WO2015022862A1

WO2015022862A1 - Separator for electrochemical devices, and electrochemical device

Info

Publication number: WO2015022862A1
Application number: PCT/JP2014/070105
Authority: WO
Inventors: 雅一満永; 良幸高森; 野家　明彦; 松本　修明
Original assignee: 日立マクセル株式会社
Priority date: 2013-08-13
Filing date: 2014-07-30
Publication date: 2015-02-19

Abstract

This separator for electrochemical devices is characterized by being provided with: a microporous first separator layer which is mainly formed of a thermoplastic resin and shuts down at a predetermined temperature; a microporous second separator layer which has heat resistance; and a microporous third separator layer which contains a low-melting-point material that melts at a lower temperature than the thermoplastic resin of the first separator layer, and which shuts down at a temperature that is lower than the shutdown temperature of the first separator layer. This separator for electrochemical devices is also characterized in that the low-melting-point material of the third separator layer has a melt viscosity of from 5 mPa·s to 100,000 mPa·s (inclusive) at 140°C.

Description

Electrochemical element separator and electrochemical element

The present invention relates to an electrochemical element separator and 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. In addition, with lithium ion secondary batteries, the risk of thermal runaway, such as abnormal heat generation, increases with increasing energy density, and thus safety measures are also strongly required.

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

Since most of the thermal runaway of lithium ion secondary batteries is triggered by internal short circuit of the battery, it can be said that the functioning to the separator occupies an important position in the safety measures of the lithium ion secondary battery. . As a function to the separator considering the safety of the lithium ion secondary battery, until now, when the battery generates heat, the separator melts when the melting point of the thermoplastic resin such as polyolefin is exceeded. It is common to provide a shutdown function that suppresses further heat generation of the battery by closing the through hole and cutting off 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 battery is safely stopped, the temperature does not start to decrease immediately after the shutdown temperature is reached, but starts to decrease after the shutdown temperature is exceeded to some extent.

A separator used in a lithium ion secondary battery is a microporous film made of a thermoplastic resin (hereinafter referred to as a microporous film). In order to improve porosity and strength, uniaxial stretching or biaxial stretching is performed. Applied. Due to the stretching, the microporous membrane is distorted, which may cause film breakage due to thermal contraction when the battery temperature rises. The temperature at which this film breaks is higher than the shutdown temperature but is very close.

The separator using only the microporous membrane described above exhibits the shutdown function after the temperature reaches the shutdown temperature due to the rise in battery temperature, and cuts off the current. However, due to the above circumstances, the temperature of the battery continues to rise while the rate of rise is suppressed. When the temperature at which film breakage occurs due to heat shrinkage is reached, the separator is broken, which may cause an internal short circuit due to contact between the positive electrode and the negative electrode.

Therefore, the separator disclosed in Patent Document 1 does not use the microporous film as described above, and uses a woven fabric or a non-woven fabric that does not cause a membrane breakage. And since such a woven fabric or nonwoven fabric does not have a shutdown function, a resin having a shutdown function is included in the woven fabric or nonwoven fabric.

A conventional separator using a microporous membrane has the above-mentioned problem of membrane breakage. Moreover, in the separator described in Patent Document 1, the problem of film breakage is eliminated, but when the battery temperature rises to a temperature considerably higher than the shutdown temperature, the resin having the shutdown function flows out from the woven fabric or the nonwoven fabric. There is.

Japanese Unexamined Patent Publication No. 2007-157723

As described above, when there is only one configuration having a shutdown function, there is a problem that the temperature rise is not sufficiently suppressed.

(1) According to the first aspect of the present invention, the separator for an electrochemical element is mainly composed of a thermoplastic resin, has a microporous first separator layer that shuts down at a predetermined temperature, and has heat resistance. And a microporous second separator layer and a microporous material that contains a low melting point material that melts at a temperature lower than the thermoplastic resin of the first separator layer, and performs shutdown at a temperature lower than the shutdown temperature of the first separator layer. The low-melting-point material of the third separator layer has a melt viscosity at 140 ° C. of 5 mPa · s or more and 100000 mPa · s or less.
(2) According to the second aspect of the present invention, the electrochemical element separator is the electrochemical element separator according to the first aspect, wherein the second separator layer is laminated on one surface of the first separator layer, and the other The third separator layer is preferably laminated on the surface.
(3) According to the third aspect of the present invention, the electrochemical element separator in the electrochemical element separator according to the second aspect is a melt filling rate at 140 ° C. with respect to the first separator layer of the third separator layer. Is preferably 3% or more and 200% or less.
(4) According to the fourth aspect of the present invention, the electrochemical element separator is formed of a plurality of microporous films having different melting points in the electrochemical element separator according to any of the first to third aspects. Is preferred.
(5) According to the fifth aspect of the present invention, the separator for an electrochemical element according to any one of the first to fourth electrochemical element separators, the melting point of the thermoplastic resin is 125 ° C. or more and 170 ° C. or less, The melting point of the low melting point material is preferably 80 ° C. or higher and 140 ° C. or lower.
(6) According to the sixth aspect of the present invention, in the electrochemical element separator according to any one of the first to fifth aspects, the second separator layer preferably contains an inorganic filler. .
(7) According to the seventh aspect of the present invention, the electrochemical element separator is the electrochemical element separator according to the sixth aspect, wherein the inorganic filler is aluminum hydroxide, boehmite, alumina, magnesium hydroxide, magnesium oxide. And at least one selected from the group consisting of silica.
(8) According to an eighth aspect of the present invention, the electrochemical element separator is the electrochemical element separator according to any one of the first to seventh aspects, wherein the first separator layer is formed by a stretching method and a pore forming method. It is a microporous film formed using at least one, and the second separator layer and the third separator layer are formed by applying a separator layer forming composition to the first separator layer. Is preferred.
(9) According to a ninth aspect of the present invention, the electrochemical element separator is the electrochemical element separator according to any one of the first to seventh aspects, wherein the thickness of the first separator layer is 4 to 20 μm, The thickness of the second separator layer is preferably 3 to 10 μm, and the thickness of the third separator layer is preferably 3 to 10 μm.
(10) According to the tenth aspect of the present invention, the electrochemical element separator is the electrochemical element separator according to any one of the first to seventh aspects, wherein the second separator layer comprises an inorganic filler and an organic binder. And the inorganic filler content is 40% by volume or more and 95% by volume or less per total volume of the second separator layer, and the organic binder content is 0.5% by volume or more and 10% by volume per total volume of the second separator layer. The following is preferable.
(11) According to an eleventh aspect of the present invention, the electrochemical element separator is the electrochemical element separator according to any one of the first to seventh aspects, wherein the third separator layer comprises a thermoplastic resin and an organic binder. The content of the thermoplastic resin is 70% by volume or more per total volume of the components of the third separator layer, and the content of the organic binder is 0.5% by volume per total volume of the components of the third separator layer The above is preferable.
(12) According to the twelfth aspect of the present invention, the electrochemical element has a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, and the separator is the first to eleventh separator for an electrochemical element.
(13) According to the thirteenth aspect of the present invention, in the electrochemical element according to the twelfth aspect, the third separator layer preferably faces the negative electrode.
(14) According to the fourteenth aspect of the present invention, in the electrochemical element according to the eleventh or twelfth aspect, the separator is preferably integrated with at least one of the positive electrode and the negative electrode. .

According to the present invention, a highly safe separator for an electrochemical element and an electrochemical element can be obtained.

Sectional drawing of the separator of this invention. Sectional drawing of the separator of this invention. The comparison table of an Example and a comparative example about a separator and a battery. Temperature dependence of the resistance value of the separator of the present invention. Temperature dependence of the resistance value of a conventional separator.

The separator is interposed between the positive electrode and the negative electrode and overlaps to constitute an electrode group of an electrochemical element such as a lithium ion secondary battery. After describing the embodiment of the separator of the present invention, the embodiment of the electrochemical device of the present invention on which the separator is mounted will be described.

--Embodiment of separator--
Hereinafter, the separator of the present invention will be described. The separator of the present invention has at least three layers of a first separator layer, a second separator layer, and a third separator layer, and has a multilayer structure that performs shutdown at each of a plurality of set shutdown temperatures. In addition, it has resistance to membrane breakage due to heat shrinkage and melting of the material. First, each separator layer will be described, and then the configuration of the separator of the present invention will be described.

<First separator layer>
A 1st separator layer becomes a base material of a separator and the positive electrode and negative electrode which an electrochemical element has are mainly isolated by the 1st separator layer. The separator has a plurality of vacancies through which lithium ions communicating between the one surface side and the other surface side can pass. The first separator layer is mainly composed of a thermoplastic resin, and when the internal temperature of the electrochemical element using the separator is equal to or higher than the melting point of the thermoplastic resin constituting the first separator layer, the first separator layer is heated. The plastic resin melts and closes the micropores of the first separator layer, thereby causing a shutdown that suppresses the progress of the electrochemical reaction. This shutdown layer by the first separator layer is called a secondary shutdown layer. The 1st separator layer is good also as a structure provided with porous substrates, such as a nonwoven fabric. The separator according to the present invention includes a primary shutdown layer that melts at a temperature lower than that of the secondary shutdown layer, that is, a low-temperature shutdown layer. The primary shutdown layer or the low-temperature shutdown layer will be described later. .

