Secondary battery containing gel polymer electrolyte and method for manufacturing the same

Abstract

The present invention relates to a method for manufacturing a secondary battery, the method comprising the steps of: (S1) preparing a first gel polymer electrolyte composition containing a first oligomer and a second gel polymer electrolyte composition containing a second oligomer; (S2) injecting the first gel polymer electrolyte composition into a battery case containing an electrode assembly to impregnate the inside of the electrode assembly with the first gel polymer electrolyte composition; (S3) injecting the second gel polymer electrolyte composition into the battery case; and (S4) curing the first gel polymer electrolyte composition and the second gel polymer electrolyte composition injected into the battery case, wherein the content of the first oligomer in the first gel polymer electrolyte composition is lower than the content of the second oligomer in the second gel polymer electrolyte composition.

Description

[Technical Field]

[0001] This application claims the benefit of the filing date of Korean Patent Application No. 10-2021-0132112, filed with the Korean Intellectual Property Office on October 6, 2021, the entire contents of which are incorporated herein by reference. The present invention relates to a secondary battery containing a gel polymer electrolyte and a method for producing the same. [Background technology]

[0002] As technological development and demand for electronic devices increases, the demand for secondary batteries as energy sources is rapidly increasing. Among such secondary batteries, lithium secondary batteries, which have high energy density and voltage, have been commercialized and are widely used.

[0003] Conventionally, liquid electrolytes, particularly ion-conductive organic liquid electrolytes in which a salt is dissolved in a non-aqueous organic solvent, have been mainly used as electrolytes for lithium secondary batteries. However, such liquid electrolytes have the disadvantages of low stability due to the high possibility of the organic solvent volatilizing and the risk of combustion caused by an increase in the ambient temperature or the temperature of the battery itself.

[0004] Therefore, in recent years, research has been conducted to commercialize polymer electrolytes such as gel polymer electrolytes instead of liquid electrolytes. The gel polymer electrolyte has superior electrochemical stability compared to liquid electrolytes, and therefore, not only can the thickness of the battery be maintained constant, but also the inherent adhesive strength of the gel allows the production of a thin-film battery with excellent stability.

[0005] Batteries using such gel polymer electrolytes are manufactured by mixing a polymerizable monomer or oligomer and a polymerization initiator with a liquid electrolyte solution in which a salt is dissolved in a non-aqueous organic solvent to prepare a composition, and then injecting the composition into a battery containing an electrode assembly in which a positive electrode, a negative electrode, and a separator are wound or stacked, and gelling (crosslinking) the composition under appropriate temperature and time conditions.

[0006] Meanwhile, gel polymer electrolytes with a high degree of hardness have been researched to prevent electrolyte leakage even if the lithium secondary battery is damaged and to increase safety. However, when the degree of hardness of the gel polymer electrolyte is increased, there are problems in that the interfacial resistance increases and the ionic conductivity decreases, resulting in a decrease in the battery performance of the lithium secondary battery. Therefore, there is a need to develop a secondary battery that uses a gel polymer electrolyte, which improves both the stability and performance of the battery. Summary of the Invention [Problem to be solved by the invention]

[0007] One object of the present invention is to solve the above problems and to provide a method for manufacturing a secondary battery using a first gel polymer electrolyte composition and a second gel polymer electrolyte composition having different oligomer contents.

[0008] Another object of the present invention is to provide a secondary battery that can improve the electrochemical performance of the secondary battery, improve rigidity, and prevent electrolyte leakage by disposing a first gel polymer electrolyte and a second gel polymer electrolyte, which have different interfacial resistances, at specific positions in the secondary battery. [Means for solving the problem]

[0009] The present invention provides a method for manufacturing a secondary battery, the method comprising the steps of: (S1) preparing a first gel polymer electrolyte composition containing a first oligomer and a second gel polymer electrolyte composition containing a second oligomer; (S2) injecting the first gel polymer electrolyte composition into a battery case containing an electrode assembly to impregnate the inside of the electrode assembly with the first gel polymer electrolyte composition; (S3) injecting the second gel polymer electrolyte composition into the battery case; and (S4) curing the first gel polymer electrolyte composition and the second gel polymer electrolyte composition, wherein the content of the first oligomer in the first gel polymer electrolyte composition is lower than the content of the second oligomer in the second gel polymer electrolyte composition.

[0010] The present invention also provides a secondary battery including an electrode assembly in which a positive electrode, a separator, and a negative electrode are alternately arranged, a battery case that houses the electrode assembly, and an electrolyte, wherein the electrolyte includes a first gel polymer electrolyte disposed inside the electrode assembly and a second gel polymer electrolyte disposed outside the electrode assembly, and the interface resistance of the first gel polymer electrolyte is lower than the interface resistance of the second gel polymer electrolyte. [Effects of the Invention]

[0011] A method for manufacturing a secondary battery according to the present invention is characterized in that a first gel polymer electrolyte composition having a low oligomer content is first injected and a second gel polymer electrolyte composition is subsequently injected, so that the gel polymer electrolyte formed from the first gel polymer electrolyte composition is impregnated into the inside of an electrode assembly and the gel polymer electrolyte formed from the second gel polymer electrolyte composition is disposed outside the electrode assembly. As a result, the secondary battery manufactured by this manufacturing method can improve both interfacial resistance and rigidity by forming a gel polymer electrolyte by hardening the first gel polymer electrolyte composition and the second gel polymer electrolyte composition, which have different oligomer contents, inside and outside the electrode assembly, respectively.

