JP5841510B2 - Metal ion secondary battery separator coating liquid and metal ion secondary battery separator - Google Patents

Description

  The present invention relates to a coating solution for a metal ion secondary battery separator and a metal ion secondary battery separator.

A metal ion secondary battery which is one of electrochemical elements has a feature of high energy density. For example, a lithium ion secondary battery which is one of them is a mobile phone, a portable music player, a notebook type. Widely used as a power source for portable electric devices such as personal computers. In addition, the movement to use lithium ion secondary batteries is spreading in large equipment such as electric bicycles, hybrid cars, and electric cars. In addition, other metal ion secondary batteries such as sodium ion secondary batteries have attracted attention. For this reason, metal ion secondary batteries are required to have high capacity and performance such as charge / discharge characteristics at a large current. However, since metal ion secondary batteries are generally non-aqueous batteries, compared to aqueous batteries, It is known that there is a high risk of smoking, ignition, rupture, etc., and improvement in safety is also required.

  In a metal ion secondary battery, the risk of smoke generation increases due to temperature rise due to external heat, overcharge, internal short circuit, external short circuit, and the like. These can be prevented to some extent by an external protection circuit. In addition, the polyolefin resin porous film used as a metal ion secondary battery separator melts at around 120 ° C, and the pores are blocked to block current and ion flow, thereby suppressing battery temperature rise. Is done. This is called a shutdown function. However, when the temperature rises due to external heat or when a chemical reaction occurs inside the battery due to the temperature rise, even if the shutdown function works, the battery temperature rises further, and the battery temperature reaches 150 ° C or higher. In some cases, the porous film contracts to cause an internal short circuit, resulting in ignition and the like.

  As described above, it is difficult to suppress the ignition of the battery by the shutdown function of the separator. Therefore, by increasing the heat shrinkage temperature more than the polyolefin resin porous film, it is difficult to cause an internal short circuit and suppresses the ignition of the battery. Nonwoven fabric separators containing aramid fibers, which are heat resistant fibers, have been proposed (for example, see Patent Documents 1 to 3). An internal short circuit or a micro short circuit due to dendrite formed on the negative electrode is likely to occur, and it is difficult to say that it is practical. In order to suppress these short circuits and further improve the heat resistance, examples in which a pigment or resin is supported on a substrate such as a nonwoven fabric or a woven fabric are disclosed (for example, Patent Documents 4 to 4). 5). However, even if a pigment or resin is applied, if the hole in the substrate is large, it is easy to cause a back-through of the coating liquid or a coating defect called pinhole, and the effect of preventing a micro short circuit becomes insufficient. There was a case.

JP 2003-123728 A JP 2007-317675 A JP 2006-19191 A JP 2005-536857 A JP 2007-157723 A

  The object of the present invention is to produce a metal ion secondary battery battery separator having high heat resistance, which is excellent in coating suitability when a pigment is applied to a non-woven fabric, has little back-through, and is excellent in prevention of micro short circuit. Another object is to provide a secondary battery separator coating liquid and a metal ion secondary battery separator manufactured using the coating liquid.

As a result of intensive studies, the present inventors have invented a coating solution for a metal ion secondary battery separator and a metal ion secondary battery separator that can solve the problem. That is,
(1) Ri greens contain pigment, the coating liquid metal ion secondary battery separator for coating the nonwoven substrate, and wherein the static surface tension of the coating solution is 45 mN / m or more Coating solution for metal ion secondary battery separator,
(2) A metal ion secondary battery separator, wherein the metal ion secondary battery separator coating liquid according to (1) is applied to a nonwoven fabric substrate and dried.
It is.

  In a coating solution for a metal ion secondary battery separator containing a pigment, when the static surface tension of the coating solution is 45 mN / m or more, the coating property is excellent, and when coated on a nonwoven fabric substrate, It is possible to provide a coating liquid with little show-through.

  By applying the coating liquid onto a non-woven fabric and drying it, a metal ion secondary battery separator excellent in preventing micro short-circuits can be obtained.

  The coating liquid of the present invention contains a pigment, and the static surface tension of the coating liquid is 45 mN / m or more.

