Electrode composite film, manufacturing method therefor, and lithium secondary battery comprising same

Abstract

The present invention provides an electrode composite film comprising: an electrode active material containing lithium iron phosphate; a conductive material; and a fibrillizable binder, wherein the thickness variation obtained from thickness measurement results of a plurality of arbitrary points is 1.5% or less, and the weight variation obtained from weight measurement results of a plurality of arbitrary points is 1.5% or less.

Description

Electrode composite film, method for manufacturing the same, and lithium secondary battery comprising the same Cross-citation with related applications This application claims the benefit of priority from Korean Patent Application No. 10-2023-0133821, dated October 6, 2023, the entire contents of which are incorporated herein by reference. Technology field The present invention relates to an electrode composite film, a method for producing the same, and a lithium secondary battery including the same. Secondary batteries are used not only in small products such as digital cameras, P-DVDs, MP3 players, mobile phones, PDAs, portable game devices, power tools, and e-bikes, but also in large products requiring high output such as electric vehicles and hybrid vehicles, as well as in power storage devices that store surplus generated power or renewable energy and power storage devices for backup purposes. Typically, secondary batteries are manufactured by applying electrode active material slurry to a positive electrode current collector and a negative electrode current collector to form an electrode active material layer, then manufacturing a positive electrode and a negative electrode through a drying and rolling process, and then laminating these on both sides of a separator to form an electrode assembly of a predetermined shape, and then housing the electrode assembly in a battery case, injecting electrolyte, and sealing the electrode assembly. Meanwhile, during the drying process of the electrode active material slurry, the solvent contained in the slurry may evaporate, causing defects such as pinholes or cracks in the electrode active material layer formed on the current collector. In addition, since the inside and outside of the electrode active material slurry are not uniformly dried during the drying process, there is a concern that the powder floating phenomenon due to the difference in solvent evaporation rate may occur, i.e., the powder in the area that dries first may rise and form a gap with the area that dries relatively later, which may deteriorate the electrode quality. To solve the above problem, a drying device capable of controlling the evaporation rate of the solvent so that the inside and outside of the electrode active material slurry can be dried evenly is being considered, but such drying devices are very expensive and require considerable cost and time to operate, which is disadvantageous in terms of manufacturing process. On the other hand, the solvent typically used in electrode active material slurries is N-methyl-2-pyrrolidone (NMP). Its high boiling point necessitates high heat energy and a very long drying process for drying, making it highly unsuitable for mass production. Furthermore, NMP is toxic and harmful to living organisms, making it unfriendly to the environment. Accordingly, there has been a recent trend of active research on dry electrodes that manufacture electrodes without using solvents. The dry electrode is generally manufactured by laminating a free-standing electrode composite film manufactured in the form of a sheet containing an electrode active material, a binder, a conductive material, etc., onto a current collector. This electrode composite film includes a process of first mixing an electrode active material, a carbon material as a conductive material, and a fiberizable binder together using a blender, etc., and then applying a shear force through a process such as jet milling or kneading to fiberize the binder, and then calendering the obtained mixture into a film form to manufacture a free-standing film. Meanwhile, in the conventional electrode composite film manufacturing process, electrode powder is fed into a high-temperature calendering roll to manufacture an electrode composite film. However, the electrode composite film manufactured in this manner has a problem in that the uniformity of thickness and weight is low, which deteriorates the characteristics of the battery. Therefore, there is a need for the development of an electrode composite film that can realize uniform battery characteristics by having high uniformity in thickness and weight. The present invention is intended to solve the above problems, and provides an electrode composite film having low thickness deviation and weight deviation, a method for manufacturing the same, and a lithium secondary battery including the same. [1] The present invention provides an electrode composite film comprising an electrode active material including lithium iron phosphate, a conductive material, and a fiberizable binder, wherein a thickness deviation obtained from thickness measurement results at a plurality of arbitrary points is 1.5% or less, and a weight deviation obtained from weight measurement results at a plurality of arbitrary points is 1.5% or less. [2] In the present invention, in the above [1], the thickness deviation may be 1.0% or less. [3] In the present invention, in the above [1] or [2], the weight deviation may be 1.0% or less. [4] In at least one of the above [1] to [3], the tensile strength of the electrode composite film may be 0.30 MPa to 1.30 MPa. [5] In at least one of the above [1] to [4], the lithium iron phosphate can be represented by the following chemical formula 1. [Chemical Formula 1] Li 1+x1 [Mn 1-a1-b1 Fe a1 M 1 b1 ]PO4 In the above chemical formula 1, M 1 It contains at least one selected from the group consisting of Al, Mg, Ni, Co, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn and Y, and -0.1≤x1≤0.1, 0.5≤a1≤1.0, 0.0≤b1≤0.1. [6] In at least one of the above [1] to [5], the average particle diameter of the electrode active material may be 0.1 µm to 3.0 µm. [7] The present invention is characterized in that in at least one of the above [1] to [6], the electrode active material has a BET specific surface area of ​​0.5 m 2 / g to 30m 2 / g may be. [8] In at least one of the above [1] to [7], the fiberizable binder may include polytetrafluoroethylene (PTFE). [9] The present invention provides a method for manufacturing an electrode composite film, comprising the steps of (S1) preparing an electrode powder comprising an electrode active material including lithium iron phosphate, a conductive material, and a fiberizable binder; and (S2) calendering the electrode powder so that the temperature difference between the electrode powder and a calendering roll is 60°C or less, wherein the temperature of the electrode powder is 30°C to 100°C, and the temperature of the calendering roll is 30°C to 90°C.

