JP5876375B2 - Metal ion secondary battery separator - Google Patents

Description

  The present invention relates to 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 personal computer. Widely used as a power source for portable electric devices such as 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. Therefore, metal ion secondary batteries are required to have high capacity and high rate discharge characteristics (high rate characteristics). However, since metal ion secondary batteries are generally non-aqueous batteries, they are compared with aqueous batteries. Therefore, 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, the battery temperature further rises even if the shutdown function works, and when the battery temperature reaches 150 ° C or higher, The porous film contracted, causing an internal short circuit, which could cause ignition.

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 (see, for example, Patent Documents 1 to 3) . However, although these nonwoven fabric separators are excellent in heat shrinkability, the pore diameter is large, and internal short circuit due to contact of the bipolar active material or micro short circuit due to dendrite generated 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 to further improve the heat resistance, examples in which a non-woven fabric or a woven fabric is supported by applying a pigment or a resin are disclosed (for example, see Patent Documents 4 to 5). However, even when a pigment or resin is applied, the substrate has a large hole, so that the coating liquid is easily exposed and a coating defect called a pinhole is likely to occur, and the effect of preventing a micro short circuit is insufficient. Moreover, in order to prevent a micro short circuit, there existed a subject that a metal ion permeability fell by applying a pigment and resin thickly, and a high rate characteristic was impaired.

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

  An object of the present invention is to provide a metal ion secondary battery separator that is excellent in high rate characteristics when producing a metal ion secondary battery separator having high heat resistance.

As a result of intensive studies, the present inventors have invented a metal ion secondary battery separator that can solve the problem. That is,
(1) In a metal ion secondary battery separator in which an inorganic pigment and an adhesive are supported on a nonwoven fabric base material, the nonwoven fabric base material has a density of 0.55 to 0.75 g / cm ³ and a fragile air permeability of 5.5. ~13.5cc ^/ cm is 2 · sec, also, an average particle size 1.5~5.0μm secondary particles inorganic pigment is formed by agglomerating primary particles of particle size 0.4~1.0μm Ah is, 30 to 70% by weight of the total solid content amount of the separator of inorganic pigment contained in the separator, the coating weight of the coating layer containing an inorganic pigment and adhesive in 5 to 30 g / m ² There, the metal-ion secondary battery separators amount of adhesive coating layer is characterized by 3-15% by mass Rukoto in solids,
(2) The metal ion secondary battery separator according to (1), wherein the inorganic pigment is α-alumina or boehmite,
It is.

In a metal ion secondary battery separator in which an inorganic pigment and an adhesive are supported on a nonwoven fabric substrate, the nonwoven fabric substrate has a density of 0.55 to 0.75 g / cm ³ and a fragile permeability of 5.5 to 13. 5 cc / cm ² · sec, and the inorganic pigment is a secondary particle having an average particle size of 1.5 to 5.0 μm formed by agglomerating primary particles having a particle size of 0.4 to 1.0 μm. It is possible to produce a highly safe metal ion secondary battery separator that is excellent in suppressing internal short circuit and excellent in high-rate characteristics.

  Moreover, the high rate characteristic can be further enhanced by using α-alumina or boehmite as the inorganic pigment.

The nonwoven fabric substrate according to the present invention has a density of 0.55 to 0.75 g / cm ³ and a fragile air permeability of 5.5 to 13.5 cc / cm ² · sec. The porosity, pore diameter, pore distribution, etc. of the nonwoven fabric substrate have a complex effect on the permeability of the coating liquid to the nonwoven fabric substrate and the ion permeability inside the separator. By controlling both, it is possible to obtain a nonwoven fabric base material suitable for achieving both internal short circuit suppression and high rate characteristics. By setting the substrate density to 0.55 g / cm ³ or more and the Frazier air permeability to 13.5 cc / cm ² · sec or less, the back-through of the coating liquid during coating can be suppressed, and the occurrence of pinholes can be suppressed. As a result, an internal short circuit is less likely to occur. In addition, by setting the substrate density to 0.75 g / cm ³ or less and the fragile air permeability to 5.5 cc / cm ² · sec or more, a metal ion secondary battery separator having good ion permeability and excellent high-rate characteristics. (Hereinafter sometimes abbreviated as “separator”). More preferably the density of the nonwoven substrate is 0.57~0.73g / cm ^3, further preferably 0.59~0.71g / cm ^3. Moreover, Frazier air permeability is more preferably from 6.0~13.0cc ^/ cm 2 · sec, more preferably from 6.5~12.5cc ^/ cm 2 · sec.

