JP6343468B2 - Electrochemical element separator and electrochemical element - Google Patents

Description

  The present invention relates to a separator for an electrochemical element that can constitute an electrochemical element excellent in safety and can suppress an increase in air permeability resistance, and an electrochemical element having the separator for an electrochemical element.

  Electrochemical elements such as lithium ion secondary batteries are used in various applications such as mobile phones, notebook computers, electric vehicles, large storage batteries for power supplies, etc., due to the need for longer power supply time and increased output. There are demands for higher capacity, higher energy density, higher voltage, and the like. Electrochemical elements also have a strong demand for safety measures because the risk of thermal runaway such as abnormal heat generation increases with increasing energy density.

  For example, an electrochemical device has a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte as main members, and the separator is made of an insulating porous film and is disposed between the positive electrode and the negative electrode. By separating, it prevents the internal short circuit of the battery, and plays a role of allowing ions in the non-aqueous electrolyte to permeate through the through hole.

  Since most of the thermal runaway of the electrochemical element is triggered by an internal short circuit of the battery, it can be said that the functional addition to the separator occupies an important position in the safety measures of the electrochemical element. As a function to the separator considering the safety of the electrochemical element, until now, when the battery generates heat, the separator melts when it exceeds the melting point of the thermoplastic resin such as polyolefin, which is a through hole. It is common to provide a shutdown function that suppresses further heat generation of the device by closing and closing the current.

  The temperature at which the separator performs the shutdown function is called the shutdown temperature. When the shutdown temperature is reached due to the battery temperature rise, the current is cut off by the shutdown function. However, even when the electrochemical device is safely stopped, the temperature does not immediately turn down after the shutdown temperature is reached, but the temperature starts to fall after the shutdown temperature is exceeded to some extent.

  Separators used in electrochemical elements such as lithium ion secondary batteries are usually microporous membranes (microporous membranes) made of thermoplastic resin, and are uniaxially stretched or biaxially to improve porosity and strength. Stretching has been performed. Due to this stretching, the microporous film is distorted, and this may cause film breakage due to thermal contraction when the temperature of the element rises. This film breakage can occur in a very close temperature range, although it is higher than the shutdown temperature.

  The separator using only the microporous film as described above exhibits a shutdown function and cuts off the current after reaching the shutdown temperature due to the temperature rise of the element. However, due to the above circumstances, the temperature of the element continues to rise while the speed decreases. When the temperature at which the separator breaks due to thermal contraction is reached, this breakage occurs, which may cause an internal short circuit due to contact between the positive electrode and the negative electrode.

  For this reason, attempts have been made to further improve the safety of electrochemical elements such as lithium ion secondary batteries by imparting higher functions to the separator. For example, Patent Document 1 mainly includes a base material layer (I) composed of a microporous film mainly composed of a thermoplastic resin, a filler layer (II) mainly composed of an inorganic filler, and particles of a low melting point resin. A lithium ion secondary comprising a separator having a resin layer (III), a filler layer (II) disposed on one surface of the substrate layer (I), and a resin layer (III) disposed on the other surface Batteries have been proposed.

  In the lithium ion secondary battery described in Patent Document 1, in the separator, for example, when a shutdown function is ensured by using polyolefin as a constituent resin of the base material layer (I), the heat resistance is supplemented by the filler layer (II). In addition, since the resin layer (III) serves as a margin for the shutdown function, it has high safety.

JP 2011-198532 A

  However, as described in Patent Document 1, when a layer containing particles of a low melting point resin is provided on the separator, the air resistance is likely to increase. In an electrochemical device using such a separator, There is a possibility that the ion permeability of the separator is lowered, and in this respect, the technique described in Patent Document 1 still has room for improvement.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an electrochemical element separator capable of constituting an electrochemical element excellent in safety and capable of suppressing an increase in air resistance, It is to provide an electrochemical element having a separator for an electrochemical element.

  The separator for an electrochemical element of the present invention that can achieve the above object is a microporous first separator layer mainly composed of a thermoplastic resin (A) and melted at a temperature lower than that of the thermoplastic resin (A). It has the 2nd separator layer containing the composite particle containing the thermoplastic resin (B) to perform and resin (C) other than the said thermoplastic resin (B), It is characterized by the above-mentioned.

  The electrochemical device of the present invention has a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, and the separator is the electrochemical device separator of the present invention.

  ADVANTAGE OF THE INVENTION According to this invention, the electrochemical element which can comprise the electrochemical element excellent in safety | security and can suppress the increase in an air permeability resistance, and the electrochemical element which has the said separator for electrochemical elements are provided. can do.

It is sectional drawing which represents typically an example of the separator for electrochemical elements of this invention. It is sectional drawing which represents typically the other example of the separator for electrochemical elements of this invention. It is sectional drawing which represents typically the other example of the separator for electrochemical elements of this invention. It is a graph which shows the measurement result of the resistance change of the separator for electrochemical elements of Example a2. It is a graph which shows the measurement result of the resistance change of the separator for electrochemical elements of comparative example b3. It is a longitudinal cross-sectional view which represents typically an example of the electrochemical element (lithium ion secondary battery) of this invention.

<Electrochemical element separator>
The separator for electrochemical elements of the present invention (hereinafter sometimes simply referred to as “separator”) has a multilayer structure having at least a first separator layer and a second separator layer.

<First separator layer>
A 1st separator layer becomes a base material of the separator of this invention, and the positive electrode and negative electrode which an electrochemical element has are mainly isolated by the 1st separator layer.

  The first separator layer is microporous and has many holes (communication holes) from one surface side to the other surface side. When the internal temperature of the electrochemical element using the separator of the present invention is equal to or higher than the melting point of the thermoplastic resin (A) constituting the first separator layer, the thermoplastic resin (A) is melted. Shutdown that blocks the pores of the first separator and suppresses the progress of the electrochemical reaction occurs.

  The first separator layer is mainly composed of the thermoplastic resin (A). The thermoplastic resin (A) has an electrical insulation property, an electrical insulation property, is stable with respect to the non-aqueous electrolyte held in the electrochemical device, and further has an operating voltage range of the electrochemical device. It is preferable to use an electrochemically stable material that is hardly oxidized and reduced. Specific examples of such thermoplastic resins include, for example, polyethylene (low density polyethylene (LDPE), high density polyethylene (HDPE), modified polyethylene (modified PE), etc.), polypropylene (PP), paraffin, wax, and copolymerization. Polyolefins such as polyolefins, polyolefin derivatives (such as chlorinated polyethylene), polyvinylidene chloride, polyvinyl chloride and fluororesins; polyvinyl alcohols; polyimides; aramids and the like. Further, as the copolymer polyolefin, ethylene-vinyl monomer copolymer (EVA), more specifically, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, ethylene-methyl acrylate copolymer, ethylene- Acrylic acid copolymers, ethylene-methacrylic acid copolymers, ethylene-vinyl alcohol copolymers, and the like can be mentioned. For the first separator layer, only one of the above-exemplified thermoplastic resins may be used, or two or more of them may be used in combination.

  As the thermoplastic resin (A), it is preferable to use a resin having a melting point of 125 ° C. or higher and 170 ° C. or lower among the thermoplastic resins exemplified above. In this case, the shutdown in the separator appears under more preferable conditions. The melting point of the resin as used herein means a melting temperature measured using a differential scanning calorimeter (DSC) in accordance with JISK7121.

  Further, two or more thermoplastic resins having different melting points are used in combination with the thermoplastic resin (A). More specifically, for example, a thermoplastic resin (A1) having a low melting point and a thermoplastic resin (A1). It is preferable to use in combination with a thermoplastic resin (A2) having a higher melting point than In the case of the first separator layer containing the thermoplastic resin (A1) and the thermoplastic resin (A2), after the shutdown occurs due to the melting of the thermoplastic resin (A1), the melting point of the thermoplastic resin (A2) is reached. Until then, the shape of the first separator layer (the shape of the separator) can be maintained. Therefore, even when the temperature of the electrochemical device continues to rise after the occurrence of shutdown, the state where the positive electrode and the negative electrode are isolated can be maintained, and the safety of the electrochemical device can be further improved. When the temperature in the electrochemical element exceeds the melting point of the thermoplastic resin (A2), the thermoplastic resin (A2) also melts, and the thermoplastic resin (A1) and the thermoplastic resin (A2) after melting. The shutdown function is enhanced by the formation of a thick layer formed by.

  When the thermoplastic resin (A1) and the thermoplastic resin (A2) are used in combination as the thermoplastic resin (A), the thermoplastic resin (A1) has a melting point of 125 ° C. in the exemplified thermoplastic resin. A thermoplastic resin (A2) having a melting point of 130 ° C. or higher and 200 ° C. or lower is used as the thermoplastic resin (A2). However, the thermoplastic resin (A2) has a melting point of 130 ° C. or higher and 200 ° C. or lower. It is preferable to use those having a high melting point. The melting point of the thermoplastic resin (A2) may be higher than that of the thermoplastic resin (A1), but for example, it is preferably higher by 10 ° C. than the melting point of the thermoplastic resin (A1).

  For the thermoplastic resin (A1), for example, one kind of thermoplastic resin having the above melting point may be used alone, or two or more kinds may be used in combination. The thermoplastic resin (A2) may be a single thermoplastic resin having the above melting point [however, a melting point higher than the melting point of the thermoplastic resin (A1) used in combination]. May be used in combination.

