Composition for electrolyte of lithium secondary battery, gel polymer electrolyte, and lithium secondary battery including gel polymer electrolyte

Abstract

The present invention relates to a composition for an electrolyte of a lithium secondary battery, a gel polymer electrolyte including a polymerization reactant of the composition, and a lithium secondary battery including the gel polymer electrolyte, the composition including a lithium salt, a polyalkylene carbonate-based first polymer having a weight average molecular weight of 1,000 g / mol to 1,500,000 g / mol, a polyethylene oxide-based second polymer having a weight average molecular weight of 200 g / mol to 2,000 g / mol, and an organic solvent, wherein the weight average molecular weight of the second polymer is in the range of 1 / 3,000 to 1 / 3 of the weight average molecular weight of the first polymer, and the amount of the first polymer is in the range of 0.1 wt% to 30 wt% based on the total weight of the composition.

Description

TECHNICAL FIELD

[0001] This application claims priority to Korean Patent Application No. 10-2020-0183055, filed on December 24, 2020, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety.

[0002] The present application relates to a composition for an electrolyte for a lithium secondary battery, a gel polymer electrolyte including a polymerization reactant of the composition, and a lithium secondary battery including the gel polymer electrolyte. BACKGROUND

[0003] The application of a lithium secondary battery, which generates or consumes electric energy using the principle of oxidation / reduction reactions caused by the intercalation and deintercalation of lithium ions in a negative electrode and a positive electrode, is rapidly expanding, and the lithium secondary battery is not only used as a portable power source for a mobile phone, a notebook computer, a digital camera, a camcorder, etc., but also used as a medium / large power source for a power tool, an electric bicycle, a hybrid electric vehicle (HEV), a plug-in HEV (PHEV), etc. As the application field expands and the demand increases, various changes in the outer shape and size of the battery have occurred, and superior performance and stability to those of conventional small batteries are required.

[0004] An ion-conductive non-aqueous electrolyte solution in which a salt is dissolved in a non-aqueous organic solvent is mainly used, but the non-aqueous electrolyte solution has disadvantages in that the electrode material is deteriorated and the organic solvent is highly likely to be volatilized, and combustion caused by an increase in the environmental temperature and the battery itself temperature results in low safety.

[0005] Therefore, there is a need to develop an electrolyte for a lithium secondary battery in which performance and safety are ensured by compensating for these disadvantages. SUMMARY

[0006] TECHNICAL PROBLEM

[0007] One aspect of the present application provides a composition for an electrolyte for a lithium secondary battery having improved safety and durability, a gel polymer electrolyte including a polymerization reactant of the composition, and a lithium secondary battery including the gel polymer electrolyte.

[0008] Technical solution

[0009] According to one aspect of the present application, there is provided a composition for an electrolyte for a lithium secondary battery, the composition including a lithium salt,

[0010] a polyalkylene carbonate-based first polymer having a weight average molecular weight of 1,000 g / mol to 1,500,000 g / mol,

[0011] a polyalkylene oxide-based second polymer; and

[0012] an organic solvent, wherein

[0013] the weight average molecular weight of the second polymer is in the range of 1 / 3,000 to 1 / 3 of the weight average molecular weight of the first polymer, and

[0014] the amount of the first polymer is in the range of 0.1 wt% to 30 wt% based on the total weight of the composition.

[0015] According to another aspect of the present application, there is provided a gel polymer electrolyte for a lithium secondary battery, the gel polymer electrolyte including a polymerization reactant of the composition of the electrolyte for a lithium secondary battery.

[0016] According to another aspect of the present application, there is provided a lithium secondary battery including a cathode including a cathode active material, an anode including an anode active material, a separator interposed between the cathode and the anode, and the gel polymer electrolyte for a lithium secondary battery.

[0017] Beneficial effects

[0018] The composition of the electrolyte for a lithium secondary battery according to the present application includes a polyalkylene carbonate-based polymer, and thus can have improved wettability, and further includes a PEO-based compound having a lower molecular weight than the polymer, and thus, due to the formation of a Semi-IPN between the polymer and the compound, has an effect of improving battery safety. DETAILED DESCRIPTION

[0019] Hereinafter, the present application will be described in more detail.

[0020] Recently, in order to improve the performance and safety of lithium secondary batteries, electrolytes that increase the concentration of lithium salts or change solvents are being developed. In the case of such electrolytes, as the viscosity and surface tension increase, the wettability of electrodes widely used in the art including polyolefin-based separators and PVdF binders decreases, thereby increasing the activation process time in the battery manufacturing process, and increasing the high-temperature aging step, which leads to the problem of an increase in processing costs.

[0021] Accordingly, the present inventors have attempted to improve the wettability of a high-concentration electrolyte by including a polyalkylene carbonate-based polymer that can be used as a surfactant for reducing the surface tension in a composition for an electrolyte and manufacturing an electrolyte from the polymer.

[0022] However, when such a polymer is introduced, there is a problem in that the polymer matrix inhibits the movement of some lithium ions, resulting in a decrease in ionic conductivity, thereby causing deterioration in the output of a battery. To solve the above problem, the present inventors introduced a polyethylene oxide (PEO)-based polymer, and found that the polyethylene oxide (PEO)-based polymer can increase the mobility of lithium ions in an electrolyte by acting as a plasticizer, thereby reducing the crystallinity of the polymer.

[0023] Further, the present inventors have also found that, since a semi-interpenetrating polymer network (Semi-IPN, Inter-penetrating polymer network) is formed between the polyalkylene carbonate-based polymer and the PEO-based polymer, the durability of maintaining the matrix structure is improved, thereby solving the safety problem due to leakage and achieving effects such as improvement in low-temperature output, improvement in oxidation stability, and improvement in exothermic performance.

[0024] In the present application, unless otherwise specified, the molecular weight refers to the weight average molecular weight, and the weight average molecular weight is measured by gel permeation chromatography (GPC). Specifically, WATERS STYRAGEL HR3 / HR4 (THF) is used as a chromatographic column, tetrahydrofuran (THF) (used with 0.45 m filtration) is used as a solvent, the measurement is performed at a flow rate of 1.0 mL / min and a sample concentration of 1 mg / mL. 100 μL is injected, and the column temperature is set to 40℃. A Waters RI detector is used as a detector, and polystyrene (PS) is set as a standard. Data processing is performed by the Empower 3 program.

[0025] The composition of the electrolyte for a lithium secondary battery according to the present application includes a lithium salt, a polyalkylene carbonate-based first polymer, a polyethylene oxide (PEO)-based second polymer, and an organic solvent.

