Electrode for electrochemical element including dry electrode film and method for manufacturing the same

Abstract

To provide a method for manufacturing a dry electrode.SOLUTION: The method for manufacturing a dry electrode according to the present invention can determine the degree of fibrillation of a binder resin from the crystallinity of the binder resin, and can control process conditions of a mixed powder for electrode or an electrode film on the basis of the determination. Therefore, the confirmation and the control of the process conditions become easy and efficient. The method for manufacturing a dry electrode according to the present invention is also advantageous for mass production, because kneading using a kneader at high temperature and low speed and a pulverizing step solve the problem of clogging of a flow path due to agglomeration of components.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This application claims priority based on Korean Patent Application No. 10-2021-0104169, filed on August 6, 2021. The present invention relates to an electrode for an electrochemical element including a dry electrode film, and a method for manufacturing the same. The present invention also relates to the dry electrode film and a method for manufacturing the same. Furthermore, the present invention relates to an electrode mixed powder used in the manufacture of the dry electrode film, and a method for manufacturing the same. [Background technology]

[0002] The rapid increase in the use of fossil fuels has led to a growing demand for alternative and clean energy sources. One of the most actively researched areas in this field is electrochemical power generation and energy storage. A prime example of an electrochemical element using electrochemical energy is the secondary battery, whose applications are expanding rapidly. Lithium-ion batteries, a representative example of such secondary batteries, are not only used as an energy source for mobile devices, but have also recently been found to power electric vehicles and hybrid electric vehicles, replacing fossil fuel-using vehicles such as gasoline and diesel vehicles, which are major causes of air pollution. Furthermore, their applications are expanding to include power supply assistance through grid integration. The manufacturing process for such lithium-ion batteries is broadly divided into three stages: electrode manufacturing, electrode assembly manufacturing, and aging. The electrode manufacturing process is further divided into electrode mixture mixing, electrode coating, drying, rolling, slitting, and winding processes. Of these steps, the electrode mixture mixing step is the process of blending components to form the electrode active layer where the actual electrochemical reaction takes place in the electrode. More specifically, it is the process of mixing the electrode active material, which is an essential element of the electrode, other additives such as conductive materials and fillers, a binder for binding the powders together and adhering them to the current collector, and a solvent for providing viscosity and dispersing the powders, in the form of a fluid slurry.

[0003] The composition mixed in this way to form the electrode active layer is also broadly referred to as an electrode mixture. Subsequently, an electrode coating process is carried out in which the electrode mixture is applied onto an electrically conductive current collector, and a drying process is carried out to remove the solvent contained in the electrode mixture. The electrode is then further rolled to produce a predetermined thickness.

[0004] On the other hand, during the drying process, the evaporation of the solvent contained in the electrode mixture may induce defects such as pinholes and cracks in the already formed electrode active layer. Furthermore, if the inside and outside of the active layer are not dried uniformly, a powder suspension phenomenon may occur due to the difference in the evaporation rate of the solvent. That is, powder in the areas that are dried first may float up, forming a gap with the areas that are dried relatively later, which may degrade the electrode quality.

[0005] Therefore, in order to solve the above problems, drying equipment that can uniformly dry the inside and outside of the active layer while controlling the evaporation rate of the solvent has been considered. However, such drying equipment is very expensive and requires considerable cost and time to operate, making it disadvantageous in terms of manufacturing process efficiency. For this reason, research into manufacturing dry electrodes that do not use solvents has been actively conducted recently.

[0006] Dry electrodes are generally manufactured by laminating a free-standing film, which is manufactured in film form and contains an active material, binder, and conductive material, onto a current collector. First, the active material, a carbon material as a conductive material, and a fibrous binder are mixed together in a blender or the like, and the binder is fibrousized through a high-shear mixing process such as jet milling. After that, the mixture is calendered into a film to produce a free-standing film. Subsequently, the free-standing film manufactured after calendering is laminated onto the current collector.

[0007] However, when the above-described high-shear mixing step is applied to fragile active materials, a large amount of fine powder with small powder size is generated, which tends to degrade mechanical performance and electrochemical performance; and when high-shear mixing is excessive, the generated binder fibers may be cut, which may reduce the flexibility of the free-standing film.

[0008] Accordingly, there is an urgent need for the development of dry electrode manufacturing technology that can solve such problems. In particular, there is a need for providing a method capable of quantitatively analyzing the mixing uniformity of a mixture in which components for dry electrode film production are mixed and the state of a binder (such as the degree of fiberization) and for establishing process conditions. Summary of the Invention Problems to be Solved by the Invention

[0009] In order to solve the above problems, an object of the present invention is to provide a dry electrode that minimizes pulverization of the active material and maximizes binder fiberization, and a method for producing the same.

[0010] Another object of the present invention is to provide a dry electrode with improved mechanical properties such as flexibility and strength, and a method for producing the same.

[0011] A further object of the present invention is to provide a method for producing a dry electrode to which process conditions based on the crystallinity of a binder resin are applied. Means for Solving the Problems

[0012] A first aspect of the present invention relates to an electrode for an electrochemical device, wherein the electrode includes a dry electrode film produced by a dry production process that does not use a solvent, the dry electrode film includes an electrode active material, a conductive material, and a binder resin, and the binder resin contained in the dry electrode film has a crystallinity of 10% or less.

[0013] According to a second embodiment of the present invention, in the first embodiment, the tensile strength of the dry electrode film in the mechanical direction (MD) is 0.5 MPa or more.

[0014] According to a third embodiment of the present invention, in the first or second embodiment, the tensile elongation of the dry electrode film is 2% or more.

[0015] According to the fourth embodiment of the present invention, in any one of the first to third embodiments, the porosity of the dry electrode film is 20 vol% to 50 vol%.

[0016] A fifth embodiment of the present invention relates to a method for manufacturing an electrode for an electrochemical element, wherein the electrode is according to one of the first to fourth embodiments, and the method is (a) A step of producing a powdered mixture containing an electrode active material, a conductive material, and a binder resin, (b) A step of kneading the powdered mixture in the range of 70°C to 200°C to produce a mixture mass, (c) A step of crushing the mixture mass to obtain a mixed powder for electrodes, (d) The step of calendering the electrode mixture powder to obtain a free-standing dry electrode film, wherein the degree of crystallinity (d) of the binder resin contained in the dry electrode film obtained in step (d) is 10% or less.

[0017] According to the sixth embodiment of the present invention, in the fifth embodiment, the degree of crystallinity (c) of the binder resin contained in the electrode mixed powder obtained in step (c) is 20% or less.

[0018] According to the seventh embodiment of the present invention, in the fifth or sixth embodiment, the degree of crystallinity (a) of the binder resin contained in the mixture obtained in step (a) is 50% or less.

[0019] According to the eighth embodiment of the present invention, in any one of the fifth to seventh embodiments, step (a) is performed under conditions of 500 rpm to 30,000 rpm.

[0020] According to the ninth embodiment of the present invention, in any one of the fifth to eighth embodiments, step (b) is performed at a speed of 100 rpm or less.

[0021] According to the tenth embodiment of the present invention, in any one of the fifth to ninth embodiments, step (b) is 0.5 kgf / cm 2 ~10 kgf / cm² 2 It is carried out under pressure.

