Method for producing negative electrode composition for secondary battery

Abstract

The method of preparing a negative active material for a secondary battery according to an exemplary embodiment of the present application includes adding a negative active material powder and a first binder powder to a mixer, adding a first solvent and performing first mixing to form a primary negative electrode composition, and after forming the primary negative electrode composition, adding a second binder powder to the mixer and performing second mixing to form a negative electrode composition.

Description

Technical Field

[0001] The disclosure of this application relates to a method for preparing a negative electrode composition for a secondary battery, a negative electrode for a secondary battery manufactured using the negative electrode composition, and a secondary battery including the negative electrode. Background Technology

[0002] Rechargeable batteries are batteries that can be recharged and discharged repeatedly. With the development of the information communication and display industries, rechargeable batteries are widely used as power sources for portable electronic communication devices such as portable cameras, mobile phones, and laptops. In addition, in recent years, battery packs that include rechargeable batteries have been developed for use as power sources for environmentally friendly vehicles such as electric vehicles.

[0003] Secondary batteries can be categorized into lithium secondary batteries, nickel-cadmium batteries, and nickel-metal hydride batteries. Among them, lithium secondary batteries have high operating voltage and energy density per unit weight, and are advantageous for charging speed and lightweight design, so they are being actively developed and applied.

[0004] In recent years, with the expansion of applications for secondary batteries, manufacturing methods for negative electrodes used in secondary batteries with higher reliability and process stability are being developed. For example, depending on the order of raw material addition and the types of raw materials in the manufacturing process of the negative electrode, the resistance, adhesion, and life characteristics of the secondary battery may deteriorate. Summary of the Invention

[0005] (a) Technical problems to be solved According to one aspect of the present invention, a method for preparing a negative electrode composition for a secondary battery having improved dispersibility, stability, and adhesion, as well as reduced resistance, can be provided.

[0006] According to one aspect of the present invention, a negative electrode for a secondary battery with improved stability and lifespan characteristics and reduced resistance can be provided.

[0007] According to one aspect of the present invention, a secondary battery having improved stability and lifespan characteristics as well as reduced resistance can be provided.

[0008] (II) Technical Solution A method for preparing a negative electrode composition for a secondary battery according to an embodiment of the present invention includes: adding negative electrode active material powder and first binder powder to a mixer, adding a first solvent and performing a first mixing to form a primary negative electrode composition, and after forming the primary negative electrode composition, adding a second binder powder to the mixer and performing a second mixing to form a negative electrode composition.

[0009] In some implementations, the negative electrode active material powder and the first binder powder may be added to the operating mixer to form a powder mixture, and then the first solvent may be added.

[0010] In some embodiments, between the step of forming the primary negative electrode composition and the step of forming the negative electrode composition, a step of adding a second solvent to the mixer may be further included.

[0011] In some implementations, the second binder powder may be added to the mixer in two or more separate additions.

[0012] In some embodiments, the total content of solids, i.e., the first solids, in the primary negative electrode composition may be 65% to 75% by weight.

[0013] In some embodiments, the total content of solids, i.e., the second solids, in the primary negative electrode composition in which the second solvent is added may be 3% to 9% less by weight than the total content of the first solids.

[0014] In some embodiments, the first adhesive powder and the second adhesive powder may each independently comprise a compound containing repeating units represented by the following chemical formula 1: [Chemical Formula 1] In the chemical formula 1, M1 and M2 are each independently Na or Li, at least one of R1 to R4 is a group represented by the following chemical formula 2, and the rest are each independently H or a group represented by the following chemical formula 2, where n is an integer.

[0015] [Chemical Formula 2] In the chemical formula 2, R5 is -CHO, -CH2CHO, -COCH3, or -CH2COCH3. - Indicates the binding site where oxygen binds.

[0016] In some embodiments, the first adhesive powder and the second adhesive powder may each independently contain less than 20% by weight of a compound containing repeating units represented by the following chemical formula 3, based on the total content of each adhesive powder, or may not contain said compound: [Chemical Formula 3] In the chemical formula 3, M4 and M5 are each independently Na or Li, and n is an integer.

[0017] In some embodiments, the negative electrode active material may include at least one selected from artificial graphite and natural graphite.

[0018] In some embodiments, the first solvent and the second solvent may each independently include at least one selected from water, pure water, deionized water, distilled water, ethanol, isopropanol, methanol, acetone, n-propanol and tert-butanol.

[0019] In some embodiments, in the step of forming the negative electrode composition, after the second mixing, at least one of a third solvent and a third binder may be further added to the mixer and a third mixing may be performed to form the negative electrode composition.

[0020] In some embodiments, the third binder may be added to the mixer after the third solvent is added and the third mixing is performed to form the negative electrode composition.

[0021] In some embodiments, the viscosity of the first adhesive powder, i.e., the first viscosity, can be from 200 cP to 6500 cP.

[0022] In some embodiments, the viscosity of the second adhesive powder, i.e., the second viscosity, can be from 1500 cP to 9500 cP.

[0023] In some implementations, the first viscosity can be from 500 cP to 3500 cP.

[0024] In some implementations, the second viscosity can be from 3000 cP to 7000 cP.

[0025] In some implementations, the ratio of the second viscosity to the first viscosity can be from 1 to 10.

[0026] In some implementations, the ratio of the second viscosity to the first viscosity can be from 1 to 6.

[0027] According to an embodiment of the present invention, a negative electrode for a secondary battery comprises: a negative electrode current collector; and a negative electrode active material layer disposed on at least one side of the negative electrode current collector, wherein the negative electrode active material layer is formed from a negative electrode composition prepared by the above-described preparation method.

[0028] According to an embodiment of the present invention, a secondary battery includes: a negative electrode for the secondary battery; and a positive electrode, wherein the positive electrode is disposed opposite to the negative electrode.

[0029] (III) Beneficial Effects According to one embodiment of the present invention, a negative electrode composition for secondary batteries with improved dispersibility, stability and adhesion, and reduced resistance can be prepared.

[0030] According to one embodiment of the present invention, the lifespan and power characteristics of the negative electrode for a secondary battery manufactured using the aforementioned negative electrode composition can be improved.

[0031] According to one embodiment of the present invention, the lifetime and power characteristics of the secondary battery including the negative electrode can be improved.

[0032] The preparation method of the negative electrode composition for secondary batteries, the negative electrode, and the secondary battery of the present invention can be widely used in green technology fields such as electric vehicles, battery charging stations, and other battery-based solar power generation and wind power generation. The preparation method of the negative electrode composition for secondary batteries, the negative electrode, and the secondary battery of the present invention can be used in eco-friendly electric vehicles and hybrid vehicles to prevent climate change by suppressing air pollution and greenhouse gas emissions. Attached Figure Description

[0033] Figure 1 This is a schematic flowchart illustrating a method for preparing a negative electrode composition for a secondary battery according to an exemplary embodiment.

[0034] Figure 2 This is a schematic flowchart illustrating a method for preparing a negative electrode composition for a secondary battery according to another exemplary embodiment.

[0035] Figure 3 and Figure 4 These are schematic plan views and schematic cross-sectional views of a secondary battery according to an exemplary embodiment.

[0036] Figure 5 This is an internal image of the stirrer taken after the negative electrode composition was prepared according to Comparative Example 1. Detailed Implementation

[0037] This invention provides a method for preparing a negative electrode composition for secondary batteries (hereinafter, simply referred to as "negative electrode composition"). This invention provides a negative electrode composition prepared using the method described above. This invention provides a secondary battery manufactured using the negative electrode composition.

[0038] The embodiments of the present invention will now be described in detail. However, these are merely exemplary embodiments, and the present invention is not limited to the specific embodiments described herein.

[0039] <Preparation method of negative electrode composition> Figure 1This is a schematic flowchart illustrating a method for preparing a negative electrode composition for a secondary battery according to an exemplary embodiment.

[0040] Reference Figure 1 The negative electrode active material powder and the first binder powder can be added to the mixer (e.g., step S10), and the first solvent can be added to the mixer and a first mixing can be performed (e.g., step S20) to form a primary negative electrode composition.

[0041] For example, the mixer may be an automatic mixer driven by electric current.

[0042] The mixer can be driven at a constant speed by varying the maximum drive current until the negative electrode slurry is prepared.

[0043] For example, the first adhesive powder can be added in a solid state.

[0044] In an exemplary embodiment, the first adhesive powder and the first solvent are not added to the mixer in the form of an adhesive solution in which they are premixed.

[0045] In some embodiments, the first solvent may be added before the addition of the negative electrode active material powder and the first binder powder is complete. For example, the first solvent may be added together when the addition of the first binder powder is three-quarters complete, but this is not a limitation.

[0046] In some embodiments, the negative electrode active material powder and the first binder powder can be added to the running mixer to form a powder mixture, followed by the addition of the first solvent. For example, the mixer can be set to a constant speed (e.g., maximum speed) and driven, and the negative electrode active material powder and the first binder powder can be added to the driven mixer. Subsequently, the first solvent can be added to the driven mixer and a first mixing process can be performed.

[0047] Therefore, solvent shock, a phenomenon where the surface of the aggregate formed by the first binder powder swells, preventing the first solvent from penetrating, can be further suppressed. Consequently, the dispersibility of the negative electrode active material and the first binder, as well as the lifespan characteristics of the secondary battery, can be further improved, and internal resistance can be reduced.

[0048] For example, the first solvent can be added 1 to 20 seconds after the addition of the negative electrode active material powder and the first binder powder is completed. Within this range, the solvent shock phenomenon can be sufficiently mitigated.

[0049] In some embodiments, the total content of the solids in the primary negative electrode composition, i.e., the first solids, may be from 65% to 75% by weight.

[0050] For example, the first mixing may be carried out at 20°C to 60°C.

[0051] In one embodiment, the first mixing may be carried out by a kneading process. For example, the primary negative electrode composition may be formed into a kneaded form.

[0052] The negative electrode active material powder (hereinafter, may be simply referred to as "negative electrode active material") may include a material capable of adsorbing and desorbing lithium ions. For example, the negative electrode active material may use carbon-based materials such as crystalline carbon, amorphous carbon, carbon composites, carbon fibers, etc.; lithium metal; lithium alloys; silicon (Si)-containing substances or tin (Sn)-containing substances, etc. These may be used alone or in combination of two or more.

[0053] The amorphous carbon may include hard carbon, soft carbon, coke, mesocarbon microbead (MCMB), mesophase pitch-based carbon fiber (MPCF), etc.

[0054] The crystalline carbon may include graphite-based carbons such as natural graphite, artificial graphite, graphitized coke, graphitized MCMB, graphitized MPCF, etc.

