KR102023732B1 - Electrode and electrochemical device including the same - Google Patents

Abstract

The present invention relates to an electrode capable of improving the output of the electrochemical device by lowering the resistance due to the movement of electrons during a relatively high current discharge, and more particularly, an electrode current collector; A first electrode active material layer including a first electrode active material, a first binder, and a first conductive material, and formed on at least one surface of the electrode current collector; And a second electrode active material layer including a second electrode active material, a second binder, and a second conductive material, and formed on an upper surface of the first electrode active material layer. An electrode having a content 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, and including the same. It relates to an electrochemical device.

Description

Electrode and electrochemical device including the same {Electrode and electrochemical device including the same}

The present invention relates to an electrode and an electrochemical device including the same, and more particularly, to an electrode and a electrochemical device including the type of the type capable of improving the output at a high current.

Recently, interest in energy storage technology is increasing. As the field of application extends to the energy of mobile phones, camcorders, notebook PCs, and even electric vehicles, efforts for research and development of electrochemical devices are becoming more concrete. The electrochemical device is the area that is receiving the most attention in this respect, and the development of a secondary battery capable of charging and discharging has been the focus of attention, and in recent years in the development of such a battery in order to improve the capacity density and specific energy R & D on the design of electrodes and batteries is underway.

Among the secondary batteries currently applied, lithium secondary batteries developed in the early 1990s have a higher operating voltage and greater energy density than conventional batteries such as Ni-MH, Ni-Cd, and sulfuric acid-lead batteries that use an aqueous electrolyte solution. I am in the spotlight.

On the other hand, the electrode used for an electrochemical element is manufactured by apply | coating the electrode active material slurry containing an electrode active material to at least one surface of an electrode collector, and drying it.

However, the conventional electrochemical device may affect the output of the electrochemical device due to the difference in the movement speed of electrons and lithium ions during high current discharge, and the resistance of the cell rises rapidly, resulting in a decrease in output. have.

Accordingly, the problem to be solved by the present invention is to provide an electrode and an electrochemical device comprising the same that can achieve the output improvement of the electrochemical device at high current discharge.

In order to solve the above problems, according to an aspect of the present invention, the electrode current collector; A first electrode active material layer including a first electrode active material, a first binder, and a first conductive material, and formed on at least one surface of the electrode current collector; And a second electrode active material layer including a second electrode active material, a second binder, and a second conductive material, and formed on an upper surface of the first electrode active material layer. An electrode is characterized in that the content 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 higher than the content of the first conductive material in the first electrode active material layer. This is provided.

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, the content of the second conductive material may be 0.1 to 10% by weight relative to the total weight of the second electrode active material layer.

Preferably, the ratio of the thickness of the first electrode active material layer and 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 positive electrode, 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 oxide is 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 It may be one or a mixture of two or more thereof.

Preferably, the electrode is a negative electrode, and the first electrode active material and the second electrode active material may each independently be any one selected from the group consisting of lithium metal, carbon material and 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, Mg, Sr and Ba. It may be any one selected or a mixture of two or more thereof.

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, and organic conductive material It may be a mixture of two or more kinds.

In addition, according to an aspect of the present invention, an electrode assembly including a positive electrode, a negative electrode and a separator interposed between the positive electrode and the negative electrode; A nonaqueous electrolyte solution for impregnating the electrode assembly; And a battery case incorporating the electrode assembly and the nonaqueous electrolyte solution, wherein at least one of the positive electrode and the negative electrode is an electrode as described above.

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

The organic solvent is ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3 Pentylene carbonate, vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methylpropyl Carbonate, ethylpropyl carbonate, dimethyl ether, diethyl ether, dipropyl ether, methylethyl ether, methylpropyl ether, ethylpropyl ether, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl prop With cypionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone and ε-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 -, It may comprise any one selected from the group consisting of SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- or two or more thereof.

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 relatively high current discharge.

The following drawings, which are attached to this specification, illustrate exemplary embodiments of the present invention, and together with the contents of the present invention serve to further understand the technical spirit of the present invention, the present invention is limited to the matters described in such drawings. It should not be construed as limited.
1 is a graph showing the results of analyzing the resistance through the EIS of the battery according to the embodiment and the comparative example of the present invention.