[0012] Furthermore, a secondary battery according to the present invention includes a first gel polymer electrolyte disposed inside an electrode assembly and a second gel polymer electrolyte disposed outside the electrode assembly, wherein the first gel polymer electrolyte has a lower interfacial resistance than the second gel polymer electrolyte. Because the first gel polymer electrolyte has a relatively low interfacial resistance, it can improve lithium mobility between the positive electrode and the negative electrode when impregnated inside the electrode assembly. Because the second gel polymer electrolyte has a relatively high interfacial resistance but high rigidity, it can effectively protect the electrode assembly from external impacts and prevent electrolyte leakage when disposed outside the electrode assembly. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 3 is a schematic diagram illustrating step (S2) of the method for producing a secondary battery according to the present invention. [Figure 2] FIG. 3 is a schematic diagram illustrating step (S2) of the method for producing a secondary battery according to the present invention. [Figure 3] FIG. 3 is a schematic diagram illustrating step (S3) of the method for producing a secondary battery according to the present invention. [Figure 4] FIG. 4 is a schematic diagram illustrating step (S4) of the method for producing a secondary battery according to the present invention. [Figure 5] 1 is a schematic plan view of a secondary battery according to the present invention; [Figure 6] 1 is a schematic side view of a secondary battery according to the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0014] The terms and words used in this specification and claims should not be interpreted in a limited way to their ordinary or dictionary meanings, but should be interpreted in a way that is consistent with the technical idea of ​​the present invention, based on the principle that the inventors can appropriately define the concepts of terms in order to best explain their inventions.

[0015] Hereinafter, a method for manufacturing a secondary battery and a secondary battery according to the present invention will be described in detail with reference to the drawings. When assigning reference numerals to components in each drawing, the same reference numerals are assigned to identical components in other drawings whenever possible. Furthermore, when describing the present invention, if it is determined that a detailed description of related well-known configurations or functions may unnecessarily obscure the gist of the present invention, such detailed description will be omitted.

[0016] Secondary battery manufacturing method The method for producing a secondary battery according to the present invention includes the steps of: (S1) preparing a first gel polymer electrolyte composition comprising a first oligomer and a second gel polymer electrolyte composition comprising a second oligomer; (S2) injecting the first gel polymer electrolyte composition into a battery case containing an electrode assembly to impregnate the inside of the electrode assembly with the first gel polymer electrolyte composition; (S3) injecting a second gel polymer electrolyte composition into the battery case; (S4) curing the first gel polymer electrolyte composition and the second gel polymer electrolyte composition injected into the battery case, The first gel polymer electrolyte composition is characterized in that the content of the first oligomer in the first gel polymer electrolyte composition is lower than the content of the second oligomer in the second gel polymer electrolyte composition.

[0017] (1) Step (S1) of Preparing a First Gel Polymer Electrolyte Composition and a Second Gel Polymer Electrolyte Composition First, a first gel polymer electrolyte composition containing a first oligomer and a second gel polymer electrolyte composition containing a second oligomer are prepared (S1).

[0018] The gel polymer electrolyte compositions, such as the first gel polymer electrolyte composition and the second gel polymer electrolyte composition, may be cured by crosslinking oligomers, polymers, etc. contained therein to form a gel-like solidified electrolyte (gel polymer electrolyte).

[0019] The oligomers such as the first oligomer and the second oligomer may refer to compounds in which about 10 or less monomers are polymerized. The content of the first oligomer in the first gel polymer electrolyte composition may be less than the content of the second oligomer in the second gel polymer electrolyte composition.

[0020] The oligomer contained in the gel polymer electrolyte composition can affect the rigidity and interfacial resistance of the gel polymer electrolyte depending on its content. For example, when the oligomer content in the gel polymer electrolyte is high, the rigidity of the gel polymer electrolyte increases, but the interfacial resistance increases and the ionic conductivity decreases. On the other hand, when the oligomer content in the gel polymer electrolyte is low, the interfacial resistance of the gel polymer electrolyte decreases and the ionic conductivity increases, but the rigidity of the gel polymer electrolyte decreases.

[0021] According to the present invention, since the content of the first oligomer in the first gel polymer electrolyte composition is lower than the content of the second oligomer in the second gel polymer electrolyte composition, the first gel polymer electrolyte formed from the first gel polymer electrolyte composition can have lower interfacial resistance than the second gel polymer electrolyte formed from the second gel polymer electrolyte composition. In particular, as described below, the gel polymer electrolyte formed from the first gel polymer electrolyte composition (e.g., the first gel polymer electrolyte) can be impregnated into the inside of an electrode assembly and then cured, thereby reducing the interfacial resistance of the electrode assembly or secondary battery. Meanwhile, the gel polymer electrolyte formed from the second gel polymer electrolyte composition (e.g., the second gel polymer electrolyte) has superior rigidity compared to the gel polymer electrolyte formed from the first gel polymer electrolyte composition. When placed outside the electrode assembly and cured, the gel polymer electrolyte can improve the rigidity of the secondary battery, preventing leakage from the secondary battery and further improving the safety of the secondary battery.

[0022] Specifically, the content of the first oligomer in the first gel polymer electrolyte composition may be 0.5 wt % to 5 wt %, and preferably 1 wt % to 3 wt %, based on the weight of the first gel polymer electrolyte composition. When the content is within this range, the ionic conductivity of the first gel polymer electrolyte can be further improved, thereby further improving the effect of reducing the interfacial resistance when impregnated into the electrode assembly, and facilitating the movement of lithium ions between the positive electrode and the negative electrode in the electrode assembly.

[0023] In addition, the content of the second oligomer in the second gel polymer electrolyte composition may be 5 wt % to 30 wt %, specifically 7 wt % to 10 wt %, based on the weight of the second gel polymer electrolyte composition. When the content is within this range, the effect of improving the rigidity of the second gel polymer electrolyte can be further improved, the viscosity of the second polymer electrolyte composition can be appropriately controlled, and the gel polymer electrolyte formed from the second gel polymer electrolyte composition can be uniformly distributed outside the electrode assembly.

