Gel polymer electrolyte and electrochemical device containing said gel polymer electrolyte

Abstract

The gel polymer electrolyte according to one embodiment of the present invention includes a matrix polymer made of an oligomer including a fluorine-substituted polyether unit and at least one acrylate unit at its terminal, which increases the degree of freedom of Li ions through immobilization and stabilization of anions, thereby reducing battery resistance and achieving high lithium ion conductivity. In addition, the matrix polymer structure in the gel polymer electrolyte increases high-temperature durability, allowing the manufacture of a lithium secondary battery with improved stability at high voltages and high temperatures.

Description

[Technical Field]

[0001] This application claims priority to Korean Patent Application No. 10-2022-0046564, filed on April 14, 2022. The present invention relates to a gel polymer electrolyte and a lithium secondary battery including the gel polymer electrolyte. [Background technology]

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

[0003] A lithium secondary battery is manufactured by applying a positive electrode active material and a negative electrode active material to a current collector in an appropriate thickness, or by forming the active material itself into a film of an appropriate length, and then winding or laminating the film together with a separator, which is an insulator, to manufacture an electrode assembly. The electrode assembly is then placed in a can or a similar container, and an electrolyte is then injected into the electrode assembly.

[0004] The positive electrode active material is lithium metal oxide, and the negative electrode active material is lithium metal, lithium alloy, crystalline carbon, amorphous carbon, or a carbon composite. The electrolyte is typically a liquid electrolyte, particularly an ion-conductive liquid electrolyte prepared by dissolving a salt in a non-aqueous organic solvent.

[0005] However, with the growing interest in energy storage technology, there is a demand for the development of secondary batteries that are small and lightweight, capable of high-capacity charging and discharging, and safe at high temperatures and voltages. Therefore, in recent years, the development of batteries using gel polymer electrolytes, which are made of gel polymers rather than liquid electrolytes, has attracted attention.

[0006] It is generally known that the safety of batteries improves in the order of liquid electrolyte < gel polymer electrolyte < solid polymer electrolyte, while the performance of the batteries decreases.

[0007] That is, gel polymer electrolytes have the disadvantage of lower lithium ion conductivity compared to liquid electrolytes consisting only of an electrolyte solution. To address this issue, methods have been proposed for reducing the thickness of the gel polymer electrolyte. However, this reduces the mechanical strength and can cause problems with battery performance and safety, such as short circuits between the positive and negative electrodes and the gel polymer electrolyte during battery manufacturing.

[0008] Therefore, there is a need for the development of gel polymer electrolytes that improve both the safety and performance of batteries. Summary of the Invention [Problem to be solved by the invention]

[0009] An object of the present invention is to provide a gel polymer electrolyte that can achieve the effects of increasing high voltage stability and reducing battery resistance.

[0010] Another object of the present invention is to provide the gel polymer electrolyte composition.

[0011] It is yet another object of the present invention to provide a lithium secondary battery containing the gel polymer electrolyte.

[0012] It will be readily apparent to those skilled in the art that other objects and advantages of the present invention can be realized by the means recited in the claims and combinations thereof. [Means for solving the problem]

[0013] A first aspect of the present invention relates to a gel polymer electrolyte, the gel polymer electrolyte including a matrix polymer and an electrolyte solution impregnated in the matrix polymer, the matrix polymer being formed into a three-dimensional network structure by polymerization of an oligomer represented by the following Chemical Formula 1, the electrolyte solution including a lithium salt and a non-aqueous solvent, the non-aqueous solvent including at least one selected from the group consisting of a cyclic carbonate-based compound, a linear carbonate-based compound, an alkyl ether-based compound, an alkyl acetate-based compound, an alkyl propionate-based compound, and a nitrile-based compound:

[0014] [ka]

[0015] In Chemical Formula 1, r is an integer equal to or greater than 1, R1 is an aliphatic hydrocarbon group or an aromatic hydrocarbon group, R2 and R5 each independently represent an alkyl group having 1 to 3 carbon atoms in which at least one hydrogen atom is substituted with a fluorine atom, R3 is an alkyl group having n carbon atoms in which all hydrogen atoms have been substituted with fluorine atoms, R4 is an alkyl group having n-1 carbon atoms in which all hydrogen atoms have been substituted with fluorine atoms, and n is 2 or 3; Either one of p and q may be 0 or both may be integers of 1 or more. When both p and q are integers of 1 or more, p / q has a value of 1 / 9 to 9 / 1; R6 and R7 each independently represent a linear or branched alkyl group having 1 to 5 carbon atoms; R8 is null or a methyl group, and m is any one of integers 1, 2, 3, 4, and 5.

[0016] According to a second aspect of the present invention, in the first aspect, the oligomer includes a unit A represented by the following chemical formula 2, a unit B represented by the following chemical formula 3, and a unit C represented by the following chemical formula 4:

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[0020] In Chemical Formula 2, Chemical Formula 3 and Chemical Formula 4, r is an integer equal to or greater than 1, R1 is an aliphatic hydrocarbon group or an aromatic hydrocarbon group, R2 and R5 each independently represent an alkyl group having 1 to 3 carbon atoms in which at least one hydrogen atom is substituted with a fluorine atom, R3 is an alkyl group having n carbon atoms in which all hydrogen atoms have been substituted with fluorine atoms, R4 is an alkyl group having n-1 carbon atoms in which all hydrogen atoms have been substituted with fluorine atoms, and n is 2 or 3; Either one of p and q may be 0 or both may be integers of 1 or more. When both p and q are integers of 1 or more, p / q has a value of 1 / 9 to 9 / 1; R6 and R7 each independently represent a linear or branched alkyl group having 1 to 5 carbon atoms; The R8 is null or a methyl group, and the m is any one of integers 1, 2, 3, 4, and 5.

[0021] According to a third aspect of the present invention, in the second aspect, the chemical formula 2 can be divided into a unit represented by the following chemical formula 2-1 and a unit represented by the following chemical formula 2-2.

[0022] [ka]

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[0024] In Chemical Formula 2-2, R1 is an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, or an aromatic hydrocarbon group.

[0025] According to a fourth aspect of the present invention, in the third aspect, the aliphatic hydrocarbon group is an alkylene group having 1 to 20 carbon atoms; an alkylene group having 1 to 20 carbon atoms and containing an isocyanate group (NCO); an alkoxylene group having 1 to 20 carbon atoms; an alkenylene group having 2 to 20 carbon atoms; or an alkynylene group having 2 to 20 carbon atoms, the alicyclic hydrocarbon group is a substituted or unsubstituted cycloalkylene group having 4 to 20 carbon atoms; a substituted or unsubstituted cycloalkylene group containing an isocyanate group (NCO) and having 4 to 20 carbon atoms; a cycloalkenylene group having 4 to 20 carbon atoms; or a heterocycloalkylene group having 2 to 20 carbon atoms, The aromatic hydrocarbon group is a substituted or unsubstituted arylene group having 6 to 20 carbon atoms; or a heteroarylene group having 2 to 20 carbon atoms.

[0026] According to a fifth aspect of the present invention, in the fourth aspect, the structure represented by chemical formula 2-2 is derived from any one of compounds represented by the following chemical formulas a to n.

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[0041] According to a sixth aspect of the present invention, in the fourth aspect, the structure represented by the chemical formula 2-2 is any one of structures represented by the following chemical formulas o to x.

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[0052] According to a seventh aspect of the present invention, in any one of the second to sixth aspects, the Chemical Formula 4 provides (meth)acryloyl groups at both ends of the oligomer of the Chemical Formula 1.

[0053] According to an eighth aspect of the present invention, in any one of the first to seventh aspects, the oligomer includes a compound represented by the following chemical formula 5:

[0054] [ka]

[0055] According to a ninth aspect of the present invention, in any one of the first to eighth aspects, the oligomer has a weight average molecular weight (Mw) of about 1,000 g / mol to 500,000 g / mol.

[0056] According to a 10th aspect of the present invention, in any one of the 1st to 9th aspects, the matrix polymer further contains 5 to 700 parts by weight of inorganic particles relative to 100 parts by weight of the oligomer.

[0057] According to an eleventh aspect of the present invention, in any one of the first to tenth aspects, the gel polymer electrolyte has a gel content of about 1 wt % or more at a temperature of 25°C.

[0058] A twelfth aspect of the present invention relates to a lithium ion secondary battery, the secondary battery including a negative electrode, a positive electrode, and a gel polymer electrolyte, the gel polymer electrolyte being according to any one of the first to eleventh aspects.

