WO2020116583A1

WO2020116583A1 - Electrolyte and electrochemical device

Info

Publication number: WO2020116583A1
Application number: PCT/JP2019/047696
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: JPWO2020116583A1; TW202032846A; TWI835941B

Abstract

The present invention provides an electrolyte containing: a compound indicated by formula (1); and a nitrile compound that does not have a silicon atom. [In formula (1), R¹–R³ each independently indicate an alkyl group or a fluorine atom, R⁴ indicates an alkylene group, and R⁵ indicates an organic group including a nitrogen atom or a sulfur 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 nitrile compound having no silicon atom.

[In the 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 or a sulfur atom. ]

With this electrolyte, in one aspect, as the performance of the electrochemical device, the capacity retention rate after the electrochemical device is stored at high temperature can be improved. Further, according to this electrolytic solution, in another aspect, it is possible to improve the capacity recovery rate after storing the electrochemical device at a high temperature. Further, according to this electrolytic solution, in another aspect, it is possible to suppress an increase in volume after the electrochemical device is stored at a high temperature. Further, according to this electrolytic solution, in another aspect, the cycle characteristics of the electrochemical device can be improved.

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 an organic group containing a nitrogen atom. R ⁵ may be 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. ]

R ⁵ may be an organic group containing a sulfur atom. R ⁵ may be a group represented by the following formula (3), formula (4) or formula (5).

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

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

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

The nitrile compound may have two cyano groups. The nitrile compound may be succinonitrile.

The total content of the compound represented by the formula (1) and the content of the nitrile 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 contains a compound represented by the following formula (1), a nitrile compound having no silicon atom, an electrolyte salt, and a nonaqueous solvent.

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 or a sulfur atom.

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.

In one embodiment, R ⁵ is an organic group containing a nitrogen atom, and is preferably a group represented by the following formula (2) from the viewpoint of further improving the performance of the electrochemical device.

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

In another embodiment, R ⁵ is an organic group containing a sulfur atom and is preferably a compound represented by the following formula (3), formula (4) or formula from the viewpoint that the performance of the electrochemical device can be further improved. It may be a group represented by any of (5).

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

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

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

The content of the compound represented by the formula (1) is preferably 0.001% by mass or more and 0.005% by mass, based on the total amount of the electrolytic solution, from the viewpoint 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, preferably 8 mass% or less, 5 mass% or less, 3 mass% or less, 2 mass% or less, Alternatively, it is 1% by mass or less.

A nitrile compound is a compound having at least one cyano group (nitrile group). The nitrile compound is a compound other than the compound represented by the above formula (1). In other words, the nitrile compound is a compound having no silicon atom. The nitrile compound may have 1 or 2 or more cyano groups, and may have 2 or 3 cyano groups. The nitrile compound having one cyano group may be, for example, butyronitrile, valeronitrile, n-heptanenitrile or the like. The nitrile compound having two cyano groups may be, for example, succinonitrile, glutarnitrile, adiponitrile, pimelonitrile, suberonitrile and the like. The nitrile compound having three cyano groups may be, for example, 1,2,3-propanetricarbonitrile, 1,3,5-pentanetricarbonitrile and the like. The nitrile compound has two or more cyano groups and excludes carbon atoms in the cyano group from the viewpoint that a stable film is formed on the positive electrode or the negative electrode and the expansion of the battery due to the decomposition of the electrolytic solution can be suppressed. Compounds having 2 or more carbon atoms are preferred. The nitrile compound is more preferably a compound having 2 or 3 cyano groups, and the number of carbon atoms excluding carbon atoms in the cyano group is 2 or more. The nitrile compound is more preferably succinonitrile, Glutarnitrile, adiponitrile, pimelonitrile, suberonitrile, 1,2,3-propanetricarbonitrile, or 1,3,5-pentanetricarbonitrile.

The content of the nitrile 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 of further improving the performance of the electrochemical device. % Or more, 0.05% by mass or more, or 0.1% by mass or more, preferably 5% by mass or less, 3% by mass or less, 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 nitrile compound is preferably 0.001 based on the total amount of the electrolytic solution, from the viewpoint that the performance of the electrochemical device can be further improved. % 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 nitrile compound (the content of the compound represented by the formula (1)/the content of the nitrile 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, 3 or less, 2 or less, or 1 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.

