KR101834324B1 - Electrode using lithium secondary battery and lithium secondary battery including the same - Google Patents

Abstract

The present invention provides an electrode slurry comprising an electrode active material, a conductive material and a dispersion medium, wherein the conductive material has a BET nitrogen surface area of 50 to 100 m < 2 > / g and at least one hydrophilic polymer selected from amylose, amylopectin and cyclodextrin And the intensity ratio (ID / IG) of the D band to the G band through Raman spectroscopy is less than 0.05. The present invention relates to an electrode slurry for a lithium secondary battery.

Description

[0001] The present invention relates to an electrode slurry for a lithium secondary battery and a lithium secondary battery including the electrode slurry.

The present invention relates to an electrode slurry for a lithium secondary battery and a lithium secondary battery including the electrode slurry. More particularly, the present invention relates to an electrode slurry for a lithium secondary battery, which increases the purity of a carbonaceous material as a conductive material to increase the capacity of the secondary battery, An electrode slurry for a secondary battery, and a lithium secondary battery including the electrode slurry.

Due to the rapid increase in the use of fossil fuels, the demand for the use of alternative energy or clean energy is increasing. As a part of this, the most active field of research is electric power generation and storage.

At present, a typical example of an electrochemical device utilizing such electrochemical energy is a secondary battery, and the use area thereof is gradually increasing.

Recently, as technology development and demand for portable devices such as smart phones, notebooks, wearable devices, and cameras have increased, the demand for secondary batteries as energy sources has increased rapidly, and the secondary batteries have high energy density and operating potential A lot of research has been conducted on a lithium secondary battery having a long cycle life and low self-discharge rate, and it has been commercialized and widely used.

In addition, as the interest in environmental issues grows, researches on electric vehicles and hybrid electric vehicles that can replace fossil fuel-based vehicles such as gasoline vehicles and diesel vehicles, which are one of the main causes of air pollution, , Lithium secondary batteries are also used as power sources for such electric vehicles and hybrid electric vehicles.

Such a lithium secondary battery has a structure in which a lithium electrolyte is impregnated into an electrode assembly composed of a cathode including a lithium transition metal oxide as an electrode active material, a cathode including a carbonaceous active material, and a separator. The positive electrode is prepared by coating a positive electrode mixture containing a lithium transition metal oxide on an aluminum foil, and the negative electrode is prepared by coating a copper foil with a negative electrode mixture containing a carbonaceous active material. The electrode mixture is prepared by mixing an electrode mixture composed of an electrode active material for storing energy, a conductive material for imparting electrical conductivity, and a binder (PVdF) for adhering it to an electrode foil, in water and NMP (N-methyl pyrrolidone) And a dispersion medium.

Generally, the conductive material is added to the positive electrode mixture and the negative electrode mixture for the purpose of improving the electrical conductivity of the active material. The conductive material is added in an amount of about 0% by weight to 20% by weight based on the weight of the electrode material mixture. If the conductive material is used in too small an amount, the internal resistance of the electrode increases and the performance of the battery deteriorates. The content of the binder must be increased at the same time, which leads to a problem such as a reduction in the battery capacity due to the reduction of the electrode active material.

Examples of the conductive material include graphite such as natural graphite and artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Carbon fibers such as carbon nanotubes and fullerene; conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

In the case of spherical carbon black which is generally applied, it has a hydrophobic surface, low specific gravity, and small nano-level. Therefore, when the aqueous slurry is prepared, the miscibility with the dispersion medium is low, so that the dispersion of the solid content and the diffusion rate are lowered, and it is difficult to secure uniform slurry production. When the electrode slurry is prepared by increasing the amount of the dispersion medium to compensate for these characteristics, it is difficult to coat the electrode slurry due to low viscosity, and the amount of evaporation increases in the drying process of the electrode, so that the light conductive material becomes higher than water, Thereby deteriorating the battery characteristics.

In order to solve such a problem, conventionally, there has been an attempt to use a carbon nanotube (CNT) as a conductive material. However, when the carbon nanotubes are also lighter than water, dispersion of the carbon nanotubes is still uneven when using an aqueous dispersion medium, and there arises an area in which the particles are not in contact with the active material particles locally. Carbon nanotubes are manufactured through synthesis for mass production. In the synthesized carbon nanotubes, metal particles, carbon impurities, and the like are present. These impurities are factors that degrade efficiency as a conductive material .

The above problems are exacerbated in the high loading region of the conductive material and have a disadvantage of increasing the waiting time for coating the slurry. Therefore, there is an increasing need to develop a technology capable of fundamentally solving such problems.

Korean Patent Publication No. 10-2015-0083635 (July 20, 2015) Korean Patent Publication No. 10-2013-0030660 (March 27, 2013)

Disclosure of the Invention The present invention has been conceived to solve the problems as described above. It is an object of the present invention to increase the purity of the carbon component, which is the conductive material, to increase the capacity of the secondary battery, and to provide a hydrophilic polymer And a lithium secondary battery comprising the electrode slurry.

