Electrode for Electrochemical Element Containing Dry-Type Electrode Film and Method for Manufacturing the Same

Abstract

In the method for manufacturing a dry electrode according to the present invention, the degree of fiberization of the binder resin can be determined from the crystallinity of the binder resin, and the process conditions of the mixed powder for the electrode and the electrode film can be controlled based on the degree of fiberization, so that the process conditions can be easily and efficiently confirmed and controlled. In addition, the method for manufacturing a dry electrode according to the present invention is advantageous for mass production since it does not have a problem of clogging of the flow path due to the agglomeration of the components by kneading using a high-temperature and low-speed kneader and pulverizing steps.

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 device including a dry electrode film and a method for manufacturing the same. Further, the present invention relates to the dry electrode film and a method for manufacturing the same. Further, the present invention relates to a mixed powder for an electrode used in the manufacture of the dry electrode film and a method for manufacturing the same.

Background Art

[0002] Due to the rapid increase in the use of fossil fuels, the demand for the use of alternative energy and clean energy is increasing. As part of this, the most actively studied field is the field of power generation and power storage using electrochemistry. As a typical example of an electrochemical device using such electrochemical energy, currently, a secondary battery can be mentioned, and its use area is increasingly expanding. A typical lithium secondary battery among such secondary batteries is not only an energy source for mobile devices, but recently, it has been realized as a power source for electric vehicles and hybrid electric vehicles that replace vehicles using fossil fuels such as gasoline vehicles and diesel vehicles, which are one of the main causes of air pollution. In addition, its use area is also expanding as an application such as a power assist power source through grid connection. The manufacturing process of such a lithium secondary battery is roughly divided into three stages: an electrode manufacturing process, an electrode assembly manufacturing process, and an aging process. The electrode manufacturing process is further divided into an electrode binder mixing process, an electrode coating process, a drying process, a rolling process, a slitting process, a winding process, and the like. Among these, the electrode binder mixing process is a process of blending components for forming an electrode active layer in which an actual electrochemical reaction occurs in the electrode. Specifically, it is a process of mixing an electrode active material, which is an essential element of the electrode, a conductive material and a filler, which are other additives, a binder for binding between powders and adhesion to a current collector, and a solvent for imparting viscosity and dispersing powders to manufacture a slurry having fluidity.

[0003] The composition thus mixed for forming the electrode active layer is also referred to as an electrode mixture in a broad sense. Subsequently, an electrode coating process of applying the electrode mixture onto an electrically conductive current collector and a drying process for removing the solvent contained in the electrode mixture are performed. Additionally, the electrode is rolled to be manufactured with a predetermined thickness.

[0004] On the other hand, in the drying process, defects such as pinholes and cracks may be induced in the already formed electrode active layer due to the evaporation of the solvent contained in the electrode mixture. Also, the inside and outside of the active layer are not dried uniformly, and there is a risk of a powder floating phenomenon due to the difference in the evaporation rate of the solvent, that is, the powder at the site dried first floats while forming a gap with the site dried relatively later, resulting in a deterioration of the electrode quality.

[0005] Therefore, in order to solve the above problems, a drying device capable of adjusting the evaporation rate of the solvent while drying the inside and outside of the active layer uniformly has been considered, but such a drying device is very expensive and requires a considerable cost and time for operation, which is disadvantageous in terms of manufacturing processability. Therefore, recently, research on manufacturing dry electrodes without using solvents has been actively conducted.

[0006] A dry electrode is generally manufactured by laminating a free-standing film manufactured in a film form containing an active material, a binder, a conductive material, etc. on a current collector. First, an active material, a carbon material as a conductive material, and a fiberizable binder are mixed together with a blender or the like, and after the binder is fiberized through a high shear mixing process such as jet-milling, a process of calendaring such a mixture into a film form to manufacture a free-standing film is included. Subsequently, it is manufactured by laminating the free-standing film manufactured after calendaring on a current collector.

[0007] However, when applying the high-shear mixing process as described above to a fragile active material, a large amount of fine powder with a small particle size is generated, and the mechanical performance and electrochemical performance are likely to deteriorate. When the high-shear mixing becomes excessive, there is a risk of cutting the generated binder fibers and reducing the flexibility of the free-standing film.

[0008] Therefore, there is an urgent need to develop a dry electrode manufacturing technology that can solve such problems. In particular, it is necessary to provide a method capable of quantitatively analyzing the mixing uniformity of the mixture in which the components for manufacturing the dry electrode film are mixed and the state of the binder (such as the degree of fibrillation), and establishing process conditions.

Summary of the Invention

Problems to be Solved by the Invention

[0009] An object of the present invention is to provide a dry electrode that minimizes the pulverization of the active material and maximizes the binder fibrillation, and a method for manufacturing the same, in order to solve the above problems.

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

[0011] Furthermore, an object of the present invention is to provide a method for manufacturing a dry electrode to which process conditions based on the crystallinity of the binder resin are applied.

Means for Solving the Problems

[0012] A first aspect of the present invention relates to an electrode for an electrochemical element, the electrode including a dry electrode film manufactured by a dry manufacturing process that does not use a solvent, the dry electrode film including an electrode active material, a conductive material, and a binder resin, and the binder resin included in the dry electrode film having a crystallinity of 10% or less.

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

[0014] According to the 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] The fifth embodiment of the present invention relates to a method for manufacturing an electrode for an electrochemical element, the electrode being according to any one of the first to fourth embodiments, and the method comprising: (a) manufacturing a powdery mixture containing an electrode active material, a conductive material, and a binder resin; (b) kneading the powdery mixture in the range of 70°C to 200°C to produce a mixture mass; (c) pulverizing the mixture mass to obtain a mixed powder for an electrode; (d) calendering the mixed powder for an electrode to obtain a free-standing dry electrode film, wherein the 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 crystallinity (c) of the binder resin contained in the mixed powder for an electrode 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 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 the conditions of 500 rpm to 30,000 rpm.

