Film for dry electrodes of secondary batteries

Abstract

The present invention relates to a composite film for manufacturing a dry electrode for a secondary battery, a dry electrode including the same, and a manufacturing method thereof. The composite electrode film according to one aspect of the present invention is characterized in that two or more electrode unit films each including a fiberized binder and an active material are laminated, and the machine directions (MD) of the two or more electrode unit films facing each other are misaligned with each other.

Description

[Technical Field]

[0001] This invention relates to an electrode film, a dry electrode, and a secondary battery containing the same.

[0002] This application claims priority based on Korean Patent Application No. 10-2022-0032853, filed on 16 March 2022, and all contents disclosed in the specification and drawings of said application are incorporated into this application. [Background technology]

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

[0004] Currently, a typical example of an electrochemical device that uses this type of electrochemical energy is the secondary battery, and its fields of application are gradually expanding.

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

[0006] The manufacturing process for such lithium secondary batteries can be broadly divided into three stages: the electrode process, the assembly process, and the chemical 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 mixing coating materials for forming an electrode active layer where an actual electrochemical reaction occurs in the electrode. Specifically, it is to mix an 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 a fluid slurry.

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

[0009] Thereafter, an electrode coating process of coating the electrode mixture on an electrically conductive current collector and a drying process for removing the solvent contained in the electrode mixture are carried out, and further the electrode is rolled to be manufactured to a predetermined thickness.

[0010] On the other hand, due to the evaporation of the solvent contained in the electrode mixture during the drying process, defects such as pinholes and cracks may occur in the already formed electrode active layer. Also, since the inside and outside of the active layer are not uniformly dried, a powder floating phenomenon due to the difference in the evaporation rate of the solvent, that is, the powder at the site dried first floats up and forms a gap with the site dried relatively later, may also cause a deterioration in electrode quality.

[0011] Therefore, recently, research on manufacturing dry electrodes without using a solvent has been actively conducted.

[0012] The dry electrode is generally manufactured by laminating a free-standing film, which contains an active material, a binder, a conductive material, etc. on a current collector and is manufactured in a film form. In the process, in order to fiberize the binder, a high shear mixing process such as jet milling is performed. At this time, when applying the high shear mixing process as described above to the easily broken active material, a large amount of fine powder with a small particle size is generated, and the mechanical performance and electrochemical performance are likely to deteriorate. When the high shear mixing becomes excessive, the generated binder fibers may be cut, resulting in a decrease in the flexibility of the free-standing film. In addition, during the jet milling process, components adhere to the inside of the equipment, hindering the flow of high-pressure air and causing problems such as clogging of the flow path, so it is not easy for mass production.

[0013] 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

[0014] Therefore, the problem to be solved by the present invention is a free-standing film that can be used for manufacturing a dry electrode with improved flexibility and mechanical physical properties by minimizing the pulverization of the active material and maximizing the fiberization of the binder, a film with improved mechanical physical properties in the machine direction (MD) and the orthogonal direction (TD) thereto, and a manufacturing method thereof.

[0015] In addition, it is to provide a dry electrode including a free-standing film with improved mechanical physical properties in the machine direction and the orthogonal direction as described above and a manufacturing method thereof.

Means for Solving the Problems

[0016] In order to solve the above problems, according to one aspect of the present invention, a film for a dry electrode of the following embodiment is provided.

[0017] According to the first embodiment, a composite electrode film is provided, comprising two or more layers of electrode unit films containing a fibrous binder and an active material, wherein the machine directions (MD) of the electrode unit films facing each other among the two or more layers of laminated electrode unit films are offset from each other.

[0018] According to the second embodiment, in the first embodiment, the angle between the mechanical directions of the two or more electrode unit films that face each other may be greater than 0° and less than or equal to 90°.

[0019] According to the third embodiment, in the first or second embodiment, the angle between the mechanical directions of the two or more electrode unit films that face each other can be 45° to 90°.

[0020] According to the fourth embodiment, in any of the first to third embodiments, the average thickness of the composite electrode film may be 50 μm to 600 μm.

[0021] According to the fifth embodiment, in any of the first to fourth embodiments, when measuring the tensile strength of the composite electrode film in accordance with the ASTM D 638 standard, the ratio of the tensile strength measured in a direction perpendicular to the reference mechanical direction to the tensile strength measured with respect to the mechanical direction of one of the two or more laminated electrode unit films may be 0.3 or more.

[0022] According to the sixth embodiment, in any of the first to fifth embodiments, when measuring the modulus of the composite electrode film according to the ASTM D 638 standard, the ratio of the modulus of elasticity measured in a direction perpendicular to the reference mechanical direction to the modulus of elasticity measured in a direction perpendicular to the reference mechanical direction of one of the two or more laminated electrode unit films is 0.3 or more.

