Separator for secondary battery and lithium secondary battery comprising the same

Abstract

The present invention relates to a separator for a secondary battery and a lithium secondary battery comprising the same, the separator comprising a substrate and a coating layer formed on a surface of the substrate, wherein the coating layer comprises an organic binder and inorganic particles, and the organic binder contains an ethylenically unsaturated group.

Description

[0001] This application is a divisional application of the invention patent application filed on January 17, 2019, with application number 201980005942.X and entitled "Separator for Secondary Battery and Lithium Secondary Battery Including the Separator". Technical Field

[0002] Cross-reference to related applications

[0003] This application claims the benefit of Korean Patent Application No. 10-2018-0006795, filed on January 18, 2018, with the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0005] The present invention relates to a separator for a secondary battery and a lithium secondary battery including the separator, and more specifically, to a separator for a secondary battery and a lithium secondary battery including the separator that can improve the performance and safety of a lithium secondary battery. Background Technology

[0006] With the development of mobile device technology and increasing demand, the demand for secondary batteries as an energy source has increased rapidly. Among these secondary batteries, lithium secondary batteries, which have high energy density and operating potential, long cycle life and low self-discharge rate, have been commercialized and are widely used.

[0007] In recent years, due to increasing concern about environmental issues, much research has been conducted on electric vehicles (EVs) and hybrid electric vehicles (HEVs) that can replace fossil fuel-powered vehicles (such as gasoline and diesel vehicles), which are one of the main causes of air pollution.

[0008] Electric vehicles (EVs) and hybrid electric vehicles (HEVs) use nickel-metal hydride (Ni-MH) batteries or lithium batteries with high energy density, high discharge voltage, and output stability as their power source. When lithium batteries are used in electric vehicles, since the batteries must be used for more than 10 years under harsh conditions, in addition to high energy density and the ability to generate a large output in a short time, they inevitably need to have significantly better energy density, safety, and long-term lifespan characteristics than traditional small lithium batteries.

[0009] Typically, lithium-ion batteries are manufactured using a positive electrode, a negative electrode, a separator between the two, and an electrolyte that serves as the lithium-ion transport medium.

[0010] The separator, being an inert material that does not participate in electrochemical reactions, provides a path for lithium ions to move through, enabling the battery to function, and is the material that separates the physical contact between the anode and cathode. The separator is one of the key materials that significantly impacts the performance and stability of the battery.

[0011] Methods for preparing separators are classified into wet and dry methods. The wet method involves mixing polymer materials and low-molecular-weight waxes to extrude a film at high temperature, and then extracting the wax with a solvent to form a microporous structure. The dry method involves forming pores in a multilayer structure of two or three layers of film bonded together using polyethylene (PE) and polypropylene (PP) without the use of wax, through only physical stretching and heat treatment.

[0012] Meanwhile, lithium-ion batteries can be easily heated due to the kinetic energy generated during repeated charging / discharging, and the separator is susceptible to this heat. In particular, separators made of polyethylene (PE) begin to melt at around 130°C, which can lead to a "shutdown" phenomenon where the pores close, and can completely melt at 150°C or higher, potentially resulting in meltdown due to the inability to prevent internal short circuits.

[0013] To overcome these limitations, research has been conducted in recent years to improve durability, for example, using dip coating, which involves coating inorganic particles and polymer adhesives onto the surface of the separator.

[0014] In addition, in typical secondary batteries, liquid electrolytes are mainly used, especially ion-conducting organic liquid electrolytes in which salts are dissolved in non-aqueous organic solvents.

[0015] However, when using a liquid electrolyte as described above, there is a significant possibility of electrode material degradation and organic solvent evaporation. Furthermore, the increased temperature of the battery and its surroundings can lead to safety issues such as combustion. In particular, the problem with lithium-ion secondary batteries is that during charging / discharging, the decomposition of carbonate organic solvents and / or side reactions between the organic solvents and the electrodes result in the generation of gas inside the battery, thus increasing its thickness. Consequently, degradation of battery performance and safety is unavoidable.

[0016] Generally speaking, the safety of known batteries increases in the order of liquid electrolyte < gel polymer electrolyte < solid polymer electrolyte, while battery performance decreases. Solid polymer electrolytes are known to have low battery performance and therefore have not yet been commercialized.

[0017] On the other hand, gel polymer electrolytes possess excellent electrochemical safety, thus maintaining a constant battery thickness. Furthermore, the inherent adhesiveness of the gel ensures excellent adhesion between the electrode and the electrolyte. Therefore, thin-film batteries can be manufactured. Consequently, gel polymer electrolytes have been widely used in recent years.

[0018] However, when using separators with coatings including gel polymer electrolytes and inorganic particles, the low adhesion between the coating and the electrolyte leads to a deterioration in the stability and performance of the secondary battery.

[0019] Therefore, there is a need to develop a separator for lithium secondary batteries that exhibits excellent adhesion to gel polymer electrolytes and excellent durability, thereby improving battery safety, capacity characteristics, and lifespan characteristics.

[0020] (Patent Document 1) Korean Patent Publication No. 10-2015-0131513 (Pending Examination) Summary of the Invention

[0021] Technical issues

[0022] One aspect of the present invention provides a separator capable of increasing adhesion to a gel polymer electrolyte, thereby improving the output characteristics and safety of the battery, and a lithium secondary battery including the separator.

[0023] Technical solution

[0024] According to one aspect of the present invention, a separator for a secondary battery is provided, the separator comprising a substrate and a coating formed on the surface of the substrate, wherein the coating comprises an organic binder and inorganic particles, and the organic binder comprises olefinic unsaturated groups.

[0025] In this case, the olefinic unsaturated group can be at least one selected from the group consisting of vinyl, acryloyloxy, and methacryloyloxy.

[0026] According to another aspect of the present invention, a lithium secondary battery is provided, comprising a positive electrode, a negative electrode, and a gel polymer electrolyte disposed between the positive electrode, the negative electrode, and a separator and formed by polymerization of an oligomer containing (meth)acrylate groups, wherein a three-dimensional polymer network is formed by polymerization reaction between an organic binder comprising an olefinic unsaturated group included in the separator and the oligomer containing (meth)acrylate groups.

