Conductive agent dispersion, and electrode and lithium secondary battery prepared by using same

Abstract

Disclosed are a conductive agent dispersion, and an electrode and a lithium secondary battery prepared by using the same, the conductive agent dispersion comprising single-walled carbon nanotubes, a fluorine-based polymer, and an organic solvent, in which the fluorine-based polymer has a dispersion index (D) of 0.10 to 0.90, the dispersion index reflects the characteristics of unsaturated functional groups and comonomers or saturated functional groups in the polymer; wherein the conductive agent dispersion including the fluorine-based polymer has the advantages of low viscosity, excellent dispersibility due to fewer particles aggregated in a dispersed state, and excellent storage stability due to small change in viscosity over time.

Description

TECHNICAL FIELD

[0001] The present application relates to a conductive agent dispersion including single-walled carbon nanotubes and a fluorine-based polymer, in which a dispersion index defined by factors affecting dispersion satisfies a certain value, and an electrode and a lithium secondary battery using the same. BACKGROUND

[0002] Due to the rapid increase in the use of fossil fuels, there is an increasing demand for the use of alternative or clean energy, and as part of this trend, power generation and power storage using electrochemical reactions are the most active fields of research.

[0003] Currently, a typical example of an electrochemical device using electrochemical energy can be a secondary battery, and its use field has a tendency to increase. In recent years, as technology development and demand for portable devices such as portable computers, mobile phones, and cameras have increased, the demand for secondary batteries as energy sources has significantly increased, and, among these secondary batteries, a great deal of research has been conducted on lithium secondary batteries having high energy density (i.e., high capacity), and has been commercialized and widely used.

[0004] An electrode of a secondary battery includes an electrode active material, a conductive agent, and a binder. Carbon nanotubes can be used as a conductive agent to improve the conductivity of the electrode, and particularly in the case of using carbon nanotubes having a large specific surface area, the effect of improving the conductivity is excellent even with a small amount.

[0005] In the case of using single-walled carbon nanotubes instead of multi-walled carbon nanotubes, the resistance of the electrode can be further reduced, and since their specific surface area is relatively large, single-walled carbon nanotubes have the effect of easily ensuring the conductivity using a small amount. In order to uniformly distribute the single-walled carbon nanotubes in the electrode, after a conductive agent dispersion in which single-walled carbon nanotubes are dispersed is first formed in the electrode preparation process, an electrode slurry is prepared by using the conductive agent dispersion.

[0006] A high-pressure homogenizer is used to prepare the conductive agent dispersion. Specifically, in the high-pressure homogenizer, a pre-mixed solution containing bundle-type single-walled carbon nanotubes, a dispersant, and a dispersion medium is passed through a nozzle having a diameter of 80 to 800 μm at a high pressure of 100 to 2,500 bar, thereby applying a shearing force to the bundle-type single-walled carbon nanotubes to disperse the single-walled carbon nanotubes.

[0007] In a state in which a solution containing bundle-type single-walled carbon nanotubes, a dispersant, and a dispersion medium is premixed, only when the bundle-type carbon nanotubes in the solution are effectively de-bundled by the dispersant, it is possible to perform a dispersion process using a high-pressure homogenizer, and finally it is possible to prepare a conductive agent dispersion in which single-walled carbon nanotubes are uniformly dispersed. In contrast, if de-bundling is not smoothly performed in the premixing process, the nozzle of the high-pressure homogenizer is clogged by the bundle-type carbon nanotubes due to phase separation between the bundle-type carbon nanotubes in the solution and the dispersion medium, and thus it is not possible to perform a dispersion process by the high-pressure homogenizer.

[0008] To solve this dispersibility problem, a method of including, as a dispersant, hydrogenated nitrile rubber and an auxiliary dispersant in the conductive agent dispersion is generally used. However, when carbon nanotubes having a large specific surface area, such as single-walled carbon nanotubes, are used, this problem becomes more prominent, and various problems occur due to high viscosity. Therefore, there is a need to research a conductive agent dispersion that can improve the dispersibility of single-walled carbon nanotubes. SUMMARY

[0009] TECHNICAL PROBLEM

[0010] An aspect of the present application provides a conductive agent dispersion in which the amount of carbon nanotubes having a large particle size is small, and a dispersibility index is adjusted by using a dispersant having a controlled weight average molecular weight and a controlled amount of functional groups to achieve excellent dispersibility and storage stability.

[0011] Further, the present application aims to provide a conductive agent dispersion containing a modified polysiloxane-based material, capable of further maximizing the dispersibility in a dispersion having excellent dispersibility.

[0012] Another aspect of the present application provides an electrode and a secondary battery prepared by using the above-described conductive agent dispersion.

[0013] TECHNICAL SOLUTION

[0014] [1] According to an embodiment of the present application, a conductive agent dispersion is provided, which includes single-walled carbon nanotubes and a fluorine-based polymer, wherein the fluorine-based polymer has a dispersibility index (D) defined by Formula 1 of 0.10 to 0.90.

[0015] [Formula 1]

[0016] D = [10 6 (1+W u )] / [M w (1+W s )(1+M H )]

[0017] In Formula 1, M wis a unitless number of weight average molecular weight (g / mol) of the fluorine-based polymer, W u is a weight fraction of unsaturated functional group units in the fluorine-based polymer, W s is a weight fraction of saturable residual compound units in the fluorine-based polymer, M H is a mole number of heteroatoms in the saturable residual compound units, wherein the saturable residual compound units are at least one selected from the group consisting of saturated functional group units and comonomer units.

