Powder for electrodes used to manufacture dry electrodes for secondary batteries, a method for manufacturing the same, and a method for manufacturing dry electrodes using the same.

Abstract

One embodiment of the present invention provides an electrode powder 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. The electrode powder also provides a method for manufacturing the electrode powder, a method for manufacturing a dry electrode using the electrode powder, a dry electrode, a secondary battery including the dry electrode, an energy storage device, and an apparatus for manufacturing the dry electrode.

Description

[Technical Field]

[0001] The present invention relates to an electrode powder for manufacturing a dry electrode for a secondary battery, a method for manufacturing the same, a method for manufacturing a dry electrode using the same, a dry electrode, a secondary battery containing 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 21 October 2020, and all contents disclosed in the specification and drawings of said application are incorporated herein by reference. [Background technology]

[0003] The rapid increase in fossil fuel use is driving a growing demand for alternative and clean energy sources. Among the most actively researched areas in this field is electrochemical power generation and energy storage.

[0004] A typical example of an electrochemical element that utilizes this type of electrochemical energy is the secondary battery, and its range of applications is steadily expanding.

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

[0006] The manufacturing process for such lithium secondary batteries can be broadly divided into three stages: the electrode process, the assembly process, and the aging process. The electrode process can be further divided into the active material mixing process, the electrode coating process, the drying process, the rolling process, the slitting process, the winding process, and so on.

[0007] Among these, the active material mixing process is a process of blending a coating material for forming an electrode active layer where actual electrochemical reactions occur in the electrode. Specifically, it is a process of mixing the electrode active material, which is an essential element of the electrode, a conductive material and a filler as other additives, a binder for binding between powders and adhesion to the current collector, and a solvent for imparting viscosity and dispersing powders, etc., to produce in the form of a slurry having fluidity.

[0008] The composition thus mixed for forming the electrode active layer is also referred to as an electrode mixture in a broad sense.

[0009] Thereafter, an electrode coating process of applying the electrode mixture onto an electrically conductive current collector and a drying process for removing the solvent contained in the electrode mixture are performed, and additionally the electrode is rolled to be manufactured with a predetermined thickness.

[0010] On the other hand, in the drying process, when the solvent contained in the electrode mixture evaporates, defects such as pinholes and cracks may be induced in the already formed electrode active layer. Also, the inside and outside of the active layer are not dried uniformly, and there is a risk that the electrode quality may deteriorate due to a powder floating phenomenon caused by the difference in the evaporation rate of the solvent, that is, the powder at the site dried first floats while forming a gap with the site dried relatively later.

[0011] Therefore, in order to solve the above problems, a drying device capable of adjusting the evaporation rate of the solvent while the inside and outside of the active layer are dried uniformly is considered, but such a drying device is very expensive and requires a considerable cost and time for operation, which is disadvantageous in terms of manufacturing processability.

[0012] Therefore, recently, research on manufacturing dry electrodes without using a solvent has been actively conducted. Dry electrodes are generally manufactured by laminating a free-standing film containing an active material, a binder, a conductive material, etc. in film form on a current collector.

[0013] Fig. 1 schematically shows the steps of manufacturing a conventional dry electrode.

[0014] Referring to Fig. 1, first, an active material, a carbon material as a conductive material, and a fibrillatable binder are mixed together using a blender or the like, and the binder is fibrillated through a high shear mixing process such as jet - milling. Then, the mixture is calendered into a film to produce a free - standing film. After that, it is manufactured by laminating the produced free - standing film after calendering onto a current collector.

[0015] However, when applying the above - mentioned high shear mixing process to the easily - broken active material, a large amount of fine powder with a small powder size is generated, and the mechanical performance and electrochemical performance are likely to deteriorate. When the high shear mixing becomes excessive, there is a risk of cutting the produced binder fibers and reducing the flexibility of the free - standing film. In addition, during the jet - milling process, components adhere to the inside of the equipment, causing problems such as clogging of the flow path by obstructing the flow of high - pressure air, so it is not suitable for mass production.

