KR20130117350A - Electrode of enhanced adhesive force and lithium secondary battery comprising the same - Google Patents

Abstract

PURPOSE: An electrode is provided to increase the binding strength between the electrode current collector and electrode mixture layer and to reduce the content of the binder included in the electrode mixture layer, thereby improving both cyclic and output characteristics of a lithium secondary battery. CONSTITUTION: An electrode (100) in which an electrode mixture containing an electrode active material is coated on an electrode collector (110). The electrode mixture includes two or more kinds of binders having different gravity. The content of the binder having low gravity (150) is 50% or greater in the upper layer and the content of the binder having high gravity (140) is 50% or greater in the lower layer based on the height (H) corresponding to 50% of the thickness of the electrode mixture coating layer (120). The quantity of the binder in the lower layer is 100% or greater than the quantity of the binder in the upper layer. The melting point of the binders is 100-250°C.

Description

Electrode having improved adhesion and a lithium secondary battery comprising the same {Electrode of Enhanced Adhesive Force and Lithium Secondary Battery Comprising The Same}

The present invention relates to an electrode for lithium secondary batteries that can be repeatedly charged and discharged, and more particularly, to a lithium secondary battery electrode including two or more kinds of binders having different specific gravity.

The increase in the price of energy sources due to the depletion of fossil fuels, the increase of interest in environmental pollution, and the demand for environmentally friendly alternative energy sources are becoming indispensable factors for future life. Various researches on power generation technologies such as nuclear power, solar power, wind power, and tidal power have been continuing, and electric power storage devices for more efficient use of such generated energy have also been attracting much attention.

Particularly, in the case of a lithium secondary battery, the demand for an energy source is rapidly increasing due to an increase in technology development and demand for a mobile device. Recently, the use of a lithium secondary battery as a power source for an electric vehicle (EV) and a hybrid electric vehicle , And the area of use is also expanding for applications such as power assisted power supply through gridization.

A binder is used in order to ensure the adhesive force or binding force between an active material and an active material, and between an active material and an electrical power collector in forming an electrode for lithium secondary batteries.

The adhesive force between the active material and the current collector may be lower than the adhesive force between the active material and the active material depending on the type of the binder, the active material, and the surface state of the current collector.

In this case, in order to secure the adhesive force between the active material and the current collector, an excessive amount of binder is used as a whole. However, such an excess amount of binder may adversely affect the capacity and conductivity of the electrode.

Accordingly, there is a need for an electrode design capable of realizing effective adhesion and performance by differentiating the type and distribution of a binder between the active material and the active material, and the active material and the current collector.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-described problems of the prior art and the technical problems required from the past.

After extensive research and various experiments, the inventors of the present application increase the binding force between the electrode current collector and the electrode mixture layer when using a binder mixture in which two or more binders having different physical properties are mixed. It was confirmed that the binder content contained could be reduced, and the present invention was completed.

Electrode according to the present invention,

An electrode mixture including an electrode active material is coated on an electrode current collector, and the electrode mixture includes two or more kinds of binders having different specific gravity.

The two or more binders may be homogeneous or heterogeneous binders.

When the two or more binders are the same kind of binders, the specific gravity may be different by different molecular weights.

The two or more binders may have a melting point in the range of 100 ° C. or higher to 250 ° C. or lower.

Based on the height (H / 2) corresponding to 50% of the thickness (H) of the electrode mixture coating layer, the content of the binder having a small specific gravity may be 50% or more in the upper layer, the content of the binder with a large specific gravity in the lower layer 50 It may be more than%.

The amount of the binder in the lower layer may be 100% or more relative to the amount of the binder in the upper layer.

As described above, since the electrode according to the present invention includes two or more binders having different specific gravity, when applying the electrode mixture slurry on the electrode current collector, the binder having a high specific gravity is mainly located at a position close to the electrode current collector. Since it is distributed, the adhesion between the electrode current collector and the electrode mixture coating layer can be greatly improved, and at the same time, when controlling the content of the binders having a low specific gravity, these binders are mainly located far from the electrode current collector, which leads to unnecessary consumption. The resistance can be reduced by reducing the amount of binder.

The present invention provides a lithium secondary battery having a structure in which an electrode assembly having a structure in which a polymer film is interposed between a cathode, an anode, and a cathode and an anode is housed in a battery case and sealed. The lithium secondary battery may include a lithium salt-containing non-aqueous electrolyte.

The lithium secondary battery may be a lithium ion battery, may be a lithium ion polymer battery, may be a lithium polymer battery.

