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 to 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. The present invention also relates to the dry electrode film and a method for manufacturing the same. The present invention also relates to a mixed powder for an electrode used in manufacturing the dry electrode film and a method for manufacturing the same. [Background technology]

[0002] The rapid increase in fossil fuel use has led to an increasing demand for alternative and clean energy. One of the most actively researched fields is the field of electrochemical power generation and storage. A representative example of an electrochemical device using electrochemical energy is a secondary battery, whose range of use is expanding. Lithium secondary batteries, a representative example of such secondary batteries, are not only used as a power source for mobile devices, but are also being used as a power source for electric vehicles and hybrid electric vehicles, replacing fossil fuel-powered vehicles such as gasoline and diesel vehicles, which are major causes of air pollution. Their range of use is also expanding, including as an auxiliary power source for grid-connected vehicles. The manufacturing process for lithium secondary batteries can be broadly divided into three steps: an electrode manufacturing process, an electrode assembly manufacturing process, and an aging process. The electrode manufacturing process can be further divided into an electrode mix mixing process, an electrode coating process, a drying process, a rolling process, a slitting process, and a winding process. Among these, the electrode mixture mixing process is a process of blending components for forming an electrode active layer where the 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, other additives such as a conductive material and a filler, a binder for binding the powder particles together and adhering them to the current collector, and a solvent for imparting viscosity and dispersing the powder, to produce a fluid slurry.

[0003] The composition mixed to form the electrode active layer is broadly referred to as an electrode mixture. The electrode mixture is then applied to an electrically conductive current collector in an electrode coating process, followed by a drying process to remove the solvent contained in the electrode mixture. The electrode is then rolled to a predetermined thickness.

[0004] Meanwhile, during the drying process, 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, the inside and outside of the active layer may not be dried uniformly, and a powder floating phenomenon may occur due to the difference in solvent evaporation rate, i.e., powder in the area that is dried first may float up and form gaps with the area that is dried later, which may result in a deterioration in electrode quality.

[0005] To solve these problems, drying devices capable of uniformly drying the inside and outside of the active layer while controlling the evaporation rate of the solvent have been considered, but such drying devices are very expensive and require considerable cost and time to operate, which is disadvantageous in terms of manufacturing process. Therefore, active research has recently been conducted into manufacturing dry electrodes that do not use solvents.

[0006] Dry electrodes are generally manufactured by laminating a free-standing film containing active material, binder, and conductive material onto a current collector. The process involves first mixing the active material, conductive carbon material, and fiberizable binder together in a blender, then fiberizing the binder through a high-shear mixing process such as jet milling. This mixture is then calendered into a film to produce a free-standing film. The free-standing film produced after calendering is then laminated onto a current collector.

[0007] However, when the high shear mixing process is applied to fragile active materials, a large amount of fine powder with small particle size is generated, which can lead to reduced mechanical and electrochemical performance. Moreover, excessive high shear mixing can cut the binder fibers, reducing the flexibility of the free-standing film.

[0008] Therefore, there is a pressing need for the development of a dry electrode manufacturing technology that can solve these problems. In particular, it is necessary to provide a method for quantitatively analyzing the mixing uniformity of the mixture containing the ingredients for manufacturing dry electrode films and the state of the binder (such as the degree of fiberization), and to establish the process conditions. Summary of the Invention [Problem to be solved by the invention]

[0009] SUMMARY OF THE INVENTION In order to solve the above problems, the present invention aims to provide a dry electrode that minimizes pulverization of an active material and maximizes binder fiberization, and a manufacturing method thereof.

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

[0011] Another object of the present invention is to provide a method for manufacturing a dry electrode in which process conditions are applied based on the crystallinity of the binder resin. [Means for solving the problem]

[0012] A first aspect of the present invention relates to an electrode for an electrochemical element, the electrode comprising a dry electrode film manufactured by a dry manufacturing process without using a solvent, the dry electrode film comprising an electrode active material, a conductive material, and a binder resin, the binder resin contained in the dry electrode film having a crystallinity of 10% or less.

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

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

[0015] According to a fourth aspect of the present invention, in any one of the first to third aspects, the dry electrode film has a porosity of 20 vol % to 50 vol %.

[0016] A fifth aspect of the present invention relates to a method for producing an electrode for an electrochemical device, the electrode being according to any one of the first to fourth aspects, the method comprising: (a) preparing a powder mixture containing an electrode active material, a conductive material, and a binder resin; (b) kneading the powder mixture at a temperature ranging from 70°C to 200°C to prepare a mixture mass; (c) pulverizing the mixture mass to obtain a mixed powder for an electrode; (d) calendering the electrode powder mixture 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 a sixth aspect of the present invention, in the fifth aspect, the degree of crystallinity (c) of the binder resin contained in the mixed powder for an electrode obtained in the step (c) is 20% or less.

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

[0019] According to an eighth aspect of the present invention, in any one of the fifth to seventh aspects, the step (a) is carried out under the condition of 500 rpm to 30,000 rpm.

