Current collector for dry electrode, electrode including same, and lithium secondary battery including same

Abstract

The present invention relates to a current collector for a dry electrode, comprising: a metal thin film for a current collector; and a primer layer formed on at least one surface of the metal thin film, wherein the primer layer comprises a binder resin and a conductive material, and the conductive material has a bulk density of 0.055 g / ml or more and a BET specific surface area of 100 m2 / g or less.

Description

Current collector for dry electrode, electrode including same, and lithium secondary battery including same

[0001] The present invention relates to a current collector for a dry electrode, an electrode including the same, and a lithium secondary battery including the same, and more particularly, to a current collector for a dry electrode having excellent resistance characteristics and high electrode-current collector adhesion, an electrode including the same, and a lithium secondary battery including the same.

[0002] This application claims priority to Korean Patent Application No. 10-2023-0158612, filed on November 15, 2023, and all contents disclosed in the specification and drawings of that application are incorporated herein by reference.

[0003] The manufacturing process of lithium secondary batteries is largely divided into three stages: electrode process, assembly process, and formation process. The electrode process is further divided into active material mixing process, electrode coating process, drying process, rolling process, slitting process, and winding process. Among these, the active material mixing process is a process of mixing a coating material for forming an electrode active layer where an actual electrochemical reaction occurs in the electrode. The electrode active material, which is an essential element of the electrode, and a solvent for imparting viscosity and dispersing powder are mixed to produce a slurry composition having fluidity. Thereafter, an electrode coating process for applying the slurry composition onto an electrically conductive current collector and a drying process for removing the solvent contained in the slurry composition are performed, and the electrode is additionally rolled to produce a predetermined thickness.

[0004] Meanwhile, during the drying process, the solvent contained in the slurry composition may evaporate, causing defects such as pinholes or cracks in the already formed electrode active layer. In addition, since the inside and outside of the active layer are not uniformly dried, a powder floating phenomenon may occur due to differences in the solvent evaporation rate, that is, powders in the area that dries first may float and form a gap with the area that dries relatively later, which may deteriorate the electrode quality. To solve this problem, drying devices that can control the evaporation rate of the solvent while ensuring that the inside and outside of the active layer are dried uniformly are being considered. However, these drying devices are very expensive and require considerable cost and time to operate, which is disadvantageous in terms of manufacturing processability. Accordingly, research into manufacturing dry electrodes that do not use solvents has been actively conducted recently.

[0005] Unlike wet electrodes, dry electrodes require a primer layer that provides interfacial adhesion between the current collector and the electrode active material layer and has electrical conductivity. To ensure electrical conductivity, the primer layer must contain a conductive agent or a certain amount of a conductive material, and to ensure sufficient interfacial adhesion between the electrode and the current collector, it must contain a binder or a certain amount of a binder. However, excessive inclusion of a conductive agent to enhance electrical conductivity can degrade battery performance. Furthermore, excessive use of a binder to enhance interfacial adhesion can lead to process issues such as meandering of the current collector metal film, electrode transfer and detachment, and adhesion of the primer layer to the roll during the roll-to-roll process. Therefore, there is a growing need for a current collector for dry electrodes that exhibits excellent resistance characteristics and adhesive strength without excessive inclusion of a conductive agent or binder in the primer layer.

[0006] The present invention was invented to solve the above problems, and its purpose is to provide a current collector for a dry electrode having excellent resistance characteristics and excellent adhesion to an electrode, an electrode including the same, and a lithium secondary battery including the same.

[0007] According to one aspect of the present invention, a current collector comprises a metal thin film, and a primer layer formed on at least one surface of the metal thin film, wherein the primer layer comprises a binder resin and a conductive material, and the conductive material has a bulk density of 0.055 g / ml or more and a BET specific surface area of ​​100 m 2 A current collector for a dry electrode having a mass of / g or less is provided.

[0008] The bulk density ratio of the conductive material to the true density of the binder resin may be 0.06 or more.

[0009] The above primer layer may include a binder resin and a conductive material in a weight ratio of 20:80 to 80:20.

[0010] The above challenge material has an average particle diameter d 50 This can be 30 nm or more.

[0011] The above-mentioned conductive material may have a concentration gradient that increases in the direction of the thickness of the primer layer toward the current collector.

[0012] The above-mentioned challenge material may include a carbon material.

[0013] The above primer layer may contain at least 20 wt% of binder resin relative to the total weight of the primer layer.

[0014] The glass transition temperature (Tg) of the above binder resin may be -40°C to 25°C, -30°C to 20°C, -25°C to 10°C, or -20°C to 0°C. When the glass transition temperature of the binder resin satisfies the above-described range, the adhesive strength with the electrode may be further improved.

[0015] The above binder resin may include at least one selected from the group consisting of styrene butadiene rubber (SBR), butadiene rubber (BR), nitrile butadiene rubber (NBR), styrene butadiene styrene block polymer (SBS), styrene ethylene butadiene block polymer (SEB), styrene-(styrene butadiene)-styrene block polymer, natural rubber (NR), and isoprene rubber (IR).

[0016] According to another aspect of the present invention, an electrode is provided, which includes a current collector for a dry electrode as described above and an electrode active material layer disposed on at least one surface of the current collector for the dry electrode.

[0017] The above electrode active material layer may include composite particles for electrodes, powder for electrodes, or a combination thereof.

[0018] According to another aspect of the present invention, a lithium secondary battery is provided, which includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein at least one of the positive electrode and the negative electrode includes a current collector for a dry electrode as described above.

[0019] The current collector for a dry electrode according to the present invention can have excellent resistance characteristics while also having excellent adhesion between the current collector and the electrode interface.

[0020] The current collector for a dry electrode according to the present invention can have excellent resistance characteristics between the current collector and the electrode interface even when a large-sized conductive material is used by controlling the bulk density of the conductive material and the true density of the binder resin.

[0021] In addition, the electrode according to the present invention can exhibit battery characteristics with excellent resistance characteristics while having excellent adhesive strength between the current collector and the electrode interface, as the conductive material is distributed in a large amount near the metal thin film for the current collector and the binder resin is distributed in a large amount on the electrode active material side.

[0022] The electrode according to the present invention can have excellent resistance characteristics between the interface between the current collector and the electrode active material layer even when a large-sized conductive material is used by controlling the bulk density of the conductive material and the true density of the binder resin in the current collector.

[0023] The electrode according to the present invention may include an electrode active material layer manufactured by a dry method on a current collector for a dry electrode, and thus may have superior resistance characteristics compared to a case where an electrode active material layer manufactured by a wet method is included.

[0024] In addition, the lithium secondary battery according to the present invention can have excellent battery characteristics by including the current collector according to the present invention.

[0025] The attached drawings illustrate preferred embodiments of the invention and, together with the detailed description, serve to explain the principles of the invention, without limiting the scope of the invention. Furthermore, the shape, size, scale, or ratio of elements in the drawings included in this specification may be exaggerated for clarity.

[0026] Figure 1 illustrates a cross-section of an electrode according to one embodiment of the present invention.

[0027] Figures 2a to 2c show the discharge resistance by SoC by performing a HPPC (hybrid pulse power characterization) test on the monocells of Experimental Example 5 and Comparative Example 3.

[0028] Hereinafter, the present invention will be described in detail. Terms and words used in this specification and claims should not be construed as limited to their conventional or dictionary meanings. Rather, they should be interpreted with meanings and concepts consistent with the technical spirit of the present invention, based on the principle that the inventor can appropriately define the concept of a term to best explain his or her invention.

[0029] Accordingly, the configurations described in the embodiments described in this specification are only the most preferred embodiments of the present invention, and do not represent all of the technical ideas of the present invention. Therefore, it should be understood that there may be various equivalents and modified examples that can replace them at the time of filing this application.

[0030] Justice

[0031] Throughout this specification, whenever a part is referred to as "comprises" or "has" a component, this does not exclude other components, but rather includes other components, unless otherwise specifically stated. The term "comprises" explicitly includes the meanings "consist of" and "essentially comprising," although not necessarily limited thereto.

[0032] In addition, the terms "about", "substantially", etc. used throughout this specification are used in the sense of numerical values ​​or near numerical values ​​when manufacturing and material tolerances inherent to the meanings stated are presented, and are used to prevent unscrupulous infringers from unfairly exploiting disclosures that mention exact or absolute values ​​to aid understanding of this specification.