[0026] (a) First Polymer

[0027] In one embodiment of the present application, the amount of the polyalkylene carbonate-based first polymer can be in the range of 0.1 to 30% by weight, preferably 0.1 to 20% by weight, most preferably 0.1 to 5% by weight, based on the total weight of the composition for the electrolyte of a lithium secondary battery. When the amount of the polyalkylene carbonate-based first polymer is in the above range, it is preferable in terms of mechanical physical properties, ionic conductivity, and viscosity.

[0028] Specifically, when the amount of the polyalkylene carbonate-based first polymer is less than 0.1% by weight, the addition effect is not significant, and improvement in battery performance is difficult to expect, and when the amount of the polyalkylene carbonate-based first polymer is greater than 30% by weight, an excess polymer inhibits activity on the surface of an electrode and dissolving of a lithium salt is difficult, and thus is not suitable for use as an electrolyte of a lithium secondary battery.

[0029] In one embodiment of the present application, the polyalkylene carbonate-based first polymer includes a unit represented by the following Formula 1.

[0030] [Formula 1]

[0031]

[0032] In the above Formula 1,

[0033] R1 to R4 are the same as or different from each other, and each is independently hydrogen, or an alkyl group having 1 to 5 carbon atoms,

[0034] * is a site connected to a main chain or an end group of a polymer, and

[0035] n is a repeating number, and is any one integer in the range of 1 to 1,000.

[0036] Preferably, R1 to R4 of the above Formula 1 can each be hydrogen. That is, the first polymer can be a polyethylene carbonate (PEC)-based polymer.

[0037] Further, preferably, m can be any one integer in the range of 1 to 500, and most preferably, m can be any one integer in the range of 1 to 200.

[0038] In one embodiment of the present application, the first polymer can include a unit represented by the following Formula 3.

[0039] [Formula 3]

[0040]

[0041] In the above Formula 3,

[0042] R and R' are the same as or different from each other, and each is independently an alkylene group having 1 to 5 carbon atoms,

[0043] A is a unit represented by the above formula 1,

[0044] B is a unit including one or more amide groups,

[0045] * is a site connected to a main chain or a terminal group of a polymer, and

[0046] m and k are the number of repetitions, wherein

[0047] m is any one integer from 1 to 1,000, and

[0048] k is any one integer from 1 to 100.

[0049] The amide group refers to a group represented by

[0050] In one embodiment of the present application, B can be represented by the following formula B-1.

[0051] [Formula B-1]

[0052]

[0053] In the above formula B-1,

[0054] R" is a substituted or unsubstituted alkylene group having 1 to 10 carbon atoms, a substituted or unsubstituted cycloalkylene group having 3 to 10 carbon atoms, a substituted or unsubstituted bicycloalkylene group having 6 to 20 carbon atoms, or a substituted or unsubstituted aralkylene group having 6 to 20 carbon atoms.

[0055] Specifically, R" can be any one selected from the following formulas R"-1 to R"-6.

[0056] [Formula R"-1]

[0057]

[0058] [Formula R"-2]

[0059]

[0060] [Formula R"-3]

[0061]

[0062] [Formula R"-4]

[0063]

[0064] [Formula R"-5]

[0065]

[0066] ​[Formula R"-6]

[0067]

[0068] In the above Formulae R"-1 to R"-6, * is a site of attachment to the main chain or end group of the polymer.

[0069] The two end groups of the first polymer of the present application are the same as or different from each other, and although not particularly limited, can be, for example, each independently an alkyl group, an alkoxy group, a hydroxyl group, an aldehyde group, an ester group, a halogen group, a halide group, a vinyl group, a (meth)acrylate group, a carboxyl group, a phenyl group, an amine group, an amide group, or a sulfonyl group. Specifically, the end group is a vinyl group or a (meth)acrylate group.

[0070] Further, the end group can be represented by any one of the following Formulae E-1 to E-6. In this case, the end group can react with a polymerization initiator to cause a polymer crosslinking reaction.

[0071] [Formula E-1]

[0072]

[0073] [Formula E-2]

[0074]

[0075] [Formula E-3]

[0076]

[0077] [Formula E-4]

[0078]

[0079] [Formula E-5]

[0080]

[0081] [Formula E-6]

[0082]

[0083] In one embodiment of the present application, the polyalkylene carbonate-based first polymer can be represented by the following Formula 3-1 or Formula 3-2, and preferably, can be represented by the following Formula 3-2.

[0084] [Formula 3-1]

[0085]

[0086] In the above Formula 3-1,

[0087] n1, m1, k1 are the number of repetitions, wherein

[0088] n1 is any one integer from 1 to 1,000,

[0089] ml is any one integer from 1 to 1,000, and

[0090] k1 is any one integer from 1 to 100, and

[0091] E1 and E2 are the same as or different from each other, and each is independently alkyl, alkoxy, hydroxyl, aldehyde, ester, halogen, halide, vinyl, (meth)acrylate, carboxyl, phenyl, amine, amide, or sulfonyl.

[0092] Specifically, E1 and E2 can each be vinyl or (meth)acrylate, more specifically (meth)acrylate.

[0093] [Formula 3-2]

[0094]

[0095] In the above Formula 3-2,

[0096] n2, m2, and k2 are the number of repetitions, wherein

[0097] n2 is any one integer from 1 to 1,000,

[0098] m2 is any one integer from 1 to 1,000, and

[0099] k2 is any one integer from 1 to 100, and

[0100] a and a' are the same as or different from each other, and each is independently an integer of 1 or 2, and

[0101] b and b' are the same as or different from each other, each is independently any one integer from 1 to 3.

[0102] In one embodiment of the present application, the above Formula 3-1 can be represented by the following Formula 3-A.

[0103] [Formula 3-A]

[0104]

[0105] In the above Formula 3-A,

[0106] n1, m1, and k1 are defined the same as in the above Formula 3-1.

[0107] In one embodiment of the present application, the above Formula 3-2 can be represented by the following Formula 3-B.

[0108] [Formula 3-B]

[0109]

[0110] In the above Formula 3-B,

[0111] n2, m2, and k2 are defined identically as in the above Formula 3-2.

