WO2020116582A1

WO2020116582A1 - Electrolyte and electrochemical device

Info

Publication number: WO2020116582A1
Application number: PCT/JP2019/047695
Authority: WO
Inventors: 馨今野; 薫平山田
Original assignee: 日立化成株式会社
Priority date: 2018-12-05
Filing date: 2019-12-05
Publication date: 2020-06-11
Also published as: JP7415946B2; KR20210096213A; KR20210096214A; WO2020116580A1; CN113396500A; CN113396496A; TWI830831B; JPWO2020116582A1; JPWO2020116580A1; TW202032847A; TW202032844A; JP7415947B2

Abstract

One aspect of this invention is an electrolyte comprising a compound represented by formula (1) and a cyclic compound having a ring containing a sulfur atom. 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

Electrolyte and electrochemical device

The present invention relates to an electrolytic solution and an electrochemical device.

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

JP, 2005-005329, A

The present invention aims to provide an electrolytic solution capable of improving the performance of an electrochemical device.

One aspect of the present invention is an electrolytic solution containing a compound represented by the following formula (1) and a cyclic compound having a ring containing a sulfur atom.

In formula (1), R ¹ to R ³ each 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.

With this electrolyte, in one aspect, as the performance of the electrochemical device, it is possible to suppress the voltage drop after the electrochemical device is stored at 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 the electrochemical device is stored at a high temperature. In addition, according to this electrolytic solution, in another aspect, it is possible to improve the capacity retention rate of the electrochemical device after the electrochemical device is stored at a high temperature. In addition, according to this electrolytic solution, in another aspect, it is possible to improve the capacity recovery rate after the electrochemical device of the electrochemical device 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 formula (1) may be one.

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 * represents a bond.

The cyclic compound may include a cyclic sulfonate compound. The cyclic sulfonic acid ester compound may include a compound represented by the following formula (X).

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

The compound represented by the formula (X) may include at least one selected from the group consisting of 1,3-propane sultone and 1-propene-1,3-sultone.

The cyclic compound may include at least one selected from the group consisting of the compound represented by the formula (Y) and the compound represented by the formula (Z).

In formula (Y), A ² represents an alkylene group having 3 to 5 carbon atoms or an alkenylene group having 3 to 5 carbon atoms, and the hydrogen atom in the alkylene group and the alkenylene group is an alkyl group, a cycloalkyl group or an aryl group. It may be substituted with a group.

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

The sum of the content of the compound represented by the formula (1) and the content of the cyclic sulfonate compound 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, it is possible to provide an electrolytic solution capable of improving the performance of an electrochemical device.

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

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 one 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 including a positive electrode, a negative electrode, and a separator, and a bag-shaped battery exterior body 3 that houses the electrode group 2. A positive electrode current collecting tab 4 and a negative electrode current collecting tab 5 are provided on the positive electrode and the negative electrode, respectively. The positive electrode current collecting tab 4 and the negative electrode current collecting tab 5 project from the inside of the battery case 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. .. An electrolyte solution (not shown) is filled in the battery exterior body 3. 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 “laminate type” as described above.

The battery outer casing 3 may be a container formed of, for example, a laminated film. The laminated film may be, for example, a laminated film in which a resin film such as a 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 such that the surfaces on the positive electrode mixture layer 10 side and the negative electrode mixture layer 12 side face the separator 7, respectively.

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 the positive electrode current collector tab 4.

The positive electrode current collector 9 is made of, for example, aluminum, titanium, stainless steel, nickel, baked carbon, conductive polymer, conductive glass, or the like. The positive electrode current collector 9 may be one in which the surface of aluminum, copper, or the like 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 material mixture layer 10 contains a positive electrode active material, a conductive agent, and a binder. The thickness of the positive electrode mixture layer 10 is, for example, 20 to 200 μm.

