Electrode film, electrode containing the same, secondary battery, and method for manufacturing the same

Abstract

The present invention provides an electrode film, comprising an active material and a fluorine-containing binder, the fluorine-containing binder comprising a polytetrafluoroethylene (PTFE) binder, the active material comprising a lithium transition metal oxide, the content of the fluorine-containing binder being 0.5 parts by weight to 10 parts by weight based on a total of 100 parts by weight of the electrode film, and having a breaking elongation of 7% or more, and an electrode, secondary battery, and energy storage device each including the electrode film.

Description

[Technical Field]

[0001] The present invention relates to an electrode film, an electrode containing the same, a secondary battery, and a method for manufacturing the same, and more specifically, to an electrode film with improved mechanical properties, an electrode containing the same, a secondary battery, and a method for manufacturing the same.

[0002] This application claims priority based on Korean Patent Application No. 10-2022-0049211, filed on April 20, 2022, and all content disclosed in the specification and drawings of said application is incorporated herein. [Background technology]

[0003] With the rapid increase in fossil fuel use, the demand for alternative and clean energy sources is growing, and one of the most active research areas in this field is electrochemical power generation and energy storage. Currently, a representative example of an electrochemical element that uses such electrochemical energy is the secondary battery, and its range of applications is expanding more and more. Lithium-ion secondary batteries, a representative example of such secondary batteries, are not only used as an energy source for mobile devices, but are also increasingly being used as a power source for electric vehicles and hybrid electric vehicles that can replace vehicles that use fossil fuels such as gasoline and diesel vehicles, which are one of the main causes of air pollution. Their range of applications is also expanding to include power supply auxiliary power sources in grid systems.

[0004] The manufacturing process for such lithium secondary batteries can be broadly divided into three stages: electrode manufacturing, electrode assembly manufacturing, and chemical conversion. The electrode manufacturing stage can be further divided into electrode mixture mixing, electrode coating, drying, rolling, slitting, and winding processes.

[0005] Among these, the electrode mixture preparation process is a process of blending components for forming an electrode active layer where an actual electrochemical reaction occurs in the electrode. Specifically, it involves mixing an electrode active material, which is an essential element of the electrode, a conductive material and a filler, which are other additives, a binder for binding between powders and adhering to a current collector, a solvent for imparting viscosity and dispersing powders, etc., to produce a slurry having fluidity.

[0006] An electrode coating process of applying such a slurry onto an electrically conductive current collector and a drying process for removing the solvent contained in the electrode mixture slurry are performed. Additionally, the electrode is rolled to produce an electrode with a predetermined thickness.

[0007] On the other hand, when the solvent contained in the electrode mixture evaporates during the drying process, defects such as pinholes and cracks may be induced in the formed electrode active layer. Also, when the inside and outside of the active layer are not dried uniformly, a floating phenomenon of powders due to the evaporation rate difference of the solvent, that is, the powders at the site dried first float up, forming a gap with the site dried relatively later, may deteriorate the quality of the electrode.

[0008] Therefore, in order to solve the above-mentioned problems, a drying device with an adjustable evaporation rate of the solvent can be considered while ensuring that the inside and outside of the active layer are dried uniformly. However, such a drying device is very expensive and requires a considerable amount of cost and time for operation, so there are disadvantages in terms of manufacturing processability.

[0009] Therefore, in recent years, research on manufacturing dry electrodes without using solvents has been actively conducted.

[0010] The manufacturing method of a dry electrode includes a process of obtaining a free-standing electrode film by performing a roll calendering process on a mixture of a binder capable of being fibrillated (for example, polytetrafluoroethylene (PTFE)), an active material, and a conductive material. However, at this time, if the mechanical strength of the electrode film is weak, it may act as a cause of defects in the subsequent electrode manufacturing process. Summary of the Invention [Problems that the invention aims to solve]

[0011] This invention has been made in view of the above-mentioned problems, and aims to provide an electrode film with improved mechanical properties, an electrode containing the same, a secondary battery, and a method for manufacturing the same. [Means for solving the problem]

[0012] To achieve the above objectives, according to one aspect of the present invention, an electrode as shown in the following embodiment is provided. According to the first concrete example, Equipped with an active material and a fluorine-containing binder, The fluorine-containing binder comprises a polytetrafluoroethylene (PTFE) binder. The active material includes a lithium transition metal oxide, The fluorine-containing binder content is 0.5 to 10 parts by weight, based on a total of 100 parts by weight of the electrode film. An electrode film is provided that has a break elongation of 7% or more.

[0013] According to the second example, in the first example, The lithium transition metal oxide may include lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium nickel-manganese-cobalt oxide, lithium nickel-manganese-cobalt-aluminum oxide, lithium copper oxide, or two or more of these.

[0014] According to the third example, in the second example, The aforementioned lithium nickel-manganese-cobalt-aluminum oxide can be represented by the following chemical formula 1. [Chemical formula 1] Li a [Ni b Co c Mn d Al e ]1-f M 1 f O2 In the above Chemical Formula 1, said M 1 is one or more selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, and 0.8 ≦ a ≦ 1.2, 0.5 ≦ b ≦ 0.99, 0 < c < 0.5, 0 < d < 0.5, 0.01 ≦ e ≦ 0.1, 0 ≦ f ≦ 0.1.

[0015] According to the fourth embodiment, in the second embodiment or the third embodiment, said lithium nickel-manganese-cobalt-aluminum oxide can be represented by the following Chemical Formula 2. [Chemical Formula 2] Li a [Ni b Co<\(0000012\)>Mn d Al<\(0000014\)> 1-f O2 In the above Chemical Formula 2, 0.8 ≦ a ≦ 1.2, 0.5 ≦ b ≦ 0.99, 0 < c < 0.5, 0 < d < 0.5, 0.01 ≦ e ≦ 0.1, 0 ≦ f ≦ 0.1.

