KR102258831B1 - Negative electrode slurry and negative electrode using the slurry - Google Patents

Abstract

The present invention provides a negative electrode slurry in which a mixture of a negative electrode active material, an aqueous binder, and a thickener is dispersed in an aqueous solvent in order to improve the dispersibility of the negative electrode slurry and at the same time to improve the adhesion of the negative electrode, wherein the negative electrode slurry contains sodium ions in a predetermined range. It is included in a concentration of, and the negative electrode prepared therefrom has excellent electrode adhesion and resistance.

Description

Negative electrode slurry and negative electrode using the slurry

The present invention relates to a negative electrode slurry and a negative electrode using the slurry.

Lithium secondary batteries generally include a positive electrode having a positive electrode active material layer formed on at least one surface of a positive electrode current collector, a negative electrode having a negative active material layer formed on at least one surface of the negative electrode current collector, and interposed between the positive electrode and the negative electrode to electrically insulate them. A separator is provided. As a method of forming the negative active material layer on the current collector, a negative active material slurry in which negative active material particles and a binder are dispersed in a solvent is directly applied and dried on the current collector, or a negative active material slurry is applied and dried on a separate support. Then, the film peeled off from this support is formed by a method of laminating on a current collector. Since the binder performs a function of maintaining the binding between the negative active material particles as well as the negative active material particles and the current collector, it has a great influence on the performance of the electrode.

Polyvinylidene fluoride polymer used as a binder for lithium secondary batteries has the advantage of being electrochemically stable. However, there is an environmental problem that must be prepared as a negative electrode active material slurry by dissolving in an organic solvent such as NMP (N-methyl-2-pyrrolidone). Accordingly, recently, a method of forming an anode active material layer using an aqueous solvent such as water as a dispersion medium and a synthetic rubber such as styrene-butadiene rubber (SBR) as an aqueous binder has been used. Compared to PVdF, the SBR-based binder exhibits the same effect even when a small amount is used, and the SBR-based binder is electrochemically stable. When SBR-based binder is used, SBR can be dispersed in water, and water can be used as a slurry solvent for the electrode active material, so it is environmentally friendly.

Meanwhile, viscosity control is essential in the coating process, and viscosity, solid content concentration, coating layer thickness, coating rate, solvent evaporation rate, and solvent evaporation amount all organically influence each other. Therefore, when the SBR-based binder is used, a thickener is used to control the viscosity of the electrode slurry, and in particular, a cellulose-based thickener such as carboxymethylcellulose (CMC) or carboxymethylcellulose sodium salt (CMCNa) is being studied. As described above, when styrene-butadiene rubber (SBR) is used as a binder and a cellulose polymer is used as a thickener, an appropriate amount of sodium ions and counter ions contained in the binder and thickener generate COULOMB FORCE on the particle surface. So that the dispersibility of the slurry can be improved.

However, the present inventors have found that as the total content of sodium salt contained in the active material slurry increases, the electrode adhesion, that is, the adhesion between the active materials, and the adhesion between the active material and the electrode current collector decrease.

In this regard, the present inventors have found that the content of the sodium salt contained in the negative electrode slurry is mostly derived from the binder and the thickener, and that the content of the sodium salt that can be derived from the conductive material or the active material is insignificant or almost none.

In addition, the present inventors believe that sodium ions have a pure function of improving the solubility of the thickener and the phase stability of the binder, while the sodium salt contained in the thickener lowers the viscosity of the active material slurry and tends to impair the phase stability of the artificial graphite slurry. Also, it was found that the sodium salt contained in the binder increased the ionic strength, causing the slurry to agglomerate.

Accordingly, the present inventors have found that it is necessary to appropriately control the total content of sodium salt contained in the negative electrode slurry, and at the same time, it is desirable to control the content of each of the sodium salt derived from the binder and the sodium salt derived from the thickener. .

Accordingly, a problem to be solved by the present invention is to provide a negative electrode slurry and a negative electrode including the same, which secures the phase stability of the negative electrode slurry and improves the adhesion of the negative electrode while having an appropriate range of resistance.

