KR101592193B1 - Electrode Having Improved Electric Conductivity - Google Patents

Abstract

The present invention provides an electrode having a structure in which an electrically conductive layer is formed on a part or all of an electrode slurry layer. The electrode according to the present invention can improve the electric conductivity of the electrode from the above-described structure. Accordingly, the present invention can provide a lithium secondary battery having improved high output characteristics and a battery pack including the same.

Description

[0001] Electrode Having Improved Electric Conductivity [

TECHNICAL FIELD The present invention relates to an electrode constituting a battery, and more particularly, to an electrode having improved electrical conductivity as an electrode constituting a lithium secondary battery.

As information technology (IT) technology has developed remarkably, various portable information and communication devices have been spreading, so that the 21st century is being developed into a "ubiquitous society" capable of providing high quality information services regardless of time and place.

As a development base for such a ubiquitous society, a lithium secondary battery occupies an important position. Specifically, the rechargeable lithium secondary battery is widely used as an energy source for wireless mobile devices, and is proposed as a solution for air pollution of existing gasoline vehicles and diesel vehicles using fossil fuels And also as an energy source for electric vehicles, hybrid electric vehicles, and the like.

As described above, as the devices to which the lithium secondary battery is applied are diversified, the lithium secondary battery has been diversified to provide an appropriate output and capacity for the applied device. In addition, miniaturization is strongly demanded.

In order to improve high-output characteristics, the resistance existing inside the battery must be minimized. The resistance inside the battery is caused by various factors such as precipitation of by-products of the interfacial reaction, deterioration of the electrode active material and electrolyte, and increase of the contact resistance of the electrode.

The resistance of the battery can be divided into resistance by electrons and resistance by lithium ions. In the case of the resistance by electrons, the contribution is increased when a very high current flows, and the resistance generated in the electrical contact portion is a major factor.

Particularly, in the case of a battery applied to a hybrid electric vehicle or the like, it is necessary to minimize the thickness of the current collector and the resistance of the electrical connection portion because the increase in resistance by electrons contributes greatly.

On the other hand, a relatively low rate characteristic is required in a small-sized battery such as a mobile phone or a notebook computer, so that an increase in resistance by lithium ions contributes more.

Generally, the electrode can be manufactured by applying an electrode slurry containing an electrode active material, a conductive material, and a binder on a current collector, followed by drying.

The conductive material is added for the purpose of improving the electron conductivity between the electrode active material particles or the current collector. In particular, it is necessary to prevent the binder from acting as an electromagnetic nonconductor and to compensate for insufficient electron conductivity of the electrode active material.

Generally, the resistance of the content of the conductive material is inversely proportional. That is, as the content of the conductive material increases, the resistance decreases.

It is presumed that the conductive material is uniformly mixed with the electrode active material in order to exhibit the effect of reducing the resistance as the content of the conductive material increases. However, the fine carbon powder used as the conductive material has a limitation in improving the electromagnetism by increasing the content of the conductive material because it is easy to coagulate with each other.

SUMMARY OF THE INVENTION In order to solve the problems of the prior art described above, it is an object of the present invention to provide an electrode structure with improved electrical conductivity.

In order to achieve the above object,

An electrode collector for transferring electrons between the outer lead and the electrode active material; An electrode slurry layer coated on the electrode current collector; And an electrically conductive layer formed on the electrode slurry layer; And an electrode.

At this time, the electrically conductive layer may be in a state of covering the entire surface of the electrode slurry layer, or in a state of covering the entire surface of the electrode slurry layer and extending to the electrode current collector to which the electrode slurry is not applied.

In a specific embodiment of the present invention, the electrically conductive layer may extend to an electrode current collector on which the electrode slurry layer is not coated, while covering the entire surface of the electrode slurry layer. In this case, since an electron conduction path directly connected to the current collector and the conductive layer can be formed, the electrical conductivity of the electrode can be further improved.

Further, according to the present invention,

An electrode collector for transferring electrons between the outer lead and the electrode active material; An electrode slurry layer formed on the electrode current collector; And an electrically conductive portion in contact with the electrode current collector and the electrode slurry layer; Wherein the electrode slurry layer comprises a coating portion in contact with the electrode current collector and a non-coating portion in which the electrode current collector is exposed to the outside, and the electrically conductive layer is located in a non-coating portion of the electrode slurry layer As shown in Fig.

