KR100458583B1 - Electrode for lithium secondary battery, lithium secondary battery, and method of preparing electrode - Google Patents

Abstract

The present invention provides an electrode and a battery using a binder aqueous dispersion for a secondary battery suitable for a nonaqueous electrolyte secondary battery using a lithium compound.

An amorphous polypropylene homopolymer or a copolymer of propylene and an olefin having 2 to 8 carbon atoms, an amorphous polymer having a propylene content of 50% by weight or more as a binder, and a copolymer of (meth) acrylic acid and (meth) acrylic acid alkyl ester By providing a binder composed of a dispersant and an electrode made of a water-soluble polymer and an active material powder, cycle characteristics superior to conventional secondary batteries can be obtained.

Description

ELECTRODE FOR LITHIUM SECONDARY BATTERY, LITHIUM SECONDARY BATTERY, AND METHOD OF PREPARING ELECTRODE

[Industrial use]

The present invention relates to an electrode for a lithium secondary battery, a manufacturing method thereof and a lithium secondary battery.

[Prior art]

Recently, carbon materials such as coke and graphite, in which lithium dendrites do not occur instead of lithium metal, have been proposed as negative electrode active materials for lithium secondary batteries.

In the negative electrode using the carbon material, a carbon material which is a negative electrode active material and a conductive material and a binder are mixed and stirred as necessary to prepare a paste, and the paste is applied to a metal current collector by a doctor-blade method or the like. It is prepared by the method of drying.

Conventionally, polyvinylidene fluoride is mainly used as a negative electrode binder of a lithium secondary battery, and N-methyl-2-pyrrolidone (NMP), which can dissolve polyvinylidene fluoride, is mainly used as a dispersion medium of the paste. It became.

However, when polyvinylidene fluoride is used as the binder, there is a problem in that the polyvinylidene fluoride fiber coats the negative electrode active material and cannot exhibit the performance inherent in the negative electrode active material.

In addition, when polyvinylidene fluoride is used, the binding force between the metal current collector and the active material is not sufficient. After repeated charging and discharging, the carbon powder is peeled from the metal current collector and the battery capacity gradually decreases, that is, the cycle characteristics are reduced. There is a problem of shortening.

Furthermore, since NMP, which is an organic solvent, is used as the dispersion medium of the paste, NMP vapor generated during electrode drying must be recovered, and there is a problem in safety.

On the other hand, styrene butadiene rubber (SBR), polytetrafluoroethylene (PTFE), and the like hardly cover the negative electrode active material, and can be used as an aqueous dispersion, which is a problem when using the polyvinylidene fluoride. Although not generated, the binding force between the metal current collector and the active material is lower than that of the polyvinylidene fluoride, resulting in a shorter cycle characteristic.

SUMMARY OF THE INVENTION The present invention has been made to solve the problems of the prior art, and an object of the present invention is to provide a lithium secondary battery electrode having excellent binding properties and excellent cycle characteristics, a manufacturing method thereof, and a lithium secondary battery.

In order to achieve the above object, the present invention is a metal current collector; And an electrode layer comprising at least an active material powder, a binder, and a water-soluble polymer formed on the metal current collector, wherein the binder is an amorphous polypropylene homopolymer or an amorphous copolymer made of propylene and an olefin having 2 to 8 carbon atoms. ; And it provides the electrode for lithium secondary batteries which is a copolymer of (meth) acrylic acid and (meth) acrylic-acid alkylester.

In another aspect, the present invention provides a lithium secondary battery comprising the electrode.

In addition, the present invention is an amorphous polypropylene homopolymer or an amorphous copolymer composed of propylene and an olefin having 2 to 8 carbon atoms in water by a dispersing agent consisting of a copolymer of (meth) acrylic acid and (meth) acrylic acid alkyl ester. A paste is prepared by mixing the dispersed binder aqueous dispersion with the electrode active material powder and the water-soluble polymer; Provided is a method of manufacturing an electrode for a lithium secondary battery, including a step of coating the paste onto a metal current collector and drying the paste at a temperature of 60 ° C. to 180 ° C. or less.