[0010] In the present invention, in the above [9], the temperature of the electrode powder may be 60°C to 80°C.

[0011] In the present invention, in the above [9] or

[0010] , the temperature of the calendaring roll may be 60°C to 80°C.

[0012] In at least one of the above [9] to

[0011] , the surface roughness (Ra) of the calendaring roll may be 0.01 µm to 0.10 µm.

[0013] In at least one of the above [9] to

[0012] , the calendering is performed by feeding the electrode powder into a roll press section including a plurality of calendering rolls, and the force applied between the calendering rolls may be 50 kg / cm to 500 kg / cm.

[0014] In at least one of the above [9] to

[0013] , the calendering is performed by introducing the electrode powder into a roll press section including a plurality of calendering rolls, and the gap between the calendering rolls may be 10 µm to 300 µm.

[0015] The present invention provides a lithium secondary battery including the electrode composite film of the above [1]. The electrode composite film according to the present invention is characterized by improved uniformity in thickness and weight. Accordingly, it prevents local concentration of electrode reactions due to uneven thickness and weight of the electrode composite film, thereby improving uneven discharge capacity. Hereinafter, the present invention will be described in more detail. Terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical spirit of the present invention, based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best possible manner. In this specification, the term "composite composition" means a mixture comprising an electrode active material, a conductive material, and a fiberizable binder, which is physically mixed to form a uniform dispersion phase, and may be a powder mixture as a product of the mixing process (mixing process) according to this specification, and may be substantially solvent-free. Here, substantially solvent-free means that no solvent is added or only a very small amount of solvent is added during mixing of the composite composition. In this specification, the “mixed aggregate” is a product of the kneading process (kneading process) according to this specification in which the above composite composition is subjected to a shear force, the binder is fiberized, and the powder mixture is combined or linked to each other to convert into a paste-like aggregate, and may be a product of the kneading process according to this specification with a solid content of 100%. In this specification, “electrode powder” may mean a powder-type electrode material that is a material in which the above mixed aggregate is pulverized to form smaller particles and is in a powder form, and includes an electrode active material, a binder, and optionally a conductive material. In this specification, the "electrode composite film" may refer to an electrode composite layer manufactured in the form of a free-standing single sheet using an "electrode composite" including an electrode active material, a conductive material, and a binder without the involvement of a solvent, or in a state of being laminated on a current collector. The term "free-standing" in this specification means that it can maintain its own form without relying on other members and can be moved or handled by itself. The electrode composite film may be formed by compressing the electrode powder as described below. For example, the electrode powder may have a shape in which a layered structure is formed by compressing. In this specification, the term "powder-sheeting film" refers to a film formed from the time the electrode powder is first passed through a rolling roll in a roll-to-roll process to the time before passing through the last rolling roll in the process, and may be a self-supporting sheet, but may have relatively weak self-supporting force. Here, the "powder-sheeting" refers to the process in which the electrode powder is formed into a self-supporting sheet by a rolling roll in the roll-to-roll process, and the "sheeting" refers to a process performed in the process in which the powder-sheeting film is manufactured into an electrode composite film, and may refer to a process in which the powder-sheeting film is rolled. In the present invention, the MD direction (Machine Direction) refers to the longitudinal direction of the electrode composite film, and the TD direction (Transverse Direction) refers to the width direction of the electrode composite film. In the present invention, "average particle diameter" refers to the particle diameter corresponding to 50% of the volume accumulation amount in the particle diameter distribution curve. The average particle diameter can be measured using, for example, the laser diffraction method. The laser diffraction method is generally capable of measuring particle diameters from the submicron range to several millimeters, and can obtain results with high reproducibility and high resolution. In the present invention, the “BET specific surface area” is measured by the BET method, and specifically, can be calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77 K) using BELSORP-mino II of BEL Japan. The inventors of the present invention have conducted continuous research to realize uniform physical properties and excellent tensile strength of an electrode composite film, and as a result, have found that when the temperature difference between the electrode powder and the calendering roll is controlled within a certain range while simultaneously controlling the temperature of the electrode powder and the calendering roll, the uniformity of the thickness and weight of the electrode composite film can be improved while also realizing excellent tensile strength, thereby completing the present invention. Hereinafter, the present invention will be described in detail. The electrode composite film according to the present invention, the method for manufacturing the same, and the lithium secondary battery including the same comprise at least one of the following disclosed configurations, and may comprise any combination between technically possible configurations among the following configurations. Electrode composite film Hereinafter, an electrode composite film according to the present invention will be described. An electrode composite film according to the present invention comprises an electrode active material including lithium iron phosphate, a conductive material, and a fiberizable binder, and has a thickness deviation of 1.5% or less obtained from thickness measurement results at a plurality of arbitrary points, and a weight deviation of 1.5% or less obtained from weight measurement results at a plurality of arbitrary points. In the conventional electrode composite film manufacturing process, electrode powder is fed into a high-temperature calendering roll to manufacture the electrode composite film. However, if the electrode composite film is manufactured in a state where the temperature difference between the electrode powder and the calendering roll and the temperature of each of the electrode