KR102298292B1 - Composition for gel polymer electrolyte, gel polymer electrolyte prepared therefrom, and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a gel polymer electrolyte composition, a gel polymer electrolyte prepared by polymerizing the same, and a secondary battery comprising the same, and more particularly, to a gel polymer electrolyte composition with improved high temperature stability, a gel polymer electrolyte formed by polymerizing the same in an inert atmosphere, and It relates to a lithium secondary battery including the same.

Description

A gel polymer electrolyte composition, a gel polymer electrolyte prepared thereby, and a lithium secondary battery comprising the same

The present invention relates to a gel polymer electrolyte composition, a gel polymer electrolyte prepared thereby, and a lithium secondary battery comprising the same.

Recently, with the rapid development of electric, electronic, communication and computer industries, the demand for high-performance and high-stability secondary batteries is gradually increasing. In particular, in accordance with the trend of miniaturization and weight reduction of these electronic (communication) devices, thin film and miniaturization of lithium secondary batteries, which are core components in this field, are required.

As an electrolyte for an electrochemical device such as a battery using an electrochemical reaction and an electric double layer capacitor, a liquid electrolyte, particularly an ion conductive organic liquid electrolyte obtained by dissolving a salt in a non-aqueous organic solvent, has been mainly used.

However, such a liquid electrolyte has a disadvantage in that the organic solvent is highly likely to be volatilized, and stability is low due to combustion due to an increase in ambient temperature and the temperature of the battery itself.

Accordingly, research to commercialize polymer electrolytes such as gel polymer electrolytes instead of liquid electrolytes has recently been on the rise.

The gel polymer electrolyte has excellent electrochemical stability compared to the liquid electrolyte, so that it is possible to maintain a constant thickness of the battery, and a thin film battery having excellent stability due to the inherent adhesive force of the gel can be manufactured.

A battery to which such a gel polymer electrolyte is applied is prepared by mixing a polymerizable monomer or oligomer and a polymerization initiator in a liquid electrolyte in which a salt is dissolved in a non-aqueous organic solvent, and then a positive electrode, a negative electrode, and an electrode assembly in which a separator is wound or laminated. It is prepared by injecting into the battery and gelling (crosslinking) it under appropriate temperature and time conditions.

On the other hand, when moisture is included in the lithium secondary battery, it may cause deterioration of the battery performance. For example, moisture present in the electrolyte composition reacts with the organic solvent by the potential energy provided during the charging process to generate gas to expand the thickness of the battery. can

Furthermore, when _{lithium salts such as LiPF 6} react with water, they form strong acid HF, which spontaneously reacts with the electrode active material exhibiting weak basicity to elute the electrode active material component, resulting in battery degradation. . In addition, lithium fluoride (LiF) is formed on the surface of the positive electrode to increase electrical resistance in the electrode and generate gas, thereby reducing the lifespan of the battery. In particular, since the HF attacks the main chain of the oligomer forming the polymer network during the preparation of the gel polymer electrolyte and prevents cross-linking, gelation is suppressed and the mechanical strength of the gel polymer electrolyte is reduced.

Accordingly, there is a need to develop a composition capable of maximally suppressing the formation of HF in the electrolyte solution.

Japanese Laid-Open Patent Publication No. 2001-313073

The present invention has been devised to solve such a problem.

A first object of the present invention is to provide a gel polymer electrolyte composition having improved long-term storage stability by including an additive capable of suppressing hydrofluoric acid production.

Another object of the present invention is to provide a gel polymer electrolyte with improved mechanical strength prepared by polymerizing the gel polymer electrolyte composition.

In addition, a third technical object of the present invention is to provide a lithium secondary battery having an improved initial capacity by including the gel polymer electrolyte.

In order to solve the above problems, in one embodiment of the present invention

lithium salt,

organic solvents;

polymerization initiator;

a dicarboimide-based compound represented by the following formula (1); and

It provides a gel polymer electrolyte composition comprising; an oligomer represented by the following formula (2).

[Formula 1]

In Formula 1,

R ₁ and R ₂ are each independently an alicyclic hydrocarbon group, and R ₁ and R ₂ may be the same as or different from each other.

[Formula 2]

In Formula 1,

R ₃ is a substituted or unsubstituted C 1 to C 5 alkylene group,

R ₄ , R ₅ , R ₆ and R ₇ are each independently a substituted or unsubstituted C1-C3 alkyl group,

R' and R" are each independently hydrogen or an alkyl group having 1 to 3 carbon atoms,

R is an aliphatic, alicyclic or aromatic hydrocarbon group,

a is an integer of any one of 1 to 3,

b is an integer of any one of 0 to 2,

n, m and x are the number of repeating units,

n is an integer of any one of 1 to 10,

m is an integer of any one of 1 to 5,

x is an integer of any one of 1 to 15.

In this case, in the dicarboimide-based compound represented by Formula 1, the alicyclic hydrocarbon group is a substituted or unsubstituted cycloalkylene group having 3 to 8 carbon atoms.

In addition, in R of the oligomer represented by Formula 2, the aliphatic hydrocarbon group may include an alkylene group having 1 to 20 carbon atoms; an alkylene group having 1 to 20 carbon atoms containing an isocyanate group (NCO); an alkoxyylene 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; wherein the alicyclic hydrocarbon group is a substituted or unsubstituted cycloalkylene group having 4 to 20 carbon atoms; a substituted or unsubstituted C4-C20 cycloalkylene group containing an isocyanate group (NCO); a cycloalkenylene group having 4 to 20 carbon atoms; Or a heterocycloalkylene group having 2 to 20 carbon atoms; wherein the aromatic hydrocarbon group is a substituted or unsubstituted arylene group having 6 to 20 carbon atoms; Or it may be a heteroarylene group having 2 to 20 carbon atoms.

In the gel polymer electrolyte composition of the present invention, the compound represented by Chemical Formula 1 may be at least one selected from the group consisting of compounds represented by the following Chemical Formulas 1a to 1f.

[Formula 1a]

[Formula 1b]

[Formula 1c]

[Formula 1d]

[Formula 1e]

[Formula 1f]

The compound represented by Formula 1 may be included in an amount of 0.001 wt% to 4 wt%, specifically 0.01 wt% to 3 wt%, more specifically 0.01 wt% to 2 wt%, based on the total weight of the gel polymer electrolyte composition have.

In addition, in the gel polymer electrolyte composition of the present invention, the oligomer represented by Formula 2 may be an oligomer represented by Formula 2a below.

[Formula 2a]

In Formula 2a,

n1 and x1 are the number of repeating units,

n1 is an integer of 1 or 10,

x1 is an integer in any one of 1 to 15.

The oligomer represented by Formula 2 may be included in an amount of 0.5 wt% to 20 wt%, specifically 0.7 wt% to 15 wt%, more specifically 1.0 wt% to 10 wt%, based on the total weight of the gel polymer electrolyte composition have.

The weight average molecular weight (MW) of the oligomer represented by Formula 2 may be 1,000 to 100,000, specifically 1,000 to 50,000, and more specifically 1,000 to 10,000.

