Pre-dispersion liquid, electrode composition, electrode slurry, electrode, and lithium ion secondary battery

Abstract

The present application relates to: a pre-dispersion liquid containing SWCNTs, in which the content of SWCNTs having a length of more than 0 [mu] m and less than 0.2 [mu] m is more than 0 parts by weight and 1 parts by weight or less with respect to 100 parts by weight of all SWCNTs; and an electrode composition, an electrode paste, an electrode, and a lithium ion secondary battery containing the pre-dispersion liquid, in which the content of SWCNTs having a length of more than 0 [mu] m and less than 0.2 [mu] m is more than 0 parts by weight and 1 parts by weight or less with respect to 100 parts by weight of all SWCNTs. The content of single-walled carbon nanotubes having a length of 10 [mu] m or more and less than 100 [mu] m is 15 parts by weight or more. Since the dispersibility of the pre-dispersion liquid of the present exemplary embodiment is controlled, the pre-dispersion liquid may contribute to improving the phase stability of an electrode composition and / or an electrode slurry, and the stability, lifespan, safety, and the like of an electrode and / or a lithium ion secondary battery in the future.

Description

Technical Field

[0001] The present application relates to a pre-dispersion liquid, an electrode composition, an electrode paste, an electrode, and a lithium secondary battery.

[0002] The present application claims the priority and benefits of Korean Patent Application No. 10-2023-0042673, filed with the Korean Intellectual Property Office on March 31, 2023, the entire content of which is incorporated herein by reference. Background Art

[0003] Due to the rapid increase in the use of fossil fuels, the demand for alternative or clean energy is increasing day by day. As part of this trend, the most actively studied field is the field of power generation and power storage using electrochemical reactions.

[0004] Currently, representative examples of electrochemical devices using such electrochemical energy include secondary batteries, and their fields of use are increasing.

[0005] Meanwhile, with the development of technology and the increasing demand for mobile devices, the demand for secondary batteries has also increased rapidly. Therefore, lithium secondary batteries having characteristics of high energy density and voltage, long cycle life, and low self-discharge rate have been commercialized and widely used. Therefore, as an electrode for a high-capacity lithium secondary battery, research has been actively conducted to prepare an electrode having a higher energy density per unit volume.

[0006] Generally, a secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, and a separator. Specifically, the negative electrode includes a negative electrode active material, and silicon-based particles having a large charge-discharge capacity can be used as the negative electrode active material.

[0007] In particular, recently, due to the demand for secondary batteries with high-energy electrodes, research has been actively conducted on methods for improving the capacity by using silicon-based compounds such as Si / C or SiO x (0 < x < 2) etc. as the negative electrode active material. However, compared with existing graphite-based materials, silicon-based compounds have the following problems: due to the generation of hydrogen during repeated charge and discharge processes, volume expansion blocks the conductive path, resulting in deterioration of battery characteristics.

[0008] To solve the volume expansion caused by the above-mentioned repeated charge and discharge processes, research has also been conducted on the composition of the binder. As a result, binder polymers with strong stress have been studied. However, these binder polymers themselves have limitations in preventing the increase in electrode thickness caused by the shrinkage and expansion of the negative electrode active material and the resulting deterioration of the performance of the lithium secondary battery.

[0009] In addition, in order to ensure the conductivity of the negative electrode, the secondary battery further includes a conductive material. Although carbon black etc. are mainly used in the prior art, single-walled carbon nanotubes (SWCNTs) having an elongated shape have been used in order to improve the capacity of the secondary battery.

[0010] However, when single-walled carbon nanotubes are used as the conductive material, it is necessary to use single-walled carbon nanotubes in the form of a single-walled carbon nanotube dispersion liquid in order to uniformly arrange the single-walled carbon nanotubes in the active material layer. However, as the degree of dispersion of the dispersion liquid increases, the density difference between the conductive material containing the dispersion liquid and the active material deepens, resulting in the migration of the conductive material from the current collector to the upper layer, and thus there are problems such as deterioration of the phase stability and conductivity of the electrode composition.

[0011] Therefore, in order to control the degree of dispersion of the dispersion liquid, various methods have been explored in terms of the dispersion medium, the active material, and the conductive material. As one of these methods, a method of controlling the dispersion by changing the particle size distribution of the single-walled carbon nanotubes used as the conductive material has been explored. [Summary of the Invention]

[0012] [Technical Problem]

[0013] The present inventors have found that during the charge and discharge process of the electrode, excellent conductive network connectivity is maintained between the active materials, so that the battery has excellent life performance. In order to control the dispersion stability and excellent coating property of the single-walled carbon nanotubes used as the conductive material, the above problems can be solved by classifying the single-walled carbon nanotubes based on their length and restricting their respective contents.

[0014] Moreover, the present inventors have found that by specifying the content range of a specific compound (i.e., acrylamide) in the copolymer constituting the binder as a method for improving the commerciality of single-walled carbon nanotubes, the above problems can be solved, and furthermore, the phase stability and the volume expansion problem of the negative electrode can be solved.

[0015] Therefore, the present invention is directed to providing a pre-dispersion liquid in which, for the electrode composition, the single-walled carbon nanotubes contained in the conductive material have a specific particle size distribution, so that the dispersibility is controlled.

[0016] In addition, the present invention is also directed to providing an electrode composition, an electrode paste, an electrode, and a lithium ion secondary battery, which can solve the future volume expansion problem of the negative electrode while maintaining the characteristic of controlling the dispersibility of single-walled carbon nanotubes by using a (meth)acrylamide-containing binder having high compatibility with the pre-dispersion liquid.

[0017] [Technical Solution]

[0018] One exemplary embodiment of the present specification provides a pre-dispersion liquid containing single-walled carbon nanotubes (SWCNTs), wherein, relative to 100 parts by weight of all single-walled carbon nanotubes, the content of single-walled carbon nanotubes having a length greater than 0 μm and less than 0.2 μm is greater than 0 part by weight and 1 part by weight or less, and the content of single-walled carbon nanotubes having a length of 10 μm or more and less than 100 μm is 15 parts by weight or more.

[0019] In another exemplary embodiment, there is provided an electrode composition comprising: an electrode active material; a conductive material; and a binder, wherein the conductive material contains the pre-dispersion liquid, and the binder is a copolymer containing repeating units derived from (meth)acrylamide (AM).

[0020] In yet another exemplary embodiment, there is provided an electrode paste containing the electrode composition and a solvent.

[0021] In yet another exemplary embodiment, there is provided an electrode comprising: a current collector layer; and an electrode active material layer provided on one surface or both surfaces of the current collector layer, wherein the electrode active material layer contains the electrode paste or a dried product thereof.

[0022] Finally, one exemplary embodiment of the present specification provides a lithium-ion secondary battery comprising: a first electrode; a second electrode; a separator interposed between the first electrode and the second electrode; and an electrolyte, wherein either the first electrode or the second electrode is the electrode.

