Dry electrode, method for manufacturing same, and secondary battery comprising same

Abstract

Presented are a dry electrode, a method for manufacturing same, and a secondary battery comprising same. The dry electrode comprises an electrode current collector and an electrode active material layer positioned on at least one surface of the electrode current collector, wherein the electrode active material layer comprises a composite in which an electrode active material, a conductive material, and a first binder polymer are composited, and a fibrillated second binder polymer. The first binder polymer comprises a polyvinylidene fluoride (PVDF)-based material, the second binder polymer comprises polytetrafluoroethylene (PTFE), and the aspect ratio of the first binder polymer is 1:1 to 1:3.

Description

Dry electrode, method for manufacturing same, and secondary battery including same

[0001] The present invention relates to a dry electrode, a method for manufacturing the same, and a secondary battery including the same.

[0002] This application claims priority to Korean Application No. 10-2024-0107885, filed August 12, 2024, the entire disclosure of which is incorporated herein by reference.

[0003] Due to the rapid increase in fossil fuel use, the demand for alternative and clean energy is increasing, and as part of this, the most actively researched field is the field of power generation and storage using electrochemistry.

[0004] A representative example of an electrochemical device that currently utilizes this type of electrochemical energy is the secondary battery, and its application area is gradually expanding.

[0005] Among these secondary batteries, lithium secondary batteries are representative not only as an energy source for mobile devices, but recently, they are being used as a power source for electric vehicles and hybrid electric vehicles that can replace vehicles that use fossil fuels such as gasoline and diesel vehicles, which are one of the main causes of air pollution. Their use areas are also expanding to purposes such as auxiliary power sources through gridization.

[0006] The manufacturing process for these lithium secondary batteries is broadly divided into three stages: the electrode process, the assembly process, and the formation process. The electrode process is further subdivided into the active material mixing process, the electrode coating process, the drying process, the rolling process, the slitting process, and the coiling process.

[0007] Among these, the active material mixing process is a process of mixing a coating material for forming an electrode active layer where an actual electrochemical reaction occurs in the electrode. Specifically, it mixes the electrode active material, which is an essential element of the electrode, and other additives such as a conductive material and a filler, a binder for inter-powder bonding and adhesion to a current collector, and a solvent for viscosity imparting and powder dispersion, to manufacture a slurry having fluidity.

[0008] A composition mixed in this way to form an electrode active layer is also referred to as an electrode mixture in a broad sense.

[0009] Afterwards, an electrode coating process is performed to apply the electrode mixture onto an electrically conductive current collector, and a drying process is performed to remove the solvent contained in the electrode mixture, and additionally, the electrode is rolled to be manufactured to a predetermined thickness.

[0010] Meanwhile, during the drying process, the solvent contained in the electrode mixture may evaporate, causing defects such as pinholes or cracks in the already formed electrode active material layer. Furthermore, since the inside and outside of the active layer are not uniformly dried, the difference in solvent evaporation rates may cause powder floating, i.e., powders in areas that dry first may float to form gaps with areas that dry relatively later, which may deteriorate electrode quality.

[0011] Therefore, research on manufacturing dry electrodes that do not use solvents has been actively conducted recently.

[0012] The above dry electrode is generally manufactured by laminating a free-standing film containing an active material, a binder polymer, a conductive material, etc., and manufactured in a film form onto a current collector. In addition, PTFE, which can be fiberized as a binder polymer, is used to manufacture the film form.

[0013] However, the above dry electrode has a problem in that the bonding force between the electrode active material and PTFE is not good, and the electrode active material, binder polymer, and conductive material are not well dispersed, resulting in low stability of the conductive network of the electrode.

[0014] Therefore, there is an urgent need to develop a dry electrode that can solve these problems.

[0015] The present invention aims to provide a dry electrode with improved conductivity by improving the dispersibility of the electrode active material, conductive agent, and binder polymer. Furthermore, the present invention aims to provide a dry electrode with improved stability by improving the adhesive strength of the electrode active material and binder polymer.

[0016] The present invention provides dry electrodes of the following embodiments, a secondary battery including the same, and a method for manufacturing the dry electrode.

[0017] The dry electrode according to the first embodiment of the present invention is

[0018] It comprises an electrode current collector and an electrode active material layer positioned on at least one surface of the electrode current collector,

[0019] The electrode active material layer includes a composite in which an electrode active material, a conductive material, and a first binder polymer are complexed, and a fiberized second binder polymer,

[0020] The first binder polymer comprises polyvinylidene fluoride (PVDF),

[0021] The second binder polymer comprises polytetrafluoroethylene (PTFE),

[0022] The above first binder polymer is characterized in that the average aspect ratio is 1:1 to 1:3.

[0023] The second embodiment is, in the first embodiment,

[0024] The average aspect ratio of the first binder polymer may be 1:1 to 1:2.5.

[0025] The third embodiment is, in the first embodiment or the second embodiment,

[0026] The average particle diameter (D50) of the above first binder polymer may be 500 nm or less.

[0027] The fourth embodiment is, in any one of the first to third embodiments,

[0028] The average particle diameter (D50) of the above first binder polymer may be 400 nm or less.

[0029] The fifth embodiment is, in any one of the first to fourth embodiments,

[0030] The above first binder polymer may include primary particles.

[0031] The sixth embodiment is, in any one of the first to fifth embodiments,

[0032] The first binder polymer may comprise primary particles in an amount of at least 50% by weight based on 100% by weight of the total.

[0033] The seventh embodiment is, in any one of the first to sixth embodiments,

[0034] In the above complex, at least a portion of the first binder polymer can be plastically deformed and attached to the surface of the electrode active material.

[0035] The eighth embodiment is, in any one of the first to seventh embodiments,

[0036] The above complex is one in which the first binder polymer and the conductive material are attached to the surface of the electrode active material,

[0037] The complex may be dispersed within the fiberized fibril structure of the second binder polymer.

[0038] The ninth embodiment is, in any one of the first to eighth embodiments,

[0039] With respect to the total 100 parts by weight of the electrode active material layer, the first binder polymer may be included in an amount of 0.1 to 3 parts by weight.

[0040] The tenth embodiment is any one of the first to ninth embodiments,

[0041] With respect to the total 100 parts by weight of the electrode active material layer, the second binder polymer may be included in an amount of 0.5 to 5 parts by weight.

[0042] The secondary battery according to the 11th embodiment,

[0043] A positive electrode; a negative electrode; a separator positioned between the positive electrode and the negative electrode; and an electrolyte,

[0044] At least one of the positive and negative electrodes may be a dry electrode according to any one of the first to tenth embodiments.

[0045] The dry electrode manufacturing method according to the 12th embodiment is:

[0046] A step of preparing a composite by dry mixing and mixing an electrode active material, a conductive material, and a first binder polymer without a solvent;

[0047] A step of dry mixing and kneading the above complex and the second binder polymer without a solvent to prepare a mixture mass;

[0048] A step of crushing the above mixture lump to obtain a mixed powder for electrode;

[0049] A step of forming an electrode sheet by injecting the above electrode mixed powder between a plurality of rolls and performing a calendaring process; and

[0050] A step of laminating the above electrode sheet onto a current collector may be included.

