KR20140134541A - Electrode of Improved Electrode Conductivity and Method For Manufacturing The Same - Google Patents

Abstract

The present invention relates to an electrode with improved electrode conductivity for a lithium secondary battery and a manufacturing method thereof and, more specifically, to an electrode for a lithium secondary battery including a method to manufacture electrodes with improved binding strength between particles of an electrode active material and conductive materials; a particle of an electrode active material and conductive material; and particles of electrode active material and current collectors or the particles of conductive material and current collectors, where the process of drying an electrode over the melting point of a binder enables the melted binder to permeate into an electrode active material particle and the space between the particles of the conductive materials and current collectors including a binder comprising a re-crystalization structure having chemically and physically different properties compared to an existing binder.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to an electrode having improved electrode conductivity,

The present invention relates to an electrode for a lithium secondary battery and a method of manufacturing the same, and more particularly, to an electrode for a lithium secondary battery having improved electrode conductivity and a method for manufacturing the same.

Due to the rapid increase in the use of fossil fuels, the demand for the use of alternative energy or clean energy is increasing. As a part of this, the most active field of research is electric power generation and storage.

At present, a typical example of an electrochemical device utilizing such electrochemical energy is a secondary battery, and the use area thereof is gradually increasing.

2. Description of the Related Art [0002] Recently, as technology development and demand for portable devices such as portable computers, portable phones, and cameras have increased, the demand for secondary batteries as energy sources has increased sharply. Among such secondary batteries, they exhibit high energy density and operating potential, Many studies have been made on a lithium secondary battery having a long self discharge rate, and it has been commercialized and widely used.

In addition, as the interest in environmental issues grows, researches on electric vehicles and hybrid electric vehicles that can replace fossil fuel-based vehicles such as gasoline vehicles and diesel vehicles, which are one of the main causes of air pollution, , Lithium secondary batteries are also used as power sources for such electric vehicles and hybrid electric vehicles.

Generally, in a lithium secondary battery, charging and discharging proceed while repeating the process in which lithium ions in the positive electrode are inserted into the negative electrode and desorbed. Such insertion and desorption of lithium ions repeatedly progresses, so that the bond between the electrode active material or the conductive material is loosened and the contact resistance between the particles is increased. As a result, the electrode conductivity may be deteriorated and the battery characteristics may be deteriorated.

Further, the binder is required to have an adhesive strength enough to maintain the binding force between the electrode active material and the current collector during the drying process of the electrode plate. Particularly, in order to increase the discharge capacity, when a material such as silicon, tin, silicon-tin alloy having a large discharging capacity is mixed with natural graphite having a theoretical discharge capacity of 372 mAh / g is used, The volume expansion of the negative electrode material significantly increases. As a result, deterioration of the negative electrode material occurs. As a result, the capacity of the battery may be drastically deteriorated as a repetitive cycle progresses.

In order to maximize the capacity and the energy density, it is desirable to increase the content of the electrode active material and reduce the content of the binder as low as possible.

Representative binders currently commercialized include polyvinylidene fluoride (PVdF), styrene-butadiene rubber (SBR), carboxy methyl cellulose (CMC), and the like. In the case of a negative electrode having a large volume expansion, SBR / CMC, which has a smaller amount of use and has a better binding force than PVdF, is used.

The inventors of the present application have found that the electrode for a lithium secondary battery manufactured by a conventional electrode manufacturing process has a problem in that insertion and desorption of lithium ions are repeatedly performed because the binder partially exists in the space between the electrode active material particles, The bonding between the electrode active material or the conductive material is loosened and the contact resistance between the particles is increased.

Accordingly, the present invention is intended to solve the above problems. Specifically, the problem as described above can be solved by melting the binder while using the conventional electrode process as it is, as will be described later.

The inventors of the present application have found that when the temperature is raised to above the melting point of the binder, unlike the conventional electrode manufacturing process, while using the conventional electrode manufacturing process as it is, when the molten binder solution is mixed with the electrode active material particles, The present invention has been accomplished based on the idea that the electrode active material particles can uniformly permeate between the spaces between the electrode active material particles and the conductive material particles and the current collector.

Further, the inventors of the present application thought that when the temperature is raised above the recrystallization temperature, the battery characteristics can be improved due to the binder of physico-chemical properties different from conventional ones, and the present invention has been accomplished.

Therefore, in the electrode manufacturing method according to the present invention,

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; And

And drying the binder at a temperature higher than the melting point of the binder.

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 having a melting point of 150 to 200 ° C in NMP (N-methyl pyrrolidone), or a styrene-butadiene rubber (SBR) / CMC (Carboxy Methyl Cellulose) may be dispersed / dissolved in water to prepare a negative electrode binder solution. The melting point of the SBR is in the range of 80 to 150 ° C.

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 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, Bi ₂ O ₅ and the like; Conductive polymers such as polyacetylene; Li-Co-Ni-based material, or 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 for drying the slurry coated on the metal current collector, as well as drying the slurry coated on the metal current collector in a vacuum oven at a temperature of 50 to 250 degrees Celsius So that the impurities contained in the electrode slurry can be removed.

The drying temperature can be appropriately selected depending on the kind of the binder. The drying time can be appropriately selected depending on the kind of the binder and the like. In a specific embodiment of the present invention, the electrode can be dried within one day.

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.

Prior to passing the electrode between two hot, heated rolls, the electrode may be preheated at a temperature above the melting point of the binder. 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 be dried within one day in a vacuum oven at a temperature of 50 to 600 degrees Celsius as a range that satisfies a temperature equal to or higher than the melting point of the binder. 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 electrode for a lithium secondary battery according to the present invention manufactured by the above-

And an electrode mixture layer containing an electrode active material, a conductive material and a binder is formed on the current collector. The binder is characterized in that it is a binder containing a recrystallization structure unlike a conventional binder.