[0112] In one embodiment of the present application, the polyalkylene carbonate-based first polymer can have a weight average molecular weight of 1,000 g / mol to 1,500,000 g / mol, preferably 2,000 g / mol to 1,000,000 g / mol, and most preferably 2,000 g / mol to 10,000 g / mol. When the weight average molecular weight of the first polymer is less than 1,000 g / mol, the affinity between the polymer and the electrode decreases, the mechanical properties of the film derived from the polymer deteriorate, and when it is greater than 1,500,000 g / mol, there is a problem in that it is difficult to dissolve in the electrolyte solvent.

[0113] (b) the second polymer

[0114] In one embodiment of the present application, the composition for electrolyte includes a polyethylene oxide (PEO)-based second polymer having a weight average molecular weight of 200 g / mol to 2,000 g / mol.

[0115] The ethylene oxide backbone of the second polymer has a high dielectric constant, thus helping to dissociate the lithium salt, and in addition, the high mobility of the polymer chain resulting from the low Tg improves the lithium ion migration characteristics. Thus, the addition of the second polymer in an appropriate ratio can help to improve the electrolyte performance.

[0116] The weight average molecular weight of the second polymer is in the range of 1 / 3,000 to 1 / 3 of the weight average molecular weight of the first polymer, preferably 1 / 1,000 to 1 / 5, and more preferably 1 / 100 to 1 / 6.

[0117] When the weight average molecular weight of the second polymer is in the above range, it is preferable that a Semi-IPN structure is easily formed between the first polymer and the second polymer having different molecular weights, and the polymer matrix can be appropriately dispersed.

[0118] When the weight average molecular weight of the second polymer is less than 1 / 3,000 of the weight average molecular weight of the first polymer, the affinity between the second polymer and the first polymer is low, thus it is difficult to sufficiently obtain the effect due to the introduction of the second polymer, and when it is greater than 1 / 3, the dispersion of the first polymer is inhibited, thus it is difficult to form a suitable structure.

[0119] In one embodiment of the present application, the weight average molecular weight of the second polymer can preferably be 200 g / mol to 1,000 g / mol.

[0120] In one embodiment of the present application, the polyethylene oxide (PEO)-based second polymer includes a unit represented by the following Formula 2.

[0121] [Formula 2]

[0122]

[0123] In the above Formula 2,

[0124] R5 to R8 are the same as or different from each other, and each is independently hydrogen, or an alkyl group having 1-5 carbon atoms,

[0125] * is a site connected to a main chain or an end group of a polymer, and

[0126] h is a repeating number, and is any one integer from 1 to 200.

[0127] Preferably, R6 to R8 of the above Formula 2 can each be hydrogen.

[0128] Further, preferably, h can be any one integer from 1 to 100, more preferably, h can be any one integer from 1 to 50.

[0129] The two end groups of the second polymer of the present application are the same as or different from each other, although not particularly limited, and may, for example, each be independently an alkyl group, an alkoxy group, a hydroxyl group, an aldehyde group, an ester group, a halogen group, a halide group, a vinyl group, a (meth)acrylate group, a carboxyl group, a phenyl group, an amine group, an amide group, or a sulfonyl group. Specifically, the end group is an alkyl group having 1-5 carbon atoms.

[0130] In one embodiment of the present application, the amount of the second polymer can be in the range of 0.01 to 50% by weight, preferably 0.02 to 40% by weight, more preferably 0.05 to 30% by weight, based on the total weight of the first polymer. When the amount of the second polymer with respect to the first polymer is less than 0.01% by weight, the effect due to the introduction of the second polymer is insignificant, and thus it is difficult to expect the effect, and when it is greater than 50% by weight, the formation of the network structure of the polymer is inhibited, and thus there is a problem in that the functionality of the electrolyte is further deteriorated.

[0131] (c) additives

[0132] According to necessity, in order to prevent the electrolyte from being decomposed in a high voltage environment to cause electrode collapse, or to further improve the effects of low temperature high rate discharge characteristics, high temperature stability, prevention of overcharging, suppression of battery swelling at high temperature, etc., the composition of the electrolyte for a lithium secondary battery according to the present application can optionally include the following additives.

[0133] The additive can be one or more selected from the group consisting of carbonate compounds, halogen-substituted carbonate compounds, sulfonic acid lactone compounds, sulfate compounds, phosphate or phosphite compounds, nitrile compounds, amine compounds, silane compounds, benzene compounds, and lithium salt compounds.

[0134] The carbonate compound can be one or more selected from the group consisting of vinylene carbonate (VC) and vinyl ethylene carbonate (VEC), and specifically, can be vinylene carbonate.

[0135] The halogen-substituted carbonate compound can be fluoroethylene carbonate (FEC).

[0136] The sulfonic acid lactone compound is a material capable of forming a stable SEI film on the surface of the negative electrode by a reduction reaction, and can be one or more compounds selected from the group consisting of 1,3-propane sulfonic acid lactone (PS), 1,4-butane sulfonic acid lactone, ethylene sulfonic acid lactone, 1,3-propylene sulfonic acid lactone (PRS), 1,4-butylene sulfonic acid lactone, and 1-methyl-1,3-propylene sulfonic acid lactone, and specifically, can be 1,3-propane sulfonic acid lactone (PS).

[0137] The sulfate compound is a material that can be electrochemically decomposed on the surface of the negative electrode to form a stable SEI film that does not break even during high-temperature storage, and can be one or more selected from the group consisting of ethylene sulfate (Esa), trimethylene sulfate (TMS), and methyl trimethylenesulfate (MTMS).

[0138] The phosphate or phosphite compound can be one or more selected from the group consisting of lithium difluoro(bisoxalato)phosphate, lithium difluorophosphate, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite, tris(2,2,2-trifluoroethyl)phosphate, and tris(trifluoroethyl)phosphite.

[0139] The nitrile compound can be one or more selected from the group consisting of butanedinitrile, hexanedinitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, octanonitrile, heptanonitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

[0140] The amine compound can be one or more selected from triethanolamine and ethylenediamine, and the silane compound can be tetraethenylsilane.

[0141] The benzene compound can be one or more selected from monofluorobenzene, difluorobenzene, trifluorobenzene, and tetrafluorobenzene.

[0142] The lithium salt compound is a compound different from a lithium salt included in a nonaqueous electrolyte, and can be one or more compounds selected from LiPO2F2, lithium bis(oxalato)borate (LiB(C2O4)2) (LiBOB), lithium tetrafluoroborate (LiBF4), and lithium tetraphenylborate.