[0022] According to the 11th embodiment of the present invention, in any one of the 5th to 10th embodiments, step (b) is carried out under conditions of atmospheric pressure or higher.

[0023] According to the twelfth embodiment of the present invention, in any one of the first to fourth embodiments, the binder resin comprises polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyolefin, or a mixture of two or more of these.

[0024] According to the thirteenth embodiment of the present invention, in any one of the first to fourth embodiments, the electrode further includes a current collector, and the dry electrode film is disposed on at least one or both sides of the current collector.

[0025] According to the 14th embodiment of the present invention, any one of the 5th to 11th embodiments further includes the step of preparing a current collector and arranging and laminating the dry electrode film on at least one surface of the current collector.

[0026] A fifteenth embodiment of the present invention relates to a secondary battery and includes a dry electrode according to any one of the first to fourth embodiments, 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 in a battery case together with a lithium-containing non-aqueous electrolyte.

[0027] A sixteenth embodiment of the present invention relates to an energy storage device and includes a secondary battery according to the fifteenth embodiment as a unit battery.

[0028] A 17th embodiment of the present invention relates to a method for producing a mixed powder for electrodes to manufacture a dry electrode film, wherein the manufacturing method is: (a) A step of producing a powdered mixture containing an electrode active material, a conductive material, and a binder resin, (b) A step of kneading the powdered mixture in the range of 70°C to 200°C to produce a mixture mass, (c) A step of crushing the mixture mass to obtain a mixed powder for electrodes, The degree of crystallinity of the binder resin contained in the electrode mixture powder is 20% or less. The binder resin comprises polytetrafluoroethylene (PTFE), polyolefin, or a mixture thereof.

[0029] According to the 18th embodiment of the present invention, the electrode mixed powder is manufactured by the method of the 17th embodiment, wherein the electrode mixed powder comprises an electrode active material, a conductive material, and a binder resin, the binder resin comprises polytetrafluoroethylene (PTFE), PVdF, polyolefin, or a mixture of two or more of these, and the degree of crystallinity of the binder resin contained in the electrode mixed powder is 20% or less.

[0030] A 19th embodiment of the present invention relates to a method for producing a dry electrode film, comprising the step of calendering an electrode mixture powder to obtain a free-standing dry electrode film, wherein the electrode mixture powder is obtained by the method according to the 17th embodiment, and the degree of crystallinity (d) of the binder resin contained in the dry electrode film is 10% or less.

[0031] According to the 20th embodiment of the present invention, a dry electrode film manufactured by the method of the 19th embodiment has a tensile strength in the mechanical direction (MD) of 0.5 MPa or more, a tensile elongation of 2% or more, and a porosity of 20 vol% to 50 vol%. [Effects of the Invention]

[0032] The dry electrode manufacturing process according to the present invention minimizes the pulverization of the active material and prevents the cutting of the fibrous binder by introducing a pulverization step after a high-temperature, low-shear mixing step when manufacturing the electrode mixed powder. Furthermore, manufacturing dry electrodes using such an electrode mixed powder has the effect of improving the mechanical properties of the dry electrodes, such as flexibility and strength.

[0033] Furthermore, the method for manufacturing a dry electrode according to the present invention allows for the determination and confirmation of the degree of microfiberization of the binder resin and the completion of each step based on the degree of crystallinity of the binder resin at each step. Based on this, the process conditions for the electrode mixture powder and electrode film can be controlled, making it easy and efficient to confirm and control the process conditions and the completion time.

[0034] Furthermore, the method for manufacturing dry electrodes according to the present invention is advantageous for fine fiber formation by going through low-shear kneading and pulverization stages using a kneader, and is advantageous for mass production as it eliminates the problem of the flow path becoming clogged with clumps of constituent components. [Brief explanation of the drawing]

[0035] [Figure 1] This is a thermal analysis graph using a DSC (Differential Scanning Calorimeter) for Example 1 of the present invention. [Figure 2] This is a thermal analysis graph using DSC for Example 2 of the present invention. [Figure 3] This is a flow chart showing the manufacturing sequence of the dry electrode of the present invention. [Modes for carrying out the invention]

[0036] The present invention will be described in more detail below to aid in understanding it.

[0037] Terms and words used in this specification and claims should not be interpreted in a manner limited to their ordinary and dictionary meanings, but rather in a manner and concept corresponding to the technical idea of ​​the present invention, in accordance with the principle that the inventor himself can appropriately define the concept of a term in order to best describe the invention.

[0038] The terms used herein are for illustrative purposes only and do not limit the invention. Unless otherwise specified, singular expressions include plural expressions.

[0039] Furthermore, throughout the specification, when a part "includes" other components, unless otherwise specified, it means that it may include other components, rather than excluding them.

[0040] One aspect of the present invention relates to an electrode for an electrochemical element and a method for manufacturing the same. The electrochemical element may be, for example, a secondary battery, and more specifically, a lithium-ion secondary battery.

[0041] In the present invention, the electrode includes a dry electrode film manufactured by a dry manufacturing process in which no solvent is used to disperse the electrode components during the electrode manufacturing process. The dry electrode film includes an electrode active material, a conductive material, and a binder resin, and the binder resin contained in the dry electrode film has a degree of crystallinity of 10% or less. For example, the degree of crystallinity may be 5% or less.

[0042] When the degree of crystallinity is within the range of 10% or less, the binder resin is highly fibrous, ensuring the flexibility of the dry electrode film. As a result, as described later, it is easier to manufacture strip-type dry electrode films in the calendering process to which a roll-to-roll continuous process is applied, and when the electrode film is wound into a roll form or unwound again after manufacturing, the form is stably maintained without damage such as breakage or cracking. It is also advantageous in ensuring a bonding force with the current collector that is greater than a predetermined strength.

[0043] Furthermore, in the present invention, it is desirable that the dry electrode film has a tensile strength in the mechanical direction (MD) of 0.5 MPa or more. On the other hand, the dry electrode film may have a tensile strength in the mechanical direction (MD) of 10.0 MPa or less, 5.0 MPa or less, or 3.0 MPa or less. When the tensile strength satisfies the above range, sufficient mechanical strength can be ensured when manufacturing a free-standing type dry electrode, making manufacturing and handling easy. On the other hand, if it does not fall within the above range, the mechanical strength is weak and it is prone to breakage. On the other hand, if the tensile strength is too high, the tensile elongation also increases, which reduces processability and results in uneven film thickness, as described below.

[0044] On the other hand, it is desirable that the dry electrode film has a tensile elongation of 2% or more.

[0045] The dry electrode film may have a tensile elongation of 30% or less, 20% or less, or 10% or less.

[0046] When the tensile elongation satisfies the above range, sufficient morphological stability and flexibility can be ensured during the manufacture of free-standing dry electrodes, making manufacturing and handling easy. If the tensile elongation is too low, flexibility and morphological stability are low, making it undesirable as it is prone to breakage during manufacturing and transport. On the other hand, if it exceeds the above range, the flexibility is too high, and the dry electrode film may be excessively stretched between the rolls in the calendering process described later, potentially resulting in an uneven thickness of the obtained film.

[0047] On the other hand, the dry electrode film may have a porosity of 20 vol% to 50 vol%.

