Method for manufacturing a curved secondary battery

Abstract

The present disclosure relates to a method of manufacturing a curved secondary battery having a target radius of curvature, the method comprising the steps of: (a) housing an electrode assembly comprising a cathode, an anode, and a separator interposed between the cathode and the anode, together with an electrolyte, into a battery case to manufacture a secondary battery; (b) performing a first activation and degassing of the secondary battery; (c) performing a first heat pressing of the degassed secondary battery so as to have a first radius of curvature; (d) performing a second activation of the secondary battery after the first heat pressing step; and (e) performing a second heat pressing of the secondary battery after the second activation so as to have a second radius of curvature.

Description

Technical Field

[0001] Cross-reference with related applications

[0002] This application claims the benefit of Korean Patent Application No. 10-2021-0162144, filed with the Korean Patent Office on November 23, 2021, the entire contents of which are incorporated herein by reference.

[0003] This disclosure relates to a method for manufacturing a curved secondary battery. Background Technology

[0004] With the development of technology and increasing demand for mobile devices, the demand for secondary batteries as an energy source is growing rapidly. Among these secondary batteries, lithium secondary batteries, which exhibit high energy density and operating voltage, long cycle life and low self-discharge rate, have been commercialized and are widely used.

[0005] As examples, due to the characteristics of battery shape, there is a high demand for prismatic and pouch-shaped secondary batteries that are thin and suitable for use in products such as mobile phones. Furthermore, due to the characteristics of the materials used, there is a high demand for lithium secondary batteries such as lithium-ion batteries and lithium-ion polymer batteries that possess high energy density, discharge voltage, and output stability.

[0006] Based on consumer preferences, these rechargeable batteries in electronic devices tend to become increasingly smaller and thinner. Consequently, to minimize unnecessary space waste, the battery shape also needs to be miniaturized and thinner. Therefore, rechargeable batteries need to have a variety of shapes that fit the shape of the device, while also making efficient use of the device's internal space.

[0007] Specifically, in recent years, device design itself has played a crucial role in consumers' product choices. Therefore, various design forms have been developed to replace flat designs that consider factors such as productivity. For example, for ergonomic purposes, devices such as mobile phones and laptops can be designed with specified curved shapes.

[0008] In this context, various designs with curved outer surfaces have been developed and put into practical application. Correspondingly, curved secondary batteries with curved surfaces are currently under active development.

[0009] Currently, in order to form curved surfaces in secondary batteries, a technique is used to deform the shape of the secondary battery by means of external force while the electrode assembly and electrolyte are housed together in the battery casing and placed in a hot press fixture or the like.

[0010] The flowchart of this type of process is shown in Figure 1 middle.

[0011] Reference Figure 1 First, a first activation (S11) is performed on the secondary battery in which the electrode assembly and electrolyte are housed together in the battery casing. Then, a degassing step is performed to remove the gas generated in the first activation step (S12).

[0012] Then, in order to manufacture a curved secondary battery, a hot pressing step is performed to have a target radius of curvature (S13).

[0013] After that, a second activation is performed to check the capacity of the secondary battery and transport it for charging (S14), a quality check is performed, and then the battery is transported.

[0014] However, there is a problem that the target radius of curvature changes during the second activation step due to springback that occurs immediately after hot pressing, and it is difficult to achieve the target radius of curvature in the final product after activations such as capacity verification for shipping, activation shipping charging, and the like.

[0015] Therefore, there is an urgent need to develop technologies for manufacturing methods of flexible secondary batteries that can solve these problems. Summary of the Invention

[0016] The problem the invention aims to solve

[0017] The purpose of this disclosure is to provide a method for manufacturing a curved secondary battery that maintains a radius of curvature nearly identical to a target radius of curvature even after capacity verification for transport and activation such as transport charging.

[0018] Problem Solving Methods

[0019] According to one embodiment of this disclosure, a method for manufacturing a curved secondary battery having a target radius of curvature is provided, the method comprising the following steps:

[0020] (a) Containing an electrode assembly comprising a cathode, an anode, and a separator inserted between the cathode and the anode, together with an electrolyte, in a battery casing to manufacture a secondary battery.

[0021] (b) The secondary battery is first activated and then degassed.

[0022] (c) The degassed secondary battery is subjected to a first hot pressing to have a first radius of curvature.

[0023] (d) The secondary battery that has undergone the first hot-pressing step is then subjected to a second activation, and

[0024] (e) The secondary battery that has been second activated is subjected to a second hot pressing to have a second radius of curvature.

