WO2017164701A1 - Composition for forming secondary battery cathode, and secondary battery cathode and secondary battery, which are manufactured using same - Google Patents

Abstract

The present invention provides a composition for forming a secondary battery cathode, and a secondary battery cathode and a secondary battery, which are manufactured using the same, the composition comprising a cathode active material, a conductive material, and a dispersant, wherein the conductive material contains, on the basis of the total weight of the composition for forming a cathode, 0.1-2 wt% of a carbon-based material having a specific surface area of 130 m²/g or more and an oil absorption amount of 220 mL/100 g or more, the dispersant is introduced into the conductive material so as to form a conductive material-dispersant composite, and the D₅₀ of the particle size distribution of the conductive material-dispersant composite is 0.8-1.2 μm.

Description

A composition for forming a cathode of a secondary battery, and a cathode and secondary battery for a secondary battery manufactured using the same

Citation with Related Applications

This application claims the benefit of priority based on Korean Patent Application No. 2016-0035562 dated March 24, 2016 and Korean Patent Application No. 2017-0036956 dated March 23, 2017. The contents are included as part of this specification.

Technical Field

The present invention relates to a composition for forming a cathode of a secondary battery capable of improving battery performance by increasing dispersibility of a conductive material, and a cathode and a secondary battery for a secondary battery manufactured using the same.

Fine carbon materials such as carbon black, ketjen black, fullerene, graphene or carbon nanotubes are widely used in the fields of energy, aerospace and the like due to their excellent electrical properties and thermal conductivity. However, in order to apply these fine carbon materials, the uniform dispersion should be preceded, but it has not been easy to prepare a high concentration of fine carbon material dispersion by methods such as conventional mechanical dispersion, dispersion using a dispersant, and surface functionalization.

Recently, with the development of technology and demand for mobile devices, the demand for secondary batteries as a source of energy is rapidly increasing. Among such secondary batteries, lithium secondary batteries having high energy density and voltage, long cycle life, and low self discharge rate have been commercialized and widely used.

In the lithium secondary battery, the electrodes of the positive electrode and the negative electrode are manufactured by applying an electrode forming composition prepared by mixing an electrode active material and a binder with a solvent to a current collector and then drying them. At this time, in order to secure the conductivity between the active material and the current collector, the conductive material of the fine carbon material is included in the composition for forming an electrode, and among these, the active material filling rate can be increased, and even a small amount can suppress an increase in battery internal resistance. Carbon black is widely used in that it can be.

However, since the conductive material is used as fine particles of several tens of nm level, the cohesive force is strong, and aggregation between the conductive material fine particles is likely to occur when dispersed in a solvent. Such non-uniform dispersion of the conductive material in the electrode active material layer leads to a decrease in conductivity and a decrease in output characteristics of the battery. Further, since the aggregate of the simply aggregated conductive material has a low structure holding force, the conductivity between the active materials can be degraded. In addition, since the conductive material has a large specific surface area, the binder may be adsorbed, resulting in non-uniform distribution of the binder in the active material layer and consequent decrease in adhesive strength.

On the other hand, a conductive material was previously dispersed together with a binder and a solvent to make a paste, and an electrode active material was added thereto, and stirred and mixed to solve the problem related to dispersion of the conductive material. However, in the dispersion liquid containing resin binders, such as a fluororesin and a cellulose resin, dispersion stability of electroconductive material particle was bad and sufficient effect was not acquired, for example, a conductive material particle reaggregated.

Moreover, the addition of the vinyl pyrrolidone type polymer as a dispersing agent to an electrically conductive material and a solvent has made the attempt to improve the dispersibility of an electrically conductive material, and to maintain favorable battery load characteristics and cycling characteristics through this. In this case, however, the added vinyl pyrrolidone-based polymer has a problem of impairing battery characteristics, such as insulation coating of the electrode active material or deterioration and deterioration of discharge characteristics when stored for a long time in a charged state.

In order to expand the use of the fine carbon particles in various fields including such lithium secondary batteries, it is necessary to develop a method capable of uniformly dispersing the fine carbon particles.

The first problem to be solved by the present invention is to provide a composition for forming a positive electrode of a secondary battery that can improve the battery performance by increasing the dispersibility of the conductive material and a method of manufacturing the same.

The second problem to be solved by the present invention is to provide a positive electrode and a secondary battery for a secondary battery is prepared using the composition for forming the positive electrode, the conductive material is uniformly dispersed.

According to an embodiment of the present invention to solve the above problems, comprising a cathode active material, a conductive material, and a dispersant, the conductive material has a specific surface area of 130 m ² / g or more, oil absorption amount 220 ml / 100 g or more carbon 0.1 wt% to 2 wt% of the base material based on the total weight of the composition for forming an anode, wherein the dispersant is introduced into the conductive material to form a conductive material-dispersant composite, and the conductive material-dispersant composite has a particle size distribution. It provides a composition for forming a positive electrode of a secondary battery having a D ₅₀ of 0.8 μm to 1.2 μm.

In addition, according to another embodiment of the present invention, by preparing a conductive material dispersion by milling a mixture of the conductive material and the dispersant in a solvent; And adding a positive electrode active material to the conductive material dispersion and mixing the conductive material, wherein the conductive material has a specific surface area of 130 m ² / g or more and an oil absorption amount of 220 ml / 100g or more. 0.1 wt% to 2 wt% of the conductive material dispersion, wherein the conductive material dispersion includes a conductive material-dispersant composite in which the dispersant is introduced into the conductive material, and the conductive material-dispersant composite has a D ₅₀ of a particle size distribution of 0.8 μm. It provides a method for producing a composition for forming a cathode of a secondary battery that is to 1.2㎛.

According to another embodiment of the present invention, there is provided a cathode for a secondary battery manufactured using the composition for forming a cathode of the secondary battery, and a lithium secondary battery including the same.

Other specific details of the embodiments of the present invention are included in the following detailed description.

The composition for forming a cathode of a secondary battery according to the present invention can greatly improve the performance, such as resistance characteristics, life characteristics, capacity characteristics and rate characteristics of the battery by uniformly dispersing the dispersibility conductive material in the composition.

Hereinafter, the present invention will be described in more detail to aid in understanding the present invention.

The terms or words used in this specification and claims are not to be construed as being limited to their ordinary or dictionary meanings, and the inventors may appropriately define the concept of terms in order to best describe their invention. It should be interpreted as meaning and concept corresponding to the technical idea of the present invention based on the principle that the present invention.

As high capacity and high output characteristics of secondary batteries are required, application of a highly conductive conductive material having a large specific surface area and a structure of secondary particles is required. Highly conductive conductive material is difficult to disperse uniformly by the mixing method in the conventional slurry mixing process because the cohesive force between the particles is stronger than the conventional commercially available conductive material. For example, in the case of carbon black in which primary particles are agglomerated as unit particles, conductivity is improved by developing a bonding structure of primary particles. However, in the case of carbon black having improved conductivity, the size of the primary particles is small and the surface area is large to easily form aggregates, and the oil absorption amount is high, so that dispersion is not easy. When the dispersion of the conductive material in the electrode is insufficient, the conductive material may not be properly distributed on the surface of the active material, thereby degrading the performance of the battery cell and increasing the performance variation between the cells. In addition, when the conductive material is excessively dispersed, the dispersed conductive material may be advantageously distributed on the surface of the active material, but the network formation between the conductive materials is not easy, and thus the resistance in the cell is increased.

In addition, the conductive material is contained in the form of a conductive material-dispersant composite in which the dispersant is introduced through a physical or chemical bond to the surface of the conductive material when mixed with the dispersant. The particle size distribution of the conductive material-dispersant composite formed at this time indicates the dispersibility of the conductive material in the composition.

Accordingly, in the present invention, the physical properties of the conductive material and the dispersant are controlled by combining the conductive materials and the dispersant in order to exhibit the optimum degree of dispersion in the electrode. By controlling the particle size distribution of the conductive material-dispersant composite, the dispersion of the hardly dispersible conductive material can be uniformly dispersed in the composition, and as a result, the performances such as resistance characteristics, life characteristics, capacity characteristics and rate characteristics of the battery can be greatly improved.