In addition, in one embodiment of the present invention

It is possible to provide a gel polymer electrolyte prepared by polymerizing the gel polymer electrolyte composition of the present invention.

In addition, in one embodiment of the present invention

It is possible to provide a lithium secondary battery comprising a positive electrode, a negative electrode, a separator, and the gel polymer electrolyte of the present invention.

As described above, according to the present invention, storage stability is improved by suppressing the decomposition reaction of the oligomer main chain by hydrofluoric acid by including the dicarboimide-based compound capable of suppressing hydrofluoric acid production together with the oligomer of a specific structure as an additive. An improved gel polymer electrolyte composition can be provided. In addition, it is possible to manufacture a gel polymer electrolyte having excellent mechanical strength using the same, and by including the same, electrolyte volatilization and leakage are improved, and a lithium secondary battery with improved initial capacity.

1 and 2 are graphs showing the storage stability evaluation results of the gel polymer electrolyte composition according to Experimental Example 1 of the present invention.
3 is a graph showing the initial capacity of the lithium secondary battery according to Experimental Example 5 of the present invention.
4 is a graph showing resistance (reference performance test, RPT) measured during initial evaluation of a lithium secondary battery according to Experimental Example 6 of the present invention.
5 is a graph showing electrochemical impedance spectroscopy (EIS) values of a lithium secondary battery according to Experimental Example 7 of the present invention.

Hereinafter, the present invention will be described in more detail.

The terms or words used in the present specification and claims should not be construed as being limited to their ordinary or dictionary meanings, and the inventor may properly define the concept of the term in order to best describe his invention. It should be interpreted as meaning and concept consistent with the technical idea of the present invention based on the principle that there is.

In general, it is known that one of the causes of performance degradation of lithium secondary batteries is moisture contained therein. That is, when a _{lithium salt such as LiPF 6} reacts with water, it forms hydrofluoric acid (HF), which is a strong acid. This HF attacks the main chain of the oligomer that forms the polymer network during the preparation of the gel polymer electrolyte and blocks cross-linking. , there is a problem that the formation of gelation is suppressed and the mechanical strength of the gel polymer electrolyte is lowered.

Accordingly, the present invention provides a gel polymer electrolyte composition with improved long-term storage stability by including an additive capable of inhibiting the generation of HF, and a gel polymer electrolyte with improved mechanical strength therefrom and a lithium secondary battery including the same. .

Specifically, in one embodiment of the present invention

lithium salt,

organic solvents;

polymerization initiator;

a dicarboimide-based compound represented by the following formula (1); and

It provides a gel polymer electrolyte composition comprising; an oligomer represented by the following formula (2).

[Formula 1]

In Formula 1,

R ₁ and R ₂ are each independently an alicyclic hydrocarbon group, and R ₁ and R ₂ may be the same as or different from each other.

[Formula 2]

In Formula 1,

R ₃ is a substituted or unsubstituted C 1 to C 5 alkylene group,

R ₄ , R ₅ , R ₆ and R ₇ are each independently a substituted or unsubstituted C1-C3 alkyl group,

R' and R" are each independently hydrogen or an alkyl group having 1 to 3 carbon atoms,

R is an aliphatic, alicyclic or aromatic hydrocarbon group,

a is an integer of any one of 1 to 3,

b is an integer of any one of 0 to 2,

n, m and x are the number of repeating units,

n is an integer of any one of 1 to 10,

m is an integer of any one of 1 to 5,

x is an integer of any one of 1 to 15.

In this case, in the dicarboimide-based compound represented by Formula 1, the alicyclic hydrocarbon group is a substituted or unsubstituted cycloalkylene group having 3 to 8 carbon atoms.

In addition, in R of the oligomer represented by Formula 2, the aliphatic hydrocarbon group may include an alkylene group having 1 to 20 carbon atoms; an alkylene group having 1 to 20 carbon atoms containing an isocyanate group (NCO); an alkoxyylene 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; wherein the alicyclic hydrocarbon group is a substituted or unsubstituted cycloalkylene group having 4 to 20 carbon atoms; a substituted or unsubstituted C4-C20 cycloalkylene group containing an isocyanate group (NCO); a cycloalkenylene group having 4 to 20 carbon atoms; Or a heterocycloalkylene group having 2 to 20 carbon atoms; wherein the aromatic hydrocarbon group is a substituted or unsubstituted arylene group having 6 to 20 carbon atoms; Or it may be a heteroarylene group having 2 to 20 carbon atoms.

In addition, in the gel polymer electrolyte composition according to an embodiment of the present invention, lithium salts commonly used in electrolytes for lithium secondary batteries may be used without limitation, for example ^{, including Li +} as the cation, and an anion. F ^- , Cl ^- , Br ^- , I ^- , NO ₃ ^- , N(CN) ₂ ^- , BF ₄ ^- , ClO ₄ ^- , AlO ₄ ^- , AlCl ₄ ^- , PF ₆ ^- , SbF ₆ ^- , AsF ₆ ^- , BF ₂ C ₂ O ₄ ^- , BC ₄ O ₈ ^- , (CF ₃ ) ₂ PF ₄ ^- , (CF ₃ ) ₃ PF ₃ ^- , (CF ₃ ) ₄ PF ₂ ^- , (CF ₃ ) ₅ PF ^- , (CF ₃ ) ₆ P ^- , CF ₃ SO ₃ ^- , C ₄ F ₉ SO ₃ ^- , CF ₃ CF ₂ SO ₃ ^- , (CF ₃ SO ₂ ) ₂ N ^- , (F ₂ SO ₂ ) ₂ N ^- , CF ₃ CF ₂ (CF ₃ ) ₂ CO ^- , (CF ₃ SO ₂ ) ₂ CH ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- , CF ₃ CO ₂ ^- , CH ₃ CO ₂ ^- , SCN ^- and ( CF ₃ CF ₂ SO ₂ ) ₂ N ⁻ may include at least one selected from the group consisting of. The lithium salt may be used alone or as a mixture of two or more as needed. Specifically, the lithium salt is LiCl, LiBr, LiClO ₄ , LiBF ₄ , LiPF ₆ , LiCF ₃ SO ₃ , LiCH ₃ CO ₂ , LiCF ₃ CO ₂ , LiCH ₃ SO ₃ , LiN(SO ₂ F) ₂ ), and LiN(SO ₂ CF ₃ ) ₂ may include a single material or a mixture of two or more thereof.

The lithium salt may be appropriately changed within the range that can be used in general, but may be included in an amount of 1M to 6M in the gel polymer electrolyte composition in order to obtain an optimal effect of forming a film for preventing corrosion of the electrode surface.

When the lithium salt concentration is 1M or more, proper lithium ions can be supplied during the charging and discharging process, thereby securing the driving performance of the secondary battery. can be obtained

In addition, in the gel polymer electrolyte composition according to an embodiment of the present invention, the organic solvent can be minimized decomposition due to oxidation reaction during the charging and discharging process of the secondary battery, and if it can exhibit the desired properties together with the additive no limits. For example, an ether-based solvent, an ester-based solvent, or an amide-based solvent may be used alone or in combination of two or more.

