KR20130140395A - Anode for lithium secondary battery, method for preparing the same, and lithium secondary battery using the same - Google Patents

Abstract

The present invention relates to a negative electrode for a lithium secondary battery having excellent electrical conductivity, a high output secondary battery including the same, and a manufacturing method thereof, and more particularly, to a secondary battery including a lithium oxide layer in a negative electrode and a method of manufacturing the same. The lithium secondary battery according to the present invention has a high capacity, excellent cycle characteristics, low internal resistance, excellent rate characteristics, and excellent battery safety while exhibiting high output characteristics.

Description

Anode for lithium secondary battery and manufacturing method thereof and lithium secondary battery using same {Anode for lithium secondary battery, method for preparing the same, and lithium secondary battery using the same}

The present invention relates to a negative electrode for a lithium secondary battery having excellent electrical conductivity, a high output secondary battery including the same, and a manufacturing method thereof.

As technology development and demand for mobile devices are increasing, the demand for secondary batteries as energy sources is rapidly increasing. Among such secondary batteries, lithium secondary batteries having high energy density and voltage have been commercialized and widely used. When a secondary battery is used as a power source for a mobile phone or a laptop, a secondary battery that provides a stable output is required, while when used as a power source of a power tool such as an electric drill, a high output can be instantaneously provided. And, there is a need for a secondary battery that can be stable against external physical shocks such as vibration and dropping.

In addition, as the interest in environmental issues grows, researches on electric vehicles and hybrid electric vehicles that can replace fossil fuel-based vehicles such as gasoline vehicles and diesel vehicles, which are one of the main causes of air pollution, . Although nickel-metal hydride secondary batteries are mainly used as power sources for such electric vehicles and hybrid electric vehicles, researches using lithium secondary batteries having high energy density and discharge voltage are being actively carried out, and they are in the commercialization stage.

The lithium secondary battery has a structure in which a non-aqueous electrolyte containing a lithium salt is impregnated in an electrode assembly having a porous separator interposed between a positive electrode and a negative electrode coated with an active material on a current collector. The positive electrode active material is mainly composed of lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium composite oxide and the like, and the negative electrode active material is mainly composed of a carbon-based material.

However, in a lithium secondary battery using a carbon-based material as a negative electrode active material, irreversible capacity occurs in some lithium ions inserted into the layered structure of the carbon-based material during initial charge and discharge, resulting in a decrease in discharge capacity. In addition, the carbon material has a oxidation / reduction potential as low as 0.1 V with respect to the Li / Li ⁺ potential, so that the decomposition of the non-aqueous electrolyte occurs on the surface of the cathode, and reacts with lithium to cover the surface of the carbon material (passivating layer or solid). electrolyte interface (SEI membrane) is formed. Such SEI membranes have different thickness and interface states depending on the electrolyte system used, and thus affect the charge and discharge characteristics. In addition, in a secondary battery used in a field requiring high output characteristics such as a power tool, even a thin SEI film may increase resistance and become a rate determining step (RDS). In addition, since the lithium compound is generated on the surface of the negative electrode, the reversible capacity of lithium gradually decreases as the charge and discharge are repeated, thereby causing a problem that the discharge capacity decreases and cycle degradation occurs.

Japanese Patent Application Publication No. 1998-069922 Japanese Patent Application Publication No. 2001-216962 United States Patent Application Publication No. 2011-0135564

The present invention has been made to overcome the problems of the prior art as described above, the object of the present invention is to provide a negative electrode for a lithium secondary battery that can be manufactured by easily changing the desired performance and safety while exhibiting high output characteristics and excellent battery safety. It is done.

Still another object of the present invention is to provide a method of manufacturing a negative electrode for a lithium secondary battery.

The negative electrode for a lithium secondary battery of the present invention comprises a first active material layer on the current collector; And a second active material layer having a charging potential of 0.1V or more relative to the lithium charging potential.

In one embodiment of the present invention, the current collector may be selected from aluminum foil or copper foil.

In an embodiment of the present invention, the second active material layer may include lithium titanium oxide, and the lithium titanium oxide may be Li ₄ Ti ₅ O ₁₂ .

In addition, in one embodiment of the present invention, the second active material layer may have a thickness of 2 to 100 μm and a density of 0.2 to 2.0 g / cm ³ .

In one embodiment of the present invention, the first active material layer may include a carbon material, a binder, and a conductive material.