[0033] In this specification, the description of “A and / or B” means “A or B or both.”

[0034] Certain terms used in this specification are for convenience and are not intended to be limiting. Terms such as "upper," "lower," "left," "right," "front," "back," "inner," and "outer" may be used to describe relative positions or directions between components, rather than absolute positions. These terms include, in addition to themselves, words containing them, derivatives thereof, and words with similar meanings.

[0035] The "glass transition temperature (Tg)" used in the present specification is measured by a conventional method known in the art, and may be measured by, for example, differential scanning calorimetry (DSC). For example, the measurement of the glass transition temperature by the differential scanning calorimetry may be performed by using a Discovery DSC 250 device from TA Instruments and measuring the amount of heat while changing the temperature in the range of -80°C to 300°C. Specifically, the temperature may be changed at a rate of 10°C / min in the order of 1st heating -> 1st cooling -> 2nd heating for the sample to be measured, from 25°C (start) -> 250°C (1st heating) -> -80°C (1st cooling) -> 300°C. At this time, the purpose is to evaporate moisture remaining in the sample during the first heating process, and to analyze thermal behavior from a heat thermogram during the first cooling and second heating processes.

[0036] In the present specification, the “specific surface area” is measured by the BET method, and can be specifically calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77K) using BELSORP-mini II of BEL Japan.

[0037] In the original specification, "diameter (particle size) d 50 " means the particle size based on 50% of the volume cumulative particle size distribution of the particles. The particle size d 50can be measured using a laser diffraction method. For example, after dispersing the particles in a dispersion medium, the particles are introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), and ultrasonic waves of about 28 kHz are irradiated with an output of 60 W, and then a volume-cumulative particle size distribution graph is obtained, and then the particle size corresponding to 50% of the volume-cumulative amount is measured. Or, in one embodiment of the present invention, the particle diameter d 50 can be measured according to ISO 9276.

[0038] The "thickness" of each layer included in the electrode used in the present specification may refer to a value measured by a known method for measuring thickness. The method for measuring thickness is not limited thereto, but may be, for example, a value measured using a thickness gauge (Mitutoyo, VL-50S-B).

[0039] In the present specification, the term "porosity" means the ratio of the volume occupied by pores to the total volume in a certain structure, and its unit is vol%, and can be used interchangeably with terms such as porosity, porosity, etc. In the present invention, the measurement of the porosity is not particularly limited, and according to an embodiment of the present invention, for example, it can be measured according to the BET (Brunauer-Emmett-Teller) measurement method using nitrogen gas or the mercury penetration method (Hg porosimeter) and ASTM D-2873. Alternatively, the true density of the electrode can be calculated from the density (bulk density) of the electrode and the composition ratio of materials included in the electrode and the density of each component, and the porosity of the electrode can be calculated from the difference between the bulk density and the true density (net density). For example, the porosity can be calculated by the following Equation 1.

[0040] [Formula 1]

[0041] Porosity (volume %) = {1-(bulk density / true density)}x100

[0042] In the above equation 1, the bulk density (e.g., the bulk density of the electrode) can be calculated from the following equation 2.

[0043] [Formula 2]

[0044] Bulk density (g / cm) 3 ) = (Weight of electrode (g)) / {(Thickness of electrode (cm))x(Area of ​​electrode (cm) 2 ))}

[0045] Bulk density, or more commonly known as apparent density, is a measure of how much space a material occupies per unit volume, including the voids or empty space contained within it. In other words, bulk density includes both the solid material and the voids within its volume. Bulk density can be calculated by dividing the mass of a material by its total volume, which includes all pores or empty space within the material. For example, the bulk density of a material can be calculated using Equation 3 below.

[0046] [Formula 3]

[0047] Bulk density (g / ml) = mass (g) / total volume (ml)

[0048] The mass can be measured using a scale. For materials of regular shape (e.g., a cube, a cylinder, etc.), the dimensions can be measured using appropriate tools such as a tape measure or calipers, which are well known in the art. For irregularly shaped samples, the volume can be measured by measuring the displacement of a liquid to determine the change in a known volume. The change in volume can be equal to the volume of the material. Those skilled in the art can apply other known methods for measuring the volume or bulk density.

[0049] Net density (true density) refers to the density of a material without considering the voids or pores contained within it. It is the mass of a solid material divided by its actual volume, excluding empty space. True density can be calculated by dividing the mass of a material by its solid, non-empty volume. For example, the true density of a material can be calculated using Equation 4 below.

[0050] [Formula 4]

[0051] True density (g / ml) = mass (g) / solid volume (not considering pore volume, unit: ml)

[0052] Unlike bulk density, true density, which does not take into account the total volume (excluding voids), represents the intrinsic density of a material. True density can be determined using the methods mentioned above, the gas volcanometry method according to ISO 12154:2014, or another measurement method known to experts in the field.

[0053] The lithium secondary battery according to the present invention can be included in a battery module as a unit battery, and the battery module can be used in a battery pack and a device that includes the battery pack as a power source. Specific examples of the device include, but are not limited to, an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or a power storage system.

[0054]

[0055] <Current collector for dry electrode>

[0056] The present invention provides a current collector for a dry electrode.

[0057] In one embodiment of the present invention, a current collector for a dry electrode includes a metal thin film for the current collector and a primer layer formed on at least one surface of the metal thin film, wherein the primer layer includes a binder resin and a conductive material.

[0058] Figure 1 is a schematic diagram illustrating a cross-section of a dry electrode according to one embodiment of the present invention. Referring to this, the dry electrode includes a current collector including a metal thin film (100) and a primer layer (200), and an electrode active material layer (300) formed on the surface of the current collector, wherein the primer layer (200) includes a binder resin (210) and a conductive material (220).

[0059] In the present specification, the direction closer to the metal thin film (100) is referred to as the lower part, and the direction closer to the electrode active material layer (300) is referred to as the upper part, based on the thickness direction of the primer layer (200). In the present invention, the upper part may refer to a portion corresponding to the upper 50% of the thickness of the primer layer (200), and the lower part may refer to a portion corresponding to the lower 50% of the thickness of the primer layer (200). In addition, the surface of the primer layer (200) facing the electrode active material layer (300) may be referred to as the first surface (electrode active material layer facing portion), and the surface facing the metal thin film (100) may be referred to as the second surface (metal thin film facing portion).

[0060] In one embodiment of the present invention, the metal thin film for the current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used.

[0061] The current collector may also form fine irregularities on its surface to enhance the adhesive strength of the active material, and may take various forms, such as films, sheets, foils, nets, porous bodies, foams, and non-woven fabrics. Meanwhile, in one embodiment of the present invention, the current collector may have a thickness of 4 μm to 25 μm, but is not particularly limited thereto. For example, the current collector may have a thickness of 6 μm to 20 μm.

[0062] In one embodiment of the present invention, the sum of the contents of the binder and the conductive material relative to the total weight of the primer layer may be specifically 91 wt% or more, 92 wt% or more, 93 wt% or more, 94 wt% or more, 95 wt% or more, 96 wt% or more, 97 wt% or more, 98 wt% or more, 99 wt% or more, 100 wt% or less, 99 wt% or less, 98 wt% or less, 95 wt% or less, or 93 wt% or less.

[0063] In one embodiment of the present invention, the primer layer includes a binder and a conductive material, and may further include a dispersant.

[0064] In one embodiment of the present invention, the primer layer may include a binder and a conductive material, but may substantially not include a dispersant. The phrase "substantially not including a dispersant in the primer layer" means not only that the primer layer does not include a dispersant at all, but also that even if the primer layer includes a dispersant, the primer layer includes a trace amount of the dispersant such that the function of the dispersant, that is, the function of dispersing the binder and the conductive material, is not realized. For example, when the primer layer includes a dispersant, the content of the dispersant may be 6 wt% or less, 5 wt% or less, 4 wt% or less, 3 wt% or less, 2 wt% or less, 1 wt% or less, 0.5 wt% or less, or 0.05 wt% or less, based on the total weight of the primer layer, and preferably 0 wt% (i.e., not including at all).

[0065] In one embodiment of the present invention, the dispersant may be capable of decomposing when exposed to the air, thereby causing changes in the primer layer over time. The dispersant may include, for example, a cellulose-based polymer, an emulsifying surfactant, or two or more thereof.