The thermoplastic resin constituting the first separator layer is electrically insulating, stable against non-aqueous electrolyte held in the electrochemical element, and redox within the operating voltage range of the electrochemical element. An electrochemically stable material is preferred. Specific examples of such thermoplastic resins include, for example, low density polyethylene (LDPE), high density polyethylene (HDPE), modified polyethylene (modified PE), polypropylene (PP), paraffin, wax copolymer polyolefin, polyolefin derivative ( Polyolefins such as chlorinated polyethylene, polyvinylidene chloride, polyvinyl chloride, fluororesin); polyvinyl alcohol; polyimide; aramid and the like. Examples of the copolymer polyolefin include ethylene-vinyl monomer copolymer (EVA), more specifically, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, ethylene-methyl acrylate copolymer, ethylene- Examples thereof include acrylic acid copolymers, ethylene-methacrylic acid copolymers, and ethylene-vinyl alcohol copolymers. For the first separator layer, only one of the exemplified thermoplastic resins may be used, or two or more may be used in combination.

Among the exemplified thermoplastic resins, it is preferable to use a resin having a melting point of 125 ° C. or higher and 170 ° C. or lower measured using a differential scanning calorimeter (DSC) in accordance with JISK 7121. . In this case, the shutdown in the separator appears under more preferable conditions.

The first separator layer includes a thermoplastic resin having a melting point of 125 ° C. or higher and 170 ° C. or lower (hereinafter referred to as “resin (A)”) and a thermoplastic resin having a higher melting point (hereinafter referred to as “resin (B)”. ) "]] Is preferably used in combination. In the case of the first separator layer containing the resin (A) and the resin (B), after the shutdown occurs due to the melting of the resin (A), the first separator layer is reached until the melting point of the resin (B) is reached. The layer shape (separator shape) can be maintained. Therefore, even when the device temperature 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. Further, when the temperature in the electrochemical element exceeds the melting point of the resin (B), the resin (B) is also melted, and a thick layer formed of the resin (A) and the resin (B) after melting is formed. By being formed, the shutdown function is enhanced. Furthermore, the separator has a stable shape at a high temperature as compared with a single layer structure.

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

The melting point of the resin (B) may be higher than the melting point of the resin (A). For example, the melting point of the resin (A) is preferably 10 ° C. or higher. Furthermore, the specific melting point of the resin (B) is preferably 130 ° C. or higher, and preferably 200 ° C. or lower.

The content of the thermoplastic resin in the first separator layer [when the above resin (A) and resin (B) are used in combination, the total content thereof) is the total volume of the components of the first separator layer ( The total volume excluding the void portion) is 50% by volume or more, preferably 70% by volume or more, and may be 100% by volume, that is, only thermoplastic resin.

As 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. For example, a microporous film can be formed by a stretching method. In other words, the film or sheet formed using the thermoplastic resin mixed with an inorganic filler is uniaxially or biaxially stretched to form fine pores, and then manufactured by removing the inorganic filler as necessary. can do. A microporous film can also be formed by a pore formation method using a solvent. That is, the thermoplastic resin exemplified above and other resin or paraffin are mixed to form a film or sheet, and then the film or sheet is immersed in a solvent that dissolves only the other resin or paraffin. It is also possible to manufacture by forming pores by dissolving only other resins and paraffin. Furthermore, a microporous film made of a thermoplastic resin produced by a method combining a stretching method and a pore forming method can also be used.

Among such microporous membranes made of thermoplastic resin, specific examples of using only the resin (A) include, for example, a microporous membrane composed of a single layer containing PE and a single layer containing PP. A microporous membrane is mentioned. Moreover, as a specific example of the combination of the resin (A) and the resin (B), for example, a microporous membrane having a two-layer structure having a layer containing PP on one side of a layer containing PE, PE is contained. Examples thereof include a microporous membrane having a three-layer structure having layers containing PP on both sides of the layer.

In particular, when two types of resin (A) and resin (B) are used in combination, a three-layer structure is preferable. When the two-layer structure is used, there may be a problem in battery manufacture, such as the separator layer being curved due to the difference in physical properties of each resin. However, the three-layer structure is easy to handle. In addition, in the case of a three-layer structure in which two kinds of resins (A) and resin (B) are used in combination, the melting point of the resin constituting the outer layer is preferably higher than the melting point of the resin constituting the inner layer. It is most preferable to provide a layer composed of the resin (B) on both sides of the layer composed of A). As such a multilayer structure, a combination of high density polyethylene and polypropylene is exemplified. For high density polyethylene, the melting point is preferably 125 ° C. to 140 ° C., and for polypropylene, it is preferably 160 ° C. to 170 ° C. In addition, in order to provide the function of maintaining the shape stabilizing function at high temperatures, it is preferable to employ a material (polypropylene or the like) having a melting point of 140 ° C. or higher for at least one layer.

In addition, the first separator layer, together with the resin (A) and the resin (B), has a melting point of 125 ° C. or higher and 170 ° C. or lower and a higher melting point than the resin (B) [hereinafter, “resin ( C) "] can be used in combination. Examples of combinations of resin (A), resin (B), and resin (C) include low density polyethylene having a melting point of 80 ° C. to 125 ° C., high density polyethylene having a melting point of 125 ° C. to 140 ° C., melting point of 160 ° C. A three-layer structure of polypropylene at 170 ° C. is illustrated. It is preferable to provide at least one layer having a melting point of 140 ° C. or higher in the first separator layer because it has a shape stabilizing function for maintaining the structure at high temperature.

The degree of porosity of the first separator layer can be expressed as porosity. The porosity is obtained by using the actual volume (v) occupied by the actual resin with respect to the apparent volume (V) obtained from the thickness (t) × width (w) × length (l) of the separator (V -V) / V. When the specific gravity of the resin is known, the weight of the cut-out separator is measured, and the actual volume (v) is obtained from the specific gravity. When the apparent volume (V) is obtained, 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 measurement, an ultra pycnometer and a mercury porosimeter should just be used. The porosity of the first separator layer is preferably 30% or more, and more preferably 35% or more. When it is 30% or less, the separator becomes a resistance, and the output of the electrochemical device produced using the separator is lowered. The porosity is preferably 90% or less, more preferably 80% or less. When the porosity is 90% or more, the risk of internal short circuit increases.

<Second separator layer>

The second separator layer 20 has a heat resistant material and has an action of suppressing an internal short circuit due to a film breakage of the separator by suppressing heat shrinkage. The second separator layer may be composed only of an inorganic filler of a heat resistant material, or may include an inorganic filler and an organic binder, and the inorganic filler may have a structure bound with an organic binder. Good.

A separator including a second separator layer having an inorganic filler with high heat resistance is capable of shrinking 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 contracts. Breaking membrane can be suppressed. Moreover, even if the first separator layer breaks, the second separator layer having an inorganic filler acts as a spacer that partitions the positive electrode and the negative electrode, so that an effect of suppressing an internal short circuit of the electrochemical element can be expected. In addition, the inorganic filler can improve the piercing strength of the separator, and even when lithium dendrite crystals are generated, the separator can be prevented from being broken and short-circuited. Therefore, the separator including the second separator layer that also has an inorganic filler can further enhance the safety of the electrochemical element.

As the inorganic filler, those having a heat resistant temperature of 150 ° C. or higher are preferable. The “heat-resistant temperature is 150 ° C. or higher” in the inorganic filler and the fibrous material described later in this specification means that no shape change is visually confirmed at least at 150 ° C.

Specific examples of the constituent material of the inorganic filler having such a heat-resistant temperature include, for example, iron oxide, magnesium oxide, SiO ₂ (silica), Al ₂ O ₃ (alumina), TiO ₂ , BaTiO ₂ , ZrO _{2 and the} like. Inorganic oxides; inorganic hydroxides such as Al (OH) ₃ (aluminum hydroxide) and magnesium hydroxide; inorganic nitrides such as aluminum nitride and silicon nitride; poorly soluble such as calcium fluoride, barium fluoride and barium sulfate Ionic crystals; covalently bonded crystals such as silicon and diamond; and 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 metal; conductive oxide such as SnO ₂ and tin-indium oxide (ITO); carbonaceous material such as carbon black and graphite; For example, it may be a particle that is 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, magnesium hydroxide, magnesium oxide, and boehmite are more preferable, and boehmite is more preferable. 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 particle size of the inorganic filler is an average particle size measured by a method described later, preferably 0.01 μm or more, more preferably 0.1 μm or more, and preferably 20 μm or less, More preferably, it is 5 μm or less.