  In the first separator layer, when the thermoplastic resin (A1) and the thermoplastic resin (A2) are used in combination, for example, a layer composed of the thermoplastic resin (A1) [for example, a polyethylene (PE) layer] and It is composed of a thermoplastic resin (A2) on both sides of a layer composed of a thermoplastic resin (A2) (for example, a PP layer) and a layer composed of a thermoplastic resin (A1) (for example, a PE layer). A layer made of thermoplastic resin (A1) on both sides of a layer made of thermoplastic resin (A2) (eg PP layer) or a layer made of thermoplastic resin (A1) (eg PE layer) It is preferable to have a multilayer structure such as a three-layer structure. In this case, the above-mentioned effect by using the thermoplastic resin (A1) and the thermoplastic resin (A2) in combination can be ensured better.

  The first separator layer is mainly composed of the thermoplastic resin (A), and the content of the thermoplastic resin (A) [when a plurality of types of resins are used as the thermoplastic resin (A), the total content thereof. The same applies to the content of the thermoplastic resin (A) in the first separator layer. ] Is 50% by volume or more and 70% by volume or more in the total volume of the constituent components of the first separator layer (the total volume excluding the void portion. The same applies to the contents of the constituent components of the separator layers). It is preferable that it is 100 volume%, that is, it may be composed of only a thermoplastic resin.

  In addition to the thermoplastic resin (A), the first separator layer is a filler (for example, an inorganic filler contained in a third separator layer to be described later) or a fibrous material (for example, a fiber that can be used for a second separator layer to be described later). Or the like).

  For the first separator layer, a microporous film made of a thermoplastic resin used as a separator in an electrochemical element such as a normal lithium ion secondary battery, for example, a microporous film made of polyolefin can be used.

  As the microporous film, for example, one produced by a stretching method can be used. That is, the microporous film is formed as follows: after forming a fine pore by uniaxially or biaxially stretching a film or sheet formed using a thermoplastic resin (A) mixed with an inorganic filler or the like. It may be manufactured by removing the inorganic filler.

  Moreover, what was manufactured by the following void | hole formation method using a solvent can also be used for the said microporous film. That is, the microporous membrane is a film or sheet obtained by mixing the thermoplastic resin (A) with another resin or paraffin, and then, in a solvent that dissolves only the other resin or paraffin, It may be manufactured by dipping a film or sheet and dissolving only the other resin or paraffin to form pores.

  Furthermore, what was manufactured by the method which combined the said extending | stretching method and the void | hole formation method using the said solvent can also be used for the said microporous film.

  The degree of porosity of the first separator layer can be expressed as porosity. The porosity is an apparent volume (V) obtained from the thickness (t) × width (w) × length (l) of the first separator layer, and the actual occupancy of all components of the first separator layer. Using volume (v), it can be expressed as (V−v) / V. When the specific gravity of each component of the first separator layer is known, the mass of the first separator layer can be measured from the cut-out separator, and the actual volume (v) can be obtained from the specific gravity. When obtaining the apparent volume (V), the thickness of the first separator layer can be measured using, for example, a Mitutoyo Digimatic Indicator “547-401”. Moreover, when calculating | requiring a porosity by actual measurement, what is necessary is just to use an ultra pycnometer and a mercury porosimeter.

  The porosity of the first separator layer can suppress the increase in the air permeability resistance of the separator more favorably (that is, improve the ion permeability better), and can maintain the output of the electrochemical device using the same. From the viewpoint of doing so, it is preferably 30% or more, and more preferably 35% or more. Further, by limiting the porosity of the first separator layer, it is possible to better suppress the occurrence of internal short circuit in the electrochemical device using this separator, so the porosity of the first separator is 90%. Or less, more preferably 80% or less.

<Second separator layer>
The second separator layer according to the separator of the present invention is a composite particle containing a thermoplastic resin (B) that melts at a temperature lower than that of the thermoplastic resin (A) and a resin (C) other than the thermoplastic resin (B). It is porous and has ion permeability.

  Since the thermoplastic resin (B) related to the composite particles contained in the second separator layer melts at a temperature lower than that of the thermoplastic resin (A) related to the first separator layer, electrochemical using the separator of the present invention When the internal temperature of the element rises, first, the thermoplastic resin (B) melts and shuts down the pores of the separator, thereby suppressing further temperature rise of the electrochemical element. And when the suppression of the temperature rise of the electrochemical element due to the shutdown of the thermoplastic resin (B) is not sufficient, the thermoplastic resin (A) according to the first separator layer is melted to cause the shutdown, thereby causing the electrochemical Suppresses further temperature rise of the device.

  As described above, in the electrochemical device using the separator of the present invention, shutdown occurs in a plurality of stages, and the temperature rise can be suppressed in a plurality of stages. Therefore, due to the melting of the thermoplastic resin (A) in the first separator layer. It is possible to prevent contact between the positive electrode and the negative electrode due to the internal temperature of the electrochemical element rising excessively before the shutdown sufficiently proceeds and the entire separator thermally contracts and breaks.

  Further, if the shutdown function by the separator is to be ensured only by the thermoplastic resin (B), for example, even if the thermoplastic resin (B) melts due to the temperature rise in the electrochemical element and the shutdown occurs, If the temperature rise continues further, the thermoplastic resin (B) closing the pores of the separator may flow out of the pores, and the shutdown state may not be continued well. However, in the case of the separator of the present invention, even if the temperature rise in the device continues after the onset of shutdown due to the melting of the thermoplastic resin (B) related to the composite particles contained in the second separator layer, the first separator layer Shutdown occurs again due to the melting of the thermoplastic resin (A) contained in.

  Therefore, according to the separator of the present invention, it is possible to constitute an electrochemical element with extremely excellent safety.

  However, when the resin particles contained in the second separator layer are composed only of the thermoplastic resin (B) that melts at a lower temperature than the thermoplastic resin (A), the air resistance of the separator is likely to increase. If such a separator is used, there is a possibility that the ion permeability of the separator in the electrochemical element is lowered, and for example, the output characteristics of the electrochemical element cannot be maintained high.

  However, in the separator of the present invention, the resin particles contained in the second separator layer are composite particles containing the thermoplastic resin (B) and the resin (C) other than the thermoplastic resin (B). The increase in the air resistance of the separator can be suppressed.

  The reason for this is not clear, but when the separator layer is formed using particles composed only of a thermoplastic resin that melts at a low temperature, these particles aggregate to make the pores of the separator layer non-uniform. However, when the second separator layer is formed using the composite particles, the aggregation of these particles can be satisfactorily suppressed. It is thought that it is possible to form pores with high homogeneity throughout the layer.

The composite particles according to the second separator layer contains a thermoplastic resin (B) and the resin (C), either core of the thermoplastic resin (B) and resin (C) It takes the form of a core-shell structure that is formed and the other forms a shell .

  The thermoplastic resin (B) and the resin (C) have electrical insulation properties, are stable with respect to the non-aqueous electrolyte held in the electrochemical element, and are oxidized and reduced within the operating voltage range of the electrochemical element. An electrochemically stable material is preferred.

  When the thermoplastic resin (A) related to the first separator layer is one having a melting point of 125 to 170 ° C., the thermoplastic resin (B) related to the composite particles contained in the second separator layer has a melting point of 80. It is preferable to use a resin having a melting point of 100 to 170 ° C. It is preferable to use a resin having a melting point of 100 to 170 ° C. By using the thermoplastic resin (A), the thermoplastic resin (B) and the resin (C) in combination with the above-mentioned characteristics, while suppressing the increase in the air resistance of the separator more favorably, The effect | action which improves the safety | security of an electrochemical element can be improved more.

  Specific examples of the thermoplastic resin (B) include LDPE, low molecular weight PE, modified PE (such as (anhydrous) maleic acid modified PE), ionomer resin, etc., and only one of them may be used. Two or more kinds may be used in combination.

  The thermoplastic resin (B) has a melt viscosity at 140 ° C. of preferably 5 mPa · s or more, and more preferably 8 mPa · s or more. In this way, by using a thermoplastic resin (B) having a somewhat high melt viscosity, when the shutdown occurs, the thermoplastic resin (B) is prevented from flowing out of the pores of the separator. It becomes possible to draw out the shutdown action by the plastic resin (B) more satisfactorily. However, if the melt viscosity of the thermoplastic resin (B) is too high, the fluidity at the time of melting of the thermoplastic resin (B) is low, so that when the shutdown occurs, the thermoplastic resin (B) becomes empty in the separator. There is a possibility that the action of closing the hole is reduced. Therefore, the melt viscosity at 140 ° C. of the thermoplastic resin (B) is preferably 100000 mPa · s or less, more preferably 2000 mPa · s or less, and still more preferably less than 1000 mPa · s.

  In addition, it is preferable that the melt viscosity of the thermoplastic resin (B) is lower than the melt viscosity of the thermoplastic resin (A) constituting the first separator layer. It becomes possible to improve performance.

  As a specific example of the resin (C), among the various thermoplastic resins (A) exemplified as the thermoplastic resin (A), those that melt at a higher temperature than the thermoplastic resin (B) (that is, the melting point is high). And modified PP [(anhydrous) maleic acid modified PP etc.], and only one of them may be used, or two or more may be used in combination.