Specifically, the composition for forming a cathode of a secondary battery according to an embodiment of the present invention includes a cathode active material, a conductive material and a dispersant, the conductive material has a specific surface area of 130 m ² / g or more, oil absorption amount 220 ml / A carbon-based material of 100g or more is contained in an amount of 0.1% to 2% by weight based on the total weight of the composition for forming an anode, wherein the dispersant is introduced into the conductive material to form a conductive material-dispersant composite, and the conductive material-dispersant composite is D ₅₀ of the particle size distribution is 0.8 μm to 1.2 μm. In the present invention, the content of the carbonaceous material is a value based on the total weight of solids in the composition for forming an anode, unless otherwise specified.

As described above, in the composition for forming a positive electrode of a secondary battery according to an embodiment of the present invention, when D ₅₀ of the particle size distribution of the conductive material-dispersant composite satisfies the above range, the dispersibility of the conductive material is greatly improved. As a result, it is possible to improve battery performance by reducing the resistance characteristics within the electrode during electrode formation. If the D ₅₀ of the particle size distribution of the conductive material-dispersant composite is less than 0.8 μm, the conductive material may be over-dispersed, so that the conductive material network may not be easily formed between the active materials in the electrode during the formation of the anode, and as a result, the cell resistance may increase. . In addition, when the D ₅₀ of the particle size distribution of the conductive material-dispersant composite exceeds 1.2 μm, the dispersion of the conductive material is not sufficient, and the conductive material is not properly distributed on the surface of the active material, resulting in increased cell performance and inter-cell performance variation. In consideration of the optimum dispersibility of the conductive material and the remarkable improvement effect thereof, the conductive material-dispersant composite included in the anode-forming composition has a particle size distribution of D ₅₀ of 0.8 μm to 1.2 μm and D ₉₀ of 2.0 μm to It may be 5.0 μm or less.

The particle size distribution condition of the conductive material-dispersant composite is influenced by the physical properties and content of the conductive material and the dispersant, and in particular, the physical properties and content of the conductive material are greatly affected. In addition, when the amount of the conductive material included in the positive electrode forming composition is large, the dispersion may not be easy, so the difference according to the dispersion particle size may be insignificant. However, when the amount of the conductive material is less than a predetermined level, the optimum dispersion particle size according to the physical properties of the conductive material May exist.

Specifically, in the composition for forming a positive electrode of a secondary battery according to an embodiment of the present invention, the conductive material has a specific surface area (SSA) of 130 m ² / g or more, and an oil absorption amount (OAN) of 220 ml / 100g or more of carbon The base material is included in an amount of 0.1% by weight to 2% by weight based on the total weight of the composition for forming an anode.

In the present invention, "specific surface are" (SSA) of the carbonaceous material may be defined as a value measured by nitrogen adsorption method, and "Oil Absorption number (OAN)" is a liquid (oil The specific surface area and the oil absorption number may be used as a numerical value indicating the structural characteristics of the carbonaceous material or the degree of structural development. In the carbon-based material having a secondary particle structure usually formed by granulation of primary particles, it means that the smaller the size of the primary particles, the larger the specific surface area and the oil absorption of the secondary particles, the more developed the structure. In this case, while exhibiting excellent conductivity, dispersibility may be lowered. Accordingly, considering the conductivity and dispersibility in the electrode, the developmental structure in the carbon-based material should be optimized.

Specifically, in the composition for forming a cathode of a secondary battery according to an embodiment of the present invention, the conductive material includes a carbonaceous material of secondary particles made by assembling primary particles, and the carbonaceous material has a specific surface area. The 130 m ² / g or more, the oil absorption may be 220 ml / 100g or more. By having such a developed structure, it can exhibit dispersibility with better conductivity.

More specifically, the carbonaceous material has an average particle diameter (D ₅₀ ) of the primary particles of 15 nm to 35 nm, and the specific surface area of the secondary particles formed by assembling the primary particles is 130 m ² / g to 270 m ² / g, having a highly developed structure with an oil absorption amount of 220 ml / 100g to 400 ml / 100g, thereby exhibiting better conductivity and dispersibility, and in particular, three phases of the positive electrode active material and the electrolyte when applied in the positive electrode Reactivity can be improved by improving the electron supply property in an interface. If the average particle diameter of the primary particles of the carbonaceous material is less than 15 nm, or if the specific surface area and oil absorption of the secondary particles exceed 270 m ² / g and 400 ml / 100g, respectively, aggregation of the carbonaceous material may occur. In this case, dispersibility may decrease. In addition, if the average particle diameter exceeds 35 nm or the specific surface area and oil absorption of the secondary particles are less than 130 m ² / g and less than 220 ml / 100g, respectively, the primary particles are too large in size and dispersed due to the lack of structural development of the conductive material. Although it may be easy, the volume of the conductive material per weight is not small enough to cover the surface of the active material, and as a result there is a concern that the cell performance degradation and inter-cell performance deviations increase. More specifically, the average particle diameter of the primary particles of the carbonaceous material, considering the remarkable effects of the specific surface area and oil absorption of the secondary particles on the conductivity and dispersibility, D _50), and a 20nm to 35nm, and the specific surface area of the secondary particles 130 m ² / g to 270 m ² / g, oil absorption may be one of 220 ml / 100g to 400 ml / 100g.

Meanwhile, in the present invention, the average particle diameter (D ₅₀ ) of the primary particles in the carbonaceous material may be defined as the particle size based on 50% of the particle size distribution. In addition, the average particle diameter (D ₅₀ ) of the carbonaceous material can be measured using, for example, a laser diffraction method. More specifically, the carbonaceous material is dispersed in a solvent and then sold. Introduced into a laser diffraction particle size measuring device (e.g., Microtrac MT 3000) and irradiating an ultrasonic wave of about 28 kHz with an output of 60 W, and then calculating the average particle diameter (D ₅₀ ) based on 50% of the particle size distribution in the measuring device. Can be.

Specifically, the carbon-based material may be graphite such as natural graphite or artificial graphite; Carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black or thermal black; Or carbonaceous materials such as carbon fibers. More specifically, the carbonaceous material may be carbon black.

In addition, the carbon black may be classified in various ways depending on the production method and the raw materials used. Carbon black usable in the present invention may be acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, or denka black and the like, any one or a mixture of two or more may be used.

More specifically, in consideration of excellent conductivity and dispersibility in the preparation of the composition for forming the anode, the carbon black is prepared using acetylene gas, specifically, is prepared by thermal decomposition of the acetylene gas under an oxygen-free atmosphere, The average particle diameter (D ₅₀ ) may be 20 nm to 30 nm.

In addition, the carbon black may control the content of metal impurities in the carbon black through an impurity control during the manufacturing process or a purification process after manufacture, specifically, the purity may be 99.5% or more.

As an example, a lithium secondary battery degrades its life characteristics as components deteriorate due to various causes. One of the main causes is due to incorporation of metal impurities in a battery into a battery. Specifically, metal impurities such as iron (Fe) contained in the conductive material are dissolved in the electrolyte by reacting at an operating voltage range of about 3.0V to 4.5V of the lithium secondary battery, and the dissolved metal impurities are in the form of metal at the negative electrode. Is reprecipitated. The precipitated metal penetrates the separator and shorts with the positive electrode, causing a low voltage failure, and deteriorating the capacity characteristics and life characteristics of the secondary battery, thereby preventing its function as a battery. Therefore, it is important to prevent the incorporation of impurities, particularly metal impurities, in the application of the secondary battery of the conductive material. Accordingly, the carbon black usable in the present invention may be carbon black having high purity in the above range in which the content of metal impurities is removed to the maximum.

In the present invention, the content of impurities in the carbon black, particularly metal impurities, may be determined by using magnetic, X-ray diffraction (XRD), differential thermal analysis (DTA), differential scanning Differential Scanning Calorimetry (DSC), Modulated Differential Scanning Calorimetry (MDSC), Thermogravimetric Analysis (TGA), Thermogravimetric-infrared (TG-IR) Analysis and Melting Point It can be analyzed or confirmed by a method that includes one or more thermal assays, including measurements. Specifically, the content of metal impurities in carbon black can be measured through the main peak intensity of the metal impurities obtained by X-ray diffraction (XRD).