[0059] A thirteenth aspect of the present invention relates to a composition for a gel polymer electrolyte, the composition comprising a lithium salt, a non-aqueous solvent, a polymerization initiator, and an oligomer represented by the following chemical formula 1, the oligomer being contained in an amount of 0.5 wt % to 20 wt % based on the total weight of the composition for the gel polymer electrolyte:

[0060] [ka]

[0061] In Chemical Formula 1, r is an integer equal to or greater than 1, R1 is an aliphatic hydrocarbon group or an aromatic hydrocarbon group, R2 and R5 each independently represent an alkyl group having 1 to 3 carbon atoms in which at least one hydrogen atom is substituted with a fluorine atom, R3 is an alkyl group having n carbon atoms in which all hydrogen atoms have been substituted with fluorine atoms, R4 is an alkyl group having n-1 carbon atoms in which all hydrogen atoms have been substituted with fluorine atoms, and n is 2 or 3; Either one of p and q may be 0 or both may be integers of 1 or more. When both p and q are integers of 1 or more, p / q has a value of 1 / 9 to 9 / 1; R6 and R7 each independently represent a linear or branched alkyl group having 1 to 5 carbon atoms; The R8 is null or a methyl group, and the m is any one of integers 1, 2, 3, 4, and 5. [Effects of the Invention]

[0062] The gel polymer electrolyte according to one embodiment of the present invention includes a matrix polymer composed of an oligomer having a fluorine-substituted polyether unit and at least one acrylate unit at its terminal, which immobilizes and stabilizes anions, thereby increasing the degree of freedom of Li ions and reducing battery resistance, thereby achieving high lithium ion conductivity. Furthermore, the matrix polymer structure within the gel polymer electrolyte increases high-temperature durability, allowing the production of a lithium secondary battery with improved stability at high voltages and high temperatures.

[0063] The drawings attached to this specification illustrate preferred embodiments of the present invention and serve to further understand the technical ideas of the present invention as well as the contents of the invention, and therefore the present invention should not be interpreted as being limited to only the matters depicted in the drawings. Meanwhile, the shape, size, scale, or ratio of elements in the drawings attached to this specification may be exaggerated to emphasize a clearer description. [Brief explanation of the drawings]

[0064] [Figure 1] 1 is a graph showing experimental results of heat generation safety of batteries according to Example 1 and Comparative Example 1. [Figure 2] 1 is a graph showing a comparison of experimental results of capacity retention rate and resistance increase rate of batteries according to Example 1 and Comparative Example 1. [Figure 3] 10 shows the results of a hot box test of the battery according to Example 2. [Figure 4] 10 shows the results of a hot box test of the battery according to Comparative Example 2. [Figure 5] 10 is a graph showing the capacity and thickness change rate when the batteries according to Example 2 and Comparative Example 2 are repeatedly charged and discharged. FIG. [Figure 6] 1 is a photographic image of the battery of Example 2 subjected to hot box testing. [Figure 7] 10 is a photographic image of the battery of Comparative Example 2 subjected to a hot box test. DETAILED DESCRIPTION OF THE INVENTION

[0065] The present invention will be described in detail below. Prior to this, the terms and words used in this specification and claims should not be construed as being limited to their ordinary and dictionary meanings, but should be construed as having meanings and concepts that correspond to the technical ideas of the present invention, based on the principle that the inventor himself can appropriately define the concepts of terms in order to best describe the invention. Therefore, it should be understood that the embodiments described in this specification and the configurations shown in the drawings are merely the most preferred embodiments of the present invention and do not represent the entire technical ideas of the present invention, and therefore, various equivalents and modifications that can be substituted therefor may exist at the time of filing this application.

[0066] Throughout the specification, when a part "comprises" another component, it does not mean excluding the other component, but rather means that the part may further include the other component, unless otherwise specified.

[0067] Furthermore, the terms "about," "substantially," and the like used throughout this specification, when given manufacturing and material tolerances inherent in the stated meaning, are used to mean a numerical value or a value close to that numerical value, in order to prevent unscrupulous infringers from unfairly using disclosure content in which precise or absolute numerical values ​​are stated to aid in the understanding of this application.

[0068] Throughout this specification, the phrase "A and / or B" means "A, B, or all of these."

[0069] On the other hand, in this specification, the term "repeating unit" refers to a unit formed by polymerizing a monomer and derived from the monomer. The repeating unit may be a unit formed directly by a polymerization reaction, or may be a unit in which a part of the unit is converted into a different structure by treating the polymer.

[0070] In the present invention, unless otherwise specified, "*" means the same or different atoms or the linked portions between the ends of a chemical formula.

[0071] In general, gel-type polymer electrolytes are weaker in terms of high voltage safety and mechanical properties than solid polymer electrolytes, and have disadvantages such as lower battery resistance and ionic conductivity than liquid electrolytes.

[0072] Therefore, in recent years, research has been conducted to improve lithium ion conductivity while ensuring high voltage stability by using copolymers such as oligomers. However, when using oligomer compounds, it is not easy to control physical properties and it is difficult to form a uniform polymer within the battery, making it difficult to apply them to high-capacity and large-scale batteries.

[0073] Therefore, the present invention aims to solve these problems by providing a gel polymer electrolyte containing a matrix polymer formed from an oligomer compound produced by polymerizing compounds having physical properties that can mutually complement each other in electrochemical properties and mechanical properties.

[0074] Specifically, one embodiment of the present invention comprises a matrix polymer; an electrolyte solution impregnated in the matrix polymer; The matrix polymer is formed into a three-dimensional network structure by polymerization of an oligomer represented by the following chemical formula 1: The oligomer provides a gel polymer electrolyte including a unit A represented by the following Chemical Formula 2, a unit B represented by the following Chemical Formula 3, and a unit C represented by the following Chemical Formula 4:

[0075] [ka]

[0076] In Chemical Formula 1, r is an integer equal to or greater than 1, R1 is an aliphatic hydrocarbon group or an aromatic hydrocarbon group, R2 and R5 each independently represent an alkyl group having 1 to 3 carbon atoms in which at least one hydrogen atom is substituted with a fluorine atom, R3 is an alkyl group having n carbon atoms in which all hydrogen atoms have been substituted with fluorine atoms, R4 is an alkyl group having n-1 carbon atoms in which all hydrogen atoms have been substituted with fluorine atoms, and n is 2 or 3; Either one of p and q may be 0 or both may be integers of 1 or more. When both p and q are integers of 1 or more, p / q may have a value of 1 / 9 to 9 / 1; R6 and R7 may each independently be a linear or branched alkyl group having 1 to 5 carbon atoms. In a more specific embodiment, R6 may be a linear or branched alkyl group having 2 to 4 carbon atoms.

[0077] In addition, R8 is null or a methyl group, and m is any one of integers 1, 2, 3, 4, and 5.

[0078] In the present invention, the explanations about R1 to R7, r, p, and q also apply to the following chemical formulas 2, 3, 4, and 5.

[0079] Hereinafter, Chemical Formula 1 will be described in detail by dividing it into the unit A (Chemical Formula 2), unit B (Chemical Formula 3), and unit C (Chemical Formula 4) that constitute Chemical Formula 1.

[0080] [ka]

[0081] In the above Chemical Formula 2, p, q, and r each represent the number of repeating units. The unit A can be divided into a unit A-1 represented by Chemical Formula 2-1 and a unit A-2 represented by Chemical Formula 2-2 as follows, and will be described below separately for Chemical Formula 2-1 and Chemical Formula 2-2. In Chemical Formula 2, r is an integer of 1 or more and can have a value of 1 to 20. The molecular weight (Mw) of the unit A represented by Chemical Formula 2 can have a value of 100 to 100,000.

[0082] [ka]

[0083] In Chemical Formula 2-1, R2 and R5 are each independently an alkyl group having 1 to 3 carbon atoms in which at least one hydrogen atom has been substituted with a fluorine atom. R3 is an alkyl group having n carbon atoms in which all hydrogen atoms have been substituted with fluorine atoms, and R4 is an alkyl group having n-1 carbon atoms in which all hydrogen atoms have been substituted with fluorine atoms, where n is 2 or 3. In Chemical Formula 2-1, either p or q may be 0, or both may be integers of 1 or greater. If both p and q are integers of 1 or greater, p / q may have a value of 1 / 9 to 9 / 1.

[0084] [ka]

[0085] In Chemical Formula 2-2, R1 can be an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, or an aromatic hydrocarbon group.

[0086] In one embodiment of the present invention, the aliphatic hydrocarbon group is an alkylene group having 1 to 20 carbon atoms; an alkylene group having 1 to 20 carbon atoms and containing an isocyanate group (NCO); an alkoxylene group having 1 to 20 carbon atoms; an alkenylene group having 2 to 20 carbon atoms; or an alkynylene group having 2 to 20 carbon atoms, the alicyclic hydrocarbon group is a substituted or unsubstituted cycloalkylene group having 4 to 20 carbon atoms; a substituted or unsubstituted cycloalkylene group containing an isocyanate group (NCO) and having 4 to 20 carbon atoms; a cycloalkenylene group having 4 to 20 carbon atoms; or a heterocycloalkylene group having 2 to 20 carbon atoms, The aromatic hydrocarbon group may be a substituted or unsubstituted arylene group having 6 to 20 carbon atoms; or a heteroarylene group having 2 to 20 carbon atoms.