[0025] In one specific implementation, the first activation in step (b) may include charging and discharging processes, and specifically, the charging and discharging may be performed two or more times, respectively.

[0026] In one specific implementation, the first hot pressing in step (c) can be performed so that the first radius of curvature is equal to the target radius of curvature. The first hot pressing in step (c) can be performed at 70°C to 90°C, and the first hot pressing in step (c) can be performed by applying pressure to the secondary battery for 1 to 10 seconds using a hot pressing fixture.

[0027] In one specific implementation, the second activation in step (d) may include a first charging, a first discharging, and a second charging process.

[0028] In one specific implementation, the second hot pressing in step (e) can be performed such that the second radius of curvature is 2% to 8% smaller than the target radius of curvature. The second hot pressing in step (e) can be performed at 70°C to 90°C. The second hot pressing in step (e) can be performed by applying pressure to the secondary battery for 1 to 10 seconds using a hot pressing fixture.

[0029] Furthermore, the method for manufacturing a curved battery may further include (f) cooling the secondary battery after the second hot-pressing step.

[0030] At this point, during the cooling step, the surface of the secondary battery can be partially restored to have the target radius of curvature. Attached Figure Description

[0031] Figure 1 A flowchart illustrating a method for manufacturing a curved secondary battery according to existing technology.

[0032] Figure 2 This is a flowchart illustrating a method for manufacturing a secondary battery having a curved shape according to an embodiment of the present disclosure.

[0033] Figure 3 An experimental example 1 based on the present disclosure shows a graph of the radius of curvature after the first hot pressing according to Example 1.

[0034] Figure 4 A graph showing the radius of curvature of the final secondary battery according to Example 1 is provided for Experimental Example 1 of this disclosure.

[0035] Figure 5 To illustrate the curve of the radius of curvature after the first hot pressing according to Comparative Example 1 in Experimental Example 1 of this disclosure.

[0036] Figure 6 To illustrate the curve of the radius of curvature of the final secondary battery according to Comparative Example 1 in Experimental Example 1 of this disclosure. Detailed Implementation

[0037] The terms and vocabulary used in this specification and claims should not be construed as limited to their common or dictionary meanings, but rather as meanings and concepts used by the inventors to best describe the invention, based on the principle of appropriately defining terms and concepts and conforming to the technical concept of the invention. Therefore, the embodiments described in this specification and the configurations shown in the accompanying drawings are merely the most preferred embodiments of the invention and do not represent the entirety of the technical concept of the invention. Furthermore, those skilled in the art will recognize that various equivalent substitutions and modifications may exist to replace the above embodiments and configurations at the time of filing this application, and the invention is not limited to the embodiments described below.

[0038] The present invention will now be described in detail with reference to the accompanying drawings. The terms and vocabulary used in this specification and claims should not be construed as limited to their common or dictionary meanings, but rather as meanings and concepts used by the inventors in order to best describe the invention, based on the principle that terms and concepts can be appropriately defined and consistent with the technical concept of the invention.

[0039] Furthermore, the embodiments described in this specification and the configurations shown in the accompanying drawings are merely the most preferred embodiments of the present invention and do not represent the entirety of the technical concept of the present invention. Moreover, those skilled in the art will recognize that various equivalent substitutions and modifications may exist to replace the above-described embodiments and configurations at the time of submission of this application.

[0040] According to one embodiment of this disclosure, a method for manufacturing a curved secondary battery having a target radius of curvature is provided, the method comprising the following steps:

[0041] (a) Containing an electrode assembly comprising a cathode, an anode, and a separator inserted between the cathode and the anode, together with an electrolyte, in a battery casing to manufacture a secondary battery.

[0042] (b) The secondary battery is first activated and then degassed.

[0043] (c) The degassed secondary battery is subjected to a first hot pressing to have a first radius of curvature.

[0044] (d) The secondary battery that has undergone the first hot-pressing step is then subjected to a second activation, and

[0045] (e) The secondary battery that has been second activated is subjected to a second hot pressing to have a second radius of curvature.

[0046] In step (a), the electrode assembly is manufactured by stacking a cathode, an anode, and a separator.

[0047] Here, the cathode is manufactured by applying a cathode slurry containing cathode active material, conductive material and binder to a cathode current collector, followed by drying and rolling.

