KR20130117222A - Electrode having enhanced adhesive force and lithium secondary battery comprising the same - Google Patents

Abstract

PURPOSE: An electrode with an improved adhesive force and a lithium secondary battery including the same are provided to remarkably improve an adhesive force between an electrode current collecting body and electrode slurry as considerable binders of the electrode are arranged near to the electrode current collecting body and to reduce resistance by reducing the amount of the unnecessary binders inside an electrode compound. CONSTITUTION: Electrode slurry is made by mixing an electrode compound including electrode activating materials and binders into an organic solvent. An electrode is obtained by spreading the electrode slurry on an electrode current collecting body. The amount of the binders which are melt at a temperature range of a -5 to 40°C and dispersed on the electrode current collecting body and a lower layer of an electrode slurry coating layer adjacent to the electrode current collecting body is 50 wt% or greater in respect to the weight of the whole binders. A melting point of the binder is 100-250 °C or less. The binder includes two or more kinds of binders of which the melting points are different.

Description

Electrode Having Enhanced Adhesive Force and Lithium Secondary Battery Comprising The Same

The present invention relates to an electrode having improved adhesion and a lithium secondary battery including the same, and more particularly, to apply an electrode slurry prepared by mixing an electrode mixture including an electrode active material and a binder to an organic solvent on an electrode current collector. As an electrode, a binder (melt binder) that is melted in the temperature range of −5 ° C. to + 40 ° C. of the melting point of the binder and distributed on the electrode current collector and under the electrode slurry coating adjacent to the electrode current collector. The amount relates to an electrode and a lithium secondary battery comprising the same, which is 50% by weight or more based on the total weight of the binder.

The increase in the price of energy sources due to the depletion of fossil fuels, the increase of interest in environmental pollution, and the demand for environmentally friendly alternative energy sources are becoming indispensable factors for future life. Various researches on power generation technologies such as nuclear power, solar power, wind power, and tidal power have been continuing, and electric power storage devices for more efficient use of such generated energy have also been attracting much attention.

Particularly, in the case of a lithium secondary battery, the demand for an energy source is rapidly increasing due to an increase in technology development and demand for a mobile device. Recently, the use of a lithium secondary battery as a power source for an electric vehicle (EV) and a hybrid electric vehicle , And the area of use is also expanding for applications such as power assisted power supply through gridization.

A binder is used for ensuring the adhesive force or binding force between an active material and an active material, and an active material and an electrical power collector, when constructing the electrode for lithium secondary batteries.

The adhesive force between the active material and the current collector may be lower than the adhesive force between the active material and the active material depending on the type of the binder, the active material, and the surface state of the current collector. In this case, in order to secure the adhesive force between the active material and the current collector, an excessive amount of binder is used as a whole. However, such an excess amount of binder may adversely affect the capacity and conductivity of the electrode.

Accordingly, there is a need for an electrode design capable of realizing effective adhesion and performance by differentiating the type and distribution of a binder between the active material and the active material, and the active material and the current collector.

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.

After extensive research and various experiments, the inventors of the present application increase the binding force between the electrode current collector and the electrode mixture layer when the binder included in the electrode mixture melts during the electrode drying process and is located close to the electrode current collector. It was confirmed that the binder content contained in the electrode mixture can be reduced, and the present invention has been completed.

Accordingly, the electrode according to the present invention is an electrode obtained by applying an electrode slurry formed by mixing an electrode mixture containing an electrode active material and a binder into an organic solvent on an electrode current collector, and the melting point of the binder is from -5 ° C to +40. The amount of the binder (melt binder) which melts in the temperature range of ° C and is distributed on the electrode current collector and under the electrode slurry coating adjacent to the electrode current collector is 50% by weight or more relative to the weight of the total binder.

In a specific embodiment of the present invention, the binder is a fluorine resin, polyolefin, styrene-butadiene rubber, carboxymethyl cellulose, mussel protein (dopamine), silane having a melting point in the range of 100 ℃ to 250 ℃ or less It may be selected from the group consisting of ethyl cellulose, methyl cellulose, hydroxypropyl cellulose, polyethylene glycol, polyvinyl alcohol, acrylic copolymer.