[0018] [2] The conductive agent dispersion of the above [1], wherein the conductive agent dispersion can further include a modified polysiloxane-based material.

[0019] [3] The conductive agent dispersion of the above [2], wherein a molecular weight of the modified polysiloxane-based material can be 4,000 g / mol to 8,000 g / mol.

[0020] [4] The conductive agent dispersion of at least one of the above [2] and / or [3], wherein the modified polysiloxane-based material can include a polydialkylsiloxane, and the alkyl group can have 1 to 5 carbon atoms.

[0021] [5] The conductive agent dispersion of at least one of the above [1] to [4], wherein the fluorine-based polymer can be a polyvinylidene fluoride.

[0022] [6] The conductive agent dispersion of at least one of the above [1] to [5], wherein the unsaturated functional group of the fluorine-based polymer can include a carboxyl group.

[0023] [7] The conductive agent dispersion of at least one of the above [1] to [6], wherein the saturated functional group can include an alkoxy group having 1 to 5 carbon atoms, and the comonomer unit can include a hexafluoropropylene unit.

[0024] [8] The conductive agent dispersion of at least one of the above [1] to [7], wherein the unsaturated functional group of the fluorine-based polymer can be included in an amount of 0.01% to 1.0% by weight, based on the total weight of the polymer.

[0025] [9] The conductive agent dispersion of at least one of the above [1] to [8], wherein the saturable residual compound units of the fluorine-based polymer are included in an amount of 0.01% to 5.0% by weight, based on the total weight of the polymer.

[0026]

[10] The conductive agent dispersion of at least one of the above [1] to [9], wherein the weight average molecular weight of the fluorine-based polymer can be 1,000,000 g / mol to 2,000,000 g / mol.

[0027]

[11] According to another embodiment of the present application, there is provided an electrode including 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 Formula 1 of 0.10 to 0.90.

[0028] [Formula 1]

[0029] D = [10 6 (1+W u )] / [M w (1+W s )(1+M H )]

[0030] In Formula 1, M w is a unitless number of a weight average molecular weight (g / mol) of the fluorine-based polymer, W u is a weight fraction of an unsaturated functional group unit in the fluorine-based polymer, W s is a weight fraction of a saturable residual compound unit in the fluorine-based polymer, and M H is a mole number of a heteroatom in the saturable residual compound unit, wherein the saturable residual compound unit is at least one selected from a saturated functional group unit and a comonomer unit.

[0031]

[12] According to another embodiment of the present application, there is provided a lithium secondary battery having a structure in which electrodes and separators are alternately stacked, wherein the electrode is the above-described electrode.

[0032] Advantageous Effects

[0033] The conductive agent dispersion according to the present application can have excellent dispersibility due to a small amount of carbon nanotubes having a large particle size and a low viscosity achieved by controlling a dispersion index defined by establishment of a relationship between factors affecting dispersibility in a fluorine-based polymer included as a dispersant, and can have excellent storage stability since a change in viscosity over time is small.

[0034] Further, by including the conductive agent dispersion in a slurry, phase stability of an electrode slurry can be improved, and since conductivity can be sufficiently ensured even using a small amount of carbon nanotubes, an electrode having a high energy density can be achieved.

[0035] Further, even if the amount of the conductive agent in the slurry is reduced due to excellent dispersibility, resistance can be improved, and thus a high-power battery can be achieved. DETAILED DESCRIPTION

[0036] It should be understood that the words or terms used in this specification and claims should not be interpreted as having the meanings defined in a conventional dictionary. It should be further understood that, based on the principle that the inventors may appropriately define the meanings of words or terms for the best interpretation of the invention, these words or terms should be interpreted as having meanings consistent with their meanings in the context of the relevant art and the technical concept of the invention.

[0037] It should be further understood that the terms “comprising,” “including,” or “having” in this specification specify the presence of the claimed features, quantities, steps, elements, or combinations thereof, but do not exclude the presence or addition of one or more other features, quantities, steps, elements, or combinations thereof.

[0038] In this specification, "specific surface area" is measured by the BET method, wherein, specifically, the specific surface area can be calculated from the amount of nitrogen adsorbed using BELSORP-mino II of BEL Japan Inc. at liquid nitrogen temperature (77 K).

[0039] D in this instruction manual 10 D 50 and D 90 These can be defined as the particle diameter at the 50% and 90% cumulative volume points in the particle diameter distribution curve, respectively. D 50 and D 90 For example, this can be measured using the laser diffraction method. Laser diffraction can typically measure particle diameters ranging from submicron to several millimeters and provides highly repeatable and high-resolution results.

[0040] In this specification, “weight-average molecular weight (Mw)” refers to the equivalent value of standard polystyrene as measured by gel permeation chromatography (GPC). Specifically, the weight-average molecular weight is obtained by converting values ​​measured using GPC under the conditions described below, and standard polystyrene from the Agilent system was used to prepare calibration curves.

[0041] <Measurement Conditions>

[0042] Measuring instrument: Agilent GPC (Agulent 1200 series, USA)

[0043] Column: Connects two PL Mixed B

[0044] Column temperature: 40℃

[0045] Eluent: Tetrahydrofuran

[0046] Flow rate: 1.0 mL / min

[0047] Concentration: ~1 mg / mL (100 μL injection)

[0048] Hereinafter, the present application will be described in detail.

[0049] In the present specification, each of the conductive agent dispersion, the electrode, and the lithium secondary battery includes at least one of the technical features and / or technical configurations described below, and these technical features and / or technical configurations can be combined in various ways.

