KR102287766B1 - Manufacturing method of secondary battery - Google Patents

Abstract

The present invention relates to a method for manufacturing a secondary battery including a gel polymer electrolyte, in which a composition for a gel polymer electrolyte is injected, and then a formation step and a curing step are sequentially performed.
According to the manufacturing method of the secondary battery of the present invention, it is possible to manufacture an improved lithium secondary battery having excellent high-temperature storage characteristics and capacity retention according to cycles.

Description

Secondary battery manufacturing method {MANUFACTURING METHOD OF SECONDARY BATTERY}

The present invention relates to a method for manufacturing a lithium secondary battery comprising a gel polymer electrolyte having excellent high-temperature storage characteristics and capacity retention according to cycle.

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.

For lithium secondary batteries, a liquid electrolyte, for example, an ion conductive organic liquid electrolyte obtained by dissolving a salt in a non-aqueous organic solvent, has been mainly used as an electrolyte. However, when a liquid electrolyte is used, there is a disadvantage in that the electrode material is deteriorated and the organic solvent is highly likely to be volatilized, and the safety is low due to combustion due to an increase in ambient temperature and the temperature of the battery itself. In particular, lithium secondary batteries have a problem in that gas is generated inside the battery due to the decomposition of the carbonate organic solvent and/or the side reaction between the organic solvent and the electrode during charging and discharging to expand the battery thickness, and this reaction is accelerated when stored at high temperature. This will further increase the amount of gas generated. The continuously generated gas causes an increase in the internal pressure of the battery and causes the central portion of a specific surface of the battery to be deformed, such as the prismatic battery swells in a specific direction, as well as local differences in the adhesion between the electrode surfaces within the battery. This causes a problem that the electrode reaction does not occur equally on the entire electrode surface. Accordingly, the performance and safety of the battery are inevitably deteriorated.

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 safety compared to a liquid electrolyte, so that the thickness of the battery can be kept constant, and a thin film battery having excellent safety due to the inherent adhesive strength of the gel can be manufactured.

A secondary battery including such a gel polymer electrolyte is prepared by mixing a salt, a polymerization initiator, and a polymerizable monomer or oligomer in a non-aqueous organic solvent, and then injecting it into a battery containing an electrode assembly in which a positive electrode, a negative electrode, and a separator are wound or stacked. and gelation (crosslinking) under appropriate temperature and time conditions, followed by a formation process.

However, if the formation process is performed after gelation as described above, since it is difficult to stably form a passivation layer on the electrode surface, the capacity retention rate is deteriorated according to the cycle.

Accordingly, there is a need to develop a method for manufacturing a secondary battery having excellent high-temperature storage characteristics and capacity retention according to cycles.

Republic of Korea Patent Publication No. 1586199

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

An object of the present invention is to provide a method for manufacturing a secondary battery having excellent high-temperature storage characteristics and capacity retention according to cycles.

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

manufacturing an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode;

inserting the electrode assembly into a battery case;

preparing a lithium secondary battery by injecting a composition for a gel polymer electrolyte into a battery case in which the electrode assembly is inserted;

performing a formation with a voltage of 2.5V to 4.5V at a temperature of 25°C to 70°C with respect to the lithium secondary battery; and

It provides a method for manufacturing a secondary battery comprising; curing the lithium secondary battery to prepare a gel polymer electrolyte by polymerization of a composition for a gel polymer electrolyte.

The composition for a gel polymer electrolyte may include an electrolyte salt, an organic solvent, a polymerization initiator, and an oligomer represented by Formula 1 below.

[Formula 1]

In Formula 1,

R is an aliphatic, alicyclic or aromatic hydrocarbon group,

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

n is an integer of 1 or 2,

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

z is an integer of any one of 1 to 10,000, specifically 1 to 1,000, and more specifically 1 to 500.

K is an integer of any one of 1 to 100, specifically 1 to 50, and more specifically 1 to 30.

Specifically, in Formula 1, the aliphatic hydrocarbon group is an alkyl group having 1 to 20 carbon atoms; an alkoxy group having 1 to 20 carbon atoms; an alkenyl group having 2 to 20 carbon atoms; an alkenyloxy group having 2 to 20 carbon atoms; or an alkynyl group having 2 to 20 carbon atoms, wherein the alicyclic hydrocarbon group is a cycloalkyl group having 4 to 20 carbon atoms; a cycloalkenyl group having 4 to 20 carbon atoms; or a heterocycloalkyl group having 2 to 20 carbon atoms, wherein the aromatic hydrocarbon group is an aryl group having 6 to 20 carbon atoms; Or it may be a heteroaryl group having 2 to 20 carbon atoms.

The polymerization initiator may be included in an amount of 0.01 parts by weight to 20 parts by weight based on 100 parts by weight of the oligomer represented by Formula 1 above.

In addition, the oligomer represented by Formula 1 may be at least one selected from the group consisting of compounds represented by Formulas 1a to 1c.

[Formula 1a]

In Formula 1a,

z1 is an integer of any one of 1 to 500;

K1 is an integer of any one of 1 to 30.

[Formula 1b]

In Formula 1b,

z2 is an integer of any one of 1 to 500;

K2 is an integer in any one of 1-30.

[Formula 1c]

In Formula 1c,

z3 is an integer of any one of 1 to 500;

K3 is an integer in any one of 1 to 30.

The oligomer represented by Formula 1 may be included in an amount of 0.5 wt% to 25 wt% based on the total weight of the composition for a gel polymer electrolyte.

The weight average molecular weight (Mw) of the oligomer represented by Formula 1 may be 1,000 g/mol to 20,000 g/mol, specifically 1,000 g/mol to 10,000 g/mol.

