JP7619259B2 - Electrolyte composition for electrochemical device and electrochemical device - Google Patents

Description

The present invention relates to an electrolyte composition for electrochemical devices and an electrochemical device.

Conventionally, organic solvent electrolytes obtained by dissolving a supporting electrolyte in an organic solvent have been used in electrochemical devices such as 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; redox flow 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 (see, for example, Patent Document 1).

For example, Patent Document 2 discloses an electrolyte composition for lithium ion secondary batteries having low viscosity and high specific conductivity, which is obtained by dissolving a lithium salt in an organic solvent containing at least one nitrile compound selected from the group consisting of a chain saturated hydrocarbon dinitrile compound, a chain ether nitrile compound, and a cyanoacetate ester, and at least one of a cyclic carbonate, a cyclic ester, and a chain carbonate.

JP 2011-192888 A JP 2010-165653 A

Here, from the perspective of enhancing safety, electrolyte compositions used in electrochemical devices are required to have reduced flammability while maintaining ionic conductivity.

However, the conventional electrolyte compositions described above were unable to achieve both low flammability and good ionic conductivity.

Therefore, an object of the present invention is to provide an electrolyte composition for electrochemical devices which has both low flammability and good ion conductivity.
Another object of the present invention is to provide an electrochemical device which is excellent in safety and can exhibit good electrochemical properties.

As a result of extensive research into achieving the above-mentioned object, the inventors have discovered that an electrolyte composition containing a specified proportion of compounds that are solid at a temperature of 5°C under atmospheric pressure, including succinonitrile and organic compounds other than succinonitrile, can achieve both low flammability and good ionic conductivity, and have thus completed the present invention.

That is, the present invention aims to advantageously solve the above problems, and the electrolyte composition for electrochemical devices of the present invention is an electrolyte composition for electrochemical devices containing at least one ionic substance and an organic composition, characterized in that the organic composition contains 80% by mass or more of a compound that is solid at a temperature of 5°C under atmospheric pressure, and the compound contains succinonitrile and an organic compound other than succinonitrile. In this way, by using an organic composition containing 80% by mass or more of a compound that is solid at a temperature of 5°C under atmospheric pressure, including succinonitrile and an organic compound other than succinonitrile, it is possible to achieve both low flammability and good ionic conductivity.

Here, in the electrolyte composition for electrochemical devices of the present invention, the organic compound is preferably at least one selected from the group consisting of ethylene carbonate, N-methyloxazolidone, N,N-dimethylimidazolidinone, fluoroethylene carbonate, glycolide, lactide, sulfolane, dimethyl sulfone, ethyl methyl sulfone, methyl methylsulfonyl acetate, dimethyl oxalate, dimethyl succinate, succinic anhydride, itaconic anhydride, glutaric anhydride, maleic anhydride, diglycolic anhydride, and N-methylsuccinimide. If the organic compound other than succinonitrile is one of the above-mentioned compounds, the flammability of the electrolyte composition for electrochemical devices can be further reduced.

In addition, in the electrolyte composition for electrochemical devices of the present invention, it is preferable that the organic composition contains three or more types of compounds that are solid at a temperature of 5° C. and atmospheric pressure. The more types of compounds that are solid at a temperature of 5° C. and atmospheric pressure, the easier it is for the ionic substance to dissolve and the ionic conductivity of the electrolyte composition for electrochemical devices to improve.

Furthermore, in the electrolyte composition for electrochemical devices 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 electrolyte composition for electrochemical devices can be made even more difficult to burn.

In addition, in the electrolyte composition for electrochemical devices of the present invention, it is preferable that the organic composition contains succinonitrile in a proportion of 45 mass% or less. If the content of succinonitrile in the organic composition is 45 mass% or less, the electrolyte composition for electrochemical devices can be made even more difficult to burn.

