KR20170014299A - Electrode and electrochemical device including the same - Google Patents

Abstract

The present invention relates to an electrode capable of increasing the output of an electrochemical device by reducing resistance by the movement of electrons upon discharge of a relatively high current, and also relates to an electrochemical device comprising the same. More specifically, the electrode according to the present invention comprises: an electrode current collector; a first electrode active material; a first binder; a first conductive material; a first electrode active material layer formed on at least one surface of the electrode current collector; a second electrode active material; a second binder; a second conductive material; and a second electrode active material formed on the upper surface of the first electrode active material layer; wherein the content of the first conductive material in the first electrode active material is higher than the content of the second conductive material in the second electrode active material, or the content of the second conductive material in the second electrode active material is higher than the content of the first conductive material in the first electrode active material.

Description

ELECTRODE AND ELECTROCHEMICAL DEVICE INCLUDING THE Same,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode and an electrochemical device including the electrode, and more particularly, to an electrode of a type capable of improving the output at a high current and an electrochemical device including the same.

Recently, interest in energy storage technology is increasing. As the application fields of cell phones, camcorders, notebook PCs and even electric vehicles are expanding, efforts for research and development of electrochemical devices are becoming more and more specified. The electrochemical device has received the most attention in this respect. Of these, the development of a rechargeable secondary battery has become a focus of attention. Recently, in developing such a battery, Research and development on the design of electrodes and batteries are underway.

Among the currently applied secondary batteries, the lithium secondary battery developed in the early 1990s has advantages such as higher operating voltage and higher energy density than conventional batteries such as Ni-MH, Ni-Cd and sulfuric acid-lead batteries using an aqueous electrolyte solution .

On the other hand, an electrode used in an electrochemical device is manufactured by applying an electrode active material slurry containing an electrode active material on at least one surface of an electrode current collector, followed by drying.

However, the conventional electrochemical device has a problem in that the output of the electrochemical device can be influenced by the difference in the moving speed of electrons and lithium ions during a high current discharge, and the resistance of the cell is rapidly increased, have.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an electrode and an electrochemical device including the same capable of achieving an improvement in output of an electrochemical device during a high current discharge.

According to an aspect of the present invention, there is provided an electrode collector, A first electrode active material layer including a first electrode active material, a first binder, and a first conductive material, the first electrode active material layer being formed on at least one surface of the electrode current collector; And a second electrode active material layer formed on the upper surface of the first electrode active material layer, the second electrode active material layer including a second electrode active material, a second binder, and a second conductive material, Wherein the content of the second conductive material in the second electrode active material layer is greater than the content of the second conductive material in the second electrode active material layer or the content of the second conductive material in the second electrode active material layer is greater than the content of the first conductive material in the first electrode active material layer. / RTI >

Preferably, the content of the first conductive material is 0.1 to 10% by weight based on the total weight of the first electrode active material layer, and the content of the second conductive material is 0.1 to 10% by weight based on the total weight of the second electrode active material layer.

Preferably, the ratio of the thickness of the first electrode active material layer to the thickness of the second electrode active material layer may be 20:80 to 80:20.

Preferably, the specific surface area of the electrode active material layer may be 0.01 to 20 m ² / g.

Preferably, the electrode is a cathode, and the first electrode active material and the second electrode active material may each independently be a lithium-containing oxide.

The lithium-containing oxide may be a lithium-containing transition metal oxide.

The lithium-containing transition metal _{oxides, Li x CoO 2 (0.5 <} x <1.3), Li x NiO 2 (0.5 <x <1.3), Li x MnO 2 (0.5 <x <1.3), Li x Mn 2 O 4 (0.5 <x <1.3), Li x (Ni a Co b Mn c) O 2 (0.5 <x <1.3, 0 <a <1, 0 <b <1, 0 <c <1, a + b + c _{= 1), Li x Ni 1} -y Co y O 2 (0.5 <x <1.3, 0 <y <1), Li x Co 1 - y Mn y O 2 (0.5 <x <1.3, 0≤y <1 _{), Li x Ni 1 -y Mn} y O 2 (0.5 <x <1.3, O≤y <1), Li x (Ni a Co b Mn c) O 4 (0.5 <x <1.3, 0 <a <2 , 0 <b <2, 0 <c <2, a + b + c = 2), Li x Mn 2 - z Ni z O 4 (0.5 <x <1.3, 0 <z <2), Li x Mn 2 _- a _{z Co z O 4 (0.5 <} x <1.3, 0 <z <2), Li x CoPO 4 (0.5 <x <1.3) and _{Li x FePO 4 (0.5 <x} <1.3) which is selected from the group consisting of Or a mixture of two or more thereof.

