers. This is to provide adhesion to the conductors, which have a relatively very small particle size compared to the active materials. Furthermore, this is because more binder polymer is required when the conductor content increases, while less binder polymer can be used when the conductor content decreases.

[0160] The negative electrode has a structure in which a layer of negative electrode active material is stacked on one or both surfaces of the negative electrode current collector. In one example, the layer of negative electrode active material includes a negative electrode active material, a conductor, a binder polymer, and the like, and may further include, if necessary, negative electrode additives commonly used in the art.

[0161] Negative electrode active materials can include carbon materials, lithium metal, silicon, or tin. When carbon materials are used as negative electrode active materials, both low-crystallinity carbon and high-crystallinity carbon can be used. Low-crystallinity carbon typically includes soft carbon and hard carbon, while high-crystallinity carbon typically includes high-temperature calcined carbon, such as natural graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesophase carbon microbeads, mesophase pitch, and petroleum orcoal tarp-derived cokes.

[0162] Non-limiting examples of current collectors for the negative electrode include foils made of copper, gold, nickel, or copper alloys or combinations thereof. Alternatively, current collectors can be used by stacking substrates made of the above materials.

[0163] In addition, the negative electrode may include conductors and adhesives commonly used in the art.

[0164] The separator can be any porous substrate used in lithium secondary batteries, and for example, a polyolefin-based porous membrane or a non-woven fabric can be used, but it is not particularly limited to this.

[0165] Examples of polyolefin-based porous membranes include polyethylene such as high-density polyethylene, linear low-density polyethylene, low-density polyethylene, and ultra-high molecular weight polyethylene, and membranes formed from polyolefin-based polymers such as polypropylene, polybutene, and polypentene, either alone or in combination with these polymers.

[0166] Besides polyolefin-based nonwoven fabrics, nonwoven fabrics include, for example, nonwoven fabrics formed from polymers such as polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, polyethylene naphthalene, or similar polymers, alone or in mixtures thereof. The structure of nonwoven fabrics can be spunbond nonwoven fabrics composed of long fibers or meltblown nonwoven fabrics.

[0167] There are no particular limitations on the thickness of the porous substrate, but it can be from 5 μm to 50 μm. There are also no particular limitations on the pore size and porosity present in the porous substrate, but they can be from 0.01 μm to 50 μm and 10% to 95%, respectively.

[0168] Meanwhile, in order to improve the mechanical strength of the separator made of porous substrate and suppress short circuits between the positive and negative electrodes, a porous coating including inorganic particles and binder polymers may be further included on at least one surface of the porous substrate.

[0169] The electrolyte may include an organic solvent and an electrolyte salt, wherein the electrolyte salt is a lithium salt. As a lithium salt, those commonly used in non-aqueous electrolytes for lithium secondary batteries can be used without limitation. For example, those containing Li... + As a cation, and containing F selected from - Cl - ,Br - I - NO3 - N(CN)2 - BF4 - ClO4 - AlO4 - AlCl4 - PF6 - SbF6 - AsF6 - BF2C2O4 - BC4O8 - (CF3)2PF4 - (CF3)3PF3- (CF3)4PF2 - (CF3)5PF - (CF3)6P-, CF3SO3 - C4F9SO3 - CF3CF2SO3 - (CF3SO2)2N - (FSO2)2N - CF3CF2(CF3)2CO - , (CF3SO2)2CH-, (SF5)3C-, (CF3SO2)3C-, CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - One or more of the group consisting of SCN- and (CF3CF2SO2)2 are used as anions.

[0170] As organic solvents included in the aforementioned electrolytes, those commonly used in secondary battery electrolytes may be used without limitation, and for example, ethers, esters, amides, straight-chain carbonates, cyclic carbonates, etc., may be used alone or in combination of two or more. Among them, cyclic carbonates, straight-chain carbonates, or carbonate compounds as mixtures of these may be typically included.

[0171] Specific examples of cyclic carbonate compounds may be one or a mixture of two or more of the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butenyl carbonate, 2,3-butenyl carbonate, 1,2-pentenyl carbonate, 2,3-pentenyl carbonate, vinylene carbonate, vinyl ethylene carbonate, and their halides. Examples of these halides include, for example, fluoroethylene carbonate (FEC), but are not limited thereto.

