Dry electrode and lithium secondary battery comprising same

Abstract

The present invention relates to a dry electrode including: a current collector; and an electrode mixture film, wherein the electrode mixture film includes an electrode active material, a conductive material, and a binder having a three-dimensional fiber network structure, and the electrode mixture film has an overlap mapping index (OMI) of 17 or more, represented by equation 1 according to the present invention.

Description

Dry electrode and lithium secondary battery including same

[0001] Cross-citation with related applications

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2024-0079211, filed June 18, 2024, and Korean Patent Application No. 10-2024-0079212, filed June 18, 2024, the entire contents of which are incorporated herein by reference.

[0003]

[0004] Technology field

[0005] The present invention relates to a dry electrode and a lithium secondary battery including the same.

[0006]

[0007] Secondary batteries are used not only in small products such as digital cameras, P-DVDs, MP3 players, mobile phones, PDAs, portable game devices, power tools, and e-bikes, but also in large products requiring high output such as electric vehicles and hybrid vehicles, as well as in power storage devices that store surplus generated power or renewable energy and power storage devices for backup purposes.

[0008] Typically, secondary batteries are manufactured by applying electrode active material slurry to a positive electrode current collector and a negative electrode current collector to form an electrode active material layer, then manufacturing a positive electrode and a negative electrode through a drying and rolling process, and then laminating these on both sides of a separator to form an electrode assembly of a predetermined shape, and then housing the electrode assembly in a battery case, injecting electrolyte, and sealing the electrode assembly.

[0009] Meanwhile, during the drying process of the electrode active material slurry, the solvent contained in the slurry may evaporate, causing defects such as pinholes or cracks in the electrode active material layer formed on the current collector. In addition, since the inside and outside of the electrode active material slurry are not uniformly dried during the drying process, there is a concern that the powder floating phenomenon due to the difference in solvent evaporation rate may occur, i.e., the powder in the area that dries first may rise and form a gap with the area that dries relatively later, which may deteriorate the electrode quality.

[0010] To solve the above problem, a drying device capable of controlling the evaporation rate of the solvent so that the inside and outside of the electrode active material slurry can be dried evenly is being considered, but such drying devices are very expensive and require considerable cost and time to operate, which is disadvantageous in terms of manufacturing process.

[0011] On the other hand, the solvent typically used in electrode active material slurries is N-methyl-2-pyrrolidone (NMP). Its high boiling point necessitates high heat energy and a very long drying process for drying, making it highly unsuitable for mass production. Furthermore, NMP is toxic and harmful to living organisms, making it unfriendly to the environment.

[0012] Accordingly, there has been a recent trend of active research on dry electrodes that manufacture electrodes without using solvents. The dry electrode is generally manufactured by laminating a free-standing electrode composite film manufactured in the form of a sheet containing an electrode active material, a binder, a conductive material, etc., onto a current collector. This electrode composite film includes a process of first mixing an electrode active material, a carbon material as a conductive material, and a fiberizable binder together using a blender, etc., and then applying a shear force through a process such as jet milling or kneading to fiberize the binder, and then calendering the obtained mixture into a film form to manufacture a free-standing film.

[0013] However, when manufacturing the dry electrode, unlike the wet electrode in which the electrode active material, conductive material, and fiberizable binder are mixed in a solvent, there is a problem in that the dispersibility of the fiberizable binder and conductive material is poor because they are mixed in a solvent-free state. For example, if the conductive material is locally aggregated or not sufficiently mixed with the binder, the mechanical strength of the electrode composite film may be reduced or the adhesion to the current collector may be reduced, resulting in a peeling phenomenon. In addition, since the electrically conductive path is not continuously and sufficiently secured, there is a problem in that the electrical resistance increases or the uniformity of the conductivity is reduced.

[0014] Therefore, there is a need for a dry electrode formed by balancing the constituent materials within the electrode composite film.

[0015]

[0016] One object of the present invention is to solve the above-described problem, and to provide a dry electrode having excellent mechanical strength of the electrode composite film, excellent processability, and excellent lifespan and output characteristics by controlling the electrode composite film so that the OMI (Overlap Mapping Index) expressed by Equation 1 according to the present invention satisfies a specific range.

[0017]

[0018] [1] The present invention provides a dry electrode comprising a current collector; and an electrode composite film; wherein the electrode composite film comprises an electrode active material, a conductive material, and a binder having a three-dimensional fiber network structure, and wherein the electrode composite film has an OMI of 17 or more, as represented by the following formula 1.

[0019] [Formula 1]

[0020] OMI = {(CFAR) / (FAR)} x 100

[0021] In the above equation 1, CFAR is the area ratio of pixel regions where 30 wt% or more of carbon element and 15 wt% or more of fluorine element are simultaneously detected when analyzing the element content within pixels of the electrode composite film cross-section using SEM-EDS, and FAR is the area ratio of pixel regions where 15 wt% or more of fluorine element is detected when analyzing the element content within pixels of the electrode composite film cross-section using SEM-EDS.

[0022] [2] In the present invention, in the above [1], the electrode composite film may have an OMI of 23 to 27 as expressed by the following formula 1.

[0023] [Formula 1]

[0024] OMI = {(CFAR) / (FAR)} x 100

[0025] In the above equation 1, CFAR is the area ratio of pixel regions where 30 wt% or more of carbon element and 15 wt% or more of fluorine element are simultaneously detected when analyzing the element content within pixels of the electrode composite film cross-section using SEM-EDS, and FAR is the area ratio of pixel regions where 15 wt% or more of fluorine element is detected when analyzing the element content within pixels of the electrode composite film cross-section using SEM-EDS.

[0026] [3] In the present invention, in the above [1] or [2], the CFAR may be 2% to 10%.

[0027] [4] In at least one of the above [1] to [3], the FAR may be 1% to 20%.

[0028] [5] In at least one of the above [1] to [4], the electrode composite film may have a tensile strength of 0.30 MPa to 0.70 MPa.

[0029] [6] In at least one of the above [1] to [5], the electrode composite film may have an elongation of 1.5% to 5.5%.

[0030] [7] In at least one of the above [1] to [6], the electrode composite film may have an electrode layer resistivity of 500 Ωcm or less.

[0031] [8] The present invention is characterized in that in at least one of the above [1] to [7], the electrode composite film has an interfacial resistivity of 9ⅹ10 -1 Ωcm 2 It could be as follows:

[0032] [9] In at least one of the above [1] to [8], the conductive material may include an expandable carbon nanotube.

[0033]

[0010] In at least one of the above [1] to [9], the expanded carbon nanotube may include a multi-walled carbon nanotube unit.

[0034]

[0011] In at least one of the above [1] to

[0010] , the multi-walled carbon nanotube unit may have an average diameter of 5 nm to 200 nm.

[0035]

[0012] The present invention is characterized in that in at least one of the above [1] to

[0011] , the BET specific surface area of ​​the multi-walled carbon nanotube unit is 50 m 2 / g to 500m 2 / g may be.

[0036]

[0013] In at least one of the above [1] to

[0012] , the multi-walled carbon nanotube unit may have three or more graphene layers arranged in parallel with respect to the axis of the multi-walled carbon nanotube unit.

[0037]

[0014] The present invention provides a lithium secondary battery including at least a dry electrode among the above [1] to

[0013] .

[0038]

[0039] The dry electrode according to the present invention forms a uniform conductive network by controlling the electrode composite film to have an OMI expressed by Equation 1 according to the present invention of 17 or more, while simultaneously forming a uniform three-dimensional fiber network structure, and at the same time, maintaining the mechanical strength of the electrode composite film above a certain level through interaction between the conductive material and the binder having the three-dimensional fiber network structure. Due to the above-mentioned characteristics, the dry electrode according to the present invention can realize excellent mechanical strength and excellent electrical conductivity, while also realizing high uniformity of the conductive network.

[0040]

[0041] The drawings attached to this specification illustrate preferred embodiments of the present invention and, together with the contents of the invention described above, serve to further enhance the understanding of the technical spirit of the present invention. Therefore, the present invention is not limited to the matters described in these drawings. Meanwhile, the shape, size, scale, or ratio of elements in the drawings included in this specification may be exaggerated to emphasize a clearer explanation.

[0042] Figure 1 is an example of a cross-sectional sample produced by ion milling on a dry electrode, and pixels with a carbon element content of 30 wt% or more are indicated as white areas through SEM-EDS analysis.

[0043] Figure 2 is an example of a cross-sectional sample prepared by ion milling on a dry electrode, and pixels with a fluorine element content of 15 wt% or more are indicated as white areas through SEM-EDS analysis.

[0044] Figure 3 is an example of a cross-sectional sample produced by ion milling on a dry electrode, and then pixels with a carbon element content of 30 wt% or more and a fluorine element content of 15 wt% or more are indicated as white areas through SEM-EDS analysis.

[0045] Figures 4 and 6 are SEM images of densely packed carbon nanotubes.

[0046] Figures 5 and 7 are SEM photographs of expanded carbon nanotube powder.

[0047]

[0048] Terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical spirit of the present invention, based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best possible manner.

[0049] In this specification, "volume cumulative average particle diameter D 50 "In the particle size distribution curve of silver particles, it means the particle size corresponding to 50% of the volume accumulation amount. The above D 50 For example, it can be measured using the laser diffraction method. The laser diffraction method can generally measure particle diameters from the submicron range to several mm, and can obtain results with high reproducibility and high resolution.

[0050] In this specification, "average particle diameter" means the arithmetic average value calculated by measuring the particle diameters of at least 30 particles observed in a scanning electron microscope image when observed at a magnification of 5,000 to 20,000 times using a scanning electron microscope. In this case, the particle diameter means the longest axis diameter of the particle. The above "volume cumulative average particle diameter D 50" and "average particle size" have different measurement methods, but their values ​​can be derived similarly, and the volume cumulative average particle size D measured in the powder state 50 The powder may have a similar value to the average particle size observed in the scanning electron microscope image of the electrode after it is manufactured into an electrode, within the error range.

[0051] In this specification, the term "composite composition" means a mixture including an electrode active material and a binder and optionally a conductive material, which is physically mixed to form a uniform dispersion phase, and may be a powder mixture as a product of the mixing process (mixing process) according to this specification, and may be substantially solvent-free. Here, substantially solvent-free means that no solvent is added or only a very small amount of solvent is added during mixing of the composite composition.

[0052] In this specification, the “mixed aggregate” refers to a mixture of powders that are converted into a dough-like aggregate by binding or connecting each other when the binder is fiberized by applying a shear force to the composite composition, and is a product of the kneading process (kneading process) according to this specification, which may have a solid content substantially close to 100% and may contain a small amount of solvent in some cases.

[0053] In this specification, “electrode powder” may mean a powder-type electrode material that is a material in which the above mixed aggregate is pulverized to form smaller particles and is in a powder form, and includes an electrode active material, a binder, and optionally a conductive material.

[0054] In this specification, the "electrode composite film" may mean an electrode composite layer manufactured in the form of a free-standing single sheet using an "electrode composite" including an electrode active material, a conductive material, and a binder without involving a solvent, or in a state of being laminated on a current collector. The term "free-standing" in this specification means that it can maintain a single shape without relying on other members and can be moved or handled by itself. The electrode composite film may be formed by compressing the electrode powder as described below. For example, the electrode powder may have a shape in which a layered structure is formed by being accumulated by compressing.