[0050] Conductive agent dispersion

[0051] The conductive agent dispersion according to the embodiment of the present application includes a single-walled carbon nanotube 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.

[0052] [Formula 1]

[0053] D = [10 6 (1+W u )] / [M w (1+W s )(1+M H )]

[0054] In Formula 1, M w is a unitless number of a weight average molecular weight (g / mol) of the fluorine-based polymer, W u is a weight fraction of an unsaturated functional group in the fluorine-based polymer, W s is a weight fraction of a saturable residual compound unit in the fluorine-based polymer, M H is a mole number of a heteroatom in the saturable residual compound unit, wherein the saturable residual compound unit is at least one selected from a saturated functional group unit and a comonomer unit.

[0055] (1) Single-walled carbon nanotube

[0056] The graphite sheet of the carbon nanotube has a cylindrical shape, has a diameter of a nanometer size, and has sp 2The carbon nanotube has a key structure in which the carbon nanotube has a conductor or semiconductor property depending on the angle at which the structure and the graphite sheet are rotated. The carbon nanotube can be classified into a single-walled carbon nanotube (SWCNT), a double-walled carbon nanotube (DWCNT), and a multi-walled carbon nanotube (MWCNT) depending on the number of walls formed by the bond.

[0057] According to one embodiment of the present application, the conductive agent dispersion includes a single-walled carbon nanotube. Since the specific surface area of the single-walled carbon nanotube is greater than that of the multi-walled carbon nanotube, sufficient conductivity can be ensured even with the addition of a small amount, and thus the reduction in the electrode resistance can be significantly increased.

[0058] The D of the single-walled carbon nanotube can be 2 μm or less, specifically, 1.5 μm or less, 1.2 μm or less, 1.0 μm or less, 0.8 μm or less, 0.6 μm or less, or 0.5 μm or less. 50 The D can be 2 μm to 8 μm, specifically, 3 μm to 7 μm, 4 μm to 6 μm, or 5 μm to 6 μm. 50 The D can be 3 μm or more or 4 μm or more, specifically, 4 μm or more, 5 μm or more, 6 μm or more, or 7 μm or more. 50 The D can also be 7 μm or less or 6 μm or less, specifically, 6 μm or less, 5 μm or less, 4 μm or less, or 3 μm or less. 90 The D of the single-walled carbon nanotube can be 10 μm to 30 μm, specifically, 12 μm to 28 μm, 14 μm to 26 μm, 16 μm to 24 μm, or 18 μm to 22 μm. 90 The D can be 12 μm or more, 14 μm or more, 16 μm or more, or 18 μm or more, specifically, 18 μm or more, 20 μm or more, 22 μm or more, or 24 μm or more. 90 The D can also be 28 μm or less, 26 μm or less, 24 μm or less, or 22 μm or less, specifically, 22 μm or less, 20 μm or less, 18 μm or less, or 16 μm or less. Satisfying the above range means that the bundle-type carbon nanotube used as a raw material is effectively dispersed and present in the conductive agent dispersion, and thus the electrode and battery resistance is effectively improved.

[0059] The content of the carbon nanotube can be 0.4 parts by weight to 2.0 parts by weight, specifically, 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, and also 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, based on 100 parts by weight of the conductive agent dispersion. When the above range is satisfied, the electrode slurry is easily added and transferred while maintaining high productivity. In addition, since the solid content of the prepared electrode slurry is not excessively low, the occurrence of binder migration during the electrode drying process can be inhibited. Thus, the electrode adhesion can be improved, and since the packing of the electrode active material layer can be effectively achieved, an electrode having a small thickness can be prepared.

[0060] (2) Fluorine-based polymer

[0061] The conductive agent dispersion according to the embodiment of the present application includes a fluorine-based polymer, wherein the fluorine-based polymer is characterized in that a dispersion index (D) defined by the following Formula 1 satisfies a range of 0.10 to 0.90.

[0062] [Formula 1]

[0063] D = [10 6 (1+W u )] / [M w (1+W s )(1+M H )]

[0064] In Formula 1, M w is a unitless number of a weight average molecular weight (g / mol) of the fluorine-based polymer, W u is a weight fraction of an unsaturated functional group in the fluorine-based polymer, W s is a weight fraction of a saturable residual compound unit in the fluorine-based polymer, and M H is a mole number of a heteroatom in the saturable residual compound unit, wherein the saturable residual compound unit is at least one selected from a saturated functional group unit and a comonomer unit.

[0065] Regarding the dispersion index, a relationship between factors capable of affecting dispersion of the single-walled carbon nanotube by using the fluorine-based polymer as a dispersant is established, wherein the weight average molecular weight of the fluorine-based polymer, the amount of the unsaturated functional group in the fluorine-based polymer, and the amount of the saturable residual compound unit are considered.

[0066] How well a polymer used as a dispersant disperses the single-walled carbon nanotube can depend on how polar and nonpolar portions present in the polymer as a dispersant interact with the nonpolar carbon nanotube and the polar organic solvent.

[0067] The dispersion index reflects the weight fraction of the unsaturated functional group having a high degree of polarity in the fluorine-based polymer, while also reflecting the weight fraction of the saturable residual compound unit having a polarity but a relatively low degree of polarity than the unsaturated functional group, but in relation to the saturable residual compound unit, the mole number of the heteroatom (such as fluorine (F), nitrogen (N), phosphorus (P), or oxygen (O)) included in the unit also has an effect, which is balanced with the effect of the unsaturated functional group.