[0066] In one embodiment of the present invention, the cellulose-based polymer may be, for example, carboxymethylcellulose (CMC), an alkali metal salt of carboxymethylcellulose, hydroxymethylcellulose (HMC), an alkali metal salt of hydroxymethylcellulose, hydroxyethylcellulose (HEC), an alkali metal salt of hydroxyethylcellulose, hydroxypropylcellulose (HPC), an alkali metal salt of hydroxypropylcellulose, ethylhydroxyethylcellulose (EHEC), methylhydroxymethylcellulose (MHMC), methylhydroxyethylcellulose (MHEC), ethylhydroxymethylcellulose (EHMC), methylcellulose (MC), ethylcellulose (EC), hydroxypropylmethylcellulose (HPMC), hydroxyethylmethylcellulose (HEMC), or a mixture of two or more thereof.

[0067] In one embodiment of the present invention, the emulsifying surfactant may be, for example, but not limited to, a nonionic surfactant, an anionic surfactant, an amphoteric surfactant, or a mixture of two or more thereof. The nonionic surfactant may be, for example, but not limited to, ethoxylates, amide ethoxylates, amine oxides, alkyl glucosides, or a mixture of two or more thereof. The anionic surfactant may be, for example, but not limited to, phosphate esters, isothionates, sulfates, sulfonates, taurates, or a mixture of two or more thereof. The amphoteric surfactant may be, for example, but not limited to, betaines, glycinates, alkylamido alkylamines, or a mixture of two or more thereof.

[0068] In one embodiment of the present invention, the primer layer may substantially not contain a cellulose-based polymer as a dispersant.

[0069] In one embodiment of the present invention, the primer layer may substantially not contain carboxymethylcellulose, hydroxypropylmethylcellulose or a mixture thereof as a dispersant.

[0070] In one embodiment of the present invention, the primer layer may substantially not contain an emulsifying surfactant as a dispersant.

[0071] In one embodiment of the present invention, the conductive material is not particularly limited in type as long as it is a known conductive material used in a primer layer.

[0072] In one embodiment of the present invention, the conductive material has a bulk density of 0.055 g / ml or more.

[0073] In one embodiment of the present invention, the bulk density of the conductive material may be 0.06 g / ml or more, or 0.065 g / ml or more, and may be 0.5 g / ml, 0.4 g / ml, 0.3 g / ml, or 0.2 g / ml or less. Since the bulk density of the conductive material is not an inherent value of the conductive material, the bulk density of the conductive material may vary depending on a method of processing the conductive material. At this time, when the bulk density of the conductive material satisfies the above-described range, the conductive material may move in the second surface direction, and the binder resin may move in the first surface direction, so that the adhesive force between the current collector and the electrode active material layer may be improved, and the resistance characteristics may be enhanced. Specifically, when the bulk density of the conductive material satisfies the above numerical range, the binder resin may be more distributed relatively in the first surface direction of the electrode active material layer (i.e., opposite to the direction of gravity), and the conductive material may be more distributed in the second surface direction of the interface between the current collector and the primer layer (i.e., in the direction of gravity). Meanwhile, in the manufacturing process of a dry electrode, a process is involved in which the primer layer and the electrode active material layer among the current collectors for the dry electrode come into contact and are compressed. At this time, the binder resin comes into contact with the electrode active material layer, so that the adhesive strength between the current collector and the electrode interface is excellent, and the distance between the conductive materials is shortened by the compression, so that the resistance characteristics can be improved. Meanwhile, if the bulk density of the conductive material exceeds the upper limit, the dispersibility may be reduced when forming the primer layer, or it may be difficult to control the thickness of the primer layer. In addition, if the density difference with the binder becomes too large, the distribution of the conductive material and the binder may be extremely polarized, so that the conductivity of the primer layer itself may not be good.

[0074] In one embodiment of the present invention, the BET specific surface area of ​​the conductive material is 100 m 2 / g or less.

[0075] In one embodiment of the present invention, the BET surface area of ​​the conductive material is 90 m 2 / g or less, or 80 m 2 / g or less, and the BET specific surface area is 5 m 2 / g or more, 10 m 2 / g or more, 15 m 2 / g or more. The BET specific surface area may refer to the specific surface area of ​​the conductive material measured by adsorbing gas on the conductive material. At this time, when the BET specific surface area satisfies the above-described range, the conductive material may move in the second surface direction and the binder resin may move in the first surface direction, so that the adhesive force between the current collector and the electrode active material layer may be improved and the resistance characteristics may be improved. Specifically, when the BET specific surface area of ​​the conductive material satisfies the above numerical range, the binder resin may be more distributed relatively in the first surface direction of the electrode active material layer (i.e., opposite to the direction of gravity), and the conductive material may be more distributed in the second surface direction of the interface between the current collector and the primer layer (i.e., in the direction of gravity). Meanwhile, in the manufacturing process of the dry electrode, a process in which the primer layer and the electrode active material layer among the current collectors for the dry electrode come into contact and are compressed is accompanied. At this time, the binder resin comes into contact with the electrode active material layer, so that the adhesive force between the current collector and the electrode interface is excellent, and the distance between the conductive materials is shortened by the compression, so that the resistance characteristics may be improved.

[0076] In one embodiment of the present invention, the binder resin may have a density of 0.9 g / ml to 1.1 g / ml.

[0077] In one embodiment of the present invention, the bulk density ratio of the conductive material to the true density of the binder resin (bulk density of the conductive material / true density of the binder resin) may be, for example, 0.06 or more, 0.065 or more, 0.07 or more, 0.08 or more, 0.09 or more, or 0.1 or more, and may be 0.6 or less, 0.5 or less, 0.4 or less, 0.3 or less, or 0.25 or less. When the bulk density ratio of the conductive material to the true density of the binder resin satisfies the above numerical range, even if the particle size of the conductive material increases, the conductive material and the binder resin are mainly distributed to the second surface and the first surface, respectively, so that the contact area between the conductive materials increases, thereby enabling the formation of a uniform conductive network, and increasing the contact area with the active material so that the conductive network can be formed. Accordingly, a current collector for a dry electrode having excellent interfacial resistance can be provided even when a conductive material having a large particle size is used. In addition, when the particle size of the binder resin increases and the bulk density ratio of the conductive material to the true density of the binder resin (bulk density of the conductive material / true density of the binder resin) satisfies the above-described range, the adhesive strength (electrode-current collector adhesive strength) and electrode interfacial resistance can be further improved.

[0078] In one embodiment of the present invention, the true density is not limited to the measurement method, but can be measured, for example, using a Pycnometer (AccuPycII 1340). The true density refers to the density of the volume of the solid material itself excluding pores in a porous solid. Meanwhile, the bulk density refers to the density of the volume of an object including the pores created between particles when a powder, fiber, etc. is filled in a container. The bulk density is not limited to the measurement method, but can be derived by calculating the mass (g) of the conductive material for the volume (ml) of the conductive material. The bulk density can be measured, for example, using a bulk density tester (cylinder volume 100cm) from JJ-Test. 3 ) can be measured.

[0079] The primer layer of the present invention includes a binder resin and a conductive material, and the content ratio of the conductive material and the binder resin according to the thickness of the primer layer may vary depending on the ratio of the density (particularly, bulk density) of the conductive material to the density (particularly, true density) of the binder resin. Specifically, as the ratio of the density (particularly, bulk density) of the conductive material to the density (particularly, true density) of the binder resin increases, the conductive material within the primer layer may have a distribution in which the content increases in the direction of gravity (typically, in the direction of the current collector) during manufacturing. At this time, the true density of the binder resin may have the above-mentioned range, and since the true density of the binder resin and the bulk density of the conductive material are relatively large in difference, when the conductive material satisfies a predetermined bulk density and BET specific surface area, it can be said that the effects of the present invention, that is, excellent battery characteristics with excellent resistance characteristics and excellent adhesion between the current collector and the electrode interface, are achieved. Meanwhile, in another embodiment of the present invention, the ratio (bulk density of conductive material / true density of binder resin) obtained by dividing the bulk density ratio of the conductive material to the true density of the binder resin may be more consistent with the tendency of the conductive material content to increase in the direction of gravity (generally in the direction of the current collector) during manufacturing within the primer layer.