In order to solve the above problem, according to an aspect of the present invention, in a negative electrode slurry in which a mixture of a negative electrode active material, an aqueous binder, and a thickener is dispersed in an aqueous solvent, the ^{concentration of sodium ions (Na +} ) in the negative electrode slurry is the following equation: A negative electrode slurry satisfying 1 is provided:

[Equation 1]

40 ppmS <Na ⁺ ions <3000 ppmS

S represents the ratio (%) occupied by solid content in the total negative electrode slurry based on weight.

The sodium ion concentration may be based on the sum of the content of sodium ions derived from the aqueous binder and the thickener.

The aqueous binder is provided with a negative electrode slurry of styrene-butadiene rubber (SBR) containing 0.02 to 8% by weight of sodium.

The thickener may be a cellulose-based compound having a substituent including sodium having a degree of substitution of 0.6 to 1.4.

The cellulose-based compounds include methylcellulose, ethylcellulose, hydroxyethylcellulose, benzylcellulose, tritylcellulose, cyanoethylcellulose, carboxymethylcellulose, carboxyethylcellulose, aminoethylcellulose, nitrocellulose, cellulose ether, and carboxymethylcellulose. It may be any one selected from the group consisting of the salts or a mixture of two or more of them, and these compounds have a degree of substitution of 0.6 to 1.4 as described above.

The weight average molecular weight of the cellulose-based compound may be 20,000 to 4,000,000.

The negative electrode slurry may include 92 to 99% by weight of the negative active material, 0.5 to 4% by weight of the aqueous binder, and 0.5 to 2% by weight of the thickener based on the solid content constituting the negative electrode slurry.

The negative active material may be a carbon-based material.

The negative electrode slurry may further include a conductive material.

The conductive material may include two or more selected from the group consisting of carbon nanotubes, carbon nanowires, carbon nanofibers, graphite, activated carbon, and graphene.

The aqueous solvent may be one or more selected from the group consisting of water, methanol, ethanol, ethylene glycol, diethylene glycol, and glycerol.

According to another aspect of the present invention, in the negative electrode slurry in which a mixture of a negative active material, an aqueous binder, and a thickener is dispersed in an aqueous solvent, the aqueous binder is styrene-butadiene rubber (SBR), and the thickener is carboxy. Methylcellulose sodium salt (CMCNa), and the sodium ion content (F _Na ) in the negative electrode slurry satisfies the following Equation 2, thereby providing a negative electrode slurry.

[Equation 2]

(F _CMCNa * A + F _SBR * 0.02) S ≤ F _Na ≤ (23 * F _CMCNa + F _SBR *0.5) S

In the above, S represents the ratio (%) of the total negative electrode slurry on a weight basis, F _SBR represents the SBR weight content ratio (%) in the electrode, and FCMCNa is the CMCNa weight content ratio (%) in the electrode, ^{A is the content of Na +} ions contained in CMCNa, A= 23 * D _sub / (80 * D _sub +162), and D _sub is the degree of substitution of CMCNa.

According to another aspect of the present invention, a negative electrode current collector; And a negative electrode mixture layer formed on at least one surface of the negative electrode current collector, wherein the negative electrode mixture layer is made of the aforementioned negative electrode slurry.

According to an embodiment of the present invention, by appropriately controlling the total content of sodium salt contained in the negative electrode slurry, electrode resistance may be lowered, electrode adhesion may be improved, and electrode rolling roll contamination generated during electrode rolling may be reduced. I can.

In addition, by controlling the sodium salt derived from the binder within a predetermined range, agglomeration of the binder can be suppressed to have improved slurry dispersibility, and by controlling the sodium salt derived from the thickener within a predetermined range, a decrease in slurry viscosity can be suppressed.

The following drawings attached to the present specification illustrate preferred embodiments of the present invention, and serve to further understand the technical idea of the present invention together with the contents of the above-described invention, so the present invention is limited to the matters described in such drawings. It is limited and should not be interpreted.
1 is a graph showing the results of measuring the resistance of the negative electrode prepared according to Examples 3, 4 and 6 to 8 and Comparative Examples 1 and 2.

