JP7647766B2 - Electrolytes and electrochemical devices - Google Patents

Description

The present disclosure relates to electrolytes and electrochemical devices.

In recent years, the spread of portable electronic devices, electric vehicles, and the like has created a need for high-performance electrochemical devices, such as nonaqueous electrolyte secondary batteries, such as lithium-ion secondary batteries, and capacitors. As a means for improving the performance of electrochemical devices, for example, a method of adding a specific additive to the electrolyte has been considered. Patent Document 1 discloses an electrolyte for nonaqueous electrolyte batteries that contains a specific siloxane compound in order to improve cycle characteristics and internal resistance characteristics.

JP 2015-005329 A

One aspect of the present invention aims to provide an electrolyte solution that can improve the performance of electrochemical devices.

式（１）中、Ｒ^１及びＲ^２は、それぞれ独立に、ハロゲン原子で置換されていてもよい１価の炭化水素基、又はハロゲン原子を表し、Ｒ^３はアルキレン基を表し、Ｒ^４は、水素原子、ハロゲン原子、又はシリル基を表す。 One aspect of the present invention is an electrolyte solution containing a compound represented by the following formula (1) and a lithium salt.

In formula (1), ^R1 and ^R2 each independently represent a monovalent hydrocarbon group which may be substituted with a halogen atom, or a halogen atom, ^R3 represents an alkylene group, and ^R4 represents a hydrogen atom, a halogen atom, or a silyl group.

^R1 and ^R2 may each independently represent an unsubstituted monovalent hydrocarbon group. ^R3 may represent a linear alkylene group. ^R3 may represent an alkylene group having 2 or more carbon atoms. ^R4 may represent a hydrogen atom. ^R4 may represent a halogen atom.

式（１ａ）中、Ｒ^４１～Ｒ^４３は、それぞれ独立に、ハロゲン原子で置換されていてもよい１価の炭化水素基、又はハロゲン原子を表す。 ^R4 may represent a silyl group. The silyl group may be represented by the following formula (1a):

In formula (1a), R ⁴¹ to R ⁴³ each independently represent a monovalent hydrocarbon group which may be substituted with a halogen atom, or a halogen atom.

The total number of carbon atoms in the compound represented by formula (1) may be 4 or more.

^R1 and ^R2 may represent a methyl group, ^R3 may represent a linear alkylene group having 2 or more carbon atoms, and ^R4 may represent a hydrogen atom or a halogen atom. ^R4 may be a hydrogen atom.

The lithium salt may _include at least one selected from _the group consisting of LiPF6, _LiBF4 , _LiClO4 , LiB( _C6H5 ) ₄ , _LiCH3SO3 , _CF3SO2OLi , LiN( _SO2F ) ₂ , LiN( _SO2CF3 ) ₂ , and LiN( _SO2CF2CF3 ) ₂ . _{The lithium} salt may include a lithium salt of _a cyclic compound having a ring containing a boron atom or _a phosphorus atom _. The lithium salt may include a lithium salt of a compound having a fluorine atom, an oxygen atom, and a phosphorus atom.

The electrolyte may further contain an additive other than the compound represented by formula (1) and the lithium salt, and the content of the additive may be 10 mass% or less based on the total amount of the electrolyte.

The additive may include a cyclic compound having a carbon-carbon double bond. The additive may include a cyclic compound having a fluorine atom. The additive may include a cyclic compound having a sulfur atom. The additive may include a nitrile compound.

Another aspect of the present invention is an electrochemical device comprising a positive electrode, a negative electrode, and the above-described electrolyte.

According to one aspect of the present invention, an electrolyte solution capable of improving the performance of an electrochemical device can be provided.

FIG. 1 is a perspective view showing a nonaqueous electrolyte secondary battery as an electrochemical device according to one embodiment. FIG. 2 is an exploded perspective view showing an electrode group of the secondary battery shown in FIG. 1 .

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiment.

FIG. 1 is a perspective view showing an electrochemical device according to one embodiment. In this embodiment, the electrochemical device is a nonaqueous electrolyte secondary battery. As shown in FIG. 1, the nonaqueous electrolyte secondary battery 1 includes an electrode group 2 consisting of a positive electrode, a negative electrode, and a separator, and a bag-shaped battery exterior 3 that houses the electrode group 2. The positive electrode and the negative electrode are provided with a positive electrode current collector tab 4 and a negative electrode current collector tab 5, respectively. The positive electrode current collector tab 4 and the negative electrode current collector tab 5 protrude from the inside of the battery exterior 3 to the outside so that the positive electrode and the negative electrode can be electrically connected to the outside of the nonaqueous electrolyte secondary battery 1, respectively. The battery exterior 3 is filled with an electrolyte (not shown). The nonaqueous electrolyte secondary battery 1 may be a battery (coin type, cylindrical type, laminated type, etc.) of a shape other than the so-called "laminated type" as described above.

The battery exterior body 3 may be a container formed of, for example, a laminate film. The laminate film may be a laminate film in which, for example, a resin film such as a polyethylene terephthalate (PET) film, a metal foil such as aluminum, copper, or stainless steel, and a sealant layer such as polypropylene are laminated in this order.

2 is an exploded perspective view showing one embodiment of the electrode group 2 in the nonaqueous electrolyte secondary battery 1 shown in FIG. 1. As shown in FIG. 2, the electrode group 2 includes a positive electrode 6, a separator 7, and a negative electrode 8, in this order. The positive electrode 6 and the negative electrode 8 are arranged such that the surfaces facing the positive electrode mixture layer 10 and the negative electrode mixture layer 12, respectively, face the separator 7.