[0048] There are no particular limitations on the cathode current collector, as long as it has high conductivity and does not cause chemical changes to the corresponding battery. For example, materials such as stainless steel, aluminum, nickel, titanium, sintered carbon, and aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., can be used. Furthermore, the thickness of the cathode current collector is typically from 3 μm to 500 μm, and it can have fine random structures formed on its surface to improve the bonding strength with the cathode active material. For example, it can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven structures.

[0049] Cathode active materials may include layered compounds such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or compounds substituted with one or more of these transition metals; such as those with the chemical formula Li 1+x Mn 2-x Lithium manganese oxides such as O4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxides (Li2CuO2); vanadium oxides such as LiV3O8, LiFe3O4, V2O5, and Cu2V2O7; and LiNi 1-x M x Ni-site type lithium nickel oxide represented by O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, x = 0.01 to 0.3); chemical formula LiMn 2-x M x Lithium manganese composite oxides represented by O2 (where M = Co, Ni, Fe, Cr, Zn or Ta, x = 0.01 to 0.1) or Li2Mn3MO8 (where M = Fe, Co, Ni, Cu or Zn); LiMn2O4 with the Li part of the chemical formula replaced by alkaline earth metal ions; disulfide compounds; and Fe2(MoO4)3; and similar, but not limited thereto.

[0050] Conductive materials are used to impart conductivity to the electrodes, and there are no particular restrictions on the use of conductive materials, as long as they are electronically conductive and do not cause chemical changes in the battery in which they are formed. Specific examples include carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fibers; graphite such as natural graphite and artificial graphite; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and any single one or mixtures of two or more of them may be used. Based on the total weight of the cathode material, the conductive material may be included in an amount from 1% to 30% by weight, specifically from 1% to 10% by weight, and more specifically from 1% to 5% by weight.

[0051] The adhesive serves to improve the adhesion between cathode active material particles and the adhesion between the cathode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), PVDF-co-HFP copolymer, polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any single one or mixtures of two or more thereof may be used. Based on the total weight of the cathode material, the adhesive may be included in an amount from 1% to 30% by weight, specifically from 1% to 10% by weight, and more specifically from 1% to 5% by weight.

[0052] The anode is manufactured by applying an anode slurry containing an anode active material, a conductive material and a binder to an anode current collector, followed by drying and rolling.

[0053] There are no particular limitations on the anode current collector, as long as it has high conductivity and does not cause chemical changes to the corresponding battery. For example, materials such as copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloys, and the like can be used. Furthermore, the thickness of the anode current collector is typically from 3 μm to 500 μm, and similar to the cathode current collector, the anode current collector can have fine random structures formed on its surface to improve the bonding strength with the anode active material. For example, it can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven structures.

[0054] As the anode active material, compounds capable of reversible intercalation and deintercalation can be used. Specific examples of the anode active material may include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fibers or amorphous carbon; metal compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; such as SiO x (0<x<2), metal oxides capable of doping and dedoping lithium such as SnO₂, vanadium oxides, and lithium vanadium oxides; composites containing a metal compound and a carbonaceous material such as Si-C composites or Sn-C composites, and any one of them alone or a mixture of two or more thereof may be used. In addition, metallic lithium thin films may be used as the anode active material. Further, the carbonaceous material may be both low-crystalline carbon and high-crystalline carbon. Soft carbon and hard carbon are typical low-crystalline carbons. Typical examples of high-crystalline carbon include amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, high-temperature sintered carbon such as mesophase pitches and petroleum or coaltar pitch derived cokes.

[0055] The separator separates the anode and the cathode from each other and provides a passage for the movement of lithium ions. The separator can be used without particular limitation as long as it is used as a separator in typical lithium secondary batteries. In particular, the separator is preferably having low resistance to ion migration of the electrolyte and excellent ability to impregnate the electrolyte. Specifically, the separator may be a porous polymer membrane, for example, a porous polymer membrane made of polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof. Further, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of glass fiber with a high melting point, polyethylene terephthalate fiber, or the like can be used. In addition, in order to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer material can be used, and can be selectively used as a single-layer or multi-layer structure.

[0056] After the electrode assembly manufactured as described above is housed in a battery case together with the electrolyte and sealed, a curved secondary battery in a flat state is manufactured without going through a forming process.

[0057] Examples of electrolytes used in this disclosure may include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, or the like that can be used in the production of lithium secondary batteries.

[0058] Specifically, electrolytes can contain organic solvents and lithium salts.

