Dry electrode, method of preparing the same, and lithium secondary battery including the same

Abstract

This invention relates to a dry electrode comprising a current collector; and an electrode material mixture film disposed on the current collector, wherein the electrode material mixture film comprises an electrode active material and a fiberizable binder, wherein the C3H7 content of the current collector is measured by time-of-flight secondary ion mass spectrometry (ToF-SIMS). + Peak intensity (I) B ) and C2H3O + Peak intensity (I) A The ratio of (I) B / I A The carbon content at the interface of the current collector, as measured by scanning electron microscopy-energy dispersive X-ray spectroscopy, is 1.3 or less, and the ratio of carbon content in the electrode material mixture film to carbon content in the current collector is 1.03 or less.

Description

Technical Field

[0001] Cross-reference to related applications

[0002] This application claims priority to Korean Patent Application No. 10-2023-0189907, filed on December 22, 2023, and Korean Patent Application No. 10-2023-0189908, filed on December 22, 2023, the disclosure of which is incorporated herein by reference. Technical Field

[0004] This invention relates to dry electrodes, methods for their preparation, and lithium secondary batteries comprising them. Background Technology

[0005] Secondary batteries are now used not only in small products such as digital cameras, P-DVDs, MP3 players, mobile phones, PDAs, portable gaming devices, power tools, and electric bicycles, but also in large products that require high output, such as electric vehicles and hybrid vehicles, as well as energy storage devices and backup energy storage devices that store surplus generated electricity or renewable energy.

[0006] Typically, secondary batteries are prepared by the following method: after forming electrode active material layers by coating positive and negative current collectors with electrode active material slurry, positive and negative electrodes are prepared by drying and rolling processes, and electrode assemblies with a predetermined shape are formed by stacking the positive and negative electrodes on both sides of a separator. These assemblies are then housed in a battery case, and the battery case is sealed after electrolyte is injected.

[0007] During the drying process of the electrode active material slurry, defects such as pinholes or cracks may appear in the electrode active material layer formed on the current collector as the solvent contained in the slurry evaporates. Furthermore, since the electrode active material slurry is not dried uniformly inside and out during the drying process, there is a concern that the quality of the electrode may deteriorate due to powder buoyancy caused by differences in solvent evaporation rates. In this buoyancy phenomenon, particles in the first-dried areas move upwards, creating gaps with the relatively later-dried areas.

[0008] To address the above issues, drying devices capable of controlling the solvent evaporation rate are being considered, allowing for uniform drying of the electrode active material slurry both inside and out. However, these drying devices are very expensive and require considerable cost and time to operate, thus presenting a manufacturability disadvantage.

[0009] On the other hand, the solvent contained in conventional electrode active material slurries is N-methyl-2-pyrrolidone (NMP). Due to its high boiling point, it requires high thermal energy and a long drying oven to dry, which is very unfavorable for large-scale production. In addition, N-methyl-2-pyrrolidone (NMP) is an environmentally unfriendly substance because it is toxic and harmful to living organisms.

[0010] Therefore, research has recently been actively conducted on dry electrodes, which are prepared without the use of solvents. Dry electrodes are typically prepared by laminating a self-supporting electrode material mixture film containing electrode active materials, binders, or conductive agents onto a current collector and preparing it in sheet form. The electrode material mixture film is prepared by a process in which the electrode active materials, carbon materials as conductive agents, and fiberizable binders are first mixed together using a mixer or the like, the binder is fiberized by applying shear force through processes such as jet milling or kneading, and then the self-supporting film is prepared by calendering the resulting mixture into a film shape.

[0011] Conventionally, dry electrodes are prepared by forming a conductive underlayer on a current collector to prevent delamination between the electrode material mixture film and the current collector, followed by laminating the electrode material mixture film. However, with the conductive underlayer formed, the increased electrode thickness leads to reduced battery energy density and processability. When the current collector and electrode material mixture film are laminated without a conductive underlayer to address these issues, delamination of the electrode material mixture film occurs due to reduced adhesion.

[0012] Therefore, in order to prevent battery performance degradation due to delamination between the current collector and electrode material mixture film without a conductive underlayer, there is a need for a dry electrode with low interfacial resistance between the current collector and electrode material mixture film, and without delamination between the current collector and electrode material mixture film. Summary of the Invention

[0013] Technical issues

[0014] One aspect of the present invention provides a dry electrode having excellent adhesion and low interfacial resistance between a current collector and electrode material mixture film without a conductive underlay, a method for preparing the same, and a lithium secondary battery including the same.

[0015] Technical solution

[0016] [1] According to one embodiment of the present invention, a dry electrode is provided, the dry electrode comprising: a current collector; and an electrode material mixture film disposed on the current collector, wherein the electrode material mixture film comprises an electrode active material and a fiberizable binder, wherein the C3H7 content measured on the surface of the current collector by time-of-flight secondary ion mass spectrometry (ToF-SIMS) is... + Peak intensity (I) B ) and C2H3O + Peak intensity (I) A The ratio of (I) B / I A The carbon content at the interface of the current collector, as measured by scanning electron microscopy-energy dispersive X-ray spectroscopy, is 1.3 or less, and the ratio of carbon content in the electrode material mixture film to carbon content in the current collector is 1.03 or less.

[0017] [2] The dry electrode of [1] above, wherein the surface of the current collector is measured by time-of-flight secondary ion mass spectrometry (ToF-SIMS) for C3H7 + Peak intensity (I) B ) and total ion count (I T The ratio of (I) B / I T (can be 230×10) -5 Or smaller.

[0018] [3] The dry electrodes of [1] and / or [2] above, wherein the surface of the current collector is measured by time-of-flight secondary ion mass spectrometry (ToF-SIMS) for C2H3O + Peak intensity (I) A ) and total ion count (I T The ratio of (I) A / I T (can be 1,000 × 10) -5 Or smaller.

[0019] [4] The dry electrode of any one or more of [1] to [3] above, wherein the current collector may include aluminum.

[0020] [5] The dry electrode of any one or more of [1] to [4] above, wherein the tensile strength of the current collector can be 5 kgf / mm. 2 Or larger.

[0021] [6] The dry electrode of any one or more of [1] to [5] above, wherein the water contact angle of the surface of the current collector can be in the range of 10° to 100°.

[0022] [7] The dry electrode of any one or more of [1] to [6] above, wherein the surface of the current collector may include rolling oil.

[0023] [8] According to one embodiment of the present invention, a method for preparing a dry electrode is provided, the method comprising: subjecting the surface of a current collector to atmospheric pressure plasma treatment, wherein the loading rate of the current collector in the atmospheric pressure plasma treatment is in the range of 1 m / min to 100 m / min.

[0024] [9] In the method of [8] above, in atmospheric pressure plasma processing, the injection flow rate of inert gas can be in the range of 500 L / min to 1000 L / min, and the injection flow rate of oxygen-containing gas can be in the range of 0.1 L / min to 10 L / min.

[0025]

[10] The methods described above [8] and / or [9], wherein the ratio of the injection flow rate of the inert gas to the injection flow rate of the oxygen-containing gas in atmospheric pressure plasma processing can be in the range of 50 to 10,000.

[0026]

[11] Any one or more of the methods in [8] to

[10] above, wherein the voltage of the atmospheric pressure plasma treatment can be in the range of 10 kV to 20 kV.

[0027]

[12] Any one or more of the methods described in [8] to

[11] above, wherein the power of the atmospheric pressure plasma treatment can be in the range of 3 kW to 5 kW.

[0028]

[13] Any one or more of the methods described in [8] to

[12] above, wherein atmospheric pressure plasma treatment can be performed with the current collector and the plasma nozzle spaced apart from each other by 0.01 mm to 3.00 mm.

[0029]

[14] According to one embodiment of the present invention, a lithium secondary battery comprising at least one dry electrode as described in [1] to [7] above is provided.

