KR20210059969A - Binder for manufacturing a positive electrode of lithium secondary battery, positive electrode of lithium secondary battery and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a binder for manufacturing a positive electrode of a lithium secondary battery, a positive electrode for a lithium secondary battery including the same, and a lithium secondary battery. The present invention can improve the lifespan characteristics of a lithium-sulfur battery.

Description

BACKGROUND OF THE INVENTION Binder for manufacturing anodes of lithium secondary batteries, anodes and lithium secondary batteries for lithium secondary batteries including the same {BINDER FOR MANUFACTURING A POSITIVE ELECTRODE OF LITHIUM SECONDARY BATTERY, POSITIVE ELECTRODE OF LITHIUM SECONDARY BATTERY AND LITHIUM SECONDARY BATTERY COMPRISING THE SAME}

The present invention relates to a binder for manufacturing a positive electrode of a lithium secondary battery, a positive electrode for a lithium secondary battery including the same, and a lithium secondary battery.

As the application area of secondary batteries expands to electric vehicles (EV) and energy storage devices (ESS), lithium-ion secondary batteries with relatively low weight-to-energy storage density (~250 Wh/kg) are suitable for these products. There is a limit to the application. In contrast, the lithium-sulfur battery is in the spotlight as a next-generation secondary battery technology because it can theoretically realize a high energy storage density (~2,600 Wh/kg) compared to its weight.

The lithium-sulfur battery refers to a battery system using a sulfur-based material having an S-S bond (Sulfur-Sulfur Bond) as a positive electrode active material and lithium metal as a negative electrode active material. Sulfur, which is the main material of the positive electrode active material, has the advantage of having abundant resources, non-toxic, and low weight per atom worldwide.

In a lithium-sulfur battery, lithium, which is a negative electrode active material, is oxidized while ionizing and releasing electrons during discharge, and a sulfur-based material, which is a positive electrode active material, receives electrons and is reduced. Here, the oxidation reaction of lithium is a process in which lithium metal releases electrons and is converted into lithium cation form. In addition, the reduction reaction of sulfur is a process in which the SS bond accepts two electrons and is converted into a sulfur anion form. The lithium cation generated by the oxidation reaction of lithium is transferred to the positive electrode through the electrolyte, and forms a salt by combining with the sulfur anion generated by the reduction reaction of sulfur. Specifically, sulfur before discharge has a cyclic S ₈ structure, which is converted into lithium polysulfide (LiS _{x) by a reduction reaction.} When lithium polysulfide is completely reduced, lithium sulfide (Li ₂ S) is produced.

Although the lithium-sulfur battery has the advantage of high energy storage density, there are several problems in practical application. Specifically, there may be a problem of instability of lithium metal used as a negative electrode, a problem of low conductivity of the positive electrode, a problem of sublimation of a sulfur-based material during electrode manufacturing, and a problem of loss of a sulfur-based material during repetitive charging and discharging.

The binder used for the conventional lithium-sulfur battery positive electrode was prepared by using styrene butadiene rubber/carboxymethyl cellulose (SBR/CMC), which is the same binder as the lithium ion battery, as a binder. The binder maintains high adhesion, but since sodium (Na) is contained in a high content in styrene butadiene rubber and carboxymethyl cellulose, there is a problem in that long-term stability is deteriorated due to deterioration of the anode due to the progress of charging and discharging.

In order to solve the above problem, an additive capable of increasing the life of the battery may be additionally used, but in this case, the content of the positive electrode active material in the positive electrode decreases, resulting in a problem that the performance of the battery is deteriorated.

Therefore, there is a need for a binder capable of solving the above problems.