[0027] Beneficial effects

[0028] The separator according to the invention includes an organic binder containing olefinic unsaturated groups in a coating, such that the organic binder of the separator coating and the oligomers included in the gel polymer electrolyte composition undergo a polymerization reaction to improve the adhesion between the separator and the gel polymer electrolyte, thereby improving the performance and safety of the lithium secondary battery.

[0029] Best practice

[0030] The invention will be described in more detail below.

[0031] It will be understood that the terms or words used in this specification and claims should not be construed as having the meanings defined in commonly used dictionaries. It will be further understood that, based on the principle that the inventors may appropriately define the meanings of terms or words to best interpret the invention, these terms or words should be interpreted as having meanings consistent with the technical concept of the invention and the context of related art.

[0032] The terminology used herein is for the purpose of describing particular exemplary embodiments only and is not intended to limit the invention. Singular terms may include plural forms unless the context clearly indicates otherwise.

[0033] It will be further understood that when the terms “comprising,” “including,” or “having” are used in this specification, they specifically describe the presence of the said features, numbers, steps, elements, or combinations thereof, but do not exclude the presence or addition of one or more other features, numbers, steps, elements, or combinations thereof.

[0034] Furthermore, unless otherwise stated in this invention, "*" indicates a portion connected at the ends of the same or different atoms or between chemical formulas.

[0035] In this specification, weight-average molecular weight (MAM) may refer to the standard polystyrene conversion value measured by gel permeation chromatography (GPC), and unless otherwise specified, molecular weight may refer to weight-average molecular weight. In this case, MAM can be measured by gel permeation chromatography (GPC). For example, a sample of a predetermined concentration is prepared, and the GPC measurement system Alliance 4 is stabilized. Once the system is stable, the standard sample and the sample are injected into the system to obtain chromatography, and the weight-average molecular weight is calculated according to the analytical method (System: Alliance 4, Column: Ultrahydrogel linear × 2, Eluent: 0.1M NaNO3 pH 7.0 phosphate buffer, Flow rate: 0.1 mL / min, Temp: 40°C, Injection: 100 μL).

[0036] Separator for secondary batteries

[0037] The separator for a secondary battery according to the present invention comprises a substrate and a coating formed on the surface of the substrate, wherein the coating comprises an organic binder and inorganic particles, and the organic binder contains olefinic unsaturated groups.

[0038] The thickness of the separator can be 0.1-20 μm, preferably 0.5-20 μm, and more preferably 1.0-20 μm. When the thickness of the separator is within the above range, it prevents an increase in resistance in the battery and promotes the movement of lithium ions. Therefore, it is desirable for the thickness of the separator to be within the above range.

[0039] The substrate can be a porous substrate, and any porous substrate can be used without particular limitation, as long as it can be used as a separator material for an electrochemical device. Examples of such porous substrates may include, but are not particularly limited to, nonwoven fabrics or porous polymer films formed from at least one, or two or more, of polymer resins such as polyolefins, polyethylene, polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene ether, polyphenylene sulfide, and polyvinylnaphthalene.

[0040] The coating is used to enhance the durability of the separator substrate and is formed on the surface of the substrate, comprising an organic binder and inorganic particles. The organic binder contains olefinically unsaturated groups.

[0041] Typically, inorganic particles and similar materials are coated onto the surface of a substrate to improve the durability and conductivity of the separator. However, inorganic particles do not react with the electrolyte, thus deteriorating the adhesion between the electrolyte and the separator, and posing safety issues such as causing internal short circuits in the battery.

[0042] The separator according to the invention has a coating that uses inorganic particles and an organic binder together, wherein the organic binder comprises olefinically unsaturated groups. The organic binder comprising olefinically unsaturated groups can undergo free radical polymerization with oligomers included in the composition for the gel polymer electrolyte.

[0043] More specifically, the composition for the gel polymer electrolyte may include oligomers containing (meth)acrylate groups, and these functional groups are capable of undergoing free radical polymerization with olefinic unsaturated groups contained in the organic binder. Therefore, the oligomers and the organic binder can be coupled via free radical polymerization during the curing process of the composition for the gel polymer electrolyte, forming a three-dimensional polymer network, thereby improving the adhesion between the separator and the gel polymer electrolyte. When the adhesion between the separator and the gel polymer electrolyte is improved, the internal resistance of the battery decreases, and the lithium-ion transport characteristics are improved. Therefore, the output characteristics and lifespan characteristics of the battery can be improved.

[0044] Furthermore, when the adhesion between the separator and the gel polymer electrolyte is improved, the mechanical strength of the secondary battery is improved, thereby preventing internal short circuits even under external impacts and preventing thermal runaway or fire. As a result, the safety of the battery can also be improved.

[0045] Organic adhesives contain olefinically unsaturated groups. For example, the olefinically unsaturated groups may include at least one selected from the group consisting of vinyl, acryloyloxy, and methacryloxy.

[0046] Furthermore, the organic adhesive may further comprise a unit comprising at least one of the following groups: an alkyl group having at least one substituted halogen element (F, Cl, Br, I), an alkyloxy group, an alkyloxy group having at least one substituted halogen element (F, Cl, Br, I), an imide group, and a celluloid.

[0047] At this point, the olefinic unsaturated groups may be located at the ends or sides of the polymer backbone composed of these units, and the number or location of the connected functional groups is not specified.

[0048] For example, a unit containing an alkyl group having at least one substituted halogen element can be represented by at least one of the units selected from the following formulas X-1 and X-2.

[0049] [Formula X-1]

[0050]

[0051] In equation X-1, m1 is an integer from 1 to 100.

[0052] [Formula X-2]

[0053]

[0054] In equation X-2, m2 and m3 are each an independent integer from 1 to 100.

[0055] For example, a unit containing an alkyloxy group can be represented by the following formula X-3.

[0056] [Formula X-3]

[0057]

[0058] In equation X-3, m4 is an integer from 1 to 100.

[0059] For example, a unit containing an alkyloxy group substituted with a halogen element can be represented by the following formula X-4.

[0060] [Formula X-4]

[0061]

[0062] In equation X-4, m5 is an integer from 1 to 100.

[0063] For example, a unit containing an imide group can be represented by the following formula X-5.

