KR20170009097A - Cathode improved conductivity and electrochemical device including the same - Google Patents

Abstract

The purpose of the present invention is to provide a positive electrode with excellent electrochemical properties such as capacity properties of a battery, lifespan, discharge potential, electric energy, etc. by forming a conductive network in the battery. The positive electrode for a lithium secondary battery comprises: a current collector; and a positive electrode active material layer formed on at least one surface of the current collector and including a positive electrode active material, a conductive material and a binder, wherein the specific surface ratio of the conductive material to the positive electrode active material is three or more; the conductive material comprises a dot-like conductive material and a plate-shaped conductive material; and the weight ratio of the dot-like conductive material and the plate-shaped conductive material is 1:0.9 to 1:1.

Description

[0001] The present invention relates to a positive electrode having improved conductivity and an electrochemical device including the same,

The present invention relates to a positive electrode having improved conductivity and an electrochemical device including the same, and more particularly, to a positive electrode and an electrochemical device including the same that improve the capacity and life characteristics of an electrochemical device.

Recently, interest in energy storage technology is increasing. The demand for electrochemical devices as energy sources is rapidly increasing as technology development and demand for mobile devices such as mobile phones, camcorders, and notebook PCs are increasing rapidly. Among such electrochemical devices, they have high energy density and voltage, , A lithium secondary battery having a low self-discharge rate has been commercialized and widely used.

In addition, as interest in environmental issues has increased recently, studies on electric vehicles and hybrid electric vehicles capable of replacing fossil fuel-based vehicles such as gasoline vehicles and diesel vehicles, which are one of the main causes of air pollution, have. Although a nickel metal hydride secondary battery is mainly used as a power source for such electric vehicles and hybrid electric vehicles, researches using a lithium secondary battery having a high energy density and a discharge voltage, a long cycle life and a low self-discharge rate are actively conducted And is in the commercialization stage.

As a cathode active material of such a lithium secondary battery, a carbon material is mainly used, and the use of lithium metal, a sulfur compound and the like is also considered. In addition, lithium-containing cobalt oxide (LiCoO ₂ ) is mainly used as the positive electrode active material, and a lithium-containing manganese oxide such as LiMnO _{2 having a} layered crystal structure and LiMn ₂ O _{4 having a} spinel crystal structure and a lithium- ₂ ) is also considered.

Since the above-mentioned cathode active materials have low electrical conductivity, conductive materials are used together to improve the conductivity. Such a conductive material can be used by using a point-like conductive material or by adding a conductive material of a plate shape. However, if the content of the plate-like conductive material is increased, a conductive network is not formed well and the output of the battery is reduced.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made in order to solve the above-mentioned problems, and it is an object of the present invention to provide a positive electrode having excellent electrochemical characteristics such as capacity characteristics, life span, discharge potential, And to provide a chemical device.

According to an aspect of the present invention, there is provided a current collector comprising: a current collector; And a cathode active material layer formed on at least one surface of the current collector and including a cathode active material, a conductive material, and a binder, wherein a ratio of a specific surface area of the conductive material to a specific surface area of the cathode active material is 3 or more, Wherein the conductive material comprises a point conductive material and a plate-like conductive material, wherein a content of the conductive material is 1 to 5 parts by weight and a content of the binder is 2 to 5 parts by weight based on 100 parts by weight of the positive electrode active material, / RTI >

Preferably, the pointed conductive material may be carbon black or a carbon material.

Preferably, the plate-like conductive material may be a graphite conductive material.

Preferably, the pointed conductive material has an aspect ratio of 0.7 to 1 and may have an average particle size of 20 to 50 nm.

Preferably, the plate-like conductive material has an aspect ratio of 0.4 to 0.9 and may have an average particle diameter of 1 to 7 mu m.

Preferably, the weight ratio of the spot-like conductive material and the plate-like conductive material may be 1: 0.8 to 1: 1.

Preferably, the cathode active material is selected from the group consisting of LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiCoPO ₄ , LiFePO ₄ , LiNiMnCoO ₂ and LiNi _{1 -xy- z} Co _x M _y M2 _z O ₂ X, y and z are independently selected from the group consisting of Al, Ni, Co, Fe, Mn, V, Cr, Ti, W, Ta, Mg and Mo; x <0.5, 0? y <0.5, 0? z <0.5 and 0 <x + y + z? 1) or a mixture of two or more thereof.