[0048] Another aspect of the present invention relates to a method for manufacturing the electrode. The method for manufacturing the electrode is such that the degree of crystallinity of the binder resin contained in the dry electrode film is controlled to 10% or less. In the present invention, the degree of crystallinity in the dry electrode is zero (0) or 10% or less.

[0049] In one specific embodiment, the method for manufacturing the electrode is: (a) A step of producing a powdered mixture containing an electrode active material, a conductive material, and a binder resin, (b) A step of kneading the powdered mixture to produce a mixture mass, (c) A step of crushing the mixture mass to obtain a mixed powder for electrodes, (d) The step of calendering the electrode mixture powder to obtain a free-standing dry electrode film.

[0050] On the other hand, in one embodiment of the present invention, step (b) may be carried out under temperature conditions of 70°C to 200°C. For example, the temperature of the object to which the kneading step is applied may be controlled to 70°C to 200°C.

[0051] Here, in the powdered mixture obtained in step (a), the degree of crystallinity (a) of the binder resin is 60% or less, preferably 50% or less. Furthermore, in the mixed powder for electrodes obtained in step (c), the degree of crystallinity (c) of the binder resin is 20% or less, and in the dry electrode film obtained in step (d), the degree of crystallinity (d) of the binder resin is 10% or less.

[0052] In one embodiment of the present invention, each of the steps (a) to (d) is determined to be complete by checking the degree of crystallinity of the resulting product obtained at each step. If the degree of crystallinity of the binder resin of the product at each step satisfies the degree of crystallinity predetermined at each step, the next step is performed.

[0053] Specifically, in step (a), if the degree of crystallinity of the binder resin in the powdered mixture is 60% or less, preferably 50% or less, the process in step (a) is terminated and the obtained result is added to step (b).

[0054] Furthermore, if the degree of crystallinity of the binder resin in the electrode mixed powder is 20% or less, the process in step (c) is terminated and the obtained result is put into step (d).

[0055] Further, in step (d), when the crystallinity of the binder resin in the produced dry electrode film is 10% or less, it is determined that the production is completed.

[0056] Alternatively, in steps (a), (b) and (d), process conditions capable of controlling the crystallinity within the above-mentioned limited range in each step may be experimentally confirmed, and the experimentally set processes may be applied to each step.

[0057] In the present invention, the crystallinity (Xc) can be measured by Differential Scanning Calorimetry (DSC), and is based on the temperature (peak temperature) at the point when the highest enthalpy is exhibited during crystallization. Specifically, the crystallinity is the melting enthalpy (ΔH m ) value measured actually by DSC divided by the theoretical melting enthalpy (ΔH m 0 )(equilibrium heat of fusion) of a perfect crystal (100% crystallinity), expressed as a percentage, and can be calculated by the following Mathematical Formula 1. Here, the theoretical melting enthalpy value of a perfect crystal (ΔH m 0 ) can be referred to academic documents such as "Polymer Handbook" (J. Brandrup et al., 2003) and "Polymer". For example, the theoretical melting enthalpy value of a perfect PTFE crystal is 85.4 J / g (Polymer, Volume 46 (2005), pages 8872 to 8882). Meanwhile, thermal analysis of polymers such as DSC can generally be measured and calculated in accordance with ASTM D3418-21.

[0058] [Mathematical Formula 1] Xc(%)=(ΔH m ÷ΔH m 0 )×100

[0059] Hereinafter, the method for producing a dry electrode according to the present invention will be described in more detail.

[0060] First, a powdered mixture containing electrode active material, conductive material, and binder is manufactured (step (a)).

[0061] In this case, the mixing for producing the powdered mixture is performed to obtain a homogeneous mixture of the electrode active material, conductive material, and binder resin, and preferably to adjust the degree of crystallinity of the binder resin in the obtained powdered mixture to 50% or less. Since the materials are mixed in powder form, a variety of methods can be applied without limitation, as long as they can be mixed uniformly. However, in this invention, since a dry electrode is manufactured without the use of solvents, the mixing can be performed by dry mixing. For example, the substances can be placed in a device such as a mixer or blender.

[0062] In one embodiment of the present invention, the mixing time is not particularly limited, but can be performed for 1 second to 20 minutes. For example, it can be performed for 1 second to 10 minutes. On the other hand, the mixing speed is not particularly limited, but can be appropriately controlled within the range of approximately 500 rpm to 30,000 rpm. For example, it can be controlled within the range of 500 rpm to 20,000 rpm.

[0063] On the other hand, in one embodiment of the present invention, the temperature of the mixture can be controlled to 70°C or lower, or 60°C or lower. If the mixing temperature exceeds 70°C, the material adheres to the mixing apparatus, making it difficult to obtain a uniform mixture. On the other hand, the lower limit of the temperature of the mixture is not particularly limited, and in one embodiment of the present invention, it can be carried out at a temperature of 20°C or higher.

[0064] Specifically, the mixing can be performed using a mixer at a temperature of 70°C or lower for 30 seconds to 10 minutes at 500 rpm to 20,000 rpm, or at a temperature of 70°C or lower for 30 seconds to 2 minutes at 5,000 rpm to 20,000 rpm, or at a temperature of 60°C or lower for 30 seconds to 1 minute or 30 seconds to 7 minutes at 1,000 rpm to 15,000 rpm or 10,000 rpm to 15,000 rpm.

[0065] In the present invention, the degree of crystallinity of the binder resin in the mixture obtained by the above mixing is 60% or less, preferably 50% or less. On the other hand, if the degree of crystallinity of the binder resin in the obtained mixture exceeds 60% or 50%, it is desirable to increase the speed (rpm) and / or increase the process time to pulverize the binder into primary particles so that the clumps do not aggregate, thereby partially promoting the formation of thick fibers.

[0066] If the degree of crystallinity of the mixture obtained in step (a) above does not fall within the above range, it may be difficult to fiberize the binder resin in the low-shear kneading step (step (b)) described later, resulting in insufficient fiber formation on the binder surface or an increase in the process time required for fiberization of the binder resin.

[0067] On the other hand, if the mixing time is too long or the mixing speed is too fast, or both, the electrode active material may be pulverized / damaged or the fibers may be cut. This may also lead to non-uniformity of the binder fiber formation. Taking these points into consideration, in one embodiment of the present invention, the degree of crystallinity of the binder resin in the mixture can be controlled to 30% or more, 35% or more, or 40% or more.

[0068] In the present invention, the binder resin is not limited to any particular type, as long as it can be fibrousized by step (a) and / or step (b) described later.

[0069] On the other hand, although the binder resin may undergo fibrosis in stage (a), the fibers formed in stage (a) are thick and difficult to finen to a degree that can achieve the tensile strength and tensile elongation required by the dry electrode. In the present invention, preferably, the fine fibrosis of the binder resin is carried out mainly through stage (b) described later.

[0070] The term "fibrosis" refers to a process of dividing a polymer into smaller parts, which can be carried out, for example, by using mechanical shear force. The fibrous polymer fibers dissolve on their surface, generating numerous fine fibers (fibrils). Non-limiting examples of such binder resins include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyolefins, or mixtures of two or more of these, more specifically polytetrafluoroethylene (PTFE), and more specifically, polytetrafluoroethylene (PTFE). Specifically, the polytetrafluoroethylene (PTFE) may be present in an amount of 30% by weight or more based on the total weight of the binder resin. Of course, in this case, the binder resin may also contain polyethylene oxide (PEO) and / or polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), in addition to the components mentioned above.