  In general, in a nonwoven fabric base material having large pores, back-through due to penetration of the coating liquid is likely to occur, and thereby pinholes are likely to occur. Further, when the back-through coating liquid adheres to and accumulates on a guide roll or the like of the coating machine, the back surface is easily rubbed, which causes a stain. In general, when applying a coating liquid to a porous separator, it is effective to lower the static surface tension of the coating liquid and increase the leveling property. However, in the present invention, the static surface tension of the coating liquid is set to 45 mN / m or more. Thus, it has been found that when applied to a nonwoven fabric substrate, penetration of the coating liquid can be suppressed, coating suitability can be improved, and pinholes can be suppressed. The static surface tension is more preferably 50 mN / m or more, and further preferably 55 mN / m or more. A static surface tension of 65 mN / m or less is preferable because a flat coating surface can be easily obtained.

  By applying the coating liquid of the present invention to a nonwoven fabric substrate, a separator having no pinholes and excellent in suppressing short-circuiting can be obtained regardless of the size of the holes in the nonwoven fabric substrate.

  In the present invention, a method of setting the static surface tension of the coating liquid to 45 mN / m or more is arbitrarily selected, but can be adjusted by selecting an additive such as an interfacial agent, for example.

  Examples of the inorganic pigment used in the present invention include alumina such as α-alumina, β-alumina and γ-alumina, hydrated alumina such as boehmite, magnesium oxide, calcium oxide and the like. These may be used alone or in combination of two or more. Of these, α-alumina or alumina hydrate is preferably used from the viewpoint of thermal stability. Moreover, it is preferable that the inorganic pigment contained in the separator of this invention is 30-70 mass% in the total solid of a separator from the point of thermal stability.

  The particle size of the pigment used in the present invention is preferably 0.1 to 10.0 μm, more preferably 0.2 to 7.5 μm, and still more preferably 0.3 to 5.0 μm. When the particle size is 0.1 μm or more, the stability of the coating liquid is increased, and when the particle size is 10.0 μm or less, a flat coating surface is easily obtained. In addition, the average particle diameter here refers to the average particle diameter (D50) measured by a laser diffraction scattering method.

  In the present invention, the static surface tension can be adjusted with various interfacial agents. As the interfacial agent, alkyl interfacial agents, silicone interfacial agents, fluorine interfacial agents and the like can be used. The addition amount of the interfacial agent is preferably about 0 to 1% with respect to the inorganic pigment.

In the coating liquid of the present invention, it is preferable that the viscosity at 1 sec ⁻¹ is 800 mPa · s or more because the penetration of the coating liquid into the base material is further suppressed.

  The coating liquid of the present invention may contain various synthetic resins such as styrene-butadiene resin, acrylic ester resin, methacrylic ester resin, and fluororesin such as polyvinylidene fluoride as a binder. In the present invention, the amount of the binder in the coating layer is preferably 20% by mass or less, more preferably 10% by mass or less in the solid content from the viewpoint of the internal resistance of the separator.

  In the present invention, various additives such as a dispersant, a thickener, an antifoaming agent, and an antiseptic can be used as long as the effects of the invention are not impaired.

  The coating liquid of the present invention can be applied to a substrate such as a porous film, a woven fabric, or a nonwoven fabric, but is preferably applied to a woven fabric substrate or a nonwoven fabric substrate, and more preferably to a nonwoven fabric substrate. Coated. As the nonwoven fabric substrate, those produced by a conventionally known method can be used. For example, what was manufactured by methods, such as the spun bond method, the melt blow method, the dry method, the wet method, and the electrospinning method, can be used.

  In the present invention, the nonwoven fabric substrate may be smoothed by calendaring or thermal calendaring for the purpose of controlling the surface and thickness of the nonwoven fabric substrate.

  Non-woven fabric base materials include polyethylene terephthalate, polybutylene terephthalate and derivatives thereof, polyesters such as aromatic polyester and wholly aromatic polyester, polyolefin, acrylic, polyacetal, polycarbonate, aliphatic polyketone, aromatic polyketone, aliphatic Polyamide, aromatic polyamide, wholly aromatic polyamide, polyimide, polyamideimide, polyphenylene sulfide, polybenzimidazole, polyetheretherketone, polyethersulfone, poly (para-phenylenebenzobisthiazole), poly (para-phenylene-2, 6-benzobisoxazole), polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol, polyurethane and polyvinyl chloride Such that fibers and cellulose fibers, and the like. The non-woven fabric substrate may contain two or more of these constituent materials.