powder and the calendering roll are not controlled within a certain range, the uniformity of the thickness and weight of the electrode composite film is low, which deteriorates the electrochemical properties of the battery and causes a problem in the process of not being able to continuously manufacture a uniform electrode composite film. In addition, even if manufactured in the form of a film, problems such as pinholes or breakage may occur, or an uneven wave pattern may appear. Accordingly, the present invention aims to provide an electrode composite film having high uniformity in thickness and weight and being easy to form into a film by controlling the temperature difference between the electrode powder containing lithium iron phosphate and the calendaring roll and the temperature of each of the electrode powder and the calendaring roll within a certain range. The thickness deviation obtained from the thickness measurement results of the above multiple arbitrary points is 1.5% or less. Preferably, it may be 1.4% or less, 1.3% or less, 1.2% or less, 1.1% or less, or 1.0% or less. When the thickness deviation exceeds 1.5%, the surface of the electrode composite film is uneven, which limits the reaction between the electrode composite film and the electrolyte, and causes a problem of increased resistance or a voltage drop during battery operation due to the microscopic space between the current collector and the electrode composite film. In addition, the electrode reaction is locally concentrated, which causes a problem of uneven discharge capacity, and in severe cases, a problem of reduced safety occurs due to local lithium metal precipitation. Therefore, when the above range is satisfied, the surface of the electrode composite film is uniform, which allows for excellent reaction between the electrode composite film and the electrolyte, and the space between the current collector and the electrode composite film is small, which allows for excellent resistance and output characteristics, and prevents local electrode reaction, thereby allowing for uniform discharge capacity and excellent safety. The weight deviation obtained from the weight measurement results of the above multiple arbitrary points is 1.5% or less. Preferably, it may be 1.4% or less, 1.3% or less, 1.2% or less, 1.1% or less, or 1.0% or less. If the weight deviation exceeds 1.0%, the electrode active material is concentrated in a specific area, so that the energy density of the battery becomes non-uniform, and accordingly, the possibility of dendrite resin growth increases, so that the capacity of the battery is reduced or the life performance is lowered, and the initial life characteristics of the battery are deteriorated. Therefore, if the above range is satisfied, the energy density of the battery can become uniform, so that the initial life characteristics can be improved. The thickness deviation and weight deviation obtained from the thickness or weight measurement results of a plurality of arbitrary points according to the present invention can be calculated by manufacturing a total of five samples by punching the electrode composite film in a MD direction of 10 mm × TD direction of 10 mm, and then measuring the thickness and weight of each sample. Specifically, the thickness deviation can be calculated using the following mathematical formula A through a total of five thickness values ​​measured in each sample. [Mathematical Formula A] Thickness deviation (%) = [{(maximum measured thickness) - (minimum measured thickness)} / {2×(average measured thickness)}]×100 In the case of weight deviation, it can be calculated using the following mathematical formula B through a total of five weight values ​​measured from each sample. [Equation B] Weight deviation (%) = [{(maximum measured weights) - (minimum measured weights)} / {2×(average measured weights)}]×100 Therefore, when the above range is satisfied, an electrode composite film of uniform quality can be manufactured, breakage of the electrode composite film can be prevented, excellent processability can be exhibited in mass or continuous processes, and resistance characteristics and life characteristics of the battery can be improved. The tensile strength of the electrode composite film may be 0.30 MPa to 1.30 MPa, and preferably, 0.30 MPa or more, 0.35 MPa or more, 0.40 MPa or more, 0.45 MPa or more, 0.46 MPa or more, or 0.48 MPa or more, and 1.30 MPa or less, 1.20 MPa or less, 1.10 MPa or less, 1.00 MPa or less, or 0.90 MPa or less. When the above range is satisfied, the electrode composite film is not torn or broken during manufacture, so that excellent uniformity can be exhibited, thereby realizing excellent battery characteristics, and at the same time, no contamination occurs in the calendaring roll, so that excellent processability can be realized. In addition, since an excessive amount of binder is not included in the electrode composite film, the resistance is low, side reactions are small, and the lifespan can be excellent. Meanwhile, in the present invention, the electrode composite film may have a porosity of 20% to 50% by volume, specifically 20% to 40% by volume, and more specifically 25% to 35% by volume. When the above range is satisfied, the electrolyte impregnation is excellent, so that the lifespan characteristics and output characteristics can be improved, and the energy density can be excellent. The above porosity can be obtained by measuring the apparent density of the electrode composite film and using the actual density calculated based on the actual density and composition of each component, as shown in [Relational Formula 1] below. [Relationship 1] Porosity (%) = [1-{(apparent density) / (actual density)}]×100 The above electrode active material comprises lithium iron phosphate. Satisfying the above conditions is desirable because it can achieve excellent uniformity and tensile strength, while also demonstrating high thermal stability. Furthermore, forming an electrode composite film using lithium iron phosphate is desirable because it can achieve excellent economic efficiency, lifespan characteristics, and stability. Preferably, the lithium iron phosphate may be represented by the following chemical formula 1. [Chemical Formula 1] Li 1+x1 [Mn 1-a1-b1 Fe a1 M 1 b1 ]PO4 In the above chemical formula 1, M 1 It includes at least one selected from the group consisting of Al, Mg, Ni, Co, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn and Y, preferably, it may include at least one selected from the group consisting of Mg, Ti, V and Nb, and more preferably, it may include at least one selected from the group consisting of Ti and V. When the above conditions are satisfied, effects such as suppression of structural change during repeated charge and discharge of the positive electrode active material can be obtained. The above x1 is -0.1 to 0.1. When the above range is satisfied, high capacity characteristics and high energy density per unit volume can be realized. The above a1 is the molar fraction of iron (Fe) among the total metals excluding lithium in the lithium iron phosphate, and is 0.5 to 1.0. Preferably, it may be 0.5 or more, 0.6 or more, 0.7 or more, 0.8 or more, or 0.9 or more, and more preferably, the above a1 may be 1.0. When the above range is satisfied, the electronic conductivity and lithium ion conductivity in the lithium iron phosphate are excellent, so that the output characteristics can be excellent, and it is preferable in that an appropriate average particle size can be implemented. The above b1 is M among all metals except lithium in the first phosphate. 