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

[0017] An object of the present invention is to provide a powder for a dry electrode that minimizes the pulverization of the active material and maximizes the fibrillation of the binder, and a method for manufacturing the same, in order to solve the above problems.

[0018] Another object of the present invention is to provide a method for manufacturing a dry electrode that improves the mechanical performance of the electrode and is suitable for mass production by including it.

[0019] The present invention further aims to provide a dry electrode manufactured by the above manufacturing method, a secondary battery containing the same, and an apparatus for manufacturing the dry electrode. [Means for solving the problem]

[0020] To solve the problems of the present invention, one aspect of the present invention provides an electrode powder as described in the following embodiment.

[0021] According to the first embodiment, an electrode powder that can be made into a film for manufacturing a dry electrode for a secondary battery is provided, wherein the powder comprises an active material, a conductive material, and a binder, and has a resistivity of 700 Ω·cm or less when pressurized at a pressure of 50 MPa.

[0022] According to the second embodiment, a method for producing electrode powder according to the first embodiment is provided, comprising: (a) the step of producing a mixture containing an active material, a conductive material, and a binder; (b) the step of kneading the mixture at a temperature in the range of 70°C to 200°C and at a pressure of normal pressure or higher in order to fibrousize the binder, thereby producing a mixture mass; and (c) the step of crushing the mixture mass to obtain electrode powder.

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

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

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

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

[0027] According to the 7th embodiment example, in any one of the 2nd to 6th embodiment examples, The kneading in step (b) above may be carried out at a temperature of 90°C to 180°C.

[0028] According to the 8th embodiment, in any one of the 2nd to 7th embodiments, the kneading in step (b) may be carried out under a pressure of 1 atm to 60 atm.

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

[0030] According to the 10th embodiment, in any one of the 2nd to 9th embodiments, the step of classifying the pulverized electrode powder may be further included after step (c).

[0031] One aspect of the present invention provides a method for manufacturing a dry electrode as described in the following embodiment.

[0032] According to the 11th embodiment, a method for manufacturing a dry electrode is provided, comprising the steps of (d) calendering an electrode powder from any one of the 2nd to 10th embodiments to produce a composite film, and (e) positioning the composite film on at least one surface of a current collector and laminating it.

[0033] According to the 12th embodiment, in the 11th embodiment, the porosity of the composite film may be 20-35%.

[0034] According to the 13th embodiment, in the 11th or 12th 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 in the composite film is 3 mAh / cm². 2 ~15mAh / cm 2 It is possible.

[0036] According to the 15th embodiment, in any one of the 11th to 14th embodiments, the interfacial resistance between the composite film and the current collector is 5 Ω·cm. 2 The following are possible:

[0037] According to the 16th embodiment, in any one of the 11th to 15th embodiments, a conductive primer may be coated on the current collector, either entirely or partially. Another aspect of the present invention provides a dry electrode as described in the following embodiment.

[0038] According to the 17th embodiment, a dry electrode manufactured by the manufacturing method of any one of the 11th to 16th embodiments is provided.

[0039] According to the 18th embodiment, a dry electrode is provided 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, having a bending resistance of less than Φ (diameter) 10 mm.

[0040] According to the 19th embodiment, in the 18th embodiment, the dry electrode may have a bending resistance of Φ (diameter) 2 to 8 mm.

[0041] According to the 20th embodiment, in the 18th or 19th embodiment, the bending resistance of the dry electrode can be evaluated according to the measurement standard JIS K5600-5-1 method.

[0042] According to the 21st embodiment, in any one of the 18th to 20th embodiments, the bending resistance of the dry electrode can be evaluated by the following steps: manufacturing a rectangular electrode sample measuring 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 to bring the electrode sample into contact with the measuring rod, then lifting both ends of the electrode sample to determine whether or not cracks occur in the composite film of the electrode sample; and if no cracks occur in the previous step, repeating the step of determining whether or not cracks occur in the composite film of the electrode sample in the same manner as the previous step using the next largest diameter measuring rod, and determining the minimum diameter value of the measuring rod that does not cause cracks in the composite film of the electrode sample as the bending resistance.

