JPWO2020027004A1 - Electrolytes and electrochemical devices - Google Patents

Abstract

As one aspect, the present invention provides an electrolytic solution containing a compound represented by the following formula (1) and a fluorine-containing cyclic carbonate. [Chemical formula 1] [In formula (1), R1 to R3 independently represent an alkyl group or a fluorine atom, R4 represents an alkylene group, and R5 represents an organic group containing a nitrogen 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

In order to apply electrochemical devices to in-vehicle applications, it is important to improve heat resistance at high temperatures. As an index of the heat resistance of the electrochemical device, for example, expansion of the electrochemical device after high temperature storage is suppressed. Another example is that deterioration of various performances of the electrochemical device, such as the degree of capacity decrease after high-temperature storage and the degree of increase in direct current resistance (DCR) during discharge, is suppressed. Suppressing the expansion of the electrochemical device is especially important because if the electrochemical device expands and explodes during high temperature storage, it poses a safety problem.

Therefore, an object of the present invention is to provide an electrolytic solution capable of suppressing expansion of an electrochemical device even at a high temperature. Another object of the present invention is to provide an electrochemical device whose expansion is suppressed even at a high temperature.

The present inventors have found that the expansion of an electrochemical device can be remarkably suppressed by containing a specific compound containing a silicon atom and a nitrogen atom and a fluorine-containing cyclic carbonate in an electrolytic solution. In particular, the present inventors remarkably suppress the expansion of the electrochemical device by using these compounds in combination, although the electrochemical device tends to expand when each compound is contained alone. I found out what I could do.

［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、窒素原子を含む有機基を示す。］The present invention provides, as a first aspect, an electrolytic solution containing a compound represented by the following formula (1) and a fluorine-containing cyclic carbonate.

[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. ]

［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 is preferably 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. ]

At ^{least one of R 1 to} R ³ is preferably a fluorine atom.

The fluorine-containing cyclic carbonate is preferably 4-fluoro-1,3-dioxolane-2-one.

The total content of the compound represented by the formula (1) and the content of the fluorine-containing cyclic carbonate is preferably 10% by mass or less based on the total amount of the electrolytic solution.

The present invention provides, as a second aspect, an electrochemical device including a positive electrode, a negative electrode, and the above-mentioned electrolytic solution.

In the second aspect, the negative electrode preferably contains a carbon material. The carbon material preferably contains graphite. The negative electrode preferably further contains a material containing at least one element selected from the group consisting of silicon and tin.

The electrochemical device is preferably a non-aqueous electrolyte secondary battery or capacitor.

According to the present invention, it is possible to provide an electrolytic solution capable of suppressing expansion of an electrochemical device even at a high temperature. Further, according to the present invention, it is possible to provide an electrochemical device in which expansion is suppressed even at a high temperature.

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 measurement result of the volume increase amount 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 electrolyte 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 be formed of aluminum, copper, or the like whose surface is 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 lithium phosphate 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, a carbon material such as graphite or 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 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 can be mentioned.

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 be formed of copper, aluminum, or the like whose surface is 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 lithium compounds, 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 substance, _{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) with respect to 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, and 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. From the viewpoint of coatability of the negative electrode mixture layer, 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. , 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 positive electrode mixture layer from the viewpoint of suppressing a decrease in battery capacity or an increase in resistance between 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、窒素原子を含む有機基を示す。In one embodiment, the electrolytic solution contains a compound represented by the following formula (1), a fluorine-containing cyclic carbonate, an electrolyte salt, and a non-aqueous 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.

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.

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.

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。R ⁵ may be a group represented by the following formula (2) in one embodiment from the viewpoint of further suppressing the expansion 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.

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.

The content of the compound represented by the formula (1) is preferably 0.001% by mass or more, 0.005% by mass or more, based on the total amount of the electrolytic solution, from the viewpoint of further suppressing the expansion of the electrochemical device. 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. be.

The fluorine-containing cyclic carbonate is a cyclic carbonate that contains a fluorine atom in the molecule. In one embodiment, the fluorine-containing cyclic carbonate is a cyclic carbonate containing a fluoro group. The fluorine-containing cyclic carbonate is not particularly limited as long as it is a cyclic carbonate containing a fluoro group. 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. The fluorine-containing cyclic carbonate is preferably 4-fluoro-1,3-dioxolane-2-one (fluoroethylene carbonate; FEC) from the viewpoint of suppressing side reactions when a stable film is formed on the negative electrode. be.

