JP6172910B2 - Electrochemical element separator - Google Patents

Description

  The present invention relates to a separator for an electrochemical element.

In recent years, along with the reduction in size and weight of electric devices, there is a strong demand for reduction in size, weight, and increase in capacity of batteries that are power sources. For example, an electrochemical element having a high energy density such as a lithium ion secondary battery is expected to satisfy such a demand.

On the other hand, when the electrochemical element generates heat or is heated, the electrochemical element separator existing between the electrodes of the electrochemical element contracts or melts, thereby causing an internal short circuit in the electrochemical element. It sometimes occurred. When an abnormally large current flows to the electrochemical element due to the occurrence of an internal short circuit, the battery characteristics change, such as decomposition of the electrolyte solution, causing the electrochemical element to further rise in temperature and run out of heat, causing flammability. There was a risk of causing gas generation or rupture or ignition of the electrochemical element.
Therefore, the electrochemical element separator that constitutes the electrochemical element is resistant to shrinkage or melting due to its heat resistance, and can prevent an internal short circuit from occurring in the electrochemical element and prevent thermal runaway. Is required.

As a separator for an electrochemical element that is expected to have the above-mentioned performance, for example, JP 2008-210541A (hereinafter referred to as Patent Document 1) includes inorganic particles such as silica particles in a fibrous material. A battery separator prepared by applying a liquid composition is disclosed, and it is disclosed that the battery separator is excellent in short circuit resistance.
Further, it is disclosed that shutdown performance can be imparted by adding heat-meltable fine particles such as polyolefin resin particles to a battery separator.

JP 2008-210541 A (claims, 0010, 0015-0016, 0024-0028, 0034, 0037-0040, 0058-0068, etc.)

The inventors of the present application studied a method disclosed in Patent Document 1 in order to obtain an electrochemical element separator that can prevent an internal short circuit from occurring in an electrochemical element.
However, an internal short circuit may still occur in the electrochemical element assembled using the electrochemical element separator thus prepared.

As a result of examining the cause of this problem, the present inventors have found that an electrolysis device comprising an electrochemical device separator prepared using the slurry when an aggregate containing inorganic particles is present in the slurry. It has been found that chemical elements tend to be susceptible to internal short circuits.
In other words, when the agglomerates are present in the separator for electrochemical devices, the separator for electrochemical devices does not contain inorganic particles or has few inorganic particles (hereinafter, inorganic particles are unevenly present). Part). And since the separator for electrochemical elements is easy to shrink | contract or melt | dissolve in the part in which an inorganic particle exists unevenly, it was thought that the electrochemical element provided with the said separator for electrochemical elements was easy to carry out an internal short circuit.
In particular, the problem of being easily short-circuited tends to occur remarkably in a separator for an electrochemical device using a nonwoven fabric, a woven fabric, or a knitted fabric as an ion-permeable support. The reason for this is thought to be that the surface of the fabric has more irregularities than a porous film and the like, and a portion where inorganic particles are present unevenly tends to occur.

In order to prevent the presence of agglomerates in the separator for electrochemical devices, the present inventors agglomerated by dispersing them in a slurry, such as a combination of silica particles and styrene-butadiene rubber (SBR) particles. The present inventors studied to prepare slurry by mixing inorganic particles and polymer particles, which are difficult to form, and to prepare a separator for an electrochemical device using the slurry.
However, although the electrochemical device provided with the electrochemical device separator prepared as described above is less likely to cause an internal short circuit, the capacity retention rate tends to decrease when it is repeatedly charged and discharged. It was.

An object of this invention is to provide the separator for electrochemical elements which can prevent that an internal short circuit generate | occur | produces in an electrochemical element and can prepare the electrochemical element which is excellent in a capacity | capacitance maintenance factor.

The present invention
“A separator for electrochemical elements prepared by applying a slurry obtained by mixing inorganic particles and polyolefin resin particles to an ion-permeable support, wherein the inorganic particles and polyolefin resin particles are contained in the slurry. Dispersing separator for electrochemical elements. "
It is.

Since the separator for electrochemical devices of the present invention is a separator for electrochemical devices prepared by applying inorganic particles, it is excellent in heat resistance and hardly shrinks or melts under high temperature conditions. Therefore, it is possible to prevent an internal short circuit from occurring in the electrochemical element.
Further, the separator for an electrochemical element of the present invention is a combination of inorganic particles and polyolefin resin particles (hereinafter referred to as inorganic particles and polyolefin resin particles of the present invention) in which the inorganic particles and the polyolefin resin particles are dispersed in a slurry. , A separator for electrochemical devices).
The present inventors have found that a combination of inorganic particles and polyolefin resin particles dispersed in a slurry hardly forms an aggregate. Therefore, since the separator for electrochemical elements of the present invention can prevent a portion where inorganic particles are present non-uniformly, it can prevent an internal short circuit from occurring in the electrochemical element. In particular, even when a cloth such as a nonwoven fabric, a woven fabric, or a knitted fabric is used as the ion-permeable support, it is possible to effectively prevent an internal short circuit from occurring in the electrochemical element.

Moreover, the present inventors have found that an electrochemical element having an excellent capacity retention ratio can be prepared by using an electrochemical element separator to which polyolefin resin particles are applied.

As described above, the present invention is an electrochemical element separator that can prevent an internal short circuit from occurring in an electrochemical element and has an excellent capacity retention rate.

It is the graph which put together the behavior of the viscosity change while increasing the shear rate about the slurry used in Example 1 from the static state. It is the graph which put together the behavior of the viscosity change while reducing the shear rate from the high shear rate to the static state about the slurry used in Example 1. It is the graph which put together the behavior of the viscosity change while increasing the shear rate about the slurry used in comparative example 3 from the static state. It is the graph which put together the behavior of the viscosity change while reducing the shear rate from the high shear rate to the static state about the slurry used in Comparative Example 3.

Details of the separator for an electrochemical element of the present invention will be described below.

The inorganic particles impart heat resistance to the separator for an electrochemical element, thereby preventing the separator for an electrochemical element from shrinking or melting even when the electrochemical element generates heat or is heated. To do.
Further, as described later, when the ion-permeable support includes a thermoplastic resin, the inorganic particles, together with the thermoplastic resin, block the micropores of the ion-permeable support so as to be used for electrochemical devices. The function of improving the shutdown performance of the separator can also be exhibited.

