Conductive material slurry, positive electrode, and secondary battery comprising same

Abstract

Disclosed is a conductive material slurry having excellent dispersion stability. According to one aspect, provided is a conductive material slurry comprising a conductive material, dispersants, and a solvent, wherein the dispersants include a first dispersant and a second dispersant which is different from the first dispersant, the first dispersant comprises a polymer having a heteroatom, and the second dispersant comprises a polymer having a group which is capable of hydrogen bonding.

Description

Challenger slurry, cathode, and secondary battery containing the same

[0001] The present disclosure relates to a conductive material slurry, and more specifically, to a conductive material slurry, a positive electrode, and a secondary battery including the same.

[0002] Since their emergence in the 1990s, secondary batteries have undergone steady research and development. Research and development is ongoing not only on the key components of secondary batteries—the cathode / anode active materials, electrolytes, and separators—but also on auxiliary components that complement and enhance their properties. To develop high-capacity secondary batteries, increased electrode thickness is essential, along with the formation of effective conductive paths to receive electrons from the current collector.

[0003] However, the electrical conductivity of the cathode active material is very low, limiting battery performance when used alone. To address this issue, a method has been developed that disperses the conductive material in a solvent and wet-mixes it to produce a conductive material slurry.

[0004] Meanwhile, graphene, a type of conductive material, has many functional groups (-OH, -COOH) on its surface, so when using a general dispersant, there was a problem that the dispersion stability of the conductive material slurry was low due to the high polarity and low hydrogen bonding strength of the solvent.

[0005] Furthermore, during the manufacturing process of the positive electrode, graphene, which should adhere to the surface of the positive electrode active material particles to exhibit conductivity, formed aggregations due to carbon-carbon attraction, resulting in graphitization. Consequently, to impart a conductive effect, a large amount of graphene had to be added when manufacturing the conductive material slurry. However, this large amount of graphene could not contribute to the battery's capacity, resulting in a lower energy density.

[0006] According to one aspect of the present invention, a conductive material slurry capable of improving dispersion stability of the conductive material slurry is provided.

[0007] According to another aspect of the present invention, a conductive slurry capable of lowering the internal resistance of a cell and increasing the capacity retention rate is provided.

[0008] According to another aspect of the present invention, a positive electrode is provided in which a conductive material is evenly disposed on the surface of positive electrode active material particles.

[0009] Another object of the present invention is to provide a secondary battery with improved electrochemical performance.

[0010] The purposes of the present invention are not limited to those mentioned above, and other unmentioned purposes and advantages of the present invention can be understood through the following description and will be more clearly understood through the embodiments of the present invention. Furthermore, it will be readily apparent that the purposes and advantages of the present invention can be realized by the means and combinations thereof described in the specification.

[0011] According to a first aspect of the present invention, a conductive material slurry is provided, comprising: a conductive material; a dispersant; and a solvent, wherein the dispersant comprises a first dispersant and a second dispersant different from the first dispersant, wherein the first dispersant comprises a polymer having a heteroatom, and the second dispersant comprises a polymer having a hydrogen-bondable group.

[0012] According to a second aspect of the present invention, in the first aspect, the conductive material may have a full width at half maximum (FWHM) of a peak attributable to a (002) crystal plane of 0.3 to 100 based on XRD (X-ray diffraction) analysis.

[0013] According to a third aspect of the present invention, in the first or second aspect, the conductive material may include at least one of graphene and carbon nanotubes.

[0014] According to a fourth aspect of the present invention, in the third aspect, the weight ratio of the graphene and the carbon nanotube may be 1:9 to 9:1.

[0015] According to a fifth aspect of the present invention, in the third or fourth aspect, the oxygen content of the graphene may be 10% or less based on EA (Elemental Analysis).

[0016] According to a sixth aspect of the present invention, in any one of the first to fifth aspects, the heteroatom may include at least one of a nitrogen atom, an oxygen atom, a sulfur atom, and a fluorine atom.

[0017] According to the seventh aspect of the present invention, in any one of the first to sixth aspects, the weight average molecular weight (M) of the first dispersant w ) can be 5,000 to 500,000 g / mol.

[0018] According to an eighth aspect of the present invention, in any one of the first to seventh aspects, the first dispersant is nitrile butadiene rubber, poly(ethylene oxide), poly(propylene oxide), poly(vinyl acetate), poly(butylene terephthalate), poly(ethylene naphthalate), polyvinylidene fluoride, polyetherimide, polyaryleneethernitrile, polyaryleneethersulfone, polyetheretherketone, polysulfone, polytetrafluoroethylene, polyphenylene sulfide. Poly(pentafluorostyrene), poly(phenylene oxide), polyacrylonitrile, poly(vinyl fluoride), polychlorotrifluoroethylene, polyimide, polycarbonate, poly(vinyl sulfone), poly(ethersulfone), poly(vinyl nitrile), polyacrylate, polymethacrylate, poly(vinyl acetate), polycaprolactone,It may include at least one selected from the group consisting of cellulose triacetate and polyvinylpyrrolidone.

[0019] According to a ninth aspect of the present invention, in any one of the first to eighth aspects, the hydrogen bondable group is a hydroxy group, a carboxyl group, a hydroperoxy group, a hemiacetal group, a hemiketal group, an oxime group, a phosphono group, a phosphate group, a carboxamide group, an amine group, a primary ketimine group, a primary aldimine group, a ketone group, a carbonate ester group, a carboalkoxy group, a methoxy group, a peroxy group, an ether group, an acetal group, a ketal group, an ortho-ester group, methylenedioxy group, ortho carbonate ester group, cyanic acid salt group, nitrate salt group, nitro-oxy group, sulfo group, thiono ester group, boronate group, borinate group, quaternary ammonium ion group, secondary ketimine group, secondary aldimine group, imide group, azide group, azo group,It may include at least one of an isocyanic acid salt group, an isonitrile group, a nitro group, a nitroso group, a carbam acid salt group, and an isothiocyanate group, and specifically, it may include at least one of a hydroxyl group and an amine group.

[0020] According to the tenth aspect of the present invention, in any one of the first to ninth aspects, the weight average molecular weight (M) of the second dispersant w ) can be from 10,000 to 350,000 g / mol.

[0021] According to an eleventh aspect of the present invention, in any one of the first to tenth aspects, the second dispersant is cellulose, ethyl cellulose, poly(vinyl alcohol), poly(acrylic acid), poly(methacrylic acid), cellulose acetate, cellulose nitrate, chitosan, cellulose propionate, cellulose acetate propionate, cellulose acetate butyrate, methyl cellulose, ethyl methyl cellulose, hydroxyethyl cellulose, Hydroxypropyl Cellulose, Hydroxyethylmethyl Cellulose, Hydroxypropylmethyl Cellulose, Ethyl Hydroxyethyl Cellulose, Polyhydroxyethylmethacrylate, Polyethyleneimine, Alginate, Polyhydroxyethylacrylate, Starch, Hyaluronic Acid, Pullulan, Pectin, Polyglycerol, Lignin, Xylan, Galactomannan,and may include at least one selected from the group consisting of polyhydroxystyrene.

[0022] According to a twelfth aspect of the present invention, in any one of the first to eleventh aspects, the weight ratio of the first dispersant and the second dispersant may be 1:0.4 to 1:2.3.

[0023] According to the 13th aspect of the present invention, in any one of the first to twelfth aspects, the content of the first dispersant may be 2.2 to 200 parts by weight, and the content of the second dispersant may be 1 to 90 parts by weight, with respect to 100 parts by weight of the conductive material.

[0024] According to a fourteenth aspect of the present invention, in any one of the first to thirteenth aspects, the solvent may include a polar aprotic solvent.

[0025] According to a fifteenth aspect of the present invention, in any one of the first to fourteenth aspects, the carbon content may be 82 wt% or more based on the total solid content of the conductive slurry.

[0026] According to a sixteenth aspect of the present invention, a positive electrode is provided, comprising: a conductive material; a dispersant; a positive electrode active material; and a binder; wherein the dispersant comprises a first dispersant and a second dispersant different from the first dispersant, the first dispersant comprises a polymer having a heteroatom, and the second dispersant comprises a polymer having a hydrogen-bondable group. Here, the positive electrode may be characterized by any one of the first to fifteenth aspects.