Hereinafter, the present invention will be described in detail with reference to the drawings. The terms or words used in this specification and claims are not to be construed as limiting in their usual or dictionary meanings, and the inventors may appropriately define the concept of terms in order to best explain their invention in the best way possible. It should be interpreted as meaning and concept corresponding to the technical idea of the present invention based on the principle that the present invention.

Accordingly, the embodiments described in the specification and the drawings described in the drawings are only the most preferred embodiments of the present invention, and do not represent all of the technical idea of the present invention. It should be understood that there may be equivalents and variations.

Electrode according to the present invention, the electrode current collector; A first electrode active material layer including a first electrode active material, a first binder, and a first conductive material, and formed on at least one surface of the electrode current collector; And a second electrode active material layer including a second electrode active material, a second binder, and a second conductive material, and formed on an upper surface of the first electrode active material layer. The content 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, an electrode active material slurry in which electrode active material particles are dispersed is applied to an electrode current collector as a single layer to form an electrode. In this case, a resistance is generated due to a difference in the moving speed of electrons and lithium ions during a high current discharge of 10C or higher. There was a problem affecting. However, according to the present invention, by biasing the conductive material of the electrode to one side, it is possible to reduce the resistance due to the movement of electrons during high current discharge and to improve the output of the electrochemical device.

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 may be 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 may be 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 second electrode active material layer may be 20:80 to 80:20.

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

According to an embodiment of the present invention, the electrode is a positive electrode, 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 oxide is 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 It may be any one selected from or a mixture of two or more thereof, and the lithium-containing transition metal oxide may be coated with a metal or metal oxide such as aluminum (Al). In addition to the lithium-containing transition metal oxides, sulfides, selenides, and halides may also be used.

According to an embodiment of the present invention, the electrode is a negative electrode, and the first electrode active material and the second electrode active material are each independently any one selected from the group consisting of lithium metal, carbon material and metal compound or two of them. It may be a mixture of species or more.

Specifically, as the carbon material, both low crystalline carbon and high crystalline carbon may be used. Soft crystalline carbon and hard carbon are typical low crystalline carbon, and high crystalline carbon is natural graphite, Kish graphite, pyrolytic carbon, liquid crystal pitch-based carbon fiber. High temperature calcined carbon such as (mesophase pitch based carbon fiber), meso-carbon microbeads, Mesophase pitches and petroleum or coal tar pitch derived cokes.

As the metal compound, metal elements such as Si, Ge, Sn, Pb, P, Sb, Bi, Al, Ga, In, Ti, Mn, Fe, Co, Ni, Cu, Zn, Ag, Mg, Sr, Ba, etc. The compound containing 1 or more types is mentioned. These metal compounds can be used in any form, such as simple materials, alloys, oxides (TiO 2, SnO 2, etc.), nitrides, sulfides, borides, and alloys with lithium, but alloys with simple materials, alloys, oxides, and lithium may become high in capacity. Can be. Among them, one or more elements selected from Si, Ge, and Sn may be contained, and one or more elements selected from Si and Sn may further increase the capacity of the battery.

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, etc., and are currently commercially available as conductive materials. Products include acetylene black series (Chevron Chemical Company or Gulf Oil Company), Ketjen Black EC series (Armak Company), Vulcan XC-72 (manufactured by Cabot Company) and Super P (manufactured by MMM).

As the first binder and the second binder, a binder that is commonly used may be used without limitation. For example, polyvinylidene fluoride-hexafluorofluoropropylene (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate Various kinds of binders may be used, such as (polymethyl methacrylate), styrene-butadiene rubber (SBR), and carboxyl methyl cellulose (CMC).