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

[0021] According to the tenth aspect of the present invention, in any one of the fifth to ninth aspects, the step (b) is performed under a pressure of 0.5 kgf / cm 2 to 10 kgf / cm 2 .

[0022] According to the eleventh aspect of the present invention, in any one of the fifth to tenth aspects, the step (b) is performed under conditions of normal pressure or higher.

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

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

[0025] According to the fourteenth aspect of the present invention, in any one of the fifth to eleventh aspects, the method further includes preparing a current collector and laminating the dry electrode film on at least one surface of the current collector.

[0026] The fifteenth aspect of the present invention relates to a secondary battery and includes a dry electrode according to any one of the first to fourth aspects. The dry electrode is a positive electrode, and an electrode assembly including the positive electrode, a negative electrode, and a separator is housed in a battery case together with a lithium-containing non-aqueous electrolyte.

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

[0028] The 17th aspect of the present invention relates to a method for producing a mixed powder for an electrode for manufacturing a dry electrode film, and the manufacturing method includes: (a) producing a powdery mixture containing an electrode active material, a conductive material, and a binder resin; (b) kneading the powdery mixture in the range of 70°C to 200°C to produce a mixture mass; (c) pulverizing the mixture mass to obtain a mixed powder for an electrode. The crystallinity of the binder resin contained in the mixed powder for an electrode is 20% or less. The binder resin includes polytetrafluoroethylene (PTFE), polyolefin, or a mixture thereof.

[0029] According to the 18th aspect of the present invention, there is provided a mixed powder for an electrode produced by the method according to the 17th aspect. The mixed powder for an electrode contains an electrode active material, a conductive material, and a binder resin. The binder resin includes polytetrafluoroethylene (PTFE), PVdF, polyolefin, or a mixture of two or more of them. The crystallinity of the binder resin contained in the mixed powder for an electrode is 20% or less.

[0030] The 19th aspect of the present invention relates to a method for manufacturing a dry electrode film including a step of calendering a mixed powder for an electrode to obtain a free-standing dry electrode film. The mixed powder for an electrode is obtained by the method according to the 17th aspect, and the crystallinity (d) of the binder resin contained in the dry electrode film is 10% or less.

[0031] According to the 20th aspect of the present invention, there is provided a dry electrode film produced by the method according to the 19th aspect, having a tensile strength in the machine direction (MD) of 0.5 MPa or more, a tensile elongation of 2% or more, and a porosity of 20 vol% to 50 vol%.

Advantages of the Invention

[0032] In the dry electrode manufacturing process according to the present invention, when manufacturing the mixed powder for the electrode, by introducing a pulverizing process after the high-temperature low-shear mixing process, it is possible to minimize the pulverization of the active material and prevent the cutting of the fibrillated binder. Further, by manufacturing a dry electrode using such a mixed powder for the electrode, there is an effect of improving mechanical properties such as the flexibility and strength of the dry electrode.

[0033] In addition, in the method for manufacturing a dry electrode according to the present invention, the degree of fine fibrillation of the binder resin and the completion of each step can be judged and confirmed from the crystallinity of the binder resin at each step, and based on this, the process conditions of the mixed powder for the electrode and the electrode film can be controlled. Therefore, it is easy and efficient to confirm and control the process conditions and the completion time of the process.

[0034] In addition, the method for manufacturing a dry electrode according to the present invention is advantageous for fine fibrillation by passing through a low-shear kneading and pulverizing stage using a kneader, and there is no problem of clogging the flow path due to agglomeration of the constituent components, which is also advantageous for mass production.

Brief Description of the Drawings

[0035]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0036] Hereinafter, in order to assist the understanding of the present invention, the present invention will be described in more detail.

[0037] In this specification and the claims, the terms and words used shall not be construed in a limited sense based on their ordinary and dictionary meanings. Instead, in accordance with the principle that the inventor can appropriately define the concept of the terms in order to best explain the invention, they shall be construed in accordance with the meaning and concept corresponding to the technical idea of the present invention.

[0038] The terms used in this specification are for illustrative purposes in explaining the exemplary embodiments and do not limit the present invention. Singular expressions include plural expressions unless otherwise explicitly stated.

[0039] Also, throughout the specification, when a certain part "includes" other components, it means that, unless otherwise specifically mentioned, it does not exclude other components but may further include other components.

[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, the secondary battery may be 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 a solvent for dispersing electrode components is not used in 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 crystallinity of 10% or less. For example, the crystallinity may be 5% or less.

[0042] When the crystallinity is in the range of 10% or less, the binder resin can be highly fibrillated to ensure the flexibility of the dry electrode film. As a result, as described later, it is easy to manufacture a strip-shaped dry electrode film in a calendering process to which a roll-to-roll continuous process is applied. After manufacturing the electrode film, when it is wound up in a roll form or unwound again, its form can be stably maintained without damage such as breakage or cracking. Also, it is advantageous for ensuring the adhesion strength to the current collector to be equal to or greater than a predetermined strength.

[0043] Further, in the present invention, it is desirable that the dry electrode film has a tensile strength in the machine direction (MD) of 0.5 MPa or more. On the other hand, the dry electrode film may have a tensile strength in the machine 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 dry electrode, and the manufacturing and handling are easy. On the other hand, when it does not reach the above range, the mechanical strength is weak and it is easily broken. On the other hand, when the tensile strength is too high, the tensile elongation increases together, so that the processability deteriorates and the film thickness becomes non-uniform 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 the free-standing dry electrode, and the manufacturing and handling are easy. If the tensile elongation is too low, the flexibility and morphological stability are low and it is easily broken during manufacturing or movement, which is not desirable. On the other hand, when exceeding the above range, the flexibility is too high, and the dry electrode film may be excessively stretched between rolls in the calendering process described below, and the thickness of the obtained film may become non-uniform.

[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 crystallinity of the binder resin contained in the dry electrode film is controlled to 10% or less. In the present invention, the crystallinity in the dry electrode is zero (0) or 10% or less.