[0023] [Advantageous Effects]

[0024] In the pre-dispersion liquid of the exemplary embodiment of the present invention, the carbon nanotubes have a particle size distribution with a specific length, and thus have an effect of controlling dispersibility.

[0025] Specifically, when the content of single-walled carbon nanotubes having a length greater than 0 μm and less than 0.2 μm is 1 part by weight or less relative to 100 parts by weight of all single-walled carbon nanotubes, damage to the single-walled carbon nanotubes caused by excessive pre-dispersion can be suppressed, and deterioration of the connectivity performance of the conductive network can be prevented.

[0026] Specifically, as long as the content of single-walled carbon nanotubes having a length of 10 μm or more and less than 100 μm satisfies 15 parts by weight or more relative to 100 parts by weight of all single-walled carbon nanotubes, during charge and discharge, due to excellent connectivity of the conductive network caused by volume expansion of the electrode, the life can be improved.

[0027] In addition, when the content of single-walled carbon nanotubes having a length of 0.2 μm or more and less than 10 μm is 30 parts by weight or more and 80 parts by weight or less with respect to 100 parts by weight of all single-walled carbon nanotubes, it is advantageous in terms of the viscosity and / or processability of the slurry, and the conductive connectivity of the electrode can be further improved.

[0028] Furthermore, when the content of single-walled carbon nanotubes having a length of 100 μm or more is 1 part by weight or less with respect to 100 parts by weight of all single-walled carbon nanotubes, during the charge and discharge process, due to the volume expansion of the electrode, while having better conductive network connectivity, the dispersion stability is improved. Therefore, in the future, good coatability in the slurry state can be ensured, and it can be advantageous in terms of viscosity and / or processability.

[0029] The electrode composition according to another exemplary embodiment of the present invention can provide an electrode composition that can solve the problem of volume expansion of future electrodes while maintaining the effects provided by the pre-dispersion liquid.

[0030] Compared with classifying the composition of single-walled carbon nanotubes based on particle size, classifying the composition of single-walled carbon nanotubes based on length helps to maintain the connectivity of the conductive network. In particular, when used together with an electrode active material containing a silicon-based active material with a large volume expansion, which increases the spacing between the active materials of the charge and discharge battery due to a large porosity, it helps to effectively maintain the connectivity of the conductive network.

[0031] In addition, since the electrode slurry, electrode, and lithium-ion secondary battery according to the exemplary embodiments of the present invention contain the electrode composition, they have the above effects and can improve the life characteristics, thereby ensuring the safety and stability of the lithium-ion secondary battery. [Detailed Embodiments]

[0032] Before describing the present invention, some terms are first defined.

[0033] When a part of this specification "includes" a component, unless otherwise specifically stated, this does not mean excluding other components, but means that other components can also be included.

[0034] In this specification, "p to q" refers to the range of "p or more and q or less".

[0035] In this specification, a polymer containing a certain monomer as a monomer unit means that the monomer participates in the polymerization reaction and is included in the polymer as a repeating unit.

[0036] In this specification, when a polymer contains a monomer, this should be understood to be the same as when the polymer contains the monomer as a monomer unit.

[0037] In this specification, "polymer" should be understood to be used in a broad sense, including copolymers, unless otherwise specified as "homopolymer".

[0038] In this specification, the weight-average molecular weight (Mw) and the number-average molecular weight (Mn) are polystyrene-converted molecular weights measured by gel permeation chromatography (GPC) using commercially available monodisperse polystyrene polymers (standard samples) with various degrees of polymerization for measuring molecular weights as standard substances.

[0039] In this specification, unless otherwise specified, the molecular weight refers to the weight-average molecular weight.

[0040] Hereinafter, the present invention will be described in detail with reference to the accompanying drawings so that those of ordinary skill in the art to which the present invention pertains can easily implement the present invention. However, the present invention can be implemented in various different forms and is not limited to the following description.

[0041] <Predispersion liquid>

[0042] An exemplary embodiment of this specification provides a predispersion liquid containing single-walled carbon nanotubes (SWCNT), wherein, relative to 100 parts by weight of all single-walled carbon nanotubes, the content of single-walled carbon nanotubes with a length greater than 0 μm and less than 0.2 μm is greater than 0 part by weight and 1 part by weight or less, and the content of single-walled carbon nanotubes with a length of 10 μm or more and less than 100 μm is 15 parts by weight or more.

[0043] In this specification, the predispersion liquid can be prepared by adding a dispersant (additionally, a dispersion medium, a viscosity regulator, etc.) to single-walled carbon nanotubes having the above composition and content, mixing the resulting mixture, and then grinding the mixture.

[0044] In another exemplary embodiment of this specification, the predispersion liquid may further contain a dispersant.

[0045] In some cases, the viscosity can be adjusted by adding additives such as tannic acid (i.e., a viscosity regulator) to the predispersion liquid.

[0046] In this specification, the predispersion liquid is prepared by preparing single-walled carbon nanotubes and then using a method such as a high-pressure homogenizer to prepare the predispersion liquid.

[0047] In this specification, "100 parts by weight of all single-walled carbon nanotubes" refers to the solid content, in other words, the solid component of the predispersion liquid. The weight part basis of the solid content and the solid content of each component can be measured by general analytical means used in the art, such as liquid chromatography or gas chromatography.

[0048] In this specification, for grinding, a grinding method using a ball mill, a bead mill, a disk mill, a basket mill, or a high-pressure homogenizer can be employed. Preferably, a high-pressure homogenizer capable of effectively achieving dispersion without damaging single-walled carbon nanotubes can be used.

[0049] In this specification, grinding by a high-pressure homogenizer can be carried out by pressurizing a mixture using, for example, a plunger pump of the high-pressure homogenizer and pushing the mixture into the gap of a homogenizing valve. When the mixture passes through the gap, forces such as cavitation, shear, impact, and explosion are utilized.

[0050] In this specification, the particle size of single-walled carbon nanotubes (SWCNT) can be measured by a laser diffraction method using a particle size analyzer (manufactured by Malvern Panalytical Ltd.). The laser diffraction method can generally measure particle sizes (especially lengths) in a wide range from sub-microns to several millimeters, and high-reproducibility and high-resolution analysis results can be obtained.

[0051] The pre-dispersion liquid of the exemplary embodiment can control the dispersibility by classifying single-walled carbon nanotubes based on length and specifying their content, and thus the conductivity can be effectively improved.

[0052] Another exemplary embodiment of this specification is that, relative to 100 parts by weight of all single-walled carbon nanotubes, the content of single-walled carbon nanotubes having a length greater than 0 μm and less than 0.2 μm can be 0.05 parts by weight or more, 0.1 parts by weight or more, 0.2 parts by weight, or can be 0.95 parts by weight or less, 0.90 parts by weight or less, or 0.85 parts by weight or less.

[0053] When the above content range is satisfied, damage to single-walled carbon nanotubes caused by excessive pre-dispersion can be suppressed, and deterioration of the connectivity performance of the conductive network can be prevented.

