Negative electrode mixture slurry, negative electrode for secondary battery produced therefrom, and lithium ion battery comprising same

Abstract

The present embodiment relates to a negative electrode mixture slurry, a negative electrode manufactured from the negative electrode mixture slurry, and a lithium ion battery comprising the negative electrode, and provides a negative electrode mixture slurry comprising a silicon-based negative electrode active material and a photocurable binder, the photocurable adhesive includes: a first acrylate monomer or oligomer having two or less functional groups and having an acrylate terminal; and a second acrylate monomer or oligomer having three or more functional groups and having an acrylate terminal.

Description

Technical Field

[0001] The present invention relates to a negative electrode mixture slurry, a negative electrode for a secondary battery manufactured from the negative electrode mixture slurry, and a lithium ion battery including the negative electrode. Background Art

[0002] In recent years, with the increase in the technological development and demand for portable devices such as portable computers, portable phones, cameras, and electric vehicles, the demand for secondary batteries as an energy source has also been rapidly increasing. Among such secondary batteries, a great deal of research has been conducted on lithium secondary batteries that exhibit high energy density, working potential, long cycle life, and low self-discharge rate, and they have been commercialized and widely used.

[0003] Generally, a lithium secondary battery is charged and discharged by repeating the process of lithium ions being intercalated into and deintercalated from the positive electrode. As this repetition of intercalation and deintercalation of lithium ions proceeds, the bonding between the electrode active material or the conductive material becomes loose, and the contact resistance between the particles increases. As a result, the ohmic resistance of the electrode increases, and thus the battery characteristics may deteriorate. Therefore, an elastic polymer that can buffer the expansion and contraction of the electrode active material caused by the intercalation and deintercalation of lithium ions in the electrode can be used as the binder.

[0004] With the increase in the technological development and demand for electric vehicles, the demand for secondary batteries as an energy source is rapidly increasing. Among such secondary batteries, a great deal of research has been conducted on lithium secondary batteries having high energy density and discharge voltage, and they have been commercialized and widely used. Such lithium secondary batteries generally use lithium transition metal oxides as the positive electrode active material and carbon-based materials as the negative electrode active material.

[0005] The theoretical maximum capacity of a negative electrode formed of a carbon-based material is limited, so the improvement of the capacity is restricted. Therefore, a great deal of research is being conducted on using silicon, which has a larger theoretical maximum capacity than carbon-based active materials, as the negative electrode active material.

[0006] However, the problem with silicon is that during charge and discharge, due to the reaction with lithium, the volume change is very large. Therefore, during continuous charge and discharge, the negative electrode active material detaches from the negative electrode current collector, or due to the large change in the contact interface between the negative electrode active materials, the resistance increases, and thus, as the charge and discharge cycles proceed, the capacity decreases rapidly, and the cycle life becomes short.

[0007] Therefore, there is a high demand for the development of an adhesive and a negative electrode material as described below. The adhesive and the negative electrode material can firmly bond the negative electrode active materials to each other or between the negative electrode active material and the current collector during the manufacture of the negative electrode to prevent separation, and can control the volume expansion of the negative electrode active material that occurs during repeated charge and discharge, thereby enabling the structural stability of the electrode and improving the performance of the battery accordingly.

[0008] In view of these problems, in some prior arts, a technique as described below has been proposed. In this technique, in order to suppress a decrease in the bonding force with the current collector and the bonding force between the active materials due to the volume change of the silicon-based negative electrode active material, polyamic acid is used as an adhesive, and a negative electrode mixture containing this adhesive is coated on the current collector and then heat-treated at a high temperature (above 300 °C) and converted into polyimide through an imidization reaction. This method requires a long-time heat treatment (for example, 10 hours) at a high temperature.

[0009] In addition, Japanese Patent Application Laid-Open No. Hei 10-162832 discloses a technique as described below. In this technique, a monomer having a polymerizable functional group at the molecular chain end and containing a fluoroalkyl group in the molecular structure is used as an adhesive, and the positive electrode or negative electrode of a solid electrolyte battery is manufactured by photopolymerization.

[0010] In addition, Japanese Patent Application Laid-Open No. 2005-44681 discloses a technique as described below. In this technique, a urethane (meth)acrylate compound (A) having a (meth)acryloyl group at the molecular chain end and / or a polyisocyanate derivative (B) having at least one (meth)acryloyl group at the molecular chain end and the rest being a hydrocarbon group is used as an adhesive, and the positive electrode or negative electrode of a lithium secondary battery having a polymer solid electrolyte is manufactured by photopolymerization or thermal polymerization. Summary of the Invention

[0011] (I) Technical Problems to be Solved

[0012] In a lithium secondary battery using a silicon-based negative electrode active material, a manufacturing technique as described below is highly desired. The manufacturing technique provides a strong bonding force sufficient to prevent large volume changes of the negative electrode active material during charge and discharge and is economical in terms of process.

[0013] Therefore, an object of a specific embodiment of the present invention is to improve the adhesion force between negative electrode active materials by increasing the cross-linking density in a negative electrode containing a silicon-based negative electrode active material.

