Dry electrode and method of manufacturing the same

Abstract

The dry electrode according to the present disclosure contains a first binder polymer that is a fibrillated polymer including polytetrafluoroethylene and a second binder polymer having a complex viscosity of 1 Pa-sec to 1500 Pa-sec at 170°C and 0.1 Hz, and ensures sufficient tensile strength and has improved indentation stiffness such as elastic indentation modulus and indentation hardness.

Description

Technical Field

[0001] This disclosure relates to dry electrodes and their manufacturing methods.

[0002] This application is based on and claims priority to Korean Patent Application No. 10-2024-0168749, filed with the Korean Intellectual Property Office on November 22, 2024, the disclosure of which is incorporated herein by reference in its entirety. Background Technology

[0003] With the increasing use of fossil fuels and the growing demand for alternative and clean energy sources, much research is underway in the field of energy generation and storage utilizing electrochemistry.

[0004] Currently, the representative example of an electrochemical device that utilizes electrical and chemical energy is the secondary battery, and the application scope of secondary batteries is gradually expanding.

[0005] One typical type of secondary battery (lithium secondary battery) is used not only as an energy source for mobile devices, but also as a power source for electric vehicles and hybrid electric vehicles that serve as alternatives to vehicles using fossil fuels, such as gasoline and diesel vehicles, which are considered one of the main causes of air pollution. Furthermore, the application of lithium secondary batteries is expanding to auxiliary power sources through the power grid.

[0006] The manufacturing process of lithium-ion batteries can be broadly divided into the electrode process, the assembly process, and the formation / aging process. The electrode process is further subdivided into the active material mixing process, the electrode coating process, the drying process, the rolling process, the cutting process, and the winding process.

[0007] The active material mixing process is a process of mixing coating materials used to form an electrode active layer in which an electrochemical reaction actually occurs in the electrode, and specifically, it involves mixing electrode active materials (which are key elements of the electrode) with additives (e.g., conductive materials, fillers, binders for binding and adhering powder particles to the current collector, and solvents for imparting viscosity and dispersing powder to prepare a flowable slurry).

[0008] Compositions used to form the active layer of an electrode are broadly referred to as electrode mixtures.

[0009] Subsequently, an electrode coating process is performed to apply the electrode mixture to a conductive current collector, followed by a drying process to remove the solvent from the electrode mixture, and additionally, rolling is performed to manufacture an electrode with a predetermined thickness.

[0010] Meanwhile, defects such as pinholes or cracks may appear in the electrode active layer because the solvent contained in the electrode mixture evaporates during drying. In addition, the active layer is not dried uniformly throughout the internal / external region, and due to differences in solvent evaporation rates, some areas dry earlier and the powder in those areas floats, while other areas dry later at different intervals, resulting in low electrode quality.

[0011] Recently, many studies have been conducted to manufacture dry electrodes that do not use solvents.

[0012] Dry electrodes are typically manufactured by laminating a self-supporting film containing active materials, fibrillable binder polymers, and conductive materials onto a current collector.

[0013] However, when using fibrillable binder polymers to manufacture dry electrodes, the dry electrodes have very low indentation stiffness, and the cycle life and capacity retention of the secondary cells that include them decrease while the resistance increases.

[0014] Therefore, there is an urgent need to develop dry electrode manufacturing technology to solve the above problems. Summary of the Invention

[0015] Technical issues

[0016] This disclosure relates to providing dry electrodes manufactured by binder polymer fibrillation that have improved indentation stiffness, cycle life, capacity retention, and resistance.

[0017] Technical solution

[0018] One aspect of this disclosure provides a dry electrode with the following embodiments and a method for manufacturing the same. Another aspect of this disclosure provides a secondary battery including a dry electrode.

[0019] The dry electrode according to the first embodiment includes:

[0020] An electrode current collector; and an electrode active material layer disposed on at least one surface of the electrode current collector.

[0021] The electrode active material layer comprises an electrode active material, a conductive material, a first binder polymer, and a second binder polymer.

[0022] The first adhesive polymer is a fibrillated polymer comprising polytetrafluoroethylene, and

[0023] The second binder polymer has a complex viscosity of 1 Pa·s to 1500 Pa·s at 170°C and 0.1 Hz.

[0024] According to the second implementation plan, in the first implementation plan...

[0025] The complex viscosity of the second binder polymer at 170°C and 0.1 Hz can range from 1 Pa·s to 1000 Pa·s.

[0026] According to the third implementation scheme, in the first or second implementation scheme...

[0027] The average particle size (D50) of the second binder polymer can be 50 μm or smaller.

[0028] According to the fourth implementation plan, in any of the first to third implementation plans,

[0029] The average particle size (D50) of the second binder polymer can be from 0.1 μm to 50 μm.

[0030] According to the fifth implementation plan, in any of the first to fourth implementation plans,

[0031] The melt index of the second binder polymer at 230°C and 2.16 kg load can be 100 g / 10 min or greater.

[0032] According to the sixth implementation plan, in any of the first to fifth implementation plans,

[0033] Based on a total of 100 parts by weight of electrode active material layer, the first binder polymer and the second binder polymer may be included in an amount of 1 to 5 parts by weight.

[0034] According to the seventh implementation scheme, in any of the first to sixth implementation schemes,

[0035] The weight ratio of the first binder polymer to the second binder polymer can be from 6:1 to 2:1.

[0036] According to the eighth implementation plan, in any of the first to seventh implementation plans,

[0037] The second binder polymer may include at least one of a polyolefin-based polymer or a polyvinylidene fluoride-based polymer.