1The molar fraction may be from 0.0 to 0.1. Preferably, it may be 0.001 or more, 0.002 or more, 0.003 or more, 0.004 or more, 0.005 or more, 0.006 or more, 0.007 or more, 0.008 or more, or 0.009 or more, and may be 0.1 or less, 0.09 or less, 0.08 or less, 0.07 or less, 0.06 or less, 0.05 or less, 0.04 or less, 0.03 or less, 0.02 or less, or 0.01 or less. When the above range is satisfied, ionic conductivity and electrical conductivity may be improved. More preferably, the chemical formula 1 may be represented by the following chemical formula 1-1. [Chemical Formula 1-1] LiFePO4 The above electrode active material may further include a coating layer comprising carbon disposed on the lithium iron phosphate. When the above conditions are satisfied, the electronic conductivity of the positive electrode powder may be improved. The content of carbon included in the coating layer including carbon disposed on the lithium iron phosphate may be 0.1 wt% to 5.0 wt%, preferably 0.25 wt% to 4.0 wt%, and more preferably 0.5 wt% to 3.0 wt%, based on the total weight of the electrode active material. When the above range is satisfied, it may be preferable in that it may improve the electronic conductivity of the electrode active material while not acting as a resistor. The average particle diameter of the above electrode active material may be 0.1 µm to 3.0 µm, preferably 0.5 µm to 2.0 µm, and more preferably 0.6 µm to 1.5 µm. When the above range is satisfied, excellent uniformity and tensile strength can be achieved, while also achieving excellent energy density. The above electrode active material has a BET specific surface area of ​​0.5 m 2 / g to 30m 2 / g can be, preferably 1m 2 / g to 20m 2 / g can be, more preferably 5m 2 / g to 15m 2 / g. When the above range is satisfied, excellent energy density and electrolyte impregnation properties can be achieved, while also achieving excellent uniformity and tensile strength. The conductive agent is a component for further improving the conductivity of the electrode active material, and the conductive agent is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and examples thereof include carbon powder such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powder such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; conductive fibers such as carbon fibers or metal fibers; fluorinated carbon powder; conductive powder such as aluminum powder or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives. Specifically, the conductive agent may include at least one selected from the group consisting of activated carbon, graphite, carbon black, and carbon nanotubes (CNTs) for uniform mixing of the conductive agent and improvement of conductivity. The above-mentioned fiberizable binder is not specifically defined as long as it is fibrillizable, and the fibrillation refers to a process of dividing a polymer into small pieces. For example, it can be performed using a mechanical shear force, etc., and the surface of the fibrillated polymer fiber is loosened to generate a large number of fine fibers (fibrils). The fiberizable binder may preferably include at least one selected from the group consisting of polytetrafluoroethylene (PTFE) and polyolefin, more preferably polytetrafluoroethylene (PTFE), and even more preferably polytetrafluoroethylene (PTFE). Specifically, the polytetrafluoroethylene (PTFE) may be included in an amount of 60 wt% or more based on the total binder weight. At this time, the binder may additionally include at least one of PEO (polyethylene oxide), PVdF (polyvinylidene fluoride), PVdF-HFP (polyvinylidene fluoride-cohexafluoropropylene), and a polyolefin-based binder. Method for manufacturing electrode composite film Hereinafter, the method for manufacturing the electrode composite film will be described. The method for manufacturing an electrode composite film according to the present invention comprises the steps of (S1) preparing an electrode powder comprising an electrode active material including lithium iron phosphate, a conductive material, and a fiberizable binder; and (S2) calendering the electrode powder so that the temperature difference between the electrode powder and a calendering roll is 60°C or less, wherein the temperature of the electrode powder is 30°C to 100°C, and the temperature of the calendering roll is 30°C to 90°C. Next, we will explain each step in more detail. ((S1) step) The electrode active material, conductive material and fiberizable binder including the above lithium iron phosphate have been described above, so a detailed description thereof will be omitted. An electrode powder including the above electrode active material, conductive material and fiberizable binder can be prepared as follows. First, the aforementioned electrode active material, conductive material, and fiberizable binder are mixed to obtain a composite composition. At this time, the mixing is performed so that the electrode active material, conductive material, and fiberizable binder can be uniformly distributed. Since they are mixed in powder form, any method that allows simple mixing thereof is not limited and can be mixed by various methods. However, since the present invention is manufactured as a dry electrode that does not use a solvent, the mixing can be performed by dry mixing, and the materials can be mixed by putting them into a device such as a mixer or blender. At this time, the mixing can be performed in a mixer at 100 rpm to 3000 rpm for 5 to 60 minutes, and more specifically, at 600 rpm to 2000 rpm for 8 to 20 minutes. When performed within the above range, the materials can be uniformly mixed, thereby improving battery performance. Next, a fiberization process can be performed on the composite composition obtained from the above mixture to fiberize the fiberizable binder. The above fiberization process is not particularly limited as long as it is a generally performed mixing process, but preferably, it can be performed by high-temperature, low-shear kneading (kneading), and can be performed using a kneader, for example. By such kneading, the fiberizable binder is fiberized, thereby combining or linking the electrode active material and conductive powders, thereby forming a mixed aggregate with a solid content of 100%. The above mixing can be performed at a speed of 10 rpm to 100 rpm, and more specifically, at a speed of 20 rpm to 70 rpm. In addition, the mixing can be performed for 1 minute to 120 minutes, and more specifically, for 2 minutes to 60 minutes. When the above range is satisfied, appropriate fiberization can occur, thereby