[0087] In one embodiment of the present invention, the structure represented by Chemical Formula 2-2 may be derived from any one of the compounds represented by the following Chemical Formulas a to n:

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[0102] The unit A contains a fluorine-substituted ether in its structure, which can improve high-voltage safety, reduce battery resistance, and improve ionic conductivity through anion stabilization and increased oxidation stability.

[0103] Meanwhile, in a specific embodiment of the present invention, the structure of the formula 2-2 may be any one of the following formulas o to x.

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[0114] In one embodiment of the present invention, the unit B may be represented by the following Chemical Formula 3:

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[0116] In Chemical Formula 3, * on both sides represents a portion connecting to the unit A-1 and the unit C described below. For details about R1 in Chemical Formula 3, please refer to the description of R1 in Chemical Formula 2-2 above.

[0117] Meanwhile, in a specific embodiment of the present invention, the structure represented by Chemical Formula 3 may be any of the structures represented by Chemical Formulas o to x as described above. In one embodiment of the present invention, the unit C may be represented by the following Chemical Formula 4:

[0118] [ka]

[0119] The unit C is bonded to both ends of the oligomer and provides functional groups capable of reacting with a crosslinker at both ends of the oligomer. In Chemical Formula 4, R6 and R7 may each independently be a linear or branched alkyl group having 1 to 5 carbon atoms. In a more specific embodiment, R6 may be a linear or branched alkyl group having 2 to 4 carbon atoms. R8 may be null or a methyl group. m is an integer of 1, 2, 3, 4, or 5. That is, the unit C is capable of providing (meth)acryloyl groups at both ends of the oligomer.

[0120] In the gel polymer electrolyte of the present invention, the oligomer may include, as a representative example, a compound represented by the following Chemical Formula 5:

[0121] [ka]

[0122] The present invention will be described in more detail below with reference to examples. However, the examples described below are for illustrative purposes only and are not intended to limit the scope of the present invention.

[0123] The weight-average molecular weight (Mw) of the oligomer for forming the gel polymer electrolyte of the present invention may be about 1,000 g / mol to 500,000 g / mol, specifically 1,000 g / mol to 100,000 g / mol. When the weight-average molecular weight of the oligomer is within the above range, the mechanical strength of the battery containing it can be effectively improved.

[0124] When the weight-average molecular weight of the copolymer is within the above range, it is possible to ensure mechanical properties, processability (moldability), electrochemical stability, etc. In this regard, in the unit A represented by Chemical Formula 1, p, q, and r may be appropriately changed within the above range depending on the weight-average molecular weight of the copolymer.

[0125] The weight-average molecular weight can be measured using gel permeation chromatography (GPC). For example, a sample of a certain concentration is prepared, and then the GPC measurement system Alliance 4 is stabilized. Once the instrument is stabilized, a standard sample and a sample are injected into the instrument to obtain a chromatogram, and the molecular weight is calculated according to the analytical method (system: Alliance 4, column: Ultrahydrogel linear x 2, eluent: 0.1 M NaNO3 (pH 7.0 phosphate buffer), flow rate: 0.1 mL / min, temperature: 40°C, injection volume: 100 μL).

[0126] Meanwhile, when the gel polymer electrolyte of the present invention is embodied as a coating type gel polymer electrolyte, the matrix polymer may further include 5 to 700 parts by weight, specifically 100 to 400 parts by weight, of inorganic particles relative to 100 parts by weight of the oligomer.

[0127] The inorganic particles are preferably included in an amount of 700 parts by weight or less to effectively prevent an increase in interfacial resistance with the electrode. If the inorganic particles are included in an amount exceeding 700 parts by weight, pores may be formed within the electrolyte, resulting in a decrease in ionic conductivity. Furthermore, if the inorganic particles are included in an amount less than 5 parts by weight, the effect of improving electrochemical stability while maintaining mechanical properties is reduced.

[0128] The inorganic particles are impregnated into the matrix polymer, allowing the high-viscosity solvent to penetrate well through the pores formed by the spaces between the inorganic particles. That is, the inclusion of inorganic particles can have the effect of further improving wettability with high-viscosity solvents due to the affinity between polar substances and capillary action.

[0129] Such inorganic particles have a high dielectric constant and are within the operating voltage range of lithium secondary batteries (e.g., Li / Li +Inorganic particles that do not undergo oxidation and / or reduction reactions at a reference of 0 to 5 V can be used. Specifically, representative examples of the inorganic particles include BaTiO3, BaTiO3, Pb(Zr,Ti)O3 (PZT), Pb 1-x La x Zr 1-y Ti y O3 (PLZT, 0 < x < 1, 0 < y < 1), Pb(Mg 1 / 3 Nb 2 / 3 )O3 - PbTiO3 (PMN - PT), hafnia (HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, Al2O3, TiO2, SiC, lithium phosphate (Li3PO4), lithium titanium phosphate (Li x1 Ti y1 (PO4)3, 0 < x1 < 2, 0 < y1 < 3), lithium aluminum titanium phosphate (Li x2 Al y2 Ti z2 (PO4)3, 0 < x2 < 2, 0 < y2 < 1, 0 < z2 < 3), (LiAlTiP) x3 O y3 -based glass (0 < x3 < 4, 0 < y3 < 13), lithium lanthanum titanate (Li x4 La y4 TiO3, 0 < x4 < y4 < 3), Li 3.25 Ge 0.25 P 0.75 S4 such as lithium germanium thiophosphate (Li x5 Ge y5 P z S w , (Li x6 N<00,00025>), lithium nitride such as Li3N (0 < x6 < 4, 0 < y6 < 2), SiS2 - based glass such as Li3PO4 - Li2S - SiS2 (Li x7 Si y7 S z2 , 0 < x7 < 3, 0 < y7 < 2, 0 < z2 < 4), P2S5 - based glass such as LiI - Li2S - P2S5 (Li x8 P y8 Sz3 , 0 < x8 < 3, 0 < z3 < 7), and a single substance or a mixture of two or more selected from the group consisting of lithium lanthanum zirconium oxide (Li7La3Zr2O 12 , LLZO).

[0130] The average particle size of the inorganic particles is preferably about 0.001 to 10 μm so that they are present in a uniform thickness in the gel polymer electrolyte and have an appropriate porosity. When the average particle size of the inorganic particles is less than 0.001 μm, the dispersibility decreases. When it exceeds 10 μm, not only does the thickness of the porous coating layer increase, but a phenomenon of agglomeration of the inorganic particles occurs, and there is a risk that the mechanical strength decreases while being exposed outside the gel polymer electrolyte. The gel polymer electrolyte of the present invention as described above, when measured with an impedance measurement analysis system at a temperature of 25 °C, has a Li -4 ionic conductivity of 2.5×10 + S / cm or more. At this time, the ionic conductivity was measured through an alternating current impedance measurement method after sandwiching the produced gel polymer electrolyte between a pair of platinum electrode disks with a diameter of 1 cm. The measuring device used was the VMP3 model manufactured by Bio Logic, and the measurement was performed at room temperature under the conditions of 10,000 - 0.1 Hz and an amplitude of 10 mV.

[0131] In addition, the gel polymer electrolyte may have a Li + ion migration coefficient of 0.3 or more based on the NMR measurement method at a temperature of 25 °C. At this time, the Li + ion migration coefficient can be defined as "Li + ion diffusivity / (Li + ion diffusivity + anion diffusivity)". At this time, the Li + ion diffusivity and anion diffusivity can be measured through the following devices and methods. For example, using a Varian 500 MHz NMR / dual probe, the Li + ion (cation) diffusion constant was 7 measured by Li diffusion NMR, and the anion diffusion constant was 19Measurements were performed using F diffusion NMR. The solvent used was acetone-d6. To measure the diffusion value within the sample itself, an inner tube (acetone-d6) was used to prevent mixing of the sample with the deuterium solvent. A stimulated echo with gradient pulse sequence was used in the measurement experiment. The gradient amplitude was adjusted so that the peak intensity at the highest gradient power was approximately 2-5% of the peak intensity at the lowest gradient power. This range was divided into 16 steps, as in solution NMR, and 16 different amplitudes were applied to each sample.

[0132] The gel polymer electrolyte may have a gel content of about 1 wt % or more, specifically about 20 wt % or more, at a temperature of 25° C. The gel content may refer to the weight of other components in the gel polymer electrolyte excluding the electrolyte solution.

[0133] In addition, the gel polymer electrolyte preferably has an unreacted oligomer content of 20 wt % or less based on the total amount of reactive oligomers added at a temperature of 25°C.

