Method for manufacturing dry electrode for secondary battery

Abstract

To provide a dry electrode for a secondary battery, a method for manufacturing the same, and a secondary battery including the same.SOLUTION: A method for manufacturing a dry electrode according to an embodiment of the present invention includes the steps of: (S1) obtaining a first electrode powder from a mixture containing an active material and a binder; (S2) kneading the first electrode powder and a reuse electrode powder to obtain a mixture mass; (S3) pulverizing the mixture mass to obtain a second electrode powder; (S4) calendaring the second electrode powder to obtain an electrode film; and (S5) positioning and laminating the electrode film on at least one surface of a current collector.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present application relates to a dry electrode and a secondary battery including the same.

[0002] This application claims priority based on Korean Patent Application No. 2022-0049195, filed on April 20, 2022, the entire contents of which are incorporated herein by reference in their entirety in the specification and drawings thereof. [Background technology]

[0003] The rapid increase in the use of fossil fuels has led to an increasing demand for alternative and clean energy sources, and one of the most actively researched areas of this is the field of electrochemical power generation and storage.

[0004] Currently, a typical example of an electrochemical element that uses such electrochemical energy is a secondary battery, and the fields in which it is used are gradually expanding.

[0005] Lithium secondary batteries, a typical example of such secondary batteries, are not only used as an energy source for mobile devices, but are also increasingly being used as a power source for electric vehicles and hybrid electric vehicles that can replace vehicles that use fossil fuels such as gasoline and diesel vehicles, which are one of the main causes of air pollution. Their use is also expanding to include auxiliary power sources for grid-connected vehicles.

[0006] The manufacturing process of such a lithium secondary battery can be roughly divided into three steps: electrode process, assembly process, and chemical formation process. The electrode process can be further divided into active material mixing process, electrode coating process, drying process, rolling process, slitting process, and winding process.

[0007] Among these, the active material mixing process is a process of mixing coating materials to form an electrode active layer where an electrochemical reaction actually occurs in the electrode. More specifically, the active material, which is an essential element of the electrode, other additives such as conductive materials and fillers, binders for binding the powder particles together and adhering them to the current collector, and solvents for imparting viscosity and dispersing the powder, are mixed together to produce a fluid slurry.

[0008] The composition mixed to form the electrode active layer is also broadly called an electrode mixture.

[0009] This is followed by an electrode coating process in which the electrode mixture is coated onto an electrically conductive current collector, and a drying process in which the solvent contained in the electrode mixture is removed. The electrode is then rolled to a predetermined thickness.

[0010] Meanwhile, evaporation of the solvent contained in the electrode mixture during the drying process may cause defects such as pinholes and cracks in the already formed electrode active layer. Furthermore, since the inside and outside of the active layer are not dried uniformly, a powder floating phenomenon may occur due to differences in the evaporation rate of the solvent, i.e., powder in the first dried area may float up and form gaps with the later dried area, resulting in a deterioration in electrode quality.

[0011] Therefore, recently, much research has been conducted into the production of dry electrodes without using solvents.

[0012] Dry electrodes are typically manufactured by laminating a free-standing film containing an active material, binder, conductive material, etc., onto a current collector. To fiberize the binder, a high-shear mixing process, such as jet milling, is performed. However, applying such a high-shear mixing process to a fragile active material can result in the generation of a large amount of fine powder, potentially reducing mechanical and electrochemical properties. Excessive high-shear mixing can also sever the resulting binder fibers, reducing the flexibility of the free-standing film. Furthermore, the jet milling process can cause problems, such as components adhering to the interior of the equipment and obstructing the flow of high-pressure air, clogging the flow passages, making mass production difficult. Therefore, technological development is ongoing to address these issues and produce dry electrodes.

[0013] Meanwhile, in the manufacturing process of freestanding films for dry electrodes, problems of loss due to defective products and loss due to edge slitting continue to occur. To solve these problems, research and development of technologies to reuse these lost portions during electrode film manufacturing is being conducted. However, when reused portions are used, other problems have been reported, such as a decrease in the appearance quality of the electrode film and a decrease in the mechanical properties of the film.

[0014] This has created an urgent need for the development of a manufacturing technology for freestanding films that can reuse these lost portions while improving the quality of the electrode film. Summary of the Invention [Problem to be solved by the invention]

[0015] Therefore, an object of the present invention is to provide a method for manufacturing a dry electrode that minimizes loss of raw materials by reusing defective products and slitting on edges that occur during the manufacturing process of a free-standing film for manufacturing a dry electrode.

[0016] Another object of the present invention is to provide a method for producing a dry electrode that is excellent in appearance quality and mechanical performance while using recycled raw materials. [Means for solving the problem]

[0017] In order to solve the above problems, according to one aspect of the present invention, there is provided a method for manufacturing a dry electrode according to the following embodiment.

[0018] According to a first embodiment, there is provided a method for manufacturing a dry electrode, comprising: (S1) obtaining a powder for a first electrode from a mixture containing an active material and a binder; (S2) kneading the powder for the first electrode and the powder for a reused electrode to obtain a mixture mass; (S3) pulverizing the mixture mass to obtain a powder for a second electrode; (S4) calendaring the powder for the second electrode to obtain an electrode film; and (S5) positioning the electrode film on at least one surface of a current collector and laminating it.

[0019] According to the second embodiment, in the first embodiment, the powder for the reusable electrode may be obtained by pulverizing a defective film or a cut film generated in a process for obtaining an electrode film in a method for manufacturing a dry electrode.

[0020] According to the third embodiment, in the first or second embodiment, the reusable electrode powder may be obtained by pulverizing an electrode film obtained from a first electrode powder through the following steps: (S1-1) kneading the first electrode powder to obtain a mixture mass, (S1-2) pulverizing the mixture mass to obtain an electrode powder, and (S1-3) calendaring the electrode powder to obtain an electrode film.

