Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
  • H01M50/403—Manufacturing processes of separators, membranes or diaphragms
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
  • H01M50/409—Separators, membranes or diaphragms characterised by the material
  • H01M50/431—Inorganic material
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B33/00—Silicon; Compounds thereof
  • C01B33/113—Silicon oxides; Hydrates thereof
  • C01B33/12—Silica; Hydrates thereof, e.g. lepidoic silicic acid
  • C01B33/14—Colloidal silica, e.g. dispersions, gels, sols
  • C01B33/157—After-treatment of gels
  • C01B33/159—Coating or hydrophobisation
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
  • H01M50/409—Separators, membranes or diaphragms characterised by the material
  • H01M50/411—Organic material
  • H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
  • H01M50/417—Polyolefins
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
  • H01M50/409—Separators, membranes or diaphragms characterised by the material
  • H01M50/431—Inorganic material
  • H01M50/434—Ceramics
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
  • H01M50/409—Separators, membranes or diaphragms characterised by the material
  • H01M50/44—Fibrous material
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
  • H01M50/409—Separators, membranes or diaphragms characterised by the material
  • H01M50/443—Particulate material
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
  • H01M50/409—Separators, membranes or diaphragms characterised by the material
  • H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
  • H01M50/409—Separators, membranes or diaphragms characterised by the material
  • H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
  • H01M50/451—Separators, membranes or diaphragms characterised by the material having a layered structure comprising layers of only organic material and layers containing inorganic material
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
  • H01M50/409—Separators, membranes or diaphragms characterised by the material
  • H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
  • H01M50/454—Separators, membranes or diaphragms characterised by the material having a layered structure comprising a non-fibrous layer and a fibrous layer superimposed on one another
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
  • H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
  • H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
  • H01M50/491—Porosity
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/10—Energy storage using batteries

Definitions

• the present invention relates to a coating material for a secondary battery separator, a manufacturing method thereof, a secondary battery separator, and a secondary battery.
• secondary batteries that can be used many times by recharging are used in various devices.
• secondary batteries include nickel-cadmium batteries, nickel-hydrogen batteries, lithium ion batteries and the like.
• a secondary battery has a structure in which two electrodes, that is, an anode and a cathode, are constantly immersed in an electrolyte solution, and a separator is laminated to separate them.
• the type of secondary battery is optimized according to the electrode material, electrolyte, and separator used. must have the ability to electrically insulate the electrodes of Also, the separator must have the ability to permeate ions in order to carry out the electrochemical reaction between the anode and cathode.
• separators are required to have as low an internal resistance as possible in order to increase the ability to transmit ions.
• the separator is required to have such high ion permeability, and at the same time, thinness is also pursued from the aspect of the device to which it is applied.
• separators based on nonwoven fabrics have been developed.
• the non-woven fabric separator is more heat resistant than the commonly used polyolefin separator, and has a high porosity, so a high current density can be obtained. This advantage is very effective for secondary batteries. However, such a high porosity may cause a micro-short circuit or a short-circuit in an environment where long-term charge/discharge cycles are repeated.
• non-woven fabric separators are required to have the ability to prevent short circuits without impairing high ion permeability.
• a technology that satisfies both performances there is a method of appropriately controlling the porosity.
• lithium-ion batteries It is also important to prevent combustion in lithium-ion batteries.
• thin laminate-type lithium-ion batteries have individual battery units adjacent to each other, and there is a concern that they may ignite due to short circuit or overheating, and combustion may spread widely.
• the anode and cathode must remain electrically isolated from each other in the event of ignition. Therefore, the separator is required to have the ability to remain in a state of maintaining insulation without being extinguished by combustion even in the event of a fire.
• Patent Document 1 proposes a separator having a structure in which various fillers are applied to a polyolefin-based resin porous film.
• Patent Document 2 proposes a film in which inorganic spherical particles such as titanium oxide are applied to a polypropylene film.
• inorganic spherical particles such as titanium oxide are applied to a polypropylene film.
• JP 2013-173283 A Japanese Patent Publication No. 2018-538164
• the present invention has been made in view of the above circumstances, and provides a secondary battery separator coating that does not impair battery characteristics in long-term charge-discharge cycles and that can maintain insulation even when combustion occurs.
• the purpose is to provide materials.
• the present inventors have found that coating a separator with a coating material containing specific surface-treated spherical silica particles does not impair battery characteristics even in long-term charge-discharge cycles. , found that it is possible to realize a secondary battery capable of maintaining insulation even when combustion occurs, and completed the present invention.
• R 1 SiO 3/2 units wherein R 1 is a substituted or unsubstituted C 1-20 monovalent hydrocarbon group
• R 2 3 SiO 1/2 units wherein , R 2 are the same or different substituted or unsubstituted monovalent hydrocarbon groups having 1 to 6 carbon atoms
• the median diameter in the volume-based particle size distribution is 0.01 to 0.5 ⁇ m and a coating material for a secondary battery separator containing surface-treated spherical silica particles having a circularity of 0.8 to 1.0; 2.