improving the characteristics of the battery. In addition, the above mixing can be performed under conditions of high temperature and pressure higher than atmospheric pressure, and more specifically, under conditions of pressure higher than atmospheric pressure. More specifically, the mixing can be performed at a temperature of 50°C to 230°C, preferably 90°C to 200°C. When mixing is performed at a high temperature such as the above range, the fiberization and lump formation of the binder through mixing can be effectively achieved, and the problem of breakage of the fiberized binder can be appropriately prevented. In addition, it can be performed at a pressure higher than atmospheric pressure, specifically at a pressure of 1 atm to 3 atm, more specifically at 1.1 atm to 3 atm. When performed within the above range, the problem of breakage of the binder in which fiberization has progressed can be appropriately prevented, and the problem of the density of the mixed aggregate becoming too high can be prevented. That is, according to the present invention, when a high-temperature-low-shear mixing process is performed under high-temperature and higher-than-normal pressure conditions instead of high-shear mixing, the intended effect of the present invention can be achieved. Next, a step of pulverizing the mixed aggregate manufactured through the above mixing step to obtain powder for electrodes can be performed. The mixed aggregates produced through the above mixing process can be directly calendered. However, in this case, the mixed aggregates must be pressed under high pressure and high temperature to form a thin film. This may result in problems such as the film density becoming too high or the inability to obtain a uniform film. Therefore, the mixed aggregates produced as described above are pulverized to produce powder for electrodes. The device used for the above crushing is not particularly limited, but it can preferably be performed by a device such as a blender or grinder. The above grinding can be performed at a speed of 1000 rpm to 15000 rpm for 5 seconds to 30 minutes, preferably at a speed of 3000 rpm to 8000 rpm for 30 seconds to 15 minutes. When performed within the above range, sufficient grinding can be achieved to produce powder of a size suitable for filming, and a large amount of fine powder can be prevented from being generated in the mixed aggregate. The average particle size of the above electrode powder may be 10 µm to 3000 µm, specifically 50 µm to 1500 µm, and more specifically 100 µm to 700 µm. When the above range is satisfied, an electrode composite film having a uniform thickness and density can be formed, and excellent electrode composite film properties can be secured. Meanwhile, the electrode powder according to the present invention may additionally include fillers, although not essential, to suppress electrode expansion. The fillers are not particularly limited as long as they are fibrous materials that do not cause chemical changes in the battery, and examples thereof include at least one selected from olefin polymers such as polyethylene and polypropylene; and fibrous materials such as glass fiber and carbon fiber. ((S2) step) A step of calendering the electrode powder manufactured in the above (S1) and the temperature difference between the calendering roll and the electrode powder is 60°C or less; the temperature of the electrode powder is 30°C to 100°C, and the temperature of the calendering roll is 30°C to 90°C, thereby manufacturing an electrode composite film. An electrode composite film can be manufactured by a calendering method in which the electrode powder according to the present invention is supplied to a calendering device and the supplied material is thermally compressed using calendering roll(s) included in the calendering device. Specifically, the electrode powder according to the present invention can be supplied to a calendering roll and thermally compressed to manufacture a sheet-shaped electrode composite film. For example, the calendering can be performed by feeding the electrode powder into a roll press section including a plurality of the calendering rolls. The temperature difference between the above electrode powder and the calendaring roll is 60°C or less, and preferably 58°C or less, 56°C or less, 55°C or less, 54°C or less, 53°C or less, 52°C or less, 51°C or less, 50°C or less, 49°C or less, 48°C or less, 47°C or less, 46°C or less, 45°C or less, 44°C or less, 43°C or less, 42°C or less, 41°C or less, 40°C or less, 39°C or less, 38°C or less, 37°C or less, 36°C or less, 35°C or less, 30°C or less, 25°C or less, 20°C or less, 15°C or less, 10°C or less, 5°C or less. When the temperature difference between the electrode powder and the calendaring roll exceeds 60℃, the temperature difference between the electrode powder and the calendaring roll is excessive, which may cause excessive fiberization in the electrode composite film being manufactured, resulting in a problem of reduced tensile strength. In addition, since the electrode powder is a powder in which various materials are mixed, the thermal expansion coefficients of the materials are different, and when the temperature difference is excessive, thermal stress occurs between different materials, which may increase the thickness deviation and weight deviation of the electrode composite film. Therefore, when the above range is satisfied, the thickness deviation and weight deviation of the electrode composite film can be reduced, and an appropriate tensile strength of the electrode composite film can be maintained, thereby improving the resistance and voltage characteristics of the battery. The temperature of the above electrode powder is 30°C to 100°C, preferably 35°C to 80°C, more preferably 40°C to 80°C, even more preferably 45°C to 80°C, even more preferably 50°C to 80°C, even more preferably 55°C to 80°C, and even more preferably 60°C to 80°C. When the above range is satisfied, an electrode composite film having an appropriate degree of fiberization can be manufactured, thereby having high tensile strength, and since the residual stress is not excessive, the thickness deviation and weight deviation of the electrode composite film can be reduced. The temperature of the above-mentioned calendering roll is 30℃ to 90℃, and specifically, it may be 35℃ or higher, 40℃ or higher, 45℃ or higher, 55℃ or higher, 60℃ or higher, 85℃ or lower, 80℃ or lower, and preferably 60℃ to 80℃. When the temperature of the calendering roll exceeds 90℃ or lower than 30℃, a problem occurs in which the thickness deviation and weight deviation of the electrode composite film increase. Therefore, when the above range is satisfied, the thickness deviation and weight deviation of the electrode composite film can be reduced, and an electrode composite film that is uniform and has excellent mechanical stability can be manufactured, and the electrode composite film is not torn during the manufacture of the electrode composite film, so it can be excellent in terms of process. The above-mentioned calendering roll may be included in the