[0024] The first oligomer and the second oligomer may be the same substance or different substances. Specifically, the first oligomer and the second oligomer may each independently include at least one selected from the group consisting of polyether-based oligomers, polycarbonate-based oligomers, acrylate-based oligomers, polysiloxane-based oligomers, phosphazene-based oligomers, polyethylene-based oligomers, urethane-based oligomers, epoxy-based oligomers, fluorine-based oligomers, polyethylene oxide, polyester sulfide, polyvinyl alcohol, and polyvinylidene fluoride.

[0025] Specifically, the first oligomer and the second oligomer may contain units derived from a fluorine-based monomer, and in this case, the fluorine-based functional group contained in the first oligomer or the second oligomer may suppress the generation of oxygen radicals caused by decomposition of the positive electrode active material, thereby further improving the stability of the battery.More specifically, the first oligomer and the second oligomer may each independently include at least one selected from tetrafluoroethylene (TFE)-vinyl acetate copolymer, (allyl 1,1,2,2-tetrafluoroethyl ether)-(2,2,2-trifluoroethyl acrylate) copolymer, tetrafluoroethylene-(2-vinyl-1,3-dioxolane) copolymer, and tetrafluoroethylene-vinyl methacrylate copolymer.

[0026] The first gel polymer electrolyte composition and the second gel polymer electrolyte composition may, independently of each other, further comprise a solvent. The solvent is one that is commonly used in secondary batteries, and may be, for example, ether, ester (acetates, propionates), amide, linear or cyclic carbonate, nitrile (acetonitrile, SN, etc.), etc., which may be used alone or in combination of two or more. Among these, typically, carbonate solvents containing carbonate compounds such as cyclic carbonates, linear carbonates, or mixtures thereof may be used.

[0027] Specific examples of the cyclic carbonate compound include a single compound or a mixture of at least two compounds 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, and halides thereof. Specific examples of the linear carbonate compound include, but are not limited to, a compound or a mixture of at least two compounds selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC).

[0028] In particular, among the carbonate solvents, propylene carbonate and ethylene carbonate, which are cyclic carbonates, are preferred because they are high-viscosity organic solvents with high dielectric constants that effectively dissociate lithium salts in the electrolyte solution. When such cyclic carbonates are mixed with a linear carbonate having low viscosity and low dielectric constant, such as ethyl methyl carbonate, diethyl carbonate, or dimethyl carbonate, in an appropriate ratio, an electrolyte solution having high electrical conductivity can be prepared, and therefore these cyclic carbonates are even more preferred.

[0029] The ester of the solvent may be a single compound or a mixture of at least two compounds selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, α-valerolactone, and ε-caprolactone, but is not limited thereto.

[0030] At least one of the first gel polymer electrolyte composition and the second gel polymer electrolyte composition may contain a lithium salt, which can be used to provide lithium ions to a secondary battery.

[0031] Specifically, either one of the first gel polymer electrolyte composition or the second gel polymer electrolyte composition may contain a lithium salt. For example, either one of the first gel polymer electrolyte composition or the second gel polymer electrolyte composition may contain a lithium salt. Alternatively, both the first gel polymer electrolyte composition and the second gel polymer electrolyte composition may contain a lithium salt.

[0032] The lithium salt may be any compound capable of providing lithium ions used in secondary batteries. Specifically, the lithium salt may be LiPF, LiClO, LiAsF, LiBF, LiSbF, LiAlO, LiAlCl, LiCF, SO, LiCF, SO, LiN(C, F, SO), LiN(C, F, SO), LiN(CF, SO), LiCl, LiI, or LiB(C, O) . The lithium salt concentration is preferably in the range of 0.1 M to 5.0 M, and more preferably 0.1 M to 3.0 M. When the lithium salt concentration is within this range, the electrolyte has suitable conductivity and viscosity, resulting in excellent electrolyte performance and efficient lithium ion migration.

[0033] At least one of the first gel polymer electrolyte composition and the second gel polymer electrolyte composition may include a polymerization initiator that can be used to polymerize the first oligomer and / or the second oligomer to form a polymer network connected in a three-dimensional structure.

[0034] Specifically, a polymerization initiator may be included in either the first gel polymer electrolyte composition or the second gel polymer electrolyte composition. For example, the first gel polymer electrolyte composition may contain a polymerization initiator, while the second gel polymer electrolyte composition may not. In this case, the first oligomer and the second oligomer may be polymerized and cured by the polymerization initiator included in the first gel polymer electrolyte composition. Alternatively, a polymerization initiator may be included in both the first gel polymer electrolyte composition and the second gel polymer electrolyte composition.

[0035] The polymerization initiator may be a photopolymerization initiator or a thermal polymerization initiator depending on the polymerization method. Specifically, representative examples of the photopolymerization initiator include 2-hydroxy-2-methylpropiophenone (HMPP), 1-hydroxy-cyclohexylphenyl-ketone, benzophenone, 2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1-propanone, oxy-phenylacetic acid 2-[2-oxo-2phenyl-acetoxy-ethoxy]-ethyl ester, oxy-phenylacetic acid 2-[2-hydroxyethoxy]-ethyl ester, α-dimethoxy-α-phenylacetophenone, 2-benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl)phenyl]-1 4-isobutylphenyl-4′-methylphenyliodonium hexafluorophosphate, and at least one compound selected from the group consisting of methyl benzoylformate, ...

[0036] Representative examples of the thermal polymerization initiator include at least one compound selected from the group consisting of benzoyl peroxide, acetyl peroxide, dilauryl peroxide, di-tert-butyl peroxide, t-butyl peroxy-2-ethyl-hexanoate, cumyl hydroperoxide, hydrogen peroxide, 2,2'-azobis(2-cyanobutane), 2,2'-azobis(methylbutyronitrile), 2,2'-azobis(isobutyronitrile) (AIBN), and 2,2'-azobisdimethyl-valeronitrile (AMVN).

