KR20150029054A - Electrode of Improved Electrolyte Wetting Property and Lithium Secondary Battery Comprising the Same - Google Patents

Abstract

The present invention relates to an electrode having improved electrolyte impregnating property and a lithium secondary battery comprising the same. More specifically, provided is an electrode which comprises a first electrode mixture layer coated on the surface of a current collector and a second electrode mixture layer coated on the first electrode mixture layer, wherein the first electrode mixture layer comprises a first electrode active material, and the second electrode mixture layer comprises a second electrode active material; the first electrode active material and the second electrode active material are formed by particles of different composition having different diameters (D50), or particles of same composition having different diameters (D50); and the diameter of the first electrode active material is in the size range of 5 to 50% based on the diameter of the second electrode active material; and a lithium secondary battery comprising the same.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode having improved electrolyte impregnability and a lithium secondary battery including the electrode.

The present invention relates to an electrode having improved electrolyte impregnability and a lithium secondary battery comprising the same, and more particularly, to a lithium secondary battery comprising a first electrode mixture layer coated on a surface of a current collector and a second electrode mixture layer coated on the first electrode mixture layer A second electrode mixture layer; Wherein the first electrode material mixture layer comprises a first electrode active material and the second electrode material mixture layer comprises a second electrode active material; The first electrode active material and the second electrode active material may be composed of particles having different particle diameters (D50) or particles of the same composition having different particle diameters (D50); And the particle size of the first electrode active material ranges from 5 to 50% based on the particle diameter of the second electrode active material, and a lithium secondary battery comprising the electrode.

As technology development and demand for mobile devices have increased, the demand for secondary batteries as energy sources is rapidly increasing. In recent years, the use of secondary batteries as a power source for electric vehicles (EV) and hybrid electric vehicles (HEV) Among such secondary batteries, there is a high demand for a lithium secondary battery having a high energy density, a high discharge voltage and an output stability.

The lithium secondary battery is manufactured by using a metal oxide such as LiCoO ₂ as a cathode active material and a carbon material as a negative electrode active material and a polyolefin porous separator between the anode and the cathode and a nonaqueous electrolytic solution containing a lithium salt such as LiPF ₆ . During charging, the lithium ions of the positive electrode active material are released and inserted into the carbon layer of the negative electrode. In discharging, lithium ions of the negative electrode carbon layer are released and inserted into the positive electrode active material, And serves as a medium for transferring ions. Such a lithium secondary battery should basically be stable in the operating voltage range of the battery, and have a capability of transferring ions at a sufficiently high speed.

The nonaqueous electrolyte solution is injected into the battery at the final stage of the lithium secondary battery manufacturing process. At this time, the electrode is quickly and completely wetted by the electrolyte solution, so that the time required for manufacturing the battery can be shortened and battery performance can be optimized.

However, as the non-aqueous electrolyte of the lithium secondary battery, a non-protonic organic solvent such as ethylene carbonate, ethyl carbonate, or 2-methyltetrahydrofuran is generally used. Such an electrolyte is a polar solvent having a polarity sufficient to dissolve and dissociate the electrolyte salt Is an aprotic solvent that does not have active hydrogens and often has high viscosity and surface tension due to extensive interactions within the electrolyte. Therefore, the non-aqueous electrolytic solution of the lithium secondary battery has a low affinity with the electrode material including the polytetrafluoroethylene and the polyvinylidene fluoride binder or the like, so that the electrode material can not be easily wetted.

In addition, when the electrode material including the electrode active material and the organic compound is coated on the current collector for drying the electrode, the electrode active material having a relatively small particle size rises up to the coated surface during the drying process do.

In this regard, FIG. 1 schematically shows a single-layered electrode 10 coated with a conventional electrode active material. Referring to FIG. 1, an electrode mixture layer 14 including relatively small particles 16 and large particles 18 is coated on the upper surface of the collector 12. The small particles 16 are concentrated on the upper portion of the electrode 10 due to the upward movement of the small particles 16 in the drying process, It is distributed in the lower part. Therefore, the upper portion of the electrode 10 has a porosity lower than that of the bottom portion, which makes it more difficult to uniformly penetrate the electrolyte into the electrode 10.