The present invention relates to an electrode slurry for a lithium secondary battery and a lithium secondary battery comprising the same.

One aspect of the present invention is an electrode slurry comprising an electrode active material, a conductive material and a dispersion medium, wherein the conductive material has a BET nitrogen surface area of 50 to 100 m < 2 > / g and one or two selected from amylose, amylopectin and cyclodextrin (ID / IG) of the D band to the G band through Raman spectroscopy is less than 0.05. The present invention relates to an electrode slurry for a lithium secondary battery.

In the present invention, the dispersion medium is any one or more selected from water, N-methylpyrrolidine, methanol, ethanol, n-propanol and isopropanol, and amylase, amyloglucosidase and cyclodextrin Glokoton And the enzyme may be one or two or more enzymes selected from the group consisting of < RTI ID = 0.0 >

The conductive material may be any one or more selected from natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanotube, graphene and fullerene.

In the present invention, the active material may be a cathode active material or an anode active material, and more specifically, the cathode active material may be represented by the following general formula (1), (2), or a mixture thereof.

≪ Formula 1 >

Li [Li _a M _1-a ] O _{2 + d}

(2)

Li [Li _b M1 _c M _{2 e} ] O _{2 + d}

0 <b <1, 0 <c <1, 0? D? 0.1, 0 <e <0.1, where 0 <a <1, b + c + e = 1,

Wherein M1 and M2 are selected from Ni, Co, Mn, Fe, Na, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, It is either.)

In the present invention, the negative electrode active material may be any one or more selected from the group consisting of lithium metal, lithium-alloyable metal, transition metal oxide, non-transition metal oxide, and carbon- SnO ₂ , SiO _x (0 < x < 2), natural graphite, artificial graphite, soft carbon, graphite, Hard carbon, mesophase pitch carbide, and fired coke,

Z is at least one element selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, Se , Te, and Po, respectively.

The hydrophilic polymer may have a coating thickness of 1 to 10 nm.

Another aspect of the present invention relates to a lithium secondary battery comprising the electrode slurry for the lithium secondary battery.

The electrode slurry for a lithium secondary battery according to the present invention includes a conductive material having a surface coated with a hydrophilic polymer, thereby improving compatibility with a water-based dispersion medium, which is a disadvantage of a hydrophobic conductive material, and it is not necessary to increase the viscosity of the dispersion medium, Can greatly increase. In addition, the dispersion medium further contains an enzyme capable of decomposing the hydrophilic polymer, whereby the hydrophilic polymer can be easily removed, if necessary, so that the performance of the conductive material can be enhanced.

In addition, impurities contained in the conductive material can be easily removed by heating in an inert gas or a vacuum atmosphere in a subsequent step of the conductive material, thereby increasing the specific surface area and purity and greatly improving the performance of the battery.

The electrode slurry for a lithium secondary battery according to the present invention is easy to manufacture electrodes with high loading due to the above characteristics and can increase the content of solid content, thereby providing a lithium rechargeable battery having a high capacity.

Hereinafter, an electrode slurry for a lithium secondary battery including a metal substrate according to the present invention and a lithium secondary battery including the electrode slurry will be described in detail with reference to specific examples. The following specific embodiments are provided by way of example so that those skilled in the art can fully understand the spirit of the present invention.

Therefore, the present invention is not limited to the embodiments shown below, but may be embodied in other forms. The embodiments shown below are only for clarifying the spirit of the present invention, and the present invention is not limited thereto.

Here, unless otherwise defined, technical terms and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. In the following description, the gist of the present invention is unnecessarily blurred And a description of the known function and configuration will be omitted.

Also, the singular forms as used in the specification and the appended claims are intended to include the plural forms as well, unless the context clearly indicates otherwise.

In describing the components of the present invention, terms such as first, second, A, B, (a), and (b) may be used. These terms are intended to distinguish the constituent elements from other constituent elements, and the terms do not limit the nature, order or order of the constituent elements. When a component is described as being "connected", "coupled", or "connected" to another component, the component may be directly connected to or connected to the other component, It should be understood that an element may be "connected," "coupled," or "connected."

The inventors of the present invention have found that the disadvantage of the conductive material included in the conventional lithium secondary battery is that the specific gravity is small and the compatibility with the aqueous dispersion medium is poor due to hydrophobicity and that the impurities contained after the synthesis reduce the efficiency of the battery, In the course of research, it has been found that when the hydrophilic polymer is coated on the surface of the conductive material to enhance the compatibility with the aqueous dispersion medium and annealing is performed at a high temperature in a vacuum or an inert gas atmosphere, the impurities are effectively removed without structural destruction of the conductive material, The efficiency of the secondary battery is increased, and the present invention has been completed.