[0055] The lithium metal may include pure lithium metal and / or lithium metal formed with a protective layer for inhibiting dendrite growth, etc. In one embodiment, a lithium metal-containing layer deposited or coated on the negative electrode current collector may be used as the negative electrode active material layer. In one embodiment, a lithium thin film layer may also be used as the negative electrode active material layer.

[0056] As the elements contained in the lithium alloy, aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, indium, etc. may be cited. These may be used alone or in combination of two or more.

[0057] The silicon-containing substance may provide further improved capacity characteristics. The silicon-containing substance may include Si, SiO x (0 < x < 2), metal-doped SiO x (0 < x < 2), silicon-carbon composites, etc.

[0058] The metal may include lithium and / or magnesium, and metal-doped SiO x (0 < x < 2) may include metal silicates.

[0059] In some embodiments, the content of silicon-based active material particles in the negative electrode active material can be from 5% to 15% by weight, for example, from 9% to 13% by weight, based on the total weight of the negative electrode active material.

[0060] In an exemplary embodiment, the negative electrode active material may include at least one selected from artificial graphite and natural graphite. Therefore, power characteristics can be improved and costs reduced.

[0061] In an exemplary embodiment, the first adhesive powder may comprise carboxymethyl cellulose and / or its salts comprising a hemiacetal functional group derived from the reaction of at least one free hydroxyl group with an aldehyde compound.

[0062] The first adhesive powder may comprise a product formed by a noncyclic hemiacetal reaction (hereinafter referred to as hemiacetal reaction) between at least one free hydroxyl group (-OH) of carboxymethyl cellulose (CMC) and / or its salt and an aldehyde compound. The metal contained in the salt may be an alkali metal, such as lithium, sodium, calcium, etc.

[0063] Specifically, the free hydroxyl group reacts with the -CHO group of the aldehyde compound, and one hydroxyl group and one ether bond (-O-) form a direct bond on the same carbon atom.

[0064] A group comprising a carbon atom that forms one hydroxyl group and one ether bond (-O-) through the hemiacetal reaction can be defined as an acyclic hemiacetal functional group (hereinafter, simply referred to as a hemiacetal functional group). That is, the product can be carboxymethyl cellulose and / or its salts in the form of the hydroxyl group participating in the hemiacetal reaction being replaced by the hemiacetal functional group.

[0065] For example, carboxymethyl cellulose and / or its salts containing the hemiacetal functional group can be prepared by mixing CMC and / or its salts, which are etherified solely by methyl carboxylic acid and / or its salts, with an aldehyde compound and heating. The aldehyde compound may include monoaldehyde and / or dialdehyde compounds. The aldehyde compound may include, for example, glyoxal, methyl glyoxal, etc.

[0066] Carboxymethyl cellulose or its salts containing the hemiacetal functional group can be represented, for example, by the following chemical formula A.

[0067] [Chemical Formula A] In the chemical formula A, CMC represents a repeating unit constituting the main chain of carboxymethyl cellulose or its salt, and the functional group associated with CMC represents a hemiacetal functional group. R can be, for example, an alkyl group, or an alkyl group with an aldehyde or ketone group at the end.

[0068] Compared to compositions using only CMCs and / or their salts whose hydroxyl groups are not substituted with the aforementioned hemiacetal functional groups, the negative electrode compositions according to embodiments of the present invention contain compounds containing the hemiacetal functional groups, thereby more effectively improving the dispersibility of the negative electrode active material in the negative electrode composition through the repulsive forces between ether bonds. Therefore, when the negative electrode composition prepared by the aforementioned method is applied to a negative electrode, the lifespan and low resistance characteristics of the secondary battery including the negative electrode can be improved.

[0069] In some embodiments, the first adhesive powder may contain a compound comprising repeating units represented by the following chemical formula 1.

[0070] [Chemical Formula 1] In the chemical formula 1, M1 and M2 are each independently Na or Li, at least one of R1 to R4 is a group represented by the following chemical formula 2, and the rest are each independently H or a group represented by the following chemical formula 2, where n is an integer.

[0071] [Chemical Formula 2] In the chemical formula 2, R5 is -CHO, -CH2CHO, -COCH3, or -CH2COCH3. - Indicates the binding site where oxygen binds.

[0072] In some embodiments, R5 in chemical formula 2 can be -CHO or -COCH3.

[0073] In some embodiments, the hemiacetal functional group may be a group represented, for example, by the following chemical formula A-1 or chemical formula A-2.

[0074] In the chemical formula A-1 or chemical formula A-2, - indicates the binding position of the hemiacetal functional group to the main chain of carboxymethyl cellulose or its salt, which is the same as the binding position of the free hydroxyl group before the hemiacetal reaction.

[0075] Therefore, the first adhesive powder may contain at least one compound selected from any one, two, three or four compounds that are groups represented by the chemical formula 2.

[0076] M1 and M2 can be the same as each other.

[0077] In the chemical formula 1, M1 and M2 in -OCH2COOM1 and -OCH2COOM2 can exist as carboxylate salts formed by ionic bonds, or as -OCH2COO - M1 + and -OCH2COO - M2 + It exists in the form of.

[0078] The number n can be, for example, 300 to 15000 or 500 to 10000.

[0079] In some embodiments, one or two of R1 to R4 may be groups represented by the chemical formula 2, and the remainder may be H.

[0080] In some embodiments, at least one of R2 and R4 may be a group represented by the chemical formula 2, and the remainder may be H.

[0081] In some embodiments, the first adhesive powder may comprise a compound in which R2 of R1 to R4 in Formula 1 is a group represented by Formula 2 and the remainder is H. The first adhesive powder may, for example, be a compound in which R2 of R1 to R4 is a group represented by Formula 2 and the remainder is H.

[0082] In some embodiments, the first adhesive powder may comprise: a compound in which R2 of R1 to R4 is a group represented by the chemical formula 2 and the remainder is H; and a compound in which R4 of R1 to R4 is a group represented by the chemical formula 2 and the remainder is H.

[0083] Compounds containing repeating units represented by the chemical formula 1 can be, for example, compounds represented by the following chemical formula 1-1, but are not limited thereto.

[0084] [Chemical Formula 1-1] In the aforementioned chemical formula 1-1, M1, M2, R1 to R4, and n refer to the contents described above in chemical formula 1. E1 and R E2 Each is independently H or CH2COOM3, M3 is Na or Li, and n is an integer. For example, R E1 It can be hydrogen, R E2 It can be CH2COOM3.

[0085] As a non-restrictive instance, M1 to M3 can be the same as each other.

[0086] In some embodiments, the first binder powder and the second binder powder may each independently contain at least one of carboxymethyl cellulose and its salts, having a degree of substitution (DS) of 0.6 or less for hydroxyl groups caused by methyl carboxylic acid or its salts and a weight-average molecular weight of 3,000,000 g / mol or more. The term "degree of substitution" as used herein can refer to the average number of substituted carboxymethyl groups per molecule of anhydrous glucose.

[0087] Even when using carboxymethyl cellulose and / or its salts with the above-mentioned degree of substitution and weight-average molecular weight range as binders, the dispersibility of the first binder powder and the second binder powder can be improved by the above-mentioned method for preparing the negative electrode composition, and the life characteristics and low resistance characteristics of the secondary battery can be improved simultaneously.

[0088] In some embodiments, the degree of substitution can be from 0.4 to 0.6, and the weight-average molecular weight can be from 3,000,000 g / mol to 5,000,000 g / mol. Therefore, excessive viscosity increase of the negative electrode slurry can be further suppressed, and the lifespan and low-resistance characteristics of the secondary battery can be further improved.

[0089] In some embodiments, the first solvent may include at least one selected from water, pure water, deionized water, distilled water, ethanol, isopropanol, methanol, acetone, n-propanol, and tert-butanol.

[0090] Figure 2 This is a schematic flowchart illustrating a method for preparing a negative electrode composition for a secondary battery according to another exemplary embodiment.

[0091] In some embodiments, between the step of forming the primary negative electrode composition and the step of forming the negative electrode composition, a step of adding a second solvent to the mixer may be further included (e.g., step S30). Therefore, the solid content of the primary negative electrode composition can be appropriately reduced, thereby preventing the aforementioned solvent shock phenomenon and suppressing the formation of solid aggregates (lumps) within the mixer. Thus, the lifespan and low-resistance characteristics of the secondary battery can be improved.

[0092] In some embodiments, the second solvent may include a solvent of the same kind as the first solvent.

[0093] In some embodiments, the total content of solids, i.e., the second solids, in the primary negative electrode composition with the addition of the second solvent can be 3% to 9% less by weight than the total content of the first solids. As described above, with the addition of the second solvent, the total content of solids in the primary negative electrode composition can be reduced.

[0094] For example, the total content of the second solids can be reduced by 3% to 9% or 3% to 5% compared to the total content of the first solids. Within the above range, the formation of binder aggregates in the second mixture can be further suppressed, and the life characteristics of the secondary battery can be further improved.

[0095] For example, the total content of the second solids can be from 56% to 72% by weight.

[0096] In an exemplary embodiment, after the primary negative electrode composition is formed, a second binder powder may be added to the mixer and a second mixing may be performed to form the negative electrode composition (e.g., step S40). In one embodiment, the second mixing may be performed by a kneading process.

[0097] In some embodiments, the second binder can be added to the mixer in two or more batches. For example, the second binder can be added in 2 to 10 batches, 2 to 7 batches, or 2 to 5 batches. Therefore, the dispersibility and adsorption of the second binder powder contained in the negative electrode composition can be further improved. Secondary batteries comprising a negative electrode formed from the negative electrode composition can achieve improved power characteristics and lifetime characteristics.

[0098] For example, the second adhesive powder can be added in a solid state.

[0099] In some embodiments, the first adhesive powder and the second adhesive powder may each independently comprise a compound containing a repeating unit represented by the chemical formula 1. The first adhesive powder and the second adhesive powder may be the same as or different from each other.

[0100] In some embodiments, the first adhesive powder and the second adhesive powder may contain the same compound.

[0101] In some embodiments, the first adhesive powder and the second adhesive powder may each independently contain less than 20% by weight of a compound containing repeating units represented by the following chemical formula 3, or may not contain said compound, based on the total content of each adhesive powder. For example, the first adhesive powder may contain less than 20% by weight of a compound containing repeating units represented by the following chemical formula 3, or may not contain said compound, based on the total content of the second adhesive powder; similarly, the second adhesive powder may contain less than 20% by weight of a compound containing repeating units represented by the following chemical formula 3, or may not contain said compound.

[0102] [Chemical Formula 3] In the chemical formula 3, M4 and M5 are Na or Li, and n is an integer. The n can be, for example, 300 to 15000 or 500 to 10000.

[0103] Compounds containing repeating units represented by the chemical formula 3 can be, for example, compounds represented by the following chemical formula 3-1, but are not limited thereto.