Specific examples of the organic binder include, for example, EVA (with a structural unit derived from vinyl acetate of 20 to 35 mol%), ethylene-acrylic acid copolymer such as ethylene-ethyl acrylate copolymer (EEA), fluorine-based 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 Acetamide (PNVA), butyl acrylate-acrylic acid copolymer, cross-linked acrylic resin, polyurethane, epoxy resin and the like can be mentioned, and in particular, a heat-resistant binder having a heat-resistant temperature of 150 ° C. or higher is preferably used. As the organic binder, those exemplified above may be used alone 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 “Evaflex Series (EVA)” from Mitsui DuPont Polychemical, EVA from Nihon Unicar, and “Evaflex-EEA Series (Ethylene) from Mitsui DuPont Polychemical. -Acrylic acid copolymer) ", EEA of Nihon Unicar," Daiel Latex Series (Fluororubber) "of Daikin Industries," TRD-2001 (SBR) "of JSR," BM-400B of Nippon Zeon " (SBR) ".

When the above 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.

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.

The average particle size of the fine particles (inorganic filler and low melting point material to be described later) referred to in this specification is, for example, using an aqueous dispersion of fine particles and using a dense particle size analyzer “FPAR-1000” manufactured by Otsuka Electronics Co., Ltd. Then, it can be defined as D ₅₀ (particle diameter with a volume cumulative frequency of 50%) measured by dynamic light scattering.

When the second separator layer contains an organic binder, the content is 0.2% by volume in the total volume of the constituent components of the second separator layer from the viewpoint of better ensuring the effect of the organic binder. It is preferable that the amount be 0.5% by 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 effect 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.

When the inorganic filler is contained in the second separator layer, the content is 10% by volume in the total volume of the constituent components of the second separator layer, from the viewpoint of ensuring the above-described effect by the inorganic filler better. It is preferable that it is above, and it is more preferable that it is 40 volume% or more. However, if the amount of the inorganic filler in the second 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. Therefore, the inorganic filler in the second separator layer 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 second separator layer.

When the fibrous material is contained in the second separator layer, the content is 5 out of the total volume of the constituent components of the second separator layer, from the viewpoint of ensuring the above-described effect by the fibrous material better. The volume is preferably at least volume%, more preferably at least 10 volume%. However, if the amount of the fibrous material in the second separator layer is too large, the amount of other components becomes too small, and there is a possibility that the effect by them cannot be sufficiently secured. The content of the shaped 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 second separator layer.

Note that the above-described inorganic filler, organic binder, and fibrous material may be contained in the first separator layer.

In addition, as can be seen from the measurement results of air permeability resistance at room temperature in the examples described later, the second separator layer has ion permeability.

<Third separator layer>
The thermoplastic resin constituting the third separator layer is a material having a melting point lower than the melting point of “resin (A)” exemplified above as a thermoplastic resin layer (secondary shutdown layer) that causes shutdown [hereinafter, “ It is called “low melting point material”. This resin layer is called a primary shutdown layer (or a low temperature shutdown layer). This resin layer has electrical insulation, is stable with respect to the non-aqueous electrolyte retained in the electrochemical element, and is not easily oxidized or reduced in the operating voltage range of the electrochemical element, and is electrochemically stable. Are preferred. The third separator layer melts while the first separator layer is maintained, and forms a film that blocks the passage of lithium ions on the surface of the separator.

Specific examples of such a thermoplastic resin include, for example, low density polyethylene from the viewpoint of affinity with other layers (for example, adhesiveness and non-reactivity) and resistance to an electrolytic solution used in a lithium ion battery. (LDPE), high density polyethylene (HDPE), modified polyethylene, polypropylene (PP), paraffin, wax, copolymer polyolefin such as ethylene-propylene copolymer, polyolefin derivatives (chlorinated polyethylene, polyvinylidene chloride, polyvinyl chloride, Polyolefin such as fluororesin; polyvinyl alcohol; polyimide; aramid and the like. Examples of the copolymer polyolefin include ethylene-vinyl monomer copolymer (EVA), more specifically, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, ethylene-methyl acrylate copolymer, ethylene. -Acrylic acid copolymer, ethylene-methacrylic acid copolymer, ethylene-vinyl alcohol copolymer and the like. For the third separator layer, only one of the thermoplastic resins exemplified above may be used, or two or more may be used in combination. A plurality of layers made of these thermoplastic resins and having different melting temperatures may be used in combination.

Among the thermoplastic resins exemplified above, those having a melting point of 80 to 140 ° C., particularly 125 ° C. or less, measured using a differential scanning calorimeter (DSC) according to JISK 7121. It is preferable to use it. In this case, the shutdown in the separator appears under more preferable conditions. More preferably, the melting temperature is in the range of 100 ° C to 120 ° C. The difference in melting point between the thermoplastic resins constituting the secondary shutdown layer and the third separator layer of the first separator layer is preferably within 30 ° C., particularly within 20 ° C.

Furthermore, there is no particular limitation on increasing the number of shutdown layers having different melting points such as the third and fourth shutdown layers.

The content of the thermoplastic resin in the third separator layer is 50% by volume or more and preferably 70% by volume or more in the total volume (total volume excluding the voids) of the constituent components of the third separator layer. 100 volume%, that is, it may be composed of only a thermoplastic resin. The third separator layer may be composed of only a low melting point material, or may include a low melting point material and an organic binder, and the low melting point material may be bonded to each other with an organic binder. .

The organic binder used for the third separator layer is appropriately used from the organic binders mentioned as the organic binder used for the second separator layer. 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 where an organic binder is contained in the third separator layer, the content is 0.2% by volume or more in the total volume of the constituent components of the third separator layer, from the viewpoint of ensuring a better effect 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 effect 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 coating amount (w) of the third separator containing at least a low melting point material, a binder, and a surfactant is the ratio of the volume (melting volume) when melted at high temperature to the pore volume of the first separator layer (melting filling) It is preferable to set the ratio to be within a predetermined range. For example, at 140 ° C., the melt filling rate is preferably 3% or more, and more preferably 10% or more. If it is less than 3%, the shutdown effect is weakened, and the effect of suppressing the heat generation of the electrochemical device produced using the electrochemical device separator is weakened. The melt filling rate is preferably 200% or less, and more preferably 150% or less. When the melt filling rate exceeds 200%, the separator becomes a resistance, and the output of an electrochemical element manufactured using the separator is lowered.

When the melt volume is expressed by a formula using the weight (w) of the third separator layer per 1 m ^{2 of} the first separator layer, the melt filling rate is expressed by the following formula (1).

The melt filling rate is expressed by the following formula (2).

here,
w: Weight of the third separator layer formed per 1 m ^{2 of} the first separator layer d: Specific gravity (true density) of the third separator layer
α: Linear expansion coefficient of the third separator layer β: Volume expansion coefficient of the third separator layer T: Shutdown temperature t: Room temperature V: Apparent volume per 1 m ^{2 of} the first separator layer v: 1 m of the first separator layer The actual volume per ² units.

The specific gravity (true density) of the third separator layer (including the third separator layer forming composition such as a binder and a surfactant) can be determined, for example, by measuring the dried product with an ultra pycnometer.

The melt viscosity of the low melting point material used for the third separator layer is preferably 5 mPa · s or more at 140 ° C., more preferably 8 mPa · s or more. When it is less than 5 mPa · s, the low melting point material melted at the time of shutdown easily flows out of the separator. The melt viscosity of the low melting point material is preferably 100,000 mPa · s or less at 140 ° C., more preferably 2000 mPa · s or less. When it is larger than 100,000 mPa · s, when the low melting point material is melted, the fluidity is small and the pores of the separator cannot be closed. Particularly, less than 1000 mPa · s is most preferable because it easily closes the pores of the separator. Moreover, the melt viscosity of the low melting point material used for the third separator layer is lower than that of the thermoplastic resin constituting the first separator layer, so that both the applicability and the shutdown performance can be improved. It becomes.

In addition, as can be seen from the measurement results of air permeability resistance at room temperature in the examples described later, the third separator layer has ion permeability.

Hereinafter, the configuration, thickness, air permeability, strength, and manufacturing method of the separator will be described.
<Configuration of separator>
FIG. 1 is a cross-sectional view showing an example of a typical configuration of a separator in the present embodiment. In the separator 1, the second separator layer 20 is provided on one surface of the first separator layer 10, and the third separator layer 30 is provided on the other surface of the first separator layer 10. The first separator layer 10 has a three-layer structure having B layers 12 and 12 made of a resin (B) on both surfaces of an A layer 11 made of a resin (A). The A layer 11 uses, for example, PE having a melting point of 137 ° C. as the resin (A), and performs a shutdown that melts at a shutdown temperature equal to or higher than the melting point to close the micropores. The B layer 12 uses, for example, PP having a melting point of 170 ° C. as the resin (B), maintains the structure up to the melting point when the element temperature rises, and then shuts down to close the micropores by melting.