Korean Patent Registration No. 10-1583948

In order to solve the above problems, the present inventors conducted various studies, and as a result of conducting a research on a lithium secondary battery, polyethyleneimine and polyvinylpyrrolidone having a weight average molecular weight of 2,500 to 270,000 were used as a binder for manufacturing a positive electrode of a lithium secondary battery. When applied to the positive electrode, it is possible to improve the adhesion of the positive electrode active material layer to the current collector due to the high viscosity of polyethyleneimine, and lithium generated during the discharge reaction of the lithium-sulfur battery due to the pyrrolidone functional group of polyvinylpyrrolidone. The present invention was completed by confirming that it was possible to suppress the elution of polysulfide, thereby increasing the life of the lithium-sulfur battery.

Accordingly, an object of the present invention is to provide a binder for manufacturing a positive electrode of a lithium secondary battery, which can improve the life characteristics of a lithium secondary battery, preferably a lithium-sulfur battery.

In addition, an object of the present invention is to provide a positive electrode for a lithium secondary battery and a lithium secondary battery including the binder.

To achieve the above object,

The present invention is a binder for manufacturing a positive electrode of a lithium secondary battery comprising polyethyleneimine and polyvinylpyrrolidone,

The polyethyleneimine has a weight average molecular weight of 2,500 to 270,000, providing a binder for manufacturing a positive electrode of a lithium secondary battery.

In addition, the present invention is a current collector; And

A positive electrode for a lithium secondary battery comprising a positive electrode active material layer formed on at least one surface of the current collector,

The positive electrode active material layer includes a positive electrode active material, a binder, and a conductive material,

The binder provides a positive electrode for a lithium secondary battery, which is a binder for manufacturing the positive electrode of the lithium secondary battery of the present invention.

In addition, the present invention is a positive electrode; cathode; A separator interposed between the anode and the cathode; And a lithium secondary battery containing an electrolyte,

The positive electrode provides a lithium secondary battery, characterized in that the positive electrode of the present invention.

As the binder for manufacturing a positive electrode of a lithium secondary battery of the present invention contains polyethyleneimine and polyvinylpyrrolidone having a weight average molecular weight of 2,500 to 270,000, adhesion of the positive electrode active material layer to the positive electrode current collector can be improved, and lithium- When applied to a sulfur battery, it is possible to suppress lithium polysulfide that is eluted, thereby improving the life performance of a lithium-sulfur battery.

1 is a graph of life characteristics of a lithium-sulfur battery of Experimental Example 1.

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

In lithium secondary batteries, especially lithium-sulfur batteries, styrene butadiene rubber/carboxymethyl cellulose (SBR/CMC) was mainly used as a binder when manufacturing a positive electrode. The carboxymethyl cellulose is an additive used to improve the dispersibility of the binder as a thickener, and if only styrene butadiene rubber is used without the carboxymethyl cellulose, the dispersibility decreases and the processability of the binder decreases, and the anode deteriorates during charging and discharging. The stability is reduced. In order to solve the above problem, carboxymethyl cellulose was used together with styrene butadiene rubber, but there is a problem that satisfactory lifespan characteristics are not obtained due to deterioration of the battery due to sodium contained in the carboxymethyl cellulose.

Accordingly, in the present invention, it is intended to provide a binder for manufacturing a positive electrode of a lithium secondary battery that does not cause deterioration and can improve lifespan characteristics.

Binder for manufacturing positive electrode of lithium secondary battery

The present invention is a binder for manufacturing a positive electrode of a lithium secondary battery comprising polyethyleneimine and polyvinylpyrrolidone,

The polyethyleneimine has a weight average molecular weight of 2,500 to 270,000, and relates to a binder for manufacturing a positive electrode of a lithium secondary battery.

The binder for manufacturing the positive electrode of the lithium secondary battery is included in the positive electrode active material layer formed on the positive electrode current collector, and the polyethyleneimine (PEI) improves the adhesion of the positive electrode active material to the positive electrode current collector due to its high viscosity. I can. Therefore, it is possible to prevent the desorption of the positive electrode active material, thereby improving the life performance of a lithium secondary battery, preferably a lithium-sulfur battery.

