Dry electrode, secondary battery including the same, energy storage device, and apparatus for manufacturing dry electrode

Abstract

Exemplary embodiments of the present invention provide an electrode powder for manufacturing a dry electrode for a secondary battery, a method of manufacturing the same, a method of manufacturing a dry electrode using the same, a dry electrode, a secondary battery including the same, an energy storage device, and an apparatus for manufacturing a dry electrode.SOLUTION: The powder includes an active material, a conductive material, and a binder, and has a specific resistance of 700 Ω·cm or less when pressurized by a pressure of a 50MPa.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electrode powder for manufacturing a dry electrode for a secondary battery, a manufacturing method thereof, a manufacturing method of a dry electrode using the same, a dry electrode, a secondary battery including the same, an energy storage device, and an apparatus for manufacturing a dry electrode.

[0002] This application claims priority based on Korean Patent Application No. 10-2020-0136913, filed on October 21, 2020, 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 fossil fuel use has led to an increasing demand for alternative and clean energy sources, with electrochemical power generation and storage being one of the most actively researched areas.

[0004] A typical example of an electrochemical element that uses such electrochemical energy is currently a secondary battery, and the range of its use is becoming increasingly wider.

[0005] Lithium secondary batteries, which are representative of such secondary batteries, are not only used as an energy source for mobile devices, but also as a power source for electric vehicles and hybrid electric vehicles, which are replacing vehicles that use fossil fuels such as gasoline and diesel vehicles, which are one of the main causes of air pollution, in recent years. Furthermore, their range of use is expanding to include auxiliary power sources through grid integration.

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

[0007] Among these, the active material mixing process is a process of blending a coating material for forming an electrode active layer where the actual electrochemical reaction occurs in the electrode. More specifically, it is a process of mixing an electrode active material, which is an essential element of an electrode, other additives such as a conductive material and a filler, a binder for binding between powder particles and adhering to a current collector, and a solvent for imparting viscosity and dispersing powder, to prepare a fluid slurry.

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

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

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

[0011] In order to solve the above problems, drying devices that can adjust the evaporation rate of the solvent while uniformly drying the inside and outside of the active layer have been considered. However, such drying devices are very expensive and require considerable cost and time to operate, which is disadvantageous in terms of manufacturing process efficiency.

[0012] Therefore, recently, active research has been conducted into the production of dry electrodes that do not use solvents. Dry electrodes are generally manufactured by laminating a free-standing film containing an active material, a binder, a conductive material, etc. onto a current collector.

[0013] The steps for manufacturing a conventional dry electrode are shown schematically in FIG.

[0014] Referring to Figure 1, the process includes first mixing the active material, the carbon material as a conductive material, and the fiberizable binder together in a blender, fiberizing the binder through a high shear mixing process such as jet milling, and then calendering the mixture into a film to produce a free-standing film.Then, the free-standing film produced after calendering is laminated onto a current collector to produce the battery.

[0015] However, when high-shear mixing is applied to fragile active materials, a large amount of fine powder is generated, which can reduce mechanical and electrochemical performance. Excessive high-shear mixing can cut the binder fibers, reducing the flexibility of the free-standing film. Furthermore, during the jet milling process, components can adhere to the inside of the equipment, obstructing the flow of high-pressure air and causing blockages in the flow passages, making it unsuitable for mass production.

[0016] Therefore, there is an urgent need to develop a dry electrode manufacturing technology that can solve these problems. Summary of the Invention [Problem to be solved by the invention]

[0017] In order to solve the above problems, the present invention aims to provide a powder for a dry electrode that minimizes pulverization of an active material and maximizes fibrous binder, and a method for manufacturing the same.

[0018] Another object of the present invention is to provide a method for manufacturing a dry electrode that includes the same, thereby improving the mechanical performance of the electrode and making it suitable for mass production.

[0019] Another object of the present invention is to provide a dry electrode manufactured by the manufacturing method, a secondary battery including the same, and an apparatus for manufacturing the dry electrode. [Means for solving the problem]

[0020] In order to achieve the above object, one aspect of the present invention provides a powder for an electrode according to the following embodiment.

[0021] According to a first embodiment, there is provided an electrode powder that can be formed into a film for manufacturing a dry electrode for a secondary battery, the electrode powder including an active material, a conductive material, and a binder, and having a resistivity of 700 Ω cm or less when pressed at a pressure of 50 MPa.

[0022] According to a second embodiment, there is provided a method for producing an electrode powder according to the first embodiment, the method including: (a) preparing a mixture containing an active material, a conductive material, and a binder; (b) kneading the mixture at a temperature in the range of 70°C to 200°C under a pressure equal to or higher than atmospheric pressure to prepare a mixture mass in order to fiberize the binder; and (c) pulverizing the mixture mass to obtain an electrode powder.

[0023] According to a third embodiment, in the second embodiment, the conductive material may include at least one selected from the group consisting of activated carbon, graphite, carbon black, and carbon nanotubes.

[0024] According to a fourth embodiment, in the second or third embodiment, the binder may include polytetrafluoroethylene (PTFE), polyolefin, or a mixture thereof.

[0025] According to a fifth embodiment, in any one of the second to fourth embodiments, the kneading in step (b) may be performed at a speed of 10 rpm to 100 rpm for 1 minute to 30 minutes.

[0026] According to a sixth embodiment, in any one of the second to fifth embodiments, the kneading in step (b) may be performed at a shear rate of 10 / s to 500 / s for 1 minute to 30 minutes.

[0027] According to a seventh embodiment, in any one of the second to sixth embodiments, the kneading in step (b) may be performed at a temperature of 90 to 180°C.

[0028] According to an eighth embodiment, in any one of the second to seventh embodiments, the kneading in step (b) may be performed under a pressure of 1 atm to 60 atm.