[0014] (II) Technical Solutions

[0015] According to a specific embodiment of the present invention, a negative electrode mixture slurry is provided. The negative electrode mixture slurry contains a silicon-based negative electrode active material and a photocurable binder. Among them, the photocurable binder includes: a first monomer or oligomer having 2 or less functional groups; and a second monomer or oligomer having 3 or more functional groups.

[0016] The photocurable binder may be an acrylate monomer or oligomer having an acrylate functional group at the end.

[0017] The weight ratio of the first monomer or oligomer to the second monomer or oligomer may be 50 to 95 wt%: 5 to 50 wt%.

[0018] The photocurable binder may have a viscosity of 10000 cps or less at 25 °C.

[0019] The photocurable binder may be at least one selected from the following: an acrylate monomer or oligomer having an acrylate end in an ethylene glycol repeating unit; an acrylate monomer or oligomer having an acrylate end in a urethane repeating unit; an acrylate monomer or oligomer having an acrylate end in a carboxylic acid structure repeating unit; and an acrylate monomer or oligomer having an acrylate end in a hydroxyl structure repeating unit.

[0020] The photocurable binder may be 1 to 20 wt% based on the total content of the solids of the negative electrode mixture slurry.

[0021] The negative electrode mixture slurry may further contain a carbon-based negative electrode active material.

[0022] In the negative electrode mixture slurry, the weight ratio of the content of the carbon-based negative electrode active material to the silicon-based negative electrode active material may be 60 to 98: 2 to 40 based on the total content of the negative electrode active material.

[0023] The negative electrode mixture slurry may further contain a photoinitiator.

[0024] The content of the photoinitiator may be 10 wt% or less based on the weight of the photocurable binder.

[0025] The photoinitiator may be at least one selected from azobisisobutyronitrile, benzoyl peroxide, di-tert-butyl peroxide, cumene hydroperoxide, and diisobutyl peroxide.

[0026] Another aspect of the present invention provides a negative electrode, which comprises: a negative electrode current collector; and a negative electrode mixture layer located on the negative electrode current collector, and the negative electrode mixture layer contains a silicon-based negative electrode active material and a photocurable binder, wherein the binder comprises: a photocurable binder, the photocurable binder contains a monomer or oligomer having at least one functional group; and a photopolymerized binder, the photopolymerized binder is formed by polymerizing the photocurable binder.

[0027] The photocurable binder may be an acrylate monomer or oligomer having an acrylate functional group at the end.

[0028] The acrylate monomer or oligomer may include a first acrylate monomer or oligomer having 2 or less functional groups and a second acrylate monomer or oligomer having 3 or more functional groups.

[0029] The content of the photocurable binder may be 0.1-15% by weight based on the total weight of the binder.

[0030] The weight average molecular weight of the photocurable binder may be 100 to 10,000.

[0031] The negative electrode may further contain a photoinitiator.

[0032] The content of the photoinitiator may be 0.01% by weight to 5% by weight based on the weight of the photocurable binder.

[0033] The negative electrode may have a second negative electrode mixture layer between the negative electrode current collector and the negative electrode mixture layer, and the second negative electrode mixture layer may contain a carbon-based negative electrode active material and a second binder different from the photocurable binder.

[0034] The second binder may include at least one selected from styrene-butadiene rubber, polyvinylidene fluoride, and polyacrylic acid.

[0035] At least one of the negative electrode mixture layer and the lower negative electrode mixture layer may further contain at least one thickener selected from carboxymethyl cellulose, methyl cellulose, hydroxypropyl cellulose, methyl hydroxypropyl cellulose, and cellulose gum.

[0036] (III) Beneficial effects

[0037] According to a specific embodiment of the present invention, the crosslinking density is increased through the crosslinking reaction of the curable binder, thereby the adhesion between active substances can be improved, and thus the volume shrinkage / swelling of silicon can be controlled. Brief description of the drawings

[0038] Figure 1It is a diagram schematically showing the concept of polymerizing a curable binder by photo-curing or electron beam curing in a negative electrode mixture layer containing a photo-curable binder to bond a negative electrode active material.

[0039] Figure 2 It is a photograph of a cross-section of the negative electrode manufactured in Example 1. Best Mode

[0040] The present invention provides a negative electrode mixture slurry. Specifically, the present invention relates to a negative electrode mixture slurry for manufacturing a negative electrode, the negative electrode mixture slurry containing a silicon-based negative electrode active material as a negative electrode active material to increase the capacity, and the present invention provides a negative electrode mixture slurry as follows, the negative electrode mixture slurry capable of preventing the detachment of the negative electrode active material due to volume expansion in a negative electrode containing a silicon-based negative electrode active material with a large volume expansion during charge and discharge of a battery.

[0041] The negative electrode mixture slurry contains a silicon-based negative electrode active material as a negative electrode active material, the silicon-based negative electrode active material containing silicon, and there is no particular limitation as long as it can generally be used as a negative electrode active material. For example, the silicon-based negative electrode active material can use at least any one selected from SiOx (0≤x<2) particles, Si-C composites, and Si-Y alloys (where Y is an element selected from alkali metals, alkaline earth metals, transition metals, Group 13 elements, Group 14 elements, rare earth elements, and combinations thereof), and for example, it can be SiO.