[0143] Meanwhile, the amount of the additive can be in the range of 0.1 to 10% by weight, preferably 1 to 5% by weight, based on the total weight of the composition for the electrolyte. When the amount of the additive is less than 0.1% by weight, the effect of improving the low-temperature capacity of the battery and the high-temperature storage performance and high-temperature life performance of the battery is not significant, and when it is greater than 10% by weight, the side reaction in the electrolyte can excessively occur during the charging and discharging of the battery. In particular, when the additive for forming the SEI film is excessively added, the additive can not be sufficiently decomposed at a high temperature, and thus can exist as an unreacted substance or be precipitated in the electrolyte at room temperature. Therefore, a side reaction that causes the life or resistance characteristics of the battery to deteriorate can occur.

[0144] (d) an organic solvent

[0145] As the organic solvent, various organic solvents commonly used in lithium electrolytes can be used without limitation. For example, the organic solvent can include one or more selected from cyclic carbonate solvents, linear carbonate solvents, cyclic ester solvents, linear ester solvents, and nitrile solvents, and preferably can include cyclic carbonate solvents and linear ester solvents. When the cyclic carbonate solvents and linear ester solvents are used together, it is preferable to form a suitable solvation sheath in the lithium ion dissociation process, thereby facilitating the dissociation of the lithium salt, reducing the viscosity of the electrolyte, thereby improving the ionic conductivity, and increasing the low-temperature ionic conductivity, thereby improving the low-temperature output performance, and also improving the stability at a high voltage, so that the battery life can be improved.

[0146] The cyclic carbonate-based solvent is a high-viscosity organic solvent having a high dielectric constant, and thus can well dissociate a lithium salt in an electrolyte, and can be one or more selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, and vinylene carbonate. Among them, ethylene carbonate (EC) and propylene carbonate (PC) can be included from the viewpoint of securing a high ionic conductivity.

[0147] Further, the linear carbonate-based solvent is a low-viscosity, low-dielectric constant organic solvent, and a representative example thereof can be one or more organic solvents selected from dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate, and ethyl propyl carbonate, and specifically, ethyl methyl carbonate (EMC) can be included.

[0148] The linear ester-based solvent can be at least one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), and butyl propionate (BP), and specifically, ethyl propionate (EP) and propyl propionate (PP) can be included.

[0149] Further, as the cyclic ester-based solvent, one or more selected from γ-butyrolactone, γ-valerolactone, γ-hexalactone, σ-valerolactone, and ε-hexalactone can be used.

[0150] When the linear ester-based solvent and / or the cyclic ester-based solvent are included as the organic solvent of the composition for the electrolyte, stability at high temperature can be improved.

[0151] The nitrile-based solvent can be one or more selected from butanedinitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, octanitrile, heptanitrile, cyclopentanitrile, cyclohexanitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile, and preferably, can be butanedinitrile.

[0152] Unless otherwise specified, the remaining portion of the composition of the electrolyte for the lithium secondary battery, excluding other components (e.g., lithium salt other than the organic solvent, the first polymer, the second polymer, the additive, and the polymerization initiator described later) can be the organic solvent.

[0153] (e) lithium salt

[0154] As the lithium salt, any lithium salt generally used in an electrolyte for a lithium secondary battery can be used without limitation, and for example, the lithium salt includes LiPF6, LiBF4, LiSbF6, LiAsF6, LiCF3SO3, LiC4F9SO3, LiAlCl4, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiClO4, Li2CrO4, Li3FeCl6, Li3P, Li2B10Cl10, and Li2B12H12. + As the cation, and includes one selected from F- Cl - Br - I - NO3 - N(CN)2 - BF4 - ClO4 - B 10 Cl 10 - AlCl4 - AIO4 - PF6 - CF3SO3 - CH3CO2 - CF3CO2 - AsF6 - SbF6 - CH3SO3 - (CF3CF2SO2)2N - (CF3SO2)2N - (FSO2)2N - BF2C2O4 - BC4O8 - BF2C2O4CHF - PF4C2O4 - PF2C4O8 - PO2F2 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - C4F9SO3 - CF3CF2SO3 - CF3CF2(CF3)2CO - (CF3SO2)2CH - CF3(CF2)7SO3 - and SCN - one or more of the group consisting of

[0155] Specifically, the lithium salt can be one or more selected from the group consisting of LiPF6, LiClO4, LiBF4, lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), LiSO3CF3, LiPO2F2, lithium bis(oxalate)borate (LiBOB), lithium difluoro(oxalate)borate (LiDFOB), lithium difluoro(bisoxalato)phosphate (LiDFBP), lithium tetrafluoro(oxalate)phosphate (LiTFOP), and lithium fluoromalonato(difluoro)borate (LiFMDFB), and preferably, can be LiPF6.

[0156] In one embodiment of the present application, the concentration of the lithium salt in the composition for the electrolyte can be 0.1 M to 4.0 M, specifically 0.5 M to 3.0 M, and more specifically 0.8 M to 2.5 M. When the concentration of the lithium salt is within the above range, the effects of improving low-temperature output and improving cycle performance are sufficiently secured, and excessive increase in viscosity and surface tension is prevented, so that appropriate electrolyte impregnation properties can be obtained.

[0157] (f) polymerization initiator

[0158] The electrolyte for a lithium secondary battery of the present application can further include a typical polymerization initiator known in the art, for example, one or more polymerization initiators selected from the group consisting of azo compounds and peroxide compounds. The polymerization initiator serves to initiate the polymerization reaction of the first polymer and the second polymer of the present application.

[0159] The azo compound can be one or more 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'-azobisdimethyl-valeronitrile (AMVN), but is not limited thereto.

[0160] The peroxide compound can be one or more selected from the group consisting of benzoyl peroxide, acetyl peroxide, dilauryl peroxide, di-tert-butyl peroxide, t-butyl peroxy-2-ethyl-hexanoate, cumyl hydroperoxide, and hydrogen peroxide, but is not limited thereto.

[0161] The polymerization initiator can be decomposed by heat, a non-limiting example of which can be heat of 30°C to 100°C, or at room temperature (5°C to 30°C) to form free radicals, and by radical polymerization, the first polymer and the second polymer can react with the acrylate-based end group to form a gel polymer electrolyte.

[0162] The polymerization initiator can be included in an amount of 0.1 parts by weight to 5 parts by weight based on 100 parts by weight of the first polymer and the second polymer. When the polymerization initiator is included within the above range, the amount of residual unreacted polymerization initiator can be minimized, and gelation higher than a predetermined level can be achieved.