[0030] Beneficial effects

[0031] The dry electrode according to the present invention is characterized by low interfacial resistance, excellent energy density, and excellent adhesion between the current collector and the electrode material mixture film. Therefore, the dry electrode according to the present invention can prevent delamination between the current collector and the electrode material mixture film, while possessing low interfacial resistance and excellent electrode energy density, and can improve the battery's resistance characteristics, fast charge / discharge characteristics, and lifespan characteristics. Attached Figure Description

[0032] The accompanying drawings illustrate preferred embodiments of the invention and, together with the detailed description, serve to illustrate the principles of the invention, but are not intended to limit the scope of the invention thereto. On the other hand, for clarity, the shapes, dimensions, scales, or proportions of the elements in the drawings as described herein may be enlarged.

[0033] Figure 1 This is a diagram showing the region mapped when the ratio of carbon content at the current collector interface to the carbon content in the electrode material mixture film is measured by scanning electron microscopy-energy dispersive X-ray spectroscopy. Detailed Implementation

[0034] The invention will be described in more detail below.

[0035] It should be understood that the words or terms used in the specification and claims should not be interpreted as having the meaning defined in a common dictionary, and it should be further understood that the words or terms should be interpreted as having a meaning consistent with their meaning in the context of the relevant field and technical concept of the invention, based on the principle that the inventor can appropriately define the meaning of the words or terms to best illustrate the invention.

[0036] In this invention, the MD direction (machine direction) refers to the longitudinal direction of the current collector or electrode material mixture film, and the TD direction (transverse direction) refers to the width direction of the current collector or electrode material mixture film.

[0037] In this specification, "material mixture composition" means a mixture comprising electrode active materials, a binder, and optionally a conductive agent, which is physically mixed to form a homogeneous dispersed phase. This mixture may be a powder mixture, a product of the mixing process according to this specification, and may be a mixture substantially free of solvents. Herein, the fact that it is substantially free of solvents means that no solvent is added or only trace amounts of solvent are added when mixing the material mixture composition.

[0038] In this specification, "mixed aggregate" means an aggregate in which the mixture of powders is transformed into a dough-like aggregate by bonding or joining together while the binder is fiberized by applying shear force to the mixture of materials, wherein it, as a product of the kneading process according to this specification, may have a solids content substantially close to 100% and may contain a small amount of solvent in some cases.

[0039] In this specification, "electrode powder" refers to a material in which a mixed aggregate is ground to form a powder by reducing the particle size, and may mean an electrode material in powder form containing an electrode active material as well as a binder and optionally a conductive agent.

[0040] In this specification, "electrode material mixture film" can refer to a film prepared in a self-supporting monolithic form using an "electrode material mixture" containing electrode active materials, conductive agents, and binders but without solvents, or it can refer to an electrode material mixture layer laminated on a current collector. The term "self-supporting" in this specification means that it can independently maintain its form without relying on other components and can be moved or handled on its own. Electrode material mixture films can be formed by pressing electrode powder, as described later. For example, electrode powder can be integrally formed by pressing to create a layered structure.

[0041] In this specification, "powder-pressed film" means a film formed into a sheet form after passing through a powder pressing process (where electrode powder first passes through the rollers in a roll-to-roll process) (e.g., a calendering process) and before passing through the last roller in the roll-to-roll process, wherein it can be a self-supporting sheet, but can also be a sheet with relatively weak self-supporting capabilities. In this document, "powder pressing" means the formation of a self-supporting sheet form from electrode powder through the rollers in a roll-to-roll process, and "pressing" is a process performed during the preparation of an electrode material mixture film from the powder-pressed film, wherein it can mean the process of rolling the powder-pressed film.

[0042] In this specification, "volume cumulative average particle size D" 50 "This refers to the particle size at 50% cumulative volume in the particle size distribution curve." 50 For example, this can be measured using laser diffraction. Laser diffraction can typically measure particle sizes ranging from submicron to several millimeters and can yield highly repeatable and high-resolution results.

[0043] In this specification, "average particle size" means the arithmetic mean of particle sizes calculated after measuring the particle sizes of at least 30 particles observed in a scanning electron microscope image at a field of view of 5,000 to 20,000x. In this case, particle size refers to the diameter of the longest axis of the particle. While "volume cumulative average particle size D" is used... 50 The methods for measuring “average particle size” and “powder average particle size” are different, but their values ​​can be obtained similarly, and the volumetric cumulative average particle size D measured in the powder state is... 50 Within the error range, it can have values ​​similar to the average particle size observed in scanning electron microscope images of the electrodes after the powder has been prepared into electrodes.

[0044] In this specification, porosity can be calculated using the following equation A.

[0045] [Equation A]

[0046] Porosity (%) = {1 - (electrode density / actual density)} × 100

[0047] In Equation A, the true density is the calculated density derived from the density and mass ratio of the component materials constituting the powder-pressed film or electrode material mixture film, assuming that pores are not included, and the electrode density is the measured density of the powder-pressed film or electrode material mixture film measured by sampling the powder-pressed film or electrode material mixture film at a predetermined size.

[0048] As a result of ongoing research aimed at achieving low interfacial resistance and excellent adhesion between the current collector and electrode material mixture film without a conductive underlayer, the inventors have discovered that C3H7, as measured by time-of-flight secondary ion mass spectrometry (ToF-SIMS) on the surface of the current collector, exhibits... + Peak intensity (I) B ) and C2H3O + Peak intensity (I) A The ratio of (I) B / I A When the ratio of carbon content at the interface of the current collector to the carbon content in the electrode material mixture film, as measured by scanning electron microscopy-energy dispersive X-ray spectroscopy, meets specific conditions, the energy density can be excellent, while adhesion and interfacial resistance are improved, thereby enabling the completion of the present invention.

[0049] dry electrode

[0050] The dry electrode according to the present invention comprises: a current collector; and an electrode material mixture film disposed on the current collector, wherein the electrode material mixture film comprises an electrode active material and a fiberizable binder, wherein the C3H7 content measured on the surface of the current collector by time-of-flight secondary ion mass spectrometry (ToF-SIMS) is... + Peak intensity (I) B ) and C2H3O + Peak intensity (I) A The ratio of (I) B / I A The carbon content at the interface of the current collector, as measured by scanning electron microscopy-energy dispersive X-ray spectroscopy, is 1.3 or less, and the ratio of carbon content in the electrode material mixture film to carbon content in the current collector is 1.03 or less.

[0051] Conventionally, dry electrodes are prepared by forming a conductive underlayer on a current collector to prevent delamination between the electrode material mixture film and the current collector, followed by laminating the electrode material mixture film. In this case, since the current collector is typically a high-strength foil with a thickness in the micrometer range, a large amount of rolling oil may remain on the current collector during its preparation.

[0052] However, if a large amount of rolling oil remains on the current collector, delamination may occur between the current collector and the electrode material mixture film due to the residual rolling oil.

[0053] In cases where a conductive underlayer is formed on the current collector to prevent delamination between the current collector and the electrode material mixture film, the electrode thickness increases, thereby reducing the battery's energy density. Furthermore, because the conductive underlayer contains a large amount of binder which is wetted and swollen by the electrolyte, breaking the conductive network, there is a problem that the battery resistance may increase rapidly. Additionally, the binder in the conductive underlayer may be oxidized or degraded at high potentials, further increasing battery resistance, and processability may be reduced due to additional costs and processes involved in forming the conductive underlayer.

[0054] To prevent these problems, in the case where a dry electrode is prepared by simply laminating a film of the current collector and electrode material mixture without a conductive underlayer, there is an advantage of increased energy density due to the reduced electrode thickness since no conductive underlayer is formed. However, due to the low adhesion between the current collector and electrode material mixture film, delamination occurs, which prevents the battery from operating or causes problems such as deterioration of the battery's resistance characteristics, fast charge / discharge characteristics, and lifespan characteristics.

[0055] Therefore, in order to achieve excellent electrochemical characteristics of the battery by improving the adhesion between the current collector and the electrode material mixture film without a conductive underlayer, the present invention aims to change the composition of the rolling oil remaining on the current collector by performing plasma treatment on the current collector under specific conditions.

