JP6942952B2 - Battery separator, battery and battery separator coating - Google Patents

Description

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

Lithium-ion secondary batteries have a feature of high energy density, and are widely used as a power source 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, as a battery separator, a porous film made of polyethylene or polypropylene has been used. However, the porous film made of polyethylene or polypropylene has low heat resistance, and when the porous film shrinks and an internal short circuit occurs, local heat is generated inside the battery, causing ignition, bursting, etc. for safety. I have a problem.

To solve such problems, battery separators containing inorganic fine particles have been developed. In a battery separator containing inorganic fine particles, by controlling the pore diameter with the inorganic fine particles, it is possible to suppress an internal short circuit and improve heat resistance. For example, Patent Document 1 discloses a battery separator having an active layer containing inorganic fine particles and a binder polymer. Here, the inorganic fine particles are bound to each other by the binder polymer, and the gaps between the inorganic fine particles have a pore structure.

When forming the active layer as described above, 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 or an organic solvent, they tend to settle in the slurry containing the inorganic fine particles, and once settled, the inorganic fine particles may aggregate with each other, which is a problem. Further, if the dispersed state of the inorganic fine particles is not good, there is a problem that coating unevenness occurs when the porous film is coated, and it has been required to improve the stability of the inorganic fine particles in the coating liquid.

In order to improve 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. Further, in Patent Document 2, it is studied to use a cellulose fiber as a thickener. Patent Document 2 discloses a separator coating solution for a battery containing cellulose fibers, in which bacterial cellulose fibers and nanocellulose fibers produced by dissociating crystalline cellulose are used as a thickener. ..

Japanese Patent Application Laid-Open No. 2008-524824 Japanese Unexamined Patent Publication No. 2015-84318

Excellent fine particle dispersibility and coatability are required for the battery separator coating liquid. Further, since the lithium ion secondary battery is used for various purposes, excellent mechanical strength may be required depending on the application. Therefore, the present invention provides a battery separator coating liquid having both excellent fine particle dispersibility and coatability, which can form a battery separator having excellent mechanical strength. The purpose is.

As a result of diligent studies to solve the above problems, the present inventors have made fibrous cellulose having a fiber width of 1000 nm or less in the fiber-containing layer and having an ionic substituent in a battery separator coating solution. By containing the fine particles and the binder resin, a battery separator coating liquid having excellent fine particle dispersibility and coatability is formed, and a battery separator having excellent mechanical strength is formed. It has been found that a separator coating liquid for batteries can be obtained.
Specifically, the present invention has the following configuration.

[1] A battery having a base material and a fiber-containing layer, and the fiber-containing layer contains fibrous cellulose having a fiber width of 1000 nm or less and having an ionic substituent, fine particles, and a binder resin. Separator for.
[2] The battery separator according to [1], wherein the fibrous cellulose is phosphorylated cellulose.
[3] The battery separator according to [1] or [2], wherein the total content of the fibrous cellulose and the binder resin is 0.1 part by mass or more and 5.0 parts by mass or less with respect to 100 parts by mass of the fine particles.
[4] The battery separator according to any one of [1] to [3], wherein the mass ratio of the content of the fibrous cellulose to the content of the binder resin is 1:99 to 99: 1.
[5] The battery separator according to any one of [1] to [4], wherein the binder resin contains at least one selected from acrylic resin, polyolefin resin, urethane resin and silicone resin.
[6] The battery separator according to any one of [1] to [5], wherein the base material contains a polyolefin resin.
[7] A battery comprising the battery separator according to any one of [1] to [6].
[8] A battery separator coating solution containing fibrous cellulose having a fiber width of 1000 nm or less and having an ionic substituent, fine particles, and a binder resin.
[9] The battery separator coating solution according to [8], wherein the fibrous cellulose is phosphorylated cellulose.
[10] The battery separator coating according to [8] or [9], wherein the total content of the fibrous cellulose and the binder resin is 0.1 part by mass or more and 5.0 parts by mass or less with respect to 100 parts by mass of the fine particles. liquid.
[11] The battery separator coating solution according to any one of [8] to [10], wherein the mass ratio of the content of the fibrous cellulose to the content of the binder resin is 1:99 to 99: 1.
[12] The separator coating solution for a battery according to any one of [8] to [11], wherein the binder resin contains at least one selected from an acrylic resin, a polyolefin resin, a urethane resin, and a silicone resin.

According to the present invention, it is possible to obtain a battery separator coating liquid having both excellent fine particle dispersibility and coatability. Further, the battery separator formed from the battery separator coating liquid of the present invention is excellent in mechanical strength.

FIG. 1 is a graph showing the relationship between the amount of NaOH added dropwise to a fiber raw material having a phosphoric acid group and the electrical conductivity. FIG. 2 is a graph showing the relationship between the amount of NaOH added to the fiber raw material having a carboxyl group and the electrical conductivity.

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

(Battery separator)
The present invention also relates to a battery separator having a base material and a fiber-containing layer. The fiber-containing layer contains fibrous cellulose having a fiber width of 1000 nm or less and having an ionic substituent, fine particles, and a binder resin. In the present specification, fibrous cellulose having a fiber width of 1000 nm or less is also referred to as fine fibrous cellulose.

Since the battery separator of the present invention has the above configuration, it is excellent in mechanical strength. Specifically, the battery separator of the present invention is a battery separator that suppresses the occurrence of an explosion even when an external impact is applied and is also excellent in safety.

The fiber-containing layer of the battery separator of the present invention is formed by applying a battery separator coating liquid having excellent fine particle dispersibility and coatability onto a base material. Therefore, the fine particles are uniformly dispersed in the formed fiber-containing layer, and uneven coating of the fiber-containing layer does not occur. In this specification, the evaluation of coatability can be determined by the presence or absence of coating unevenness in the fiber-containing layer.
Further, the battery separator of the present invention is also characterized in that uniform pores are formed over the entire fiber-containing layer. As described above, in the fiber-containing layer of the battery separator of the present invention, the occurrence of coating unevenness is suppressed, the dispersibility of fine particles is excellent, and uniform pores are formed, so that the battery can be used. In addition to having good performance as a separator, it is highly safe.

(Fiber-containing layer)
The battery separator of the present invention has a fiber-containing layer. The fiber-containing layer contains fibrous cellulose having a fiber width of 1000 nm or less and having an ionic substituent, fine particles, and a binder resin.
The battery separator may have a fiber-containing layer on at least one surface of the base material, and may have a fiber-containing layer on both sides of the base material, but the fiber-containing layer may be provided on one side of the base material. It is preferable that the fiber has. Such a fiber-containing layer is formed by applying a battery separator coating solution to the surface of the base material. In the present specification, such a fiber-containing layer may be referred to as a coating layer. A part of the battery separator coating liquid forming the fiber-containing layer (coating layer) may have penetrated into the microporous portion of the base material. Such a state can be said to be a state in which a part of the battery separator coating liquid has permeated into the surface layer region of the base material.

The thickness of the fiber-containing layer varies depending on the pore size 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 even more preferable. Further, it is preferably 20 μm or less, more preferably 15 μm or less, and further preferably 10 μm or less.

<Fine fibrous cellulose>
The fiber-containing layer contains fibrous cellulose (fine fibrous cellulose) having a fiber width of 1000 nm or less.

The content of the fine fibrous cellulose in the fiber-containing layer is preferably 0.01 parts by mass or more and 40 parts by mass or less with respect to 100 parts by mass of the fine particles contained in the fiber-containing layer. The content of the fine fibrous cellulose is more preferably 0.05 parts by mass or more, and further preferably 0.1 parts by mass or more. The content of the fine fibrous cellulose is more preferably 30 parts by mass or less, further preferably 20 parts by mass or less, and 10 parts by mass with respect to 100 parts by mass of the fine particles contained in the fiber-containing layer. The following is particularly preferable.

The average degree of polymerization of the fine fibrous cellulose is preferably 100 or more, more preferably 150 or more, and even more preferably 200 or more. The average degree of polymerization of the fine fibrous cellulose is preferably 2000 or less, more preferably 1500 or less, further preferably 1200 or less, further preferably 1000 or less, and 750 or less. It is particularly preferable to have. The average degree of polymerization of the fine fibrous cellulose is preferably less than 400. By setting the average degree of polymerization of the fine fibrous cellulose to less than 400, it is possible to suppress the occurrence of coating unevenness when the fiber-containing layer is made into a thin film (for example, the basis weight of the fiber-containing layer is 2.5 g / m ^2). be able to.