The electrode may be an anode or a cathode, and may be manufactured by a manufacturing method including the following processes.

The electrode manufacturing method,

Preparing a binder solution by dispersing or dissolving the binder in a solvent;

Preparing an electrode mixture slurry by mixing the binder solution with an electrode active material and a conductive material;

Coating the electrode mixture slurry on a current collector;

Drying the electrode; And

Compressing the electrode to a constant thickness.

In some cases, the method may further include drying the rolled electrode.

The binder solution manufacturing process is a process of preparing a binder solution by dispersing or dissolving a binder in a solvent.

The binder may be all binders known in the art, and specifically, fluorine resin, polyolefin, styrene-butadiene rubber, carboxy methyl cellulose, mussel protein (dopamine), silane, ethyl cellulose, methyl cellulose , Hydroxypropyl cellulose, polyethylene glycol, polyvinyl alcohol, may be selected from the group consisting of an acrylic copolymer.

The solvent may be selectively used according to the type of the binder. For example, an organic solvent such as isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, water, and the like may be used.

As one specific embodiment of the present invention, PVdF may be dispersed / dissolved in NMP (N-methyl pyrrolidone) to prepare a binder solution for the positive electrode, and SBR (Styrene-Butadiene Rubber) / CMC (Carboxy Methyl Cellulose) may be used. It is also possible to prepare a binder solution for the negative electrode by dispersing / dissolving in.

An electrode mixture slurry may be prepared by mixing / dispersing an electrode active material and a conductive material in the binder solution. The electrode mixture slurry thus prepared may be transferred to a storage tank and stored until the coating process. In the said storage tank, in order to prevent an electrode mixture slurry from hardening, an electrode mixture slurry can be stirred continuously.

The electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; Lithium manganese oxides such as Li _{1 + y} Mn _2-y O ₄ (where y is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ and LiMnO ₂ ; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ and Cu ₂ V ₂ O ₇ ; Formula _{LiNi 1-y M y O 2} ( where, the M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, y = 0.01 ~ 0.3 Im) Ni site type lithium nickel oxide which is represented by; Formula LiMn _2-y M _y O ₂ , wherein M = Co, Ni, Fe, Cr, Zn or Ta and y = 0.01 to 0.1, or Li ₂ Mn ₃ MO ₈ , where M = Fe, Co, Lithium manganese composite oxide represented by Ni, Cu or Zn); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with an alkaline earth metal ion; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ , and the like. However, the present invention is not limited to these.

In a non-limiting embodiment of the present invention, the electrode active material may include a lithium metal oxide having a spinel structure represented by the following formula (1) as a cathode active material.

Li _x M _y Mn _{2 - y} O _{4 - z z} (1)

Wherein 0 < y < 2, 0 z < 0.2,

M is at least one element selected from the group consisting of Al, Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, ;

A is one or more of an anion of -1 or -2.

The maximum substitution amount of A may be less than 0.2 mol%, and in a specific embodiment of the present invention, A may be at least one anion selected from the group consisting of halogen, S and N, such as F, Cl, Br, and I.

By substituting these anions, the binding force with the transition metal is improved and the structural transition of the compound is prevented, so that the lifetime of the battery can be improved. On the other hand, if the amount of substitution of the anion A is too large (t ≧ 0.2), it is not preferable because the life characteristics are lowered due to the incomplete crystal structure.

Specifically, the oxide of Formula (1) may be a lithium metal oxide represented by the following Formula (2).

Li _x Ni _y Mn _2-y O ₄ (2)

In the above formula, 0.9? X? 1.2 and 0.4? Y? 0.5.

More specifically, the lithium metal oxide may be LiNi _0.5 Mn _1.5 O ₄ or LiNi _0.4 Mn _1.6 O ₄ .

The electrode active material may be, for example, carbon such as hardly graphitized carbon or graphite carbon; _{Li x Fe 2 O 3 (0≤x≤1} ), Li x WO 2 (0≤x≤1), Sn x Me 1-x Me 'y O z (Me: Mn, Fe, Pb, Ge; Me' : Metal complex oxides such as Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, Halogen, 0 &lt; x &lt; Lithium metal; Lithium alloy; Silicon-based alloys; Tin alloy; _{SnO, SnO 2, PbO, PbO} 2, Pb 2 O 3, Pb 3 O 4, Sb 2 O 3, Sb 2 O 4, Sb 2 O 5, GeO, GeO 2, Bi 2 O 3, Bi 2 O 4, Bi ₂ O ₅ and the like; Conductive polymers such as polyacetylene; Li-Co-Ni-based material, and the like.