[0038] According to the ninth implementation plan, in any of the first to eighth implementation plans,

[0039] The second binder polymer may include polypropylene or polyvinylidene fluoride.

[0040] According to the tenth implementation plan, in any of the first to ninth implementation plans,

[0041] The tensile strength of the dry electrode can be 30 gf / mm. 2 Or larger.

[0042] According to the eleventh implementation plan, in any of the first to tenth implementation plans...

[0043] The elastic indentation modulus can be 3 GPa or greater.

[0044] The secondary battery according to the twelfth implementation plan includes:

[0045] Positive electrode; negative electrode; a separator between the positive and negative electrodes; and an electrolyte solution.

[0046] At least one of the positive and negative electrodes is an electrode according to any one of the first to twelfth embodiments.

[0047] The dry electrode manufacturing method according to the thirteenth implementation plan includes:

[0048] (S1) The electrode active material, the conductive material, the first binder polymer, and the second binder polymer are dry-mixed in the absence of solvent to obtain a mixture;

[0049] (S2) Knead the mixture to form a mixture block;

[0050] (S3) Grind the mixture block to obtain electrode mixture powder;

[0051] (S4) The electrode mixture powder is fed between a plurality of rollers for calendering to produce an electrode sheet; and

[0052] (S5) The electrode sheet is laminated onto at least one surface of the electrode current collector to manufacture an electrode.

[0053] The first binder polymer includes polytetrafluoroethylene, and

[0054] The second binder polymer has a complex viscosity of 1 Pa·s to 1500 Pa·s at 170°C and 0.1 Hz.

[0055] Beneficial effects

[0056] According to one aspect of this disclosure, the dry electrode comprises a fibrillable binder polymer and a binder polymer having a complex viscosity of 1 Pa·s to 1500 Pa·s at 170°C and 0.1 Hz, thereby improving indentation stiffness.

[0057] Specifically, the dry electrode has an improved elastic indentation modulus. Furthermore, the dry electrode has improved indentation hardness. Detailed Implementation

[0058] The present disclosure will be described in detail below with reference to the accompanying drawings. The terms or words used in the specification and appended claims should not be construed as limited to their general or dictionary meanings, but rather should be interpreted based on the principle of allowing the inventors to appropriately define terms for best description, and on the meanings and concepts corresponding to the technical aspects of the present disclosure.

[0059] Therefore, the embodiments described herein and the illustrations in the accompanying drawings are provided to illustrate the disclosure by way of example but not in a limiting manner. It should be understood that many other equivalents and modifications may be made thereto at the time of filing this application.

[0060] It should also be understood that, unless otherwise expressly stated, “comprising,” “including,” or “having” as used in this specification specifies the presence of the said element and does not exclude the presence or addition of one or more other elements.

[0061] Furthermore, when given the manufacturing and material tolerances inherent in said circumstances, the terms 'about' and 'substantially' are used herein in the sense of being at or close to precise or absolute figures, and are used to prevent unethical infringers from unfairly exploiting the precise or absolute figures stated herein to aid in understanding this disclosure.

[0062] In this specification, 'A and / or B' means A or B or both.

[0063] Unless otherwise stated, the temperature used in this document refers to temperature on the Celsius scale and is in °C.

[0064] In this specification, "particle size Dn" refers to the particle size at the n% point of the cumulative volume particle size distribution. That is, D50 refers to the particle size at the 50% point of the cumulative volume particle size distribution, D90 refers to the particle size at the 90% point of the cumulative volume particle size distribution, and D10 refers to the particle size at the 10% point of the cumulative volume particle size distribution. Dn can be measured using laser diffraction. Specifically, after dispersing the powder in a dispersion medium and introducing it into a commercially available laser diffraction particle size measuring instrument (e.g., Malvern; Mastersizer 3000), the particle size distribution is calculated by measuring the difference in diffraction patterns as a function of particle size when the particles pass through a laser beam. D10, D50, and D90 can be measured by calculating the particle diameter at the 10%, 50%, and 90% points of the cumulative volume particle size distribution in the measuring instrument.

[0065] In this specification, unless otherwise stated, complex viscosity is measured using an Advanced Rheometric Expansion System (ARES-G2) at 170°C with a gradual frequency variation from 0.01 Hz to 100 Hz. Furthermore, complex viscosity is measured within the strain range (1% to 10%) where the polymer exhibits linear viscoelastic properties according to the viscosity of each polymer.

[0066] Unless otherwise specified, the melt flow index (MFI) is measured according to ASTM D-1238 at 230°C and 2.16 kg.

[0067] The first aspect of this disclosure relates to dry electrodes.

[0068] According to one aspect of this disclosure, the dry electrode includes:

[0069] An electrode current collector; and an electrode active material layer disposed on at least one surface of the electrode current collector.

[0070] The electrode active material layer comprises an electrode active material, a conductive material, a first binder polymer, and a second binder polymer, and

[0071] The first adhesive polymer is a fibrillated polymer including polytetrafluoroethylene (PTFE), and

[0072] The second binder polymer has a complex viscosity of 1 Pa·s to 1500 Pa·s at 170°C and 0.1 Hz.

[0073] The electrode active material layer used in dry electrodes typically employs fibrillable binder polymers and has a structure in which the fibrillable binder polymer holds the active and conductive materials together. The fibrillable polymer improves the flexibility of the electrode active material layer and the electrode due to its high elongation in the length direction. However, dry electrodes made using fibrillable binder polymers exhibit very low indentation stiffness.