[0029] According to a ninth embodiment, in any one of the second to eighth embodiments, the grinding in step (c) may be performed at a speed of 500 rpm to 20,000 rpm for 30 seconds to 10 minutes.

[0030] According to a tenth embodiment, in any one of the second to ninth embodiments, after step (c), the method may further include a step of classifying the pulverized electrode powder.

[0031] One aspect of the present invention provides a method for manufacturing a dry electrode according to the following embodiment.

[0032] According to an eleventh embodiment, there is provided a method for manufacturing a dry electrode, the method including: (d) calendaring the electrode powder of any one of the second to tenth embodiments to manufacture a composite film; and (e) positioning the composite film on at least one surface of a current collector and laminating the film.

[0033] According to a twelfth embodiment, in the eleventh embodiment, the porosity of the composite film may be 20 to 35%.

[0034] According to a thirteenth embodiment, in the eleventh or twelfth embodiment, the bending resistance of the dry electrode may be less than Φ (diameter) 10 mm.

[0035] According to the 14th embodiment, in any one of the 11th to 13th embodiments, the loading amount of the active material of the composite film is 3 mAh / cm 2 ~15mAh / cm 2 It could be.

[0036] According to a fifteenth embodiment, in any one of the eleventh to fourteenth embodiments, the interface resistance between the composite film and the current collector is 5 Ω cm 2 It can be the following:

[0037] According to a sixteenth embodiment, in any one of the eleventh to fifteenth embodiments, the current collector may be entirely or partially coated with a conductive primer. Another aspect of the present invention provides a dry electrode according to the following embodiment.

[0038] According to a seventeenth embodiment, there is provided a dry electrode manufactured by the manufacturing method of any one of the eleventh to sixteenth embodiments.

[0039] According to an eighteenth embodiment, there is provided a dry electrode having a bending resistance of less than 10 mm in diameter, the dry electrode comprising: an electrode current collector; and a composite film disposed on the electrode current collector and including an active material, a conductive material, and a binder.

[0040] According to a nineteenth embodiment, in the eighteenth embodiment, the dry electrode may have a bending resistance of Φ (diameter) 2 to 8 mm.

[0041] According to the twentieth embodiment, in the eighteenth or nineteenth embodiment, the bending resistance of the dry electrode can be evaluated according to the measurement standard JIS K5600-5-1 method.

[0042] According to a 21st embodiment, in any one of the 18th to 20th embodiments, the bending resistance of the dry electrode may be evaluated by the steps of: preparing a rectangular electrode sample of 100 mm x 50 mm; preparing measuring rods having diameters of 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 8 mm, 10 mm, 12 mm, 16 mm, 20 mm, 25 mm, and 32 mm; bringing the electrode sample into contact with the measuring rod using the measuring rod with the largest diameter among the measuring rods; and determining whether cracks occur in the composite film of the electrode sample when both ends of the electrode sample are lifted; and if no cracks occur in the previous step, repeating the step of determining whether cracks occur in the composite film of the electrode sample using the measuring rod with the next largest diameter, and determining the smallest diameter of the measuring rod at which no cracks occur in the composite film of the electrode sample as the bending resistance.

[0043] According to a 22nd embodiment, in any one of the 18th to 21st embodiments, the porosity of the composite film may be 20 to 35%.

[0044] According to the 23rd embodiment, in any one of the 18th to 22nd embodiments, the loading amount of the active material of the composite film is 3 mAh / cm 2 ~15mAh / cm 2 It could be.

[0045] According to a 24th embodiment, in any one of the 18th to 23rd embodiments, the interface resistance between the composite film and the current collector is 5 Ω cm 2 It can be the following:

[0046] According to a 25th embodiment, in any one of the 18th to 24th embodiments, the current collector may be entirely or partially coated with a conductive primer.

[0047] One aspect of the present invention provides a secondary battery according to the following embodiment.

[0048] According to a 26th embodiment, there is provided a secondary battery including a dry electrode according to any one of the 17th to 25th embodiments, wherein the dry electrode is a positive electrode, and an electrode assembly including the positive electrode, the negative electrode, and a separator is housed in a battery case together with a lithium-containing non-aqueous electrolyte.

[0049] One aspect of the present invention provides an energy storage device according to the following embodiment.

[0050] According to a twenty-seventh embodiment, there is provided an energy storage device including the secondary battery of the twenty-sixth embodiment as a unit battery.

[0051] One aspect of the present invention provides a dry electrode manufacturing apparatus according to the following embodiment.

[0052] According to a 28th embodiment, there is provided an apparatus for manufacturing a dry electrode, the apparatus including: a blender for mixing raw composite materials including an active material, a conductive material, and a binder; a kneader for kneading the mixture to produce a mixture mass in order to fiberize the binder; a pulverizer for pulverizing the mixture mass to form an electrode powder; a calender for forming the electrode powder into a composite film; and a lamination roll for positioning the composite film on at least one surface of a current collector and laminating it.

[0053] According to a 29th embodiment, in the 28th embodiment, the kneader may be set to a temperature range of 70°C to 200°C and a pressure condition equal to or higher than atmospheric pressure. [Effects of the Invention]

[0054] According to the present invention, by introducing a high-temperature low-shear kneading process followed by a pulverization process instead of a high-shear mixing process, it is possible to minimize pulverization of the active material, maximize binder fiberization, and minimize shearing of the fiberized binder.

[0055] Furthermore, by manufacturing a dry electrode using such an electrode powder, the flexibility of the dry electrode can be ensured.

