KR102314626B1 - Electrode for secondary battery, method for preparing the same, and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention comprises the steps of adding a linear conductive material, a dotted conductive material, a dispersing agent and a solvent to a disperser; and dispersing the linear conductive material and the dotted conductive material in a solvent at the same time to prepare a conductive material linear dispersion; a method for manufacturing an electrode for a secondary battery comprising, an electrode for a secondary battery manufactured through the same, and a lithium secondary battery including the same will be.

Description

Electrode for secondary battery, manufacturing method thereof, and lithium secondary battery comprising same

The present invention relates to an electrode for a secondary battery, a manufacturing method thereof, and a lithium secondary battery including the same.

As technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, a lithium secondary battery having a high energy density and voltage, a long cycle life, and a low self-discharge rate has been commercialized and widely used.

Lithium secondary batteries are manufactured by using a material capable of inserting and deintercalating lithium ions as the negative electrode and positive electrode, and filling an organic electrolyte or polymer electrolyte between the positive electrode and the negative electrode. It generates electrical energy through oxidation and reduction reactions.

As the usage area of lithium secondary batteries gradually expands, it is required to manufacture batteries with superior performance such as high capacity, high output, long lifespan, and fast charging. In order to further improve the capacity of the lithium secondary battery, it is necessary to decrease the content of the conductive material of the electrode and increase the content of the electrode active material.

Accordingly, it was attempted to reduce the conductive material content by using a linear conductive material instead of the existing spherical conductive material. However, the linear conductive material has a problem in that physical cohesion and chemical cohesion caused by surface attraction such as Van der Waals force occur severely.

In a lithium secondary battery, if the conductive material present in the electrode does not have an even dispersion state, a channel through which current can flow is not locally formed in the electrode, so that the resistance inside the battery increases or a current concentration phenomenon occurs, and thus the battery performance and There is a problem that may impair stability. Therefore, there is a demand for the development of a lithium secondary battery with improved performance and stability of the battery by evenly dispersing the conductive material.

In addition, when a linear conductive material is used, the viscosity of the conductive material dispersion is greatly increased and fluidity is poor, so that there is a difficulty in the electrode manufacturing process. Accordingly, there is a need for a method for improving processability by lowering the viscosity of the linear conductive material dispersion and increasing the fluidity.

Korean Patent Publication No. 2006-0111092

In the present invention, by using a linear conductive material, conductivity can be secured even with a small amount of conductive material, so that a high capacity can be realized by increasing the content of the electrode active material as the content of the conductive material is decreased, and furthermore, a point-shaped conductive material together with the linear conductive material An object of the present invention is to provide an electrode for a secondary battery with improved performance and stability of the battery by reducing the aggregation of the linear conductive material and allowing the conductive material to be evenly distributed.

Another object of the present invention is to provide a method for manufacturing an electrode for a secondary battery that improves the processability of electrode manufacturing by lowering the viscosity of the conductive material dispersion and increasing the fluidity compared to the conventional linear conductive material dispersion.

The present invention comprises the steps of adding a linear conductive material, a dotted conductive material, a dispersing agent and a solvent to a disperser; and dispersing the linear conductive material and the dotted conductive material in a solvent at the same time to prepare a conductive material linear dispersion.

In addition, the present invention provides a conductive material linear dispersion for forming a secondary battery electrode comprising a linear conductive material, a dotted conductive material, a dispersing agent, and a solvent, and having a viscosity of 8,000 to 12,000 cps (25° C.).

In addition, the present invention provides an electrode for a secondary battery manufactured using the conductive material wire dispersion, and a lithium secondary battery including the same.

According to the present invention, by simultaneously dispersing the linear conductive material and the dotted conductive material in the solvent, the conductive material does not agglomerate and has an even dispersion state, thereby preventing an increase in internal resistance of the battery and securing the performance and stability of the battery.

In addition, compared to the conventional linear conductive material dispersion, the process yield can be improved by lowering the viscosity of the conductive material dispersion and increasing the fluidity, thereby improving the processability of manufacturing the electrode, and increasing the solid content in the conductive material dispersion.