The content of the fluorine-containing 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 suppressing the expansion of the electrochemical device. As mentioned above, it is 0.05% by mass or more, or 0.1% by mass or more, and is 5% by mass or less, 3% by mass or less, 2% by mass or less, or 1% by mass or less.

The total content of the compound represented by the formula (1) and the content of the fluorine-containing cyclic carbonate is preferably 0.001 mass based on the total amount of the electrolytic solution from the viewpoint of further suppressing the expansion of the electrochemical device. % Or more, 0.005% by mass or more, 0.01% by mass or more, 0.1% by mass or more, or 0.5% by mass or more, preferably 10% by mass or less, 7% by mass or less, 5% by mass. Hereinafter, it is 3% by mass or less, 2% by mass or less, 1.5% by mass or less, or 1% by mass or less. From the same viewpoint, the total content of the compound represented by the formula (1) and the content of the fluorine-containing cyclic carbonate are preferably 0.001 to 10% by mass and 0.001 based on the total amount of the electrolytic solution. ~ 7% by mass, 0.001 to 5% by mass, 0.001 to 3% by mass, 0.001 to 2% by mass, 0.001 to 1.5% by mass, 0.001 to 1% by mass, 0.005 10% by mass, 0.005 to 7% by mass, 0.005 to 5% by mass, 0.005 to 3% by mass, 0.005 to 2% by mass, 0.005 to 1.5% by mass, 0.005 ~ 1% by mass, 0.01-10% by mass, 0.01-7% by mass, 0.01-5% by mass, 0.01-3% by mass, 0.01-2% by mass, 0.01-1% .5% by mass, 0.01 to 1% by mass, 0.1 to 10% by mass, 0.1 to 7% by mass, 0.1 to 5% by mass, 0.1 to 3% by mass, 0.1 to 2 Mass%, 0.1 to 1.5% by mass, 0.1 to 1% by mass, 0.5 to 10% by mass, 0.5 to 7% by mass, 0.5 to 5% by mass, 0.5 to 3 It is by mass%, 0.5 to 2% by mass, 0.5 to 1.5% by mass, or 0.5 to 1% by mass.

The mass ratio of the content of the compound represented by the formula (1) to the content of the fluorine-containing cyclic carbonate (content of the compound represented by the formula (1) / content of the fluorine-containing cyclic carbonate) is an electrochemical device. From the viewpoint of further suppressing the expansion of the compound, 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 100 or less and 50 or less. , Or 20 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 the compound represented by the formula (1), a fluorine-containing cyclic carbonate, an electrolyte salt, and other materials other than the non-aqueous solvent. The other material may be, for example, a cyclic carbonate having a carbon-carbon double bond, and a nitrogen atom, a sulfur atom, a heterocyclic compound containing a nitrogen atom and a sulfur atom other than the above-mentioned compounds, and a cyclic carboxylic compound. It may be an acid ester or the like. The other material may be a compound having an unsaturated bond in the molecule other than these compounds.

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 vinylene carbonate, vinylene carbonate, methylvinylene carbonate, dimethylvinylene carbonate (4,5-dimethylvinylene carbonate), ethylvinylene carbonate (4,5-diethylvinylene carbonate), diethylvinylene carbonate or the like, and may be electric. From the viewpoint of improving the performance of the chemical device, vinylene carbonate is preferable.

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 fluorine-containing cyclic carbonate to the electrolytic solution, thereby increasing the temperature of the electrochemical device. It was clarified that the expansion underneath can be suppressed. In particular, when either the compound represented by the formula (1) or the fluorine-containing cyclic carbonate is applied to the electrolytic solution, the present inventors cannot suppress the expansion of the electrochemical device, but rather promote the expansion. Nevertheless, it was clarified that the expansion of the electrochemical device can be remarkably suppressed when both compounds are applied to the electrolytic solution. The present inventors infer the action and effect of using the compound represented by the formula (1) and the fluorine-containing cyclic carbonate in the electrolytic solution as follows. That is, the compound and the fluorine-containing cyclic carbonate each act in a place in the lithium ion secondary battery where the effect is most likely to be exhibited, and contribute to, for example, stable film formation of the positive electrode or the negative electrode or stabilization of the electrolytic solution. Conceivable. Alternatively, it is considered that the electrolytic solution is stabilized by the interaction between the compound represented by the formula (1) and the fluorine-containing cyclic carbonate, and the gas generation caused by the decomposition of the electrolyte salt is suppressed. As a result, the expansion of the electrochemical device such as the non-aqueous electrolyte secondary battery 1 under high temperature is suppressed.

