JP6710920B2 - Ceramic slurry and battery separator using the same - Google Patents

Description

The present invention provides a ceramic slurry capable of forming a porous layer that has both a low water content and shape stability when heated at a low temperature and in a short drying step, and a non-porous ceramic layer having the porous layer formed from the ceramic slurry. The present invention relates to a separator for a water electrolyte secondary battery and a non-aqueous electrolyte secondary battery using the separator.

BACKGROUND ART Porous membranes made of thermoplastic resin are widely used as materials for separating substances, selectively permeating and separating substances, and the like. For example, lithium secondary batteries, nickel-hydrogen batteries, nickel-cadmium batteries, battery separators for polymer batteries, separators for electric double layer capacitors, reverse osmosis filtration membranes, ultrafiltration membranes, various filters such as microfiltration membranes. It is used in breathable waterproof clothing, medical materials, etc. In particular, a polyethylene porous film is preferably used as a separator for a lithium ion secondary battery, because it has excellent electrical insulation properties, has ion permeability when impregnated with an electrolytic solution, and has electrolyte resistance and acid resistance. This is because it has not only the characteristic of being excellent in chemical conversion property, but also the hole blocking effect of blocking the current at a temperature of about 120 to 150° C. at the time of abnormal temperature rise of the battery to suppress excessive temperature rise. However, if the temperature continues to rise even after the pores are closed for some reason, the membrane may break at a certain temperature due to the decrease in the viscosity of the melted polyethylene that constitutes the membrane and the shrinkage of the membrane. When left at a constant high temperature, the viscosity of molten polyethylene may decrease and the membrane may shrink, which may cause membrane rupture after a certain period of time. This phenomenon is not limited to polyethylene, and even when another thermoplastic resin is used, it cannot be avoided at a temperature equal to or higher than the melting point of the resin forming the porous film.

Lithium ion secondary battery separators are closely related to battery characteristics, battery productivity and battery safety, and have excellent mechanical characteristics, heat resistance, permeability, low water content, dimensional stability, pore blocking characteristics (shutdown). Properties), melt film breakage prevention properties (meltdown prevention properties), and the like. In particular, when the heat resistance is low, there is a risk of battery ignition due to thermal contraction of the separator in a high temperature environment, contact between the positive electrode and the negative electrode, and a short circuit. It is also known that when the water content is high, the battery constituent material reacts with water to deteriorate the battery performance. Therefore, it is desired that the separator has a high thermal contraction and a low water content.

On the other hand, non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries have been widely used in recent years as power sources for portable electronic devices and transportation equipment. In particular, a lithium-ion secondary battery that is lightweight and has a high energy density is suitably used as a high-output power source for driving a vehicle, and further cost reduction is required while ensuring safety.

Against this background, various separators for lithium ion secondary batteries have been studied so far. For example, in Patent Documents 1 to 6, a laminated porous membrane in which a porous layer containing an insulating inorganic filler is formed on the surface of a resin porous membrane containing a thermoplastic resin to improve heat resistance is used as a separator. Is proposed. However, in any of the separators described in any of the documents, it is essential to reduce the particle size of the inorganic filler in order to obtain the required heat resistance. To reduce the particle size of the inorganic filler, the crushing process using various crushers such as a ball mill, a vibration mill, a jet mill, and a media stirring mill, sieving, and classification processes such as airflow classification are bulky, so the inorganic filler productivity is high. To increase the cost, which in turn leads to an increase in the cost of the separator using the inorganic filler. Further, by reducing the particle size of the inorganic filler, the specific surface area increases and the surface adsorbed water increases, so that the water content of the laminated porous membrane is high, and there is a concern that it may affect the battery characteristics.

JP, 2008-123996, A JP, 2004-227972, A JP, 2008-186721, A JP, 2013-101954, A JP, 2014-2954, A International Publication No. 2013/073011

It is very important to control the particle size distribution of the inorganic filler in order to form a porous layer that has both a low water content and a stable shape when heated in a drying process at low temperature and for a short time. In order to achieve a low water content, it is conceivable to increase the particle size of the inorganic filler, and to achieve shape stability during heating, sharply control the particle size distribution of the inorganic filler. However, in order to obtain the inorganic filler, classification processes such as sieving and air flow type classification are essential, so that the productivity of the inorganic filler is deteriorated and the cost is increased, which is not realistic.

An object of the present invention is to provide a ceramic slurry capable of forming a porous layer having both a low water content and a shape stability at the time of heating at a low temperature and a short drying step, and a porous layer formed from the ceramic slurry. It is to provide a non-aqueous electrolyte secondary battery separator having the same at low cost.