[0051] The 13th embodiment is, in the 12th embodiment,

[0052] The steps of manufacturing the above complex are:

[0053] A composite may be manufactured by mixing an electrode active material, a conductive material, and a first binder polymer, which is a secondary particle, to prepare a mixture, mixing the mixture to pulverize the first binder polymer, which is a secondary particle, into primary particles, and attaching the conductive material and the primary particles of the first binder polymer to the surface of the electrode active material.

[0054] The 14th embodiment is, in the 12th embodiment or the 13th embodiment,

[0055] In the step of manufacturing the above complex, at least a portion of the first binder polymer may be plastically deformed.

[0056] According to one aspect of the present invention, a dry electrode comprises a composite in which an electrode active material, a conductive material, and a first binder polymer are complexed, and a fiberized second binder polymer, wherein the first binder polymer comprises a polyvinylidene fluoride (PVDF) system, the second binder polymer comprises polytetrafluoroethylene (PTFE), and the average aspect ratio of the first binder polymer is controlled to 1:1 to 1:3, so that the adhesive strength between the electrode active material and the binder polymer and the electrolyte stability of the active material can be improved by the PVDF binder polymer as the primary particle. In addition, since the composite is first manufactured and then mixed with the second binder polymer including PTFE, the composite is well dispersed between the fiberized PTFE binder polymers, so that the conductivity of the electrode can be improved. In addition, since the composite is manufactured by a dry method, low resistance can be secured.

[0057] The following drawings attached to this specification illustrate preferred embodiments of the present invention and, together with the contents of the invention described above, serve to further understand the technical concept of the present invention. Therefore, the present invention should not be interpreted as being limited to the matters described in these drawings. Meanwhile, the shape, size, scale, or ratio of elements in the drawings included in this specification may be exaggerated to emphasize a clearer explanation.

[0058] Figure 1 is an SEM image of a composite manufactured using the method of Manufacturing Example 1.

[0059] Figure 2 is an SEM image of a composite manufactured using the method of Manufacturing Example 1.

[0060] Figure 3 is an SEM image of a composite manufactured using the method of Manufacturing Example 2.

[0061] Figure 4 is an SEM image of a composite manufactured using the method of Manufacturing Example 2.

[0062] Figure 5 shows an SEM image of the composite of Manufacturing Example 1, and the aspect ratio is calculated by randomly selecting a composite from the SEM image.

[0063] Figure 6 shows an SEM image of the composite of Manufacturing Example 1, and the aspect ratio is calculated by randomly selecting a composite from the SEM image.

[0064] Figure 7 shows an enlarged SEM image of the composite manufactured in Manufacturing Example 1.

[0065] Figure 8 shows an enlarged SEM image of the composite manufactured in Manufacturing Example 1.

[0066] Figure 9 shows an enlarged SEM image of the composite manufactured in Manufacturing Example 1.

[0067] Figure 10 is an SEM image of the composite manufactured in Manufacturing Example 3.

[0068] Figure 11 is an SEM image of the composite manufactured in Manufacturing Example 3.

[0069] Figure 12 is an SEM image of the composite manufactured in Manufacturing Example 4.

[0070] Figure 13 is an SEM image of the composite manufactured in Manufacturing Example 4.

[0071] Figure 14 is an SEM image of the composite manufactured in Manufacturing Example 5.

[0072] Figure 15 is an SEM image of the composite manufactured in Manufacturing Example 5.

[0073] Figure 16 shows the results of measuring the discharge capacity of a secondary battery according to one embodiment of the present invention and a comparative example.

[0074] Hereinafter, the present invention will be described in detail with reference to the drawings. Terms and words used in this specification and claims should not be construed as limited to their conventional or dictionary meanings. Based on the principle that the inventor can appropriately define the concept of a term to best explain his or her invention, they should be interpreted in the sense and concept that conforms to the technical spirit of the present invention.

[0075] Accordingly, the embodiments described in this specification and the configurations described in the drawings are only the most preferred embodiments of the present invention and do not represent all of the technical ideas of the present invention. Therefore, it should be understood that there may be various equivalents and modified examples that can replace them at the time of filing this application.

[0076] Additionally, throughout the specification, whenever a part is said to “include,” “comprise,” “have,” or “have” a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise stated.

[0077] In addition, the terms 'about', 'substantially', etc. used throughout this specification are used in the sense of or near to the numerical values ​​when manufacturing and material tolerances inherent to the meanings stated are presented, and are used to prevent unscrupulous infringers from unfairly exploiting the disclosure where exact or absolute values ​​are mentioned to aid understanding of this specification.

[0078] Throughout this specification, references to 'A and / or B' mean 'A or B or both.'

[0079] Unless otherwise specified throughout this specification, temperature refers to Celsius temperature, and the unit is ℃.

[0080]

[0081] The first aspect of the present invention relates to a dry electrode.

[0082] According to one aspect of the present invention, a dry electrode comprises:

[0083] It comprises an electrode current collector and an electrode active material layer positioned on at least one surface of the electrode current collector,

[0084] The electrode active material layer includes a composite in which an electrode active material, a conductive material, and a first binder polymer are complexed, and a fiberized second binder polymer,

[0085] The first binder polymer comprises polyvinylidene fluoride (PVDF),

[0086] The second binder polymer comprises polytetrafluoroethylene (PTFE),

[0087] The above first binder polymer is characterized in that the average aspect ratio is 1:1 to 1:3.

[0088]

[0089] In one embodiment of the present invention, the electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. The current collector may be, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, copper, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. The current collector may also have fine unevenness on its surface to increase the adhesiveness of the active material, and may be in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric. Meanwhile, in one embodiment of the present invention, the current collector may have a thickness of 10 μm to 50 μm, but is not particularly limited thereto. The current collector may have a thickness of, for example, 10 μm to 20 μm.

[0090]

[0091] The above electrode active material layer includes an electrode active material, a conductive material, a first binder polymer, and a second binder polymer.

[0092] The above electrode active material, conductive material, and first binder polymer are combined to form a composite. The composite may be one in which the first binder polymer and the conductive material are attached to the surface of the electrode active material.

[0093] The above second binder polymer is fiberized by shear force, and the composite can be dispersed between the fiberized second binder polymers.

[0094] In the above composite, at least a portion of the first binder polymer may be present while attached to the surface of the electrode active material, and preferably, most of the first binder polymer may be present while attached to the surface of the electrode active material. When the first binder polymer is present while attached to the surface of the electrode active material, it can mainly bind between the electrode active material and / or the conductive material constituting the composite, and the composite can be well bound to the fiberized second binder polymer and maintain a dispersed state. In addition, it also has the effect of binding the composites together. In addition, it can improve the tensile strength of the second binder polymer and minimize deformation caused by an external force.

[0095] The above second binder polymer may be in a fiberized state due to shear force, and primarily allows the composite to remain well dispersed within the electrode active material layer.

