JPWO2020116578A1 - Electrolytes and electrochemical devices - Google Patents

Abstract

［式（１）中、Ｒ^１〜Ｒ^３は、それぞれ独立に、アルキル基又はフッ素原子を示し、Ｒ^４はアルキレン基を示し、Ｒ^５は、窒素原子又は硫黄原子を含む有機基を示す。］
One aspect of the present invention provides an electrolytic solution containing a compound represented by the following formula (1) and a cyclic carbonate having a carbon-carbon double bond.
[Chemical 1]

[In the formula (1), R ^{1 to} R ³ independently represent an alkyl group or a fluorine atom, R ⁴ represents an alkylene group, and R ⁵ represents an organic group containing a nitrogen atom or a sulfur atom. ]

Description

The present invention relates to electrolytes and electrochemical devices.

In recent years, with the spread of portable electronic devices, electric vehicles and the like, high-performance electrochemical devices such as non-aqueous electrolyte secondary batteries typified by lithium ion secondary batteries and capacitors have been required. As a means for improving the performance of the electrochemical device, for example, a method of adding a predetermined additive to the electrolytic solution has been studied. Patent Document 1 discloses an electrolytic solution for a non-aqueous electrolytic solution battery containing a specific siloxane compound in order to improve cycle characteristics and internal resistance characteristics.

Japanese Unexamined Patent Publication No. 2015-005329

An object of the present invention is to provide an electrolytic solution capable of improving the performance of an electrochemical device.

［式（１）中、Ｒ^１〜Ｒ^３は、それぞれ独立に、アルキル基又はフッ素原子を示し、Ｒ^４はアルキレン基を示し、Ｒ^５は、窒素原子又は硫黄原子を含む有機基を示す。］One aspect of the present invention is an electrolytic solution containing a compound represented by the following formula (1) and a cyclic carbonate having a carbon-carbon double bond.

[In the formula (1), R ^{1 to} R ³ independently represent an alkyl group or a fluorine atom, R ⁴ represents an alkylene group, and R ⁵ represents an organic group containing a nitrogen atom or a sulfur atom. ]

According to this electrolytic solution, in one aspect, the cycle characteristics can be improved as the performance of the electrochemical device. Further, according to this electrolytic solution, it is possible to reduce the DC resistance (discharge DCR) at the time of discharging the electrochemical device in another aspect. Further, according to this electrolytic solution, in another aspect, it is possible to improve the capacity retention rate after the electrochemical device is stored at a high temperature. Further, according to this electrolytic solution, in another aspect, it is possible to suppress an increase in volume of the electrochemical device after it is stored at a high temperature.

At ^{least one of R 1 to} R ³ may be a fluorine atom.

The number of silicon atoms in one molecule of the compound represented by the formula (1) may be one.

［式（２）中、Ｒ^６及びＲ^７は、それぞれ独立に、水素原子又はアルキル基を示し、＊は結合手を示す。］R ⁵ may be an organic group containing a nitrogen atom. R ⁵ may be a group represented by the following formula (2).

[In formula (2), R ⁶ and R ⁷ each independently represent a hydrogen atom or an alkyl group, and * indicates a bond. ]

［式（３）中、Ｒ^８はアルキル基を示し、＊は結合手を示す。］

［式（４）中、Ｒ^９はアルキル基を示し、＊は結合手を示す。］

［式（５）中、Ｒ^１０はアルキル基を示し、＊は結合手を示す。］R ⁵ may be an organic group containing a sulfur atom. R ⁵ may be a group represented by any of the following formulas (3), (4) or (5).

[In formula (3), R ⁸ represents an alkyl group and * represents a bond. ]

[In formula (4), R ⁹ represents an alkyl group and * represents a bond. ]

[In formula (5), R ¹⁰ represents an alkyl group and * represents a bond. ]

The cyclic carbonate may be vinylene carbonate.

The total content of the compound represented by the formula (1) and the content of the cyclic carbonate may be 10% by mass or less based on the total amount of the electrolytic solution.

Another aspect of the present invention is an electrochemical device including a positive electrode, a negative electrode, and the electrolytic solution.

The negative electrode may contain a carbon material. The carbon material may contain graphite. The negative electrode may further contain a material containing at least one element selected from the group consisting of silicon and tin.

The electrochemical device may be a non-aqueous electrolyte secondary battery or a capacitor.

According to the present invention, there is provided an electrolytic solution capable of improving the performance of an electrochemical device.

It is a perspective view which shows the non-aqueous electrolyte secondary battery as an electrochemical device which concerns on one Embodiment. It is an exploded perspective view which shows the electrode group of the secondary battery shown in FIG. It is a graph which shows the result of the cycle test in an Example and a comparative example. It is a graph which shows the measurement result of the discharge DCR in an Example and a comparative example.