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

MEANS TO SOLVE THE PROBLEM As a result of earnestly examining the problem of the said prior art, the amorphous polymer and acryl-type nose which made the content rate of propylene more than a specific amount in the amorphous polypropylene homopolymer or the copolymer of propylene and the olefin of 2-8 carbon atoms When the polymer is used as the binder and the water-soluble polymer is used as the thickener, the present inventors have found that an electrode for a secondary battery, particularly a lithium secondary battery, can be provided.

That is, in the lithium secondary battery electrode of the present invention, an electrode layer including at least an active material powder, a binder, and a water-soluble polymer is formed on a metal current collector, and the binder has an amorphous polypropylene homopolymer or propylene having 2 to 8 carbon atoms. Amorphous copolymers of olefins; And a copolymer of (meth) acrylic acid and (meth) acrylic acid alkyl ester.

Since the electrode of the present invention has sufficient adhesiveness of the active material powder to the metal current collector and also high binding properties of the active material powders, it is possible to prevent the active material powder from falling off due to the volume change of the active material powder during charging and discharging. Capacity deterioration due to the inversion cycle can be prevented.

In particular, the binder used in the present invention has better binding properties than conventional polyvinylidene fluoride and the like, so that sufficient binding properties can be obtained even with a small amount of addition. Therefore, the amount of the binder can be reduced to increase the amount of the active material powder added, and the battery charge / discharge capacity can be improved. Moreover, since the ratio of the binder which is an electrical nonconductor in an electrode is small, the impedance of an electrode is reduced and the high rate current characteristic of a battery improves.

The content of propylene contained in the amorphous polymer is characterized in that more than 50% by weight. Thus, when the content rate of the propylene contained in an amorphous polymer is 50 weight% or more, the binding property of a binder can be improved.

The electrode of the present invention comprises the binder in the range of 0.1 wt% or more and 10 wt% or less with respect to the active material powder. When the addition amount of the binder is in the above range, there is no fear that the electrode active material may drop off, and there is no fear that the battery characteristics may decrease.

In addition, in the electrode of the present invention, the water-soluble polymer is characterized in that it is included in the range of 0.1% by weight or more, 10% by weight or less based on the active material powder.

The water-soluble polymer is used as a thickener, and if the amount of the water-soluble polymer is included in the above range, there is no fear that the electrode active material will drop off, and there is no fear that the battery characteristics will deteriorate. The water-soluble polymers include carboxymethyl cellulose (CMC), polyvinyl alcohol, polyvinylpyrrolidone, polyacrylic acid, polymethacrylic acid, polyethylene oxide, polyacrylamide, poly-N-isopropylacrylamide, poly- N, N-dimethylacrylamide, polyethyleneimine, polyoxyethylene, poly (2-methoxyethoxyethylene), poly (3-molpyridylethylene), polyvinylsulfonic acid, polyvinylidene fluoride, amylose ( amylose) and the like, but CMC is most preferred. Since CMC has high viscosity, imparts excellent coating properties, and is excellent in adhesive force, the CMC can prevent the active material from falling off from the current collector and achieve excellent cycle characteristics.

The lithium secondary battery of the present invention includes the above-mentioned electrode, and particularly preferably includes a negative electrode. Since the lithium secondary battery includes the electrode excellent in the adhesion between the active material powder and the binding of the active material powders to the metal current collector, it is possible to prevent the active material powder from falling off due to the volume change of the active material powder during charging and discharging. Capacity deterioration accompanying the discharge cycle can be prevented. In addition, since the amount of the binder, which is an insulator of the electrode, can be reduced in the electrode, the impedance of the electrode is reduced, thereby improving the high rate current characteristic of the battery.

Subsequently, in the method for producing an electrode for a lithium secondary battery of the present invention, an amorphous polypropylene homopolymer or an amorphous copolymer made of propylene and an olefin having 2 to 8 carbon atoms is a combination of (meth) acrylic acid and (meth) acrylic acid alkyl ester. A binder is prepared by mixing a binder aqueous dispersion dispersed in water with a copolymer dispersant and a water-soluble polymer as an electrode active material powder and a thickener, and the paste is coated on a metal current collector and at the same time, 60 ° C. or more and 180 ° C. or less. It is characterized by drying at a temperature of.

