KR20190012843A - Manufacturing method of secondary battery - Google Patents

Abstract

The present invention relates to a method for manufacturing a secondary battery comprising a gel polymer electrolyte. More particularly, the present invention relates to a method for manufacturing a secondary battery in which a composition for a gel polymer electrolyte is injected, and a curing step is sequentially performed after a forming step. According to the method for manufacturing the secondary battery of the present invention, an enhanced lithium secondary battery having excellent high-temperature storage characteristics and capacity retention ratio according to cycles.

Description

TECHNICAL FIELD [0001] The present invention relates to a manufacturing method of a secondary battery,

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

BACKGROUND ART [0002] With the recent rapid development of the electrical, electronic, communication and computer industries, demand for high-performance, high-stability secondary batteries is gradually increasing. Particularly, as these electronic (communication) devices are becoming smaller and lighter, there is a demand for thinning and miniaturization of lithium secondary batteries, which are key components in this field.

In lithium secondary batteries, an electrolyte is used as an electrolyte, and an ion conductive organic liquid electrolyte in which a salt is dissolved in a non-aqueous organic solvent has been mainly used. However, when a liquid electrolyte is used, there is a disadvantage that the electrode material is degraded and the organic solvent is volatilized, and safety is low due to the ambient temperature and the combustion due to the temperature rise of the battery itself. Particularly, lithium secondary batteries have problems in that decomposition of a carbonate organic solvent and / or side reaction between an organic solvent and an electrode occur during charging and discharging, gas is generated inside the battery, thereby expanding the thickness of the battery. And the amount of generated gas is further increased. The gas generated continuously causes an increase in the internal pressure of the battery, so that the prismatic cell swells up in a specific direction, and the central part of the specific surface of the battery is deformed. In addition, So that the electrode reaction does not occur uniformly on the entire electrode surface. Therefore, the performance and safety of the battery deteriorate.

Recently, studies have been made to commercialize a polymer electrolyte such as a gel polymer electrolyte instead of a liquid electrolyte.

The gel polymer electrolyte is excellent in electrochemical stability as compared with a liquid electrolyte, so that the thickness of the cell can be kept constant, and a thin film type cell having excellent safety due to the inherent adhesive force in the gel state can be produced.

The secondary battery comprising the gel polymer electrolyte can be produced by mixing a salt, a polymerization initiator and a polymerizable monomer or oligomer with a non-aqueous organic solvent, and then subjecting the battery containing the positive electrode, negative electrode, Followed by gelation (crosslinking) under appropriate temperature and time conditions, followed by a forming process.

However, if the forming process after the gelling process is performed as described above, it is difficult for the passivation layer to be stably formed on the surface of the electrode, resulting in degradation of the capacity retention rate depending on the cycle.

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

Korean Patent Publication No. 1586199

The present invention has been made in order to solve such a problem.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of manufacturing a secondary battery having excellent high-temperature storage characteristics and cycle retention.

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

A method for manufacturing an electrode assembly, comprising: preparing 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 gel polymer electrolyte composition into a battery case having the electrode assembly inserted therein;

Subjecting the lithium secondary battery to a formation at a voltage of 2.5 V to 4.5 V at a temperature of 25 캜 to 70 캜; And

And curing the lithium secondary battery to prepare a gel polymer electrolyte by polymerization of the gel polymer electrolyte composition.

The composition for the gel polymer electrolyte may include an electrolyte salt, an organic solvent, a polymerization initiator, and an oligomer represented by the following general formula (1).

[Chemical 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 1 to 3,

z is an integer of 1 to 10,000, specifically 1 to 1,000, more specifically 1 to 500;

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

Specifically, in Formula 1, the aliphatic hydrocarbon group may be 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; and 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, and the aromatic hydrocarbon group is an aryl group having 6 to 20 carbon atoms; Or a heteroaryl group having 2 to 20 carbon atoms.

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

The oligomer represented by the formula (1) may be at least one selected from the group consisting of the compounds represented by the formulas (1a) to (1c).

[Formula 1a]

In formula (1a)

z1 is an integer of 1 to 500;

K1 is an integer from 1 to 30;

[Chemical Formula 1b]

In the above formula (1b)

z2 is an integer of 1 to 500;

And K2 is an integer of any one of 1 to 30.

[Chemical Formula 1c]

In the above formula (1c)

z3 is an integer of 1 to 500;

And K3 is any integer of 1 to 30. [

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

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 comprise a multifunctional (meth) acrylate compound having at least one acrylate group in the molecule.

In addition, the method of the present invention may further include an initial charging step to improve the wetting of the electrolyte solution to the electrode assembly after the composition for the gel polymer electrolyte is injected.

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

Further, in the method of the present invention, the forming step may be performed at a constant current of 1 C / 10 or more to 1 C / 3 or less at a temperature of 25 DEG C to 70 DEG C, specifically, at 25 DEG C to 65 DEG C, State of Charge) 30% to 100%, specifically, SOC 30% to 70%.