Hereinafter, embodiments of the present invention will be described with reference to the drawings as appropriate. However, the present invention is not limited to the following embodiments.

FIG. 1 is a perspective view showing an electrochemical device according to an embodiment. In this embodiment, the electrochemical device is a non-aqueous electrolyte secondary battery. As shown in FIG. 1, the non-aqueous electrolytic solution secondary battery 1 includes an electrode group 2 composed of a positive electrode, a negative electrode, and a separator, and a bag-shaped battery exterior body 3 accommodating the electrode group 2. The positive electrode and the negative electrode are provided with a positive electrode current collecting tab 4 and a negative electrode current collecting tab 5, respectively. The positive electrode current collecting tab 4 and the negative electrode current collecting tab 5 project 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 non-aqueous electrolyte secondary battery 1, respectively. .. The battery exterior 3 is filled with an electrolytic solution (not shown). The non-aqueous electrolyte secondary battery 1 may be a battery (coin type, cylindrical type, laminated type, etc.) having a shape other than the so-called “laminated type” as described above.

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

FIG. 2 is an exploded perspective view showing an embodiment of the electrode group 2 in the non-aqueous electrolyte secondary battery 1 shown in FIG. 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 so that the surfaces of the positive electrode mixture layer 10 side and the negative electrode mixture layer 12 side face each other with 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 current collector 9 is made of, for example, aluminum, titanium, stainless steel, nickel, calcined carbon, a conductive polymer, conductive glass, or the like. The positive electrode current collector 9 may have a surface of aluminum, copper or the like treated with carbon, nickel, titanium, silver or the like for the purpose of improving adhesiveness, conductivity and oxidation resistance. The thickness of the positive electrode current 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, a lithium oxide. The lithium oxide, for _{example, Li x CoO 2, Li x} NiO 2, Li x MnO 2, Li x Co y Ni 1-y O 2, Li x Co y M 1-y O z, Li x Ni 1- _{y M y O z, Li x} Mn 2 O 4 and _{Li x Mn 2-y M y} O 4 ( in each formula, M represents, Na, Mg, Sc, Y , Mn, Fe, Co, Cu, Zn, Al , Cr, Pb, Sb, V and B indicate at least one element selected from the group (where M is an element different from the other elements in each equation). X = 0 to 1.2. , Y = 0 to 0.9, z = 2.0 to 2.3). Li _x Ni _1-y lithium oxide represented by M y _{O z is, Li x Ni 1- (y1 +} y2) Co y1 Mn y2 O z ( here, 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), for example, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ,. It may be LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , LiNi _0.6 Co _0.2 Mn _0.2 O _2, LiNi _0.8 Co _0.1 Mn _0.1 O _2. Li _x Ni _1-y lithium oxide represented by M y _{O z is, Li x Ni 1- (y3 +} y4) Co y3 Al y4 O z ( here, 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 . There may be.

The positive electrode active material may be, for example, a phosphate of lithium. Examples of the phosphate of lithium include 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 ) can be mentioned.

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

The conductive agent may be carbon black such as acetylene black or Ketjen black, or a carbon material such as graphite, graphene or carbon nanotube. 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 is 50% by mass or less and 30% by mass, based on the total amount of the positive electrode mixture layer. It may be less than or equal to 15% by mass or less.

The binder is, for example, a resin such as polyethylene, polypropylene, polyethylene terephthalate, polymethylmethacrylate, polyimide, aromatic polyamide, cellulose, nitrocellulose; SBR (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), fluororubber. , Isoprene rubber, butadiene rubber, ethylene-propylene rubber and other rubbers; styrene-butadiene-styrene block copolymer or its hydrogen additive, EPDM (ethylene-propylene-diene ternary copolymer), styrene-ethylene-butadiene- Thermoplastic elastomers such as ethylene copolymers, styrene / isoprene / styrene block copolymers or hydrogenated products thereof; syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene / vinyl acetate copolymers, propylene / α -Soft resins such as olefin copolymers; polyvinylidene fluoride (PVDF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, polytetrafluoroethylene / ethylene copolymer, polytetrafluoroethylene / vinylidene fluoride copolymer, etc. Fluorine-containing resin; a resin having a nitrile group-containing monomer as a monomer unit; a polymer composition having ionic conductivity of an alkali metal ion (for example, lithium ion) and the like.

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

The separator 7 is particularly limited as long as it electronically insulates between the positive electrode 6 and the negative electrode 8 while allowing ions to permeate and has resistance to oxidizing property on the positive electrode 6 side and reducing property on the negative electrode 8 side. Not done. Examples of the material (material) of such a separator 7 include resins and inorganic substances.