In addition, in the conductive material dispersion according to an embodiment of the present invention, the carbon black may be surface treated to increase the dispersibility in the dispersion.

Specifically, the carbon black imparts hydrophilicity by introducing an oxygen-containing functional group on the surface of the carbon black by oxidation treatment; Alternatively, hydrophobicity may be imparted by fluorination treatment or siliconization treatment on carbon black. The carbon black may be coated with a phenol resin or subjected to a mechanical chemical treatment. For example, when the carbon black is oxidized, it may be performed by heat treating the carbon black at about 500 ° C. to 700 ° C. for about 1 to 2 hours in air or under an oxygen atmosphere. However, if the surface treatment for the carbon black is excessive, since the electrical conductivity and strength characteristics of the carbon black itself may be greatly deteriorated, it may be desirable to control properly.

More specifically, the carbon black may be iodine number (iodine number) measured according to ASTM D-1510 (200 mg / g to 400 mg / g), if the iodine number of the carbon black is 200 mg / If it is less than g it may be difficult to sufficiently disperse the carbon black, if it exceeds 400 mg / g may cause a problem that the conductivity is lowered.

As used herein, the term "iodine number" is absorbed in 100 g of a sample by converting the amount of halogen absorbed into iodine when halogen is applied to a fat or fatty acid using a reaction in which a halogen is added to a double bond. The amount of iodine is expressed in g, which is used as a numerical value indicating the number of double bonds of unsaturated fatty acids in a sample. The higher the iodine number, the higher the number of double bonds.

The carbonaceous material may be included in an amount of 0.1 wt% to 2 wt% based on the total weight of solids in the composition for forming an anode. If the content of the carbon-based material is less than 0.1% by weight, the conductivity improvement effect by using the carbon-based material is insignificant, and when the content of the carbon-based material is more than 2% by weight, the dispersibility is lowered and there is a fear of lowering the cell capacity. In consideration of the remarkable improvement effect of using the carbonaceous material, the carbonaceous material may be included in an amount of 0.5% by weight to 1.5% by weight based on the total weight of solids in the composition for forming an anode.

In addition, in the composition for forming a cathode according to an embodiment of the present invention, the conductive material may further include a conventional conductive material together with the carbon-based material to improve conductivity.

Specifically, the conductive material may further include a fibrous conductive material that is easier to form a conductive network when used in combination with the carbon-based material, and easily forms a three-phase interface with the active material when the battery is applied. The fibrous conductive material may be a fibrous conductive material having an aspect ratio (a ratio of the length of the long axis passing through the center of the fibrous conductive material and the diameter perpendicular to the long axis) such as carbon nanorods or carbon nanofibers.

In addition, the length of the fibrous conductive material affects the electrical conductivity, strength, and dispersibility of the dispersion. Specifically, the longer the length of the fibrous conductive material, the higher the electrical conductivity and the strength characteristics may be, but if the length is too long, there is a fear that the dispersibility is lowered. Accordingly, the aspect ratio of the fibrous conductive material usable in the present invention may be 5 to 50,000, more specifically 10 to 15,000.

The fibrous conductive material as described above may be used in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the carbonaceous material. If the content of the fibrous conductive material is too low compared to the content of the carbonaceous material, the effect of improving conductivity due to the mixed use is insignificant, and if it exceeds 10 parts by weight, the dispersibility of the fibrous conductive material may be reduced.

In addition, during the preparation of the electrode-forming composition using a dispersant, the conductive material is dispersed in the dispersion medium in the form of a composite physically or chemically bonded to the dispersant.

Accordingly, in the present invention, the content of the repeating unit region of the structure capable of interacting with the conductive material and the repeating unit region of the structure capable of interacting with the dispersion medium when the composition for forming the anode using the conductive material is controlled is controlled. By using partially hydrogenated nitrile rubber as the dispersant, the conductive material is uniformly dispersed in the dispersion medium, and further, low viscosity can be exhibited even at the time of dispersing a high concentration of the conductive material.

Specifically, in the composition for forming a positive electrode according to an embodiment of the present invention, the dispersing agent is a repeating unit having an α, β-unsaturated nitrile-derived structure as a repeating unit region (A) of a structure capable of interacting with a carbon-based material; The repeating unit region (B) of the structure capable of interacting with the dispersion medium may include a partially hydrogenated nitrile rubber comprising a repeating unit of a conjugated diene derived structure and a repeating unit of a hydrogenated conjugated diene derived structure. The partially hydrogenated nitrile rubber may optionally further comprise additional comonomers copolymerizable under conditions such that the conductive material-dispersant composite has the above particle size distribution.

The partially hydrogenated nitrile rubber may be prepared by specifically copolymerizing α, β-unsaturated nitrile, conjugated diene and optionally other copolymerizable comonomers, followed by hydrogenation of the C = C double bond in the copolymer. In this case, the polymerization reaction process and the hydrogenation process may be performed according to a conventional method.

Specific examples of the α, β-unsaturated nitrile that can be used in the preparation of the partially hydrogenated nitrile rubber include acrylonitrile or methacrylonitrile, and one or more of these may be used.

Moreover, the conjugated diene which can be used at the time of manufacture of the said partially hydrogenated nitrile rubber can specifically mention conjugated diene of 4 to 6 carbon atoms, such as 1, 3- butadiene, isoprene, and 2, 3- methyl butadiene, Any one of these Or mixtures of two or more may be used.

Other copolymerizable comonomers which may optionally be used include, for example, aromatic vinyl monomers (for example, styrene, α-methylstyrene, vinylpyridine, fluoroethyl vinyl ether, etc.), α, β-unsaturated carboxylic acids. (Eg, acrylic acid, methacrylic acid, maleic acid, fumaric acid, etc.), esters or amides of α, β-unsaturated carboxylic acids (eg methyl (meth) acrylate, ethyl (meth) acrylate, n-dodecyl (meth) acrylate, methoxymethyl (meth) acrylate, hydroxyethyl (meth) acrylate, or polyethylene glycol (meth) acrylate), and anhydrides of α, β-unsaturated dicarboxylic acids (For example, maleic anhydride, itaconic anhydride, citraconic anhydride, etc.), but is not limited thereto.

More specifically, the partially hydrogenated nitrile rubber further comprises esters of α, β-unsaturated carboxylic acids as comonomers, such as (meth) acrylate based monomers. Examples of the (meth) acrylate monomers include methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-amyl acrylate, iso amyl acrylate, n-ethylhexyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, 2-hydroxyethyl methacrylate, or hydroxy Propyl methacrylate and the like.

In the partially hydrogenated nitrile butadiene rubber prepared according to the above method, a repeating unit of α, β-unsaturated nitrile derived structure, a repeating unit of conjugated diene derived structure, a repeating unit of hydrogenated conjugated diene derived structure and optionally The content ratio of repeating units of other copolymerizable comonomer-derived structures may vary within a wide range, in each case the total sum of repeating units of the structure is 100% by weight.

Specifically, in consideration of the improved dispersibility of the carbon-based material and the miscibility with the dispersion medium, the content of the repeating unit of the α, β-unsaturated nitrile-derived structure is 20% based on the total weight of the partially hydrogenated nitrile rubber. It may be 50% to 50% by weight, more specifically 20% to 30% by weight. When the repeating unit having an α, β-unsaturated nitrile-derived structure is included in the above content range, the dispersibility of the conductive material can be increased, and even if the amount of the conductive material added is small, high conductivity can be given.

In the present invention, the content of the repeating unit of the α, β-unsaturated nitrile-derived structure in the partially hydrogenated nitrile rubber is the weight ratio of the entire rubber of the repeating unit of the structure derived from the α, β-unsaturated nitrile. The measurement of is the median of the value which measures the amount of nitrogen which generate | occur | produced according to the mill oven method of JISK6364, converts the amount of its binding from the acrylonitrile molecular weight, and quantifies.

