Method for manufacturing gel polymer electrolyte secondary battery and gel polymer electrolyte secondary battery manufactured by the method

Abstract

The present invention relates to a method for manufacturing a gel polymer secondary battery, which can easily remove gas generated inside the secondary battery, greatly improve resistance and life characteristics, and improve mechanical properties to improve both the rigidity and safety of the battery, and a gel polymer secondary battery manufactured by the method.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a lithium secondary battery including a gel polymer electrolyte, and a gel polymer electrolyte secondary battery manufactured thereby.This application claims priority to Korean Patent Application Nos. 10-2022-0006079, 10-2022-0006080, 10-2022-0006081, and 10-2022-0006082, filed on January 14, 2022, the entire contents of which are incorporated herein by reference. [Background technology]

[0002] Recently, interest in energy storage technology has been growing. In particular, as its application fields expand to mobile phones, video cameras, laptops, and even electric vehicle energy, research and development efforts into electrochemical devices have become more concrete. Electrochemical devices are the most popular field in the field of energy storage technology, and among them, interest in rechargeable secondary batteries has been growing.

[0003] Among the currently used secondary batteries, lithium secondary batteries, which were developed in the early 1990s, are attracting attention for their advantages of higher operating voltage and much higher energy density compared to conventional batteries that use aqueous electrolyte solutions, such as Ni-MH, Ni-Cd, and sulfuric acid-lead batteries.

[0004] Such lithium secondary batteries are classified into lithium ion batteries using a liquid electrolyte and lithium polymer batteries using a polymer electrolyte, depending on the dedicated electrolyte.

[0005] Lithium ion batteries have the advantage of high capacity, but have the disadvantage of using a liquid electrolyte containing lithium salt, which can cause leakage and explosion, making battery design complicated to prevent this.

[0006] Meanwhile, lithium polymer batteries use solid polymer electrolytes or gel polymer electrolytes containing an electrolyte solution, which improves safety and flexibility. This allows them to be developed in various forms, such as small or thin-film batteries. Gel polymer electrolytes are classified into coating and injection types depending on the manufacturing method. Injection-type gel polymer electrolytes can be manufactured by injecting a liquid electrolyte solution containing a crosslinking monomer into a cell, uniformly wetting the electrode assembly with the liquid electrolyte, and then performing a crosslinking process. During the crosslinking process, the electrolyte solution forms a matrix and transforms into a non-flowing gel electrolyte. Such gel electrolytes have the advantages of being heat-resistant and free of leakage issues due to their non-flowing electrolyte, and also of being highly physical safe due to improved cell strength and resistance to external impacts.

[0007] Meanwhile, lithium secondary batteries are generally manufactured through an assembly process and an activation process. The assembly process includes stacking electrodes and separators, laminating to bond the separators and electrodes, and injecting electrolyte. The activation process involves charging and / or discharging under conditions required for activation. However, during the activation process, a large amount of gas is generated inside the secondary battery. If the generated gas is not removed, it becomes trapped inside the secondary battery and occupies a certain amount of space, causing deformation of the battery and reducing its performance, such as capacity and output, and its lifespan.

[0008] In a secondary battery using a liquid electrolyte, gas generated inside the battery can be removed by applying pressure during or after the activation process.

[0009] However, secondary batteries using gel polymer electrolytes have a problem in that gas cannot be removed even when pressure is applied during or after the activation process because the electrolyte is already in a gel state. In particular, in the case of gel polymer secondary batteries that are laminated to bond the separator and electrode, the separator and electrode are tightly adhered. For this reason, gas generated within the secondary battery cannot be released to the outside and is trapped at the interface between the separator and electrode, forming bubbles or inhibiting lithium migration, which increases the concentration of lithium ions near the bubbles and causes problems such as lithium precipitation.

[0010] For this reason, there is a need to develop a method for manufacturing a gel polymer secondary battery that can remove the gas generated during the activation process. Summary of the Invention [Problem to be solved by the invention]

[0011] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a method for manufacturing a gel polymer secondary battery that can easily remove gas generated inside the secondary battery and significantly improve resistance and life characteristics.

[0012] Another object of the present invention is to provide a method for manufacturing a gel polymer secondary battery that can improve both the rigidity and safety of the battery by improving mechanical properties, and a gel polymer secondary battery manufactured by the method.

[0013] It will be readily apparent that other objects and advantages of the present invention can be realized by the means or methods recited in the claims, and combinations thereof. [Means for solving the problem]

[0014] The present inventors have found that the above-mentioned problems can be solved by the following method for producing a gel polymer secondary battery and a gel polymer secondary battery produced thereby.

[0015] The first embodiment includes: (S1) preparing a ceramic-coated separator and an electrode, the ceramic-coated separator comprising a porous substrate and a ceramic coating layer, the ceramic coating layer including a first binder polymer and ceramic particles; (S2) laminating the separator and the electrode to fabricate an electrode assembly, the separator and the electrode being folded in a zigzag pattern to coat a composition including a second binder polymer in a pattern on at least one surface of the separator or the electrode, and the electrode being inserted into the overlapping portion of the separator; (S3) injecting a composition for a gel polymer electrolyte into the electrode assembly to fabricate a battery; and (S4) fabricating a battery under a temperature condition of 50°C or higher and a pressure of 0.1 kgf / cm. 2 to 5kgf / cm 2 and activating the battery by charging it at least twice under the pressure condition.

[0016] The second embodiment relates to the method for producing a gel polymer secondary battery according to the first embodiment, wherein the lamination in the step (S2) is carried out at a temperature of 30° C. or lower.

[0017] The third embodiment is the first or second embodiment, wherein the lamination in the step (S2) is performed under normal pressure conditions, or the pressure applied to the electrode assembly is 3 kgf / cm. 2 The present invention relates to a method for producing a gel polymer secondary battery, which is carried out under the following conditions:

[0018] A fourth embodiment relates to a method for producing a gel polymer secondary battery according to any one of the first to third embodiments, wherein the step (S2) does not include a lamination step under pressurized conditions.

[0019] A fifth embodiment relates to a method for manufacturing a gel polymer secondary battery according to any one of the first to fourth embodiments, wherein the content of the first binder polymer is 0.1 wt % to 10 wt % relative to the total weight of the ceramic coating layer.

[0020] A sixth embodiment relates to a method for producing a gel polymer secondary battery according to any one of the first to fifth embodiments, wherein the first binder polymer is an acrylate-based binder polymer.

[0021] A seventh embodiment relates to a method for manufacturing a gel polymer secondary battery according to any one of the first to sixth embodiments, wherein the pattern shape includes one or more of a dot, a stripe, and a grid shape.

[0022] An eighth embodiment relates to a method for producing a gel polymer secondary battery according to any one of the first to seventh embodiments, wherein the composition for a gel polymer electrolyte contains a polymerization initiator having a 10-hour half-life temperature of 60°C or less, a polymerizable compound, a lithium salt, and a non-aqueous organic solvent.

[0023] A ninth embodiment relates to a method for producing a gel polymer secondary battery according to any one of the first to eighth embodiments, wherein the 10-hour half-life temperature of the polymerization initiator is 55° C. or lower.

[0024] A tenth embodiment relates to the method for producing a gel polymer secondary battery according to any one of the first to ninth embodiments, wherein the content of the polymerization initiator is 0.1 to 10 parts by weight with respect to 100 parts by weight of the composition for gel polymer electrolyte.

[0025] An eleventh embodiment relates to a method for producing a gel polymer secondary battery according to any one of the first to tenth embodiments, wherein the application of pressure in the step (S4) is carried out at least once by a pressure device.

[0026] A twelfth embodiment is any one of the first to eleventh embodiments, wherein the step (S4) is performed under the following conditions: (S4a) a temperature of 50 to 60°C and a pressure of 0.1 kgf / cm 2 to 1 kgf / cm 2(S4b) applying a pressure condition of 3 kgf / cm and performing primary charging within a range of 20% of the secondary battery state of charge (SOC); and (S4c) applying a temperature condition of 50 to 60°C and a pressure condition of 3 kgf / cm 2 to 5kgf / cm 2 and performing secondary charging at 15% to 60% of the secondary battery state of charge (SOC).

[0027] The thirteenth embodiment is, in any one of the first to twelfth embodiments, (S5) the battery activated in the step (S4) is heated under a temperature condition of 60° C. or higher and a pressure of 3 kgf / cm 2 and storing the gel polymer secondary battery under the above pressure conditions.

[0028] A fourteenth embodiment relates to a method for producing a gel polymer secondary battery according to any one of the first to thirteenth embodiments, wherein the step (S5) is carried out for 30 minutes to 5 hours.

[0029] The fifteenth embodiment relates to a method for producing a gel polymer secondary battery according to any one of the first to fourteenth embodiments, wherein the application of pressure in the step (S5) is carried out at least once by a pressure device.

[0030] The sixteenth embodiment relates to a method for producing a gel polymer secondary battery according to any one of the first to fifteenth embodiments, further comprising, after the (S3) step, a step of vacuum sealing the battery under a pressure condition of less than -95 kPa.