[0134] Here, the content of the unreacted oligomer can be determined by preparing a gel polymer electrolyte, extracting the gel polymer electrolyte with a solvent (acetone), and measuring the extracted solvent with NMR.

[0135] Meanwhile, in the gel polymer electrolyte of the present invention, the electrolyte solution impregnated in the matrix polymer contains a conventional lithium salt-containing non-aqueous solvent, and in this case, the lithium salt may include any one selected from the group consisting of LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiN(C2F5SO2)2, LiN(CF3SO2)2, CF3SO3Li, LiC(CF3SO2)3, LiC4BO8, LiTFSI, LiFSI, and LiClO4, or a mixture of two or more thereof, but is not limited thereto.

[0136] The lithium salt may be contained in the electrolyte at a molar concentration (M) to 2M, or at a concentration of 10 wt % to 50 wt % based on the total content of the oligomer. The electrolyte solvent of the present invention may be a non-aqueous solvent commonly used in electrolytes for lithium secondary batteries, and representative examples thereof may include at least one compound selected from the group consisting of cyclic carbonate compounds, linear carbonate compounds, alkyl ether compounds, alkyl acetate compounds, alkyl propionate compounds, and nitrile compounds. Examples of the cyclic carbonate compounds include at least one compound selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and fluoroethylene carbonate (FEC).

[0137] The alkyl ether compound may include at least one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, and ethyl propyl ether.

[0138] The alkyl acetate compound may include at least one selected from the group consisting of methyl acetate, ethyl acetate, and propyl acetate.

[0139] The alkyl propionate compound may include at least one selected from the group consisting of methyl propionate, ethyl propionate, propyl propionate, and butyl propionate.

[0140] The nitrile-based compound may include at least one selected from the group consisting of acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

[0141] In particular, propylene carbonate and ethylene carbonate, which are cyclic carbonates among the carbonate-based electrolyte solvents, are highly viscous organic solvents with high dielectric constants, and are therefore suitable for use because they effectively dissociate lithium salts in the electrolyte. When such cyclic carbonates are mixed with linear carbonates having low viscosity and low dielectric constants, such as ethyl methyl carbonate, diethyl carbonate, or dimethyl carbonate, in an appropriate ratio, an electrolyte having high electrical conductivity can be produced, making them more suitable for use.

[0142] In addition, the electrolyte solvent can be supplemented with common additives used in electrolytes to improve performance, such as vinylene carbonate (VC), 1,3-propane sultone (PS), succinonitrile (SN), ethylene sulfate (ESa), 1,3-propene sultone (PRS), fluoroethylene carbonate (FEC), adiponitrile (ADN), LiPO2F2, lithium difluorobis(oxalato)phosphate (LiODFB), lithium bis(oxalato)borate (LiBOB), (trimethylsilyl)propyl phosphate (TMSPa), (trimethylsilyl)propyl phosphate (TMSPi), TFEPa, and TFEPi, without limitation.

[0143] While conventional electrolytes result in metal ions leaching from the positive electrode and depositing at the negative electrode, the gel polymer electrolyte of the present invention contains a matrix polymer formed from an oligomer, thereby improving ionic conductivity through not only mechanical properties but also high-voltage safety and reduced battery resistance. This allows for the production of lithium secondary batteries with improved life and capacity characteristics. Furthermore, by forming a protective layer composed of a polymer on the surfaces of the positive and negative electrodes or stabilizing anions using a polymer structure, side reactions can be suppressed and the adhesion between the electrodes can be increased, thereby suppressing gas generation inside the battery at high temperatures. Furthermore, the gel polymer strengthens the separator, thereby improving permeation stability, improving flame retardancy, and reducing volatility, thereby improving stability during overcharging and other events.

[0144] According to another embodiment of the present invention, a composition for a gel polymer electrolyte can be provided, which comprises a lithium salt, an electrolyte solvent, a polymerization initiator, and the oligomer containing the units A to C.

[0145] The oligomer may be included in an amount of 0.5 wt % to 20 wt %, more preferably 0.5 wt % to 10 wt %, based on the total weight of the gel polymer electrolyte composition. If the oligomer content is less than 0.5 wt %, gelation is difficult and the properties of the gel polymer electrolyte are difficult to exhibit. If the oligomer content exceeds 20 wt %, the excess oligomer may increase resistance, resulting in reduced battery performance.

[0146] In the present invention, the gel polymer electrolyte of the present invention can be produced from the gel polymer electrolyte composition by using a conventionally known polymerization method.

[0147] As the polymerization initiator used in such a reaction, any ordinary polymerization initiator well known in the art can be used.

[0148] Non-limiting examples of the polymerization initiator include organic peroxides and hydroperoxides such as benzoyl peroxide, acetyl peroxide, dilauroyl peroxide, di-tert-butyl peroxide, t-butylperoxy-2-ethyl-hexanoate, cumyl hydroperoxide, and hydrogen peroxide, and azo compounds such as 2,2′-azobis(2-cyanobutane), 2,2′-azobis(methylbutyronitrile), AIBN (2,2′-azobis(isobutyronitrile)), and AMVN (2,2′-azobisdimethylvaleronitrile), but are not limited thereto.

[0149] The polymerization initiator is decomposed in the battery by heat, for example, at 30°C to 100°C, or at room temperature (5°C to 30°C) to form radicals, and the polymerizable oligomer reacts with the acrylate compound through free radical polymerization to form a gel polymer electrolyte.

[0150] The polymerization initiator may be used in an amount of 0.01 to 5 parts by weight based on 100 parts by weight of the oligomer. If the amount of the polymerization initiator exceeds 5 parts by weight, gelation may occur too quickly during injection of the gel polymer electrolyte composition into the battery, or unreacted initiator may remain, adversely affecting subsequent battery performance. If the amount of the polymerization initiator is less than 0.01 part by weight, gelation may not occur smoothly.

[0151] Meanwhile, as described above, the lithium salt may include any one selected from the group consisting of LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiN(C2F5SO2)2, LiN(CF3SO2)2, CF3SO3Li, LiC(CF3SO2)3, LiC4BO8, LiTFSI, LiFSI, and LiClO4, or a mixture of two or more thereof, but is not limited thereto.

[0152] In addition, as described above, the electrolyte solvent may be a non-aqueous solvent commonly used in electrolytes for lithium secondary batteries, and may include, for example, at least one compound selected from the group consisting of cyclic carbonate-based compounds, linear carbonate-based compounds, alkyl ether-based compounds, alkyl acetate-based compounds, alkyl propionate-based compounds, and nitrile-based compounds.

[0153] Among these, typically, carbonate compounds such as cyclic carbonates, linear carbonates, or mixtures thereof may be included.

[0154] In addition, the composition for a gel polymer electrolyte according to one embodiment of the present invention may optionally further include, in addition to the above-mentioned components, other additives known in the art that can achieve the above-mentioned physical properties in order to further impart performance such as an increase in gel reaction efficiency and an effect of reducing resistance.

[0155] As described above, the additive may be any of the commonly used additives such as VC, VEC, PS, SN, AdN, ESa, PRS, FEC, LiPO2F2, LiODFB, LiBOB, TMSPa, TMSPi, TFEPa, and TFEPi, without limitation.

[0156] Furthermore, still another embodiment of the present invention is a positive electrode and a negative electrode; a polymer electrolyte disposed between the positive electrode and the negative electrode; A lithium secondary battery is provided, which includes a gel polymer electrolyte according to an embodiment of the present invention as the polymer electrolyte.

[0157] The gel polymer electrolyte is formed by polymerizing a composition for a gel polymer electrolyte by a conventional method known in the art. For example, the gel polymer electrolyte may be formed by in-situ polymerization of the composition for a gel polymer electrolyte inside a secondary battery.

[0158] According to a more preferred embodiment, the method may include the steps of: (a) inserting an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode into a battery case; and (b) injecting a composition for a gel polymer electrolyte according to one embodiment of the present invention into the battery case and polymerizing the composition to form a gel polymer electrolyte.

[0159] In-situ polymerization in a lithium secondary battery can be achieved through E-BEAM, gamma ray, or room temperature / high temperature aging processes, and according to one embodiment of the present invention, it can be achieved through thermal polymerization, where the polymerization time is about 2 minutes to 12 hours and the thermal polymerization temperature is 30°C to 100°C.

[0160] More specifically, the in-situ polymerization reaction in a lithium secondary battery is carried out by adding a predetermined amount of a polymerization initiator and the oligomer to an electrolyte solution containing a lithium salt, mixing them, and then injecting the mixture into a battery cell. After sealing the inlet of the battery cell, the mixture is heated at 40 to 80°C for 1 to 20 hours to polymerize the lithium salt-containing electrolyte solution, which undergoes gelation to produce a gel polymer electrolyte.

