Conductive material dispersion, electrodes manufactured using the same, and lithium secondary battery

Abstract

The present invention discloses a conductive material dispersion, an electrode manufactured using the conductive material dispersion, and a secondary battery, wherein the conductive material dispersion comprises single-walled carbon nanotubes, a fluorine-based polymer, and an organic solvent, and the fluorine-based polymer has a dispersion index (D) of 0.10 to 0.90, which reflects the properties of the unsaturated functional groups and copolymers or saturated functional groups in the polymer, and the conductive material dispersion containing the fluorine-based polymer has the advantages of low viscosity, excellent dispersibility with few aggregated particles in the dispersed state, and excellent storage stability with little change in viscosity over time.

Description

Technical Field

[0001] The present invention relates to a conductive material dispersion liquid containing a fluorine-based polymer in which a dispersion index defined by factors affecting dispersibility satisfies a specific value, a single-walled carbon nanotube, an electrode to which this dispersion liquid is applied, and a lithium secondary battery.

Background Art

[0002] Due to the rapid increase in the use of fossil fuels, the demand for the use of alternative energy and clean energy has been increasing. As part of this, the fields most actively studied are power generation and power storage using electrochemical reactions.

[0003] Currently, a typical example of an electrochemical device that utilizes such electrochemical energy is a secondary battery, and its usage area is increasingly expanding. In recent years, with the increase in technology development and demand for portable devices such as portable computers, mobile phones, and cameras, the demand for secondary batteries as their energy source has been rapidly increasing. Among such secondary batteries, many studies have been conducted on lithium secondary batteries with high energy density, that is, high capacity, and they have also been commercialized and widely used.

[0004] The electrode of a secondary battery includes an electrode active material, a conductive material, and a binder. In order to improve the conductivity of the electrode, carbon nanotubes can be used as the conductive material. In particular, when applying those with a large specific surface area, even a small amount can exhibit an excellent effect of improving conductivity.

[0005] On the other hand, when using single-walled carbon nanotubes instead of multi-walled carbon nanotubes, the resistance of the electrode can be further reduced. Since the specific surface area is relatively large, there is an effect that conductivity can be easily ensured with only a small amount. In order to make the single-walled carbon nanotubes uniformly distributed in the electrode, during the manufacture of the electrode, a conductive material dispersion liquid in which the single-walled carbon nanotubes are dispersed is first formed, and then an electrode slurry is manufactured using the conductive material dispersion liquid.

[0006] A high-pressure homogenizer is used to manufacture the conductive material dispersion. Specifically, a premixed solution containing bundled single-walled carbon nanotubes, a dispersant, and a dispersion medium is passed through a nozzle with a diameter of 80 μm to 800 μm under a high pressure of 100 bar to 2,500 bar. This applies shear force to the bundled single-walled carbon nanotubes, causing them to disperse.

[0007] On the other hand, for a dispersion process using a high-pressure homogenizer to be possible, the solution containing bundled single-walled carbon nanotubes, a dispersant, and a dispersion medium must be pre-mixed, and the bundled carbon nanotubes in the solution must be effectively debundled by the dispersant, ultimately producing a conductive material dispersion in which single-walled carbon nanotubes are uniformly dispersed. Conversely, if debunding is not smooth during the pre-mixing, phase separation of the bundled carbon nanotubes and the dispersion medium will occur in the solution, causing the nozzle of the high-pressure homogenizer to clog with the bundled carbon nanotubes, making the dispersion process using the high-pressure homogenizer impossible.

[0008] To address these dispersibility issues, conventional methods have involved including an auxiliary dispersant in the conductive material dispersion along with the dispersant hydrogenated nitrile butadiene rubber. However, this problem becomes particularly pronounced when using carbon nanotubes with a large specific surface area, such as single-walled carbon nanotubes, and the high viscosity causes a variety of problems. Therefore, there is a need for research on conductive material dispersions that can improve the dispersibility of single-walled carbon nanotubes. [Overview of the project] [Problems that the invention aims to solve]

[0009] One objective of the present invention is to provide a conductive material dispersion with an adjusted dispersion index by using a dispersant with a low content of large-grained carbon nanotubes and controlled weight-average molecular weight and functional group content to achieve excellent dispersibility and storage stability.

[0010] Furthermore, the objective is to provide a conductive material dispersion containing a modified polysiloxane-based substance that can further maximize the dispersibility of the dispersion liquid, which has excellent dispersibility.

[0011] Another object of the present invention is to provide electrodes and secondary batteries manufactured using the conductive material dispersion. [Means for solving the problem]

[0012] [1] According to one embodiment of the present invention, a conductive material dispersion is provided, comprising single-walled carbon nanotubes and a fluorine-based polymer, wherein the fluorine-based polymer has a dispersion index (D) defined by the following formula 1 of 0.10 to 0.90.

[0013] [Formula 1] D=[10 6 (1+W u )] / [M w (1+W s )(1+M H )]

[0014] In the above formula 1, Mw is the unitless number of the weight-average molecular weight (g / mol) of the fluorine-based polymer, and W u This is the weight fraction of unsaturated functional group units in a fluorinated polymer, and W s This is the weight fraction of saturated residual compound units in the fluorinated polymer, and M H is the number of moles of heteroatoms in a saturated residual compound unit, where the saturated residual compound unit is one or more selected from saturated functional group units and copolymer units.