And further aging for 1 to 24 hours under the condition of 25 DEG C to 70 DEG C, specifically 30 DEG C to 65 DEG C before the curing step after the formation step.

In the method of the present invention, the curing step may be carried out by performing a photo-curing by thermal curing, electron beam, or gamma irradiation.

Specifically, the curing step may include a thermal curing step and may be performed at a temperature in the range of 70 占 폚 or less, specifically 30 占 폚 to 70 占 폚, more specifically, 40 占 폚 to 65 占 폚 for 5 hours to 24 hours .

Further, in the method of the present invention, after the curing step, it may further include a step of aging for 1 hour to 24 hours under the condition of 25 ° C to 70 ° C, specifically 30 ° C to 60 ° C.

Further, the method of the present invention may further include a degas step of removing the gas generated through the forming step after the forming 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, more specifically -95 kPa, to the battery case.

As described above, according to the method of the present invention, the composition for a gel polymer electrolyte is injected, followed by forming and curing at a temperature of 70 ° C or lower. Thereby, a stable ionic conductivity A lithium secondary battery including a gel polymer electrolyte having a coating formed thereon can be produced. Therefore, the high temperature storage characteristics of the lithium secondary battery and the capacity retention ratio according to the cycle can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments of the invention and, together with the description of the invention, It should not be construed as 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 a change in thickness of the secondary battery according to Experimental Example 2 of the present invention at high temperature storage.
5 is a graph showing a resistance change of the secondary battery according to Experimental Example 2 of the present invention at high temperature storage.
6 is a graph showing the results of measuring the amount of generated gas of the lithium secondary battery according to Experimental Example 3 of the present invention.
7 is a graph showing the initial interface resistance of a lithium secondary battery according to Experimental Example 4 of the present invention.
8 is a graph showing the degree of change in interfacial resistance of a lithium secondary battery according to Experimental Example 4 of the present invention.
9 is a graph showing the cycle characteristics of a lithium secondary battery according to Experimental Example 5 of the present invention.

Hereinafter, the present invention will be described in detail in order to facilitate understanding of the present invention.

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

Generally, a cell to which a gel polymer electrolyte is applied is prepared by mixing a polymerization initiator together with a polymerizable monomer and / or an oligomer and a polymerizable monomer in a non-aqueous organic solvent in which a salt is dissolved to prepare a composition, injecting the composition into a battery containing the electrode assembly, Curing (gelling) at a temperature and time condition, and then performing a forming process. That is, in the conventional secondary battery manufacturing method, the post-gelation forming step is performed so that the oligomer can not react with the negative electrode interface by electrons (e ^- ) to cause side reactions.

However, when a curing (gelling) 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 occurring between the electrode interface and the electrolyte Is suppressed compared with the liquid electrolyte. As a result, since the ion conductive film formed by the decomposition reaction of the electrolyte and the additive, for example, the passivation layer or the SEI film, is not stably formed, the decomposition reaction of the electrolyte is continuously generated, . This eventually causes high temperature storage and cycle performance degradation of the secondary battery.

Thus, the present invention provides a method including a step of performing a post-forming (gelling) process after a preforming process at a temperature of 70 ° C or lower after the composition for a gel polymer electrolyte is injected, To provide a lithium ion secondary battery having excellent storage characteristics at high temperature and excellent capacity retention according to cycles.

Specifically, in one embodiment of the present invention

A method for manufacturing an electrode assembly, comprising: preparing 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 gel polymer electrolyte composition into a battery case having the electrode assembly inserted therein;

Subjecting the lithium secondary battery to a formation at a voltage of 2.5 V to 4.5 V at a temperature of 25 캜 to 70 캜; And

And curing the gel polymer electrolyte composition to prepare a gel polymer electrolyte by polymerization of the gel polymer electrolyte composition.

First, in the method of the present invention, the method of manufacturing the electrode assembly is not particularly limited, and may be manufactured by a conventional method in which a separator is interposed between a cathode and an anode, followed by winding in the form of a jellyroll. Alternatively, in addition to the general winding method, a separator may be laminated and stacked between an anode and a cathode, followed by folding.

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

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

The positive electrode collector is not particularly limited as long as it has electrical conductivity without causing chemical change in the battery. For example, the positive electrode collector may be formed of a metal such as carbon, stainless steel, aluminum, nickel, titanium, sintered carbon, , Nickel, titanium, silver, or the like may be used.

The cathode active material is a compound capable of reversibly intercalating and deintercalating lithium, and may specifically include a lithium composite metal oxide including lithium and at least one metal such as cobalt, manganese, nickel, or aluminum have. More specifically, the lithium composite metal oxide may be at least one selected from the group consisting of lithium-manganese-based oxides (for example, LiMnO ₂ and LiMn ₂ O ₄ ), lithium-cobalt oxides (for example, LiCoO ₂ ), lithium- (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 (e.g., Ni _p Co _q Mn _r1 (Li) 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 (here, 0 <p1 <2, 0 <q1 <2, 0 <r2 <2, p1 + q1 + r2 = 2) , etc.), or a lithium- nickel-cobalt-transition metal (M) oxide (e.g., Li (Ni Co _{p2 q2} Mn _r3 M _S2) O ₂ (here Wherein M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, p2, q2, r3 and s2 are atomic fractions of independent elements, 0 <p2 < (Q2 <1, 0 <r3 <1, 0 <s2 <1, p2 + q2 + r3 + s2 = 1)), and any one or two or more of these compounds may be included.