When calculating the average degree of polymerization of the fine fibrous cellulose in the fiber-containing layer, the fine fibrous cellulose is isolated from the battery separator by the following procedure, and then the measurement is performed.
In this case, first, the surface of the fiber-containing layer is observed with a transmission electron microscope to confirm the presence of fine fibrous cellulose. Then, solid-state NMR is used to detect type I crystals of cellulose.

When the presence of fine fibrous cellulose is confirmed on the surface of the fiber-containing layer, the fine fibrous cellulose is isolated according to the following procedure.
First, the battery separator is cut into 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 crushed product of the battery separator at a ratio of 100 ml, and the mixture is stirred to dissolve the fine fibrous cellulose. The obtained solution is filtered to remove the residue, and then added dropwise to 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 then dried.

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

The average degree of polymerization of the fine fibrous cellulose contained in the battery separator 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.

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 capacity screw tube to prepare a 0.5 mol / L copper ethylenediamine solution. 10 ml of the above 0.5 mol / L copper ethylenediamine solution is placed in a Canon Fenceke viscometer, left for 5 minutes, and then the drop time at 25 ° C. is measured to determine the solvent drop time.

The regenerated cellulose obtained as described above is separated into a centrifuge tube and allowed to stand in a freezer overnight to freeze. Further, it is dried in a freeze-dryer for 5 days or more, and then heated in a constant temperature dryer set at 105 ° C. for 3 hours or more and 4 hours or less to obtain fine fibrous cellulose in an absolutely dry state. To 0.14 g or more and 0.16 g or less of the dried product of regenerated cellulose obtained as described above, 30 ml of a 0.5 mol / L copper ethylenediamine solution is added, and the mixture is stirred to dissolve the cellulose again. The obtained solution is filtered to remove the residue. Then, 10 ml of the prepared filtrate is placed in a Canon Fenceke viscometer, left for 5 minutes, and then the drop time at 25 ° C. is measured. The fall time is measured three times, and the average value is taken as the fall 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 drop time, and the fall time of the fine fibrous cellulose solution using the following formula. The following average degree of polymerization is the average value of each measurement when measured twice or more.
Absolutely dry fine fibrous cellulose mass used for measurement: a (g) (where a is 0.14 or more and 0.16 or less)
Cellulose concentration in solution: c = a / 30 (g / mL)
Solvent drop time: t ₀ (sec)
Falling time of fine fibrous cellulose solution: t (sec)
Relative viscosity of solution: η _rel = t / t ₀
Specific viscosity of solution: η _sp = η _rel- 1
Intrinsic viscosity: [η] = η _{sp /} c (1 + 0.28 _{η sp} )
Degree of polymerization: DP = [η] /0.57
Since the average degree of polymerization of fine fibrous cellulose is calculated by the above method, it is sometimes called the average degree of polymerization of viscosity.

The fibrous cellulose raw material for obtaining fine fibrous cellulose is not particularly limited, but pulp is preferably used because it is easily available and inexpensive. Examples of the pulp include wood pulp, non-wood pulp, and deinked pulp. Examples of wood pulp include broadleaf kraft pulp (LBKP), coniferous kraft pulp (NBKP), sulfite pulp (SP), dissolved pulp (DP), soda pulp (AP), unbleached kraft pulp (UKP), and oxygen bleached craft. Examples thereof include chemical pulp such as pulp (OKP). Further, semi-chemical pulp such as semi-chemical pulp (SCP) and chemiground wood pulp (CGP), mechanical pulp such as crushed wood pulp (GP) and thermomechanical pulp (TMP, BCTMP) and the like can be mentioned, but are not particularly limited. Examples of the non-wood pulp include cotton pulp such as cotton linter and cotton lint, non-wood pulp such as hemp, straw and bagasse, and cellulose, chitin and chitosan isolated from sea squirts and seaweed, but are not particularly limited. .. Examples of the deinked pulp include deinked pulp made from used paper, but the deinking pulp is not particularly limited. As the pulp of the present embodiment, one of the above types may be used alone, or two or more types may be mixed and used. 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 refining (defibration) is high, the decomposition of cellulose in the pulp is small, and the fine fibers with a large axial ratio are fine. It is preferable in that fibrous cellulose can be obtained. Of these, kraft pulp and sulfite pulp are most preferably selected. High viscosity tends to be obtained by using long-fiber fine fibrous cellulose having a large axial ratio.

The average fiber width of the fine fibrous cellulose is 1000 nm or less when 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. If the average fiber width of the fine fibrous cellulose is less than 2 nm, it is dissolved in water as a cellulose molecule, so that the physical properties (strength, rigidity, dimensional stability) of the fine fibrous cellulose tend to be difficult to develop. .. The fine fibrous cellulose is, for example, a monofibrous cellulose having a fiber width of 1000 nm or less.

The average fiber width of the fine fibrous cellulose is measured by electron microscopy 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 was prepared, and this suspension was cast on a hydrophilized carbon film-coated grid to form a sample for TEM observation. do. If it contains wide fibers, an SEM image of the surface cast on the glass may be observed. Observation with an electron microscope image is performed at a magnification of 1000 times, 5000 times, 10000 times, or 50,000 times depending on the width of the constituent fibers. However, the sample, observation conditions and magnification should be adjusted so as to satisfy the following conditions.

(1) A straight line X is drawn at an arbitrary position in the observation image, and 20 or more fibers intersect the straight line X.
(2) A straight line Y that intersects the straight line perpendicularly is drawn in the same image, and 20 or more fibers intersect the straight line Y.

The width of the fiber intersecting the straight line X and the straight line Y is visually read with respect to the observation image satisfying the above conditions. In this way, at least three sets of images of the non-overlapping surface portions are observed, and the widths of the fibers intersecting the straight lines X and Y are read for each image. In this way, at least 20 fibers × 2 × 3 = 120 fibers are read. The average fiber width of the fine fibrous cellulose (sometimes simply referred to as "fiber width") is the 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 setting the fiber length within the above range, the destruction of the crystal region of the fine fibrous cellulose can be suppressed, and the slurry viscosity of the fine fibrous cellulose can be set within an appropriate range. The fiber length of the fine fibrous cellulose can be obtained by image analysis by TEM, SEM, or AFM.

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

Fine fibrous cellulose has an ionic substituent. The ionic substituent is preferably an anionic group or a cationic group. Examples of the anion 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), and the like. 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 phosphoric acid group is particularly preferable. That is, the fine fibrous cellulose used in the present invention is preferably phosphorylated cellulose.

The fine fibrous cellulose preferably has a phosphoric acid group or a substituent derived from the phosphoric acid group. The phosphoric acid group is a divalent functional group obtained by removing the hydroxyl group from phosphoric acid. Specifically, it is a group represented by _{−PO 3} H _2. Substituents derived from phosphoric acid groups include substituents such as a group obtained by decomposing a phosphoric acid group, a salt of a phosphoric acid group, and a phosphoric acid ester group, and even if it is an ionic substituent, it is a nonionic substituent. It may be a group.

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

In equation (1), a, b, m and n each independently represent an integer (where a = b × m); α ⁿ (an integer of n = 1 or more and n or less) and α'are independent of each other. to O ^-, represents R or oR. R is a hydrogen atom, a saturated-linear hydrocarbon group, a saturated-branched chain hydrocarbon group, a saturated-cyclic hydrocarbon group, an unsaturated-linear hydrocarbon group, an unsaturated-branched chain hydrocarbon group. , Aromatic groups, or inducing groups thereof; β ^{b +} is a monovalent or higher cation consisting of an organic or inorganic substance.

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

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

As an example of the method of allowing the compound A to act on the fiber raw material in the coexistence of the compound B, a method of mixing the powder or the aqueous solution of the compound A and the compound B with the fiber raw material in a dry state or a wet state can be mentioned. Another example is a method of adding a powder or an aqueous solution of Compound A and Compound B to a slurry of a fiber raw material. Of these, since the reaction uniformity is high, a method of adding an aqueous solution of compound A and compound B to a dry fiber raw material, or adding a powder or aqueous solution of compound A and compound B to a wet fiber raw material. The method is preferred. Further, compound A and compound B may be added at the same time or separately. Alternatively, compound A and compound B to be tested in the reaction may be added as an aqueous solution first, and the excess chemical solution may be removed by squeezing. The form of the fiber raw material is preferably cotton-like or thin sheet-like, but is not particularly limited.

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

Of these, from the viewpoints of high efficiency of introduction of phosphoric acid group, easy improvement of defibration efficiency in the defibration step described later, low cost, and easy industrial application, phosphoric acid and phosphoric acid A sodium salt, a potassium salt of phosphoric acid, or an ammonium salt of phosphoric acid is preferable. Sodium dihydrogen phosphate or disodium hydrogen phosphate is more preferred.