Further, as a characteristic other than the heat resistance required for the electrochemical device, it is also required to suppress an increase in DCR at the time of discharge. By incorporating the compound represented by the formula (1) in the electrolytic solution, it is possible to suppress an increase in DCR at the time of discharging the electrochemical device. The compound represented by the formula (1) forms a stable film on the positive electrode or the negative electrode. It is presumed that this suppresses the decrease in DCR caused by the deposition of the decomposed product of the electrolytic solution on the positive electrode or the negative electrode.

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.

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 multilayer structure positive electrode mixture layer by performing the above-mentioned steps from application of the positive electrode mixture to 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 electrolyte 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]
Lithium cobalt oxide (95% by mass) as a positive electrode active material, fibrous graphite (1% by mass) and acetylene black (AB) (1% by mass) as a conductive agent, and a binder (3% by mass). Were added sequentially 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 volatilizing the dispersion medium, it ^{was compacted to a density of 3.6 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. Regarding these mass ratios, the negative electrode active material: 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 volatilizing the dispersion medium, 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]
A positive electrode cut into a 13.5 cm ² quadrangle is sandwiched between a polyethylene porous sheet (trade name: Hypore (registered trademark), manufactured by Asahi Kasei Co., Ltd., thickness 30 μm), which is a separator, and further a 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. The electrolytic solution is a mixed solution of ethylene carbonate, dimethyl carbonate and diethyl carbonate containing 1 mol / L LiPF ₆ , and vinylene carbonate (VC) is 1% by mass based on the total amount of the mixed solution, which is represented by the following formula (3). Compound A to be added was used in an amount of 0.5% by mass and 0.5% by mass (based on the total amount of the electrolytic solution) of 4-fluoro-1,3-dioxolane-2-one (fluoroethylene carbonate; FEC).

(Example 2)
A lithium ion secondary battery was produced in the same manner as in Example 1 except that compound A was added in an amount of 0.8% by mass and FEC was added in an amount of 0.2% by mass (based on the total amount of the electrolytic solution).

(Example 3)
A lithium ion secondary battery was produced in the same manner as in Example 1 except that 0.2% by mass of Compound A and 0.8% by mass of FEC (based on the total amount of the electrolytic solution) were added in Example 1.

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

(Comparative Example 2)
In Example 1, a lithium ion secondary battery was produced in the same manner as in Example 1 except that Compound A was not used and 1.0% by mass of FEC was added.

(Reference example 1)
In Example 1, a lithium ion secondary battery was produced in the same manner as in Example 1 except that FEC was not used and compound A was added in an amount of 1.0% by mass.

[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 4.45 V, and then constant voltage charging was performed at 4.45 V. The charging termination condition was a current value of 0.01C. Then, a constant current discharge with a final voltage of 2.5 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)”).

[High temperature storage test]
The secondary batteries of Examples 1 to 3, Comparative Examples 1 and 2, and Reference Example 1 were constantly charged with a current value of 0.1 C in an environment of 25 ° C. up to an upper limit voltage of 4.45 V, followed by 4 Constant voltage charging was performed at .45 V. The charging termination condition was a current value of 0.01C. Then, those secondary batteries were stored in a constant temperature bath at 80 ° C. for 4 hours.

[Measurement of volume increase]
The volumes of the secondary batteries of Examples 1 to 3, Comparative Examples 1 and 2, and Reference Example 1 were measured by a hydrometer based on the Archimedes method (electronic hydrometer MDS-300, manufactured by Alpha Mirage Co., Ltd.). The difference between the volume of the secondary battery before the high temperature storage test and the volume of the secondary battery held in an environment of 25 ° C. for 30 minutes after the high temperature storage test was determined, and the degree of expansion of the secondary battery was evaluated. The results are shown in FIG.