[0163] Gel polymer electrolyte

[0164] The present application provides a gel polymer electrolyte for a lithium secondary battery, including a polymerization reactant of a composition for an electrolyte of a lithium secondary battery, and specifically, the gel polymer electrolyte can be a polymerization reactant of a composition for an electrolyte. That is, the gel polymer electrolyte can include a polymer network formed by polymerization reaction of the polymerization reactant of the composition for an electrolyte. Specifically, the gel polymer electrolyte can be manufactured by injecting the composition for an electrolyte into a secondary battery and then curing the composition by thermal polymerization reaction. For example, the gel polymer electrolyte can be formed by in-situ polymerization of the electrolyte composition within the secondary battery.

[0165] More specifically, the gel polymer electrolyte can be manufactured by:

[0166] (a) inserting an electrode assembly composed of a cathode, an anode, and a separator interposed between the cathode and the anode, into a battery case,

[0167] (b) injecting the composition of the present application into the battery case,

[0168] (c) wetting and aging the electrode assembly, and

[0169] (d) polymerizing the composition to form a gel polymer electrolyte.

[0170] At this time, the in-situ polymerization reaction in the lithium secondary battery can be performed by E-BEAM, gamma rays, room temperature / high temperature aging processes, and can be performed by thermal polymerization according to the embodiment of the present application. At this time, the polymerization takes about 2 minutes to 24 hours, and the thermal polymerization temperature can be 50°C to 100°C, specifically 60°C to 80°C.

[0171] More specifically, the gel polymer electrolyte of the present application can be manufactured by injecting the composition for electrolyte into a battery cell, then sealing the injection port, and performing thermal polymerization at about 60°C to 80°C for 1 to 20 hours.

[0172] Lithium secondary battery

[0173] Next, a lithium secondary battery according to the present application will be described.

[0174] The lithium secondary battery according to the present application includes a cathode including a cathode active material, an anode including an anode active material, a separator interposed between the cathode and the anode, and the above-described gel polymer electrolyte for a lithium secondary battery. The gel polymer electrolyte has been described above, so its description will be omitted, and the other components will be described hereinafter.

[0175] (a) Cathode

[0176] The cathode can be manufactured by coating a cathode mixture slurry including a cathode active material, a binder, a conductive material, a solvent, etc. on a cathode current collector.

[0177] The cathode current collector is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, silver, and the like can be used.

[0178] The cathode active material is a compound capable of reversibly intercalating and deintercalating lithium, and can be one or more selected from the group consisting of LCO (LiCoO2), LNO (LiNiO2), LMO (LiMnO2), LiMn2O4, LiCoPO4, LFP (LiFePO4), and LiNi 1-x-y-z Co x M 1 y M 2 z O2(M 1 and M 2each independently selected from any one of the group consisting of Al, Ni, Co, Fe, Mn, V, Cr, Ti, W, Ta, Mg, and Mo, x, y, z are each independently an atomic fraction of an oxide constituent element, wherein 0≤x<0.5, 0≤y<0.5, 0≤z<0.5, and x+y+z=1), including LiNiMnCoO2, LiNiCoMnO2(NMC), and the like.

[0179] Specifically, the positive active material can include a lithium metal oxide containing lithium and one or more metals such as cobalt, manganese, nickel, or aluminum.

[0180] More specifically, the lithium metal oxide can be a lithium-manganese-based oxide (such as LiMnO2, LiMnO3, LiMn2O3, and LiMn2O4), a lithium-cobalt-based oxide (such as LiCoO2), a lithium-nickel-based oxide (such as LiNiO2), a lithium-nickel-manganese-based oxide (such as LiNi 1-Y Mn y O2(0 2-z Ni z O4(0 1- y 1Co y1 O2(0 1-y2 Mn y2 O2(0 2-z1 Co z1 O4(0 p Co q Mn r1 )O2(0 p1 Co q1 Mn r2 )O4(0 p2 Co q2 Mn r3 M s2 )O2(wherein M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r3, and s2 are atomic fractions of independent elements, respectively, wherein 0

[0181] Among them, since the capacity and stability of the battery can be improved, the lithium metal oxide can be LiCoO2, LiMnO2, LiNiO2, lithium-nickel-manganese-cobalt oxide (e.g., 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, Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, etc.), or lithium nickel cobalt aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05 )O2, etc.). When considering a significant improvement effect according to the type and content ratio control of the constituent elements forming the lithium metal oxide, the lithium metal oxide can be one or more selected from 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.

[0182] The cathode active material can be included in an amount of 60 to 99% by weight, preferably 70 to 99% by weight, more preferably 80 to 99% by weight, based on the total weight of the solids excluding the solvent in the cathode mixture slurry.

[0183] The binder is a component for helping the binding between the active material and the conductive material and the binding with the current collector.

[0184] Examples of the binder can include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene (PE), polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene butadiene rubber (SBR), fluororubber, and various copolymers thereof.

[0185] Generally, the binder can be included in an amount of 1 to 20% by weight, preferably 1 to 15% by weight, more preferably 1 to 10% by weight, based on the total weight of solids excluding the solvent in the positive electrode mixture slurry.

[0186] The conductive material is a component for further improving the conductivity of the positive electrode active material.

[0187] The conductive material is not particularly limited as long as it has conductivity without causing chemical changes in the battery. For example, 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 fibers and metal fibers; metal powders such as carbon fluoride powder, aluminum powder, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyaniline derivatives and the like can be used.

[0188] Generally, the conductive material can be included in an amount of 1 to 20% by weight, preferably 1 to 15% by weight, more preferably 1 to 10% by weight, based on the total weight of solids excluding the solvent in the positive electrode mixture slurry.

[0189] The solvent can include an organic solvent such as N-methyl-2-pyrrolidone (NMP), and can be used in an amount such that a preferred viscosity is achieved when the positive electrode active material, and optionally the binder and the conductive material, etc. are included. For example, the solvent can be included in an amount such that the concentration of solids including the positive electrode active material, and optionally the binder and the conductive material, is in the range of 50 to 95% by weight, preferably 50 to 80% by weight, more preferably 55 to 70% by weight.

[0190] (b) Negative electrode

[0191] The negative electrode can be prepared by coating a negative electrode slurry including a negative electrode active material, a binder, a conductive material, a solvent, etc. on a negative electrode current collector, and then drying and roll-pressing.

[0192] The negative electrode current collector generally has a thickness of 3 to 500 μm. The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper; stainless steel; aluminum; nickel; titanium; baked carbon; copper or stainless steel subjected to surface treatment using one of carbon, nickel, titanium, silver, and the like; aluminum-cadmium alloy; or the like can be used. Furthermore, as in the case of the positive electrode current collector, a micro-irregularity 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 a film, a sheet, a foil, a mesh, a porous body, a foam, and a nonwoven fabric.