[0172] In addition, specific examples of linear carbonate compounds may be selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, methyl ethyl carbonate (EMC), methyl propyl carbonate, and ethyl propyl carbonate, or mixtures of two or more of them may be used, but are not limited thereto.

[0173] In particular, among carbonate-based organic solvents, ethylene carbonate and propylene carbonate, as cyclic carbonates, are high-viscosity organic solvents with high dielectric constants, allowing for better dissociation of lithium salts in electrolytes. Furthermore, when low-viscosity, low-dielectric-constant linear carbonates such as dimethyl carbonate and diethyl carbonate are mixed in appropriate proportions with these cyclic carbonates, electrolytes with higher conductivity can be produced.

[0174] In addition, the ether used as an organic solvent may be any one of 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 them, but is not limited thereto.

[0175] In addition, as an organic solvent, the ester includes, but is not limited to, any one of the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, α-valerolactone, and β-caprolactone, or a mixture of two or more of them.

[0176] The electrode assembly can be a laminated / stacked structure in which the cell units are stacked with spacers inserted therebetween, or a stacked / folded structure in which the cell units are wound with spacers.

[0177] In the electrode assembly, electrode active materials are applied to the positive and negative current collectors to form a mixed layer. Then, the positive and negative electrodes, in which pinholes are formed on the electrode contacts and electrode plates, are manufactured using a notching device, and the positive and negative electrodes are manufactured by bonding them to a separator that does not contain pinholes. There are no restrictions on the type of separator, but it can be an organic / inorganic composite porous safety-reinforcing separator (SRS).

[0178] Specifically, the SRS separator is manufactured by using inorganic particles and binder polymers as active layer components on a polyolefin-based separator substrate. It features a porous structure and a uniform porous structure formed by the interstitial volume between the inorganic particles that form the active layer. Using this organic / inorganic composite porous separator offers the advantage of suppressing the increase in battery thickness caused by swelling during the formation process, compared to conventional separators. When using a polymer capable of gelling during liquid electrolyte impregnation as the binder polymer component, it can also be used as the electrolyte. Furthermore, since the organic / inorganic composite porous separator exhibits excellent adhesion properties by adjusting the content of inorganic particles and binder polymers as active layer components in the separator, battery assembly processes can be easily performed.

[0179] Invention Implementation Form

[0180] The invention will be described in more detail below by way of examples and the like. Since the invention can have various modifications and forms, specific embodiments are illustrated and described in detail in the text. However, it should be understood that this is not intended to limit the invention to the specific forms disclosed, but rather to include all modifications, equivalents, and alternatives included within the spirit and scope of the invention.

[0181] Example 1

[0182] LiPF6, as a lithium salt, was dissolved at a concentration of 1 M in a solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 3:7, and a gel polymer electrolyte composition was prepared by adding additives according to the contents of each additive based on the total weight of the gel polymer electrolyte as shown in Table 1 below.

[0183] Specifically, the oligomer is added in an amount of 4% by weight, and the oligomer has the structural formula in Formula 1, where R is a methyl-substituted alkyl group having 2 carbon atoms, and m is an integer in the range of 2 to 3.

[0184] The curing accelerator is added in an amount of 1% by weight, and the structural formula of the curing accelerator is shown in the following formula 1-c.

[0185] [Equation 1-c]

[0186]

[0187] As a polymerization initiator, the azo initiator V-59 product manufactured by FUJIFILM WAKO Co. is used as a thermal initiator at a rate of 1% by weight.

[0188] LiNi with a particle size of 5 μm was prepared as a positive electrode active material. 0.5 Mn 1.5 O4 was mixed with a carbon-based conductor and polyvinylidene fluoride as a binder in N-methylpyrrolidone (NMP) at a weight ratio of 94:3:3 to form a slurry. The slurry was cast onto a thin aluminum plate, dried in a vacuum oven at 120°C, and then rolled to prepare the positive electrode.

[0189] Separately, a negative electrode active material in which artificial graphite and silicon oxide (SiO2) are mixed in a weight ratio of 9:1 is prepared, and 97 parts by weight of the negative electrode active material and 3 parts by weight of styrene-butadiene rubber (SBR) are mixed in water to form a slurry. The slurry is cast onto a thin copper plate, dried in a vacuum oven at 130°C, and then rolled to prepare the negative electrode.