[0015] [2] In the above [1], the conductive material dispersion may further contain a modified polysiloxane-based substance.

[0016] [3] In the above [2], the modified polysiloxane-based substance may have a molecular weight of 4,000 g / mol to 8,000 g / mol.

[0017] [4] In either [2] and / or [3] above, the modified polysiloxane-based material may contain a polydialkylsiloxane, and the alkyl group may have 1 to 5 carbon atoms.

[0018] [5] In any of the above [1] to [4], the fluorine-based polymer may be polyvinylidene fluoride.

[0019] [6] In any of the above [1] to [5], the unsaturated functional group of the fluorine polymer may include a carboxyl group.

[0020] [7] In any of [1] to [6] above, the saturated functional group may include an alkoxy group having 1 to 5 carbon atoms, and the copolymer unit may include a hexafluoropropylene unit.

[0021] [8] In any of the above [1] to [7], the unsaturated functional groups of the fluorine polymer may be present in an amount of 0.01% to 1.0% by weight relative to the total weight of the polymer.

[0022] [9] In any of the above [1] to [8], the saturated residual compound units of the fluorine polymer may be present in an amount of 0.01% to 5.0% by weight relative to the total weight of the polymer.

[0023]

[10] In any of the above [1] to [9], the fluorine-based polymer may have a weight-average molecular weight of 1,000,000 g / mol to 2,000,000 g / mol.

[0024]

[11] According to another embodiment of the present invention, an electrode is provided comprising an electrode active material, a single-walled carbon nanotube, and a fluorine-based polymer, wherein the fluorine-based polymer has a dispersion index (D) represented by the following formula 1 of 0.10 to 0.90.

[0025] [Formula 1] D = [10 6 (1 + W u )] / [M w (1 + W s )(1 + M H )]

[0026] In the above Formula 1, Mw is the unitless number of the weight-average molecular weight (g / mol) of the fluorine-based polymer, W u is the weight fraction of the unsaturated functional group units in the fluorine-based polymer, and W s is the weight fraction of the saturated residual compound units in the fluorine-based polymer, M H is the number of moles of heteroatoms in the saturated residual compound units, where the saturated residual compound units are one or more selected from saturated functional group units and comonomer units.

[0027]

[12] According to still another embodiment of the present invention, a lithium secondary battery is provided which has a structure in which electrodes and separators are alternately laminated, and the electrodes are the aforementioned electrodes.

Advantages of the Invention

[0028] The conductive material dispersion liquid according to the present invention controls the dispersion index defined from the relationship of factors affecting the dispersibility in the fluorine-based polymer contained as a dispersant, so that the content of carbon nanotubes having a large particle size is small, the viscosity is low, the dispersibility is excellent, and the change in viscosity over time is small. Therefore, it can have excellent storage stability.

[0029] Also, by including the conductive material dispersion liquid in the electrode slurry, the phase stability of the slurry can be improved, and sufficient conductivity can be ensured even with a small amount of carbon nanotubes, and an electrode with a high energy density can be realized.

[0030] Furthermore, because it has excellent dispersibility, even though the content of the conductive material in the slurry is reduced, the resistance can be improved, so that a high-power battery can be realized. [Modes for carrying out the invention]

[0031] The terms and words used in this specification and in the claims should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather in a manner consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may appropriately define the concepts of terms in order to best describe their invention.

[0032] In this specification, terms such as “includes,” “completion,” or “having” are intended to indicate the presence of implemented features, figures, steps, components, or combinations thereof, and do not preclude the presence or possibility of adding one or more other features, figures, steps, components, or combinations thereof.

[0033] In this specification, "specific surface area" is measured by the BET method, and specifically, it can be calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77K) using BELSORP-mino II from BEL Japan.

[0034] In this specification, D 10 , D 50 , and D 90 These can be defined as particle sizes corresponding to 50% and 90% of the cumulative volume, respectively, in the particle size distribution curve. 50 and D 90 This can be measured, for example, by laser diffraction. Generally, laser diffraction can measure particle sizes ranging from the submicron region to several millimeters in size, and can yield highly reproducible and high-resolution results.

[0035] In this specification, "weight-average molecular weight (Mw)" refers to the converted value relative to standard polystyrene measured by gel permeation chromatography (GPC). Specifically, the weight-average molecular weight is a value converted from the value measured using GPC under the following conditions, and standard polystyrene from the Agilent system was used to prepare the calibration curve. <Measurement conditions> Measurement equipment: Agilent GPC (Agilent 1200 series, USA) Column: PL Mixed B (2 columns linked) Column temperature: 40℃ Eluent: Tetrahydrofuran Flow rate: 1.0mL / min Concentration: ~1mg / mL (100μL injection)

[0036] The present invention will be described in detail below.

[0037] In this specification, each of the conductive material dispersion, the electrode, and the lithium secondary battery includes one or more of the technical features and / or technical configurations described below, and these technical features and / or technical configurations can be combined in various ways.

[0038] Conductive material dispersion A conductive material dispersion according to one embodiment of the present invention comprises single-walled carbon nanotubes and a fluorine-based polymer, wherein the fluorine-based polymer has a dispersion index (D) of 0.10 to 0.90 as defined by the following formula 1.