The positive electrode active material may be, for example, lithium oxide. Examples of the lithium oxide include 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 , and 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 is Na, Mg, Sc, Y, Mn, Fe, Co, Cu, Zn, Al. , At least one element selected from the group consisting of Cr, Pb, Sb, V and B (provided that M is an element different from the other elements in each formula), x=0 to 1.2. , Y=0 to 0.9 and z=2.0 to 2.3). The lithium oxide represented by Li _x Ni _1-y M _y O _z is Li _x Ni _1-(y1+y2) Co _y1 Mn _y2 O _z (where x and z are the same as those described above, and 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 , _{_{_{_{LiNi 0.5 Co 0.2 Mn 0.3 O 2}}}} , LiNi 0.6 Co 0.2 Mn 0.2 O 2, may be _{_{_{LiNi 0.8 Co 0.1 Mn 0.1 O 2}}} . The lithium oxide represented by Li _x Ni _1-y M _y O _z is Li _x Ni _1-(y3+y4) Co _y3 Al _y4 O _z (where x and z are the same as those described above, and 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 . It may be.

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

The content of the positive electrode active material may be 80% by mass or more, or 85% by mass or more, and 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 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 50% by mass or less, 30% by mass, based on the total amount of the positive electrode mixture layer. Or less, or 15% by mass or less.

Examples of the binder include resins such as polyethylene, polypropylene, polyethylene terephthalate, polymethylmethacrylate, polyimide, aromatic polyamide, cellulose and nitrocellulose; SBR (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), fluororubber. , Isoprene rubber, butadiene rubber, ethylene-propylene rubber and the like; styrene/butadiene/styrene block copolymers or hydrogenated products thereof, EPDM (ethylene/propylene/diene terpolymer), 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 resin such as olefin copolymer; polyvinylidene fluoride (PVDF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, polytetrafluoroethylene/ethylene copolymer, polytetrafluoroethylene/vinylidene fluoride copolymer, etc. And a fluorine-containing resin, a resin having a nitrile group-containing monomer as a monomer unit, a polymer composition having an alkali metal ion (for example, lithium ion) ion conductivity, 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, based on the total amount of the positive electrode mixture layer, 30% by mass or less, 20% by mass. % Or less, or 10% by mass or less.

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

Examples of resins include olefin polymers, fluorine polymers, cellulosic polymers, polyimides and nylons. The separator 7 is preferably a porous sheet or a non-woven fabric formed of polyolefin such as polyethylene or polypropylene from the viewpoint of being stable with respect to the electrolytic solution and excellent in liquid retaining property.

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 thin film substrate such as a nonwoven fabric, a woven fabric, or a microporous film to which a fibrous or particulate inorganic substance is attached.

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, baked carbon, conductive polymer, conductive glass, aluminum-cadmium alloy, or the like. The negative electrode current collector 11 may be one in which the surface of copper, aluminum, or the like is treated with carbon, nickel, titanium, silver, or the like for the purpose of improving adhesion, conductivity, and reduction resistance. The thickness of the negative electrode current collector 11 is, for example, 1 to 50 μm from the viewpoint 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 can absorb and release lithium ions. Examples of the negative electrode active material include carbon materials, metal composite oxides, oxides or nitrides of Group IV elements such as tin, germanium, and silicon, simple substances of lithium, lithium alloys such as lithium aluminum alloys, Sn, Si, and the like. And a metal capable of forming an alloy 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 type of these alone or a mixture of two or more types. The shape of the negative electrode active material may be, for example, a particle shape.

As the carbon material, amorphous carbon material, natural graphite, composite carbon material obtained by forming a film of amorphous carbon material on natural graphite, artificial graphite (resin raw material such as epoxy resin, phenol resin, or petroleum, coal, etc. 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 one or both of titanium and lithium, and more preferably contains lithium.

Among the negative electrode active materials, carbon materials have high conductivity and are particularly excellent in low temperature characteristics and cycle stability. Among the carbon materials, graphite is preferable from the viewpoint of high capacity. In graphite, the carbon network plane 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 that satisfies such conditions may be referred to as pseudo-anisotropic 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, silver. , An alloy containing at least one selected from the group consisting of 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 oxide such as SiO, SiO ₂ , and LiSiO. A silicon nitride such as Si ₃ N ₄ or Si ₂ N ₂ O, a silicon carbide such as SiC, a tin oxide such as SnO, SnO ₂ or LiSnO.

