Negative electrode, method of manufacturing this electrode, and electrochemical equipment including this electrode.

Abstract

The invention relates to a cathode comprising a current collector and a cathode active material layer situated on at least one surface of the current collector, wherein the cathode active material layer consists of particles comprising a silicon-based active material, a linear conductive material and a binder; and a fluorine-containing fibrous binder that joins and holds large particles together, and an electrochemical device comprising such an electrode.

Description

Cathode, method for manufacturing same, and electrochemical device including same

[0001] The present invention relates to a cathode, a method for manufacturing the same, and an electrochemical device including the same, and more particularly, to a cathode having improved cohesion between active materials in the electrode and improved dispersibility of a conductive material, a method for manufacturing the same, and an electrochemical device including the same.

[0002] This application claims priority to Korean Application No. 10-2024-0015221, filed January 31, 2024, the entire disclosure of which is incorporated herein by reference.

[0003] The rapid increase in fossil fuel use has led to a growing demand for alternative and clean energy sources. As part of this, the most actively researched area is the field of electrochemical power generation and storage. Secondary batteries are a prime example of electrochemical devices that utilize electrochemical energy, and their applications are expanding. Lithium secondary batteries, a representative type of secondary battery, are not only used as an energy source for mobile devices, but are also increasingly being used as a power source for electric and hybrid electric vehicles, replacing gasoline and diesel vehicles, which are major sources of air pollution. Their applications are also expanding to include auxiliary power sources through grid integration.

[0004] The manufacturing process for these lithium secondary batteries is broadly divided into three stages: the electrode manufacturing process, the electrode assembly manufacturing process, and the formation process. The electrode manufacturing process is further divided into the electrode compound mixing process, the electrode coating process, the drying process, the rolling process, the slitting process, and the coiling process.

[0005] Among these, the electrode mixture mixing process is a process of mixing components for forming an electrode active layer in which an actual electrochemical reaction occurs in the electrode. Specifically, it mixes the electrode active material, which is an essential element of the electrode, and other additives such as conductive materials and fillers, a binder for inter-powder bonding and adhesion to a current collector, and a solvent for imparting viscosity and dispersing powder, to manufacture a slurry having fluidity.

[0006] An electrode coating process is performed to apply the slurry onto an electrically conductive current collector, a drying process is performed to remove the solvent contained in the electrode mixture slurry, and additionally, the electrode is rolled to manufacture the electrode to a predetermined thickness.

[0007] In the conventional electrode manufacturing process, the drying process for drying the solvent included in the slurry causes uneven shrinkage of the electrode or migration of materials, especially binder, to the electrode surface due to differences in the evaporation rate of the solvent, resulting in uneven distribution of the binder in the direction of the thickness of the electrode layer, which in turn causes problems such as surface defects, edge defects, and reduced adhesion to the current collector.

[0008] To address the challenges of wet electrode processes, which involve a drying process that dries the solvent contained in such slurries, numerous attempts have been made to develop technologies for manufacturing dry anodes for various lithium-ion secondary batteries. A representative example is the production of dry anodes by mixing active materials with binders such as polytetrafluoroethylene (PTFE) and then feeding the mixture between calendaring rolls.

[0009] In the case of these dry negative electrodes, as the content of polytetrafluoroethylene binder increases, capacity decline due to irreversible loss occurs, so a small amount of polytetrafluoroethylene binder (for example, less than 1 wt%) compared to the negative electrode active material is used to minimize capacity loss. In particular, when the negative electrode active material contains an active material with low conductivity, such as silicon, and a large shrinkage and expansion during charge and discharge, when manufacturing an electrode using a polytetrafluoroethylene binder, additional binder, and conductive material using a dry mixing method, the dispersibility of the conductive material is poor, so a secondary battery using such a negative electrode is prone to capacity degradation when cycling. At this time, when applying a linear conductive material, such as a single-walled carbon nanotube or a multi-walled carbon nanotube, there is a problem that it is more difficult to secure the dispersibility of the conductive material in a dry mixing method.

[0010] The present invention is intended to solve the above-mentioned problem, and provides an anode in which cohesion between active materials in an electrode is improved, volume expansion of a silicon-based active material is prevented, and dispersibility of a conductive material is improved, thereby forming a uniform and stable conductive network within a layer of an anode active material, a method for manufacturing the same, and an electrochemical device including the same.

[0011] In order to solve the problem of the present invention, according to one aspect of the present invention, a secondary battery of the following embodiment is provided.

[0012] According to the first implementation example,

[0013] It comprises a negative electrode active material layer positioned on at least one surface of the entire collector,

[0014] A negative electrode is provided, wherein the negative active material layer comprises a granule comprising a silicon-based active material, a linear conductive material, and a binder; and a fiberized fluorine-containing binder that connects and fixes the granules to each other.

[0015] According to the second embodiment, in the first embodiment,

[0016] The above silicon-based active material is silicon (Si), silicon oxide (SiOx (0 <x≤2), Si / C 복합체, 또는 이들 중 2 이상을 포함할 수 있다.

[0017] According to the third embodiment, in the first embodiment or the second embodiment,

[0018] The linear conductive material may include a single-walled carbon nanotube (SWCNT), a multi-walled carbon nanotube (MWCNT), a carbon nanofiber, or two or more thereof.

[0019] According to the fourth embodiment, in any one of the first to third embodiments,

[0020] The above binder may include at least one of a linear binder and a point-shaped binder.

[0021] According to the fifth embodiment, in the fourth embodiment,

[0022] The above binder may include a linear binder and a dot-shaped binder.

[0023] According to the sixth embodiment, in the fourth embodiment or the fifth embodiment,

[0024] The linear binder may include an acrylate polymer, and the dot-shaped binder may include a diene polymer, a styrene polymer, or two or more thereof.

[0025] According to the seventh embodiment, in any one of the first to sixth embodiments,

[0026] The above granules may have a central portion including a silicon-based active material and a linear conductive material; and a surface portion including a binder that binds the silicon-based active material and the linear conductive material and is located on all or part of the outer side of the central portion.

[0027] According to the eighth embodiment, in the seventh embodiment,

[0028] The content (wt%) of the dot-shaped binder relative to the total weight of 100 wt% of the above silicon-based active material, linear conductive material, and binder is greater on the surface than in the center of the granules,

[0029] The above surface portion is an area near the surface of the granule from the surface of the granule to a predetermined depth toward the center of the granule, and the center may be a portion other than the surface portion.

[0030] According to the ninth embodiment, in any one of the first to eighth embodiments,

[0031] The above granules may include 80 to 98 parts by weight of a silicon-based active material, 0.2 to 10 parts by weight of a linear conductive material, and 0.5 to 10 parts by weight of a binder.

[0032] According to the tenth embodiment, in any one of the first to ninth embodiments,

[0033] The above granules may further include a carbon-based active material.

[0034] According to the eleventh embodiment, in any one of the first to tenth embodiments,

[0035] The above fluorine-containing binder may include polytetrafluoroethylene (PTFE).

[0036] According to the 12th embodiment, in any one of the 1st to 11th embodiments,

[0037] The above negative electrode active material layer may include 5 to 30 parts by weight of a fluorine-containing binder based on 100 parts by weight of the granules.

[0038] According to the 13th embodiment, in any one of the first to twelfth embodiments,

[0039] A primer layer is formed on all or part of at least one side surface of the above-mentioned collector,

[0040] The above primer layer includes a primer layer binder and a primer layer conductive material,

[0041] The sum of the contents of the primer layer binder and the primer layer conductive material may be 90 wt% or more based on the total weight of the primer layer.

[0042] According to the 14th implementation example,

[0043] A step of preparing a mixture comprising a granule comprising a silicon-based active material, a linear conductive material, and a dot-shaped binder; and a fluorine-containing binder;

[0044] A step of kneading the mixture at a temperature ranging from 70°C to 200°C and under a pressure higher than atmospheric pressure to produce a mixture lump;

[0045] A step of crushing the above mixture lump to obtain a mixed powder for a cathode;

[0046] A step of forming a negative electrode film by injecting the above negative electrode mixed powder between a plurality of rolls and performing a calendaring process; and

[0047] A method for manufacturing a negative electrode according to any one of the first to thirteenth embodiments is provided, comprising the step of attaching the negative electrode film to at least one surface of a current collector.

[0048] According to the 15th embodiment, in the 14th embodiment,

[0049] The above granules,

[0050] It can be manufactured through a step of preparing a slurry by mixing the above silicon-based active material, linear conductive material, and binder with a dispersion medium; and a step of spray drying the slurry.

[0051] According to the 16th implementation example,

[0052] An electrochemical device is provided comprising a cathode according to any one of the first to thirteenth embodiments.

[0053] According to the 17th embodiment, in the 16th embodiment,

[0054] The above electrochemical device may be a secondary battery.

[0055] According to one embodiment of the present invention, by manufacturing granules containing a silicon-based active material, a linear conductive material, and a binder (binder for granules) in advance and using the granules, and simultaneously manufacturing an electrode by a dry method using a fiberizable fluorine-containing binder when forming a negative electrode layer, a synergistic effect can be created by combining individual advantages.

[0056] First, the method of utilizing granules can contribute to ensuring the uniformity of the conductive network by forming an electrode layer in a state where the silicon-based active material and linear conductive agent are uniformly combined. Silicon-based active materials have high capacity characteristics, but they can cause severe volume expansion during the charge / discharge process, which may make the electrode structure unstable. In one embodiment of the present invention, granules including linear conductive agents are formed in advance, and a binder within the granules is utilized to fix the silicon-based active material and linear conductive agent in a physically and chemically combined state, thereby effectively buffering the volume expansion of the silicon-based active material. In addition, since the linear conductive agent is uniformly dispersed within the granules to form conductive paths on the surface of the silicon-based active material, excellent electrical connectivity is maintained throughout the electrode, and the movement path of lithium ions can be optimized.

[0057] Here, the fluorine-containing binder not only provides high chemical stability and electrochemical durability, but also has a fiber-forming property, so it can be evenly distributed within the electrode layer while forming a fine fiber structure during the dry mixing process. As a result, the fiber-forming fluorine-containing binder forms a more flexible network within the negative active material layer, enabling the silicon-based active material and linear conductive material to be uniformly fixed, and can play a role in enhancing the mechanical stability of the electrode layer during the charge and discharge process. In particular, even if the silicon-based active material repeatedly expands and contracts during charge and discharge, the fiber-forming binder flexibly accommodates this and suppresses structural collapse of the electrode, significantly improving long-term cycle characteristics.

[0058] Consequently, the present invention combines two elements: a uniform conductive network formed by utilizing granules containing a silicon-based active material and a linear conductive agent, and a flexible bonding structure formed within the electrode through a fiberizable fluorine-containing binder, thereby creating a synergistic effect that surpasses the individual strengths of each. This allows the electrode to maintain a certain resistance level or higher while stably demonstrating electrochemical performance, and in particular, significantly improving long-term cycle life. Furthermore, the method of the present invention can be applied as a dry process, thereby simplifying the process and enhancing productivity. Furthermore, it can be easily applied to the production of large-area electrodes, thereby securing a technological advantage suitable for the commercial production of high-capacity lithium-ion batteries.

[0059] The following drawings attached to this specification illustrate preferred embodiments of the present invention, and serve to further understand the technical idea of ​​the present invention together with the contents of the invention described above, and therefore the present invention should not be interpreted as being limited to matters described in such drawings.

[0060] Figure 1 is a schematic diagram showing the surface and center of a granule included in a cathode according to one embodiment of the present invention.

[0061] Figures 2a and 2b are schematic diagrams of a manufacturing process of a cathode according to one embodiment of the present invention.

[0062] FIG. 3 is a schematic diagram of a step of laminating a negative electrode film on both sides of a current collector according to one embodiment of the present invention.

[0063] Hereinafter, the present invention will be described in more detail to help understand the present invention.

[0064] 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 idea 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 way.

[0065] The terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

[0066] Additionally, throughout this specification, when it is said that a part "includes" a component, this does not mean that other components are excluded, but rather that other components may be included, unless otherwise specifically stated.

[0067] In addition, the terms "about", "substantially", etc. used throughout this specification are used in the sense of numerical values ​​or near numerical values ​​when manufacturing and material tolerances inherent to the meanings stated are presented, and are used to prevent unscrupulous infringers from unfairly exploiting disclosures that mention exact or absolute values ​​to aid understanding of this specification.

[0068] Throughout this specification, the description of “A and / or B” means “A or B or both.”

[0069] Certain terminology used in this specification is for convenience and not limitation. Terms such as "upper," "lower," "front," "back," "inner," and "outer" are used to describe relative positions or directions between components rather than absolute positions, or may indicate positions or directions in drawings to which reference is made. These terms include, in addition to themselves, words containing them, derivatives thereof, and words of similar meaning.

[0070] As used herein, the term "glass transition temperature (T g )" is measured by a conventional method known in the art, and may be measured by, for example, differential scanning calorimetry (DSC).

[0071] In this specification, the term "porosity" means the ratio of the volume occupied by pores to the total volume in a certain structure, and its unit is vol%, and can be used interchangeably with terms such as porosity, porosity, etc. In the present invention, the measurement of the porosity is not particularly limited, and according to an embodiment of the present invention, for example, it can be measured according to the BET (Brunauer-Emmett-Teller) measurement method using nitrogen gas or the mercury penetration method (Hg porosimeter) and ASTM D-2873. Alternatively, the true density of the membrane can be calculated from the density (apparent density) of the membrane and the composition ratio of materials included in the membrane and the density of each component, and the porosity of the membrane can be calculated from the difference between the apparent density and the true density (net density).