Furthermore, the electrolyte composition for electrochemical devices of the present invention preferably has an ionic conductivity of 1.0 × 10 ^-4 S/cm or more at a temperature of -10° C. When the electrolyte composition for electrochemical devices has an ionic conductivity of the above-mentioned lower limit or more, electrochemical reactions can proceed smoothly in the electrochemical device.
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.

Moreover, the electrolyte composition for electrochemical devices of the present invention preferably has an ionic conductivity of 1.0 × 10 ^-4 S/cm or more at a temperature of -20° C. When the electrolyte composition for electrochemical devices has an ionic conductivity of the above-mentioned lower limit or more, electrochemical reactions can proceed smoothly in the electrochemical device.

Furthermore, the electrolyte composition for electrochemical devices of the present invention preferably further contains a polymer component. If the electrolyte composition for electrochemical devices contains a polymer component, the electrolyte composition for electrochemical devices can be made even more resistant to combustion.
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.

The electrolyte composition for electrochemical devices of the present invention is preferably in the form of a chemical gel obtained by crosslinking the polymer component or in the form of a physical gel obtained by depositing the polymer component. An electrolyte composition for electrochemical devices in the form of a chemical gel obtained by crosslinking the polymer component or in the form of a physical gel obtained by depositing the polymer component can be advantageously used for forming a free-standing membrane or the like.

The present invention also aims to advantageously solve the above problems, and the electrochemical device member of the present invention is characterized in that it contains any of the above-mentioned electrolyte compositions for electrochemical devices. In this way, by incorporating the above-mentioned electrolyte composition for electrochemical devices into the electrochemical device member, it is possible to provide an electrochemical device that is safe and can exhibit good electrochemical properties.

Furthermore, the present invention aims to advantageously solve the above problems, and the electrochemical device of the present invention is characterized by including any one of the above-mentioned electrolyte compositions for electrochemical devices. In this way, by using the above-mentioned electrolyte composition for electrochemical devices, the safety of the electrochemical device can be improved and the electrochemical device can exhibit good electrochemical properties.

According to the present invention, it is possible to provide an electrolyte composition for electrochemical devices which has both low flammability and good ion conductivity.
Furthermore, according to the present invention, it is possible to provide an electrochemical device which is excellent in safety and can exhibit good electrochemical properties.

The electrolyte composition for electrochemical devices and the member for electrochemical devices of the present invention are not particularly limited and can be used in 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, redox flow 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. In particular, the electrolyte composition for electrochemical devices and the member for electrochemical devices of the present invention can be suitably used in non-aqueous secondary batteries, particularly lithium ion secondary batteries.
The electrochemical device of the present invention uses the electrolyte composition for electrochemical devices of the present invention.
The electrolyte composition for electrochemical devices of the present invention has low flammability and can exhibit good ion conductivity. Therefore, by using the electrolyte composition for electrochemical devices and/or the electrochemical device member of the present invention, an electrochemical device that is excellent in safety and can exhibit good electrochemical properties can be obtained. Furthermore, the electrochemical device of the present invention has excellent in safety and can exhibit good electrochemical properties.

(Electrolyte composition for electrochemical devices)
The electrolyte composition for electrochemical devices of the present invention contains at least one ionic substance and an organic composition, and may further contain a polymer component and/or an additive, as desired. The electrolyte composition for electrochemical devices of the present invention is preferably liquid at a temperature of 20° C. and atmospheric pressure. When the electrolyte composition for electrochemical devices is liquid at a temperature of 20° C. and atmospheric pressure, it can exhibit excellent ion conductivity. In the present invention, "liquid" includes, in addition to a single liquid phase state, a state in which one or more other liquid phases are present in a main liquid phase at a ratio of 5% by volume or less, and a state in which a liquid phase contains a small amount of solid phase of 5% by volume or less.