[0021] According to a fourth embodiment, in any of the first to third embodiments, the step (S4) further includes an edge slitting step of edge slitting a spare electrode film obtained by calendaring the powder for the second electrode to obtain an electrode film, and the steps (S1) to (S4) are repeated n times (where n is an integer of 2 or more), and the powder for the reused electrode used in the nth step (S2) may be obtained by pulverizing the spare electrode film cut in the edge slitting steps of the 1st to (n-1)th steps (S4).

[0022] According to a fifth embodiment, in any of the first to fourth embodiments, the step (S2) may further include a step of mixing the first electrode powder and the reuse electrode powder before the kneading to obtain an electrode powder mixture, and kneading the obtained electrode powder mixture to obtain a mixture mass.

[0023] According to the sixth embodiment, in any of the first to fifth embodiments, in the step (S2), the weight of the powder for the first electrode may be 30% by weight or more, based on a total of 100% by weight of the powder for the first electrode and the powder for the reuse electrode.

[0024] According to a seventh embodiment, in any of the first to sixth embodiments, in the step (S2), the weight ratio of the first electrode powder to the reuse electrode powder may be 30:70 to 99:1.

[0025] According to an eighth embodiment, in any one of the first to seventh embodiments, the first electrode powder may be a mixture obtained by a step of obtaining a mixture containing the active material and a binder.

[0026] According to a ninth embodiment, in any of the first to eighth embodiments, the kneading in the step (S2) can be carried out at a temperature of 70° C. to 200° C. and under a pressure equal to or higher than atmospheric pressure.

[0027] According to a tenth embodiment, in any of the first to ninth embodiments, the kneading in the step (S2) can be carried out at a shear rate of 10 / s to 500 / s for 1 minute to 30 minutes.

[0028] According to the eleventh embodiment, in any of the first to tenth embodiments, after the step (S3) and before the calendaring process of the step (S4), a step of classifying the pulverized powder for the second electrode can be further included.

[0029] According to another aspect of the present invention, there is provided a dry electrode having the following embodiments.

[0030] The dry electrode according to the twelfth embodiment includes an electrode current collector and an electrode film located on the electrode current collector and including an active material and a binder, and may be manufactured by the manufacturing method according to any one of the first to eleventh embodiments.

[0031] According to still another aspect of the present invention, there is provided a secondary battery having the following embodiment.

[0032] The secondary battery according to the thirteenth embodiment is a secondary battery in which an electrode assembly including a positive electrode, a negative electrode, and a separator is housed in a battery case together with a lithium-containing nonaqueous electrolyte, and at least one of the positive electrode and the negative electrode may be the dry electrode according to the twelfth embodiment.

[0033] According to still another aspect of the present invention, there is provided an energy storage device having the following embodiments.

[0034] The energy storage device according to the fourteenth embodiment may include the secondary battery according to the thirteenth embodiment as a unit battery. [Effects of the Invention]

[0035] According to the present invention, the loss rate of raw materials during the production of free-standing electrode films for dry electrodes can be reduced.

[0036] Furthermore, it is possible to provide a dry electrode that is excellent in appearance quality and mechanical properties.

[0037] 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 concepts of the present invention. Therefore, the present invention should not be interpreted as being limited to the matters described in the drawings. [Brief explanation of the drawings]

[0038] [Figure 1] 1A-1C are schematic diagrams illustrating a process for the fabrication of a conventional free-standing electrode film. [Figure 2] 1A to 1C are schematic diagrams illustrating a procedure for manufacturing a dry electrode according to an embodiment of the present invention. [Figure 3] Photographs of the appearance of the electrode films of Example 1 (left) and Comparative Example 2 (right) in the present specification. DETAILED DESCRIPTION OF THE INVENTION

[0039] The present invention will be described in detail below.

[0040] Throughout this specification, the phrase "A and / or B" means "either A or B, or both."

[0041] The present application relates to a method for manufacturing an electrode including a free-standing dry electrode film, and an electrode for an electrochemical device obtained by the method. The electrochemical device includes all devices that perform electrochemical reactions, and specific examples include all types of primary and secondary batteries, fuel cells, solar cells, and capacitors such as supercapacitors. The secondary battery includes a lithium-ion secondary battery in which lithium ions act as ion conductors.

[0042] A method for manufacturing a dry electrode according to one embodiment of the present invention includes: (S1) obtaining a first electrode powder from a mixture containing an active material and a binder; (S2) kneading the first electrode powder and the reuse electrode powder to obtain a mixture mass; (S3) pulverizing the mixture mass to obtain a second electrode powder; (S4) calendaring the second electrode powder to obtain an electrode film; and (S5) positioning the electrode film on at least one surface of a current collector and laminating it.

[0043] FIG. 2 is a schematic diagram illustrating a method for manufacturing a dry electrode according to one embodiment of the present invention.

[0044] Referring to FIG. 2, according to the present invention, a powder for a first electrode is obtained from a mixture containing an active material, a binder, and optionally a conductive material. The powder for the first electrode and the powder for a reused electrode are kneaded to obtain a mixture mass, which is then pulverized and calendered to obtain an electrode film.

[0045] According to one embodiment of the present invention, the powder for reused electrodes may be obtained by pulverizing defective films or cut films generated by edge slitting during a process of obtaining an electrode film for manufacturing any dry electrode.

[0046] According to one embodiment of the present invention, the reusable electrode powder may be obtained by pulverizing defective films and / or cut films generated in a process of obtaining an electrode film using only the first electrode powder.

[0047] According to one embodiment of the present invention, the reusable electrode powder may be obtained by pulverizing an electrode film obtained from a first electrode powder through the following steps: (S1-1) kneading the first electrode powder to obtain a mixture mass, (S1-2) pulverizing the mixture mass to obtain an electrode powder, and (S1-3) calendering the electrode powder to obtain an electrode film.