The composition for a gel polymer electrolyte may further include a multifunctional (meth)acrylate-based compound containing at least one acrylate group in a molecule.

In addition, in the method of the present invention, an initial charging step may be additionally performed in order to improve the wetting of the electrolyte to the electrode assembly after the injection of the composition for a gel polymer electrolyte and before the formation step.

The initial charging step may be performed at a voltage of 1.4V to 4.0V with a constant current of 1/100C or more to 1/10C or less, specifically, 1/50C or more to 1/10C or less.

In addition, in the method of the present invention, the formation step is SOC ( SOC ( State of Charge) 30% to 100%, specifically, the charging may be carried out to 30% to 70% of SOC.

After the formation step, before the curing step, 25° C. to 70° C., specifically, aging at 30° C. to 65° C. for 1 hour to 24 hours may be further included.

In the method of the present invention, the curing step may be performed by thermal curing, electron beam, or photocuring by irradiation with gamma rays.

Specifically, the curing step may include a thermal curing step, in a temperature range of 70° C. or less, specifically 30° C. to 70° C., more specifically 40° C. to 65° C. for 5 hours to 24 hours. can be carried out.

In addition, after the curing step in the method of the present invention, it may further include the step of aging for 1 hour to 24 hours under conditions of 25 ℃ to 70 ℃, specifically 30 ℃ to 60 ℃.

In addition, the method of the present invention may further include a degassing step of removing gas generated through the formation step after the formation step and before the curing step, or after the aging step.

The degassing step may be performed by applying a pressure of -80 kPa to -100 kPa, specifically -90 kPa to -100 kPa, and more specifically -95 kPa to the battery case.

As described above, according to the method of the present invention, after the composition for a gel polymer electrolyte is injected, formation is performed at a temperature of 70° C. or less, and curing is sequentially performed, thereby providing stable ion conductivity on the electrode film. A lithium secondary battery including a gel polymer electrolyte having a film formed thereon may be manufactured. Therefore, it is possible to improve the high-temperature storage characteristics of the lithium secondary battery and the capacity retention rate according to the cycle.

The following drawings attached to the present specification illustrate preferred embodiments of the present invention, and serve to further understand the technical spirit of the present invention together with the above-described content of the present invention, so the present invention is limited to the matters described in those drawings It should not be construed as being limited.
1 to 3 are graphs showing electrochemical safety measurement results of a secondary battery according to Experimental Example 1 of the present invention.
4 is a graph showing the thickness change during high-temperature storage of the secondary battery according to Experimental Example 2 of the present invention.
5 is a graph showing a change in resistance during high-temperature storage of a secondary battery according to Experimental Example 2 of the present invention.
6 is a graph showing a gas generation amount measurement result of a lithium secondary battery according to Experimental Example 3 of the present invention.
7 is a graph showing the initial interface resistance of the lithium secondary battery according to Experimental Example 4 of the present invention.
8 is a graph showing the degree of change in the interfacial resistance of the lithium secondary battery according to Experimental Example 4 of the present invention.
9 is a graph showing cycle characteristics of a lithium secondary battery according to Experimental Example 5 of the present invention.

Hereinafter, the present invention will be described in more detail to help the understanding of the present invention.

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, a battery to which a gel polymer electrolyte is applied is prepared by mixing a polymerization initiator with a polymerizable monomer and/or oligomer in a non-aqueous organic solvent in which a salt is dissolved, and then injecting it into a battery containing an electrode assembly, It is prepared by curing (gelling) under the conditions of temperature and time, and then performing a formation process. That is, in the conventional secondary battery manufacturing method, the formation step is performed after gelation so that the oligomer cannot cause a side reaction by reacting with the negative electrode interface by ^{electrons (e − ).}

However, when the curing (gelation) process is performed before the formation of the secondary battery, the mass transfer reaction is suppressed by the properties of the formed gel polymer electrolyte, and the electrolyte decomposition reaction that occurs between the electrode interface and the electrolyte is reduced. compared to liquid electrolytes. As a result, since the ion conductive film formed by the decomposition reaction of the electrolyte and the additive, such as the passivation layer or the SEI film, is not stably formed, the decomposition reaction of the electrolyte continuously occurs, generating gas and increasing resistance inside the secondary battery. causes This eventually causes high-temperature storage and deterioration of cycle performance of the secondary battery.

Accordingly, in the present invention, after injecting the composition for a gel polymer electrolyte, after a pre-formation process at a temperature of 70° C. or less, and then performing a post-curing (gelation) process, the electrode surface It is intended to manufacture a lithium secondary battery with excellent high-temperature storage characteristics and capacity retention according to cycles by forming a stable ion-conducting film in the

Specifically, in one embodiment of the present invention

manufacturing an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode;

inserting the electrode assembly into a battery case;

preparing a lithium secondary battery by injecting a composition for a gel polymer electrolyte into a battery case in which the electrode assembly is inserted;

performing a formation with a voltage of 2.5V to 4.5V at a temperature of 25°C to 70°C with respect to the lithium secondary battery; and

It provides a method of manufacturing a secondary battery comprising; curing the composition for a gel polymer electrolyte to prepare a gel polymer electrolyte by polymerization of the composition for a gel polymer electrolyte.

First, in the method of the present invention, the method for manufacturing the electrode assembly is not particularly limited, and may be manufactured by a conventional method of winding in the form of a jelly roll after interposing a separator between the negative electrode and the positive electrode. Alternatively, in addition to the general winding method, the separator may be manufactured by lamination and stacking between the positive electrode and the negative electrode and then folding.

The positive electrode and the negative electrode constituting the electrode assembly of the present invention may be manufactured by the following method, respectively.