In order to solve the above problems, the ceramic slurry of the present invention has the following constitution.
That is,
(1) A compound containing an inorganic filler, a water-soluble binder resin, an additive and a solvent, wherein the additive has a cationic or amphoteric character and is a compound that causes the inorganic filler to coagulate, and the average particle size of the aggregate of the inorganic filler in the ceramic slurry. Is 1.0 μm or more and 2.5 μm or less, and the volume distribution of less than 1.0 μm is less than 17 vol%.
(2) In the ceramic slurry of the present invention, the inorganic filler preferably has an average particle size of 1.0 μm or more and 2.5 μm or less, and a volume distribution of less than 1.0 μm is 17 vol% or more.
(3) In the ceramic slurry of the present invention, the additive preferably has a weight average molecular weight of 50,000 or less.
(4) In the ceramic slurry of the present invention, the water-soluble binder resin is selected from the group consisting of a hydroxyl group and an acetic acid group, a carboxyl group or an ammonium salt or amine salt thereof, a sulfonic acid group or an ammonium salt or amine salt thereof. And a second polymer having a main chain of an alkyl chain and at least one selected from the group consisting of an amide group, a carboxyl group or its ammonium salt or amine salt in the side chain. It is preferably a molecular compound.
(5) In the ceramic slurry of the present invention, the first polymer compound is polyvinyl alcohol, ethylene-vinyl alcohol copolymer, acrylic acid-vinyl alcohol copolymer or its ammonium salt or amine salt, sulfonic acid-vinyl alcohol. It is preferably at least one selected from the group consisting of a copolymer or its ammonium salt or amine salt, carboxymethyl cellulose or its ammonium salt or amine salt.
(6) In the ceramic slurry of the present invention, the second polymer compound preferably has a weight average molecular weight of 50,000 or less.
(7) The ceramic slurry of the present invention preferably contains the water-soluble binder resin in an amount of 0.8 or more and less than 2.0 parts by mass with respect to 100 parts by mass of the inorganic filler.
(8) In the ceramic slurry of the present invention, the inorganic filler is preferably alumina.
In order to solve the above problems, the battery separator of the present invention has the following configuration.
That is,
(9) An inorganic filler, a water-soluble binder resin, a cationic or amphoteric additive is included, and the average particle size of the inorganic filler is 1.0 μm or more and 2.5 μm or less, and the volume distribution of less than 1.0 μm is less than 17 vol %. Is a battery separator.
(10) The battery separator of the present invention is preferably used in a non-aqueous electrolyte secondary battery.
In order to solve the above-mentioned subject, the manufacturing method of the battery separator of the present invention has the following composition.
That is,
(11) A method for manufacturing a battery separator, in which the ceramic slurry is applied onto a porous membrane and the solvent is removed to form a porous layer.

It is possible to inexpensively provide a battery separator having a porous layer that has both a low water content and shape stability when heated at a low temperature and in a short drying process.

The present inventor diligently studied a material capable of forming a porous layer which is inexpensive, has high productivity by a drying process at low temperature, and has low moisture content and shape stability at the time of heating. The agent is a compound which has a cationic or amphoteric property and coagulates the inorganic filler. By condensing the inorganic filler with the additive, the particle size distribution of the inorganic filler in the ceramic slurry is controlled, and the inorganic filler in the ceramic slurry is controlled. By setting the filler aggregate to have an average particle size of 1.0 μm or more and 2.5 μm or less and a volume distribution of less than 1.0 μm of less than 17 vol%, a low water content in a low-temperature and short-time drying step and heating can be achieved. It was found that a ceramic slurry capable of forming a porous layer having both shape stability can be provided at low cost. In addition, to condense the inorganic filler as referred to herein means to repel the inorganic filler that is electrically repelled in the slurry and drifts by the force of ions to form a small aggregate by intermolecular force. .. The inorganic filler aggregate is an aggregate of inorganic fillers obtained by weak interaction.

Details of the present invention will be described below.
1. Ceramic Slurry [1] Inorganic Filler As the inorganic filler used in the present invention, an inorganic filler generally called a filler can be used. As the inorganic filler, alumina, boehmite, calcium carbonate, calcium phosphate, amorphous silica, crystalline glass filler, kaolin, talc, titanium dioxide, silica-alumina composite oxide particles, barium sulfate, calcium fluoride, lithium fluoride. , Zeolite, molybdenum sulfide, mica and the like. In particular, alumina is preferable. The surface of alumina has a negative charge in the pH range (6 to 9) of the present ceramic slurry, and the particle size distribution can be easily controlled by a coagulant having a cationic property or an amphoteric property.

