KR20150071452A - A method for manufacturing a slurry an anode of lithium ion secondary battery - Google Patents

Abstract

The present invention relates to a manufacturing method of an anode slurry for a secondary battery and, more specifically, to a manufacturing method of a water-based anode slurry in which a conductor in a solvent is evenly dispersed in a process of manufacturing a water-based electrode. According to the present invention, a manufacturing method of a slurry for an anode has an effect of having a conductor evenly dispersed inside the water-based anode slurry. In addition, the anode manufactured according to the manufacturing method has an effect in improving conductive properties compared to the anode manufactured by a conventional method, thus can be effectively used for power for a device requiring high output.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a negative electrode slurry for secondary batteries,

The present invention relates to a method for producing an anode slurry for a secondary battery. More particularly, the present invention relates to a method for producing a water-based negative electrode slurry in which a conductive material in a solvent is uniformly dispersed in a water-based electrode manufacturing process.

Lithium secondary batteries are increasingly used in small electronic devices for electric vehicles and electric power storage, and there is a growing demand for cathode materials for secondary batteries having high stability, long life, high energy density and high output characteristics. Electrode binders that are currently commercially used in the manufacture of secondary batteries include polyvinylidene fluoride (PVDF) -based polymers such as PVDF homopolymer and polyvinylidene fluoride hexafluoropropylene copolymer (Korean Patent Laid-Open Publication No. 2001-0055968), polyvinylidene fluoride-chlorotrifluoroethylene copolymer, etc. These PVDF polymers have advantages of being stable chemically and electrochemically, N-methyl-2-pyrrolidone) to be used as a binder composition, there may be an environmental problem due to an organic solvent. Further, since the safety is deteriorated and the affinity with the liquid electrolyte is low This is a fundamental cause of deterioration of the performance of the electrode. Further, But has a disadvantage in that a large amount of the binder must be added in order to exhibit and maintain a sufficient adhesive force because the adhesive strength with the current collector such as metal is not good.

In order to solve the above problems, a water-dispersible electrode composition using water as a dispersion medium (i.e., a solvent) has been proposed. In this case, an aqueous dispersion binder is used in place of the PVDF binder described above. As such an aqueous dispersion binder, styrene butadiene rubber (SBR) is mainly used. The electrode using the water-dispersed binder has a larger binding effect even in a small amount compared to the non-aqueous (organic solvent) binder, so that the ratio of the active material per volume can be increased, so that a high capacity and long life time characteristics can be given.

Reference 1 discloses a conventional process for producing a negative electrode of a secondary battery using water as a dispersion medium. Document 1 describes the effect of carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR) on the stability of suspension in the aqueous suspension preparation of natural graphite, a lithium ion battery anode material; Electrokinetic behavior and rheological behavior to evaluate the dispersion stability of suspensions with organic additives; as well as the microstructure, porosity and interrelation of the as-castsheet.

[Literature 1] Lee, Jin-Hun, " Process for manufacturing an aqueous suspension of a lithium ion battery anode material and evaluation of battery characteristics ", Master Thesis, Graduate School of Hanyang University, 2005.

As described above, in order to solve the problems of the prior art relating to a negative electrode made of a nonaqueous solvent, a technique of manufacturing a negative electrode using an aqueous dispersion solvent has been proposed. However, when water is used as a solvent for an electrode slurry and an aqueous dispersion binder is used The cathode of the electrode deteriorates the electrical conductivity of the electrode if various conditions are not optimized during the drying of the electrode. Therefore, it is necessary to add a conductive material to the aqueous anode. However, there is a problem that the charged conductive material is agglomerated without being uniformly dispersed in the aqueous slurry, so that the conductive effect is less effective than the amount of the charged conductive material.

It is an object of the present invention to provide a method for producing a negative electrode slurry having a uniform dispersion state of CNTs while minimizing aggregation of a conductive material in the preparation of a water-based negative electrode slurry containing a conductive material. Other objects and advantages of the present invention will become apparent from the following description. It is also to be easily understood that the objects and advantages of the present invention can be realized by the means or method described in the claims, and the combination thereof.

The present invention provides a novel negative electrode slurry production method for solving the above problems. The method comprises: (S10) mixing a conductive material with a dispersion medium to prepare a first mixture; (S20) mixing the first mixture and the negative electrode active material to prepare a second mixture; (S30) further adding a dispersion medium to the second mixture to prepare a third mixture; And (S40) mixing the third mixture with a binder to prepare a fourth mixture. Here, the dispersion medium includes a solvent and a thickener.