[0043] According to the 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 in the composite film is 3 mAh / cm². 2 ~15mAh / cm 2 It is possible.

[0045] According to the 24th embodiment, in any one of the 18th to 23rd embodiments, the interfacial resistance between the composite film and the current collector is 5 Ω·cm. 2 The following are possible:

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

[0047] One aspect of the present invention provides a secondary battery as described below.

[0048] According to the 26th embodiment, a secondary battery is provided which includes a dry electrode according to any one of the 17th to 25th embodiments, wherein the dry electrode is a positive electrode, and the electrode assembly including the positive electrode, negative electrode, and separator membrane 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 as described below.

[0050] According to the 27th embodiment, an energy storage device is provided that includes the secondary battery of the 26th embodiment as a unit battery.

[0051] One aspect of the present invention provides a manufacturing apparatus for dry electrodes as described below.

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

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

[0054] According to the present invention, by introducing a pulverization step after a high-temperature, low-shear kneading step instead of a high-shear mixing step, it is possible to minimize the micronization of the active material, maximize the formation of binder fibers, and minimize the cutting of the fibrous binder.

[0055] Furthermore, by manufacturing dry electrodes using such electrode powders, the flexibility of the dry electrodes can be ensured.

[0056] Furthermore, by using a kneading and grinding stage with a kneader instead of a high-shear jet milling process, the problem of the flow path becoming clogged with clumps of constituent components is eliminated, which is advantageous for mass production. [Brief explanation of the drawing]

[0057] [Figure 1] This is a flowchart illustrating a conventional method for manufacturing dry electrodes for secondary batteries. [Figure 2] This is a flowchart illustrating a method for manufacturing a dry electrode for a secondary battery according to one embodiment of the present invention. [Figure 3] This is an SEM image of the electrode powder used in Example 1 of the present invention, according to Experimental Example 1. [Figure 4] This is an SEM image of the electrode powder of Comparative Example 1 according to Experimental Example 1 of the present invention. [Modes for carrying out the invention]

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

[0059] Terms and words used in this specification and claims should not be interpreted in a manner limited to their ordinary and dictionary meanings, but rather in a manner and concept corresponding to the technical idea of ​​the present invention, in accordance with the principle that the inventor himself can appropriately define the concept of a term in order to best describe the invention.

[0060] The terms used herein are for illustrative purposes only and do not limit the invention. Unless otherwise specified, singular expressions include plural expressions.

[0061] Furthermore, throughout the specification, when a part "includes" other components, unless otherwise specified, it means that it may include other components, rather than excluding them.

[0062] According to one embodiment of the present invention, there is an electrode powder that can be made into a film for manufacturing a dry electrode for a secondary battery, wherein the powder comprises an active material, a conductive material, and a binder, and has a resistivity of 700 Ω·cm or less when pressurized at a pressure of 50 MPa.

[0063] In order to achieve the characteristics described above, the dispersion of the active material, conductive material, and binder within the electrode powder must be maximized, while the generation of fine powder must be minimized.

[0064] The electrode powder according to the present invention is manufactured by a new manufacturing method described later, which minimizes the generation of fine particles. As a result, it has a low resistivity as described above, and is easy to form into a film for the manufacture of dry electrodes.

[0065] If the resistivity is high and falls outside the above range, it may increase the resistance of the subsequently manufactured composite film and dry electrode, potentially degrading battery performance, which is undesirable.

[0066] The resistivity can be calculated by placing 2g of electrode powder into a 22mm diameter ceramic container with four built-in probes at the bottom, applying a force of 2,000kgf, or a pressure of approximately 50MPa, measuring the resistance, and multiplying this by the thickness of the pressurized electrode powder.