[0037] The polymerization initiator can be decomposed by heat at 30°C to 100°C in the secondary battery or by light such as UV at room temperature (5°C to 30°C) to form radicals, which can form crosslinks through free radical polymerization, thereby polymerizing the oligomer.

[0038] Meanwhile, the polymerization initiator may be used in an amount of 0.001 to 0.1 parts by weight, preferably 0.0015 to 0.015 parts by weight, and more preferably 0.002 to 0.01 parts by weight, relative to 100 parts by weight of the oligomer (the first oligomer or the second oligomer). When the amount of the polymerization initiator used is within this range, the amount of unreacted polymerization initiator, which may adversely affect battery performance, can be minimized. Furthermore, when the polymerization initiator is used within this range, gelation of the electrolyte composition can be appropriately achieved.

[0039] In addition to the above components, the first gel polymer electrolyte composition and the second gel polymer electrolyte composition may further contain additives to improve battery life characteristics, suppress battery capacity loss, and improve battery discharge capacity. For example, the additives may include, but are not limited to, haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, and aluminum trichloride, used alone or in combination. The additives may be present in an amount of 0.1 to 10 wt %, preferably 0.1 to 5 wt %, based on the total weight of the electrolyte.

[0040] The viscosity of the first gel polymer electrolyte composition at 25° C. may be 6 cP or less, preferably 1 cP to 5 cP. When the viscosity of the first gel polymer electrolyte composition satisfies the above range, the gel polymer electrolyte formed from the first gel polymer electrolyte composition can smoothly promote the movement of lithium ions between the positive electrode and the negative electrode in the electrode assembly.

[0041] The viscosity of the second gel polymer electrolyte composition at 25° C. may be 10 cP or more, and preferably 11 cP to 20 cP. When the viscosity of the second gel polymer electrolyte composition satisfies the above-mentioned range, the rigidity of the gel polymer electrolyte formed from the second gel polymer electrolyte composition can be further improved, thereby improving the stability of the secondary battery.

[0042] (2) First gel polymer electrolyte injection and impregnation step (S2) Referring to Figures 1 and 2, the first gel polymer electrolyte composition 310 is injected into the battery case 100 containing the electrode assembly 200, and the inside of the electrode assembly 200 is impregnated with the first gel polymer electrolyte composition 310 (S2).

[0043] The battery case 100 can be used to house the electrode assembly 200 and the electrolyte therein. The battery case 100 may be a pouch-shaped case made of a flexible material, for example, an aluminum pouch battery case.

[0044] When the battery case 100 is an aluminum pouch battery case, the battery case 100 may be formed from a pouch film in which, for example, a polypropylene layer (PP layer), an aluminum layer, and a polyethylene terephthalate layer (PET layer) are laminated in this order from the inside.

[0045] The battery case 100 may include a storage space 110 for storing the electrode assembly. The battery case 100 may include a cover (not shown), and after the electrode assembly is housed and the gel polymer electrolyte composition is hardened and gelled, the battery case 100 can be sealed with the cover to manufacture a sealed secondary battery.

[0046] The electrode assembly 200 is housed inside the battery case 100. Specifically, the electrode assembly 200 may be housed in the housing space 110 of the battery case 100. The electrode assembly 200 may have positive electrodes 210, separators 230, and negative electrodes 220 arranged alternately.

[0047] Specifically, the electrode assembly 200 may be a laminated structure including two types of electrodes, a positive electrode 210 and a negative electrode 220, and a separator 230 that is disposed between the electrodes or on the top or bottom of one of the electrodes to insulate the electrodes from each other. The laminated structure may be formed by stacking the positive electrode 210 and the negative electrode 220 of a predetermined specification with the separator 230 between them, and may have various shapes without limitation, such as being wound up like a jelly roll.

[0048] More specifically, the electrode assembly 200 may be a stack type electrode assembly, and may include a positive electrode 210, a separator 230, a negative electrode 220, and a separator 230, which are sequentially stacked, as shown in Fig. 2. Meanwhile, the electrode assembly 200 may be formed by stacking two or more units, each of which is a structure in which the positive electrode 210, the separator 230, the negative electrode 220, and the separator 230 are sequentially stacked.

[0049] The positive electrode 210 and the negative electrode 220 may each have a structure in which an active material slurry is applied to a metal foil or metal mesh current collector containing aluminum and copper. The positive electrode 210 and the negative electrode 220 may each have a structure in which the active material slurry is applied to both sides of a current collector, dried, and rolled. The active material slurry may be formed by adding a granular active material, a conductive material, a binder, and the like to a solvent and stirring the mixture. The active material, conductive material, binder, and the like used in the positive electrode 210 and the negative electrode 220 may be any material commonly used in the relevant fields without any limitations.

[0050] 1 and 2, the electrode assembly may be connected to a positive electrode tab 400 and a negative electrode tab 500. Specifically, the positive electrode tab 400 and the negative electrode tab 500 are connected to the positive electrode 210 and the negative electrode 220 of the electrode assembly 200, respectively, and protrude to the outside of the battery case 100 to serve as paths through which electrons can move. Although the positive electrode tab 400 and the negative electrode tab 500 are shown in FIGS. 1 and 2 as being arranged in different directions relative to the electrode assembly 200, the present invention is not limited thereto and may protrude side by side in the same direction from one side of the electrode assembly 200.

[0051] The first gel polymer electrolyte composition 310 is injected into the battery case 100, and the inside of the electrode assembly 200 is impregnated with the first gel polymer electrolyte composition 310. Specifically, the first gel polymer electrolyte composition 310 may impregnate the positive electrode 210, the negative electrode 220, and the separator 230 of the electrode assembly 200, thereby ensuring the mobility of ions between the positive electrode 210 and the negative electrode 220.