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

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

[0022] According to an eleventh embodiment of the present invention, in any one of the fifth to tenth embodiments, the step (b) is carried out under a condition of atmospheric pressure or higher.

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

[0024] According to a 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 a 14th aspect of the present invention, in any one of the 5th to 11th aspects, the method further comprises the step of preparing a current collector, and disposing the dry electrode film on at least one surface of the current collector and laminating it.

[0026] A fifteenth aspect of the present invention relates to a secondary battery, comprising the dry electrode according to any one of the first to fourth aspects, 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 nonaqueous electrolyte.

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

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

[0029] According to an eighteenth aspect of the present invention, there is provided a powder mixture for an electrode manufactured by the method according to the seventeenth aspect, the powder mixture for an electrode comprising an electrode active material, a conductive material and a binder resin, the binder resin comprising polytetrafluoroethylene (PTFE), PVdF, polyolefin, or a mixture of two or more thereof, and a crystallinity of the binder resin contained in the powder mixture for an electrode being 20% ​​or less.

[0030] A 19th aspect of the present invention relates to a method for manufacturing a dry electrode film, comprising the step of calendering a powder mixture for an electrode to obtain a free-standing dry electrode film, wherein the powder mixture for an electrode is obtained by the method according to the 17th aspect, and the degree of crystallinity (d) of a binder resin included 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 manufactured by the method according to the 19th aspect, which has 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%. [Effects of the Invention]

[0032] In the dry electrode manufacturing process according to the present invention, a high-temperature, low-shear mixing process is performed followed by a pulverization process when preparing a powder mixture for an electrode, thereby minimizing pulverization of the active material and preventing breakage of the fibrous binder. Furthermore, by manufacturing a dry electrode using such a powder mixture for an electrode, mechanical properties such as flexibility and strength of the dry electrode can be improved.

[0033] In addition, the method for manufacturing a dry electrode according to the present invention can determine and confirm the degree of fiberization of the binder resin and the completion of each process step based on the crystallinity of the binder resin at each step, and can control the process conditions for the electrode powder mixture and the electrode film based on the determination and confirmation, thereby making it easy and efficient to check 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 producing fine fibers by undergoing low-shear kneading and pulverization steps using a kneader, and is advantageous for mass production since it does not cause problems such as clogging of flow channels due to clumps of components. [Brief explanation of the drawings]

[0035] [Figure 1] 1 is a thermal analysis graph using a DSC (Differential Scanning Calorimeter) for Example 1 of the present invention. [Figure 2] 1 is a thermal analysis graph using DSC for Example 2 of the present invention. [Figure 3] FIG. 2 is a flow chart showing the manufacturing sequence of the dry electrode of the present invention. DETAILED DESCRIPTION OF THE INVENTION

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

[0037] The terms and words used in this specification and claims should not be interpreted limited to their ordinary and dictionary meanings, but should be interpreted in terms and concepts that correspond to the technical idea of ​​the present invention, in accordance with the principle that the inventor himself can appropriately define the concept of the term in order to explain the invention in the best way.

[0038] The terms used in this specification are used to describe exemplary embodiments and are not intended to limit the present invention. Unless otherwise specified, the singular includes the plural.

[0039] Furthermore, throughout the specification, when a part "comprises" another component, it does not mean that the other component is excluded, but that the part may further include the other component, unless otherwise specified.

[0040] TECHNICAL FIELD One aspect of the present invention relates to an electrode for an electrochemical device and a method for manufacturing the same. The electrochemical device 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 no solvent is used to disperse electrode components. The dry electrode film includes an electrode active material, a conductive material, and a binder resin, and the binder resin included 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 10% or less, the binder resin is highly fibrous, ensuring the flexibility of the dry electrode film. This facilitates the production of strip-shaped dry electrode films in a roll-to-roll continuous calendering process, as described below. After the electrode film is manufactured, it maintains its shape stably without damage such as breakage or cracking when wound into a roll or unwound. This also helps ensure a predetermined level of adhesive strength with the current collector.

[0043] In addition, in the present invention, the dry electrode film preferably has a tensile strength in the machine direction (MD) of 0.5 MPa or more. The tensile strength of the dry electrode film in the machine direction (MD) may be 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 is ensured when manufacturing a free-standing dry electrode, making it easy to manufacture and handle. On the other hand, when the tensile strength does not reach the above range, the mechanical strength is weak and the film is easily broken. On the other hand, when the tensile strength is too high, the tensile elongation also increases, resulting in poor processability and uneven film thickness, as described below.

[0044] On the other hand, the dry electrode film preferably 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 dimensional stability and flexibility can be ensured during the manufacture of a free-standing dry electrode, making it easy to manufacture and handle. If the tensile elongation is too low, the flexibility and dimensional stability are low, making it prone to breakage during manufacture or transportation, which is undesirable. On the other hand, if the tensile elongation exceeds the above range, the flexibility is too high, and the dry electrode film may be overstretched between rolls in the calendering process described below, resulting in an uneven thickness of the obtained film.

