Dry electrode and manufacturing method thereof

Abstract

A dry electrode according to the present invention employs: a first binder polymer in which a polymer including polytetrafluoroethylene is fibrillated; and a second binder polymer which has a complex viscosity of 1 Pa·s to 1500 Pa·s at 170°C and 0.1 Hz, thereby improving indentation stiffness, such as the elastic indentation modulus and indentation hardness, while ensuring sufficient tensile strength.

Description

Dry electrode and method of manufacturing the same

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

[0002] This application claims priority based on Korean Application No. 10-2024-0168749 filed on November 22, 2024, and all contents disclosed in the specification of said application are incorporated into this application.

[0003] Due to the rapid increase in the use of fossil fuels, there is a growing demand for alternative and clean energy. As part of this effort, the fields of power generation and energy storage utilizing electrochemistry are the most actively researched.

[0004] Currently, a representative example of an electrochemical device utilizing such electrochemical energy is the secondary battery, and its scope of application is steadily expanding.

[0005] Among these secondary batteries, the representative lithium-ion battery is not only used as an energy source for mobile devices, but recently, its use as a power source for electric vehicles and hybrid electric vehicles capable of replacing fossil fuel-using vehicles such as gasoline and diesel cars, which are one of the major causes of air pollution, is being realized, and its scope of application is expanding to include uses such as auxiliary power sources through grid integration.

[0006] The manufacturing process of such lithium secondary batteries is broadly divided into three stages: electrode process, assembly process, and formation process. The electrode process is further divided into active material mixing process, electrode coating process, drying process, rolling process, slitting process, and winding process.

[0007] Among these, the active material mixing process is a process for mixing a coating material for forming an electrode active layer where actual electrochemical reactions occur at the electrode, and more 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 between powders and adhesion to a current collector, and a solvent for imparting viscosity and dispersing powders, to produce a fluid slurry.

[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] Subsequently, 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. Additionally, the electrode is rolled to produce a predetermined thickness.

[0010] Meanwhile, as the solvent contained in the electrode mixture evaporates during the drying process, defects such as pinholes or cracks may be induced in the pre-formed electrode active layer. Additionally, since the inner and outer surfaces of the active layer are not dried uniformly, powder floating may occur due to differences in solvent evaporation rates; that is, powders from the areas that dry first may rise to form gaps with the areas that dry relatively later, potentially degrading the electrode quality.

[0011] Therefore, research on manufacturing solvent-free dry electrodes has been actively conducted recently.

[0012] The above dry electrode is generally manufactured by laminating a free-standing film, which is manufactured in the form of a film and includes an active material, a fiberizable binder polymer, a conductive material, etc., onto a current collector.

[0013] However, when using a binder polymer that can be fiberized, the manufactured dry electrode has the problem of having excessively weak compression stiffness, and when applied to a secondary battery, there were problems with poor cycle life and capacity retention rate, and increased resistance.

[0014] Therefore, there is an urgent need to develop dry electrode manufacturing technology capable of solving these problems.

[0015] The problem that the present invention aims to solve is to provide a dry electrode with improved compression stiffness while manufacturing the dry electrode using a binder polymer fiberization method, and to provide a battery with improved cycle life, capacity retention rate, and resistance.

[0016] In one aspect of the present invention, a dry electrode of the following embodiments and a method for manufacturing the same are provided. In another aspect of the present invention, a secondary battery comprising the dry electrode is provided.

[0017] The dry electrode according to the first embodiment is,

[0018] The electrode current collector; and an electrode active material layer formed on at least one surface of the electrode current collector, comprising

[0019] The above electrode active material layer comprises an electrode active material, a conductive material, a first binder polymer, and a second binder polymer, and

[0020] The first binder polymer mentioned above is a polymer containing polytetrafluoroethylene that has been fiberized, and

[0021] The second binder polymer is characterized by having a composite viscosity of 1 Pa·s to 1500 Pa·s at 170°C and 0.1 Hz.

[0022] The dry electrode according to the second embodiment is, in the first embodiment,

[0023] The second binder polymer may have a composite viscosity of 1 Pa·s to 1000 Pa·s at 170°C and 0.1 Hz.

[0024] The dry electrode according to the third embodiment is, in the first embodiment or the second embodiment,

[0025] The above second binder polymer may have an average particle size (D50) of 50㎛ or less.

[0026] The dry electrode according to the fourth embodiment is, in any one of the first to third embodiments,

[0027] The above second binder polymer may have an average particle size (D50) of 0.1 μm to 50 μm.

[0028] The dry electrode according to the fifth embodiment is, in any one of the first to fourth embodiments,

[0029] The above second binder polymer may have a melt index of 100 g / 10 min or more when a load of 2.16 kg is applied at 230°C.

[0030] The dry electrode according to the 6th embodiment is, in any one of the 1st to 5th embodiments,

[0031] The first binder polymer and the second binder polymer may be included in an amount of 1 to 5 parts by weight per 100 parts by weight of the total electrode active material layer.

[0032] The dry electrode according to the seventh embodiment is, in any one of the first to sixth embodiments,

[0033] The weight ratio of the first binder polymer and the second binder polymer may be 6:1 to 2:1.

[0034] The dry electrode according to the 8th embodiment is, in any one of the 1st to 7th embodiments,

[0035] The second binder polymer may include one or more of a polyolefin-based polymer and a polyvinylidene fluoride-based polymer.