[0027] According to the 17th aspect of the present invention, in the 16th aspect, the positive electrode active material includes a lithium transition metal oxide, and the lithium transition metal oxide is Li x1 CoO2(0.5 <x1<1.3), Li x2 NiO2(0.5 <x2<1.3), Lix3 MnO2(0.5 <x3<1.3), Li x4 Mn2O4(0.5 <x4<1.3), Li x5 (Ni a1 Co b1 Mn c1 )O2(0.5 <x5<1.3, 0<a1<1, 0<b1<1, 0<c1<1, a1+b1+c1=1), Li x6 Ni 1-y1 Co y1 O2(0.5 <x6<1.3, 0<y1<1), Li x7 Co 1-y2 Mn y2 O2(0.5 <x7<1.3, 0≤y2<1), Li x8 Ni 1-y3 Mn y3 O2(0.5 <x8<1.3, O≤y3<1), Li x9 (Ni a2 Co b2 Mn c2 )O4(0.5 <x9<1.3, 0<a2<2, 0<b2<2, 0<c2<2, a2+b2+c2=2), Li x10 Mn 2-z1 Ni z1 O4(0.5 <x10<1.3, 0<z1<2), Li x11 Mn 2-z2 Co z2 O4(0.5 <x11<1.3, 0<z2<2), Li x12 CoPO4(0.5 <x12<1.3), Li x13 FePO4(0.5 <x13<1.3), Li A1 Ni B1 Co C1 Mn D1 Al E1 O2(A1=0.5 or more and 1.3 or less, B1+C1+D1+E1=1, 0 <B1<1, 0<C1<1, 0<D1<1, 0<E1<1), Li A2 Ni B2 Co C2 Al D2 O2(A2=0.5 or more and 1.3 or less, B2+C2+D2=1, 0 <B2<1, 0<C2<1, 0<D2<1) 및 Li A3 Mn B3Fe C3 PO4(0.5 <A3<1.3, B3+C3=1, 0<B3<1, 0<C3<1)로 이루어진 군에서 선택되는 적어도 하나 이상을 포함할 수 있다.

[0028] According to an eighteenth aspect of the present invention, a secondary battery is provided, comprising: a positive electrode according to the sixteenth or seventeenth aspect; a negative electrode; a separator interposed between the positive electrode and the negative electrode; and an electrolyte. Here, the secondary battery may be characterized by any one of the first to fifteenth aspects.

[0029] The solutions to the above problems do not enumerate all the features of the present invention. The various features of the present invention, along with their corresponding advantages and effects, can be understood in more detail by referring to the detailed description below.

[0030] According to one aspect of the present invention, the dispersion stability of a conductive material slurry can be improved by minimizing the phenomenon of conductive material agglomeration. Consequently, the internal resistance of a secondary battery can be reduced while simultaneously increasing capacity retention.

[0031] According to another aspect of the present invention, a positive electrode can be implemented in which a conductive material is evenly disposed on the surface of positive electrode active material particles.

[0032] According to another aspect of the present invention, a secondary battery having excellent electrochemical performance can be implemented.

[0033] In addition to the aforementioned effects, the specific effects of the present invention are described below along with the specific details for implementing the invention. Furthermore, the effects of the present invention are not limited to the effects described above and can be readily achieved by the means and combinations thereof described in the specification.

[0034] In this specification, singular expressions include plural expressions unless the context clearly indicates otherwise.

[0035] In this specification, “At least one of a, b and c” may include a, b or c alone, or a combination of two or more selected from the group consisting of a, b and c.

[0036] If multiple embodiments are described in this specification, the embodiments may be combined unless specifically stated otherwise. In this case, the effects of the present invention may be defined as including the effects derived from each embodiment and the effects resulting from the organic combination of the embodiments. For example, even if Embodiments 1 and 2 are described independently in this specification, Embodiments 1 and 2 may be organically combined with each other, unless the context clearly indicates otherwise, and the effects of the present invention may include the effects resulting from the combination of Embodiments 1 and 2.

[0037] The numerical range indicated by the term "to" in this specification refers to a numerical range that includes the values ​​described before and after the term as the lower limit and the upper limit, respectively. When multiple numerical values ​​are disclosed as the upper and lower limits of an arbitrary numerical range, the numerical range disclosed in this specification can be understood as any numerical range that has any one of the multiple lower limit values ​​and any one of the multiple upper limit values ​​as the lower limit and the upper limit, respectively. For example, when a to b, or c to d is described in the specification, it can be understood that a or more and b or less, a or more and d or less, c or more and d or less, or c or more and b or less is described.

[0038] As used herein, terms such as "about" or "substantially" mean a reasonable amount of variation from the term that does not significantly alter the final result. These terms may be interpreted to include a variation of at least ±5% or at least ±10%, provided that such variation does not alter the meaning of the term and render it invalid.

[0039] In this specification, "weight average molecular weight" or "number average molecular weight" refers to a standard polystyrene-converted molecular weight, which can be analyzed using a GPC (Gel permeation chromatography) device. For example, in the case of a GPC analysis method, the developing solvent may be Tetrahydrofuran (THF), the column may be PL Olexis from Polymer Laboratories, the sample concentration may be 5 mg / mL, the sample injection amount may be 100 ㎕, the flow rate may be 1 mL / min, the detector may be Agilent High Temperature RI detector, and the column temperature may be set to 40°C.

[0040] According to one aspect of the present invention, a conductive material slurry is provided, which comprises a conductive material; a dispersant; and a solvent, wherein the dispersant comprises a first dispersant and a second dispersant different from the first dispersant, wherein the first dispersant comprises a polymer having a heteroatom, and the second dispersant comprises a polymer having a hydrogen-bondable group. According to one aspect of the present invention, since the conductive material slurry comprises the first dispersant comprising a polymer having a heteroatom and the second dispersant comprising a polymer having a hydrogen-bondable group, the phenomenon of the conductive material agglomerating can be minimized, thereby improving the dispersion stability of the conductive material slurry. Accordingly, the internal resistance of a secondary battery can be lowered while simultaneously increasing the capacity retention rate.

[0041] Below, the configuration of the present invention is described in more detail.

[0042] 1. Challenger slurry

[0043] Challenge

[0044] The conductive material according to the present invention can have the function of increasing the conductivity between positive electrode active material particles or with a metal current collector, and can minimize the electrode binder included in the electrode slurry from acting as an insulator.

[0045] In some embodiments of the present invention, the conductive material may have a full width at half maximum (FWHM) of a peak attributable to the (002) crystal plane of 0.2 to 100, 0.3 to 99, 0.3 to 95, or 5 to 95, based on XRD (X-ray diffraction) analysis. Here, the full width at half maximum may refer to a width at a point where the maximum peak corresponding to the (002) crystal plane is half. According to some embodiments of the present invention, when the full width at half maximum in the (002) crystal plane of the conductive material satisfies the above numerical range, re-stacking within the graphene is reduced, and thus the effect of increasing conductivity between positive electrode active material particles or with a metal current collector can be further expressed.

[0046] The conductive material according to the present invention may include at least one of graphene and carbon nanotubes, specifically graphene and carbon nanotubes, and more specifically graphene and multi-walled carbon nanotubes. According to some embodiments of the present invention, by including graphene and multi-walled carbon nanotubes in the conductive material, the dispersion stability of the conductive material slurry is further improved, and at the same time, the conductivity between positive electrode active material particles or with a metal current collector is further increased, thereby significantly reducing the internal resistance of the cell.

[0047] In some embodiments of the present invention, the weight ratio of the graphene and the carbon nanotube (graphene: carbon nanotube) may be 0.5:9.5 to 9.5:0.5, 1:9 to 9:1, or 3:7 to 7:3. According to some embodiments of the present invention, when the weight ratio of the graphene and the carbon nanotube (graphene: carbon nanotube) satisfies the numerical range, the dispersion stability of the conductive slurry may be further improved, and at the same time, the internal resistance of the cell may be further reduced and the capacity retention rate may be further increased.

[0048] The graphene according to the present invention may include at least one of multilayer graphene, graphene oxide, and reduced graphene oxide, and specifically may include reduced graphene oxide. Here, the reduced graphene oxide is a two-dimensional planar structure having a hexagonal shape and having conductivity formed by reducing graphene oxide, and may be distinguished from multilayer graphene and graphene oxide. In some examples, the multilayer graphene may refer to graphene exfoliated by physical force, mainly graphene dispersed in a solvent and exfoliated by shear stress.

[0049] In some examples, the graphene may be thin-layer graphene manufactured by various exfoliation methods, such as graphene exfoliated using physical energy or shear stress, graphene synthesized by an epitaxy method, graphene synthesized by a chemical vapor deposition method, or Scotch tape of HOPG graphene.

[0050] In some embodiments of the present invention, the oxygen content of the graphene may be 10 wt% or less, 9 wt% or less, 8 wt% or less, 7 wt% or less, 6 wt% or less, 5 wt% or less, 3 wt% or less, 2 wt% or less, or 0.5 to 2 wt%. In some embodiments of the present invention, when the oxygen content of the graphene satisfies the numerical range, the rigidity and ductility of the graphene can be controlled, so that the performance of the conductive material can be better expressed. For example, the oxygen content in the graphene can be analyzed through an EA (Elemental Analysis) analysis method.

[0051] In some embodiments of the present invention, the carbon content of the graphene may be 80 wt% or more, 85 wt% or more, 90 wt% or more, or 92 to 98 wt%. In some embodiments of the present invention, the carbon content of the graphene satisfies the above numerical range, so that the sp of carbon 2 Bonding can facilitate the movement of electrons and ions. For example, the carbon content within the graphene can be analyzed using the Elemental Analyzer (EA) method.