From the viewpoint of further improving the performance of the electrochemical device such as low temperature input characteristics, the negative electrode 8 preferably contains a carbon material, more preferably graphite, and further preferably a carbon material, silicon and 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 based on the total amount of the mixture, or 3 It may be not less than 30% by mass and not more than 30% by mass.

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

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

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

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, and 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. , And 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, and more preferably 2% by mass or less.

In one embodiment, the electrolytic solution is a compound represented by the following formula (1), a cyclic compound having a ring containing a sulfur atom (hereinafter, also simply referred to as “cyclic compound”), an electrolyte salt, and a non-aqueous solvent. Contains and.

The alkyl group represented by R ¹ to R ³ may have 1 or more carbon atoms and 3 or less carbon atoms. 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 ~ ^{R ^3,} it may be any two of a fluorine atom of R 1 ~ ^{R ^3,} all of R 1 ~ ^{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 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 formula (1) is one. That is, in one embodiment, the organic group represented by R ⁵ does not include a silicon atom.

R ⁵ is preferably a group represented by the following formula (2) from the viewpoint that the performance of the electrochemical device can be further improved.

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.

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 that the performance of the electrochemical device can be further improved. % Or more, 0.01 mass% or more, 0.05 mass% or more, or 0.1 mass% or more, 8 mass% or less, 5 mass% or less, 3 mass% or less, 2 mass% or less, or 1 mass. % Or less.

A cyclic compound is a compound having a ring (heterocycle) containing a sulfur atom. The cyclic compound is a compound other than the compound represented by the above formula (1). In other words, the cyclic compound is a compound having no silicon atom.

The cyclic compound may include, for example, at least one cyclic sulfonate compound (also referred to as a sultone compound). The cyclic sulfonate compound is a compound having a ring containing an —OSO ₂ — group. The cyclic sulfonic acid ester compound has a ring containing one or two —OSO ₂ — groups.

The cyclic sulfonic acid ester compound having a ring containing one —OSO ₂ — group may be, for example, a compound represented by the following formula (X).

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

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

A ¹ is preferably an alkylene group having 3 carbon atoms or an alkenylene group having 3 carbon atoms. That is, the cyclic sulfonate compound is preferably a compound represented by the following formula (X-1) or formula (X-2).

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

Examples of the cyclic sulfonate compound represented by the formula (X) include 1,3-propane sultone, 1,4-butane sultone, 2,4-butane sultone, 1,3-propene sultone, 1,4-butene sultone, Monosulfonic acid esters such as 1-methyl-1,3-propane sultone, 3-methyl-1,3-propane sultone, 1-fluoro-1,3-propane sultone and 3-fluoro-1,3-propane sultone Is mentioned. Of these, 1,3-propane sultone (a compound in which all of R ¹¹ to R ^{16 in} the formula (X-1) are hydrogen atoms) or 1 from the viewpoint that the performance of the electrochemical device can be further improved. -Propene-1,3-sultone (a compound in which all of R ¹⁷ to R ^{20 in} the formula (X-2) are hydrogen atoms) is preferable.

The cyclic sulfonic acid ester compound having a ring containing two —OSO ₂ — groups may be, for example, a compound represented by the following formula (X-3).

In the formula, B ¹ and B ² each independently represent an alkylene group having 1 to 5 carbon atoms or an alkenylene group having 1 to 5 carbon atoms, and the hydrogen atom in the alkylene group and the alkenylene group is an alkyl group, cycloalkyl It may be substituted with an alkyl group, an aryl group, or a fluoro group.

B ¹ and B ² are preferably unsubstituted alkylene groups having 1 or 2 carbon atoms. Such cyclic sulfonic acid ester compound may be a disulfonic acid ester such as methylene methane disulfonic acid ester and ethylene methane disulfonic acid ester.

The cyclic compound may include, for example, at least one selected from the group consisting of the compound represented by the formula (Y) and the compound represented by the formula (Z).

In formulas (Y) and (Z), A ² and A ³ each independently represent an alkylene group having 3 to 5 carbon atoms or an alkenylene group having 3 to 5 carbon atoms, and hydrogen in the alkylene group and the alkenylene group. Atoms may be substituted with alkyl, cycloalkyl or aryl groups.