[0193] Further, the negative active material can include one or more selected from the group consisting of a lithium metal, a carbon material capable of reversibly intercalating / deintercalating lithium ions, a metal or an alloy of a metal and lithium, a metal composite oxide, a material capable of doping and undoping lithium, and a transition metal oxide.

[0194] As the carbon material capable of reversibly intercalating / deintercalating lithium ions, a carbon-based negative active material commonly used in lithium ion secondary batteries can be used without particular limitation, and representative examples thereof can include crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon can include graphite such as irregular, planar, flake, spherical, or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon can include soft carbon (low-temperature fired carbon) or hard carbon, mesophase pitch carbide, fired coke, and the like.

[0195] As the metal or the alloy of a metal and lithium, a metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn, or an alloy of the metal and lithium can be used.

[0196] As the metal composite oxide, one selected from the group consisting of PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, Bi2O5, Li x Fe2O3(0≤x≤1), Li x WO2(O≤x≤1), and Sn x Me l-x Me′ y O z (Me: Mn, Fe, Pb, Ge; Me′: Al, B, P, Si, each element of Group 1, Group 2, Group 3 of the periodic table, halogen; 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8).

[0197] The material capable of doping and undoping lithium can be Si, SiO x(0 < x < 2), Si-Y alloys (where Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, but not Si), Sn, Sn02, Sn-Y (where Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, but not Sn), and the like, or at least one of them can be mixed with Si02and used. The element Y can be selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

[0198] The transition metal oxide can be lithium-containing titanium composite oxide (LTO), vanadium oxide, lithium vanadium oxide, and the like.

[0199] In the present application, the negative electrode active material is preferably graphite.

[0200] The negative electrode active material can be included in an amount of 60 to 99% by weight, preferably 70 to 99% by weight, more preferably 80 to 99% by weight, based on the total weight of solids excluding the solvent in the negative electrode mixture slurry.

[0201] The binder is a component for assisting the binding between the conductive material, the active material, and the current collector. Examples of the binder can include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene butadiene rubber (SBR), fluoro rubber, and various copolymers thereof.

[0202] Generally, the binder can be included in an amount of 1 to 20% by weight, preferably 1 to 15% by weight, more preferably 1 to 10% by weight, based on the total weight of solids excluding the solvent in the negative electrode mixture slurry.

[0203] The conductive material is not particularly limited as long as it has conductivity without causing chemical changes in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride powder, aluminum powder, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyaniline derivatives can be used.

[0204] The conductive material can be included in an amount of 1 to 20% by weight, preferably 1 to 15% by weight, more preferably 1 to 10% by weight, based on the total weight of solids other than the solvent in the negative electrode mixture slurry.

[0205] The solvent can include water; or an organic solvent such as N-methyl-2-pyrrolidone (NMP), and can be used in an amount such that a preferred viscosity is achieved when the negative electrode active material and, optionally, the binder and the conductive material, etc. are included. For example, the solvent can be included in an amount such that the concentration of solids including the negative electrode active material and, optionally, the binder and the conductive material is in the range of 50 to 95% by weight, preferably 70 to 90% by weight.

[0206] When a metal itself is used as the negative electrode, the negative electrode can be manufactured by physically bonding, rolling, or depositing the metal on a metal thin film itself or a negative electrode current collector. The deposition method can be electro-gas deposition or chemical vapor deposition.

[0207] For example, the metal bonded / rolled / deposited on the metal thin film itself or the negative electrode current collector can be one metal selected from the group consisting of nickel (Ni), tin (Sn), copper (Cu), and indium (In), or an alloy of two of them.

[0208] (c) Separator

[0209] The lithium secondary battery according to the present application includes a separator disposed between the positive electrode and the negative electrode.

[0210] The separator serves to separate the negative electrode and the positive electrode and to provide a path for movement of lithium ions, and any separator can be used without particular limitation as long as it is a separator commonly used in secondary batteries. In particular, a separator having excellent electrolyte impregnability and a low resistance to ion movement in the electrolyte is preferred.

[0211] Specifically, as the separator, a porous polymer film, for example, a porous polymer film manufactured using a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure having two or more layers thereof can be used. In addition, a typical porous nonwoven fabric, for example, a nonwoven fabric formed of glass fibers, polyethylene terephthalate fibers, or the like having a high melting point can be used. Furthermore, a separator including or coated with a ceramic component or a polymer material in the form of a film, a fiber, or a powder can be used to ensure heat resistance or mechanical strength, and can be used in a single layer or a multilayer structure.

[0212] The lithium secondary battery according to the present application as described above can be advantageously used in portable devices such as mobile phones, notebook computers, and digital cameras, and in electric vehicles such as hybrid electric vehicles (HEVs).

[0213] Accordingly, according to another embodiment of the present application, there are provided a battery module including the lithium secondary battery as a unit cell, and a battery pack including the battery module.

[0214] The battery module or the battery pack can be used as a power source for one or more medium- and large-sized devices, for example, Power Tools, electric vehicles (EVs), hybrid electric vehicles, and Plug-in Hybrid Electric Vehicles (PHEVs), and power storage systems.

[0215] The lithium secondary battery of the present application is not particularly limited in outer shape, and can be cylindrical, square, pouch-shaped, coin-shaped, or the like using a can.

[0216] The lithium secondary battery according to the present application can be used in a battery unit as a power source for small-sized devices, and can be preferably used as a unit cell in a medium- and large-sized battery module including a plurality of battery units.

[0217] Hereinafter, the present application will be described in detail with reference to specific examples.

[0218] Embodiment

[0219] <Example: Manufacture of lithium secondary battery>

[0220] Example 1.

[0221] (1) Preparation of a composition for an electrolyte

[0222] A 1.0 M LiPF6, 5 wt% of a PEC-based first polymer represented by the following formula 3-B (Mw: 3,000 g / mol, n2=10, m2=10, k2=2), 0.0025 wt% (0.05 wt% based on the first polymer) of a PEO-based second polymer represented by the following formula P2 (Mw: 500 g / mol, h=10), 0.4 wt% of 2,2'-azobis(2,4-dimethylvaleronitrile) (V-65, Wako Co., Ltd.), and the remaining organic solvent were mixed to prepare a composition for an electrolyte in a total amount of 100 wt%. At this time, as the organic solvent, a mixed non-aqueous organic solvent including ethylene carbonate (EC): propylene carbonate (PC): ethyl propionate (EP): propyl propionate (PP) at a volume ratio of 20:10:25:45 was used.