Further, the compound A is preferably used as an aqueous solution because the uniformity of the reaction is enhanced and the efficiency of introducing the phosphoric acid group 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 introducing a phosphoric acid group is high, and more preferably 3 or more and pH 7 or less from the viewpoint of suppressing hydrolysis of pulp fibers. The pH of the aqueous solution of the compound A may be adjusted, for example, by using a compound having a phosphoric acid group that exhibits acidity and an alkalinity in combination and changing the amount ratio thereof. The pH of the aqueous solution of the compound A may be adjusted by adding an inorganic alkali or an organic alkali to the compound having a phosphoric acid group and showing acidity.

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 the phosphorus atomic weight, the amount of phosphorus atom added to the fiber raw material (absolute dry mass) is 0.5% by mass or more and 100% by mass. The following is preferable, 1% by mass or more and 50% by mass or less is more preferable, and 2% by mass or more and 30% by mass or less is most preferable. When the amount of phosphorus atom added to the fiber raw material is within the above range, the yield of fine fibrous cellulose can be further improved. By setting the addition amount of phosphorus atoms to the fiber raw material to 100% by mass or less, the effect of improving the yield and the cost can be balanced. On the other hand, the yield can be increased by setting the addition amount of phosphorus atoms to the cellulose fibers to be equal to or higher than the above lower limit value.

Examples of 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 like compound A. Further, since the uniformity of the reaction is enhanced, it is preferable to use an 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. It is more preferably 150% by mass or more, and particularly preferably 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 in particular is known to act as a good reaction catalyst.

It is preferable to perform heat treatment in the phosphoric acid group introduction step. The heat treatment temperature is preferably selected so that the phosphoric acid group can be efficiently introduced while suppressing the 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. Further, a vacuum dryer, an infrared heating device, and a microwave heating device may be used for heating.

During the heat treatment, if the fiber raw material is allowed to stand for a long time while the fiber raw material slurry to which the compound A is added contains water, the water molecules and the dissolved compound A move to the surface of the fiber raw material as it dries. do. Therefore, the concentration of the compound A in the fiber raw material may be uneven, and the introduction of the phosphoric acid group to the fiber surface may not proceed uniformly. In order to suppress the occurrence of uneven concentration of compound A in the fiber raw material due to drying, a very thin sheet-shaped fiber raw material is used, or the fiber raw material and compound A are kneaded or agitated with a kneader or the like and dried by heating or under reduced pressure. You can take the method.

The heating device used for the heat treatment is preferably a device capable of constantly discharging the water retained by the slurry and the water generated by the addition reaction of fibers such as phosphoric acid groups to the hydroxyl groups to the outside of the device system. For example, a ventilation type oven. Etc. are preferable. If the water in the apparatus system is constantly discharged, not only the hydrolysis reaction of the phosphate ester bond, which is the reverse reaction of the phosphate esterification, can be suppressed, but also the acid hydrolysis of the sugar chain in the fiber can be suppressed. , Fine fibers having a high axial ratio can be obtained.

Although the heat treatment time is affected by the heating temperature, it is preferably 1 second or more and 300 minutes or less after the water is substantially removed from the fiber raw material slurry, and more preferably 1 second or more and 1000 seconds or less. It is preferable, and it is more preferably 10 seconds or more and 800 seconds or less. In the present invention, the amount of the phosphoric acid group introduced can be within a preferable range by setting the heating temperature and the heating time within an appropriate range.

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

The amount of the phosphoric acid 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 the fine fibrous cellulose. It is more preferable, and it is particularly preferable that it is 1.00 mmol / g or more. The amount of phosphoric acid group 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. Is more preferable. By setting the amount of the phosphoric acid group introduced within the above range, it is possible to facilitate the miniaturization of the fiber raw material and enhance the stability of the fine fibrous cellulose. Further, by setting the amount of the phosphoric acid group introduced within the above range, good characteristics can be exhibited as a thickener for a battery separator coating liquid. In the present specification, the content of the phosphoric acid group (the amount of the phosphoric acid group introduced) contained in the fine fibrous cellulose is equal to the amount of the strongly acidic group of the phosphoric acid group possessed by the fine fibrous cellulose, as will be described later.

The amount of the phosphoric acid group introduced into the fiber raw material can be measured by the conductivity titration method. Specifically, it is refined by a defibration treatment step, the obtained fine fibrous cellulose-containing slurry is treated with an ion exchange resin, and then the change in electrical conductivity is obtained while adding an aqueous sodium hydroxide solution. The amount introduced can be measured.

In the conductivity titration, the addition of alkali gives the curve shown in FIG. Initially, the electrical conductivity drops sharply (hereinafter referred to as the "first region"). After that, the conductivity begins to increase slightly (hereinafter referred to as "second region"). After that, the increment of conductivity increases (hereinafter referred to as "third region"). The boundary point between the second region and the third region is defined by the point at which the second derivative value of the conductivity, that is, the amount of change in the increment (slope) of the conductivity is maximized. That is, three regions appear. Of these, the amount of alkali required in the first region is equal to the amount of strong acid groups in the slurry used for titration, and the amount of alkali required in the second region is equal to the amount of weakly acidic groups in the slurry used for titration. Become equal. When the phosphoric acid group causes condensation, the weakly acidic group is apparently lost, and the amount of alkali required for the second region is smaller than the amount of alkali required for the first region. On the other hand, since the amount of strongly acidic groups is the same as the amount of phosphorus atoms regardless of the presence or absence of condensation, it is simply referred to as the amount of phosphate groups introduced (or the amount of phosphate groups) or the amount of substituents introduced (or the amount of substituents). When it is said, it means the amount of strongly acidic groups. That is, the amount of alkali (mmol) required in the first region of the curve shown in FIG. 1 is divided by the solid content (g) in the slurry to be titrated to obtain the amount of substituent introduced (mmol / g).

<Carboxyl group introduction process>
When the fine fibrous cellulose has a carboxyl group, the carboxyl group can be introduced into the fine fibrous cellulose by going through the carboxyl group introduction step. In the carboxyl group introduction step, the fiber raw material is treated with an oxidation treatment such as TEMPO oxidation treatment, a compound having a group derived from a carboxylic acid, a derivative thereof, or an acid anhydride thereof or a derivative thereof, thereby forming a carboxyl group into 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, and examples thereof include acid anhydrides of dicarboxylic acid compounds such as maleic anhydride, succinic anhydride, phthalic anhydride, glutaric anhydride, adipic anhydride, and itaconic anhydride. Be done.

The derivative of the compound having a carboxyl group is not particularly limited, and examples thereof include an imide of an acid anhydride of a compound having a carboxyl group and a derivative of an acid anhydride of a compound having a carboxyl group. The imide of the acid anhydride of the compound having a carboxyl group is not particularly limited, and examples thereof include an imide of a dicarboxylic acid compound such as maleimide, succinateimide, and phthalateimide.

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

When the TEMPO oxidation treatment is carried out in the carboxyl group introduction step, it is also preferable to carry out the treatment under the conditions of pH 6 or more and 8 or less. Such a treatment step is also referred to as a neutral TEMPO oxidation treatment. The neutral TEMPO oxidation treatment involves, for example, adding a sodium phosphate buffer (pH = 6.8), pulp, and a reagent such as TEMPO (2,2,6,6-tetramethylpiperidin-1-oxyl) as a catalyst. This can be done by adding sodium hypochlorite as a radical or sacrificial reagent. Further, by coexisting with sodium chlorite, the aldehyde generated in the oxidation process can be efficiently oxidized to the carboxyl group.

The amount of the carboxyl 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 the fine fibrous cellulose. Is more preferable, and 0.90 mmol / g or more is particularly preferable. The amount of the carboxyl group introduced is preferably 3.65 mmol / g or less, more preferably 3.50 mmol / g or less, and even more preferably 3.00 mmol / g or less.

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

In the conductivity titration method, the addition of alkali gives the curve shown in FIG. This curve is divided into a first region after the electrical conductivity decreases until the increment (slope) of the conductivity becomes almost constant, and then a second region where the increment (slope) of the conductivity increases. The boundary point between the first region and the second region is defined by the point at which the second derivative value of the conductivity, that is, the amount of change in the increment (slope) of the conductivity is maximized. The amount of alkali (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 / mmol /). g).

<Alkaline treatment>
When producing fine fibrous cellulose, an alkali treatment may be performed between the ionic substituent introduction step such as the phosphoric acid group introduction step and the carboxyl group introduction step and the defibration treatment step described later. The alkaline treatment method is not particularly limited, and examples thereof include a method of immersing the ionic substituent-introduced fiber in an alkaline solution.
The alkaline compound contained in the alkaline solution is not particularly limited, but may be an inorganic alkaline compound or an organic alkaline compound. The solvent in the alkaline solution may be either water or an organic solvent. The solvent is preferably a polar solvent (water or a polar organic solvent such as alcohol), and more preferably an aqueous solvent containing at least water.
Further, among the alkaline solutions, an aqueous solution of sodium hydroxide or an aqueous solution of potassium hydroxide is particularly preferable because of its high versatility.