[0064] [Formula X-5]

[0065]

[0066] For example, a cell containing celluloid can be represented by the following formula X-6.

[0067] [Formula X-6]

[0068]

[0069] In equation X-6, m7 is an integer from 1 to 100.

[0070] Specifically, the compound used as an organic adhesive is a compound having an olefinic unsaturated group at the end or side of the polymer backbone formed by at least one unit selected from the group consisting of formulas X-1 to X-6.

[0071] For example, polymers or copolymers comprising units represented by formulas X-1 to X-6 are typically formed by free radical polymerization or similar reactions. In this case, at the end of the polymerization reaction, functional groups including halogen elements, hydroxyl groups, alkoxy groups, and alkyl groups are attached to the ends or sides of the main chain constituting the polymer or copolymer by end-capping, so that no further polymerization reaction occurs.

[0072] For example, when treating the ends with functional groups including halogen elements, halogen compounds such as sodium chloride (NaCl) can be used as end-capping agents. However, the present invention is not limited to the methods described above, nor is the type of end-capping agent limited to the materials described above.

[0073] Specifically, when functional groups including halogen elements are located at the ends or sides, these functional groups can react with (meth)acrylate compounds or vinyl compounds. Through this reaction, organic adhesives having halogen elements and olefinic unsaturated groups (such as (meth)acryloyloxy or vinyl groups) can be prepared.

[0074] Based on 100 parts by weight of the coating, the organic binder may be included in an amount of 1 to 80 parts by weight, preferably 5 to 60 parts by weight, and more preferably 5 to 40 parts by weight. When the organic binder is included within the above range, it can prevent the deintercalation of inorganic particles included in the coating and can provide a separator for secondary batteries with improved mechanical properties.

[0075] Inorganic particles form interstitial volumes between themselves, thus creating pores within micro-units and simultaneously acting as spacers that maintain their physical shape. Furthermore, inorganic particles can transport and move lithium ions, thereby improving lithium-ion conductivity. The formation of these micro-unit pores can be achieved by controlling the size and content of the inorganic particles, as well as the composition of the inorganic particles and the polymer. Additionally, the size and porosity of the pores can be controlled.

[0076] The inorganic particles can be inorganic particles commonly used in the art. For example, the inorganic particles may include at least one element selected from the group consisting of Si, Al, Ti, Zr, Sn, Ce, Mg, Ca, Zn, Y, Pb, Ba, Hf, and Sr, and preferably may include at least one element selected from the group consisting of Si, Al, Ti, and Zr.

[0077] More specifically, examples of inorganic particles may include SiO2, Al2O3, TiO2, ZrO2, SnO2, CeO2, MgO, CaO, ZnO, Y2O3, Pb(Zr,Ti)O3(PZT), Pb (1-a1) Laa1 Zr (1-b1) Ti b1 O3(0≤a1≤1,0≤b1≤1,PLZT), PB(Mg3Nb 2 / 3 The inorganic materials, including PbTiO3 (PMN-PT), BaTiO3, HfO2 (hafnium dioxide), SrTiO3, and the like, are characterized in that their physical properties remain unchanged even at temperatures of 200°C or higher. More preferably, the inorganic particles may include at least one inorganic material selected from the group consisting of SiO2, Al2O3, TiO2, and ZrO2.

[0078] Based on 100 parts by weight of coating, inorganic particles may be included in an amount of 20 to 99 parts by weight, preferably 40 to 95 parts by weight, and more preferably 60 to 90 parts by weight. When inorganic particles are included within the above range, it can prevent inorganic particles from being extracted from the coating and can improve the durability of the separator used in secondary batteries.

[0079] <Manufacturing of Lithium Secondary Batteries>

[0080] Next, a lithium secondary battery according to the present invention will be described. A lithium secondary battery according to another embodiment of the present invention includes a positive electrode, a negative electrode, a separator interposed between the positive and negative electrodes and including a coating, and a gel polymer electrolyte disposed between the positive electrode, the negative electrode, and the separator.

[0081] A positive electrode can be prepared by coating a slurry of positive active materials, including positive active materials, binders, conductive agents, and solvents, onto a positive current collector.

[0082] There are no particular restrictions on the positive current collector, as long as it is conductive and does not cause chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel that has been surface-treated with one of the following: carbon, nickel, titanium, silver, or the like can be used.

[0083] The positive electrode active material is a compound capable of reversibly inserting and deintercalating lithium, and specifically, may include lithium composite metal oxides comprising one or more metals such as cobalt, manganese, nickel, or aluminum, and lithium. More specifically, the lithium composite metal oxide may be: lithium manganese-based oxides (e.g., LiMnO2, LiMn2O4, etc.); lithium cobalt-based oxides (e.g., LiCoO2, etc.); lithium nickel-based oxides (e.g., LiNiO2, etc.); lithium nickel manganese-based oxides (e.g., LiNi... 1-Y1 Mn Y1 O2 (where 0) <Y1<1)、LiMn 2-Z1 Ni Z1 O4 (where 0 < Z1 < 2), etc.; lithium nickel cobalt-based oxides (e.g., LiNi).1-Y2 Co Y2 O2 (where 0 < Y2 < 1), etc.; lithium manganese cobalt-based oxides (e.g., LiCo 1-Y3 Mn Y3 O2 (where 0 < Y3 < 1), LiMn 2-Z2 Co Z2 O4 (where 0 < Z2 < 2), etc.; lithium nickel manganese cobalt-based oxides (e.g., Li(Ni p1 Co q1 Mn r1 )O2 (where 0 < p1 < 1, 0 < q1 < 1, 0 < r1 < 1, p1 + q1 + r1 = 1), or Li(Ni p2 Co q2 Mn r2 )O4 (where 0 < p2 < 2, 0 < q2 < 2, 0 < r2 < 2, p2 + q2 + r2 = 2), etc.; or lithium nickel cobalt transition metal (M) oxides (e.g., Li(Ni p3 Co q3 Mn r3 M s1 )O2 (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p3, q3, r3, and s1 are each the atomic fraction of an independent element, and 0 < p3 < 1, 0 < q3 < 1, 0 < r3 < 1, 0 < s1 < 1, p3 + q3 + r3 + s1 = 1), etc.) and analogs, and may include any one of them or a mixture of two or more of them.