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. there is. More specifically, the lithium composite metal oxide is a lithium-manganese 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, in terms of improving the capacity characteristics and safety of the battery, 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 ) /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 80% to 99% by weight based on the total weight of the solid content in the positive electrode 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 such that the solid content concentration in the slurry including the positive electrode active material and, optionally, the binder and the conductive material is 50 wt% to 95 wt%, preferably 70 wt% to 90 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 a negative electrode current collector, drying and rolling.

The negative electrode current collector generally has a thickness of 3 μm 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 non-graphitizable carbon and graphitic carbon; 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 active material, and optionally the binder and the conductive material is 50 wt% to 95 wt%, preferably 70 wt% to 90 wt%.

The separator serves to block the internal short circuit of the both electrodes and impregnate the electrolyte, and commonly used porous films, for example, ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and A porous film made of a polyolefin-based polymer such as an ethylene/methacrylate copolymer may be used alone or by laminating them, or a conventional porous nonwoven fabric, for example, a high-melting-point glass fiber, polyethylene terephthalate fiber, etc. A nonwoven fabric may be used, but is not limited thereto.

The pore diameter of the porous separator is generally 0.01 μm 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 battery case is not particularly limited in appearance, and may be at least one of a battery case having an external shape of a cylindrical, prismatic, pouch, or coin type, and specifically may be a pouch type case. .

In addition, in the method for manufacturing a secondary battery of the present invention according to an embodiment, the composition for a gel polymer electrolyte may include an electrolyte salt, an organic solvent, a polymerization initiator, and an oligomer represented by the following Chemical Formula 1.

[Formula 1]

In Formula 1,

R is an aliphatic, alicyclic or aromatic hydrocarbon group,

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

n is an integer of 1 or 2,

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

z is an integer of any one of 1 to 10,000, specifically 1 to 1,000, and more specifically 1 to 500.

K is an integer of any one of 1 to 100, specifically 1 to 50, and more specifically 1 to 30.

Specifically, in Formula 1, the aliphatic hydrocarbon group is an alkyl group having 1 to 20 carbon atoms; an alkoxy group having 1 to 20 carbon atoms; an alkenyl group having 2 to 20 carbon atoms; an alkenyloxy group having 2 to 20 carbon atoms; or an alkynyl group having 2 to 20 carbon atoms;

The alicyclic hydrocarbon group is a cycloalkyl group having 4 to 20 carbon atoms; a cycloalkenyl group having 4 to 20 carbon atoms; Or a heterocycloalkyl group having 2 to 20 carbon atoms;

The aromatic hydrocarbon group is an aryl group having 6 to 20 carbon atoms; Or it may be a heteroaryl group having 2 to 20 carbon atoms.

The electrolyte salt ^{contains Li +} as a ^{cation, and F -} , Cl ^- , Br ^- , I ^- , NO ₃ ^- , N(CN) ₂ ^- , ClO ₄ ^- , BF ₄ ^- , AlO ₄ ^- , AlCl as an anion. 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 ^- , (FSO ₂ ) ₂ N ^- , CF ₃ CF ₂ (CF ₃ ) ₂ CO ^- , (CF ₃ SO ₂ ) ₂ CH ^- , (SF ₅ ) ₃ C ^- , (CF ₃ SO ₂ ) ₃ C ^- , 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 any one selected from the group consisting of there is.

The electrolyte salt may be used alone or as a mixture of two or more as needed. The electrolyte salt may be appropriately changed within the range that can be used in general, but may be included in the composition for a gel polymer electrolyte at a concentration of 0.3M to 2.0M in order to obtain an optimal effect of forming a film for preventing corrosion of the electrode surface.

In addition, the organic solvent is not limited as long as it can minimize the decomposition due to oxidation reaction during the charging and discharging process of the secondary battery, and can exhibit desired properties together with the additive. 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 the lithium salt 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 a high electrical conductivity can be prepared, which can be used more preferably.

In addition, the polymerization initiator is a component that is decomposed by heat at 30°C to 100°C in the battery, or is decomposed by photocuring by e-beam or gamma irradiation at room temperature (5°C to 30°C) to form radicals. , the oligomer represented by Formula 1 may react by such free radical polymerization to form a gel polymer electrolyte.

The polymerization initiator may be a conventional polymerization initiator known in the art, for example, benzoyl peroxide (benzoyl peroxide), acetyl peroxide (acetyl peroxide), dilauryl peroxide (dilauryl peroxide), di -tert-butyl peroxide, t-butyl peroxy-2-ethyl-hexanoate, cumyl hydroperoxide and Organic peroxides or hydroperoxides such as hydrogen peroxide, 2,2'-azobis(2-cyanobutane), 2,2'-azobis(methylbutyronitrile), 2,2 '-Azobis(isobutyronitrile) (AIBN; 2,2'-Azobis(iso-butyronitrile)) and 2,2'-azobisdimethyl-valeronitrile (AMVN; 2,2'-Azobisdimethyl-Valeronitrile) There are at least one azo compound selected from the group consisting of, but is not limited thereto.

The polymerization initiator may be included in an amount of 0.01 to 20 parts by weight, specifically 0.1 to 10 parts by weight, based on 100 parts by weight of the oligomer represented by Formula 1.

When the polymerization initiator is included in the range of 0.01 to 20 parts by weight, it is possible to prevent the pre-gelation reaction from proceeding before electrode wetting, and the unreacted initiator remains after the polymerization reaction to cause a side reaction, thereby affecting battery performance. It is possible to prevent the disadvantages affecting it, and to bring about an excellent polymer conversion rate, the gelation reaction can be easily carried out.

