TWI835942B - Electrolytes and electrochemical devices - Google Patents

Abstract

One aspect of the present invention is an electrolyte solution comprising: a compound represented by the following formula (1); and a cyclic compound having no silicon atom and 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 sulfur atom.

Description

Electrolyte and electrochemical device

The invention relates to an electrolyte solution and an electrochemical device.

In recent years, due to the 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, capacitors, and the like are in demand. As a means for improving the performance of an electrochemical device, a method of adding a predetermined additive to an electrolytic solution is being studied, for example. Patent Document 1 discloses an electrolyte for a nonaqueous electrolyte battery that contains a specific siloxane compound in order to improve cycle characteristics and internal resistance characteristics. [Prior technical literature] (patent document)

Patent Document 1: Japanese Patent Application Publication No. 2015-005329

[Problem to be solved by the invention] The object of the present invention is to provide an electrolyte that can improve the performance of an electrochemical device. [Technical means to solve the problem]

One aspect of the present invention is an electrolyte solution containing: a compound represented by the following formula (1); and a cyclic compound that does not have a silicon atom and has a ring containing a sulfur 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 sulfur atom.

According to this electrolyte solution, in one aspect, the performance of the electrochemical device can be suppressed from increasing in volume after the electrochemical device is stored at high temperature. In addition, by using this electrolyte, in another aspect, it is possible to improve the cycle characteristics of the electrochemical device (in particular, to improve the capacity retention rate after the cycle test and to suppress the DC resistance during discharge after the cycle test ( Discharge DCR) rises). In addition, with this electrolyte solution, in another aspect, the discharge DCR after the electrochemical device is stored at high temperature can be reduced.

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 any one of the following formula (3), formula (4) and formula (5): In formula (3), R ⁸ represents an alkyl group, and * represents a bond; In formula (4), R ⁹ represents an alkyl group, and * represents a bond; In formula (5), R ¹⁰ represents an alkyl group, and * represents a bond.

Cyclic compounds may include cyclic sulfonate compounds. The cyclic sulfonate 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. The hydrogen atoms in the alkylene group and the alkenylene group may be Alkyl, cycloalkyl, aryl or fluoro substitution.

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

The cyclic compound may include at least one selected from the group consisting of the compound represented by formula (Y) and the compound represented by formula (Z): 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. The hydrogen atoms in the alkylene group and the alkenylene group may be alkyl groups, rings Substituted by alkyl or aryl groups; 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. The hydrogen atoms in the alkylene group and the alkenylene group may be alkyl groups, ring Alkyl or aryl substitution.

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

Another aspect of the present invention is an electrochemical device, which comprises: a positive electrode, a negative electrode, and the above-mentioned electrolyte.

The negative electrode may contain carbon materials. Carbon material, which 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.

Electrochemical device, which may be a non-aqueous electrolyte secondary battery or capacitor. [Effects]

According to the present invention, an electrolyte can be provided which can improve the performance of an electrochemical device.

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 embodiments described below.

FIG. 1 is an oblique view of an electrochemical device showing an embodiment. In this embodiment, the electrochemical device is a non-aqueous electrolyte secondary battery. As shown in FIG. 1, the non-aqueous electrolyte secondary battery 1 comprises: an electrode group 2, which is composed of a positive electrode, a negative electrode and a spacer; and a bag-shaped battery casing 3, which is used to accommodate the electrode group 2. A positive electrode collector terminal (tab) 4 and a negative electrode collector terminal 5 are provided at the positive electrode and the negative electrode, respectively. The positive electrode collector terminal 4 and the negative electrode collector terminal 5 protrude from the inside of the battery casing 3 to the outside in a manner that the positive electrode and the negative electrode can be electrically connected to the outside of the non-aqueous electrolyte secondary battery 1. The battery casing 3 is filled with an electrolyte (not shown). The non-aqueous electrolyte secondary battery 1 may be a battery in a shape other than the above-mentioned so-called "stacked type" (such as a coin type, a cylindrical type, a laminate type, etc.).

The battery casing 3 may be, for example, a container formed by a laminated film. The laminated film may be, for example, a laminated film formed by laminating the following in order: a resin film such as a polyethylene terephthalate (PET) film; a metal foil such as aluminum, copper, or stainless steel; and a sealant layer such as polypropylene.