The kind of the inorganic compound constituting the inorganic particles is not limited because it can be appropriately selected. For example, SiO ₂ (silica), Al ₂ O ₃ (alumina), alumina-silica composite oxide, Oxides such as TiO ₂ , SnO ₂ , BaTiO ₂ , ZrO, tin-indium oxide (ITO); nitrides such as aluminum nitride and silicon nitride; sparingly soluble ions such as calcium fluoride, barium fluoride and barium sulfate Crystals; Covalent crystals such as silicon and diamond; Clays such as talc and montmorillonite; Mineral resources derived from minerals such as boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, mica or their artifacts Etc. can be used.

When preparing inorganic particles by using two or more inorganic compounds in combination, prepare inorganic particles by mixing two or more inorganic compounds, or coat one inorganic compound with the other inorganic compound. Thus, inorganic particles can be prepared.

  The shape of the inorganic particles to be used is not limited. For example, spherical (substantially spherical or true spherical), fibrous, needle-like (for example, tetrapot-like), flat plate, polyhedron, feather, irregular shape The shape can be selected as appropriate.

In addition, it is preferable that the separator for electrochemical elements is configured to include true spherical inorganic particles, since the contact area between the inorganic particles and the polyolefin resin particles becomes smaller, so that formation of aggregates can be further prevented.

In particular, a method of producing inorganic particles by detonating a dust cloud of a raw material capable of preparing inorganic particles as an inorganic particle in a reaction gas atmosphere such as air, oxygen, chlorine, nitrogen or the like (for example, JP-A-60-255602). It is preferable to use inorganic particles (hereinafter referred to as deflagration inorganic particles) obtained by the method disclosed in the Japanese Patent Publication No.

It is known that the deflagration inorganic particles have a true spherical shape, and since the contact area between the inorganic particles and the polyolefin resin particles becomes smaller, further formation of aggregates can be prevented.
Moreover, when preparing the separator for electrochemical elements which uses nonaqueous electrolyte solutions, such as a lithium ion secondary battery, it is preferable to use a deflagration inorganic particle as an inorganic particle carry | supported by an ion-permeable support body. It is known that the amount of water present in the deflagration inorganic particles is small, and it is possible to prevent the deterioration of the function of the electrochemical element caused by the mixing of water into the non-aqueous electrolyte solution.

As such deflagration inorganic particles, for example, silica particles (Admafine: registered trademark, trade names: SO-E1, SO-E2, SO-E3, SO-E4, SO-E5, SO, manufactured by Admatechs Co., Ltd.) -E6, SO-C1, SO-C2, SO-C3, SO-C4, SO-C5, SO-C6, etc.), Admatex Corporation alumina particles (Admafine: registered trademark, trade name: AO-802) , AO-809, AO-820, AO-502, AO-509, AO-520 and the like.

The particle size of the inorganic particles is not particularly limited, but if the particle size of the inorganic particles is too large, the function of imparting heat resistance to the ion-permeable support may not be exhibited efficiently.
Therefore, the particle diameter of the inorganic particles is preferably 3 μm or less, more preferably 2 μm or less, and most preferably 1 μm or less. In addition, the lower limit of the particle diameter of the inorganic particles is appropriately prepared and should not be limited, but is practically 0.1 μm or more.

The particle diameter of the particles referred to in the present invention is determined by subjecting the particles to FPRA1000 (measurement range: 3 nm to 5000 nm) manufactured by Otsuka Electronics Co., Ltd., and performing continuous measurement for 3 minutes by the dynamic light scattering method. The value obtained from the obtained particle diameter measurement data. That is, particle size measurement is performed five times, and the particle size measurement data obtained by the measurement are arranged in the order of the narrowest particle size distribution width, and the accumulation of particles in the data showing the third narrowest particle size distribution width. The particle diameter D _{50 at the} 50% value (hereinafter abbreviated as D ₅₀ ) is defined as the particle diameter. In addition, the measurement liquid used for the measurement is adjusted to a temperature of 25 ° C., and pure water at 25 ° C. is used as a blank for scattering intensity.

In addition, the particle size distribution of the inorganic particles is not particularly limited, but if the particle size distribution of the inorganic particles is too wide, there is a tendency that a portion where the inorganic particles are present unevenly tends to occur.
Therefore, the particle size distribution of the inorganic particles is preferably in the range of less than _(D 50/2) or more _{(D 50} × 2). The particle size distribution of the particles referred to in the present invention is measured by the above-mentioned dynamic light scattering method and is determined from particle size measurement data obtained from the measured intensity.

The polyolefin resin particles of the present invention play a role of supporting inorganic particles on the ion-permeable support by interposing between the ion-permeable support and the inorganic particles and interposing between the inorganic particles. .
The type of polyolefin resin constituting the polyolefin resin particles is not limited, and examples thereof include polypropylene, polyethylene, and polymethylpentene.
Further, it is preferable to use a polyolefin resin having a molecular weight in the range of 10,000 to 50,000, and more preferable to use a polyolefin resin having a molecular weight in the range of 20,000 to 30,000.

Further, as a polyolefin-based resin, for example, a polyolefin having a compound structure represented by any structural formula shown below as (Chemical Formula 1) as a copolymer unit disclosed in JP-A No. 2003-119328, etc. And a resin derived from an unsaturated carboxylic acid or an unsaturated carboxylic acid-derived compound disclosed in JP-A-2005-2137, for example, as a copolymer unit. It is preferable to use a chlorinated polyolefin resin (hereinafter referred to as polyolefin resin B) containing chlorine.

Since the polyolefin resin A and the polyolefin resin B are excellent in hydrophilicity, they can be prevented from forming aggregates by being dispersed in the slurry.
As such polyolefin resin A particles, for example, in a modified polyolefin resin aqueous dispersion (Arrowbase (registered trademark), SA-1200, SB-1200, SE-1200, SB-1010, etc.) manufactured by Unitika Ltd. Anion-modified polyolefin resin particles dispersed in the resin can be used. Examples of the polyolefin resin B particles include a cation-modified polyolefin resin aqueous dispersion (Arrowbase (registered trademark), CB-) manufactured by Unitika Ltd. 1200, CD-1200, etc.) and modified polyolefin resin particles dispersed therein.