[0067] On the other hand, according to another embodiment of the present invention, a method for producing electrode powder is provided, comprising: (a) a step of producing a mixture containing an active material, a conductive material, and a binder; (b) a step of kneading the mixture at a temperature in the range of 70°C to 200°C and at a pressure of normal pressure or higher in order to fibrousize the binder, in order to produce a mixture mass; and (c) a step of crushing the mixture mass to obtain electrode powder.

[0068] Furthermore, according to yet another embodiment of the present invention, a method for manufacturing a dry electrode using the electrode powder is provided, comprising the steps of (d) calendering the electrode powder to produce a composite film, and (e) positioning the composite film on at least one surface of a current collector and laminating it to produce a dry electrode.

[0069] Figure 2 schematically shows a flow chart illustrating a method for manufacturing a dry electrode, including a method for manufacturing electrode powder according to one embodiment of the present invention.

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

[0071] In this case, the mixing for producing the mixture is carried out so that the active material, conductive material, and binder are uniformly distributed, and since they are mixed in a powder form, they can be mixed in a variety of ways without limitation, as long as simple mixing of these materials is possible. However, in this invention, since a solvent-free dry electrode is to be manufactured, the mixing can be carried out by dry mixing, and can be done by putting the materials into equipment such as a blender or supermixer.

[0072] Furthermore, in order to ensure uniformity, the mixing may be carried out using a mixer at 5,000 rpm to 20,000 rpm for 30 seconds to 20 minutes, or 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 lithium transition metal oxides or lithium metallic iron phosphorus oxides, or metal oxides, and is, 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; chemical formula Li 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); LiMn2O4 in which part of the 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 graphitizable carbon and graphite-based carbon; 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) and other 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 and the like can be used.

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

[0078] The conductive material is not particularly limited as long as it does not induce a chemical change in the battery and is conductive. For example, graphite such as natural graphite or 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 fibers and metal fibers; 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, to ensure uniform mixing of the conductive material and improve conductivity, it may include one or more selected from the group consisting of activated carbon, graphite, carbon black, and carbon nanotubes, and more specifically, it may include activated carbon.

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

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

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

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

[0083] If the binder content exceeds the above range, the binder may be excessively fibrous during the subsequent kneading process, potentially affecting the process. If the content is too low, it may not fibrous sufficiently, resulting in insufficient aggregation to form a mixture lump, difficulty in manufacturing the composite film, or a decrease in the physical properties of the composite film.

[0084] Furthermore, if the conductive material content exceeds the above range, the relative content of the active material may decrease, leading to a decrease in capacity or a deterioration of the physical properties of the composite film. Conversely, if the content is too low, sufficient conductivity cannot be ensured, which is undesirable.

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

[0086] After producing the mixture in this manner, a process may be carried out to fibrousize the binder using this mixture.

[0087] Conventionally, high-shear mixing such as jet milling was performed to fibrousize the binder. However, such mixing may cause the active material to be pulverized and 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 can be carried out using a kneading machine, such as a kneader, although this is not limited to this method.

[0089] Such kneading is a step in which the binder is fibrousized while bonding or linking the active material and conductive material powder to form a mixture mass with 100% solid content.

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

[0091] Furthermore, such mixing steps can be carried out under high temperature and pressure conditions above atmospheric pressure, or more specifically, under pressure conditions higher than atmospheric pressure.

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

[0093] If the process is carried out at a temperature outside the above range, the binder will not fiberize or agglomerate sufficiently during kneading, resulting in poor film formation during calendering. Conversely, if the process is carried out at a temperature that is too high, the binder will fiberize too rapidly, and then the already formed fibers will be cut by excessive shear force, which is undesirable.

[0094] Furthermore, the tests may be conducted at or above atmospheric pressure, specifically under pressures 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] Performing the process at excessively high pressures outside the above range is undesirable because it can lead to problems such as excessive shear force and pressure, causing the formed fibers to break or the density of the mixture to become excessively high.