Examples of the resin include olefin polymers, fluoropolymers, cellulosic polymers, polyimides, nylons and the like. The separator 7 is preferably a porous sheet or a non-woven fabric made of a polyolefin such as polyethylene or polypropylene from the viewpoint of being stable to the electrolytic solution and having excellent liquid retention.

Examples of the inorganic substance 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. The separator 7 may be, for example, a separator in which a fibrous or particulate inorganic substance is attached to a thin film-like base material such as a non-woven 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 made of copper, stainless steel, nickel, aluminum, titanium, calcined carbon, a conductive polymer, conductive glass, an aluminum-cadmium alloy, or the like. The negative electrode current collector 11 may have a surface of copper, aluminum, or the like treated with carbon, nickel, titanium, silver, or the like for the purpose of improving adhesiveness, 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 substance that can occlude and release 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, simple substances of lithium, lithium alloys such as lithium aluminum alloys, Sn, Si, and the like. Examples include metals that can form alloys with lithium. 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 the carbon material include amorphous carbon material, natural graphite, composite carbon material in which a film of amorphous carbon material is formed on natural graphite, artificial graphite (resin raw material such as epoxy resin and phenol resin, petroleum, coal, etc.). It is obtained by firing a pitch-based raw material obtained from the above). 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 lithium.

Among the negative electrode active materials, the carbon material has high conductivity, and is particularly excellent in low temperature characteristics and cycle stability. Among the carbon materials, graphite is preferable from the viewpoint of increasing the capacity. In graphite, the carbon network layer (d002) in the X-ray wide-angle diffraction method is preferably less than 0.34 nm, and more preferably 0.3354 nm or more and 0.337 nm or less. A carbon material satisfying such conditions may be referred to as 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, in addition to silicon and tin, nickel, copper, iron, cobalt, manganese, zinc, indium and silver. , Titanium, germanium, bismuth, antimony and chromium. The compound containing at least one element selected from the group consisting of silicon and tin may be an oxide, a nitride, or a carbide, and specifically, for example, _{silicon oxidation of SiO, SiO 2} , LiSiO, etc. It may be a compound, _{a silicon nitride such as Si 3} N ₄ , Si ₂ N ₂ O, a silicon carbide such as SiC _{, a tin oxide such as SnO, SnO 2} , LiSnO, or the like.

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 graphite, still more preferably a carbon material, silicon and the negative electrode active material. It contains a mixture with a material containing at least one element selected from the group consisting of tin, and particularly preferably contains a mixture of graphite and silicon oxide. The content of the carbon material (graphite) in the material (silicon oxide) containing at least one element selected from the group consisting of silicon and tin in the mixture is 1% by mass or more, or 3 based on the total amount of the mixture. It may be 3% by mass or more, and 30% by mass or less.

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

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

The negative electrode mixture layer 12 may contain a thickener in order to adjust the viscosity. The thickener is not particularly limited, but may be carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, salts thereof and the like. The thickener may be one of these alone or a mixture of two or more.

When the negative electrode mixture layer 12 contains a thickener, the content thereof is not particularly limited. The content of the thickener may be 0.1% by mass or more, preferably 0.2% by mass or more, based on the total amount of the negative electrode mixture layer from the viewpoint of coatability of the negative electrode mixture layer. , More preferably 0.5% by mass or more. The content of the thickener may be 5% by mass or less, preferably 3% by mass, 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. % Or less, more preferably 2% by mass or less.

式（１）中、Ｒ^１〜Ｒ^３は、それぞれ独立に、アルキル基又はフッ素原子を示し、Ｒ^４はアルキレン基を示し、Ｒ^５は、窒素原子又は硫黄原子を含む有機基を示す。In one embodiment, the electrolytic solution includes a compound represented by the following formula (1), a cyclic carbonate having a carbon-carbon double bond (hereinafter, also simply referred to as “cyclic carbonate”), an electrolyte salt, and non-water. Contains a solvent.

In the formula (1), R ^{1 to} R ³ independently represent an alkyl group or a fluorine atom, R ⁴ represents an alkylene group, and R ⁵ represents an organic group containing a nitrogen atom or a sulfur atom.

The ^{number of carbon atoms of the alkyl group represented by R 1 to} R ³ may be 1 or more, and may be 3 or less. R ^{1 to} R ³ may be a methyl group, an ethyl group, or a propyl group, and may be linear or branched. At ^{least one of R 1 to} R ³ is preferably a fluorine atom. May be any one of fluorine atom of R ¹ to R ^3, it may be any two of a fluorine atom of R 1 to R ^3, all R 1 to R ³ may be a fluorine atom.

The carbon number of the alkylene group represented by R ⁴ may be 1 or more or 2 or more, and may be 5 or less or 4 or less. The ^{alkylene group represented by R 4} may be a methylene group, an ethylene group, a propylene group, a butylene group, or a pentylene group, and may be linear or branched.