[0054] Another exemplary embodiment of this specification is that, relative to 100 parts by weight of all single-walled carbon nanotubes, the content of single-walled carbon nanotubes having a length of 10 μm or more and less than 100 μm can be 16 parts by weight or more, 18 parts by weight or more, 20 parts by weight or more, or can be 25 parts by weight or more. There is no particular limitation on the upper limit, but it can preferably be 80 parts by weight or less.

[0055] When the above content range is satisfied, due to excellent connectivity of the conductive network caused by volume expansion of the electrode during the charge and discharge process, the lifespan can be improved.

[0056] The predispersion liquid of this exemplary embodiment may contain single-walled carbon nanotubes within the above length and content ranges, thereby suppressing damage to the single-walled carbon nanotubes caused by excessive predispersion, preventing deterioration of the conductive network connectivity performance, and having excellent conductive network connectivity due to the volume expansion of the electrode during the charge and discharge process, which can improve the lifespan.

[0057] The predispersion liquid of this exemplary embodiment can improve the performance of an electrode containing a silicon-based active material.

[0058] In an exemplary embodiment of this specification, it further contains single-walled carbon nanotubes with a length of 100 μm or more. With respect to 100 parts by weight of all single-walled carbon nanotubes, the content of single-walled carbon nanotubes with a length of 100 μm or more can be greater than 0 part by weight and 1 part by weight or less.

[0059] The predispersion liquid of this exemplary embodiment further contains single-walled carbon nanotubes with the above length. By satisfying this content range, while having better connectivity of the conductive network due to the volume expansion of the electrode during the charge and discharge process, the dispersion stability is improved, and thus good coatability in the slurry state can be ensured in the future, which can be advantageous in terms of viscosity and / or processability.

[0060] In an exemplary embodiment of this specification, it further contains single-walled carbon nanotubes with a length of 0.2 μm or more and less than 10 μm. With respect to 100 parts by weight of all single-walled carbon nanotubes, the content of single-walled carbon nanotubes with a length of 0.2 μm or more and less than 10 μm can be 30 parts by weight or more and 80 parts by weight or less.

[0061] The predispersion liquid of this exemplary embodiment is advantageous in terms of the viscosity and / or processability of the slurry and can further improve the conductive connectivity of the electrode.

[0062] According to another exemplary embodiment of this specification, when the length of the single-walled carbon nanotubes is greater than 0 μm and less than 0.2 μm, greater than or equal to 2 μm and less than 10 μm, greater than or equal to 10 μm and less than 100 μm, and greater than or equal to 100 μm, with respect to 100 parts by weight of all single-walled carbon nanotubes, the content of single-walled carbon nanotubes with a length of greater than or equal to 10 μm and less than 100 μm can be 15 parts by weight or more and 60 parts by weight or less, 15 parts by weight or more and 50 parts by weight or less, or 15 parts by weight or more and 46 parts by weight or less.

[0063] The predispersion liquid of this exemplary embodiment is advantageous in terms of the viscosity and / or processability of the slurry and can further improve the conductive connectivity of the electrode.

[0064] In an exemplary embodiment of the present specification, the predispersion liquid further includes a dispersion medium, and the dispersion medium may be at least one of water and an organic solvent.

[0065] In the present specification, examples of the organic solvent used as the dispersion medium include N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide (DMAc), N-dimethylformamide (DMF), alcohols, etc., but are not limited thereto.

[0066] The predispersion liquid of this exemplary embodiment may have improved dispersibility.

[0067] According to a preferred exemplary embodiment of the present specification, the dispersion medium may be water.

[0068] The predispersion liquid of this exemplary embodiment may have improved compatibility with the binder.

[0069] In an exemplary embodiment of the present specification, the predispersion liquid may further include a dispersant.

[0070] In another exemplary embodiment of the present specification, the dispersant may be selected from the group consisting of hydrogenated nitrile rubber (H-NBR), polyvinylidene fluoride (PVDF), polyvinylpyrrolidone (PVP), polyvinyl butyral (PVB), and carboxymethyl cellulose (CMC), and may preferably be PVP or CMC, but is not limited thereto.

[0071] The predispersion liquid of this exemplary embodiment may further have improved dispersibility.

[0072] <Electrode composition>

[0073] An exemplary embodiment of the present specification provides an electrode composition, which includes: an electrode active material; a conductive material; and a binder, wherein the conductive material includes the above-mentioned predispersion liquid, and the binder is a copolymer including repeating units derived from (meth)acrylamide (AM).

[0074] In the present specification, unless otherwise specified, the copolymer is a concept including all alternating copolymers, random copolymers, block copolymers, and graft copolymers.

[0075] In an exemplary embodiment of the present specification, the electrode active material may include one or more selected from the group consisting of silicon-based active materials and carbon-based active materials.

[0076] In an exemplary embodiment of the present specification, based on 100 parts by weight of the electrode composition, the amount of the electrode active material present may be 30 parts by weight or more, preferably 35 parts by weight or more, more preferably 40 parts by weight or more, and 95 parts by weight or less, preferably 90 parts by weight or less.

[0077] In this specification, the silicon-based active material may exist, for example, in a crystalline or amorphous form. Specifically, the silicon particles of the silicon-based active material may preferably be spherical particles, but are not limited thereto.

[0078] In another exemplary embodiment of this specification, the electrode active material may be a silicon-based active material. In other words, the electrode active material may consist only of the silicon-based active material.

[0079] In yet another exemplary embodiment of this specification, the electrode active material may include a silicon-based active material and a carbon-based active material.

[0080] In still another exemplary embodiment of this specification, the electrode active material contains a silicon-based active material as a main component (content greater than about 50 parts by weight based on 100 parts by weight of the total electrode active material), and may contain a carbon-based active material as a minor component (content less than about 50 parts by weight based on 100 parts by weight of the total electrode active material).

[0081] In still another exemplary embodiment of this specification, the electrode active material contains a carbon-based active material as a main component (content greater than about 50 parts by weight based on 100 parts by weight of the total electrode active material), and may contain a silicon-based active material as a minor component (content less than about 50 parts by weight based on 100 parts by weight of the total electrode active material).

[0082] In another exemplary embodiment of this specification, the electrode active material contains a carbon-based active material as a main component (content being about 50 parts by weight based on 100 parts by weight of the total electrode active material), and may contain a silicon-based active material as a minor component (content being about 50 parts by weight based on 100 parts by weight of the total electrode active material).

[0083] In one exemplary embodiment of this specification, the silicon-based active material may include SiO x (x = 0), SiO x (0 < x < 2), SiC, and one or more of Si alloys.

[0084] In this specification, the case of SiO2 where x is 2 in SiO x is not included. This SiO2 does not react with lithium ions and thus cannot store lithium. Therefore, it is preferred that x falls within the range of the exemplary embodiment.

[0085] In this specification, the silicon-based active material may be Si / C composed of a composite of Si and C, or Si.

[0086] In this specification, two or more silicon-based active materials may be used in combination.