[0084] Among them, due to the fact that the capacity characteristics and stability of the battery can be increased, the lithium composite metal oxide can be LiCoO2, LiMnO2, LiNiO2, lithium nickel manganese cobalt oxide (e.g., Li(Ni 1 / 3 Co 1 / 3 Mn 1 / 3 )O2, Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, or Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, etc.), or lithium nickel cobalt aluminum oxide (e.g., LiNi 0.8 Co 0.15 Al 0.05 O2, etc.), and analogs. When considering the significant improvement effect according to the control of the type and content ratio of the constituent elements forming the lithium composite metal oxide, the lithium composite metal oxide can be Li(Ni 0.6Mn 0.2 Co 0.2) O2, Li(Ni) 0.5 Mn 0.3 Co 0.2) O2, Li(Ni) 0.7 Mn 0.15 Co 0.15) O2, or Li(Ni) 0.8 Mn 0.1 Co 0.1) O2, and analogues, and any one of them or a mixture of two or more of them may be used.

[0085] Based on the total weight of solids other than solvent in the positive electrode active material slurry, the positive electrode active material may be included in an amount of 60% to 98% by weight, preferably 70% to 98% by weight, and more preferably 80% to 98% by weight.

[0086] Adhesives are components that facilitate the bonding between the active material and the conductive agent, and also facilitate bonding to the current collector. Specifically, examples of adhesives may include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene (PE), polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile rubber, fluororubber, various copolymers thereof, and the like. Typically, based on the total weight of solids other than solvents in the positive electrode active material slurry, the adhesive may be included in an amount from 1% to 20% by weight, preferably from 1% to 15% by weight, more preferably from 1% to 10% by weight.

[0087] Conductive agents are components used to further improve the conductivity of the positive electrode active material. There are no particular limitations on conductive agents, as long as they are conductive and do not cause chemical changes in the battery. Examples of conductive agents can include graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lampblack, and thermal black; conductive fibers such as carbon fibers and metal fibers; metal powders such as fluorinated carbon powder, aluminum powder, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive materials such as polyphenylene derivatives; and the like. Specific examples of commercially available conductive materials include: Chevron Chemical Company's acetylene black series, Denka Black from Denka Singapore Private Limited, Gulf Oil Company, etc., Armak Company's Ketjen black and EC series, Cabot Company's Vulcan XC-72, and Timcal Company's Super P. Based on the total weight of solids other than solvent in the positive electrode active material slurry, the conductive agent may be included in an amount of 1% to 20% by weight, preferably 1% to 15% by weight, more preferably 1% to 10% by weight.

[0088] The solvent may include organic solvents such as N-methyl-2-pyrrolidone (NMP) and may be used in an amount such that a preferred viscosity is obtained when the positive electrode active material is included, as well as binders and conductive agents and the like are selectively included. For example, the solvent may be included in an amount such that the concentration of the solids including the positive electrode active material and selectively including binders and conductive agents is 50% to 95% by weight, preferably 70% to 95% by weight, more preferably 70% to 90% by weight.

[0089] In addition, a negative electrode can be prepared by coating a negative electrode active material slurry, including a negative electrode active material, a binder, a conductive agent, and a solvent, onto the negative electrode current collector.

[0090] Negative electrode current collectors typically have a thickness of 3-500 μm. There are no particular limitations on the negative electrode current collector, as long as it has high conductivity and does not cause chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or copper or stainless steel, aluminum-cadmium alloys, and the like surface-treated with one of carbon, nickel, titanium, silver, and the like can be used. Furthermore, similar to the positive electrode current collector, microscopic irregularities can be formed on the surface of the negative electrode current collector to improve the adhesion of the negative electrode active material, and the negative electrode current collector can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0091] Examples of negative electrode active materials may include one or more negative electrode active materials selected from the group consisting of: natural graphite, artificial graphite, carbonaceous materials; metals (Me) such as lithium titanium oxide (LTO), Si, Sn, Li, Zn, Mg, Cd, Ce, Ni, or Fe; alloys composed of metals (Me); oxides of metals (MeO). x ); and complexes of metal (Me) and carbon.

[0092] Based on the total weight of solids other than solvent in the negative electrode active material slurry, the negative electrode active material may be included in an amount of 60% to 98% by weight, preferably 70% to 98% by weight, more preferably 80% to 98% by weight.

[0093] The descriptions of adhesives, conductive agents, and solvents are the same as those above, therefore their detailed descriptions will be omitted.

[0094] A separator is inserted between the positive and negative electrodes and includes a coating comprising an organic binder and inorganic particles. The coating is located on the surface facing the gel polymer electrolyte. The descriptions of the coating and electrolyte are the same as those above, and therefore their detailed descriptions will be omitted.

[0095] The gel polymer electrolyte is disposed between the positive electrode, the negative electrode, and the separator, and is formed by polymerizing oligomers containing (meth)acrylate groups. When oligomers containing (meth)acrylate groups are used, they undergo free radical polymerization with an organic binder containing olefinic unsaturated groups included in the coating to form a three-dimensional polymer network.

[0096] For example, oligomers may further include oxyalkylene groups. Specifically, oligomers may be represented by Formula 1 below.

[0097] [Formula 1]

[0098] A-C1-A'

[0099] In Formula 1, A and A' are each independently a unit containing a (meth)acrylate group, and C1 is a unit containing an oxane group.

[0100] Specifically, units A and A' are each units comprising (meth)acrylate groups, allowing the oligomers to polymerize to form a polymer. When (meth)acrylate groups are included, polymerization occurs with organic binders containing olefinically unsaturated groups to form a polymer network. Units A and A' can be derived from monomers comprising monofunctional or polyfunctional (meth)acrylates or (meth)acrylic acid.

[0101] For example, units A and A' may each independently contain at least one unit represented by the following formulas A-1 to A-5.

[0102] [Formula A-1]

[0103]

[0104] [Formula A-2]

[0105]

[0106] [Formula A-3]

[0107]

[0108] [Formula A-4]

[0109]

[0110] [Formula A-5]

[0111]

[0112] Unit C1 may include units represented by equation C1-1.