[0104] [Chemical Formula 3-1] In the aforementioned chemical formula 3-1, M4 and M5 are each independently Na or Li, and R E3 and R E4 One of them is H, the other is CH2COOM6, M6 is Na or Li, and n is an integer. The n can be, for example, 300 to 15000 or 500 to 10000. For example, R E3 It can be H, R E4 It can be CH2COOM6.

[0105] As a non-restrictive instance, M4 to M6 can be the same as each other.

[0106] In one embodiment, the first adhesive powder and the second adhesive powder may contain 80% to 100% by weight of a compound containing repeating units represented by the chemical formula 1, based on the total content of each adhesive powder.

[0107] For example, the second mixing can be carried out at 20°C to 60°C.

[0108] In some embodiments, the viscosity of the first adhesive powder measured in an aqueous solution at a concentration of 1.2% by weight, i.e., the first viscosity, can be from 200 cP to 6500 cP. The first viscosity can be, for example, from 300 cP to 6000 cP, 400 cP to 4000 cP, or 500 cP to 3000 cP.

[0109] In some embodiments, the viscosity of the second adhesive powder measured in an aqueous solution at a concentration of 1.2% by weight, i.e., the second viscosity, can be from 1500 cP to 9500 cP. The second viscosity can be, for example, from 2000 cP to 9000 cP, from 3000 cP to 6000 cP, or from 3000 cP to 5000 cP.

[0110] The first and second viscosities of the first and second adhesive powders refer to the viscosities measured in an aqueous solution with a concentration of 1.2% by weight. The first and second viscosities can be measured, for example, at room temperature. In this case, the 1.2% by weight aqueous solution can be formed by dissolving either the first or second adhesive powder in water at a concentration of 1% by weight.

[0111] In some embodiments, the ratio of the second viscosity to the first viscosity can be from 1 to 10. For example, the ratio of the second viscosity to the first viscosity can be from 1 to 8, 1 to 6, or 1 to 3. Therefore, the first binder and the second binder contained in the negative electrode composition can be more uniformly dispersed.

[0112] In some embodiments, in the step of forming the negative electrode composition, after the second mixing, at least one of a third solvent and a third binder may be added to the mixer and a third mixing may be performed to form the negative electrode composition.

[0113] The third solvent refers to the above description of the first or second solvent. The third solvent may include solvents of the same type as the first solvent.

[0114] In some embodiments, the third solvent and the third binder may not be added to the mixer at the same time.

[0115] In some embodiments, the third adhesive may be added to the mixer after the third solvent is added, followed by a third mixing.

[0116] For example, after the second mixing, the third solvent can be added to the driven mixer for dilution. After adding the third solvent, mixing can be carried out for 10 to 60 minutes, but is not limited to this.

[0117] The third adhesive may include styrene-butadiene-rubber (SBR) based adhesives, styrene-acrylate based adhesives, polyacrylic acid based adhesives, and poly(3,4-ethylenedioxythiophene) (PEDOT) based adhesives, etc. These can be used alone or in combination of two or more.

[0118] The third adhesive can be added in either a solid or liquid form, without any particular limitation.

[0119] As a non-limiting example, additional components such as conductive materials, thickeners, and dispersants that can be further added to the negative electrode composition can be added to the mixer at any time before or after the first mixing or before or after the second mixing.

[0120] By adjusting the amount of the above-mentioned components added, the solid content or viscosity of the negative electrode composition can be controlled according to the technical objectives.

[0121] The solid content in the negative electrode composition can be, for example, 40% to 65% by weight, 45% to 63% by weight, 50% to 61% by weight, 52% to 60% by weight, 53% to 60% by weight, or 56% to 60% by weight.

[0122] For example, based on the total content of the solids contained in the negative electrode composition, the total amount of the negative electrode active material can be appropriately adjusted to the range of 80% to 98.9% by weight, the total amount of the binder can be appropriately adjusted to the range of 1.0% to 10% by weight, for example, 1.1% to 10% by weight, and the total amount of other components such as the conductive material can be appropriately adjusted to the range of 0.1% to 10% by weight.

[0123] The viscosity of the negative electrode composition at 23°C can be, for example, 6000 cP to 15000 cP, 7000 cP to 13000 cP, 8000 cP to 11000 cP, 8500 cP to 10000 cP, or 9000 cP to 9500 cP.

[0124] In some embodiments, the total content of the first adhesive and the second adhesive can be from 1.5% to 5% by weight. For example, the total content obtained by adding the contents of the first adhesive and the second adhesive can be from 2% to 5% by weight or from 3% to 5% by weight. According to the preparation method of the embodiments of the present invention, the amount of adhesive powder added can be increased without the anode active material and / or adhesive powder agglomeration, thus further improving the lifespan characteristics of the anode and the secondary battery, as well as the electrode adhesion. Furthermore, when the anode active material contains a silicon-based active material, the thickness change and swelling phenomenon of the battery due to repeated charging and discharging of the secondary battery can be further suppressed. In some embodiments, the content of the first adhesive powder in the total weight of the first adhesive powder and the second adhesive powder can be from 30% to 90% by weight, for example, from 60% to 90% by weight or from 70% to 80% by weight.

[0125] Based on the total weight of the first adhesive powder and the second adhesive powder, the content of the second adhesive powder can be from 10% to 70% by weight, for example, from 10% to 40% by weight or from 20% to 30% by weight.

[0126] Therefore, the resistance of the secondary battery can be further reduced, and its lifespan characteristics can be further improved.

[0127] In an exemplary embodiment, the maximum drive current of the mixer in the first mixing process can be greater than or equal to the maximum drive current of the mixer in the second mixing process. Therefore, the maximum performance of the mixer can be achieved, while further improving the driving stability of the mixer and the dispersibility of the negative electrode composition.

[0128] The maximum drive current of the mixer can refer to the maximum value of the drive current of the mixer that varies according to the added substance while the drive speed of the mixer is kept at a constant speed (e.g., the maximum drive speed).

[0129] The mixer may be, for example, a mixer manufactured by Primix. As a non-limiting example, the mixer may be a 2000L-class PD mixer, a planetary Despa mixer, etc.

[0130] In one embodiment, the drive speed of the mixer can be kept constant, for example, during the first mixing and the second mixing.

[0131] For example, the maximum drive current of the mixer can be changed by adjusting the amount and ratio of the first and second binder powders, the amount of the first solvent, the second solvent and / or the third solvent, the addition time, the viscosity of the mixture and the solid content, etc.

[0132] In some embodiments, the difference (ΔC = C1 - C2) between the maximum drive current of the mixer in the first mixing and the maximum drive current of the mixer in the second mixing can be, for example, 10A to 130A. ΔC can be, for example, 20A to 100A, 30A to 80A, or 40A to 60A. Therefore, the dispersibility of the negative electrode composition can be further improved.

[0133] In some implementations, for example, the maximum drive current of the mixer in the first mixing process can be from 180A to 220A.

[0134] In some implementations, for example, the maximum drive current of the mixer in the second mixing process can be from 80A to 160A.

[0135] <Negative electrode for secondary batteries and secondary batteries> Figure 3 and Figure 4 These are schematic plan views and schematic cross-sectional views illustrating a secondary battery according to an exemplary embodiment. For example, Figure 4 It is along Figure 3 A cross-sectional view taken along the thickness direction of the I-I' line.

[0136] Figure 3 and Figure 4 The structure shown is an example for illustrative purposes, and the structure of the secondary battery according to the embodiments of the present invention is not limited thereto.

[0137] Reference Figure 3 and Figure 4 The secondary battery may include a negative electrode 130 manufactured using the above-described negative electrode composition and a positive electrode 100 disposed opposite to the negative electrode 130.

[0138] The negative electrode 130 can be formed using the negative electrode composition prepared according to the above preparation method.

[0139] For example, a method for manufacturing a negative electrode for a secondary battery, including the preparation method described above, can be provided. The method for manufacturing the negative electrode for a secondary battery may include coating the negative electrode composition onto at least one side of the negative electrode current collector 125 and then drying and calendering it.

[0140] The negative electrode 130 can be formed by coating the negative electrode composition onto at least one side of the negative electrode current collector 125 and then drying and calendering it.

[0141] The positive electrode 100 may include a positive electrode current collector 105 and a positive electrode active material layer 110, wherein the positive electrode active material layer 110 is formed on at least one side of the positive electrode current collector 105.

[0142] The positive electrode current collector 105 may comprise stainless steel, nickel, aluminum, titanium, or alloys thereof. The positive electrode current collector 105 may also comprise aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver. For example, the thickness of the positive electrode current collector 105 may be from 10 μm to 50 μm.

[0143] The positive electrode active material layer 110 may contain a positive electrode active material. The positive electrode active material may contain compounds that enable reversible insertion and extraction of lithium ions.

[0144] According to an exemplary embodiment, the positive electrode active material may comprise a lithium-nickel metal oxide. The lithium-nickel metal oxide may further comprise at least one of cobalt (Co), manganese (Mn), and aluminum (Al).

[0145] In some embodiments, the positive electrode active material or the lithium-nickel metal oxide may comprise a layered structure or a crystal structure represented by the following chemical formula 4.

[0146] [Chemical Formula 4] Li x Ni a M b O 2+z In chemical formula 4, the values ​​can be 0.9≤x≤1.2, 0.5≤a≤0.99, 0.01≤b≤0.5, and -0.5≤z≤0.1. As mentioned above, M can contain Co, Mn, and / or Al.

[0147] The chemical structure represented by Formula 4 indicates the bonding relationships contained in the layered or crystalline structure of the positive electrode active material, and does not exclude other additional elements. For example, M may contain Co and / or Mn, and Co and / or Mn may be provided together with Ni as the main active element of the positive electrode active material. Formula 4 is provided to represent the bonding relationships of the main active elements, and it should be understood that Formula 4 includes the introduction and substitution of additional elements.

[0148] In one embodiment, in addition to the primary active element, auxiliary elements may be further included to enhance the chemical stability of the positive electrode active material or the layered / crystal structure. These auxiliary elements may be incorporated into the layered / crystal structure and form bonds; this should be understood to also include the chemical structures represented by Formula 4.

[0149] The auxiliary element may include at least one selected from, for example, Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra, P, and Zr. The auxiliary element may function as an auxiliary active element, together with Co or Mn, to contribute to the capacity / power activity of the positive electrode active material; for example, Al.

[0150] For example, the positive electrode active material or the lithium-nickel metal oxide may contain a layered structure or a crystal structure represented by the following chemical formula 4-1.

[0151] [Chemical Formula 4-1] Li x Ni a M1 b1 M2 b2 O 2+z In chemical formula 4-1, M1 may contain Co, Mn, and / or Al. M2 may contain the aforementioned auxiliary elements. In chemical formula 4-1, the following conditions may be met: 0.9≤x≤1.2, 0.5≤a≤0.99, 0.01≤b1+b2≤0.5, -0.5≤z≤0.1.