[0161] The lithium secondary battery according to one embodiment of the present invention has a charging voltage in the range of 3.0V to 5.0V, and has excellent capacity characteristics in both normal voltage and high voltage ranges.

[0162] Meanwhile, according to one embodiment of the present invention, the electrode constituting the lithium secondary battery may be prepared by a conventional method known in the art. For example, an electrode may be prepared by mixing and stirring an electrode active material with a solvent, and optionally a binder, a conductive material, and a dispersant to prepare a slurry, and then coating the slurry onto a metal current collector, compressing the coated material, and drying the resulting mixture.

[0163] The positive electrode may be fabricated by forming a positive electrode mixture layer on a positive electrode current collector. The positive electrode mixture layer may be formed by coating a positive electrode slurry containing a positive electrode active material, a binder, a conductive material, and a solvent on the positive electrode current collector, followed by drying and rolling.

[0164] The positive electrode current collector is not particularly limited as long as it has conductivity without inducing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or those obtained by surface treatment of the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. can be used.

[0165] The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium. Specifically, it may include a lithium composite metal oxide containing one or more metals such as cobalt, manganese, nickel, or aluminum and lithium. More specifically, the lithium composite metal oxide includes 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-Y9 Mn Y9 O2 (0 < Y9 < 1), LiMn 2-z4 [[ID=z]]Ni z 4O4 (0 < Z4 < 2), etc.), lithium-nickel-cobalt-based oxides (e.g., LiNi 1-Y10 Co Y10 O2 (0 < Y10 < 1), etc.), lithium-manganese-cobalt-based oxides (e.g., LiCo 1-Y11 Mn Y11 O2 (0 < Y11 < 1), LiMn 2-z5 Co z5 O4 (0 < Z5 < 2), etc.), lithium-nickel-manganese-cobalt-based oxides (e.g., Li(Ni a Co b Mn c )O2 (0 < a < 1, 0 < b < 1, 0 < c < 1, a + b + c = 1) or Li(Ni a1 Co b1 Mn c1 )O4 (0 < a1 < 2, 0 < b1 < 2, 0 < c1 < 2, a1 + b1 + c1 = 2), etc.), or lithium-nickel-cobalt-transition metal (M) oxides (e.g., Li(Ni a2 Co b2 Mn c2 M d ]])O2 (M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and a2, b2, c2, and d are atomic fractions of independent elements, where 0 < a2 < 1, 0 < b2 < 1, 0 < c2 < 1, 0 < d < 1, and a2 + b2 + c2 + d = 1), etc.) etc. are included, and one or more of these compounds may be contained.

[0166] Among them, in terms of enhancing the capacity characteristics and stability of the battery, the lithium composite metal oxide is LiCoO2, LiMnO2, LiNiO2, lithium nickel manganese cobalt oxide (for example, Li(Ni 1 / 3 Mn 1 / 3 Co 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, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2, and Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, etc.), or nickel manganese cobalt aluminum compound (for example, Li(Ni 0.86 Mn 0.045 CoAl 0.045 Al 0.05 )O2, or lithium nickel cobalt aluminum oxide (for example, Li(Ni 0.8 Co 0.15 Al 0.05 )O2, etc.) can be.

[0167] The positive electrode active material may be contained at 80% to 99% by weight based on the total weight of the solid content in the positive electrode slurry.

[0168] The binder is a component that aids in binding between the active material and the conductive material, etc., and to the current collector, and is typically added in an amount of 1 to 30 wt % based on the total weight of the solids in the positive electrode slurry. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymers.

[0169] The conductive material is usually added in an amount of 1% by weight to 30% by weight based on the total weight of the solid content in the positive electrode slurry.

[0170] Such a conductive material is not particularly limited as long as it does not induce chemical changes in the battery and is conductive, and examples thereof include graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber and metal fiber; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives. Specific examples of commercially available conductive materials include acetylene black (manufactured by Chevron Chemical), Denka Black (manufactured by Denka Singapore Private Limited, Gulf Oil Company Limited, etc.), Ketjen Black EC (manufactured by Almac), Vulcan XC-72 (manufactured by Cabot Corporation), and Super P (manufactured by Timcal Corporation).

[0171] The solvent may include an organic solvent such as NMP (N-methyl-2-pyrrolidone) and may be used in an amount that provides a suitable viscosity when the slurry contains the positive electrode active material, and optionally a binder and a conductive material, etc. For example, the solvent may be added so that the solids concentration in the slurry containing the positive electrode active material, and optionally a binder and a conductive material, is 40 wt % to 60 wt %, preferably 40 wt % to 50 wt %.

[0172] The negative electrode may be fabricated by forming a negative electrode mixture layer on a negative electrode current collector. The negative electrode mixture layer may be formed by coating a negative electrode current collector with a negative electrode slurry including a negative electrode active material, a binder, a conductive material, and a solvent, followed by drying and rolling.

[0173] The negative electrode current collector generally has a thickness of 3 μm to 500 μm. Such a negative electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and has high conductivity, and examples of such a negative electrode current collector include copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys. Similarly to the positive electrode current collector, the surface may be formed with fine irregularities to strengthen the binding force of the negative electrode active material, and the negative electrode current collector may be used in various forms such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0174] The negative electrode active material may be a lithium-containing titanium composite oxide (LTO); a carbon-based material such as non-graphitizable carbon or graphite-based carbon; x10 Fe2O3(0≦x10≦1), Li x11 WO2(0≦x11≦1), Sn x12 Me 1-x12 Me' y12 O z(Me: Mn, Fe, Pb, Ge; Me’: Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen; 0 < x12 ≤ 1; 1 ≤ y12 ≤ 3; 1 ≤ z12 ≤ 8), etc. metal composite oxides; lithium metal; lithium alloy; silicon-based alloy; tin-based alloy; metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5; and may contain a single substance or a mixture of two or more selected from the group consisting of conductive polymers such as polyacetylene.

[0175] The negative electrode active material may be contained at 80% to 99% by weight based on the total weight of the solid content in the negative electrode slurry.

[0176] The binder is a component that aids in the bonding of the conductive material and the active material and the bonding to the current collector, and is usually added at 1% to 30% by weight based on the total weight of the solid content in the negative electrode slurry. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, fluorine rubber, various copolymers thereof, and the like.

[0177] The conductive material is a component for further improving the conductivity of the negative electrode active material and may be added in an amount of 1 wt % to 20 wt % based on the total weight of the solid content in the negative electrode slurry. The conductive material is not particularly limited as long as it does not induce chemical changes in the battery and has conductivity. Examples of such conductive materials include graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber and metal fiber; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0178] The solvent may include water or an organic solvent such as NMP or alcohol, and may be used in an amount that provides a suitable viscosity when the negative electrode active material and, optionally, a binder and a conductive material are contained. For example, the solvent may be contained so that the solids concentration in the slurry containing the negative electrode active material and, optionally, a binder and a conductive material is 50 wt % to 75 wt %, preferably 50 wt % to 65 wt %.

[0179] Then, a separator is selectively inserted between the positive electrode and the negative electrode. The separator serves to block internal short circuits between the electrodes and to impregnate the electrolyte. The separator may be prepared by mixing a polymer resin, a filler, and a solvent to prepare a separator composition, and then coating and drying the separator composition directly on the top of the electrode to form a separator film. Alternatively, the separator may be prepared by casting the separator composition on a support, drying the composition, and then peeling the separator film from the support and laminating it on the top of the electrode.

[0180] The polymer resin is not particularly limited, and examples thereof include chemically resistant and hydrophobic olefin polymers such as polypropylene; composite porous separators in which inorganic materials are added to a porous separator substrate; and sheets or nonwoven fabrics made of glass fiber or polyethylene.

[0181] The porous separation membrane may generally have a pore size of 0.01 μm to 50 μm, a porosity of 5% to 95%, and a thickness of 5 μm to 300 μm.

[0182] The shape of the lithium secondary battery according to an embodiment of the present invention is not particularly limited, and may be a cylindrical shape using a can, a prismatic shape, a pouch shape, a coin shape, or the like.

[0183] [Example] Example 1 (positive electrode active material: NCMA) (1) Preparation of a composition for gel polymer electrolyte Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 3:7, and 0.5M LiPF6 and 0.5M LiFSI were added to prepare a mixed solvent. An oligomer represented by Formula 5 (weight average molecular weight 6,000, p:q=2:1, r=3) was then added to the mixed solvent at a content of 5 wt% based on 100 wt% of the gel polymer electrolyte composition. 0.1 wt% of a polymerization initiator (AIBN), 1.5 wt% of vinylene carbonate (VC), and 1 wt% of propane sultone (PS) were then added to prepare a gel polymer electrolyte composition. Table 1 below summarizes the ingredients and contents of the gel polymer electrolyte composition of Example 1.