[0048] According to one embodiment of the present invention, the "kneading" step (S1-1) can incorporate the "kneading" step (S2) described below, the "pulverizing" step (S1-2) can incorporate the "pulverizing" step (S3) described below, and the "calendering" step (S1-3) can incorporate the "calendering" step (S4) described below. Furthermore, the "pulverization" of the electrode film can also incorporate the "pulverizing" step described below, but is not limited to this.

[0049] According to another embodiment of the present invention, a reuseable electrode film may be obtained again by pulverizing defective films and / or cut films generated in the process of obtaining an electrode film using the first electrode powder and the reuseable electrode powder. That is, the reuseable electrode powder may include raw materials for manufacturing an electrode film that are reused not only once but also n times, such as two or three times.

[0050] According to one embodiment of the present invention, the powder for reused electrodes may be obtained by pulverizing defective films and / or cut films generated in the process of obtaining the electrode film (S4).

[0051] In another embodiment of the present invention, steps (S1) to (S4) are repeated n times (where n is an integer greater than or equal to 2), and the reusable electrode powder used in the nth step (S2) may be obtained by pulverizing defective and / or cut films generated in the processes for obtaining electrode films obtained in the first to (n-1)th steps (S4). Specifically, step (S4) may obtain an electrode film by further including an edge slitting process of edge slitting a spare electrode film obtained by calendering the second electrode powder, and the reusable electrode powder used in the nth step (S2) may be obtained by pulverizing the spare electrode film cut in the edge slitting process of the first to (n-1)th steps (S4).

[0052] The reuse electrode powder can be introduced into a kneading process for the first electrode powder, i.e., the newly produced electrode powder, and kneaded with the first electrode powder to form a mixture mass.

[0053] At this time, according to one embodiment of the present invention, the method may further include a step of mixing the first electrode powder and the reusable electrode powder to obtain a powder mixture for an electrode before kneading the first electrode powder and the reusable electrode powder. That is, the step (S2) may include a step of obtaining the first electrode powder, mixing the reusable electrode powder with the first electrode powder to obtain a powder mixture for an electrode, and then kneading the obtained electrode powder mixture to obtain a mixture mass.

[0054] Before kneading the first electrode powder and the reusable electrode powder, first obtaining a powder mixture for an electrode by mixing the first electrode powder and the reusable electrode powder may have an advantageous effect in that the powders are uniformly mixed and the final electrode exhibits uniform physical properties, but the present invention is not limited thereto.

[0055] According to an embodiment of the present invention, in the step (S2), the weight of the powder for the first electrode may be 30 wt % or more based on 100 wt % of the total weight of the powder for the first electrode and the powder for the reuse electrode.

[0056] For example, based on 100% by weight of the total of the first electrode powder and the reuse electrode powder, the weight of the first electrode powder may be 30% by weight or more, 35% by weight or more, 40% by weight or more, 45% by weight or more, 50% by weight or more, 55% by weight or more, 60% by weight or more, 65% by weight or more, 70% by weight or more, 75% by weight or more, or 80% by weight or more. When the weight of the first electrode powder is within the above range, advantageous effects can be obtained in terms of the mechanical properties of the manufactured electrode film, but the present invention is not limited thereto.

[0057] According to one embodiment of the present invention, in step (S2), the weight ratio of the powder for the first electrode to the powder for the reuse electrode may be, for example, 30:70 to 99:1, 30:70 to 95:5, 30:70 to 90:10, 35:75 to 85:15, 40:60 to 80:20, 45:55 to 75:25, 50:50 to 70:30, 50:50 to 60:40, or 60:40 to 80:20.

[0058] According to one embodiment of the present invention, when the weight ratio of the first electrode powder to the reusable electrode powder is within the above range, not only is the quality of the manufactured electrode film excellent, but there is also an effect that an electrode film of excellent quality can be manufactured regardless of the number of times the reusable electrode powder is reused.

[0059] According to one embodiment of the present invention, the means for pulverization to obtain the reusable electrode powder is not limited, and for example, equipment such as a blender and a grinder such as a cutter mill or a fine impact mill can be used. It may be preferable to pulverize the reusable electrode powder to a size corresponding to the size of the first electrode powder in terms of uniformity of the powder in the resulting mixture. Therefore, the first electrode powder will be described in detail below.

[0060] First, powder for the first electrode is obtained from a mixture containing an active material, a conductive material, and a binder.

[0061] According to one embodiment of the present invention, the reusable electrode powder and the first electrode powder both include an active material and a binder. According to one embodiment of the present invention, at least one of the reusable electrode powder and the first electrode powder may further include a conductive material, if necessary. In this case, the types of the active material, conductive material, and binder included in the reusable electrode powder and the first electrode powder may be the same or different, but are not limited thereto.

[0062] According to another embodiment of the present invention, obtaining the first electrode powder using the same active material and binder, and if necessary, the same type of conductive material as those contained in the reuse electrode powder used in step (S2), can have an advantageous effect in terms of the quality of the electrode film.

[0063] According to one embodiment of the present invention, the first electrode powder may be a mixture obtained by mixing the active material and the binder. That is, the first electrode powder may be a powder mixture formed by mixing the active material and the binder in a powder state. The first electrode powder may further include a conductive material as needed, but the present invention is not limited thereto.

[0064] The above process is a process of mixing an active material and a binder to prepare a mixture for producing a powder for a first electrode. The mixing for preparing the mixture is performed so that the active material and the binder are uniformly distributed. Since the active material and the binder are mixed in powder form, various methods can be used as long as they allow simple mixing. However, since the present invention is a dry electrode that does not use a solvent, the above mixing can be performed by dry mixing, which can be performed by putting the materials into a device such as a blender or super mixer.