• the SiO2 unit is converted to After obtaining a mixed solvent dispersion of hydrophilic spherical silica particles containing R1Si ( OR4 ) 3 (II) (In the formula, R 1 is the same as above, and R 4 is the same or different monovalent hydrocarbon group having 1 to 6 carbon atoms.)
• R 1 SiO is formed on the surfaces of the hydrophilic spherical silica particles.
• a mixed solvent dispersion of the first surface-treated spherical silica particles into which 3/2 units (in the formula, R 1 is the same as above) is prepared, and then the first surface-treated spherical silica particles Part of the hydrophilic organic solvent and water is removed from the mixed solvent dispersion of and concentrated to obtain a mixed solvent concentrated dispersion of the first surface-treated spherical silica particles, and then the first surface treatment Formula (III) below is added to a mixed solvent concentrated dispersion of spherical silica particles R23SiNHSiR23 ( III ) (In the formula, R 2 is the same as above.)
• Manufacture of coating material for secondary battery separator comprising the step of obtaining surface-treated spherical silica particles as second surface-treated spherical silica particles by introducing units (wherein R 2 is the same as above) Method, 3.
• a secondary battery separator having a substrate and a coating of the secondary battery separator coating material according to claim 1 formed on the surface of the substrate or inside the pores of the substrate, wherein the substrate a secondary battery separator in which the amount of the surface-treated spherical silica particles per 1 cm 2 of the material is 0.07 to 0.29 mg; 4.
• a secondary battery comprising the secondary battery separator according to 3 or 4 is provided.
• a coating material containing specific surface-treated spherical silica particles is applied to a secondary battery separator to improve battery characteristics in long-term charge-discharge cycles, and to prevent the spread of fire on the separator in the event of ignition. It is possible to electrically separate the anode and the cathode and maintain insulation even after combustion, so that a highly reliable secondary battery can be provided.
• the secondary battery separator coating material according to the present invention has R 1 SiO 3/2 units and R 2 3 SiO 1/2 units on the surface, and has a median diameter and a predetermined circularity in a predetermined volume-based particle size distribution. It contains surface-treated spherical silica particles with
• the surface-treated spherical silica particles used in the present invention are excellent in dispersibility, they can be uniformly coated on the separator substrate.
• the surface-treated spherical silica particles used in the present invention penetrate into the pores of the separator base material, thereby suppressing a significant increase in the thickness of the separator due to deposition of agglomerated particles on the coated surface. It is extremely important not to increase the thickness of the separator from the problem of internal electrical resistance and the requirements of the device to which it is applied.
• R 1 SiO 3/2 units and R 2 3 SiO 1/2 units on the surface of silica particles are trifunctional silane compounds represented by the following formula (II), partial hydrolysis products thereof, or A mixture of these, a silazane compound represented by the following formula (III), a monofunctional silane compound represented by the following formula (IV), a hydrolyzate thereof, a condensate thereof, or a mixture thereof is bound to the silica surface. It can be formed by R1Si ( OR4 ) 3 (II) R23SiNHSiR23 ( III ) R23SiX ( IV)
• R 1 is a substituted or unsubstituted monovalent hydrocarbon having 1 to 20 carbon atoms, preferably 1 to 6 carbon atoms, more preferably 1 to 3 carbon atoms, still more preferably 1 or 2 carbon atoms. is the base.
• monovalent hydrocarbon groups for R 1 include alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl and n-hexyl groups, among which methyl and ethyl are preferred. , n-propyl and isopropyl groups, and particularly preferably methyl and ethyl groups.
• some or all of the hydrogen atoms in these monovalent hydrocarbon groups may be substituted with halogen atoms such as fluorine, chlorine and bromine atoms, preferably fluorine atoms.
• R 2 is the same or different substituted or unsubstituted monovalent hydrocarbon group having 1 to 6 carbon atoms, preferably 1 to 4 carbon atoms, more preferably 1 or 2 carbon atoms.
• monovalent hydrocarbon groups for R 2 include alkyl groups such as methyl, ethyl, n-propyl, isopropyl and n-butyl groups, among which methyl, ethyl and propyl groups are preferred. and particularly preferably a methyl group or an ethyl group.
• some or all of the hydrogen atoms of these monovalent hydrocarbon groups may be substituted with halogen atoms such as fluorine, chlorine and bromine atoms, preferably fluorine atoms.
• R 4 is the same or different monovalent hydrocarbon group having 1 to 6 carbon atoms, preferably 1 to 3 carbon atoms, more preferably 1 or 2 carbon atoms.
• monovalent hydrocarbon groups for R4 include alkyl groups such as methyl, ethyl, n-propyl and n-butyl groups, among which methyl, ethyl and propyl groups are preferred.
• a methyl group and an ethyl group are particularly preferred.
• X is an OH group or a hydrolyzable group.
