KR20180092520A - Negative electrode slurry and negative electrode using the slurry - Google Patents

Abstract

The present invention relates to negative electrode slurry in which a mixture, composed of a negative electrode active material, a water-based binder, and a viscosity agent, is dispersed in a water-based solvent, in an attempt to improve adhesiveness in a negative electrode while increasing dispersibility of the negative electrode slurry. The negative electrode slurry contains sodium ions in a predetermined range of concentration, and the negative electrode produced therefrom has excellent electrode adhesiveness and resistance.

Description

[0001] The present invention relates to a negative electrode slurry and a negative electrode using the slurry,

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

The lithium secondary battery generally includes a cathode having a cathode active material layer formed on at least one surface of a cathode current collector, a cathode having a cathode active material layer formed on at least one surface of the anode current collector, and a cathode interposed between the anode and the cathode, And a separator. The negative electrode active material layer may be formed on the current collector by coating the negative electrode active material slurry in which the negative electrode active material particles and the binder are dispersed in a solvent directly on the current collector and drying or by applying the negative electrode active material slurry on a separate support , And then the film peeled off from the support is laminated on the current collector. The binder plays a role of binding the negative electrode active material particles and maintaining the binding between the negative electrode active material particles and the current collector, thereby greatly affecting the performance of the electrode.

The polyvinylidene fluoride polymer used as the binder of the lithium secondary battery has an advantage of being electrochemically stable. However, there is an environmental problem in that it must be dissolved in an organic solvent such as NMP (N-methyl-2-pyrrolidone) to prepare an anode active material slurry. Recently, a method of forming an anode active material layer by 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. SBR-based binders exhibit the same effect when used in a small amount compared with PVdF, and SBR-based binders are electrochemically stable. When an SBR system is used as a binder, the SBR can be dispersed in water, which makes it possible to use water as an electrode active material slurry solvent, which is environmentally friendly.

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

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

In this connection, the present inventors have found that the sodium salt content contained in the negative electrode slurry is mostly derived from a binder and a thickener, and that the sodium salt content that can be derived from the conductive material or the active material is insignificant or small.

Further, the present inventors have found that 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, while sodium ions have a net effect of improving the solubility of the thickener and the phase stability of the binder , And also found that the sodium salt contained in the binder increases the ionic strength and causes slurry aggregation.

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

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a negative electrode slurry which secures the phase stability of the negative electrode slurry and has an appropriate range of resistance while improving the adhesion of the negative electrode, and a negative electrode including the negative electrode slurry.

According to an aspect of the present invention, there is provided an anode slurry in which a mixture of an anode active material, an aqueous binder, and a thickener is dispersed in an aqueous solvent, wherein a sodium ion (Na ⁺ Lt; RTI ID = 0.0 > 1: < / RTI &

[Equation 1]

40 ppmS < Na ⁺ ion < 3000 ppmS

S is the weight percentage of the solid content in the entire negative electrode slurry.

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

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

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

The cellulose-based compound may be selected from the group consisting of methylcellulose, ethylcellulose, hydroxyethylcellulose, benzylcellulose, tritethylcellulose, cyanoethylcellulose, carboxymethylcellulose, carboxyethylcellulose, aminoethylcellulose, nitrocellulose, cellulose ether, carboxymethylcellulose A salt thereof, or a mixture of two or more thereof, and these compounds have a degree of substitution of 0.6 to 1.4 as described above.

The weight average molecular weight of the cellulosic compound may be 20,000 to 4,000,000.

The negative electrode slurry may include 92 to 99% by weight of the negative electrode 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 electrode active material may be a carbon-based material.

The negative electrode slurry may further include a conductive material.

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

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

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

&Quot; (2) &quot;

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

S represents the ratio of the solid content in the whole negative electrode slurry on a weight basis, F _SBR represents the SBR weight content ratio (%) in the electrode, FCMCNa represents the weight content ratio (%) of CMCNa 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, there is provided a negative electrode current collector comprising: a negative electrode collector; And a negative electrode mixture layer formed on at least one side of the negative electrode collector, wherein the negative electrode mixture layer is made of the negative electrode slurry described above.

According to an embodiment of the present invention, the total content of the sodium salt contained in the negative electrode slurry is appropriately controlled to lower the electrode resistance, improve the electrode adhesiveness, and reduce the electrode rolling roll contamination .

Further, by controlling the sodium salt derived from the binder to a predetermined range, the binder aggregation phenomenon can be suppressed and the slurry dispersibility can be improved, and the sodium salt derived from the thickener can be controlled to a predetermined range, whereby the slurry viscosity reduction can be suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate preferred embodiments of the invention and, together with the description of the invention given above, serve to further the understanding of the technical idea of the invention, It should not be construed as limited.
FIG. 1 is a graph showing the results of measuring the resistance of a negative electrode manufactured according to Examples 3, 4 and 6 to 8 and Comparative Examples 1 and 2. FIG.