[0072] As used herein, the "average particle diameter (D50)" refers to the particle diameter at the 50% point of the cumulative distribution of particle numbers according to particle diameter, and the particle diameter may be measured using a laser diffraction method. Specifically, the powder to be measured is dispersed in a dispersion medium, and then introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500), and the difference in diffraction patterns according to particle size is measured when the particles pass through the laser beam, thereby calculating the particle size distribution. By calculating the particle diameter at the point where the cumulative distribution of particle numbers according to particle diameter in the measuring device becomes 50%, the D50 particle diameter can be measured.

[0073] The "thickness" of each layer included in the electrode used in this specification may refer to a value measured by a known method for measuring thickness. The method for measuring thickness is not limited thereto, but may be, for example, a value measured using a thickness gauge (Mitutoyo, VL-50S-B).

[0074] As used herein, "specific surface area" may refer to a value measured by a known method for measuring specific surface area. The method for measuring specific surface area is not limited thereto, but may be, for example, a value measured by a fluidized or fixed method.

[0075] In the conventional manufacturing process of positive and negative electrodes applied to secondary batteries, a slurry containing an active material, a binder, a conductive agent, and a solvent (dispersant) was applied to at least one surface of a current collector, and a drying process for drying the dispersion medium included in the slurry was essentially included. The electrode manufactured by this electrode manufacturing process was called a wet electrode. These wet electrodes had the disadvantage of uneven distribution of the binder in the direction of the thickness of the electrode layer due to uneven shrinkage of the electrode or differences in the evaporation rate of the solvent as they went through the drying process during manufacturing, which caused the binder to migrate to the electrode surface due to uneven distribution of the binder in the direction of the thickness of the electrode layer. In order to solve the problems of secondary batteries equipped with such conventional wet electrodes, a dry process that does not use a solvent or dispersant was attempted. However, in this case, the linear conductive agent had significantly poor dispersibility within the active material layer of the dry process, and thus the electrochemical devices such as secondary batteries that applied such electrodes had limitations in terms of life characteristics and resistance characteristics.

[0076] The inventors of the present invention have devised the present invention to solve the problem of reduced dispersibility of binders and conductive materials in conventional wet electrodes and dry electrodes attempted to solve the problem.

[0077] In view of the above, according to one aspect of the present invention,

[0078] It comprises a negative electrode active material layer positioned on at least one surface of the entire collector,

[0079] A negative electrode is provided, wherein the negative active material layer comprises a granule comprising a silicon-based active material, a linear conductive material, and a binder; and a fiberized fluorine-containing binder that connects and fixes the granules to each other.

[0080] The above granules include a silicon-based active material, a linear conductive material, and a binder.

[0081] That is, in the present invention, in order to solve the problem of significantly poor dispersibility of linear conductive materials within an active material layer in a conventional dry process that does not use a solvent or dispersion medium, granules containing linear conductive materials together with silicon-based active materials and dot-shaped binders are prepared in advance, and then mixed with a fluorine-containing binder described later to prepare a dry electrode, thereby enabling the linear conductive materials to be uniformly distributed in the thickness direction of the negative electrode active material layer.

[0082] The above granules may be composite particles including a silicon-based active material, a linear conductive material, and a binder. In addition, the granules may further include optional components added as needed.

[0083] In one embodiment of the present invention, the granules may be secondary particles formed by bonding and assembling silicon-based active material particles and linear conductive materials using a binder. In the present invention, the granules may refer to an aggregate of particles, and the diameter of the granules may be 0.05 μm to 2 μm.

[0084] The above silicon-based active material is silicon (Si), silicon oxide (SiOx (0 <x≤2), Si / C 복합체, 또는 이들 중 2 이상을 포함할 수 있다. 상기 규소계 활물질의 구체적인 예로는 Si, SiO, SiO / C, SiO2등이 있고, 여기에 한정되지는 않는다.

[0085] The above Si / C composite (silicon-carbon composite) comprises silicon particles (e.g., silicon (Si), silicon oxide (SiOx (0)) within a carbon-based support (carbon matrix). <x≤2) 등)가 물리적으로 분산되거나 화학적으로 결합된 구조를 포함할 수 있다. 상기 탄소 담지체는 비정질 탄소(카본블랙, 활성탄, 하드 카본 등), 흑연, 카본나노튜브, 카본나노파이버, 그래핀 등을 포함할 수 있고, 또는 이들 중 2 이상을 포함할 수 있다. 또한, 상기 탄소 담지체는 비정질 탄소, 흑연, 카본나노튜브, 카본나노파이버, 그래핀 등으로 이루어질 수 있고, 또는 이들 중 2 이상으로 이루어질 수 있다.

[0086] According to one embodiment of the present invention, the content of the silicon-based particles relative to 100 parts by weight of the carbon carrier may be 5 to 45 parts by weight, or 10 to 40 parts by weight, or 15 to 35 parts by weight, or 20 to 30 parts by weight, or 5 to 20 parts by weight, or 20 to 45 parts by weight. According to one embodiment of the present invention, the carbon carrier may include activated carbon, and the silicon-based particles may include pure Si particles. The granules may further include another type of negative active material in addition to the silicon-based active material.

[0087] When the silicon-based particles compared to the carbon carrier satisfy this content range, the lithium storage capacity can be increased while maintaining sufficient electrical conductivity, and the carbon carrier can effectively buffer the volume expansion of silicon to suppress cracking and detachment of the electrode structure, thereby improving the mechanical stability of the electrode and the charge / discharge characteristics (life characteristics) of the secondary battery.

[0088] Examples of the above other types of negative electrode active materials include carbon-based active materials such as non-graphitizable carbon, graphitic carbon (natural graphite, artificial graphite); Li x Fe2O3(0≤x≤1), Li x WO2(0≤x≤1), Sn x Me 1-x Me'y O z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, elements of group 1, group 2, group 3 of the periodic table, halogen; 0≤x≤1; 1≤y≤3; 1≤z≤8) and other metal composite oxides; lithium metal; lithium alloy; silicon-based alloy; tin-based alloy; metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4 and Bi2O5; conductive polymers such as polyacetylene; Li-Co-Ni-based materials, etc. According to one embodiment of the present invention, the granules may further include one or more carbon-based active materials such as natural graphite and artificial graphite.

[0089] The linear conductive material may include a single-walled carbon nanotube (SWCNT), a multi-walled carbon nanotube (MWCNT), a carbon nanofiber, or two or more thereof.

[0090] The above carbon nanotubes include carbon allotropes and aggregates thereof, in which graphite sheets have a cylindrical shape with a nano-sized diameter and an sp2 bonding structure. The carbon nanotube aggregate refers to a secondary structure formed by arranging or agglomerating a plurality of carbon nanotubes. For example, the carbon nanotube aggregate may be a bundle-type carbon nanotube in which a plurality of carbon nanotubes are arranged or aligned in a bundle or rope shape in a certain direction, or an entangled-type carbon nanotube in which a plurality of carbon nanotubes are entangled in a sphere or potato shape without a certain direction.

[0091] At this time, the multi-walled carbon nanotube is a small hollow tube composed of coaxial cylindrical surface sleeves of several hexagonal lattices of carbon atoms, and the single-walled carbon nanotube may be composed of a single carbon cylindrical surface. The wall of this tubular structure is composed of a hexagonal lattice similar to a graphite sheet, and the intersections of the hexagonal lattices are where carbon atoms are located, and each carbon atom is adjacent to a surrounding carbon atom, and at the same time, both ends (end caps) of the tube can be closed with a polygonal structure composed of pentagonal carbon rings.

[0092] The above linear conductive materials, especially single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs), have a dielectric constant of 500 m. 2 / g or more, or 500m 2 / g to 5,000m 2 / g, or 800m 2 / g or more, or 800m 2 / g to 5,000m 2 / g, or 900 m 2 / g to 2000 m 2 / g of BET surface area. By using a linear conductive material having a BET surface area as described above, a conductive network is formed between silicon-based negative electrode active materials, thereby further improving the cycle characteristics of a secondary battery.

[0093] The linear conductive material may have a length of 0.5 μm to 100 μm. For example, the single-walled carbon nanotube may have an average length of 2 μm to 100 μm, and the multi-walled carbon nanotube may have an average length of 0.3 μm to 30 μm. Meanwhile, the linear conductive material may have a cross-sectional diameter of 1 nm to 100 nm.

[0094] According to one embodiment of the present invention, the content of the linear conductive agent may be 0.2 to 10 parts by weight, or 0.2 to 5 parts by weight, or 0.3 to 5 parts by weight, or 0.2 to 3 parts by weight, or 0.2 to 2 parts by weight, or 0.2 to 1.6 parts by weight, or 0.3 to 1.6 parts by weight, based on 100 parts by weight of the granules. When the content of the linear conductive agent satisfies this range, the linear conductive agent effectively forms a conductive network between silicon-based negative electrode active materials in the granules, and the cycle characteristics of a secondary battery using such granules can be further improved.

[0095] When the linear conductive material is directly added in solid form during the manufacture of the above granules, it may clump together and not be uniformly mixed with the silicon-based active material, binder, etc., and thus the desired effect of adding the linear conductive material may not be achieved. Therefore, the granules may be manufactured by adding the linear conductive material in the form of a linear conductive material dispersion solution containing a dispersant and a dispersion medium in addition to the linear conductive material.

[0096] According to one embodiment of the present invention, the linear conductive material dispersion may include a linear conductive material, a polymer dispersant containing an amine, and a dispersion medium.

[0097] Or, according to one embodiment of the present invention, the linear conductive material dispersion may include a linear conductive material, a polymer dispersant containing an amine, a phenolic compound containing two or more aromatic rings, and a dispersion medium.

[0098] In the case where the linear conductive material is added in the form of a dispersion as described above, even though a linear conductive material having a large specific surface area is used, the initial viscosity of the dispersion is low due to the excellent dispersibility of the linear conductive material, such as carbon nanotubes, and the change in viscosity over time is suppressed. In addition, when applied to the production of a slurry for producing granules, the linear conductive material is uniformly positioned between the active materials, so that the micro-spaces between the electrode active materials can be maintained consistently even during the drying of the slurry to produce granules. In addition, the linear conductive material is uniformly distributed without agglomeration, so that a sufficient conductive path can be formed even with a small amount of the linear conductive material. The average diameter of the linear conductive material can be measured by photographing the linear conductive material powder with a scanning electron microscope, and the average length of the linear conductive material can be measured by photographing the linear conductive material dispersion with a scanning electron microscope. In addition, the linear conductive material included in the electrode active material layer can also be measured using a scanning electron microscope. That is, when an electrode active material layer including a linear conductive agent is dissolved and dispersed in a solvent such as a dispersion medium (e.g., water) and then separated into a supernatant and a lower layer through centrifugation, the active material mainly settles in the lower layer, and the supernatant contains the linear conductive agent. Therefore, the supernatant can be used to measure the average diameter and average length of the linear conductive agent in the electrode active material layer by observing it with a scanning electron microscope (SEM).

[0099] The linear conductive agent may be included in an amount of 0.01 to 5 wt%, preferably 0.01 to 3 wt%, more preferably 0.1 to 2 wt%, and even more preferably 0.1 to 1 wt%, based on the total weight of the linear conductive agent dispersion. When the content of the linear conductive agent satisfies the above range, the effect of improving the viscosity of the dispersion and the effect of improving the cycle characteristics of the secondary battery are excellent.

[0100] The above dispersant is intended to enable the linear conductive material to be evenly dispersed without agglomeration within the linear conductive material dispersion. The linear conductive material dispersion may use a polymer dispersant containing an amine as a dispersant and a phenolic compound containing two or more aromatic rings together. When the two specific dispersants are used together, the change in viscosity over time of the linear conductive material dispersion can be significantly reduced.

[0101] In one embodiment of the present invention, the dispersant may be included in an amount of 10 to 2000 parts by weight, preferably 50 to 1000 parts by weight, and more preferably 70 to 500 parts by weight, relative to 100 parts by weight of the linear conductive material. When the content of the dispersant satisfies this range, the viscosity of the linear conductive material dispersion is appropriately maintained, and the problem of the dispersant acting as an impurity and thus deteriorating the physical properties of the secondary battery can be prevented.

[0102] The polymer dispersant containing the above amine may be, for example, at least one selected from the group consisting of polyvinylpyrrolidone, polyacrylic acid hydrazide, poly-N-vinyl-5-methoxazolidon, N-alkyl polyimine, N-acetyl polyimine, polyacrylamide, poly-L-lysine hydrobromide, benzyl-dodecyl-dimethylammonium chloride, and polyethylenimine.

[0103] As described above, when a specific polymer dispersant containing amine in the polymer structure is applied, a further enhanced viscosity improvement effect and an effect of suppressing viscosity changes over time can be achieved.

[0104] The phenolic compound containing two or more aromatic rings can reduce the viscosity of a linear conductive dispersion, particularly an aqueous linear conductive dispersion, compared to a conventional one, and significantly improve the increase in viscosity over time due to the bulky structure generated by the two or more aromatic rings and the influence of a hydroxyl group contained in the phenol group.

[0105] The above phenolic compound may include at least one structure selected from the group consisting of a phenol structure, a catechol structure, a galol structure, and a naphthol structure in at least one of the aromatic rings, and specifically, may include at least one structure selected from the group consisting of a catechol structure and a galol structure in at least one of the aromatic rings. The phenol structure is a structure in which one hydroxyl group is bonded to a benzene ring, the catechol structure is a structure in which two hydroxyl groups are bonded to a benzene ring, the galol structure is a structure in which three hydroxyl groups are bonded to a benzene ring, and the naphthol structure is a structure in which one hydroxyl group is bonded to naphthalene.

[0106] When the phenolic compound containing two or more of the above aromatic rings includes the above structure, the interaction between the aromatic ring and the linear conductive material in the linear conductive material dispersion and the interaction by hydrogen bonding between the -OH of the phenolic compound and the polymer dispersant are appropriately balanced, thereby exhibiting the effect of reducing the viscosity of the linear conductive material dispersion and suppressing the increase in viscosity due to changes over time.