Preferably, the binder is selected from the group consisting of polyvinylidene fluoride (PVDF), hexafluoro propylene (HFP), polyvinylidene fluoride-co hexafluoro propylene, polyvinylidene fluoride-co-trichlorethylene, polymethyl methacrylate, polybutylacrylate, polyacrylonitrile, But are not limited to, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, , Cellulose acetate butyrate (cellulose acetate butyrate), cellulose acetate propyl But are not limited to, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, A carboxyl methyl cellulose, an acrylonitrile-styrene-butadiene copolymer, and a polyimide, or a mixture of two or more thereof.

According to an aspect of the present invention, there is provided an electrochemical device including a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte solution, wherein the positive electrode is the positive electrode described above.

The electrochemical device may be a lithium secondary battery.

According to an embodiment of the present invention, it is possible to secure the mobility of lithium ions by well forming the conductive network, and to improve the electrochemical characteristics such as the capacity characteristics, life span, discharge potential, and electric power characteristics of the battery.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate preferred embodiments of the invention and together with the description of the invention serve to further the understanding of the technical idea of the invention, It should not be construed as limited.
Fig. 1 is a graph showing the results of measurement of conductance against the frequency of an anode according to Examples and Comparative Examples 1 to 3. Fig.
Fig. 2 is a graph showing the results of measuring the resistance of the pouch type mono cell according to the embodiment and Comparative Examples 1 to 3. Fig.
3 is a graph showing the results of measurement of the EIS of the pouch type mono cell of Example and Comparative Example 1. Fig.

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.

A positive electrode for a lithium secondary battery according to the present invention comprises: a current collector; And a cathode active material layer formed on at least one surface of the current collector, the cathode active material layer including a cathode active material, a conductive material, and a binder.

By adding a plate-like conductive material to the positive electrode active material layer, it is possible to form pores having a uniform size in the active material layer. However, when the content of the plate-like conductive material increases, the conductive network is not well formed and the output of the battery decreases.

However, in the present invention, the ratio of the specific surface area of the conductive material to the specific surface area of the cathode active material is 3 or more, and the conductive material includes the point conductive material and the plate-like conductive material, Is contained in an amount of 1 to 5 parts by weight and the binder is contained in an amount of 2 to 5 parts by weight so that a conductive network is well formed and the electrochemical characteristics such as the capacity characteristics, life span, discharge potential and electric power characteristics of the battery can be improved.

The weight ratio of the spot-like conductive material and the plate-like conductive material may be 1: 0.8 to 1: 1.

Examples of the point-like conductive material include carbon black such as ketchen black, denka black, acetylene black, carbon black, thermal black, and channel black; Carbon materials such as activated carbon; And the like, but are not limited thereto. The point-like conductive material may have an aspect ratio of 0.7 to 1 and an average particle diameter of 20 to 50 nm.

The plate-like conductive material may be a graphite-based conductive material, and examples of the graphite-based conductive material include natural graphite and artificial graphite. The plate-like conductive material may have an aspect ratio of 0.4 to 0.9 and an average particle diameter of 1 to 7 mu m.

Wherein the positive electrode active material is selected from the group consisting of LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiCoPO ₄ , LiFePO ₄ , LiNiMnCoO _2, and LiNi _{1 -xy- z} Co _x M _{y y} M2 _z O ₂ X, y and z are independently selected from the group consisting of Co, Fe, Mn, V, Cr, Ti, W, Ta, Mg and Mo, 0 < y < 0.5, 0 < z < 0.5, and 0 &lt; x + y + z 1).

The binder may be selected from the group consisting of polyvinylidene fluoride (PVDF), hexafluoro propylene (HFP), polyvinylidene fluoride-co-hexafluoro propylene Polyvinylidene fluoride-co-trichlorethylene, polymethyl methacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylpyrrolidone, Polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyl Cellulose acetate butyrate, cellulose acetate propionate sodium acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxymethylcellulose a carboxyl methyl cellulose, an acrylonitrile-styrene-butadiene copolymer, and a polyimide, or a mixture of two or more thereof.

According to an embodiment of the present invention, there is also provided an electrochemical device comprising a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte solution, wherein the positive electrode comprises the above-described positive electrode.

Here, the electrochemical device includes all devices that perform an electrochemical reaction, and specific examples thereof include capacitors such as all kinds of secondary cells, fuel cells, solar cells, or super-capacitor devices. Particularly, a lithium secondary battery including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery among the above secondary batteries is preferable.

In addition, the electrochemical device according to the present invention is capable of stacking, lamination, folding, and stacking / folding processes of separators and electrodes in addition to a general winding process.