  The shape of the polyolefin resin particles is not limited, and can be appropriately selected from, for example, a spherical shape (substantially spherical or true spherical shape), a fibrous shape, a needle shape, a flat plate shape, a polyhedral shape, a feather shape, and the like.

The particle diameter of the polyolefin resin particles (D ₅₀ ) is not particularly limited and should be adjusted as appropriate, but if it is too large, the distance between the electrodes is increased and the resistance value between the electrodes is increased. There is a possibility that the electrochemical device may not be able to exhibit desired discharge characteristics, and a large amount of inorganic particles are likely to be present outside the polyolefin resin particles due to the large surface area of the polyolefin resin particles. As a result, the electrochemical device There exists a tendency for the part which an inorganic particle exists in the separator for water to produce unevenly.
Therefore, the particle diameter (D ₅₀ ) of the polyolefin resin particles is preferably 500 nm or less, more preferably 300 nm or less, and most preferably 200 nm or less. Further, the lower limit value of the particle diameter (D ₅₀ ) of the polyolefin resin particles is not particularly limited, and should be adjusted as appropriate, but it is realistic to be 10 nm or more.

The size of the particle diameter of the polyolefin resin particles (D ₅₀₎ determined appropriately adjusted in accordance with the particle diameter of the inorganic particles (D ₅₀₎ to be used, the polyolefin resin to the particle diameter of the inorganic particles (D ₅₀₎ When the particle size (D ₅₀ ) of the particles is 1 to 0.09 times, the mass of the polyolefin resin particles applied to the separator for an electrochemical element is reduced, and the ion-permeable support is efficiently inorganic. It is preferable because it can carry particles.

The ion-permeable support of the present invention can be made of a material such as a nonwoven fabric, a woven fabric, or a knitted fabric, a microporous film, a foamed material, etc. that can pass ions from one main surface to the other main surface. Can do. These materials can be used alone as an ion-permeable support, but can also be used as an ion-permeable support by combining a plurality of materials, for example.

The component constituting the ion-permeable support is not particularly limited, and may be electrochemically stable and stable with respect to the electrolyte. For example, polyolefin resin (polyethylene, polypropylene, polymethylpentene, carbonized) Polyolefin resin having a structure in which a part of hydrogen is substituted with cyano group or halogen such as fluorine or chlorine), styrene resin, polyvinyl alcohol resin, polyether resin (polyether ether ketone, polyacetal, phenol resin, melamine) Resin, urea resin, epoxy resin, modified polyphenylene ether, aromatic polyether ketone, etc.), polyester resin (polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, Ribylene naphthalate, polycarbonate, polyarylate, wholly aromatic polyester resin, unsaturated polyester resin, etc.), polyimide resin, polyamideimide resin, polyamide resin (for example, aromatic polyamide resin, aromatic polyetheramide resin, nylon) Resin), nitrile group-containing resin (eg, polyacrylonitrile), urethane resin, epoxy resin, polysulfone resin (polysulfone, polyethersulfone, etc.), fluorine resin (polytetrafluoroethylene, polyvinylidene fluoride) Etc.), cellulose resin, polybenzimidazole resin, acrylic resin (for example, polyacrylonitrile resin copolymerized with acrylic acid ester or methacrylic acid ester, acrylonitrile and vinyl chloride) Or a known organic resin such as a modacrylic resin copolymerized with vinylidene chloride), a known non-conductive inorganic compound such as glass, alumina, or silica, or an oxide of a non-conductive inorganic compound. be able to.

These organic resins may be either a linear polymer or a branched polymer, and the polymer may be a block copolymer or a random copolymer, and the polymer has a three-dimensional structure or crystallinity. Anything is not particularly limited.
Further, organic resins other than those exemplified above can be used, and two or more organic resins including those other than those exemplified may be used.

  In addition, when the separator for electrochemical elements which comprises an electrochemical element is equipped with the ion-permeable support body containing a thermoplastic resin, when an electrochemical element heat | fever-generates or is heated, it will be melted thermoplastic resin By closing the micropores of the ion-permeable support, the micropores of the separator for electrochemical devices can be closed at the initial stage when the internal temperature of the electrochemical device rises, resulting in an electrochemical device separator having shutdown performance. preferable.

In addition, since the polyolefin resin is electrochemically stable and stable with respect to the electrolytic solution, it is more preferable to be a separator for an electrochemical element provided with an ion-permeable support including a polyolefin resin as a thermoplastic resin. preferable. Furthermore, the ion-permeable support containing the polyolefin resin makes it easier for the inorganic resin to be supported on the ion-permeable support by the polyolefin resin particles, and the inorganic particles are effectively removed from the separator for electrochemical devices. Therefore, it is possible to prevent a portion where inorganic particles are present non-uniformly in the separator for an electrochemical element.
In particular, when the ion-permeable support is composed only of a polyolefin-based resin, the above-described effect is effectively exhibited, and is most preferable.

Although the mass percentage of the thermoplastic resin in the mass of the ion-permeable support can be adjusted as appropriate, it is preferably 5 to 100% by mass, for example.
Further, the melting point of the thermoplastic resin should be appropriately adjusted and is not limited. However, when a separator for an electrochemical element having shutdown performance is required, it is 160 ° C. or lower. Is preferable, it is more preferably 150 ° C. or less, and most preferably 140 ° C. or less.
In addition, melting | fusing point as used in the field of this invention means the temperature of the peak of the melting peak in the differential thermal analysis curve (DTA curve) obtained by using for the differential thermal analysis prescribed | regulated to JISK7121.

In addition, when the electrochemical element generates heat or is heated, the ion-permeable support is prevented from unintentionally deforming to cause an internal short circuit, so that the above-described thermoplastic resin melts in the ion-permeable support. A component that does not melt or disappear at temperature (hereinafter referred to as a heat-resistant component) may be included.
Examples of the heat-resistant component include organic polymers having a melting point or glass transition temperature higher than those of the above-described thermoplastic resins, and inorganic fibers such as glass fibers.

  The constituent fibers of the fabric that can constitute the ion-permeable support are, for example, melt spinning method, dry spinning method, wet spinning method, direct spinning method (melt blow method, spunbond method, electrostatic spinning method, etc.), composite fiber, etc. It can be obtained by a known method such as a method of extracting a fiber having a small fiber diameter by removing one or more kinds of resin components, or a method of obtaining a divided fiber by beating a fiber.