[0071] The dry electrode may be a positive electrode, and the electrode active material may be a positive electrode active material.

[0072] The positive electrode active material is not limited to any specific component, as long as it is in the form of a lithium transition metal oxide or lithium metallic iron phosphate compound or metal oxide. Such positive electrode active materials include layered compounds such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), or compounds substituted with one or more transition metals; chemical formula Li 1+x Mn 2-x Lithium manganese oxides such as O4 (x=0~0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, Cu2V2O7; chemical formula LiNi 1-x M x Ni-site type lithium nickel oxide represented as O2(M=Co, Mn, Al, Cu, Fe, Mg, B or Ga, x=0.01~0.5), for example, Li(Ni,Co,Mn,Al)O2 in which the fraction of Ni in the metal excluding Li is 50% or more; chemical formula LiMn 2-x M xLithium manganese composite oxides represented by O₂ (M=Co, Ni, Fe, Cr, Zn or Ta, x=0.01~0.1) or Li₂Mn₃MO₈ (M=Fe, Co, Ni, Cu or Zn); LiMn₂O₄ in which a part of Li in the chemical formula is substituted with alkaline earth metal ions; lithium metal phosphate compounds LiMPO₄ (M=Fe, Co, Ni or Mn), disulfide compounds; Fe₂(MoO₄)₃, etc., may be mentioned, and one or more of these may be included. However, the present invention is not limited thereto.

[0073] Alternatively, the dry electrode may be a negative electrode, and the active material may be a negative electrode active material. The negative electrode active material includes carbons such as non-graphitizable carbon and graphite-based carbon; Li x Fe₂O₃ (0≦x≦1), Li x WO₂ (0≦x≦1), Sn x Me 1-x Me’ y O z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, elements of Group 1, Group 2, and Group 3 of the periodic table, halogens; 0<x≦1; 1≦y≦3; 1≦z≦8); lithium metal; lithium alloys; silicon-based alloys; tin-based alloys; silicon-based oxides such as SiO, SiO / C, SiO₂; metal oxides such as SnO, SnO₂, PbO, PbO₂, Pb₂O₃, Pb₃O₄, Sb₂O₃, Sb₂O₄, Sb₂O₅, GeO, GeO₂, Bi₂O₃, Bi₂O₄ and Bi₂O₅; conductive polymers such as polyacetylene; Li-Co-Ni based materials, etc., may be used.

[0074] However, the dry electrode may more specifically be a positive electrode, and accordingly, the active material may more specifically be a positive electrode active material, and more specifically, may be a lithium transition metal oxide, a lithium nickel-manganese-cobalt oxide, an oxide obtained by substituting a part of the lithium nickel-manganese-cobalt oxide with another transition metal, lithium iron phosphate, or the like.

[0075] The conductive material is not particularly limited as long as it does not induce a chemical change in the battery and is conductive. For example, graphite such as natural graphite or artificial graphite; carbon blacks such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives may be used. More specifically, to ensure uniform mixing of the conductive material and improve conductivity, it may include one or more selected from the group consisting of activated carbon, graphite, carbon black, and carbon nanotubes, and more specifically, it may include activated carbon.

[0076] The mixing ratio of the electrode active material, conductive material, and binder may be 80-98% by weight:0.5-10% by weight:0.5-10% by weight of the electrode active material:conductive material:binder resin, and more specifically, 85-98% by weight:0.5-5% by weight:0.5-10% by weight.

[0077] If the binder resin content exceeds the above range, the binder resin may be excessively fibrous during subsequent kneading processes, potentially affecting the process. If the content is too low, sufficient fibrous formation may not occur, resulting in insufficient aggregation to form a mixture mass, difficulty in manufacturing a dry electrode film, or a decrease in the physical properties of the dry electrode film.

[0078] Furthermore, if the conductive material content exceeds the above range, there is a problem in that the active material content decreases relatively, resulting in a decrease in capacity. Conversely, if it is too low, sufficient conductivity cannot be ensured, or the physical properties of the dry electrode film may deteriorate, which is undesirable.

[0079] On the other hand, depending on the circumstances, a filler, which is a component that suppresses the expansion of the electrodes, may be further added to the mixture. The filler is not particularly limited as long as it is a fibrous material that does not induce a chemical change in the battery, and for example, olefin polymers such as polyethylene and polypropylene; fibrous materials such as glass fibers and carbon fibers may be used.

[0080] In one embodiment of the present invention, the degree of crystallinity of the binder resin in the powdered mixture obtained in step (a) can be checked, and if the checked degree of crystallinity is 60% or less, preferably 50% or less, the process in step (a) can be terminated and the obtained result can be added to step (b). The degree of crystallinity can be checked at each step while performing steps (a) to (d).

[0081] Alternatively, in another embodiment, process conditions that can control the degree of crystallinity of the binder resin of the powdered mixture to 60% or less or 50% or less can be experimentally confirmed in step (a), and the experimentally set process can be applied to step (a).

[0082] Next, the resulting mixture is subjected to a kneading step (step (b)) as a process to fibrousize the binder resin.

[0083] In this mixing stage, as will be described later, a relatively low shear force is applied at a high temperature, so problems such as pulverization / damage of the electrode active material and cutting of binder fibers are avoided, and electrode mixed particles with finely fibrous binder resin can be obtained. In addition, the fibrous binder has high uniformity in fiber thickness and / or length.

[0084] The kneading is not limited to any particular method. In one specific embodiment of the present invention, the kneading may be performed using a kneader, for example. For example, the kneader may be a twin-screw extruder, a single-screw extruder, a batch kneader, a continuous kneader, etc.

[0085] Such kneading is a step in which the binder resin is fibroused while bonding or linking the electrode active material and conductive material powder to form a lump-like mixture with 100% solid content.

[0086] Specifically, the kneading in step (b) above 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 above range.

[0087] On the other hand, in one embodiment of the present invention, the kneading may be performed for 1 to 30 minutes. For example, it may be performed for 3 to 10 minutes at a speed of 20 rpm to 70 rpm within the above range.

[0088] On the other hand, in one embodiment of the present invention, the kneading step is performed with a shear rate of 5s -1 ~1,000s -1 It can be controlled within the range. In one specific embodiment of the present invention, the kneading may be carried out for 1 to 30 minutes, and the shear rate may be 10s -1 ~500s -1 It can be controlled within a certain range.

[0089] The aforementioned mixing step may be carried out under high temperature and pressure conditions above atmospheric pressure.

[0090] Specifically, the kneading may be carried out in the range of 70°C to 200°C, more precisely, 90°C to 150°C. The temperature may be the temperature inside the kneader or the temperature of the material being kneaded. Alternatively, both of these may be controlled to temperatures within the above range.

[0091] If the process is carried out at a temperature outside the above range, the binder will not fiberize or agglomerate sufficiently during the kneading process, resulting in poor film formation during calendering. Conversely, if the process is carried out at a temperature that is too high, the binder will fiberize too rapidly, and then the already formed fibers will be cut by excessive shear force, which is undesirable.