The current collector used for the positive electrode and the negative electrode is a metal having high conductivity, and may be any metal as long as it is a metal to which the electrode active material slurry can easily adhere and is not reactive in the voltage range of the electrochemical device. Specifically, a non-limiting example of a positive electrode current collector is a foil prepared by aluminum, nickel or a combination thereof, and a non-limiting example of a negative electrode current collector is copper, gold, nickel or a copper alloy or a combination thereof There is a foil produced by. In addition, the current collector may be used by stacking substrates made of the 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 types of electrode active material slurry with different contents of the conductive material, and then, each electrode active material slurry is formed into two layers on the current collector. After coating, drying, and press molding, the mixture may be prepared by heat treatment under vacuum at a temperature of about 50 to 250 ° C. for about 2 hours.

In addition, according to one embodiment of the present invention, an electrode assembly including a positive electrode, a negative electrode and a separator interposed between the positive electrode and the negative electrode; A nonaqueous electrolyte solution for impregnating the electrode assembly; And a battery case incorporating the electrode assembly and the nonaqueous electrolyte solution, 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 may be used as long as it is a porous substrate used in an electrochemical device. For example, a polyolefin-based porous membrane or a nonwoven fabric may be used, but is not particularly limited thereto.

Examples of the polyolefin-based porous membrane, polyolefin-based polymers such as polyethylene, polypropylene, polybutylene, polypentene, such as high density polyethylene, linear low density polyethylene, low density polyethylene, ultra high molecular weight polyethylene, respectively, or a mixture thereof One membrane may be mentioned.

The nonwoven fabric may be, for example, polyethylene terephthalate, polybutyleneterephthalate, polyester, polyacetal, polyamide, polycarbonate, or polycarbonate. ), Polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfide, polyethylenenaphthalene, etc., alone or separately The nonwoven fabric formed from the polymer which mixed these is mentioned. The structure of the nonwoven can be a spunbond nonwoven or melt blown nonwoven 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 pore 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 suppress the short circuit between the positive electrode and the negative electrode, a porous coating layer including inorganic particles and a polymer binder may be further included on at least one surface of the porous substrate.

In the porous coating layer, the polymer binder is attached to each other (that is, the polymer binder is connected and fixed between the inorganic particles) so that the inorganic particles are bound to each other, and the porous coating layer is bound to the porous substrate by the polymer binder. Stay intact. The inorganic particles of the porous coating layer are present in the closest-filled structure substantially in contact with each other, and the interstitial volume generated when the inorganic particles are in contact with each other becomes 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 inorganic particles are not oxidized and / or reduced in the operating voltage range (for example, 0 to 5 V on the basis of Li / Li ⁺ ). In particular, in the case of using the inorganic particles having the ion transport ability, it is possible to improve the performance by increasing the ion conductivity in the electrochemical device.

In addition, when inorganic particles having a high dielectric constant are used as the inorganic particles, the ionic conductivity of the electrolyte may be improved by contributing to an increase in the dissociation degree of the electrolyte salt such as lithium salt in the liquid electrolyte.

For the foregoing reasons, the inorganic particles may include high dielectric constant inorganic particles having a dielectric constant of 5 or more, or 10 or more, inorganic particles having a lithium ion transfer 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), (1-x) Pb (Mg _1/3 Nb _2/3 ) O ₃ -xPbTiO ₃ (PMN-PT, where 0 < 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 Etc. can be used individually or in mixture of 2 or more types, respectively.

In particular, 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), (1-x) Pb (Mg _1/3 Nb _2/3 ) O _{3 - x} PbTiO ₃ (PMN-PT, where 0 <x <1), hafnia ( Inorganic particles such as HfO ₂ ) not only exhibit high dielectric constants with a dielectric constant greater than 100, but also have piezoelectricity in which electric charges are generated when a tension or tension is applied under a constant pressure, thereby causing a potential difference between both surfaces. The occurrence of internal short circuit of the positive electrode due to the impact can be prevented and the safety of the electrochemical device can be improved. In addition, synergistic effects of the high dielectric constant inorganic particles and the inorganic particles having lithium ion transfer ability may be doubled.