The outer shape of the electrochemical device is not particularly limited, but may be a cylindrical shape, a square shape, a pouch shape, a coin shape, or the like using a can.

The negative electrode may include a current collector and a negative electrode active material layer formed on the current collector. The current collector used for the negative electrode may be a highly conductive metal. The negative active material layer may be easily bonded, Any material that is not reactive in the voltage range of the electrochemical device can be used. Specifically, non-limiting examples of the current collector for a negative electrode include a foil manufactured by copper, gold, nickel or a copper alloy or a combination thereof. In addition, the current collector may be used by laminating the substrates made of the above materials.

At this time, as the negative electrode active material, a lithium metal, a carbon material, a metal compound, or a mixture thereof can be used, in which lithium ions can be occluded and released.

Examples of the metal compound include metal elements such as Si, Ge, Sn, Pb, P, Sb, Bi, Al, Ga, In, Ti, Mn, Fe, Co, Ni, Cu, Zn, Ag, Mg, , And the like. These metal compounds can be used in any form such as a single body, an alloy, an oxide (TiO 2, SnO 2, etc.), a nitride, a sulfide, a boride and an alloy with lithium. However, the alloy with a single body, alloy, . In particular, it may contain at least one element selected from Si, Ge, and Sn, and the element containing at least one element selected from Si and Sn can further increase the capacity of the electrochemical device.

The thickness of the negative electrode active material layer may be 1 to 100 mu m, or 3 to 70 mu m. When the negative electrode active material layer satisfies such a thickness range, the amount of the active material in the negative electrode active material layer is sufficiently secured, the capacity of the electrochemical device can be prevented from being reduced, and the cycle characteristics and rate characteristics can be improved.

Here, the conductive material and the polymer binder may be the above-mentioned materials used for the anode.

On the other hand, the separator can be used as a porous substrate used for an electrochemical device. For example, a polyolefin porous membrane or a nonwoven fabric may be used. However, the separator is not particularly limited to this.

Examples of the polyolefin-based porous film include polyolefin-based polymers such as polyethylene, polypropylene, polybutylene, and polypentene, such as high-density polyethylene, linear low-density polyethylene, low-density polyethylene and ultra-high molecular weight polyethylene, One membrane can be mentioned.

The nonwoven fabric may include, in addition to the polyolefin nonwoven fabric, for example, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate ), Polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylenesulfide, and polyethylene naphthalene, which may be used alone or in combination, And nonwoven fabrics formed by mixing these polymers. The structure of the nonwoven fabric may be a spun bond nonwoven fabric or a meltblown nonwoven fabric composed of long fibers.

The thickness of the porous substrate is not particularly limited, but may be 5 to 50 μm, and the pore size and porosity present in the porous substrate are also not particularly limited, but may be 0.01 to 50 μm and 10 to 95%, respectively.

The porous substrate may further include a porous coating layer having inorganic particles and a polymeric binder on at least one surface of the porous substrate so as to improve the mechanical strength of the separator composed of the porous substrate and to prevent a short circuit between the anode and the cathode.

In the porous coating layer, the polymer binder binds the inorganic particles together (that is, the polymer binder binds and fixes the inorganic particles) so that the inorganic particles can remain bonded to each other, and the porous coating layer binds the porous substrate with the polymer binder . The inorganic particles of the porous coating layer exist in a closely packed state in substantially contact with each other and the interstitial volume generated when the inorganic particles are in contact with each other can be pores of the porous coating layer.

At this time, the inorganic particles used are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles are not particularly limited as long as the oxidation and / or reduction reaction does not occur in the operating voltage range of the applied electrochemical device (for example, 0 to 5 V based on Li / Li ⁺ ). Particularly, when inorganic particles having ion transfer ability are used, the ion conductivity in the electrochemical device can be increased to improve the performance.

When inorganic particles having a high dielectric constant are used as the inorganic particles, dissociation of an electrolyte salt, for example, a lithium salt, in the liquid electrolyte is also increased, and ion conductivity of the electrolyte can be improved.

For the reasons stated above, the inorganic particles may include high-permittivity inorganic particles having a dielectric constant of 5 or more, or 10 or more, inorganic particles having lithium ion-transporting ability, or a mixture thereof.