[0031] The seventeenth embodiment relates to a method for producing a gel polymer secondary battery according to any one of the first to sixteenth embodiments, wherein the pressure condition in the vacuum sealing step is in the range of −100 kPa to −120 kPa.

[0032] The eighteenth embodiment relates to a method for producing a gel polymer secondary battery according to any one of the first to seventeenth embodiments, wherein the vacuum sealing step is carried out for 5 to 30 seconds.

[0033] The 19th embodiment relates to a method for producing a gel polymer secondary battery according to any one of the first to 18th embodiments, further comprising, after the (S4) step, a step of degassing the battery under a pressure condition of less than -95 kPa.

[0034] A twentieth embodiment relates to a method for producing a gel polymer secondary battery according to any one of the first to nineteenth embodiments, wherein the pressure condition in the degassing step is in the range of −100 kPa to −120 kPa.

[0035] The twenty-first embodiment relates to a gel polymer secondary battery manufactured by any one of the first to twentieth embodiments, which has a stiffness of 4.0 MPa or more. [Effects of the Invention]

[0036] A method for manufacturing a gel polymer secondary battery according to an embodiment of the present invention mainly includes the steps of: applying a binder polymer in a pattern on one surface of a separator or an electrode, folding the separator in a zigzag pattern, inserting an electrode where the separator overlaps, and stacking the separator and the electrode to manufacture an electrode assembly; injecting a gel polymer electrolyte composition into the manufactured electrode assembly to manufacture a battery; and activating the battery under high temperature and high pressure conditions.

[0037] This manufacturing method of the present invention can provide sufficient adhesion between the separator and the electrode, facilitate the discharge of gas generated inside the secondary battery, and allow further hardening of the gel polymer, thereby improving the resistance, lifespan, and mechanical properties of the gel polymer secondary battery.

[0038] In addition, in the method for manufacturing a gel polymer secondary battery according to one embodiment of the present invention, by using a composition for a gel polymer electrolyte containing a predetermined polymerization initiator, the electrolyte solution can be sufficiently impregnated and the impregnation time of the electrolyte can be shortened, thereby suppressing the pre-gelation reaction.

[0039] In addition, the method for manufacturing a gel polymer secondary battery according to an embodiment of the present invention may further include a step of storing the activated battery under high temperature and high pressure conditions, thereby further improving the above-mentioned effects of the present invention.

[0040] In addition, the method for manufacturing a gel polymer secondary battery according to an embodiment of the present invention may further include a step of sealing and degassing the battery under a pressure condition of less than -95 kPa, thereby further improving the above-mentioned effects of the present invention. In particular, since a higher degree of vacuum can be applied in the sealing and degassing steps, the mechanical properties of the battery may be improved.

[0041] The following drawings attached to this specification illustrate preferred embodiments of the present invention and, together with the detailed description of the invention, serve to further understand the technical concept of the present invention, so the present invention should not be interpreted as being limited to the matters depicted in the drawings. Meanwhile, the shape, size, scale, or ratio of elements in the drawings attached to this specification may be exaggerated to emphasize a clearer description. [Brief explanation of the drawings]

[0042] [Figure 1] 1 is a process flow diagram illustrating a method for manufacturing a secondary battery according to an embodiment of the present invention. [Figure 2] 2A to 2F are schematic diagrams illustrating steps for manufacturing an electrode assembly according to an embodiment of the present invention. [Figure 3] 1 is an image showing traces of binder applied in dots (DOT) after disassembling the battery prepared in Example A-1 of the present invention. [Figure 4]1 is an image of an exploded view of a battery produced in Comparative Example A-3 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0043] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, the terms and words used in this specification and claims should not be construed as being limited to their ordinary and dictionary meanings, but should be construed as meanings and concepts corresponding to the technical ideas of the present invention, based on the principle that the inventors themselves can appropriately define the concepts of terms in order to best describe the invention. Therefore, it should be understood that the configurations shown in the embodiments described in this specification are merely the most preferred embodiment of the present invention and do not represent the entire technical ideas of the present invention, and therefore various equivalents and modifications that can be substituted therefor may exist at the time of filing this application.

[0044] Throughout this specification, when a part is said to "include" or "comprise" a certain element, this means that it can further include other elements, rather than excluding other elements, unless otherwise specified.

[0045] Furthermore, the terms "about," "substantially," and the like used throughout this specification are used to mean a numerical value or a value close to that numerical value when manufacturing and material tolerances inherent in the stated meaning are given, and are used to prevent unscrupulous infringers from unfairly exploiting the disclosure content in which precise and absolute numerical values ​​are stated for the understanding of this application.

[0046] Throughout this specification, the phrase "A and / or B" means "A or B, or both."

[0047] Generally, the manufacturing process of a secondary battery essentially includes an activation step in which charging and / or discharging is performed. During the activation step, gas is generated inside the secondary battery, which affects the performance of the secondary battery. Therefore, in order to improve the performance of the secondary battery, it is important to remove the gas inside the secondary battery.

[0048] Meanwhile, secondary batteries using gel electrolytes have the advantage of improved safety and physical strength compared to secondary batteries using liquid electrolytes. However, since the interior of a secondary battery using gel electrolytes is already in a gel state during the activation step, there is a problem in that it is difficult to discharge gas present inside the battery.

[0049] Therefore, the inventors of the present invention aim to provide a method for manufacturing a secondary battery using a gel polymer electrolyte that can improve the performance of the secondary battery by efficiently removing gas generated inside the secondary battery.

[0050] Manufacturing method of gel polymer secondary battery In one embodiment of the present invention, a method for manufacturing a gel polymer secondary battery includes: (S1) preparing a ceramic-coated separator and an electrode, the ceramic-coated separator comprising a porous substrate and a ceramic coating layer, the ceramic coating layer including a first binder polymer and ceramic particles; (S2) laminating the separator and the electrode to manufacture an electrode assembly, the separator and the electrode being folded in a zigzag pattern to coat a composition including a second binder polymer in a pattern on at least one surface of the separator or the electrode, and inserting the electrode into a portion where the separator overlaps; (S3) injecting a gel polymer electrolyte composition into the electrode assembly to manufacture a battery; and (S4) manufacturing the battery under conditions of a temperature of 50°C or higher and a pressure of 0.1 kgf / cm. 2 to 5kgf / cm 2 and activating the battery by charging it at least twice under this pressure condition.

[0051] Each step will be described in detail below.

[0052] First, a ceramic-coated separator and an electrode are prepared (S1). In the present invention, the ceramic-coated separator includes a porous substrate and a ceramic coating layer, and the ceramic coating layer includes a first binder polymer and ceramic particles.

[0053] Ceramic coated separation membrane In the present invention, the ceramic-coated separator includes a porous substrate and a ceramic coating layer. The ceramic-coated separator is inserted between the negative electrode and the positive electrode to physically and electrically separate the two electrodes, thereby preventing internal short circuits, providing a path for ion migration, and impregnating an electrolyte.

[0054] The porous substrate is not limited as long as it has a pore structure, and examples thereof include porous polymer films made of polyolefin polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminate structures of two or more layers thereof, and also includes ordinary porous nonwoven fabrics such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers.

[0055] The ceramic coating layer may be disposed on at least one or both surfaces of the porous substrate and may include a binder polymer and ceramic particles. A separator having such a ceramic coating layer has excellent electrical insulation properties, thereby preventing short circuits and, even if a short circuit occurs, preventing the shorted area from expanding significantly, thereby improving battery safety.

[0056] The ceramic coating layer is an organic / inorganic composite film containing ceramic particles and a binder resin, and the organic / inorganic composite film has porous properties due to pores formed by the interstitial volume between the ceramic particles. The interstitial volume refers to the space defined by the ceramic particles that are substantially in contact with each other in a packed structure of the ceramic particles.

[0057] The ceramic particles have the role of forming micropores by enabling the formation of empty spaces between the ceramic particles, and also serve as a kind of spacer that can maintain the physical shape. Generally, the ceramic particles have excellent heat resistance because their physical properties do not change even at high temperatures of 200°C or higher. Such ceramic particles are not particularly limited as long as they are electrochemically stable. In particular, the ceramic particles can be used in a range of the operating voltage of the battery to be used (for example, Li / Li + There are no particular limitations on the ceramic particles as long as they do not undergo oxidation and / or reduction reactions at temperatures between 0 and 5 V relative to the reference voltage. Examples include Al2O3, AlOOH, Al(OH)3, AlN, BN, MgO, Mg(OH)2, SiO2, ZnO, TiO2, BaTiO3, and mixtures thereof.

[0058] In the present invention, the first binder polymer is not particularly limited as long as it can provide binding strength between ceramic particles and between the porous coating layer and the electrode.

[0059] Specifically, the first binder polymer may be a polymer that is not dissolved in an organic solvent and can maintain dispersibility, or a particulate binder polymer that is not dissolved in an organic solvent and can maintain dispersibility and a particulate shape.