[0049] In a specific embodiment, the method for manufacturing the electrode includes: (a) manufacturing a powdery mixture including an electrode active material, a conductive material, and a binder resin; (b) kneading the powdery mixture to manufacture a mixture mass; (c) pulverizing the mixture mass to obtain a mixed powder for an electrode; and (d) calendering the mixed powder for an electrode to obtain a free-standing dry electrode film.

[0050] On the other hand, in an embodiment of the present invention, the step (b) can be performed under a temperature condition of 70°C to 200°C. For example, the object to which the kneading process is applied can be controlled to a temperature of 70°C to 200°C.

[0051] Here, in the powdery mixture obtained in the step (a), the crystallinity (a) of the binder resin is 60% or less, desirably 50% or less. Further, the crystallinity (c) of the binder resin in the mixed powder for an electrode obtained in the step (c) is 20% or less, and the crystallinity (d) of the binder resin in the dry electrode film obtained in the step (d) is 10% or less.

[0052] In an embodiment of the present invention, for each of the steps (a) to (d), the completion of the process is determined by checking the crystallinity of the resultant obtained in each step. When the crystallinity of the binder resin of the product in each process step satisfies the predetermined crystallinity in each step, the process of the next step is performed.

[0053] Specifically, in the step (a), when the crystallinity of the binder resin of the powdery mixture is 60% or less, desirably 50% or less, the process of the step (a) is terminated, and the obtained resultant is input into the step (b).

[0054] Further, in the step (c), when the crystallinity of the binder resin in the mixed powder for an electrode is 20% or less, the process of the step (c) is terminated, and the obtained resultant is input into the step (d).

[0055] Also, in the case where the crystallinity of the binder resin in the manufactured dry electrode film is 10% or less in the step (d), it is determined that the manufacturing is completed.

[0056] Alternatively, in the steps (a), (b), and (d), the process conditions controllable to the limited crystallinity within the above ranges can be experimentally confirmed at each step, and the experimentally set processes can be applied to each step.

[0057] In the present invention, the crystallinity (Xc) can be measured through a Differential Scanning Calorimetrer (DSC), and is based on the temperature (peak temperature) at the time when the highest enthalpy is shown during crystallization. Specifically, the crystallinity is the melting enthalpy (ΔH m ) value measured by DSC divided by the melting enthalpy (ΔH m 0 )(equilibrium melting heat) value of theoretically perfect crystals (crystallinity 100%) and is expressed in %, and can be calculated by the following formula 1. Here, the melting enthalpy value (ΔH m 0 ) of theoretically perfect crystals can be referred to academic papers such as "Polymer Handbook" (J. Brandrup, etc., 2003) and "Polymer". For example, the melting enthalpy value of theoretically perfect crystals of PTFE is 85.4 J / g (Polymer, Vol. 46 (2005), 8872 - 8882). On the other hand, usually, thermal analysis of polymers such as DSC can be measured and calculated according to ASTM D3418 - 21.

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

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

[0060] First, a powdery mixture containing an electrode active material, a conductive material, and a binder is produced ((a) step).

[0061] At this time, the mixing for producing the powdery mixture is performed to obtain a uniform mixture of the electrode active material, the conductive material, and the binder resin, and desirably to adjust the crystallinity of the binder resin in the obtained powdery mixture to 50% or less. Since these materials are mixed in a powdery form, various methods can be applied without limitation as long as they can be uniformly mixed. However, in the present invention, for producing a dry electrode without using a solvent, the mixing can be performed by dry mixing. For example, it can be performed by charging the substances into a device such as a mixer or a 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 about 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. When the mixing temperature exceeds 70°C, the material adheres to the mixing device and it is 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 performed at a temperature of 20°C or higher.

[0064] Specifically, the mixing is performed using a mixer at 500 rpm to 20,000 rpm for 30 seconds to 10 minutes at a temperature of 70°C or lower, or at 5,000 rpm to 20,000 rpm for 30 seconds to 2 minutes at a temperature of 70°C or lower, or at 1,000 rpm to 15,000 rpm or 10,000 rpm to 15,000 rpm for 30 seconds to 1 minute or 30 seconds to 7 minutes at a temperature of 60°C or lower, in terms of high uniformity and control of the crystallinity of the binder resin.

[0065] In the present invention, the crystallinity of the binder resin in the mixture obtained by the mixing is 60% or less, desirably 50% or less. On the other hand, in the obtained mixture, when the crystallinity of the binder resin exceeds 60% or exceeds 50%, it is desirable to increase the speed (rpm) and / or increase the process time to grind it into primary particles so that the binder mass does not aggregate, and to partially proceed with thick fibrillation.

[0066] When the crystallinity of the mixture obtained in the step (a) does not fall within the above range, it is difficult to fibrillate the binder resin in the subsequent low-shear kneading step (step (b)), and fibers may not be sufficiently formed on the binder surface or the process time required for fibrillating the binder resin may increase.

[0067] On the other hand, when the mixing time is too long or the mixing speed is too fast, or both, there is a risk that the electrode active material may be pulverized / damaged or the fibers may be cut instead. Along with this or independently, there is a risk of causing non-uniformity in binder fibrillation. Considering such points, in one embodiment of the present invention, the crystallinity of the binder resin in the mixture can be controlled to be 30% or more, 35% or more, or 40% or more.

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

[0069] On the other hand, fibrillation can proceed in the step (a) for the binder resin, but the fibers formed in the step (a) are thick and difficult to refine to an extent that can achieve the tensile strength and elongation required for a dry electrode. In the present invention, desirably, the fine fibrillation of the binder resin is mainly carried out through the step (b) described later.

[0070] The fibrillation means a process of thinning and dividing a polymer, and can be performed, for example, using mechanical shearing force or the like. The surface of the fibrillated polymer fibers unfolds and a large number of fine fibers (fibrils) are generated. Such non-limiting examples of the binder resin include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyolefin, or a mixture of two or more of these. Specifically, polytetrafluoroethylene (PTFE) is included, and more specifically, it can be polytetrafluoroethylene (PTFE). Specifically, the polytetrafluoroethylene (PTFE) can be contained in an amount of 30% by weight or more based on the weight of the total binder resin. Of course, at this time, in addition to the components described above, the binder resin may further contain polyethylene oxide (PEO) and / or polyvinylidene fluoride - hexafluoropropylene (PVdF-HFP) or the like.

