JPWO2018070472A1 - Thickener for battery separator coating liquid, battery separator coating liquid and battery separator - Google Patents

Abstract

This invention makes it a subject to provide the separator coating liquid for batteries with favorable coating property, when forming a coating layer thinly. The present invention relates to a thickener for battery separator coating liquid containing fibrous cellulose having a fiber width of 1000 nm or less and an average degree of polymerization of less than 400.

Description

  The present invention relates to a thickener for battery separator coating liquid, a battery separator coating liquid, and a battery separator.

  Lithium ion secondary batteries are characterized by high energy density, and are widely used as power sources for portable electric devices such as mobile phones, portable music players, and notebook personal computers. A normal lithium ion secondary battery is provided with a separator to prevent contact between the positive and negative electrodes.

  Conventionally, a porous film made of polyethylene or polypropylene has been used as a battery separator. However, a porous film made of polyethylene or polypropylene has low heat resistance, and when the porous film contracts and an internal short circuit occurs, local heat is generated inside the battery, and ignition or rupture occurs. I have a problem.

  In response to such problems, battery separators containing inorganic fine particles have been developed. In the battery separator containing the inorganic fine particles, it is possible to suppress a short circuit due to an external impact. In addition, it is possible to suppress a short circuit due to thermal contraction of the film serving as the base material, that is, it is possible to improve the heat resistance of the battery separator.

  In order to contain inorganic fine particles in a porous film, a coating liquid containing inorganic fine particles is applied to the surface of the porous film. However, since the inorganic fine particles have a higher specific gravity than water and organic solvents, they tend to settle in the inorganic fine particle-containing slurry, and once settled, the inorganic fine particles may aggregate to cause a problem. In addition, when the dispersion state of the inorganic fine particles is not good, there is a problem that uneven coating occurs when applied to the porous film, and improvement of the stability of the inorganic fine particles in the coating liquid has been demanded.

  In order to increase the dispersibility of the inorganic fine particles in the coating liquid, a thickener is added to the coating liquid. As such a thickener, for example, a thickener such as xanthan gum is used. Moreover, in patent document 1 and 2, using a cellulose fiber as a thickener is examined. Patent Document 1 discloses a battery separator coating solution containing cellulose fibers. Here, bacterial cellulose fibers or nanocellulose fibers prepared by dissociating crystalline cellulose are used as thickeners. . Patent Document 2 discloses a battery separator coating solution containing fine cellulose fibers having an I-type crystal form to which a carboxyl group is added.

JP-A-2015-84318 JP 2014-175232 A

A battery separator may be required to be thin in order to reduce the size of the battery or improve efficiency. In recent years, in order to achieve a reduction in the thickness of battery separators, it may be required to thin the coating layer provided on a substrate such as a porous film.
Accordingly, an object of the present invention is to provide a battery separator coating solution having good coating properties even when the coating layer is formed thin.

As a result of intensive studies to solve the above problems, the present inventors have used fine fibrous cellulose having a fiber width of 1000 nm or less and an average polymerization degree within a predetermined range for battery separator coating liquid. It has been found that a battery separator coating solution with good coating properties can be obtained even when the coating layer is formed thin by containing it as a thickener in the battery separator coating solution.
Specifically, the present invention has the following configuration.

[1] A thickener for battery separator coating liquid containing fibrous cellulose having a fiber width of 1000 nm or less and an average degree of polymerization of less than 400.
[2] The thickener for battery separator coating liquid according to [1], wherein the fibrous cellulose is phosphorylated cellulose.
[3] A battery separator coating solution comprising fibrous cellulose having a fiber width of 1000 nm or less and an average degree of polymerization of less than 400, fine particles, and a dispersion medium.
[4] The battery separator coating liquid according to [3], wherein the fibrous cellulose is phosphorylated cellulose.
[5] The battery separator coating liquid according to [3] or [4], wherein the content of fibrous cellulose is 0.1 parts by mass or more and 1.3 parts by mass or less with respect to 100 parts by mass of the dispersion medium. .
[6] The battery separator coating liquid according to any one of [3] to [5], wherein the fine particles are inorganic fine particles.
[7] A battery separator having a base material and a coating layer, wherein the coating layer includes fibrous cellulose having a fiber width of 1000 nm or less and an average degree of polymerization of less than 400, and fine particles. Separator for use.
[8] The battery separator according to [7], wherein the fibrous cellulose is phosphorylated cellulose.
[9] The battery separator according to [7] or [8], wherein the basis weight of the coating layer is 4.5 g / m ² or less.
[10] The battery separator according to any one of [7] to [9], wherein the fine particles are inorganic fine particles.
[11] The battery separator according to any one of [7] to [10], wherein the substrate includes a polyolefin resin.

  According to the present invention, even when the coating layer is formed thin, a battery separator coating solution having good coating properties can be obtained.

FIG. 1 is a graph showing the relationship between the amount of dropped NaOH and electrical conductivity for a fiber material having a phosphate group. FIG. 2 is a graph showing the relationship between the amount of dropped NaOH and electrical conductivity for a fiber material having a carboxyl group.

  Hereinafter, the present invention will be described in detail. The description of the constituent elements described below may be made based on representative embodiments and specific examples, but the present invention is not limited to such embodiments.

(Thickener for battery separator coating liquid)
The present invention relates to a thickener for battery separator coating liquid containing fibrous cellulose having a fiber width of 1000 nm or less and an average degree of polymerization of less than 400.

Since the thickener for battery separator coating liquid of the present invention has the above-described configuration, a battery separator coating liquid having good coating properties can be obtained even when the coating layer is formed thin. In the coating layer formed from the battery separator coating liquid containing the battery separator coating liquid thickener of the present invention, even when the coating layer is thin, the occurrence of coating unevenness or the like occurs. It is suppressed. In the present specification, the applicability can be evaluated based on the presence or absence of coating unevenness in the coating layer.
A battery separator including a coating layer formed from a battery separator coating liquid has high coating safety because it has a coating layer without coating unevenness. In the present invention, since the coating layer can be formed thin, the thickness of the battery separator itself can be reduced.

  Since the thickener in the battery separator coating solution may become an impurity after coating, it is preferable that the amount added is small. The present invention is also characterized in that the addition amount can be reduced by using the thickener for battery separator coating liquid. In the present invention, the dispersibility of the fine particles can be enhanced even when the addition amount of the thickener for the battery separator coating liquid is small. Moreover, in this invention, since the addition amount of the said battery separator coating liquid thickener can be suppressed, it can also suppress that the microporous of a battery separator base material is block | closed.

  The thickener for battery separator coating liquid of the present invention contains fibrous cellulose having a fiber width of 1000 nm or less and an average polymerization degree of less than 400. In the present specification, fibrous cellulose having a fiber width of 1000 nm or less is also referred to as fine fibrous cellulose. The thickener for battery separator coating liquid preferably contains 60% by mass or more, more preferably 70% by mass or more, and more preferably 80% by mass or more of such fine fibrous cellulose with respect to the total solid mass. More preferably, it is more preferably 90% by mass or more. The thickener for the battery separator coating liquid may be composed of the above-mentioned fine fibrous cellulose, but the thickener for the battery separator coating liquid contains water in addition to the above fine fibrous cellulose. And other solvents, water-soluble polymers and the like may be contained.

  Examples of the form of the thickener for battery separator coating liquid of the present invention include powder, gel, slurry, solution, and sheet.

The average degree of polymerization of the fine fibrous cellulose contained in the thickener for battery separator coating liquid may be less than 400, preferably 395 or less, and more preferably 380 or less. The average degree of polymerization of the fine fibrous cellulose is preferably 100 or more, more preferably 150 or more, and further preferably 200 or more.
By making the average degree of polymerization of the fine fibrous cellulose within the above range, even when the coating layer is formed thin, the coating property of the battery separator coating liquid can be improved, and coating unevenness is small. A coating layer can be formed.

The average degree of polymerization of the fine fibrous cellulose contained in the battery separator coating liquid thickener is calculated with reference to the following paper.
TAPPI International Standard; ISO / FDIS 5351, 2009.
Smith, DK; Bampton, RF; Alexander, WJ Ind. Eng. Chem., Process Des. Dev. 1963, 2, 57-62.

Specifically, 30 g of a suspension obtained by diluting fine fibrous cellulose with ion-exchanged water so as to have a content of 2 ± 0.3% by mass is collected in a centrifuge tube and left in a freezer overnight. Freeze. Further, after drying for 5 days or more with a freeze dryer, heating is performed for 3 hours or more and 4 hours or less with a constant temperature dryer set at 105 ° C. to obtain absolutely dry fine fibrous cellulose.
In order to measure the reference, 15 ml of pure water and 15 ml of 1 mol / L copper ethylenediamine are added to an empty 50 ml screw tube to prepare a 0.5 mol / L copper ethylenediamine solution. Put 10 ml of the above 0.5 mol / L copper ethylenediamine solution into a Canon Fenske viscometer and leave it for 5 minutes, then measure the drop time at 25 ° C. to make the solvent drop time.

  Next, in order to measure the viscosity of the fine fibrous cellulose, 0.14 g or more and 0.16 g or less of the dried fine fibrous cellulose is weighed into an empty 50 ml capacity screw tube, and 15 ml of pure water is added. Further, 15 ml of 1 mol / L copper ethylenediamine is added, and stirred at 1000 rpm for 10 minutes with a rotation / revolution supermixer to obtain a 0.5 mol / L copper ethylenediamine solution in which fine fibrous cellulose is dissolved. Similarly to the measurement of the reference, 10 ml of a 0.5 mol / L copper ethylenediamine solution prepared in a Cannon-Fenske viscometer is added and left for 5 minutes, and then the drop time at 25 ° C. is measured. The drop time is measured three times, and the average value is taken as the drop time of the fine fibrous cellulose solution.