  In the present invention, fragile air permeability means air permeability based on the fragile method defined in JIS L 1096.

  The method for adjusting the density and fragile air permeability of the nonwoven fabric substrate is arbitrarily selected. For example, the fiber type and fiber diameter can be selected, the drying temperature can be adjusted, and the paper can be processed by calendering or heat calendering after drying. Can be adjusted.

  As the nonwoven fabric substrate used in the present invention, 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 calendering or thermal calendering for the purpose of controlling the surface and density 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. The density is a value obtained by dividing the basis weight by the thickness.

  The inorganic pigment according to the present invention is a secondary particle having an average particle diameter of 1.5 to 5.0 μm formed by agglomerating primary particles having a particle diameter of 0.4 to 1.0 μm. The dispersion stability of the particles and the flatness of the coating layer depend on the particle size of the secondary particles, the “average particle size” referred to here, but the coating has a large effect on the separator pore size and high rate characteristics that affect internal short circuit suppression. The porosity in the layer depends on the layer structure and the particle size of the primary particles. When the average particle diameter is 1.5 μm or more, the dispersion stability of the particles is improved, and a uniform coating layer can be formed. Moreover, it becomes easy to obtain the flatness of a coating layer because an average particle diameter is 5.0 micrometers or less. The average particle diameter is more preferably 1.7 to 4.5 μm, and further preferably 2.0 to 4.0 μm.

  Since the particles have a secondary shape, fine voids are formed between the agglomerated particles, and the specific surface area is increased compared to the primary particles having the same average particle diameter, and the voids in the coating layer are increased. It becomes easy to obtain. In this case, when the particle diameter of the primary particles is 0.4 to 1.0 μm, it is easy to control the pore diameter of the entire separator, which is effective for both internal short circuit suppression and high rate characteristics. The particle diameter of the primary particles is more preferably 0.5 to 0.9 μm, and further preferably 0.6 to 0.8 μm.

  By providing this non-woven fabric base material with a uniform, flat, and high porosity coating layer, the metal ion secondary battery separator is excellent in high-rate characteristics, allowing easy passage of metal ions without biasing current density. Is obtained. The “particle size of primary particles” as used in the present invention refers to the observation of inorganic pigment particles with an electron microscope, and the average particle size is determined by using the diameter of a circle equal to the projected area of each primary particle as the particle size. It is a thing. The “average particle diameter of secondary particles” is an average particle diameter (D50) measured by a laser diffraction scattering method.

  Further, the 90% particle diameter (D90) measured by the laser diffraction scattering method of the inorganic pigment is 1/2 to 1/4 of the thickness of the coating layer from the viewpoint of coexistence of internal short-circuit suppression and high-rate characteristics. desirable. The thickness of the coating layer is measured by observing and measuring an arbitrary five points in the cross section of the separator with a scanning electron microscope, an optical microscope, or the like, and is calculated as an average value thereof. In addition, even if it is a case where a part of inorganic pigment has penetrated the inside of a nonwoven fabric base material, let the thickness of the layer only of an inorganic pigment be the thickness of a coating layer.

  Examples of the inorganic pigment used in the present invention include kaolin, calcined kaolin, heavy calcium carbonate, light calcium carbonate, magnesium carbonate, zinc oxide, alumina, boehmite, aluminum hydroxide, magnesium hydroxide, titanium dioxide, barium sulfate, zinc sulfate, Examples thereof include amorphous silica and calcium silicate. These may be used alone or in combination of two or more. Of these, α-alumina or boehmite 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 oil absorption of the inorganic pigment of the present invention is preferably 40 to 100 ml / 100 g because an effective specific surface area and voids in the coating layer are easily obtained.

  As the primary particle shape of the inorganic pigment used in the present invention, any shape such as a plate shape, a granular shape, a needle shape, a cubic shape, a spherical shape, a spindle shape, and a scale shape may be used, and the cubic shape is particularly preferred. It is preferable because voids in the coating layer are easily obtained.

  As an inorganic pigment which is a secondary particle having an average particle diameter of 1.5 to 5.0 μm formed by agglomeration of primary particles having a particle diameter of 0.4 to 1.0 μm, a corresponding commercially available product may be used. It may be synthesized according to the method.