[0052] In some embodiments of the present invention, the purity of the graphene may be 85% or more, 90% or more, or 95% or more. Here, impurities including metals, ash, and moisture may affect the purity of the graphene. According to some embodiments of the present invention, since the purity of the graphene satisfies the numerical range, the stability of the graphene may be improved and conductivity may be sufficiently implemented. For example, metal impurities included in the graphene may be analyzed through an inductively coupled plasma (ICP) analysis method, and non-metallic impurities may be analyzed through an elemental analyzer (EA) analysis method.

[0053] In some examples, the thickness of the graphene is not particularly limited, but may be 1 to 1,000 nm, 1 to 800 nm, 1 to 500 nm, 1 to 100 nm, 1 to 50 nm, 1 to 10 nm, or 1 to 3 nm. For example, in order to measure the thickness of the graphene, a method may be used in which a graphene dispersion liquid in which the graphene is dispersed is coated on a silicon wafer, and then the thickness is measured by scraping it with an atomic force microscope (AFM) tip.

[0054] In some examples, the method for producing the above graphene is not particularly limited, and may be a physical exfoliation method based on shear stress, a physical exfoliation method additionally using a surfactant or dispersant, an electrical exfoliation method using an electrode, or an oxidative exfoliation method using an oxidizing agent.

[0055] In some examples, the shape of the graphene is not particularly limited and may be any one selected from the group consisting of single-layer graphene, multi-layer graphene, and combinations thereof.

[0056] The carbon nanotube according to the present invention has a structure distinct from graphene, and has a large surface area, high electrical conductivity, and light weight, so that the conductivity of the conductive material slurry can be further improved.

[0057] The carbon nanotube according to the present invention may include at least one of a single-walled carbon nanotube and a multi-walled carbon nanotube, and specifically may include a multi-walled carbon nanotube.

[0058] In some examples, the length of the carbon nanotube is not particularly limited, but may be 10 to 20,000 nm, 10 to 2,000 nm, 10 to 1,000 nm, or 10 to 500 nm. Here, the length of the carbon nanotube may be the length of the major axis passing through the center of the carbon nanotube. For example, the length of the carbon nanotube may be measured by any one method selected from the group consisting of a transmission electron microscope, a Raman spectroscopy, and a combination thereof.

[0059] In some examples, the diameter of the carbon nanotube is not particularly limited, but may be 1 to 200 nm, 2 to 200 nm, 5 to 200 nm, or 50 to 200 nm. Here, the diameter of the carbon nanotube may refer to the diameter of a hollow tube shape. If the carbon nanotube is multi-walled, the diameter may be measured based on the outermost wall of the carbon nanotube. For example, the diameter of the carbon nanotube may be measured by any one method selected from the group consisting of a transmission electron microscope, a Raman spectroscopy, and a combination thereof.

[0060] In some embodiments of the present invention, the content of the conductive material may be 1 to 6 wt%, 2 to 6 wt%, 3 to 6 wt%, 3 to 5 wt%, or 3 to 4 wt% based on the total weight of the conductive material slurry. In some embodiments of the present invention, when the content of the conductive material satisfies the numerical range, the phenomenon of the conductive material being excessively aggregated in the conductive material slurry can be prevented, while the conductivity between positive electrode active material particles or with the metal current collector can be increased, and the binder can effectively be minimized from acting as an insulator.

[0061] dispersant

[0062] The dispersant according to the present invention can effectively prevent excessive agglomeration of the conductive material within the conductive material slurry, thereby improving the dispersion stability of the conductive material slurry. Accordingly, by manufacturing an electrode slurry using a conductive material slurry with excellent dispersion stability, a secondary battery with low internal cell resistance and excellent cycle stability can be realized.

[0063] The dispersant according to the present invention comprises a first dispersant comprising a polymer having a heteroatom. Specifically, by comprising a polymer having a heteroatom, the first dispersant can partially function as a hydrogen bond acceptor. Here, since the hydrogen bond acceptor of the first dispersant has polar properties, the dispersibility of the conductive material slurry can be further improved through interaction with the intramolecular polar groups of the solvent included in the conductive material slurry.

[0064] In some embodiments of the present invention, the heteroatom of the first dispersant may include at least one of a nitrogen atom, an oxygen atom, a sulfur atom, and a fluorine atom. According to some embodiments of the present invention, since the heteroatom includes at least one of a nitrogen atom, an oxygen atom, a sulfur atom, and a fluorine atom, the dispersibility of the conductive material slurry may be further improved through interaction with the polar group in the molecule of the solvent.

[0065] In some embodiments of the present invention, the weight average molecular weight (M) of the first dispersant w ) may be 4,000 to 600,000 g / mol, specifically 5,000 to 500,000 g / mol. Specifically, when the weight average molecular weight of the first dispersant satisfies the above numerical range, the dispersant is dissolved in the solvent, thereby further improving the dispersion stability of the conductive slurry, while lowering the internal resistance of the cell and increasing the capacity retention rate of the secondary battery.

[0066] In some examples, the first dispersant is not particularly limited, and specifically, Nitrile Butadiene Rubber, Poly(ethylene oxide), Poly(propylene oxide), Poly(vinyl acetate), Poly(butylene terephthalate), Poly(ethylene naphthalate), Polyvinylidene fluoride, Polyetherimide, Polyaryleneethernitrile, Polyaryleneethersulfone, Polyetheretherketone, Polysulfone, Polytetrafluoroethylene, Poly(phenylene sulfide), Poly(pentafluorostyrene), poly(phenylene oxide), polyacrylonitrile, poly(vinyl fluoride), polychlorotrifluoroethylene, polyimide, polycarbonate, poly(vinyl sulfone), poly(ethersulfone), poly(vinyl nitrile), polyacrylate, polymethacrylate, poly(vinyl acetate), polycaprolactone, cellulose triacetate,It may include at least one selected from the group consisting of polyvinylpyrrolidone, and specifically, it may include at least one of nitrile butadiene rubber, polyvinylidene fluoride, and polyetherimide.

[0067] The dispersant according to the present invention comprises a second dispersant different from the first dispersant. Herein, the second dispersant comprises a polymer having a hydrogen bondable group.

[0068] In this specification, the term "hydrogen-bonding group" may refer to a functional group capable of forming a hydrogen bond with a second dispersant and another intramolecular group. Specifically, the hydrogen-bonding group may be 1 H-NMR, 13 It can be analyzed through a combination of various chemical analysis methods such as C-NMR or FT-IR.

[0069] The second dispersant according to the present invention can form a hydrogen bond with the hydrogen bond acceptor of the first dispersant and the hydrogen bond acceptor of the solvent in the conductive material slurry by including a hydrogen bond-capable group, and can promote interaction (e.g., van der Waals attraction) with the conductive material by including a non-polar site as the main skeletal structure in the molecule. In addition, the second dispersant can also form a hydrogen bond with the conductive material. Accordingly, by minimizing aggregation of the conductive material in the conductive material slurry, the dispersion stability of the conductive material slurry can be further improved. Consequently, by combining the first and second dispersants according to the present invention, the conductive material can be evenly distributed on the surface of the positive electrode active material particles, and the conductivity of the positive electrode can be further improved, so that the internal resistance of the cell can be significantly reduced while at the same time exhibiting a high capacity retention rate at a high rate.

[0070] In some examples, the hydrogen bonding group of the second dispersant is not particularly limited and may be a functional group capable of forming a hydrogen bond with another molecule, and specifically, a hydroxy group, a carboxyl group, a hydroperoxy group, a hemiacetal group, a hemiketal group, an oxime group, a phosphono group, a phosphate group, a carboxamide group, an amine group, a primary ketimine group, a primary aldimine group, a ketone group, a carbonate ester group, a carboalkoxy group, a methoxy group, a peroxy group, an ether group, an acetal group, a ketal group, Ortho-ester group, methylenedioxy group, ortho carbonate ester group, cyanic acid salt group, nitrate salt group, nitro-oxy group, sulfo group, thiono ester group, boronate group, borinate group, quaternary ammonium ion group, secondary ketimine group, secondary aldimine group, imide group, azide group, azo group,It may include at least one of an isocyanic acid salt group, an isonitrile group, a nitro group, a nitroso group, a carbam acid salt group, and an isothiocyanate group.

[0071] In some examples, when the second dispersant comprises a main skeletal structure and one or more side chain groups bonded to the main skeletal structure, the hydrogen bondable group may be included in at least one of the side chain groups.

[0072] In some embodiments of the present invention, the weight average molecular weight (M) of the second dispersant w ) may be 5,000 to 500,000 g / mol, 5,000 to 450,000 g / mol, more than 5,000 g / mol and less than 450,000 g / mol, or 10,000 to 350,000 g / mol. Specifically, when the weight average molecular weight of the second dispersant satisfies the numerical range, the dispersion stability of the conductive slurry is excellent, the internal resistance of the cell is further reduced, and the capacity retention rate of the secondary battery can be further increased.