The degree of polymerization is calculated from the mass of the absolutely dry fine fibrous cellulose used for the measurement, the solvent dropping time, and the dropping time of the fine fibrous cellulose solution using the following equation. In addition, when the following average degree of polymerization is measured twice or more, it is an average value of each time.
Absolutely dry fine fibrous cellulose used for measurement Mass: a (g) (where a is 0.14 to 0.16)
Cellulose concentration of the solution: c = a / 30 (g / mL)
Solvent falling time: t ₀ (sec)
Drop time of fine fibrous cellulose solution: t (sec)
Relative viscosity of the solution: η _rel = t / t ₀
Specific viscosity of the solution: η _sp = η _rel -1
Intrinsic viscosity: [η] = η _sp /c(1+0.28η _sp )
Degree of polymerization: DP = [η] /0.57
In addition, since the average degree of polymerization of the fine fibrous cellulose is calculated by the above method, it may be called the viscosity average degree of polymerization.

In addition, when components other than fine fibrous cellulose are contained in the thickener for battery separator coating liquids, after the fine fibrous cellulose is isolated, the average degree of polymerization of the fine fibrous cellulose is calculated.
In this case, first, the battery separator coating liquid thickener is diluted and dried, and then observed with a transmission electron microscope to confirm the presence of fine fibrous cellulose. Subsequently, the type I crystal | crystallization of a fine fibrous cellulose is detected using solid state NMR.

When the presence of fine fibrous cellulose is confirmed in the thickener for battery separator coating liquid, the fine fibrous cellulose is isolated according to the following procedure.
First, 20 ± 5 g of thickener for battery separator coating liquid is weighed into a 50 ml capacity aluminum cup. Similarly, a plurality of aluminum cups prepared by measuring the thickener for battery separator coating liquid are prepared. It heats at 105 degreeC with a ventilation constant temperature dryer for 16 hours, and dries the thickener for battery separator coating liquids. A 0.5 mol / L copper ethylenediamine solution is added to 1 g of the thickening agent for battery separator coating liquid thus dried so as to have a ratio of 200 ml, and stirred to dissolve the fine fibrous cellulose. The obtained solution is filtered to remove the residue, and then dropped into water to obtain regenerated cellulose. This regenerated cellulose is obtained by dissolving fine fibrous cellulose in a copper ethylenediamine solution and regenerating it in water. The obtained regenerated cellulose is filtered off, washed thoroughly with water and dried.

  And the dry weight of the obtained regenerated cellulose is measured. From this weight and the weight of the thickener for battery separator coating solution used to obtain this weight, the content of fine fibrous cellulose contained in the thickener for battery separator coating solution is determined.

  30 ml of 0.5 mol / L copper ethylenediamine solution is added to 0.14 g or more and 0.16 g or less of the dried regenerated cellulose obtained as described above, and stirred to dissolve the cellulose again. The resulting solution is filtered to remove the residue. Then, 10 ml of the prepared filtrate is put into a Canon Fenceke viscometer, and after 5 minutes, the drop time at 25 ° C. is measured. From the measured dropping time, the intrinsic viscosity is determined according to the method described above and converted to the degree of polymerization.

<Fine fibrous cellulose>
Although it does not specifically limit as a fibrous cellulose raw material for obtaining a fine fibrous cellulose, It is preferable to use a pulp from the point of being easy to acquire and cheap. Examples of the pulp include wood pulp, non-wood pulp, and deinked pulp. Examples of wood pulp include hardwood kraft pulp (LBKP), softwood kraft pulp (NBKP), sulfite pulp (SP), dissolved pulp (DP), soda pulp (AP), unbleached kraft pulp (UKP), oxygen bleached craft Chemical pulps such as pulp (OKP) are listed. Further, semi-chemical pulps such as semi-chemical pulp (SCP) and chemiground wood pulp (CGP), mechanical pulps such as ground wood pulp (GP), and thermomechanical pulp (TMP, BCTMP) are exemplified, but not limited thereto. Non-wood pulp includes cotton pulp such as cotton linter and cotton lint, non-wood pulp such as hemp, straw and bagasse, cellulose isolated from sea squirts and seaweed, chitin, chitosan, etc., but is not particularly limited. . The deinking pulp includes deinking pulp made from waste paper, but is not particularly limited. The pulp of this embodiment may be used alone or in combination of two or more. Among the above pulps, wood pulp containing cellulose and deinked pulp are preferable in terms of availability. Among wood pulps, chemical pulp has a large cellulose ratio, so the yield of fine fibrous cellulose during fiber refinement (defibration) is high, and the degradation of cellulose in the pulp is small, and the fineness of long fibers with a large axial ratio is high. It is preferable at the point from which fibrous cellulose is obtained. Of these, kraft pulp and sulfite pulp are most preferably selected. When long fiber fine fibrous cellulose having a large axial ratio is used, high viscosity tends to be obtained.

  The average fiber width of the fine fibrous cellulose is 1000 nm or less as observed with an electron microscope. The average fiber width is preferably 2 nm or more and 1000 nm or less, more preferably 2 nm or more and 100 nm or less, more preferably 2 nm or more and 50 nm or less, and further preferably 2 nm or more and 10 nm or less, but is not particularly limited. When the average fiber width of the fine fibrous cellulose is less than 2 nm, the physical properties (strength, rigidity, dimensional stability) as the fine fibrous cellulose tend to be difficult to be expressed because the cellulose molecules are dissolved in water. . The fine fibrous cellulose is monofilamentous cellulose having a fiber width of 1000 nm or less, for example.

  Measurement of the average fiber width of the fine fibrous cellulose by observation with an electron microscope is performed as follows. An aqueous suspension of fine fibrous cellulose having a concentration of 0.05% by mass or more and 0.1% by mass or less is prepared, and the suspension is cast on a carbon film-coated grid subjected to a hydrophilic treatment to prepare a sample for TEM observation. To do. When a wide fiber is included, an SEM image of the surface cast on glass may be observed. Observation with an electron microscope image is performed at a magnification of 1000 times, 5000 times, 10000 times, or 50000 times depending on the width of the constituent fibers. However, the sample, observation conditions, and magnification are adjusted to satisfy the following conditions.

(1) One straight line X is drawn at an arbitrary location in the observation image, and 20 or more fibers intersect the straight line X.
(2) A straight line Y perpendicular to the straight line is drawn in the same image, and 20 or more fibers intersect the straight line Y.

  The width of the fiber that intersects with the straight line X and the straight line Y is visually read from the observation image that satisfies the above conditions. In this way, at least three sets of images of the surface portion that do not overlap each other are observed, and the width of the fiber intersecting with the straight line X and the straight line Y is read for each image. Thus, at least 20 × 2 × 3 = 120 fiber widths are read. The average fiber width (sometimes simply referred to as “fiber width”) of fine fibrous cellulose is an average value of the fiber widths read in this way.

  The fiber length of the fine fibrous cellulose is not particularly limited, but is preferably 0.1 μm or more and 1000 μm or less, more preferably 0.1 μm or more and 800 μm or less, and particularly preferably 0.1 μm or more and 600 μm or less. By making the fiber length within the above range, the destruction of the crystalline region of the fine fibrous cellulose can be suppressed, and the slurry viscosity of the fine fibrous cellulose can be made an appropriate range. Note that the fiber length of the fine fibrous cellulose can be determined by image analysis using TEM, SEM, or AFM.

The fine fibrous cellulose preferably has an I-type crystal structure. Here, the fact that the fine fibrous cellulose has a type I crystal structure can be identified in a diffraction profile obtained from a wide-angle X-ray diffraction photograph using CuKα (λ = 1.5418Å) monochromatized with graphite. Specifically, it can be identified by having typical peaks at two positions of 2θ = 14 ° to 17 ° and 2θ = 22 ° to 23 °.
The proportion of the I-type crystal structure in the fine fibrous cellulose is preferably 30% or more, more preferably 50% or more, and further preferably 70% or more. In this case, further superior performance can be expected in terms of heat resistance and low linear thermal expansion coefficient. The degree of crystallinity is obtained by measuring an X-ray diffraction profile and determining the crystallinity by a conventional method (Seagal et al., Textile Research Journal, 29, 786, 1959).

  The fine fibrous cellulose is preferably one having a substituent, and the substituent is preferably an anionic group. Examples of the anionic group include a phosphate group or a substituent derived from a phosphate group (sometimes simply referred to as a phosphate group), a carboxyl group or a substituent derived from a carboxyl group (sometimes simply referred to as a carboxyl group), In addition, it is preferably at least one selected from a sulfone group or a substituent derived from a sulfone group (sometimes simply referred to as a sulfone group), and at least one selected from a phosphate group and a carboxyl group Is more preferable, and a phosphate group is particularly preferable. That is, the fine fibrous cellulose used in the present invention is preferably phosphorylated cellulose.

The fine fibrous cellulose is preferably one having a phosphate group or a substituent derived from a phosphate group. The phosphoric acid group is a divalent functional group equivalent to the phosphoric acid obtained by removing the hydroxyl group. Specifically, it is a group represented by —PO ₃ H ₂ . Substituents derived from phosphoric acid groups include substituents such as groups obtained by polycondensation of phosphoric acid groups, salts of phosphoric acid groups, and phosphoric acid ester groups. It may be a group.

In the present invention, the phosphate group or the substituent derived from the phosphate group may be a substituent represented by the following formula (1).

In the formula (1), a, b and n are natural numbers (where a = b × m). Of α ¹ , α ² ,..., α ⁿ and α ′, a is O ⁻ and the rest is either R or OR. Note that all α ⁿ and α ′ may be O ⁻ . R is a hydrogen atom, a saturated-linear hydrocarbon group, a saturated-branched hydrocarbon group, a saturated-cyclic hydrocarbon group, an unsaturated-linear hydrocarbon group, an unsaturated-branched hydrocarbon group, respectively. A hydrogen group, an unsaturated-cyclic hydrocarbon group, an aromatic group, or a derivative thereof.