The non-aqueous solvent is, for example, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyl lactone, 1,2-dimethoxyethane, dimethoxymethane, tetrahydrofuran, dioxolane, methylene chloride, methyl acetate, etc. You may. 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 nitrile compound, the electrolyte salt and the non-aqueous solvent. Other materials include, for example, a cyclic carbonate such as a fluorine-containing cyclic carbonate, a cyclic carbonate having a carbon-carbon double bond, a nitrogen atom other than the compound represented by the formula (1), a sulfur atom, or a nitrogen atom and a sulfur atom. It may be a compound containing, 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 or the like, 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 sulfur atom other than the compound represented by the formula (1) may be, for example, a cyclic sulfonate compound such as 1,3-propane sultone and 1-propene-1,3-sultone.

As a result of examining compounds having various structures and functional groups, the present inventors have improved the performance of an electrochemical device by applying the compound represented by the above formula (1) and a nitrile compound to an electrolytic solution. Revealed that can be made. The present inventors presume the action and effect of using the compound represented by the formula (1) and the nitrile compound in the electrolytic solution as follows. That is, the compound represented by the formula (1) and the nitrile compound act on the place where the effect is most likely to be exhibited in the lithium ion secondary battery, for example, to form a stable coating film 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. For example, by using this electrolytic solution, the capacity retention rate after storing the electrochemical device at high temperature can be improved. In another aspect, by using this electrolytic solution, it is possible to improve the capacity recovery rate after storing the electrochemical device at high temperature. In another aspect, by using this electrolytic solution, it is possible to suppress an increase in volume of the electrochemical device after storage at high temperature. In another aspect, the use of this electrolytic solution can improve the cycle characteristics of the electrochemical device.

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. The order of the first to fourth steps is arbitrary.

In the first step, the material used for the positive electrode mixture layer 10 is dispersed in a dispersion medium using a kneader, a disperser or the like to obtain a 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 a conductive agent, and a binder (3% by mass). Were 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 applied uniformly and uniformly 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 ethylmethyl carbonate containing 1 mol/L of LiPF ₆ , 1% by mass of vinylene carbonate (VC) based on the total amount of the mixed solution, 4-fluoro-1, Addition of 1% by mass of 3-dioxolan-2-one (fluoroethylene carbonate; FEC), 1% by mass of compound A represented by the following formula (6) and 1% by mass of succinonitrile (on the basis of the total amount of electrolytic solution). I used what I did.

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

(Example 3)
A lithium ion secondary battery was prepared in the same manner as in Example 1 except that Compound B represented by the following formula (7) was added in place of Compound A in an amount of 0.5% by mass based on the total amount of the electrolytic solution. A battery was produced.

(Example 4)
A lithium ion secondary battery was prepared in the same manner as in Example 1 except that Compound C represented by the following formula (8) was added in place of Compound A in an amount of 0.1% by mass based on the total amount of the electrolytic solution. A battery was produced.

(Example 5)
A lithium ion secondary battery was produced in the same manner as in Example 1 except that adiponitrile was used instead of succinonitrile.

(Comparative Example 1)
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the compound A and succinonitrile 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 (1% by mass of succinonitrile was added).

[First charge/discharge]
The lithium-ion battery thus prepared was subjected to initial charge/discharge by the method described below. 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 charging/discharging cycle was repeated 3 times (“C” used as a unit of current value means “current value (A)/battery capacity (Ah)”). The discharge capacity at the third cycle was defined as the capacity Q1 of this battery.

[High temperature storage test (1)]
Each of the secondary batteries of Examples 1 to 5 and Comparative Examples 1 and 2 was subjected to constant current charging up to an upper limit voltage of 4.45 V at a current value of 0.1 C under an environment of 25° C., and then at 4.45 V. Voltage charging was performed. The charge termination condition was a current value of 0.01C. Then, the secondary batteries were stored for 1 week in a constant temperature bath at 60°C.

