KR102144878B1 - Separator coating slurry for secondary battery and seperator for secondary battery comprising the same - Google Patents

Abstract

The present invention provides a slurry for coating a secondary battery separator comprising inorganic particles, a binder, a solvent, and a dispersant, and the dispersant comprises two or more fatty acid compounds, and the dispersant comprises two or more fatty acid compounds having different carbon atoms. It may be to include.

Description

Slurry for secondary battery separator coating and secondary battery separator using the same {SEPARATOR COATING SLURRY FOR SECONDARY BATTERY AND SEPERATOR FOR SECONDARY BATTERY COMPRISING THE SAME}

The present invention relates to a secondary battery separator coating slurry prepared by adding a dispersant including two or more fatty acid compounds, a secondary battery separator coated with the secondary battery separator coating slurry, and a secondary battery including the same.

With the recent rise of environmental issues and increasing interest in renewable energy that can replace nuclear power and fossil fuels, rechargeable and dischargeable secondary batteries have been developed that can be used repeatedly. Demand is increasing rapidly. Among secondary batteries, lithium secondary batteries are a field that secures safety and reliability compared to other types of batteries and is price-competitive. In recent years, design of new electrodes and batteries to improve capacity, degree and specific energy in developing lithium secondary batteries In addition to research and development on the lithium secondary battery, research and development on the separator constituting the lithium secondary battery is also actively progressing.

In general, a lithium secondary battery is composed of a positive electrode, a negative electrode, and a separator and an electrolyte positioned between the positive electrode and the negative electrode.

The separator constituting the secondary battery enables the electrical blocking function of the negative electrode and the positive electrode and lithium ions to move constantly in the electrolyte of the lithium secondary battery. In general, the separator is a mixture of inorganic particles and a binder to prepare a slurry, and then the slurry It is prepared by coating a substrate and then drying to form a coating layer on the substrate.

At this time, if the inorganic particles contained in the slurry are not properly dispersed, aggregation may be caused between the inorganic particles, and adhesion to the substrate may be reduced due to not being uniformly coated on the surface of the substrate. When the coating layer is formed in a state in which the slurry is not properly adhered to the substrate, as charging and discharging proceeds, separation between inorganic particles constituting the coating layer or between inorganic particles and the substrate may occur, thereby deteriorating physical properties of the secondary battery. In order to solve this problem, research has been conducted to improve the dispersibility of inorganic particles in the coating layer constituting the separation membrane. For example, referring to Korean Patent Publication No. 10-2014-0070465, A method of initiating dispersibility of inorganic particles by controlling the diameter and controlling the viscosity of the slurry for coating a separator was proposed.

However, simply controlling the diameter of the inorganic particles cannot completely block the aggregation of the inorganic particles, and as the battery is repeatedly charged and discharged, the adhesion between the coating layer constituting the separator and the substrate decreases, resulting in lower battery performance. The problem continues to occur. Accordingly, many studies are being conducted to improve the performance of the separator by maintaining a certain level or more of adhesion between the substrate and the coating layer even in the case of repeated charging and discharging.

Korean Patent Publication No. 10-2104-0070465

The present invention was conceived to solve the problems of the prior art, and powder of the slurry by adding a dispersant containing two or more fatty acid compounds so that inorganic particles constituting the slurry forming the coating layer of the separator can be uniformly dispersed. To provide a secondary battery separator coating slurry that improves acidity and thus has improved adhesion to a substrate, a secondary battery separator prepared by coating the secondary battery separator coating slurry, and a secondary battery including the secondary battery separator To do.

According to an embodiment of the present invention for solving the above problems, the present invention provides a separator for a secondary battery comprising inorganic particles, a binder, a solvent, and a dispersant, and the dispersant comprises two or more fatty acid compounds. can do.

According to an embodiment of the present invention, the dispersant may include two or more fatty acid compounds having different carbon numbers.

According to an embodiment of the present invention, the fatty acid compound may be two or more fatty acid compounds selected from the group consisting of C15 to C30 unsaturated fatty acid compounds and C15 to C30 saturated fatty acid compounds.