The temperature of the alkaline solution in the alkaline treatment step is not particularly limited, but is preferably 5 ° C. or higher and 80 ° C. or lower, and more preferably 10 ° C. or higher and 60 ° C. or lower.
The immersion time in the alkaline solution in the alkaline treatment step is not particularly limited, but is preferably 5 minutes or more and 30 minutes or less, and more preferably 10 minutes or more and 20 minutes or less.
The amount of the alkaline solution used in the alkaline treatment is not particularly limited, but is preferably 100% by mass or more and 100,000% by mass or less, preferably 1000% by mass or more and 10000% by mass or less, based on the absolute dry mass of the ionic substituent-introduced fiber. More preferably.

In order to reduce the amount of the alkaline solution used in the alkaline treatment step, the ionic substituent-introduced fiber may be washed with water or an organic solvent before the alkaline 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 defibration treatment step.

<Acid treatment>
When producing fine fibrous cellulose, acid treatment may be performed between the ionic substituent introduction step and the defibration treatment step described later. Further, the ionic substituent introduction step, the acid treatment, the alkali treatment and the defibration treatment may be carried out in this order.

The method of the acid treatment is not particularly limited, and examples thereof include a method of immersing the ionic substituent-introduced fiber in an acidic liquid containing an acid. The concentration of the acidic liquid used is not particularly limited, but is preferably 10% by mass or less, and more preferably 5% by mass or less. The pH of the acidic liquid used is not particularly limited, but is preferably 0 to 4, and 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, chloric 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, tartaric acid and the like. Of these, hydrochloric acid is preferably used as the acid.

The temperature of the acid solution in the acid treatment step is not particularly limited, but is preferably 5 ° C. or higher and 100 ° C. or lower, and more preferably 20 ° C. or higher and 90 ° C. or lower.
The immersion time in the acid solution in the acid treatment step is not particularly limited, but is preferably 5 minutes or more and 120 minutes or less, and more preferably 10 minutes or more and 60 minutes or less.
The amount of the acid solution used in the acid treatment is not particularly limited, but is preferably 100% by mass or more and 100,000% by mass or less, preferably 1000% by mass or more and 10,000% by mass or less, based on the absolute dry mass of the ionic substituent-introduced fiber. More preferably.

<Fiber processing>
Cellulose fibers are defibrated in the defibration treatment step. In the defibration treatment step, the fibers are usually defibrated using a defibration treatment device to obtain a fine fibrous cellulose-containing slurry, but the treatment device and the treatment method are not particularly limited. In the defibration treatment step, it is preferable to perform the defibration treatment on the cellulose fiber having an ionic substituent from the viewpoint of defibration efficiency.
As the defibration processing apparatus, a high-speed defibrator, a grinder (stone mill type crusher), a high-pressure homogenizer, an ultra-high pressure homogenizer, a high-pressure collision type crusher, a ball mill, a bead mill and the like can be used. Alternatively, as the defibration processing device, use a wet pulverizing device such as a disc type refiner, a conical refiner, a twin-screw kneader, a vibration mill, a homomixer under high-speed rotation, an ultrasonic disperser, or a beater. You can also. The defibration processing apparatus is not limited to the above. Preferred defibration treatment methods include a high-speed defibrator, a high-pressure homogenizer, and an ultra-high-pressure homogenizer, which are less affected by crushed media and less likely to cause contamination.

In the defibration treatment, the fiber raw material is preferably diluted with water and an organic solvent alone or in combination to form a slurry, but is not particularly limited. As the dispersion medium, a polar organic solvent can be used in addition to water. Preferred polar organic solvents include, but are not limited to, alcohols, ketones, ethers, dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAc) and the like. Examples of alcohols include methanol, ethanol, n-propanol, isopropanol, n-butanol, t-butyl alcohol and the like. Examples of the ketones include acetone, methyl ethyl ketone (MEK) and the like. Examples of ethers include diethyl ether and tetrahydrofuran (THF). The dispersion medium may be one kind or two or more kinds. Further, the dispersion medium may contain a solid content other than the fiber raw material, for example, urea having a hydrogen bond property.

In the present invention, the defibration treatment may be performed after the fine fibrous cellulose is concentrated and dried. In this case, the method of concentration and drying is not particularly limited, and examples thereof include a method of adding a concentrating agent to a slurry containing fine fibrous cellulose, a method of using a commonly used dehydrator, press, and dryer. In addition, known methods such as those described in WO2014 / 024876, WO2012 / 107642, and WO2013 / 121086 can be used. Further, the concentrated fine fibrous cellulose may be made into a sheet. The sheet can also be crushed for defibration treatment.

Equipment used for crushing fine fibrous cellulose includes high-speed defibrator, grinder (stone mill type crusher), high-pressure homogenizer, ultra-high pressure homogenizer, high-pressure collision type crusher, ball mill, bead mill, disc type refiner, and conical. Wet pulverizers such as refiners, twin-screw kneaders, vibration mills, homomixers under high-speed rotation, ultrasonic dispersers, beaters, etc. can also be used, but are not particularly limited. Further, the treatment conditions are not particularly limited as long as a preferable degree of polymerization can be obtained.

<Fine particles>
Examples of the fine particles include organic fine particles and inorganic fine particles. Among them, 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. Resins polymerized by combining one or more vinyl cyanide compounds such as (meth) acrylic acid esters, (meth) acrylonitrile, vinyl halide compounds such as vinyl chloride and vinylidene chloride, and vinyl monomers such as butadiene. Can be 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 , and so on. CeO ₂ , MgO, NiO, CaO, ZnO, Y ₂ O ₃ , Pb (Zr, Ti) O ₃ (PZT), Pb _1-x La _x Zr _1-y T _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 T _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), CaF 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 S _{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 can be mentioned. Covalently bonded crystalline fine particles such as silicone and diamond; clay fine particles such as talc and montmorillonite; mineral resource-derived substances such as boehmite (AlOOH), zeolite, apatite, kaolin, mulite, spinel, olivine, sericite and bentonite or theirs. Artificial products; carbonaceous fine particles such as carbon black and graphite; and the like can also be used. Among them, at least one kind of inorganic fine particles selected from _{BaTiO 3} , Li ₃ PO _{4 , alumina, silica and boehmite is preferable, and at least one kind selected from BaTiO 3} , alumina and silica is particularly preferable. ..
Further, by coating the surface of the fine particles with a material having an electrically insulating property (for example, a material constituting the insulating fine particles), the fine particles having an electrically insulating property can be obtained.

The form of the fine particles may be any of a spherical shape, a polyhedral shape, a plate shape, and the like. The primary average particle size of the fine particles is preferably 0.01 μm or more, and preferably 5 μm or less. When the fine particles are not spherical, it is preferable that the value obtained by calculating the primary average particle diameter on the assumption that the fine particles are spherical in the same volume is within the above range.

The content of the fine particles is preferably 5% by mass or more, more preferably 10% by mass or more, based on the total mass of the fiber-containing layer. The content of the fine particles is preferably 99% by mass or less, and more preferably 96% by mass or less. By setting the content of the fine particles within the above range, the heat resistance of the battery separator can be increased more effectively.

<Binder resin>
The fiber-containing layer contains a binder resin. As the binder resin, it is preferable to use a polymer having ionic conductivity. In the present invention, the binder resin refers to a resin capable of exerting a binding action with fine fibrous cellulose. Examples of the resin capable of exerting a binding action include a heat-sealing synthetic polymer. For example, carboxymethyl cellulose is not included in the binder resin because it does not exert a binding action with fine fibrous cellulose.

The binder resin is preferably at least one selected from an acrylic resin, a polyolefin resin, a urethane resin, and a silicone resin.