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

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

[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 carbon such as graphitizable carbon and graphite-based carbon; Li x Fe2O3 (0 ≦ x ≦ 1), Li x WO2 (0 ≦ x ≦ 1), Sn x Me 1-x Me’ y O z (Me: Mn, Fe, Pb, Ge; Me’: Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen; 0 < x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8) and other metal composite oxides; lithium metal; lithium alloy; silicon-based alloy; tin-based alloy; silicon-based oxides such as SiO, SiO / C, SiO2; metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4 and Bi2O5; conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used.

[0074] However, the dry electrode may be a positive electrode in detail, and thus, the active material may be a positive electrode active material in detail, and more specifically, it may be a lithium transition metal oxide, a lithium nickel-manganese-cobalt oxide, an oxide in which part of the lithium nickel-manganese-cobalt oxide is substituted with another transition metal, lithium iron phosphate, and the like.

[0075] The conductive material is not particularly limited as long as it has conductivity without inducing chemical changes in the battery. For example, graphite such as natural graphite and artificial graphite; carbon blacks such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives can be used. Specifically, for uniform mixing of the conductive material and improvement of conductivity, it may contain one or more selected from the group consisting of activated carbon, graphite, carbon black, and carbon nanotubes, and more specifically, it may contain activated carbon.

[0076] The mixing ratio of the electrode active material, conductive material, and binder can be such that the electrode active material: conductive material: binder resin is contained in a weight ratio of 80 to 98 wt%: 0.5 to 10 wt%: 0.5 to 10 wt%, and specifically, it can be contained in a ratio of 85 to 98 wt%: 0.5 to 5 wt%: 0.5 to 10 wt%.

[0077] When the content of the binder resin exceeds the above range and is too high, the binder resin may affect the process while being overly fibrillated in the subsequent kneading process. When it is too low, it may not be fibrillated sufficiently, may not aggregate enough to form a mixture mass, may make it difficult to manufacture the dry electrode film, or may cause a decrease in the physical properties of the dry electrode film.

[0078] Also, when the content of the conductive material exceeds the above range and is too high, there is a problem that the content of the active material relatively decreases and the capacity decreases. When it is too low, sufficient conductivity may not be ensured or the physical properties of the dry electrode film may deteriorate, which is not desirable.

[0079] On the one hand, depending on the circumstances, a filler, which is a component for suppressing the expansion of the electrode, 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. For example, olefin polymers such as polyethylene and polypropylene; fibrous substances such as glass fiber and carbon fiber can be used.

[0080] In one embodiment of the present invention, in the powdery mixture obtained in the step (a), the crystallinity of the binder resin is confirmed. If the confirmed crystallinity is 60% or less, desirably 50% or less, the process of step (a) is terminated, and the obtained product can be introduced into step (b). The crystallinity can be confirmed at each step while performing steps (a) to (d).

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

[0082] Next, a kneading step is performed on the obtained mixture as a process for fibrillating the binder resin ((b) step).

[0083] In this kneading step, since a relatively low shear force is applied at a high temperature as described later, there are no problems such as pulverization / damage of the electrode active material and cutting of the binder fibers, and mixed particles for an electrode in which the binder resin is finely fibrillated can be obtained. In addition, the fibrillated binder has high uniformity in the thickness and / or length of the fibers.

[0084] The kneading is not limited to a specific method. In a specific embodiment of the present invention, the kneading can be performed using a kneader such as a kneader. For example, as the kneader, a twin-screw extruder, a single-screw extruder, a batch kneader, a continuous kneader, etc. can be used.

[0085] Such kneading is a stage of forming a solid content 100% massive mixture by binding or connecting the electrode active material and the conductive material powder while the binder resin is being fiberized.

[0086] Specifically, the kneading in the step (b) 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 can be performed for 1 minute to 30 minutes. For example, it can be performed for 3 minutes to 10 minutes at a speed of 20 rpm to 70 rpm within the above range.

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

[0089] The kneading step can be performed under high temperature and pressure conditions equal to or higher than normal pressure.

[0090] Specifically, the kneading can be performed in the range of 70°C to 200°C, specifically, 90°C to 150°C. The temperature can be the temperature inside the kneader or the temperature of the kneaded object. Or both of them can be controlled at the temperature within the above range.

[0091] When performing at a temperature lower than the above range, the fiberization of the binder and the lumping by kneading during the kneading process become insufficient, and the film formation during calendering is not smoothly performed. When performing at a temperature too high, the binder is rapidly fiberized, and then there is a problem that the fibers already formed are cut by excessive shear force, which is not desirable.

[0092] Also, the kneading process is 0.5 kgf / cm 2~10kgf / cm 2 More specifically, under a pressure of 1kgf / cm 2 ~8kgf / cm 2 Under pressure, for example, 8kgf / cm above normal pressure 2 If the pressure is too high outside the above range, excessive shear force and pressure are applied, which is undesirable since it may cause problems such as cutting the formed fibers or excessively high density of the mixture mass. That is, according to the present invention, when the low shear kneading process is performed under high temperature and pressure conditions of atmospheric pressure or higher, the intended effect of the present invention can be achieved. Alternatively, it may be performed under atmospheric pressure or higher, specifically, at 1 atm to 3 atm, or 1.1 atm to 3 atm.

[0093] Meanwhile, in one embodiment of the present invention, the process conditions in the kneading step may be controlled according to the characteristics of the input materials. In a specific embodiment, the process conditions may be appropriately adjusted according to the particle size of the input electrode active material particles. When the particle size of the electrode active material particles is large, fiberization proceeds relatively easily compared to an electrode active material having a small 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. Meanwhile, the temperature and pressure may also be adjusted in consideration of the characteristics of the materials. Next, the lump mixture produced through the kneading in step (b) is further pulverized to obtain a mixed powder for an electrode (step (c)).