Hereinafter, the present invention will be described in detail. The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

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.

&Quot; (2) &quot;

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

S represents the ratio of the solid content in the whole negative electrode slurry on a weight basis, F _SBR represents the SBR weight content ratio (%) in the electrode, FCMCNa represents the weight content ratio (%) of CMCNa 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 water-based binder and the thickener includes 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-mentioned condition, the dispersibility of CMC and SBR can not be ensured. If the concentration of sodium ion exceeds the above-mentioned condition,

The aqueous binder may be a styrene-butadiene rubber (SBR), and the styrene-butadiene rubber may be prepared by using a surfactant containing sodium ions for polymerization or by substituting one or more hydrogen atoms constituting the styrene-butadiene rubber compound with sodium ions . Such a styrene-butadiene rubber may include 0.02 to 8% by weight sodium ion based on the weight of the styrene-butadiene rubber. When the sodium content of the styrene-butadiene rubber is lower than 0.02% by weight, the coulombic force of the surface of the aqueous binder particle is lowered and the dispersibility between the particles is lowered. Aggregation between the aqueous rubber particles inhibits the stability of the slurry phase, Which may cause deterioration of the physical properties of the electrode. When the sodium content of the styrene-butadiene rubber is more than 8% by weight, there is a problem that the adhesive strength of the electrode is lowered due to the lowering of the dispersibility of the thickener and the migration of the binder together with the water in which the binder evaporates 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-mentioned range, it is necessary to reduce the content of sodium acrylate, which is a salt form of acrylic acid among the monomers constituting the styrene-butadiene rubber (Meth) acrylate, methyl acrylate, ethyl acrylate and sodium acrylate with a monomer such as methyl methacrylate (MMA), or a method in which a part of the styrene-butadiene rubber is styrene-butadiene And the like.

Surfactants may also be used for the aqueous polymerization of the styrene-butadiene rubber. For example, anionic surfactants include carboxylic acid salts, amino acid salts, sulfates, sulfonates, alpha sulfonated fatty acid salts, phosphoric ester salts and the like, including sodium and hydrocarbons.

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

Non-limiting examples of such a cellulosic compound include methylcellulose, ethylcellulose, hydroxyethylcellulose, benzylcellulose, tritylcellulose, cyanoethylcellulose, carboxymethylcellulose, carboxyethylcellulose, aminoethylcellulose, nitrocellulose, cellulose Ether, and carboxymethylcellulose and salts thereof, or a mixture of two or more thereof. The substitution degree by sodium in each of these compounds may be in the range of 0.6 to 1.4 as described above.

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

The average number of substitution groups substituted on cellulose per cellulosic repeating unit is referred to as a degree of substitution (DS). (1) according to the degree of substitution of carboxymethylcellulose sodium salt (CMCNa). When a CMC monomer unit has x degree of substitution,

_{C 6+ 2x H 10 + x O} 5 + 2x Na x ... The empirical formula (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 may contain 92 to 99% by weight of the negative electrode 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 the solid component constituting the negative electrode slurry, Or may be dispersed or dissolved therein.

The negative electrode active material may be a carbonaceous negative electrode active material such as crystalline carbon, amorphous carbon, or carbon composite. The carbonaceous negative electrode active material may be used alone or as a mixture of two or more thereof. Preferably, the carbonaceous active material is graphite, such as natural graphite and artificial graphite, Carbon.

The aqueous solvent may be at least one 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 is conductive 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, summer black, carbon nanotube, fullerene, carbon fiber, metal fiber, carbon fluoride, Powder, zinc oxide, potassium titanate, titanium oxide and polyphenylene derivative, or a mixture of two or more thereof may be used.

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

&Quot; (2) &quot;

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

S represents the ratio of the solid content in the whole negative electrode slurry on a weight basis, F _SBR represents the SBR weight content ratio (%) in the electrode, FCMCNa represents the weight content ratio (%) of CMCNa 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 negative electrode slurry solids may range from 500 to 2000 ppm. When the sodium content is lower than the lower limit, the stability of the carboxymethyl cellulose dissolution and the styrene-butadiene rubber is deteriorated. When the sodium content is larger than the upper limit, the electrode process becomes disadvantageous. In addition, the sodium content can be determined differently depending on the cathode and other electrode components, for example, whether the adhesive force can be sufficiently ensured. In the case where the adhesive force can be sufficiently secured by other components that are combined with the cathode, While increasing the sodium content helps lowering the battery resistance, it is desirable that the sodium content of the negative electrode slurry is minimized so as not to adversely affect the adhesive strength when the adhesive strength by other components that are bonded to the negative electrode is insufficient.