The carbon material may be artificial graphite in the form of potato or MCMB (MesoCarbon MicroBead), hard carbon, coke, and needle coke or pitch obtained by pyrolysing natural graphite, phenolic resin, or furan resin treated with surface treatment. One or two or more mixtures selected from the group consisting of soft carbon carbonized) may be used, and the conductive material may be graphite, carbon black, conductive fiber, metal powder, conductive whiskey, conductive metal oxide, poly One or a mixture of two or more selected from phenylene derivatives can be used. The binder is polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), cellulose, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, Selected from polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene copolymer (EPDM), sulfonated ethylene-propylene-diene copolymer (EPDM), styrene butylene rubber, fluorine rubber One kind or a mixture of two or more kinds may be used, and the carbon material, the binder, and the conductive material may be included in the first active material layer in a weight ratio of 4 to 6000: 0.1 to 1500: 1.

The lithium secondary battery according to the present invention includes the negative electrode for the lithium secondary battery.

In addition, the method of manufacturing a negative electrode for a lithium secondary battery of the present invention comprises the steps of: coating a negative electrode mixture slurry containing a carbon material, a binder, a conductive material and a solvent on one surface of the current collector to form a first active material layer; And

And forming a second active material layer having a charging potential of 0.1V or more relative to the lithium charging potential on the carbon material layer.

In an embodiment of the present invention, the first active material layer may include a carbon material, a binder, and a conductive material in a weight ratio of 4 to 6000: 0.1 to 1500: 1, and the dry coating thickness of the first active material layer is 50 to 500 μm and specific surface area may be 0.5 to 10 m ² / g.

In an embodiment of the present invention, the second active material layer may include lithium titanium oxide, and the lithium titanium oxide may be Li ₄ Ti ₅ O ₁₂ .

In addition, in one embodiment of the present invention, the second active material layer may have a thickness of 2 to 100 μm and a density of 0.2 to 2.0 g / cm ³ .

The second active material layer according to an embodiment of the present invention may be formed by any one method selected from coating, metal sputtering, chemical vapor deposition, ion plating, electron beam vapor deposition and laser deposition, the second active material layer For the formation of the solvent, an insoluble solvent may be used for the first active material layer, and in detail, selected from pure water, n-methylpyrrolidinone (NMP), cyclohexane, methyl ethyl ketone (MEK) and tetrahydrofuran (THF) One kind or a mixture of two or more kinds thereof can be used.

The present invention is a current collector in the negative electrode for a lithium secondary battery; A first active material layer; And a second active material layer having a charging potential of 0.1 V or more relative to the lithium charging potential; having a structure in which layers are sequentially stacked, and having high capacity, excellent cycle characteristics, and low internal resistance, the battery exhibits high output characteristics while exhibiting high output characteristics. The safety of the can bring about an excellent effect.

In particular, by stacking the second active material layer having a charging potential of 0.1V or more relative to the lithium charging potential on the second active material layer, the absolute amount of SEI film formation and the internal resistance thereof are reduced, and the wettability of the electrolyte is excellent, thereby improving battery performance and lifespan. Properties can be improved.

In addition, the manufacturing method comprises the steps of forming a first active material layer; And forming a second active material layer having a charging potential of 0.1 V or more relative to the lithium charging potential on the first active material layer, and easily adjusting the thickness of the second active material layer as necessary, This can bring about the effect that can be produced by varying the desired performance and safety.

1 schematically shows a negative electrode for a lithium secondary battery according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail. The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

In addition, it will be described with reference to the accompanying Figure 1 in order to help the understanding of the present invention, Figure 1 below does not limit the scope of the present invention.

The present invention is the current collector 10, as shown in Figure 1 below; A first active material layer 20; And a second active material layer 30 having a charging potential of 0.1 V or more relative to the lithium charging potential; provides a negative electrode for a lithium secondary battery sequentially stacked.

In one embodiment of the present invention, the first active material layer 20 may be formed on at least one surface of the current collector (10).

In one embodiment of the present invention, the material of the current collector 10 may be any metal having electrical conductivity, and more specifically, an aluminum foil or a copper foil may be used. The first active material layer 20 may include a carbon material, a binder, and a conductive material. The carbon material is not particularly limited as long as lithium ions can be occluded and desorbed, and artificial graphite in a potato or MCMB (MesoCarbon MicroBead) shape, non-graphitized pyrolytically pyrolyzed natural graphite, phenolic resin, or furan resin One or a mixture of two or more selected from the group consisting of carbon, hard carbon, coke and needle coke or soft carbon carbonized pitch may be used, and the conductive material may be graphite, carbon black, One kind or a mixture of two or more kinds selected from conductive fibers, metal powders, conductive whiskeys, conductive metal oxides, and polyphenylene derivatives can be used. The binder is preferably a polymer binder, and in one embodiment of the present invention, the type of polymer resin that can be used for the binder is polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), cellulose, Polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene copolymer (EPDM), sulfonated ethylene-propylene-diene copolymer (EPDM), styrene butyrene rubber, fluororubber, and one or two or more kinds selected from them may be used, but are not particularly limited, and the carbon material, the binder and The conductive material may be included in the first active material layer 20 in a weight ratio of 4 to 6000: 0.1 to 1500: 1.