[0056] Furthermore, by going through the kneading and pulverization stages using a kneader rather than a high-shear jet milling process, there is no problem of clogging of flow paths due to clumps of constituent components, which is advantageous for mass production. [Brief explanation of the drawings]

[0057] [Figure 1] FIG. 1 is a flow chart showing a conventional method for manufacturing a dry electrode for a secondary battery. [Figure 2] 1 is a flowchart illustrating a method for manufacturing a dry electrode for a secondary battery according to an embodiment of the present invention. [Figure 3] 1 is a SEM photograph of the electrode powder of Example 1 according to Experimental Example 1 of the present invention. [Figure 4] 1 is a SEM photograph of the electrode powder of Comparative Example 1 according to Experimental Example 1 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0058] The present invention will now be described in more detail to aid in understanding the invention.

[0059] The terms and words used in this specification and claims should not be interpreted limited to their ordinary and dictionary meanings, but should be interpreted in terms and concepts that correspond to the technical idea of ​​the present invention, in accordance with the principle that the inventor himself can appropriately define the concept of the term in order to explain the invention in the best way.

[0060] The terms used in this specification are used to describe exemplary embodiments and are not intended to limit the present invention. Unless otherwise specified, the singular includes the plural.

[0061] Furthermore, throughout the specification, when a part "comprises" another component, it does not mean that the other component is excluded, but that the part may further include the other component, unless otherwise specified.

[0062] According to one embodiment of the present invention, there is provided an electrode powder that can be formed into a film for producing a dry electrode for a secondary battery, the electrode powder including an active material, a conductive material, and a binder, and having a resistivity of 700 Ω cm or less when pressed at a pressure of 50 MPa.

[0063] In order to achieve the above properties, it is necessary to maximize the dispersion of the active material, conductive material, and binder in the electrode powder and minimize the generation of fine powder.

[0064] The electrode powder according to the present invention is manufactured by a new manufacturing method described below, which can minimize the generation of fine powder, and therefore has a low resistivity as described above, and is easy to form into a film for manufacturing a dry electrode.

[0065] If the specific resistance is high and outside the above range, the resistance of the subsequently produced composite film and dry electrode may increase, which may degrade the battery performance, and this is undesirable.

[0066] The resistivity can be calculated by placing 2 g of electrode powder in a 22 mm diameter ceramic container with a built-in four-point probe at the bottom, pressurizing it with a force of 2,000 kgf, i.e., a pressure of about 50 MPa, and then measuring the resistance, and multiplying the result by the thickness of the pressed electrode powder.

[0067] Meanwhile, according to another embodiment of the present invention, there is provided a method for producing the electrode powder, comprising: (a) producing a mixture containing an active material, a conductive material, and a binder; (b) kneading the mixture at a temperature in the range of 70°C to 200°C under a pressure equal to or higher than atmospheric pressure to produce a mixture mass in order to fiberize the binder; and (c) pulverizing the mixture mass to obtain the electrode powder.

[0068] Furthermore, according to yet another embodiment of the present invention, there is provided a method for manufacturing a dry electrode using the electrode powder, the method including: (d) a step of calendaring the electrode powder to manufacture a composite film; and (e) a step of positioning the composite film on at least one surface of a current collector and laminating the film to manufacture a dry electrode.

[0069] FIG. 2 is a schematic flow diagram showing a method for manufacturing a dry electrode including a method for manufacturing an electrode powder according to one embodiment of the present invention.

[0070] Referring to FIG. 2, according to the present invention, first, a mixture containing an active material, a conductive material, and a binder is prepared.

[0071] Here, the mixing for preparing the mixture is performed so that the active material, conductive material, and binder are uniformly distributed, and since they are mixed in powder form, various methods can be used without limitation as long as simple mixing is possible. However, in the present invention, since a dry electrode is prepared without using a solvent, the mixing may be performed by dry mixing, and may be performed by putting the materials into a device such as a blender or a super mixer.

[0072] To ensure uniformity, the mixing can be carried out using a mixer 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.

[0073] In this case, the dry electrode may be a positive electrode, and the active material may be a positive electrode active material.

[0074] The positive electrode active material is not limited to a lithium transition metal oxide or a lithium metal iron phosphate, as long as it is in the form of a metal oxide, for example, a layered compound such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; 1+x Mn 2-xLithium manganese oxides such as O4(x = 0 to 0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, Cu2V2O7; chemical formula LiNi 1-x M x Ni-site type lithium nickel oxides represented by O2 (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 (M = Co, Ni, Fe, Cr, Zn or Ta, x = 0.01 to 0.1) or Li2Mn3MO8 (M = Fe, Co, Ni, Cu or Zn); LiMnTiO4 in which part of Li in the chemical formula is substituted with alkaline earth metal ions; lithium metal phosphate LiMPO4 (M = Fe, Co, Ni or Mn), disulfide compounds; Fe2(MoO4)3 and the like, but not limited thereto.

[0075] Alternatively, the dry electrode may be a negative electrode, and the active material may be a negative electrode active material.

[0076] The negative electrode active material includes carbons such as non-graphitizable carbon and graphite-based carbon; Li x [[ID=> 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), etc. Metal composite oxides; lithium metal; lithium alloy; silicon-based alloy; tin-based alloy; 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.

[0077] ​However, the dry electrode may specifically be a positive electrode, and therefore the active material may specifically be a positive electrode active material, more specifically, a lithium transition metal oxide, 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, lithium iron phosphate, etc.

[0078] The conductive material is not particularly limited as long as it does not induce chemical changes in the battery and has conductivity. For example, graphite such as natural graphite and artificial graphite; carbon blacks 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 may be used. More specifically, in order to uniformly mix the conductive material and improve conductivity, the conductive material may include one or more selected from the group consisting of activated carbon, graphite, carbon black, and carbon nanotubes, and more specifically, activated carbon.