Hereinafter, the present invention will be described in detail. The terms or words used in the specification and claims should not be construed as being limited to their usual or dictionary meanings, and the inventor may appropriately define the concept of terms in order to describe his own invention in the best way. It should be interpreted as a meaning and concept consistent with the technical idea of the present invention based on the principle that there is.

According to an embodiment of the present invention, the negative electrode slurry includes a mixture of a negative electrode active material, an aqueous binder, and a thickener, and the content of sodium ions in the negative electrode slurry satisfies the following equation.

[Equation 2]

(F _CMCNa * A + F _SBR * 0.02) S ≤ F _Na ≤ (F _CMCNa * A + F _SBR *0.5) S

In the above, S represents the ratio (%) of the total negative electrode slurry on a weight basis, F _SBR represents the SBR weight content ratio (%) in the electrode, and FCMCNa is the CMCNa weight content ratio (%) in the electrode, ^{A is the content of Na +} ions contained in CMCNa, A= 23 * D _sub / (80 * D _sub +162), and D _sub is the degree of substitution of CMCNa.

In addition, each of the aqueous binder and the thickener contains a sodium salt. When the concentration of sodium ions in the negative electrode slurry having a solid content of 50% is less than the above conditions, the dispersibility of CMC and SBR is not secured, and when the concentration of sodium ions exceeds the above conditions, a decrease in adhesion occurs.

The aqueous binder may be styrene-butadiene rubber (SBR), and the styrene-butadiene rubber uses a surfactant containing sodium ions for polymerization, or at least one hydrogen constituting the styrene-butadiene rubber compound is substituted with sodium ions. Can be. The styrene-butadiene rubber may contain 0.02 to 8% by weight of sodium ions based on the weight of the styrene-butadiene rubber. When the sodium content of the styrene-butadiene rubber is less than 0.02% by weight, the coulomb force of the surface of the aqueous binder particles decreases, resulting in poor dispersibility between the particles, and aggregation between the aqueous rubber particles impairs the slurry phase stability as well as the binder unevenness. This may cause a decrease in electrode properties. When the sodium content of the styrene-butadiene rubber is greater than 8% by weight, there is a problem in that the adhesive strength of the electrode decreases due to a decrease in the dispersibility of the thickener and a binder migration phenomenon in which the binder moves together with evaporating water during drying. Preferably, the sodium content of the styrene-butadiene rubber may be 0.05 to 8% by weight based on the weight of the styrene butadiene rubber.

In order to adjust the sodium content in the styrene-butadiene rubber to the above range, among the monomers constituting the styrene-butadiene rubber, the content of sodium acrylate, which is in the form of a salt of acrylic acid, is reduced or , Methyl acrylate (methyl acrylate), ethyl acrylate (ethyl acrylate), sodium acrylate is synthesized by replacing it with a monomer such as methyl methacrylate (MMA), or some styrene-butadiene rubber is substituted with styrene-butadiene. It can be controlled by synthesizing so that it is composed only of

In addition, a surfactant may be used for aqueous polymerization of styrene-butadiene rubber. For example, anionic surfactants include carboxylate, amino acid salts, sulfates, sulfonates, alpha sulfonated fatty acid salts, and phosphate ester salts including sodium and hydrocarbon.

The thickener used according to an embodiment of the present invention may be a cellulose-based compound having a degree of substitution of 0.6 to 1.4 by sodium.

Non-limiting examples of such cellulose-based compounds include methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, benzyl cellulose, trityl cellulose, cyanoethyl cellulose, carboxymethyl cellulose, carboxyethyl cellulose, aminoethyl cellulose, nitrocellulose, cellulose It may be any one selected from the group consisting of ether and carboxymethylcellulose and salts thereof, or a mixture of two or more thereof, and the degree of substitution by sodium in each of these compounds may range from 0.6 to 1.4 as described above.

In addition, the cellulose-based compound may have a weight average molecular weight of 20,000 to 4,000,000. In the case of using a cellulose-based compound having a molecular weight and degree of substitution within the above range, the solid content ratio of the negative active material can be increased due to the improved dispersibility of the negative electrode slurry, stabilization of the viscosity of the negative electrode slurry, and even distribution of the active material and the conductive agent. The capacity and rate characteristics of can be improved.