1 is a shear viscous modulus ( It is a graph showing shear viscosity).
2 is a conductive material linear dispersion (Example 1), a linear conductive material alone linear dispersion (Comparative Example 1), a point-shaped conductive material alone linear dispersion solution (Comparative Example 2), and a linear conductive material linear dispersion solution according to an embodiment of the present invention; It is a particle size distribution graph for a linear dispersion liquid (Comparative Example 3) in which a dotted conductive material is dispersed afterward.
Figure 3a is a photograph of the conductive material linear dispersion (Example 1) according to an embodiment of the present invention observed at a magnification of 5,000 times with a scanning electron microscope (SEM, Scanning Eletron Microscope), Figure 3b is observed at a further magnification of 30,000 times; it's one picture
FIG. 4a is a photograph observed at 5,000 times magnification with a scanning electron microscope (SEM, Scanning Eletron Microscope) of a linear dispersion liquid (Comparative Example 3) dispersed after a point-shaped conductive material is dispersed in a linear conductive material linear dispersion liquid, and FIG. 4b is further enlarged by 30,000 times. This is an enlarged view.
5 is a graph showing the capacity retention rate and resistance increase rate according to the charge/discharge cycle of the battery cells of Example 2, Comparative Examples 4 and 5.
6 is a graph showing the capacity retention rate and resistance increase rate according to time after high-temperature storage of the battery cells of Examples 2 and 4 and 5;

Hereinafter, the present invention will be described in more detail to help the understanding of the present invention. At this time, the terms or words used in the present specification and claims should not be construed as being limited to conventional or dictionary meanings, and the inventor appropriately defines the concept of the term in order to best describe his invention. Based on the principle that it can be done, it should be interpreted as meaning and concept consistent with the technical idea of the present invention.

The accompanying drawings are for clearly explaining the present invention, and are not limited to the embodiments of the drawings. The shapes and sizes of elements in the drawings may be exaggerated for a clearer description, parts irrelevant to the description are omitted, and components having the same function within the scope of the same concept will be described using the same reference numerals.

The method for manufacturing an electrode for a secondary battery of the present invention includes the steps of: adding a linear conductive material, a dotted conductive material, a dispersing agent, and a solvent to a disperser; and dispersing the linear conductive material and the dotted conductive material in a solvent at the same time to prepare a conductive material linear dispersion.

In the present invention, a linear conductive material and a dotted conductive material are put together in a disperser and dispersed in a solvent at the same time to prepare a conductive material linear dispersion. By dispersing the linear conductive material and the dotted conductive material together, it is possible to reduce the physical cohesion of the linear conductive material and the chemical aggregation phenomenon caused by surface attraction such as the Van der Waals force, and improve the dispersibility. Dispersibility can be sufficiently improved by dispersing the linear conductive material and the dotted conductive material in the solvent at the same time as compared to a method of dispersing the linear conductive material in a solvent first and then secondarily dispersing the dotted conductive material in the solvent.

In the present invention, a 'linear conductive material' means a conductive material having a fibrous structure such as a cylindrical type or a tube type, and the 'point type conductive material' means a generally used conductive material having a generally spherical particle shape. .

The linear conductive material is electrochemically stable and has good conductivity, and it is preferable to form a fibrous structure, for example, a carbon-based material such as carbon fiber; metal fibers such as copper, nickel, aluminum, and silver; and the like, and more preferably, carbon nanotubes (CNTs) as carbon fibers.

The linear conductive material may be at least one selected from the group consisting of fine fibrous carbon having a diameter of less than 100 nm and fibrous carbon having a diameter of 100 nm or more.

That is, the conductive material linear dispersion according to an embodiment of the present invention may include fine fibrous carbon having a diameter of less than 100 nm as a linear conductive material, or may include fibrous carbon having a diameter of 100 nm or more, and less than 100 nm. It may also include fine fibrous carbon having a diameter and fibrous carbon having a diameter of 100 nm or more.

The fine fiber carbon may have a diameter of less than 100 nm, more preferably 5 nm to 20 nm, and still more preferably 8 nm to 15 nm. The length of the fine fiber carbon may be 20 nm to 1 μm, and more preferably 50 nm to 400 nm.

The fibrous carbon may have a diameter of 100 nm or more, more preferably 100 nm or more and 1 μm or less, more preferably 100 nm or more and 500 nm or less, and most preferably 100 nm or more and 300 nm or less.

