KR20170111749A - Composition for preparing positive electrode of secondary battery, and positive electrode for secondary battery and secondary battery prepared using the same - Google Patents

Abstract

In the present invention, a composition for forming an anode of a secondary battery comprising a cathode active material, a conductive material, a binder, a dispersant, and a dispersion medium, wherein the binder contains a fluorine-based polymer containing 0.5 mol% to 1 mol% Wherein the dispersant is a hydrogenated nitrile rubber having a residual double bond value of 30% by weight or less according to the following formula 1 and a content of repeating units in the?,? - unsaturated nitrile-derived structure in the molecule of 20% by weight to 35% It is possible to improve the dispersibility of the conductive material in the anode during the preparation of the anode and to increase the adhesion between the active material and the active material and the collector to improve the high temperature stability of the electrode and the chemical resistance to the electrolyte, And a positive electrode and a secondary battery for a secondary battery manufactured using the same.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composition for forming a positive electrode of a secondary battery, and a positive electrode and a secondary battery for the secondary battery,

The present invention relates to a composition for forming a positive electrode of a secondary battery which can improve the dispersibility of conductive materials and improve the durability of the positive electrode and the electrolyte by increasing the adhesive force between the active materials or between the active material and the current collector, A positive electrode for a secondary battery, and a secondary battery.

Carbon black, Ketjenblack, fullerene, graphene or carbon nanotubes have been widely used in the fields of energy, aerospace, etc. due to their excellent electrical properties and thermal conductivity. However, in order to apply these fine carbon materials, uniform dispersion must be preceded. However, it has not been easy to produce a dispersion of fine carbonaceous materials in a high concentration by methods such as mechanical dispersion, dispersion using a dispersant, and dispersion through surface functionalization.

Recently, as technology development and demand for mobile devices have increased, the demand for secondary batteries as energy sources has been rapidly increasing. Of these secondary batteries, lithium secondary batteries having high energy density and voltage, long cycle life and low self discharge rate are commercialized and widely used.

In the lithium secondary battery, the electrodes for the positive electrode and the negative electrode are prepared by applying a composition for electrode formation, which is prepared by collectively mixing an electrode active material and a binder with a solvent, onto a current collector and drying the same. At this time, in order to ensure conductivity between the active material and the current collector, a conductive material of the above-described fine carbon material is contained in the electrode forming composition. Among them, the active material filling rate can be increased, Carbon black is widely used.

However, since the conductive material is used as fine particles having a size of several tens of nanometers, the cohesive force is strong, and when the conductive material is dispersed in a solvent, aggregation of the conductive fine particles tends to occur. Such uneven dispersion of the conductive material in the electrode active material layer leads to deterioration of conductivity and deterioration of the output characteristics of the battery, and the agglomerated body of such a simple agglomerated conductive material can deteriorate the conductivity between the active materials because of low structural holding power. In addition, the conductive material has a large specific surface area and adsorbs the binder, which may lead to a non-uniform distribution of the binder in the active material layer and consequently a decrease in the adhesion.

To solve this problem, a conductive material is preliminarily dispersed together with a binder and a solvent to form a paste, an electrode active material is added thereto, and the mixture is stirred and mixed. However, in a dispersion containing a resin binder such as a fluororesin or a cellulose resin, dispersion stability of the conductive material particles is poor, and sufficient effect such as re-aggregation of the conductive material particles can not be obtained.

In addition, attempts have been made to increase the dispersibility of the conductive material by adding a vinyl pyrrolidone-based polymer as a dispersant to the conductive material and the solvent, and to maintain the battery load characteristics and the cycle characteristics satisfactorily. However, in this case, there is a problem that the added vinyl pyrrolidone polymer is insulated to cover the electrode active material, or is deformed when stored for a long period of time in a charged state to deteriorate discharge characteristics.

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

Japanese Patent Laid-Open No. 2001-283835 (published on October 12, 2001) Japanese Patent Application Laid-Open No. 2003-157846 (published May 30, 2003)

The first problem to be solved by the present invention is to improve the dispersibility of the conductive material in the positive electrode and to improve the durability of the positive electrode and the electrolyte by increasing the adhesive force between the active material or between the active material and the current collector, And to provide a composition for forming the same.

A second object of the present invention is to provide a positive electrode for a secondary battery and a lithium secondary battery including the positive electrode, which are manufactured using the composition for forming an anode.

According to an embodiment of the present invention,

A cathode active material, a conductive material, a binder, a dispersant, and a dispersion medium,

Wherein the binder contains a fluorine-based polymer containing 0.5 mol% to 1 mol% of a functional group capable of hydrolysis in a molecule,

The dispersant may include a hydrogenated nitrile rubber having a residual double bond value of 30% by weight or less according to the following formula 1 and a repeating unit content of the?,? - unsaturated nitrile-derived structure in the molecule of 20% by weight to 35% by weight The composition comprising: < RTI ID = 0.0 >

[Equation 1]

 Residual double bond (RDB) = BD / (BD + HBD) x100

BD represents the content (% by weight) of the repeating units of the conjugated diene-derived structure in the hydrogenated nitrile rubber, and HBD represents the content (% by weight) of the repeating units of the hydrogenated conjugated diene-derived structure.

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

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

The composition for forming an anode of a secondary battery according to the present invention improves the dispersibility of the conductive material in the anode during the preparation of the anode and improves the durability of the anode at high temperatures and electrolytes by increasing the adhesive force between the active materials or between the active material and the collector have.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments of the invention and, together with the description of the invention, It should not be construed as limited.
1 is a graph showing the results of evaluating the rate of increase in resistance after storage at a high temperature of a lithium secondary battery manufactured using the composition for forming a positive electrode in Examples 1 and 2 and Comparative Examples 1 and 2. FIG.
2 is a graph showing the results of evaluating swelling characteristics of an electrolyte solution of the dispersant used in Examples 1 and 2 and Comparative Example 1. Fig.

Hereinafter, the present invention will be described in detail in order to facilitate understanding of the present invention.

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

In order to realize a high loading / high density anode in a lithium secondary battery, it has been attempted to enhance dispersibility and flexibility of the conductive material in the anode. To this end, hydrogenated nitrile butadiene rubber (HNBR), which is flexible and excellent in chemical resistance and abrasion resistance, has been applied. However, in the case of HNBR, the swelling of the electrolyte relative to the fluorinated polymer used as the binder in the electrode, specifically, polyvinylidene fluoride (PVDF) is 10 times or more. Therefore, There is a problem that some conductive paths are blocked, and as a result, the cell resistance is increased. When the content of the repeating units in the specific monomer-derived structure in the HNBR is too high, there is a possibility that the HNBR will be eluted into the electrolyte due to the increase in compatibility with the electrolytic solution. Therefore, the content of the repeating units constituting the HNBR needs to be controlled.