The inorganic filler used in the present invention preferably has an average particle size of 1.0 μm or more and 2.5 μm or less and a volume distribution of less than 1.0 μm of 17 vol% or more. Since the inorganic filler has a volume distribution of less than 1.0 μm in an amount of 17 vol% or more, it is possible to control the particle size distribution using an additive that causes the inorganic filler to coagulate in the ceramic slurry, and improve the packing property. This dramatically improves the shape stability of the porous layer when heated. Inorganic fillers with a volume distribution of 1.0 μm or more and 2.5 μm or less and less than 1.0 μm and less than 17 vol% have to undergo classification processes such as sieving and air flow type classification, which deteriorates the productivity of the inorganic fillers and increases the cost. Is not realistic. The average particle size and the volume distribution of less than 1.0 μm means that a ceramic slurry is added to water by using a laser scattering particle size distribution meter (“MT3300EXII” manufactured by Microtrac Bell (former Nikkiso Co., Ltd.)), and the flow rate is 3% at 45%. The particle size (D50) at 50% in the volume-based integrated fraction measured within 10 minutes after circulating for 10 minutes, and the volume-based integrated amount of particles having a particle size of less than 1.0 μm. Note that these measurement results differ greatly under different measurement conditions, so caution is required.

The average particle size of the inorganic filler aggregate in the ceramic slurry is 1.0 μm or more and 2.5 μm or less, and the volume distribution of less than 1.0 μm is preferably less than 17 vol %, more preferably 1.0 μm or more.2. The volume distribution of 5 μm or less and less than 1.0 μm is less than 15 vol %. If the average particle size is less than 1.0 μm, the specific surface area of the inorganic filler increases and the surface adsorbed water increases, so if the drying step after coating the ceramic slurry is performed at a low temperature for a short time, the water content of the porous layer will increase. Get higher When it is larger than 2.5 μm, it is difficult to control the film thickness of the porous layer to 4 μm or less. When the volume distribution of less than 1.0 μm is 17 vol% or more, the packing property of the inorganic filler aggregate is significantly reduced, and the shape stability of the porous layer during heating is deteriorated.

[2] Water-soluble binder resin As the water-soluble binder resin, the first polymer compound for the purpose of adhesion to the porous film and the binder effect of the inorganic filler, and the first polymer compound for the purpose of stabilizing the dispersion of the inorganic filler are used. Two polymer compounds are required.

The first polymer compound preferably has a hydroxyl group and at least one selected from the group consisting of an acetic acid group, a carboxyl group or its ammonium salt or amine salt, a sulfonic acid group or its ammonium salt or amine salt. Having a hydroxyl group improves the adhesion of the porous layer to the porous membrane. The presence of the carboxyl group enhances the binder effect on the inorganic filler and improves the temporal stability of the ceramic slurry. In addition, when the carboxyl group is converted to its ammonium salt or amine salt, the counter anion volatilizes and the water retention effect of the binder decreases, so that drying at low temperature and in a short time becomes possible.

In particular, the first polymer compound is polyvinyl alcohol, ethylene-vinyl alcohol copolymer, acrylic acid-vinyl alcohol copolymer or an ammonium salt or amine salt thereof, sulfonic acid-vinyl alcohol copolymer or an ammonium salt thereof. It is preferably at least one selected from the group consisting of amine salts, carboxymethyl cellulose or ammonium salts or amine salts thereof.

The first polymer compound is preferably contained in an amount of 0.6 parts by mass or more and 1.7 parts by mass or less based on 100 parts by mass of the inorganic filler. When the amount is 0.6 parts by mass or more, the adhesiveness of the porous layer to the porous film, the binder effect of the inorganic filler can be obtained, the desorption of the inorganic filler from the porous film, and the heating of the porous layer Shape stability can be improved. When the amount is 1.7 parts by mass or less, clogging of the porous membrane and voids between the inorganic fillers are reduced, and deterioration of battery characteristics due to increase in air permeation resistance can be prevented.

The second polymer compound preferably has an alkyl chain as the main chain and has at least one selected from the group consisting of an amide group, a carboxyl group, or an ammonium salt or amine salt thereof in the side chain. When the carboxyl group is converted to its ammonium salt or amine salt, the counter anion is volatilized and the water retention effect of the binder is reduced, so that drying at low temperature and in a short time is possible.