[Measurement of volume increase rate]
The volumes of the secondary batteries of Examples 1 to 5 and Comparative Examples 1 and 2 were measured by a hydrometer based on the Archimedes method (electronic hydrometer MDS-300, manufactured by Alpha Mirage). The volume increase rate was calculated by the following formula from the volume (V1) of the secondary battery before the high temperature storage test and the volume (V2) of the secondary battery kept for 30 minutes in the environment of 25° C. after the high temperature storage test. From this, the degree of expansion of the secondary battery was evaluated. The results are shown in Table 1.
Volume increase rate (%)=V2/V1×100

[Measurement of capacity maintenance rate and recovery rate]
After the high temperature storage test, each of the secondary batteries of Examples 1 to 5 and Comparative Examples 1 and 2 was taken out from the constant temperature bath and kept in an environment of 25° C. for 30 minutes, and then cut off at a current value of 0.1 C and a final voltage of 2. A constant current discharge of 5V was performed. 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 described above, the capacity retention rate and capacity recovery rate were calculated using the following formulas. The results are shown in Table 1.
(Capacity maintenance rate) (%)=Q2/Q1×100
(Capacity recovery rate) (%)=Q3/Q1×100

[Evaluation of cycle characteristics]
After the initial charge/discharge, the cycle characteristics of each secondary battery were evaluated by a cycle test in which charge/discharge was repeated. Regarding the charging pattern, in the environment of 45° C., the secondary batteries of Examples 1 to 5 and Comparative Examples 1 and 2 were subjected to constant current charging at a current value of 0.5 C up to an upper limit voltage of 4.45 V, and then 4 Constant voltage charging was performed at 0.45V. The charge termination condition was a current value of 0.05C. Regarding discharge, constant current discharge was performed up to 2.5 V at 1 C, and the discharge capacity was obtained. This series of charging/discharging was repeated 100 cycles, and the discharging capacity was measured every charging/discharging. The relative value (discharge capacity retention rate (%)) of the discharge capacity after 100 cycles with respect to the discharge capacity after charge and discharge in the first cycle was determined. The results are shown in Table 1.

As shown in Table 1, the lithium ion secondary batteries to which the electrolytic solutions of Examples 1 to 5 containing the compound A, the compound B or the compound C, and the nitrile compound (succinonitrile or adiponitrile) were applied were the compound A In comparison with the lithium ion secondary batteries of Comparative Examples 1 and 2 to which an electrolytic solution containing at least one of Compound B or Compound C and a nitrile compound is applied, the volume increase rate in the high temperature storage test is small, and the capacity retention rate is small. It was also found that the recovery rate is improved. The lithium-ion secondary battery described in Comparative Example 1 accelerated the deterioration and short-circuited during the test. Further, it was revealed that the lithium ion secondary batteries to which the electrolytic solutions of Examples 1 to 5 were applied had a higher capacity retention rate in the cycle test than the lithium ion secondary batteries of Comparative Examples 1 and 2. It is considered that this is because the nitrile compound formed a stable film on the positive electrode, and the compound A, the compound B, or the compound C contributed to the stabilization of the electrolytic solution.

(Example 6)
[Preparation of positive electrode and negative electrode]
A positive electrode and a negative electrode were obtained in the same manner as in Example 1.

[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 diethyl carbonate containing 1 mol/L of LiPF ₆ , 1 mass% of vinylene carbonate (VC) based on the total amount of the mixed solution, 4-fluoro-1,3- 0.5 mass% of dioxolan-2-one (fluoroethylene carbonate; FEC), 0.5 mass% of compound A represented by the above formula (6), and 0.5 mass% of succinonitrile (electrolysis The total amount of the liquid) was used.

[High temperature storage test (2)]
For each of the secondary batteries of Example 1 and Comparative Examples 1 and 2 described above, after performing the initial charge and discharge described above, constant current charging was performed at a current value of 0.1 C under an environment of 25° C. to obtain an upper limit voltage of 4. It was performed up to 45V, and then constant voltage charging was performed at 4.45V. 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 volume increase rate]
By the same method as the above-mentioned method, from the volume before the high temperature storage test (V1) and the volume of the secondary battery (V2) kept for 30 minutes in the environment of 25° C. after the high temperature storage test, Example 6 and Comparative Example The volume increase rate after the high temperature storage test of 1-2 was calculated.