[0039] [Formula 1] D=[10 6 (1+W u )] / [M w (1+W s )(1+M H )]

[0040] In the above formula 1, Mw is the unitless number of the weight-average molecular weight (g / mol) of the fluorine-based polymer, and Wu This is the weight fraction of unsaturated functional groups in a fluorinated polymer, and W s This is the weight fraction of saturated residual compound units in the fluorinated polymer, and M H is the number of moles of heteroatoms in a saturated residual compound unit, where the saturated residual compound unit is one or more selected from saturated functional group units and copolymer units.

[0041] (1) Single-walled carbon nanotubes Carbon nanotubes are characterized by a graphite sheet having a cylindrical shape with a nanoscale diameter and possessing an sp2 bonding structure. Depending on the angle and structure at which the graphite sheet is curled, they exhibit conductive or semiconductor properties. Carbon nanotubes can be classified into single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNTs), and multi-walled carbon nanotubes (MWCNTs) based on the number of bonds forming the wall.

[0042] According to one embodiment of the present invention, the conductive material dispersion contains single-walled carbon nanotubes. Since single-walled carbon nanotubes have a larger specific surface area than multi-walled carbon nanotubes, even if only a small amount is added, sufficient conductivity can be ensured, and the reduction in electrode resistance can be greatly increased.

[0043] The D of the single-walled carbon nanotube 50 The diameter may be 2 μm to 8 μm, specifically 3 μm or more or 4 μm or more, and 7 μm or less or 6 μm or less. The D of the single-walled carbon nanotube 90The nanotubes may be 10 μm to 30 μm in size, specifically 12 μm or larger, 14 μm or larger, 16 μm or larger, or 18 μm or larger, and also 28 μm or smaller, 26 μm or smaller, 24 μm or smaller, or 22 μm. Satisfying the above range means that the bundled carbon nanotubes used as raw materials are effectively dispersed in the conductive material dispersion, thereby effectively improving the resistance of the electrodes and batteries.

[0044] The carbon nanotubes may be included in an amount of 0.4 to 2.0 parts by weight per 100 parts by weight of the conductive material dispersion, specifically in amounts of 0.5 parts by weight or more, 0.6 parts by weight or more, 0.7 parts by weight or more, or 0.8 parts by weight or more, or 1.7 parts by weight or less, 1.5 parts by weight or less, 1.3 parts by weight or less, or 1.2 parts by weight or less. When the above ranges are met, high productivity is maintained and the transfer and input of the electrode slurry is easy. In addition, since the solid content of the manufactured electrode slurry is not excessively low, the occurrence of binder migration during electrode drying can be suppressed. As a result, the adhesion strength of the electrode can be improved, packing of the electrode active material layer can be performed effectively, and electrodes of thin thickness can be manufactured.

[0045] (2) Fluorine-based polymers A conductive material dispersion according to one embodiment of the present invention contains a fluorine-based polymer, characterized in that the fluorine-based polymer satisfies a dispersion index (D) of 0.10 to 0.90 as defined by the following formula 1.

[0046] [Formula 1] D=[10 6 (1+W u )] / [M w (1+W s )(1+M H )]

[0047] In the above formula 1, Mw is the unitless number of the weight-average molecular weight (g / mol) of the fluorine-based polymer, and W u This is the weight fraction of unsaturated functional groups in a fluorinated polymer, and Ws This is the weight fraction of saturated residual compound units in the fluorinated polymer, and M H is the number of moles of heteroatoms in a saturated residual compound unit, where the saturated residual compound unit is one or more selected from saturated functional group units and copolymer units.

[0048] The aforementioned dispersion index establishes the relationships between factors that may influence the dispersion of single-walled carbon nanotubes using a fluorine-based polymer as a dispersant, taking into account the weight-average molecular weight of the fluorine-based polymer, the content of unsaturated functional groups in the fluorine-based polymer, and the content of saturated residual compound units.

[0049] The extent to which a polymer used as a dispersant can disperse single-walled carbon nanotubes depends on the degree to which the polar and nonpolar parts of the polymer interact with the nonpolar carbon nanotubes and the polar organic solvent.

[0050] The aforementioned dispersion index reflects the weight fraction of highly polar unsaturated functional groups in the fluorinated polymer, as well as the weight fraction of saturated residual compound units, which are polar but whose polarity is relatively less than that of unsaturated functional groups. In the case of saturated residual compound units, the number of moles of heteroatoms (e.g., F, N, P, or O) contained in the unit also has an effect, and the index balances the influence of unsaturated functional groups with that of saturated residual compound units.

[0051] These factors alone make it difficult to accurately grasp the degree of dispersion of single-walled carbon nanotubes, and it may be necessary to reflect the influence of the polymer itself, rather than just the units within the polymer. For example, weight-average molecular weight was included as a factor to reflect the effects of steric hindrance and the overall size of the molecule.

[0052] The dispersion index derived in this way can be said to be an index that can more accurately confirm how well single-walled carbon nanotubes can be dispersed. The dispersion index is characterized by being between 0.10 and 0.90. Preferably, the dispersion index may be 0.11 or higher, 0.12 or higher, or 0.13 or higher, and may also be 0.85 or lower, 0.80 or lower, 0.75 or lower, 0.70 or lower, or 0.68 or lower, and most preferably 0.14 to 0.67.

