JP7567779B2 - Separator material and non-aqueous electrochemical device - Google Patents

Description

The present invention relates to a separator material and a non-aqueous electrochemical device using the separator material.

Conventionally, in non-aqueous electrochemical devices such as primary batteries such as lithium primary batteries; non-aqueous secondary batteries such as lithium ion secondary batteries, lithium metal secondary batteries, sodium ion secondary batteries, potassium ion secondary batteries, magnesium secondary batteries, and aluminum secondary batteries; solar cells such as dye-sensitized solar cells; capacitors such as electric double layer capacitors and lithium ion capacitors; electrochromic display devices; electrochemical light-emitting elements; electric double layer transistors; and electrochemical actuators, separators have been used as components that separate the positive and negative electrodes to prevent short circuits between the positive and negative electrodes.

For example, Patent Document 1 discloses a lithium ion secondary battery having an electrolyte solution made of a mixture of ethylene carbonate, dimethyl sulfone, and lithium tetrafluoroborate (LiBF ₄ ) and a separator made of a glass fiber filter (product name: Whatman (registered trademark), thickness: 675 μm).

International Publication No. 2015/188932

From the perspective of safety, non-aqueous electrochemical devices are required to be difficult to burn and to have minimal leakage of materials to the outside, even if they are ignited internally due to abnormal heat generation, or externally if caught in a fire, etc.

However, conventional non-aqueous electrochemical devices had room for improvement in terms of reducing flammability and improving safety by preventing leakage of substances to the outside in the event that the exterior is destroyed by ignition or other causes.

Therefore, the present invention aims to provide a technology that can obtain a nonaqueous electrochemical device that is difficult to burn and has little leakage of substances to the outside, even if ignited from inside or outside.

As a result of extensive research into achieving the above-mentioned objective, the inventors have discovered that by using a separator material in which a porous thin film material having specified properties is impregnated with an electrolyte composition having a specified composition, a non-aqueous electrochemical device that is highly safe even in the event of internal or external ignition can be obtained, and have thus completed the present invention.

That is, the present invention aims to advantageously solve the above problems, and the separator material of the present invention is obtained by impregnating a porous thin film material having a thickness of 300 μm or less with an electrolyte composition, the electrolyte composition containing at least one ionic substance and an organic composition, and being liquid under atmospheric pressure at a temperature of 100 ° C., the organic composition containing 80 mass % or more of a compound that is solid under atmospheric pressure at a temperature of 5 ° C., and the content of a low-boiling point organic compound having a boiling point of less than 130 ° C. under atmospheric pressure is 0 mass % or more and 20 mass % or less. In this way, by impregnating a porous thin film material having the above-mentioned predetermined thickness with an electrolyte composition having the above-mentioned predetermined composition and properties, a separator material can be obtained that has low flammability, is unlikely to cause damage to the porous thin film material such as holes caused by heating, and is unlikely to leak substances to the outside even if the exterior is destroyed by ignition or the like.
In the present invention, the "thickness" of the porous thin film material refers to a thickness measured in accordance with JIS K 7130. In addition, in the present invention, the "boiling point" can be measured by boiling and refluxing at standard atmospheric pressure and measuring the recondensation temperature of the vapor with a thermometer.

Here, in the separator material of the present invention, the organic composition preferably contains two or more types of compounds that are solid at a temperature of 5°C under atmospheric pressure, and more preferably contains three or more types. The more types of compounds that are solid at a temperature of 5°C under atmospheric pressure, the easier it is for the ionic substance to dissolve and the performance of the electrolyte composition to improve.

In addition, in the separator material of the present invention, it is preferable that the organic composition further contains a flame retardant. If the organic composition contains a flame retardant, the separator material can be made even more difficult to burn.

In the separator material of the present invention, the electrolyte composition preferably further contains a polymer component. If the electrolyte composition contains a polymer component, the separator material can be made even more difficult to burn.
In the present invention, the term "polymer component" refers to a component having a weight average molecular weight of 10,000 or more as measured in accordance with JIS K7252.

In addition, in the separator material of the present invention, it is preferable that the porous thin film material has a melting point. If the porous thin film material melts when heated, the separator material can be prevented from burning.

Furthermore, in the separator material of the present invention, it is preferable that non-flammable fine particles are attached to the surface of the porous thin film material. By using a porous thin film material having non-flammable fine particles attached to its surface, the separator material can be made even more difficult to burn.

In the separator material of the present invention, the electrolyte composition preferably has an ionic conductivity of 1.0 × 10 ^-4 S/cm or more at a temperature of −20° C. When the ionic conductivity of the electrolyte composition is equal to or higher than the above lower limit, electrochemical reactions can proceed satisfactorily in a nonaqueous electrochemical device using the separator material.
In the present invention, the "ionic conductivity" refers to the ionic conductivity measured by an AC method, and can be determined by taking the reciprocal of the volume resistivity calculated from the arc diameter of a Nyquist plot obtained by sandwiching a sample between two parallel stainless steel plates in a thermostatic chamber controlled to a measurement temperature of ±1°C and applying an AC voltage in the range of 10 to 100 mV.

In the separator material of the present invention, the organic composition preferably contains an organic compound that is liquid at atmospheric pressure and a temperature of 40° C. and has a content ratio of 0% by mass or more and 20% by mass or less. If the content ratio of the organic compound that is liquid at atmospheric pressure and a temperature of 40° C. is within the above range, the separator material can be made even more difficult to burn.