Examples of the acrylic resin include a copolymer resin of an olefin component such as ethylene, propylene, butylene, and isobutylene and (meth) acrylic acid or (meth) acrylic acid ester;
The following monomeric units (meth) acrylic acid monomer unit and copolymerizable with (meth) acrylic acid (methyl (meth) acrylic acid, ethyl (meth) acrylic acid, propyl (meth) acrylic acid, (meth) ) Acrylic acid containing butyl acrylate, isobutyl (meth) acrylate, pentyl (meth) acrylate, hexyl (meth) acrylate, -2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, etc.) Acrylic acid;
Modified alkyl acrylate resin such as the above alkyl acrylate resin modified with epoxy resin, silicone resin, styrene or a derivative thereof;
Resins made of (meth) acrylonitrile, acrylic acid ester, hydroxyalkyl acrylic acid ester, etc.; and polyacrylic acid and the like can be mentioned.
Examples of the polyolefin resin include polypropylene, polyethylene, polyisobutylene, polystyrene and the like.
Examples of the urethane-based resin include polyurethane, epoxy-modified polyurethane resin, and silicone-modified polyurethane resin.
Examples of the silicone resin include methyl silicone resin, methylphenyl silicone resin, alkyd-modified silicone resin, epoxy-modified silicone resin, acrylic-modified silicone resin, polyester-modified silicone resin and the like.

Further, as the binder resin, fluorine-based rubber, styrene-butadiene rubber (SBR), epoxy resin, polyvinyl chloride-based resin, vinyl acetate-based resin, phenol-based resin, alkyd-based resin, aminoalkyd-based resin, urea-based resin, vinyl. A based resin, a polyester resin, a silicon resin, a silazane resin, a melamine resin and the like may be used.

The content of the binder resin in the fiber-containing layer is preferably 0.1 part by mass or more and 40 parts by mass or less with respect to 100 parts by mass of the fine particles contained in the fiber-containing layer. The content of the binder resin is more preferably 0.2 parts by mass or more, and further preferably 0.5 parts by mass or more. The content of the binder resin is more preferably 30 parts by mass or less, further preferably 20 parts by mass or less, and 15 parts by mass or less with respect to 100 parts by mass of the fine particles contained in the fiber-containing layer. It is particularly preferable to have.

The content of the binder resin in the fiber-containing layer is preferably 1% by mass or more with respect to the total mass of the fiber-containing layer. The binder resin contained in the fiber-containing layer is identified and quantified as follows, for example. The binder resin contained in the fiber-containing layer is identified by thermal decomposition GC-MS or IR spectrophotometer, and then by thermogravimetric analysis (TG), it is contained from the weight loss due to thermal decomposition of the corresponding binder resin. Measure the binder resin and content.

The total content of the fine fibrous cellulose and the binder resin is preferably 0.1 part by mass or more and 40 parts by mass or less with respect to 100 parts by mass of the fine particles contained in the fiber-containing layer. The total content of the fine fibrous cellulose and the binder resin is more preferably 0.2 parts by mass or more, and further preferably 0.5 parts by mass or more. The total content of the fine fibrous cellulose and the binder resin is more preferably 30 parts by mass or less, further preferably 20 parts by mass or less, further preferably 10 parts by mass or less, and 5 parts by mass. It is particularly preferable that the amount is less than or equal to a portion. By setting the total content of the fine fibrous cellulose and the binder resin within the above range, the mechanical strength of the fiber-containing layer can be further increased.

The mass ratio of the content of the fine fibrous cellulose to the content of the binder resin is preferably 1:99 to 99: 1, and more preferably 10:90 to 90:10. By setting the mass ratio of the content of the fine fibrous cellulose to the content of the binder resin within the above range, the mechanical strength of the fiber-containing layer can be further increased.

<Other ingredients>
The fiber-containing layer can be added with an internal additive such as an internal sizing agent, an anionic, nonionic, cationic or amphoteric yield improver, and a drainage improver, if necessary. Specific examples of the internal sizing agent include alkyl ketene dimer-based, alkenyl succinic anhydride-based, styrene-acrylic, higher fatty acid-based, petroleum resin-based sizing agent, rosin-based sizing agent, polyvinyl alcohol, and the like. Specific examples of the yield improver and the drainage improver include polyvalent metal compounds such as aluminum (specifically, aluminum sulfate band, aluminum chloride, sodium aluminate, basic aluminum compounds, etc.), and various starches. Kind, flocculant, polyethyleneimine, polyamine, polyethylene oxide and the like can be exemplified. Further, additive aids such as dyes, pH adjusters, slime control agents, antifoaming agents, and viscous agents can be appropriately used depending on the intended use. The above-mentioned internal supplement may be used alone or in combination of two or more.

The fiber-containing layer may contain a flocculant, and the flocculant can increase the efficiency of supporting fine particles in the fiber-containing layer. Since the flocculant can agglomerate the fine fibrous cellulose to some extent, it is possible to easily support the fine particles in the fiber-containing layer. Further, the yield improver or the drainage improver suppresses the movement of the fine fibrous cellulose to the base material, and also functions to prevent clogging of the base material described later.

The fiber-containing layer may contain organic ions or the like in addition to the above components. Examples of the organic ion include tetraalkylammonium ion and tetraalkylphosphonium ion. Examples of the tetraalkylammonium ion include tetramethylammonium ion, tetraethylammonium ion, tetrapropylammonium ion, tetrabutylammonium ion, tetrapentylammonium ion, tetrahexylammonium ion, tetraheptylammonium ion, tributylmethylammonium ion, and lauryltrimethyl. Examples thereof include ammonium ion, cetyltrimethylammonium ion, stearyltrimethylammonium ion, octyldimethylethylammonium ion, lauryldimethylethylammonium ion, didecyldimethylammonium ion, lauryldimethylbenzylammonium ion and tributylbenzylammonium ion. Examples of the tetraalkylphosphonium ion include tetramethylphosphonium ion, tetraethylphosphonium ion, tetrapropylphosphonium ion, tetrabutylphosphonium ion, and lauryltrimethylphosphonium ion. Further, as tetrapropyl onium ion and tetrabutyl onium ion, tetra n-propyl onium ion, tetra n-butyl onium ion and the like can be mentioned, respectively. The content of the organic ion is the total mass of the fine particles in the fiber-containing layer. On the other hand, it is preferably 20% by mass or less.

(Base material)
The battery separator includes a substrate. The base material is stable with respect to the electrolytic solution and is preferably a porous base material.

Specific constituent materials of the base material include, for example, cellulose, a cellulose modified product (carboxymethyl cellulose, etc.), polyolefin (polypropylene (PP), polyethylene (PE), and a copolymerized polyolefin having an ethylene-derived structural unit 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; Examples include inorganic materials (inorganic oxides).
Among them, the constituent material of the base material is preferably a polyolefin resin, and more preferably polypropylene or polyethylene. The base material is particularly preferably a non-woven 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 papermaking polyethylene fibers by a wet papermaking method. In the non-woven fabric, the polyethylene fibers are preferably oriented at random.

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

The substrate may have an adhesive. When the base material has an adhesive, it is preferable to contain an acrylic resin as the adhesive. Examples of the acrylic resin include ethylene- (meth) acrylic acid-based resin and propylene- (meth) acrylic acid-based resin. The adhesive is preferably sprayed onto the surface of the substrate and preferably present in the surface area of the substrate. Such an adhesive serves to enhance the adhesiveness between the base material and the fiber-containing layer.
Further, if necessary, other resins can be used in combination. Resins that can be used together include vinyl chloride resin, (meth) acrylic acid ester resin, styrene / acrylic acid ester copolymer resin, vinyl acetate resin, vinyl acetate / (meth) acrylic acid ester copolymer resin, urethane resin, etc. 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 base material ^{is preferably 10 g / m 2} or more, and more preferably 20 g / m ² or more. The basis weight of the base material ^{is preferably 100 g / m 2} or less, and ^{more preferably 80 g / m 2} or less.

The density of the base material ^{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 base material ^{is preferably 3.0 g / cm 3} or less, more preferably 2.0 g / cm ³ or less, and even more preferably 1.0 g / cm ³ or less.

<Manufacturing method of battery separator>
The process for manufacturing the battery separator preferably includes a step of applying the battery separator coating liquid to at least one surface of the base material and a step of drying the base material coated with the battery separator coating liquid. When applying the battery separator coating liquid to the surface of the base material, 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 liquid is preferably applied to one side of the base material.

The coating amount (fiber-containing layer basis weight) of the battery separator coating solution ^{is preferably 1 g / m 2} or more, and more preferably 1.5 g / m ² or more. 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.

(Battery separator coating liquid)
The present invention also relates to a battery separator coating solution containing fibrous cellulose having a fiber width of 1000 nm or less and having an ionic functional group, fine particles, and a binder resin.

Since the battery separator coating liquid of the present invention has the above-mentioned structure, it has both excellent fine particle dispersibility and coatability. Therefore, in the fiber-containing layer formed from the battery separator coating liquid of the present invention, the fine particles are uniformly dispersed, and coating unevenness does not occur in the battery separator. Further, in the fiber-containing layer formed from the battery separator coating liquid of the present invention, uniform pores are formed over the entire area. Further, the fiber-containing layer formed from the battery separator coating liquid of the present invention is excellent in mechanical strength.