[0065] According to one embodiment of the present invention, when the mixing for preparing the mixture in the mixing step for obtaining the powder for the first electrode is performed in a blender, the mixing may be performed in the blender at 5,000 rpm to 20,000 rpm for 30 seconds to 20 minutes, more specifically at 10,000 rpm to 15,000 rpm for 30 seconds to 5 minutes, in order to ensure uniformity.

[0066] According to another embodiment of the present invention, when the mixing is performed using a super mixer, the mixing speed may be set to 500 rpm to 2,500 rpm, specifically 1,000 rpm to 2,000 rpm, in order to ensure uniformity, and the process time may be adjusted accordingly.

[0067] According to one embodiment of the present invention, the dry electrode to be manufactured may be a positive electrode, and the active material may be a positive electrode active material.

[0068] The positive electrode active material may include, but is not limited to, a lithium transition metal oxide, a lithium metal iron phosphate, a lithium nickel-manganese-cobalt oxide, an oxide in which a portion of the lithium nickel-manganese-cobalt oxide is substituted with another transition metal, or two or more of these. Specifically, the positive electrode active material may include, for example, a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals, and a compound having the chemical formula Li 1+x Mn 2-x Lithium manganese oxides such as LiMnO4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, and LiMnO2, lithium copper oxide (Li2CuO2), vanadium oxides such as LiV3O8, LiV3O4, V2O5, and Cu2V2O7, and oxides with the chemical formula LiNi 1-x M x O2 (where M=Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x=0.01 to 0.3), and Ni-site lithium nickel oxide represented by the chemical formula LiMn 2-x M x Lithium manganese composite oxides represented by Li2Mn3MO8 (where M is Co, Ni, Fe, Cr, Zn, or Ta, and x is 0.01 to 0.1) or Li2Mn3MO8 (where M is Fe, Co, Ni, Cu, or Zn), lithium metal phosphate LiMPO4 (where M is Fe, CO, Ni, or Mn), and lithium nickel-manganese-cobalt oxide Li 1+x (Ni a Co b Mn c ) 1-x O2 (x=0-0.03, a=0.3-0.95, b=0.01-0.35, c=0.01-0.5, a+b+c=1) and lithium nickel-manganese-cobalt oxide, Li, a [Ni b Co c Mnd Al e 1-f M1 f O2 (M1 is one or more selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, 0.8 ≦ a ≦ 1.2, 0.5 ≦ b ≦ 0.99, 0 < c < 0.5, 0 < d < 0.5, 0.01 ≦ e ≦ 0.1, 0 ≦ f ≦ 0.1), and an oxide Li 1+x (Ni a Co b Mn c M d ) 1-x O2 (x = 0 to 0.03, a = 0.3 to 0.95, b = 0.01 to 0.35, c = 0.01 to 0.5, d = 0.001 to 0.03, a + b + c + d = 1, M is any one selected from the group consisting of Fe, V, Cr, Ti, W, Ta, Mg, and Mo), a disulfide compound, and Fe2(MoO4)3, etc. are mentioned, but it is not limited only to these.

[0069] According to another embodiment of the present invention, the dry electrode to be manufactured is a negative electrode, and the active material can be a negative electrode active material.

[0070] The negative electrode active material includes carbon such as graphitizable carbon and graphite-based carbon, and Li x Fe2O3 (0 ≦ x ≦ 1), Li x WO2 (0 ≦ x ≦ 1), Sn x Me 1-x Me’ y O z ​(Me: Mn, Fe, Pb, Ge; Me’: Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen; 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8), metal composite oxides such as, lithium metal, lithium alloys, silicon-based alloys, tin-based alloys, silicon-based oxides such as SiO, SiO / C, SiO2, metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5, conductive polymers such as polyacetylene, Li-Co-Ni-based materials, etc. can be used.

[0071] According to another embodiment of the present invention, the dry electrode may specifically be a positive electrode. Therefore, the active material is specifically a positive electrode active material, and more specifically, it can be a lithium transition metal oxide, lithium nickel-manganese-cobalt oxide, an oxide in which part of the lithium nickel-manganese-cobalt oxide is substituted with other transition metals, lithium iron phosphate, etc.

[0072] According to one embodiment of the present invention, the positive electrode active material can include nickel-manganese-cobalt-aluminum (NCMA). The nickel-manganese-cobalt-aluminum (NCMA) is not limited thereto, but for example, Li[Ni 0.86 Mn 0.05 Co 0.07 Al 0.2 O2 can be included.

[0073] The binder can include polytetrafluoroethylene (PTFE), polyolefin, or a mixture thereof, specifically, it can include polytetrafluoroethylene (PTFE), and more specifically, it can be polytetrafluoroethylene (PTFE).

[0074] Specifically, the polytetrafluoroethylene (PTFE) may be contained in an amount of 60 wt % or more based on the total weight of the binder.

[0075] In still another embodiment of the present invention, the binder may further include PEO (polyethylene oxide), PVdF (polyvinylidene fluoride), PVdF-HFP (polyvinylidene fluoride-co-hexafluoropropylene), or two or more thereof.

[0076] The conductive material is not particularly limited as long as it is conductive and does not cause chemical changes in the battery. For example, graphite such as natural graphite or artificial graphite; carbon black-based carbon materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber and metal fiber; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives. More specifically, in order to uniformly mix the conductive material and improve conductivity, the conductive material may contain one or more selected from the group consisting of activated carbon, graphite, carbon black, and carbon nanotubes, and more specifically, activated carbon.

[0077] According to one embodiment of the present invention, the active material, conductive material, and binder may be mixed in a weight ratio of 80 to 98 parts by weight: 0 to 10 parts by weight: 0.5 to 10 parts by weight of the active material: conductive material: binder, and more particularly, in a weight ratio of 85 to 98 parts by weight: 0.5 to 5 parts by weight: 0.5 to 10 parts by weight.