roll press section, and preferably, a plurality of calendering rolls may be included in the roll press section, and more preferably, two calendering rolls may be included in the roll press section, and even more preferably, two calendering rolls may be included in the roll press section so as to face each other. For example, the calendar device may include a roll press section in which two of the above-described calendaring rolls are arranged facing each other, and a plurality of the above-described roll press sections may be arranged continuously. When a plurality of the above-described roll press sections are arranged continuously, the temperature of each of the calendaring rolls may be the same or may satisfy the temperature of the above-described calendaring rolls. At this time, each roll press section can be independently adjusted so that the rotation speed ratio of the two rollers is appropriately adjusted within 1:1 to 1:10. In addition, the electrode composite film manufactured above can be put into a roll press section again and subjected to heat pressing 1 to 10 times to adjust it to an appropriate thickness. The above-mentioned calendaring rolls may each independently have a surface roughness (Ra) of 0.01 µm to 0.10 µm, preferably 0.02 µm to 0.08 µm, and more preferably 0.03 µm to 0.06 µm. When the above range is satisfied, defects such as tearing of the electrode composite film can be reduced, and excellent processability and superior uniformity can be achieved. The force applied between the above-mentioned calendering rolls may be 50 kg / cm to 500 kg / cm, preferably the force applied between the above-mentioned calendering rolls may be 80 kg / cm to 400 kg / cm, and more preferably the force applied between the above-mentioned calendering rolls may be 100 kg / cm to 300 kg / cm. When the above range is satisfied, it may be easy to maintain the gap between the rolls, and excellent uniformity and tensile strength may be achieved. The gap between the calendering rolls may be 10 µm to 300 µm, preferably the gap between the calendering rolls may be 20 µm to 200 µm, and more preferably the gap between the calendering rolls may be 50 µm to 180 µm. When the above range is satisfied, the processability can be excellent, while also achieving excellent uniformity and tensile strength. dry electrode Hereinafter, a dry electrode according to the present invention will be described. A dry electrode according to the present invention comprises the electrode composite film of the present invention described above. Specifically, the dry electrode may comprise a current collector; and an electrode composite film of the present invention formed on the current collector. In addition, the dry electrode according to the present invention can be manufactured by laminating the electrode composite film on one or both sides of a current collector and laminating the resultant product. The above lamination may be a step of rolling and attaching the electrode composite film onto a current collector. The above lamination may be performed by a roll press method using a lamination roller, and at this time, the lamination roller may be maintained at a temperature of 20°C to 200°C. The current collector is not particularly limited and may be any conductive material that does not induce chemical changes in the battery. For example, the current collector may be made of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like. The thickness of the above-mentioned collector may be 3 μm to 500 μm, but is not limited thereto. In addition, fine irregularities may be formed on the surface of the collector to increase the adhesive strength of the composite film. The above-mentioned collector may be used with a conductive primer coated entirely or partially on the surface to lower resistance and improve adhesion. Here, the conductive primer may include a conductive material and a binder, and the conductive material is not limited to any conductive material, but may be, for example, a carbon-based material. The binder may include a fluorine-based binder (including PVDF and PVDF copolymer), an acrylic-based binder, and an aqueous binder that can be dissolved in a solvent. lithium secondary battery Hereinafter, a lithium secondary battery according to the present invention will be described. A lithium secondary battery according to the present invention comprises an electrode composite film according to the present invention, and more specifically, a dry electrode according to the present invention. Preferably, the lithium secondary battery comprises a positive electrode, a negative electrode, a separator, and an electrolyte, and more preferably, the lithium secondary battery comprises a dry electrode, a negative electrode, a separator, and an electrolyte according to the present invention. The negative electrode may be an electrode manufactured through a conventional wet manufacturing method, or an electrode manufactured through a conventional dry manufacturing method. The above separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without any particular restrictions, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength may be used, and may optionally be used in a single-layer or multi-layer structure. In addition, the electrolyte used in the present invention may include, but is not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, etc. that can be used in the manufacture of a lithium secondary battery. Specifically, the electrolyte may include an organic solvent and a lithium salt. The organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; Carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R represents a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, a carbonate solvent is preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery and a linear carbonate compound having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable. The above lithium salt can be used without any special limitation as long as it is a compound that can provide lithium ions used in a lithium secondary battery. Specifically, the anion of the above lithium salt is F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - At least one selected from the group consisting of, and the lithium salt is LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2) 2. LiCl, LiI, or LiB(C2O4)2 can be used. The concentration of the lithium salt is preferably within the range of 0.1M to 4.0M, preferably 0.5M to 3.0M, and more preferably 1.0M to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively. In addition to the electrolyte components, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. At this time, the additives may be included in an amount of 0.1 to 10.0 wt% based on the total weight of the electrolyte. In addition, since the lithium secondary battery according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, it is useful in portable devices such as mobile phones, laptop computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs). Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided. The above battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, such as a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system. Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein. Hereinafter, the present invention will be described in more detail through specific examples. Example 1: Preparation of electrode composite film Lithium iron phosphate (LiFePO4, average particle size: 0.9㎛, BET surface area: 11.1m) as an electrode active material 2 / g) 7.6 kg, carbon black 0.12 kg as a conductive agent, and polytetrafluoroethylene (PTFE) 0.28 kg as a fiberizable binder were added and mixed at a rotation speed of 1500 rpm for 10 minutes to prepare a composite composition. After the above composite composition was put into a kneader, it was kneaded at a rotation speed of 50 rpm at a temperature of 150°C and 1.1 atm for 5 minutes to produce a mixed aggregate. The above mixed aggregates were placed in a blender and ground at a rotation speed of 5000 rpm for 10 minutes to produce powder for electrodes. Thereafter, the electrode powder was heated to 80°C, and the heated electrode powder was fed into a roll press section including two calendaring rolls heated to 80°C to manufacture an electrode composite film (roll diameter: 250 mm, roll speed ratio: 1 / 1.5 mpm). At this time, the surface roughness (Ra) of the roll was 0.04 μm, the force applied between the calendering rolls was 100 kg / cm, and the gap between the calendering rolls was 180 μm. Comparative Example 1: Manufacturing of electrode composite film An electrode composite film was manufactured in the same manner as in Example 1, except that the electrode powder at room temperature (25°C) was fed into a calendaring roll heated to 100°C. Comparative Example 2: Manufacturing of electrode composite film An electrode composite film was manufactured in the same manner as in Example 1, except that the electrode powder heated to 100°C was fed into a calendaring roll heated to 100°C. Comparative Example 3: Manufacturing of electrode composite film An electrode composite film was manufactured in the same manner as in Example 1, except that the electrode powder at room temperature (25°C) was fed into a calendaring roll heated to 150°C. Comparative Example 4: Manufacturing of electrode composite film An electrode composite film was manufactured in the same manner as in Example 1, except that the electrode powder at room temperature (25°C) was fed into a calendaring roll heated to 80°C. Comparative Example 5: Manufacturing of electrode composite film An electrode composite film was manufactured in the same manner as in Example 1, except that the electrode powder at room temperature (25°C) was fed into a calendaring roll heated to 60°C. Comparative Example 6: Manufacturing of electrode composite film An electrode composite film was manufactured in the same manner as in Example 1, except that the electrode powder at room temperature (25°C) was fed into a calendaring roll at room temperature (25°C). At this time, comparative example 6 could not be filmed. Comparative Example 7: Manufacturing of electrode composite film An electrode composite film was manufactured in the same manner as in Example 1, except that the electrode powder heated to 120°C was fed into a calendaring roll heated to 120°C. The manufacturing method of the electrode composite film manufactured according to the above Example 1 and Comparative Examples 1 to 7 is summarized and shown in [Table 1] below. Powder temperature for electrode (℃)Calendering roll temperature (℃)Temperature difference between powder for electrode and calendering roll (℃)Example 180800Comparative example 12510075Comparative example 21001000Comparative example 325150125Comparative example 4258055Comparative example 5256035Comparative example 625250Comparative example 71201200 Experimental Example 1: Measurement of thickness deviation, weight deviation, and tensile strength <Thickness deviation and weight deviation> The electrode composite films manufactured in Example 1 and Comparative Examples 1 to 7 were cut into 10 mm in MD direction × 10 mm in TD direction to make 5 samples, and the weight and thickness of each sample were measured using an AND GR-200 scale and a TESA μ HITE precision thickness measuring instrument, respectively. At this time, the thickness deviation and weight deviation were obtained using the mathematical formulas A and B described above, respectively. The measurement results are shown in [Table 2] below. Tensile strength The electrode composite films manufactured in Example 1 and Comparative Examples 1 to 7 were cut into 10 mm × 10 mm pieces, and the tensile strength was measured using a UTM device from ZwickRoell according to the ASTM 638 method. The preload was 0.01 kg / cm, and the speed was 50 mm / min. At this time, the tensile strength was obtained as the maximum value (MPa) of the force applied until the sample did not break. The measurement results are shown in [Table 2] below. Thickness deviation (%)Weight deviation (%)Tensile strength (MPa)Example 10.940.990.58Comparative example 13.033.10.38Comparative example 21.551.510.45Comparative example 33.833.930.34Comparative example 41.941.80.31Comparative example 52.382.910.29Comparative example 6---Comparative example 71.651.720.42 As can be confirmed in the above [Table 2], in the case of Example 1, it can be seen that the thickness deviation and weight deviation are lower compared to Comparative Examples 1 to 7. That is, it can be seen that the thickness deviation and weight deviation intended by the present invention require that the temperature difference between the electrode powder and the calendaring roll be appropriately controlled, and that the temperatures of each of the electrode powder and the calendaring roll be appropriately controlled. Experimental Example 2: Evaluation of Defects in Electrode Composite Films The appearance of the electrode composite film manufactured according to Example 1 and Comparative Examples 1 to 7 and the calendaring roll used in the manufacturing was observed to evaluate the defects of the electrode composite film. Specifically, if there were no defects at all, it was evaluated as X; if contamination by the electrode composite film or tearing of the electrode composite film occurred on the surface of the calendering roll, or if an uneven wave pattern occurred to some extent, it was evaluated as △; and if contamination by the electrode composite film or tearing of the electrode composite film occurred excessively on the surface of the calendering roll, or an uneven wave pattern occurred severely, it was evaluated as ○. The evaluation results are shown in [Table 3] below. Electrode composite film defect evaluation example 1XComparative example 1△Comparative example 2△Comparative example 3OComparative example 4△Comparative example 5OComparative example 6Film formation not possibleComparative example 7X As can be confirmed in the above [Table 3], in the case of Example 1, compared to the comparative examples, no contamination occurred on the roll surface, no problem occurred with the electrode composite film being torn off, and no uneven wave pattern occurred.