[0060] For example, the first binder polymer may include an acrylate-based binder polymer. The acrylate-based binder polymer may include a homopolymer or copolymer of an acrylic acid ester-based monomer, such as polyacrylonitrile, acrylonitrile-styrene-butadiene copolymer, or polybutyl acrylate, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, butyl acrylate, isononyl acrylate, or 2-ethylhexyl acrylate, or a mixture of two or more thereof. In the present invention, when the acrylic binder polymer is used as the first binder polymer, the manufacturing process can be simplified by using water as a solvent, and the thickness of the porous coating layer can be reduced.

[0061] The content of the first binder polymer may be 0.1 wt % to 10 wt % based on the total weight of the ceramic coating layer, specifically, 0.1 wt % or more, 1 wt % or more, 3 wt % or more, 10 wt % or less, or 8 wt % or less based on the total weight of the ceramic coating layer.

[0062] Generally, when the binder polymer is contained within the above content range, sufficient adhesive strength cannot be secured when bonding to the electrode, and problems such as peeling of the separator may occur during assembly of the electrode assembly. However, the method for manufacturing a gel polymer secondary battery of the present invention can solve these problems, and by ensuring that the content of the first binder polymer satisfies the above range, the resistance of the separator can be reduced, thereby improving the energy density of the battery and reducing costs.

[0063] electrode In the present invention, the electrode is a positive electrode and / or a negative electrode, and any electrode commonly used in the manufacture of lithium secondary batteries can be used. In the present invention, the electrode can be manufactured in a form in which an electrode active material is bound to an electrode current collector by a common method known in the art.

[0064] Among the electrode active materials, non-limiting examples of the positive electrode active material may include a common positive electrode active material that can be used in the positive electrode of a conventional lithium secondary battery, and may include at least one selected from the group consisting of lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, and lithium composite oxides combining these.

[0065] Non-limiting examples of the negative electrode active material include conventional negative electrode active materials that can be used in the negative electrodes of conventional lithium secondary batteries, such as at least one selected from the group consisting of lithium metal or lithium alloys, silicon and / or silicon-based compounds, tin and / or tin-based compounds, carbon, petroleum coke, activated carbon, graphite, and other carbonaceous materials into which lithium can be inserted and released.

[0066] Non-limiting examples of negative electrode current collectors include foils made of copper, gold, nickel, copper alloys, or combinations thereof, and non-limiting examples of positive electrode current collectors include foils made of aluminum, nickel, or combinations thereof.

[0067] Then, the separator and the electrode are stacked to prepare an electrode assembly (S2). In the electrode assembly preparation step (S2), a composition containing a second binder polymer is pattern-coated on at least one surface of the separator and / or the electrode. The separator is then folded in a zigzag pattern, and the electrode is inserted into the overlapping portion of the separator.

[0068] The present invention can improve problems such as separation between the separator and the electrode and folding of the separator during the steps of assembling and transferring the electrode assembly by the step of manufacturing the electrode assembly (S2).

[0069] Generally, when manufacturing an electrode assembly, lamination is performed under high temperature and / or high pressure conditions to bond the separator and the electrode. Specifically, typical lamination involves bonding the separator and the electrode at a temperature of about 50°C to 150°C and / or under a pressure of about 5 kgf / cm. 2 The pressure is applied under the above conditions.

[0070] However, in the present invention, a composition containing a second binder polymer is applied in a pattern to one surface of a separator or an electrode, and the separator and electrode are laminated by placing the electrode between the separator folded in a zigzag pattern. This can alleviate problems such as detachment between the separator and the electrode and folding of the separator during the assembly and transfer steps of the electrode assembly, without applying high temperature and / or high pressure conditions typically used in lamination.

[0071] For example, in one embodiment of the present invention, the lamination in step (S2) can be performed at a temperature of 30° C. or less. Also, the lamination in step (S2) can be performed under atmospheric pressure, or the pressure applied to the electrode assembly can be 3 kgf / cm. 2 It may be performed under the following conditions: In addition, the lamination process under pressure may not be performed in the step (S2). That is, in the present invention, the step (S2) may be performed in a pressure-free state.

[0072] The electrode assembly of the present invention has an advantage that the resistance at the interface between the separator and the electrode is very low, and the resistance of the battery is reduced, since the lamination in step (S2) is performed under the conditions described above.

[0073] The second binder polymer is not particularly limited as long as it is soluble in the gel polymer electrolyte composition. Specifically, in the present invention, the second binder polymer may be a material that is dissolved in the electrolyte composition after the electrolyte composition is injected, thereby reducing the resistance at the interface between the separator and the electrode. The second binder polymer is applied to at least one surface of the separator or electrode, and serves to bind the electrode and separator together, while also alleviating problems such as detachment between the separator and electrode and folding of the separator.

[0074] For example, the second binder polymer may include an acrylate-based binder polymer, etc. By using an acrylate-based polymer in the present invention, dissolution into the composition for electrolyte after the composition for electrolyte is injected may be easily performed.

[0075] Specifically, the acrylate polymer may include a copolymer containing 60.1 to 79.9% by weight of an alkyl (meth)acrylate repeating unit (A) and 20.1 to 39.9% by weight of a (meth)acrylate repeating unit (B) having a terminal hydroxy group.

[0076] More specifically, in the acrylate polymer, the repeating unit (A) is represented by the following chemical formula 1, and the repeating unit (B) is represented by the following chemical formula 2.

[0077] [ka]

[0078] In the above chemical formula 1, R1 is a hydrogen atom or a methyl group, R2 is a linear or branched alkyl group having 1 to 12 carbon atoms, and n can be an integer of 450 to 850 representing the number of repeating units (A).

[0079] [ka]

[0080] In the above Chemical Formula 2, R3 is a hydrogen atom or a methyl group, R4 is a linear or branched alkyl group having 1 to 9 carbon atoms to which a hydroxy group is bonded, and m can be an integer of 200 to 350 representing the number of repeating units (B).

[0081] More specifically, the acrylate polymer may include at least one selected from the group consisting of methyl acrylate (MMA), 2-ethylhexyl acrylate (2-EHA), and 2-hydroxyethyl acrylate (2-HEA), and more specifically, the above three may be mixed and used.

[0082] The composition containing the second binder polymer may be applied in a pattern on one surface of the separator or electrode, thereby providing adhesive strength to the patterned area.

[0083] The pattern shape may be dots, stripes, grids, etc. Specifically, the pattern shape is preferably dots. In this case, the diameter of the dots may be about 0.3 mm to 1.0 mm. According to a specific embodiment, for example, about 30 dots with a diameter of about 0.5 mm may be formed on an electrode having a size of 30 cm x 10 cm. Three dots may be formed at intervals of about 10 cm along the 30 cm length, and ten dots may be formed at intervals of about 0.35 mm along the 10 cm width. In this case, the spacing and number of dots may be freely determined by those skilled in the art, and the pattern may be changed depending on the size of the battery.

[0084] In one embodiment of the present invention, the pattern may be covered at 0.0001% to 0.05% of the 100% area of ​​the separator or electrode. When the above range is satisfied, adhesive strength is imparted to the region where the pattern is formed, and the second binder may be dissolved so as not to affect the performance of the battery after the electrolyte composition is subsequently injected.

[0085] In the step (S2), the separator is folded in a zigzag shape, and the electrode is inserted into the overlapping portion of the separator, thereby stacking the separator and the electrode.

[0086] FIG. 2 is a schematic diagram illustrating a method for laminating a separator and electrodes according to the present invention.

[0087] For example, referring to FIGS. 2A to 2F in FIG. 2, a method of stacking a separator and an electrode will be described. A separator 21 wound in a roll is supplied onto a stack table 1 through a separation membrane supply unit 2. The stack table can move left and right to fold the separator in a zigzag pattern. A first electrode 31 and / or a second electrode 32 can be sequentially stacked in the section where the separator is folded in a zigzag pattern through an electrode supply unit 3. A binder coating unit 4 can apply a composition 41 containing a binder polymer in a pattern onto one side of the separator or electrode.

[0088] For example, in FIG. 2A, a first electrode is stacked on a stack table on which a separator is provided. In FIGS. 2B and 2C, the stack table is moved so that the separator is folded in a zigzag pattern, and a composition containing a binder polymer is applied in a pattern onto one side of the separator. In FIGS. 2D and 2E, a second electrode is transferred and stacked on the separator. In FIG. 2F, an electrode assembly is stacked on the stack table, with the first and second electrodes inserted in the overlapping portion of the zigzag-folded separator. The stack table is moved so that the separator is folded in a zigzag pattern, and a composition containing a binder polymer is applied in a pattern onto one side of the separator.

[0089] That is, in the electrode assembly manufactured according to the present invention, a first electrode is positioned on one side of a separator, and a second electrode is positioned on the other side of the separator, with the separator sandwiched between them.

[0090] Next, a gel polymer electrolyte composition is injected into the electrode assembly to manufacture a battery (S3).

[0091] In the method for manufacturing a lithium secondary battery according to one aspect of the present invention, the gel polymer electrolyte composition may be a composition commonly used in manufacturing a gel polymer electrolyte, and may specifically include a polymerization initiator, a polymerizable compound, a lithium salt, and a non-aqueous organic solvent.