Among the organic solvents, any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether and ethyl propyl ether or a mixture of two or more thereof may be used as the ether-based solvent among the organic solvents. , but is not limited thereto.

In addition, the ester-based solvent may include at least one compound selected from the group consisting of a cyclic carbonate compound, a linear carbonate compound, a linear ester compound, and a cyclic ester compound.

Specific examples of the cyclic carbonate compound include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate , any one selected from the group consisting of 2,3-pentylene carbonate, vinylene carbonate, and fluoroethylene carbonate (FEC), or a mixture of two or more thereof.

In addition, specific examples of the linear carbonate compound include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methylpropyl carbonate and the group consisting of ethylpropyl carbonate Any one selected from or a mixture of two or more of them may be used representatively, but is not limited thereto.

Specific examples of the linear ester compound include any one or two selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate. The above mixtures and the like may be typically used, but the present invention is not limited thereto.

Specific examples of the cyclic ester compound include any one selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, ε-caprolactone, or two or more of them. A mixture may be used, but is not limited thereto.

Among the ester-based solvents, the cyclic carbonate-based compound is a high-viscosity organic solvent and has a high dielectric constant, so it can well dissociate lithium salts in the electrolyte. When the dielectric constant linear carbonate-based compound and the linear ester-based compound are mixed in an appropriate ratio, an electrolyte having high electrical conductivity can be prepared, and thus it can be used more preferably.

In addition, in the gel polymer electrolyte composition according to an embodiment of the present invention, a conventional polymerization initiator capable of generating radicals by heat and light may be used as the polymerization initiator. For example, the polymerization initiator may use an azo polymerization initiator or a peroxide polymerization initiator, representative examples of which include benzoyl peroxide, acetyl peroxide, and dilauryl peroxide. , di-tert-butyl peroxide, t-butyl peroxy-2-ethyl-hexanoate, cumyl hydroperoxide ) and at least one peroxide compound selected from the group consisting of hydrogen peroxide, or 2,2'-azobis (2-cyanobutane), dimethyl 2,2'-azobis (2- methylpropionate), 2,2'-azobis(methylbutyronitrile), 2,2'-azobis(isobutyronitrile) (AIBN; 2,2'-Azobis(iso-butyronitrile)) and 2 and at least one azo-based compound selected from the group consisting of ,2'-azobisdimethyl-valeronitrile (AMVN; 2,2'-Azobisdimethyl-valeronitrile).

The polymerization initiator may be decomposed by heat in the secondary battery, non-limiting examples of 30°C to 100°C, specifically 60°C to 80°C, or decomposed at room temperature (5°C to 30°C) to form radicals.

The polymerization initiator may be included in an amount of from about 0.01 parts by weight to about 20 parts by weight, specifically 5 parts by weight, based on 100 parts by weight of the total oligomer, and when included in the above range, the gelation reaction is easily performed to inject the composition into the battery It is possible to prevent gelation from occurring during the process or unreacted initiator remaining after the polymerization reaction to cause side reactions.

In particular, in the case of some polymerization initiators, nitrogen or oxygen gas may be generated while radicals are generated by heat or the like. In most cases, such gas generation leads to a gas trap or gas bubbling phenomenon during the gel polymer electrolyte formation process. Because this phenomenon causes defects in the gel polymer electrolyte, it appears as electrolyte quality degradation. Therefore, when the polymerization initiator is included in the above range, it is possible to more effectively prevent disadvantages such as generation of a large amount of gas.

In addition, in the gel polymer electrolyte composition according to an embodiment of the present invention, the compound represented by Chemical Formula 1 may include at least one selected from the group consisting of compounds represented by the following Chemical Formulas 1a to 1f as representative examples thereof.

[Formula 1a]

[Formula 1b]

[Formula 1c]

[Formula 1d]

[Formula 1e]

[Formula 1f]

The compound represented by Formula 1 may be included in an amount of 0.001 wt% to 4 wt%, specifically 0.01 wt% to 3 wt%, more specifically 0.01 wt% to 2 wt%, based on the total weight of the gel polymer electrolyte composition have.

In the case of the dicarboimide-based compound represented by Chemical Formula 1, since oxidation stability is low, when an excessive amount is added, the reactivity of the oligomer main chain (acrylate functional group) is rather reduced, thereby reducing gelation formation. That is, when the content of the compound of Formula 1 is 4% by weight or less, the mechanical strength of the gel polymer electrolyte is secured and the irreversible capacity of the battery is increased or a side reaction caused by an excess of the compound, for example, mobility of lithium ions in the electrolyte solution can prevent the problem of degradation. In addition, when the content of the compound of Formula 1 is 0.001 wt % or more, the hydrofluoric acid production inhibitory effect is excellent, and the crosslinking reaction effect (gelation) of the oligomer can be improved.

Meanwhile, in the gel polymer electrolyte composition, LiPF ₆ ions or LiBF ₄ ions, which are lithium salts, are decomposed by a trace amount of water to generate acids such as hydrogen fluoride. The acid thus generated prevents gelation by cleaving (decomposing) the main chain of the oligomer when forming the gel-type polymer electrolyte. In particular, in the case of a polymer having an alkylene oxide skeleton or a siloxane (Si-O) bond, it is susceptible to attack and gelation is inhibited even by a trace amount of an acid component. In the case of a polymer having a functional group in which polymerization reaction occurs by radical reaction, such as a vinyl group, an acrylate group, or a methacrylate group, the gelation reactivity is lowered by the acid component.

In addition, moisture present in a trace amount in the gel polymer electrolyte composition also acts as a radical scavenger in the polymerization process.

Since the gel polymer electrolyte composition of the present invention contains the compound represented by Formula 1 as an additive, it can not only remove moisture by the mechanism shown in Scheme 1 below, but also suppress the generation of hydrofluoric acid (HF) in the electrolyte composition. .

[Scheme 1]

That is, water is removed by a reaction in which the dicarboimide structure of the compound of Formula 1 reacts with water _{to generate urea (CO(NH) 2 ).} Since the reaction occurs spontaneously because the energy level of the product is lower than the energy level of the reactant, moisture can be effectively removed. As a result, the decomposition reaction of the lithium salt due to moisture is greatly suppressed, so that the amount of hydrofluoric acid produced in the electrolyte may be reduced.

Therefore, the storage stability of the gel polymer electrolyte composition and the reactivity of the oligomers can be improved to form a gel polymer electrolyte having superior mechanical strength, and further, various performances such as initial capacity and stability are improved by suppressing electrolyte volatilization and leakage. A lithium secondary battery can be manufactured.

In addition, in the gel polymer electrolyte composition of the present invention, the oligomer represented by Formula 2 may be an oligomer represented by Formula 2a below.

[Formula 2a]

In Formula 2a,

n1 and x1 are the number of repeating units,

n1 is an integer of 1 or 10,

x1 is an integer in any one of 1 to 15.

The oligomer represented by Formula 2 may be included in an amount of 0.5 wt% to 20 wt%, specifically 0.7 wt% to 15 wt%, more specifically 1.0 wt% to 10 wt%, based on the total weight of the gel polymer electrolyte composition have.