[0052] The impregnation with the first gel polymer electrolyte composition 310 may be carried out at a temperature of 10°C to 30°C for 0.5 to 72 hours, and preferably at a temperature of 15°C to 30°C for 40 to 60 hours.

[0053] Meanwhile, in order to impregnate the inside of the electrode assembly 200 with the first gel polymer electrolyte composition 310 and to dispose the gel polymer electrolyte formed from the first gel polymer electrolyte composition 310 inside the electrode assembly 200, the injection amount of the first gel polymer electrolyte composition 310 can be calculated and adjusted in advance.

[0054] If necessary, the first gel polymer electrolyte composition 310 may be cured after step (S2). This step is not essential, and as will be described later, after the injection of the second gel polymer electrolyte, the first gel polymer electrolyte composition 310 and the second gel polymer electrolyte composition 320 may be cured together in step (S4). However, when the curing process is performed after the impregnation of the first gel polymer electrolyte composition 310, there are advantages in that the first gel polymer electrolyte composition 310 is prevented from flowing out of the electrode assembly 200 before the injection of the second gel polymer electrolyte composition 320, and the first gel polymer electrolyte composition 310 and the second gel polymer electrolyte composition 320 are prevented from being mixed with each other.

[0055] In this case, the curing may be carried out at a temperature of 50° C. to 100° C. for 0.5 to 48 hours, and preferably at a temperature of 60° C. to 80° C. for 0.5 to 24 hours.

[0056] (3) Injection step of second gel polymer electrolyte composition (S3) Referring to FIG. 3, thereafter, a second gel polymer electrolyte composition 320 is injected into the battery case 100 (S3).

[0057] 3, the second gel polymer electrolyte composition 320 is injected into the battery case 100. Specifically, the second gel polymer electrolyte composition 320 may be injected inside the battery case 100 and outside the electrode assembly 200 impregnated with the first gel polymer electrolyte composition 310.

[0058] In order to easily place the second gel polymer electrolyte composition 320 and the gel polymer electrolyte produced thereby on the outside of the electrode assembly 200, the injection amount of the second gel polymer electrolyte composition 320 can be calculated and adjusted in advance.

[0059] The battery case 100 may be sealed after the injection of the second gel polymer electrolyte composition 320. Specifically, the battery case 100 may further include a cover (not shown), and the battery case 100 may be sealed via the cover (not shown).

[0060] (4) Step (S4) of curing the first gel polymer electrolyte composition and / or the second gel polymer electrolyte composition Referring to FIG. 4, thereafter, the first gel polymer electrolyte composition 310 and / or the second gel polymer electrolyte composition 320 injected into the battery case is cured (S4).

[0061] The first gel polymer electrolyte composition 310 and / or the second gel polymer electrolyte composition 320 may be cured by a photocuring or heat curing process, and specifically, may be cured by a heat curing process.

[0062] As shown in FIG. 4, the first gel polymer electrolyte composition 310 and / or the second gel polymer electrolyte composition 320 can be cured to form the first gel polymer electrolyte 310a and the second gel polymer electrolyte 320a, respectively.

[0063] Even if only this step is performed without performing the curing step after the impregnation of the first gel polymer electrolyte composition 310, both the first gel polymer electrolyte composition 310 and the second gel polymer electrolyte composition 320 will be cured in this step. In this case, since only one curing step is required, the manufacturing time is shortened and the manufacturing process is relatively simplified. However, if curing is performed only in step (S4) to prevent the first gel polymer electrolyte composition 310 and the second gel polymer electrolyte composition 320 from mixing with each other before curing, it is preferable to perform the curing step immediately after injecting the second gel polymer electrolyte composition 320 into the battery case 100 (step S3).

[0064] In this case, the curing may be carried out at a temperature of 50° C. to 100° C. for 0.5 to 48 hours, and preferably at a temperature of 60° C. to 80° C. for 0.5 to 24 hours.

[0065] Meanwhile, the curing may be performed in a sealed state of the battery case 100. For example, the battery case 100 containing the electrode assembly 200, the first gel polymer electrolyte composition 310, and the second gel polymer electrolyte composition 320 may be sealed with a cover or the like and then heat-treated, thereby thermally curing the first gel polymer electrolyte composition 310 and the second gel polymer electrolyte composition 320.

[0066] After step (S4), a step of cooling the hardened first gel polymer electrolyte composition 310 and second gel polymer electrolyte composition 320 may be further performed. The cooling may be performed, for example, by placing the hardened first gel polymer electrolyte composition 310 and second gel polymer electrolyte composition 320 at room temperature.

[0067] After step (S4), the battery case 100 may be sealed to form a vacuum atmosphere inside the battery case 100. By forming the vacuum atmosphere, degassing of gases generated during curing may be performed.

[0068] secondary battery The present invention provides a secondary battery, specifically a lithium secondary battery. Explaining in more detail with reference to FIGS. 5 and 6, the secondary battery 10 includes an electrode assembly 200 in which a positive electrode 210, a separator 230, and a negative electrode 220 are alternately arranged, a battery case 100 that houses the electrode assembly 200, and an electrolyte, the electrolyte including a first gel polymer electrolyte 310a disposed inside the electrode assembly 200 and a second gel polymer electrolyte 320a disposed outside the electrode assembly 200, and the interface resistance of the first gel polymer electrolyte 310a is lower than the interface resistance of the second gel polymer electrolyte 320a.