[0042] The negative electrode mixture slurry contains a photo-curable binder. The photo-curable binder can use a binder that can be cured by light due to having a functional group and shows the property of being able to bond a negative electrode active material by curing. For example, the photo-curable binder can be a monomer or oligomer having a functional group.

[0043] In the present invention, the monomer having a functional group is a unit compound that provides a repeating unit structure constituting a polymer, and an oligomer refers to a polymerization product having a repeating unit structure obtained by polymerization of the unit compound and having a weight average molecular weight of 10,000 g / mol or less. Therefore, in addition to monomers, as long as it is a polymerization product having a weight average molecular weight within the above range, dimers, trimers, etc. are also included in the oligomers of the present invention.

[0044] The weight average molecular weight refers to the average molecular weight obtained by averaging the molecular weights of the component molecular species of a polymer compound having a molecular weight distribution according to weight fractions, and the weight average molecular weight can be measured by a light scattering method, the light scattering method using the phenomenon that light having the same frequency as the incident light is scattered after the incident light collides with polymer particles.

[0045] Hereinafter, in the present invention, unless otherwise specified, the photocurable binder contained in the negative electrode mixture slurry is a monomer or oligomer having a functional group. For example, it can be an acrylate monomer or oligomer having an acrylate functional group at the end.

[0046] As an example, the acrylate monomer or oligomer can be an acrylate monomer or oligomer having an ethylene glycol repeating unit and an acrylate end. For example, the acrylate monomer or oligomer can be polyethylene glycol diacrylate or ethoxylated trimethylolpropane triacrylate. As another example, the acrylate monomer or oligomer can be an acrylate monomer or oligomer having a urethane repeating unit and an acrylate end, which is insoluble in water and can be provided in the form of a polyurethane dispersion dispersed in water. As another example, the acrylate monomer or oligomer can be an acrylate monomer or oligomer having a carboxylic acid (-COOH) structural repeating unit containing a carboxylic acid and having an acrylate end. As another example, the acrylate monomer or oligomer can be an acrylate monomer or its oligomer having a hydroxyl (-OH) structural repeating unit containing a hydroxyl group and having an acrylate end.

[0047] Any one of the acrylate monomers or oligomers can be used alone, or two or more of them can also be used in combination.

[0048] Specifically, the photocurable binder can be used in combination with a monomer or oligomer having 2 or less functional groups (first monomer or oligomer) and a monomer or oligomer having 3 or more acrylate functional groups (second monomer or oligomer).

[0049] More specifically, an acrylate monomer or oligomer having 2 or less acrylate functional groups at the end (first acrylate monomer or oligomer) and an acrylate monomer or oligomer having 3 or more acrylate functional groups at the end (second acrylate monomer or oligomer) can be used in combination.

[0050] As described above, when a monomer or oligomer having 2 or less functional groups is used in combination with a second monomer or oligomer having 3 or more functional groups, the functional groups can crosslink with each other to form a three-dimensional network during the curing process using light. And through the formed three-dimensional network, the photocurable binder surrounds the silicon-based negative electrode active material, thereby increasing the crosslinking density. Therefore, the volume shrinkage and expansion of the silicon-based negative electrode active material during the charge and discharge process can be suppressed, and the shedding of the silicon-based negative electrode active material can be prevented.

[0051] In the photocurable adhesive, acrylate monomers or oligomers having 2 or less functional groups and acrylate monomers or oligomers having 3 or more functional groups can be mixed, for example, in a weight ratio of 50-95 wt% to 5-50 wt%, but are not limited thereto. When the content of the acrylate monomer or oligomer having 3 or more functional groups is less than 5 wt%, it may be difficult to achieve a sufficient crosslinking density. When the content of the acrylate monomer or oligomer having 3 or more functional groups exceeds 50 wt%, due to the increase in crosslinking density, a shrinkage problem of the electrode may occur.

[0052] The photocurable adhesive may have a viscosity of 10,000 cps or less at 25°C. When the viscosity of the photocurable adhesive exceeds the above range, the coating processability may be reduced due to the increase in the viscosity of the slurry.

[0053] The content of the photocurable adhesive may be 1-20 wt% based on the total weight of the solids of the negative electrode mixture slurry. When the content of the photocurable adhesive is less than 1 wt%, the dispersibility of the active material may be reduced, and the adhesion between the active material and the current collector may be insufficient. When the content of the photocurable adhesive exceeds 20 wt%, the resistance may increase.

[0054] The negative electrode mixture slurry containing the photocurable adhesive may further contain a photoinitiator. The photoinitiator initiates the polymerization reaction of the photocurable adhesive, and the photoinitiator may use a substance generally used as a photoinitiator. As the photoinitiator, for example, azobisisobutyronitrile, benzoyl peroxide, di-tert-butyl peroxide, cumene hydroperoxide, diisobutyl peroxide can be cited. The photoinitiator may use any one of them, or two or more of them may be used in combination.