  As a combination of the thermoplastic resin (B) and the resin (C) constituting the composite particle, PE or modified PE is used for the thermoplastic resin (B), and PP or modified PP is used for the resin (C). Is more preferable.

  There is no restriction | limiting in particular about the shape of the said composite particle, Any shapes, such as substantially spherical shape (a spherical shape is included), an ellipsoid shape, and plate shape, may be sufficient. Moreover, the average particle diameter of the composite particles is preferably 0.01 μm or more, and more preferably 0.1 μm or less, from the viewpoint of better suppressing the increase in the air permeability resistance of the separator. However, when the particle size of the composite particles is too large, when the second separator layer is formed, the separator becomes thick, and when a battery is manufactured, the occupied portion of the separator becomes large, and the volume energy density decreases. Therefore, the average particle size of the composite particles is preferably 15 μm or less, and more preferably 5 μm or less.

The average particle size of the particles referred to in the present specification (the composite particles and the inorganic filler according to the third separator layer described later) is, for example, an aqueous dispersion of particles, and a concentrated particle size analyzer manufactured by Otsuka Electronics Co., Ltd. Using “FPAR-1000”, it can be defined as D ₅₀ (particle size with 50% volume cumulative frequency) measured by dynamic light scattering. Measured by: Further, when measuring the average particle diameter of the particles not dispersed in water or the like, for example, the individual particle diameters of 20 particles are obtained by observing with a scanning electron microscope, and the average is obtained from these total values. What is necessary is just to obtain | require a particle diameter.

  In the composite particles, the content of the thermoplastic resin (B) is preferably 1% by mass or more, more preferably 50% by mass or more, and preferably 99% by mass or less. More preferably, it is 95 mass% or less. In the composite particles, the content of the resin (C) is preferably 1% by mass or more, more preferably 5% by mass or more, and preferably 99% by mass or less. More preferably, it is 50 mass% or less. If it is a composite particle comprising the thermoplastic resin (B) and the resin (C) in the above amounts, the effect of suppressing the increase in the air permeability resistance of the separator and the effect of improving the safety of the electrochemical element Will be improved.

  The composite particles may be composed of only the thermoplastic resin (B) and the resin (C). For example, for the purpose of increasing the compatibility of the thermoplastic resin (B) and the resin (C), 1 A seed or two or more other resins may be further contained. For the resin (C), for example, a resin (C1) having a low compatibility with the thermoplastic resin (B) and a resin (C2) having a high compatibility with the thermoplastic resin (B) and the resin (C1) are used in combination. As described above, a plurality of resins can be used in combination according to required characteristics.

  The content of the composite particles in the second separator layer is preferably 50% by volume or more, more preferably 70% by volume or more, in the total volume of the constituent components of the second separator layer, 100% by volume, That is, the second separator layer may be composed only of the composite particles. In addition, an organic binder can also be contained in the 2nd separator layer, and it is preferable that the content rate of the said composite particle in the 2nd separator layer in this case is 99.8 volume% or less.

  As described above, the second separator layer contains an organic binder in order to bind the composite particles to each other or to bond the second separator layer and another layer (such as the first separator layer). be able to.

  Specific examples of the organic binder include, for example, EVA (with a structural unit derived from vinyl acetate of 20 to 35 mol%), an ethylene-acrylic acid copolymer such as an ethylene-ethyl acrylate copolymer (EEA), and a fluorine-based binder. Rubber, styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyvinyl pyrrolidone (PVP), polyethylene oxide (PEO), poly-N-vinyl Examples include acetamide (PNVA), butyl acrylate-acrylic acid copolymer, cross-linked acrylic resin, polyurethane, and epoxy resin. As the organic binder, those exemplified above may be used singly or in combination of two or more.

  Among the organic binders exemplified above, highly flexible binders such as EVA, ethylene-acrylic acid copolymer, fluorine rubber, SBR, butyl acrylate-acrylic acid copolymer, PVP, CMC, and PNVA are preferable. Specific examples of such highly flexible organic binders include Mitsui DuPont Polychemical's “Evaflex Series (EVA)”, Nihon Unicar's EVA, Mitsui DuPont Polychemical's “Evaflex-EAA Series (Ethylene). -Acrylic acid copolymer) ", Nippon Unicar EEA, Daikin Industries" DAI-EL Latex Series (Fluororubber) ", JSR" TRD-2001 (SBR) ", Nippon Zeon" BM-400B " (SBR) ".

  When the organic binder is used, it may be used in the state of an emulsion dissolved or dispersed in a solvent of a composition for forming a second separator layer described later.

  In the case where an organic binder is contained in the second separator layer, the content is 0.2% by volume or more in the total volume of the constituent components of the second separator layer, from the viewpoint of ensuring better effects of the organic binder. It is preferable that it is 0.5 volume% or more. However, if the amount of the organic binder in the second separator layer is too large, the amount of other components becomes too small, and there is a possibility that the effects of them cannot be sufficiently secured. The content of is preferably 20% by volume or less, and more preferably 10% by volume or less, in the total volume of the constituent components of the second separator layer.

  The second separator layer may contain a fibrous material in order to ensure the shape stability and flexibility of the separator. The fibrous material preferably has a heat resistant temperature of 150 ° C. or higher.

  As the fibrous material, it has electrical insulation, is electrochemically stable, is stable to the non-aqueous electrolyte solution of the electrochemical element, and the solvent used in the production of the separator, preferably the above-mentioned The material is not particularly limited as long as it has a heat resistant temperature.

  Specific constituent materials of the fibrous material include, for example, cellulose and its modified products (carboxymethyl cellulose (CMC), hydroxypropyl cellulose (HPC), etc.), polyolefin (PP, propylene copolymer, etc.), polyester [polyethylene, etc. Resins such as terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), polyacrylonitrile (PAN), aramid, polyamideimide, polyimide; inorganic oxides such as glass, alumina, zirconia, silica; A fibrous material may be formed by using two or more of these constituent materials in combination. Further, the fibrous material may contain various additives, for example, an antioxidant when the fibrous material is a resin, as necessary.

  As the shape of the fibrous material, for example, the average diameter is preferably 0.01 to 20 μm, and the average length is preferably 0.1 to 50000 μm.

  When the fibrous material is contained in the second separator layer, the content of the fibrous material in the entire volume of the constituent components of the second separator layer is preferably 0.1 to 50% by volume.

  The second separator layer may be set such that the proportion (melting filling rate) of the volume (melting volume) when the constituent components are melted at a high temperature to the pore volume of the first separator layer falls within a predetermined range. preferable. For example, the melt filling rate at 140 ° C. of the second separator layer with respect to the first separator layer is preferably 3% or more from the viewpoint of ensuring a better shutdown effect by forming the second separator layer. More preferably, it is 10% or more. Also, from the viewpoint of satisfactorily suppressing the decrease in output of the electrochemical element caused by the separator as a resistance component, the second separator layer is melted at 140 ° C. with respect to the first separator layer. The filling rate is preferably 200% or less, and more preferably 150% or less.

  The melt filling rate is represented by the following formula (1).

In the formula (1),
w: the mass of the third separator layer formed per 1 m ^{2 of} the first separator layer,
d: specific gravity (true density) of the second separator layer,
β: Volume expansion coefficient of the second separator layer (β = 3α, where α is the linear expansion coefficient of the second separator layer),
T: shutdown temperature,
t: room temperature,
V: apparent volume per 1 m ^{2 of} the first separator layer,
v: actual volume per 1 m ^{2 of} the first separator layer,
It is. In addition, the molecule | numerator of said Formula (1) corresponds to the molten volume of a 2nd separator layer.

  The specific gravity (true density) of the second separator layer can be determined, for example, by measuring a dried product with an ultra pycnometer.

  In addition, the amount of the composite particles in the second separator layer is preferably 3 to 200% by volume, more preferably 5 to 100% by volume, based on the volume of the pores of the first separator layer. By doing in this way, the melt filling rate in 140 degreeC with respect to the 1st separator layer of a 2nd separator layer can be adjusted to the said value.

  The separator of the present invention may contain two or more second separator layers. In this case, for each layer of the plurality of second separator layers, the thermoplastic resin (B) contained in the composite particles may have a different melting point so that shutdown can occur in more stages.

<Third separator layer>
The separator of the present invention may be composed of only the first separator layer and the second separator layer, and further, as the third separator layer, a layer having a higher heat resistance temperature than the first separator layer and the second separator layer. You may contain. The third separator layer is porous and has ion permeability.

  The separator including the third separator layer having a high heat-resistant temperature suppresses shrinkage and film breakage of the first separator layer due to the action of the inorganic filler even when the temperature in the electrochemical element is such that the first separator layer shrinks. be able to. Even if the first separator layer breaks, the third separator layer having a high heat resistance acts as a spacer for partitioning the positive electrode and the negative electrode, so that an effect of suppressing an internal short circuit of the electrochemical element can be expected. Therefore, the safety | security of an electrochemical element can be improved further by making a separator of this invention also contain a 3rd separator layer.

  The “heat-resistant temperature” in the present specification refers to a temperature at which no shape deformation is visually observed with respect to the layer or filler (described later).

  The third separator layer preferably contains an inorganic filler having high heat resistance. More specifically, the third separator layer may be composed of only an inorganic filler, contains an inorganic filler and an organic binder, and contains an inorganic filler. They may have a structure in which they are bound with an organic binder.