• the hydrolyzable group for X include halogen atoms such as chlorine and bromine, alkoxy groups such as methoxy and ethoxy, amino groups such as dimethylamino and diethylamino, and acyloxy groups such as acetoxy.
• alkoxy group and an amino group are preferred, and a methoxy group and an ethoxy group are particularly preferred.
• trifunctional silane compounds represented by the above formula (II) include methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, trimethoxysilane such as silane, isopropyltrimethoxysilane, isopropyltriethoxysilane, n-butyltrimethoxysilane, n-butyltriethoxysilane, n-hexyltrimethoxysilane, trifluoropropyltrimethoxysilane, heptadecafluorodecyltrimethoxysilane, etc.
• Alkoxysilanes and the like can be mentioned, and they can be used singly or in combination of two or more. Among these, methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, and ethyltriethoxysilane are preferred, and methyltrimethoxysilane, methyltriethoxysilane, or partial hydrolysis (condensation) thereof are more preferred. ) is the product.
• silazane compound represented by the above formula (III) examples include hexamethyldisilazane, hexaethyldisilazane, and the like, which can be used singly or in combination of two or more. Among these, hexamethyldisilazane is preferred.
• Examples of the monofunctional silane compound represented by the formula (IV) include monosilanol compounds such as trimethylsilanol and triethylsilanol; monochlorosilanes such as trimethylchlorosilane and triethylchlorosilane; monoalkoxy compounds such as trimethylmethoxysilane and trimethylethoxysilane; silanes; monoaminosilanes such as trimethylsilyldimethylamine and trimethylsilyldiethylamine; monoacyloxysilanes such as trimethylacetoxysilane; Among these, trimethylsilanol, trimethylmethoxysilane and trimethylsilyldiethylamine are preferred, and trimethylsilanol and trimethylmethoxysilane are particularly preferred.
• silica Particles Synthetic silica particles are broadly classified into combustion silica, deflagration silica, wet silica, and sol-gel silica (so-called Stoeber method) according to the manufacturing method.
• silica produced by the sol-gel method has excellent monodispersity, is spherical in shape, can be controlled over a wide range of particle diameters, and is porous inside the silica core. It is suitable as the coating material for the secondary battery separator of the present invention because it does not hinder the mobility of ions under certain conditions.
• the surface-treated spherical silica particles used in the present invention are, for example, Step (A1): a step of synthesizing hydrophilic silica particles, Step (A2): surface treatment step with a trifunctional silane compound, Step (A3): concentration step, Step (A4): can be obtained by a production method including a surface treatment step with a monofunctional silane compound.
• the SiO2 unit is converted to obtaining a mixed solvent dispersion of hydrophilic silica particles containing Step (A2):
• the following formula (II) is added to the mixed solvent dispersion of the hydrophilic silica particles R1Si ( OR4 ) 3 (II) (In the formula, R 1 and R 4 are the same as above.)
• a trifunctional silane compound represented by, a partial hydrolysis product thereof, or a mixture thereof to treat the surface of the hydrophilic silica particles
• the surface of the hydrophilic silica particles has R 1 SiO 3 / introducing 2 units (wherein R 1 is the same as above) to obtain a mixed solvent dispersion of the first surface-treated silica particles;
• Step (A1) Synthesis step of hydrophilic silica particles
• formula (I) Si( OR3 ) 4
• a silica particle mixed solvent dispersion is obtained.
• R 3 is the same or different monovalent hydrocarbon group having 1 to 6 carbon atoms, preferably 1 to 4 carbon atoms, more preferably 1 or 2 carbon atoms.
• monovalent hydrocarbon groups for R 3 include alkyl groups such as methyl, ethyl, n-propyl and n-butyl groups; and aryl groups such as phenyl groups. Among them, preferred are methyl, ethyl, n-propyl and n-butyl groups, and more preferred are methyl and ethyl groups.
• Examples of the tetrafunctional silane compound represented by the above formula (I) include tetraalkoxysilanes such as tetramethoxysilane, tetraethoxysilane, tetra-n-propoxysilane and tetra-n-butoxysilane; tetraaryls such as tetraphenoxysilane; Oxysilane and the like can be mentioned, and can be used alone or in combination of two or more.
• Partial hydrolysis condensation products of the tetrafunctional silane compound represented by formula (I) include, for example, methyl silicate and ethyl silicate.
• the hydrophilic organic solvent is not particularly limited as long as it dissolves the tetrafunctional silane compound represented by the formula (I), the partial hydrolysis condensation product thereof, and water.
• cellosolves such as methyl cellosolve, ethyl cellosolve, butyl cellosolve, and cellosolve acetate; ketones such as acetone and methyl ethyl ketone; ethers such as dioxane and tetrahydrofuran; can be done.
• alcohols and cellosolves are preferred, and alcohols are more preferred.
• R 5 is a monovalent hydrocarbon group having 1 to 6 carbon atoms, preferably 1 to 4 carbon atoms, more preferably 1 or 2 carbon atoms.