In addition, the partially hydrogenated nitrile rubber is 20% to 70% by weight, more specifically 20% to 50% by weight, and more specifically, the repeating unit of the hydrogenated conjugated diene-derived structure As may be included in 30% by weight to 50% by weight. By including the repeating unit of the hydrogenated conjugated diene-derived structure in the content range as described above, the miscibility to the dispersion medium can be increased to increase the dispersibility of the carbon-based material.

In addition, when the partially hydrogenated nitrile rubber further includes additional copolymerizable comonomers, the content ratio may vary depending on the type and nature of the comonomer, but specifically, the content of the repeating unit of the comonomer-derived structure may be partially hydrogenated. It may be 30% by weight or less, more specifically 10% to 30% by weight relative to the total weight of the nitrile rubber.

More specifically, the partially hydrogenated nitrile rubber includes repeating units of the structure of Formula 1, repeating units of the structure of Formula 2, and repeating units of the structure of Formula 3, and optionally, α, β-unsaturated carbon It may be an acrylonitrile-butadiene rubber (H-NBR) further comprising a repeating unit of the ester-derived structure of the acid. At this time, the content of the repeating unit of the acrylonitrile-derived structure of Formula 1 may be 20% to 50% by weight relative to the total weight of the rubber. In addition, the content of the repeating unit of the hydrogenated butadiene-derived structure of Formula 3 may be 20% to 50% by weight relative to the total weight of the rubber. In the case in which the partially hydrogenated nitrile rubber further comprises a repeating unit of α, β- unsaturated carboxylic acid ester derived from the structure, the content of the repeating unit of the α, β- unsaturated carboxylic acid ester of the structure is derived rubber The total weight may be 30% by weight or less, more specifically 10% by weight to 30% by weight.

[Formula 1]

[Formula 2]

[Formula 3]

In addition, the partially hydrogenated nitrile rubber may have a weight average molecular weight of 10,000 g / mol to 700,000 g / mol, more specifically 10,000 g / mol to 200,000 g / mol. In addition, the partially hydrogenated nitrile rubber may have a polydispersity index PDI (ratio of Mw / Mn, Mw is weight average molecular weight and Mn is number average molecular weight) in the range of 2.0 to 6.0, specifically, 2.0 to 4.0. have. When the partially hydrogenated nitrile rubber has a weight average molecular weight and a polydispersity index in the above range, the conductive material can be uniformly dispersed in the dispersion medium by satisfying the average particle size condition of the conductive material-dispersant composite.

In the present invention, the weight average molecular weight and the number average molecular weight are polystyrene reduced molecular weights analyzed by gel permeation chromatography (GPC).

Again, The partially hydrogenated nitrile rubber may have a Mooney viscosity (ML 1 + 4 at 100 ° C.) of 10 to 120, more specifically 10 to 100. The Mooney viscosity of the partially hydrogenated nitrile rubber in the present invention can be measured according to ASTM standard D 1646.

On the other hand, in the positive electrode formation composition according to an embodiment of the present invention, the positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium (lithiated intercalation compound), specifically Is a material having a hexagonal layered rock salt structure (specifically, LiCoO ₂ , LiCo _1/3 Mn _1/3 Ni _1/3 O ₂ , or LiNiO ₂ ), a material having an olivine structure (specifically, LiFePO ₄ ), A spinel material having a cubic structure (specifically, LiMn ₂ O ₄ ), and other vanadium oxides such as V ₂ O ₅ , and a chalcone compound such as TiS or MoS.

More specifically, the cathode active material may be a lithium composite metal oxide including a metal such as cobalt, manganese, nickel or aluminum and lithium. The lithium composite metal oxide is specifically, a lithium-manganese oxide (eg, LiMnO ₂ , LiMn ₂ O Etc.), lithium-cobalt-based oxides (e.g., LiCoO _2, etc.), lithium-nickel-based oxides (e.g., LiNiO _2, etc.), lithium-nickel-manganese-based oxides (e.g., LiNi _{1 - Y} Mn _Y O ₂ (where, 0 <Y <1), LiMn _2-z Ni _z O ₄ (where, 0 <z <2) and the like), lithium-nickel-cobalt-based oxide (for example, LiNi _{1- Y} Co _Y O ₂ (where, 0 <Y <1) and the like), lithium-manganese-cobalt oxide (e.g., LiCo _1-Y Mn _Y O ₂ (where, 0 <Y <1), LiMn _{2 - z} Co _z O ₄ (here, 0 <Z <2) and the like, lithium-nickel-manganese-cobalt-based oxides (eg, Li (Ni _P Co _Q Mn _R ) O ₂ (here, 0 <P <1, 0 <Q <1, 0 <R <1, P + Q + R = 1) or Li (Ni _P Co _Q Mn _R ) O ₄ (where 0 <P <2, 0 <Q <2, 0 <R <2, P + Q + R = 2) or the like, or lithium-nickel-cobalt-manganese-metal (M) oxide (for example, Li (Ni _P Co _Q Mn _R M _S ) O ₂ , where M is selected from the group consisting of Al, Cu, Fe, V, Cr, Ti, Zr, Zn, Ta, Nb, Mg, B, W and Mo, and P, Q, R and S are Each independent As an atomic fraction of phosphorus elements, 0 <P <1, 0 <Q <1, 0 <R <1, 0 <S <1, P + Q + R + S = 1) etc.) etc. are mentioned, Any one or two or more of these may be included. In particular, considering that the method for evaluating the life of the cathode active material according to the present invention is performed under severe conditions of high temperature and high voltage, it is possible to obtain a more accurate and reliable life characteristics evaluation result without fear of deterioration of the cathode active material itself. The cathode active material may be a lithium composite metal oxide having a layered structure, and more specifically, may be a lithium cobalt oxide having a layered structure.

In the lithium composite metal oxide, at least one of the metal elements except lithium is selected from the group consisting of Al, Cu, Fe, V, Cr, Ti, Zr, Zn, Ta, Nb, Mg, B, W, and Mo. It may be doped by any one or two or more elements selected. As described above, when the above metal element is further doped into the lithium composite metal oxide of the lithium defect, the structural stability of the cathode active material may be improved, and as a result, the output characteristics of the battery may be improved. In this case, the content of the doping element included in the lithium composite metal oxide may be appropriately adjusted within a range that does not lower the characteristics of the positive electrode active material, specifically, may be 0.02 atomic% or less.

More specifically, the lithium composite metal oxide may include a compound of Formula 4 below:

[Formula 4]

Li _{1 + a} Ni _x Co _y Mn _z M _w O ₂

In Formula 4, M is one containing one or two or more elements selected from the group consisting of Al, Cu, Fe, V, Cr, Ti, Zr, Zn, Ta, Nb, Mg, B, W and Mo And a, x, y, z and w are each independently atomic fractions of the corresponding elements, -0.5≤a≤0.5, 0≤x≤1, 0 <y≤1, 0≤z≤1, 0≤ w ≦ 1 and 0 <x + y + z ≦ 1.

In addition, in view of the remarkable effect of the improved use of the combination of the optimized conductive material and dispersant, the positive electrode active material is 0 <x <1, 0 <y <1, 0 <z <1 in Formula 4, It may include a compound of y + z ≤ x, more specifically, the positive electrode active material is LiNi _{0 . 6} Mn _{0 . 2} Co _{0 . 2} O ₂ , LiNi _{0 . 5} Mn _{0 . 3} Co _{0 . 2} O ₂ , LiNi _0.7 Mn _0.15 Co _0.15 O ₂ or LiNi _{0 . 8} Mn _{0 . 1} Co _{0 . 1} O _{2 and the} like, any one or a mixture of two or more thereof may be used.

In addition, the composition for forming an anode according to an embodiment of the present invention may optionally further include a binder.

The binder serves to improve adhesion between the cathode active material particles and adhesion between the cathode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), Starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber Or various copolymers thereof, and the like may be used alone or in a mixture of two or more thereof. The binder may be included in an amount of 1% to 30% by weight based on the total weight of solids in the composition for forming an anode.