That is, when the content of the oligomer is 0.5% by weight or more, the effect of forming a gel reaction is improved to ensure sufficient mechanical strength of the gel polymer electrolyte, and when the content of the oligomer is less than 20% by weight, resistance increases and lithium ions in excess according to the oligomer content Disadvantages such as restriction of movement (reduction of ionic conductivity) can be avoided.

Specifically, the molar ratio of the compound represented by Formula 1 to the oligomer represented by Formula 2 may be 1:1 to 1:100,000, specifically 1:10 to 1:50,000, and more specifically 1:100 to 1:10,000.

When the compound represented by Formula 1 and the oligomer represented by Formula 2 are included in the above ranges in the gel polymer electrolyte composition of the present invention, a gel polymer electrolyte composition with improved long-term storage stability can be provided, and further, excellent mechanical strength is ensured A gel polymer electrolyte can be prepared.

According to an embodiment of the present invention, the weight average molecular weight (MW) of the oligomer represented by Formula 2 may be controlled by the number of repeating units, and is about 1,000 to 100,000, specifically 1,000 to 50,000, more specifically 1,000 to 10,000. When the weight average molecular weight of the oligomer is within the above range, the mechanical strength of the gel polymer electrolyte including the same can be effectively improved. If the weight average molecular weight of the oligomer is less than 1,000, adequate mechanical strength cannot be expected, and more polymerization initiators are required, or a difficult additional polymerization process is required, indicating disadvantages in the gel polymer electrolyte formation process. On the other hand, when the weight average molecular weight exceeds 100,000, the physical properties of the oligomer itself become rigid, and the affinity with the electrolyte solvent is lowered to make dissolution difficult, so that uniform and excellent gel polymer electrolyte formation cannot be expected.

In the present specification, the weight average molecular weight may mean a value converted to standard polystyrene measured by GPC (Gel Permeation Chromatograph), and unless otherwise specified, the molecular weight may mean a weight average molecular weight. For example, in the present invention, measurement is performed using Agilent's 1200 series under GPC conditions, and the column used at this time may be Agilent's PL mixed B column, and the solvent may be THF.

In addition, in the gel polymer electrolyte composition of the present invention, the oligomer represented by Formula 2 shows a balanced affinity with the positive electrode or separator (SRS layer), which is the hydrophilic part, and the negative electrode or the separator, which is the hydrophobic part, in the secondary battery. Because it is chemically stable, it is very helpful in improving the performance of lithium secondary batteries. That is, the oligomer represented by Formula 2 contains an acrylate-based functional group which is a hydrophilic moiety capable of forming cross-links by itself at both ends, and a siloxane group (-Si-O-) and urethane (- Since it contains an NC(O)O-) group, it can serve as a surfactant in the battery. Accordingly, the gel polymer electrolyte including the oligomer represented by Chemical Formula 2 can lower the surface tension of the polymer electrolyte precursor solution, thereby further improving the interfacial properties with the electrode.

Moreover, the oligomer represented by Chemical Formula 2 has the ability to dissociate lithium salts, and thus can improve lithium ion mobility, and the Si-O bond constituting the main chain of the oligomer is electrochemically very stable and interacts with Li ions. Due to the low reactivity, ^{the side reaction of lithium ions (Li +} ) and the decomposition reaction of lithium salt can be controlled, so that the generation of gases such as _{CO or CO 2 can be reduced.}

Accordingly, a polymer having an alkylene oxide backbone, such as ethylene oxide, propylene oxide, or butylene oxide, or a block copolymer having a dialkyl siloxane, a fluorosiloxane, or a unit thereof, which has been commercialized in the production of a gel polymer electrolyte And the gel polymer electrolyte prepared by the gel polymer electrolyte composition of the present invention comprising the oligomer represented by Formula 2 instead of the graft polymer, etc., reduces side reactions with the electrode, so as to realize the interfacial stability effect between the electrode and the electrolyte. can

In addition, in one embodiment of the present invention

It is possible to provide a gel polymer electrolyte prepared by polymerizing the gel polymer electrolyte composition of the present invention in an inert atmosphere.

The gel polymer electrolyte of the present invention must have an elastic modulus value of at least 100 Pa or more to maintain the shape of the gel. Specifically, in order to exhibit excellent performance in a lithium secondary battery, 1,000 Pa or more, more specifically, 3,000 Pa or more desirable.

The elastic modulus was measured within a range of 0.1 to 10 Hz using a Roatainonal Rheometer (DHR2) equipment.

Specifically, the gel polymer electrolyte may be prepared by injecting the gel polymer electrolyte composition into a secondary battery and then performing a curing reaction.

For example, the gel polymer electrolyte may be formed by in-situ polymerization of the gel polymer electrolyte composition inside the secondary battery.

More specifically, the gel polymer electrolyte is

(a) inserting an electrode assembly comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode into a battery case;

(b) injecting the gel polymer electrolyte composition of the present invention into the battery case;

(c) wetting and aging the electrode assembly; and

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

In this case, the in-situ polymerization reaction in the lithium secondary battery is possible through electron beam (E-BEAM), gamma rays, room temperature or high temperature aging process, and according to an embodiment of the present invention, thermal polymerization may be performed. In this case, the polymerization time takes about 2 minutes to 48 hours, and the thermal polymerization temperature may be 60°C to 100°C, specifically 60°C to 80°C.

More specifically, in the in-situ polymerization reaction in a lithium secondary battery, a predetermined amount of a polymerization initiator and the oligomer are added to an electrolyte containing a lithium salt, mixed, and then injected into the battery cell. After sealing the injection port of such a battery cell, when polymerization is performed by heating, for example, at 60° C. to 80° C. for 1 to 20 hours, the lithium salt-containing electrolyte is gelled to produce a gel polymer electrolyte.

In addition, in one embodiment of the present invention

It provides a lithium secondary battery comprising a negative electrode, a positive electrode, a separator interposed between the negative electrode and the positive electrode, and the gel polymer electrolyte of the present invention, manufactured by the above method.

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

In addition, the deterioration of the quality occurring during the storage and transportation of the electrolyte is reduced, so that the overall cost can be reduced and the long-term storage stability under high temperature and high voltage can be further improved.

On the other hand, specifically, in the lithium secondary battery of the present invention, a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode may be sequentially stacked to form an electrode assembly, and in this case, the positive electrode, the negative electrode, and the separator constituting the electrode assembly is manufactured by a conventional method, and all those used in manufacturing a lithium secondary battery may be used.

First, the positive electrode may be manufactured 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 including a positive electrode active material, a binder, a conductive material, and a solvent on a positive electrode current collector, followed by drying and rolling.

The positive electrode current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or carbon on the surface of aluminum or stainless steel. , nickel, titanium, silver, etc. may be used.