[0036] The dry electrode according to the ninth embodiment is, in any one of the first to eighth embodiments,

[0037] The second binder polymer may be polypropylene or polyvinylidene fluoride.

[0038] The dry electrode according to the 10th embodiment is, in any one of the 1st to 9th embodiments,

[0039] The above dry electrode has a tensile strength of 30 gf / mm 2 It could be more than that.

[0040] The dry electrode according to the 11th embodiment is, in any one of the 1st to 10th embodiments,

[0041] The elastic indentation modulus can be 3 GPa or more.

[0042] The secondary battery according to the 12th embodiment is,

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

[0044] At least one of the anode and cathode is an electrode according to any one of the first to twelfth embodiments.

[0045] The dry electrode manufacturing method according to the 13th embodiment is,

[0046] (S1) A step of obtaining a mixture by dry mixing of an electrode active material; a conductive material, a first binder polymer and a second binder polymer without a solvent;

[0047] (S2) A step of kneading the above mixture to produce a mass of the mixture;

[0048] (S3) A step of crushing the above mixture lumps to obtain a mixed powder for electrodes;

[0049] (S4) A step of manufacturing an electrode sheet by feeding the above-mentioned mixed powder between a plurality of rolls and performing calendering processing; and

[0050] (S5) A step of manufacturing an electrode by laminating the above electrode sheet onto at least one surface of an electrode current collector; comprising,

[0051] The first binder polymer above comprises polytetrafluoroethylene, and

[0052] The second binder polymer is characterized by having a composite viscosity of 1 Pa·s to 1500 Pa·s at 170°C and 0.1 Hz.

[0053] A dry electrode according to one aspect of the present invention comprises a binder polymer having a composite viscosity of 1 Pa·s to 1500 Pa·s at 170°C and 0.1 Hz together with a fiberizable binder polymer, and the compression stiffness is improved.

[0054] Specifically, the elastic indentation modulus of the dry electrode is improved. In addition, the indentation hardness of the dry electrode is improved.

[0055] 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 interpreted as being limited to their ordinary or dictionary meanings, and should be interpreted in a meaning and concept consistent with the technical spirit of the present invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0056] Therefore, the embodiments described in this specification and the configurations described in the drawings are merely the most preferred embodiments of the present invention and do not represent all of the technical ideas of the present invention; thus, it should be understood that various equivalents and modifications that can replace them may exist at the time of filing this application.

[0057] Furthermore, throughout the specification, when a part is described as "include, comprise," "have," or "possess" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0058] Additionally, terms such as 'about,' 'substantially,' etc., used throughout this specification are used to mean at or near the stated value when inherent manufacturing and material tolerances are presented in the said sense, and are used to prevent unscrupulous infringers from unfairly exploiting the disclosure in which precise or absolute values ​​are mentioned to aid in understanding this invention.

[0059] Throughout this specification, the description of 'A and / or B' means 'A or B or both.'

[0060] Throughout the entire specification, unless otherwise specifically stated, temperature refers to Celsius temperature, and the unit is °C.

[0061] In this specification, “particle size Dn” refers to the particle size at the n% point of the cumulative distribution of particle volume according to particle size. That is, D50 is the particle size at the 50% point of the cumulative distribution of particle volume according to particle size, D90 is the particle size at the 90% point of the cumulative distribution of particle volume according to particle size, and D10 is the particle size at the 10% point of the cumulative distribution of particle volume according to particle size. The above Dn can be measured using the laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g., Malvern; mastersizer 3000) and the difference in diffraction patterns according to particle size is measured as the particles pass through the laser beam to calculate the particle size distribution. D10, D50, and D90 can be measured by calculating the particle diameter at the point where the cumulative distribution of the number of particles according to the particle size in the measuring device reaches 10%, 50%, and 90%.

[0062] In this specification, unless otherwise specified, complex viscosity is measured using an Advanced Rheometric Expansion System (ARES-G2) at 170°C and with the frequency changed stepwise from 0.01 Hz to 100 Hz. Additionally, it is measured at a strain (1% to 10%) in a range where linear viscoelastic properties can be secured according to the viscosity of each polymer.

[0063] In this specification, the melt index (melt flow index, MFI) is measured under conditions of 230°C and 2.16 kg according to ASTM D-1238 unless otherwise specified.

[0064]

[0065] The first aspect of the present invention relates to a dry electrode.

[0066] A dry electrode according to one aspect of the present invention is,

[0067] The electrode current collector; and an electrode active material layer formed on at least one surface of the electrode current collector, comprising

[0068] The above electrode active material layer comprises an electrode active material, a conductive material, a first binder polymer, and a second binder polymer, and

[0069] The first binder polymer mentioned above is a polymer containing polytetrafluoroethylene (PTFE) that has been fiberized, and

[0070] The second binder polymer is characterized by having a composite viscosity of 1 to 1500 Pa·s at 170°C and 0.1 Hz.

[0071]

[0072] Conventional electrode active material layers for dry electrodes utilize a binder polymer capable of fiberization, having a structure in which the fiberized binder polymer binds the active material and the conductive material. The fiberized polymer has excellent elongation in the longitudinal direction, which has the advantage of improving the flexibility of the electrode active material layer and the electrode. However, dry electrodes manufactured using a fiberized binder polymer have a problem in that their compression stiffness is very weak.

[0073] Accordingly, in the present invention, a binder polymer having a composite viscosity of 1 Pa·s to 1500 Pa·s at 170°C and 0.1 Hz is applied together with a fiberizable binder polymer in the electrode active material layer to significantly improve compression stiffness.

