Nanocellulose-based aqueous binders and slurries for secondary battery electrodes

Abstract

The present invention provides an aqueous binder for nanocellulose-based secondary battery electrodes, comprising latex particles having a core-shell structure, the core comprising a rubber-like polymer; and a shell formed by bonding an acrylic or non-acrylic monomer to the surface of the core through a chemical reaction; and nanocellulose that interacts with functional groups on the surface of the latex particles; and a slurry for secondary battery electrodes comprising the same.

Description

[Technical Field]

[0001] The present invention relates to nanocellulose-based aqueous binders and slurries for use in the manufacture of electrodes for lithium secondary batteries. [Background technology]

[0002] Electrodes for lithium secondary batteries are generally manufactured by applying a slurry containing an active material and a binder to a metal current collector and drying it. Slurries for electrode fabrication are typically obtained by mixing and kneading a negative electrode active material, a binder, and a dispersant. Slurries for use as aqueous binders consisting of styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) are known in the art. When applying conventional SBR aqueous binders to electrodes and drying them, uniformly dispersed SBR particles migrate to the upper layer of the electrode along with the evaporated water, resulting in a decrease in the electrode's adhesive strength. Therefore, research into new binder-related technologies that can suppress this migration phenomenon is needed. Summary of the Invention [Problem to be solved by the invention]

[0003] The object of the present invention is to provide an aqueous binder and slurry for nanocellulose-based secondary battery electrodes, which contain latex particles with a core-shell structure and nanocellulose, thereby forming strong hydrogen bonds between the latex particles and nanocellulose, thereby suppressing the migration of SBR in the upper electrode layer that occurs in conventional technologies, and improving the binding strength of the electrode. [Means for solving the problem]

[0004] A nanocellulose-based aqueous binder for a secondary battery electrode according to one embodiment of the present invention can include latex particles with a core-shell structure including a core comprising a rubbery polymer; and a shell formed by a chemical reaction of one or two monomers selected from the group consisting of acrylic monomers and non-acrylic monomers on the surface of the core; and nanocellulose interacting with functional groups on the surface of the shell.

[0005] The nanocellulose may be one or more selected from the group consisting of cellulose nanofibers (CNF), cellulose nanocrystals (CNC), and bacterial cellulose (BC).

[0006] The nanocellulose may be present in an amount of 0.01% by weight to 1.0% by weight based on the total mass of the solid content of the latex particles.

[0007] The chemical reaction that forms the shell may be a polymerization reaction.

[0008] The interaction may be a hydrogen bond.

[0009] The functional group on the surface of the shell may be one or more selected from the group including a carbonyl group, a carboxy group, and a nitrile group.

[0010] The rubbery polymer may be one or more selected from the group consisting of butadiene rubber, acrylic rubber, ethylene-propylene copolymer rubber, styrene-butadiene copolymer rubber, acrylonitrile-butadiene copolymer rubber, isoprene rubber, ethylene-propylene-diene terpolymer rubber, polyorganosiloxane-polyalkyl(meth)acrylate rubber composite, and mixtures thereof.

[0011] The acrylic monomer may be one or more selected from the group consisting of methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, isobutyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 2-ethylbutyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, octadecyl (meth)acrylate, and isobornyl (meth)acrylate.

[0012] The non-acrylic monomer may be one or more selected from the group consisting of (meth)acrylamide, N-methyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, (meth)acrylonitrile, N-vinylpyrrolidone, N-vinylcaprolactam, N-vinylcaprolactone, styrene, 2-vinylpyridine, 4-vinylpyridine, and vinyl acetate.

[0013] A nanocellulose-based secondary battery electrode slurry according to one embodiment of the present invention may include the above-described aqueous binder, negative electrode active material, and thickener.

[0014] The thickener may be one or more selected from the group consisting of cellulose-based polymers such as carboxymethyl cellulose, methyl cellulose, and hydroxypropyl cellulose, and their ammonium salts and alkali metal salts; (modified) poly(meth)acrylic acid, and their ammonium salts and alkali metal salts; (modified) polyvinyl alcohols such as copolymers of acrylic acid or acrylic acid salts with vinyl alcohol, and copolymers of maleic anhydride or maleic acid or fumaric acid with vinyl alcohol; polyethylene glycol; polyethylene oxide; modified polyacrylic acid; oxidized starch; starch phosphate; casein; and hydrogenated acrylonitrile-butadiene copolymer.