[0079] The binder may include polytetrafluoroethylene (PTFE), a polyolefin, or a mixture thereof, and may specifically include polytetrafluoroethylene (PTFE), and more specifically may be polytetrafluoroethylene (PTFE).

[0080] Specifically, the polytetrafluoroethylene (PTFE) may be contained in an amount of 60 wt % or more based on the total weight of the binder.

[0081] Of course, the binder may further include polyethylene oxide (PEO), polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), and the like.

[0082] The mixing ratio of the active material, conductive material, and binder may be 80 to 98 wt %:0.5 to 10 wt %:0.5 to 10 wt %:0.5 to 10 wt %, more specifically, 85 to 98 wt %:0.5 to 5 wt %:0.5 to 10 wt %.

[0083] If the binder content is too high beyond the above range, the binder may be excessively fiberized in the subsequent kneading process, affecting the process. If the binder content is too low, the binder may not be sufficiently fiberized, and may not aggregate enough to form a mixture mass, or it may be difficult to produce a composite film, or the physical properties of the composite film may be reduced.

[0084] Furthermore, if the content of the conductive material is too high beyond the above range, the content of the active material may be relatively reduced, resulting in a decrease in capacity or a deterioration in the physical properties of the composite film. On the other hand, if the content is too low, sufficient conductivity may not be ensured, which is undesirable.

[0085] Meanwhile, depending on the case, a filler, which is a component that suppresses expansion of the electrode, may be further added to the mixture. The filler is not particularly limited as long as it does not induce chemical changes in the battery and is a fibrous material, and for example, olefin polymers such as polyethylene and polypropylene; glass fiber, carbon fiber, and other fibrous materials may be used.

[0086] After preparing the mixture in this way, a step for fiberizing the binder in such mixture can be carried out.

[0087] In order to fiberize the binder, high shear mixing such as jet milling has been conventionally performed. However, this type of mixing can pulverize the active material and cause the formed fibers to be cut. Therefore, in the present invention, this problem is solved by using a low shear kneading method instead of high shear mixing.

[0088] In this case, the kneading may be carried out using, but is not limited to, a kneading machine such as a kneader.

[0089] This kneading is a step in which the binder is fiberized to bond or connect the active material and the conductive powder, thereby forming a mixture mass with a solid content of 100%.

[0090] Specifically, the kneading in step (b) may be carried out at a speed of 10 rpm to 100 rpm for 1 minute to 30 minutes, more specifically, at a speed of 25 rpm to 50 rpm for 3 minutes to 7 minutes, and at a shear rate of 10 / s to 500 / s for 1 minute to 30 minutes. More specifically, the shear rate may be in the range of 30 / s to 100 / s.

[0091] Furthermore, this kneading step may be carried out under high temperature and pressure conditions equal to or higher than atmospheric pressure, more particularly, under pressure conditions higher than atmospheric pressure.

[0092] More specifically, the kneading can be carried out at a temperature in the range of 70°C to 200°C, more specifically, 90°C to 180°C or 90°C to 150°C.

[0093] If the temperature is lower than the above range, the binder will not be sufficiently fibrous during kneading and will not form a mass by kneading, and film formation during calendering will not be smooth. If the temperature is too high, the binder will be rapidly fibrous, and then the already formed fibers will be cut by excessive shear force, which is undesirable.

[0094] The reaction can also be carried out at atmospheric pressure or higher, specifically at a pressure of 1 atm to 60 atm, 1 atm to 30 atm, 1 atm to 10 atm, 1 atm to 3 atm, or 1.1 atm to 3 atm.

[0095] If the pressure is too high outside the above range, excessive shear force and pressure will be applied, which may result in cutting of the formed fibers or excessively high density of the mixture mass, which is undesirable.

[0096] That is, according to the present invention, when a low shear mixing step is carried out under high temperature and pressure conditions equal to or higher than atmospheric pressure instead of high shear mixing, the intended effect of the present invention can be achieved.

[0097] Next, according to the present invention, the mixture mass produced through the kneading step is crushed again to obtain powder for an electrode.

[0098] Specifically, the mixture mass produced through the kneading process may be immediately calendered, but in this case, the mixture mass must be pressed under high pressure and high temperature to form a thin film, which may result in an excessively high density of the film or an inconsistent film. Therefore, in the present invention, the produced mixture mass is subjected to a pulverization step.

[0099] 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, etc. Specifically, the pulverization may be performed 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.

[0100] If the rpm is too low or the grinding time is too short outside the above range, grinding will be insufficient and powder of a size unsuitable for film formation may be produced, while if the rpm is too high or the grinding time is too long, a large amount of fine powder may be generated from the mixture mass, which is undesirable.

[0101] According to an embodiment of the present invention, the method may further include, after step (c), classifying the pulverized electrode powder. In the classifying step, the pulverized electrode powder may be filtered through a mesh having pores of a certain size or less to obtain electrode powder having pores of a certain size or more.

[0102] In this manner, powder for an electrode is produced, and then the powder for an electrode is used to produce a dry electrode.

[0103] Specifically, the electrode powder prepared through the above-mentioned pulverization step is calendered to prepare a composite film.

[0104] The calendering is a process of processing the electrode powder into a film shape, for example, a process of rolling the electrode powder into a film shape having an average thickness of 50 μm to 300 μm.

[0105] At this time, the calendering may be performed by, for example, rolls arranged opposite to each other, and at this time, the temperature of the rolls may be 50° C. to 200° C., and the rotation speed of the rolls may be 10 rpm to 50 rpm.

[0106] Once the calendering step is completed, a composite film that serves as an electrode composite can be produced. Conventionally, such a composite film is also called a free-standing film.