[0152] The positive electrode active material may further include coating elements or doping elements. For example, elements that are substantially the same as or similar to the auxiliary elements described above can be used as coating elements or doping elements. For example, one or more combinations of the elements described above can be used as coating elements or doping elements.

[0153] The coating element or doping element may exist on the surface of the lithium-nickel metal oxide particles, or may penetrate through the surface of the lithium-nickel metal composite oxide particles and be included in the bonding structure represented by chemical formula 4 or chemical formula 4-1.

[0154] The positive electrode active material may comprise nickel-cobalt-manganese (NCM)-based lithium oxide. In this case, NCM-based lithium oxide with increased nickel content can be used.

[0155] Ni can be provided as a transition metal related to the power and capacity of lithium secondary batteries. Therefore, as described above, by using a high-content (High-Ni) composition for the positive electrode active material, a high-capacity positive electrode and a high-capacity lithium secondary battery can be provided.

[0156] However, with increasing Ni content, the long-term storage stability and lifetime stability of the cathode or secondary battery may relatively decrease, and side reactions with the electrolyte may also increase. However, according to an exemplary embodiment, conductivity can be maintained by including Co, while lifetime stability and capacity retention characteristics can be improved by including Mn.

[0157] The Ni content in the NCM-based lithium oxide (e.g., the mole fraction of nickel in the total moles of nickel, cobalt, and manganese) can be 0.5 or more, 0.6 or more, 0.7 or more, or 0.8 or more. In some embodiments, the Ni content can be 0.8 to 0.95, 0.82 to 0.95, 0.83 to 0.95, 0.84 to 0.95, 0.85 to 0.95, or 0.88 to 0.95.

[0158] In some embodiments, the positive electrode active material may further include lithium cobalt oxide-based active material, lithium manganese oxide-based active material, lithium nickel oxide-based active material, or lithium iron phosphate (LFP)-based active material (e.g., LiFePO4).

[0159] In some embodiments, the positive electrode active material may include, for example, a Li rich layered oxide (LLO) / OverLithiated Oxide (OLO)-based active material, a Mn-rich-based active material, a Co-less-based active material, etc. having a chemical structure or crystal structure represented by Chemical Formula 5. These may be used alone or in combination of two or more.

[0160] [Chemical Formula 5] p[Li2MnO3]·(1-p)[Li q JO2] In Chemical Formula 5, 0 < p < 1, 0.9 ≤ q ≤ 1.2, and J may include at least one element selected from Mn, Ni, Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, and B.

[0161] The positive electrode active material may be mixed in a solvent to prepare a positive electrode paste. The positive electrode paste may be coated on at least one surface of the positive electrode current collector 105 and then dried and calendered to prepare the positive electrode active material layer 110. The coating may include methods such as gravure coating, slot die coating, multilayer simultaneous die coating, imprinting, doctor blade coating, dip coating, bar coating, casting, etc. The positive electrode active material layer 110 may further include a binder and may optionally further include a conductive material and / or a thickener.

[0162] The solvent may be N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc.

[0163] The binder may include polyvinylidene fluoride (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) copolymer, polyacrylonitrile, polymethyl methacrylate, nitrile rubber (NBR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), etc. These may be used alone or in combination of two or more.

[0164] In one embodiment, a PVDF-based binder can be used as the positive electrode binder. In this case, the amount of binder used to form the positive electrode active material layer 110 can be reduced, and the amount of positive electrode active material can be relatively increased. Therefore, the power characteristics and capacity characteristics of the secondary battery can be improved.

[0165] The conductive material can be added to enhance the conductivity and / or the mobility of lithium ions or electrons in the positive electrode active material layer 110. For example, the conductive material may include carbon-based conductive materials such as graphite, carbon black, acetylene black, Ketjen black, graphene, carbon nanotubes, vapor-grown carbon fiber (VGCF), and carbon fibers, and / or metal-based conductive materials including perovskite materials such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3. These can be used alone or in combination of two or more.

[0166] The cathode slurry may further contain thickeners and / or dispersants. In one embodiment, the cathode slurry may contain thickeners such as carboxymethyl cellulose (CMC).

[0167] The negative electrode composition can be prepared by the preparation method of the exemplary embodiment.

[0168] The negative electrode 130 may include a negative electrode current collector 125 and a negative electrode active material layer 120, the negative electrode active material layer 120 being disposed on at least one side of the negative electrode current collector 125, and the negative electrode active material layer 120 being formed using a negative electrode composition prepared by a preparation method according to an exemplary embodiment. The negative electrode composition prepared by the preparation method of the exemplary embodiment may be in the form of a negative electrode slurry. The negative electrode active material layer 120 may be formed by coating the aforementioned negative electrode composition onto at least one side of the negative electrode current collector 125 and drying it, for example, by coating the aforementioned negative electrode composition and then drying and calendering it.

[0169] For example, the negative electrode current collector 125 may include copper foil, nickel foil, stainless steel foil, titanium foil, foam nickel, foam copper, polymer substrate coated with conductive metal, etc. These can be used alone or in combination of two or more. For example, the thickness of the negative electrode current collector 125 can be from 10 μm to 50 μm.

[0170] The negative electrode active material layer 120 may contain the aforementioned negative electrode active material. For example, the negative electrode active material may contain multiple negative electrode active material particles.

[0171] The aforementioned negative electrode composition can be coated / deposited onto the negative electrode current collector 125, followed by drying and calendering to prepare the negative electrode active material layer 120. The coating process may include gravure coating, slot extrusion coating, multilayer simultaneous die coating, embossing, blade coating, dip coating, rod coating, casting, and other methods. Optionally, the negative electrode active material layer 120 may further comprise conductive materials, thickeners, etc.

[0172] The conductive material and thickener may be any of the aforementioned substances that can be used in the manufacture of the positive electrode 100.

[0173] In an exemplary embodiment, a separator 140 may be disposed between the positive electrode 100 and the negative electrode 130. The separator 140 may be configured to prevent short circuits between the positive electrode 100 and the negative electrode 130 and to allow ion flow. For example, the thickness of the separator may be from 10 μm to 20 μm.

[0174] For example, diaphragm 140 may comprise a porous polymer membrane or a porous nonwoven fabric.

[0175] The porous polymer membrane may include polyolefin-based polymers such as ethylene polymers, propylene polymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers. These may be used alone or in combination of two or more.

[0176] The porous nonwoven fabric may include high-melting-point glass fibers, polyethylene terephthalate fibers, etc.

[0177] The diaphragm 140 may also include a ceramic-based material. For example, inorganic particles may be coated on or dispersed in the polymer membrane to improve heat resistance.

[0178] The diaphragm 140 may have a single-layer or multi-layer structure comprising the aforementioned polymer membrane and / or nonwoven fabric.

[0179] According to an exemplary embodiment, the battery cell can be defined by a positive electrode 100, a negative electrode 130, and a separator 140, and an electrode assembly 150 can be formed, for example, in the form of a jelly roll, by stacking multiple battery cells. For example, the electrode assembly 150 can be formed by winding, stacking, z-folding, stack-folding, etc. of the separator 140.

[0180] The electrode assembly 150 can be housed together with the electrolyte in the housing 160, thereby defining a lithium secondary battery. According to an exemplary embodiment, the electrolyte can be a non-aqueous electrolyte.

[0181] Non-aqueous electrolytes may contain a lithium salt as the electrolyte and an organic solvent, wherein the lithium salt may be, for example, Li... + X - This indicates that the anion (X) of the lithium salt is... - ), can be exemplified by F - Cl - ,Br - I - NO3 - N(CN)2 - BF4 - ClO4 - PF6 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - CF3SO3 - CF3CF2SO3 - (CF3SO2)2N - (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2)2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N - wait.

[0182] The organic solvent may be, for example, propylene carbonate (PC), ethylene carbonate (EC), butene carbonate, diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, vinylene carbonate, methyl acetate (MA), ethyl acetate (EA), n-propylacetate (n-PA), 1,1-dimethylethyl acetate (DMEA), methyl propionate (MP), ethyl propionate (EP), ethyl fluoroacetate (FEA), ethyl difluoroacetate (DFEA), ethyl trifluoroacetate (TFEA), dibutyl ether, tetraethylene glycol dimethyl ether (TEGDME), and diethylene glycol dimethyl ether. These include ether (DEGDME), dimethoxyethane, tetrahydrofuran (THF), 2-methyltetrahydrofuran, ethyl alcohol, isopropyl alcohol, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, sulfolane, γ-butyrolactone, and propylene sulfite, among others. These can be used alone or in combination of two or more.

[0183] The non-aqueous electrolyte may further contain additives. These additives may include, for example, cyclic carbonate compounds, fluorinated carbonate compounds, sulfonyl lactone compounds, cyclic sulfate compounds, cyclic sulfite compounds, phosphate compounds, borate compounds, etc. These may be used alone or in combination of two or more.

[0184] The cyclic carbonate-based compound may include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), etc.

[0185] The fluorine-substituted cyclic carbonate compounds may include fluoroethylene carbonate (FEC), etc.

[0186] The sulfonyl compounds may include 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, etc.

[0187] The cyclic sulfate-based compounds may include 1,2-ethylene sulfate, 1,2-propylene sulfate, etc.

[0188] The cyclic sulfite-based compounds may include ethylene sulfite, butylene sulfite, etc.

[0189] The phosphate-based compounds may include lithium difluorobis-oxalato phosphate, lithium difluorophosphate, etc.

[0190] The borate-based compounds may include lithium bis(oxalate) borate, etc.

[0191] In some embodiments, a solid electrolyte can be used instead of the non-aqueous electrolyte. In this case, the lithium secondary battery can be made into an all-solid-state battery. Furthermore, a solid electrolyte layer can be disposed between the positive electrode 100 and the negative electrode 130 instead of the separator 140.

[0192] The solid electrolyte may include a sulfide-based electrolyte. As a non-limiting example, the sulfide-based electrolyte may include Li₂S-P₂S₅, Li₂S-P₂S₅-LiCl, Li₂S-P₂S₅-LiBr, Li₂S-P₂S₅-LiCl-LiBr, Li₂S-P₂S₅-Li₂O, Li₂S-P₂S₅-Li₂O-LiI, Li₂S-SiS₂, Li₂S-SiS₂-LiI, Li₂S-SiS₂-LiBr, Li₂S-SiS₂-LiCl, Li₂S-SiS₂-B₂S₃-LiI, Li₂S-SiS₂-P₂S₅-LiI, Li₂S-B₂S₃, and Li₂S-P₂S₅-Z. m Sn (m and n are positive numbers, Z is Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (p and q are positive numbers, M is P, Si, Ge, B, Al, Ga, or In), Li7-xPS6-xCl x (0≤x≤2), Li7-xPS6-xBr x (0≤x≤2), Li7-xPS6-xI x (0≤x≤2), etc. These can be used individually or in combination of two or more.