  The constituent fibers of the fabric may be composed of one kind or plural kinds of components. As a fiber comprising a plurality of types of components, for example, a composite fiber such as a core-sheath type, a sea-island type, a side-by-side type, or an orange type can be used.

In addition, when an ion-permeable support is prepared using a composite fiber having a part of the thermoplastic resin exposed on the surface, the presence of the thermoplastic resin around the micropores of the ion-permeable support allows the It is preferable that the micropores are easily blocked by the thermoplastic resin melted from the periphery of the pores. As such a composite fiber having a part of the thermoplastic resin exposed on the surface, for example, a core-sheath type composite fiber in which the sheath component contains a thermoplastic resin, a sea-island type composite fiber in which the sea component contains a thermoplastic resin, etc. Can be mentioned.
In addition, you may prepare the fabric by mixing the fiber which contains a thermoplastic resin, and the fiber which does not contain a thermoplastic resin.

The woven fabric or knitted fabric can be prepared by weaving or knitting the fibers prepared as described above.

  Moreover, when a fabric is a nonwoven fabric, a dry method, a wet method, etc. can be used as a preparation method of the fiber web which can manufacture a nonwoven fabric, for example. In particular, it is preferable to prepare a fiber web using a wet method because a separator for an electrochemical element that hardly causes a short circuit can be produced due to uniform fiber distribution and apertures.

As a method of combining the fibers constituting the fiber web into a non-woven fabric, for example, a method of entanglement with a needle or a water flow, a method of integrating the fibers with a binder, or a fiber in which the fiber web is provided with a thermoplastic resin. When it contains, the method of fuse | melting the said thermoplastic resin by heat-processing a fiber web and integrating fibers can be mentioned.
In addition, as a method of heat-processing a fiber web, the method of using for a well-known apparatus, such as a heating roller, a hot air dryer, a hot air dryer, an electric furnace, a heat plate, an infrared heating dryer, can be mentioned, for example.

Moreover, you may prepare a nonwoven fabric by collecting the fiber spun using the direct spinning method.

The fabric prepared as described above can be used as a single product or a laminate of a plurality of sheets to form a separator for an electrochemical element. Alternatively, a separator for an electrochemical element can be configured using a laminate of a plurality of types of fabrics.

When the ion-permeable support is a microporous film or foam, for example, a resin containing a molten thermoplastic resin is poured into a mold and subjected to a known method such as foaming treatment. A support can be prepared.

  The diameter of the micropores in the ion-permeable support is not particularly limited and may be adjusted as appropriate. However, the separator for an electrochemical device comprising an ion-permeable support having micropores with a large diameter has non-uniform inorganic particles. There is a tendency that portions existing in

  Therefore, the diameter of the micropores is preferably smaller than 30 μm, more preferably smaller than 20 μm, and most preferably smaller than 15 μm. The lower limit of the diameter of the micropores is appropriately prepared and should not be limited, but it is realistic to be 10 nm or more.

The diameter of the micropore in the ion-permeable support referred to in the present invention is obtained by subjecting the ion-permeable support to a Perm-Porometer device manufactured by PMI and measuring it based on the bubble point method (ASTMF 316-86, JIS K3832). Value. That is, the measurement is performed 5 times, and the individual pore size distributions obtained by the measurement are arranged in the order of narrow pore size distribution width, and the cumulative value 50 in the plot data showing the third narrow pore size distribution width is 50. The value of the pore size distribution at the% point is defined as the diameter of the micropores in the ion-permeable support.

Various characteristics such as basis weight and thickness of the ion-permeable support are not particularly limited, but the basis weight of the ion-permeable support is preferably 5 to 15 g / m ² , and 6 to 13 g. / ^m, more preferably from ^2, most preferably a 8-12 g / ^{m 2.} The thickness of the ion-permeable support is preferably 10 to 50 μm, more preferably 15 to 40 μm, and most preferably 20 to 30 μm.

The slurry of the present invention is a mixture of inorganic particles and polyolefin resin particles in a dispersion medium. As a dispersion medium constituting the slurry, for example, pure water (for example, A1-A4 grade water specified in JISK0557), Alcohols etc. can be used alone or in combination. And the method of providing a slurry to an ion-permeable support is not particularly limited, but the following method can be adopted as an example.

1. A method of spraying slurry onto one or both main surfaces of an ion-permeable support,
2. A method of immersing an ion-permeable support in a slurry;
3. A method of adhering the foamed slurry to one main surface or both main surfaces of the ion-permeable support,
4). Known methods such as coating a slurry on one or both main surfaces of an ion-permeable support using a known coating method (for example, a kiss coating method using a gravure roll, a die coating method, etc.) The method can be selected as appropriate.

  The viscosity of the slurry when applying the slurry to the ion-permeable support is not particularly specified, but when applying the slurry to the main surface of the ion-permeable support using a gravure roll, It is preferable to adjust the viscosity of the slurry so that the viscosity when the shear rate is 100 (unit: 1 / s) is 0.01 to 1 Pas, and the viscosity of the slurry is 0.01 to 0.1 Pas. It is more preferable to adjust.

Moreover, you may provide the slurry which heated or cooled to the ion-permeable support body. The temperature of the slurry at this time (in other words, the temperature of the inorganic particles and the polyolefin resin particles) can be, for example, 5 ° C. to 50 ° C., 20 ° C. to 40 ° C., and 25 ° C. to 25 ° C. It can be 35 degreeC.

  As a method for removing the dispersion medium after applying the slurry to the ion-permeable support, a method of leaving the ion-permeable support provided with the slurry at room temperature (25 ° C.), an ion-permeable support provided with the slurry Known methods such as a method of exposing under reduced pressure and a method of exposing the ion-permeable support provided with slurry to an atmosphere at a temperature higher than the temperature at which the dispersion medium can be volatilized can be used.

Examples of the heating means include known devices such as a heating roller, a hot air dryer, a hot air dryer, an electric furnace, a heat plate, and an infrared heating dryer. The heating temperature can be selected as appropriate, but if heated at a temperature equal to or higher than the melting point of the ion-permeable support, clogging of micropores or the like occurs.