<Ionic Substances>
As the ionic substance, any ionic substance can be used depending on the type of ions used in the electrochemical reaction in the electrochemical device.
The amount of the ionic substance can be appropriately set according to the type of 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 electrochemical device in which the electrolyte composition for electrochemical devices 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, or lithium bis(trifluoromethanesulfonyl)imide. When the electrochemical device in which the electrolyte composition for electrochemical devices 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 at a temperature of 5° C. under atmospheric pressure, and may optionally further contain at least one member selected from the group consisting of a compound that is liquid at a temperature of 5° C. under atmospheric pressure, a flame retardant, and 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 is not within the above range, the flammability of the electrolyte composition for electrochemical devices cannot be sufficiently reduced. Here, the reason why the content ratio of the compound that is solid under atmospheric pressure at a temperature of 5°C can be sufficiently reduced by setting the content ratio of the compound that is solid under atmospheric pressure at a temperature of 5°C within the above range is not clear, but it is presumed that the electrolyte composition becomes highly viscous by using an organic composition mainly composed of a compound that is solid under atmospheric pressure at a temperature of 5°C, and when exposed to high temperatures such as a fire, a part of the components volatilize, causing the electrolyte composition to deviate from the range in which it can maintain a liquid state (solids precipitate). Note that if the electrolyte composition is likely to deviate from the range in which it can maintain a liquid state, it is possible to sufficiently suppress leakage of the electrolyte composition to the outside when the exterior of the electrochemical device is destroyed by ignition or the like.

[Compounds that are solid at 5°C and atmospheric pressure]
The electrolyte composition for electrochemical devices of the present invention is required to contain succinonitrile and an organic compound other than succinonitrile as compounds that are solid under atmospheric pressure at a temperature of 5° C. If the electrolyte composition does not contain both succinonitrile and an organic compound other than succinonitrile, it is not possible to achieve both low flammability and good ionic conductivity.

Here, the content of succinonitrile in the organic composition is preferably 45% by mass or less. If the content of succinonitrile in the organic composition is 45% by mass or less, the electrolyte composition for electrochemical devices can be made even more difficult to burn. From the viewpoint of increasing the ionic conductivity of the electrolyte composition for electrochemical devices, the content of succinonitrile in the organic composition is preferably 10% by mass or more, and more preferably 20% by mass or more.

In addition, it is preferable that the organic composition contains three or more types of compounds that are solid at atmospheric pressure and a temperature of 5°C. In other words, it is preferable that the organic composition contains two or more types of organic compounds other than succinonitrile that are solid at atmospheric pressure and a temperature of 5°C. This is because the more types of compounds that are solid at atmospheric pressure and a temperature of 5°C, the easier it is for the ionic substance to dissolve and the ionic conductivity of the electrolyte composition for electrochemical devices to improve.

[Organic compounds other than succinonitrile]
Here, the organic compound other than succinonitrile 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. Organic compounds other than succinonitrile that are solid under atmospheric pressure at a temperature of 5° C. are usually compounds that do not have flame retardancy and are different from flame retardants. In addition, organic compounds other than succinonitrile that are solid under atmospheric pressure at a temperature of 5° C. preferably have a molecular weight of less than 10,000.

Examples of organic compounds other than succinonitrile that are solid under atmospheric pressure at a temperature of 5° C. include glutaric anhydride, succinic anhydride, dimethyl succinate, N-methylsuccinimide, diglycolic anhydride, sulfolane, ethyl methyl sulfone, dimethyl sulfone, diethyl sulfone, sulfolane, ethylene sulfate (1,3,2-dioxathiolane-2,2-dioxide), itaconic anhydride, maleic anhydride, methylsulfonyl methyl acetate, ethylene carbonate, N-methyloxazolidone, fluoroethylene carbonate, methyl carbamate, N,N-dimethylimidazolidinone, dimethyl oxalate, vinylene carbonate, dimethyl sulfoxide, glycolide, and lactide.
These organic compounds may be used alone or in combination of two or more. Among them, it is preferable to use two or more of the organic compounds other than succinonitrile in combination.