In general, a carbon material used as a negative electrode active material for a lithium secondary battery has a high discharge capacity, but has a disadvantage of high current characteristics and low cycle characteristics.

On the other hand, by stacking the second active material layer 30 having a charging potential of 0.1 V or more relative to the lithium charging potential on the first active material layer 20, the cycle characteristics are excellent, and the redox potential has a conventional charging potential compared to the lithium charging potential. As compared with the carbon-based active material, the absolute amount of the SEI film formation and the internal resistance thereof are reduced, thereby improving the rate characteristic and the high current characteristic, and the wettability of the electrolyte may be improved, thereby improving battery performance and lifespan characteristics.

In addition, the carbon material used as a negative electrode active material for a lithium secondary battery may cause a volume change during charge and discharge. The structure in which the second active material layer 30 is coated in the form of core-shell on the particles without being sequentially stacked may cause cracks on the outside due to the volume change of the carbon material during charging and discharging of the battery. You may not lose. In the negative electrode for a lithium secondary battery according to the present invention, the positive electrode and the first active material layer 20 are formed by densely coating the carbon material by laminating the second active material layer 30 on the first active material 20 containing the carbon material. Direct contact can be prevented, and this can bring about an effect of improving safety during internal short circuits.

The second active material layer 30 according to an embodiment of the present invention may have a thickness of 2 to 100 μm and a density of 0.2 to 2.0 g / cm ³ . The thinner the thickness of the second active material layer 30, the lower the stability, but can increase the energy density, the thicker the thickness increases the stability, so if necessary, by changing the thickness of the second active material layer 30 desired performance and The safety can be easily changed to produce an effect that can be produced.

In an embodiment of the present invention, the second active material layer 30 may be formed by any one method selected from coating, metal sputtering, chemical vapor deposition, ion plating, electron beam vapor deposition, and laser deposition.

In one embodiment of the present invention, the second active material layer 30 may be a layer including a second active material having a charging potential of 0.1V or more relative to the lithium charging potential, and more specifically, a charging potential of 0.1V relative to the lithium charging potential. It may be to include a second active material up to 1.5V.

According to an embodiment of the present invention, the second active material having a charge potential higher than 0.1 to 1.5V relative to the lithium charge potential may be lithium titanium oxide (LTO).

Since the LTO can participate in the reaction as a redox site by itself, the ion conductivity is high and the output characteristics are excellent while minimizing the capacity reduction of the battery. That is, the lithium secondary battery negative electrode according to an embodiment of the present invention can improve the disadvantages of the carbon material as the negative electrode active material and maximize the advantages of low internal resistance and cycle characteristics of LTO, high efficiency, energy density and output characteristics It can bring the effect of manufacturing an excellent secondary battery.

The second active material layer 30 according to an embodiment of the present invention may include a lithium titanium oxide (LTO), a binder and a conductive material as the second active material, and the lithium titanium oxide, the binder and the conductive material are 10 to 30: It may be included in the second active material layer 30 in a weight ratio of 0.5 to 2: 1.

The conductive material may be one or a mixture of two or more selected from graphite, carbon black, conductive fibers, metal powders, conductive whiskeys, conductive metal oxides, and polyphenylene derivatives. The binder is preferably a polymer binder, and in one embodiment of the present invention, the type of polymer resin that can be used for the binder is polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), cellulose, Polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene copolymer One kind or a mixture of two or more kinds selected from (EPDM), sulfonated ethylene-propylene-diene copolymer (EPDM), styrene butyrene rubber, and fluororubber can be used, but is not particularly limited.

A method for producing lithium titanium oxide (LTO) according to an embodiment of the present invention is known in the art, for example, dissolving lithium salts such as lithium hydroxide, lithium oxide, lithium carbonate, etc. in water as a lithium source. Titanium oxide or the like is added as a titanium source according to the atomic ratio of lithium and titanium, and then stirred and dried to prepare a precursor, followed by calcining it.