The inorganic filler preferably has a heat resistant temperature of 150 ° C. or higher. Specific examples of the constituent material of the inorganic filler having such heat-resistant temperature include, for example, inorganic oxides such as iron oxide, SiO ₂ (silica), Al ₂ O ₃ (alumina), TiO ₂ , BaTiO ₂ , and ZrO ₂ . Inorganic hydroxides such as Al (OH) ₃ (aluminum hydroxide); inorganic nitrides such as aluminum nitride and silicon nitride; sparingly soluble ionic crystals such as calcium fluoride, barium fluoride and barium sulfate; silicon and diamond Covalent crystals such as; clays such as montmorillonite; Here, the inorganic oxide may be a material derived from mineral resources such as boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, mica, or these artificial products. In addition, the surface of a conductive material exemplified by a metal; a conductive oxide such as SnO ₂ or tin-indium oxide (ITO); a carbonaceous material such as carbon black or graphite; For example, the particles may be particles that have been electrically insulated by coating with the above-described inorganic oxide or the like. As the inorganic filler, only one kind of fine particles composed of the materials exemplified above may be used, or two or more kinds may be used in combination.

  Among the inorganic fillers exemplified above, alumina, silica, aluminum hydroxide, and boehmite are more preferable, and boehmite is more preferable among them. Among boehmite, synthetic boehmite that can easily control the particle size and shape and can reduce ionic impurities that adversely affect the characteristics of the electrochemical element is particularly preferable.

  There is no restriction | limiting in particular about the shape of an inorganic filler, Any shapes, such as substantially spherical shape (a spherical shape is included), an ellipsoid shape, and plate shape, may be sufficient. The average particle size of the inorganic filler is preferably 0.01 μm or more, more preferably 0.1 μm or more, more preferably 20 μm or less, and more preferably 5 μm or less. preferable.

  When an organic binder is contained in the third separator layer, the same organic binders as those exemplified above as those that can be used for the second separator layer can be used as the organic binder. When an organic binder is used for the third separator layer, it may be used in the state of an emulsion dissolved or dispersed in a solvent for a composition for forming a third separator layer described later. The third separator layer may contain a fibrous material as in the second separator layer.

  In the case of using an inorganic filler for the third separator layer, the content is 10% by volume or more in the total volume of the constituent components of the third separator layer, from the viewpoint of ensuring the above-mentioned effect by the inorganic filler better. It is preferable that it is 40 volume% or more. However, if the amount of the inorganic filler in the third separator layer is too large, the amount of the other components becomes too small, and there is a possibility that the effect by them cannot be sufficiently secured. The content of is preferably 99% by volume or less and more preferably 95% by volume or less in the total volume of the constituent components of the third separator layer.

  In addition, when an organic binder is used for the third separator layer, the effect of the organic binder (an effect of binding inorganic fillers or bonding the third separator layer to another layer) is improved. From the viewpoint of ensuring, the content is preferably 0.2% by volume or more, and more preferably 0.5% by volume or more in the total volume of the constituent components of the third separator layer. However, if the amount of the organic binder in the third separator layer is too large, the amount of other components becomes too small, and there is a possibility that the effects of these components cannot be sufficiently ensured. The content of is preferably 20% by volume or less, more preferably 10% by volume or less, in the total volume of the constituent components of the third separator layer.

  Furthermore, when using a fibrous material for the third separator layer, from the viewpoint of better ensuring the effect of the fibrous material (an effect of increasing the shape stability and flexibility of the separator), the content is The total volume of the constituent components of the three separator layers is preferably 5% by volume or more, and more preferably 10% by volume or more. However, if the amount of the fibrous material in the third separator layer is too large, the amount of other components becomes too small, and there is a possibility that the effect of them cannot be sufficiently secured. The content of the material is preferably 90% by volume or less and more preferably 60% by volume or less in the total volume of the constituent components of the third separator layer.

<Laminated structure of separator>
FIG. 1 is a sectional view schematically showing an example of the separator of the present invention. The separator shown in FIG. 1 is composed of a first separator layer 10 and a second separator layer 20.

  In FIG. 1, the first separator layer 10 is represented as a single layer, but the first separator layer 10 may have a multilayer structure such as a two-layer structure or a three-layer structure as described above. The second separator layer can also have a multilayer structure containing composite particles using thermoplastic resins (B) having different melting points for each layer.

  FIG. 2 is a sectional view schematically showing another example of the separator of the present invention. The separator in FIG. 2 has a third separator layer 30 in addition to the first separator layer 10 and the second separator layer 20.

  When the separator has a third separator layer, for example, the second separator layer can be disposed on one surface side of the first separator layer, and the third separator layer can be disposed on the other surface side of the first separator layer. In addition, it is possible to arrange the second separator layer between the first separator layer and the third separator layer. However, as shown in FIG. It is preferable to arrange on the one surface side of the layer 10 and arrange the third separator layer 30 on the other surface side of the first separator layer 10. By setting it as the separator of such arrangement | positioning, the effect | action which a shutdown occurs by lower temperature by the 2nd separator layer, and the heat shrinkage suppression effect | action of the whole separator by a 3rd separator express more favorably.

  In addition, the shutdown was completed at a temperature where the thermal contraction of the first separator layer does not occur so significantly, or the electrode (positive electrode or negative electrode) and the separator were integrated so that the separator did not contract due to friction or fixation. In this case, the safety of the electrochemical device can be sufficiently enhanced even when a separator having a two-layer structure of the first separator layer and the second separator layer is formed without forming the third separator layer.

<Separator thickness>
From the viewpoint of further improving the short-circuit preventing effect in the electrochemical element, ensuring the strength of the separator and improving the handleability, the thickness of the separator of the present invention is preferably 3 μm or more, more preferably 5 μm or more. preferable. On the other hand, from the viewpoint of further increasing the energy density of the electrochemical element, the thickness of the separator of the present invention is preferably 45 μm or less, and more preferably 30 μm or less.

  The thickness of the first separator layer is preferably 2 μm or more, preferably 4 μm or more, preferably 30 μm or less, more preferably 20 μm or less. The thickness of the second separator layer is preferably 1 μm or more, more preferably 3 μm or more, preferably 15 μm or less, more preferably 10 μm or less. The thickness of the third separator layer is preferably 1 μm or more, more preferably 3 μm or more, preferably 15 μm or less, more preferably 10 μm or less.

<Air permeability resistance of separator>
The air permeation resistance of the separator of the present invention is a Gurley value represented by the number of seconds that 100 mL of air passes through the membrane, and is preferably 10 to 500 sec. If the air permeation resistance is too large, the ion permeability decreases, whereas if it is too small, the strength of the separator may decrease. By using the separator having the configuration described so far, such air permeability can be ensured.

<Strength of separator>
The strength of the separator is desirably 50 g or more in terms of piercing strength using a needle having a diameter of 1 mm. If the piercing strength is too small, a short circuit may occur due to the piercing of the separator when lithium dendrite crystals are generated. For example, such a strength can be ensured by using a separator having a third separator layer containing an inorganic filler.

<Manufacturing method of separator>
In the separator of the present invention, for example, a composition for forming a second separator layer (slurry, paste, etc.) is applied to a microporous film made of a thermoplastic resin constituting the first separator layer, and dried at a predetermined temperature. Thus, the second separator layer can be formed.

  In the case of a separator that also has a third separator layer, a composition for forming a third separator layer (slurry,) on a surface different from the second separator layer forming surface (second separator layer forming planned surface) of the first separator layer. Or a third separator layer forming composition on the second separator layer formed on at least one surface of the first separator layer, followed by drying at a predetermined temperature. It can be manufactured by forming a three separator layer.

  In this case, before applying the second separator layer forming composition or the third separator layer forming composition, the first separator layer or the second separator layer (when the third separator layer is formed on the surface) Surface treatment (corona treatment, ozone treatment, electron beam treatment, primer treatment, etc.) may be applied.

  The composition for forming the second separator layer can be prepared by dispersing the composite particles and, if necessary, an organic binder, a fibrous material, etc. in a solvent (however, the organic binder may be dissolved in the solvent). ).

  The composite particles dispersed in the composition for forming the second separator layer are not particularly limited in shape, and may be any shape such as a substantially spherical shape (including a true spherical shape), an ellipsoid shape, and a plate shape. There may be. The average particle diameter of the composite particles in the second separator layer forming composition is preferably 0.01 μm or more, more preferably 0.1 μm or more, and 20 μm or less. Preferably, it is 5 μm or less.

  The solvent used in the composition for forming the second separator layer may be any solvent that can uniformly disperse the composite material and the fibrous material used as necessary, and can uniformly dissolve or disperse the organic binder. However, organic solvents such as aromatic hydrocarbons such as toluene, furans such as tetrahydrofuran, and ketones such as methyl ethyl ketone and methyl isobutyl ketone are generally preferably used. For the purpose of controlling the interfacial tension, alcohols (ethylene glycol, propylene glycol, etc.) or various propylene oxide glycol ethers such as monomethyl acetate may be appropriately added to these solvents. In addition, when the organic binder is water-soluble or used as an emulsion, water may be used as a solvent. In this case, alcohols (methyl alcohol, ethyl alcohol, isopropyl alcohol, ethylene glycol, etc.) are appropriately added. It is also possible to control the interfacial tension.