[0073] In some examples, the second dispersant is not particularly limited, but specifically includes Cellulose, Ethyl cellulose, Poly(vinyl alcohol), Poly(acrylic acid), Poly(methacrylic acid), Cellulose acetate, Cellulose nitrate, Chitosan, Cellulose propionate, Cellulose acetate propionate, Cellulose acetate butyrate, Methyl cellulose, Ethyl methyl cellulose, Hydroxyethyl cellulose, Hydroxypropyl cellulose, It may include at least one selected from the group consisting of Hydroxyethylmethyl Cellulose, Hydroxypropylmethyl Cellulose, Ethyl Hydroxyethyl Cellulose, Polyhydroxyethylmethacrylate, Polyethyleneimine, Alginate, Polyhydroxyethylacrylate, Starch, Hyaluronic Acid, Pullulan, Pectin, Polyglycerol, Lignin, Xylan, Galactomannan, and Polyhydroxystyrene.

[0074] In some embodiments of the present invention, when the second dispersing agent is ethyl cellulose, the degree of substitution of the ethyl cellulose may be 40 to 60%, 45 to 55%. Here, the degree of substitution may mean the ratio of R to the total -OR groups (wherein R is a hydrogen atom or an ethyl group) in the side chain of the ethyl cellulose polymer chain, in which R is substituted with an ethyl group. For example, the degree of substitution of the ethyl cellulose can be analyzed by gas chromatography analysis. According to some embodiments of the present invention, since the degree of substitution of the ethyl cellulose satisfies the numerical range, the hydroxyl group bonded to the side chain of the ethyl cellulose can act as a hydrogen bond donor and form a hydrogen bond with the hydrogen bond acceptor of the first dispersing agent and the hydrogen bond acceptor of the solvent. Furthermore, ethyl cellulose can promote interactions with the conductive agent (e.g., van der Waals forces) by incorporating non-polar carbon rings, which are non-polar sites, into its molecular backbone. This minimizes aggregation of the conductive agent within the conductive agent slurry, thereby further enhancing the dispersion stability of the conductive agent slurry.

[0075] The content of the dispersant according to the present invention may be 0.1 to 1.0 wt%, 0.2 to 0.9 wt%, 0.3 to 0.8 wt%, 0.4 to 0.7 wt%, or 0.5 to 0.6 wt% based on the total weight of the conductive material slurry. Specifically, when the content of the dispersant satisfies the above numerical range, the agglomeration of the conductive material in the conductive material slurry is minimized, thereby further improving the dispersion stability of the conductive material slurry and, at the same time, further improving the electrochemical performance of the cell.

[0076] In some embodiments of the present invention, the weight ratio of the first dispersant and the second dispersant (first dispersant:second dispersant) may be 1:0.05 to 1:4, 1:0.4 to 1:2.3, or 1:0.43 to 1:1. According to some embodiments of the present invention, when the weight ratio of the first and second dispersants satisfies the numerical range, the dispersion stability of the conductive slurry may be further improved, the internal resistance of the cell may be further reduced, and the capacity retention rate of the secondary battery may be further increased.

[0077] In some embodiments of the present invention, the content of the first dispersant may be 2.2 to 200 parts by weight, 5 to 100 parts by weight, 7 to 50 parts by weight, 10 to 30 parts by weight, or 12 to 20 parts by weight, based on 100 parts by weight of the conductive material.

[0078] In some embodiments of the present invention, the content of the second dispersant may be 1 to 90 parts by weight, 2 to 50 parts by weight, 3 to 40 parts by weight, 3 to 30 parts by weight, 3 to 10 parts by weight, or 3 to 7 parts by weight, per 100 parts by weight of the conductive material.

[0079] According to some embodiments of the present invention, when the contents of the first and second dispersants in the conductive material are within the above numerical range, the dispersion stability of the conductive material slurry can be further improved, the internal resistance of the cell can be further reduced, and the capacity retention rate of the secondary battery can be further increased.

[0080] menstruum

[0081] The solvent according to the present invention can be included in the conductive slurry to dissolve the dispersant.

[0082] In the present specification, the polar aprotic solvent may have a dielectric constant at 25°C of 5 or more, 6 or more, 7 or more, 8 or more, 9 or more, 10 or more, 11 or more, 12 or more, 13 or more, 15 or more, 20 or more, 25 or more, or 30 or more, and may have a pKa at 25°C of -2 or more, -1 or more, 0 or more, 1 or more, 5 or more, 10 or more, 15 or more, 20 or more, 25 or more, or 30 or more.

[0083] For example, the polar aprotic solvent may be a solvent having a dielectric constant of 5 or more and 40 or less at 25°C and a refractive index (nD20) of 1.35 or more and 1.5 or less.

[0084] The solvent according to the present invention may include a polar aprotic solvent that does not provide hydrogen cations when dissolved in water. In some examples, the polar aprotic solvent is not particularly limited, but may specifically include one or more of N-methyl-2-pyrrolidone, N,N-dimethylformamide, and N,N'-dimethylacetamide.

[0085] In some examples, the polar aprotic solvent may contain both a polar group capable of acting as an intramolecular hydrogen bond acceptor and an intramolecular non-polar site. According to some embodiments of the present invention, when the first and second dispersants are used as the dispersants, the affinity between the dispersants and the polar aprotic solvent is further enhanced, thereby further improving the dispersion stability of the conductive material slurry.

[0086] In some examples, the content of the solvent is not particularly limited and may be any content other than the composition described above.

[0087] Properties of the challenge slurry

[0088] In some embodiments of the present invention, based on the total solid content of the conductive slurry, the carbon content may be 82 wt% or more, 83 wt% or more, 84 wt% or more, 85 wt% or more, 86 wt% or more, 87 wt% or more, 88 wt% or more, 89 wt% or more, or 90 wt% or more. Here, the carbon content based on the total solid content of the conductive slurry may be analyzed using an elemental analyzer. According to some embodiments of the present invention, when the carbon content based on the total solid content of the conductive slurry satisfies the numerical range, the internal resistance of the cell may be further reduced and the capacity retention rate of the secondary battery may be improved.

[0089] In some embodiments of the present invention, the viscosity of the conductive slurry is 23°C and a shear rate of 50 s -1 It can be from 100 to 2,000 cps.

[0090] In some embodiments of the present invention, the dispersion stability index of the conductive slurry may be 0.72 or less, 0.65 or less, 0.60 or less, 0.50 or less, 0.45 or less, 0.42 or less, 0.41 or less, 0.40 or less, 0.39 or less, 0.31 or less, 0.30 or less, or 0.29 or less. For example, the dispersion stability index may be calculated by applying a centrifugal force of 2,100 to 2,200 G to the conductive slurry at 25°C, performing high-speed centrifugation and separation for 60 minutes, and then measuring the near-infrared transmittance profile for the conductive slurry (see Equation 1 below).

[0091] 2. Bipolar

[0092] According to another aspect of the present invention, a positive electrode is provided, comprising: a conductive material; a dispersant; a positive electrode active material; and a binder; wherein the dispersant comprises a first dispersant and a second dispersant different from the first dispersant, wherein the first dispersant comprises a polymer having a heteroatom, and the second dispersant comprises a polymer having a hydrogen-bondable group. The above-described portions and repeated descriptions are briefly described or omitted.

[0093] Specifically, the dispersant further includes a second dispersant different from the first dispersant, and the second dispersant may include a polymer having a hydrogen bondable group.

[0094] The positive electrode according to the present invention may include a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector.

[0095] For example, the positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. Specifically, the positive electrode current collector may be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, an aluminum-cadmium alloy, or the like. The positive electrode current collector may typically have a thickness of 6 to 20 μm.

[0096] For example, the positive electrode active material may include a lithium transition metal oxide. The lithium transition metal oxide may be Li x1 CoO2(0.5 <x1<1.3), Li x2 NiO2(0.5 <x2<1.3), Li x3 MnO2(0.5 <x3<1.3), Li x4 Mn2O4(0.5 <x4<1.3), Li x5 (Ni a1 Co b1 Mn c1 )O2(0.5 <x5<1.3, 0<a1<1, 0<b1<1, 0<c1<1, a1+b1+c1=1), Lix6 Ni 1-y1 Co y1 O2(0.5 <x6<1.3, 0<y1<1), Li x7 Co 1-y2 Mn y2 O2(0.5 <x7<1.3, 0≤y2<1), Li x8 Ni 1-y3 Mn y3 O2(0.5 <x8<1.3, O≤y3<1), Li x9 (Ni a2 Co b2 Mn c2 )O4(0.5 <x9<1.3, 0<a2<2, 0<b2<2, 0<c2<2, a2+b2+c2=2), Li x10 Mn 2-z1 Ni z1 O4(0.5 <x10<1.3, 0<z1<2), Li x11 Mn 2-z2 Co z2 O4(0.5 <x11<1.3, 0<z2<2), Li x12 CoPO4(0.5 <x12<1.3), Li x13 FePO4(0.5 <x13<1.3), Li A1 Ni B1 Co C1 Mn D1 Al E1 O2(A1=0.5 or more and 1.3 or less, B1+C1+D1+E1=1, 0 <B1<1, 0<C1<1, 0<D1<1, 0<E1<1), Li A2 Ni B2 Co C2 Al D2 O2(A2=0.5 or more and 1.3 or less, B2+C2+D2=1, 0 <B2<1, 0<C2<1, 0<D2<1) 및 Li A3 Mn B3 Fe C3 PO4(0.5 <A3<1.3, B3+C3=1, 0<B3<1, 0<C3<1)로 이루어진 군에서 선택되는 적어도 하나 이상을 포함할 수 있다.