For example, the C15 to C30 unsaturated fatty acid compounds include Oleic acid, Palmitoleic acid, Cis-Heptadecenoic acid, Vaccenic acid, and elaidic acid. (Elaidic acid), linolenic acid, arachidonic acid, eicosanoic acid, erucic acid, eicosapentaenoic acid (EPA), docosahexaenoic acid (Docosahexaenoic acid, DHA), nervonic acid (Nervonic acid) may be selected from the group consisting of.

For another example, the C15 to C30 saturated fatty acid compound is palmitic acid, stearic acid, arachidic acid, behenic acid, and lignoceric acid. acid) may be selected from the group consisting of.

According to an embodiment of the present invention, it is possible to provide a secondary battery separator including a substrate and a coating layer positioned on the surface of the substrate and formed of a slurry for coating the secondary battery separator.

According to another embodiment of the present invention, a secondary battery including a positive electrode, a negative electrode, the separator disposed between the positive electrode and the negative electrode, and an electrolyte may be provided.

In the slurry for coating a separator for a secondary battery according to the present invention, inorganic particles are uniformly dispersed by a dispersant including two or more fatty acid compounds, so that aggregation between the inorganic particles may be prevented. Accordingly, not only the storage stability of the slurry is improved, but also the adhesion between the substrate forming the separator and the coating layer is improved, thereby preventing detachment between the substrate and the coating layer, and providing a secondary battery with improved life and performance.

Hereinafter, the present invention will be described in more detail to aid in understanding the present invention.

The terms or words used in the description and claims of the present invention should not be construed as being limited to their usual or dictionary meanings, and the inventor appropriately explains the concept of terms in order to explain his own invention in the best way. Based on the principle that it can be defined, it should be interpreted as a meaning and concept consistent with the technical idea of the present invention.

First, a slurry for coating a secondary battery separator according to the present invention will be described.

The slurry for coating a secondary battery separator according to the present invention includes inorganic particles, a binder and a dispersant, and the dispersant includes two or more fatty acid compounds.

According to the research of the present inventors, when only one type of fatty acid compound is used as a dispersant, there is no effect of preventing aggregation of inorganic particles, and rather, a phenomenon in which inorganic particles are more agglomerated than when a dispersant is not used. However, when two or more types of fatty acid compounds are mixed and used, the dispersibility of inorganic particles is greatly improved. Particularly, when a fatty acid compound having different carbon atoms is mixed and used as a dispersant, the effect of improving the dispersibility is more excellent.

Specifically, when a dispersant containing two or more fatty acid compounds is used, the hydrocarbon portion constituting the fatty acid compound is adsorbed on the surface of the inorganic particles, and the adsorbed fatty acid compound is a layer on the surface of the inorganic particles. ) To form. Aggregation between inorganic particles in which the fatty acid compound layer is formed may be suppressed through the effect of electrostatic repulsion and steric hindrance between fatty acid compounds forming the layer. In particular, when fatty acids having different carbon numbers are mixed and used, the density and thickness of the fatty acid compound layer can be increased, and thus the dispersibility improvement effect is more excellent.

In contrast, when a dispersant containing only one fatty acid compound is used, the fatty acid compound layer is formed but is not uniformly formed, and thus aggregation between inorganic particles may be induced more than when the fatty acid compound is not used as a dispersant.

In the present invention, the fatty acid compound may mean a saturated hydrocarbon having a carboxy group (-COOH) or a carboxylic acid compound having an unsaturated hydrocarbon chain, and a fatty acid compound having a saturated hydrocarbon chain is referred to as a saturated fatty acid compound, and an unsaturated hydrocarbon chain A fatty acid compound having a is referred to as an unsaturated fatty acid compound.

In the case where the unsaturated fatty acid compound contains a double bond, both hydrocarbon groups are located in the same direction based on the double bond (cis isomer) and both hydrocarbon groups are located in opposite directions (trans isomer).

In the present invention, the dispersant may include two or more fatty acid compounds having different carbon atoms. However, in the case of two or more different fatty acid compounds, each of the fatty acid compounds included in the dispersant may have a different number of carbon atoms, but it means that all fatty acid compounds must be fatty acid compounds each having a different number of carbon atoms. no. For example, when the dispersant contains 3 or more fatty acid compounds, when the two fatty acid compounds have different carbon numbers, the remaining fatty acid compounds have the same carbon number as any one of the two fatty acid compounds, but different It may be a kind of fatty acid compound.