[0092] In step (S3), after injecting the composition for the gel polymer electrolyte, the composition can be polymerized to form a gel polymer electrolyte. For example, the polymerization can be performed at a temperature of 40° C. to 80° C., and the polymerizable compound present in the composition for the gel polymer electrolyte can be polymerized or crosslinked to form a gel polymer electrolyte.

[0093] polymerization initiator The gel polymer electrolyte composition of the present invention may contain a polymerization initiator to carry out the desired reaction during the production of the gel polymer electrolyte.

[0094] The polymerization initiator may be a conventional thermal polymerization initiator or photopolymerization initiator known in the art, for example, the polymerization initiator may be decomposed by heat to form radicals, which may react with the crosslinker by free radical polymerization to form a gel polymer electrolyte.

[0095] More specifically, non-limiting examples of the polymerization initiator include benzoyl peroxide, acetyl peroxide, dilauryl peroxide, di-tert-butylperoxide, t-butyl peroxy-2-ethyl-hexanoate, cumyl hydroperoxide, and hydrogen peroxide. peroxide), hydroperoxides, and azo compounds such as 2,2'-azobis(2-cyanobutane), 2,2'-azobis(methylbutyronitrile), 2,2'-azobis(isobutyronitrile) (AIBN), 2,2'-azobis(isobutyronitrile) (AMVN), and 2,2'-azobis-methoxy-dimethyl-valeronitrile (AMVN).

[0096] Meanwhile, in one embodiment of the present invention, the polymerization initiator contained in the composition for a gel polymer electrolyte of the present invention may have a 10-hour half-life temperature of 60°C or less, or a 10-hour half-life temperature of 55°C or less.

[0097] When the polymerization initiator having a 10-hour half-life temperature of 60°C or less is included, the gel polymer conversion rate can be increased to ensure the properties of the gel polymer electrolyte, and the pre-gelation reaction can be suppressed to improve the impregnation of the electrolyte into the electrode.

[0098] In the present invention, the 10-hour half-life temperature means a temperature at which half of the components of the existing initiator decompose within 10 hours.

[0099] In particular, the method for manufacturing a gel polymer secondary battery according to the present invention does not include a step of applying pressure exceeding atmospheric pressure during the process of manufacturing an electrode assembly, particularly before the activation step, so that the electrode and the separator do not come into close contact with each other. As a result, after the gel polymer electrolyte composition is injected, a path for electrolyte migration is well formed, and the impregnation of the electrolyte can proceed more quickly.

[0100] In addition, in the present invention, by reducing the content of the binder contained in the ceramic coating separator, the swelling time of the binder can be shortened, and the overall electrolyte impregnation time can be shortened.

[0101] That is, the method for producing a gel polymer secondary battery according to the present invention can shorten the electrolyte impregnation time, and therefore, by using a highly reactive polymerization initiator, i.e., a polymerization initiator with excellent reaction initiation performance and a 10-hour half-life temperature of 60°C or less, a secondary battery with excellent physical properties can be provided.

[0102] For example, in the present invention, a polymerization initiator having a 10-hour half-life temperature of 60°C or less may be selected from the azo compounds exemplified as the polymerization initiator. Specifically, one or more selected from 2,2-azobis-2,4-dimethylvaleronitrile (2,2'-azobis(2,4-dimethylvaleronitrile, Wako Co., Ltd. V65) and 2,2-azobis-4-methoxy-2,4-dimethylvaleronitrile (2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile, Wako Co., Ltd. V70) may be included. Specifically, the 10-hour half-life temperature of 2,2-azobis-2,4-dimethylvaleronitrile is 51°C, and the 10-hour half-life temperature of 2,2-azobis-4-methoxy-2,4-dimethylvaleronitrile is 30°C.

[0103] The polymerization initiator can be decomposed in the battery by heat, for example, at 30°C to 100°C, or at room temperature (5°C to 30°C) to form radicals, which can react with the polymerizable compound by free radical polymerization to form a gel polymer electrolyte.

[0104] 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 polymerizable compound.

[0105] When the polymerization initiator is used in an amount ranging from 0.01 to 20 parts by weight, the gel polymer conversion rate can be increased to ensure the properties of the gel polymer electrolyte, and the wettability of the electrolyte to the electrode can be improved by preventing a pre-gel reaction.

[0106] polymerizable compound The polymerizable compound is a compound that has a polymerizable functional group selected from the group consisting of a vinyl group, an epoxy group, an allyl group, and a (meth)acrylic group that can undergo polymerization reaction within the structure of a polymerizable monomer, oligomer, or copolymer, and can be converted into a gel state by polymerization or crosslinking. There is no particular limitation on the polymerizable compound as long as it is a compound that is commonly used as a polymerizable monomer, oligomer, or copolymer for producing a gel polymer electrolyte.

[0107] Among these, examples of the polymerizable monomer include, but are not limited to, tetraethylene glycol diacrylate, polyethylene 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, pentaerythritol tetraacrylate, and pentaerythritol ethoxylate tetraacrylate. tetraacrylate), dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate, poly(ethylene glycol) diglycidylether, 1,5-hexadiene diepoxide, glycerol propoxylate triglycidyl ether, vinylcyclohexene dioxide, 1,2,7,8-diepoxyoctane (1,2,7,Examples of suitable glycidyl ethers include, but are not limited to, 8-diepoxyoctane, 4-vinylcyclohexene dioxide, butyl glycidyl ether, diglycidyl 1,2-cyclohexanedicarboxylate, ethylene glycol diglycidyl ether, glycerol triglycidyl ether, and glycidyl methacrylate. These compounds may be used alone or in combination of two or more.

[0108] Representative examples of the copolymer include at least one selected from the group consisting of allyl 1,1,2,2-tetrafluoroethyl ether (TFE)-(2,2,2-trifluoroethyl acrylate) copolymer, TFE-vinyl acetate copolymer, TFE-(2-vinyl-1,3-dioxolane) copolymer, TFE-vinyl methacrylate copolymer, TFE-acrylonitrile copolymer, TFE-vinyl acrylate copolymer, TFE-methyl acrylate copolymer, TFE-methyl methacrylate (MMA) copolymer, and TFE-2,2,2-trifluoroethyl acrylate (FA) copolymer.

[0109] The polymerizable compound may be included in an amount of 0.01 wt % to 10 wt % based on the total weight of the gel polymer electrolyte composition. If the content of the polymerizable compound exceeds 10 wt %, gelation may occur too quickly or the composition may become too thick when injected into a battery, resulting in a gel with high resistance. Conversely, if the content of the polymerizable compound is less than 0.01 wt %, gelation may not occur well.

[0110] lithium salts The lithium salt is used as an electrolyte salt in a lithium secondary battery and is used as a medium for transferring ions. Generally, lithium salts contain Li as a cation. + and the anion is F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , AlO4 - , AlCl4 - , PF6 - , SbF6 - , AsF6 - , BF2C2O4 - , BC4O8 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , C4F9SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (F2SO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - It may contain at least one selected from the group consisting of:

[0111] The lithium salt may be used alone or in combination of two or more as needed. The lithium salt may be appropriately varied within a range that is normally usable, but in order to obtain an optimal effect of forming an anticorrosion coating on the electrode surface, the lithium salt may be contained in the gel polymer electrolyte composition at a concentration of 0.5 M to 2 M, specifically 0.9 M to 1.5 M.

[0112] The gel polymer electrolyte composition of the present invention contains 0.5M or more of an electrolyte salt, thereby reducing the resistance caused by the depletion of lithium ions during high-rate charge and discharge. Furthermore, in the gel polymer electrolyte composition of the present invention, when the concentration of the electrolyte salt satisfies the above range, the increase in the lithium cations present in the gel polymer electrolyte composition results in a high lithium cation (Li + ) can ensure the ion transfer characteristics (i.e., cation transfer number), thereby reducing the diffusion resistance of lithium ions and improving the cycle capacity characteristics.

[0113] Non-aqueous organic solvents The non-aqueous organic solvent is not limited as long as it can minimize decomposition due to oxidation during the charge / discharge process of the secondary battery and exhibit desired properties together with the additives, and for example, carbonate-based organic solvents, ether-based organic solvents, and ester-based organic solvents can be used alone or in combination.

[0114] The carbonate organic solvent may include at least one of a cyclic carbonate organic solvent and a linear carbonate organic solvent. Specifically, the cyclic carbonate organic solvent may include at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate, and fluoroethylene carbonate (FEC). Specifically, the cyclic carbonate organic solvent may include a mixed solvent of ethylene carbonate, which has a high dielectric constant, and propylene carbonate, which has a melting point lower than that of ethylene carbonate.

[0115] In addition, the linear carbonate organic solvent may be a solvent having low viscosity and low dielectric constant, and may include at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate, and ethyl propyl carbonate, and more specifically, may include dimethyl carbonate.

[0116] The ether-based organic solvent may be 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 of these, but is not limited thereto.

[0117] The ester-based organic solvent may include at least one selected from the group consisting of linear ester-based organic solvents and cyclic ester-based organic solvents.

[0118] Specific examples of the linear ester-based organic solvent include, but are not limited to, any one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate, or a mixture of two or more thereof.