Non-limiting examples of inorganic particles having a dielectric constant of 5 or more include BaTiO ₃ , Pb (Zr _x Ti _1-x ) O ₃ (PZT, where 0 <x <1), Pb _{1 - x} La _x Zr _{1 - y} Ti _y O ₃ (PLZT, where, 0 <x <1, 0 <y <1 Im), (1-x) Pb (Mg 1/3 Nb 2/3) O 3 -xPbTiO 3 (PMN-PT, where 0 < xO, x <1), hafnia (HfO ₂ ), SrTiO ₃ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, ZnO, ZrO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , SiC, TiO ₂ May be used alone or in combination of two or more.

In particular, the above-described _{BaTiO 3, Pb (Zr x Ti} 1-x) O 3 (PZT, where 0 <x <1), Pb 1 - x La x Zr 1 -y Ti y O 3 (PLZT, where 0 < 1, 0 <y <1), (1-x) Pb (Mg _1/3 Nb _2/3 ) O _{3 - x} PbTiO ₃ (PMN- HfO ₂ ) exhibits a high dielectric constant with a dielectric constant of 100 or more, as well as a piezoelectricity in which a potential difference is generated between both surfaces due to the generation of charge when a certain pressure is applied to the piezoelectric element by being stretched or compressed. It is possible to prevent internal short-circuiting of both electrodes due to the impact, thereby improving the safety of the electrochemical device. Further, when the above-mentioned high-permittivity inorganic particles and inorganic particles having lithium ion transferring ability are mixed, their synergistic effect can be doubled.

The inorganic particles having the lithium ion transferring ability refer to inorganic particles that contain a lithium element but do not store lithium but have a function of transferring lithium ions. The inorganic particles having lithium ion transferring ability exist in the particle structure Since lithium ions can be transferred and transferred due to a kind of defect, the lithium ion conductivity in the electrochemical device can be improved and the performance of the electrochemical device can be improved. Examples of the inorganic particles having lithium ion transferring ability include lithium phosphate (Li ₃ PO ₄ ), lithium titanium phosphate (Li _x Ti _y (PO ₄ ) ₃ , 0 <x <2, 0 <y < (Li _x Al _y Ti _z (PO ₄ ) ₃ , 0 <x <2, 0 <y <1, 0 <z <3), 14Li ₂ O-9Al ₂ O ₃ -38TiO ₂ -39P ₂ O ₅ (0 <x <4, 0 <y <13), lithium lanthanum titanate (Li _x La _y TiO ₃ , 0 <x <2, 0 <y <3), Li (LiAlTiP) _x O _y series glass (Li _x Ge _y P _z S _w , 0 <x <4, 0 <y <1, 0 <z <1, 0 <w <5) such as _3.25 Ge _0.25 P _0.75 S ₄ , (Li _x N _y , 0 <x <4, 0 <y <2) such as Li ₃ N and Li ₃ PO ₄ -Li ₂ S-SiS ₂ SiS ₂ based glass, such as _{(Li x Si y S z,} 0 <x <3, 0 <y <2, 0 <z <4), LiI-Li 2 SP 2 S 5 There is P ₂ S ₅ based glass _{(Li x P y S z,} 0 <x <3, 0 <y <3, 0 <z <7) or a mixture thereof as such.

The size of the inorganic particles is not limited. However, for proper porosity of the separator, the average particle size may be in the range of 0.001 탆 to 10 탆.

As the polymer binder used for forming the porous coating layer, a polymer commonly used in the formation of the porous coating layer in the art can be used. In particular, a polymer having a glass transition temperature (T _g ) of -200 to 200 ° C can be used because it can improve mechanical properties such as flexibility and elasticity of a finally formed porous coating layer. Such a polymer binder faithfully performs a binder function to connect and stably fix inorganic particles, thereby contributing to prevention of degradation of mechanical properties of the separator into which the porous coating layer is introduced.

Further, the polymer binder does not necessarily have ion conductivity, but when the polymer having ion conductivity is used, the performance of the electrochemical device can be further improved. Therefore, a polymer binder having a high permittivity constant can be used. Actually, the dissociation degree of the salt in the electrolytic solution depends on the permittivity constant of the solvent of the electrolyte. Therefore, the higher the permittivity constant of the polymer, the better the salt dissociation degree in the electrolyte. The permittivity constant of such a polymeric binder may be in the range of 1.0 to 100 (measurement frequency = 1 kHz), in particular, 10 or more.

In addition to the functions described above, the polymeric binder may be characterized by being capable of exhibiting a high degree of swelling of the electrolyte due to gelation upon impregnation with a liquid electrolyte. Accordingly, the solubility parameter of the polymeric binder is from 15 to 45 MPa ^1/2 or 15 to 25 MPa ^1/2, and 30 to 45 MPa ^1/2 range. Therefore, hydrophilic polymers having many polar groups can be used more than hydrophobic polymers such as polyolefins. This is because the solubility parameter can be difficult to swell (swelling) by a conventional liquid electrolyte for electrochemical device, if it exceeds 15 MPa ^1/2 and less than 45 MPa ^1/2.