The positive electrode 6 includes a positive electrode current collector 9 and a positive electrode mixture layer 10 provided on the positive electrode current collector 9. The positive electrode current collector 9 is provided with a positive electrode current collector tab 4.

The positive electrode collector 9 is formed of, for example, aluminum, titanium, stainless steel, nickel, baked carbon, conductive polymer, conductive glass, etc. The positive electrode collector 9 may be made of aluminum, copper, etc., whose surface has been treated with carbon, nickel, titanium, silver, etc., for the purpose of improving adhesion, conductivity, and oxidation resistance. The thickness of the positive electrode collector 9 is, for example, 1 to 50 μm in terms of electrode strength and energy density.

In one embodiment, the positive electrode mixture layer 10 contains a positive electrode active material, a conductive agent, and a binder. The thickness of the positive electrode mixture layer 10 is, for example, 20 to 200 μm.

The positive electrode active material may be, for example, lithium oxide. Examples of lithium oxides _{include LixCoO2} , _{LixNiO2 , LixMnO2} , _{LixCoyNi1-yO2, LixCoyM1- yOz , LixNi1 - yMyOz , LixMn2O4} and _{LixMn2 - yMyO4} (in each formula, M represents at least one element selected from _the group consisting of Na, Mg, _{Sc ,} Y, _Mn , _Fe , _Co , _Cu , Zn, Al, Cr, Pb, Sb, V _{and B} (with the proviso that M is an element different from the other elements in each formula); x = 0 to 1.2, y = 0 to 0.9, z = 2.0 to 2.3). The lithium oxide represented by Li _x Ni _1-y M _y O _z may be Li _x Ni _1-(y1+y2) Co _y1 Mn _y2 O _z (wherein x and z are the same as those described above, y1=0 to 0.9, y2=0 to 0.9, and y1+y2=0 to 0.9), and may be, for example, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , LiNi _0.6 Co _0.2 Mn _0.2 O _{2 , or} LiNi _0.8 Co _0.1 Mn _0.1 O ₂ . The lithium oxide represented by Li _x Ni _1-y M _y O _z may be Li _x Ni _1-(y3+y4) Co _y3 Al _y4 O _z (wherein x and z are the same as those described above, y3=0 to 0.9, y4=0 to 0.9, and y3+y4=0 to 0.9), for example, LiNi _0.8 Co _0.15 Al _0.05 O ₂ .

The positive electrode active material may be, for example, a lithium phosphate, such as lithium manganese phosphate (LiMnPO ₄ ), lithium iron phosphate (LiFePO ₄ ), lithium cobalt phosphate (LiCoPO ₄ ), and lithium vanadium phosphate (Li ₃ V ₂ (PO ₄ ) ₃ ).

The content of the positive electrode active material may be 80% by mass or more, or 85% by mass or more, and may be 99% by mass or less, based on the total amount of the positive electrode mixture layer.

The conductive agent may be a carbon material such as carbon black, such as acetylene black or ketjen black, graphite, graphene, or carbon nanotubes. The content of the conductive agent may be, for example, 0.01% by mass or more, 0.1% by mass or more, or 1% by mass or more, and 50% by mass or less, 30% by mass or less, or 15% by mass or less, based on the total amount of the positive electrode mixture layer.

Examples of binders include resins such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose; rubbers such as SBR (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), fluororubber, isoprene rubber, butadiene rubber, and ethylene-propylene rubber; styrene-butadiene-styrene block copolymers or hydrogenated products thereof, EPDM (ethylene-propylene-diene terpolymer), styrene-ethylene-butadiene-ethylene copolymer, and styrene-isoprene-styrene block copolymer. Examples of the polymer include thermoplastic elastomers such as polyvinyl acetate, ethylene-vinyl acetate copolymers, and propylene-α-olefin copolymers; soft resins such as syndiotactic-1,2-polybutadiene, polyvinylidene fluoride, polytetrafluoroethylene-ethylene copolymers, and polytetrafluoroethylene-vinylidene fluoride copolymers; fluorine-containing resins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, polytetrafluoroethylene-ethylene copolymers, and polytetrafluoroethylene-vinylidene fluoride copolymers; resins having a nitrile group-containing monomer as a monomer unit; and polymer compositions having ionic conductivity for alkali metal ions (for example, lithium ions).

The binder content may be, for example, 0.1 mass% or more, 1 mass% or more, or 1.5 mass% or more, and may be 30 mass% or less, 20 mass% or less, or 10 mass% or less, based on the total amount of the positive electrode mixture layer.

There are no particular limitations on the separator 7, so long as it electronically insulates the positive electrode 6 from the negative electrode 8 while allowing ions to pass through, and is resistant to oxidation on the positive electrode 6 side and reduction on the negative electrode 8 side. Examples of materials for the separator 7 include resins, inorganic substances, and the like.

Examples of the resin include olefin polymers, fluorine polymers, cellulose polymers, polyimides, nylons, etc. From the viewpoint of being stable against the electrolyte and having excellent electrolyte retention, the separator 7 is preferably a porous sheet or nonwoven fabric formed of a polyolefin such as polyethylene or polypropylene.

Examples of inorganic substances include oxides such as alumina and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates such as barium sulfate and calcium sulfate. Separator 7 may be a separator in which fibrous or particulate inorganic substances are attached to a thin-film substrate such as a nonwoven fabric, a woven fabric, or a microporous film.

The negative electrode 8 includes a negative electrode current collector 11 and a negative electrode mixture layer 12 provided on the negative electrode current collector 11. The negative electrode current collector 11 is provided with a negative electrode current collector tab 5.