[0056] According to one embodiment of the present invention, the surface of the current collector is measured by time-of-flight secondary ion mass spectrometry (ToF-SIMS) for C3H7. + Peak intensity (I) B ) and C2H3O + Peak intensity (I) A The ratio of (I) B / I A () can be 1.3 or smaller.

[0057] Measured C2H3O + Peak intensity (I) A This can be a factor indicating the amount of CHO-based organic matter present on the current collector, as well as the measured C3H7. + Peak intensity (I) BThis can be a factor indicating the amount of CH-based organic matter present on the current collector. In this case, C3H7-based organic matter is a hydrophilic material, where higher amounts may result in better adhesion, but they may also act as a factor maximizing interfacial resistance. Conversely, CH-based organic matter is a hydrophobic material, where higher amounts may result in lower adhesion. Therefore, C3H7 must be... + Peak intensity (I) B ) and C2H3O + Peak intensity (I) A The ratio of (I) B / I A The resistance is controlled within an appropriate range to achieve low resistance as well as excellent coatability and adhesion.

[0058] Preferably, the surface C3H7 of the current collector is measured by time-of-flight secondary ion mass spectrometry (ToF-SIMS). + Peak intensity (I) B ) and C2H3O + Peak intensity (I) A The ratio of (I) B / I A The ) can be 0.01 or greater, 0.02 or greater, 0.03 or greater, or 0.04 or greater, can be 1.3 or less, 1.2 or less, 1.0 or less, 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, 0.5 or less, or 0.45 or less, and can more preferably be in the range of 0.25 to 0.45.

[0059] C3H7 + Peak intensity (I) B ) and C2H3O + Peak intensity (I) A The ratio of (I) B / I A When the value is greater than 1.3, the surface energy of the current collector does not increase because the composition of the rolling oil formed on the surface of the current collector is not sufficiently changed, resulting in a decrease in the adhesion between the current collector and the electrode material mixture film. Therefore, when the above range is met, the adhesion between the current collector and the electrode material mixture film is excellent, and the amount of rolling oil remaining on the current collector can be sufficiently reduced, thereby improving the battery's resistance characteristics, fast charge / discharge characteristics, and lifespan characteristics.

[0060] According to one embodiment of the invention, the ratio of carbon content at the current collector interface of the dry electrode, as measured by scanning electron microscopy-energy dispersive X-ray spectroscopy, to the carbon content in the electrode material mixture film can be 1.03 or less. A feature of the invention is that, since the electrode does not include a conductive underlayer, an excellent electrode is achieved while maintaining excellent energy density by preventing degradation of the battery's electrochemical characteristics due to excessive binder contained in the conductive underlayer. Therefore, when the ratio of carbon content at the current collector interface, as measured by scanning electron microscopy-energy dispersive X-ray spectroscopy, to the carbon content in the electrode material mixture film is greater than 1.03, problems arise such as reduced electrode energy density, potentially increased resistance due to excessive binder, and reduced processability. Preferably, the ratio of carbon content at the current collector interface, as measured by scanning electron microscopy-energy dispersive X-ray spectroscopy, to the carbon content in the electrode material mixture film can be in the range of 0.53 to 1.03.

[0061] There are no restrictions on the intensity of carbon distribution on the electrode cross section measured by scanning electron microscopy-energy dispersive X-ray spectroscopy, as long as it can be measured by a measuring device commonly used in the art, but for example, a JSM-IT800 (JEOLLtd.) can be used for measurement.

[0062] In this case, the ratio of carbon content at the current collector interface to carbon content in the electrode material mixture film, measured by scanning electron microscopy-energy dispersive X-ray spectroscopy, can be measured under the conditions of 5 kV accelerating voltage, 2.3 nA incident current (probe current), and 10 mm working distance.

[0063] The carbon content at the interface of the current collector can be obtained as the average of the carbon content (wt%) measured by 10 mappings centered on the interface of the current collector in a rectangular shape with dimensions of 2.0 μm × 1.5 μm. The carbon content in the electrode material mixture film can be obtained as the average of the carbon content (wt%) measured by 10 mappings such that only the interior of the electrode material mixture film is included in a rectangular shape with dimensions of 2.0 μm × 1.5 μm. The total count measured during each mapping period can be 35,000 cps.

[0064] For example, refer to Figure 1Ten mappings were performed with the current collector interface as the center, using a rectangular shape (e.g., a dashed rectangle) of size 2.0 μm × 1.5 μm, to measure the carbon content (wt%) and obtain an average value, which can be evaluated as the carbon content at the current collector interface. Ten mappings were also performed such that only the interior of the electrode material mixture film was included in a rectangular shape (e.g., a solid rectangle) of size 2.0 μm × 1.5 μm, to measure the carbon content (wt%) and obtain an average value, which can be evaluated as the carbon content in the electrode material mixture film. Thus, the ratio of the evaluated carbon content at the current collector interface to the evaluated carbon content in the electrode material mixture film can be obtained.

[0065] According to one embodiment of the present invention, the surface of the current collector is measured by time-of-flight secondary ion mass spectrometry (ToF-SIMS) for C3H7. + Peak intensity (I) B ) and total ion count (I T The ratio of (I) B / I T (can be 230×10) -5 Or smaller, and preferably 1×10 -5 Or larger, 10×10 -5 Or larger, 20×10 -5 Or larger, 30×10 -5 Or larger, 40×10 -5 Or larger, 50×10 -5 Or larger, 60×10 -5 Or larger, 70×10 -5 Or larger, 72×10 -5 Or larger, 74×10 -5 Or larger, or 76×10 -5 Or larger, such as 200×10 -5 Or smaller, 150×10 -5 Or smaller, 100×10 -5 Or smaller, 90×10 -5 Or smaller, 88×10 -5 Or smaller, 86×10 -5 Or smaller, 84×10 -5 Or smaller, 82×10 -5 Or smaller, or 81×10 -5 Or smaller, and more preferably in 76×10 -5 Up to 81×10 -5Within the range specified above, since the surface energy of the current collector can be increased due to the smaller amount of low-reactivity organic matter on it, the adhesion between the current collector and the electrode material mixture film can be excellent, and excellent resistance characteristics can be achieved, while preventing the peeling of the electrode material mixture film.

[0066] According to one embodiment of the present invention, the surface C2H3O of the current collector is measured by time-of-flight secondary ion mass spectrometry (ToF-SIMS). + Peak intensity (I) A ) and total ion count (I T The ratio of (I) A / I T (can be 1,000 × 10) -5 Or smaller, and preferably 1×10 -5 Or larger, 10×10 -5 Or larger, 20×10 -5 Or larger, 40×10 -5 Or larger, 60×10 -5 Or larger, 80×10 -5 Or larger, 100×10 -5 Or larger, 120×10 -5 Or larger, 140×10 -5 Or larger, 160×10 -5 Or larger, 180×10 -5 Or larger, or 184×10 -5 Or larger, such as 900×10 -5 Or smaller, 800×10 -5 Or smaller, 700×10 -5 Or smaller, 600×10 -5 Or smaller, 500×10 -5 Or smaller, 400×10 -5 Or smaller, 350×10 -5 Or smaller, 320×10 -5 Or smaller, 310×10 -5 Or smaller, or 309×10 -5 Or smaller, and more preferably in 184×10 -5 Up to 309×10 -5 Within the range specified above, since the surface energy of the current collector can be increased due to the smaller amount of low-reactivity organic matter on it, the adhesion between the current collector and the electrode material mixture film can be excellent, and excellent resistance characteristics can be achieved, while preventing the peeling of the electrode material mixture film.