The second separator layer 20 has, for example, an inorganic filler 21 which is a heat resistant material, and the heat resistant temperature is set to 150 ° C. or higher. Thereby, the thermal contraction of the separator 1 can be suppressed at least at 150 ° C. or lower. As the heat resistant temperature of the second separator layer is higher, the thermal contraction of the separator can be suppressed even at a higher temperature, and safety is improved.

The third separator layer 30 is a low melting point material having a melting point lower than the melting point of the resin (A) of the first separator layer 10, for example, PE having a melting point of 100 ° C. to 125 ° C. When the internal temperature exceeds the melting point, a shutdown (primary shutdown) is performed to melt and close the micropores. The third separator layer 30 is such a primary shutdown layer (low-temperature shutdown layer), and performs shutdown at a temperature lower than the shutdown temperature of the secondary shutdown layer that is the first separator layer 10. Therefore, shutdown can be performed at an earlier stage, and heat generation leading to thermal runaway can be suppressed.

If further heat generation occurs due to an internal short circuit or other cause after the first-stage shutdown, the temperature of the third separator layer 30 is further lowered by further increasing the temperature after the low melting point material is dissolved. To do. At this time, the low melting point material flows out of the separator 1 and the sustaining effect may be lost. Therefore, if the first separator layer 10 does not have a secondary shutdown layer, the possibility of further heat generation increases. However, in the separator 1 of the present embodiment, since the first separator layer 10 has the secondary shutdown layer, even if the sustained shutdown effect of the primary shutdown layer disappears, the secondary shutdown layer in the first separator layer 10 When the melting temperature is reached, the shutdown can be performed again. Thus, the presence of a plurality of shutdown layers having different shutdown temperatures makes it possible to suppress heat generation in a wider temperature range, thereby contributing to an improvement in safety.

Further, as described above, the second separator layer 20 has a heat resistant material and has a function of suppressing thermal shrinkage. By suppressing the heat shrinkage, an internal short circuit due to the film breakage of the separator can be suppressed. Therefore, the separator 1 of the present invention has a structure that combines a multi-stage shutdown by a plurality of thermoplastic resin layers having different melting points and a function of preventing film breakage by a heat-resistant material.

In the electrochemical device of the present embodiment, the third separator layer is partially melted by pre-heating by utilizing the fact that the third separator layer contains a thermoplastic resin having a relatively low melting temperature, and the electrode ( At least one of a positive electrode and a negative electrode). That is, when an electrochemical device is produced by combining a separator and an electrode, heating is performed in the vicinity of the melting temperature of the thermoplastic resin contained in the third separator in advance (preferably within 10 minutes, more preferably within 3 minutes). Thus, the thermoplastic resin can be partially melted and used as an adhesive that adheres the separator and the electrode. Lithium ion secondary batteries are known to expand and contract alternately when charging and discharging are repeated, resulting in a gap between the electrode and the separator, resulting in deterioration of battery performance. However, since the third separator layer is provided near the electrode, the separator and the electrode can be easily adhered to each other, and the deterioration is suppressed by using the third separator layer to adhere the separator and the electrode. can do.

Furthermore, it is preferable that the separator 1 of this embodiment is disposed with the third separator layer 30 facing the negative electrode and the second separator layer 20 facing the positive electrode due to the following circumstances. In the electrochemical device, dendrites are deposited by long-term use and grow from the negative electrode toward the positive electrode. Since this dendrite reacts with the electrolyte, a method for suppressing this reaction at an early stage is to physically cover the dendrite. In the electrochemical device having the separator arrangement described above, the effect of shortening the shutdown time was observed. In the electrochemical device having the separator arrangement described above, when the temperature of the electrochemical device rises and the third separator layer 30 is melted, the low melting point material of the melted third separator layer 30 may directly cover the dendrite and the negative electrode. is there. By forming the film on the negative electrode side, the reaction between the dendrite and the electrolyte can be suppressed early. In addition, the second separator layer is disposed opposite to the negative electrode, and dendrites are deposited by long-term use, grow from the negative electrode toward the positive electrode, and the tip protrudes from the second separator layer to the positive electrode side. When shutting down in a state, if the third separator melts, the tip of the dendrite may reach the positive electrode and short-circuit, but insulation can be maintained by using the reverse arrangement. As mentioned above, the safety | security of an electrochemical element can be improved more by the arrangement | positioning mentioned above.

On the other hand, when the third separator layer 30 is arranged on the positive electrode side, the first separator layer 10 and the second separator layer 20 exist between the negative electrode having dendrites and the third separator layer 30. Therefore, when the third separator layer 30 is arranged on the positive electrode side, the normal effect of the present invention can be obtained, but the molten low melting point material of the third separator layer 30 directly covers the dendrite and the negative electrode. Therefore, it is presumed that it takes time to suppress the reaction between the dendrite and the electrolytic solution as compared with the case where it is arranged on the negative electrode side.

FIG. 2 is a cross-sectional view showing another example of the typical configuration of the separator in the present embodiment. In the separator 1, the second separator layer 20 is provided on one surface of the first separator layer 10, and the third separator layer 30 is provided on one surface of the second separator layer 20. The third separator layer 30 is disposed to face the negative electrode, and the first separator layer 10 is disposed to face the positive electrode. Even in this configuration, the same effects as the separator 1 shown in FIG. 1 can be obtained.

As another configuration, the second separator layer is provided on one surface of the first separator layer, the third separator layer is provided on the other surface, and the third separator layer is stacked on one surface of the second separator layer. Provide. As a result, heat is easily transmitted from both sides to the third separator layer, the shutdown response to the battery temperature is improved, and the safety of the battery is further improved.

<Separator thickness>
The thickness of the separator of the present invention is 3 μm or more from the viewpoint of sufficiently insulating the positive electrode and the negative electrode, further enhancing the short-circuit prevention effect in the electrochemical element, ensuring the separator strength, and improving the handleability. Is preferably 5 μm or more. On the other hand, the thickness of the separator of the present invention is preferably 45 μm or less, preferably 30 μm or less, from the viewpoint of preventing an excessive hindrance to the movement of lithium ions and further increasing the energy density of the electrochemical device. It is more preferable.

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 resistance of the separator of the present invention is measured by a method in accordance with JIS P 8117, and the Gurley value indicated by the number of seconds that 100 mL of air passes through the membrane at room temperature (25 ° C.) is 10 to 500 sec. It is desirable to be. If the air permeability is too high, the ion permeability is reduced, whereas if it is too low, the strength of the separator may be reduced. 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 second separator layer that also contains an inorganic filler.

<Manufacturing method of separator>

The separator can be manufactured by forming and bonding the respective separator layers, but it is preferable that the second and third separator layers are provided by coating. Since the slurry or paste-like composition binds to the first separator, which is a microporous film, with high adhesion, defects such as interfacial peeling are unlikely to occur. Further, since the third separator enters the vicinity of the opening, at the time of shutdown, the low melting point material of the melted third separator layer easily closes the opening of the other separator, and an improvement in shutdown performance can be expected. For example, a composition for forming a second separator layer (slurry, paste, etc.) and a composition for forming a third separator layer (slurry, paste, etc.) are applied to a microporous film made of a thermoplastic resin constituting the first separator layer. It can be manufactured by applying in order or simultaneously and drying at a predetermined temperature to form the second separator layer and the third separator layer. If necessary, a surfactant may be used in the paint, or the first separator layer may be applied after surface treatment (corona treatment, ozone treatment, electron beam treatment, primer treatment, etc.). The composition for forming the separator layer can be applied using a bar coater, a gravure coater, a comma coater, a slit coater, a die coater, a spray device, or the like.

The composition for forming the second separator layer is prepared by dispersing an inorganic filler, a fibrous material, or the like in a solvent, and dispersing or dissolving an organic binder or a surfactant used as necessary in the solvent.

The composition for forming the third separator layer is prepared by dispersing or dissolving a low-melting-point material, fibrous material, etc. in a solvent, and dispersing or dissolving an organic binder or surfactant used in the above solvent as necessary. Is done. When the composition of the third separator layer forming composition is a dispersion or an emulsion, the shape of the fine particles is not particularly limited, and may be any shape such as a substantially spherical shape (including a true spherical shape), an elliptical shape, or a plate shape. There may be. The particle size of the composition for forming the third separator layer is an average particle size measured by the above method, preferably 0.01 μm or more, more preferably 0.1 μm or more, and 20 μm. Or less, more preferably 5 μm or less.

The solvent used in the composition for forming the second separator layer and the composition for forming the third separator layer can uniformly disperse the inorganic filler, the low melting point material, the fibrous material, and the like, 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. To these solvents, surfactants such as alcohol (ethylene glycol, propylene glycol, etc.) or various propylene oxide glycol ethers such as monomethyl acetate are appropriately added for the purpose of controlling interfacial tension and improving dispersibility. May be. When adding, it is preferable that content of surfactant shall be 2 mass% or more with respect to a solvent. 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. When water is used as a solvent, no harmful organic solvent vapor is generated in the step of drying after applying the separator, and the operation can be performed safely.