The polymeric binder may be selected from the group consisting of polyvinylidene fluoride (PVDF), hexafluoro propylene (HFP), polyvinylidene fluoride-co-hexafluoro propylene, polyvinylidene fluoride-co-trichlorethylene, polymethyl methacrylate, polybutylacrylate, polyacrylonitrile, polyvinyl But are not limited to, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, Cellulose acetate butyrate, cellulose acetate propyl But are not limited to, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, But may be any one selected from the group consisting of carboxyl methyl cellulose, acrylonitrile-styrene-butadiene copolymer and polyimide, or a mixture of two or more thereof. But is not limited to.

The weight ratio of the inorganic particles to the polymeric binder may be 50:50 to 99: 1, or 60:40 to 90:10, or 70:30 to 80:20.

The thickness of the porous coating layer composed of the inorganic particles and the polymer binder is not particularly limited, but may be in the range of 0.01 to 20 占 퐉. The pore size and porosity are also not particularly limited, but the pore size may be in the range of 0.01 to 10 μm, and the porosity may be in the range of 5 to 90%.

Meanwhile, the non-aqueous electrolyte may include an electrolyte salt and an organic solvent, and the electrolyte salt is a lithium salt. The lithium salt may be any of those conventionally used for non-aqueous electrolytes for lithium secondary batteries. For example is the above lithium salt anion ^{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 ^- .

Examples of the organic solvent included in the non-aqueous electrolyte include those commonly used in non-aqueous electrolytes for lithium secondary batteries, such as ether, ester, amide, linear carbonate, cyclic carbonate, etc., Or more.

Among them, a carbonate compound which is typically a cyclic carbonate, a linear carbonate, or a mixture thereof may be included.

Specific examples of the cyclic carbonate compound include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, Propylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate, and halides thereof, or a mixture of two or more thereof. Examples of such halides include, but are not limited to, fluoroethylene carbonate (FEC) and the like.

Specific examples of the linear carbonate compound include any one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate and ethyl propyl carbonate A mixture of two or more thereof, and the like may be used, but the present invention is not limited thereto.

In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates in the carbonate-based organic solvent, are high-viscosity organic solvents having a high dielectric constant and can dissociate the lithium salt in the electrolyte more easily. In addition, such cyclic carbonates can be used as dimethyl carbonate and diethyl carbonate When a low viscosity, low dielectric constant linear carbonate is mixed in an appropriate ratio, an electrolyte having a higher electric conductivity can be produced.

As the ether in the organic solvent, any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether and ethyl propyl ether or a mixture of two or more thereof may be used , But is not limited thereto.

Examples of the ester in the organic solvent include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate,? -Butyrolactone,? -Valerolactone,? -Caprolactone,? -Valerolactone, ε-caprolactone, or a mixture of two or more thereof, but the present invention is not limited thereto.

The injection of the nonaqueous electrolyte solution can be performed at an appropriate stage of the manufacturing process of the electrochemical device according to the manufacturing process and required properties of the final product. That is, it can be applied before assembling the electrochemical device or in the final stage of assembling the electrochemical device.

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.

One. Example  One

1-1. Manufacture of anode

A cathode active material slurry was prepared by mixing an NMC active material as a cathode active material, styrene-butadiene rubber as a binder, natural graphite of Mitsubishi Corporation as a conductive material, and carbon conductive material of Timal Company.

At this time, the cathode active material, the binder and the conductive material were mixed in a weight ratio of 96: 2: 2, and the conductive material was mixed so that the weight ratio of the natural graphite and the carbon conductive material was 1: 1.

Then, the cathode active material slurry was coated on an aluminum (Al) foil current collector by a conventional method to prepare a cathode.

1-2. Cathode manufacturing

AGM01 (natural graphite, Mitsubishi) and MAG-XL (artificial graphite, Hitachi) were mixed at a ratio of 9: 1 to prepare an anode active material. Thereafter, the anode active material, the conductive material and the binder were mixed at a weight ratio of 89: 5: 6 to prepare a slurry. The slurry was coated on a copper (Cu) foil current collector by a conventional method and dried to prepare a negative electrode.

