KR101514314B1 - Electrode of Enhanced Adhesive Force and Lithium Secondary Battery Comprising The Same - Google Patents

Abstract

The present invention relates to an electrode in which an electrode mixture containing an electrode active material is coated on an electrode current collector, wherein the electrode mixture contains a mixture of two or more kinds of binders having different weights, And more particularly, to a lithium secondary battery including the lithium secondary battery.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode having improved adhesion and an electrode having improved adhesion,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode for a lithium secondary battery capable of repeated charge and discharge, and more particularly, to an electrode for a lithium secondary battery 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.

In forming the electrode for a lithium secondary battery, the binder is used to secure an adhesive force or binding force between the active material and the active material, or between the active material and the current collector.

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

In this case, an excessive amount of binder should be used as a whole in order to secure the adhesive force between the active material and the current collector, but such an excessive amount of binder adversely affects the capacity and conductivity of the electrode.

Therefore, it is necessary to design an electrode capable of differentiating the kind and distribution of the binder between the active material and the active material and between the active material and the current collector, thereby realizing effective adhesion and performance.

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.

The inventors of the present application have conducted intensive research and various experiments and have found that when using a binder mixture in which two or more binders having different physical properties are mixed, the binding force between the electrode current collector and the electrode mixture layer is increased, And that the content of the binder contained therein can be reduced, and the present invention has been accomplished.

In the 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 kinds of binders may be homogeneous or heterogeneous binders.

When the two or more kinds of binders are the same kind of binders, they may have a specific gravity difference by different molecular weights.

The two or more binders may have melting points in the range of 100 ° C to 250 ° C.

The content of the binder having a small specific gravity may be 50% or more and the content of the binder having a large specific gravity may be 50% or more, based on the height (H / 2) corresponding to 50% of the thickness H of the electrode mixture coating layer. % ≪ / RTI >

The amount of the binder in the lower layer may be 100% or more of 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 the electrode mixture slurry is coated on the electrode current collector, the binder having a large specific gravity is mainly The adhesion between the electrode current collector and the electrode material mixture coating layer can be greatly improved. In addition, when the content of the binder having a small specific gravity is controlled, such binders are mainly located far from the electrode collector, 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 positive electrode, a negative electrode, and a polymer film interposed between a positive electrode and a negative electrode is housed in a battery case and sealed. The lithium secondary battery may include a non-aqueous electrolyte containing a lithium salt.

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

The electrode may be a positive electrode or a negative electrode, and may be manufactured by a manufacturing method including the following processes.

In the electrode manufacturing method,

Dispersing or dissolving the binder in a solvent to prepare a binder solution;

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

Coating the electrode mixture slurry on a current collector;

Drying the electrode; And

And compressing the electrode to a predetermined thickness.

In some cases, the rolled electrode may further be dried.

The binder solution preparation process is a process of dispersing or dissolving the binder in a solvent to prepare a binder solution.

The binder may be any binder known in the art and may be selected from the group consisting of fluororesin, polyolefin, styrene-butadiene rubber, carboxymethylcellulose, mussel protein (dopamine), silane, ethylcellulose, methylcellulose , Hydroxypropylcellulose, polyethylene glycol, polyvinyl alcohol, and an acrylic copolymer.

The solvent can be selectively used depending on the type of the binder. For example, organic solvents such as isopropyl alcohol, N-methylpyrrolidone (NMP), and acetone and water can be used.

As a specific example of the present invention, a binder solution for a positive electrode may be prepared by dispersing / dissolving PVdF in NMP (N-methyl pyrrolidone), or a styrene-butadiene rubber (SBR) / carboxy methyl cellulose (CMC) To prepare a negative electrode binder solution.

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

The electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO ₂ ) or 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} ( where, M = Co, Ni, Fe , Cr, and Zn, or Ta, y = 0.01 ~ 0.1 Im) or Li ₂ Mn ₃ MO ₈ (where, M = Fe, Co, 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 chemical 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%. In a specific embodiment of the present invention, A may be at least one anion selected from the group consisting of halogens such as F, Cl, Br, I, S and N.

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 substitution amount of the anion A is too large (t? 0.2), the life characteristic is deteriorated due to the incomplete crystal structure, which is not preferable.