[0193] In one embodiment, the solid electrolyte may include oxide-based amorphous solid electrolytes such as Li2O-B2O3-P2O5, Li2O-SiO2, Li2O-B2O3, and Li2O-B2O3-ZnO.

[0194] like Figure 2 and Figure 3 As shown, the tabs (positive tab and negative tab) can protrude from the positive current collector 105 and negative current collector 125 belonging to each cell and extend to one side of the housing 160. The tabs can be fused to said side of the housing 160 to form electrode leads (positive lead 107 and negative lead 127) extending to or exposed outside the housing 160.

[0195] The lithium secondary battery can be manufactured in shapes such as cylindrical, prismatic, pouch, or coin, for example, using a can.

[0196] The embodiments of the present invention described above include the following aspects, and can be implemented by at least one of the following aspects.

[0197] A method for preparing a negative electrode composition for a secondary battery according to a first aspect of the present invention includes: adding negative electrode active material powder and a first binder powder to a mixer, adding a first solvent and performing a first mixing to form a primary negative electrode composition; after forming the primary negative electrode composition, adding a second binder powder to the mixer and performing a second mixing to form a negative electrode composition.

[0198] In the first aspect, according to the second aspect, the negative electrode active material powder and the first binder powder can be added to the operating mixer to form a powder mixture, and then the first solvent is added.

[0199] In either the first or second aspect, according to the third aspect, between forming the primary negative electrode composition and forming the negative electrode composition, the addition of a second solvent to the mixer may be further included.

[0200] In any one of the first to the third aspects, according to the fourth aspect, the second adhesive powder may be added to the mixer in two or more separate additions.

[0201] In any one of the first to the fourth aspects, according to the fifth aspect, the total content of solids, i.e. the first solids, in the primary negative electrode composition may be 65% to 75% by weight.

[0202] In the fifth aspect, according to the sixth aspect, the total content of solids, i.e., the second solids, in the primary negative electrode composition in which the second solvent is added can be 3% to 9% less by weight than the total content of the first solids.

[0203] In any one of the first to the sixth aspects, according to the seventh aspect, the first adhesive powder and the second adhesive powder may each independently contain a compound containing a repeating unit represented by the chemical formula 1.

[0204] In the seventh aspect, according to the eighth aspect, the first adhesive powder and the second adhesive powder may each independently contain less than 20% by weight of a compound containing a repeating unit represented by the chemical formula 3, based on the total content of each adhesive powder, or may not contain the compound.

[0205] In any one of the first to the eighth aspects, according to the ninth aspect, the negative electrode active material may include at least one selected from artificial graphite and natural graphite.

[0206] In any one of the first to the ninth aspects, according to the tenth aspect, the first solvent and the second solvent may each independently include at least one selected from water, pure water, deionized water, distilled water, ethanol, isopropanol, methanol, acetone, n-propanol and tert-butanol.

[0207] In any one of the first to the tenth aspects, according to the eleventh aspect, when forming the negative electrode composition, after the second mixing, at least one of a third solvent and a third binder may be further added to the mixer and a third mixing may be performed to form the negative electrode composition.

[0208] In the eleventh aspect, according to the twelfth aspect, the third binder may be added to the mixer after the third solvent is added and the third mixing is performed to form the negative electrode composition.

[0209] In any one of the first to the twelfth aspects, according to the thirteenth aspect, the viscosity of the first adhesive powder, i.e., the first viscosity, can be from 200 cP to 6500 cP.

[0210] In any one of the first to the thirteenth aspects, according to the fourteenth aspect, the viscosity of the second adhesive powder, i.e., the second viscosity, can be from 1500 cP to 9500 cP.

[0211] In the thirteenth or fourteenth aspect, according to the fifteenth aspect, the first viscosity may be from 500 cP to 3500 cP.

[0212] In any one of the fourteenth to fifteenth aspects, according to the sixteenth aspect, the second viscosity may be from 3000 cP to 7000 cP.

[0213] In any one of the fourteenth to the sixteenth aspects, according to the seventeenth aspect, the ratio of the second viscosity to the first viscosity can be from 1 to 10.

[0214] In the seventeenth aspect, according to the eighteenth aspect, the ratio of the second viscosity to the first viscosity can be from 1 to 6.

[0215] The negative electrode for a secondary battery according to the nineteenth aspect of the present invention comprises: a negative electrode current collector; and a negative electrode active material layer disposed on at least one side of the negative electrode current collector, and the negative electrode active material layer is formed by a negative electrode composition prepared by a method for preparing a negative electrode composition according to any one of the first to eighteenth aspects.

[0216] The secondary battery according to the twentieth aspect of the present invention includes: a negative electrode for the secondary battery according to the nineteenth aspect; and a positive electrode, the positive electrode being disposed opposite to the negative electrode.

[0217] The embodiments of the present invention will be further described below with reference to specific experimental examples. The embodiments and comparative examples included in the experimental examples are only for illustrating the present invention and do not limit the scope of the claims. Various changes and modifications can be made to the embodiments within the scope of the present invention and its technical concept, which is obvious to those skilled in the art, and such variations and modifications naturally fall within the scope of the claims.

[0218] Preparation Example Preparation Example 1 250g of sodium carboxymethyl cellulose (CMC-Na) (weight average molecular weight: 1,500,000, degree of substitution (DS): 0.9), 3.5g of methylglyoxal and 0.5g of oxalic acid were added to 500g of ethanol solution, stirred at 60°C for 180 minutes and dried to prepare the binder powder (hereinafter referred to as compound A powder).

[0219] The compound A powder is a compound powder containing repeating units represented by the chemical formula 1. Compound A is a compound in which M1 and M2 in chemical formula 1 are Na, R2 in R1 to R4 is a group represented by the chemical formula 2, the remainder are H, and R5 in chemical formula 2 is CH3.

[0220] The compound A powder was dissolved in water to prepare an aqueous solution with a concentration of 1.2% by weight. The viscosity of the aqueous solution was measured to be 3000 cP at 25°C using a viscometer (Brookfield DV2T viscometer (RV3 spindle) , 30 rpm).

[0221] Preparation Example 2 The adhesive powder (hereinafter referred to as compound B powder) was prepared by the same method as in Preparation Example 1, except that an equal amount of glyoxal was added instead of methylglyoxal.

[0222] The compound B powder is a compound powder containing repeating units represented by the chemical formula 1. Compound B is a compound in which M1 and M2 in chemical formula 1 are Na, R2 in R1 to R4 is a group represented by the chemical formula 2, the remainder are H, and R5 in chemical formula 2 is H.

[0223] The viscosity was measured to be 3000 cP using the same method as in Preparation Example 1, except that the compound B powder was dissolved in water to prepare an aqueous solution with a concentration of 1.2% by weight.

[0224] Preparation Example 3 250 g of sodium carboxymethyl cellulose (CMC-Na) (weight average molecular weight: 100,000, degree of substitution (DS): 0.9), 3.5 g of methylglyoxal, and 0.5 g of oxalic acid were added to 500 g of ethanol solution, stirred at 60 °C for 180 minutes, and dried to prepare the binder powder (hereinafter referred to as compound C powder). Compound C powder is a compound powder containing repeating units represented by the chemical formula 1.

[0225] The viscosity was measured to be 200 cP using the same method as in Preparation Example 1, except that the compound C powder was dissolved in water to prepare an aqueous solution with a concentration of 1.2% by weight.

[0226] Preparation Example 4 250 g of sodium carboxymethyl cellulose (CMC-Na) (weight average molecular weight: 300,000, degree of substitution (DS): 0.9), 3.5 g of methylglyoxal, and 0.5 g of oxalic acid were added to 500 g of ethanol solution, stirred at 60 °C for 180 minutes, and dried to prepare the binder powder (hereinafter referred to as compound D powder). Compound D powder is a compound powder containing repeating units represented by the chemical formula 1.

[0227] The viscosity was measured to be 500 cP using the same method as in Preparation Example 1, except that the compound D powder was dissolved in water to prepare an aqueous solution with a concentration of 1.2% by weight.

[0228] Preparation Example 5 250 g of sodium carboxymethyl cellulose (CMC-Na) (weight average molecular weight: 800,000, degree of substitution (DS): 0.9), 3.5 g of methylglyoxal, and 0.5 g of oxalic acid were added to 500 g of ethanol solution, stirred at 60 °C for 180 minutes, and dried to prepare the binder powder (hereinafter referred to as compound E powder). Compound E powder is a compound powder containing repeating units represented by the chemical formula 1.

[0229] The viscosity was measured to be 1000 cP using the same method as in Preparation Example 1, except that the compound E powder was dissolved in water to prepare an aqueous solution with a concentration of 1.2% by weight.

[0230] Preparation Example 6 250g of sodium carboxymethyl cellulose (CMC-Na) (weight average molecular weight: 1,200,000, degree of substitution (DS): 0.9), 3.5g of methylglyoxal and 0.5g of oxalic acid were added to 500g of ethanol solution, stirred at 60°C for 180 minutes and dried to prepare the binder powder (hereinafter referred to as compound F powder).

[0231] The compound F powder is a compound powder containing repeating units represented by the chemical formula 1.

[0232] The viscosity was measured to be 1500 cP using the same method as in Preparation Example 1, except that the compound F powder was dissolved in water to prepare an aqueous solution with a concentration of 1.2% by weight.

[0233] Preparation Example 7 250g of sodium carboxymethyl cellulose (CMC-Na) (weight average molecular weight: 1,800,000, degree of substitution (DS): 0.9), 3.5g of methylglyoxal and 0.5g of oxalic acid were added to 500g of ethanol solution, stirred at 60°C for 180 minutes and dried to prepare the binder powder (hereinafter referred to as compound G powder).

[0234] The compound G powder is a compound powder containing repeating units represented by the chemical formula 1.

[0235] The viscosity was measured to be 6000 cP using the same method as in Preparation Example 1, except that the compound G powder was dissolved in water to prepare an aqueous solution with a concentration of 1.2% by weight.

[0236] Preparation Example 8 250g of sodium carboxymethyl cellulose (CMC-Na) (weight average molecular weight: 2,000,000, degree of substitution (DS): 0.9), 3.5g of methylglyoxal and 0.5g of oxalic acid were added to 500g of ethanol solution, stirred at 60°C for 180 minutes and dried to prepare the binder powder (hereinafter referred to as compound H powder).

[0237] The compound H powder is a compound powder containing repeating units represented by the chemical formula 1.

[0238] The viscosity was measured to be 9000 cP using the same method as in Preparation Example 1, except that the compound H powder was dissolved in water to prepare an aqueous solution with a concentration of 1.2% by weight.