[0016] According to the fifth embodiment, in any one of the first embodiment to the fourth embodiment, <000|\(0140\)>the elongation at break of said electrode film is 7% or more, and the tensile strength of said electrode film can be 1.1 MPa or more.

[0017] According to the sixth embodiment, in the fifth embodiment, the elongation at break of said electrode film is 7.2% to 7.8%, the tensile strength (Tensile Strength) of said electrode film is 1.1MPa~ 1.4 MPa, and the modulus of said electrode film can be 38.3 MPa to 40.9 MPa.

[0018] [[ID=\\(54\)]]According to the seventh embodiment, in any one of the first embodiment to the sixth embodiment, ​The electrode film may include an active material, a fluorine-containing binder, and a conductive material.

[0019] According to the eighth example of implementation, in the seventh example of implementation, The conductive material may include activated carbon, graphite, carbon black, Ketjenblack, carbon nanotubes, or two or more of these.

[0020] According to the 9th embodiment, in the 7th or 8th embodiment, The content of the active material may be 85 to 98 parts by weight, the content of the conductive material may be 0.5 to 5 parts by weight, and the content of the fluorine-containing binder may be 0.5 to 10 parts by weight.

[0021] According to the 10th embodiment, in any one of the 1st to 9th embodiments, The electrode film can be manufactured using a dry process.

[0022] According to the 11th example, The process involves heat-treating the fluorine-containing binder at 290°C to 310°C, A step of producing a mixture containing an active material and the heat-treated fluorine-containing binder, The steps include kneading the aforementioned mixture at a temperature in the range of 70°C to 200°C and under a pressure of atmospheric pressure or higher to produce a mixture mass, The steps include crushing the aforementioned mixture mass to obtain a mixed powder for electrodes, A method for manufacturing an electrode film is provided, which is characterized by comprising the step of forming an electrode film by calendering the electrode mixed powder between a plurality of rolls, according to any one of the first to tenth embodiments.

[0023] According to the 12th embodiment, in the 11th embodiment, The aforementioned step of kneading to produce a mixture mass can be carried out in a kneader under a pressure of atmospheric pressure or higher.

[0024] According to the 13th embodiment, a method for manufacturing an electrode is provided, characterized by including the step of laminating an electrode film from any one of the 1st to 10th embodiments onto a current collector.

[0025] According to the 14th embodiment example, in the 12th embodiment example, The compression ratio of the electrode film during the lamination stage may be 30% to 50%.

[0026] According to the 15th example, Current collector and, An electrode is provided, characterized by including an electrode film of any one of the first to tenth embodiments located on at least one surface of the current collector.

[0027] According to the 16th example, in the 15th example, The current collector may further include a conductive primer layer on at least one surface.

[0028] According to the 17th example, A secondary battery is provided, comprising a positive electrode, a negative electrode, and a separator membrane interposed between the positive electrode and the negative electrode, wherein at least one of the positive electrode and the negative electrode is an electrode of the 15th embodiment or the 16th embodiment.

[0029] According to the 18th example, An energy storage device is provided that includes a secondary battery as a unit battery according to the 17th embodiment example. [Effects of the Invention]

[0030] According to one embodiment of the present invention, an electrode film is manufactured by heat-treating a fluorine-containing binder at 290°C to 310°C and then mixing it with an active material. In this case, pre-heat-treating the fluorine-containing binder improves the bonding between primary particles within secondary particles of the fluorine-containing binder (e.g., PTFE) through melt inter-diffusion on the surface between binder particles. As a result, the fiberization of the fluorine-containing binder becomes easier in subsequent electrode film manufacturing processes. Consequently, electrode films containing fluorine-containing binders with further fiberization have significantly improved mechanical properties compared to conventional electrode films, and the productivity of the film is increased.

[0031] The following drawings accompanying this specification illustrate preferred embodiments of the invention and, together with the detailed description of the invention, serve to further illustrate the technical idea of ​​the invention. Therefore, the invention should not be construed as being limited solely to what is shown in the drawings. [Brief explanation of the drawing]

[0032] [Figure 1] This is a schematic diagram of the manufacturing process for an electrode film according to one embodiment of the present invention. [Figure 2] This is a schematic diagram of the electrode lamination process according to one embodiment of the present invention. [Modes for carrying out the invention]

[0033] Preferred embodiments of the present invention will now be described in detail with reference to the attached drawings. Prior to this, terms and words used herein and in the claims should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather in a manner consistent with 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. Accordingly, it should be understood that the embodiments and configurations shown in the drawings described herein are merely the most preferred embodiments of the present invention and do not represent the entirety of the technical idea of ​​the present invention, and that there may be a variety of equivalents and modifications that can be substituted therein at the time of this application.

[0034] The terms used herein are for illustrative purposes only and do not limit the invention. Unless otherwise specified in the context, singular expressions include plural expressions.

[0035] When a part of the specification is described as "including" a certain component, unless otherwise specified, it means that it may include other components, rather than excluding them.

[0036] According to one aspect of the present invention, Equipped with an active material and a fluorine-containing binder, The fluorine-containing binder comprises a polytetrafluoroethylene (PTFE) binder. The active material includes a lithium transition metal oxide, The fluorine-containing binder content is 0.5 to 10 parts by weight, based on a total of 100 parts by weight of the electrode film. An electrode film is provided that has a break elongation of 7% or more.

[0037] The active material includes a lithium transition metal oxide.

[0038] According to one embodiment of the present invention, the lithium transition metal oxide may include lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium nickel-manganese-cobalt oxide, lithium nickel-manganese-cobalt-aluminum oxide, lithium copper oxide, or two or more of these.