  Examples of the saturated-linear hydrocarbon group include, but are not limited to, a methyl group, an ethyl group, an n-propyl group, or an n-butyl group. Examples of the saturated-branched hydrocarbon group include i-propyl group and t-butyl group, but are not particularly limited. Examples of the saturated-cyclic hydrocarbon group include a cyclopentyl group and a cyclohexyl group, but are not particularly limited. Examples of the unsaturated-linear hydrocarbon group include, but are not particularly limited to, a vinyl group or an allyl group. Examples of the unsaturated-branched hydrocarbon group include i-propenyl group and 3-butenyl group, but are not particularly limited. Examples of the unsaturated-cyclic hydrocarbon group include, but are not limited to, a cyclopentenyl group and a cyclohexenyl group. Examples of the aromatic group include, but are not limited to, a phenyl group or a naphthyl group.

  In addition, the derivative group in R is a functional group in which at least one of functional groups such as a carboxy group, a hydroxy group, or an amino group is added or substituted to the main chain or side chain of various hydrocarbon groups. However, it is not particularly limited. Further, the number of carbon atoms constituting the main chain of R is not particularly limited, but is preferably 20 or less, and more preferably 10 or less. By setting the number of carbon atoms constituting the main chain of R in the above range, the molecular weight of the phosphate group can be set in an appropriate range, and the penetration into the fiber raw material is facilitated, and the yield of fine cellulose fibers is increased. You can also.

β ^{b +} is a monovalent or higher cation composed of an organic substance or an inorganic substance. Examples of the monovalent or higher cation made of an organic substance include aliphatic ammonium or aromatic ammonium. Examples of the monovalent or higher cation made of an inorganic substance include ions of alkali metals such as sodium, potassium, or lithium, Examples include, but are not particularly limited to, a cation of a divalent metal such as calcium or magnesium, or a hydrogen ion. These can be applied alone or in combination of two or more. The monovalent or higher cation composed of an organic substance or an inorganic substance is preferably a sodium ion or potassium ion which is not easily yellowed when heated to a fiber raw material containing β ^{b +} and is industrially easy to use, but is not particularly limited. .

<Phosphate group introduction process>
In the phosphate group introduction step, the fiber raw material containing cellulose is reacted with at least one selected from a compound having a phosphate group and a salt thereof (hereinafter referred to as “phosphorylation reagent” or “compound A”). Can be performed. Such a phosphorylating reagent may be mixed in a powder or aqueous solution with a dry or wet fiber raw material. As another example, a phosphorylating reagent powder or an aqueous solution may be added to the fiber raw material slurry.

  The phosphoric acid group introduction step can be performed by reacting at least one selected from a compound having a phosphoric acid group and a salt thereof (a phosphorylating reagent or compound A) with a fiber raw material containing cellulose. This reaction may be carried out in the presence of at least one selected from urea and derivatives thereof (hereinafter referred to as “compound B”).

  As an example of a method for causing compound A to act on a fiber raw material in the presence of compound B, a method of mixing powder or an aqueous solution of compound A and compound B with a dry or wet fiber raw material can be mentioned. Another example is a method in which powders and aqueous solutions of Compound A and Compound B are added to the fiber raw material slurry. Among these, since the uniformity of the reaction is high, a method of adding an aqueous solution of Compound A and Compound B to a dry fiber material, or a powder or an aqueous solution of Compound A and Compound B to a wet fiber material The method is preferred. Moreover, the compound A and the compound B may be added simultaneously, or may be added separately. Moreover, you may add the compound A and the compound B first used for reaction as aqueous solution, and remove an excess chemical | medical solution by pressing. The form of the fiber raw material is preferably cotton or thin sheet, but is not particularly limited.

Compound A used in this embodiment is at least one selected from a compound having a phosphate group and a salt thereof.
Examples of the compound having a phosphate group include, but are not limited to, phosphoric acid, lithium salt of phosphoric acid, sodium salt of phosphoric acid, potassium salt of phosphoric acid, ammonium salt of phosphoric acid, and the like. Examples of the lithium salt of phosphoric acid include lithium dihydrogen phosphate, dilithium hydrogen phosphate, trilithium phosphate, lithium pyrophosphate, and lithium polyphosphate. Examples of the sodium salt of phosphoric acid include sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium pyrophosphate, and sodium polyphosphate. Examples of the potassium salt of phosphoric acid include potassium dihydrogen phosphate, dipotassium hydrogen phosphate, tripotassium phosphate, potassium pyrophosphate, and potassium polyphosphate. Examples of the ammonium salt of phosphoric acid include ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, ammonium pyrophosphate, and ammonium polyphosphate.

  Among these, phosphoric acid and phosphoric acid are introduced efficiently from the viewpoint that the introduction efficiency of phosphate groups is high, the fibrillation efficiency is easily improved in the fibrillation process described later, the cost is low, and the industrial application is easy. Sodium salt, potassium salt of phosphoric acid, and ammonium salt of phosphoric acid are preferable. Sodium dihydrogen phosphate or disodium hydrogen phosphate is more preferable.

  In addition, compound A is preferably used as an aqueous solution because the uniformity of the reaction is increased and the efficiency of introduction of phosphate groups is increased. The pH of the aqueous solution of Compound A is not particularly limited, but is preferably 7 or less because the efficiency of introduction of phosphate groups is increased, and more preferably pH 3 or more and pH 7 or less from the viewpoint of suppressing the hydrolysis of pulp fibers. The pH of the aqueous solution of Compound A may be adjusted by, for example, using a phosphoric acid group-containing compound that exhibits acidity and an alkalinity, and changing the amount ratio thereof. You may adjust pH of the aqueous solution of the compound A by adding an inorganic alkali or an organic alkali to the thing which shows acidity among the compounds which have a phosphoric acid group.

  The amount of compound A added to the fiber raw material is not particularly limited, but when the amount of compound A added is converted to phosphorus atomic weight, the amount of phosphorus atom added to the fiber raw material (absolute dry mass) is 0.5 mass% to 100 mass%. Or less, more preferably 1% by mass or more and 50% by mass or less, and most preferably 2% by mass or more and 30% by mass or less. If the amount of phosphorus atoms added to the fiber raw material is within the above range, the yield of fine fibrous cellulose can be further improved. By making the amount of phosphorus atoms added to the fiber raw material 100% by mass or less, it is possible to balance the effect of improving the yield and the cost. On the other hand, a yield can be raised by making the addition amount of the phosphorus atom with respect to a cellulose fiber more than the said lower limit.

  Examples of the compound B used in this embodiment include urea, biuret, 1-phenylurea, 1-benzylurea, 1-methylurea, 1-ethylurea and the like.

  Compound B is preferably used as an aqueous solution in the same manner as Compound A. Moreover, since the uniformity of reaction increases, it is preferable to use the aqueous solution in which both compound A and compound B are dissolved. The amount of Compound B added to the fiber raw material (absolute dry mass) is preferably 1% by mass or more and 500% by mass or less, more preferably 10% by mass or more and 400% by mass or less, and 100% by mass or more and 350% by mass or less. More preferably, it is more preferably 150% by mass or more and 300% by mass or less.

  In addition to Compound A and Compound B, amides or amines may be included in the reaction system. Examples of amides include formamide, dimethylformamide, acetamide, dimethylacetamide and the like. Examples of amines include methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, hexamethylenediamine, and the like. Among these, triethylamine is known to work as a good reaction catalyst.

  In the phosphoric acid group introduction step, it is preferable to perform a heat treatment. As the heat treatment temperature, it is preferable to select a temperature at which a phosphate group can be efficiently introduced while suppressing thermal decomposition and hydrolysis reaction of the fiber. Specifically, it is preferably 50 ° C. or higher and 300 ° C. or lower, more preferably 100 ° C. or higher and 250 ° C. or lower, and further preferably 130 ° C. or higher and 200 ° C. or lower. Moreover, you may use a vacuum dryer, an infrared heating apparatus, and a microwave heating apparatus for a heating.

  During the heat treatment, while water is contained in the fiber raw material slurry to which compound A is added, if the time for allowing the fiber raw material to stand still becomes long, the compound A dissolved with water molecules moves to the fiber raw material surface with drying. To do. Therefore, the concentration of the compound A in the fiber raw material may be uneven, and the introduction of phosphate groups on the fiber surface may not proceed uniformly. In order to suppress the occurrence of unevenness in concentration of Compound A in the fiber material due to drying, a very thin sheet-like fiber material is used, or the fiber material and Compound A are kneaded or stirred with a kneader or the like and dried by heating or reduced pressure. The method should be taken.

  The heating device used for the heat treatment is preferably a device that can always discharge the moisture retained by the slurry and the moisture generated by the addition reaction of the fibers such as phosphate groups to the hydroxyl group of the fiber, such as a blower oven. Etc. are preferred. If water in the system is always discharged, the hydrolysis reaction of the phosphate ester bond, which is the reverse reaction of the esterification, can be suppressed, and the acid hydrolysis of the sugar chain in the fiber can also be suppressed. A fine fiber having a high axial ratio can be obtained.

  The heat treatment time is also affected by the heating temperature, but it is preferably 1 second or more and 300 minutes or less, preferably 1 second or more and 1000 seconds or less after moisture is substantially removed from the fiber raw material slurry. Preferably, it is 10 seconds or more and 800 seconds or less. In the present invention, the amount of phosphate groups introduced can be within a preferred range by setting the heating temperature and the heating time to appropriate ranges.

  The phosphate group introduction step may be performed at least once, but may be repeated a plurality of times. In this case, more phosphoric acid groups are introduced, which is preferable. In the present invention, for example, it is also a preferred embodiment to perform the phosphate group introduction step twice.

  The amount of phosphate group introduced is preferably 0.10 mmol / g or more, more preferably 0.20 mmol / g or more, and 0.50 mmol / g or more per 1 g (mass) of fine fibrous cellulose. More preferably, it is particularly preferably 1.00 mmol / g or more. The amount of phosphate groups introduced is preferably 3.65 mmol / g or less, more preferably 3.50 mmol / g or less, and 3.00 mmol / g or less per 1 g (mass) of fine fibrous cellulose. More preferably. By making the introduction amount of the phosphoric acid group within the above range, the fiber raw material can be easily refined, and the stability of the fine fibrous cellulose can be enhanced. Moreover, by setting the introduction amount of phosphate groups within the above range, good characteristics can be exhibited as a thickener for battery separator coating liquid. In addition, in this specification, content of the phosphoric acid group which a fine fibrous cellulose has (introduction amount of a phosphoric acid group) is equal to the strongly acidic group amount of the phosphoric acid group which a fine fibrous cellulose has so that it may mention later.