[0059] Organic solvents can be used without any particular restrictions, as long as they serve as a medium for the migration of ions involved in the electrochemical reactions of the battery. Specific examples of organic solvents include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, or ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene or fluorobenzene; and solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methylethyl carbonate (MEC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), or propylene carbonate. Carbonate-based solvents such as carbonate (PC); alcohol-based solvents such as ethanol or isopropanol; nitriles such as R-CN (wherein R is a straight-chain, branched, or cyclic hydrocarbon group with 2 to 20 carbon atoms, and may contain double bonds, aromatic rings, or ether bonds); amides such as dimethylformamide; dioxolane such as 1,3-dioxolane; sulfolane; or the like. Among these, carbonate-based solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate, propylene carbonate, etc.) with high ionic conductivity and high dielectric constant and straight-chain carbonate compounds with low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, or the like) are more preferred, as they can improve the charge / discharge performance of the battery. In this case, when cyclic carbonates and chain carbonates are mixed in a volume ratio of about 1:1 to about 1:9, excellent electrolyte performance can be exhibited.

[0060] Lithium salts can be used without any particular restrictions, as long as they are compounds capable of providing lithium ions for use in lithium-ion secondary batteries. Specific examples of lithium salts include LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of lithium salts can be used in the range of 0.1M to 2.0M. When the concentration of lithium salts is within this range, the electrolyte exhibits suitable conductivity and viscosity, thus demonstrating excellent electrolyte performance and efficient lithium ion migration.

[0061] In addition to the electrolyte components mentioned above, to improve battery life characteristics, suppress battery capacity decline, and improve battery discharge capacity, the electrolyte may further include, for example, at least one additive, such as compounds like alkyl halogenated carbonates such as difluoroethylene carbonate; pyridine; triethyl phosphite; triethanolamine; cyclic ethers; ethylenediamine; n-ethylene glycol dimethyl ether (glyme); hexaphosphoric triamide; nitrobenzene derivatives; sulfur; quinone imine dyes; N-substituted oxazolidinones; N,N-substituted imidazolidinyl ethers; ethylene glycol dialkyl ethers; ammonium salts; pyrrole; 2-methoxyethanol; and aluminum trichloride. In this case, the additive may be included in an amount from 0.1% to 5% by weight, based on the total weight of the electrolyte.

[0062] Then, in order to manufacture a curved secondary battery, the battery casing can be a pouch-shaped battery casing.

[0063] As an example, the bag can consist of a three-layer structure consisting of an insulating layer, a metal layer, and an insulating layer. For example, the metal layer can be formed of aluminum, steel, stainless steel, and the like, and the insulating layer can be formed of modified polypropylene (CPP), polyethylene terephthalate (PET), nylon, and the like, but is not limited thereto.

[0064] The secondary batteries manufactured in this way then undergo a process for transportation, and a hot-pressing step is performed to give the secondary batteries a curved shape in the middle.

[0065] The flowchart for this process is shown below. Figure 2 middle.

[0066] Next, we will refer to Figure 2 A method for manufacturing a curved secondary battery according to the present disclosure is described in detail.

[0067] First, the manufactured secondary battery is activated for the first time (S110).

[0068] The first activation step is to perform charging and discharging processes to activate the internal components of the secondary battery.

[0069] In the activation step, charging and discharging can be performed once or multiple times, specifically two or more times.

[0070] More specifically, the manufactured secondary batteries are aged at room temperature for 2 to 5 days, charged to full capacity (SOC 40% to 65%), aged again at room temperature for 2 to 5 days, fully charged to 100% SOC, and then discharged to SOC 40% to 65%.

[0071] Then, a degassing step (S120) is performed to discharge the gas generated in the activation step to the outside of the secondary battery.

[0072] The degassing step can be performed by partially unsealing the sealed secondary battery. After that, it can be resealed to prevent electrolyte leakage.

[0073] After that, the first hot press is performed in the same manner as in the prior art (S130).

[0074] The first hot pressing is a step of applying pressure to a flat secondary cell so that the flat secondary cell has a first radius of curvature, thereby having a curved shape.

[0075] Here, the radius of curvature is expressed as the radius of the circle having that circumference when the curved shape of the secondary battery occupies a portion of the circumference.

[0076] In this case, the first radius of curvature can be equal to the target radius of curvature.