[0096] In other words, according to the present invention, the intended effects can be achieved when a low-shear mixing process is performed under high temperature and pressure conditions above atmospheric pressure, instead of high-shear mixing.

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

[0098] Specifically, the mixture mass produced through the kneading process may be immediately calendered, but in this case, it is necessary to press the mixture mass with high pressure and high temperature to form a thin film, which can lead to problems such as the film becoming excessively dense or not being able to obtain a uniform film. Therefore, in the present invention, the produced mixture mass is subjected to a grinding step.

[0099] In this case, the grinding may be carried out using a blender, although this is not particularly limited, or using equipment such as a cutter mill or a fine impact mill. Specifically, the grinding may be carried out at a speed of 500 rpm to 20,000 rpm for 30 seconds to 10 minutes, or more precisely 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 not be sufficient, and powder particles of an unsuitable size for film formation may be produced. Conversely, 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, which is undesirable.

[0101] According to one embodiment of the present invention, the step of classifying the pulverized electrode powder may be further included after step (c). In the classification step, the pulverized electrode powder can be filtered to obtain electrode powder of a certain size or larger using a mesh having pores of a certain size or smaller.

[0102] Electrode powder is manufactured using this method. Then, a dry electrode is manufactured using this electrode powder.

[0103] Specifically, the electrode powder, which has been manufactured up to the grinding stage as described above, is calendered to produce a composite film.

[0104] Such calendering processes the electrode powder into a film, and may involve, for example, rolling it into a film with an average thickness of 50 μm to 300 μm.

[0105] In this case, the calendering may be performed, for example, by opposing rolls, in which case 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] By performing this calendering stage, a composite film that serves as an electrode composite can be manufactured. Conventionally, such a composite film is also called a free-standing film.

[0107] The resulting composite film, being solvent-free, has very little fluidity and is easy to handle, and can be processed into desired forms for use in the manufacture of electrodes of various shapes. Furthermore, when the electrode composite of the present invention is used in the manufacture of electrodes, the drying process for removing the solvent can be omitted, which not only greatly improves the efficiency of electrode manufacturing but also eliminates problems such as the cutting of fine active material and fibrous binders that have been problematic in the manufacture of conventional dry electrodes.

[0108] Furthermore, according to the present invention, after calendering, a lamination step is performed in which the composite film is formed on at least one surface of the current collector.

[0109] The lamination may involve rolling and attaching the composite film to the current collector to a predetermined thickness.

[0110] The lamination can also be performed by a lamination roll, in which case the lamination roll can be maintained at a temperature of room temperature (25°C) to 200°C.

[0111] In dry electrodes where lamination has been performed in this manner, the porosity of the composite film can be 20-35%, 22-30%, 20-28%, 20-26%, 23.1-27.4%, 23.1-24.8%, or 24.8-27.4%. Such porosity can be slightly varied depending on the effect being emphasized.

[0112] However, being within the above range is desirable in terms of various effects. If the porosity is too small and falls outside the above range, the electrolyte will not penetrate easily, which is undesirable in terms of lifetime characteristics and output characteristics. If it is too large, the volume required to achieve the same capacity will increase, which is undesirable in terms of volume-to-energy density.

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

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

[0115] Furthermore, the bending resistance of dry electrodes manufactured as described above may be less than 10 mm in diameter, 8 mm or less, 5 mm or less, 2-8 mm, 2-5 mm, or 2-3 mm in diameter.

[0116] In other words, as described above, the dry electrode manufactured by the present invention can improve flexibility because the cutting of the fibrous binder is reduced.

[0117] The aforementioned bending resistance can be evaluated according to the method of the measurement standard JIS K5600-5-1, specifically by bringing the manufactured dry electrode into contact with measuring rods of various diameters, and then lifting both ends to measure whether cracks occur and the minimum diameter at which no cracks occur.