[0092] Furthermore, the kneading process is performed at 0.5 kgf / cm². 2~10 kgf / cm² 2 Under this pressure, more specifically 1 kgf / cm² 2 ~8 kgf / cm² 2 Under pressure, for example, above atmospheric pressure, 8 kgf / cm². 2 The process can be carried out as follows. Performing the process at excessively high pressures outside the above range is undesirable because it can lead to problems such as excessive shear force and pressure, causing the formed fibers to break or the density of the mixture to become excessively high. In other words, according to the present invention, the intended effect can be achieved when the low-shear kneading process is performed under high temperature and pressure conditions above atmospheric pressure. Alternatively, the process can be carried out at atmospheric pressure or higher, specifically at pressures of 1 atm to 3 atm, or 1.1 atm to 3 atm.

[0093] On the other hand, in one embodiment of the present invention, the above-mentioned process conditions in the kneading stage can be controlled according to the characteristics of the material introduced. In one specific embodiment, the process conditions can be appropriately adjusted according to the particle size of the electrode active material particles introduced. When the particle size of the electrode active material is large, fiber formation proceeds relatively more easily compared to electrode active material with a smaller particle size. Therefore, when the particle size of the electrode active material is large, a relatively slow rotation speed and / or shear rate may be applied, and when the particle size is small, a relatively fast rotation speed and / or shear rate may be applied. On the other hand, temperature and pressure can also be adjusted taking into account such material characteristics. Next, the lump mixture produced through the kneading in step (b) is further crushed to obtain a mixed powder for electrodes (step (c)).

[0094] Specifically, the lump mixture produced through the kneading in step (b) above may be immediately introduced into the calendering process to form a sheet. However, in this case, high pressure and high temperature are required to press the lump mixture into a thin film, which can lead to problems such as the dry electrode film becoming excessively dense or the inability to obtain a film with uniform thickness and density. Therefore, in the present invention, the lump mixture (lump mixture) produced in step (b) above is subjected to the pulverization step.

[0095] In this case, the grinding can be performed using known grinding equipment such as a blender or grinder, although this is not particularly limited. In one specific embodiment of the present invention, the grinding speed can be controlled within the range of 100 rpm to 30,000 rpm or 3,000 rpm to 30,000 rpm. On the other hand, the grinding time can be appropriately controlled within the range of 1 second to 10 minutes. However, the grinding speed and time are not particularly limited to the above ranges. Specifically, the grinding can be performed at a speed of 500 rpm to 20,000 rpm or 5,000 rpm to 20,000 rpm for 30 seconds to 10 minutes, or at a speed of 700 rpm to 18,000 rpm or 10,000 rpm to 18,000 rpm for 30 seconds to 5 minutes or 30 seconds to 1 minute.

[0096] If the rpm is too low or the grinding time is too short, outside the above range, grinding will not be sufficient, and powder particles of an unsuitable size for film formation may be produced. Conversely, if the rpm is too high or the grinding time is too long, a large amount of fine powder may be generated from the mixture, which is undesirable.

[0097] In one embodiment of the present invention, the particle size of the electrode mixed powder obtained in step (c) may preferably be in the range of 30 μm to 180 μm, taking into consideration the aspect of film formation.

[0098] In one embodiment of the present invention, the particle size can be measured using a particle size distribution analyzer (PSA) (Model Mastersizer 300, Malvern Instruments LTD). Specifically, a laser is irradiated, and the degree of light scattering caused by the scattering of the incident laser by the particles is detected, thereby measuring the particle size. The measurement method can be a wet method, in which the particles are dispersed in a solvent for measurement, or a dry method, in which the particles are measured in a powder state.

[0099] On the other hand, in the present invention, the electrode mixed powder has a degree of crystallinity (c) of the binder resin contained in the electrode mixed powder of 20% or less, which is lower than the degree of crystallinity (a) of the binder resin contained in the powdered mixture. On the other hand, it may be higher than the degree of crystallinity (d) of the binder resin contained in the dry electrode film after calendering. In other words, the degree of crystallinity may decrease further throughout the calendering stage.

[0100] On the other hand, if the degree of crystallinity (c) of the binder resin exceeds 20%, it becomes difficult to produce a film of uniform quality in the subsequent calendering process. If the degree of crystallinity of the obtained electrode mixture exceeds 20%, the degree of crystallinity can be adjusted by adjusting at least one of the conditions of the preceding process, the mixing time, the mixing temperature, the rotation speed (rpm), and the shear rate. For example, the degree of crystallinity can be adjusted by increasing the mixing time to promote the fiberization of the binder.

[0101] In one embodiment of the present invention, it is desirable that the degree of crystallinity (c) of the binder resin in the electrode mixed powder obtained in step (c) is 20% or less. If the degree of crystallinity (c) exceeds 20%, fiber formation will be insufficient, and the tensile strength and tensile elongation of the dry electrode obtained in the calendering process described later may decrease.

[0102] In one embodiment of the present invention, the degree of crystallinity of the binder resin in the electrode mixed powder obtained in step (c) can be checked, and if the confirmed degree of crystallinity (c) is 20% or less, the process in step (c) can be terminated and the obtained result can be added to step (d). The degree of crystallinity can be checked at each step while performing steps (a) to (d).

[0103] Alternatively, process conditions that can control the degree of crystallinity of the binder resin to 20% or less in the results obtained in step (c) above can be experimentally confirmed, and the set process conditions can be applied to steps (b) and / or (c) above.

[0104] Once the electrode mixture powder is obtained in this manner, a dry electrode is subsequently manufactured using this electrode powder (step (d)). Specifically, the electrode mixture powder manufactured up to the grinding stage is calendered to produce a dry electrode film.

[0105] Such calendering involves processing the electrode mixture powder into a film, and may involve, for example, pressurizing it into a film with an average thickness of 50 μm to 300 μm.

[0106] In one embodiment of the present invention, the calendering may be performed using a calendering apparatus that includes a roll press section in which two rollers are arranged opposite each other. The calendering apparatus may include at least one roll press section. For example, a plurality of the roll press sections may be arranged in a series to perform multi-stage compression of the electrode mixture powder. On the other hand, in the calendering apparatus, one or more rollers may be independently controlled to a temperature of 50°C to 200°C. Together with or independently of this, the rotational speed ratio of two rollers in the one or more roll press sections may be controlled to a ratio of 1:1 to 1:3.

[0107] If the process is carried out up to the calendering stage, a dry electrode film that acts as an electrode mixture can be manufactured. Such a dry electrode film may also be called a free-standing film or a self-supporting film. Such a dry electrode film may have sufficient mechanical strength for use in the manufacturing process of energy storage devices without any external support elements such as current collectors, support webs, or other structures. Alternatively, it may be used in combination with a support such as a current collector in the manufacture of a battery.

[0108] On the other hand, in one embodiment of the present invention, the obtained dry electrode film has a degree of crystallinity (d) of the binder resin in the dry electrode film of 10% or less. If the degree of crystallinity of the obtained dry electrode film exceeds 10%, the degree of crystallinity can be adjusted by adjusting the gap between the two rollers of the roll press section or by controlling the speed ratio. For example, the degree of fibrous formation of the binder can be increased by reducing the gap and / or increasing the speed ratio.