From the viewpoint of further increasing the ionic conductivity of the electrolyte composition for electrochemical devices, the organic compound other than the succinonitrile is preferably a polar compound having an oxygen atom and/or a nitrogen atom, and is more preferably at least one selected from the group consisting of ethylene carbonate, N-methyloxazolidone, N,N-dimethylimidazolidinone, fluoroethylene carbonate, glycolide, lactide, sulfolane, dimethyl sulfone, ethyl methyl sulfone, methyl methylsulfonyl acetate, dimethyl oxalate, dimethyl succinate, succinic anhydride, itaconic anhydride, glutaric anhydride, maleic anhydride, diglycolic anhydride and N-methylsuccinimide, and even more preferably two or more selected from the above group.

In addition, when the organic compound other than succinonitrile has a heteroatom in the molecule, the number of carbon atoms is preferably not more than twice the number of heteroatoms in the molecule in terms of reducing flammability. For the same reason, the number of carbon atoms in the organic compound other than succinonitrile is preferably not more than 5.

Furthermore, from the viewpoint of reducing flammability, it is preferable that the organic compounds other than the succinonitrile do not have carbon-carbon double bonds or carbon-carbon triple bonds in the molecule. This is because compounds with unsaturated bonds are more flammable than compounds with only single bonds.

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

[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 electrolyte composition 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 a decrease in the ionic conductivity of the electrolyte composition for 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 prevent the electrolyte composition for electrochemical devices from leaking to the outside when the exterior of the electrochemical device is destroyed by ignition or the like, the content of the low-boiling point organic compound in the organic composition is preferably 0% by mass or more and 20% by mass or less, and more preferably 0% by mass or more and 10% by mass or less.

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

It is preferable that the compounds contained in the organic composition have different boiling points. If the organic composition is made up of many types of compounds with different boiling points, the compounds that make up the organic composition will not volatilize at the same time in the event of a fire, making it less likely for the fire to intensify.

<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 the 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. The inclusion of a polymer component makes it difficult for the electrolyte composition to flow, and makes it even more difficult for the electrolyte composition to burn.

Here, the polymer component may be polymerized by using a polymerization method such as thermal polymerization inside the electrochemical device after assembly. The polymer component is preferably uniformly dissolved in the electrolyte composition at a temperature of 20° C.
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.
Additionally, the polymeric components may be advantageously used to form free-standing membranes and the like by crosslinking the entire electrolyte composition to a chemical gel and/or by precipitating the composition to a physical gel, where crosslinking may be accomplished using any method, such as, for example, ultraviolet radiation.
On the other hand, the polymer component preferably does not have a crosslinked structure from the viewpoint of dissolving well in the electrolyte composition. Also, from the viewpoint of dissolving well in the electrolyte composition, the polymer component preferably has a small 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 at 100° C. for 12 hours, filtering the insoluble matter with a membrane filter at 100° C., vacuum drying to remove the propylene carbonate, and measuring the weight of the residue.

In order to suppress a decrease in the ionic conductivity of the electrolyte composition, the content of the polymer component in the electrolyte composition is preferably 0 parts by mass or more and 100 parts by mass or less, and more preferably 0 parts by mass or more and 50 parts by mass or less, per 100 parts by mass of the organic composition.

<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 for Electrochemical Device>
From the viewpoint of exhibiting excellent ion conductivity, the electrolyte composition is preferably in a liquid state at a temperature of 20° C. under atmospheric pressure.

The electrolyte composition preferably has an ionic conductivity of 1.0×10 ⁻⁴ S/cm or more at a temperature of −20° C. The electrolyte composition preferably has an ionic conductivity of 1.0×10 −4 S/cm or more at a temperature of −10° C. Furthermore, the electrolyte composition 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 be satisfactorily promoted in an electrochemical device using the electrolyte composition.

<Preparation of Electrolyte Composition>
The electrolyte composition is not particularly limited, and can be prepared by mixing the above-mentioned compounds by any method.
Here, since the process of preparing a liquid electrolyte composition using a compound that is solid under atmospheric pressure at a temperature of 5°C is often an endothermic process, it is preferable to prepare the electrolyte composition while heating the compounds to be mixed. In particular, the preparation of the liquid electrolyte composition is smooth when it is performed at a temperature equal to or higher than the melting point of the compound contained in the organic composition. The heating temperature is preferably equal to or lower than the decomposition temperature of the compound or ionic substance contained in the electrolyte composition.
The electrolyte composition is preferably prepared in the absence of moisture and oxygen.