FIG. 2 is an exploded perspective view showing an embodiment of the electrode group 2 of the non-aqueous electrolyte secondary battery 1 shown in FIG. As shown in FIG. 2, the electrode group 2 includes, in order: a positive electrode 6, a spacer 7, and a negative electrode 8. The positive electrode 6 and the negative electrode 8 are arranged so that the surfaces of the positive electrode compound layer 10 side and the negative electrode compound layer 12 side are opposite to the spacer 7, respectively.

The positive electrode 6 includes a positive electrode current collector 9 and a positive electrode mixture layer 10 , and the positive electrode mixture layer 10 is provided on the positive electrode current collector 9 . The positive current collector 9 is provided with a positive current collecting terminal 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 surface of the positive electrode current collector 9 may be treated with carbon, nickel, titanium, silver, etc., such as aluminum or copper, for the purpose of improving adhesion, conductivity, and oxidation resistance. From the viewpoint of electrode strength and energy density, the thickness of the positive electrode current collector 9 is, for example, 1 to 50 μm.

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

The positive 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 means selected from Na, Mg, Sc, Y, Mn, Fe, Co, Cu, At least one element from the group consisting of Zn, Al, Cr, Pb, Sb, V and B (where M is an element different from other elements in each formula); x=0~1.2, y=0 ~0.9, z=2.0~2.3). The lithium oxide represented by Li _x Ni _{1 - y} M _y O _z can be Li _x Ni _{1 - (y1 + y2)} Co _y1 Mn _y2 O _z (where x and z are the same as above, y1=0~0.9, y2 =0~0.9, and y1+y2=0~0.9), which can be, for example: LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , LiNi _0.6 Co _0.2 Mn _0.2 O ₂ , 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 can be Li _x Ni _{1 - (y3 + y4)} Co _y3 Al _y4 O _z (where x and z are the same as above, y3=0~0.9, y4 =0~0.9, and y3+y4=0~0.9), for example: LiNi _0.8 Co _0.15 Al _0.05 O ₂ .

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

The content of the positive electrode active material may be 80 mass% or more, or 85 mass% or more, and may be 99 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 and Ketjen black; or carbon materials such as graphite, graphene, and carbon nanotubes. The content of the conductive agent may be, for example, 0.01 mass % or more, 0.1 mass % or more, or 1 mass % or more, based on the total amount of the positive electrode agent layer, and may be 50 mass % or less, 30 mass % or less, or 15 mass % or less.

Adhesives include, for example, resins such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, nitrocellulose, etc.; rubbers such as SBR (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), fluororubber, isoprene rubber, butadiene rubber, ethylene-propylene rubber, etc.; thermoplastic elastomers such as styrene-butadiene-styrene block copolymer or its hydrogenated product, EPDM (ethylene-propylene-diene terpolymer), styrene-ethylene-butadiene-ethylene copolymer, styrene-isoprene-styrene block copolymer or its hydrogenated product; syndiotactic 1,2-polybutadiene (syndiotactic 1,2-polybutadiene), polyvinyl acetate, ethylene-vinyl acetate copolymer, propylene-α-olefin copolymer and other soft resins; polyvinylidene fluoride (PVDF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, polytetrafluoroethylene-ethylene copolymer, polytetrafluoroethylene-vinylidene fluoride copolymer and other fluorine-containing resins; resins having nitrile-containing monomers as monomer units; polymer compositions having ion conductivity of alkaline metal ions (such as lithium ions), etc.

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

The spacer 7 is not particularly limited as long as it electrically insulates the positive electrode 6 and the negative electrode 8 and allows ions to pass therethrough, and has resistance to oxidation on the positive electrode 6 side and reduction on the negative electrode 8 side. Examples of the material of such a spacer 7 include resins, inorganic substances, and the like.

Examples of the resin include olefin polymers, fluorine polymers, cellulose polymers, polyimide, and polyester. From the perspective of stability and excellent liquid retention for the electrolyte, the spacer 7 is preferably a porous sheet or nonwoven fabric made of polyolefins such as polyethylene and polypropylene.