For example, as a method for synthesizing boehmite having a secondary form, aluminum hydroxide can be obtained by a hydrothermal treatment with a reaction accelerator and water. Aluminum hydroxide having an average particle size of about 0.1 to 10.0 μm is used. Here, it is preferable to use aluminum hydroxide whose particle size is adjusted by pulverization because secondary aggregates are easily formed. Reaction accelerators include alkali compounds and alkaline earth metal hydroxides, oxides, chlorides, carbonates, sulfates, nitrates, phosphates, boric acid, and other inorganic compounds, alkali metals and alkaline earths. Organic compounds such as metal acetates and oxalates can be used. What is necessary is just to add a reaction accelerator about 0.0001-1 mol with respect to 1 mol of aluminum hydroxide. A polyacrylic acid ester or the like may be added to promote crystal growth.

The above aluminum hydroxide, reaction accelerator and water are sealed in a pressure-resistant container such as an autoclave and reacted at a temperature of about 140 to 350 ° C. for about 1 to 50 hours, and the product after the reaction is washed, filtered and dried. Thus, the intended boehmite can be obtained. The particle size and shape of the primary particles or secondary particles can be appropriately adjusted by changing the particle size of aluminum hydroxide, the type and amount of reaction accelerator, reaction temperature, reaction time, and the like. Further, the obtained boehmite may be used as it is, or may be used after adjusting the particle diameter as necessary.

  It is also possible to obtain α-alumina by treating the boehmite obtained as described above with an electric furnace or the like at a temperature of about 1200 to 1500 ° C.

As the adhesive in the present invention, a latex polymer is preferably used. Specific examples include, for example, styrene / butadiene copolymers, acrylonitrile / butadiene copolymers, methyl acrylate / butadiene copolymers, acrylonitrile / butadiene / styrene terpolymers, polyvinyl acetate, vinyl acetate / acrylate esters. Examples include, but are not limited to, latex polymers such as copolymers, ethylene / vinyl acetate copolymers, polyacrylates, styrene / acrylate copolymers, and polyurethanes. In terms of high-rate characteristics及 beauty coating layer strength of the separator in the present invention, the adhesive of the coating layer is preferably in the solid content of 3 to 15 wt%.

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

  In the present invention, the method for supporting the inorganic pigment and the adhesive on the nonwoven fabric substrate is not particularly limited, and a known method can be used. For example, an air doctor coater, a blade coater, a knife coater, a rod coater, a squeeze coater The coating liquid can be applied with an impregnation coater, a gravure coater, a kiss roll coater, a die coater, a reverse roll coater, a transfer roll coater, a spray coater, etc., and supported by drying.

In this invention, as a coating amount of the coating layer containing an inorganic pigment and an adhesive agent, 5-30 g / m < ² > is preferable, More preferably, it is 10-20 g / m < ² >. By setting the coating amount to 5 g / m ² or more, it becomes easy to sufficiently cover the nonwoven fabric surface, and internal short circuit is easily prevented. Moreover, the raise of the thickness of a separator can be suppressed by setting it as the coating amount 30g / m < ² > or less.

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 parts are 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 an inclined paper machine, this papermaking slurry is made up by a wet method, and a PET dryer short fiber for a binder is adhered to the nonwoven fabric with a cylinder dryer at 140 ° C. to develop a nonwoven fabric strength, and a nonwoven fabric having a basis weight of 12 g / m ² did. Furthermore, this nonwoven fabric was used under the conditions of a heat roll temperature of 200 ° C., a linear pressure of 100 kN / m, and a processing speed of 80 m / min, using a 1-nip heat calender consisting of a dielectric heating jacket roll (metal heat roll) and an elastic roll. Thermal calendar treatment was performed to prepare a nonwoven fabric substrate having a thickness of 22 μm, a density of 0.55 g / cm ³ , and a fragile air permeability of 13.2 cc / cm ² · sec.

(2) Preparation of coating liquid As an inorganic pigment, 100 parts of boehmite secondary particles having an average particle diameter of 2.3 μm formed by agglomeration of primary particles having a particle diameter of 0.7 μm were mixed with a 1 mass% aqueous solution at 25 ° C. Was dispersed in 120 parts of a 0.3% aqueous solution of sodium carboxymethylcellulose having a concentration of 200 mPa · s and stirred well to prepare a boehmite dispersion. Subsequently, 300 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 was mixed and stirred, and further a latex of 45% styrene / butadiene copolymer was used as an adhesive. 15 parts of molecules were mixed and stirred to prepare a coating solution.