[0068] It is difficult to accurately determine the degree of dispersion of the single-walled carbon nanotube only with these factors, and it can also be necessary to reflect the effect of the polymer itself, rather than the effect of the unit in the polymer, for example, the weight average molecular weight is reflected as a factor reflecting the effect produced by steric hindrance or the overall size of the molecule.

[0069] The dispersion index thus derived can be regarded as an index that can more accurately confirm how well the single-walled carbon nanotubes are dispersed, and the dispersion index is characterized by 0.10 to 0.90. The dispersion index can preferably be 0.11 or more, 0.12 or more, or 0.13 or more, and can also be 0.85 or less, 0.80 or less, 0.75 or less, 0.70 or less, or 0.68 or less, and most preferably can be in the range of 0.14 to 0.67.

[0070] Since the dispersion index reflects various factors, as its value decreases, it is possible to provide a conductive agent dispersion having better dispersibility, but, in the case where the value is less than 0.10, since the weight average molecular weight is much greater than the amount of the unsaturated functional group, there is a concern that the contribution to the dispersion of the carbon nanotubes will decrease due to the attraction between the respective polymers, and since the influence of the saturable residual compound unit becomes greater than the influence of the unsaturated functional group, there is a concern that even if the viscosity of the dispersion decreases, aggregates of large particle size can be formed in the dispersion.

[0071] In the case where the dispersion index is greater than 0.90, since it is difficult to consider that the carbon nanotubes are properly dispersed, there is a problem in that the viscosity is high and the amount of particles of large particle size also increases.

[0072] The fluorine-based polymer can be at least one polymer selected from the group consisting of polyvinylidene fluoride (PVDF), polyperfluoroalkoxy (PFA), polytetrafluoroethylene (PTFE), and a copolymer thereof copolymerized with a comonomer, and can preferably be polyvinylidene fluoride. In the case where polyvinylidene fluoride is used for the dispersion of single-walled carbon nanotubes, since it has excellent affinity with the organic solvent used, it is possible to form a polymer solution, and as a result, there is an advantage of having excellent processability.

[0073] The fluorine-based polymer can include a carboxyl group as the unsaturated functional group, and the content of the unsaturated functional group can be 0.01 to 1.00% by weight based on the total weight of the polymer, the content can preferably be 0.02% by weight or more, 0.03% by weight or more, or 0.05% by weight or more, and the content can be 0.90% by weight or less, 0.80% by weight or less, preferably 0.75% by weight or less. The unsaturated functional group is a major factor that provides polarity, and it can be necessary to properly adjust the amount in order to contribute to the dispersion of the single-walled carbon nanotubes.

[0074] The fluorine-based polymer can include a saturable residual compound unit, which can refer to a saturated functional group and / or a comonomer unit. In the present invention, the expression "saturable residual compound unit" can refer to a residual compound unit other than the main monomer unit and the unsaturated functional group. The saturated functional group in the saturable residual compound unit can include an alkoxy group having 1 to 5 carbon atoms, and the comonomer unit can include at least one selected from the group consisting of hexafluoropropylene units and trifluorochloroethylene.

[0075] The content of the saturable residual compound unit can be 0.01 to 5.0% by weight, preferably 0.02% by weight or more, or 0.03% by weight or more, and also 4.0% by weight or less, 3.0% by weight or less, or 2.5% by weight or less, based on the total weight of the polymer. Furthermore, the number of moles of heteroatoms contained in the saturable residual compound unit can be in the range of 1 to 6, and this is taken together with the amount of the saturable residual compound unit, so that the effect of the saturable residual compound unit on dispersibility is reflected in proportion to the amount of the heteroatoms having a high electronegativity contained.

[0076] The weight average molecular weight of the fluorine-based polymer can be 1,000,000 to 2,000,000 g / mol. It can be desirable to control the weight average molecular weight so as not to be too small or too large to control the dispersity index to satisfy the above range.

[0077] The content of the fluorine-based polymer in the conductive agent dispersion can be 0.5 to 6.0 parts by weight, specifically 0.8 parts by weight or more, 1.0 parts 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, and also 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, based on 100 parts by weight of the conductive agent dispersion. When the above range is satisfied, the carbon-based conductive agent can be smoothly dispersed in the conductive agent dispersion, the energy density of the prepared electrode can be improved, and the resistance can be reduced.

[0078] The conductive agent dispersion can additionally include a dispersant other than the fluorine-based polymer, for example, can include a hydrogenated nitrile-based copolymer. The hydrogenated nitrile-based copolymer can be a copolymer including α,β-unsaturated nitrile-derived structural units and hydrogenated conjugated diene-derived structural units, or can be a copolymer including α,β-unsaturated nitrile-derived structural units, conjugated diene-derived structural units, and hydrogenated conjugated diene-derived structural units. The hydrogenated nitrile-based copolymer can be a hydrogenated nitrile-based butadiene rubber, specifically can be a hydrogenated acrylonitrile-butadiene rubber, more specifically can be a partially hydrogenated acrylonitrile-butadiene rubber.

[0079] (3) Modified silicone-based material

[0080] The conductive agent dispersion according to the embodiment of the present application can further include a modified polysiloxane-based material. The modified polysiloxane-based material can have a molecular weight of 4,000 g / mol to 8,000 g / mol, preferably 4,500 g / mol to 7,500 g / mol.