In a non-limiting example of the present invention, the electrode active material may include a lithium metal oxide as a negative electrode active material, and the lithium metal oxide may be preferably represented by the following formula (3).

Li _a M ' _b O _{4-ca c} (3)

In the above formula, M 'is at least one element selected from the group consisting of Ti, Sn, Cu, Pb, Sb, Zn, Fe, In, Al and Zr;

a and b are 0.1? a? 4; Is determined according to the oxidation number of M 'in the range of 0.2? B? 4;

c is determined according to the oxidation number in the range of 0? c <0.2;

A is one or more of an anion of -1 or -2.

The oxide of formula (3) may be represented by the following formula (4).

Li _a Ti _b O ₄ (4)

In the above formula, 0.5? A? 3, 1? B? 2.5.

The lithium metal oxide may be Li _0.8 Ti _2.2 O ₄ , Li _2.67 Ti _1.33 O ₄ , LiTi ₂ O ₄ , Li _1.33 Ti _1.67 O ₄ , Li _1.14 Ti _1.71 O _4, or the like. However, it is not limited only to these.

In a non-limiting embodiment of the present invention, the lithium metal oxide may be Li _1.33 Ti _1.67 O ₄ or LiTi ₂ O ₄ . Li _1.33 Ti _1.67 O ₄ has a spinel structure with little change in crystal structure during charge and discharge and excellent reversibility.

The lithium metal oxide can be produced by a production method known in the art, for example, can be produced by a solid phase method, hydrothermal method, sol-gel method and the like. A detailed description thereof will be omitted.

The lithium metal oxide may be in the form of secondary particles in which primary particles are aggregated.

The particle diameter of the secondary particles may be 200 nm to 30 ㎛.

If the particle diameter of the secondary particles is less than 200 nm, since a large amount of solvent is required in the negative electrode slurry production process, productivity is lowered and it is not preferable because it is difficult to control the water content. If the particle diameter of the secondary particles is more than 30 μm, the diffusion rate of lithium ions is low, and thus it is difficult to realize high output, which is not preferable.

The lithium metal oxide may be included in more than 50% by weight or less than 100% by weight relative to the weight of the entire negative electrode active material.

When the content of the lithium titanium oxide is 100% by weight based on the total weight of the negative electrode active material, it means a case in which the negative electrode active material is composed of only lithium titanium oxide.

The conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery. 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; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskeys 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.

Fillers and the like may be optionally added to the electrode mixture slurry as necessary.

The filler is not particularly limited as long as it is a fibrous material without causing chemical change in the battery. Examples of the filler include olefinic polymers such as polyethylene and polypropylene; Fibrous materials, such as glass fiber and carbon fiber, etc. can be used.

The coating of the electrode mixture slurry on a current collector is a process of coating the electrode mixture slurry on a current collector in a predetermined pattern and a predetermined thickness by passing through a coater head.

The method of coating the electrode mixture slurry on the current collector, the electrode slurry may be distributed on the current collector and uniformly dispersed using a doctor blade, die casting, comma coating ( comma coating, screen printing, and the like. In addition, the electrode mixture slurry may be bonded to the current collector by pressing or lamination after molding on a separate substrate.

The current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery. For example, the surface of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel Surface-treated with carbon, nickel, titanium, silver, and the like, aluminum-cadmium alloy, and the like can be used. The positive electrode current collector may be formed into various shapes such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven fabric, or the like by forming fine irregularities on the surface to enhance the bonding force of the positive electrode active material. Specifically, the positive electrode current collector may be a metal current collector including aluminum, and the negative electrode current collector may be a metal current collector including copper. The electrode current collector may be a metal foil, and may be an aluminum (Al) foil or a copper (Cu) foil.

The drying process is a process of removing the solvent and water in the slurry to dry the slurry coated on the metal current collector, in a specific embodiment, is dried within 1 day in a vacuum oven of 50 to 200 ℃.

After the drying process, a cooling process may be further included, and the cooling process may be slow cooling to room temperature so that the recrystallized structure of the binder is well formed.

In order to increase the capacity density of the electrode after the coating process and to increase the adhesion between the current collector and the active materials, the electrode may be compressed into a desired thickness by passing it between two hot-rolled rolls. This process is called a rolling process.