[0078] When the binder is contained in an amount such that the mixing ratio of the active material, the conductive material, and the binder falls within the above range, it is possible to prevent excessive fiberization of the binder in the subsequent kneading process, thereby improving process operability, or to induce sufficient fiberization, thereby improving the physical properties of the composite film, but the present invention is not limited thereto.

[0079] When the conductive material is contained in an amount such that the mixing ratio of the active material, the conductive material, and the binder falls within the above range, excellent effects can be exhibited in terms of the capacity of the electrode to be manufactured, and the physical properties and conductivity of the composite film, but the present invention is not limited thereto.

[0080] According to another embodiment of the present invention, the powder for the first electrode may be a powder obtained by kneading and pulverizing the mixture obtained in step (S1-1). Specifically, the powder for the first electrode may be obtained by a method including: (S1-2) kneading the mixture obtained in step S1-1 to obtain a lump of mixture; and (S1-3) pulverizing the lump of mixture.

[0081] The step (S1-2) is a step for fiberizing the binder in the mixture produced as described above to obtain a mixture mass, and can be referred to as, for example, a kneading step.

[0082] According to one embodiment of the present invention, in terms of the appearance characteristics of the electrode film to be manufactured, it may be preferable to use, as the powder for the first electrode, a mixture itself obtained by mixing an active material, a binder, and optionally a conductive material, i.e., a powder mixture; however, the present invention is not limited thereto.

[0083] As described above, according to the present invention, the process includes (S2) kneading the first electrode powder obtained from a mixture containing an active material, a binder, and, if necessary, a conductive material with the reuse electrode powder to obtain a mixture mass.

[0084] In one embodiment of the present invention, after the step (S1) and before the kneading step (S2), a step of classifying the obtained first electrode powder may be further included. In the classifying step, the pulverized electrode powder may be filtered using a mesh having pores of a certain size or less to obtain electrode powder having pores of a certain size or more.

[0085] The kneading in the step (S2) is a step of fiberizing the binder contained in the first electrode powder and the reusable electrode powder, and bonding or connecting these powders to form a mixture mass in which the first electrode powder and the reusable electrode powder are uniformly distributed.

[0086] The kneading in step (S2) can be performed using a kneading machine such as, but not limited to, a kneader. This kneading is a step in which the binder is fibrous to bond or connect the active material and conductive material powder, thereby forming a mixture mass with a solid content of 100%.

[0087] Specifically, the kneading in step (S2) can be carried out at a speed of 10 to 100 rpm for 1 to 30 minutes, more specifically, at a speed of 25 to 50 rpm for 3 to 7 minutes, with a shear rate in the range of 10 / s to 500 / s for 1 to 30 minutes, more specifically, at a shear rate in the range of 30 / s to 100 / s.

[0088] Furthermore, such a kneading step can be carried out under conditions of high temperature and pressure equal to or higher than atmospheric pressure, more specifically, under conditions of pressure higher than atmospheric pressure.

[0089] More specifically, the kneading of the mixture in the step (S2) can be carried out at a temperature of 70°C to 200°C, more specifically, 90°C to 180°C or 90°C to 150°C.

[0090] In one embodiment of the present invention, the kneading in step (S2) can be carried out at atmospheric pressure or higher, specifically, under a pressure of 1 atm to 60 atm, or 1 atm to 30 atm, or 1 atm to 10 atm, or 1 atm to 10 atm, or 1.1 atm to 10 atm, or 1.1 atm to 6 atm, or 1.1 atm to 3 atm.

[0091] When the kneading is carried out under the above-mentioned conditions, the binder is sufficiently fibrous and agglomerated during kneading, and film formation during calendering is facilitated, but the present invention is not limited to this.

[0092] In one embodiment of the present invention, when an electrode film is manufactured by calendaring without performing a step of kneading (kneading process) after mixing the first electrode powder and the reusable electrode powder, or when an electrode film is manufactured by kneading and pulverizing only the first electrode powder, mixing it with the reusable electrode powder (which has already been manufactured by performing the kneading process), and then calendaring, unevenness may be observed in the appearance of the electrode film, resulting in poor appearance characteristics.

[0093] Furthermore, if the appearance characteristics of the electrode film are poor, the active material may not be uniformly distributed in the electrode film, the binder may be partially agglomerated, or the conductive material may not be uniformly distributed, or the degree of fiberization of the binder in the electrode film may vary, which may result in a decrease in the uniformity of the powder in the electrode film produced, thereby causing poor quality of the electrode, but the effects of the present invention are not limited to this.

[0094] The mixture mass produced by the kneading process can then be immediately subjected to calendering. However, in this case, it may be necessary to press the mixture mass under strong pressure and high temperature to produce a thin film, which may result in problems such as the film being too dense or not being uniform. Therefore, according to the present invention, a step (S3) is carried out in which the produced mixture mass is pulverized to obtain powder for the second electrode.

[0095] The pulverization in step (S3) may be performed to obtain a second electrode powder, which is the final electrode powder, before obtaining an electrode film by the method of the present invention. In this case, the pulverization may be performed using, but is not limited to, a blender or a grinder such as a cutter mill or a fine impact mill.

[0096] In one embodiment of the present invention, when the grinding is carried out using a blender, the grinding can be carried out specifically at a speed of 500 rpm to 20,000 rpm for 30 seconds to 10 minutes, more specifically at a speed of 1,000 rpm to 10,000 rpm for 30 seconds to 1 minute.

[0097] In another embodiment of the present invention, when the pulverization is carried out using a cutter mill, the pulverization can be carried out specifically at a speed of 500 rpm or less, for example, 400 rpm to 500 rpm, for 10 to 60 seconds.

[0098] In yet another embodiment of the present invention, when the grinding is carried out using an impact mill, the grinding can be carried out specifically at a speed of 3,000 rpm to 8,000 rpm, for example, 4,000 rpm to 7,000 rpm, for 10 to 60 seconds.