The positive active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically may include a lithium composite metal oxide including lithium and one or more metals such as cobalt, manganese, nickel or aluminum. have. More specifically, the lithium composite metal oxide is a lithium-manganese-based oxide (eg, LiMnO ₂ , LiMn ₂ O _{4 ,} etc.), a lithium-cobalt-based oxide (eg, LiCoO _{2 ,} etc.), lithium-nickel-based oxide (for example, LiNiO ₂ and the like), lithium-nickel-manganese-based oxide (for example, LiNi _1-Y Mn _Y O ₂ (where, 0 <Y <1), LiMn _2-z Ni _z O ₄ ( here, 0 <Z <2) and the like), lithium-nickel-cobalt oxide (e.g., LiNi _1-Y1 Co _Y1 O ₂ (here, 0 <Y1 <1) and the like), lithium-manganese-cobalt oxide (e. g., LiCo _1-Y2 Mn _Y2 O ₂ (here, 0 <Y2 <1), LiMn 2 - z1 Co z1 O 4 ( here, 0 <z1 <2) and the like), lithium-nickel -Manganese-cobalt oxide (for example, Li(Ni _p Co _q Mn _r1 )O ₂ (here, 0<p<1, 0<q<1, 0<r1<1, p+q+r1= 1) or Li(Ni _p1 Co _q1 Mn _r2 )O ₄ (where 0<p1<2, 0<q1<2, 0<r2<2, p1+q1+r2=2), etc.), or lithium- Nickel-cobalt-transition metal (M) oxide (eg, Li(Ni _p2 Co _q2 Mn _r3 M _S2 )O ₂ , where M is Al, Fe, V, Cr, Ti, Ta, Mg and Mo selected from the group consisting of, and p2, q2, r3 and s2 are each independent atomic fractions of elements, 0<p2<1, 0<q2<1, 0<r3<1, 0<s2<1, p2+q2 +r3+s2=1)) and the like, and any one or two or more compounds may be included.

_{Among them, the lithium composite metal oxide is LiCoO 2} , LiMnO ₂ , LiNiO ₂ , lithium nickel manganese cobalt oxide (for example, Li(Ni _1/3 Mn _1/3 Co _{1 )} in that the capacity characteristics and stability of the battery can be improved. _/3 )O ₂ , Li(Ni _0.6 Mn _0.2 Co _0.2 )O ₂ , Li(Ni _0.5 Mn _0.3 Co _0.2 )O ₂ , Li(Ni _0.7 Mn _0.15 Co _0.15 )O ₂ and Li(Ni _0.8 Mn _0.1 Co _0.1 )O _{2 ,} etc.), or lithium nickel cobalt aluminum oxide (eg, Li (Ni _0.8 Co _0.15 Al _0.05 )O _{2 ,} etc.).

The positive active material may be included in an amount of 40 wt% to 90 wt%, specifically 40 wt% to 75 wt%, based on the total weight of the solid content in the cathode slurry.

The binder is a component that assists in bonding between the active material and the conductive material and bonding to the current collector, and is typically added in an amount of 1 to 30% by weight based on the total weight of the solid content in the positive electrode slurry. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoro roethylene, polyethylene, polypropylene, ethylene-propylene-diene ter polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, various copolymers, and the like.

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

Such a conductive material is not particularly limited as long as it has conductivity without causing a chemical change 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, aluminum, and nickel powder; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; A conductive material such as a polyphenylene derivative may be used. Specific examples of commercially available conductive materials include acetylene black-based Chevron Chemical Company, Denka Singapore Private Limited, Gulf Oil Company, etc.), Ketjenblack, and EC series. (product of Armak Company), Vulcan XC-72 (product of Cabot Company) and Super P (product of Timcal Company).

The solvent may include an organic solvent such as N-methyl-2-pyrrolidone (NMP), and may be used in an amount having a desirable viscosity when the positive active material and optionally a binder and a conductive material are included. For example, it may be included so that the solid content concentration in the slurry including the positive electrode active material, and optionally the binder and the conductive material is 10 wt% to 60 wt%, preferably 20 wt% to 50 wt%.

In addition, the negative electrode may be manufactured by forming a negative electrode mixture layer on the negative electrode current collector. The negative electrode mixture layer may be formed by coating a slurry including a negative electrode active material, a binder, a conductive material, and a solvent on an anode current collector, followed by drying and rolling.

The negative electrode current collector generally has a thickness of 3 to 500 μm. Such a negative current collector is not particularly limited as long as it has high conductivity without causing a chemical change in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel. The surface treated with carbon, nickel, titanium, silver, etc., an aluminum-cadmium alloy, etc. may be used. In addition, like the positive electrode current collector, the bonding force of the negative electrode active material may be strengthened by forming fine irregularities on the surface, and may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a non-woven body.

In addition, the negative active material is lithium-containing titanium composite oxide (LTO); carbon-based substances such as Cu-based substances, Ni-based substances, non-graphitizable carbons, and graphite-based carbons; Li _x Fe ₂ O ₃ (0≤x≤1), Li _x WO ₂ (0≤x≤1), Sn _x Me _{1 - x} Me' _y O _z (Me: Mn, Fe, Pb, Ge; Me' : metal composite oxides such as Al, B, P, Si, elements of Groups 1, 2, and 3 of the periodic table, halogen; 0 < x ≤ 1; 1 ≤ y ≤ 3; lithium metal; lithium alloy; silicon-based alloys; tin-based alloys; SnO, SnO ₂ , PbO, PbO ₂ , Pb ₂ O ₃ , Pb ₃ O ₄ , Sb ₂ O ₃ , Sb ₂ O ₄ , Sb ₂ O ₅ , GeO, GeO ₂ , Bi ₂ O ₃ , Bi ₂ O ₄ , and metal oxides such as _{Bi 2} O _{5 ;} and a single substance or a mixture of two or more selected from the group consisting of conductive polymers such as polyacetylene.

The negative active material may be included in an amount of 80% to 99% by weight based on the total weight of the solids in the negative electrode slurry.

The binder is a component that assists in bonding between the conductive material, the active material, and the current collector, and is typically added in an amount of 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, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoro roethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, fluororubber, and various copolymers thereof.

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 to 20 wt % based on the total weight of the solid content in the negative electrode slurry. Such a conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery. 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, aluminum, and nickel powder; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; A conductive material such as a polyphenylene derivative may be used.

The solvent may include water or an organic solvent such as NMP or alcohol, and may be used in an amount having a desirable viscosity when the negative electrode active material and, optionally, a binder and a conductive material are included. For example, it may be included so that the solid content concentration in the slurry including the negative electrode active material, and optionally the binder and the conductive material is 50 wt% to 75 wt%, preferably 50 wt% to 65 wt%.

In addition, the separator serves to block the internal short circuit of both electrodes and impregnate the electrolyte. A separator composition is prepared by mixing a polymer resin, a filler, and a solvent, and then the separator composition is directly coated on the electrode and dried. A separator film may be formed, or the separator composition may be cast and dried on a support, and then formed by laminating a separator film peeled off from the support on an electrode.

The separator is a porous polymer film commonly used, for example, 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. The polymer film may be used alone or by laminating them, or a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, or the like may be used, but is not limited thereto.

In this case, the pore diameter of the porous separator is generally 0.01 to 50 μm, and the porosity may be 5 to 95%. In addition, the thickness of the porous separator may be generally in the range of 5 to 300㎛.

The external shape of the lithium secondary battery of the present invention is not particularly limited, but may be a cylindrical shape using a can, a prismatic shape, a pouch type, or a coin type.