[0055] In this specification, “powder-sheeting film” means a film formed from the time the electrode powder is first passed through a calender roll in a roll-to-roll process (e.g., a calendering process) into a sheet shape through a powder-sheeting process until it passes through the last calender roll in the roll-to-roll process. The film may be a self-supporting sheet, but may have relatively weak self-supporting force. Here, the “powder-sheeting” means that the electrode powder is formed into a self-supporting sheet shape by a calender roll in the roll-to-roll process, and the “sheeting” is a process performed in the process of manufacturing the powder-sheeting film into an electrode composite film, and may mean a process of roll-rolling the powder-sheeting film.

[0056] In this specification, the term "three-dimensional fiber network structure" may refer to a structure that can be formed by fiberization of a binder during the process of forming a sheet into an electrode composite film from a composite composition including an electrode active material and a binder. Specifically, the three-dimensional fiber network structure may refer to various structures in which fine fibers formed by fiberization of the binder form a skeleton, thereby functioning as a support that enables the electrode composite film to be a self-supporting film. In this case, the electrode active material and, optionally, a conductive material may be accommodated within the pores formed in the three-dimensional fiber network structure.

[0057] In this specification, the porosity can be calculated using the following mathematical formula A.

[0058] [Mathematical Formula A]

[0059] Porosity (%) = {1-(electrode density / true density)} x 100

[0060] In the above mathematical formula A, the true density is a calculated density derived from the density and mass ratio of each component material forming the electrode composite film under the assumption that no pores are included, and the electrode density is a measured density of the electrode composite film measured by sampling the electrode composite film to a certain size.

[0061] In this specification, “specific surface area (m 2 / g)” is measured by the BET method, and specifically, it can be calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77K) using BELSORP-mino II of BEL Japan.

[0062] In this specification, MD direction (Machine Direction) means the longitudinal direction of the electrode composite film, and TD direction (Transverse Direction) means the width direction of the electrode composite film.

[0063]

[0064] In the case of manufacturing a dry electrode, unlike a wet electrode where the electrode active material, conductive material, and fiberizable binder are mixed in a solvent, the dry electrode is mixed in a solvent-free state, which causes the problem of poor dispersibility of the fiberizable binder and conductive material. For example, if the conductive material is locally aggregated, the electrically conductive path is not sufficiently secured or the durability of the electrically conductive path is weakened, which increases the electrical resistance, and the electrically conductive path is not formed uniformly and continuously, which reduces the uniformity of the conductive network. On the other hand, as the dispersibility of the binder decreases, the mechanical strength of the electrode composite film is reduced, and the problem of poor uniformity of the three-dimensional fiber network of the binder occurs.

[0065] The inventors of the present invention have conducted continuous research to solve such problems and have found that by controlling the electrode composite film so that the OMI (Overlap Mapping Index) expressed by Equation 1 according to the present invention satisfies a specific range, a dry electrode can be provided that maintains the mechanical strength of the electrode composite film above a certain level while also realizing excellent electrical conductivity and high uniformity of the conductive network, thereby completing the present invention.

[0066]

[0067] dry electrode

[0068] A dry electrode according to the present invention comprises a current collector; and an electrode composite film; wherein the electrode composite film comprises an electrode active material, a conductive material, and a binder having a three-dimensional fiber network structure, and the electrode composite film has an OMI of 17 or more, as expressed by the following formula 1.

[0069] [Formula 1]

[0070] OMI = {(CFAR) / (FAR)} x 100

[0071] In the above equation 1, CFAR is the area ratio of pixel regions where 30 wt% or more of carbon element and 15 wt% or more of fluorine element are simultaneously detected when analyzing the element content within pixels of the electrode composite film cross-section using SEM-EDS, and FAR is the area ratio of pixel regions where 15 wt% or more of fluorine element is detected when analyzing the element content within pixels of the electrode composite film cross-section using SEM-EDS.

[0072] The above OMI is measured using a commonly used SEM-EDS. For example, Apreo2S (Thermofisher) can be used for SEM, and Extreme (Oxford) can be used for EDS.

[0073] For example, for a dry electrode, a cross-sectional sample is produced by ion milling using Hitachi's IM5000, and then the cross-section of the electrode composite film among the cross-sections of the dry electrode is measured using the SEM-EDS to measure the area where a specific element is distributed, and the content of each element present in one pixel can be measured. Specifically, if a specific element contained in one pixel is higher than a specific content through SEM-EDS analysis, the pixels can be displayed as a white area.

[0074] At this time, the observation conditions may be an acceleration voltage of 3 kV, a magnification of 3000 times, and 1024 pixels x 400 pixels, but the number of pixels measured may vary depending on the size and / or thickness of the electrode composite film. In addition, the detection elements measured during SEM-EDS analysis may be C, O, F, and Ni, and other trace elements may be additionally detected. In the case of the content of a specific element contained in one pixel, the content of the specific element may be determined based on the total weight of the detection elements contained in one pixel. At this time, the size of one pixel may be 135 nm x 135 nm, but may vary depending on the magnification.

[0075] Referring to Figure 1, after fabricating a cross-sectional sample by ion milling on a dry electrode, SEM-EDS analysis reveals that pixels with a carbon element content of 30 wt% or more within a pixel can be designated as white areas. Through this processing, the area ratio of the white area to the total area can be derived.

[0076] Referring to Figure 2, after fabricating a cross-sectional sample by ion milling on a dry electrode, SEM-EDS analysis reveals that pixels with a fluorine element content of 15 wt% or more within a pixel can be designated as white areas. Through this processing, the area ratio of the white area to the total area can be derived.

[0077] Referring to Fig. 3, after fabricating a cross-sectional sample by ion milling on a dry electrode, SEM-EDS analysis reveals that pixels with a carbon element content of 30 wt% or more and a fluorine element content of 15 wt% or more can be displayed as white areas. Through such processing, the area ratio of the white area to the total area can be derived.

[0078]

[0079] Since no solvent is used in dry electrode manufacturing, the dispersing and buffering effects of the solvent, as expected in wet processes, cannot be expected. This prevents the strong cohesive forces between the constituent particles within the electrode composite film from being resolved, resulting in localized clumping of the conductive material or insufficient mixing with the binder.

[0080] Accordingly, in the present invention, by controlling the electrode composite film to have an OMI of 17 or more as expressed by Equation 1 according to the present invention, a uniform conductive network is formed while forming a uniform three-dimensional fiber network structure, and at the same time, through interaction between a conductive material and a binder having a three-dimensional fiber network structure, the mechanical strength of the electrode composite film is maintained above a certain level, while achieving excellent electrical conductivity and uniformity of an excellent conductive network.

[0081]

[0082] The electrode composite film according to the present invention has an OMI of 17 or more, represented by the following formula 1. Preferably, the OMI represented by the following formula 1 may be 18 or more, 19 or more, 20 or more, 21 or more, 22 or more, or 23 or more, and may be 40 or less, 39 or less, 38 or less, 37 or less, 36 or less, 35 or less, 34 or less, 33 or less, 32 or less, 31 or less, 30 or less, 29 or less, 28 or less, or 27 or less, and more preferably 23 to 27.

[0083] [Formula 1]

[0084] OMI = {(CFAR) / (FAR)} x 100

[0085] In the above equation 1, CFAR is the area ratio of pixel regions where 30 wt% or more of carbon element and 15 wt% or more of fluorine element are simultaneously detected when analyzing the element content within pixels of the electrode composite film cross-section using SEM-EDS, and FAR is the area ratio of pixel regions where 15 wt% or more of fluorine element is detected when analyzing the element content within pixels of the electrode composite film cross-section using SEM-EDS.

[0086] The above OMI is a ratio of the area ratio (CFAR) of the area in which 30 wt% or more of carbon element and 15 wt% or more of fluorine element are simultaneously detected to the area ratio (FAR) of the area in which 15 wt% or more of fluorine element is detected in the electrode composite film, and is a parameter that can indicate the degree of spatial overlap and formation of a solid network between the conductive material and the binder in the electrode composite film.

[0087] For example, in the case of FAR (Fluorine Area Ratio) corresponding to the denominator, it means an area in which 15 wt% or more of fluorine element is detected in the electrode composite film, and thus it can mean an area of ​​the binder that forms a three-dimensional fiber network structure overall in the electrode composite film.

[0088] In addition, in the case of CFAR (Carbon Fluorine Area Ratio) corresponding to a molecule, it means an area where 30 wt% or more of carbon element and 15 wt% or more of fluorine element are detected simultaneously in the electrode composite film, and therefore, it can mean an area where the carbon element included in the conductive material overlaps with the fluorine element included in the binder, and an area where the binder having a three-dimensional fiber network distributed throughout the electrode composite film overlaps with the conductive material forming a conductive network.

[0089] Accordingly, the above OMI can mean the ratio of the overlapping area of ​​the binder having a three-dimensional fiber network distributed throughout the electrode composite film and the conductive material forming a conductive network to the area of ​​the binder having a three-dimensional fiber network distributed throughout the electrode composite film, and thus can indicate the dispersibility of the conductive material and the binder within the electrode composite film, while also indicating how well the degree of dispersion and interaction between the binder having a three-dimensional fiber network structure and the conductive material forming a conductive network are implemented.

[0090] When the OMI is less than 18, the dispersibility of the conductive material deteriorates due to reasons such as local agglomeration of the conductive material, thereby compromising the uniformity of the conductive network within the electrode and increasing the resistivity. In this case, when used as a battery in the future, local overcurrent or overreaction may occur in some areas, which may aggravate the deterioration of the electrode. In addition, the resistance may not be uniform and the quality deviation between batteries may increase, which may deteriorate the electrochemical characteristics and processability.

[0091] Therefore, when the OMI satisfies the above-described range, the conductive material can have excellent dispersibility while also forming a conductive network uniformly and continuously, thereby realizing excellent resistance characteristics and resistance uniformity. In addition, the binder forming a three-dimensional fiber network structure can be distributed throughout the electrode composite film, thereby improving the mechanical strength of the electrode composite film and the adhesive strength between the current collector and the electrode composite film. In addition, the uniformity and hardness of the binder having a three-dimensional fiber network are improved, thereby realizing excellent dispersibility of the binder while maintaining a certain level of mechanical strength of the electrode composite film. In addition, the binder having a three-dimensional fiber network can be appropriately dispersed to facilitate the manufacture of the electrode composite film, thereby realizing excellent processability. Meanwhile, the above-described numerical range may be a unique numerical range of a dry electrode manufactured through a process of mixing, kneading, and calendering in a solvent-free state, unlike a wet electrode using a solvent.

[0092]

[0093] On the other hand, since it measures the area where 30 wt% or more of carbon elements are detected, rather than simply the area where carbon elements are measured, it has the advantage of being able to more clearly measure the area where the conductive material is mainly distributed, and since it measures the area where 15 wt% or more of fluorine elements are detected, rather than simply the area where fluorine elements are measured, it has the advantage of being able to more clearly measure the area of ​​the binder forming the three-dimensional fiber network.

[0094] For example, when polytetrafluoroethylene (PTFE) is used as a binder, since the PTFE has a repeated fluorine (F)-carbon (C)-fluorine (F) structure, the carbon (C) content is derived to be approximately 24 wt%. On the other hand, since most conductive materials have a carbon (C) content close to 100 wt%, when measuring an area where more than 30 wt% of the carbon element is detected per pixel, the conductive network area formed by the conductive material can be clearly measured.