As a nonwoven fabric base material used for the metal ion secondary battery separator of this invention, it is preferable that a fabric weight is 5-30 g / m < ² >, More preferably, it is 7-20 g / m < ² >. By setting the basis weight to 5 g / m ² or more, it becomes easy to obtain uniformity as a nonwoven fabric, and by setting it to 30 g / m ² or less, the thickness is suitable for a metal ion secondary battery separator. The basis weight means the basis weight based on the method defined in JIS P 8124 (paper and paperboard—basis weight measurement method).

  There is no particular limitation on the method for applying the coating liquid of the present invention to the nonwoven material, for example, a conventionally known air doctor coater, blade coater, knife coater, rod coater, squeeze coater, impregnation coater, gravure coater, kiss roll coater, Examples include a die coater, a reverse roll coater, a transfer roll coater, and a spray coater. In particular, an impregnation coater, a gravure coater, and a die coater are preferably used from the viewpoint of uniform coating.

In this invention, as a coating amount of a coating layer, 5-30 g / m < ² > is preferable, More preferably, it is 10-20 g / m < ² >. When the coating amount is 5 g / m ² or more, the surface of the nonwoven fabric substrate can be sufficiently covered, and an internal short circuit can be easily prevented. Moreover, the raise of the internal resistance of a separator can be suppressed by making a coating amount into 30 g / m < ² > or less.

  In the present invention, the method of drying after coating is not particularly limited, and a known drying method can be used. In particular, a method of drying by heating, such as a method of blowing hot air or a method of irradiating infrared rays, is productivity. Is preferably used.

In the metal ion secondary battery separator of the present invention, the basis weight of the separator is preferably 10 to 50 g / m ² , and more preferably 17 to 40 g / m ² . Moreover, 10-50 micrometers is preferable and, as for the thickness of a separator, More preferably, it is 15-40 micrometers. The density of the separator is preferably 0.4 to 1.2 g / cm ³ , more preferably 0.5 to 1.0 g / cm ³ .

  In the present invention, after coating and drying, the metal ion secondary battery separator may be smoothed by calendaring for the purpose of controlling the flatness and thickness of the coating layer surface.

  EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples. In Examples,% and part are all based on mass unless otherwise specified. The coating amount is an absolutely dry coating amount.

Example 1
(1) Production of Nonwoven Fabric Base Material 40 parts by mass of oriented crystallized polyethylene terephthalate (PET) short fibers having a fineness of 0.06 dtex (average fiber diameter of 2.4 μm) and a fiber length of 3 mm and a fineness of 0.1 dtex (average fiber diameter of 3. 0 μm), 20 mass parts of oriented crystallized PET short fibers with a fiber length of 3 mm, a fineness of 0.2 dtex (average fiber diameter 4.3 μm), and a fiber length of 3 mm PET short fibers for a single-component binder (softening point 120 ° C. , Melting point 230 ° C.) and 40 parts by mass were mixed together, disaggregated in water by a pulper, and a uniform papermaking slurry having a concentration of 1% by mass was prepared under stirring by an agitator. Using cylinder paper machine, raising the paper making the sheet-forming slurry by a wet method, the cylinder dryer of 130 ° C., and to adhere the PET-based short fibers binders were expressed nonwoven fabric strength, and basis weight 12 g / m ² nonwoven did. Further, this nonwoven fabric was subjected to heat treatment at a roll temperature of 200 ° C., a linear pressure of 800 N / cm, and a conveying speed of 40 m / min using a 1-nip thermal calendar composed of a metal roll and a metal roll, and a nonwoven fabric base having a thickness of 17 μm. A material was prepared.

(2) Preparation of coating liquid 100 parts of boehmite having a volume average particle size of 2.3 μm and a specific surface area of 3 m ² / g, carboxymethyl cellulose sodium salt having a viscosity of 200 mPa · s at 25 ° C. Dispersed in 120 parts of an aqueous solution and stirred well to prepare a boehmite dispersion. Next, 300 parts of a 0.5% aqueous solution of carboxymethylcellulose sodium salt having a viscosity of 7000 mPa · s at 25 ° C. of the 1% by mass aqueous solution was mixed and stirred, and further 10 parts of 49% styrene butadiene latex was mixed and stirred. A coating liquid was prepared.