The dotted conductive material is electrochemically stable, has good conductivity, and preferably has a particulate form, for example, graphite such as natural graphite or artificial graphite; carbon-based substances such as carbon black, acetylene black, oil furnace black, ketjen black, channel black, furnace black, lamp black, and summer black; metal powders such as copper, nickel, aluminum, and silver; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; Alternatively, a conductive polymer such as a polyphenylene derivative may be used, and more preferably carbon black and/or acetylene black may be used.

The dotted conductive material may have an average particle diameter of 5 to 150 nm, more preferably 30 to 100 nm, and most preferably 50 to 80 nm.

In the preparation of the conductive material linear dispersion according to an embodiment of the present invention, the linear conductive material and the dotted conductive material may be included in a weight ratio of 1:0.25 to 1:0.75.

When the dotted conductive material is included in a weight ratio of less than 0.25 times that of the linear conductive material, the effect of improving the dispersibility due to the dotted conductive material is insignificant, so that aggregation of the linear conductive material may occur, and the viscosity of the conductive material linear dispersion is greatly increased to improve fairness. may be lowered, and the process yield may be reduced due to a decrease in the solids content As this increases, the content of the electrode active material may be relatively decreased.

The dispersant preferably uses a material having a thickener or surfactant function, for example, carboxymethyl cellulose (CMC), hydroxyethyl cellulose, pectin, alginic acid, guar gum, locust bean gum, gum arabic, dextrin , polysaccharides and monosaccharides such as altose, sorbit, lactose, unstarch and sucrose; sodium cholate, gelatin and polyvinyl alcohol; Anionic surfactants such as naphthalenesulfonic acid-formaldehyde condensates and alkylbenzenesulfonates, cationic surfactants, nonionic surfactants, polyether-modified silicone surfactants, and Hydrogenated Nitrile Butadiene Rubber (HNBR) ) and the like, and more preferably, using Hydrogenated Nitrile Butadiene Rubber (HNBR) may be effective in improving dispersibility.

The dispersant may include 5 to 50 parts by weight, more preferably 15 to 50 parts by weight, based on 100 parts by weight of the total weight of the linear conductive material and the dotted conductive material.

When the dispersant is included in less than 5 parts by weight, the linear conductive material and the dotted conductive material are not sufficiently dispersed, so that the resistance inside the battery may be greatly increased, and the battery performance and stability may be reduced due to the current concentration phenomenon, and the dispersant When included in excess of 5 parts by weight, electrode resistance may be increased, and may become electrochemically unstable.

The solvent used in preparing the conductive material linear dispersion may be water or an organic solvent, for example, water, N-methylpyrrolidone (NMP), methyl alcohol, ethyl alcohol, propanol, isopropanol, dimethylformamide (DMF). ) and mixtures of two or more thereof.

An embodiment of the present invention may further include the step of milling the prepared conductive material pre-dispersion using beads (beads). Dispersibility may be further improved by milling the conductive material pre-dispersion with beads. More preferably, the milling may be performed twice or more for sufficient dispersion.

In this way, by simultaneously dispersing the linear conductive material and the dotted conductive material in a solvent to prepare a conductive material linear dispersion, the aggregation of the linear conductive material can be reduced and the dispersibility can be improved, and the internal resistance of the battery is increased because the conductive material has an even dispersion state and to improve battery performance and stability. In addition, since the conductive material linear dispersion prepared as described above has low viscosity and fluidity is secured, processability may be increased, and the solid content in the conductive material linear dispersion may be increased to improve process yield.

The viscosity of the conductive material linear dispersion prepared according to an embodiment of the present invention may be 8,000 to 12,000 cps (25° C.). The conductive material linear dispersion prepared according to an embodiment of the present invention was able to significantly lower the viscosity compared to the existing linear conductive material linear dispersion liquid by dispersing the linear conductive material and the dotted conductive material in a solvent at the same time. This can increase significantly.

If the viscosity of the conductive material line dispersion is less than 8,000 cps, the linear conductive material and the dotted conductive material are not sufficiently dispersed, which may cause an increase in resistance inside the battery. This can be.