[0095] In addition, the PTFE does not clearly fiberize in the wet electrode, but in the dry electrode, the PTFE is appropriately fiberized and thinned to form a three-dimensional fiber network. Therefore, the area where 15 wt% or more of fluorine element is detected per pixel must be measured to clearly measure the area of ​​the binder that forms the three-dimensional fiber network. In particular, in the case of the area where 15 wt% or more of fluorine element is detected per pixel, a reaction area (X-ray interaction volume) of around 100 nm is shown when measured with SEM-EDS under an acceleration voltage of 3 kV. At this time, the appropriately fiberized binder can be clearly measured when 15 wt% or more of fluorine element is detected per pixel.

[0096]

[0097] The above OMI can be controlled in various ways. For example, it can be controlled according to the composition of the electrode active material, the conductive material, and the binder, the content of the electrode active material, the conductive material, and the binder, the physical properties of the conductive material, the method for manufacturing the electrode composite film, and the method for manufacturing the conductive material, and preferably, it can be controlled according to the physical properties of the electrode active material, the content of the conductive material, and the binder, the composition of the conductive material, the manufacturing method, and the shape (expandable type).

[0098] In particular, the above OMI numerical range may be a numerical range that is unique to a dry electrode rather than a wet electrode. For example, a dry electrode is manufactured in a virtually solvent-free state, and the binder is fiberized to form a binder having a three-dimensional fiber network structure, and the conductive material forms a conductive network in a virtually solvent-free state. Therefore, the above OMI numerical range may be a numerical range that is unique to a dry electrode rather than a wet electrode.

[0099] In addition, the above-described numerical range can be reached by considering the characteristics of the dry electrode described above and the dispersibility and / or network of the binder and the conductive material having a three-dimensional fiber network structure. When considering the dispersibility and / or network, it may be preferable to use an expandable carbon nanotube as the conductive material, but the present invention is not limited thereto.

[0100]

[0101] Hereinafter, the present invention will be described in more detail.

[0102]

[0103] (electrode composite film)

[0104] A dry electrode according to the present invention includes an electrode composite film.

[0105]

[0106] The above electrode composite film comprises an electrode active material, a conductive material, and a binder having a three-dimensional fiber network structure. The electrode active material, the conductive material, and the binder having a three-dimensional fiber network structure are described below.

[0107]

[0108] According to one embodiment of the present invention, the CFAR (Carbon Fluorine Area Ratio) may be 2% to 10%, preferably 2.0% or more, 2.1% or more, 2.2% or more, 2.3% or more, 2.4% or more, 2.5% or more, 2.6% or more, 2.7% or more, 2.8% or more, or 2.9% or more, and may be 10% or less, 9% or less, 8% or less, 7% or less, 6% or less, 5% or less, 4% or less, 3.5% or less, or 3.1% or less, and preferably 2.9% to 3.1%. When the above range is satisfied, the conductive material forming the conductive network and the binder having the three-dimensional fiber network structure can be appropriately dispersed, thereby preventing the conductive material from locally clumping or the three-dimensional fiber network from becoming excessively thin, thereby enabling the network to be implemented while maintaining the continuity of the conductive path, while increasing the mechanical strength of the electrode composite film. In addition, since the conductive material and the binder can be appropriately overlapped, the binder can appropriately fix the electrical connection between the well-dispersed conductive networks, so that the electrode composite film can have low resistivity, high resistance uniformity, and a certain level or higher of mechanical strength. Therefore, when the electrode composite film according to the present invention is included in a battery, the life characteristics and output characteristics can be excellent.

[0109]

[0110] According to one embodiment of the present invention, the FAR (Fluorine Area Ratio) may be 1% to 20%, preferably 1% or more, 2% or more, 3% or more, 4% or more, 5% or more, 6% or more, 7% or more, 8% or more, 9% or more, or 10% or more, and may be 20% or less, 19% or less, 18% or less, 17% or less, 16% or less, 15% or less, or 14% or less, and more preferably 10% to 14%. When the above range is satisfied, the conductive path can form a uniform network while allowing the binder to appropriately form a three-dimensional fiber network structure, and can exhibit excellent electrical conductivity characteristics while maintaining the mechanical strength of the electrode composite film at a certain level or more.

[0111]

[0112] According to one embodiment of the present invention, when the element content within a pixel of the electrode composite film is analyzed by SEM-EDS for a cross-section of the electrode composite film, the area ratio of pixel regions in which 30 wt% or more of carbon elements are detected may be 1% to 30%, preferably 1% or more, 2% or more, 3% or more, 4% or more, 5% or more, 6% or more, 7% or more, 8% or more, 9% or more, or 10% or more, and may be 30% or less, 28% or less, 26% or less, 24% or less, 22% or less, 20% or less, 18% or less, 17% or less, 16% or less, 15% or less, or 14% or less, and more preferably 10% to 14%. When the above range is satisfied, a conductive network with a uniform conductive path can be implemented, and the conductive material has excellent dispersibility, so that the resistivity is low and the uniformity of the resistance is excellent.

[0113] When analyzing the element content within the pixels of the cross-section of the above electrode composite film using SEM-EDS, the area ratio of pixel regions where carbon elements of 30 wt% or more are detected can be measured similarly to the CFAR and FAR described above.

[0114]

[0115] According to one embodiment of the present invention, the electrode composite film may have a tensile strength of 0.30 MPa to 0.70 MPa, preferably 0.30 MPa or more, 0.35 MPa or more, 0.36 MPa or more, 0.37 MPa or more, 0.38 MPa or more, 0.39 MPa or more, 0.40 MPa or more, or 0.41 MPa or more, and may have a tensile strength of 0.70 MPa or less, 0.65 MPa or less, 0.60 MPa or less, 0.55 MPa or less, 0.50 MPa or less, 0.48 MPa or less, 0.47 MPa or less, or 0.46 MPa or less, and preferably 0.41 MPa to 0.46 MPa. When the above range is satisfied, excellent processability can be achieved by preventing tearing or breakage of the electrode composite film during production, and contamination of the calendaring roll can be avoided, thereby achieving excellent processability. In addition, since excessive amounts of binder are not included in the electrode composite film, resistance can be low, side reactions can be minimal, and the lifespan can be excellent.

[0116]

[0117] According to one embodiment of the present invention, the electrode composite film may have an elongation of 1.5% to 5.5%, preferably 1.5% or more, 1.6% or more, 1.7% or more, 1.8% or more, 1.9% or more, 2.0% or more, 2.1% or more, 2.2% or more, 2.3% or more, 2.4% or more, 2.5% or more or 2.6% or more, and 5.5% or less, 5.4% or less, 5.3% or less, 5.2% or less, 5.1% or less, 5.0% or less, 4.9% or less, 4.8% or less or 4.7% or less, and more preferably 2.6% to 4.7%. When the above range is satisfied, it may be desirable in that process uniformity can be secured while preventing breakage of the electrode composite film, and the electrode composite film may have low resistivity and excellent resistance uniformity while maintaining appropriate mechanical strength.

[0118]

[0119] According to one embodiment of the present invention, the electrode composite film may have an electrode layer resistivity of 500 Ωcm or less, preferably 450 Ωcm or less, 400 Ωcm or less, 350 Ωcm or less, 300 Ωcm or less, 250 Ωcm or less, 200 Ωcm or less, 150 Ωcm or less, 100 Ωcm or less, or 50 Ωcm or less, and may be 1 Ωcm or more, 2 Ωcm or more, 3 Ωcm or more, or 4 Ωcm or more, and more preferably 4 Ωcm to 50 Ωcm. When the above range is satisfied, the conductivity of the electrode composite film is excellent, so that the resistance characteristics of the battery can be excellent, and it may be preferable in that the electrode composite film can maintain appropriate mechanical strength.

[0120] At this time, the electrode layer resistivity may refer to the resistivity inside the electrode composite film, and for example, may refer to the average value obtained by measuring the resistivity at any point inside the electrode composite film six times.

[0121]

[0122] According to one embodiment of the present invention, the electrode composite film may have a ratio of the standard deviation of the electrode layer resistivity to the average value of the electrode layer resistivity of the electrode composite film of 40% or less, and preferably 35% or less, 30% or less, 25% or less, 20% or less, 19% or less, 18% or less, 17% or less, or 16.5% or less. The ratio of the standard deviation of the electrode layer resistivity to the average value of the electrode layer resistivity of the electrode composite film may be a parameter indicating the uniformity of the conductive network within the electrode. When the above range is satisfied, it may be preferable in that the conductive network within the electrode is uniformly formed, thereby improving electrode durability and cell durability.

[0123] At this time, the average value and standard deviation of the electrode layer resistivity may be values ​​derived by measuring the resistivity at any point inside the electrode composite film six or more times.

[0124]

[0125] According to one embodiment of the present invention, the electrode composite film has an interfacial resistivity of 9ⅹ10 -1 Ωcm 2 It can be less than or equal to 8x10, preferably -1 Ωcm 2 Below, 7x10 -1 Ωcm 2 Below, 6x10 -1 Ωcm 2 Below, 5x10 -1 Ωcm 2 Below, 4x10 -1 Ωcm 2 Below, 3x10 -1 Ωcm 2 Below, 2x10 -1 Ωcm 2 Below, 1x10 -1 Ωcm 2 Below, 9x10 -2 Ωcm 2 Below, 8x10 -2 Ωcm 2 Below, 7x10 -2 Ωcm2 Below or 6x10 -2 Ωcm 2 It can be less than 5x10 -3 Ωcm 2 Ideal, 7x10 -3 Ωcm 2 Ideal, 9x10 -3 Ωcm 2 Ideal, 1x10 -2 Ωcm 2 Ideal, 2x10 -2 Ωcm 2 Ideal, 3x10 -2 Ωcm 2 Ideal or 3.5x10 -2 Ωcm 2 This may be ideal. When the above range is satisfied, the resistance between the current collector and the electrode composite film is low, which may be desirable in that the resistance characteristics of the battery may be excellent and the appropriate mechanical strength of the electrode composite film may be maintained.

[0126] At this time, the interfacial resistivity may mean the interfacial area resistivity between the current collector and the electrode composite film, and for example, may mean the average value of the resistivity measured six times at any point between the current collector and the electrode composite film layer.

[0127]

[0128] According to one embodiment of the present invention, the electrode composite film may have a ratio of the standard deviation of the interfacial resistivity to the average value of the interfacial resistivity of the electrode composite film of 25% or less, preferably 22% or less, 20% or less, 18% or less, or 16% or less, more preferably 1% or more, 5% or more, or 7% or more, and more preferably 7% to 16%. The ratio of the standard deviation of the interfacial resistivity to the average value of the interfacial resistivity of the electrode composite film may be a parameter indicating the uniformity of the conductive network between the electrode composite film and the current collector. When the above range is satisfied, it may be preferable in that the conductive network between the electrode composite film and the current collector is uniformly formed, thereby improving electrode durability and cell durability.

[0129] At this time, the average value and standard deviation of the interfacial resistivity may be values ​​derived by measuring the interfacial resistivity at any point between the current collector and the electrode composite film layer six or more times.