(Electrochemical device components)
The electrochemical device member of the present invention contains the above-mentioned electrolyte composition for electrochemical devices of the present invention. Since the electrochemical device member of the present invention contains the electrolyte composition for electrochemical devices of the present invention, it has low flammability and excellent ion conductivity. Therefore, by using the electrochemical device member of the present invention, it is possible to provide an electrochemical device that is excellent in safety and can exhibit good electrochemical properties.

Here, the electrochemical device components are not particularly limited and may include, for example, electrodes (positive and negative electrodes) and separators.

<Electrodes>
The electrode containing the electrolyte composition for electrochemical devices of the present invention is not particularly limited, and examples thereof include electrodes having an electrode mixture layer containing the electrolyte composition for electrochemical devices of the present invention.
Here, an electrode having an electrode mixture layer can be produced by forming an electrode mixture layer on a current collector. The electrode mixture layer is not particularly limited, and may be, for example, an electrode mixture layer that contains an electrode active material (positive electrode active material, negative electrode active material) and the electrolyte composition for electrochemical devices of the present invention, and optionally further contains at least one selected from the group consisting of a conductive material, a binder, and an additive. The current collector, electrode active material, conductive material, binder, and additive may be any of those used in the field of electrochemical devices.

<Separator>
Furthermore, the separator containing the electrolyte composition for electrochemical devices of the present invention is not particularly limited, and examples thereof include porous thin film materials impregnated with the electrolyte composition for electrochemical devices of the present invention.
Here, the porous thin film material is not particularly limited, and may be, for example, a material used in the field of electrochemical devices, such as a polyolefin porous film, a polyolefin nonwoven fabric, a fluororesin porous film, paper, a cellulose nonwoven fabric, an aramid nonwoven fabric, and a glass fiber filter.The impregnation of the porous thin film material with the electrolyte composition is not particularly limited, and may be performed by 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.

(Electrochemical Devices)
The electrochemical device of the present invention includes the electrolyte composition for electrochemical devices of the present invention. Specifically, the electrochemical device of the present invention usually includes a positive electrode and a negative electrode, a separator that separates the positive electrode and the negative electrode, and an electrolyte. The electrochemical device of the present invention usually uses the electrolyte composition for electrochemical devices of the present invention as the electrolyte. In this way, by using the electrolyte composition for electrochemical devices of the present invention, an electrochemical device that is difficult to burn and has excellent safety and can exhibit good electrochemical properties can be obtained. In addition, the electrochemical device using the electrolyte composition for electrochemical devices of the present invention can sufficiently suppress leakage of the electrolyte composition to the outside even if the exterior is destroyed by ignition or the like.

Here, the positive electrode, negative electrode, and separator are not particularly limited, and any positive electrode, negative electrode, and separator that can be used in the field of electrochemical devices can be used.

First, the following Reference Examples 1 to 3 were carried out to attempt to prepare a composition that is liquid at a temperature of 20°C and atmospheric pressure using a compound that is solid at a temperature of 5°C and atmospheric pressure.

(Reference Example 1)
Equal masses of ethylene carbonate and succinonitrile were weighed out and mixed at room temperature, whereupon the mixture melted while absorbing heat from the surroundings to form a homogeneous liquid composition.

(Reference Example 2)
Equal masses of ethylene carbonate and dimethyl sulfone were weighed out and mixed at room temperature, but the mixture remained solid. When the mixture was heated to 60° C. on a hot plate, it melted and became a homogeneous liquid composition.
However, when the resulting liquid composition was left in an atmosphere at 20° C., the entire composition solidified.