The electrode slurry for a lithium secondary battery according to the present invention may include an electrode active material, a conductive material, and a dispersion medium.

In the present invention, the electrode active material is a material capable of reversibly storing and releasing lithium, and includes a cathode active material and an anode active material.

In the present invention, the cathode active material may be a lithium transition metal oxide. The lithium transition metal oxide can be used for the positive electrode of a lithium battery, and any lithium metal can be used as long as it can be used in the related art. For example, the lithium transition metal oxide may have a spinel structure, a layered structure, or an olivine structure.

The lithium transition metal oxide may be a single composition or a compound having two or more compositions. For example, a complex of a compound having two or more layered structures, and may be a complex of a compound having a layered structure and a compound having a spinel structure.

In the lithium transition metal oxide, the raw material of the lithium transition metal is at least one selected from the group consisting of Ni, Co, Mn, Fe, Na, Ca, Ti, (V), Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, A metal salt of at least one element selected from the group consisting of molybdenum (Mo), aluminum (Al), gallium (Ga), boron (B) and combinations thereof. The metal salt may be sulfate, nitrate, acetate, halide, hydroxide or the like, and is not particularly limited as long as it can be dissolved in a solvent.

More specifically, the cathode active material may be represented by the following general formula (1), (2), or a mixture thereof.

&Lt; Formula 1 >

Li [Li _a M _1-a ] O _{2 + d}

(2)

Li [Li _b M1 _c M _{2 e} ] O _{2 + d}

0 <b <1, 0 <c <1, 0? D? 0.1, 0 <e <0.1, where 0 <a <1, b + c + e = 1,

Wherein M1 and M2 are selected from Ni, Co, Mn, Fe, Na, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, It is either.)

More specifically, M1 may be nickel, M2 may be cobalt, and M3 may be manganese. Further, the transition metal raw material can be mixed by adjusting the molar ratio so as to have a high capacity characteristic. This molar ratio can be easily controlled according to the metal composition of the center portion to be obtained.

The cathode active material is not limited to the production method. For example, the cathode active material may be prepared by simultaneously mixing a lithium source material, at least one transition metal source material, a chelating agent, and a basic aqueous solution, followed by firing the same. Particularly, when co-mixing the above materials, coprecipitation can be applied to obtain a slurry.

In the present invention, the cathode active material may have an average particle diameter of 10 nm to 100 탆. The workability is improved in the above-mentioned average particle size range, and the charging / discharging efficiency of the secondary battery is maximized.

In the present invention, the negative electrode active material may be a lithium metal, an alloy of lithium and other elements, a transition metal oxide, a non-transition metal oxide, etc., in addition to a carbon material generally used as a material capable of absorbing and desorbing lithium ions.

Sn-Z alloy, lithium titanium oxide, vanadium oxide, lithium vanadium oxide, SnO ₂ , SiO _x (0, 0, 0, <x <2), natural graphite, artificial graphite, soft carbon, hard carbon, mesophase pitch carbide, and fired cokes.

In the present invention, examples of Z include Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, (Zr), hafnium (Hf), ruthenium (Rf), vanadium (V), niobium (Nb), tantalum (Ta), dibonium (Db), chromium (Cr), molybdenum (Si), technetium (Tc), rhenium (Re), boron (Bh), iron (Fe), lead (Pb), rubidium (Ru), osmium (Os) (Rh), Ir, Ir, Pd, Pt, Cu, Ag, Au, Zn, (Al), Ga, Sn, In, Ti, Ge, Ph, As, Sb, Bi, , Sulfur (S), selenium (Se), telenium (Te), and polonium (Po).

In the present invention, the negative electrode active material is more preferably LTO (Li ₄ Ti ₅ O ₁₂ ). The LTO is advantageous for fast charging and high output characteristics at room temperature and low temperature when lithium ions are absorbed into the cathode because the lithium ions are absorbed into the cathode and maintains the original crystal structure during charging and discharging, This is because the life of the lithium secondary battery is increased.

Even when the negative electrode active material is a lithium-metal oxide, it is preferable to manufacture the negative electrode active material in a similar manner to the positive electrode active material. For example, in the case of LTO, a lithium raw material, a titanium raw material, a chelating agent, and a basic aqueous solution may be simultaneously mixed and then fired. Particularly, when co-mixing the above materials, coprecipitation can be applied to obtain a slurry.

In the present invention, the conductive material plays a role to improve the electrical conductivity between the electrode active material or between the active material and the current collector. If the amount of the conductive material is insufficient or does not act properly, The capacity of the battery is decreased, the fast charge / discharge characteristics, the charge / discharge efficiency, especially the initial charge / discharge efficiency are adversely affected.

The conductive material is a carbon-based material, and can be divided into a carbon representative area structure and a carbon sub-surface structure based on the shape.

The term "carbon representative area structure" used in the present invention means a material having a surface area of at least 5000 nm ² of a particle composed of carbon atoms arranged in a hexagonal shape and is mainly composed of a two-dimensional surface or a three- And may include any carbon structure that does not have a shape.