The carbon numbers of the alkyl group, cycloalkyl group and aryl group in A ² and A ³ are the same as the carbon numbers of the alkyl group, cycloalkyl group and aryl group described for formula (X), respectively.

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

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

The cyclic compound may contain at least one selected from the group consisting of a cyclic sulfonate compound, a compound represented by the formula (Y) and a compound represented by the formula (Z), and is represented by the formula (X). Compound represented by the formula (Y) and a compound represented by the formula (Z) may be included in the compound represented by the formula (X) and the formula (Z). At least one selected from the group consisting of compounds represented by

The content of the cyclic compound is preferably 0.001 mass% or more, 0.005 mass% or more, 0.01 mass, based on the total amount of the electrolytic solution, from the viewpoint that the performance of the electrochemical device can be further improved. % Or more, 0.05 mass% or more, or 0.1 mass% or more, and 5 mass% or less, 3 mass% or less, 2 mass% or less, or 1 mass% or less.

From the viewpoint that the performance of the electrochemical device can be further improved, the total content of the compound represented by formula (1) and the content of the cyclic compound is preferably 0.001 based on the total amount of the electrolytic solution. % By mass, 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 % 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 compound (content of the compound represented by the formula (1)/content of the cyclic compound) further improves 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, It is 50 or less, 20 or less, 10 or less, 5 or less, or 4 or less.

The electrolyte salt may be, for example, a lithium salt. The lithium salt is, 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. Fluorosulfonylimide), LiN(SO ₂ CF ₃ ) ₂ (Li[TFSI], lithium bistrifluoromethanesulfonylimide), and at least one selected from the group consisting of 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.

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

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

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

Examples of the fluorine-containing cyclic carbonate include 4-fluoro-1,3-dioxolan-2-one (fluoroethylene carbonate; FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2. It may be trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, etc., preferably 4-fluoro-1,3-dioxolan-2-one (fluoroethylene carbonate; FEC). The cyclic carbonate having a carbon-carbon double bond may be vinylene carbonate, for example. The compound containing a nitrogen atom other than the compound represented by formula (1) may be a nitrile compound such as succinonitrile.

As a result of examining compounds having various structures and functional groups, the present inventors applied the compound represented by the above formula (1) and the cyclic compound to an electrolytic solution to improve the performance of an electrochemical device. Revealed that can be made. The present inventors presume the action and effect of using the compound represented by formula (1) and the cyclic compound in the electrolytic solution as follows. That is, the compound represented by the formula (1) and the cyclic compound each act on the place where the effect is most likely to be exhibited in the lithium ion secondary battery, for example, stable film formation of the positive electrode or the negative electrode, or the electrolytic solution. Is considered to contribute to the stabilization of As a result, the performance of the electrochemical device such as the non-aqueous electrolyte secondary battery 1 is improved.

Specifically, according to the electrolytic solution of one embodiment, as the performance of the electrochemical device, it is possible to suppress the voltage drop after the electrochemical device is stored at a high temperature. Moreover, according to the electrolytic solution of one embodiment, it is possible to suppress an increase in volume of the electrochemical device after the electrochemical device is stored at a high temperature. Moreover, according to the electrolytic solution of one embodiment, it is possible to improve the capacity retention rate of the electrochemical device after the electrochemical device is stored at a high temperature. Moreover, according to the electrolytic solution of one embodiment, it is possible to improve the capacity recovery rate after the electrochemical device of the electrochemical device is stored at high temperature.

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

In the first step, the material used for the positive electrode mixture layer 10 is dispersed in a dispersion medium using a kneader, a disperser or the like to obtain a positive electrode mixture in a slurry state, and then this positive electrode mixture is treated by a doctor blade method, The positive electrode current collector 9 is coated with a dipping method, a spray method, or the like, and then the dispersion medium is volatilized to obtain the positive electrode 6. After volatilizing the dispersion medium, a compression molding step using a roll press may be provided, if necessary. The positive electrode mixture layer 10 may be formed as a positive electrode mixture layer having a multi-layer structure by performing the above-described 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 above-mentioned first step, 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 above-mentioned first step. ..