[0047] Meanwhile, 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, in which the crystallinity of the binder resin contained in the dry electrode film is controlled to 10% or less. In the present invention, the crystallinity of the dry electrode is zero (0) or 10% or less.

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

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

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

[0052] In one embodiment of the present invention, the completion of each step (a) to (d) is determined by checking the crystallinity of the resultant product of each step. If the crystallinity of the binder resin product of each step satisfies the predetermined crystallinity of each step, the next step is carried out.

[0053] Specifically, in step (a), if the crystallinity of the binder resin in the powder mixture is 60% or less, preferably 50% or less, the process of step (a) is terminated and the obtained resultant is introduced into step (b).

[0054] In addition, in the step (c), if the crystallinity of the binder resin in the electrode powder mixture is 20% or less, the step (c) is terminated and the obtained resultant is input to the step (d).

[0055] In addition, in the step (d), the manufacturing is determined to be completed when the crystallinity of the binder resin in the manufactured dry electrode film is 10% or less.

[0056] Alternatively, in steps (a), (b), and (d), process conditions that can control the crystallinity to the limited range described above can be experimentally confirmed, and the experimentally determined process can be applied to each step.

[0057] In the present invention, the crystallinity (Xc) can be measured using a differential scanning calorimeter (DSC) and is based on the temperature (peak temperature) at which the highest enthalpy is observed during crystallization. Specifically, the crystallinity can be calculated based on the melting enthalpy (ΔH m ) value is the theoretical melting enthalpy (ΔH m 0 ) (equilibrium heat of fusion) and expressed as a percentage, and can be calculated by the following formula 1. Here, the theoretical enthalpy of fusion of a perfect crystal (ΔH m 0 For details on the melting enthalpy of PTFE, refer to academic papers such as "Polymer Handbook" (J. Brandrup et al., 2003) and "Polymer." For example, the theoretical melting enthalpy of PTFE for perfect crystals is 85.4 J / g (Polymer, Vol. 46 (2005), pp. 8872-8882). Meanwhile, thermal analysis of polymers, such as DSC, can usually be measured and calculated according to ASTM D3418-21.

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

[0059] The method for manufacturing a dry electrode according to the present invention will now be described in more detail.

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

[0061] Here, the mixing for preparing the powder mixture is performed to obtain a uniform mixture of the electrode active material, conductive material, and binder resin, and preferably to adjust the crystallinity of the binder resin in the obtained powder mixture to 50% or less. Since the materials are mixed in powder form, various methods can be applied without limitation as long as they can be mixed uniformly. However, in the present invention, since a dry electrode is prepared without using a solvent, the mixing may be performed by dry mixing. For example, the materials may 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 may be 1 second to 20 minutes. For example, it may be 1 second to 10 minutes. Meanwhile, the mixing speed is not particularly limited, but may be appropriately controlled within a range of about 500 rpm to 30,000 rpm. For example, it may be controlled within a range of 500 rpm to 20,000 rpm.

[0063] Meanwhile, in one embodiment of the present invention, the temperature of the mixture may be controlled to 70°C or less or 60°C or less. If the mixing temperature exceeds 70°C, the materials may adhere to the mixer, making it difficult to obtain a uniform mixture. Meanwhile, the lower limit of the temperature of the mixture is not particularly limited, and in one embodiment of the present invention, the mixture may be mixed at a temperature of 20°C or more.

[0064] Specifically, in terms of high uniformity and control of the crystallinity of the binder resin, the mixing can be carried out using a mixer at 500 rpm to 20,000 rpm for 30 seconds to 10 minutes at a temperature of 70°C or less, or at 5,000 rpm to 20,000 rpm for 30 seconds to 2 minutes at a temperature of 70°C or less, 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 less.

[0065] In the present invention, the crystallinity of the binder resin in the mixture obtained by the mixing is 60% or less, preferably 50% or less. On the other hand, if the crystallinity of the binder resin in the obtained mixture is more than 60% or more than 50%, it is preferable to increase the speed (rpm) and / or process time to crush the binder clumps into primary particles to prevent agglomeration and partially promote thick fiberization.

[0066] If the crystallinity of the mixture obtained in step (a) is below the above range, it may be difficult to fiberize the binder resin in the low-shear kneading process (step (b)) described below, and the fibers may not be sufficiently formed on the binder surface, or the process time required for fiberization of the binder resin may increase.

[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, or independently, may result in non-uniform binder fiberization. In consideration of this, in one embodiment of the present invention, the crystallinity of the binder resin in the mixture may 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 a specific one as long as it can be fiberized in the step (a) and / or the step (b) described below.

[0069] Meanwhile, the binder resin may be fiberized in step (a), but the fibers formed in step (a) are thick and difficult to be thinned to a degree that can achieve the tensile strength and tensile elongation required for a dry electrode. In the present invention, it is preferable that the fiberization of the binder resin is mainly performed through step (b) described below.