The final solids content of the conductive material linear dispersion prepared according to an embodiment of the present invention may be 3.0 wt% or more. The conductive material linear dispersion prepared according to an embodiment of the present invention improves dispersibility compared to the existing linear conductive material linear dispersion liquid by dispersing the linear conductive material and the dotted conductive material in a solvent at the same time, and the solid content can be increased. , thus, the process yield may be improved.

According to an embodiment of the present invention, the method comprising: preparing an electrode slurry by mixing an electrode active material and a binder with the conductive material line dispersion; And coating the electrode slurry on the current collector, drying and rolling to prepare an electrode; may further include a secondary battery electrode can be manufactured.

The electrode for a secondary battery manufactured according to an embodiment of the present invention includes both a linear conductive material and a dotted conductive material, and a conductive material linear dispersion prepared by dispersing the linear conductive material and the dotted conductive material in a solvent at the same time as described above is used. By being manufactured by using the method, the dispersibility is excellent, the current flow in the electrode is smooth, the increase in resistance inside the battery is suppressed, and the battery performance and stability can be improved.

The electrode active material may use a lithium transition metal oxide typically used as a positive electrode active material, for example, lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ) Layered compounds such as, or one or more transitions a compound substituted with a metal; Formula _{Li 1 + x1 Mn 2 - x1} O 4 ( here, x ₁ is 0 to 0.33), LiMnO _3, the lithium manganese oxide such as LiMn ₂ O _3, LiMnO _2; lithium copper oxide (Li ₂ CuO ₂ ); vanadium oxides such as LiV ₃ O ₈ , LiV ₃ O ₄ , V ₂ O ₅ , and Cu ₂ V ₂ O _{7 ;} Formula LiNi _{1 - x2} M ¹ _x2 O ₂ (here, M ¹ = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x ₂ = 0.01 ~ 0.3) Ni site type lithium nickel oxide represented by; Formula LiMn _{2 - x3} M _x3 O ₂ (where M ² = Co, Ni, Fe, Cr, Zn or Ta and x ₃ = 0.01 to 0.1) or Li ₂ Mn ₃ M ³ O ₈ (where M ^{3 )} = lithium manganese composite oxide represented by Fe, Co, Ni, Cu or Zn; LiNi _x4 Mn _{2 - x4} O ₄ (here, x ₄ = 0.01 ~ 1) spinel structure lithium manganese composite oxide; _{LiMn 2} O _{4 in} which a part of Li in the formula is substituted with an alkaline earth metal ion; disulfide compounds; And the like Fe ₂ (MoO _{4) 3,} but is not limited to these.

In addition, the cathode active material may include a lithium transition metal oxide represented by the following formula (1).

[Formula 1]

Li _a Ni _1-xy Co _x Mn _y M _z O ₂

In the above formula, M is any one or more elements selected from the group consisting of Al, Zr, Ti, Mg, Ta, Nb, Mo and Cr, 0.9≤a≤1.5, 0≤x≤0.5, 0≤y≤0.5, 0≤z≤0.1, 0≤x+y≤0.7.

By using the positive electrode active material as described above as the electrode active material, a positive electrode of a lithium secondary battery may be manufactured according to the manufacturing method according to an embodiment of the present invention.

Alternatively, as the electrode active material, a compound capable of reversible intercalation and deintercalation of lithium, which is typically used as an anode active material, may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metal compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; metal oxides capable of doping and dedoping lithium, such as SiO _q (0 < q < 2), SnO _{2 , vanadium oxide, and lithium vanadium oxide;} Alternatively, a composite including the above-mentioned metallic compound and a carbonaceous material such as a Si-C composite or a Sn-C composite may be used, and any one or a mixture of two or more thereof may be used. As the carbon material, both low crystalline carbon and high crystalline carbon may be used. As low crystalline carbon, soft carbon and hard carbon are representative, and as high crystalline carbon, natural or artificial graphite of amorphous, plate-like, flaky, spherical or fibrous shape, and Kish graphite (Kish) graphite), pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, liquid crystal pitches (Mesophase pitches), and petroleum and coal tar pitch (petroleum or coal tar pitch) High-temperature calcined carbon such as derived cokes) is a representative example.

By using the negative electrode active material as described above as the electrode active material, a negative electrode of a lithium secondary battery can be manufactured according to the manufacturing method according to an embodiment of the present invention.