[0107] Specific examples of the phenolic compound containing two or more of the above aromatic rings may include at least one selected from the group consisting of baicalin, luteolin, taxifolin, myricetin, quercetin, rutin, catechin, epigallocatechin gallate, butein, piceatenol, and tannic acid, and preferably tannic acid, quercetin, epigallocatechin gallate, or a combination thereof.

[0108] In one embodiment of the present invention, the aromatic ring included in the phenolic compound including two or more aromatic rings may be one aromatic ring that is not fused with another aromatic ring or a structure in which two aromatic rings are fused to each other, and a structure in which three or more aromatic rings are fused to each other may not be included.

[0109] That is, the scope of phenolic compounds containing two or more aromatic rings may exclude those containing a structure in which three or more aromatic rings are fused within the molecular structure.

[0110] When the phenolic compound containing two or more aromatic rings has a structure in which three or more aromatic rings are fused within its molecular structure, the structure in which three or more aromatic rings are fused may exert a strong bonding force that is stronger than an appropriate level with the linear conductive material in the linear conductive material dispersion, thereby inducing coagulation between the linear conductive materials, and thus may not be suitable for improving the dispersibility of the linear conductive material. In addition, since the balance between the interaction between the aromatic ring and the linear conductive material in the linear conductive material dispersion and the interaction through hydrogen bonding between the -OH of the phenolic compound and the polymer dispersant is broken, it may be difficult to exert an appropriate viscosity reduction effect of the linear conductive material dispersion and an effect of suppressing viscosity increase due to changes over time.

[0111] Meanwhile, the phenolic compound may be included in an amount of 1 to 100 parts by weight, or 5 to 100 parts by weight, or 10 to 100 parts by weight, based on 100 parts by weight of the polymeric dispersant containing the amine. When the content of the polymeric dispersant containing the amine and the phenolic compound satisfies the above range, the effect of reducing the viscosity of the dispersion and increasing the storage stability is more excellent.

[0112] The above dispersion medium (solvent) is a liquid medium for dispersing the linear conductive material, the polymer dispersant, and the phenolic compound containing two or more aromatic rings. When the linear conductive material is directly mixed with a negative electrode active material, etc. and used as a slurry for granules, it is used to supply the linear conductive material dispersion liquid by pre-dispersing it to prevent agglomeration.

[0113] The above dispersion medium may be any liquid medium used in the technical field of the present invention, as long as it can dissolve or disperse the linear conductive material, polymer dispersant, and phenolic compound containing two or more aromatic rings to a certain level or higher. The above dispersion medium may be an aqueous solvent, for example, water.

[0114]

[0115] The linear conductive dispersion of the present invention as described above can be manufactured by a manufacturing method comprising: (1) a step of manufacturing a mixture by mixing a linear conductive material (e.g., carbon nanotubes, etc.), a polymer dispersant, a phenolic compound containing two or more aromatic rings, and a dispersion medium; and (2) a step of milling the mixture.

[0116] In step (1), a mixture is prepared by mixing a linear conductive material, a polymer dispersant, a phenolic compound containing two or more aromatic rings, and a dispersion medium.

[0117] The above mixture preparation step can be performed under temperature conditions in which the physical properties of the mixture, including viscosity, do not change due to evaporation of the dispersion medium. For example, it can be performed at a temperature of 50°C or lower, more specifically, from 5°C to 50°C.

[0118] In step (2), the above mixture is dispersed to prepare a linear conductive dispersion.

[0119] The above milling can be performed by a method such as a ball mill, a bead mill, a disc mill, a basket mill, a high pressure homogenizer, etc., and more specifically, it can be performed by a milling method using a disc mill or a high pressure homogenizer.

[0120] When milling using the above disk mill, the size of the beads can be appropriately determined depending on the type and amount of the linear conductive material and the type of the dispersant, and specifically, the diameter of the beads can be 0.1 mm to 5 mm, more specifically, 0.5 mm to 4 mm. In addition, the bead milling process can be performed at a speed of 2,000 rpm to 10,000 rpm, and more specifically, can be performed at a speed of 5,000 rpm to 9,000 rpm.

[0121] Milling by the high-pressure homogenizer is achieved by pressurizing the mixture with a plunger pump of the high-pressure homogenizer, for example, and pushing it through the gap of the homogenization valve, thereby generating forces such as cavitation, shear, impact, and explosion when passing through the gap.

[0122] The above milling process can be performed depending on the degree of dispersion of the linear conductive material dispersion, and can be performed specifically for 30 to 120 minutes, more specifically for 60 to 90 minutes.

[0123] According to one embodiment of the present invention, instead of directly adding the linear conductive material to a mixture for producing a dry negative electrode film, the linear conductive material is mixed in advance with a negative electrode active material including a silicon-based active material having a large volume change and a binder in a dispersion medium, and dried to produce granules, and the dry negative electrode film is produced using the granules thus obtained. As a result, the linear conductive material is uniformly dispersed in the dispersion medium, thereby obtaining granules having excellent dispersibility of the linear conductive material, and since these granules are included in the negative electrode film, the dispersibility of the linear conductive material in the final negative electrode active material layer can be significantly improved.

[0124] In addition, since the anode active material including the silicon-based active material, which has excellent capacity but has a large volume change and thus has limited application, is manufactured in advance as a granule, and the silicon-based active material is connected and fixed by the linear conductive material and binder uniformly dispersed within the granule, even if the volume of the silicon-based active material changes later within the anode active material layer, the silicon-based active material is uniformly dispersed and a conductive network within the anode active material layer can be stably formed by the linear conductive material connecting it through line contact, and as a result, the electrical properties such as the life characteristics of an electrochemical device such as a secondary battery employing such a cathode can be significantly improved.

[0125] In one embodiment of the present invention, the content of the binder may be 0.5 to 10 parts by weight, or 0.5 to 8 parts by weight, or 0.5 to 7 parts by weight, or 0.5 to 6 parts by weight, or 0.5 to 5 parts by weight, or 0.5 to 4 parts by weight, or 0.5 to 2 parts by weight, or 1 to 8 parts by weight, or 1 to 7 parts by weight, or 1 to 6 parts by weight, or 1 to 5 parts by weight, or 1 to 4 parts by weight, or 1 to 2 parts by weight, based on 100 parts by weight of the granules. When the content of the above binder satisfies this range, it plays a role in connecting and fixing the silicon-based active material and the linear conductive material within the granules, thereby minimizing the effect of volume expansion of the silicon-based active material, and at the same time, when the granules are later applied to the negative electrode of a secondary battery, it does not cause the problem of increasing resistance by impeding the movement of lithium ions, thereby improving the cycle characteristics of the secondary battery. At this time, the binder included in the granules can be called a binder for the granules.

[0126] In one embodiment of the present invention, the binder may include at least one of a linear binder and a dot-shaped binder.

[0127] The linear binder may refer to a polymer compound characterized by a structure in which polymer chains are linearly arranged, acting as a binding agent in a composition containing an active material. Such a linear binder has flexible polymer chains, stably bonding the active material and conductive material to the current collector, and absorbing the volume expansion and contraction of the electrode that occurs during the charge and discharge process, thereby maintaining the mechanical stability and electrical contact of the electrode.

[0128] The above dot-shaped binder may refer to a binder that, when dispersed in a solvent, does not completely dissolve in the solvent, maintains a dot-shaped form while having a size of several hundred nanometers, has good dispersibility and can well surround the surface of an active material, and has a low viscosity compared to the solid content, making it easy to control the binder content compared to the active material. By using such a dot-shaped binder together with a silicon-based active material and a linear conductive material in a granular body, the surface of the active material can be sufficiently covered while maintaining the dispersibility of the linear conductive material.

[0129] The above-mentioned dot-shaped binder has no particular limitations on its shape, but is preferably in the form of particles, as it has good binding properties and can suppress deterioration due to reduction in the electrostatic capacity of the formed electrode or repeated charge / discharge cycles. Examples of the dot-shaped binder in the form of particles include those in which dispersed binder particles are dispersed in a solvent such as water, such as latex, or those in the form of powder obtained by drying such a dispersion.

[0130] The above linear binder may include an acrylate polymer.

[0131] Examples of the above acrylate polymer may include a polymer containing monomer units derived from acrylic acid ester and / or methacrylic acid ester. The proportion of monomer units derived from acrylic acid ester and / or methacrylic acid ester in the acrylate polymer may usually be 40 wt% or more, preferably 50 wt% or more, and more preferably 60 wt% or more. Specific examples of acrylate polymers include cross-linked acrylate polymers such as acrylamide-acrylate copolymer, 2-ethylhexyl acrylate-methacrylic acid-acrylonitrile-ethylene glycol dimethacrylate copolymer, 2-ethylhexyl acrylate-methacrylic acid-methacrylonitrile-diethylene glycol dimethacrylate copolymer, 2-ethylhexyl acrylate-styrene-methacrylic acid-ethylene glycol dimethacrylate copolymer, butyl acrylate-acrylonitrile-diethylene glycol dimethacrylate copolymer, and butyl acrylate-acrylic acid-trimethylolpropane trimethacrylate copolymer; Examples thereof include copolymers of ethylene and (meth)acrylic acid esters, such as ethylene-methyl acrylate copolymers, ethylene-methyl methacrylate copolymers, ethylene-ethyl acrylate copolymers, and ethylene-ethyl methacrylate copolymers; graft polymers obtained by grafting a radically polymerizable monomer onto the above copolymers of ethylene and (meth)acrylic acid esters; and the like. Meanwhile, examples of the radically polymerizable monomer used in the graft polymers include methyl methacrylate, acrylonitrile, and methacrylic acid. In addition, copolymers of ethylene and (meth)acrylic acid, such as ethylene-acrylic acid copolymers and ethylene-methacrylic acid copolymers, can be used as dispersion-type binders.

[0132] According to one embodiment of the present invention, the acrylate polymer may include an acrylamide-acrylate copolymer.

[0133] The above dot-shaped binder may include a diene polymer, a styrene polymer, or two or more thereof.

[0134] Examples of the diene polymer include polymers containing monomer units derived from conjugated dienes such as butadiene and isoprene, and hydrogenated products thereof. The proportion of monomer units derived from conjugated dienes in the diene polymer may usually be 40 wt% or more, preferably 50 wt% or more, and more preferably 60 wt% or more. Specifically, examples thereof include conjugated diene homopolymers such as polybutadiene or polyisoprene; aromatic vinyl-conjugated diene copolymers such as styrene-butadiene copolymers (SBRs), which may be carboxyl-modified; cyanated vinyl-conjugated diene copolymers such as acrylonitrile-butadiene copolymers (NBRs); hydrogenated SBRs, hydrogenated NBRs, and the like.

[0135] The above styrene polymer is a polymer having a repeating unit derived from a styrene monomer, and may include a styrene homopolymer (polystyrene), a styrene copolymer, etc. Examples of the above styrene copolymers may include block copolymers such as styrene-ethylene-butadiene copolymer, styrene-butadiene-propylene copolymer, styrene-isoprene copolymer, styrene-n-butyl acrylate-itaconic acid-methyl methacrylate-acrylonitrile copolymer, styrene-n-butyl acrylate-itaconic acid-methyl methacrylate-acrylonitrile copolymer, styrene-butadiene block copolymer, styrene-butadiene-styrene block copolymer, styrene-ethylene-butylene-styrene block copolymer, styrene-isoprene block copolymer, and styrene-ethylene-propylene-styrene block copolymer.

[0136] In addition, in one embodiment of the present invention, the binder may include a linear binder and a dot-shaped binder. In one embodiment of the present invention, the binder may include an acrylate polymer (e.g., an acrylamide-acrylate copolymer, an acrylamide-acrylic acid-acrylonitrile copolymer, etc.) as a linear binder and a diene polymer or a styrene polymer (e.g., a styrene-butadiene copolymer (SBR), etc.) as a dot-shaped binder.

[0137] When the above binder includes both a linear binder and a point-like binder, it provides a synergistic effect that comprehensively improves mechanical, electrical, and chemical stability in electrodes and secondary batteries, which may be advantageous in the design of secondary batteries requiring high energy density, long life, and high reliability.

[0138] First, the linear binder has a long and continuous molecular structure, which increases the bonding strength between the active material and the current collector in the electrode, effectively dispersing the mechanical stress that may occur during electrode manufacturing and secondary battery operation, thereby preventing peeling or cracking of the electrode. The dot-shaped binder has a three-dimensional bonding structure, and in addition to improving local adhesive strength, it absorbs the stress caused by volume expansion during charge and discharge, thereby preventing physical damage to the electrode caused by repeated charge and discharge. Therefore, by using these linear binders and dot-shaped binders together, the mechanical stability of the electrode is improved, and the stability is maintained even during repeated charge and discharge cycles, which can result in extending the life of the battery.

[0139] In addition, the linear binder enables uniform dispersion of the active material within the electrode, thereby improving the conductivity and electrical contact of the electrode, and the point-like binder forms high-strength bonds at small contact points, thereby optimizing the contact between the active material and the electrolyte, thereby contributing to reducing the ion migration resistance. Therefore, the combination of the linear binder and the point-like binder can form a more efficient migration path of ions and electrons within the electrode, thereby improving the energy density and output characteristics.

[0140] According to one embodiment of the present invention, when the binder includes a linear binder and a dot-shaped binder, the weight ratio of the linear binder and the dot-shaped binder may be 70:30 to 30:70, or 60:40 to 40:60, or 70:50 to 50:70. When the weight ratio of the linear binder and the dot-shaped binder satisfies this range, the synergy effect resulting from the mixed use of the linear binder and the dot-shaped binder is further maximized, thereby improving the mechanical stability of the electrode and exhibiting the effect of improving the lifespan of the battery even in repeated charge / discharge cycles.

[0141] Figure 1 is a schematic diagram showing the surface and center of a granule according to one embodiment of the present invention.