[0107] The electrode mixture film thus produced is solvent-free, has little fluidity, and is easy to handle, and can be processed into a desired form for use in the manufacture of various electrodes. Furthermore, when the electrode mixture of the present invention is used in the manufacture of an electrode, the drying process for removing the solvent can be omitted, which not only significantly improves the efficiency of the electrode manufacturing process but also eliminates problems that have arisen in the manufacture of conventional dry electrodes, such as the generation of fine powder of the active material and the cutting of fibrous binders.

[0108] According to the present invention, after the calendering, a lamination step is performed to form the composite film on at least one surface of a current collector.

[0109] The lamination may be a step of rolling and attaching the composite film onto a current collector to a predetermined thickness.

[0110] The lamination may also be performed using a lamination roll, which may be maintained at a temperature between room temperature (25°C) and 200°C.

[0111] The porosity of the composite film in the dry electrode thus laminated may be 20-35%, 22-30%, 20-28%, 20-26%, 23.1-27.4%, 23.1-24.8%, or 24.8-27.4%, and the porosity may be varied slightly depending on the desired effect.

[0112] However, being within the above range is desirable in terms of various effects, but if the porosity is too small outside the above range, it is difficult for the electrolyte to penetrate, which is undesirable in terms of life characteristics, output characteristics, etc., and if it is too large, the volume required to achieve the same capacity increases, which is undesirable in terms of energy density per volume.

[0113] The porosity can be calculated by the following Equation 1 using the true density calculated based on the true density and composition of each component by measuring the apparent density of only the composite film by subtracting the volume and weight of the current collector from the volume and weight of the electrode.

[0114] [Formula 1] Porosity (%)={1-(apparent density / true density)}×100

[0115] Furthermore, the bending resistance of the dry electrode manufactured as described above may be Φ (diameter) less than 10 mm, Φ (diameter) 8 mm or less, Φ (diameter) 5 mm or less, Φ (diameter) 2 to 8 mm, Φ (diameter) 2 to 5 mm, or Φ (diameter) 2 to 3 mm.

[0116] That is, as described above, the dry electrode manufactured according to the present invention can improve flexibility because the cutting of the fibrous binder is reduced.

[0117] The bending resistance can be evaluated according to the method of measurement standard JIS K5600-5-1. Specifically, the prepared dry electrode is brought into contact with measuring rods of various diameters, and then both ends are lifted to measure whether cracks occur and the minimum diameter at which cracks do not occur.

[0118] According to one embodiment of the present invention, the bending resistance of the dry electrode can be evaluated by the following steps: preparing a rectangular electrode sample of 100 mm x 50 mm; preparing measuring rods having diameters of 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 8 mm, 10 mm, 12 mm, 16 mm, 20 mm, 25 mm, and 32 mm; bringing the electrode sample into contact with the measuring rod having the largest diameter among the measuring rods; and determining whether cracks occur in the composite film of the electrode sample when both ends of the electrode sample are lifted; and if no cracks occur in the previous step, repeating the step of determining whether cracks occur in the composite film of the electrode sample using the measuring rod with the next largest diameter, and determining the smallest diameter of the measuring rod at which no cracks occur in the composite film of the electrode sample as the bending resistance.

[0119] The loading amount of the active material in the composite film is 3 mAh / cm 2 ~15mAh / cm 2 Specifically, 4mAh / cm 2 ~10mAh / cm 2 , 4mAh / cm 2 ~6mAh / cm 2 , 4mAh / cm 2 ~5mAh / cm 2 , or 4.8mAh / cm 2 ~4.9mAh / cm 2 It could be.

[0120] Here, the loading amount of the active material is a value calculated according to the following Equation 2.

[0121] [Formula 2] Loading amount (mAh / cm 2) = Capacity of active material (mAh / g) × Weight ratio of active material in the composite film (wt%) × Weight per unit area of ​​composite film (g / cm 2 )

[0122] The interface resistance between the composite film and the current collector is 5 Ω cm 2 Below, 4.3Ω cm 2 Below, 4Ω cm 2 Below, 3Ω cm 2 Below, 1.3~4.3Ω·cm 2 , 1.3~1.8Ω·cm 2 , or 1.8 to 4.3 Ω·cm 2 It could be.

[0123] Here, the interfacial resistance was measured by applying a current of 100 μA to the electrodes using a multi-probe (MP) resistance measurement method, and calculating the resistance between the composite film and the current collector layer from the potential difference measured between 46 probes.

[0124] If the interface resistance is too high and falls outside the above range, it is undesirable because it may degrade the battery performance of the secondary battery that is subsequently manufactured.

[0125] Meanwhile, the current collector is not particularly limited as long as it does not induce chemical changes in the battery and has high conductivity, and may be made of, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, copper, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. In addition, the current collector may have fine irregularities on its surface to increase adhesion of the positive electrode active material, and may be used in various forms such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0126] Furthermore, the current collector may be entirely or partially coated with a conductive primer to reduce surface resistance and improve adhesion.

[0127] Here, the conductive primer may include a conductive material and a binder. The conductive material is not limited as long as it has conductivity, and may be, for example, a carbon-based material.

[0128] The binder may include a solvent-soluble fluorine-based binder (including PVdF and PVdF copolymers), an acrylic binder, and a water-based binder.

[0129] According to another embodiment of the present invention, there is provided a dry electrode manufactured by the method for manufacturing a dry electrode.

[0130] According to the present invention, there is provided a dry electrode having a bending resistance of less than 10 mm in diameter, the dry electrode comprising: an electrode current collector; and a composite film located on the electrode current collector and containing an active material, a conductive material, and a binder.

[0131] At this time, the mixture film and the current collector are as described above.

[0132] According to one embodiment of the present invention, the bending resistance of the dry electrode may be Φ (diameter) less than 10 mm, Φ (diameter) 8 mm or less, Φ (diameter) 5 mm or less, Φ (diameter) 2 to 8 mm, Φ (diameter) 2 to 5 mm, or Φ (diameter) 2 to 3 mm.