The type of fatty acid compound that can be used in the dispersant according to the present invention is not particularly limited, and the fatty acid compound may be selected from C15 to C30 unsaturated fatty acid compounds and C15 to C30 saturated fatty acid compounds.

For example, C15 to C30 unsaturated fatty acid compounds include oleic acid (C ₁₈ H ₃₄ O ₂ ), palmitoleic acid (C ₁₆ H ₃₀ O ₂ ), cis-heptadecenoic acid (Cis-Heptadecenoic). acid, C ₁₇ H ₃₂ O ₂ ), Vaccenic acid (C ₁₈ H ₃₄ O ₂ ), Elaidic acid (C ₁₈ H ₃₄ O ₂ ), Linolenic acid, C ₁₈ H ₃₂ O ₂ ), Arachidonic acid (C ₂₀ H ₃₂ O ₂ ), Eicosanoic acid (C ₂₀ H ₄₀ O ₂ ), Erucic acid (C ₂₂ H ₄₂ O ₂ ), Eicosapentaenoic acid (Eicosapentaenoic acid, EPA, C ₂₀ H ₃₀ O ₂ ), Docosahexaenoic acid (DHA, C ₂₂ H ₃₂ O ₂ ), Nervonic acid (Nervonic acid C ₂₄ H ₄₆ O ₂ ) Selected from the group consisting of It can be.

For another example, C15 to C30 saturated fatty acid compounds include palmitic acid (C ₁₆ H ₃₂ O ₂ ), stearic acid (C ₁₈ H ₃₆ O ₂ ), arachidic acid (C ₂₀ H ₄₀ O ₂ ), Behenic acid (C ₂₂ H ₄₄ O ₂ ), Lignoceric acid (Lignoceric acid, C ₂₄ H ₄₈ O ₂ ) It may be selected from the group consisting of.

According to an embodiment of the present invention, as a dispersant, only two or more types of unsaturated fatty acid compounds may be included, or only two or more types of saturated fatty acid compounds may be included, and each of a saturated fatty acid compound and an unsaturated fatty acid compound may be used as a dispersant. have.

As an embodiment of the present invention, the dispersant may include oleic acid, stearic acid, palmitic acid, and nervonic acid.

The oleic acid is a C18 unsaturated fatty acid, which can be represented by the formula C ₁₈ H ₃₄ O ₂ , and is also called oleic acid, as a single unsaturated fatty acid, which has one double bond between carbon atoms, and all the remaining carbon atoms Are unitary.

The nerbonic acid is a C24 unsaturated fatty acid, which is also expressed as a chain product of oleic acid. Like oleic acid, it is a single unsaturated fatty acid having one double bond between carbon atoms, and all the remaining carbon atoms are single bonded.

The stearic acid may be represented by the C18 saturated fatty acid, C ₁₈ H ₃₆ O ₂ formula, and palmitic acid may be represented by the C16 saturated fatty acid, C ₁₆ H ₃₂ O ₂ formula.

For example, the dispersing agent of the fatty acid compound mixed in a weight ratio of oleic acid: stearic acid: palmitic acid: nerbonic acid = (5 to 25): (5 to 25): (5 to 25): (5 to 25) It may contain mixtures. Specifically, the dispersant is oleic acid: stearic acid: palmitic acid: nerbonic acid = (5 to 15): (5 to 15): (5 to 15): (5 to 15): (5 to 15) in a weight ratio of It may contain a mixture of mixed fatty acid compounds, more preferably, oleic acid: stearic acid: palmitic acid: nerbonic acid = (9-10): (9-10): (9-10): (8- It may include a mixture of fatty acid compounds mixed in a weight ratio of 9). The dispersant including the mixture of fatty acid compounds as described above may form a uniform and dense fatty acid compound layer on the surface of the inorganic particles, thereby further improving the dispersibility of the inorganic particles.

In another embodiment of the present invention, the acid value (　酸價) of the dispersant may be 20 to 600 mg-KOH/g, 30 to 500 mg-KOH/g, and 40 to 400 mg-KOH /g may be, it may be 50 to 300 mg-KOH / g. In the present invention,'acid value' is a numerical value representing the amount of fatty acids contained in 1 g of oils and fats or petroleum products, and in general, the number of mg of potassium hydroxide (KOH) required to neutralize fatty acids contained in 1 g of oils and fats or petroleum products is the acid value. It can be defined as (mg-KOH/g). When the dispersant has an acid value less than the above range, the inorganic particles may not be properly dispersed because the dispersant is not contained above a certain level, and when the dispersant has an acid value exceeding the above range, an aggregation phenomenon between the dispersants occurs. It can turn back and inhibit dispersion. Therefore, it is more preferable to use a dispersant having an acid value within the above range as the dispersant.