Lithium titanium oxide (LTO) according to an embodiment of the present invention may be in detail Li ₄ Ti ₅ O ₁₂ .

As described above, the negative electrode for a lithium secondary battery according to an embodiment of the present invention includes a first active material layer 20 in the current collector 10; And a second active material layer 30 having a charging potential of 0.1 V or more relative to the lithium charging potential; excellent cycle characteristics due to the stacked structure, and the redox potential of the charging potential is lower than that of a conventional carbon-based active material. The relatively high amount of SEI film formation and its internal resistance is reduced, thereby improving rate characteristics and high current characteristics, and excellent wettability of the electrolyte, resulting in improved battery performance and lifespan characteristics. The coating may prevent the direct contact between the positive electrode and the first active material layer 20, thereby bringing an effect of improving safety during internal short circuit.

In addition, the second active material layer 30 according to an embodiment of the present invention may use lithium titanium oxide (LTO) as a second active material having a higher charging potential than 0.1 V to 1.5 V as compared to a lithium charging potential, thereby providing a capacity of a battery. It can have the effect of high ion conductivity and excellent output characteristics while minimizing degradation.

The electrochemical cell of the present invention is composed of the negative electrode for a lithium secondary battery.

The electrochemical cell is a device for providing electricity through an electrochemical reaction, preferably a high output lithium secondary battery containing a lithium salt-containing nonaqueous electrolyte. The lithium secondary battery may have a structure in which a lithium salt-containing non-aqueous electrolyte solution is impregnated into an electrode assembly having a separator interposed between the negative electrode and the positive electrode material.

Other components of the lithium secondary battery according to the present invention will be described in detail below.

The positive electrode material may be manufactured by, for example, applying a positive electrode mixture containing a positive electrode active material onto a positive electrode current collector and then drying it.

The positive electrode current collector in the present invention is not particularly limited as long as it has high conductivity without causing chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel Surface-treated with carbon, nickel, titanium, silver, and the like may be used. The current collector may have fine irregularities on the surface thereof to increase the adhesive force of the cathode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric are possible.

In the present invention, the positive electrode active material may be a conventional positive electrode active material that can be used for the positive electrode of a conventional electrochemical device, and in particular, lithium manganese oxide (lithiated magnesium oxide), lithium cobalt oxide (lithiated cobalt oxide), lithium nickel oxide (lithiated nickel) Lithium intercalation materials and the like are preferred, such as a composite oxide formed by an oxide or a combination thereof. The positive electrode active material described above is made of a positive electrode current collector, i.e., a foil and a negative electrode current collector, i.e., copper, gold, nickel or a copper alloy, or a combination thereof. The positive electrode is constituted in a form bound to the foil produced by the combination of.

The separation membrane is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally 0.01 ~ 10 ㎛, the thickness may be generally 5 ~ 300 ㎛.

Such separation membranes include, for example, olefinic polymers such as polypropylene, which are chemically resistant and hydrophobic; Sheets or nonwovens made of fiberglass or polyethylene may be used.

The electrolyte solution used in one embodiment of the present invention is a salt having a structure such as A + B-, A + includes an ion composed of an alkali metal cation such as Li ⁺ , Na ⁺ , K ⁺ or a combination thereof, and B ^- it is _{^{PF 6 -, BF 4 -,}} Cl -, Br -, I -, ClO 4 -, ASF 6 -, CH 3 CO 2 -, CF 3 SO 3 -, N (CF 3 SO 2) 2 -, C Salts containing ions consisting of anions such as (CF ₂ SO ₂ ) ₃ ^- or combinations thereof include propylene carbonate (PC), ethylene carbonate (EC) and diethyl carbonate (DEC). , Dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, diethoxyethane, tetrahydro Furan (tetrahydrofuran), N-methyl-2-pyrrolidone (N-methyl-2-pyrrolidone, NMP), ethylmethyl carbo Sites (ethyl methyl carbonate, EMC), may be useful in an organic solvent consisting of lactones (γ-butyrolactone) or their mixtures of gamma -butyrolactone dissolved and dissociated.

In addition, the method of manufacturing a negative electrode for a lithium secondary battery of the present invention comprises the steps of forming a first active material layer 20 on one surface of the current collector 10; And

And forming a second active material layer 30 having a charging potential of 0.1 V or more relative to the lithium charging potential on the first active material layer 20.

In one embodiment of the present invention, the material of the current collector 10 may be any metal having electrical conductivity, and more specifically, an aluminum foil or a copper foil may be used.

In one embodiment of the present invention, the first active material layer 20 may be formed by applying a first active material slurry including a carbon material, a binder and a conductive material.