[0239] Preparation Example 9 250g of sodium carboxymethyl cellulose (CMC-Na) (weight average molecular weight: 5,000,000, degree of substitution (DS): 0.4), 3.5g of methylglyoxal and 0.5g of oxalic acid were added to 500g of ethanol solution, stirred at 60°C for 180 minutes and dried to prepare the binder powder (hereinafter referred to as compound J powder).

[0240] The compound J powder is a compound powder containing repeating units represented by the chemical formula 1. Compound J is a compound in which M1 and M2 in chemical formula 1 are Na, R2 in R1 to R4 is a group represented by the chemical formula 2, the remainder are H, and R5 in chemical formula 2 is CH3.

[0241] Preparation Example 10 The binder powder (hereinafter referred to as compound K powder) was prepared by the same method as in Preparation Example 9, except that an equal amount of glyoxal was added instead of methylglyoxal.

[0242] The compound K powder is a compound powder containing repeating units represented by the chemical formula 1. The compound K is a compound in which M1 and M2 in chemical formula 1 are Na, R2 in R1 to R4 is a group represented by the chemical formula 2, the remainder are H, and R5 in chemical formula 2 is H.

[0243] Preparation Example 11 The binder powder (hereinafter referred to as compound L powder) was prepared by the same method as in Preparation Example 1, except that 250 g of sodium carboxymethyl cellulose (CMC-Na) (weight average molecular weight: 3,000,000, degree of substitution (DS): 0.6) was used.

[0244] Preparation Example 12 The binder powder (hereinafter referred to as compound M powder) was prepared by the same method as in Preparation Example 1, except that 250 g of sodium carboxymethyl cellulose (CMC-Na) (weight average molecular weight: 4,000,000, degree of substitution (DS): 0.5) was used.

[0245] Preparation Example 13 The binder powder (hereinafter referred to as compound N powder) was prepared by the same method as in Preparation Example 1, except that 250 g of sodium carboxymethyl cellulose (CMC-Na) (weight average molecular weight: 5,000,000, degree of substitution (DS): 0.3) was used.

[0246] Preparation Example 14 The binder powder (hereinafter referred to as compound O powder) was prepared by the same method as in Preparation Example 1, except that 250 g of sodium carboxymethyl cellulose (CMC-Na) (weight average molecular weight: 6,000,000, degree of substitution (DS): 0.4) was used.

[0247] Example Example 1 (1) Preparation of negative electrode composition The planetary mixer (Pleximix, 2000L class PD mixer) is set and maintained at maximum drive speed, and natural graphite as the negative electrode active material, carbon black as the conductive material, and compound A powder as the first binder powder are added to the mixer in a weight ratio of 98.9:0.5:0.6 (step S10).

[0248] Subsequently, water, serving as the first solvent, is added to the mixer and a first mixing is performed to form a kneaded primary negative electrode composition (step S20). The total content of the solids, i.e., the first solids, in the primary negative electrode composition is 70% by weight.

[0249] Water, as a second solvent, is added to the mixer to reduce the solid content of the primary negative electrode composition by about 5% (step S30).

[0250] Add an equal amount of compound A powder as the compound A powder added in step S10 to the mixer as a second binder powder, and perform a second mixing (step S40).

[0251] After the second mixing, water, as a third solvent, is added to the mixer for dilution, and then styrene-butadiene rubber (SBR), as a third binder, is added and a third mixing is performed to prepare a negative electrode composition in slurry form.

[0252] Based on the total solids content of the prepared negative electrode composition, the total content of natural graphite, carbon black and compound A powder is 98.5% by weight, and the content of SBR is 1.5% by weight.

[0253] Based on the total solids content in the negative electrode composition, the total content of the first binder powder and the second binder powder, i.e., the total content of compound A, is 1.2% by weight. The weight ratio of the first binder powder to the second binder powder is 1:1.

[0254] (2) Manufacturing of secondary batteries The negative electrode composition is coated onto a copper current collector and then dried and rolled to manufacture the negative electrode.

[0255] LiNi will be used as the positive electrode active material 0.8 Co 0.1 Mn 0. O2, carbon black as a conductive material, and polyvinylidene fluoride (PVDF) as a binder are mixed in a mass ratio of 95:3:2 to prepare a slurry-like positive electrode composition. The positive electrode slurry is coated onto an aluminum current collector and then dried and calendered to manufacture the positive electrode.

[0256] Forty-three positive electrodes and forty-four negative electrodes are cut (notched) to predetermined sizes and stacked. A separator (polyethylene, 25 μm thick) is placed between the positive and negative electrodes to form a cell. Then, the tab portions of the positive and negative electrodes are welded together. The welded positive / separator / negative electrode assembly is placed in a soft case, and the three sides except for the electrolyte injection surface are sealed. At this point, the portion with the tabs is included in the sealed portion. Electrolyte is injected through the electrolyte injection surface, and the electrolyte injection surface is sealed. Then, it is immersed for at least 12 hours to manufacture a secondary battery.

[0257] The electrolyte used was a 1M LiPF6 solution prepared using a mixed solvent of EC / EMC (25 / 75; volume ratio), with 1% by weight of vinylene carbonate (VC) and 0.5% by weight of 1,3-propenesulfonyl lactone (PRS) added relative to the total weight of the solution.

[0258] The lithium secondary battery was pre-charged for 36 minutes at a current (5A) corresponding to 0.25C. After 1 hour, it was degassed and aged for more than 24 hours, followed by formation charge-discharge (charging conditions: CC-CV 0.2C 4.2V 0.05C cut-off; discharging conditions: CC 0.2C 2.5V cut-off).

[0259] Example 2 The negative electrode composition and the secondary battery were prepared by the same method as in Example 1, except that the second solvent was not added to the mixer (step S30 was omitted), and the compound A powder was added in five portions during the second mixing (step S40).

[0260] Example 3 The negative electrode composition and secondary battery were prepared using the same method as in Example 1, except that an equal amount of compound B powder was used instead of compound A powder.

[0261] Example 4 The negative electrode composition and secondary battery were prepared using the same method as in Example 1, except that an equal amount of artificial graphite was used instead of natural graphite as the negative electrode active material.

[0262] Example 5 The negative electrode composition and secondary battery were prepared using the same method as in Example 1, except that an equal amount of unetherified sodium carboxymethyl cellulose (CMC-Na) powder (a compound containing repeating units represented by the chemical formula 3, referred to as compound I powder) was used instead of compound A powder. In the chemical formula 3, M4 and M5 are Na.

[0263] The viscosity was measured to be 3000 cP using the same method as in Preparation Example 1, except that the compound I powder was dissolved in water to prepare an aqueous solution with a concentration of 1.2% by weight.

[0264] Example 6 The negative electrode composition and secondary battery were prepared using the same method as in Example 1, except that an equal amount of compound I powder was used instead of compound A powder as used in Example 5, and an equal amount of artificial graphite was used instead of natural graphite as the negative electrode active material.

[0265] Example 7 The negative electrode composition and the secondary battery were prepared by the same method as in Example 1, except that the second solvent was not added to the mixer (step S30 was omitted).

[0266] Examples 8 to 17 The negative electrode composition and the secondary battery were prepared by the same method as in Example 1, except that the first binder powder and the second binder powder were changed to compound powders of the types shown in Table 1 below.

[0267] Comparative Example 1 (One-time addition of adhesive powder) The negative electrode composition and secondary battery were prepared by the same method as in Example 1, except that steps S10 to S40 in Example 1 were combined into one step, and all the components added to the mixer in each step were added at the same time, i.e., added and mixed at one time.

[0268] The mixing time after adding all the above components into the mixer at once is the same as the total time obtained by adding the mixing times of each of steps S10 to S40 in Example 1.

[0269] Comparative Example 2 (adding adhesive solution in batches) The negative electrode composition and the secondary battery were prepared by the same method as in Example 1, except that in steps S10 and S20 of Example 1, after adding the negative electrode active material and the conductive material to the mixer, a first binder solution prepared by mixing the first binder powder (compound A powder) with the first solvent was added and mixed (corresponding to the first mixture), and in steps S30 and S40, a second binder solution prepared by mixing the second binder powder (compound A powder) with the second solvent was added and mixed (corresponding to the second mixture).

[0270] Comparative Example 3 (adhesive solution added in one step) The negative electrode composition and the secondary battery were prepared by the same method as in Comparative Example 2, except that the steps in Comparative Example 2 were combined into one step, and all the components added to the mixer in each step were added at the same time, that is, added and mixed at one time.

[0271] The mixing time after adding all the above components into the mixer at once is the same as the total time obtained by adding the mixing times of each of steps S10 to S40 in Example 1.

[0272] [Table 1] Example 18 The negative electrode composition and secondary battery were prepared by the same method as in Example 1, except that in step S10, a planetary mixer (Pleximix, 2000L class PD mixer) was set and maintained at maximum drive speed, and artificial graphite and SiO as negative electrode active materials, compound A powder as first binder powder, and carbon nanotubes (CNTs) as conductive material were added to the mixer in a weight ratio of 86.8:10:0.75:0.5, and the solid content was adjusted as follows.

[0273] Based on the total solids content in the negative electrode composition, the total content of artificial graphite, SiO, compound A powder, and carbon nanotubes (CNTs) is 98.8% by weight, and the content of SBR is 1.2% by weight. Furthermore, based on the total solids content in the negative electrode composition, the total content of the first binder powder and the second binder powder, i.e., the total content of compound A, is 1.5% by weight.

[0274] Example 19 The negative electrode composition and secondary battery were prepared by the same method as in Example 18, except that in step S10, artificial graphite and SiO as negative electrode active materials, compound A powder as first binder powder, and carbon nanotubes (CNTs) as conductive material were added to the mixer in a weight ratio of 85.3:10:1.5:0.5. In step S40, an equal amount of compound A powder was added as second binder powder, such that, based on the total solid content in the negative electrode composition, the total content of artificial graphite, SiO, compound A powder, and carbon nanotubes (CNTs) was 98.8% by weight, and the content of SBR was 1.2% by weight.

[0275] Based on the total solids content in the negative electrode composition, the total content of the first binder powder and the second binder powder, i.e., the total content of compound A, is 3 by weight.

[0276] Example 20 The negative electrode composition and secondary battery were prepared by the same method as in Example 18, except that in step S10, artificial graphite and SiO as negative electrode active materials, compound A powder as first binder powder, and carbon nanotubes (CNTs) as conductive material were added to the mixer in a weight ratio of 83.3:10:2.5:0.5. In step S40, an equal amount of compound A powder was added as second binder powder, such that, based on the total solid content in the negative electrode composition, the total content of artificial graphite, SiO, compound A powder, and carbon nanotubes (CNTs) was 98.8% by weight, and the content of SBR was 1.2% by weight.