[0074]

[0075] 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. For example, the current collector may be made of 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 irregularities formed on its surface to increase the adhesion of the active material, and may take various forms such as a film, sheet, foil, net, porous body, foam, or nonwoven 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. For example, the current collector may have a thickness of 10 μm to 20 μm.

[0076]

[0077] In one embodiment of the present invention, the electrode active material may be a positive electrode active material or a negative electrode active material. The positive electrode active material is not limited to lithium transition metal oxides or lithium metal iron phosphate, provided it is in the form of a metal oxide, and may include, for example, a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound 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, etc.; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiFe3O4, V2O5, Cu2V2O7, etc.; 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 ~ 0.3); chemical formula LiMn 2-x M xLithium manganese composite oxides represented by O2 (where M = Co, Ni, Fe, Cr, Zn, or Ta, and x = 0.01–0.1) or Li2Mn3MO8 (where M = Fe, Co, Ni, Cu, or Zn); LiMn2O4 in which part of the Li in the chemical formula is substituted with alkaline earth metal ions; lithium metal phosphate LiMPO4 (where M = Fe, CO, Ni, or Mn), LiNi 1-x-y-z Co x M1 y M2 z O2(M1 and M2 are independently selected from the group consisting of Al, Ni, Fe, Mn, V, Cr, Ti, W, Ta, Mg and Mo, and x, y and z are independently atomic fractions of oxide composition elements as 0 <x<0.5, 0<y<0.5, 0<z<0.5, 0<x+y+z≤1), 디설파이드 화합물; Fe2(MoO4)3 등을 들 수 있지만, 이들만으로 한정되는 것은 아니다.

[0078] In addition, the above-mentioned negative electrode active material is carbon such as non-graphitizable carbon, graphite-based carbon, etc.; Li x Fe2O3(0≤x≤1), Li x WO2(0≤x≤1), Sn x Me 1-x Me y O z Metal composite oxides of (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, Group 1, 2, and 3 elements of the periodic table, halogens; 0≤x≤1; 1≤y≤3; 1≤z≤8), etc.; lithium metal; lithium alloy; silicon alloy; tin alloy; SiO, SiO / C, SiO 2　 Silicon-based 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.

[0079]

[0080] According to one embodiment of the present invention, the electrode active material may, in detail, be a positive electrode active material, and more specifically, may be a lithium transition metal oxide, a lithium nickel-manganese-cobalt oxide, an oxide in which a portion of the lithium nickel-manganese-cobalt oxide is substituted with Al or another transition metal, a lithium iron phosphate, etc.

[0081]

[0082] In one embodiment of the present invention, the conductive material is not particularly limited as long as it is conductive without causing chemical changes 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 thermal black; conductive fibers such as carbon fibers or metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; carbon nanotubes; conductive whiskies 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.

[0083]

[0084] In one embodiment of the present invention, the first binder polymer and the second binder polymer may be included in an amount of 1 to 5 parts by weight per 100 parts by weight of the total electrode active material layer. When the content of the binder polymer is within the above range, strong adhesion can be produced between the components of the electrode active material layer.

[0085]

[0086] In one embodiment of the present invention, the first binder polymer and the second binder polymer may be included in a weight ratio of 6:1 to 2:1, 5:1 to 2:1, 6:1 to 3:1, 5:1 to 3:1, or 4:1 to 3:1. When the first binder polymer and the second binder polymer are included in the above weight ratios, the compression strength of the dry electrode can be significantly improved.

[0087]

[0088] In one embodiment of the present invention, the average particle size (D50) of the second binder polymer may be 50 μm or less, 45 μm or less, 40 μm or less, 35 μm or less, 30 μm or less, 25 μm or less, 20 μm or less, 15 μm or less, 0.1 μm or more, or 0.2 μm or more. When the average particle size of the second binder polymer falls within the above range, the compression stiffness of the electrode active material layer is greatly improved, and excellent dispersibility is achieved so that it can be well dispersed between the electrode active material layers.

[0089]

[0090] In one embodiment of the present invention, the second binder polymer may have a composite viscosity of 1500 Pa·s or less, 1000 Pa·s or less, 500 Pa·s or less, 300 Pa·s or less, 144 Pa·s or less, or 70 Pa·s or less at 170°C and 0.1 Hz, and may have a viscosity of 0.1 Pa·s or more, 0.5 Pa·s or more, 1 Pa·s or more, 3 Pa·s or more, 5 Pa·s or more, 10 Pa·s or more, or 18 Pa·s or more. For example, the second binder polymer may have a composite viscosity of 0.1 to 1500 Pa·s, 1 to 1000 Pa·s, 3 to 500 Pa·s, 5 to 300 Pa·s, 10 to 300 Pa·s, or 18 to 144 Pa·s at 170°C and 0.1 Hz.

[0091] When the second binder polymer has a composite viscosity within the above range, it has high fluidity and excellent dispersibility, so it can be well mixed with the conductive material and electrode active material even in an environment where no solvent is present. Accordingly, the electrode containing the second binder polymer can have improved indentation stiffness, such as elastic indentation modulus and indentation hardness, and can secure appropriate life characteristics and discharge capacity characteristics of the secondary battery.