[0015] The secondary battery electrode according to an embodiment of the present invention may be manufactured using the above-described slurry.

[0016] The secondary battery electrode according to one embodiment of the present invention may have a peel strength of 8.5 gf / cm or more before vacuum drying and a peel strength of 9.0 gf / cm or more after vacuum drying during the manufacturing process. [Effects of the Invention]

[0017] The nanocellulose-based aqueous binder for secondary battery electrodes according to one embodiment of the present invention inhibits binder migration as the electrode dries, resulting in uniform binder distribution in the electrode and excellent electrode binding strength.

[0018] In addition, the nanocellulose-based secondary battery electrode slurry according to one embodiment of the present invention has improved viscosity and excellent slurry stability. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a photograph showing the presence or absence of aggregation and the surface state of binders produced in Comparative Example 3, Example 1, and Example 2 of the present invention, observed with the naked eye. [Figure 2]1 is a graph showing the relationship between shear deformation rate and viscosity of slurries of Comparative Example 2 and Examples 1 to 3 of the present invention on a logarithmic scale. [Figure 3] 1 is a graph comparing the binding strength of the electrodes before and after vacuum drying in the manufacturing process of Comparative Example 2, Comparative Example 3, and Examples 1 to 3 of the present invention. [Figure 4] FIG. 1 is a schematic diagram of a SAICAS measurement method carried out in Experimental Example 5 of the present invention. [Figure 5] 10 is a graph comparing horizontal forces acting during SAICAS measurement at different cutting depths of composite layers manufactured using Comparative Example 2, Comparative Example 3, and Examples 1 to 3 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0020] Terms such as "first," "second," and "third" are used to describe various parts, components, regions, layers, and / or sections, but are not limited thereto. These terms are used only to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Thus, a first part, component, region, layer, or section described below can be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0021] The terminology used herein is merely for the purpose of referring to particular embodiments and is not intended to limit the present invention. As used herein, the singular forms "a," "an," and "the" include the plural forms unless the context clearly dictates otherwise. As used herein, the term "comprises" refers to the inclusion of specific properties, regions, integers, steps, operations, elements, and / or components, and does not exclude the presence or addition of other properties, regions, integers, steps, operations, elements, and / or components.

[0022] When a part is described as being "on" or "above" another part, it may be exactly on or above the other part, or it may have other parts between them. In contrast, when a part is described as being "directly above" another part, there are no other parts between them.

[0023] Unless otherwise specified, % means % by weight, and 1 ppm is 0.0001% by weight. Unless otherwise defined, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by those of ordinary skill in the art to which this invention pertains. Terms defined in commonly used dictionaries are further interpreted to have a meaning consistent with the relevant technical literature and the presently disclosed content, and are not interpreted in an idealized or very formal sense unless defined.

[0024] DETAILED DESCRIPTION OF THE INVENTION The present invention will now be described in detail with reference to exemplary embodiments thereof, so that those skilled in the art can easily understand and practice the invention. However, the present invention may be embodied in many different forms and is not limited to the exemplary embodiments set forth herein.

[0025] [Nanocellulose-based aqueous binder for secondary battery electrodes]

[0026] A nanocellulose-based aqueous binder for a secondary battery electrode according to one embodiment of the present invention can include core-shell latex particles including a core containing a rubbery polymer and a shell formed on the surface of the core by a chemical reaction of one or two monomers selected from the group consisting of acrylic monomers and non-acrylic monomers; and nanocellulose interacting with functional groups on the surface of the shell. Specifically, the shell can be formed on the surface of the core by a polymerization reaction of one or two monomers selected from the group consisting of acrylic monomers and non-acrylic monomers. The inclusion of nanocellulose fixes the core-shell latex particles, which can form strong hydrogen bonds with the nanocellulose as described below, thereby preventing migration of the core-shell latex particles to the upper layer of the electrode along with the evaporation of water during electrode fabrication. Therefore, the binder distribution within the electrode can be maintained uniformly even during the drying process during electrode fabrication.