[0087] Generally, the capacity of known silicon-based active materials is more than 10 times higher than that of carbon-based active materials. Therefore, when silicon-based active materials are applied to electrodes, especially anodes, it is expected that electrodes with a high level of energy density can be achieved even with a small thickness.

[0088] In an exemplary embodiment of the present specification, when the electrode active material is composed of a silicon-based active material, the silicon-based active material includes one or more selected from the group consisting of SiO x (x = 0) and SiO x (0 < x < 2), and based on 100 parts by weight of the silicon-based active material, it may contain 70 parts by weight or more of SiO x (x = 0).

[0089] In another exemplary embodiment, based on 100 parts by weight of the silicon-based active material, the content of SiO x (x = 0) in the silicon-based active material may be 70 parts by weight or more, preferably 80 parts by weight or more, more preferably 90 parts by weight or more, or 100 parts by weight or less, preferably 99 parts by weight or less, more preferably 95 parts by weight or less.

[0090] In another exemplary embodiment of the present invention, the average particle size (D 50 ) of the silicon-based active material may be 3 μm to 10 μm.

[0091] When the above particle size range is satisfied, it is further ensured that the active material is structurally stable during charge and discharge, and problems such as an increase in volume expansion / shrinkage level due to excessive increase in particle size and a decrease in initial efficiency due to too small particle size can be prevented.

[0092] The particle size of the anode active material can be adjusted by methods such as ball mills, jet mills, or air classifiers, and the method is not limited thereto.

[0093] In the present specification, "Dn" represents the particle size distribution, which refers to the particle size at the n% point in the cumulative distribution of the number of particles according to the particle size. That is, D 50 is the particle size (average particle size) at the 50% point in the cumulative distribution of the number of particles according to the particle size, D 90 is the particle size at the 90% point in the cumulative distribution of the number of particles according to the particle size, D 10 is the particle size at the 10% point in the cumulative distribution of the number of particles according to the particle size. At the same time, the particle size distribution can be measured by the laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, the particle size distribution is calculated by measuring the difference in the diffraction pattern that changes with the particle size when the obtained dispersion is introduced into a commercially available laser diffraction type particle size measuring device (such as Microtrac S3500) as the particles pass through the laser beam.

[0094] In this specification, in some cases, in addition to the above-mentioned silicon-based active material, a carbon-based active material may also be included. The carbon-based active material can further contribute to improving the excellent cycle characteristics or battery life performance of the negative electrode or secondary battery of the present invention.

[0095] In an exemplary embodiment of this specification, the carbon-based material may include at least one selected from the group consisting of artificial graphite, natural graphite, hard carbon, and soft carbon.

[0096] In an exemplary embodiment of the present invention, when the electrode active material includes a silicon-based active material and a carbon-based active material, the weight ratio of the silicon-based active material to the carbon-based active material may be from 2:98 to 30:70.

[0097] The electrode active material of this exemplary embodiment contains a carbon-based active material as the main component, and thus can further provide the following effects: Since the volume expansion of the active material during charge and discharge is small, swelling occurs slightly, and the conductive connectivity of the electrode is excellent.

[0098] In an exemplary embodiment of this specification, based on 100 parts by weight of the electrode composition, the amount of the conductive material present may be 0.03 parts by weight or more and 60 parts by weight or less.

[0099] In another exemplary embodiment of this specification, based on 100 parts by weight of the electrode composition, the content of the conductive material may be 0.03 parts by weight or more and 60 parts by weight or less, preferably 0.05 parts by weight or more and 59 parts by weight or less, more preferably 0.5 parts by weight or more and 58 parts by weight or less.

[0100] In another exemplary embodiment of this specification, the electrode composition refers to a negative electrode composition. Therefore, the electrode active material, the conductive material, and the binder may respectively refer to the negative electrode active material, the negative electrode conductive material, and the negative electrode binder.

[0101] In this specification, the negative electrode conductive material has a completely different composition from the positive electrode conductive material applied to the positive electrode. That is, the negative electrode conductive material of the present application serves to capture the contact points between the silicon-based active materials with a very large volume expansion of the electrode during charge and discharge, and the positive electrode conductive material serves to play a buffering role during rolling and impart partial conductivity at the same time, and its composition and function are completely different from those of the negative electrode conductive material of the present invention.

[0102] In addition, when the electrode active material contains a silicon-based active material, the negative electrode conductive material of the present application has a structure completely different from that of the conductive material applied to a graphite-based active material (i.e., an electrode active material containing only graphite). That is, the conductive material used for an electrode having a graphite-based active material simply has small particles with respect to the active material, and thus has the characteristics of improving output characteristics and imparting partial conductivity, and its composition and function are completely different from those of the negative electrode conductive material applied together with the silicon-based active material in the present invention.

[0103] In an exemplary embodiment of the present invention, the conductive material may further include one or more selected from the group consisting of a dot-shaped conductive material, a planar conductive material, and a linear conductive material.

[0104] In an exemplary embodiment of the present invention, the conductive material may further contain a planar conductive material.

[0105] In an exemplary embodiment of the present application, the dot-shaped conductive material can be used to enhance the conductivity of the negative electrode, and refers to a dot-shaped or spherical conductive material having conductivity and not causing chemical changes. Specifically, the dot-shaped conductive material may be at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking carbon black, conductive fiber, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives. In terms of achieving high conductivity and excellent dispersibility, carbon black may be preferably included.

[0106] In an exemplary embodiment of the present application, the BET specific surface area of the dot-shaped conductive material may be 40 m 2 / g or more and 70 m 2 / g or less, preferably 45 m 2 / g or more and 65 m 2 / g or less, and more preferably 50 m 2 / g or more and 60 m 2 / g or less.

[0107] In an exemplary embodiment of the present application, the functional group content (volatile matter) of the dot-shaped conductive material may satisfy 0.01% or more and 1% or less, preferably 0.01% or more and 0.3% or less, and more preferably 0.01% or more and 0.1% or less.

[0108] In particular, when the functional group content in the dot-shaped conductive material satisfies the above range, there are functional groups present on the surface of the dot-shaped conductive material, so that when water is used as a solvent, the dot-shaped conductive material can be smoothly dispersed in the solvent. In particular, in the present invention, since silicon particles and a specific binder are used, the functional group content of the dot-shaped conductive material can be reduced, and thus the present invention has an excellent effect of improving dispersibility.

[0109] In an exemplary embodiment of the present invention, the dot-shaped conductive material having a functional group content within the above range is characterized in that it is included together with the silicon-based active material, and the functional group content can be adjusted according to the heat treatment degree of the dot-shaped conductive material.

[0110] In an exemplary embodiment of the present invention, the particle size of the dot-shaped conductive material can be from 10 nm to 100 nm, preferably from 20 nm to 90 nm, and more preferably from 20 nm to 60 nm.

[0111] The planar conductive material can improve conductivity and simultaneously inhibit the disconnection of the conduction path caused by volume expansion by increasing the surface contact between silicon particles in the negative electrode. The planar conductive material can be in the form of a plate-shaped conductive material or a block-shaped conductive material.