The inorganic particles having a lithium ion transfer capacity refers to inorganic particles containing lithium elements but having a function of transferring lithium ions without storing lithium, and the inorganic particles having lithium ion transfer ability are present in the particle structure. Since the lithium ions can be transferred and moved due to a kind of defect, the lithium ion conductivity in the battery is improved, thereby improving battery performance. Non-limiting examples of the inorganic particles having a lithium ion transfer capacity is lithium phosphate (Li ₃ PO ₄ ), lithium titanium phosphate (Li _x Ti _y (PO ₄ ) ₃ , 0 <x <2, 0 <y <3) , Lithium aluminum titanium phosphate (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 (LiAlTiP) _x O _y series glass such as 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 _{3 . 25} Ge _{0 .25} P _{0. 75} S ₄ Lithium germanium thiophosphate 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, etc. SiS ₂ series glasses (Li _x Si _y S _z , 0 <x <3) such as Ride (Li _x N _y , 0 <x <4, 0 <y <2), Li ₃ PO ₄ -Li ₂ S-SiS _2, etc. P ₂ S ₅ series glasses (Li _x P _y S _z , 0 <x <3, 0 <y <3), 0 <y <2, 0 <z <4, and LiI-Li ₂ SP ₂ S ₅ 0 <z <7) or mixtures thereof.

As the polymer binder used for forming the porous coating layer, a polymer commonly used in forming a porous coating layer in the art may be used.

Non-limiting examples of such polymeric binders include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, and polyvinylidene fluoride-co-hexafluoropropylene. Methyl methacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, ethylene vinyl acetate copolymer (polyethylene-co- vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullul Cyanoethylpullulan, cyanoethylpolybi Cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan and carboxyl methyl cellulose.

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

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

Meanwhile, the nonaqueous electrolyte may include an organic solvent and an electrolyte salt, and the electrolyte salt is a lithium salt. The lithium salt may be used without limitation those conventionally used in the non-aqueous electrolyte 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 -, It may comprise any one selected from the group consisting of SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- or two or more thereof.

In addition, as the organic solvent included in the nonaqueous electrolyte solution described above, those conventionally used in the nonaqueous electrolyte solution for a lithium secondary battery may be used without limitation. It can mix and use 2 or more types.

Among them, carbonate compounds which are typically cyclic carbonates, linear carbonates, or mixtures 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, 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate and any one selected from the group consisting of halides thereof or mixtures of two or more thereof. These halides include, for example, fluoroethylene carbonate (FEC), but are not limited thereto.

In addition, specific examples of the linear carbonate compound may be any one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methylpropyl carbonate and ethylpropyl carbonate. Mixtures of two or more of them may be representatively used, but are not limited thereto.

In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates among the carbonate-based organic solvents, are high viscosity organic solvents and have a high dielectric constant, which may dissociate lithium salts in the electrolyte more effectively. By using a low viscosity, low dielectric constant linear carbonate mixed in an appropriate ratio it can be made an electrolyte having a higher electrical conductivity.

In addition, as the ether in the organic solvent, any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methylethyl ether, methylpropyl ether, and ethylpropyl ether, or a mixture of two or more thereof may be used. It is not limited to this.

And esters in the organic solvent include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ Any one or a mixture of two or more selected from the group consisting of -valerolactone and ε-caprolactone may be used, but is not limited thereto.

The injection of the nonaqueous electrolyte may be performed at an appropriate step in the manufacturing process of the electrochemical device, depending on the manufacturing process and the required physical properties of the final product. That is, it may be applied before the electrochemical device assembly or the final step of the electrochemical device assembly.

In this case, the electrochemical device includes all devices that undergo an electrochemical reaction, and specific examples thereof include capacitors such as all kinds of secondary batteries, fuel cells, solar cells, or super capacitor devices. In particular, 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 secondary batteries is preferable.

Hereinafter, the present invention will be described in detail with reference to Examples. However, embodiments according to the present invention can be modified in many different forms, the scope of the present invention should not be construed as limited to the embodiments described below. Embodiments of the present invention are provided to more fully explain the present invention to those skilled in the art.

Example

(1) manufacture of positive electrode

As a positive electrode active material, 93.5% by weight of Li (NiCoMn) O ₂ , 4.5% by weight of carbon black (conductive agent), and 2% by weight of PVdF (binder) were added to NMP (N-methyl-2-pyrrolidone) as a solvent. A positive electrode active material slurry was prepared.