[0067] According to one embodiment of the invention, time-of-flight secondary ion mass spectrometry (ToF-SIMS) can be performed using commonly used equipment, and preferably using the TOF-SIMS 5 from Ion-TOF GmbH under specific conditions. For example, time-of-flight secondary ion mass spectrometry (ToF-SIMS) can be performed under the following conditions: it is performed in positive mode, the measured mass range is 1 u to 873 u, the primary ion (source ion) type is Bi3, and the primary ion dose is 3.81 × 10⁻⁶. 8 ions / cm 2 The voltage was 30 KeV, the detection time was 100 seconds, and the field of view (FOV) was 100 μm × 100 μm.

[0068] Next, the current collector will be described in detail.

[0069] When the dry electrode is the positive electrode, there are no particular restrictions on the current collector, as long as it is conductive and will not cause chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel that has been surface-treated with one of carbon, nickel, titanium, silver, etc. can be used as the current collector.

[0070] When the dry electrode is the negative electrode, there are no particular restrictions on the current collector, as long as it has high conductivity and will not cause changes in the battery. For example, copper; stainless steel; aluminum; nickel; titanium; sintered carbon; copper or stainless steel that has been surface treated with one of carbon, nickel, titanium, silver, etc.; aluminum-cadmium alloy; etc.

[0071] Specifically, the current collector may include aluminum, and more specifically, aluminum alloy A1100. When the current collector is formed of aluminum or aluminum alloy A1100, current collector breakage due to intense plasma treatment can be prevented, and the problem of reduced adhesion due to residual rolling oil can be improved.

[0072] According to one embodiment of the invention, the thickness of the current collector can be in the range of 5 µm to 30 µm, preferably 8 µm to 20 µm, and more preferably 10 µm to 15 µm. When these ranges are met, it is desirable to prevent short circuits because defects such as pinholes are not present in the current collector, and to improve energy density because the thickness is not excessive. Furthermore, the current collector can have a fine surface roughness to improve adhesion to the electrode material mixture film.

[0073] According to one embodiment of the present invention, the tensile strength of the current collector can be 5 kgf / mm. 2 Or greater, preferably 6 kgf / mm 2or greater, and more preferably 7 kgf / mm 2 within the range of or greater. When the above range is satisfied, since the current collector has high strength, even if the current collector is thin, it is less likely to break and can withstand the impact from strong plasma treatment. In addition, regarding the current collector with high strength and high stiffness, different from the conventional current collector substrate, a large amount of rolling oil can be used to prepare the current collector. Therefore, the effects of improving the coatability and adhesiveness due to plasma treatment can be more excellent.

[0074] According to an embodiment of the present invention, the water contact angle of the surface of the current collector can be within the range of 10° to 100°, preferably 10° to 80°, and more preferably 10° to 70°. When the above range is satisfied, since the surface energy of the current collector can be excellent while the processing cost and complexity are not too high, the adhesiveness between the current collector and the electrode material mixture film can be excellent.

[0075] The water contact angle can be measured by conventional methods in the art. For example, it can be measured by the tangent angle method by dropping 3 μl of droplets at a rate of 3 μl / second using DSA100 of KRUSS GmbH.

[0076] Next, the electrode material mixture film will be described in detail.

[0077] According to an embodiment of the present invention, the electrode material mixture film may include an electrode active material and a fibrillatable binder, and the electrode material mixture film may preferably include an electrode active material, a conductive agent, and a fibrillatable binder.

[0078] There is no particular limitation on the electrode active material as long as it is a commonly used electrode active material. For example, the electrode active material can be a positive electrode active material or a negative electrode active material.

[0079] The positive electrode active material is a compound capable of reversibly inserting and extracting lithium, and the positive electrode active material may preferably include a lithium metal oxide, and the lithium metal oxide contains lithium and at least one metal such as cobalt, manganese, nickel, or aluminum. More preferably, the lithium metal oxide may include lithium-manganese-based oxides (such as LiMnO2, LiMn2O4, etc.), lithium-cobalt-based oxides (such as LiCoO2, etc.), lithium-nickel-based oxides (such as LiNiO2, etc.), lithium-nickel-manganese-based oxides (such as LiNi 1-Y Mn Y O2 (where 0 < Y < 1), LiMn 2-Z Ni z O4 (where 0 < Z < 2), etc.), lithium-nickel-cobalt-based oxides (such as LiNi 1-Y1 CoY1 O2 (where 0 < Y1 < 1), etc., lithium-manganese-cobalt-based oxides (e.g., LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-Z1 Co Z1 O4 (where 0 < Z1 < 2), etc., lithium-nickel-manganese-cobalt-based oxides (e.g., Li(Ni p Co q Mn r )O2 (where 0 < p < 1, 0 < q < 1, 0 < r < 1 and p + q + r = 1) or Li(Ni p1 Co q1 Mn r1 )O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r1 < 2 and p1 + q1 + r1 = 2), etc., lithium-nickel-cobalt-transition metal (M) oxides (e.g., Li(Ni p2 Co q2 Mn r2 M s2 )O2 (where M is selected from aluminum (Al), iron (Fe), vanadium (V), chromium (Cr), titanium (Ti), tantalum (Ta), magnesium (Mg) and molybdenum (Mo), and p2, q2, r2 and s2 are atomic fractions of each independent element, where 0 < p2 < 1, 0 < q2 < 1, 0 < r2 < 1, 0 < s2 < 1 and p2 + q2 + r2 + s2 = 1), etc.), or lithium iron phosphate (e.g., Li 1+a Fe 1-x M x (PO 4-b )X b (where M is at least one selected from Al, Mg and Ti, and X is at least one selected from fluorine (F), sulfur (S) and nitrogen (N), where -0.5 ≤ a ≤ 0.5, 0 ≤ x ≤ 0.5 and 0 ≤ b ≤ 0.1), and may include a composite of any one of them or both or more of them.)

[0080] Among these materials, in terms of improving the capacity characteristics and stability of the battery, the lithium metal oxide can be LiCoO2, LiMnO2, LiNiO2, lithium nickel manganese cobalt oxide (e.g., Li(Ni 1 / 3 Mn 1 / 3 Co 1 / 3 )O2, Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15Co 0.15 )O2 and Li(Ni 0.8 Mn 0.1 Co 0.1 O2, etc.), lithium nickel cobalt aluminum oxides (e.g., Li(Ni) 0.8 Co 0.15 Al 0.05 O2, etc.), lithium nickel manganese cobalt aluminum oxides (e.g., Li(Ni) 0.86 Co 0.05 Mn 0.07 Al 0.02 (O2) or lithium iron phosphate (e.g., LiFePO4), and either or a mixture of both or more thereof may be used.

[0081] For example, electrode active materials may include phosphates represented by Formula 1 below.

[0082] [Formula 1]

[0083] Li 1+x [Fe 1-a-b Mn a M 1 b ]PO4

[0084] In Equation 1, M 1 The element is selected from at least one element chosen from Al, Mg, nickel (Ni), cobalt (Co), Ti, gallium (Ga), copper (Cu), V, Mo, niobium (Nb), tungsten (W), zirconium (Zr), cerium (Ce), indium (In), zinc (Zn), and yttrium (Y), and has the properties -0.5 ≤ x ≤ 0.5, 0 ≤ a ≤ 0.9, and 0 ≤ b ≤ 0.1. Under these conditions, excellent economic efficiency and stability are desirable.

[0085] For example, in terms of preparing electrode material mixture films in a uniform and stable film form, the electrode active material may include lithium nickel cobalt manganese aluminum oxide.

[0086] The negative electrode active material may include at least one of the following: lithium metal, carbon material capable of reversibly inserting / de-inserting lithium ions, metal or an alloy of lithium and the metal, metal composite oxide, material capable of being doped and de-doped with lithium, and transition metal oxide.

[0087] As a carbon material capable of reversibly embedding / extracting lithium ions, carbon-based negative electrode active materials commonly used in lithium ion secondary batteries can be used without particular limitation, and as typical examples, crystalline carbon, amorphous carbon, or both can be used. Examples of crystalline carbon can be graphite, such as irregular, planar, flaky, spherical, or fibrous natural graphite or artificial graphite, and examples of amorphous carbon can be soft carbon (low-temperature sintered carbon) or hard carbon, mesophase pitch carbide, and calcined coke.