[0109] In one embodiment of the present invention, the degree of crystallinity of the binder resin in the dry electrode film obtained in step (d) can be checked, and if the confirmed degree of crystallinity (d) is 10% or less, the process in step (d) can be terminated. The degree of crystallinity can be checked at each step while performing steps (a) to (d).

[0110] Alternatively, in the dry electrode film obtained in step (d), process conditions that can control the degree of crystallinity of the binder resin to 10% or less can be experimentally confirmed, and the set process conditions can be applied to step (d).

[0111] The dry electrode film produced in this manner contains no solvent, has almost no fluidity, is easy to handle, and can be processed into desired shapes for use in the manufacture of various types of electrodes. Furthermore, when the dry electrode film of the present invention is used in the manufacture of electrodes, the drying process for removing the solvent can be omitted, which not only greatly improves the efficiency of electrode manufacturing but also eliminates problems that have plagued conventional dry electrode manufacturing, such as the pulverization of the active material and the cutting of fibrous binders.

[0112] Furthermore, the dry electrode film according to the present invention has the advantage of increased flexibility because the degree of crystallinity of the binder resin contained in the dry electrode film is controlled to 10% or less, preventing breakage or cracking when it is wound up for storage or unwound again. In addition, the mechanical strength can be improved, such as by improving tensile strength and tensile elongation due to the increased flexibility.

[0113] On the other hand, in the present invention, the dry electrode film may have a porosity of 20 vol% to 50 vol%, and can be controlled to a value of preferably 45 vol% or less or 40 vol% or less within the above range. When the porosity satisfies the above range, it is desirable in terms of various effects. On the other hand, if the porosity is too small and falls outside the above range, the electrolyte is difficult to impregnate, which is undesirable in terms of life characteristics and output characteristics, and if it is too large, the volume required to achieve the same capacity increases, which is undesirable in terms of volume-to-energy density. In one embodiment of the present invention, the porosity can be calculated by measuring the apparent density of the dry electrode film and using the true density calculated based on the true density and composition of each constituent component, using the following formula 2.

[0114] [Formula 2] Porosity (vol%) = {1 - (Apparent density / True density)} × 100

[0115] Furthermore, according to the present invention, after calendering, a lamination step may be performed to form the dry electrode film on at least one surface of the current collector. The lamination may be a step of rolling and adhering the dry electrode film onto the current collector to a predetermined thickness. The lamination may also be performed by a lamination roll, in which case the lamination roll may be maintained at a temperature of 20°C to 200°C.

[0116] On the other hand, in one embodiment of the present invention, the bending resistance of the manufactured dry electrode may be less than Φ (diameter) 10 mm, more specifically Φ (diameter) 8 mm or less, and more specifically Φ (diameter) 5 mm or less. That is, as described above, the dry electrode manufactured by the present invention can improve flexibility because the cutting of the fibrous binder is reduced. The bending resistance can be evaluated according to the method of the measurement standard JIS K5600-5-1, specifically by bringing the manufactured dry electrode into contact with measuring rods of various diameters, and then lifting both ends to measure whether cracks occur and the minimum diameter at which cracks do not occur.

[0117] Furthermore, the loading amount of the active material in the dry electrode film is 3 mAh / cm².2 ~15mAh / cm 2 It could be 4mAh / cm², for more details. 2 ~10mAh / cm 2 It is possible. Here, the loading amount of the active material is a value calculated using the method shown in equation 3 below.

[0118] [Formula 3] Loading capacity (mAh / cm³) 2 ) = Active material capacity (mAh / g) × Weight ratio of active material in dry electrode film (wt%) × Weight of dry electrode film per unit area (g / cm²) 2 )

[0119] On the other hand, the current collector is not particularly limited as long as it does not induce chemical changes in the battery and has high conductivity. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, copper, or aluminum or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc., can be used. Furthermore, the current collector may have fine irregularities formed on its surface to enhance the adhesion to the positive electrode active material, and can be used in a variety of forms such as films, sheets, foils, nets, porous materials, foams, and nonwoven fabrics.

[0120] Furthermore, the current collector may be coated entirely or partially with a conductive primer to reduce surface resistance and improve adhesion. Here, the conductive primer may include a conductive substance and a binder, the conductive substance being not limited to any conductive substance, but for example, a carbon-based substance. The binder may include solvent-soluble fluorine-based (including PVdF and PVdF copolymers), acrylic binders, and aqueous binders.

[0121] A further aspect of the present invention provides a dry electrode manufactured by the method for manufacturing a dry electrode. The electrode further includes a current collector, the dry electrode film being disposed on at least one or both sides of the current collector. The present invention also provides a secondary battery comprising the dry electrode, wherein the dry electrode is the positive electrode, and the electrode assembly comprising the positive electrode, the negative electrode, and the separator membrane is housed in a battery case together with a lithium-containing non-aqueous electrolyte, and an energy storage device comprising the secondary battery as a unit battery.

[0122] At this time, the specific structure of the secondary battery and energy storage device is well known, so a description is omitted in this specification.

[0123] On the other hand, in a specific embodiment of the present invention, a dry electrode manufacturing system is provided. The system includes a blender device for mixing raw materials including an electrode active material, a conductive material, and a binder resin; a kneader device for kneading the mixture to produce a mixture mass; a grinding device for grinding the mixture mass to form an electrode mixed powder; a calendar device for forming the electrode powder as a dry electrode film; and a laminating device for laminating the dry electrode film and a current collector.

[0124] Each device of the system and each process performed using the device may have pre-set process conditions such that the binder resin can have the above-mentioned degree of crystallinity at each stage.

[0125] Furthermore, after each step of the process, a sample is taken and the degree of crystallinity is measured. If it does not meet the standard, the already established process conditions can be modified and reflected.

[0126] For example, if the crystallinity measurement result for the powdered mixture obtained by the blender device exceeds 50%, or if the crystallinity measurement result for the obtained electrode mixed powder exceeds 20%, the respective process time may be increased. Also, if the crystallinity of the electrode film obtained after the calendering process exceeds 10%, the crystallinity may be controlled by reducing the gap between the rollers in the roll press section or by increasing the speed ratio.

[0127] On the other hand, the blender device is a mixer for mixing raw materials, and as described above, it is capable of mixing the raw materials for the mixture at a speed of 500 rpm to 30,000 rpm.

[0128] The kneading apparatus kneads the mixture into a mass and promotes the fiberization of the binder. For this purpose, the kneading apparatus can be set to a temperature range of 70°C to 200°C and a pressure above atmospheric pressure. Specifically, 90°C to 150°C and 0.5 kgf / cm². 2 ~10 kgf / cm² 2 For pressure conditions, see more specifically, 1 kgf / cm². 2 ~8 kgf / cm² 2 The pressure conditions can be set to these.

[0129] The aforementioned crushing device is a device that crushes the mixture mass obtained by the kneading device to form electrode powder, and may use, for example, a blender or a grinder.

[0130] The calendering apparatus is a device for pressing the electrode powder into a film. In one specific embodiment of the present invention, the calendering apparatus includes a roll press section in which two rollers are arranged opposite each other, and a plurality of these roll press sections are arranged in a continuous manner so that the powder can be pressed in multiple stages.