In addition, the oligomer represented by Formula 1 is a compound having a cross-linkable substituent capable of forming a polymer matrix, which is the basic skeleton of a gel polymer electrolyte, while being oxidized by a polymerization reaction when the temperature rises, specifically represented by Formula 1 The oligomer may be at least one selected from the group consisting of compounds represented by the following Chemical Formulas 1a to 1c.

[Formula 1a]

In Formula 1a,

z1 is an integer of any one of 1 to 500;

K1 is an integer of any one of 1 to 30.

[Formula 1b]

In Formula 1b,

z2 is an integer of any one of 1 to 500;

K2 is an integer in any one of 1-30.

[Formula 1c]

In Formula 1c,

z3 is an integer of any one of 1 to 500;

K3 is an integer in any one of 1 to 30.

The oligomer represented by Formula 1 may be included in an amount of 0.5 wt% to 25 wt%, specifically 0.5 wt% to 20 wt%, more specifically 0.5 wt% to 15 wt%, based on the total weight of the composition for a gel polymer electrolyte. .

When the oligomer represented by Formula 1 is contained in 0.5 wt% to 25 wt%, the gel polymer electrolyte has excellent mechanical strength, ionic conductivity and flame retardancy, has low interfacial resistance, and has improved wetting properties by securing appropriate viscosity can be manufactured. Since the gel polymer electrolyte has improved adhesion to the electrode and suppressed electrolyte decomposition reaction at the electrode interface to reduce gas generation, a stable ion conductive film can be formed. The lithium secondary battery of the present invention including such a gel polymer electrolyte prevents electrolyte leakage, has excellent capacity retention according to cycle, and can implement the effect of improving safety at high temperature.

The weight average molecular weight (Mw) of the oligomer represented by Formula 1 may be 1,000 g/mol to 20,000 g/mol, specifically 1,000 g/mol to 10,000 g/mol.

When the weight average molecular weight (Mw) of the oligomer represented by Formula 1 is 1,000 g/mol to 20,000 g/mol, a gel polymer electrolyte having improved mechanical properties, processability (formability) and battery safety can be prepared.

The weight average molecular weight may be measured using gel permeation chromatography (GPC). For example, after preparing a sample sample of a certain concentration, the GPC measurement system alliance 4 device is stabilized. When the instrument is stabilized, a standard sample and a sample sample are injected into the instrument to obtain a chromatogram, and then the molecular weight is calculated according to the analytical method (system: Alliance 4, column: Ultrahydrogel linear x 2, eluent: 0.1M NaNO ₃ (pH 7.0) phosphate buffer, flow rate: 0.1 mL/min, temp: 40℃, injection: 100μL)

In addition, the composition for a gel polymer electrolyte may further include a multifunctional (meth)acrylate-based compound containing at least one acrylate group in a molecule so that a polymer matrix, which is a basic skeleton, can be more easily formed.

Specifically, the multifunctional (meth) acrylate-based compound is a representative example of which is a phosphate-based compound or pyrophosphate-based compound containing at least one acrylate group known to be useful as a flame retardant, methyl acrylate, methyl meta acrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, butyl acrylate, butyl methacrylate, hexyl acrylate, hexyl methacrylate, ethylhexyl acrylate, ethylhexyl methacrylate, 2,2,2-trifluoroethyl acrylate, 2,2,2-trifluoroethyl methacrylate, 2,2,3,3-tetrafluoropropyl acrylate, and 2,2,3,3 -Tetrafluoropropyl methacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate (molecular weight 50~20,000), 1,4-butanediol diacrylate (1, 4-butanediol diacrylate, 1,6-hexanediol diacrylate, trimethylolpropane triacrylate, trimethylolpropane ethoxylate triacrylate, Trimethylolpropane propoxylate triacrylate, ditrimethylolpropane tetraacrylate, pentaerythritol tetraacrylate, pentaerythritol ethoxylate tetraacrylate), dipentaerythritol pentaa crylate), dipentaerythritol hexaacrylate, poly(ethylene glycol) diglycidylether, 1,5-hexadiene diepoxide, glycerol glycerol propoxylate triglycidyl ether, vinylcyclohexene dioxide, 1,2,7,8-diepoxyoctane, 4-vinylcyclo Hexene dioxide (4-vinylcyclohexene dioxide), butyl glycidyl ether (butyl glycidyl ether), diglycidyl 1,2-cyclohexanedicarboxylate (diglycidyl 1,2-cyclohexanedicarboxylate), ethylene glycol diglycidyl ether ( and at least one compound selected from the group consisting of ethylene glycol diglycidyl ether), glycerol triglycidyl ether, and glycidyl methacrylate.

In addition, in the method of the present invention, an initial charging step may be additionally performed in order to improve the wetting property of the electrolyte to the electrode assembly after the injection of the composition for a gel polymer electrolyte and before the formation step.

The initial charging step may be performed at a reference voltage of 1.4V to 4.0V with a constant current of 1/100C or more to 1/10C or less, specifically, 1/50C or more to 1/10C or less.

The pre-gelation reaction can be suppressed by preventing Cu elution from the negative electrode by the initial charging step.

In addition, in the method of the present invention, the formation step is SOC ( SOC ( State of Charge) 30% to 100%, specifically, the charging may be carried out to 30% to 70% of SOC.

In addition, after the formation step, 25 ℃ to 70 ℃, specifically 30 ℃ to 65 ℃ conditions may further include the step of aging for 1 hour to 24 hours.

At this time, by charging the formation process to 30% to 70% SOC at a constant current of 1C/3 or less, a sufficient SEI film can be formed, and the wetting property can be further improved in the additionally performed aging step.