If the electrolyte does not sufficiently wet the surface of the active material constituting the electrode due to the above-mentioned phenomenon, the delivery path of the lithium ions is limited, causing problems such as deterioration of the rate characteristic and capacity reduction, and contact between the active materials The resistance is increased and the output characteristic is also reduced.

Therefore, there is a high need for a technique for improving the performance of the battery by increasing the impregnation property of the electrode with respect to the electrolyte solution.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-described problems of the prior art and the technical problems required from the past.

The inventors of the present application have conducted intensive research and various experiments,

It has been confirmed that the performance of the secondary battery including the active material particles having the different particle diameter D50 is improved by impregnating the electrode with the electrolytic solution when the electrode is manufactured by arranging the active material particles having a different particle size D50 in a two- It came.

According to an aspect of the present invention, there is provided an electrode comprising a first electrode compound layer coated on a surface of a current collector and a second electrode compound layer coated on the first electrode compound layer;

Wherein the first electrode material mixture layer comprises a first electrode active material and the second electrode material mixture layer comprises a second electrode active material;

The first electrode active material and the second electrode active material may be composed of particles having different particle diameters (D50) or particles of the same composition having different particle diameters (D50);

The particle size of the first electrode active material ranges from 5 to 50% based on the particle diameter of the second electrode active material.

The inventors of the present application have found that when an electrode mixture is coated on a current collector for the production of an electrode and dried, the electrode active material having a small particle size during drying rises above the coated surface, and the porosity of the upper portion of the electrode is lowered, The present inventors have recognized that there is a problem that they are not uniformly penetrated into the electrodes and that the above problems can be solved in the case where electrodes are manufactured by double coating an active material having different particle sizes after an in-depth study.

Therefore, as described above, the electrode according to the present invention is characterized in that the particle size of the first electrode active material is always smaller than the particles of the second electrode active material in a size range of 5 to 50% based on the particle diameter of the second electrode active material (D50) ratio of the first electrode active material and the second electrode active material may be in the range of 1: 9 to 4: 5.

If the particle diameter of the second electrode active material is smaller than or equal to the particle diameter of the first electrode active material, impregnation of the electrolyte up to the first electrode mixture layer including the first electrode active material is not easy.

In this structure, the electrolyte impregnation property is proportional to the porosity of the second electrode material mixture layer. In one specific example, the porosity of the second electrode material mixture layer may be 10% to 70%.

When the porosity of the second electrode material mixture layer is 10% or less, it is difficult to uniformly penetrate into the particles due to viscosity and surface tension of the electrolyte. When the porosity of the second electrode material mixture layer is 70% or more, the electrode density is lowered, .

On the other hand, it is preferable that the first electrode material mixture layer has lower porosity and higher electrode density than the second electrode material mixture layer in order to lower the contact resistance by smooth movement of electrons and to increase the energy density of the whole electrode.

In one specific example, the electrode density of the second electrode active material may range from 5% to 95% of the electrode density of the first electrode active material, and the porosity of the first electrode material mixture layer may be in the range of 5% May range from 5% to 95%.

As a result, the second electrode material mixture layer at the upper part of the electrode can maintain the porosity at a high level by using the active material having a large particle diameter, so that the electrolyte impregnation property into the electrode can be enhanced. On the other hand, It is possible to make the porosity small and increase the electrode density by using the active material having a small particle size, thereby improving the electrolyte impregnability and increasing the energy density. Therefore, the capacity and output characteristic of the secondary battery including the electrode of the present invention , The charge / discharge speed, and the like can be improved.

It is preferable that the first electrode material mixture layer is thinner than the second electrode material mixture layer. The thickness ratio of the first electrode material mixture layer and the second electrode material mixture layer may be 1: 9 to 4: 6. If the first electrode material mixture layer is too thick and out of the above range, the electrode active material may not come into contact with the current collector in the first electrode material mixture layer, and may rise upward.