  The amount of phosphate group introduced into the fiber material can be measured by a conductivity titration method. Specifically, by performing the defibration process step, after treating the resulting fine fibrous cellulose-containing slurry with an ion exchange resin, by determining the change in electrical conductivity while adding an aqueous sodium hydroxide solution, The amount introduced can be measured.

  In conductivity titration, when alkali is added, the curve shown in FIG. 1 is given. Initially, the electrical conductivity rapidly decreases (hereinafter referred to as “first region”). Thereafter, the conductivity starts to increase slightly (hereinafter referred to as “second region”). Thereafter, the conductivity increment increases (hereinafter referred to as “third region”). The boundary point between the second region and the third region is defined as a point at which the amount of change in conductivity twice, that is, the increase (inclination) in conductivity is maximized. That is, three areas appear. Among these, the amount of alkali required in the first region is equal to the amount of strongly acidic groups in the slurry used for titration, and the amount of alkali required in the second region is the amount of weakly acidic groups in the slurry used for titration. Will be equal. When the phosphoric acid group undergoes condensation, apparently weakly acidic groups are lost, and the amount of alkali required in the second region is reduced compared to the amount of alkali required in the first region. On the other hand, the amount of strongly acidic groups coincides with the amount of phosphorus atoms regardless of the presence or absence of condensation, so that the amount of phosphate groups introduced (or the amount of phosphate groups) or the amount of substituent introduced (or the amount of substituents) is simply When said, it represents the amount of strongly acidic group. That is, the alkali amount (mmol) required in the first region of the curve shown in FIG. 1 is divided by the solid content (g) in the titration target slurry to obtain the substituent introduction amount (mmol / g).

<Carboxyl group introduction step>
When the fine fibrous cellulose has a carboxyl group, the carboxyl group can be introduced into the fine fibrous cellulose through a carboxyl group introduction step. In the carboxyl group introduction step, the fiber raw material is treated with an oxidation treatment such as a TEMPO oxidation treatment or a compound having a group derived from a carboxylic acid, a derivative thereof, or an acid anhydride or a derivative thereof, whereby a carboxyl group is added to the fine fibrous cellulose. Can be introduced.

  The compound having a carboxyl group is not particularly limited, and examples thereof include dicarboxylic acid compounds such as maleic acid, succinic acid, phthalic acid, fumaric acid, glutaric acid, adipic acid and itaconic acid, and tricarboxylic acid compounds such as citric acid and aconitic acid. .

  The acid anhydride of the compound having a carboxyl group is not particularly limited, but examples thereof include acid anhydrides of dicarboxylic acid compounds such as maleic anhydride, succinic anhydride, phthalic anhydride, glutaric anhydride, adipic anhydride, and itaconic anhydride. It is done.

  Although it does not specifically limit as a derivative of the compound which has a carboxyl group, The derivative of the acid anhydride of the compound which has a carboxyl group and the acid anhydride imidation of a compound which has a carboxyl group are mentioned. Although it does not specifically limit as an acid anhydride imidation thing of a compound which has a carboxyl group, Imidation thing of dicarboxylic acid compounds, such as maleimide, succinic acid imide, and phthalic acid imide, is mentioned.

  The acid anhydride derivative of the compound having a carboxyl group is not particularly limited. For example, at least some of the hydrogen atoms of the acid anhydride of the compound having a carboxyl group, such as dimethylmaleic anhydride, diethylmaleic anhydride, diphenylmaleic anhydride, etc. are substituted (for example, alkyl group, phenyl group, etc. ) Are substituted.

  In the carboxyl group introduction step, when TEMPO oxidation treatment is performed, it is also preferable to perform the treatment under conditions where the pH is 6 or more and 8 or less. Such a treatment process is also called neutral TEMPO oxidation treatment. Neutral TEMPO oxidation treatment includes, for example, sodium phosphate buffer (pH = 6.8), nitroxy such as pulp and TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) as a catalyst. This can be done by adding sodium hypochlorite as a radical or sacrificial reagent. Furthermore, by allowing sodium chlorite to coexist, an aldehyde generated during the oxidation process can be efficiently oxidized to a carboxyl group.

  The amount of carboxyl groups introduced is preferably 0.10 mmol / g or more, more preferably 0.20 mmol / g or more, and 0.50 mmol / g or more per 1 g (mass) of fine fibrous cellulose. Is more preferable, and particularly preferably 1.00 mmol / g or more. The amount of carboxyl group introduced is preferably 3.65 mmol / g or less, more preferably 3.50 mmol / g or less, and further preferably 3.00 mmol / g or less.

  The amount of carboxyl group introduced can be measured by a conductivity titration method. In the measurement by the conductivity titration method, the introduction amount is measured by obtaining a change in conductivity while adding an aqueous sodium hydroxide solution to the obtained fine fibrous cellulose-containing slurry.

  In the conductivity titration method, the curve shown in FIG. 2 is given when alkali is added. This curve is divided into a first region until the conductivity increment (slope) becomes substantially constant after the electrical conductivity decreases, and then a second region where the conductivity increment (slope) increases. Note that the boundary point between the first region and the second region is defined as the point at which the amount of change in conductivity twice, that is, the increase (inclination) in conductivity is maximized. The alkali amount (mmol) required in the first region of the curve shown in FIG. 2 is divided by the solid content (g) in the fine fibrous cellulose-containing slurry to be titrated, and the amount of carboxyl group introduced (mmol / g).

<Alkali treatment>
In the case of producing fine fibrous cellulose, an alkali treatment may be performed between an ionic substituent introduction step such as a phosphate group introduction step or a carboxyl group introduction step and a defibration treatment step described later. Although it does not specifically limit as a method of an alkali treatment, For example, the method of immersing an ionic substituent introduction | transduction fiber in an alkaline solution is mentioned.
The alkali compound contained in the alkali solution is not particularly limited, but may be an inorganic alkali compound or an organic alkali compound. The solvent in the alkaline solution may be either water or an organic solvent. The solvent is preferably a polar solvent (polar organic solvent such as water or alcohol), and more preferably an aqueous solvent containing at least water.
Of the alkaline solutions, a sodium hydroxide aqueous solution or a potassium hydroxide aqueous solution is particularly preferred because of its high versatility.

Although the temperature of the alkali solution in an alkali treatment process is not specifically limited, 5 to 80 degreeC is preferable and 10 to 60 degreeC is more preferable.
The immersion time in the alkaline solution in the alkali treatment step is not particularly limited, but is preferably 5 minutes or longer and 30 minutes or shorter, and more preferably 10 minutes or longer and 20 minutes or shorter.
Although the usage-amount of the alkali solution in an alkali treatment is not specifically limited, It is preferable that it is 100 mass% or more and 100,000 mass% or less with respect to the absolute dry mass of an ionic substituent introduction | transduction fiber, and is 1000 mass% or more and 10000 mass% or less. More preferably.

  In order to reduce the amount of the alkaline solution used in the alkali treatment step, the ionic substituent-introduced fiber may be washed with water or an organic solvent before the alkali treatment step. After the alkali treatment, in order to improve the handleability, it is preferable to wash the alkali-treated ionic substituent-introduced fiber with water or an organic solvent before the defibrating treatment step.

<Acid treatment>
In the production process of fine fibrous cellulose having a predetermined average degree of polymerization, an acid treatment step may be further provided. The acid treatment step is preferably provided after the ionic substituent introduction step, and an alkali treatment step is preferably provided after the acid treatment step. In such an acid treatment step, an acid hydrolysis treatment of cellulose having an ionic substituent may be performed. In the present invention, the average degree of polymerization of the fine fibrous cellulose can be controlled within a preferable range by appropriately selecting the raw material and production conditions of the fine fibrous cellulose, and the fine fiber can be provided by providing an acid treatment step. The average degree of polymerization of the cellular cellulose may be controlled within a preferable range.

  Although it does not specifically limit as a method of an acid treatment, For example, the method of immersing an ionic substituent introduction | transduction fiber in the acidic liquid containing an acid is mentioned. Although the density | concentration of the acidic liquid to be used is not specifically limited, 10 mass% or less is preferable, More preferably, it is 5 mass% or less. Moreover, the pH of the acidic solution to be used is not particularly limited, but is preferably 0 to 4, more preferably 1 to 3. As the acid contained in the acidic liquid, for example, an inorganic acid, a sulfonic acid, a carboxylic acid, or the like can be used. Examples of the inorganic acid include sulfuric acid, nitric acid, hydrochloric acid, hydrobromic acid, hydroiodic acid, hypochlorous acid, chlorous acid, chloric acid, perchloric acid, phosphoric acid, boric acid and the like. Examples of the sulfonic acid include methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, trifluoromethanesulfonic acid, and the like. Examples of the carboxylic acid include formic acid, acetic acid, citric acid, gluconic acid, lactic acid, oxalic acid, and tartaric acid. Of these, hydrochloric acid is preferably used as the acid.

Although the temperature of the acid solution in an acid treatment process is not specifically limited, 5 to 100 degreeC is preferable and 20 to 90 degreeC is more preferable.
Although the immersion time in the acid solution in an acid treatment process is not specifically limited, 5 minutes or more and 120 minutes or less are preferable, and 10 minutes or more and 60 minutes or less are more preferable.
Although the usage-amount of the acid solution in an acid treatment is not specifically limited, It is preferable that it is 100 mass% or more and 100,000 mass% or less with respect to the absolute dry mass of an ionic substituent introduction | transduction fiber, and is 1000 mass% or more and 10000 mass% or less. More preferably.