(3) Production of Separator On the nonwoven fabric produced in (1), the coating liquid produced in (2) was applied and dried so that the absolutely dry coating amount was 15 g / m ^2, and the metal ion secondary. A battery separator was obtained.

(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, the positive and negative electrode area is 15 cm ² , and the electrolyte is lithium hexafluorophosphate. A laminate type lithium ion battery having a design capacity of 30 mAh, which is a 7/3 (capacity ratio) mixed solvent solution (1 mol / L) of diethyl carbonate, was produced.

Example 2
In the production of the nonwoven fabric substrate of Example 1 (1), the nonwoven fabric substrate having a thickness of 16 μm, a density of 0.75 g / cm ³ , and a fragile air permeability of 5.7 cc / cm ² · sec, with a thermal calendar treatment speed of 30 m / min. A metal ion secondary battery separator and a lithium ion battery were produced in the same manner as in Example 1 except that was produced.

Example 3
Example 1 (2) In preparation of the coating liquid, Example 1 was used except that boehmite secondary particles having an average particle diameter of 1.6 μm formed by agglomerating primary particles having a particle diameter of 0.4 μm were used as inorganic pigments. Similarly, a metal ion secondary battery separator and a lithium ion battery were produced.

Example 4
Example 1 (2) In the preparation of the coating liquid, Example 1 was used except that boehmite secondary particles having an average particle diameter of 4.8 μm formed by agglomerating primary particles having a particle diameter of 1.0 μm were used as the inorganic pigment. Similarly, a metal ion secondary battery separator and a lithium ion battery were produced.

Example 5
Example 1 (2) In the preparation of the coating liquid, Example 1 was used except that α-alumina secondary particles having an average particle size of 2.3 μm formed by agglomeration of primary particles having a particle size of 0.7 μm were used as the inorganic pigment. In the same manner, a metal ion secondary battery separator and a lithium ion battery were produced.

Example 6
Example 1 (2) In the preparation of the coating liquid, Example 1 was used except that calcium carbonate secondary particles having an average particle size of 2.3 μm formed by agglomerating primary particles of 0.7 μm in particle size were used as inorganic pigments. In the same manner, a metal ion secondary battery separator and a lithium ion battery were produced.

Comparative Example 1
In preparation of the nonwoven fabric substrate of Example 1 (1), 30 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: 3.0 μm), 30 mass parts of oriented crystallized PET short fibers having a fiber length of 3 mm, thermal calendering speed of 70 m / min, thickness of 22 μm, density of 0.55 g / cm ³ , Frazier ventilation A metal ion secondary battery separator and a lithium ion battery were produced in the same manner as in Example 1 except that a nonwoven fabric substrate having a degree of 14.3 cc / cm ² · sec was produced.

Comparative Example 2
In preparation of the nonwoven fabric substrate of Example 1 (1), 50 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: 3.0 μm), 10 mass parts of oriented crystallized PET short fibers having a fiber length of 3 mm, thermal calendering speed of 100 m / min, thickness of 24 μm, density of 0.50 g / cm ³ , Frazier ventilation A metal ion secondary battery separator and a lithium ion battery were produced in the same manner as in Example 1 except that a nonwoven fabric substrate having a degree of 13.5 cc / cm ² · sec was produced.

Comparative Example 3
In preparation of the nonwoven fabric substrate of Example 1 (1), 50 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: 3.0 μm), 10 mass parts of oriented crystallized PET short fibers having a fiber length of 3 mm, thermal calendering speed of 40 m / min, thickness of 16 μm, density of 0.75 g / cm ³ , Frazier ventilation A metal ion secondary battery separator and a lithium ion battery were produced in the same manner as in Example 1 except that a nonwoven fabric substrate having a degree of 5.0 cc / cm ² · sec was produced.

Comparative Example 4
In preparation of the nonwoven fabric substrate of Example 1 (1), 30 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: 3.0 μm), 30 mass parts of oriented crystallized PET short fibers having a fiber length of 3 mm, thermal calendering speed of 20 m / min, thickness of 15 μm, density of 0.80 g / cm ³ , Frazier ventilation A metal ion secondary battery separator and a lithium ion battery were produced in the same manner as in Example 1 except that a nonwoven fabric substrate having a degree of 5.8 cc / cm ² · sec was produced.