Whether or not the inorganic particles and the polyolefin resin particles of the present invention are dispersed in the slurry can be confirmed by the method described below.
1. The prepared slurry is visually checked to determine whether aggregates are present.
When aggregates are present in the slurry, it means that the inorganic particles and polyolefin resin particles of the present invention are not dispersed in the slurry. Moreover, when the aggregate does not exist in a slurry, it means that the inorganic particle and polyolefin resin particle of this invention disperse | distribute in a slurry.
2. The viscosity of the slurry that has been visually confirmed to be free of aggregates is measured.

For example, when the aggregate formed in the slurry is physically crushed and refined and diffused in the slurry, the inorganic particles of the present invention and the polyolefin-based resin can be obtained only by visually confirming the prepared slurry. It may be difficult to confirm whether the particles are dispersed.
Therefore, among the slurries that have been confirmed to be free of agglomerates by visual inspection, those that are suspected of having agglomerates in the slurry are subjected to the following (viscosity measurement method). Thus, it is determined whether or not the inorganic particles and polyolefin resin particles of the present invention are dispersed in the slurry.

(Measurement method of viscosity)
2 ml of the prepared slurry was subjected to a viscometer (Rheo Stress 6000 manufactured by Thermo scientific, plate shape: cone type with a diameter of 60 mm, measurement temperature: 25 ° C., gap: 0.103 mm), and the value of the obtained stress (N) was The viscosity (Pas) of the slurry is calculated by substituting into the following equation.
・ Shear rate (1 / s) = plate speed (m / s) × gap (m)
・ Shear stress (Pa) = stress (N) / plate area (m ² )
Viscosity (Pas) = shear stress (pa) / shear rate (1 / s)
And the behavior of the viscosity change during the acceleration of the plate speed from 10 ⁻⁷ (m / s) to 10 ⁻¹ (m / s), and then the plate speed from 10 ⁻¹ (m / s) to 10 ^−7. The behavior of the viscosity change during deceleration to (m / s) is measured.

  As a result of measuring the viscosity of the slurry, the behavior of the viscosity change during acceleration of the plate speed (for example, the behavior disclosed in FIG. 1) and the behavior of the viscosity change during deceleration of the plate speed (for example, In the case where the behavior disclosed in FIG. 2 shows a similar behavior, the inorganic particles present in the slurry during acceleration of the plate speed and subsequent deceleration of the plate speed. And the change of the aspect of the polyolefin resin particles are prevented, and the combination of the inorganic particles and the polyolefin resin particles is a combination that hardly forms an agglomerate, and is a combination that is dispersed in the slurry. It means that.

On the other hand, as a result of measuring the viscosity of the slurry, the behavior of the viscosity change while the plate speed is accelerated (for example, the behavior disclosed in FIG. 3) and the behavior of the viscosity change while the plate speed is decelerated. If (for example, the behavior disclosed in FIG. 4) shows a different mode of behavior, it is present in the slurry while accelerating the plate speed and subsequently decelerating the plate speed. This means that the aspect of the inorganic particles and the polyolefin resin particles changed, and the combination of the inorganic particles and the polyolefin resin particles is a combination that easily forms an aggregate and is a combination that does not disperse in the slurry. Means that.

1-4, the horizontal axis is the shear rate (1 / S, indicated as GP [1 / S] in the graph), and the vertical axis is the shear stress (Pa, indicated as Tau [Pa] in the graph). ) And viscosity (Pas, indicated as Eta [Pas] in the graph). In addition, the graph represented by the white triangle and inverted white triangle markers represents the behavior of the shear stress (Pa) accompanying the fluctuation of the shear rate (1 / S), and is represented by the black circle and black rhombus markers. Represents the behavior of the viscosity (Pas) accompanying the fluctuation of the shear rate (1 / S).

Examples of the combination of inorganic particles and polyolefin resin particles of the present invention include a combination of silica particles and polyolefin resin A particles, a combination of alumina particles and polyolefin resin B particles, and the like.

Although not characteristics will be particularly restricted, such as basis weight and thickness of the separator for an electrochemical device, the basis weight of the separator for an electrochemical element is preferably from ^{5g / m 2 ~60g / m 2} , 10g / ^m, more preferably from 2 to 50 g / ^{m 2,} and even most preferably 15 g / m 2 to 40 g / ^{m 2.} In the present invention, the basis weight refers to the mass per 1 m ² of area on the main surface.

The thickness of the separator for an electrochemical element is not particularly limited, but a thin separator for an electrochemical element tends to improve the discharge characteristics of the electrochemical element, but tends to be inferior in the performance of preventing an internal short circuit. On the other hand, thick separators for electrochemical devices tend to be inferior in discharge characteristics, although they tend to be excellent in performance of preventing internal short circuits.
Therefore, the thickness of the separator for electrochemical elements is preferably 10 μm to 80 μm, more preferably 20 μm to 60 μm, and most preferably 20 μm to 40 μm. In the present invention, the thickness is 5 thicknesses measured at a load of 500 g, measured with a thickness measuring instrument (Digimatic standard outer micrometer (MCC-MJ / PJ) 1/1000 mm, Mitutoyo Corporation). This is the arithmetic average value.

  The mass of the inorganic particles included in the separator for electrochemical elements may be any separator for electrochemical elements that can prevent the occurrence of internal short circuit in the electrochemical element and improve the discharge characteristics of the electrochemical element. Adjust appropriately according to the type and shape.

However, the value obtained by dividing the mass (g / m ² ) of the inorganic particles applied to the separator for electrochemical elements by the specific gravity (g / cm ³ ) of the substance constituting the inorganic particles is 1 to 1 per 1 m ² . It is preferable to apply inorganic particles to the separator for electrochemical elements so as to be within the range of 8, since the heat resistance of the separator for electrochemical elements tends to be improved. The range is more preferably in the range of 2-6, and most preferably in the range of 3-5.

  Further, the mass of the polyolefin resin particles provided in the separator for an electrochemical element varies depending on the mass and the particle size of the inorganic particles applied to the ion-permeable support, and is not particularly limited and is appropriately adjusted. However, if the mass of the polyolefin resin particles applied to the separator for electrochemical devices is too small, the inorganic particles are likely to fall off from the separator for electrochemical devices, and the inorganic particles are unevenly present in the separator for electrochemical devices. Tend to occur. On the other hand, if the mass of the polyolefin resin particles applied to the separator for electrochemical devices is too large, the pores of the separator for electrochemical devices are likely to be blocked by the polyolefin resin particles, resulting in a high resistance between the electrodes. In addition, the electrochemical element may not exhibit desired discharge characteristics and may deteriorate.