Examples of inorganic substances include oxides such as aluminum oxide and silicon dioxide; nitrides such as aluminum nitride and silicon nitride; and sulfates such as barium sulfate and calcium sulfate. The spacer 7 may be, for example, a spacer in which a fibrous or particulate inorganic substance is adhered to a film-like base material, and the film-like base material may be a nonwoven fabric, a woven fabric, a microporous film, or the like.

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

The negative electrode collector 11 is formed of the following: copper, stainless steel, nickel, aluminum, titanium, carbon (baked carbon), conductive polymer, conductive glass, aluminum-cadmium alloy, etc. The negative electrode collector 11 can be treated with carbon, nickel, titanium, silver, etc. on the surface of aluminum, copper, etc. for the purpose of improving adhesion, conductivity, and reduction resistance. From the perspective of electrode strength and energy density, the thickness of the negative electrode collector 11 is, for example, 1 to 50 μm.

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

The negative electrode active material is not particularly limited as long as it is a material that can adsorb 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; lithium monomers; lithium alloys such as lithium aluminum alloys; metals such as Sn and Si that can form alloys with lithium, etc. From the perspective 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 a single type or a mixture of two or more of these. The shape of the negative electrode active material may be, for example, particulate.

Examples of the carbon material include amorphous carbon materials, natural graphite, composite carbon materials in which natural graphite is made into an amorphous carbon material, artificial graphite (resin raw materials such as epoxy resin and phenol resin, or petroleum). Graphite obtained by calcining pitch-based raw materials obtained from coal, etc.), etc. From the viewpoint of high current density charge and discharge characteristics, the metal composite oxide preferably contains one or both of titanium and lithium, and more preferably contains lithium.

Among negative electrode active materials, carbon materials have high electrical conductivity and are particularly excellent in low-temperature characteristics and cycle stability. From the viewpoint of increasing the capacity, graphite is preferred among carbon materials. Among graphite, it is preferable that the interlayer (d002) of the carbon mesh surface measured by X-ray wide-angle diffraction method is less than 0.34 nm, and more preferably it is 0.3354 nm or more and 0.337 nm or less. A carbon material that satisfies such conditions is sometimes called quasi-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 monomer 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, it may be an alloy containing, in addition to silicon and tin, an alloy selected from the group consisting of nickel, copper, iron, cobalt, manganese, and zinc. , at least one of the group consisting of indium, silver, titanium, germanium, bismuth, antimony and chromium. The compound containing at least one element selected from the group consisting of silicon and tin may be an oxide, a nitride, or a carbide. Specifically, it may be a silicon oxide such as SiO, SiO ₂ , LiSiO, etc. ;Si ₃ N ₄ , Si ₂ N ₂ O and other silicon nitrides; SiC and other silicon carbides; SnO, SnO ₂ , LiSnO and other tin oxides, etc.

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 as the negative electrode active material, more preferably contains graphite, and further more preferably contains a mixture containing The carbon material and the material containing at least one element selected from the group consisting of silicon and tin are particularly preferably a mixture containing graphite and silicon oxide. In the mixture, the content of the carbon material (graphite) relative to the material (silicon oxide) of at least one element selected from the group consisting of silicon and tin, based on the total amount of the mixture, may be 1 mass% or more or 3 mass% or more, and may be 30 mass% or less.

The content of the negative electrode active substance 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 compound.

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

The negative electrode mixture layer 12 may contain a thickener to adjust the viscosity. The tackifier is not particularly limited and can be: carboxymethylcellulose, methylcellulose, hydroxymethylcellulose, ethylcellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and salts thereof wait. The thickening agent may be one type alone or a mixture of two or more types among these.

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

In one embodiment, the electrolyte solution contains: a compound represented by the following formula (1), a cyclic compound having no silicon atom and having a ring containing a sulfur atom (hereinafter also simply referred to as "cyclic compound"), an electrolyte salt, and a non-aqueous 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 sulfur atom.

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

The number of carbon atoms in the alkylene group represented by R ⁴ may be 1 or more or 2 or more, and may be 5 or less or 4 or less. The alkylene group represented by R ⁴ may be methylene, ethylene, propylene, butylene, or pentylene, 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. In other words, in one embodiment, the organic group represented by R ⁵ does not contain silicon atoms.