The composition for forming a cathode according to an embodiment of the present invention having the above composition may be prepared by dissolving and dispersing a cathode active material, a conductive material, a dispersant and optionally a binder in a solvent by mixing. Accordingly, the positive electrode forming composition may further include a solvent.

The solvent may be used without particular limitation as long as it is usually used in the preparation of the composition for forming an anode. Specifically, the solvent is an amide polar organic solvent such as dimethylformamide (DMF), diethyl formamide, dimethyl acetamide (DMAc) or N-methyl pyrrolidone (NMP); Methanol, ethanol, 1-propanol, 2-propanol (isopropyl alcohol), 1-butanol (n-butanol), 2-methyl-1-propanol (isobutanol), 2-butanol (sec-butanol), 1-methyl Alcohols such as 2-propanol (tert-butanol), pentanol, hexanol, heptanol or octanol; Glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,5-pentanediol, or hexylene glycol; Polyhydric alcohols such as glycerin, trimetholpropane, pentaerythritol, or sorbitol; Ethylene glycol mono methyl ether, diethylene glycol mono methyl ether, triethylene glycol mono methyl ether, tetra ethylene glycol mono methyl ether, ethylene glycol mono ethyl ether, diethylene glycol mono ethyl ether, triethylene glycol mono ethyl ether, tetra ethylene glycol Glycol ethers such as mono ethyl ether, ethylene glycol mono butyl ether, diethylene glycol mono butyl ether, triethylene glycol mono butyl ether, or tetra ethylene glycol mono butyl ether; Ketones such as acetone, methyl ethyl ketone, methylpropyl ketone, or cyclopentanone; Ester, such as ethyl acetate, (gamma) -butyl lactone, (epsilon) -propiolactone, etc. are mentioned, Any one or a mixture of two or more of these may be used. More specifically, the solvent may be an amide polar organic solvent when considering the effect of improving dispersibility for the carbon black and the dispersant.

In the composition for forming a positive electrode according to an embodiment of the present invention having the configuration as described above, the content of the positive electrode active material, the conductive material, the dispersant, the solvent, and optionally the binder may improve the processability and positive electrode characteristics at the time of manufacturing the positive electrode. It may be appropriately determined depending on the like.

Specifically, the conductive material including the carbonaceous material for uniform dispersion of the conductive material in the positive electrode forming composition may be included in an amount of 0.1% to 10% by weight relative to the total weight of solids in the positive electrode forming composition. When included in the content of the above range of the conductive material can exhibit a good balance of electronic conductivity and dispersibility. If the content of the conductive material is less than 0.1% by weight out of the above range, for example, when forming the electrode of a lithium secondary battery, the composition for forming an electrode includes a large amount of organic solvent, and as a result, the voids in the electrode increase, and the active material filling rate is increased. The battery capacity can be lowered by being lowered. In addition, the drying time for removing the organic solvent may be long. Moreover, when content of an electrically conductive material exceeds 10 weight%, there exists a possibility that a dispersibility may fall. More specifically, the conductive material including the carbonaceous material may be included in an amount of 0.1% by weight to 2% by weight based on the total weight of solids in the composition for forming an anode.

In addition, the dispersant may be included in 10 parts by weight to 50 parts by weight with respect to 100 parts by weight of the conductive material. If the content of the dispersant is less than 10 parts by weight, it is difficult to uniformly disperse the conductive material in the dispersion. If the content of the dispersant is more than 50 parts by weight, the viscosity of the composition may increase, leading to a decrease in processability.

More specifically, the dispersant may be included in an amount of 0.1% to 10% by weight based on the total weight of solids in the composition for forming the positive electrode. If the content of the dispersant is less than 0.1% by weight, the effect of improving the dispersibility of the conductive material according to the use of the dispersant may be insignificant. If the content of the dispersant is more than 10% by weight, there is a concern that the capacity characteristics of the battery may be deteriorated due to the increase in the anode resistance and the decrease of the relative active material. There may be.

In addition, the cathode active material may be included in an amount of 80% by weight to 98% by weight based on the total weight of solids in the composition for forming an anode. If the content of the positive electrode active material is less than 80% by weight, the capacity characteristics may be lowered. If the content of the positive electrode active material is more than 98% by weight, the battery characteristics may be deteriorated due to the relative decrease of the content of the conductive material and the dispersant.

In addition, the solvent may be included in an amount such that the composition for forming the positive electrode has an appropriate viscosity to enable easy application and uniform coating during application of the composition for forming the positive electrode.

In addition, the positive electrode forming composition according to an embodiment of the present invention may further include a dispersion stabilizer for increasing the dispersion stability of the conductive material.

The dispersion stabilizer may prevent the agglomeration of carbon black by adsorbing the surface of the conductive material to exhibit a lapping effect surrounding the conductive material. Accordingly, the dispersion stabilizer may be excellent in affinity for the conductive material and at the same time excellent in miscibility with the dispersant and the solvent. Specifically, the dispersion stabilizer may be polyvinylpyrrolidone or the like.

In addition, the dispersion stabilizer may be a weight average molecular weight of 20,000g / mol to 5,000,000g / mol. If the molecular weight of the dispersion stabilizer is too small, less than 20,000 g / mol, it is difficult to exhibit a sufficient lapping effect for carbon black, and if the molecular weight is too large, exceeding 5,000,000 g / mol, the molecular motion of the dispersion stabilizer in the dispersion medium may be reduced. It is hard to wrap carbon black enough. More specifically, the dispersion stabilizer may have a weight average molecular weight of 70,000 g / mol to 2,000,000 g / mol.

In addition, the dispersion stabilizer may be used in 1 to 10 parts by weight with respect to 100 parts by weight of the conductive material. If the content of the dispersion stabilizer is too low compared to the content of the conductive material, it is difficult to obtain a sufficient lapping effect, and as a result, there is a fear that aggregation between the conductive materials occurs.

The composition for forming a positive electrode according to an embodiment of the present invention having the above composition comprises the steps of preparing a conductive material dispersion by milling a mixture of the conductive material and the dispersant in a solvent (step 1); And adding and mixing a cathode active material, and optionally a binder and other additives to the conductive material dispersion (step 2). At this time, the conductive material comprises a carbon-based material having a specific surface area of 130 m ² / g or more, oil absorption of 220 ml / 100 g or more of 0.1% by weight to 2% by weight relative to the total weight of solids in the composition for forming an anode, and The conductive material dispersion includes a conductive material-dispersant composite in which the dispersant is introduced into the conductive material, and the conductive material-dispersant composite has a D ₅₀ of a particle size distribution of 0.8 μm to 1.2 μm.

Hereinafter, each step will be described in more detail. A first step for preparing a composition for forming an anode according to an embodiment of the present invention is preparing a conductive material dispersion.

The conductive material dispersion may be prepared by specifically preparing a mixture by mixing the conductive material and the dispersant in a solvent and then milling it.

The mixing process may be performed by a conventional mixing or dispersing method, and specifically, may be performed by a homogenizer, a bead mill, a ball mill, a basket mill, an attention mill, a universal stirrer, a clear mixer, or a TK mixer. have.

In addition, the milling process may be performed using a conventional milling method such as a ball mill, a bead mill, a basket mill, and more specifically, a bead mill. Can be performed by

In addition, since the dispersibility of the conductive material and the dispersion particle size of the conductive material-dispersant composite may vary depending on the conditions such as the diameter and filling rate of the bead mill, the rotational speed of the rotor, the discharge speed of the conductive material dispersion during the milling process, It is preferable to carry out at the milling conditions optimized according to the kind and content of the electrically conductive material and dispersing agent used.

Specifically, in the production of a cathode active material for a secondary battery according to an embodiment of the present invention, the milling process according to the use of the conductive material and the dispersant as described above may be a diameter of the bead mill 0.5mm to 2mm, More specifically, it may be 0.7mm to 1.5mm.

In addition, the filling rate of the bead mill may be 50% to 90% by weight, and more specifically 80% to 90% by weight relative to the total weight of the conductive material dispersion.

In addition, the circumferential speed during the bead mill process may be 6 m / s to 12 m / s, more specifically 7 m / s to 12 m / s.