[0119] Specific examples of the cyclic ester-based organic solvent include, but are not limited to, any one selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone, or a mixture of two or more of these.

[0120] Among the ester-based solvents, cyclic carbonate-based compounds are preferred because they are highly viscous organic solvents with a high dielectric constant and can easily dissociate lithium salts in the electrolyte. When such cyclic carbonate-based compounds are mixed in an appropriate ratio with linear carbonate-based compounds and linear ester-based compounds having low viscosity and low dielectric constant, such as dimethyl carbonate and diethyl carbonate, a gel polymer electrolyte having high electrical conductivity can be prepared, and thus the cyclic carbonate-based compounds are more preferred.

[0121] additives The gel polymer electrolyte composition of the present invention may further contain an additional additive capable of forming a more stable ion-conductive coating on the electrode surface, if necessary, in order to prevent the collapse of the negative electrode due to decomposition in a high-power environment during the preparation of the gel polymer electrolyte, or to further improve low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, and swelling improvement effects during high-temperature storage.

[0122] Specifically, the additional additive may include at least one first additive selected from the group consisting of sultone-based compounds, sulfite-based compounds, sulfone-based compounds, sulfate-based compounds, halogen-substituted carbonate-based compounds, nitrile-based compounds, cyclic carbonate-based compounds, phosphate-based compounds, borate-based compounds, and lithium salt-based compounds, as representative examples thereof.

[0123] The sultone-based compound may be at least one compound selected from the group consisting of 1,3-propane sultone (PS), 1,4-butane sultone, ethene sultone, 1,3-propene sultone (PRS), 1,4-butene sultone, and 1-methyl-1,3-propene sultone, and may be included in an amount of 0.3 to 5 wt %, specifically 1 to 5 wt %, based on the total weight of the gel polymer electrolyte composition. If the content of the sultone-based compound in the gel polymer electrolyte composition exceeds 5 wt %, a thick coating may form on the electrode surface, resulting in increased resistance and reduced output power. An excessive amount of additives in the gel polymer electrolyte composition may increase resistance and reduce output power characteristics.

[0124] The sulfite-based compound may be one or more compounds selected from the group consisting of ethylene sulfite, methyl ethylene sulfite, ethyl ethylene sulfite, 4,5-dimethyl ethylene sulfite, 4,5-diethyl ethylene sulfite, propylene sulfite, 4,5-dimethyl propylene sulfite, 4,5-diethyl propylene sulfite, 4,6-dimethyl propylene sulfite, 4,6-diethyl propylene sulfite, and 1,3-butylene glycol sulfite, and may be contained in an amount of 3 wt % or less based on the total weight of the composition for the gel polymer electrolyte.

[0125] The sulfone-based compound may be one or more compounds selected from the group consisting of divinyl sulfone, dimethyl sulfone, diethyl sulfone, methyl ethyl sulfone, and methyl vinyl sulfone, and may be contained in an amount of 3 wt % or less based on the total weight of the composition for the gel polymer electrolyte.

[0126] The sulfate-based compound may be ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS), and may be contained in an amount of 3 wt % or less based on the total weight of the composition for the gel polymer electrolyte.

[0127] The halogen-substituted carbonate-based compound may be fluoroethylene carbonate (FEC), and may be contained in an amount of 5 wt% or less based on the total weight of the gel polymer electrolyte composition. If the content of the halogen-substituted carbonate-based compound in the gel polymer electrolyte composition exceeds 5 wt%, cell swelling performance may be reduced.

[0128] Examples of the nitrile compound include at least one compound selected from the group consisting of succinonitrile, adiponitrile (Adn), acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

[0129] The cyclic carbonate-based compound may be vinylene carbonate (VC) or vinylethylene carbonate, and may be contained in an amount of 3 wt% or less based on the total weight of the gel polymer electrolyte composition. If the content of the cyclic carbonate-based compound in the gel polymer electrolyte composition exceeds 3 wt%, the cell swelling suppression performance may be reduced.

[0130] The phosphate-based compound may be one or more compounds selected from the group consisting of lithium difluoro(bisoxalato)phosphate, lithium difluorophosphate, tetramethyltrimethylsilylphosphate, trimethylsilylphosphite, tris(2,2,2-trifluoroethyl)phosphate, and tris(trifluoroethyl)phosphite, and may be contained in an amount of 3 wt % or less based on the total weight of the composition for the gel polymer electrolyte.

[0131] The borate-based compound may be lithium oxalyl difluoroborate, which may be contained in an amount of 3 wt % or less based on the total weight of the composition for the gel polymer electrolyte.

[0132] The lithium salt-based compound is a compound different from the lithium salt contained in the composition for a gel polymer electrolyte, and may include one or more compounds selected from the group consisting of LiPO2F2, LiODFB, LiBOB (lithium bis(oxalatoborate) (LiB(C2O4)2)), and LiBF4, and may be contained in an amount of 3 wt% or less based on the total weight of the composition for a gel polymer electrolyte.

[0133] The additional additives may be mixed and included in an amount of 20 wt % or less, specifically 0.1 wt % to 10 wt %, based on the total weight of the gel polymer electrolyte composition. If the content of the additional additive is less than 0.01 wt %, the effect of improving the low-temperature output, high-temperature storage characteristics, and high-temperature life characteristics of the battery is small. If the content of the additional additive is more than 20 wt %, excessive side reactions may occur in the gel polymer electrolyte composition during battery charge and discharge. In particular, the additive may not be fully decomposed at high temperatures and may remain unreacted or precipitated in the gel polymer electrolyte composition at room temperature. This may result in side reactions that reduce the life or resistance characteristics of the secondary battery.

[0134] In one embodiment of the present invention, after the step (S3), the method may further comprise the step of vacuum sealing the battery under a pressure condition of less than -95 kPa.

[0135] After injecting the gel polymer electrolyte composition in step (S3), a gel polymer electrolyte is formed, and a vacuum sealing process can be performed at a high degree of vacuum. Specifically, the vacuum sealing process can be performed by applying a predetermined high degree of vacuum to a battery including the electrode assembly manufactured in step (S2) and a battery case in which the gel polymer electrolyte composition is the main liquid.

[0136] In the case of batteries filled with liquid electrolyte, applying a high degree of vacuum causes the electrolyte to volatilize, resulting in a decrease in long-term cycle characteristics and a shortened battery life. For this reason, when filling with liquid electrolyte, a pressure of -95 kPa or higher must be applied during the sealing process.

[0137] However, in the present invention, the sealing step can be performed in a relatively high vacuum environment compared to the conventional method. Therefore, the volatility of the gel polymer electrolyte is lower than that of the liquid electrolyte, and the adhesion between the battery case and the electrode assembly is improved, thereby further improving the rigidity and lifespan.

[0138] Specifically, the battery fabricated in step (S3) can be subjected to a vacuum sealing step under a pressure condition of less than -95 kPa or a pressure condition in the range of -100 kPa to -120 kPa. When vacuum sealing is performed under pressure conditions satisfying the above range, it is possible to prevent water from penetrating into the injected gel polymer electrolyte composition and air from entering the battery from the outside to the inside. Furthermore, the remaining amount and degree of hardening of the electrolyte after the vacuum sealing step increases, improving cell rigidity and thereby improving life characteristics.

[0139] The vacuum sealing process may be carried out for 5 to 30 seconds.

[0140] Furthermore, the vacuum sealed battery can be cured by a polymerization or crosslinking reaction under appropriate temperature and time conditions to form a gel polymer electrolyte.

[0141] For example, the gelation can be carried out at a temperature of about 50° C. to 100° C., or about 60° C. to 80° C. The gelation can be carried out within the above temperature range for 0.5 to 48 hours, or 0.5 to 24 hours, thereby allowing the polymerizable compound present in the gel polymer electrolyte composition to undergo a polymerization or crosslinking reaction to form a gel polymer electrolyte.

[0142] Next, the temperature was increased to 50°C or higher and the pressure was increased to 0.1 kgf / cm 2 to 5kgf / cm 2 The battery is charged at least twice under this pressure condition to perform activation (S4).

[0143] The application of pressure in step (S4) may include at least one application by a pressure device. The pressure device is not limited as long as it can apply an appropriate pressure to the battery, and may be, for example, a jig. Specifically, the pressure can be applied by a method in which the battery is sandwiched between a pair of opposing jigs and pressurized. When applying pressure, for example, the pressure device may apply a pressure of 0.1 kgf / cm. 2 to 5kgf / cm 2 The battery can be pressurized under the pressure conditions of 1 minute to 10 hours, or 1 hour to 5 hours.

[0144] Battery activation is a step of initially charging a battery to activate the electrode active material and form an SEI film on the electrode surface. In the case of a gel polymer secondary battery according to the present invention, this step can be performed by applying a current up to a predetermined voltage to an electrode assembly impregnated with a gel polymer electrolyte composition. During the battery activation step, gas generation inside the battery is unavoidable due to the decomposition reaction of the electrolyte. However, in the present invention, the battery is activated under predetermined high-temperature and high-pressure conditions to remove the gas generated inside. In particular, in the case of a secondary battery using a gel polymer electrolyte, the electrolyte is already in a gel state during the activation step, so gas cannot be removed even by applying high pressure. However, in the present invention, the manufacturing process of a secondary battery does not include a step of applying pressure exceeding atmospheric pressure to the electrode assembly before the activation step. This prevents adhesion between the electrode and the separator, and allows the high pressure applied during the activation step to facilitate gas removal.