[0023] According to another aspect of the present invention, a method for manufacturing a composite electrode film is provided as described below.

[0024] According to the seventh embodiment, a method for manufacturing a composite electrode film is provided, comprising the steps of: mixing an active material and a binder to produce a mixture; kneading the mixture at a high temperature and low shear rate to produce a mixture mass; crushing the mixture mass at a high shear to produce an electrode mixed powder; feeding the electrode mixed powder between a plurality of rolls and calendering it to produce an electrode unit film; stacking two or more electrode unit films so that the axes of the machine direction (MD) of the electrode unit films facing each other are offset from each other to obtain a film laminate; and calendering the film laminate.

[0025] According to the eighth embodiment, in the seventh embodiment, the two or more electrode unit films can be laminated such that the angle between the mechanical directions of the electrode unit films facing each other is greater than 0° and less than or equal to 90°.

[0026] According to the ninth embodiment, in the seventh or eighth embodiment, the average thickness of the composite electrode film may be 50 μm to 600 μm.

[0027] According to another aspect of the present invention, electrodes of the following embodiments are provided.

[0028] According to the tenth embodiment, an electrode is provided that includes a current collector and a composite electrode film according to any of the first to sixth embodiments, which is located on at least one surface of the current collector.

[0029] According to yet another aspect of the present invention, a method for manufacturing electrodes of the following embodiments is provided.

[0030] According to the 11th embodiment, a method for manufacturing an electrode is provided, characterized by including the step of laminating a composite electrode film described in any of the first to sixth embodiments onto at least one surface of a current collector.

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

[0032] According to the 12th embodiment, a secondary battery is provided in which an electrode assembly including a positive electrode, a negative electrode, and a separator membrane is incorporated into a battery case together with a lithium-containing non-aqueous electrolyte, wherein at least one of the positive electrode and the negative electrode is the electrode described in the 10th embodiment. [Effects of the Invention]

[0033] According to the present invention, it is possible to provide a freestanding film for use in dry electrodes, in which the mechanical properties are improved not only in the mechanical direction but also in the direction deviating from the mechanical direction, and a method for manufacturing the same.

[0034] Furthermore, by using the film described above, it is possible to provide a dry electrode and a method for manufacturing the same with improved productivity and physical properties.

[0035] Furthermore, according to one embodiment of the present invention, by introducing a process of grinding after a high-temperature, low-shear kneading process instead of a high-shear mixing process, it is possible to provide a dry electrode in which the micronization of the active material is minimized, the fibrousization of the binder is maximized, and the cutting of the fibrous binder is minimized. Moreover, since the process involves kneading and grinding using a kneader without performing a high-shear jet milling process, there is no problem of the flow path becoming blocked due to the aggregation of constituent components, which is advantageous for mass production. [Brief explanation of the drawing]

[0036] [Figure 1] This is a schematic diagram of the process for manufacturing electrode unit films according to one embodiment of the present invention. [Figure 2] This is a schematic diagram of a structure in which two electrode unit films are stacked with their mechanical directions (MDs) offset from each other, according to one embodiment of the present invention. [Figure 3] This is an explanatory diagram of the angle (θ) between the mechanical directions (MD) of two electrode unit films according to one embodiment of the present invention. [Modes for carrying out the invention]

[0037] The present invention will be described in detail below.

[0038] In this specification, "machine direction (MD) of electrode unit film" refers to the production travel direction of the electrode unit film in the manufacturing process of the electrode unit film.

[0039] Figure 1 shows a schematic diagram of a process for manufacturing an electrode unit film by calendering an electrode mixed powder according to one embodiment of the present invention. Referring to Figure 1, when the electrode mixed powder 10 is fed between a plurality of rolls 1, an electrode unit film 100 is formed in one direction. At this time, the direction of travel of the manufactured electrode unit film can be defined as the mechanical direction (MD) of the electrode unit film.

[0040] The mechanical orientation (MD) of the electrode unit film coincides with the orientation direction of the fibers within the film, and can therefore be confirmed by the orientation direction of the fibers within the manufactured film. For example, the mechanical orientation of the electrode unit film can be confirmed by a scanning electron microscope (SEM) image of the electrode unit film. It can also be confirmed by an SEM image of the composite film manufactured using the electrode unit film. The fiber orientation direction confirmed by the SEM image can be confirmed as the mechanical orientation (MD) of each of the electrode unit films.

[0041] As described above, the manufacturing of conventional dry electrodes includes a process of producing a freestanding film by a roll calendering process. In this process, the freestanding film produced has different mechanical properties in the machine direction (MD) and in the transverse direction (TD).