[0053] The aforementioned dispersion index reflects a variety of factors, and the smaller the value, the better the dispersibility of the conductive material dispersion. However, if the dispersion index is less than 0.10, the weight-average molecular weight is too large compared to the content of unsaturated functional groups. As a result, the attractive forces between these polymers may reduce the contribution of carbon nanotubes to dispersion, and the influence of saturated residual compound units may become greater than the influence of unsaturated functional groups. This may lead to the formation of large clumps in the dispersion even if the viscosity of the dispersion is low.

[0054] If the aforementioned dispersion index is greater than 0.90, it cannot be said that the carbon nanotubes are properly dispersed, resulting in problems such as high viscosity and a high content of larger particles.

[0055] The fluorine-based polymer may be one or more polymers selected from the group consisting of polyvinylidene fluoride (PVDF), polyperfluoroalkoxy (PFA), polytetrafluoroethylene (PTFE), and copolymers obtained by copolymerizing these with a comonmer, and preferably polyvinylidene fluoride. When polyvinylidene fluoride is applied in the dispersion of single-walled carbon nanotubes, a polymer solution can be formed with excellent affinity to the organic solvent used, which has the advantage of excellent processability.

[0056] The fluorine-based polymer may contain carboxyl groups as unsaturated functional groups. The unsaturated functional groups may be present in an amount of 0.01% to 1.00% by weight relative to the total weight of the polymer, preferably 0.02% or more by weight, 0.03% or more by weight, or 0.05% or more by weight, and may be present in an amount of 0.90% or less by weight, 0.80% or less by weight, preferably 0.75% or less by weight. The unsaturated functional groups are the main factors that cause the polymer to exhibit polar properties, and it is preferable that their content be appropriately adjusted in order to contribute to the dispersion of single-walled carbon nanotubes.

[0057] The fluorinated polymer may contain saturated residual compound units, and these saturated residual compound units may represent saturated functional groups and / or comonomer units. In the present invention, "saturated residual compound units" may mean the remaining compound units after removing the main monomer units and unsaturated functional groups. Among such saturated residual compound units, the saturated functional groups may include alkoxy groups having 1 to 5 carbon atoms, and the comonomer units may include one or more selected from the group consisting of hexafluoropropylene units and chlorotrifluoroethylene.

[0058] The saturated residual compound units may be present in an amount of 0.01% to 5.0% by weight relative to the total weight of the polymer, preferably 0.02% or more, 0.03% or more by weight, and also 4.0% or less by weight, 3.0% or less by weight, or 2.5% or less by weight. Furthermore, the number of moles of heteroatoms contained in the saturated residual compound units may be 1 to 6, and this is considered together with the content of the saturated residual compound units so that the effect of the saturated residual compound units on dispersibility is reflected in proportion to how many highly electronegative heteroatoms are present.

[0059] The fluorinated polymer may have a weight-average molecular weight of 1,000,000 g / mol to 2,000,000 g / mol. It is preferable to control the weight-average molecular weight so that it is not excessively small or large, thereby ensuring that the variance index satisfies the above range.

[0060] The fluorine-based polymer may be contained in the conductive material dispersion in an amount of 0.5 to 6.0 parts by weight per 100 parts by weight of the conductive material dispersion. Specifically, it may be contained in an amount of 0.8 parts by weight or more, 1.0 part by weight or more, 1.5 parts by weight or more, 2.0 parts by weight or more, or 2.4 parts by weight or more, or 5.0 parts by weight or less, 4.0 parts by weight or less, 3.0 parts by weight or less, or 2.6 parts by weight or less. When the above ranges are met, the carbon-based conductive material can be smoothly dispersed in the conductive material dispersion, improving the energy density of the manufactured electrode and reducing its resistance.

[0061] The conductive material dispersion may further contain a dispersant in addition to the fluorine-based polymer, for example, a hydrogenated nitrile copolymer. The hydrogenated nitrile copolymer may be a copolymer containing structural units derived from α,β-unsaturated nitrile and structural units derived from hydrogenated conjugated diene, or a copolymer containing structural units derived from α,β-unsaturated nitrile, structural units derived from conjugated diene, and structural units derived from hydrogenated conjugated diene. The hydrogenated nitrile copolymer may be hydrogenated nitrile butadiene rubber, more specifically hydrogenated acrylonitrile-butadiene rubber, and more specifically partially hydrogenated acrylonitrile-butadiene rubber.

[0062] (3) Modified polysiloxane-based substances A conductive material dispersion according to one embodiment of the present invention may further contain a modified polysiloxane-based substance. The modified polysiloxane-based substance may have a molecular weight of 4,000 g / mol to 8,000 g / mol, preferably 4,500 g / mol to 7,500 g / mol.

[0063] The modified polysiloxane-based substance can be affected by the dispersibility index of the aforementioned fluorine-based polymer. When added together with a fluorine-based polymer whose dispersibility index is not within the range of 0.10 to 0.90, a viscosity reduction effect can be expected, but there is a risk that the content of larger particles will increase, leading to a deterioration in dispersibility. However, when added together with a fluorine-based polymer that satisfies the dispersibility index, a viscosity reduction effect can be expected without deterioration in dispersibility, and the effect of adding the modified polysiloxane-based substance can be maximized. Therefore, it is preferable to add the modified polysiloxane-based substance for viscosity reduction, taking the dispersibility index into consideration.