• monovalent hydrocarbon groups for R 5 include alkyl groups such as methyl, ethyl, n-propyl, isopropyl and n-butyl groups, among which methyl, ethyl, n-propyl, It is an isopropyl group, more preferably a methyl group or an ethyl group.
• Examples of the alcohol represented by the above formula (V) include methanol, ethanol, propanol, isopropanol, butanol, etc. Among them, methanol and ethanol are preferred. As the number of carbon atoms in the alcohol increases, the particle size of the produced silica particles tends to increase. Therefore, methanol is preferable for obtaining the desired small-diameter silica particles.
• examples of the basic substance include ammonia, dimethylamine, diethylamine, etc. Among them, ammonia and diethylamine are preferred, and ammonia is more preferred.
• the obtained aqueous solution may be mixed with the hydrophilic organic solvent.
• the amount of water used at this time is 0.5 to 0.5 to 1 mol of total hydrocarbyloxy groups of the tetrafunctional silane compound represented by the above formula (I), its partial hydrolysis condensation product, or mixture thereof. It is preferably 5 mol, more preferably 0.6 to 2 mol, still more preferably 0.7 to 1 mol.
• the molar ratio of the hydrophilic organic solvent to water is preferably from 0.5 to 10, more preferably from 3 to 9, and even more preferably from 5 to 8 by mass. The larger the amount of the hydrophilic organic solvent, the smaller the desired silica particles.
• the amount of the basic substance is 0.01 to 2 mol per 1 mol of the total hydrocarbyloxy group of the tetrafunctional silane compound represented by the above formula (I), its partial hydrolysis condensation product or mixture thereof. It is preferably 0.02 to 0.5 mol, and still more preferably 0.04 to 0.12 mol. The smaller the amount of the basic substance, the easier it is to obtain the desired small-sized silica particles.
• Hydrolysis and condensation of the tetrafunctional silane compound represented by the above formula (I) can be carried out by a well-known method, that is, in a mixture of a hydrophilic organic solvent containing a basic substance and water, the above formula (I). It is carried out by adding a tetrafunctional silane compound or the like shown.
• the reaction can be carried out under well-known conditions, and the reaction is usually preferably carried out at about 10 to 80° C. for about 1 to 20 hours.
• the concentration of silica particles in the hydrophilic silica particle mixed solvent dispersion obtained in this step (A1) is generally 3 to 15% by mass, preferably 5 to 10% by mass.
• Step (A2) Surface treatment step with a trifunctional silane compound
• the following formula (II) is added to the hydrophilic silica particle mixed solvent dispersion obtained in step (A1).
• R1Si ( OR4 ) 3 (II) By adding a trifunctional silane compound represented by, a partial hydrolysis product thereof, or a mixture thereof to treat the surface of the hydrophilic silica particles with this, R 1 SiO 3/2 is formed on the surface of the hydrophilic silica particles.
• a unit (wherein R 1 is the same as above) is introduced to obtain a mixed solvent dispersion of the first surface-treated silica particles.
• This step (A2) is essential for suppressing aggregation of silica particles in the next step, the concentration step (A3). If this aggregation cannot be suppressed, the individual particles of the resulting silica-based powder cannot maintain their primary particle diameters. As a result, when coated on a separator, the silica particles may aggregate or become uneven. be.
• R 1 and R 4 in formula (II) and the trifunctional silane compound represented by formula (II) are the same as those described for the surface treatment agent for fine silica particles.
• the addition amount of the trifunctional silane compound represented by the above formula (II) is preferably 0.001 to 1 mol, more preferably 0.01 to 0.1 mol, per 1 mol of Si atom of the hydrophilic silica particles. mol, more preferably 0.01 to 0.05 mol. If the amount added is 0.001 mol or more, the dispersibility is improved. Further, if the amount added is 1 mol or less, aggregation of silica particles does not occur.
• the reaction conditions are preferably about 10 to 80° C. for about 1 to 20 hours.
• the concentration of the silica particles in the mixed solvent dispersion of the first surface-treated silica particles obtained in this step (A2) is usually 3% by mass or more and less than 15% by mass, preferably 5 to 10% by mass. be. If the concentration is 3% by mass or more, productivity is improved, and if it is less than 15% by mass, aggregation of silica particles does not occur.
• Step (A3) Concentration step In this step, part of the hydrophilic organic solvent and water is removed from the first surface-treated silica particle mixed solvent dispersion obtained in step (A2), followed by concentration. Thus, a mixed solvent concentrated dispersion of the first surface-treated silica particles that is desired to be concentrated is obtained.
• a hydrophobic organic solvent may be added in advance or during the process. Hydrocarbon solvents, ketone solvents and the like are preferable as the hydrophobic solvent. Specific examples thereof include toluene, xylene; methyl ethyl ketone, methyl isobutyl ketone, etc., which can be used singly or in combination of two or more.