[0077] The target radius of curvature can be appropriately selected according to the requirements of this secondary battery device, but is not limited thereto. However, if the target radius of curvature is too small, it may lead to safety issues with the secondary battery, and therefore it should be selected within a range that does not cause such problems.

[0078] Therefore, the first radius of curvature can also be equal to the target radius of curvature.

[0079] This first hot press can be formed by mounting a flat secondary battery in a hot press fixture to have a first radius of curvature and then pressing it.

[0080] At this point, it can be performed by applying pressure to the secondary battery for 1 to 10 seconds using a hot press clamp.

[0081] If the secondary battery is pressurized for too short a time outside the above range, it will be difficult for it to bend sufficiently to achieve the first radius of curvature. If the secondary battery is pressurized for too long, the stress applied to the secondary battery will increase, which will have an adverse effect on the component or the like and is not preferred.

[0082] Pressure can also be appropriately selected while minimizing its impact on secondary battery components, taking into account the applied stress, wrinkling, or similar factors. Specifically, 16 kgf / cm² can be applied. 2 Up to 28 kgf / cm 2 More specifically, 18 kgf / cm 2 Up to 24 kgf / cm 2 The pressure.

[0083] Furthermore, the first hot pressing can apply heat while applying pressure to promote shape deformation. Specifically, it can be performed at 70°C to 90°C, and more specifically, 75°C to 85°C.

[0084] If heat is applied at excessively high temperatures beyond the above range, the component may deform, which is not preferred. If heat is applied at low temperatures, the effect resulting from the applied heat may not be sufficient, which is also not preferred.

[0085] Here, temperature refers to the temperature of the hot press fixture used to perform the hot press.

[0086] After the first hot pressing, the second activation step (S140) is performed.

[0087] Unlike the first activation step, a second activation step can be performed to confirm the actual discharge capacity of the secondary battery and to partially charge it for shipping purposes.

[0088] Therefore, the second activation may include a first charging, a first discharging, and a second charging process.

[0089] Specifically, the second activation can perform charging and discharging once or multiple times, or two or more times, but can be performed until the secondary battery is finally charged, because the number of charging times is one more than the number of discharging times.

[0090] However, at this point, the final charge can be either a full charge or a partial charge. Specifically, for shipping purposes, the final charge can be between 20% and 80%, or more specifically, between 30% and 50%.

[0091] Normally, shipping is carried out immediately after that, but according to this disclosure, a second hot pressing (S150) is performed after the second activation.

[0092] After the second activation, the radius of curvature of the secondary battery changes more significantly. Therefore, the original target radius of curvature is not met and may even exceed the target radius of curvature, causing problems. However, according to this disclosure, a second hot pressing is performed after the second activation, thereby enabling manufacturing within a range that further satisfies the target radius of curvature.

[0093] At this point, a second hot pressing can be performed so that the secondary battery has a second radius of curvature, and specifically, the second radius of curvature can be 2% to 8% smaller than the target radius of curvature.

[0094] Typically, springback occurs immediately after hot pressing. Therefore, in order to ultimately meet the target radius of curvature, a second hot pressing can be performed to achieve a second radius of curvature smaller than the target radius of curvature, taking into account the springback phenomenon.

[0095] At this point, taking into account the degree of springback, the second radius of curvature can be 2% to 8% smaller than the target radius of curvature, and more specifically, it can be 4% to 6% smaller, or more specifically, about 5% smaller.

[0096] If the second radius of curvature decreases by more than 8% outside the above range, it may be too small compared to the target radius of curvature. Conversely, if the second radius of curvature decreases by less than 2%, it may be larger than the target radius of curvature, which is not preferred. Therefore, in order to have a range closest to the target radius of curvature after the springback phenomenon, the second radius of curvature can be relatively small to satisfy the above range.

[0097] Similar to the first hot press, the second hot press can also be formed by mounting a flat secondary cell in a hot press fixture to have a second radius of curvature and then pressing it.

[0098] At this point, since the second hot press should also have a smaller radius of curvature than the first hot press, the curvature of the hot press fixture can have a second curvature.

[0099] Specifically, the second hot pressing can be performed by applying pressure to the secondary battery for 1 to 10 seconds using a clamp.

[0100] If the secondary battery is pressurized for too short a time outside the above range, it will be difficult for the secondary battery to bend sufficiently to have a second radius of curvature. If the secondary battery is pressurized for too long, it can have an adverse effect on the secondary battery, which is not preferred.