On the other hand, in the present invention, the content of the repeating unit of the monomer-derived structure constituting the hydrogenated nitrile rubber used as the dispersant of the conductive material in the production of the anode is controlled to improve the dispersibility of the conductive material and, at the same time, The increase in the ring resistance and thus the cell resistance can be minimized, and the high temperature storage characteristics can be improved. In addition, by optimizing the binder in accordance with the characteristics of the hydrogenated nitrile rubber, it is possible to improve the durability against high temperature and electrolytic solution by increasing the adhesive force in the electrode.

Specifically, a composition for forming an anode of a secondary battery according to an embodiment of the present invention includes:

A cathode active material, a conductive material, a binder, a dispersant, and a dispersion medium,

Wherein the binder contains a fluorine-based polymer containing 0.5 mol% to 1 mol% of a functional group capable of hydrolysis in a molecule,

Wherein the dispersant has a residual double bond value of 30% by weight or less according to the following formula (1) and a repeating unit content of the?,? - unsaturated nitrile-derived structure in the molecule is 20% by weight to 35% Includes rubber:

[Equation 1]

 Residual double bond (RDB) = BD / (BD + HBD) x100

BD represents the content (% by weight) of the repeating units of the conjugated diene-derived structure in the hydrogenated nitrile rubber, and HBD represents the content (% by weight) of the repeating units of the hydrogenated conjugated diene-derived structure.

In the preparation of the composition for electrode formation usually using a dispersant, the conductive material is dispersed in the dispersion medium in the form of a composite physically or chemically bonded to the dispersing agent.

Accordingly, in the present invention, a hydrogenated nitrile rubber, which controls the content of a repeating unit region of a structure capable of interacting with a conductive material and a repeating unit region of a structure capable of interacting with a dispersion medium, By using the conductive material, the conductive material in the dispersion medium is uniformly dispersed, and even when the conductive material is dispersed at a high concentration, a low viscosity can be exhibited. In addition, the dispersant can minimize the swelling of the electrolyte solution of the hydrogenated nitrile rubber at a high temperature, thereby increasing the cell resistance and improving the high temperature storage characteristics.

Specifically, in the composition for forming an anode according to an embodiment of the present invention, the dispersant may include a repeating unit having an α, β-unsaturated nitrile-derived structure as a repeating unit region (A) having a structure capable of interacting with a carbonaceous material; And a hydrogenated nitrile rubber including a repeating unit of a conjugated diene-derived structure and a repeating unit of a hydrogenated conjugated diene-derived structure as a repeating unit region (B) of a structure capable of interacting with a dispersion medium. The hydrogenated nitrile rubber may optionally further comprise additional comonomer capable of copolymerizing under conditions such that the conductive material-dispersant composite has an optimal particle size distribution.

The hydrogenated nitrile rubber can be specifically prepared by copolymerizing an?,? - unsaturated nitrile, a conjugated diene, and optionally other comonomerizable comonomers, and then hydrogenating the carbon-carbon double bond in the copolymer. At this time, the polymerization reaction and the hydrogenation process can be carried out according to a conventional method.

Specific examples of the?,? - unsaturated nitrile that can be used in the production of the hydrogenated nitrile rubber include acrylonitrile and methacrylonitrile. One, two, or more of these may be used.

Specific examples of the conjugated diene which can be used in the production of the hydrogenated nitrile rubber include conjugated dienes having 4 to 6 carbon atoms such as 1,3-butadiene, isoprene and 2,3-methylbutadiene. Two or more mixtures may be used.

Examples of other copolymerizable comonomers which can be selectively used include aromatic vinyl monomers such as styrene,? -Methylstyrene, vinylpyridine, and fluoroethyl vinyl ether),?,? - unsaturated carboxylic acids (Meth) acrylate, ethyl (meth) acrylate, isobutyl (meth) acrylate, isobutyl (meth) acrylate, (meth) acrylate, methoxymethyl (meth) acrylate, hydroxyethyl (meth) acrylate or polyethylene glycol (meth) acrylate), anhydrides of?,? - unsaturated dicarboxylic acids (For example, maleic anhydride, itaconic anhydride, citraconic anhydride, etc.), and any one or a mixture of two or more thereof may be used. More specifically, the comonomer may be an ester of an alpha, beta -unsaturated carboxylic acid, such as a (meth) acrylate-based monomer. Specific examples of the (meth) acrylate monomers include methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-amyl acrylate, Ethylhexyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, 2-hydroxyethyl methacrylate, or And hydroxypropyl methacrylate. Any one or a mixture of two or more of them may be used.

In the hydrogenated nitrile rubber produced according to the above process, the repeating unit of the?,? -Unsaturated nitrile-derived structure, the repeating unit of the conjugated diene-derived structure, the repeating unit of the hydrogenated conjugated diene-derived structure, The content ratio of the repeating units in the monomer-derived structure may vary within a wide range, and in each case, the total sum of the repeating units of the above structure is 100% by weight.

Specifically, considering improvement in dispersibility of the carbon-based material and compatibility with the dispersion medium, the hydrogenated nitrile rubber preferably has a repeating unit of the?,? - unsaturated nitrile structure in an amount of 20% by weight or more based on the total weight of the hydrogenated nitrile rubber, By weight, preferably 20% by weight to 35% by weight, more specifically 30% by weight to 35% by weight. When the recurring units of the?,? - unsaturated nitrile-derived structure are contained in the above-mentioned content range, swelling for an electrolytic solution at a high temperature is relatively small, which is advantageous for decreasing the cell resistance. In particular, when the compatibility with the electrolytic solution is good in the anode composition having a small conductive material content, it may cause disconnection of the conductive path due to swelling. Therefore, it is preferable to repeat the structure derived from the?,? - unsaturated nitrile Unit. ≪ / RTI >

 In the present invention, the repeating unit content of the?,? - unsaturated nitrile derived structure in the hydrogenated nitrile rubber is preferably such that the weight ratio (percentage) of the repeating unit derived from?,? - unsaturated nitrile to the total weight in the hydrogenated nitrile rubber, , And the content thereof is a median value of quantities determined by measuring the amount of nitrogen generated and converting the amount of bonding thereof from the molecular weight of acrylonitrile in accordance with the wheat oven method of JIS K 6364.

