KR102014115B1 - Negative electrode for secondary battery and secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a negative electrode for a secondary battery and a secondary battery including the same. Specifically, the copper current collector, a conductive polymer layer, and a negative electrode active material layer are sequentially included, and the conductive polymer is PEDOT / PSS (poly (3,4, Provided is a negative electrode for a secondary battery which is -ethylenedioxythiophene) polystyrene sulfonate).
In the negative electrode according to the present invention, the PEDOT / PSS polymer layer is disposed between the copper current collector and the negative electrode active material layer, thereby increasing the contact area with the negative electrode active material due to the unevenness of the PEDOT / PSS polymer layer, thereby increasing the copper current collector and the negative electrode active material layer. There is an effect of increasing the adhesion. Furthermore, the PEDOT / PSS polymer is a conductive polymer, it is effective to maintain the resistance of the negative electrode.

Description

A negative electrode for a secondary battery and a secondary battery including the same {NEGATIVE ELECTRODE FOR SECONDARY BATTERY AND SECONDARY BATTERY COMPRISING THE SAME}

The present invention relates to a negative electrode for a secondary battery and a secondary battery including the same.

Due to the rapid increase in the use of fossil fuels, the demand for the use of alternative energy or clean energy is increasing, and the most actively researched fields are power generation and storage using electrochemical reactions.

A representative example of an electrochemical device using such electrochemical energy is a secondary battery, and its use area is gradually increasing. Recently, as the development and demand of portable devices such as portable computers, portable telephones, and cameras increases, the demand for secondary batteries as a source of energy is rapidly increasing, and these secondary batteries exhibit high energy density and operating potential, and have a cycle life. Many researches have been conducted on this long, low self-discharge rate lithium battery and are commercially available and widely used.

In general, a secondary battery is composed of a positive electrode, a negative electrode, and an electrolyte, and transfers energy while reciprocating both electrodes such that lithium ions from the positive electrode active material are inserted into a negative electrode active material such as carbon particles and are detached again during discharge by the first charge. Since it plays a role, it becomes possible to charge and discharge.

For example, a lithium secondary battery has a structure in which a lithium electrolyte is impregnated into an electrode assembly including a cathode including a lithium transition metal oxide as an electrode active material, a cathode including a graphite-based active material, and a porous separator. The positive electrode is prepared by coating a positive electrode mixture containing a lithium transition metal oxide on an aluminum foil, and the negative electrode is prepared by coating a negative electrode mixture including a graphite-based active material on a copper foil.

Recently, many studies have been conducted to increase the adhesion of the negative electrode of a lithium secondary battery. If the negative electrode has insufficient adhesive strength between the negative electrode active material and the current collector, the negative electrode active material and the negative electrode plate may be detached due to the tension in the winding process during battery manufacturing. In addition, when the secondary battery is used, the negative electrode active material layer and the negative electrode plate are partially detached due to shrinkage or relaxation due to repeated charging and discharging, thereby increasing resistance and causing abnormal heat generation, thereby reducing the capacity of the battery. There is this.

As described above, in order to solve the problem of adhesion between the negative electrode active material and the electrode plate, the coating of a specific material or surface treatment is performed on the copper foil used as the electrode plate, but this has a problem that leads to an increase in resistance of the negative electrode.

Therefore, development of a negative electrode capable of maintaining the resistance of the electrode while increasing the adhesion between the negative electrode active material and the current collector is required.

Republic of Korea Patent No. 10-0490543

The first technical problem to be solved of the present invention, by placing the PEDOT / PSS polymer in the layer between the negative electrode active material and the current collector, the bonding force between the negative electrode active material layer and the current collector is improved, further improved resistance characteristics for secondary batteries It is to provide a negative electrode.

The second technical problem to be solved of the present invention is to provide a secondary battery, a battery module and a battery pack including the secondary battery negative electrode.

In order to solve the above problems, the present invention includes a copper current collector, a conductive polymer layer, and a negative electrode active material layer in sequence, the conductive polymer is PEDOT / PSS (poly (3,4-ethylenedioxythiophene) polystyrene sulfonate) for secondary batteries Provide a cathode.

The present invention also provides a secondary battery, a battery module, and a battery pack including the negative electrode, the positive electrode, and the electrolyte.