[0118] According to one embodiment of the present invention, the bending resistance of the dry electrode can be evaluated by the following steps: manufacturing a rectangular electrode sample measuring 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 or not cracks occur in the composite film of the electrode sample; and if no cracks occur in the previous step, repeating the step of determining whether or not cracks occur in the composite film of the electrode sample in the same manner as the previous step using the measuring rod with the next largest diameter, and determining the minimum diameter value of the measuring rod that does not cause cracks in the composite film of the electrode sample as the bending resistance.

[0119] Furthermore, the loading amount of the active material in the aforementioned composite film is 3 mAh / cm². 2 ~15mAh / cm 2 It could be 4mAh / cm², for more details. 2 ~10mAh / cm 2 4mAh / cm² 2 ~6mAh / cm 2 4mAh / cm² 2 ~5mAh / cm 2 , or 4.8mAh / cm² 2 ~4.9mAh / cm 2 It is possible.

[0120] Here, the loading amount of the active material is the value calculated using the following formula 2.

[0121] [Formula 2] Loading capacity (mAh / cm³) 2) = Active material capacity (mAh / g) × Weight ratio of active material in the mixture film (wt%) × Weight of the mixture film per unit area (g / cm²) 2 )

[0122] Furthermore, the interfacial 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 1.8~4.3Ω·cm 2 It is possible.

[0123] Here, the interfacial resistance was calculated by applying a current of 100 μA to the electrodes using the MP (Multi Probe) resistance measurement method and determining the resistance between the composite film and the current collector layer based on the potential difference measured between 46 probes.

[0124] If the interfacial resistance is high outside the above range, it may degrade the battery performance of subsequent secondary batteries, which is undesirable.

[0125] On the other hand, the current collector is not particularly limited as long as it does not induce chemical changes in the battery and has high conductivity. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, copper, or aluminum or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc., can be used. Furthermore, the current collector may have fine irregularities formed on its surface to enhance the adhesion to the positive electrode active material, and can be used in a variety of forms such as films, sheets, foils, nets, porous materials, foams, and nonwoven fabrics.

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

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

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

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

[0130] According to the present invention, a dry electrode is provided that comprises 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, and having a bending resistance of less than Φ (diameter) 10 mm.

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

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

[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: manufacturing a rectangular electrode sample measuring 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, and using the measuring rod with the largest diameter to bring the electrode sample into contact with the measuring rod, then lifting both ends of the electrode sample to determine whether or not cracks occur in the composite film of the electrode sample; and, if no cracks occur in the previous step, repeating the step of determining whether or not cracks occur in the composite film of the electrode sample in the same manner as the previous step using the measuring rod with the next largest diameter, and determining the minimum diameter value of the measuring rod that does not cause cracks 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 occurred in the composite film of the electrode sample when using measuring rods ranging from 32 mm in diameter to 3 mm in diameter. However, 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, cracks occur in the composite film of the electrode sample. In this case, the bending resistance of this dry electrode is determined to be Φ (diameter) 3 mm, which is the smallest diameter of measuring rod in which no cracks occurred 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 20-35%, 22-30%, 20-28%, 20-26%, 23.1-27.4%, 23.1-24.8%, or 24.8-27.4%. 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 in the composite film is 3 mAh / cm². 2 ~15mAh / cm 2 It could be 4mAh / cm², for more details. 2 ~10mAh / cm 2 4mAh / cm² 2 ~6mAh / cm 2 4mAh / cm² 2~5mAh / cm 2 , or 4.8mAh / cm² 2 ~4.9mAh / cm 2 This is possible. The method for evaluating the loading amount of the active material is as described above.

[0138] The interfacial 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 1.8~4.3Ω·cm 2 This is possible. The method for evaluating the interfacial resistance is as described above.

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

[0140] At this time, the specific structure of the secondary battery and energy storage device is already well known, so a description of it will be omitted in this specification.