In some cases, the binder may include two or more binders having different melting points. In this case, the two or more binders will melt sequentially in the temperature range of -5 ° C to + 40 ° C of each melting point.

At this time, based on the height (H / 2) corresponding to 50% of the thickness (H) of the electrode slurry coating layer, a binder having a high melting point is distributed at least 50%, and a binder having a low melting point is at least 50% in the lower layer. It is preferable to distribute, and it is more preferable that the amount of binder of the lower layer is 100% or more with respect to the amount of binder of the upper layer.

Meanwhile, the two or more kinds of binders may be homogeneous or heterogeneous binders.

In a specific embodiment of the present invention, the electrode active material may be a lithium nickel manganese composite oxide as a positive electrode active material, the lithium nickel manganese composite oxide may be a lithium manganese oxide of the spinel structure represented by the formula (1).

Li _x M _y Mn _{2 - y} O _{4 - z z} (1)

Wherein 0 ≦ x ≦ 0.1; 0 <y ≦ 0.5; 0 ≦ z <0.2; M is a transition metal cation having an oxidation number of +2; A is an anion of oxidation number -1 or -2.

The spinel-structure lithium manganese oxide represented by Chemical Formula 1 is a part of manganese (Mn) that is substituted with a transition metal cation having an oxidation number of +2, and in a specific embodiment of the present invention, M is nickel (Ni) And the maximum substitution amount of nickel may be 0.5 mol%. In this case, the lithium manganese oxide represented by Chemical Formula 1 is LiNi _0.5 Mn _1.5 O ₄ .

Meanwhile, in Chemical Formula 1, the oxygen element may be partially substituted with an anion of -1 or -divalent oxidation number, and the maximum substitution amount may be less than 0.2 mol%. In a specific embodiment of the present invention, the anion is F, Cl It may be at least one anion selected from the group consisting of halogen, such as Br, I, S and N.

By substituting these anions, the binding force with the transition metal is improved and the structural transition of the compound is prevented, so that the lifetime of the battery can be improved. On the other hand, if the amount of substitution of the anion A is too large (t ≧ 0.2), it is not preferable because the life characteristics are lowered due to the incomplete crystal structure.

In another specific embodiment of the present invention, the electrode active material may include lithium titanium oxide represented by Formula 2 as a negative electrode active material.

Li _x Ti _y O ₄ (0.5≤x≤3; 1≤y≤2.5) (2)

For example, the negative electrode active material represented by Chemical Formula 2 may be Li _0.8 Ti _2.2 O ₄ , Li _2.67 Ti _1.33 O ₄ , LiTi ₂ O ₄ , Li _1.33 Ti _1.67 O ₄ , Li _1.14 Ti _1.71 O _4, or the like. It is not limited only to these.

More preferably, Li _1.33 Ti _1.67 O ₄ , which has a spinel structure with little change in crystal structure and excellent reversibility during charge and discharge, may be used.

The method for producing lithium titanium oxide represented by Chemical Formula 2 is well known in the art, for example, lithium and a lithium salt in a solution in which lithium salts such as lithium hydroxide, lithium oxide, lithium carbonate and the like are dissolved in water. According to the atomic ratio of titanium, titanium oxide or the like is added as a titanium source, followed by stirring and drying to prepare a precursor and then firing it.

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

The lithium secondary battery according to the present invention can be used not only in a battery cell used as a power source of a small device but also as a unit cell in a middle- or large-sized battery module including a plurality of battery cells.

Also, the present invention provides a battery pack including the battery module as a power source of a middle- or large-sized device, wherein the middle- or large-sized device is an electric vehicle (EV), a hybrid electric vehicle (HEV) An electric vehicle including a plug-in hybrid electric vehicle (PHEV), a power storage device, and the like, but the present invention is not limited thereto.

The structure of the battery module and the battery pack and the method of manufacturing the battery module and the battery pack are well known in the art, so a detailed description thereof will be omitted herein.

The present invention also provides a method of manufacturing the above electrode.

The manufacturing method may include applying an electrode slurry, which is formed by mixing an electrode mixture including an electrode active material and a binder with an organic solvent, onto an electrode current collector; And drying the electrode slurry coating layer by raising the temperature to a temperature range of −5 ° C. to + 40 ° C. of the melting point of the binder. .