The term &quot; carbon sub-surface structure &quot; used in the present invention means a material having a surface area of one particle of carbon atoms arranged in a hexagonal shape of less than 5000 nm ^2, . &Lt; / RTI &gt;

In the present invention, an example of the carbon representative area structure may be at least one selected from graphene, single-walled carbon nanotubes, and multi-walled carbon nanotubes.

Examples of the carbon sub-surface structure in the present invention include fullerene; Graphite such as graphite, natural graphite, and artificial graphite; Carbon black, acetylene black, ketjen black, denka black, thermal black, channel black, furnace black, lamp black, summer black and super-P.

In the present invention, conductive materials such as carbon fibers and metal fibers, in addition to the carbon representative area structure and the carbon sub-surface structure, may be used as the conductive material raw material. Carbon fluoride; Metal powders such as aluminum and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive oxides such as titanium oxide; And polyphenylene derivatives may be used singly or in combination of two or more, but the present invention is not limited thereto.

As the conductive material raw material used in the present invention, more specifically, it may be a mixture of carbon nanotubes and carbon black. This is to induce formation of a three-dimensional network structure by forming point, line and surface contact between conductive materials by mixing conductive materials having different structural characteristics. That is, the shape of the carbon nanotubes is cylindrical and has a large specific surface area, whereas the shape of the carbon black is a nanoscale spherical shape, so that carbon black can be easily adsorbed on the surface of the carbon nanotubes to form a three-dimensional network structure. In the case of forming such a three-dimensional network structure, the π-π interaction between the conductive material materials can be reduced, and as a result, it is possible to inhibit the electrical characteristics from being reduced due to the re-agglomeration of the respective conductive material materials.

In the present invention, the mixing ratio of the conductive material raw material is in the range of 70 to 10:30 to 90 weight ratio of the carbon representative area structure and the carbon sub-surface structure, more specifically, the carbon representative area structure and the carbon sub- 80 weight ratio. When the carbon representative area structure is less than 10 parts by weight or the carbon sub-surface structure is added in an amount greater than 90 parts by weight, the contact between the conductive material and the active material is lowered and the discharge output and the low temperature characteristics are decreased. Even when the carbon sub-surface structure is added in an amount of less than 30 parts by weight, contact between the conductive material and the active material decreases, which is not preferable.

The conductive material preferably has a BET nitrogen surface area of 50 to 100 m &lt; 2 &gt; / g. In this range, the surface area of the conductive material itself is increased, so that the contact between the conductive material and the active material can be maintained, excessive use of the solvent can be prevented, and workability is improved.

The conductive material may include heating before mixing into the slurry to completely remove metal impurities remaining after the production.

In general, metal catalysts are indispensable for synthesizing conductive materials, particularly carbon nanotubes. However, such a metal catalyst remains in the carbon layer during the synthesis of carbon nanotubes, and acts as an impurity. As the impurity increases, lattice strain of the carbon structure becomes a factor to decrease the capacity of the cell.

In order to remove these impurities, a method of oxidizing the conductive material with an acid is generally used. However, when impurities are present in the carbon layer, it is impossible to remove all metal impurities by the chemical acid treatment.

The present invention proposes a high temperature annealing method to solve this disadvantage. Carbon can be effectively removed without destroying the conductive material structure because the metal is removed by evaporation at a temperature above the evaporation temperature, while the structure is not changed even if a high temperature of 1,400 ° C or more is applied in a vacuum or an inert gas atmosphere.

In the present invention, the conductive material is preferably heated in an inert gas atmosphere such as vacuum or nitrogen or argon to 1,400 to 3,000 DEG C, and is preferably heated at the above temperature for 10 minutes to 2 hours. It is possible to achieve evaporation and removal of metal impurities in the above range.

In addition, the conductive material may be coated with a hydrophilic polymer on its surface to improve affinity with the dispersion medium. In detail, in general, the conductive material is hydrophobic and does not mix well with an aqueous solvent. In addition, when the specific gravity is small, it floats on the surface of the dispersion medium when it is mixed with the dispersion medium. In this case, the efficiency of the electrode is greatly decreased because the conductive material is stuck to one side. In order to solve this problem, a binder is conventionally added to the slurry. However, since the binder is basically an insulator, the efficiency of the electrode deteriorates.

In order to solve the above-mentioned problems, the present invention provides a hydrophilic polymer on the surface of a conductive material to impart affinity to the dispersion medium and to increase the specific gravity of the conductive material so that the dispersion medium can be uniformly mixed with the slurry. If necessary, an enzyme capable of decomposing the hydrophilic polymer may be further added to the dispersion medium to remove the hydrophilic polymer, which is an insulator, to prevent reduction in the efficiency of the electrode.