[0097] For example, the binder used in the above anode is poly(vinylidene fluoride co-hexafluoropropylene), poly(vinylidene fluoride-co-trichloroethylene), poly(methylmethacrylate), poly(ethylhexylacrylate), poly(butylacrylate), poly(acrylonitrile), poly(vinylpyrrolidone), poly(vinyl acetate), poly(ethylene-co-vinyl acetate), poly(ethylene oxide), polyacrylate, cellulose acetate, cellulose acetate butyrate. Examples of such polymers include, but are not limited to, cellulose acetate propionate, cyano ethyl pullulan, cyano ethyl poly(vinylalcohol), cyanoethylcellulose, cyano ethylsucrose, pullulan, and carboxyl methyl cellulose.

[0098] 3. Secondary batteries

[0099] According to another aspect of the present invention, a secondary battery is provided, comprising: a cathode; a separator interposed between the cathode and the anode; and an electrolyte.

[0100] cathode

[0101] A method for manufacturing a negative electrode according to the present invention may include the steps of preparing a negative electrode slurry including a negative electrode active material, a conductive material, and a negative electrode binder; coating and drying the negative electrode slurry on at least one surface of a negative electrode current collector to form a negative electrode active material layer; and rolling the current collector on which the negative electrode active material layer is formed.

[0102] The above-described negative electrode current collector can serve as a passage to transfer electrons from the outside to cause an electrochemical reaction in the negative electrode active material or to receive electrons from the negative electrode active material and send them to the outside. For example, the negative electrode current collector may be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. Specifically, a transition metal that adsorbs carbon well, such as copper or nickel, may be used as the current collector. For example, the thickness of the negative electrode current collector may be 6 μm to 55 μm, but the thickness of the negative electrode current collector is not limited thereto.

[0103] In some embodiments of the present invention, the negative electrode slurry may further include at least one of a silicon-based negative electrode active material and a graphite-based active material. For example, the silicon-based negative electrode active material may be Si, SiOx(0 <x≤2), Si-C 복합체 및 Si-Y 합금(Y는 알칼리금속, 알칼리토금속, 전이금속, 13족 원소, 14족 원소 및 희토류 원소로 이루어진 군에서 선택된 어느 하나의 원소이다)으로 이루어진 군에서 선택되는 1종 이상을 포함할 수 있다. 예를 들어, 상기 흑연계 활물질은 인조흑연, 천연흑연, 흑연화탄소 섬유 및 흑연화 메조카본마이크로비드로 이루어진 군에서 선택되는 1종 이상을 포함할 수 있다.

[0104] The above-described negative electrode binder can suppress separation between negative electrode active material (silicon negative electrode active material) particles, or between the negative electrode and the current collector. A polymer commonly used in electrodes in the relevant technical field can be used as the negative electrode binder. This negative electrode binder may be, without limitation, the same as or different from the positive electrode binder.

[0105] membrane

[0106] The separation membrane according to the present invention may be composed of a porous substrate or may include a porous substrate and a coating layer.

[0107] The porous substrate according to the present invention can be a porous structure having high resistance to electrolyte and fine pore diameters, capable of providing a path for lithium ions to move while electrically insulating the negative electrode and the positive electrode to prevent short circuits.

[0108] Any organic or inorganic material having electrical insulation properties may be used as a constituent material of the porous substrate without particular limitation. The porous substrate may include, for example, at least one selected from the group consisting of polyolefin, polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyvinyl variether ether ketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalene, and may specifically include polyolefin. Polyolefin not only has excellent coatability, but also can increase the ratio of the electrode active material layer in the battery by making the separator thinner, thereby increasing the capacity per volume.

[0109] Specifically, the weight average molecular weight (Mw) of the polyolefin may be 100,000 to 500,000 g / mol. If the weight average molecular weight of the polyolefin is less than the above numerical range, it may be difficult to secure sufficient mechanical properties, and if it exceeds the above numerical range, the shutdown function may not be implemented or molding may become difficult. The shutdown function refers to the function of blocking the movement of ions and preventing thermal runaway of the battery by melting the thermoplastic resin and closing the pores of the porous substrate when the temperature of the secondary battery increases.

[0110] The thickness of the porous substrate may be, for example, 3 to 50 μm or 4 to 30 μm. If the thickness of the porous substrate is less than the numerical range, the function of the conductive barrier may not be sufficient, and if it exceeds the numerical range, the resistance of the separator may excessively increase.

[0111] The average diameter of the pores included in the porous substrate may be, for example, 10 to 100 nm. The pores included in the porous substrate have a structure that is interconnected with each other, so that gas or liquid can pass from one side of the porous substrate to the other side.

[0112] A separator according to another embodiment of the present invention can improve the mechanical strength and heat resistance of a separator for a secondary battery and can include a coating layer disposed on at least one surface of a porous substrate of a water-soluble polymer to increase ionic conductivity within the secondary battery.

[0113] The coating layer according to the present invention may include a binder polymer and inorganic particles.

[0114] The binder polymer according to the present invention can connect inorganic particles and stably fix them. The binder polymer may be, for example, polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, poly(ethylene-co-vinyl acetate), polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, One or more selected from the group consisting of cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methyl cellulose, acrylonitrile-styrene butadiene copolymer, polyimide, and styrene-butadiene rubber may be used in combination.

[0115] According to another embodiment of the present invention, the weight ratio of the inorganic particles and the binder polymer (inorganic particles: binder polymer) may be 50:50 to 99:1, specifically 70:30 to 95:5. If the content ratio of the inorganic particles to the binder polymer is less than the above numerical range, the content of the binder polymer may increase, thereby deteriorating the thermal stability improvement performance of the separator, and the pore size and porosity may decrease due to a decrease in the empty space formed between the inorganic particles, thereby causing a deterioration in the performance of the final battery, and if the content of the binder polymer is exceeded, the content of the binder polymer may be too small, thereby weakening the peeling resistance of the coating layer.

[0116] The inorganic particles according to the present invention can contribute to improving the mechanical strength and heat resistance of a separator for a secondary battery. Specifically, the inorganic particles are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles that can be used in the present invention can be used within the operating voltage range of the secondary battery to which they are applied (e.g., Li / Li). + There are no particular restrictions as long as no oxidation and / or reduction reaction occurs at a reference voltage of 0 to 5 V. For example, when using inorganic particles with a high dielectric constant, the ionic conductivity of the electrolyte can be improved by contributing to an increase in the degree of dissociation of the electrolyte salt, such as a lithium salt, in the liquid electrolyte.

[0117] For the reasons described above, the inorganic particles may be inorganic particles having a dielectric constant of 5 or more, inorganic particles having lithium ion transport capability, or a mixture thereof.

[0118] The inorganic particles having the dielectric constant of 5 or more are Al2O3, SiO2, ZrO2, AlO(OH), Al(OH)3, Mg(OH)2, BaSO4, TiO2, BaTiO3, Pb(Zr x Ti 1-x )O3(PZT, where 0 <x<1), Pb 1-x La x Zr 1-y Tiy O3(PLZT, where 0 < x < 1, 0 < y < 1), (1-x)Pb(Mg 1 / 3 Nb 2 / 3 )O 3-x It may be a mixture of one or more selected from the group consisting of PbTiO3 (PMN-PT, where 0 < x < 1), HfO2, SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, and SiC.