[0055] The content of the photoinitiator may be 10 wt% or less based on the weight of the photocurable adhesive, and more specifically, it may be 0.01-5 wt%. When the content of the photoinitiator is less than 0.01 wt% based on the weight of the photocurable adhesive, there is a problem that it is difficult to perform chain growth due to low reactivity. When the content of the photoinitiator exceeds 10 wt% based on the weight of the photocurable adhesive, due to overuse, the cost increases, and the resistance may increase due to the remaining unreacted photoinitiator.

[0056] The negative electrode mixture paste of the present invention can further contain a carbon-based negative electrode active material while containing the silicon-based negative electrode active material. The carbon-based negative electrode active material is not particularly limited, but for example, it can be one or more selected from artificial graphite, natural graphite, and graphitized mesophase carbon microspheres. More specifically, artificial graphite can be used, and artificial graphite and natural graphite can be used in combination.

[0057] When the silicon-based negative electrode active material and the graphite-based negative electrode active material are used in combination, the graphite-based negative electrode active material and the silicon-based negative electrode active material can be contained in a weight ratio of 60 to 98:2 to 40. When the content of the silicon-based negative electrode active material is less than 2% by weight, the effect of increasing the capacity is low. When the content of the silicon-based negative electrode active material exceeds 40% by weight, electrode detachment may occur due to the volume shrinkage and expansion of the excessive silicon-based active material.

[0058] In addition, the negative electrode mixture paste can contain a conductive agent. Carbon nanotubes (CNT) can be used as the conductive agent to further suppress the volume expansion of the silicon-based negative electrode active material. Any one of single-walled carbon nanotubes (SWCNT), double-walled carbon nanotubes (TWCNT), and multi-walled carbon nanotubes (MWCNT) can be used as the CNT, and there is no particular limitation.

[0059] The content of the conductive agent can be 0.1 - 10% by weight based on the total weight of the solid matter. When the content of the conductive agent is less than 0.1% by weight, the resistance may increase. When the content of the conductive agent exceeds 10% by weight, a decrease in capacity and an increase in cost may occur.

[0060] The negative electrode mixture paste can further contain a second binder commonly used to form the negative electrode mixture layer while containing a photocurable binder.

[0061] The second binder can contain, for example, at least one selected from styrene-butadiene rubber (SBR), acrylated styrene-butadiene rubber, nitrile rubber, acrylic rubber, butyl rubber, ethylene-propylene copolymer, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, ethylene-propylene-diene copolymer, polyvinylidene fluoride (PVDF), polyvinyl pyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol resin, acrylate-based resin, polyaniline (PANI), polythiophene (PT), polyacetylene, polypyrrole (PPy), and poly(3,4-ethylene dioxythiophene) (PEDOT).

[0062] When the negative electrode mixture paste further contains the second binder, the content of the second binder is not particularly limited. For example, the content of the second binder may be 0.1-10% by weight based on the total weight of the solid content. When the content of the second binder is less than 0.1% by weight, there is a problem of reduced adhesion. When the content of the second binder exceeds 10% by weight, a reduction in capacity may be caused.

[0063] The negative electrode mixture paste of the present invention may further contain a thickener. The thickener may be one or more selected from carboxymethyl cellulose (CMC), methyl cellulose (MC), hydroxypropyl cellulose (HPC), methyl hydroxypropylcellulose (MHPC), ethyl hydroxyethyl cellulose (EHEC), methyl ethyl hydroxyethyl cellulose (MEHEC), and cellulose gum, but is not limited thereto.

[0064] The content of the thickener may be 0.1-10% by weight based on the total content of the solid content of the negative electrode mixture paste. When the content of the thickener is less than 0.1% by weight, the thickening effect is very small. When the content of the thickener exceeds 10% by weight, an increase in resistance and a reduction in capacity may be caused.

[0065] As described above, the paste can be prepared by mixing a silicon-based negative electrode active material, a photocurable binder, a photoinitiator as needed, and an additive component as needed with a solvent. Water can be used as the solvent. At this time, water can be added to the paste so that the solid content is 20-70% by weight.

[0066] When manufacturing the negative electrode according to the present invention, it includes a step of coating the negative electrode mixture paste containing the photocurable binder on a negative electrode current collector.

[0067] The negative electrode current collector can be appropriately used as long as it does not cause chemical changes in the battery and has conductivity, and there is no particular limitation. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon can be used as the negative electrode current collector; substances obtained by surface-treating the surface of copper or stainless steel with, including but not limited to, carbon, nickel, titanium, or silver can be used; or an aluminum-cadmium alloy can be used, but it is not limited thereto. In addition, the negative electrode current collector can form fine irregularities on the surface of the substrate as described above, and the binding force between the negative electrode active material and the current collector can be enhanced through the irregularities as described above. In addition, the negative electrode current collector can have various forms, and the negative electrode current collector can be in the form of a film, sheet, foil, net, porous body, foam, or non-woven fabric, but it is not limited thereto.

[0068] When manufacturing a negative electrode using the negative electrode mixture paste containing a photocurable binder provided by the present invention, it includes a step of coating the negative electrode mixture paste on a negative electrode current collector and then drying it. The drying is used to remove the solvent contained in the paste, and the process conditions are not particularly limited and can be carried out under the process conditions commonly used for drying negative electrode pastes. For example, the drying can be carried out at a temperature condition of 80 - 220°C.

