KR20120054243A - Negative electrode for secondary battery, method for preparing thereof and secondary battery comprising the same - Google Patents

Abstract

PURPOSE: A negative electrode for a secondary battery comprises a crystalline carbon-based active material layer and an amorphous carbon active material layer coated on a current collector, thereby having high discharging capacity, and preventing overcharge. CONSTITUTION: A negative electrode(100) for a secondary battery comprises: a current collector(110); a first negative electrode active material layer(120) formed on at least one side of the current collector, comprising crystalline carbon-based active material; and a second negative electrode active material layer(130) containing amorphous carbon-based material, formed on the outside of the first negative electrode active material layer. A manufacturing method of the negative electrode comprises: a step of forming a first negative electrode active material layer by coating slurry containing the crystalline carbon-based active material layer on at least one side of the current collector, and drying the same; and a step of forming a second negative electrode active material layer by coating slurry containing the amorphous carbon-based active material layer on one side of the first negative electrode active material layer, and drying the same.

Description

A negative electrode for a secondary battery, a method of manufacturing the same, and a secondary battery including the same {NEGATIVE ELECTRODE FOR SECONDARY BATTERY, METHOD FOR PREPARING THEREOF AND SECONDARY BATTERY COMPRISING THE SAME}

The present invention relates to a secondary battery negative electrode having a high discharge capacity, and excellent in output characteristics and impregnation of the electrolyte solution.

Recently, lithium secondary batteries have received the most attention as batteries with high energy density and long lifespan. Typically, a lithium secondary battery includes an anode made of a carbon material or a lithium metal alloy, a cathode made of a lithium metal oxide, and an electrolyte in which lithium salt is dissolved in an organic solvent.

Lithium metal was initially used as a negative electrode active material constituting the negative electrode of a lithium secondary battery. However, lithium has a problem of low reversibility and safety, and carbon-based active materials are mainly used as negative electrode active materials of lithium secondary batteries. Carbon materials have a smaller capacity than lithium metal, but have a small volume change, excellent reversibility, and an advantageous price.

Such carbon-based active materials may be classified into amorphous carbon-based active materials and crystalline carbon-based active materials such as graphite. The amorphous carbon-based active material has a high discharge capacity and excellent rate characteristics, but has a high irreversible capacity, low charge and discharge efficiency, and low energy density due to low bulk density and electrical conductivity. On the other hand, the crystalline carbon-based active material has a low discharge capacity, but has excellent electrical conductivity and energy density, good electric potential flatness, and relatively good reversibility in charge / discharge process compared to the amorphous carbon-based compound. Thus, in order to compensate for the disadvantages of these carbon-based active materials, a technique of using a mixture of crystalline carbon and amorphous carbon has been studied, but these negative electrodes have increased initial charging and discharging efficiency, but do not solve the problem of overcharging.

Accordingly, an object of the present invention is to provide a negative electrode having a high discharge capacity and capable of preventing overcharge.

In order to solve the above problem, a current collector; A first negative electrode active material layer comprising a crystalline carbon-based active material formed on at least one surface of the current collector; And it provides a negative electrode for a secondary battery having a second negative electrode active material layer comprising an amorphous carbon-based active material formed on the outer surface of the first negative electrode active material layer.

It is preferable that the thickness of this 1st negative electrode active material layer is 10-100 micrometers. In addition, it is preferable that the thickness of such a 2nd negative electrode active material layer is 10-100 micrometers.

In addition, as the crystalline carbon-based active material of the present invention, natural graphite or artificial graphite may be used.

The amorphous carbon-based active material of the present invention may be sucrose, phenol resin, naphthalene resin, polyvinyl alcohol resin, furfuryl alcohol resin, polyacrylonitrile resin, polyamide resin, furan resin, cellulose resin, styrene Hard carbon raw materials of resin, polyimide resin, epoxy resin or vinyl chloride resin; And one or two or more amorphous carbon precursors selected from the group consisting of coal-based pitches, petroleum-based pitches, polyvinyl chloride, mesophase pitch, tar, or soft carbon raw materials of low molecular weight heavy oil.