Particularly, the second polymer compound is polyacrylamide, ethylene-acrylic acid copolymer or its ammonium salt or amine salt, polyacrylic acid or its ammonium salt or amine salt, acrylamide-acrylic acid copolymer or its ammonium salt. Alternatively, at least one selected from the group consisting of amine salts is preferable.

The weight average molecular weight of the second polymer compound is preferably 50,000 or less. By setting it to 50,000 or less, sedimentation of the inorganic filler can be suppressed.

The second polymer compound is preferably contained in an amount of 0.1 part by mass or more and 0.6 part by mass or less based on 100 parts by mass of the inorganic filler. When the amount is 0.1 part by mass or more, the dispersion stabilizing effect can be obtained, and it is possible to prevent the insufficient temporal stability of the ceramic slurry due to the sedimentation of the inorganic filler. When the amount is 0.6 parts by mass or less, clogging of the porous film and voids between the inorganic fillers are reduced, and deterioration of battery characteristics due to increase in air permeation resistance can be prevented.

The water-soluble binder resin is preferably contained in an amount of 0.8 parts by mass or more and less than 2.0 parts by mass with respect to 100 parts by mass of the inorganic filler, more preferably 1.0 part by mass or more and less than 2.0 parts by mass. is there. By the amount of 0.8 parts by mass or more, the adhesiveness of the porous layer to the porous film, the binder effect of the inorganic filler, and the dispersion stabilizing effect can be obtained, and the desorption of the inorganic filler from the porous film and the porosity. It is possible to improve the shape stability of the quality layer during heating and prevent the ceramic slurry from being insufficiently stable over time due to sedimentation of the inorganic filler. When the amount is less than 2.0 parts by mass, the clogging of the porous film and the voids between the inorganic fillers are reduced, and the deterioration of the battery characteristics due to the increase in air permeation resistance can be prevented.

[3] Additive The additive is a compound or mixture having a cationic property or an amphoteric property that coagulates the inorganic filler. The term "cationic or amphoteric compound" as used herein refers to any of an organic compound, an inorganic compound, and an organometallic compound, and in the case of an organic compound, a cationic functional group, or a cationic functional group and an anionic functional group. A water-soluble compound having a polyvalent metal ion, which is a compound having both groups and is an inorganic compound or an organometallic compound. By having a cationic property, it becomes possible to neutralize the negatively charged inorganic filler and the binder charge adsorbed to the periphery of the inorganic filler for the purpose of stabilizing the dispersion, and efficiently condense the inorganic filler.

The weight average molecular weight of the additive is preferably 50,000 or less. When the weight average molecular weight is 50,000 or less, the particle size distribution can be controlled, the packing property of the inorganic filler aggregate is increased, and the shape stability of the porous layer upon heating is improved.

Additives that coagulate the inorganic filler include organic coagulants and inorganic coagulants. Examples of the organic coagulant include dimethyldiallylammonium chloride polymer, alkylamine-epichlorohydrin condensate, alkylenedichloride-polyalkylenepolyamine condensate, alkylaminomethacrylate quaternary salt polymer, alkylaminoacrylate quaternary salt/acrylamide copolymer, Examples thereof include cationic organic polymer compounds such as polyamidine hydrochloride, and amphoteric organic polymer compounds such as acrylamide/acrylic acid/alkylaminomethacrylate quaternary salt copolymers. As the inorganic coagulant, for example, polyaluminum chloride, aluminum sulfate, ferric chloride, ferrous sulfate, polysulfate, titanium triethanolaminate, titanium lactate, titanium lactate ammonium salt, titanium diethanolaminate, titanium aminoethyl. Examples thereof include cationic or amphoteric metal compounds such as aminoethanolate, ammonium peroxocitrate tetrahydrate, zirconium tetraacetylacetonate, zirconyl chloride compounds, zirconium lactate ammonium salts, and polyvalent metal salts. These coagulants may be used alone or in combination of two or more.

[4] Solvent The solvent preferably contains water as a main component from the viewpoint of solubility of the water-soluble binder resin and dispersibility of the inorganic filler, and more preferably water.

2. Method for Manufacturing Ceramic Slurry The ceramic slurry of the present invention is manufactured by mixing and dispersing an inorganic filler, a water-soluble binder resin and a water-soluble compound containing water, and then adding an additive and mixing. The details will be described below.