[0074] To improve indentation stiffness, this disclosure applies both a fibrillable binder polymer and a binder polymer with a complex viscosity of 1 Pa·s to 1500 Pa·s at 170°C and 0.1 Hz to the electrode active material layer.

[0075] In one embodiment of the present disclosure, the electrode current collector is not limited to a specific electrode current collector, and may include those having high conductivity without causing chemical changes in the corresponding battery. For example, the current collector may include stainless steel; aluminum; nickel; titanium; calcined carbon; copper; or aluminum or stainless steel surface-treated with carbon, nickel, titanium or silver. The current collector may have a micro-rough surface to increase the adhesion strength of the active material, and may be in different forms such as a film, a sheet, a foil, a mesh, a porous body, a foam or a non-woven fabric. Meanwhile, in one embodiment of the present disclosure, the thickness of the current collector may be 10 μm to 50 μm, but the thickness is not limited to a specific range. The thickness of the current collector may be, for example, 10 μm to 20 μm.

[0076] In one embodiment of the present disclosure, the electrode active material may be a positive electrode active material or a negative electrode active material. The positive electrode active material may include, without limitation, any type of lithium transition metal oxide, lithium metal iron phosphate or metal oxide, and may include, for example: layered compounds such as lithium cobalt oxide (LiCoO₂) or lithium nickel oxide (LiNiO₂) or compounds substituted with one or more transition metals; lithium manganese oxides such as the chemical formula Li 1+x Mn 2-x O₄ (wherein x is 0 to 0.33), LiMnO₃, LiMn₂O₃, LiMnO₂; lithium copper oxide (Li₂CuO₂); vanadium oxides such as LiV₃O₈, LiFe₃O₄, V₂O₅, Cu₂V₂O₇; LiNi of the chemical formula 1-x M x O₂ (M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, x = 0.01 to 0.3) represented Ni-site type lithium nickel oxide; LiMn represented by the chemical formula 2-x M x O₂ (M = Co, Ni, Fe, Cr, Zn or Ta, x = 0.01 to 0.1) or Li₂Mn₃MO₈ (M = Fe, Co, Ni, Cu or Zn) represented lithium manganese composite oxide; LiMn₂O₄ partially substituted with alkaline earth metal ions in the chemical formula; lithium metal phosphate LiMPO₄ (M = Fe, Co, Ni or Mn); LiNi 1-x-y-z Co x M1 y M2 z O₂ (each of M1 and M2 is independently any one selected from the group consisting of Al, Ni, Fe, Mn, V, Cr, Ti, W, Ta, Mg and Mo, x, y and z independently represent the atomic fraction of elements in the oxide, 0<x<0.5, 0<y<0.5, 0<z<0.5, 0<x+y+z≤1); disulfide compounds; or Fe₂(MoO₄)₃, but is not limited thereto.

[0077] Negative electrode active materials may include: carbon, such as non-graphitized carbon or graphite-based carbon; metal composite oxides, such as Li x Fe2O3 (0≤x≤1), Li x WO2 (0≤x≤1), Sn x Me 1-x Me' y O z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, Group 1, Group 2 and Group 3 elements in the periodic table, halogens; 0≤x≤1; 1≤y≤3; 1≤z≤8); lithium metal; lithium alloys; silicon-based alloys; tin-based alloys; silicon-based oxides, such as SiO, SiO / C, SiO2; metal oxides, such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4 and Bi2O5; conductive polymers, such as polyacetylene; Li-Co-Ni based materials.

[0078] According to one embodiment of this disclosure, specifically, the electrode active material can be a positive electrode active material, and more specifically, it can include lithium transition metal oxides, lithium nickel-manganese-cobalt oxides, Al or other transition metal-substituted lithium nickel-manganese-cobalt oxides, or lithium iron phosphate.

[0079] In one embodiment of this disclosure, the conductive material is not limited to a specific type and may include any material that is conductive without causing chemical changes in the corresponding battery. Non-limiting examples of conductive materials may include: graphite, such as natural or artificial graphite; carbon black-based carbon compounds, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lampblack, or thermally cracked black; conductive fibers, such as carbon fibers or metal fibers; fluorocarbon compounds; metal powders, such as aluminum or nickel powder; carbon nanotubes; conductive whiskers, such as zinc oxide whiskers or potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or conductive materials, such as polyphenylene derivatives. In a specific embodiment, the conductive material may include one, two, or more of these materials.

[0080] In one embodiment of this disclosure, based on a total of 100 parts by weight of the electrode active material layer, the first binder polymer and the second binder polymer may be included in an amount of 1 to 5 parts by weight. When the amount of the binder polymer falls within the aforementioned range, strong adhesive strength can be formed between the components of the electrode active material layer.

[0081] In one embodiment of this disclosure, 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 aforementioned weight ratios, the indentation stiffness of the dry electrode can be significantly improved.

[0082] In one embodiment of this disclosure, the average particle size D50 of the second binder polymer can 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, or 15 μm or less, and can be 0.1 μm or greater, or 0.2 μm or greater. When the average particle size of the second binder polymer falls within the aforementioned range, the indentation stiffness of the electrode active material layer can be significantly improved, and good dispersion can ensure uniform distribution within the electrode active material layer.

[0083] In one embodiment of this disclosure, the complex viscosity of the second binder polymer at 170°C and 0.1 Hz can be 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, and can be 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 complex viscosity of the second binder polymer at 170°C and 0.1 Hz can be from 0.1 Pa·s to 1500 Pa·s, from 1 Pa·s to 1000 Pa·s, from 3 Pa·s to 500 Pa·s, from 5 Pa·s to 300 Pa·s, from 10 Pa·s to 300 Pa·s, or from 18 Pa·s to 144 Pa·s.