The current collector of the present invention is stainless steel, aluminum, nickel, titanium, calcined carbon, copper; Stainless steel surface-treated with carbon, nickel, titanium, or silver; Aluminum-cadmium alloys; Non-conductive polymer surface-treated with a conductive material; Alternatively, a conductive polymer may be used, and as the conductive material, polyacetylene, polyaniline, polypyrrole, polythiophene and polysulfuritride, indium thin oxide (ITO), silver, palladium and nickel may be used.

Method of manufacturing a negative electrode of the present invention comprises the steps of coating and drying a slurry containing a crystalline carbon-based active material on at least one surface of the current collector to form a first negative electrode active material layer; And coating and drying a slurry including an amorphous carbon-based active material on one surface of the first negative electrode active material layer to form a second negative electrode active material layer.

The present invention also relates to a secondary battery including such a negative electrode.

The negative electrode of the present invention having the crystalline carbon-based active material layer and the amorphous carbon-based active material layer coated on the current collector prevents the occurrence of overcharge.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments of the invention and, together with the description of the invention, It should not be construed as limited.
1 is a diagram of a cathode according to an embodiment.
2 is a graph of charging graphite and hard carbon at 0.2 C rate.
3 is a graph of charging graphite and hard carbon at 1 C rate.
4 is a charge graph of graphite and hard carbon at 3 C rate.
5 is a graph of charging graphite and hard carbon at 5 C rate.

Hereinafter, the present invention will be described in detail. Prior to this, terms or words used in the specification and claims should not be construed as having a conventional or dictionary meaning, and the inventors should properly explain the concept of terms in order to best explain their own invention. Based on the principle that can be defined, it should be interpreted as meaning and concept corresponding to the technical idea of the present invention. Therefore, the configurations described in the embodiments described herein are only one of the most preferred embodiments of the present invention and do not represent all of the technical ideas of the present invention, and various equivalents may be substituted for them at the time of the present application. It should be understood that there may be variations.

Referring to Figure 1, the secondary battery negative electrode 100 of the present invention is a current collector (110); A first negative electrode active material layer 120 formed on at least one surface of the current collector and including a crystalline carbon-based active material; And a second negative electrode active material layer 130 formed on an outer surface of the first negative electrode active material layer and including an amorphous carbon-based active material. It is preferable that the thickness of this 1st negative electrode active material layer is 10-100 micrometers. In addition, it is preferable that the thickness of such a 2nd negative electrode active material layer is 10-100 micrometers.

In general, the crystalline carbon-based compound has a path in which lithium ions are inserted and desorbed into the carbon layer structure in approximately two dimensions, so that charging does not proceed as the charging current increases. On the other hand, the amorphous carbonated compound has a relatively large number of pathways for insertion of lithium ions and is relatively limited, and thus exhibits excellent rate characteristics and thus enables fast charging (see FIGS. 2, 3, 4 and 5). Therefore, the negative electrode of the present invention having the crystalline carbon-based active material layer coated on the current collector and the amorphous carbon-based active material layer thereon, when a strong current flow due to overcharging occurs, that is, an extremely high level of high rate ( In the case of high rate charging, the crystalline carbon-based active material layer directly coated on the current collector serves to hinder the flow of charge. Due to the role of hindering the flow of the filling of the crystalline carbon-based active material layer, it is possible to prevent overcharge as a result. In addition, the negative electrode of the present invention has a multi-layered structure of a layer made of an amorphous carbon-based active material and a layer made of a crystalline carbon-based active material, and complements the disadvantages of the amorphous carbon-based active material and the crystalline carbon-based active material, and thus has a high discharge capacity and output characteristics. This is excellent.

The amorphous carbon-based active material is not particularly limited as long as the carbon atoms have an amorphous crystal structure and exhibit excellent rate characteristics. Sucrose, phenol resin, naphthalene resin, polyvinyl alcohol resin, furfuryl alcohol Hard carbon raw materials of resin, polyacrylonitrile resin, polyamide resin, furan resin, cellulose resin, styrene resin, polyimide resin, epoxy resin or vinyl chloride resin; And one or two or more amorphous carbon precursors selected from the group consisting of coal-based pitches, petroleum-based pitches, polyvinyl chloride, mesophase pitch, tar, or soft carbon raw materials of low molecular weight heavy oil.