In one embodiment, the number of silicon atoms in one molecule of the compound represented by the formula (1) is one. That is, in one embodiment, the organic group represented by R ⁵ does not contain silicon atoms.

式（２）中、Ｒ^６及びＲ^７は、それぞれ独立に、水素原子又はアルキル基を示す。Ｒ^６又はＲ^７で表されるアルキル基は、上述したＲ^１〜Ｒ^３で表されるアルキル基と同様であってよい。＊は結合手を示す。In ^{one embodiment, R 5} is an organic group containing a nitrogen atom, and is preferably a group represented by the following formula (2) from the viewpoint of further improving the performance of the electrochemical device.

In formula (2), R ⁶ and R ⁷ each independently represent a hydrogen atom or an alkyl group. The ^{alkyl group represented by R 6} or R ⁷ may be the same as the alkyl group represented by R ^{1 to} R ³ described above. * Indicates a bond.

式（３）中、Ｒ^８はアルキル基を示す。アルキル基は、上述したＲ^１〜Ｒ^３で表されるアルキル基と同様であってよい。＊は結合手を示す。

式（４）中、Ｒ^９はアルキル基を示す。アルキル基は、上述したＲ^１〜Ｒ^３で表されるアルキル基と同様であってよい。＊は結合手を示す。

式（５）中、Ｒ^１０はアルキル基を示す。アルキル基は、上述したＲ^１〜Ｒ^３で表されるアルキル基と同様であってよい。＊は結合手を示す。In ^{another embodiment, R 5} is an organic group containing a sulfur atom, and is preferably the following formula (3), formula (4) or formula from the viewpoint of further improving the performance of the electrochemical device. It may be a group represented by any of (5).

In formula (3), R ⁸ represents an alkyl group. The alkyl group may be the same as the alkyl group represented by ^{R 1 to} R ^{3 described above.} * Indicates a bond.

In formula (4), R ⁹ represents an alkyl group. The alkyl group may be the same as the alkyl group represented by ^{R 1 to} R ^{3 described above.} * Indicates a bond.

In formula (5), R ¹⁰ represents an alkyl group. The alkyl group may be the same as the alkyl group represented by ^{R 1 to} R ^{3 described above.} * Indicates a bond.

The content of the compound represented by the formula (1) is preferably 0.001% by mass or more and 0.005% by mass based on the total amount of the electrolytic solution from the viewpoint of further improving the performance of the electrochemical device. % Or more, 0.01% by mass or more, 0.05% by mass or more, or 0.1% by mass or more, 8% 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.

A cyclic carbonate having a carbon-carbon double bond is a cyclic carbonate having a carbon-carbon double bond. In one embodiment, in the cyclic carbonate, the two carbons constituting the ring may form a double bond. The cyclic carbonate may be, for example, vinylene carbonate, methylvinylene carbonate, dimethylvinylene carbonate (4,5-dimethylvinylene carbonate), ethylvinylene carbonate (4,5-diethylvinylene carbonate), diethylvinylene carbonate and the like, and may be electrochemical. From the viewpoint of further improving the performance of the device, vinylene carbonate is preferable.

The content of the cyclic carbonate is preferably 0.001% by mass or more, 0.005% by mass or more, and 0.01% by mass based on the total amount of the electrolytic solution from the viewpoint of further improving the performance of the electrochemical device. % Or more, 0.05% by mass or more, or 0.1% by mass or more, preferably 5% by mass or less, 3% by mass or less, or 2% by mass or less.

The total content of the compound represented by the formula (1) and the content of the cyclic carbonate is preferably 0.001 based on the total amount of the electrolytic solution from the viewpoint of further improving the performance of the electrochemical device. Mass% or more, 0.005 mass% or more, 0.01 mass% or more, 0.1 mass% or more, 0.5 mass% or more, or 1 mass% or more, preferably 10 mass% or less, 7 mass% or more. % Or less, 5% by mass or less, 3% by mass or less, or 2% by mass or less.

The mass ratio of the content of the compound represented by the formula (1) to the content of the cyclic carbonate (content of the compound represented by the formula (1) / content of the cyclic carbonate) further enhances the performance of the electrochemical device. From the viewpoint of being able to improve, it is preferably 0.01 or more, 0.05 or more, 0.1 or more, 0.2 or more, or 0.25 or more, and preferably 500 or less, 100 or less. 50 or less, 20 or less, 10 or less, 5 or less, 3 or less, or 1 or less.