The present invention also aims to advantageously solve the above problems, and the nonaqueous electrochemical device of the present invention is characterized by comprising any one of the separator materials described above. In this way, by using the separator material described above, a nonaqueous electrochemical device can be obtained that is difficult to burn and has little leakage of substances to the outside, even if ignited from the inside or outside.

According to the present invention, a non-aqueous electrochemical device is obtained which is less likely to burn and has less leakage of substances to the outside, even if ignited from the inside or outside.

The separator material of the present invention is not particularly limited and can be used for, for example, primary batteries such as lithium primary batteries; nonaqueous secondary batteries such as lithium ion secondary batteries, lithium metal secondary batteries, sodium ion secondary batteries, potassium ion secondary batteries, magnesium secondary batteries, and aluminum secondary batteries; solar cells such as dye-sensitized solar cells; capacitors such as electric double layer capacitors and lithium ion capacitors; electrochromic display devices; electrochemical light-emitting devices; electric double layer transistors; and nonaqueous electrochemical devices such as electrochemical actuators. Among these, the separator material of the present invention can be suitably used for nonaqueous secondary batteries, particularly lithium ion secondary batteries.
The separator material of the present invention has low flammability and is unlikely to leak substances to the outside even if the exterior is destroyed by ignition, etc. Furthermore, the nonaqueous electrochemical device of the present invention is unlikely to burn and is unlikely to leak substances to the outside even if ignited from the inside or outside.

(Separator material)
The separator material of the present invention is obtained by impregnating a porous thin film material having a thickness of 300 μm or less with an electrolyte composition.

<Porous thin film materials>
The porous thin film material of the separator material of the present invention is not particularly limited, and examples of thin film materials having a large number of pores, such as polyolefin porous membranes, polyolefin nonwoven fabrics, fluororesin porous membranes, paper, cellulose nonwoven fabrics, aramid nonwoven fabrics, and glass fiber filters, can be used.

The porous thin film material must have a thickness of 300 μm or less, preferably 200 μm or less, and more preferably 50 μm or less. If the thickness of the porous thin film material exceeds 300 μm, it becomes easy to burn and easy to leak substances to the outside. On the other hand, if the thickness of the porous thin film material is equal to or less than the upper limit, a separator material that is low in combustibility and difficult to leak substances to the outside can be obtained.
The reason why the flammability of the separator material decreases when the thickness of the porous thin film material is set to 300 μm or less is not clear, but it is presumed that this is because the amount of electrolyte composition retained is reduced and the movement of the electrolyte composition is suppressed, thereby preventing the electrolyte composition from contributing to combustion.

The porous thin film material preferably has a melting point, and more preferably has a melting initiation temperature of 100° C. or more and 400° C. or less. If the ends of the porous thin film material melt when heated and lose their porous shape, the porous thin film material can act as a core to prevent the separator material from burning when the electrochemical device is ignited from inside or outside.
In the present invention, the "melting initiation temperature" can be determined from the melting peak when the temperature is raised at 3°C/min by differential scanning calorimetry (DSC).

The porous thin film material preferably has non-combustible fine particles attached to its surface, and more preferably has non-combustible fine particles attached to the surface of the porous thin film material other than the outer edge portion. If non-combustible fine particles are attached to the surface, the separator material can be made even more difficult to burn.
In the present invention, "non-flammable" means that it will not ignite or catch fire even when heated up to 800°C.

Here, the non-flammable fine particles are not particularly limited, and examples thereof include inorganic fine particles such as silica fine particles and alumina fine particles, as well as fine particles of oxides, sulfates and carbonates of other metals.
The particle size of the fine particles is not particularly limited, but is preferably 10 μm or less, and more preferably 0.1 μm or more and 5 μm or less. In the present invention, the "particle size" can be measured in accordance with JIS K8825.

The porous thin film material may be subjected to a hydrophilic treatment. The hydrophilic treatment can increase the wettability of the porous thin film material with respect to the electrolyte composition. The method for hydrophilicizing the porous thin film material is not particularly limited, and may be, for example, a corona treatment, a plasma treatment, a surfactant treatment, a hydrophilic polymer coating treatment, or the addition of an inorganic filler.

<Electrolyte Composition>
The electrolyte composition of the present invention contains at least one ionic substance and an organic composition containing a predetermined compound in a predetermined ratio, and may further contain a polymer component and/or an additive, and is required to be liquid at a temperature of 100° C. under atmospheric pressure.

[Ionic substances]
Here, as the ionic substance, any ionic substance can be used depending on the type of ions utilized in the electrochemical reaction in the nonaqueous electrochemical device in which the separator material is used.
The amount of the ionic substance can be appropriately set according to the type of non-aqueous electrochemical device. Specifically, the concentration of the ionic substance in the electrolyte composition is preferably 0.01 mol/L or more and less than 2.5 mol/L from the viewpoint of making the electrolyte composition in a viscosity range that is easy to handle. On the other hand, from the viewpoint of improving the safety, heat resistance, and life of the electrochemical device, the concentration of the ionic substance in the electrolyte composition is preferably 2.5 mol/L or more.