[0088] As the metal or an alloy of lithium and the metal, a metal selected from Cu, Ni, sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), beryllium (Be), Mg, calcium (Ca), strontium (Sr), silicon (Si), antimony (Sb), lead (Pb), In, Zn, barium (Ba), radium (Ra), germanium (Ge), Al, and tin (Sn), or an alloy of lithium and the metal can be used.

[0089] As the metal composite oxide, one selected from the following can be used: PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, Bi2O5, Li x Fe2O3 (0 ≤ x ≤ 1), Li x WO2 (0 ≤ x ≤ 1), and Sn x Me 1- x Me' y O z (Me: manganese (Mn), Fe, Pb, or Ge; Me': Al, boron (B), phosphorus (P), Si, elements of Group I, Group II, and Group III of the periodic table, or halogen; 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8).

[0090] Materials that can be doped and undoped with lithium can include Si, SiO x (0 < x ≤ 2), Si-Y alloy (where Y is an element selected from the following: alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, and not Si), Sn, SnO2, and Sn-Y (where Y is an element selected from the following: alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, and not Sn), and mixtures of SiO2 and at least one of them can also be used. Element Y can be selected from Mg, Ca, Sr, Ba, Ra, scandium (Sc), Y, Ti, Zr, hafnium (Hf), (Rf), V, Nb, Ta, (Db), Cr, Mo, W, (Sg), Technetium (Tc), Rhenium (Re) (Bh), Fe, Pb, Ruthenium (Ru), Osmium (Os) (Hs), rhodium (Rh), iridium (Ir), palladium (Pd), platinum (Pt), Cu, silver (Ag), gold (Au), Zn, cadmium (Cd), B, Al, Ga, Sn, In, Ge, P, arsenic (As), Sb, bismuth (Bi), S, selenium (Se), tellurium (Te), polonium (Po), and combinations thereof.

[0091] Transition metal oxides can include lithium-containing titanium composite oxides (LTO), vanadium oxides, and lithium vanadium oxides.

[0092] Preferably, the electrode active material may include at least one selected from lithium nickel cobalt manganese aluminum oxide and lithium iron phosphate, and more preferably includes lithium nickel cobalt manganese aluminum oxide.

[0093] The conductive agent is a component used to further improve the conductivity of the electrode active material. There are no particular limitations on the conductive agent, as long as it is conductive and does not cause chemical changes in the battery. For example, conductive materials such as: carbon powder (e.g., carbon black, acetylene black, Ketjen black, channel black, furnace black, lampblack, or thermally cracked black); graphite powder (e.g., natural graphite, artificial graphite, or graphite with a well-formed crystal structure); conductive fibers (e.g., carbon fibers or metal fibers); fluorocarbon powder; conductive powders (e.g., aluminum powder and nickel powder); conductive whiskers (e.g., zinc oxide whiskers and potassium titanate whiskers); conductive metal oxides (e.g., titanium oxide); or polyphenylene derivatives. Specifically, for uniform mixing and improved conductivity, the conductive agent may include at least one selected from activated carbon, graphite, carbon black, and carbon nanotubes (CNTs).

[0094] There are no particular restrictions on the type of fiberizable adhesive, as long as it can be fiberized, and fiberization refers to a process that finely separates the polymer. For example, fiberization can be carried out using mechanical shear forces, and the surface of the fiberized polymer fibers is loose, thereby producing a large number of fine fibers (fibrils). The fiberizable adhesive may preferably contain at least one selected from polytetrafluoroethylene (PTFE) and polyolefins, more preferably polytetrafluoroethylene (PTFE), and even more preferably polytetrafluoroethylene (PTFE). Preferably, based on the total weight of the adhesive, polytetrafluoroethylene (PTFE) may be included in an amount of 60% by weight or more. In this case, the adhesive may additionally contain at least one selected from PEO (polyethylene oxide), PVdF (polyvinylidene fluoride), PVdF-HFP (polyvinylidene fluoride-copolymer-hexafluoropropylene), and polyolefin-based adhesives.

[0095] The weight ratio of the electrode active material, conductive agent, and fiberizable binder can be 80% to 98% by weight: 0.5% to 10% by weight: 0.5% to 10% by weight, and is preferably 85% to 98% by weight: 0.5% to 5% by weight: 0.5% to 10% by weight. When the above ranges are met, sufficient fiberization can be achieved because the amount of binder can be appropriately included. Therefore, the fiberized binder can aggregate to form an electrode powder, can aggregate to form an electrode material mixture film, and can improve the physical properties of the electrode material mixture film.

[0096] In this invention, the porosity of the electrode material mixture film can be 20% to 50%, specifically 20% to 40%, and more specifically 25% to 35%. When the above ranges are met, the lifetime and output characteristics can be improved due to the excellent electrolyte impregnation, and the energy density can be excellent.

[0097] Dry electrodes may include rolling oil on the surface of the current collector. There are no particular limitations on the rolling oil, as long as it can lubricate and remove foreign matter during rolling, while cooling the high-temperature frictional heat generated during rolling.

[0098] Dry electrodes may not include a conductive underlayer. In this document, the conductive underlayer may comprise a conductive material and a binder, wherein the conductive material is not limited as long as it is conductive, but may, for example, be a carbon-based material. The binder may include fluorine-based binders (including PVDF and PVDF copolymers), acrylic binders, and water-based binders that are soluble in solvents. By omitting the conductive underlayer, the energy density of the electrode can be increased, and the resistance can be reduced.

[0099] Methods for preparing dry electrodes

[0100] The method for preparing a dry electrode according to the present invention includes the step of subjecting the surface of a current collector to atmospheric pressure plasma treatment, wherein the loading rate of the current collector during atmospheric pressure plasma treatment is in the range of 1 m / min to 100 m / min.

[0101] The atmospheric pressure plasma processing will be described in detail below, and since the current collector has already been described above, a detailed description of the current collector will be omitted.

[0102] (S1) Steps for performing atmospheric pressure plasma treatment

[0103] The method for preparing a dry electrode according to the present invention includes the step of treating the surface of a current collector with atmospheric pressure plasma. The specific peak intensity measured on the surface of the current collector by time-of-flight secondary ion mass spectrometry (ToF-SIMS) can be achieved by various methods, but is preferably achieved by atmospheric pressure plasma treatment.

[0104] Conventionally, plasma treatment is carried out in a vacuum. However, there are disadvantages to plasma treatment in a vacuum: continuous processing is not possible because the plasma treatment takes place in a closed space. That is, the need to use a vacuum chamber leads to increased processing time and makes plasma treatment unsuitable for large-scale or continuous production. Therefore, atmospheric pressure plasma treatment can provide an efficient continuous process with excellent machinability.

[0105] In atmospheric pressure plasma processing, the loading rate of the current collector is in the range of 1 m / min to 100 m / min, preferably 2 m / min or greater, 3 m / min or greater, 4 m / min or greater, 5 m / min or greater, 6 m / min or greater, 7 m / min or greater, 8 m / min or greater, 9 m / min or greater, 10 m / min or greater, 11 m / min or greater, 12 m / min or greater, 13 m / min or greater, 14 m / min or greater, or 15 m / min or greater, and can be 95 m / min or less, 90 m / min or less, 85 m / min or less, 80 m / min or less, 75 m / min or less, 70 m / min or less, 65 m / min or less, or 60 m / min or less. When the loading speed of the current collector is less than 1 m / min, the following problems exist: cracking occurs in the current collector due to excessive plasma treatment, all rolling oil is lost due to excessive surface etching, and machinability is reduced due to the low loading speed. When the loading speed of the current collector is greater than 100 m / min, the following problems exist: sufficient plasma treatment cannot be achieved due to the high speed, and adhesion is reduced because the composition of the rolling oil is not sufficiently altered. Therefore, when the above ranges are met, adhesion can be improved by altering the rolling oil through sufficient plasma treatment while appropriately preventing current collector cracking.