The electrically conductive layer may be formed to have a thickness corresponding to the thickness of the electrode slurry layer or may be in a state of covering the entire surface of the electrode slurry layer, And may be in a state of extending to the electrode current collector which is not coated.

In one specific embodiment of the present invention, the electrically conductive layer may extend to the current collector while covering the electrode slurry layer.

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The electrode slurry layer may be pattern coated by a known method, and the non-coated portions may be formed in a uniform shape and / or an array of uniform intervals, or may be formed in disordered shapes or arrangements.

The uncoated portion may be located on the front surface of the electrode slurry layer. If the uncoated portion is located only in a part of the electrode slurry layer, there is a problem that unevenness of dislocation occurs in the electrode.

The shape of the uncoated portion on the plane or the shape of the electrode on the vertical section is not particularly limited. That is, the shape on the plane and the shape on the vertical section may be circular, polygonal, or the like.

In a specific embodiment of the present invention, the shape of the uncoated portion on the plane may be circular, and the shape on the vertical section may be rectangular.

That is, the non-coated portion may have a cylindrical shape, and the cylindrical non-coated portion may form a through hole in the electrode slurry layer. Therefore, according to the above-described embodiment, the electrode slurry layer may have two or more through-holes, and the through-holes may be located on the front surface of the electrode slurry layer in a uniform gap or disordered arrangement.

The following contents are commonly applicable to the two or more aspects of the present invention described above.

The electrode slurry layer may be formed on one surface or both surfaces of the electrode current collector. The electrode slurry layer may be formed to have a uniform thickness in order to eliminate unevenness of the potential in the electrode.

The electrically conductive layer may be formed to a thickness of 1 to 10% of the thickness of the electrode slurry layer. When the thickness of the electrically conductive layer is less than 1% or more than 10% of the thickness of the electrode slurry layer, it is not preferable because it can act as a resistance.

The electrically conductive layer may be a microporous film capable of intercalating and deintercalating lithium ions. Specifically, the microporous membrane may have pores having a size of 0.03 to 1 micrometer (m) and may have a porosity of 30 to 50% in order not to interfere with the mobility of lithium ions.

The electrically conductive layer may include one or more selected from the group consisting of carbon powder, metal powder, carbon fiber, metal fiber, and conductive polymer.

The carbon powder may be one or more selected from the group consisting of graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black and thermoplastic black. The conductive polymer may be at least one selected from the group consisting of polyacetylene, polypyrrole, Polyaniline, polythiophene, and polythiophene.

In a specific embodiment of the present invention, the electrically conductive layer may be a carbon coating layer or a graphen layer, and the electrically conductive layer may be formed by using a known coating method or a deposition method. More specifically, the carbon coating layer may be formed by dissolving or dispersing carbon powders and a binder used as a conductive material in an organic solvent to prepare a suspension, and then coating the electrode active material layer with the suspension.

The electrode may be a positive electrode or a negative electrode, and may be manufactured by a manufacturing method including the following processes.

In the electrode manufacturing method,

Dispersing or dissolving the binder in a solvent to prepare a binder solution;

Preparing an electrode slurry by mixing the binder solution, the electrode active material, and the conductive material;

Coating the electrode slurry on a current collector;

Drying the electrode; And

And compressing the electrode to a predetermined thickness.

In some cases, the rolled electrode may further be dried.

The binder solution preparation process is a process of dispersing or dissolving the binder in a solvent to prepare a binder solution.

The binder may be any binder known in the art and specifically includes a fluororesin binder including polyvinylidene fluoride (PVdF) or polytetrafluoroethylene (PTFE), a binder such as styrene-butadiene But are not limited to, cellulose-based binders including carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, poly Or a mixture or copolymer of one or more binders selected from the group consisting of polyolefin binders, polyolefin binders, polyimide binders, polyester-based binder mussel adhesives, and silane-based binders.

The solvent can be selectively used depending on the type of the binder. For example, organic solvents such as isopropyl alcohol, N-methylpyrrolidone (NMP), and acetone and water can be used.