(Reference Example 3)
80 g of ethylene carbonate and 20 g of dimethyl sulfone were mixed at room temperature, but the mixture remained solid. When the mixture was heated to 60° C. on a hot plate, it melted and became a homogeneous liquid composition.
However, when the resulting liquid composition was left in an atmosphere at 20° C., the entire composition solidified.
Then, 7.5 g of _LiBF4 was added to the solidified composition and the composition was heated and dissolved again to obtain a homogeneous liquid composition. This liquid composition did not precipitate a solid even when left at 20°C.

Next, the following Reference Examples 4 and 5 were carried out to investigate the flammability of various compounds on their own.

(Reference Example 4)
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 burner flame for 1 second to check for ignition. 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-allyl glycidyl ether copolymer (powder form)
<Compounds that did not ignite>
Flame retardants such as succinonitrile, ethylene carbonate, N-methyloxazolidone, N,N-dimethylimidazolidinone, fluoroethylene carbonate, glycolide, lactide, sulfolane, dimethyl sulfone, ethyl methyl sulfone, 4,4-dioxo-1,4-oxathiane, methyl methylsulfonylacetate, dimethyl oxalate, dimethyl succinate, succinic anhydride, itaconic anhydride, glutaric anhydride, maleic anhydride, diglycolic anhydride, N-methylsuccinimide, adiponitrile, tetraglyme, propylene carbonate, and N-methylpyrrolidone trimethyl phosphate, hydrin rubber (bulk), and acrylic rubber (bulk).

(Reference Example 5)
Of the compounds that did not ignite in Reference Example 4, a test was carried out in which a flame was continuously applied to the following compounds until they ignited: succinonitrile, ethylene carbonate, N-methyloxazolidone, N,N-dimethylimidazolidinone, fluoroethylene carbonate, glycolide, lactide, sulfolane, dimethyl sulfone, ethyl methyl sulfone, 4,4-dioxo-1,4-oxathiane, methyl methylsulfonylacetate, dimethyl oxalate, dimethyl succinate, succinic anhydride, itaconic anhydride, glutaric anhydride, maleic anhydride, diglycolic anhydride, N-methylsuccinimide, adiponitrile, tetraglyme, propylene carbonate, and N-methylpyrrolidone.
As a result, all of the compounds ignited. Table 1 shows the height of the flame during combustion, as well as whether or not there was leakage outside the container and whether or not there was combustion outside the container.

Finally, the following Reference Example 6 was carried out to investigate the volatility of various compounds on their own.

(Reference Example 6)
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.

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.

<Evaluation of flammability of electrolyte composition>
100 mg of the prepared electrolyte composition was placed in a stainless steel dish having a diameter of 2 cm and exposed to a flame from a burner. The time until ignition, the presence or absence of fluidity during combustion, the size of the flame, and the resistance to combustion (self-extinguishing property) were evaluated.
<Ionic Conductivity of Electrolyte Composition>
The measurements were carried out at temperatures of -20°C and -10°C using an impedance analyzer (manufactured by Solartron).

Example 1
7.5 g of _LiBF4 as an ionic compound, 60 g of succinonitrile as an organic composition, and 40 g of ethylene carbonate were weighed out and mixed to prepare a homogeneous solution of an electrolyte composition.
The flammability and ionic conductivity were then measured. The results are shown in Table 2.

(Examples 2 to 6)
An electrolyte composition was prepared in the same manner as in Example 1, except that the amounts of succinonitrile and ethylene carbonate were changed to those shown in Table 2. Then, various evaluations were performed in the same manner as in Example 1. The results are shown in Table 2.

(Examples 7 to 11)
An electrolyte composition was prepared in the same manner as in Example 1, except that 30 g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was used as the ionic compound instead of 7.5 g of LiBF ₄ , and the compounds shown in Table 2 were used in the amounts shown in Table 2 as the organic composition. Various evaluations were then performed in the same manner as in Example 1. The results are shown in Table 2.