[0142] Referring to Fig. 1, the granule (10) has a greater amount of binder contained in the surface portion (12) of the granule than the amount of dot-shaped binder contained in the center portion (11) of the granule. The amount of binder may refer to weight or volume.

[0143] Together with or independently of this, the granule (10) has a content (wt%) of binder included in the center (101) of the granule relative to 100 wt% of the total weight of the granule (B c / G t ) compared to the content (wt%) of point-shaped binder included in the surface portion (102) of the granule (B s / G t ) is more. Here, Bc is the weight of the point-shaped binder included in the center, Bs is the weight of the binder included in the surface part, and G t refers to the total weight of the granular particles.

[0144] Together with or independently of this, the granules (10) contain a binder content (vol%) (B) contained in the center (11) of the granules relative to 100 vol% of the total volume of the granules. c / G t) compared to the content (vol%) of binder included in the surface part (12) of the granules (B s / G t ) is higher. Here, Bc is the volume of binder included in the center, Bs is the volume of binder included in the surface, and G t refers to the total volume of granular particles.

[0145] Here, the surface portion refers to an area near the surface of the granule from the surface of the granule to a predetermined depth toward the center of the granule, and the center may refer to a portion other than the surface portion. In one embodiment of the present invention, the surface portion may refer to an area from the center of the granule to the surface of the granule after 70% of the radius toward the outside of the granule. In one embodiment of the present invention, the surface portion may refer to an area from 80%, 85%, 90%, or 95% of the radius to the surface of the granule, for example.

[0146] In one embodiment of the present invention, the center of the granules may mean a point at half the longest diameter of the granules.

[0147] In one embodiment of the present invention, the binder content in a region from the center of the granule particle to the surface of the granule at a radius of 90% relative to 100 wt% of the total weight of the granule in that region may be 50 wt% or more, 60 wt% or more, 70 wt% or more, 80 wt% or more, or 90 wt% or more.

[0148] In another embodiment of the present invention, the binder content in a region from the center of the granule to the surface of the granule at 95% of the particle radius may be 50 wt% or more, 60 wt% or more, 70 wt% or more, 80 wt% or more, or 90 wt% or more, based on 100 wt% of the total weight of the granule in that region.

[0149] In another embodiment of the present invention, the binder content in a region from the center of the granule particle to the surface of the granule after 99% of the radius may be 50 wt% or more, 60 wt% or more, 70 wt% or more, 80 wt% or more, or 90 wt% or more, based on 100 wt% of the total weight of the granule in that region.

[0150] In one embodiment of the present invention, the binder content in a region from the center of the granule particle to the surface of the granule at a radius of 90% relative to 100 vol% of the total volume of the granule in that region may be 50 vol% or more, 60 vol% or more, 70 vol% or more, 80 vol% or more, or 90 vol% or more.

[0151] In another embodiment of the present invention, the binder content in a region from the center of the granule to the surface of the granule at 95% of the particle radius may be 50 vol% or more, 60 vol% or more, 70 vol% or more, 80 vol% or more, or 90 vol% or more, based on 100 vol% of the total volume of the granule in that region.

[0152] In another embodiment of the present invention, the binder content in a region from the center of the granule particle to the surface of the granule at a radius of 99% relative to 100 vol% of the total volume of the granule in that region may be 50 vol% or more, 60 vol% or more, 70 vol% or more, 80 vol% or more, or 90 vol% or more.

[0153] To describe the above granules in more detail, the granules may have a central portion including one or more silicon-based active materials; and a surface portion including a binder that is positioned on all or part of the outer side of the central portion and binds the silicon-based active materials. That is, in the central portion of the granules, a plurality of silicon-based active materials are in surface contact, line contact, point contact, or two or more of these contacts with each other to form an aggregate, and in the surface portion of the granules, a binder is positioned on all or part of the outer side of the aggregate, thereby fixing and binding the plurality of silicon-based active materials in the central portion of the granules with each other.

[0154] According to one embodiment of the present invention, a small amount of binder may be further included in the central portion of the granule, which may serve to connect and fix the plurality of silicon-based active materials in the central portion. However, as previously described, it is preferable that the binder content ratio be greater in the surface portion than in the central portion.

[0155] Meanwhile, in one embodiment of the present invention, the granules may have an aspect ratio of 0.5 to 1.0, preferably 0.75 to 1.0. The aspect ratio may refer to the ratio of the major axis length to the minor axis length of the granules. In another embodiment of the present invention, the average aspect ratio of the granules may have a value of 0.5 to 1.0, preferably 0.75 to 1.0, and in this case, the average aspect ratio may refer to the ratio of the average major axis length to the average minor axis length of the granule particles. At this time, the average minor axis length may refer to the average value of the length in the axial direction having the shortest length of the granules, and the average major axis length may refer to the average value of the length in the axial direction having the longest length of the granules. When the aspect ratio of the granules satisfies this range, it is advantageous in terms of having sufficient fluidity suitable for the process.

[0156] In one embodiment of the present invention, the particle diameter of the granules may range from 0.1 to 1,000 μm based on the longest particle diameter. In another embodiment of the present invention, the average particle diameter (D50) of the granules may range from 0.1 to 1,000 μm.

[0157] According to one embodiment of the present invention, the granules may comprise 80 to 98 parts by weight of a silicon-based active material, 0.5 to 10 parts by weight of a linear conductive material, and 0.5 to 10 parts by weight of a binder. Alternatively, the granules may comprise 85 to 95 parts by weight of a silicon-based active material, 0.5 to 5 parts by weight of a linear conductive material, and 0.5 to 8 parts by weight, or 0.5 to 7 parts by weight, or 0.5 to 6 parts by weight, or 0.5 to 5 parts by weight, or 0.5 to 4 parts by weight, or 1 to 8 parts by weight, or 1 to 7 parts by weight, or 1 to 6 parts by weight, or 1 to 5 parts by weight, or 1 to 4 parts by weight of a binder.

[0158] When the contents of the above silicon-based active material, linear conductive material, and binder satisfy this range, the cohesion between the active materials in the negative electrode increases, and the dispersibility of the linear conductive material and binder is significantly improved, so that the cell performance, such as the life characteristics of an electrochemical device equipped with such a negative electrode, can be greatly improved.

[0159] The above granules may further include other types of negative electrode active materials in addition to the above silicon-based active material.

[0160] Examples of the above other types of negative electrode active materials include carbon-based active materials such as non-graphitizable carbon, graphitic carbon (natural graphite, artificial graphite); Li x Fe2O3(0≤x≤1), Li x WO2(0≤x≤1), Sn x Me 1-x Me' y O z(Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, elements of group 1, group 2, group 3 of the periodic table, halogen; 0≤x≤1; 1≤y≤3; 1≤z≤8) and other metal composite oxides; lithium metal; lithium alloy; silicon-based alloy; tin-based alloy; metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4 and Bi2O5; conductive polymers such as polyacetylene; Li-Co-Ni-based materials, etc. According to one embodiment of the present invention, the granules may further include one or more carbon-based active materials such as natural graphite and artificial graphite.

[0161] According to one embodiment of the present invention, the granules may include 30 to 70 parts by weight of a silicon-based active material, 30 to 70 parts by weight of a negative electrode active material other than the silicon-based active material, 0.5 to 10 parts by weight of a linear conductive material, and 0.5 to 10 parts by weight of a binder.

[0162] Alternatively, the granules may include 35 to 70 parts by weight of a silicon-based active material, 35 to 70 parts by weight of a carbon-based active material, and other types of negative active material, 0.5 to 5 parts by weight of a linear conductive material, and 0.5 to 5 parts by weight of a binder.

[0163] The above-described negative active material layer includes a granule comprising the above-described silicon-based active material, a linear conductive material, and a binder; and a fiberized fluorine-containing binder that connects and fixes the granules to each other.

[0164] The above fluorine-containing binder is not particularly limited as long as it can be microfiberized during the step of manufacturing the mixed powder for the negative electrode. The microfiberization refers to a process of dividing a polymer into small pieces and can be performed using, for example, mechanical shear force. Specific examples of such fluorine-containing binders may include polytetrafluoroethylene (PTFE), etc.

[0165] In addition, according to one embodiment of the present invention, the negative electrode active material layer may further include at least one of a PVdF-based copolymer such as PVdF (polyvinylidene fluoride), PVdF-HFP (polyvinylidene fluoride-co-hexafluoropropylene), and a fluoroelastomer such as an FKM-based copolymer as an additional binder.

[0166] According to one embodiment of the present invention, the negative electrode active material layer may include 5 to 30 parts by weight, or 5 to 25 parts by weight, or 10 to 25 parts by weight, or 10 to 30 parts by weight, or 10 to 20 parts by weight of a fluorine-containing binder based on 100 parts by weight of the granules.

[0167] According to one embodiment of the present invention, the negative electrode active material layer may include 0.1 to 2 parts by weight, or 0.2 to 1 part by weight, or 0.5 to 1 part by weight, or 0.1 to 0.5 part by weight of a fluorine-containing binder based on 100 parts by weight of the negative electrode active material.

[0168] When the content of the fluorine-containing binder satisfies this range based on the content of the above granules and negative electrode active material, the fluorine-containing binder can be sufficiently fiberized in a subsequent mixing process to form a mixture lump, and a negative electrode film can be easily manufactured through the molding of the mixed powder formed through a pulverizing process, and the physical properties of the negative electrode film can be secured, the content of the silicon-based active material is secured to prevent the problem of capacity reduction, and sufficient conductivity can be secured.

[0169] When a fluorine-containing binder such as polytetrafluoroethylene (PTFE) is used as the fluorine-containing binder, there is a problem that the capacity of an electrochemical device, for example, a secondary battery, is reduced due to a side reaction with electrons flowing into the negative electrode. However, since the content of polytetrafluoroethylene (PTFE) can be reduced as in the present invention, such side reactions and performance problems of the secondary battery can be prevented.

[0170] According to one embodiment of the present invention, the negative electrode active material layer may further include other necessary additives such as an additional binder, an additional conductive material, or a filler in addition to the aforementioned granules and fluorine-containing binder.

[0171] The above additional binder may further include at least one of PVdF (polyvinylidene fluoride); PVdF-based copolymers such as PVdF-HFP (polyvinylidene fluoride-co-hexafluoropropylene); fluoroelastomers such as FKM-based copolymers; and olefin-based polymers such as polyethylene and polypropylene.

[0172] The additional conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and examples thereof include graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; activated carbon; conductive fibers such as carbon fiber or metal fiber; metal powder such as fluorinated carbon, aluminum, and nickel powder; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0173] The above filler can play a role in suppressing expansion of the electrode, and the filler is not particularly limited as long as it is a fibrous material that does not cause a chemical change in the battery, and for example, an olefin polymer such as polyethylene or polypropylene; a fibrous material such as glass fiber or carbon fiber can be used.

[0174] In addition, the active material loading amount of the negative electrode active material layer is 3 mAh / cm 2 Up to 15 mAh / cm 2 It can be 4 mAh / cm in detail. 2 10 mAh / cm 2 , or 4mAh / cm 2 6 mAh / cm 2 , or 4mAh / cm 2 5 mAh / cm 2 or 4.8mAh / cm 2 4.9 mAh / cm 2 It could be.

[0175] Here, the loading amount of the active material is a value calculated using the following method.

[0176] Loading capacity (mAh / cm 2 ) = [Capacity of active material (mAh / g)] Х [Weight content ratio of active material in the negative electrode active material layer (wt%) x Weight per unit area of ​​the negative electrode active material layer (g / cm 2 )]

[0177] The porosity of the negative electrode active material layer of the above negative electrode may be 18 to 50%, or 20 to 45%, or 20 to 40%, or 20 to 35%, or 22 to 30%, or 20 to 29%, or 23.1 to 28%. This porosity may vary slightly depending on which effect is focused on, etc.

[0178] However, when the porosity of the negative electrode active material layer is within this range, the electrolyte impregnation property is improved, so that the life characteristics and output characteristics are excellent, and the volume does not need to increase to express the same capacity, so it is advantageous in terms of energy density per volume.

[0179] The porosity of the above negative electrode active material layer can be obtained by measuring the apparent density of the negative electrode active material layer and using the actual density calculated based on the actual density and composition of each component, using the following relationship.

[0180] Porosity (%) = {1 - (apparent density / actual density)} Х 100

[0181] In one embodiment of the present invention, the crystallinity of the fluorine-containing binder in the negative electrode active material layer may be 10% or less.

[0182] In the present invention, the crystallinity (Xc) can be measured through differential scanning calorimetry (DSC), and is based on the temperature (peak temperature) at which the highest enthalpy is observed during crystallization. Specifically, the crystallinity is measured by the melting enthalpy (△H) actually measured in DSC. m ) value is theoretically the melting enthalpy (△H) of a perfect crystal (crystallization degree 100%) m 0)(equilibrium heat of fusion) and expressed as a %, which can be calculated by the following equation 1. Here, the theoretical melting enthalpy value of a perfect crystal can be found and used in the polymer handbook for known polymers, and for unknown or newly synthesized substances, it can be calculated by the extrapolation method that extends the crystallinity by two or more points.

[0183] [Relationship 1]

[0184] Xc(%) = (△H m ÷ △H m 0 ) x 100

[0185]

[0186] The above-described negative electrode active material layer may further include other additional conductive materials in addition to the linear conductive material included in the granules described above. The additional conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and each independently includes, for example, graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black; conductive fibers such as carbon fiber or metal fiber; metal powder such as fluorocarbon, aluminum, nickel powder; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives, etc. However, specifically, in order to uniformly mix the conductive material and improve conductivity, the negative electrode active material may include at least one selected from the group consisting of activated carbon, graphite, carbon black, and carbon nanotubes.

[0187] The current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, copper, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. can be used. The current collector can also form fine unevenness on its surface to increase the adhesive strength of the positive electrode active material, and various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric are possible.

[0188] A primer layer may be formed on all or part of at least one side surface of the above-mentioned collector.