The method of mixing and dispersing the inorganic filler to obtain the ceramic slurry is not particularly limited as long as it is a method of obtaining a homogeneous ceramic slurry. For example, a mechanical stirring method, an ultrasonic dispersion method, a high pressure dispersion method, a media dispersion method and the like can be mentioned. Among them, the media dispersion method is preferable because the inorganic filler can be highly dispersed and the inorganic filler and the water-soluble binder resin can be made compatible with each other in a short time.

The order of mixing is not limited as long as there are no particular obstacles such as the occurrence of precipitates in the ceramic slurry, but it is possible to mix and disperse the inorganic filler, the water-soluble binder resin and water, and then add the additives and mix. is necessary. If a strong shearing force is applied after the addition of the additive, for example, a media dispersion method, the aggregate of the inorganic filler aggregated by the additive is crushed and the particle size distribution cannot be controlled.

3. Battery Separator The battery separator of the present invention comprises a porous film and a porous layer formed from the above ceramic slurry on at least one surface thereof. The details will be described below.

[1] Porous Membrane As the resin constituting the porous membrane, the melting point (softening point) of the resin is preferably 70 to 150 from the viewpoint of the function of pores being closed when the charge/discharge reaction is abnormal (pore closing function). C., more preferably 80 to 140.degree. C., most preferably 100 to 130.degree.

Examples of the porous film include a polyolefin microporous film whose constituent resin is a polyolefin resin. In particular, a polyethylene microporous membrane whose constituent resin is a polyethylene resin is preferable from the viewpoint of electrical insulation, ion permeability, or pore blocking effect.

The weight average molecular weight of the polyolefin resin is preferably 300,000 or more, from the viewpoint of process workability and mechanical strength (for example, tensile strength, elastic modulus, elongation, puncture strength) that can withstand various external pressures generated when the electrode and the electrodes are relieved. , More preferably 400,000 or more, most preferably 500,000 or more. When a polyolefin resin is used, it is preferable that the polyolefin component having a weight average molecular weight in the above range is contained in an amount of 50% by weight or more, and more preferably 60% by weight or more. If the content is less than the above range, the melt viscosity is low, so the mechanical properties are significantly reduced when the temperature is raised above the hole blocking temperature, and due to the pressure and the burr at the electrode end even near the hole closing temperature. Melt rupture may occur.

The layer structure of the porous membrane differs depending on the manufacturing method. Within the range where the above-mentioned various characteristics are satisfied, a layered structure can be freely provided according to the purpose by the manufacturing method. Methods for producing porous membranes include foaming method, phase separation method, dissolution recrystallization method, stretch opening method, powder sintering method, etc. Among these methods, phase separation is performed in terms of uniformization of fine pores and cost. Method is preferred.

The upper limit of the air permeation resistance (JIS-P8117) of the porous membrane is preferably 500 seconds/100 ccAir, more preferably 400 seconds/100 ccAir, most preferably 300 seconds/100 ccAir, and the lower limit is preferably 50 seconds/100 ccAir. , More preferably 70 seconds/100 ccAir, most preferably 100 seconds/100 ccAir.

[2] Porous Layer The porous layer is formed by applying a ceramic slurry to at least one surface of the porous membrane and removing the solvent.
The method for applying the ceramic slurry to the porous film is not particularly limited as long as it is a method capable of uniformly performing wet coating, and a conventionally known method can be adopted. For example, gravure coater method, small diameter gravure coater method, reverse roll coater method, transfer roll coater method, kiss coater method, dip coater method, knife coater method, air doctor coater method, blade coater method, rod coater method, squeeze coater method, cast Examples thereof include a coater method, a die coater method, a screen printing method, and a spray coating method.

The method for removing the solvent is not particularly limited as long as it does not adversely affect the porous membrane. Specific examples include a method of heating and drying the porous membrane at a temperature below its melting point while fixing the porous membrane, and a method of drying under reduced pressure. However, the method of heating and drying is preferable because it simplifies the process.

The heating and drying temperature is preferably 70° C. or lower, more preferably 60° C. or lower, and most preferably 50° C. or lower. The heating and drying time is preferably several seconds to several minutes. When the heating and drying temperature is higher than 70° C., the pore blocking function of the porous membrane may be exhibited and the battery characteristics may be deteriorated. Further, when the heating and drying temperature is higher than 70° C. and the heating and drying time exceeds several minutes, the amount of heat used in the drying step increases and the manufacturing cost increases.