The electrolyte salt may be, for example, a lithium salt. Lithium salts include, for example, 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 bis. At least one selected from the group consisting of fluorosulfonylimide), LiN (SO ₂ CF ₃ ) ₂ (Li [TFSI], lithium bistrifluoromethanesulfonylimide), and LiN (SO ₂ CF ₂ CF ₃ ) _2. good. _{The lithium salt preferably contains LiPF 6} from the viewpoint of further excellent solubility in a solvent, charge / discharge characteristics of a secondary battery, output characteristics, cycle characteristics, and the like.

The concentration of the electrolyte salt is preferably 0.5 mol / L or more, more preferably 0.7 mol / L or more, still more preferably 0.8 mol / L or more, based on the total amount of the non-aqueous solvent, from the viewpoint of excellent charge / discharge characteristics. It is preferably 1.5 mol / L or less, more preferably 1.3 mol / L or less, and further preferably 1.2 mol / L or less.

Non-aqueous solvents include, for example, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyl lactone, acetonitrile, 1,2-dimethoxyethane, dimethoxymethane, tetrahydrofuran, dioxolane, methylene chloride, methyl acetate and the like. May be. The non-aqueous solvent may be one of these alone or a mixture of two or more, and is preferably a mixture of two or more.

The electrolytic solution may further contain a compound represented by the formula (1), a cyclic carbonate having a carbon-carbon double bond, an electrolyte salt, and other materials other than a non-aqueous solvent. Other materials may be, for example, a fluorine-containing cyclic carbonate, a nitrogen atom other than the compound represented by the formula (1), a sulfur atom, a compound containing a nitrogen atom and a sulfur atom, a cyclic carboxylic acid ester, and the like.

Fluorine-containing cyclic carbonates include, for example, 4-fluoro-1,3-dioxolan-2-one (fluoroethylene carbonate; FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2. -Trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate and the like may be used, and 4-fluoro-1,3-dioxolan-2-one (fluoroethylene carbonate; FEC) is preferable. The compound containing a nitrogen atom other than the compound represented by the formula (1) may be a nitrile compound such as succinonitrile. The compound containing a sulfur atom other than the compound represented by the formula (1) may be, for example, a cyclic sulfonic acid ester compound such as 1,3-propane sultone or 1-propen-1,3-sultone.

As a result of examining compounds having various structures and functional groups, the present inventors have applied the compound represented by the above formula (1) and the cyclic carbonate having a carbon-carbon double bond to the electrolytic solution. , Clarified that the performance of electrochemical devices can be improved. The present inventors infer the action and effect of using the compound represented by the formula (1) and the cyclic carbonate having a carbon-carbon double bond in the electrolytic solution as follows. That is, the compound represented by the formula (1) and the cyclic carbonate having a carbon-carbon double bond each act on a place in the lithium ion secondary battery where the effect is most likely to be exhibited, and for example, a positive electrode or a negative electrode. It is considered to contribute to stable film formation or stabilization of the electrolytic solution. As a result, the performance of the electrochemical device such as the non-aqueous electrolyte secondary battery 1 is improved. For example, by using this electrolytic solution, the cycle characteristics of the electrochemical device can be improved in one aspect. In another aspect, the use of this electrolyte can reduce the discharge DCR of the electrochemical device. In another aspect, the use of this electrolyte can improve the capacity retention of the electrochemical device after storage at high temperatures. In another aspect, the volume increase after the electrochemical device is stored at a high temperature can be suppressed.

Subsequently, a method for manufacturing the non-aqueous electrolyte secondary battery 1 will be described. The method for manufacturing the non-aqueous electrolyte secondary battery 1 includes a first step of obtaining a positive electrode 6, a second step of obtaining a negative electrode 8, and a third step of accommodating the electrode group 2 in the battery exterior body 3. A fourth step of injecting the electrolytic solution into the battery exterior 3 is provided. The order of the first to fourth steps is arbitrary.

In the first step, the material used for the positive electrode mixture layer 10 is dispersed in a dispersion medium using a kneader, a disperser, or the like to obtain a slurry-like positive electrode mixture, and then this positive electrode mixture is used by the doctor blade method. A positive electrode 6 is obtained by applying the mixture onto the positive electrode current collector 9 by a dipping method, a spray method, or the like, and then volatilizing the dispersion medium. After volatilizing the dispersion medium, a compression molding step by a roll press may be provided, if necessary. The positive electrode mixture layer 10 may be formed as a multi-layered positive electrode mixture layer by performing the steps from the application of the positive electrode mixture to the volatilization of the dispersion medium a plurality of times. The dispersion medium may be water, 1-methyl-2-pyrrolidone (hereinafter, also referred to as NMP) or the like.

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

In the third step, the separator 7 is sandwiched between the produced positive electrode 6 and the negative electrode 8 to form the electrode group 2. Next, the electrode group 2 is housed in the battery exterior body 3.