[0106] In atmospheric pressure plasma processing, the injection flow rate of inert gas can be in the range of 650 L / min to 1,000 L / min, preferably 675 L / min to 950 L / min, more preferably 700 L / min to 900 L / min, and even more preferably 725 L / min to 900 L / min.

[0107] Atmospheric pressure plasma treatment can be performed by injecting oxygen-containing gas. Preferably, atmospheric pressure plasma treatment can be performed using oxygen-containing gas as the plasma activation gas. When the above conditions are met, the processability can be excellent because plasma treatment can be performed at atmospheric pressure without the need for plasma treatment in a vacuum chamber.

[0108] In atmospheric pressure plasma processing, the injection flow rate of oxygen-containing gas can be in the range of 0.1 L / min to 10 L / min, preferably 0.5 L / min to 6 L / min, and more preferably 1 L / min to 4 L / min. In this case, the oxygen-containing gas can have an oxygen content of 80% by weight or more, and can preferably be dry air free of foreign matter.

[0109] In atmospheric pressure plasma processing, the injection flow rate (F) of inert gas N ) and oxygen-containing gas injection flow rate (F O The ratio of (F) N / F O The value can be in the range of 50 to 10,000, preferably 60 to 5,000, and more preferably 90 to 1,000.

[0110] The voltage for atmospheric pressure plasma treatment can be in the range of 10 kV to 20 kV, preferably 11 kV to 19 kV, and more preferably 12 kV to 18 kV. When these ranges are met, an appropriate level of plasma can be effectively generated.

[0111] The power for atmospheric pressure plasma processing can be in the range of 3 kW to 5 kW, preferably 3.2 kW to 4.8 kW, and more preferably 3.4 kW to 4.6 kW. When these ranges are met, the processability can be excellent because plasma can be generated with efficient power.

[0112] Atmospheric pressure plasma treatment can be carried out with the current collector and the plasma nozzle spaced 0.01 mm to 3.00 mm apart, and preferably with the current collector and the plasma nozzle spaced 0.05 mm to 2.90 mm apart, more preferably 0.1 mm to 2.5 mm apart, and even more preferably 0.5 mm to 2.5 mm apart.

[0113] Atmospheric pressure plasma treatment can be performed 1 to 10 times, preferably 1 to 8 times, more preferably 1 to 6 times, even more preferably 1 to 4 times, and even more preferably 1 to 3 times. When the above ranges are met, excellent adhesion can be achieved because the surface of the current collector can be adequately plasma-treated.

[0114] This invention may exclude the step of forming a conductive underlayer on the current collector. Since the specific composition of the conductive underlayer has already been described above, its description will be omitted.

[0115] The method for preparing a dry electrode according to the present invention may further include the step of preparing the electrode by laminating an electrode material mixture film onto one or both sides of the current collector and laminating the resulting product after atmospheric pressure plasma treatment of the surface of the current collector. Lamination may be a step of attaching the electrode material mixture film to the current collector by rolling. Lamination can be performed by rolling using laminating rollers, and in this case, the laminating rollers can be maintained at a temperature of 20°C to 200°C.

[0116] Since the specific composition of the electrode material mixture film has been described above, its description will be omitted, and the electrode material mixture film can be prepared by including the following steps: (a) mixing the electrode active material with a fiberizable binder to obtain a material mixture composition; (b) kneading the material mixture composition to prepare a mixed aggregate; (c) grinding the mixed aggregate to prepare an electrode powder; and (d) calendering the electrode powder.

[0117] The steps will preferably be described below.

[0118] Step (a) will be described as mixing an electrode active material with a fiberizable binder to obtain a material mixture composition. Preferably, step (a) can be a step of obtaining a material mixture composition by mixing the electrode active material, the conductive agent, and the fiberizable binder. Since the specific compositions of the electrode active material, the conductive agent, and the fiberizable binder have already been described above, their descriptions will be omitted.

[0119] Mixing allows the electrode active material, the fiberizable binder, and the optional conductive agent to be uniformly distributed. Since they are mixed in powder form, they can be mixed without limitation by various methods, as long as they can be easily mixed. However, since the electrode in this invention is prepared as a dry electrode without the use of solvents, mixing can be carried out as a dry mixture and can be performed by adding the above materials to a device such as a mixer or blender.

[0120] In this case, mixing can be carried out in a mixer at 500 rpm to 20,000 rpm for 1 to 60 minutes, preferably at 600 rpm to 1,800 rpm for 2 to 30 minutes, more preferably at 800 rpm to 1,600 rpm for 3 to 20 minutes, and even more preferably at 1,000 rpm to 1,400 rpm for 5 to 15 minutes. When mixing is carried out within the above ranges, battery performance can be improved because the materials can be uniformly mixed.

[0121] Next, step (b) of kneading the material mixture composition to prepare a mixed assembly will be described. For the material mixture composition obtained in the mixing, a fiberization process for fiberizing the fiberizable binder can be carried out, and preferably, the mixed assembly can be prepared by kneading.

[0122] Kneading can be performed at a speed of 50 rpm to 300 rpm, and preferably at a speed of 70 rpm to 200 rpm. Furthermore, kneading can be performed by loading the material mixture composition at a rate of 5 kg / h to 40 kg / h, and preferably by loading the material mixture composition at a rate of 10 kg / h to 30 kg / h. When the above ranges are met, the battery characteristics can be improved because appropriate fibrosis can be achieved.

[0123] Furthermore, kneading can be performed at temperatures ranging from 150°C to 250°C, preferably from 160°C to 200°C. When kneading is performed at these high temperatures, the fiberization and aggregation of the binder resulting from kneading can be effectively achieved, and the problem of the fiberized binder breaking off can be appropriately prevented.

[0124] Next, the step (c) of grinding the mixed aggregate to prepare powder for electrodes will be described.

[0125] The mixed aggregate prepared by kneading can also be added immediately to the calendering process to form an electrode material mixture film. However, in this case, the mixed aggregate must be pressed under high pressure and high temperature to prepare a thin film, which may result in excessively high film density or failure to obtain a uniform film. Therefore, the mixed aggregate prepared as described above is ground to prepare an electrode powder.

[0126] There are no particular restrictions on the grinding machine used for grinding, but it is preferable to use a device such as a mixer or grinder for grinding.

[0127] Milling can be performed at a speed of 1,000 rpm to 6,000 rpm and a rate of 5 kg / h to 200 kg / h, preferably at a speed of 1,500 rpm to 4,000 rpm and a rate of 10 kg / h to 150 kg / h. When milling is performed within these ranges, sufficient milling can be achieved to prepare a powder of a size suitable for film formation, and a large amount of fine powder is not generated in the mixed aggregate.

[0128] The average particle size of the electrode powder can range from 10 μm to 3000 μm, specifically from 50 μm to 1500 μm, and more specifically from 100 μm to 700 μm. Within these ranges, a material mixture film with uniform thickness and density can be formed, ensuring excellent physical properties of the material mixture film.

[0129] While not strictly necessary, the electrode powder according to the invention may additionally contain fillers to suppress electrode expansion. The fillers are not particularly limited, provided they are fibrous materials that will not cause chemical changes in the battery; however, for example, the fillers may include at least one selected from: olefin polymers, such as polyethylene and polypropylene; and fibrous materials, such as glass fibers and carbon fibers.

[0130] Next, step (d) of calendering the electrode powder will be described. The electrode material mixture film can be prepared by calendering in which the electrode powder is supplied to a calendering apparatus and the supplied material is hot-pressed using a roller press included in the calendering apparatus.

[0131] Preferably, the electrode powder according to the invention can be supplied to a calendering roll and hot-pressed to prepare a material mixture film in sheet form. In this case, the temperature of the calendering roll can be in the range of 50°C to 200°C.

[0132] A calendering roll comprises a roll pressing unit in which two rolls are arranged facing each other, and a plurality of roll pressing units can be arranged continuously. In this case, the speed ratio of the two rolls in each roll pressing unit can be appropriately adjusted independently within the range of 1:1 to 1:10.