In the case of using the conventional organic solvent-based binder-dispersion solution by using the aqueous binder and the aqueous thickener dispersed in the aqueous dispersion, no special equipment for treating the organic solvent is required, and thus it is an excellent production method in terms of environment at low cost.

[Embodiment of the Invention]

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described in detail.

The electrode for lithium secondary batteries which concerns on this invention is especially used as a negative electrode, and is an electrode in which the electrode layer containing at least a negative electrode active material powder (active material powder), a binder, and a water-soluble polymer is formed on a metal current collector. The form of such an electrode is generally a sheet-like electrode, but is not limited thereto, and a columnar, disk-shaped, plate-like or columnar electrode can also be used.

The negative electrode active material is preferably one capable of reversibly occluding and releasing lithium. Carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, graphitized mesocarbon microbeads, fullerene, and amorphous carbon may be used. It can be illustrated. Moreover, the composite material which mix | blended the metal material which can be alloyed with lithium alone, and this metal material and carbonaceous material can also be illustrated as a negative electrode active material. Examples of the metal that can be alloyed with lithium include Al, Si, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, and Ge.

In addition, a conductive assistant may be added to the negative electrode. Examples of the conductive assistant may include nickel powder, cobalt oxide, titanium oxide, and carbon. As carbon, Ketjen black, acetylene black, furnace black rack, graphite, carbon fiber, a preene etc. can be illustrated.

Examples of the metal current collector include punching metal, ex punching metal, gold foil, foamed metal, reticulated metal fiber sintered body, nickel foil, and copper foil.

The binder is an amorphous polypropylene homopolymer or a copolymer of propylene and an olefin having 2 to 8 carbon atoms, a binder made of an amorphous polymer having a propylene content of 50% by weight or more, (meth) acrylic acid and (meth) acrylic acid alkyl ester And a dispersant composed of a copolymer of S, wherein the binder is dispersed in water by the dispersant.

If the propylene component in the amorphous polymer is less than 50% by weight, compatibility with other materials is lowered and the adhesive force is lowered as a binder, which is not preferable.

It is preferable that the binder which concerns on this invention is used with the aqueous dispersion which disperse | distributed the said binder in water, In this case, the copolymer of (meth) acrylic acid and (meth) acrylic-acid alkylester is used as a dispersing agent, (meth) It is preferable that acrylic acid contains 10-80 mol% and (meth) acrylic-acid alkylester contains 2 or more types 90-20 mol%. This dispersant is contained in the negative electrode together with a binder as a binder.

By including the water-soluble polymer in the range of 0.1% by weight or more and 10% by weight or less with respect to the active material powder as the thickener, the coating property is improved, the electrode active material is not dropped, and the battery properties are not reduced. can do.

Examples of the water-soluble polymer include carboxymethyl cellulose (CMC), polyvinyl alcohol, polyvinylpyrrolidone, polyacrylic acid, polymethacrylic acid, polyethylene oxide, polyacrylamide, poly-N-isopropylacrylamide, poly-N, Examples include N-dimethylacrylamide, polyethyleneimine, polyoxyethylene, poly (2-methoxyethoxyethylene), poly (3-molpyridylethylene), polyvinylsulfonic acid, polyvinylidene fluoride, amylose, and the like. However, CMC is most preferred.

In the present invention, when the binder aqueous dispersion for secondary batteries containing the above-described amorphous homopolymer or amorphous copolymer is used for the negative electrode, a binder is added in an amount of 0.05 to 20.0 parts by weight based on 100 parts by weight of the negative electrode active material such as graphite. Preferably it is 0.1-10.0 weight part. If the binder is less than 0.05 part by weight, the negative electrode active material cannot be sufficiently bound to the metal current collector, and the negative electrode active material is dropped from the metal current collector, resulting in a decrease in battery capacity. On the other hand, when the binder exceeds 20 parts by weight, the impedance of the electrode is increased, battery characteristics are deteriorated, and flexibility of the electrode is very low, which is not preferable.