[0070] The fiberization refers to a process of finely dividing a polymer, and can be performed, for example, using mechanical shearing force. The fiberized polymer fibers have their surfaces disintegrated to generate numerous fine fibers (fibrils). Non-limiting examples of such binder resins include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyolefin, or a mixture of two or more of these. Specifically, polytetrafluoroethylene (PTFE) can be included in an amount of 30 wt% or more based on the total weight of the binder resin. In this case, the binder resin can further include polyethylene oxide (PEO) and / or polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP) in addition to the above-mentioned components.

[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 a specific component as long as it is in the form of a lithium transition metal oxide or a lithium metal iron phosphate compound, or a metal oxide. Examples of 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; 1+x Mn 2-x Lithium manganese oxides such as O4 (x=0~0.33), LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, and Cu2V2O7; chemical formula LiNi 1-x M x Ni-site lithium nickel oxides represented by the formula Li(Ni,Co,Mn,Al)O2 (M=Co, Mn, Al, Cu, Fe, Mg, B or Ga, x=0.01-0.5), such as Li(Ni,Co,Mn,Al)O2, in which the fraction of Ni in the metals excluding Li is 50% or more; 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, etc., and may include one or more of these. 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 carbons 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), etc. 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, etc. can be used.

[0074] However, the dry electrode may specifically be a positive electrode, and thus, the active material may specifically be a positive electrode active material, 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, etc.

[0075] The conductive material is not particularly limited as long as it does not induce chemical changes in the battery and has conductivity. 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, and thermal black; conductive fibers such as carbon fiber and metal fiber; 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, in order to uniformly mix the conductive material and improve conductivity, the conductive material may include one or more selected from the group consisting of activated carbon, graphite, carbon black, and carbon nanotubes, and more specifically, activated carbon.

[0076] The mixing ratio of the electrode active material, conductive material, and binder may be 80 to 98 wt %:0.5 to 10 wt %:0.5 to 10 wt % (electrode active material:conductive material:binder resin), specifically 85 to 98 wt %:0.5 to 5 wt %:0.5 to 10 wt %.

[0077] If the binder resin content is too high beyond the above range, the binder resin may be excessively fibrous in the subsequent kneading process, which may affect the process. If the binder resin content is too low, the binder resin may not be sufficiently fibrous, and may not aggregate to form a mixture mass, making it difficult to produce a dry electrode film, or the physical properties of the dry electrode film may be deteriorated.

[0078] In addition, if the content of the conductive material is too high beyond the above range, the content of the active material is relatively reduced, resulting in a problem of reduced capacity, while if the content is too low, sufficient conductivity may not be ensured or the physical properties of the dry electrode film may be deteriorated, which is undesirable.

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

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

[0081] Alternatively, in another embodiment, the process conditions for controlling the crystallinity of the binder resin in the powder mixture to 60% or less or 50% or less in step (a) may be experimentally confirmed, and the experimentally determined process may be applied to step (a).

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

[0083] In this kneading step, as described below, a relatively low shear force is applied at a high temperature, so that problems such as pulverization / damage of the electrode active material and cutting of the binder fibers are avoided, and it is possible to obtain a mixed particle for an electrode in which the binder resin is made into fine fibers. Furthermore, the fiberized binder has high uniformity in thickness and / or length.

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

[0085] This kneading is a step in which the binder resin is fiberized to bind or connect the electrode active material and the conductive powder, thereby forming a lumpy mixture with a solid content of 100%.

[0086] Specifically, the kneading in the step (b) can be controlled to a speed of 10 rpm to 100 rpm. For example, the kneading can be controlled to a speed of 20 rpm or more or 70 rpm or less within the above range.

[0087] Meanwhile, in one embodiment of the present invention, the kneading may be carried out for 1 minute to 30 minutes, for example, at a speed of 20 rpm to 70 rpm within the above range for 3 minutes to 10 minutes.

[0088] Meanwhile, in one embodiment of the present invention, the kneading step is carried out at a shear rate of 5 s -1 ~1,000s -1 In a specific embodiment of the present invention, the kneading may be carried out for 1 minute to 30 minutes, and the shear rate may be controlled within a range of 10 s -1 ~500s -1 The temperature can be controlled within the range of

[0089] The kneading step may be carried out under high temperature and pressure conditions equal to or higher than atmospheric pressure.

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

[0091] If the temperature is lower than the above range, the binder fiberization and kneading-induced agglomeration during the kneading process will be insufficient, and film formation during calendaring will not be smooth. If the temperature is too high, the binder will be rapidly fiberized, and then the already formed fibers will be cut by excessive shear force, which is undesirable.