The overall structure of the electrode including the first electrode mix layer and the second electrode mix layer according to the present invention is such that, in one specific example, at the interface between the first electrode mix layer and the second electrode mix layer, The particles and the second electrode active material particles may be a structure that forms a perfect interface without being mixed with each other.

In another specific example, a portion of the first electrode active material particles is introduced into the second mixture layer at a contact surface of the first and second mixture layers to form a concentration gradient of the first electrode active material particles .

The present invention also provides a method of manufacturing an electrode according to the above description.

A method of manufacturing the electrode,

(a) fabricating a second electrode mixture comprising a first electrode mixture comprising a first electrode active material and a second electrode active material;

(b) forming a first electrode material mixture layer by applying a first electrode material mixture onto a surface of an electrode collector and drying the first electrode material mixture;

(c) applying a second electrode mixture onto the surface of the first electrode material mixture layer and then drying to form a second electrode material mixture layer;

.

At this time, the first electrode active material and the second electrode active material are composed of particles having different particle diameters (D50) regardless of the composition. That is, they may be composed of particles having different compositions or particles having the same composition.

The electrode according to the present invention can be applied to both the positive electrode and the negative electrode.

When the electrode is an anode, the first electrode mixture layer and the second electrode mixture layer coated on the surface of the cathode current collector are a mixture of the first electrode active material, the second electrode active material, the conductive material, and the binder If necessary, the mixture may further contain a filler.

The cathode active material may be a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; Lithium manganese oxides such as Li _{1 + x} Mn _{2 -x} O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ and the like; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ and Cu ₂ V ₂ O ₇ ; A Ni-site type lithium nickel oxide expressed by the formula LiNi _1-x M _x O ₂ (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga and x = 0.01 to 0.3); Formula _{LiMn 2-x M x O 2} ( where, M = Co, Ni, Fe , Cr, and Zn, or Ta, x = 0.01 ~ 0.1 Im) or Li ₂ Mn ₃ MO ₈ (where, M = Fe, Co, Ni, Cu, or Zn); A lithium manganese composite oxide having a spinel structure represented by LiNi _x Mn _2-x O ₄ ; LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with an alkaline earth metal ion; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ , and the like. However, the present invention is not limited to these.

At this time, the types of the first electrode active material and the second electrode active material may be the same or different.

The cathode current collector generally has a thickness of 3 to 500 mu m. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. Examples of the positive electrode current collector include stainless steel, aluminum, nickel, titanium, sintered carbon, aluminum or stainless steel A surface treated with carbon, nickel, titanium, silver or the like may be used. The current collector may have fine irregularities on the surface thereof to increase the adhesive force of the cathode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric are possible.

The conductive material is usually added in an amount of 1 to 30% by weight based on the total weight of the mixture including the cathode active material. Such a conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, for example, graphite such as natural graphite or artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The binder is a component which assists in bonding of the active material and the conductive material and bonding to the current collector, and is usually added in an amount of 1 to 30% by weight based on the total weight of the mixture containing the cathode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers and the like.

The filler is optionally used as a component for suppressing the expansion of the anode, and is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery. Examples of the filler include olefin polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

When the electrode is a negative electrode, the first electrode mixture layer and the second electrode mixture layer coated on the surface of the negative electrode collector include the first electrode active material and the second electrode active material as the negative electrode active material, A binder, a filler, and the like as in the first embodiment.

The negative electrode active material may include, for example, carbon such as non-graphitized carbon or graphite carbon; _{Li x Fe 2 O 3 (0≤x≤1} ), Li x WO 2 (0≤x≤1), Sn x Me 1-x Me 'y O z (Me: Mn, Fe, Pb, Ge; Me' : Metal complex oxides such as Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, Halogen, 0 < x < Lithium metal; Lithium alloy; Silicon-based alloys; Tin alloy; _{SnO, SnO 2, PbO, PbO} 2, Pb 2 O 3, Pb 3 O 4, Sb 2 O 3, Sb 2 O 4, Sb 2 O 5, GeO, GeO 2, Bi 2 O 3, Bi 2 O 4, and Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials; Titanium oxide; Lithium titanium oxide, and the like.