[0141] On the other hand, according to one embodiment of the present invention, a dry electrode manufacturing apparatus is provided, comprising: a blender for mixing a mixture raw material containing an active material, a conductive material, and a binder; a kneader for kneading the mixture to produce a mixture mass; a pulverizer for crushing the mixture mass to form electrode powder; a calender for forming the electrode powder as a mixture film; and a lamination roll for positioning the mixture film on at least one surface of a current collector and laminating it.

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

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

[0144] In this case, in order to obtain the results intended by the present invention, the kneader may be set to a temperature range of 70°C to 200°C and a pressure condition of atmospheric pressure or higher. Specifically, it may be set to 90°C to 180°C, or 90°C to 150°C, and pressure conditions 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 aforementioned pulverizer is a device that pulverizes a mixture mass to form electrode powder, and may use 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, and may be, for example, a pair of opposing rollers, the thickness of the film can be adjusted by the distance between them.

[0147] The lamination roll plays the role of adhering and rolling the composite film formed by the calender to at least one surface of the current collector.

[0148] In other words, the dry electrode manufacturing apparatus according to the present invention is characterized by not including a jet milling machine, but including a kneader and a pulverizer.

[0149] Since the specific structures of the blender, kneader, calender, and lamination rolls are well known, a detailed explanation is omitted in this specification.

[0150] The present invention will be described in detail below with reference to examples, comparative examples, and experimental examples, so that it can be easily understood by those who have ordinary skill in the art to which the present invention pertains.

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

[0152] The aforementioned mixture was placed in a blender and ground at 10,000 rpm for 1 minute to obtain electrode powder.

[0153] <Comparative Example 1> In Example 1, the mixing and grinding steps using a kneader were omitted, and the mixture was subjected to a jet milling process (feed pressure 50 psi, grinding pressure 45 psi) to obtain the electrode powder.

[0154] <Experimental Example 1> SEM images of the electrode powder produced in Example 1 and the electrode powder produced in Comparative Example 1 are shown in Figures 3 and 4.

[0155] Figures 3 and 4 allow us to confirm the degree of pulverization of the active material.

[0156] It can be confirmed that even greater pulverization occurs with the dry electrode in Comparative Example 1.

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

[0158] <Example 3> Except for using only 3.5g of carbon black as the conductive material and setting the kneader temperature to 150°C, electrode powder was obtained in the same manner as in Example 1.

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

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

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

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

[0163] Subsequently, the electrode powders produced in Examples 1-3 and Comparative Examples 1-3 were fed into a wrap calender (roll diameter: 88 mm, roll temperature: 85°C, 20 rpm) under the following active material loading conditions to produce a composite film. This composite film was used as a conductive primer layer, and the electrode was produced by laminating it onto one side of an aluminum foil (19 μm) coated with a primer layer of carbon black and acrylic binder mixed in a weight ratio of 5:6, using a lamination roll maintained at 120°C.

[0164] At this time, the target porosity was set to 23-30%, 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, Comparative Examples 2 and 3 evaluated the feasibility of manufacturing composite films through calendering. The measurement methods were as follows, and the results are shown in Table 1 below.

[0166] Porosity: The apparent density of the composite film alone was measured by subtracting the volume and weight of the current collector from the volume and weight of the electrode. The actual porosity of each electrode was then determined using the true density calculated based on the true density and composition of each component, as shown in Equation 1 below.

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

[0168] Flexural resistance: Following 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 no cracks occurred.