[0277] Based on the total solids content in the negative electrode composition, the total content of the first binder powder and the second binder powder, i.e., the total content of compound A, is 5% by weight.

[0278] Example 21 The negative electrode composition and secondary battery were prepared by the same method as in Example 1, except that in step S10, a planetary mixer (Pleximix, 2000L class PD mixer) was set and maintained at maximum drive speed, and natural graphite, artificial graphite and SiO as negative electrode active materials, the compound J powder as the first binder powder and carbon nanotubes (CNTs) as the conductive material were added to the mixer in a weight ratio of 48:48:3:0.4:0.2, the compound J powder was used as the second binder powder, and the solid content was adjusted as follows.

[0279] Based on the total solids content of the negative electrode composition, the total content of natural graphite, artificial graphite, SiO, compound J powder and carbon nanotubes (CNT) is 98.8% by weight, and the content of SBR is 1.2% by weight.

[0280] Example 22 The negative electrode composition and the secondary battery were prepared by the same method as in Example 21, except that the second solvent was not added to the mixer (step S30 was omitted), and the compound J powder was added in five portions during the second mixing (step S40).

[0281] Example 23 The negative electrode composition and secondary battery were prepared using the same method as in Example 21, except that an equal amount of compound K powder was used instead of compound J powder.

[0282] Example 24 The negative electrode composition and secondary battery were prepared by the same method as in Example 21, except that the second solvent was not added to the mixer (step S30 is omitted).

[0283] Example 25 The negative electrode composition and secondary battery were prepared by the same method as in Example 21, except that compound L powder was used as the first binder powder and the second binder powder.

[0284] Example 26 The negative electrode composition and secondary battery were prepared by the same method as in Example 21, except that compound M powder was used as the first binder powder and the second binder powder.

[0285] Example 27 The negative electrode composition and the secondary battery were prepared by the same method as in Example 21, except that compound N powder was used as the first binder powder and the second binder powder.

[0286] Example 28 The negative electrode composition and secondary battery were prepared by the same method as in Example 21, except that compound O powder was used as the first binder powder and the second binder powder.

[0287] Example 29 (content of the first adhesive in the first adhesive and the second adhesive: 30% by weight) The negative electrode composition and secondary battery were prepared by the same method as in Example 1, except that in step S10, a planetary mixer (Pleximix, 2000L class PD mixer) was set and maintained at maximum drive speed, and natural graphite, carbon black as negative electrode active material and compound A powder as first binder powder were added to the mixer in a weight ratio of 99.14:0.5:0.36, and the solid content was adjusted as follows.

[0288] Based on the total solids content of the negative electrode composition, the total content of natural graphite, carbon black, and compound A powder is 98.5% by weight, and the content of SBR is 1.5% by weight. Furthermore, after the second mixing in step S40, the weight ratio of natural graphite, carbon black, first binder powder, and second binder powder is 98.3:0.5:0.36:0.84.

[0289] Example 30 (content of the first adhesive in the first adhesive and the second adhesive: 40% by weight) The negative electrode composition and the secondary battery were prepared by the same method as in Example 29, except that the natural graphite, carbon black, first binder powder and second binder powder were mixed in a weight ratio of 98.3:0.5:0.48:0.72.

[0290] Example 31 (content of the first adhesive in the first adhesive and the second adhesive: 60% by weight) The negative electrode composition and the secondary battery were prepared by the same method as in Example 29, except that the natural graphite, carbon black, first binder powder and second binder powder were mixed in a weight ratio of 98.3:0.5:0.72:0.48.

[0291] Example 32 (content of the first adhesive in the first adhesive and the second adhesive: 70% by weight) The negative electrode composition and the secondary battery were prepared by the same method as in Example 29, except that the natural graphite, carbon black, first binder powder and second binder powder were mixed in a weight ratio of 98.3:0.5:0.84:0.36.

[0292] Example 33 (content of the first adhesive in the first adhesive and the second adhesive: 90% by weight) The negative electrode composition and the secondary battery were prepared by the same method as in Example 29, except that the natural graphite, carbon black, first binder powder and second binder powder were mixed in a weight ratio of 98.3:0.5:1.08:0.12.

[0293] Comparative Example 4 (One-time addition of adhesive powder) The negative electrode composition and secondary battery were prepared by the same method as in Example 18, except that steps S10 to S40 in Example 18 were combined into one step, and all the components added to the mixer in each step were added at the same time, i.e., added and mixed at one time.

[0294] The mixing time after adding all the above components into the mixer at once is the same as the total time obtained by adding the mixing times of each of steps S10 to S40 in Example 18.

[0295] Comparative Example 5 (Adding adhesive solution in batches) The negative electrode composition and the secondary battery were prepared by the same method as in Example 18, except that in steps S10 and S20 of Example 18, after adding the negative electrode active material and the conductive material to the mixer, a first binder solution prepared by mixing the first binder powder (compound A powder) with the first solvent was added and mixed (corresponding to the first mixture), and in steps S30 and S40, a second binder solution prepared by mixing the second binder powder (compound A powder) with the second solvent was added and mixed (corresponding to the second mixture).

[0296] Comparative Example 6 (adhesive solution added in one step) The negative electrode composition and the secondary battery were prepared by the same method as in Comparative Example 5, except that the steps in Comparative Example 5 were combined into one step, and all the components added to the mixer in each step were added at the same time, that is, added and mixed at one time.

[0297] The mixing time after adding all the above components into the mixer at once is the same as the total time obtained by adding the mixing times of each of steps S10 to S40 in Example 18.

[0298] Comparative Example 7 (One-time addition of adhesive powder) The negative electrode composition and secondary battery were prepared by the same method as in Example 21, except that steps S10 to S40 in Example 21 were combined into one step, and all the components added to the mixer in each step were added at the same time, i.e., added and mixed at one time.

[0299] The mixing time after adding all the above components into the mixer at once is the same as the total time obtained by adding the mixing times of each of steps S10 to S40 in Example 21.

[0300] Comparative Example 8 (Adding adhesive solution in batches) The negative electrode composition and the secondary battery were prepared by the same method as in Example 21, except that in steps S10 and S20 of Example 21, after adding the negative electrode active material and the conductive material to the mixer, a first binder solution prepared by mixing the first binder powder (compound J powder) with the first solvent was added and mixed (corresponding to the first mixture), and in steps S30 and S40, a second binder solution prepared by mixing the second binder powder (compound J powder) with the second solvent was added and mixed (corresponding to the second mixture).

[0301] Comparative Example 9 (adhesive solution added in one step) The negative electrode composition and the secondary battery were prepared by the same method as in Comparative Example 2, except that the steps in Comparative Example 8 were combined into one step, and all the components added to the mixer in each step were added at the same time, that is, added and mixed at one time.

[0302] The mixing time after adding all the above components into the mixer at once is the same as the total time obtained by adding the mixing times of each of steps S10 to S40 in Example 21.

[0303] Comparative Example 10 (One-time addition of adhesive powder) The negative electrode composition and secondary battery were prepared by the same method as in Example 32, except that steps S10 to S40 were combined into one step, and all the components added to the mixer in each step were added at the same time, i.e., added and mixed at one time.

[0304] The mixing time after adding all the above components into the mixer at once is the same as the total time obtained by adding the mixing times of each of steps S10 to S40 in Example 29.

[0305] Comparative Example 11 (Adding adhesive solution in batches) The negative electrode composition and the secondary battery were prepared by the same method as in Example 32, except that in steps S10 and S20, after adding the negative electrode active material and the conductive material to the mixer, a first binder solution prepared in advance by mixing the first binder powder (compound A powder) with the first solvent was added and mixed (corresponding to the first mixture), and in steps S30 and S40, a second binder solution prepared in advance by mixing the second binder powder (compound A powder) with the second solvent was added and mixed (corresponding to the second mixture).

[0306] Comparative Example 12 (Adhesive solution added in one step) The negative electrode composition and the secondary battery were prepared by the same method as in Comparative Example 2, except that the steps in Comparative Example 2 were combined into one step, and all the components added to the mixer in each step were added at the same time, that is, added and mixed at one time.

[0307] The mixing time after adding all the above components into the mixer at once is the same as the total time obtained by adding the mixing times of each of steps S10 to S40 in Example 29.

[0308] Experimental Example (1) Measurement of the maximum drive current of the mixer In Examples 1 to 7, 18, 21 to 24 and 29 above, the maximum drive current in step S20 and the maximum drive current in step S40 are measured respectively.

[0309] In the above measurements, the values ​​measured and displayed by the mixer itself are used. If necessary, additional components for measuring current can be installed on the mixer to measure the maximum drive current. When the mixer is a dual-motor mixer including two motors, the larger of the maximum drive currents measured by the two motors can be evaluated as the maximum drive current of the mixer.

[0310] The results are shown in Table 2 below.

[0311] [Table 2] (2) Measurement of negative electrode adhesion force For the negative electrodes of the above embodiments and comparative examples, the adhesive force was measured by a 90° peel test. The measuring device used was a DS2-N model from IMADA.

[0312] Specifically, the negative electrode is cut into 18mm lengths to obtain a sample. Adhesive tape is attached to the sample, and the force (90°) required to peel off the tape is measured, expressed in N / 18mm.

[0313] The results are shown in Table 3 below.

[0314] (3) Measurement of internal resistance For the secondary batteries of the above embodiments and comparative examples, the internal resistance of the secondary batteries was measured using a WONIK PNE 200A class charge-discharge machine.

[0315] Specifically, at 50% SOC, a current corresponding to 1C is applied for 10 seconds, and the direct current internal resistance (DCIR) is measured.

[0316] The results are shown in Table 3 below.

[0317] (4) Evaluation of capacity retention For the lithium half-cells of the examples and comparative examples, they were charged (CC-CV 0.33C 4.2V 0.05C cutoff) and discharged (CC 0.33C 2.5V cutoff) 800 times each in a chamber maintained at 25°C. The capacity retention rate was evaluated by dividing the discharge capacity of the 800th discharge by the discharge capacity of the 1st discharge and multiplying by 100.

[0318] The results are shown in Table 3 below.

[0319] (5) Evaluation of cell expansion rate Battery cells were prepared using the same method as the manufacturing method of the secondary batteries in Examples 18 to 20 and Comparative Examples 4 to 6 described above.

[0320] Prepare and adjust the compression jig so that the device can apply a uniform force of 500N. Prepare the battery cell, place it on the compression jig, and fix it in place so that it will not move during charging and discharging.

[0321] The thickness of the battery cell in its initial state was measured using a thickness measuring device and set as a reference value.

[0322] The battery cell is subjected to 100 charge-discharge cycles under the following conditions.