Example 12
10 g of _LiBF4 as an ionic compound, 50 g of succinonitrile and 50 g of ethylene carbonate as organic compositions, and 10 g of ethylene oxide (EO)-propylene oxide (PO)-allyl glycidyl ether (AGE) copolymer as a polymer component were weighed out and mixed to prepare a homogeneous solution of an electrolyte composition.
The flammability and ionic conductivity were then measured. The results are shown in Table 2.

Example 13
An electrolyte composition was prepared in the same manner as in Example 1, except that 40 g of magnesium bis(trifluoromethanesulfonyl)imide (Mg(TFSI) ₂ ) was used as the ionic compound instead of 7.5 _g of LiBF4, and the compounds shown in Table 2 were used in the amounts shown in Table 2 as the organic composition. Various evaluations were then performed in the same manner as in Example 1. The results are shown in Table 2.

(Example 14)
30 g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as an ionic compound, 40 g of succinonitrile as an organic composition, 40 g of ethylene carbonate, and 20 g of trimethyl phosphate (flame retardant) were weighed out and mixed to prepare a homogeneous solution of an electrolyte composition.
The flammability and ionic conductivity were then measured. The results are shown in Table 2.

(Examples 15 to 16)
An electrolyte composition was prepared in the same manner as in Example 14, except that the amounts of succinonitrile, ethylene carbonate, and trimethyl phosphate were changed to those shown in Table 2. Various evaluations were then performed in the same manner as in Example 1. The results are shown in Table 2.

(Example 17)
30 g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as an ionic compound, 40 g of succinonitrile as an organic composition, 40 g of ethylene carbonate, and 20 g of propylene carbonate (a compound that is liquid under atmospheric pressure at a temperature of 5° C.) were weighed out and mixed to prepare a homogeneous solution of an electrolyte composition.
The flammability and ionic conductivity were then measured. The results are shown in Table 2.

(Comparative Example 1)
10 g of LiBF ₄ as an ionic compound and 100 g of succinonitrile as an organic composition were weighed out and mixed to prepare a solid electrolyte composition.
The flammability and ionic conductivity were then measured. The results are shown in Table 2.

(Comparative Example 2)
A solid electrolyte composition was prepared in the same manner as in Comparative Example 1, except that 30 g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was used as the ionic compound instead of 10 g of LiBF _4. Various evaluations were then performed in the same manner as in Example 1. The results are shown in Table 2.

(Comparative Example 3)
10 g of _LiBF4 as an ionic compound, 40 g of succinonitrile as an organic composition, and 60 g of diethyl carbonate (a low boiling point organic compound) were weighed out and mixed to prepare a homogeneous solution of an electrolyte composition.
The flammability and ionic conductivity were then measured. The results are shown in Table 2.

(Comparative Example 4)
10 g of _LiBF4 as an ionic compound, 75 g of succinonitrile as an organic composition, and 25 g of propylene carbonate (a compound that is liquid under atmospheric pressure at a temperature of 5°C) were weighed out and mixed to prepare a homogeneous solution of an electrolyte composition.
The flammability and ionic conductivity were then measured. The results are shown in Table 2.

(Comparative Example 5)
7.5 g of _LiBF4 as an ionic compound, 80 g of ethylene carbonate as an organic composition, and 20 g of dimethyl sulfone were weighed out and mixed to prepare a homogeneous solution of an electrolyte composition.
The flammability and ionic conductivity were then measured. The results are shown in Table 2.

From Table 2, it can be seen that the electrolyte compositions of Examples 1 to 17 can achieve both low flammability and good ionic conductivity. Also, from Table 2, it can be seen that the electrolyte compositions of Comparative Examples 1 and 2, which do not contain organic compounds other than succinonitrile as compounds that are solid at a temperature of 5°C under atmospheric pressure, have low ionic conductivity, the electrolyte compositions of Comparative Examples 3 and 4, which contain less than 80 mass% of compounds that are solid at a temperature of 5°C under atmospheric pressure, have a short time to ignition and high flammability, and the electrolyte composition of Comparative Example 5, which does not contain succinonitrile as a compound that is solid at a temperature of 5°C under atmospheric pressure, has low ionic conductivity.