[0039] For example, the lithium transition metal oxide may be 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-x Lithium manganese oxides such as O4 (where x is between 0 and 0.33), LiMnO3, LiMn2O3, LiMnO2, LiMn2O4; lithium copper oxide (Li2CuO2); chemical formula LiNi 1-x M x Ni-site type lithium nickel oxide represented by O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x = 0.01 to 0.3); chemical formula LiMn 2-x M x Possible examples include lithium manganese composite oxide represented by O2 (where M = Co, Ni, Fe, Cr, Zn, or Ta, and x = 0.01 to 0.1), Li2Mn3MO8 (where M = Fe, Co, Ni, Cu, or Zn), and lithium nickel-manganese-cobalt-aluminum oxide represented by chemical formula 1.

[0040] [Chemical formula 1] Li a [Ni b Co c Mn d Al e ] 1-f M 1 f O2 In the aforementioned chemical formula 1, Said M 1is one or more elements selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, and 0.8 ≤ a ≤ 1.2, 0.5 ≤ b ≤ 0.99, 0 <c<0.5、0<d<0.5、0.01≦e≦0.1、0≦f≦0.1である。

[0041] According to one embodiment of the present invention, The aforementioned lithium nickel-manganese-cobalt-aluminum oxide can be represented by the following chemical formula 2. [Chemical formula 2] Li a [Ni b Co c Mn d Al e ] 1-f O2 In the above chemical formula 2, 0.8 ≤ a ≤ 1.2, 0.5 ≤ b ≤ 0.99, 0 <c<0.5、0<d<0.5、0.01≦e≦0.1、0≦f≦0.1である。

[0042] Specifically, the lithium nickel-manganese-cobalt-aluminum oxide is Li[Ni 0.73 Co 0.05 Mn 0.15 Al 0.02 May contain O2, etc.

[0043] According to one embodiment of the present invention, the electrode film may include an active material, a fluorine-containing binder, and a conductive material.

[0044] The conductive material is not particularly limited as long as it does not induce a chemical change in the battery and is conductive. Examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; needle-shaped or branched conductive whiskers such as zinc oxide whiskers, calcium carbonate whiskers, titanium dioxide whiskers, silicon oxide whiskers, silicon carbide whiskers, aluminum borate whiskers, magnesium borate whiskers, potassium titanate whiskers, silicon nitride whiskers, silicon carbide whiskers, and alumina whiskers; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. These can be used individually or in mixtures of two or more. More specifically, to ensure uniform mixing of conductive materials and improve conductivity, the material includes 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.

[0045] The fluorine-containing binder may be a fluorine-containing polymer, specifically polytetrafluoroethylene (PTFE). The fluorine-containing binder may contain polytetrafluoroethylene alone, or it may further contain polytetrafluoroethylene with one or more PVdF-based copolymers such as PVdF (polyvinylidene fluoride) and PVdF-HFP (polyvinylidene fluoride-co-hexafluoropropylene).

[0046] In this context, the break elongation of the electrode film refers to the elongation rate at the time of breakage of the electrode film. Specifically, it refers to the deformation rate at the point when the electrode film breaks, after the load applied to deform the length of the electrode film of a predetermined standard has been increased and no further deformation occurs.

[0047] According to one embodiment of the present invention, the elongation at break of the electrode film can be measured using a UTM (ZwickRoell) device under the following test conditions. Test conditions: ASTM D 638, Pre-load 0.01 kg / cm, Test Speed ​​50 mm / min

[0048] Furthermore, in this specification, the tensile strength of the electrode film means the maximum stress until the electrode film breaks. Specifically, it means the value obtained by dividing the maximum tensile load at the point when the electrode film breaks without further deformation during the process of increasing the load applied to deform the length of the electrode film of a predetermined standard by the original cross-sectional area of ​​the specimen.

[0049] The modulus of elasticity is a constant that represents the ratio of deformation force (stress) to strain in an elastic material, and is also called the elastic modulus. When an external force is applied to an object and it is deformed, the deformation force caused by the external force and the strain caused by the deformation are proportional in the range where the deformation is not too large (Hooke's Law), and the constant of proportionality at this time is called the modulus of elasticity.

[0050] In this specification, the elastic modulus of the electrode film means the proportionality constant of the deformation force with respect to the strain caused by the deformation of the electrode film.

[0051] According to one embodiment of the present invention, the tensile strength and elastic modulus of the electrode film can be measured using a UTM (ZwickRoell) apparatus under the following test conditions. Test conditions: ASTM D 638, Pre-load 0.01 kg / cm, Test Speed ​​50 mm / min

[0052] The break elongation of the electrode film is 7% or more, and according to one embodiment of the present invention, the break elongation of the electrode film may be 7% to 10%, or 7% to 9%, or 7% to 8%, or 7.2% to 7.8%, or 7.2% to 7.4%, or 7.4% to 7.8%.

[0053] The tensile strength of the electrode film may be 1.1 MPa or more, or 1.1 MPa to 1.4 MPa.

[0054] The modulus of the electrode film may be 32.7 MPa or higher, 32.7 MPa to 40.9 MPa, or 38.3 MPa to 40.9 MPa.

[0055] The content of the fluorine-containing binder is 0.5 to 10 parts by weight based on 100 parts by weight of the electrode film of the present invention. According to one embodiment of the present invention, the content of the fluorine-containing binder may be 0.5 to 5 parts by weight, or 0.5 to 3 parts by weight, or 3 to 10 parts by weight based on 100 parts by weight of the electrode film.

[0056] If the fluorine-containing binder content is less than 0.5 parts by weight, it is impossible to manufacture the electrode film by molding the mixed powder formed by the grinding process. If it exceeds 10 parts by weight, it is undesirable because the non-uniformity of the mixed powder causes a decrease in the physical properties of the film.

[0057] The electrode film may include an active material, a fluorine-containing binder, and a conductive material.