[0113] [Equation C1-1]

[0114]

[0115] In formula C1-1, R is a substituted or unsubstituted linear or branched alkyl group having 1 to 10 carbon atoms, and k1 is an integer from 1 to 30.

[0116] In another example, in equation C1-1, R can be independently -CH2CH2- or -CHCH3CH2-.

[0117] For example, according to one embodiment of the invention, the oligomers forming the polymer network may be at least one compound selected from the group consisting of Formulas 1-1 to 1-5.

[0118] [Equation 1-1]

[0119]

[0120] In Equation 1-1, n1 is an integer from 1 to 20,000.

[0121] [Equation 1-2]

[0122]

[0123] In Equation 1-2, n2 is an integer from 1 to 20,000.

[0124] [Equation 1-3]

[0125]

[0126] In Equations 1-3, n3 is an integer from 1 to 20,000.

[0127] [Equations 1-4]

[0128]

[0129] In Equations 1-4, n4 is an integer from 1 to 20,000.

[0130] [Equations 1-5]

[0131]

[0132] In Equations 1-5, n5 is an integer from 1 to 20,000.

[0133] In Equations 1-1 to 1-5, n1 to n5 are each independently an integer from 1 to 20,000, preferably an integer from 1 to 10,000, and more preferably an integer from 1 to 5,000.

[0134] In another example, oligomers can be represented by Equation 2.

[0135] [Equation 2]

[0136]

[0137] In Formula 2, A and A' are each independently a unit containing the same (meth)acrylate group as described above, B and B' are each independently a unit containing an amide group, C2 and C2' are each independently a unit containing an oxane group, D is a unit containing a siloxane group, and l is an integer from 1 to 200.

[0138] Furthermore, l can preferably be an integer from 10 to 200, more preferably from 20 to 200. When l is within the above range, although the polymer formed from oligomers has high mechanical properties, its flowability remains above a predetermined level, so that the polymer can be uniformly dispersed in the battery.

[0139] Furthermore, B and B' are each independently units containing amide groups, which control ion transport properties and impart mechanical properties when realizing polymer electrolytes.

[0140] For example, B and B' can each independently include a unit represented by the following formula B-1.

[0141] [Formula B-1]

[0142]

[0143] In formula B-1, R' is selected from at least one of the group consisting of a straight-chain or non-straight-chain alkyl group having 1 to 10 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 10 carbon atoms, a substituted or unsubstituted bicycloalkyl group having 6 to 20 carbon atoms, a substituted or unsubstituted aryl group having 6 to 20 carbon atoms, a unit represented by the following formula R"-1, and a unit represented by the following formula R"-2.

[0144] [Formula R"-1]

[0145]

[0146] [Equation R"-2]

[0147]

[0148] In another example, in equation B-1,

[0149] R" may include at least one of the units represented by formulas R"-3 to R"-8.

[0150] [Formula R"-3]

[0151]

[0152] [Formula R"-4]

[0153]

[0154] [Formula R"-5]

[0155]

[0156] [Formula R"-6]

[0157]

[0158] [Formula R"-7]

[0159]

[0160] [Formula R"-8]

[0161]

[0162] Furthermore, in realizing the polymer electrolyte of the present invention, units C2 and C2' are each independently units containing oxoalkyl groups. Units C2 and C2' are used to control the dissociation of salts and ion transport capabilities in the polymer network.

[0163] For example, C2 and C2' can each independently include the unit represented by the following formula C2-1.

[0164] [Equation C2-1]

[0165]

[0166] In formula C2-1, R' is a substituted or unsubstituted linear or branched alkyl group having 1 to 10 carbon atoms, and k2 is an integer from 1 to 30.

[0167] In another example, in equation C2-1, R' can be -CH2CH2- or -CHCH3CH2-.

[0168] Furthermore, unit D contains siloxane groups and is used to control mechanical properties and affinity with the separator. Specifically, structures can be formed in the polymer network to ensure flexibility in regions other than the rigid structural regions caused by amide bonds.

[0169] For example, element D may include elements represented by equation D-1.

[0170] [Formula D-1]

[0171]

[0172] In formula D-1, R1 and R2 are straight-chain or non-straight-chain alkyl groups having 1 to 5 carbon atoms, R3, R4, R5 and R6 are each independently hydrogen, an alkyl group having 1 to 5 carbon atoms, or an aryl group having 6 to 12 carbon atoms, and g1 is an integer from 1 to 400.

[0173] Furthermore, g1 can preferably be an integer from 1 to 300, and more preferably an integer from 1 to 200.

[0174] In another example, element D may include elements represented by the following formula D-2.

[0175] [Formula D-2]

[0176]

[0177] In formula D-2, R3, R4, R5 and R6 are each independently hydrogen, an alkyl group having 1 to 5 carbon atoms, or an aryl group having 6 to 12 carbon atoms, and g2 can be an integer from 1 to 400, preferably an integer from 1 to 300, more preferably an integer from 1 to 200.

[0178] More specifically, D-1 can be at least one of the units represented by the following formulas D-3 and D-4.

[0179] [Formula D-3]

[0180]

[0181] [Formula D-4]

[0182]

[0183] In formulas D-3 and D-4, g3 and g4 can each be an integer from 1 to 400, preferably an integer from 1 to 300, and more preferably an integer from 1 to 200.

[0184] For example, according to one embodiment of the invention, the oligomers forming the polymer network may be at least one compound selected from the group consisting of compounds represented by formulas 2-1 to 2-5 below.

[0185] [Equation 2-1]

[0186]

[0187] In Equation 2-1, k3 and k4 are each independent integers from 1 to 30, and g5 is an integer from 1 to 400. l1 is an integer from 1 to 200.

[0188] [Equation 2-2]

[0189]

[0190] In Equation 2-2, k5 and k6 are each independent integers from 1 to 30, and g6 is an integer from 1 to 400. l2 is an integer from 1 to 200.

[0191] [Equation 2-3]

[0192]

[0193] In Equation 2-3, k7 and k8 are each independent integers from 1 to 30, and g7 is an integer from 1 to 400. l3 is an integer from 1 to 200.

[0194] [Equation 2-4]

[0195]

[0196] In Equation 2-4, k9 and k10 are each independent integers from 1 to 30, and g8 is an integer from 1 to 400. l4 is an integer from 1 to 200.