[0133] In this case, the bending resistance of the dry electrode can be evaluated according to the measurement standard JIS K5600-5-1 method as described above.

[0134] According to one embodiment of the present invention, the bending resistance of the dry electrode can be evaluated by the following steps: preparing a rectangular electrode sample of 100 mm x 50 mm; preparing measuring rods having diameters of 2, 3, 4, 5, 6, 8, 10, 12, 16, 20, 25, and 32 mm; bringing the electrode sample into contact with the measuring rod having the largest diameter among the measuring rods; and determining whether cracks occur in the composite film of the electrode sample when both ends of the electrode sample are lifted; and if no cracks occur in the previous step, repeating the step of determining whether cracks occur in the composite film of the electrode sample using the measuring rod with the next largest diameter, and determining the smallest diameter of the measuring rod at which no cracks occur in the composite film of the electrode sample as the bending resistance.

[0135] For example, when a dry electrode sample is brought into contact with a measuring rod and then both ends of the electrode sample are lifted, no cracks occur in the composite film of the electrode sample for measuring rods with diameters ranging from 32 mm to 3 mm, but when the electrode sample is brought into contact with a measuring rod with a diameter of 2 mm and then both ends of the electrode sample are lifted, if cracks occur in the composite film of the electrode sample, the bending resistance of this dry electrode is determined to be Φ (diameter) 3 mm, which is the smallest diameter value of the measuring rod at which no cracks occur in the composite film of the electrode sample.

[0136] According to one embodiment of the present invention, the porosity of the composite film may be 20 to 35%, 22 to 30%, 20 to 28%, 20 to 26%, 23.1 to 27.4%, 23.1 to 24.8%, or 24.8 to 27.4%. The method for evaluating the porosity is as described above.

[0137] According to one embodiment of the present invention, the loading amount of the active material of the composite film is 3 mAh / cm 2 ~15mAh / cm 2 Specifically, 4mAh / cm 2 ~10mAh / cm 2 , 4mAh / cm 2 ~6mAh / cm 2 , 4mAh / cm 2~5mAh / cm 2 , or 4.8mAh / cm 2 ~4.9mAh / cm 2 The method for evaluating the loading amount of the active material is as described above.

[0138] The interface resistance between the composite film and the current collector is 5 Ω cm 2 Below, 4.3Ω cm 2 Below, 4Ω cm 2 Below, 3Ω cm 2 Below, 1.3~4.3Ω·cm 2 , 1.3~1.8Ω·cm 2 , or 1.8 to 4.3 Ω·cm 2 The method for evaluating the interface resistance is as described above.

[0139] The present invention also provides a secondary battery including the dry electrode, wherein the dry electrode is a positive electrode, and an electrode assembly including the positive electrode, the negative electrode, and a separator is housed in a battery case together with a lithium-containing non-aqueous electrolyte. Also provided is an energy storage device including the same as a unit battery.

[0140] At this time, the specific structures of the secondary battery and the energy storage device are well known and therefore will not be described in this specification.

[0141] Meanwhile, according to one embodiment of the present invention, there is provided a dry electrode manufacturing apparatus including: a blender that mixes raw material composites including an active material, a conductive material, and a binder; a kneader that kneads the mixture to produce a lump of mixture; a pulverizer that pulverizes the lump of mixture to form a powder for an electrode; a calender that forms the powder for an electrode into a film of composite; and a lamination roll that positions the film of composite on at least one surface of a current collector and laminates it.

[0142] The blender is a mixer for mixing raw materials, and can mix the raw materials for the combination at a speed of 5,000 rpm to 20,000 rpm as described above.

[0143] The kneader is a binder fiberizing device used in place of a jet mill in the present invention, and the mixture can be obtained as a mixture mass through kneading using the kneader.

[0144] In order to obtain the intended results of the present invention, the kneader may be set to a temperature in the range of 70°C to 200°C and a pressure equal to or higher than atmospheric pressure. Specifically, the kneader may be set to a temperature of 90°C to 180°C or 90°C to 150°C and a pressure of 1 atm to 60 atm, 1 atm to 30 atm, 1 atm to 10 atm, 1 atm to 3 atm, or 1.1 atm to 3 atm.

[0145] The pulverizer is a device for pulverizing the mixture mass to form powder for an electrode, and may be a blender or a grinder such as a cutter mill or a fine impact mill.

[0146] The calender is a device for forming the electrode powder into a film shape, and may be, for example, a pair of rollers facing each other, and the thickness of the film can be adjusted by adjusting the gap between them.

[0147] The lamination roll serves to attach and roll the composite film formed by the calendar onto at least one surface of the current collector.

[0148] That is, the dry electrode manufacturing apparatus according to the present invention is characterized in that it does not include a jet milling device, but includes a kneader and a pulverizer.

[0149] The specific structures of the blender, kneader, calendar, and lamination roll are well known, and therefore, detailed explanations thereof will be omitted in this specification.

[0150] The present invention will now be described in detail with reference to examples, comparative examples and experimental examples so that those skilled in the art can easily understand the present invention.

[0151] Example 1 94g of LiMnO2 as a positive electrode active material, 0.5g of activated carbon as a conductive material, 3g of carbon black, and 2.5g of polytetrafluoroethylene (PTFE) as a binder were added to a blender and mixed at 15,000 rpm for 1 minute to prepare a mixture. The temperature of the kneader was stabilized at 90°C, and the mixture was then added to the kneader. The kneader was then operated at a pressure of 1.1 atm and a speed of 50 rpm for 5 minutes to obtain a mixture mass.

[0152] The mixture mass was put into a blender and pulverized at 10,000 rpm for 1 minute to obtain powder for electrodes.