The hydrophilic polymer is a hydrophilic polymer having a high affinity with a dispersion medium, and is not limited to a polysaccharide that can be hydrolyzed through an enzyme. Amylose, amylopectine and cyclodextrin can be mentioned as preferred examples, and all hydrophilic polymers capable of hydrolyzing through enzymes can be used.

In the present invention, the hydrophilic polymer may be coated on the surface of the conductive material to a thickness of 1 to 10 nm. When the enzyme is added to the dispersion medium in the above range, the hydrophilic polymer can be removed without leaving a hydrophilic polymer on the surface of the conductive material.

The hydrophilic polymer may be coated on the surface of the conductive material by non-covalent bonding. Therefore, even if the conductive material and the hydrophilic polymer are mixed without any other binder or special treatment, the hydrophilic polymer can naturally cover the surface of the conductive material.

The dispersion medium may be any one or a mixture of two or more selected from water, an alcohol compound, a ketone compound, an ether compound, and a lactam compound, provided that the dispersion medium is a liquid at normal temperature and normal pressure.

Examples of the dispersion medium include water; Alcohols such as methanol, ethanol, propanol, isopropanol, butanol, isobutanol, s-butanol, t-butanol, pentanol, isopentanol and hexanol; Ketones such as acetone, methyl ethyl ketone, methyl propyl ketone, ethyl propyl ketone, cyclopentanone, cyclohexanone, and cycloheptanone; Methyl ethyl ether, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, diisobutyl ether, di-n-amyl ether, diisobutyl ether, methylpropyl ether, methylisopropyl ether, Ethers such as ethyl propyl ether, ethyl isobutyl ether, ethyl n-amyl ether, ethyl isoamyl ether and tetrahydrofuran; Lactones such as gamma-butylolactone and delta-butylolactone; Lactams such as beta-lactam; , But they are not limited to these, and two or more kinds of them may be mixed. However, considering the cost and the kind of the active material, the dispersion medium is preferably an aqueous dispersion medium.

The solvent may include an enzyme capable of removing the hydrophilic polymer on the surface of the conductive material as required.

The enzyme is not limited to any kind as long as it can hydrolyze the polysaccharide, which is the hydrophilic polymer, even in a small amount. For example, one or two or more selected from amylase, amyloglucosidase and cyclodextrin glucokonate can be used. In the present invention, the addition amount is not limited, and it is preferable to appropriately adjust the rate in consideration of the decomposition rate of the hydrophilic polymer.

The present invention also provides a lithium secondary battery comprising the electrode for a secondary battery, wherein the electrode slurry is coated on a current collector and dried.

In the present invention, the electrode for a secondary battery may be manufactured as an anode or a cathode according to an active material contained in the slurry. The slurry may be prepared by including an active material, a conductive material, and a solvent, and then directly coating and drying the slurry on a current collector. Alternatively, the slurry may be cast on a separate support, May also be produced by laminating on a current collector.

The current collector is a region where electrons move in an electrochemical reaction, and a positive electrode collector and a negative electrode collector exist depending on the type of the electrode.

The cathode current collector is generally made to have a thickness of 3 to 500 mu m. For example, stainless steel, aluminum (Al), nickel (Ni), titanium (Ti), or the like may be used as the positive electrode current collector as long as it has high conductivity without causing chemical changes in the battery. , Fired carbon, or a surface treated with carbon, nickel, titanium, or silver on the surface of aluminum or stainless steel, or the like may be used.

The negative electrode current collector is generally made to have a thickness of 3 [mu] m to 500 [mu] m. Such an anode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, and may be formed of a material such as copper, stainless steel, aluminum, nickel, titanium, fired carbon, surface of copper or stainless steel A surface treated with carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used.

These current collectors may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven fabric, or the like, by forming minute irregularities on the surface of the current collectors to enhance the binding force of the electrode active material no.

When the electrode slurry obtained by drying the electrode slurry in the electrode is thick, the electrode slurry can be dispersed relatively uniformly, have high conductivity, and can secure a high-capacity excellent battery. 20 mg / cm &lt; 2 &gt;.

The lithium secondary battery according to the present invention may have a structure in which an electrode stacked body in which a plurality of positive and negative electrodes opposed to each other with a separator interposed therebetween is impregnated with an electrolyte.

Specifically, the lithium secondary battery according to the present invention may include an electrode assembly in which an anode and a cathode are stacked alternately with each other with a separator interposed therebetween, an electrolyte in which the electrode assembly is impregnated, and a battery case for sealing the electrolyte and the electrolyte assembly .

Each anode of the electrode assembly may be connected in series, parallel, or series-parallel, and each cathode may be connected in series, parallel, or series-parallel. The positive electrode may include a current collector and a positive electrode active material layer containing the positive electrode active material on the current collector. The positive electrode may include an uncoated portion on which the positive electrode active material layer is not formed. The negative electrode may further include a current collector and a negative electrode active material layer containing the negative electrode active material on the current collector, and may include an uncoated portion in which the negative electrode active material layer is not formed. Electrical connection between each anode or each cathode of the electrode assembly can be accomplished through this igniter.