Hereinafter, examples will be given to describe the present invention in detail. However, the embodiments according to the present invention may be modified in various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described in detail below. The embodiments of the present invention are provided to more completely explain the present invention to those of ordinary skill in the art.

Example

<Manufacture of lithium secondary battery>

Example One

(Preparation of gel polymer electrolyte composition)

In 94.86 g of ethylene carbonate (EC) and ethyl propionate (EP) solvent (3:7 volume ratio) dissolved in 1M LiPF _{6 , 0.13 g of a compound represented by Formula 1d, an oligomer represented by Formula 2a (n1=9, x1)} = 10, weight average molecular weight (Mw): 3,000) 5 g, polymerization initiator dimethyl 2,2'-azobis (2-methylpropionate) (CAS No. 2589-57-3) 0.01 g by adding 0.01 g of a gel polymer An electrolyte composition was prepared.

(electrode manufacturing)

_{(LiNi 1 / 3} Co _{1 / 3} Mn _{1 / 3} O ₂ ; NCM) 94 wt% as a cathode active material, 3 wt% of carbon black as a conductive material, 3 wt% of polyvinylidene fluoride (PVDF) as a binder % was added to N-methyl-2-pyrrolidone (NMP) as a solvent to prepare a positive electrode mixture slurry. The positive electrode mixture slurry was applied to an aluminum (Al) thin film as a positive electrode current collector having a thickness of about 20 μm, dried to prepare a positive electrode, and then a positive electrode was prepared by roll press.

Carbon powder as an anode active material, PVDF as a binder, and carbon black as a conductive material in 96 wt%, 3 wt%, and 1 wt%, respectively, were added to NMP as a solvent to prepare an anode 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 to prepare a negative electrode, and then roll press was performed to prepare a negative electrode.

A battery was assembled using the positive electrode, the negative electrode, and a separator consisting of three layers of polypropylene/polyethylene/polypropylene (PP/PE/PP).

(Secondary battery manufacturing)

After injecting the gel polymer electrolyte composition into the assembled battery, it was stored at room temperature for 2 days, and then heated at 65° C. for 5 hours to prepare a lithium secondary battery including the gel polymer electrolyte.

Example 2.

The same method as in Example 1, except that 0.001 g of the compound represented by Formula 1d and 20 g of the compound represented by Formula 2a were included in 79.989 g of the organic solvent when preparing the gel polymer electrolyte composition in Example 1 Thus, a lithium secondary battery including a gel polymer electrolyte composition and a gel polymer electrolyte prepared therefrom was prepared.

Example 3.

The same method as in Example 1, except that 4 g of the compound represented by Formula 1d and 0.5 g of the compound represented by Formula 2a were included in 94.49 g of the organic solvent when preparing the gel polymer electrolyte composition in Example 1 Thus, a lithium secondary battery including a gel polymer electrolyte composition and a gel polymer electrolyte prepared therefrom was prepared.

Example 4.

The same method as in Example 1, except that 4 g of the compound represented by Formula 1d and 0.4 g of the compound represented by Formula 2a were included in 95.59 g of the organic solvent when preparing the gel polymer electrolyte composition in Example 1 Thus, a lithium secondary battery including a gel polymer electrolyte composition and a gel polymer electrolyte prepared therefrom was prepared.

Example 5.

In Example 1, in the preparation of the gel polymer electrolyte composition, in the same manner as in Example 1, except that 4 g of the compound represented by Formula 1d and 21 g of the compound represented by Formula 2a were included in 74.99 g of the organic solvent. A lithium secondary battery including a gel polymer electrolyte composition and a gel polymer electrolyte prepared therefrom was prepared.

Example 6.

In Example 1, in the preparation of the gel polymer electrolyte composition, in the same manner as in Example 1, except that 5 g of the compound represented by Formula 1d and 5 g of the compound represented by Formula 2a were included in 89.99 g of the organic solvent. A lithium secondary battery including a gel polymer electrolyte composition and a gel polymer electrolyte prepared therefrom was prepared.

comparative example One.

A gel polymer electrolyte composition and a gel polymer electrolyte prepared therefrom were included in the same manner as in Example 1, except that the compound represented by Formula 1d was not added when preparing the gel polymer electrolyte composition in Example 1 A lithium secondary battery was prepared.

comparative example 2.

In the same manner as in Example 1, except for adding the compound represented by the following formula (3) instead of the compound represented by the formula (1d) during the preparation of the gel polymer electrolyte composition in Example 1, the gel polymer electrolyte composition and the A lithium secondary battery including the prepared gel polymer electrolyte was prepared.

[Formula 3]

comparative example 3.

The gel polymer electrolyte composition and from the same method as in Example 1, except that the oligomer represented by the following formula (4) was added instead of the compound represented by the formula (2a) when preparing the gel polymer electrolyte composition in Example 1 A lithium secondary battery including the prepared gel polymer electrolyte was prepared.

[Formula 4]

Experimental example

Experimental example 1: gel polymer Storage stability evaluation of electrolyte composition (1)

Storage stability of the gel polymer electrolyte compositions prepared in Examples 1 and 2 and Comparative Example 1, respectively, was evaluated.

First, the main chain (Si-O) of the oligomers included in the gel polymer electrolyte compositions prepared in Examples 1 and 2 and Comparative Example 1, respectively, using NMR (Bruker 700 MHz NMR, 1H NMR, Solvent: Aceton-d6) before storage. The integrated area of the peak corresponding to the binding) structure was measured.

Then, the gel polymer electrolyte compositions prepared in Examples 1 and 2 and Comparative Example 1 were stored at room temperature of 20° C. for 10 weeks, and then the main chain (Si-O bond) structure of the oligomer included in each gel polymer electrolyte composition The integral area of the peak corresponding to was measured.

The area ratio of the two peaks was compared and shown in FIG. 1 .

In this case, the peak area corresponding to the main chain structure of the oligomer before storage was set to 100, and the peak area corresponding to the main chain structure of the oligomer after storage was calculated in a relative ratio.

In addition, the weight average molecular weight of the oligomers contained in the gel polymer electrolyte compositions prepared in Examples 1 and 2 and Comparative Example 1 was measured through GPC analysis (Agilent's 1200 series, Agilent's PL mixed B column, THF solvent) before storage. did.

Then, the gel polymer electrolyte composition was stored at room temperature of 20° C. for 10 weeks, and then the weight average molecular weight of the oligomers included in the gel polymer electrolyte compositions prepared in Examples 1 and 2 and Comparative Example 1 was measured.

The weight average molecular weights of the measured oligomers were compared and shown in FIG. 2 .

In this case, the weight average molecular weight of the oligomer before storage was set to 100, and the weight average molecular weight of the oligomer obtained after storage was calculated as a relative ratio.

1 and 2, it can be seen that in the gel polymer electrolyte of Comparative Example 1, which does not contain the compound of Formula 1, the oligomer structure is decomposed after 10 weeks, so that the area ratio of the main chain structure and the weight average molecular weight are rapidly reduced.

On the other hand, in the case of the gel polymer electrolyte compositions of Examples 1 and 2, the hydrofluoric acid production is suppressed by the compound of Formula 1 and the decomposition of the oligomer main chain structure can be prevented, so that the main chain structure and weight average of the oligomer even after storage It can be seen that the molecular weight is maintained as it is.