Specifically, when the non-aqueous electrochemical device in which the separator material is used is a lithium ion secondary battery or a lithium ion capacitor, the ionic substance is not particularly limited and may be, for example, a lithium salt such as LiBF ₄ , LiPF ₆ , lithium bis(oxalate)borate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, etc. When the non-aqueous electrochemical device in which the separator material is used is a magnesium secondary battery, the ionic substance is not particularly limited and may be, for example, a magnesium salt such as magnesium bis(trifluoromethanesulfonyl)imide.
These ionic substances may be used alone or in combination of two or more.

[Organic Composition]
The organic composition is required to contain 80% by mass or more of a compound that is solid under atmospheric pressure at a temperature of 5° C., and may optionally further contain at least one selected from the group consisting of a compound that is liquid under atmospheric pressure at a temperature of 5° C. and a flame retardant. In addition, the organic composition is required to contain 0% by mass or more and 20% by mass or less of a low-boiling organic compound having a boiling point of less than 130° C. under atmospheric pressure.
If the content ratio of the compound that is solid under atmospheric pressure at a temperature of 5° C. and the low boiling point organic compound is not within the above range, it is not possible to sufficiently prevent the electrolyte composition from leaking to the outside when the exterior is destroyed by ignition, etc. By setting the content ratio of the compound that is solid under atmospheric pressure at a temperature of 5° C. and the low boiling point organic compound within the above range, it is possible to prevent the electrolyte composition from leaking to the outside when the exterior is destroyed by ignition, etc. It is not clear why the electrolyte composition can be prevented from leaking to the outside when the exterior is destroyed by ignition, etc., by using an organic composition mainly composed of a compound that is solid under atmospheric pressure at a temperature of 5° C., the electrolyte composition becomes highly viscous, and when exposed to high temperatures such as a fire, part of the components volatilize, causing the electrolyte composition to deviate from the range in which it can remain liquid (solids precipitate).

[Compounds that are solid at 5°C and atmospheric pressure]
Here, the compound that is solid under atmospheric pressure at a temperature of 5° C. is not particularly limited, and examples thereof include high-boiling organic compounds having a boiling point of 130° C. or more under atmospheric pressure. Moreover, a compound that is solid under atmospheric pressure at a temperature of 5° C. is usually a compound that does not have flame retardancy and is different from a flame retardant. Furthermore, it is preferable that the compound that is solid under atmospheric pressure at a temperature of 5° C. has a molecular weight of less than 10,000.
Examples of compounds that are solid under atmospheric pressure at a temperature of 5° C. include glutaric anhydride, succinic anhydride, succinonitrile, diglycolic anhydride, sulfolane, ethyl methyl sulfone, dimethyl sulfone, diethyl sulfone, sulfolene, ethylene sulfate (1,3,2-dioxathiolane-2,2-dioxide), itaconic anhydride, ethylene carbonate, N-methyloxazolidone, fluoroethylene carbonate, methyl carbamate, N,N-dimethylimidazolidinone, dimethyl oxalate, vinylene carbonate, and dimethyl sulfoxide.
These compounds may be used alone or in combination of two or more. Among them, it is preferable to use two or more compounds that are solid at a temperature of 5° C. under atmospheric pressure, and it is more preferable to use three or more compounds in combination.

Among these, from the viewpoint of improving the solubility of the ionic substance and improving the performance of the electrolyte composition, it is preferable to use a polar compound having an oxygen atom and/or a nitrogen atom as the compound that is solid under atmospheric pressure at a temperature of 5° C., and it is more preferable to use one or more compounds selected from the group consisting of ethylene carbonate, dimethyl sulfone, succinonitrile, itaconic anhydride, diglycolic anhydride, sulfolene, 1,3,2-dioxathiolane 2,2-dioxide, vinylene carbonate, and fluoroethylene carbonate, it is even more preferable to use two or more compounds selected from the above group, and it is particularly preferable to use three or more compounds selected from the above group.
From the viewpoint of reducing the heat generated during combustion, the compound that is solid at a temperature of 5° C. under atmospheric pressure is preferably a compound having 8 or less carbon atoms, and more preferably a compound having 5 or less carbon atoms.
When it is desired to know a composition that will become liquid using compounds that are solid at a temperature of 5°C under atmospheric pressure, equal amounts of all compounds to be used in the composition are mixed, and the whole is heated to a temperature equal to or higher than the melting point of the compound with the highest melting point among those compounds until it is melted, and then cooled to a temperature at which it is desired to use it as a liquid. If the whole remains liquid, it can be used as is, but if only part of it becomes solid, the composition of the supernatant can be quantified by gas chromatography or liquid chromatography to determine the composition that will become liquid.

The content of the compound that is solid at a temperature of 5°C under atmospheric pressure in the organic composition is 80% by mass or more and 100% by mass or less, and preferably 85% by mass or more and 100% by mass or less.

[Compounds that are liquid at 5°C and atmospheric pressure]
The compound that is liquid under atmospheric pressure at a temperature of 5° C. is not particularly limited, and examples thereof include high-boiling organic compounds having a boiling point of 130° C. or higher under atmospheric pressure. Compounds that are liquid under atmospheric pressure at a temperature of 5° C. are generally compounds that do not have flame retardancy and are different from flame retardants. Furthermore, it is preferable that the compound that is liquid under atmospheric pressure at a temperature of 5° C. has a molecular weight of less than 10,000.
Examples of compounds that are liquid at a temperature of 5° C. under atmospheric pressure include trisethylhexyl phosphate, adiponitrile, 1,3-propane sultone, tributyl phosphate, tetraglyme, trisbutoxyethyl phosphate, vinyl ethylene carbonate, propylene carbonate, triglyme, triethyl phosphate, citraconic anhydride, N-methylpyrrolidone, γ-butyrolactone, and trimethyl phosphate.
These compounds may be used alone or in combination of two or more.
Among these, from the viewpoint of ease of handling and preparation of the electrolyte composition, it is preferable to use propylene carbonate as a compound that is liquid at a temperature of 5° C. under atmospheric pressure.