In the present invention, the dispersant may be included in an amount of 0.1 to 40 parts by weight based on 100 parts by weight of the inorganic particles, for example, 0.2 to 30 parts by weight, 0.3 to 20 parts by weight, 0.4 to 10 parts by weight, 0.5 to It may be included in 10 parts by weight and 1.0 to 5 parts by weight. When the dispersant is included in an amount of the weight part exceeding the above range, aggregation is formed due to the bonding between the inorganic particles-dispersant-inorganic particles, and thus dispersion may be inhibited. On the other hand, when the dispersant is included in an amount of parts by weight less than the above range, the dispersant is not sufficiently adsorbed on the surface of the inorganic particles, and the repulsive force between the dispersants is weak, so it is difficult to prevent aggregation between the inorganic particles. Therefore, it is preferable that the dispersant is contained within the range of the content by weight.

In one embodiment of the present invention, the slurry for coating a secondary battery separator may include two or more inorganic particles having different surface areas.

The inorganic particles included in the slurry for coating the secondary battery separator are included in order to improve the strength of the separator by the coating layer formed by the coating slurry. In general, when only a substrate formed of an organic material is used as a separator of a secondary battery, the separator may be easily damaged by electric charges of metal particles moving between the separators during the charging and discharging process of the secondary battery. Therefore, even when charging/discharging continues in the secondary battery, when the slurry containing inorganic particles is coated on the surface of a substrate and used as a separator, a separator with improved strength is formed compared to the case of simply using the substrate. can do.

For example, the slurry for coating a secondary battery separator may include first inorganic particles and second inorganic particles having a larger surface area than the first inorganic particles.

In the present invention, inorganic particles having a relatively larger surface area are defined as second inorganic particles, and inorganic particles having a relatively smaller surface area are defined as first inorganic particles. The use of mixing inorganic particles having different surface areas is to improve the storage stability of the slurry and to improve the electrochemical performance of the formed separator by improving the adhesion to the substrate.

In the present invention, the inorganic particles may be measured by the BET surface area measurement method, and the surface area measured by the method may be referred to as the BET surface area.

For example, BET surface area refers to the surface area measured by a measurement method using a formula developed by Brunauer, Emmett, Teller, and measures the amount of adsorption by partial pressure by adsorbing and desorbing a specific gas on the surface of a solid sample. It means the specific surface area of the measured material.

In the present invention, the BET surface area may be measured through calculation of the amount of adsorbed nitrogen after adding nitrogen gas to inorganic particles using BELSORP-MAX (BEL Japan, Inc.).

In an embodiment of the present invention, the BET surface area of the first inorganic particles is less than 20 m ² /g, preferably less than 10 m ² /g, and the BET surface area of the second inorganic particles is 5 to 35 m ² /g, preferably 10 to 30 m ² /g may be. When the first inorganic particles and the second inorganic particles having the BET surface area as described above are used, the electrochemical performance of the separator may be improved.

In an embodiment of the present invention, the second inorganic particles may be 0.1 to 40 parts by weight based on 100 parts by weight of the first inorganic particles, 5 to 30 parts by weight may be included, and 10 to 20 parts by weight. It may be included in parts by weight, and may be included in 15 to 18 parts by weight. When the second inorganic particles are contained within the range of the weight part relative to the first inorganic particles to form the slurry for coating a secondary battery separator, dispersion between the inorganic particles may be made more uniformly in the separator.

In an embodiment of the present invention, the inorganic particles may be included in an amount of 0.5 to 40 wt% based on the total weight of the slurry for coating a secondary battery separator, preferably 5 to 30 wt%, more preferably 10 To 20 wt%, even more preferably 13 to 15 wt%. When the coating layer of the separation membrane is formed with a slurry in which the content of inorganic particles satisfies the above range, the separation membrane having the coating layer may have strength enough to maintain a long-term life.