Among them, the lithium composite metal oxide may be 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 ), or lithium nickel cobalt aluminum oxide (e.g., Li (Ni _0.8 Co _0.15 Al _0.05 ) O _2, etc.).

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

The binder is a component that assists in bonding of the active material to the conductive material and bonding to the current collector, and is usually added in an amount of 1 to 30 wt% 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, tetrafluoroethylene (Ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluorine rubber, various copolymers and the like.

The conductive material is usually 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 electrical conductivity without causing a chemical change in the battery, and includes, 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 fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used. Concrete examples of commercially available conductive materials include acetylene black series such as Chevron Chemical Company, Denka Singapore Private Limited and Gulf Oil Company products), Ketjenblack, EC series (Available from Armak Company), Vulcan XC-72 (from Cabot Company) and Super P (from Timcal).

The solvent may include an organic solvent such as N-methyl-2-pyrrolidone (NMP), and may be used in an amount that provides a preferable viscosity when the positive electrode active material and optionally a binder and a conductive material are included. For example, the solid content in the slurry containing the positive electrode active material, and optionally the binder and the conductive material may be in the range of 50 wt% to 95 wt%, preferably 70 wt% to 90 wt%.

The negative electrode may be manufactured by forming a negative electrode mixture layer on the negative electrode collector. The negative electrode material mixture layer may be formed by coating a negative electrode current collector with a slurry containing a negative electrode active material, a binder, a conductive material, a solvent, and the like, followed by drying and rolling.

The negative electrode collector generally has a thickness of 3 to 500 mu m. The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery. Examples of the negative electrode current collector include copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel Surface-treated with carbon, nickel, titanium, silver or the like, aluminum-cadmium alloy, or the like can be used. In addition, like the positive electrode collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams and nonwoven fabrics.

In addition, the negative electrode active material may include a lithium-containing titanium composite oxide (LTO); Carbon-based materials such as graphitized carbon and graphite 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, : Metal complex oxides such as Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, Halogen, 0 &lt; x &lt; Lithium metal; Lithium alloy; Silicon-based alloys; Tin alloy; _{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 Bi ₂ O ₅ ; And conductive polymers such as polyacetylene, or a mixture of two or more thereof.

The negative active material may be contained in an amount of 80% by weight to 99% by weight based on the total weight of the solid content 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 usually 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, tetrafluoroethylene Examples thereof include ethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, fluorine rubber 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 electrical conductivity without causing chemical changes 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 fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The solvent may include water or an organic solvent such as NMP, alcohol, etc., and may be used in an amount in which the negative electrode active material and, optionally, a binder, a conductive material, and the like are contained in a desired viscosity. For example, the slurry containing the negative electrode active material and, optionally, the binder and the conductive material may be contained to have a solid concentration of 50 wt% to 95 wt%, preferably 70 wt% to 90 wt%.

The separator interrupts the internal short circuit of both electrodes and impregnates the electrolyte. The separator may be a commonly used porous film such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / A porous film made of a polyolefin-based polymer such as an ethylene / methacrylate copolymer can be used alone or as a laminate thereof, or a porous nonwoven fabric made of a common porous nonwoven fabric such as a glass fiber having a high melting point or a polyethylene terephthalate fiber Nonwoven fabrics may be used, but are not limited thereto.

The pore diameter of the porous separator is generally 0.01 탆 to 50 탆, and the porosity may be 5% to 95%. The thickness of the porous separator may generally be in the range of 5 탆 to 300 탆.

The battery case may be at least one of a cylindrical shape, a square shape, a pouch shape, or a coin shape, and may be a pouch type case. .

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

[Chemical Formula 1]

In Formula 1,

R is an aliphatic, alicyclic or aromatic hydrocarbon group,

R 'and R &quot; 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 1 to 3,

z is an integer of 1 to 10,000, specifically 1 to 1,000, more specifically 1 to 500;

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

Specifically, in Formula 1, the aliphatic hydrocarbon group may be 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 heteroaryl group having 2 to 20 carbon atoms.

The electrolytic salt contains Li ⁺ as a cation and an anion such as F ^- , Cl ^- , Br ^- , I ^- , NO ₃ ^- , N (CN) ₂ ^- , ClO ₄ ^- , BF ₄ ^- , AlO ₄ ^{- _{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 ^- have.

The electrolytic salts may be used alone or in combination of two or more as necessary. The electrolyte salt may be appropriately changed within a usable range, but it may be contained in the composition for a gel polymer electrolyte at a concentration of 0.3M to 2.0M in order to obtain an effect of forming an anti-corrosive film on an optimum electrode surface.