[0099] In one embodiment of the present invention, when the pulverization is performed under the above-described conditions, the size of the powder for the second electrode is suitable for film formation and may be preferable in that generation of fine powder is minimized, but the present invention is not limited thereto.

[0100] In one embodiment of the present invention, after step (S3) and before calendering in step (S4), a step of classifying the pulverized second electrode powder may be further included. In the classifying step, the pulverized electrode powder may be filtered using a mesh with pores of a certain size or less to obtain electrode powder having a certain size or greater. The additional step of classifying may have beneficial effects in terms of improving the appearance characteristics and surface uniformity of the film, as well as the physical properties of the film. For example, if the electrode powder produced above is too large or agglomerated, bridges may form in the subsequent calendering step, increasing the likelihood of producing a film with poor appearance and uneven surface characteristics, such as pinholes, but the present invention is not limited thereto.

[0101] Thereafter, (S4) the second electrode powder obtained as described above or the supplied second electrode powder is used to perform calendaring to obtain an electrode film.

[0102] The calendering process is a process of processing the second electrode powder into a film, and may be a step of rolling the powder into a film having an average thickness of, for example, 50 μm to 300 μm.

[0103] In this case, the calendering can be performed, for example, by using opposing rolls. In this case, the roll temperature is 50°C to 200°C, and the opposing rolls can rotate at different speeds, and the rotation speed is not particularly limited.

[0104] In one embodiment of the present invention, the gap between the opposing rolls is, for example, 20 to 500 μm, and can be variably adjusted depending on the number of times the calendering process is repeated and the desired film thickness, but is not particularly limited thereto.

[0105] In one embodiment of the present invention, the calendering can be repeated one or more times, for example, three or four or more times.

[0106] According to an embodiment of the present invention, the step (S4) of obtaining an electrode film may further include an edge slitting step after calendering. Specifically, the step (S4) may further include a step of edge slitting a preliminary electrode film obtained by calendering the second electrode powder to obtain an electrode film.

[0107] The film obtained by the calendering process (i.e., the preliminary electrode film) may have problems such as a thinner edge or an inconsistent edge shape. To address this issue, an edge slitting process may be further performed to cut out the edge of the film obtained by the calendering process to make the thickness of the film uniform across the entire surface or to make the edge shape uniform, but the present invention is not limited thereto.

[0108] The edge slitting can be performed by any means commonly used in the manufacture of a self-supporting (or free-standing) electrode film, and the means is not particularly limited.

[0109] According to one embodiment of the present invention, the electrode film obtained by the calendering process may have poor quality or may be cut by the edge slits, and may be pulverized and used as a powder for a reused electrode.

[0110] According to an embodiment of the present invention, the powder for reused electrodes may be obtained by pulverizing defective films generated in the process of obtaining the electrode film (S4).

[0111] According to one embodiment of the present invention, the electrode film having poor quality may mean, for example, that the tensile strength of the electrode film is 0.7 MPa or less, specifically less than 0.7 MPa. For example, it may also mean that the tensile strength of the electrode film is less than 0.7 MPa, less than 0.8 MPa, or less than 1 MPa. For example, if the tensile strength of the electrode film is below the above range, the film may break and be difficult to wind up. Therefore, an electrode film having such quality may be pulverized and used as a powder for a reusable electrode.

[0112] The tensile strength is measured by a known method, and the measurement method is not limited thereto. For example, the tensile strength may be evaluated by cutting the electrode film into a size of 1 cm × 5 cm and pulling it at a rate of 5 cm / min using a UTM device, where the maximum stress value at break is the tensile strength and the rate of change in length at break is the elongation.

[0113] According to one embodiment of the present invention, the step (S4) may further include a step of edge-slitting a preliminary electrode film obtained by calendering the second electrode powder, whereby the reused electrode powder may be obtained by pulverizing the preliminary electrode film cut in the edge-slitting step.

[0114] In one embodiment of the present invention, the area of ​​the preliminary electrode film cut by the edge slitting process is, for example, 20% or less, specifically 1% to 20%, 5% to 20%, 10% to 20%, 10% to 15%, or 15% to 20%, based on the total area of ​​the preliminary electrode film, but is not limited thereto.

[0115] By proceeding to step S4, a composite film that functions as an electrode composite, i.e., an electrode film, can be manufactured. Such an electrode film is also known as a free-standing film.

[0116] As described above, the steps (S1) to (S4) can be repeated once or twice or more (n times). For example, if a defective film is generated in the step (S4), it can be pulverized to obtain a powder for a primary reuse electrode, and the steps (S1) to (S4) can be repeated.

[0117] As described above, in another embodiment of the present invention, the reusable electrode powder can be obtained by a process of manufacturing an electrode film using the first electrode powder.

[0118] The electrode film produced in this manner does not contain a solvent, so it has almost no fluidity, is easy to handle, and can be processed into a desired shape to produce electrodes of various shapes. Furthermore, when the electrode film is used in the production of an electrode, the drying step for removing the solvent can be omitted, which not only significantly improves the efficiency of the electrode production process but also solves problems such as fine powder of the active material and broken fibrous binder that have been issues in the production of conventional dry electrodes.

[0119] The step (S5) is a step of laminating the electrode film onto at least one surface of a current collector.

[0120] In one embodiment of the present invention, the current collector may be any material that has high conductivity without causing chemical changes in the battery. Examples of such materials include stainless steel, aluminum, nickel, titanium, calcined carbon, copper, or aluminum or stainless steel surfaces treated with carbon, nickel, titanium, silver, etc. The current collector may also be formed with fine irregularities on its surface to improve adhesion of the positive electrode active material. Various forms are available, including films, sheets, foils, nets, porous materials, foams, and nonwoven fabrics. The current collector may be fully or partially coated with a conductive primer to reduce surface resistance and improve adhesion. The conductive primer may include a conductive material and a binder. The conductive material may be any material that is conductive, including, for example, a carbon-based material.