The first active material slurry may include a carbon material, a binder and a conductive material in a weight ratio of 4 to 6000: 0.1 to 1500: 1, more specifically, 40 to 60% by weight carbon material, 1 to 15% by weight binder, It may be prepared including 0.01 to 10% by weight of the conductive agent and 30 to 70% by weight of the solvent.

The carbon material may be artificial graphite in the form of potato or MCMB (MesoCarbon MicroBead), hard carbon, coke, and needle coke or pitch obtained by pyrolysing natural graphite, phenolic resin, or furan resin treated with surface treatment. One or two or more mixtures selected from the group consisting of soft carbon carbonized) may be used, and the conductive material may be graphite, carbon black, conductive fiber, metal powder, conductive whiskey, conductive metal oxide, poly One or a mixture of two or more selected from phenylene derivatives can be used. The binder is polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), cellulose, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, Polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene copolymer (EPDM), sulfonated ethylene-propylene-diene copolymer (EPDM), styrene butylene rubber (SBR), fluororubber One or a mixture of two or more selected may be used, and the solvent may be used without limitation as long as it can dissolve the binder of the first active material layer 20, but in one embodiment of the present invention, pure water, One or a mixture of two or more selected from n-methylpyrrolidinone (NMP), cyclohexane, methyl ethyl ketone (MEK) and tetrahydrofuran (THF) can be used as a solvent.

In one embodiment of the present invention, the first active material layer 20 may be formed by applying the first active material slurry on one surface of the current collector 10, and the first active material slurry is formed on one surface of the current collector 10. After drying in a dry oven may be formed as a first active material layer (20). The temperature and time of the drying may be adjusted to those skilled in the art as needed to form the first active material layer 20.

The first active material layer 20 has a specific surface area of 0.5 to 10 m ² / g and a thickness of 10 to 100 μm may have an effect of having high conductivity without causing chemical change in the battery.

In general, a carbon material used as a negative electrode active material for a lithium secondary battery has a high discharge capacity, but has a disadvantage of high current characteristics and low cycle characteristics.

On the other hand, by stacking the second active material layer 30 having a charging potential of 0.1 V or more relative to the lithium charging potential on the first active material layer 20, the cycle characteristics are excellent, and the redox potential has a conventional charging potential compared to the lithium charging potential. As compared with the carbon-based active material, the absolute amount of the SEI film formation and the internal resistance thereof are reduced, thereby improving the rate characteristic and the high current characteristic, and the wettability of the electrolyte may be improved, thereby improving battery performance and lifespan characteristics.

In addition, the carbon material used as a negative electrode active material for a lithium secondary battery may cause a volume change during charge and discharge. The structure in which the second active material layer 30 is coated in the form of core-shell on the particles without being sequentially stacked may cause cracks on the outside due to the volume change of the carbon material during charging and discharging of the battery. You may not lose. In the negative electrode for a lithium secondary battery according to the present invention, the positive electrode and the first active material layer 20 are formed by densely coating the carbon material by laminating the second active material layer 30 on the first active material 20 containing the carbon material. Direct contact can be prevented, and this can bring about an effect of improving safety during internal short circuits.

The second active material layer 30 according to an embodiment of the present invention may have a thickness of 2 to 100 μm and a density of 0.2 to 2.0 g / cm ³ . The thinner the thickness of the second active material layer 30, the lower the stability, but can increase the energy density, the thicker the thickness increases the stability, so if necessary, by changing the thickness of the second active material layer 30 desired performance and The safety can be easily changed to produce an effect that can be produced.

In an embodiment of the present invention, the second active material layer 30 may be formed by any one method selected from coating, metal sputtering, chemical vapor deposition, ion plating, electron beam vapor deposition, and laser deposition.

In one embodiment of the present invention, the second active material layer 30 may be a layer including a second active material having a charging potential of 0.1V or more relative to the lithium charging potential, and more specifically, a charging potential of 0.1V relative to the lithium charging potential. It may be to include a second active material up to 1.5V.

According to an embodiment of the present invention, the second active material having a charge potential higher than 0.1 to 1.5V relative to the lithium charge potential may be lithium titanium oxide (LTO).

Since the LTO can participate in the reaction as a redox site by itself, the ion conductivity is high and the output characteristics are excellent while minimizing the capacity reduction of the battery. That is, the lithium secondary battery negative electrode according to an embodiment of the present invention can improve the disadvantages of the carbon material as the negative electrode active material and maximize the advantages of low internal resistance and cycle characteristics of LTO, high efficiency, energy density and output characteristics It can bring the effect of manufacturing an excellent secondary battery.