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

In another embodiment, the electrochemical device may be a capacitor. Similar to the non-aqueous electrolytic solution secondary battery 1 described above, the capacitor may include an electrode group composed of a positive electrode, a negative electrode, and a separator, and a bag-shaped battery exterior body accommodating the electrode group. The details of each component in the capacitor may be the same as those of the non-aqueous electrolyte secondary battery 1.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples.

(Example 1)
[Preparation of positive electrode]
To lithium nickel-cobalt manganate (92% by mass) as a positive electrode active material, acetylene black (AB) (4% by mass) as a conductive agent and a binder (4% by mass) were sequentially added and mixed. NMP as a dispersion medium was added to the obtained mixture and kneaded to prepare a slurry-like positive electrode mixture. A predetermined amount of this positive electrode mixture was evenly and uniformly applied to an aluminum foil having a thickness of 20 μm as a positive electrode current collector. Then, after the dispersion medium was volatilized, it ^{was compacted to a density of 2.8 g / cm 3} by pressing to obtain a positive electrode.

[Preparation of negative electrode]
A binder and carboxymethyl cellulose as a thickener were added to graphite as a negative electrode active material. The mass ratios of these were graphite: binder: thickener = 98: 1: 1. Water as a dispersion medium was added to the obtained mixture and kneaded to prepare a slurry-like negative electrode mixture. A predetermined amount of this negative electrode mixture was evenly and uniformly applied to a rolled copper foil having a thickness of 10 μm as a negative electrode current collector. Then, after the dispersion medium was volatilized, it ^{was compacted to a density of 1.6 g / cm 3} by pressing to obtain a negative electrode.

[Manufacturing of lithium-ion secondary battery]
The positive electrode cut into a 13.5 cm ² quadrangle is sandwiched between polyethylene porous sheets (trade name: Hypore (registered trademark), manufactured by Asahi Kasei Corporation, thickness 30 μm), which is a separator, and further 14.3 cm ² quadrangle. An electrode group was prepared by superimposing the negative electrodes cut in the above. This electrode group was housed in a container (battery outer body) formed of an aluminum laminated film (trade name: aluminum laminated film, manufactured by Dai Nippon Printing Co., Ltd.). Next, 1 mL of the electrolytic solution was added into the container, and the container was heat-welded to prepare a lithium ion secondary battery for evaluation. As the electrolytic solution, 1% by mass of compound A represented by the following formula (6) and 1% by mass of vinylene carbonate were added to a mixed solution of ethylene carbonate, dimethyl carbonate and diethyl carbonate containing _{1 mol / L LiPF 6.} (Based on the total amount of electrolytic solution) was added.

(Example 2)
In Example 1, lithium ion secondary was obtained in the same manner as in Example 1 except that Compound B represented by the following formula (7) was added in place of Compound A in an amount of 0.3% by mass based on the total amount of the electrolytic solution. A battery was manufactured.

(Example 3)
In Example 1, lithium ion secondary was obtained in the same manner as in Example 1 except that Compound C represented by the following formula (8) was added in place of Compound A in an amount of 0.1% by mass based on the total amount of the electrolytic solution. A battery was manufactured.

(Comparative Example 1)
A lithium ion secondary battery was produced in the same manner as in Example 1 except that compound A and vinylene carbonate were not used in Example 1.

(Comparative Example 2)
A lithium ion secondary battery was produced in the same manner as in Example 1 except that compound A was not used in Example 1.

[First charge / discharge]
The produced lithium-ion battery was charged and discharged for the first time by the method shown below. First, in an environment of 25 ° C., constant current charging was performed at a current value of 0.1 C up to an upper limit voltage of 4.2 V, and then constant voltage charging was performed at 4.2 V. The charging termination condition was a current value of 0.01C. Then, a constant current discharge with a final voltage of 2.7 V was performed with a current value of 0.1 C. This charge / discharge cycle was repeated three times (“C” used as a unit of the current value means “current value (A) / battery capacity (Ah)”). The discharge capacity of the third cycle was defined as the capacity Q1 of this battery.

[Evaluation of cycle characteristics]
The cycle characteristics of each secondary battery were evaluated by a cycle test in which charging and discharging were repeated after the initial charging and discharging. As a charging pattern, in an environment of 45 ° C., the secondary batteries of Examples 1 to 3 and Comparative Examples 1 and 2 are constantly charged with a current value of 0.5 C up to an upper limit voltage of 4.2 V, and subsequently. Constant voltage charging was performed at 4.2 V. The charging termination condition was a current value of 0.05C. Regarding the discharge, a constant current discharge was performed at 0.5 C up to 2.7 V, and the discharge capacity was determined. This series of charge / discharge was repeated for 300 cycles, and the discharge capacity was measured for each charge / discharge. The relative value (discharge capacity retention rate (%)) of the discharge capacity in each cycle was obtained with respect to the discharge capacity after the charge / discharge in the first cycle. The results of the cycle test are shown in FIG. 3 (a), 3 (b), and 3 (c) show the results of Example 1, Example 2, and Example 3, respectively, and for comparison, FIGS. 3 (a) to 3 (a). The results of Comparative Example 1 and Comparative Example 2 are shown in all the graphs of FIG. 3C.