[0197] [Equation 2-5]

[0198]

[0199] In Equation 2-5, k11 and k12 are each independent integers from 1 to 30, and g9 is an integer from 1 to 400. l5 is an integer from 1 to 200.

[0200] Furthermore, in Formulas 2-1 to 2-5, l1 to l5 are preferably each an integer from 1 to 200, more preferably an integer from 1 to 150. When l1 to l5 are within the above range, although the polymer formed from the oligomer has high mechanical properties, its flowability remains above a predetermined level, allowing the polymer to be uniformly dispersed within the battery.

[0201] Furthermore, the oligomers of the present invention may have a weight-average molecular weight of about 1,000 to about 100,000. When the weight-average molecular weight of the oligomer is within the above range, the mechanical strength of the battery, including the oligomer, can be effectively improved.

[0202] Furthermore, the gel polymer electrolyte is preferably formed by injecting a gel polymer electrolyte composition including the oligomer into a battery casing and then curing the composition.

[0203] More specifically, the secondary battery according to the invention can be manufactured by: (a) inserting an electrode assembly consisting of a positive electrode, a negative electrode, and a separator inserted between the positive and negative electrodes into a battery casing; and (b) injecting a composition according to the invention for a gel polymer electrolyte into the battery casing, followed by polymerization to form a gel polymer electrolyte.

[0204] At this point, the polymerization reaction can be carried out using E-BEAM, gamma rays, and room temperature / high temperature aging processes.

[0205] Furthermore, various battery casings used in this art can be used as the battery casing without limitation. For example, cylindrical, square, pouch-shaped, coin-shaped, or similar shaped battery casings can be used.

[0206] In addition to oligomers, compositions for gel polymer electrolytes may include lithium salts, non-aqueous organic solvents, and polymerization initiators.

[0207] Any lithium salt can be used without particular limitation, as long as it is commonly used in electrolytes for lithium secondary batteries. For example, lithium salts may include Li. + As a positive ion, and may include F - 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 - (F2SO2)2N - CF3CF2(CF3)2CO - (CF3SO2)2CH - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N - At least one of the constituent groups serves as a negative ion. When necessary, the lithium salt may comprise a single material or a mixture of two or more materials. The content of the lithium salt can be suitably varied within the generally available range. However, for optimal effect in forming an anti-corrosion coating on the electrode surface, the lithium salt may be included in the electrolyte at a concentration of 0.8M to 2M, specifically 0.8M to 1.5M. However, the content of the lithium salt is not limited to the above range, and depending on the other components in the composition for the gel polymer electrolyte, the lithium salt may be included at a high concentration of 2M or higher.

[0208] Any non-aqueous organic solvent commonly used in electrolytes for lithium secondary batteries may be used without limitation. For example, ether compounds, ester compounds, amide compounds, linear carbonate compounds, or cyclic carbonate compounds may be used alone or in combination of two or more thereof. Typical examples of the above compounds may include cyclic carbonate compounds, linear carbonate compounds, or mixtures thereof.

[0209] Specific examples of cyclic carbonate compounds may include any one selected from 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, and fluoroethylene carbonate (FEC), or mixtures of two or more thereof. Furthermore, specific examples of linear carbonate compounds may include, but are not limited to, any one 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 thereof.

[0210] Specifically, in carbonate organic solvents, cyclic carbonates (such as ethylene carbonate and propylene carbonate), which are organic solvents with high viscosity and high dielectric constant, can be used to effectively dissociate lithium salts in the electrolyte. When linear carbonates (such as dimethyl carbonate and diethyl carbonate) with low viscosity and low dielectric constant are mixed with such cyclic carbonates in appropriate proportions, electrolytes with high conductivity can be prepared.

[0211] Furthermore, in non-aqueous organic solvents, the ether compound may be any one selected from the group consisting of: dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, and ethyl propyl ether, or a mixture of two or more of them, but is not limited thereto.

[0212] Furthermore, in non-aqueous organic solvents, the ester compound can be any one of the following groups of compounds: straight-chain esters, such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate; and cyclic esters, such as γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone, and ε-caprolactone, or mixtures of two or more of them, but not limited thereto.

[0213] The polymerization initiator decomposes upon heating in the battery, with non-limiting examples including 30°C to 100°C, specifically 60°C to 80°C, or at room temperature (5°C to 30°C) to form free radicals. The oligomers can then form gel polymer electrolytes through free radical polymerization.

[0214] The polymerization initiator can be any typical polymerization initiator known in the art, and can be at least one selected from the group consisting of azo compounds, peroxide compounds, or mixtures thereof.

[0215] For example, polymerization initiators can be organic peroxides or hydroperoxides, such as benzoyl peroxide, acetyl peroxide, dilauryl peroxide, di-tert-butyl peroxide, t-butyl peroxy-2-ethyl-hexanoate, cumyl hydroperoxide, and hydrogen peroxide. The peroxide, or at least one azo compound selected from the group consisting of 2,2'-azobis(2-cyanobutane), dimethyl 2,2'-azobis(2-methylpropionate), 2,2'-azobis(methylbutyronitrile), 2,2'-azobis(isobutyronitrile) (AIBN), and 2,2'-azobis(dimethylvaleronitrile) (AMVN), but not limited thereto.

[0216] The polymerization initiator can be included in an amount from 0.1% to 5% by weight based on the total weight of the oligomers. When the content of the polymerization initiator is greater than 5% by weight, unreacted polymerization initiator may remain during the preparation of the gel polymer electrolyte, thereby adversely affecting the battery performance. On the other hand, when the content of the polymerization initiator is less than 0.01% by weight, gelation may not be achieved even under conditions above the predetermined temperature.

[0217] According to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell is provided, and a battery pack including the battery module is provided. The battery module and the battery pack include lithium secondary batteries with high capacity, high-speed characteristics, and cycle characteristics, and therefore can be used as power sources for medium and large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and energy storage systems. Detailed Implementation

[0218] The present invention will be described in more detail below with reference to specific embodiments. However, the following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. It will be apparent to those skilled in the art that various changes and modifications can be made without departing from the scope and spirit of the invention, and such changes and modifications obviously fall within the scope of the appended claims.