[0130]

[0131] Below, the components included in the electrode composite film are described in detail.

[0132]

[0133] 1) Electrode active material

[0134] The above electrode composite film includes an electrode active material.

[0135] There is no special limitation on the above electrode active material as long as it is a commonly used electrode active material. For example, the above electrode active material may be a positive electrode active material or a negative electrode active material.

[0136] The above-mentioned positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically may include a lithium metal oxide containing lithium and one or more metals such as cobalt, manganese, nickel or aluminum. More specifically, the lithium metal oxide may be a lithium-manganese oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt oxide (e.g., LiCoO2, etc.), a lithium-nickel oxide (e.g., LiNiO2, etc.), a lithium-nickel-manganese oxide (e.g., LiNi 1-Y Mn Y O2 (here, 0 <Y<1), LiMn 2-Z Ni Z O4 (where 0<Z<2), etc.), lithium-nickel-cobalt oxides (e.g., LiNi 1-Y1 Co Y1 O2 (here, 0 <Y1<1) 등), 리튬-망간-코발트계 산화물(예를 들면, LiCo 1-Y2 Mn Y2 O2 (here, 0 <Y2<1), LiMn 2-Z1 Co Z1 O4 (wherein, 0<Z1<2) etc.), lithium-nickel-manganese-cobalt oxides (e.g., Li(Ni p Co q Mn r )O2(wherein, 0<p<1, 0<q<1, 0<r<1, p+q+r=1) or Li(Ni p1 Co q1 Mn r1 )O4 (wherein, 0<p1<2, 0<q1<2, 0<r1<2, p1+q1+r1=2) etc.), or lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r2 M s2)O2 (wherein, M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, and p2, q2, r2 and s2 are atomic fractions of independent elements, respectively, 0<p2<1, 0<q2<1, 0<r2<1, 0<s2<1, p2+q2+r2+s2=1), etc.), lithium iron phosphate (e.g., Li 1+a Fe 1-x M x (PO 4-b )X b (Here, M is at least one selected from Al, Mg, and Ti, X is at least one selected from F, S, and N, -0.5≤a≤0.5, 0≤x≤0.5, 0≤b≤0.1), and any one or two or more compounds thereof may be included.

[0137] Among these, the lithium metal oxides are LiCoO2, LiMnO2, LiNiO2, lithium nickel manganese cobalt oxide (e.g., Li(Ni)) in that they can improve the capacity characteristics and stability of the battery. 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 0.15 Co 0.15 )O2 and Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, etc.), lithium nickel cobalt aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05 )O2, etc.), or lithium nickel cobalt manganese aluminum oxide (e.g. Li(Ni 0.86 Co 0.05 Mn 0.07 Al 0.02)O2), lithium iron phosphate (e.g., LiFePO4), etc., and any one or a mixture of two or more of these may be used. More specifically, the electrode active material may include lithium nickel cobalt manganese aluminum oxide in terms of being able to produce a uniform and stable film-shaped electrode composite film.

[0138]

[0139] The above negative active material may include at least one selected from the group consisting of lithium metal, a carbon material capable of reversibly intercalating / deintercalating lithium ions, a metal or an alloy of these metals and lithium, a metal composite oxide, a material capable of doping and dedoping lithium, and a transition metal oxide.

[0140] As the carbon material capable of reversibly intercalating / deintercalating the lithium ions, any carbon-based negative electrode active material commonly used in lithium-ion secondary batteries can be used without particular limitation, and representative examples thereof include crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as natural graphite or artificial graphite in an amorphous, plate-like, flake-like, spherical, or fibrous form, and examples of the amorphous carbon include soft carbon (low-temperature calcined carbon) or hard carbon, mesophase pitch carbide, calcined coke, etc.

[0141] As the above metal or an alloy of these metals with lithium, a metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al and Sn or an alloy of these metals with lithium may be used.

[0142] The above metal composite oxides include 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: 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) 로 이루어진 군에서 선택되는 것이 사용될 수 있다.

[0143] Materials capable of doping and dedoping the above lithium include Si, SiO x (0 <x≤2), Si-Y 합금(상기 Y는 알칼리 금속, 알칼리 토금속, 13족 원소, 14족 원소, 전이금속, 희토류 원소 및 이들의 조합으로 이루어진 군에서 선택되는 원소이며, Si은 아님), Sn, SnO2, Sn-Y(상기 Y는 알칼리 금속, 알칼리 토금속, 13족 원소, 14족 원소, 전이금속, 희토류 원소 및 이들의 조합으로 이루어진 군에서 선택되는 원소이며, Sn은 아님) 등을 들 수 있고, 또한 이들 중 적어도 하나와 SiO2를 혼합하여 사용할 수도 있다. 상기 원소 Y로는 Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ge, P, As, Sb, Bi, S, Se, Te, Po 및 이들의 조합으로 이루어진 군에서 선택될 수 있다.

[0144] Examples of the above transition metal oxides include lithium-containing titanium composite oxide (LTO), vanadium oxide, and lithium vanadium oxide.

[0145]

[0146] According to one embodiment of the present invention, the electrode active material may be included in an amount of 80 to 99 parts by weight, and preferably 90 to 99 parts by weight, based on the total weight of the electrode composite film. When the above range is satisfied, it is preferable in terms of increasing the capacity and energy density of the electrode.

[0147]

[0148] 2) Challenge

[0149] The above electrode composite film includes a conductive material.

[0150]

[0151] According to one embodiment of the present invention, the conductive material may include expandable carbon nanotubes. When the above conditions are satisfied, the conductive material forms a conductive network in which it is appropriately dispersed within the electrode composite film, and through the interaction between the conductive material and a binder having a three-dimensional fiber network structure, the reinforcing effect in terms of the mechanical strength of the electrode composite film and the continuity of the conductive network are maintained, which may be preferable in that the electrode composite film can exhibit excellent mechanical strength and resistance characteristics.

[0152] A detailed description of the above expandable carbon nanotubes will be provided below.

[0153]

[0154] According to one embodiment of the present invention, the conductive material may be included in an amount of 0.1 to 10 parts by weight, and preferably 0.1 to 5.0 parts by weight, based on the total weight of the electrode composite film. When the above range is satisfied, it is preferable in that an excellent conductive path can be formed while also implementing an excellent capacity density.

[0155]

[0156] 3) Binder

[0157] The above electrode composite film includes a binder having a three-dimensional fiber network structure.

[0158] The above binder has the function of forming a three-dimensional fiber network structure so that the electrode composite film can be self-supporting. The binder is not specified as a specific one as long as it is fiberizable, that is, can form a three-dimensional fiber network structure in the electrode composite film through fiberization and provide pores that can accommodate an electrode active material and optionally a conductive material.

[0159] The fiberization of the above binder refers to a process of dividing and finely dividing the polymer applied as the binder, and can be performed, for example, by applying a mechanical shear force, etc., and as a result, the surface is loosened and fiberized, thereby forming a plurality of fine fibers, and thereby including a three-dimensional fiber network structure.

[0160] The above-mentioned fiberizable binder is not specifically defined as long as it is fibrillizable, and the fibrillation refers to a process of dividing a polymer into small pieces. For example, it can be performed using a mechanical shear force, etc., and the surface of the fibrillated polymer fiber is loosened to generate a large number of fine fibers (fibrils). The fiberizable binder may preferably include at least one selected from the group consisting of polytetrafluoroethylene (PTFE) and polyolefin, more preferably polytetrafluoroethylene (PTFE), and even more preferably polytetrafluoroethylene (PTFE). When the above conditions are satisfied, excellent conductive material dispersibility can be realized, while appropriately reducing resistance.

[0161]

[0162] According to one embodiment of the present invention, the polytetrafluoroethylene (PTFE) may be included in an amount of 60 wt% or more based on the total binder weight. At this time, the binder may additionally include at least one of polyethylene oxide (PEO), polyvinylidene fluoride (PVdF), polyvinylidene fluoride-cohexafluoropropylene (PVdF-HFP), and a polyolefin-based binder.

[0163]

[0164] According to one embodiment of the present invention, the fiberizable binder may be included in an amount of 0.1 to 10 parts by weight, and preferably 0.1 to 5.0 parts by weight, based on the total weight of the electrode composite film. When the above range is satisfied, it is preferable in that it is possible to realize a degree of fiberization appropriate for producing a self-supporting sheet, while also exhibiting excellent resistance characteristics.

[0165]

[0166] According to one embodiment of the present invention, the content of the conductive material within the electrode composite film may be higher than the content of the binder within the electrode composite film. When the above range is satisfied, an excellent conductive network can be formed, resulting in low resistivity and excellent resistance uniformity.

[0167]

[0168] Meanwhile, a dry electrode according to the present invention can be manufactured by including a step S1 of obtaining a composite composition by mixing an electrode active material, a conductive material, and a fiberizable binder; a step S2 of kneading the composite composition while applying a shear force to form a mixed aggregate; a step S3 of pulverizing the mixed aggregate to manufacture an electrode powder; and a step S4 of sheet-forming the electrode powder into an electrode composite film by roll-rolling.

[0169]

[0170] (Stage S1)

[0171] This is a step of forming a composite composition by mixing an electrode active material, a conductive material, and a fiberizable binder. A detailed description of the electrode active material, the conductive material, and the fiberizable binder is omitted as described above, and at this time, the mixing is performed so that the electrode active material, the conductive material, and the binder can be uniformly distributed. Since they are mixed in a powder form, they can be mixed by various methods without limitation as long as they enable simple mixing thereof. However, since the present invention is manufactured as a dry electrode that does not use a solvent, the mixing can be performed by dry mixing, and the materials can be mixed by putting them into a device such as a mixer or blender.

[0172]

[0173] At this time, the mixing can be performed in a mixer at 100 rpm to 5,000 rpm for 1 to 60 minutes. Preferably, it can be performed at 500 rpm to 4,000 rpm for 3 to 45 minutes, and more preferably, it can be performed at 100 rpm to 3,000 rpm for 5 to 30 minutes. When performed within the above range, the materials can be uniformly mixed, thereby improving battery performance.

[0174]

[0175] The control conditions of the above mixing process can determine how uniformly the binder is fiberized in the subsequent mixing process of step S2. If the mixing is not uniform, even if fiberization occurs uniformly, non-uniform parts may occur on the entire side of the film. Therefore, it may be desirable to perform the mixing process under the conditions described above.

[0176]

[0177] (S2 stage)

[0178] Next, a fiberization process using a binder capable of forming a three-dimensional fiber network structure can be performed on the composite material composition obtained from the above mixing to produce a mixed aggregate. Preferably, a step of kneading the composite material composition while applying a shear force to form a mixed aggregate can be performed.

[0179] The above fiberization process can be performed, for example, through mechanical milling or kneading, and there are no particular limitations as long as it is generally performed, but preferably, it can be performed through high-temperature, low-shear kneading, and can be performed, for example, through a kneader. By such kneading, the binder capable of forming the three-dimensional fiber network structure is fiberized, thereby combining or linking the electrode active material and conductive powders, so that a mixed aggregate with a solid content of 100% can be formed.

[0180] The above mixing can be performed at a speed of 10 rpm to 100 rpm, and more specifically, at a speed of 20 rpm to 70 rpm. In addition, the mixing can be performed for 1 minute to 120 minutes, and more specifically, for 2 minutes to 60 minutes. When the above range is satisfied, appropriate fiberization can proceed, and a three-dimensional fiber network structure that is uniformly fiberized overall and structurally stable can be formed.