The hydrogenated nitrile rubber may have a residual double bond value of 30% by weight or less, more specifically, 1% by weight to 20% by weight based on the following formula (1)

[Equation 1]

Residual double bond (RDB) = BD% / (BD + HBD) x100

(BD and HBD in the above formula (1) are as defined above)

When exhibiting the residual double bond value in the above-mentioned range, it is possible to exhibit a better effect of improving the dispersibility of the conductive material.

Further, the hydrogenated nitrile rubber can be produced by reacting the repeating unit of the hydrogenated conjugated diene-derived structure with a hydrogenated nitrile rubber-based structure under the condition that the content of the repeating units in the?,? - unsaturated nitrile- More preferably from 50% by weight to 80% by weight, and even more specifically from 50% by weight to 70% by weight, based on the weight of the composition. By incorporating the repeating unit of the hydrogenated conjugated diene-derived structure in the above-mentioned content range, the miscibility with the dispersion medium is increased, and the dispersibility of the conductive material can be increased.

When the hydrogenated nitrile rubber further contains other comonomerizable comonomer, the content ratio may vary depending on the type and nature of the comonomer. Specifically, the content of the repeating unit in the comonomer-derived structure is preferably in the range of from 0.1% May be 20 wt% or less, more specifically 1 wt% to 10 wt%, based on the total weight.

More specifically, the hydrogenated nitrile rubber may be an acrylonitrile-butadiene rubber comprising a repeating unit having a structure represented by the following formula (1), a repeating unit represented by the following formula (2), and a repeating unit represented by the following formula (3). At this time, the content of the repeating unit of the acrylonitrile-derived structure of Formula 1 may be 20 wt% to 35 wt%, more specifically 30 wt% to 35 wt% with respect to the total weight of the acrylonitrile-butadiene rubber. The residual double bond value according to Equation 1 may be 30 wt% or less, more specifically 1 wt% to 20 wt%. The content of the repeating unit of the hydrogenated butadiene-derived structure represented by the following formula (3) in the acrylonitrile-butadiene rubber-based structure satisfies the range of the content of the repeating unit of the acrylonitrile- By weight, more preferably 50% by weight to 80% by weight, and still more preferably 50% by weight to 70% by weight.

[Chemical Formula 1]

(2)

(3)

The hydrogenated nitrile rubber may have a weight average molecular weight (Mw) of 100,000 g / mol to 700,000 g / mol, more specifically 150,000 g / mol to 350,000 g / mol. The hydrogenated nitrile rubber has a polydispersion 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 . When the hydrogenated nitrile rubber has the weight average molecular weight and the polydispersity index in the above range, the conductive material can be uniformly dispersed in the dispersion medium by satisfying the average particle size requirement of the conductive material-dispersant composite.

In the present invention, the weight average molecular weight and the number average molecular weight are molecular weight in terms of polystyrene which is analyzed by gel permeation chromatography (GPC).

The hydrogenated nitrile rubber may have a Mooney viscosity (ML 1 + 4 at 100 캜) of 10 to 100, more specifically 50 to 80. The Mooney viscosity of the hydrogenated nitrile rubber in the present invention can be measured according to ASTM Standard D 1646.

Meanwhile, in the composition for forming an anode of a secondary battery according to an embodiment of the present invention, the conductive material exhibiting excellent dispersibility when mixed with the dispersing agent described above and easily forming a conductive path in the electrode may be carbon black.

In general, when the dispersion of the conductive material in the electrode is insufficient, the conductive material is not appropriately distributed on the surface of the active material, thereby deteriorating the performance of the battery cell and increasing the performance deviation between cells. In addition, when the dispersion of the conductive material is excessive, the dispersed conductive material can be advantageously distributed on the surface of the active material. However, the formation of a network between the conductive materials is not easy and resistance in the cell is rather increased.

Carbon black is a secondary particle formed by granulation of primary particles, and improves the conductivity by improving the bonding structure of primary particles. However, in the case of the carbon black having improved conductivity as described above, the size of the primary particles is small and the surface area is large, so that it is easy to form aggregates and dispersion is not easy. Accordingly, considering the dispersibility and conductivity of the carbon black in the electrode, the structure development of the carbon black should be optimized.

On the other hand, in the present invention, by controlling the structure of carbon black, conductivity and dispersibility in the electrode can be improved. Specifically, the carbon black preferably has an average particle diameter (D ₅₀ ) of the primary particles of 15 nm to 25 nm and a BET specific surface area of the secondary particles composed of aggregation of the primary particles of 130 m ² / g to 380 m ² / g .

As described above, the carbon black usable in the present invention can exhibit better conductivity by having a highly developed structure having a small primary particle size and a large BET specific surface area of secondary particles. Particularly, when used in the production of an electrode of a lithium secondary battery, the electron availability at the three phase interface between the positive electrode active material and the electrolyte can be enhanced and the reactivity can be improved. If the average particle diameter of the primary particles of the carbon black is less than 15 nm, there is a possibility that the dispersibility of the carbon black is significantly lowered due to aggregation of the carbon black particles. In addition, when the average particle diameter exceeds 25 nm, the particle size is excessively large, so that the dispersion property itself is low and can be partially concentrated in the dispersion. Further, the wider the specific surface area of the conductive material, the larger the contact area with the cathode active material, and as a result, the conductive path is easily formed between the cathode active material particles. However, when the specific surface area is excessively large, specifically, when the specific surface area exceeds 380 m ² / g, the energy density of the anode may deteriorate due to the bulky structural feature. On the other hand, when the specific surface area of the conductive material is excessively small, specifically less than 130 m ² / g, the contact area with the cathode active material may decrease and the conductive material may aggregate. More specifically, considering the remarkable effect of the average particle diameter of the primary particles of the carbon black and the specific surface area of the secondary particles on the conductivity and dispersibility, the average particle diameter (D ₅₀ ) of the primary particles of the carbon black is preferably from 15 nm to And a specific surface area of 130 m ² / g to 250 m ² / g.

In the present invention, the specific surface area of carbon black can be defined as a value (BET specific surface area) measured by a nitrogen adsorption method. The average particle diameter (D ₅₀ ) of the primary particles of the carbon black can be defined as the particle diameter on the basis of 50% of the particle diameter distribution in the non-agglomerated carbon black particles. The average particle diameter (D ₅₀ ) of the primary particles of the carbon black can be measured through, for example, scanning electron microscopy or electron microscope observation such as transmission electron microscopy.