In the third step, the separator 7 is sandwiched between the produced positive electrode 6 and negative electrode 8 to form the electrode group 2. Next, the electrode group 2 is housed in the battery case 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 an electrolyte salt in a solvent and then dissolving other materials.

In another embodiment, the electrochemical device may be a capacitor. Like the above-described non-aqueous electrolyte secondary battery 1, the capacitor may include an electrode group including a positive electrode, a negative electrode, and a separator, and a bag-shaped battery exterior body that houses the electrode group. The details of each component of 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)
[Production 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 conductive agents, and a binder (3% by mass). Sequentially added and mixed. NMP as a dispersion medium was added to the obtained mixture, and the mixture was kneaded to prepare a slurry-like positive electrode mixture. A predetermined amount of this positive electrode mixture was uniformly and uniformly applied to an aluminum foil having a thickness of 20 μm as a positive electrode current collector. Then, the dispersion medium was volatilized and then pressed to consolidate it to a density of 3.6 g/cm ³ to obtain a positive electrode.

[Fabrication of negative electrode]
A binder and carboxymethyl cellulose as a thickener were added to graphite as a negative electrode active material. Regarding the mass ratio of these materials, the negative electrode active material:binder:thickener=98:1:1. Water as a dispersion medium was added to the obtained mixture, and the mixture was kneaded to prepare a slurry negative electrode mixture. A predetermined amount of this negative electrode mixture was uniformly and uniformly applied to a rolled copper foil having a thickness of 10 μm as a negative electrode current collector. After that, the dispersion medium was volatilized and then pressed to consolidate to a density of 1.6 g/cm ³ to obtain a negative electrode.

[Preparation of lithium-ion secondary battery]
The positive electrode cut into a 13.5 cm ² square was sandwiched by 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 square. The negative electrodes cut into pieces were stacked to prepare an electrode group. This electrode group was housed in a container (battery outer casing) formed of an aluminum laminate film (trade name: aluminum laminate film, manufactured by Dai Nippon Printing Co., Ltd.). Next, 1 mL of the electrolytic solution was added to the container, and the container was heat-welded to produce a lithium ion secondary battery for evaluation. As the electrolytic solution, a mixed solution of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate containing 1 mol/L of LiPF ₆ , and 1% by mass of vinylene carbonate (VC) and 4-fluoro-1,3 with respect to the total amount of the mixed solution. -Dioxolan-2-one (fluoroethylene carbonate; FEC) 0.5% by mass, compound A represented by the following formula (6) 0.5% by mass, and 1,3-propanesultone 0.5% by mass (electrolysis The liquid added was used.

(Example 2)
A lithium ion secondary battery was produced in the same manner as in Example 1 except that 1,3-propene sultone was used instead of 1,3-propane sultone.

(Example 3)
A lithium ion secondary battery was produced in the same manner as in Example 1 except that methylene methane disulfonic acid ester (MMDS) was used instead of 1,3-propane sultone.

(Example 4)
A lithium ion secondary battery was produced in the same manner as in Example 1 except that ethylene sulfite was used instead of 1,3-propane sultone.

(Comparative Example 1)
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the compound A and 1,3-propane sultone were not used.

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

[Evaluation of high temperature storage characteristics]
(First charge/discharge)
Initial charging/discharging was implemented by the method shown below about each produced secondary battery. First, in a 25° C. environment, 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 charge termination condition was a current value of 0.01C. After that, constant current discharge with a final voltage of 2.5 V was performed at a current value of 0.1 C. This charge/discharge cycle was repeated 3 times. The discharge capacity at the third cycle was defined as the capacity Q1 of the secondary battery. Note that "C" used as a unit of current value means "current value (A)/battery capacity (Ah)" (the same applies hereinafter).

(High temperature storage)
Each of the manufactured secondary batteries was subjected to constant current charging at a current value of 0.1 C under an environment of 25° C. up to an upper limit voltage of 4.45 V, and then at 4.45 V. The charge termination condition was a current value of 0.01C. After that, these secondary batteries were stored for 4 hours in an 80° C. constant temperature bath.