Preferably, the electrode is a cathode, and the first electrode active material and the second electrode active material may be independently selected from the group consisting of a lithium metal, a carbonaceous material, and a metal compound, or a mixture of two or more thereof have.

The metal compound is selected from the group consisting of Si, Ge, Sn, Pb, P, Sb, Bi, Al, Ga, In, Ti, Mn, Fe, Co, Ni, Cu, Zn, Ag, Any one selected or a mixture of two or more thereof may be used.

Preferably, the first conductive material and the second conductive material are each independently selected from the group consisting of carbon black, graphite, carbon fiber, carbon nanotube, metal powder, conductive metal oxide, organic conductive material, It may be a mixture of two or more.

According to an aspect of the present invention, there is also provided an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; A nonaqueous electrolytic solution for impregnating the electrode assembly; And a battery case containing the electrode assembly and the non-aqueous electrolyte, wherein at least one of the positive electrode and the negative electrode is the above-described electrode.

Preferably, the nonaqueous electrolytic solution may include an organic solvent and an electrolyte salt.

Examples of the organic solvent include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, (DEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate A solvent such as methanol, ethanol, propanol, isopropanol, isopropanol, butanol, isopropanol, butanol, isopropanol, Pyronate,? -Butyrolactone,? -Valerolactone,? -Caprolactone,? -Valerolactone and? -Caprolactone Luer may be any one or a binary mixture of two or more of those selected from the group.

The electrolyte salt includes, as ^{anions, 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 ^- , or two or more of them.

Preferably, the electrochemical device may be a lithium secondary battery.

According to one embodiment of the present invention, the output of the electrochemical device can be improved by lowering the resistance due to the movement of electrons during a relatively high current discharge.

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 given above, serve to further the understanding of the technical idea of the invention, It should not be construed as limited.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing a result of analyzing resistance of a battery according to an embodiment of the present invention and a comparative example through an EIS. FIG.

Hereinafter, the present invention will be described in detail with reference to the drawings. 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.

Therefore, the embodiments described in the present specification and the constitutions described in the drawings are merely the most preferred embodiments of the present invention, and are not intended to represent all of the technical ideas of the present invention. Therefore, It is to be understood that equivalents and modifications are possible.

An electrode according to the present invention includes: an electrode collector; A first electrode active material layer including a first electrode active material, a first binder, and a first conductive material, the first electrode active material layer being formed on at least one surface of the electrode current collector; And a second electrode active material layer formed on the upper surface of the first electrode active material layer, the second electrode active material layer including a second electrode active material, a second binder, and a second conductive material, The content of the second conductive material in the second electrode active material layer is greater than the content of the second conductive material in the second electrode active material layer or the content of the second conductive material in the second electrode active material layer is greater than the content of the first conductive material in the first electrode active material layer.

Conventionally, a slurry of an electrode active material in which electrode active material particles are dispersed is applied only to a current collector in a single layer. In this case, resistance is generated due to a difference in moving speed of electrons and lithium ions during a high current discharge of 10 C or more, And the like. However, according to the present invention, by thickening the conductive material of the electrode to one side, the resistance due to the movement of electrons during high current discharge can be reduced and the output of the electrochemical device can be improved.

The content of the first conductive material may be 0.1 to 10% by weight based on the total weight of the first electrode active material layer, and the content of the second conductive material may be 0.1 to 10% by weight based on the total weight of the second electrode active material layer. Preferably, the content of the first conductive material is 1 to 8% by weight based on the total weight of the first electrode active material layer, and the content of the second conductive material is 1 to 8% by weight based on the total weight of the second electrode active material layer.

The ratio of the thickness of the first electrode active material layer and the thickness of the second electrode active material layer may be 20:80 to 80:20.

The specific surface area of the electrode active material may be 0.01 to 20 m ² / g. Preferably, the specific surface area of the electrode active material may be 0.1 to 3.0 m ² / g.