The inorganic particles used in the present invention are, for example, BaTiO ₃ , BaTiO ₃ , Pb(Zr,Ti)O ₃ (PZT), Pb _1-x La _x Zr _1-y Ti _y O ₃ (PLZT, where, 0<x<1, 0<y<1), Pb(Mg _1/3 Nb _2/3 )O ₃ -PbTiO ₃ (PMN-PT), Hafnia(HfO ₂ ), SrTiO ₃ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, ZnO, ZrO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , TiO ₂ , SiC, and a mixture of two or more selected from the group consisting of a mixture thereof. In addition, in addition to the compounds listed above, compounds having lithium ion transfer ability, that is, lithium phosphate (Li ₃ PO ₄ ), lithium titanium phosphate (Li _p Ti _q (PO ₄ ) ₃ , 0<p<2, 0<q<3) , Lithium aluminum titanium phosphate (Li _a Al _b Ti _c (PO ₄ ) ₃ , 0<a<2, 0<b<1, 0<c<3), 14 Li ₂ O ₉ Al ₂ O ₃ 38 TiO ₂ 39P ₂ O ₅ (LiAlTiP) _d O _e series glass (0<d<4, 0<e<13), lithium lanthanum titanate (Li _e La _f TiO ₃ , 0<e<2, 0<f<3), Lithium germanium thiophosphate such as Li _3.25 Ge _0.25 P _0.75 S ₄ (Li _g Ge _h P _i S _j , 0<g<4, 0<h<1, 0<i<1, 0<j<5), Li lithium nitride such as _{3 N (Li k N l,} 0 <k <4, 0 <l <2), Li 3 PO 4 -Li 2 S-SiS 2 SiS 2 based glass (Li Si _n S _{m o,} such as , 0<m<3, 0<n<2, 0<o<4), P ₂ S ₅ series glass such as LiI-Li ₂ SP ₂ S ₅ or a mixture thereof may be further included. However, it is not limited to the above compound, and any material may be used as long as it has a particle shape as an inorganic compound and can exhibit its function as a composition for forming a separator.

The slurry for coating a secondary battery separator according to an embodiment of the present invention may contain a binder. The binder may improve adhesion between the coated separator and the electrode, and a compound of a component that is not easily dissolved by an electrolyte may be used as the binder.

In one embodiment of the present invention, the binder is not particularly limited as long as it is a polymer used to improve the bonding strength between the separator and the electrode, and representative examples thereof are polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexa Fluoropropylene, polyvinylpyrrolidone, polyacrylonitrile, polyvinylidenefluoride-trichloroethylene, polyvinylidenefluoride-chlorotrifluoroethylene (PVdF-CTFE), polymethylmethacrylate, polyvinyl Acetate, ethylene-co-vinyl acetate copolymer, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethylpolyvinyl alcohol, cyanoethylcellulose, cyanoethyl sucrose , Pullulan, carboxyl methyl cellulose, acrylonitrile styrene butadiene copolymer, and a water-based or non-aqueous (organic) polymer comprising a mixture of two or more selected from the group consisting of polyimide, specifically aqueous polyvinyl Lidenfluoride (PVdF) can be used.

In one embodiment of the present invention, the binder may be included in 3 to 20 wt%, 5 to 10 wt%, based on the total weight of the slurry for coating the secondary battery separator. When the binder within the above range is included, the adhesion between the coating layer formed of the slurry and the surface of the substrate on which the coating layer is formed may be improved to prevent the coating layer from peeling off.

According to an embodiment of the present invention, the slurry for coating the secondary battery separator may include a solvent. As the solvent used in the present invention, it is preferable to use a solvent having a non-solvent property for a substrate on which the slurry is coated while being capable of dissolving inorganic particles constituting the slurry, a binder, and a dispersant at a certain level or more. Specific examples include acetone, tetrahydrofuran, acetonitrile, dimethylformamide, dimethyl sulfoxide, dimethylacetamide, N-methylpyrrole, or water, and two or more of them may be used in combination.

In one embodiment of the present invention, the solvent may be included in 50 to 90 wt%, 60 to 85 wt%, based on the total weight of the slurry for coating a secondary battery separator.

Next, a secondary battery separator according to the present invention will be described.

According to an embodiment, the separator of the present invention is located on a substrate and a surface of the substrate, and comprises a slurry for coating the secondary battery separator, that is, an inorganic particle, a binder, a solvent, and a dispersant including two or more fatty acid compounds. It includes a coating layer formed of a slurry.