The second active material layer 30 according to an embodiment of the present invention may include a lithium titanium oxide (LTO), a binder and a conductive material as the second active material, and the lithium titanium oxide, the binder and the conductive material are 10 to 30: It may be included in the second active material layer 30 in a weight ratio of 0.5 to 2: 1.

The conductive material may be one or a mixture of two or more selected from graphite, carbon black, conductive fibers, metal powders, conductive whiskeys, conductive metal oxides, and polyphenylene derivatives. The binder is preferably a polymer binder, and in one embodiment of the present invention, the type of polymer resin that can be used for the binder is polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), cellulose, Polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene copolymer One kind or a mixture of two or more kinds selected from (EPDM), sulfonated ethylene-propylene-diene copolymer (EPDM), styrene butyrene rubber, and fluororubber can be used, but is not particularly limited.

A method for producing lithium titanium oxide (LTO) according to an embodiment of the present invention is known in the art, for example, dissolving lithium salts such as lithium hydroxide, lithium oxide, lithium carbonate, etc. in water as a lithium source. Titanium oxide or the like is added as a titanium source according to the atomic ratio of lithium and titanium, and then stirred and dried to prepare a precursor, followed by calcining it.

Lithium titanium oxide (LTO) according to an embodiment of the present invention may be in detail Li ₄ Ti ₅ O ₁₂ .

In the embodiment of the present invention, in the preparation of the first active material slurry and the second active material slurry, the same polymer resin and solvent used as the binder may not be used, and the solvent contained in the second active material slurry is the first active material layer. The insoluble solvent may be selected and used for the carbon material and the binder of (20).

In the formation of the second active material layer 30, when a solvent having the same solubility as the solvent used to form the first active material layer 20 is used, the binder in the first active material layer 20 is dissolved to form a first active material layer. The coated surface of 20 may be irregular or mixed when the second active material layer is applied, and thus the structure in which the first active material layer 20 and the second active material layer 30 are sequentially stacked may be modified. On the other hand, in the present invention, by using a solvent having different solubility in forming the first active material layer and the second active material layer 30, the laminated surface of the first active material layer 20 and the second active material layer 30 is not deformed. Can be imported.

In one embodiment of the present invention, the solvent used in the formation of the second active material layer 30 is a pure solvent, n-methylpyrrolidinone (NMP), cyclohexane, methyl ethyl ketone (MEK) and tetrahydrofuran It may be one or a mixture of two or more selected from (THF).

In an embodiment of the present invention with a specific example, the first active material layer 20 uses a mixture of styrene butyrene rubber (SBR) and carboxymethylcellulose (CMC) as a binder, and as a solvent Pure water was used to prepare and apply a first active material slurry to form a first active material layer 20, and the second active material layer 30 was polyvinylidene fluoride (PVDF) as a binder, and n-methylpi A second active material slurry may be prepared and coated using lollidinone (NMP) as a solvent to form the second active material layer 30, and conversely, polyvinyl is added to the first active material slurry to form the first active material layer 20. The second active material slurry, which uses lithium fluoride (PVDF) as a binder, n-methylpyrrolidinone (NMP) as a solvent, and forms the second active material layer 30, includes styrene butyrene rubber (SBR) and Using a mixture of carboxymethylcellulose (CMC) as a binder As the solvent, pure water can be used.

After forming the second active material slurry may be dried in a dry oven may be formed as a second active material layer (30). The temperature and time of the drying may be adjusted to those skilled in the art as needed to form the second active material layer 30.

As described above, a method of manufacturing a negative electrode for a lithium secondary battery according to an embodiment of the present invention includes forming a first active material layer 20 on one surface of a current collector 10; And

Forming a second active material layer 30 having a charging potential of 0.1 V or more relative to the lithium charging potential on the first active material layer 20; and including the first active material layer 20 and the second active material layer ( 30) Each of the thickness and density can be produced in various ways, and thus, it is possible to easily change the performance and safety, such as the density of the battery, can be produced.

BEST MODE FOR CARRYING OUT THE INVENTION 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 enable those skilled in the art to more fully understand the present invention.

Example 1

Preparation of First Active Material Slurry

45% by weight of graphite (Mitsubishi Chemical, MPG) as a carbon material, 1% by weight of styrene butyrene rubber (SBR, ZEON BM400B), 1% by weight of carboxymethyl cellulose (CMC, Daicel-2D) The first active material slurry was prepared by mixing 3% by weight of carbon black and 50% by weight of pure water with a solvent.