Before passing the electrode between two hot heated rolls, the electrode can be preheated. The preheating process is a process of preheating the electrode before it is introduced into the roll in order to increase the compression effect of the electrode.

The electrode after the rolling process is completed as described above, may be dried within a day in a vacuum oven at 50 to 200 ℃ as a range satisfying the temperature of the melting point or more of the binder. The rolled electrode may be cut to a constant length and then dried.

After the drying process, a cooling process may be further included, and the cooling process may be slow cooling to room temperature so that the recrystallized structure of the binder is well formed.

The polymer membrane is a separator that separates between the positive electrode and the negative electrode. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as the separator.

As the separator, an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally 0.01 to 10 mu m and the thickness is generally 5 to 300 mu m.

Such separation membranes include, for example, olefinic polymers such as polypropylene, which are chemically resistant and hydrophobic; A sheet or nonwoven fabric made of glass fiber, polyethylene or the like; Kraft paper and the like are used. Representative examples currently on the market include the Celgard ^R 2400, 2300 (from Hoechest Celanese Corp.), polypropylene separator (from Ube Industries Ltd. or Pall RAI), and polyethylene series (from Tonen or Entek).

In some cases, a gel polymer electrolyte may be coated on the separation membrane to increase the stability of the cell. Representative examples of such a gel polymer include polyethylene oxide, polyvinylidene fluoride, and polyacrylonitrile.

The electrode assembly may include a jelly-roll electrode assembly (or wound electrode assembly), a stacked electrode assembly (or a stacked electrode assembly), or a stack & folding electrode assembly having a structure known in the art.

In the present specification, the stack & folding type electrode assembly is a method of folding or winding a separator sheet after arranging unit cells having a structure in which a separator is interposed between an anode and a cathode on a separator sheet. It can be understood as a concept including a stack & folding type electrode assembly to be manufactured.

In addition, the electrode assembly may include an electrode assembly having a structure in which any one of an anode and a cathode is laminated by a method such as thermal fusion in a state in which a structure is interposed between the separators.

As the non-aqueous electrolyte, a non-aqueous electrolyte, an organic solid electrolyte, an inorganic solid electrolyte, and the like are used.

Examples of the nonaqueous electrolyte include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate , Gamma -butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, Diethyl ether, formamide, dimethyl formamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane A non-protonic organic solvent such as an ether, a methyl pyrophosphate, or an ethyl propionate is used as the solvent, a sulfone, a methyl sulfolane, a 1,3-dimethyl-2-imidazolidinone, a propylene carbonate derivative, a tetrahydrofuran derivative, .

Examples of the organic solid electrolyte include a polymer electrolyte such as a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, Polymers containing ionic dissociation groups, and the like can be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides, sulfates, and the like of Li, such as Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ , and the like, may be used.

The lithium salt is a material that is readily soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO 4, LiBF 4, LiB 10 Cl 10, LiPF 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF _{6, LiSbF 6, LiAlCl 4,} CH 3 SO 3 Li, CF 3 SO 3 Li, LiSCN, LiC (CF 3 SO 2) 3, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, 4-phenylborate, imide, and the like can be used.

For the purpose of improving the charge / discharge characteristics and the flame retardancy, the electrolytic solution is preferably mixed with an organic solvent such as pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, . In some cases, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further added to impart nonflammability. In order to improve the high-temperature storage characteristics, carbon dioxide gas may be further added. FEC (fluoro-ethylene carbonate, PRS (propene sultone), FPC (fluoro-propylene carbonate), and the like.

The lithium secondary battery according to the present invention can be used not only in a battery cell used as a power source of a small device but also as a unit cell in a middle- or large-sized battery module including a plurality of battery cells.

Also, the present invention provides a battery pack including the battery module as a power source of a middle- or large-sized device, wherein the middle- or large-sized device is an electric vehicle (EV), a hybrid electric vehicle (HEV) An electric vehicle including a plug-in hybrid electric vehicle (PHEV), a power storage device, and the like, but the present invention is not limited thereto.

The structure of the battery module and the battery pack and the method of manufacturing the battery module and the battery pack are well known in the art, so a detailed description thereof will be omitted herein.

As described above, since the electrode according to the present invention includes two or more binders having different specific gravity, when applying the electrode mixture slurry on the electrode current collector, the binder having a high specific gravity is mainly located at a position close to the electrode current collector. Since the distribution, the adhesion between the electrode current collector and the electrode mixture can be greatly improved, and at the same time, when controlling the content of the binders having a low specific gravity, these binders are mainly located far from the electrode current collector, thereby reducing the amount of unnecessary binder. Can reduce the resistance.