[0219] [Example]

[0220] 1. Example 1

[0221] (1) Preparation of organic adhesives

[0222] In a nitrogen atmosphere, vinylidene fluoride (VDF) as a monomer, diisopropyl peroxydicarbonate as a free radical initiator, and 1,1,2-trichlorotrifluoroethane as a solvent were introduced into a reactor cooled to -15°C. Then, while maintaining the temperature at 45°C to initiate polymerization, the reactants were stirred at 200 rpm to polymerize a compound in which the unit represented by formula X-1 was repeatedly applied. After 10 hours, the polymerization was terminated by introducing NaCl by substituting Cl at the end of the polymerized compound, and unreacted monomers were removed.

[0223] The polymerized compound was dispersed in N-methylpyrrole as a solvent, and then acrylic acid was introduced at a molar ratio of 1:1.1 based on the polymerized compound. The mixture was stirred at 200 rpm in the presence of NaOH while maintaining a temperature of 45°C. After 10 hours, it was dried at 120°C to obtain an organic binder substituted with an acryloxy group and a Cl group at its terminal.

[0224] (2) Preparation of separators for lithium secondary batteries

[0225] A coating composition was prepared by adding 27g of alumina (Al2O3) as inorganic particles and 3g of the organic binder from Example 1 to 72.1ml of N-methylpyrrole.

[0226] The coating composition was applied to a polyethylene substrate with a thickness of 10 μm and then dried to prepare a separator (total thickness = 20 μm) for lithium secondary batteries, the separator having a coating with a thickness of 10 μm.

[0227] 2. Example 2

[0228] In a nitrogen atmosphere, a mixture of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) in a 7:3 weight ratio as monomers, diisopropyl peroxydicarbonate as a free radical initiator, and 1,1,2-trichlorotrifluoroethane as a solvent were introduced into a reactor cooled to -15°C. The polymerization reaction was then carried out by stirring the reactants at 200 rpm while maintaining a temperature of 45°C to initiate polymerization, thus repeating the unit represented by Formula X-2. After 10 hours, the polymerization reaction was terminated by introducing NaCl to replace Cl at the end of the polymerized compound, and the unreacted monomers were discharged.

[0229] The polymerized compound was dispersed in N-methylpyrrole as a solvent, and then acrylic acid was introduced at a molar ratio of 1:1.1 based on the polymerized compound. The mixture was stirred at 200 rpm in the presence of NaOH while maintaining a temperature of 45°C. After 10 hours, it was dried at 120°C to obtain an organic binder substituted with an acryloxy group and a Cl group at its terminal.

[0230] A separator for a lithium secondary battery was prepared in the same manner as in Example 1, except that the organic adhesive prepared according to Example 2 was used.

[0231] Comparative example

[0232] Comparative Example 1

[0233] Uncoated polyethylene substrates are used as separators for lithium secondary batteries.

[0234] Comparative Example 2

[0235] A separator for a lithium secondary battery was prepared in the same manner as in Example 2, except that unsubstituted polyvinylidene fluoride-hexafluoropropylene copolymer (PvDF-co-HFP) (weight average molecular weight = 100,000) was used as an organic binder.

[0236] [Manufacturing Example] Manufacturing of Lithium-ion Secondary Batteries

[0237] 94% by weight of Li(Ni) will be used as the positive electrode active material. 1 / 3 Co 1 / 3 Mn 1 / 3O2, 3% by weight of carbon black as a conductive agent, and 3% by weight of polyvinylidene fluoride (PVDF) as a binder were added to N-methyl-2-pyrrolidone (NMP) as a solvent to prepare a positive electrode active material slurry. The positive electrode active material slurry was applied to an aluminum (Al) film with a thickness of about 20 μm, which served as the positive electrode current collector, dried, and then rolled to manufacture the positive electrode.

[0238] A negative electrode active material slurry was prepared by adding 96 wt% carbon powder as the negative electrode active material, 3 wt% PVDF as the binder, and 1 wt% carbon black as the conductive agent to NMP as the solvent. The negative electrode active material was applied to a copper (Cu) film with a thickness of about 10 μm, which served as the negative electrode current collector, dried, and then rolled to manufacture the negative electrode.

[0239] The battery is assembled using the positive electrode, the negative electrode, and the separator according to Examples 1 and 2 and Comparative Examples 1 and 2.

[0240] 5 g of the compound represented by Formula 1-1 (n1 = 3) and 0.01 g of dimethyl 2,2'-azobis(2-methylpropionate) (CAS No.: 2589-57-3) as a polymerization initiator were added to 94.99 g of an organic solvent in which 1 M LiPF6 was dissolved in ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 3:7 (volume ratio) to prepare a gel polymer electrolyte composition.

[0241] The gel polymer electrolyte composition was introduced into the assembled battery, and the electrode assembly was stored at room temperature for 2 days and then heated at 65°C for 5 hours to manufacture a lithium secondary battery.

[0242] [Experimental Example]

[0243] 1. Experimental Example 1: Initial Capacity Determination Experiment

[0244] The lithium secondary batteries manufactured in Examples 1 and 2, and the lithium secondary batteries manufactured in Comparative Examples 1 and 2, were each subjected to a formation process at a current of 100 mA (0.1C rate). Then, a CC / CV charge of 4.2V, 333mA (0.3C, 0.05C cut-off) and a CC discharge of 3V, 333mA (0.3C) were repeated three times, and the capacity of the third discharge was defined as the initial capacity. The results are shown in Table 1 below.

[0245] Table 1

[0246] Initial capacity (mAh) Example 1 1027±5 Example 2 1018±5 Comparative Example 1 985±5 Comparative Example 2 1002±5

[0247] Referring to Table 1, the lithium secondary batteries of Examples 1 and 2 exhibit high adhesion between the gel polymer electrolyte and the separator, thereby achieving higher initial capacity at high voltage.

[0248] Meanwhile, as shown in Table 1, compared with the lithium secondary batteries of Examples 1 and 2, the lithium secondary batteries of Comparative Examples 1 and 2 have lower adhesion between the electrolyte and the separator and lack interfacial characteristics, and therefore their initial capacity is relatively low.