The inorganic filler aggregate in the porous film has an average particle size of 1.0 μm or more and 2.5 μm or less, and a volume distribution of less than 1.0 μm is preferably less than 17 vol %, more preferably 1.0 μm or more 2 The volume distribution of 0.5 μm or less and less than 1.0 μm is less than 15 vol %. When the average particle size is 1.0 μm or more and 2.5 μm or less, the specific surface area of the inorganic filler becomes small, and the surface adsorbed water decreases, so that the water content of the porous layer becomes low and the film thickness of the porous layer becomes small. It becomes possible to control to 4 μm or less. When the volume distribution of less than 1.0 μm is less than 17 vol %, the packing property of the inorganic filler aggregate is improved and the shape stability of the porous layer during heating is improved. The average particle size and the volume distribution of less than 1.0 μm used herein means a laser scattering particle size distribution meter (“MT3300EXII” manufactured by Microtrac Bell (formerly Nikkiso) Co., Ltd.), and a battery separator is dipped in the inorganic filler. After the extraction, the extract was added, and while circulating at a flow rate of 45%, ultrasonic waves were output at 25 W for 10 minutes, and then the particle size at 50% in the volume-based cumulative fraction measured within 10 minutes. (D50) and the volume-based integrated amount of particles having a particle size of less than 1.0 μm. Note that these measurement results differ greatly under different measurement conditions, so caution is required.

The thickness of the porous layer is preferably 1 to 10 μm, more preferably 2 to 5 μm. When the film thickness is within the above-mentioned preferred range, it is possible to secure the film rupture strength and the insulating property when the porous film is melted and contracted at the melting point or more, and the pore blocking function can be obtained. Further, the winding volume can be suppressed to be small, which is suitable for increasing the capacity of the battery which will be advanced in the future. The porous layer may be formed on one surface of the porous membrane or on both surfaces thereof.

[3] Physical Properties of Battery Separator The water content of the battery separator of the present invention is preferably 500 ppm or less, more preferably 450 ppm or less. When it is 500 ppm or less, the reaction between the battery constituent material and water can be suppressed, and the deterioration of the battery performance can be prevented.

Regarding the shape stability of the battery separator of the present invention when heated (heat shrinkage when heated at 130° C.), the smaller value in the machine direction (MD) or the width direction (TD) is preferably 3% or less. And more preferably 2% or less. When the content is 3% or less, it is possible to prevent a short circuit due to contact between the positive electrode and the negative electrode due to thermal contraction of the separator during abnormal battery heat generation.

[4] Battery The battery separator of the present invention can be suitably used for both a battery using an aqueous electrolytic solution and a battery using a non-aqueous electrolyte. Specifically, it can be preferably used as a separator for secondary batteries such as nickel-hydrogen batteries, nickel-cadmium batteries, nickel-zinc batteries, silver-zinc batteries, lithium secondary batteries and lithium polymer secondary batteries. Especially, it is preferable to use it as a separator of a lithium ion secondary battery. In a lithium ion secondary battery, a positive electrode and a negative electrode are laminated via a separator, and the separator contains an electrolytic solution (electrolyte). The structure of the electrode is not particularly limited, and a conventionally known structure can be used. For example, an electrode structure (coin type) in which a disk-shaped positive electrode and a negative electrode are arranged so as to face each other, a flat plate-shaped positive electrode and a negative electrode are used. The electrode structure may be alternately laminated (laminated type), or the laminated strip-shaped positive electrode and negative electrode may be wound around an electrode structure (wound type). The current collector, the positive electrode, the positive electrode active material, the negative electrode, the negative electrode active material, and the electrolytic solution used in the lithium ion secondary battery are not particularly limited, and conventionally known materials can be appropriately combined and used.

Next, examples of the present invention will be described, but the present invention is not limited to these examples.

Example 1
1.2 parts by mass of polyvinyl alcohol (PVA) and ammonium polycarboxylic acid salt (weight) relative to 100 parts by mass of alumina (A-1) having an average particle size of 1.5 μm and a volume distribution of less than 1.0 μm of 22 vol%. An average molecular weight of 30,000) 0.4 parts by mass was added, and a ceramic slurry prepared by adjusting water so that the alumina solid content was 50 wt% was mixed using a high-speed shear stirrer (DESPA, manufactured by Asada Iron Works Co., Ltd.), Further, the particles were dispersed by a continuous media disperser (NANO GRAIN MILL, manufactured by Asada Iron Works Co., Ltd.). Thereafter, 0.3 parts by mass of dimethylaminoethyl acrylate methyl chloride quaternary salt/acrylamide copolymer (weight average molecular weight 30,000) was added to 100 parts by mass of alumina and mixed using a three-one motor with a propeller blade. , A ceramic slurry was obtained.