• Methods for removing a portion of the hydrophilic organic solvent and water include, for example, distillation, distillation under reduced pressure, and the like. The conditions at this time are preferably about 10 to 150° C. and about 1 to 20 hours.
• the resulting concentrated dispersion preferably has a silica particle concentration of 15 to 40% by mass, more preferably 20 to 35% by mass, and still more preferably 25 to 30% by mass.
• silica particle concentration is 15% by mass or more, the surface treatment in the post-process goes well, and when it is 40% by mass or less, aggregation of the silica particles does not occur.
• the silazane compound represented by the formula (III) and the monofunctional silane compound represented by the formula (IV) used as surface treatment agents in the next step (A4) are mixed with alcohol or water. It is indispensable for suppressing the problem that the surface treatment becomes insufficient due to the reaction with and the subsequent drying causes agglomeration and the resulting silica powder cannot maintain the primary particle size.
• Step (A4) Surface treatment step with a monofunctional silane compound
• the mixed solvent concentrated dispersion of the first surface-treated silica particles obtained in step (A3) is added with the following formula (III ), a monofunctional silane compound represented by the following formula (IV), or a mixture thereof is added to further surface-treat the surface of the first surface-treated silica particles, thereby obtaining the first surface Second surface-treated silica particles are obtained by introducing R 2 3 SiO 1/2 units (wherein R 2 is the same as above) onto the surface of the treated silica particles.
• R23SiNHSiR23 ( III ) R23SiX ( IV) In this step, the R 2 O 3 SiO 1/2 units are introduced to the surface by triorganosilylating the silanol groups remaining on the surfaces of the first surface-treated silica particles by the above treatment.
• R 2 , X, the silazane compound represented by formula (III), and the monofunctional silane compound represented by formula (IV) in the above formula are the same as those described for the surface treatment agent for silica fine particles. be.
• the amount of the silazane compound and monofunctional silane compound used is preferably 0.1 to 0.5 mol, more preferably 0.2 to 0.4 mol, per 1 mol of Si atoms in the hydrophilic silica particles. mol, particularly preferably 0.25 to 0.35 mol. If the amount used is 0.1 mol or more, the dispersibility will be good. Moreover, if the amount used is 0.5 mol or less, it is economically advantageous.
• the reaction conditions are preferably about 10 to 150° C. for about 1 to 20 hours.
• the obtained surface-treated spherical silica particles can be used as they are as a coating material for secondary battery separators, but it is preferable to use a mixture obtained by mixing and dispersing appropriate amounts of the surface-treated spherical silica particles and a solvent.
• the surface-treated spherical silica particles have excellent dispersibility and maintain a highly dispersed state even when mixed with a solvent, so that they can be applied not only easily to the separator substrate but also uniformly.
• the surface-treated spherical silica particles are preferably dehydrated in advance, and the dehydration is preferably performed by heating. Specifically, it is preferable to provide a dehydration treatment step of drying at a temperature of 160 to 260° C. under normal pressure or reduced pressure for 12 hours or more.
• the surface-treated spherical silica particles used in the present invention have a median diameter (50% cumulative diameter) in the volume-based particle size distribution of 0.01 to 0.5 ⁇ m, preferably 0.01 to 0.4 ⁇ m, and more It is preferably 0.01 to 0.35 ⁇ m.
• the method for measuring the median diameter in the volume-based particle size distribution is as described later.
• the shape of the surface-treated silica particles used in the present invention is spherical.
• spherical means that the degree of circularity is 0.8 to 1.0.
• the circularity is preferably between 0.8 and 0.95.
• a method for measuring the degree of circularity is as described later.
• the coating material for a secondary battery separator of the present invention contains the surface-treated spherical silica particles.
• the content of the surface-treated spherical silica particles is preferably 1-50% by mass, more preferably 2-40% by mass, based on the total amount of the coating material.
• solvent it is preferable to use a solvent in the secondary battery separator coating material of the present invention in order to disperse the surface-treated spherical silica particles in the coating material.
• Alcohols, esters, carbonates, ketones, lactones, ethers, sulfoxides, amides and the like can be used as solvents.
• alcohols include methanol, ethanol, isopropanol, and the like.
• esters include ethyl acetate, methyl propionate, butyl acetate and the like.
• Carbonates include, for example, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, methylethyl carbonate, diethyl carbonate and the like.
• ketones examples include methyl ethyl ketone, methyl isobutyl ketone, methyl propyl ketone, diethyl ketone and the like.
• Lactones include, for example, ⁇ -butyl lactone.
• Ethers include, for example, trimethoxymethane, 1,2-dimethoxyethane, diethyl ether, 2-ethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran and the like.
• sulfoxides examples include dimethylsulfoxide and the like.
• amides examples include N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide, N,N-dimethylacetamide and the like.
• amides such as N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide and N,N-dimethylacetamide are preferred.
• NMP N-methyl-2-pyrrolidone
• N,N-dimethylformamide N,N-dimethylacetamide
• its content is preferably 10 to 80% by mass, more preferably 20 to 70% by mass, based on the total amount of the coating material.