[0189] The above primer layer includes a primer layer binder and a primer layer conductive material, and the sum of the contents of the primer layer binder and the primer layer conductive material in the primer layer may be 90 wt% or more.

[0190] At this time, the primer layer includes a primer layer binder and a primer layer conductive material, and the sum of the contents of the primer layer binder and the primer layer conductive material is 90 wt% or more, thereby ensuring stability over time of the primer layer, and thus exhibiting excellent physical properties such as adhesive strength and lifespan characteristics, but the present invention is not limited thereto.

[0191] First, the primer layer will be described in detail.

[0192] According to one embodiment of the present invention, the sum of the contents of the primer layer binder and the primer layer conductive material in the primer layer may be specifically 91 wt% or more, 92 wt% or more, 93 wt% or more, 94 wt% or more, 95 wt% or more, 96 wt% or more, 97 wt% or more, 98 wt% or more, 99 wt% or more, 100 wt% or less, 99 wt% or less, 98 wt% or less, 95 wt% or less, or 93 wt% or less.

[0193] According to one embodiment of the present invention, the primer layer includes a primer layer binder and a primer layer conductive material, and may further include a dispersant.

[0194] According to another embodiment of the present invention, the primer layer may include a primer layer binder and a primer layer conductive material, but may substantially not include a dispersant.

[0195] In this specification, the term "substantially not including" means not only that the component is not included at all, but also that the component is included in a trace amount so that the function of the component is not implemented. For example, the content of the component that is not substantially included may be 6 wt% or less, 5 wt% or less, 4 wt% or less, 3 wt% or less, 2 wt% or less, 1 wt% or less, 0.5 wt% or less, or 0 wt% (i.e., not included at all).

[0196] Accordingly, the primer layer being “substantially free of dispersant” means not only that the primer layer does not contain any dispersant at all, but also that the primer layer contains a trace amount of dispersant in such a quantity that the function of the dispersant, i.e., the function of dispersing the binder and the conductive agent, is not realized. For example, the content of the dispersant in the primer layer may be 6 wt% or less, 5 wt% or less, 4 wt% or less, 3 wt% or less, 2 wt% or less, 1 wt% or less, 0.5 wt% or less, or 0 wt% (i.e., not containing at all).

[0197] According to one embodiment of the present invention, the substantially non-included dispersant may be capable of decomposing when exposed to the air, thereby causing a change in the primer layer over time.

[0198] The dispersant may include, but is not limited to, a cellulose-based polymer, an emulsifying surfactant, or two or more thereof.

[0199] The above cellulose polymer may include, but is not limited to, carboxymethylcellulose (CMC), alkali metal salts of carboxymethylcellulose, hydroxymethylcellulose (HMC), alkali metal salts of hydroxymethylcellulose, hydroxyethylcellulose (HEC), alkali metal salts of hydroxyethylcellulose, hydroxypropylcellulose (HPC), alkali metal salts of hydroxypropylcellulose, ethylhydroxyethylcellulose (EHEC), methylhydroxymethylcellulose (MHMC), methylhydroxyethylcellulose (MHEC), ethylhydroxymethylcellulose (EHMC), methylcellulose (MC), ethylcellulose (EC), hydroxypropylmethylcellulose (HPMC), hydroxyethylmethylcellulose (HEMC), or mixtures of two or more thereof.

[0200] The emulsifying surfactant may be, for example, but not limited to, a nonionic surfactant, an anionic surfactant, an amphoteric surfactant, or a mixture of two or more thereof. The nonionic surfactant may be, for example, but not limited to, ethoxylates, amide ethoxylates, amine oxides, alkyl glucosides, or a mixture of two or more thereof. The anionic surfactant may be, for example, but not limited to, phosphate esters, isothionates, sulfates, sulfonates, taurates, or a mixture of two or more thereof. The amphoteric surfactant may be, for example, but not limited to, betaines, glycinates, alkylamido alkylamines, or a mixture of two or more thereof.

[0201] According to another embodiment of the present invention, the primer layer may substantially not contain a cellulose-based polymer as a dispersant.

[0202] According to another embodiment of the present invention, the primer layer may substantially not contain carboxymethylcellulose, hydroxypropylmethylcellulose or a mixture thereof as a dispersant.

[0203] According to another embodiment of the present invention, the primer layer may substantially not contain an emulsifying surfactant.

[0204] According to one embodiment of the present invention, the primer layer binder may be used without particular limitation as long as it is a known binder used in a primer layer.

[0205] According to another embodiment of the present invention, it may be preferable to use a binder that can secure stability of the primer layer over time as the primer layer binder. Specifically, the binder has a glass transition temperature (T) of 45°C or less. g ) may have. More specifically, the glass transition temperature of the binder may be -40°C to 45°C. The glass transition temperature of the binder may be, for example, -35°C to 45°C, or -30°C to 40°C, or -25°C to 35°C, or -20°C to 30°C, or -15°C to 25°C.

[0206] According to another embodiment of the present invention, the primer layer binder is, for example, styrene butadiene rubber (SBR), butadiene rubber (BR), nitrile butadiene rubber (NBR), styrene butadiene styrene block polymer (SBS), styrene ethylene butadiene block polymer (SEB), styrene-(styrene butadiene)-styrene block polymer, natural rubber (NR), isoprene rubber (IR), ethylene-propylene-diene terpolymer (EPDM), poly(ethylene-co-propylene-co-5-methylene-2-norbornene) polytetrafluoroethylene (PTFE), polyvinylidene fluoride, polyvinyl chloride, polyvinylidene fluoride-hexafluoropropylene fluoride-co-hexafluoropropylene), polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polyethylhexylacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene, polypropylene, polyethylene-co-vinyl acetate, polyethylene oxide, polypropylene oxide, polyarylate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, or two or more thereof.Specifically, the binder may include styrene butadiene rubber (SBR), nitrile butadiene rubber (NBR), polymethylmethacrylate, polyethylhexylacrylate, polybutylacrylate, or two or more thereof.

[0207] According to another embodiment of the present invention, the primer layer binder may be a mixture of one or two or more types selected from the above-described types while having the above-described glass transition temperature value.

[0208] According to another embodiment of the present invention, the binder for the primer layer may be a styrene butadiene copolymer (SBR) having a glass transition temperature (Tg) of -40°C to 45°C, a nitrile butadiene rubber (NBR) having a glass transition temperature (Tg) of -40°C to 45°C, or a mixture thereof.

[0209] According to one embodiment of the present invention, the primer layer conductive material is 10 m 2 / g to 1,400 m 2 / g of surface area. For example, the conductive material may have a surface area of ​​10 m 2 / g to 400 m 2 / g or 30 m 2 / g to 1,400 m 2 It may have a specific surface area of ​​ / g.

[0210] According to another embodiment of the present invention, the primer layer conductive material has a specific surface area of ​​30 m 2 / g to 1,400 m 2 / g and may have a spherical shape. At this time, the size of the primary particle of the conductive material having a spherical shape may be, for example, 10 nm to 100 nm, specifically 15 nm to 70 nm, but is not limited thereto.

[0211] According to another embodiment of the present invention, the primer layer conductive material has a specific surface area of ​​10 m 2 / g to 400 m 2 / g may have a tubular shape. At this time, the conductive material having a tubular shape may have a cross-sectional diameter in a direction orthogonal to the longitudinal direction of 0.1 to 3 nm, specifically 0.3 to 1.5 nm, but is not limited thereto.

[0212] The primer layer conductive material is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black-based carbon compounds such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; conductive fibers such as carbon fibers or metal fibers; metal powders such as fluorocarbon, aluminum, and nickel powders; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives may be used. However, specifically, in order to uniformly mix the conductive material and improve conductivity, the conductive material may include activated carbon, graphite, carbon black, carbon nanotubes, or a mixture of two or more thereof, and more specifically, the conductive material may include activated carbon.

[0213] According to one embodiment of the present invention, the primer layer includes the above-described composition and may have a thickness of 300 nm to 1.5 ㎛, specifically 700 nm to 1.3 ㎛, but is not limited thereto.

[0214]

[0215] According to one aspect of the present invention,

[0216] A step of preparing a mixture comprising a granule comprising a silicon-based active material, a linear conductive material, and a binder; and a fluorine-containing binder;

[0217] A step of kneading the mixture at a temperature ranging from 70°C to 200°C and under a pressure higher than atmospheric pressure to produce a mixture lump;

[0218] A step of crushing the above mixture lump to obtain a mixed powder for a cathode;

[0219] A step of forming a negative electrode film by injecting the above negative electrode mixed powder between a plurality of rolls and performing a calendaring process; and

[0220] A method for manufacturing a negative electrode according to one embodiment of the present invention is provided, including a step of attaching the negative electrode film to at least one surface of a current collector.

[0221]

[0222] According to one embodiment of the present invention, the granules are

[0223] It can be manufactured through a step of preparing a slurry by mixing the above silicon-based active material, linear conductive material, and binder with a dispersion medium; and a step of spray drying the slurry.

[0224] First, the silicon-based active material, linear conductive material, and binder are dispersed or dissolved in a dispersion medium (a solvent for the binder) to obtain a slurry in which the silicon-based active material, linear conductive material, and binder are dispersed or dissolved.

[0225] As the dispersion medium used to obtain the above slurry, water is most preferably used, but an organic solvent may also be used. Examples of the organic solvent include alkyl alcohols such as methyl alcohol, ethyl alcohol, and propyl alcohol; alkyl ketones such as acetone and methyl ethyl ketone; ethers such as tetrahydrofuran, dioxane, and diglyme; amides such as diethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone (hereinafter also referred to as NMP), and dimethylimidazolidinone; sulfur-based solvents such as dimethyl sulfoxide and sulfolane; and the like, but alcohols are preferred. When an organic solvent having a boiling point lower than water is used in combination, the drying speed during fluid granulation can be accelerated. In addition, since the dispersibility or solubility of the binder can be changed, the viscosity or fluidity of the slurry can be adjusted depending on the amount or type of the dispersion medium, thereby improving production efficiency.

[0226] The amount of dispersion medium used when preparing the above slurry may be such that the solid concentration of the slurry is usually in the range of 1 to 50 wt%, or 5 to 50 wt%, or 10 to 30 wt%.

[0227] The method or order of dispersing or dissolving the above silicon-based active material, linear conductive material, and binder in the dispersion medium is not particularly limited, and examples thereof include a method of adding the silicon-based active material, linear conductive material, and binder to the dispersion medium and mixing them, a method of dissolving or dispersing the binder in the dispersion medium, and then finally adding the silicon-based active material and linear conductive material and mixing them, etc.

[0228] According to one embodiment of the present invention, the slurry may further include another type of negative electrode active material in addition to the silicon-based active material.

[0229] Examples of the above other types of negative electrode active materials include carbon-based active materials such as non-graphitizable carbon, graphitic carbon (natural graphite, artificial graphite); Li x Fe2O3(0≤x≤1), Li xWO2(0≤x≤1), Sn x Me 1-x Me' y O z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, elements of group 1, group 2, group 3 of the periodic table, halogen; 0≤x≤1; 1≤y≤3; 1≤z≤8) and other metal composite oxides; lithium metal; lithium alloy; silicon-based alloy; tin-based alloy; metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4 and Bi2O5; conductive polymers such as polyacetylene; Li-Co-Ni-based materials, etc. According to one embodiment of the present invention, the granules may further include one or more carbon-based active materials such as natural graphite and artificial graphite.

[0230] At this time, a conductive agent other than a linear conductive agent or other additives can be optionally added to the dispersion medium.

[0231] Examples of mixing means include mixing devices such as ball mills, sand mills, bead mills, pigment dispersers, stone mills, ultrasonic dispersers, homogenizers, and planetary mixers. Mixing is usually performed at a temperature ranging from room temperature to 80°C for 10 minutes to several hours.

[0232] Next, the slurry is spray-dried to produce the initial granules.

[0233] Spray drying is a method of drying by spraying slurry into hot air. The spraying method of the device used in spray drying includes a rotating disc method and a nozzle pressurization method. The rotating disc method is a method in which the slurry is introduced almost to the center of a high-speed rotating disc, and the slurry is placed outside the disc by the centrifugal force of the disc, and then dried in the form of a mist. The rotation speed of the disc depends on the size of the disc, but is usually 5,000 rpm to 35,000 rpm, and preferably 15,000 rpm to 30,000 rpm. On the other hand, the nozzle pressurization method is a method in which the slurry is passed through a thin nozzle while being sprayed with a high-pressure fluid such as air or another liquid to form a mist and dry.

[0234] In one embodiment of the present invention, the temperature of the hot air can be controlled to 80°C to 250°C based on the reactor inlet temperature (at the time of injection) in terms of forming a granular structure with a high binder content on the surface. In one embodiment of the present invention, it can be controlled to 175°C to 220°C, or 180°C to 220°C, considering the content gradient and aspect ratio of the first binder. In the spray drying method, the method of sucking the hot air is not particularly limited, and examples thereof include a method in which the hot air and the spray direction are parallel to each other horizontally, a method in which the hot air is sprayed at the top of the drying tower and then descends together with the hot air, a method in which the sprayed droplets come into countercurrent contact with the hot air, and a method in which the sprayed droplets initially come into parallel with the hot air and then fall under gravity to come into countercurrent contact. Meanwhile, in one embodiment of the present invention, the outlet temperature of the reactor during the spray drying (the temperature of the hot air discharged from the reactor) can be controlled to 90°C to 130°C.

[0235] If the outlet temperature and / or the difference between the inlet and outlet temperatures, △T, is low, drying may not be performed properly, resulting in the formation of particles with a large amount of residual solvent, which may result in the formation of spherical particles of a uniform shape and the formation of granules that may be agglomerated or irregularly shaped. On the other hand, if the inlet temperature is too high and △T is large, overdrying may result in poor assembly and the formation of particles with an extremely small D50 and a low aspect ratio. Therefore, in order to achieve a high degree of sphericity, minimize binder agglomeration, and control the particle size to an appropriate level, it is necessary to control the inlet temperature and outlet temperature within an appropriate range.