Moreover, in the negative electrode of this invention, it is preferable to add 0.1-10.0 weight part (0.1-10 weight%) of water-soluble polymer as a thickener with respect to 100 weight part of negative electrode active materials, such as graphite. When the amount of the water-soluble polymer is less than 0.1 part by weight, the viscosity of the paste is lowered, the applicability is remarkably lowered, and the negative electrode active material cannot be sufficiently bound to the metal current collector, so that the negative electrode active material is dropped from the metal current collector and the battery The capacity of may be lowered. On the other hand, when the amount of the dispersant is more than 10 parts by weight, the impedance of the electrode is increased, the battery coatability is lowered, and the flexibility of the electrode is significantly lowered, which is not preferable.

The negative electrode constructed by using the binder of the present invention is, for example, the binder aqueous dispersion liquid in which the binder is dispersed in water by the dispersing agent and the water-soluble polymer dissolved in water, and then mixed and stirred, and then the mixture and the negative electrode active material powder The paste is prepared by mixing, and the paste is coated on a metal current collector and dried at a temperature of 60 ° C. or higher and 180 ° C. or lower.

Furthermore, after dipping a metal current collector in the said paste, it can also manufacture by drying.

If the drying time of the paste is less than 60 ° C, the paste cannot be dried sufficiently, and a large amount of water remains in the electrode, which is undesirable because the water reacts with lithium in the battery to generate hydrogen, and the drying temperature When the temperature exceeds 180 ° C., some of the binder and the water-soluble polymer may be pyrolyzed, which is not preferable.

The positive electrode for a lithium secondary battery according to the present invention can be used as long as it is a positive electrode normally used in a lithium secondary battery. A positive electrode active material powder is mixed with a binder such as polyvinylidene fluoride and a conductive additive such as carbon black to form a paste or a flat plate. The thing shape | molded in the shape etc. is mentioned.

As a cathode active material is, for example, such as _{LiMn 2 O 4, LiCoO 2,} LiNiO 2, LiFeO 2, V 2 O 5 is preferred. Moreover, it is good to use what can occlude and desorb lithium, such as TiS, MoS, an organic disulfide compound, or an organic polysulfide compound. Moreover, as a conductive support material, conductive crude materials, such as Ketchen black, acetylene black, furnace black, graphite, carbon fiber, and a preene, are preferable. In addition, as the binder, in addition to polyvinylidene fluoride, water-soluble polymers such as carboxymethyl cellulose, methyl cellulose and sodium polyacrylate can also be used.

The positive electrode is formed by using a roll press after applying and drying a paste obtained by mixing a positive electrode active material powder, a binder, and a conductive aid to a metal substrate.

Any separator may be used as long as it is used in a lithium secondary battery, and examples thereof include polyethylene nonwoven fabric, polypropylene nonwoven fabric, polyamide nonwoven fabric, and glass fiber.

As a lithium secondary battery electrolyte, the organic electrolyte solution in which lithium salt was melt | dissolved in the non-aqueous solvent is mentioned, for example.

Non-aqueous solvents include propylene carbonate, ethylene carbonate, butylene carbonate, benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, dioxolane, 4-methyldioxolane, N, N -Dimethylformamide, dimethylacetoamide, dimethyl sulfoxide, dioxane, 1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate , Non-aqueous solvents such as methyl isopropyl carbonate, ethyl butyl carbonate, dipropyl carbonate, diisopropyl carbonate, dibutyl carbonate, diethylene glycol, dimethyl ether, or a mixed solvent in which two or more of these solvents are mixed, and also lithium As a solvent for secondary batteries, what was conventionally known can be mentioned, In particular, propylene carbonate and ethylene It is a mixture of carbonate, dimethyl carbonate that comprises one of butyl carbonate, one of the methyl ethyl carbonate, diethyl carbonate, is preferred.

Examples of the lithium salt include LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiSbF ₆ , LiAlO ₄ , LiAlCl ₄ , LiN (C _x F _{2x + 1} SO ₂ ) (C _y F _{2y + 1} SO ₂ ) (where x and y are natural water), LiCl, LiI, etc. And those conventionally known as lithium salts for lithium secondary batteries are mentioned, and it is particularly preferable to include one of LiPF ₆ and LiBF ₄ .