The substrate serves to prevent physical contact between the negative electrode and the positive electrode while passing metal ions such as lithium ions through the pores, and generally, a porous polyolefin may be used. In one embodiment of the present invention, the 　 base is not particularly limited as long as it is formed of a conventional polyolefin-based polymer, and specific examples include polyolefin-based resin, fluorine-based resin, polyester-based resin, polyacrylonitrile resin, and cellulose. A microporous membrane or nonwoven fabric composed of one or two or more components selected from the group consisting of materials, and more specifically polyethylene, polypropylene, polyvinylidene fluoride, polytetrafluoroethylene, polyethylene terephthalate And a microporous membrane or nonwoven fabric composed of one or two or more components selected from the group consisting of polybutylene terephthalate may be used as the substrate.

However, in many cases, a separator containing a polyolefin does not have a strength enough to withstand when the battery continues to be charged/discharged due to its material properties and characteristics of a process manufactured by stretching. Accordingly, in the present invention, a slurry containing an inorganic particle, a binder, a solvent, and a dispersant including two or more fatty acid compounds is coated on the substrate to form a coating layer, thereby improving the strength of the separator. Since the detailed contents of the slurry for coating the secondary battery separator are the same as described above, a detailed description will be omitted.

The separation membrane according to the present invention as described above contains inorganic particles in the coating layer, so it has excellent mechanical properties such as strength, and by using a slurry in which inorganic particles are uniformly dispersed by using a dispersant containing two or more fatty acid compounds, inorganic substances The separation between the substrate and the coating layer due to the aggregation of particles is effectively suppressed.

Next, a secondary battery according to the present invention will be described.

The secondary battery of the present invention includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte, and the separator according to the present invention described above is used as the separator.

The positive electrode may be prepared by coating a positive electrode mixture prepared by mixing a positive electrode material including a positive electrode active material with a solvent such as NMP on a positive electrode current collector, followed by drying and rolling. The positive electrode agent may include a positive electrode active material and, optionally, a conductive material, a binder, a filler, and the like.

As the positive electrode active material, positive electrode active materials well known in the art may be used without limitation. For example, lithium cobalt-based oxide, lithium nickel-based oxide, lithium manganese-based oxide, lithium iron phosphate, lithium nickel manganese cobalt-based Oxide or a combination thereof and the like may be used. Specifically, as the positive electrode active material, LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiCoPO ₄ , LiFePO ₄ and LiNiaMnbCocO ₂ (here, 0 <a, b, c <1), etc. may be used, but limited thereto It is not. When the lithium cobalt oxide and lithium-metal oxide are used as the positive electrode active material, since cracks hardly occur on the surface of the active material particles during charging and discharging, gas generation by reaction with the electrolyte and reaction between the core and the electrolyte-derived hydrofluoric acid Thus, the cathode active material can be prevented from being dissolved in the electrolyte.

The 　 conductive material is not particularly limited as long as it has conductivity without causing chemical changes to the battery, and examples thereof include graphite; Carbon blacks such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used. Specific examples of commercially available conductive materials include acetylene black-based Chevron Chemical Company, Denka Singapore Private Limited, Gulf Oil Company, etc.), Ketjenblack, EC The group (Armak Company), Vulcan XC-72 (Cabot Company) and Super P (Timcal).

The binder is a component that aids in bonding of an active material and a conductive material and bonding to a current collector, and is typically added in an amount of 1 to 30% by weight based on the total weight of the mixture including the positive electrode active material. Examples of such a binder include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butyrene rubber, fluorine rubber, and various copolymers.

The filler is selectively used as a component that suppresses the expansion of the electrode, and is not particularly limited as long as it is a fibrous material without causing chemical changes to the battery, and examples thereof include olefinic polymerizers such as polyethylene and polypropylene; Fibrous materials such as glass fiber and carbon fiber are used.

The negative electrode is manufactured by, for example, coating a negative electrode mixture prepared by mixing a negative electrode agent containing a negative electrode active material with a solvent on a negative electrode current collector, followed by drying and rolling, and the negative electrode agent as described above, if necessary. Components such as a conductive material, a binder, and a filler may be included.