In the negative electrode according to the present invention, the PEDOT / PSS polymer layer is disposed between the copper current collector and the negative electrode active material layer, thereby increasing the contact area with the negative electrode active material due to the unevenness of the PEDOT / PSS polymer layer, thereby increasing the copper current collector and the negative electrode active material layer. There is an effect of increasing the adhesion. Furthermore, the PEDOT / PSS polymer is a conductive polymer, it is effective to maintain the resistance of the negative electrode.

1 is a schematic diagram showing a negative electrode according to an embodiment of the present invention.

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

The terms or words used in this specification and claims are not to be construed as being limited to their ordinary or dictionary meanings, and the inventors may appropriately define the concept of terms in order to best describe their invention. It should be interpreted as meaning and concept corresponding to the technical idea of the present invention based on the principle that the present invention.

The terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to be limiting of the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

As used herein, the terms "comprise", "comprise" or "have" are intended to indicate that there is a feature, number, step, component, or combination thereof, that is, one or more other features, It should be understood that it does not exclude in advance the possibility of the presence or addition of numbers, steps, components, or combinations thereof.

According to an embodiment of the present invention, a copper current collector, a conductive polymer layer, and a negative electrode active material layer are sequentially included, and the conductive polymer is PEDOT / PSS (poly (3,4-ethylenedioxythiophene) polystyrene sulfonate) negative electrode for secondary batteries To provide.

The copper current collector may have a thickness of 6 μm to 20 μm. The negative electrode active material of the negative electrode active material layer may be one selected from the group consisting of natural graphite, artificial graphite, and mixtures thereof. The average particle diameter (D ₅₀ ) of the negative electrode active material may be 5 μm to 23 μm. When the negative electrode active material particles in the above range is used, since it can contact the unevenness of the conductive polymer layer to exhibit the widest contact area, it can exhibit excellent adhesion between the current collector and the negative electrode active material.

Conventionally, in order to improve the adhesion between the copper current collector and the negative electrode active material, it was overcome by providing a polymer layer therebetween. However, there is a problem that the resistance of the negative electrode increases as the polymer layer is added.

The present invention provides a polymer layer using PEDOT / PSS to solve the problem of high resistance. PEDOT / PSS polymer is composed of electrostatic attraction between PEDOT (poly (3,4-ethylenedioxythiophene)), a conductive polymer having ethylene dioxy group in the form of thiophene, and polystyrene sulfonate (PSS) for atmospheric stability. It is a combined polymer. Therefore, when the conductive polymer layer is positioned between the copper current collector and the negative electrode active material layer, it is possible to provide a negative electrode having excellent adhesion and maintaining a low negative electrode resistance and excellent chemical stability against air or heat.

The conductive polymer layer may have a thickness of about 10 nm to about 500 nm. If the thickness of the conductive polymer layer is less than 10 nm, since the unevenness of the conductive polymer layer is not sufficiently formed, the contact area between the negative electrode active materials may be small, which may cause a problem that the adhesion between the negative electrode active materials is lowered, which is greater than 500 nm. In this case, a problem of increasing resistance may occur.

On the other hand, the conductive polymer layer is formed with a concave-convex state on the copper current collector, thereby widening the surface area, it is possible to exhibit a more excellent adhesion since the area in contact with the negative electrode active material.

Specifically, one surface of the conductive polymer layer, the average surface roughness (Ra) of the surface in contact with the negative electrode active material layer may be 130 nm to 800 nm. If the average surface roughness (Ra) of one surface of the conductive polymer layer is less than 130 nm, since the unevenness of the polymer layer is not sufficiently formed, the contact area between the negative electrode active materials is small, which may cause a problem that the adhesion between the negative electrode active materials is reduced. In case of more than 800 nm, a problem of increasing resistance may occur.

The average surface roughness can be measured using AFM (Atomic Force Microscopy) measuring equipment.

The weight ratio of the conductive polymer layer and the negative electrode active material layer may be 0.01: 99.99 to 0.5: 99.50.

If the weight ratio of the conductive polymer layer is less than 0.01, there is a slight improvement in adhesion between the negative electrode active materials, and if the weight ratio of the conductive polymer layer is more than 0.5, a problem of increasing resistance may occur.