[0121] In one embodiment of the present invention, the lamination may be a step of rolling and adhering the electrode film to a predetermined thickness onto a current collector. The lamination may also be performed using a lamination roll, which may be maintained at a temperature of, but not limited to, room temperature (25°C) to 200°C.

[0122] A dry electrode according to another aspect of the present invention comprises an electrode current collector and an electrode film located on the electrode current collector and including an active material, a conductive material, and a binder, and is manufactured by the above-described manufacturing method.

[0123] The dry electrode according to one embodiment of the present invention not only exhibits an appearance similar to that of a dry electrode manufactured using only a new electrode powder without using a reusable electrode powder, but also exhibits similar mechanical properties such as tensile strength and elongation.

[0124] According to another aspect of the present invention, there is provided a secondary battery in which an electrode assembly including a positive electrode, a negative electrode, and a separator is housed in a battery case together with a lithium-containing nonaqueous electrolyte, and at least one of the positive electrode and the negative electrode is used as the dry electrode.

[0125] The specific structure of the secondary battery is well known, and therefore a description thereof will be omitted in this specification.

[0126] An energy storage device according to still another aspect of the present invention includes the above-described secondary battery as a unit battery.

[0127] The specific structure of the energy storage device is well known, and therefore will not be described in this specification.

[0128] The present invention will be described in more detail below with reference to examples. However, the following examples are for illustrative purposes only and the scope of the present invention is not limited to these examples.

[0129] [Dry electrode manufacturing] Example 1 Dry electrodes were fabricated by the following steps.

[0130] Step 1. Preparation of powder for the first electrode The positive electrode active material was lithium nickel cobalt manganese aluminum oxide (NCMA) Li[Ni 0.86 Mn 0.05 Co 0.07 ]Al 0.02 965 g of O2, 10 g of carbon black as a conductive material, and 25 g of polytetrafluoroethylene (PTFE) as a binder were placed in a blender and mixed at 10,000 rpm for 3 minutes to obtain a powder for the first electrode in the form of a mixture.

[0131] Step 2. Manufacturing powder for reusable electrodes The temperature of the kneader (Shin-Nihon Dispersion Machine) was stabilized at 150°C, and the powder for the first electrode prepared in step 1 above was placed in the kneader. The kneader was then operated at a speed of 40 rpm under a pressure of 1.1 atm for 5 minutes to obtain a mixture mass.

[0132] The mixture mass was placed in a blender (Waring) and pulverized at 10,000 rpm for 1 minute. The resulting powder was then pulverized to an active material loading of 5.0 mAh / cm. 2 The film was then placed in a wrap calender (roll diameter: 160 mm, roll temperature: 100°C) three times under the conditions described above to produce a film with a thickness of 85 μm. The film thus produced was then edge-slit to a width of 270 mm to produce an electrode film.

[0133] The part cut by the edge slit was put into a blender (Waring) and pulverized at 10,000 rpm for 1 minute to obtain powder for reused electrodes.

[0134] Step 3. Preparation of powder for the second electrode 800 g of the powder for the first electrode obtained in step 1 above and 200 g of the powder for the reused electrode obtained in step 2 above were placed in a blender (Waring) and mixed at 10,000 rpm for 1 minute to obtain an electrode powder mixture.

[0135] The temperature of a kneader (Shin-Nichi Dispersion Machine) was stabilized at 150°C, and the obtained electrode powder mixture was placed in the kneader, which was then operated at a speed of 40 rpm under a pressure of 1.1 atm for 5 minutes to obtain a mixture mass.

[0136] The mixture mass was placed in a blender (Waring) and pulverized at 10,000 rpm for 1 minute to obtain powder for the second electrode.

[0137] Step 4. Fabrication of electrode film The powder for the second electrode obtained in step 3 above was charged to a battery with an active material loading of 5.0 mAh / cm 2The film was then placed in a wrap calender (roll diameter: 160 mm, roll temperature: 100°C) three times under the conditions described above to produce a film with a thickness of 85 μm. The film thus produced was then edge-slit to a width of 270 mm to produce an electrode film.

[0138] Step 5. Fabrication of electrodes The electrode film obtained in step 4 was placed on one side of a coated aluminum foil (16 μm) and laminated with a laminating roll maintained at 150° C. to prepare an electrode.

[0139] Example 2 An electrode was manufactured in the same manner as in Example 1, except that in step 3, 600 g of the powder for the first electrode and 400 g of the powder for the reused electrode were added.

[0140] Example 3 An electrode was manufactured in the same manner as in Example 1, except that in step 3, 400 g of the powder for the first electrode and 600 g of the powder for the reused electrode were added.

[0141] Comparative Example 1 An electrode was manufactured in the same manner as in Example 1, except that in step 3 above, the first electrode powder was not mixed and 1,000 g of the reuse electrode powder was used.

[0142] Comparative Example 2 Dry electrodes were fabricated by the following steps.

[0143] Step 1. Preparation of powder for the first electrode The positive electrode active material was lithium nickel cobalt manganese aluminum oxide (NCMA) Li[Ni 0.86 Mn 0.05 Co 0.07 ]Al 0.02 965 g of O2, 10 g of carbon black as a conductive material, and 25 g of polytetrafluoroethylene (PTFE) as a binder were placed in a blender and mixed at 10,000 rpm for 3 minutes to obtain a powder mixture.

[0144] The temperature of the kneader (Shin-Nichi Dispersion Machine) was stabilized at 150° C., and the powder mixture was placed in the kneader, which was then operated at a speed of 40 rpm under a pressure of 1.1 atm for 5 minutes to obtain a mixture mass.

[0145] The mixture mass was placed in a blender (Waring) and pulverized at 10,000 rpm for 1 minute to obtain powder for the first electrode.

[0146] Step 2. Fabrication of electrode film 800 g of the powder for the first electrode obtained in step 1 above and 200 g of the powder for the reuse electrode obtained in step 2 of Example 1 above were mixed together to obtain a powder mixture.