Carbon black can be variously classified according to its production method and raw materials to be used. The carbon black usable in the present invention may be acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, And any one or a mixture of two or more thereof may be used. More specifically, considering the conductivity and dispersibility of the conductive material, the carbon black is prepared using acetylene gas, specifically, by pyrolysis of an acetylene gas in an oxygen-free atmosphere, and the average particle diameter (D ₅₀ ) of the primary particles is And may be 15 nm to 25 nm.

The carbon black may have a purity of 99.5% or more, in which the content of metal impurities in the carbon black is controlled through the control of the impurities in the production process or the purification process after the production.

For example, lithium secondary batteries deteriorate in life characteristics due to deterioration of components due to various causes. One of the main causes is due to the incorporation of metal impurities contained in the conductive material into the battery. Specifically, metal impurities such as iron (Fe) contained in the conductive material are dissolved in the electrolyte solution at a reaction voltage range of about 3.0 V to 4.5 V, which is the operating voltage range of the lithium secondary battery, and the dissolved metal impurities are dissolved in the form of metal . The metal thus precipitated is short-circuited with the positive electrode through the separator, causing a low voltage failure, and deteriorating the capacity characteristics and lifetime characteristics of the secondary battery, thereby failing to fulfill its role as a battery. Therefore, it is important to prevent the incorporation of impurities, especially metal impurities, in the application of the conductive material to the secondary battery. Accordingly, the carbon black usable in the present invention may be carbon black having a high purity within the above range in which the content of the metal impurities is removed as much as possible.

In the present invention, the content of impurities, particularly metal impurities, in the carbon black may be determined by using magnetism, X-ray diffraction (XRD), differential thermal analysis (DTA) (DSC), Modulated Differential Scanning Calorimetry (MDSC), Thermogravimetric Analysis (TGA), Thermogravimetric-infrared (TG-IR) analysis, and Melting Point Or by one or more methods including thermal analysis, including measurement. Specifically, the content of the metal impurity in the carbon black can be measured through the main peak intensity of the metal impurity obtained by the X-ray diffraction method (XRD).

In addition, the carbon black may be surface-treated to enhance dispersibility in the composition for forming an anode.

Specifically, the carbon black has an oxygen-containing functional group introduced into the surface of the carbon black by an oxidation treatment to impart hydrophilicity thereto; Or may be imparted with hydrophobicity by fluorination treatment or silicone treatment on carbon black. The carbon black may be coated with a phenolic resin or mechanochemically treated. For example, in the case of oxidation treatment of carbon black, it can be carried out by heat-treating carbon black at about 500 ° C to 700 ° C for about 1 hour to 2 hours in air or under an oxygen atmosphere. However, if the surface treatment for carbon black is excessive, the electrical conductivity and strength characteristics of the carbon black itself may be significantly deteriorated, so that it may be desirable to control it appropriately.

The above carbon black is dispersed in the form of a composite in which the dispersant is introduced into the carbon black when the composition for forming an anode is produced. At this time, the dispersibility and the particle size distribution of the conductive material-dispersant composite dispersed in the composition for anode formation can be optimized through the control of the dispersant and the carbon black.

Specifically, in the composition for forming an anode of a secondary battery according to an embodiment of the present invention, the conductive material-dispersant composite may have a D ₅₀ of a particle size distribution of 0.5 μm to 2 μm.

When the D ₅₀ of the particle size distribution of the conductive material-dispersant composite satisfies the above-described range, the dispersibility of the conductive material is greatly improved, and as a result, the battery performance can be improved by reducing the resistance property in the electrode at the time of electrode formation. If the D ₅₀ of the particle size distribution of the conductive material-dispersant composite is less than 0.5 탆, the dispersion of the conductive material may not be sufficient and the conductive material may not be properly distributed on the surface of the active material. Also, when the D ₅₀ of the particle size distribution of the conductive material-dispersant composite exceeds 2 탆, the conductive material is dispersed over the conductive material, so that the in-electrode conductive material is not easily formed in forming the anode, resulting in an increase in cell resistance. In view of the optimum dispersibility of the conductive material and the remarkable improvement effect of the conductive material, the conductive material-dispersant composite contained in the composition for anode formation has a D ₅₀ of the particle size distribution of 0.5 탆 to 1.2 탆, more specifically 0.5 탆 To 0.7 [mu] m. By having such a developed structure, it is possible to exhibit dispersibility with better conductivity.

The particle size distribution D ₅₀ of the conductive material-dispersant composite can be defined as a particle size at a 50% of the particle size distribution. The particle size distribution of the conductive material-dispersant composite may be measured using a laser diffraction method. More specifically, the conductive material and the dispersant may be dispersed in a dispersion medium, and then a commercially available laser diffraction particle size analyzer (For example, Microtrac MT 3000), and an ultrasonic wave of about 28 kHz is irradiated at an output of 60 W, and the average particle size (D ₅₀ ) based on the 50% of the particle diameter distribution in the measuring apparatus can be calculated.

In addition, in the composition for forming an anode according to an embodiment of the present invention, the conductive material may further include a conventional conductive material together with the carbon black for improving conductivity.

More specifically, the conductive material may further include a fibrous conductive material which is easier to form a conductive network when mixed with carbon black, and can easily form 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 (ratio of the length of the long axis passing through the center of the fibrous conductive material to the diameter perpendicular to the long axis), such as carbon nanorod or carbon nanofiber.

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 greater the electrical conductivity and the strength characteristic. However, if the length is too long, the dispersibility may deteriorate. 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 may be used in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the carbon black. If the content of the fibrous conductive material is too low as compared with the content of the carbon black, the effect of improving the conductivity by mixing is small. If the content is more than 10 parts by weight, the dispersibility of the fibrous conductive material may be deteriorated.

Meanwhile, in the composition for forming an anode according to an embodiment of the present invention, the binder may be a fluoropolymer containing 0.5 to 1 mol% of a positive electrode active material or a functional group capable of hydrogen bonding with a hydroxyl group on the surface of the current collector . The hydrogen-bonding synthetic functional group may specifically be a carboxyl group, a hydroxyl group, a sulfonic acid group, a carbonyl group, an ester group (-COOR, R is an alkyl group) or a glycidyl group, and any one or two or more of them may be included. More specifically, it may be a carbonyl group or a hydroxy group.

It is preferable that the binder is excellent in compatibility with the positive electrode active material and the conductive material, and excellent in compatibility with the dispersant and the dispersion medium.