In addition, the discharge rate of the mixture may be 0.5 kg / min to 1.5 kg / min, more specifically 0.5 kg / min to 1 kg / min under the conditions that meet all the bead mill process conditions. When the discharge rate of the conductive material dispersion is out of the above range, the conductive material-dispersant composite particle size distribution conditions in the composition for forming an anode may not be satisfied, and as a result, the effect of the present invention may be insignificant due to the decrease in the dispersibility of the conductive material.

Next, the second step for producing a composition for forming a positive electrode according to an embodiment of the present invention is a positive electrode active material, and optionally a binder and other additives to the conductive material dispersion prepared in step 1 to add and mix the positive electrode It is a step of preparing a composition for forming.

The mixing process may be carried out by a conventional mixing or dispersing method, specifically, homogenizer, bead mill, ball mill, basket mill, attrition mill, universal stirrer, clear mixer or TK mixer Can be performed by

By the above-described manufacturing method, a positive electrode forming composition in which a positive electrode active material, a conductive material, and a dispersant is uniformly dispersed in a solvent is prepared.

In this case, the conductive material and the dispersant may be included in a dispersant is dispersed in the form of a conductive material-dispersant composite introduced into the surface of the conductive material through a physical or chemical bond. Specifically, the conductive material-dispersant composite may have a distribution in which D ₅₀ of the particle size distribution is 0.8 μm to 1.2 μm and D ₉₀ is 2.0 μm to 5.0 μm or less.

The particle size distributions D ₅₀ and D ₉₀ of the conductive material-dispersant composite may be defined as particle diameters based on 50% and 90% of the particle size distribution, respectively. In addition, the particle size distribution D ₅₀ of the complex can be measured using, for example, a laser diffraction method, and more specifically, a commercially available laser diffraction particle size measuring apparatus after dispersing the complex in a solvent. after examining the ultrasound of about 28kHz is introduced (for example Microtrac MT 3000) to the output 60 W, it is possible to calculate the average particle diameter (D ₅₀₎ of from 50% based on the particle size distribution of the measuring device.

As described above, the composition for forming an anode according to the exemplary embodiment of the present invention is a uniform dispersion of a conductive material having excellent conductivity, and thus may exhibit excellent conductivity throughout the electrode when manufacturing the electrode. In addition, performance such as capacity characteristics and rate characteristics can be greatly improved.

Accordingly, according to another embodiment of the present invention, a positive electrode manufactured using the positive electrode forming composition is provided. In the present invention, that the positive electrode is manufactured using the positive electrode forming composition described above means that the positive electrode forming composition, a dried material thereof, or a cured product thereof is included.

The positive electrode according to an embodiment of the present invention may be manufactured according to a conventional method except for forming a positive electrode active material layer using the positive electrode forming composition. Specifically, the positive electrode is applied to the positive electrode current collector and the composition for forming the positive electrode and dried; Alternatively, the composition for forming the cathode may be cast on a separate support, and then the film obtained by peeling from the support may be manufactured by laminating on a cathode current collector.

Specifically, the positive electrode manufactured according to the above-described manufacturing method includes a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector, in which a composite of a conductive material-dispersant is uniformly dispersed.

In addition, the positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or carbon on the surface of aluminum or stainless steel Surface treated with nickel, titanium, silver, or the like may be used. In addition, the current collector may have a thickness of typically 3 μm to 500 μm, and may form fine irregularities on the surface of the current collector to increase adhesion of the positive electrode active material. For example, it can be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven body.

According to another embodiment of the present invention, an electrochemical device including the anode is provided. The electrochemical device may be specifically a battery, a capacitor, or the like, and more specifically, a lithium secondary battery.

The lithium secondary battery specifically includes a positive electrode, a negative electrode positioned to face the positive electrode, a separator and an electrolyte interposed between the positive electrode and the negative electrode, and the positive electrode is as described above. The lithium secondary battery may further include a battery container for accommodating the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member for sealing the battery container.

The negative electrode includes a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector. The negative electrode active material layer may include at least one of a negative electrode active material and optionally a binder, a conductive material, and other additives.

The negative electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, including carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; Metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys or Al alloys; Metal oxides capable of doping and undoping lithium such as SiO _x (0 <x <2), SnO ₂ , vanadium oxide, lithium vanadium oxide; Or an anode active material such as a composite including the metallic compound and a carbonaceous material, such as a Si-C composite or a Sn-C composite, and any one or a mixture of two or more thereof may be used. In addition, a metal lithium thin film may be used as the anode active material. As the carbon material, both low crystalline carbon and high crystalline carbon can be used. Soft crystalline carbon and hard carbon are typical low crystalline carbon, and high crystalline carbon is amorphous, plate, scaly, spherical or fibrous natural graphite or artificial graphite, Kish graphite (Kish) graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar pitch High-temperature calcined carbon such as derived cokes is typical.

In addition, the binder and the conductive material are the same as described above for the positive electrode.

On the other hand, in the lithium secondary battery, the separator is to separate the negative electrode and the positive electrode and to provide a passage for the movement of lithium ions, if it is usually used as a separator in a lithium secondary battery can be used without particular limitation, in particular to the ion movement of the electrolyte It is desirable to have a low resistance against the electrolyte and excellent electrolytic solution-moisture capability. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer or the like Laminate structures of two or more layers may be used. In addition, conventional porous nonwoven fabrics such as nonwoven fabrics made of high melting point glass fibers, polyethylene terephthalate fibers and the like may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may be optionally used as a single layer or a multilayer structure.

In addition, examples of the electrolyte used in the present invention include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, and the like, which can be used in manufacturing a lithium secondary battery. It doesn't happen.

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

The organic solvent may be used without particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may be an ester solvent such as methyl acetate, ethyl acetate, γ-butyrolactone or ε-caprolactone; Ether solvents such as dibutyl ether or tetrahydrofuran; Ketone solvents such as cyclohexanone; Aromatic hydrocarbon solvents such as benzene and fluorobenzene; Dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate, Carbonate solvents such as PC) and the like.

Of these, carbonate-based solvents are preferable, and cyclic carbonates having high ionic conductivity and high dielectric constant (for example, ethylene carbonate or propylene carbonate) that can improve the charge and discharge performance of a battery, and low viscosity linear carbonate compounds ( For example, a mixture of ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate and the like is more preferable.

In addition, the lithium salt may be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt is LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAl0 ₄ , LiAlCl ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (C ₂ F ₅ SO ₃ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ . LiCl, LiI, or LiB (C ₂ O ₄ ) ₂ and the like can be used. The lithium salt is preferably included at a concentration of approximately 0.6 mol% to 2 mol% in the electrolyte.

In addition to the electrolyte components, the electrolyte includes, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity. -Glyme, hexaphosphate triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2 One or more additives such as -methoxy ethanol or aluminum trichloride may be included. In this case, the additive may be included in an amount of 0.1% to 5% by weight based on the total weight of the electrolyte.

The lithium secondary battery having the above configuration may be manufactured by manufacturing an electrode assembly through a separator between a positive electrode and a negative electrode, placing the electrode assembly inside a case, and then injecting an electrolyte solution into the case. Alternatively, the electrode assembly may be stacked, and then impregnated in the electrolyte, and the resultant may be manufactured by sealing it in a battery case.

As described above, the lithium secondary battery including the cathode manufactured by using the composition for forming a cathode according to an embodiment of the present invention may stably exhibit excellent discharge capacity, output characteristics, and capacity retention rate due to uniform dispersion of the conductive material in the cathode. have. As a result, it is useful for portable devices, such as a mobile telephone, a notebook computer, a digital camera, and the electric vehicle field | area, such as a hybrid electric vehicle (HEV).

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

The battery module or the battery pack is a power tool (Power Tool); Electric vehicles including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); Or it can be used as a power source for any one or more of the system for power storage.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily practice the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

Example  One

In the N-methylpyrrolidone (NMP) solvent, carbon black (SSA = 135m ² / g, OAN = 220ml / 100g) shown in Table 1 below as a conductive material, and partially hydrogenated nitrile rubber shown in Table 2 below as a dispersant were added. After mixing to the composition ratio shown in Table 3, the bead milling process was performed under the following conditions to prepare a conductive material dispersion.