From the viewpoint of further improving the performance of the electrochemical device, ^R5 is preferably a group represented by any one of the following formulas (3), (4) and (5): In formula (3), R ⁸ represents an alkyl group, which may be the same as the alkyl groups represented by R ¹ to R ³ above, and * represents a bond; In formula (4), R ⁹ represents an alkyl group, which may be the same as the alkyl groups represented by R ¹ to R ³ above, and * represents a bond; In formula (5), R ¹⁰ represents an alkyl group, which may be the same as the alkyl groups represented by R ¹ to R ³ above, and * represents a bond.

From the viewpoint of being able to further improve the performance of the electrochemical device, the content of the compound represented by formula (1) is preferably 0.001 mass % or more, 0.005 mass % or more, 0.01 mass % or more, 0.05 mass % or more, or 0.1 mass % or more, and 8 mass % or less, 5 mass % or less, 3 mass % or less, 2 mass % or less, or 1 mass % or less, based on the total amount of the electrolyte.

Cyclic compounds are compounds having a ring (heterocycle) containing sulfur atoms. In addition, the cyclic compound is a compound other than the compound represented by the said formula (1). In other words, the cyclic compound is a compound that does not have a silicon atom.

The cyclic compound may include, for example, at least one of cyclic sulfonate compounds (also called sultone compounds). The cyclic sulfonate compound is a compound having a ring containing an -OSO ₂ - group. The cyclic sulfonate compound has a ring containing one or two -OSO ₂ - groups.

The cyclic sulfonate compound having a ring containing one -OSO ₂ - group may be, for example, a compound represented by the following formula (X): In formula (X), ^A1 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 may be substituted by an alkyl group, a cycloalkyl group, an aryl group or a fluoro group.

The number of carbon atoms in the alkyl group may be, for example, 1 to 12. The number of carbon atoms in the cycloalkyl group may be, for example, 3 to 6. The 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. In other words, the cyclic sulfonate compound is preferably a compound represented by the following formula (X-1) or (X-2).

In formulas (X-1) and (X-2), R ¹¹ to R ²⁰ each independently represents a hydrogen atom, an alkyl group, a cycloalkyl group, an aryl group, or a fluoro group; an alkyl group represented by R ¹¹ to R ²⁰ , the carbon number of the cycloalkyl group and the aryl group is the same as the carbon number of the alkyl group, cycloalkyl group and aryl group described in the formula (X) respectively. R ¹¹ to R ²⁰ are preferably hydrogen atoms.

Examples of the cyclic sulfonate compound represented by formula (X) include monosulfonates such as 1,3-propane sultone, 1,4-butane sultone, 2,4-butane sultone, 1,3-propylene sultone, 1,4-butene sultone, 1-methyl-1,3-propane sultone, 3-methyl-1,3-propane sultone, 1-fluoro-1,3-propane sultone, and 3-fluoro-1,3-propane sultone. Among these, 1,3-propane sultone (a compound in which all R ¹¹ to R ¹⁶ in formula (X-1) are hydrogen atoms) or 1-propylene-1,3-sultone (a compound in which all R ¹⁷ to R ²⁰ in formula (X-2) are hydrogen atoms) is preferred from the viewpoint of further improving the performance of the electrochemical device.

The cyclic sulfonate compound having a ring containing two -OSO ₂ - groups may be, for example, a compound represented by the following formula (X-3): In formula (X-3), 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. In the alkylene group and the alkenylene group, Hydrogen atoms may be substituted by alkyl, cycloalkyl, aryl or fluoro groups.

B ¹ and B ² are preferably unsubstituted alkylene groups having 1 or 2 carbon atoms. Such cyclic sulfonate compounds may be disulfonate esters such as methylene methane disulfonate and ethyl methane disulfonate.

The cyclic compound may include, for example, at least one selected from the group consisting of a compound represented by formula (Y) and a compound represented by formula (Z): In formula (Y) and (Z), ^A2 and ^A3 represent 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 may be substituted by an alkyl group, a cycloalkyl group or an aryl group.