[0092] The kneading step is carried out at a pressure of 0.5 kgf / cm 2~10kgf / cm 2 Under pressure of 1kgf / cm 2 ~8kgf / cm 2 Under pressure, for example, 8kgf / cm above normal pressure 2 The low shear mixing process can be carried out at or below the atmospheric pressure. If the pressure is too high, outside the above range, excessive shear force and pressure are applied, which can result in problems such as cutting of the formed fibers or excessively high density of the mixture mass, which is undesirable. That is, according to the present invention, the intended effect of the present invention can be achieved when the low shear mixing process is carried out under high temperature and pressure conditions above atmospheric pressure. Alternatively, the process can be carried out at atmospheric pressure or above, specifically at a pressure of 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 depending on 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 more easily compared to electrode active material particles with small particle sizes. 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 taking into account the characteristics of the materials. Next, the lumpy mixture prepared through the kneading in step (b) is further pulverized to obtain a mixed powder for an electrode (step (c)).

[0094] Specifically, the mixture mass produced through the kneading in step (b) may be directly subjected to a calendering process to form a sheet, but in this case, high pressure and high temperature are required to press the mixture mass 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 mixture mass (mixture mass) produced in step (b) is subjected to a pulverization process.

[0095] The grinding may be performed using known grinding equipment such as a blender or grinder, but is not limited thereto. In a specific embodiment of the present invention, the grinding speed may be controlled within a range of 100 rpm to 30,000 rpm or 3,000 rpm to 30,000 rpm. Meanwhile, the grinding time may be appropriately controlled within a range of 1 second to 10 minutes. However, the grinding speed and time are not particularly limited to the above ranges. Specifically, the grinding may 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 be insufficient and powder of a size unsuitable for film formation may be produced, while 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 mass, which is undesirable.

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

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

[0099] Meanwhile, in the present invention, the crystallinity (c) of the binder resin contained in the electrode mixture is 20% or less, which is lower than the crystallinity (a) of the binder resin contained in the powder mixture. However, it may be higher than the crystallinity (d) of the binder resin contained in the dry electrode film after calendering. That is, the crystallinity may be further reduced through the calendering step.

[0100] On the other hand, if 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 electrode powder mixture exceeds 20%, the crystallinity can be adjusted by adjusting at least one of the conditions of the preceding process, such as the kneading time, kneading temperature, rotation speed (rpm), and shear rate. For example, the crystallinity can be adjusted by increasing the kneading time to promote fiberization of the binder.

[0101] In one embodiment of the present invention, the crystallinity (c) of the binder resin in the electrode powder mixture obtained in step (c) is preferably 20% or less. If the crystallinity (c) exceeds 20%, fiberization may be insufficient, and the tensile strength and tensile elongation of the dry electrode obtained in the calendering process described below may be reduced.

[0102] In one embodiment of the present invention, the crystallinity of the binder resin in the electrode powder mixture obtained in step (c) is confirmed, and if the confirmed crystallinity (c) is 20% or less, step (c) is terminated and the obtained resultant product is introduced into step (d). The crystallinity may be confirmed at each step while performing steps (a) to (d).

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

[0104] Once the electrode powder mixture is obtained in this manner, it is used to manufacture a dry electrode (step (d)). Specifically, the electrode powder mixture manufactured through the pulverization step is calendered to manufacture a dry electrode film.

[0105] The calendering is a process for processing the electrode powder mixture into a film shape, and may be a step of compressing the electrode powder mixture into a film shape having an average thickness of 50 μm to 300 μm.

[0106] In one embodiment of the present invention, the calendering may be performed using a calender including a roll press unit in which two rollers are arranged facing each other. The calender may include at least one roll press unit. For example, a plurality of roll press units may be arranged in series to perform multi-stage compression of the electrode powder mixture. Meanwhile, in the calender, one or more rollers may be independently controlled to a temperature of 50°C to 200°C. Additionally or independently, the rotational speed ratio of the two rollers in the one or more roll press units may be controlled to a ratio of 1:1 to 1:3.

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

[0108] Meanwhile, 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 two rollers of the roll press unit or by controlling the speed ratio. For example, the degree of fiberization 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 crystallinity of the binder resin in the dry electrode film obtained in step (d) is confirmed, and if the confirmed crystallinity (d) is 10% or less, step (d) may be terminated. The crystallinity may be confirmed at each step while performing steps (a) to (d).

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

[0111] The dry electrode film thus produced is solvent-free, has little fluidity, and is easy to handle, and can be processed into a desired form for use in the manufacture of various electrodes. Furthermore, when the dry electrode film of the present invention is used in the manufacture of an electrode, the drying process for removing the solvent can be omitted, thereby significantly improving the efficiency of the electrode manufacturing process and eliminating problems that have arisen in the manufacture of conventional dry electrodes, such as pulverization of the active material and cutting of fibrous binders.

[0112] In addition, the dry electrode film according to the present invention has an advantage that the crystallinity of the binder resin contained in the dry electrode film is controlled to 10% or less, which increases flexibility and prevents breakage or cracks when wound and stored or unwound.In addition, the increased flexibility can improve mechanical strength, such as tensile strength and tensile elongation.