[0058] According to one embodiment of the present invention, the content of the active material may be 85 to 98 parts by weight, the content of the conductive material may be 0.5 to 5 parts by weight, and the content of the fluorine-containing binder may be 0.5 to 10 parts by weight. Alternatively, the content of the active material may be 85 to 96 parts by weight, or 90 to 98 parts by weight, or 90 to 96 parts by weight, or 96 to 98 parts by weight, the content of the conductive material may be 0.5 to 5 parts by weight, or 0.5 to 1 part by weight, or 1 to 5 parts by weight, and the content of the fluorine-containing binder may be 0.5 to 5 parts by weight, or 5 to 3 parts by weight, or 3 to 10 parts by weight.

[0059] When the contents of the active material, conductive material, and fluorine-containing binder meet these ranges, the fluorine-containing binder can be sufficiently fiberized in the subsequent kneading process to form a mixture mass, facilitating the production of an electrode film by molding the mixed powder formed in the pulverization process, ensuring the physical properties of the electrode film, preventing volume reduction problems by ensuring the content of the active material, and ensuring sufficient conductivity.

[0060] On the other hand, in some cases, a filler that suppresses electrode expansion may be further added to the electrode layer, and the filler is not particularly limited as long as it does not induce a chemical change in the battery and is a fibrous material. For example, olefin polymers such as polyethylene and polypropylene; fibrous materials such as glass fiber and carbon fiber may be used.

[0061] According to one aspect of the present invention, Current collector and, An electrode is provided, characterized by comprising an electrode film of an embodiment of the present invention located on at least one surface of the current collector.

[0062] 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 surfaces treated with carbon, nickel, titanium, silver, etc. can be used. Furthermore, the current collector can have fine irregularities formed on its surface to enhance the adhesion of the positive electrode active material, and can take various forms such as films, sheets, foils, nets, porous materials, foams, and nonwoven fabrics.

[0063] Furthermore, the current collector may be one which is coated all or partially with a conductive primer layer on its surface to reduce resistance and improve adhesion. Here, the conductive primer layer may contain a conductive material and a binder. The conductive material is not limited as long as it is conductive. Examples include carbon-based materials, metallic materials (metal powder or metal fibers), conductive whiskers, conductive metal oxides, conductive polymers, and the like. Carbon-based materials include natural graphite, artificial graphite, graphene, carbon black, Denka Black, acetylene black, Ketjen Black, Super P, Channel Black, Furnace Black, Lamp Black, Thermal Black, carbon nanotubes, graphite nanofibers, and carbon nanofibers. Metallic materials include copper, nickel, aluminum, and silver. Conductive whiskers include zinc oxide whiskers, calcium carbonate whiskers, titanium dioxide whiskers, silicon oxide whiskers, silicon carbide whiskers, aluminum borate whiskers, magnesium borate whiskers, potassium titanate whiskers, silicon nitride whiskers, silicon carbide whiskers, and alumina whiskers. Conductive metal oxides include titanium oxide, and conductive polymers include polyphenylene derivatives. These can be used individually or as mixtures of two or more.

[0064] The binder may be a fluorine-based binder (including PVDF and PVDF copolymers) or an acrylic-based binder that dissolves in a solvent, and may also include an aqueous binder such as styrene-butadiene rubber (SBR).

[0065] According to one aspect of the present invention, The process involves heat-treating the fluorine-containing binder at 290°C to 310°C, A step of producing a mixture containing an active material and the heat-treated fluorine-containing binder, The steps include kneading the aforementioned mixture at a temperature in the range of 70°C to 200°C and under a pressure of atmospheric pressure or higher to produce a mixture mass, The steps include crushing the aforementioned mixture mass to obtain a mixed powder for electrodes, A method for manufacturing an electrode film according to one embodiment of the present invention is provided, characterized by comprising the step of forming an electrode film by calendering the electrode mixed powder between a plurality of rolls.

[0066] The method for manufacturing electrodes according to the present invention will be described in detail below. First, the fluorine-containing binder is heat-treated at 290°C to 310°C.

[0067] Pre-heating the fluorine-containing binder separately before mixing it with the active material allows for melt inter-diffusion at the surface between the binder particles, firmly binding the primary particles within the secondary particles of the fluorine-containing binder (e.g., PTFE), thereby facilitating the fiberization of the fluorine-containing binder in the subsequent manufacturing process of the electrode film.

[0068] Compared to conventional electrode films, electrode films containing a fluorine-containing binder with further fibrous structure exhibit significantly improved mechanical properties and increased film productivity.

[0069] The heat treatment of the fluorine-containing binder can be carried out in an air atmosphere using equipment such as a furnace.

[0070] The heat treatment temperature of the fluorine-containing binder is 290°C to 310°C, and according to one embodiment of the present invention, it may be 290°C to 300°C, or 300°C to 310°C, or 292°C to 308°C, or 293°C to 307°C.

[0071] If the heat treatment temperature of the fluorine-containing binder is below 290°C, there is no heat treatment effect, and if it exceeds 310°C, sheeting is not possible, which is disadvantageous in terms of film processability.

[0072] Next, a mixture comprising the active material and the heat-treated fluorine-containing binder is prepared.

[0073] In this case, the mixing for producing the mixture is carried out so that the active material and the heat-treated fluorine-containing binder are uniformly distributed, and since they are mixed in powder form, they can be mixed by a variety of methods, as long as they enable simple mixing. However, since the electrode film of the present invention is manufactured by a dry manufacturing method that does not use a dispersion medium, the mixing is carried out by dry mixing, and can be done by putting the substances into equipment such as a blender. According to one embodiment of the present invention, the mixture can be manufactured by further including a conductive material in addition to the active material and the heat-treated fluorine-containing binder.