Cathode manufacturing

The first active material layer was prepared by applying the first active material slurry on top of a copper foil (thickness 10 μm) as a current collector to have a dry coating thickness of 100 μm.

Li ₄ Ti ₅ O ₁₂ as lithium titanium oxide, N-methylpyrrolidone (NMP) as a solvent, PVDF (polyvinylidene fluoride) as a binder, and carbon as a conductive material The second active material slurry in which the black was mixed in a weight ratio of 45: 50: 2.5: 2.5 was coated by a slot-die coating method so that the second active material layer became 2 μm. The drying temperature during the coating was gradually raised from 100 ℃ to 150 ℃ dried, and dried for about 12 hours at 150 degrees, 10 ^-2 torr level in a vacuum drying process to prepare a lithium secondary battery negative electrode.

Lithium Secondary Battery Manufacturing

The manufactured negative electrode and the positive electrode material were LiNiMnCoO ₂ , Celgard 2400 was used as a separator, and a lithium secondary battery was manufactured by applying an aluminum exterior material. The battery standard size was 4.5 mm thick x 64 mm wide x 95 mm in length, and the design capacity was 2000 mAh.

[Example 2]

The preparation of the negative electrode was carried out in the same manner as in Example 1, except that the second active material layer was manufactured to be 10 μm.

[Example 3]

The preparation of the negative electrode was carried out in the same manner as in Example 1, except that the second active material layer was manufactured to be 50 μm.

Example 4

The preparation of the negative electrode was carried out in the same manner as in Example 1, except that the second active material layer was manufactured to be 100 μm.

[Example 5]

The preparation of the negative electrode was carried out in the same manner as in Example 1, except that the second active material layer was manufactured to be 1 μm.

[Example 6]

The preparation of the negative electrode was carried out in the same manner as in Example 1, except that the second active material layer was manufactured to be 150 μm.

Comparative Example 1

Except for not using lithium titanium oxide in the preparation of the negative electrode was carried out in the same manner as in Example 1.

Comparative Example 2

Preparation of Anode Active Material Slurry

45 wt% graphite (Mitsubishi Chemical, MPG) as carbon material, 3 wt% polyvinylidene fluoride (PVDF, mw.100,000) as binder, 2 wt% carbon black as conductive material, Li ₄ Ti ₅ O as lithium titanium oxide ₁₂ was mixed with 5% by weight of N-methylpyrrolidone and 45% by weight of a solvent to prepare a negative electrode active material slurry.

Cathode manufacturing

The negative electrode mixture slurry was coated on top of a copper foil (thickness 10 μm) as a current collector to prepare a dry coating thickness of 100 μm, and the same process as in Example 1 was performed thereafter.

 [Test Example 1]

Electrochemical properties

The batteries manufactured according to Examples 1 to 6 and Comparative Examples 1 and 2 were charged at 25 ° C., 4.2 V charging voltage, and 400 mAh current density using a charge / discharge cycle apparatus (manufacturer: TOYO, model: TOYO-5200). After the initial charge with CC-CV (Constant Current-Constant Voltage), the battery is discharged to 2.7V with a discharge capacity of 1000 mAh with a 10 minute rest period, and thus the charge potential, initial charge / discharge efficiency, and specific capacity which are electrochemical characteristics And initial resistance (IR) was evaluated, the results are shown in Table 1 below.

As shown in Table 1, the lithium secondary battery according to the present invention was found to be excellent in high charge potential, specific capacity and initial charge / discharge efficiency.

[Test Example 2]

Cycle characteristics

The charging capacity in the CC section was compared with the total charging capacity according to the current density, and cycle characteristics and post-cycle resistance values were evaluated at 1C / 1C at room temperature.

The test results are shown in Table 2 below.

As can be seen from the results of Table 2, the lithium secondary battery using the lithium secondary battery according to the present invention did not significantly increase the resistance value even after 100 charge / discharge cycles, and thus a low cycle rate compared to the capacity of the initial battery was excellent. Showed characteristics.

[Test Example 3]

Safety evaluation

Overcharge characteristics, high temperature standing characteristics and nail penetration tests of the prepared negative electrode active material were evaluated. In the overcharge test, 18V, 24V, and 30V were performed at a current of 2000 mA, and the shape change of the battery according to the overcharge was measured by A to D as follows according to the shape, and the surface temperature of the battery was measured. .

A-no change

B-smoke

C-fire

D-explosion

In addition, after the nail penetration test evaluation, the surface temperature of the battery was investigated and shown in Table 3.