[0113] Meanwhile, in the present invention, the porosity of the dry electrode film may be 20 vol% to 50 vol%, and may be controlled within the above range, preferably to 45 vol% or less, or 40 vol% or less. A porosity within the above range 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 undesirable in terms of life characteristics, output characteristics, etc., while if the porosity is too large, it is undesirable in terms of volume-specific energy density, as the volume required to achieve the same capacity increases. In one embodiment of the present invention, the porosity can be calculated using the following Equation 2, which is obtained by measuring the apparent density of the dry electrode film and using the true density calculated based on the true density of each component and the composition:

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

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

[0116] Meanwhile, in one embodiment of the present invention, the flex resistance of the prepared dry electrode may be less than 10 mm (diameter), specifically 8 mm (diameter) or less, and more specifically 5 mm (diameter) or less. That is, as described above, the dry electrode prepared according to the present invention may have improved flexibility due to reduced shearing of the fibrous binder. The flex resistance may be evaluated according to the method of measurement standard JIS K5600-5-1. Specifically, the prepared dry electrode is brought into contact with measuring rods of various diameters, and then both ends are lifted to measure whether cracks occur and the minimum diameter at which cracks do not occur.

[0117] The loading amount of the active material of the dry electrode film is 3 mAh / cm2 ~15mAh / cm 2 Specifically, 4mAh / cm 2 ~10mAh / cm 2 It could be. Here, the loading amount of the active material is a value calculated by the following Equation 3.

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

[0119] Meanwhile, the current collector is not particularly limited as long as it does not induce chemical changes in the battery and has high conductivity, and may be made of, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, copper, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. In addition, the current collector may have fine irregularities on its surface to increase adhesion of the positive electrode active material, and may be used in various forms such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0120] Furthermore, the current collector may be fully or partially coated with a conductive primer to reduce surface resistance and improve adhesion. Here, the conductive primer may include a conductive material and a binder. The conductive material may be any conductive material, such as a carbon-based material. The binder may include solvent-soluble fluorine-based binders (including PVdF and PVdF copolymers), acrylic binders, and water-based binders.

[0121] In yet another aspect of the present invention, there is provided a dry electrode manufactured by the dry electrode manufacturing method. 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. The present invention also provides a secondary battery including the dry electrode, in which 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 nonaqueous electrolyte, and an energy storage device including the secondary battery as a unit battery.

[0122] At this time, the specific structures of the secondary battery and the energy storage device are well known, and therefore will not be described in this specification.

[0123] Meanwhile, in one specific embodiment of the present invention, there is provided a system for manufacturing a dry electrode, which includes a blender device that mixes raw materials including an electrode active material, a conductive material, and a binder resin, a kneader device that kneads the mixture to prepare a mixture mass, a grinder device that grinds the mixture mass to form an electrode mixed powder, a calender device that forms the electrode powder into a dry electrode film, and a laminator 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 so that the binder resin has the above-mentioned crystallinity at each stage.

[0125] In addition, after each process step, a sample is taken and the crystallinity is measured. If the crystallinity does not meet the standard, the process conditions can be adjusted accordingly.

[0126] For example, if the crystallinity of the powder mixture obtained in the blender exceeds 50% or if the crystallinity of the electrode powder mixture obtained exceeds 20%, the time of each process 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 rollers in the roll press unit or increasing the speed ratio.

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

[0128] The kneader kneads the mixture to form a mass of the mixture and promotes the fiberization of the binder. For this purpose, the kneader can be set to a temperature range of 70°C to 200°C and a pressure higher than atmospheric pressure. More specifically, the kneader can be set to a temperature range of 90°C to 150°C and a pressure of 0.5 kgf / cm. 2 ~10kgf / cm 2 Pressure condition, more specifically, 1kgf / cm 2 ~8kgf / cm 2 The pressure condition can be set as follows.

[0129] The pulverizing device is a device that pulverizes the mixture mass obtained by the kneading device to form electrode powder, and may be, for example, a blender or a grinder.

[0130] The calendering device is a device for compressing the electrode powder into a film shape. In a specific embodiment of the present invention, the calendering device includes a roll press unit having two rollers arranged opposite to each other, and a plurality of roll press units may be arranged in succession to compress the powder in multiple stages.

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

[0132] The calender and laminators may determine the porosity of the dry electrode film according to the present invention. The specific structures of the blender, kneader, calender, and laminator are well known, and therefore, detailed description thereof will be omitted herein.

[0133] FIG. 3 is a flow chart showing the steps of a method for manufacturing an electrode using the above-described apparatus. First, an electrode active material, a binder resin, and a conductive material are mixed to prepare a powder 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 powder mixture is introduced into the next kneading process. However, if the crystallinity exceeds 50%, the mixing time can be increased by subjecting the powder mixture to a second mixing process. During this process, binder clumps are pulverized into primary particles, which can lead to thick fiberization.