[0147] The obtained powder mixture was mixed with an active material loading of 5.0 mAh / cm 2 The film was then placed in a wrap calender (roll diameter: 160 mm, roll temperature: 100°C) three times under the conditions described above to produce a film with a thickness of 85 μm. The film thus produced was then edge-slit to a width of 270 mm to produce an electrode film.

[0148] Step 3. Fabrication of electrodes The electrode film obtained in step 2 was placed on one side of a coated aluminum foil (15 μm) and laminated using a laminating roll maintained at 150° C. to prepare an electrode.

[0149] [Physical property evaluation] The tensile strength and appearance characteristics of the electrode films contained in the dry electrodes of Examples 1 to 3, Comparative Examples 1 and 2 prepared above were evaluated by the following methods, and the results are shown in Table 1 below and FIG. 3.

[0150] The evaluation results also include the results of evaluating the physical properties of the electrode film produced in step 2 of Example 1 as a comparative group.

[0151] Tensile strength Using a UTM (Zwick), electrode films cut to 1 cm x 5 cm were pulled at a rate of 5 cm / min to measure stress and strain values, and the maximum stress value just before breakage was evaluated as the tensile strength.

[0152] To prevent breakage in subsequent processes, the target physical property value was set to 0.7 MPa or higher.

[0153] exterior The appearance was checked by visual observation, and if unevenness was observed on the film, it was rated as having poor appearance. The results of the appearance evaluation for Example 1 and Comparative Example 2 are shown in FIG.

[0154] [Table 1]

[0155] As a result of the above, it was confirmed that the mechanical properties of the electrode film were poor in Comparative Example 1, which used only the reusable electrode powder. Also, in Comparative Example 2, when the electrode film was manufactured by mixing the first electrode powder manufactured by pulverization after the kneading process with the reusable electrode powder and then calendering it, not only did the uniformity of the powder in the film decrease, resulting in poor appearance characteristics, but also the use of the reusable electrode powder required the binder fiberization process (kneading process) to be repeated, compared to using only the first electrode powder, and the tensile strength of the electrode film was also confirmed to be low.

[0156] On the other hand, in Examples 1 to 3, in which the reusable electrode powder was used at a ratio of 70% or less, it was confirmed that mechanical properties and appearance characteristics similar to those of the comparison group using only the new electrode powder could be achieved.

[0157] The present invention has been described above with reference to the embodiments and drawings. However, a person having ordinary knowledge in the field to which the present invention pertains will be able to make various applications and modifications within the scope of the present invention based on the above content.

Claims

1. (S1) obtaining a powder for a first electrode from a mixture containing an active material and a binder; (S2) kneading the first electrode powder and the reuse electrode powder to obtain a mixture mass; (S3) pulverizing the mixture mass to obtain powder for a second electrode; (S4) a step of calendering the second electrode powder to obtain an electrode film; (S5) a step of positioning the electrode film on at least one surface of a current collector and laminating the electrode film.

2. 2. The method for producing a dry electrode according to claim 1, wherein the reusable electrode powder is obtained by pulverizing defective films generated in a step of obtaining an electrode film in the method for producing a dry electrode.

3. 2. The method for producing a dry electrode according to claim 1, wherein the reusable electrode powder is obtained by pulverizing an electrode film obtained by the steps of: (S1-1) kneading a first electrode powder to obtain a mixture lump; (S1-2) pulverizing the mixture lump to obtain an electrode powder; and (S1-3) calendaring the electrode powder to obtain an electrode film.

4. The step (S4) further includes an edge slitting step of edge-slitting a preliminary electrode film obtained by calendering the second electrode powder, The steps (S1) to (S4) are repeated n times, where n is an integer of 2 or more; The method for producing a dry electrode according to claim 1, wherein the reusable electrode powder used in the n-th step (S2) is obtained by pulverizing a spare electrode film cut in the edge slitting steps in the 1st to (n-1)th steps (S4).

5. 2. The method for manufacturing a dry electrode according to claim 1, wherein the step (S2) includes a step of mixing the first electrode powder and the reuse electrode powder to obtain an electrode powder mixture before kneading, and kneading the obtained electrode powder mixture to obtain a mixture mass.

6. 6. The method for manufacturing a dry electrode according to claim 1, wherein in the step (S2), a weight of the first electrode powder is 30% by weight or more based on 100% by weight of the total of the first electrode powder and the reuse electrode powder.

7. 7. The method for manufacturing a dry electrode according to claim 6, wherein in the step (S2), a weight ratio of the first electrode powder to the reuse electrode powder is 30:70 to 99:

1.

8. The method for producing a dry electrode according to claim 1 , wherein the first electrode powder is a mixture obtained by a step of obtaining a mixture containing the active material and a binder.

9. The method for producing a dry electrode according to claim 1 , wherein the kneading in the step (S2) is carried out at a temperature of 70° C. to 200° C. under a pressure equal to or higher than atmospheric pressure.

10. 2. The method for producing a dry electrode according to claim 1, wherein the kneading in the step (S2) is carried out at a shear rate of 10 / s to 500 / s for 1 minute to 30 minutes.

11. 2. The method for manufacturing a dry electrode according to claim 1, further comprising a step of classifying the pulverized powder for the second electrode after the step (S3) and before the calendering in the step (S4).

12. a current collector; and an electrode film located on the current collector and including an active material and a binder; A dry electrode manufactured by the method for manufacturing a dry electrode according to claim 1.

13. A secondary battery in which an electrode assembly including a positive electrode, a negative electrode, and a separator is housed in a battery case together with a lithium-containing non-aqueous electrolyte, A secondary battery, wherein at least one of the positive electrode and the negative electrode is the dry electrode according to claim 12.

14. An energy storage device comprising the secondary battery according to claim 13 as a unit battery.

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