[0096] That is, in the electrode active material layer according to one aspect of the present invention, the composite can be evenly dispersed between the fiberized second binder polymer and can exist while being bound to the second binder polymer. In addition, the first binder polymer included in the composite can bind between the electrode active material and / or the conductive material, and can allow the composite to be better bound to the second binder polymer. The first binder polymer allows the second binder polymer to better maintain the fiberized form. Therefore, the tensile strength of the electrode can be improved.

[0097]

[0098] In one embodiment of the present invention, the electrode active material may be a cathode active material. The cathode active material is not limited to a specific component as long as it can be used as a cathode active material of a lithium ion secondary battery. Non-limiting examples thereof include layered compounds such as lithium manganese oxide (LiMn2O4, LiMnO2, etc.), lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or compounds substituted with one or more transition metals; chemical formula Li 1+x Mn 2-x Lithium manganese oxides such as O4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, Cu2V2O7; chemical formula LiNi 1-x M x Ni-site type lithium nickel oxide represented by O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga and x = 0.01 to 0.3); chemical formula LiMn 2-x M x Lithium manganese complex oxides represented by O2 (wherein, M = Co, Ni, Fe, Cr, Zn or Ta, and x = 0.01 to 0.1) or Li2Mn3MO8 (wherein, M = Fe, Co, Ni, Cu or Zn); Li where some of the Li in the chemical formula is replaced by aluminum ions. 1+x (Ni a Co b Mn c Al d ) 1-x O2(x = 0 ~ 0.03, a = 0.3 ~ 0.95, b = 0.01 ~ 0.35, c = 0.01 ~ 0.5, d = 0.001 ~ 0.03, a+b+c+d=1); disulfide compound; may include one or a mixture of two or more of Fe2(MoO4)3.

[0099]

[0100] In one embodiment of the present invention, the electrode active material may be a negative electrode active material. A compound capable of reversible intercalation and deintercalation of lithium may be used as the negative electrode active material. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; SiO β (0 < β < 2), SnO2, vanadium oxide, lithium vanadium oxide, and other metal oxides capable of doping and dedoping lithium; or composites containing the above metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and one or a mixture of two or more of these may be used. In addition, a metallic lithium thin film may be used as the negative electrode active material. In addition, both low-crystalline carbon and high-crystalline carbon may be used as the carbonaceous material. Representative examples of low-crystalline carbon include soft carbon and hard carbon, and representative examples of high-crystalline carbon include natural graphite or artificial graphite in the form of amorphous, plate-like, flaky, spherical, or fiber-like forms, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch derived cokes.

[0101]

[0102] In one embodiment of the present invention, the conductive material is not particularly limited as long as it is conductive and does not cause a chemical change in the battery. Non-limiting examples thereof include graphite such as natural graphite or artificial graphite; carbon black-based carbon compounds such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; conductive fibers such as carbon fibers or metal fibers; metal powders such as fluorinated carbon, aluminum, and nickel powders; carbon nanotubes; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives. In a specific embodiment, the conductive material may include one or more selected from these.

[0103]

[0104] The above first binder polymer includes a polyvinylidene fluoride-based (PVDF-based) polymer.

[0105] In one embodiment of the present invention, for example, the polyvinylidene fluoride-based polymer may include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE), polyvinylidene fluoride-tetrafluoroethylene (PVDF-TFE), polyvinylidene fluoride-chlorofluoroethylene (PVDF-CTFE), or a mixture of two or more thereof. Since the electrode active material and PTFE have poor compatibility, when the polyvinylidene fluoride-based polymer is attached to the surface of the electrode active material, the polyvinylidene fluoride-based polymer can more strongly bind between the electrode active material and the PTFE. In addition, by reducing the area where the electrode active material is exposed to the electrolyte, side reactions can be reduced, thereby improving battery stability.

[0106]

[0107] In one embodiment of the present invention, the first binder polymer may include primary particles, and preferably, primary particles. PVDF-based polymers, which are typically manufactured by emulsion polymerization or suspension polymerization, are manufactured in the form of secondary particles. However, the first binder polymer according to one embodiment of the present invention may have a sufficiently small average particle diameter (D50) because the secondary particles are pulverized into primary particles. When the first binder is a primary particle or the proportion of primary particles is high so that the average particle diameter (D50) is sufficiently small, complexation with the electrode active material and the conductive material may occur well.

[0108]

[0109] In one embodiment of the present invention, the first binder polymer may be present in the form of primary particles at 50 wt% or more, 60 wt% or more, 70 wt% or more, 80 wt% or more, 90 wt% or more, or 95 wt% or more based on the total weight of the entire first binder polymer. When the proportion of the primary particles falls within the above range, complexation with the electrode active material and the conductive material can occur smoothly. When a process of filtering out particles larger than a specific particle size is performed after manufacturing the composite, the first binder polymer remaining in the form of secondary particles can be removed.

[0110]

[0111] In one embodiment of the present invention, the average particle diameter (D50) of the first binder polymer may be 500 nm or less, 400 nm or less, 320 nm or less, 200 nm or less, 190 nm or less, 180 nm or less, 170 nm or less, 160 nm or less, and may be 50 nm or more, 60 nm or more, 70 nm or more, or 80 nm or more. When the average particle diameter (D50) of the first binder polymer falls within the above range, complexation with the electrode active material and the conductive material may occur well. The first binder polymer may be present in the wrinkles formed on the surface of the electrode active material. However, when the average particle diameter (D50) of the first binder polymer exceeds 500 nm, it is difficult for it to be present in the wrinkles formed on the surface of the electrode active material, and thus it does not adhere well to the surface of the electrode active material, and the first binder polymers become tangled with each other to form lumps. Such lumps cause a problem of increasing the resistance of the battery.

[0112] The above average particle diameter (D50) can be measured, for example, using a laser diffraction method. The laser diffraction method can generally measure particle diameters from the submicron range to several mm, and can obtain highly reproducible and highly resolvable results. The average particle diameter (D50) of the artificial graphite can be defined as the particle diameter at 50% of the particle diameter distribution. For example, a method for measuring the average particle diameter (D50) of the artificial graphite includes dispersing artificial graphite in an ethanol / water solution, introducing the dispersion into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), irradiating the dispersion with ultrasonic waves of about 28 kHz at an output of 60 W, and then calculating the average particle diameter (D50) at 50% of the particle diameter distribution in the measuring device.

[0113]

[0114] In one embodiment of the present invention, at least a portion of the first binder polymer may have undergone plastic deformation. The first binder polymer undergoes plastic deformation during the composite process with the electrode active material and the conductive material, and is pressed and adhered to the surface of the electrode active material. Therefore, compared to a binder polymer that has not undergone plastic deformation, a first binder polymer that has undergone at least a portion of plastic deformation can secure superior bonding strength.

[0115]

[0116] In one embodiment of the present invention, among the entire first binder polymer, 80 wt% or more, 85 wt% or more, 90 wt% or more, 95 wt% or more, or 98 wt% or more of the first binder polymer may have undergone plastic deformation, and preferably, close to 100 wt% of the first binder polymer has undergone plastic deformation. When plastic deformation occurs in the first binder polymer, it can better adhere to the electrode active material. Therefore, when the proportion of the first binder polymer that has undergone plastic deformation falls within the above range, the bonding strength of the composite can be sufficiently secured.