In addition, the crystalline carbon-based active material of the present invention is a graphite-based carbon material, natural graphite or artificial graphite can be used.

The current collector of the present invention is stainless steel, aluminum, nickel, titanium, calcined carbon, copper; Stainless steel surface-treated with carbon, nickel, titanium, or silver; Aluminum-cadmium alloys; Non-conductive polymer surface-treated with a conductive material; Alternatively, a conductive polymer may be used, and as the conductive material, polyacetylene, polyaniline, polypyrrole, polythiophene and polysulfuritride, indium thin oxide (ITO), silver, palladium and nickel may be used.

The negative electrode of the present invention comprises the steps of coating and drying a slurry containing an amorphous carbon-based active material on at least one surface of the current collector to form a first negative electrode active material layer; And coating and drying a slurry including the crystalline carbon-based active material on one surface of the first negative electrode active material layer to form a second negative electrode active material layer.

These slurries are prepared by mixing an active material, a polymer binder and the like in a predetermined solvent.

The polymer binder may be polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoro Ethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, fluorine rubber and various copolymers thereof may be used.

In addition, preferred examples of the solvent include dimethyl sulfoxide (DMSO), alcohol, N-methylpyrrolidone (NMP), acetone or water, and the like, and are removed in a drying process.

The method of coating such a slurry can be selected from known methods or carried out by a new suitable method in consideration of the properties of materials and the like. For example, it is preferable to distribute the slurry on the current collector and then to uniformly disperse the same using a doctor blade or the like. In some cases, a method of distributing and dispersing in one process may be used. In addition, a method of die casting, comma coating, screen printing, or the like may be selected.

After coating the slurry, it is dried. In particular, the negative electrode of the present invention is characterized in that the second negative electrode active material layer is formed after drying after forming the first negative electrode active material layer.

When the negative electrode is manufactured, a lithium secondary battery having a separator and an electrolyte interposed between the positive electrode and the negative electrode, which is commonly used in the art, may be manufactured using the negative electrode.

In the electrolytic solution used in the present invention, the lithium salt that may be included as an electrolyte may be used, without limitation, those which are commonly used in a lithium secondary battery electrolyte, such as the lithium salt, the anion is 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 -, 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 ^- .

In the electrolyte solution used in the present invention, as the organic solvent included in the electrolyte solution, those conventionally used in the electrolyte for lithium secondary batteries may be used without limitation, and typically, propylene carbonate (PC), ethylene carbonate (ethylene carbonate, EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), methylpropyl carbonate, dipropyl carbonate, dimethylsulfuroxide, acetonitrile, dimethoxyethane, diethoxy Ethylene, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite, tetrahydrofuran, any one selected from the group consisting of, or a mixture of two or more thereof may be representatively used. In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates among the carbonate-based organic solvents, are highly viscous organic solvents, and thus may be preferably used because they dissociate lithium salts in electrolytes well. Dimethyl carbonate and diethyl When a low viscosity, low dielectric constant linear carbonate, such as carbonate, is mixed and used in an appropriate ratio, an electrolyte having high electrical conductivity can be prepared, and thus it can be more preferably used.

Optionally, the electrolyte solution stored according to the present invention may further include additives such as an overcharge inhibitor included in a conventional electrolyte solution.

In addition, as the separator, conventional porous polymer films conventionally used as separators, for example, polyolefins such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer, etc. The porous polymer film made of the polymer may be used alone or by laminating them, or a conventional porous nonwoven fabric, for example, a non-woven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, or the like may be used. It is not.

The positive electrode to be applied together with the negative electrode of the present invention is not particularly limited, and according to conventional methods known in the art, the positive electrode active material may be prepared in a form bound to the electrode current collector. Non-limiting examples of the positive electrode active material may be used a conventional positive electrode active material that can be used for the positive electrode of the conventional electrochemical device, in particular lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide or a combination thereof Preference is given to using oxides. Non-limiting examples of the positive electrode current collector include a foil made of aluminum, nickel, or a combination thereof.