The weight average molecular weight of the polyethyleneimine is 2,500 to 270,000, preferably 40,000 to 100,000. If the weight average molecular weight of the polyethyleneimine is less than 2,500, the viscosity of the composition for forming the positive electrode active material layer in the form of a slurry is low compared to the content of the polyethyleneimine used, and the effect of improving adhesion cannot be obtained, and if the weight average molecular weight exceeds 270,000, it is in the form of a slurry. The viscosity of the composition for forming a positive electrode active material layer of is increased, so that the content of the solid content in the entire slurry is lowered, and thus the fairness of the positive electrode manufacturing process of coating and drying the slurry on the positive electrode current collector may be lowered.

Accordingly, in the present invention, by using polyethyleneimine having a weight average molecular weight of 2,500 to 270,000, it is possible to obtain an effect of improving the life of the lithium-sulfur battery.

The polyvinylpyrrolidone (PVP) can suppress the elution of lithium polysulfide due to the pyrrolidone functional group present in the polyvinylpyrrolidone. More specifically, the lithium-sulfur battery generates lithium polysulfide during charging and discharging, and the lithium polysulfide is eluted to reduce the life of the battery. However, Li-O bonds are formed by the strong interaction between the carbonyl functional group inside the pyrrolidone monomer of the polyvinylpyrrolidone and the lithium ions inside the lithium polysulfide, thereby inhibiting the elution of lithium polysulfide. It can improve the life of the sulfur battery.

The weight average molecular weight of the polyvinylpyrrolidone is 10,000 to 1,300,000, preferably 55,000 to 1,300,000.

When the weight average molecular weight of the polyvinylpyrrolidone is less than 10,000, the viscosity of the composition for forming a slurry-type positive active material layer decreases, and when the weight average molecular weight exceeds 1,300,000, the viscosity of the composition for forming the slurry-type positive active material layer increases. The content of the solid content in the entire slurry is lowered, and thus, the processability of a positive electrode manufacturing process in which the slurry is coated and dried on a positive electrode current collector may be deteriorated.

The polyethyleneimine and polyvinylpyrrolidone may be mixed in a weight ratio of 5:1 to 1:5, preferably in a weight ratio of 7:3 to 3:7.

If the polyethyleneimine is contained in an amount less than the weight ratio, the effect of increasing adhesion is insignificant, and if it is contained in an amount exceeding the weight ratio, the viscosity of the composition for forming the positive electrode active material layer in the form of a slurry increases, so that the content of solid content in the slurry may be lowered.

The binder for manufacturing the positive electrode of the lithium secondary battery may be preferably used as a binder for manufacturing the positive electrode of the lithium-sulfur battery.

Anode for lithium secondary battery

In addition, the present invention is a current collector; And

It relates to a positive electrode for a lithium secondary battery comprising; a positive electrode active material layer formed on at least one surface of the current collector,

The positive electrode active material layer includes a positive electrode active material, a binder, and a conductive material,

The binder may be a binder for manufacturing the positive electrode of the lithium secondary battery of the present invention described above.

The current collector is not particularly limited as long as it is generally used in the manufacture of a positive electrode. According to one embodiment of the present invention, the type of the positive electrode current collector may be one or more materials selected from stainless steel, aluminum, nickel, titanium, calcined carbon, and aluminum, and if necessary, carbon, nickel, and titanium on the surface of the material. Alternatively, it can be used by treating silver. According to one embodiment of the present invention, the shape of the positive electrode current collector may be selected from a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric. The thickness of the positive electrode current collector is not particularly limited, and may be set in an appropriate range in consideration of the mechanical strength of the positive electrode, productivity, and capacity of a battery, and is preferably 3 to 500 μm.

The positive active material layer may include a positive active material, a binder, and a conductive material.