[0092]

[0093] In one embodiment of the present invention, the melt index of the second binder polymer when a load of 2.16 kg is applied at 230°C may be 100 g / 10 min or more, 200 g / 10 min or more, 300 g / 10 min or more, 400 g / 10 min or more, 500 g / 10 min or more, 600 g / 10 min or more, 700 g / 10 min or more, 800 g / 10 min or more, 900 g / 10 min or more, 1000 g / 10 min or more, 1300 g / 10 min or more, or 1500 g / 10 min or more. When the melt index of the second binder polymer falls within the above range, the compression strength of the electrode can be improved.

[0094]

[0095] In one embodiment of the present invention, the second binder polymer may include one or more of a polyolefin-based polymer and a polyvinylidene fluoride-based polymer.

[0096] For example, it may include polyethylene, polypropylene, polybutylene, polypentene, or two or more of these. And, 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), polytetrafluoroethylene (PTFE), or two or more of these.

[0097]

[0098] In one embodiment of the present invention, the electrode active material layer may further include other binder polymers in addition to the first binder polymer and the second binder polymer described above.Binder polymers that may be further included in the electrode active material layer include styrene butadiene rubber (SBR), butadiene rubber (BR), nitrile butadiene rubber (NBR), styrene butadiene styrene block polymer (SBS), styrene ethylene butadiene block polymer (SEB), styrene-(styrene butadiene)-styrene block polymer, natural rubber (NR), isoprene rubber (IR), ethylene-propylene-diene terpolymer (EPDM), poly(ethylene-co-propylene-co-5-methylene-2-norbornene) polytetrafluoroethylene (PTFE), polyvinylidene fluoride, polyvinyl chloride, and polyvinylidene fluoride-co-hexafluoropropylene copolymer. It may be polyvinylidene fluoride-co-trichloroethylene copolymer, polymethylmethacrylate, polyethylhexylacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene, polypropylene, polyethylene-co-vinyl acetate copolymer, polyethylene oxide, polypropylene oxide, polyarylate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, or may contain two or more of these.Specifically, the binder polymer may include styrene butadiene rubber (SBR), nitrile butadiene rubber (NBR), polymethylmethacrylate, polyethylhexyl acrylate, and polybutyl acrylate. Additionally, the binder polymer may include one or more selected from these.

[0099]

[0100] In one embodiment of the present invention, the tensile strength of the dry electrode is 20 gf / mm 2 Above, 30gf / mm 2 Above, 40gf / mm 2 ≥ 50gf / mm 2 It may be more than that. Even if a second binder polymer is further included in addition to the fiberized first binder polymer, the dry electrode of the present invention can secure sufficient tensile strength because the second binder polymer has the composite viscosity described above.

[0101] The above tensile strength can be obtained by fabricating a sheet specimen for dry electrodes with a width of 50 mm, a length of 15 mm, and a thickness of 85 μm to 90 μm, fixing it to a jig for measuring tensile strength, and then using a universal testing machine (LLOYD LS1, load cell 10N) to pull it in a 180° direction at a speed of 2 mm / min at 25°C, drawing a stress-strain graph, and measuring the stress value at the highest point on the graph.

[0102]

[0103] In one embodiment of the present invention, the elastic indentation modulus of the dry electrode may be 2.5 GPa or more, 3.0 GPa or more, or 3.5 GPa or more.

[0104] In one embodiment of the present invention, the indentation hardness of the dry electrode is 120 N / mm 2 Above, 130N / mm 2Above, 140N / mm 2 Above, or 150 N / mm 2 It could be more than that.

[0105] The above elastic indentation modulus and indentation hardness can be measured using nano-indentation (NHT, Anton Paar, Austria) under conditions of a maximum load range of 40 mN, a loading rate of 40 mN / min, a pause of 10 sec, and an unloading rate of 40 mN / min.

[0106]

[0107] A second aspect of the present invention relates to a secondary battery.

[0108] A secondary battery according to one aspect of the present invention is,

[0109] A positive electrode; a negative electrode; a separator disposed between the positive electrode and the negative electrode; and an electrolyte, comprising

[0110] At least one of the anode and cathode is characterized as being a dry electrode according to one aspect of the present invention.

[0111]

[0112] 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 cylindrical using a can, prismatic, pouch-type, or coin-type.

[0113]

[0114] In one embodiment of the present invention, the cathode may include a cathode current collector; and a cathode active material layer formed on at least one surface of the cathode current collector, and the cathode active material layer may include a cathode active material, a binder polymer, and a conductive material.

[0115] The above negative electrode active material layer may include graphite and a silicon-based compound as negative electrode active materials, wherein the graphite and the silicon-based compound may be included in a weight ratio in the range 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 Chemical Formula 1 below.

[0116]

[0117] [Chemical Formula 1]

[0118] SiO x

[0119] In the above chemical formula 1, 0 ≤ x < 2. In the above chemical formula 1, since SiO2 (where x=2 in the above chemical formula 1) does not react with lithium ions and therefore cannot store lithium, it is preferable that x be less than 2. Specifically, in terms of the structural stability of the electrode active material, x may be 0.5 ≤ x ≤ 1.5.

[0120] The silicon-based compound may further include a carbon coating layer that covers the surface of the active material particles in whole or at least part of it. The carbon coating layer may function as a protective layer that suppresses volume expansion of the negative electrode active material particles containing the silicon-based compound and prevents adverse reactions with the electrolyte. The carbon coating layer may be included in the silicon-based compound in an amount of 0.1% to 10% by weight, preferably 3% to 7% by weight. This range is preferable in that the carbon coating layer can control the volume expansion of the negative electrode active material particles containing the silicon-based compound to an excellent level while preventing adverse reactions with the electrolyte.