Therefore, the mass (g / m ² ) of the polyolefin resin particles included in the electrochemical element separator is adjusted to 1 to 10% by mass with respect to the inorganic particles included in the electrochemical element separator. It is preferable to prepare such that it is 2 to 5% by mass.

The electrochemical element prepared using the electrochemical element separator of the present invention can be composed of the same material as the conventional one. Specifically, in the case of a lithium ion secondary battery, as a positive electrode, for example, a lithium or sodium-containing transition metal compound or a slurry of a sulfur compound supported on a current collector can be used, and as a negative electrode, For example, lithium metal and materials that can be alloyed with lithium (for example, materials such as tin alloys and silicon alloys), and polyacene and carbon materials that can occlude and release lithium (for example, carbon, natural graphite, and artificial graphite) , A vanadium compound, a lithium titanate compound supported on a current collector, and the like can be used. As an electrolyte, for example, a non-aqueous electrolyte (for example, LiPF _{6 in} a mixed solvent of ethylene carbonate and diethyl carbonate is used. A dissolved electrolytic solution) or the like can be used. Further, the cell structure of the lithium ion secondary battery that can be prepared is not particularly limited, and can be, for example, a cylindrical shape, a square shape, a coin shape, or the like.

EXAMPLES Hereinafter, the present invention will be specifically described by way of examples, but these do not limit the scope of the present invention.

Example 1
70% by mass of a core-sheath composite fiber (fineness: 0.8 dtex, fiber length: 10 mm) having a core component of polypropylene (melting point: 170 ° C.) and a sheath component of polyethylene (melting point: 135 ° C.), and a polypropylene extra fine fiber (melting point: 160 ° C., fiber diameter: 2 μm, fiber length: 2 mm) and 30% by mass were mixed, and a fiber web was prepared by a wet papermaking method.
Thereafter, the fiber web was treated with hot air at a temperature of 140 ° C. for 10 seconds, and then subjected to a roll calender at 80 ° C., whereby a wet nonwoven fabric (micropore diameter: 11 μm, thickness: 26 μm, basis weight: 10 g / m ² ) Was prepared.

Next, silica particles (manufactured by Admatechs Co., Ltd., product number: SO-C1, particle size (D ₅₀ ): 250 nm, shape: true spherical shape) 97% by mass as inorganic particles, and a dispersion of polyolefin resin particles ( Unitika Co., Ltd., product number: SB-1200, melting point: 100 ° C., particle size (D ₅₀ ): 90 nm, solid content mass of polyolefin resin in the dispersion: 3% by mass is mixed with pure water. Then, stirring was performed at 1200 rpm for 1 hour using a disper type stirring blade, and a slurry having a solid content concentration of 50 mass% was prepared. As a result of visual confirmation, no aggregates were formed in the slurry.

And the said slurry adjusted to 25 degreeC was coated to one main surface of the wet nonwoven fabric prepared as mentioned above by the kiss coater method using a gravure roll. Thereafter, the wet nonwoven fabric coated with the slurry is subjected to an IR heater, and then subjected to a heating apparatus equipped with a floating dryer to remove pure water, and silica particles and polyolefin resin particles are supported on the wet nonwoven fabric. A separator for an electrochemical element (thickness: 30 μm, basis weight: 26 g / m ² ) was produced.

(Example 2)
Silica particles as inorganic particles, except for using (manufactured by Admatechs Co., No.: SO-C2, the particle diameter _(D 50):: 450 nm, shape spherical shape), in the same manner as in Example 1, A separator for an electrochemical element (thickness: 30 μm, basis weight: 26 g / m ² ) was produced. As a result of visual confirmation, no aggregates were formed in the slurry.

(Example 3)
Silica particles as inorganic particles were prepared by grinding (manufactured by Admatechs Co., No.: SO-C6, particle diameter _(D 50):: 2000 nm, shape spherical shape), ground silica particles (particle diameter (D ₅₀ ): 1000 nm, shape: amorphous shape) was used in the same manner as in Example 1 to produce an electrochemical element separator (thickness: 30 μm, basis weight: 26 g / m ² ). As a result of visual confirmation, no aggregates were formed in the slurry.

Example 4
70% by mass of polyethylene terephthalate fiber (melting point: 220 ° C., fineness: 0.8 dtex, fiber length: 10 mm), and 30% by mass of low melting point polyethylene terephthalate fiber (melting point: 170 ° C., fineness: 0.8 dtex, fiber length: 10 mm) And a fiber web was prepared by a wet papermaking method.
Thereafter, the fiber web was treated with hot air at a temperature of 200 ° C. for 10 seconds to prepare a wet nonwoven fabric (micropore diameter: 14 μm, thickness: 20 μm, basis weight: 10 g / m ² ).
A separator for an electrochemical element (thickness: 27 μm, basis weight: 26 g / m ² ) was produced in the same manner as in Example 1 except that the wet nonwoven fabric prepared in this way was used.

(Example 5)
As inorganic particles, alumina particles (manufactured by Admatechs Co., Ltd., product number: AO-802, D ₅₀ = 800 nm, shape: true spherical shape) 97% by mass and a dispersion of polyolefin resin particles (manufactured by Unitika Ltd., product number) : CB-1200, melting point: 102 ° C., particle size (D ₅₀ ): 90 nm, solid content mass of polyolefin resin in the dispersion: 23 mass%) 3% by mass was mixed with pure water, and the solid content concentration was A 55% by mass slurry was prepared. As a result of visual confirmation, no aggregates were formed in the slurry.

Then, a separator for an electrochemical element (thickness: 30 μm, basis weight: 35 g / m ² ) was produced in the same manner as in Example 1 except that the prepared slurry was used.

(Example 6)
Except for using alumina particles (manufactured by Showa Denko KK, product number: AL-45-A, particle diameter (D ₅₀ ): 700 nm, shape: irregular shape) as inorganic particles, A separator for an electrochemical element (thickness: 35 μm, basis weight: 35 g / m ² ) was produced. As a result of visual confirmation, no aggregates were formed in the slurry.