When the binder includes two or more binders having different melting points, the melting point of the binder having the lowest melting point to the melting point of the binder having the highest melting point is -5 ° C to + 40 ° C based on the melting point of each binder. It is preferable to heat up sequentially to the temperature range of and dry an electrode slurry coating layer.

The structure of the battery module and the battery pack and the method of manufacturing the battery module and the battery pack are well known in the art, so a detailed description thereof will be omitted herein.

As described above, in the electrode according to the present invention, since the amount of the binder contained in the electrode mixture melts during the electrode drying process and is located close to the electrode current collector, the adhesion between the electrode current collector and the electrode slurry can be greatly improved, and the electrode The resistance can be reduced by reducing the amount of unnecessary binder in the mixture.

Therefore, in the lithium secondary battery including the electrode according to the present invention, both cycle characteristics and output characteristics are improved.

Hereinafter, the present invention will be described in detail with reference to the following examples. However, the following examples are intended to illustrate the present invention, and the scope of the present invention is not limited thereto.

In addition to the lithium manganese oxide of Chemical Formula 1, the positive electrode active material according to the present invention may further include other lithium-containing transition metal oxides.

Examples of the other lithium-containing transition metal oxides include layered compounds such as lithium cobalt oxide (LiCoO ₂ ) and lithium nickel oxide (LiNiO ₂ ), or compounds substituted with one or more transition metals; Lithium manganese oxides such as Li _{1 + y} Mn _2-y O ₄ (where y is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ and LiMnO ₂ ; 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 ; Formula _{LiNi 1-y M y O 2} ( where, the M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, y = 0.01 ~ 0.3 Im) Ni site type lithium nickel oxide which is represented by; Formula LiMn _2-y M _y O ₂ , wherein M = Co, Ni, Fe, Cr, Zn or Ta and y = 0.01 to 0.1, or Li ₂ Mn ₃ MO ₈ , where M = Fe, Co, Lithium manganese composite oxide represented by Ni, Cu or Zn); 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.

The positive electrode may be prepared by applying a slurry prepared by mixing a positive electrode mixture containing the positive electrode active material with a solvent such as NMP, coating the positive electrode collector, followed by drying and rolling.

In addition to the cathode active material, the cathode mixture may optionally include a conductive material, a binder, a filler, and the like.

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, and examples thereof include copper, stainless steel Surface-treated with carbon, nickel, titanium, silver or the like, aluminum-cadmium alloy, or the like can be used. The positive electrode current collector may be formed into various shapes such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven fabric, or the like by forming fine irregularities on the surface to enhance the bonding force of the positive electrode active material.

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 whiskeys 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 added to the binder in an amount of 1 to 30% by weight, based on the total weight of the mixture containing the cathode active material, as a component that assists in bonding between the active material and the conductive agent and bonding to the current collector. 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, and various copolymers.

The filler is optionally used as a component for suppressing 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-based polymerizers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

Typical examples of the dispersion include isopropyl alcohol, N-methyl pyrrolidone (NMP), and acetone.

The method of evenly applying the paste of the electrode material to the metal material can be selected from known methods or performed by a new suitable method in consideration of the properties of the material. For example, the paste can be uniformly dispersed by using a doctor blade or the like after being distributed on the current collector. In some cases, a method of performing the distribution and dispersion processes in a single process may be used. In addition, a die casting method, a comma coating method, a screen printing method, or the like may be used. Alternatively, the resin may be formed on a separate substrate, and then pressed or laminated by a pressing or laminating method. .

It is preferable that the paste applied on the metal plate is dried in a vacuum oven at 50 to 200 DEG C within one day.

The negative electrode may be formed by coating a negative electrode active material on a negative electrode collector and drying the negative electrode active material. If necessary, the negative electrode may further include components such as a conductive agent, a binder, and a filler as described above.

The negative electrode 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 conductivity without causing chemical change in the battery, and may be formed of a material such as copper, stainless steel, aluminum, nickel, titanium, fired carbon, 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 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 &lt; 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, Bi ₂ O ₅ and the like; Conductive polymers such as polyacetylene; Li-Co-Ni-based material, and the like.