The positive electrode active material may be selected from elemental sulfur (S ₈ ), a sulfur-carbon composite, a sulfur-based compound, or a mixture thereof, but is not limited thereto. Specifically, the sulfur-based compound may be Li ₂ S _n (n≥1), an organosulfur compound or a carbon-sulfur polymer ((C ₂ S _x ) _n : x=2.5 to 50, n≥2). These can be applied in combination with a conductive material because the sulfur material alone has no electrical conductivity.

In addition, the sulfur-carbon composite is an aspect of a positive electrode active material in which carbon and sulfur are mixed to reduce the leakage of sulfur into the electrolyte and increase the electrical conductivity of the sulfur-containing electrode.

The carbon material constituting the sulfur-carbon composite may be crystalline or amorphous carbon, or may be conductive carbon. Specifically, graphite, graphene, super P, carbon black, denka black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, carbon a nanofiber, carbon nanotube, carbon nanowire, carbon nano-rings, carbon fabric, and fullerene (C ₆₀₎ may be selected from the group consisting of.

Examples of such a sulfur-carbon composite include a sulfur-carbon nanotube composite. Specifically, the sulfur-carbon nanotube composite includes a carbon nanotube aggregate having a three-dimensional structure, and a sulfur or sulfur compound provided on at least a portion of an inner surface and an outer surface of the carbon nanotube aggregate.

The positive electrode active material may be included in an amount of 30 to 95% by weight based on the total weight of the positive electrode active material layer.

As the positive electrode active material is used, the positive electrode for a lithium secondary battery of the present invention may be a positive electrode for a lithium-sulfur battery.

The conductive material is graphite such as natural graphite or artificial graphite; Carbon black, such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, or thermal black; Conductive fibers such as carbon fibers or metal fibers; Metal powders such as carbon fluoride, aluminum or nickel powder; Conductive whiskey such as zinc oxide or potassium titanate; Conductive metal oxides such as titanium oxide; Or it may be a polyphenylene derivative, but is not limited thereto. The conductive material may preferably be included in an amount of 5 to 20% by weight based on the total weight of the positive electrode active material layer. If the content of the conductive material is less than 5% by weight, the effect of improving the conductivity due to the use of the conductive material is insignificant, whereas if the content of the conductive material is more than 20% by weight, the content of the positive electrode active material is relatively small, and the capacity characteristics may be deteriorated.

As the binder, the binder of the present invention described above may be used, and the binder may be included in an amount of 0.1 to 10% by weight based on the total weight of the positive electrode active material layer. When the binder is contained in an amount of less than 0.1% by weight, the effect of improving the binding strength between the positive electrode active material or between the positive electrode active material and the current collector according to the use of the binder is insignificant, and if it exceeds 10% by weight, the content of the positive electrode active material is relatively reduced, resulting in the capacity and capacity of the battery. Life characteristics may be deteriorated.

The positive electrode as described above may be manufactured according to a conventional method, and specifically, a composition for forming a positive electrode active material layer prepared in a slurry state by mixing a positive electrode active material, a conductive material, and a binder in a solvent is applied on a current collector and then dried. And it can be produced by selectively rolling.

At this time, the positive electrode active material, the binder, and the conductive material may be uniformly dispersed as the solvent, and it is preferable to use one that evaporates easily. Specific examples include acetonitrile, methanol, ethanol, tetrahydrofuran, water, and isopropyl alcohol.

As the coating method, for example, a bar coating method, a screen coating method, a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, or an extrusion method may be applied. The amount of the composition for forming a positive electrode active material layer on the current collector is not particularly limited, and is finally adjusted in consideration of the thickness of the desired positive electrode active material layer. In addition, a known process required for manufacturing a positive electrode may be performed before or after the positive electrode active material layer forming process, for example, a rolling or drying process. The thickness of the active layer formed by the composition for forming the positive active material layer may be appropriately selected in consideration of desired performance, and is not particularly limited. According to one embodiment of the present invention, it may be preferable that the thickness of the positive electrode active material layer is 1 to 200 μm.