[0042] The inventors of the present invention recognized that differences in the physical properties of a freestanding film between the mechanical direction (MD) and the orthogonal direction (TD) could subsequently act as a cause of defects in the electrode manufacturing process. They discovered that electrode films manufactured by calendering electrode mixed powders have the characteristic that the mechanical properties in directions not parallel to the mechanical direction are lower than those in the mechanical direction, and thus completed the present invention.

[0043] A composite electrode film according to one aspect of the present invention is characterized in that two or more electrode unit films containing a fibrous binder and an active material are laminated together, and the machine directions (MD) of the two or more laminated electrode unit films that face each other are offset from each other.

[0044] Figure 2 shows a schematic diagram of a structure in which two electrode unit films 100 are stacked offset in the mechanical direction (MD) according to one embodiment of the present invention. Referring to Figure 2, the composite electrode film according to the present invention has a structure in which at least two electrode unit films are stacked with their mechanical directions (MD) not parallel but offset.

[0045] In this specification, "the mechanical directions (MDs) of two or more electrode unit films facing each other are offset from each other" means that when two or more electrode unit films are laminated, the mechanical directions of the opposing electrode unit films are not parallel to each other.

[0046] Figure 3 shows the angle (θ) between the mechanical directions (MD) of two electrode unit films that are stacked with their mechanical directions (MD) offset from each other according to one embodiment of the present invention.

[0047] Referring to Figure 3, a composite electrode film according to one aspect of the present invention includes two or more electrode unit films that are laminated such that the angle (θ) between the mechanical directions (MD) of opposing electrode unit films is offset from 0° (or 180°).

[0048] According to one embodiment of the present invention, the angle between the mechanical directions of two or more electrode unit films that face each other is, for example, greater than 0° and less than or equal to 90°, specifically 10° to 90°, specifically 45° to 90°, and more specifically 60° to 90°, 70° to 90°, 80° to 90°, 85° to 90°, or 90°. When the angle between the mechanical directions of the facing electrode unit films is within the above range, it may be advantageous in that it provides a composite electrode film having improved mechanical properties in any direction.

[0049] According to one embodiment of the present invention, the average thickness of the composite electrode film is the general thickness of a freestanding film and is not particularly limited. For example, the average thickness of the composite electrode film may be 50 μm to 600 μm, but is not limited thereto. The composite electrode film has the advantage of improving mechanical properties by including two or more electrode unit films such that their mechanical directions are offset from each other, and maintaining the excellent electrical and chemical properties of the electrode film by maintaining the average thickness of the composite electrode film at a normal level.

[0050] The average thickness of the composite electrode film can be measured by known means in the art for measuring the thickness of each component, such as a thickness gauge or SEM imaging. In one embodiment of the present invention, the thickness of the composite electrode film can be measured using a thickness gauge (Mitutoyo, VL-50S-B), but is not limited thereto.

[0051] As described above, the electrode unit films, which are stacked in two or more layers, each independently contain a fibrous binder and an active material.

[0052] In this specification, the “fibrous” binder means a binder used in the manufacture of a film that has been stretched into a fibril shape by a predetermined process for the manufacture of an electrode film. The fibrous binder can form a network and provide binding force between the active materials, which are essential elements of the electrode. The fibrous binder can also provide adhesive force for the electrode film to the current collector, but the shape and function of the fibrous binder are not limited thereto.

[0053] In one embodiment of the present invention, the structure in which the fibrous binder forms a fibril-like network to bind the active material can be confirmed, for example, by SEM images of the electrode unit film and / or the composite electrode film.

[0054] According to one embodiment of the present invention, the electrode unit film may further include a conductive material in addition to a binder and an active material that are independently fibrousized.

[0055] In one embodiment of the present invention, the binder is not particularly limited as long as it is used to uniformly disperse powdered substances such as active materials contained in the composite electrode film without causing a chemical change in the battery.

[0056] In one embodiment of the present invention, the binder comprises, for example, polytetrafluoroethylene (PTFE), polyolefin, or a mixture thereof, more specifically, polytetrafluoroethylene (PTFE), and more specifically, polytetrafluoroethylene (PTFE).

[0057] In another embodiment of the present invention, if the binder contains polytetrafluoroethylene (PTFE), the polytetrafluoroethylene content may be 60% by weight or more based on the total weight of the binder.

[0058] In yet another embodiment of the present invention, the binder may further include PEO (polyethylene oxide), PVdF (polyvinylidene fluoride), PVdF-HFP (polyvinylidene fluoride-co-hexafluoropropylene), or two or more of these.