[0169] Specifically, the evaluation of flexural resistance was carried out by manufacturing a rectangular electrode sample measuring 100 mm x 50 mm; preparing measuring rods with 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; using the measuring rod with the largest diameter, the electrode sample was brought into contact with the measuring rod, and then both ends of the electrode sample were lifted to determine whether or not cracks occurred in the composite film of the electrode sample; if no cracks occurred in the previous step, the next step of determining whether or not cracks occurred in the composite film of the electrode sample was repeated using the measuring rod with the next largest diameter, and the minimum diameter of the measuring rod that did not cause cracks in the composite film of the electrode sample was determined as the flexural 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 occurred in the composite film of the electrode sample when using measuring rods ranging from 32 mm in diameter to 3 mm in diameter. However, 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, cracks occur in the composite film of the electrode sample. In this case, the bending resistance of this dry electrode is determined to be Φ (diameter) 3 mm, which is the smallest diameter of measuring rod in which no cracks occurred 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 electrodes, and the resistance value between the composite film and the current collector layer was calculated from the potential difference measured between 46 probes.

[0172] [Table 1]

[0173] Referring to Table 1, it can be confirmed that the dry electrodes manufactured by the present invention have a bending resistance of Φ (diameter) 3 mm or less. However, dry electrodes manufactured by conventional methods have a diameter of Φ (diameter) of 10 mm, and it can be confirmed that they do not easily form a film under the aforementioned calendering conditions when the kneader temperature is low, making them unsuitable for the electrode manufacturing process.

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

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

[0176] After placing the electrode assembly into a battery case, a liquid electrolyte in which LiPF6 was dissolved at 1M in a solvent mixture of ethylene carbonate, dimethylene carbonate, and diethyl carbonate in a 1:2:1 (volume ratio) was poured in, and the case was sealed to manufacture a secondary battery.

[0177] The aforementioned secondary battery was charged to 4.3V at 0.1C using a constant current (CC)-constant voltage (CV) method, and then discharged to 3.0V at 0.1C. 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 confirmed that products manufactured using the method according to the present invention exhibit charge and discharge efficiencies similar to or better than those manufactured using conventional methods.

Claims

1. A powder for electrodes that can be formed into a film for manufacturing dry electrodes for secondary batteries, The electrode powder comprises an active material, a conductive material, and a binder. The aforementioned active material is a positive electrode active material, The binder is polytetrafluoroethylene, polyolefin, or a mixture thereof. An electrode powder having a resistivity of 700 Ω·cm or less when pressurized at a pressure of 50 MPa.

2. A method for producing electrode powder according to claim 1, (a) A process for producing a mixture comprising an active material, a conductive material, and a binder, (b) A step of kneading the mixture in the range of 70°C to 200°C and under a pressure of normal pressure or higher in order to fibrousize the binder, (c) A method for producing electrode powder, comprising the step of crushing the mixture mass to obtain electrode powder.

3. The method for producing electrode powder according to claim 2, wherein the conductive material comprises one or more 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 kneading in step (b) is performed at a speed of 10 rpm to 100 rpm for 1 minute to 30 minutes.

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

6. The method for producing electrode powder according to claim 2, wherein the kneading in step (b) is performed at a temperature of 90°C to 180°C.

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

8. The method for producing electrode powder according to claim 2, wherein the grinding in step (c) is performed at a speed of 500 rpm to 20,000 rpm for 30 seconds to 10 minutes.

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

10. A method for manufacturing a dry electrode, (d) A step of producing a composite film by calendering the electrode powder produced by the method for producing electrode powder according to claim 2, (e) A method for manufacturing a dry electrode, comprising the steps of (e) placing the composite film on at least one surface of a current collector and laminating it to manufacture a dry electrode.

11. The method for manufacturing a dry electrode according to claim 10, wherein the porosity of the composite film is 20 to 35%.

12. The method for manufacturing a dry electrode according to claim 10, wherein the bending resistance of the dry electrode is less than Φ10 mm.

13. The loading amount of the active material in the aforementioned composite film is 3 mAh / cm². ２ ~15mAh / cm² ２ The method for manufacturing a dry electrode according to claim 10.

14. The interfacial resistance between the composite film and the current collector is 5 Ω·cm ２ The method for manufacturing a dry electrode according to claim 10 is as follows:

15. The method for manufacturing a dry electrode according to claim 10, wherein a conductive primer is coated on the current collector, either entirely or partially.

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