Also in the negative electrode active material, the first electrode active material and the second electrode active material may be the same kind or different.

The negative electrode current collector is generally made to have a thickness of 3 to 500 mu m. Such an anode current collector is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, and examples of the anode current collector include copper, stainless steel, aluminum, nickel, titanium, sintered carbon, a surface of copper or stainless steel A surface treated with carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used. In addition, like the positive electrode collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams and nonwoven fabrics.

The present invention also provides a lithium secondary battery comprising the electrode.

The lithium secondary battery may be composed of the positive electrode, the negative electrode, the separator, and the non-aqueous electrolyte containing a lithium salt, and may be manufactured by putting a porous separator between the positive electrode and the negative electrode by a conventional method known in the art, .

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

The separation membrane is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally 0.01 to 10 mu m and the thickness is generally 5 to 300 mu m. Such separation membranes include, for example, olefinic polymers such as polypropylene, which are chemically resistant and hydrophobic; A sheet or nonwoven fabric made of glass fiber, polyethylene or the like is used. When a solid electrolyte such as a polymer is used as an electrolyte, the solid electrolyte may also serve as a separation membrane.

The lithium salt-containing nonaqueous electrolyte is composed of a nonaqueous electrolyte and lithium. Nonaqueous organic solvents, organic solid electrolytes, inorganic solid electrolytes, and the like are used as the nonaqueous electrolyte, but the present invention is not limited thereto.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma -Butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane , Acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate Nonionic organic solvents such as tetrahydrofuran derivatives, ethers, methyl pyrophosphate, ethyl propionate and the like can be used.

Examples of the organic solid electrolyte include a polymer electrolyte such as a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, A polymer containing an ionic dissociation group and the like may be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides and sulfates of Li such as Li ₄ SiO ₄ -LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ can be used.

The lithium salt is a material that is readily soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO 4, LiBF 4, LiB 10 Cl 10, LiPF 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF _{6, LiSbF 6, LiAlCl 4,} CH 3 SO 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide.

For the purpose of improving the charge / discharge characteristics and the flame retardancy, the electrolytic solution is preferably mixed with an organic solvent such as pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, . In some cases, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further added to impart nonflammability. In order to improve the high-temperature storage characteristics, carbon dioxide gas may be further added. FEC (Fluoro-Ethylene Carbonate, PRS (Propene sultone), and the like.

In a preferred _{embodiment, LiPF 6, LiClO 4, LiBF} 4, LiN (SO 2 CF 3) 2 , such as a lithium salt, a highly dielectric solvent of DEC, DMC or EMC Fig solvent cyclic carbonate and a low viscosity of the EC or PC of And then adding it to a mixed solvent of linear carbonate to prepare a lithium salt-containing non-aqueous electrolyte.

The present invention also provides a battery pack comprising the lithium secondary battery as a unit battery, and the battery pack can be used in a vehicle requiring high capacity and output characteristics.

In one specific example, the vehicle includes an electric vehicle (EV); An electric vehicle including a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), and an extended range electric vehicle (EREV); And an electric motorcycle including an E-bike and an E-scooter.

As described above, the electrode according to the present invention comprises a first electrode mixture layer containing a first electrode active material having a relatively small particle diameter and a second electrode mixture layer containing a second electrode active material having a relatively large particle diameter, The porosity of the upper portion of the electrode can be maintained at a high level, so that the impregnability of the electrolyte into the electrode can be enhanced. At the same time, the porosity at the lower portion of the electrode can be made small and the electrode density can be increased .

Further, the lithium secondary battery based thereon has an effect of improving battery performance such as capacity and output characteristics.

1 is a schematic view of a single-layer electrode having a conventional electrode active material coated thereon;
2 is a schematic diagram of an electrode according to one specific example of the present invention;
3 is a schematic view of an electrode according to another specific example of the present invention.

Hereinafter, the present invention will be described with reference to the drawings, but the present invention is not limited by the scope of the present invention.