In addition, the organic solvent is not limited as long as it can minimize decomposition due to an oxidation reaction during charging and discharging of the secondary battery, and can exhibit desired properties together with additives. For example, an ether solvent, an ester solvent or an amide solvent may be used alone or in combination of two or more.

As the ether solvent in the organic solvent, 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 , But is not limited thereto.

In addition, the ester 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 , 2,3-pentylene carbonate, vinylene carbonate, and fluoroethylene carbonate (FEC), or a mixture of two or more thereof.

Specific examples of the linear carbonate compound include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate and ethyl propyl carbonate , Or a mixture of two or more thereof, but the present invention is not limited thereto.

Specific examples of the linear ester compound include any one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate, And mixtures thereof, but the present invention is not limited thereto.

Specific examples of the cyclic ester compound include any one selected from the group consisting of? -Butyrolactone,? -Valerolactone,? -Caprolactone,? -Valerolactone and? -Caprolactone, or two or more Mixtures may be used, but are not limited thereto.

The cyclic carbonate-based compound in the ester-based solvent is a highly viscous organic solvent having a high dielectric constant and can dissociate the lithium salt in the electrolyte well. The cyclic carbonate-based compound has a low viscosity such as dimethyl carbonate and diethyl carbonate, The dielectric constant linear carbonate compound and the linear ester compound are mixed in an appropriate ratio, an electrolyte having a high electric conductivity can be prepared, and thus it can be more preferably used.

The polymerization initiator is decomposed by heat at 30 to 100 DEG C in a battery or decomposed by e-beam or gamma irradiation at room temperature (5 to 30 DEG C) to form radicals , The oligomer represented by the general formula (1) may react with the free radical polymerization to form a gel polymer electrolyte.

The polymerization initiator may be a conventional polymerization initiator known in the art. Examples of the polymerization initiator include benzoyl peroxide, acetyl peroxide, dilauryl peroxide, di di-tert-butyl peroxide, t-butyl peroxy-2-ethyl-hexanoate, cumyl hydroperoxide and Organic peroxides such as hydrogen peroxide, hydroperoxides and 2,2'-azobis (2-cyanobutane), 2,2'-azobis (methylbutyronitrile), 2,2'-azobis Azobis (iso-butyronitrile) and 2,2'-azobisdimethyl-valeronitrile (AMVN), which are known in the art, , And the like, but the present invention is not limited thereto.

The polymerization initiator may be contained 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 the formula (1).

When the polymerization initiator is contained in the range of 0.01 to 20 parts by weight, it is possible to prevent the pre-gelation reaction from proceeding before the electrode wetting, and the unreacted initiator remains after the polymerization reaction, It is possible to prevent the disadvantages that influence the polymerization reaction, and it is possible to carry out the gelation reaction with an excellent polymer conversion rate.

The oligomer represented by Formula 1 is a compound having a crosslinkable substituent capable of forming a polymer matrix which is a basic skeleton of a gel polymer electrolyte while being oxidized by a polymerization reaction at a temperature rise, The oligomer may be at least one selected from the group consisting of compounds represented by the following general formulas (1a) to (1c).

[Formula 1a]

In formula (1a)

z1 is an integer of 1 to 500;

K1 is an integer from 1 to 30;

[Chemical Formula 1b]

In the above formula (1b)

z2 is an integer of 1 to 500;

And K2 is an integer of any one of 1 to 30.

[Chemical Formula 1c]

In the above formula (1c)

z3 is an integer of 1 to 500;

And K3 is any integer of 1 to 30. [

The oligomer represented by Formula 1 may be contained 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 gel polymer electrolyte composition .

When the oligomer represented by Formula 1 is contained in an amount of 0.5 wt% to 25 wt%, gel polymer electrolyte having excellent mechanical strength, ionic conductivity and flame retardancy, low interface resistance, Can be prepared. Such a gel polymer electrolyte improves adhesion with the electrode, inhibits the decomposition reaction of the electrolyte at the electrode interface, and reduces the generation of gas, so that a stable ion conductive film can be formed. The lithium secondary battery of the present invention including the gel polymer electrolyte can prevent leakage of electrolytes, improve the capacity retention ratio according to the cycle, and improve the high temperature safety.

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 in the range of 1,000 g / mol to 20,000 g / mol, a gel polymer electrolyte improved in mechanical properties, processability (moldability) and cell safety can be produced.

The weight average molecular weight can be measured by Gel Permeation Chromatography (GPC). For example, after a sample of a certain concentration is prepared, the GPC measurement system alliance 4 apparatus is stabilized. When the instrument is stabilized, the standard and sample are injected into the instrument to obtain a chromatogram, and the molecular weight is calculated according to the analytical method (System: Alliance 4, column: Ultrahydrogel linear x 2, eluent: 0.1M NaNO ₃ phosphate buffer, flow rate: 0.1 mL / min, temp: 40 ° C, injection: 100 μL)

The composition for a gel polymer electrolyte may further comprise a multifunctional (meth) acrylate compound having at least one acrylate group in the molecule so that the polymer matrix as a basic skeleton can be more easily formed.