Specifically, the oxide of the 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 non-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 embodiment of the present invention, the electrode active material may include a lithium metal oxide as an anode active material, and the lithium metal oxide may preferably be 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 the 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, the present invention is not limited 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 less change in crystal structure during charging and discharging and excellent reversibility.

The lithium metal oxide can be produced by a production method known in the art and can be produced by, for example, a solid phase method, a hydrothermal method, a sol-gel method, or 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 size of the secondary particles may be 200 nm to 30 탆.

If the particle diameter of the secondary particles is less than 200 nm, a large amount of solvent is required in the negative electrode slurry production process, which lowers productivity and is not preferable because it is difficult to control the moisture content. When the particle size of the secondary particles is more than 30 占 퐉, the diffusion rate of lithium ions is slow and it is difficult to realize a high output, which is not preferable.

The lithium metal oxide may be contained in an amount of 50 wt% or more to 100 wt% or less based on the weight of the entire negative electrode active material.

When the content of lithium titanium oxide is 100 wt% with respect to the weight of the entire negative electrode active material, it means that the negative active material is composed of lithium titanium oxide alone.

The conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, for example, graphite such as natural graphite or artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; 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.

A filler or the like may be optionally added to the electrode mixture slurry as required.

The filler is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery, and examples thereof include olefin-based polymerizers such as polyethylene and polypropylene; Fibrous materials such as glass fiber, carbon fiber and the like can be used.

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

The method of coating the electrode mixture slurry on the current collector may include a method of uniformly dispersing the electrode slurry on the current collector using a doctor blade or the like, a method of die casting, comma coating, screen printing, and the like. Alternatively, the electrode mixture slurry may be bonded to a collector by molding on a separate substrate and then pressing or laminating.

The current collector is not particularly limited as long as it has high conductivity without causing a chemical change in the battery. For example, the current collector may be made of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, a 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. 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 cathode current collector may be a metal current collector including aluminum, and the anode current collector may be a metal current collector including copper. The electrode current collector may be a metal foil, and may be an aluminum foil or a copper foil.

The drying process is a process of removing the solvent and moisture in the slurry to dry the slurry coated on the metal current collector. In a specific example, the drying process is performed within one day in a vacuum oven at 50 to 200 ° C.

After the drying process, a cooling process may be further included, and the cooling process may be a slow cooling process to room temperature to form a recrystallized structure of the binder.

In order to increase the capacity density of the coated electrode and increase the adhesion between the current collector and the active materials, an electrode can be passed between two rolls heated at a high temperature and compressed to a desired thickness. This process is called the rolling process.

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

The electrode having completed the rolling process as described above can be dried within one day in a vacuum oven at 50 to 200 DEG C in a range satisfying a temperature equal to or higher than the melting point of the binder. The rolled electrode may be cut to a certain length and then dried.

After the drying process, a cooling process may be further included, and the cooling process may be a slow cooling process to room temperature to form a recrystallized structure of the binder.

The polymer membrane is a separator separating the anode and the cathode. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.

The separator is made of an insulating thin film having high ion permeability and mechanical strength. 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 both a jelly-roll type electrode assembly (or a wound electrode assembly), a stacked electrode assembly (or a stacked electrode assembly), or a stacked & folded electrode assembly having a structure known in the art.

In this specification, the stacked & folded type electrode assembly is a method of arranging unit cells having a structure in which a separator is interposed between an anode and a cathode on a separator sheet, folding and winding the separator sheet A stack &amp; folding type electrode assembly.

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

As the non-aqueous electrolyte, a non-aqueous electrolyte, an organic solid electrolyte, an inorganic solid electrolyte, or the like is 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 and sulfates of Li such as Li ₄ SiO ₄ -LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ can 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 differing in specific gravity from each other, when the electrode mixture slurry is coated on the electrode current collector, the binder having a large specific gravity It is possible to greatly improve the adhesive force between the electrode current collector and the electrode mixture, and at the same time, when the content of the binder having a small specific gravity is controlled, these binders are mainly located far from the electrode collector. Therefore, by reducing the amount of unnecessary binders The resistance can be reduced.