The functional groups contained in the binder form a hydrogen bond with the positive electrode active material or the hydroxyl group on the surface of the current collector, thereby enhancing adhesion between the positive active material particles as a binder and adhesion between the positive active material and the current collector. As a result, the durability of the anode at high temperatures and electrolytes can be improved. The functional groups form a selective permeable coating of lithium ions on the surface of the cathode active material and inhibit the formation of lithium compounds synthesized by the reaction of the electrolytic solution and lithium ions on the surface of the cathode active material at the first discharge, Even if it is increased by a short circuit or the like, a thermally unstable lithium compound is less likely to be decomposed and heat generation is suppressed, and direct reaction of the lithium ion and the electrolytic solution in the active material can be suppressed. It is also possible to prevent the agglomeration of the conductive material by exhibiting a lapping effect that adsorbs on the surface of the conductive material and surrounds the conductive material.

However, if the content of the hydrogen-sintering synthetic functional groups is excessively high, it may be preferable that the content of the sintering synthetic functional group is included in the optimum amount because there is a fear of decrease in the adhesive strength. Specifically, the functional group may be contained in an amount of 0.5 mol% to 1 mol%, more specifically, 0.5 mol% to 0.7 mol% in the fluorine-based polymer.

More specifically, the binder may be selected from the group consisting of polyvinylidene fluoride (PVDF), polytetrafluoroethylene, polyhexafluoropropylene vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP) And various copolymers thereof. One kind or a mixture of two or more kinds may be used. Among these, the binder may be more specifically a homopolymer of vinylidene fluoride containing the above-mentioned hydrogen bonding functional groups in view of the remarkable effect of increasing the adhesive force and thus improving the durability against high temperatures and electrolytes. More specifically, May be a homopolymer of vinylidene fluoride containing a hydroxy group or a carboxy group as the hydrogen-bonding functional group. When the fluorine-based polymer is in the form of a homopolymer, the effect of increasing the adhesive strength is high, and thus it is possible to exhibit higher durability against high temperature and electrolytic solution.

The binder may have a weight average molecular weight (Mw) of 300,000 g / mol to 1,000,000 g / mol. If the molecular weight of the binder is too small or less than 20,000 g / mol, it is difficult to exhibit a sufficient lapping effect on the conductive material. If the molecular weight exceeds 5,000,000 g / mol, It is difficult to wrap enough. More specifically, the binder may have a weight average molecular weight of 70,000 g / mol to 2,000,000 g / mol. In the present invention, the weight average molecular weight of the binder is the polystyrene reduced molecular weight as analyzed by gel permeation chromatography (GPC).

The binder is in powder form, and its shape is not particularly limited. Specifically, it may be spherical, fibrous, platy or polygonal.

In the composition for forming an anode according to an embodiment of the present invention, the cathode active material is a compound capable of reversibly intercalating and deintercalating lithium (a lithiated intercalation compound) (Specifically, LiCoO ₂ , LiCo _1/3 Mn _1/3 Ni _1/3 O ₂ , or LiNiO ₂ ) having a hexagonal layered bed salt structure, a material having an olivine structure (specific examples include LiFePO ₄ ), A spinel material having a cubic structure (specifically, LiMn ₂ O ₄ ), a vanadium oxide such as V ₂ O ₅ , and a chalcocene compound such as TiS or MoS.

More specifically, the cathode active material may be a lithium composite metal oxide including lithium and a metal such as cobalt, manganese, nickel or aluminum. The lithium composite metal oxide is specifically a lithium-manganese oxide (for example, LiMnO ₂ , LiMn ₂ O And the like), lithium-cobalt oxide (e.g., LiCoO ₂ and the like), lithium-nickel-based oxide (for example, LiNiO ₂ and the like), lithium-nickel-manganese-based oxide (for example, 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 (where, 0 <Z <2), and the like), lithium-nickel-manganese-cobalt oxide (e.g., Li (Ni Co _{P Q R} Mn) 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 ( here, 0 <P <2, 0 <Q <2, 0 <R <2 , P + Q + R = 2) , etc.), or lithium-nickel-cobalt-manganese-metal (M) oxide (e.g., Li (Ni _P Co _Q Mn _R M _S) O ₂ (here, M is Al, Cu, Fe, V, Cr, Ti, is selected from the group consisting of Zr, Zn, Ta, Nb, Mg, B, W and Mo, P, Q, R and S is Independent 1, 0 <R <1, 0 <S <1, and P + Q + R + S = 1), and the like, Any one or two or more of these compounds may be included. Considering that the method for evaluating the lifetime 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 characteristic evaluation result without worrying about deterioration of the cathode active material itself The cathode active material may be a layered lithium composite metal oxide, and more specifically, a layered lithium cobalt oxide.

At least one of the metal elements other than lithium in the lithium composite metal oxide is selected from the group consisting of Al, Cu, Fe, V, Cr, Ti, Zr, Zn, Ta, Nb, Mg, B, And may be doped by any one or two or more elements selected. When the lithium metal composite oxide of lithium deficiency is further doped with the metal element, the structural stability of the cathode active material is improved, and as a result, the output characteristics of the battery can be improved. At this time, the content of the doping element contained in the lithium composite metal oxide may be appropriately controlled within a range not to deteriorate the characteristics of the cathode active material, and may be 0.02 atomic% or less.

More specifically, the lithium composite metal oxide may include a compound represented by the following formula (4):

[Chemical Formula 4]

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

Wherein M is at least one element selected from the group consisting of Al, Cu, Fe, V, Cr, Ti, Zr, Zn, Ta, Nb, Mg, B, A, x, y, z, and w each independently represent an atomic fraction of the corresponding elements, -0.5? A? 0.5, 0? X? 1, 0? Y? 1, 0? Z? 1 and 0 < x + y + z &lt; 1.

Also, in consideration of the remarkable improvement effect of the combination of the conductive material and the dispersant, the positive electrode active material satisfies 0 <x <1, 0 <y <1, 0 <z < y + a z≤x may include a compound, wherein the cathode active material in that more specifically, to improve the capacity characteristics of the battery, and reliability 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, etc., and any one or a mixture of two or more thereof may be used.

The composition for forming an anode according to an embodiment of the present invention having the above composition may be prepared by adding a cathode active material, a conductive material, a binder, and a dispersant to a dispersion medium and dispersing the mixture through mixing. Accordingly, the composition for forming an anode may further include a dispersion medium.