[0069] In the secondary battery according to the present invention, the first gel polymer electrolyte 310a has a relatively low interfacial resistance, and therefore, when impregnated inside the electrode assembly 200, it can improve the mobility of lithium between the positive electrode 210 and the negative electrode 220. On the other hand, the second gel polymer electrolyte 320a has a relatively high interfacial resistance but also high rigidity, and when disposed outside the electrode assembly 200, it can effectively protect the electrode assembly 200 from external impact. In addition, since the second gel polymer electrolyte 320a is disposed outside the electrode assembly 200, there is an advantage that the electrolyte does not leak to the outside even if a portion of the surface of the secondary battery 10 is cut open. The battery case 100 and the electrode assembly 200 have been described above.

[0070] As shown in FIGS. 5 and 6, the first gel polymer electrolyte 310a is disposed inside the electrode assembly 200, and the second gel polymer electrolyte 320a is disposed outside the electrode assembly 200.

[0071] The first gel polymer electrolyte 310a has a lower interfacial resistance than the second gel polymer electrolyte 320a. The first gel polymer electrolyte 310a is impregnated into the electrode assembly 200 of the secondary battery 10 and has a low interfacial resistance, thereby improving the mobility of lithium ions between the positive electrode 210 and the negative electrode 220 of the electrode assembly 200. The second gel polymer electrolyte 320a is disposed outside the electrode assembly 200 and has a somewhat higher interfacial resistance, but its high hardness and rigidity improve the physical stability of the secondary battery 10 and prevent electrolyte leakage.

[0072] The interfacial resistance of the first gel polymer electrolyte 310a and the second gel polymer electrolyte 320a can be achieved, for example, by adjusting the oligomer content of the gel polymer electrolyte composition used to form them. Specifically, increasing the oligomer content of the gel polymer electrolyte composition can decrease lithium ion mobility but increase rigidity, whereas decreasing the oligomer content of the gel polymer electrolyte composition can decrease rigidity but increase lithium ion mobility. More specifically, the first gel polymer electrolyte 310a can be formed by curing the first gel polymer electrolyte composition described above, and the second gel polymer electrolyte 320a can be formed by curing the second gel polymer electrolyte composition described above.

[0073] The interface resistance of the first gel polymer electrolyte 310a may be 2.0 mΩ to 2.6 mΩ, and preferably 2.32 mΩ to 2.51 mΩ. When the interface resistance of the first gel polymer electrolyte 310a satisfies the above numerical range, the mobility of lithium ions in the secondary battery 10 can be improved.

[0074] The interfacial resistance of the second gel polymer electrolyte 320a may be 2.6 mΩ to 3.0 mΩ, and preferably 2.70 mΩ to 2.90 mΩ. Since there is a trade-off between the interfacial resistance and rigidity of the gel polymer electrolyte, when the interfacial resistance of the second gel polymer electrolyte 320a satisfies the above numerical range, it can be understood that the second gel polymer electrolyte 320a has a preferable level of rigidity.

[0075] The "interfacial resistance of the gel polymer electrolyte" herein can be defined as the resistance of the interface between the gel polymer electrolyte and the electrode assembly. Specifically, the interfacial resistance of the gel polymer electrolyte can be calculated using the voltage change (ΔV) measured when a battery including the gel polymer electrolyte and the electrode assembly is discharged for 10 seconds at a 2.5C rate at 50% SOC. However, because the secondary battery of the present invention includes a first gel polymer electrolyte and a second gel polymer electrolyte, it is difficult to measure the interfacial resistance of each of the first and second gel polymer electrolytes. Therefore, the interfacial resistance of each of the first and second gel polymer electrolytes according to the present invention is defined as the interfacial resistance of the first gel polymer electrolyte or the second gel polymer electrolyte, respectively, by manufacturing a secondary battery sample containing only the first gel polymer electrolyte or the second gel polymer electrolyte, and measuring the interfacial resistance of the secondary battery sample.

[0076] The rigidity of the secondary battery 10 may be 5 MPa / 2 mm to 10 MPa / 2 mm, and preferably 6 MPa / 2 mm to 8 MPa / 2 mm. When the rigidity of the secondary battery 10 satisfies the above numerical range, the electrode assembly 200 can be stably protected from external impact, and even if a portion of the surface of the battery case 100 is cut open, the electrolyte will not leak. The stiffness of the secondary battery 10 is a stress value measured when a displacement of 2 mm is applied to the center of the cell at a rate of 10 mm / min using a universal testing machine (UTM).

[0077] The present invention may be embodied in various different forms and should not be construed as being limited to the embodiments set forth herein, although the present invention may be embodied in various different forms and should not be construed as being limited to the embodiments set forth herein. [Example]

[0078] Example 1 S1: Preparation of first gel polymer electrolyte composition and second gel polymer electrolyte composition The first gel polymer electrolyte composition was prepared by mixing tetrafluoroethylene (TFE)-vinyl acetate copolymer as an oligomer, a solvent, LiPF6 as a lithium salt, and AIBN (Azobisisobutyronitrile) as a polymerization initiator in a solvent.

[0079] The solvent was a mixture of ethyl carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7, the lithium salt was contained in the first gel polymer electrolyte composition at a concentration of 1.0 M, the oligomer was contained in an amount of 2 wt % based on the weight of the first gel polymer electrolyte composition, and the polymerization initiator was contained in an amount of 0.02 wt % based on the weight of the first gel polymer electrolyte composition.

[0080] The second gel polymer electrolyte composition was prepared in the same manner as the first gel polymer electrolyte composition, except that the oligomer was added in an amount of 8 wt % based on the weight of the second gel polymer electrolyte composition.

[0081] S2: Injection and impregnation of the first gel polymer electrolyte An electrode assembly was prepared in which 19 units each having a positive electrode, a separator, a negative electrode, and a separator stacked in sequence were stacked.

[0082] A pouch-type battery case made of aluminum was prepared as the battery case, and the electrode assembly was housed in the housing space of the battery case. Then, 65 g of the prepared first gel polymer electrolyte composition was injected into the battery case containing the electrode assembly, and after the injection, the battery case was vacuum sealed and the inside of the electrode assembly was allowed to be impregnated at room temperature for 48 hours.