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 10 to 40% by mass, for example. For example, in the composition for forming the third separator layer, the surfactant may be 0.1 to 3% by mass, the binder is 1 to 10% by volume, and the low melting point material is 6 to 40% by mass. In particular, by setting the concentration of the low melting point material to 15 to 40% by mass or more, a uniform layer is formed and the amount of the low melting point material per unit area necessary for shutdown is secured, and the holes of the first separator are formed. Do not block. *

--Embodiment of electrochemical element--
<Configuration example of electrochemical element>
Hereinafter, as an example of an electrochemical element using the separator of the present invention, application to a lithium ion secondary battery (hereinafter also simply referred to as “battery”) will be described in detail. 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.

As the positive electrode, for example, one having a structure in which a positive electrode mixture layer containing a lithium-containing transition metal oxide, which is a positive electrode active material, a binder, a conductive auxiliary agent, and the like is provided on one side or both sides of the 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 , LiMn _{3 / 5} Ni _1/5 Co _1/5 O ₂ etc.).

As the positive electrode binder, for example, a fluororesin such as polyvinylidene fluoride (PVDF) is used. As the positive electrode conductive aid, 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 said method, You may manufacture by another method.

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

The lead part on the positive electrode side is usually provided by leaving the exposed part of the current collector without forming the positive electrode mixture layer on a part of the current collector and forming the lead part 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, as a negative electrode active material, lithium, such as graphite, pyrolytic carbons, cokes, glassy carbons, fired organic polymer compounds, mesocarbon microbeads (MCMB), and carbon fibers, can be occluded and released. 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 prepared by appropriately adding a conductive additive (carbon material such as carbon black) or a binder such as PVDF to these negative electrode active materials is finished into a molded body (negative electrode mixture layer) using the current collector as the 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 composition obtained by dispersing a negative electrode active material and a binder, and further 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 the electrode body, the separator may be integrated with at least one of the positive electrode and the negative electrode. 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 above lithium salt and does not cause a side reaction such as decomposition in the 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, cyclohexyl benzene, biphenyl, and fluorobenzene are used for the purpose of improving the safety, charge / discharge cycleability, and high-temperature storage properties of these non-aqueous electrolytes. Additives such as t-butylbenzene can also 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.

The electrochemical device of the present invention has a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, and the separator only needs to be the separator of the present invention. Other configurations and structures are not particularly limited. Various configurations and structures employed in known electrochemical elements can be applied. The electrochemical device to which the separator of the present invention can be applied is not particularly limited as long as it uses a non-aqueous electrolyte. In addition to a lithium ion secondary battery, a lithium ion primary battery, a super capacitor, etc. Any application that requires safety can be preferably applied. That is, the electrochemical device 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 of the present invention, and there is no particular limitation on the other configuration and structure, Various configurations and structures provided in various electrochemical elements (lithium ion secondary battery, lithium ion primary battery, supercapacitor, etc.) having a conventional non-aqueous electrolyte can be employed.

In the electrochemical device of the present invention, the separator of the present invention may have a configuration in which it is fixed and integrated with at least one of the positive electrode and the negative electrode.

The electrochemical element of the present invention can be applied to the same applications as conventionally known electrochemical elements.

--Example--
Hereinafter, the present invention will be described in detail based on examples. FIG. 3 shows a list of this embodiment. The following examples do not limit the present invention.

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

This slurry was applied to one side of a three-layered microporous film (thickness 16 μm, porosity 49%) of PP / high density PE / PP subjected to corona discharge treatment on both sides, and dried to provide one side of the first separator layer. A separator r1 having a second separator layer having a thickness of 5 μm was obtained.

Modified polyethylene: 97 parts by mass, and 3 parts by mass of an acrylate copolymer as a binder were added and dispersed water as a solvent to prepare a third separator layer forming slurry having a solid pigment of 30% by mass. Modified polyethylene having a melt viscosity of 300 mPa · s at 140 ° C. was used. The melting point of the modified polyethylene used here is 110 ° C. to 115 ° C. The melt viscosity at 140 ° C. used in this example is, for example, using a capillograph (manufactured by Toyo Seiki Co., Ltd.), using a nozzle with a length (L) of 10 mm and a diameter (D) of 1.0 mm. A value measured with a shear rate of 100 s ⁻¹ can be used.

The slurry was applied to a third separator layer having a thickness of 5 μm on the surface opposite to the second separator layer of the separator r1 having a second separator layer having a thickness of 5 μm on one side of the first separator layer, and dried. A separator a1 having second and third separator layers on both sides of one separator layer was obtained. As a result of calculating the melt filling rate, it was 23.3%. The schematic diagram of the separator configuration is the same as in FIG.

(Example a2)
Boehmite fine particles: 97 parts by mass, 3 parts by mass of an acrylate copolymer as a binder (a commercially available acrylate copolymer having butyl acrylate as a main component as a monomer component), water as a solvent is added and dispersed to obtain a solid content. A slurry for forming a second separator layer having a pigment content of 22% by mass was prepared.

This slurry was applied to one side of a three-layered microporous film (thickness 16 μm, porosity 49%) of PP / high density PE / PP subjected to corona discharge treatment on both sides, and dried to provide one side of the first separator layer. A separator r2 having a second separator layer having a thickness of 5 μm was obtained.

Modified polyethylene: 97 parts by mass, and 3 parts by mass of an acrylate copolymer as a binder were added and dispersed in water as a solvent to prepare a third separator layer forming slurry having a solid pigment of 30% by mass. Modified polyethylene having a melt viscosity of 300 mPa · s at 140 ° C. was used. The melting point of the modified polyethylene used here is 110 ° C. to 115 ° C.

The slurry was applied to a third separator layer having a thickness of 9 μm on the surface opposite to the second separator layer of the separator r2 having a second separator layer having a thickness of 5 μm on one side of the first separator layer, and dried. A separator a2 having second and third separator layers on both surfaces of the one separator layer was obtained. As a result of calculating the melt filling rate, it was 49.3%. The schematic diagram of the separator configuration is the same as in FIG.

(Example a3)
Boehmite fine particles: 97 parts by mass, 3 parts by mass of an acrylate copolymer as a binder (a commercially available acrylate copolymer having butyl acrylate as a main component as a monomer component), water as a solvent is added and dispersed to obtain a solid content. A slurry for forming a second separator layer having a pigment content of 22% by mass was prepared.

This slurry was applied to one side of a three-layered microporous film (thickness 16 μm, porosity 49%) of PP / high density PE / PP subjected to corona discharge treatment on both sides, and dried to provide one side of the first separator layer. A separator r3 having a second separator layer with a thickness of 3 μm was obtained.

Modified polyethylene: 97 parts by mass, and 3 parts by mass of an acrylate copolymer as a binder were added and dispersed with water as a solvent to prepare a third separator layer forming slurry having a solid content pigment of 35% by mass. Modified polyethylene having a melt viscosity of 20 mPa · s at 140 ° C. was used. The melting point of the modified polyethylene used here is 110 ° C. to 115 ° C.

The slurry was applied to a surface of the separator r3 having a second separator layer having a thickness of 3 μm on one side of the first separator layer, and a second separator layer having a thickness of 2 μm was applied to the surface opposite to the second separator layer, followed by drying. A separator a3 having second and third separator layers on both sides of one separator layer was obtained. As a result of calculating the melt filling rate, it was 10.2%. The schematic diagram of the separator configuration is the same as in FIG.

(Example a4)
Boehmite fine particles: 97 parts by mass, 3 parts by mass of an acrylate copolymer as a binder (a commercially available acrylate copolymer having butyl acrylate as a main component as a monomer component), water as a solvent is added and dispersed to obtain a solid content. A slurry for forming a second separator layer having a pigment content of 22% by mass was prepared.

This slurry was applied to one side of a three-layered microporous film (thickness 16 μm, porosity 49%) of PP / high density PE / PP subjected to corona discharge treatment on both sides, and dried to provide one side of the first separator layer. A separator r4 having a second separator layer with a thickness of 3 μm was obtained.

The slurry was applied to the surface on the opposite side of the second separator layer of the separator r4 having a second separator layer having a thickness of 3 μm on one side of the first separator layer, dried, and dried. A separator a4 having second and third separator layers on both surfaces of one separator layer was obtained. As a result of calculating the melt filling rate, it was 27.9%. The schematic diagram of the separator configuration is the same as in FIG.

(Example a5)
Boehmite fine particles: 97 parts by mass, 3 parts by mass of an acrylate copolymer as a binder (a commercially available acrylate copolymer having butyl acrylate as a main component as a monomer component), water as a solvent is added and dispersed to obtain a solid content. A slurry for forming a second separator layer having a pigment content of 22% by mass was prepared.