Lithium secondary battery

In addition, the present invention is a positive electrode; cathode; A separator interposed between the anode and the cathode; And it relates to a lithium secondary battery comprising an electrolyte,

The positive electrode may be the positive electrode for a lithium secondary battery of the present invention described above.

Accordingly, the lithium secondary battery of the present invention may be a lithium-sulfur battery.

The negative electrode may include a current collector and a negative active material layer formed on one or both surfaces thereof. Alternatively, the negative electrode may be a lithium metal plate.

The current collector is for supporting the negative active material, and is not particularly limited as long as it has excellent conductivity and is electrochemically stable in the voltage range of a lithium secondary battery. For example, copper, stainless steel, aluminum, nickel, titanium, palladium , Calcined carbon, surface treated with carbon, nickel, silver, etc. on the surface of copper or stainless steel, aluminum-cadmium alloy, etc. may be used.

The negative electrode current collector may form fine irregularities on its surface to enhance the bonding strength with the negative electrode active material, and various forms such as films, sheets, foils, meshes, nets, porous bodies, foams, and nonwoven fabrics may be used.

The negative active material is a material capable of reversibly intercalating or deintercalating lithium ions, a material capable of reversibly forming a lithium-containing compound by reacting with lithium ions, a lithium metal or a lithium alloy Can be used.

The material capable of reversibly intercalating or deintercalating lithium ions may be, for example, crystalline carbon, amorphous carbon, or a mixture thereof.

A material capable of reversibly forming a lithium-containing compound by reacting with the lithium ions may be, for example, tin oxide, titanium nitrate, or silicon.

The lithium alloy is, for example, lithium (Li) and sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), beryllium (Be), magnesium (Mg), calcium ( It may be an alloy of a metal selected from the group consisting of Ca), strontium (Sr), barium (Ba), radium (Ra), aluminum (Al), and tin (Sn).

A separator may be additionally included between the above-described anode and cathode. The separator separates or insulates the positive and negative electrodes from each other and enables transport of lithium ions between the positive and negative electrodes, and may be made of a porous non-conductive or insulating material. This separator may be an independent member such as a film, or may be a coating layer added to the anode and/or the cathode.

Materials constituting the separation membrane include, for example, polyolefins such as polyethylene and polypropylene, glass fiber filter paper, and ceramic materials, but are not limited thereto, and the thickness thereof is about 5 to 50 µm, preferably about 5 to 25 µm. I can.

The electrolyte is a non-aqueous electrolyte containing a lithium salt and is composed of a lithium salt and an electrolyte, and as the electrolyte, a non-aqueous organic solvent, an organic solid electrolyte, an inorganic solid electrolyte, and the like are used.

The lithium salt may be used without limitation as long as it is commonly used in an electrolytic solution for a lithium secondary battery, preferably a lithium-sulfur battery. For example, LiSCN, LiBr, LiI, LiPF ₆ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiSO ₃ CF ₃ , LiCl, LiClO ₄ , LiSO ₃ CH ₃ , LiB(Ph) ₄ , LiC(SO ₂ CF ₃ ) _{3 , LiN (SO 2 CF 3)} 2, LiCF 3 CO 2, LiAsF 6, LiSbF 6, LiAlCl 4, may be included are one or more from LiFSI, chloro group consisting of borane lithium, lower aliphatic carboxylic acid lithium or the like.

In addition, the concentration of the lithium salt in the electrolyte may be 0.2 to 2 M, specifically 0.6 to 2 M, more specifically 0.7 to 1.7 M. When the concentration of the lithium salt is less than 0.2 M, the conductivity of the electrolyte solution may be lowered and thus the electrolyte performance may be deteriorated, and when the concentration of the lithium salt exceeds 2 M, the viscosity of the electrolyte solution may increase, thereby reducing the mobility of lithium ions.