As a specific example of the present invention, a binder solution for a positive electrode may be prepared by dispersing / dissolving PVdF in NMP (N-methyl pyrrolidone), or a styrene-butadiene rubber (SBR) / carboxy methyl cellulose (CMC) To prepare a negative electrode binder solution.

An electrode active material and a conductive material may be mixed / dispersed in the binder solution to prepare an electrode slurry. The electrode slurry thus prepared can be transferred to a storage tank and stored until the coating process. In order to prevent the electrode slurry from hardening in the storage tank, the electrode slurry can be agitated continuously.

The electrode active material may be a positive electrode active material or a negative electrode active material.

Specifically, 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 + 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} ( where, M = Co, Ni, Fe , Cr, and Zn, or Ta, y = 0.01 ~ 0.1 Im) or Li ₂ Mn ₃ MO ₈ (where, M = Fe, Co, 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 negative electrode active material may contain, in addition to the above-described negative electrode active material, 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, Bi ₂ O ₅ and the like; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials, and the like.

The 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.

A filler or the like may be optionally added to the electrode slurry as required. The filler is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery, and examples thereof include olefin-based polymerizers such as polyethylene and polypropylene; Fibrous materials such as glass fiber, carbon fiber and the like can be used.

The process of coating the electrode slurry on the current collector is a process in which the electrode slurry is passed through a coater head to coat the current collector with a predetermined pattern and a constant thickness.

The method of coating the electrode slurry on the current collector includes a method of uniformly dispersing the electrode slurry on a current collector using a doctor blade or the like, a method of die casting, comma coating coating, screen printing, and the like. Alternatively, the electrode slurry may be bonded to the current collector by molding on a separate substrate, followed by pressing or lamination.

The current collector is not particularly limited as long as it has high conductivity without causing a chemical change in the battery. For example, the current collector may be made of 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. 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. Specifically, the cathode current collector may be a metal current collector including aluminum, and the anode current collector may be a metal current collector including copper.

The drying step is a step of removing the solvent and moisture in the slurry to dry the slurry coated on the metal current collector. In a specific embodiment, the drying step is performed within one day in a vacuum oven at 50 to 200 degrees Celsius.

After the drying process, a cooling process may be further included, and the cooling process may be a slow cooling process to room temperature to form a recrystallized structure of the binder.

In order to increase the capacity density of the coated electrode and increase the adhesion between the current collector and the active materials, an electrode can be passed between two rolls heated at a high temperature and compressed to a desired thickness. This process is called the rolling process.

The electrode can be preheated before passing the electrode between two heated, heated rolls. The preheating process is a process of preheating the electrode before it is introduced into the roll to increase the compression effect of the electrode.

The electrode having completed the rolling process as described above can form an electrically conductive layer using a known evaporation method or coating method.

The electrode on which the electrically conductive layer is formed can be dried within one day in a vacuum oven at 50 to 200 degrees Celsius (DEG C). The rolled electrode may be cut to a certain length and then dried.

After the drying process, a cooling process may be further included, and the cooling process may be a slow cooling process to room temperature to form a recrystallized structure of the binder.

The present invention also provides a lithium secondary battery comprising a positive electrode, a negative electrode, and an electrode assembly including a separator interposed between the positive electrode and the negative electrode, into a battery case of a metal can or a laminate sheet, And a battery pack including the secondary battery and the lithium secondary battery.

The separator is made of an insulating thin film having high ion permeability and mechanical strength. The pore diameter of the separator is generally 0.01 to 10 micrometers (m) and the thickness is generally 5 to 300 micrometers (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 electrolyte is a non-aqueous electrolyte containing a lithium salt. As the non-aqueous electrolyte, a non-aqueous electrolyte, a solid electrolyte, an inorganic solid electrolyte, or the like is 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 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 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, 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), FPC (fluoro-propylene carbonate), and the like.

The battery pack including the lithium secondary battery may be an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV) Can be used as the power source of the device.

The structure of the electrode assembly, the structure of the lithium secondary battery, the structure of the battery pack, and the manufacturing method thereof are well known in the art, and therefore, detailed description thereof will be omitted.

The present invention can improve the electrical conductivity of an electrode from an electrode structure in which an electrically conductive layer is formed on an electrode slurry layer.