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; Kraft paper and the like are used. Representative examples currently on the market include the Celgard ^R 2400, 2300 (from Hoechest Celanese Corp.), polypropylene separator (from Ube Industries Ltd. or Pall RAI), and polyethylene series (from Tonen or Entek).

In some cases, a gel polymer electrolyte may be coated on the separation membrane to increase the stability of the cell. Representative examples of such a gel polymer include polyethylene oxide, polyvinylidene fluoride, and polyacrylonitrile.

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 non-aqueous electrolyte is composed of a nonaqueous electrolyte and lithium. As the non-aqueous electrolyte, a non-aqueous electrolyte, a solid electrolyte, an inorganic solid electrolyte and the like are used.

Examples of the nonaqueous electrolyte include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate , Gamma -butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, Diethyl ether, formamide, dimethyl formamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane A non-protonic organic solvent such as an ether, a methyl pyrophosphate, or an ethyl propionate is used as the solvent, a sulfone, a methyl sulfolane, a 1,3-dimethyl-2-imidazolidinone, a propylene carbonate derivative, a tetrahydrofuran derivative, .

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, Polymers containing ionic dissociation groups, and the like can 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, sulfates, and the like of Li, such as Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ , and the like, may 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 3 Li, LiSCN, LiC (CF 3 SO 2) 3, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, 4-phenylborate, imide, and the like can be used.

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, in order to impart nonflammability, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further included, and in order to improve high temperature storage characteristics, a carbon dioxide gas may be further included, and fluoro-ethylene carbonate), propene sultone (PRS), and fluoro-propylene carbonate (FPC).

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 (14)

As an electrode which apply | coated the electrode slurry formed by mixing the electrode mixture containing an electrode active material and a binder to an organic solvent,
The amount of the binder (melt binder) that melts at a temperature range of -5 ° C to + 40 ° C of the melting point of the binder and is distributed on the electrode current collector and under the electrode slurry coating in proximity to the electrode current collector is the total binder. Electrode, characterized in that more than 50% by weight relative to the weight of. The electrode of claim 1, wherein the melting point of the binder is 100 ° C or more and 250 ° C or less. The method of claim 1, wherein the binder is a fluororesin, polyolefin, styrene-butadiene rubber, carboxy methyl cellulose, mussel protein (dopamine), silane, ethyl cellulose, methyl cellulose, hydroxypropyl cellulose, polyethylene glycol, Electrode, characterized in that selected from the group consisting of polyvinyl alcohol, acrylic copolymer. The electrode of claim 1, wherein the binder includes two or more binders having different melting points. The electrode of claim 4, wherein the two or more binders are sequentially melted at a temperature range of −5 ° C. to + 40 ° C. of each melting point. The binder according to claim 4, wherein a binder having a high melting point is distributed at least 50% in the upper layer, and a binder having a low melting point in the lower layer, based on a height (H / 2) corresponding to 50% of the thickness (H) of the electrode slurry coating layer. Electrode, characterized in that more than 50% distribution. The electrode of claim 5, wherein the amount of the binder in the lower layer is 100% or more relative to the amount of the binder in the upper layer. The electrode of claim 4, wherein the two or more binders are homogeneous or heterogeneous binders. A lithium secondary battery comprising the electrode according to any one of claims 1 to 8. A battery module comprising the lithium secondary battery according to claim 9 as a unit cell. A battery pack comprising the battery module according to claim 10. A device comprising the battery pack according to claim 11 as a power source. A method of manufacturing an electrode according to claim 1, comprising: applying an electrode slurry formed by mixing an electrode mixture including an electrode active material and a binder into an organic solvent on an electrode current collector; And
Drying the electrode slurry coating layer by raising the temperature to a temperature range of -5 ° C to + 40 ° C of the melting point of the binder;
Electrode manufacturing method comprising a. The binder of claim 13, wherein the binder comprises two or more binders having different melting points, and from the melting point of the binder having the lowest melting point to the melting point of the binder having the highest melting point, the binder is −5 based on the melting points of the binders. Sequentially raising the temperature to a temperature range of + 40 ° C. to dry the electrode slurry coating layer;
Electrode manufacturing method comprising a.