The non-aqueous organic solvent should dissolve the lithium salt well, and the non-aqueous organic solvent of the present invention includes, for example, N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, di Ethyl carbonate, ethylmethyl carbonate, gamma-butyrolactone, 1,2-dimethoxy ethane, 1,2-diethoxy ethane, tetrahydroxyfranc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1, 3-dioxolane, 4-methyl-1,3-dioxene, diethyl ether, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate tryster, trimer Aprotic, such as oxymethane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl pyropionate, ethyl propionate, etc. An organic solvent may be used, and the organic solvent may be one or a mixture of two or more organic solvents.

Examples of the organic solid electrolyte include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, poly etch lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, ionic dissociation. Group-containing polymers and the like can be used.

As the inorganic solid electrolyte, for example, 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 , Li ₄ Nitrides, halides, and sulfates of Li such as SiO ₄ -LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS _{2 may be used.}

The electrolyte of the present invention includes pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, and nitro for the purpose of improving charge/discharge properties and flame retardancy. Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol, aluminum trichloride, etc. may be added. . In some cases, in order to impart non-flammability, a halogen-containing solvent such as carbon tetrachloride and ethylene trifluoride may be further included, and carbon dioxide gas may be further included to improve high-temperature storage characteristics. carbonate), PRS (Propene sultone), FPC (Fluoro-propylene carbonate), etc. may be further included.

The electrolyte may be used as a liquid electrolyte or may be used in the form of a solid electrolyte membrane. When used as a liquid electrolyte, a separator made of porous glass, plastic, ceramic, or polymer as a physical separator having a function of physically separating the electrode may be further included.

The lithium secondary battery of the present invention, preferably a lithium-sulfur battery, includes the binder of the present invention described above in the positive electrode active material layer. Accordingly, the adhesion of the positive electrode active material layer to the current collector is excellent, the elution of lithium polysulfide can be suppressed, and the life characteristics of the lithium-sulfur battery can be improved. In addition, it is possible to solve problems such as battery deterioration occurring in the conventional styrene butadiene rubber/carboxymethyl cellulose binder, thereby improving the life characteristics of the lithium-sulfur battery by about 100% or more compared to the use of the conventional binder.

Hereinafter, preferred embodiments are presented to aid in the understanding of the present invention, but the following examples are only illustrative of the present invention, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and spirit of the present invention. It is natural that changes and modifications fall within the scope of the appended claims.

<Manufacture of positive electrode for lithium-sulfur battery>

Example 1.

A binder was prepared by mixing polyethyleneimide having a weight average molecular weight of 70,000 and polyvinylpyrrolidone having a weight average molecular weight of 360,000 in a weight ratio of 3:7. Sulfur (manufactured by Sigma-Aldrich) was mixed with CNT (Carbon Nanotube) using a ball mill and then heat-treated at 155°C to prepare a sulfur-carbon composite cathode active material. Denka black was prepared as a conductive material.

The above-described positive electrode active material, conductive material, and binder were added to water as a solvent and mixed in a beads milling method to prepare a composition for forming a positive electrode active material layer. At this time, the mixing ratio was a weight ratio of 90:5:5 of the positive electrode active material: the conductive material: the binder. The prepared composition for forming a positive electrode active material layer was applied to an aluminum foil current collector and then dried at 50° C. for 2 hours to prepare a positive electrode.

Comparative Example 1.

A positive electrode for a lithium-sulfur battery was prepared in the same manner as in Example 1, except that a binder obtained by mixing styrene butadiene rubber and carboxymethyl cellulose in a weight ratio of 3.5:1.5 was used.

Experimental Example 1. Evaluation of life characteristics of lithium-sulfur battery

A lithium foil having a thickness of about 100 μm was used as a negative electrode, and polyethylene was used as a separator. _{An electrolyte in which 0.38M LiTFSI and 0.31M LiNO 3} were added to a mixed solvent (1:1, v/v) of 1,3-dioxolane (DOL) and 1,2-dimethoxyethane (DME) as an electrolyte. Was used.