  In addition, for example, a solvent (water, organic solvent, mixed solvent thereof or the like) is added to the thermoplastic resin (B) and the resin (C), and the mixture is stirred for a certain time at a temperature equal to or higher than the melting point of the resin (C) and then cooled. By doing so, a dispersion (emulsion) containing the composite particles can be prepared. Therefore, when preparing the composition for forming the second separator layer, the dispersion containing the composite particles may be used.

  Here, the stirring for preparing the dispersion containing the composite particles may be performed in a heat and pressure resistant container, and in that case, a compatibilizing agent or a surfactant is added to the system. May be.

  The composition for forming the third separator layer can be prepared by dispersing an inorganic filler and, if necessary, an organic binder, a fibrous material, etc. in a solvent (however, the organic binder may be dissolved in the solvent). .

  As the solvent used for the composition for forming the third separator layer, the same solvents as those exemplified above as those that can be used for the composition for forming the second separator layer can be used.

  Moreover, you may add surfactant to the composition for 2nd separator layer formation, and the composition for 3rd separator layer formation as needed.

  The solid content (total content of all components excluding the solvent) in the second separator layer forming composition and the third separator layer forming composition is preferably 5 to 40% by mass, for example.

<Electrochemical element>
The electrochemical element of the present invention has a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, and the separator may be the separator for electrochemical elements of the present invention, and there are no particular restrictions on the other configurations and structures. Various configurations and structures employed in electrochemical devices such as conventionally known lithium ion secondary batteries can be applied.

  The electrochemical element of the present invention includes an electrochemical element having a non-aqueous electrolyte, such as a lithium ion primary battery, a lithium ion secondary battery, and a supercapacitor. A lithium ion secondary battery which is a typical embodiment of will be described in detail.

  As the positive electrode, for example, a structure having a positive electrode mixture layer containing a lithium-containing transition metal oxide, which is a positive electrode active material, a binder, a conductive additive and the like, on one side or both sides of a current collector can be used.

The positive electrode active material is not particularly limited as long as it is an active material used in a conventional lithium ion secondary battery, that is, an active material capable of occluding and releasing Li ions. Specifically, for example, a lithium-containing transition metal oxide having a layered structure represented by Li _{1 + x} MO ₂ (−0.1 <x <0.1, M: Co, Ni, Mn, Al, Mg, etc.), It is possible to use LiMn ₂ O ₄ , a spinel-structure lithium manganese oxide obtained by substituting some of its elements with other elements, or an olivine type compound represented by LiMPO ₄ (M: Co, Ni, Mn, Fe, etc.). Is possible. Specific examples of the lithium-containing transition metal oxide having a layered structure include LiCoO ₂ and LiNi _1-x Co _xy Al _y O ₂ (0.1 ≦ x ≦ 0.3, 0.01 ≦ y ≦ 0. 2) and other oxides containing at least Co, Ni and Mn (LiMn _1/3 Ni _1/3 Co _1/3 O ₂ , LiMn _5/12 Ni _5/12 Co _1/6 O ₂ , LiNi _{3 / 5} Mn _1/5 Co _1/5 O ₂ etc.).

  As the binder for the positive electrode, for example, a fluororesin such as polyvinylidene fluoride (PVDF) is used, and as the conductive additive for the positive electrode, for example, a carbon material such as carbon black is used.

  For the positive electrode, for example, a positive electrode mixture containing a positive electrode active material, a conductive additive and a binder is dispersed in a solvent such as N-methyl-2-pyrrolidone (NMP), and a positive electrode mixture-containing composition (slurry, paste, etc.) Can be produced by applying it to a current collector, drying it, and then subjecting it to press treatment such as calendering if necessary. However, the manufacturing method of a positive electrode is not necessarily limited to the said method, You may manufacture by another method.

  As the current collector of the positive electrode, a metal foil such as aluminum, a punching metal, a net, an expanded metal, or the like can be used. Usually, an aluminum foil having a thickness of 10 to 30 μm is preferably used.

  The lead portion on the positive electrode side is normally provided by leaving the exposed portion of the current collector without forming the positive electrode mixture layer on a part of the current collector and forming the lead portion at the time of producing the positive electrode. However, the lead portion is not necessarily integrated with the current collector from the beginning, and may be provided by connecting an aluminum foil or the like to the current collector later.

  The negative electrode is not particularly limited as long as it is a negative electrode used in a conventional lithium ion secondary battery, that is, a negative electrode containing an active material capable of occluding and releasing Li ions. For example, it can occlude and release lithium such as graphite, pyrolytic carbons, cokes, glassy carbons, fired organic polymer compounds, mesophase carbon microbeads (MCMB), carbon fibers, etc., as the negative electrode active material One type or a mixture of two or more types of carbon-based materials are used. In addition, elements such as Si, Sn, Ge, Bi, Sb, In and alloys thereof, lithium-containing nitrides, compounds that can be charged and discharged at a low voltage close to lithium metal such as lithium-containing oxides, or lithium metal or lithium / An aluminum alloy can also be used as the negative electrode active material. A negative electrode mixture in which a conductive additive (carbon material such as carbon black) or a binder such as PVDF is appropriately added to these negative electrode active materials is finished into a molded body (negative electrode mixture layer) using the current collector as a core material. Or a laminate of the above various alloys and lithium metal foil alone or on a current collector is used as the negative electrode.

  In the case of a negative electrode having a negative electrode mixture layer, for example, a negative electrode mixture containing a negative electrode active material, a binder, and a negative electrode mixture containing a conductive auxiliary agent, if necessary, in a solvent such as NMP or water. An article (slurry, paste, etc.) is prepared, applied to a current collector, dried, and further subjected to a press treatment such as a calendar treatment as necessary. However, the manufacturing method of the negative electrode having the negative electrode mixture layer is not limited to the above method, and may be manufactured by other methods.

  When a current collector is used for the negative electrode, a copper or nickel foil, a punching metal, a net, an expanded metal, or the like can be used as the current collector, but a copper foil is usually used. In the negative electrode current collector, when the thickness of the entire negative electrode is reduced in order to obtain a battery having a high energy density, the upper limit of the thickness is preferably 30 μm, and the lower limit is preferably 5 μm. Further, the lead portion on the negative electrode side may be formed in the same manner as the lead portion on the positive electrode side.

  The positive electrode and the negative electrode can be used in the form of an electrode body such as a laminated body laminated via the separator of the present invention or a wound body obtained by winding the laminated body. In addition, in the said electrode body, it is preferable to arrange | position a separator so that the 2nd separator layer of a separator may oppose a negative electrode. In this case, the time at which the second separator layer is shut down becomes shorter, and the safety of the lithium ion secondary battery (electrochemical element) is further improved. Further, when the separator also contains a third separator layer containing an inorganic filler, in the electrode body, the separator is disposed so that the third separator layer faces the positive electrode, thereby oxidative degradation of the separator. Can be suppressed.

  In the electrode body, the separator may be integrated with at least one of the positive electrode and the negative electrode. By doing in this way, position shift with a separator, a positive electrode, and a negative electrode can be prevented, and the effect | action which suppresses the contact with a positive electrode and a negative electrode becomes more favorable. In order to integrate the separator with the positive electrode, for example, a method of applying a positive electrode mixture-containing composition to a current collector to form a coating film, and stacking the separator on this coating film before drying can be employed. In addition, when the separator is integrated with the negative electrode, for example, there is a method in which the negative electrode mixture-containing composition is applied to a current collector to form a coating film, and the separator is stacked on this coating film before drying. Can be adopted.

As the non-aqueous electrolyte, a solution in which a lithium salt is dissolved in an organic solvent is used. The lithium salt is not particularly limited as long as it dissociates in a solvent to form Li ⁺ ions and hardly causes side reactions such as decomposition in a voltage range used as a battery. For example, inorganic lithium salts such as LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ ; LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li ₂ C ₂ F ₄ (SO ₃ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiC _n F _{2n + 1} SO ₃ (2 ≦ n ≦ 5), LiN (RfOSO ₂ ) ₂ [where Rf is a fluoroalkyl group] or the like is used. Can do.

  The organic solvent used for the non-aqueous electrolyte is not particularly limited as long as it dissolves the lithium salt and does not cause a side reaction such as decomposition in a voltage range used as a battery. For example, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; chain esters such as methyl propionate; cyclic esters such as γ-butyrolactone; Chain ethers such as dimethoxyethane, diethyl ether, 1,3-dioxolane, diglyme, triglyme and tetraglyme; cyclic ethers such as dioxane, tetrahydrofuran and 2-methyltetrahydrofuran; nitriles such as acetonitrile, propionitrile and methoxypropionitrile Sulfites such as ethylene glycol sulfite; etc., and these should be used as a mixture of two or more. It can be. In order to obtain a battery with better characteristics, it is desirable to use a combination that can obtain high conductivity, such as a mixed solvent of ethylene carbonate and chain carbonate.

  In addition, vinylene carbonates, 1,3-propane sultone, diphenyl disulfide, cyclohexylbenzene, biphenyl, and fluorobenzene are used for the purpose of improving safety, charge / discharge cycleability, and high-temperature storage properties of these non-aqueous electrolytes. An additive such as t-butylbenzene may be added as appropriate.

  The concentration of the lithium salt in the non-aqueous electrolyte is preferably 0.5 to 1.5 mol / L, and more preferably 0.9 to 1.25 mol / L.