In the step (S10), the solid content of the first mixture is 1 wt% to 10 wt% based on 100 wt% of the first mixture and the solid content of the first mixture is 100 wt% .

In the step (S20), the solid content of the second mixture is 40% by weight to 90% by weight based on 100% by weight of the second mixture, and the solid content includes all the components except for the solvent in the second mixture .

In the step (S30), the solid content of the third mixture is 40% by weight to 75% by weight based on 100% by weight of the third mixture, and the solid content includes all the components other than the solvent in the third mixture .

In the step (S40), the solid content of the fourth mixture is 40% by weight to 70% by weight based on 100% by weight of the fourth mixture, wherein the solid content of all of the remaining components .

The negative electrode active material composition according to claim 1, wherein the content of the negative electrode active material, the conductive material, the thickener, and the binder in the negative electrode slurry is 90-99, the conductive material is 0.1-0.3, the thickener is 0.1-3, .

The negative electrode active material is selected from the group consisting of carbon materials including graphitic carbon such as non-graphitized carbon, natural graphite, artificial graphite, and graphite.

Further, in the cathode described above, the thickening agent is a cellulose-based polymer, and the binder is an aqueous dispersion binder.

In the above-mentioned negative electrode, the conductive material is at least one selected from the group consisting of carbon nanotubes, acetylene black, carbon black, natural graphite, artificial graphite, ketjen black, and carbon fiber.

The method for producing a slurry for a negative electrode according to the present invention has the effect of uniformly dispersing a conductive material in a water-based negative electrode slurry. In addition, the negative electrode prepared according to the above-described method has an effect of improving the conductivity as compared with the negative electrode manufactured by the conventional method, and can be effectively used for a power source for a device requiring a high output.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. On the other hand, the shape, size, scale or ratio of the elements in the drawings incorporated herein can be exaggerated to emphasize a clearer description.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a process flow chart illustrating a method of manufacturing a water-based negative electrode slurry according to the present invention in a time-series manner.
2 is a graphical representation of the dispersion state of a water-based negative electrode slurry according to Examples and Comparative Examples.

The terms or words used in the present specification and claims should not be construed to be limited to ordinary or dictionary terms and the inventor shall properly define the concept of the term in order to best explain its invention The present invention should be construed in accordance with the meaning and concept consistent with the technical idea of the present invention. In addition, since the embodiments described in the present specification and the configurations shown in the drawings are only the most preferred embodiments of the present invention and do not represent all the technical ideas of the present invention, It is to be understood that equivalents and modifications are possible.

The present invention provides a method for producing a negative electrode slurry for a secondary battery in which a conductive material is uniformly dispersed in an anode slurry. The method comprises: mixing a conductive material with a dispersion medium to prepare a first mixture; Mixing the first mixture and the negative electrode active material to prepare a second mixture; Further adding a dispersion medium to the second mixture to produce a third mixture; And mixing the third mixture with a binder to prepare a fourth mixture.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a process flow chart showing each step of the method for producing the negative electrode slurry of the present invention in a time-wise manner. Hereinafter, the slurry producing method of the present invention will be described in detail with reference to Fig.

First, the dispersion medium will be described. Herein, the dispersion medium means a dispersion medium for dispersing a solute such as a conductive material, an anode active material, a binder and a thickener contained in the negative electrode slurry of the present invention. In one specific embodiment of the present invention, the dispersion medium is a mixture of a solvent and a thickener. For example, water is used as the solvent. Generally, the negative electrode is prepared by uniformly mixing the negative electrode active material, the binder, etc. with the solvent at a suitable ratio to prepare an anode slurry, applying the slurry to the current collector, and drying and pressing the slurry. Usually, non-aqueous solvents are used as the solvent. This is because the non-aqueous solvent is advantageous in terms of ensuring adhesion between the active materials. However, organic solvents can pose a risk to the health or the natural environment of workers exposed to the work environment such as VOC generation. Further, due to the low affinity with the liquid electrolyte, it may be a fundamental cause of deterioration of electrode performance. Accordingly, the present invention produces an anode slurry according to a water-based electrode manufacturing process using water as a solvent.

As described later, a conductive material such as a carbon material such as CNT is difficult to uniformly disperse in an aqueous solution such as water because it exists as an aggregate of fine primary particles having a particle diameter of several tens to several hundreds of nanometers. In this case, if a predetermined amount of a thickener is added to the solvent, the dispersed phase is stabilized and the re-agglomeration of the particles is prevented, so that the dispersibility of the conductive material can be increased.