<Defibration processing>
The ionic substituent-introduced fiber is defibrated in the defibrating process. In the defibrating process, the fiber is usually defibrated using a defibrating apparatus to obtain a fine fibrous cellulose-containing slurry, but the processing apparatus and the processing method are not particularly limited.
As the defibrating apparatus, a high-speed defibrator, a grinder (stone mill type pulverizer), a high-pressure homogenizer, an ultra-high pressure homogenizer, a high-pressure collision type pulverizer, a ball mill, a bead mill, or the like can be used. Alternatively, as a defibrating apparatus, a device for wet grinding such as a disk type refiner, a conical refiner, a twin-screw kneader, a vibration mill, a homomixer under high-speed rotation, an ultrasonic disperser, or a beater should be used. You can also. The defibrating apparatus is not limited to the above. Preferable defibrating treatment methods include a high-speed defibrator, a high-pressure homogenizer, and an ultra-high pressure homogenizer that are less affected by the grinding media and less worried about contamination.

  In the defibrating treatment, it is preferable to dilute the fiber raw material with water and an organic solvent alone or in combination to form a slurry, but there is no particular limitation. As the dispersion medium, in addition to water, a polar organic solvent can be used. Preferable polar organic solvents include alcohols, ketones, ethers, dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAc), and the like, but are not particularly limited. Examples of alcohols include methanol, ethanol, n-propanol, isopropanol, n-butanol, and t-butyl alcohol. Examples of ketones include acetone and methyl ethyl ketone (MEK). Examples of ethers include diethyl ether and tetrahydrofuran (THF). The dispersion medium may be one type or two or more types. Further, the dispersion medium may contain a solid content other than the fiber raw material, such as urea having hydrogen bonding property.

  In the present invention, the fibrillation treatment may be performed after the fine fibrous cellulose is concentrated and dried. In this case, the concentration and drying methods are not particularly limited, and examples thereof include a method of adding a concentrating agent to a slurry containing fine fibrous cellulose, a generally used dehydrator, a press, and a method using a dryer. Moreover, a well-known method, for example, the method described in WO2014 / 024876, WO2012 / 107642, and WO2013 / 121086 can be used. Further, the concentrated fine fibrous cellulose may be formed into a sheet. The sheet can be pulverized to perform a defibrating process.

  The equipment used for pulverization of fine fibrous cellulose includes high-speed fibrillators, grinders (stone mill type pulverizers), high-pressure homogenizers, ultra-high pressure homogenizers, high-pressure collision type pulverizers, ball mills, bead mills, disk type refiners, conicals. An apparatus for wet pulverization such as a refiner, a twin-screw kneader, a vibration mill, a homomixer under high-speed rotation, an ultrasonic disperser, a beater, and the like can be used, but is not particularly limited. The treatment conditions are not particularly limited as long as a preferable degree of polymerization is obtained.

  In the present invention, it is possible to control the average degree of polymerization of the fine fibrous cellulose within a preferable range by appropriately selecting the raw materials and production conditions of the fine fibrous cellulose. Such production conditions are not particularly limited, and examples thereof include adjusting pressure conditions and the number of treatments in the defibrating process, and selecting the type of production apparatus. For example, when performing a defibrating process at a pressure of 200 MPa using a wet atomizer, the number of treatments is preferably 8 times or more, more preferably 9 times or more, and preferably 10 times or more. Further preferred. Further, the upper limit value of the number of times of processing is not particularly limited, but can be, for example, 30 times.

(Battery separator coating liquid)
The present invention also relates to a battery separator coating solution containing fine fibrous cellulose having a fiber width of 1000 nm or less and an average degree of polymerization of less than 400, fine particles, and a dispersion medium. That is, the battery separator coating liquid contains a thickener for battery separator coating liquid, preferably contains the fine fibrous cellulose described above, and preferably contains phosphorylated cellulose.

  The average degree of polymerization of the fine fibrous cellulose may be less than 400, preferably 395 or less, and more preferably 380 or less. The average degree of polymerization of the fine fibrous cellulose is preferably 100 or more, more preferably 150 or more, and further preferably 200 or more.

In addition, when calculating the average degree of polymerization of the fine fibrous cellulose in the battery separator coating liquid, the measurement is performed after the fine fibrous cellulose is isolated from the battery separator coating liquid by the following procedure.
In this case, first, the battery separator coating solution is diluted and dried, and then observed with a transmission electron microscope to confirm the presence of fine fibrous cellulose. Subsequently, the type I crystal of cellulose is detected using solid-state NMR.

When the presence of fine fibrous cellulose is confirmed in the battery separator coating liquid, the fine fibrous cellulose is isolated according to the following procedure.
First, 20 ± 5 g of battery separator coating solution is weighed into a 50 ml capacity aluminum cup. Similarly, a plurality of aluminum cups prepared by weighing battery separator coating liquid are prepared. It heats at 105 degreeC with a ventilation constant temperature dryer for 16 hours, and dries the separator coating liquid for batteries. A 0.5 mol / L copper ethylenediamine solution is added to 1 g of the dried battery separator coating solution so as to have a ratio of 100 ml and stirred to dissolve the fine fibrous cellulose. The obtained solution is filtered to remove the residue, and then dropped into water to obtain regenerated cellulose. This regenerated cellulose is obtained by dissolving fine fibrous cellulose in a copper ethylenediamine solution and regenerating it in water. The obtained regenerated cellulose is filtered off, sufficiently washed with water, and dried.

  And the dry weight of the obtained regenerated cellulose is measured. The content of fine fibrous cellulose contained in the battery separator coating solution is determined from this weight and the weight of the battery separator coating solution used to obtain this weight.

  30 ml of 0.5 mol / L copper ethylenediamine solution is added to 0.14 g or more and 0.16 g or less of the dried regenerated cellulose obtained as described above, and stirred to dissolve the cellulose again. The resulting solution is filtered to remove the residue. Then, 10 ml of the prepared filtrate is put into a Canon Fenceke viscometer, and after 5 minutes, the drop time at 25 ° C. is measured. From the measured dropping time, the intrinsic viscosity is determined according to the method described above and converted to the degree of polymerization.

  The content of the fine fibrous cellulose is preferably 0.1 parts by mass or more and 2.0 parts by mass or less with respect to 100 parts by mass of the dispersion medium of the battery separator coating liquid. The content of fine fibrous cellulose is more preferably 0.2 parts by mass or more, and further preferably 0.3 parts by mass or more. Further, the content of fine fibrous cellulose is more preferably 1.3 parts by mass or less, and further preferably 1.1 parts by mass or less, with respect to 100 parts by mass of the dispersion medium of the battery separator coating liquid. preferable.

  In the present invention, even when the content of fine fibrous cellulose in the battery separator coating liquid is within the above range, the dispersibility of fine particles and the ease of coating are compatible. In the coating layer formed from the battery separator coating liquid of the present invention, the occurrence of coating unevenness is suppressed. Moreover, in this invention, since content of the fine fibrous cellulose in the battery separator coating liquid can be made into the said range, it can also suppress that the microporous of a battery separator base material is block | closed.

  The viscosity of the battery separator coating liquid is preferably 100 mPa · s or more, more preferably 300 mPa · s or more, and further preferably 400 mPa · s or more. The viscosity of the battery separator coating liquid is preferably 40000 mPa · s or less, more preferably 20000 mPa · s or less, and further preferably 10000 mPa · s or less. The viscosity of the battery separator coating solution was adjusted so that the concentration of the fine fibrous cell roll contained in the battery separator coating solution was 0.4% by mass. -LVT), and measured at a rotation speed of 3 rpm, a measurement time of 3 minutes, and a liquid temperature of 23 ° C.

<Fine particles>
Examples of the fine particles contained in the battery separator coating liquid include organic fine particles and inorganic fine particles. Among these, the fine particles are preferably inorganic fine particles.

  Examples of the resin constituting the organic fine particles include aromatic vinyl compounds such as styrene, α-methylstyrene, and p-methylstyrene, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, and the like. (Meth) acrylic acid esters, vinyl cyanides such as (meth) acrylonitrile, vinyl halide compounds such as vinyl chloride and vinylidene chloride, and vinyl monomers such as butadiene, and a polymer obtained by combining one or more types Is mentioned.

Examples of the inorganic fine particles include iron oxide, Al ₂ O ₃ (alumina), SiO ₂ (silica), TiO ₂ , BaTiO ₃ , ZrO ₂ , Li ₃ PO ₄ (trilithium phosphate), SrTiO ₃ , SnO ₂ , _{CeO 2, MgO, NiO, CaO} , ZnO, Y 2 O 3, Pb (Zr, Ti) O 3 (PZT), Pb 1-x La x Zr 1-y Ti y O 3 (PLZT), Pb (Mg 1 _{/ 3} Nb _2/3 ) O ₃ —PbTiO ₃ (PMN-PT), HfO ₂ , Li ₃ PO ₄ , Li _x Ti _y (PO ₄ ) ₃ (0 <x <2, 0 <y <3), Li _{x Al y Ti z (PO 4} ) 3 (0 <x <2,0 <y <1,0 <z <3), (LiAlTiP) x O y (0 <x <4,0 <y <13), _{li x La y TiO 3 (0} <x <2,0 <y <3), AlN ( aluminum nitride), Si ₃ N ₄ (silicon nitride), C F ₂ (calcium fluoride), BaF ₂ (barium fluoride), BaSO ₄ (barium _{sulfate), SiC, Li x Ge y} P z S w (0 <x <4,0 <y <1,0 <z < 1, 0 <w <5), Li _x N _y (0 <x <4, 0 <y <2), SiS ₂ (Li _x Si _y S _z , 0 <x <3, 0 <y <2, 0 <Z <4), P ₂ S ₅ (Li _x P _y S _z ) (0 <x <3, 0 <y <3, 0 <z <7) and the like. Also, covalently bonded crystalline fine particles such as silicon and diamond; clay fine particles such as talc and montmorillonite; substances derived from mineral resources such as boehmite (AlOOH), zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite or the like Or carbonaceous fine particles such as carbon black and graphite can be used. Among these, at least one kind of fine particles selected from alumina, silica and boehmite is preferable, and silica or boehmite is particularly preferable.
Further, the surface of the fine particles may be coated with a material having electrical insulating properties (for example, a material constituting the insulating fine particles, etc.) to obtain fine particles having electrical insulating properties.