In particular, by performing the formation process and the aging process at 70° C. or less, it is possible to prevent side reactions by controlling the wetting property improvement effect and the electrolyte salt decomposition reaction. Accordingly, it is possible to manufacture a secondary battery with improved overall performance, such as excellent capacity retention according to cycle, by preventing gas generation reduction and increasing interfacial resistance.

In addition, in the method for manufacturing a secondary battery of the present invention according to an embodiment, the curing (gelling) step may be performed through a conventional photocuring process by heat, e-beam, or gamma irradiation.

Specifically, the curing (gelling) step may be carried out by thermal curing for 5 hours to 24 hours at a temperature range of 30° C. to 70° C., specifically 40° C. to 65° C. under an inert condition.

When the curing process is performed under an inert atmosphere as described above, the reaction between oxygen in the atmosphere, which is a radical scavenger, and radicals is fundamentally blocked, and the extent of reaction is increased to such an extent that unreacted oligomers hardly exist. can do it Therefore, it is possible to improve the gel conversion rate, and it is possible to prevent deterioration of the performance of the secondary battery caused by a large amount of unreacted oligomer remaining inside the battery. As the inert atmosphere condition, a gas with low reactivity known in the art may be used, and in particular, at least one inert gas selected from the group consisting of nitrogen, argon, helium and xenon may be used.

In addition, in the curing (gelation) step, side reactions due to Cu elution and side reactions due to decomposition of electrolyte salts can be prevented.

By this curing (gelling) step, the oligomers represented by Formula 1 are cross-linked with each other to form a gel-type polymer network, and the electrolyte salt dissociated from the electrolyte solvent may be uniformly impregnated in the polymer network.

In addition, in the method of the present invention, after the curing step, it may further include the step of aging for 1 hour to 24 hours under conditions of 25 ℃ to 70 ℃, specifically 30 ℃ to 60 ℃.

In the aging process, an additional SEI film may be formed by leaving the battery after the charging/discharging and curing processes completed at room temperature for a certain period of time, thereby inducing additional gas generation.

On the other hand, in the formation process, a large amount of gas may be generated due to a side reaction between the gas resulting from the cathode active material and the cathode active material and the electrolyte through the charging/discharging and aging process, so it is necessary to remove these gases from the battery. If the gas generated inside the battery cell is not efficiently removed during the formation process, the gas occupies a certain space inside the battery cell, thereby preventing uniform formation, and adversely affecting battery performance such as capacity and output and battery life. In addition, due to the residual gas inside the battery cell, the capacity of the battery is rapidly reduced as the number of times of charging and discharging increases, and there are problems such as swelling of the battery cell.

Accordingly, in the method of the present invention, after the formation step, before the curing step, a degassing step of removing the gas generated through the formation may be further included.

The gas removal step may be performed through a degassing process including discharging through an outlet formed in the battery case, and fusing the outlet through which the gas is discharged.

The gas removal step may be performed while applying pressure to the battery case. In this case, the pressure may be performed by applying a pressure of -80 kPa to -100 kPa, specifically -90 kPa to -100 kPa, and more specifically -95 kPa.

As described above, in the case of a secondary battery including a conventional gel polymer electrolyte, when the gel polymer electrolyte polymerization reaction proceeds by electrons (e-) in addition to the radical polymerization reaction of the oligomer forming the gel during the preparation of the gel polymer electrolyte, the negative electrode As a large amount of oligomer is consumed non-uniformly, the gelation reaction occurs non-uniformly or causes pre-gelation. In order to prevent this, the formation process was performed after the curing (gelation) step.

On the other hand, in the present invention, by using the oligomer represented by Chemical Formula 1, which has excellent electrochemical stability compared to the conventional oligomer, the gelation reaction caused by the electron (e-) can be prevented. Therefore, since pre-gelation can be prevented, a curing (gelling) step after the formation step is possible. As a result, it is possible to form a uniform ion conductive film on the electrode surface, thereby suppressing the electrolyte decomposition reaction between the electrode, the electrolyte, and the interface. Therefore, by forming a stable ion conductive film, it is possible to reduce the amount of gas generated during high-temperature storage, as well as reduce the interfacial resistance, thereby improving the capacity retention rate according to the cycle of the secondary battery.

In addition, in one embodiment of the present invention, prepared by the method of the present invention

It provides a lithium secondary battery comprising a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a gel polymer electrolyte.

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

Example One.

_{A cathode mixture slurry was prepared by adding 94 wt% of LiCoO 2} as a cathode active material, 3 wt% of carbon black as a conductive agent, and 3 wt% of PVDF as a binder to N-methyl-2-pyrrolidone (NMP) as a solvent. did. 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, and then roll press was performed to prepare a positive electrode.

Then, 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 serving as a negative electrode current collector, dried, and then roll press was performed to prepare a negative electrode.

Next, a separator film made of polyethylene (PE) having a thickness of 20 μm was interposed between the prepared electrodes, wound and compressed to prepare an electrode assembly, and then inserted into a pouch-type battery case.

_{Then, 1M LiPF 6} was dissolved in an organic solvent of ethylene carbonate (EC):propylene carbonate (PC): diethyl carbonate (DEC) (3:2:5 vol%) to prepare a mixed solution, and then the mixed solution To 93.95 g, 7 g of the oligomer represented by Formula 1a (weight average molecular weight (Mw) 8,000, z=10, K=9) and 0.05 g of AIBN as a polymerization initiator were added to prepare a composition for a gel polymer electrolyte.

A lithium secondary battery was prepared by injecting the composition for a gel polymer electrolyte into the pouch-type battery case.