[0181] In addition, the above mixing can be performed under conditions of high temperature and pressure higher than atmospheric pressure, and more specifically, under conditions of pressure higher than atmospheric pressure.

[0182] More specifically, the mixing can be performed at a temperature of 50°C to 230°C, preferably 90°C to 200°C. When mixing is performed at a high temperature such as the above range, the fiberization and lump formation of the binder through mixing can be effectively achieved, and the problem of breakage of the fiberized binder can be appropriately prevented.

[0183] Additionally, the process can be performed under a pressure higher than atmospheric pressure, specifically, a pressure of 1 to 3 atm. When performed within the above range, the problem of breakage of the binder undergoing fiberization can be appropriately prevented, and the problem of the density of the aggregates becoming excessively high can be prevented.

[0184] That is, according to the present invention, when a high-temperature-low-shear mixing process is performed under high-temperature and higher-than-normal pressure conditions instead of high-shear mixing, the intended effect of the present invention can be achieved.

[0185]

[0186] (S3 stage)

[0187] Next, a step of pulverizing the mixed aggregate produced through the above mixing step to obtain powder for electrodes may be performed. Preferably, a step of pulverizing the mixed aggregate to produce powder for electrodes may be performed.

[0188] The mixed aggregates produced through the above mixing process can be directly pressed into a sheet shape (sheeting, for example, using a calendaring process). However, in this case, the mixed aggregates may need to be pressed under strong pressure and high temperature to produce a thin film, which may result in problems such as the film density becoming too high or the inability to obtain a uniform film. Therefore, the mixed aggregates produced as described above are pulverized to produce a powder for electrodes.

[0189] The device used for the above crushing is not particularly limited, but it can preferably be performed by a device such as a blender or grinder.

[0190] The above grinding can be performed at a speed of 1000 rpm to 15000 rpm for 1 to 30 minutes, preferably at a speed of 3000 rpm to 10000 rpm for 5 to 20 minutes. When performed within the above range, sufficient grinding can be achieved to produce powder of a size suitable for film formation, and a large amount of fine powder can be prevented from being generated in the mixed aggregate.

[0191] The average particle size of the above electrode powder may be 10 µm to 3,000 µm, specifically 50 µm to 1,500 µm, and more specifically 100 µm to 700 µm. When the above range is satisfied, an electrode composite film having a uniform thickness and density can be formed, and excellent electrode composite film properties can be secured.

[0192]

[0193] Meanwhile, the electrode powder may additionally include fillers, although not essential, to suppress electrode expansion. The fillers are not particularly limited as long as they are fibrous materials that do not cause chemical changes in the battery, and examples thereof include at least one selected from olefin polymers such as polyethylene and polypropylene; and fibrous materials such as glass fiber and carbon fiber.

[0194]

[0195] (Stage S4)

[0196] Next, the electrode powder is rolled into a sheet and formed into an electrode composite film. Preferably, this may be a process of manufacturing an electrode composite film in the form of a self-supporting sheet by heat-pressing the electrode powder using a calendar roll in a roll-to-roll process including two or more pairs of calendar rolls.

[0197] The above roll-to-roll process may include a roll press section in which roll rolling is performed, and the roll press section may have calender rolls arranged in pairs facing each other, and may have a plurality of calender rolls arranged continuously, and such calender rolls may be arranged continuously in the roll press section. When a plurality of calender rolls are arranged continuously, the temperature and main speed ratio (rotation speed ratio of a pair of calender rolls) of each calender roll may be the same or different.

[0198]

[0199] According to one embodiment of the present invention, the temperature of the calender roll may be 50°C to 200°C, preferably the temperature of the calender roll may be 50°C to 180°C, and more preferably the temperature of the calender roll may be 60°C to 150°C. When the above range is satisfied, an electrode composite film having excellent processability and uniformity can be obtained.

[0200]

[0201] The rotation speed ratio of the calendar rolls provided in the roll-to-roll process of the above step S4 can be appropriately adjusted independently within a range of 1:1 to 1:10. In addition, the manufactured electrode composite film can be again fed into a roll press section and subjected to heat pressing 1 to 10 times to adjust it to an appropriate thickness.

[0202]

[0203] According to one embodiment of the present invention, the step S4 may include a step (S4a) of pre-sheeting the electrode powder to obtain a powder-sheeting film; and a step (S4b) of sheeting the powder-sheeting film two or more times to produce an electrode composite film. That is, after the powder is converted into a sheet in step S4a, the sheet may be rolled in step S4b to improve strength and satisfy the porosity and loading required for the electrode.

[0204]

[0205] Meanwhile, according to one embodiment of the present invention, a step of laminating the electrode composite film on one or both sides of a current collector and then inserting it into a lamination unit for lamination may be further included. Through this, the electrode composite film is rolled onto the current collector, thereby manufacturing a dry electrode in which the electrode composite film is arranged on the current collector.

[0206] The above lamination may be performed by rolling and attaching the electrode composite film onto a current collector. The above lamination may be performed by a roll press method using a lamination unit including a lamination roll.

[0207]

[0208] According to one embodiment of the present invention, the lamination roll can be maintained at a temperature of 20°C to 200°C.

[0209]

[0210] The above lamination may preferably be performed after one or more, or two or more, heat pressings, and then one or more additional heat pressings may be performed to achieve the desired porosity. When lamination is performed in the middle of calendering in this manner, the appearance of the electrode and the calendering processability may be superior to lowering the porosity in the composite film state before lamination. Control of the porosity through additional heat pressing can be achieved by controlling the compression ratio by adjusting the roll gap, and the compression ratio can be derived by the following equation 2.

[0211] [Relationship 2]

[0212] Compression ratio (%) = [(electrode thickness) - (roll gap)] / [(electrode thickness) - (collector thickness)]

[0213]

[0214] (entire house)

[0215] When the above dry electrode is a positive electrode, the current collector may be any material that is conductive and does not cause chemical changes in the battery, and is not particularly limited. For example, the current collector may be stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc.

[0216] The thickness of the above current collector may be from 8 μm to 500 μm, but is not limited thereto. In addition, fine irregularities may be formed on the surface of the current collector to increase the adhesive strength of the electrode composite film.

[0217]

[0218] When the above dry electrode is a negative electrode, the current collector is not particularly limited as long as it has high conductivity without causing changes 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.

[0219] The above current collector may typically have a thickness of 3 ㎛ to 500 ㎛, and, as in the case where the dry electrode is used as a positive electrode, fine irregularities may be formed on the surface of the current collector to increase the adhesive strength of the electrode composite film.

[0220]

[0221] The above-mentioned collector may be used with a conductive primer coated entirely or partially on the surface to lower resistance and improve adhesion. Here, the conductive primer may include a conductive material and a binder. The conductive material is not limited to any conductive material, but may be, for example, a carbon-based material. The binder may include a solvent-soluble fluorine-based binder (including PVDF and PVDF copolymer), an acrylic-based binder, and an aqueous binder.

[0222]

[0223] Hereinafter, the above-mentioned expandable carbon nanotubes will be described in detail.

[0224]

[0225] Expandable carbon nanotubes

[0226] According to one embodiment of the present invention, the conductive material may include an expandable carbon nanotube.

[0227] Unlike wet electrodes, which undergo a process of dispersing and / or mixing in a solvent, in the manufacture of dry electrodes, conductive materials (e.g., carbon nanotubes) are dispersed and / or mixed in a solvent-free state. When dispersing and / or mixing in a solvent-free state, the buffering and dispersing effects of the solvent cannot occur, so there is a problem that excessive cutting of the conductive material occurs due to excessive shear force, or it is difficult to achieve the desired degree of swelling. In particular, when a dry electrode is manufactured using a conductive material that has excessive cutting or is not properly dispersed, the formation of a conductive path within the electrode is limited, and the contact area with the electrode active material is reduced, which may cause disadvantages in that it deteriorates cell performance.

[0228] The above-mentioned expanded carbon nanotubes are different from densely aggregated carbon nanotubes or high-density carbon nanotube aggregates generally used in large-scale industries, and can be characterized by forming a kind of pop-type having an expanded structure without excessive breakage of the carbon nanotubes. Preferably, unlike carbon nanotubes dispersed using an aqueous dispersion, the above-mentioned expanded carbon nanotubes can be characterized by forming a pop-type having an expanded structure without excessive breakage of the carbon nanotubes in a dry, solvent-free state.

[0229] The above-mentioned pop-type may refer to a form in which densely packed carbon nanotube aggregates are disassembled, visually loosely separated, the space between carbon nanotubes increases, and the connections between carbon nanotubes become loose, increasing the overall volume. For example, the expanded structure may form a honeycomb structure with a reduced density between carbon nanotubes, thereby exposing more of the carbon nanotube surfaces to the outside.

[0230] Therefore, when the conductive material includes expandable carbon nanotubes, it may be preferable in that it can realize excellent mechanical strength and resistance characteristics by forming an excellently dispersed conductive network while maintaining the continuity of the conductive network. For example, in the case of expandable carbon nanotubes having an expandable structure that is appropriately dispersed while minimizing cutting, excellent dispersibility can be maintained while minimizing cutting during the subsequent dry electrode manufacturing process, thereby forming an excellent conductive network between and / or within the electrode active materials in the electrode composite film, and sufficiently preventing agglomeration of the conductive material that reduces the conductive effect, thereby realizing excellent resistance characteristics and life characteristics.

[0231]

[0232] At this time, expanded carbon nanotubes having a pop-type shape can be achieved by various methods, but preferably, it can be achieved by controlling the characteristics of the carbon nanotubes such as shape, diameter, length and / or number of walls, or the conditions for disintegrating the carbon nanotubes.

[0233]

[0234] According to one embodiment of the present invention, when the electrical conductivity (S / cm) and the packing density (g / cc) of the expanded carbon nanotube are plotted on the y-axis and the x-axis, respectively, the slope may be 90 or more, and preferably, the slope may be 91 or more, 92 or more, 93 or more, 94 or more, 95 or more, 96 or more, 97 or more, or 98 or more, and may be 150 or less, 145 or less, 140 or less, 135 or less, 130 or less, 129 or less, 128 or less, 127 or less, 126 or less, or 125 or less, and more preferably, the slope may be 98 to 125. When the above range is satisfied, the occurrence of cutting is minimized, and the expanded carbon nanotube having an expanded structure can be formed, thereby realizing excellent resistance characteristics and life characteristics when used as a conductive material in the future. In particular, since the above slope is measured in the powder state of the expanded carbon nanotube, it is a parameter that is very difficult to measure in a conductive dispersion liquid manufactured under general wet conditions.