[0094] Specifically, the lump mixture produced through the kneading in step (b) may be directly fed to a calendaring process to be formed into a sheet, but in this case, high pressure and high temperature are required to press the lump mixture into a thin film, which may result in an excessively high density of the dry electrode film or an inconsistent film in terms of thickness, density, etc. Therefore, in the present invention, the lump mixture (lump mixture) produced in step (b) is subjected to a pulverization step.

[0095] At this time, the pulverization is not particularly limited, but can be performed using known pulverization equipment such as a blender or a grinder. In a specific embodiment of the present invention, the speed of the pulverization 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 pulverization time can be appropriately controlled within the range of 1 second to 10 minutes. However, the pulverization speed and time are not particularly limited to the above ranges. Specifically, the pulverization is 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 pulverization time is too short outside the above range, the pulverization is not sufficiently performed, and powders of a size unsuitable for film formation may be generated. If the rpm is too high or the pulverization time is too long, a large amount of fine powder may be generated from the mixture mass, which is not desirable.

[0097] In one embodiment of the present invention, considering the film formation aspect, the particle size of the mixed powder for the electrode obtained in the step (c) may desirably have a range of 30 μm to 180 μm.

[0098] In one embodiment of the present invention, the measurement of the particle size can be performed using a particle size distribution analyzer (PSA) (Model Mastersizer 300, Malvern Instruments LTD). Specifically, by irradiating a laser and detecting the degree of light scattering of the incident laser scattered by the particles, the particle size can be measured through this. As the measurement method, a wet method in which the particles are dispersed in a solvent for measurement and a dry method in which the measurement is performed in a powder state can be applied.

[0099] On the one hand, in the present invention, the mixed powder for electrodes has a crystallinity (c) of the binder resin contained in the mixed powder for electrodes of 20% or less, which is lower than the crystallinity (a) of the binder resin contained in the powdery mixture. On the other hand, it can be higher than the crystallinity (d) of the binder resin contained in the dry electrode film after calendering. That is, the crystallinity can further decrease through the calendering stage.

[0100] On the other hand, when the crystallinity (c) of the binder resin exceeds 20%, it is difficult to produce a film of uniform quality in the subsequent calendering process. If the crystallinity of the obtained mixed powder for electrodes exceeds 20%, at least one of the conditions of the preceding process, kneading time, kneading temperature, rotation speed (rpm), and shear rate can be adjusted to adjust the crystallinity. For example, the crystallinity can be adjusted by increasing the kneading time to promote the fibrillation of the binder.

[0101] In one embodiment of the present invention, in the mixed powder for electrodes obtained in the step (c), the crystallinity (c) of the binder resin is desirably 20% or less. When the crystallinity (c) exceeds 20%, the fibrillation becomes 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, in the mixed powder for electrodes obtained in the step (c), when the crystallinity of the binder resin is confirmed and the confirmed crystallinity (c) is 20% or less, the process of the step (c) can be terminated, and the obtained product can be introduced into the step (d). The crystallinity can be confirmed at each stage while performing the steps (a) to (d).

[0103] Alternatively, in the product obtained in the step (c), the process conditions capable of controlling the crystallinity of the binder resin to 20% or less are experimentally confirmed, and the set process conditions can be applied to the step (b) and / or (c).

[0104] If the mixed powder for electrodes is obtained in such a manner, then a dry electrode is subsequently manufactured using such powder for electrodes ((step (d))). Specifically, the mixed powder for electrodes that has been manufactured and completed up to the pulverization step is calendared to manufacture a dry electrode film.

[0105] Such calendaring processes the mixed powder for electrodes into a film form. For example, it can be a step of manufacturing by pressing the mixed powder for electrodes into a film form so as to have an average thickness of 50 μm to 300 μm.

[0106] In one embodiment of the present invention, the calendaring can be performed using a calender device including a roll press section in which two rollers are arranged to face each other. The calender device can include at least one roll press section. For example, a plurality of roll press sections may be continuously arranged so that the crimping of the mixed powder for electrodes is performed in multiple stages. On the other hand, in the calender device, one or more rollers can each be independently controlled to a temperature of 50°C to 200°C. Together with or independently of this, the rotation speed ratio of the two rollers in the one or more roll press sections can be controlled at a ratio of 1:1 to 1:3.

[0107] Once the calendaring step is completed, a dry electrode film that serves as an electrode binder can be manufactured. Such a dry electrode film can also be referred to as a free-standing film or a self-supporting film. Such a dry electrode film can have sufficient mechanical strength to be used in the manufacturing process of an energy storage device even without any external support elements such as a current collector, a support web, or other structures. Alternatively, it may be combined with a support such as a current collector and used in the manufacture of a battery.

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

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

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

[0111] The dry electrode film manufactured in this way does not contain a solvent, so it has almost no fluidity and is easy to handle. It can be processed into a desired form and used for manufacturing various forms of electrodes. Furthermore, when the dry electrode film of the present invention is used for manufacturing an electrode, since the drying process for removing the solvent can be omitted, not only can the manufacturability of the electrode be greatly improved, but also problems such as the pulverization of the active material and the cutting of the fibrillated binder, which were problems in the manufacture of conventional dry electrodes, can be solved.

[0112] In addition, the dry electrode film according to the present invention has increased flexibility because the crystallinity of the binder resin contained in the dry electrode film is controlled to 10% or less. When it is wound up and stored or unwound again, there is an advantage that breakage or cracks do not occur. Also, the mechanical strength can be improved, such as by improving the tensile strength and elongation at break due to the increased flexibility.

[0113] On the one hand, in the present invention, the dry electrode film may have a porosity of 20 vol% to 50 vol%, and within the above range, it can be preferably controlled to a value of 45 vol% or less or 40 vol% or less. 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 outside the above range, it is difficult for the electrolyte to be impregnated, which is not desirable in terms of life characteristics, output characteristics, etc. If it is too large, the volume for expressing the same capacity increases, so it is not desirable in terms of volume-specific energy density. In one embodiment of the present invention, the porosity can be calculated by the following formula 2 using the measured apparent density of the dry electrode film and the true density calculated based on the true density and composition of each constituent component.