[0112] In an exemplary embodiment of the present invention, the planar conductive material can include at least one selected from the group consisting of plate-shaped graphite, graphene, graphene oxide, and graphite flakes, and can preferably be plate-shaped graphite.

[0113] In an exemplary embodiment of the present invention, the average particle size (D 50 ) of the plate-shaped conductive material can be from 2 μm to 7 μm, specifically from 3 μm to 6 μm, and more specifically from 3.5 μm to 5 μm. When the average particle size satisfies the above range, a sufficient particle size is beneficial for dispersion without causing an excessive increase in the viscosity of the negative electrode slurry. Therefore, when dispersing particles using the same equipment and time, the dispersion effect is excellent.

[0114] In an exemplary embodiment of the present invention, a negative electrode composition is provided, wherein D 10 of the planar conductive material is 0.5 μm or more and 2.0 μm or less, D 50 is 2.5 μm or more and 3.5 μm or less, and D 90 is 6.5 μm or more and 15.0 μm or less.

[0115] In an exemplary embodiment of the present invention, as the planar conductive material, a high specific surface area planar conductive material having a high BET specific surface area or a low specific surface area planar conductive material can be used.

[0116] In an exemplary embodiment of the present invention, a high specific surface area planar conductive material or a low specific surface area planar conductive material can be used without limitation as the planar conductive material. However, particularly, the planar conductive material of the present application may be affected to a certain extent by the dispersion effect in terms of electrode performance. Therefore, it can be particularly desirable to use a low specific surface area planar conductive material that does not cause dispersion problems.

[0117] In an exemplary embodiment of the present invention, the BET specific surface area of the sheet-like conductive material may be 1 m 2 / g or more.

[0118] In another exemplary embodiment, the BET specific surface area of the sheet-like conductive material may be 1 m 2 / g or more and 500 m 2 / g or less, preferably 5 m 2 / g or more and 300 m 2 / g or less, more preferably 5 m 2 / g or more and 250 m 2 / g or less.

[0119] As the sheet-like conductive material of the present invention, a high specific surface area sheet-like conductive material or a low specific surface area sheet-like conductive material may be used.

[0120] In another exemplary embodiment, the sheet-like conductive material is a high specific surface area sheet-like conductive material, and the BET specific surface area may satisfy 50 m 2 / g or more and 500 m 2 / g or less, preferably 80 m 2 / g or more and 300 m 2 / g or less, more preferably 100 m 2 / g or more and 300 m 2 / g or less.

[0121] In yet another exemplary embodiment, the sheet-like conductive material is a low specific surface area sheet-like conductive material, and the BET specific surface area may satisfy 1 m 2 / g or more and 40 m 2 / g or less, preferably 5 m 2 / g or more and 30 m 2 / g or less, more preferably 5 m 2 / g or more and 25 m 2 / g or less.

[0122] In an exemplary embodiment of the present invention, the binder may contain repeating units derived from (meth)acrylamide in an amount of 30% by weight or more and 80% by weight or less based on the total copolymer.

[0123] By containing the above content of (meth)acrylamide, the electrode composition of this exemplary embodiment can improve phase stability and improve the life performance in terms of batteries in the future.

[0124] In another exemplary embodiment of the present invention, the aqueous adhesive may include repeating units derived from (meth)acrylamide in an amount of about 30% by weight or more, about 35% by weight or more, or about 40% by weight or more based on the total amount of the copolymer.

[0125] In yet another exemplary embodiment of the present invention, there is no particular limitation on the upper limit of the adhesive, as long as the adhesive contains (meth)acrylamide (AM) in an amount of about 80% by weight or less based on the total amount of the copolymer.

[0126] Since the electrode composition of this exemplary embodiment uses an (meth)acrylamide-containing adhesive having high compatibility with the pre-dispersion liquid, it can simultaneously solve the problem of volume expansion of the future negative electrode while controlling the dispersibility of single-walled carbon nanotubes, and thus can contribute to improving the battery life of future lithium-ion secondary batteries.

[0127] In this specification, the term “(meth)acrylamide” may include methacrylamide or acrylamide.

[0128] In addition, with respect to the copolymer contained in the adhesive, (meth)acrylamide may be referred to as a monomer or a compound.

[0129] In this specification, a copolymer refers to a substance polymerized from two or more monomers and may be a concept compared with a homopolymer.

[0130] In this specification, a copolymer may refer to at least one of an alternating copolymer, a random copolymer, a block copolymer, a graft copolymer, and combinations thereof.

[0131] In this specification, the adhesive may contain additional monomers such as (meth)acrylic acid and acrylonitrile as the remaining components (repeating units) in addition to (meth)acrylamide.

[0132] In this specification, a polymerization initiator is used to prepare a copolymer, and ammonium persulfate may be used as an example of the polymerization initiator, but the polymerization initiator is not limited thereto.

[0133] In this specification, to prepare an aqueous adhesive, a copolymer is first prepared, and then it may be neutralized with an acid or a base having a predetermined concentration if necessary.

[0134] In one exemplary embodiment of this specification, based on 100 parts by weight of the electrode composition, the amount of the aqueous adhesive present may be 2 parts by weight or more and 30 parts by weight or less.

[0135] In another exemplary embodiment of the present specification, based on 100 parts by weight of the electrode composition, the content of the aqueous binder may be 30 parts by weight or less, preferably 25 parts by weight or less, more preferably 20 parts by weight or less, or the content may be 2 parts by weight or more, 3 parts by weight or more, 4 parts by weight or more.

[0136] In yet another exemplary embodiment of the present specification, the weight average molecular weight of the binder may be 100,000 g / mol or more and 1,500,000 g / mol or less.

[0137] The electrode composition of this exemplary embodiment can ensure the following characteristics: Since the weight average molecular weight of the binder satisfies the above range, the mechanical strength is excellent, and since the intermolecular interaction is high, the adhesion strength of the electrode is excellent. In addition, when the above range is satisfied, the viscosity of the binder can be controlled within an appropriate range, so that when the negative electrode is manufactured using this binder, the negative electrode has excellent coating properties of the electrode.

[0138] <Preparation method of the predispersion liquid>

[0139] An exemplary embodiment of the present invention provides a method for preparing a predispersion liquid, the method including introducing single-walled carbon nanotubes (SWCNTs) and a dispersant and mixing the resulting mixture, and grinding the mixture, and relative to 100 parts by weight of all single-walled carbon nanotubes (SWCNTs), the single-walled carbon nanotubes may respectively contain more than 0 parts by weight and 1 part by weight or less of single-walled carbon nanotubes having a length greater than 0 μm and less than 0.2 μm and 15 parts by weight or more of single-walled carbon nanotubes having a length of 10 μm or more and less than 100 μm.

[0140] The above content can be applied to other exemplary embodiments.

[0141] In the present specification, grinding is as described above, but preferably, a high-pressure homogenizer that can effectively achieve dispersion and does not damage the single-walled carbon nanotubes can be used.