The present invention can also improve the electrical conductivity of the electrode from the structure in which the electrode slurry layer extends to the current collector.

Accordingly, the present invention can provide a lithium secondary battery having improved high output characteristics and a battery pack including the same.

FIG. 1 schematically shows a vertical cross-sectional view of an electrode according to a first embodiment of the present invention; FIG.
FIG. 2 is a schematic vertical cross-sectional view of an electrode according to a second embodiment of the present invention; FIG.
3 schematically shows a vertical cross-sectional view of an electrode according to a third embodiment of the present invention;
Fig. 4 schematically shows a top view of the electrode of Fig. 3; Fig.
5 is a schematic vertical cross-sectional view of an electrode according to a fourth embodiment of the present invention;

Hereinafter, the contents of the present invention will be described in detail with reference to the drawings. However, the following drawings are for illustrating the present invention, and the scope of the present invention is not limited thereto.

1, the electrode 100 has an electrode slurry layer 20 formed on one upper surface of the current collector 10, and an electrode layer 30 is formed on the upper surface of the electrode slurry layer 20 And pores 31 are formed in the conductive layer 30.

An electrode slurry layer 20 is formed on one upper surface of the current collector 10 and an electrode layer 30 is formed on the upper surface of the electrode slurry layer 20, The conductive layer 30 extends to the current collector 10 and is in direct contact with the current collector 10. The conductive layer 30 has pores 31 formed therein.

3 and 4, the electrode 100 has an electrode slurry layer 20 formed on one upper surface of the current collector 10, and the electrode slurry layer 20 is formed with electrode slurry An electrically conductive layer 30 penetrating the layer 20 and in direct contact with the current collector 10 is formed. The electrically conductive layer 30 is circular in plan view. Pores (not shown) are formed in the electrically conductive layer 30 penetrating through the electrode slurry layer 20.

An electrode slurry layer 20 is formed on one upper surface of the current collector 10 and an electrode slurry layer 20 is formed on the electrode slurry layer 20 at regular intervals, And the electric conductive layer 30 extends to the current collector 10 and is in direct contact with the current collector 10. The current collector 10 is formed of an electrically conductive layer 30 which is in direct contact with the current collector 10, And pores 31 are formed in the electrically conductive layer 30. Pores (not shown) are formed in the electrically conductive layer 30 penetrating through the electrode slurry layer 20.

Claims (18)

delete delete An electrode collector for transferring electrons between the outer lead and the electrode active material;
An electrode slurry layer formed on the electrode current collector; And
An electrically conductive layer in contact with the electrode current collector and the electrode slurry layer;
Lt; / RTI >
Wherein the electrode slurry layer comprises a coating portion in contact with the electrode current collector and a non-coating portion in which the electrode current collector is exposed to the outside,
Wherein the electrically conductive layer is located in an uncoated portion of the electrode slurry layer,
Wherein the uncoated portion comprises two or more through-holes, and
The through-holes are located in front of the electrode slurry layer in a uniformly spaced or disordered arrangement,
Wherein the electrically conductive layer is a microporous membrane capable of intercalating and deintercalating lithium ions and the microporous membrane has a porosity of 30 to 50%
Wherein the microporous membrane has a pore size of 0.03 to 1 占 퐉. delete delete delete The electrode according to claim 3, wherein the electrode slurry layer is formed on one surface or both surfaces of the current collector. delete The electrode according to claim 3, wherein the electrically conductive layer comprises one or more selected from the group consisting of carbon powder, metal powder, carbon fiber, metal fiber, and conductive polymer. The electrode according to claim 9, wherein the carbon powder is at least one selected from the group consisting of graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black. The electrode according to claim 9, wherein the conductive polymer is one or more selected from the group consisting of polyacetylene, polypyrrole, polyaniline, and polythiophene. delete delete The electrode according to claim 3, wherein the electrically conductive layer is formed to a thickness of 1 to 10% of the thickness of the electrode slurry layer. delete A lithium secondary battery comprising the electrode according to claim 3. A battery pack comprising the lithium secondary battery according to claim 16. The battery pack according to claim 17, wherein the battery pack is an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV) Wherein the battery pack is a power supply of the battery pack.

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