[0027] The nanocellulose may be one or more selected from the group consisting of cellulose nanofibers (CNF), cellulose nanocrystals (CNC), and bacterial cellulose (BC). Specifically, the nanocellulose may be cellulose nanocrystals (CNC).

[0028] The functional groups on the shell surface may be one or more selected from the group including carbonyl groups, carboxy groups, and nitrile groups. Specifically, they may be one or two selected from the group including carbonyl groups and nitrile groups. By including the functional groups on the shell surface, they can form strong hydrogen bonds with the hydroxyl groups (-OH) of nanocellulose.

[0029] The amount of nanocellulose may be 0.01% to 1.0% by weight based on the total mass of the solid content of the latex particles. Specifically, it may be 0.05% to 0.9% by weight, and more specifically, it may be 0.05% to 0.8% by weight. If the amount of nanocellulose added is too small, the effects of improving the dispersibility of the binder, suppressing the migration of core-shell structured latex particles during the electrode manufacturing process, and improving the binding strength of the electrode manufactured using the nanocellulose may not be fully achieved. However, if the amount of nanocellulose added is too large, the hydrogen bonding between the nanocellulose and between the nanocellulose and the core-shell structured latex particles within the binder may become significantly increased, leading to the formation of agglomerates, which may significantly reduce the dispersibility of the binder and the binding strength of the electrode manufactured using the nanocellulose.

[0030] The rubbery polymer may be one or more selected from the group consisting of butadiene rubber, acrylic rubber, ethylene-propylene copolymer rubber, styrene-butadiene copolymer rubber, acrylonitrile-butadiene copolymer rubber, isoprene rubber, ethylene-propylene-diene terpolymer rubber, polyorganosiloxane-polyalkyl(meth)acrylate rubber composite, and mixtures thereof. Specifically, the rubbery polymer may be styrene-butadiene copolymer rubber.

[0031] The acrylic monomer may be one or more selected from the group consisting of methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, isobutyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 2-ethylbutyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, octadecyl (meth)acrylate, and isobornyl (meth)acrylate. Specifically, the acrylic monomer may be one or more selected from the group consisting of n-butyl (meth)acrylate, t-butyl (meth)acrylate, isobutyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate, more specifically, one or more of butyl (meth)acrylate and 2-ethylhexyl methacrylate, more specifically, butyl (meth)acrylate and 2-ethylhexyl methacrylate.

[0032] The non-acrylic monomer may be one or more selected from the group consisting of (meth)acrylamide, N-methyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, (meth)acrylonitrile, N-vinylpyrrolidone, N-vinylcaprolactam, N-vinylcaprolactone, styrene, 2-vinylpyridine, 4-vinylpyridine, and vinyl acetate. Specifically, the non-acrylic monomer may be (meth)acrylonitrile.

[0033] [Nanocellulose-based slurry for secondary battery electrodes]

[0034] The slurry for the nanocellulose-based secondary battery electrode according to an embodiment of the present invention can include the above-described aqueous binder for the nanocellulose-based secondary battery electrode, the negative electrode active material, and the thickener. By including the above-described aqueous binder for the nanocellulose-based secondary battery electrode in the slurry, the viscosity of the slurry is improved.

[0035] Since the nanocellulose-based aqueous binder is the same as described above, repeated description is omitted. The amount of the nanocellulose-based aqueous binder added to the slurry production may be 1 to 5 parts by weight with respect to 100 parts by weight of the slurry solid content. Specifically, it may be 1 to 3 parts by weight with respect to 100 parts by weight of the slurry solid content.

[0036] The negative electrode active material may be one or more selected from the group consisting of carbon and graphite materials capable of insertion and deintercalation of lithium ions, Si-based materials, metals and compounds capable of alloying with lithium, composites of metals and their compounds with carbon and graphite materials, lithium-containing nitrides, and the like.

[0037] Examples of the carbon and graphite materials include natural graphite, artificial graphite, expanded graphite, carbon fiber, graphitizable carbon, carbon black, carbon nanotube, fullerene, activated carbon, hard carbon, and soft carbon.