[0084] When the second binder polymer has a complex viscosity within the aforementioned range, its high flowability and dispersibility ensure miscibility with conductive and electrode active materials in a solvent-free environment. Therefore, electrodes incorporating the second binder polymer can exhibit improved indentation stiffness, such as elastic indentation modulus and indentation hardness, and ensure appropriate lifetime and discharge capacity characteristics of the secondary battery.

[0085] In one embodiment of this disclosure, the melt index of the second binder polymer at 230°C under a load of 2.16 kg can be 100 g / 10 min or greater, 200 g / 10 min or greater, 300 g / 10 min or greater, 400 g / 10 min or greater, 500 g / 10 min or greater, 600 g / 10 min or greater, 700 g / 10 min or greater, 800 g / 10 min or greater, 900 g / 10 min or greater, 1000 g / 10 min or greater, 1300 g / 10 min or greater, or 1500 g / 10 min or greater. When the melt index of the second binder polymer falls within the aforementioned range, the indentation stiffness of the electrode can be improved.

[0086] In one embodiment of this disclosure, the second adhesive polymer may include at least one of a polyolefin-based polymer or a polyvinylidene fluoride-based polymer.

[0087] For example, the second binder polymer may include polyethylene, polypropylene, polybutene, polypentene, or both or more thereof. Polyvinylidene fluoride-based polymers 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 both or more thereof.

[0088] In one embodiment of this disclosure, in addition to the first and second binder polymers, the electrode active material layer may further comprise another binder polymer. The binder polymers that may also be included in the electrode active material layer may include styrene-butadiene rubber (SBR), butadiene rubber (BR), nitrile 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-copolymer-propylene-copolymer-5-methylene-2-propene ... The adhesive polymer may include borneol, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinyl chloride (PVC), PVDF-copolymer-hexafluoropropylene copolymer, PVDF-copolymer-trichloroethylene copolymer, polymethyl methacrylate (PMMA), polyethylhexyl acrylate (PEHJ), polybutyl acrylate (PBMA), polyacrylonitrile (PAA), polyvinylpyrrolidone (PVP), polyvinyl acetate (PVC), polyethylene, polypropylene, polyethylene-copolymer-vinyl acetate (PVC), polyethylene oxide (PEO), polypropylene oxide (PEO), polyarylates, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol (PEE), or both or more thereof. Specifically, the adhesive polymer may include styrene-butadiene rubber (SBR), nitrile rubber (NBR), polymethyl methacrylate (PMMA), polyethylhexyl acrylate (PEHJ), or polybutyl acrylate (PBMA). Furthermore, the adhesive polymer may include one or more selected from these categories.

[0089] In one embodiment of this disclosure, the tensile strength of the dry electrode can be 20 gf / mm². 2 Or larger, 30gf / mm 2 Or larger, 40 gf / mm 2 Or larger, or 50 gf / mm 2 Or even greater. In addition to the fibrillated first binder polymer, a second binder polymer is also included, but the second binder polymer has the aforementioned complex viscosity, so the dry electrode of this disclosure can have sufficient tensile strength.

[0090] Tensile strength can be determined by the following steps: preparing a dry electrode sample with a width of 50 mm, a length of 15 mm, and a thickness of 85 μm to 90 μm, fixing the sample to a fixture for tensile strength measurement, and measuring the stress value at the highest point on the stress-strain diagram when stretched 180° at a speed of 2 mm / min using a universal testing machine (LLOYD LS1, load cell 10 N) at 25°C.

[0091] In one embodiment of this disclosure, the elastic indentation modulus of the dry electrode may be 2.5 GPa or greater, 3.0 GPa or greater, or 3.5 GPa or greater.

[0092] In one embodiment of this disclosure, the indentation hardness of the dry electrode can be 120 N / mm. 2 Or larger, 130 N / mm 2 Or larger, 140 N / mm 2 Or larger, or 150 N / mm 2 Or larger.

[0093] Elastic indentation modulus and indentation hardness can be measured using a nanoindenter (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 seconds, and an unloading rate of 40 mN / min.

[0094] The second aspect of this disclosure relates to secondary batteries.

[0095] According to one aspect of this disclosure, the secondary battery includes:

[0096] Positive electrode; negative electrode; a separator between the positive and negative electrodes; and an electrolyte solution.

[0097] At least one of the positive and negative electrodes is a dry electrode according to one aspect of this disclosure.

[0098] In one embodiment of this disclosure, 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 lithium secondary battery is not limited to a specific shape, but may have a cylindrical shape, a prism shape, a bag shape, or a coin shape suitable for use in a can.

[0099] In one embodiment of this disclosure, the negative electrode may include a negative electrode current collector; and a negative electrode active material layer disposed 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.

[0100] The negative electrode active material layer may comprise graphite and a silicon-based compound as the negative electrode active material, and in this case, the graphite and the silicon-based compound may be included in a weight ratio of 70:30 to 99:1. Furthermore, the silicon-based compound may comprise silicon and / or silicon oxide, and the silicon oxide may comprise at least one type of compound represented by the following chemical formula 1.

[0101] [Chemical Formula 1]

[0102] SiO x

[0103] In the above chemical formula 1, 0 ≤ x < 2. In the above chemical formula 1, SiO2 (x = 2 in the above chemical formula 1) does not react with lithium ions and cannot store lithium. Preferably, x is less than 2. Specifically, in terms of the structural stability of the electrode active material, 0.5 ≤ x ≤ 1.5.