[0153] <Comparative Example 1> In Example 1, the kneading and pulverizing steps using a kneader were not performed, and the mixture was subjected to a jet milling process (feeding pressure 50 psi, pulverizing pressure 45 psi) to obtain powder for an electrode.

[0154] <Experimental Example 1> SEM photographs of the electrode powder produced in Example 1 and the electrode powder produced in Comparative Example 1 are shown in FIGS.

[0155] 3 and 4, the degree of pulverization of the active material can be confirmed.

[0156] It can be seen that the dry electrode of Comparative Example 1 was more pulverized.

[0157] <Example 2> A powder for an electrode was obtained in the same manner as in Example 1, except that the temperature of the kneader was set to 150°C.

[0158] Example 3 An electrode powder was obtained in the same manner as in Example 1, except that 3.5 g of carbon black alone was used as the conductive material and the kneader temperature was set to 150°C.

[0159] <Comparative Example 2> Powder for an electrode was obtained in the same manner as in Example 1, except that the temperature of the kneader was set to 25°C.

[0160] <Comparative Example 3> Powder for an electrode was obtained in the same manner as in Example 1, except that the temperature of the kneader was set to 60°C.

[0161] <Experimental Example 2> The pressure resistivity of the electrode powders produced in Examples 1 to 3 and Comparative Examples 1 to 3 was measured by the following method, and the results are shown in Table 1 below.

[0162] Pressurized resistivity of electrode powder: 2 g of electrode powder was placed in a 22 mm diameter ceramic container with a built-in four-point probe at the bottom, and the resistance was measured after applying a force of 2,000 kgf, or a pressure of approximately 50 MPa, and the powder resistivity was calculated by multiplying this by the thickness of the pressed electrode powder.

[0163] Then, the electrode powders prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were fed into a wrap calender (roll diameter: 88 mm, roll temperature: 85°C, 20 rpm) under the following active material loading conditions to prepare composite films. The composite films were used as a conductive primer layer and placed on one side of an aluminum foil (19 μm) coated with a primer layer made of a carbon black:acrylic binder mixture in a weight ratio of 5:6. The foil was then laminated using a lamination roll maintained at 120°C to prepare an electrode.

[0164] At this time, the target porosity was set to 23 to 30%, and the gap of the lamination roll was adjusted based on the initial density and thickness of the composite film so that it fell within the above range.

[0165] The following parameters were measured for the manufactured electrodes. Meanwhile, in Comparative Examples 2 and 3, the feasibility of producing composite films through calendering was evaluated. The measurement methods were as follows, and the results are shown in Table 1 below.

[0166] Porosity: The volume and weight of the current collector were subtracted from the volume and weight of the electrode to measure the apparent density of the composite film alone. The actual porosity of each electrode was calculated using the true density of each component and the true density calculated based on the composition according to the following equation 1.

[0167] [Formula 1] Porosity (%)={1-(apparent density / true density)}×100

[0168] Bending resistance: According to the measurement standard JIS K5600-5-1 method, each electrode was brought into contact with measuring rods of various diameters and then both ends were lifted to measure whether cracks occurred and the minimum diameter at which cracks did not occur.

[0169] Specifically, the bending resistance was evaluated by preparing rectangular electrode samples of 100 mm x 50 mm; preparing measuring rods having diameters of 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 8 mm, 10 mm, 12 mm, 16 mm, 20 mm, 25 mm, and 32 mm; and using the measuring rod with the largest diameter among these, bringing the electrode sample into contact with the measuring rod and then lifting both ends of the electrode sample to determine whether cracks occurred in the composite film of the electrode sample; if no cracks occurred in the previous step, the next largest diameter measuring rod was used to repeat the step of determining whether cracks occurred in the composite film of the electrode sample in the same manner as in the previous step, and the smallest diameter of the measuring rod at which no cracks occurred in the composite film of the electrode sample was determined as the bending resistance.

[0170] For example, when a dry electrode sample is brought into contact with a measuring rod and then both ends of the electrode sample are lifted, no cracks occur in the composite film of the electrode sample for measuring rods with diameters ranging from 32 mm to 3 mm, but when the electrode sample is brought into contact with a measuring rod with a diameter of 2 mm and then both ends of the electrode sample are lifted, if cracks occur in the composite film of the electrode sample, the bending resistance of this dry electrode is determined to be Φ (diameter) 3 mm, which is the smallest diameter value of the measuring rod at which no cracks occur in the composite film of the electrode sample.

[0171] Interfacial resistance between the composite film and the current collector: Using the MP (Multi-Probe) resistance measurement method, a current of 100 μA was applied to the electrode, and the resistance between the composite film and the current collector layer was calculated from the potential difference measured between the 46 probes.

[0172] [Table 1]

[0173] Referring to Table 1, it can be seen that the dry electrode manufactured according to the present invention has a bending resistance of Φ (diameter) 3 mm or less, whereas the dry electrode manufactured by the conventional method has a Φ (diameter) of Φ 10 mm, and it can be seen that if the kneader temperature is low, it is not easily formed into a film under the above calendering conditions, and is therefore not suitable for the electrode manufacturing process.

[0174] <Experimental Example 3> A negative electrode was prepared by depositing lithium metal on a copper foil to a thickness of 70 μm.

[0175] An electrode assembly was prepared by interposing a polyethylene film (manufactured by Celgard, thickness: 20 μm) between the dry electrodes prepared in Examples 1 to 3 and Comparative Example 1 and the negative electrode.

[0176] The electrode assembly was placed in a battery case, and a liquid electrolyte solution in which LiPF6 was dissolved at 1M in a solvent in which ethylene carbonate, dimethylene carbonate, and diethyl carbonate were mixed in a volume ratio of 1:2:1 was poured into the battery case, and the battery case was sealed to manufacture a secondary battery.