(Comparative Example 1)
Silica particles (manufactured by Admatechs Co., Ltd., product number: SO-C1, particle size (D ₅₀ ): 250 nm, shape: true spherical shape) 97% by mass as inorganic particles, SBR particles (manufactured by Zeon Corporation, product number) : BM-400, particle size _(D 50): 120nm) to 3 wt% were mixed in pure water, the solid content concentration to prepare a 50 wt% slurry. As a result of visual confirmation, no aggregates were formed in the slurry.
Then, a separator for an electrochemical element (thickness: 30 μm, basis weight: 26 g / m ² ) was produced in the same manner as in Example 1 except that the prepared slurry was used.

(Comparative Example 2)
As inorganic particles, alumina particles (manufactured by Admatechs Co., Ltd., product number: AO-802, particle diameter (D ₅₀ ): 800 nm, shape: true spherical shape) 97% by mass, SBR resin particles (manufactured by Zeon Corporation, No.: BM-400, particle size _(D 50): 120nm) to 3 wt% were mixed in pure water, the solid content concentration to prepare a 50 wt% slurry. In addition, when visually confirmed, aggregates were formed and precipitated in the slurry.
When coating was performed using the prepared slurry, agglomerates were formed in the slurry during coating, and coating was impossible. Therefore, in Comparative Example 2, an electrochemical element separator could not be manufactured.

(Comparative Example 3)
Silica particles (manufactured by Admatechs Co., Ltd., product number: SO-C1, particle size (D ₅₀ ): 250 nm, shape: true spherical shape) 97% by mass as inorganic particles and a dispersion of polyolefin resin particles (Unitika Co., Ltd.) Made by company, product number: CB-1200, melting point: 102 ° C., particle size (D ₅₀ ): 90 nm, solid content mass of polyolefin resin in dispersion: 23% by mass) 3% by mass was mixed with pure water, A slurry having a solid content concentration of 50% by mass was prepared. In addition, when visually confirmed, aggregates were formed and precipitated in the slurry.

Then, the slurry prepared as described above was subjected to a homogenizer, whereby the aggregates that had been precipitated were physically crushed and finely dispersed in the slurry. In addition, when the slurry which performed the homogenizer process was confirmed visually, presence of the aggregate was not confirmed in the slurry.

A separator for an electrochemical element (thickness: 30 μm, basis weight: 26 g / m ² ) was produced in the same manner as in Example 1 except that the slurry thus prepared was used.

  The slurry prepared in Comparative Example 3 was subjected to the above-described (Measurement Method of Viscosity). Moreover, in order to compare with the result of Comparative Example 3, the slurry prepared in Example 1 was subjected to the above-described (viscosity measurement method) as a reference.

A graph summarizing the behavior of the viscosity of the slurry used in Example 1 while increasing the shear rate from the static state is shown in FIG. Moreover, about the slurry used in Example 1, the graph which summarized the behavior of the viscosity change while reducing the shear rate from the high shear rate to the static state is illustrated in FIG.
And about the slurry used by the comparative example 3, the graph which put together the behavior of the viscosity change while making the shear rate increase the slurry from a static state is illustrated in FIG. FIG. 4 is a graph summarizing the behavior of the viscosity of the slurry used in Comparative Example 3 while reducing the shear rate from a high shear rate to a static state.

1-4, the horizontal axis is the shear rate (1 / S, indicated as GP [1 / S] in the graph), and the vertical axis is the shear stress (Pa, indicated as Tau [Pa] in the graph). ) And viscosity (Pas, indicated as Eta [Pas] in the graph). In addition, the graph represented by the white triangle and inverted white triangle markers represents the behavior of the shear stress (Pa) accompanying the fluctuation of the shear rate (1 / S), and is represented by the black circle and black rhombus markers. Represents the behavior of the viscosity (Pas) accompanying the fluctuation of the shear rate (1 / S).

As a result of measuring the viscosity of the slurry used in Example 1 from FIG. 1-2, the behavior of the viscosity change while accelerating the plate speed is the same as the behavior of the viscosity change while decelerating the plate speed. The behavior was shown. Therefore, it was found that the combination of inorganic particles and polyolefin resin particles used in Example 1 is a combination that hardly forms an aggregate in the slurry at any shear rate, that is, a combination that disperses in the slurry. .
As a result of measuring the viscosity of the slurry used in Comparative Example 3 from FIG. 3-4, the behavior of the viscosity change during acceleration of the plate speed and the behavior of the viscosity change during deceleration of the plate speed are different. The behavior was shown. Therefore, the combination of inorganic particles and polyolefin resin particles used in Comparative Example 3 is a combination that easily forms aggregates in the slurry when the shear rate is changed, that is, a combination that does not disperse in the slurry. There was found.

From each of the separators for electrochemical elements of Examples 1-6, Comparative Example 1 and Comparative Example 3 produced as described above, round test pieces having a diameter of 16 mm were collected, and the test pieces were used in the following manner. A lithium secondary battery was produced.

(Production of lithium ion secondary battery)
1. Preparation of positive electrode 87% by mass of spinel lithium manganate (LiMn ₂ O ₄ ) powder and 6% by mass of acetylene black were mixed therewith, and polyvinylidene fluoride (PVdF) dissolved in an N-methyl-2-pyrrolidone solution. A solution (manufactured by Kureha Chemical Co., Ltd., # 1120, PVdF concentration: 12% by mass) was added so that the dry mass ratio of PVdF was 7% by mass to obtain a mixed solution. Then, the positive electrode material paste was prepared by adding N-methyl-2-pyrrolidone solution to a liquid mixture and stirring with a defoaming stirrer so that the viscosity of the obtained liquid mixture might be 2000 cp.
The obtained positive electrode material paste was applied to one main surface of an aluminum foil (thickness: 20 μm), then heated at 80 ° C. for 2 hours, and then heated at 150 ° C. under reduced pressure for 6 hours. N-methyl-2-pyrrolidone was removed from the prepared positive electrode material paste.
And the positive electrode sheet (thickness: 90 micrometers) was prepared by pressing the aluminum foil which apply | coated the positive electrode material paste after a drying process with the linear pressure of 200 kg using the roll press machine.