In addition, the content of compounds that are liquid at a temperature of 5°C under atmospheric pressure in the organic composition is typically 0% by mass or more and 20% by mass or less, and preferably 0% by mass or more and 15% by mass or less.

[Flame retardant]
As the flame retardant, phosphates having 24 or less carbon atoms, phosphites having 24 or less carbon atoms, phosphazenes, etc. can be used. If the organic composition contains a flame retardant, the separator material can be made even more difficult to burn.

Examples of phosphate esters having 24 or less carbon atoms include alkyl phosphate esters such as trimethyl phosphate, triethyl phosphate, triphenyl phosphate, tricresyl phosphate, and trixylenyl phosphate; and fluorinated phosphate esters such as tris(trifluoroethyl)phosphate, bis(trifluoroethyl)methyl phosphate, and tris(hexafluoroisopropyl)phosphate.
Examples of phosphites having 24 or less carbon atoms include alkyl phosphites such as triethyl phosphite, triisopropyl phosphite, and tributyl phosphite.
Furthermore, examples of phosphazenes include monoethoxypentafluorocyclotriphosphazene, diethoxytetrafluorocyclotriphosphazene, and monophenoxypentafluorocyclotriphosphazene.
The above-mentioned compounds may be used alone or in combination of two or more.

In addition, since it is better for the flame-retardant compound to move together with the electrolyte rather than being separated from it in the event of a fire, etc., it is preferable for the flame-retardant compound to be liquid at atmospheric pressure and a temperature of 5°C. In addition, it is preferable for the flame-retardant compound to have a boiling point of 130°C or higher at atmospheric pressure.

The content of the flame retardant in the organic composition is typically 0% by mass or more and 20% by mass or less, and from the viewpoint of suppressing deterioration in the performance of non-aqueous electrochemical devices, it is preferably 0% by mass or more and 10% by mass or less, and from the viewpoint of minimizing the impact on human health when a phosphorus compound is used as a flame retardant, it is more preferably 0% by mass or more and 5% by mass or less.

[Low boiling point organic compound]
The low boiling point organic compound is not particularly limited as long as it has a boiling point of less than 130° C. under atmospheric pressure, and examples thereof include dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl acetate, ethyl propionate, and propyl propionate. These compounds may be used alone or in combination of two or more.
The low-boiling point organic compound preferably has a molecular weight of less than 10,000.

In order to adequately prevent the electrolyte composition from leaking to the outside when the exterior is destroyed by fire or the like, the content of the low-boiling point organic compound in the organic composition must be 0% by mass or more and 20% by mass or less, and preferably 0% by mass or more and 10% by mass or less.

In addition, from the viewpoint of making the separator material more difficult to burn, it is preferable that the organic composition contains organic compounds that are liquid at a temperature of 40°C and atmospheric pressure in an amount of 0% by mass or more and 20% by mass or less, and it is more preferable that the amount of organic compounds that are liquid at a temperature of 40°C and atmospheric pressure in an amount of 0% by mass or more and 10% by mass or less.

Here, examples of organic compounds that are liquid at atmospheric pressure and a temperature of 40°C include, but are not limited to, high-boiling organic compounds with a boiling point of 130°C or higher at atmospheric pressure, such as sulfolane, ethyl methyl sulfone, ethylene carbonate, N-methyloxazolidone, fluoroethylene carbonate, dimethylimidazolidinone, vinylene carbonate, and dimethyl sulfoxide. These compounds may be used alone or in combination of two or more.

In addition, organic compounds that are liquid at atmospheric pressure and a temperature of 40°C are usually compounds that do not have flame retardancy and are different from flame retardants. In addition, organic compounds that are liquid at atmospheric pressure and a temperature of 40°C are preferably solid at atmospheric pressure and a temperature of 5°C. Furthermore, organic compounds that are liquid at atmospheric pressure and a temperature of 40°C preferably have a molecular weight of less than 10,000.

And, examples of organic compositions containing the above-mentioned compounds include, but are not limited to, ethylene carbonate alone, a mixture of ethylene carbonate and dimethyl sulfone, a mixture of ethylene carbonate and propylene carbonate, a mixture of ethylene carbonate and succinonitrile, a mixture of dimethyl sulfone and succinonitrile, a mixture of succinonitrile and itaconic anhydride, a mixture of ethylene carbonate and fluoroethylene carbonate, a mixture of ethylene carbonate, dimethyl sulfone and succinonitrile, a mixture of ethylene carbonate, dimethyl sulfone and vinylene carbonate, a mixture of ethylene carbonate, dimethyl sulfone and a flame retardant (e.g., trimethyl phosphate), and the like.

[Polymer component]
The optional polymer component is not particularly limited, and examples thereof include polymers having an ethylene oxide chain which may have a substituent, and epichlorohydrin-based polymers. Examples of polymers having an ethylene oxide chain which may have a substituent include ethylene oxide-based polymers such as polyethylene oxide, ethylene oxide-propylene oxide copolymers, ethylene oxide-propylene oxide-allyl glycidyl ether copolymers, ethylene oxide-allyl glycidyl ether copolymers, and polyacrylate-based polymers having an oxyethylene chain. These polymers may be used alone or in combination of two or more. If the electrolyte composition contains a polymer component, the separator material can be made even more difficult to burn.