  Moreover, what was gelatinized using gelling agents, such as a well-known polymer (gel electrolyte), can also be used for a non-aqueous electrolyte.

  Examples of the form of the lithium ion secondary battery include a cylindrical shape (such as a rectangular tube shape or a cylindrical shape) using a steel can or an aluminum can as an outer can. Moreover, it can also be set as the soft package battery which used the laminated film which vapor-deposited the metal as an exterior body.

  The electrochemical device of the present invention can be applied to the same use as a conventionally known electrochemical device such as a lithium ion secondary battery.

  Hereinafter, the present invention will be described in detail based on examples. However, the following examples do not limit the present invention. In addition, in each separator of the comparative example to be described later, instead of the second separator layer, there is one in which a layer containing resin particles composed of a single resin is formed instead of composite particles. The particle-containing layer is also referred to as a second separator layer for convenience.

In addition, the melt viscosity at 140 ° C. of the thermoplastic resin used in this example is “Capillograph” manufactured by Toyo Seiki Co., Ltd., and a nozzle with a length (L) of 10 mm and a diameter (D) of 1.0 mm is used. It is a value measured using a shear rate of 100 s ⁻¹ . Furthermore, the porosity of the microporous membrane used in this example is a value measured using an ultra pycnometer.

<Production of composite particles>
Production Example 1
LDPE (melting point: 113 ° C., melt viscosity at 140 ° C .: 20 mPa · s): 28 parts by mass, maleic anhydride-modified PP (melting point: 135 ° C.): 12 parts by mass, and water: 60 parts by mass are mixed and sealed In a container, after heating and stirring at 150 ° C., the mixture was cooled to obtain a dispersion containing composite particles P having a modified PP content of 30% by mass at a solid content concentration of 40%. When the sample of the composite particle P sliced with osmium tetroxide is observed with a transmission electron microscope (TME), it has a core-shell structure having a core with a high degree of staining and a dark core and a shell with a low degree of staining and a light color. It was. From the above observation results, it is presumed that in the composite particles P, LDPE constitutes a core and modified PP constitutes a shell.

Production Example 2
LDPE (melting point: 120 ° C., melt viscosity at 140 ° C .: 20000 mPa · s): 13.5 parts by mass, maleic anhydride-modified PP (melting point: 135 ° C.): 1.5 parts by mass, and water: 85 parts by mass The mixture was mixed, heated and stirred at 150 ° C. in an airtight container, and then cooled to obtain a dispersion containing composite particles Q having a modified PP content of 10 mass% at a solid content concentration of 15%. When the sample of the composite particle Q sliced with osmium tetroxide is observed with a transmission electron microscope (TME), it has a core-shell structure having a core with a high degree of staining and a dark core and a shell with a low degree of staining and a light color. It was. From the above observation results, it is presumed that the composite particle Q also has a core-shell structure in which LDPE constitutes the core and modified PP constitutes the shell, similarly to the composite particle P.

<Example of separator production>
Example a1
Boehmite fine particles: 97 parts by mass, and acrylate copolymer as an organic binder (commercially available acrylate copolymer having butyl acrylate as a main component as a monomer component): 3 parts by mass of water as a solvent are added and dispersed. A slurry for forming a third separator layer having a solid content of 22% by mass was prepared.

  Corona discharge treatment was performed on both sides of a microporous membrane (first separator layer, thickness: 16 μm, porosity: 49%) having a three-layer structure in which a PP layer / HDPE layer / PP layer were sequentially laminated, The slurry for forming the third separator layer was applied and dried to obtain a laminate having a third separator layer having a thickness of 3.5 μm on one side of the first separator layer.

  A dispersion of composite particles P, a binder (the same acrylate copolymer used for the third separator layer), and water as a solvent are mixed to form a second separator layer having a solid content of 35% by mass. A slurry was prepared. In this second separator layer forming slurry, the amount of the composite particles was 97 parts by mass, and the binder was 3 parts by mass.

  This second separator layer forming slurry is applied to the surface of the first separator layer of the laminate of the first separator layer and the third separator layer and dried to form a second separator layer having a thickness of 1 μm. Thus, a separator a1 having a second separator layer on one side of the first separator layer and a third separator layer on the other side was obtained. As a result of calculating the melt filling rate of this separator a1, it was 11.6%. Moreover, in the 2nd separator layer, the content rate of the composite particle P was 97 volume%, and the content rate of the organic binder was 3 volume%. Furthermore, in the third separator layer, the boehmite content was 91.5% by volume, and the binder content was 8.5% by volume.

  A cross-sectional view schematically showing a cross section of the separator a1 is shown in FIG. The separator a1 has a second separator layer 20 containing composite particles P on one side of a first separator layer 10 made of a microporous film having a three-layer structure of PP layer 11 / HDPE layer 12 / PP layer 11; It has the 3rd separator layer 30 containing the boehmite which is an inorganic filler in the surface.

Example a2
Except for changing the thickness of the second separator layer to 2 μm, in the same manner as in Example a1, composite particles P were formed on one side of the first separator layer composed of a microporous film having a three-layer structure of PP layer / HDPE layer / PP layer. The separator a2 which has the 2nd separator layer containing this and has the 3rd separator layer containing the boehmite which is an inorganic filler on the other surface was produced. As a result of calculating the melt filling rate of this separator a2, it was 17.7%.

Example a3
Except for changing the thickness of the second separator layer to 4 μm, in the same manner as in Example a1, composite particles P were formed on one side of the first separator layer composed of a microporous film having a three-layer structure of PP layer / HDPE layer / PP layer. The separator a3 which has the 2nd separator layer containing this and has the 3rd separator layer containing the boehmite which is an inorganic filler on the other surface was produced. As a result of calculating the melt filling rate of this separator a3, it was 35.6%.

Example a4
A slurry for forming a second separator layer having a solid content of 7% by mass was prepared in the same manner as in Example 1 except that the dispersion of composite particles Q was used instead of the dispersion of composite particles P.

  And the said 2nd separator layer formation slurry is apply | coated to the surface of the 1st separator layer of the laminated body of the same 1st separator layer and 3rd separator layer as what was produced in Example a1, and it dries. And a second separator layer containing composite particles Q on one side of the first separator layer formed of a microporous film having a three-layer structure of PP layer / HDPE layer / PP layer by forming a second separator layer having a thickness of 3 μm A separator a4 having a third separator layer containing boehmite as an inorganic filler on the other surface was obtained. As a result of calculating the melt filling rate of this separator a4, it was 16.3%. In the second separator layer, the content of the composite particles Q was 97% by volume, and the content of the organic binder was 3% by volume.

Comparative Example b1
A third separator layer forming slurry was prepared in the same manner as in Example a1, except that the solid content was changed to 30% by mass.

  A corona discharge treatment was performed on one side of a microporous film having the same three-layer structure of PP layer / HDPE layer / PP layer as used in Example a1. Then, using the microporous membrane as a first separator layer, the third separator layer forming slurry is applied to the corona discharge treatment surface and dried to form a third separator layer having a thickness of 5 μm. A separator b1 having a third separator layer containing boehmite as an inorganic filler on one surface of a first separator layer composed of a microporous film having a three-layer structure of layer / HDPE layer / PP layer was produced.

Comparative Example b2
A third separator layer forming slurry was prepared in the same manner as in Example a1, except that the solid content was changed to 25% by mass.

  A corona discharge treatment is applied to one side of a microporous membrane (first separator layer, thickness: 20 μm, porosity: 52%) having a three-layer structure in which a PP layer / HDPE layer / PP layer are sequentially laminated. The third separator layer forming slurry is applied, dried, and boehmite, which is an inorganic filler, is applied to one side of the first separator layer made of a microporous film having a three-layer structure of PP layer / HDPE layer / PP layer. A separator b2 containing a third separator layer containing 5 μm in thickness was produced.

Comparative Example b3
The microporous membrane having a three-layer structure in which the PP layer / HDPE layer / PP layer used as the first separator layer in Example a1 was sequentially laminated was designated as a separator b3.

Comparative Example b4
A microporous membrane having a three-layer structure in which the PP layer / HDPE layer / PP layer used as the first separator layer in Comparative Example b2 was sequentially laminated was designated as a separator b4.

Comparative Example b5
A HDPE microporous membrane (single-layer microporous membrane, thickness: 16 μm, porosity: 45%) was designated as separator b5.

Comparative Example b6
Except having changed the thickness of the 3rd separator layer into 3 micrometers, it carried out similarly to Example a1, and produced the laminated body of the 1st separator layer and the 3rd separator layer.

  Maleic anhydride-modified PE (melting point: 113 ° C., melt viscosity at 140 ° C .: 20 mPa · s): 97 parts by mass, binder (the same acrylate copolymer used for the third separator layer): 3 parts by mass Then, water as a solvent was mixed to prepare a second separator layer forming slurry having a solid content of 35% by mass.

  This second separator layer forming slurry is applied to the surface of the first separator layer of the laminate of the first separator layer and the third separator layer and dried to form a second separator layer having a thickness of 2 μm. And having a second separator layer containing modified PE particles on one side of the first separator layer composed of a microporous film having a three-layer structure of PP layer / HDPE layer / PP layer, and an inorganic filler on the other side. A separator b6 having a third separator layer containing boehmite was obtained. As a result of calculating the melt filling rate of this separator b6, it was 10.2%.