[0064] The polysiloxane portion of the modified polysiloxane-based substance may contain dialkylsiloxane as a monomer unit, and in the dialkylsiloxane, the alkyl group may have 1 to 5 carbon atoms. Examples of applicable polysiloxane-based portions include polydimethylsiloxane, polymethylethylsiloxane, and polymethylpropylsiloxane.

[0065] Preferably, the modified polysiloxane material may be a polyether-modified polysiloxane material modified with a polyether material, in which case it can be modified in a form in which the polyether material is bonded to the alkyl group. The polyether material may include homopolymers such as polyethylene glycol, propoxylated polyethylene glycol, polypropylene glycol, and ethoxylated polypropylene glycol; random copolymers thereof; or block copolymers thereof.

[0066] The polyether-based modified polysiloxane material may, for example, be in the form of a block copolymer of a polyether material and a polysiloxane material. The modified polysiloxane material may be in the form of a polyether material distributed on one side and a polysiloxane material distributed on the other side, with these two materials linked by covalent bonds.

[0067] For example, the weight ratio of the polysiloxane-based material to the polyether-based material in the modified polysiloxane-based material may be about 95:5 to 5:95, preferably 70:30 to 10:90, 60:40 to 10:90, 50:50 to 10:90, 40:60 to 10:90, and more preferably 30:70 to 10:90.

[0068] As described above, the modified polysiloxane-based material, through modification, possesses both polar and nonpolar parts within its molecule. This allows for more active interaction with fluorinated polymers and conductive materials, thereby improving dispersibility. In particular, the interaction with the functional group portion of the fluorinated polymer can significantly influence the dispersion index, leading to the expectation of considerable synergistic effects.

[0069] (4) Organic solvents The organic solvent may be an organic solvent containing one or more heteroatoms selected from the group consisting of nitrogen atoms (N) and oxygen atoms (O) having lone pairs of electrons.

[0070] Specifically, the organic solvents include amide-based polar organic solvents such as dimethylformamide (DMF), diethylformamide, dimethylacetamide (DMAc), and N-methylpyrrolidone (NMP); alcohols such as methanol, ethanol, 1-propanol, 2-propanol (isopropyl alcohol), 1-butanol (n-butanol), 2-methyl-1-propanol (isobutanol), 2-butanol (sec-butanol), 1-methyl-2-propanol (tert-butanol), pentanol, hexanol, heptanol, or octanol; glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,5-pentanediol, or hexylene glycol; and glycerin, trimethylolpropane, pentaerythritol, or sorbitol. Examples include polyhydric alcohols such as ethanol; glycol ethers such as ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, tetraethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, tetraethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, or tetraethylene glycol monobutyl ether; ketones such as acetone, methyl ethyl ketone, methyl propyl ketone, or cyclopentanone; and esters such as ethyl acetate, γ-butyl lactone, and ε-propiolactone. Any one or a mixture of two or more of these can be used. Considering miscibility with the electrode slurry, N-methylpyrrolidone (NMP) is particularly preferred.

[0071] In the conductive material dispersion, the solid content of the conductive material dispersion may be 1% to 10% by weight, specifically 2% to 8% by weight, and more specifically 3.5% to 5.5% by weight. When the above range is satisfied, the viscosity of the conductive material dispersion can be kept at a low level, and the dispersion of the conductive material can be effectively achieved. Here, the solid content may refer to single-walled carbon nanotubes and fluorinated polymers contained in the conductive material dispersion.

[0072] The conductive material dispersion can be produced by mixing single-walled carbon nanotubes, a fluorine-based polymer, and an organic solvent. In this case, the mixing may be carried out using a conventional mixing method, specifically a mixing device such as a homogenizer, bead mill, ball mill, basket mill, attrition mill, universal stirrer, clear mixer, spike mill, or TK mixer, and the mixing order of each component is not particularly limited. That is, the conductive material dispersion according to the present invention may be produced by adding single-walled carbon nanotubes to an organic solvent and then adding and mixing the fluorine-based polymer, or by adding the fluorine-based polymer to the organic solvent first and then mixing the single-walled carbon nanotubes, or by adding both single-walled carbon nanotubes and the fluorine-based polymer to the organic solvent and then mixing them.

[0073] On the other hand, in the mixing process, cavitation dispersion treatment may be performed to improve the dispersibility of single-walled carbon nanotubes. The cavitation dispersion treatment is a dispersion method that uses shock waves generated when vacuum bubbles generated in water burst when high energy is applied to the liquid, and by this method, single-walled carbon nanotubes can be dispersed without impairing their properties. Specifically, the cavitation dispersion treatment can be performed by ultrasound, jet milling, or shear dispersion treatment.

[0074] electrode An electrode according to another embodiment of the present invention comprises an electrode active material, a single-walled carbon nanotube, and a fluorine-based polymer, wherein the dispersion index of the fluorine-based polymer is as described above.

[0075] The electrode comprises a current collector and an electrode active material layer disposed on the current collector, the electrode active material layer may contain an electrode active material, a single-walled carbon nanotube, and a fluorine-based polymer.

[0076] The electrode active material layer may be formed from an electrode slurry composition comprising an electrode active material, a conductive material dispersion, and a binder. Specifically, the electrode comprises an electrode current collector and an electrode active material layer formed on the electrode current collector, and the electrode active material layer may be formed from an electrode slurry composition comprising an electrode active material, a conductive material dispersion, and a binder.