[0134] The obtained powder mixture is then kneaded to obtain a mixture mass, which is then pulverized to obtain an electrode mixture. If the crystallinity of the binder resin in the obtained electrode mixture is confirmed to be 20% or less, the electrode mixture is subjected to the subsequent calendering process. However, if the crystallinity exceeds 20%, the electrode mixture is subjected to a second kneading process.

[0135] The obtained electrode powder mixture is then 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 subjected to a lamination process to produce an electrode. However, if the crystallinity exceeds 10%, the crystallinity is adjusted by adjusting the roller gap, controlling the roller speed ratio, or both. Meanwhile, the flow chart shown in FIG. 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 now be described in detail with reference to examples, comparative examples and experimental examples so that those skilled in the art can easily understand the present invention.

[0137] Example 1 The positive electrode active material, Li(Ni,Mn,Co,Al)O2, activated carbon, and polytetrafluoroethylene (PTFE) were mixed in a weight ratio of 96:1:3 into a blender and mixed at 15,000 rpm for 1 minute to prepare a powder mixture. The temperature of the kneader was then stabilized at 150°C, and the mixture was then added to the kneader under a pressure of 1 kgf / cm. 2 The mixture was then mixed at 10,000 rpm for 5 minutes to obtain a mixture mass. The mixture mass was then placed in a blender and pulverized at 10,000 rpm for 30 seconds to obtain a mixed powder for an electrode. The mixed powder for an electrode was then placed in a wrap calender (roll diameter: 200 mm, roll temperature: 100°C, roll speed ratio: 1.5) to prepare a dry electrode film. 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 mixed in a ratio of 94:1.5:4.5 into a blender and mixed at 10,000 rpm for 1 minute to prepare a powder mixture. The temperature of the kneader was then stabilized at 150°C, and the mixture was then added to the kneader at a pressure of 1 kgf / cm. 2 The mixture was then mixed at 10,000 rpm for 5 minutes to obtain a mixture mass. The mixture mass was then placed in a blender and pulverized at 10,000 rpm for 20 seconds to obtain a mixed powder for an electrode. The mixed powder for an electrode was then placed in a wrap calender (roll diameter: 200 mm, roll temperature: 100°C, roll speed ratio: 1.75) to prepare a dry electrode film. The particle size of the positive electrode active material was approximately 2 μm to 3 μm.

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

[0140] Next, the temperature of the kneader is stabilized at 150°C, and the powder mixture is charged into the kneader, and then the kneading is continued at a pressure of 1 kgf / cm. 2 The mixture was then mixed at 10,000 rpm for 2 minutes at 25 rpm to obtain a mixture mass. The mixture mass was then placed in a blender and pulverized at 10,000 rpm for 30 seconds to obtain an electrode mixture powder. The electrode mixture powder was then placed in 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 mixed in a ratio of 94:1.5:4.5 into a blender and mixed at 10,000 rpm for 1 minute to prepare a powder mixture. The temperature of the kneader was then stabilized at 150°C, and the mixture was then added to the kneader at a pressure of 1 kgf / cm. 2 The mixture was then mixed at 10,000 rpm for 2 minutes to obtain a mixture mass. The mixture mass was then placed in a blender and pulverized at 10,000 rpm for 20 seconds to obtain an electrode mixture powder. The electrode mixture powder was then placed in a wrap calender (roll diameter: 200 mm, roll temperature: 100°C, roll speed ratio: 1.75) to produce a dry electrode film. 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 super mixer in a ratio of 96:1:3 (weight ratio) and mixed at 400 rpm for 2 minutes to produce a powder mixture.

[0143] Next, the temperature of the kneader was stabilized at 150°C, and the mixture was charged into the kneader, and then the pressure was 1 kgf / cm 2The mixture was then mixed at 10,000 rpm for 5 minutes to obtain a mixture mass. The mixture mass was then placed in a blender and pulverized at 10,000 rpm for 30 seconds to obtain a mixed powder for an electrode. The mixed powder for an electrode was then placed in a wrap calender (roll diameter: 200 mm, roll temperature: 100°C, roll speed ratio: 1.5) to prepare a dry electrode film. The particle size of the positive electrode active material was approximately 5 μm to 12 μm.