2. Production of Negative Electrode A natural graphite powder and a polyvinylidene fluoride (PVdF) solution (manufactured by Kureha Chemical Co., Ltd., # 9130, PVdF concentration: 13% by mass) dissolved in an N-methyl-2-pyrrolidone solution having a mixing ratio of 90 % And 10% (dry weight of PVdF), and then the viscosity was adjusted appropriately while adding the N-methyl-2-pyrrolidone solution and stirred with a defoaming stirrer to prepare a negative electrode material paste.
The obtained negative electrode material paste was applied to one main surface of a copper foil (thickness: 15 μm), dried at 80 ° C. for 2 hours, and then heated at a reduced pressure of 150 ° C. for 6 hours. N-methyl-2-pyrrolidone was removed from the negative electrode material paste.
And the negative electrode sheet (thickness: 70 micrometers) was prepared by pressing the copper foil which apply | coated the negative electrode material paste after a drying process with the linear pressure of 200 kg using the roll press machine.

3. Preparation of non-aqueous electrolyte solution LiPF ₆ was dissolved to a concentration of 1 mol / L in a mixed solvent prepared by mixing ethylene carbonate and diethyl carbonate so that the volume ratio was (50:50), A non-aqueous electrolyte solution was prepared.

4). Assembly of Lithium Ion Secondary Battery Each collected specimen was immersed in the non-aqueous electrolyte solution prepared as described above.
Next, the test piece impregnated with the electrolytic solution is laminated on the main surface side of the positive electrode sheet coated with the positive electrode material paste, and the test piece immersed in the electrolytic solution is coated on the main surface side of the negative electrode sheet coated with the negative electrode material paste. By stacking as described above, a lithium ion secondary battery (2030 type coin cell) using each test piece was produced.

Each lithium ion secondary battery prepared as described above was allowed to stand at room temperature (25 ° C.) for one day, and then charged with a constant current to a final voltage of 4.2 V over 5 hours, and then over 5 hours. A constant current discharge was performed. This charging / discharging was performed 10 cycles.
Thereafter, the battery was charged with a constant current to a final voltage of 4.2 V over 5 hours, then charged with a constant voltage until the charge current value reached 0.02 mA, and discharged to 3.0 V over a period of 1/4 hour. This charge / discharge was performed as 5 cycles for 5 cycles.

(Measurement method of capacity maintenance rate)
In each lithium ion secondary battery that was charged and discharged as described above, the ratio of the discharge capacity at the fifteenth cycle to the discharge capacity at the fifteenth cycle was converted into a percentage, whereby the capacity retention rate ( %) Was calculated.

In addition, about the lithium ion secondary battery prepared using the separator for electrochemical elements which concerns on the comparative example 3, since the internal short circuit generate | occur | produced in the middle of charging / discharging in the measurement of a capacity | capacitance maintenance factor (%), charging / discharging became impossible. The capacity retention rate (%) could not be calculated.
The reason for this is that in Comparative Example 3, a slurry for forming an agglomerate was applied to a wet nonwoven fabric to produce a separator for an electrochemical element, which resulted in a portion in which silica particles were non-uniformly present in the separator for an electrochemical element. It was thought that it was because of it.
Further, the lithium ion secondary battery prepared using the electrochemical device separator according to Comparative Example 3 will be described below because the positive electrode and the negative electrode are connected due to an internal short circuit. The cell resistance (Ω) was not measured.

(Measurement method of cell resistance)
Each lithium ion secondary battery after being subjected to the above-described (Method for measuring high rate discharge characteristics) was heated from room temperature (25 ° C.) to 200 ° C. at a temperature rising rate of 5 ° C./min. The resistance value (cell resistance value (Ω) between the positive electrode and the negative electrode when an alternating current of ± 0.01 V (1 KHz) was passed through each lithium ion secondary battery at room temperature (25 ° C.) and 200 ° C. )) Was measured.
In addition, when the value of cell resistance (Ω) increases when the lithium ion secondary battery is heated from room temperature (25 ° C.) to 200 ° C., the separator for an electrochemical element constituting the lithium ion secondary battery This means that the micropores are closed by the melted polyolefin-based ion-permeable support and are in a state where ions are difficult to pass through (a state in which the shutdown performance is exhibited).
And the larger the increase value of the cell resistance (Ω) means that the electrochemical device separator has more excellent shutdown performance.

Table 1 shows the capacity retention ratio (%) and the cell resistance value (Ω) of the lithium ion secondary battery according to Example 1-6 and the lithium ion secondary battery according to Comparative Example 1 measured as described above. Summarized in

The lithium ion secondary battery prepared using the electrochemical device separator according to Example 1-6 can be charged / discharged without causing an internal short circuit during charging, and the electrochemical device separator according to Comparative Example 1 is used. It was found that the lithium ion secondary battery had a higher capacity retention rate (%) than the lithium ion secondary battery prepared by using the battery.

As described above, the electrochemical element separator of the present invention is an electrochemical element separator that can prevent an internal short circuit from occurring in the electrochemical element and can prepare an electrochemical element that is excellent in capacity retention.

In addition, the lithium ion secondary battery according to Example 1 increased the resistance value between the electrodes by 197.9Ω when heated from 25 ° C. to 200 ° C., whereas the lithium ion secondary battery according to Example 4 When the ion secondary battery was heated from 25 ° C. to 200 ° C., the resistance value between the electrodes increased only by 7.8Ω.
That is, the electrochemical element separator according to Example 1 is more excellent than the electrochemical element separator according to Example 4 because the increase in cell resistance (Ω) when heated from 25 ° C. to 200 ° C. is larger. It was found to be a separator for electrochemical devices having a shutdown performance.
The reason for this was considered that the electrochemical element separator according to Example 1 was provided with an ion-permeable support including a polyolefin resin.

  The separator for electrochemical elements of the present invention can be used, for example, as a separator for electrochemical elements such as alkaline batteries, lithium batteries or capacitors.

Claims (1)

A separator for an electrochemical element in which inorganic particles and polyolefin resin particles are supported on an ion-permeable support including a polyolefin resin having a melting point of 150 ° C. or less. The inorganic particles and the polyolefin resin particles are Or a combination of a silica particle and a polyolefin-based resin having a compound structure represented by any of the following structural formulas as a copolymer unit, or an alumina particle and an unsaturated carboxylic acid or a compound derived from an unsaturated carboxylic acid. Electrochemical composition comprising a combination of chlorinated polyolefin-based resin which is provided as a polymerization unit and contains chlorine, and wherein the ion-permeable support is composed of a single fabric or a combination of fabrics selected from non-woven fabrics, woven fabrics and knitted fabrics. Element separator.
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