The prepared lithium secondary battery was formed by charging it at a voltage of 3V at a voltage of 3V at 65°C at 1C/10 for 3 hours to form an SOC, followed by aging at 30°C for 24 hours .

Subsequently, after degassing at a pressure of -95 kPa, thermal curing was performed at 65° C. for 5 hours.

Then, after aging at 25° C. for 2 days and at 60° C. for 1 day, the degassing process was performed again at a pressure of -95 kpa.

Then, the cell was completed by charging to 4.15V and discharging to 3V at a constant current of 1C/3.

Example 2.

Except for using the oligomer represented by Formula 1b (weight average molecular weight (Mw) 8,000, z=5, K=9) instead of the oligomer represented by Formula 1a when preparing the composition for a gel polymer electrolyte in Example 1 was prepared in the same manner as in Example 1 above.

Example 3.

Except for using the oligomer represented by Formula 1c (weight average molecular weight (Mw) 8,000, z=5, K=9) instead of the oligomer represented by Formula 1a when preparing the composition for a gel polymer electrolyte in Example 1 was prepared in the same manner as in Example 1 above.

comparative example One

A ratio prepared by dissolving _{1M LiPF 6} in an organic solvent of ethylene carbonate (EC): propylene carbonate (PC): diethyl carbonate (DEC) (3: 2: 5 vol%) instead of the gel polymer electrolyte composition in Example 1 A lithium secondary battery was manufactured in the same manner as in Example 1, except that a thermal curing step was not performed while using an aqueous electrolyte solution.

comparative example 2

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the formation process was performed after thermal curing in Example 1.

comparative example 3

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the formation process in Example 1 was performed at 75°C.

Experimental example

Experimental example One: cyclic voltammetry ( cyclicVoltammetry ) measurement

A slurry was prepared by mixing graphite as an anode active material, an aqueous binder, SBR, and a thickener, CMC, at a ratio of 95:3:2 (wt%), and then applied to a 10㎛-thick copper (Cu) thin film as an anode current collector, , dried and rolled to prepare a negative electrode.

The negative electrode was used as a working electrode, and the lithium electrode was used as a reference electrode and a counter electrode.

Ethylene carbonate (EC): propylene carbonate (PC): diethyl carbonate (DEC) (3: 2: 5 vol%) _{by dissolving 1 M LiPF 6} in an organic solvent to prepare a mixed solution, and then to 93.95 g of the mixed solution The composition for a gel polymer electrolyte prepared in Example 1 was prepared by adding 7 g of the oligomer represented by Formula 1a (weight average molecular weight (Mw) 8,000, z=10, K=9) and 0.05 g of AIBN as a polymerization initiator.

Next, a second gel polymer electrolyte composition was prepared in the same manner as in the method for preparing the first composition for a gel polymer electrolyte, except for adding the oligomer represented by the following formula (2) instead of the oligomer represented by the formula (1).

[Formula 2]

Next, a third gel polymer electrolyte composition was prepared in the same manner as in the method for preparing the composition for the first gel polymer electrolyte, except that the oligomer represented by the following formula (3) was added instead of the oligomer represented by the formula (1).

[Formula 3]

The three-phase electrodes (working electrode, reference electrode, counter electrode) prepared in each of the first to third gel polymer electrolyte compositions were put and bubbled with nitrogen for 30 minutes to remove residual oxygen in the solution. Cyclic voltammetry analysis was performed in the range of 0-3V (vs. NHE) using a constant potential electrolyzer and a constant current electrolyzer (Potentiostat/galvanostat) to measure current density values (mA/cm 2 ). The results are shown in FIGS. 1 to 3, respectively.

1 shows the evaluation result of the first electrolyte composition using the oligomer represented by Formula 1a, FIG. 2 shows the evaluation result of the second electrolyte composition using the oligomer represented by Formula 2, and FIG. 3 is the chemical formula The evaluation results for the third electrolyte composition using the oligomer represented by 3 are shown.

At this time, in Figs. 1 to 3, ethylene carbonate (EC): propylene carbonate (PC): diethyl carbonate (DEC) (3: 2: 5 vol%) in an organic solvent of 1M without including an oligomer for relative comparison. The three-phase electrodes (working electrode, reference electrode, counter electrode) were put into a non-aqueous electrolyte solution in which _{LiPF 6 was dissolved, and the measured values are also shown as reference examples.}

Referring to this, unlike the case of using the conventional oligomer represented by Formula 2 (see FIG. 2) and the case of using the oligomer represented by Formula 3 (see FIG. 3), when the oligomer represented by Formula 1a is used (see FIG. 1) The degree of irreversibility according to the intensity of the reduction peak (anodic peak) and the cathodic peak according to the repetition of the cycle 5 times was small. That is, it can be seen that the oligomer represented by Formula 1a is electrochemically stable compared to the oligomer represented by Formulas 2 and 3. Therefore, in the case of the oligomer represented by Formula 1a, it is predicted that the degree of gelation at room temperature due to electrons (e-) is low.

Experimental example 2: Safety test in high temperature storage

Each of the secondary batteries prepared in Examples 1 to 3 and Comparative Examples 1 to 3 was fully charged at room temperature at 0.33C/4.15V constant current-constant voltage, and discharged at 50% SOC at 5C for 10 seconds to perform initial charge/discharge. . After initial charging and discharging, each was charged to 4.15V and stored at 60 for 10 weeks (SOC (state of charge) 100%), while measuring the thickness increase rate (%) and resistance increase rate (%) at 60.

The thickness increase rate (%) is shown in FIG. 4, and the resistance increase rate (%) is shown in FIG. 5 .

In this case, the thickness increase rate (%) of the battery was calculated using Equation 1 below.