[0069] After completing the drying process, a calendering process can be carried out. The calendering can make the negative electrode mixture layer have a predetermined electrode density and can contribute to flattening the negative electrode mixture layer. The calendering can be selected according to the desired electrode density and there is no particular limitation, and it can be carried out according to the process conditions commonly carried out.

[0070] In addition, it includes a curing process for polymerizing the photocurable binder contained in the negative electrode mixture layer. Through the curing process, the photocurable binder polymerizes, and thus a network is formed between the functional groups, so that the negative electrode active material can be bonded. Figure 1 The concept of forming a network through the curing of the photocurable binder and thereby bonding the negative electrode active material is schematically shown.

[0071] The curing process can be carried out after the drying process, and can also be carried out after the calendering process, and there is no particular limitation. However, if the curing step is carried out after calendering, the light transmittance can be increased during the process of irradiating light to polymerize the photocurable binder, so that the photo-polymerization efficiency can be further improved.

[0072] As Figure 1As shown, the monomers and / or oligomers of the photocurable binder contained in the negative electrode mixture slurry are polymerized by irradiation with light (ultraviolet (UV) light) or an electron beam to form a network. More specifically, through the curing process, the photocurable binder is polymerized, so as to cross-link with each other between functional groups to form a network, and the silicon-based negative electrode active material is located within the network, thereby volume expansion can be inhibited, and thus shedding of the negative electrode active material can be prevented.

[0073] The curing process can be carried out by ultraviolet (UV) light irradiation or electron beam (E-Beam) irradiation. More specifically, when the photoinitiator is included, the curing process can be carried out by UV light irradiation.

[0074] The negative electrode mixture layer obtained according to the present invention is formed on a negative electrode current collector. The negative electrode mixture layer contains a silicon-based negative electrode active material and a binder. The binder contains a photopolymerizable binder and a photopolymerized binder. The photopolymerizable binder is a monomer or oligomer having at least one functional group, and the photopolymerized binder is a polymer obtained by photopolymerization of the monomer or oligomer having a functional group as the photopolymerizable binder.

[0075] For example, the photopolymerizable binder is a monomer or oligomer having at least one functional group. For example, it can be an acrylate monomer or oligomer having an acrylate group as a functional group at the end, and the polymer obtained by photopolymerization of the monomer or oligomer can be an acrylate-based polymer.

[0076] The acrylate-based polymer is generated by photopolymerization of the acrylate monomer or oligomer having an acrylate end. Through cross-linking between the functional groups of the acrylate monomer or oligomer, a three-dimensional network structure can be formed, and the silicon-based negative electrode active material can be located within the network structure, thereby shedding of the negative electrode active material can be inhibited, and further volume expansion of the silicon-based negative electrode active material during charge and discharge can be inhibited.

[0077] The negative electrode mixture slurry used to form the negative electrode mixture layer contains a monomer or oligomer as a photocurable binder. Specifically, it contains the acrylate monomer or oligomer having acrylate terminals as the photocurable binder, and its content is relatively small, being 1-20% by weight based on the total content of the entire solid matter. Therefore, the chain growth of the photocurable binder through the photocuring reaction may be partially hindered by the negative electrode active material, so that the crosslinking between the photocurable binders may not occur completely, and thus it may remain in the state of acrylate monomer or oligomer. Therefore, the negative electrode mixture layer provided by the present invention may contain a part of the acrylate monomer or oligomer having acrylate terminals. That is, it can be considered that the negative electrode mixture layer according to the present invention has a relatively wide binder molecular weight distribution characteristic from monomer to polymer.

[0078] The content of the uncured acrylate monomer or oligomer present in the negative electrode mixture layer may be 20% by weight or less of the total content of the photocurable binder, and more specifically may be 0.1-15% by weight or 1-10% by weight. When the content of the uncured acrylate monomer or oligomer exceeds 20% by weight of the total content of the photocurable binder, there is a problem that the increase in adhesive force is limited due to the low crosslinking degree.

[0079] The measurement of the content of the unreacted acrylate monomer or oligomer present in the negative electrode mixture layer can be carried out by dissolving the acrylate monomer and oligomer from the negative electrode mixture layer using a solvent that can dissolve the acrylate monomer or oligomer having acrylate terminals. At this time, the solvents that can be used may be selected from, for example, distilled water, ethanol, acetone, and N-methyl-2-pyrrolidone (NMP), but are not limited thereto.

[0080] The content of the unreacted acrylate monomer or oligomer in the entire binder present in the negative electrode mixture layer can be measured by comparing the content after removing the acrylate monomer or oligomer having acrylate terminals from the negative electrode mixture layer as described above with the content before removing the acrylate monomer or oligomer having acrylate terminals as described above.

[0081] Specifically, a solvent that can dissolve the unreacted acrylate monomer or oligomer can be used to dissolve and remove the unreacted acrylate monomer or oligomer, and then the electrode is completely dried again in an oven at 140°C, and while raising the temperature to 500°C using a thermogravimetric analysis (TGA) device and burning, as described above, the content reduced by burning under the condition of 500°C or less in the total content of the negative electrode mixture layer (reduction amount: Wa) can be measured.