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

[0115] Moreover, according to the present invention, after calendering, a lamination step of forming the dry electrode film on at least one surface of the current collector can be performed. The lamination can be a step of rolling and adhering the dry electrode film on the current collector with a predetermined thickness. The lamination can also be performed by a lamination roll, and at this time, the lamination roll can be maintained at a temperature of 20°C to 200°C.

[0116] On the one hand, in one embodiment of the present invention, the bending resistance of the manufactured dry electrode can be less than Φ (diameter) 10 mm, 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 according to 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 measurement standard JIS K5600-5-1. Specifically, after the manufactured dry electrode is brought into contact with measurement rods of various diameters, the occurrence of cracks and the minimum diameter at which no cracks occur are measured by lifting both ends.

[0117] Also, the loading amount of the active material of the dry electrode film is 3 mAh / cm2 ~15 mAh / cm 2 can be, specifically 4 mAh / cm 2 ~10 mAh / cm 2 can be. Here, the loading amount of the active material is a value calculated by the method as shown in the following Mathematical Formula 3.

[0118] [Mathematical Formula 3] Loading amount (mAh / cm 2 ) = Capacity of active material (mAh / g) × Weight ratio (wt%) of active material in dry electrode film × Weight per unit area of dry electrode film (g / cm 2 )

[0119] On the other hand, the current collector is not particularly limited as long as it does not induce a chemical change in the battery and has high conductivity. For example, stainless steel, aluminum, nickel, titanium, fired carbon, copper, or those obtained by surface treatment of the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. can be used. Further, the current collector may form fine irregularities on its surface to enhance the adhesive force of the positive electrode active material, and can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven bodies, etc.

[0120] Furthermore, as the current collector, those obtained by entirely or partially coating a conductive primer for reducing the surface resistance and improving the adhesive force can be used. Here, the conductive primer may contain a conductive substance and a binder. The conductive substance is not limited as long as it is a conductive substance, and can be, for example, a carbon-based substance. The binder may include fluorine-based (including PVdF and PVdF copolymers), acrylic-based binders, and aqueous binders that are soluble in solvents.

[0121] Yet another 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, and the dry electrode film is disposed on at least one or both surfaces of the current collector. Further provided is a secondary battery including the dry electrode, wherein the dry electrode is a positive electrode, and an electrode assembly including the positive electrode, a negative electrode, and a separator is housed in a battery case together with a lithium-containing non-aqueous electrolyte, and an energy storage device including the secondary battery as a unit cell.

[0122] At this time, since the specific structures of the secondary battery and the energy storage device are well known, descriptions thereof are 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 that mixes raw material substances including an electrode active material, a conductive material, and a binder resin, a kneader device that kneads the mixture to produce a mixture mass, a pulverizing device that pulverizes the mixture mass to form a mixed powder for an electrode, a calender device that forms the powder for the electrode into a dry electrode film, and a laminating device that laminates the dry electrode film and a current collector.

[0124] The process conditions of each device of the system and each process performed using the device may be preset such that the binder resin can have the crystallinity described above at each stage.

[0125] Further, after performing the process for each stage, a sample may be taken to measure the crystallinity, and if it does not meet the standard, the already set process conditions may be corrected and reflected.

[0126] For example, when the measurement result of the crystallinity of the powdery mixture obtained by the blender device exceeds 50%, or when the measurement result of the crystallinity of the mixed powder for the electrode obtained exceeds 20%, the respective process times can be increased. Further, after the calendaring process, when the crystallinity of the obtained electrode film exceeds 10%, the crystallinity can be controlled by reducing the gap between the rollers or increasing the speed ratio in the roll press section.

[0127] On the other hand, the blender device is a mixer for mixing raw material substances, and can mix the compound raw material substances at a speed of 500 rpm to 30,000 rpm as described above.

[0128] The kneader device forms a mixture into a mass through kneading and progresses the fibrillation of the binder. For such a purpose, the kneader device can be set to pressure conditions of normal pressure or higher in the range of 70°C to 200°C. Specifically, it can be set to pressure conditions of 90°C to 150°C, 0.5 kgf / cm 2 ~10 kgf / cm 2 and more specifically, it can be set to pressure conditions of 1 kgf / cm 2 ~8 kgf / cm 2 .

[0129] The pulverizing device is a device for pulverizing the mass of the mixture obtained by the kneader device to form a powder for an electrode, and for example, a blender or a grinder can be used.

[0130] The calendaring device is a device for pressing the powder for the electrode into a film form. In a specific embodiment of the present invention, the calendaring device includes a roll press section in which two rollers are arranged opposite to each other, and a plurality of the roll press sections are continuously arranged so that the pressing of the powder can be performed in multiple stages.

[0131] The laminating device serves to attach and roll the dry electrode film formed by the calendaring device to at least one surface of the current collector, and for example, a roll press device can be used.

[0132] The porosity of the dry electrode film according to the present invention can be determined by such a calendar device and a laminating device. Since the specific structures of the blender device, kneader device, calendar device, and laminating device are well-known, specific descriptions thereof are omitted in this specification.

[0133] Figure 3 is a flowchart showing the electrode manufacturing method performed using the above-described device in order of steps. Referring to this, first, an electrode active material, a binder resin, and a conductive material are mixed to produce a powdery mixture, and the crystallinity of the binder resin is measured. If the crystallinity of the binder resin is confirmed to be 50% or less, the powdery mixture is put into the next kneading step. However, if the crystallinity exceeds 50%, the mixing time can be increased by, for example, performing the mixing step again on the powdery mixture. At this time, the lumps of the binder can be pulverized into primary particles, and thick fibrillation can proceed.

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

[0135] Thereafter, the obtained mixed powder for an electrode is calendared 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 put into the lamination step to manufacture an electrode. However, if the crystallinity exceeds 10%, the crystallinity is adjusted by adjusting the interval between rollers, controlling the speed ratio of the rollers, or both of these methods. On the other hand, the flowchart shown in Figure 3 can also be utilized to establish the process conditions for achieving the required crystallinity at each stage during electrode manufacturing.