The negative electrode current collector 11 is formed of copper, stainless steel, nickel, aluminum, titanium, baked carbon, conductive polymer, conductive glass, aluminum-cadmium alloy, etc. The negative electrode current collector 11 may be made of copper, aluminum, etc., whose surface has been treated with carbon, nickel, titanium, silver, etc., for the purpose of improving adhesion, conductivity, and reduction resistance. The thickness of the negative electrode current collector 11 is, for example, 1 to 50 μm in terms of electrode strength and energy density.

The negative electrode mixture layer 12 contains, for example, a negative electrode active material and a binder.

The negative electrode active material is not particularly limited as long as it is a material capable of absorbing and releasing lithium ions. Examples of the negative electrode active material include carbon materials, metal composite oxides, oxides or nitrides of Group 4 elements such as tin, germanium, and silicon, lithium alone, lithium alloys such as lithium-aluminum alloys, and metals capable of forming alloys with lithium such as Sn and Si. From the viewpoint of safety, the negative electrode active material is preferably at least one selected from the group consisting of carbon materials and metal composite oxides. The negative electrode active material may be one of these alone or a mixture of two or more of them. The shape of the negative electrode active material may be, for example, particulate.

Examples of carbon materials include amorphous carbon materials, natural graphite, composite carbon materials in which a coating of amorphous carbon material is formed on natural graphite, and artificial graphite (obtained by firing resin raw materials such as epoxy resins and phenolic resins, or pitch-based raw materials obtained from petroleum, coal, etc.). From the viewpoint of high current density charge/discharge characteristics, the metal composite oxide preferably contains either one or both of titanium and lithium, and more preferably contains lithium.

Among the negative electrode active materials, carbon materials have high electrical conductivity and are particularly excellent in low-temperature characteristics and cycle stability. Among carbon materials, graphite is preferred from the viewpoint of increasing capacity. In graphite, the carbon net surface interlayer distance (d002) in the wide-angle X-ray diffraction method is preferably less than 0.34 nm, and more preferably 0.3354 nm or more and 0.337 nm or less. Carbon materials that satisfy these conditions are sometimes called pseudoanisotropic carbon.

The negative electrode active material may further contain a material containing at least one element selected from the group consisting of silicon and tin. The material containing at least one element selected from the group consisting of silicon and tin may be a simple substance of silicon or tin, or a compound containing at least one element selected from the group consisting of silicon and tin. The compound may be an alloy containing at least one element selected from the group consisting of silicon and tin, for example, an alloy containing at least one element selected from the group consisting of nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony, and chromium in addition to silicon and tin. The compound containing at least one element selected from the group consisting of silicon and tin may be an oxide, nitride, or carbide, and specifically may be, for example, a silicon oxide such as SiO, _SiO2 , or _LiSiO , a silicon nitride such as _Si3N4 or _Si2N2O , a silicon carbide such as SiC, or _a tin oxide such as SnO, _SnO2 , or LiSnO.

From the viewpoint of further improving the performance of the electrochemical device, such as low-temperature input characteristics, the negative electrode 8 preferably contains a carbon material, more preferably contains graphite, and even more preferably contains a mixture of a carbon material and a material containing at least one element selected from the group consisting of silicon and tin, and particularly preferably contains a mixture of graphite and silicon oxide, as the negative electrode active material. The content of the carbon material (graphite) relative to the material (silicon oxide) containing at least one element selected from the group consisting of silicon and tin in the mixture may be 1% by mass or more, or 3% by mass or more, and may be 30% by mass or less, based on the total amount of the mixture.

The content of the negative electrode active material may be 80% by mass or more, or 85% by mass or more, and may be 99% by mass or less, based on the total amount of the negative electrode mixture layer.

The binder and its content may be similar to the binder and its content in the positive electrode mixture layer described above.

The negative electrode mixture layer 12 may contain a thickener to adjust the viscosity. The thickener is not particularly limited, but may be carboxymethylcellulose, methylcellulose, hydroxymethylcellulose, ethylcellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, salts thereof, etc. The thickener may be one of these alone or a mixture of two or more of them.

When the negative electrode mixture layer 12 contains a thickener, its content is not particularly limited. From the viewpoint of the coatability of the negative electrode mixture layer, the content of the thickener may be 0.1 mass% or more, preferably 0.2 mass% or more, and more preferably 0.5 mass% or more, based on the total amount of the negative electrode mixture layer. From the viewpoint of suppressing a decrease in battery capacity or an increase in resistance between the negative electrode active materials, the content of the thickener may be 5 mass% or less, preferably 3 mass% or less, and more preferably 2 mass% or less, based on the total amount of the negative electrode mixture layer.

式（１）中、Ｒ^１及びＲ^２は、それぞれ独立に、ハロゲン原子で置換されていてもよい１価の炭化水素基、又はハロゲン原子を表し、Ｒ^３はアルキレン基を表し、Ｒ^４は、水素原子、ハロゲン原子、又はシリル基を表す。 In one embodiment, the electrolyte solution contains a compound represented by the following formula (1), a lithium salt, and a non-aqueous solvent.

In formula (1), ^R1 and ^R2 each independently represent a monovalent hydrocarbon group which may be substituted with a halogen atom, or a halogen atom, ^R3 represents an alkylene group, and ^R4 represents a hydrogen atom, a halogen atom, or a silyl group.

The "monovalent hydrocarbon group which may be substituted with a halogen atom" represented by ^R1 and ^R2 is an unsubstituted monovalent hydrocarbon group or a monovalent hydrocarbon group in which at least one hydrogen atom has been substituted with a halogen atom (hereinafter also referred to as a "halogen-substituted monovalent hydrocarbon group").