[0223] [Formula 3-B]

[0224]

[0225] [Formula P2]

[0226]

[0227] (2) Manufacture of lithium secondary battery

[0228] To an N-methyl-2-pyrrolidone (NMP) solvent, 96 parts by weight of LiCoO2 as a positive electrode active material, 2 parts by weight of carbon black as a conductive material, and 2 parts by weight of polyvinylidene fluoride (PVdF) as a binder were added, respectively, to prepare a positive electrode mixture slurry. The positive electrode mixture slurry was applied to an aluminum (Al) thin film having a thickness of about 20 μm as a positive electrode current collector, dried, and then roll-pressed, thereby manufacturing a positive electrode.

[0229] Graphite as a negative electrode active material, styrene butadiene rubber (SBR) as a binder, CMC as a thickening agent, and carbon black as a conductive material were mixed in a weight ratio of 96.3:1:1.5:1.2, and then added to an NMP solvent to prepare a negative electrode mixture slurry. The negative electrode mixture slurry was applied to a copper (Cu) thin film having a thickness of about 10 μm as a negative electrode current collector, dried, and then roll-pressed, thereby manufacturing a negative electrode.

[0230] A lithium secondary battery was manufactured in the same manner as in Example 1, except that, in the preparation of the composition for electrolyte of Example 1, the amount of the first polymer was changed to 0.5% by weight based on the total amount of the composition, and the amount of the second polymer was changed to 0.5% by weight based on the amount of the first polymer.

[0231] Example 2.

[0232] A lithium secondary battery was manufactured in the same manner as in Example 1, except that, in the preparation of the composition for electrolyte of Example 1, the amount of the second polymer was changed to 20% by weight based on the total amount of the first polymer.

[0233] Example 3.

[0234] A lithium secondary battery was manufactured in the same manner as in Example 1, except that, in the preparation of the composition for electrolyte of Example 1, the amount of the first polymer was changed to 0.5% by weight based on the total amount of the composition, and the amount of the second polymer was changed to 0.5% by weight based on the amount of the first polymer.

[0235] Example 4.

[0236] A lithium secondary battery was manufactured in the same manner as in Example 1, except that, in the preparation of the composition for electrolyte of Example 1, the amount of the first polymer was changed to 30% by weight based on the total amount of the composition, and the amount of the second polymer was changed to 0.5% by weight based on the amount of the first polymer.

[0237] Comparative Example 1.

[0238] A lithium secondary battery was manufactured in the same manner as in Example 1, except that, in the preparation of the composition for electrolyte of Example 1, the first polymer and the second polymer were not included.

[0239] Comparative Example 2.

[0240] A lithium secondary battery was manufactured in the same manner as in Example 1, except that, in the preparation of the composition for electrolyte of Example 1, the second polymer was not included.

[0241] Comparative Example 3.

[0242] A lithium secondary battery was manufactured in the same manner as in Example 1, except that, in the preparation of the composition for the electrolyte of Example 1, the amount of the first polymer was changed to 0.05% by weight based on the total amount of the composition, and the amount of the second polymer was changed to 20% by weight based on the amount of the first polymer.

[0243] Comparative Example 4.

[0244] A lithium secondary battery was manufactured in the same manner as in Example 1, except that, in the preparation of the composition for the electrolyte of Example 1, the amount of the first polymer was changed to 40% by weight based on the total amount of the composition, and the amount of the second polymer was changed to 0.5% by weight based on the amount of the first polymer.

[0245] Comparative Example 5.

[0246] A lithium secondary battery was manufactured in the same manner as in Example 2, except that, in the preparation of the composition for the electrolyte of Example 2, a polymer having a weight average molecular weight of 3,000 g / mol (h = 60 in the above Formula P2) was used as the second polymer.

[0247] Comparative Example 6.

[0248] The same operation was performed in the same manner as in Example 1, except that, in the preparation of the composition for the electrolyte of Example 1, a polymer having a weight average molecular weight of 2,000,000 g / mol (n2 = 10, m2 = 10, k2 = 1,000 in the above Formula 3-B) was used as the first polymer, and the amount of the second polymer was changed to 0.5% by weight based on the amount of the first polymer, but the first polymer was not dissolved, so that the composition for the electrolyte could not be manufactured.

[0249] Comparative Example 7.

[0250] A lithium secondary battery was manufactured in the same manner as in Example 1, except that, in the preparation of the composition for the electrolyte of Example 1, a PEO-based polymer (Mw: 3,000 g / mol, n = 68) represented by the following Formula C was used as the first polymer.

[0251] [Formula C]

[0252]

[0253] Comparative Example 8.

[0254] A lithium secondary battery was manufactured in the same manner as in Example 1, except that, in the preparation of the composition for the electrolyte of Example 1, a compound represented by the above Formula C (n = 4) having a weight average molecular weight of 196 g / mol was used instead of the compound represented by the above Formula P2 as the second polymer.

[0255] <Test example>

[0256] Test Example 1: Thermal safety evaluation

[0257] The lithium secondary batteries prepared in the examples and comparative examples were heated to 150°C at a temperature increase rate of 5°C / min in a full charged state of SOC 100% (4.45V), and then each of them was left to stand for one hour, and a thermal oven evaluation test was performed to determine whether or not ignition occurred.

[0258] The results are shown in Table 1 below, and FAIL is recorded when the battery ignites, and PASS is recorded when it does not ignite.

[0259] Test Example 2: Heat value evaluation

[0260] Each of the lithium secondary batteries of the examples and comparative examples was charged in a full charged state of SOC 100% (4.45V) under the condition of 150°C, and was stored therein for 4 hours to measure the heat value of each battery using a multi-module calorimeter (MMC) (NETZSCH Co. Ltd., MMC274 MMC 274). When the heat value of the battery of Comparative Example 1 was set to 100%, the relative heat values of each battery are shown in Table 1.

[0261] Test Example 3: Evaluation of leakage generation

[0262] In manufacturing the lithium secondary batteries in the examples and comparative examples, 15% excess of electrolyte was injected thereto, and the batteries were stored at room temperature for 4 days to perform an impregnation process.