Comparative Example 5
A metal ion secondary battery separator and a lithium ion battery were prepared in the same manner as in Example 1 except that boehmite having a single particle shape and an average particle diameter of 2.0 μm was used as the inorganic pigment in the preparation of the coating liquid of Example 1 (2). Was made.

Comparative Example 6
In the preparation of the coating liquid of Example 1 (2), the same procedure as in Example 1 was used, except that boehmite secondary particles having an average particle size of 6.1 μm formed by agglomerating primary particles of 0.7 μm were used as the inorganic pigment. Thus, a metal ion secondary battery separator and a lithium ion battery were produced.

Comparative Example 7
In the preparation of the coating liquid in Example 1 (2), the same procedure as in Example 1 was used, except that boehmite secondary particles having an average particle diameter of 1.3 μm formed by agglomerating primary particles of 0.3 μm were used as the inorganic pigment. Thus, a metal ion secondary battery separator and a lithium ion battery were produced.

<Evaluation>
The following evaluation was performed about the coating liquid obtained by the Example and the comparative example, the metal ion secondary battery separator, and the lithium ion battery, and the result was shown in Table 1.

[Coulomb efficiency during initial charge / discharge]
About the produced battery, when it becomes 30mA constant current charge-> 4.3V constant voltage charge-> charge current 3mA, it carries out constant current discharge to 2.8V at 30mA, A 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.

[High-rate battery characteristics]
About the produced battery, when 30 mA constant current charge → 4.2 V constant voltage charge → charge current 3 mA, 30 mA constant current discharge to 2.8 V → 30 mA constant current charge → 4.2 V constant voltage charge → charge current 3 mA Then, a constant current discharge was performed at 2.8 V at 90 mA, and the discharge capacity ratio was determined as [(discharge capacity at 90 mA) / (discharge capacity at 30 mA)] × 100 (%) to obtain high rate characteristics.

As is apparent from Table 1, the nonwoven fabric substrate has a density of 0.55 to 0.75 g / cm ³ and a fragile permeability of 5.5 to 13.5 cc / cm ² · sec, and the inorganic pigment has a particle size of Examples 1 to 6, which are secondary particles having an average particle diameter of 1.5 to 5.0 μm formed by agglomeration of primary particles of 0.4 to 1.0 μm, are excellent in coulomb efficiency at the first charge / discharge and are high rate. Excellent characteristics.

In Comparative Example 1 in which the fragile air permeability of the nonwoven fabric substrate exceeds 13.5 cc / cm ² · sec and in Comparative Example 2 in which the density of the nonwoven fabric substrate is less than 0.55 g / cm ³ , the Coulomb efficiency at the first charge / discharge Is small. In Comparative Example 3 in which the fragile air permeability of the nonwoven fabric substrate is less than 5.5 cc / cm ² · sec and Comparative Example 4 in which the density of the nonwoven fabric substrate is more than 0.75 g / m ³ , the high rate characteristics are poor. In Comparative Example 5 using single particle boehmite as the inorganic pigment and Comparative Example 7 in which the particle diameter of the inorganic pigment is less than 0.4 μm and the average particle diameter of the secondary particles is less than 1.5 μm, the high rate characteristics are poor, In Comparative Example 6 in which the average particle diameter of the secondary particles of the inorganic pigment exceeds 5.0 μm, the Coulomb efficiency at the first charge / discharge is small.

  From the comparison of Examples 1, 5 and 6, when the inorganic pigment is α-alumina or boehmite, the Coulomb efficiency and the high rate characteristics are more excellent.

  The 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)

In a metal ion secondary battery separator in which an inorganic pigment and an adhesive are supported on a nonwoven fabric substrate, the nonwoven fabric substrate has a density of 0.55 to 0.75 g / cm ³ and a fragile air permeability of 5.5 to 13.5 cc. / ^cm is 2 · sec, also, Ri Oh an average particle size 1.5~5.0μm secondary particles inorganic pigment is formed by agglomerating primary particles of particle size 0.4～1.0Myuemu, separator The amount of the inorganic pigment contained in the separator is 30 to 70% by mass in the total solid content of the separator, the coating amount of the coating layer containing the inorganic pigment and the adhesive is 5 to 30 g / m ² , and the coating layer metal ion secondary battery separators amount adhesive is characterized 3-15% by mass Rukoto in solids in.   The metal ion secondary battery separator according to claim 1, wherein the inorganic pigment is α-alumina or boehmite.