[0236] Additionally, the surface of the result obtained by optionally spray drying, i.e., the granules, can be heat-treated to harden them. At this time, the heat treatment temperature can usually be 80°C to 300°C.

[0237] According to one embodiment of the present invention, the span value of the initial granule, expressed by the following mathematical formula, may be 0.5 to 1.5, or 0.7 to 1.3.

[0238] Span = (D90-D10) / D50.

[0239] At this time, the above D10, D50 and D90 refer to the equivalent circle diameters of the initial granules at the 10%, 50% and 90% points of the cumulative distribution of the number according to the equivalent circle diameter of the initial granules. Here, the equivalent circle diameter (CE diameter) of the initial granules refers to the diameter of a circle having the same area as the two-dimensional image of the initial granules.

[0240] The span value of the above equation is an indicator showing the distribution ratio (particle size distribution) of the equivalent circle diameter of the initial granules. That is, it is about the proportion in which the initial granules with different equivalent circle diameters are composed. If the composition ratio of the initial granules having an equivalent circle diameter smaller than the average equivalent circle diameter and the initial granules having an equivalent circle diameter larger than the average equivalent circle diameter is high, the span value is higher than 1, and if the initial granules are composed only of the initial granules having the same average equivalent circle diameter, the span value is 0. That is, the smaller the span value of the above equation, the narrower the width of the equivalent circle diameter distribution of the initial granules is.

[0241] The above initial granules may have an aspect ratio of 0.5 to 1.0. The aspect ratio refers to the ratio of the average major axis length to the average minor axis length of the granules.

[0242] At this time, the average short axis length represents the average value of the length in the direction of the axis having the shortest length of the initial granules, and the average long axis length represents the average value of the length in the direction of the axis having the longest length of the initial granules. When the aspect ratio of the initial granules satisfies this range, the granules have sufficient fluidity, which is advantageous.

[0243]

[0244] The method for manufacturing the cathode of the present invention using the aforementioned granules will be examined step by step below.

[0245] First, a mixture is prepared, which includes a granule comprising a silicon-based active material, a linear conductive agent, and a binder; and a fluorine-containing binder. Optionally, the mixture may further include other necessary additives, such as an additional binder, an additional conductive agent, or a filler.

[0246] At this time, the mixing for manufacturing the mixture is performed so that the granules and the fluorine-containing binder, optionally an additional conductive agent or other necessary additives (fillers, etc.) can be uniformly distributed, and since they are mixed in powder form, as long as they enable simple mixing thereof, there is no limitation and they can be mixed by various methods. However, since the negative electrode film of the present invention is manufactured by a dry manufacturing method that does not use a dispersion medium, the mixing can be performed by dry mixing, and can be performed by putting the materials into a device such as a blender.

[0247] In addition, the above mixture can be prepared by mixing in a mixer at 5,000 rpm to 20,000 rpm for 30 seconds to 5 minutes, specifically at 10,000 rpm to 15,000 rpm for 30 seconds to 3 minutes, to ensure uniformity.

[0248] As described above, the fluorine-containing binder is not particularly limited as long as it can be microfiberized by the step of manufacturing the mixed powder for the negative electrode. The microfiberization refers to a process of dividing a polymer into small pieces and can be performed using, for example, mechanical shear force. Specific examples of such fiberizable fluorine-containing binders may include polytetrafluoroethylene (PTFE), etc.

[0249] In addition, according to one embodiment of the present invention, the negative electrode active material layer may further include at least one of a PVdF-based copolymer such as PVdF (polyvinylidene fluoride), PVdF-HFP (polyvinylidene fluoride-co-hexafluoropropylene), and a fluoroelastomer such as an FKM-based copolymer as an additional binder.

[0250] The above additional binder may further include at least one of PVdF (polyvinylidene fluoride); PVdF-based copolymers such as PVdF-HFP (polyvinylidene fluoride-co-hexafluoropropylene); fluoroelastomers such as FKM-based copolymers; and olefin-based polymers such as polyethylene and polypropylene.

[0251] The additional conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and examples thereof include graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; activated carbon; conductive fibers such as carbon fiber or metal fiber; metal powder such as fluorinated carbon, aluminum, and nickel powder; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0252] The above filler can play a role in suppressing expansion of the electrode, and the filler is not particularly limited as long as it is a fibrous material that does not cause a chemical change in the battery, and for example, a fibrous material such as glass fiber or carbon fiber can be used.

[0253] The above mixing step may be carried out in a one-step manner in which the above-mentioned granules, fluorine-containing binder, optionally added additional binder, additional conductive agent, or other necessary additives are mixed at once. The above mixing step may also be carried out in a two-step manner in which the above-mentioned granules, additional binder (PVDF, PE, etc.), additional conductive agent, or other necessary additives are first mixed, and then polytetrafluoroethylene as a fluorine-containing binder is mixed thereto.

[0254] Next, the mixture is kneaded at a temperature ranging from 70°C to 200°C and under a pressure higher than normal pressure to produce a mixture lump.

[0255] In conventionally known techniques, high-shear mixing, such as in a jet mill, is performed to fiberize a fluorine-containing binder. However, problems arise in that the active material is finely divided by the mixing and the formed fibers may be cut. In the present invention, the above problems are solved by a low-shear kneading method rather than high-shear mixing.

[0256] The above mixing is not limited to a specific method. In a specific embodiment of the present invention, the mixing may be performed using a kneader, for example.

[0257] This mixing is a step in which the fluorine-containing binder is fiberized and the granules and optionally additional conductive material or other necessary additives are combined or linked to form a mixture mass having a solid content of 100%.

[0258] Specifically, the mixing can be controlled at a speed of 10 rpm to 100 rpm. For example, the mixing can be controlled at a speed of 20 rpm or more or 70 rpm or less within the above range. The mixing can be performed for 1 minute to 30 minutes. For example, the mixing can be performed at a speed of 40 rpm to 70 rpm within the above range for 3 minutes to 10 minutes. Meanwhile, the mixing can be controlled at a shear rate in the range of 10 / s to 500 / s. In one specific embodiment of the present invention, the mixing can be performed for 1 minute to 30 minutes, and the shear rate can be controlled in the range of 30 / s to 100 / s.

[0259] Additionally, this mixing step 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.

[0260] More specifically, the mixing can be performed at a temperature ranging from 70°C to 200°C, specifically, from 90°C to 150°C.

[0261] If the process is performed at a low temperature outside the above temperature range, the fiberization and lump formation by kneading of the fluorine-containing binder during kneading are not performed well, so film formation is not easily performed during calendaring, and if the process is performed at too high a temperature, the fiberization of the fluorine-containing binder occurs rapidly and thereafter, there is a problem that the already formed fibers may be cut by excessive shear force, which is not preferable.

[0262] In addition, it can be performed under a pressure higher than atmospheric pressure, specifically under a pressure of 1 to 100 atm, and more specifically under a pressure of 10 to 80 atm. When the above pressure range is satisfied, the problem of excessive shear force and pressure being applied, which may cause the formed fibers to break or the density of the mixture mass to become too high can be prevented. That is, according to the present invention, when a low-shear mixing process is performed under conditions of high temperature and pressure higher than atmospheric pressure instead of high-shear mixing, the intended effect of the present invention can be achieved.

[0263] Next, the above mixture lump is pulverized to obtain a mixed powder for the cathode.

[0264] Specifically, the mixture lump manufactured through the above mixing may be directly calendered, but in this case, the mixture lump may have to be pressed to manufacture it into a thin film form, and thus, a problem may arise in that the density of the film becomes too high or a uniform film cannot be obtained. Therefore, according to the present invention, the manufactured mixture lump undergoes the above pulverizing step.

[0265] At this time, the grinding step is not limited, but can be performed with a device such as a blender or grinder, and the grinding step can be specifically performed at a speed of 5,000 rpm to 20,000 rpm for 30 seconds to 5 minutes, and specifically at a speed of 10,000 rpm to 18,000 rpm for 30 seconds to 2 minutes.

[0266] When the above grinding speed and time are satisfied, sufficient grinding can be achieved to form powder of a size suitable for filming, and the problem of excessive fine particles being generated in the mixture mass can be prevented. If necessary, a classification process can be performed to filter out powder exceeding a certain size or powder below a certain size.

[0267] Next, the above-mentioned mixed powder for the negative electrode is fed between a plurality of rolls and subjected to calendaring processing to form a negative electrode film.

[0268] Referring to FIGS. 2A and 2B, a process (100) for forming a film for an electrode is performed by placing a plurality of rolls (110) spaced apart from each other, inserting the electrode mixed powder (120) obtained in the previous step between the adjacent rolls (100), and rotating the rolls (100) in an facing direction so that the mixed powder (120) is rolled and formed into a sheet or film through a powder sheeting step, and then, through a plurality of calenderings, a film for an electrode having a final target thickness can be obtained. Only one calendering is illustrated in FIGS. 2A and 2B, and a plurality of rolls can be further arranged to perform a plurality of calenderings.

[0269] Specifically, such calendaring may be a step of processing the mixed powder for the cathode into a film form, for example, manufacturing it into a film form with an average thickness of 50 ㎛ to 300 ㎛.

[0270] At this time, the calendaring can be performed, for example, by a roll that exists face to face, and at this time, the roll temperature can be 50°C to 200°C, and the rotation speed ratio of the roll can be controlled in the range of 1.0 to 3.0.

[0271] By proceeding to this calendering step, a dry cathode film capable of functioning as a cathode layer can be manufactured. Such cathode films are also conventionally referred to as free-standing films.

[0272] The cathode film manufactured in this manner does not contain a solvent, has almost no fluidity, and is thus easy to handle and can be processed into a desired shape to be used in manufacturing various types of cathodes. Furthermore, the manufacturing process of the cathode film according to one embodiment of the present invention can omit the drying process for solvent removal, thereby significantly improving the manufacturing processability of the cathode layer and resolving problems such as breakage of the active material or disconnection of the fiberized binder, which were problems in the manufacturing of existing dry electrodes.

[0273]

[0274] Afterwards, the above-mentioned negative electrode film is attached (laminated) to at least one surface of the current collector.

[0275] The negative electrode film manufactured in the previous process is attached (laminated) to at least one surface of the current collector.

[0276] According to one embodiment of the present invention, after manufacturing a negative electrode film, it may be subjected to a separate lamination step with a current collector in a free-standing film state.

[0277] Alternatively, according to one embodiment of the present invention, a lamination roll may be placed directly in contact with (or spaced apart from) the end of the roll on which the film is manufactured in the calendaring process, so that the step of laminating the current collector directly without a free-standing film section may be performed. In the latter case of performing the step of laminating the current collector directly without a free-standing film section, other auxiliary devices, such as a predetermined tension control mechanism, may be omitted in order to smoothly transport the negative electrode film (free-standing film) manufactured through the calendaring process to the lamination step.

[0278] In the method of manufacturing a negative electrode film, which is a free-standing film as described above, and then performing a separate lamination step, the negative electrode film can be cut to a desired width before being attached to the current collector.

[0279] The above lamination step may be a step of rolling and attaching the negative electrode film obtained in the previous step to a predetermined thickness on a current collector. The lamination step may be performed using a lamination roll, and at this time, the lamination roll may be maintained at a temperature of 25 to 250°C.

[0280] According to one embodiment of the present invention, the compression ratio of the negative electrode film in the lamination step may be 10 to 50%, or 20 to 50%, or 30 to 50%.

[0281] The compression ratio of the above cathode film can be defined as the ratio of the thickness to which the cathode film is compressed at the moment of lamination, and can be expressed by the following equation 1.

[0282] [Formula 1]

[0283] Compression ratio (%) = T p / T1Х 100

[0284] In equation 1,

[0285] T p In the lamination step, it refers to the pressing thickness of the negative electrode film,

[0286] T1 refers to the thickness of the cathode film before the lamination step.

[0287] By controlling the compression ratio in the above lamination step to satisfy a specific range, it is possible to provide an appropriate density and porosity of the negative electrode film and excellent adhesion between the negative electrode film and the current collector.

[0288] When the compression ratio of the above negative electrode film satisfies the range of 10 to 50%, the pressure applied to the negative electrode film is sufficient to improve the adhesive strength between the negative electrode film and the current collector, the problem of the negative electrode film being peeled off from the current collector after the lamination process can be prevented, and the problem of the density of the negative electrode film being increased more than necessary, resulting in a lower porosity than the target porosity or damage to the current collector can be resolved.

[0289] Additionally, the rolling ratio of the cathode film that has undergone the lamination step may be in the range of 20% or less, or 18% or less, or 15% or less, or 5% to 15%, or 6% to 15%, or 7% to 15%, or 9% to 13%.

[0290] Here, the rolling ratio can be defined as the ratio of the thickness of the negative electrode film after the lamination step to the thickness of the negative electrode film before the lamination step, and can be expressed by Equation 2 below.

[0291] [Formula 2]

[0292] Rolling rate (%) = (T1-T2) / T1Х100

[0293] In the above equation 2,

[0294] T1 refers to the thickness of the cathode film before the lamination step,

[0295] T2 represents the thickness of the cathode film after the lamination step.

[0296] When the above rolling ratio satisfies the above-described range, it is possible to achieve an appropriate density and porosity of the negative electrode film and an adhesive strength between the negative electrode film and the current collector.

[0297] Figure 3 is a schematic diagram of a step of laminating a negative electrode film on both sides of a current collector according to one embodiment of the present invention. That is, the lamination step (200) can ultimately obtain a negative electrode (240) by rolling and attaching the negative electrode film (230) obtained in the previous step to a predetermined thickness on a current collector (220) using a pair of lamination rolls (210).