As shown in FIG. 3, a lithium ion secondary battery of Comparative Example 2 to which an electrolytic solution containing fluorine-containing cyclic carbonate and not containing compound A was applied, and an electrolytic solution containing compound A and not containing fluorine-containing cyclic carbonate. The volume increase of the lithium ion secondary battery of Reference Example 1 applied was larger than the volume increase of the lithium ion secondary battery of Comparative Example 1 to which an electrolytic solution containing neither compound A nor a fluorine-containing cyclic carbonate was applied. rice field. This is because the fluorine-containing cyclic carbonate or compound A undergoes oxidative decomposition in an environment of high voltage (about 4.45 V) and high temperature (80 ° C.) to generate gas, or the decomposed product reacts with the electrolyte component. It is probable that gas was generated. On the other hand, the lithium ion secondary batteries of Examples 1 to 3 to which the electrolytic solution containing both compound A and the fluorine-containing cyclic carbonate are applied have a volume as compared with the lithium ion secondary batteries of Comparative Examples 1 and 2 and Reference Example 1. The amount of increase was dramatically reduced, confirming the effect of suppressing the expansion of the lithium-ion secondary battery due to gas generation. The mechanism of this volume increase reduction is not always clear, but it is considered that the decomposition _{of the electrolytic solution or LiPF 6} could be suppressed because a stable film was formed on the positive electrode or the negative electrode by the interaction between the compound A and the fluorine-containing cyclic carbonate. Be done. Or, compounds according to the interaction of the compound A and the fluorine-containing cyclic carbonate electrolyte or to stabilize LiPF _6, since that suppresses decomposition of the electrolyte or LiPF _6, is considered.

[Measurement of discharge DCR]
For the secondary battery after the initial charge and discharge, 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 4.45 V, and then constant voltage charging was performed at 4.45 V. The charging termination condition was a current value of 0.02C. After that, constant current discharge with a final voltage of 2.5 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 4.45 V, and then a constant voltage charge of 4.45 V was performed (the charge termination condition was a current value of 0.02 C), and then 0. A constant current discharge with a final voltage of 2.5 V was performed with a current value of 5 _{C, and 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 results are shown in FIG.

As shown in FIG. 4, the lithium ion secondary battery of Comparative Example 2 to which the electrolytic solution containing fluorine-containing cyclic carbonate and not containing compound A was applied contains an electrolytic solution containing neither compound A nor fluorine-containing cyclic carbonate. The discharge DCR was good (decreased) as compared with the applied lithium ion secondary battery of Comparative Example 1. It is considered that the discharge DCR of Comparative Example 2 was lowered because the film formed by the fluorine-containing cyclic carbonate formed a stable film mainly on the negative electrode and suppressed the excessive decomposition of the electrolytic solution. On the other hand, in the lithium ion secondary batteries of Examples 1 to 3 to which the electrolytic solution containing both compound A and the fluorine-containing cyclic carbonate was applied, the discharge DCR was much higher than that of the lithium ion secondary batteries of Comparative Examples 1 and 2. It was good. The mechanism by which the discharge DCR is good in the lithium ion secondary batteries of Examples 1 to 3 is not always clear, but it is stable at the positive electrode or the negative electrode as in the lithium ion secondary battery of Reference Example 1 containing only compound A. It is considered that this is because a film having good ionic conductivity was formed.

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

Claims (10)

An electrolytic solution containing a compound represented by the following formula (1) and a fluorine-containing cyclic carbonate.

[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. ] The electrolytic solution according to claim 1, 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 claim 1 or 2, wherein ^{at least one of R 1 to} R ^{3 is a fluorine atom.} The electrolytic solution according to any one of claims 1 to 3, wherein the fluorine-containing cyclic carbonate is 4-fluoro-1,3-dioxolane-2-one. Any one of claims 1 to 4, wherein the total content of the compound represented by the formula (1) and the content of the fluorine-containing cyclic carbonate is 10% by mass or less based on the total amount of the electrolytic solution. The electrolytic solution described in. An electrochemical device comprising a positive electrode, a negative electrode, and an electrolytic solution according to any one of claims 1 to 5. The electrochemical device according to claim 6, wherein the negative electrode contains a carbon material. The electrochemical device according to claim 7, wherein the carbon material contains graphite. The electrochemical device according to claim 7 or 8, 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 6 to 9, wherein the electrochemical device is a non-aqueous electrolyte secondary battery or a capacitor.

Images