[0081] The modified polysiloxane-based material can be affected by the dispersion index of the fluorine-based polymer described above. In the case where the modified polysiloxane-based material is added together with the fluorine-based polymer having a dispersion index outside the range of 0.10 to 0.90, the effect of reducing viscosity can be expected, but the amount of particles having a large particle size can increase, thereby causing a problem of reduced dispersibility. However, in the case where the modified polysiloxane-based material is added together with the fluorine-based polymer satisfying the dispersion index, since the effect of reducing viscosity can be expected without reducing dispersibility, the effect of adding the modified polysiloxane-based material can be maximized, and thus, it is preferable to additionally add the modified polysiloxane-based material to reduce viscosity in consideration of the dispersion index.

[0082] The polysiloxane-based portion in the modified polysiloxane-based material can include a dialkylsiloxane as a monomer unit, and for the dialkylsiloxane, the alkyl group can have 1 to 5 carbon atoms. For example, polydimethylsiloxane, polymethylethylsiloxane, or polymethylpropylsiloxane can be used as the polysiloxane-based portion.

[0083] Preferably, the modified polysiloxane-based material can be a polyether-based modified polysiloxane-based material modified from a polyether-based material, in which case, the material can be modified in a form in which the polyether-based material is combined with an alkyl group. The polyether-based material can include homopolymers such as polyethylene glycol, propoxylated polyethylene glycol, polypropylene glycol, and ethoxylated polypropylene glycol; random copolymers thereof; or block copolymers thereof.

[0084] For example, the polyether-based modified polysiloxane-based material can be in the form of a block copolymer of the polyether-based material and the polysiloxane-based material. The modified polysiloxane-based material can be in the form in which the polyether-based material is distributed on one side, the polysiloxane-based material is distributed on the other side, and the two materials are connected by a covalent bond.

[0085] For example, the weight ratio of the polyether-based material to the polysiloxane-based material of the modified polysiloxane-based material can be in the range of about 95:5 to about 5:95, preferably 70:30 to 10:90, 60:40 to 10:90, 50:50 to 10:90, or 40:60 to 10:90, and more preferably 30:70 to 10:90.

[0086] Since the modified polysiloxane-based material has a polar portion and a non-polar portion in the molecule by the modification as described above, it can more actively interact with the fluorine-based polymer and the conductive agent, can further improve the dispersibility, and in particular, can significantly affect the dispersion index by interacting with the functional group portion of the fluorine-based polymer, so a significant synergistic effect can be expected.

[0087] (4) Organic solvent

[0088] The organic solvent can be an organic solvent containing one or more heteroatoms selected from the group consisting of a nitrogen atom (N) and an oxygen atom (O) having a lone pair of electrons.

[0089] Specifically, the organic solvent can 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 (isopropanol), 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 hexanediol; polyhydric alcohols such as glycerol, trimethylolpropane, pentaerythritol, or sorbitol; 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 cyclohexanone; and esters such as ethyl acetate, γ-butyrolactone, and ε-propylolactone, and any one of them or a mixture of two or more of them can be used. N-methylpyrrolidone (NMP) is particularly preferred in view of the compatibility with the electrode slurry.

[0090] In the conductive agent dispersion, the solid content of the conductive agent dispersion can be in the range of 1 to 10% by weight, particularly 2 to 8% by weight, more particularly 3.5 to 5.5% by weight. When the above range is satisfied, the dispersion of the conductive agent dispersion can be effectively achieved while the viscosity of the conductive agent dispersion can be maintained at a low level. Here, the solid content can mean the single-walled carbon nanotube and the fluorine-based polymer included in the conductive agent dispersion.

[0091] The conductive agent dispersion can be prepared by mixing the single-walled carbon nanotube, the fluorine-based polymer, and the organic solvent. In this case, the mixing can be performed using a general mixing method, specifically, a mixing device such as a homogenizer, a bead mill, a ball mill, a basket mill, a pin mill, or a TK mixer, and the mixing order of each component is not particularly limited. That is, the conductive agent dispersion according to the present application can be prepared by a method of adding and mixing the fluorine-based polymer after adding the single-walled carbon nanotube to the organic solvent, can be prepared by a method of mixing the single-walled carbon nanotube after first adding the fluorine-based polymer to the organic solution, and can be prepared by a method of adding the single-walled carbon nanotube and the fluorine-based polymer together to the organic solvent and then mixing.

[0092] The cavitation dispersion treatment can be performed in order to increase the dispersibility of the single-walled carbon nanotube in the above mixing process. The cavitation dispersion treatment is a dispersion treatment method using a shock wave generated by the rupture of a vacuum bubble formed in water when high energy is applied to a liquid, in which the above method can disperse the single-walled carbon nanotube without damaging the properties of the single-walled carbon nanotube. Specifically, the cavitation dispersion treatment can be performed by ultrasonic waves, jet milling, or shear dispersion treatment.

[0093] Electrode

[0094] The electrode according to another embodiment of the present application includes an electrode active material, a single-walled carbon nanotube, and a fluorine-based polymer, in which the dispersion index of the fluorine-based polymer is the same as described above.

[0095] The electrode can include a current collector and an electrode active material layer disposed on the current collector, which can include an electrode active material, a single-walled carbon nanotube, and a fluorine-based polymer.

[0096] The electrode active material layer can be formed of an electrode slurry composition including an electrode active material, a conductive agent dispersion, and a binder. Specifically, the electrode includes an electrode current collector and an electrode active material layer formed on the electrode current collector, and the electrode active material layer can be formed of an electrode slurry composition including an electrode active material, a conductive agent dispersion, and a binder.