Comparative Example b7
Modified PE particles on one side of the first separator layer composed of a microporous film having a three-layer structure of PP layer / HDPE layer / PP layer in the same manner as in Comparative Example b6 except that the thickness of the second separator layer was changed to 4 μm. The separator b7 which has the 2nd separator layer containing this and has the 3rd separator layer containing the boehmite which is an inorganic filler on the other surface was obtained. As a result of calculating the melt filling rate of this separator b7, it was 27.9%.

Comparative Example b8
A third separator layer forming slurry was prepared in the same manner as in Example a1, except that the solid content was changed to 30% by mass.

  The HDPE microporous membrane (first separator layer, single-layer microporous membrane, thickness: 16 μm, porosity: 45%) is subjected to corona discharge treatment, and the third separator layer is formed on one side. The slurry for coating was applied and dried to prepare a laminate having a third separator layer having a thickness of 3.5 μm on one side of the first separator layer.

  Maleic anhydride-modified PE (melting point: 120 ° C., melt viscosity at 140 ° C .: 20000 mPa · s): 97 parts by mass, binder (the same acrylate copolymer used for the third separator layer): 3 parts by mass Then, water as a solvent was mixed to prepare a slurry for forming a second separator layer having a solid content of 25% by mass.

  This second separator layer forming slurry is applied to the surface of the first separator layer of the laminate of the first separator layer and the third separator layer and dried to form a second separator layer having a thickness of 3 μm. And having a second separator layer containing modified PE particles on one side of the first separator layer composed of a microporous film having a three-layer structure of PP layer / HDPE layer / PP layer, and an inorganic filler on the other side. A separator b8 having a third separator layer containing boehmite was obtained. As a result of calculating the melt filling rate of this separator b8, it was 24.8%.

  About each separator of an Example and a comparative example, the following air permeability resistance measurement and the heat shrinkage rate measurement were performed.

(Measurement of air resistance of separator)
About each separator of an Example and a comparative example, air permeability resistance (air permeability resistance at room temperature) kept at room temperature, and air resistance in a state where it was returned to room temperature after being stored at 110 ° C. for 30 minutes (Air permeability resistance after storage at 110 ° C. for 30 minutes) was measured. These air resistances were measured by a method based on JISP 8117 as described above.

(Measurement of thermal shrinkage of separator)
Each separator of the example and the comparative example was cut into a size of 10 cm × 5 cm to prepare a test piece. In this test piece, the direction of 10 cm (longitudinal direction) was made parallel to the longitudinal direction of the microporous membrane according to the separator (stretching direction during the production of the microporous membrane). Each test piece was put in a thermostat adjusted to 150 ° C., taken out after 30 minutes, and the degree of heat shrinkage was measured.

  Moreover, about each separator of Example a2 and Comparative Example b3, the resistance change at the time of heating in the state immersed in the non-aqueous electrolyte between electrodes was performed by the following method.

(Measurement of resistance change of separator)
Aluminum foil and copper foil are used as electrodes, and a laminate with each separator sandwiched between them is placed in a pressure vessel (10 atm), and a non-aqueous electrolyte (ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate and A solution obtained by dissolving LiPF ₆ at a concentration of 1.2 mol / l in a mixed solvent having a volume ratio of 2: 4: 4 was filled in a pressure vessel and sealed. A terminal connected to the inner electrode was pulled out of the pressure vessel so that the resistance between the electrodes could be measured, and a thermometer was installed so that the tip of the thermocouple was placed at the separator. Then, the pressure vessel was placed in a thermostatic bath, the temperature was raised at a rate of 100 ° C. per hour, and the resistance value and temperature of the separator sandwiched between the electrodes were monitored.

  Table 1 shows the configuration of each separator in Examples and Comparative Examples, and Table 2 shows the results of measurement of air resistance and thermal shrinkage of each separator. The “melt viscosity” in Table 1 means the melt viscosity at 140 ° C. In addition, in Table 2, “Impossible to measure” in the column of “Air resistance after storage at 110 ° C. for 30 minutes” means that even when the separator is installed in the apparatus and measurement is started, the inner cylinder hardly moves. This means that measurement has not started.

  As shown in Table 2, Example a1 having a first separator layer mainly composed of the thermoplastic resin (A) and a second separator layer containing composite particles containing the thermoplastic resin (B) and the resin (C). The separator of ~ a4 has an increase in air resistance after storage at 110 ° C for 30 minutes compared to the air resistance at room temperature, and shutdown has started at a relatively low temperature such as 110 ° C. There was found. In particular, in the separator of Example a3, the air permeability resistance after storage at 110 ° C. for 30 minutes is not measurable, and it can be seen that the closure of the pores of the separator has progressed considerably and the shutdown has been well developed.

  On the other hand, in the separators of Comparative Examples b1 to b5 having no second separator layer, the difference between the air resistance at room temperature and the air resistance after storage at 110 ° C. for 30 minutes is small, and the start of shutdown is almost recognized. There wasn't.

  In addition, among those having the second separator layer, the separators of Examples a1 to a3 and the thermoplastic resin having the same melt viscosity as the thermoplastic resin (B) related to the composite particles contained in these separators were used. When the separators of Comparative Examples b6 and b7 containing resin particles are compared, the separators of Examples a1 to a3 have lower air resistance at room temperature than the separators of Comparative Examples b6 and b7. The increase in the air resistance due to the formation of the separator layer containing the resin particles could be suppressed by using the composite particles.

  In addition, the separator of Example a4 was compared with the separator of Comparative Example b8 containing resin particles composed of the same type (melt viscosity) as the thermoplastic resin (B) related to the composite particles contained in these separators. Even in the case, the separator of Example a4 had a lower air resistance at room temperature than the separator of Comparative Example b8. Therefore, also in the separator of Example a4, like the separators of Examples a1 to a3, the increase in the air resistance due to the formation of the separator layer containing the resin particles could be suppressed by using the composite particles.

  Moreover, the separator of Examples a1-a4 also has the 3rd separator layer with high heat-resistant temperature, and, thereby, the thermal contraction rate in 150 degreeC was small. Therefore, with these separators, it can be said that even if the internal temperature rises, an internal short circuit due to contact between the positive electrode and the negative electrode hardly occurs, and an electrochemical device with higher safety can be configured.

  Furthermore, the graph showing the measurement result of the resistance change in each separator of Example a2 and Comparative Example b3 is shown in FIGS. 4 and 5, respectively. In these graphs, the horizontal axis represents temperature, and the vertical axis represents resistance value.

  As shown in FIG. 4, in the separator a <b> 2 of Example a <b> 2, the resistance value increase corresponding to the shutdown started near 100 ° C., and the first-stage resistance value increase reached saturation near 110 ° C. The second-stage resistance value increase started at around 120 ° C. and reached saturation at around 130 ° C.

  On the other hand, as shown in FIG. 5, in the separator b3 of the comparative example b3 that does not have the second separator layer (and the third separator layer), the temperature at which the increase in the resistance value is saturated is around 128 ° C. It was higher than the saturation temperature (shutdown temperature) of the first-stage resistance increase in the separator a2 of a2.

  Also from these results, the separator a2 of Example a2 having the second separator layer containing the composite particles containing the thermoplastic resin (B) and the resin (C) is the same as that of Comparative Example b3 having no second separator layer. It was found that shutdown at a lower temperature is possible compared to the separator b3.

<Example of production of lithium ion secondary battery (electrochemical element)>
Example A1
A negative electrode mixture-containing paste was prepared by mixing 95 parts by mass of graphite as a negative electrode active material and 5 parts by mass of PVDF as a binder so as to be uniform using NMP as a solvent. This negative electrode mixture-containing paste is intermittently applied on both sides of a 10 μm thick copper foil serving as a current collector to a coating length of 630 mm, dried, and calendered to a total thickness of 131 μm. The thickness of the negative electrode mixture layer was adjusted so that the width was 56 mm, and a negative electrode having a length of 650 mm and a width of 56 mm was produced. Further, a tab was welded to the exposed portion of the copper foil of the negative electrode to form a lead portion.

The positive electrode active material LiCoO ₂ : 85 parts by mass, the conductive auxiliary agent acetylene black: 10 parts by mass, and the binder PVDF: 5 parts by mass are mixed uniformly using NMP as a solvent. An agent-containing paste was prepared. This paste was applied to both sides of a 20 μm thick aluminum foil serving as a current collector, dried, and then subjected to calendering to adjust the thickness of the positive electrode mixture layer so that the total thickness was 125 μm. A positive electrode having a length of 610 mm and a width of 54 mm was produced by cutting to 54 mm. Further, a tab was welded to the exposed portion of the aluminum foil of the positive electrode to form a lead portion.

The positive electrode and the negative electrode were overlapped with the separator a1 prepared in Example a1 interposed, and wound in a spiral shape to prepare a wound electrode body. In this wound electrode body, the second separator layer of the separator was made to face the negative electrode. This wound electrode body was loaded into a battery container of 18650 specifications. Further, after injecting a nonaqueous electrolytic solution (a solution obtained by dissolving LiPF ₆ at a concentration of 1 mol / L in a solvent in which ethylene carbonate and propylene carbonate are mixed at a volume ratio of 3: 7) into a battery container, sealing is performed. Thus, a lithium ion secondary battery A1 having the structure shown in FIG. 6 was obtained.