[0074] Furthermore, in order to ensure uniformity, the mixture may be manufactured by mixing in a mixer at 5,000 rpm to 20,000 rpm for 30 seconds to 2 minutes, or more specifically at 10,000 rpm to 15,000 rpm for 30 seconds to 1 minute.

[0075] The fluorine-containing binder can be microfibrillated during the manufacturing process of the mixed powder, and as mentioned above, it is not limited to any particular type as long as it contains fluorine. Microfibrillation refers to a process of finely dividing a polymer, which can be done, for example, by using mechanical shear force. As a specific example of such a fluorine-containing binder, as mentioned above, a fluorine-containing polymer can be used, and specifically, it may contain polytetrafluoroethylene (PTFE) alone, or polytetrafluoroethylene may further contain one or more PVdF-based copolymers such as PVdF (polyvinylidene fluoride) or PVdF-HFP (polyvinylidene fluoride-co-hexafluoropropylene).

[0076] Next, the mixture is kneaded at a temperature in the range of 70°C to 200°C and under a pressure equal to or greater than atmospheric pressure to produce a mass of the mixture.

[0077] Conventional techniques have involved high-shear mixing, such as jet milling, to fibrousize the binder. However, this mixing can cause problems such as the active material being pulverized and the formed fibers being cut. Therefore, in the present invention, these problems are resolved by using a low-shear kneading method instead of high-shear mixing.

[0078] The kneading is not limited to any particular method. In one specific embodiment of the present invention, the kneading may be performed, for example, by a kneading machine such as a kneader.

[0079] This kneading process involves the fluorine-containing binder becoming fibrous while bonding or linking the active material and conductive material powders to form a 100% solid mixture mass.

[0080] Specifically, the kneading can be controlled at a speed of 10 rpm to 100 rpm. For example, the kneading can be controlled at a speed of 20 rpm or more or 70 rpm or less within the range. The kneading can be performed for 1 minute to 30 minutes. For example, it can be performed for 3 minutes to 10 minutes at a speed of 40 rpm to 70 rpm within the range. On the other hand, the shear rate of the kneading can be controlled in the range of 10 / s to 500 / s. In one specific embodiment of the present invention, the kneading can be performed for 1 minute to 30 minutes, and the shear rate can be controlled in the range of 30 / s to 100 / s.

[0081] Furthermore, such mixing steps can be carried out under high temperature and pressure conditions above atmospheric pressure. More specifically, they can be carried out under pressure conditions higher than atmospheric pressure.

[0082] More specifically, the kneading may be carried out at a temperature of 70°C to 200°C, more precisely, 90°C to 150°C, for the mixture.

[0083] If the process is carried out at a temperature outside the aforementioned temperature range, it becomes difficult for the fluorine-containing binder to fiberize and for lumps to form during kneading, making it difficult to form a film during calendering. Conversely, if the process is carried out at a temperature that is too high, the fluorine-containing binder will fiberize rapidly, and the pre-formed fibers may be cut by excessive shear force, which is undesirable.

[0084] Furthermore, the process can be carried out at atmospheric pressure or higher, more specifically at a pressure of 1 to 100 atmospheres, and more specifically at a pressure of 10 to 80 atmospheres. When the aforementioned pressure range is met, it is possible to prevent problems such as the formation of fibers being cut by excessive shear force and pressure, or the density of the mixture mass becoming excessively high. In other words, according to the present invention, the intended effects of the present invention can be achieved when a low-shear mixing process is performed under high temperature and atmospheric pressure or higher conditions instead of high-shear mixing.

[0085] Next, the mixture mass is crushed to obtain a mixed powder for electrodes. Specifically, the mixture mass produced by the kneading may be immediately calendered, but in this case, it is necessary to press the mixture mass to produce a thin film, which may result in problems such as the film becoming excessively dense or not being able to obtain a uniform film. Therefore, according to the present invention, the produced mixture mass undergoes the grinding step.

[0086] In this case, the grinding step is not limited, but may be performed using equipment such as a blender or grinder. Specifically, the grinding step may be performed at a speed of 5,000 rpm to 20,000 rpm for 30 seconds to 10 minutes, or more precisely, at a speed of 10,000 rpm to 18,000 rpm for 30 seconds to 2 minutes.

[0087] When the aforementioned grinding speed and time are met, sufficient grinding is performed to form powders of a size suitable for film formation, preventing the problem of a large amount of fine powder being generated in the mixture clumps. If necessary, a classification process can be carried out to separate powders that exceed a certain size or fall below a certain size.

[0088] Next, the electrode mixture powder is fed between multiple rolls and calendered to form an electrode film.

[0089] Referring to Figure 1, in the step 100 for forming the electrode film, multiple rolls 110 are arranged spaced apart. Mixed electrode powder 120 obtained in the previous step is fed between adjacent rolls 110, and the rolls 110 are rotated in opposing directions to roll the mixed powder 120, which is then formed into a sheet or film through a powder sheeting step. After that, an electrode film having the target thickness is finally obtained through multiple calendering steps.

[0090] Specifically, such calendering may involve processing the electrode mixture powder into a film, for example, to produce a film with an average thickness of 50 μm to 300 μm.

[0091] In this case, the caraging is performed, for example, by opposing rolls, the temperature of the rolls being 50°C to 200°C, and the rotation speed ratio of the rolls being controlled to be in the range of 1.0 to 2.0.

[0092] When the process reaches this calendering stage, a dry electrode film that acts as an electrode mixture can be manufactured. Such a dry electrode film is conventionally also called a free-standing film.

[0093] Since the dry electrode film produced in this manner does not contain solvents, it has almost no fluidity and is easy to handle, and can be processed into desired shapes and used in the manufacture of electrodes of various forms. Furthermore, when the dry electrode film of the present invention is used in the manufacture of electrodes, the drying process for solvent removal can be omitted, which not only greatly improves the processability of electrode manufacturing but also eliminates problems that have occurred in the manufacture of existing dry electrodes, such as cracking of the active material and cutting of fibrous fluorine-containing binders.