[0059] In one embodiment of the present invention, the binder may be included in an amount of 0.5 to 15 parts by weight based on 100 parts by weight of the active material. Specifically, the binder content may be 0.5 to 15 parts by weight, 0.5 to 10 parts by weight, 1 to 5 parts by weight, or 1 to 3 parts by weight based on 100 parts by weight of the active material. When the binder content satisfies such a range, the binder can be sufficiently fiberized in a later kneading step and aggregated to the extent that it can form a mixture mass, making it easy to manufacture the electrode film and improving the physical properties of the electrode film. In one embodiment of the present invention, if the composite electrode film is for manufacturing a positive electrode, the active material may be a positive electrode active material.

[0060] The positive electrode active material may include, but is not limited to, two or more of the following: lithium transition metal oxide, lithium metallic iron phosphate, lithium nickel-manganese-cobalt oxide, and an oxide in which a portion of the lithium nickel-manganese-cobalt oxide is substituted with another transition metal. Specifically, the positive electrode active material may include, for example, layered compounds such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), or compounds substituted with one or more transition metals, and a compound with the chemical formula Li 1+x Mn2-x O4 (where x is from 0 to 0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, LiMnO2, lithium copper oxide (Li2CuO2), vanadium oxides such as LiV3O8, LiV3O4, V2O5, Cu2V2O7, and the chemical formula LiNi 1-x M x O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga and x = 0.01 to 0.3), Ni-site type lithium nickel oxides represented by the chemical formula, and the chemical formula LiMn 2-x M x O2 (where M = Co, Ni, Fe, Cr, Zn or Ta and x = 0.01 to 0.1), or lithium manganese composite oxides represented by Li2Mn3MO8 (where M = Fe, Co, Ni, Cu or Zn), and lithium nickel cobalt manganese aluminum oxide (NCMA) Li in which part of the Li in the chemical formula is substituted with aluminum ions 1+x (Ni a Co b Mn c Al d ) 1-x O2 (x = 0 to 0.03, a = 0.3 to 0.95, b = 0.01 to 0.35, c = 0.01 to 0.5, d = 0.001 to 0.03, a + b + c + d = 1), for example, Li[Ni 0.73 Co 0.05 Mn 0.15 Al 0.02 O2, and lithium metal phosphates LiMPO4 (where M = Fe, CO, Ni, or Mn), disulfide compounds, Fe2(MoO4)3, etc., but are not limited thereto.

[0061] In another embodiment of the present invention, when the film for the combined electrode is for manufacturing a negative electrode, the active material can be a negative electrode active material.

[0062] The negative electrode active material is, for example, carbon such as graphitizable carbon and graphite-based carbon, and Li x Fe2O3 (0 ≤ x ≤ 1), Li x WO2 (0 ≤ x ≤ 1), Sn x Me1-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 alloys, silicon-based alloys, tin-based alloys, silicon-based oxides such as SiO, SiO / C, SiO2, metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5, conductive polymers such as polyacetylene, Li-Co-Ni-based materials, etc. can be used, but are not limited thereto.

[0063] In one embodiment of the present invention, the conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, graphite such as natural graphite and artificial graphite, carbon black-based carbon compounds such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, 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, conductive materials such as polyphenylene derivatives, etc. can be used. Specifically, for uniform mixing of the conductive material and improvement of conductivity, it can include activated carbon, graphite, carbon black, carbon nanotubes, or a mixture of two or more of these. More specifically, it can include carbon black.

[0064] In one embodiment of the present invention, each electrode unit film may independently contain an active material, conductive material, and binder in a weight ratio of 80 to 99 parts by weight, 0 to 10 parts by weight, and more specifically, 90 to 99 parts by weight, 0 to 5 parts by weight, and 0.5 to 10 parts by weight. Alternatively, the active material, conductive material, and binder may be contained in a weight ratio of 80 to 99 parts by weight, 0.5 to 10 parts by weight, and more specifically, 90 to 99 parts by weight, 0.5 to 5 parts by weight, and 0.5 to 10 parts by weight.

[0065] In one embodiment of the present invention, each electrode unit film may independently further contain a filler, which is a component that suppresses the expansion of the electrodes. The filler is not particularly limited as long as it is a fibrous material that does not cause chemical changes in the battery, and for example, fibrous materials such as polyethylene, polypropylene or other olefin polymers, glass fibers, or carbon fibers can be used.

[0066] In one embodiment of the present invention, the composite electrode film is characterized in that, when the mechanical direction of one of the electrode unit films is taken as the reference direction, the mechanical properties are improved not only in the reference direction but also in other directions that are not parallel to the reference direction.

[0067] The improved mechanical properties of the composite electrode film according to one embodiment of the present invention refer to tensile strength, modulus, elongation at break, etc., which are normally required for electrode films, and the types of mechanical properties are not particularly limited.