Example 2
A ceramic slurry was obtained in the same manner as in Example 1 except that PVA was a vinyl acetate copolymer (EVA).

Example 3
A ceramic slurry was obtained in the same manner as in Example 1 except that PVA was changed to a carboxylic acid-modified PVA ammonium salt.

Example 4
A ceramic slurry was obtained in the same manner as in Example 1 except that PVA was changed to sulfonic acid-modified PVA ammonium salt.

Example 5
A ceramic slurry was obtained in the same manner as in Example 1 except that PVA was changed to carboxymethyl cellulose (CMC) ammonium salt.

Example 6
A ceramic slurry was obtained in the same manner as in Example 1 except that PVA was 0.8 part by mass.
Example 7
A ceramic slurry was obtained in the same manner as in Example 1 except that PVA was 1.4 parts by mass.

Example 8
A ceramic slurry was obtained in the same manner as in Example 1, except that the weight average molecular weight of the polycarboxylic acid ammonium salt was 10,000.

Example 9
A ceramic slurry was obtained in the same manner as in Example 1, except that the weight average molecular weight of the polycarboxylic acid ammonium salt was changed to 50,000.

Example 10
A ceramic slurry was obtained in the same manner as in Example 1 except that the average particle size was 2.4 μm and the volume distribution of less than 1.0 μm was 18 vol% alumina (A-2).

Example 11
A ceramic slurry was obtained in the same manner as in Example 1 except that aluminum sulfate (weight average molecular weight 342) was used as the dimethylaminoethyl acrylate methyl chloride quaternary salt/acrylamide copolymer.

Example 12
A ceramic slurry was obtained in the same manner as in Example 1 except that titanium lactate (weight average molecular weight 260) was used as the dimethylaminoethyl acrylate methyl chloride quaternary salt/acrylamide copolymer.

Example 13
A ceramic slurry was obtained in the same manner as in Example 1 except that the dimethylaminoethyl acrylate methyl chloride quaternary salt/acrylamide copolymer had a weight average molecular weight of 50,000.

Example 14
Example 1 except that the dimethylaminoethyl acrylate methyl chloride quaternary salt/acrylamide copolymer was changed to dimethylaminoethyl acrylate methyl chloride quaternary salt/acrylamide/sodium acrylate copolymer (weight average molecular weight 30,000). Similarly, a ceramic slurry was obtained.

Example 15
A ceramic slurry was obtained in the same manner as in Example 1 except that PVA was carboxylic acid-modified PVA sodium salt.

Example 16
A ceramic slurry was obtained in the same manner as in Example 1 except that sodium polycarboxylic acid was used instead of ammonium polycarboxylic acid.

Example 17
A ceramic slurry was obtained in the same manner as in Example 1 except that 0.4 part by mass of PVA was used.

Example 18
A ceramic slurry was obtained in the same manner as in Example 1 except that PVA was 1.8 parts by mass.

Comparative Example 1
A ceramic slurry was obtained in the same manner as in Example 1 except that alumina having an average particle size of 0.8 μm and a volume distribution of less than 1.0 μm of 70 vol% was used.

Comparative example 2
A ceramic slurry was obtained in the same manner as in Example 1 except that the acrylamide/sodium acrylate polymer (weight average molecular weight 30,000) was used as the dimethylaminoethyl acrylate methyl chloride quaternary salt/acrylamide copolymer.

Comparative Example 3
A ceramic slurry was obtained in the same manner as in Example 1 except that the weight average molecular weight of the polycarboxylic acid ammonium salt was 70,000.

Comparative Example 4
A ceramic slurry was obtained in the same manner as in Example 1 except that the dimethylaminoethyl acrylate methyl chloride quaternary salt/acrylamide copolymer had a weight average molecular weight of 70,000.

Comparative Example 5
A ceramic slurry was obtained in the same manner as in Example 1 except that dimethylaminoethyl acrylate methyl chloride quaternary salt/acrylamide copolymer was not added.

The ceramic slurry before and after the additive addition was evaluated by the following method.
1. Average particle size D50 measurement After adding to water using a laser scattering particle size distribution meter ("MT3300EXII" manufactured by Microtrac Bell (formerly Nikkiso Co., Ltd.)), circulating for 3 minutes at a flow rate of 45% and measuring within 10 minutes based on volume The particle size at 50% in the integrated fraction was defined as the average particle size (D50).