In the cellulose-based compound, the average number of substitution groups substituted in cellulose per cellulose repeating unit is referred to as the degree of substitution (DS). For example, it has the following empirical formula (1) according to the degree of substitution of sodium carboxymethylcellulose salt (CMCNa). When one CMC monomer unit has a degree of substitution x,

C _{6+ 2x} H _{10 + x} O _{5 + 2x} Na _x … Experimental equation (1)

At this time, the Na content in CMCNa is expressed as 23x/(80x+162).

The negative electrode slurry according to an embodiment of the present invention comprises 92 to 99% by weight of the negative active material, 0.5 to 4% by weight of the aqueous binder, and 0.5 to 2% by weight of the thickener based on 100% by weight of solids constituting the negative electrode slurry. It may be formed by dispersing or dissolving in.

The negative active material may be a carbon-based negative active material such as crystalline carbon, amorphous carbon, or a carbon composite alone or in combination of two or more, and graphite such as natural graphite and artificial graphite as crystalline carbon It can be carbon.

The aqueous solvent may be one or more selected from the group consisting of water, methanol, ethanol, ethylene glycol, diethylene glycol, and glycerol. Preferably, the aqueous solvent is water.

According to another embodiment of the present invention, the negative electrode slurry may further include a conductive material. Such a conductive material is not particularly limited as long as it has conductivity without causing side reactions with other elements of the battery. For example, natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon nanotube, fullerene, carbon fiber, metal fiber, carbon fluoride, aluminum, nickel Any one selected from the group consisting of powder, zinc oxide, potassium titanate, titanium oxide and polyphenylene derivatives, or a mixture of two or more of them may be used.

Further, according to another aspect of the present invention, in the negative electrode slurry in which a mixture of a negative active material, an aqueous binder, and a thickener is dispersed in an aqueous solvent, the aqueous binder is styrene-butadiene rubber (SBR), and the The thickener is carboxymethylcellulose sodium salt (CMCNa), and the sodium content (F _Na ) in the negative electrode slurry is provided with a negative electrode slurry that satisfies the following equation.

[Equation 2]

(F _CMCNa * A + F _SBR * 0.02) S ≤ F _Na ≤ (F _CMCNa * A + F _SBR *0.5) S

In the above, S represents the ratio (%) of the total negative electrode slurry on a weight basis, F _SBR represents the SBR weight content ratio (%) in the electrode, and FCMCNa is the CMCNa weight content ratio (%) in the electrode, ^{A is the content of Na +} ions contained in CMCNa, A= 23 * D _sub / (80 * D _sub +162), and D _sub is the degree of substitution of CMCNa.

In another embodiment of the present invention, preferably, the sodium content in the solids of the negative electrode slurry may range from 500 to 2000 ppm. If the sodium content is less than the lower limit, the dissolution of carboxymethyl cellulose and the phase stability of the styrene-butadiene rubber are detrimental, and if it is greater than the upper limit, the electrode process is detrimental. In addition, the sodium content may be determined differently depending on whether the negative electrode and other electrode components, for example, sufficient adhesion can be secured. If the adhesion can be sufficiently secured by the other components bonded to the negative electrode, the negative electrode slurry While increasing the sodium content is helpful in lowering the battery resistance, when the adhesion by other components that bind to the negative electrode is insufficient, it is preferable to minimize the sodium content of the negative electrode slurry so as not to impair the adhesion.

In addition, according to another aspect of the present invention, there is provided a negative electrode current collector, a negative electrode formed on at least one surface of the negative electrode current collector and made of the above-described negative electrode slurry.

The negative electrode current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, the surface of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel For the surface treatment with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloys and the like may be used. In addition, like the positive electrode current collector, it is possible to enhance the bonding strength of the negative electrode active material by forming fine irregularities on the surface thereof, and it may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

Hereinafter, examples will be described in detail in order to describe the present invention in detail. However, the embodiments according to the present invention may be modified in 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 more clearly and completely describe the present invention to those of ordinary skill in the art.