  The form of the fine particles may be any form such as a spherical shape, a polyhedral shape, and a plate shape. The primary average particle diameter of the fine particles is preferably 0.01 μm or more, and preferably 5 μm or less. In addition, when the fine particles are not spherical, it is preferable that the value obtained by calculating the primary average particle diameter assuming that the fine particles are spherical with the same volume is within the above range.

The content of the fine particles is preferably 5% by mass or more, and more preferably 10% by mass or more with respect to the total mass of the battery separator coating liquid. The content of the fine particles is preferably 90% by mass or less, more preferably 80% by mass or less, and further preferably 70% by mass or less. By making content of microparticles | fine-particles in the said range, the heat resistance of the battery separator base material mentioned later can be improved more effectively.
In addition, when the content of the fine particles is, for example, 10% by mass or less, the collision probability between the fine particles decreases, and a tendency to settle more easily is observed. However, since the battery separator coating liquid of the present invention contains fine fibrous cellulose having a predetermined condition, sedimentation of fine particles can be suppressed even when the content of fine particles is small.

<Dispersion medium>
The battery separator coating liquid contains a dispersion medium. Examples of the dispersion medium include water, organic solvents, and mixtures thereof. Of these, the dispersion medium is preferably water. Examples of the organic solvent include toluene, tetrahydrofuran, methyl ethyl ketone, methyl isobutyl ketone, isopropyl alcohol and the like. In the present specification, the dispersion medium refers to the remaining part of the battery separator coating liquid excluding the solid content remaining upon drying when the coating layer is formed.

  The content of the dispersion medium is preferably 10% by mass or more, more preferably 20% by mass or more, and further preferably 30% by mass or more with respect to the total mass of the battery separator coating liquid. . Further, the content of the dispersion medium is preferably 90% by mass or less, and more preferably 80% by mass or less.

<Other ingredients>
The battery separator coating liquid may further contain a binder component in addition to the above components. Specific examples of the binder component include, for example, ethylene-vinyl acetate copolymer; (meth) acrylic acid copolymer such as ethylene-ethyl acrylate copolymer, ethylene-ethyl methacrylate copolymer; fluorine-based rubber; styrene -Butadiene rubber (SBR); Polyvinyl alcohol (PVA); Polyvinyl butyral (PVB); Polyvinyl pyrrolidone (PVP); Poly N-vinyl acetamide; Cross-linked acrylic resin; Polyurethane; Epoxy resin; These binder components may be used individually by 1 type, and may use 2 or more types together. When the battery separator coating liquid further contains a binder component, adhesion to the battery separator substrate described later can be enhanced. The content of the binder component is preferably 15% by mass or less based on the total mass of the fine particles in the battery separator coating solution.

  Examples of other components contained in the battery separator coating liquid include hydrophilic polymers and organic ions. Examples of hydrophilic polymers include polyethylene glycol, cellulose derivatives (hydroxyethyl cellulose, carboxyethyl cellulose, carboxymethyl cellulose, etc.), casein, dextrin, starch, modified starch, polyvinyl alcohol, modified polyvinyl alcohol (acetoacetylated polyvinyl alcohol, etc.), Examples thereof include polyethylene oxide, polyvinyl pyrrolidone, polyvinyl methyl ether, polyacrylates, polyacrylamide, alkyl acrylate copolymer, urethane copolymer, and the like. Examples of organic ions include tetraalkylammonium ions and tetraalkylphosphonium ions. Examples of tetraalkylammonium ions include tetramethylammonium ion, tetraethylammonium ion, tetrapropylammonium ion, tetrabutylammonium ion, tetrapentylammonium ion, tetrahexylammonium ion, tetraheptylammonium ion, tributylmethylammonium ion, and lauryltrimethyl. Examples include ammonium ion, cetyltrimethylammonium ion, stearyltrimethylammonium ion, octyldimethylethylammonium ion, lauryldimethylethylammonium ion, didecyldimethylammonium ion, lauryldimethylbenzylammonium ion, and tributylbenzylammonium ion. Examples of tetraalkylphosphonium ions include tetramethylphosphonium ions, tetraethylphosphonium ions, tetrapropylphosphonium ions, tetrabutylphosphonium ions, and lauryltrimethylphosphonium ions. In addition, examples of the tetrapropylonium ion and the tetrabutylonium ion include a tetra n-propylonium ion and a tetra n-butylonium ion, respectively. The content of the hydrophilic polymer or organic ion is preferably 20% by mass or less based on the total mass of the fine particles in the battery separator coating liquid.

(Separator for battery)
The present invention also relates to a battery separator having a substrate and a coating layer. The coating layer includes fibrous cellulose having a fiber width of 1000 nm or less and an average degree of polymerization of less than 400, and fine particles. A coating layer is a layer formed from the battery separator coating liquid described above.

  The battery separator is not limited as long as it has a coating layer on at least one surface of the substrate, and may have a coating layer on both surfaces of the substrate. It is preferable that it has. In addition, although the battery separator has a coating layer, a part of the battery separator coating liquid forming the coating layer may penetrate into the microporous interior of the substrate. Such a state can also be said to be a state in which a part of the battery separator coating solution is infiltrated into the surface layer region of the substrate.

  The battery separator is formed by coating the above-described battery separator coating liquid on a substrate. The coating layer formed by coating contains a thickener for battery separator coating liquid and contains the above-described fine fibrous cellulose. The fine fibrous cellulose is preferably phosphorylated cellulose.

  The average degree of polymerization of the fine fibrous cellulose may be less than 400, preferably 395 or less, and more preferably 380 or less. The average degree of polymerization of the fine fibrous cellulose is preferably 100 or more, more preferably 150 or more, and further preferably 200 or more.

In addition, when calculating the average degree of polymerization of the fine fibrous cellulose in the battery separator, the measurement is performed after the fine fibrous cellulose is isolated from the battery separator by the following procedure.
In this case, first, the surface of the battery separator is observed with a transmission electron microscope to confirm the presence of fine fibrous cellulose. Subsequently, the type I crystal of cellulose is detected using solid-state NMR.

When the presence of fine fibrous cellulose is confirmed on the surface of the battery separator, the fine fibrous cellulose is isolated according to the following procedure.
First, the battery separator is cut to about 1 cm square, and then pulverized to about 1 mm square using a cutter mill. Next, a 0.5 mol / L copper ethylenediamine solution is added to 1 g of the pulverized product of the battery separator so as to have a ratio of 100 ml and stirred to dissolve the fine fibrous cellulose. The obtained solution is filtered to remove the residue, and then dropped into water to obtain regenerated cellulose. This regenerated cellulose is obtained by dissolving fine fibrous cellulose in a copper ethylenediamine solution and regenerating it in water. The obtained regenerated cellulose is filtered off, sufficiently washed with water, and dried.

  And the dry weight of the obtained regenerated cellulose is measured. The content of the fine fibrous cellulose contained in the battery separator is determined from this weight and the weight of the battery separator used to obtain this weight.

  30 ml of 0.5 mol / L copper ethylenediamine solution is added to 0.14 g or more and 0.16 g or less of the dried regenerated cellulose obtained as described above, and stirred to dissolve the cellulose again. The resulting solution is filtered to remove the residue. Then, 10 ml of the prepared filtrate is put into a Canon Fenceke viscometer, and after 5 minutes, the drop time at 25 ° C. is measured. From the measured dropping time, the intrinsic viscosity is determined according to the method described above and converted to the degree of polymerization.

  The coating layer contains fine particles. The fine particles described above can be listed as the fine particles, and inorganic fine particles are preferable. Preferred specific examples are as described above.

The basis weight of the coating layer is not particularly limited, but the present invention is characterized in that a coating layer without coating unevenness can be formed even when the basis weight of the coating layer is small. There is. For example, in the present invention, the basis weight of the coating layer can be 4.5 g / m ² or less, can be 4.0 g / m ² or less, and can be 3.0 g / m ² or less. You can also. In this invention, even if it is a case where the basic weight of a coating layer is made into the said range, a surface property is favorable and a coating layer without a coating nonuniformity is formed.

  The thickness of the coating layer varies depending on the pore diameter and thickness on the substrate side, but is preferably 0.1 μm or more, more preferably 0.5 μm or more, and 1 μm or more, for example. Is more preferable. Further, it is preferably 20 μm or less, more preferably 15 μm or less, and further preferably 10 μm or less. In addition, the thickness of the coating layer can be 4.5 μm or less, 4.0 μm or less, or 3.0 μm or less. In the present invention, the coating layer can be thinned, and a coating layer having no coating unevenness can be obtained even when the coating layer is thinned.

<Base material>
The battery separator includes a base material. The base material is stable with respect to the electrolytic solution, and is preferably a porous base material.

Specific examples of the constituent material of the substrate include, for example, cellulose, modified cellulose (such as carboxymethyl cellulose), polyolefin (polypropylene (PP), polyethylene (PE), and copolymerized polyolefin having a structural unit derived from ethylene of 85 mol% or more. Etc.), polyester (polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), etc.), polyacrylonitrile (PAN), aramid, polyamideimide, polyimide and other resins; glass, alumina, silica, etc. An inorganic material (inorganic oxide) is mentioned.
Among them, the constituent material of the substrate is preferably a polyolefin resin, and more preferably polypropylene or polyethylene. The substrate is particularly preferably a nonwoven fabric or film made of polypropylene or polyethylene.

  When the base material is a non-woven fabric made of polyethylene, it is preferable to form a non-woven fabric by making paper using polyethylene fibers by a wet paper making method. In the nonwoven fabric, the polyethylene fibers are preferably oriented randomly.

  When the base material is a film made of polyethylene, the film is preferably a stretched film, and more preferably a biaxially stretched film.