[0097] In this case, the conductive agent dispersion is the above-described conductive agent dispersion according to the present application. Since the contents of the conductive agent dispersion are the same as those described above, a detailed description thereof will be omitted, and hereinafter, only the other components will be described.

[0098] The electrode current collector is not particularly limited as long as it has electrical conductivity and does not cause chemical changes in the battery, and, for example, copper, stainless steel, aluminum, nickel, titanium, alloys thereof, these materials subjected to surface treatment with carbon, nickel, titanium, silver, or the like, or sintered carbon can be used.

[0099] The electrode current collector can typically have a thickness of 3 μm to 500 μm, and micro irregularities can be formed on the surface of the current collector to improve adhesion of the negative electrode active material. In addition, the electrode current collector, for example, can be used in various shapes such as films, sheets, foils, meshes, porous bodies, foam bodies, non-woven fabric bodies, and the like.

[0100] The electrode active material (a) included in the electrode active material layer can be a positive electrode active material or a negative electrode active material generally used in the art, but the type thereof is not particularly limited.

[0101] For example, as the positive electrode active material, a lithium oxide including lithium and at least one metal such as cobalt, manganese, nickel, or aluminum can be used. Specifically, the lithium oxide can include a lithium manganese-based oxide (e.g., LiMnO2, LiMn2O4, or the like), a lithium cobalt-based oxide (e.g., LiCoO2, or the like), a lithium nickel-based oxide (e.g., LiNiO2, or the like), a lithium nickel-manganese-based oxide (e.g., LiNi 1- Y1 Mn Y1 O2(wherein 0 < Y1 < 1), LiMn 2-Z1 Ni Z1 O4(wherein 0 < Z1 < 2), or the like), a lithium nickel-cobalt-based oxide (e.g., LiNi 1-Y2 Co Y2 O2(wherein 0 < Y2 < 1), a lithium manganese-cobalt-based oxide (e.g., LiCo 1-Y3 Mn Y3 O2(wherein 0 < Y3 < 1), LiMn 2-Z2 Co Z2 O4(wherein 0 < Z2 < 2), or the like), a lithium nickel-manganese-cobalt-manganese-based oxide (e.g., Li(Ni P1 Co Q1 Mn R1 )O2(wherein 0 < P1 < 1, 0 < Q1 < 1, 0 < R1 < 1, and P1 + Q1 + R1 = 1) or Li(Ni P2 Co Q2 Mn R2 )O4(wherein 0 < P2 < 2, 0 < Q2 < 2, 0 < R2 < 2, and P2 + Q2 + R2 = 2), or the like), or a lithium nickel-cobalt-manganese transition metal (M) oxide (e.g., Li(Ni P3 Co Q3 Mn R3 M1 S )O2(wherein M 1 is 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 each independent element, wherein 0 < P3 < 1, 0 < Q3 < 1, 0 < R3 < 1, 0 < S < 1, and P3 + Q3 + R3 + S = 1), and can include any one thereof or a mixture of two or more thereof.

[0102] The negative active material, for example, can include a carbonaceous material such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; a metal compound that can form an alloy with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; a metal oxide that can be doped with or without lithium such as SnO (0 < v < 2), SnO2, vanadium oxide, and lithium vanadium oxide; or a composite including a metal compound and a carbonaceous material such as a Si-C composite or a Sn-C composite, and any one thereof or a mixture of two or more thereof can be used. In addition, a metal lithium thin film can be used as the negative active material. Furthermore, both low-crystalline carbon and high-crystalline carbon can be used as the carbon material. v (0 < v < 2), SnO2, vanadium oxide, and lithium vanadium oxide; or a composite including a metal compound and a carbonaceous material such as a Si-C composite or a Sn-C composite, and any one thereof or a mixture of two or more thereof can be used. In addition, a metal lithium thin film can be used as the negative active material. Furthermore, both low-crystalline carbon and high-crystalline carbon can be used as the carbon material.

[0103] The electrode active material can be included in an amount of 90 to 99% by weight, preferably 95 to 99% by weight, based on the total solid content of the electrode slurry composition. When the amount of the electrode active material satisfies the above range, excellent energy density, electrode adhesion, and electrical conductivity can be achieved.

[0104] The binder serves to secure adhesion between the electrode active materials and adhesion of the electrode active material to the current collector, wherein a conventional binder used in the art can be used, and the type thereof is not particularly limited. The binder, for example, can include polyvinylidene fluoride (PVDF), vinylidene-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluoro rubber, or various copolymers thereof, and any one thereof or a mixture of two or more thereof can be used.

[0105] The binder can be included in an amount of 5% by weight or less, preferably 1 to 3% by weight, based on the total solid content of the electrode slurry composition. In the case where the amount of the binder satisfies the above range, excellent electrode adhesion can be achieved while minimizing an increase in electrode resistance.

[0106] If necessary, the electrode slurry composition can further include a solvent for viscosity control. In this case, the solvent can be water, an organic solvent, or a mixture thereof. The organic solvent, for example, can include an amide-based polar organic solvent such as dimethylformamide (DMF), diethylformamide, dimethylacetamide (DMAc), and N-methylpyrrolidone (NMP); an alcohol such as methanol, ethanol, 1-propanol, 2-propanol (isopropanol), 1-butanol (n-butanol), 2-methyl-1-propanol (isobutanol), 2-butanol (sec-butanol), 1-methyl-2-propanol (tert-butanol), pentanol, hexanol, heptanol, or octanol; a glycol such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,5-pentanediol, or hexanediol; a polyol such as glycerol, trimethylolpropane, pentaerythritol, or sorbitol; a glycol ether 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; a ketone such as acetone, methyl ethyl ketone, methyl propyl ketone, or cyclohexanone; and an ester such as ethyl acetate, γ-butyrolactone, and ε-propylolactone, and any one thereof or a mixture of two or more thereof can be used, but the present application is not limited thereto.