Therefore, in the lithium secondary battery including the electrode according to the present invention, both cycle characteristics and output characteristics are improved.

1 is a schematic cross-sectional view of an electrode according to a non-limiting embodiment of the present invention.

Hereinafter, the content of the present invention will be described in detail with reference to the drawings and examples, but the drawings and embodiments are provided to illustrate the present invention, and the scope of the present invention is not limited thereto.

1 is a schematic cross-sectional view of an electrode according to a non-limiting embodiment of the present invention. Referring to FIG. 1, an electrode mixture slurry coating layer 120 is formed on an electrode current collector 110, and an electrode mixture slurry coating layer 120 is formed of an electrode active material 130 and a binder 140. It includes a binder 150 having a smaller molecular weight than the binder 140.

The binder 140 and the binder 150 may be the same kind of binders, or the binder 140 and the binder 150 may be different kinds of binders. The relatively large molecular weight binder 140 is mainly distributed at a position close to the electrode current collector, and the relatively small molecular weight binder 150 is mainly distributed at a position far from the electrode current collector.

Example 1 Use of Binders of the Same Type with Different Molecular Weights

Li _1.33 Ti _1.67 O ₄ : Carbon black: PVDF (molecular weight: 250,000): PVDF (molecular weight: 1,000,000): NMP is weighed in a weight ratio of 90: 5: 2.5: 2.5: 85 and mixed ( mixing) to prepare an electrode mixture slurry (viscosity: 12,000 cps).

The electrode mixture slurry was applied to a thickness of 80 μm on a 20 μm thick aluminum foil. The electrode was manufactured by rolling to a porosity of 40% and drying at 60 ° C. for 24 hours.

The electrode was punched into a coin shape, lithium metal was used as a counter electrode, a polyethylene membrane (Celgard, thickness: 20 μm) as a separator, and 1 mol of LiPF ₆ were dissolved in an electrolyte, and ethylene carbonate (EC): propylene carbonate (PC) A coin-type battery was manufactured using a carbonate electrolyte having a quantity of 1: 1.

Example 2 Use of Heterogeneous Binders of Different Molecular Weights

Cells were prepared in the same manner as in Example 1, except that PVDF-HFP (poly (vinylidene fluoride-hexafluoro propylene, molecular weight: 250,000) and PVDF-CTFE (poly (vinylidene fluoride-chloro trifluoro ethylene, molecular weight: 750,000)) were used as binders. The viscosity of the electrode mixture slurry is 10,000 cps.

&Lt; Comparative Example 1 &

Li _1.33 Ti _1.67 O ₄ : Carbon black: PVDF (molecular weight: 250,000): The amount of NMP was measured in a weight ratio of 90: 5: 5: 85 and mixed to prepare an electrode mixture slurry. Except that, a battery was manufactured in the same manner as in Example 1. The viscosity of the electrode mixture slurry is 8,000 cps.

Comparative Example 2

Li _1.33 Ti _1.67 O ₄ : Carbon black: PVDF (molecular weight: 1,000,000): NMP was weighed in a weight ratio of 90: 5: 5: 85 and mixed to prepare an electrode mixture slurry. Except that, a battery was manufactured in the same manner as in Example 1. The viscosity of the electrode mixture slurry is 25,000 cps.

&Lt; Comparative Example 3 &

Li _1.33 Ti _1.67 O ₄ : Carbon black: PVDF-HFP (molecular weight: 250,000): The amount of NMP was measured in a weight ratio of 90: 5: 5: 85 and then mixed to prepare an electrode mixture slurry. A battery was manufactured in the same manner as in Example 2, except for manufacturing. The viscosity of the electrode mixture slurry is 6,500 cps.

&Lt; Comparative Example 4 &

Li _1.33 Ti _1.67 O ₄ : Carbon black: PVDF-CTFE (Molecular Weight: 750,000): NMP was weighed in a weight ratio of 90: 5: 5: 85 and mixed to mix the electrode mixture slurry. A battery was manufactured in the same manner as in Example 2, except for manufacturing. The viscosity of the electrode mixture slurry is 135,000 cps.

<Experimental Example 1>

The adhesion test was performed using the electrode of Example 1, Example 2, and Comparative Examples 1-4. After cutting the surface of the electrode of Example 1, Example 2, and Comparative Examples 1-4, and fixing it to the slide glass, peeling strength of 180 degree was measured, peeling off an electrode collector. Evaluation was made into the average value by measuring five or more peeling strengths.