The battery separator substrate may have an adhesive. When the battery separator substrate has an adhesive, it is preferable to contain an acrylic resin as the adhesive. Examples of the acrylic resin include ethylene- (meth) acrylic acid resin, propylene- (meth) acrylic acid resin, and the like. The adhesive is preferably sprayed on the surface of the substrate, and is preferably present in the surface layer region of the substrate. Such an adhesive acts to increase the adhesion between the substrate and the coating layer.
Moreover, other resin can also be used together as needed. Resins that can be used in combination include vinyl chloride resin, (meth) acrylic ester resin, styrene / acrylic ester copolymer resin, vinyl acetate resin, vinyl acetate / (meth) acrylic ester copolymer resin, urethane resin, Examples thereof include silicone resins, epoxy resins, ethylene / vinyl acetate copolymer resins, polyester resins, polyvinyl alcohol resins, ethylene vinyl alcohol copolymer resins, and rubber emulsions such as SBR and NBR.

The basis weight of the substrate is preferably 10 g / m ² or more, and more preferably 20 g / m ² or more. The basis weight of the substrate is preferably 100 g / m ² or less, more preferably 80 g / m ² or less.

The density of the substrate is preferably 0.1 g / cm ³ or more, more preferably 0.2 g / cm ³ or more, and further preferably 0.3 g / cm ³ or more. The density of the substrate is preferably 3.0 g / cm ³ or less, more preferably 2.0 g / cm ³ or less, and further preferably 1.0 g / cm ³ or less.

<Method for producing battery separator>
The battery separator manufacturing process preferably includes a step of applying the battery separator coating liquid to at least one surface of the substrate and a step of drying the substrate coated with the battery separator coating liquid. When applying the battery separator coating solution to the surface of the substrate, a conventionally known coating machine can be used. Examples of the coating machine include a die coater, a gravure coater, a reverse roll coater, a squeeze roll coater, a curtain coater, a blade coater, and a knife coater. The battery separator coating solution is preferably applied to one side of the substrate.

The coating amount (coating layer basis weight) of the battery separator coating liquid is preferably 1 g / m ² or more, and more preferably 1.5 g / m ² or more. Further, the coating amount of the battery separator coating liquid is preferably 50 g / m ² or less, and more preferably 20 g / m ² or less. The coating amount of the battery separator coating liquid may be 4.5 g / m ² or less, 4.0 g / m ² or less, or 3.0 g / m ² or less.

(Use)
The battery separator of the present invention is preferably used for an electrochemical element typified by a lithium secondary battery. As an electrochemical element, it can be used for applications such as supercapacitors as well as lithium batteries (primary batteries and secondary batteries) using organic electrolytes.

  Lithium secondary batteries can be in the form of cylinders (such as square cylinders or cylinders) that use steel cans or aluminum cans as exterior canisters, or soft package forms that use metal-deposited laminated films as exterior bodies. You can also.

  The members constituting the lithium ion battery can be roughly divided into a positive electrode, a negative electrode, a separator, and an electrolytic solution. Each of the positive electrode and the negative electrode contains an active material that performs an oxidation / reduction reaction for sending and receiving electrons. The positive electrode and the negative electrode can be used in the form of an electrode group having a laminated structure laminated via a battery separator, or an electrode group having a wound structure in which this is wound.

The positive electrode is not particularly limited as long as it is a positive electrode used in a conventionally known lithium secondary battery. The positive electrode contains an active material capable of occluding and releasing Li ⁺ ions.
The negative electrode is not particularly limited as long as it is a negative electrode used in a conventionally known lithium secondary battery. The negative electrode contains an active material capable of occluding and releasing Li ⁺ ions.

  The positive electrode and the negative electrode can be used in the form of a laminated electrode group laminated via the battery separator of the present invention, or a wound electrode group in which this is wound.

As the electrolytic solution, a solution in which a lithium salt is dissolved in an organic solvent is used. The lithium salt is not particularly limited as long as it dissociates in a solvent to form Li ⁺ ions and does not cause a side reaction such as decomposition in a voltage range used as a battery. The organic solvent is not particularly limited as long as it dissolves a lithium salt and does not cause a side reaction such as decomposition in a voltage range used as a battery.

  Lithium-ion batteries have been known for many years in addition to power supplies for portable devices such as mobile phones and notebook personal computers, electric vehicles, hybrid vehicles, electric motorcycles, electric assist bicycles, electric tools, shavers, etc. It is used for various applications.

  The features of the present invention will be described more specifically with reference to examples and comparative examples. The materials, amounts used, ratios, processing details, processing procedures, and the like shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

<Production of Fine Fibrous Cellulose 1 (for Examples)>
Impregnated kraft pulp with a dry mass of 100 parts by weight is impregnated with a mixed aqueous solution of ammonium dihydrogen phosphate and urea, and compressed to 49 parts by weight of ammonium dihydrogen phosphate and 130 parts by weight of urea. Got. The obtained chemical solution-impregnated pulp was dried with a dryer at 105 ° C. to evaporate the moisture and pre-dried. Then, it heated for 10 minutes with the ventilation dryer set to 140 degreeC, the phosphate group was introduce | transduced into the cellulose in a pulp, and the phosphorylated pulp was obtained.

  The obtained phosphorylated pulp was fractionated by 100 g, and 10 L of ion-exchanged water was poured, stirred and dispersed uniformly, and then subjected to filtration and dehydration to obtain a dehydrated sheet, which was repeated twice. Next, the obtained dehydrated sheet was diluted with 10 L of ion-exchanged water, and a 1N sodium hydroxide aqueous solution was added little by little while stirring to obtain a pulp slurry having a pH of 12 or more and 13 or less. Thereafter, the pulp slurry was dehydrated to obtain a dehydrated sheet, and then 10 L of ion exchange water was added. The step of stirring and dispersing uniformly, followed by filtration and dehydration to obtain a dehydrated sheet was repeated twice.

In the same manner as described above, the step of introducing phosphate groups and the step of filtration and dehydration were repeated for the obtained dehydrated sheet to obtain a twice-phosphorylated cellulose dehydrated sheet 1. The infrared absorption spectrum of the obtained dehydration sheet 1 was measured by FT-IR. As a result, absorption based on phosphate groups was observed at 1230 cm ⁻¹ or more and 1290 cm ⁻¹ or less, and addition of phosphate groups was confirmed.

  Ion exchange water was added to the obtained dehydrated sheet 1 (twice phosphorylated cellulose) to prepare a slurry having a solid content concentration of 2% by mass. This slurry was processed 15 times at a pressure of 200 MPa with a wet atomization apparatus (manufactured by Sugino Machine Co., Ltd., an optimizer) to obtain fine fibrous cellulose 1. It was confirmed by X-ray diffraction that this fine fibrous cellulose 1 maintained the cellulose I type crystal.

<Manufacture of fine fibrous cellulose 2 (for Examples)>
Fine fibrous cellulose 2 was obtained in the same manner as in the production of fine fibrous cellulose 1 except that the number of pressure treatments of 200 MPa in the wet atomization apparatus was set to 12. It was confirmed by X-ray diffraction that the fine fibrous cellulose 2 maintained the cellulose I type crystal.

<Manufacture of fine fibrous cellulose 3 (for Examples)>
Fine fibrous cellulose 3 was obtained in the same manner as in the production of fine fibrous cellulose 1 except that the number of pressure treatments of 200 MPa in the wet atomization apparatus was set to 10. It was confirmed by X-ray diffraction that the fine fibrous cellulose 3 maintained the cellulose I type crystal.

<Manufacture of fine fibrous cellulose A (for comparative example)>
Fine fibrous cellulose A was obtained in the same manner as in the production of fine fibrous cellulose 1 except that the pressure treatment in the wet atomization apparatus was changed to 6 times at 245 MPa. It was confirmed by X-ray diffraction that this fine fibrous cellulose A maintained the cellulose I type crystal.

<Manufacture of fine fibrous cellulose B (for comparative example)>
Fine fibrous cellulose B was obtained in the same manner as in the production of fine fibrous cellulose 1 except that the pressure treatment in the wet atomization apparatus was changed to 3 times at 245 MPa. It was confirmed by X-ray diffraction that this fine fibrous cellulose B maintained the cellulose I type crystal.

<Manufacture of fine fibrous cellulose C (for comparative example)>
<Neutral TEMPO oxidation treatment> (Hereinafter, M represents mol concentration mol / L)
Undried softwood bleached kraft pulp equivalent to 100 parts by weight of dry weight, 1.6 parts by weight of TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl), and 113 parts by weight of 80% sodium chlorite Were suspended in 9000 parts by mass of 0.05 M sodium phosphate buffer (pH = 6.8) (Liquid A).
To 50 mL of 2M sodium hypochlorite, 0.05M sodium phosphate buffer (pH = 6.8) was added to 0.1M (solution B).
Liquid B was poured into liquid A and immediately sealed, and then reacted at a temperature of 60 ° C. for 72 hours while stirring at 500 rpm using a magnetic stirrer to obtain a pulp slurry.

Thereafter, this pulp slurry is dehydrated to obtain a dehydrated sheet, and then, 5000 parts by mass of ion-exchanged water is poured, stirred and dispersed uniformly, and then subjected to filtration and dehydration to obtain a dehydrated sheet 2 twice. Repeated. The obtained dehydration sheet 2 was measured for infrared absorption spectrum by FT-IR. As a result, absorption based on a carboxyl group was observed at 1730 cm ⁻¹ , confirming the addition of a carboxyl group. Using this dehydrated sheet 2 (TEMPO oxidized cellulose), fine fibrous cellulose was prepared.

  Ion exchange water was added to the resulting dehydrated sheet 2 (TEMPO oxidized cellulose) to prepare a slurry having a solid content concentration of 2 mass%. This slurry was treated three times at a pressure of 245 MPa with a wet atomization apparatus (manufactured by Sugino Machine, Optimizer) to obtain fine fibrous cellulose C. It was confirmed by X-ray diffraction that this fine fibrous cellulose C maintained the cellulose I type crystal.