[0080] In one embodiment of the present invention, the primer layer may include a binder resin and a conductive material in a weight ratio of 20:80 to 80:20, 25:75 to 75:25, or 30:70 to 70:30. When the weight ratio of the binder resin and the conductive material satisfies the above range, the adhesive strength between the current collector and the electrode interface may be excellent, and the resistance characteristics may be excellent.

[0081] In one embodiment of the present invention, the conductive material has an average particle diameter d 50This may be 30 nm or more, 33 nm or more, or 35 nm or more, or 5000 nm or less, 4500 nm or less, or 4000 nm or less. When the average particle diameter of the conductive material satisfies the above-described range, the conductive material may have an excellent contact area, form a uniform conductive network, and have an excellent contact area with the electrode active material.

[0082] In one embodiment of the present invention, the conductive material may have a spherical, pseudo-spherical, plate-shaped or tubular shape.

[0083] In one embodiment of the present invention, the conductive material may include a carbon material. The conductive material may include, as the carbon material, graphite such as natural graphite or artificial graphite; carbon black-based carbon compounds such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; conductive fibers such as carbon fibers or metal fibers; metal powders such as fluorocarbon, aluminum, and nickel powders; conductive whiskies such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives. Preferably, the conductive material may include acetylene black, carbon black, or a combination thereof.

[0084] In one embodiment of the present invention, since the conductive material satisfies a predetermined bulk density and BET specific surface area, when the slurry for the primer layer is dried, the conductive material can move toward the surface of the current collector (generally in the direction of gravity) and the binder resin can move toward the electrode active material, so that the conductive material can have a concentration gradient that increases in the thickness direction of the primer layer toward the current collector.

[0085] In one embodiment of the present invention, the binder resin may be used without particular limitation as long as it is a known binder used in a primer layer.

[0086] In one embodiment of the present invention, the primer layer may contain a binder resin in an amount of 20 wt% or more, 25 wt% or more, or 27 wt% or more, and may contain 80 wt% or less, 75 wt% or less, or 70 wt% or less, based on the total weight of the primer layer. When the content of the binder resin in the primer layer satisfies the above-described range, the stability of the primer layer over time can be secured.

[0087] In one embodiment of the present invention, the glass transition temperature (Tg) of the binder resin may be -40°C to 25°C, -30°C to 20°C, -25°C to 10°C, or -20°C to 0°C. When the glass transition temperature of the binder resin satisfies the above-described range, the stability of the primer layer over time can be secured, and the adhesive strength between the current collector and the electrode interface can be excellent.

[0088] In one embodiment of the present invention, the binder resin may include at least one selected from the group consisting of styrene butadiene rubber (SBR), butadiene rubber (BR), nitrile butadiene rubber (NBR), styrene butadiene styrene block polymer (SBS), styrene ethylene butadiene block polymer (SEB), styrene-(styrene butadiene)-styrene block polymer, natural rubber (NR), and isoprene rubber (IR).

[0089]

[0090] <Method for manufacturing a current collector for a dry electrode>

[0091] In one embodiment of the present invention, a current collector for a dry electrode can be manufactured by a method including the steps of: preparing a slurry for a primer layer by mixing a conductive material and a binder resin in a dispersion medium; applying the slurry for the primer layer to at least one surface of a metal thin film; and heating and drying the metal thin film on which the slurry is applied.

[0092] First, the conductive material, the binder resin, and optionally the dispersant are dispersed or dissolved in the dispersion medium to obtain a slurry. Since the conductive material, binder resin, and dispersant are the same as those described above, they will be replaced.

[0093] In one embodiment of the present invention, the binder resin may be mixed into a dispersion medium in the form of an aqueous emulsion. At this time, the binder resin may maintain a particulate form.

[0094] In one embodiment of the present invention, the conductive agent may be mixed into a dispersion medium in the form of an aqueous emulsion. In this case, the conductive agent may maintain a particulate form.

[0095] As the dispersion medium used to obtain the above slurry, water is most preferably used, but an organic solvent may also be used. Examples of the organic solvent include alkyl alcohols such as methyl alcohol, ethyl alcohol, and propyl alcohol; alkyl ketones such as acetone and methyl ethyl ketone; ethers such as tetrahydrofuran, dioxane, and diglyme; amides such as diethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone (hereinafter also referred to as NMP), and dimethylimidazolidinone; sulfur-based solvents such as dimethyl sulfoxide and sulfolane; and the like, but alcohols are preferred. When an organic solvent having a boiling point lower than water is used in combination, the drying speed can be accelerated. In addition, since the dispersibility or solubility of the binder resin can be changed, the viscosity or fluidity of the slurry can be adjusted depending on the amount or type of the dispersion medium, thereby improving production efficiency.

[0096] The method or order of dispersing or dissolving the conductive material and binder resin, etc. in the dispersion medium is not particularly limited, and examples thereof include a method of adding the conductive material and binder resin to the dispersion medium and mixing them, a method of dissolving or dispersing the conductive material in the dispersion medium and then adding the binder resin and mixing them, etc. As a mixing means, mixing devices such as a ball mill, a sand mill, a bead mill, a pigment disperser, a stone mill, an ultrasonic disperser, a homogenizer, and a planetary mixer can be mentioned. The mixing can be performed, for example, at a temperature ranging from room temperature to 80°C for 10 minutes to several hours.

[0097] Next, the slurry is applied to at least one surface of the metal film. Since the metal film is the same as described above, this will be replaced.

[0098] Next, the metal thin film coated with the slurry is dried by heating at a temperature range of 80°C to 140°C for less than 5 minutes. In the heating and drying step, as the dispersion medium in the slurry evaporates, the bulk density and specific surface area of ​​the conductive material contained in the primer layer or the conductive material and binder resin are rearranged by the difference in density, particularly, the difference (ratio) in the bulk density of the conductive material to the true density of the binder resin, so that the conductive material can move in the direction of gravity toward the second surface, and the binder resin can move relatively toward the first surface, thereby improving the adhesive strength between the current collector and the electrode active material layer, and enhancing the resistance characteristics.

[0099] Meanwhile, in the above heating and drying step, the dispersion medium within the primer layer may evaporate, reducing the thickness of the primer layer and increasing the bulk density of the primer layer.

[0100] Meanwhile, even in the above heating and drying step, the content ratio of the conductive material and binder resin in the slurry may be the same as the content ratio of the conductive material and binder resin in the primer layer formed thereafter.

[0101] In one embodiment of the present invention, the conductive material may maintain a particle shape within the primer layer or may be in a partially collapsed particle shape.

[0102] In one embodiment of the present invention, the binder resin may maintain a particle shape within the primer layer, or may be in a partially collapsed particle shape.

[0103] In one embodiment of the present invention, the step of heating the metal thin film to which the slurry is applied may further include a step of pressing simultaneously with the heating step and / or before or after the heating step.

[0104]

[0105] Dry electrode

[0106] The present invention provides an electrode including the current collector for the above-described dry electrode and an electrode active material layer disposed on at least one surface of the current collector for the dry electrode.

[0107] The above electrode active material layer includes an electrode active material and an electrode binder, and may further include an electrode conductive material as needed.

[0108] In a specific embodiment of the present invention, the electrode active material layer includes electrode composite particles, and the electrode composite particles include an electrode active material and an electrode binder, and may further include an electrode conductive material as needed. When the electrode composite particles are introduced into the electrode, the aspect ratio or particle size range may not be maintained in the initial state due to the calendaring process described below. The electrode active material layer may include 80 wt% or more, 90 wt% or more, 95 wt% or more, or 99 wt% or more of the composite particles relative to 100 wt% of the electrode active material layer. Meanwhile, in one embodiment, the electrode active material layer may further include an electrode active material, an electrode binder, an electrode conductive material, etc., which are not assembled and included in the composite particles but are present in a free state.

[0109] In a specific embodiment of the present invention, the electrode active material layer includes an electrode powder, the electrode powder includes an electrode active material, an electrode conductive material, and an electrode binder, and the electrode powder can be formed into a film and included in a dry electrode.

[0110] The electrode active material layer has pores provided by the interstitial volume, which is the space between the composite particles, and exhibits porous characteristics derived from this structure. In one embodiment of the present invention, the electrode active material layer preferably has a porosity of 20 vol% to 40 vol%, considering aspects such as electrolyte impregnation ability, shape stability, and ionic conductivity.