Specifically, the multifunctional (meth) acrylate compound is a phosphate compound or a pyrophosphate compound containing at least one acrylate group which is known to be useful as a flame retardant, methyl acrylate, methyl methacrylate Acrylates such as methyl 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 acrylate. - tetrafluoropropyl methacrylate, tetraethylene glycol diacrylate, polyethyl &lt; RTI ID = 0.0 &gt; Poly (ethylene glycol) diacrylate (molecular weight 50 to 20,000), 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate ), Trimethylolpropane triacrylate, trimethylolpropane ethoxylate triacrylate, trimethylolpropane propoxylate triacrylate, ditrimethylolpropane tetraacrylate, trimethylolpropane triacrylate, ditrimethylolpropane tetraacrylate, pentaerythritol tetraacrylate, pentaerythritol ethoxylate tetraacrylate, dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate, pentaerythritol tetraacrylate, (dipentaerythritol hexaacrylate), poly Poly (ethylene glycol) diglycidylether, 1,5-hexadiene diepoxide, glycerol propoxylate triglycidyl ether, vinyl But are not limited to, vinylcyclohexene dioxide, 1,2,7,8-diepoxyoctane, 4-vinylcyclohexene dioxide, butylglycidyl ether, butyl glycidyl ether, diglycidyl 1,2-cyclohexanedicarboxylate, ethylene glycol diglycidyl ether, glycerol triglycidyl ether, glycerol triglycidyl ether, ), And glycidyl methacrylate. The term &quot; a &quot;

In addition, the method of the present invention may further include an initial charging step to improve the wettability of the electrolyte solution to the electrode assembly after the composition for the gel polymer electrolyte is injected.

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

The pre-gelling reaction can be suppressed by preventing the elution of Cu from the anode by the initial charging step.

Further, in the method of the present invention, the forming step may be performed at a constant current of 1 C / 10 or more to 1 C / 3 or less at a temperature of 25 DEG C to 70 DEG C, specifically, at 25 DEG C to 65 DEG C, State of Charge) 30% to 100%, specifically, SOC 30% to 70%.

Further, after the formation step, aging may be further carried out at 25 ° C to 70 ° C, specifically at 30 ° C to 65 ° C for 1 hour to 24 hours.

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

Particularly, by performing the forming process and the aging process at 70 캜 or less, the wetting property improving effect and the electrolytic salt decomposition reaction can be controlled to prevent the side reaction. Therefore, it is possible to manufacture a secondary battery in which the gas generation reduction effect and the interface resistance increase are prevented, and the performance such as excellent capacity retention ratio according to the cycle is improved.

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

Specifically, the curing (gelling) step may be performed by thermosetting under inert conditions at a temperature of 30 ° C to 70 ° C, specifically 40 ° C to 65 ° C for 5 hours to 24 hours.

When the curing process is carried out in an inert atmosphere, the reaction between oxygen and radicals in the atmosphere, which is radical scavenging agent, is fundamentally blocked, thereby increasing the extent of reaction of the polymerization to such an extent that unreacted oligomers are hardly present . Therefore, it is possible to improve the gel conversion rate and to prevent deterioration of performance of the secondary battery caused by a large amount of unreacted oligomer remaining in the battery. The inert gas may be at least one inert gas selected from the group consisting of nitrogen, argon, helium, and xenon.

In addition, in the curing (gelation) step, side reaction by Cu elution and side reaction by decomposition reaction of electrolyte salt can be prevented.

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

Further, in the method of the present invention, after the curing step, it may further include a step of aging for 1 to 24 hours under the condition of 25 ° C to 70 ° C, specifically 30 ° C to 60 ° C.

In the aging process, an additional SEI film can be formed by allowing the battery having undergone charge / discharge and curing processes to be left at a room temperature for a certain period of time, from which additional gas generation can be induced.

On the other hand, in the forming process, gas generated from the cathode active material through charge / discharge and aging processes, and gas generated due to a side reaction between the cathode active material and the electrolyte may be generated in a large amount. If the gas generated in the battery cell is not efficiently removed in the forming process, the gas occupies a certain space in the battery cell, thereby hindering formation of uniformity, and adversely affecting battery performance such as capacity and output, and battery life And the capacity of the battery is rapidly lowered as the number of times of charging and discharging is increased due to the residual gas inside the battery cell, and the battery cell is inflated.

Accordingly, the method of the present invention may further include a degassing step of removing the gas generated through the formation after the forming step and before the curing step.

The degassing step may be performed through a degassing process including discharging the gas through a discharge port formed in the battery case and fusing the discharge port through which the gas is discharged.

The gas removing step may be performed while applying pressure to the battery case. At this time, the pressure can be performed by applying a pressure of -80 kPa to -100 kPa, specifically -90 kPa to -100 kPa, more specifically -95 kPa.