[0068] In one embodiment of the present invention, when measuring the tensile strength of the composite electrode film according to the ASTM D 638 standard, the tensile strength (TS) measured with reference to the mechanical direction of one of the two or more laminated electrode unit films is measured. MD ) and the tensile strength (TS) measured in a direction perpendicular to the aforementioned reference machine direction TD The ratio of ) that is, TS TD / TS MD The value of may be 0.3 or greater. For example, if the composite electrode film includes a first electrode unit film and a second electrode unit film laminated on the first electrode unit film such that the mechanical direction of the first electrode unit film is offset from the mechanical direction of the first electrode unit film, the tensile strength (TS) of the composite electrode film measured with respect to the mechanical direction of the first electrode unit film may be 0.3 or greater. MD The tensile strength (TS) of the composite electrode film measured in the direction perpendicular to the mechanical direction of the first electrode unit film, relative to the given tensile strength (TS) TD ) ratio TS TD / TS MD The value may be 0.3 or greater.

[0069] In one embodiment of the present invention, the above ratio TS TD / TS MD Specifically, this can be 0.3 or more, 0.4 or more, 0.5 or more, 0.6 or more, 0.7 or more, 0.8 or more, 0.9 or more, or 1 or less. The more electrode unit films are laminated such that the mechanical directions of the electrode unit films facing the composite electrode film are offset from each other, the more uniformly the mechanical properties of the composite electrode film can be improved in any direction. As a result, the more the number of laminated electrode unit films increases, the higher the ratio TS is. TD / TS MD It can converge to 1.

[0070] In one embodiment of the present invention, when measuring the elastic modulus of the composite electrode film according to the ASTM D 638 standard, the elastic modulus (M) measured with reference to the mechanical direction of one of the two or more laminated electrode unit films is MD The elastic modulus (M) measured in the direction perpendicular to the reference mechanical direction for ) TD The ratio of ) that is, M TD / M MDThe value of may be 0.3 or greater. For example, if the composite electrode film includes a first electrode unit film and a second electrode unit film laminated on the first electrode unit film such that the mechanical direction of the first electrode unit film is offset from the mechanical direction of the first electrode unit film, the elastic modulus (M) of the composite electrode film measured with respect to the mechanical direction of the first electrode unit film is... MD The elastic modulus (M) of the composite electrode film measured in the direction perpendicular to the mechanical direction of the first electrode unit film. TD ) ratio M TD / M MD The value may be 0.3 or greater.

[0071] In one embodiment of the present invention, the ratio M TD / M MD Specifically, this can be 0.3 or more, 0.4 or more, 0.5 or more, 0.6 or more, 0.7 or more, 0.8 or more, 0.9 or more, or 1 or less. The more electrode unit films are laminated such that the mechanical directions of the electrode unit films facing the composite electrode film are offset from each other, the more uniformly the mechanical properties of the composite electrode film can be improved in any direction. As a result, the more the number of laminated electrode unit films increases, the higher the ratio M TD / M MD It can converge to 1.

[0072] In another embodiment of the present invention, the number of electrode unit films laminated on the composite electrode film is two or more, specifically two to five layers, two to four layers, or two to three layers. When the number of electrode unit films laminated is within this range, the thickness of the composite electrode film is appropriately maintained, so that the pressure applied during the manufacture of the composite electrode film increases, preventing problems such as tearing of the active material, and improving the electrical and mechanical properties of the composite electrode film.

[0073] An electrode according to another aspect of the present invention includes a current collector and the above-described composite electrode film located on at least one surface of the current collector.

[0074] In one embodiment of the present invention, the current collector is not particularly limited as long as it has high conductivity without causing a chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, copper, or aluminum or stainless steel with a surface treatment using carbon, nickel, titanium, silver, etc., can be used. Furthermore, the current collector can improve the adhesion strength to the positive electrode active material by forming fine irregularities on its surface, and can take various forms such as films, sheets, foils, nets, porous materials, foams, and nonwoven fabrics. In addition, the current collector can be coated entirely or partially with a conductive primer to reduce surface resistance and improve adhesion. Here, the conductive primer may contain a conductive substance and a binder, and the conductive substance is not limited as long as it is a conductive material, but may be a carbon-based material, for example.

[0075] A method for manufacturing a composite electrode film according to another aspect of the present invention includes the steps of: obtaining a mixture containing an active material and a binder; kneading the mixture at a high temperature and low shear rate to produce a mixture mass; crushing the mixture mass at a high shear to produce a mixed powder for electrodes; feeding the mixed powder for electrodes between a plurality of rolls and calendering it to produce a unit film for electrodes; stacking two or more of the unit films for electrodes so that the machine directions (MD) of the opposing unit films for electrodes are offset from each other to obtain a film laminate; and calendering the film laminate.

[0076] The step of obtaining a mixture containing the active material and binder involves mixing the active material and binder, and optionally conductive material and other additives, in a certain ratio to obtain a mixture as components of an electrode unit film.