The battery case used in the present invention may be adopted that is commonly used in the art, there is no limitation on the appearance according to the use of the battery, for example, cylindrical, square, pouch type or coin using a can (coin) type and the like.

Hereinafter, the present invention will be described in detail with reference to Examples. However, the embodiments according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

Example

Manufacturing example  1. Preparation of negative electrode having a natural graphite coating layer

Natural graphite and PVdF polymer binder were mixed in an organic solvent in a weight ratio of 95: 5 to prepare a crystalline carbon-based slurry.

A current collector made of copper foil was prepared. The prepared crystalline carbon-based slurry was coated on one surface of the copper foil so as to have a thickness of an active material layer of 50 μm and then dried.

Manufacturing example  2. Hard carbon  Cathode Preparation with Coating Layer

Hard carbon and SBR polymer binder was mixed in water at a weight ratio of 95: 5 to prepare an amorphous carbon-based slurry.

A current collector made of copper foil was prepared. The prepared amorphous carbon-based slurry was coated on one surface of the copper foil so as to have a thickness of an active material layer of 50 μm, and then dried.

Test Example  1. Overcharge test

An overcharge test at 0.2, 1, 3 and 5 C rates of the negative electrode of Preparation Example 1-2 was shown in FIGS. 2-5. As the filling rate increased, it was found that Preparation Example 1 using natural graphite, which is crystalline carbon, converged more quickly to the maximum charging value than Preparation Example 2 using Hard Carbon, which was amorphous carbon. .

100: cathode 110: current collector
120: first negative electrode active material layer 130: second negative electrode active material layer

Claims (9)

Current collector;
A first negative electrode active material layer formed on at least one surface of the current collector and including a crystalline carbon-based active material; And
The negative electrode for secondary batteries which is formed in the outer surface of the said 1st negative electrode active material layer, and comprises the 2nd negative electrode active material layer containing an amorphous carbon type active material. The method of claim 1,
The thickness of the first negative electrode active material layer is a secondary battery negative electrode, characterized in that 10 to 100 ㎛. The method of claim 1,
The thickness of the second negative electrode active material layer is a secondary battery negative electrode, characterized in that 10 to 100 ㎛. The method of claim 1,
The crystalline carbon-based active material is a negative electrode for a secondary battery, characterized in that the compound or a mixture of one kind selected from natural graphite or artificial graphite. The method of claim 1,
The amorphous carbon-based active material may be sucrose, phenol resin, naphthalene resin, polyvinyl alcohol resin, furfuryl alcohol resin, polyacrylonitrile resin, polyamide resin, furan resin, cellulose resin, styrene resin, Hard carbon raw materials of polyimide resin, epoxy resin or vinyl chloride resin; And one or two or more amorphous carbon precursors selected from the group consisting of coal-based pitch, petroleum-based pitch, polyvinyl chloride, mesophase pitch, tar, or low-carbon heavy oil soft carbon raw material. The method of claim 1,
The current collector is stainless steel, aluminum, nickel, titanium, calcined carbon, copper; Stainless steel surface-treated with carbon, nickel, titanium, or silver; Aluminum-cadmium alloys; Non-conductive polymer surface-treated with a conductive material; Or a negative electrode for a secondary battery, which is made of a conductive polymer. The method according to claim 6,
The conductive material is a negative electrode for a secondary battery, characterized in that one or a mixture of polyacetylene, polyaniline, polypyrrole, polythiophene and polysulfuride, ITO (Indum Thin Oxide), silver, palladium and nickel. Coating and drying a slurry including a crystalline carbon-based active material on at least one surface of the current collector to form a first negative electrode active material layer; And
Coating a slurry comprising an amorphous carbon-based active material on one surface of the first negative electrode active material layer and drying to form a second negative electrode active material layer. anode; The negative electrode of any one selected from claim 1 to claim 7; A secondary battery having a separator and an electrolyte interposed between the positive electrode and the negative electrode.

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