[0038] Examples of the Si-based materials include Si, SiOx (0 < x < 2), Si-Y alloy (where Y is an alkali metal, alkaline earth metal, Group 13 element, Group 14 element, transition metal, rare earth element, or a combination thereof), Si-C composite, or Si-based compounds of these combinations.

[0039] Examples of the metals and elements capable of alloying with lithium include Al, Si, Sn, Ag, Bi, Mg, Zn, In, Ge, Pb, Pd, Pt, Ti, and the like. Specifically, the negative electrode active material may be a carbon and graphite material.

[0040] The amount of the negative electrode active material added to the prepared slurry may be 95 to 99 parts by weight relative to 100 parts by weight of the slurry.

[0041] The thickener may be one or more selected from the group consisting of cellulose-based polymers such as carboxymethyl cellulose, methyl cellulose, and hydroxypropyl cellulose, and their ammonium salts and alkali metal salts; (modified) poly(meth)acrylic acid and their ammonium salts and alkali metal salts; (modified) polyvinyl alcohols such as copolymers of acrylic acid or acrylic acid salts with vinyl alcohol, and copolymers of maleic anhydride or maleic acid or fumaric acid with vinyl alcohol; polyethylene glycol; polyethylene oxide; modified polyacrylic acid; oxidized starch; starch phosphate; casein; and hydrogenated acrylonitrile-butadiene copolymer. Specifically, the thickener may be carboxymethyl cellulose.

[0042] If the viscosity of the slurry is too low, layer separation occurs, and if the viscosity of the slurry is too high, uniform electrode application is not possible. Therefore, by adding a thickener to the slurry, the viscosity of the slurry can be adjusted to an appropriate level, thereby imparting electrode application properties.

[0043] The amount of thickener added to the slurry preparation may be 0.5 to 1.5 parts by weight per 100 parts by weight of the slurry.

[0044] The slurry according to one embodiment of the present invention may further contain a solvent, if necessary, such as, but not limited to, N-methylpyrrolidone, acetone, or water, and any solvent available in the art may be used.

[0045] [Secondary battery electrode]

[0046] A secondary battery electrode according to one embodiment of the present invention may be prepared using the above-described slurry. The slurry is the same as described above, so a repeated description will be omitted. By using the above-described slurry, a secondary battery electrode with excellent binding strength can be prepared.

[0047] The secondary battery electrode may be a negative electrode. The negative electrode can be prepared by applying a negative electrode slurry containing a mixture of distilled water, a negative electrode active material, carboxymethyl cellulose, and the nanocellulose-based aqueous binder for secondary battery electrodes onto a conductive negative electrode current collector using an applicator, a doctor blade, immersion, brush coating, or the like, and then vacuum drying the slurry at 80°C to 150°C for 5 to 60 minutes. The thickness of the negative electrode after vacuum drying may be 20 μm to 150 μm.

[0048] The current collector is the site where electrons move during the electrochemical reaction of the active material. The negative electrode current collector can be manufactured to a thickness of 5 μm to 30 μm. The negative electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and is conductive. For example, copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or a combination thereof can be used.

[0049] The secondary battery electrode may have a peel strength of 8.5 gf / cm or more before vacuum drying and a peel strength of 9.0 gf / cm or more after vacuum drying during the manufacturing process. [Example]

[0050] DETAILED DESCRIPTION OF THE INVENTION The present invention will now be described in detail with reference to exemplary embodiments thereof so that those skilled in the art can easily understand and practice the invention. However, the present invention may be embodied in many different forms and is not limited to the exemplary embodiments set forth herein.

[0051] [Comparative Example 1] (1) Binder preparation Using a high-pressure reactor, 140 parts by weight of distilled water was emulsified with 1-0.5 parts by weight of sodium dodecylbenzenesulfonate as an anionic surfactant, 3 parts by weight of a 4:6 mixture of 1,3-butadiene and styrene as an SBR seed, and 1-3 parts by weight of itaconic acid. An additional 100 parts by weight of the 4:6 mixture of 1,3-butadiene and styrene was added and emulsified with stirring. 0.3 parts by weight of potassium sulfate as a decomposition initiator was added, and an emulsion polymerization reaction was carried out to prepare the SBR binder.