[0121] The negative electrode active material particles containing the above silicon-based compound have a particle size (D 50 ) may be 3㎛ to 10㎛, preferably 3㎛ to 10㎛. The particle size (D 50If the specific surface area is less than 3㎛, the reaction area with the electrolyte increases due to the high specific surface area, which may increase the frequency of side reactions with the electrolyte during charging and discharging, and consequently, the battery life may be reduced. On the other hand, if it exceeds 10㎛, the volume change due to the volume expansion / contraction of active material particles during charging and discharging is large, which may lead to problems such as the active material particles breaking or cracking, resulting in a decrease in battery performance due to degradation.

[0122] The graphite may include at least one type selected from artificial graphite and natural graphite. The natural graphite may be unprocessed natural graphite such as flake graphite, sculpted graphite, or earthy graphite, or spherical natural graphite. Flake graphite and sculpted graphite exhibit nearly perfect crystals, while earthy graphite has lower crystallinity. Flake graphite and sculpted graphite with high crystallinity may be used in consideration of electrode capacitance. For example, the flake graphite may be spherical for use. In the case of spherical natural graphite, the particle size may have a particle diameter of 5 to 30 μm, preferably 10 to 25 μm.

[0123] 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-based heavy oils are sintered at 2,500°C or higher, and after such graphitization, it is used as a negative electrode active material after undergoing particle size adjustment such as grinding and secondary particle formation.

[0124] Typically, artificial graphite has crystals randomly distributed within the particles and has a lower degree of sphericity and a somewhat pointed shape compared to natural graphite. The artificial graphite may be in powder, flake, block, plate, or rod form, but it is desirable for the degree of grain orientation to be isotropic so that the travel distance of lithium ions is shortened to improve output characteristics. Considering this aspect, it may be in flake and / or plate form.

[0125] The above artificial graphite includes commercially widely used MCMB (mesophase carbon microbeads), MPCF (mesophase pitch-based carbon fiber), artificial graphite graphitized in block form, and artificial graphite graphitized in powder form. In addition, the above artificial graphite may have a particle size of 5 to 30 μm, preferably 10 to 25 μm.

[0126] The specific surface area of ​​the above artificial graphite can be measured by the BET (Brunauer-Emmett-Teller) method. For example, it can be measured by the BET 6-point method using a pore analysis analyzer (Bell Japan Inc, Belsorp-II mini) via the nitrogen gas adsorption flow method. The measurement of the specific surface area of ​​natural graphite described below also follows this.

[0127] The tap density of the artificial graphite above may be 0.7 g / cc to 1.1 g / cc, and more specifically, 0.8 g / cc to 1.05 g / cc. If the tap density is outside the above range and is less than 0.7 g / cc, the contact area between particles is insufficient, resulting in reduced adhesion characteristics and reduced capacity per volume; if it exceeds 1.1 g / cc, the tortuosity of the electrode and the wet-ability of the electrolyte are reduced, which is undesirable as it causes a problem of reduced output characteristics during charging and discharging.

[0128] Here, the tap density is determined by placing 50g of precursor into a 100cc tapping cylinder and applying 3,000 taps using a JV-1000 measuring instrument from COPLEY or a SEISHIN (KYT-4000) measuring instrument. This applies to the measurement of tap density of natural graphite described below.

[0129] Additionally, the artificial graphite may have an average particle size (D50) of 8 μm to 30 μm, specifically 12 μm to 25 μm. If the average particle size (D50) of the artificial graphite is less than 8 μm, the initial efficiency of the secondary battery may decrease due to an increase in the specific surface area, and thus the battery performance may be degraded. If the average particle size (D50) exceeds 30 μm, the adhesive strength may decrease and the capacity may be reduced because the packing density is low.

[0130] The average particle size of the artificial graphite can be measured, for example, using a laser diffraction method. The laser diffraction method generally enables the measurement of particle sizes ranging from the submicron region to several millimeters, and allows for the acquisition of results with high reproducibility and high resolution. The average particle size (D50) of the artificial graphite can be defined as the particle size at 50% of the particle size distribution. A method for measuring the average particle size (D50) of the artificial graphite can be, for example, by dispersing the artificial graphite in an ethanol / water solution, introducing it into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), irradiating it with ultrasound of approximately 28 kHz at an output of 60 W, and then calculating the average particle size (D50) at 50% of the particle size distribution in the measuring device.

[0131] The conductive material may be, for example, any one selected from the group consisting of graphite, carbon black, carbon nanotubes, carbon fibers or metal fibers, metal powder, conductive whiskers, conductive metal oxides, activated carbon, and polyphenylene derivatives, or a mixture of two or more of these conductive materials. More specifically, it 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, thermal black, Denka black, aluminum powder, nickel powder, zinc oxide, potassium titanate, and titanium oxide, or a mixture of two or more of these conductive materials.

[0132] The above-mentioned 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 a surface treated with carbon, nickel, titanium, silver, etc. on the surface of copper, aluminum, or stainless steel may be used. The thickness of the above-mentioned current collector is not particularly limited, but it may have a thickness of 3 to 500 μm, which is commonly applied.

[0133] The above binder polymer may be a polymer commonly used in the industry for electrodes. 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 copolymer, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, and cellulose acetate propionate. Examples include acetatepropionate), cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, and carboxyl methyl cellulose, but are not limited thereto.