(3) Production of Separator On the nonwoven fabric substrate produced in (1), the coating liquid produced in (2) was applied with a kiss reverse gravure coater so that the absolute dry coating amount was 16 g / m ^2. Coating and drying were performed to obtain a metal ion secondary battery separator having a thickness of 34 μm.

(4) Production of Battery Using the separator produced in (3), the positive electrode active material is lithium manganate, the negative electrode active material is artificial graphite, and the electrolyte is lithium hexafluorophosphate 1 of ethylene carbonate, diethyl carbonate, and dimethyl carbonate. A laminate type lithium ion secondary battery having a design capacity of 100 mAh, which is a 1/1/1 (capacity ratio) mixed solvent solution (1 mol / L), was produced.

Example 2
A metal ion secondary battery separator and a lithium ion secondary battery were produced in the same manner as in Example 1 except that 0.1 part of the silicone-based surfactant was added in the production of (2) the coating liquid of Example 1.

Example 3
A metal ion secondary battery separator and a lithium ion secondary battery were produced in the same manner as in Example 1 except that 0.2 part of the silicone surfactant was added in the production of (2) the coating liquid of Example 1.

Comparative Example 1
In the preparation of the coating liquid of (2) in Example 1, 100 parts of a 0.5% aqueous solution of carboxymethyl cellulose sodium salt having a viscosity of 7000 mPa · s at 25 ° C. in a 1% by mass aqueous solution and 0.25 parts of a silicone surfactant A metal ion secondary battery separator and a lithium ion secondary battery were produced in the same manner as in Example 1 except that.

Comparative Example 2
In the preparation of the coating liquid of (2) in Example 1, 100 parts of a 0.5% aqueous solution of carboxymethylcellulose sodium salt having a viscosity of 7000 mPa · s at 25 ° C. in a 1% by mass aqueous solution, and a polyoxyethylene surfactant 0. A metal ion secondary battery separator and a lithium ion secondary battery were produced in the same manner as in Example 1 except that 5 parts were added.

<Evaluation>
The coating liquid, metal ion secondary battery separator, and lithium ion secondary battery obtained in the examples and comparative examples were evaluated as follows, and the results are shown in Table 1.

[Coating liquid surface tension]
The static surface tension at 23 ° C. of the prepared coating solution was measured with a fully automatic surface tension meter CBVP-Z manufactured by Kyowa Interface Science Co., Ltd.

[Through coating liquid]
In the production of the separators of (3) each example and comparative example, the amount of dried coating liquid deposited on the guide roll immediately after the gravure roll in the gravure coater after 500 m coating was visually evaluated. Evaluation criteria were as follows.
A: Sediment is hardly seen on the guide roll.
○: Slight deposits are observed, but at a level that does not cause any operational problems.
(Triangle | delta): There is a concern that a deposit may be much and the dirt of a separator may occur.
X: A lot of deposits are transferred to the separator.

[Coulomb efficiency during initial charge / discharge]
About the produced battery, 100mA constant current charge-> 4.2V constant voltage charge (1 hour)-> Conduct constant current discharge to 2.8V at 100mA, charge capacity and discharge capacity are measured, (Coulomb efficiency) = (discharge capacity) ) / (Charge capacity) was calculated. Those with low Coulomb efficiency are considered to have a micro short circuit.

  As apparent from Table 1, in Examples 1 to 3 in which the static surface tension of the coating liquid is 45 mN / m or more, there is little occurrence of back-through during coating, and the coating suitability is excellent. In addition, the coulomb efficiency at the first charge / discharge is excellent. On the other hand, in Comparative Examples 1 and 2 in which the static surface tension of the coating liquid is less than 45 mN / m, back-through occurs at the time of coating, the Coulomb efficiency at the first charging is low, and a micro short-circuit occurs. The result was considered.

  The coating solution for metal ion secondary battery separator and metal ion secondary battery separator of the present invention can be used for metal ion polymer batteries, metal ion capacitors and the like in addition to metal ion secondary battery applications.

Claims (2)

Pigment Ri Na contain, in the metal-ion secondary battery separator coating solution for coating the nonwoven substrate, the metal static surface tension of the coating liquid is characterized in that it is 45 mN / m or more ions Coating solution for secondary battery separator.   A metal ion secondary battery separator, wherein the coating solution for a metal ion secondary battery separator according to claim 1 is applied to a nonwoven fabric substrate and dried.