The monovalent hydrocarbon group may be, for example, an alkyl group or an aryl group. The alkyl group may be linear or branched. The number of carbon atoms in the monovalent hydrocarbon group may be 1 or more, 2 or more, 3 or more, 4 or more, 5 or more, or 6 or more, and may be 8 or less, 7 or less, 6 or less, 5 or less, 4 or less, 3 or less, or 2 or less.

The halogen atoms in the halogen-substituted monovalent hydrocarbon group may be, for example, fluorine atoms, chlorine atoms, bromine atoms, or iodine atoms, or may be fluorine atoms or chlorine atoms, or may be fluorine atoms. The number of halogen atoms in the halogen-substituted monovalent hydrocarbon group may be 1 or more, 2 or more, 3 or more, or 4 or more, and may be 6 or less, 5 or less, 4 or less, 3 or less, or 2 or less.

The halogen atom represented by R ¹ and R ² may be, for example, a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom, or may be a fluorine atom or a chlorine atom.

The alkylene group represented by ^R3 may be linear or branched. The number of carbon atoms in the alkylene group may be 1 or more, 2 or more, 3 or more, 4 or more, 5 or more, or 6 or more, and may be 12 or less, 11 or less, 10 or less, 9 or less, 8 or less, 7 or less, 6 or less, 5 or less, 4 or less, or 3 or less.

The halogen atom represented by ^R4 may be, for example, a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom, and may be a fluorine atom or a chlorine atom, or may be a fluorine atom.

式（１ａ）中、Ｒ^４１～Ｒ^４３は、それぞれ独立に、ハロゲン原子で置換されていてもよい１価の炭化水素基、又はハロゲン原子を表す。 The silyl group represented by ^R4 is represented, for example, by the following formula (1a).

In formula (1a), R ⁴¹ to R ⁴³ each independently represent a monovalent hydrocarbon group which may be substituted with a halogen atom, or a halogen atom.

The "monovalent hydrocarbon group which may be substituted with a halogen atom" represented by R ⁴¹ to R ⁴³ is an unsubstituted monovalent hydrocarbon group or a halogen-substituted monovalent hydrocarbon group. The monovalent hydrocarbon group may be, for example, an alkyl group or an aryl group. The alkyl group may be linear or branched. The number of carbon atoms in the monovalent hydrocarbon group may be 1 or more, 2 or more, 3 or more, 4 or more, 5 or more, or 6 or more, and may be 8 or less, 7 or less, 6 or less, 5 or less, 4 or less, 3 or less, or 2 or less.

The halogen atoms in the halogen-substituted monovalent hydrocarbon group may be, for example, fluorine atoms, chlorine atoms, bromine atoms, or iodine atoms, or may be fluorine atoms or chlorine atoms, or may be fluorine atoms. The number of halogen atoms in the halogen-substituted monovalent hydrocarbon group may be 1 or more, 2 or more, 3 or more, or 4 or more, and may be 6 or less, 5 or less, 4 or less, 3 or less, or 2 or less.

The halogen atom represented by R ⁴¹ to R ⁴³ may be, for example, a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom, and may be a fluorine atom or a chlorine atom, or may be a fluorine atom.

The total number of carbon atoms in the compound represented by formula (1) may be 4 or more, 5 or more, 6 or more, 7 or more, 8 or more, 9 or more, or 10 or more, and may be 20 or less, 19 or less, 18 or less, 17 or less, 16 or less, 15 or less, 14 or less, 13 or less, 12 or less, 11 or less, 10 or less, 9 or less, or 8 or less.

In a preferred embodiment of the compound represented by formula (1), R ¹ and R ² each independently represent a methyl group or a halogen atom, R ³ represents a linear alkylene group having 2 or more carbon atoms, and R ⁴ represents a hydrogen atom or a halogen atom. In another preferred embodiment of the compound represented by formula (1), R ¹ and R ² represent a methyl group, R ³ represents a linear alkylene group having 2 or more carbon atoms, and R ⁴ represents a hydrogen atom or a halogen atom. In another preferred embodiment of the compound represented by formula (1), R ¹ and R ² represent a methyl group, R ³ represents a linear alkylene group having 2 or more carbon atoms, and R ⁴ represents a hydrogen atom.

Specific examples of the compound represented by formula (1) include compounds represented by the following formulas.

The compound represented by formula (1) may be a solid or liquid at 25°C. When the compound represented by formula (1) is a liquid at 25°C, the viscosity of the compound represented by formula (1) at 25°C may be 10 mPa·s or less, 5 mPa·s or less, or 1 mPa·s or less, or may be 0.2 mPa·s or more. The viscosity of the compound represented by formula (1) at 25°C is measured using a differential pressure microviscometer (for example, a differential pressure microviscometer Microvisc manufactured by RheoSense (applied with low viscosity sensor cartridge HA01-01)).

The content of the compound represented by formula (1) may be, based on the total amount of the electrolyte, 0.1% by mass or more, 0.3% by mass or more, 0.5% by mass or more, 0.7% by mass or more, 1% by mass or more, 2% by mass or more, 3% by mass or more, 5% by mass or more, 10% by mass or more, 15% by mass or more, or 20% by mass or more, and may be 50% by mass or less, 40% by mass or less, 30% by mass or less, 20% by mass or less, 15% by mass or less, 10% by mass or less, 9% by mass or less, 8% by mass or less, 7% by mass or less, 6% by mass or less, or 5% by mass or less.