[0077] In the step of producing the mixture, the mixing to obtain the mixture is carried out so that the active material and binder, and optionally conductive material and other additives, are uniformly distributed. Since these components are mixed in powder form, the method is not particularly limited as long as it allows for simple mixing, and they can be mixed by various methods. However, since the above method is intended to produce a dry electrode without the use of a solvent, the mixing can be carried out by dry mixing, and can be done by putting the substances into a device such as a blender or supermixer.

[0078] In one embodiment of the present invention, the mixture can be produced by mixing it in 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, in order to ensure uniformity.

[0079] The step of producing the aforementioned mixture mass is a step of fiberizing the binder with the mixture produced as described above, and can be called, for example, a kneading step.

[0080] In one embodiment of the present invention, high-shear mixing, such as in a jet mill, can be performed to fiberize the binder, but preferably, low-shear kneading can be performed to solve the problem of the active material being pulverized and the formed fibers being cut.

[0081] In this case, the above-mentioned mixing is not particularly limited and can be carried out using a mixing machine such as a kneader.

[0082] Such kneading is a step in which the binder becomes fibrous and binds or connects the active material, conductive material and porous carbon powder to form a mixture mass with 100% solid content.

[0083] Specifically, the kneading for producing the aforementioned mixture mass can 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, during which the shear rate can be in the range of 10 / s to 500 / s for 1 to 30 minutes. More specifically, the shear rate can be in the range of 30 / s to 100 / s. Furthermore, such a kneading step can be carried out under high temperature and pressures above atmospheric pressure, and more specifically, under pressures higher than atmospheric pressure.

[0084] In one embodiment of the present invention, in the step of producing the mixture mass, the kneading can be carried out in the range of 70°C to 200°C, more specifically, in the range of 90°C to 180°C, or 90°C to 150°C. If the kneading is carried out at a temperature lower than the above temperature range, the fibrosis of the binder and the aggregation by kneading will not occur well, so film formation will not occur easily when calendering is carried out in the next step. If the kneading is carried out at an excessively high temperature, the fibrosis of the binder will occur rapidly, and there is a risk that the already formed fibers will be cut by excessive shear force, which is undesirable.

[0085] In one embodiment of the present invention, in the step of producing the mixture mass, the kneading can be carried out at atmospheric pressure or higher, more specifically, at a pressure of 1 atm to 60 atm, or 1 atm to 30 atm, or 1 atm to 10 atm, or 1 atm to 3 atm, or 1.1 atm to 3 atm. If the kneading is carried out at an excessively high pressure outside the above pressure range, it may be undesirable because excessive shear force and pressure may be applied, causing the formed fibers to break or resulting in a mixture mass that is too dense.

[0086] Thus, in one embodiment of the present invention, it may be preferable to perform a low-shear mixing process under high temperature and pressure conditions above atmospheric pressure, instead of high-shear mixing.

[0087] The step of producing electrode mixed powder from the aforementioned mixture mass is to crush the mixture mass to obtain electrode powder. To immediately process the mixture mass into a film, a process with high pressure and high temperature is required. This can lead to problems such as the film becoming too dense or not being able to obtain a uniform film. Therefore, after crushing the mixture mass to obtain electrode powder, the obtained powder is calendered.

[0088] In one embodiment of the present invention, the grinding can be performed by a blender, or by a grinder such as a cutter mill or a fine impact mill, and the grinding can be performed at a speed of 500 rpm to 20000 rpm for 30 seconds to 10 minutes, more specifically at a speed of 1000 rpm to 10000 rpm for 30 seconds to 1 minute. If the grinding is performed at an rpm that is too low or for too short a time, the grinding will not be sufficient, resulting in the problem of producing powder particles of a size unsuitable for film formation. If the grinding is performed at an rpm that is too high or for too long a time, it will result in the problem of producing a large amount of fine powder from the mixture clumps, which is undesirable.

[0089] In one embodiment of the present invention, the step of classifying the pulverized electrode powder may be further included after the step of manufacturing the electrode mixed powder and before calendering. In the classifying step, the pulverized electrode powder can be obtained by filtering out electrode powder of a certain size or larger through a mesh having voids of a certain size or less.

[0090] Subsequently, electrode unit films are manufactured by calendering the electrode powder obtained as described above, or the classified electrode powder.

[0091] The calendering process involves processing the electrode mixture powder into a film, and may involve, for example, rolling it into a film with an average thickness of 50 μm to 600 μm.

[0092] In this case, the calendering process can be performed, for example, by opposing rolls, with a roll temperature of 25°C to 200°C and a roll rotation speed of 10 rpm to 50 rpm.

[0093] Once the calendering process is complete, a composite film that acts as an electrode mixture can be manufactured. Such films are also conventionally known as freestanding films.