According to an embodiment of the present invention, the electrode is an anode, and the first electrode active material and the second electrode active material may each independently be a lithium-containing oxide. As the lithium-containing oxide, a lithium-containing transition metal oxide can be preferably used. For example, the lithium-containing transition metal _{oxides, Li x CoO 2 (0.5 <} x <1.3), Li x NiO 2 (0.5 <x <1.3), Li x MnO 2 (0.5 <x <1.3), Li x _{Mn 2 O 4 (0.5 <x} <1.3), Li x (Ni a Co b Mn c) O 2 (0.5 <x <1.3, 0 <a <1, 0 <b <1, 0 <c <1, a + b + c = 1), Li x Ni 1 - y Co y O 2 (0.5 <x <1.3, 0 <y <1), Li x Co 1 - y Mn y O 2 (0.5 <x <1.3, 0 _{≤y <1), Li x Ni} 1 - y Mn y O 2 (0.5 <x <1.3, O≤y <1), Li x (Ni a Co b Mn c) O 4 (0.5 <x <1.3, 0 <a <2, 0 <b <2, 0 <c <2, a + b + c = 2), Li x Mn 2 - z Ni z O 4 (0.5 <x <1.3, 0 <z <2), the group consisting of _{z Co z O 4 (0.5 <} x <1.3, 0 <z <2), Li x CoPO 4 (0.5 <x <1.3) and _{Li x FePO 4 (0.5 <x} <1.3) - Li x Mn 2 Or a mixture of two or more thereof. The lithium-containing transition metal oxide may be coated with a metal such as aluminum (Al) or a metal oxide. In addition to the lithium-containing transition metal oxide, sulfide, selenide and halide may also be used.

According to an embodiment of the present invention, the electrode is a cathode, and the first electrode active material and the second electrode active material are each independently selected from the group consisting of lithium metal, carbonaceous material and metal compound, or 2 Or more.

Concretely, as the carbon material, both low-crystalline carbon and highly-crystalline carbon may be used. Examples of the low crystalline carbon include soft carbon and hard carbon. Examples of highly crystalline carbon include natural graphite, Kish graphite, pyrolytic carbon, liquid crystal pitch carbon fiber high temperature sintered carbon such as mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar pitch derived cokes.

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, . Among them, it may contain at least one element selected from Si, Ge and Sn, and it may further increase the capacity of the battery including at least one element selected from Si and Sn.

The first conductive material and the second conductive material are not particularly limited as long as they are electron conductive materials that do not cause chemical changes in the electrochemical device. The first conductive material and the second conductive material may each independently use carbon black, graphite, carbon fiber, carbon nanotube, metal powder, conductive metal oxide, organic conductive material, (Manufactured by Chevron Chemical Company or Gulf Oil Company), Ketjen Black EC series (manufactured by Armak Company), acetylene black series (Chevron Chemical Company, Gulf Oil Company, etc.) Vulcan XC-72 (Cabot Company) and Super P (MMM).

The first binder and the second binder can be used without any limitations in the binders that are commonly used. For example, polyvinylidene fluoride-hexafluoropropylene (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate various kinds of binders such as polymethyl methacrylate, styrene butadiene rubber (SBR), and carboxyl methyl cellulose (CMC) can be used.

The current collector used for the positive electrode and the negative electrode may be any metal having a high conductivity and being a metal capable of easily adhering the electrode active material slurry but not reactive in the voltage range of the electrochemical device. Specifically, non-limiting examples of the current collector for a positive electrode include aluminum, nickel, or a foil produced by a combination thereof. Non-limiting examples of the current collector for a negative electrode include copper, gold, nickel or a copper alloy, And the like. In addition, the current collector may be used by laminating the substrates made of the above materials.

The positive electrode and the negative electrode are kneaded using an active material, a conductive material, a binder and a high boiling point solvent to prepare two kinds of electrode active material slurries having different contents of conductive material, Drying, pressure-forming, and then heat-treating under vacuum at a temperature of about 50 to 250 ° C for about 2 hours, respectively.

According to an embodiment of the present invention, there is also provided an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; A nonaqueous electrolytic solution for impregnating the electrode assembly; And a battery case containing the electrode assembly and the non-aqueous electrolyte, wherein at least one of the positive electrode and the negative electrode is an electrode of the present invention.

The separator according to the present invention can be used as a porous substrate used in an electrochemical device. For example, a polyolefin porous membrane or a nonwoven fabric may be used, but the present invention is not limited thereto.

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.