[0145] Specifically, the step (S4) is performed under the following conditions: (S4a) a temperature of 50 to 60°C and a pressure of 0.1 kgf / cm 2 to 1 kgf / cm 2 (S4b) performing primary charging at a temperature of 50 to 60°C and a pressure of 3 kgf / cm within a range of 20% of the secondary battery capacity (SOC, state of charge); 2 to 5kgf / cm 2 and applying a pressure condition of 15% to 60% of the secondary battery state of charge (SOC). More specifically, the step (S4a) can be performed at a rate-determining (C-rate) of 0.01C to 0.15C, and the step (S4b) can be performed at a rate-determining (C-rate) of 0.2C to 1C.

[0146] As described above, by dividing the charging step in the activation step into multiple stages to satisfy predetermined conditions, in step (S4a), uniform charging is possible with an initial low rate charge, and a large amount of gas can be generated because an SEI film is uniformly formed. In step (S4b), a higher rate can be applied to shorten the time, and increasing the pressure has the advantage of easily removing the generated gas to the outside.

[0147] In one embodiment of the present invention, the battery activated in step (S4) is heated under a temperature condition of 60°C or higher and 3 kgf / cm 2 The method may further include a step (S5) of storing the mixture under the above pressure conditions.

[0148] Step (S5) refers to a step of leaving the activated battery under high temperature and pressure conditions for a predetermined time, which softens the binder present in the separator, improves the adhesive strength between the electrode and the separator, and effectively releases gas trapped inside the electrode and / or at the interface between the electrode and the separator.

[0149] The step (S5) may be referred to as a clamp and bake (CB) process, which will be described in detail below.

[0150] In one embodiment of the present invention, gas generated inside a secondary battery can be removed by storing an activated battery under predetermined high temperature and high pressure conditions. In particular, in the case of a secondary battery using a gel polymer electrolyte, the electrolyte is already in a gel state during the activation step, so applying high pressure after the activation step does not remove gas. However, the present invention does not include a step of applying pressure exceeding atmospheric pressure to an electrode assembly before the activation step in the manufacturing process of a secondary battery. This prevents adhesion between the electrodes and the separator, and allows the high pressure applied during the clamping and baking process after the activation step to facilitate gas removal.

[0151] Specifically, the activated battery can be stored under temperature conditions of 60°C or higher, 60°C to 100°C, or 70°C to 90°C. Furthermore, the application of pressure in step (S5) can include at least one application using a pressure device. The pressure device is not limited as long as it can apply an appropriate pressure to the battery, and can be, for example, a jig. Specifically, the battery can be clamped between a pair of opposing jigs and pressurized. When applying pressure, for example, the pressure device can be set to 3 kgf / cm 2 or more, or 3kgf / cm 2 to 10 kgf / cm 2 The battery can be pressurized under these pressure conditions. The pressurization can be performed for 1 minute to 5 hours, or 30 minutes to 1 hour. Pressurization under these conditions can remove activated gas trapped at the electrode and electrode / separator interfaces, reducing resistance and preventing lithium precipitation due to trapped gas and the resulting shortening of battery life. Another advantage is that the gel polymer can be further hardened, improving the rigidity of the battery.

[0152] In one embodiment of the present invention, after the step (S4), the battery can be degassed under a pressure condition of less than -95 kPa.

[0153] The degassing step can remove gas generated during the activation step. Specifically, the degassing step can be performed on the activated battery under a pressure of less than -95 kPa or in the range of -100 kPa to -120 kPa.

[0154] In the case of batteries filled with liquid electrolyte, applying a high degree of vacuum during the degassing step causes the electrolyte to volatilize, degrading long-term cycle characteristics and shortening the battery's lifespan. For this reason, when filling with liquid electrolyte, a pressure of -95 kPa or higher must be applied during the sealing process.

[0155] However, in the present invention, the degassing step can be performed in a relatively high vacuum environment compared to the conventional method. This reduces the volatility of the gel polymer electrolyte compared to the liquid electrolyte, and improves the adhesion between the battery case and the electrode assembly, thereby further improving the rigidity and lifespan.

[0156] The degassing step is carried out for 5 to 30 seconds to remove any remaining gas in the battery case.

[0157] Meanwhile, in one embodiment of the present invention, after the electrode assembly is fabricated as described above, a process of surrounding the electrode assembly with a separator film may be further performed.

[0158] The separator film is a porous insulating film and may include a polymer material. For example, the separator film may refer to the porous substrate of the separator described above. When the electrode assembly is surrounded by the separator film, the separator film may not be applied to the side portion of the electrode assembly from which the electrode tabs are pulled out. Alternatively, the end of the separator film may be fixed with a fixing tape or a binder material. When the electrode assembly is surrounded by the separator film in this manner, the structure of the electrode assembly can be more stably maintained.

[0159] In the present invention, the secondary battery is preferably a lithium secondary battery, and non-limiting examples of the lithium secondary battery include a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, and a lithium ion polymer secondary battery.

[0160] Meanwhile, according to one aspect of the present invention, there is provided a gel polymer secondary battery manufactured by the method for manufacturing a gel polymer secondary battery according to an embodiment of the present invention, wherein the secondary battery has a stiffness of 4.0 MPa or more, or 4.5 MPa or more.

[0161] The stiffness can be measured using a UTM device. For example, a 3 mm x 3 mm jig is placed on top of the fabricated secondary battery, and the secondary battery is pressed at the center with a force of 30 gf and a speed of 10 mm / min. The maximum force (maximum bending stress, MPa) during the cell displacement (extension from preload, the extent to which the cell is pushed from the reference value) of 2 mm can be measured.

[0162] Hereinafter, the present invention will be described in detail with reference to examples. However, the examples according to the present invention can be modified into various other forms, and the scope of the present invention is not limited to the examples described in detail below. The examples of the present invention are provided to more completely explain the present invention to those skilled in the art.

[0163] Example SET 1 Example A-1 (Preparation of ceramic coated separator and electrodes) Ceramic particles Al2O3, a first binder polymer (a mixture of TRD 202A manufactured by JSR and AP-0821 manufactured by APEC) were added to a solvent in a weight ratio of 96:4 to prepare a ceramic coating slurry.

[0164] The ceramic coating slurry was applied to both sides of a polyethylene porous film (thickness 9 μm, porosity 45%) and then dried to prepare a separator with a ceramic coating layer. The thickness of the ceramic coating layer was approximately 1.5 μm on each side.

[0165] As a positive electrode active material (LiNi 0.8 Co 0.1 Mn 0.1A positive electrode active material slurry was prepared by adding 97 wt% of O2 (NCM), 1 wt% of carbon black as a conductive material, and 2 wt% of polyvinylidene fluoride (PVDF) as a binder to a solvent, N-methyl-2-pyrrolidone (NMP). The positive electrode active material slurry was applied to a thin aluminum (Al) film of a positive electrode current collector having a thickness of approximately 20 μm, dried, and then roll pressed to prepare a positive electrode.

[0166] A negative electrode active material slurry was prepared by adding 96 wt % of carbon powder as a negative electrode active material, 3 wt % of PVDF as a binder, and 1 wt % of carbon black as a conductive material to a solvent, NMP. The negative electrode active material slurry was applied to a 10 μm-thick copper (Cu) thin film of a negative electrode current collector, dried, and then roll-pressed to prepare a negative electrode.

[0167] (Production of Gel Polymer Electrolyte Composition) LiPF6 was dissolved in a non-aqueous organic solvent having a composition of ethylene carbonate (EC):ethyl methyl carbonate (EMC) = 30:70 (volume ratio) to a concentration of 1.0 M. A gel polymer electrolyte composition was prepared by adding 5 parts by weight of trimethylolpropane triacrylate as a polymerizable compound to 100 parts by weight of the solution and 0.06 parts by weight of azobisisobutyronitrile (AIBN, V59) as a polymerization initiator to 100 parts by weight of the solution.

[0168] (Manufacturing of electrode assemblies and secondary batteries) The ceramic-coated separator was folded in a zigzag pattern, and the negative and positive electrodes were inserted in order into the overlapping portions. An acrylate-based polymer composition, a copolymer containing repeating units derived from methyl methacrylate (MMA), 2-ethylhexyl acrylate (2-EHA), and 2-hydroxyethyl acrylate (2-HEA) in a weight ratio of 40:30:30, was applied to one side of the ceramic-coated separator in the form of 0.5 mm diameter dots. The separator measured 306.5 mm (width) x 104.5 mm (length), and the coating was applied in three locations spaced 100 mm apart in the horizontal direction and 0.35 mm apart in the vertical direction. The electrode assembly was fabricated at room temperature and pressure.