Example One

A negative active material was prepared by mixing spherical graphite and flaky graphite as a negative electrode active material at a weight ratio of 9:1. Subsequently, (1) the prepared negative electrode active material, (2) spherical and flaky graphite having a particle diameter of 30 nm as a conductive material, (3) a styrene-butadiene rubber having a sodium content of 0.2% by weight as a binder, and (4) a thickener. Carboxymethylcellulose (molecular weight 1.6 million g/mol), which has a degree of sodium substitution of 1.1 and does not contain sodium, is mixed in a weight ratio of 95.7:1:2.2:1.1 and mixed with water as a solvent to prepare a uniform negative electrode slurry. I did. The sodium concentration in the 50% solid negative electrode slurry was 20 ppm.

The prepared negative electrode slurry was coated on a copper foil having a thickness of 10 μm at a weight of 350 mg/25 cm 2, and then dried and rolled in a vacuum oven at 100° C. to prepare a negative electrode.

_{LiNi 1/3 Co 1/3} Mn 1/3 O 2, the PVdF as a Super-P, a binder 98 as the conductive material as a positive electrode active material: 1: After producing the positive electrode material mixture slurry was mixed in a 1, this positive electrode mixture slurry After coating on aluminum foil, which is a metal current collector, it was dried in a vacuum oven at 120° C. for 2 hours or more to prepare a positive electrode.

Using the negative electrode and the positive electrode prepared above, interposing a polypropylene separator between the negative electrode and the positive electrode, and then injecting a 1:1 ethylene carbonate (EC) and dimethyl carbonate (DMC) solution in a volume ratio of 1 M _{LiPF 6 dissolved therein.} A rectangular monocell (cathode 17.34 cm 2 / anode 16.5 cm 2) was prepared.

Example 2

The negative electrode active material of Example 1, the conductive material of Example 1, a styrene-butadiene rubber having a sodium content of 0.4% by weight as a binder, carboxymethylcellulose (CMC, degree of substitution 1.1, molecular weight 1.6 million g/mol) and carboxy as a thickener The same negative electrode as in Example 1 was prepared, except that methylcellulose sodium (CMCNa, sodium substitution degree 1.1, molecular weight 1.6 million g/mol) was used in a weight composition ratio of 95.7:1:2.2:0.5:0.6. In the above, the CMCNa Na content was 10%, and the concentration of sodium ions in the 50% solid negative electrode slurry was 350 ppm.

Example 3

The negative electrode active material of Example 1, the conductive material of Example 1, a styrene-butadiene rubber having a sodium content of 0.02% by weight as a binder, and carboxymethylcellulose sodium (CMCNa, degree of substitution 0.8, molecular weight 3 million g/mol) as a thickener A negative electrode was prepared in the same manner as in Example 1, except that it was used in a weight composition ratio of 95.7:1:2.2:1.1. In the above, the CMCNa Na content was 8%, and the concentration of sodium ions in the 50% solid negative electrode slurry was 450 ppm.

Example 4

The negative electrode active material of Example 1, the conductive material of Example 1, a styrene-butadiene rubber having a sodium content of 0.1% by weight as a binder, and sodium carboxymethylcellulose (CMCNa, degree of substitution: 0.9, molecular weight 1.8 million g/mol) as a thickener A negative electrode was prepared in the same manner as in Example 1, except that it was used in a weight composition ratio of 95.7:1:2.2:1.1. In the above, the CMCNa Na content was 9%, and the concentration of sodium ions in the 50% solid negative electrode slurry was 500 ppm.

Example 5

The negative electrode active material of Example 1, the conductive material of Example 1, a styrene-butadiene rubber having a sodium content of 0.8% by weight as a binder, and sodium carboxymethylcellulose (CMCNa, degree of substitution 1.1, molecular weight 1.6 million g/mol) as a thickener A negative electrode was prepared in the same manner as in Example 1, except that it was used in a weight composition ratio of 95.7:1:2.2:1.1. In the above, the CMCNa Na content was 10%, and the concentration of sodium ions in the 50% solid negative electrode slurry was 650 ppm.