(Example 18)
A positive electrode having a positive electrode composite layer (positive electrode active material: lithium iron phosphate) and a negative electrode made of lithium metal were laminated together with a separator made of a glass fiber filter (Whatman (registered trademark) GF/A, manufactured by GE Healthcare Life Sciences) interposed therebetween, and the electrolyte composition prepared in Example 10 was filled as an electrolyte solution to produce a lithium ion secondary battery. Immediately after production, repeated charging and discharging were performed under conditions of a voltage of 3.8 to 3.0 V, and it was confirmed that charging and discharging were possible.

(Example 19)
First, 10 g of the electrolyte composition prepared in Example 12 and 40 g of graphite (604A, manufactured by Nippon Carbon Co., Ltd.) as a negative electrode active material were mixed in an open mortar to obtain a uniform clay-like molding material. The molding material was then spread into a sheet on a copper foil to obtain a negative electrode having a thickness of 50 μm.
Next, 10 g of the electrolyte composition prepared in Example 12, 25 g of lithium cobalt oxide (Cellseed C, manufactured by Nippon Chemical Industry Co., Ltd.) as a positive electrode active material, and 5 g of acetylene black as a conductive material were kneaded in an open mortar to obtain a uniform clay-like molding material. The molding material was then spread into a sheet on aluminum foil to obtain a positive electrode with a thickness of 50 μm.
Further, 0.5 parts of Irg651 as an ultraviolet crosslinking agent was added to 100 parts of the electrolyte composition prepared in Example 12, and the mixture was irradiated with ultraviolet light to produce an electrolyte film having a thickness of 50 μm.
The positive and negative electrodes were bonded together with an electrolyte film interposed therebetween to produce a lithium ion battery. Immediately after production, the battery was repeatedly charged and discharged at a voltage of 4.2 to 3.0 V, and it was confirmed that the battery was capable of charging and discharging.

According to the present invention, it is possible to provide an electrolyte composition for electrochemical devices which has both low flammability and good ion conductivity.
Furthermore, according to the present invention, it is possible to provide an electrochemical device which is excellent in safety and can exhibit good electrochemical properties.

Claims (8)

An electrolyte composition for electrochemical devices comprising at least one ionic substance, an organic composition, and a polymer component,
The polymer component is crosslinked to form a chemical gel,
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,
the compound comprises succinonitrile and an organic compound other than succinonitrile,
The organic composition comprises succinonitrile in an amount of 45 mass % or less . The electrolyte composition for electrochemical devices according to claim 1, wherein the organic compound is at least one selected from the group consisting of ethylene carbonate, N-methyloxazolidone, N,N-dimethylimidazolidinone, fluoroethylene carbonate, glycolide, lactide, sulfolane, dimethyl sulfone, ethyl methyl sulfone, methyl methylsulfonyl acetate, dimethyl oxalate, dimethyl succinate, succinic anhydride, itaconic anhydride, glutaric anhydride, maleic anhydride, diglycolic anhydride, and N-methylsuccinimide. The electrolyte composition for electrochemical devices according to claim 1 or 2, wherein the organic composition contains three or more compounds that are solid at a temperature of 5°C and atmospheric pressure. The electrolyte composition for electrochemical devices according to any one of claims 1 to 3, wherein the organic composition further contains a flame retardant. 5. The electrolyte composition for electrochemical devices according to claim 1 , which has an ionic conductivity of 1.0×10 ^-4 S/cm or more at a temperature of -10° C. 6. The electrolyte composition for electrochemical devices according to claim 1 , which has an ionic conductivity of 1.0×10 ^-4 S/cm or more at a temperature of -20°C. A member for electrochemical devices, comprising the electrolyte composition for electrochemical devices according to any one of claims 1 to 6 . An electrochemical device comprising the electrolyte composition for electrochemical devices according to any one of claims 1 to 6 .