As a result, the discharge capacity retention rates at the 300th cycle in Examples 1 to 3 were 90%, 89%, and 89%, respectively, and the discharge capacity retention rates at the 300th cycle in Comparative Example 1 and Comparative Example 2 (67, respectively). %, 86%) was found to be better than. The reason for this is that compound A, compound B, or compound C and vinylene carbonate form a stable film on the positive electrode or negative electrode, and this film suppresses the decomposition of the electrolytic solution, thus extending the life of the secondary battery. Is considered to have been achieved.

[Measurement of discharge DCR]
For each secondary battery after the cycle test, the DC resistance (discharge DCR) at the time of discharge was measured as follows.
First, constant current charging at 0.2 C was performed up to an upper limit voltage of 4.2 V, and then constant voltage charging was performed at 4.2 V. The charging termination condition was a current value of 0.02C. After that, constant current discharge with a final voltage of 2.7 V was performed with a current value of _{0.2 C} , the current value at this time was I 0.2 C, and the voltage change 10 seconds after the start of discharge was ΔV _{0.2 C.} Next, a constant current charge of 0.2 C was performed up to an upper limit voltage of 4.2 V, and then a constant voltage charge was performed at 4.2 V (the charge termination condition was a current value of 0.02 C). After that, constant current discharge with a final voltage of 2.7 V was performed with a current value of _{0.5 C} , the current value at this time was I 0.5 C, and the voltage change 10 seconds after the start of discharge was ΔV _{0.5 C.} From the same charge / discharge, the current value of _1C was evaluated as _{I 1C} , and the voltage change ΔV 1C 10 seconds after the start of discharge was evaluated. The current value-voltage change is first-order using the least squares method on _{the three-point plots (I 0.2C} , ΔV _0.2C ), (I _0.5C , ΔV _0.5C ), and (I _1C , ΔV _1C). An approximate straight line was drawn, and the slope was taken as the value of the discharge DCR. The measurement result of the discharge DCR after 300 cycles is shown in FIG.

As a result, the discharge DCRs of Examples 1 to 3 were 2.6Ω, 2.5Ω, and 2.5Ω, respectively, which were higher than the discharge DCRs of Comparative Example 1 and Comparative Example 2 (4.9Ω and 4.0Ω, respectively). It was revealed that the resistance was reduced. The reason for this is that compound A, compound B, or compound C and vinylene carbonate form a stable film on the positive electrode or the negative electrode, and this film suppresses excessive decomposition of the electrolytic solution, so that the secondary battery has a secondary battery. It is considered that the increase in resistance could be suppressed.

[High temperature storage test]
After the above-mentioned initial charge and discharge of each of the secondary batteries of Example 1 and Comparative Examples 1 and 2, constant current charging is performed at a current value of 0.1 C in an environment of 25 ° C. up to an upper limit voltage of 4.2 V. Then, constant voltage charging was performed at 4.2 V. The charging termination condition was a current value of 0.01C. Then, those secondary batteries were stored in a constant temperature bath at 60 ° C. for 4 weeks.

[Measurement of volume increase rate]
The volumes of the secondary batteries of Examples 1 and Comparative Examples 1 and 2 were measured by a hydrometer based on the Archimedes method (electronic hydrometer MDS-300, manufactured by Alpha Mirage Co., Ltd.). The volume increase rate was calculated from the volume (V1) before the high temperature storage test and the volume (V2) of the secondary battery held in an environment of 25 ° C. for 30 minutes after the high temperature storage test by the following formula.
Volume increase rate (%) = V2 / V1 × 100

As a result, the volume increase rate of Example 1 was 105.5%, the volume increase rate of Comparative Example 1 was 107.1%, and the volume increase rate of Comparative Example 2 was 108.9%. The lithium ion secondary battery of Comparative Example 2 to which the electrolytic solution containing only vinylene carbonate was applied was compared with the lithium ion secondary battery of Comparative Example 1 to which the electrolytic solution containing neither compound A nor vinylene carbonate was applied. The volume increase rate has increased. It is considered that this is because vinylene carbonate was decomposed in an environment of high temperature (60 ° C.) and gas was generated. On the other hand, the lithium ion secondary battery of Example 1 to which the electrolytic solution containing both compound A and vinylene carbonate was applied had a reduced volume increase rate as compared with the lithium ion secondary batteries of Comparative Example 1 and Comparative Example 2. It is considered that this is because the compound A contributes to the stabilization of the electrolytic solution containing vinylene carbonate and can suppress the gas generation.