(Measurement of voltage after high temperature storage)
Each secondary battery after high temperature storage was allowed to stand in an environment of 25° C. for 30 minutes, and then the voltage of each secondary battery was measured. The results are shown in Table 1.

(Measurement of volume change rate)
The volume (V1) of each rechargeable battery before high temperature storage and the volume (V2) of each rechargeable battery that was allowed to stand in an environment of 25°C for 30 minutes after high temperature storage were measured by a densitometer (electronic specific gravity) based on the Archimedes method. MDS-300, manufactured by Alpha Mirage). A volume change rate (%)=V2/V1×100 was calculated using the measured V1 and V2. The results are shown in Table 1.

(Cycle test)
After each high temperature storage secondary battery was allowed to stand in an environment of 25° C. for 30 minutes, constant current discharge with a final voltage of 2.5 V was performed at a current value of 0.1 C. The discharge capacity at this time was defined as Q2. Next, 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 charge termination condition was a current value of 0.01C. After that, constant current discharge with a final voltage of 2.5 V was performed at a current value of 0.1 C. The discharge capacity at this time was set to Q3. Using Q1, Q2 and Q3 above, the capacity retention rate and capacity recovery rate were calculated by the following formulas. The results are shown in Table 1.
Capacity maintenance rate (%) = Q2/Q1 x 100
Capacity recovery rate (%)=Q3/Q1×100

As can be seen from Table 1, the lithium-ion secondary batteries to which the electrolytic solutions of Examples 1 to 4 containing the compound represented by the formula (1) and the cyclic compound were applied were the compound represented by the formula (1) and the cyclic compound. Compared to the lithium ion secondary batteries of Comparative Examples 1 and 2 to which an electrolytic solution containing neither one or both of the compounds is applied is superior in high temperature storage characteristics (the voltage drop and volume change rate after high temperature storage are small, and high temperature storage is possible). High capacity retention rate and capacity recovery rate after). It is considered that this is because the cyclic compound formed a stable film on the positive electrode or the negative electrode, and the compound represented by the formula (1) contributed to the stabilization of the electrolytic solution.

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

Claims

A compound represented by the following formula (1):
An electrolyte solution containing a cyclic compound having a ring containing a sulfur atom.

[In the formula (1), R 1 to R 3 each independently represents 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 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 claim 3, wherein R 5 is a group represented by the following formula (2).

[In the formula (2), R 6 and R 7 each independently represent a hydrogen atom or an alkyl group, and * represents a bond. ]
The electrolytic solution according to any one of claims 1 to 4, wherein the cyclic compound contains a cyclic sulfonate compound.
The electrolytic solution according to claim 5, wherein the cyclic sulfonate compound includes a compound represented by the following formula (X).

[In the formula (X), A 1 represents a group containing an alkylene group having 3 to 5 carbon atoms or an alkenylene group having 3 to 5 carbon atoms, the hydrogen atom in the alkylene group and the alkenylene group is an alkyl group, It may be substituted with an alkyl group, an aryl group, or a fluoro group. ]
The electrolytic solution according to claim 6, wherein the compound represented by the formula (X) contains at least one selected from the group consisting of 1,3-propane sultone and 1-propene-1,3-sultone.
8. The electrolysis according to claim 1, wherein the cyclic compound contains at least one selected from the group consisting of a compound represented by formula (Y) and a compound represented by formula (Z). liquid.

[In the formula (Y), A 2 represents an alkylene group having 3 to 5 carbon atoms or an alkenylene group having 3 to 5 carbon atoms, and hydrogen atoms in the alkylene group and the alkenylene group are an alkyl group, a cycloalkyl group or It may be substituted with an aryl group. ]

[In the formula (Z), A 3 represents an alkylene group having 3 to 5 carbon atoms or an alkenylene group having 3 to 5 carbon atoms, and hydrogen atoms in the alkylene group and the alkenylene group are an alkyl group, a cycloalkyl group or It may be substituted with an aryl group. ]
The total content of the compound represented by the formula (1) and the content of the cyclic compound 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 the 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.