[0184] [Table 1]

[0185] (2) Manufacture of lithium secondary batteries As a positive electrode active material (LiNi 0.86 Co 0.045 Mn 0.045 Al 0.05A cathode mixture slurry was prepared by adding 94 wt% of O2, 3 wt% of carbon black as a conductive material, and 3 wt% of PVDF as a binder to a solvent, N-methyl-2-pyrrolidone (NMP). The cathode mixture slurry was applied to an approximately 20 μm-thick aluminum (Al) thin film as a cathode current collector, dried, and then roll-pressed to prepare a cathode.

[0186] Carbon powder as a negative electrode active material, PVDF as a binder, and carbon black as a conductive material were mixed at 96 wt%, 3 wt%, and 1 wt%, respectively, and added to NMP as a solvent to prepare a negative electrode mixture slurry. The negative electrode mixture slurry was applied to a 10 μm-thick copper (Cu) thin film as a negative electrode current collector, dried, and then roll-pressed to prepare a negative electrode.

[0187] An electrode assembly was prepared using the positive electrode, negative electrode, and a separator consisting of three layers of polypropylene / polyethylene / polypropylene (PP / PE / PP). The gel polymer electrolyte composition prepared above was poured into the electrode assembly, and the assembly was left for two days and then heated at 60°C for 24 hours to prepare a lithium secondary battery containing a gel polymer electrolyte. The nominal voltage of the obtained battery was 2.5V to 4.2V.

[0188] Example 2 (Positive electrode active material: LCO) (1) Preparation of a composition for gel polymer electrolyte A gel polymer electrolyte composition was produced in the same manner as in Example 1, except that the composition was as shown in Table 2 below.

[0189] [Table 2]

[0190] (2) Manufacture of lithium secondary batteries A cathode mixture slurry was prepared by adding 94 wt% of LiCoO2 (LCO) as a cathode active material, 3 wt% of carbon black as a conductive material, and 3 wt% of PVDF as a binder to a solvent, N-methyl-2-pyrrolidone (NMP). The cathode mixture slurry was applied to an approximately 20 μm-thick aluminum (Al) thin film as a cathode current collector, dried, and then roll-pressed to prepare a cathode.

[0191] Carbon powder as a negative electrode active material, PVDF as a binder, and carbon black as a conductive material were mixed at 96 wt%, 3 wt%, and 1 wt%, respectively, and added to NMP as a solvent to prepare a negative electrode mixture slurry. The negative electrode mixture slurry was applied to a 10 μm-thick copper (Cu) thin film as a negative electrode current collector, dried, and then roll-pressed to prepare a negative electrode.

[0192] An electrode assembly was prepared using the positive electrode, negative electrode, and a separator consisting of three layers of polypropylene / polyethylene / polypropylene (PP / PE / PP). The gel polymer electrolyte composition prepared above was poured into the electrode assembly, and the assembly was left for two days and then heated at 60°C for 24 hours to prepare a lithium secondary battery containing a gel polymer electrolyte. The nominal voltage of the battery was 3.0V to 4.45V.

[0193] Example 3 (positive electrode active material: LFP) (1) Preparation of a composition for gel polymer electrolyte Ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 3:4:3 and 1M of LiPF6 was added to prepare a mixed solvent. An oligomer represented by Formula 5 (weight average molecular weight 6,000, p:q=2:1r=3) was then added to the mixed solvent at a content of 3 wt% based on 100 wt% of the gel polymer electrolyte composition. 0.1 wt% of a polymerization initiator (AIBN) and 2.5 wt% of vinylene carbonate (VC) were also added to prepare a gel polymer electrolyte composition. Table 3 below summarizes the ingredients and contents of the gel polymer electrolyte composition of Example 3.

[0194] [Table 3]

[0195] (2) Manufacture of lithium secondary batteries A cathode mixture slurry was prepared by adding 94 wt% of LiFePO4 (LFP) as a cathode active material, 3 wt% of carbon black as a conductive material, and 3 wt% of PVDF as a binder to a solvent, N-methyl-2-pyrrolidone (NMP). The cathode mixture slurry was applied to an approximately 20 μm-thick aluminum (Al) thin film as a cathode current collector, dried, and then roll-pressed to prepare a cathode.

[0196] Carbon powder as a negative electrode active material, PVDF as a binder, and carbon black as a conductive material were mixed at 96 wt%, 3 wt%, and 1 wt%, respectively, and added to NMP as a solvent to prepare a negative electrode mixture slurry. The negative electrode mixture slurry was applied to a 10 μm-thick copper (Cu) thin film as a negative electrode current collector, dried, and then roll-pressed to prepare a negative electrode.

[0197] An electrode assembly was prepared using the positive electrode, negative electrode, and a separator consisting of three layers of polypropylene / polyethylene / polypropylene (PP / PE / PP). The gel polymer electrolyte composition prepared above was poured into the electrode assembly, left for two days, and then heated at 60°C for 24 hours to prepare a lithium secondary battery containing a gel polymer electrolyte. The nominal voltage of the battery was 2.5V to 3.6V, and the capacity was 720mAh.

[0198] Comparative Example 1 (using liquid electrolyte, NCMA) (1) Electrolyte production An electrolyte solution was prepared by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7, adding 1.0M LiPF6 to 97g of the mixed solvent, and adding 1.5g of VC and 1.5g of PS as other additives. Table 4 below summarizes the components and contents of the electrolyte composition of Comparative Example 1.

[0199] [Table 4]

[0200] (2) Manufacture of lithium secondary batteries As a positive electrode active material (LiNi 0.86 Co 0.045 Mn 0.045 Al 0.05 A cathode mixture slurry was prepared by adding 94 wt% of O2, 3 wt% of carbon black as a conductive material, and 3 wt% of PVDF as a binder to a solvent, N-methyl-2-pyrrolidone (NMP). The cathode mixture slurry was applied to an approximately 20 μm-thick aluminum (Al) thin film as a cathode current collector, dried, and then roll-pressed to prepare a cathode.

[0201] Carbon powder as a negative electrode active material, PVDF as a binder, and carbon black as a conductive material were mixed at 96 wt%, 3 wt%, and 1 wt%, respectively, and added to NMP as a solvent to prepare a negative electrode mixture slurry. The negative electrode mixture slurry was applied to a 10 μm-thick copper (Cu) thin film as a negative electrode current collector, dried, and then roll-pressed to prepare a negative electrode.

[0202] An electrode assembly was prepared using the positive electrode, the negative electrode, and a separator consisting of three layers of polypropylene / polyethylene / polypropylene (PP / PE / PP), and the electrolyte prepared as described above was injected into the electrode assembly to prepare a lithium secondary battery.

[0203] Comparative Example 2 (Liquid Electrolyte Used, LCO) A lithium secondary battery was manufactured in the same manner as in Comparative Example 1, except that (LiCoO2; LCO) was used as the positive electrode active material.

[0204] Comparative Example 3 (liquid electrolyte, LFP) (1) Electrolyte production An electrolyte solution was prepared according to the composition shown in Table 5 below.

[0205] [Table 5]

[0206] (2) Manufacture of lithium secondary batteries A cathode mixture slurry was prepared by adding 94 wt% of LiFePO4 (LFP) as a cathode active material, 3 wt% of carbon black as a conductive material, and 3 wt% of PVDF as a binder to a solvent, N-methyl-2-pyrrolidone (NMP). The cathode mixture slurry was applied to an approximately 20 μm-thick aluminum (Al) thin film as a cathode current collector, dried, and then roll-pressed to prepare a cathode.

[0207] Carbon powder as a negative electrode active material, PVDF as a binder, and carbon black as a conductive material were mixed at 96 wt%, 3 wt%, and 1 wt%, respectively, and added to NMP as a solvent to prepare a negative electrode mixture slurry. The negative electrode mixture slurry was applied to a 10 μm-thick copper (Cu) thin film as a negative electrode current collector, dried, and then roll-pressed to prepare a negative electrode.

[0208] An electrode assembly was fabricated using the positive electrode, negative electrode, and a three-layer separator made of polypropylene / polyethylene / polypropylene (PP / PE / PP), and the electrolyte solution prepared as described above was injected into the electrode assembly to fabricate a lithium secondary battery. The nominal voltage of the battery was 2.5 V to 3.6 V, and the capacity was 720 mAh.

[0209] Comparative Example 4 (using gel polymer electrolyte, LFP) (1) Preparation of a composition for gel polymer electrolyte Ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 3:4:3 and LiPF6 was added at 1M to prepare a mixed solvent. An oligomer (weight average molecular weight 6,000, m2:n2 = 2:1, o2 = 6) represented by the following chemical formula z was then added to the mixed solvent at a content of 3 wt% based on 100 wt% of the gel polymer electrolyte composition. 0.1 wt% of a polymerization initiator (AIBN) and 2.5 wt% of vinylene carbonate (VC) were also added to prepare a gel polymer electrolyte composition.