[Measurement of capacity retention rate]
The secondary batteries of Example 1 and Comparative Examples 1 and 2 stored in a constant temperature bath at 60 ° C. for 4 weeks were taken out from the constant temperature bath, held in an environment of 25 ° C. for 30 minutes, and then at a current value of 0.1 C. A constant current discharge with a final voltage of 2.7 V was performed. The discharge capacity at this time was set to Q2. Using the above Q1 and Q2, the capacity retention rate was calculated using the following formula.
Capacity retention rate (%) = Q2 / Q1 x 100

As a result, the capacity retention rate of Example 1 was 92.9%, the capacity retention rate of Comparative Example 1 was 90.7%, and the capacity retention rate of Comparative Example 2 was 92.3%. The lithium ion secondary battery of Comparative Example 2 to which the electrolytic solution containing only vinylene carbonate was applied maintained its capacity as compared with the lithium ion battery of Comparative Example 1 to which the electrolytic solution containing neither compound A nor vinylene carbonate was applied. The rate was good. It is considered that this is because vinylene carbonate formed a stable film on the negative electrode and the decrease in the capacity retention rate due to the decomposition of the electrolytic solution in the high temperature (60 ° C.) environment was suppressed. Further, the lithium ion secondary battery of Example 1 to which the electrolytic solution containing both compound A and vinylene carbonate was applied was compared with the lithium ion secondary battery of Comparative Example 2 to which the electrolytic solution containing only vinylene carbonate was applied. The capacity retention rate has been further improved. It is considered that this is because the vinylene carbonate formed a stable film on the negative electrode and the compound A stabilized the electrolytic solution, so that the decomposition of the electrolytic solution was further suppressed.

As described above, the lithium ion secondary batteries of Examples 1 to 3 to which the electrolytic solution containing both the compound A or the cyclic carbonate having a carbon-carbon double bond are applied are cyclics having a carbon-carbon double bond. A lithium ion secondary battery of Comparative Example 1 to which an electrolytic solution containing no carbonate and compound A was applied, and lithium of Comparative Example 2 to which an electrolytic solution containing cyclic carbonate having a carbon-carbon double bond and not containing compound A was applied. It shows superior performance compared to ion secondary batteries.

1 ... Non-aqueous electrolyte secondary battery (electrochemical device), 6 ... Positive electrode, 7 ... Separator, 8 ... Negative electrode.

Claims (14)

An electrolytic solution containing a compound represented by the following formula (1) and a cyclic carbonate having a carbon-carbon double bond.

[In the formula (1), R ^{1 to} R ³ independently represent an alkyl group or a fluorine atom, R ⁴ represents an alkylene group, and R ⁵ represents an organic group containing a nitrogen atom or a sulfur atom. ] The electrolytic solution according to claim 1, wherein ^{at least one of R 1 to} R ^{3 is a fluorine atom.} The electrolytic solution according to claim 1 or 2, wherein the number of silicon atoms in one molecule of the compound represented by the formula (1) is one. The electrolytic solution according to any one of claims 1 to 3, wherein R ^{5 is an organic group containing a nitrogen atom.} The electrolytic solution according to claim 4, wherein R ⁵ is a group represented by the following formula (2).

[In formula (2), R ⁶ and R ⁷ each independently represent a hydrogen atom or an alkyl group, and * indicates a bond. ] The electrolytic solution according to any one of claims 1 to 3, wherein R ^{5 is an organic group containing a sulfur atom.} The electrolytic solution according to claim 6, wherein R ⁵ is a group represented by any of the following formulas (3), (4) or (5).

[In formula (3), R ⁸ represents an alkyl group and * represents a bond. ]

[In formula (4), R ⁹ represents an alkyl group and * represents a bond. ]

[In formula (5), R ¹⁰ represents an alkyl group and * represents a bond. ] The electrolytic solution according to any one of claims 1 to 7, wherein the cyclic carbonate is vinylene carbonate. The item according to any one of claims 1 to 8, wherein the total content of the compound represented by the formula (1) and the content of the cyclic carbonate is 10% by mass or less based on the total amount of the electrolytic solution. Electrolyte. An electrochemical device comprising a positive electrode, a negative electrode, and an electrolytic solution according to any one of claims 1 to 9. The electrochemical device according to claim 10, wherein the negative electrode contains a carbon material. The electrochemical device according to claim 11, wherein the carbon material contains graphite. The electrochemical device according to claim 11 or 12, wherein the negative electrode further contains a material containing at least one element selected from the group consisting of silicon and tin. The electrochemical device according to any one of claims 10 to 13, wherein the electrochemical device is a non-aqueous electrolyte secondary battery or a capacitor.

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