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

Examples of the compound represented by the formula (Y) include: cyclotetrane, 2-methylcyclotetrane, 3-methylcyclotetrane, 2-ethylcyclotetrane, 3-ethylcyclotetrane, 2,4-dimethylcyclobutane, 2-phenylcyclobutane, 3-phenylcyclobutene, sulfolene, 3-methylcyclobutene, etc. From the viewpoint of being able to further improve the performance of the electrochemical device, the compound represented by the formula (Y) is preferably cyclotenine.

Examples of the compound represented by formula (Z) include ethylene sulfide, propane sulfide, butane sulfide, vinyl sulfide, and phenylethylene sulfide. From the viewpoint of further improving the performance of the electrochemical device, the compound represented by formula (Z) is preferably ethylene sulfide.

The cyclic compound may include at least one selected from the group consisting of a cyclic sulfonate compound, a compound represented by formula (Y), and a compound represented by formula (Z), and may include at least one selected from the group consisting of a compound represented by formula (X) ), at least one of the group consisting of a compound represented by formula (Y) and a compound represented by formula (Z), may include a compound selected from a compound represented by formula (X) and a compound represented by formula (Z) At least one member of the group consisting of the represented compounds.

From the perspective of being able to further improve the performance of the electrochemical device, the content of the cyclic compound is preferably 0.001 mass % or more, 0.005 mass % or more, 0.01 mass % or more, 0.05 mass % or more, or 0.1 mass % or more, and 5 mass % or less, 3 mass % or less, 2 mass % or less, or 1 mass % or less, based on the total amount of the electrolyte.

From the viewpoint of being able to further improve the performance of the electrochemical device, the total amount of the compound represented by formula (1) and the content of the cyclic compound, based on the total amount of the electrolyte, is preferably 0.001 mass % or more, 0.005 mass % or more, 0.01 mass % or more, 0.1 mass % or more, or 0.5 mass % or more, and is preferably 10 mass % or less, 7 mass % or less, 5 mass % or less, 3 mass % or less, or 2 mass % or less.

From the viewpoint of being able to further improve the performance of the electrochemical device, the mass ratio of the content of the compound represented by formula (1) to the content of the cyclic compound (content of the compound represented by formula (1)/content of the cyclic compound) is preferably greater than 0.01, greater than 0.05, greater than 0.1, greater than 0.2, or greater than 0.25, and is preferably less than 500, less than 100, less than 50, less than 20, less than 10, less than 5, or less than 4.

The electrolyte salt may be, for example, a lithium salt. The lithium salt may be at least one selected from the group consisting of: LiPF ₆ , LiBF ₄ , LiClO ₄ , LiB(C ₆ H ₅ ) ₄ , LiCH ₃ SO ₃ , CF ₃ SO ₂ OLi, and LiN. (SO ₂ F) ₂ (Li[FSI], lithium bis(fluoromethanesulfonyl)imide), LiN(SO ₂ CF ₃ ) ₂ (Li[TFSI], lithium bis(trifluoromethanesulfonyl)imide), and LiN(SO ₂ CF ₂ CF ₃ ) ₂ . The lithium salt preferably contains LiPF ₆ from the viewpoint of being more excellent in solubility in solvents, charge and discharge characteristics, output characteristics, and cycle characteristics of secondary batteries.

From the viewpoint of excellent charge and 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 even more preferably 0.8 mol/L or more based on the total amount of non-aqueous solvent. , and it is preferably 1.5 mol/L or less, more preferably 1.3 mol/L or less, and more preferably 1.2 mol/L or less.

The non-aqueous solvent may be, for example, ethyl carbonate, propyl carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, acetonitrile, 1,2-dimethoxyethane, dimethoxymethane, tetrahydrofuran, dioxolane, dichloromethane, methyl acetate, etc. The non-aqueous solvent may be one alone or a mixture of two or more thereof, preferably a mixture of two or more.

The electrolyte may further contain other materials other than the compound represented by formula (1), the cyclic compound, the electrolyte salt and the non-aqueous solvent. Examples of other materials include: cyclic carbonates such as fluorine-containing cyclic carbonates and cyclic carbonates having a carbon-carbon double bond; compounds having nitrogen atoms; compounds other than the compound represented by formula (1) and the cyclic compound having sulfur atoms; cyclic carboxylates, etc.