The thickening agent is a cellulose-based polymer. Non-limiting examples of the thickening agent include carboxyl methyl cellulose (CMC). Carboxyl methyl cellulose is excellent in thickening, spreading and adhesion. These characteristics increase the binding force between the active materials and prevent the active material from falling off the current collector, thereby exhibiting excellent cycle characteristics. In addition, CMC has a high water solubility and is easy to ionize, and is suitable for dispersing water in water together with an aqueous binder such as styrene-butadiene rubber (SBR) to carry out an aqueous electrode manufacturing process.

In one specific embodiment of the present invention, the content of the thickening agent in the dispersion medium may be in the range of 1.0 wt% to 2.0 wt% based on 100 wt% of the dispersion medium. However, the amount of the solvent and the thickener and / or the ratio thereof may vary depending on the content of the negative electrode active material and other components contained in the finally produced negative electrode, as described later.

Next, a conductive material is added to the dispersion medium and mixed to prepare a first mixture (S10).

The conductive material may be any of those conventionally used in the production of electrodes, and examples thereof include non-limiting examples of carbon nanotubes, acetylene black, carbon black, natural graphite, artificial graphite, ketjen black, carbon fiber, . In the present invention, the conductive material has a particle diameter of 1 탆 to 100 탆, preferably 3 탆 to 30 탆. When the diameter of the conductive material is less than the above-mentioned range, it is difficult to control the generation of agglomerates of the conductive material particles. On the other hand, when the diameter of the conductive material exceeds the above-mentioned range, the phase stability of the slurry may be deteriorated.

Preferably, the conductive material is a carbon nanotube (CNT). Carbon nanotubes are excellent materials in terms of strength, thermal conductivity, thermal stability and copper conductivity. However, this characteristic can be achieved when the carbon nanotubes can be homogeneously distributed and the contact between the carbon nanotubes and the active material is maximally formed. Therefore, it is necessary that the carbon nanotubes are dispersed in the form as isolated as possible, that is, without agglomerates.

For this purpose, the mixing may preferably be carried out with stirring or mechanical stirring using a magnetic stick. This agitation helps to disassemble and separate the conductive re-agglomerates and suppress the tendency to re-agglomerate.

In this step, the solid content of the first mixture is 1 wt% to 10 wt%, preferably 2 wt% to 7 wt%, based on 100 wt% of the first mixture. Hereinafter, in the present invention, the solid content refers to all the components except for the solvent in the mixture. In this step, the solid content includes the conductive material and the thickening agent. In the case where the content of the solid content is less than the above range, that is, when the content of the solid content in the first mixture is lower than the above-mentioned range, the conductive material tends to aggregate without being uniformly dispersed in the unit of primary particles. Further, even if agitation is involved for dispersing the active material in addition to the introduction of the active material in the later-described step, agglomeration between primary particles of the conductive material generated in this step tends to remain in a coagulated state without being solved.

Next, a second mixture is prepared by adding and mixing the negative active material into the first mixture (S20). The mixing can be performed preferably with stirring using a magnetic stick or mechanical stirring.

According to a specific embodiment of the present invention, the negative electrode active material may be a carbon-based material such as natural graphite, artificial graphite, expanded graphite, carbon fiber, non-graphitizable carbon, carbon black, carbon nanotube, fullerene and activated carbon; Metals such as Al, Si, Sn, Ag, Bi, Mg, Zn, In, Ge, Pb, Pd, Pt and Ti which can be alloyed with lithium and compounds containing these elements; Complexes of metals and their compounds and carbon and graphite materials; Lithium-containing nitride, and the like may be used, but the present invention is not limited thereto. Among them, a carbon-based material is more preferable.

Further, the carbon-based material is preferably consisting of a spherical particle, R value of Raman spectrum _{[R = I 1350 / I 1580} ] (I 1350 is 1350 cm ^- Raman intensity, I ₁₅₈₀ in the vicinity of ¹ 1580 cm ^{- 1} < / RTI > is a natural graphite having a degree of crystallinity of 0.30 to 1.0.

Such natural graphite can be manufactured into a spherical shape by pulverizing and assembling scaly natural graphite raw materials. The spherical natural graphite thus produced has a minimized specific surface area, so that the decomposition reaction of the electrolyte on the active material surface can be reduced. Therefore, when the spherical granulated natural graphite is mixed with natural graphite in scaly form, the filling density of the electrode increases and the energy density can be improved.