[0119] The inorganic particles having the above lithium ion transfer capability include lithium phosphate (Li3PO4), lithium titanium phosphate (Li x Ti y (PO4)3, 0< x < 2, 0 < y < 3), lithium aluminum titanium phosphate (Li x Al y Ti z (PO4)3, 0 < x < 2, 0 < y < 1, 0 < z < 3), (LiAlTiP) x O y Series glass (0 < x < 4, 0 < y < 13), lithium lanthanum titanate (Li x La y TiO3, 0 < x < 2, 0 < y < 3), lithium germanium thiophosphate (Li x Ge y P z S w , 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), lithium nitride (Li x N y , 0 < x <4, 0 < y < 2), SiS2 series glass(Li x Si y S z , 0 < x < 3, 0 < y < 2, 0 < z < 4) and P2S5 series glass(Li x P y S z, 0 < x < 3, 0 < y < 3, 0 < z < 7) may be a mixture of one or more selected from the group consisting of:

[0120] For example, the average particle diameter (D) of the above inorganic particles 50 ) may be 1 nm to 10 μm, specifically 10 nm to 2 μm, and more specifically 50 nm to 1 μm, for forming a coating layer of uniform thickness and having an appropriate porosity. The "average particle diameter (D 50 )" means the particle diameter at the 50% point of the cumulative distribution of the number of particles according to particle diameter. The above average particle diameter can be measured using the laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500) and measuring the difference in diffraction pattern according to particle size when the particles pass through the laser beam, thereby calculating the particle size distribution.

[0121] Specifically, the thickness of the coating layer may be 0.1 to 10 μm, specifically 1 to 3 μm, and more specifically 1.4 to 1.6 μm. When the thickness of the coating layer satisfies the above numerical range, the insulation and thermal stability of the separator can be increased, and the energy density of the battery can be improved.

[0122] electrolyte

[0123] The electrolyte according to the present invention may include a solvent and a lithium salt.

[0124] The solvent according to the present invention is, for example, propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone, ethyl methyl carbonate (EMC), gamma-buturolactone (GBL), fluoroethylene carbonate (FEC), methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, pentyl acetate, methyl propionate, propionic acid. It may be one or a mixture of two or more selected from the group consisting of ethyl, ethyl propionate and butyl propionate.

[0125] Lithium salt according to the present invention is, for example, NO3 - , F - , Cl - , Br - , I - , or PF6 - It may contain anions such as:

[0126] Performance

[0127] In some embodiments of the present invention, based on a half-cell sample including the positive electrode and lithium metal (Li metal) as an anode, the internal resistance of the cell measured in accordance with the cell internal resistance analysis method (Direct Current Internal Resistance, DCIR) may be about 27 Ω or less, about 24 Ω or less, about 15 Ω or less, about 11 Ω or less, about 10 Ω or less, about 9 Ω or less, about 8 Ω or less, about 7 Ω or less, about 6 Ω or less, about 5 Ω or less, or about 4.9 Ω or less, and specifically may be greater than 0 Ω and less than any one of the plurality of upper limits.

[0128] In some embodiments of the present invention, based on a half-cell sample including the positive electrode and lithium metal as an anode as described above, when 50 charge / discharge cycles are performed at a C-rate of 1C, the capacity retention may be about 71% or more, about 80% or more, about 85% or more, about 90% or more, about 91% or more, about 92% or more, about 93% or more, about 94% or more, about 95% or more, about 96% or more, or about 97% or more, and any one or more of the plurality of lower limits may be 100% or less.

[0129] Application

[0130] The secondary battery according to the present invention may be a cylindrical, square, or pouch-shaped secondary battery, but is not particularly limited as long as it corresponds to a charging / discharging device.

[0131] Another embodiment of the present invention can provide a battery module including the secondary battery as a unit cell and a battery pack including the same. The battery pack can be used as a power source for one or more medium- to large-sized devices selected from the group consisting of, for example, power tools; electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0132] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the present invention. However, this is merely an example, and the scope of the present invention is not limited by the following contents.

[0133] [Manufacturing Example 1: Manufacturing of a conductive slurry]

[0134] <Examples 1 to 11: Preparation of a conductive slurry containing first and second dispersants>

[0135] Step of preparing a first dispersant solution by dissolving the first dispersant in a solvent:

[0136] After adding 950 g of NMP (N-methyl-2-pyrrolidone) and 50 g of nitrile-butadiene rubber (NBR), which is a first dispersant, to a round-bottom flask, the mixture was stirred at 70°C for 5 hours to prepare a 5 wt% first dispersant solution.

[0137] Step of preparing a second dispersant solution by dissolving the second dispersant in a solvent:

[0138] After adding 950 g of NMP (N-methyl-2-pyrrolidone) and 50 g of ethyl cellulose (EC), a second dispersant, to a round bottom flask, the mixture was stirred at 70°C for 5 hours to prepare a 5 wt% solution of the second dispersant.

[0139] Step of stirring the challenge agent and the first and second dispersant solutions:

[0140] After mixing the conductive agent and the first and second dispersant solutions to have the composition and content described in Table 1 below, a preliminary conductive agent slurry was prepared by stirring at 1,000 to 2,000 rpm for 60 minutes using Dispermat (LC 55-E) equipment.

[0141] Step of manufacturing a conductive material slurry by high-pressure dispersing the above preliminary conductive material slurry:

[0142] The above preliminary conductive slurry was dispersed at 2,000 bar for 8 passes using a high-pressure disperser (MN400BF, Micronox) to produce a conductive slurry.

[0143] <Comparative Examples 1 to 4: Preparation of a conductive slurry containing only one of the first dispersant and the second dispersant>

[0144] A conductive slurry having the contents described in Table 1 below was prepared in the same manner as in Example 1, except that only one of the first and second dispersants was used.

[0145] Graphene (wt%) CNT 1) (wt%)Carbon black(wt%)First dispersant(NBR)(wt%) 2) Second dispersant (EC) (wt%) 3) Carbon content 4) Graphene (FWHM) 5)Graphene oxygen content (%) Comparative example 101.51.50.60 Comparative example 20300.60 Comparative example 33000.60 89.5% 112% Comparative example 430000.68 6.8% 112% Example 13000.57 0.039 0.0% 112% Example 23000.42 0.18 90.1% 112% Example 33000.30.38 9.9% 112% Example 43000.18 0.42 86.0% 112% Example 53000.120.48 87.2% 112% Example 63000.42 0.18--10% Example 73000.42 0.18 11% Example 8 3000.420.18 0.2 Example 9 3000.420.18 0.3 Example 10 3000.420.18 95 Example 11 3000.420.18 99 1) The aspect ratio is 15,000 and the BET surface area is 200 m 2 / g multi-walled carbon nanotubes2) NBR: Nitrile-butadiene rubber with a nitrile content of 60 wt% and a weight-average molecular weight of 120,000 g / mol3) EC: Ethyl cellulose with a degree of substitution (content of ethoxy groups) of 47.5 to 49.5% and a weight-average molecular weight of 70,000 g / mol4) Carbon content (wt%) relative to the total solids of the conductive slurry: analyzed using an elemental analyzer5) Half-width in the (002) crystal plane of graphene: analyzed by XRD analysis6) Oxygen content (wt%) of graphene: analyzed using an elemental analyzer

[0146] [Experimental Example 1: Evaluation of Dispersion Stability of a Conductive Slurry and Electrochemical Performance of a Half-Cell]

[0147] Measurement of the dispersion stability index of the challenge slurry

[0148] Using a dispersion stability analyzer (Lumisizer), a centrifugal force of 2,100 to 2,200 G was applied to the conductive material slurry at 25°C, and high-speed centrifugation and separation were performed for 60 minutes. The near-infrared transmittance profile of the conductive material slurry was then measured. Then, the dispersion stability index was calculated using Equation 1 below. A lower dispersion stability index indicates better dispersion stability of the conductive material slurry.

[0149] [Formula 1]

[0150] Dispersion stability index = [(A n -A f ) / (A l -A f )]

[0151] In the above equation 1, A n is the nth area in the silver transmittance profile, and A f is the area of ​​the initial profile in the transmittance profile and A l is the area of ​​the last profile in the transmittance profile, where n is an arbitrary value, the initial profile means the first profile after 5 seconds, and the last profile means the 720th profile after 60 minutes.

[0152] Electrochemical performance evaluation of half-cells

[0153] Preparation of half-cell samples:

[0154] The conductive slurry, cathode active material (NCM), and electrode binder (polyvinylidene fluoride, PVDF) manufactured by the method according to Manufacturing Example 1 were mixed in a weight ratio of 2:95:3, and then added to a solvent (N-methyl 2-pyrrolidone, NMP) to manufacture a cathode slurry having a total solid content of 70 wt%. The cathode slurry was coated on a cathode current collector (aluminum) having a thickness of 10 μm, and then dried at 90 ° C. for 30 minutes to manufacture a cathode. Lithium metal (Li metal) was used as the anode, and a polyethylene separator (thickness: 80 μm) was used as the separator, and an electrolyte (1.3 mol LiPF6, EC:EMC=3:7 (v / v) 95 vol% + FEC 5 vol%) was injected to manufacture a coin-type half-cell.

[0155] Evaluation method:

[0156] The internal resistance of the above half-cell was measured using the cell internal resistance analysis method (Direct Current Internal Resistance, DCIR), and the capacity retention was measured by performing 50 charge / discharge cycles at a C-rate of 1C, which is shown in Table 2 below.