• Binder A binder may be added to the secondary battery separator coating material of the present invention in order to bind the surface-treated spherical silica particles to the separator substrate.
• binders include copolymers of vinylidene fluoride (VDF) and hexafluoropropylene (HFP), copolymers of vinylidene fluoride (VDF), tetrafluoroethylene (TFE), and hexafluoropropylene (HFP); Resin of vinylidene fluoride copolymer such as copolymer of vinylidene chloride (VDF), hexafluoropropylene (HFP), perfluoromethyl vinyl ether (PFMV) and tetrafluoroethylene (TFE); polytetrafluoroethylene (PTFE) Fluorine-based resins such as; fluorine rubber; styrene-butadiene rubber (SBR), ethylene-propylene rubber (EPDM); polymers such as
• vinylidene fluoride copolymer resins are preferred.
• a binder When a binder is used, its content is preferably 1-20% by mass, more preferably 2-10% by mass.
• the coating material for a secondary battery separator of the present invention comprises surface-treated silica particles produced by a method including the above steps (A1) to (A4), etc., optionally together with a solvent, a binder, etc. It can be obtained by mixing according to the method and performing defoaming treatment or the like.
• the method for applying the secondary battery separator coating material of the present invention to the separator substrate is not particularly limited, but for example, bar coater method, spin coating method, dip coating method, offset printing method, screen printing. law, etc.
• the secondary battery separator coating material of the present invention After coating or impregnating the secondary battery separator coating material of the present invention on one side or both sides of the separator base material, it is dried and the excess solvent is removed. When it has pores, a film of a coating material can be formed inside the pores. As a result, it is possible to obtain a separator in which the surface-treated spherical silica particles are bound to the surface of the separator substrate or inside the pores.
• the base material of the separator is not particularly limited as long as it is commonly used in secondary batteries, but nonwoven fabrics can be preferably used.
• the non-woven fabric may have a fiber diameter of 0.1 to 5 ⁇ m (eg, 0.1 ⁇ m, 1 ⁇ m, 5 ⁇ m, etc.), and may vary depending on various methods, but is not particularly limited in the present invention. Examples of fibers include cellulose fiber, pulp fiber, carbon fiber, glass fiber, ceramic fiber, aramid fiber, vinylon fiber, and polyamide fiber. becomes expensive.
• the thickness of the substrate is preferably 30 ⁇ m or less, more preferably 20 ⁇ m or less. Although the lower limit is not particularly limited, it is preferably 1 ⁇ m or more.
• the nonwoven fabric is preferably dehydrated in advance before applying the secondary battery separator coating material of the present invention, specifically, at a temperature of 130 to 260 ° C., particularly 140 to 200 ° C., normal pressure or reduced pressure. It is preferable to provide a dehydration treatment step of drying for 12 hours or more under a low temperature environment.
• the amount of the surface-treated spherical silica particles applied to the separator substrate is 0.07 to 0.29 mg/cm 2 , preferably 0.11 to 0.29 mg/cm 2 . If it is less than 0.07 mg/cm 2 , the resulting secondary battery separator will be inferior in battery characteristics and flame retardancy in long-term charge-discharge cycles, and if it exceeds 0.29 mg/cm 2 , the thickness of the separator will increase. , a problem arises that the internal electric resistance increases.
• the thickness of the obtained separator is preferably 30 ⁇ m or less, more preferably 25 ⁇ m or less, and even more preferably 24 ⁇ m or less. Although the lower limit is not particularly limited, it is preferably 1 ⁇ m or more.
• the secondary battery using the separator coated with the coating material of the present invention is not particularly limited, but includes a positive electrode and a negative electrode, a separator inserted between these electrodes, and a non-aqueous electrolyte.
• Preferred are lithium ion secondary batteries.
• Positive Electrode Positive electrode materials include positive electrode active materials, conductive agents, binders, viscosity modifiers, and the like.
• the positive electrode active material may be lithium or a compound containing lithium, and may be used singly or in combination of two or more.
• Specific examples of lithium-containing compounds include lithium composite oxides containing lithium.
• a lithium composite oxide mainly composed of Li p MetO 2 is preferable in order to increase the energy density.
• Met is preferably at least one of cobalt, nickel, iron and manganese, and p is usually a value within the range of 0.05 ⁇ p ⁇ 1.10.
• lithium composite oxides include LiCoO 2 , LiNiO 2 , LiFeO 2 and Li q Ni r Co 1-r O 2 having a layer structure (wherein the values of q and r are 0 ⁇ q ⁇ 1, 0.7 ⁇ r ⁇ 1, depending on the discharge state), LiNi 0.8 Co 0.1 Mn 0.1 O 2 , spinel structure LiMn 2 O 4 , orthorhombic LiMnO 2 and the like. be done.