[0107] The solvent can be included in an amount such that the solid content in the electrode slurry is in the range of 60 to 85% by weight, preferably 65 to 80% by weight. When the above range is satisfied, binder migration can be inhibited to improve electrode adhesion, the drying temperature can be lowered to improve coatability, and the coating speed can be increased to improve productivity.

[0108] The electrode according to the present application can be prepared by coating and drying the electrode slurry composition including the above-described components to form an electrode active material layer. Specifically, the electrode active material layer can be prepared by a method of coating the electrode slurry on an electrode current collector and drying the coated electrode current collector, or can be manufactured by a method of casting the electrode slurry on a separate carrier and then laminating the film separated from the carrier on the electrode current collector. If necessary, the electrode active material layer is formed by the above-described method, and then a rolling process can be further performed. In this case, the drying and rolling can be performed under suitable conditions in consideration of the physical properties of the finally prepared electrode, and are not particularly limited.

[0109] <Secondary lithium battery>

[0110] A lithium secondary battery according to another embodiment of the present application has a structure in which electrodes and separators are alternately stacked, and the electrode includes the above-described electrode. Specifically, a secondary battery according to the present application can include a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte, and in this case, the positive electrode can be the electrode of the above-described embodiment.

[0111] Since the electrode according to the present application has been described above, a detailed description thereof will be omitted, and hereinafter, only other components will be described.

[0112] The separator separates the negative electrode and the positive electrode and provides a moving path of lithium ions, and any separator can be used as the separator without particular limitation as long as it is typically used in a secondary battery. Specifically, a porous polymer film, for example, a porous polymer film prepared from a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butylene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminate structure having two or more layers thereof can be used as the separator. In addition, a typical nonwoven fabric, for example, a nonwoven fabric formed of high-melting point glass fibers or polyethylene terephthalate fibers can be used. In addition, a coated separator including a ceramic component or a polymer material can be used to secure heat resistance or mechanical strength, and a separator having a single layer or a multi-layer structure can be selectively used.

[0113] The electrolyte can include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, or a molten-type inorganic electrolyte, which can be used in the preparation of a lithium secondary battery, but the present application is not limited thereto.

[0114] Specifically, the electrolyte can include a non-aqueous organic solvent and a metal salt.

[0115] As the non-aqueous organic solvent, for example, an aprotic solvent such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate can be used.

[0116] In particular, in carbonate-based organic solvents, since ethylene carbonate and propylene carbonate, which are cyclic carbonates, dissociate lithium salts well due to high dielectric constants as highly viscous organic solvents, cyclic carbonates can be preferably used, and since when the above cyclic carbonates are mixed with low-viscosity, low-dielectric constant linear carbonates such as dimethyl carbonate and diethyl carbonate in an appropriate ratio and used, electrolytes having high electric conductivity can be prepared, cyclic carbonates can be more preferably used.

[0117] A lithium salt can be used as the metal salt, and the lithium salt is a material that is easily dissolved in a nonaqueous organic solvent, in which, for example, at least one selected from the group consisting of 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 - may be used as the anion of the lithium salt.

[0118] To improve the life characteristics of the battery, suppress the decrease in the battery capacity, and increase the discharge capacity of the battery, in addition to the above-mentioned electrolyte components, at least one of the following additives can be further included in the electrolyte: for example, a halogenated alkylene carbonate-based compound such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, a cyclic ether, ethylenediamine, glyme, triamide hexaphosphate, a nitrobenzene derivative, sulfur, a quinonimine dye, an N-substituted oxazolidinone, an N,N-substituted imidazolidine, a glycol dialkyl ether, an ammonium salt, a pyrrole, 2-methoxyethanol, or aluminum trichloride.

[0119] EMBODIMENT

[0120] Hereinafter, embodiments of the present application will be described in detail in a manner that can be easily practiced by one of ordinary skill in the art to which the present application pertains. However, the present application can be embodied in many different forms, and should not be construed as being limited to the embodiments set forth herein.

[0121] Examples 1-1 to 1-3 and Comparative Examples 1-1 to 1-3

[0122] Two weight parts of polyvinylidene fluoride (PVDF) having the properties listed in Table 1 below as a fluorine-based polymer, one weight part of single-walled carbon nanotubes (Tuball, OcSiAl), and 97 weight parts of N-methylpyrrolidone were mixed, and then mixed using a mixer (BTM-50, disperser 1000 rpm / anchor 100 rpm) for 180 minutes. The mixed mixture was stirred for 30 minutes using a high-pressure homogenizer (MICRONOX, Picomax MN230A, pressure: 1,500 bar), thereby obtaining each conductive agent dispersion.

[0123] [Table 1]

[0124]

[0125] Experimental Example 1: Particle size analysis

[0126] The particle size of each conductive agent dispersion of the examples and comparative examples was analyzed by laser diffraction and is presented in Table 2. Specifically, after the conductive agent dispersion was dispersed in a solvent, the particle size distribution was calculated by measuring the difference in diffraction pattern due to particle size as the solution was introduced into a laser diffraction particle size measurement instrument (Malvern, Mastersizer 3000) and the particles passed through a laser beam. D 10 , D 50 , and D 90 .