[0157] Stability index of the cell internal resistance (DCIR, Ω) at 50 cycles Capacity retention rate (%) (1C / 1C) Comparative example 10.58 12.38 8.9 Comparative example 20.62 10.59 0.3 Comparative example 30.44 8.79 2.9 Comparative example 40.76 9.49 1.8 Exemplary example 10.41 7.79 3.1 Exemplary example 20.417.79 3.2 Exemplary example 30.47.69 3.1 Exemplary example 40.65 9.19 2.1 Exemplary example 50.72 9.39 1.9 Exemplary example 60.47.8 93.3 Exemplary example 70.62 3.97 1.3 Exemplary example 80.52 6.78 3.6 Exemplary example 90.417.89 3.2 Exemplary example 100.47.79 3.1 Exemplary example 110.417.99 3.3

[0158] Comparing Comparative Examples 1 to 4 and several Examples according to the combination relationship of the first dispersant including a polymer having a heteroatom and the second dispersant including a polymer having a hydrogen-bondable group in Table 2 above, several Examples including a conductive slurry including both the first and second dispersants showed superior dispersion stability compared to Comparative Examples 1 to 4, low internal resistance of cells manufactured with the conductive slurry, and relatively high capacity retention.

[0159] Comparing Examples 1 to 5 in terms of dispersion stability and cell performance of the conductive slurry according to the optimal weight ratio of the first and second dispersants in Table 2 above, Examples 1 to 3, which satisfy the weight ratio of the first and second dispersants of 1:2.3 or less, exhibited better dispersion stability, lower internal resistance of the cell, and higher capacity retention compared to Examples 4 and 5.

[0160] Comparing Examples 2, 6, and 7 in terms of the internal resistance and capacity retention rate of the cell according to the oxygen content of the graphene, it can be confirmed that the internal resistance of the cell is lowered and the capacity retention rate of the half-cell is increased when the oxygen content of the graphene is satisfied to be 10% or less.

[0161] [Manufacturing Example 2: Manufacturing of conductive slurries with different molecular weights of NBR]

[0162] A conductive slurry was prepared using the same method as Example 1, but containing the composition (unit: weight %) described in Table 3 below and the remaining solvent (N-methyl-2-pyrrolidone, NMP).

[0163] Graphene (wt%) CNT (wt%) Carbon black (wt%) NBR (wt%) EC (wt%) NBR Weight average molecular weight (g / mol) Example 1 2 3000.42 0.184,000 g / mol Example 1 3 000.42 0.185,000 g / mol Example 1 4 3000.42 0.185 00,000 g / mol Example 1 5 3000.42 0.186 00,000 g / mol Weight average molecular weight of EC: 70,000 g / mol

[0164] [Experimental Example 2: Evaluation of Dispersion Stability of a Conductive Slurry and Electrochemical Performance of a Half-Cell]

[0165] After evaluating the performance in the same manner as Experimental Example 1 above, the results are shown in Table 4 below.

[0166] Weight average molecular weight of NBR (g / mol) Dispersion stability index (Stability index) Cell internal resistance (DCIR, Ω) Capacity retention rate at 50 cycles (%) (1C / 1C) Example 1 24,000 g / mol 0.5 10.69 1.3 Example 1 35,000 g / mol 0.4 2 7.99 3.3 Example 1 45 00,000 g / mol 0.4 7.69 3 Example 1 5 600,000 g / mol Slurry cannot be manufactured (non-dissolved) Cell cannot be assembled Cell cannot be assembled

[0167] Referring to Table 4 above, when Examples 12 to 15 are compared with each other in terms of the dispersion stability of the conductive slurry and cell performance according to the weight average molecular weight of the nitrile-butadiene rubber, Examples 13 and 14, which satisfy the weight average molecular weight of the nitrile-butadiene rubber of more than 4,000 g / mol and less than 600,000 g / mol, exhibited superior dispersion stability of the conductive slurry, lower internal resistance of the cell, and higher capacity retention rate compared to Examples 12 and 15.

[0168] [Manufacturing Example 3: Manufacturing of a conductive slurry with different molecular weights of EC]

[0169] A conductive slurry was prepared using the same method as Example 1, but including the composition (unit: weight %) described in Table 5 below and the remaining solvent (N-methyl-2-pyrrolidone, NMP).

[0170] Graphene (wt%) CNT (wt%) Carbon black (wt%) NBR (wt%) EC (wt%) Weight average molecular weight of EC (g / mol) Example 16 3000.42 0.185,000 g / mol Example 17 3000.42 0.1810,000 g / mol Example 18 3000.42 0.18350,000 g / mol Example 19 3000.42 0.18450,000 g / mol Weight average molecular weight of NBR: 120,000 g / mol

[0171] [Experimental Example 3: Evaluation of Dispersion Stability of a Conductive Slurry and Electrochemical Performance of a Half-Cell]

[0172] After evaluating the performance in the same manner as Experimental Example 1 above, the results are shown in Table 6 below.

[0173] Weight average molecular weight of EC (g / mol) Dispersion stability index (Stability index) Cell internal resistance (DCIR, Ω) Capacity retention rate at 50 cycles (%) (1C / 1C) Example 16 5,000 g / mol 0.6 9.5 9 1 Example 17 10,000 g / mol 0.4 7.7 9 3.2 Example 18 350,000 g / mol 0.3 9 7.6 9 2.9 Example 19 450,000 g / mol Slurry cannot be manufactured (non-dissolved) Cell cannot be assembled Cell cannot be assembled

[0174] In Table 6 above, Examples 17 and 18, which satisfy the weight average molecular weight of ethyl cellulose of more than 5,000 g / mol and less than 450,000 g / mol, exhibited excellent dispersion stability of the conductive slurry, low internal resistance of the cell, and high capacity retention compared to Examples 16 and 19.

[0175] [Manufacturing Example 4: Manufacturing of a conductive slurry with different molecular weights of EC]

[0176] A conductive slurry was prepared using the same method as Example 1, but including the composition (unit: weight %) described in Table 7 below and the remaining solvent (N-methyl-2-pyrrolidone, NMP).

[0177] Here, the degree of substitution of ethyl cellulose can mean the ratio of R to the total -OR groups (where R is a hydrogen atom or an ethyl group) in the side chain of the polymer chain of ethyl cellulose, in which R is substituted with an ethyl group. Here, the degree of substitution of ethyl cellulose can be analyzed by gas chromatography analysis.

[0178] Graphene (wt%) CNT (wt%) Carbon black (wt%) NBR (wt%) EC (wt%) Degree of substitution of EC (%) Example 20 3000.42 0.18 40~45% Example 21 3000.42 0.18 45~50% Example 22 3000.42 0.18 50~55% Example 23 3000.42 0.18 55~60% Weight average molecular weight of NBR: 120,000 g / mol Weight average molecular weight of EC: 70,000 g / mol

[0179] [Experimental Example 4: Evaluation of Dispersion Stability of a Conductive Slurry and Electrochemical Performance of a Half-Cell]

[0180] After evaluating the performance in the same manner as Experimental Example 1 above, the results are shown in Table 8 below.

[0181] Classification EC Substitution Degree (%) Dispersion Stability Index Cell Internal Resistance (DCIR, Ω) 50 Cycle Capacity Retention Rate (%) (1C / 1C) Example 2 40~45% 0.417.79 3.2 Example 2 1 45~50% 0.47.69 3.1 Example 2 50~55% 0.47.89 3.2 Example 2 3 55~60% 0.417.793

[0182] [Manufacturing Example 5: Manufacturing of conductive slurry using different types of dispersants]

[0183] A conductive slurry was prepared using the same method as Example 1, but the dispersant was changed to the composition described in Table 9 below.

[0184] Graphene (wt%)CNT (wt%)Carbon black (wt%)First dispersant (wt%)Second dispersant (wt%)Example 243000.48(PVDF)0.12(EC)Example 253000.48(PEI)0.12(EC)Example 263000.51(NBR)0.09(PAA)Example 273000.54(NBR)0.06(PVA)PVDF: Polyvinylidene fluoride with a weight average molecular weight of 1,300,000 g / molEC: Ethyl cellulose with a weight average molecular weight of 70,000 g / molPEI: Polyetherimide with a weight average molecular weight of 25,000 g / molNBR: Nitrile-butadiene rubber with a weight average molecular weight of 120,000 g / molPVA: Polyvinyl alcohol with a molecular weight of 31,000 to 50,000 g / mol

[0185] [Experimental Example 5: Evaluation of Dispersion Stability of a Conductive Slurry and Electrochemical Performance of a Half-Cell]

[0186] After evaluating the performance in the same manner as Experimental Example 1 above, the results are shown in Table 10 below.

[0187] Dispersion stability index (Stability index) Cell internal resistance (DCIR, Ω) 50 cycle capacity retention rate (%) (1C / 1C) Example 240.427.993.1 Example 250.41893 Example 260.47.793.1 Example 270.417.993.1

[0188] [Manufacturing Example 6: Manufacturing of conductive slurry using two types of conductive materials and two types of dispersants]

[0189] A conductive slurry was prepared using the same method as Example 1, but with the composition described in Table 11 below.