Specifically, the binder is melted at a temperature equal to or higher than the melting point of the binder and is at least partly recrystallized after penetrating into the space between the electrode active material particles, the conductive material particles, and the current collector. Further, the binder is characterized in that it has changed physico-chemical properties compared to that before the recrystallization.

The present invention also provides a lithium secondary battery having a structure in which an electrode assembly including the above-described electrode and having a separator interposed between an anode and a cathode is embedded in a battery case and impregnated with an electrolyte and the battery case is sealed, A battery pack including a secondary battery is provided.

The battery pack may be used as a power source for an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), and a power storage device .

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 manufacturing method according to the present invention is characterized in that the electrode is dried at a temperature equal to or higher than the melting point of the binder so that the electrode active material particles and the conductive material particles, the electrode active material particles and the conductive material particles, Or the space between the conductive material particles and the current collector allows the molten binder to be impregnated, thereby improving the binding force between the electrode active material particles, the conductive material particles, and the current collector.

As a result, the electrical conductivity of the electrode is improved, the electrode resistance can be reduced, and the swelling phenomenon of the electrode during charge / discharge of the battery can be remarkably reduced. It was also possible to remove impurities and moisture present in the electrode slurry.

The manufacturing method according to the present invention can provide the electrode with price competitiveness compared with the technique of changing the material of the electrode active material, the binder and the conductive material in order to improve the electrode conductivity because the conventional electrode manufacturing process can be used as it is It is effective.

In addition, the electrode for a lithium secondary battery according to the present invention includes a recrystallization structure having physicochemical properties completely different from those of a conventional binder, and has the effect of improving the characteristics of the battery due to the changed physicochemical properties.

1 is a schematic view of an electrode manufactured according to a conventional electrode manufacturing method;
2 is a schematic view of an electrode manufactured according to a manufacturing method according to a specific embodiment of the present invention.

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.

FIG. 1 schematically shows an electrode manufactured according to a conventional electrode manufacturing method, and FIG. 2 illustrates an electrode manufactured according to a manufacturing method according to a specific embodiment of the present invention.

Referring to FIGS. 1 and 2, when the electrode is manufactured according to the method of manufacturing an electrode according to the present invention, molten binder particles permeate into the space between the electrode active material particles, the conductive material particles, and the current collector, It can be confirmed that the binding force between the conductive material particles and the current collector can be improved.

1, an electrode 100 manufactured by a conventional electrode manufacturing method includes an electrode slurry 50 including electrode active material particles 10, conductive material particles 20, and a binder 30 And is coated on the collector 70. It can be confirmed that the binder 30 is in partial contact with the electrode active material particles 10, the conductive material particles 20 and the current collector 70.

2, an electrode 200 manufactured by an electrode manufacturing method according to the present invention includes an electrode slurry 150 including electrode active material particles 110, conductive particles 120, and a binder 130 Is coated on the current collector 170 and the binder 130 penetrates into the space between the electrode active material particles 110, the conductive material particles 120 and the current collector 170 The electrode active material particles 110, the conductive material particles 120, and the current collector 170. In the present embodiment,

Claims (18)

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; And
Drying at a temperature equal to or higher than the melting point of the binder;
Wherein the first electrode and the second electrode are electrically connected to each other. The method according to claim 1, wherein the binder is selected from the group consisting of a fluororesin binder, a rubber binder, a cellulose binder, a polyalcohol binder, a polyolefin binder, a polyimide binder, a polyester binder mussel adhesive, and a silane binder A mixture of one or more binders, or a copolymer. The electrode manufacturing method according to claim 2, wherein the fluororesin binder comprises polyvinylidene fluoride (PVdF) or polytetrafluoroethylene (PTFE). The method of claim 3, wherein the PVdF has a melting point of 150 to 200 ° C. The electrode manufacturing method according to claim 2, wherein the rubber binder includes styrene-butadiene rubber, acrylonitrile-butadiene rubber, and styrene-isoprene rubber. The method of claim 5, wherein the styrene-butadiene rubber has a melting point of 80 to 150 degrees Celsius. The method of manufacturing an electrode according to claim 1, wherein the drying step is performed within a day in a vacuum oven at 50 to 250 degrees Celsius as a range satisfying a temperature equal to or higher than a melting point of the binder. The method of claim 1, further comprising a cooling process after the drying process. 9. The method of claim 8, wherein the cooling process is slow cooling to room temperature. The method of claim 1, further comprising: compressing the electrode to a predetermined thickness; And drying the rolled electrode at a temperature equal to or higher than the melting point of the binder. Wherein an electrode mixture layer containing an electrode active material, a conductive material, and a binder including a recrystallization structure is formed on a current collector. The electrode for a lithium secondary battery according to claim 11, wherein the binder is melted at a temperature equal to or higher than the melting point of the binder and is at least partially recrystallized after penetrating into a space between the electrode active material, . 12. The electrode for a lithium secondary battery according to claim 11, wherein the binder has a physicochemical property that is changed compared with that before recrystallization. 12. The electrode for a lithium secondary battery according to claim 11, wherein the electrode active material is a cathode active material, and the electrode current collector is a metal current collector containing aluminum. The electrode for a lithium secondary battery according to claim 11, wherein the electrode active material is a negative active material, and the current collector is a metal current collector including copper. A lithium secondary battery having a structure in which the electrode according to any one of claims 11 to 15 is embedded in a battery case and impregnated with an electrolyte and then the battery case is sealed. 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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