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

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

Hereinafter, the contents of the present invention will be described in detail with reference to the drawings and examples. However, the drawings and examples are for illustrating 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. 1, the electrode 100 includes an electrode mixture slurry coating layer 120 formed on an electrode collector 110, and an electrode mixture slurry coating layer 120 includes an electrode active material 130, a binder 140, And a binder 150 having a relatively small molecular weight as compared to the binder 140.

The binder 140 and the binder 150 may be the same type of binder. The binder 140 and the binder 150 may be different binders. The binder 140 having a relatively large molecular weight is mainly distributed near the electrode current collector and the binder 150 having a relatively small molecular weight is distributed mainly at a position far from the electrode current collector.

&Lt; Example 1 > - Use of the same kind of binder having 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 was weighed to a weight ratio of 90: 5: 2.5: 2.5: to prepare an electrode mixture slurry (viscosity: 12,000 cps).

The electrode mixture slurry was applied to an aluminum foil having a thickness of 20 mu m to a thickness of 80 mu m. Rolled to a porosity of 40% and dried at 60 DEG C for 24 hours to prepare an electrode.

The electrode was punched out in the form of a coin, and a lithium metal as a counter electrode, a polyethylene film (Celgard, thickness: 20 탆) as a separation membrane, and 1 mol of LiPF ₆ dissolved in an electrolyte were mixed, and ethylene carbonate (EC) A coin type cell was fabricated using a 1: 1 carbonate electrolyte.

&Lt; Example 2 > - Use of different kinds of binders having different molecular weights

Except that PVDF-HFP (polyvinylidene fluoride-hexafluoro propylene, molecular weight: 250,000) and polyvinylidene fluoride-chloro trifluoroethylene (PVDF-CTFE, molecular weight: 750,000) were used as the binder. The viscosity of the electrode slurry was 10,000 cps.

&Lt; Comparative Example 1 &

Li: _1.33 Ti _1.67 O ₄ : carbon black: PVDF (molecular weight: 250,000): NMP was weighed to a weight ratio of 90: 5: 5: 85 and mixed to prepare an electrode mixture slurry A battery was fabricated in the same manner as in Example 1 except for the following. The viscosity of the electrode mixture slurry is 8,000 cps.

&Lt; Comparative Example 2 &

Li: _1.33 Ti _1.67 O ₄ : Carbon black: PVDF (molecular weight: 1,000,000): NMP was weighed to a weight ratio of 90: 5: 5: 85 and mixed to prepare an electrode mixture slurry A battery was fabricated in the same manner as in Example 1 except for the following. 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): NMP was weighed to a weight ratio of 90: 5: 5: 85 and mixed to prepare an electrode mixture slurry A battery was produced in the same manner as in Example 2, except that the battery was manufactured. 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 to a weight ratio of 90: 5: 5: 85 and mixed to prepare an electrode mixture slurry A battery was produced in the same manner as in Example 2, except that the battery was manufactured. The viscosity of the electrode mixture slurry is 135,000 cps.

<Experimental Example 1>

An adhesive strength test was conducted using the electrodes of Example 1, Example 2, and Comparative Examples 1 to 4. The surfaces of the electrodes of Example 1, Example 2, and Comparative Examples 1 to 4 were cut and fixed on a slide glass, and the peel strength of 180 degrees was measured while peeling the electrode collector. The evaluation was made by measuring the peel strengths of 5 or more and calculating the average value.

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

<Experimental Example 2>

The batteries of Examples 1 and 2 and Comparative Examples 1 to 4 were charged at a charging current of 0.2 C at a temperature of 25 캜 up to a charging end voltage of 2.5 V and then discharged at a discharging rate of 0.2 C and 3 C, A charge / discharge test was performed to discharge the voltage to 1.0 V. Table 2 below shows the 3C discharge capacity versus 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%

As a result of the above experiment, Comparative Example 1 shows that the 3C discharge capacity is 96% compared to the 0.2C discharge capacity, but the adhesion is not excellent as 8 gf / cm. In Comparative Example 2, the adhesion is 60 gf / cm However, the 3C discharge capacity was not as good as 93% compared with the 0.2C discharge capacity. In Comparative Example 3, the 3C discharge capacity versus the 0.2C discharge capacity was 95%, but the adhesion was not excellent as 30 gf / cm. Example 4 demonstrates that the adhesive strength is excellent at 77 gf / cm, but the 3C discharge capacity as compared with the 0.2C discharge capacity is not excellent as 93%.