As a result, the volume increase rate of Example 1 was 102.3%, the volume increase rate of Comparative Example 1 was 107.8%, and the volume increase rate of Comparative Example 2 was 103.7%. The lithium ion secondary battery of Comparative Example 2 to which the electrolytic solution containing succinonitrile and not containing Compound A was applied was the lithium ion secondary battery of Comparative Example 1 to which the electrolytic solution containing neither Compound A nor succinonitrile was applied. The volume increase rate was reduced as compared with the battery. It is considered that this is because in the lithium ion secondary battery of Comparative Example 2, the gas derived from the electrolytic solution generated under a high temperature (80° C.) environment was reduced. On the other hand, in the lithium ion secondary battery of Example 6 to which the electrolytic solution containing both the compound A and succinonitrile was applied, the volume increase rate was further reduced as compared with the lithium ion secondary batteries of Comparative Examples 1 and 2.

[Measurement of capacity retention rate]
The secondary batteries of Example 6 and Comparative Examples 1 and 2 stored for 4 hours in a constant temperature bath of 80° C. were taken out from the constant temperature bath and kept in an environment of 25° C. for 30 minutes, and then the same method as the above-mentioned method. Thus, the capacity retention rate after the high temperature storage test of Example 6 and Comparative Examples 1 and 2 was calculated.

As a result, the capacity retention rate of Example 6 was 95.8%, the capacity retention rate of Comparative Example 1 was 94.5%, and the capacity retention rate of Comparative Example 2 was 94.8%. The lithium ion secondary battery of Example 1 to which the electrolytic solution containing both the compound A and succinonitrile was applied was the lithium ion battery of Comparative Example 1 to which the electrolytic solution containing neither compound A nor succinonitrile was applied, and The capacity retention rate was better than that of the lithium ion secondary battery of Comparative Example 2 to which the electrolytic solution containing succinonitrile and containing no compound A was applied. The reason for this is considered that, in addition to the nitrile compound forming a stable film on the positive electrode, the compound A contributed to the stabilization of the electrolytic solution. It is also considered that the side reaction at the positive electrode or the negative electrode was suppressed and the electrolytic solution was stabilized.

As described above, the lithium ion secondary batteries of Examples 1 to 6 to which the electrolytic solution containing both the compound A, the compound B or the compound C, and the nitrile compound were applied were prepared by using the electrolytic solution containing neither the nitrile compound nor the compound A. Compared to the applied lithium ion secondary battery of Comparative Example 1 and the lithium ion secondary battery of Comparative Example 2 to which the electrolytic solution containing the nitrile compound and not containing the compound A was applied, excellent performance is exhibited.

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

Claims

An electrolytic solution containing a compound represented by the following formula (1) and a nitrile compound having no silicon atom.

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

[In 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 3, wherein R 5 is an organic group containing a sulfur atom.
The electrolytic solution according to claim 6, wherein R 5 is a group represented by the following formula (3), formula (4), or formula (5).

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

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

[In the formula (5), R 10 represents an alkyl group, and * represents a bond. ]
The electrolytic solution according to any one of claims 1 to 7, wherein the nitrile compound has two cyano groups.
The electrolytic solution according to any one of claims 1 to 8, wherein the nitrile compound is succinonitrile.
10. The total of the content of the compound represented by the formula (1) and the content of the nitrile compound is 10% by mass or less based on the total amount of the electrolytic solution, according to any one of claims 1 to 9. Electrolyte.
An electrochemical device comprising a positive electrode, a negative electrode, and the electrolytic solution according to any one of claims 1 to 10.
The electrochemical device according to claim 11, wherein the negative electrode contains a carbon material.
The electrochemical device according to claim 12, wherein the carbon material contains graphite.
The electrochemical device according to claim 12 or 13, 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 11 to 14, wherein the electrochemical device is a non-aqueous electrolyte secondary battery or a capacitor.