[0117] The ratio of the first binder polymer in which the above plastic deformation occurred can be calculated by observing an image of the electrode active material layer using a transmission electron microscope (TEM) and measuring the number of first binder polymers in which plastic deformation occurred when 50 random first binder polymers are selected.

[0118]

[0119] The average aspect ratio of the first binder polymer is 1:1 to 1:3.

[0120] In one embodiment of the present invention, the average aspect ratio of the first binder polymer may be 1:1 to 1:3, 1:1 to 1:2.5, 1:1.1 to 1:3, 1:1.1 to 1:2.5, 1:1.1 to 1:2, or 1:1.2 to 1:2. When the average aspect ratio of the first binder polymer is out of the above range, it means that the first binder polymers, which are primary particles, aggregate to form large lumps. The large lumps do not adhere well to the surface of the electrode active material and act as resistance in the electrode. When the average aspect ratio of the first binder polymer falls within the above range, the first binder polymer exists in the form of primary particles and thus can adhere well to the surface of the electrode active material.

[0121]

[0122] The above average aspect ratio can be calculated by the method described in Equation 1 below.

[0123] (Formula 1) Aspect ratio = major axis / minor axis

[0124] The above “major axis” means the longest distance (d) among the vertical distances between two parallel tangent lines of the 2D image (cross-section) of the first binder polymer particle, and the “minor axis” means the shortest distance (d) among the vertical distances between two parallel tangent lines of the 2D image (cross-section) of the first binder polymer particle.

[0125] The above 2D image may be an image taken with a SEM (scanning electron microscope), and 10 random first binder polymers may be selected from the taken image, and the aspect ratio may be calculated for each of the selected first binder polymers using the above formula 1, and then the average value may be used as the “average aspect ratio of the first binder polymer” according to the present invention.

[0126]

[0127] In one embodiment of the present invention, the first binder polymer may be included in an amount of 0.1 to 3 parts by weight, 0.1 to 2.5 parts by weight, 0.3 to 2 parts by weight, or 0.5 to 1.5 parts by weight, based on 100 parts by weight of the total electrode active material layer. When the amount of the first binder polymer falls within the above range, the composite can be stably bound, and the composite can be bound to the second binder polymer with sufficient force.

[0128]

[0129] In one embodiment of the present invention, the second binder polymer may have a fiberized fibril structure. Accordingly, an electrode comprising the second binder polymer can secure flexibility, and when manufacturing an electrode, it can be easy to manufacture an electrode sheet.

[0130] The composite including the electrode active material, the conductive material, and the first binder polymer can be dispersed and positioned between the fiberized fibril structures, and the composite can exist by being bound to the second binder polymer.

[0131]

[0132] In one embodiment of the present invention, the second binder polymer may be included in an amount of 0.5 to 5 parts by weight, 1 to 3 parts by weight, or 1 to 2 parts by weight, based on a total of 100 parts by weight of the electrode active material layer. When the amount of the second binder polymer falls within the above range, the second binder polymer can well maintain a fibril structure and secure sufficient bonding strength with the composite.

[0133]

[0134] The second aspect of the present invention relates to a secondary battery.

[0135] A secondary battery according to one aspect of the present invention comprises a positive electrode; a negative electrode; a separator positioned between the positive electrode and the negative electrode; and an electrolyte.

[0136] It is characterized in that at least one of the above positive and negative electrodes is a dry electrode according to one aspect of the present invention.

[0137]

[0138] In one embodiment of the present invention, the secondary battery may include a lithium secondary battery. The lithium secondary battery may include a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery. The external shape of the lithium secondary battery is not particularly limited, but may be a cylindrical shape using a can, a square shape, a pouch shape, or a coin shape.

[0139]

[0140] In one embodiment of the present invention, when the dry electrode is a positive electrode, a negative electrode used in a conventional secondary battery can be applied as the negative electrode, and such a negative electrode will be described below.

[0141] In one embodiment of the present invention, the negative electrode may include a negative electrode current collector; and a negative electrode active material layer formed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer may include a negative electrode active material, a binder polymer, and a conductive material.

[0142] The above-described negative electrode active material layer may include graphite and a silicon-based compound as the negative electrode active material, and at this time, the graphite and the silicon-based compound may be included in a weight ratio of 70:30 to 99:1. In addition, the silicon-based compound may include silicon and / or silicon oxide, and the silicon oxide may include one or more compounds represented by the following chemical formula 1.

[0143]

[0144] [Chemical Formula 1]

[0145] SiO x

[0146] In the above chemical formula 1, 0≤x<2. In the above chemical formula 1, since SiO2 (when x=2 in the above chemical formula 1) does not react with lithium ions and thus cannot store lithium, it is preferable that x is less than 2. Specifically, in terms of the structural stability of the electrode active material, x may be 0.5≤x≤1.5.

[0147] The silicon-based compound may further include a carbon coating layer covering all or at least a portion of the surface of the active material particles. The carbon coating layer may function as a protective layer that suppresses volume expansion of the negative electrode active material particles including the silicon-based compound and prevents side reactions with the electrolyte. The carbon coating layer may be included in the silicon-based compound in an amount of 0.1 wt% to 10 wt%, preferably 3 wt% to 7 wt%, and when within the above range, the carbon coating layer is preferable in that it can control volume expansion of the negative electrode active material particles including the silicon-based compound at an excellent level while preventing side reactions with the electrolyte.

[0148] The negative active material particles containing the above silicon compound have a particle diameter (D 50 ) may be 3㎛ to 10㎛, preferably 3㎛ to 10㎛. The particle diameter (D 50 ) is less than 3㎛, the specific surface area is high, so the reaction area with the electrolyte increases, which may increase the frequency of side reactions with the electrolyte during charge and discharge, which may reduce the battery life. On the other hand, if it exceeds 10㎛, the volume change due to expansion / contraction of the active material particles during charge and discharge is large, which may cause problems such as deterioration of the battery performance due to breakage or cracking of the active material particles.

[0149] The graphite may include at least one selected from artificial graphite and natural graphite. The natural graphite may be unprocessed natural graphite such as flake graphite, spheroidal graphite, and earthy graphite, or spheroidal natural graphite. Flake graphite and spheroidal graphite exhibit almost complete crystallinity, while earthy graphite has lower crystallinity. In consideration of the aspect of electrode capacity, flake graphite and spheroidal graphite with high crystallinity may be used. For example, the flake graphite may be spheroidized and used. In the case of spheroidal natural graphite, the particle size may be 5 to 30 μm, preferably 10 to 25 μm.

[0150] The above artificial graphite can generally be manufactured by a graphitization method in which raw materials such as coal tar, coal tar pitch, and petroleum heavy oils are sintered at 2,500°C or higher, and after this graphitization, the particles are adjusted through grinding and secondary particle formation, and then used as a negative electrode active material.

[0151] Typically, artificial graphite has crystals randomly distributed within the particles, has a lower sphericity than natural graphite, and has a somewhat pointed shape. The artificial graphite may be in the form of powder, flakes, blocks, plates, or rods. However, it is preferable that the crystal grains have an isotropic orientation so that the migration distance of lithium ions is shortened to improve output characteristics. Considering these aspects, the artificial graphite may be in the form of flakes and / or plates.