[Equation 1]

Battery thickness increase rate (%) = (final thickness - initial thickness / initial thickness) × 100 (%)

Looking at the thickness increase rate (%) of FIG. 4 , in the case of the secondary battery of Example 1 using the gel polymer electrolyte containing the oligomer represented by Formula 1a of the present invention, the secondary battery of Comparative Example 1 using a non-aqueous electrolyte, curing step It can be seen that the thickness increase rate is low even after storage at 60° C. for 7 weeks compared to the secondary battery of Comparative Example 2 subjected to the post-formation process and the secondary battery of Comparative Example 3 subjected to the formation at high temperature. In particular, in the case of the secondary battery of Example 1 using the gel polymer electrolyte containing the oligomer represented by Formula 1a of the present invention, the formation and curing steps were performed at 75° C. at 60° C. compared to the secondary battery of Comparative Example 3 It can be seen that the thickness increase rate is significantly reduced after storage for 7 weeks.

Specifically, as can be seen in FIG. 4 , in the case of the secondary battery of Example 1 using the gel polymer electrolyte including the oligomer represented by Formula 1a, the thickness increase rate after 7 weeks of storage is less than about 5%, whereas the non-water In the case of the secondary battery of Comparative Example 1 using the electrolyte, it can be seen that the thickness increase rate increased from the initial 1 week, and after 7 weeks of storage, the thickness increase rate was about 15%.

In addition, in the case of the secondary battery of Comparative Example 2, in which the formation process was performed after the curing step, the thickness increase rate increased after 2 weeks, and it can be seen that the thickness increase rate was about 10% after storage for 7 weeks.

On the other hand, in the case of the secondary battery of Comparative Example 3, in which the formation and curing steps were performed at a temperature of 75° C., a side reaction was caused due to decomposition of electrolyte salt, etc., and the thickness increase rate increased by about 15% from the initial 1 week, and after 7 weeks of storage, It can be seen that the thickness increase rate is about 25%.

In addition, looking at the resistance increase rate (%) in FIG. 5, in the case of the secondary battery of Example 1 using the gel polymer electrolyte containing the oligomer represented by Formula 1a of the present invention, the resistance increase rate (%) after 5 weeks of storage was 10% or less. On the other hand, in the case of the secondary battery of Comparative Example 1 using the non-aqueous electrolyte, the resistance increase rate (%) after storage for 5 weeks was about 12%, and in the case of the secondary battery of Comparative Example 2 in which the formation process was performed after the curing step, the resistance after storage for 5 weeks It can be seen that the increase rate (%) increased to about 33%.

In addition, in the case of the secondary battery of Comparative Example 3, in which the formation and curing steps were performed at a temperature of 75° C., it can be seen that the resistance increase rate (%) after storage for 5 weeks was the highest at about 90%.

As can be seen from FIG. 5 , in the case of the secondary battery of Example 1, the resistance increase rate during storage at a high temperature is the lowest, and thus it can be seen that the secondary battery is stable.

Experimental example 3: Measurement of gas content

After charging and discharging the lithium secondary batteries prepared in Example 1 and Comparative Examples 1 and 2 in the same manner as in Experimental Example 2, CO and CO ₂ generated inside the battery were generated using a gas chromatography (GC) analysis method. The gas content was measured. The comparison results are shown in FIG. 6 below.

As shown in FIG. 6 , the lithium secondary battery of Example 1 using the gel polymer electrolyte including the oligomer represented by Formula 1a according to an embodiment of the present invention is CO, CO ₂ , CH ₄ and C ₂ H inside the battery. ₆ While almost no gas was generated, in the case of the secondary battery of Comparative Example 1 using the non-aqueous electrolyte, 1700 μl and 1000 μl of _{CO and CO 2 gas were released, respectively.} In addition, in the case of the secondary battery of Comparative Example 2 in which the formation process was performed after the curing step, it can be seen that 500 μl and 1000 μl of _{CH 4} and C ₂ H _{6 gas were released, respectively.}

Therefore, since the gel electrolyte including the oligomer according to the embodiment of the present invention showed excellent oxidation stability, it can be seen that the amount of gas generated inside the battery could be significantly reduced.

Experimental example 4: Interfacial resistance evaluation

After discharging the lithium secondary batteries prepared in Examples 1 to 3 and Comparative Examples 2 and 3 at a temperature of 25° C. and an SOC of 50% at 5° C. for 10 seconds, the initial resistance was calculated through the amount of voltage drop that appeared at that time. The results are shown in FIG. 7 .

Then, after storage (SOC (state of charge) 50%) at 60° C. for 2 weeks, the degree of increase in interfacial resistance after high-temperature storage was calculated from the amount of voltage drop that appeared after formation at 5 C for 10 seconds. The results are shown in FIG. 8 .

7 and 8, in the case of the secondary jersey of Example 1, the SEI film initially formed by the pre-formation process suppresses additional electrolyte decomposition reactions, etc., and suppresses unnecessary oligomer decomposition reactions on the surface of the anode. It can be seen that the increase is suppressed and the voltage drop phenomenon hardly appears.

On the other hand, in the case of the secondary battery of Comparative Example 2, it can be seen that the SEI film formation reaction is insignificant due to the application of the pre-curing process, and the interfacial resistance increases as the electrolyte decomposition reaction intensifies during the cycle, resulting in a voltage drop. .

In particular, in the case of the secondary battery of Comparative Example 3, it can be seen that the high-temperature formation process causes side reactions such as decomposition of electrolyte salts, and since it is difficult to form an SEI film, the degree of voltage drop is the greatest.