The negative electrode active material layer includes a binder, the binder being styrene-butadiene rubber (SBR), nitrile-butadiene rubber, methyl (meth) acrylate-butadiene rubber, chloroprene rubber, carboxy-modified styrene-butadiene rubber, carboxymethylcellulose (CMC) ) And one or more selected from the group consisting of modified polyorganosiloxane polymers. In particular, when styrene-butadiene is used, adhesion of the negative electrode active material layer and the conductive polymer layer is easier.

The negative electrode active material layer may include a conductive material. The conductive material is used to impart conductivity to the electrode, and any battery can be used as long as it is an electronic conductive material without causing chemical changes in the battery. For example, natural graphite, artificial graphite, carbon black, acetylene black, and ketjen. Metal powders, such as black, carbon fiber, copper, nickel, aluminum, silver, a metal fiber, etc. can be used, and also conductive materials, such as a polyphenylene derivative, can be mixed and used.

According to an embodiment of the present invention, a secondary battery including the negative electrode, the positive electrode, and an electrolyte is provided. Since the negative electrode is excellent in adhesion and conductivity, the secondary battery manufactured by the same may exhibit excellent stability and capacity characteristics.

The manufacturing method of the negative electrode according to the present invention is not particularly limited, and may be prepared by applying and drying a conventional method known in the art, that is, an electrode slurry including a negative electrode active material, a binder, and a conductive polymer on a current collector. At this time, a dispersing agent or surfactant may be used as needed.

On the other hand, the positive electrode according to the present invention, for example, may be prepared by applying a positive electrode mixture made by mixing the positive electrode active material particles, conductive material and binder, a filler and a solvent such as NMP on a positive electrode current collector and then dried and rolled have. In the present invention, a lithium-containing transition metal oxide may be preferably used as the cathode active material, for example, LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li (Ni _a Co _b Mn _c ) O ₂ ( 0 <a <1, 0 <b <1,0 <c <1, a + b + c = 1), LiNi _{1 -y} Co _y O ₂ , LiCo _{1 - y} Mn _y O ₂ , LiNi _{1 - y} Mn _y O ₂ (O ≦ y <1), Li (Ni _a Co _b Mn _c ) O ₄ (0 <a <2, 0 <b <2, 0 <c <2, a + b + c = 2), _{LiMn 2 - z Ni z O 4} (0 <z <2), LiMn 2 - z Co z O 4 (0 <z <2), LiCoPO 4 , and two of either or both selected from the group consisting of LiFePO ₄ jong The above mixture can be used. In addition to these oxides, sulfides, selenides, and halides may also be used.

The electrolyte may include a non-aqueous organic solvent and a metal salt.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, and gamma Butyl lactone, 1,2-dimethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxorone, formamide, dimethylformamide, dioxolon , Acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxy methane, dioxorone derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbo Aprotic organic solvents such as nate derivatives, tetrahydrofuran derivatives, ethers, methyl pyroionate and ethyl propionate can be used.

The metal salt may use a lithium salt, and in the electrolyte solution used in the present invention, lithium salt that may be included as an electrolyte may be used without limitation those conventionally used in the electrolyte for lithium secondary batteries, for example, anion of the lithium salt include ^{F -, Cl -, Br -} , I -, NO 3 -, N (CN) 2 -, BF 4 -, ClO 4 -, PF 6 -, (CF 3) 2 PF 4 -, (CF 3) _{^{3 PF 3 -, (CF 3}} ) 4 PF 2 -, (CF 3) 5 PF -, (CF 3) 6 P -, CF 3 SO 3 -, CF 3 CF 2 SO 3 -, (CF 3 SO 2) _{^{2 N -, (FSO 2)}} 2 N -, CF 3 CF 2 (CF 3) 2 CO -, (CF 3 SO 2) 2 CH -, (SF 5) 3 C -, (CF 3 SO 2) 3 C ^- it may be any one selected from the group consisting of ^{_{-, CF 3 (CF 2)}} 7 SO 3 -, CF 3 CO 2 -, CH 3 CO 2 -, SCN - , and _{(CF 3 CF 2 SO 2)} 2 N.