As described above, in the case of a secondary cell comprising a conventional gel polymer electrolyte, when the gel polymer electrolyte reaction is proceeded by the electrons (e) in addition to the radical polymerization reaction of the oligomer forming the gel at the time of preparing the gel polymer electrolyte, Since a large amount of oligomers are consumed unevenly, gelation reaction occurs unevenly or pre-gelation is caused. To prevent this, formation process is performed after curing (gelation) step.

On the other hand, in the present invention, by using the oligomer represented by the above formula (1), which is superior in electrochemical stability to the conventional oligomer, the gelation reaction by the electron (e-) can be prevented. Therefore, since the pre-gelation can be prevented, a curing (gelation) step after the forming step is possible. As a result, a uniform ion conductive film is formed on the surface of the electrode, and the decomposition reaction of the electrolyte between the electrode and the electrolyte and the interface can be suppressed. Therefore, by forming a stable ion conductive film, it is possible not only to reduce the amount of gas generated in high-temperature storage, but also to 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,

There is provided a lithium secondary battery including 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, a square shape, a pouch shape, a coin shape, or the like using a can.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to examples. However, the embodiments according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

Example

Example  One.

94 wt% of LiCoO ₂ as a positive electrode active material, 3 wt% of carbon black as a conductive agent, and 3 wt% of PVDF as a binder were added to N-methyl-2-pyrrolidone (NMP) as a solvent to prepare a positive electrode mixture slurry Respectively. The positive electrode mixture slurry was applied to an aluminum (Al) thin film as a positive electrode collector having a thickness of about 20 mu m, dried, and then rolled to produce a positive electrode.

Subsequently, a negative electrode mixture slurry was prepared by adding carbon powder as a negative active material, PVDF as a binder and carbon black as a conductive agent to 96 wt%, 3 wt% and 1 wt%, respectively, as a solvent. The negative electrode mixture slurry was applied to a copper (Cu) thin film as an anode current collector having a thickness of 10 mu m, dried, and then rolled to produce a negative electrode.

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

Then, 1 M 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, 7 g of the oligomer (weight average molecular weight (Mw) 8,000, z = 10, K = 9) represented by the general formula (1a) and 0.05 g of AIBN as a polymerization initiator were added to 93.95 g of the polyolefin resin composition to prepare a gel polymer electrolyte composition.

A composition for the gel polymer electrolyte was injected into the pouch-shaped battery case to prepare a lithium secondary battery.

The prepared lithium secondary battery was filled up to 30% SOC at a voltage of 3 V at 65 C for 3 hours for 3 hours, and then aged at 30 deg. C for 24 hours .

Subsequently, the substrate was subjected to a degassing process at a pressure of -95 kPa, followed by thermal curing 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 again carried out at a pressure of -95 kPa.

Subsequently, the cell was filled up to 4.15 V with a constant current of 1 C / 3, and discharged to 3 V to complete the cell.

Example  2.

Except that the oligomer (weight average molecular weight (Mw) 8,000, z = 5, K = 9) represented by the general formula (1b) was used instead of the oligomer represented by the general formula (1a) in the preparation of the gel polymer electrolyte composition in Example 1 , A cell was fabricated in the same manner as in Example 1 above.

Example  3.

Except that the oligomer (weight average molecular weight (Mw) 8,000, z = 5, K = 9) represented by the formula 1c was used instead of the oligomer represented by the formula 1a in the preparation of the gel polymer electrolyte composition in Example 1 , A cell was fabricated in the same manner as in Example 1 above.

Comparative Example  One

The procedure of Example 1 was repeated except that 1M LiPF ₆ was dissolved 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 A lithium secondary battery was produced in the same manner as in Example 1, except that the aqueous electrolyte solution was used and the heat curing step was not carried out.

Comparative Example  2

A lithium secondary battery was produced in the same manner as in Example 1 except that the forming process was performed after the heat curing in Example 1.

Comparative Example  3

A lithium secondary battery was produced in the same manner as in Example 1 except that the forming process was performed at 75 캜 in Example 1.

Experimental Example

Experimental Example  One: Cyclic Boltmetry ( cyclicVoltammetry ) Measure

SBR as an anode active material, SBR as an aqueous binder, and CMC as a thickening agent were mixed at a ratio of 95: 3: 2 (wt%) to prepare a slurry, which was then applied to a Cu thin film having a thickness of 10 μm , Dried and rolled to produce a negative electrode.

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

1 M 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. 93.95 g 7 g of the oligomer (weight average molecular weight (Mw) 8,000, z = 10, K = 9) represented by the general formula (1a) and 0.05 g of AIBN as a polymerization initiator were added to prepare a gel polymer electrolyte composition prepared in Example 1.

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

(2)

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

(3)

A three-phase electrode (working electrode, reference electrode, and counter electrode) prepared in each of the first to third gel polymer electrolyte compositions was placed and bubbled with nitrogen for 30 minutes to remove residual oxygen in the solution. The current density values (mA / cm 2) were measured by cyclic voltammetry analysis in a range of 0 to 3 V (vs. NHE) using a constant potential electrolytic apparatus and a constant current electrolysis apparatus (potentiostat / galvanostat). The results are shown in Figs. 1 to 3, respectively.