[0142] The specific content of each component in the method for preparing the predispersion liquid is as described above.

[0143] Through the method for preparing the predispersion liquid of this exemplary embodiment, the dispersibility of the single-walled carbon nanotubes as a conductive material can be controlled, and the shape of the carbon nanotube structure formed according to the above dispersion can be easily maintained.

[0144] <Preparation method of the electrode composition>

[0145] An exemplary embodiment of the present invention provides a method for preparing an electrode composition, the method comprising: mixing a conductive material and a binder; and adding an electrode active material thereto and mixing the resulting mixture, wherein the conductive material is the above-mentioned predispersion liquid, and the binder is a copolymer containing repeating units derived from (meth)acrylamide (AM).

[0146] In the present specification, based on 100 parts by weight of the binder, the content of (meth)acrylamide may be about 30 parts by weight or more, about 40 parts by weight or more, or about 45 parts by weight or more, or about 80 parts by weight or less, about 75 parts by weight or less, or about 70 parts by weight or less.

[0147] The specific contents of the components in the method for preparing the electrode composition are as described above.

[0148] According to this exemplary embodiment, while maintaining the property that the shape of the controlled-dispersion conductive material and the carbon nanotube structure formed thereby is easy to maintain, the compatibility with the (meth)acrylamide-based binder is improved, the phase stability of the electrode paste is improved, and the life characteristics of the battery can be improved.

[0149] <Electrode paste>

[0150] In another exemplary embodiment of the present invention, an electrode paste containing the electrode composition and a solvent is provided.

[0151] The electrode paste of the present invention is a negative electrode paste. Therefore, the electrode composition may relate to a negative electrode paste.

[0152] The specific contents of the components in the electrode paste are as described above.

[0153] In the present specification, a solvent can be used without limitation as long as it can dissolve the electrode composition. For example, water or an organic solvent can be used. Preferably, the solvent can be water.

[0154] According to this exemplary embodiment, while maintaining the property that the shape of the controlled-dispersion conductive material and the carbon nanotube structure formed thereby is easy to maintain, the compatibility with the (meth)acrylamide-based binder is improved, so that the phase stability of the electrode paste can be improved, and the life characteristics of the future battery can be improved.

[0155] <Electrode>

[0156] Another exemplary embodiment of the present invention provides an electrode, which includes: a current collector layer; and an electrode active material layer provided on one surface or both surfaces of the current collector layer, wherein the electrode active material layer contains the electrode paste or its dried product.

[0157] In another exemplary embodiment of the present invention, the electrode is a negative electrode. Therefore, the current collector layer, the electrode paste, and the electrode active material layer can be referred to as the negative current collector layer, the negative electrode paste, and the negative electrode active material layer, respectively.

[0158] In an exemplary embodiment of the present application, the solid content of the negative electrode paste can satisfy not less than 3% and not more than 50%.

[0159] In another exemplary embodiment, the solid content of the negative electrode paste can satisfy the range of not less than 3% and not more than 50%, preferably not less than 5% and not more than 45%, and more preferably not less than 7% and not more than 40%.

[0160] The solid content of the electrode paste can refer to the content of the negative electrode composition contained in the negative electrode paste, and can refer to the content of the negative electrode composition based on 100 parts by weight of the negative electrode paste.

[0161] When the solid content of the negative electrode paste satisfies the above range, the present invention has the characteristic that since the viscosity is appropriate when forming the negative electrode active material layer, the negative electrode active material layer can be effectively formed by minimizing the particle aggregation phenomenon of the negative electrode composition.

[0162] In an exemplary embodiment of the present application, the slurry solvent can be used without limitation as long as the slurry solvent can dissolve the negative electrode composition. Specifically, water or NMP can be used.

[0163] In an exemplary embodiment of the present application, the thickness of the negative current collector layer is generally 1 μm to 100 μm. The negative current collector layer is not particularly limited as long as the negative current collector layer has high conductivity and does not cause chemical changes to the battery. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, or copper or stainless steel, aluminum-cadmium alloy whose surface is treated with carbon, nickel, titanium, silver, etc. can be used. In addition, the negative current collector layer can also improve the bonding strength of the negative electrode active material by forming fine irregularities on its surface. The negative current collector layer can be used in various forms, such as films, sheets, foils, nets, porous bodies, foams, and non-woven fabrics.

[0164] In an exemplary embodiment of the present application, a negative electrode for a lithium secondary battery is provided, wherein the thickness of the negative current collector layer is not less than 1 μm and not more than 100 μm, and the thickness of the negative electrode active material layer is not less than 20 μm and not more than 500 μm.

[0165] However, the thickness can be variously modified according to the type and use of the negative electrode used, and is not limited thereto.

[0166] <Lithium Ion Secondary Battery>

[0167] In an exemplary embodiment of the present invention, a lithium ion secondary battery is provided, which includes: a first electrode; a second electrode; a separator disposed between the first electrode and the second electrode; and an electrolyte. Any one of the first electrode and the second electrode may be the above-mentioned electrode.

[0168] The first electrode may be a negative electrode, the second electrode may be a positive electrode, or the first electrode may be a positive electrode and the second electrode may be a negative electrode.

[0169] Since the electrode (negative electrode) has been described in detail, its specific description is omitted.

[0170] The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and containing a positive electrode active material.

[0171] In the positive electrode, the positive electrode current collector is not particularly limited as long as it has conductivity and does not cause chemical changes to the battery. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or aluminum or stainless steel with its surface treated with carbon, nickel, titanium, silver, etc. can be used. In addition, the thickness of the positive electrode current collector can generally be 3 μm to 500 μm, and the adhesion of the positive electrode active material can also be improved by forming fine irregularities on the surface of the current collector. For example, the positive electrode current collector can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam body, and a non-woven fabric body.

[0172] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material includes: layered compounds such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), or compounds substituted with one or more transition metals; lithium iron oxides such as LiFe3O4; lithium manganese oxides such as the chemical formula Li 1+c1 Mn 2-c1 O4 (0 ≤ c1 ≤ 0.33), LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, and Cu2V2O7; the chemical formula LiNi 1-c2 M c2 O2 (here, M is at least any one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and c2 satisfies 0.01 ≤ c2 ≤ 0.3) represents Ni-site type lithium nickel oxide; the chemical formula LiMn 2-c3 M c3A lithium manganese composite oxide represented by O2 (where M is at least any one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and c3 satisfies 0.01 ≤ c3 ≤ 0.1) or Li2Mn3MO8 (where M is at least any one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); LiMn2O4 in which Li in the chemical formula is partially substituted by alkaline earth metal ions, etc., but not limited thereto. The positive electrode may be lithium metal.

[0173] The positive electrode active material layer may include a positive electrode conductive material and a positive electrode binder together with the above positive electrode active material.