Here, the polymer component contained in the separator material of the present invention may be polymerized using a polymerization method such as thermal polymerization inside the nonaqueous electrochemical device after assembly. It is preferable that the polymer component is uniformly dissolved in the electrolyte composition at the operating temperature for manufacturing the nonaqueous electrochemical device.

The weight average molecular weight of the polymer component is not particularly limited as long as it is 10,000 or more, but is preferably 100,000 or more and 30,000,000 or less.
Furthermore, the polymer component may have a crosslinked structure, but from the viewpoint of good dissolution in the electrolyte composition, it is preferable that the polymer component does not have a crosslinked structure. Here, the crosslinked structure can be introduced into the polymer component using any crosslinking method such as ultraviolet irradiation. Also, from the viewpoint of good dissolution in the electrolyte composition, it is preferable that the polymer component has a low gel content. The gel content is preferably 20% by mass or less of the polymer component, more preferably 10% by mass or less, and even more preferably 5% by mass or less. The gel content of the polymer component can be determined by adding the polymer component to propylene carbonate at a ratio of 5% by mass, stirring and dissolving it at 100 ° C. for 12 hours, filtering the insoluble matter with a membrane filter at 100 ° C., vacuum drying to remove propylene carbonate, and measuring the weight of the residue.

The content ratio of the polymer component in the electrolyte composition is typically 0 parts by mass or more and 100 parts by mass or less per 100 parts by mass of the organic composition, and from the viewpoint of suppressing a decrease in the ionic conductivity of the electrolyte composition, it is preferable that the content ratio is 0 parts by mass or more and 50 parts by mass or less.

[Additives]
The optional additive is not particularly limited, and any additive that can be used in the field of electrochemical devices, such as a wetting agent, can be used.

[Wetting agent]
Here, the wetting agent is not particularly limited as long as it has a hydrophilic part and a hydrophobic part in the molecule, and examples thereof include long-chain alkyl carboxylates having 8 or more carbon atoms, long-chain alkyl sulfonates having 8 or more carbon atoms, long-chain perfluoroalkyl carboxylates having 8 or more carbon atoms, long-chain perfluoroalkyl sulfonates having 8 or more carbon atoms, long-chain alkyl phosphates having 8 or more carbon atoms, long-chain perfluoroalkyl phosphates having 8 or more carbon atoms, fluorine-substituted ethers, ethylene oxide polymers having terminal alkyl groups having 8 or more carbon atoms, and ethylene oxide (EO)-propylene oxide (PO) block copolymers. The alkyl groups of the above compounds may have unsaturated bonds in part or may have branched chains. These wetting agents may be used alone or in combination of two or more.

The amount of wetting agent is not particularly limited, but for example, it is preferable to use 5 parts by weight or less, and more preferably 3 parts by weight or less, per 100 parts by weight of the organic composition.

[Properties of Electrolyte Composition]
The electrolyte composition is required to be in a liquid state under atmospheric pressure at a temperature of 100° C. Here, the term "liquid state" includes not only a single liquid phase state, but also a state in which a main liquid phase contains one or more other liquid phases at a ratio of 5% by volume or less, and a state in which a liquid phase contains a small amount of a solid phase at 5% by volume or less.

The electrolyte composition preferably has an ionic conductivity of 1.0×10 ⁻⁴ S/cm or more at a temperature of −20° C., and preferably has an ionic conductivity of 1.0×10 ⁻³ S/cm or more at a temperature of 25° C. When the ionic conductivity of the electrolyte composition is equal to or more than the above lower limit, the electrochemical reaction can proceed satisfactorily in a nonaqueous electrochemical device using the separator material.

In addition, the electrolyte composition preferably has a viscosity of 10 mPa·s or more, more preferably 20 mPa·s or more, and even more preferably 50 mPa·s or more. If the viscosity of the electrolyte composition is equal to or more than the lower limit, the electrolyte composition is more unlikely to leak to the outside when the exterior is destroyed by ignition or the like, and even if the electrolyte composition burns, the entire amount is less likely to burn, so that the flammability is reduced.
In the present invention, the term "viscosity" refers to a viscosity measured at a temperature of 25°C using an EMS viscometer (Kyoto Electronics Manufacturing Co., Ltd., EMS-1000S) under sealed conditions with a motor speed of 1000 rpm so that the organic composition does not volatilize and moisture in the air does not get mixed in. The viscosity measured by this measurement method is basically the same as the value measured in accordance with JIS Z8803. The viscosity of the electrolyte composition can be adjusted by changing the composition of the electrolyte composition. Specifically, for example, the viscosity of the electrolyte composition can be increased by blending a high-viscosity compound or increasing the concentration of an ionic substance.

<Preparation of separator material>
The impregnation of the porous thin film material with the electrolyte composition is not particularly limited, and can be carried out using any method, such as immersing the porous thin film material in the electrolyte composition or pouring the electrolyte composition into the porous thin film material.