[0190] A separator made of 18 μm polypropylene was inserted between the positive and negative electrodes obtained above, inserted into the casing, and then the prepared gel polymer electrolyte composition was injected. A pouch-type lithium secondary battery was then prepared by curing at 65°C for 30 minutes.

[0191] Examples 2-6

[0192] The curing accelerator was added in an amount of 1% by weight, and the gel polymer electrolyte composition was prepared in the same manner as in Example 1, except that the following formulas 2-e, 2-i, 3-a, 4-b and 5-c were applied to the structural formula of the curing accelerator, respectively.

[0193] [Equation 2-e]

[0194]

[0195] [Formula 2-i]

[0196]

[0197] [Equation 3-a]

[0198]

[0199] [Equation 4-b]

[0200]

[0201] [Equation 5-c]

[0202]

[0203] The prepared gel polymer electrolyte composition was used to prepare a lithium secondary battery in the same manner as in Example 1.

[0204] Comparative Example 1

[0205] The electrolyte composition was prepared by dissolving LiPF6, as a lithium salt, at a concentration of 1 M in a solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 3:7.

[0206] LiNi with a particle size of 5 μm was prepared as a positive electrode active material. 0.5 Mn 1.5 O4 was mixed with a carbon-based conductor and polyvinylidene fluoride as a binder in N-methylpyrrolidone (NMP) at a weight ratio of 94:3:3 to form a slurry. The slurry was cast onto a thin aluminum plate, dried in a vacuum oven at 120°C, and then rolled to prepare the positive electrode.

[0207] Separately, a negative electrode active material in which artificial graphite and silicon oxide (SiO2) are mixed in a weight ratio of 9:1 is prepared, and 97 parts by weight of the negative electrode active material and 3 parts by weight of styrene-butadiene rubber (SBR) are mixed in water to form a slurry. The slurry is cast onto a thin copper plate, dried in a vacuum oven at 130°C, and then rolled to prepare the negative electrode.

[0208] A pouch-type lithium secondary battery was prepared by inserting a separator made of 18 μm polypropylene onto the obtained positive and negative electrodes, inserting it into a casing, and then injecting the prepared electrolyte composition.

[0209] Comparative Example 2

[0210] LiPF6, as a lithium salt, was dissolved at a concentration of 1 M in a solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 3:7, and a gel polymer electrolyte composition was prepared by adding additives according to the contents of each additive based on the total weight of the gel polymer electrolyte as shown in Table 1 below.

[0211] The prepared gel polymer electrolyte composition was used to prepare a lithium secondary battery in the same manner as in Example 1, but the curing time was set to 30 minutes.

[0212] Comparative Example 3

[0213] LiPF6, as a lithium salt, was dissolved at a concentration of 1 M in a solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 3:7, and a gel polymer electrolyte composition was prepared by adding additives according to the contents of each additive based on the total weight of the gel polymer electrolyte as shown in Table 1 below.

[0214] The prepared gel polymer electrolyte composition was used to prepare a lithium secondary battery in the same manner as in Example 1, but the curing time was set to 100 minutes.

[0215] Comparative Example 4

[0216] LiPF6, as a lithium salt, was dissolved at a concentration of 1 M in a solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 3:7, and a gel polymer electrolyte composition was prepared by adding additives according to the contents of each additive based on the total weight of the gel polymer electrolyte as shown in Table 1 below.

[0217] The prepared gel polymer electrolyte composition was used to prepare a lithium secondary battery in the same manner as in Example 1, but the curing time was set to 300 minutes.

[0218] [Table 1]

[0219]

[0220]

[0221] Experimental example: Evaluation of leakage

[0222] Electrolyte leakage was evaluated for each secondary battery manufactured in Examples 1 to 4 and Comparative Examples 1 to 3. Each secondary battery was a large-size 100Ah battery.

[0223] The evaluation process is shown in Figure 1 (See also:) Figure 1 Each pouch-type secondary battery 100 is a large-size battery cell in the 100Ah class. The pouch-type secondary battery 100 has a structure in which electrode assemblies are housed within a pouch-type casing. Based on the pouch-type casing, a sealing region 120 is formed by heat-sealing the four surfaces surrounding the electrode assembly housing 110, and electrode terminals 130 are pulled out on both sides. One side of the lower end of each pouch-type secondary battery 100 is cut by up to d (d = 25 cm), and the battery is stored at room temperature for one week while tilted at an angle θ (θ = 5°). The electrolyte leakage of each pouch-type secondary battery 100 is then measured.