[0152] The above artificial graphite includes MCMB (mesophase carbon microbeads), MPCF (mesophase pitch-based carbon fiber), artificial graphite graphitized in block form, and artificial graphite graphitized in powder form, which are widely used commercially. In addition, the artificial graphite may have a particle size of 5 to 30 μm, preferably 10 to 25 μm.

[0153] The specific surface area of ​​the above artificial graphite can be measured using the Brunauer-Emmett-Teller (BET) method. For example, it can be measured using the BET 6-point method by nitrogen gas adsorption flow using a porosimetry analyzer (Bell Japan Inc., Belsorp-II mini). This also applies to the measurement of the specific surface area of ​​natural graphite described below.

[0154] The tap density of the above artificial graphite may be 0.7 g / cc to 1.1 g / cc, and specifically 0.8 g / cc to 1.05 g / cc. If the tap density is less than 0.7 g / cc outside the above range, the contact area between particles is insufficient, resulting in a decrease in adhesive properties and a decrease in volumetric capacity. If the tap density exceeds 1.1 g / cc, the tortuosity of the electrode deteriorates and the wettability of the electrolyte deteriorates, resulting in a decrease in output properties during charge and discharge, which is not preferable.

[0155] Here, the tap density is obtained by placing 50 g of precursor in a 100 cc tapping cylinder using a COPLEY JV-1000 measuring instrument and a SEISHIN (KYT-4000) measuring instrument and performing 3000 tappings. This also applies to the tap density measurement of natural graphite described below.

[0156] In addition, the artificial graphite may have an average particle diameter (D50) of 8 ㎛ to 30 ㎛, specifically 12 ㎛ to 25 ㎛. When the average particle diameter (D50) of the artificial graphite is less than 8 ㎛, the initial efficiency of the secondary battery may decrease due to an increase in the specific surface area, thereby deteriorating the battery performance. When the average particle diameter (D50) exceeds 30 ㎛, the adhesive strength may decrease and the packing density may be low, thereby deteriorating the capacity.

[0157] The average particle diameter of the artificial graphite can be measured, for example, using a laser diffraction method. The laser diffraction method can generally measure particle diameters from the submicron range to several mm, and can obtain highly reproducible and highly resolvable results. The average particle diameter (D50) of the artificial graphite can be defined as the particle diameter at 50% of the particle diameter distribution. For example, a method for measuring the average particle diameter (D50) of the artificial graphite includes dispersing the artificial graphite in an ethanol / water solution, introducing the dispersion into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), irradiating the dispersion with ultrasonic waves of about 28 kHz at an output of 60 W, and then calculating the average particle diameter (D50) at 50% of the particle diameter distribution in the measuring device.

[0158] The conductive material may be, for example, one selected from the group consisting of graphite, carbon black, carbon nanotubes, carbon fibers or metal fibers, metal powders, conductive whiskers, conductive metal oxides, activated carbon, and polyphenylene derivatives, or a mixture of two or more conductive materials thereof. More specifically, the conductive material may be one selected from the group consisting of natural graphite, artificial graphite, super-p, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, Denka black, aluminum powder, nickel powder, zinc oxide, potassium titanate, and titanium oxide, or a mixture of two or more conductive materials thereof.

[0159] The negative current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, stainless steel, copper, aluminum, nickel, titanium, calcined carbon, or copper, aluminum, or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. can be used. The thickness of the negative current collector is not particularly limited, but can have a thickness of 3 to 500 ㎛, which is typically applied.

[0160] The above binder polymer may be a polymer commonly used in electrodes in the art. Non-limiting examples of such binder polymers include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-cotrichloroethylene, polymethylmethacrylate, polyethylhexyl acrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, and cellulose acetate propionate. Examples thereof include, but are not limited to, cellulose acetatepropionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, and carboxyl methyl cellulose.

[0161]

[0162] In one embodiment of the present invention, the separator may include a porous polymer substrate and a porous coating layer formed on at least one surface of the porous polymer substrate.

[0163] The above separator is not particularly limited as long as it is used as a separator for a secondary battery. As long as the separator has electrical insulating properties and can provide an ion conductive path, any separator that can be used as a separator for an electrochemical device in the present technical field may be used without limitation. For example, a porous sheet containing a polymer material such as a polymer film or non-woven fabric may be used as the separator. In one embodiment of the present invention, the separator may further have a heat-resistant coating layer containing inorganic particles or the like formed on the surface of the porous sheet.

[0164]

[0165] In one embodiment of the present invention, in the present invention, the electrolyte is A + B - As a salt with the same structure as A + is Li + , Na + , K + B containing an ion composed of an alkali metal cation or a combination thereof; - is PF6 - , BF4 - , Cl - , Br - , I - , ClO4 - , AsF6 - , CH3CO2 - , CF3SO3 - , N(CF3SO2)2 - , C(CF2SO2)3 -Salts containing anions such as or combinations thereof are dissolved or dissociated in organic solvents such as propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), gamma butyrolactone (g-butyrolactone) or mixtures thereof, but are not limited thereto.

[0166]

[0167] The third aspect of the present invention relates to a method for manufacturing a dry electrode.

[0168] A method for manufacturing a dry electrode according to one aspect of the present invention is as follows:

[0169] A step of preparing a composite by dry mixing and mixing an electrode active material, a conductive material, and a first binder polymer without a solvent;

[0170] A step of dry mixing and kneading the above complex and the second binder polymer without a solvent to prepare a mixture mass;

[0171] A step of crushing the above mixture lump to obtain a mixed powder for electrode;

[0172] A step of forming an electrode sheet by injecting the above electrode mixed powder between a plurality of rolls and performing a calendaring process is included, and a dry electrode manufactured according to the above manufacturing method is the dry electrode described above.

[0173]

[0174] Below, the manufacturing method of the dry electrode is explained in more detail.

[0175] First, a step of dry mixing and mixing an electrode active material, a conductive material, and a first binder polymer without a solvent to obtain a composite is performed.

[0176] This step is a step of mixing an active material, a conductive material, and a first binder polymer as components of an electrode sheet at a certain mixing ratio, attaching the conductive material and the first binder polymer to the surface of the electrode active material, and pulverizing at least a portion of the first binder polymer from secondary particles into primary particles.

[0177] When manufacturing a composite using a wet process using a solvent, the binder polymer must be dissolved in the solvent and then removed. However, this process can cause the binder polymer to agglomerate, increasing the average particle diameter (D50). Furthermore, the binder polymer's shape can become distorted, resulting in an amorphous shape, making it impossible to calculate the aspect ratio. These binder polymers can increase the resistance of the electrode.

[0178] However, in the present invention, a composite is obtained by mixing and mixing the electrode active material, conductive material, and first binder polymer in a dry manner without a solvent. Therefore, the first binder polymer can exist in the form of particles having a predetermined average aspect ratio, thereby achieving low resistance.