Further examples of the electrolyte include polymers such as polyethylene oxide, polypropylene oxide, polyacetonitrile, polyvinylidene fluoride, polymethacrylate, polymethylmethacrylate, etc., which have excellent swelling properties with respect to the organic electrolyte and the organic electrolyte. Examples thereof include polymer electrolytes containing this polymer.

The lithium secondary battery according to the present invention is produced by encapsulating the positive electrode, the negative electrode, the separator, and the electrolyte in a metal container in a general manner.

Since the electrode for lithium secondary batteries of the present invention configured as described above is used, the binding force of the negative electrode active material is sufficient for the metal current collector, and the dropping of the negative electrode active material from the metal current collector accompanying charging and discharging can be prevented. Cycle characteristics that could not be obtained can be obtained.

EXAMPLE

Hereinafter, the present invention will be described in more detail with reference to Examples. However, this invention is not limited by the following Example.

[Production of Cathode Electrode]

(Example 1)

Propylene / 1-butene copolymer amorphous copolymer (propylene content 60 wt%, heptane insoluble content; 0.1 wt%, density (25 ° C.); 0.87 g / cm 3, number average molecular weight: 7,000, melt viscosity (190 ° C.); 20,000 mPa · s) was added to 26.8 parts by weight of an acrylic copolymer aqueous solution. The acrylic copolymer aqueous solution was synthesized by mixing 21 parts by weight of acrylic acid, 30 parts by weight of ethyl acrylate, 56.8 parts by weight of butyl methacrylate, and 0.6 parts by weight of 2,2'-azobisisobutyronitrile.

To the obtained mixture was added 113.8 parts by weight of water. The mixture was stirred to prepare a binder aqueous dispersion, and the binder aqueous dispersion was added to 97 parts by weight of natural graphite having an average particle diameter of 18 µm so that the solid content was 1.5 parts by weight.

Subsequently, 1.5 parts by weight of carboxymethyl cellulose (CMC) and 110 parts by weight of water were added to the obtained mixture, and stirred for 30 minutes with a homogenizer to prepare a negative electrode slurry, which was applied to copper foil. Subsequently, after drying at 130 degreeC for 10 minutes, it rolled by roll press so that the thickness of an electrode layer might be set to 100 micrometers, and density was 1.6 g / cm <3>.

The electrode was cut to a width of 2.5 cm and a length of 15 cm, bonded to a plastic plate with copper foil down, and a pressure-sensitive adhesive tab having a length of 17 cm was attached to the graphite surface, and one end of the tab was pulled between the fixtures of the tester. The tensile strength was measured by pulling in the direction perpendicular to the electrode.

(Comparative Example 1)

A negative electrode was manufactured in the same manner as in Example 1 except that 97 parts by weight of natural graphite, 1.5 parts by weight of styrene butadiene rubber (SBR), 1.5 parts by weight of CMC, and water were mixed to prepare a negative electrode slurry. Using this electrode, a tensile test was conducted in the same manner as in Example 1.

(Comparative Example 2)

A negative electrode was prepared in the same manner as in Example 1 except that 92 parts by weight of natural graphite and 8 parts by weight of polyvinylidene fluoride were mixed and stirred to prepare a negative electrode slurry. Using this electrode, a tensile test was conducted in the same manner as in Example 1.

Table 1 shows the tensile test results of Example 1 and Comparative Examples 1 and 2.

Tensile Strength (mN / cm) Example 1 1213 Comparative Example 1 666 Comparative Example 2 1057

As shown in Table 1, the electrode tensile strength of Example 1 is higher than that of Comparative Examples 1 and 2, it can be seen that the binder composed of the olefinic amorphous copolymer and the acrylic dispersant used in Example 1 has excellent adhesion have. The CMC used as a thickener also has adhesive properties, but the same CMC was used in Example 1 and Comparative Example 1, and the electrode was manufactured using the same amount, so that the olefinic amorphous copolymer was compared with SBR, which is widely known as an aqueous adhesive. It can be seen that the binder composed of and the acrylic dispersant has a higher adhesive force.