[0082] In addition, for an electrode in which the unreacted acrylate monomer or oligomer is not eluted and removed, the reduced content (reduction amount: Wb) can be measured using a TGA apparatus under the same combustion conditions as described above.

[0083] By calculating the difference between the reduction amount (Wb) during TGA combustion before the elution and the reduction amount (Wa) during TGA combustion after the elution, the content of the unreacted acrylate monomer and oligomer can be obtained.

[0084] In addition, during the process of eluting the unreacted acrylate monomer and oligomer contained in the negative electrode mixture layer using the solvent as described above, the unreacted photoinitiator selectively contained can also be eluted. Based on the photocurable binder present in the negative electrode mixture layer at 100% by weight, the content of the unreacted photoinitiator can be 5% by weight or less. For example, it can be 0.01 - 5% by weight.

[0085] In the present invention, the negative electrode can be a multi-layer negative electrode. For example, two or more negative electrode mixture layers can be included on the negative electrode current collector. More specifically, a second negative electrode mixture layer can be present between the negative electrode current collector and the negative electrode mixture layer. For example, when the negative electrode is a multi-layer negative electrode including two negative electrode mixture layers, one of the two negative electrode mixture layers can be a negative electrode mixture layer containing the photocurable binder provided by the present invention, and the negative electrode mixture layer containing the photocurable binder provided by the present invention can be located on the surface side of the negative electrode.

[0086] More specifically, a second negative electrode mixture layer having a different composition can be included between the negative electrode current collector and the negative electrode mixture layer provided by the present invention. The second negative electrode mixture layer can have a composition different from that of the negative electrode mixture layer of the present invention. For example, the second negative electrode mixture layer can be a negative electrode mixture layer formed from a negative electrode mixture slurry containing a carbon-based active material, a particulate binder, a thickener, and a conductive agent. At this time, the carbon-based active material, particulate binder, thickener, and conductive agent are the same as those described above, so repeated description is omitted.

[0087] The second negative electrode mixture layer can be formed on the negative electrode current collector. The photocurable binder can form a three-dimensional network through cross-linking of the binder, thereby restricting the silicon-based negative electrode active material inside the network. Therefore, an effect of suppressing volume expansion and preventing detachment can be provided. However, the particulate binder can more effectively prevent the negative electrode mixture layer from peeling off from the current collector by providing a high adhesive force to the current collector.

[0088] In addition, the second negative electrode mixture layer can also contain a silicon-based negative electrode active material, and the content of the silicon-based negative electrode active material can be less than the content of the silicon-based negative electrode active material contained in the negative electrode mixture layer.

[0089] In addition, when the second negative electrode mixture layer contains a silicon-based negative electrode active material, the photocurable adhesive may be included or the photocurable adhesive may not be included. At this time, when the photocurable adhesive is included, the content of the photocurable adhesive may be less than the content of the photocurable adhesive included in the negative electrode mixture layer. Detailed Description of the Invention

[0090] Hereinafter, the present invention will be described in more detail by way of examples. However, the following examples are for showing an example according to the present invention and are not intended to limit the present invention.

[0091] Example 1

[0092] Based on the weight of the solid content, 15% by weight of silicon oxide SiOx (0 < x < 2) as the negative electrode active material, 78% by weight of graphite, 3% by weight of a curable adhesive as the binder, 2% by weight of styrene-butadiene rubber (SBR) as the particulate binder, and 2% by weight of carboxymethyl cellulose (CMC) as the thickener were mixed with water. The curable adhesive was composed of a polyethylene glycol diacrylate monomer (viscosity at 25 °C: 50 cps) and an ethoxylated trimethylolpropane triacrylate monomer (viscosity at 25 °C: 100 - 200 cps) mixed at a weight ratio of 75:25 to prepare a negative electrode mixture slurry. At this time, the solid content of the negative electrode mixture slurry was 40% by weight.

[0093] A copper foil (thickness: 8 μm) was prepared as the negative electrode current collector, and the negative electrode mixture slurry was coated on both sides of the copper foil at a coating amount of 10 mg / cm 2 to manufacture a negative electrode sheet having a negative electrode mixture slurry coating formed thereon. The negative electrode sheet having the negative electrode mixture slurry coating formed thereon was placed in a drying oven and dried at 190 °C to remove water.

[0094] Next, the dried negative electrode sheet was calendered to manufacture a negative electrode (total thickness: 188 μm) having a negative electrode mixture layer with a thickness of 90 μm formed on both sides of the copper foil, and then the binder was cured by electron beam irradiation (surface irradiation dose: 100 kGy).

[0095] The cross-section of the negative electrode thus manufactured was photographed, and the photograph is shown in Figure 2 In Figure 2 , 3 represents the copper foil as the negative electrode current collector, and 5 represents the negative electrode mixture layer.

[0096] The adhesion force (kN / m) of the negative electrode mixture layer of the obtained negative electrode before and after electron beam irradiation was measured, and the results are shown in Table 1.