The binder serves to improve adhesion between the electrode active material particles and adhesion between the electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC) ), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one of them or a mixture of two or more thereof may be used. The binder may be included in an amount of 1% to 30% by weight based on the total weight of the electrode slurry.

The solvent may be a solvent commonly used in the art, dimethyl sulfoxide (DMSO), isopropyl alcohol (isopropyl alcohol), N-methylpyrrolidone (NMP), acetone (acetone) or water and the like, and any one of them or a mixture of two or more thereof may be used. The amount of the solvent used is enough to dissolve or disperse the electrode active material, the conductive material, and the binder in consideration of the application thickness of the slurry and the production yield, and to have a viscosity that can exhibit excellent thickness uniformity when applied for subsequent electrode production. do.

The current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery. For example, in the case of a positive electrode current collector, stainless steel, aluminum, nickel, titanium, calcined carbon, or carbon on the surface of aluminum or stainless steel , nickel, titanium, silver, etc. may be used. In addition, for example, in the case of a negative electrode current collector, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface treated with carbon, nickel, titanium, silver, etc., aluminum- A cadmium alloy or the like may be used. The current collector may typically have a thickness of 3 to 500 μm, and may increase the adhesion of the electrode active material by forming fine irregularities on the surface of the current collector. For example, it may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven body, and the like.

Alternatively, the electrode may be manufactured by casting the electrode slurry on a separate support and then laminating a film obtained by peeling it from the support on a current collector.

In addition, an embodiment of the present invention provides an electrochemical device including the electrode. The electrochemical device may specifically be a battery, a capacitor, or the like, and more specifically, a lithium secondary battery.

The lithium secondary battery specifically includes a positive electrode, a negative electrode positioned to face the positive electrode, a separator and an electrolyte interposed between the positive electrode and the negative electrode, and the positive electrode and the negative electrode are as described above. In addition, the lithium secondary battery may optionally further include a battery case for accommodating the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member for sealing the battery case.

On the other hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move, and as long as it is used as a separator in a lithium secondary battery, it can be used without any particular limitation, especially for the movement of ions in the electrolyte It is preferable to have a low resistance to and excellent electrolyte moisture content. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene/butene copolymer, an ethylene/hexene copolymer, and an ethylene/methacrylate copolymer, or these A laminate structure of two or more layers of may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, in order to secure heat resistance or mechanical strength, a coated separator including a ceramic component or a polymer material may be used, and may optionally be used in a single-layer or multi-layer structure.

In addition, examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes, which can be used in the manufacture of lithium secondary batteries, and are limited to these. it's not going to be

Specifically, the electrolyte may include an organic solvent and a lithium salt.

The organic solvent may be used without particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, as the organic solvent, ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate, carbonate-based solvents such as PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (R is a C2 to C20 linear, branched or cyclic hydrocarbon group, which may include a double bond aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; Or sulfolane may be used. Among these, a carbonate-based solvent is preferable, and a cyclic carbonate (eg, ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant capable of increasing the charge/discharge performance of the battery, and a low-viscosity linear carbonate-based compound ( For example, a mixture of ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) is more preferable. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1:1 to 9, the electrolyte may exhibit excellent performance.

The lithium salt may be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt is LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAl0 ₄ , LiAlCl ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN(C ₂ F ₅ SO ₃ ) ₂ , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiN(CF ₃ SO ₂ ) ₂ . LiCl, LiI, or LiB(C ₂ O ₄ ) ₂ and the like may be used. The concentration of the lithium salt is preferably used within the range of 0.1M to 2.0M. When the concentration of the lithium salt is included in the above range, the electrolyte may exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions may move effectively.

The electrolyte may include, in addition to the electrolyte components, a haloalkylene carbonate-based compound such as difluoroethylene carbonate for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity; or pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N One or more additives such as -substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol or aluminum trichloride may be further included. In this case, the additive may be included in an amount of 0.1 wt% to 5 wt% based on the total weight of the electrolyte.

As described above, since the lithium secondary battery including the positive electrode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics and capacity retention rate, portable devices such as mobile phones, notebook computers, digital cameras, and hybrid electric vehicles ( It is useful in the field of electric vehicles such as hybrid electric vehicle, HEV).

Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

The battery module or battery pack is a power tool (Power Tool); electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); Alternatively, it may be used as a power source for any one or more medium and large-sized devices in a system for power storage.

Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the art can easily carry out the present invention. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein.

Example One

1.9 parts by weight of carbon nanotubes (CNT) having an average diameter of 10 nm and an average length of 100 μm as a linear conductive material, 0.9 parts by weight of carbon black having an average particle diameter of 20 nm as a point-shaped conductive material, and 0.5 weight of hydrogenated nitrile butadiene rubber (HNBR) as a dispersant Parts and 96.7 parts by weight of N-methylpyrrolidone (NMP) as a solvent were put into a disperser BTM-50, and the mixture was uniformly stirred.

Then, the conductive material pre-dispersion was put into a spike-mill, and milling was performed twice through beads to prepare a conductive material pre-dispersion.

The solid content of the conductive material linear dispersion prepared as described above was about 3.27%.

comparative example One

A conductive material linear dispersion was prepared in the same manner as in Example 1, except that 2 parts by weight of carbon nanotubes (CNTs) having an average diameter of 10 nm and an average length of 100 μm were added as a linear conductive material, and a dotted conductive material was not added. did.

The solid content of the linear conductive material linear dispersion prepared as described above was about 2.4%.

comparative example 2

A conductive material linear dispersion was prepared in the same manner as in Example 1, except that 3 parts by weight of carbon black having an average particle diameter of 20 nm was added as a dotted conductive material, and a linear conductive material was not added.

comparative example 3

2 parts by weight of carbon nanotubes (CNT) having an average diameter of 10 nm and an average length of 100 μm as a linear conductive material, 0.4 parts by weight of hydrogenated nitrile butadiene rubber (HNBR) as a dispersant, and N-methylpyrrolidone (NMP) 97.6 as a solvent A weight part was put into a disperser BTM-50, and uniformly stirred to prepare a linear conductive material linear dispersion. Then, 1 part by weight of carbon black having an average particle diameter of 20 nm as a point-shaped conductive material was added to the primary linear conductive material linear dispersion and stirred again to prepare a conductive material linear dispersion in which a linear/point-shaped conductive material was mixed. Example 1 Conductive material line dispersion was prepared in the same manner as described above.

The solid content of the conductive material linear dispersion prepared as described above was about 2.97%.

[ Experimental example 1] shear viscosity (Shear viscosity) and viscosity measurement

The shear viscosity of the conductive material wire dispersions prepared in Example 1 and Comparative Examples 1 to 3 was measured using a TA Instruments Rheometer (DHR2). And the viscosity was measured using a Brookfield DV2T viscometer. For the measurement method, the DHR2 equipment concentric cylinder type accessory was used, and after 10 ml of the dispersion was added, the shear viscosity was measured. The DV2T viscometer put the dispersion in a 250 ml beaker and measured the viscosity (25° C.). The results are shown in Table 1 and FIG. 1 below. Specifically, FIG. 1 is a graph showing the shear viscosity of the conductive material linear dispersion of Example 1, the linear conductive material alone linear dispersion of Comparative Example 1, and the dotted conductive material alone linear dispersion of Comparative Example 2;

Shear viscosiry (Pa s) Viscosity (Type B Viscosity) (cps)
0.1/s 1/s 100/s Example 1 1,639 122 0.48 11,330 Comparative Example 1 4,507 40 0.99 20,580 Comparative Example 2 791 10 0.25 4,433 Comparative Example 3 624 15 0.42 7,800

Referring to Table 1 and FIG. 1 , it can be seen that the shear viscosity and viscosity are lowered in Example 1 in which the linear/point-shaped conductive material is included as compared to Comparative Example 1 in which the linear conductive material is included alone. Furthermore, in Comparative Example 3, in which a linear conductive material was pre-injected and dispersed, and then a dotted conductive material was added and dispersed, the viscosity was significantly lower than 8,000 cps. This may be a state in which the linear/point-shaped conductive material is not evenly dispersed, but is agglomerated in some parts. That is, it can be seen that the dispersion characteristics are further improved when the linear conductive material and the dotted conductive material are simultaneously dispersed. As in the embodiment, when the viscosity of the conductive material line dispersion is in the range of 8,000 to 12,000 cps, the dispersion is sufficiently achieved, and the flowability is increased to increase the fairness.