[0101] Similar to the first hot pressing, the pressure can also be appropriately selected while minimizing the impact on the secondary battery components, taking into account the applied stress, wrinkling, or similar factors. However, it can be performed at a relatively higher pressure to meet the second radius of curvature. Specifically, 16 kgf / cm² can be applied. 2 Up to 28 kgf / cm 2More specifically, 18 kgf / cm 2 Up to 24 kgf / cm 2 The pressure.

[0102] In addition, the first hot pressing can apply heat while pressurizing to further promote shape deformation, and specifically, it can be performed at 70°C to 90°C, specifically 75°C to 85°C.

[0103] If heat is applied at excessively high temperatures beyond the above range, the component may deform, which is not preferred. If heat is applied at low temperatures, sufficient effect from the applied heat may not be obtained, which is also not preferred.

[0104] Here, temperature refers to the temperature of the hot press fixture used to perform the hot press.

[0105] Meanwhile, the method for manufacturing a bent secondary battery according to this disclosure includes a step (f) of cooling the secondary battery after the second hot pressing step.

[0106] During this cooling process, the surface of the secondary battery can be partially restored to have the target radius of curvature.

[0107] That is, since springback occurs immediately after the second hot pressing, these second hot presses will have a quadratic curvature smaller than the target radius of curvature, thereby eliminating this problem.

[0108] Therefore, when the second hot pressing is performed in this manner, the secondary battery according to this disclosure can achieve the desired radius of curvature almost identically.

[0109] Following that, performance testing and shipping of the secondary batteries for transport purposes were carried out, details of which are omitted here.

[0110] The present disclosure will now be described in more detail with reference to embodiments. These embodiments are intended to be illustrative and are not intended to limit the scope of the invention in any way.

[0111] <Example 1>

[0112] Manufacturing of flat secondary batteries

[0113] A cathode active material composition slurry was prepared by dispersing LiCoO2 powder (manufactured by Umicore Corporation) with an average particle size of 5 μm, carbon black as a conductive material, and polyvinylidene fluoride as a binder in an N-methylpyrrolidone solvent at a weight ratio of 96:2:2. The cathode active material composition slurry was applied to an aluminum foil to a thickness of approximately 166 μm using a doctor blade (slit: 170 mm), heat-treated in a vacuum at 130°C for 5 hours, and then dried. The aluminum foil with the cathode active material composition slurry applied was then rolled using a roller press to manufacture a cathode with a cathode active material layer formed.

[0114] Artificial graphite, carbon black as a conductive material, carboxymethyl cellulose as a thickener, and styrene-butadiene rubber as a binder were dispersed in an aqueous solvent at a weight ratio of 94:1:2:3, and then mixed to prepare an anodic active material composition slurry. The anodic active material composition slurry was applied to a copper foil with a thickness of approximately 225 μm using a doctor blade (slit: 160 mm), heat-treated in a vacuum oven at 130°C for 5 hours, and then dried. The copper foil coated with the anodic active material composition slurry was then rolled using a roller press to manufacture an anode with an anodic active material layer.

[0115] The electrode assembly is prepared using polyethylene as a separator, then sealed in a bag, and an electrolyte containing 1.2 M LiPF6 dissolved in a solvent with an EC:PC:PP weight ratio of 3:1:6 is injected into the bag to manufacture a secondary battery.

[0116] First hot pressing and degassing

[0117] The secondary battery was tested at 60°C, constant current (CC), and 0.5 kgf / cm². 2 Under these conditions, pressure was applied and charged at 0.2C until SOC reached 1%, at 0.5 kgf / cm². 2 Apply pressure and charge at 2.0C until the SOC reaches 17%, then charge at 5 kgf / cm². 2 Apply pressure and charge at 2.0C until SOC reaches 49%, then charge at 5 kgf / cm². 2 The system is pressurized and charged at 1.5C until the SOC reaches 65% mAh. It is then aged for 72 hours at room temperature, fully charged again at room temperature and constant current / constant voltage (CC / CV) (4.4V / 0.7C, 0.05C cutoff), fully discharged at constant current (CC) (0.7C, 3V, cutoff), and then recharged at 0.7C until the SOC reaches 66%. The airbag is degassed by puncturing it and then sealed to remove the airbag.

[0118] First hot pressing

[0119] The degassed secondary battery is installed in a hot-pressing fixture with a curvature radius of R95mm inside the battery, at a pressure of 22kgf / cm. 2 Apply pressure for 3 seconds and set the temperature of the fixture to 80℃.