96.5% by weight of Li (NiCoMn) O ₂ , 1.5% by weight of carbon black (conductor), and 2% by weight of PVdF (binder) were added to NMP (N-methyl-2-pyrrolidone) as a positive electrode active material. A positive electrode active material slurry was prepared.

The first positive electrode active material slurry was first coated on aluminum foil with a loading amount of 240 mg / 25 cm ² and then vacuum dried. Then, the second positive electrode active material slurry was coated with the same loading amount.

(2) Preparation of Cathode

As the negative electrode active material, natural graphite was used, and 96.1% by weight of natural graphite, 1% by weight of Super-P (conductor), 2.2% by weight of SBR (binder), and 0.7% of CMC were added to water as a solvent to prepare a negative electrode active material slurry. After the preparation, the negative electrode was prepared by coating, drying and pressing on copper foil once.

(3) Preparation of separator

Polypropylene was uniaxially stretched using a dry method to prepare a separator having a microporous structure having a melting point of 165 ° C and a width of one side of 200 mm.

(4) lithium secondary battery manufacturing

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

Comparative example

As the cathode active material, 95% by weight of Li (NiCoMn) O ₂ , 3% by weight of carbon black (conductor), and 2% by weight of PVdF (binder) were added to NMP (N-methyl-2-pyrrolidone), a solvent, to form a cathode active material. A slurry was prepared, and a battery was manufactured in the same manner as in Example, except that the cathode active material slurry was coated on aluminum foil with a loading amount of 480 mg / 25 cm ² and then vacuum dried to prepare a cathode.

EIS Resistance Comparison

The battery according to the Examples and Comparative Examples was analyzed for resistance through the EIS, and the measured results are shown in FIG. 1. Electrochemical impedance spectroscopy (EIS) measurement is a method of calculating the resistance by applying an 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 above description is merely illustrative of the technical idea of the present invention, and those skilled in the art to which the present invention pertains may make various modifications and changes without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention but to describe 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 interpreted by the following claims, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of the present invention.

Claims (15)

Electrode current collectors;
A first electrode active material layer including a first electrode active material, a first binder, and a first conductive material, and formed on at least one surface of the electrode current collector; And
And a second electrode active material layer including a second electrode active material, a second binder, and a second conductive material, and formed on an upper surface of the first electrode active material layer.
The first electrode active material and the second electrode active material are the same, and 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),
Each of the first binder and the second binder is polyvinylidene fluoride,
Each of the first conductive material and the second conductive material is carbon black,
The specific surface area of each of the first electrode active material layer and the second electrode active material layer is 0.1 to 3.0 m ² / g,
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,
The content of the first conductive material is 0.1 to 8% by weight based on the total weight of the first electrode active material layer, the content of the second conductive material is 0.1 to 8% by weight relative to the total weight of the second electrode active material layer,
The ratio of the thickness of the first electrode active material layer and the second electrode active material layer is an electrode, characterized in that 20:80 to 80:20.
The method of claim 1,
The content of the first conductive material is an electrode, characterized in that three times the content of the second conductive material by weight. delete delete delete delete delete delete delete delete An electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode;
A nonaqueous electrolyte solution for impregnating the electrode assembly; And
Includes; a battery case containing the electrode assembly and the non-aqueous electrolyte;
Electrochemical device wherein the anode is the electrode of claim 1. The method of claim 11,
The non-aqueous electrolyte, the electrochemical device comprising an organic solvent and an electrolyte salt. The method of claim 12,
The organic solvent is ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3 Pentylene carbonate, vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methylpropyl Carbonate, ethylpropyl carbonate, dimethyl ether, diethyl ether, dipropyl ether, methylethyl ether, methylpropyl ether, ethylpropyl ether, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl prop With cypionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone and ε-caprolactone The electrochemical device according to claim any one or a mixture of two or more of those selected from the group true luer. 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 -, An electrochemical device comprising any one selected from the group consisting of SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- or two or more thereof. The method of claim 11,
The electrochemical device is an electrochemical device, characterized in that the lithium secondary battery.

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