• LiMet s Mn 1-s O 4 (0 ⁇ s ⁇ 1) is also used as a substituted spinel manganese compound as a high voltage type, where Met is titanium, chromium, iron, cobalt, nickel, copper, Zinc etc. are mentioned.
• Lithium composite oxides are produced, for example, by pulverizing and mixing lithium carbonates, nitrates, oxides or hydroxides and transition metal carbonates, nitrates, oxides or hydroxides according to the desired composition, and oxygen It can be prepared by firing at a temperature within the range of 600 to 1,000° C. in an atmosphere.
• the negative electrode material includes a negative electrode active material, a conductive agent, a binder, a viscosity modifier, and the like.
• One of the negative electrode active materials can be used alone, or two or more of them can be appropriately selected and used.
• Specific examples of the negative electrode active material include non-graphitizable carbon, graphitizable carbon, graphite, pyrolytic carbons, cokes, vitreous carbons, baked organic polymer compounds, and carbon fibers. , carbon materials such as activated carbon, and the like. Also included are materials that are capable of intercalating and deintercalating lithium and that contain at least one element selected from metallic elements and metalloid elements as constituent elements.
• metal powders and metal fibers such as Al, Ti, Fe, Ni, Cu, Zn, Ag, Sn, and Si, or natural graphite, artificial graphite, various coke powders, mesophase carbon, and vapor-grown carbon fibers.
• pitch-based carbon fiber, PAN-based carbon fiber, graphite such as various resin sintered bodies, and the like can be used. These can be used singly or in combination of two or more.
• binders examples include polyimide resin, polyamide resin, polyamideimide resin, polyvinylidene fluoride (PVDF) resin, styrene-butadiene rubber (SBR), and the like. These can be used singly or in combination of two or more.
• PVDF polyvinylidene fluoride
• SBR styrene-butadiene rubber
• viscosity modifiers examples include carboxymethylcellulose, sodium polyacrylate, other acrylic polymers, fatty acid esters, and the like. These can be used singly or in combination of two or more.
• Preferable content (solid content mass%) of each component in the positive electrode material is 90 to 98% by mass of the positive electrode active material, 0.5 to 5.0% by mass of the conductive agent, and 0.5 to 5.0% by mass of the binder. %, and the viscosity modifier is 0 to 3.0% by mass.
• Preferred contents of each component in the negative electrode material (solid content mass%) are negative electrode active material 75 to 98 mass%, conductive agent 1 to 20 mass%, binder 1 to 20 mass%, viscosity modifier 0 mass%. ⁇ 3.0% by mass.
• Non-aqueous electrolyte examples include light metal salts.
• Light metal salts include alkali metal salts such as lithium salts, sodium salts and potassium salts; alkaline earth metal salts such as magnesium salts and calcium salts; and aluminum salts.
• specific examples of lithium salts include LiBF4 , LiClO4 , LiPF6 , LiAsF6 , CF3SO3Li , ( CF3SO2 ) 2NLi , C4F9SO3Li , and CF3CO2Li .
• the non-aqueous solvent for the electrolyte is not particularly limited as long as it can be used as a non-aqueous electrolyte.
• aprotic high dielectric constant solvents such as ethylene carbonate, propylene carbonate, butylene carbonate, ⁇ -butyrolactone; dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, methylpropyl carbonate, dipropyl carbonate, diethyl ether, tetrahydrofuran, 1,2 -Aprotic low viscosity such as dimethoxyethane, 1,2-diethoxyethane, 1,3-dioxolane, sulfolane, methylsulfolane, acetonitrile, propionitrile, anisole, acetate esters such as methyl acetate, propionate esters, etc.
• a solvent etc. are mentioned. It is desirable to use these aprotic high dielectric constant solvents and aprotic low viscosity solvents together in a proper mixing ratio. Additionally, ionic liquids with imidazolium, ammonium, and pyridinium type cations can be used. Counter anions include, but are not limited to, BF 4 ⁇ , PF 6 ⁇ , (CF 3 SO 2 ) 2 N ⁇ and the like. The ionic liquid can be used by mixing with the non-aqueous electrolyte solvent described above.
• polymer materials such as glass-based inorganic solid electrolytes, polyether gels, silicone gels, silicone polyether gels, acrylic gels, silicone acrylic gels, acrylonitrile gels, poly(vinylidene fluoride), etc. It can be contained as In addition, these may be polymerized in advance, or may be polymerized after injection. These can be used singly or as a mixture of two or more.
• additives may be added to the non-aqueous electrolyte as necessary.
• vinylene carbonate, methylvinylene carbonate, ethylvinylene carbonate, 4-vinylethylene carbonate, etc. for the purpose of improving cycle life
• biphenyl, alkylbiphenyl, cyclohexylbenzene, t-butylbenzene, diphenyl ether, etc. for the purpose of overcharge prevention
• examples include benzofuran, various carbonate compounds such as carbon dioxide gas, various carboxylic acid anhydrides, and various nitrogen-containing and sulfur-containing compounds for the purpose of deoxidizing and dehydrating.