[0169] The electrode assembly was inserted into a battery case, and the gel polymer electrolyte composition was poured into the battery case to prepare a secondary battery. The battery case was then wetting-tested at room temperature for 2 days, and the gel polymer electrolyte composition was then left in a chamber at 60°C for 10 hours to polymerize.

[0170] (Battery activation step) The secondary battery prepared above was activated in two stages.

[0171] Primary charge: 0.1 kgf / cm at 60°C 2 The secondary battery was charged to 20% of its capacity at a rate of 0.1 C by applying a pressure of 0.1 C.

[0172] Secondary charge: 5kgf / cm at 60℃ 2 The secondary battery was charged to 60% of its capacity at a rate of 0.2 C by applying a pressure of 0.2 C.

[0173] At this time, pressure was applied during the primary charging and secondary charging by clamping the battery between a pair of opposing jigs.

[0174] Example A-2 After the battery activation step, the battery was clamped between a pair of opposing jigs and then heated to 80°C with 5 kgf / cm2 A battery was fabricated in the same manner as in Example A-1, except that a clamping and baking process was further performed in which the battery was stored for 30 minutes under a pressure of 1000 kJ / cm2.

[0175] Comparative example A-1 A battery was manufactured in the same manner as in Example A-1, except that in the battery activation step, the battery was charged once under the following conditions.

[0176] Primary charging: The secondary battery was charged to 60% of its capacity at a rate of 0.2 C without applying pressure at room temperature (25°C).

[0177] Comparative example A-2 A battery was manufactured in the same manner as in Example A-1, except that in the battery activation step, the battery was charged once under the following conditions.

[0178] Primary charging: The secondary battery was charged to 60% of its capacity at a rate of 0.2 C without applying pressure at a temperature of 60°C.

[0179] Comparative example A-3 The content of binder polymer in the ceramic coating separator is 30% by weight, and the electrode assembly is assembled under high temperature (80°C) and high pressure (3kgf / cm 2 A battery was produced in the same manner as in Example A-1, except that normal lamination was carried out under the conditions of

[0180] Comparative example A-4 A battery was fabricated in the same manner as in Example A-1, except that the following battery activation step and clamp & bake process were performed.

[0181] (Battery activation step) Primary charging: The secondary battery was charged to 60% of its capacity at a rate of 0.2 C without applying pressure at room temperature (25°C).

[0182] (Clamping and baking process) The sample is sandwiched between a pair of opposing jigs and baked at 80°C with 2 kgf / cm 2The mixture was stored for 30 minutes under a pressure of 0.05 MPa.

[0183] Evaluation results The gel polymer secondary batteries manufactured according to the examples and comparative examples of SET A were evaluated for physical properties as follows, and the results are shown in Table 1.

[0184] [Table 1]

[0185] (1) Resistance measurement method The secondary batteries manufactured according to the example and comparative example of SET A were discharged at a rate of 2.5C for 10 seconds at an SOC of 50%, and the resistance was measured using the voltage change (ΔV).

[0186] (2) Life measurement method The secondary batteries manufactured according to the example and comparative example of SET A were initially charged and discharged once using an electrochemical charger / discharger. Charging was performed by applying a current at a current density of 0.33 C up to a voltage of 4.2 V, and discharging was performed at the same current density down to 2.5 V. This charging and discharging cycle was repeated a total of 100 times.

[0187] During the above charge and discharge process, the voltage and capacity of the positive and negative electrodes included in each battery were measured.

[0188] From this, the capacity retention rate of each battery was calculated as follows:

[0189] Capacity retention rate (%) = (Capacity after 100 cycles / Initial capacity) x 100

[0190] (3) Stiffness evaluation method The rigidity of the secondary batteries manufactured according to the SET A Example and Comparative Example was measured using a UTM device. A 3mm x 3mm jig was placed on top of the secondary battery, and the secondary battery was pressed at the center with a force of 30gf at a speed of 10mm / min. The maximum force (maximum bending stress, MPa) was measured during the cell displacement (extension from preload, the extent to which the cell was pushed from the reference value, mm) of 2mm.

[0191] (4) Safety evaluation by nail penetration test The secondary batteries manufactured according to the example and comparative example of SET A were fully charged to 4.4 V at room temperature, and then subjected to a nail penetration test under GB / T conditions (nail diameter 2.5 mm, penetration speed 6 m / min). The results are shown in Table 1.

[0192] As can be seen from Table 1 above, comparing Example A-1 and Comparative Examples A-1 to A-3, which used a gel polymer electrolyte composition as the electrolyte, it was confirmed that Example A-1, in which high temperature and high pressure were applied in the battery activation step, exhibited easier gas removal and was superior in resistance, life characteristics, rigidity, and safety compared to Comparative Example A-1, in which activation was performed at room temperature, and Comparative Example A-2, in which activation was performed at high temperature without applying pressure.

[0193] Furthermore, comparing Example A-1 and Example A-2, Example A-2, which further performed a clamping and baking process after the same battery activation step, was found to have a more excellent effect on the overall battery performance because the high pressure applied in the clamping and baking process promoted gas discharge.

[0194] In addition, Comparative Example A-3 was subjected to the same battery activation step as Example A-1, but the ceramic coating separator contained a higher binder content in Comparative Example A-3 than in Example A-1, resulting in poor resistance characteristics. Furthermore, unlike Example A-1, Comparative Example A-3 was subjected to lamination under high temperature and high pressure conditions. Even though the same battery activation step as Example A-1 was performed, it was confirmed that gas generated inside the battery was not easily removed, resulting in poor life characteristics.

[0195] SET 2 Example B-1 A battery was produced in the same manner as in Example A-1. The 10-hour half-life of the polymerization initiator AIBN (V59) used in Example A-1 is 67°C.

[0196] Example B-2 A battery was manufactured in the same manner as in Example B-1, except that 2,2-azobis-2,4-dimethylvaleronitrile (V65) having a 10-hour half-life of 51° C. was used as the polymerization initiator.

[0197] Example B-3 As a post-process after the battery activation step, the battery is sandwiched between a pair of opposing jigs and subjected to 5 kgf / cm at a temperature of 80°C. 2 A battery was fabricated in the same manner as in Example B-1, except that a clamping and baking process was further performed in which the battery was stored for 30 minutes under a pressure of 1000 kJ / cm².

[0198] Example B-4 As a post-process after the battery activation step, the battery is sandwiched between a pair of opposing jigs and subjected to 5 kgf / cm at a temperature of 80°C. 2 A battery was fabricated in the same manner as in Example B-2, except that a clamping and baking process was further performed in which the battery was stored for 30 minutes under a pressure of 1000 kJ / cm2.

[0199] Comparative example B-1 The content of binder polymer in the ceramic coating separator is 30% by weight, and high temperature (80°C) and high pressure (3kgf / cm) are required when assembling the electrode assembly. 2 A battery was produced in the same manner as in Example B-1, except that ordinary lamination was carried out in the same manner as in Example B-1.

[0200] Evaluation results The gel polymer secondary batteries manufactured according to the examples and comparative examples of SET B were evaluated for physical properties as follows.

[0201] The results for the polymer curing rate are shown in Table 2, and the results for the performance of the gel polymer secondary battery are shown in Table 3. The method for evaluating the physical properties in Table 3 is the same as the method presented in SET A.

[0202] [Table 2]

[0203] (1) Measurement method at the time of completion of impregnation The time point at which the resistance converged was measured using EIS (Electrochemical Impedance Spectroscopy).

[0204] (2) Pre-gelation (%) at the completion of impregnation and polymer conversion rate (%) after curing The pregelation rate (%) and polymer conversion rate (%) were calculated using the following mathematical formula 1. Specifically, the polymerizable compound present in the composition for a gel polymer electrolyte was quantitatively analyzed by NMR to confirm the difference in the polymer before and after polymerization. Specifically, the reactive sites of the polymer and the remaining reactive sites were quantitatively analyzed using NMR. The results are shown in Table 2 above.

[0205] [Mathematical formula 1] Polymer conversion rate (%) = 100 - (remaining reactive sites of polymer after polymerization / reactive sites of polymer before polymerization) x 100

[0206] [Table 3]

[0207] As can be seen from Table 2 above, it was confirmed that impregnation was completed more quickly in Examples B-1 to B-4, the pre-gelation rate was lower, and the polymer conversion rate after curing was higher compared to Comparative Example B-1. Furthermore, it was confirmed that Comparative Example B-1, unlike Examples B-1 to B-4, was subjected to lamination under high temperature and pressure conditions, resulting in closer adhesion between the separator and the electrodes, resulting in a longer electrolyte impregnation time.

[0208] Furthermore, as can be seen from Table 3 above, in Comparative Example B-1, even when the same battery activation step as in Examples B-1 and B-2 was performed, it was confirmed that the gas generated inside the battery was not easily removed, resulting in poor life and resistance characteristics. On the other hand, in Examples B-3 and B-4, it was confirmed that the cell rigidity was improved by performing the clamping and baking process.

[0209] SET 3 Example C-1 A battery was produced in the same manner as in Example A-1.