[0136] Hereinafter, the present invention will be described in detail with reference to examples, comparative examples, and experimental examples so that those having ordinary knowledge in the technical field to which the present invention pertains can easily understand it.

[0137] Example 1 As the positive electrode active material, Li(Ni,Mn,Co,Al)O2, activated carbon, and polytetrafluoroethylene (PTFE) were charged into a blender at a ratio (weight ratio) of 96:1:3, and mixed at 15,000 rpm for 1 minute to produce a powdery mixture. Next, the temperature of the kneader was stabilized at 150 °C. After charging the mixture into the kneader, the pressure was 1 kgf / cm 2 , and it was operated at a speed of 25 rpm for 5 minutes to obtain a mixture mass. The mixture mass was charged into a blender and pulverized at 10,000 rpm for 30 seconds to obtain a mixed powder for the electrode. Then, the mixed powder for the electrode was charged into a wrap calendar (roll diameter: 200 mm, roll temperature: 100 °C, roll speed ratio 1.5 condition) to produce a dry electrode film. On the other hand, the particle size of the positive electrode active material was about 5 μm to 12 μm.

[0138] Example 2 As the positive electrode active material, lithium iron phosphate (LFP), activated carbon, and polytetrafluoroethylene (PTFE) were charged into a blender at a ratio of 94:1.5:4.5, and mixed at 10,000 rpm for 1 minute to produce a powdery mixture. Next, the temperature of the kneader was stabilized at 150 °C. After charging the mixture into the kneader, the pressure was 1 kgf / cm 2 , and it was operated at a speed of 50 rpm for 5 minutes to obtain a mixture mass. The mixture mass was charged into a blender and pulverized at 10,000 rpm for 20 seconds to obtain a mixed powder for the electrode. Then, the mixed powder for the electrode was charged into a wrap calendar (roll diameter: 200 mm, roll temperature: 100 °C, roll speed ratio 1.75 condition) to produce a dry electrode film. On the other hand, the particle size of the positive electrode active material was about 2 μm to 3 μm.

[0139] Example 3 As the positive electrode active material, Li(Ni,Mn,Co,Al)O2, activated carbon, and polytetrafluoroethylene (PTFE) were charged into a blender at a ratio (weight ratio) of 96:1:3, and mixed at 15,000 rpm for 1 minute to produce a powdery mixture. The particle size of the positive electrode active material was about 5 μm to 12 μm.

[0140] Next, the temperature of the kneader was stabilized at 150°C. After the powdered mixture was charged into the kneader, the pressure was 1 kgf / cm 2 , and it was operated at a speed of 25 rpm for 2 minutes to obtain a mixture mass. The mixture mass was charged into a blender and pulverized at 10,000 rpm for 30 seconds to obtain a mixed powder for the electrode. Then, the mixed powder for the electrode was charged into a wrap calendar (roll diameter: 200 mm, roll temperature: 100°C, roll speed ratio 1.5 condition) to produce a dry electrode film.

[0141] Comparative Example 1 As the positive electrode active material, lithium iron phosphate (LFP), activated carbon, and polytetrafluoroethylene (PTFE) were charged into a blender at a ratio of 94:1.5:4.5 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. After the mixture was charged into the kneader, the pressure was 1 kgf / cm 2 , and it was operated at a speed of 25 rpm for 2 minutes to obtain a mixture mass. The mixture mass was charged into a blender and pulverized at 10,000 rpm for 20 seconds to obtain a mixed powder for the electrode. Then, the mixed powder for the electrode was charged into a wrap calendar (roll diameter: 200 mm, roll temperature: 100°C, roll speed ratio 1.75 condition) to produce a dry electrode film. On the other hand, the particle size of the positive electrode active material was about 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 charged into a super mixer at a ratio (weight ratio) of 96:1:3 and mixed at 400 rpm for 2 minutes to produce a powdered mixture.

[0143] Next, the temperature of the kneader was stabilized at 150°C. After the mixture was charged into the kneader, the pressure was 1 kgf / cm 2, It was operated at a speed of 25 rpm for 5 minutes to obtain a mixture mass. The obtained mixture mass was put into a blender and pulverized at 10,000 rpm for 30 seconds to obtain a mixed powder for the electrode. Then, the mixed powder for the electrode was put into a wrap calendar (roll diameter: 200 mm, roll temperature: 100 °C, roll speed ratio 1.5 condition) to manufacture a dry electrode film. On the other hand, the particle size of the positive electrode active material was about 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 put into a blender at a ratio (weight ratio) of 96:1:3 and mixed at 15,000 rpm for 1 minute. Then, it was mixed at 800 rpm for 30 seconds using a super mixer. At this time, the temperature was maintained at 23 °C and the pressure was controlled to about 85 psi. A powdery mixture was obtained in such a manner. Then, the mixed powder for the electrode was put into a wrap calendar (roll diameter: 200 mm, roll temperature: 100 °C, roll speed ratio 1.5 condition) to manufacture a dry electrode film. On the other hand, the particle size of the positive electrode active material was about 5 μm to 12 μm.

[0145]

Table 1

[0146]

Table 2

[0147] As can be confirmed from Table 1, in Examples 1 to 3, the crystallinity of the powdery mixture was controlled to 50% or less, the crystallinity of the mixed powder for the electrode was controlled to 20% or less, and the crystallinity of the dry electrode film was controlled to 10% or less. Figure 1 is a graph showing the DSC thermal analysis results of Example 1. According to Figure 1, it was confirmed that the crystallinity of the mixed powder for the electrode (ground) and the dry electrode film (sheet) processed in the subsequent steps was lower than that of the powdery mixture (mixed). Further, Figure 2 is a graph showing the DSC thermal analysis results of Example 2. Also in Example 2, it was confirmed that the crystallinity of the mixed powder for the electrode (ground) and the dry electrode film (sheet) processed in the subsequent steps was lower than that of the powdery mixture (mixed). Further, in the dry electrode films obtained in each example, the tensile strength was confirmed to be 0.5 Mpa or more in all cases, and the tensile elongation also showed a value of 2% or more. On the other hand, PTFE in Figure 2 is the measurement of the inherent crystallinity of 100% PTFE before processing, and is shown for comparison with the degree of crystallization of PTFE after processing.