[0077] In this case, the conductive material dispersion is the conductive material dispersion according to the present invention as described above. Since the details of the conductive material dispersion are the same as described above, a detailed explanation will be omitted, and the other components will be described below.

[0078] The electrode current collector is not particularly limited as long as it is made of a material that does not cause chemical changes in the battery and is conductive. For example, copper, stainless steel, aluminum, nickel, titanium, alloys thereof, materials with surface treatments such as carbon, nickel, titanium, or silver, or calcined carbon may be used.

[0079] The electrode current collector typically has a thickness of 3 μm to 500 μm, and the bonding force of the active material may be strengthened by forming fine irregularities on the surface of the current collector. Furthermore, the electrode current collector can be used in various forms such as film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0080] On the other hand, the electrode active material (a) contained in the electrode active material layer may be a positive electrode active material or a negative electrode active material commonly used in the art, and its type is not particularly limited.

[0081] For example, as the positive electrode active material, a lithium oxide containing one or more metals such as cobalt, manganese, nickel, or aluminum and lithium may be used. More specifically, the lithium oxide is a lithium-manganese-based oxide (e.g., LiMnO2, LiMn2O, etc.), a lithium-cobalt-based oxide (e.g., LiCoO2, etc.), a lithium-nickel-based oxide (e.g., LiNiO2, etc.), a lithium-nickel-manganese-based oxide (e.g., LiNi 1-Y1 Mn Y1 O2 (where 0 < Y1 < 1), LiNi Z1 Mn 2-Z1 O4 (where 0 < Z1 < 2), etc.), a lithium-nickel-cobalt-based oxide (e.g., LiNi 1-Y2 Co Y2 O2 (where 0 < Y2 < 1), etc.), a lithium-manganese-cobalt-based oxide (e.g., LiCo 1-Y3 Mn Y3 O2 (where 0 < Y3 < 1), LiMn 2-Z2 Co Z2 O4 (where 0 < Z2 < 2), etc.), a lithium-nickel-cobalt-manganese-based oxide (e.g., Li(Ni P1 Co Q1 Mn R1 )O2 (where 0 < Pⱼ < 1, 0 < Qⱼ < 1, 0 < Rⱼ < 1, Pⱼ + Qⱼ + Rⱼ = 1) or Li(Ni P2 Co Q2 Mn R2 )O4 (where 0 < P₂ < 2, 0 < Q₂ < 2, 0 < R₂ < 2, P₂ + Q₂ + R₂ = 2), etc., or a lithium-nickel-cobalt-manganese-other metal (M) oxide (e.g., Li(Ni P3 Co Q3 Mn R3 M 1 S )O2 (where M 1is selected from the group consisting of Al, Cu, Fe, V, Cr, Ti, Zr, Zn, Ta, Nb, Mg, B, W, and Mo, and P3, Q3, R3, and S are atomic fractions of independent elements, respectively, where 0 < P3 < 1, 0 < Q3 < 1, 0 < R3 < 1, 0 < S < 1, and P3 + Q3 + R3 + S = 1 (etc.), and any one or two or more of these compounds may be included.

[0082] On the other hand, examples of the negative electrode active material include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; v (0 < v < 2), metal oxides capable of doping and undoping lithium, such as SnO2, vanadium oxides, and lithium vanadium oxides; or composites containing the metallic compound and the carbonaceous material, such as Si-C composites or Sn-C composites. Any one or two or more of these mixtures can be used. Further, a thin film of metallic lithium may be used as the negative electrode active material. Also, any of low-crystalline carbon and high-crystalline carbon may be used as the carbon material.

[0083] The electrode active material may be contained in an amount of 90% to 99% by weight, preferably 95% to 99% by weight, based on the content of the total solid matter in the electrode slurry composition. When the content of the electrode active material satisfies the above range, excellent energy density, electrode adhesion, and electrical conductivity can be achieved.

[0084] The binder is used to ensure adhesion between electrode active materials or between electrode active materials and current collectors, and any general binder used in the art can be used, and its type is not particularly limited. Examples of the binder include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these can be used alone, or a mixture of two or more can be used.

[0085] The binder may be present in an amount of 5% by weight or less, based on the total solid content in the electrode slurry composition, and preferably in an amount of 1% to 3% by weight. When the binder content satisfies the above range, the increase in electrode resistance can be minimized while achieving excellent electrode adhesion.

[0086] On the other hand, the electrode slurry composition may further contain a solvent as needed for viscosity adjustment or the like. In this case, the solvent may be water, an organic solvent, or a mixture thereof. Examples of the aforementioned organic solvents include amide-based polar organic solvents such as dimethylformamide (DMF), diethylformamide, dimethylacetamide (DMAc), and N-methylpyrrolidone (NMP); alcohols such as methanol, ethanol, 1-propanol, 2-propanol (isopropyl alcohol), 1-butanol (n-butanol), 2-methyl-1-propanol (isobutanol), 2-butanol (sec-butanol), 1-methyl-2-propanol (tert-butanol), pentanol, hexanol, heptanol, or octanol; glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,5-pentanediol, or hexylene glycol; and polyvalent organic solvents such as glycerin, trimethylolpropane, pentaerythritol, or sorbitol. Examples include alcohols; glycol ethers such as ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, tetraethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, tetraethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, or tetraethylene glycol monobutyl ether; ketones such as acetone, methyl ethyl ketone, methyl propyl ketone, or cyclopentanone; and esters such as ethyl acetate, γ-butyl lactone, and ε-propiolactone. Any one or more of these mixtures may be used, but are not limited to these.