As a positive electrode, the positive electrodes for lithium-sulfur batteries of Example 1 and Comparative Example 1 were used, respectively, to prepare lithium-sulfur batteries in the form of respective coin cells. At this time, the loading amount of the positive electrode of Example 1 and Comparative Example 1 was adjusted to a value between ^{4.5 and 5 mAh/cm 2.}

The galvanostatic charge/discharge analysis of the coin cell type lithium-sulfur battery was carried out in a voltage range of 0.2 C, 1.5 V to 2.6 V (vs Li/Li ⁺ ) to measure lifespan characteristics, and the results are shown in the following figure. It is shown in 1.

The lithium-sulfur battery including the positive electrode of Example 1 was measured by repeating three times.

As a result of measuring the lifetime of a lithium-sulfur battery in a coin cell unit, polyethyleneimide (weight average molecular weight 70,000) and polyvinylpyrrolidone (weight average molecular weight 360,000) (3:7 weight ratio) were used as binders for the positive electrode for lithium-sulfur batteries. The lithium-sulfur battery of Example 1 used showed a lifespan performance of maintaining a discharge capacity of 800 mAh/g or more for 100 cycles or more.

On the other hand, the lithium-sulfur battery of Comparative Example 1 using styrene butadiene rubber and carboxymethyl cellulose as binders for the lithium-sulfur battery positive electrode maintained a discharge capacity of about 500mAh/g after 50 cycles with 0.2C discharge.

It is judged that this is because the chemical properties of polyethyleneimine and polyvinylpyrrolidone, which are binders for manufacturing the positive electrode of the lithium secondary battery of the present invention, helped the adsorption and reduction reaction of polysulfide, effectively inhibiting the elution of sulfur-based substances into the electrolyte. do. In addition, it can be seen that through the use of the binder for manufacturing the positive electrode of the lithium secondary battery of the present invention, it is possible to suppress the deterioration of the battery life due to sodium ions contained in a large amount in carboxymethyl cellulose, a thickener used in the related art.

From this, it was found that the binder of the present invention can improve the life performance of a lithium secondary battery, preferably a lithium-sulfur battery.

Claims (8)

As a binder for manufacturing a positive electrode of a lithium secondary battery containing polyethyleneimine and polyvinylpyrrolidone,
The weight average molecular weight of the polyethyleneimine is 2,500 to 270,000, a binder for manufacturing a positive electrode of a lithium secondary battery. The method of claim 1,
A binder for manufacturing a positive electrode of a lithium secondary battery, characterized in that the weight average molecular weight of the polyvinylpyrrolidone is 10,000 to 1,300,000. The method of claim 1,
The polyethyleneimine and polyvinylpyrrolidone are mixed in a weight ratio of 5:1 to 1:5. A binder for manufacturing a positive electrode for a lithium secondary battery. The method of claim 1,
The binder for manufacturing a positive electrode for a lithium secondary battery is a binder for manufacturing a positive electrode for a lithium secondary battery, characterized in that the binder for manufacturing a positive electrode for a lithium-sulfur battery. Current collector; And
A positive electrode for a lithium secondary battery comprising a positive electrode active material layer formed on at least one surface of the current collector,
The positive electrode active material layer includes a positive electrode active material, a binder, and a conductive material,
The binder is a binder for manufacturing a positive electrode of a lithium secondary battery according to any one of claims 1 to 4, a positive electrode for a lithium secondary battery. The method of claim 5,
The positive electrode for a lithium secondary battery is a positive electrode for a lithium secondary battery, characterized in that the positive electrode for a lithium-sulfur battery. anode; cathode; A separator interposed between the anode and the cathode; And a lithium secondary battery containing an electrolyte,
The lithium secondary battery, characterized in that the positive electrode is the positive electrode of any one of claims 5 or 6. The method of claim 7,
The lithium secondary battery is a lithium secondary battery, characterized in that the lithium-sulfur battery.

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