[0210] [ka]

[0211] Here, m2, n2, and o2 are the numbers of repeating units, m2 is any one integer from 1 to 10, n2 is any one integer from 1 to 10, and o2 is any one integer from 1 to 500.

[0212] [Table 6]

[0213] (2) Manufacture of lithium secondary batteries A cathode mixture slurry was prepared by adding 94 wt% of LiFePO4 (LFP) as a cathode active material, 3 wt% of carbon black as a conductive material, and 3 wt% of PVDF as a binder to a solvent, N-methyl-2-pyrrolidone (NMP). The cathode mixture slurry was applied to an approximately 20 μm-thick aluminum (Al) thin film as a cathode current collector, dried, and then roll-pressed to prepare a cathode.

[0214] Carbon powder as a negative electrode active material, PVDF as a binder, and carbon black as a conductive material were mixed at 96 wt%, 3 wt%, and 1 wt%, respectively, and added to NMP as a solvent to prepare a negative electrode mixture slurry. The negative electrode mixture slurry was applied to a 10 μm-thick copper (Cu) thin film as a negative electrode current collector, dried, and then roll-pressed to prepare a negative electrode.

[0215] An electrode assembly was prepared using the positive electrode, negative electrode, and a three-layer separator made of polypropylene / polyethylene / polypropylene (PP / PE / PP). The gel polymer electrolyte composition prepared above was poured into the electrode assembly, left for two days, and then heated at 60°C for 24 hours to prepare a lithium secondary battery containing a gel polymer electrolyte. The nominal voltage of the battery was 2.5V to 3.6V, and the capacity was 720mAh.

[0216] [Experimental Example] Experimental Example 1: Experiment on heat generation safety (Example 1 and Comparative Example 1) After the battery was fabricated, an additional exothermic reaction was observed while the temperature was increased in a fully charged state. The heat flux was measured using a multiple module calorimetry (MMC) at a heating rate of 0.2°C / min up to 300°C. Referring to Fig. 1 and Table 7, the first peak was measured at 137.4 J for the example and 156.9 J for the comparative example, and the second peak was measured at 127.4 J for the example and 166.4 J for the comparative example.

[0217] [Table 7]

[0218] In the case of the beaker cell prepared according to Example 1, it was confirmed that the current increased sharply at a voltage range lower than the voltage range at which a typical electrolyte would decompose. This is believed to be due to the increase in current (A) caused by the decomposition of the overcharge prevention additive contained in the electrolyte. On the other hand, in the case of the beaker cell prepared according to Comparative Example 1, it was confirmed that the current increased at a voltage range higher than that of the examples.

[0219] Experimental Example 2: Evaluation experiment of high-temperature capacity retention rate and resistance increase rate (Example 1 and Comparative Example 1) The batteries of Example 1 and Comparative Example 1 were charged to SOC 100% and then maintained at 60° C. for 4 weeks.

[0220] The capacity retention rate was measured as follows. At the start of the experiment, the battery was charged to 4.2 V at 1 C in a thermostatic chamber at 60°C, and then discharged to 2.5 V, at which point the capacity was measured. Thereafter, while maintaining the battery in the chamber, it was charged to 4.2 V at 1 C and discharged to 2.5 V at predetermined intervals, and the capacity at each interval was measured. This was repeated for four weeks. The first measured capacity was set to 100%, and each subsequent capacity value was calculated as a percentage.

[0221] Meanwhile, the resistance increase rate was measured as follows: For the batteries obtained in each Example 1 and Comparative Example 1, pulse discharge (DC-IR measurement) was performed for each SOC section using the Hybrid Pulse Power Characterization (HPPC) method, and the resistance was recorded. The resistance was calculated by dividing the voltage change that occurred during discharge by the discharge current, as shown in Equation 1 below. R=V / I … Equation 1 Here, R is the resistance, V is the voltage change that occurs during discharge, and I is the discharge current.

[0222] [Table 8]

[0223] The results are summarized in Table 8 and Figure 2. Table 8 and Figure 2 confirm that the gel polymer electrolyte of the present invention does not affect the capacity or resistance of the battery compared to when a liquid electrolyte is used.

[0224] Experimental Example 3: Evaluation of low-temperature life characteristics (Example 2 and Comparative Example 2) The batteries of Example 2 and Comparative Example 2 were charged / discharged at an ambient temperature of 15° C. to measure the capacity. -Charging conditions: 2C, CC (constant current) / CV (constant voltage) (4.45V, 0.05C current cutoff) -Discharge conditions: 1C, CC (constant current) conditions, 3V The battery was then charged and discharged 200 times at the same current and voltage. The capacity retention rate was calculated using the following formula 2. Capacity retention rate (%) = [discharge capacity after 200 cycles / charge capacity after 1 cycle] x 100 ... Formula 2

[0225] Experimental Example 4: Evaluation of room temperature life characteristics (Example 2 and Comparative Example 2) The batteries of Example 2 and Comparative Example 2 were charged / discharged at an ambient temperature of 25° C. to measure the capacity. -Charging conditions: 2C, CC (constant current) / CV (constant voltage) (4.45V, 0.05C current cutoff) -Discharge conditions: 1C, CC (constant current) conditions, 3V

[0226] The battery was then charged and discharged 300 times at the same current and voltage. The capacity retention rate was calculated using the following formula 3. Capacity retention rate (%) = [discharge capacity after 300 cycles / charge capacity after 1 cycle] x 100 ... Formula 3

[0227] [Table 9]

[0228] Referring to Table 9, the battery according to Example 2 exhibited a capacity retention rate comparable to that of a battery using a conventional liquid electrolyte. In particular, it was confirmed that the battery according to Example 2 exhibited a better capacity retention rate after repeated charge / discharge at low temperature than the battery according to Comparative Example 2.

[0229] Experimental Example 5: High-temperature storage characteristics (Example 2 and Comparative Example 2) The batteries of Example 2 and Comparative Example 2 were left in a chamber at 60° C. and 90% relative humidity for 7 days, and the capacity retention rate and capacity recovery rate were evaluated.

[0230] The capacity retention rate was measured as follows. At the start of the experiment, the battery was charged and discharged once under the charge-discharge conditions of Experimental Example 4, and the capacity at this time was measured. Next, the battery was left in a chamber at 60°C and 90% relative humidity for 7 days, then removed from the chamber and charged to 4.45 V at 0.2 C, and discharged to 3 V, and the capacity at this time was measured. The initially measured capacity was set to 100%, and the remaining capacity was calculated as a percentage.

[0231] After that, each battery was left at room temperature for a certain period of time, and then charged and discharged from 3V to 4.45V at 0.2C and 0.1C, respectively, to measure the capacity. The capacity relative to the initially measured capacity of 100% was calculated as the capacity recovery rate (%).

[0232] [Table 10]

[0233] Referring to Table 10, the battery according to Example 2 exhibited a capacity retention rate comparable to that of a battery using a conventional liquid electrolyte. In particular, it was confirmed that the battery according to Example 2 exhibited a better capacity retention rate after repeated charge / discharge at low temperature than the battery according to Comparative Example 2.

[0234] Experimental Example 6: Hot Box Profile (Example 2 and Comparative Example 2) The batteries of Example 2 and Comparative Example 2 were subjected to a hot box test. The batteries of Example 2 and Comparative Example 2 were charged to 100% SOC, placed in a temperature-controllable chamber, heated to 140°C at a rate of 5°C / min, and maintained at that temperature for at least 1 hour. Figure 3 shows the hot box test results for the batteries of Example 2 and Figure 4 shows the hot box test results for the batteries of Comparative Example 2.

[0235] 3 and 4, it can be seen that the battery of Example 2 maintained its voltage for a significantly longer time than the battery of Comparative Example 2. On the other hand, the battery of Comparative Example 2 suddenly rose in temperature after 30 minutes, causing it to explode and become unable to operate. This confirmed that the battery of Example 2 had superior heat resistance compared to the battery of Comparative Example 2.

[0236] Figure 6 is a photographic image of the battery of Example 2 that underwent the hot box test, and Figure 7 is a photographic image of the battery of Comparative Example 2 that underwent the hot box test. The battery in Figure 7 was damaged by an explosion.

[0237] Experimental Example 7: Comparison of life characteristics and thickness increase rate (Example 2 and Comparative Example 2) The batteries of Example 2 and Comparative Example 2 were charged / discharged at an ambient temperature of 25°C to measure the capacity. Each battery was charged in CC (constant current) / CV (constant voltage) mode up to 4.45 V, with the charge rate varied between 2 C, 1.5 C, and 1 C, with a cutoff current of 0.05 C. Discharge was performed under 1 C and CC (constant current) conditions down to 3 V. Charge / discharge was repeated 400 times under the same conditions.