[0133] In addition, in order to adjust the prepared material mixture film to have an appropriate thickness, the prepared material mixture film can be reintroduced into the rolling unit and hot-pressed 1 to 10 times.

[0134] Lithium secondary batteries

[0135] The lithium secondary battery according to the present invention includes a dry electrode according to the present invention. More specifically, the lithium secondary battery according to the present invention includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode and / or the negative electrode can be a dry electrode, and preferably, the lithium secondary battery according to the present invention can be a lithium secondary battery including a dry electrode, a negative electrode, a separator, and an electrolyte according to the present invention. Where only one of the positive or negative electrodes is a dry electrode according to the present invention, the other electrode can be an electrode prepared by a conventional wet preparation method.

[0136] The separator separates the negative and positive electrodes and provides a path for lithium ions to move. Any separator can be used without particular limitation, as long as it is commonly used in lithium secondary batteries. In particular, separators with high electrolyte retention capacity and low resistance to electrolyte ion transfer are preferred. Preferably, porous polymer membranes can be used, such as porous polymer membranes prepared from polyolefin-based polymers (e.g., ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers) or laminated structures having two or more layers thereof. Furthermore, typical porous nonwoven fabrics can be used, such as nonwoven fabrics formed from high-melting-point glass fibers or polyethylene terephthalate fibers. Additionally, coated separators containing ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and separators with single-layer or multi-layer structures can optionally be used.

[0137] Furthermore, the electrolyte used in this invention may include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, or melt inorganic electrolytes that can be used to prepare lithium secondary batteries, but this invention is not limited thereto.

[0138] Preferably, the electrolyte may contain an organic solvent and a lithium salt.

[0139] Any organic solvent can be used without particular restriction, as long as it can serve as a medium through which the ions involved in the electrochemical reactions of the battery can move. Specifically, the following can be used as organic solvents: ester-based solvents, such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents, such as dibutyl ether or tetrahydrofuran; ketone-based solvents, such as cyclohexanone; aromatic hydrocarbon-based solvents, such as benzene and fluorobenzene; or carbonate-based solvents, such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-based solvents, such as ethanol and isopropanol; nitriles, such as R-CN (where R is a linear, branched, or cyclic C2-C20 hydrocarbon group and may contain a double bond, aromatic ring, or ether bond); amides, such as dimethylformamide; dioxolane, such as 1,3-dioxolane; or sulfolane. Among these solvents, carbonate-based solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant and low viscosity linear carbonate-based compounds (e.g., ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) that can improve the charge / discharge performance of the battery are even more preferred.

[0140] Lithium salts can be used without particular restrictions, as long as they are compounds capable of providing lithium ions used in lithium secondary batteries. Specifically, the anion of the lithium salt can be selected from at least one of the following: F - Cl - ,Br - I - NO3 - N(CN)2 - BF4 - CF3CF2SO3 - (CF3SO2)2N - (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2)2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N -As lithium salts, LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2 can be used. The lithium salt can be used in concentrations ranging from 0.1 M to 4.0 M, preferably from 0.5 M to 3.0 M, and more preferably from 1.0 M to 2.0 M. If the concentration of the lithium salt is within the above range, excellent electrolyte performance can be obtained because the electrolyte can have suitable conductivity and viscosity, and lithium ions can move efficiently.

[0141] To improve battery life characteristics, suppress battery capacity reduction, and improve battery discharge capacity, in addition to the electrolyte components mentioned above, the electrolyte may also contain at least one additive, such as compounds based on alkylene carbonates, such as ethylene difluorocarbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol dimethyl ether (n-glyme), triammonium hexaphosphate, nitrobenzene derivatives, sulfur, quinone imine dyes, and N-substituted compounds. Alzolidinediones, N,N-substituted imidazolidinyl ethers, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be included in an amount from 0.1% to 10.0% by weight, based on the total weight of the electrolyte.

[0142] Furthermore, since the lithium secondary battery according to the present invention stably exhibits excellent capacity characteristics, output characteristics and lifespan characteristics, the lithium secondary battery is suitable for portable devices such as mobile phones, laptops and digital cameras, as well as electric vehicles such as hybrid electric vehicles (HEVs).

[0143] Therefore, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit battery and a battery pack including the battery module are provided.

[0144] Battery modules or battery packs can be used as a power source for at least one of the following medium and large-sized devices: power tools; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or energy storage systems.

[0145] In the following description, embodiments of the invention will be described in detail in a manner that enables those skilled in the art to readily implement the invention. However, the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

[0146] In the following description, the present invention will be more preferably described with reference to specific embodiments.

[0147] Example 1: Dry Electrode Preparation

[0148] (Preparation of current collectors)

[0149] A current collector (aluminum alloy film) with rolling oil on its surface is subjected to plasma treatment under atmospheric pressure to prepare an atmospheric pressure plasma-treated current collector.

[0150] Preferably, atmospheric pressure plasma treatment is performed once while moving the current collector at a speed of 40 m / min, with an inert gas (N2) injection flow rate of 800 LPM, a dry oxygen-containing gas injection flow rate of 2 LPM, a voltage of 14 kV, a power of 3.9 kW, and a distance of 1.5 mm between the current collector and the plasma nozzle.

[0151] (Preparation of electrode material mixture film)

[0152] 96 g of lithium nickel cobalt manganese aluminum oxide as the electrode active material, 1.5 g of carbon black as the conductive agent, and polytetrafluoroethylene (PTFE) as the binder were introduced into a mixer and mixed at 10,000 rpm for 1 minute to prepare a material mixture composition.

[0153] Subsequently, the material mixture composition was placed in a kneader and kneaded for 5 minutes at 50 rpm at a temperature of 150°C and a pressure of 1.1 atmospheres to prepare a mixed aggregate. The mixed aggregate was then introduced into a blender and ground at 10,000 rpm for 40 seconds to obtain electrode powder.

[0154] Electrode powder is formed into a sheet by roller pressing during a roller-to-roll process, and then rolled using a roller pressing roller (roller diameter: 200 mm, roller temperature: 100 °C, rotation speed: 20 rpm) to prepare an electrode material mixture film.

[0155] (Preparation of dry electrodes)

[0156] Subsequently, a dry electrode is prepared by laminating a film of electrode material mixture onto a current collector treated with atmospheric pressure plasma via a roller press.

[0157] Example 2: Dry Electrode Preparation

[0158] The dry electrode was prepared in the same manner as in Example 1, except that the atmospheric pressure plasma treatment was performed twice while the current collector was moved at a speed of 40 m / min, with an inert gas (N2) injection flow rate of 800 LPM, a dry oxygen-containing gas injection flow rate of 2 LPM, a voltage of 14 kV, a power of 3.9 kW, and a distance of 1.5 mm between the current collector and the plasma nozzle.

[0159] Example 3: Dry Electrode Preparation

[0160] The dry electrode was prepared in the same manner as in Example 1, except that the atmospheric pressure plasma treatment was performed once while the current collector was moved at a speed of 20 m / min, with an inert gas (N2) injection flow rate of 800 LPM, a dry oxygen-containing gas injection flow rate of 2 LPM, a voltage of 14 kV, a power of 3.8 kW, and a distance of 1.5 mm between the current collector and the plasma nozzle.

[0161] Example 4: Dry Electrode Preparation

[0162] The dry electrode was prepared in the same manner as in Example 1, except that the atmospheric pressure plasma treatment was performed twice while the current collector was moved at a speed of 20 m / min, with an inert gas (N2) injection flow rate of 800 LPM, a dry oxygen-containing gas injection flow rate of 2 LPM, a voltage of 14 kV, a power of 3.9 kW, and a distance of 1.5 mm between the current collector and the plasma nozzle.

[0163] Comparative Example 1: Dry Electrode Preparation

[0164] The dry electrode was prepared in the same manner as in Example 1, except that atmospheric pressure plasma treatment was not performed.