[0298]

[0299] According to one aspect of the present invention, an electrochemical device comprising the aforementioned cathode is provided. The electrochemical device includes any device that undergoes an electrochemical reaction, and specific examples thereof include capacitors such as all types of primary batteries, secondary batteries, fuel cells, solar cells, or supercapacitor devices. In the present invention, the electrochemical device may preferably be a secondary battery, and more preferably, a lithium-ion secondary battery.

[0300] According to another embodiment of the present invention, a secondary battery is provided, in which an electrode assembly including the aforementioned negative electrode, positive electrode, and separator is housed in a battery case (cylindrical case, square case, pouch, etc.) together with a lithium-containing non-aqueous electrolyte, and an energy storage device including the secondary battery as a unit battery. The secondary battery may more preferably be a lithium-ion secondary battery.

[0301] The above positive electrode comprises a positive electrode current collector, and a positive electrode active material layer positioned on the positive electrode current collector, containing a positive electrode active material, a positive electrode conductive material, and a positive electrode binder, and in which the positive electrode binder is fiberized to bind the positive electrode active material and the positive electrode conductive material.

[0302] The positive electrode of the present invention comprises a fiberized binder as a means for binding the positive electrode active material and the positive electrode conductive material in the positive electrode active material layer. This fiberized binder exhibits less breakage than conventional non-fiberized binders and has excellent longitudinal stretchability, thereby significantly improving the flexibility of the positive electrode active material layer and the positive electrode itself including the same. The fiberization process of the binder will be discussed in detail in the positive electrode manufacturing method described below.

[0303] The above cathode active material is not limited to a lithium transition metal oxide or a lithium metal iron phosphate, as long as it is in the form of a metal oxide, and for example, a layered compound such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; chemical formula Li 1+x Mn 2-x Lithium manganese oxides such as O4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, Cu2V2O7; chemical formula LiNi 1-x M x Ni-site type lithium nickel oxide represented by O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga and x = 0.01 to 0.3); chemical formula LiMn 2-x M x Lithium manganese complex oxides represented by O2 (wherein, M = Co, Ni, Fe, Cr, Zn or Ta, and x = 0.01 to 0.1) or Li2Mn3MO8 (wherein, M = Fe, Co, Ni, Cu or Zn); Li where some of the Li in the chemical formula is replaced by aluminum ions. 1+x (Ni a Co b Mn c Al d ) 1xO2(x = 0 ~ 0.03, a = 0.3 ~ 0.95, b = 0.01 ~ 0.35, c = 0.01 ~ 0.5, d = 0.001 ~ 0.03, a+b+c+d=1); lithium metal phosphate LiMPO4 (wherein, M is M = Fe, CO, Ni, or Mn); disulfide compounds; Fe2(MoO4)3, etc., but are not limited thereto.

[0304] The above-mentioned positive electrode conductive material is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black; conductive fiber such as carbon fiber or metal fiber; metal powder such as fluorocarbon, aluminum, nickel powder; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxide such as titanium oxide; conductive materials such as polyphenylene derivatives, etc. may be used. However, specifically, in order to uniformly mix the conductive material and improve conductivity, the positive electrode conductive material may include at least one selected from the group consisting of activated carbon, graphite, carbon black, and carbon nanotubes, and more specifically, the positive electrode conductive material may include activated carbon.

[0305] The positive electrode binder may include polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HEP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyacrylic acid, polymethacrylic acid, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene (PTFE), polyethylene oxide (PEO), polyethylene, polypropylene, polyacrylic acid, styrene butylene rubber (SBR), fluoroelastomer, or two or more thereof.

[0306] According to one embodiment of the present invention, the content of the positive electrode active material may be 85 to 98 parts by weight, the content of the positive electrode conductive material may be 0.5 to 5 parts by weight, and the content of the positive electrode binder may be 0.5 to 10 parts by weight. In addition, the content of the positive electrode active material may be 90 to 98 parts by weight, the content of the positive electrode conductive material may be 0.5 to 5 parts by weight, and the content of the positive electrode binder may be 0.5 to 5 parts by weight.

[0307] The above separator may be a conventional porous polymer film used as a conventional separator, for example, a porous polymer film made of a polyolefin polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, which may be used alone or in a laminated manner. In addition, an insulating thin film having high ion permeability and mechanical strength may be used. The separator may include a safety reinforced separator (SRS) in which a ceramic material is thinly coated on the surface of the separator. In addition, a conventional porous non-woven fabric, for example, a non-woven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used, but is not limited thereto.

[0308] The above electrolyte solution includes a lithium salt as an electrolyte and an organic solvent for dissolving the same.

[0309] The above lithium salt can be used without limitation as long as it is one commonly used in electrolytes for secondary batteries, and for example, the anion of the above lithium salt is F - , Cl - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C -, (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - One type selected from the group consisting of can be used.

[0310] As the organic solvent included in the above electrolyte, any commonly used one can be used without limitation, and representative examples thereof include at least one selected from the group consisting of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, methylpropyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite, and tetrahydrofuran.

[0311] In particular, among the above carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents with high dielectric constants and thus can be preferably used because they easily dissociate lithium salts in the electrolyte. In addition, when a low-viscosity, low-dielectric constant linear carbonate such as dimethyl carbonate and diethyl carbonate is mixed and used in an appropriate ratio with these cyclic carbonates, an electrolyte having high electrical conductivity can be produced, so that the electrolyte can be used even more preferably.

[0312] Optionally, the electrolyte stored according to the present invention may further include additives such as an overcharge prevention agent included in a conventional electrolyte.

[0313] According to one embodiment of the present invention, a lithium secondary battery is formed by placing a separator between a positive electrode and a negative electrode to form an electrode assembly, placing the electrode assembly in, for example, a pouch, a cylindrical battery case, or a square battery case, and then injecting an electrolyte to complete the secondary battery. Alternatively, the electrode assembly may be laminated, then impregnated with an electrolyte, and the resulting product may be placed in a battery case and sealed to complete the lithium secondary battery.

[0314]

[0315] At this time, since the specific structure of the secondary battery and energy storage device is known in the past, a description thereof is omitted in this specification.

[0316]

[0317] Hereinafter, the present invention will be described in detail with examples to specifically illustrate it. However, the examples according to the present invention may be modified in various ways, and the scope of the present invention should not be construed as being limited to the examples described below. These examples are provided to more fully explain the present invention to those of average skill in the art.

[0318]

[0319] [Example 1]

[0320] (1) Preparation of granules

[0321] As a silicon-based active material, SiO (average particle diameter (D50): 17㎛), as a linear conductive material, single-walled carbon nanotubes (SWCNTs) and a dispersant for SWCNTs (PVP (polyvinylpyrrolidone), K90 grade)), as a binder (binder for granules), styrene-butadiene rubber (SBR, SBR copolymer containing styrene and butadiene, LG Chemical) and acrylamide-acrylate copolymer (acrylamide (AM): acrylic acid (AA): acrylonitrile (AN) = molar ratio 60:30:10), and as a dispersant, carboxymethyl cellulose (CMC, Daicel2200) were mixed with water as a dispersion medium in a weight ratio of 91:1.6:2.4:2:2:1, and a composition having a viscosity of about 9000 cPs was manufactured through a homogenizer. At this time, the solid content in the composition was 26.4 wt%.

[0322] At this time, single-wall carbon nanotubes (SWCNTs) were introduced in the form of a dispersion, and the dispersion contained single-wall carbon nanotubes (SWCNTs), a dispersant for SWCNTs, and water as a dispersion medium.

[0323] The manufactured composition was introduced into a spray dryer with hot air under a pressure range of -40 mmH2O and dried. At this time, the conditions of the spray dryer were controlled such that the inlet temperature was 250°C, the outlet temperature was 105°C, the pressure of the two fluid nozzles of the spray dryer was 2.5 bar, and the feed rate of the spray dryer was 10 cc / min.

[0324] Half of the above dried product was sieved using an industrial sieve to remove particles larger than 150 μm, thereby obtaining granules. The D90 of the obtained granules was 35 μm.

[0325] The above granules have a central portion including a plurality of silicon-based active materials and linear conductive materials, and a surface portion including a binder (binder for granules) located outside the central portion and binding the plurality of silicon-based active materials and linear conductive materials.

[0326]

[0327] (2) Manufacturing of electrode (cathode)

[0328] Artificial graphite and natural graphite as carbon-based active materials, the obtained granules, carbon black (C65) as a conductive material for an electrode layer, and polyethylene (PE), polyvinylidene fluoride (PVDF), and polytetrafluoroethylene (PTFE) as binders for an electrode layer were placed in a blender at a weight ratio of 46.5:46.5:3.2:1.0:0.3:2.0:0.5 and mixed at 10,000 rpm for 1 minute to prepare a mixture.

[0329] At this time, the mixing step was carried out in a two-step manner by first mixing artificial graphite, natural graphite, the obtained granules, the conductive material for the electrode layer, polyethylene, and polyvinylidene fluoride, and then adding and mixing polytetrafluoroethylene.

[0330] Thereafter, the temperature of the kneader was stabilized at 140°C, and the prepared mixture was placed in the kneader, and then operated at a speed of 10 rpm for 20 minutes under a cover pressure of 50 atm to obtain a mixture lump. The mixture lump was placed in a blender, ground at 10,000 rpm for 30 seconds, and classified with a sieve having pores of 1 mm in size to obtain a mixed powder for electrodes. Thereafter, the prepared mixed powder for electrodes was placed in a wrap calender (roll diameter: 88 mm, roll temperature: 130°C) to manufacture a negative electrode film. Two sheets of the negative electrode film were placed on both sides of a copper foil (12 μm) coated with a conductive primer layer containing a mixture of carbon black and an acrylic binder in a weight ratio of 5:5, and laminated through a compression roll maintained at 130°C to manufacture a negative electrode.

[0331] At this time, in the lamination step, the compression ratio of the negative electrode film was 35.6%, and the rolling ratio of the negative electrode film was 16.4%.

[0332] At this time, the compression ratio of the cathode film is defined as the ratio of the thickness to which the cathode film is compressed at the moment of lamination, and is calculated using the following equation 1.

[0333] [Formula 1]

[0334] Compression ratio (%) = T p / T1Х 100

[0335] In equation 1,

[0336] T p In the lamination step, it refers to the pressing thickness of the negative electrode film,

[0337] T1 refers to the thickness of the cathode film before the lamination step.

[0338] In addition, the rolling rate of the above-mentioned negative electrode film is defined as the ratio of the thickness of the negative electrode film after the lamination step to the thickness of the negative electrode film before the lamination step, and is calculated using the following equation 3.

[0339] [Formula 3]

[0340] Rolling rate (%) = ((T1-T2) / T1X 100

[0341] In the above equation 3,

[0342] T1 refers to the thickness of the cathode film before the lamination step,

[0343] T2 represents the thickness ratio of the cathode film after the lamination step.

[0344] The total thickness of the final manufactured negative electrode was 175 ㎛, the thickness of the negative electrode active material layer was 81.5 ㎛, and the porosity of the negative electrode was 25.1%.

[0345] At this time, the porosity of the negative electrode was measured by subtracting the volume and weight of the current collector from the volume and weight of the negative electrode to obtain the apparent density of only the negative electrode active material layer, and the actual porosity of each negative electrode was obtained by the following relationship using the actual density calculated based on the actual density and composition of each component.

[0346] Porosity (%) = {1 - (Apparent density / Actual density)} X 100

[0347] The apparent density increase rate before and after lamination of the above negative electrode film with the current collector was 19%.

[0348] At this time, the apparent density increase rate before and after lamination of the negative electrode film with the current collector was calculated using the following equation 4, and the apparent density before and after lamination of the negative electrode film with the current collector was calculated by measuring the weight and thickness of the negative electrode film before lamination, measuring the weight and thickness of the negative electrode after lamination, and obtaining the weight and thickness of the film by subtracting the weight and thickness of the current collector.

[0349] [Formula 4]

[0350] Apparent density increase rate (%) = (D2-D1) / D1Х 100

[0351] D1 is the apparent density (g / cm) of the cathode film before the lamination step. 3 ) represents,

[0352] D2 is the apparent density (g / cm) of the cathode film after the lamination step. 3 ) is indicated.

[0353] (3) Manufacturing of anode

[0354] Li[Ni as a cathode active material 0.88 Co 0.07 Mn 0.04 ]Al 0.01 O2), a pre-dispersed solution of carbon black as a cathode conductive material and polyvinylidene fluoride (PVdF) as a binder for cathode powder were added to the dispersion medium NMP at a weight ratio of 96.5:1.5:2, and the mixture was stirred at 3500 rpm for 1 hour using a homogenizer to prepare a cathode active material slurry. The solid content of the carbon black pre-dispersed solution was 16%, and the final solid content of the slurry was prepared as 68%. The slurry was coated on both sides of an aluminum current collector having a thickness of 12 μm, and the coated slurry was dried using a drying device equipped with a hot air blower and an IR heater to form a cathode active material layer.

[0355] Afterwards, the above-mentioned positive electrode active material layer was rolled using a roll pressing method, and the weight after drying per unit area was 590 mg / 25 cm 2A positive electrode having a positive electrode active material layer having a loading amount of was manufactured.

[0356]

[0357] (4) Manufacturing of secondary batteries

[0358] An electrode assembly was manufactured using a porous polyethylene film (thickness: 10 μm) as a separator between the previously manufactured positive and negative electrodes. After the electrode assembly was embedded in a pouch-type battery case, a liquid electrolyte containing 1 M LiPF6 dissolved in a solvent containing ethylene carbonate and ethyl methyl carbonate in a volume ratio of 1:4 was used to inject, seal, and form a pouch-type secondary battery cell.