The slurry was applied to one side of a three-layered microporous film (thickness 20 μm, porosity 52%) of PP / high-density PE / PP subjected to corona discharge treatment on both sides, and dried to provide one side of the first separator layer. A separator r5 having a second separator layer with a thickness of 3 μm was obtained.

The slurry was applied to a surface of the first separator layer opposite to the second separator layer of the separator r5 having a second separator layer having a thickness of 3 μm on one side, dried, and then dried. A separator a5 having second and third separator layers on both surfaces of one separator layer was obtained. As a result of calculating the melt filling rate, it was 11.3%. The schematic diagram of the separator configuration is the same as in FIG.

(Example a6)
Boehmite fine particles: 97 parts by mass, 3 parts by mass of an acrylate copolymer as a binder (a commercially available acrylate copolymer having butyl acrylate as a main component as a monomer component), water as a solvent is added and dispersed to obtain a solid content. A slurry for forming a second separator layer having a pigment content of 30% by mass was prepared.

This slurry is applied to one side of a single layer microporous membrane (thickness 16 μm, porosity 45%) of high density PE that has been subjected to corona discharge treatment on both sides and dried, and the first separator layer has a thickness of 5 μm on one side. A separator r6 having a second separator layer was obtained.

Modified polyethylene: 97 parts by mass, and 3 parts by mass of an acrylate copolymer as a binder were added and dispersed in water as a solvent to prepare a third separator layer forming slurry having a solid pigment of 30% by mass. Modified polyethylene having a melt viscosity of 300 mPa · s at 140 ° C. was used. The melting point of the modified polyethylene used here is 110 ° C. to 115 ° C. The slurry was applied to a third separator layer having a thickness of 5 μm on the surface opposite to the second separator layer of the separator r6 having a second separator layer having a thickness of 5 μm on one side of the first separator layer, and dried. The separator a6 which has a 2nd, 3rd separator layer on both surfaces of 1 separator layer, respectively was obtained. As a result of calculating the melt filling rate, it was 49.3%.

(Example a7)
Boehmite fine particles: 97 parts by mass, 3 parts by mass of an acrylate copolymer as a binder (a commercially available acrylate copolymer having butyl acrylate as a main component as a monomer component), water as a solvent is added and dispersed to obtain a solid content. A slurry for forming a second separator layer having a pigment content of 30% by mass was prepared.

This slurry was applied to one side (corona discharge treatment surface) of a microporous film (thickness 16 μm, porosity 49%) of PP / high density PE / PP having a corona discharge treatment on one side and dried, A separator r7 having a second separator layer having a thickness of 5 μm on one surface of the first separator layer was obtained.

The slurry was applied to the upper surface of the second separator layer of the separator r7 having the second separator layer having a thickness of 5 μm on one side of the first separator layer, and then applied to the first separator layer, followed by drying. A separator a7 having a separator layer in which a second separator layer and a third separator layer were sequentially applied on one side of the separator layer was obtained. A schematic diagram of the separator configuration is shown in FIG. As a result of calculating the melt filling rate, it was 44.6%.

(Comparative Example b1)
Boehmite fine particles: 97 parts by mass, 3 parts by mass of an acrylate copolymer as a binder (a commercially available acrylate copolymer having butyl acrylate as a main component as a monomer component), water as a solvent is added and dispersed to obtain a solid content. A slurry for forming a second separator layer having a pigment content of 30% by mass was prepared.

This slurry was applied to one side (corona discharge treatment surface) of a microporous film (thickness 16 μm, porosity 49%) of PP / high density PE / PP having a corona discharge treatment on one side and dried, A separator b1 having a second separator layer having a thickness of 5 μm on one surface of the first separator layer was obtained.

(Comparative Example b2)
Boehmite fine particles: 97 parts by mass, 3 parts by mass of an acrylate copolymer as a binder (a commercially available acrylate copolymer having butyl acrylate as a main component as a monomer component), water as a solvent is added and dispersed to obtain a solid content. A slurry for forming a second separator layer having a pigment content of 25% by mass was prepared.

This slurry was applied to one side (corona discharge treatment surface) of a three-layered microporous film (thickness 20 μm, porosity 52%) of PP / high density PE / PP treated on one side with corona discharge, and dried. A separator b2 having a second separator layer having a thickness of 5 μm on one surface of the first separator layer was obtained.

(Comparative Example b3)
A separator b3 having only a first separator layer made of a microporous membrane (thickness: 16 μm) having a three-layer structure of PP / high density PE / PP was used in various experiments. As a result of measuring the porosity with an ultra pycnometer, it was 49%.

(Comparative Example b4)
A separator b4 having only a first separator layer made of a microporous film (thickness 20 μm) having a three-layer structure of PP / high density PE / PP was used in various experiments. As a result of measuring the porosity with an ultra pycnometer, it was 52%.

(Comparative Example b5)
A separator having only a first separator layer composed of a single layer microporous film of high density PE (thickness 16 μm, porosity 45%) is defined as a separator b5.

The configuration of the above separators a1 to a7 and b1 to b5 is shown in the column of FIG.

<Example of electrochemical device>
(Preparation of negative electrode) Production Example 1
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.

(Preparation of positive electrode) Production Example 2
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.

(Example A1)
The negative electrode produced in Production Example 1 and the positive electrode produced in Production Example 2 were overlapped with the separator a1 produced in Example a1 interposed, and wound in a spiral shape to produce a wound electrode body. In this wound electrode body, the second separator layer of the separator was made to face the positive electrode. The above wound electrode body was loaded into a battery container of 18650 specifications. In addition, after injecting a non-aqueous electrolyte, that is, a solution in which LiPF ₆ was dissolved at a concentration of 1 mol / L in a solvent in which ethylene carbonate and propylene carbonate were mixed at a volume ratio of 3: 7, into the battery container, sealing was performed. As a result, a lithium ion secondary battery A1 was obtained.

(Example A2)
The negative electrode produced in Production Example 1 and the positive electrode produced in Production Example 2 were overlapped with the separator a2 produced in Example a2 interposed, and wound in a spiral shape to produce a wound electrode body. In this wound electrode body, the second separator layer of the separator was made to face the positive electrode. The above wound electrode body was loaded into a battery container of 18650 specifications. In addition, after injecting a non-aqueous electrolyte, that is, a solution in which LiPF ₆ was dissolved at a concentration of 1 mol / L in a solvent in which ethylene carbonate and propylene carbonate were mixed at a volume ratio of 3: 7, into the battery container, sealing was performed. As a result, a lithium ion secondary battery A2 was obtained.

(Example A3)
The negative electrode produced in Production Example 1 and the positive electrode produced in Production Example 2 were overlapped with the separator a3 produced in Example a3 interposed, and wound in a spiral shape to produce a wound electrode body. In this wound electrode body, the second separator layer of the separator was made to face the positive electrode. The above wound electrode body was loaded into a battery container of 18650 specifications. In addition, after injecting a non-aqueous electrolyte, that is, a solution in which LiPF ₆ was dissolved at a concentration of 1 mol / L in a solvent in which ethylene carbonate and propylene carbonate were mixed at a volume ratio of 3: 7, into the battery container, sealing was performed. As a result, a lithium ion secondary battery A3 was obtained.

(Example A4)
The negative electrode produced in Production Example 1 and the positive electrode produced in Production Example 2 were overlapped with the separator a4 produced in Example a4 interposed, and wound into a spiral shape to produce a wound electrode body. In this wound electrode body, the second separator layer of the separator was made to face the positive electrode. The above wound electrode body was loaded into a battery container of 18650 specifications. In addition, after injecting a non-aqueous electrolyte, that is, a solution in which LiPF ₆ was dissolved at a concentration of 1 mol / L in a solvent in which ethylene carbonate and propylene carbonate were mixed at a volume ratio of 3: 7, into the battery container, sealing was performed. As a result, a lithium ion secondary battery A4 was obtained.

(Example A5)
The negative electrode produced in Production Example 1 and the positive electrode produced in Production Example 2 were overlapped with the separator a5 produced in Example a5 interposed, and wound in a spiral shape to produce a wound electrode body. In this wound electrode body, the second separator layer of the separator was made to face the positive electrode. The above wound electrode body was loaded into a battery container of 18650 specifications. In addition, after injecting a non-aqueous electrolyte, that is, a solution in which LiPF ₆ was dissolved at a concentration of 1 mol / L in a solvent in which ethylene carbonate and propylene carbonate were mixed at a volume ratio of 3: 7, into the battery container, sealing was performed. As a result, a lithium ion secondary battery A5 was obtained.