[0083] S3: Injection of the second gel polymer electrolyte composition The prepared second gel polymer electrolyte composition was poured into the battery case. 15 g of the prepared second gel polymer electrolyte composition was poured into the battery case containing the electrode assembly, and the battery case was sealed.

[0084] S4: Curing of the first gel polymer electrolyte composition and the second gel polymer electrolyte composition Thereafter, the first gel polymer electrolyte composition and the second gel polymer electrolyte composition injected into the battery case were cured by heat treatment at a temperature of 60°C for 5 hours. Thereafter, the heat-treated battery case was cooled, sealed, and degassed to manufacture a secondary battery.

[0085] Example 2 A first gel polymer electrolyte composition was prepared in the same manner as in Example 1, except that 2 wt % of (allyl 1,1,2,2-tetrafluoroethyl ether (TFE))-(2,2,2-trifluoroethyl acrylate) copolymer was used instead of 2 wt % of TFE-vinyl acetate copolymer. A secondary battery was manufactured in the same manner as in Example 1, except that the first gel polymer electrolyte composition prepared above was used.

[0086] Comparative Example 1 The first gel polymer electrolyte composition and the second gel polymer electrolyte composition were prepared in the same manner as in Example 1, except that the first gel polymer electrolyte composition and the second gel polymer electrolyte composition did not contain an oligomer. A secondary battery was manufactured in the same manner as in Example 1, except that the first and second gel polymer electrolyte compositions prepared above were used.

[0087] Comparative Example 2 A first gel polymer electrolyte composition was prepared in the same manner as in Example 1, except that the content of the oligomer TFE-vinyl acetate copolymer was 5 wt % based on the weight of the first gel polymer electrolyte composition.

[0088] In addition, a second gel polymer electrolyte composition was prepared in the same manner as in Example 1, except that the content of the oligomer TFE-vinyl acetate copolymer was 5 wt % based on the weight of the second gel polymer electrolyte composition.

[0089] A secondary battery was manufactured in the same manner as in Example 1, except that the first and second gel polymer electrolyte compositions prepared above were used.

[0090] Comparative Example 3 A first gel polymer electrolyte composition was prepared in the same manner as in Example 1, except that an (allyl 1,1,2,2-tetrafluoroethyl ether (TFE))-(2,2,2-trifluoroethyl acrylate) copolymer was used as the oligomer instead of the TFE-vinyl acetate copolymer, and the content of the copolymer was 5 wt % based on the weight of the first gel polymer electrolyte composition.

[0091] In addition, a second gel polymer electrolyte composition was prepared in the same manner as in Example 1, except that an (allyl 1,1,2,2-tetrafluoroethyl ether (TFE))-(2,2,2-trifluoroethyl acrylate) copolymer was used as the oligomer instead of the TFE-vinyl acetate copolymer, and the content of the copolymer was 5 wt % based on the weight of the second gel polymer electrolyte composition.

[0092] A secondary battery was manufactured in the same manner as in Example 1, except that the first and second gel polymer electrolyte compositions prepared above were used.

[0093] Experimental Example 1 - Measurement of interface resistance of gel polymer electrolyte (1) Preparation of Reference Examples 1 and 2 Reference Example 1: Manufacture of a secondary battery containing gel polymer electrolyte X A gel polymer electrolyte composition was prepared containing a solvent, a lithium salt, an oligomer, and a polymerization initiator. The solvent was a mixture of ethyl carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7. The lithium salt was LiPF6, which was included in the gel polymer electrolyte composition at a concentration of 1.0 M. The oligomer was TFE-vinyl acetate copolymer, which was included in the gel polymer electrolyte composition at 5 wt% by weight, and the polymerization initiator was AIBN, which was included in the gel polymer electrolyte composition at 0.02 wt% by weight.

[0094] A secondary battery was manufactured in the same manner as in Example 1, except that the first gel polymer electrolyte composition and the second gel polymer electrolyte composition were not used, and 80 g of the gel polymer electrolyte composition alone was injected into a battery case and cured to form a gel polymer electrolyte X.

[0095] Reference Example 2: Production of a secondary battery containing gel polymer electrolyte Y A secondary battery was manufactured in the same manner as in Reference Example 1, except that a gel polymer electrolyte composition was formed by adding 10 wt % of TFE-vinyl acetate copolymer as an oligomer instead of 5 wt % of TFE-vinyl acetate copolymer, and then curing the gel polymer electrolyte Y.

[0096] (2) Measurement of interface resistance The 10s resistance in a cell reference performance test (RPT) was measured for the secondary batteries of Reference Examples 1 and 2. Specifically, the resistance value calculated based on the voltage change (ΔV) measured when the secondary batteries of Reference Examples 1 and 2 were discharged for 10 seconds at a 2.5C rate at an SOC of 50% was used as the interface resistance value of Reference Examples 1 and 2.

[0097] [Table 1]

[0098] Referring to Table 1, it can be seen that the oligomer content of gel polymer electrolyte X is lower than that of gel polymer electrolyte Y, resulting in lower interfacial resistance. Because gel polymer electrolyte X has low interfacial resistance, impregnating the interior of an electrode assembly with a gel polymer electrolyte composition having a low oligomer content is expected to further facilitate lithium ion migration within a secondary battery. Meanwhile, the high interfacial resistance of gel polymer electrolyte Y leads to increased cell rigidity, which is a trade-off. Therefore, when a gel polymer electrolyte prepared from a gel polymer electrolyte composition having a high oligomer content is disposed on the exterior of an electrode assembly, it is expected that the stability of the secondary battery against external impacts can be improved. Therefore, by disposing a first gel polymer electrolyte having a relatively low interfacial resistance and a second gel polymer electrolyte having a relatively high interfacial resistance on the interior and exterior of an electrode assembly, respectively, the secondary battery according to the present invention can simultaneously improve lithium ion mobility and secondary battery stability. This effect can be confirmed in Experimental Examples 2 to 4, which will be described later.