Since the conductive material dispersion prepared LiNi _{0 . 7} Co _{0 . 15} Mn _{0 . 15} O ₂ (average particle diameter (D ₅₀ ) = 10 μm) and polyvinylidene fluoride (PVdF) were added, and mixed for 1 hour using a homo mixer to prepare a composition for forming an anode.

<Milling process conditions>

Rotor diameter: 150 mm

Rotor speed 1000rpm

Rotor speed: 7.9 m / s

Bead diameter: 1.25mm

Bead filling rate: 80% by weight

Discharge Rate: 1kg / min

Example  2

In the same manner as in Example 1, except that each component is used in the formulations described in Tables 1 to 3, and the discharge rate is 0.5 kg / min during the bead milling process for preparing the conductive material dispersion. It carried out to manufacture the composition for positive electrode formation.

Example  3

In the same manner as in Example 1, except that each component is used in the formulations described in Tables 1 to 3, and the discharge rate is 1.2 kg / min in the bead milling process for preparing the conductive material dispersion. It carried out to manufacture the composition for positive electrode formation.

Comparative example  One

In the same manner as in Example 1 except that each component is used in the formulations described in Tables 1 to 3 below, and the discharge rate is 2 kg / min during the bead milling process for preparing the conductive material dispersion. To prepare a composition for forming an anode.

Comparative example  2

In the same manner as in Example 1, except that each component is used in the formulations described in Tables 1 to 3, and the discharge rate is 0.3 kg / min during the bead milling process for preparing the conductive material dispersion. It carried out to manufacture the composition for positive electrode formation.

Comparative example  3

Except for using each of the components in the formulation described in Tables 1 to 3, was carried out in the same manner as in Example 1 to prepare a composition for forming a positive electrode.

Comparative example  4

Each component was used in the formulations described in Tables 1 to 3, except that polyvinyl alcohol (PVA) was used as the dispersant, and the composition for forming the anode was prepared in the same manner as in Example 1. .

	Conductive material
	Kinds	Primary particle average particle diameter (nm)	Secondary Particle SSA (m 2 / g)	OAN (ml / 100g)
Example 1	Carbon black	30	135	220
Example 2	Carbon black	22	230	362
Example 3	Carbon black	26	170	272
Comparative Example 1	Carbon black	30	135	220
Comparative Example 2	Carbon black	30	135	220
Comparative Example 3	Carbon black	36	63	190
Comparative Example 4	Carbon black	30	135	220

	Partially Hydrogenated Nitrile Rubber Dispersant
	AN (% by weight)	BD (% by weight)	HBD (% by weight)	BA (% by weight)	Mw (x 1000 g / mol)	PDI
Example 1	21	One	50	28	300	3.1
Example 2
Example 3
Comparative Example 1
Comparative Example 2
Comparative Example 3

In Table 2, AN is a repeating unit of acrylonitrile-derived structure in partially hydrogenated nitrile rubber, BD is a repeating unit of butadiene-derived structure, HBD is a repeating unit of hydrogenated butadiene-derived structure, and BA is n-butylacryl It means the repeat unit of the rate-derived structure, the weight percent content of the repeat unit of each structure is a value based on the total weight of the partially hydrogenated nitrile rubber.

	Composition for Anode Formation (parts by weight)
	Cathode active material	Conductive material	Dispersant	bookbinder
Example 1	96.67	2.0	0.2	1.13
Example 2	97.34	1.3	0.23	1.13
Example 3	97.05	1.6	0.22	1.13
Comparative Example 1	96.67	2.0	0.2	1.13
Comparative Example 2	96.67	2.0	0.2	1.13
Comparative Example 3	96.67	2.0	0.2	1.13
Comparative Example 4	96.67	2.0	0.2	1.13

Production Example  : Fabrication of positive electrode and lithium secondary battery

The positive electrode forming compositions prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were respectively coated on one surface of an aluminum foil, dried and rolled, and then punched to a predetermined size to prepare a positive electrode.

In addition, a negative electrode slurry was prepared by adding carbon powder as a negative electrode active material, carboxymethyl cellulose as a thickener, styrene-butadiene rubber as a binder, and carbon black as a conductive material, respectively, in a weight ratio of 96: 1: 2: 1. Was prepared. The negative electrode slurry was applied to a thin copper (Cu) thin film, which is a negative electrode current collector having a thickness of 10 μm, and dried, followed by roll press to prepare a negative electrode.

After the positive electrode and the negative electrode thus prepared were faced to each other, a battery assembly was manufactured through a separator composed of three layers of polypropylene / polyethylene / polypropylene (PP / PE / PP) between the positive electrode and the negative electrode. After storing the battery assembly in a battery case, the non-aqueous organic solvent having a composition of ethylene carbonate (EC): ethyl methyl carbonate (EMC): dimethyl carbonate (DMC) = 3: 3: 4 (volume ratio) and non-aqueous as lithium salt LiPF ₆ based on total aqueous electrolyte To A non-aqueous electrolyte solution added with 1 mol / l was poured into a lithium secondary battery.

Experimental Example  One

The particle size distribution of the conductive material was measured for the compositions for positive electrode formation prepared in Examples 1 to 3 and Comparative Examples 1 to 4 above.

Particle size: The prepared positive electrode composition was diluted 500-fold using NMP solvent, and the D ₅₀ and D ₉₀ values of the particle size distribution of the carbon black-dispersant composite dispersed in the dispersion were measured using Malvern's Mastersizer 3000 equipment. It was. The results are shown in Table 4 below.

	Particle size (㎛)
	D 50	D 90
Example 1	1.0	2.9
Example 2	0.85	2.1
Example 3	1.1	3.2
Comparative Example 1	1.8	7.5
Comparative Example 2	0.7	1.6
Comparative Example 3	1.13	3.0
Comparative Example 4	0.97	2.05

As a result, the carbon black-dispersant composite in the positive electrode composition of Examples 1 to 3 showed a more uniform particle size distribution than Comparative Example 1, and showed a larger particle size distribution than Comparative Example 2. For Comparative Examples 3 and 4, the particle size distribution was similar to that of Examples 1 to 3. This is because, in Comparative Examples 3 and 4, the milling was performed under the same conditions as in Example 1, and it was confirmed that the particle size distribution could be adjusted according to the milling conditions.

Experimental Example  2

The resistance characteristics of the batteries prepared according to the above production examples were evaluated using the compositions for positive electrode formation prepared in Examples 1 to 3 and Comparative Examples 1 to 4 above.

Specifically, the prepared lithium secondary battery was charged and discharged 1.0C / 1.0C three times at 25 ° C., and SOC (charge depth) was set based on the final discharge capacity. The 10 second resistance was measured by applying a discharge pulse at 6.5C at SOC15, SOC30 and SOC50, respectively. The results are shown in Table 5 below.

	Resistance (mOhm)
	SOC15	SOC30	SOC50
Example 1	1.3320	1.1721	1.1125
Example 2	1.3411	1.1854	1.1205
Example 3	1.3365	1.1803	1.1179
Comparative Example 1	1.4459	1.2755	1.2222
Comparative Example 2	1.3895	1.2285	1.1646
Comparative Example 3	1.4924	1.3251	1.2873
Comparative Example 4	1.3702	1.2091	1.1595

As a result, when the particle size of the carbon black-dispersant composite is large as in Comparative Example 1 and when the particle size of the carbon black-dispersant composite is too small as in Comparative Example 2, the resistance was large. On the contrary, in the case of Examples 1 to 3, it can be seen that the cell resistance during high rate discharge is reduced compared to Comparative Examples 1 and 2. It can be seen from this that there is an optimum dispersion particle size of the conductive material-dispersant composite. In addition, when the specific surface area of the carbon black is less than 130m ² / g as in Comparative Example 3, it can be seen that the conductivity of the electrode decreases as the volume of the conductive material decreases, thereby increasing the resistance, and PVA as a dispersant as in Comparative Example 4 When used, it was confirmed that the PVA increased the resistance compared to the present example using the H-NBR dispersant by insulating coating the positive electrode active material.