• partially fluorine-substituted compounds of these compounds are also preferably used.
• the non-aqueous electrolyte secondary battery has a battery case that seals the above battery configuration, and the shape is arbitrary, and there are no particular restrictions.
• a coin-type battery in which a coin-shaped electrode and a separator are laminated, and a prismatic or cylindrical battery in which an electrode sheet and a separator are spirally wound can be used.
• Step (S2) Surface treatment step with a trifunctional silane compound
• a trifunctional silane compound To the suspension obtained in the above step (S1), 4.4 g (0.03 mol) of methyltrimethoxysilane was added at 25°C to 0.5. After dropping, stirring was continued for 12 hours to treat the surface of the silica particles, thereby obtaining a first surface-treated silica particle dispersion.
• Step (S4) Surface treatment step with a monofunctional silane compound
• a monofunctional silane compound To the concentrated dispersion obtained in the previous step, 138.4 g (0.86 mol) of hexamethyldisilazane was added at 25°C, and then this dispersion was added. The liquid was heated to 50 to 60° C. and reacted for 9 hours to trimethylsilylate the silica particles in the dispersion. Then, the solvent in this dispersion was distilled off at 130° C. under reduced pressure (6,650 Pa) to obtain 186 g of second surface-treated silica particles [1].
• Step (S2) Surface treatment step with a trifunctional silane compound
• Add 11.6 g of methyltrimethoxysilane (molar ratio to tetramethoxysilane) to the suspension obtained in the step (S1) at 25°C 0.01 equivalent) was added dropwise over 0.5 hours, and the mixture was stirred for 12 hours after the dropwise addition to obtain the first surface-treated silica particles.
• ⁇ Step (S3) Concentration step Next, an ester adapter and a cooling pipe are attached to the glass reactor, and 1,440 g of methyl isobutyl ketone is added to the dispersion obtained in the previous step, and then heated to 80 to 110 ° C. Then, the mixture of methanol and water was distilled off over 7 hours to obtain a mixed solvent concentrated dispersion of the first surface-treated silica particles.
• step (S4) the same operation as in Synthesis Example 1 was performed except that the solvent in this dispersion was distilled off at 130° C. under reduced pressure (6,650 Pa) without adding hexamethyldisilazane. 179 g of treated silica particles [8] were obtained.
• ⁇ Particle size ⁇ Surface-treated silica particles were added to methanol so as to be 0.5% by mass, and ultrasonic waves were applied for 10 minutes to disperse the particles, and a dynamic light scattering method/laser Doppler method nanotrack particle size distribution measuring device ( The volume-based particle size distribution was measured using UPA-EX150 (trade name, manufactured by Nikkiso Co., Ltd.), and the median diameter (50% cumulative diameter) in the particle size distribution was calculated.
• Tables 2 and 3 show the thickness of the obtained secondary battery separator, the results of the combustion test test, and the characteristics of the lithium ion battery. Comparative Example 2-31 shows the result of a secondary battery separator in which the coating material is not applied to the nonwoven fabric.
• the thickness of the resulting secondary battery separator was measured with a thickness gauge. When the thickness was 24 ⁇ m or less, it was evaluated as ⁇ ;
• Battery characteristics were evaluated for lithium ion secondary batteries manufactured by the following procedure.
• negative electrode material Graphite as a negative electrode active material was layered and adhered to a metal plate, and a lead-out electrode (tab) was electrically welded to a metal portion not coated with the negative electrode active material to form a negative electrode material.
• a polyimide tape was attached to the entire back side, which was not in close contact with the separator, to provide electrical insulation.
• the laminate was filled with an electrolytic solution in a glove box filled with dry N 2 from the end face that was not crimped.
• the electrolytic solution used was a LiPF 6 1 mol/L [ethylene carbonate:ethylene carbonate (1:1% by volume)] solution.
• the release portion was welded with a vacuum heating laminator in a glove box to obtain a lithium ion battery.
• the lithium ion battery obtained above is subjected to preliminary charge and discharge (chemical conversion treatment), then charged to 4.1 V at a current value of 0.2 cA in a 30 ° C. constant temperature bath, and then the current value is 0. It was charged at a constant voltage of 4.1 V to 0.02 cA. After charging, the battery was repeatedly discharged to 2.7 V at a current value of 0.2 cA.
• the battery capacity after 500 charging/discharging cycles was obtained when the initial capacity was assumed to be 100%, and the retention rate was calculated.
• a maintenance rate of 85% or more was indicated by ⁇
• a maintenance rate of 80% or more was indicated by ⁇
• a maintenance rate of less than 80% was indicated by ⁇ .
• the coating amount of the separator was within the range of 0.07 to 0.29 mg/cm
• the thickness of the battery, the combustion test, and the battery characteristics were all good (Examples 2-1 to 2-15).
• the results of the battery characteristic test showed that the battery capacity retention rate after 500 charge-discharge cycles was insufficient. became.
• the result of the combustion test was insufficient.

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