[0052] (2) Slurry and electrode preparation Based on a total of 100 parts by weight of slurry solids, 97.4 parts by weight of graphite as an active material, 1.5 parts by weight of the binder particles obtained above, and 1.1 parts by weight of carboxymethyl cellulose were mixed, and distilled water was added thereto to adjust the solids content of the slurry to 20% to 80% by weight. The slurry was then uniformly applied to a 10 μm-thick Cu thin film using an applicator, dried, and rolled using a roll press to prepare a negative electrode.

[0053] Comparative Example 2 An SBR binder was prepared in the same manner as in Comparative Example 1. After 4 hours, 4 parts by weight of acrylic monomer (0.6 parts by weight of butyl (meth)acrylate, 0.2 parts by weight of acrylonitrile, and 3.2 parts by weight of 2-ethylhexyl methacrylate) and 0.2 parts by weight of a decomposition initiator potassium sulfate were added to 1 part by weight of the SBR binder to carry out an emulsion polymerization reaction, polymerizing an SBR-Acryl binder with a core-shell structure. Using the obtained binder, a slurry and an electrode were prepared in the same manner as in Comparative Example 1.

[0054] [Comparative Example 3] A binder was prepared by adding 5% by weight of nanocellulose (CNC) based on the SBR-Acryl solid content to an SBR-Acryl core-shell structured binder prepared in the same manner as in Comparative Example 2. Using the obtained binder, a slurry and an electrode were prepared in the same manner as in Comparative Example 1.

[0055] [Example 1] A binder was prepared by adding 0.1% by weight of nanocellulose (CNC) based on the SBR-Acryl solid content to an SBR-Acryl core-shell structure binder prepared in the same manner as in Comparative Example 2. Using the obtained binder, a slurry and an electrode were prepared in the same manner as in Comparative Example 1.

[0056] [Example 2] A binder was prepared by adding 0.5% by weight of nanocellulose (CNC) based on the SBR-Acryl solid content to an SBR-Acryl core-shell structured binder prepared in the same manner as in Comparative Example 2. Using the obtained binder, a slurry and an electrode were prepared in the same manner as in Comparative Example 1.

[0057] [Example 3] A binder was prepared by adding 0.75 wt% nanocellulose (CNC) to the SBR-Acryl core-shell structure binder prepared in the same manner as in Comparative Example 2. Using the obtained binder, a slurry and an electrode were prepared in the same manner as in Comparative Example 1.

[0058] [Experimental Example 1] The presence or absence of aggregation and surface condition of the binders prepared in Comparative Example 3, Example 1, and Example 2 were observed with the naked eye and are shown in Figure 1. From this, it can be seen that the binders of Example 1 and Example 2 have smooth surfaces, but the binder of Comparative Example 3 has a lot of curvature on the surface due to internal aggregation. This is the result of the amount of nanocellulose (CNC) added being excessive relative to the SBR-Acryl solid content, which significantly increased the hydrogen bonds between nanocellulose within the binder and between nanocellulose and the carbonyl or nitrile groups of the SBR-Acryl binder, resulting in aggregation.

[0059] [Experimental Example 2] The binders prepared in Comparative Example 1, Comparative Example 2, and Example 1 were mixed with distilled water to prepare binder suspension compositions containing 0.05 to 0.1 wt % of binder solids. The zeta potential of the binder suspension compositions was measured at room temperature, and the results are shown in Table 1 below.

[0060] Zeta potential is generally measured by measuring the surface potential of the electric double layer of particles. When the zeta potential value is ±30mV to ±60mV (absolute value 30 to 60mV), the dispersibility is judged to be stable, and the larger the absolute value, the higher the surface potential value, and therefore the more stable it can be judged to be.