Natural graphite, artificial graphite, carbonaceous material as the negative active material; Lithium-containing titanium composite oxide (LTO), Si, Sn, Li, Zn, Mg, Cd, Ce, Ni, or Fe metals (Me); Alloys composed of the metals (Me); Oxides of the metals (Me) (MeOx); And one or two or more negative active materials selected from the group consisting of a composite of the metals (Me) and carbon.

The electrolytic solution refers to an electrolytic solution composed of a high dielectric constant, a high viscosity organic solvent, a low viscosity organic solvent, a lithium salt, etc. used in a secondary battery, and may further include various kinds of additives to improve the performance of the battery. . However, in the present invention, the use of a specific electrolyte is not a technical feature, and all commonly used electrolytes may be used, and the type of electrolyte is not limited.

Hereinafter, the present invention will be described in more detail by examples. However, the following examples are for illustrative purposes only, and the scope of the present invention is not limited thereto.

Example

Example 1

(1) Preparation of dispersant

BYK-P104 (product name) manufactured by BYK was prepared as a dispersant. BYK-P104 is a mixture of fatty acid compounds mixed in a weight ratio of oleic acid: stearic acid: palmitic acid: nerbonic acid (9-10): (9-10): (9-10): (8-9). It includes 50 parts by weight based on the weight, and 50 parts by weight of the solvent mixed with xylene: ethylbenzene: isobutyl ketone = 65:27:8 based on the total weight.

(2) Preparation of slurry for membrane coating

11.9 parts by weight of alumina particles having an average particle diameter (D ₅₀ ) of 0.5 μm and a BET surface area of 6 m ² /g, 2.1 parts by weight of alumina particles having an average particle diameter (D ₅₀ ) of 0.25 μm and a BET surface area of 20 m ² /g , 0.2 parts by weight of dispersant (BYK-P104), PVdF-HFP (polyvinylidene fluoride-hexafluoropropylene) and PVdF-CTFE (polyvinylidene fluoride-chlorotrifluoroethylene) are mixed in a mass ratio of 7:3 After 3.8 parts by weight of a binder and 82 parts by weight of an acetone solution were mixed, mixing was performed for 30 minutes using a homo mixer (product name: Dispermat LC, manufacturer: VMA) to prepare a slurry for membrane coating.

(3) Dispersion of slurry for membrane coating

After putting the prepared slurry for membrane coating in an Orbital Shaker (Beads size 1mm), a dispersion process was performed at 300 rpm for 3 hours.

Comparative example

Comparative Example 1

11.9 parts by weight of alumina particles having an average particle diameter (D ₅₀ ) of 0.5 μm and a BET surface area of 6 m ² /g, 2.1 parts by weight of alumina particles having an average particle diameter (D ₅₀ ) of 0.25 μm and a BET surface area of 20 m ² /g , PVdF-HFP (polyvinylidene fluoride-hexafluoropropylene) and PVdF-CTFE (polyvinylidene fluoride-chlorotrifluoroethylene): 4.0 parts by weight of a binder mixed in a mass ratio of 7:3 and 82 parts by weight of acetone solution After mixing the parts, mixing was carried out for 30 minutes using a homo mixer (manufacturer: VMA, product name: Dispermat LC) to prepare a slurry for coating a separator. The analysis results of the thus prepared slurry for coating a separator are shown in Table 1 below.

Comparative Example 2

It was carried out in the same manner as in Example 1, except that 0.2 parts by weight of stearic acid was added instead of BYK-P104 as a dispersant. The analysis results of the thus prepared slurry for coating a separator are shown in Table 1 below.

Comparative Example 3

In Example 1, it was carried out in the same manner as in Example 1, except that 0.2 parts by weight of oleic acid was added instead of the dispersant (BYK-P104). The analysis results of the thus prepared slurry for coating a separator are shown in Table 1 below.

Comparative Example 4

In Example 1, it was carried out in the same manner as in Example 1, except that 0.2 parts by weight of palmitic acid was added instead of the dispersant (BYK-P104). The analysis results of the thus prepared slurry for coating a separator are shown in Table 1 below.

Experimental example

Experimental Example 1

The average particle diameter (μm) and sedimentation speed (μm/s) of the inorganic particles in the slurry prepared in Example 1 and Comparative Examples 1 to 4 were measured, respectively, and the results are shown in Table 1 below.