The above-mentioned dispersion medium can be used without particular limitation, as long as it is usually used in the production of a composition for forming a positive electrode. Specifically, the solvent may be an amide-based polar organic solvent such as dimethylformamide (DMF), diethylformamide, dimethylacetamide (DMAc) or N-methylpyrrolidone (NMP); Propanol (isobutanol), 2-butanol (sec-butanol), 1-methyl -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, trimethylol propane, pentaerythritol, or sorbitol; Ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, tetraethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, tetraethylene glycol Glycol ethers such as monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, and tetraethylene glycol monobutyl ether; Ketones such as acetone, methyl ethyl ketone, methyl propyl ketone, or cyclopentanone; And esters such as ethyl acetate,? -Butyllactone, and? -Propiolactone. Any one or a mixture of two or more of them may be used. More specifically, the dispersion medium may be an amide compound in consideration of the effect of improving the dispersibility of the carbon black and the dispersant.

The content of the positive electrode active material, the conductive material, the binder, the dispersant, and the dispersion medium in the composition for forming an anode according to an embodiment of the present invention having the above-described structure, Can be properly controlled.

The particle size distribution condition of the conductive material-dispersant composite is affected by the physical properties and content of the conductive material and the dispersant, and in particular, the physical properties and the content of the conductive material are greatly influenced. When the amount of the conductive material contained in the composition for forming an anode is large, dispersion is not easy and the difference depending on the dispersed particle size may be small. However, when the amount of the conductive material is less than a certain level, Can exist.

 Specifically, in order to uniformly disperse the conductive material in the composition for forming an anode, the conductive material may be contained in an amount of 5% by weight or less based on the total solid content in the composition for forming an anode. When the conductive material is included in the above range, the conductivity and dispersibility can be well balanced. If the content of the conductive material is out of the above range and exceeds 5% by weight, the dispersibility may deteriorate. More specifically, the conductive material may be included in an amount of 0.4% by weight to 2.5% by weight based on the total weight of the composition for forming an anode.

The dispersant may be included in an amount of 5 to 50 parts by weight based on 100 parts by weight of the conductive material. If the content of the dispersing agent is less than 5 parts by weight, the dispersibility of the conductive material may be deteriorated. If the amount exceeds 50 parts by weight, excess dispersing agent may remain in the anode and increase resistance in the anode. There is a fear of deterioration. More specifically, the dispersant may be included in an amount of 5 to 20 parts by weight based on 100 parts by weight of the conductive material.

More specifically, the dispersant may be contained in an amount of 0.1% by weight to 10% by weight based on the total weight of solids in the composition for forming an anode. If the content of the dispersing agent is less than 0.1% by weight, the dispersibility of the conductive material may not be improved by the use of the dispersing agent. If the content exceeds 10% by weight, the resistance of the anode may increase, Can be.

The binder may be included in an amount of 1 part by weight to 30 parts by weight based on 100 parts by weight of the cathode active material. If the content of the binder is less than 1 part by weight, it is difficult to exhibit the necessary adhesion effect in the electrode. If the content of the binder is more than 30 parts by weight, there is a fear of deterioration of capacity characteristics of the battery. More specifically, the binder may be included in an amount of 10 parts by weight to 20 parts by weight based on 100 parts by weight of the cathode active material.

The positive electrode active material may be contained in an amount of 80 wt% to 96 wt% based on the total weight of the solid content 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 deteriorated. If the content is more than 96% by weight, the relative content of the conductive material and the dispersant may decrease.

The dispersion medium may be contained in an amount such that the composition for forming an anode has an appropriate viscosity so that the coating composition can be easily applied and uniformly applied when the composition for forming an anode is applied.

The composition for forming an anode according to an embodiment of the present invention having the above composition may be prepared by adding and mixing the above-mentioned cathode active material, conductive material, binder and dispersant in a dispersion medium.

At this time, in order to improve the dispersibility of the conductive material, the conductive material and the dispersant may be linearly dispersed in the dispersion medium, and then the binder and the cathode active material may be sequentially added to and mixed with the resulting linear dispersion.

The mixing step may be performed by a conventional mixing or dispersing method, and specifically concretely, a milling (milling) process such as a ball mill, a bead mill, a basket mill, ) Method, or a homogenizer, a bead mill, a ball mill, a basket mill, an impact mill, a universal stirrer, a clear mixer or a TK mixer. More specifically, it can be performed by a milling method using a bead mill. At this time, the size of the bead mill may be suitably determined according to the kind and amount of the carbon black and the kind of the dispersant, and specifically, the diameter of the bead mill may be 0.5 mm to 2 mm.

According to the above-described production method, a composition for forming a positive electrode, in which a positive electrode active material, a conductive material, a binder and a dispersing agent are uniformly dispersed in a solvent, is produced.

The conductive material and the dispersant are dispersed in the form of a conductive material-dispersant composite in which the dispersant is introduced into the surface of the conductive material through physical or chemical bonding. Specifically, the conductive material-dispersant composite has a particle size distribution as described above .

As described above, in the composition for forming an anode of a secondary battery according to an embodiment of the present invention, the degree of hydrogenation in the hydrogenated nitrile rubber used as the dispersant for the conductive material and the content of the repeating unit in the acrylonitrile- It is possible to improve the dispersibility of the conductive material and at the same time to minimize the swelling of the electrolytic solution of the hydrogenated nitrile rubber at a high temperature and hence the cell resistance increase and to improve the high temperature storage characteristics.

Accordingly, according to another embodiment of the present invention, there is provided a positive electrode manufactured using the composition for forming an anode. In the present invention, the fact that the positive electrode is manufactured using the above-mentioned composition for forming an anode means that the positive electrode composition, the dried material thereof, or a cured product thereof.

The positive electrode according to an embodiment of the present invention may be manufactured according to a conventional method except that the positive electrode active material layer is formed using the composition for forming an anode. Specifically, the positive electrode may be formed by applying the positive electrode composition to the positive electrode collector and drying the positive electrode collector; Or by casting the composition for anode formation on a separate support, and then peeling the support from the support to laminate a film on the cathode current collector.

Specifically, the positive electrode produced according to the above-described production method includes a positive electrode collector and a positive electrode active material layer disposed on the positive electrode collector and having a composite of a conductive material and a dispersant uniformly dispersed.

The positive electrode collector is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, , Nickel, titanium, silver, or the like may be used. In addition, the current collector may have a thickness of 3 to 500 탆, and fine unevenness may be formed on the surface of the current collector to increase the adhesive force 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, and a nonwoven fabric.