From these results, it can be seen that the storage stability of the gel polymer electrolyte composition of the present invention is improved.

Experimental example 2: gel polymer Evaluation of storage stability of electrolyte composition (2)

The storage stability of the gel polymer electrolyte compositions prepared in Example 1 and Comparative Examples 1 and 3 was evaluated.

First, the main chain of the oligomer contained in the gel polymer electrolyte composition prepared in Example 1 and Comparative Examples 1 and 3 using NMR (Bruker 700 MHz NMR, 1H NMR, Solvent: Aceton-d6) before storage (acrylate bond) The integral area of the peak corresponding to the structure was measured.

Then, the gel polymer electrolyte compositions prepared in Example 1 and Comparative Examples 1 and 3 were stored at 30° C. for 1 month, and then the oligomers contained in the gel polymer electrolyte compositions prepared in Example 1 and Comparative Examples 1 and 3 were removed. The integral area of the peak corresponding to the main chain (acrylate bond) structure was measured.

The two area ratios are compared and shown in Table 2 below.

At this time, based on the area ratio of the main chain structure of the oligomer contained in the gel polymer electrolyte composition before storage, the area ratio of the main chain structure of the oligomer contained in the gel polymer electrolyte composition after storage for one month was calculated as a relative ratio (%).

According to Table 2, the gel polymer electrolyte composition of Comparative Example 1 not containing the compound of Formula 1 and the gel polymer electrolyte composition of Comparative Example 3 containing the oligomer of Formula 4 having low affinity with the urea compound were all prepared for 1 month. It can be seen that the main chain (acrylate bond) structure of the oligomer is decomposed after storage, and storage stability is deteriorated.

On the other hand, in the case of the gel polymer electrolyte composition of Example 1, it can be seen that the oligomer main chain (acrylate bond) structure is maintained without decomposition even after 1 month.

That is, the compound of Formula 1 contained in the gel polymer electrolyte composition of the present invention reacts with moisture to generate urea. By this reaction mechanism, moisture is removed from the gel polymer electrolyte composition and the generation of hydrofluoric acid is also suppressed.

Furthermore, since the produced urea compound forms a polymer entanglement structure while bonding with the oligomer represented by Formula 2 containing functional groups of Si-O and NH-CO in the main chain, the main chain of the oligomer (acryl It has excellent ability to protect the structure (rate bond).

Therefore, it can be seen that the storage stability of the gel polymer electrolyte composition of the present invention is improved.

Experimental example 3. Gel polymer in the electrolyte acrylate Bond conversion rate measurement

Before carrying out the gelation process, NMR analysis (Bruker 700MHz NMR, 1H NMR, Solvent: Aceton-d6) was performed on the gel polymer electrolyte compositions prepared in Examples 1 to 6 and Comparative Examples 1 and 2, Example 1 The integral area of the peak corresponding to the oligomer main chain (acrylate bond) structure included in the gel polymer electrolyte composition prepared in Examples 1 to 3 and Comparative Examples 1 to 3 was measured.

Next, NMR analysis (Bruker 700 MHz NMR, 1H NMR, Solvent: Aceton-d6) was performed for each of the gel polymer electrolytes of Examples 1 to 6 and Comparative Examples 1 and 2 prepared by performing the gelation process to polymer The integral area of the peak corresponding to the acrylate bond structure remaining after network formation was measured.

The acrylate bond conversion (%) was calculated from the measured peak area, and the results are shown in Table 3 below.

In Table 3, the acrylate conversion rate is an index for measuring the gelation efficiency (degree of polymerization), and the gel polymer electrolyte compositions of Examples 1 to 3 had an acrylate conversion rate of 93% or more after gelation, and the gel polymers of Comparative Examples 1 and 2 It can be seen that significantly improved compared to the electrolyte composition.

On the other hand, in the case of the gel polymer electrolyte of Example 4 containing a small amount of the oligomer of Formula 2 and the gel polymer electrolyte of Example 6 containing an excessive amount of the compound of Formula 1, the amount of urea generated from Formula 1 increases compared to the oligomer, respectively. The entanglement (twisting) phenomenon of the polymer network increases, which reduces the reactivity of the acrylate functional groups contained in the oligomer, so that the acrylate conversion rate is higher than that of the gel polymer electrolytes of Comparative Examples 1 and 2, but the gels of Examples 1 to 3 It can be seen that it is lower than that of the polymer electrolyte.

In addition, the gel polymer electrolyte composition of Example 5 containing an excess of the oligomer of Formula 2 has the ability to protect the main chain (acrylate bond) of the oligomer during storage as the amount of urea produced from Formula 1 is reduced compared to the oligomer. Since it is lowered, it can be seen that the acrylate conversion rate is higher than that of the gel polymer electrolytes of Comparative Examples 1 and 2 during preparation of the gel polymer electrolyte, but is decreased compared to Examples 1 to 3.

Experimental example 4: gel polymer Electrolyte mechanical strength measurement experiment

The elastic modulus of each of the gel polymer electrolytes prepared in Examples 1 to 3, 5 and 6 and Comparative Examples 1 and 3 was measured within a range of 0.1 to 10 Hz using a Roatainonal Rheometer (DHR2) equipment. The results are shown in Table 4 below.

The elastic modulus shown in Table 3 is an index for measuring mechanical strength, and it can be seen that the elastic modulus (Pa) of the gel polymer electrolytes of Examples 1 to 3 is excellent at 3357 or more.

On the other hand, in the gel polymer electrolyte of Comparative Example 1, which does not contain the compound of Formula 1, as the main chain of the oligomer is decomposed by the generated hydrofluoric acid, the gelation formation efficiency is lowered, and the elastic modulus compared to the gel polymer electrolyte of Examples 1 to 3 It can be seen that is low.

In addition, even in the case of the gel polymer electrolyte of Comparative Example 3 including the oligomer of Chemical Formula 4 having a small molecular weight, it is difficult to form a polymer network structure having excellent mechanical strength, so it can be seen that the elastic modulus value is low.

On the other hand, the gel polymer electrolyte of Example 5 containing an excess of the oligomer of Formula 2 has the best elastic modulus, and the gel polymer electrolyte of Example 6 containing an excess of the compound of Formula 1 has a high hydrofluoric acid inhibitory effect, which prevents the formation of a polymer network. It can be seen that, more easily, it has a high elastic modulus value.

Experimental example 5: Initial dose measurement experiment

For each lithium secondary battery prepared in Examples 1 and 6 and Comparative Examples 1 to 3, 4.2 V 333mA (0.3 C, 0.05 C cut-off) CC after formation at 100mA current (0.1 C rate) When the /CV charge and 3 V 333 mA (0.3 C) CC discharge were repeated three times, the third discharge capacity was selected as the initial capacity. The results are shown in FIG. 3 .

Referring to FIG. 3 , in the case of the lithium secondary batteries of Examples 1 to 3, a stable gel polymer electrolyte is formed to obtain a higher initial capacity at a high voltage.