Examples of lithium salts include lithium salts that function as electrolyte salts (first lithium salts), lithium salts of cyclic compounds having a ring containing a boron atom or a phosphorus atom (second lithium salts), and lithium salts of compounds having a fluorine atom, an oxygen atom, and a phosphorus atom (third lithium salts). Note that lithium salts that fall under the second lithium salt or the third lithium salt are not included in the first lithium salt. Also, lithium salts that fall under the second lithium salt are not included in the third lithium salt.

The first lithium salt may be, for example, at least one selected from the group consisting of LiPF ₆ , LiBF ₄ , LiClO ₄ , LiB(C ₆ H ₅ ) ₄ , LiCH ₃ SO ₃ , CF ₃ SO ₂ OLi, LiN(SO ₂ F) ₂ (Li[FSI], lithium bisfluorosulfonylimide), LiN(SO ₂ CF ₃ ) ₂ (Li[TFSI], lithium bistrifluoromethanesulfonylimide), and LiN(SO ₂ CF ₂ CF ₃ ) _2. The lithium salt preferably contains LiPF ₆ from the viewpoint of further improving solubility in a solvent, and the charge/discharge characteristics, output characteristics, cycle characteristics, and the like of the secondary battery.

From the viewpoint of excellent charge/discharge characteristics, the concentration of the first lithium salt is preferably 0.5 mol/L or more, more preferably 0.7 mol/L or more, and even more preferably 0.8 mol/L or more, based on the total amount of the nonaqueous solvent, and is preferably 1.5 mol/L or less, more preferably 1.3 mol/L or less, and even more preferably 1.2 mol/L or less.

式中、Ｍは、ホウ素原子又はリン原子を表し、Ｘは、ハロゲン原子又はフルオロアルキル基を表し、ｐは１～３の整数を表す。Ｍがホウ素原子である場合、（ｑ，ｒ）＝（１，２）又は（２，０）であり、Ｍがリン原子である場合、（ｑ，ｒ）＝（１，４）、（２，２）又は（３，０）である。 The second lithium salt may be, for example, a lithium salt represented by the following formula (2).

In the formula, M represents a boron atom or a phosphorus atom, X represents a halogen atom or a fluoroalkyl group, and p represents an integer of 1 to 3. When M is a boron atom, (q, r) = (1, 2) or (2, 0), and when M is a phosphorus atom, (q, r) = (1, 4), (2, 2) or (3, 0).

p is preferably 2. The number of carbon atoms of the fluoroalkyl group represented by X may be, for example, 1 to 4. X is preferably a fluorine atom or a trifluoromethyl group, and more preferably a fluorine atom.

Specific examples of the second lithium salt include lithium salts represented by the following formula:

The content of the second lithium salt may be, based on the total amount of the electrolyte, 0.001% by mass or more, 0.005% by mass or more, 0.01% by mass or more, 0.05% by mass or more, or 0.1% by mass or more, and may be 10% by mass or less, 5% by mass or less, 3% by mass or less, 2% by mass or less, or 1% by mass or less.

The compound having a fluorine atom, an oxygen atom and a phosphorus atom that constitutes the third lithium salt may be, for example, a compound having a P=O bond and a P-F bond, or a compound having a P=O bond, a P-O bond and a P-F bond.

Specific examples of the third lithium salt include lithium salts represented by the following formula:

The content of the third lithium salt may be, based on the total amount of the electrolyte, 0.001% by mass or more, 0.005% by mass or more, 0.01% by mass or more, 0.05% by mass or more, or 0.1% by mass or more, and may be 10% by mass or less, 5% by mass or less, 3% by mass or less, 2% by mass or less, or 1% by mass or less.

The lithium salt may include any one of the first lithium salt, the second lithium salt, and the third lithium salt, or may include two or more. When the lithium salt includes two or more lithium salts, the lithium salt may include, for example, the first lithium salt and the second lithium salt, the first lithium salt and the third lithium salt, or the first lithium salt, the second lithium salt, and the third lithium salt.

When the electrolyte solution contains a first lithium salt and a second lithium salt and/or a third lithium salt, the content of the second lithium salt and/or the third lithium salt may be 1 part by mass or more, 3 parts by mass or more, or 5 parts by mass or more per 100 parts by mass of the total amount of the first lithium salt, the second lithium salt, and the third lithium salt, and may be 20 parts by mass or less, 15 parts by mass or less, or 10 parts by mass or less.

The non-aqueous solvent is a non-aqueous solvent capable of dissolving a lithium salt. The non-aqueous solvent may be, for example, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, acetonitrile, 1,2-dimethoxyethane, dimethoxymethane, tetrahydrofuran, dioxolane, methylene chloride, methyl acetate, etc. The non-aqueous solvent may be one of these alone or a mixture of two or more of them, and is preferably a mixture of two or more of them.

The content of the non-aqueous solvent may be 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, or 90% by mass or more, based on the total amount of the electrolyte, and may be 99% by mass or less.

The electrolyte solution described above can improve the performance of an electrochemical device by containing a compound represented by formula (1). Specifically, for example, the electrolyte solution contains a compound represented by formula (1), thereby reducing the viscosity of the electrolyte solution. This improves the diffusion rate of the lithium salt cation (Li ⁺ ) in the electrolyte solution, and as a result, the rate characteristics of the electrochemical device can be improved. In addition, the reduced viscosity of the electrolyte solution can improve the permeability of the electrolyte solution to the high-density electrode and suppress the bubbling of the electrolyte solution.