FIG. 1 shows the evaluation results of the first electrolyte composition using the oligomer represented by the formula (Ia). FIG. 2 shows the evaluation results of the second electrolyte composition using the oligomer represented by the formula (2) 3 shows the results of evaluation of the third electrolyte composition using an oligomer represented by the following formula.

1 to 3 show graphs showing the relative mobility of oligomers in the organic solvent of ethylene carbonate (EC): propylene carbonate (PC): diethyl carbonate (DEC) (3: 2: 5 vol% A three-phase electrode (working electrode, reference electrode, and counter electrode) was placed in the nonaqueous electrolyte solution in which LiPF ₆ was dissolved, and the measured values are shown together as a reference example.

Referring to FIG. 1, when the oligomer represented by Formula 1 is used (see FIG. 2) and the oligomer represented by Formula 3 is used (see FIG. 3) The degree of irreversibility with the anodic peak and the intensity of the cathodic peak according to the repeating cycle of 5 cycles was small. That is, it can be seen that the oligomer represented by the formula (1a) is electrochemically stable as compared with the oligomers represented by the formulas (2) and (3). Therefore, it is expected that the degree of gelation at room temperature due to the electron (e-) in the case of the oligomer represented by formula (Ia) is low.

Experimental Example  2: Safety test at high temperature storage

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

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

At this time, the growth rate (%) of the thickness of the battery was calculated using the following equation (1).

[Formula 1]

(%) = (Final thickness - initial thickness / initial thickness) x 100 (%)

In the case of the secondary battery of Example 1 using the gel polymer electrolyte comprising the oligomer represented by Formula 1a of the present invention, the secondary battery of Comparative Example 1 using the non-aqueous electrolyte, the curing step It can be confirmed that the thickness increase rate is low even after storage at 60 ° C for 7 weeks as compared with the secondary battery of Comparative Example 2 subjected to the post forming process and the secondary battery of Comparative Example 3 formed at a high temperature. In particular, in the case of the secondary battery of Example 1 using the gel polymer electrolyte comprising the oligomer represented by Formula 1a of the present invention, the forming and curing steps were performed at 60 ° C It can be confirmed that the thickness increase rate is remarkably decreased after 7 weeks storage.

Specifically, as can be seen from FIG. 4, in the case of the secondary battery of Example 1 using the gel polymer electrolyte containing the oligomer represented by Formula 1a, the thickness increase rate after storage for 7 weeks was less than about 5% In the case of the secondary battery of Comparative Example 1 using the electrolytic solution, the thickness increase rate was increased from the initial one week, and the thickness increase rate was about 15% after 7 weeks of storage.

In addition, in the case of the secondary battery of Comparative Example 2 in which the forming process was performed after the curing step, the thickness increase rate was increased from 2 weeks, and the thickness increase rate was about 10% after 7 weeks storage.

On the other hand, in the case of the secondary battery of Comparative Example 3 in which the forming and curing steps were carried out at a temperature of 75 ° C, side reactions were caused by decomposition of the electrolyte salt and the like, And a thickness increase rate of about 25%.

5, the resistance increase rate (%) of the secondary battery of Example 1 using the gel polymer electrolyte containing the oligomer represented by Formula 1a of the present invention was 10% or less after 5 weeks of storage On the other hand, in the case of the secondary battery of Comparative Example 1 in which the non-aqueous electrolyte was used, the resistance increase rate (%) after 5 weeks storage 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, The growth rate (%) increased to about 33%.

In the case of the secondary battery of Comparative Example 3 in which the forming and curing steps were carried out at a temperature of 75 ° C, 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 at the time of high-temperature storage is lowest and stable.

Experimental Example  3: Measurement of gas content

The lithium secondary batteries manufactured in Example 1 and Comparative Examples 1 and 2 were charged and discharged in the same manner as in Experimental Example 2, and then CO and CO ₂ The gas content was measured. The comparison result is shown in Fig.

As shown in FIG. 6, the lithium secondary battery of Example 1 using the gel polymer electrolyte comprising the oligomer represented by Formula 1a according to an embodiment of the present invention has CO, CO ₂ , CH _4, and C ₂ H ₆ gas was hardly generated. On the other hand, in the case of the secondary battery of Comparative Example 1 using the non-aqueous electrolyte, 1700 占 퐇 and 1000 占 퐇 of CO and CO ₂ gas were emitted, respectively. In addition, in the case of the secondary battery of Comparative Example 2 in which the forming process was performed after the curing step, it was found that 500 μl and 1000 μl of CH ₄ and C ₂ H ₆ gases were emitted, respectively.

Therefore, it can be seen that the gel electrolyte containing the oligomer according to the embodiment of the present invention exhibits excellent oxidation stability, so that the gas generation amount in the battery can be remarkably reduced.

Experimental Example  4: Evaluation of interface resistance

The lithium secondary batteries manufactured in Examples 1 to 3 and Comparative Examples 2 and 3 were discharged at a temperature of 25 DEG C and an SOC of 50% at 5C for 10 seconds, and the initial resistance was calculated based on the voltage drop at that time. The results are shown in Fig.