[0061] [Table 1]

[0062] Referring to Table 1, the absolute value of the zeta potential for Comparative Example 2 is higher than that for Comparative Example 1, confirming that the dispersibility of the binder was improved by forming an SBR-Acrylic core-shell structure. However, in the case of Comparative Example 3, in which an excessive amount of nanocellulose (CNC) was added, a large amount of aggregation occurred within the binder, as confirmed with the naked eye in Experimental Example 1, confirming that dispersibility was significantly reduced. Examples 1 to 3, which show a much higher absolute value of the zeta potential than Comparative Example 2, which had relatively stable dispersibility, demonstrate that adding an appropriate amount of nanocellulose (CNC) to a binder with an SBR-Acrylic core-shell structure further improves the dispersibility of the binder.

[0063] [Experimental Example 3] Figure 2 is a graph showing the relationship between shear deformation rate and viscosity of the slurries of Comparative Example 2 and Examples 1 to 3 on a logarithmic scale. It can be seen from this graph that the viscosities of the slurries of Examples 1 to 3, which were prepared by adding an appropriate amount of nanocellulose (CNC) to the SBR-Acrylic core-shell binder, were higher than that of the slurry of Comparative Example 2. This is because the viscosity of the slurry was improved due to the formation of hydrogen bonds between the SBR-Acrylic core-shell binder and the nanocellulose (CNC). This indicates that the stability of the slurry was increased, and the increased viscosity enabled more uniform application.

[0064] [Experimental Example 4] The electrodes prepared in Comparative Examples 2, 3, and Examples 1 to 3 were cut to a size of 25 mm wide and 100 mm long. A 20 mm wide, 40 mm long double-sided tape was attached to a 40 mm wide, 100 mm long acrylic plate. The prepared electrode was attached to the double-sided tape and gently pressed five times with a hand roller. The electrode was then placed in a UTM (20 kgf load cell). Approximately 25 mm of one side of the negative electrode was peeled off. The electrode was then attached to the upper clip of a tensile strength meter and the tape attached to one side of the electrode was attached to the lower clip. The peel strength was measured at a rate of 100 mm / min, and the peel strength is shown in Figure 3. At least five specimens were prepared for each sample, and the electrode strengths were measured before and after vacuum drying (before VD (vacuum drying)) and after VD (vacuum drying), and the average was calculated. Vacuum drying was performed at 110°C for 4 hours. The results of Figure 3 are summarized in Table 2 below.

[0065] [Table 2]

[0066] From the results in Table 2, it can be seen that when nanocellulose (CNC) is added to an SBR-Acryl core-shell structured binder in the amount proposed in the present invention, the electrode binding strength of the binder is improved compared to when no nanocellulose (CNC) is added, while when excessive nanocellulose (CNC) is added, the electrode binding strength of the binder is actually lower than when no nanocellulose (CNC) is added.

[0067] [Experimental Example 5] The binder dispersibility was compared for Comparative Example 2, Comparative Example 3, and Examples 1-3 using SAICAS (Surface and Interfacial Cutting Analysis System). Specifically, appropriate amounts of the slurries from Comparative Example 2, Comparative Example 3, and Examples 1-3 were uniformly applied to a 10 μm Cu thin film and dried to form a composite layer of 1-1000 μm. The composite layer was then cut and peeled to analyze its adhesive properties. The composite layer was cut to a specific depth with a micro-blade, and the horizontal force acting while peeling at a constant speed in a direction parallel to the interface between the Cu thin film and the composite layer was converted into adhesive force. This process is shown diagrammatically in Figure 4. The composite layer was cut to depths of 30%, 60%, and 90% from the top surface, and the horizontal force was measured while peeling horizontally. The results are shown in Figure 5 and summarized in Table 3 below. This allows for an analogy of binder dispersibility.

[0068] [Table 3] (unit: kN / m)

[0069] As can be seen from Table 3, Examples 1 to 3, unlike Comparative Examples 2 and 3, have small deviations in the horizontal force regardless of the cutting depth, confirming excellent binder dispersion. This is because adding nanocellulose (CNC) in the amount proposed in this invention to the SBR-Acrylic core-shell structured binder forms strong hydrogen bonds between the binder and nanocellulose (CNC) in the slurry, suppressing binder migration during electrode drying. Therefore, even after the electrode is dried, the binder remains uniformly distributed throughout the composite layer, just as it was before the electrode was dried.