Furthermore, for example, the Si-F bond in the compound represented by formula (1) can trap the anion of the lithium salt (e.g., PF ₆ ^- ) and improve the dissociation property of the lithium salt, resulting in a reduction in the interfacial charge transfer resistance in an electrochemical device (secondary battery). Furthermore, for example, the Si-F bond in the compound represented by formula (1) can stabilize the anion of the lithium salt and suppress the decomposition of the anion on an electrode. Furthermore, for example, since the compound represented by formula (1) has excellent electrochemical stability, the above-mentioned effects can be exhibited for a long period of time, as compared with conventional film-forming additives such as vinylene carbonate and fluoroethylene carbonate.

The electrolyte may further contain an additive in addition to the compound represented by formula (1), the lithium salt, and the non-aqueous solvent. By further containing an additive in the electrolyte, it is expected that the effect of the compound represented by formula (1) described above can be more significantly obtained. In this specification, the additive means a component other than the compound represented by formula (1), the lithium salt, and the non-aqueous solvent, the content of which is 10 mass% or less based on the total amount of the electrolyte.

The additive may include a cyclic compound having a carbon-carbon double bond. The cyclic compound having a carbon-carbon double bond may be, for example, a cyclic carbonate having a carbon-carbon double bond. In one embodiment, in the cyclic carbonate, two carbons constituting the ring may form a double bond.

Examples of cyclic carbonates having a carbon-carbon double bond include vinylene carbonate, methylvinylene carbonate, dimethylvinylene carbonate (4,5-dimethylvinylene carbonate), ethylvinylene carbonate (4,5-diethylvinylene carbonate), and diethylvinylene carbonate. The cyclic carbonate having a carbon-carbon double bond is preferably vinylene carbonate, from the viewpoint of further improving the performance of the electrochemical device.

The content of the cyclic compound having a carbon-carbon double bond may be 0.001% by mass or more, 0.005% by mass or more, 0.01% by mass or more, 0.05% by mass or more, or 0.1% by mass or more, based on the total amount of the electrolyte, and may be 10% by mass or less, 5% by mass or less, 3% by mass or less, or 2% by mass or less.

The additive may include a cyclic compound having a fluorine atom. The cyclic compound having a fluorine atom may be, for example, a cyclic carbonate having a fluorine atom. In one embodiment, the cyclic carbonate having a fluorine atom is a cyclic carbonate ester having a fluoro group.

Examples of cyclic carbonates having fluorine atoms include 4-fluoro-1,3-dioxolane-2-one (fluoroethylene carbonate; FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, and 1,1,2,2-tetrafluoroethylene carbonate. The cyclic carbonate having fluorine atoms is preferably 4-fluoro-1,3-dioxolane-2-one (fluoroethylene carbonate; FEC), from the viewpoint of suppressing side reactions when a stable coating is formed on the negative electrode.

The content of the cyclic compound having a fluorine atom may be 0.001 mass% or more, 0.005 mass% or more, 0.01 mass% or more, 0.05 mass% or more, or 0.1 mass% or more, based on the total amount of the electrolyte, and is 10 mass% or less, 5 mass% or less, 3 mass% or less, 2 mass% or less, or 1 mass% or less.

The additive may include a cyclic compound having a sulfur atom. The cyclic compound having a sulfur atom may be, for example, a cyclic sulfonate compound (also called a sultone compound). The cyclic sulfonate compound is a compound having a ring containing an —OSO ₂ — group. The cyclic sulfonate compound has a ring containing one or two —OSO ₂ — groups.

式（Ｘ）中、Ａ^１は、炭素数３～５のアルキレン基又は炭素数３～５のアルケニレン基を表し、該アルキレン基及び該アルケニレン基における水素原子は、アルキル基、シクロアルキル基、アリール基、又はフルオロ基で置換されていてもよい。 The cyclic sulfonate compound having a ring containing one —OSO ₂ — group may be, for example, a compound represented by the following formula (X) (monosulfonate ester).

In formula (X), A ¹ represents an alkylene group having 3 to 5 carbon atoms or an alkenylene group having 3 to 5 carbon atoms, and a hydrogen atom in the alkylene group or alkenylene group may be substituted with an alkyl group, a cycloalkyl group, an aryl group, or a fluoro group.

The number of carbon atoms in the alkyl group may be, for example, 1 to 12. The number of carbon atoms in the cycloalkyl group may be, for example, 3 to 6. The number of carbon atoms in the aryl group may be, for example, 6 to 12.

^A1 is preferably an alkylene group having 3 carbon atoms or an alkenylene group having 3 carbon atoms. That is, the monosulfonic acid ester is preferably a compound represented by the following formula (X-1) or formula (X-2).

In the formula, R ¹¹ to R ²⁰ each independently represent a hydrogen atom, an alkyl group, a cycloalkyl group, an aryl group, or a fluoro group. The carbon numbers of the alkyl group, cycloalkyl group, and aryl group represented by R ¹¹ to R ²⁰ are the same as the carbon numbers of the alkyl group, cycloalkyl group, and aryl group described for formula (X), respectively. ^{R 11} to R ²⁰ are preferably hydrogen atoms.

Examples of the monosulfonic acid ester include 1,3-propane sultone, 1,4-butane sultone, 2,4-butane sultone, 1,3-propene sultone, 1,4-butene sultone, 1-methyl-1,3-propane sultone, 3-methyl-1,3-propane sultone, 1-fluoro-1,3-propane sultone, and 3-fluoro-1,3-propane sultone. From the viewpoint of further improving the performance of the electrochemical device, the monosulfonic acid ester is preferably 1,3-propane sultone (a compound in which all of R ¹¹ to R ¹⁶ in formula (X-1) are hydrogen atoms) or 1-propene-1,3-sultone (a compound in which all of R ¹⁷ to R ²⁰ in formula (X-2) are hydrogen atoms).