[0111] Meanwhile, according to one embodiment of the present invention, the thickness of the electrode active material layer may be, for example, 30 μm to 300 μm, but is not limited thereto.

[0112] According to another embodiment of the present invention, the electrode active material layer may be composed of a single layer including one unit active material layer.

[0113] According to another embodiment of the present invention, the electrode active material layer may have a multilayer structure in which two or more unit active material layers are laminated. At this time, the electrode materials included in each unit active material layer, for example, the electrode active material and the electrode binder, may be the same or different for each layer, but are not limited thereto. In addition, if necessary, each layer may include an electrode conductive material, and at this time, the electrode conductive materials of each layer may also be the same or different.

[0114] Meanwhile, in the present invention, the electrode may be a cathode or an anode, and preferably a cathode.

[0115] In one embodiment of the present invention, the negative electrode active material is carbon such as graphite carbon such as non-graphitizable carbon, natural graphite or artificial graphite; Lix 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, elements of group 1, 2, and 3 of the periodic table, halogens; 0 <x≤1; 1≤y≤3; 1≤z≤8) 등의 금속 복합 산화물; 리튬 금속; 리튬 합금; 규소계 합금; 주석계 합금; SiO, SiO / C, SiO2등의 실리콘계 산화물; SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, 및 Bi2O5 등의 금속 산화물; 폴리아세틸렌 등의 도전성 고분자; Li-Co-Ni 계 재료 등을 사용할 수 있으나, 이들만으로 한정되는 것은 아니다.

[0116] In one embodiment of the present invention, the positive electrode active material may include, but is not limited to, a lithium transition metal oxide; a lithium metal iron phosphate; a lithium nickel-manganese-cobalt oxide; an oxide in which a portion of the lithium nickel-manganese-cobalt oxide is substituted with another transition metal; or two or more thereof. Specifically, the positive electrode active material may include, but is not limited to, a layered compound such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; a compound having the chemical formula Li 1+x Mn 2-x Lithium manganese oxides such as O4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, Cu2V2O7; chemical formula LiNi 1-x M xNi-site type lithium nickel oxide represented by O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga and x = 0.01 to 0.3); chemical formula LiMn 2-x M x Lithium manganese complex oxides represented by O2 (wherein, M = Co, Ni, Fe, Cr, Zn or Ta, and x = 0.01 to 0.1) or Li2Mn3MO8 (wherein, M = Fe, Co, Ni, Cu or Zn); Li where some of the Li in the chemical formula is replaced by aluminum ions. 1+x (Ni a Co b Mn c Al d ) 1-x O2(x = 0 ~ 0.03, a = 0.3 ~ 0.95, b = 0.01 ~ 0.35, c = 0.01 ~ 0.5, d = 0.001 ~ 0.03, a+b+c+d=1); lithium metal phosphate LiM P O4 (wherein M = Fe, CO, Ni, or Mn), disulfide compounds; Fe2(MoO4)3, etc., but are not limited to these.

[0117] In one embodiment of the present invention, the electrode conductive material is not particularly limited as long as it has conductivity without causing chemical changes in the battery.

[0118] The electrode conductive material is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black; conductive fiber such as carbon fiber or metal fiber; metal powder such as fluorocarbon, aluminum, nickel powder; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxide such as titanium oxide; conductive materials such as polyphenylene derivatives, etc. may be used. Specifically, in order to uniformly mix the electrode conductive material and improve conductivity, it may include at least one selected from the group consisting of activated carbon, graphite, carbon black, and carbon nanotubes, and more specifically, it may include activated carbon.

[0119] In one embodiment of the present invention, the electrode binder is not particularly limited as long as it uniformly disperses the powder-based electrode active material and conductive material without causing chemical changes in the battery. For example, the electrode binder may include a diene polymer, an acrylate polymer, a fluorine polymer, a styrene polymer, or two or more thereof.

[0120] Examples of the diene polymer include polymers containing monomer units derived from conjugated dienes such as butadiene and isoprene, and hydrogenated products thereof. The proportion of monomer units derived from conjugated dienes during the diene polymerization may usually be 40 wt% or more, preferably 50 wt% or more, and more preferably 60 wt% or more.

[0121] Specifically, examples thereof include conjugated diene homopolymers such as polybutadiene or polyisoprene; aromatic vinyl-conjugated diene copolymers such as styrene-butadiene copolymer (SBR), which may also be carboxyl-modified; cyanated vinyl-conjugated diene copolymers such as acrylonitrile-butadiene copolymer (NBR); hydrogenated SBR, hydrogenated NBR, and the like.

[0122] The above styrene polymer is a polymer having a repeating unit derived from a styrene monomer, and may include a styrene homopolymer (polystyrene), a styrene copolymer, etc. Examples of the styrene copolymer may include a styrene-ethylene-butadiene copolymer, a styrene-butadiene-propylene copolymer, a styrene-isoprene copolymer, a styrene-n-butyl acrylic acid-itaconic acid-methyl methacrylate-acrylonitrile copolymer, a styrene-butadiene block copolymer, a styrene-butadiene-styrene block copolymer, a styrene-ethylene-butylene-styrene block copolymer, a styrene-isoprene block copolymer, a styrene-ethylene-propylene-styrene block copolymer, and other block copolymers.

[0123] Examples of the above acrylate polymer may include a polymer containing monomer units derived from acrylic acid ester and / or methacrylic acid ester. The proportion of monomer units derived from acrylic acid ester and / or methacrylic acid ester in the acrylate polymer may usually be 40 wt% or more, preferably 50 wt% or more, and more preferably 60 wt% or more. Specific examples of acrylate polymers include crosslinked acrylate polymers such as 2-ethylhexyl acrylate-methacrylic acid-acrylonitrile-ethylene glycol dimethacrylate copolymer, 2-ethylhexyl acrylate-methacrylic acid-methacrylonitrile-diethylene glycol dimethacrylate copolymer, 2-ethylhexyl acrylate-styrene-methacrylic acid-ethylene glycol dimethacrylate copolymer, butyl acrylate-acrylonitrile-diethylene glycol dimethacrylate copolymer, and butyl acrylate-acrylic acid-trimethylolpropane trimethacrylate copolymer; Examples thereof include copolymers of ethylene and (meth)acrylic acid esters, such as ethylene-methyl acrylate copolymers, ethylene-methyl methacrylate copolymers, ethylene-ethyl acrylate copolymers, and ethylene-ethyl methacrylate copolymers; graft polymers obtained by grafting a radically polymerizable monomer onto the above copolymers of ethylene and (meth)acrylic acid esters; and the like. Meanwhile, examples of the radically polymerizable monomer used in the graft polymers include methyl methacrylate, acrylonitrile, and methacrylic acid. In addition, copolymers of ethylene and (meth)acrylic acid, such as ethylene-acrylic acid copolymers and ethylene-methacrylic acid copolymers, can be used as dispersion-type binders.

[0124] The above fluorine-based polymer may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and polyvinylidene fluoride copolymers such as PVDF-HFP, and specifically, may include polytetrafluoroethylene (PTFE), and more specifically, may be polytetrafluoroethylene (PTFE).

[0125] In one embodiment of the present invention, the mixing ratio of the electrode active material, electrode conductive material, and electrode binder may be 80 to 99 parts by weight: 0.5 to 10 parts by weight: 0.5 to 10 parts by weight of electrode active material: electrode conductive material: electrode binder, and specifically, 90 to 99 parts by weight: 0.5 to 5 parts by weight: 0.5 to 10 parts by weight.

[0126] In one embodiment of the present invention, the electrode active material layer may include electrode composite particles, electrode powder, or a combination thereof. In the present invention, when a dry electrode, i.e., electrode composite particles, electrode powder, or a combination thereof, is included as an electrode active material on a dry electrode current collector, the electrode interfacial resistance characteristics may be excellent. In this case, the dry electrode composite particles and the dry electrode powder are substituted for the above-described types of dry electrodes.

[0127]

[0128] <Method for manufacturing composite particles for electrodes>

[0129] In one embodiment of the present invention, the electrode composite particle included in the electrode active material layer can be manufactured by a method including a step of preparing a slurry by mixing an electrode active material and an electrode binder with a dispersion medium; and a step of spray drying the slurry.