[0249] 2. Test Example 2: Cyclic (Life) Measurement

[0250] The lithium secondary batteries manufactured in Examples 1 and 2, and those manufactured in Comparative Examples 1 and 2, were each subjected to a forming process at a current of 100 mA (0.1C rate). Subsequently, 100 cycles of CC / CV charging at 4.2V, 333mA (0.3C, 0.05C cut-off) and CC discharging at 3V, 333mA (0.3C) were repeated, and the capacity retention was determined by comparing the capacity at the 100th discharge with the initial capacity. The results are shown in Table 2 below.

[0251] Table 2

[0252] Capacity retention rate (%) after 100 cycles Example 1 93±2 Example 2 94±2 Comparative Example 1 88±2 Comparative Example 2 90±2

[0253] Referring to Table 2, the lithium secondary batteries of Examples 1 and 2 exhibit excellent interfacial adhesion between the gel polymer electrolyte and the separator, as well as excellent gel polymer electrolyte distribution, thereby suppressing additional degradation reactions of the electrolyte and thus improving cycle life.

[0254] Meanwhile, as shown in Table 2, compared with the lithium secondary batteries of Examples 1 to 2, the lithium secondary batteries of Comparative Examples 1 and 2 have lower adhesion between the electrolyte and the separator and lack interfacial characteristics, thus causing additional degradation of the electrolyte and resulting in a decrease in capacity retention after cycling.

[0255] 3. Test Example 3: Nail Penetration Test

[0256] Each fully charged lithium secondary battery manufactured in Examples 1 and 2, as well as Comparative Examples 1 and 2, was pierced with a metal nail of 2.5 mm in diameter at a speed of 600 mm / min to conduct a safety assessment test on the secondary battery through mechanical impact and internal short circuit.

[0257] At this point, the metal nail caused an internal short circuit in the lithium secondary battery, leading to battery heating. The higher the temperature, the higher the likelihood of fire; therefore, the safety level was determined to be low. Furthermore, when this heating resulted in a fire, the safety of the secondary battery was determined to be very low. The test results are shown in Table 3 below.

[0258] Table 3

[0259]

[0260] As shown in Table 3, compared to the lithium secondary batteries of the comparative examples, the lithium secondary batteries of Examples 1 and 2 have a lower heat generation temperature of approximately 60°C. On the other hand, the lithium secondary batteries of Comparative Examples 1 and 2 have higher heat generation temperatures of 100°C and 95°C, respectively, thus confirming a reduction in safety. Furthermore, even when safety is assessed based on the number of batteries that caught fire, it can be seen that the lithium secondary batteries of Examples 1 and 2 are safer.

Claims

1. A lithium secondary battery, comprising: positive electrode; negative electrode; The partition includes: substrate; and A coating formed on the surface of the substrate, wherein The coating comprises an organic binder and inorganic particles, and The organic adhesive contains olefinically unsaturated groups. The olefinic unsaturated group is located at the end or side of the main chain of a polymer comprising at least one unit selected from the group consisting of formulas X-4 to X-6: [Formula X-4] In equation X-4, m5 is an integer from 1 to 100. [Formula X-5] In equation X-5, m6 is an integer from 1 to 100. [Formula X-6] In equation X-6, m7 is an integer from 1 to 100; and A gel polymer electrolyte, disposed between the positive electrode, the negative electrode and the separator, and formed by polymerization of an oligomer containing (meth)acrylate groups, wherein a three-dimensional polymer network is formed by polymerization of an organic binder containing olefinic unsaturated groups included in the separator and the oligomer containing (meth)acrylate groups.

2. The lithium secondary battery of claim 1, wherein the olefinic unsaturated group is at least one selected from the group consisting of vinyl, acryloyloxy, and methacryloxy.

3. The lithium secondary battery of claim 1, wherein the organic binder is included in an amount of 1 to 80 parts by weight based on 100 parts by weight of the coating.

4. The lithium secondary battery of claim 1, wherein the oligomer further comprises an oxyalkylene group.

5. The lithium secondary battery of claim 1, wherein the oligomer is represented by formula 1: [Formula 1] A-C1-A' In Formula 1, A and A' are each independently a unit containing a (meth)acrylate group, and C1 is a unit containing an oxane group.

6. The lithium secondary battery of claim 1, wherein the oligomer comprises at least one compound selected from compounds represented by formulas 1-1 to 1-5: [Equation 1-1] In Equation 1-1, n1 is an integer from 1 to 20,000. [Equation 1-2] In Equation 1-2, n2 is an integer from 1 to 20,000. [Equation 1-3] In equations 1-3, n3 is an integer from 1 to 20,000. [Equations 1-4] In equations 1-4, n4 is an integer from 1 to 20,000. [Equations 1-5] In Equations 1-5, n5 is an integer from 1 to 20,000.

7. The lithium secondary battery of claim 1, wherein the oligomer is represented by formula 2: [Equation 2] In Formula 2, A and A' are each independently a unit containing a (meth)acrylate group, B and B' are each independently a unit containing an amide group, C2 and C2' are each independently a unit containing an oxoalkyl group, D is a unit containing a siloxane group, and l is an integer from 1 to 200.

8. The lithium secondary battery of claim 1, wherein the oligomer comprises at least one compound selected from compounds represented by formulas 2-1 to 2-5: [Equation 2-1] In Equation 2-1, k3 and k4 are each independent integers from 1 to 30, g5 is an integer from 1 to 400, and l1 is an integer from 1 to 200. [Equation 2-2] In Equation 2-2, k5 and k6 are each independent integers from 1 to 30, g6 is an integer from 1 to 400, and l2 is an integer from 1 to 200. [Equation 2-3] In Equation 2-3, k7 and k8 are each independent integers from 1 to 30, g7 is an integer from 1 to 400, and l3 is an integer from 1 to 200. [Equation 2-4] In Equation 2-4, k9 and k10 are each independent integers from 1 to 30, g8 is an integer from 1 to 400, and l4 is an integer from 1 to 200. [Equation 2-5] In Equation 2-5, k11 and k12 are each independent integers from 1 to 30, g9 is an integer from 1 to 400, and l5 is an integer from 1 to 200.

9. The lithium secondary battery of claim 1, wherein the gel polymer electrolyte is formed by injecting a gel polymer electrolyte composition comprising the oligomer into a battery casing and then curing the composition.

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