[0104] The silicon-based compound may also include a carbon coating covering all or at least a portion of the surface of the active material particles. The carbon coating acts as a protective layer to suppress volume expansion of the negative electrode active material particles containing the silicon-based compound and to prevent side reactions with the electrolyte solution. The carbon coating may be included in the silicon-based compound in an amount from 0.1% to 10% by weight, and preferably from 3% to 7% by weight. When the amount of carbon coating falls within the aforementioned range, the carbon coating can very effectively control the volume expansion of the negative electrode active material particles containing the silicon-based compound and prevent side reactions with the electrolyte solution.

[0105] Particle size D of anode active material particles containing silicon-based compounds 50 It can range from 3 μm to 10 μm. When the particle size D... 50 At particle sizes smaller than 3 μm, the high specific surface area may result in a larger reaction area with the electrolyte solution and more frequent side reactions with the electrolyte solution during charging and discharging, leading to a shorter battery life. Conversely, when the particle size D... 50 When the particle size is greater than 10 μm, large volume changes may be caused by the expansion / contraction of the active material particles during charging and discharging, leading to fragmentation or breakage of the active material particles and resulting in low battery performance.

[0106] Graphite may include at least one selected from synthetic graphite and natural graphite. Natural graphite may include unprocessed natural graphite (e.g., flake graphite, block graphite, or amorphous graphite) or spherical natural graphite. Flake and block graphite exhibit near-perfect crystals, while amorphous graphite has lower crystallinity. When considering electrode capacity, flake and block graphite with higher crystallinity can be used. For example, flake graphite can be transformed into spherical shapes. The particle size of spherical natural graphite can be from 5 μm to 30 μm, and preferably from 10 μm to 25 μm.

[0107] Artificial graphite is typically produced by graphitization methods involving calcining raw materials such as coal tar, coal tar pitch, and petroleum-based heavy oil at 2,500°C or higher, and can be used as a negative electrode active material after graphitization by particle size adjustment such as grinding and secondary particle formation.

[0108] Typically, synthetic graphite exhibits a random distribution of intragranular grains, has a lower sphericity than natural graphite, and possesses a pointed shape. Synthetic graphite can be in the form of powder, flakes, blocks, plates, or rods; however, to improve output characteristics, synthetic graphite is preferably characterized by isotropic grain orientation to reduce the migration distance of lithium ions. From this perspective, synthetic graphite can be in flake and / or plate form.

[0109] Artificial graphite includes mesophase carbon microbeads (MCMB) widely used in commercial applications, mesophase pitch-based carbon fiber (MPCF), and artificial graphite produced by graphitization into bulk form or by graphitization into powder form. Furthermore, the particle size of artificial graphite can range from 5 μm to 30 μm, and preferably from 10 μm to 25 μm.

[0110] The specific surface area of ​​synthetic graphite can be measured using the Brunauer-Emmett-Teller (BET) method. For example, the specific surface area of ​​synthetic graphite can be measured using a porosity analyzer (Bell JaPan Inc., Belserp-II mini) via nitrogen adsorption flow method through a BET 6-point analysis. The same applies to the measurement of the specific surface area of ​​natural graphite, as described below.

[0111] The tap density of artificial graphite can range from 0.7 g / cc to 1.1 g / cc, and specifically from 0.8 g / cc to 1.05 g / cc. When the tap density is less than 0.7 g / cc outside the aforementioned range, insufficient contact area between particles leads to poor adhesion properties and low capacity per volume. When the tap density is greater than 1.1 g / cc, electrode curvature decreases and electrolyte wettability deteriorates, resulting in low output characteristics during charging and discharging.

[0112] Here, the tap density is determined by placing 50 g of the precursor into a 100 cc tapping cylinder and tapping it 3000 times using a COPLEY JV-1000 measuring instrument and a SEISHIN (KYT-4000) measuring instrument. This also applies to the tap density measurement of natural graphite as described below.

[0113] Furthermore, the average particle size D50 of artificial graphite can range from 8 μm to 30 μm, and specifically from 12 μm to 25 μm. When the average particle size D50 of artificial graphite is less than 8 μm, the specific surface area increases and the initial efficiency of the secondary battery decreases, resulting in low battery performance. When the average particle size D50 is greater than 30 μm, the adhesion strength decreases and the packing density decreases, resulting in small capacity.

[0114] The average particle size of synthetic graphite can be measured, for example, using laser diffraction. Laser diffraction typically measures particle sizes from submicron to several millimeters and yields results with high reproducibility and high resolution. The average particle size D50 of synthetic graphite can be defined as the particle size at 50% of the particle size distribution. For example, a method for measuring the average particle size D50 of synthetic graphite may include: dispersing synthetic graphite in an ethanol / aqueous solution, introducing it into a commercially available laser diffraction particle size measuring instrument (e.g., Microtrac MT 3000), emitting ultrasonic waves at approximately 28 kHz with an output of 60 W, and calculating the average particle size D50 at 50% of the particle size distribution in the measuring instrument.

[0115] Conductive materials may include, for example, any of the following: graphite, carbon black, carbon nanotubes, carbon fibers or metal fibers, metal powders, conductive whiskers, conductive metal oxides, activated carbon and polyphenylene derivatives, or mixtures thereof. More specifically, conductive materials may include any of the following: natural graphite, artificial graphite, super-p, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking black, Tenca black, aluminum powder, nickel powder, zinc oxide, potassium titanate and titanium oxide, or mixtures thereof.