[0097] For the adhesion force before and after the electron beam irradiation, it was measured using SAICAS (EN-EX model (Model)). The horizontal force applied when the composite electrode was cut to a specific depth using a microblade and the negative electrode mixture layer was peeled off in a direction parallel to the current collector was measured, and this value was recorded as the adhesion force before and after the electron beam irradiation.

[0098] The copper foil serving as the negative electrode current collector was removed from the manufactured electrode, and the negative electrode mixture layer was recovered. The negative electrode mixture layer was dissolved in distilled water at a concentration of 20% by weight, and then stirred at a temperature of 60 °C for 24 hours. Thus, a mixed solution in which the negative electrode mixture layer was dissolved was obtained.

[0099] The negative electrode active material in the negative electrode mixture layer was dissolved into fine particles, and the negative electrode active material was filtered off from the mixed solution using a 0.4 μm filter, and the filtrate passing through the filter was recovered. The contents of ethylene glycol diacrylate monomer and ethoxylated trimethylolpropane triacrylate monomer in the above-mentioned recovered filtrate were measured by liquid chromatography.

[0100] It was confirmed that the ethylene glycol diacrylate monomer was eluted in an amount of about 5% by weight relative to the amount used when manufacturing the electrode, and it was confirmed that the ethoxylated trimethylolpropane triacrylate monomer was eluted in an amount of about 8% by weight relative to the amount used when manufacturing the electrode.

[0101] Example 2

[0102] Based on the weight of the solid content, 94% by weight of graphite as the negative electrode active material, 3% by weight of SBR as the particulate binder, and 3% by weight of CMC as the thickener were mixed with water to prepare a first negative electrode mixture slurry. At this time, the solid content of the first negative electrode mixture slurry was 45% by weight.

[0103] 15% by weight of silicon oxide SiOx (0 < x < 2) as the negative electrode active material, 78% by weight of graphite, 3% by weight of a curable binder as the binder, 2% by weight of SBR as the particulate binder, and 2% by weight of CMC as the thickener were mixed with water. The curable binder was composed of ethylene glycol diacrylate monomer (viscosity at 25 °C: 50 cps) and ethoxylated trimethylolpropane triacrylate monomer (viscosity at 25 °C: 100 - 200 cps) mixed at a weight ratio of 75:25 to prepare a second negative electrode mixture slurry. At this time, the solid content of the second negative electrode mixture slurry was 40% by weight.

[0104] Prepare a copper foil as the negative electrode current collector, and coat the first negative electrode mixture slurry on both sides of the copper foil at a coating amount of 5 mg / cm 2 to form a first negative electrode mixture slurry coating. Then, coat the second negative electrode mixture slurry on the first negative electrode mixture slurry coating at a coating amount of 5 mg / cm 2 to form a second negative electrode mixture slurry coating.

[0105] Put the negative electrode sheet with two layers of negative electrode mixture slurry coatings formed above into a drying furnace, and dry it under the same conditions as in Example 1 to remove water as the solvent.

[0106] Next, calender the dried negative electrode sheet in the same method as in Example 1 and then perform electron beam curing, so as to manufacture a negative electrode having a first negative electrode mixture layer and a second negative electrode mixture layer formed on both sides of the copper foil with a thickness ratio of 5:5 and a thickness of 90 μm for the negative electrode mixture layer.

[0107] Measure the adhesion force (kN / m) of each thickness of the negative electrode mixture layer of the obtained negative electrode, and show the results in Table 1.

[0108] Comparative Example 1

[0109] Except that the negative electrode mixture slurry does not contain a curable binder, use the same negative electrode mixture slurry as in Example 1 (15 wt% silicon oxide, 78 wt% graphite, 2 wt% SBR as a particulate binder, 5 wt% CMC as a thickener), coat it on both sides of the copper foil by the same method as in Example 1 and dry it, so as to manufacture a dried negative electrode sheet.

[0110] In addition, calender the above dried negative electrode sheet to manufacture a negative electrode having a negative electrode mixture layer with a thickness of 90 μm formed on both sides of the copper foil (total thickness: 188 μm).

[0111] Measure the adhesion force (kN / m) of each thickness of the negative electrode mixture layer of the obtained negative electrode, and show the results in Table 1.

[0112] Comparative Example 2

[0113] When preparing the second negative electrode mixture slurry, as a curable binder, ethoxylated trimethylolpropane triacrylate monomer (viscosity at 25 °C is 100 - 200 cps) is excluded, and only 3 wt% of polyethylene glycol diacrylate monomer (viscosity at 25 °C is 50 cps) is used alone to prepare the negative electrode mixture slurry (15 wt% silicon oxide, 78 wt% graphite, 3 wt% polyethylene glycol diacrylate monomer, 2 wt% SBR as a particulate binder, 2 wt% CMC as a thickener). It is coated on both sides of a copper foil and dried by the same method as in Example 1, thereby manufacturing a dried negative electrode sheet.

[0114] Furthermore, the above-mentioned dried negative electrode sheet is calendered, thereby manufacturing a negative electrode (total thickness: 188 μm) having negative electrode mixture layers with a thickness of 90 μm formed on both sides of the copper foil.

[0115] The adhesion force (kN / m) of each thickness of the negative electrode mixture layer of the obtained negative electrode is measured, and the results are shown in Table 1.