[0263] For the impregnated batteries, a formation process was performed by charging at a rate of 0.1C to SOC 30% for 3 hours at 25°C, and then a degassing process was performed after aging for 24 hours. The battery after degassing was charged to 4.45V at a rate of 0.1C under constant current-constant voltage (CC-CV) conditions at 25°C, and then was discharged to 3.0V at a rate of 0.1C under CC conditions. The above charging and discharging were set to 1 cycle, and 2 initial charging and discharging cycles were performed.

[0264] After that, the battery was discharged to SOC 0%, and the lower end of the battery was cut by 10 mm while the battery was placed upright, and then the battery was stored inclined at an angle of 1° for 24 hours to confirm the leakage of the electrolyte. Whether there was leakage is shown in Table 1 below.

[0265] [Table 1]

[0266]

[0267] Referring to the results of Table 1, it can be seen that when the electrolyte is manufactured using the composition including the optimal amount of the PEC-based polymer and the PEO-based polymer according to the embodiment of the present application, there is an effect of improving thermal safety and durability.

[0268] Meanwhile, it can be confirmed that Comparative Example 1, which does not include the PEC-based polymer or the PEO-based polymer, is vulnerable to heat and has low durability, and thus has a high risk of leakage. Further, it can be confirmed that in the case of including the PEC-based polymer but not the PEO-based polymer (Comparative Example 2), the heat value is high.

[0269] As described above, in the case where the molecular weight of the PEC-based polymer is excessively high (Comparative Example 6), the PEC-based polymer is not dissolved in the solvent, so that the composition for the electrolyte cannot be prepared, in the case where the PEC-based polymer is used in excess (Comparative Example 4), the battery cannot be driven, and in the case where the amount of the PEC-based polymer is too small (Comparative Example 3), there is no effect on improving thermal safety and durability.

[0270] Further, in the case of Comparative Example 7 in which the PEO-based polymer is used instead of the PEC-based polymer, the oxidation stability is reduced, and since the battery using LCO as the positive electrode is not charged to SOC 100% (4.45V), it is impossible to evaluate.

[0271] Further, it can be seen that in the case where the molecular weight of the PEO-based polymer is greater than 1 / 3 of the molecular weight of the PEC-based polymer (Comparative Example 5), the dispersion of the PEC-based polymer is inhibited, and thus both the discharge capacity and the durability are reduced. Further, it can be confirmed that in the case where the molecular weight of the PEO-based polymer is less than 200 g / mol (Comparative Example 8), the second polymer having a low molecular weight causes a side reaction on the surface of the positive electrode, thereby increasing the heat generated by the positive electrode, so that the heat value is increased.

Claims

1. A composition for an electrolyte used in a lithium secondary battery, comprising: Lithium salts; A first polymer of polyalkylene carbonate, the first polymer having a weight-average molecular weight of 1,000 g / mol to 1,500,000 g / mol; A second polyethylene oxide polymer having a weight-average molecular weight of 200 g / mol to 2,000 g / mol; and Organic solvents, The weight-average molecular weight of the second polymer is in the range of 1 / 3,000 to 1 / 3 of the weight-average molecular weight of the first polymer. Based on the total weight of the composition, the amount of the first polymer is in the range of 0.1% to 30% by weight, and The amount of the second polymer is in the range of 0.01% to 50% by weight, based on the total weight of the first polymer.

2. The composition according to claim 1, wherein the first polymer comprises a unit represented by formula 1: [Formula 1] In equation 1 above, R1 to R4 may be the same as or different from each other and are each independently hydrogen or an alkyl group having 1 to 5 carbon atoms. * indicates a site where the polymer backbone or end group is attached, and n is a repeated number and is any integer from 1 to 1,000.

3. The composition according to claim 1, wherein the second polymer comprises a unit represented by formula 2: [Equation 2] In equation 2 above, R5 to R8 may be the same as or different from each other and are each independently hydrogen or an alkyl group having 1-5 carbon atoms. * is the site attached to the polymer backbone or end group, and h is a repetition number and is any integer from 1 to 200.

4. The composition according to claim 2, wherein the first polymer comprises a unit represented by formula 3: [Formula 3] In equation 3 above, R and R' may be the same as or different from each other, and each is an alkyl group with 1-5 carbon atoms. A is the unit represented by Equation 1 above. B is a unit that includes one or more amide groups. * indicates a site where the polymer backbone or end group is attached, and m and k are the repetition numbers, where: m is any integer from 1 to 1,000, and k is any integer from 1 to 100.

5. The composition according to claim 4, wherein B is represented by the formula B-1: [Formula B-1] In equation B-1 above, R” is a substituted or unsubstituted alkyl group having 1-10 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3-10 carbon atoms, a substituted or unsubstituted bicycloalkyl group having 6-20 carbon atoms, or a substituted or unsubstituted aryl group having 6-20 carbon atoms.

6. The composition according to claim 1, wherein the first polymer is represented by formula 3-1 or formula 3-2: [Equation 3-1] In equation 3-1 above, n1, m1, and k1 are the repetition numbers, where: n1 is any integer from 1 to 1,000. m1 is any integer from 1 to 1,000, and k1 is any integer from 1 to 100, and E1 and E2 may be the same as or different from each other, and each is independently an alkyl, alkoxy, hydroxyl, aldehyde, ester, halogen, halide, vinyl, (meth)acrylate, carboxyl, phenyl, amino, amide, or sulfonyl group. [Equation 3-2] In equation 3-2 above, n², m², and k² are repeating numbers, where: n2 is any integer from 1 to 1,000. m2 is any integer from 1 to 1,000, and k2 is any integer from 1 to 100, and a and a' are either the same or different from each other, and are each an independent integer of 1 or 2. b and b' are either the same or different from each other, and each is an independent integer from 1 to 3.

7. The composition according to claim 1, wherein the weight-average molecular weight of the second polymer is in the range of 1 / 1,000 to 1 / 5 of the weight-average molecular weight of the first polymer.

8. The composition according to claim 1, wherein the amount of the first polymer is in the range of 0.1% to 20% by weight based on the total weight of the composition.

9. The composition of claim 1, wherein the amount of the second polymer is in the range of 0.02% by weight to 40% by weight, based on the total weight of the first polymer.

10. The composition according to claim 1, wherein the composition further comprises a polymerization initiator.

11. A gel polymer electrolyte for lithium secondary batteries, said gel polymer electrolyte comprising the polymeric reactant of the composition for electrolyte of claim 1.

12. A lithium secondary battery, comprising: A positive electrode containing positive electrode active material; A negative electrode containing a negative electrode active material; A partition inserted between the positive electrode and the negative electrode; and The gel polymer electrolyte of claim 11.

Images