[0116] The negative electrode current collector is not limited to a specific negative electrode current collector, and may include those with high conductivity without causing chemical changes in the corresponding battery, and may include, for example, stainless steel; copper; aluminum; nickel; titanium; calcined carbon; copper, aluminum, or stainless steel treated with carbon, nickel, titanium, or silver on the surface. The thickness of the current collector is not limited to a specific range, but is typically in the range of 3 μm to 500 μm.

[0117] The binder polymer can include any polymer commonly used for electrodes in this art. Non-limiting examples of binder polymers include, but are not limited to, polyvinylidene fluoride-copolyhexafluoropropylene, polyvinylidene fluoride-copolytrichloroethylene, polymethyl methacrylate, polyethylhexyl acrylate, polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, polyethylene-copolyvinyl acetate copolymer, polyethylene oxide, polyarylates, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, or carboxymethyl cellulose.

[0118] In one embodiment of this disclosure, the separator may include a porous polymer substrate and a porous coating disposed on at least one surface of the porous polymer substrate.

[0119] The separator is not limited to a specific type and can include any type of separator used in secondary batteries. The separator can include any commonly used type of separator for electrochemical devices without limitation, as long as it has electrically insulating properties and provides a pathway for ion conduction. For example, the separator can include a porous sheet containing a polymer, such as a polymer membrane or nonwoven fabric. In one embodiment of this disclosure, the separator may also have a heat-resistant coating containing inorganic particles on the surface of the porous sheet.

[0120] In one embodiment of this disclosure, the electrolyte solution may contain A + B - The structure of a salt and the organic solvent therein that dissolves or dissociates the salt, wherein A + It can include alkali metal cations, such as Li. + Na + K + or combinations thereof, and B - It can include anions, such as PF6. - BF4 - Cl - ,Br - I - ClO4 - AsF6 - CH3CO2 - CF3SO3 - N(CF3SO2)2 - C(CF2SO2)3 - The organic solvent may include, but is not limited to, 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), γ-butyrolactone, or mixtures thereof.

[0121] The third aspect of this disclosure relates to a method for manufacturing dry electrodes.

[0122] A method for manufacturing a dry electrode according to one aspect of this disclosure includes the following steps:

[0123] (S1) The electrode active material, the conductive material, the first binder polymer, and the second binder polymer are dry-mixed in the absence of solvent to obtain a mixture;

[0124] (S2) Knead the mixture to form a mixture block;

[0125] (S3) Grind the mixture block to obtain electrode mixture powder;

[0126] (S4) The electrode mixture powder is fed between a plurality of rollers for calendering to produce an electrode sheet; and

[0127] (S5) The electrode sheet is laminated onto at least one surface of the electrode current collector to manufacture an electrode.

[0128] The first binder polymer includes polytetrafluoroethylene, and

[0129] The average particle size D90 of the second binder polymer is 50 μm or smaller.

[0130] The dry electrode manufacturing method will be described in more detail below.

[0131] First, a step (S1) is performed in which the electrode active material, the conductive material, the first binder polymer, and the second binder polymer are dry-mixed in the absence of solvent to obtain a mixture.

[0132] Step (S1) includes mixing the components of the electrode sheet (i.e., active material, conductive material, first binder polymer and second binder polymer) at a predetermined mixing ratio to obtain a mixture.

[0133] In step (S1), mixing is performed to obtain a mixture, thereby achieving a uniform distribution of the active material, conductive material, and binder polymer. Since the components are mixed in powder form, any method for simple mixing can be used, and the mixing method is not limited to a specific method. However, because the method is used to manufacture solvent-free dry electrodes, mixing can be performed through a dry mixing process, and can be carried out by feeding the material into a mixer or a supermixer.

[0134] In one embodiment of this disclosure, when mixing is carried out in a mixer, in order to ensure uniformity, mixing may be carried out in the mixer at 5,000 rpm to 20,000 rpm for 30 seconds to 20 minutes, and specifically at 10,000 rpm to 15,000 rpm for 30 seconds to 5 minutes.

[0135] In another embodiment of this disclosure, when mixing is carried out in a super mixer, in order to ensure uniformity, mixing can be carried out in the super mixer at 500 rpm to 2,500 rpm, and specifically 1,000 rpm to 2,000 rpm, and the process time can be adjusted accordingly.

[0136] Then, the mixture is kneaded to form a mixture block (S2).

[0137] Step (S2) includes forming a 100% solids mixture block in which active material particles and conductive material particles are linked and held together by fibrillation of a first binder polymer.

[0138] Kneading is not limited to a specific method. In one specific embodiment of this disclosure, kneading can be performed, for example, using a kneading machine. Specifically, kneading can be controlled at a speed of 10 rpm to 100 rpm. For example, kneading can be controlled at a speed of 20 rpm or greater, or 70 rpm or less within the aforementioned range. Kneading can be performed for 1 minute to 30 minutes. For example, kneading can be performed for 3 minutes to 10 minutes at a speed of 40 rpm to 70 rpm within the aforementioned range. Simultaneously, kneading can be controlled at a shear rate of 10 / sec to 500 / sec. In one specific embodiment of this disclosure, kneading can be performed for 1 minute to 30 minutes, and the shear rate can be controlled within the range of 30 / sec to 100 / sec.

[0139] Furthermore, the kneading step can be carried out under high temperature and pressure conditions above atmospheric pressure, and more specifically, under pressure conditions above atmospheric pressure. More specifically, the mixture can be kneaded within a range of 70°C to 200°C, and more specifically, 90°C to 150°C. When kneading is carried out within the aforementioned temperature range, blocks can be effectively formed through fibrillation and kneading of the first binder polymer.