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

7 and 8, in the case of the secondary prevention of Example 1, the SEI coating formed in the early formation process suppresses additional electrolyte decomposition reaction and suppresses unnecessary oligomer decomposition reaction on the cathode surface, Increase is suppressed, and a voltage drop phenomenon hardly occurs.

On the other hand, in the case of the secondary battery of Comparative Example 2, the SEI film formation reaction is insignificant due to application of the pre-curing process, and the electrolyte decomposition reaction in the cycle is deepened, so that the interfacial resistance increases and voltage drop appears .

Particularly, in the case of the secondary battery of Comparative Example 3, since the SEI film formation is difficult due to the side reactions caused by decomposition of the electrolyte salt or the like by the high temperature forming process, the voltage drop is greatest.

Experimental Example  5: Cycle capacity evaluation

Improvement in cycle performance was confirmed by continuing charge / discharge of the lithium secondary battery manufactured in Example 1 and Comparative Examples 2 and 3 at 25 ° C, 0.5C, 4.35V / 0.5C, and 3V.

The results are shown in Fig.

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

This is because, in the case of the secondary battery of Example 1, the SEI film stably formed by the preceding formation process is not decomposed by the additional electrolyte decomposition reaction and is maintained well, while in the case of the secondary battery of Comparative Example 2, It is predicted that the SEI film formation reaction is insignificant and the cycle degradation is caused by the decomposition reaction of the electrolyte in the cycle.

In addition, in the case of the secondary battery of Comparative Example 3, side reaction was caused by decomposition of the electrolyte salt or the like by the high-temperature forming process, and the capacity retention ratio according to the cycle was lowest.

Claims (15)

A method for manufacturing an electrode assembly, comprising: preparing 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 gel polymer electrolyte composition into a battery case having the electrode assembly inserted therein;
Subjecting the lithium secondary battery to a formation at a voltage of 2.5 V to 4.5 V at a temperature of 25 캜 to 70 캜; And
And curing the composition for the gel polymer electrolyte to prepare a gel polymer electrolyte by polymerization of the composition for a gel polymer electrolyte.
The method according to claim 1,
Wherein the composition for the gel polymer electrolyte comprises an electrolyte salt, an organic solvent, a polymerization initiator, and an oligomer represented by the following Formula 1:
[Chemical Formula 1]

In Formula 1,
R is an aliphatic, alicyclic or aromatic hydrocarbon group,
R 'and R &quot; 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 1 to 3,
and z is an integer of 1 to 10,000.
And K is an integer of any one of 1 to 100.
The method of claim 2,
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 heteroaryl group having 2 to 20 carbon atoms.
The method of claim 2,
Wherein the oligomer represented by the formula (1) is at least one selected from the group consisting of compounds represented by the following formulas (1a) to (1c).
[Formula 1a]

In formula (1a)
z1 is an integer of 1 to 500;
K1 is an integer from 1 to 30;

[Chemical Formula 1b]

In the above formula (1b)
z2 is an integer of 1 to 500;
And K2 is an integer of any one of 1 to 30.

[Chemical Formula 1c]

In the above formula (1c)
z3 is an integer of 1 to 500;
And K3 is any integer of 1 to 30. [
The method of claim 2,
Wherein the oligomer represented by Formula 1 is contained in an amount of 0.5 wt% to 25 wt% based on the total weight of the gel polymer electrolyte composition.
The method of claim 2,
Wherein the polymerization initiator is contained in an amount of 0.01 to 20 parts by weight based on 100 parts by weight of the oligomer represented by the formula (1).
The method of claim 2,
Wherein the composition for a gel polymer electrolyte further comprises a polyfunctional (meth) acrylate compound having at least one acrylate group in the molecule.
The method according to claim 1,
Wherein the method further comprises an initial charging step after the composition liquid for the gel polymer electrolyte and before the forming step.
The method of claim 8,
Wherein the initial charging step is performed at a voltage of 1.4V to 4.0V at a constant current of 1 / 100C or more to 1 / 10C or less.
The method according to claim 1,
Wherein the forming step is carried out by charging at a constant current of 1 C / 10 or more to 1 C / 3 or less at a temperature of 25 DEG C to 70 DEG C and a SOC (State of Charge) of 30% to 100% A method of manufacturing a secondary battery.
The method according to claim 1,
Wherein the curing step is performed by thermosetting by irradiation of heat, electron beam, or gamma radiation.
The method according to claim 1,
Wherein the curing step is performed in a temperature range of 30 ° C to 70 ° C for 5 hours to 24 hours.
The method according to claim 1,
Wherein the method further comprises aging for 1 hour to 24 hours under a temperature condition of 25 占 폚 to 70 占 폚 after the curing step.
The method according to claim 1,
Wherein the method further comprises, after the forming step, a degassing step prior to the curing step.
The method according to claim 1,
Wherein the degassing step is performed by applying a pressure of -80 kPa to -100 kPa to the battery case.

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