[0235]

[0236] In the case of the expandable carbon nanotubes according to the present invention, the electrical conductivity (S / cm) and the packing density (g / cc) may be measured while applying a pressure of 50 MPa to 420 MPa to the expandable carbon nanotubes. Preferably, the electrical conductivity may be measured while applying a pressure of 60 MPa to 420 MPa, and more preferably, the electrical conductivity may be measured while applying a pressure of 70 MPa to 420 MPa. Since the expandable carbon nanotubes may have a low bulk density while forming an expanded structure, when a low pressure is applied, sufficient electrical contact between the expandable carbon nanotubes may not be achieved, making it difficult to clearly measure the conductive properties inherent in the expandable carbon nanotubes. That is, when a low pressure is applied, it may be difficult to measure the slope intended by the present invention. In addition, since the conductivity of the expandable carbon nanotubes is measured under a high pressure range that is applied when actually manufacturing an electrode, one of the characteristics of the present invention is that the conductivity in the electrode state can be more clearly determined. Therefore, when the electrical conductivity and packing density are measured by applying a pressure in the above range, the electrical conductivity and packing density can be measured with sufficient electrical contact between the expanded carbon nanotubes, and thus a slope that can clearly represent the conductive properties inherent in the expanded carbon nanotubes can be measured.

[0237]

[0238] According to one embodiment of the present invention, the bulk density of the expanded carbon nanotube may be 0.022 g / cc or less, preferably 0.020 g / cc or less, 0.018 g / cc or less, 0.016 g / cc or less, 0.014 g / cc or less, 0.012 g / cc or less, 0.010 g / cc or less, or 0.009 g / cc or less, and may be 0.001 g / cc or more or 0.002 g / cc or more, and more preferably 0.001 g / cc to 0.009 g / cc. When the above range is satisfied, an appropriately expanded structure can be formed while excessive cutting can be prevented, so that excellent resistance characteristics and life characteristics can be realized.

[0239]

[0240] According to one embodiment of the present invention, when the packing density of the expandable carbon nanotube is 1.0 g / cc, the electrical conductivity may be 70 S / cm or more, preferably 70 S / cm or more, 71 S / cm or more, 72 S / cm or more, 73 S / cm or more, 74 S / cm or more, or 75 S / cm or more, and may be 125 S / cm or less, 123 S / cm or less, 120 S / cm or less, 117 S / cm or less, or 115 S / cm or less. More preferably, it may be 75 S / cm to 115 S / cm. When the above range is satisfied, it may be preferable in that the expandable carbon nanotube has an appropriate expanded shape and can form an excellent expandable structure.

[0241]

[0242] According to one embodiment of the present invention, the ratio of true density (TD) to bulk density (BD) of the expanded carbon nanotube (TD / BD) may be 91 to 673, preferably 134 to 505, and more preferably 200 to 405. When the above range is satisfied, the expanded carbon nanotube may be preferable in that it can appropriately expand and simultaneously implement excellent dispersibility.

[0243] The above bulk density (BD) can be measured by filling an expandable carbon nanotube into a container of known weight, measuring the weight, and then converting the density.

[0244] The above true density (TD) is different from bulk density in that it is the density of the volume of the material itself, excluding the pores within the porous material. As a device for measuring the above true density (TD), an example of a dry automatic density meter (Accupick II 1340 series, Shimadzu Corporation) can be mentioned. When using the above device, the true density can be automatically measured by introducing a small amount of expandable carbon nanotubes. The above true density can also be obtained using other measuring methods and / or devices in addition to the above-described measuring methods and / or devices.

[0245]

[0246] According to one embodiment of the present invention, the true density (TD) of the expanded carbon nanotube may be 1.850 g / cc to 2.500 g / cc, preferably 1.900 g / cc to 2.300 g / cc, and more preferably 1.950 g / cc to 2.150 g / cc. When the above range is satisfied, the density may be such that a sufficient conductive path can be formed within the electrode, and may be preferable in that an expanded structure can be easily formed.

[0247]

[0248] According to one embodiment of the present invention, the BET specific surface area of ​​the expanded carbon nanotube is 200 m 2 / g to 1000m 2 / g can be, preferably 250m 2 / g to 950m 2 / g can be, more preferably 300m 2 / g to 900m 2 / g may be. If the above range is satisfied, it may be desirable in that an appropriately expanded structure can be formed while also implementing excellent dispersibility.

[0249]

[0250] According to one embodiment of the present invention, the expanded carbon nanotube powder may include carbon nanotube units. The graphite sheet of the carbon nanotube has a cylindrical shape with a nano-sized diameter, and sp 2 It has a bonding structure. At this time, depending on the angle and structure at which the graphite plane is rolled, it can exhibit the characteristics of a conductor or a semiconductor. The carbon nanotube can be classified into a single-walled carbon nanotube (SWCNT, single-walled FARbon nanotube) unit, a double-walled carbon nanotube (DWCNT, double-walled FARbon nanotube) unit, and a multi-walled carbon nanotube (MWCNT, multi-walled FARbon nanotube) unit depending on the number of bonds forming the wall.

[0251]

[0252] According to one embodiment of the present invention, the carbon nanotube unit may be a multi-walled carbon nanotube unit. If the carbon nanotube unit is a single-walled carbon nanotube or a double-walled carbon nanotube, the battery manufacturing cost may be excessively high, which may lower the processability, and the carbon nanotube unit may exist in an excessively aggregated state, making it difficult to form an expanded carbon nanotube with an expanded structure. On the other hand, if the carbon nanotube unit is a multi-walled carbon nanotube unit, the manufacturing cost is relatively low, and the cohesion between them is not excessive, so that the formation of an appropriate expanded structure may be possible.

[0253]

[0254] According to one embodiment of the present invention, the aspect ratio of the multi-walled carbon nanotube unit may be 30 to 10,000, preferably 60 to 2,000, and more preferably 100 to 1,000. When the above range is satisfied, the dispersibility of the multi-walled carbon nanotube unit may be excellent, and when used as a conductive material in the future, the contact area between electrode active materials may be increased. The aspect ratio may be defined as the ratio of the length and diameter of the multi-walled carbon nanotube unit.

[0255]

[0256] According to one embodiment of the present invention, the average length of the multi-walled carbon nanotube units may be 0.1 μm to 100 μm, preferably 0.1 μm to 50 μm, and more preferably 0.1 μm to 3 μm. When the above range is satisfied, appropriate dispersion of the multi-walled carbon nanotube units may be possible, and when used as a conductive material in the future, the formation of a conductive network may be maximized. The above average length corresponds to the average value of the top 100 multi-walled carbon nanotube units with the longest lengths and the bottom 100 multi-walled carbon nanotube units observed through SEM or TEM.

[0257]

[0258] According to one embodiment of the present invention, the average diameter of the multi-walled carbon nanotube units may be 5 nm to 200 nm, preferably 5 nm or more, 6 nm or more, 7 nm or more, 8 nm or more, 9 nm or more, or 10 nm or more, 200 nm or less, 180 nm or less, 160 nm or less, 140 nm or less, 120 nm or less, 100 nm or less, 80 nm or less, 60 nm or less, or 50 nm or less, and more preferably 10 nm to 50 nm. When the above range is satisfied, dispersion is easy, so that conductivity can be improved when used as a conductive material in the future. The above average diameter corresponds to the average value of the top 100 multi-walled carbon nanotube units with large diameters and the bottom 100 multi-walled carbon nanotube units observed through SEM or TEM.

[0259]

[0260] According to one embodiment of the present invention, the BET specific surface area of ​​the multi-walled carbon nanotube unit is 50 m 2 / g to 500m 2 / g can be, preferably 100m 2 / g to 400m 2 / g can be, more preferably 150m 2 / g to 350m 2 / g. When the above specific surface area range is satisfied, appropriate dispersion between the multi-walled carbon nanotube units is possible, thereby maintaining the manufacturing processability. The BET specific surface area can be measured through the nitrogen adsorption BET method.

[0261]

[0262] According to one embodiment of the present invention, the multi-walled carbon nanotube unit may have three or more graphene layers arranged in parallel with respect to the axis of the multi-walled carbon nanotube unit. Preferably, it may have three to twenty graphene layers, more preferably, it may have three to ten graphene layers, and even more preferably, it may have three to five graphene layers. When the above range is satisfied, it is preferable in that the multi-walled carbon nanotube unit is appropriately dispersed, enabling the production of an expandable carbon nanotube powder having an expandable structure, while improving the conductivity of the expandable carbon nanotube powder.

[0263]

[0264] Hereinafter, a method for manufacturing the above-mentioned expandable carbon nanotube will be described.

[0265]

[0266] Method for manufacturing expandable carbon nanotubes

[0267] According to one embodiment of the present invention, the method for producing the expanded carbon nanotube powder includes a step of colliding carbon nanotube aggregates with each other in a disintegrating device in a solvent-free state to disintegrate them, wherein the disintegration is performed by the rotation of two or more rotors provided in the disintegrating device and high-pressure gas injected from an injection port provided in the disintegrating device, the rotation speed of the rotor is 3000 rpm or more, and the injection port injects high-pressure gas at a pressure of 3.5 bar or more.

[0268]

[0269] Unlike wet electrodes that undergo a process of dispersing and / or mixing in a solvent, in the production of dry electrodes, conductive materials (e.g., carbon nanotubes) are dispersed and / or mixed in a solvent-free state. When dispersing and / or mixing in a solvent-free state, the buffering and dispersing effects of the solvent cannot occur, so there is a problem that excessive cutting of the conductive material occurs due to excessive shear force, or it is difficult to achieve the desired degree of disintegration. In particular, when attempting to disintegrate carbon nanotubes in a solvent-free state, aggregation of carbon nanotubes occurs due to van der Waals forces, making disintegration even more difficult. In addition, since carbon nanotubes have a linear shape, there is a problem that excessive pulverization of carbon nanotubes occurs due to excessive shear force when dispersing and / or mixing in a solvent-free state.

[0270] Accordingly, the present invention provides a method for manufacturing an expanded carbon nanotube powder having excellent dispersibility by colliding carbon nanotube aggregates with each other in a solvent-free state and controlling the disintegration conditions to satisfy specific conditions, thereby forming an expanded structure without excessive cutting.

[0271] Specifically, devices such as jaw crushers and hammer crushers that can apply a strong shear force in a solvent-free state cause excessive crushing that damages carbon nanotubes, making it difficult to produce carbon nanotubes with an expanded structure. However, in the present invention, carbon nanotubes can be crushed with an appropriate force while minimizing cutting by colliding with each other in a solvent-free state, thereby producing carbon nanotubes with an expanded structure. Therefore, excellent resistance characteristics and life characteristics can be realized when manufacturing electrode powders and dry electrodes containing the same thereafter.

[0272] Since the above-mentioned expandable carbon nanotubes have been described above, detailed information on the expandable carbon nanotube powders will be omitted.

[0273]

[0274] According to one embodiment of the present invention, a method for manufacturing an expandable carbon nanotube comprises the step of colliding carbon nanotube aggregates with each other in a disintegrating device in a solvent-free state to disintegrate them, wherein the disintegration is performed by the rotation of two or more rotors provided in the disintegrating device and high-pressure gas injected from an injection port provided in the disintegrating device. Preferably, the disintegration can be performed by a swirling airflow generated by the rotation of two or more rotors provided in the disintegrating device and a high-pressure gas injected from an injection port provided in the disintegrating device, and more preferably, the disintegration can be performed by a swirling airflow and impact force generated by the rotation of two or more rotors provided in the disintegrating device and a high-pressure gas injected from an injection port provided in the disintegrating device.