[0140] Subsequently, a step (S3) is performed to grind the mixture block to obtain electrode mixture powder. The mixture block formed by kneading can be immediately subjected to calendering, but in this case, it may be necessary to press the mixture block into a film shape, and therefore, the film density may be too high, or a film with uniform density may not be obtained. According to this disclosure, the mixture block is subjected to a grinding step.

[0141] In this case, the grinding step can be performed, for example, using a mixer or a grinder, but not limited thereto, and specifically, the grinding step can be performed at a speed of 5,000 rpm to 20,000 rpm for 30 seconds to 10 minutes, and more specifically at a speed of 10,000 rpm to 18,000 rpm for 30 seconds to 2 minutes.

[0142] Subsequently, a step (S4) is performed whereby the electrode mixture powder is fed between a plurality of rolls for calendering to manufacture an electrode sheet. Calendering may involve processing the electrode mixture powder into a film shape, and may, for example, involve rolling the mixture into a film shape with an average thickness of 50 μm to 300 μm. Calendering may be performed, for example, by one or more pairs of opposing rolls, and the rolling conditions may be controlled at a temperature of 25°C to 250°C, or a rotational speed of 5 rpm to 20 rpm, at a temperature of 100°C to 200°C.

[0143] Subsequently, a step (S5) is performed to laminate the electrode sheet onto at least one surface of the electrode current collector to manufacture an electrode. To form an electrode film on at least one surface of the current collector during the lamination step, the method may further include rolling the electrode film to a predetermined thickness and attaching it to the current collector. Lamination can be performed using lamination rollers, and in this case, the lamination rollers can be controlled at a temperature of 25°C to 250°C.

[0144] The present disclosure will be described in more detail below by way of examples, but the following examples are provided for illustrative purposes and the scope of the disclosure is not limited thereto.

[0145] Example 1

[0146] Prepare 96.5 parts by weight of lithium nickel-cobalt-manganese-aluminum oxide (NCMA, Li[Ni 0.88 Co 0.07 Mn 0.04 Al 0.01 O2) as the positive electrode active material, 1.5 parts by weight of carbon black as the conductive material, 1.5 parts by weight of polytetrafluoroethylene (PTFE, Daikin, 601X) as the first binder polymer, and 0.5 parts by weight of polypropylene (LGChem., H7918) as the second binder polymer.

[0147] The complex viscosity of the second binder polymer was 18 Pa·s when measured using an advanced rheological extension system (ARES-G2) at 170°C and 0.1 Hz, and the D50 was 8 μm when measured.

[0148] Subsequently, the positive electrode active material, conductive material, first binder polymer, and second binder polymer were fed into a mixer 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 then run at 25 rpm for 5 minutes under a cap pressure of 1.1 atm to obtain a mixture block. The mixture block was fed into a mixer and ground at 10,000 rpm for 30 seconds to obtain an electrode mixture powder. The electrode mixture powder was separated into particle sizes of 150 μm or larger and 1,000 μm or smaller in a multi-stage classifier. Subsequently, the sieved electrode powder was fed into a laboratory calender (conditions: roll diameter 200 mm, roll temperature 100°C, roll speed ratio 1.5) and subjected to multiple calendering processes to manufacture electrode sheets.

[0149] Two electrode sheets were placed on the two surfaces of an aluminum foil (15.8 μm) coated with a conductive underlayer containing a 5:6 (weight ratio) mixture of carbon black and acrylic binder, and laminated by pressing rollers at 150°C to produce an 81 μm thick positive electrode.

[0150] Example 2

[0151] The positive electrode was manufactured using the same method as in Example 1, except that polypropylene (LG Chem., H7914) was prepared as the second binder polymer. The thickness of the positive electrode was 81 μm at the time of measurement.

[0152] The complex viscosity of the second binder polymer was 144 Pa·s when measured using an advanced rheological extension system (ARES-G2) at 170°C and 0.1 Hz, and the D50 was 8 μm when measured.

[0153] Comparative Example 1

[0154] The positive electrode was manufactured using the same method as in Example 1, except that a second binder polymer was not used, and 2 parts by weight of a first binder polymer were prepared. The thickness of the positive electrode was 81 μm at the time of measurement.

[0155] Comparative Example 2

[0156] The positive electrode was manufactured using the same method as in Example 1, except that a second binder polymer was not used. 97 parts by weight of the positive electrode active material and 1.5 parts by weight of the first binder polymer were prepared. The thickness of the positive electrode was 80 μm at the time of measurement.

[0157] Comparative Example 3

[0158] The positive electrode was manufactured using the same method as in Example 1, except that polypropylene (LG Chem., M1500) was prepared as the second binder polymer. At the time of measurement, the second binder polymer had an average particle size (D50) of 8 μm and a complex viscosity of 1850 Pa·s. The thickness of the positive electrode at the time of measurement was 80 μm.

[0159] Comparative Example 4

[0160] The positive electrode was manufactured using the same method as in Example 1, except that polypropylene (TIANSHI WAX, PPW-0901) was used as the second binder polymer. At the time of measurement, the second binder polymer had an average particle size (D50) of 6 μm and a complex viscosity of 0.2 Pa·s. The thickness of the positive electrode at the time of measurement was 80 μm.

[0161] The thickness of the positive electrode was measured using a thickness gauge (VL-50S-B (Mitutoyo)).