[0094] On the other hand, in the present invention, the porosity of the dry electrode film is 20% to 50%, and preferably can be controlled to a value of 40% or less or 30% or less within the above range. When the porosity satisfies such a range, impregnation of the electrolyte becomes easier, improving the lifetime characteristics and output characteristics, and since it is not necessary to increase the volume to achieve the same capacity, the energy density relative to the volume is improved. In one embodiment of the present invention, the porosity can be determined by measuring the apparent density of the dry electrode film and using the actual density calculated based on the actual density and composition of each constituent component, using the following formula. Porosity (%) = {1 - (Apparent density / Actual density)} × 100

[0095] According to one aspect of the present invention, A method for manufacturing an electrode is provided, characterized by including the step of laminating an electrode film, an embodiment of the present invention, onto a current collector.

[0096] The lamination step may be a step in which the electrode film obtained by the method for manufacturing an electrode film according to one embodiment of the present invention is rolled to a predetermined thickness and attached to a current collector. The lamination may also be performed by a laminating roll, in which case the laminating roll may be maintained at a temperature of 25°C to 250°C.

[0097] According to one embodiment of the present invention, the compression ratio of the electrode film may be 30% to 50%, or 35% to 50%, or 40% to 50%.

[0098] The compression ratio of the electrode film is defined as the ratio of the thickness of the electrode film compressed at the moment of lamination, and can be expressed by the following equation 1.

[0099] [Formula 1] Compression ratio (%) = T p / T1×100 In Equation 1, T p This refers to the pressure thickness of the electrode film during the lamination stage. T1 refers to the thickness of the electrode film before the lamination stage.

[0100] In this invention, by adjusting the compression ratio to satisfy a specific range during the lamination stage, it is possible to provide the electrode film with appropriate density and porosity, as well as excellent adhesion between the electrode film and the current collector.

[0101] When the compression ratio of the electrode film is within the range of 30% to 50%, the pressure applied to the electrode film becomes sufficient, improving the adhesion between the electrode film and the current collector. This prevents the electrode film from peeling off the current collector after the lamination process, and eliminates problems such as the density of the electrode film increasing excessively, resulting in a lower porosity than the target porosity, or damage to the current collector.

[0102] In one embodiment of the present invention, when electrode films are laminated to both sides of the current collector, the compression ratio (%) in formula 1 may mean the following formula 2. [Formula 2] 30 ≤ (T1 + 0.5T) c -0.5T gap ) / T1×100≦50 In Equation 2, T1 represents the thickness of the electrode film before the lamination step, and T c This refers to the thickness of the current collector, T gap This refers to the distance between the first rolling roll and the second rolling roll.

[0103] Furthermore, the rolling ratio of the electrode film after the lamination step may be in the range of 20% or less, 18% or less, 15% or less, 5% to 15%, 6% to 15%, 7% to 15%, or 9% to 13%.

[0104] Here, the rolling ratio is defined as the ratio of the thickness of the electrode film after the lamination stage to the thickness of the electrode film before the lamination stage, and can be expressed by the following equation 3.

[0105] [Formula 3] Rolling ratio (%) = (T1 - T2) / T1 × 100 In the above formula 3, T1 indicates the thickness of the electrode film before the lamination stage. T2 indicates the thickness of the electrode film after the lamination stage.

[0106] When the rolling ratio satisfies the range described above, appropriate density and porosity of the electrode film and adhesive strength between the electrode film and the current collector can be achieved.

[0107] The apparent density increase rate before and after lamination of the electrode film with the current collector can be expressed by the following equation 4.

[0108] [Formula 4] The rate of increase in apparent density (%) = (D2 - D1) / D1 × 100 D1 is the apparent density (g / cm³) of the electrode film before the lamination stage. 3 ) indicates, D2 is the apparent density (g / cm³) of the electrode film after the lamination stage. 3 ) indicates.

[0109] The increase in apparent density of the electrode film before and after lamination with the current collector may be 5% to 30%, 7% to 25%, or 10% to 20%. In this case, D1 and D2 are 2.75 g / cm³. 3 ~3.5g / cm 3 It may be within this range. On the other hand, if the rate of increase in the apparent density of the electrode film satisfies the above range, the adhesion between the electrode film and the current collector is improved, and problems such as the porosity falling outside the target range or damage to the positive electrode active material or current collector can be prevented.

[0110] The apparent density of the electrode film before and after lamination with the current collector can be calculated by measuring the weight and thickness of the electrode film before lamination, measuring the weight and thickness of the electrode after lamination, and then determining the weight and thickness of the film excluding the weight and thickness of the current collector.

[0111] Furthermore, the load amount of the active material in the dry electrode film is 3 mAh / cm². 2 ~15mAh / cm 2For more details, see 4mAh / cm². 2 ~10mAh / cm 2 It is possible.

[0112] Here, the load amount of the active material is the value calculated by the following equation 5. [Formula 5] Loading capacity of active material (mAh / cm²) 2 ) = Active material capacity (mAh / g) × Active material content ratio in dry electrode film (wt%) × Weight per unit area of ​​dry electrode film (g / cm²) 2 )

[0113] Furthermore, the interfacial resistance between the dry electrode film and the current collector is 5 Ω·cm. 2 For more details, see below: 2Ω·cm 2 The following is possible. Here, the interfacial resistance can be calculated by applying a current of 100 μA to the electrode using the MP (Multi Probe) resistance measurement method and measuring the resistance between the dry electrode film and the current collector layer using the potential difference measured between multiple probes. If the interfacial resistance range is met, the battery performance of subsequently manufactured secondary batteries can be improved.