[0144] Comparative Example 3 The positive electrode active material, Li(Ni,Mn,Co,Al)O2, activated carbon, and polytetrafluoroethylene (PTFE), were added to a blender in a weight ratio of 96:1:3 and mixed at 15,000 rpm for 1 minute. The mixture was then mixed at 800 rpm for 30 seconds using a super mixer. The temperature was maintained at 23°C and the pressure was controlled at approximately 85 psi. A powdery mixture was obtained in this manner. The electrode powder mixture was then placed in a wrap calender (roll diameter: 200 mm, roll temperature: 100°C, roll speed ratio: 1.5) to prepare a dry electrode film. 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 powder mixture was controlled to 50% or less, the crystallinity of the electrode powder mixture was controlled to 20% or less, and the crystallinity of the dry electrode film was controlled to 10% or less. FIG. 1 is a graph showing the results of DSC thermal analysis of Example 1. As shown in FIG. 1, it was confirmed that the crystallinity of the electrode powder mixture (pulverized) and the dry electrode film (sheet) processed in the subsequent steps was lower than that of the powder mixture (mixed). Also, FIG. 2 is a graph showing the results of DSC thermal analysis of Example 2. It was also confirmed that the crystallinity of the electrode powder mixture (pulverized) and the dry electrode film (sheet) processed in the subsequent steps was lower than that of the powder mixture (mixed). Furthermore, the dry electrode films obtained in each Example all had a tensile strength of 0.5 MPa or more and a tensile elongation of 2% or more. On the other hand, the PTFE in Figure 2 is a measurement of the inherent crystallinity of 100% PTFE before processing, and is shown for comparison with the degree of crystallinity of PTFE after processing.

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

[0149] Crystallinity measurement In each example and comparative example, samples for measuring the crystallinity were prepared from the powder mixture, the electrode powder mixture, and the dry electrode film. For each sample, the crystallinity (Xc) was measured by weighing out approximately 5 mg to 12 mg of the sample and placing it in a differential scanning calorimeter (DSC) manufactured by TA Corp. The heat of fusion (ΔHm) corresponding to the temperature was measured in a nitrogen atmosphere in the temperature range of 25 to 360°C while increasing the temperature at a rate of 10°C / min.

[0150] Using the TROIS program from TA, the melting point (T m ) and enthalpy of fusion (ΔH m The crystallinity of each sample was analyzed based on the melting enthalpy (ΔH m ) value is the theoretical melting enthalpy (ΔH m 0 ) and expressed as a percentage, and was calculated using the above formula 1. The theoretical melting enthalpy value of perfect crystal of PTFE was determined to be 85.4 J / g by referring to Polymer, 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, and the average values ​​were shown. The tensile strength was measured as the stress applied until breakage, and the tensile elongation was the ratio of the specimen elongation until breakage (%; length change rate relative to the original length).

Claims

1. The dry electrode film is manufactured by a dry manufacturing 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 crystallinity of the binder resin included in the dry electrode film is 10% or less.

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

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

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

5. A method for producing the electrode for an electrochemical element according to claim 1, comprising: The method comprises: (a) preparing a powder mixture containing an electrode active material, a conductive material, and a binder resin; (b) kneading the powder mixture under a temperature condition of 70°C to 200°C to prepare a mixture mass; (c) pulverizing the mixture mass to obtain a mixed powder for an electrode; (d) calendering the electrode powder mixture to obtain a free-standing dry electrode film; The method, wherein the crystallinity of the binder resin contained in the dry electrode film obtained in step (d) is 10% or less.

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

7. The method according to claim 5, wherein the binder resin contained in the mixture obtained in step (a) has a crystallinity of 50% or less.

8. The method according to claim 5, wherein the step (a) is carried out at a speed of 500 rpm to 30,000 rpm.

9. 6. The method of claim 5, wherein step (b) is carried out at a speed of 100 rpm or less.

10. The step (b) is 0.5 kgf / cm ２ ~10 kgf / cm ２ 6. The process of claim 5, wherein the process is carried out under a pressure of

11. The method according to claim 5, wherein step (b) is carried out under atmospheric pressure or higher.

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

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

14. The method of claim 5 , further comprising the steps of: providing a current collector; and disposing and laminating the dry electrode film on at least one surface of the current collector.

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

16. An energy storage device comprising the secondary battery according to claim 15 as a unit battery.

17. A method for producing an electrode powder mixture for producing a dry electrode film, comprising: (a) preparing a powder mixture containing an electrode active material, a conductive material, and a binder resin; (b) kneading the powder mixture at a temperature ranging from 70°C to 200°C to prepare a mixture mass; (c) pulverizing the mixture mass to obtain an electrode powder mixture; The crystallinity of the binder resin contained in the electrode powder mixture is 20% or less, The method, wherein the binder resin comprises polytetrafluoroethylene, a polyolefin, or a mixture thereof.

18. 18. A mixed powder for an electrode produced by the method according to claim 17, The mixed powder for an electrode includes an electrode active material, a conductive material, and a binder resin, the binder resin including polytetrafluoroethylene, polyvinylidene fluoride, polyolefin, or a mixture of two or more thereof, and the degree of crystallinity of the binder resin included in the mixed powder for an electrode is 20% or less.

19. 20. A method for producing a dry electrode film, comprising: calendering an electrode powder mixture to obtain a free-standing dry electrode film, wherein the electrode powder mixture is obtained by the method of claim 17, and a crystallinity of a binder resin contained in the dry electrode film is 10% or less.

20. 20. A dry electrode film produced by the method of claim 19, having a machine direction tensile strength of 0.5 MPa or more, a tensile elongation of 2% or more, and a porosity of 20 vol% to 50 vol%.

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