[0131] The laminating apparatus plays the role of adhering and rolling the dry electrode film formed by the calender apparatus to at least one surface of the current collector, and for example, a roll press apparatus may be used.

[0132] The porosity of the dry electrode film according to the present invention can be determined by such a calendering and laminating apparatus. Since the specific structures of the blender apparatus, kneading apparatus, calendering apparatus, and laminating apparatus are well known, a detailed explanation is omitted in this specification.

[0133] Figure 3 is a flowchart showing the step-by-step process for manufacturing electrodes using the above-described apparatus. Referring to this, first, the electrode active material, binder resin, and conductive material are mixed to produce a powdered mixture, and the degree of crystallinity of the binder resin is measured. If the degree of crystallinity of the binder resin is confirmed to be 50% or less, the powdered mixture is added to the next kneading step. However, if the degree of crystallinity exceeds 50%, the mixing time can be increased by performing a mixing step again on the powdered mixture. At this time, the binder clumps may be pulverized into primary particles, and the formation of thicker fibers may proceed.

[0134] Next, the obtained powdered mixture is kneaded to obtain a mixture mass, which is then pulverized to obtain electrode mixed powder. If the degree of crystallinity of the binder resin in the obtained electrode mixed powder is confirmed to be 20% or less, the electrode mixed powder is put into the next calendering step. However, if the degree of crystallinity exceeds 20%, the electrode mixed powder is put back into the kneading step.

[0135] Subsequently, the obtained electrode mixture powder is calendered to produce a dry electrode film. If the crystallinity of the produced dry electrode film is confirmed to be 10% or less, the dry electrode film is fed into the lamination process to produce the electrode. However, if the crystallinity exceeds 10%, the crystallinity is adjusted by adjusting the spacing between rollers, controlling the roller speed ratio, or both. Meanwhile, the flow chart shown in Figure 3 can also be used to establish process conditions for achieving the required crystallinity at each stage of electrode production.

[0136] The present invention will be described in detail below with reference to examples, comparative examples, and experimental examples, so that it can be easily understood by those who have ordinary skill in the art to which the present invention pertains.

[0137] Example 1 As the positive electrode active material, Li(Ni,Mn,Co,Al)O2, activated carbon, and polytetrafluoroethylene (PTFE) were added to a blender in a ratio of 96:1:3 (by weight) and mixed at 15,000 rpm for 1 minute to produce a powdered mixture. Next, the temperature of the kneader was stabilized at 150°C, and the mixture was added to the kneader, followed by mixing at a pressure of 1 kgf / cm². 2 The mixture was operated at a speed of 25 rpm for 5 minutes to obtain a mass of mixture. The mass of mixture was put into a blender and crushed at 10,000 rpm for 30 seconds to obtain a mixed powder for electrodes. Then, the mixed powder for electrodes was put into a wrap calender (roll diameter: 200 mm, roll temperature: 100 °C, roll speed ratio: 1.5) to produce a dry electrode film. Meanwhile, the particle size of the positive electrode active material was approximately 5 μm to 12 μm.

[0138] Example 2 Lithium iron phosphate (LFP), activated carbon, and polytetrafluoroethylene (PTFE) were added to a blender in a ratio of 94:1.5:4.5 as the positive electrode active material, and mixed at 10,000 rpm for 1 minute to produce a powdered mixture. Next, the temperature of the kneader was stabilized at 150°C, and the mixture was added to the kneader, followed by mixing at a pressure of 1 kgf / cm². 2 The mixture was operated at a speed of 50 rpm for 5 minutes to obtain a mass of mixture. The mass of mixture was put into a blender and crushed at 10,000 rpm for 20 seconds to obtain a mixed powder for electrodes. Then, the mixed powder for electrodes was put into a lap calender (roll diameter: 200 mm, roll temperature: 100 °C, roll speed ratio: 1.75) to produce a dry electrode film. Meanwhile, the particle size of the positive electrode active material was approximately 2 μm to 3 μm.

[0139] Example 3 A powdered mixture was prepared by adding Li(Ni,Mn,Co,Al)O2, activated carbon, and polytetrafluoroethylene (PTFE) in a ratio of 96:1:3 (by weight) to a blender and mixing at 15,000 rpm for 1 minute. The particle size of the positive electrode active material was approximately 5 μm to 12 μm.

[0140] Next, the kneader temperature is stabilized at 150°C, the powdered mixture is added to the kneader, and then the pressure is increased to 1 kgf / cm². 2 The mixture was operated at a speed of 25 rpm for 2 minutes to obtain a mass of mixture. The mass of mixture was put into a blender and crushed at 10,000 rpm for 30 seconds to obtain a mixed powder for electrodes. Then, the mixed powder for electrodes was put into a wrap calender (roll diameter: 200 mm, roll temperature: 100 °C, roll speed ratio: 1.5) to produce a dry electrode film.

[0141] Comparative Example 1 Lithium iron phosphate (LFP), activated carbon, and polytetrafluoroethylene (PTFE) were added to a blender in a ratio of 94:1.5:4.5 as the positive electrode active material, and mixed at 10,000 rpm for 1 minute to produce a powdered mixture. Next, the temperature of the kneader was stabilized at 150°C, and the mixture was added to the kneader, followed by mixing at a pressure of 1 kgf / cm². 2 The mixture was operated at a speed of 25 rpm for 2 minutes to obtain a mass of mixture. The mass of mixture was put into a blender and crushed at 10,000 rpm for 20 seconds to obtain a mixed powder for electrodes. Then, the mixed powder for electrodes was put into a lap calender (roll diameter: 200 mm, roll temperature: 100 °C, roll speed ratio: 1.75) to produce a dry electrode film. Meanwhile, the particle size of the positive electrode active material was approximately 2 μm to 3 μm.

[0142] Comparative Example 2 As the positive electrode active material, Li(Ni,Mn,Co,Al)O2, activated carbon, and polytetrafluoroethylene (PTFE) were added to a supermixer in a ratio of 96:1:3 (by weight) and mixed at 400 rpm for 2 minutes to produce a powdered mixture.

[0143] Next, the temperature of the kneader is stabilized at 150°C, and the mixture is added to the kneader, followed by a pressure of 1 kgf / cm². 2The mixture was operated at a speed of 25 rpm for 5 minutes to obtain a mass of mixture. The mass of mixture was put into a blender and crushed at 10,000 rpm for 30 seconds to obtain a mixed powder for electrodes. Then, the mixed powder for electrodes was put into a wrap calender (roll diameter: 200 mm, roll temperature: 100 °C, roll speed ratio: 1.5) to produce a dry electrode film. Meanwhile, the particle size of the positive electrode active material was approximately 5 μm to 12 μm.

[0144] Comparative Example 3 As the positive electrode active material, Li(Ni,Mn,Co,Al)O2, activated carbon, and polytetrafluoroethylene (PTFE) were placed in a blender in a ratio of 96:1:3 (by weight) and mixed at 15,000 rpm for 1 minute. Then, the mixture was mixed using a supermixer at 800 rpm for 30 seconds. During this time, the temperature was maintained at 23°C and the pressure was controlled to approximately 85 psi. A powdered mixture was obtained using this method. Subsequently, the electrode mixture powder was fed into a wrap calender (roll diameter: 200 mm, roll temperature: 100°C, roll speed ratio: 1.5) to produce a dry electrode film. Meanwhile, the particle size of the positive electrode active material was approximately 5 μm to 12 μm.