[0323] One cycle (5 minutes): CC / CV charging (0.5C 4.3V 0.05C cutoff) and CC discharging (1.0C 3.0V cutoff) at room temperature (25℃). The charging and discharging equipment is linked with the data collection system so that the thickness change data can be recorded synchronously in real time. During the charging and discharging process, the thickness change rate of the cell is measured every 5 minutes. The thickness change rate after 100 cycles is evaluated as the cell expansion rate.

[0324] Thickness change rate (%) = (T2 - T1) / T1 × 100 T1 is the thickness of the cell in the initial state, and T2 is the thickness of the cell after 100 cycles.

[0325] The results are shown in Table 4 below.

[0326] (6) Measurement of degree of substitution For each compound used as the first binder powder and the second binder powder (hereinafter referred to as the binder compound), the degree of substitution described above due to methyl carboxylic acid or its salt shall be measured according to ASTM D 1439-03 by the following method.

[0327] Specifically, 1g of the adhesive compound was added to a 500mL Erlenmeyer flask, and 100mL of distilled water and 25mL of 0.5N (equivalent concentration) NaOH were added to the Erlenmeyer flask. The mixture was stirred at 120°C for 30 minutes.

[0328] Add excess NaOH aqueous solution to the conical flask and perform back titration with 0.5N HCl. Confirm the endpoint using phenolphthalein indicator and calculate the degree of substitution according to Equations 1 and 2 below.

[0329] [Formula 1] DS=0.162Y A / (1-0.58Y A ) [Equation 2] A={(Y B ×Y C )-(Y D ×Y E )} / Y F In Equations 1 and 2, Y A Y represents the equivalent amount (millomoles (mmol) / g) consumed per 1g of adhesive compound. B Y represents the volume (mL) of NaOH added. C Y represents the concentration (N) of the NaOH aqueous solution. D Y represents the volume (mL) of HCl used in the back titration. E Y represents the concentration (N) of the HCl solution. F The mass (g) of the adhesive used.

[0330] (7) Measurement of weight-average molecular weight For each compound used as the first binder powder and the second binder powder, the samples treated with gel permeation chromatograph (GPC) were analyzed using Tosoh's EcoSEC HLC-8320 GPC, and the weight-average molecular weight was measured according to the following method.

[0331] In the above sample processing, without separate sample pretreatment, the solution in which the sample is completely dissolved is filtered through a 0.45 μm nylon filter to obtain the sample.

[0332] The sample was analyzed under the following analytical equipment / conditions to measure the weight-average molecular weight of the adhesive compound.

[0333] i) Analytical instrument: Tosoh's EcoSEC HLC-8320 GPC ii) Detector: RI detector iii) Developing solution: 0.1M NaNO3 iv) Column: TSKgel GMPWxl (7.8mm × 300mm) 2ro v) Temperature: 40℃ vi) Flow rate: 1 mL / min vii) Sample injection volume: 200 mL, 0.5 mg / mL viii) Standard substance: Polysaccharide ix) Data processing software: EcoSEC software (8) Measurement of solids content of negative electrode composition For the negative electrode compositions of the examples and comparative examples, the weight of the negative electrode compositions was measured and dried in an oven.

[0334] Measure the weight of the dried solids.

[0335] Calculate the percentage of the measured weight of the solids divided by the measured weight of the negative electrode composition.

[0336] (9) Measurement of the phase angle of the negative electrode composition The negative electrode composition was kept at 25°C, and each phase angle was measured using a rheometer (model name: Kinexus rotary type, manufacturer: Malvern) as the measuring device. After setting the distance between the circular rotating plates of the rheometer to a constant 1 mm, a negative electrode composition corresponding to the volume filling the gap was placed in, and the temperature was increased to 10°C. -2 Hz to 10 2 Within the Hz range, the amplitude was increased by approximately 2 times each time, and the phase angle was measured simultaneously. The results at 1Hz are shown in Table 5 below.

[0337] In Table 3 below, the column corresponding to the binder (chemical formula) lists the chemical formulas of the repeating units contained in each binder compound. Additionally, in the column corresponding to the addition method, "single addition" indicates that in the addition process for preparing the negative electrode composition, all components are simultaneously added to the mixer in one step.

[0338] [Table 3] [Table 4] [Table 5] Referring to Tables 2 and 3, in the embodiments, negative electrode active material powder and first binder powder are first added to the mixer, then a first solvent is added and a first mixing is performed, then a second binder powder is added and a second mixing is performed. Compared with the comparative example, the overall electrode adhesion and capacity retention are improved, and the internal resistance is reduced.

[0339] In Examples 5 and 6, a compound containing repeating units represented by the chemical formula 3 (unetherified sodium carboxymethyl cellulose (CMC-Na)) was used instead of a compound containing repeating units represented by the chemical formula 1 as the first binder powder and the second binder powder. Compared with other examples, the electrode adhesion and capacity retention were relatively reduced, and the internal resistance was relatively increased.

[0340] In Examples 7 and 24, the maximum drive current of the mixer in the first mixture is less than the maximum drive current of the mixer in the second mixture. Compared with other examples, the electrode adhesion and capacity retention are reduced, and the internal resistance is increased.

[0341] Referring to Table 4, the cell expansion rate was evaluated as low for the cells according to Examples 18 to 20, while the cell expansion rate was evaluated as high for the cells according to Comparative Examples 4 to 6.

[0342] Referring to Table 5, in Examples 29 to 33, the phase angle was evaluated as 45° or higher, indicating that the dispersion between active materials was improved. As shown in Comparative Examples 10 to 12, when the phase angle was less than 45°, it indicated a high degree of aggregation of the components in the negative electrode composition.

[0343] In Comparative Examples 1, 4, 7 and 10, the binder powder was added in a single step instead of in two separate steps. Compared with the examples, the electrode adhesion and capacity retention were reduced, and the internal resistance was increased. Figure 5 This is an internal image of the stirrer taken after the negative electrode composition was prepared according to Comparative Example 1. (Refer to...) Figure 5 In Comparative Example 1, the adhesive powder aggregated in the adhesive solution, resulting in solvent shock, which led to a decrease in negative electrode adhesion, mechanical stability and processability.

[0344] In Comparative Examples 2, 3, 5, 6, 8, and 9, an adhesive solution was used instead of solid adhesive powder. Compared with the examples, the electrode adhesion and capacity retention decreased, and the internal resistance increased. In Comparative Example 3, where the adhesive solution was added in a single step, the electrode adhesion, internal resistance, and capacity retention further deteriorated.

Claims

1. A method for preparing a negative electrode composition for a secondary battery, comprising the following steps: Add negative electrode active material powder and first binder powder to a mixer, add a first solvent and perform a first mixing to form a primary negative electrode composition; and After the primary negative electrode composition is formed, a second binder powder is added to the mixer and a second mixing is performed to form the negative electrode composition.

2. The method for preparing the negative electrode composition for secondary batteries according to claim 1, wherein, The negative electrode active material powder and the first binder powder are added to the operating mixer to form a powder mixture, and then the first solvent is added.

3. The method for preparing the negative electrode composition for secondary batteries according to claim 1, wherein, Between the step of forming the primary negative electrode composition and the step of forming the negative electrode composition, a further step of adding a second solvent to the mixer is included.

4. The method for preparing the negative electrode composition for secondary batteries according to claim 1 or 3, wherein, The second adhesive powder is added to the mixer in two or more portions.

5. The method for preparing the negative electrode composition for secondary batteries according to claim 3, wherein, The total content of solids, i.e. the first solids, in the primary negative electrode composition is 65% to 75% by weight.

6. The method for preparing the negative electrode composition for secondary batteries according to claim 5, wherein, The total content of solids, i.e., the second solids, in the primary negative electrode composition with the addition of the second solvent is 3% to 9% less by weight than the total content of the first solids.

7. The method for preparing the negative electrode composition for secondary batteries according to claim 1, wherein, The first adhesive powder and the second adhesive powder each independently comprise a compound containing repeating units represented by the following chemical formula 1: [Chemical Formula 1] ， In the chemical formula 1, M1 and M2 are each independently Na or Li, at least one of R1 to R4 is a group represented by the following chemical formula 2, and the rest are each independently H or a group represented by the following chemical formula 2, where n is an integer. [Chemical Formula 2] ， In the chemical formula 2, R5 is -CHO, -CH2CHO, -COCH3, or -CH2COCH3. - Indicates the binding site where oxygen binds.

8. The method for preparing the negative electrode composition for a secondary battery according to claim 7, wherein, The first adhesive powder and the second adhesive powder each independently contain less than 20% by weight of a compound containing repeating units represented by the following chemical formula 3, based on the total content of each adhesive powder, or do not contain said compound: [Chemical Formula 3] ， In the chemical formula 3, M4 and M5 are each independently Na or Li, and n is an integer.

9. The method for preparing the negative electrode composition for a secondary battery according to claim 1, wherein, The negative electrode active material includes at least one selected from artificial graphite and natural graphite.

10. The method for preparing the negative electrode composition for a secondary battery according to claim 1, wherein, The first solvent and the second solvent each independently include at least one selected from water, pure water, deionized water, distilled water, ethanol, isopropanol, methanol, acetone, n-propanol and tert-butanol.

11. The method for preparing the negative electrode composition for a secondary battery according to claim 1, wherein, In the step of forming the negative electrode composition, after the second mixing, at least one of a third solvent and a third binder is further added to the mixer and a third mixing is performed to form the negative electrode composition.

12. The method for preparing the negative electrode composition for a secondary battery according to claim 11, wherein, The third solvent is added to the mixer, followed by the addition of the third binder and the third mixing to form the negative electrode composition.

13. The method for preparing the negative electrode composition for a secondary battery according to claim 1, wherein, The viscosity of the first adhesive powder, i.e. the first viscosity, is 200 cP to 6500 cP.

14. The method for preparing the negative electrode composition for a secondary battery according to claim 1, wherein, The viscosity of the second adhesive powder, i.e. the second viscosity, is 1500 cP to 9500 cP.

15. The method for preparing the negative electrode composition for a secondary battery according to claim 13, wherein, The first viscosity is 500 cP to 3500 cP.

16. The method for preparing the negative electrode composition for a secondary battery according to claim 14, wherein, The second viscosity is 3000 cP to 7000 cP.

17. The method for preparing the negative electrode composition for a secondary battery according to claim 14, wherein, The ratio of the second viscosity to the first viscosity is 1 to 10.

18. The method for preparing the negative electrode composition for a secondary battery according to claim 17, wherein, The ratio of the second viscosity to the first viscosity is 1 to 6.

19. A negative electrode for a secondary battery, comprising: Negative electrode current collector; as well as A negative electrode active material layer is disposed on at least one side of the negative electrode current collector, and the negative electrode active material layer is formed from a negative electrode composition prepared by the preparation method according to claim 1.

20. A secondary battery, comprising: The negative electrode for a secondary battery as described in claim 19; as well as The positive electrode is positioned opposite the negative electrode.

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