On the other hand, in order 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, a porous coating layer containing inorganic particles and a polymeric binder may be further provided on at least one surface of the porous substrate.

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 a state of being substantially in contact with each other, and the interstitial volume generated when the inorganic particles are in contact becomes the 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 oxidation and / or reduction reactions do 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 moving 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 battery is improved and the battery performance 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 as such (LiAlTiP) _x O _y series glass (0 <x <4, 0 <y <13), lithium lanthanum titanate _{(Li x La y TiO 3,} 0 <x <2, 0 <y <3 ), Li _{3 . 25 Ge 0 .25 P 0. 75 S} 4 Lithium, such as germanium Mani help thiophosphate lithium nitro, such as _{(Li x Ge y P z S} w, 0 <x <4, 0 <y <1, 0 <z <1, 0 <w <5), Li 3 N fluoride _{(Li x N y, 0 <} x <4, 0 <y <2), 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 , etc., such as 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 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.

Non-limiting examples of such polymeric binders include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichlorethylene, poly But are not limited to, polymethylmethacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co- polyvinyl acetate, vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, Cyanoethylpullulan, cyanoethylpolybi Cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, and carboxyl methyl cellulose can be given.

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 mu m, and the porosity may be in the range of 5 to 90%.

Meanwhile, the non-aqueous electrolyte may include an organic solvent and an electrolyte salt, 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 ^- , or two or more of them.

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., Two or more of them may be used in combination.

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 And mixtures of two or more of them may be used as typical examples, 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, propyl propionate,? -Butyrolactone,? -Valerolactone,? -Caprolactone,? -Valerolactone and? -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.

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.

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. Embodiments of the present invention are provided to more fully describe the present invention to those skilled in the art.

Example

(1) Preparation of positive electrode

93.5 wt% of Li (NiCoMn) O ₂ , 4.5 wt% of carbon black (conductive agent) and 2 wt% of PVdF (binder) were added to NMP (N-methyl-2-pyrrolidone) To prepare a cathode active material slurry.

96.5 wt% of Li (NiCoMn) O ₂ , 1.5 wt% of carbon black (conductive agent) and 2 wt% of PVdF (binder) were added to NMP (N-methyl-2-pyrrolidone) To prepare a cathode active material slurry.

The first positive electrode active material slurry was first dried 240mg / 25cm then coated on an aluminum foil as a loading amount of the ^second vacuum, after which the first coating was a second positive electrode active material slurry in the same loading amount.

(2) Manufacture of cathodes

Natural graphite was used as the negative electrode active material, and 96.1 wt% of natural graphite and 1 wt% of Super-P (conductive agent), 2.2 wt% of SBR (binder) and 0.7 wt% of CMC were added to water as a solvent to prepare a negative electrode active material slurry And then coated, dried and pressed once on a copper foil to prepare a negative electrode.

(3) Preparation of separator

Polypropylene was uniaxially stretched by a dry method to prepare a membrane having a microporous structure having a melting point of 165 DEG C and a width of 200 mm on one side.

(4) Production of lithium secondary battery

An electrode assembly was prepared between the positive electrode and the negative electrode through the separator, the electrode assembly was embedded in a pouch-shaped battery case, and a 1M LiPF ₆ carbonate solution electrolyte was injected to complete the battery.

Comparative Example

95% by weight of Li (NiCoMn) O ₂ , 3% by weight of carbon black (conductive agent) and 2% by weight of PVdF (binder) as a cathode active material were added to NMP (N-methyl-2-pyrrolidone) A slurry was prepared, and the cathode active material slurry was coated on an aluminum foil with a loading amount of 480 mg / 25 cm &lt; ^{2 &} gt ;, followed by vacuum drying to prepare a positive electrode.

EIS resistance comparison

The resistance of the battery according to the above Examples and Comparative Examples through EIS was analyzed and the measured results are shown in FIG. Electrochemical impedance spectroscopy (EIS) is a method of calculating the resistance by applying alternating current of 10 mV at a frequency of 500 kHz to 50 mHz, and the size of the semicircle means the charge transfer resistance. Referring to FIG. 1, it can be seen that the charge transfer resistance of the embodiment is lower than that of the comparative example.

The foregoing description is merely illustrative of the technical idea of the present invention, and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas within the scope of equivalents should be construed as falling within the scope of the present invention.