[0177] The secondary battery was charged at 0.1C up to 4.3V using CC (constant current)-CV (constant voltage) charging, and then discharged at 0.1C down to 3.0V. The capacity and efficiency were calculated, and the results are shown in Table 2.

[0178] [Table 2]

[0179] Referring to Table 2, it can be seen that the charge / discharge efficiency produced by the method of the present invention is the same as or better than that produced by the conventional method.

Claims

1. An electrode powder that can be formed into a film for producing a dry electrode for a secondary battery, the electrode powder contains an active material, a conductive material, and a binder; The electrode powder has a resistivity of 700 Ω·cm or less when pressed at a pressure of 50 MPa.

2. A method for producing the electrode powder according to claim 1, (a) preparing a mixture including an active material, a conductive material, and a binder; (b) kneading the mixture at a temperature in the range of 70°C to 200°C under a pressure equal to or higher than atmospheric pressure to produce a mixture mass in order to fiberize the binder; (c) pulverizing the mixture mass to obtain the electrode powder.

3. The method for producing a powder for an electrode according to claim 2 , wherein the conductive material comprises at least one material selected from the group consisting of activated carbon, graphite, carbon black, and carbon nanotubes.

4. The method for producing electrode powder according to claim 2 , wherein the binder comprises polytetrafluoroethylene, polyolefin, or a mixture thereof.

5. 3. The method for producing a powder for an electrode according to claim 2, wherein the kneading in the step (b) is carried out at a speed of 10 rpm to 100 rpm for 1 minute to 30 minutes.

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

7. The method for producing a powder for an electrode according to claim 2, wherein the kneading in the step (b) is carried out at 90°C to 180°C.

8. 3. The method for producing a powder for an electrode according to claim 2, wherein the kneading in the step (b) is carried out under a pressure of 1 atm to 60 atm.

9. 3. The method for producing an electrode powder according to claim 2, wherein the pulverization in the step (c) is carried out at a speed of 500 rpm to 20,000 rpm for 30 seconds to 10 minutes.

10. The method for producing electrode powder according to claim 2 , further comprising the step of classifying the pulverized electrode powder after the step (c).

11. A method for manufacturing a dry electrode, comprising: (d) producing a composite film by calendering the electrode powder produced by the method for producing an electrode powder according to claim 2; (e) placing the mixture film on at least one surface of a current collector and laminating it to produce a dry electrode.

12. The method for producing a dry electrode according to claim 11, wherein the porosity of the composite film is 20 to 35%.

13. The method for producing a dry electrode according to claim 11, wherein the dry electrode has a bending resistance of less than Φ10 mm.

14. The loading of the active material of the composite film is 3 mAh / cm ２ ~15mAh / cm ２ The method for producing a dry electrode according to claim 11,

15. The interface resistance between the composite film and the current collector is 5 Ω cm ２ The method for producing a dry electrode according to claim 11, wherein:

16. The method for manufacturing a dry electrode according to claim 11, wherein the current collector is entirely or partially coated with a conductive primer.

17. A dry electrode manufactured by the method for manufacturing a dry electrode according to claim 11.

18. A current collector; a composite film located on the current collector and including an active material, a conductive material, and a binder; A dry electrode with bending resistance of less than Φ10 mm.

19. The dry electrode according to claim 18, wherein the dry electrode has a bending resistance of Φ2 to 8 mm.

20. The dry electrode according to claim 18, wherein the flex resistance of the dry electrode is evaluated according to the measurement standard JIS K5600-5-1 method.

21. The bending resistance of the dry electrode is producing a rectangular electrode sample of 100 mm x 50 mm; preparing measuring rods having diameters of 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 8 mm, 10 mm, 12 mm, 16 mm, 20 mm, 25 mm, and 32 mm, respectively, and determining whether cracks occur in the composite film of the electrode sample when the measuring rod with the largest diameter is used to contact the electrode sample with the measuring rod and then lifting both ends of the electrode sample; 21. The dry electrode according to claim 20, wherein, if no cracks occur in the previous step, a step of determining whether or not cracks occur in the composite film of the electrode sample in the same manner as in the previous step is repeated using a measuring rod with a next larger diameter, and the minimum diameter value of the measuring rod at which no cracks occur in the composite film of the electrode sample is determined as the bending resistance.

22. 19. The dry electrode according to claim 18, wherein the porosity of the composite film is 20 to 35%.

23. The loading amount of the active material of the composite film is 3 to 15 mAh / cm ２ 19. The dry electrode of claim 18, wherein:

24. The interface resistance between the composite film and the current collector is 5 Ω cm ２ 20. The dry electrode of claim 18, wherein:

25. 20. The dry electrode of claim 18, wherein the current collector is wholly or partially coated with a conductive primer.

26. A secondary battery comprising the dry electrode according to any one of claims 17 to 25, The dry electrode is a positive electrode, and an electrode assembly including the positive electrode, the negative electrode, and a separator is housed in a battery case together with a lithium-containing non-aqueous electrolyte.

27. An energy storage device comprising the secondary battery according to claim 26 as a unit battery.

28. A dry electrode manufacturing apparatus, comprising: a blender for mixing raw materials for a mixture including an active material, a conductive material, and a binder to produce a mixture; a kneader for kneading the mixture to produce a mixture mass in order to fiberize the binder; a grinder for grinding the mixture mass to form an electrode powder; a calender for forming the electrode powder into a mixture film; and a lamination roll that places the composite film on at least one surface of a current collector and laminates it.

29. The dry electrode manufacturing apparatus according to claim 28, wherein the kneader is set at a temperature in the range of 70°C to 200°C and a pressure condition of atmospheric pressure or higher.

Images