[0162] Experimental Example 1: Evaluation of the Positive Electrode

[0163] [Table 1]

[0164]

[0165] Tensile strength can be determined by: preparing the electrode sheets of each embodiment and comparative example into dimensions of 50 mm (width) × 15 mm (length), fixing them to a fixture for tensile strength measurement, and measuring the stress value at the highest point on the stress-strain diagram when stretched 180° at 2 mm / min using a universal testing machine (LLOYD LS1, load cell 10 N) at 25°C.

[0166] For each of the positive electrodes according to the examples and comparative examples, which were prepared with dimensions of 50 mm (width) × 15 mm (length), the elastic indentation modulus and indentation hardness were measured using a nanoindenter (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 seconds, and an unloading rate of 40 mN / min.

[0167] Referring to Table 1, it was determined that the cathodes according to Examples 1 and 2 showed significant improvements in elastic indentation modulus and indentation hardness compared to the cathodes according to Comparative Examples 1 and 2 that used PTFE binder polymer alone.

[0168] Furthermore, it was determined that the cathode according to Example 1 showed significant improvement in elastic indentation modulus and indentation hardness compared to the cathodes according to Comparative Examples 3 and 4 which used a second binder polymer with excessively high or low complex viscosity.

[0169] In addition to the fibrillated binder polymer, the cathodes according to Examples 1 and 2 also contain a second binder polymer, but despite this, sufficient tensile strength is still ensured.

[0170] Experiment Example 2: Battery Evaluation

[0171] A negative electrode slurry was prepared by mixing a 5:5 mixture of artificial graphite and natural graphite as the negative electrode active material, superC as the conductive material, and SBR / CMC as the binder in a weight ratio of 96:1:3. The negative electrode slurry was applied to one surface of a copper current collector, dried at 130°C, and rolled to a porosity of 26% to manufacture the negative electrode.

[0172] A porous polyethylene separator is placed between the positive and negative electrodes prepared as described in each embodiment and comparative example to manufacture an electrode assembly. The electrode assembly is then placed in a box, and an electrolyte solution is injected into the box to manufacture a lithium secondary battery.

[0173] In this case, the electrolyte solution used is prepared by dissolving 1.0 M lithium hexafluorophosphate (LiPF6) in an organic solvent of ethylene carbonate / ethyl methyl carbonate / diethyl carbonate (mixed volume ratio of EC / EMC / DEC = 3 / 4 / 3).

[0174] The prepared lithium secondary battery single cell was charged to 4.25V at 0.7C in CC-CV mode at 25°C and discharged to 2.5V at a constant current of 0.5C. The initial capacity and capacity retention were measured during repeated charge and discharge cycles.

[0175] [Table 2]

[0176]

[0177] Referring to Table 2, it was determined that the secondary battery having the positive electrode according to Example 1 and Example 2 has sufficient initial capacity and capacity retention.

[0178] While the present disclosure has been described above with reference to a number of embodiments and figures, the present disclosure is not limited thereto, and various changes and modifications will be apparent to those skilled in the art to which the present disclosure pertains.

Claims

1. A dry electrode, comprising: Electrode current collector; as well as An electrode active material layer disposed on at least one surface of the electrode current collector. The electrode active material layer comprises an electrode active material, a conductive material, a first binder polymer, and a second binder polymer. The first adhesive polymer is a fibrillated polymer comprising polytetrafluoroethylene, and The second binder polymer has a complex viscosity of 1 Pa·s to 1500 Pa·s at 170°C and 0.1 Hz.

2. The dry electrode according to claim 1, The second binder polymer has a complex viscosity of 1 Pa·s to 1000 Pa·s at 170°C and 0.1 Hz.

3. The dry electrode according to claim 1, The average particle size (D50) of the second binder polymer is 50 μm or smaller.

4. The dry electrode according to claim 1, The average particle size (D50) of the second binder polymer is 0.1 μm to 50 μm.

5. The dry electrode according to claim 1, The second binder polymer has a melt index of 100 g / 10 min or greater at 230°C and a load of 2.16 kg.

6. The dry electrode according to claim 1, The first binder polymer and the second binder polymer are included in an amount of 1 to 5 parts by weight, based on a total of 100 parts by weight of the electrode active material layer.

7. The dry electrode according to claim 1, The weight ratio of the first adhesive polymer to the second adhesive polymer is 6:1 to 2:

1.

8. The dry electrode according to claim 1, The second adhesive polymer includes at least one of a polyolefin-based polymer or a polyvinylidene fluoride-based polymer.

9. The dry electrode according to claim 1, The second adhesive polymer includes polypropylene or polyvinylidene fluoride.

10. The dry electrode according to claim 1, The tensile strength of the dry electrode is 30 gf / mm. 2 Or larger.

11. The dry electrode according to claim 1, The elastic indentation modulus of the dry electrode is 2.5 GPa or greater.

12. A secondary battery, comprising: Positive electrode; negative electrode; a separator located between the positive electrode and the negative electrode; And electrolyte solutions, The positive electrode and the negative electrode are at least one of the electrodes according to any one of claims 1 to 11.

13. A method for manufacturing a dry electrode, comprising: (S1) The electrode active material, the conductive material, the first binder polymer, and the second binder polymer are dry-mixed in the absence of solvent to obtain a mixture; (S2) Knead the mixture to form a mixture block; (S3) Grind the mixture block to obtain electrode mixture powder; (S4) The electrode mixture powder is fed between a plurality of rollers for calendering to produce an electrode sheet; as well as (S5) The electrode sheet is laminated onto at least one surface of the electrode current collector to manufacture an electrode. The first adhesive polymer includes polytetrafluoroethylene, and The second binder polymer has a complex viscosity of 1 Pa·s to 1500 Pa·s at 170°C and 0.1 Hz.

Images