[0094] In this specification, one electrode film produced by the calendering process is referred to as an electrode unit film.

[0095] The step of obtaining the film laminate after calendering is to laminate two or more electrode unit films so that the machine directions (MD) of the electrode unit films facing each other are offset from each other.

[0096] According to one embodiment of the present invention, the lamination can be carried out such that the angle between the mechanical directions of two or more electrode unit films facing each other is greater than 0° and 90°. The angle between the mechanical directions of two or more electrode unit films facing each other is, for example, greater than 0° and 90° or less, specifically 10° to 90°, specifically 45° to 90°, and more specifically 85° to 90° or 90°.

[0097] According to one embodiment of the present invention, electrode unit films can be laminated such that the number of opposing surfaces in the film laminate that are offset from each other in mechanical directions is one to three.

[0098] According to one embodiment of the present invention, the electrode unit film can be laminated in two or more layers, for example, two to five layers, two to four layers, or two to three layers, but the present invention is not limited to these.

[0099] Subsequently, the film laminate obtained as described above is calendered to produce a film for the composite electrode.

[0100] The calendering process of the film laminate allows the film laminate to be rolled to have the thickness of a single-layer electrode film. For example, the film laminate can be rolled so that the average thickness of the manufactured composite electrode film is between 50 μm and 300 μm.

[0101] In this case, the calendering process can be performed, for example, by opposing rolls, with a roll temperature of 25°C to 200°C and a roll rotation speed of 0.1 rpm to 50 rpm.

[0102] The composite electrode film produced in this manner contains no solvent, has almost no fluidity, is easy to handle, and can be processed into desired shapes for use in the manufacture of electrodes of various forms. Furthermore, when this composite electrode film is used in electrode manufacturing, the drying process to remove the solvent can be omitted, which not only greatly improves the efficiency of electrode manufacturing but also solves problems that have plagued the manufacture of existing dry electrodes, such as the breaking of fine active material and fibrous binders.

[0103] Furthermore, a composite electrode film containing two or more electrode unit films laminated so that their mechanical directions are offset from each other has improved mechanical properties in all directions, resulting in a significant reduction in the defect rate during electrode manufacturing.

[0104] A method for manufacturing an electrode according to another aspect of the present invention includes the step of laminating the above-mentioned composite electrode film onto at least one surface of a current collector.

[0105] In one embodiment of the present invention, the lamination may be a step of rolling and adhering the composite electrode film to a predetermined thickness onto the current collector. The lamination may also be performed by a laminating roll, in which case the laminating roll is maintained at a temperature of room temperature (25°C) to 200°C, but is not limited thereto.

[0106] According to one embodiment of the present invention, the electrode manufactured by the above manufacturing method includes a solvent-free composite electrode film and is therefore also called a dry electrode.

[0107] A secondary battery according to yet another aspect of the present invention is a secondary battery in which an electrode assembly including a positive electrode, a negative electrode, and a separator membrane is incorporated into a battery case together with a lithium-containing non-aqueous electrolyte, wherein at least one of the positive electrode and the negative electrode is used as the electrode described above.

[0108] Since the specific structure of the aforementioned secondary battery is well known, a detailed explanation is omitted in this specification.

[0109] The secondary battery according to the present invention can be included as a unit battery in an energy storage device, but the applications of the present invention are not limited to these.

[0110] Since the specific structure of the aforementioned energy storage device is well known, a detailed explanation is omitted in this specification.

[0111] The present invention will be described in more detail below with reference to examples, but the following examples are for illustrative purposes only and the scope of the present invention is not limited thereto.

[0112] [Manufacturing of dry electrodes] Comparative Example 1 Lithium nickel cobalt manganese aluminum oxide (NCMA, Li[Ni) is used as the positive electrode active material. 0.73 Co 0.05 Mn 0.15 Al 0.0297g of O2, 1g of carbon black as a conductive material, and 2g of polytetrafluoroethylene (PTFE) as a binder were placed in a blender and mixed at 15,000 rpm for 1 minute to obtain a mixture.

[0113] Next, the temperature of the kneader (irie-shokai, PBV0.1) was stabilized at 150°C, and the mixture prepared above was placed into the kneader. The mixture was then operated at a speed of 50 rpm for 5 minutes under a pressure of 1.1 atm to obtain a mass of the mixture.

[0114] The aforementioned mixture was placed in a blender (Hanil, HMF-3260s) and ground at 10,000 rpm for 1 minute to obtain electrode powder.

[0115] Next, the manufactured electrode powder was fed into a wrap roll press (roll temperature: 100°C, roll diameter: 160 mm, roll speed ratio: 1.4) to produce an electrode film with a thickness of 90 μm.