According to another embodiment of the present invention, a battery module including the secondary battery as a unit cell and a battery pack used as a power source for a medium-large device including the same are provided. Since the secondary battery exhibits excellent stability and capacity characteristics, the secondary battery may be used as a power source for medium and large devices selected from the group consisting of an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, and a power storage system.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily practice the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

<Example 1>

Step 1: Conductive Of polymer layer  formation

A solution of 100 g of water and 2 g of PEDOT: PSS as a solvent for 1 hour was coated with a thickness of 200 nm on a copper mesh foil, which is a negative electrode current collector, using a slit coating method. Thereafter, a conductive polymer layer was formed on the copper current collector by drying at a temperature of 130 ° C., with an average surface roughness of 450 nm.

Step 2: Preparation of the Cathode

On the copper current collector on which the conductive polymer layer is formed, a mixture of 96 g of artificial graphite having a diameter of 30 to 150 μm, 1 g of CMC, 2 g of SBR, 1 g of acetylene black as a conductive material, and 220 g of water as a solvent are prepared. After applying one negative electrode mixture, the negative electrode was prepared by drying and rolling in a vacuum oven at 130 ° C.

Comparative Example 1

An anode was manufactured in the same manner as in Example 1, except that the conductive polymer layer was not formed in Step 1 of Example 1.

Experimental Example 1 Adhesion

In order to find out the adhesive strength of the negative electrode prepared in Example 1 and Comparative Example 1, the adhesion was measured by a commonly known 180 ^o peel test. The results are shown in Table 1 below.

Adhesive force (gf) Example 1 72.32 Comparative Example 1 65.24

As shown in Table 1, it can be seen that the adhesion of Example 1 was increased by 10.8% compared to Comparative Example 1 without the conductive polymer layer of the present invention.

Through this, it can be seen that by providing the conductive polymer layer of the present invention, the adhesive strength of the electrode is increased.

Experimental Example 2 Electrode Resistance Measurement

After measuring the resistance of the negative electrode prepared in Example 1 and Comparative Example 1 with a four-probe sheet resistance measuring apparatus, the results are shown in Table 2.

Sheet resistance (mΩ / □) Example 1 1.0 Comparative Example 1 1.1

As shown in Table 2, it can be seen that the sheet resistance of Comparative Example 1 without the conductive polymer layer is 10% higher than that of Example 1 with the conductive polymer layer of the present invention.

Through this, it can be seen that by providing the conductive polymer layer of the present invention, not only the adhesive strength of the electrode is increased but also the resistance of the electrode is also low.

Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of the invention.

Claims (12)

Sequentially comprising a copper current collector, a conductive polymer layer, and a negative electrode active material layer,
The conductive polymer is PEDOT / PSS (poly (3,4-ethylenedioxythiophene) polystyrene sulfonate),
The thickness of the conductive polymer layer is a secondary battery negative electrode 10 to 500 nm.
The method of claim 1,
The negative electrode active material is a negative electrode for a secondary battery, characterized in that one selected from the group consisting of natural graphite, artificial graphite, and mixtures thereof.
delete The method of claim 1,
The weight ratio of the conductive polymer layer and the negative electrode active material layer is a secondary battery negative electrode, characterized in that 0.01: 99.99 to 0.5: 99.5.
The method of claim 1,
The negative electrode active material layer comprises a binder, the binder is a secondary battery negative electrode, characterized in that the styrene-butadiene rubber (SBR).
The method of claim 1,
One surface of the conductive polymer layer, the surface in contact with the negative electrode active material layer is a negative electrode for a secondary battery, characterized in that the irregularities are formed.
The method of claim 1,
One surface of the conductive polymer layer, the average surface roughness (R _a ) of the surface in contact with the negative electrode active material layer is a negative electrode for a secondary battery, characterized in that 130 nm to 800 nm.
The method of claim 1,
An average particle diameter (D ₅₀ ) of the negative electrode active material is a secondary battery negative electrode, characterized in that 5 ㎛ to 23 ㎛.
A secondary battery comprising the negative electrode, the positive electrode, and the electrolyte of claim 1.
A battery module comprising the secondary battery of claim 9 as a unit cell.
A battery pack comprising the battery module of claim 10 and used as a power source for medium and large devices.
The method of claim 11,
The medium-to-large device is a battery pack is selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles and power storage systems.

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