In this step, the solid content of the second mixture is 40 wt% to 90 wt%, preferably 50 wt% to 80 wt%, based on 100 wt% of the second mixture. In this step, the solid content includes the conductive material, the thickener, and the negative active material as the components other than the solvent in the second mixture.

Next, a third mixture is prepared by further adding a dispersion medium to the second mixture (S30). Since the dispersion medium is the same as the above-mentioned contents, detailed description is omitted. In this step, the solid content of the third mixture is 40 wt% to 75 wt%, preferably 45 wt% to 70 wt%, based on 100 wt% of the third mixture. In this step, the solid content includes a conductive material, a thickener, and a negative active material as a component other than the solvent in the third mixture.

Next, a binder is added to the third mixture to prepare a fourth mixture (S40). The binder is an aqueous dispersion binder for binding the negative electrode active material. The water-dispersed binder may be any of conventionally widely used water-dispersed binders. The water-dispersed binder may be one selected from the group consisting of styrene butadiene rubber, acrylonitrile-butadiene rubber, acrylonitrile-butadiene-styrene rubber, and hydroxypropyl methylcellulose, polyvinyl alcohol, hydroxypropylcellulose, and diacetylcellulose. And a combination of two or more thereof may be used. Particularly preferably, the binder is a styrene butadiene rubber.

At this stage, the solid content of the fourth mixture is 40 wt% to 70 wt%, preferably 45 wt% to 65 wt%, relative to 100 wt% of the third mixture. In this step, the solid content includes a conductive material, a thickener, a negative electrode active material, and a binder as a component excluding the solvent in the fourth mixture.

When the concentration of the solid component is less than the above-mentioned value, that is, when the content of the solid component is low, the productivity of the electrode is lowered, and the solvent may not be sufficiently removed during drying. On the other hand, if the solid content is excessively high, the coating on the current collector is not performed well, and the electrode quality may be deteriorated due to drying.

As described above, the negative electrode slurry production method according to the present invention has been described. The production method has the effect of obtaining a solid dispersion, particularly a uniformly dispersed phase of the conductive material, by a method of sequentially adding and mixing various kinds of solid components into the dispersion medium and adjusting the concentration of the mixture to be produced in each step.

FIG. 2 is a graphical representation of the dispersion state (a) of the aqueous negative electrode slurry according to the present invention and the dispersion states (b, c) of the comparative examples. (a), the conductive material and the negative electrode active material in the negative electrode slurry are dispersed very uniformly. However, in the cases of (b) and (c) in which the concentrations of the mixtures in the preparation of the first mixture and the second mixture are low or very low as compared with the present invention, the conductive material and the active material in the finally obtained negative electrode slurry are uniformly dispersed They can not be formed and are concentrated in one part of the conductive materials. In the case of manufacturing the negative electrode through the slurry in which the agglomerates remain, a predetermined conductive effect may not be obtained as compared with the amount of the conductive material, and resistance may be increased.

The negative electrode slurry obtained by the above method preferably has the following composition. The content ratio of the negative electrode active material, the conductive material, the thickener and the binder in the negative electrode slurry excluding the solvent is 90 to 99, the conductive material is 0.1 to 5, the thickener is 0.1 to 3, and the binder is 0.1 to 3 . However, it is apparent to those skilled in the art that the ratio between the solids content may be suitably changed within the object of the present invention depending on the final required cathode or the characteristics of the battery including such cathode. The negative electrode slurry of the present invention may further contain additives such as a stabilizer, a flame retardant, a lubricant, an antioxidant, a plasticizer, a dispersant, and an antistatic agent within the allowable range.

According to another aspect of the present invention, a negative electrode using the negative electrode slurry according to the present invention and an electrochemical device including the same can be manufactured. In the present invention, the electrochemical device includes all devices that perform an electrochemical reaction. Examples of the electrochemical device include capacitors such as all kinds of primary cells, secondary cells, fuel cells, solar cells, and super capacitors . Particularly, a lithium secondary battery including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery is preferable among the above secondary batteries.

According to a specific embodiment of the present invention, the lithium secondary battery includes a positive electrode, a negative electrode, and a separator interposed between the negative electrode and the positive electrode.