[0130] First, the electrode active material and electrode binder, and optionally an electrode conductive material or additive, are dispersed or dissolved in a dispersion medium (a solvent for the electrode binder), thereby obtaining a slurry in which the electrode active material and electrode binder, together with the electrode conductive material and / or other additives, are dispersed or dissolved.

[0131] As the dispersion medium used to obtain the above slurry, water is most preferably used, but an organic solvent may also be used. Examples of the organic solvent include alkyl alcohols such as methyl alcohol, ethyl alcohol, and propyl alcohol; alkyl ketones such as acetone and methyl ethyl ketone; ethers such as tetrahydrofuran, dioxane, and diglyme; amides such as diethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone (hereinafter also referred to as NMP), and dimethylimidazolidinone; sulfur-based solvents such as dimethyl sulfoxide and sulfolane; and the like, but alcohols are preferred. When an organic solvent having a boiling point lower than water is used in combination, the drying speed during fluid granulation can be accelerated. In addition, since the dispersibility or solubility of the negative electrode binder can be changed, the viscosity and fluidity of the slurry can be adjusted depending on the amount or type of the dispersion medium, thereby improving production efficiency.

[0132] The amount of the dispersion medium used when preparing the above slurry may be an amount such that the solid concentration of the slurry is usually in the range of 1 to 50 wt%, or 5 to 50 wt%, or 10 to 30 wt%.

[0133] The method or order of dispersing or dissolving the electrode active material and electrode binder, etc. in the dispersion medium is not particularly limited, and examples thereof include a method of adding the electrode active material and electrode binder to the dispersion medium and mixing them, a method of dissolving or dispersing the electrode binder in the dispersion medium, and then finally adding the electrode active material and mixing them, etc. When the slurry contains an electrode conductive material and / or additive, these components may be added when the electrode active material is added. Examples of the mixing means include mixing devices such as a ball mill, a sand mill, a bead mill, a pigment disperser, a stone mill, an ultrasonic disperser, a homogenizer, and a planetary mixer. The mixing may be performed, for example, at a temperature ranging from room temperature to 80°C for 10 minutes to several hours.

[0134] Next, the slurry is spray-dried. Spray drying is a method of drying by spraying the slurry into hot air. The spraying method of the device used in the spray drying method includes a rotating disc method and a nozzle pressurization method. The rotating disc method is a method in which the slurry is introduced almost to the center of a high-speed rotating disc, and the slurry is placed outside the disc by the centrifugal force of the disc, and then dried in the form of a mist. The rotation speed of the disc depends on the size of the disc, but is usually 5,000 rpm to 35,000 rpm, preferably 15,000 rpm to 30,000 rpm. On the other hand, the nozzle pressurization method is a method in which the slurry is passed through a thin nozzle and a high-pressure fluid such as air or another liquid is sprayed together to spray in the form of a mist, thereby drying.

[0135] In one embodiment of the present invention, the temperature of the hot air can be controlled to 80°C to 250°C, preferably 175°C to 220°C, based on the reactor inlet temperature (at the time of injection) in terms of forming a composite particle structure having a high content of electrode binder on the surface. In the spray drying method, the method of sucking the hot air is not particularly limited, and examples thereof include a method in which the hot air and the spray direction are parallel to each other in the horizontal direction, a method in which the hot air is sprayed from the top of the drying tower and then descends together with the hot air, a method in which the sprayed droplets come into countercurrent contact with the hot air, a method in which the sprayed droplets initially come into parallel with the hot air and then fall by gravity and come into countercurrent contact, etc. Meanwhile, in one embodiment of the present invention, the outlet temperature of the reactor during the spray drying (the temperature of the hot air discharged from the reactor) can be controlled to 90°C to 130°C.

[0136] If the outlet temperature and / or the difference between the inlet and outlet temperatures, ΔT, is low, drying is not performed properly, resulting in the formation of particles with a large amount of residual solvent, which prevents the formation of spherical particles of uniform shape and may result in the formation of composite particles that are agglomerated or irregular. On the other hand, if the inlet temperature is too high and ΔT is large, over-drying may occur and assembly may not occur, resulting in d 50 These extremely small, low-aspect-ratio particles can be produced. Therefore, to achieve a high aspect ratio, minimal binder agglomeration, and optimal particle size control, the inlet and outlet temperatures must be controlled within appropriate ranges.

[0137] Additionally, the result obtained by optionally spray drying, i.e. the composite particles, can be heat treated to harden the surface, and at this time, the heat treatment temperature can usually be 80°C to 300°C.

[0138] In one embodiment of the present invention, the electrode powder included in the electrode active material layer can be manufactured by a method including the steps of: manufacturing a mixture including an electrode active material, an electrode conductive material, and an electrode binder; kneading the mixture at a temperature range of 70°C to 200°C and under a pressure higher than normal pressure to fiberize the electrode binder to manufacture a mixture lump; and pulverizing the mixture lump to obtain an electrode powder.

[0139]

[0140] <Method for manufacturing dry electrodes>

[0141] According to one embodiment of the present invention, the method for manufacturing the dry electrode includes the steps of dispersing a plurality of electrode composite particles manufactured by the above-described method on a dry electrode current collector; and the step of pressing the dispersed electrode composite particles to form an electrode active material layer (pressurizing step).

[0142] First, composite particles for electrodes are dispersed on a current collector. At this time, a primer layer including a conductive material and a binder is provided on at least one side of the dry electrode current collector, as described above.

[0143] In one embodiment of the present invention, prepared composite particles for electrodes can be supplied to a roll-type pressurizing molding device by a supply device such as a screw feeder to form an electrode active material layer, and at this time, a dry electrode current collector can be sent to the roll of the pressurizing molding device at the same time as the supply of the composite particles for electrodes, thereby directly laminating the electrode active material layer on the dry electrode current collector. Alternatively, the composite particles for electrodes can be dispersed on a current collector, the thickness can be adjusted evenly with a blade or the like, and then formed by a pressurizing device in a pressurizing step to form an electrode active material layer.

[0144] In one embodiment of the present invention, the pressurizing step may be performed by a roll press process. The roll press process may be performed by arranging two cylindrical rolls in parallel, vertically, with a narrow gap between them, rotating them in opposite or identical directions, and interlocking a pressurized object (e.g., an electrode) between them.

[0145] In one embodiment of the present invention, the method for manufacturing the dry electrode may include a step of manufacturing a composite film by calendering the electrode powder manufactured by the above-described method, manufacturing an electrode active material layer, and a step of positioning the electrode active material layer including the composite film on at least one surface of a current collector for a dry electrode of the present invention and laminating the electrode active material layer to manufacture a dry electrode.

[0146]

[0147] Lithium secondary battery

[0148] The present invention provides a lithium secondary battery.

[0149] In one embodiment of the present invention, a lithium secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and at least one of the positive electrode and the negative electrode may include the current collector for a dry electrode as described above in the present invention. Preferably, the negative electrode may include the current collector for a dry electrode.

[0150] The above separator is interposed between the positive and negative electrodes, electrically insulating them while simultaneously allowing lithium ions to pass through. Any separator commonly used in lithium secondary batteries may be used as the separator, and there are no particular limitations.

[0151] The above separator may be a conventional porous polymer film used as a conventional separator, for example, a porous polymer film made of a polyolefin polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, which may be used alone or in a laminated manner. In addition, an insulating thin film having high ion permeability and mechanical strength may be used. The separator may include a safety reinforced separator (SRS) in which a ceramic material is thinly coated on the surface of the separator. In addition, a conventional porous non-woven fabric, for example, a non-woven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used, but is not limited thereto.

[0152] The above electrolyte solution includes a lithium salt as an electrolyte and an organic solvent for dissolving the same.

[0153] The above lithium salt can be used without limitation as long as it is one commonly used in electrolytes for secondary batteries, and for example, the anion of the above lithium salt is F - , Cl - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C -, (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - One type selected from the group consisting of can be used.

[0154] As the organic solvent included in the above electrolyte, any commonly used one can be used without limitation, and representative examples thereof include at least one selected from the group consisting of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, methylpropyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite, and tetrahydrofuran.

[0155] In particular, among the above carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents with high dielectric constants and thus can be preferably used because they easily dissociate lithium salts in the electrolyte. In addition, when a low-viscosity, low-dielectric constant linear carbonate such as dimethyl carbonate and diethyl carbonate is mixed and used in an appropriate ratio with these cyclic carbonates, an electrolyte having high electrical conductivity can be produced, so that the electrolyte can be used even more preferably.