[ Experimental example 2] Particle size measurement

The particle size distribution of the conductive material linear dispersion prepared in Example 1 and Comparative Examples 1 to 3 was measured using a Malvern Mastersizer 3000. As for the measurement method, the particle size of the dispersion was measured by diluting 1000 times in 3 ml of the dispersion. The results are shown in Table 2 and FIG. 2 below. Specifically, FIG. 2 shows the conductive material linear dispersion of Example 1, the linear conductive material alone linear dispersion of Comparative Example 1, the dotted conductive material alone linear dispersion of Comparative Example 2, and the dotted conductive material after the linear conductive material linear dispersion of Comparative Example 3 It is a particle size graph for the post-dispersed linear dispersion.

Particle size (㎛) D10 D50 D90 Example 1 2.07 7.22 22.6 Comparative Example 1 2.33 6.84 18.8 Comparative Example 2 0.35 1.25 7.48 Comparative Example 3 1.95 8.14 34.7

Referring to Table 1 and FIG. 1 , in the case of Example 1 in which the linear/point-shaped conductive material is simultaneously dispersed, it can be seen that the particle size is generally similar to the tendency of the linear conductive material linear dispersion (Comparative Example 1). On the other hand, in Comparative Example 3, in which the linear conductive material was pre-injected and dispersed, and then the dotted conductive material was added and dispersed, the particle size of D90 was significantly larger than that of the example in which the linear/point-shaped conductive material was simultaneously dispersed in the solvent. It can be seen that the dispersion is not sufficiently achieved.

On the other hand, Figure 3a is a photograph observed at 5,000 times magnification of the linear/point-shaped conductive material linear dispersion of Example 1 with a scanning electron microscope (SEM), and Figure 3b is a photograph observed at a further magnification of 30,000 times. It is a photograph observed at 5,000 times magnification with a scanning electron microscope (SEM) of the linear dispersion solution obtained by dispersing the dotted conductive material after linear dispersion of the linear conductive material of Example 3, and FIG. 4B is a photograph observed at a further 30,000 times magnification.

In the case of FIGS. 3A and 3B, it can be seen that the point-shaped conductive material is uniformly dispersed, whereas in the case of FIGS. 4A and 4B, it can be seen that the point-shaped conductive material is partially agglomerated. That is, the linear/point-shaped conductive material line dispersion according to the present invention in which the linear conductive material and the point-shaped conductive material are simultaneously dispersed is dispersed compared to the linear/point-shaped conductive material line dispersion liquid prepared by post-dispersing the dotted conductive material after the linear conductive material line dispersion. characteristics are excellent.

Example 2

_{The positive active material LiNi 0} in the conductive material linear dispersion prepared in Example 1 _{. 6} Mn _{0 . 2} Co _{0 . 2} O ₂ and PVdF binder were mixed in N-methylpyrrolidone solvent to prepare a positive electrode slurry. The positive electrode slurry was applied to an aluminum current collector, dried at 130° C., and then rolled to prepare a positive electrode.

In addition, a negative electrode slurry was prepared by mixing the negative electrode active material natural graphite and PVdF binder in the N-methylpyrrolidone solvent with the conductive material linear dispersion prepared in Example 1. The negative electrode slurry was applied to a copper current collector, dried at 130° C., and then rolled to prepare a positive electrode.

An electrode assembly was prepared by interposing a separator of porous polyethylene between the prepared positive electrode and the negative electrode, the electrode assembly was placed inside the case, and the electrolyte was injected into the case to prepare a lithium secondary battery. At this time, the electrolyte is prepared by dissolving _{lithium hexafluorophosphate (LiPF 6} ) at a concentration of 1.0 M in an organic solvent consisting of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate (mixed volume ratio of EC / DMC / EMC = 3 / 4 / 3) did.

comparative example 4 and 5

A secondary battery was manufactured in the same manner as in Example 2, except that the conductive material line dispersion prepared in Comparative Examples 1 and 2 was used, respectively.