As shown in Table 3, the lithium secondary battery negative electrode and the lithium secondary battery manufactured using the same according to the present invention was found to have excellent safety as a result of the overcharge test and the nail penetration test.

100: lithium secondary battery negative electrode
10: The whole house
20: first active material layer
30: second active material layer

Claims (24)

A first active material layer on the current collector; And a second active material layer having a charging potential of 0.1 V or more relative to the lithium charging potential.
The method of claim 1,
The first active material layer is a lithium secondary battery negative electrode comprising a carbon material, a binder and a conductive material.
3. The method of claim 2,
The carbonaceous material may be artificial graphite in the form of potato, artificial graphite in the form of MCMB (MesoCarbon MicroBead), natural graphite subjected to surface treatment, hard carbon obtained by pyrolyzing phenolic resin, hard carbon obtained by pyrolyzing furan resin (Hard carbon), coke, needle coke and pitch (carbon) carbon dioxide (carbon) carbon dioxide (soft carbon) is one or a mixture of two or more selected from the group consisting of a negative electrode for a lithium secondary battery.
The method of claim 1,
The second active material layer is a lithium secondary battery negative electrode having a thickness of 2 to 100㎛.
The method of claim 1,
The second active material layer is a lithium secondary battery negative electrode having a density of 0.2 to 2.0 g / cm3.
The method of claim 1,
The second active material layer is a lithium secondary battery negative electrode containing lithium titanium oxide.
The method according to claim 6,
The lithium titanium oxide is Li 4 Ti 5 O 12 A negative electrode for a lithium secondary battery.
The method of claim 1,
The current collector is a lithium secondary battery negative electrode selected from aluminum foil or copper foil.
3. The method of claim 2,
The binder is polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), cellulose, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, Selected from polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene copolymer (EPDM), sulfonated ethylene-propylene-diene copolymer (EPDM), styrene butylene rubber and fluorine rubber The negative electrode for lithium secondary batteries which is 1 type, or 2 or more types of mixtures.
3. The method of claim 2,
The conductive material is a negative electrode for a lithium secondary battery which is one or a mixture of two or more selected from graphite, carbon black, conductive fibers, metal powder, conductive whiskey, conductive metal oxide and polyphenylene derivative.
3. The method of claim 2,
The first active material layer is a negative electrode for a lithium secondary battery containing a carbon material, a binder and a conductive material in a weight ratio of 4 to 6000: 0.1 to 1500: 1.
A lithium secondary battery comprising the negative electrode of any one of claims 1 to 11.
Forming a first active material layer on one surface of the current collector; And
And forming a second active material layer having a charging potential of 0.1 V or more relative to a lithium charging potential on the first active material layer.
The method of claim 13,
The second active material layer is a method for producing a negative electrode for a lithium secondary battery having a thickness of 2 to 100㎛.
The method of claim 13,
The second active material layer is a density of 0.2 to 2.0 g / cm 3 The method of manufacturing a negative electrode for a lithium secondary battery.
The method of claim 13,
The second active material layer is a method of manufacturing a negative electrode for a lithium secondary battery containing lithium titanium oxide.
17. The method of claim 16,
The lithium titanium oxide is Li 4 Ti 5 O 12 The manufacturing method of the negative electrode for a lithium secondary battery.
The method of claim 13,
The current collector is a method of manufacturing a negative electrode for a lithium secondary battery is selected from aluminum foil or copper foil.
The method of claim 13,
The first active material layer is 40 to 60% by weight of a carbon material, 1 to 15% by weight of the binder, 0 to 10% by weight of the conductive material and 30 to 70% by weight of a solvent for a lithium secondary battery negative electrode manufacturing method.
The method of claim 13,
The thickness of the first active material layer is 50 to 500㎛ manufacturing method of a negative electrode for a lithium secondary battery.
The method of claim 13,
The manufacturing method of the negative electrode for lithium secondary batteries whose specific surface area of the said 1st active material layer is 0.5-10 m <2> / g.
The method of claim 13,
The second active material layer is formed by any one method selected from coating, metal sputtering, chemical vapor deposition, ion plating, electron beam vapor deposition and laser deposition.
The method of claim 13,
Formation of the second active material layer is a method for producing a negative electrode for a lithium secondary battery using a solvent insoluble to the first active material layer.
24. The method of claim 23,
The solvent is pure water, n-methylpyrrolidinone (NMP), cyclohexane, methyl ethyl ketone (MEK) and tetrahydrofuran (THF) is one or a mixture of two or more selected from the manufacturing method of the negative electrode for a lithium secondary battery.

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