Electrode Assembly The collector of each anode and / or cathode may be a porous conductor, and more particularly the collector may be a foam, a film, a mesh, a felt or a porous Or may be a perforated film. More specifically, the current collector may be a conductive material including graphite, graphene, titanium, copper, platinum, aluminum, nickel, silver, gold, or carbon nanotubes that is excellent in conductivity and chemically stable at the time of charge / And may be in the form of a foam, a film, a mesh, a felt or a perforated foil of such a conductive material, or may be a composite coated or laminated with a different conductive material .

Electrode Assembly The negative electrode active material of each negative electrode can be used as an active material conventionally used for a negative electrode of a secondary battery. As an example of the lithium secondary battery, the negative electrode active material may be a lithium intercalable material. As a non-limiting example, the negative electrode active material may be selected from the group consisting of lithium (metal lithium), graphitizable carbon, graphitizable carbon, graphite, silicon, Sn alloy, Si alloy, Sn oxide, Si oxide, Ti oxide, Ni oxide, FeO) and a lithium-titanium oxide (LiTiO _2, Li ₄ Ti ₅ O ₁₂₎ can be one or more selected materials in the negative electrode active material group, and the negative electrode active material group the selected materials (at least two first cathode active material and second cathode active material) Lt; / RTI &gt; Such a composite body may have a structure in which a first anode active material and a second anode active material are simply mixed, a core shell structure of a core of a first anode active material and a shell of a second anode active material, a structure in which a second anode active material is supported on a matrix of the first anode active material , A structure in which a second negative electrode active material is coated or supported on a first negative electrode active material having a zero-dimensional or one-dimensional or two-dimensional nanostructure, or a structure in which a first negative electrode active material and a second negative electrode active material are stacked.

In the electrode assembly, the separation membrane positioned between the anodes and the cathodes adjacent to each other may be different from or different from each other depending on the stacking direction of the anodes and the cathodes, and in order to prevent shorting between the cathodes and the anodes in a conventional secondary battery, The separator used is sufficient. As a non-limiting example of a lithium secondary battery, the separation membrane may be a material selected from one or more of polyethylene, polypropylene, polyolefin, and polyester, and may be a microporous membrane structure. In this case, the microporous membrane may be coated with an inorganic material, and may have a laminated structure in which a plurality of organic films such as a polyethylene membrane, a polypropylene membrane, and a nonwoven fabric are laminated for the purpose of preventing overcurrent, have.

The electrode assembly may be manufactured by a conventional method of manufacturing a jelly roll type electrode assembly. For example, a plurality of anodes and cathodes alternately and alternately disposed on one surface of a separator may be formed by rolling. However, it goes without saying that the present invention can not be limited by the above-described method of manufacturing an electrode assembly.

The electrolyte in which the electrode assembly is impregnated may be a conventional aqueous or non-aqueous electrolyte capable of smoothly conducting lithium ions involved in charging and discharging of the battery and maintaining battery characteristics for a long period of time in a conventional lithium secondary battery.

Examples of the electrolyte in the present invention may be a non-aqueous electrolyte, and the non-aqueous electrolyte may include a non-aqueous solvent and a lithium salt. As a non-limiting example, the lithium salt contained in the electrolyte may be a lithium cation and a cation selected from the group consisting of NO ₃ ^- , N (CN) ₂ ^- , BF ₄ ^- , ClO ₄ ^- , PF ₆ ^- , (CF ₃ ) ₂ PF ₄ ^{- _{3) 3 PF 3 -, (}} CF 3) 4 PF 2 -, (CF 3) 5 PF -, (CF 3) 6 P -, CF 3 SO 3 -, CF 3 CF 2 SO 3 -, (CF 3 SO ^{_{2) 2 N -, (FSO}} 2) 2 N -, CF 3 CF 2 (CF 3) 2 CO -, (CF 3 SO 2) 2 CH -, (SF 5) 3 C -, (CF 3 SO 2) ^{_{3 C -, CF 3 (CF}} 2) 7 SO 3 -, CF 3 CO 2 -, CH 3 CO 2 -, SCN - , and _{(CF 3 CF 2 SO 2)} 2 N - providing an anion selected at least one from It can be a salt.