[0210] Example C-2 As a post-process after the battery activation step, the battery is sandwiched between a pair of opposing jigs and subjected to 5 kgf / cm at a temperature of 80°C. 2 A battery was fabricated in the same manner as in Example C-1, except that a clamping and baking process was further performed in which the battery was stored for 30 minutes under a pressure of 1000 kJ / cm2.

[0211] Comparative example C-1 A separator similar to the ceramic-coated separator of Example C-1 was used, except that the content of the binder polymer in the ceramic-coated separator was 30 wt %.

[0212] When assembling the electrode assembly, high temperature (80°C) and high pressure (3 kgf / cm 2An electrode assembly was manufactured in the same manner as in Example C-1, except that normal lamination was performed under the conditions of

[0213] A battery was produced in the same manner as in Example C-1, except that a non-aqueous electrolyte solution having the following composition was injected.

[0214] (Production of non-aqueous electrolyte) A non-aqueous electrolyte solution was prepared by dissolving LiPF6 to 1.0 M in a non-aqueous organic solvent having a composition of ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 30:70 (volume ratio).

[0215] Comparative example C-2 A separator similar to the ceramic-coated separator of Example C-1 was used, except that the content of the binder polymer in the ceramic-coated separator was 30 wt %.

[0216] When assembling the electrode assembly, high temperature (80°C) and high pressure (3 kgf / cm 2 An electrode assembly was manufactured in the same manner as in Example C-1, except that normal lamination was performed under the conditions of

[0217] Comparative example C-3 A battery was produced in the same manner as in Example C-1, except that a non-aqueous electrolyte solution having the following composition was injected.

[0218] (Production of non-aqueous electrolyte) A non-aqueous electrolyte solution was prepared by dissolving LiPF6 to 1.0 M in a non-aqueous organic solvent having a composition of ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 30:70 (volume ratio).

[0219] Evaluation results The gel polymer secondary batteries manufactured according to the example and comparative example of SET C were subjected to a vacuum sealing and degassing process under conditions of -95 kPa and -105 kPa for 5 to 30 seconds, respectively.

[0220] The results of the physical property evaluation under each condition are shown in Table 4.

[0221] [Table 4]

[0222] (1) Method for measuring remaining electrolytes The total pore volume present in the cathode material, anode material, and separator was set to 100%, and the excess factor was set to 125% taking into account the dead space present inside the battery and the amount of electrolyte required for cycle consumption, and the remaining amount of electrolyte after the degassing step was calculated.

[0223] (2) Stiffness measurement method The method for measuring the stiffness of the secondary battery is the same as the method presented in SET A. The stiffness value measured in the above Comparative Example C-1 was set to 100%, and the stiffness values ​​of Example C-1 and Comparative Examples C-2 and C-3 were shown in percentage.

[0224] (3) Resistance and lifespan measurement method The method for measuring the resistance and lifespan of the secondary battery was the same as that presented in SET A.

[0225] (4) Measurement of Ramp-up Ignition Temperature The temperature of the cell was increased at a rate of 0.5°C / min, and the temperature at the center of the cell was measured when the cell ignited.

[0226] As can be seen from Table 4 above, Examples C-1 and C-2 and Comparative Example C-2, which used the gel polymer electrolyte composition, were confirmed to have superior electrolyte residual amount and cell rigidity compared to Comparative Examples C-1 and C-3, which were injected with a non-aqueous electrolyte solution.

[0227] In particular, when sealing and degassing at a pressure of -95 kPa was compared with sealing and degassing at a pressure of -105 kPa, it was confirmed that in Examples C-1 and C-2 and Comparative Example C-2, in which a gel polymer electrolyte composition was injected, the remaining amount of electrolyte and resistance were maintained at the same level even when the degree of vacuum increased, and cell rigidity was further improved, whereas in Comparative Examples C-1 and C-3, in which a liquid electrolyte was injected, the remaining amount of electrolyte decreased and the cell resistance increased.

[0228] On the other hand, Comparative Example C-2 had a higher binder content in the ceramic-coated separator than Examples C-1 and C-2 during electrode assembly fabrication, and unlike Examples C-1 and C-2, it was subjected to a lamination process at high temperature and pressure, resulting in inferior resistance characteristics and safety. In Examples C-1 and C-2, the physical shape of the separator was maintained even at high temperatures, thereby delaying thermal shrinkage as much as possible and providing excellent safety. In particular, Example C-2 was confirmed to further apply a clamping and baking process, thereby improving interfacial adhesion between the separator and electrode, reducing resistance and further improving cell rigidity. [Explanation of symbols]

[0229] 1 Stack Table 2 Separation membrane supply section 21 Separation membrane 3 Electrode supply section 31 1st electrode 32 2nd electrode 4. Binder application section 41 Composition containing a binder polymer

Claims

1. (S1) preparing a ceramic-coated separator and an electrode, the ceramic-coated separator including a porous substrate and a ceramic coating layer, the ceramic coating layer including a first binder polymer and ceramic particles; (S2) a step of manufacturing an electrode assembly by stacking the separator and the electrode, wherein a composition including a second binder polymer is applied in a pattern on at least one surface of the separator or the electrode, and the separator is folded in a zigzag pattern and the electrode is inserted into an overlapping portion of the separator; (S3) injecting a gel polymer electrolyte composition into the electrode assembly to manufacture a battery; (S4) Temperature conditions of 50°C or higher and 0.1 kgf / cm ２ to 5 kgf / cm ２ Activating the battery by charging it at least twice under this pressure condition; Including, The method for manufacturing a gel polymer secondary battery, wherein the step (S4) does not include discharging.

2. The method for manufacturing a gel polymer secondary battery according to claim 1 , wherein the lamination in step (S2) is performed at a temperature of 30° C. or less.

3. The lamination in step (S2) is performed under normal pressure, or the pressure applied to the electrode assembly is 3 kgf / cm ２ The method for producing the gel polymer secondary battery according to claim 1, which is carried out under the following conditions:

4. The method for manufacturing a gel polymer secondary battery according to claim 1 , wherein the step (S2) does not include a lamination process under pressure.

5. The method of claim 1 , wherein the content of the first binder polymer is 0.1 wt % to 10 wt % based on the total weight of the ceramic coating layer.

6. The method for manufacturing a gel polymer secondary battery according to claim 1 , wherein the first binder polymer is an acrylate-based binder polymer.

7. The method for manufacturing a gel polymer secondary battery according to claim 1 , wherein the pattern shape includes at least one of a dot shape, a stripe shape, and a grid shape.

8. 2. The method for producing a gel polymer secondary battery according to claim 1, wherein the gel polymer electrolyte composition comprises a polymerization initiator having a 10-hour half-life temperature of 60° C. or less, a polymerizable compound, a lithium salt, and a non-aqueous organic solvent.

9. The method for producing a gel polymer secondary battery according to claim 8 , wherein the polymerization initiator has a 10-hour half-life temperature of 55° C. or lower.

10. The method for manufacturing a gel polymer secondary battery according to claim 8 , wherein the content of the polymerization initiator is 0.1 to 10 parts by weight based on 100 parts by weight of the polymerizable compound.

11. The method for manufacturing a gel polymer secondary battery according to claim 1 , wherein the application of pressure in the step (S4) includes applying the pressure at least once using a pressure device.

12. The step (S4) (S4a) Temperature conditions of 50 to 60°C and 0.1 kgf / cm ２ to 1 kgf / cm ２ applying a pressure condition of the above and performing primary charging within a range of 20% of the secondary battery capacity (SOC); (S4b) Temperature conditions of 50 to 60°C and 3 kgf / cm ２ to 5 kgf / cm ２ and performing secondary charging at 15 to 60% of the secondary battery capacity (SOC); The method for producing the gel polymer secondary battery according to claim 1 , comprising:

13. (S5) The battery activated in step (S4) is subjected to a temperature condition of 60°C or higher and a pressure of 3 kgf / cm ２ The method for producing a gel polymer secondary battery according to claim 1 , further comprising a step of storing the battery under the above pressure conditions.

14. The method for manufacturing a gel polymer secondary battery according to claim 13, wherein the step (S5) is performed for 30 minutes to 5 hours.

15. The method for manufacturing a gel polymer secondary battery according to claim 13 , wherein the application of pressure in the step (S5) includes applying the pressure at least once using a pressure device.

16. The method for producing a gel polymer secondary battery according to claim 1, further comprising the step of vacuum sealing the battery under a pressure condition of less than -95 kPa after the step (S3) and before the step (S4).

17. The method for producing a gel polymer secondary battery according to claim 16, wherein the pressure condition in the vacuum sealing step is in the range of −100 kPa to −101.33 kPa.

18. The method for producing a gel polymer secondary battery according to claim 16, wherein the vacuum sealing step is carried out for 5 to 30 seconds.

19. The method for producing a gel polymer secondary battery according to claim 1, further comprising the step of degassing the battery under a pressure condition of less than -95 kPa after the step (S4).

20. 20. The method for producing a gel polymer secondary battery according to claim 19, wherein the pressure condition in the degassing step is in the range of −100 kPa to −120 kPa.

Images