(Example A6)
The negative electrode produced in Production Example 1 and the positive electrode produced in Production Example 2 were overlapped with the separator a6 produced in Example a6 interposed, and wound into a spiral shape to produce a wound electrode body. In this wound electrode body, the second separator layer of the separator was made to face the positive electrode. The above wound electrode body was loaded into a battery container of 18650 specifications. In addition, after injecting a non-aqueous electrolyte, that is, a solution in which LiPF ₆ was dissolved at a concentration of 1 mol / L in a solvent in which ethylene carbonate and propylene carbonate were mixed at a volume ratio of 3: 7, into the battery container, sealing was performed. Then, a lithium ion secondary battery A6 was obtained.

(Comparative Example B1)
The negative electrode produced in Production Example 1 and the positive electrode produced in Production Example 2 were stacked while interposing the separator b1 produced in Comparative Example b1, and wound into a spiral shape to produce a wound electrode body. In this wound electrode body, the second separator layer of the separator was made to face the positive electrode. The above wound electrode body was loaded into a battery container of 18650 specifications. In addition, after injecting a non-aqueous electrolyte, that is, a solution in which LiPF ₆ was dissolved at a concentration of 1 mol / L in a solvent in which ethylene carbonate and propylene carbonate were mixed at a volume ratio of 3: 7, into the battery container, sealing was performed. As a result, a lithium ion secondary battery B1 was obtained.

(Comparative Example B2)
The negative electrode produced in Production Example 1 and the positive electrode produced in Production Example 2 were stacked while interposing the separator b2 produced in Comparative Example b2, and wound in a spiral shape to produce a wound electrode body. In this wound electrode body, the second separator layer of the separator was made to face the positive electrode. The above wound electrode body was loaded into a battery container of 18650 specifications. In addition, after injecting a non-aqueous electrolyte, that is, a solution in which LiPF ₆ was dissolved at a concentration of 1 mol / L in a solvent in which ethylene carbonate and propylene carbonate were mixed at a volume ratio of 3: 7, into the battery container, sealing was performed. As a result, a lithium ion secondary battery B2 was obtained.

Measurements and tests were performed using the separators of Examples a1 to a7, the separators of Comparative Examples b1 to b5, the lithium ion secondary batteries of Examples A1 to A6, and the lithium ion secondary batteries of Comparative Examples B1 and B2. In particular,
(I) With respect to the separators of Example a1 and Comparative Example b3, the resistance change due to heating in the electrolytic solution of the separator sandwiched between the electrodes was measured.
(II) The air permeability was measured for the separators of Examples a1 to a7 and Comparative Examples b1 to b5.
(III) For Examples a1 to a7 and Comparative Examples b1 to b5, the following heat shrinkage ratio was measured.
(IV) The following overcharge tests were conducted on the lithium ion secondary batteries of Examples A1 to A6 and Comparative Examples B1 and B2.

(I) <Measurement of resistance change due to heating in an electrolyte solution of a separator sandwiched between electrodes>
The resistance change shown below was measured for the separator a1 produced in Example a1 and the separator b3 produced in Comparative Example b3.

A separator is placed between an aluminum foil and a copper foil placed as an electrode, placed in a pressure vessel (10 atm), and a non-aqueous electrolyte, ie, ethylene carbonate, ethylmethyl carbonate, dimethyl carbonate, is added to the separator in a volume ratio. A solution in which LiPF6 was dissolved at a concentration of 1.2 mol / L was added to the solvent mixed at 2: 4: 4 and sealed. A terminal that connects to the internal electrode from the outside of the pressure vessel is provided, and it is configured to be able to measure the resistance between the electrodes by contacting the internal electrode. At the same time, a thermometer is connected so that the tip of the thermocouple is placed at the separator site did. The pressure vessel was placed in a thermostatic bath, and the resistance and temperature of the separator sandwiched between the electrodes were monitored at a rate of temperature increase of about 100 ° C. per hour.

FIG. 4 and FIG. 5 show the measurement results of resistance change regarding the separators of Example a1 and Comparative Example b3, respectively. In the separator a1 of Example a1, the increase in the resistance value corresponding to shutdown starts near 100 ° C. and reaches saturation near 110 ° C. On the other hand, in the separator b3 of the comparative example b3, the temperature indicating the saturation value of the resistance is around 128 ° C., which is higher than the shutdown temperature of the separator a1. The separator a1 having the first, second and third separator layers is shut down at around 110 ° C. by the modified polyethylene which is a low melting point material forming the third separator layer. On the other hand, the separator b3 formed only from the first separator layer is shut down at a high temperature due to melting of the high-density polyethylene. From the above, it is considered that the separator a1 of Example a1 is a battery separator that can be shut down at a low temperature and has higher safety than the separator b3 of Comparative Example b3.

The temperature at which the resistance value in this measurement reaches saturation is considered to be the shutdown temperature of the separator. FIG. 3B shows the temperatures of the separator a1 and the separator b3 in the column “d)“ Shutdown temperature as seen from the resistance value (° C.) ”in the“ Separator characteristics ”column.

(II) <Measurement of air resistance of separator>
For the separators of Examples a1 to a7 and Comparative Examples b1 to b5, the non-heated air resistance and the air resistance at room temperature after heating at 110 ° C. for 30 minutes while being kept at room temperature were measured. did. The measurement result of the air resistance is shown in the column of FIG.

First, the air resistance at room temperature will be described. As shown in the column of FIG. 3 (e), a separator composed only of the first separator layer tends to exhibit the lowest air resistance. The value is 270 to 290.6 seconds. Then, the separator comprised only by the 1st separator layer and the 2nd separator layer tends to show the result according to it. The value is 278 to 318.1 seconds. Finally, a separator having all of the first separator layer, the second separator layer, and the third separator layer tends to exhibit the highest air resistance. The value is 329 to 414 seconds. Since there are other differences in the configuration of the separator, the value of the air resistance may vary, but it can be seen that the air resistance increases as the separator layer increases as a whole. However, it has not reached the result that measurement is impossible, and it can be seen that even if all of the first, second, and third separator layers are provided, there is ion permeability. This indicates that not only the first separator layer but also the second separator layer and the third separator layer have ion permeability.

Next, the air resistance when heated at 110 ° C. for 30 minutes will be described. As shown in the column of FIG. 3 (e), in Examples a2, a4, a6, and a7, it became impossible to measure after heating at 110 ° C. for 30 minutes, indicating that the separator was blocked (shut down). “Unmeasurable” means that even when the separator was set in the apparatus and measurement was started, the inner cylinder hardly moved and measurement was not started. This means that the separator membrane is blocked. Example a1 also rose significantly to 1990, and Examples a3 and a5 also rose significantly to 646 and 539, respectively. In contrast, Comparative Examples b1 to b5 were 342.8, 285, 315.2, 280, 325.2, respectively, and it was found that the separator was not clogged at 110 ° C. Thereby, the blockage | closure of the separator by the low melting-point material layer was confirmed at 110 degreeC.

Further, in Examples a1 to a5, when considering the measurement results of the air permeability resistance including the melt filling rate, it can be seen that the separator having a high melt filling rate shows higher values at both room temperature and 110 ° C. .

(III) <Measurement of heat shrinkage rate of separator>
The separators of Examples a1 to a7 and Comparative Examples b1 to b5 were cut into a size of 10 cm × 5 cm to prepare test pieces. In this test piece, the direction of 10 cm (longitudinal direction) was made parallel to the longitudinal direction of the microporous membrane having a three-layer structure 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.

In the column of FIG. 3 (f), the thermal shrinkage rate measurement results of Examples a1 to a7 and Comparative Examples b1 to b5 are shown. The separators b3 and b4 of Comparative Examples b3 and b4, which are three-layer microporous membranes, contracted by 40% in the longitudinal direction, and the single-layer separator b5 of Comparative Example b5 contracted by 50% in the longitudinal direction. The separators a1 and a2 of a1 and a2 are within 3%, the separator a3 of Example a3 is 6%, the separator a4 of Example a4 is 8%, the separator a5 of Example a5 is 13%, and the separator a6 of Example a6 is The separator a7 of Example a7 was 26%, the separator b1 of Comparative Example b1 was within 3%, and the separator b2 of Comparative Example b2 was 4%. The separators a1 to a5 have a second separator layer that is a heat-resistant material layer and a third separator layer that is a low-melting-point material layer, and can ensure good heat shrinkage due to the action of the inorganic filler related to the second separator layer. Yes. In addition, it can be said that the separators a6 and a7 have a certain heat shrinkage resistance compared to the separators b3, b4, and b5. By using the separator having the first, second, and third separator layers, an electrochemical element such as a lithium ion secondary battery can suppress the occurrence of an internal short circuit and can reduce the temperature rise.

(IV) <Overcharge test>
An overcharge test was performed on the lithium ion secondary batteries A1 to A6, B1, and B2 manufactured in Examples A1 to A6 and Comparative Examples B1 and B2. Each lithium ion secondary battery was fully charged, and further overcharged by CC / CV charging with a charging rate of 2 C and an upper limit voltage of 8.4 V. The lithium ion secondary batteries A1 to A6 of Examples A1 to A6 are lithium ion secondary batteries manufactured using the separators a1 to a6 of Examples a1 to a6, respectively. Similarly, the lithium ion secondary batteries B1 and B2 of Comparative Examples B1 and B2 are lithium ion secondary batteries manufactured using the separators b1 and b2 of Comparative Examples b1 and b2, respectively.