[0116] Example 1 The electrode film produced in Comparative Example 1 above was prepared as an electrode unit film. Two layers of the prepared electrode unit films were laminated so that their mechanical orientations were 90° apart, and then fed into a lap roll press (roll temperature: 100°C, roll diameter: 160 mm, roll speed ratio: 1.4) and re-rolled to produce a composite electrode film with a thickness of 90 μm.

[0117] Example 2 The electrode film produced in Comparative Example 1 above was prepared as an electrode unit film. Two layers of the prepared electrode unit films were laminated so that their mechanical orientations were at a 45° angle to each other. Then, they were fed into a lap roll press (roll temperature: 100°C, roll diameter: 160 mm, roll speed ratio: 1.4) and re-rolled to produce a composite electrode film with a thickness of 90 μm.

[0118] [Material property evaluation] The density, modulus, tensile strength, and elongation at break of the electrode films produced in Comparative Example 1 and Examples 1 and 2, respectively, were evaluated using the following methods, and the results are shown in Tables 1 and 2 below.

[0119] In Table 1 below, the MD direction for Comparative Example 1 indicates the direction in which the film travels during manufacturing (see Figure 1), and the TD direction indicates the direction perpendicular to the MD direction of the manufactured film. In Example 1, the MD direction indicates the machine direction of the lower layer, and the TD direction indicates the direction perpendicular to the MD direction of the lower layer.

[0120] - Measurement of density The manufactured film was cut into 5cm x 5cm pieces to prepare test specimens. The weight of the film in the test specimen was calculated as the volume of the film (thickness x 25cm). 2 The density was measured by dividing by ).

[0121] - Measurement of tensile strength The manufactured film was cut into pieces measuring 1 cm wide by 10 cm long to prepare test specimens. In accordance with the ASTM (American Society for Testing and Materials) D 638 standard, both ends of the prepared test specimens were pulled using a UTM (Universal Testing Machine) (ZwichRoell) under the conditions of a pre-load of 0.01 kg / cm and a test speed of 50 mm / min.

[0122] In this case, the tensile strength was measured by dividing the force applied to the specimen at the time of fracture by the initial cross-sectional area of ​​the specimen.

[0123] - Measurement of the elastic modulus The manufactured film was cut into pieces measuring 1 cm wide by 10 cm long to prepare test specimens. In accordance with the ASTM (American Society for Testing and Materials) D 638 standard, both ends of the prepared test specimens were pulled using a UTM (ZwichRoell) apparatus under the conditions of a pre-load of 0.01 kg / cm and a test speed of 50 mm / min.

[0124] In this case, the elastic modulus was measured by dividing the tensile strength by the deformation ratio over a linear interval of the tensile strength with respect to the deformation ratio.

[0125] - Elongation at break Test specimens were prepared by cutting the manufactured film into pieces measuring 1 cm wide x 10 cm long. In accordance with the ASTM (American Society for Testing and Materials) D 638 standard, the elongation at break (%) was measured using a UTM (ZwichRoell) apparatus under the conditions of a pre-load of 0.01 kg / cm and a test speed of 50 mm / min, by pulling both ends of the prepared test specimens and using the following formula. Elongation at break (ε) = ΔL / L0 × 100 (%) In the above formula, L0 is the initial length of the specimen, and ΔL represents the change in length until the specimen breaks.

[0126] [Table 1]

[0127] [Table 2]

[0128] As shown in the results above, the electrode film according to Comparative Example 1 had very poor mechanical properties in the TD direction, while the electrode films according to Example 1 and Example 2 showed significantly improved mechanical properties in both the MD and TD directions.

[0129] The higher the elastic modulus, tensile strength, and elongation at break, the better the stability of the electrode film and the processability during electrode manufacturing. It was confirmed that the electrode films produced in Examples 1 and 2 not only exhibited excellent stability but also improved the processability when using them to manufacture electrodes. [Explanation of symbols]

[0130] 1 roll 10 Mixed powder for electrodes 100 Unit Films for Electrodes

Claims

1. A step of mixing the active material and the binder to produce a mixture, The steps include kneading the mixture at a high temperature and low shear rate to produce a mass of the mixture while fibrousizing the binder, A step of producing an electrode mixed powder without using a solvent, comprising the step of crushing the mixture mass with high shear to produce the electrode mixed powder, The steps include: feeding the electrode mixture powder between multiple rolls and calendering it to manufacture an electrode unit film; The steps include: stacking two or more electrode unit films so that the angles between the mechanical directions (MD) of the opposing electrode unit films are between 10° and 90° to obtain a film laminate; A method for manufacturing a composite electrode film which is a free-standing film, comprising the step of calendering the aforementioned film laminate.

2. The method for manufacturing a composite electrode film according to claim 1, wherein the average thickness of the composite electrode film is 50 μm to 600 μm.

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