式中、Ｂ^１及びＢ^２は、それぞれ独立に、炭素数１～５のアルキレン基又は炭素数１～５のアルケニレン基を表し、該アルキレン基及び該アルケニレン基における水素原子は、アルキル基、シクロアルキル基、アリール基、又はフルオロ基で置換されていてもよい。 The cyclic sulfonate compound having a ring containing two --OSO ₂ -- groups may be, for example, a compound (disulfonate) represented by the following formula (X-3).

In the formula, ^B1 and ^B2 each independently represent an alkylene group having 1 to 5 carbon atoms or an alkenylene group having 1 to 5 carbon atoms, and a hydrogen atom in the alkylene group or alkenylene group may be substituted with an alkyl group, a cycloalkyl group, an aryl group, or a fluoro group.

^B1 and ^B2 are preferably an unsubstituted alkylene group having 1 or 2 carbon atoms. Examples of disulfonic acid esters include methylenemethane disulfonic acid ester and ethylenemethane disulfonic acid ester.

式（Ｙ），（Ｚ）中、Ａ^２及びＡ^３は、それぞれ独立に、炭素数３～５のアルキレン基又は炭素数３～５のアルケニレン基を表し、該アルキレン基及び該アルケニレン基における水素原子は、アルキル基、シクロアルキル基又はアリール基で置換されていてもよい。 The cyclic compound having a sulfur atom may be, for example, a compound represented by formula (Y) or a compound represented by formula (Z).

In formulae (Y) and (Z), ^A2 and ^A3 each independently represent an alkylene group having 3 to 5 carbon atoms or an alkenylene group having 3 to 5 carbon atoms, and a hydrogen atom in the alkylene group or alkenylene group may be substituted with an alkyl group, a cycloalkyl group, or an aryl group.

The numbers of carbon atoms of the alkyl group, cycloalkyl group and aryl group in ^A2 and ^A3 are the same as the numbers of carbon atoms of the alkyl group, cycloalkyl group and aryl group explained in relation to formula (X), respectively.

Examples of the compound represented by formula (Y) include sulfolane, 2-methylsulfolane, 3-methylsulfolane, 2-ethylsulfolane, 3-ethylsulfolane, 2,4-dimethylsulfolane, 2-phenylsulfolane, 3-phenylsulfolane, sulfolene, and 3-methylsulfolene. The compound represented by formula (Y) is preferably sulfolane, from the viewpoint of further improving the performance of the electrochemical device.

Examples of compounds represented by formula (Z) include ethylene sulfite, propylene sulfite, butylene sulfite, vinylene sulfite, and phenylethylene sulfite. The compound represented by formula (Z) is preferably ethylene sulfite, from the viewpoint of further improving the performance of the electrochemical device.

The content of the cyclic compound having a sulfur atom may be 0.001% by mass or more, 0.005% by mass or more, 0.01% by mass or more, 0.05% by mass or more, or 0.1% by mass or more, based on the total amount of the electrolyte, and may be 10% by mass or less, 5% by mass or less, 3% by mass or less, 2% by mass or less, or 1% by mass or less.

The additive may include a nitrile compound. The nitrile compound is a compound having at least one cyano group (nitrile group). The nitrile compound may have one or more cyano groups, or may have two or three cyano groups.

Examples of nitrile compounds having one cyano group include butyronitrile, valeronitrile, and n-heptanenitrile. Examples of nitrile compounds having two cyano groups include succinonitrile, glutarnitrile, adiponitrile, pimelonitrile, and suberonitrile. Examples of nitrile compounds having three cyano groups include 1,2,3-propanetricarbonitrile and 1,3,5-pentanetricarbonitrile.

From the viewpoint of forming a stable coating on the positive electrode or negative electrode and suppressing expansion of the battery due to decomposition of the electrolyte, the nitrile compound is preferably a nitrile compound having two or more cyano groups and having two or more carbon atoms excluding the carbon atom in the cyano group. More preferably, the nitrile compound is a compound having two or three cyano groups and having two or more carbon atoms excluding the carbon atom in the cyano group. More preferably, the nitrile compound is succinonitrile, glutaric nitrile, adiponitrile, pimelonitrile, suberonitrile, 1,2,3-propanetricarbonitrile, or 1,3,5-pentanetricarbonitrile.

The content of the nitrile compound may be 0.001% by mass or more, 0.005% by mass or more, 0.01% by mass or more, 0.05% by mass or more, or 0.1% by mass or more, based on the total amount of the electrolyte, and may be 10% by mass or less, 5% by mass or less, 3% by mass or less, 2% by mass or less, or 1% by mass or less.

The content of the additives (the total content of the additives when the electrolyte contains two or more types of additives) may be, based on the total amount of the electrolyte, 0.001% by mass or more, 0.005% by mass or more, 0.01% by mass or more, 0.05% by mass or more, or 0.1% by mass or more, and may be 10% by mass or less, 5% by mass or less, 3% by mass or less, 2% by mass or less, or 1% by mass or less.

The viscosity of the electrolyte at 25°C may be 20 mPa·s or less, 10 mPa·s or less, or 5 mPa·s or less, or may be 0.5 mPa·s or more. The viscosity of the electrolyte at 25°C is measured using a differential pressure microviscometer (for example, a differential pressure microviscometer Microvisc manufactured by RheoSense (using low viscosity sensor cartridge HA01-01)).

Next, a method for manufacturing the nonaqueous electrolyte secondary battery 1 will be described. The method for manufacturing the nonaqueous electrolyte secondary battery 1 includes a first step of obtaining a positive electrode 6, a second step of obtaining a negative electrode 8, a third step of housing the electrode group 2 in a battery exterior body 3, and a fourth step of injecting an electrolyte into the battery exterior body 3.