The fine fibrous cellulose functions as a thickener for the battery separator coating liquid in the battery separator coating liquid, and functions to enhance the dispersibility of fine particles and the like. Since the fine fibrous cellulose contained in the fiber-containing layer may become impurities after coating, it is preferable that the amount added is small. The present invention is also characterized in that the amount of fine fibrous cellulose added can be reduced by using it as a thickener for a battery separator coating liquid. In the present invention, the dispersibility of the fine particles can be improved even when the amount of the thickener for the battery separator coating liquid added is small. Further, in the present invention, the ease of coating can be improved by suppressing the amount of the thickener for the battery separator coating liquid added.

Further, in the present invention, by using fine fibrous cellulose as a thickener for a battery separator coating liquid, it is possible to suppress the microporous of the base material from being blocked. Normally, there is a trade-off relationship between suppressing the microporous blockage of the base material and preventing the occurrence of strike-through. However, in the present invention, fine fibrous cellulose is used as a thickener for a battery separator coating liquid. , Both suppression of microporous blockage of the substrate and prevention of strike-through are achieved.

The fine fibrous cellulose contained in the battery separator coating liquid is the above-mentioned fine fibrous cellulose. The fine fibrous cellulose is preferably phosphorylated cellulose.

The average degree of polymerization of the fine fibrous cellulose is preferably 100 or more, more preferably 150 or more, and even more preferably 200 or more. The average degree of polymerization of the fine fibrous cellulose is preferably 2000 or less, more preferably 1500 or less, further preferably 1200 or less, further preferably 1000 or less, and 750 or less. It is particularly preferable to have. The average degree of polymerization of the fine fibrous cellulose is preferably less than 400. By setting the average degree of polymerization of the fine fibrous cellulose to less than 400, it is possible to suppress the occurrence of coating unevenness when the fiber-containing layer is made into a thin film (for example, the basis weight of the fiber-containing layer is 2.5 g / m ^2). be able to.

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

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, weigh 20 ± 5 g of the battery separator coating solution into a 50 ml capacity aluminum cup. In the same manner, prepare a plurality of aluminum cups from which the battery separator coating liquid has been weighed. The battery separator coating liquid is dried by heating at 105 ° C. for 16 hours in a blower constant temperature dryer. A 0.5 mol / L copper ethylenediamine solution is added to 1 g of the dried battery separator coating solution at a ratio of 100 ml, and the mixture is stirred to dissolve the fine fibrous cellulose. The obtained solution is filtered to remove the residue, and then added dropwise to 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 then dried.

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

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

The content of the fine fibrous cellulose is preferably 0.01 parts by mass or more and 40 parts by mass or less with respect to 100 parts by mass of the fine particles contained in the battery separator coating liquid. The content of the fine fibrous cellulose is more preferably 0.05 parts by mass or more, and further preferably 0.1 parts by mass or more. The content of the fine fibrous cellulose is more preferably 30 parts by mass or less, further preferably 20 parts by mass or less, and 10 parts by mass with respect to 100 parts by mass of the fine particles contained in the fiber-containing layer. The following is particularly preferable.

The content of the binder resin is preferably 0.1 part by mass or more and 40 parts by mass or less with respect to 100 parts by mass of the fine particles contained in the battery separator coating liquid. The content of the binder resin is more preferably 0.2 parts by mass or more, and further preferably 0.5 parts by mass or more. The content of the binder resin is more preferably 30 parts by mass or less, still more preferably 20 parts by mass or less, and 15 parts by mass with respect to 100 parts by mass of the fine particles contained in the battery separator coating liquid. The following is particularly preferable.

The total content of the fine fibrous cellulose and the binder resin is preferably 0.1 part by mass or more and 40 parts by mass or less with respect to 100 parts by mass of the fine particles contained in the battery separator coating liquid. The total content of the fine fibrous cellulose and the binder resin is more preferably 0.2 parts by mass or more, and further preferably 0.5 parts by mass or more. The total content of the fine fibrous cellulose and the binder resin is more preferably 30 parts by mass or less, further preferably 20 parts by mass or less, further preferably 10 parts by mass or less, and 5 parts by mass. It is particularly preferable that the amount is less than or equal to a portion.

The mass ratio of the content of the fine fibrous cellulose contained in the battery separator coating liquid to the content of the binder resin is preferably 1:99 to 99: 1, and preferably 10:90 to 90:10. More preferred.

The battery separator coating liquid contains fine particles. As the fine particles, the above-mentioned fine particles can be listed, and preferable specific examples are as described above.

The battery separator coating liquid contains a binder resin. As the binder resin, the above-mentioned flocculants can be listed.

<Dispersion medium>
The battery separator coating solution preferably contains a dispersion medium. Examples of the dispersion medium include water, an organic solvent, and a mixture 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 portion of the battery separator coating liquid excluding the solid content remaining during drying when the fiber-containing layer is formed.

The content of the dispersion medium is preferably 10% by mass or more, more preferably 20% by mass or more, still more preferably 30% by mass or more, based on the total mass of the battery separator coating liquid. .. The content of the dispersion medium is preferably 90% by mass or less, and more preferably 80% by mass or less.

(Use)
The present invention may relate to a battery provided with the battery separator described above. The battery of the present invention is preferably a lithium battery (primary battery and secondary battery) using an organic electrolytic solution or a supercapacitor.

As for the form of the lithium secondary battery, a tubular shape (square tubular shape, cylindrical shape, etc.) using a steel can or an aluminum can as an outer can, or a soft package type with a metal-deposited laminated film as an outer body. 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. The positive electrode and the negative electrode each contain an active material that undergoes an oxidation / reduction reaction that sends and receives electrons. The positive electrode and the negative electrode can be used in the form of a group of electrodes having a laminated structure laminated via a battery separator, or a group of electrodes having a wound structure in which the electrodes are further 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 that can occlude and release ^{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 that can occlude and release ^{Li + ions.}

The positive electrode and the negative electrode can be used in the form of an electrode group having a laminated structure laminated via the battery separator of the present invention, or an electrode group having a wound structure in which the positive electrode and the negative electrode are further 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 side reactions such as decomposition in the 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 the voltage range used as a battery.

Lithium-ion batteries have been known in the past, in addition to power applications for mobile devices such as mobile phones and notebook personal computers, electric vehicles, hybrid vehicles, electric bikes, electrically assisted bicycles, electric tools, and shavers. It is used for various purposes.

The features of the present invention will be described in more detail with reference to Examples and Comparative Examples. The materials, amounts used, ratios, treatment contents, treatment procedures, etc. shown in the following examples can be appropriately changed as long as they do not deviate from the gist of the present invention. Therefore, the scope of the present invention should not be construed as limited by the specific examples shown below.

<Manufacturing of fine fibrous cellulose 1 (for examples)>
100 parts by mass of dry coniferous kraft pulp is impregnated with a mixed aqueous solution of ammonium dihydrogen phosphate and urea, and squeezed so that ammonium dihydrogen phosphate is 49 parts by mass and urea is 130 parts by mass, and the pulp is impregnated with a chemical solution. Got The obtained chemical-impregnated pulp was dried in a dryer at 105 ° C. to evaporate the water content and pre-dried. Then, it was heated for 10 minutes in a blower dryer set at 140 ° C., and a phosphoric acid group was introduced into the cellulose in the pulp to obtain phosphorylated pulp.

100 g of the obtained phosphorylated pulp was taken out by the pulp mass, 10 L of ion-exchanged water was poured, the mixture was stirred and uniformly dispersed, and then filtered and dehydrated to obtain a dehydrated sheet. The process was repeated twice. Next, the obtained dehydrated sheet was diluted with 10 L of ion-exchanged water, and a 1N aqueous sodium hydroxide solution was added little by little with stirring to obtain a pulp slurry having a pH of 12 or more and 13 or less. Then, this pulp slurry was dehydrated to obtain a dehydrated sheet, and then 10 L of ion-exchanged water was added. After stirring and uniformly dispersing, the steps of filtering and dehydrating to obtain a dehydrated sheet were repeated twice.

The dehydrated sheet 1 of phosphorylated cellulose was obtained twice by repeating the steps of introducing a phosphoric acid group and filtering and dehydrating the obtained dehydrated sheet in the same manner as above. The infrared absorption spectrum of the obtained dehydrated sheet 1 was measured by FT-IR. As a result, ^{absorption based on the phosphate group was observed at 1230 cm -1} or more and 1290 cm ^-1 or less, and the addition of the phosphate group was confirmed.

Ion-exchanged 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 treated 15 times at a pressure of 200 MPa with a wet atomizer (Ultimizer manufactured by Sugino Machine Limited) to obtain fine fibrous cellulose 1. By X-ray diffraction, it was confirmed that the fine fibrous cellulose 1 maintained the cellulose type I crystal.