[0114] Figure 2 is a schematic diagram of the step of laminating electrode films to both sides of a current collector according to one embodiment of the present invention. Specifically, in the lamination step 200, the electrode film 230 obtained in the previous step is rolled to a predetermined thickness and attached to the current collector 220 using a pair of laminating rolls 210, thereby ultimately obtaining the electrode 240.

[0115] According to yet another embodiment of the present invention, a dry electrode manufactured by the method for manufacturing a dry electrode is provided. Furthermore, a secondary battery including the dry electrode is provided, wherein the dry electrode is a positive electrode, and the electrode assembly including the positive electrode, a negative electrode, and a separator membrane is housed together with a lithium-containing non-aqueous electrolyte in a battery case (cylindrical case, rectangular case, pouch type, etc.), and an energy storage device including the same as a unit battery is also provided.

[0116] In this case, the specific structure of the secondary battery and energy storage device is as conventionally known, so a detailed explanation will be omitted in this specification.

[0117] 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 of raw materials including an active material, a conductive material, and a fluorine-containing binder; a kneader for kneading the mixture to produce a mixture mass; a pulverizer for crushing the mixture mass to form an electrode mixture powder; a calendar for forming the electrode mixture powder into a dry electrode film; and a laminating roll for positioning the dry electrode film on at least one surface of a current collector and laminating it.

[0118] 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. The kneader is a device for fiberizing the fluorine-containing binder and dispersing the raw materials for the mixture in the present invention, and the mixture can be obtained as a mixture mass by kneading with the kneader. In this case, the kneader for obtaining the results according to the present invention can be set to a temperature range of 70°C to 200°C and a pressure condition of atmospheric pressure or higher. More specifically, it can be set to a temperature range of 90°C to 180°C and a pressure condition of 1 to 100 atmospheres, and more specifically, a pressure condition of 10 to 80 atmospheres.

[0119] The aforementioned pulverizer is a device that pulverizes such a mixture mass to form a mixed powder for electrodes, and may use a blender or a grinder.

[0120] The calender is a device for forming the electrode mixture 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.

[0121] The laminating roll plays the role of attaching the dry electrode film formed by the calender to at least one surface of the current collector and rolling it.

[0122] The porosity of the dry electrode film according to the present invention can be determined by such a calender and laminating roll.

[0123] In other words, the dry electrode manufacturing apparatus according to the present invention is characterized by including a kneader and a pulverizer.

[0124] The specific structures of the aforementioned blender, kneader, calender, and laminating roll are conventionally known, and therefore, a detailed explanation is omitted in this specification.

[0125] The present invention will be described in detail below with reference to examples. However, the examples of the present invention can be modified in various forms, and the scope of the present invention is not limited by the examples described below. The examples of the present invention are provided to give a more complete explanation of the present invention to a person of average knowledge in the art.

[0126] Comparative Example 1 <Manufacturing of electrode films> Lithium nickel cobalt manganese aluminum oxide (Li[Ni 0.73 Co 0.05 Mn 0.15 Al 0.02 96g of ¹O₂;NCMA, 1g of carbon black as a conductive material, and 3g of polytetrafluoroethylene (PTFE) as a fluorine-containing binder were placed in a blender and mixed at 50 rpm for 5 minutes to produce a mixture. The kneader temperature was maintained at 150°C, and after placing the mixture in the kneader, it was operated at a speed of 50 rpm for 5 minutes under a lid pressure of 1.1 atmospheres to obtain a mixture mass. The mixture mass was placed in a blender and pulverized at 10,000 rpm for 1 minute, and then classified using a sieve with 1 mm openings to obtain an electrode mixed powder. Subsequently, the produced electrode mixed powder was placed in a wrap calender (roll diameter: 160 mm, roll temperature: 100°C) to produce an electrode film. The thickness of the produced electrode film was 80 μm.

[0127] Examples 1-3 <Manufacturing of electrode films> An electrode film was manufactured in the same manner as in Comparative Example 1, except that polytetrafluoroethylene (PTFE) was heat-treated with a fluorine-containing binder at the heat treatment temperature and time listed in Table 1 below, using a furnace in an air atmosphere, and then cooled to room temperature of 25°C.

[0128] Comparative Examples 2 and 3 <Manufacturing of electrode films> An electrode film was manufactured in the same manner as in Comparative Example 1, except that polytetrafluoroethylene (PTFE) was heat-treated in a furnace under an air atmosphere with a fluorine-containing binder at the heat treatment temperature and heat treatment time shown in Table 1 below, and then cooled to room temperature of 25°C.

[0129] Comparative Example 4 <Manufacturing of electrode films> Lithium nickel cobalt manganese aluminum oxide (Li[Ni 0.73 Co 0.05 Mn 0.15 Al 0.02 An electrode film was manufactured in the same manner as in Comparative Example 1, except that 87 g of 2000 (O2;NCMA), 1 g of carbon black as a conductive material, and 12 g of polytetrafluoroethylene (PTFE) as a fluorine-containing binder were used, and the polytetrafluoroethylene (PTFE) was heat-treated in a furnace under an air atmosphere at the heat treatment temperature and heat treatment time listed in Table 1 below, and then cooled to room temperature of 25°C.

[0130] Performance evaluation The electrode films produced in Examples 1-3 and Comparative Examples 1-4 were evaluated as follows, and the results are shown in Table 1.

[0131] (1) Elongation at break (%) Measurements were taken using a UTM (ZwickRoell) instrument under the following test conditions. Test conditions: ASTM D 638, Pre-load 0.01 kg / cm, Test Speed ​​50 mm / min (2) Modulus of elasticity (MPa) Measurements were taken using a UTM (ZwickRoell) instrument under the following test conditions. Test conditions: ASTM D 638, Pre-load 0.01 kg / cm, Test Speed ​​50 mm / min (3) Tensile Strength (MPa) Measurements were taken using a UTM (ZwickRoell) instrument under the following test conditions. Test conditions: ASTM D 638, Pre-load 0.01 kg / cm, Test Speed ​​50 mm / min

[0132] (4) Table 1 below shows the percentage increase in the physical properties of the examples compared to the physical properties of the comparative examples. The rate of increase was calculated using the formula [(Physical properties of the example - Physical properties of the comparative example) / (Physical properties of the comparative example) × 100 (%)].