On the other hand, in the case of the lithium secondary batteries of Comparative Examples 1 to 3, it can be seen that the initial capacity is lower than that of the lithium secondary batteries of Examples 1 to 3. In particular, in the case of the lithium secondary battery of Comparative Example 2, the unreacted acrylate functional group remaining from the oligomer of Chemical Formula 2 is reduced and decomposed during the charging/discharging process of the secondary battery, and the initial irreversible reaction increases to promote cell deterioration. It can be seen that the capacity is low.

On the other hand, in the case of the lithium secondary battery of Example 4, since the content of the oligomer of Chemical Formula 2 is low and the effect of forming a gel polymer electrolyte is low as shown in Experimental Example 4, it can be seen that the stability is lowered and the performance improvement is insignificant.

In addition, in the case of the lithium secondary battery of Example 5 having the gel polymer electrolyte containing an excess of the oligomer of Formula 2 and the lithium secondary battery of Example 6 having the gel polymer electrolyte containing the compound of Formula 1 in excess, irreversible reaction As this increases, it can be seen that the initial capacity is lower than that of the lithium secondary batteries of Examples 1 to 3.

Experimental example 6. Initial resistance measurement experiment

For each lithium secondary battery prepared in Examples 1 to 6 and Comparative Examples 1 to 3, after the formation at 100mA current (0.1 C rate), 4.2 V 333mA (0.3 C, 0.05 C cut-off) CC /CV charge and 3 V 333 mA (0.3 C) CC discharge are repeated 3 times, and the voltage drop that occurs when discharging for 10 seconds with a current of 2A (2 C) is recorded, and R=V/I (Ohm’s Law) ), the resistance (reference performance test, RPT) value measured during the initial evaluation calculated using the ) is shown in FIG. 4 below.

At this time, RPT resistance can be said to be DC resistance, and RPT is closely related to the output characteristics of the secondary battery.

Referring to FIG. 4 , it can be seen that, in the case of the lithium secondary batteries of Examples 1 to 3, a stable gel polymer electrolyte is formed and the initial resistance is low.

On the other hand, in the case of the lithium secondary batteries of Comparative Examples 1 to 3, it can be seen that the initial resistance is higher than that of the lithium secondary batteries of Examples 1 to 3.

On the other hand, in the case of the lithium secondary battery of Example 4, since the acrylate conversion rate is low, the unreacted acrylate causes irreversible reductive decomposition in the battery, thereby increasing the initial resistance compared to the lithium secondary batteries of Examples 1 to 3. .

In addition, in the case of the lithium secondary battery of Example 5 having the gel polymer electrolyte containing an excess of the oligomer of Formula 2 and the lithium secondary battery of Example 6 having the gel polymer electrolyte containing the compound of Formula 1 in excess, Examples It can be seen that the initial resistance is increased compared to the lithium secondary batteries of 1 to 3.

Experimental example 7. EIS measurement experiment

Electrochemical impedance spectroscopy (EIS) of the lithium secondary batteries prepared in Example 1 and Comparative Example 1 was measured. EIS resistance was measured in the range of 10 mHz to 100 kHz at the shipping SOC of 61 using a potentiostat device. EIS can be called AC resistance and is closely related to the electrode surface state and electrolyte state inside the secondary battery. The results are shown in FIG. 5 .

In this case, in the graph of FIG. 5 , the smaller the diameter of the semicircle, the smaller the induced resistance is.

That is, as shown in FIG. 5, in the case of a lithium secondary battery having a gel polymer containing the oligomer of Formula 2, the electrode and electrolyte interface characteristics are improved, and the internal resistance of the battery is significantly lowered, so that the EIS resistance of the lithium secondary battery is a comparative example It can be seen that the lithium secondary battery of No. 1 is significantly improved.

Claims (12)

lithium salt; organic solvents; polymerization initiator;
a dicarboimide-based compound represented by the following formula (1); and
As a gel polymer electrolyte prepared by polymerizing a gel polymer electrolyte composition comprising an oligomer represented by the following formula (2),
The gel polymer electrolyte has an elastic modulus value of 3,000 pa to 5,210 pa:
[Formula 1]

In Formula 1,
R ₁ and R ₂ are each independently an alicyclic hydrocarbon group, wherein R ₁ and R ₂ may be the same as or different from each other;

[Formula 2]

In Formula 1,
R ₃ is a substituted or unsubstituted C 1 to C 5 alkylene group,
R ₄ , R ₅ , R ₆ and R ₇ are each independently a substituted or unsubstituted C1-C3 alkyl group,
R' and R" are each independently hydrogen or an alkyl group having 1 to 3 carbon atoms,
R is an aliphatic, alicyclic or aromatic hydrocarbon group,
a is an integer of any one of 1 to 3,
b is an integer of any one of 0 to 2,
n, m and x are the number of repeating units,
n is an integer of any one of 1 to 10,
m is an integer of any one of 1 to 5,
x is an integer of any one of 1 to 15.
The method according to claim 1,
In the dicarboimide-based compound represented by Formula 1, the alicyclic hydrocarbon group is a substituted or unsubstituted cycloalkylene group having 3 to 8 carbon atoms.
The method according to claim 1,
In R of the oligomer represented by Formula 2, the aliphatic hydrocarbon group is an alkylene group having 1 to 20 carbon atoms; an alkylene group having 1 to 20 carbon atoms containing an isocyanate group (NCO); an alkoxyylene 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 C 4 to C 20 cycloalkylene group; a substituted or unsubstituted C4-C20 cycloalkylene group containing an isocyanate group (NCO); 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 C 6 to C 20 arylene group; Or a gel polymer electrolyte of a heteroarylene group having 2 to 20 carbon atoms.
The method according to claim 1,
The compound represented by Formula 1 is a gel polymer electrolyte selected from the group consisting of compounds represented by Formulas 1a to 1f.
[Formula 1a]

[Formula 1b]

[Formula 1c]

[Formula 1d]

[Formula 1e]

[Formula 1f]

The method according to claim 1,
The compound represented by Formula 1 is 0.001 wt% to 4 wt% based on the total weight of the gel polymer electrolyte composition.
6. The method of claim 5,
The compound represented by Formula 1 is 0.01 wt% to 3 wt% based on the total weight of the gel polymer electrolyte composition.
The method according to claim 1,
The oligomer represented by the formula (2) is an oligomer represented by the following formula (2a), a gel polymer electrolyte:
[Formula 2a]

In Formula 2a,
n1 and x1 are the number of repeating units,
n1 is an integer of 1 or 10,
x1 is an integer in any one of 1 to 15.
The method according to claim 1,
The oligomer represented by Formula 2 is 0.5 wt% to 20 wt% based on the total weight of the gel polymer electrolyte composition.
9. The method of claim 8,
The oligomer represented by Formula 2 is 0.7 wt% to 15 wt% based on the total weight of the gel polymer electrolyte composition.
The method according to claim 1,
The weight average molecular weight (MW) of the oligomer represented by Formula 2 is 1,000 to 100,000 gel polymer electrolyte.
delete A lithium secondary battery comprising a positive electrode, a negative electrode, a separator, and the gel polymer electrolyte of claim 1.

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