2 schematically shows an electrode 100 according to one specific example of the present invention.

2, the electrode 100 includes a first electrode mix layer 140 coated on the current collector 120 and a second electrode mix layer 142 coated on the first electrode mix layer 140 ). ≪ / RTI >

At this time, the first electrode mixture layer 140 includes the first electrode active material 161 having a relatively small particle size and the second electrode mixture layer 142 includes the second electrode active material 162 having a relatively large particle size. And the first electrode material mixture layer 140 and the second electrode material mixture layer 142 form an interface without being mixed with each other.

Fig. 3 schematically shows an electrode according to another specific example of the present invention.

3, the electrode 200 includes a first electrode material mixture layer 240 coated on the current collector 220 and a second electrode material mixture layer 242 coated on the first electrode material mixture layer 240 , The first electrode material mixture layer 240 includes a relatively small particle first electrode active material 260 and the second electrode material mixture layer 242 includes a relatively large particle material Electrode active material 162. The two-

Unlike the electrode 100 of FIG. 2, the lower portion of the second electrode compound layer 242 may be formed of a portion 260a of the first electrode compound layer 240 on the basis of the imaginary step line A-A ' ) Are introduced and incorporated.

As a result, the first electrode material mixture layer 240 exhibits lower and upper grain concentration gradients with respect to the virtual step line A-A ', and the porosity of the first electrode material mixture layer 240 is further secured .

Although the electrodes 100 and 200 according to FIGS. 2 and 3 are slightly different in configuration, since the porosity of the upper portion of each of the two electrodes 100 and 200 is relatively large, can do.

Those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims (13)

A first electrode material mixture layer applied on the surface of the current collector and a second electrode material mixture layer coated on the first electrode material mixture layer;
Wherein the first electrode material mixture layer comprises a first electrode active material and the second electrode material mixture layer comprises a second electrode active material;
The first electrode active material and the second electrode active material may be composed of particles having different particle diameters (D50) or particles of the same composition having different particle diameters (D50);
Wherein a particle diameter of the first electrode active material ranges from 5 to 50% based on a particle diameter of the second electrode active material. The electrode according to claim 1, wherein the first electrode active material particles and the second electrode active material particles are not mixed with each other at an interface between the first and second mixture layers. The method according to claim 1, wherein a part of the first electrode active material particles is introduced into the second mixture layer at a contact surface of the first mixture layer and the second mixture layer to form a concentration gradient of the first electrode active material particles Characterized by the electrodes. The electrode according to claim 1, wherein the ratio of the particle diameter (D50) of the first electrode active material and the second electrode active material ranges from 1: 9 to 4: 5. The electrode according to claim 1, wherein the first electrode material mixture layer and the second electrode material mixture layer are applied in a thickness ratio of 1: 9 to 4: 6. The electrode according to claim 1, wherein the porosity of the first electrode material mixture layer is 5% to 95% of the porosity of the second electrode material mixture layer. The electrode according to claim 1, wherein the porosity of the second electrode material mixture layer is 10% to 70%. The electrode according to claim 1, wherein an electrode density of the second electrode active material is 5% to 95% of an electrode density of the first electrode active material. A method of manufacturing an electrode according to claim 1,
(a) fabricating a second electrode mixture comprising a first electrode mixture comprising a first electrode active material and a second electrode active material;
(b) forming a first electrode material mixture layer by applying a first electrode material mixture onto a surface of an electrode collector and drying the first electrode material mixture;
(c) applying a second electrode mixture onto the surface of the first electrode material mixture layer and then drying to form a second electrode material mixture layer;
Wherein the electrode is made of a metal. A lithium secondary battery comprising the electrode according to claim 1. A battery pack comprising a lithium secondary battery according to claim 10 as a unit battery. A vehicle comprising the battery pack according to claim 11. The system of claim 12, wherein the vehicle is an electric vehicle (EV); An electric vehicle including a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), and an extended range electric vehicle (EREV); And an electric motorcycle including an E-bike and an E-scooter.

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