[ Experimental example 3] Battery performance evaluation

With respect to the secondary battery mono cells prepared in Example 2, Comparative Examples 4 and 5, while performing 200 cycles of charging and discharging at 45 ° C. under 1.0 C / 1.0 C conditions, capacity retention (Capacity Retention [%]) and resistance increase rate (DCIR) [%]) was measured. The measurement results are shown in FIG. 5 .

In addition, the secondary battery mono cells prepared in Example 2 and Comparative Examples 4 and 5 were stored at a high temperature of 60° C., and then HPPC was measured in units of one week. The capacity of 0.33C was checked every week, and the pulse discharge resistance was checked at SOC 50% and 2.5C. The measurement results are shown in FIG. 6 .

5 and 6 , it can be seen that in the case of the battery cell of Example 2, the resistance increase rate at the time of charging and discharging 200 times or for 4 weeks is significantly lower than that of the battery cells of Comparative Examples 4 and 5.

Claims (21)

adding a linear conductive material, a point-shaped conductive material, a dispersing agent, and a solvent to a disperser; and
dispersing the linear conductive material and the dotted conductive material in a solvent at the same time to prepare a conductive material linear dispersion;
including,
The linear conductive material and the dotted conductive material are included in a weight ratio of 1:0.25 to 1:0.75,
The dispersant is hydrogenated nitrile butadiene rubber (HNBR),
The dispersant is included in an amount of 5 to 50 parts by weight based on 100 parts by weight of the total weight of the linear conductive material and the dotted conductive material,
A method of manufacturing an electrode for a secondary battery, wherein the final solid content of the conductive material line dispersion is 3.0% by weight or more.
According to claim 1,
The method of manufacturing an electrode for a secondary battery, wherein the linear conductive material is a carbon nano tube (CNT).
According to claim 1,
The linear conductive material is a method of manufacturing an electrode for a secondary battery at least one selected from the group consisting of fine fibrous carbon having a diameter of less than 100 nm and fibrous carbon having a diameter of 100 nm or more.
According to claim 1,
The dotted conductive material is at least one selected from the group consisting of carbon black, acetylene black, oil furnace black, Ketjen black, channel black, furnace black, lamp black, and summer black.
delete delete delete According to claim 1,
The method of manufacturing an electrode for a secondary battery further comprising the step of milling the prepared conductive material line dispersion using beads (beads).
9. The method of claim 8,
The method of manufacturing an electrode for a secondary battery, wherein the milling is performed two or more times.
According to claim 1,
The viscosity of the conductive material linear dispersion is 8,000 to 12,000 cps (25° C.) of a method for manufacturing an electrode for a secondary battery.
delete According to claim 1,
preparing an electrode slurry by mixing an electrode active material, a binder, and a solvent with the conductive material predispersion; and
The method of manufacturing an electrode for a secondary battery further comprising; coating the electrode slurry on a current collector, drying and rolling to prepare an electrode.
It contains a linear conductive material, a dotted conductive material, a dispersant and a solvent,
a viscosity of 8,000 to 12,000 cps (25° C.),
The linear conductive material and the dotted conductive material are included in a weight ratio of 1:0.25 to 1:0.75,
The dispersant is hydrogenated nitrile butadiene rubber (HNBR),
The dispersant is included in an amount of 5 to 50 parts by weight based on 100 parts by weight of the total weight of the linear conductive material and the dotted conductive material,
The final solid content is 3.0% by weight or more of the conductive material for forming the electrode of the secondary battery line dispersion.
delete An electrode for a secondary battery manufactured using the conductive material linear dispersion according to claim 13.
16. The method of claim 15,
The secondary battery electrode is a secondary battery electrode comprising a carbon nano tube (Carbon Nano Tube, CNT) as a linear conductive material.
16. The method of claim 15,
The secondary battery electrode is a secondary battery electrode comprising fine fibrous carbon having a diameter of less than 100 nm and fibrous carbon having a diameter of 100 nm or more as a linear conductive material.
16. The method of claim 15,
The electrode for a secondary battery comprising at least one selected from the group consisting of carbon black, acetylene black, oil furnace black, ketjen black, channel black, furnace black, lamp black and summer black as a point-shaped conductive material.
delete delete an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode;
a battery case housing the electrode assembly; and
Including; electrolyte injected into the battery case;
At least one of the positive electrode and the negative electrode is a lithium secondary battery according to any one of claims 15 to 18.

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