(Physical properties of fine fibrous cellulose)
<Measurement of fiber width>
The fiber width of the fine fibrous cellulose was measured by the following method.
The supernatant of the fine fibrous cellulose treated with the wet atomization apparatus was diluted with water so that the concentration of the fine fibrous cellulose was 0.01% by mass or more and 0.1% by mass or less, and subjected to a hydrophilic treatment. It was dripped on the carbon grid film. After drying, it was stained with uranyl acetate and observed with a transmission electron microscope (JEOL-2000EX, manufactured by JEOL Ltd.). It was confirmed that the fine fibrous celluloses 1 to 3 and the fine fibrous celluloses A to C were fine fibrous cellulose having a fiber width of about 4 nm.

<Measurement of substituent amount>
The introduction amount of the substituent is the introduction amount of the phosphoric acid group or carboxylic acid group to the fiber raw material, and the larger this value, the more phosphoric acid groups or carboxylic acid groups are introduced. The amount of substituent introduced was measured by diluting the target fine fibrous cellulose with ion-exchanged water so that the content was 0.2% by mass, and then treating with ion-exchange resin and titration with alkali. In the treatment with an ion exchange resin, 1/10 by volume of a strongly acidic ion exchange resin (Amberjet 1024; Organo Co., Ltd., conditioned) is added to the 0.2 mass% fibrous cellulose-containing slurry and shaken for 1 hour. Went. Thereafter, the mixture was poured onto a mesh having an opening of 90 μm to separate the resin and the slurry. In the titration using an alkali, the change in the value of electrical conductivity exhibited by the slurry was measured while adding a 0.1 N sodium hydroxide aqueous solution to the fine fibrous cellulose-containing slurry after ion exchange. That is, the alkali amount (mmol) required in the first region of the curves shown in FIG. 1 (phosphate group) and FIG. 2 (carboxyl group) is divided by the solid content (g) in the titration target slurry, The amount of substituent introduced (mmol / g). The calculated results are shown in Table 1 below.

<Measurement of degree of polymerization>
The average degree of polymerization of cellulose molecules constituting fine fibrous cellulose was evaluated with reference to the following paper.
TAPPI International Standard; ISO / FDIS 5351, 2009.
Smith, DK; Bampton, RF; Alexander, WJ Ind. Eng. Chem., Process Des. Dev. 1963, 2, 57-62.

30 g of the suspension obtained by diluting the target fine fibrous cellulose with ion-exchanged water so that the content becomes 2 ± 0.3% by mass is collected in a centrifuge tube and left overnight in a freezer. I let you. Furthermore, after drying with a freeze dryer for 5 days or more, it was heated for 3 hours or more and 4 hours or less with a constant temperature dryer set at 105 ° C. to obtain absolutely dry fine fibrous cellulose.
In order to measure the reference, 15 ml of pure water and 15 ml of 1 mol / L copper ethylenediamine were added to an empty screw tube having a capacity of 50 ml to prepare a 0.5 mol / L copper ethylenediamine solution. 10 ml of the above 0.5 mol / L copper ethylenediamine solution was put into a Cannon-Fenske viscometer and left for 5 minutes, and then the drop time at 25 ° C. was measured as the solvent drop time.

  Next, in order to measure the viscosity of the fine fibrous cellulose, 0.14 g or more and 0.16 g or less of the dried fine fibrous cellulose was weighed into an empty 50 ml capacity screw tube, and 15 ml of pure water was added. Furthermore, 15 ml of 1 mol / L copper ethylenediamine was added, and the mixture was stirred at 1000 rpm for 10 minutes with a rotation / revolution super mixer to obtain a 0.5 mol / L copper ethylenediamine solution. Similarly to the measurement of the reference, 10 ml of a 0.5 mol / L copper ethylenediamine solution prepared in a Cannon Fenceke viscometer was added and left for 5 minutes, and then the drop time at 25 ° C. was measured. The drop time was measured three times, and the average value was taken as the drop time of the fine fibrous cellulose solution.

The degree of polymerization was calculated from the mass of the absolutely dry fine fibrous cellulose used for the measurement, the solvent dropping time, and the dropping time of the fine fibrous cellulose solution using the following equation. In addition, the following average degree of polymerization is an average value of the values measured three times.
Absolutely dry fine fibrous cellulose used for measurement Mass: a (g) (where a is 0.14 to 0.16)
Cellulose concentration of the solution: c = a / 30 (g / mL)
Solvent falling time: t ₀ (sec)
Drop time of fine fibrous cellulose solution: t (sec)
Relative viscosity of the solution: η _rel = t / t ₀
Specific viscosity of the solution: η _sp = η _rel -1
Intrinsic viscosity: [η] = η _sp /c(1+0.28η _sp )
Degree of polymerization: DP = [η] /0.57

<Example 1>
51 g of water was added as a dispersion medium to 100 g of silica fine particles (Fuji Silysia Chemical Co., Ltd., Sylycia 310, particle size: 1.4 μm) K. The mixture was stirred for 15 minutes at 3000 rpm with a homodisper (manufactured by Tokushu Kika Kogyo). Thereafter, 50 g of a suspension of fine fibrous cellulose 1 having a solid content concentration of 2 mass% (a suspension of 1 g of the solid content of fine fibrous cellulose 1 and 49 g of water) was added, and the mixture was further stirred for 1 hour with a disperser. In this way, a battery separator coating liquid was obtained in which the solid content concentration of fine fibrous cellulose was 1 part by mass with respect to 50% by mass of silica fine particles and 100 parts by mass of the dispersion medium (51 g of the dispersion medium + 49 g of water).

<Example 2>
A battery separator coating solution was obtained in the same manner as in Example 1 except that the fine fibrous cellulose 1 was replaced with the fine fibrous cellulose 2.

<Example 3>
A battery separator coating solution was obtained in the same manner as in Example 1 except that the fine fibrous cellulose 1 was replaced with the fine fibrous cellulose 3.

<Comparative Example 1>
A battery separator coating solution was obtained in the same manner as in Example 1 except that the fine fibrous cellulose 1 was replaced with the fine fibrous cellulose A.

<Comparative example 2>
A battery separator coating solution was obtained in the same manner as in Example 1 except that the fine fibrous cellulose 1 was replaced with the fine fibrous cellulose B.

<Comparative Example 3>
A battery separator coating solution was obtained in the same manner as in Example 1 except that the fine fibrous cellulose 1 was replaced with the fine fibrous cellulose C.

<Reference Example 1>
A battery separator coating solution was obtained in the same manner as in Comparative Example 1. However, in Reference Example 1, the coating layer basis weight after drying was set to 5.0 g / m ² as described later (production of battery separator), and coating evaluation was performed.

<Reference Example 2>
A battery separator coating solution was obtained in the same manner as in Comparative Example 3. However, in Reference Example 2, the coating layer basis weight after drying in the later-described (production of battery separator) was set to 5.0 g / m ^2, and coating evaluation was performed.

(Preparation of base material)
Polyethylene fiber (fiber length: 5 mm, fiber strength: 28 cN / dtex, elastic modulus: 900 cN / dtex) is dispersed in water so as to be 0.2% by mass, and a randomly oriented web is formed by wet papermaking. did. Ethylene- (meth) acrylic acid resin (manufactured by Toho Chemical Co., Ltd., Hitech S-3148, ethylene / acrylic acid = 80 parts by mass / 20 parts by mass, having a urethane group at the resin end) as an adhesive on this web, and polyethylene After spraying so that the fiber ratio was 10% by mass, it was dried with a hot air dryer set at 110 ° C. to obtain a nonwoven fabric of 30 g / m ² . The nonwoven fabric was calendered to obtain a nonwoven fabric having a density of 0.64 g / cm ³ . This non-woven fabric was used as a non-woven fabric substrate for applying a battery separator coating solution.

(Preparation of battery separator)
A battery separator coating solution was applied to the nonwoven fabric substrate so that the basis weight of the coating layer after drying was 2.5 g / m ² to prepare a battery separator. In Reference Examples 1 and 2, a battery separator coating solution was applied so that the basis weight of the coating layer after drying was 5.0 g / m ² to prepare a battery separator.

(Evaluation of battery separator)
<Coating property>
A battery separator coating solution is applied to the nonwoven fabric base so that the basis weight of the coating layer after drying is 2.5 g / m ² (Examples and Comparative Examples) or 5.0 g / m ² (Reference Examples). The coatability was evaluated according to the following criteria.
○: There is no unevenness on the entire surface in the appearance observation after coating.
(Triangle | delta): There exists a nonuniformity part in the external appearance observation after coating.
X: Unevenness is observed on the entire surface by appearance observation after coating. Or coating itself is not possible.

  As can be seen from Table 2, the battery separator coating liquid obtained in the examples had good coating properties even when the coating layer was thinned. On the other hand, in the battery separator coating solution obtained in the comparative example, the coating property when the coating layer was thinned was poor.

Claims (11)

  A thickener for battery separator coating liquid containing fibrous cellulose having a fiber width of 1000 nm or less and an average degree of polymerization of less than 400.   The thickener for battery separator coating liquid according to claim 1, wherein the fibrous cellulose is phosphorylated cellulose.   A battery separator coating solution comprising fibrous cellulose having a fiber width of 1000 nm or less and an average degree of polymerization of less than 400, fine particles, and a dispersion medium.   The battery separator coating liquid according to claim 3, wherein the fibrous cellulose is phosphorylated cellulose.   The battery separator coating liquid according to claim 3 or 4, wherein the content of the fibrous cellulose is 0.1 parts by mass or more and 1.3 parts by mass or less with respect to 100 parts by mass of the dispersion medium.   The battery separator coating liquid according to claim 3, wherein the fine particles are inorganic fine particles. A battery separator having a substrate and a coating layer,
The coating layer is a battery separator including fibrous cellulose having a fiber width of 1000 nm or less and an average degree of polymerization of less than 400, and fine particles.   The battery separator according to claim 7, wherein the fibrous cellulose is phosphorylated cellulose. The battery separator according to claim 7 or 8, wherein a basis weight of the coating layer is 4.5 g / m ² or less.   The battery separator according to claim 7, wherein the fine particles are inorganic fine particles.   The battery separator according to any one of claims 7 to 10, wherein the base material contains a polyolefin-based resin.

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