[0179] The above first binder polymer may be manufactured by emulsion polymerization or suspension polymerization and then pulverized into primary particles.

[0180]

[0181] In one embodiment of the present invention, the mixing is performed so that the electrode active material, the conductive material, and the first binder polymer can be uniformly distributed. Since these components are mixed in powder form, any method that allows simple mixing thereof is not limited and can be mixed by various methods. The mixing can be performed by dry mixing, and can be performed by putting the materials into a device such as a blender or a supermixer.

[0182] In one embodiment of the present invention, when the mixing is performed in a blender, the mixture may be prepared by mixing in the blender at 5,000 rpm to 20,000 rpm for 30 seconds to 20 minutes, specifically at 10,000 rpm to 15,000 rpm for 30 seconds to 5 minutes, to ensure uniformity.

[0183] In another embodiment of the present invention, when the mixing is performed in a supermixer, the mixing may be performed in the supermixer at 500 rpm to 2,500 rpm, specifically 1,000 rpm to 2,000 rpm, to ensure uniformity, and the process time may be adjusted accordingly.

[0184]

[0185] In one embodiment of the present invention, the mixing may be a process of uniformly distributing the electrode active material, the conductive material, and the first binder polymer, attaching the conductive material and the first binder polymer to the surface of the electrode active material, and pulverizing at least a portion of the first binder polymer, which is a secondary particle, into primary particles. In this process, the first binder polymer may be pulverized into primary particles and attached to the surface of the electrode active material.

[0186] The above mixing can be performed using a mechanofusion method or a mechanofusion device. The mechanofusion method involves placing a mixture into a rotating vessel, centrifugal force to secure the mixture to the inner wall of the vessel, and then compressing it through a gap between an arm head and the inner wall of the vessel, which is positioned slightly apart from the inner wall. For example, the mixing can be performed using a Nobilta device (Hosokawa Micron).

[0187] When the above mixing is performed by a mechanofusion method, at least a portion of the first binder polymer undergoes plastic deformation and can be attached to the electrode active material.

[0188] In one embodiment of the present invention, the mixing may be performed at 500 rpm to 7000 rpm, 500 to 5000 rpm, 1000 to 4000 rpm, or 2000 to 3000 rpm. When the mixing is performed at the above speed, the first binder polymer and the conductive material can be well bonded to the surface of the electrode active material to form a complex. In addition, when the mixing is performed at an excessively high speed, the surface of the electrode active material may be damaged.

[0189]

[0190] In one embodiment of the present invention, the mixing may be performed for a period of 5 to 60 minutes, 5 to 50 minutes, or 10 to 40 minutes. When the mixing is performed for the period of time, the first binder polymer and the conductive material may be well bonded to the surface of the electrode active material to form a composite.

[0191]

[0192] In one embodiment of the present invention, the mixing may be performed at a temperature of 10°C to 60°C, 10°C to 50°C, 10°C to 40°C, or 15°C to 30°C. When the mixing is performed at the above temperature, the first binder polymer has appropriate fluidity, so that the first binder polymer and the conductive material can be well bound to the surface of the electrode active material to form a composite.

[0193]

[0194] In one embodiment of the present invention, both mixing and blending can be performed through a mechanofusion device without using a separate mixing device.

[0195]

[0196] Next, a step of dry mixing and kneading the complex and the second binder polymer without a solvent to produce a mixture mass is performed.

[0197] The above step is a step of forming a mixture mass with 100% solid content by combining or connecting composite particles while the second binder polymer is fiberized through mixing.

[0198] The above mixing is not limited to a specific method. In a specific embodiment of the present invention, the mixing may be performed using a kneader, for example. Specifically, the mixing may be controlled at a speed of 10 rpm to 100 rpm or 20 rpm to 50 rpm. For example, the mixing may be controlled at a speed of 20 rpm or more or 70 rpm or less within the above range. The mixing may be performed for 1 minute to 30 minutes or 3 to 10 minutes. For example, the mixing may be performed at a speed of 20 rpm to 50 rpm within the above range for 3 minutes to 10 minutes. Meanwhile, the mixing may be controlled at a shear rate in the range of 10 / s to 500 / s. In a specific embodiment of the present invention, the mixing may be performed for 1 minute to 30 minutes, and the shear rate may be controlled in the range of 30 / s to 100 / s.

[0199] In addition, this mixing step can be performed under conditions of high temperature and pressure higher than atmospheric pressure, and more specifically, can be performed under conditions of pressure higher than atmospheric pressure. More specifically, the mixing can be performed at a temperature of 70°C to 200°C, and specifically, at a temperature of 90°C to 150°C. When the mixing is performed within the above temperature range, the fiberization and agglomeration of the second binder polymer due to mixing can be well achieved.

[0200]

[0201] Next, a step is performed to pulverize the mixture lump to obtain a mixed powder for electrodes. The mixture lump produced through the above-described kneading can be directly calendered, but in this case, the mixture lump may need to be pressed to produce a thin film, which may result in problems such as the film density becoming too high or the inability to obtain a uniform film. Therefore, according to the present invention, the produced mixture lump undergoes the above-described pulverization step.

[0202] At this time, the grinding step is not limited, but can be performed with a device such as a blender or grinder, and the grinding step can be specifically performed at a speed of 5,000 rpm to 20,000 rpm, or 10,000 rpm to 18,000 rpm. In addition, the grinding step can be performed for 5 seconds to 10 minutes, 5 seconds to 5 minutes, or 10 seconds to 2 minutes.

[0203]

[0204] Thereafter, a step of manufacturing an electrode sheet by feeding the mixed powder between a plurality of rolls and performing a calendering process is performed. The calendering may be a step of processing the mixed powder into a film form, and may be a step of manufacturing a film form through rolling so as to have an average thickness of, for example, 50 ㎛ to 300 ㎛. The calendering may be performed, for example, by one or more pairs of rolls facing each other, and the roll rotation may be controlled to have a rotation speed of 5 rpm to 20 rpm at a temperature of 25°C to 250°C or a temperature of 100°C to 200°C.

[0205]

[0206] Next, a step of manufacturing an electrode is performed by laminating the electrode sheet on at least one surface of an electrode current collector. In order to form an electrode film on at least one surface of the current collector in the lamination step, a step of rolling and attaching the electrode film to a predetermined thickness on the current collector may be further included. The lamination may be performed by a lamination roll, and at this time, the lamination roll may be controlled at a temperature of 25 to 250°C.

[0207]

[0208] Hereinafter, the present invention will be described in more detail through examples, but the following examples are intended to illustrate the present invention, and the scope of the present invention is not limited to these examples.

[0209]

[0210] Manufacturing Example 1: Dry method

[0211] Lithium nickel cobalt manganese aluminum composite oxide (Li(Ni, Co, Mn, Al)O2) was prepared as a cathode active material, PVDF with an average particle size of 160 nm was prepared as a first binder polymer, and carbon nanotubes were prepared as a conductive material. The cathode active material, the first binder polymer, and the carbon nanotubes were mixed in a dry manner without a solvent at a weight ratio of 98.5:0.5:1, and placed in Nobilta, and mixed at 23°C and 2500 rpm for 30 minutes to prepare a composite.