[0190] Classification Graphene (wt%) CNT (wt%) Carbon Black (wt%) NBR (wt%) EC (wt%) Example 28 2.85 0.15 00.42 0.18 Example 29 2.7 0.30 0.42 0.18 Example 30 2.10 9 0.42 0.18 Example 31 1.5 1.5 00.42 0.18 Example 320.9 2.10 0.42 0.18 Example 33 0.32 7 00.42 0.18 Example 34 0.15 2.8 5 00.42 0.18

[0191] [Experimental Example 6: Evaluation of Dispersion Stability of a Conductive Slurry and Electrochemical Performance of a Half-Cell]

[0192] After evaluating the performance in the same manner as Experimental Example 1 above, the results are shown in Table 12 below.

[0193] Weight ratio (graphene: CNT) Dispersion stability index (Stability index) Cell internal resistance (DCIR, Ω) 50 cycle capacity retention rate (%) (1C / 1C) Example 28 9.5: 0.5 0.4 5 9.1 94.2 Example 299: 10.2 95.7 97.7 Example 307: 30.3 5.2 97.6 Example 315: 50.3 15 97.6 Example 323: 70.3 4.9 97.7 Example 331: 90.2 94.9 97.6 Example 340.5: 9.5 0.4 6 7.6 91.3

[0194] Referring to Table 12 above, Examples 29 to 33, in which the weight ratio of graphene and CNT was 9:1 to 1:9, showed better dispersion stability of the conductive slurry, lower internal resistance of the cell, and higher capacity retention rate compared to Examples 28 and 34.

[0195] Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concept of the present invention defined in the following claims also fall within the scope of the present invention.

Claims

1. Challenge; dispersant; and solvent; including, The above dispersant is, Comprising a first dispersant and a second dispersant different from the first dispersant, The first dispersant comprises a polymer having a heteroatom, The second dispersant comprises a polymer having a hydrogen bonding capable group. Challenger slurry.

2. In paragraph 1, The above challenge is, According to XRD (X-ray diffraction) analysis, the full width at half maximum (FWHM) of the peak due to the (002) crystal plane is 0.3 to 100. Challenger slurry.

3. In paragraph 1, The above challenge is, Comprising at least one of graphene and carbon nanotube, Challenger slurry.

4. In paragraph 3, The weight ratio of the above graphene and the above carbon nanotube is 1:9 to 9:1, Challenger slurry.

5. In paragraph 3, According to EA (Elemental Analysis), the oxygen content of the graphene is 10 wt% or less. Challenger slurry.

6. In paragraph 1, The above heteroatoms are, Containing at least one of a nitrogen atom, an oxygen atom, a sulfur atom, and a fluorine atom, Challenger slurry.

7. In paragraph 1, The weight average molecular weight (M) of the first dispersant w ) is 5,000 to 500,000 g / mol, Challenger slurry.

8. In paragraph 1, The above first dispersant is, Nitrile Butadiene Rubber, Poly(ethylene oxide), Poly(propylene oxide), Poly(vinyl acetate), Poly(butylene terephthalate), Poly(ethylene naphthalate), Polyvinylidene fluoride, Polyetherimide, Polyaryleneethernitrile, Polyaryleneethersulfone, Polyetheretherketone, Polysulfone, Polytetrafluoroethylene, Poly(phenylene sulfide), Poly(pentafluorostyrene), Poly(phenylene oxide) oxide), polyacrylonitrile, poly(vinyl fluoride), polychlorotrifluoroethylene, polyimide, polycarbonate, poly(vinyl sulfone), poly(ethersulfone), poly(vinyl nitrile), polyacrylate, polymethacrylate, poly(vinyl acetate), polycaprolactone, cellulose triacetate,and at least one selected from the group consisting of polyvinylpyrrolidone, Challenger slurry.

9. In paragraph 1, The above hydrogen bondable group is, Hydrox group, carboxyl group, hydroperoxy group, hemiacetal group, hemiketal group, oxime group, phosphono group, phosphate group, carboxamide group, amine group, primary ketimine group, primary aldimine group, ketone group, carbonate ester group, carboalkoxy group, methoxy group, peroxy group, ether group, acetal group, ketal group, ortho-ester group, methylenedioxy group, ortho carbonate ester group, A cyanic acid salt group, a nitrate salt group, a nitro-oxy group, a sulfo group, a thiono ester group, a boronate group, a borinate group, a quaternary ammonium ion group, a secondary ketimine group, a secondary aldimine group, an imide group, an azide group, an azo group, an isocyanic acid salt group, an isonitrile group, a nitro group,Containing at least one of a nitroso group, a carbamate salt group, and an isothiocyanate group, Challenger slurry.

10. In paragraph 1, The weight average molecular weight (M) of the second dispersant w ) is 10,000 to 350,000 g / mol, Challenger slurry.

11. In paragraph 1, The second dispersant is, Cellulose, Ethyl cellulose, Poly(vinyl alcohol), Poly(acrylic acid), Poly(methacrylic acid), Cellulose acetate, Cellulose nitrate, Chitosan, Cellulose propionate, Cellulose acetate propionate, Cellulose acetate butyrate, Methyl cellulose, Ethyl methyl cellulose, Hydroxyethyl cellulose, Hydroxypropyl cellulose, Hydroxyethylmethyl A composition comprising at least one selected from the group consisting of Cellulose, Hydroxypropylmethyl Cellulose, Ethyl hydroxyethyl cellulose, Polyhydroxyethylmethacrylate, Polyethyleneimine, Alginate, Polyhydroxyethylacrylate, Starch, Hyaluronic acid, Pullulan, Pectin, Polyglycerol, Lignin, Xylan, Galactomannan, and Polyhydroxystyrene. Challenger slurry.

12. In paragraph 1, The weight ratio of the first dispersant and the second dispersant is 1:0.4 to 1:2.

3. Challenger slurry.

13. In paragraph 1, For 100 parts by weight of the above challenge material, The content of the first dispersant is 2.2 to 200 parts by weight, The content of the second dispersant is 1 to 90 parts by weight, Challenger slurry.

14. In paragraph 1, The solvent comprises a polar aprotic solvent, Challenger slurry.

15. In paragraph 1, Based on the total solid content of the above challenge slurry, the carbon content is 82 wt% or more. Challenger slurry.

16. Challenge; dispersant; positive electrode active material; and Binder; including; The above dispersant comprises a first dispersant and a second dispersant different from the first dispersant, The first dispersant comprises a polymer having a heteroatom, The second dispersant comprises a polymer having a hydrogen bonding capable group. anode.

17. In paragraph 16, The above positive electrode active material comprises a lithium transition metal oxide, The above lithium transition metal oxide is, Li x1 CO 2 (0.5 <x1<1.3), Li x2 NiO 2 (0.5 <x2<1.3), Li x3 MnO 2 (0.5 <x3<1.3), Li x4 Mr 2 O 4 (0.5 <x4<1.3), Li x5 (Ni a1 Co b1 Mr c1 )O 2 (0.5 <x5<1.3, 0<a1<1, 0<b1<1, 0<c1<1, a1+b1+c1=1), Li x6 Ni 1-y1 Co y1 O 2 (0.5 <x6<1.3, 0<y1<1), Li x7 Co 1-y2 Mr y2 O 2 (0.5 <x7<1.3, 0≤y2<1), Li x8 Ni 1-y3 Mr y3 O 2 (0.5 <x8<1.3, O≤y3<1), Li x9 (Ni a2 Co b2 Mr c2 )O 4 (0.5 <x9<1.3, 0<a2<2, 0<b2<2, 0<c2<2, a2+b2+c2=2), Li x10 Mr 2-z1 Ni z1 O 4 (0.5 <x10<1.3, 0<z1<2), Li x11 Mr 2-z2 Co z2 O 4 (0.5 <x11<1.3, 0<z2<2), Li x12 COPO 4 (0.5 <x12<1.3), Li x13 FePO 4 (0.5 <x13<1.3), Li A1 Ni B1 Co C1 Mr D1 Al E1 O 2 (A1=0.5 or more and 1.3 or less, B1+C1+D1+E1=1, 0 <B1<1, 0<C1<1, 0<D1<1, 0<E1<1), Li A2 Ni B2 Co C2 Al D2 O 2 (A2=0.5 or more and 1.3 or less, B2+C2+D2=1, 0 <B2<1, 0<C2<1, 0<D2<1) 및 Li A3 Mn B3 Fe C3 PO 4 (0.5 <A3<1.3, B3+C3=1, 0<B3<1, 0<C3<1)로 이루어진 군에서 선택되는 적어도 하나 이상을 포함하는, anode.

18. Anode according to Article 16; cathode; a separator interposed between the anode and the cathode; and containing an electrolyte; Secondary battery.