Claims (15)

Electrode collector;
A first electrode active material layer including a first electrode active material, a first binder, and a first conductive material, the first electrode active material layer being formed on at least one surface of the electrode current collector; And
And a second electrode active material layer formed on an upper surface of the first electrode active material layer, the second electrode active material layer including a second electrode active material, a second binder, and a second conductive material,
Wherein the content of the first conductive material in the first electrode active material layer is greater than the content of the second conductive material in the second electrode active material layer, and the content of the second conductive material in the second electrode active material layer is greater than the content of the second conductive material in the first electrode active material layer. 1 &lt; / RTI &gt; conductive material. The method according to claim 1,
Wherein the content of the first conductive material is 0.1 to 10 wt% based on the total weight of the first electrode active material layer, and the content of the second conductive material is 0.1 to 10 wt% based on the total weight of the second electrode active material layer. The method according to claim 1,
Wherein the ratio of the thickness of the first electrode active material layer to the thickness of the second electrode active material layer is 20:80 to 80:20. The method according to claim 1,
Wherein the electrode active material layer has a specific surface area of 0.01 to 20 m ² / g. The method according to claim 1,
Wherein the electrode is an anode, and the first electrode active material and the second electrode active material are each independently a lithium-containing oxide. 6. The method of claim 5,
Wherein the lithium-containing oxide is a lithium-containing transition metal oxide. The method according to claim 6,
The lithium-containing transition metal _{oxides, Li x CoO 2 (0.5 <} x <1.3), Li x NiO 2 (0.5 <x <1.3), Li x MnO 2 (0.5 <x <1.3), Li x Mn 2 O 4 (0.5 <x <1.3), Li x (Ni a Co b Mn c) O 2 (0.5 <x <1.3, 0 <a <1, 0 <b <1, 0 <c <1, a + b + c _{= 1), Li x Ni 1} -y Co y O 2 (0.5 <x <1.3, 0 <y <1), Li x Co 1 - y Mn y O 2 (0.5 <x <1.3, 0≤y <1 _{), Li x Ni 1 -y Mn} y O 2 (0.5 <x <1.3, O≤y <1), Li x (Ni a Co b Mn c) O 4 (0.5 <x <1.3, 0 <a <2 , 0 <b <2, 0 <c <2, a + b + c = 2), Li x Mn 2 - z Ni z O 4 (0.5 <x <1.3, 0 <z <2), Li x Mn 2 _- a _{z Co z O 4 (0.5 <} x <1.3, 0 <z <2), Li x CoPO 4 (0.5 <x <1.3) and _{Li x FePO 4 (0.5 <x} <1.3) which is selected from the group consisting of One or a mixture of two or more thereof. The method according to claim 1,
Wherein the electrode is a cathode, and the first electrode active material and the second electrode active material are independently selected from the group consisting of lithium metal, carbonaceous material, and metal compound, or a mixture of two or more thereof. . 9. The method of claim 8,
The metal compound is selected from the group consisting of Si, Ge, Sn, Pb, P, Sb, Bi, Al, Ga, In, Ti, Mn, Fe, Co, Ni, Cu, Zn, Ag, Or a mixture of two or more thereof. The method according to claim 1,
Wherein the first conductive material and the second conductive material are each independently selected from the group consisting of carbon black, graphite, carbon fiber, carbon nanotube, metal powder, conductive metal oxide, and organic conductive material or a mixture of two or more thereof . An electrode assembly including an anode, a cathode, and a separator interposed between the anode and the cathode;
A nonaqueous electrolytic solution for impregnating the electrode assembly; And
And a battery case housing the electrode assembly and the non-aqueous electrolyte,
Wherein at least one of the positive electrode and the negative electrode is the electrode of claim 1. 12. The method of claim 11,
Wherein the non-aqueous electrolyte comprises an organic solvent and an electrolyte salt. 13. The method of claim 12,
Examples of the organic solvent include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, (DEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate A solvent such as methanol, ethanol, propanol, isopropanol, isopropanol, butanol, isopropanol, butanol, isopropanol, Pyronate,? -Butyrolactone,? -Valerolactone,? -Caprolactone,? -Valerolactone and? -Caprolactone The electrochemical device according to claim any one or a mixture of two or more of those selected from the group true luer. 13. The method of claim 12,
The electrolyte salt includes, as ^{anions, 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 ^- , or two or more of them. 12. The method of claim 11,
Wherein the electrochemical device is a lithium secondary battery.

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