  Here, the battery shown in FIG. 6 will be described. In the lithium ion secondary battery shown in FIG. 6, the positive electrode 101 and the negative electrode 102 are spirally wound via the separator 103, and non-aqueous electrolysis is used as the wound electrode body. It is accommodated in the battery container 105 together with the liquid 104. Note that in FIG. 6, in order to avoid complication, the current collectors used for manufacturing the positive electrode 101 and the negative electrode 102 are not illustrated, and each layer of the separator is not illustrated.

  The battery container 105 is made of stainless steel, and an insulator 106 made of PP is disposed at the bottom of the battery container 105 prior to the insertion of the wound electrode body. The sealing plate 107 is made of aluminum and has a disk shape. A thin portion 107a is provided at the center of the sealing plate 107, and a pressure introduction port 107b for allowing the internal pressure of the battery to act on the explosion-proof valve 109 around the thin portion 107a. As a hole. And the protrusion part 109a of the explosion-proof valve 109 is welded to the upper surface of this thin part 107a, and the welding part 111 is comprised. The thin-walled portion 107a provided on the sealing plate 107, the protruding portion 109a of the explosion-proof valve 109, etc., only show a cut surface for easy understanding on the drawing, and the contour behind the cut surface is The illustration is omitted. In addition, the welded portion 111 of the thin-walled portion 107a of the sealing plate 107 and the protruding portion 109a of the explosion-proof valve 109 is also shown in an exaggerated state for the sake of easy understanding on the drawing.

  The terminal plate 108 is made of rolled steel, has a nickel-plated surface, and has a hat shape with a peripheral edge portion. The terminal plate 108 is provided with a gas discharge port 108a. The explosion-proof valve 109 is made of aluminum and has a disk shape. A projection 109a having a tip portion is provided on the power generation element side (lower side in FIG. 7) at the center thereof, and a thin-walled portion 109b is provided. As described above, the lower surface of the protruding portion 109a is welded to the upper surface of the thin portion 107a of the sealing plate 107 to constitute the welded portion 111. The insulating packing 110 is made of PP and has an annular shape. The insulating packing 110 is disposed at the upper portion of the peripheral edge of the sealing plate 107, and the explosion-proof valve 109 is disposed on the upper portion thereof, and insulates the sealing plate 107 and the explosion-proof valve 109. The gap between the two is sealed so that the non-aqueous electrolyte does not leak between the two. The annular gasket 112 is made of PP, the lead body 113 is made of aluminum, the sealing plate 107 and the positive electrode 101 are connected to each other, an insulator 114 is disposed on the upper part of the wound electrode body, and the negative electrode 102 and the battery container 105 are The bottom is connected by a lead body 115 made of nickel.

  In this lithium ion secondary battery, the thin portion 107a of the sealing plate 107 and the protruding portion 109a of the explosion-proof valve 109 are in contact with each other at the welded portion 111, and the peripheral portion of the explosion-proof valve 109 and the peripheral portion of the terminal plate 108 are in contact. Since the positive electrode 101 and the sealing plate 107 are connected by the positive electrode side lead body 113, in the normal state, the positive electrode 101 and the terminal plate 108 are the lead body 113, the sealing plate 107, the explosion-proof valve 109, and their welding. An electrical connection is obtained by the portion 111 and functions normally as an electric circuit.

  When an abnormal situation occurs in the battery, such as exposure of the battery to a high temperature, and gas is generated inside the battery and the internal pressure of the battery increases, the central portion of the explosion-proof valve 109 increases in the internal pressure direction due to the increase in internal pressure. (The upper direction in FIG. 7) is deformed, and accordingly, the thin portion 107a integrated with the welded portion 111 is subjected to a shearing force to break the thin portion 107a, or the protruding portion of the explosion-proof valve 109. After the welded portion 111 between the 109a and the thin portion 107a of the sealing plate 107 is peeled off, the thin portion 109b provided on the explosion-proof valve 109 is cleaved to discharge the gas from the gas discharge port 108a of the terminal plate 108 to the outside of the battery. It is designed to prevent the battery from bursting.

Example A2
A lithium ion secondary battery A2 was produced in the same manner as in Example A1, except that the separator was changed to the separator a2 produced in Example a2.

Example A3
A lithium ion secondary battery A3 was produced in the same manner as in Example A1, except that the separator was changed to the separator a3 produced in Example a3.

Example A4
A lithium ion secondary battery A4 was produced in the same manner as in Example A1, except that the separator was changed to the separator a4 produced in Example a4.

Comparative Example B1
A lithium ion secondary battery B1 was produced in the same manner as in Example A1, except that the separator was changed to the separator b1 produced in Comparative Example b1.

Comparative Example B2
A lithium ion secondary battery B2 was produced in the same manner as in Example A1, except that the separator was changed to the separator b2 produced in Comparative Example b2.

Comparative Example B3
A lithium ion secondary battery B3 was produced in the same manner as in Example A1, except that the separator was changed to the separator b3 produced in Comparative Example b3.

Comparative Example B4
A lithium ion secondary battery B4 was produced in the same manner as in Example A1, except that the separator was changed to the separator b4 produced in Comparative Example b4.

Comparative Example B5
A lithium ion secondary battery B5 was produced in the same manner as in Example A1, except that the separator was changed to the separator b5 produced in Comparative Example b5.

Comparative Example B6
A lithium ion secondary battery B6 was produced in the same manner as in Example A1, except that the separator was changed to the separator b6 produced in Comparative Example b6.

Comparative Example B7
A lithium ion secondary battery B7 was produced in the same manner as in Example A1, except that the separator was changed to the separator b7 produced in Comparative Example b7.

Comparative Example B8
A lithium ion secondary battery B8 was produced in the same manner as in Example A1, except that the separator was changed to the separator b8 produced in Comparative Example b8.

  The following overcharge tests were conducted on the lithium ion secondary batteries of Examples and Comparative Examples. The results are shown in Table 3.

(Overcharge test)
About each lithium ion secondary battery of an Example and a comparative example, it carried out constant current charge until it became 4.2V with the electric current value of 1C, and then performed constant voltage charging until the electric current value became 0.05C with 4.2V. And fully charged. Each of the batteries thereafter was charged at a constant current until the current value of 2C reached 8.4 V, and then charged at a constant voltage of 8.4 V to obtain an overcharged state. The maximum temperature (peak temperature) was measured by monitoring the external temperature of each battery in the process of overcharging.

  Although the external temperature of the battery gradually increased by the overcharge test, as shown in Table 3, a separator having a second separator layer containing composite particles containing the thermoplastic resin (B) and the resin (C) was used. The lithium ion secondary batteries of Examples A1 to A4 are the same as the batteries of Comparative Examples B6 to B8 using separators having separator layers containing resin particles composed only of the thermoplastic resin (B). The peak temperature was lower than the batteries of Comparative Examples B1 to B5 using a separator having no separator layer, further heat generation was suppressed, and the battery had good safety.

DESCRIPTION OF SYMBOLS 10 1st separator layer 11 Polypropylene layer 12 Polyethylene layer 20 2nd separator layer 30 3rd separator layer 101 Positive electrode 102 Negative electrode 103 Separator 104 Non-aqueous electrolyte 105 Battery container

Claims (11)

A microporous first separator layer mainly composed of a thermoplastic resin (A) having a melting point of 125 to 170 ° C. ,
A thermoplastic resin (B) that has a melting point of 80 to 140 ° C. and melts at a temperature lower than that of the thermoplastic resin (A), and a melting point of 100 to 170 ° C., which is higher than the thermoplastic resin (B). second separator layer containing composite particles comprising a resin which melts (C) even at high temperatures, as well as
Have a third separator layer having a higher heat resistance temperature than the first separator layer and the second separator layer,
The composite particles, electrochemical, characterized in that either one of the thermoplastic resin (B) and the resin (C) forms a core and the other to have a core-shell structure forming the shell Element separator.   The separator for an electrochemical element according to claim 1, wherein the thermoplastic resin (B) has a melt viscosity at 140 ° C. of 5 to 100,000 mPa · s. The separator for an electrochemical element according to claim 1 or 2 , wherein the second separator layer is disposed on one surface of the first separator layer, and the third separator layer is disposed on the other surface. The separator for an electrochemical element according to any one of claims 1 to 3 , wherein a melt filling rate of the second separator layer at 140 ° C with respect to the first separator layer is 3 to 200%. The said 1st separator layer is a separator for electrochemical elements in any one of Claims 1-4 containing 2 or more types of thermoplastic resins from which melting | fusing point differs as said thermoplastic resin (A). The composite particles of the second separator layer contain polyethylene or modified polyethylene as the thermoplastic resin (B), and contain polypropylene or modified polypropylene as the resin (C). The separator for electrochemical elements according to any one of 5 . The separator for an electrochemical element according to any one of claims 1 to 6, wherein the third separator layer contains an inorganic filler. The separator for an electrochemical element according to claim 7 , wherein the third separator layer contains at least one selected from the group consisting of aluminum hydroxide, boehmite, alumina, and silica as the inorganic filler. An electrochemical element having a positive electrode, a negative electrode, a separator and a non-aqueous electrolyte,
The said separator is an electrochemical element separator in any one of Claims 1-8 , The electrochemical element characterized by the above-mentioned. The electrochemical device according to claim 9 , wherein the second separator layer in the separator faces the negative electrode. The separator, the positive electrode and at least one electrochemical device according to claim 9 or 1 0 is integral of the negative electrode.