[0275] The above manufacturing method is characterized by colliding carbon nanotube aggregates with each other to break them apart, unlike pulverizing methods that apply excessive direct impact, such as ball milling. Accordingly, excessive cutting and agglomeration of carbon nanotube aggregates can be prevented, and the densely aggregated carbon nanotubes of FIGS. 4 and 6 can be formed into expanded carbon nanotubes having an expanded structure, as shown in FIGS. 5 and 7. When the expanded carbon nanotubes having an expanded structure are formed as described above, when manufacturing a powder for an electrode and / or a dry electrode thereafter, the carbon nanotubes can form an excellent conductive network while appropriately connecting electrode active material particles, and can exhibit excellent dispersibility even in a solvent-free state, so that excellent resistance characteristics and life characteristics can be realized.

[0276] When the above conditions are satisfied, it may be desirable in that the degree of disintegration can be increased by strengthening the collision between carbon nanotube aggregates due to the swirling airflow and the high-pressure gas, and it may be desirable in that the degree of disintegration can be increased by causing the carbon nanotube aggregates to collide with the rotor due to the impact force by the rotor and / or the pressure injected from the nozzle.

[0277] According to one embodiment of the present invention, the carbon nanotube aggregate may be an aggregate in which carbon nanotubes are densely assembled, and may be, for example, a bundled carbon nanotube or an entangled carbon nanotube.

[0278]

[0279] According to one embodiment of the present invention, the rotation speed of the rotor is 3000 rpm or more. Preferably, the rotation speed of the rotor may be 3100 rpm or more, 3200 rpm or more, 3300 rpm or more, 3400 rpm or more, 3500 rpm or more, 3600 rpm or more, 3700 rpm or more, 3800 rpm or more, 3900 rpm or more, 4000 rpm or more, 4100 rpm or more, 4200 rpm or more, 4300 rpm or more, 4400 rpm or more, 4500 rpm or more, 4600 rpm or more, 4700 rpm or more, 4800 rpm or more, 4900 rpm or more or 5000 rpm or more, and 7000 rpm or less, 6900 rpm or less, 6800 rpm or less, 6700 rpm or less, 6600 rpm or less, 6500 rpm or less, 6400 rpm or less, 6300 rpm or less, 6200 rpm Below, it may be 6100 rpm or less, 5900 rpm or less, 5800 rpm or less, 5700 rpm or less, 5600 rpm or less, 5500 rpm or less, or 5400 rpm or less, and more preferably, it may be 5000 rpm to 5400 rpm. When the rotation speed of the rotor is less than 3000 rpm, the van der Waals force of the carbon nanotube aggregates cannot be overcome, so there is a problem that the carbon nanotube aggregates aggregate and the expanded carbon nanotube powder of the expanded structure cannot be manufactured. Therefore, when the above range is satisfied, the cutting of the carbon nanotube aggregates can be minimized, and the expanded carbon nanotube powder of the expanded structure with sufficient disintegration can be manufactured, thereby realizing excellent resistance characteristics and life characteristics.

[0280]

[0281] In the method for manufacturing an expandable carbon nanotube powder according to the present invention, the injection port injects high-pressure gas at a pressure of 3.5 bar or more. Preferably, the injection port can inject high-pressure gas at a pressure of 3.6 bar or more, 3.7 bar or more, 3.8 bar or more, 3.9 bar or more, 4.0 bar or more, 4.1 bar or more, 4.2 bar or more, 4.3 bar or more, 4.4 bar or more, 4.5 bar or more, 4.6 bar or more, 4.7 bar or more, 4.8 bar or more, 4.9 bar or more, or 5.0 bar or more, and can inject high-pressure gas at a pressure of 7.5 bar or less. More preferably, the high-pressure gas can be injected at a pressure of 5.0 bar to 7.5 bar. The above nozzle is a nozzle that injects a gas and / or fluid that can generate pressure, such as water vapor, air, steam, nitrogen, and / or argon gas, and can disintegrate carbon nanotube aggregates through collisions between carbon nanotube aggregates or between carbon nanotube aggregates and the rotor. When the nozzle injects high-pressure gas at a pressure of less than 3.5 bar, it is difficult to form carbon nanotubes of an expanded structure because the carbon nanotube aggregates cannot apply enough pressure to overcome the van der Waals force. Therefore, when the above range is satisfied, the cutting of the carbon nanotube aggregates may not occur, and an expanded carbon nanotube powder of an expanded structure in which disintegration has progressed sufficiently may be manufactured, thereby realizing excellent resistance characteristics and life characteristics.

[0282]

[0283] According to one embodiment of the present invention, the crushing device is not particularly limited as long as it is a crushing device that can apply a non-excessive force, but may be, for example, a Galaxy jet mill (JEM Corporation).

[0284]

[0285] Hereinafter, the carbon nanotube aggregate used in the manufacturing method according to the present invention will be described in more detail.

[0286]

[0287] Among carbon nanotube aggregates, bundle-type carbon nanotubes refer to a form in which carbon nanotubes are aggregated into a bundle due to interactions between carbon nanotube units, rather than a form in which carbon nanotubes exist in the form of single strands. Preferably, it can refer to a form in which carbon nanotube units are attached or entangled with each other due to interactions between each other.

[0288]

[0289] According to one embodiment of the present invention, the bulk density of the carbon nanotube aggregate is 0.011 g / cm 3 0.900g / cm 3 It may be, and preferably, the bulk density of the carbon nanotube aggregates is 0.020 / cm 3 0.500g / cm 3 It may be, and more preferably, the bulk density of the carbon nanotube aggregate is 0.030 g / cm 3 0.150g / cm 3 If the above range is satisfied, it may be a carbon nanotube aggregate suitable for implementing the degree of disintegration according to the manufacturing method of the present invention.

[0290] The above bulk density can be measured by filling an expanded carbon nanotube powder into a container of known weight, measuring the weight, and then converting the density.

[0291]

[0292] According to one embodiment of the present invention, the volume cumulative average particle diameter of the carbon nanotube aggregate may be 100 ㎛ to 600 ㎛, preferably 200 ㎛ to 580 ㎛, and more preferably 300 ㎛ to 560 ㎛. When the above range is satisfied, an appropriate number of carbon nanotube units are aggregated, so that the carbon nanotube aggregate may be suitable for implementing the degree of disintegration according to the manufacturing method of the present invention. The volume cumulative average particle diameter is not limited as long as it is measured by a conventional method, such as measuring using a scanning electron microscope or measuring using laser diffraction, but preferably, it may be measured through the volume cumulative particle diameter distribution using laser diffraction.

[0293]

[0294] The above carbon nanotube aggregate may include carbon nanotube units. The graphite sheet of the carbon nanotube has a cylindrical shape with a nano-sized diameter, and sp 2 It has a bonding structure. At this time, depending on the angle and structure at which the graphite plane is rolled, it can exhibit the characteristics of a conductor or a semiconductor. The carbon nanotube can be classified into a single-walled carbon nanotube (SWCNT) unit, a double-walled carbon nanotube (DWCNT) unit, and a multi-walled carbon nanotube (MWCNT) unit, depending on the number of bonds forming the wall.

[0295] According to one embodiment of the present invention, the carbon nanotube aggregate may include a multi-walled carbon nanotube unit. When the carbon nanotube unit is a single-walled carbon nanotube unit or a double-walled carbon nanotube unit, the manufacturing cost of the battery may be excessively high, which may lower the processability, and the carbon nanotube unit may exist in an excessively aggregated state, which may make it difficult to disintegrate. On the other hand, when the carbon nanotube unit is a multi-walled carbon nanotube unit, the manufacturing cost is relatively low, and the cohesion between the carbon nanotube units is not excessive, which allows for appropriate disintegration, and thus the processability may be excellent.

[0296] In particular, in the case of multi-walled carbon nanotube units, the structural defects are high due to the mechanism of node growth (nodes exist due to defects that occur during the growth process, not in a smooth linear manner). Therefore, during the disintegration process, the multi-walled carbon nanotube units can be more easily cut, and the short-cut multi-walled carbon nanotube units are prone to aggregation due to π-π stacking caused by the carbon surface bonding structure (sp2) of the units. However, when disintegration is performed through the manufacturing method according to the present invention, the multi-walled carbon nanotube units may not be agglomerated, and the effect of the present invention can be maximized in that the length of the carbon nanotube units may not be shortened due to excessive cutting, thereby preventing the electrical conductivity from being deteriorated.

[0297] When the above carbon nanotube aggregate includes a multi-walled carbon nanotube unit, the same applies as described above with respect to the multi-walled carbon nanotube unit.

[0298]

[0299] lithium secondary battery

[0300] Hereinafter, a lithium secondary battery according to the present invention will be described.

[0301]

[0302] A lithium secondary battery according to the present invention may include a dry electrode according to the present invention. For example, the lithium secondary battery may include a secondary battery including a liquid electrolyte and an all-solid-state battery including a solid electrolyte.

[0303] Specifically, it includes a positive electrode, a negative electrode, a separator, and an electrolyte, and the positive electrode and / or the negative electrode may be a dry electrode, and specifically, it may be a lithium secondary battery including the dry electrode, negative electrode, separator, and electrolyte according to the present invention. When only one of the positive electrode or the negative electrode is a dry electrode according to the present invention, the other electrode may be an electrode manufactured through a conventional wet manufacturing method.

[0304]

[0305] In the case where the lithium secondary battery according to one embodiment of the present invention is a secondary battery including a liquid electrolyte, a separator may be included between a plurality of electrodes. The separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator commonly used in lithium secondary batteries may be used without particular limitation, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fibers, polyethylene terephthalate fibers, etc. may also be used. Additionally, a coated separator containing ceramic components or polymeric materials may be used to secure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

[0306] Additionally, if the lithium secondary battery is an all-solid-state battery, the solid electrolyte membrane can be manufactured to perform the function of the separator.

[0307]

[0308] The above separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without any particular restrictions, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength may be used, and may optionally be used in a single-layer or multi-layer structure.

[0309]

[0310] In addition, the electrolyte used in the present invention may include, but is not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, etc. that can be used in the manufacture of a lithium secondary battery.

[0311] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0312] The organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; Carbonate solvents such as dimethylFARbonate (DMC), diethylFARbonate (DEC), methylethylFARbonate (MEC), ethylmethylFARbonate (EMC), ethylene carbonate (EC), and propylene FARbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R represents a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes, etc., can be used. Among these, a carbonate solvent is preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery and a linear carbonate compound having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable.

[0313]

[0314] The above lithium salt can be used without any special limitation as long as it is a compound that can provide lithium ions used in a lithium secondary battery. Specifically, the anion of the above lithium salt is 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 - At least one selected from the group consisting of, and the lithium salt is LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2) 2. LiCl, LiI, or LiB(C2O4)2 can be used. The concentration of the lithium salt is preferably within the range of 0.1M to 4.0M, preferably 0.5M to 3.0M, and more preferably 1.0M to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0315]

[0316] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. At this time, the additives may be included in an amount of 0.1 to 10.0 wt% based on the total weight of the electrolyte.

[0317]

[0318] In addition, since the lithium secondary battery according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, it is useful in portable devices such as mobile phones, laptop computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0319] Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

[0320] The above battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, such as a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0321]

[0322] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0323]

[0324] Examples and Comparative Examples

[0325] Example 1: Preparation of dry electrodes

[0326] A composite composition was prepared by placing 488 g of lithium nickel cobalt manganese oxide (LNF) as a positive electrode active material, 7 g of expandable carbon nanotubes as a conductive material, and 5 g of polytetrafluoroethylene (PTFE) as a fiberizable binder into a blender and mixing at 1500 rpm for 4 minutes.