The negative electrode may be prepared by applying the above-described negative electrode slurry onto an anode current collector and then drying. The negative electrode current collector may be any of metals having high conductivity, which can easily adhere to the negative electrode mixture and have no reactivity in the voltage range of the electrochemical device. The kind of the current collector is not particularly limited. For example, the surface of the stainless steel, aluminum, nickel, titanium, sintered carbon, aluminum or stainless steel surface treated with carbon, nickel, titanium or silver Etc. may be used. In addition, the current collector may have fine irregularities on its surface to increase the adhesive force of the cathode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric are possible. Specifically, the current collector may be formed of aluminum, nickel, or a combination thereof, and may be formed by laminating substrates made of the above materials.

The anode may be prepared by applying a mixture of a cathode active material, a conductive material and a binder on a cathode current collector, followed by drying. If necessary, the mixture may further contain a filler. The cathode active material may be a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; Lithium manganese oxides such as Li _{1 + x} Mn _{2 - x} O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ 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 ; A Ni-site type lithium nickel oxide represented by the formula LiNi _{1 -x} MxO ₂ (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga and x = 0.01 to 0.3); Formula _{LiMn 2-x M x O 2} ( where, M = Co, Ni, Fe , Cr, and Zn, or Ta, x = 0.01 ~ 0.1 Im) or Li ₂ Mn ₃ MO ₈ (where, M = Fe, Co, Ni, Cu, or Zn); 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 cathode current collector generally has a thickness of 3 to 500 mu m. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery, and may be formed of a material such as stainless steel, aluminum, nickel, titanium, sintered carbon, or a surface of aluminum or stainless steel Treated with carbon, nickel, titanium, silver or the like may be used. The current collector may have fine irregularities on the surface thereof to increase the adhesive force of the cathode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric are possible.

The binder for the positive electrode active material is a component that assists in bonding of the active material to the conductive material and bonding to the current collector, and is usually added in an amount of 1 to 50 wt% based on the total weight of the positive electrode mixture. As such a binder, the high molecular weight polyacrylonitrile-acrylic acid copolymer may be used, but is not limited thereto. Other examples include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers and the like.

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

The secondary battery of the present invention can be manufactured by storing and sealing the electrode assembly in which the positive electrode and the negative electrode are laminated alternately with the separator together with the electrolytic solution on the casing material such as the battery case. The secondary battery can be manufactured by any conventional method without limitation.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to examples. However, the embodiments according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

Claims (10)

(S10) mixing a conductive material with a dispersion medium to prepare a first mixture;
(S20) mixing the first mixture and the negative electrode active material to prepare a second mixture;
(S30) further adding a dispersion medium to the second mixture to prepare a third mixture; And
(S40) mixing the third mixture with a binder to prepare a fourth mixture,
Wherein the dispersion medium comprises a solvent and a thickener.
The method according to claim 1,
In the step (S10), the solid content of the first mixture is 1 wt% to 10 wt% based on 100 wt% of the first mixture, wherein the solid content of the first mixture And all other components are contained in the negative electrode slurry.
The method according to claim 1,
In the step (S20), the solid content of the second mixture is 40% by weight to 90% by weight based on 100% by weight of the second mixture, wherein the solid content includes all the components except for the solvent By weight based on the total weight of the negative electrode slurry.
The method according to claim 1,
In the step (S30), the solid content of the third mixture is 40% by weight to 75% by weight based on 100% by weight of the third mixture, wherein the solid content includes all the components other than the solvent in the third mixture By weight based on the total weight of the negative electrode slurry.
The method according to claim 1,
In the step (S40), the solid content of the fourth mixture is 40% by weight to 70% by weight based on 100% by weight of the fourth mixture, wherein the solid content of all of the remaining components Wherein the negative electrode slurry is a negative electrode slurry.
The negative electrode active material composition according to claim 1, wherein the content of the negative electrode active material, the conductive material, the thickener, and the binder in the negative electrode slurry is 90-99, the conductive material is 0.1-0.3, the thickener is 0.1-3, By weight based on the total weight of the negative electrode slurry.
7. The method according to any one of claims 1 to 6,
Wherein the negative electrode active material is selected from the group consisting of carbon materials including graphitic carbon such as non-graphitized carbon, natural graphite, artificial graphite, and graphite.
7. The method according to any one of claims 1 to 6,
Wherein the thickener is a cellulose-based polymer.
7. The method according to any one of claims 1 to 6,
Wherein the binder is an aqueous dispersion binder.
7. The method according to any one of claims 1 to 6,
Wherein the conductive material is at least one selected from the group consisting of carbon nanotubes, acetylene black, carbon black, natural graphite, artificial graphite, Ketjen black, and carbon fiber.

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