(Non-aqueous electrochemical devices)
The nonaqueous electrochemical device of the present invention includes the separator material of the present invention. Specifically, the nonaqueous electrochemical device of the present invention usually includes a positive electrode and a negative electrode, a separator material that separates the positive electrode and the negative electrode, and an electrolyte. Since the nonaqueous electrochemical device of the present invention includes the separator material of the present invention, it is difficult to burn even if ignited from the inside or outside, and there is little leakage of materials to the outside.

Here, the positive and negative electrodes are not particularly limited, and any positive and negative electrodes that can be used in the field of non-aqueous electrochemical devices can be used.

In addition, the electrolyte composition used in the separator material of the present invention can be used as the electrolyte solution.

First, we carried out Reference Examples 1 and 2 below to investigate the flammability of various compounds on their own.

(Reference Example 1)
100 mg of the compound to be evaluated was placed in a stainless steel dish having a diameter of 2 cm, and the dish was exposed to a lighter flame for 1 second to check whether or not it ignited. The results are shown below.
These results show that compounds with boiling points below 130° C. and evaluation objects with large surface areas are prone to ignition.
<Ignite compound>
Dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl acetate, ethyl propionate, propyl propionate, ethylene oxide-propylene oxide copolymer (powder form)
<Compounds that did not ignite>
Flame retardants such as succinonitrile, ethylene carbonate, dimethyl sulfone, dimethyl oxalate, glycolide, adiponitrile, tetraglyme, propylene carbonate, fluoroethylene carbonate, and trimethyl phosphate, hydrin rubber (lump), and acrylic rubber (lump)

(Reference Example 2)
Of the compounds that did not ignite in Reference Example 1, succinonitrile, ethylene carbonate, dimethyl sulfone, dimethyl oxalate, glycolide, adiponitrile, tetraglyme, propylene carbonate and fluoroethylene carbonate were subjected to a test in which a flame was continuously applied until they ignited.
As a result, all of the compounds ignited. However, the combustion of succinonitrile, ethylene carbonate, dimethyl sulfone, dimethyl oxalate, glycolide, and fluoroethylene carbonate was milder than that of adiponitrile, tetraglyme, and propylene carbonate, and the flames were contained within the dish.

Next, the following Reference Example 3 was carried out to investigate the volatility of various compounds on their own.

(Reference Example 3)
10 g of a compound that is a solid at atmospheric pressure and a temperature of 5° C., such as ethylene carbonate or dimethyl sulfone, and a compound that is a liquid at atmospheric pressure and a temperature of 5° C., such as propylene carbonate, were weighed out onto a plastic dish having a diameter of 5 cm and placed on a hot plate at 125° C. A glass plate was then placed horizontally at a position 2 cm above the dish.
As a result, compounds that are solid under atmospheric pressure at a temperature of 5°C, such as ethylene carbonate and dimethyl sulfone, remained in place even though their vapor adhered to the glass. On the other hand, compounds that are liquid under atmospheric pressure at a temperature of 5°C, such as propylene carbonate, showed a behavior in which, after their vapor adhered to the glass, they migrated to the surroundings as the amount of vapor adhering increased.
This shows that compounds that are solid under atmospheric pressure at a temperature of 5°C are less likely to flow in the event of a fire, and are less likely to cause the combustion to spread.

Furthermore, the following Reference Examples 4 and 5 were carried out to confirm the change in the state of the electrolyte composition due to the volatilization of the compounds.

(Reference Example 4)
45 g of ethylene carbonate, 45 g of dimethyl sulfone, and 10 g of LiBF ₄ were weighed out and mixed to prepare a homogeneous solution of an electrolyte composition.
1 g of this electrolyte composition was placed on a glass plate and left on a hot plate at 60° C., whereupon the organic compounds evaporated and a loss in weight was observed.
It was observed that the viscosity increased with the weight loss, and when about 20% of the weight was lost, the mixture was removed from the hot plate and observed. A solid was precipitated and the mixture had lost fluidity.
This is believed to be because the composition became unbalanced due to partial volatilization of the organic compound constituting the electrolyte composition, and the organic compound and the salt could no longer maintain a mutually dissolved state.

(Reference Example 5)
90 g of dimethyl carbonate and 10 g of LiBF ₄ were weighed out and mixed to prepare a homogeneous solution of an electrolyte composition.
When the test was carried out in the same manner as in Reference Example 4, the rate of weight loss was extremely fast because the boiling point of dimethyl carbonate is as low as 90°C.
When 60% of the weight had been lost, the sample was removed from the hot plate and observed, but no solid was precipitated.

Finally, Reference Example 6 below was carried out, and an ignition test was performed on the porous thin film material alone.

(Reference Example 6)
The porous thin film materials shown in Table 1 were cut into squares of 2 cm x 2 cm, one side of which was pinched with tweezers and exposed to a flame from below for 3 seconds. Then, it was confirmed whether or not the material ignited and whether or not the shape changed. The results are shown in Table 1.

The present invention will be specifically described below based on examples, but the present invention is not limited to these examples. In the following description, "%" and "parts" expressing amounts are based on mass unless otherwise specified.
In the examples and comparative examples, various evaluations were carried out by the following methods.