[0133] [Table 1]

[0134] Referring to Table 1 above, it can be seen that the electrode films of Examples 1 to 3, which were manufactured by heat-treating a fluorine-containing binder at 290°C to 310°C and then mixing it with an active material, showed a significant improvement in mechanical properties such as elongation at break, modulus of elasticity, and tensile strength compared to the electrode films of Comparative Examples 1 to 3, which were either not heat-treated or did not meet the heat-treatment temperature conditions. Furthermore, although the electrode film of Comparative Example 4 met the elongation at break requirement of 7% or more, the content of the fluorine-containing binder was 12 parts by weight relative to 100 parts by weight of the electrode film, which fell outside the range of 0.5 parts by weight to 10 parts by weight relative to 100 parts by weight of the electrode film, resulting in very low tensile strength characteristics. [Explanation of symbols]

[0135] 110 rolls 120 Mixed powder 210 Laminating Rolls 220 Current collector 230 Electrode Film 240 electrodes

Claims

1. An electrode film comprising an active material and a fluorine-containing binder, The fluorine-containing binder mainly consists of a fibrous polytetrafluoroethylene (PTFE) binder. The active material includes a lithium transition metal oxide, The fluorine-containing binder content is 0.5 to 10 parts by weight, based on a total of 100 parts by weight of the electrode film. An electrode film characterized by having an elongation at break of 7% or more and less than 10%.

2. The electrode film according to claim 1, characterized in that the lithium transition metal oxide comprises lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium nickel-manganese-cobalt oxide, lithium nickel-manganese-cobalt-aluminum oxide, lithium copper oxide, or two or more of these.

3. The electrode film according to claim 2, characterized in that the lithium nickel-manganese-cobalt-aluminum oxide is represented by the following chemical formula 1. [Chemical formula 1] Li ａ [Ni ｂ Co ｃ Mn ｄ Al ｅ ] １－ｆ M １ ｆ O ２ In the aforementioned chemical formula 1, Said M １ is one or more elements selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, and satisfies the following conditions: 0.8 ≤ a ≤ 1.2, 0.5 ≤ b ≤ 0.99, 0 < c < 0.5, 0 < d < 0.5, 0.01 ≤ e ≤ 0.1, and 0 ≤ f ≤ 0.

1.

4. The electrode film according to claim 3, characterized in that the lithium nickel-manganese-cobalt-aluminum oxide is represented by the following chemical formula 2. [Chemical formula 2] Li ａ [Ni ｂ Co ｃ Mn ｄ Al ｅ ] １－ｆ O ２ In the above chemical formula 2, 0.8 ≤ a ≤ 1.2, 0.5 ≤ b ≤ 0.99, 0 < c < 0.5, 0 < d < 0.5, 0.01 ≤ e ≤ 0.1, and 0 ≤ f ≤ 0.

1.

5. The electrode film according to claim 1, characterized in that the elongation at break of the electrode film is 7% or more and less than 10%, and the tensile strength of the electrode film is 1.1 MPa to 1.4 MPa.

6. The electrode film according to claim 5, characterized in that the electrode film has a break elongation of 7.2% to 7.8%, a tensile strength of 1.1 MPa to 1.4 MPa, and an elastic modulus of 38.3 MPa to 40.9 MPa.

7. The electrode film according to claim 1, characterized in that the electrode film comprises an active material, a fluorine-containing binder, and a conductive material.

8. The electrode film according to claim 7, characterized in that the conductive material includes activated carbon, graphite, carbon black, Ketjenblack, carbon nanotubes, or two or more of these.

9. The electrode film according to claim 7, characterized in that the content of the active material is 85 to 98 parts by weight, the content of the conductive material is 0.5 to 5 parts by weight, and the content of the fluorine-containing binder is 0.5 to 10 parts by weight.

10. A method for manufacturing an electrode film according to claim 1, The process involves heat-treating polytetrafluoroethylene (PTFE) at 290°C to 310°C, A step of producing a mixture containing an active material and the heat-treated polytetrafluoroethylene (PTFE), The steps include kneading the aforementioned mixture at a temperature in the range of 70°C to 200°C and a pressure of normal or higher to produce a mixture mass, The steps include crushing the aforementioned mixture mass to obtain a mixed powder for electrodes, A method for manufacturing an electrode film, comprising the step of forming an electrode film by calendering the electrode mixture powder between a plurality of rolls.

11. The method for manufacturing an electrode film according to claim 10, characterized in that the step of kneading to produce a mixture mass is performed in a kneader under a pressure of atmospheric pressure or higher.

12. A method for manufacturing an electrode, characterized by including the step of laminating an electrode film according to any one of claims 1 to 9 onto a current collector.

13. The method for manufacturing an electrode according to claim 12, characterized in that the compression ratio of the electrode film at the lamination stage is 30% to 50%.

14. Current collector and, An electrode characterized by comprising an electrode film according to any one of claims 1 to 9, which is located on at least one surface of the current collector.

15. The electrode according to claim 14, characterized in that the current collector further comprises a conductive primer layer on at least one surface.

16. A secondary battery comprising a positive electrode, a negative electrode, and a separation membrane interposed between the positive electrode and the negative electrode, wherein at least one of the positive electrode and the negative electrode is the electrode described in claim 14.

17. An energy storage device comprising the secondary battery described in claim 16 as a unit battery.

18. The electrode according to claim 14, characterized in that it is a dry electrode.

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