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 negative electrode current collector may have a surface of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, A surface treated with carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used. In addition, like the positive electrode collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams and nonwoven fabrics.

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 above-described embodiments. The embodiments of the present invention are provided so that those skilled in the art can explain the present invention more clearly and completely.

Example  One

Spherical graphite and scaly graphite were mixed as a negative electrode active material in a weight ratio of 9: 1 to prepare an anode active material. (3) a styrene-butadiene rubber having a sodium content of 0.2 wt% as a binder, and (4) a thickener as a binder. Carboxymethylcellulose (molecular weight: 1.6 million g / mol) having a sodium substitution degree of 1.1 and no sodium content was mixed at 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 Respectively. The sodium concentration in the solid 50% negative electrode slurry was 20 ppm.

The prepared negative electrode slurry was coated on a copper foil having a thickness of 10 mu m to a weight of 350 mg / 25 cm &lt; 2 &gt;, followed by drying and rolling in a vacuum oven at 100 DEG 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 Coated on an aluminum foil as a metal current collector, and then dried in a vacuum oven at 120 DEG C for 2 hours or more to prepare a positive electrode.

The prepared cathode and anode were used, and a polypropylene separator was interposed between the anode and the cathode. Then, ethylene carbonate (EC) and dimethyl carbonate (DMC) solutions having a volume ratio of 1: 1 in which 1 M of LiPF ₆ was dissolved were injected A monocell of a rectangular shape (cathode 17.34 cm 2 / anode 16.5 cm 2) was prepared.

Example  2

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

Example  3

(CMCNa, degree of substitution of 0.8, molecular weight: 3,000,000 g / mol) as a thickener was added to the negative active material of Example 1, the conductive material of Example 1, a styrene-butadiene rubber having a sodium content of 0.02% 95.7: 1: 2.2: 1.1 The same negative electrode as in Example 1 was prepared, except that the weight ratio was used. In the above, the content of CMCNa Na was 8%, and the concentration of sodium ions in the solid fraction 50% negative electrode slurry was 450 ppm.

Example  4

(CMCNa, degree of substitution of 0.9, molecular weight of 180,000 g / mol) as a thickener was added to the negative active material of Example 1, the conductive material of Example 1, the styrene-butadiene rubber having a sodium content of 0.1% by weight and the carboxymethylcellulose sodium 95.7: 1: 2.2: 1.1 The same negative electrode as in Example 1 was prepared, except that the weight ratio was used. In the above, the content of CMCNa Na was 9%, and the concentration of sodium ion in the solid fraction 50% negative electrode slurry was 500 ppm.

Example  5

(CMCNa, degree of substitution: 1.1, molecular weight: 1,600,000 g / mol) as a thickener was added to the negative active material of Example 1, the electroconductive material of Example 1, the styrene-butadiene rubber having a sodium content of 0.8% by weight and the carboxymethylcellulose sodium 95.7: 1: 2.2: 1.1 The same negative electrode as in Example 1 was prepared, except that the weight ratio was used. In the above, the content of CMCNa Na was 10%, and the concentration of sodium ion in the solid fraction 50% negative electrode slurry was 650 ppm.

Example  6

(CMCNa, degree of substitution 1.1, molecular weight: 1,600,000 g / mol) as a thickener was added to the negative 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 carboxymethylcellulose sodium 95.7: 1: 2.2: 1.1 The negative electrode was prepared in the same manner as in Example 1 except that the weight ratio was used. In the above, the content of CMCNa Na was 10%, and the concentration of sodium ion in the above 50% solid negative electrode slurry was 750 ppm.

Example  7

(CMCNa, degree of substitution 1.1, molecular weight: 1,600,000 g / mol) as a thickener was added to the negative active material of Example 1, the conductive material of Example 1, a styrene-butadiene rubber having a sodium content of 2.7% 95.7: 1: 2.2: 1.1 The negative electrode was prepared in the same manner as in Example 1 except that the weight ratio was used. In the above, the content of CMCNa Na was 10%, and the concentration of sodium ions in the solid fraction 50% negative electrode slurry was 850 ppm.

Example  8

(CMCNa, degree of substitution: 1.2, molecular weight: 700,000 g / mol) as a thickening agent was added to 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 and a carboxymethylcellulose sodium 95.7: 1: 2.2: 1.1 The negative electrode was prepared in the same manner as in Example 1 except that the weight ratio was used. In the above, the content of CMCNa Na was 11%, and the concentration of sodium ions in the solid fraction 50% negative electrode slurry was 1050 ppm.