[0134]

[0135] 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.

[0136] The above separator is not particularly limited as long as it is used as a separator for a secondary battery. The above separator may be used without limitation as long as it has electrical insulation properties and can provide an ion conduction path, and can be used as a separator for an electrochemical device in the art. For example, a porous sheet containing a polymer material, such as a polymer film or a nonwoven fabric, may be used as a separator. In one embodiment of the present invention, the separator may further have a heat-resistant coating layer containing inorganic particles, etc., formed on the surface of the porous sheet.

[0137]

[0138] In one embodiment of the present invention, in the present invention, the electrolyte is A + B - As a salt with a structure like that, A + is Li + , Na + , K + It includes alkali metal cations such as or ions composed of combinations thereof, and B - is PF6 - , BF4 - , Cl - , Br - , I - , ClO4 - , AsF6 - , CH3CO2 - , CF3SO3 - , N(CF3SO2)2 - , C(CF2SO2)3 -Salts comprising anions such as or combinations thereof are dissolved or dissociated in organic solvents composed of 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), ethylmethyl carbonate (EMC), gamma butyrolactone (g-butyrolactone), or mixtures thereof, but are not limited thereto.

[0139]

[0140] A third aspect of the present invention relates to a method for manufacturing a dry electrode.

[0141] A method for manufacturing a dry electrode according to one aspect of the present invention is,

[0142] (S1) A step of obtaining a mixture by dry mixing of an electrode active material; a conductive material, a first binder polymer and a second binder polymer without a solvent;

[0143] (S2) A step of kneading the above mixture to produce a mass of the mixture;

[0144] (S3) A step of crushing the above mixture lumps to obtain a mixed powder for electrodes;

[0145] (S4) A step of manufacturing an electrode sheet by feeding the above-mentioned mixed powder between a plurality of rolls and performing calendering processing; and

[0146] (S5) A step of manufacturing an electrode by laminating the above electrode sheet onto at least one surface of an electrode current collector; comprising,

[0147] The first binder polymer above comprises polytetrafluoroethylene, and

[0148] The above second binder polymer is characterized by having an average particle size (D90) of 50㎛ or less.

[0149]

[0150] The method for manufacturing a dry electrode is described in more detail below.

[0151] First, a step is performed to obtain a mixture by dry mixing (S1) an electrode active material; a conductive material, a first binder polymer and a second binder polymer without a solvent.

[0152] The above step (S1) is a step of obtaining a mixture by mixing an active material, a conductive material, a first binder polymer, and a second binder polymer in a constant mixing ratio as components of an electrode sheet.

[0153] In the above step (S1), the mixing to obtain the mixture is performed so that the active material, conductive material, and binder polymer are uniformly distributed. Since these components are mixed in powder form, they can be mixed by various methods that enable simple mixing, without limitation. However, since the above method is intended to manufacture a dry electrode that does not use a solvent, the mixing can be performed as a dry mixing and can be carried out by introducing the materials into a device such as a blender or a supermixer.

[0154] In one embodiment of the present invention, when the mixing is performed in a blender, in order to ensure uniformity, it may be manufactured by mixing in a 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.

[0155] In another embodiment of the present invention, when the mixing is performed in a supermixer, the mixing can be performed at 500 rpm to 2,500 rpm, specifically 1,000 rpm to 2,000 rpm, in order to ensure uniformity, and the process time can be adjusted accordingly.

[0156]

[0157] Next, (S2) a step of kneading the above mixture to produce a mass of the mixture is performed.

[0158] The above step (S2) is a step of forming a mixture mass of 100% solid content by combining or connecting the active material and conductive material powders as the first binder polymer is fiberized.

[0159] 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 dough mixer, such as a kneader, for example. Specifically, the mixing may be controlled at a speed of 10 rpm to 100 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. For example, it may be performed for 3 minutes to 10 minutes at a speed of 40 rpm to 70 rpm within the above range. 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 at a range of 30 / s to 100 / s.

[0160] In addition, this mixing step can be performed under high temperature and pressure conditions above atmospheric pressure, and more specifically, under pressure conditions higher than atmospheric pressure. More specifically, the mixing can be performed on the mixture in a range of 70°C to 200°C, specifically 90°C to 150°C. When the mixing is performed in the above temperature range, the fiberization of the first binder polymer and the agglomeration by mixing can be effectively achieved.

[0161]

[0162] Next, (S3) a step of crushing the mixture lump to obtain a mixed powder for electrodes is performed. Although the mixture lump produced through the above kneading may be calendered immediately, in this case, the mixture lump may need to be pressed to produce a thin film, and consequently, problems may arise such as the film density becoming too high or a uniform film not being obtained. According to the present invention, the prepared mixture lump undergoes the crushing step.

[0163] At this time, the grinding step may be performed using a device such as a blender or a grinder, although it is not limited to this method. Specifically, the grinding step may be performed for 30 seconds to 10 minutes at a speed of 5,000 rpm to 20,000 rpm, and more specifically, for 30 seconds to 2 minutes at a speed of 10,000 rpm to 18,000 rpm.

[0164]

[0165] Subsequently, (S4) a step of manufacturing an electrode sheet is performed by feeding the mixed powder between a plurality of rolls and processing it by calendering. The calendering process is a step of processing the mixed powder into a film form, for example, by manufacturing it into a film form through rolling to have an average thickness of 50 μm to 300 μm. The calendering can be performed, for example, by one or more pairs of rolls facing each other, and the rolls can be controlled to have a rotational 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.