[0145] [Table 1]

[0146] [Table 2]

[0147] As can be seen from Table 1, in Examples 1 to 3, the crystallinity of the powdered mixture was controlled to 50% or less, the crystallinity of the electrode mixed powder to 20% or less, and the crystallinity of the dry electrode film to 10% or less. Figure 1 is a graph showing the DSC thermal analysis results for Example 1. According to Figure 1, it was confirmed that the crystallinity of the electrode mixed powder (crushed) and dry electrode film (sheet) processed in subsequent stages was lower than that of the powdered mixture (mixed). Figure 2 is a graph showing the DSC thermal analysis results for Example 2. In Example 2 as well, it was confirmed that the crystallinity of the electrode mixed powder (crushed) and dry electrode film (sheet) processed in subsequent stages was lower than that of the powdered mixture (mixed). Furthermore, in the dry electrode films obtained in each example, the tensile strength was confirmed to be 0.5 MPa or higher, and the tensile elongation was also shown to be 2% or higher. On the other hand, the PTFE in Figure 2 represents the intrinsic crystallinity of 100% unprocessed PTFE, and is shown for comparison with the degree of crystallinity of processed PTFE.

[0148] On the other hand, in Comparative Examples 1 and 2, it was confirmed that the crystallinity of the binder resin in the obtained electrode mixed powder exceeded 20%. This means that the fiberization in the obtained electrode mixed powder was insufficient, making it difficult to produce a sheet-like dry electrode film in the subsequent calendering process. In particular, in Comparative Example 2, it was confirmed that the crystallinity of the binder resin in the powdered mixture exceeded 60%, and sufficient fiberization was not achieved even as the subsequent processes proceeded. On the other hand, in Comparative Example 3, the kneading process according to the present invention was not applied, and it was confirmed that the fine fiberization was insufficient, making it impossible to produce a sheet even after calendering.

[0149] Measurement of crystallinity In each example and comparative example, samples for measuring the degree of crystallinity were prepared from the powdered mixture, the electrode mixed powder, and the dry electrode film, respectively. For each sample, the degree of crystallinity (Xc) was measured by weighing approximately 5 mg to 12 mg of the sample and placing it into a Differential Scanning Calorimeter (DSC) manufactured by TA Corporation. The heat of fusion (ΔHm) was measured in a nitrogen atmosphere while increasing the temperature at a rate of 10°C / min in the temperature range of 25 to 360°C.

[0150] Using TA's TROIS program, the melting point (T) is determined based on the temperature at which the highest enthalpy is observed during melting (peak temperature). m ) and enthalpy of fusion (ΔH m The crystallinity of each sample was analyzed using the melt enthalpy (ΔH) measured by DSC. m Theoretically, the enthalpy of fusion (ΔH) of a perfect crystal (100% crystallinity) can be calculated using this value. m 0 This is expressed as a percentage after dividing by the value of ), and was calculated using the above formula 1. The melting enthalpy value of theoretically perfect crystal PTFE was set to 85.4 J / g, referring to Polymer journal, Vol. 46 (2005), pp. 8872-8882.

[0151] Measurement of tensile strength and tensile elongation The dry electrode films obtained in each example and comparative example were cut to a width of 10 mm, and then measured three times using a tensile strength tester at a tensile speed of 5 mm / min. The average of these measurements is shown. Tensile strength is the stress applied until fracture, and tensile elongation is the percentage (%) of length change relative to the original length that the specimen stretched before fracture.

Claims

1. comprising a dry electrode film, The dry electrode film comprises an electrode active material, a conductive material, and a binder resin, wherein the degree of crystallinity of the binder resin contained in the dry electrode film is 0 to 5%, and is an electrode for an electrochemical element.

2. The electrode for an electrochemical element according to claim 1, wherein the degree of crystallinity of the binder resin contained in the dry electrode film is 0 to 2.85%.

3. The electrode for an electrochemical element according to claim 1, wherein the tensile strength of the dry electrode film in the mechanical direction (MD) is 0.5 MPa or more.

4. The electrode for an electrochemical element according to claim 1, wherein the tensile elongation of the dry electrode film is 2% or more.

5. The electrode for an electrochemical element according to claim 1, wherein the porosity of the dry electrode film is 20 vol% to 50 vol%.

6. The electrode for an electrochemical element according to claim 1, wherein the binder resin comprises polytetrafluoroethylene, polyvinylidene fluoride, polyolefin, or a mixture of two or more of these.

7. The electrode for an electrochemical element according to claim 1, further comprising a current collector, wherein the dry electrode film is disposed on at least one or both sides of the current collector.

8. A method for manufacturing an electrode for an electrochemical element according to any one of claims 1 to 7, The aforementioned method, (a) A step of producing a powdered mixture containing an electrode active material, a conductive material, and a binder resin, (b) A step of kneading the powdered mixture under a temperature of 70°C to 200°C to produce a mixture mass, (c) A step of crushing the mixture mass to obtain a mixed powder for electrodes, (d) The step of calendering the electrode mixture powder to obtain a free-standing dry electrode film, The method wherein the degree of crystallinity of the binder resin contained in the dry electrode film obtained in step (d) is 0 to 5%.

9. The method according to claim 8, wherein the degree of crystallinity of the binder resin contained in the electrode mixed powder obtained in step (c) is 20% or less.

10. The method according to claim 8, wherein the degree of crystallinity of the binder resin contained in the mixture obtained in step (a) is 50% or less.

11. The method according to claim 8, wherein step (a) is performed under conditions of 500 rpm to 30,000 rpm.

12. The method according to claim 8, wherein step (b) is performed at a speed of 100 rpm or less.

13. The above step (b) is 0.5 kgf / cm ２ ~10 kgf / cm² ２ The method according to claim 8, performed under pressure.

14. The method according to claim 8, wherein step (b) is performed under conditions of atmospheric pressure or higher.

15. The method according to claim 8, further comprising the steps of preparing a current collector and arranging the dry electrode film on at least one surface of the current collector and laminating it.

16. Includes an electrode for an electrochemical element according to any one of claims 1 to 7, A secondary battery in which the electrode for the electrochemical element is the positive electrode, and the electrode assembly including the positive electrode, negative electrode and separator membrane is housed in a battery case together with a lithium-containing non-aqueous electrolyte.

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

18. It comprises a finely fibrous binder resin, an electrode active material, and a conductive agent powder. A mixed powder for electrodes, wherein the electrode active material and conductive powder are bonded or connected by the finely fibrous binder resin, and the degree of crystallinity of the binder resin is 20% or less.

19. The electrode mixed powder according to claim 18, wherein the electrode mixed powder contains electrode mixed particles in which the binder resin has been finely fibrousized, and the particle size of the electrode mixed particles is 30 μm to 180 μm.

20. The electrode mixed powder according to claim 19, wherein the electrode mixed particles include an electrode active material and a conductive agent powder.

21. The electrode mixed powder according to claim 18, wherein the binder resin comprises polytetrafluoroethylene, polyvinylidene fluoride, polyolefin, or a mixture of two or more of these.

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