[0165] Comparative Example 2: Dry Electrode Preparation

[0166] The dry electrode was prepared in the same manner as in Example 1, except that the atmospheric pressure plasma treatment was performed while the current collector was moving at a speed of 200 m / min.

[0167] The preparation methods of the dry electrodes prepared according to Examples 1 to 4 and Comparative Examples 1 and 2 are summarized and given in Table 1 below.

[0168] [Table 1]

[0169]

[0170] Experimental Example 1: ToF-SIMS and SEM-EDX Analysis

[0171] 1) ToF-SIMS Analysis

[0172] ToF-SIMS analysis was performed on the current collectors prepared in Examples 1 to 4 and Comparative Examples 1 and 2 to analyze the organic components remaining on the surface of the current collectors.

[0173] Specifically, the current collectors prepared in Examples 1 to 4 and Comparative Examples 1 and 2 were stamped into a size of 50 mm × 50 mm and then analyzed using a TOF-SIMS 5 from Ion-TOF GmbH under the following conditions.

[0174] 1) Positive Mode

[0175] 2) Measurement mass range: 1 u to 873 u

[0176] 3) Primary ion: Bi3,

[0177] 4) Single ion dose: 3.81 × 10 8 ions / cm 2

[0178] 5) Voltage: 30 KeV

[0179] 6) Detection time: 100 seconds

[0180] 7) FOV (Field of View): 100 μm × 100 μm

[0181] The measured C2H3O + Peak intensity and C3H7 + Peak intensities and the total number of ions measured are given in Table 2 below.

[0182] 2) SEM-EDX measurement

[0183] The carbon content at the interface of the current collector and the ratio of the carbon content in the electrode material mixture film were measured using scanning electron microscopy-energy dispersive X-ray spectroscopy on the dry electrodes prepared in Examples 1 to 4 and Comparative Examples 1 and 2.

[0184] 1) Instrument: JSM-IT800 (JEOL Ltd.)

[0185] 2) Accelerating voltage: 5 kV

[0186] 3) Incident current: 2.3 nA, high current mode

[0187] 4) Working distance: 10 mm

[0188] 5) Total counts during mapping: 35,000 cps

[0189] The measurement results are given in Table 2 below.

[0190] [Table 2]

[0191]

[0192] Experiment Example 2: Measurement of Electrode Layer Resistance and Interface Resistance

[0193] 1) Electrode layer resistance (Ωcm)

[0194] After cutting each dry electrode prepared in Examples 1 to 4 and Comparative Examples 1 and 2 into a size of 50 mm × 50 mm to make five samples, a current of 100 μA was applied to the electrodes using a multi-probe (MP) resistance measurement method, and the resistance value of the electrode material mixture film surface was measured by the potential difference measured between 46 probes.

[0195] Table 3 below lists the average values ​​of the measured resistance values.

[0196] 2) Interface resistance (Ωcm)

[0197] After cutting each dry electrode prepared in Examples 1 to 4 and Comparative Examples 1 and 2 into 50 mm × 50 mm sizes to make five samples, a current of 100 μA was applied to the electrodes using the MP resistance measurement method, and the resistance between the electrode material mixture film and the current collector was measured by the potential difference measured between 46 probes.

[0198] Table 3 below lists the average values ​​of the measured resistance values.

[0199] Experimental Example 3: Evaluation of the adhesion of electrode material mixture films and evaluation of electrode appearance

[0200] (Evaluation of the adhesion of the electrode material mixture film)

[0201] The 90° peel strength of the current collector-electrode material mixture film was measured for the dry electrodes prepared in Examples 1 to 4 and Comparative Examples 1 and 2.

[0202] Specifically, the dry electrodes prepared in Examples 1 to 4 and Comparative Examples 1 and 2 were immersed in electrolyte, sealed, and stored in an oven at 70°C for 4 weeks. After being removed from the oven, they were rinsed with dimethyl carbonate (DMC) and then cut into 20 mm widths. Subsequently, the adhesion was evaluated by measuring the average value of the 90° peel strength at a displacement of 20 mm to 80 mm using a universal testing machine (UTM) to peel the electrode material mixture film from the current collector.

[0203] The measurement results are given in Table 3 below.

[0204] (Electrode appearance evaluation)

[0205] The dry electrodes prepared in Examples 1 to 4 and Comparative Examples 1 and 2 were immersed in electrolyte, sealed, and then stored in an oven at 70°C for 4 weeks.

[0206] Afterward, the stored dry electrodes were removed from the oven and rinsed, and then an appearance evaluation was performed.

[0207] Specifically, regarding appearance evaluation, if there is peeling of the electrode material mixture film in the dry electrode rinsed with dimethyl carbonate (DMC), it is evaluated as X, and if there is no peeling, it is evaluated as O.

[0208] The evaluation results are given in Table 3 below.

[0209] [Table 3]

[0210]

[0211] Referring to Table 3, regarding Examples 1 to 4, it can be determined that, unlike Comparative Examples 1 and 2, the resistivity characteristics are excellent, the adhesion of the electrode material mixture film is excellent, and the appearance of the electrode does not peel off.

Claims

1. A dry electrode, comprising: current collector; and an electrode material mixture film disposed on the current collector, The electrode material mixture film comprises an electrode active material and a fiberizable binder. The surface of the current collector was measured using time-of-flight secondary ion mass spectrometry (ToF-SIMS) for C3H7. + Peak intensity (I) B ) and C2H3O + Peak intensity (I) A The ratio of (I) B / I A ) is 1.3 or less, and The ratio of carbon content at the interface of the current collector to the carbon content in the electrode material mixture film, as measured by scanning electron microscopy-energy dispersive X-ray spectroscopy, is 1.03 or less.

2. The dry electrode according to claim 1, wherein the C3H7 measured on the surface of the current collector by time-of-flight secondary ion mass spectrometry (ToF-SIMS) + Peak intensity (I) B ) and total ion count (I T The ratio of (I) B / I T ) is 230×10 -5 Or smaller.

3. The dry electrode according to claim 1, wherein the C2H3O measured on the surface of the current collector by time-of-flight secondary ion mass spectrometry (ToF-SIMS) + Peak intensity (I) A ) and total ion count (I T The ratio of (I) A / I T ) is 1,000 × 10 -5 Or smaller.

4. The dry electrode according to claim 1, wherein the current collector comprises aluminum.

5. The dry electrode according to claim 1, wherein the tensile strength of the current collector is 5 kgf / mm². 2 Or larger.

6. The dry electrode according to claim 1, wherein the water contact angle of the surface of the current collector is in the range of 10° to 100°.

7. The dry electrode according to claim 1, wherein the surface of the current collector comprises rolling oil.

8. A method for preparing a dry electrode, the method comprising: The surface of the current collector is treated with atmospheric pressure plasma. The loading speed of the current collector in the atmospheric pressure plasma treatment is in the range of 1 m / min to 100 m / min.

9. The method for preparing a dry electrode according to claim 8, wherein, In the atmospheric pressure plasma treatment, the injection flow rate of the inert gas is in the range of 500 L / min to 1,000 L / min, and the injection flow rate of the oxygen-containing gas is in the range of 0.1 L / min to 10 L / min.

10. The method for preparing a dry electrode according to claim 8, wherein the ratio of the injection flow rate of the inert gas to the injection flow rate of the oxygen-containing gas in the atmospheric pressure plasma treatment is in the range of 50 to 10,000.

11. The method for preparing a dry electrode according to claim 8, wherein the voltage of the atmospheric pressure plasma treatment is in the range of 10 kV to 20 kV.

12. The method for preparing a dry electrode according to claim 8, wherein the power of the atmospheric pressure plasma treatment is in the range of 3 kW to 5 kW.

13. The method for preparing a dry electrode according to claim 8, wherein the atmospheric pressure plasma treatment is performed with the current collector and the plasma nozzle spaced 0.01 mm to 3.00 mm apart.

14. A lithium secondary battery comprising the dry electrode according to claim 1.

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