[0212]

[0213] Manufacturing Example 2: Wet Method

[0214] Lithium nickel cobalt manganese aluminum composite oxide (Li(Ni, Co, Mn, Al)O2) was prepared as a positive electrode active material, PVDF with an average particle size of 160 nm was prepared as a first binder polymer, and carbon nanotubes were prepared as a conductive material. The positive electrode active material, the first binder polymer, and the carbon nanotubes were mixed in a weight ratio of 98.5:0.5:1 in a solvent NMP, and dried at 130°C for 30 minutes to prepare a composite.

[0215]

[0216] Manufacturing Example 3: Dry method

[0217] A composite was manufactured in the same manner as in Manufacturing Example 1, except that PVDF-HFP (Polyvinylidene Fluoride-co-hexafluoropropylene) with an average particle diameter of 200 nm was used as the first binder polymer.

[0218]

[0219] Manufacturing Example 4: Dry method

[0220] A composite was manufactured in the same manner as in Manufacturing Example 1, except that PVDF with an average particle diameter of 320 nm was used as the first binder.

[0221]

[0222] Manufacturing Example 5: Dry method

[0223] A composite was manufactured in the same manner as in Manufacturing Example 1, except that PVDF with an average particle diameter of 140 μm was used as the first binder polymer.

[0224]

[0225] Figures 1 and 2 are SEM images of a composite manufactured using the method of Manufacturing Example 1. It was confirmed that the first binder polymer was attached to the wrinkles formed on the surface of the electrode active material.

[0226]

[0227] Figures 3 and 4 are SEM images of a composite manufactured using the method of Manufacturing Example 2. It was confirmed that the PVDF polymer was attached to the surface of the electrode active material in a molten state. It was confirmed that the PVDF polymer had lost its original spherical shape.

[0228]

[0229] Figures 5, 6, 10 to 13 are SEM images of composites manufactured in each manufacturing example, and the aspect ratio of the first binder polymer was measured by randomly selecting the composites.

[0230] Specifically, FIGS. 5 and 6 are for Manufacturing Example 1, FIGS. 10 and 11 are for Manufacturing Example 3, and FIGS. 12 and 13 are for Manufacturing Example 4. The aspect ratio measured in FIG. 5 was 1:1.97, the aspect ratio measured in FIG. 6 was 1:1.29, the aspect ratio measured in FIG. 10 was 1:1.16, the aspect ratio measured in FIG. 11 was 1:1.67, the aspect ratio measured in FIG. 12 was 1:2.76, and the aspect ratio measured in FIG. 13 was 1:1.62. In addition, it was confirmed that the first binder polymer was attached to the curves formed on the surface of the electrode active material in the composites of Manufacturing Examples 1, 3, and 4.

[0231]

[0232] Fig. 14 is a SEM image of the composite of Manufacturing Example 5, and Fig. 15 is an image taken by further enlarging the square portion of Fig. 14. Referring to Figs. 14 and 15, it can be confirmed that the size of the first binder polymer is much larger than the size of the electrode active material, and thus the electrode active material is attached to the surface of the first binder polymer. Therefore, the first binder polymer was unable to secure a bonding force between the electrode active material and / or the conductive material.

[0233]

[0234] The above aspect ratio was calculated by selecting any binder polymer particle from the SEM image, measuring the length of the major axis and the minor axis, and using Equation 1 below.

[0235] (Formula 1) Aspect ratio = major axis / minor axis

[0236] The above “major axis” means the longest distance (d) among the vertical distances between two parallel tangent lines of the 2D image (cross-section) of the first binder polymer particle, and the “minor axis” means the shortest distance (d) among the vertical distances between two parallel tangent lines of the 2D image (cross-section) of the first binder polymer particle.

[0237]

[0238] Example 1

[0239] The composite manufactured in Manufacturing Example 1 was mixed with PTFE in a dry manner without a solvent at a weight ratio of 98:2, placed in a blender, mixed at about 10,000 rpm for about 1 minute, placed in a kneader stabilized at about 150°C, and kneaded under about 1.1 atm to produce a mixture mass. At this time, the kneading was performed at a speed of about 25 rpm for about 5 minutes.

[0240] The above mixture lump was placed in a blender and ground for about 15 seconds under conditions of about 10,000 rpm to obtain a mixed powder for electrodes.

[0241] Then, the above electrode-use mixed powder was pressed into a roll calendar (roll diameter: 80 mm, roll temperature: about 80°C, about 10 rpm) to manufacture an electrode-use film, and the manufactured electrode-use film was subjected to a roll milling process twice to make the thickness about 90 μm.

[0242] The above electrode film was placed on one side of an aluminum thin film (approximately 16 ㎛ thick), bonded through a lamination process maintained at approximately 150°C, and rolled to manufacture a dry electrode having a thickness of approximately 80 ㎛.

[0243]

[0244] Example 2

[0245] A dry electrode was manufactured in the same manner as in Example 1, except that the composite manufactured in Manufacturing Example 3 was used.

[0246]

[0247] Example 3

[0248] A dry electrode was manufactured in the same manner as in Example 1, except that the composite manufactured in Manufacturing Example 4 was used.

[0249]

[0250] Comparative Example 1

[0251] A dry electrode was manufactured in the same manner as in Example 1, except that the composite manufactured in Manufacturing Example 2 was used.

[0252]

[0253] Comparative Example 2

[0254] A lithium nickel cobalt manganese aluminum composite oxide (Li(Ni, Co, Mn, Al)O2) was prepared as a cathode active material, carbon nanotubes as a conductive material, and PTFE as a binder polymer. The cathode active material, conductive material, and binder polymer were mixed in a dry manner without a solvent at a weight ratio of 96:2:2, placed in a blender, mixed at about 10,000 rpm for about 1 minute, placed in a kneader stabilized at about 150°C, and kneaded under about 1.1 atm to produce a mixture lump. At this time, the kneading was performed at a speed of about 25 rpm for about 5 minutes.

[0255] The above mixture lump was placed in a blender and ground for about 15 seconds under conditions of about 10,000 rpm to obtain a mixed powder for electrodes.

[0256] Then, the above electrode-use mixed powder was pressed into a roll calendar (roll diameter: 80 mm, roll temperature: about 80°C, about 10 rpm) to manufacture an electrode-use film, and the manufactured electrode-use film was subjected to a roll milling process twice to make the thickness about 90 μm.

[0257] The above electrode film was placed on one side of an aluminum thin film (approximately 16 ㎛ thick), bonded through a lamination process maintained at approximately 150°C, and rolled to manufacture a dry electrode having a thickness of approximately 80 ㎛.

[0258]

[0259] Comparative Example 3

[0260] An attempt was made to manufacture a dry electrode using the same method as Example 1, except that the composite manufactured in Manufacturing Example 5 was used, but electrode formation failed.

[0261]

[0262] Experimental Example 1: Tensile strength measurement

[0263] The tensile strength was measured using the electrodes manufactured in Example 1 and Comparative Example 2, and the results are shown in Table 1 below.