In the first step, the material used for the positive electrode mixture layer 10 is dispersed in a dispersion medium using a kneader, disperser, etc. to obtain a slurry-like positive electrode mixture, and then this positive electrode mixture is applied to the positive electrode current collector 9 by a doctor blade method, a dipping method, a spray method, etc., and then the dispersion medium is evaporated to obtain the positive electrode 6. After the dispersion medium is evaporated, a compression molding process using a roll press may be provided as necessary. The positive electrode mixture layer 10 may be formed as a multi-layered positive electrode mixture layer by performing the above-mentioned process from application of the positive electrode mixture to evaporation of the dispersion medium multiple times. The dispersion medium may be water, 1-methyl-2-pyrrolidone (hereinafter also referred to as NMP), etc.

The second step may be the same as the first step described above, and the method for forming the negative electrode mixture layer 12 on the negative electrode current collector 11 may be the same as the first step described above.

In the third step, a separator 7 is sandwiched between the prepared positive electrode 6 and negative electrode 8 to form an electrode group 2. Next, this electrode group 2 is housed in a battery outer casing 3.

In the fourth step, the electrolyte is injected into the battery exterior body 3. The electrolyte can be prepared, for example, by first dissolving a lithium salt in a non-aqueous solvent and then further dissolving other materials in the non-aqueous solvent.

In another embodiment, the electrochemical device may be a capacitor. The capacitor may include an electrode group consisting of a positive electrode, a negative electrode, and a separator, and a bag-shaped battery exterior body that houses the electrode group, similar to the nonaqueous electrolyte secondary battery 1 described above. The details of each component of the capacitor may be similar to those of the nonaqueous electrolyte secondary battery 1.

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[Preparation of electrolyte solution]
Example 1
An electrolyte solution was prepared by adding 1 mass% vinylene carbonate (VC) and 0.5 mass% of a compound represented by the following formula (A) (corresponding to 0.033 mol per 1 mol of LiPF ₆ ) to a mixed solution (EC/DMC/EMC = 1:1:1 (volume ratio)) of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) containing 1 mol/L of LiPF _6. The viscosity of the compound represented by formula (A) at 25°C was 0.48 mPa·s.

Example 2
An electrolyte solution was prepared in the same manner as in Example 1, except that the content of the compound represented by formula (A) was changed to 5 mass % (corresponding to 0.33 mol per 1 mol of LiPF ₆ ) based on the total mass of the electrolyte solution.

(Comparative Example 1)
An electrolyte solution was prepared in the same manner as in Example 1, except that the compound represented by formula (A) was not added.

[Measurement of viscosity of electrolyte]
The viscosity of each of the electrolyte solutions in the Examples and Comparative Examples at 25° C. was measured using a differential pressure type microviscometer Microvisc (applied with low viscosity sensor cartridge HA01-01) manufactured by RheoSense. The results are shown below.
Example 1: 3.00 mPa·s
Example 2: 2.77 mPa·s
Comparative example 1: 3.07 mPa・s

As described above, the electrolyte solution contains the compound represented by formula (1), thereby reducing the viscosity of the electrolyte solution. This improves the diffusion rate of the lithium salt cation (Li ⁺ ) in the electrolyte solution, and as a result, the rate characteristics of the electrochemical device can be improved. In other words, the electrolyte solution contains the compound represented by formula (1), thereby improving the performance of the electrochemical device.

1... nonaqueous electrolyte secondary battery (electrochemical device), 6... positive electrode, 7... separator, 8... negative electrode.

Claims (11)

An electrolyte solution containing a compound represented by the following formula (1) and a lithium salt ,

[In formula (1), ^R1 and ^R2 represent a methyl group , ^R3 represents an alkylene group having 2 to 5 carbon atoms , and ^R4 represents a hydrogen atom .]
The content of the compound represented by the formula (1) is 3 mass% or more based on the total amount of the electrolyte solution. The electrolyte according to claim 1 , wherein R ³ represents a linear alkylene group. _3. The electrolyte solution according to claim 1 _or 2 _, wherein the lithium salt comprises at least one selected from _the group consisting of _LiPF6 , _LiBF4 , _LiClO4 , LiB( _C6H5 ) ₄ , _LiCH3SO3 , _CF3SO2OLi , LiN( _{SO2F ) 2} , LiN( _SO2CF3 ) ₂ , and LiN( _SO2CF2CF3 ) _{2 .} The electrolyte solution according to claim 1 , wherein the lithium salt comprises a lithium salt of a cyclic compound having a ring containing a boron atom or a phosphorus atom. The electrolyte solution according to any one of claims 1 to 4 , wherein the lithium salt comprises a lithium salt of a compound having a fluorine atom, an oxygen atom, and a phosphorus atom. The composition further contains an additive different from the compound represented by formula (1) and the lithium salt,
The electrolyte solution according to any one of claims 1 to 5 , wherein the content of the additive is 10 mass % or less based on the total amount of the electrolyte solution. The electrolyte according to claim 6 , wherein the additive comprises a cyclic compound having a carbon-carbon double bond. The electrolyte solution according to claim 6 or 7 , wherein the additive comprises a cyclic compound having a fluorine atom. The electrolyte solution according to claim 6 , wherein the additive comprises a cyclic compound having a sulfur atom. The electrolyte solution according to claim 6 , wherein the additive comprises a nitrile compound. An electrochemical device comprising a positive electrode, a negative electrode, and the electrolyte solution according to any one of claims 1 to 10 .

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