2. Volume measurement of less than 1.0 μm Using a laser scattering particle size distribution meter (“MT3300EXII” manufactured by Microtrac Bell (formerly Nikkiso Co., Ltd.)), water was added and then circulated at a flow rate of 45% for 3 minutes and then within 10 minutes. The volume-based integrated amount of the measured particles having a particle size of less than 1.0 μm was defined as a volume distribution of less than 1.0 μm.
Table 1 shows the evaluation results of each ceramic slurry.

Next, battery separators were produced using the ceramic slurries of Examples 1 to 18 and Comparative Examples 1 to 5 by the following method. A ceramic heat-resistant layer is formed on the porous film by coating the above ceramic slurry on one surface using a gravure coater on the substrate porous film (film thickness 12 μm) and drying at 50° C. for 1 minute. A battery separator was obtained. The porous heat-resistant layer of the obtained battery separator had a film thickness of 4 μm and had a good appearance.

The battery separator was evaluated by the following method.
1. Moisture Content Evaluation 1 g of the battery separator was cut out and left standing for 12 hours in an environment with a dew point of −30° C. The sample was placed in a Karl Fischer method moisture content measuring device, treated at 150° C. for 5 minutes in a nitrogen atmosphere, and the moisture content generated was calculated by the following formula. The calculated value was evaluated as ◯ when the water content was 450 ppm or less, Δ when it was more than 450 ppm and 500 ppm or less, and as X when it was more than 500 ppm.
Moisture content (ppm)=measured moisture content-nitrogen-containing moisture content

2. Evaluation of Shape Stability During Heating A battery separator was cut into a piece of 5 cm×5 cm and placed in an oven heated to 130° C. After 1 hour, the battery separator is taken out of the oven, cooled, and the shorter side length d (mm) is measured. Then, the heat shrinkage rate (%) is calculated by the following formula. From the calculated values, less than 2% was evaluated as ◯, 2% or more and 3% or less as Δ, and values greater than 3% were evaluated as x.
Thermal shrinkage rate (%)={(50-d)/50}×100
Table 1 shows the results of moisture content evaluation and shape stability evaluation during heating.
Examples 1 to 18 using the ceramic slurry within the scope of the present invention had excellent evaluation results, but comparative examples 1 to 5 using the ceramic slurry outside the scope of the present invention had poor evaluation results. became.

Claims (10)

A compound containing an inorganic filler, a water-soluble binder resin, an additive and a solvent, wherein the additive is a cationic or amphoteric compound that coagulates the inorganic filler, and the average particle size of the inorganic filler aggregate in the ceramic slurry is 1. A ceramic slurry having a volume distribution of 0 μm or more and 2.5 μm or less and less than 1.0 μm of less than 17 vol %. The ceramic slurry according to claim 1, wherein the inorganic filler has an average particle size of 1.0 μm or more and 2.5 μm or less, and a volume distribution of less than 1.0 μm is 17 vol% or more. The ceramic slurry according to claim 1 or 2, wherein the additive has a weight average molecular weight of 50,000 or less. The water-soluble binder resin is a first polymer compound having a hydroxyl group and at least one selected from the group consisting of an acetic acid group, a carboxyl group or an ammonium salt or amine salt thereof, a sulfonic acid group or an ammonium salt or amine salt thereof. And a second polymer compound whose main chain is an alkyl chain, and whose side chain has at least one selected from the group consisting of an amide group, a carboxyl group, or an ammonium salt or an amine salt thereof. Item 4. The ceramic slurry according to any one of items 1 to 3. The first polymer compound is polyvinyl alcohol, ethylene-vinyl alcohol copolymer, acrylic acid-vinyl alcohol copolymer or its ammonium salt or amine salt, sulfonic acid-vinyl alcohol copolymer or its ammonium salt or amine salt. 5. The ceramic slurry according to claim 4 , wherein the ceramic slurry is at least one selected from the group consisting of carboxymethyl cellulose, ammonium salt or amine salt thereof. The ceramic slurry according to claim 4 or 5 , wherein the second polymer compound has a weight average molecular weight of 50,000 or less. The ceramic slurry according to any one of claims 1 to 6, wherein the water-soluble binder resin is contained in an amount of 0.8 or more and less than 2.0 parts by mass based on 100 parts by mass of the inorganic filler. The ceramic slurry according to any one of claims 1 to 7, wherein the inorganic filler is alumina. An inorganic filler, a water-soluble binder resin, a cationic or amphoteric additive is included, and the average particle size of the inorganic filler is 1.0 μm or more and 2.5 μm or less, and the volume distribution of less than 1.0 μm is less than 17 vol%. A battery separator characterized by: A non-aqueous electrolyte secondary battery comprising the battery separator according to claim 9.