The solvent of the electrolyte is selected from the group consisting of ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, Dimethyl carbonate, diethyl carbonate, di (2,2,2-trifluoroethyl) carbonate, dipropyl carbonate, dibutyl carbonate, ethyl methyl carbonate, 2,2,2-trifluoroethyl methyl carbonate, methyl propyl carbonate , Ethyl propyl carbonate, 2,2,2-trifluoroethyl propyl carbonate, methyl formate, ethyl formate, propyl formate, butyl formate, dimethyl ether, diethyl ether, di Propyl ether, methyl ethyl ether, methyl propyl ether, ethyl propyl ether, methyl acetate, ethyl acetate, propyl acetate, butyl acetate Butyrate, butyl butyrate, gamma -butyrolactone (gamma-butyrolactone), ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, butyrolactone, 2-methyl- gamma -butyrolactone, 3-methyl- gamma -butyrolactone, 4-methyl- gamma -butyrolactone, gamma -thiobutyrolactone, ? -valerolactone,? -valerolactone,? -caprolactone,? -caprolactone,? -propiolactone (? -caprolactone,? -caprolactone, propiolactone), tetrahydrofuran, 2-methyltetrahydrofuran, 3-methyltetrahydrofuran, trimethylphosphate, triethylphosphate, tris (2-chloroethyl) 2-trifluoroethyl) phosphate, tripropyl phosphate, triisopropyl &lt; RTI ID = 0.0 &gt; But are not limited to, sulfates, triesters, tributyl phosphate, trihexyl phosphate, triphenyl phosphate, tritolyl phosphate, methyl ethylene phosphate, ethyl ethylene phosphate, dimethyl sulfone, ethyl methyl sulfone, methyl trifluoromethyl sulfone, Sulfone, methylpentafluoroethylsulfone, ethyl pentafluoroethylsulfone, di (trifluoromethyl) sulfone, di (pentafluoroethyl) sulfone, trifluoromethylpentafluoroethylsulfone, trifluoromethyl nonafluoro One or more selected solvents selected from butyl sulfone, pentafluoroethyl nonafluorobutyl sulfone, sulfolane, 3-methyl sulfolane, 2-methyl sulfolane, 3-ethyl sulfolane and 2- .

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, the following examples are intended to illustrate the most preferred embodiments of the present invention, but the present invention is not limited to the following examples and comparative examples.

The physical properties of the specimens prepared through Examples and Comparative Examples were measured as follows, and each battery was prepared as follows.

(Discharge output)

The output characteristics of the batteries manufactured through Examples and Comparative Examples were measured by HPPC (Hybrid Pulse Power Characterization by Freedom Car Battery Test Manual).

(Low temperature characteristics)

The batteries prepared in Examples and Comparative Examples were tested for low temperature characteristics at room temperature (25 ° C) and at room temperature (-20 ° C) at 0.5 ° C and 0.5C discharge capacity.

(Electrolytic solution)

A 1M LiPF6 solution was prepared by mixing ethylene carbonate (EC) / ethylmethyl carbonate (EMC) / diethyl carbonate (DEC) in a volume ratio of 25/45/30 by volume, and then 1 weight part of vinylene carbonate (VC) , 0.5% by weight of 1,3-propensulfone (PRS), and 0.5% by weight of bis (oxalate) borate (LiBOB).

(battery)

The positive electrode plate and the negative electrode plate were each laminated by notching, and a cell was formed between the positive electrode plate and the negative electrode plate through a separator (polyethylene, thickness: 25 μm), and the tab portions of the positive electrode and the negative electrode were respectively welded .

Next, the welded anode / separator / cathode combination was put into the pouch, and the three sides of the electrolytic solution except for the liquid injection side were sealed. At this time, the portion with the tab was included in the sealing portion, the electrolyte was injected into the other portion, and the injection portion was sealed and impregnated for 12 hours.

Thereafter, pre-charging was carried out for 36 minutes at a current of 0.25C (2.5 A). After precharging, the gas was removed and aging was performed for 24 hours. Then, charge-discharge was performed under the condition of charging condition CC-CV 0.2C 4.2V 0.05C cut-off, discharge condition CC 0.5C 2.5V cut-off (Charging condition CC-CV 0.5C 4.2V cut-off, discharge condition CC 0.5C 2.5V cut-off).

(Example 1)

Denken black (Denka) was prepared as a conductive material. The denka black was charged into a heating furnace, and nitrogen was charged into the furnace, followed by heating at a temperature of 1500 캜 for one hour. The heated Denka black was mixed with an aqueous amylose solution (concentration 5%) having a weight average molecular weight of 30,000 and stirred at room temperature for 30 minutes at 500 rpm in an oxygen atmosphere to perform a hydrophilic polymer coating process.

As a cathode active material in the coating Denka Black as described above LiNi _{0. 8} Co _{0 . 1} Mn _{0 . 1} O ₂ , polyvinylidene fluoride having a weight average molecular weight of 750,000 as a binder, and water as a dispersion medium. The weight ratio of the solids was 92: DENKA BLACK 5: Binder 3. The content of the solid content was 56% by weight in 100% by weight of the total slurry.

Also, slurry for negative electrode was prepared by using LTO (Li ₄ Ti ₅ O ₁₂ ) as a negative electrode active material, polyvinylidene fluoride as a positive electrode as a binder, and water as a dispersion medium in the coated denka black, Active material 92: Denka black 5: Binder 3. The content of the solid content was 56% by weight in 100% by weight of the total slurry.