[0327] The above composite composition was placed in a kneader and kneaded at a rotation speed of 40 rpm at a temperature of 160°C and 1.1 atm for 10 minutes to produce a mixed aggregate.

[0328] The above mixed aggregates were placed in a blender and ground at a rotation speed of 1500 rpm for 1 minute to prepare powder for electrodes.

[0329] The above electrode powder was sheeted onto a calender roll (roll diameter: 160 mm, roll temperature: 80°C) in a roll-to-roll process to produce a powder-sheeting film. Thereafter, the powder-sheeting film was produced by running the two calender rolls at a speed ratio of 1:2 while maintaining a gap of 80 μm between the two rolls, and then placing it on one side of an aluminum foil (thickness: 12 μm) having a conductive primer layer formed thereon, and laminating it using a roll press maintained at 80°C to produce a dry electrode.

[0330] At this time, the porosity of the electrode composite film was 23.5%.

[0331]

[0332] In the case of the above expanded carbon nanotubes, bundled carbon nanotubes (BET specific surface area: 256 m) containing multi-walled carbon nanotube units (average diameter: 10 nm) 2 / g, bulk density: 0.110 g / cc, volume cumulative average particle size: 530 μm) was placed in a crushing device (Galaxy Jet Mill, JEM Co.) and crushed in a solvent-free state to manufacture the product.

[0333] At this time, the rotation speed of the rotor included in the disintegrator was 5400 rpm, and the injection pressure of the nozzle included in the disintegrator was 5.2 bar.

[0334]

[0335] Example 2: Preparation of dry electrodes

[0336] A dry electrode was manufactured in the same manner as in Example 1, except that 488 g of lithium nickel cobalt manganese oxide (LNF) was used as the positive electrode active material, 8 g of expandable carbon nanotubes as the conductive material, and 4 g of polytetrafluoroethylene (PTFE) as the fiberizable binder.

[0337]

[0338] Comparative Example 1: Manufacturing of dry electrodes

[0339] Instead of using expandable carbon nanotubes as a conductive material, bundled carbon nanotubes (BET surface area: 256 m) containing multi-walled carbon nanotube units (average diameter: 10 nm) 2 A dry electrode was manufactured in the same manner as in Example 1, except that a bulk density of 0.110 g / cc, volume cumulative average particle size of 530 μm were used.

[0340]

[0341] Comparative Example 2: Manufacturing of dry electrodes

[0342] A dry electrode was manufactured in the same manner as in Example 1, except that 488 g of lithium nickel cobalt manganese oxide (LNF) was used as the positive electrode active material, 2 g of expandable carbon nanotubes was used as the conductive material, and 10 g of polytetrafluoroethylene (PTFE) was used as the fiberizable binder.

[0343]

[0344] Experimental Example 1: OMI (Overlap Mapping Index) Measurement

[0345] For the dry electrodes manufactured in Examples 1 to 2 and Comparative Examples 1 to 2, cross-sectional samples were manufactured by ion milling using Hitachi's IM5000, and then the Overlap Mapping Index (OMI) was measured using Scanning Electron Microscope-Energy Dispersive X-ray Spectroscopy (SEM-EDS).

[0346] In detail, for each cross-sectional sample, the area where carbon elements were detected and the area where fluorine elements were detected were mapped using SEM-EDS.

[0347] More specifically, a mapping result including the content of each element per pixel was obtained, and the pixel area ratio in which the content of the fluorine element within the measurement area is 15 wt% or more and the pixel area ratio in which the content of the carbon element is 30 wt% or more and the content of the fluorine element is 15 wt% or more were extracted through image processing.

[0348] At this time, the pixel area ratio in which the content of the fluorine element is 15 wt% or more is expressed as FAR expressed in Equation 1 according to the present invention, and the pixel area ratio in which the content of the carbon element is 30 wt% or more and the content of the fluorine element is 15 wt% or more is expressed as CFAR expressed in Equation 1 according to the present invention.

[0349]

[0350] The equipment and measurement conditions used for SEM-EDS were as follows.

[0351] 1) Equipment (SEM): Apreo2S (Thermofisher)

[0352] 2) Equipment (EDS): Extreme (Oxford)

[0353] 3) Acceleration voltage: 3kV

[0354] 4) Incident current: 1.6nA

[0355] 5) Working Distance: 5nm

[0356] 6) Magnification: 3000x

[0357] 7) Area: 1024 pixels x 400 pixels

[0358] 8) Detected elements: C, O, F, Ni

[0359] 9) Pixel size: 135nm x 135nm

[0360]

[0361] The OMI derived from the measured CFAR and FAR above is shown in Table 1 below.

[0362]

[0363] CFAR(%)FAR(%)OMI(%)Example 12.911.525.1Example 23.111.128.4Comparative Example 11.06.915.2Comparative Example 22.414.416.5

[0364] Experimental Example 2: Measurement of tensile strength of electrode composite film

[0365] The electrode composite films manufactured in Examples 1 to 2 and Comparative Example 1 were cut into 50 mm (MD direction) x 10 mm (TD direction), and the tensile strength was measured using UTM equipment (ZwickRoell) according to ASTM 638, with a preload of 0.01 kg / cm and a speed of 50 mm / min. At this time, the tensile strength (MPa) was obtained as the maximum value of the force applied until the sample did not break in each of the MD and TD directions.

[0366] The measured tensile strength is shown in Table 2 below.

[0367]

[0368] Experimental Example 3: Measurement of electrode layer resistivity and interface resistivity

[0369] 1) Measurement of electrode layer resistivity: For the dry electrodes manufactured in Examples 1 to 2 and Comparative Examples 1 to 2, cut into 30 mm x 50 mm, a current of 100 μA was applied to the electrode using the MP resistance measurement method, and the resistivity (Ωcm) value for an arbitrary point inside the electrode composite film was measured 6 times using the potential difference measured between 46 probes, and the average value and standard deviation were calculated.

[0370] The measurement results are shown in Table 3 below.

[0371]

[0372] 2) Measurement of interfacial resistivity: For the dry electrodes manufactured in Examples 1 to 2 and Comparative Examples 1 to 2, cut them into 30 mm x 50 mm, and then apply a current of 100 μA to the electrode using the MP resistance measurement method, and measure the electrical resistivity (Ωcm) at any point between the electrode composite film and the current collector layer by the potential difference measured between 46 probes. 2 ) The values ​​were measured six times, and the average and standard deviation were calculated.

[0373] The measurement results are shown in Table 3 below.

[0374]

[0375] The equipment used in the above resistance measurement was Hioki's Electrode Resistance Measurement System, RM2610.

[0376]

[0377] Electrode composite film tensile strength (MPa) Example 10.46 Example 20.40 Comparative example 10.33

[0378] Electrode layer resistivity (Ωcm)Interface resistivity (Ωcm) 2 )Average (Ωcm)Standard deviation (Ωcm)Standard deviation / Average (%)Average (Ωcm 2 )Standard deviation (Ωcm 2 )Standard deviation / mean (%)Example 16.560.8813.344.85ⅹ10 -2 3.60ⅹ10 -3 7.42 Example 23.820.6517.023.19ⅹ10 -2 3.20ⅹ10 -3 10.03 Comparative Example 18.184.2652.071.14ⅹ10 -1 3.35ⅹ10 -2 29.39 Comparative example 2703.82109.5215.569.33ⅹ10 -1 1.80ⅹ10 -1 19.28

[0379] Referring to Tables 2 and 3 above, in the case of Examples 1 and 2 in which the OMI represented by Equation 1 according to the present invention satisfies the range intended by the present invention, the electrode layer resistivity dispersion degree (standard deviation / average value) is at the same level or less than that of Comparative Examples 1 and 2, and since the interfacial resistivity dispersion degree (standard deviation / average value) is small, it can be confirmed that the electrode is excellent in terms of conductivity uniformity.

[0380] In addition, in the case of Examples 1 and 2 in which the OMI represented by Equation 1 according to the present invention satisfies the range intended by the present invention, it can be confirmed that excellent electrical conductivity is realized because the average values ​​of the electrode layer resistivity and the interface resistivity are lower than those of Comparative Examples 1 and 2.

[0381] That is, when the OMI represented by Equation 1 according to the present invention satisfies the range intended by the present invention, a tensile strength above a certain level is realized, thereby realizing excellent tensile properties and processability, while also ensuring that both the uniformity and electrical conductivity of the electrode are balanced and excellent. Therefore, when manufacturing a secondary battery using the dry electrode according to the present invention, excellent lifespan characteristics and output characteristics can be realized.

Claims

1. Containing a current collector; and an electrode composite film; The above electrode composite film includes an electrode active material, a conductive material, and a binder having a three-dimensional fiber network structure, The above electrode composite film is a dry electrode having an OMI of 17 or more, as represented by the following formula 1: [Formula 1] OMI = {(CFAR) / (FAR)} x 100 In the above equation 1, CFAR is the area ratio of pixel regions where 30 wt% or more of carbon element and 15 wt% or more of fluorine element are simultaneously detected when analyzing the element content within pixels of the electrode composite film cross-section using SEM-EDS, and FAR is the area ratio of pixel regions where 15 wt% or more of fluorine element is detected when analyzing the element content within pixels of the electrode composite film cross-section using SEM-EDS.

2. In claim 1, The above electrode composite film is a dry electrode having an OMI of 23 to 27, represented by the following formula 1: [Formula 1] OMI = {(CFAR) / (FAR)} x 100 In the above equation 1, CFAR is the area ratio of pixel regions where 30 wt% or more of carbon element and 15 wt% or more of fluorine element are simultaneously detected when analyzing the element content within pixels of the electrode composite film cross-section using SEM-EDS, and FAR is the area ratio of pixel regions where 15 wt% or more of fluorine element is detected when analyzing the element content within pixels of the electrode composite film cross-section using SEM-EDS.

3. In claim 1, A dry electrode having a CFAR of 2% to 10%.

4. In claim 1, The above FAR is a dry electrode of 1% to 20%.

5. In claim 1, The above electrode composite film is a dry electrode having a tensile strength of 0.30 MPa to 0.70 MPa.

6. In claim 1, The above electrode composite film is a dry electrode having an elongation of 1.5% to 5.5%.

7. In claim 1, The above electrode composite film is a dry electrode having an electrode layer resistivity of 500 Ωcm or less.

8. In claim 1, The above electrode composite film has an interfacial resistivity of 9ⅹ10 -1 Ωcm 2 Below, dry electrode.

9. In claim 1, The above-mentioned conductive material is a dry electrode comprising an expandable carbon nanotube.

10. In claim 9, The above-mentioned expanded carbon nanotube is a dry electrode comprising multi-walled carbon nanotube units.

11. In claim 10, A dry electrode wherein the multi-walled carbon nanotube unit has an average diameter of 5 nm to 200 nm.

12. In claim 10, The BET surface area of ​​the above multi-walled carbon nanotube unit is 50 m 2 / g to 500m 2 / g, dry electrode 13. In claim 10, A dry electrode, wherein the multi-walled carbon nanotube unit has three or more graphene layers arranged in parallel with respect to the axis of the multi-walled carbon nanotube unit.

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

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