[0099] Experimental Example 2 - Stiffness Measurement The stiffness of the secondary batteries manufactured in Example 1, Example 2, and Comparative Examples 1 to 3 was measured. Specifically, a downward force was applied to the center of each secondary battery using a three-point bending method, and the stress value was measured when a displacement of 2 mm was given. The experiment was carried out at room temperature, and the stress value was measured using a universal testing machine (UTM). The results are shown in Table 2 below.

[0100] Experimental Example 3: Measurement of leakage amount of gel polymer electrolyte The amount of leakage of the gel polymer electrolyte was measured for the secondary batteries manufactured in Example 1, Example 2, and Comparative Examples 1 to 3. A 5 cm cut was made in the side of each secondary battery, and the cut part was set as the bottom end. After leaving the secondary battery for 3 days, the amount of leakage of the electrolyte was measured. The results are shown in Table 2 below.

[0101] Experimental Example 4 - Measurement of interface resistance The interface resistance of the secondary batteries of Example 1, Example 2, and Comparative Examples 1 to 3 was measured. Specifically, the resistance values ​​calculated using the voltage change (ΔV) measured when the secondary batteries of Example 1, Example 2, and Comparative Examples 1 to 3 were discharged for 10 seconds at a 2.5C rate at an SOC of 50% were used as the interface resistance values ​​of the secondary batteries of Example 1, Example 2, and Comparative Examples 1 to 3. The results are shown in Table 2.

[0102] [Table 2]

[0103] Referring to Table 2, it can be seen that the secondary batteries of the examples simultaneously achieve reduced interface resistance, improved cell rigidity, and prevention of electrolyte leakage, compared to the secondary batteries of the comparative examples.

Claims

1. (S1) preparing a first gel polymer electrolyte composition including a first oligomer and a second gel polymer electrolyte composition including a second oligomer; (S2) injecting the first gel polymer electrolyte composition into a battery case containing an electrode assembly to impregnate the inside of the electrode assembly with the first gel polymer electrolyte composition; (S3) injecting the second gel polymer electrolyte composition into the battery case; (S4) curing the first gel polymer electrolyte composition and the second gel polymer electrolyte composition injected into the battery case to form a first gel polymer electrolyte and a second gel polymer electrolyte; Including, the concentration of the first oligomer in the first gel polymer electrolyte composition, based on the weight of the first gel polymer electrolyte composition, is lower than the concentration of the second oligomer in the second gel polymer electrolyte composition, based on the weight of the second gel polymer electrolyte composition; The method for manufacturing a secondary battery, wherein the interface resistance of the first gel polymer electrolyte is lower than the interface resistance of the second gel polymer electrolyte.

2. The method of claim 1 , further comprising the step of curing the first gel polymer electrolyte composition after the step (S2).

3. The method for producing a secondary battery according to claim 1 , wherein at least one of the first gel polymer electrolyte composition and the second gel polymer electrolyte composition contains a lithium salt.

4. The method for manufacturing a secondary battery according to claim 1 , wherein at least one of the first gel polymer electrolyte composition and the second gel polymer electrolyte composition contains a polymerization initiator.

5. 2. The method for producing a secondary battery according to claim 1, wherein the viscosity of the first gel polymer electrolyte composition at 25°C is 6 cP or less, and the viscosity of the second gel polymer electrolyte composition at 25°C is 10 cP or more.

6. The method for manufacturing a secondary battery according to claim 1 , wherein in the step (S4), the curing is performed immediately after the second gel polymer electrolyte composition is injected into the battery case.

7. 2. The method for producing a secondary battery according to claim 1, wherein the first oligomer and the second oligomer each independently comprise one or more oligomers selected from the group consisting of polyether-based oligomers, polycarbonate-based oligomers, polyacrylate-based oligomers, polysiloxane-based oligomers, phosphazene-based oligomers, polyethylene-based oligomers, urethane-based oligomers, epoxy-based oligomers, fluorine-based oligomers, polyethylene oxide, polyester sulfide, polyvinyl alcohol, and polyvinylidene fluoride.

8. 8. The method for producing a secondary battery according to claim 1, wherein the first oligomer and the second oligomer each independently comprise at least one selected from the group consisting of tetrafluoroethylene-vinyl acetate copolymer, (allyl 1,1,2,2-tetrafluoroethyl ether)-(2,2,2-trifluoroethyl acrylate) copolymer, tetrafluoroethylene-(2-vinyl-1,3-dioxolane) copolymer, and tetrafluoroethylene-vinyl methacrylate copolymer.

9. an electrode assembly in which a positive electrode, a separator, and a negative electrode are alternately arranged; a battery case that houses the electrode assembly; Electrolytes, Including, the electrolyte includes a first gel polymer electrolyte disposed inside the electrode assembly and a second gel polymer electrolyte disposed outside the electrode assembly; A secondary battery, wherein the interface resistance of the first gel polymer electrolyte is lower than the interface resistance of the second gel polymer electrolyte.

10. 10. The secondary battery according to claim 9, wherein the first gel polymer electrolyte has an interface resistance of 2.0 mΩ to 2.6 mΩ.

11. 10. The secondary battery according to claim 9, wherein the second gel polymer electrolyte has an interface resistance of 2.6 mΩ to 3.0 mΩ.

12. The secondary battery according to any one of claims 9 to 11, wherein the secondary battery has a rigidity of 5 MPa / 2 mm to 10 MPa / 2 mm.

Images