Claims

1. An electrode active material comprising lithium iron phosphate; a conductive material; and a fiberizable binder; The thickness deviation obtained from the thickness measurement results at multiple random points is 1.5% or less, An electrode composite film having a weight deviation of 1.5% or less obtained from weight measurement results at multiple random points.

2. In paragraph 1, An electrode composite film having a thickness deviation of 1.0% or less.

3. In paragraph 1, An electrode composite film having a weight deviation of 1.0% or less.

4. In paragraph 1, An electrode composite film having a tensile strength of 0.30 MPa to 1.30 MPa.

5. In paragraph 1, The above lithium iron phosphate is an electrode composite film represented by the following chemical formula 1: [Chemical Formula 1] Li 1+x1 [Mn 1-a1-b1 Fe a1 M 1 b1 ]PO4 In the above chemical formula 1, M 1 It contains at least one selected from the group consisting of Al, Mg, Ni, Co, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn and Y, and -0.1≤x1≤0.1, 0.5≤a1≤1.0, 0.0≤b1≤0.

1.

6. In paragraph 1, An electrode composite film in which the average particle diameter of the electrode active material is 0.1 ㎛ to 3.0 ㎛.

7. In paragraph 1, The above electrode active material has a BET specific surface area of ​​0.5 m 2 / g to 30m 2 / g electrode composite film.

8. In paragraph 1, The above fiberizable binder is an electrode composite film comprising polytetrafluoroethylene (PTFE).

9. (S1) A step of preparing a powder for an electrode including an electrode active material including lithium iron phosphate, a conductive material, and a fiberizable binder; and (S2) A step of calendering the temperature difference between the electrode powder and the calendering roll to 60°C or less; The temperature of the above electrode powder is 30°C to 100°C, A method for manufacturing an electrode composite film, wherein the temperature of the above calendaring roll is 30°C to 90°C.

10. In paragraph 9, A method for manufacturing an electrode composite film, wherein the temperature of the above electrode powder is 60°C to 80°C.

11. In paragraph 9, A method for manufacturing an electrode composite film, wherein the temperature of the above calendaring roll is 60°C to 80°C.

12. In paragraph 9, A method for manufacturing an electrode composite film having a surface roughness (Ra) of the above calendaring roll of 0.01 ㎛ to 0.10 ㎛.

13. In paragraph 9, The above calendaring is performed by putting the electrode powder into a roll press section including a plurality of the above calendaring rolls, A method for manufacturing an electrode composite film in which a force applied between the above-mentioned calendaring rolls is 50 kg / cm to 500 kg / cm.

14. In paragraph 9, The above calendaring is performed by putting the electrode powder into a roll press section including a plurality of the above calendaring rolls, A method for manufacturing an electrode composite film having a gap between the above-mentioned calendaring rolls of 10 ㎛ to 300 ㎛.

15. A lithium secondary battery comprising the electrode composite film of claim 1.