[0070] The present invention is not limited to the examples, and can be manufactured in various different forms, and a person skilled in the art to which the present invention pertains will understand that the present invention can be embodied in other specific forms without changing the technical idea or essential characteristics of the present invention. Therefore, the above-described examples should be understood to be illustrative in all respects and not limiting.

Claims

1. a core comprising a rubbery polymer; and a shell formed by bonding one or two monomers selected from the group consisting of acrylic monomers and non-acrylic monomers to the surface of the core by chemical reaction; Core-shell structured latex particles comprising: nanocellulose that interacts with the functional groups on the shell surface; The nanocellulose is 0.01% by weight to 1.0% by weight based on the total mass of the latex particle solids.

2. 2. The nanocellulose-based aqueous binder for secondary battery electrodes according to claim 1, wherein the nanocellulose is at least one selected from the group consisting of cellulose nanofibers (CNF), cellulose nanocrystals (CNC), and bacterial cellulose (BC).

3. The nanocellulose-based aqueous binder for secondary battery electrodes according to claim 1 , wherein the chemical reaction is a polymerization reaction.

4. The nanocellulose-based aqueous binder for secondary battery electrodes according to claim 1, wherein the interaction is a hydrogen bond.

5. The nanocellulose-based aqueous binder for secondary battery electrodes according to claim 1, wherein the functional group on the shell surface is one or more selected from the group consisting of a carbonyl group, a carboxy group, and a nitrile group.

6. The nanocellulose-based aqueous binder for secondary battery electrodes according to claim 1, wherein the rubber-like polymer is at least one selected from the group consisting of butadiene rubber, acrylic rubber, ethylene-propylene copolymer rubber, styrene-butadiene copolymer rubber, acrylonitrile-butadiene copolymer rubber, isoprene rubber, ethylene-propylene-diene terpolymer rubber, polyorganosiloxane-polyalkyl (meth)acrylate rubber composite, and mixtures thereof.

7. The acrylic monomer is methyl (meth) acrylate, ethyl (meth) acrylate, n- propyl (meth) acrylate, isopropyl (meth) acrylate, n- butyl (meth) acrylate, t- butyl (meth) acrylate, isobutyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, 2-ethylbutyl (meth) acrylate, pentyl (meth) acrylate, hexyl (meth) acrylate, cyclohexyl (meth) acrylate, n- octyl (meth) acrylate, isooctyl (meth) acrylate, isononyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, tridecyl (meth) acrylate, tetradecyl (meth) acrylate, octadecyl (meth) acrylate and isobornyl (meth) acrylate. The nanocellulose-based aqueous binder for secondary battery electrodes according to claim 1, which is at least one selected from the group consisting of acrylate.

8. The nanocellulose-based aqueous binder for secondary battery electrodes according to claim 1, wherein the non-acrylic monomer is at least one selected from the group consisting of (meth)acrylamide, N-methyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, (meth)acrylonitrile, N-vinylpyrrolidone, N-vinylcaprolactam, N-vinylcaprolactone, styrene, 2-vinylpyridine, 4-vinylpyridine, and vinyl acetate.

9. A nanocellulose-based secondary battery electrode slurry comprising the aqueous binder according to any one of claims 1 to 8, a negative electrode active material, and a thickener.

10. The thickener is a cellulose-based polymer such as carboxymethyl cellulose, methyl cellulose, hydroxypropyl cellulose, and their ammonium salts and alkali metal salts; (modified) poly(meth)acrylic acid, and their ammonium salts and alkali metal salts; (modified) polyvinyl alcohols such as copolymers of acrylic acid or acrylic acid salts and vinyl alcohol, copolymers of maleic anhydride or maleic acid or fumaric acid and vinyl alcohol; polyethylene glycol; polyethylene oxide; modified polyacrylic acid; oxidized starch; starch phosphate; casein; and acrylonitrile-butadiene copolymer hydrogenated; The nanocellulose-based slurry for secondary battery electrodes according to claim 9, which is at least one selected from the group consisting of:

11. A secondary battery electrode produced using the slurry of claim 10.

12. The secondary battery electrode according to claim 11 , wherein the peel strength before vacuum drying during the manufacturing process is 8.5 gf / cm or more and the peel strength after vacuum drying is 9.0 gf / cm or more.

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