[0156] Optionally, the electrolyte stored according to the present invention may further include additives such as an overcharge prevention agent included in a conventional electrolyte.

[0157] According to one embodiment of the present invention, a lithium secondary battery is formed by placing a separator between a positive electrode and a negative electrode to form an electrode assembly, placing the electrode assembly in, for example, a pouch, a cylindrical battery case, or a square battery case, and then injecting an electrolyte to complete the secondary battery. Alternatively, the electrode assembly may be laminated, then impregnated with an electrolyte, and the resulting product may be placed in a battery case and sealed to complete the lithium secondary battery.

[0158] The lithium secondary battery according to the present invention can be included in a battery module as a unit battery, and the battery module can be used in a battery pack and a device that includes the battery pack as a power source. Specific examples of the device include, but are not limited to, an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or a power storage system.

[0159]

[0160] Hereinafter, the present invention will be described in more detail through examples, but the following examples are intended to illustrate the present invention, and the scope of the present invention is not limited to these examples.

[0161] Example 1

[0162] <Manufacturing of current collectors for dry electrodes>

[0163] A slurry for a primer layer was prepared by mixing 30 parts by weight of acetylene black (Denka, Li250) as a conductive agent and 70 parts by weight of styrene-butadiene rubber (SBR, LG Chemical, AD-B31, Tg: -15℃) as a binder resin with water as a dispersion medium. At this time, the content ratio of the conductive agent and the binder resin in the slurry was the same as the content ratio of the conductive agent and the binder resin in the primer layer formed thereafter. At this time, the true density of the binder resin used was 0.9 g / ml, and the particle size, BET specific surface area, bulk density, and true density of the conductive agent used are shown in Table 1 below.

[0164] The prepared slurry for the primer layer was applied to one surface of a 10 ㎛ thick copper current collector (SK Nexilis, STN-B Grade) and dried at a temperature of 130°C for 2 minutes to form a primer layer on the entire surface of the copper current collector, thereby manufacturing a dry electrode current collector. At this time, the thickness of the primer layer formed on the entire surface of the copper current collector was confirmed to be 1.5 ㎛.

[0165] <Manufacturing of electrodes (cathode)>

[0166] Natural graphite and artificial graphite were prepared as negative active materials, carbon black as negative conductive material, carboxymethyl cellulose as negative dispersant, and modified styrene butadiene copolymer as negative binder were mixed with water as a dispersion medium in a weight ratio of 95.6:1.0:1.1:2.3, and then a slurry with a viscosity of approximately 1,000 cPs was prepared using a homogenizer. The prepared slurry was fed into a spray dryer together with hot air under a pressure range of -40 mmH2O and dried. At this time, the spray dryer was controlled at an inlet temperature of 180°C, an outlet temperature of 90°C, and a rotation speed of 18,000 rpm. The obtained electrode composite particles were sieved using an industrial sieve to remove coarse particles larger than 150 μm, and fine particles smaller than 40 μm were separated again. The separated fine particles were mixed with composite particles for electrodes from which only the coarse particles were removed, and a composite particle for cathode was finally prepared containing a larger amount of fine particles than the conventional composite particle for electrodes.

[0167] A thickness adjustment bar is used on one side of the current collector for the dry electrode having the above primer layer to adjust the current collector to 25 cm. 2 The composite particles for electrodes prepared in advance in an amount of 400 mg were evenly applied, and a roll-to-roll hot rolling molding device was used to form a negative electrode active material layer by applying pressure of 0.7 tons per cm at a speed of 2 m per minute under conditions of 60°C, thereby manufacturing a negative electrode.

[0168] Examples 2 to 4 and Comparative Examples 1 to 2

[0169] In the above Example 1, the same procedure as Example 1 was performed except that a conductive material having the properties shown in Table 1 below was used.

[0170] Classification Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Type of conductive material Li250 (carbon black) SuperC65 (carbon black) Li400 (carbon black) SFG6L (graphite) Li100 (carbon black) Li435 (carbon black) Conductive material particle size (d) 50 , nm)37404835003523BET specific surface area (m 2 / g)5863391768133 Bulk density of the challenge material (g / ml)0.080.0670.150.1870.040.05 True density of the challenge material (g / ml)1.951.951.952.231.951.95 Bulk density of the challenge material / True density of the binder resin0.0890.0740.170.210.0440.056

[0171] Experimental examples 1 and 2

[0172] Experimental Example 1: Measurement of Adhesion Between the Current Collector and the Electrode Interface

[0173] Double-sided tape was attached to a slide glass measuring 25 mm X 75 mm, and the electrodes of Examples 1 to 4 and Comparative Examples 1 to 2, which were punched out to 20 mm X 100 mm, were adhered thereon. Then, using a UTM (LLOYD) device, the force for peeling off the slide glass in a section of 80 mm in electrode length was measured by pulling at 100 mm / min, and the results are shown in Table 2 below. At this time, the adhesive force is the average value of the force measured in a section of 20 to 40 mm, and the measurement angle between the slide glass and the electrode was 90°.

[0174] Experimental Example 2: Measurement of the interface resistance of the electrode

[0175] The interface resistance of the electrodes of Examples 1 to 4 and Comparative Examples 1 to 2, which were punched out to 50 mm X 70 mm, was measured using a resistance meter (HIOKI MP Tester, RM2611, RM9003, RM9004) under 10 Ω (10 mA) and slow measurement conditions, and the results are shown in Table 2.

[0176] Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Electrode interface resistance (Ω cm) 2 )0.0300.0260.0160.0140.0540.049Adhesion (gf / 20 mm)786481833730

[0177] According to Table 2, it was confirmed that the collectors of Examples 1 to 4 had lower electrode interface resistance than the collectors of Comparative Examples 1 to 2, indicating superior resistance characteristics. In addition, it was confirmed that the collectors of Examples 1 to 4 had superior adhesion between the collector and the electrode interface than the collectors of Comparative Examples 1 to 2.

[0178] Other property measurement methods

[0179] The particle size, BET specific surface area, bulk density of the conductive material, and true density of the conductive material / binder resin were measured by the following methods:

[0180] <Intake(d) 50 ) measurement>

[0181] Particle size d of the conductive materials of Examples 1 to 4 and Comparative Examples 1 to 2 50 After being dispersed in a dispersion medium, it was introduced into a commercially available laser diffraction particle size measuring device (Microtrac MT 3000) and irradiated with ultrasonic waves of approximately 28 kHz at an output of 60 W. Then, a volume-cumulative particle size distribution graph was obtained, and the particle size corresponding to 50% of the volume-cumulative amount was measured.

[0182] <BET 비표면적의 측정>

[0183] The BET specific surface area of ​​the particle size of the conductive materials of Examples 1 to 4 and Comparative Examples 1 to 2 was measured from the nitrogen gas adsorption amount at liquid nitrogen temperature (77 K) using BELSORP-mini II of BEL Japan.

[0184] <Measurement of bulk density>

[0185] The bulk density of the conductive materials of Examples 1 to 4 and Comparative Examples 1 to 2 was measured by placing about 100 g of the conductive material into a funnel-shaped bulk density measuring device, pouring it into a 100 ml container, and then measuring the weight of the conductive material inside the container.

[0186] <Measurement of true density>

[0187] The true density of the challenge material and binder resin was measured using a true density meter (Gas Pycnometer, G PYC-100, PMI, USA).

[0188] <Measurement of glass transition temperature (Tg)>

[0189] The glass transition temperature of the binder resin was measured using DSC equipment (TA instrument, DSC 2920).

[0190]

[0191] Experimental examples 3 to 5

[0192] Example 5: Preparation of monocell

[0193] Ni as a cathode active material 0.90 Co 0.05 Mn 0.05 A positive electrode slurry was prepared by mixing carbon black as a positive electrode conductive material and PVdF as a positive electrode binder in an N-methylperolidone solvent at a ratio of 96:2:2, and the slurry was applied to one side of an aluminum current collector, followed by drying and rolling at a temperature of 130°C to prepare a positive electrode.