<Thickness of porous thin film material>
The thickness of the porous thin film material was measured using a constant pressure digital thickness gauge (manufactured by Toyo Seiki Co., Ltd.).
<Viscosity of Electrolyte Composition>
The viscosity of the electrolyte composition was measured at a temperature of 25° C. using an EMS viscometer (manufactured by Kyoto Electronics Manufacturing Co., Ltd., EMS-1000S) at a motor rotation speed of 1000 rpm.
<Ionic Conductivity of Electrolyte Composition>
The measurements were carried out at temperatures of -20°C and 25°C using an impedance analyzer (manufactured by Solartron).
<Ignition test of separator material>
The prepared separator material was sandwiched between two disk-shaped stainless steel plates having a diameter of 16 mm and a thickness of 500 μm so that the separator material protruded by 2 mm from the entire circumference to prepare a test piece.
A burner was then applied to the vicinity of the protruding portion of the test piece to check for ignition. The burner was then applied to the center of the test piece for 5 seconds to evaluate flammability. Specifically, the presence or absence of continued combustion after the burner was removed and the state of the protruding portion were visually observed.
After the test, the stainless steel plate was peeled off, and the separator material in contact with the stainless steel plate was observed to see if it was dry or wet, and whether the porous thin film material of the separator material had any damage (holes).The percentage of the wet area (wet area) was determined to reflect the amount of electrolyte composition that remained without burning.

Example 1
<Preparation of Electrolyte Composition>
10 g of _LiBF4 as an ionic substance, 80 g of ethylene carbonate and 20 g of dimethyl sulfone as an organic composition were weighed out and mixed to prepare a homogeneous solution of an electrolyte composition.
The viscosity and ionic conductivity were then measured, and the results are shown in Table 2.
<Preparation of porous thin film material>
A glass fiber filter (GA-55, manufactured by ADVANTEC) having a thickness of 210 μm was cut into a circular shape having a diameter of 20 mm to prepare a porous thin film material.
<Preparation of separator material>
A porous thin film material was immersed in the electrolyte composition to impregnate the porous thin film material with the electrolyte composition, and the porous thin film material impregnated with the electrolyte composition was then pulled out and the excess electrolyte was scraped off to obtain a separator material.
An ignition test was then carried out, and the results are shown in Table 2.

(Examples 2 to 3)
During the preparation of the porous thin film material, the glass fibers of a glass fiber filter (GA-55, manufactured by ADVANTEC) were carefully peeled off from the surface with tweezers to a thickness of 100 μm (Example 2) and 50 μm (Example 3), respectively. Except for this, the electrolyte composition was prepared, the porous thin film material was prepared, and the separator material was fabricated in the same manner as in Example 1. Various evaluations were then performed in the same manner as in Example 1. The results are shown in Table 2.

(Examples 4 to 7)
In preparing the porous thin film material, instead of the glass fiber filter (GA-55, manufactured by ADVANTEC), a 25 μm thick polyolefin (PO) microporous membrane (Celgard 2325, manufactured by Polypore) (Example 4), a 29 μm thick alumina-coated polyolefin (PO) microporous membrane (Example 5), a 100 μm thick PTFE membrane filter (Omnipore JMWP04700, manufactured by Merck) (Example 7), and a 35 μm thick paper (TF4535, manufactured by Nippon Kodoshi Kogyo) (Example 8) were used, respectively. The electrolyte composition was prepared, the porous thin film material was prepared, and the separator material was produced in the same manner as in Example 1. Then, various evaluations were performed in the same manner as in Example 1. The results are shown in Table 2.
The polyolefin (PO) microporous membrane (Celgard 2325, manufactured by Polypore) of Example 4 was used after being subjected to a hydrophilization treatment according to the examples of JP 2000-103886 A. The alumina-coated polyolefin (PO) microporous membrane of Example 5 was prepared by forming an alumina particle layer having a thickness of 2 μm on both sides of the polyolefin (PO) microporous membrane of Example 4, except for a 3 mm portion at the end, according to the method described in JP 2014-149935 A.

(Examples 8 to 11)
The electrolyte composition was prepared, the porous thin film material was prepared, and the separator material was produced in the same manner as in Example 1, except that the compounds shown in Table 2 were used as the organic composition in the amounts shown in Table 2 when preparing the electrolyte composition. Various evaluations were then performed in the same manner as in Example 1. The results are shown in Table 2.
In the table, "EO-PO copolymer" refers to an ethylene oxide (EO)-propylene oxide (PO) copolymer (EO:PO=90:10) having a weight average molecular weight of 1,000,000.

(Examples 12 to 15 and 17 to 18)
In preparing the electrolyte composition, 30 g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was used as the ionic substance instead of 10 g of LiBF ₄ , and the compounds shown in Table 2 were used as the organic composition in the amounts shown in Table 2. Except for this, the electrolyte composition was prepared, the porous thin film material was prepared, and the separator material was produced in the same manner as in Example 1. Various evaluations were then performed in the same manner as in Example 1. The results are shown in Table 2.

(Example 16)
In preparing the electrolyte composition, 40 g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was used as the ionic substance instead of 10 g of LiBF ₄ , and the compounds shown in Table 2 were used as the organic composition in the amounts shown in Table 2. Except for this, the electrolyte composition was prepared, the porous thin film material was prepared, and the separator material was produced in the same manner as in Example 1. Then, various evaluations were performed in the same manner as in Example 1. The results are shown in Table 2.

(Example 19)
In preparing the electrolyte composition, 30 g of magnesium bis(trifluoromethanesulfonyl)imide (Mg(TFSI) ₂ ) was used as the ionic substance instead of 10 _g of LiBF4, and the compounds shown in Table 2 were used in the amounts shown in Table 2 as the organic composition, but the electrolyte composition was prepared, a porous thin film material was prepared, and a separator material was produced in the same manner as in Example 1. Various evaluations were then performed in the same manner as in Example 1. The results are shown in Table 2.