[0174] In this case, the positive electrode conductive material is used to impart conductivity to the electrode and can be used without particular limitation as long as the positive electrode conductive material has electron conductivity and does not cause chemical changes in the constructed battery. Specific examples thereof include: graphite, such as natural graphite or artificial graphite; carbonaceous materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking carbon black, and carbon fiber; metal powders or metal fibers, such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; or conductive polymers, such as polyphenylene derivatives, and any one or a mixture of two or more thereof can be used.

[0175] Alternatively, the positive electrode binder is used to improve the binding between the positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples thereof may include: polyvinylidene fluoride (PVDF), polyvinylidene fluoride - hexafluoropropylene copolymer (PVDF - co - HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene - propylene - diene monomer (EPDM), sulfonated EPDM, styrene - butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one or a mixture of two or more thereof can be used.

[0176] The separator separates the negative electrode and the positive electrode and provides a channel for the movement of lithium ions, and can be used without particular limitation as long as it is generally used as a separator in secondary batteries. In particular, a separator having excellent ability to retain the moisture of the electrolyte and low resistance to the movement of ions in the electrolyte is preferred. Specifically, a porous polymer membrane can be used, for example, a porous polymer membrane formed of polyolefin polymers (such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer), or a laminated structure of two or more layers thereof. In addition, typical porous non-woven fabrics can also be used, for example, non-woven fabrics made of glass fibers with high melting points, polyethylene terephthalate fibers, etc. Furthermore, a coated separator containing a ceramic component or a polymer material can be used to ensure heat resistance or mechanical strength, and can be selectively used as a single layer or a multi-layer structure.

[0177] Examples of the electrolyte include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries, etc., but are not limited thereto.

[0178] Specifically, the electrolyte can include a non-aqueous organic solvent and a metal salt.

[0179] As the non-aqueous organic solvent, for example, an aprotic organic solvent such as N-methyl-2-pyrrolidone (NMP), propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate ester, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate can be used.

[0180] In particular, among carbonate organic solvents, cyclic carbonates ethylene carbonate and propylene carbonate can be preferably used because cyclic carbonates have a high dielectric constant as organic solvents with high viscosity and thus dissociate lithium salts well, and because cyclic carbonates can be mixed with chain carbonates with low viscosity and low dielectric constant, such as dimethyl carbonate and diethyl carbonate, in an appropriate proportion and used to prepare an electrolyte with high conductivity, so such cyclic carbonates can be more preferably used.

[0181] As the metal salt, a lithium salt can be used, and the lithium salt is a material that is easily soluble in non-aqueous electrolytes. For example, as the anion of the lithium salt, it can be selected from F - 、Cl - 、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 - One or more selected from the group consisting of.

[0182] In the electrolyte, in order to improve the life characteristics of the battery, suppress the reduction of the battery capacity, and increase the discharge capacity of the battery, in addition to the above electrolyte components, one or more additives may be further included, such as haloalkyl carbonate compounds (such as ethylene difluorocarbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol ethers, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride.

[0183] One exemplary embodiment of the present invention provides a battery module including the secondary battery as a unit cell and a battery pack including the battery module. The battery module and the battery include a secondary battery having high capacity, high rate characteristics, and cycle characteristics, and thus can be used as a power source for medium and large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0184] <Method for manufacturing a lithium ion secondary battery>

[0185] In another exemplary embodiment of the present invention, a method for manufacturing a lithium ion secondary battery is provided, the method comprising: preparing an electrode paste by mixing an electrode composition with a solvent; coating the electrode paste on one or both surfaces of an electrode current collector layer; and drying the electrode current collector layer coated with the electrode paste, wherein the electrode composition, the solvent, the electrode current collector layer, and the coating are the same as those described above.

[0186] In the present specification, as the drying, a method known in the art, such as air drying, is adopted.

[0187] In the present specification, steps such as calendering applied after the above steps are known in the art.

[0188] [Examples]

[0189] Hereinafter, preferred embodiments will be presented for ease of understanding of the present invention. However, only the embodiments are provided to illustrate the present invention. It is obvious to those skilled in the art that various changes and modifications can be made within the scope and technical concept of the present invention, and these changes and modifications naturally also fall within the scope of the appended claims.

[0190] Preparation Example: Preparation of a Predispersion

[0191] After mixing single-walled carbon nanotubes (SWCNTs) (manufactured by OCSiAl, Tubll) and single-walled carbon nanotubes (SWCNTs) (manufactured by Jiangsu Tiannai Technology Co., Ltd., FT202), the mixed single-walled carbon nanotubes were mixed with polyvinylpyrrolidone (PVP) (manufactured by Zhangzhou Huafu Chemical Co., Ltd., K15) and tannic acid (manufactured by Sigma-Aldrich) as a dispersant at a ratio of 1:1:0.4 (SWCNT: PVP: tannic acid) by weight, and then the resulting mixture was subjected to primary dispersion (primary mixing) using a high-shear in-line mixer.

[0192] Next, a predispersion having a specific dispersion particle size and a solids content of 1 wt% was prepared (secondary mixing) by repeatedly circulating while adjusting the pressure using a high-pressure homogenizer.

[0193] The dispersion particle size was measured using a particle size distribution measuring device manufactured by Malvern Panalytical Ltd. The results are shown in Table 1 below.

[0194] [Table 1]

[0195]

[0196] Synthesis Example: Synthesis of an Adhesive

[0197] In a reactor equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen inlet tube, acrylamide (AM, 50% aqueous solution), acrylic acid (AA, 80% aqueous solution), and acrylonitrile (AN) were mixed at the ratios shown in Table 2 below. A polymerization initiator (ammonium persulfate) was added thereto, and then the resulting mixture was reacted at 75 °C for 8 hours to prepare an aqueous polymer solution.

[0198] After that, an aqueous solution of 0.1 molar concentration of NaOH was added dropwise to the aqueous polymer solution to neutralize the solution, and then an aqueous adhesive was obtained.

[0199] [Table 2]

[0200]

[0201] Example: Preparation of Electrode Paste

[0202] As described in Table 3 below, each electrode composition was mixed with a solvent (water) to prepare an electrode paste. During the preparation of the electrode paste, the water content was adjusted in consideration of coatability, viscosity, and solids content, and the viscosity was adjusted to 5000 to 6000 cp.

[0203] [Table 3]

[0204]

[0205] Experimental Example: Battery Fabrication and Battery Characteristic Evaluation

[0206] A copper foil with a thickness of 15 μm was coated with each electrode paste shown in Table 3 and dried to form an electrode active material layer with a thickness of 48 μm on one surface of the copper foil. Then, the copper foil was punched into a circle with a diameter of 14Φ (mm) to prepare a test electrode (negative electrode).

[0207] A metal lithium foil with a thickness of 0.3 mm was used as the positive electrode, a porous polyethylene sheet with a thickness of 0.1 mm was used as the separator, and a product obtained by dissolving LiPF6 in a mixed solvent of fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) at a volume ratio of 2:1 at a concentration of about 1 mol / L was used as the electrolyte.