Example 6

The negative electrode active material of Example 1, the conductive material of Example 1, a styrene-butadiene rubber having a sodium content of 1.8% by weight as a binder, and sodium carboxymethylcellulose (CMCNa, degree of substitution 1.1, molecular weight 1.6 million g/mol) as a thickener A negative electrode was prepared in the same manner as in Example 1, except that it was used in a weight composition ratio of 95.7:1:2.2:1.1. In the above, the CMCNa Na content was 10%, and the concentration of sodium ions in the 50% solid negative electrode slurry was 750 ppm.

Example 7

The negative electrode active material of Example 1, the conductive material of Example 1, a styrene-butadiene rubber having a sodium content of 2.7% by weight as a binder, and sodium carboxymethylcellulose (CMCNa, degree of substitution 1.1, molecular weight 1.6 million g/mol) as a thickener A negative electrode was prepared in the same manner as in Example 1, except that it was used in a weight composition ratio of 95.7:1:2.2:1.1. In the above, the CMCNa Na content was 10%, and the concentration of sodium ions in the 50% solid negative electrode slurry was 850 ppm.

Example 8

The negative active material of Example 1, the conductive material of Example 1, a styrene-butadiene rubber having a sodium content of 4.2% by weight as a binder, and sodium carboxymethylcellulose (CMCNa, degree of substitution 1.2, molecular weight 700,000 g/mol) as a thickener A negative electrode was prepared in the same manner as in Example 1, except that it was used in a weight composition ratio of 95.7:1:2.2:1.1. In the above, the CMCNa Na content was 11%, and the concentration of sodium ions in the 50% solid negative electrode slurry was 1050 ppm.

Comparative example One

The negative electrode active material of Example 1, the conductive material of Example 1, a styrene-butadiene rubber having a sodium content of 10.0% by weight as a binder, and sodium carboxymethylcellulose (CMCNa, degree of substitution 1.1, molecular weight 1.8 million g/mol) as a thickener A negative electrode was prepared in the same manner as in Example 1, except that it was used in a weight composition ratio of 95.7:1:2.2:1.1. In the above, the CMCNa Na content was 10%, and the concentration of sodium ions in the 50% solid negative electrode slurry was 1650 ppm.

Comparative example 2

The negative electrode active material of Example 1, the conductive material of Example 1, a styrene-butadiene rubber having a sodium content of 46.8% by weight as a binder, and sodium carboxymethylcellulose (CMCNa, degree of substitution 1.1, molecular weight 1.6 million g/mol) as a thickener A negative electrode was prepared in the same manner as in Example 1, except that it was used in a weight composition ratio of 95.7:1:2.2:1.1. In the above, the CMCNa Na content was 10%, and the concentration of sodium ions in the 50% solid negative electrode slurry was 5500 ppm.

Cathode adhesion measurement

The adhesion (gf/15mm) of the negative electrode mixture layer was measured using the negative electrode prepared according to Examples 1 to 8 and Comparative Examples 1 and 2, and the measured results are shown in Table 1 below. The adhesive force was cut into 1.5 mm width of the electrode and fixed to the slide glass, and the peel strength was measured at 180 degrees while peeling off the electrode current collector.

Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Comparative Example 1 Comparative Example 2 Fold
Sack
Force 31.8 26.9 25 23 20 17 14 10 Tally Tally

Cathode resistance measurement

Using the negative electrodes prepared according to Examples 3 to 4 and 6 to 8 and Comparative Examples 1 and 2, the resistance of the negative electrode mixture layer according to the SOC condition was measured, and the measurement results are shown in FIG. 1. As for the discharge resistance, the prepared battery was charged with an end voltage of 4.2 V and an end of discharge voltage of 3.0 V, and the discharge resistance was measured for 30 seconds at 1C for each SOC. The measurement results of the discharge resistance of the monocell under the SOC 50% condition are shown in Table 2 below.