[0120] Second activation

[0121] The secondary battery that has completed the first hot pressing is fully charged (4.4V / 0.7C, 0.05C, cutoff) at 25°C and constant current (CC / CV), and fully discharged (0.7C, cutoff voltage 3V) at 25°C and constant current (CC). Then it is recharged at 0.5C, 50% SOC, and constant current (CC).

[0122] Second hot pressing

[0123] The rechargeable battery, which has undergone secondary activation, is installed in a thermoforming fixture with a curvature radius of R90mm inside the battery, at a pressure of 22 kgf / cm². 2 The pressure is applied for 5 seconds, and the temperature of the fixture is set to 80°C. Then, the secondary battery is cooled at room temperature to complete the manufacturing of the secondary battery.

[0124] <Comparative Example 1>

[0125] Except for the second hot-pressing step in Example 1, the secondary battery is manufactured in the same manner as in Example 1.

[0126] <Experimental Example 1>

[0127] During the manufacturing process of the secondary battery as described in Example 1 and Comparative Example 1, the curvature of the finally manufactured secondary battery, i.e., the radius of curvature of the secondary battery, was measured after the first hot-pressing step. The results are shown below. Figures 3 to 6 middle.

[0128] For the measurement of the radius of curvature, the curved surface of the cell was scanned with a 3D scanner, and then a circle was drawn with three points as reference, and the radius of the circle was measured.

[0129] Refer to the following Figures 3 to 6 After the first hot pressing, they have similar radii of curvature, but in the case of the manufacturing method according to the present disclosure, the final manufactured secondary battery has a radii of curvature that is almost the same as the target radii of curvature R95mm, while the final secondary battery according to Comparative Example 1 has a radii of curvature that is larger than the target radii of curvature.

[0130] Although exemplary embodiments of the present disclosure have been disclosed for illustrative purposes, those skilled in the art will understand that various modifications, additions, and substitutions may be made without departing from the scope and spirit of the invention as disclosed in the appended claims.

[0131] Industrial applicability

[0132] In the method for manufacturing a bent secondary battery according to this disclosure, after the first activation step, not only is a first hot pressing performed, but also a second hot pressing is performed after the second activation step for the purpose of capacity confirmation and charging. During the second hot pressing, the battery is hot-pressed to have a radius of curvature smaller than the target radius of curvature, thereby compensating for the springback phenomenon that occurs in the second activation step due to the change in the radius of curvature of the secondary battery. Thus, a secondary battery that satisfies the target radius of curvature can be manufactured.

Claims

1. A method for manufacturing a curved secondary battery having a target radius of curvature, the method comprising the following steps: (a) Containing an electrode assembly comprising a cathode, an anode, and a separator inserted between the cathode and the anode, together with an electrolyte, in a battery casing to manufacture a secondary battery. (b) The secondary battery is first activated and degassed. (c) The degassed secondary battery is subjected to a first hot pressing to have a first radius of curvature. (d) The secondary battery after the first hot-pressing step is subjected to a second activation, and (e) The secondary battery, after the second activation, is subjected to a second hot pressing to obtain a second radius of curvature. In step (c), the first hot pressing is performed so that the first radius of curvature is equal to the target radius of curvature, and In step (e), the second hot pressing is performed so that the second radius of curvature is 2% to 8% smaller than the target radius of curvature.

2. The method according to claim 1, wherein: The first activation in step (b) includes a charging process and a discharging process.

3. The method according to claim 2, wherein: The charging process and the discharging process are each performed two or more times.

4. The method according to claim 1, wherein: The first hot pressing in step (c) is performed at 70°C to 90°C.

5. The method according to claim 1, wherein: The first hot pressing in step (c) is performed by applying pressure to the secondary battery for 1 to 10 seconds using a hot pressing fixture.

6. The method according to claim 1, wherein: The second activation in step (d) includes a first charging, a first discharging, and a second charging process.

7. The method according to claim 1, wherein: The second hot pressing in step (e) is performed at 70°C to 90°C.

8. The method according to claim 1, wherein: The second hot pressing in step (e) is performed by applying pressure to the secondary battery for 1 to 10 seconds using a hot pressing clamp.

9. The method according to claim 1, wherein: The method further includes (f) cooling the secondary battery after the second hot-pressing step.

10. The method according to claim 9, wherein: During the cooling step, the surface of the secondary battery is partially restored to have the target radius of curvature.

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