(Comparative Example 1)
The electrolyte composition was prepared, the porous thin film material was prepared, and the separator material was produced in the same manner as in Example 1, except that the compounds shown in Table 2 were used as the organic composition in the amounts shown in Table 2 when preparing the electrolyte composition. Various evaluations were then performed in the same manner as in Example 1. The results are shown in Table 2.

(Comparative Example 2)
The electrolyte composition was prepared, the porous thin film material was prepared, and the separator material was fabricated in the same manner as in Comparative Example 1, except that a 25 μm-thick polyolefin (PO) microporous membrane (Celgard 2325, manufactured by Polypore) was used instead of a glass fiber filter (GA-55, manufactured by Advantec Corporation) when preparing the porous thin film material. Various evaluations were then performed in the same manner as in Example 1. The results are shown in Table 2.

(Comparative Example 3)
The electrolyte composition was prepared, the porous thin film material was prepared, and the separator material was fabricated in the same manner as in Example 1, except that a 675 μm thick glass fiber filter (Whatman (registered trademark) GF/B, manufactured by GE Healthcare Life Sciences) was used instead of the glass fiber filter (GA-55, manufactured by ADVANTEC) when preparing the porous thin film material. Various evaluations were then performed in the same manner as in Example 1. The results are shown in Table 2.

(Comparative Examples 4 to 5)
In preparing the electrolyte composition, the electrolyte composition was prepared, the porous thin film material was prepared, and the separator material was produced in the same manner as in Comparative Example 1 and Comparative Example 2, except that the compounds shown in Table 2 were used as the organic composition in the amounts shown in Table 2. Then, various evaluations were performed in the same manner as in Example 1. The results are shown in Table 2.

From Table 2, it can be seen that the separator materials of Examples 1 to 19 have a large wet area ratio after the ignition test and no holes in the porous thin film material, so that they are unlikely to burn even when ignited from the outside. Also, from Table 2, it can be seen that the separator materials of Comparative Examples 1, 3, and 4 have a small wet area ratio after the ignition test and the electrolyte composition is likely to burn. Furthermore, from Table 2, it can be seen that the separator materials of Comparative Examples 2 and 5 have holes in the porous thin film material, so that the porous thin film material is easily damaged, and therefore the electrochemical device is likely to have an internal short circuit.
Furthermore, the separator materials of Examples 1 to 19 had a high proportion of compounds that were solid at a temperature of 5° C. under atmospheric pressure, and therefore were less susceptible to leakage of substances to the outside.

(Example 20)
A lithium ion secondary battery was produced by bonding a positive electrode having a positive electrode composite layer (positive electrode active material: lithium iron phosphate) impregnated with the same electrolyte composition as the separator material, with the separator material produced in Example 10 interposed therebetween, and a negative electrode made of lithium metal. Immediately after production, the battery was repeatedly charged and discharged under conditions of a voltage of 3.8 to 3.0 V and a current value of 0.1 C, and it was confirmed that charging and discharging were possible.

According to the present invention, a non-aqueous electrochemical device is obtained which is less likely to burn and has less leakage of substances to the outside, even if ignited from the inside or outside.

Claims (10)

A porous thin film material having a thickness of 300 μm or less is impregnated with an electrolyte composition,
The electrolyte composition contains at least one ionic substance and an organic composition, and is liquid at a temperature of 100° C. under atmospheric pressure;
The organic composition contains a compound that is solid at a temperature of 5° C. under atmospheric pressure in a proportion of 80% by mass or more, and a content ratio of a low-boiling point organic compound having a boiling point of less than 130° C. under atmospheric pressure is 0% by mass or more and 20% by mass or less,
The electrolyte composition has an ionic conductivity of 1.0×10 ⁻⁴ S/cm or more at a temperature of −20° C. 2 . The separator material according to claim 1 , wherein the organic composition contains an organic compound that is liquid at a temperature of 40° C. under atmospheric pressure in an amount of 0% by mass or more and 20% by mass or less. A porous thin film material having a thickness of 300 μm or less is impregnated with an electrolyte composition,
The electrolyte composition contains at least one ionic substance and an organic composition, and is liquid at a temperature of 100° C. under atmospheric pressure;
The organic composition contains 80% by mass or more of a compound that is solid at a temperature of 5° C. under atmospheric pressure, a content of low-boiling point organic compounds having a boiling point of less than 130° C. under atmospheric pressure is 0% by mass or more and 20% by mass or less , and a content of organic compounds that are liquid at a temperature of 40° C. under atmospheric pressure is 0% by mass or more and 20% by mass or less . The separator material according to claim 1 , wherein the organic composition contains two or more compounds that are solid at a temperature of 5° C. under atmospheric pressure. The separator material according to claim 1 , wherein the organic composition contains three or more compounds that are solid at a temperature of 5° C. under atmospheric pressure. The separator material according to claim 1 , wherein the organic composition further contains a flame retardant. The separator material according to claim 1 , wherein the electrolyte composition further contains a polymer component. The separator material according to any one of claims 1 to 7 , wherein the porous thin film material has a melting point. The separator material according to any one of claims 1 to 8 , wherein non-combustible fine particles are attached to a surface of the porous thin film material. A non-aqueous electrochemical device comprising the separator material according to any one of claims 1 to 9.