Example 3 Example 4 Example 6 Example 7 Example 8 Comparative Example 1 Comparative Example 2 Resistance (ohm) 1.9 1.8 1.8 1.7 1.6 Not measurable Not measurable

In the case of Comparative Example 1 and Comparative Example 2, electrodes were not evenly distributed on the current collector due to the detachment phenomenon of the negative electrode during battery fabrication. Due to poor contact at the interface between the current collector and the electrode, the measurement could not be performed because the measurement values did not converge when measuring resistance for 5 or more battery sets made with the corresponding electrode.

The above description is merely illustrative of the technical idea of the present invention, and those of ordinary skill in the art to which the present invention pertains will be able to make various modifications and variations without departing from the essential characteristics of the present invention. Accordingly, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention, but to explain the technical idea, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be interpreted by the following claims, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of the present invention.

Claims (12)

In the negative electrode slurry in which a mixture of a negative electrode active material, an aqueous binder, and a thickener is dispersed in an aqueous solvent,
Sodium-substituted styrene-butadiene rubber so that the aqueous binder contains 0.02 to 8% by weight of sodium,
The sodium ion concentration in the negative electrode slurry is due to the sum of the content of sodium ions derived from the aqueous binder and the thickener,
A negative electrode slurry in which the sodium ion concentration in the negative electrode slurry satisfies the following Equation 1:
[Equation 1]
40 ppmS ≤ Na ⁺ ions <3000 ppmS
S represents the ratio (%) occupied by solid content in the total negative electrode slurry based on weight.
delete delete The method of claim 1,
The negative electrode slurry, characterized in that the thickener is a cellulose-based compound having a degree of substitution of 0.6 to 1.4.
The method of claim 4,
The cellulose-based compounds include methylcellulose, ethylcellulose, hydroxyethylcellulose, benzylcellulose, tritylcellulose, cyanoethylcellulose, carboxymethylcellulose, carboxyethylcellulose, aminoethylcellulose, nitrocellulose, cellulose ether, and carboxymethylcellulose. A negative electrode slurry, characterized in that it is any one selected from the group consisting of the salts or a mixture of two or more of them.
The method of claim 4,
The negative electrode slurry, characterized in that the weight average molecular weight of the cellulose-based compound is 20,000 to 4,000,000.
The method of claim 1,
The negative electrode slurry comprises 92 to 99% by weight of a negative electrode active material, 0.5 to 4% by weight of an aqueous binder, and 0.5 to 2% by weight of a thickener.
The method of claim 1,
The negative electrode slurry, characterized in that the negative active material is a carbon-based material.
The method of claim 1,
The negative electrode slurry further comprises a conductive material.
The method of claim 1,
The aqueous solvent is a negative electrode slurry, characterized in that at least one selected from the group consisting of water, methanol, ethanol, ethylene glycol, diethylene glycol and glycerol.
In the negative electrode slurry in which a mixture of a negative electrode active material, an aqueous binder, and a thickener is dispersed in an aqueous solvent,
The aqueous binder is sodium-substituted styrene-butadiene rubber (SBR) to contain 0.02 to 8% by weight of sodium, and the thickener is carboxymethylcellulose sodium salt (CMCNa), and the sodium content in the negative electrode slurry (F _Na ) is due to the sum of the content of sodium ions derived from the aqueous binder and the thickener,
The negative electrode slurry, characterized in that the sodium content (F _Na ) in the negative electrode slurry satisfies Equation 2 below.
[Equation 2]
(F _CMCNa * A + F _SBR * 0.02) S ≤ F _Na ≤ (F _CMCNa * A + F _SBR *0.5) S
In the above, S represents the ratio (%) of the total negative electrode slurry on a weight basis, F _SBR represents the SBR weight content ratio (%) in the electrode, and FCMCNa is the CMCNa weight content ratio (%) in the electrode, ^{A is the content of Na +} ions contained in CMCNa, A= 23 * D _sub / (80 * D _sub +162), and D _sub is the degree of substitution of CMCNa.
Negative electrode current collector; And a negative electrode mixture layer formed on at least one surface of the negative electrode current collector,
The negative electrode mixture layer is a negative electrode, characterized in that made of the negative electrode slurry according to any one of claims 1 and 4 to 11.

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