Fig. 3 (c) shows the result of the overcharge test. By overcharging, the temperature gradually increased, and the lithium ion secondary batteries A1 to A6 of Examples A1 to A6 were shut down at around 110 ° C., and the peak temperature was 140 ° C., and further heat generation was suppressed. In the lithium ion secondary batteries B1 and B2 of Comparative Examples B1 and B2, shutdown was performed at around 135 ° C., and the peak temperature was 160 ° C., and further heat generation was suppressed. The separators a1 to a6 can shut down the lithium ion secondary battery at a lower temperature than the separators b1 and b2. As a result, the lithium ion secondary batteries A1 to A6 having the separators a1 to a6 having the first, second, and third separator layers as members are the lithium ion secondary batteries B1, B2 having the separators b1 and b2 as members. Since the shutdown is performed at a lower temperature, it can be said that the lithium ion secondary battery has higher safety in a state where current interruption is necessary, for example, when the battery is overcharged.

The separator for an electrochemical element and the electrochemical element according to the above embodiment and examples have the following operational effects.
(1) The electrochemical element separator of the present invention can be shut down at different temperatures. That is, a microporous membrane having a microporous having ion permeability and having a first shutdown function for closing the microporous by increasing the temperature to stop the ion permeability, and a temperature at which the first shutdown function is exhibited. A low-melting-point material having a second shutdown function that melts at a lower temperature, closes the micropores, and stops ion permeability, such as the third separator layer 30.
When the battery temperature rises by shutting down at different temperatures, the low melting point material first melts to close the pores of the microporous membrane, and if the shutdown does not sufficiently suppress the battery temperature rise, The temperature rise can be suppressed by shutting down the porous membrane itself. As described above, it is possible to perform multi-stage shutdown, and it is possible to suppress the temperature increase in multiple stages.
(2) Since the melt viscosity at 140 ° C. of the low melting point material of the separator for an electrochemical element of the present invention is 5 mPa · s or more and 100000 mPa · s or less, the melted low melting point material remains in the separator 1 and It is possible to continue the state of entering the pores of the microporous membrane and closing the pores.
(3) The separator for an electrochemical element of the present invention has a three-layer structure, and has first to third separator layers 10 to 30. The first separator layer 10 includes a plurality of layers made of microporous films, and each of the plurality of

layers

11 and 12 exhibits a shutdown function at, for example, 137 ° C. and 170 ° C. The second separator 20 is provided on one surface of the first separator layer 10 and has heat resistance. The third separator layer is made of a low-melting-point material, and is provided on the other surface of the first separator layer 10 or on the second separator 20 provided on one surface of the first separator layer 10. The low melting point material of the third separator layer 30 that can suppress the temperature rise of the battery first, and if the temperature is not sufficiently suppressed, is a microporous film in which a plurality of first separator layers 10 are laminated A The layer 11 and the B layer 12 can suppress a temperature increase in multiple stages. Further, the second separator layer 20 can suppress thermal contraction of the first separator layer 10 and prevent film breakage.
In this way, it is possible to provide a safe separator and an electrochemical element that can be shut down many times and that do not break even if the temperature rises excessively.
(4) If the low melting point material of the third separator layer 30 has a melt filling rate of 3% or more with respect to the first separator layer, it is sufficient to close the holes of the first separator layer 10.
(5) The microporous film of the separator for electrochemical elements of the present invention is a thermoplastic resin having a melting point of 125 ° C. or higher and 170 ° C. or lower, and the low melting point material is lower in melting point than the microporous film and is 80 ° C. By using a thermoplastic resin in a range of 140 ° C. or less, using a microporous film that shuts down in a general shutdown temperature range, and without affecting the actual use of the battery, the low melting point material, It can be shut down with a low melting point material before the microporous membrane is shut down.
(6) If the 2nd separator layer 20 of the separator for electrochemical devices of this invention contains an inorganic filler, the thermal contraction of the 1st separator layer 10 will suppress the inorganic filler 21, and it can prevent a film breakage. .
(7) By making the inorganic filler 21 of the separator for an electrochemical device of the present invention at least one selected from the group consisting of aluminum hydroxide, boehmite, alumina, magnesium hydroxide, magnesium oxide and silica, the above compound (Group) can further suppress the thermal contraction of the first separator layer 10 and effectively prevent the film breakage.
(8) Since the electrochemical device of the present invention includes the positive electrode, the negative electrode, the separator for electrochemical devices of the present invention, and the non-aqueous electrolyte, the increase in battery temperature can be suppressed in multiple stages.
(9) By disposing the third separator layer 30 of the electrochemical device of the present invention so as to face the negative electrode, the shutdown time can be shortened.
(10) The separator of the electrochemical device of the present invention is fixed and integrated with at least one of the positive electrode and the negative electrode. Thereby, since a separator does not shift | deviate with respect to the surface of at least one electrode, the electrode surface can always be covered and the short circuit of a positive electrode and a negative electrode can be prevented.

The above description is merely an example, and the present invention is not limited to the above-described embodiments and examples.

The disclosure of the following priority application is hereby incorporated by reference.
Japanese application 2013 No. 168174 (August 13, 2013)
Japanese application 2013 No. 168724 (August 14, 2013)
Japanese Application No. 2013-205433 (September 30, 2013)

1: separator,
10: first separator layer,
11: A layer,
12: B layer
20: second separator layer,
21: inorganic filler,
30: Third separator layer,
a1 to a7: separators of Examples,
b1 to b5: separators of comparative examples,
A1 to A6: Lithium ion secondary battery of Example,
B1, B2: Lithium ion secondary batteries of comparative examples

Claims

A microporous first separator layer mainly composed of a thermoplastic resin and shut down at a predetermined temperature;
A heat-resistant and microporous second separator layer;
A low melting point material that melts at a temperature lower than that of the thermoplastic resin, and a microporous third separator layer that performs shutdown at a temperature lower than the shutdown temperature of the first separator layer,
The separator for electrochemical elements whose melt viscosity in 140 degreeC of the said low melting-point material is 5 mPa * s or more and 100,000 mPa * s or less.
The separator for an electrochemical element according to claim 1, wherein the second separator layer is laminated on one surface of the first separator layer, and the third separator layer is laminated on the other surface.
The separator for an electrochemical element according to claim 2, wherein a melt filling rate at 140 ° C of the third separator layer with respect to the first separator layer is 3% or more and 200% or less.
The separator for an electrochemical element according to any one of claims 1 to 3, wherein the first separator layer is formed of a plurality of microporous films having different melting points.
The melting point of the thermoplastic resin is 125 ° C. or more and 170 ° C. or less,
The separator for an electrochemical element according to any one of claims 1 to 4, wherein the low melting point material has a melting point of 80 属 C or higher and 140 属 C or lower.
The electrochemical device separator according to any one of claims 1 to 5, wherein the second separator layer contains an inorganic filler.
The separator for an electrochemical element according to claim 6, wherein the inorganic filler includes at least one selected from the group consisting of aluminum hydroxide, boehmite, alumina, magnesium hydroxide, magnesium oxide and silica.
The first separator layer is a microporous film formed by using at least one of a stretching method and a pore forming method, and the second separator layer and the third separator layer are formed on the first separator layer. The separator for an electrochemical element according to any one of claims 1 to 7, which is formed by applying a composition for forming a separator layer.
8. The thickness of the first separator layer is 4 to 20 μm, the thickness of the second separator layer is 3 to 10 μm, and the thickness of the third separator layer is 3 to 10 μm. The separator for an electrochemical element according to Item.
The second separator layer includes an inorganic filler and an organic binder, and the content of the inorganic filler is 40% by volume to 95% by volume with respect to the total volume of the second separator layer, and the content of the organic binder The separator for an electrochemical element according to any one of claims 1 to 7, wherein is from 0.5% by volume to 10% by volume per total volume of the second separator layer.
The third separator layer includes a thermoplastic resin and an organic binder, the content of the thermoplastic resin is 70% by volume or more per total volume of the constituent components of the third separator layer, and the content of the organic binder is The separator for an electrochemical element according to any one of claims 1 to 7, which is 0.5% by volume or more per total volume of components of the third separator layer.
Having a positive electrode, a negative electrode, a separator and a non-aqueous electrolyte,
An electrochemical element, wherein the separator is a separator for an electrochemical element according to any one of claims 1 to 11.
The electrochemical element according to claim 12, wherein the third separator layer faces the negative electrode.
The electrochemical device according to claim 11 or 12, wherein the separator is integrated with at least one of a positive electrode and a negative electrode.