Adhesion (gf / cm) Example 1 40gf / cm Example 2 55gf / cm Comparative Example 1 8gf / cm Comparative Example 2 60gf / cm Comparative Example 3 30gf / cm Comparative Example 4 77gf / cm

<Experimental Example 2>

Using the batteries of Examples 1, 2, and Comparative Examples 1 to 4 at the temperature of 25 ℃ to charge end voltage 2.5V at a charge current of 0.2C, discharge end while changing the discharge rate to 0.2C and 3C A charge and discharge test was conducted to discharge the voltage to 1.0 V. Table 2 shows the 3C discharge capacity compared to the 0.2C discharge capacity.

3C discharge capacity / 0.2C discharge capacity (%) Example 1 96% Example 2 97% Comparative Example 1 96% Comparative Example 2 93% Comparative Example 3 95% Comparative Example 4 93%

In the above experimental results, Comparative Example 1 exhibited 96% of the 3C discharge capacity compared to the 0.2C discharge capacity, but the adhesion was not excellent as 8 gf / cm, Comparative Example 2 was excellent in the adhesive strength of 60 gf / cm However, the 3C discharge capacity is not as good as 93% compared to the 0.2C discharge capacity, Comparative Example 3, the 3C discharge capacity is 95% compared to the 0.2C discharge capacity, but the adhesive strength is not excellent as 30 gf / cm, compared In Example 4, although the adhesion is excellent at 77 gf / cm, it can be seen that the 3C discharge capacity is 93% compared to the 0.2C discharge capacity.

That is, when only one binder component is used, it can be seen that the value of the 3C discharge capacity and the adhesive force are not in proportion to each other.

However, in Examples 1 and 2, it can be seen that the comparative examples, the adhesive force and the value of the 3C discharge capacity relative to the 0.2C discharge capacity is in a proportional relationship. Specifically, Examples 1 and 2 showed an adhesive force of more than 30 gf / cm and a value of 3C discharge capacity compared to 0.2C discharge capacity of more than 95%.

Those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims (17)

An electrode having an electrode mixture including an electrode active material coated on an electrode current collector, wherein the electrode mixture comprises two or more kinds of binders having different specific gravity. The binder of claim 1, wherein a binder having a low specific gravity is 50% or more in the upper layer and a binder having a high specific gravity in the lower layer, based on a height H / 2 corresponding to 50% of the thickness H of the electrode mixture coating layer. The electrode is characterized in that the content of more than 50%. The electrode of claim 1, wherein the amount of the binder in the lower layer is 100% or more relative to the amount of the binder in the upper layer. The electrode of claim 1, wherein the two or more binders are homogeneous binders. The electrode of claim 4, wherein the homogeneous binders have different molecular weights. The electrode of claim 1, wherein the two or more binders are heterogeneous binders. The electrode of claim 1, wherein the binder has a melting point of about 100 ° C. or more and about 250 ° C. or less. The electrode of claim 1, wherein the binders are aqueous or non-aqueous binders. The method of claim 1, wherein the two or more binders are fluorine resin, polyolefin, styrene-butadiene rubber, carboxy methyl cellulose, mussel protein (dopamine), silane, ethyl cellulose, methyl cellulose, hydroxypropyl cellulose, Electrode, characterized in that two or more binders selected from the group consisting of polyethylene glycol, polyvinyl alcohol, acrylic copolymer. A lithium secondary battery comprising the electrode according to any one of claims 1 to 9. A battery module comprising the lithium secondary battery according to claim 10 as a unit cell. A battery pack comprising the battery module according to claim 11. A device comprising the battery pack according to claim 12 as a power source. The lithium secondary battery of claim 10, wherein the average adhesive force and the high rate discharge characteristic of the electrode have a proportional relationship. The lithium secondary battery according to claim 10, wherein the average adhesive force of the electrode is greater than 30 gf / cm, and the 3C discharge capacity is greater than 95% relative to the 0.2C discharge capacity. The lithium secondary battery according to claim 10, wherein the average adhesive force of the electrode is 35 gf / cm or more, and the 3C discharge capacity is greater than 95% relative to the 0.2C discharge capacity. The lithium secondary battery according to claim 10, wherein the average adhesive force of the electrode is 40 gf / cm or more, and the 3C discharge capacity is 96% or more relative to the 0.2C discharge capacity.

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