[Manufacture of Battery]

(Example 2)

In order to evaluate the electrode prepared in Example 1 as a negative electrode of a lithium ion secondary battery, the electrode was cut into a 13 mm circular electrode to form a working electrode, and a metal lithium foil cut into a circular electrode was used as a counter electrode. A propylene separator was inserted, and a coin-type test cell was prepared by adding 1 mol / L of LiPF ₆ dissolved in a mixed solvent of dimethyl carbonate (DMC), diethyl carbonate (DEC) and ethylene carbonate (EC) as an electrolyte.

[Battery performance evaluation]

Charge / discharge tests were performed using the test cell of Example 2. Four charge / discharge tests were conducted with a charge and discharge current density of 0.2 C, a charge end voltage of 0 V (Li / Li ⁺ ), and a discharge end voltage of 1.5 V (Li / Li ⁺ ). Subsequently, 50 charge / discharge tests in which the charge and discharge current density was 1 C, the charge end voltage was 0 V, and the discharge end voltage were 1.5 V were performed. That is, all the charging / discharging experiments were carried out by constant current / constant voltage, and the end voltage of constant voltage charge was 0.01C. Subsequently, the discharge capacity retention rate at the 54th cycle was obtained by setting the discharge capacity at the first cycle and the discharge capacity at the first cycle as 100%, respectively. The results are shown in Table 2.

(Example 3)

A test cell was prepared in the same manner as in Example 2 except that 94 parts by weight of natural graphite and 3 parts by weight of the aqueous binder used in Example 1 and 3 parts by weight of carboxymethylcellulose were used as solids. Subsequently, a charge and discharge test was conducted in the same manner as in Example 2 using this test cell. The results are shown in Table 2.

(Example 4)

A test cell was prepared in the same manner as in Example 2, except that 99 parts by weight of natural graphite and 0.5 parts by weight of the aqueous binder used in Example 1 and 0.5 parts by weight of carboxymethylcellulose were used. Subsequently, a charge and discharge test was conducted in the same manner as in Example 2 using this test cell. The results are shown in Table 2.

(Example 5)

A negative electrode slurry was prepared and applied to the copper foil, and the test cell was prepared in the same manner as in Example 1 except that it was dried at 200 ° C. for 10 minutes. Charge and discharge tests were carried out in the same manner as in Example 2 using the test cell. The results are shown in Table 2.

(Comparative Example 3)

A test cell of Comparative Example 3 was prepared in the same manner as in Example 2, except that the electrode prepared in Comparative Example 1 was used. Using this test cell, a charge and discharge test was conducted in the same manner as in Example 2. The results are shown in Table 2.

(Comparative Example 4)

A test cell of Comparative Example 3 was prepared in the same manner as in Example 2, except that the electrode prepared in Comparative Example 2 was used. Using this test cell, a charge and discharge test was conducted in the same manner as in Example 2. The results are shown in Table 2.

Binder Drying temperature (℃) 1st cycle (0.2C) 1st cycle (1C) Capacity maintenance rate (the 54th cycle / 1 cycle) Discharge Capacity (mAh / g) Charge / discharge efficiency (%) Discharge Capacity (mAh / g) Example 2 Binder of the present invention 1.5%, CMC 1.5% 130 366 95.8 360 88.3 Example 3 Binder 3.0%, CMC 3.0% of the present invention 130 358 94.2 348 83.6 Example 4 0.5% binder of the present invention, CMC 0.5% 130 360 95.1 340 69.8 Example 5 Binder of the present invention 1.5%, CMC 1.5% 200 355 92.7 321 65.9 Comparative Example 3 SBR 1.5%, CMC 1.5% 130 365 94.5 357 81.1 Comparative Example 4 PVdF 8% 130 358 92.2 342 70.5

As shown in Table 2, the batteries of Examples 2 and 3 each had a high discharge capacity of 366 mAh / g, 358 mAh / g, and a capacity retention rate of 88.3% and 83.6%, respectively, at 0.2 C. Capacity and excellent cycle characteristics. The value of Example 3 is rather low, but this is believed to be due to the relatively reduced amount of natural graphite since the amount of binder and CMC is slightly excess compared to Example 4.

In addition, the battery of Example 4 exhibits a relatively low discharge capacity of 360 mAh / g at 0.2C at the first cycle, but has a relatively low capacity retention of 69.8%. This is considered to be because the adhesiveness between the electrode layer containing natural graphite and copper foil accompanying the progress of a cycle fell because the amount of the binder was rather low.