[0194] Afterwards, a porous polyethylene separator was interposed between the positive electrode and the negative electrode of the aforementioned Experimental Example 1 to manufacture an electrode assembly, and after positioning the electrode assembly inside a case, an electrolyte was injected into the case to manufacture a lithium secondary battery. At this time, the electrolyte was a monocell manufactured by dissolving 1.0 M lithium hexafluorophosphate (LiPF6) in an organic solvent composed of ethylene carbonate / ethyl methyl carbonate / diethyl carbonate (mixed volume ratio of EC / EMC / DEC=3 / 4 / 3).

[0195] The monocell was prepared for evaluation by performing formation charging and discharging on the above monocell and removing the initial gas.

[0196]

[0197] Comparative Example 3: Manufacturing of Monocell

[0198] Natural graphite and artificial graphite were prepared as negative active materials, carbon black as negative conductive material, carboxymethyl cellulose as negative dispersant, and modified styrene butadiene copolymer as negative binder were mixed in a weight ratio of 95.6:1.0:1.1:2.3 with water as a dispersion medium to prepare negative electrode slurry. The negative electrode slurry was applied onto the dry electrode current collector prepared in Example 1 using a thickness control bar to a current collector thickness of 25 cm. 2 The previously prepared negative electrode slurry was evenly applied in an amount of 400 mg per unit, and a roll-to-roll hot rolling forming device was used to form a negative electrode active material layer by applying pressure of 0.7 tons per cm at a speed of 2 m per minute under conditions of 60°C, thereby manufacturing a negative electrode.

[0199] Ni as a cathode active material 0.90 Co 0.05 Mn 0.05 A positive electrode slurry was prepared by mixing carbon black as a positive electrode conductive material and PVdF as a positive electrode binder in an N-methylperrolidone solvent at a ratio of 96:2:2, and the slurry was applied to one side of an aluminum current collector, followed by drying and rolling at 130°C to prepare a positive electrode.

[0200] Afterwards, a porous polyethylene separator was interposed between the positive electrode and the negative electrode to manufacture an electrode assembly, and the electrode assembly was placed inside a case, and an electrolyte was injected into the case to manufacture a lithium secondary battery. At this time, the electrolyte was a monocell manufactured by dissolving 1.0 M lithium hexafluorophosphate (LiPF6) in an organic solvent composed of ethylene carbonate / ethyl methyl carbonate / diethyl carbonate (mixed volume ratio of EC / EMC / DEC=3 / 4 / 3).

[0201] The monocell was prepared for evaluation by performing formation charging and discharging on the above monocell and removing the initial gas.

[0202]

[0203] Experimental Example 3: Initial DCIR Measurement

[0204] The monocells of Experimental Example 5 and Comparative Example 3 were charged under charging conditions of 4.2 V 0.33 C CC / CV, 0.05 C cut-off, and then discharged under discharging conditions of 2.0 V 0.33 C CC, 2.5 V cut-off. Thereafter, the initial DCIR was measured under SOC 50, 2.5 C 30 s pulse conditions, and the results are shown in Table 3.

[0205]

[0206] Experimental Example 4: HPPC Discharge

[0207] HPPC (hybrid pulse power characterization) tests were performed on the monocells of Experimental Example 5 and Comparative Example 3, and the discharge resistance was measured for each SoC. At this time, each monocell was charged under the conditions of 4.2 V 0.33 C CC / CV, 0.05 C Cut-off, and then discharged under the conditions of 2.5 C 30 s pulse at SOCs of 90, 80, 70, 60, 50, 40, 30, 20, and 10, and the batteries were stabilized for 30 minutes each. The discharge resistance (Ohm) of the monocell was measured for each SoC step, and the results are shown in FIGS. 2a to 2c.

[0208] Comparative Example 3 Example 50.1s0.8030.70610s1.1871.07930s1.5561.446

[0209] According to Table 3 and FIGS. 2a to 2c, Example 5 was confirmed to have a lower initial DCIR value compared to Comparative Example 3. That is, the initial DCIR value of Example 5, which includes a negative electrode manufactured by a dry method, was lower than that of Comparative Example 3, which includes a negative electrode manufactured by a wet method having the same composition. This confirms that when an electrode active material layer manufactured by a dry method is included on a current collector for a dry electrode, the resistance characteristics are superior to when an electrode active material layer manufactured by a wet method is included.

[0210]

[0211] Experimental Example 5: Measurement of Cycle Characteristics

[0212] For the monocells of Experimental Example 5 and Comparative Example 3, a cycle was performed in which the cells were charged at a temperature of 45°C under the charging conditions of 4.2 V, 0.33 C CC / CV, and 0.05 C Cut-off, and then discharged under the discharging conditions of 2.0 V, 0.33 C CC, and 2.5 V Cut-off. The cycle was repeated 100 and 200 times, and the initial capacity retention rate and DCIR value, the 100-cycle capacity retention rate and DCIR value, and the 200-cycle capacity retention rate and DCIR value were measured, respectively, and the results are shown in Tables 4 and 5 below. At this time, the DCIR measurement was performed under the conditions of SOC 50 and 2.5 C 30 s pulse.

[0213] Example 5 Comparative Example 3 Initial Capacity (mAh) 77.77 78.75 Capacity after 100 cycles (mAh) 72.6 173.48 Capacity retention rate after 100 cycles (%) 93.49 3.3 Capacity after 200 cycles (mAh) 69.8 470.56 Capacity retention rate after 200 cycles (%) 89.8 89.6

[0214] Example 5 Comparative Example 3 Initial DCIR (mΩ) 1.074 1.176 Initial DCIR after 100 cycles (mΩ) 1.220 1.930 Increase rate of DCIR after 100 cycles (%) 13.66 Initial DCIR after 4.1200 cycles (mΩ) 1.342 2.338 Increase rate of DCIR after 200 cycles (%) 25.09 8.8

[0215] According to Table 4, the monocells of Example 5 and Comparative Example 3 have similar capacity retention rates, but according to Table 5, the monocell of Example 5 has a reduced DCIR increase rate compared to the monocell of Comparative Example 3, confirming that when a dry electrode active material layer is included on a current collector for a dry electrode, the resistance characteristics are superior to when a wet electrode active material layer is included.

Claims

1. A metal film for the entire body, and a primer layer formed on at least one surface of the metal film, The above primer layer comprises a binder resin and a conductive material, The above challenge material has a bulk density of 0.055 g / ml or more and a BET surface area of ​​100 m 2 / g or less, current collector for dry electrode.

2. In claim 1, A current collector for a dry electrode, characterized in that the bulk density ratio of the conductive material to the true density of the binder resin is 0.06 or more.

3. In claim 1, A current collector for a dry electrode, characterized in that the primer layer comprises a binder resin and a conductive material in a weight ratio of 20:80 to 80:

20.

4. In claim 1, The above challenge material has an average particle diameter d 50 A current collector for a dry electrode characterized by a thickness of 30 nm or more.

5. In claim 1, A current collector for a dry electrode, characterized in that the above-mentioned conductive material has a concentration gradient that increases in the direction of the current collector in the thickness direction of the primer layer.

6. In claim 1, A current collector for a dry electrode, characterized in that the above-mentioned conductive material comprises a carbon material.

7. In claim 1, A current collector for a dry electrode, characterized in that the primer layer contains a binder resin in an amount of 20 wt% or more relative to the total weight of the primer layer.

8. In claim 1, A current collector for a dry electrode, characterized in that the binder resin includes a binder resin having a glass transition temperature (Tg) of -40°C to 25°C.

9. In claim 1, A current collector for a dry electrode, characterized in that the binder resin includes at least one selected from the group consisting of styrene butadiene rubber (SBR), butadiene rubber (BR), nitrile butadiene rubber (NBR), styrene butadiene styrene block polymer (SBS), styrene ethylene butadiene block polymer (SEB), styrene-(styrene butadiene)-styrene block polymer, natural rubber (NR), and isoprene rubber (IR).

10. A current collector for a dry electrode according to any one of claims 1 to 9; and An electrode characterized by comprising an electrode active material layer disposed on at least one surface of a current collector for the dry electrode.

11. In claim 10, An electrode characterized in that the electrode active material layer includes electrode composite particles, electrode powder, or a combination thereof.

12. Including a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte; A lithium secondary battery, wherein at least one of the positive and negative electrodes comprises a current collector for a dry electrode according to any one of claims 1 to 9.

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