[0224] An electrolyte leak is confirmed when the volume decreases by 3% or more compared to the initial injection volume. The evaluation results are shown in Table 2 below.

[0225] [Table 2]

[0226] Example 1 X Example 2 X Example 3 X Example 4 X Example 5 X Example 6 X Comparative Example 1 O Comparative Example 2 O Comparative Example 3 O Comparative Example 4 X

[0227] Referring to Table 2, in Examples 1 to 6, no electrolyte leakage was observed even at a curing time of 30 minutes. In contrast, in Comparative Example 1, gelation of the electrolyte was not achieved, and leakage was therefore observed. Referring to Comparative Examples 2 and 3, it can be seen that electrolyte leakage was observed at curing times of 30 minutes or 100 minutes without the addition of the curing accelerator according to the invention. Referring to Comparative Example 4, it can be seen that no leakage was observed at a curing time of 300 minutes without the addition of the curing accelerator.

[0228] [Figure Labels]

[0229] 100: Pouch-type secondary battery

[0230] 110: Electrode assembly housing

[0231] 120: Sealed area

[0232] 130: Electrode terminal

Claims

1. A gel polymer electrolyte composition, comprising: Oligomers represented by the following formula 1; As a curing accelerator for monocyclic or polycyclic amine compounds; Polymerization initiator; Non-aqueous solvents; and Lithium salts; [Formula 1] In Equation 1, R is an alkyl group having 1 to 5 carbons substituted with an alkyl group, and m is an integer from 1 to 50.

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°C to 80°C.

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

4. The gel polymer electrolyte composition according to claim 1, wherein the curing accelerator comprises one or more of pyrimidine, imidazole, purine, thiadiazole, and pyrrole curing accelerators.

5. The gel polymer electrolyte composition according to claim 4, wherein... In the curing accelerator, the pyrimidine curing accelerator is one or more of the following formulas 1-a to 1-g: [Equation 1-a] [Equation 1-b] [Equation 1-c] [Equation 1-d] [Equation 1-e] [Equation 1-f] [Formula 1-g] 6. The gel polymer electrolyte composition according to claim 4, wherein the imidazole curing accelerator is one or more of formulas 2-a to 2-i: [Equation 2-a] [Equation 2-b] [Equation 2-c] [Equation 2-d] [Equation 2-e] [Equation 2-f] [Equation 2-g] [Equation 2-h] [Formula 2-i] 7. The gel polymer electrolyte composition according to claim 4, wherein the purine-based curing accelerator in the curing accelerator is represented by the following formula 3-a: [Equation 3-a] 8. The gel polymer electrolyte composition according to claim 4, wherein the thiadiazole curing accelerator is one or more of formulas 4-a to 4-b: [Equation 4-a] [Equation 4-b] 9. The gel polymer electrolyte composition according to claim 4, wherein the pyrrole-based curing accelerator is one or more of formulas 5-a to 5-c: [Equation 5-a] [Equation 5-b] [Equation 5-c] 10. The gel polymer electrolyte composition according to claim 1, wherein the content of the curing accelerator is in the range of 0.01 parts by weight to 10 parts by weight based on a total of 100 parts by weight of the gel polymer electrolyte composition.

11. A method for manufacturing a lithium secondary battery, comprising: The gel polymer electrolyte composition according to claim 1 is injected into the battery housing while the electrode assembly, including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, is stored in the battery housing.

12. The method for manufacturing a lithium secondary battery according to claim 11, further comprising: Thermal crosslinking is performed within a range of 10 to 50 minutes after the gel polymer electrolyte composition is injected into the battery casing.

13. The method for manufacturing a lithium secondary battery according to claim 12, wherein the thermal crosslinking is performed within a temperature range of 55°C to 80°C.

14. A lithium secondary battery, comprising: An electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; A battery casing that houses and seals the electrode assembly; and The gel polymer electrolyte composition according to claim 1 is injected into a battery casing in which the electrode assembly is housed.

15. The lithium secondary battery according to claim 14, wherein the lithium secondary battery is a pouch cell.

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