That is, when only one binder component is used, it can be seen that the value of the 3C discharge capacity versus the adhesion force is not in proportion to the 0.2C discharge capacity.

However, in Examples 1 and 2, it can be confirmed that the adhesion and the value of the 3C discharge capacity are proportional to the 0.2C discharge capacity and the comparative examples. Specifically, Examples 1 and 2 showed an adhesion force of more than 30 gf / cm and a 3C discharge capacity value versus a 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 (21)

A lithium secondary battery having an electrode in which an electrode mixture containing an electrode active material is coated on an electrode current collector,
The electrode mixture contains PVDF having a molecular weight of 250,000 and PVDF having a molecular weight of 1,000,000 having different specific gravities as a binder and having a height (H / 2) corresponding to 50% of the thickness (H) of the electrode mixture coating layer , A binder having a small specific gravity in the upper layer is 50% or more based on the total weight of the binder having a small specific gravity contained in the whole electrode mixture, and a binder having a large specific gravity in the lower layer is contained in the total amount of the binder 50% or more,
The average adhesive force and the high rate discharge characteristic of the electrode are proportional to each other,
The positive electrode contains a lithium metal oxide having a spinel structure represented by the following formula (2) as an electrode active material, and the negative electrode contains Li _1.33 Ti _1.67 O ₄ as an electrode active material,
Wherein the negative electrode mixture comprises Li _1.33 Ti _1.67 O ₄ : carbon black: PVDF having a molecular weight of 250,000 and PVDF having a molecular weight of 1,000,000 in a weight ratio of 90: 5: 2.5: 2.5.
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. delete delete delete delete delete delete delete delete delete A battery module comprising the lithium secondary battery according to claim 1 as a unit cell. A battery pack comprising the battery module according to claim 11. A device according to claim 12, wherein the battery pack is used as a power source. delete The lithium secondary battery according to claim 1, wherein the average adhesion of the electrode is greater than 30 gf / cm 2 and the 3C discharge capacity is more than 95% of the 0.2C discharge capacity. The lithium secondary battery according to claim 1, wherein the average adhesion of the electrode is 35 gf / cm or more, and the 3C discharge capacity is more than 95% of the 0.2C discharge capacity. The lithium secondary battery according to claim 1, wherein the average adhesion of the electrode is 40 gf / cm or more and the discharge capacity at 3 C is 96% or more relative to 0.2 C discharge capacity. A lithium secondary battery having an electrode in which an electrode mixture containing an electrode active material is coated on an electrode current collector,
The electrode mixture contains polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) having a molecular weight of 250,000 and polyvinylidene fluoride-chloro trifluoroethylene (PVDF-CTFE) having a specific gravity of 750,000, Based on the height (H / 2) corresponding to 50% of the thickness (H) of the electrode mixture coating layer, the binder having a small specific gravity in the upper layer is 50% or more based on the total weight of the binder having a small specific gravity contained in the whole electrode mixture , The binder having a large specific gravity in the lower layer is 50% or more based on the total weight of the binder having a large specific gravity contained in the entire electrode mixture,
The average adhesive force and the high rate discharge characteristic of the electrode are proportional to each other,
The positive electrode contains a lithium metal oxide having a spinel structure represented by the following formula (2) as an electrode active material, and the negative electrode contains Li _1.33 Ti _1.67 O ₄ as an electrode active material,
The negative electrode material mixture comprises Li _1.33 Ti _1.67 O ₄ : Carbon black: PVDF-HFP having a molecular weight of 250,000 and PVDF-CTFE having a molecular weight of 750,000 in a weight ratio of 90: 5: 2.5: 2.5. Secondary battery:
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. A battery module comprising the lithium secondary battery according to claim 18 as a unit cell. A battery pack comprising the battery module according to claim 19. A device according to claim 20, wherein the battery pack is used as a power source.

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