In Example 5, the discharge capacity at the 0.2C first cycle was good at 355 mAh / g, but the capacity retention was 65.9%, indicating a relatively low value. This is considered to be because the adhesiveness between the copper foil and the electrode layer containing natural graphite deteriorated due to heat and a part of the binder deteriorated by heat because the drying temperature at the time of electrode production was high at 200 ° C.

In Comparative Example 3, the capacity retention rate is low as compared with Example 2 in which the amount of the binder is the same. This is considered to have caused a difference in cycle characteristics because the binding force of SBR is lower than that of the binder according to the present invention.

In Comparative Example 4, the addition of 8% PVdF did not reach the level of the capacity retention rate in Example 2, indicating that it was degraded compared to the binder of the present invention.

As apparent from the results of Table 2, it was determined that the battery of Example 2 had an excellent capacity retention rate when repeated charging and discharging compared to the battery of Comparative Example 3. This is because the electrode of the present invention using a binder composed of an olefinic amorphous copolymer and an acrylic dispersant has excellent binding property between the metal current collector and the active material, and the content of the binder which is an electrical nonconductor in the electrode is low. Charging and desorption of lithium ions of the active material proceeds smoothly, thereby showing excellent cycle characteristics.

As described above, the electrode for a lithium secondary battery of the present invention has sufficient adhesion of the active material powder to the metal current collector, and also excellent binding property between the active material powders. Dropping out can be prevented and capacity deterioration associated with charge and discharge cycles can be prevented.

In particular, the binder used in the present invention has better binding properties than conventional polyvinylidene fluoride and the like, and therefore sufficient binding properties are obtained even with a small amount of addition. Accordingly, the amount of the active material powder can be increased by reducing the amount of the binder, the charge / discharge capacity of the battery can be improved, and the content of the binder, which is an electrical nonconductor in the electrode, is small, so that the active material can be Insertion and desorption of lithium ions occurs smoothly and can exhibit excellent cycle characteristics.

Claims (9)

Metal current collectors; And An active material powder formed on the metal current collector, an amorphous polypropylene homopolymer, or an amorphous copolymer made of propylene and an olefin having 2 to 8 carbon atoms, and having a content ratio of propylene of 50% by weight or more; And an electrode layer comprising at least a copolymer binder of (meth) acrylic acid and (meth) acrylic acid alkyl ester and a water-soluble polymer. Containing Electrode for lithium secondary battery. delete The electrode of claim 1, wherein the binder is included in an amount of 0.1 wt% or more and 10 wt% or less with respect to the active material powder. The electrode for a lithium secondary battery of claim 1, wherein the water-soluble polymer is included in the range of 0.1 wt% or more and 10 wt% or less with respect to the active material powder. Metal current collectors; And an electrode layer comprising at least an active material powder, a binder, and a water-soluble polymer formed on the metal current collector, wherein the binder is an amorphous polypropylene homopolymer or an amorphous copolymer made of propylene and an olefin having 2 to 8 carbon atoms. ; And an electrode which is a copolymer of (meth) acrylic acid and (meth) acrylic acid alkyl ester. The lithium secondary battery according to claim 5, wherein the content of propylene contained in the amorphous copolymer is 50% by weight or more. The lithium secondary battery according to claim 5 or 6, wherein the binder is included in the range of 0.1 wt% or more and 10 wt% or less with respect to the active material powder. The lithium secondary battery according to claim 5 or 6, wherein the water-soluble polymer is included in the range of 0.1 wt% or more and 10 wt% or less with respect to the active material powder. Aqueous polypropylene homopolymer or binder aqueous dispersion in which an amorphous copolymer consisting of propylene and an olefin having 2 to 8 carbon atoms is dispersed in water by a dispersant consisting of a copolymer of (meth) acrylic acid and (meth) acrylic acid alkylester. A paste is prepared by mixing the electrode active material powder and the water-soluble polymer, The paste is coated on a metal current collector and dried at a temperature of 60 ° C. to 180 ° C. or less. Method for producing an electrode for a lithium secondary battery comprising a.