[0359]

[0360] [Example 2]

[0361] (1) Preparation of granules

[0362] As a silicon-based active material, SiO (average particle size (D50): 17 μm), as a linear conductive material, single-walled carbon nanotubes (SWCNTs) and a dispersant for SWCNTs (PVP (polyvinylpyrrolidone), (K90 grade), as a binder (binder for granules), acrylamide-acrylate copolymer (acrylamide (AM): acrylic acid (AA): acrylonitrile (AN) = molar ratio 60:30:10), as a dispersant, carboxymethyl cellulose (CMC, Daicel2200) was mixed with water as a dispersion medium at a weight ratio of 91:1.6:2.4:4:1, and the viscosity was about 9000 cPs through a homogenizer, and at this time, the composition was prepared with a solid content of 25.7 wt%, and the granules were obtained in the same manner as in Example 1, except that the obtained granules D90 was 34㎛.

[0363]

[0364] (2) A negative electrode, a positive electrode, and a secondary battery were manufactured in the same manner as in Example 1, except that the granules obtained in Example 2 were used.

[0365]

[0366] [Example 3]

[0367] (1) Preparation of granules

[0368] Active material (artificial graphite: silicon-based active material SiO (average particle size (D50): 17㎛) = weight ratio 50:50), single-walled carbon nanotubes (SWCNT) as linear conductive material and dispersant for SWCNT (PVP (polyvinylpyrrolidone), K90 grade), styrene-butadiene rubber (SBR, SBR copolymer containing styrene and butadiene, LG Chemical product) and acrylamide-acrylate copolymer (acrylamide (AM): acrylic acid (AA): acrylonitrile (AN) = molar ratio 60:30:10) as binder (binder for granules), carboxymethyl cellulose (CMC, Daicel2200) as dispersant were mixed with water as a dispersion medium in a weight ratio of 97.9:0.3:0.45:0.5:0.5:0.35 and homogenized. Granules were obtained in the same manner as in Example 1, except that the viscosity was approximately 9000 cPs and the solid content in the composition was 50 wt%. The D90 of the obtained granules was 35 μm.

[0369]

[0370] (2) A negative electrode, a positive electrode, and a secondary battery were manufactured in the same manner as in Example 1, except that the granules obtained in Example 3 were used.

[0371]

[0372] [Example 4]

[0373] (1) Preparation of granules

[0374] As a silicon-based active material, a Si / C composite (20 parts by weight of Si supported on 100 parts by weight of amorphous carbon support, average particle diameter (D50): 16㎛), a single-walled carbon nanotube (SWCNT) as a linear conductive material and a dispersant for SWCNT (PVP (polyvinylpyrrolidone), (K90 grade), styrene-butadiene rubber (SBR, SBR copolymer containing styrene and butadiene, LG Chemical product) as a binder (binder for granules) and an acrylamide-acrylate copolymer (acrylamide (AM): acrylic acid (AA): acrylonitrile (AN) = molar ratio 60:30:10), and carboxymethyl cellulose (CMC, Daicel2200) as a dispersant were mixed with water as a dispersion medium in a weight ratio of 93:1.6:2.4:1:1:1. Granules were obtained in the same manner as in Example 1, except that a composition having a viscosity of approximately 9000 cPs and a solid content of 25.7 wt% was prepared through a homogenizer. The D90 of the obtained granules was 34 μm.

[0375]

[0376] (2) A negative electrode, a positive electrode, and a secondary battery were manufactured in the same manner as in Example 1, except that the granules obtained in Example 2 were used.

[0377]

[0378] [Comparative Example 1]

[0379] (1) Manufacturing of electrode (cathode)

[0380] Artificial graphite and natural graphite as carbon-based active materials, silicon-based active materials (SiO (average particle size (D50): 17㎛), carbon black (C65) as a conductive material for the electrode layer, and polyethylene (PE), polyvinylidene fluoride (PVDF), and polytetrafluoroethylene (PTFE) as binders for the electrode layer were placed in a blender at a weight ratio of 46.66:46.66:2.89:1.0:0.3:2.0:0.5 and mixed at 10,000 rpm for 1 minute to prepare a mixture.

[0381] At this time, the mixing step was carried out in a two-step manner by first mixing artificial graphite, natural graphite, silicon-based active material, conductive material for electrode layer, polyethylene, and polyvinylidene fluoride, and then adding and mixing polytetrafluoroethylene.

[0382] Thereafter, the temperature of the kneader was stabilized at 150°C, and the prepared mixture was placed in the kneader, and then operated at a speed of 10 rpm for 20 minutes under a cover pressure of 50 atm to obtain a mixture lump. The mixture lump was placed in a blender, ground at 10,000 rpm for 30 seconds, and classified with a sieve having pores of 1 mm in size to obtain a mixed powder for an electrode. Thereafter, the prepared mixed powder for an electrode was placed in a wrap calender (roll diameter: 88 mm, roll temperature: 130°C) to manufacture a negative electrode film. Two sheets of the negative electrode film were placed on both sides of a copper foil (12 μm) coated with a conductive primer layer containing a mixture of carbon black and an acrylic binder in a weight ratio of 5:6, and laminated through a compression roll maintained at 130°C to manufacture a negative electrode.

[0383] At this time, in the lamination step, the compression ratio of the negative electrode film was 35.6%, and the rolling ratio of the negative electrode film was 16.4%.

[0384]

[0385] (2) A positive electrode and a secondary battery were manufactured in the same manner as in Example 1, except that the negative electrode manufactured in Comparative Example 1 was used.

[0386]

[0387] Performance Evaluation

[0388] resistance

[0389] The component-specific resistance (Ω), specifically Rohm (ohm resistance) (0.1 s) and Rdiff (diffusion resistance) (30 s) of the secondary batteries manufactured in Examples 1 to 4 and Comparative Example 1 were measured, and the results are shown in Table 1 below (conditions SOC 50, 25°C, the smaller the resistance value, the better).

[0390] Specifically, the component-specific resistance measurement method was conducted through electrochemical impedance spectroscopy (EIS), which separates the component-specific resistance of a secondary battery by measuring impedance by applying micro-AC signals of different frequencies to the battery cell. Since the EIS experiment is temperature-sensitive, it was conducted in a chamber at 25℃, similar to room temperature, to minimize errors.

[0391]

[0392] Life characteristics (capacity retention after 100 cycles)

[0393] The secondary batteries manufactured in Examples 1 to 4 and Comparative Example 1 were each charged at 25°C with a constant current and constant voltage of 0.33 C to 4.2 V with a 0.5% cut-off. Thereafter, they were discharged at a constant current of 0.33 C to 2.5 V. The above charging and discharging behavior was considered one cycle, and this cycle was repeated 100 times. The capacity retention rate was calculated using the following equation.

[0394] Capacity retention = [(Capacity after 100 cycles) / (Capacity after 1 cycle (initial capacity))] X 100

[0395] The evaluation results are shown in Table 1.

[0396] Rohm(ohm resistance)(0.1s)(Ω)Rdiff(diffusion resistance)(30s) (Ω)Capacity retention rate after 100 cycles(%)Example 10.621.54389.8Example 20.6951.789.2Example 30.4751.49989.5Example 40.5271.34489.0Comparative example 10.481.287.0

[0397] Referring to Table 1, the secondary batteries of Examples 1 to 4 showed similar or slightly higher Ohm resistance and diffusion resistance than the secondary battery of Comparative Example 1, but it was confirmed that the capacity retention rate after 100 cycles was greatly improved. This difference can be considered to be due to the electrode manufacturing method and whether or not the linear conductive material was dispersed. In Examples 1 to 4, a method was applied in which a granule including a silicon-based active material and a linear conductive material was manufactured in advance and then mixed with a fluorine-containing binder to form a negative electrode active material layer, whereas in Comparative Example 1, a granule was not manufactured in advance, and a silicon-based active material was dry-mixed with a fluorine-containing binder to manufacture a negative electrode active material layer.

[0398] In Comparative Example 1, a problem occurs in which the linear conductive agent is not uniformly dispersed within the negative electrode active material layer. This can be attributed to the structural characteristics of the linear conductive agent. Since the linear conductive agent has a long and thin fiber form, it is difficult to disperse it using a dry mixing method, and as a result, it becomes difficult to form a uniform conductive network. Accordingly, in Comparative Example 1, the linear conductive agent was not added, and there is a high possibility that the conductive path will be formed unevenly within the negative electrode active material layer. On the other hand, in Examples 1 to 4, the linear conductive agent was prepared in advance in a granular form together with the silicon-based active material, so that the negative electrode active material layer was formed in a state in which the linear conductive agent was uniformly dispersed, thereby securing electrical connectivity and forming a structure in which lithium ion diffusion can occur smoothly.

[0399] The granules used in Examples 1 to 4 are not simple mixtures, but contain a binder that serves to connect and fix the silicon-based active material and linear conductive agent. Due to these structural characteristics, the linear conductive agent can be uniformly distributed on the surface of the silicon-based active material within the granules, and the binder serves to fix them, thereby forming a more stable conductive network within the negative electrode active material layer. However, since the binder within the granules is a non-conductive material, it is understood that the resistance tended to increase somewhat in Examples 1 to 4. However, since the linear conductive agent is uniformly dispersed within the granules to form a conductive network, a certain level of electrical conductivity or higher can be maintained throughout the electrode layer. Accordingly, although the internal resistance of the electrode may increase to some extent, the overall lithium ion diffusion and electron transfer can be smoothly achieved, which can have a significant impact on improving electrochemical performance.

[0400] In addition, silicon-based active materials have the characteristic of experiencing large volume expansion during the charge / discharge process, and a volume change of up to about 300% has a significant impact on the electrode structure. In the case of Comparative Example 1, since granules were not applied, there was a lack of a structural mechanism capable of suppressing the volume expansion of the silicon-based active material. As a result, the silicon-based active material particles individually expanded and contracted during the charge / discharge process, which made the electrode structure unstable and ultimately caused a rapid deterioration in cycle characteristics. On the other hand, in Examples 1 to 4, the binder in the granules played a role in connecting and fixing the silicon-based active material and the linear conductive agent, so that the volume expansion of the silicon-based active material could be effectively buffered, and a flexible conductive network was formed throughout the electrode layer in a state where the linear conductive agent was uniformly dispersed, thereby maintaining a more stable electrode structure. Thanks to these characteristics, Examples 1 to 4 secured excellent capacity retention even after 100 charge / discharge cycles, and showed the effect of improving the mechanical stability of the electrode during the charge / discharge process.

Claims

1. Including a current collector and a negative electrode active material layer positioned on at least one surface of the current collector, An anode comprising a negative electrode active material layer, a granule comprising a silicon-based active material, a linear conductive material, and a binder; and a fiberized fluorine-containing binder connecting and fixing the granules to each other.

2. In paragraph 1, The above silicon-based active material is silicon (Si), silicon oxide (SiOx (0 <x≤2), Si / C 복합체 또는 이들 중 2 이상을 포함하는 것을 특징으로 하는 음극.

3. In paragraph 1, A cathode characterized in that the linear conductive material comprises a single-walled carbon nanotube (SWCNT), a multi-walled carbon nanotube (MWCNT), a carbon nanofiber, or two or more thereof.

4. In paragraph 1, A cathode characterized in that the binder comprises at least one of a linear binder and a dot-shaped binder.

5. In paragraph 4, A cathode characterized in that the binder comprises a linear binder and a dot-shaped binder.

6. In paragraph 4, A negative electrode characterized in that the linear binder comprises an acrylate polymer, and the dot-shaped binder comprises a diene polymer, a styrene polymer, or two or more thereof.

7. In paragraph 1, A negative electrode characterized in that the granules have a central portion including a silicon-based active material and a linear conductive material; and a surface portion including a binder that binds the silicon-based active material and the linear conductive material and is located on all or part of the outer side of the central portion.

8. In paragraph 7, The content (wt%) of the binder relative to the total weight of 100 wt% of the above silicon-based active material, linear conductive material, and binder is greater in the surface portion than in the center portion of the granules, A cathode characterized in that the surface portion is an area near the surface of the granule from the surface of the granule to a predetermined depth toward the center of the granule, and the center portion is a portion other than the surface portion.

9. In paragraph 1, A negative electrode characterized in that the granules comprise 80 to 98 parts by weight of a silicon-based active material, 0.2 to 10 parts by weight of a linear conductive material, and 0.5 to 10 parts by weight of a binder.

10. In paragraph 1, A negative electrode characterized in that the above granules further contain a carbon-based active material.

11. In paragraph 1, A cathode characterized in that the fluorine-containing binder comprises polytetrafluoroethylene (PTFE).

12. In paragraph 1, A negative electrode characterized in that the negative electrode active material layer comprises 5 to 30 parts by weight of a fluorine-containing binder based on 100 parts by weight of the granules.

13. In paragraph 1, A primer layer is formed on all or part of at least one side surface of the above-mentioned collector, The above primer layer includes a primer layer binder and a primer layer conductive material, A cathode characterized in that the sum of the contents of the primer layer binder and the primer layer conductive material is 90 wt% or more based on the total weight of the primer layer.

14. A step of preparing a mixture comprising a granule comprising a silicon-based active material, a linear conductive material, and a dot-shaped binder; and a fluorine-containing binder; A step of kneading the mixture at a temperature ranging from 70°C to 200°C and under a pressure higher than atmospheric pressure to produce a mixture lump; A step of crushing the above mixture lump to obtain a mixed powder for a cathode; A step of forming a negative electrode film by injecting the above negative electrode mixed powder between a plurality of rolls and performing a calendaring process; and A method for manufacturing a negative electrode according to claim 1, comprising the step of attaching the negative electrode film to at least one surface of a current collector.

15. In paragraph 14, The above granules, A method for manufacturing a negative electrode, characterized in that it is manufactured through the steps of: preparing a slurry by mixing the above silicon-based active material, linear conductive material, and binder with a dispersion medium; and spray-drying the slurry.

16. An electrochemical device comprising a cathode according to any one of claims 1 to 13.

17. In paragraph 16, An electrochemical device characterized in that the electrochemical device is a secondary battery.

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