[0208] An evaluation button cell with a thickness of 2 mm and a diameter of 32 mm was fabricated by sealing the negative electrode, positive electrode, separator, and electrolyte in a stainless steel container.

[0209] The button cell was charged at a constant current of 0.2C until the voltage reached 0.01V, and then discharged at a constant current of 0.2C until the voltage reached 1.5V to perform a capacity retention rate test. The results are shown in Table 4 below.

[0210] [Table 4]

[0211] Electrode paste Capacity retention rate (%) Example 1 85 Example 2 82 Example 3 83 Example 4 80 Comparative Example 1 62 Comparative Example 2 60 Comparative Example 3 51 Comparative Example 4 54 Comparative Example 5 57 Comparative Example 6 68 Comparative Example 7 56

[0212] - Capacity retention rate (%): The capacity retention rate test is carried out by charging the button battery at a constant current of 0.05C until the voltage reaches 0.01V, discharging the button battery at a constant current of 0.05C until the voltage reaches 1.5V, and performing cyclic characteristics at a constant current of 0.2C within the same voltage range as above, and is calculated based on 30 cycles.

[0213] As described above in Table 4, in Examples 1 to 4, with respect to 100 parts by weight of all single-walled carbon nanotubes, the content of single-walled carbon nanotubes having a length greater than 0 μm and less than 0.2 μm is greater than 0 part by weight and 1 part by weight or less, and the content of single-walled carbon nanotubes having a length of 10 μm or more and less than 100 μm satisfies 15 parts by weight or more.

[0214] In addition, Examples 2 and 3 correspond to the case where single-walled carbon nanotubes having a length of 100 μm or more are included with respect to 100 parts by weight of all single-walled carbon nanotubes, and the content is greater than 0 part by weight and less than 1 part by weight, and the remaining part satisfies the content occupied by single-walled carbon nanotubes having a length of 0.2 μm or more and less than 100 μm.

[0215] In addition, in the above Examples 1 to 4, an adhesive containing a repeating unit derived from (meth)acrylamide in an amount of 30% by weight or more and 80% by weight or less with respect to all copolymers was used. As a result, all of the capacity retention rates showed 80% or more.

[0216] In contrast, although Comparative Examples 1 and 5 used an adhesive with a (meth)acrylamide content satisfying the scope of the present invention (i.e., 30% by weight or more and 80% by weight or less with respect to all copolymers), since the dispersion particle size of the single-walled carbon nanotubes exceeded the scope of the present invention, the capacity retention rates of 62% and 57% were shown respectively.

[0217] In addition, in Comparative Examples 2 to 4 and 7, since an adhesive other than a (meth)acrylamide content of 30% by weight or more and 80% by weight or less with respect to all copolymers and the dispersion particle size of the single-walled carbon nanotubes exceeded the scope of the present invention, the capacity retention rates of 60%, 51%, 54%, and 56% were shown respectively.

[0218] In addition, in Comparative Example 6, although the dispersion particle size of the single-walled carbon nanotubes satisfied the scope of the present invention, since the content of (meth)acrylamide with respect to all copolymers was outside the range of 30% by weight or more and 80% by weight or less, the capacity retention rate of 68% was shown.

[0219] Therefore, it can be seen that when comparing Comparative Example 6 with Comparative Examples 1 and 5, the influence of the dispersion particle size factor of single-walled carbon nanotubes on improving the capacity retention rate is greater than the factor of (meth)acrylamide content. And from Comparative Examples 2 to 4 and 7, it can be seen that when the above two factors do not meet a specific range, the deterioration of the capacity retention rate becomes serious.

Claims

1. A pre-dispersion liquid containing single-walled carbon nanotubes (SWCNT), Among them, relative to 100 parts by weight of all single-walled carbon nanotubes, the content of single-walled carbon nanotubes with a length greater than 0 μm and less than 0.2 μm is greater than 0 part by weight and 1 part by weight or less, and the content of single-walled carbon nanotubes with a length of 10 μm or more and less than 100 μm is 15 parts by weight or more.

2. The pre-dispersion liquid according to claim 1, further comprising single-walled carbon nanotubes with a length of 100 μm or more, wherein, Relative to 100 parts by weight of all single-walled carbon nanotubes, the content of single-walled carbon nanotubes with a length of 100 μm or more is greater than 0 part by weight and 1 part by weight or less.

3. The pre-dispersion liquid according to claim 1, further comprising single-walled carbon nanotubes having a length of 0.2 μm or more and less than 10 μm, wherein, Relative to 100 parts by weight of all single-walled carbon nanotubes, the content of single-walled carbon nanotubes with a length of 0.2 μm or more and less than 10 μm is 30 parts by weight or more and 80 parts by weight or less.

4. The pre-dispersion liquid according to claim 1, further comprising a dispersion medium, Among them, wherein the dispersion medium is at least one of water and an organic solvent.

5. The pre-dispersion liquid according to claim 1, further comprising a dispersant.

6. An electrode composition, comprising: an electrode active material; a conductive material; and a binder, Among them, wherein the conductive material comprises the pre-dispersion liquid according to claim 1, and the binder is a copolymer containing repeating units derived from (meth)acrylamide (AM).

7. The electrode composition according to claim 6, wherein The electrode active material comprises one or more selected from the group consisting of silicon-based active materials and carbon-based active materials.

8. The electrode composition according to claim 7, wherein, The silicon-based active material includes one or more selected from SiO where x = 0 x , SiO where 0 < x < 2 x , SiC, and Si alloys.

9. The electrode composition according to claim 7, wherein, When the electrode active material is composed of a silicon-based active material, the silicon-based active material includes one or more selected from the group consisting of SiO where x = 0 x and SiO where 0 < x < 2 x and, based on 100 parts by weight of the silicon-based active material, contains 70 parts by weight or more of SiO where x = 0 x .

10. The electrode composition according to claim 7, wherein, The carbon-based active material comprises at least one selected from the group consisting of artificial graphite, natural graphite, hard carbon, and soft carbon.

11. The electrode composition according to claim 7, wherein, When the electrode active material comprises a silicon-based active material and a carbon-based active material, the weight ratio of the silicon-based active material to the carbon-based active material is 2:98 to 30:

70.

12. The electrode composition according to claim 6, wherein, The conductive material further comprises a planar conductive material.

13. The electrode composition according to claim 6, wherein The binder comprises repeating units derived from (meth)acrylamide in an amount of 30 wt% or more and 80 wt% or less relative to the total copolymer.

14. An electrode paste, comprising the electrode composition according to any one of claims 6 to 13 and a solvent.

15. An electrode, comprising: a current collector layer; and an electrode active material layer provided on one or both surfaces of the current collector layer, Among them, wherein the electrode active material layer comprises the electrode paste according to claim 14 or its dried product.

16. A lithium-ion secondary battery, comprising: a first electrode; a second electrode; a separator inserted between the first electrode and the second electrode; and an electrolyte, Among them, wherein either the first electrode or the second electrode is the electrode according to claim 15.

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