[0087] The solvent may be included in such a concentration that the solid content in the electrode slurry is 60% to 85% by weight, preferably 65% ​​to 80% by weight. When the above range is met, binder migration can be suppressed, electrode adhesion can be improved, the drying temperature can be lowered to improve coating properties, and the coating speed can be increased to improve productivity.

[0088] The electrode according to the present invention can be manufactured by applying an electrode slurry composition containing the above-mentioned components and drying it to form an electrode active material layer. Specifically, the electrode active material layer can be formed by applying the electrode slurry onto an electrode current collector and then drying it, or by applying the electrode slurry onto another support, peeling it off this support, and then laminating the resulting film onto the electrode current collector. If necessary, after forming the electrode active material layer by the above-mentioned method, a rolling step may be further performed. In this case, drying and rolling can be carried out under appropriate conditions considering the physical properties of the electrode to be ultimately manufactured, and are not particularly limited.

[0089] Lithium-ion battery A lithium secondary battery according to yet another embodiment of the present invention has a structure in which electrodes and separators are alternately stacked, and the electrodes include the electrodes described above. Specifically, the secondary battery according to the present invention includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, in which case the positive electrode may be the electrode of the above-described embodiment.

[0090] Since the electrodes according to the present invention have been described above, a detailed explanation will be omitted, and only the other components will be described below.

[0091] The separator separates the negative and positive electrodes and provides a passage for lithium ions to move. It is not particularly limited and can be used as long as it is a separator commonly used in secondary batteries. Specifically, the separator can be a porous polymer film, for example, a porous polymer film made from 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. Alternatively, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, a coated separator containing ceramic components or polymeric substances may be used to ensure heat resistance or mechanical strength, and may be selectively used as a single-layer or multi-layer structure.

[0092] Examples of the aforementioned electrolytes include, but are not limited to, 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.

[0093] Specifically, the electrolyte may contain a non-aqueous organic solvent and a metal salt.

[0094] As the non-aqueous organic solvent, for example, aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate may be used.

[0095] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are preferred because they are high-viscosity organic solvents with high dielectric constants that readily dissociate lithium salts. When such cyclic carbonates are mixed with linear carbonates with low viscosity and low dielectric constant, such as dimethyl carbonate and diethyl carbonate, in appropriate proportions, an electrolyte with high electrical conductivity can be obtained, and therefore this mixture is also preferred.

[0096] A lithium salt can be used as the metal salt, and the lithium salt is a substance that is easily soluble in the non-aqueous electrolyte, for example, the anion of the lithium salt is 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 types selected from the group consisting of the following can be used.

[0097] In addition to the components of the electrolyte, the electrolyte may further contain one or more additives for the purpose of improving the battery's lifespan, suppressing the decrease in battery capacity, and improving the battery's discharge capacity, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride.

[0098] Examples Hereinafter, embodiments of the present invention will be described in detail so that those with ordinary skill in the art to which the present invention pertains can easily implement it. However, the present invention can be realized in various different forms and is not limited to the embodiments described herein.

[0099] Examples 1-1 to 1-3 and Comparative Examples 1-1 to 1-3 As a fluorine-based polymer, 2.0 parts by weight of polyvinylidene fluoride (PVDF) having the characteristics described in Table 1 below, 1.0 part by weight of single-walled carbon nanotubes (Tuball, OcSiAl), and 97 parts by weight of N-methylpyrrolidone were mixed, and then mixed for 180 minutes using a mixer (BTM-50, disper 1000 rpm / anchor 100 rpm). The mixed mixture was stirred for 30 minutes using a high-pressure homogenizer (manufactured by MICRONOX, Picomax MN230A, pressure: 1,500 bar) to obtain conductive material dispersions respectively.

[0100]

Table 1

[0101] Experimental Example 1: Particle Size Analysis The particle sizes of the conductive material dispersions of the examples and comparative examples were analyzed by laser diffraction method and shown in Table 2. Specifically, after dispersing the conductive material dispersion in a solvent, it was introduced into a laser diffraction particle size measuring device (Malvern, Mastersizer 3000), and the diffraction pattern difference due to the particle size when the particles passed through the laser beam was measured to calculate the particle size distribution. The particle sizes at the points where the volume cumulative distribution by particle diameter was 10%, 50%, and 90% were confirmed, and D 10 、D 50 、and D 90 were measured.

[0102] Experimental Example 2: Viscosity Analysis (Immediately after manufacturing of conductive material dispersion) The viscosities of the conductive material dispersions produced in the above examples and comparative examples were measured at 25 °C and 12 rpm using a viscometer (Brookfield, viscometer DV2T, LV) and shown in Table 2.

[0103] Experimental Example 3: Confirmation of viscosity increase during long-term storage For the conductive material dispersions produced in the examples and comparative examples, the viscosity increase rate (%) was confirmed by the following formula.