The average particle diameter of inorganic particles was measured through a Particle Size Analyzer (product name: MASTERSIZER 3000, manufacturer: Malvern), and the sedimentation rate was settled with time in the state of applying a centrifugal force using a Dispersion Analyzer (product name: Lumisizer, manufacturer: LUM). The speed was measured.

Average particle diameter of inorganic particles (㎛) Settling speed (㎛/s)
D50 D90 Example 1 0.53 0.9 3.618 Comparative Example 1 1.77 4.06 7.178 Comparative Example 2 2.59 4.86 213.2 Comparative Example 3 2.20 4.07 228.1 Comparative Example 4 2.54 4.80 168

From Table 1 above, in the case of a slurry for coating a separator for preparing a separator according to the present invention, when a dispersant is not used (Comparative Example 1) and when a single fatty acid compound is used as a dispersant (Comparative Examples 2 to 4) In comparison, both the particle diameter and the sedimentation rate of the inorganic particles in the slurry were reduced to less than 1/2.

Through the decrease in the inorganic particle diameter and the sedimentation rate, it can be seen that the inorganic particles constituting the separation membrane do not aggregate and are evenly dispersed. Further, in the case of Comparative Examples 2 to 4, only one type of fatty acid compound was used as the dispersing agent, but it can be seen that the particle diameter and the sedimentation rate were remarkably increased compared to Comparative Example 1 in which the dispersant was not used. That is, if a single type of fatty acid is used as a dispersant, it can be confirmed that aggregation between inorganic particles can proceed further. Therefore, it can only play a role as a dispersant when two or more types of fatty acids are mixed and used instead of a single type of fatty acid. It can be confirmed that there is.

Claims (15)

Inorganic particles;
bookbinder;
menstruum; And
Containing a dispersant,
The dispersant is a slurry for coating a secondary battery separator consisting of a C15 to C30 unsaturated fatty acid compound and a C15 to C30 saturated fatty acid compound.
delete delete The method of claim 1,
The C15 to C30 unsaturated fatty acid compounds include Oleic acid, Palmitoleic acid, Cis-Heptadecenoic acid, Vaccenic acid, and Elaidic acid. , Linolenic acid, arachidonic acid, eicosanoic acid, erucic acid, eicosapentaenoic acid (EPA), docosahexaenoic acid, DHA), a slurry for coating a separator for a secondary battery that is selected from the group consisting of nervonic acid.
The method of claim 1,
The C15 to C30 saturated fatty acid compound is a group consisting of palmitic acid, stearic acid, arachidic acid, behenic acid, and lignoceric acid. The slurry for coating a secondary battery separator that is selected from.
The method of claim 1,
The dispersant, oleic acid (Oleic acid), stearic acid (Stearic acid), palmitic acid (palmitic acid) and nerbonic acid (nervonic acid) is a slurry for coating a secondary battery separator comprising a.
The method of claim 6,
The oleic acid, stearic acid, palmitic acid, and nerbonic acid are (5 to 25): (5 to 25): (5 to 25): a slurry for coating a secondary battery separator in a weight ratio of (5 to 25).
According to claim 1
The slurry for coating a separator for a secondary battery is contained in an amount of 0.1 to 40 parts by weight based on 100 parts by weight of the inorganic particles.
The method of claim 1,
The slurry for coating a secondary battery separator includes two or more kinds of inorganic particles having different surface areas.
The method of claim 9,
The slurry for coating a secondary battery separator includes a first inorganic particle and a second inorganic particle having a larger surface area than the first inorganic particle.
The method of claim 10,
The BET surface area of the first inorganic particles is less than 10 m ² /g, and the BET surface area of the second inorganic particles is 10 to 30 m ² /g of secondary battery separator coating slurry.
The method of claim 10,
The second inorganic particles are contained in an amount of 10 to 20 parts by weight based on 100 parts by weight of the first inorganic particles.
The method of claim 1,
The inorganic particle is a slurry for coating a secondary battery separator that is contained in an amount of 0.5 to 40 wt% in the slurry.
A secondary battery separator comprising a substrate and a coating layer positioned on the surface of the substrate and formed of the slurry for coating the secondary battery separator according to claim 1.
A secondary battery comprising a positive electrode, a negative electrode, the separator according to claim 14, and an electrolyte solution disposed between the positive electrode and the negative electrode.