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

Specifically, the lithium secondary battery includes a positive electrode, a negative electrode disposed opposite to the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, as described above. The lithium secondary battery may further include a battery container for storing the positive electrode, the negative electrode and the electrode assembly of 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 disposed 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 reversibly intercalating and deintercalating lithium, and includes carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber and amorphous carbon; Metal 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 dedoping lithium such as SiO _x (0 <x <2), SnO ₂ , vanadium oxide, and lithium vanadium oxide; Or a composite containing the metallic compound and the 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. Also, a metal lithium thin film may be used as the negative electrode active material. The carbon material may be both low-crystalline carbon and high-crystallinity carbon. Examples of the low-crystalline carbon include soft carbon and hard carbon. Examples of the highly crystalline carbon include natural graphite, artificial graphite, artificial graphite or artificial graphite, Kish graphite graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar pitches. derived cokes).

The binder and the conductive material are the same as those described above for the anode.

Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a moving path of lithium ions. The separator can be used without any particular limitation as long as it is used as a separator in a lithium secondary battery. Particularly, It is preferable to have a low resistance and an excellent ability to impregnate the electrolyte. Specifically, porous polymer films such as porous polymer films made of polyolefin-based polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers and ethylene / methacrylate copolymers, May be used. Further, a nonwoven fabric made of a conventional porous nonwoven fabric, for example, glass fiber of high melting point, polyethylene terephthalate fiber, or the like may be used. In order to secure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer material may be used, and may be optionally used as a single layer or a multilayer structure.

Examples of the electrolyte used in the present invention include an organic-based liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, and a molten inorganic electrolyte that can be used in the production of a lithium secondary battery. It is not.

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

The organic solvent may be used without limitation as long as it can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate,? -Butyrolactone and? -Caprolactone; Ether solvents such as dibutyl ether or tetrahydrofuran; Ketone solvents such as cyclohexanone; Aromatic hydrocarbon solvents such as benzene and fluorobenzene; Dimethyl carbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate PC) and the like can be used.

Among these, a carbonate-based solvent is preferable, and a cyclic carbonate (for example, ethylene carbonate or propylene carbonate) having a high ionic conductivity and a high dielectric constant, for example, such as ethylene carbonate or propylene carbonate, For example, ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) is more preferable.

In addition, the lithium salt can 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, 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 may be used. The lithium salt is preferably contained in the electrolyte at a concentration of about 0.6 mol% to 2 mol%.

The electrolytes include, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, n-propylamine, and the like for the purpose of improving lifetime characteristics of the battery, N, N-substituted imidazolidine, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-ethylhexyl glycols, - methoxyethanol or aluminum trichloride may be further included. The additive may be included in an amount of 0.1 wt% to 5 wt% based on the total weight of the electrolyte.

The lithium secondary battery having the above structure can be manufactured by manufacturing an electrode assembly with a separator interposed between the positive electrode and the negative electrode, positioning the electrode assembly inside the case, and injecting an electrolyte into the case. Or by laminating the electrode assembly, impregnating the electrode assembly with an electrolytic solution, and sealing the obtained result in a battery case.

As described above, the lithium secondary battery including the anode manufactured using the composition for forming an anode according to an embodiment of the present invention can stably exhibit excellent discharge capacity, output characteristics, and capacity retention ratio due to the uniform dispersion of the conductive material in the anode have. As a result, it is useful for portable devices such as mobile phones, notebook computers, digital cameras, and electric vehicles such as hybrid electric vehicles (HEV).

According to another embodiment of the present invention, there is provided a battery module including the lithium secondary battery as a unit cell and a battery pack including the same.

The battery module or the battery pack may include a power tool; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); Or a power storage system, as shown in FIG.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

Example 1

LiNi ₀ .2 in N-methylpyrrolidone (NMP) solvent _{. 7} Co _{0 . 15} Mn _{0 . 15} O ₂ (average particle diameter (D ₅₀₎ = 10㎛), as a conductive material of carbon black (primary particle diameter = 15 ~ 25nm, specific surface area = 135m ² / g), polyvinyl fluoride containing a hydroxyl group within the molecule as a binder (Repeating structure of acrylonitrile butadiene rubber (residual double bond (RDB) value = 1% by weight, acrylonitrile (AN)) as a dispersant, (Mw = 290,000 g / mol) was added at a weight ratio of 95.8: 2.0: 2.0: 0.2 and mixed for 1 hour using a homo mixer to prepare a composition for forming a positive electrode.

Example 2

A composition for forming an anode was prepared in the same manner as in Example 1, except that the dispersant shown in Table 1 was used.

Example 3

A composition for forming an anode was prepared in the same manner as in Example 1, except that the binder shown in Table 2 was used.

Comparative Examples 1 and 2

A composition for forming an anode was prepared in the same manner as in Example 1 except that the dispersant and the binder described in Tables 1 and 2 were used.

Hydrogenated nitrile rubber dispersant AN ¹⁾
(weight%) BD ²⁾
(weight%) HBD ^{3 )}
(weight%) RDB
(weight%) Mw
(x 1000 g / mol) Example 1 34 0.6 65.4 One 290 Example 2 33.6 11.6 54.8 17 290 Comparative Example 1 40.2 0.5 59.3 One 220 Comparative Example 2 37 9 54 14 220

In Table 1, AN represents repeating units of an acrylonitrile-derived structure in acrylonitrile butadiene rubber, BD represents repeating units of a butadiene-derived structure, and HBD represents repeating units of a hydrogenated butadiene structure. The content by weight,% by weight, is based on the total weight of the acrylonitrile butadiene rubber.

bookbinder Kinds Type of functional group Functional content (mol%) Mw
(x 1000 g / mol) Example 1 PVDF Carbonyl group 0.5 900 Example 2 PVDF Carbonyl group 0.6 900 Example 3 PVDF Hydroxy group 0.6 850 Comparative Example 1 PVDF Carbonyl group 0.3 900 Comparative Example 2 PVDF Carbonyl group 0.4 900

Preparation Example: Preparation of positive electrode and lithium secondary battery

Each of the positive electrode forming compositions prepared in Examples 1 to 3 and Comparative Examples 1 and 2 was coated on one side of an aluminum foil, dried and rolled, and then punched to a predetermined size to prepare a positive electrode.

The negative electrode slurry was prepared by adding carbon powder as a negative electrode active material, PVdF as a binder and carbon black as a conductive material to 96 wt%, 3 wt% and 1 wt%, respectively, as a solvent. The negative electrode slurry was applied to a copper (Cu) thin film as an anode current collector having a thickness of 10 mu m, dried, and then rolled to produce a negative electrode.