<Manufacturing of fine fibrous cellulose 2 (for comparative example)>
100 parts by mass of dry mass of softwood kraft pulp is beaten with a single disc refiner (KRK pressure refiner manufactured by Kumagai Riki Kogyo Co., Ltd.) until the irregular freeness reaches 100 ml, and a pulp dispersion having a solid content concentration of 2% by mass is prepared. Obtained. This is diluted with ion-exchanged water so that the solid content concentration becomes 0.2% by mass, and treated 15 times at a pressure of 200 MPa with a wet atomizing device in the same manner as in the production of fine fibrous cellulose 1, and is in the form of fine fibers. Cellulose 2 was obtained.

<Manufacturing of dispersed pulp (for comparative examples)>
100 parts by mass of dry mass of softwood kraft pulp is beaten with a single disc refiner (KRK pressure refiner manufactured by Kumagai Riki Kogyo Co., Ltd.) until the freeness (measurement conforms to JIS P 8121) reaches 400 ml, and the solid content concentration is increased. A 2% by mass pulp dispersion was obtained.

(Physical characteristics of cellulose fiber)
<Measurement of fiber width>
The fiber widths of the fine fibrous celluloses 1 and 2 were measured by the following method.
The supernatant of the fine fibrous cellulose treated with the wet atomization device 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 hydrophilized. It was added dropwise to 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.). Thirty points were randomly extracted from the observed fibers, and the average fiber diameter was calculated. The average fiber diameter of the fine fibrous cellulose 1 was 4 nm, and the fiber diameter of the fine fibrous cellulose 2 was 75 nm.
Regarding the fiber diameter of the dispersed pulp, the pulp dispersion was dropped on a slide glass, dried at 110 ° C., and then observed with a digital microscope (KH2700, manufactured by Hirox Co., Ltd.). Thirty points were randomly extracted from the observed fibers, and the average fiber diameter was calculated. The average fiber diameter was 16000 nm.

<Measurement of Substituents of Fine Fibrous Cellulose 1>
The amount of the substituent introduced is the amount of the phosphoric acid group introduced into the fiber raw material. The amount of the substituent introduced was measured by diluting the target fine fibrous cellulose with ion-exchanged water so that the content was 0.2% by mass, treating with an ion-exchange resin, and titrating with an alkali. In the treatment with an ion exchange resin, a strongly acidic ion exchange resin (Amberjet 1024; Organo Corporation, conditioned) with a volume of 1/10 is added to a slurry containing 0.2 mass% fibrous cellulose and shaken for 1 hour. Was done. Then, it was poured onto a mesh having a mesh size of 90 μm to separate the resin and the slurry. In the titration using 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 amount of alkali (mmol) required in the first region of the curve shown in FIG. 1 was divided by the solid content (g) in the slurry to be titrated to obtain the amount of substituent introduced (mmol / g). The amount of substituent was 1.60 mmol / g.

<Measurement of degree of polymerization>
The evaluation of the average degree of polymerization of the cellulose molecules constituting the fine fibrous cellulose and the dispersed pulp was carried out with reference to the following papers.
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 a suspension obtained by diluting the target fine fibrous cellulose and dispersed pulp with ion-exchanged water so that the content is 2 ± 0.3% by mass is divided into a centrifuge tube and allowed to stand in a freezer overnight. And frozen. Further, it was dried in a freeze dryer for 5 days or more, and then heated in a constant temperature dryer set at 105 ° C. for 3 hours or more and 4 hours or less to obtain fine fibrous cellulose and dispersed pulp in an absolutely dry state.
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 placed in a Canon Fenceke viscometer, left for 5 minutes, and then the drop time at 25 ° C. was measured to determine the solvent drop time.

Next, in order to measure the viscosity of the fine fibrous cellulose and the dispersed pulp, an empty 50 ml capacity screw tube is used so that the amount of the fine fibrous cellulose or the dispersed pulp in an absolutely dry state is 0.14 g or more and 0.16 g or less, respectively. Was weighed and 15 ml of pure water was added. Further, 15 ml of 1 mol / L copper ethylenediamine was added, and the mixture was stirred with a rotating and revolving supermixer at 1000 rpm for 10 minutes to prepare a 0.5 mol / L copper ethylenediamine solution. In the same manner as in the reference measurement, 10 ml of the prepared 0.5 mol / L copper ethylenediamine solution was placed in a Canon Fenceke viscometer, left for 5 minutes, and then the drop time at 25 ° C. was measured. The fall time was measured three times, and the average value was taken as the fall time of the fine fibrous cellulose solution or the dispersed pulp solution.

The degree of polymerization was calculated using the following formula from the mass of the absolutely dry fine fibrous cellulose or dispersed pulp used in the measurement, the solvent drop time, and the fall time of the fine fibrous cellulose solution or the dispersed pulp solution. The average degree of polymerization below is the average value of the values measured three times.
Absolutely dry fine fibrous cellulose mass used for measurement: a (g) (where a is 0.14 or more and 0.16 or less)
Cellulose concentration in solution: c = a / 30 (g / mL)
Solvent drop time: t ₀ (sec)
Fall time of fine fibrous cellulose solution or dispersed pulp solution: t (sec)
Relative viscosity of solution: η _rel = t / t ₀
Specific viscosity of solution: η _sp = η _rel- 1
Intrinsic viscosity: [η] = η _{sp /} c (1 + 0.28 _{η sp} )
Degree of polymerization: DP = [η] /0.57
The average degree of polymerization of the fine fibrous cellulose 1 was 370, the average degree of polymerization of the fine fibrous cellulose 2 was 850, and the average degree of polymerization of the dispersed pulp was 2200.

<Example 1>
(Preparation of barium titanate dispersion)
Barium titanate powder (manufactured by KCM Corporation, BT-HP9DX, particle size: 0.4 μm) 100 parts by mass, suspension of fine fibrous cellulose 1 (solid content concentration 2% by mass) 5 parts by mass, and water 120 parts by mass The mixture of parts was added to T.I. K. The mixture was stirred with a homodisper (manufactured by Tokushu Kagaku Kogyo Co., Ltd.) at 3000 rpm for 1 hour to obtain a barium titanate dispersion (1).

(Preparation of battery separator coating liquid)
Barium titanate dispersion (1) 225 parts by mass, Vinibran 2685 (acrylic emulsion, manufactured by Nissin Chemical Industry Co., Ltd., solid content concentration 30% by mass) 14.6 parts by mass, and 20 parts by mass of water are mixed and used for batteries. A separator coating solution was obtained.

<Example 2>
(Preparation of barium titanate dispersion (2))
In the preparation of the barium titanate dispersion of Example 1, the amount of the suspension (solid content concentration: 2% by mass) of the fine fibrous cellulose 1 was changed from 5 parts by mass to 25 parts by mass. A barium titanate dispersion (2) was prepared in the same manner.

(Preparation of battery separator coating liquid)
In the preparation of the battery separator coating solution of Example 1, 245 parts by mass of barium titanate dispersion (2) was used instead of 225 parts by mass of barium titanate dispersion (1), and the amount of Vinibran 2685 was 14.6 mass. A battery separator coating solution was prepared in the same manner as in Example 1 except that the portion was changed from 1 part to 13.3 parts by mass.

<Example 3>
(Preparation of barium titanate dispersion (3))
In the preparation of the barium titanate dispersion of Example 1, the amount of the suspension of fine fibrous cellulose 1 (solid content concentration: 2% by mass) was changed from 5 parts by mass to 100 parts by mass. A barium titanate dispersion (3) was prepared in the same manner.

(Preparation of battery separator coating liquid)
In the preparation of the battery separator coating solution of Example 1, 320 parts by mass of barium titanate dispersion (3) was used instead of 225 parts by mass of barium titanate dispersion (1), and the amount of Vinibran 2685 was 14.6 mass. A battery separator coating solution was prepared in the same manner as in Example 1 except that the portion was changed to 8.3 parts by mass.

<Example 4>
(Preparation of battery separator coating liquid)
In the preparation of the battery separator coating solution of Example 2, the battery separator coating solution was prepared in the same manner as in Example 2 except that the amount of Vinibran 2685 was changed from 13.3 parts by mass to 33 parts by mass.

<Example 5>
(Preparation of battery separator coating liquid)
In the preparation of the battery separator coating solution of Example 2, Hitec P5060P (polypropylene wax emulsion, manufactured by Toho Chemical Industry Co., Ltd., solid content concentration 40% by mass) was used instead of Vinibran 2685, and the addition amount was 10 parts by mass. Prepared a battery separator coating solution in the same manner as in Example 2.