[0127] Experimental Example 2: Viscosity analysis (immediately after preparation of the conductive agent dispersion)

[0128] The viscosity of the conductive agent dispersions prepared in the examples and comparative examples was measured using a viscometer (Brookfield, viscometer DV2T, LV) at 25°C and 12 rpm, and is presented in Table 2.

[0129] Experimental Example 3: Confirmation of viscosity increase during long-term storage

[0130] For the conductive agent dispersions prepared from the examples and comparative examples, the viscosity increase rate (%) according to the following formula was confirmed.

[0131] Viscosity increase rate (%) = { (viscosity of the conductive agent dispersion measured after storage for 4 weeks at 25°C - viscosity of the conductive agent dispersion measured immediately after preparation) / viscosity of the conductive agent dispersion measured immediately after preparation} x 100

[0132] [Table 2]

[0133]

[0134] With reference to Table 1, for Examples 1-1 to 1-3 having a dispersion index in the range of 0.1 to 0.9, it can be confirmed that the viscosity is low, the change in viscosity over time is small, and the average particle diameter at 90% of the cumulative volume is relatively small compared to the comparative examples.

[0135] Experimental Example 4: Evaluation of addition of modified polysiloxane-based material

[0136] In the conductive agent 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 as a dispersant, 0.5 parts by weight of a modified polysiloxane-based material having a molecular weight of 6,000 g / mol (modified by combining about 0.15 parts by weight of polydimethylsiloxane (PDMS) with about 0.85 parts by weight of polyethylene glycol) and 1.5 parts by weight of polyvinylidene fluoride were added to prepare the conductive agent dispersions of Examples 2-1 to 2-3 and Comparative Examples 2-1 to 2-3, and the viscosity and particle size properties were evaluated in the same manner as in Experimental Example 1-3, the results of which are presented in Table 3 below.

[0137] [Table 3]

[0138]

[0139] Referring to Table 3, it can be confirmed through Examples 2-1 to 2-3 that when the modified polysiloxane-based material is added to Examples 1-1 to 1-3 having a dispersion index of 0.10 to 0.90, there is an effect of reducing the viscosity, and it can be understood that such an effect also occurs in Comparative Examples 2-1 to 2-3, which are cases where the modified polysiloxane-based material is added to Comparative Examples 1-1 to 1-3 that do not satisfy the dispersion index.

[0140] However, for Comparative Examples 2-1 to 2-3, it can be confirmed that D 90 is significantly increased, and thus it can be understood that in the case where the dispersion index is not satisfied, the addition of the modified polysiloxane-based material can have a negative impact on the dispersibility.

Claims

1.A conductive agent dispersion including single-walled carbon nanotubes and a fluorine-based polymer, wherein the fluorine-based polymer has a dispersion index (D) defined by Formula 1 of 0.10 to 0.90: [Formula 1] D = [10 6 (1+W u ) ] / [M w (1+W s )(1+M H )] wherein In Formula 1, M w is the number of units of unsaturated functional groups in the fluorine-based polymer, W u is the number of units of unsaturated functional groups in the fluorine-based polymer, W s is the number of units of saturable residual compound in the fluorine-based polymer, M H is the number of units of saturable residual compound in the fluorine-based polymer, M 2.The conductive agent dispersion according to claim 1, further including a modified polysiloxane-based material. 3.The conductive agent dispersion according to claim 2, wherein the modified polysiloxane-based material has a molecular weight of 4,000 g / mol to 8,000 g / mol. 4.The conductive agent dispersion according to claim 2, wherein the modified polysiloxane-based material includes a polydialkylsiloxane, and the alkyl group has 1 to 5 carbon atoms. 5.The conductive agent dispersion according to claim 1, wherein the fluorine-based polymer is a polyvinylidene fluoride. 6.The conductive agent dispersion according to claim 1, wherein the unsaturated functional group of the fluorine-based polymer includes a carboxyl group. 7.The conductive agent dispersion according to claim 1, wherein the saturated functional group includes an alkoxy group having 1 to 5 carbon atoms, and the co-monomer unit includes at least one selected from the group consisting of hexafluoropropylene units and trifluorochloroethylene. 8.The conductive agent dispersion according to claim 1, wherein the unsaturated functional group of the fluorine-based polymer is included in an amount of 0.01 to 1.0% by weight, based on the total weight of the polymer. 9.The conductive agent dispersion according to claim 1, wherein the saturable residual compound unit of the fluorine-based polymer is included in an amount of 0.01 to 5.0% by weight, based on the total weight of the polymer. 10.The conductive agent dispersion according to claim 1, wherein the fluorine-based polymer has a weight average molecular weight of 1,000,000 g / mol to 2,000,000 g / mol. 11.An electrode including an electrode active material, single-walled carbon nanotubes, and a fluorine-based polymer, wherein the fluorine-based polymer has a dispersion index (D) defined by Formula 1 of 0.05 to 0.95: [Formula 1] In Formula 1, 12.A lithium secondary battery having a structure in which electrodes and separators are alternately stacked, D = [10 6 (1+W u )] / [M w (1+W s )(1+M H )] wherein, wherein the electrode is the electrode of claim 11. M w is the number of units of unsaturated functional units in the fluorine-based polymer, W u is the number of units of unsaturated functional units in the fluorine-based polymer, W s is the number of units of saturable residual compound units in the fluorine-based polymer, and M H is the number of moles of heteroatoms in the saturable residual compound units, wherein the saturable residual compound units are at least one selected from the group consisting of saturated functional units and comonomer units. ​ ​

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