[0264] Specifically, tensile properties were measured by manufacturing each test piece according to the tensile test method of ASTM 412, and measuring the tensile strength at break and the tensile stress at 300% elongation (300% modulus) of the test piece. Specifically, tensile properties were measured at room temperature at a speed of 50 mm / min using a Universal Test Machin LS1 (Ametek) tensile tester.

[0265]

[0266] Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Composite method Dry Dry Dry Wet Dry Dry Composite type Manufacturing example 1 Manufacturing example 3 Manufacturing example 4 Manufacturing example 2-Manufacturing example 5 Type of first binder polymer PVDFPVDF-HFPPVDFPVDF-PVDF First binder polymer Average particle size 160 nm 200 nm 320 nm 160 nm-140 ㎛ Average aspect ratio 1:1.6 3 1:1.4 2 1:2.19 --- Tensile strength (gf / mm) 2 )46.9(±6.6)43.3(±4.1)41.2(±5.4)5.0Less than28.4(±1.0)-

[0267] Referring to Table 1 above, it can be confirmed that the tensile strength of the electrode manufactured in Example 1 is significantly higher than the tensile strength of the electrode manufactured in Comparative Example 2. This is because the first binder polymer on the surface of the electrode active material can increase the bonding strength between the electrode active materials and also assist in the elongation of the second binder polymer.

[0268]

[0269] Experimental Example 2: Observation of Plastic Deformation

[0270] SEM images of the composite manufactured in Manufacturing 1 are shown in enlarged form in Figs. 7, 8, and 9. Referring to Figs. 7 to 9, it can be confirmed that the PVDF is pressed onto the surface of the electrode active material in a partially elongated state (plastic deformation) while maintaining the shape of the primary particle.

[0271]

[0272] Experimental Example 3: Discharge Capacity Measurement

[0273] A 5:5 mixture of artificial graphite and natural graphite as negative active materials, superC as a conductive agent, and SBR / CMC as a binder were mixed in a weight ratio of 96:1:3 to produce a negative electrode slurry, which was then applied to one side of a copper current collector, dried at 130°C, and rolled to a porosity of 30% to produce a negative electrode.

[0274] An electrode assembly was manufactured by interposing a porous polyethylene separator between each of the positive electrodes manufactured in Example 1, Example 2, Example 3, and Comparative Example 1 and the negative electrode, and the electrode assembly was positioned inside a case, and then an electrolyte was injected into the case to manufacture a lithium secondary battery.

[0275] At this time, the electrolyte was used by dissolving 1.0 M lithium hexafluorophosphate (LiPF6) and 2 wt% vinylene carbonate (VC) in an organic solvent composed of ethylene carbonate / ethyl methyl carbonate / diethyl carbonate / (mixed volume ratio of EC / EMC / DEC = 3 / 4 / 3).

[0276] For the manufactured lithium secondary battery monocell, the discharge capacity was measured by discharging at different C-rates at 25°C. The results are shown in Fig. 16.

[0277] In Fig. 16, the x-axis represents each discharge C-rate. Then, when discharging at 0.1 C-rate, it was charged at 0.1 C-rate, and when discharging at 0.33 C-rate, 1 C-rate, 1.5 C-rate, and 2.5 C-rate, it was charged at 0.33 C. At this time, the voltage during the charge and discharge was set to 3 V to 4.25 V. As the C-rate increases, the electrical conductivity within the electrode becomes more dominant than the ionic conductivity. In the case of Comparative Example 1, the electrode active material was coated with a binder polymer, so the ionic conductivity on the surface of the electrode active material was lower. Therefore, when discharging at a high C-rate (2.5 C-rate), the ion movement speed compared to the current decreased rapidly, and a significantly lower capacity was measured compared to Examples 1, 2, and 3.

[0278]

[0279] As described above, although the present invention has been described by limited embodiments and drawings, the present invention is not limited thereto, and it is obvious that various modifications and variations are possible within the scope of the technical idea of ​​the present invention and the equivalent scope of the patent claims to be described below by a person having ordinary skill in the art to which the present invention pertains.

Claims

1. Including an electrode current collector and an electrode active material layer positioned on at least one surface of the electrode current collector, The electrode active material layer includes a composite in which an electrode active material, a conductive material, and a first binder polymer are complexed, and a fiberized second binder polymer, The first binder polymer comprises polyvinylidene fluoride (PVDF), The second binder polymer comprises polytetrafluoroethylene (PTFE), A dry electrode characterized in that the average aspect ratio of the first binder polymer is 1:1 to 1:

3.

2. In paragraph 1, A dry electrode characterized in that the average aspect ratio of the first binder polymer is 1:1 to 1:2.

5.

3. In paragraph 1, A dry electrode, characterized in that the average particle diameter (D50) of the first binder polymer is 500 nm or less.

4. In paragraph 1, A dry electrode characterized in that the average particle diameter (D50) of the first binder polymer is 400 nm or less.

5. In paragraph 1, A dry electrode, characterized in that the first binder polymer comprises primary particles.

6. In paragraph 1, A dry electrode characterized in that the first binder polymer comprises primary particles at a ratio of 50% by weight or more with respect to the total 100% by weight.

7. In paragraph 1, A dry electrode characterized in that in the above complex, at least a portion of the first binder polymer is plastically deformed and attached to the surface of the electrode active material.

8. In paragraph 1, The above complex is one in which the first binder polymer and the conductive material are attached to the surface of the electrode active material, A dry electrode characterized in that the second binder polymer is dispersed in a fiberized fibril structure.

9. In paragraph 1, A dry electrode, characterized in that the first binder polymer is included in an amount of 0.1 to 3 parts by weight relative to a total of 100 parts by weight of the electrode active material layer.

10. In paragraph 1, A dry electrode, characterized in that the second binder polymer is included in an amount of 0.5 to 5 parts by weight relative to a total of 100 parts by weight of the electrode active material layer.

11. In a secondary battery comprising a positive electrode; a negative electrode; a separator positioned between the positive electrode and the negative electrode; and an electrolyte, A secondary battery characterized in that at least one of the positive and negative electrodes is a dry electrode according to any one of claims 1 to 10.

12. A step of preparing a composite by dry mixing and mixing an electrode active material, a conductive material, and a first binder polymer without a solvent; A step of dry mixing and kneading the above complex and the second binder polymer without a solvent to prepare a mixture mass; A step of crushing the above mixture lump to obtain a mixed powder for electrode; A step of forming an electrode sheet by injecting the above electrode mixed powder between a plurality of rolls and performing a calendaring process; and A method for manufacturing a dry electrode according to claim 1, comprising the step of laminating the electrode sheet on a current collector.

13. In paragraph 12, The steps of manufacturing the above complex are: A dry electrode manufacturing method characterized by preparing a mixture by mixing an electrode active material, a conductive material, and a first binder polymer as secondary particles, mixing the mixture to pulverize the first binder polymer as secondary particles into primary particles, and attaching the conductive material and the primary particles of the first binder polymer to the surface of the electrode active material to manufacture a composite.

14. In paragraph 12, A dry electrode manufacturing method characterized in that at least a portion of the first binder polymer is plastically deformed in the step of manufacturing the above complex.

Images