[0116] [Table 1]

[0117]

[0118] From the results in Table 1, it can be seen that in the case of using the curable binder provided by the present invention, the silicon-based negative electrode active material is crosslinked to form a network through the curing of the curable binder, thereby firmly bonding. For example, in the case of a thickness of 8 μm, it can be seen that the adhesion force of Example 1 and Example 2 is improved by more than 30% compared with Comparative Example 1. In addition, when comparing Example 1 and Comparative Example 2, it can be confirmed that in the case of using a curable binder having three or more functional groups in combination, due to the increase in crosslinking density, the adhesion force is further increased compared with the case of using a curable binder having two functional groups alone.

[0119] [Description of Reference Numerals]

[0120] 3: Negative electrode current collector

[0121] 5: Negative electrode mixture layer

Claims

1. A negative electrode mixture paste, which comprises a silicon-based negative electrode active material and a photocurable binder, wherein, the photocurable binder comprises: a first monomer or oligomer having 2 or less functional groups; and a second monomer or oligomer having 3 or more functional groups.

2. The negative electrode mixture paste according to claim 1, wherein, the photocurable binder is an acrylate monomer or oligomer having an acrylate functional group at the end.

3. The negative electrode mixture paste according to claim 1, wherein, the weight ratio of the first monomer or oligomer to the second monomer or oligomer is 50 to 95 wt%: 5 to 50 wt%.

4. The negative electrode mixture paste according to claim 1, wherein, the photocurable binder has a viscosity of 10000 cps or less at 25 °C.

5. The negative electrode mixture paste according to claim 1, wherein, the photocurable binder is at least one selected from the following: an acrylate monomer or oligomer having an acrylate end in an ethylene glycol repeating unit; an acrylate monomer or oligomer having an acrylate end in a urethane repeating unit; an acrylate monomer or oligomer having an acrylate end in a carboxylic acid structure repeating unit; and an acrylate monomer or oligomer having an acrylate end in a hydroxyl structure repeating unit.

6. The negative electrode mixture paste according to claim 1, wherein, the photocurable binder is 1-20 wt% based on the total content of the solids of the negative electrode mixture paste.

7. The negative electrode mixture paste according to claim 1, wherein, the negative electrode mixture paste further comprises a carbon-based negative electrode active material.

8. The negative electrode mixture paste according to claim 7, wherein, relative to the total content of the negative electrode active material, the weight ratio of the content of the carbon-based negative electrode active material to the silicon-based negative electrode active material is 60 to 98: 2 to 40.

9. The negative electrode mixture paste according to any one of claims 1 to 8, wherein, the negative electrode mixture paste further comprises a photoinitiator.

10. The negative electrode mixture paste according to claim 9, wherein, the content of the photoinitiator is 10 wt% or less based on the weight of the photocurable binder.

11. The negative electrode mixture paste according to claim 9, wherein, the photoinitiator is at least one selected from azobisisobutyronitrile, benzoyl peroxide, di-tert-butyl peroxide, cumene hydroperoxide and diisobutyl peroxide.

12. A negative electrode, which comprises: a negative electrode current collector; and a negative electrode mixture layer, the negative electrode mixture layer being located on at least one surface of the negative electrode current collector, and the negative electrode mixture layer comprising a silicon-based negative electrode active material and a binder, wherein the binder comprises: a photocurable binder, the photocurable binder comprising a monomer or oligomer having at least one functional group; and a photopolymerized binder, the photopolymerized binder being formed by photopolymerization of the photocurable binder.

13. The negative electrode according to claim 12, wherein, The photocurable adhesive is an acrylate monomer or oligomer having an acrylate functional group at the end.

14. The negative electrode according to claim 13, wherein, the acrylate monomer or oligomer includes a first acrylate monomer or oligomer having 2 or less functional groups and a second acrylate monomer or oligomer having 3 or more functional groups.

15. The negative electrode according to claim 12, wherein, the content of the photocurable adhesive is 0.1 - 15% by weight based on the total weight of the adhesive.

16. The negative electrode according to claim 12, wherein, the weight - average molecular weight of the photocurable adhesive is 100 to 10,000.

17. The negative electrode according to any one of claims 12 to 16, wherein, the negative electrode further includes a photoinitiator.

18. The negative electrode according to claim 17, wherein, the content of the photoinitiator is 0.01% by weight to 5% by weight based on the weight of the adhesive.

19. The negative electrode according to claim 12, wherein, the negative electrode further includes a second negative electrode mixture layer between the negative electrode current collector and the negative electrode mixture layer, and the second negative electrode mixture layer contains a carbon - based negative electrode active material and a second adhesive different from the adhesive.

20. The negative electrode according to claim 19, wherein, the second adhesive includes at least one selected from styrene - butadiene rubber, polyvinylidene fluoride, and polyacrylic acid.

21. The negative electrode according to claim 19, wherein, at least one of the negative electrode mixture layer and the second negative electrode mixture layer further includes at least one thickener selected from carboxymethyl cellulose, methyl cellulose, hydroxypropyl cellulose, methylhydroxypropyl cellulose, and cellulose gum.

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