[0166]

[0167] Next, (S5) a step of manufacturing an electrode by laminating the electrode sheet onto at least one surface of an electrode current collector is performed. In the lamination step, to form an electrode film on at least one surface of the current collector, the step of rolling and attaching the electrode film onto the current collector to a predetermined thickness may be further included. The lamination may be performed by a lamination roll, and the lamination roll may be controlled to a temperature of 25 to 250°C.

[0168]

[0169] The present invention will be described in more detail below through examples, but the following examples are intended to illustrate the invention and the scope of the invention is not limited thereto.

[0170]

[0171] Example 1

[0172] As a positive electrode active material, lithium nickel-cobalt-manganese-aluminum oxide (NCMA, Li[Ni]) having an average particle size (D50) of 10㎛ 0.88 Co 0.07 Mn 0.04 ]Al 0.01 96.5 parts by weight of O2, 1.5 parts by weight of carbon black as a conductive material, 1.5 parts by weight of polytetrafluoroethylene (PTFE, Daikin, 601X) as a first binder polymer, and 0.5 parts by weight of polypropylene (LG Chem, H7918) as a second binder polymer were prepared.

[0173] The above second binder polymer was measured to have a composite viscosity of 18 Pa·s and a D50 of 8 μm using an advanced rheometric expansion system (ARES-G2) under conditions of 170°C and 0.1 Hz.

[0174] Subsequently, the above-mentioned positive active material, conductive material, first binder polymer, and second binder polymer were introduced into a blender and mixed at 10,000 rpm for 1 minute to prepare a mixture. The temperature of the kneader was stabilized at 150°C, and the mixture was placed into the kneader and operated at a speed of 25 rpm for 5 minutes under a cover pressure of 1.1 atmospheres to obtain a lump of the mixture. The lump of the mixture was introduced into a blender and ground at 10,000 rpm for 30 seconds to obtain a mixed powder for electrodes. The obtained mixed powder for electrodes was classified into particles ranging from 150 µm to 1,000 µm in a multi-stage classifier. Subsequently, the classified powder for electrodes was introduced into a lab calender (conditions: roll diameter 200 mm, roll temperature 100°C, roll speed ratio 1.5) and subjected to several calendering processes to manufacture an electrode sheet.

[0175] Two of the above electrode sheets were placed on both sides of an aluminum foil (15.8 μm) coated with a conductive primer layer in which carbon black and an acrylic binder were mixed in a weight ratio of 5:6, and laminated using a compression roll maintained at 150°C to produce an anode with a thickness of 81 μm.

[0176]

[0177] Example 2

[0178] An anode was prepared in the same manner as in Example 1, except that polypropylene (LG Chem, H7914) was prepared as the second binder polymer. The thickness of the anode was measured to be 81 μm.

[0179] The above second binder polymer was measured using an advanced rheometric expansion system (ARES-G2) at 170°C and 0.1 Hz, and the composite viscosity was 144 Pa·s and the D50 was measured to be 8 μm.

[0180]

[0181] Comparative Example 1

[0182] An anode was prepared in the same manner as in Example 1, except that the second binder polymer was not used and the first binder polymer was prepared in an amount of 2 parts by weight. The thickness of the anode was measured to be 81 μm.

[0183]

[0184] Comparative Example 2

[0185] A cathode was prepared in the same manner as in Example 1, except that the second binder polymer was not used, the cathode active material was prepared in an amount of 97 parts by weight, and the first binder polymer was prepared in an amount of 1.5 parts by weight. The thickness of the cathode was measured to be 80 μm.

[0186]

[0187] Comparative Example 3

[0188] An anode was manufactured in the same manner as in Example 1, except that polypropylene (LG Chem, M1500) was prepared as the second binder polymer. The second binder polymer had an average particle size (D50) of 8 μm and a composite viscosity of 1850 Pa·s. The thickness of the anode was measured to be 80 μm.

[0189]

[0190] Comparative Example 4

[0191] An anode was prepared in the same manner as in Example 1, except that polypropylene (TIANSHI WAX, PPW-0901) was prepared as the second binder polymer. The second binder polymer had an average particle size (D50) of 6 μm and a composite viscosity of 0.2 Pa·s. The thickness of the anode was measured to be 80 μm.

[0192] The thickness of the above anode was measured using a thickness gauge (VL-50S-B (Mitutoyo)).

[0193]

[0194] Experimental Example 1: Anode Evaluation

[0195] Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Tensile strength (gf / mm² 2)524553203045 Elastic indentation modulus (GPa) 5.2 4.8 2.7 2.1 2.5 1.8 Indentation hardness (N / mm 2 )151137117111113104

[0196] The above tensile strength can be obtained by manufacturing the electrode sheets of the examples and comparative examples with a width of 50 mm and a length of 15 mm, fixing them to a jig for measuring tensile strength, and then using a universal material testing machine (LLOYD LS1, load cell 10 N) to draw a stress-strain graph while pulling in a 180° direction at a speed of 2 mm / min at 25°C, and measuring the stress value at the highest point on the graph.

[0197] The above elastic indentation modulus and indentation hardness were measured by manufacturing an anode according to the example and comparative example with a width of 50 mm and a length of 15 mm, and using nano-indentation (NHT, Anton Paar, Austria) under conditions of a maximum load range of 40 mN, a loading rate of 40 mN / min, a pause of 10 sec, and an unloading rate of 40 mN / min.