Comparative Example  One

(CMCNa, degree of substitution 1.1, molecular weight: 1,800,000 g / mol) as a thickener was added to the negative active material of Example 1, the conductive material of Example 1, the styrene-butadiene rubber having a sodium content of 10.0% by weight and the carboxymethylcellulose sodium 95.7: 1: 2.2: 1.1 The negative electrode was prepared in the same manner as in Example 1 except that the weight ratio was used. In the above, the content of CMCNa Na was 10%, and the concentration of sodium ions in the solid content slurry of 50% was 1650 ppm.

Comparative Example  2

(CMCNa, degree of substitution 1.1, molecular weight: 1,600,000 g / mol) as a thickener was added to the negative active material of Example 1, the conductive material of Example 1, a styrene-butadiene rubber having a sodium content of 46.8 wt% 95.7: 1: 2.2: 1.1 The negative electrode was prepared in the same manner as in Example 1 except that the weight ratio was used. In the above, the content of CMCNa Na was 10%, and the concentration of sodium ions in the solid fraction 50% negative electrode slurry was 5500 ppm.

Cathode adhesion measurement

The adhesive force (gf / 15 mm) 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 to a width of 1.5 mm of the electrode and fixed to the slide glass, and the peel strength of 180 degrees was measured while peeling 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
Cling
Power 31.8 26.9 25 23 20 17 14 10 Tally Tally

Cathode resistance measurement

Resistance of the negative electrode mixture layer according to the SOC condition was measured using the negative electrode prepared according to Examples 3 to 4, 6 to 8, and Comparative Examples 1 and 2, and the measurement results are shown in FIG. The discharge resistance was measured at a charging end voltage of 4.2 V and a discharge end voltage of 3.0 V, and the discharging resistance was measured for 30 seconds at 1 C for each SOC. The measurement results of the discharge resistance of the mono cell at 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, the electrodes were not evenly distributed on the current collector due to the desorption phenomenon of the cathode at the time of manufacturing the battery. Because of the poor contact between the current collector and the electrode, the measurement value could not be measured because the measured value did not converge when measuring the resistance of 5 or more battery sets made of the electrode.

The foregoing description is merely illustrative of the technical idea of the present invention, and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, 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 construed according to the following claims, and all technical ideas within the scope of equivalents should be construed as falling within the scope of the present invention.

Claims (12)

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, wherein the negative electrode slurry satisfies the following formula (1)
[Equation 1]
40 ppmS < Na ⁺ ion < 3000 ppmS
S is the weight percentage of the solid content in the entire negative electrode slurry.
The method according to claim 1,
Wherein the sodium ion concentration is based on the sum of the sodium ion content derived from the aqueous binder and the thickener.
The method according to claim 1,
Wherein the aqueous binder is a sodium substituted styrene-butadiene rubber so as to include 0.02 to 8% by weight of sodium.
The method according to claim 1,
Wherein the thickener is a cellulose compound having a substitution degree of 0.6 to 1.4.
5. The method of claim 4,
The cellulose-based compound may be selected from the group consisting of methylcellulose, ethylcellulose, hydroxyethylcellulose, benzylcellulose, tritethylcellulose, cyanoethylcellulose, carboxymethylcellulose, carboxyethylcellulose, aminoethylcellulose, nitrocellulose, cellulose ether, carboxymethylcellulose And a mixture of two or more thereof.
5. The method of claim 4,
Wherein the cellulose-based compound has a weight-average molecular weight of 20,000 to 4,000,000.
The method according to claim 1,
Wherein the negative electrode slurry comprises 92 to 99% by weight of the 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 according to claim 1,
Wherein the negative electrode active material is a carbonaceous material.
The method according to claim 1,
Wherein the negative electrode slurry further comprises a conductive material.
The method according to claim 1,
Wherein the aqueous solvent is at least one selected from the group consisting of water, methanol, ethanol, ethylene glycol, diethylene glycol, and glycerol.
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,
Wherein the aqueous binder is styrene-butadiene rubber (SBR), the thickener is carboxymethylcellulose sodium salt (CMCNa), and the sodium content (F _Na ) in the negative electrode slurry satisfies the following formula Features cathodic slurry.
&Quot; (2) &quot;
(F _CMCNa * A + F _SBR * 0.02) S? F _Na ? (F _CMCNa * A + F _SBR * 0.5) S
S represents the ratio of the solid content in the whole negative electrode slurry on a weight basis, F _SBR represents the SBR weight content ratio (%) in the electrode, FCMCNa represents the weight content ratio (%) of CMCNa 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.
Cathode collector; And a negative electrode mixture layer formed on at least one surface of the negative electrode collector,
Wherein the negative electrode material mixture layer is made of the negative electrode slurry according to any one of claims 1 to 11.

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