[0104] Viscosity increase rate (%) = {(Viscosity of conductive material dispersion measured after 4 weeks of storage at 25°C - Viscosity of conductive material dispersion immediately after manufacturing) / Viscosity of conductive material dispersion immediately after manufacturing} x 100

[0105] [Table 2]

[0106] Referring to Table 1 above, it can be confirmed that Examples 1-1 to 1-3, whose dispersion index is in the range of 0.1 to 0.9, have low viscosity and little change over time, and their average particle size, cumulatively measured at 90% by volume, is relatively smaller compared to the comparative example.

[0107] Experimental Example 4: Evaluation of the effects of adding modified polysiloxane-based substances In the conductive material dispersions of Examples 1-1 to 1-3 and Comparative Examples 1-1 to 1-3, instead of 2.0 parts by weight of polyvinylidene fluoride, which is used as a dispersant, 0.5 parts by weight of a modified polysiloxane-based substance (modified by bonding approximately 0.15 parts by weight of polydimethylsiloxane (PDMS) and approximately 0.85 parts by weight of polyethylene glycol) with a molecular weight of 6,000 g / mol and 1.5 parts by weight of polyvinylidene fluoride were added to produce the conductive material dispersions of Examples 2-1 to 2-3 and Comparative Examples 2-1 to 2-3. The viscosity and particle size characteristics were evaluated in the same manner as in Experimental Examples 1 to 3, and the results are shown in Table 3 below.

[0108] [Table 3]

[0109] Referring to Table 3 above, it can be confirmed from Examples 2-1 to 2-3 that when a modified polysiloxane-based substance is added to Examples 1-1 to 1-3, which have a dispersion index of 0.10 to 0.90, it has the effect of lowering viscosity. It can also be seen that this effect is observed in Comparative Examples 2-1 to 2-3, which are the same substance added to Comparative Examples 1-1 to 1-3, which do not meet the dispersion index requirements.

[0110] However, comparative examples 2-1 to 2-3 are D 90A significant increase in this factor was observed, indicating that if the dispersibility index is not met, adding modified polysiloxane-based substances may actually have a negative impact on dispersibility.

Claims

1. It contains single-walled carbon nanotubes and fluorine-based polymers, The fluorine-based polymer is a conductive material dispersion having a dispersion index (D) of 0.10 to 0.90 as defined by the following formula 1. [Formula 1] D=[10 ６ (1+W ｕ )] / [M ｗ (1+W ｓ )(1+M Ｈ )] (In formula 1 above, Mw is the unitless number of the weight-average molecular weight (g / mol) of the fluorine-based polymer, and W ｕ This is the weight fraction of unsaturated functional group units in a fluorinated polymer, W ｓ This is the weight fraction of saturated residual compound units in the fluorinated polymer, M Ｈ (where is the number of moles of heteroatoms in the saturated residual compound unit, and the saturated residual compound unit is one or more selected from saturated functional group units and copolymer units.)

2. The conductive material dispersion according to claim 1, further comprising a modified polysiloxane-based substance.

3. The conductive material dispersion according to claim 2, wherein the modified polysiloxane-based substance has a molecular weight of 4,000 g / mol or more and 8,000 g / mol or less.

4. The aforementioned modified polysiloxane-based material includes a polydialkylsiloxane. The conductive material dispersion according to claim 2, wherein the alkyl has 1 or more carbon atoms and 5 or less.

5. The conductive material dispersion according to claim 1, wherein the fluorine-based polymer is polyvinylidene fluoride.

6. The conductive material dispersion according to claim 1, wherein the unsaturated functional group of the fluorine-based polymer contains a carboxyl group.

7. The saturated functional group includes an alkoxy group having 1 or more carbon atoms and 5 or fewer carbon atoms. The conductive material dispersion according to claim 1, wherein the aforementioned couniter unit comprises one or more selected from the group consisting of hexafluoropropylene units and chlorotrifluoroethylene.

8. The conductive material dispersion according to claim 1, wherein the unsaturated functional groups of the fluorine-based polymer are contained in an amount of 0.01% by weight or more and 1.0% by weight or less relative to the total weight of the polymer.

9. The conductive material dispersion according to claim 1, wherein the saturated residual compound units of the fluorine-based polymer are contained in an amount of 0.01% by weight or more and 5.0% by weight or less relative to the total weight of the polymer.

10. The conductive material dispersion according to claim 1, wherein the fluorine-based polymer has a weight-average molecular weight of 1,000,000 g / mol or more and 2,000,000 g / mol or less.

11. It contains electrode active material, single-walled carbon nanotubes, and fluorine-based polymers. The fluorine-based polymer is an electrode having a dispersion index (D) represented by the following formula 1 that is 0.05 or more and 0.95 or less. [Formula 1] D=[10 ６ (1+W ｕ )] / [M ｗ (1+W ｓ )(1+M Ｈ )] (In formula 1 above, Mw is the unitless number of the weight-average molecular weight (g / mol) of the fluorine-based polymer, and W ｕ This is the weight fraction of unsaturated functional group units in a fluorinated polymer, W ｓ This is the weight fraction of saturated residual compound units in the fluorinated polymer, M Ｈ (where is the number of moles of heteroatoms in the saturated residual compound unit, and the saturated residual compound unit is one or more selected from saturated functional group units and copolymer units.)

12. It has a structure in which electrodes and separators are stacked alternately. A lithium secondary battery wherein the electrode is the electrode described in claim 11.

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