Experimental Example  3

The rate characteristic was evaluated about the battery manufactured using the composition for positive electrode formation manufactured in the said Examples 1-3 and Comparative Examples 1-4.

Specifically, two unit cells were prepared in the same manner as in Preparation Example using the compositions for forming anodes prepared in Example 1 and Comparative Examples 1 to 4, respectively, and the prepared unit cells were 0.1C at 25 ° C. The battery was charged until the constant current (CC) of 4.25V, then charged with a constant voltage (CV) of 4.25V, and the first charge was performed until the charging current became 0.05mAh. After standing for 20 minutes, the battery was discharged to a constant current of 0.1C until 3.0V, and the discharge capacity of the first cycle was measured. Thereafter, the capacity characteristics for each rate were evaluated by varying the discharge conditions at 2.0C.

Rate capacity represents the ratio of the capacity | capacitance when it discharges at 2.0C with respect to the capacity | capacitance when it discharged the battery charged at 0.1C at 0.1C as a percentage. The results are shown in Table 6 below.

		Capacity by Rate (%)
		0.1C	2.0C
Example 1	First cell	100	91.6
	2nd cell	100	91.7
Example 2	First cell	100	91.4
	2nd cell	100	91.5
Example 3	First cell	100	91.3
	2nd cell	100	91.5
Comparative Example 1	First cell	100	91.6
	2nd cell	100	90.7
Comparative Example 2	First cell	100	90.6
	2nd cell	100	90.9
Comparative Example 3	First cell	100	88.8
	2nd cell	100	88.2
Comparative Example 4	First cell	100	91.0
	2nd cell	100	90.9

As a result, the variation between cells increased in Comparative Examples 1 and 2 with a large dispersion particle size, and the variation between cells was larger in Comparative Example 1 with a larger dispersion particle size. In addition, in Comparative Example 3 using carbon black having a small specific surface area and Comparative Example 4 using PVA as the dispersant, the variation between the cells was small, but the rate characteristics were lowered as compared with Examples 1 to 3. On the other hand, in the case of Examples 1 to 3 it can be seen that there is almost no variation between cells exhibits excellent rate characteristics. Specifically, in the case of Comparative Example 3, the specific surface area and the oil absorption amount is less than 130 m ² / g and less than 220 ml / 100g, since the structure of the conductive material is less developed, the volume of the conductive material per weight is not small enough to cover the active material surface As a result, the cell performance was deteriorated. In the case of Comparative Example 4, it was considered that by using PVA as a dispersant, the PVA was insulated or denatured from the positive electrode active material to deteriorate discharge characteristics, thereby degrading cell performance.

Experimental Example  4

Capacity retention at high temperatures was evaluated for the batteries prepared using the compositions for forming a positive electrode prepared in Examples 1 to 3 and Comparative Examples 1 to 4 above.

Specifically, the prepared lithium secondary battery was charged at 1C to 4.25V under constant current / constant voltage (CC / CV) conditions at 45 ° C., and then discharged at 1C to 3.0V under constant current (CC) conditions. This cycle was repeated for 490 cycles, and the capacity retention rate at the 490th cycle was measured. The results are shown in Table 7 below.

		Capacity retention at 490 cycles (@ 45 ° C)
		Capacity maintenance rate (%)	Average
Example 1	First cell	90.1	90.0
	2nd cell	89.7
Example 2	First cell	89.8	89.7
	2nd cell	89.5
Example 3	First cell	90.1	90.1
	2nd cell	90.1
Comparative Example 1	First cell	83.5	86.0
	2nd cell	88.4
Comparative Example 2	First cell	90.0	89.4
	2nd cell	88.7
Comparative Example 3	First cell	84.1	84.5
	2nd cell	84.8
Comparative Example 4	First cell	87.1	87.3
	2nd cell	87.4

As a result, the battery containing the positive electrode produced by the composition for forming the positive electrode of Examples 1 to 3 exhibited a better high temperature capacity retention rate and the smallest cell variation. It is considered that the conductive materials included in Examples 1 to 3 form a dispersant and a conductive material-dispersant composite to stably exhibit excellent capacity retention by uniformly dispersing the conductive material in the positive electrode.

Claims (15)

1. A cathode active material, a conductive material, and a dispersant,

   The conductive material includes a carbon-based material having a specific surface area of 130 m ² / g or more and an oil absorption amount of 220 ml / 100 g or more, based on the total weight of the composition for forming an anode, in an amount of 0.1 wt% to 2 wt%,

   The dispersant is introduced into the conductive material to form a conductive material-dispersant composite, wherein the conductive material-dispersant composite has a D ₅₀ of a particle size distribution of 0.8 μm to 1.2 μm.
2. The method of claim 1,

   The conductive material-dispersant composite is a composition for forming a positive electrode of a secondary battery that D ₉₀ of the particle size distribution is 2.0㎛ to 5.0㎛.
3. The method of claim 1,

   The carbon-based material is a composition for forming a positive electrode of a secondary battery that is a secondary particle formed by assembling the primary particles.
4. The method of claim 1,

   The carbon-based material is carbon black composition for forming a positive electrode of a secondary battery.
5. The method of claim 1,

   The dispersant is a composition for forming a positive electrode of a secondary battery comprising a partially hydrogenated nitrile rubber containing 20 to 50% by weight of the repeating unit of the hydrogenated conjugated diene structure relative to the total weight of the rubber.
6. The method of claim 5,

   The partially hydrogenated nitrile rubber is a composition for forming a positive electrode of a secondary battery comprising a repeating unit of the α, β-unsaturated nitrile-derived structure in 20% to 50% by weight relative to the total weight of the rubber.
7. The method of claim 5,

   The partially hydrogenated nitrile rubber is an acryl including a repeating unit of the structure of Formula 1, a repeating unit of the structure of Formula 2, a repeating unit of the structure of Formula 3, and an ester derived structural unit of α, β-unsaturated carboxylic acid. Ronitrile-butadiene rubber,

   The acrylonitrile-butadiene rubber is a composition for forming a positive electrode of a secondary battery containing 20 to 50% by weight of the repeating unit of the structure of formula (3) based on the total weight of the rubber.

   [Formula 1]

   

   [Formula 2]

   

   [Formula 3]

   
8. The method of claim 5,

   The partially hydrogenated nitrile rubber has a weight average molecular weight of 10,000 g / mol to 700,000 g / mol composition for forming a positive electrode of a secondary battery.
9. The method of claim 1,

   The dispersant is a composition for forming a positive electrode of a secondary battery that is contained in 10 parts by weight to 50 parts by weight with respect to 100 parts by weight of the conductive material.
10. Preparing a conductive material dispersion by milling a mixture of the conductive material and the dispersant in a solvent; And

    Adding and mixing a positive electrode active material to the conductive material dispersion,

    The conductive material has a specific surface area of 130 m ² / g or more, and contains a carbon-based material having an oil absorption of 220 ml / 100g or more of 0.1% by weight to 2% by weight relative to the total weight of the composition for forming an anode,

    The conductive material dispersion includes a conductive material-dispersant composite in which the dispersant is introduced into the conductive material, wherein the conductive material-dispersant composite has a D ₅₀ of a particle size distribution of 0.8 μm to 1.2 μm. Method for producing a composition for forming.
11. The method of claim 10,

    The milling is a method of manufacturing a composition for forming a positive electrode of a secondary battery that is performed by filling a bead mill having a diameter of 0.5mm to 2mm at a filling rate of 50% by weight to 90% by weight relative to the total weight of the conductive material dispersion.
12. The method of claim 10,

    The milling method of manufacturing a composition for forming a positive electrode of a secondary battery that is performed while rotating the mixture at a circumferential speed of 6m / s to 12m / s.
13. The method of claim 10,

    The milling method of producing a composition for forming a positive electrode of a secondary battery that is performed by discharging the mixture at a discharge rate of 0.5kg / min to 1.5kg / min.
14. A secondary battery positive electrode manufactured using the positive electrode forming composition according to claim 1.
15. A lithium secondary battery comprising the positive electrode according to claim 14.