The prepared anode and cathode were faced to each other, and then a battery assembly was manufactured through a separator composed of three layers of polypropylene / polyethylene / polypropylene (PP / PE / PP) between the anode and the cathode. After the battery assembly was housed in the battery case, a nonaqueous organic solvent having a composition of ethylene carbonate (EC): ethylmethyl carbonate (EMC): dimethyl carbonate (DMC) = 3: 3: 4 (volume ratio) Based on the total amount of aqueous electrolyte, LiPF ₆ A non-aqueous electrolytic solution added with 1 mol / l was injected to prepare a lithium secondary battery.

Experimental Example 1

Using the composition for forming an anode in Examples 1 and 2 and Comparative Examples 1 and 2, the battery prepared according to the above Production Example was evaluated for battery resistance characteristics after storage at high temperature.

Specifically, the produced lithium secondary battery was stored at 60 占 폚 under a 4.2 V full charge condition for 5 weeks, and the DC-IR resistance was measured. The results are shown in Fig.

As a result of the experiment, it can be seen that the resistance characteristic can be changed according to the content of the repeating unit of the AN-derived structure in the acrylonitrile butadiene rubber and the RDB value, and in particular, the content of the repeating unit of the AN-derived structure in acrylonitrile butadiene is 34 weight %, And the RDB value was 1 wt%, the resistance increase rate of the cell was the lowest even after storage at high temperature when the content of the repeating unit of the AN-derived structure and the RDB value condition were both satisfied in the present invention.

Experimental Example 2

A film was prepared using acrylonitrile butadiene rubber as a dispersant in Examples 1 and 2 and Comparative Examples 1 and 2, and the film was impregnated with an electrolytic solution to measure the thickness and weight of the film before and after impregnation with the electrolyte, The swelling characteristics were evaluated. The nonaqueous organic solvent having a composition of ethylene carbonate (EC): ethylmethyl carbonate (EMC): propylene carbonate (PC) = 2: 6: 2 (volume ratio) and a nonaqueous organic solvent ₆ To 1 mol / l was used. The results are shown in Table 3 and FIG.

Example 1 Example 2 Comparative Example 1 Comparative Example 2 Mass increase rate (%) 356 408 Dissolved in electrolyte 704 Thickness increase rate (%) 124 146 Dissolved in electrolyte No thickness measurement

As a result of the experiment, swelling characteristics may be changed depending on the content of AN and RDB in acrylonitrile-butadiene rubber, and such swelling characteristic causes a disconnection of a conductive path in an electrode composition having a low conductive material content, It can be expected that it will affect the characteristics.

Experimental Example 3

The mixing energy required for dispersing the carbon black and the dispersant in the NMP solvent during the preparation of the composition for forming an anode prepared in Example 1 and Comparative Examples 1 and 2 and the particle size distribution of the carbon black- the D ₅₀ value was determined. The results are shown in Table 4 below.

Mixing energy required for dispersion
(Kwh / kg) Particle size D ₅₀ (占 퐉) Example 1 20 0.59 Comparative Example 1 28 0.77 Comparative Example 2 21 0.75

As a result of the experiment, in Example 1, the carbon black-dispersant composite exhibited a more uniform particle size distribution than Comparative Examples 1 and 2.

Experimental Example 4

The positive electrode was prepared using the composition for forming an anode in Examples 1 and 2 and Comparative Examples 1 and 2, and the adhesion between the positive electrode active material layer and the current collector was measured.

Specifically, the positive electrode prepared by using the composition for forming an anode in Examples 1 and 2 and Comparative Examples 1 and 2 was cut into a predetermined size and fixed on a slide glass. Then, the current collector was peeled off at an angle of 180 °, The strength was measured. The results are shown in Table 5.

Adhesion (gf) Example 1 20 Example 2 30 Comparative Example 1 14 Comparative Example 2 18

As a result of the test, the positive electrode of Examples 1 and 2 prepared using the composition for forming a positive electrode satisfying both the dispersant and the binder condition of the present invention exhibited remarkably improved adhesion properties as compared with Comparative Examples 1 and 2.

Claims (12)

A cathode active material, a conductive material, a binder, a dispersant, and a dispersion medium,
Wherein the binder contains a fluorine-based polymer containing 0.5 mol% to 1 mol% of a functional group capable of hydrolysis in a molecule,
Wherein the dispersant comprises a hydrogenated nitrile rubber having a residual double bond value of 30% by weight or less according to the following formula 1 and a content of repeating units of the?,? - unsaturated nitrile-derived structure in the molecule is 20% by weight to 35% &Lt; tb &gt;&lt; TABLE &gt;
[Equation 1]
Residual double bond (RDB) = BD% / (BD + HBD) x100
In the above formula (1), BD represents the weight% of the repeating units of the conjugated diene-derived structure in the hydrogenated nitrile rubber, and HBD represents the weight percent of the repeating units of the hydrogenated conjugated diene-derived structure.
The method according to claim 1,
Wherein the hydrogen-sintering synthetic functional group comprises any one or two or more selected from the group consisting of a carboxyl group, a hydroxyl group, a sulfonic acid group, a carbonyl group, an ester group and a glycidyl group.
The method according to claim 1,
Wherein the binder is a homopolymer of vinylidene fluoride containing a hydrogen-sintering synthetic functional group.
The method according to claim 1,
Wherein the binder has a weight average molecular weight of 300,000 g / mol to 1,000,000 g / mol.
The method according to claim 1,
Wherein the binder is contained in an amount of 1 part by weight to 30 parts by weight based on 100 parts by weight of the cathode active material.
The method according to claim 1,
Wherein the conductive material comprises carbon black.
The method according to claim 6,
The carbon black is a secondary particle formed by aggregating primary particles,
Wherein the primary particle has an average particle diameter (D ₅₀ ) of 15 nm to 25 nm and a secondary particle has a BET specific surface area of 130 m ² / g to 380 m ² / g.
The method according to claim 1,
Wherein the hydrogenated nitrile rubber comprises a repeating unit represented by the following formula (1), a repeating unit represented by the following formula (2), and a repeating unit represented by the following formula (3) And a hydrogenated acrylonitrile-butadiene rubber in which the content of repeating units having the structure of the following formula (1) is 20% by weight to 35% by weight in the molecule.
[Chemical Formula 1]

(2)

(3)

The method according to claim 1,
Wherein the hydrogenated nitrile rubber has a weight average molecular weight of 100,000 g / mol to 700,000 g / mol.
The method according to claim 1,
Wherein the dispersant is contained in an amount of 5 to 50 parts by weight based on 100 parts by weight of the conductive material.
A positive electrode for a secondary battery produced by using the composition for forming an anode according to any one of claims 1 to 10.
12. A lithium secondary battery comprising the positive electrode according to claim 11.

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