The positive electrode slurry thus prepared was coated on an aluminum substrate to a thickness of 140 탆, dried and pressed to prepare a positive electrode plate, and the negative electrode slurry was coated on a copper substrate to a thickness of 140 탆, dried and pressed to produce a negative electrode plate.

(Example 2)

A positive electrode plate and a negative electrode plate were prepared in the same manner as in Example 1, except that 0.035 g / 100 ml of amylase was further added to the dispersion medium in preparing the positive electrode slurry and negative electrode slurry.

(Example 3)

In the preparation of the positive electrode slurry and the negative electrode slurry in Example 2, the mixture of the conductive material rode black and the carbon nanotube was mixed at a composition ratio of 60 wt% and 40 wt%, respectively. A positive electrode plate and a negative electrode plate were prepared in the same manner as in Example 2. [

(Example 4)

A positive electrode plate and a negative electrode plate were prepared in the same manner as in Example 3 except that 90% by weight and 10% by weight of carbon black and carbon nanotubes were used as the conductive material.

(Example 5)

A positive electrode plate and a negative electrode plate were prepared in the same manner as in Example 3 except that 30% by weight and 70% by weight of carbon black and carbon nanotubes were used as the conductive material, respectively.

(Comparative Example 1)

A positive electrode plate and a negative electrode plate were prepared in the same manner as in Example 1, except that Denka black not subjected to heat treatment was used.

(Comparative Example 2)

A positive electrode plate and a negative electrode plate were prepared in the same manner as in Comparative Example 1, except that Denka black not coated with a hydrophilic polymer was used.

[Table 1]

It can be seen that the discharge power and the low temperature characteristic, that is, the capacity retention ratio at low temperature, are improved in the embodiment using the conductive material subjected to the heat treatment as shown in Table 1, as compared with the comparative example. It can be confirmed that the lithium secondary battery manufactured through the example has much better stability than the conventional lithium secondary battery.

In Example 2 in which a hydrophilic polymer degrading enzyme was further added to the dispersion medium, the discharge output was improved due to the increase of the contact area between the conductive material and the active material due to the removal of the hydrophilic polymer, compared with Example 1, Example 3 in which black and carbon nanotubes were mixed showed that the tube-shaped carbon nanotube and the spherical nanoparticle, denka black, were mixed at an appropriate ratio, thereby increasing the connection between the active materials and increasing the conduction path. As a result, . However, when denser black or carbon nanotubes are added in excess of a certain amount, the conductive material is deteriorated by interfering with effective contact between the conductive material and the cathode active material.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, It will be obvious to those of ordinary skill in the art.

Claims (10)

An electrode slurry comprising an electrode active material including a cathode active material and a cathode active material, a conductive material and a dispersion medium,
The negative electrode active material is Si, Sn, Al, Ge, Pb, Bi, Sb-Si-Z alloy, Sn-Z alloy, lithium-titanium oxide, vanadium oxide, lithium vanadium oxide, SnO _2, natural graphite, artificial graphite, soft carbon Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, Zr, Cr, Cr, Cr, Cu, Ag, Au, Zn, Cd, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, , B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, Se, Te,
The conductive material was annealed at 1,400 to 3,000 占 폚 for 10 minutes to 2 hours to obtain a graphite material having a BET nitrogen surface area of 50 to 100 m &lt; 2 &gt; / g, natural graphite, artificial graphite, carbon black, acetylene black, Graphene, and fullerene, and the surface is coated with one or two or more hydrophilic polymers selected from amylose, amylopectin and cyclodextrin,
The dispersion medium may be any one selected from water, an alcohol compound, a ketone compound, an ether compound, and a lactam compound, and at least one selected from amylase, amyloglucosidase and cyclodextrin glucokonotran spirase Or two or more hydrophilic polymer degrading enzymes,
Wherein the electrode slurry has an intensity ratio (ID / IG) of D band to G band through Raman spectroscopy of less than 0.05.
delete delete The method according to claim 1,
Wherein the conductive material is at least one selected from natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanotube, graphene and fullerene.
delete The method according to claim 1,
Wherein the cathode active material is represented by the following general formula (1), (2), or a mixture thereof.
&Lt; Formula 1 >
Li [Li _a M _1-a ] O _{2 + d}
(2)
Li [Li _b M1 _c M _{2 e} ] O _{2 + d}
0 <b <1, 0 <c <1, 0? D? 0.1, 0 <e <0.1, where 0 <a <1, b + c + e = 1,
Wherein M1 and M2 are selected from Ni, Co, Mn, Fe, Na, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, It is either.)
delete delete The method according to claim 1,
Wherein the coating thickness of the hydrophilic polymer is 1 to 10 nm.
A lithium secondary battery comprising an electrode obtained from the electrode slurry of any one of claims 1, 4, 6, and 9.