[0198]

[0199] Referring to Table 1 above, it can be seen that the anodes according to Example 1 and Example 2 have significantly improved elastic indentation modulus and indentation hardness compared to the anodes according to Comparative Example 1 and Comparative Example 2, which use only PTFE binder polymer.

[0200] In addition, it can be confirmed that the elastic indentation modulus and indentation hardness of the anode according to Example 1 are significantly improved compared to the anodes according to Comparative Examples 3 and 4, which use a second binder polymer with excessively high or low composite viscosity.

[0201] In addition, the anodes according to Examples 1 and 2 were able to secure sufficient tensile strength even though they contained a second binder polymer in addition to the fibrous binder polymer.

[0202]

[0203] Experimental Example 2: Battery Evaluation

[0204] A cathode slurry was prepared by mixing a mixture of artificial graphite and natural graphite in a 5:5 ratio as the cathode active material, superC as the conductive material, and SBR / CMC as the binder in a weight ratio of 96:1:3, and then coating the slurry on one side of a copper current collector, drying it at 130°C, and rolling it to a porosity of 26% to manufacture a cathode.

[0205] An electrode assembly was manufactured by interposing a porous polyethylene separator between each anode and cathode prepared in the examples and comparative examples, and after placing the electrode assembly inside a case, an electrolyte was injected into the case to manufacture a lithium secondary battery.

[0206] At this time, the electrolyte used was prepared by dissolving 1.0 M concentration lithium hexafluorophosphate (LiPF6) in an organic solvent composed of ethylene carbonate / ethylmethyl carbonate / diethyl carbonate / (mixed volume ratio of EC / EMC / DEC = 3 / 4 / 3).

[0207] For the manufactured lithium secondary battery monocell, the initial capacity and capacity retention rate were measured by repeating the process of charging at 0.7C in CC-CV mode at 25°C until it reached 4.25V, and discharging at a constant current of 0.5C until it reached 2.5V.

[0208]

[0209] Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Initial Capacity (mAh / g) 205 204 204 204 205 205 Capacity Retention Rate (%) 97 97 96 96 97 96

[0210] Referring to Table 2, it was confirmed that the secondary battery with the anode according to Example 1 and Example 2 has sufficient initial capacity and capacity retention rate.

[0211]

[0212] As described above, although the present invention has been explained 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 spirit of the present invention and the equivalent scope of the claims described below by those skilled in the art to which the present invention belongs.

Claims

1. An electrode current collector; and an electrode active material layer formed on at least one surface of the electrode current collector, and The above electrode active material layer comprises an electrode active material, a conductive material, a first binder polymer, and a second binder polymer, and The first binder polymer mentioned above is a polymer containing polytetrafluoroethylene that has been fiberized, and A dry electrode characterized in that the second binder polymer has a composite viscosity of 1 Pa·s to 1500 Pa·s at 170°C and 0.1 Hz.

2. In Paragraph 1, A dry electrode characterized in that the second binder polymer has a composite viscosity of 1 Pa·s to 1000 Pa·s at 170°C and 0.1 Hz.

3. In Paragraph 1, A dry electrode characterized in that the above-mentioned second binder polymer has an average particle size (D50) of 50㎛ or less.

4. In Paragraph 1, A dry electrode characterized in that the second binder polymer has an average particle size (D50) of 0.1㎛ to 50㎛.

5. In Paragraph 1, A dry electrode characterized in that the second binder polymer has a melt index of 100 g / 10 min or higher when a load of 2.16 kg is applied at 230°C.

6. In Paragraph 1, A dry electrode characterized in that the first binder polymer and the second binder polymer are included in an amount of 1 to 5 parts by weight per 100 parts by weight of the total electrode active material layer.

7. In Paragraph 1, A dry electrode characterized in that the weight ratio of the first binder polymer and the second binder polymer is 6:1 to 2:

1.

8. In Paragraph 1, A dry electrode characterized in that the second binder polymer comprises one or more of a polyolefin-based polymer and a polyvinylidene fluoride-based polymer.

9. In Paragraph 1, A dry electrode characterized in that the second binder polymer is polypropylene or polyvinylidene fluoride.

10. In Paragraph 1, The above dry electrode has a tensile strength of 30 gf / mm 2 A dry electrode characterized by the above.

11. In Paragraph 1, The above dry electrode is characterized by having an elastic indentation modulus of 2.5 GPa or higher.

12. A secondary battery comprising: a positive electrode; a negative electrode; a separator disposed between the positive electrode and the negative electrode; and an electrolyte, wherein A secondary battery characterized in that at least one of the anode and cathode is an electrode according to any one of claims 1 to 11.

13. (S1) A step of obtaining a mixture by dry mixing an electrode active material; a conductive material, a first binder polymer, and a second binder polymer without a solvent; (S2) A step of kneading the above mixture to produce a mass of the mixture; (S3) A step of crushing the above mixture lumps to obtain a mixed powder for electrodes; (S4) A step of manufacturing an electrode sheet by feeding the above-mentioned mixed powder between a plurality of rolls and performing calendering processing; and (S5) A step of manufacturing an electrode by laminating the above electrode sheet onto at least one surface of an electrode current collector; comprising, The first binder polymer above comprises polytetrafluoroethylene, and A method for manufacturing a dry electrode, characterized in that the second binder polymer has a composite viscosity of 1 Pa·s to 1500 Pa·s at 170℃ and 0.1 Hz.