[0238] FIG. 5 shows the capacity of the batteries of Example 2 and Comparative Example 2. From FIG. 5, it was confirmed that the batteries of Example 2 and Comparative Example 2 had similar capacity change rates. Furthermore, both the battery of Example 2 and the battery of Comparative Example 2 showed a capacity retention rate of 78% at 400 cycles. Furthermore, it was confirmed that the batteries of Example 2 and Comparative Example 2 showed an increase in thickness of less than 5.76 mm after 400 cycles. This confirms that the battery of Example 2 has electrochemical properties at a similar level to batteries using conventional liquid electrolytes.

[0239] Experimental Example 8 (Example 3, Comparative Example 3 and Comparative Example 4) The batteries of Example 3, Comparative Example 3, and Comparative Example 4 were charged / discharged three times between 2.5 V and 3.6 V, and then stored in a constant temperature chamber at 60°C for six weeks at an SOC of 100%. Then, the room temperature resistance was measured at an SOC of 50%, and the difference in the rate of increase relative to the same resistance of the initial battery was confirmed.

[0240] [Table 11]

[0241] It has been confirmed that the battery according to the present invention further improves the resistance increase rate by effectively suppressing the reaction between the electrode and the additive / electrolyte.

Claims

1. a matrix polymer and an electrolyte solution impregnated in the matrix polymer; The matrix polymer is formed into a three-dimensional network structure by polymerizing an oligomer represented by the following Chemical Formula 1: the electrolyte solution contains a lithium salt and a non-aqueous solvent; the non-aqueous solvent includes at least one selected from the group consisting of a cyclic carbonate-based compound, a linear carbonate-based compound, an alkyl ether-based compound, an alkyl acetate-based compound, an alkyl propionate-based compound, and a nitrile-based compound; 【Chemical 1】 In Chemical Formula 1, r is an integer of 1 or greater; R １ are each an aliphatic hydrocarbon group or an aromatic hydrocarbon group, R ２ and R ５ are each independently an alkyl group having 1 to 3 carbon atoms in which at least one hydrogen atom has been substituted with a fluorine atom, R ３ is an alkyl group having n carbon atoms in which all hydrogen atoms are substituted with fluorine atoms, and R ４ is an alkyl group having n-1 carbon atoms in which all hydrogen atoms have been substituted with fluorine atoms, wherein n is 2 or 3; wherein either one of p and q is 0 or both are integers of 1 or greater, and when both p and q are integers of 1 or greater, p / q has a value of 1 / 9 to 9 / 1; R ６ and R ７ are each independently a linear or branched alkyl group having 1 to 5 carbon atoms, The R ８ is null or a methyl group, and m is an integer of 1, 2, 3, 4, or 5; Gel polymer electrolyte.

2. The oligomer includes a unit A represented by the following Chemical Formula 2, a unit B represented by the following Chemical Formula 3, and a unit C represented by the following Chemical Formula 4: 【Chemistry 2】 【Chemistry 3】 【Chemistry 4】 In Chemical Formula 2, Chemical Formula 3 and Chemical Formula 4, r is an integer of 1 or greater; R １ are each an aliphatic hydrocarbon group or an aromatic hydrocarbon group, R ２ and R ５ are each independently an alkyl group having 1 to 3 carbon atoms in which at least one hydrogen atom has been substituted with a fluorine atom, R ３ is an alkyl group having n carbon atoms in which all hydrogen atoms are substituted with fluorine atoms, and R ４ is an alkyl group having n-1 carbon atoms in which all hydrogen atoms have been substituted with fluorine atoms, wherein n is 2 or 3; wherein either one of p and q is 0 or both are integers of 1 or greater, and when both p and q are integers of 1 or greater, p / q has a value of 1 / 9 to 9 / 1; R ６ and R ７ are each independently a linear or branched alkyl group having 1 to 5 carbon atoms, The R ８ The gel polymer electrolyte of claim 1 , wherein m is null or a methyl group, and m is any one of integers 1, 2, 3, 4, and 5.

3. The chemical formula 2 is divided into a unit represented by the following chemical formula 2-1 and a unit represented by the following chemical formula 2-2: 【Chemistry 5】 【Chemistry 6】 In Chemical Formula 2-2, R １ The gel polymer electrolyte according to claim 2 , wherein is an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, or an aromatic hydrocarbon group.

4. the aliphatic hydrocarbon group is an alkylene group having 1 to 20 carbon atoms; an alkylene group having 1 to 20 carbon atoms and containing an isocyanate group (NCO); an alkoxylene group having 1 to 20 carbon atoms; an alkenylene group having 2 to 20 carbon atoms; or an alkynylene group having 2 to 20 carbon atoms; the alicyclic hydrocarbon group is a substituted or unsubstituted cycloalkylene group having 4 to 20 carbon atoms; a substituted or unsubstituted cycloalkylene group containing an isocyanate group (NCO) and having 4 to 20 carbon atoms; a cycloalkenylene group having 4 to 20 carbon atoms; or a heterocycloalkylene group having 2 to 20 carbon atoms, 4. The gel polymer electrolyte according to claim 3, wherein the aromatic hydrocarbon group is a substituted or unsubstituted arylene group having 6 to 20 carbon atoms; or a heteroarylene group having 2 to 20 carbon atoms.

5. The gel polymer electrolyte according to claim 4, wherein the compound represented by Chemical Formula 2-2 is derived from any one of the compounds represented by the following Chemical Formulas a to n: 【Chemistry 7】 【Chemistry 8】 【Chemistry 9】 【Chemistry 10】 【Chemistry 11】 【Chemistry 12】 【Chemistry 13】 【Chemistry 14】 【Chemistry 15】 【Chemistry 16】 【Chemistry 17】 【Chemistry 18】 【Chemistry 19】 【Chemistry 20】

6. The gel polymer electrolyte according to claim 4, wherein the structure represented by Chemical Formula 2-2 is any one or more of the structures represented by Chemical Formulas o to x below: 【Chemical 21】 ​ 【Chemical 23】 【Chemistry 24】 【Chemistry 25】 【Chemical 26】 【Chemical 27】 【Chemical formula 28】 【Chemical 29】 【Chemistry 30】

7. The gel polymer electrolyte of claim 2 , wherein the oligomer of Chemical Formula 4 has (meth)acryloyl groups at both ends of the oligomer of Chemical Formula 1.

8. The gel polymer electrolyte of claim 1 , wherein the oligomer comprises a compound represented by the following Chemical Formula 5: 【Chemical 31】

9. 2. The gel polymer electrolyte of claim 1, wherein the weight average molecular weight (Mw) of the oligomer is from about 1,000 g / mol to 500,000 g / mol.

10. The gel polymer electrolyte of claim 1 , wherein the matrix polymer further comprises 5 to 700 parts by weight of inorganic particles relative to 100 parts by weight of the oligomer.

11. The gel polymer electrolyte according to claim 1 , wherein the gel polymer electrolyte has a gel content of about 1% by weight or more at a temperature of 25° C.

12. a negative electrode, a positive electrode, and a gel polymer electrolyte; A lithium ion secondary battery, wherein the gel polymer electrolyte is the gel polymer electrolyte according to claim 1 .

13. The composition includes a lithium salt, a non-aqueous solvent, a polymerization initiator, and an oligomer represented by the following Chemical Formula 1: The oligomer is contained in an amount of 0.5 wt % to 20 wt % based on the total weight of the composition for the gel polymer electrolyte, 【Chemical 32】 In Chemical Formula 1, r is an integer of 1 or greater; R １ are each an aliphatic hydrocarbon group or an aromatic hydrocarbon group, R ２ and R ５ are each independently an alkyl group having 1 to 3 carbon atoms in which at least one hydrogen atom has been substituted with a fluorine atom, R ３ is an alkyl group having n carbon atoms in which all hydrogen atoms are substituted with fluorine atoms, and R ４ is an alkyl group having n-1 carbon atoms in which all hydrogen atoms have been substituted with fluorine atoms, wherein n is 2 or 3; Either one of p and q may be 0 or both may be integers of 1 or greater, and when both p and q are integers of 1 or greater, p / q has a value of 1 / 9 to 9 / 1; R ６ and R ７ are each independently a linear or branched alkyl group having 1 to 5 carbon atoms, The R ８ is null or a methyl group, and m is any one of integers 1, 2, 3, 4, and 5.

14. A gel polymer electrolyte as described in claim 1, wherein when p and q are both integers greater than or equal to 1, p / q has a value of 1 / 9 to 9 / 1.

15. A gel polymer electrolyte as described in claim 2, wherein when p and q are both integers greater than or equal to 1, p / q has a value of 1 / 9 to 9 / 1.

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