Experimental example 5: Cycle capacity evaluation

Cycle performance improvement was confirmed while charging and discharging the lithium secondary batteries prepared in Example 1 and Comparative Examples 2 and 3 under the evaluation conditions of 0.5C, 4.35V / 0.5C, and 3V at a temperature of 25°C.

The results are shown in FIG. 9 .

Referring to FIG. 9 , it can be seen that the capacity retention rate according to the cycle of the secondary battery of Example 1 is the best compared to the secondary batteries of Comparative Examples 2 and 3.

This is that, in the case of the secondary battery of Example 1, the SEI film stably formed by the pre-formation process is well maintained without being decomposed by an additional electrolyte decomposition reaction, whereas in the case of the secondary battery of Comparative Example 2, pre-curing During the process, the SEI film formation reaction was insignificant and the electrolyte decomposition reaction during the cycle was intensified, which is expected to cause cycle degradation.

In addition, in the case of the secondary battery of Comparative Example 3, it can be seen that the high-temperature formation process causes side reactions due to decomposition of electrolyte salts, etc., so that the capacity retention rate according to the cycle is the lowest.

Claims (15)

manufacturing an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode;
inserting the electrode assembly into a battery case;
preparing a lithium secondary battery by injecting a composition for a gel polymer electrolyte into a battery case in which the electrode assembly is inserted;
performing a formation with a voltage of 2.5V to 4.5V at a temperature of 25°C to 70°C with respect to the lithium secondary battery; and
Including; performing curing on the composition for a gel polymer electrolyte to prepare a gel polymer electrolyte by polymerization of the composition for a gel polymer electrolyte;
The composition for a gel polymer electrolyte is an electrolyte salt, an organic solvent, a polymerization initiator, and a method for manufacturing a secondary battery comprising an oligomer represented by the following formula (1):
[Formula 1]

In Formula 1,
R is an aliphatic, alicyclic or aromatic hydrocarbon group,
R' and R'' are each independently hydrogen or an alkyl group having 1 to 3 carbon atoms,
n is an integer of 1 or 2,
m is an integer of any one of 1 to 3,
z is an integer of any one of 1 to 10,000.
K is an integer of any one of 1 to 100.
delete The method according to claim 1,
In the oligomer represented by Formula 1,
The aliphatic hydrocarbon group is an alkyl group having 1 to 20 carbon atoms; an alkoxy group having 1 to 20 carbon atoms; an alkenyl group having 2 to 20 carbon atoms; an alkenyloxy group having 2 to 20 carbon atoms; or an alkynyl group having 2 to 20 carbon atoms;
The alicyclic hydrocarbon group is a cycloalkyl group having 4 to 20 carbon atoms; a cycloalkenyl group having 4 to 20 carbon atoms; Or a heterocycloalkyl group having 2 to 20 carbon atoms;
The aromatic hydrocarbon group is an aryl group having 6 to 20 carbon atoms; Or a method of manufacturing a secondary battery that is a heteroaryl group having 2 to 20 carbon atoms.
The method according to claim 1,
The method for manufacturing a secondary battery, wherein the oligomer represented by Formula 1 is at least one selected from the group consisting of compounds represented by Formulas 1a to 1c.
[Formula 1a]

In Formula 1a,
z1 is an integer of any one of 1 to 500;
K1 is an integer of any one of 1 to 30.

[Formula 1b]

In Formula 1b,
z2 is an integer of any one of 1 to 500;
K2 is an integer in any one of 1-30.

[Formula 1c]

In Formula 1c,
z3 is an integer of any one of 1 to 500;
K3 is an integer in any one of 1 to 30.
The method according to claim 1,
The method for manufacturing a secondary battery, wherein the oligomer represented by Formula 1 is included in an amount of 0.5 wt% to 25 wt% based on the total weight of the composition for a gel polymer electrolyte.
The method according to claim 1,
The polymerization initiator is a method of manufacturing a secondary battery that is included in an amount of 0.01 parts by weight to 20 parts by weight based on 100 parts by weight of the oligomer represented by Formula 1 above.
The method according to claim 1,
The method for manufacturing a secondary battery, wherein the composition for a gel polymer electrolyte further comprises a multifunctional (meth)acrylate-based compound containing at least one acrylate group in a molecule.
The method according to claim 1,
The method of manufacturing a secondary battery further comprises an initial charging step after the injection of the composition for a gel polymer electrolyte and before the formation step.
9. The method of claim 8,
The initial charging step is a method of manufacturing a lithium secondary battery that is performed at a voltage of 1.4V to 4.0V with a constant current of 1/100C or more to 1/10C or less.
The method according to claim 1,
The formation step is carried out by charging up to 30% to 100% of SOC (State of Charge) with a constant current of 1C/10 or more to 1C/3 or less and a voltage of 2.5V to 4.5V at a temperature of 25°C to 70°C. A method for manufacturing a secondary battery.
The method according to claim 1,
The curing step is a method of manufacturing a secondary battery that is performed by performing photocuring by thermal curing, electron beam, or gamma ray irradiation.
The method according to claim 1,
The curing step is a method of manufacturing a secondary battery to perform thermal curing for 5 hours to 24 hours at a temperature range of 30 ℃ to 70 ℃.
The method according to claim 1,
The method of manufacturing a secondary battery further comprising the step of aging for 1 hour to 24 hours under a temperature condition of 25 ℃ to 70 ℃ after the curing step.
The method according to claim 1,
The method of manufacturing a secondary battery further comprising a degassing step after the formation step and before the curing step.
15. The method of claim 14,
The degassing step is a method of manufacturing a secondary battery that is carried out by applying a pressure of -80 kPa to -100 kPa to the battery case.

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