<Example 6>
(Preparation of battery separator coating liquid)
In the preparation of the battery separator coating solution of Example 2, Charine R-170BX (silicone / acrylic emulsion, manufactured by Nisshin Kagaku Kogyo Co., Ltd., solid content concentration 45% by mass) was used instead of Vinibran 2685, and the addition amount was 8. A battery separator coating solution was prepared in the same manner as in Example 2 except that the volume was 0.8 parts by mass.

<Example 7>
(Preparation of battery separator coating liquid)
In the preparation of the battery separator coating solution of Example 2, Superflex 150 (water-based urethane resin, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., solid content concentration 30% by mass) was used instead of Viniblanc 2685, and the addition amount was 13.3% by mass. A battery separator coating solution was prepared in the same manner as in Example 2 except for the portion.

<Comparative example 1>
(Preparation of battery separator coating liquid)
Fine fibrous cellulose 1 was not used in the preparation of the barium titanate dispersion of Example 1, and the amount of Vinibran 2685 was changed from 14.6 parts by mass to 15 parts by mass in the preparation of the battery separator coating solution of Example 1. A battery separator coating solution was prepared in the same manner as in Example 1.

<Comparative example 2>
(Preparation of battery separator coating liquid)
A battery separator coating solution was prepared in the same manner as in Example 2 except that 250 parts by mass of fine fibrous cellulose 2 was used instead of fine fibrous cellulose 1 in the preparation of the barium titanate dispersion in Example 2.

<Comparative example 3>
(Preparation of battery separator coating liquid)
A battery separator coating solution was prepared in the same manner as in Example 2 except that the pulp dispersion was used instead of the fine fibrous cellulose 1 in the preparation of the barium titanate dispersion in Example 2.

(Evaluation of battery separator coating liquid)
<Particle dispersibility>
After allowing the battery separator coating solution to stand at 23 ° C. for one day, the presence or absence of particle sedimentation was confirmed and evaluated according to the following criteria.
◯: There is no sedimentation of fine particles, and there is no supernatant layer.
X: There is sedimentation of fine particles, and a supernatant layer is present.

(Preparation of base material)
Polyethylene fibers (fiber length: 5 mm, fiber strength: 28 cN / dtex, elastic modulus: 900 cN / dtex) are dispersed in water so as to have a modulus of 0.2% by mass, and a web of randomly oriented webs is formed by a wet papermaking method. bottom. Ethylene- (meth) acrylic acid resin (manufactured by Toho Chemical Co., Ltd., Hi-Tech S-3148, ethylene / acrylic acid = 80 parts by mass / 20 parts by mass, having a urethane group at the resin end) is applied to this web as an adhesive to polyethylene fibers. After spraying so as to have a ratio of 10% by mass, a non-woven fabric of ^{30 g / m 2 was obtained by drying with a hot air dryer set at 110 ° C.} This non-woven fabric was subjected to calendar treatment to obtain a non-woven fabric having a ^{density of 0.64 g / cm 3.} This non-woven fabric was used as a non-woven fabric base material for coating the battery separator coating liquid.

(Making a battery separator)
A battery separator was prepared by applying the battery separator coating liquids obtained in Examples and Comparative Examples to the above-mentioned non-woven fabric base material so that the fiber-containing layer basis weight after drying was 5 g / m ^2.

(Evaluation of battery separator)
<Paintability>
A separator coating liquid for batteries was applied to the non-woven fabric base material so that the fiber-containing layer basis weight after drying was 5 g / m ^2, and the coatability was evaluated according to the following criteria.
◯: There is no unevenness on the entire surface when observing the appearance after coating.
Δ: There is some unevenness in the appearance observation after coating.
X: Unevenness is seen on the entire surface when observing the appearance after coating. Or the coating itself cannot be done.

<Surface analysis of battery separator>
The surface of the prepared battery separator was observed using a scanning electron microscope (SEM) and evaluated according to the following criteria.
◯: Fine particles are uniformly dispersed, and uniform pores are formed over all of the fiber-containing layers.
Δ: The dispersibility of the fine particles is good, but some pores are blocked by the polymer binder.
X: Fine particles are aggregated and uniform pores are not formed.

(Manufacturing of lithium secondary ion battery)
(Preparation of positive electrode)
_{A disperser containing 91 parts by mass of LiCoO 2} powder as a positive electrode active material, 4.0 parts by mass of polyvinylidene fluoride resin as a binder, 5.0 parts by mass of graphite powder as a conductive agent, and N-methylpyrrolidone as a dispersant. Prepare a slurry for coating the positive electrode active material mixture by stirring and mixing, apply it to a current collector made of aluminum foil, and dry it in an oven to remove the dispersant to apply the positive electrode active material mixture. A film was formed. This was pressed to a general density as an electrode and cut to a predetermined size to obtain a positive electrode plate.

(Preparation of negative electrode)
90 parts by mass of artificial graphite powder, 10 parts by mass of polyvinylidene fluoride resin as a binder, and N-methylpyrrolidone as a dispersant are mixed by stirring with a disperser to coat a negative electrode active material mixture. The slurry for use was prepared, applied to a current collector made of copper foil, and dried in an oven to remove the dispersant to form a negative electrode active material mixture coating film. This was pressed to a general density as an electrode and cut to a predetermined size to obtain a negative electrode plate.

(Battery manufacturing)
A positive electrode, a negative electrode, and a battery separator were assembled by a stack / folding method to prepare a battery. The electrolytic solution was injected into the battery assembled in this way. The electrolytic solution is prepared by dissolving LiPF6 in a solvent in which ethylene carbonate, ethylmethyl carbonate and diethyl carbonate are mixed in a volume ratio of 1: 1: 1 so as to have a concentration of 1.1 mol / L, and FEC (fluoroethylene) is dissolved therein. Soluble carbonate) to 1.0% by mass, VC (vinylene carbonate) to 1.0% by mass, and 2-propynyl2- (diethoxyphosphoryl) acetate to 1.0% by mass. It is an added solution.

(Battery safety evaluation)
The produced lithium secondary ion battery was subjected to a local crush test to evaluate its safety.
The local crush test is a test in which a rod-shaped jig with a diameter of 2 cm is pressed against the battery surface at a constant speed to forcibly generate an internal short circuit in which the positive electrode and the negative electrode come into contact with each other, and the presence or absence of a battery explosion is examined. ..
◯: No explosion occurred.
×: There is an explosion.

As can be seen from Table 1, the battery separator formed from the battery separator coating liquid obtained in the examples has compressibility (mechanical strength) and is highly safe. Further, the battery separator coating liquid obtained in the examples had good coatability, and a fiber-containing layer having no coating unevenness was formed from the battery separator coating liquid. Further, in the battery separator formed from the battery separator coating solution obtained in the examples, the inorganic fine particles had good dispersibility and uniform pores were formed.

Claims (10)

It has a base material and a fiber-containing layer,
The fiber-containing layer contains fibrous cellulose having a fiber width of 1000 nm or less and having an ionic substituent, fine particles, and a binder resin.
The average degree of polymerization of the fibrous cellulose Ri der 750 or less,
A battery separator in which the fibrous cellulose is phosphorylated cellulose. The battery separator according to claim 1, wherein the total content of the fibrous cellulose and the binder resin is 0.1 part by mass or more and 5.0 parts by mass or less with respect to 100 parts by mass of the fine particles. The battery separator according to claim 1 or 2 , wherein the mass ratio of the content of the fibrous cellulose to the content of the binder resin is 1:99 to 99: 1. The battery separator according to any one of claims 1 to 3 , wherein the binder resin contains at least one selected from an acrylic resin, a polyolefin resin, a urethane resin, and a silicone resin. The battery separator according to any one of claims 1 to 4 , wherein the base material contains a polyolefin-based resin. A battery comprising the battery separator according to any one of claims 1 to 5. It contains fibrous cellulose having a fiber width of 1000 nm or less and having an ionic substituent, fine particles, and a binder resin.
The average degree of polymerization of the fibrous cellulose Ri der 750 or less,
The fibrous cellulose is a phosphorylated cellulose, which is a separator coating liquid for batteries. The separator coating solution for a battery according to claim 7 , wherein the total content of the fibrous cellulose and the binder resin is 0.1 part by mass or more and 5.0 parts by mass or less with respect to 100 parts by mass of the fine particles. The battery separator coating solution according to claim 7 or 8 , wherein the mass ratio of the content of the fibrous cellulose to the content of the binder resin is 1:99 to 99: 1. The separator coating solution for a battery according to any one of claims 7 to 9 , wherein the binder resin contains at least one selected from an acrylic resin, a polyolefin resin, a urethane resin, and a silicone resin.

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