1-3. Manufacture of electrochemical devices

A pouch type mono cell was fabricated using an electrode assembly made by interposing a polyethylene porous membrane between the prepared anode and cathode.

2. Comparative Example  One

A pouch type mono cell was produced in the same manner as in Example except that only the carbon conductor material was used as the conductive material of the anode.

3. Comparative Example  2

A pouch type mono cell was produced in the same manner as in Example except that only natural graphite was used as the conductive material of the positive electrode.

4. Comparative Example 3

A pouch-type mono-cell was manufactured in the same manner as in Example 1 except that the mixture was used so that the weight ratio of natural graphite and carbon carrier to the conductive material of the anode was 5: 1.

The specific surface area and capacity of the conductive material / active material of Examples and Comparative Examples 1 to 3 were measured and shown in Table 1 below.

Conductive material / Active material Specific surface area Volume( mAh ) Example 3 33 Comparative Example  One 5 33 Comparative Example  2 0.3 27 Comparative Example  3 1.2 31

Conductivity and resistance measurement of electrodes

The conductivities of the positive and negative electrodes prepared in Examples and Comparative Examples 1 to 3 were measured and shown in FIG. 1, and the resistance of the pouch type mono cell prepared in Examples and Comparative Examples 1 to 3 was measured, Respectively. Referring to FIGS. 1, 2 and 1, it can be seen that in Comparative Examples 2 and 3 where the specific surface area of the conductive material / active material is less than 3, the conductive path is not generated well and the resistance is increased and the capacity is reduced .

Li  Ion migration resistance measurement

The resistance of the pouch type monocell of Example and Comparative Example 1 was measured by EIS (Electrochemical Impedance Spectroscopy), and the migration resistance of Li ion was shown in Fig. Referring to FIG. 3, it can be seen that the resistance of Li ions is larger because the comparative example is longer in the linear region after the A region.

It should be noted that the embodiments of the present invention disclosed in the present specification and drawings are only illustrative of specific examples for the purpose of understanding and are not intended to limit the scope of the present invention. It will be apparent to those skilled in the art that other modifications based on the technical idea of the present invention are possible in addition to the embodiments disclosed herein.

Claims (10)

Collecting house; And
And a positive electrode active material layer formed on at least one surface of the current collector and including a positive electrode active material, a conductive material, and a binder,
The ratio of the specific surface area of the conductive material to the specific surface area of the cathode active material is 3 or more,
Wherein the conductive material includes a point-like conductive material and a plate-like conductive material,
Wherein the conductive material is contained in an amount of 1 to 5 parts by weight based on 100 parts by weight of the cathode active material, and the content of the binder is 2 to 5 parts by weight based on 100 parts by weight of the cathode active material. The method according to claim 1,
Characterized in that the point-like conductive material is carbon black or a carbon material. The method according to claim 1,
Wherein the plate-like conductive material is a graphite-based conductive material. The method according to claim 1,
Wherein the point conductive material has an aspect ratio of 0.7 to 1 and an average particle diameter of 20 to 50 nm. The method according to claim 1,
Wherein the plate-like conductive material has an aspect ratio of 0.4 to 0.9 and an average particle diameter of 1 to 7 占 퐉. The method according to claim 1,
Wherein the weight ratio of the spot-like conductive material to the plate-like conductive material is 1: 0.8 to 1: 1. The method according to claim 1,
The positive electrode active material may be selected from the group consisting of LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiCoPO ₄ , LiFePO ₄ , LiNiMnCoO ₂ and LiNi _1-xyz Co _x M _{y y} M2 _z O ₂ X, y and z are independently selected from the group consisting of Fe, Mn, V, Cr, Ti, W, Ta, Mg and Mo, y <0.5, 0? z <0.5, 0 <x + y + z? 1), or a mixture of two or more of the foregoing. The method according to claim 1,
The binder may be selected from the group consisting of polyvinylidene fluoride (PVDF), hexafluoro propylene (HFP), polyvinylidene fluoride-co-hexafluoro propylene Polyvinylidene fluoride-co-trichlorethylene, polymethyl methacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylpyrrolidone, Polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyl Cellulose acetate butyrate, cellulose acetate propionate sodium acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxymethylcellulose wherein the polymer is one selected from the group consisting of carboxyl methyl cellulose, acrylonitrile-styrene-butadiene copolymer and polyimide, or a mixture of two or more thereof. anode. An electrochemical device comprising a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte solution,
The positive electrode is the positive electrode according to any one of claims 1 to 8. 10. The method of claim 9,
Wherein the electrochemical device is a lithium secondary battery.

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