[0148] On the other hand, in Comparative Example 1 and Comparative Example 2, it was confirmed that the crystallinity of the binder resin in the obtained mixed powder for the electrode exceeded 20%. This means that the fibrillation in the obtained mixed powder for the electrode was insufficient, and it was difficult to manufacture a sheet-like dry electrode film in the subsequent calendaring process. In particular, in Comparative Example 2, it was confirmed that the crystallinity of the binder resin in the powdery mixture exceeded 60%, and sufficient fibrillation was not achieved even when the subsequent process was advanced. On the other hand, in Comparative Example 3, the kneading process according to the present invention was not applied, and since the micro-fibrillation was insufficient, it was confirmed that it could not be made into a sheet even by calendaring.

[0149] Measurement of crystallinity In each of the examples and comparative examples, samples for measuring the crystallinity were prepared from the powdery mixture, the mixed powder for the electrode, and the dry electrode film, respectively. For each sample, about 5 mg to 12 mg of the sample was weighed and put into a differential scanning calorimeter (DSC) manufactured by TA Instruments, and the heat of fusion (ΔHm) corresponding to the temperature was measured while raising the temperature at a rate of 10 °C / min in a nitrogen atmosphere in the temperature range of 25 to 360 °C.

[0150] Using the TROIS program of TA Instruments, the melting point (T m ) and the heat of fusion (ΔH m ) were analyzed based on the temperature (peak temperature) at the point where the highest enthalpy was shown during melting. The crystallinity of each sample was expressed as a percentage by dividing the measured heat of fusion (ΔH m ) value by the heat of fusion (ΔH m 0 ) value of theoretically perfect crystals (crystallinity 100%) and was calculated by the above formula (1). The heat of fusion value of theoretically perfect crystals of PTFE was set to 85.4 J / g with reference to Polymer, Vol. 46 (2005), pages 8872 - 8882.

[0151] Measurement of Tensile Strength and Elongation at Break After cutting the dry electrode films obtained in each of the examples and comparative examples to a width of 10 mm, they were measured three times at a tensile speed of 5 mm / min using a tensile strength tester, and the average value was shown. The tensile strength was the stress applied until breakage was measured, and the elongation at break was the ratio (%) of the elongation of the test piece until breakage (the rate of change in length with respect to the original length).

Claims

Claim 1. An electrode for an electrochemical element, comprising a dry electrode film, wherein the dry electrode film contains an electrode active material, a conductive material, and a binder resin, and the crystallinity of the binder resin contained in the dry electrode film is 10% or less, and the porosity of the dry electrode film is 20 vol% to 50 vol%.

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

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

4. A method for manufacturing the electrode for an electrochemical element according to claim 1 by a dry manufacturing process without using a solvent, wherein the method comprises: (a) producing a powdery mixture containing an electrode active material, a conductive material, and a binder resin; (b) kneading the powdery mixture under a temperature condition of 70°C to 200°C to produce a mixture mass; (c) pulverizing the mixture mass to obtain a mixed powder for an electrode; and (d) calendering the mixed powder for an electrode to obtain a free-standing dry electrode film, wherein the crystallinity of the binder resin contained in the dry electrode film obtained in step (d) is 10% or less.

5. The method according to claim 4, wherein the crystallinity of the binder resin contained in the mixed powder for an electrode obtained in step (c) is 20% or less.

6. The method according to claim 4, wherein the crystallinity of the binder resin contained in the mixture obtained in step (a) is 50% or less.

7. The method according to claim 4, wherein step (a) is performed under a condition of 500 rpm to 30,000 rpm.

8. The method according to claim 4, wherein step (b) is performed at a speed of 100 rpm or less.

9. The step (b) is 0.5 kgf / cm ２ ~10kgf / cm ２ 5. The process of claim 4, wherein the process is carried out under a pressure of

10. The method according to claim 4, wherein step (b) is performed under a condition of normal pressure or more.

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

12. 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 surface or both surfaces of the current collector.

13. The method according to claim 4, further comprising the step of preparing a current collector and laminating the dry electrode film on at least one surface of the current collector.

14. Comprising the electrode for an electrochemical element according to claim 1, wherein the electrode for an electrochemical element is a positive electrode, and an electrode assembly including the positive electrode, a negative electrode, and a separator is housed in a battery case together with a lithium-containing non-aqueous electrolyte, a secondary battery.

15. An energy storage device including the secondary battery according to claim 14 as a unit cell.

16. A method for manufacturing a mixed powder for an electrode for manufacturing a dry electrode film, comprising: (a) manufacturing a powdery mixture including an electrode active material, a conductive material, and a binder resin; (b) kneading the powdery mixture in the range of 70°C to 200°C to manufacture a mixture mass; (c) pulverizing the mixture mass to obtain a mixed powder for an electrode, measuring the crystallinity of the binder resin contained in the mixed powder for an electrode, and if the measured crystallinity is 20% or less, terminating the manufacturing; the binder resin includes polytetrafluoroethylene, polyolefin, or a mixture thereof, a method.

17. A method for manufacturing a dry electrode film, comprising the step of calendering a mixed powder for an electrode to obtain a free-standing dry electrode film, the mixed powder for an electrode being obtained by the method according to claim 16, and the crystallinity of the binder resin contained in the dry electrode film being 10% or less.

18. A dry electrode film including an electrode active material, a conductive material, and a binder resin, wherein the crystallinity of the binder resin contained in the dry electrode film is 10% or less, and the dry electrode film has a tensile strength in the machine direction of 0.5 MPa or more, a tensile elongation of 2% or more, and a porosity of 20 vol% to 50 vol%.

Images