The fluorine-containing cyclic carbonate may be, for example, 4-fluoro-1,3-dioxacyclopentane-2-one (fluoroethyl carbonate; FEC), 1,2-difluoroethyl carbonate, 1,1-difluoroethyl carbonate, 1,1,2-trifluoroethyl carbonate, 1,1,2,2-tetrafluoroethyl carbonate, etc., preferably 4-fluoro-1,3-dioxacyclopentane-2-one (fluoroethyl carbonate; FEC). The cyclic carbonate having a carbon-carbon double bond may be, for example, vinyl carbonate. The compound containing a nitrogen atom may be, for example, a nitrile compound such as succinonitrile.

As a result of research on compounds having various structures and functional groups, the present inventors clearly found out that by applying the compound represented by the above formula (1) and the cyclic compound to the electrolyte, it is possible to improve the electrochemical device. performance. The present inventors speculate that the effects produced by using the compound represented by formula (1) and the cyclic compound in the electrolyte solution are as follows. In other words, we believe that the compound represented by formula (1) and the cyclic compound each act on the position where the effect is most likely to appear in the lithium ion secondary battery, and, for example, contribute to the formation of a stable coating on the positive electrode or the negative electrode, Or stabilize the electrolyte. As a result, the performance of electrochemical devices such as the non-aqueous electrolyte secondary battery 1 will be improved.

Specifically, if an electrolyte of one embodiment is used, as the performance of the electrochemical device, the volume increase after the electrochemical device is stored at a high temperature can be suppressed. In addition, if an electrolyte of one embodiment is used, the cycle characteristics of the electrochemical device can be improved (particularly, the capacity retention rate after the cycle test is improved, and the increase in the discharge DCR after the cycle test is suppressed). In addition, if an electrolyte of one embodiment is used, the discharge DCR after the electrochemical device is stored at a high temperature can be reduced.

Next, the manufacturing method of the non-aqueous electrolyte secondary battery 1 is described. The manufacturing method of the non-aqueous electrolyte secondary battery 1 comprises: a first step of obtaining a positive electrode 6; a second step of obtaining a negative electrode 8; a third step of placing an electrode group 2 in a battery casing 3; and a fourth step of injecting an electrolyte into the battery casing 3.

In the first step, the materials used in the positive electrode mixture layer 10 are dispersed in the dispersion medium using a kneader, a disperser, etc. to obtain a slurry positive electrode mixture, and then the materials used in the positive electrode mixture layer 10 are dispersed in a dispersion medium using a doctor blade method, a dipping method, The positive electrode mixture is applied to the positive electrode current collector 9 by a spray method or the like, and then the dispersion medium is volatilized, thereby obtaining the positive electrode 6 . After the dispersion medium is volatilized, a compression molding step by rolling can be set as needed. The positive electrode mixture layer 10 can be formed into a multi-layered positive electrode mixture layer by performing a plurality of steps from application of the positive electrode mixture to volatilization of the dispersion medium. The dispersion medium may be water, 1-methyl-2-pyrrolidone (hereinafter also referred to as NMP), or the like.

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

In the third step, the spacer 7 is sandwiched between the prepared positive electrode 6 and the negative electrode 8 to form the electrode group 2. Then, the electrode group 2 is placed in the battery casing 3.

In step 4, an electrolyte is injected into the battery casing 3. The electrolyte can be prepared, for example, by first dissolving an electrolyte salt in a solvent and then dissolving other materials.

As another embodiment, the electrochemical device may be a capacitor. The capacitor may have the same components as the above-mentioned non-aqueous electrolyte secondary battery 1: an electrode group consisting of a positive electrode, a negative electrode and a spacer; and a bag-shaped battery casing for accommodating the electrode group. The details of each component in the capacitor are the same as those of the non-aqueous electrolyte secondary battery 1. [Example]

The present invention is described in detail below by using embodiments, but the present invention is not limited to these embodiments.

(Example 1) [Preparation of positive electrode] Acetylene black (AB) (4 mass%) and a binder (4 mass%) as a conductive agent are added to lithium nickel cobalt manganate (92 mass%) as a positive electrode active material in sequence and mixed. A slurry positive electrode compound is prepared by adding NMP as a dispersion medium to the obtained mixture and kneading. A specified amount of this positive electrode compound is evenly and uniformly applied to an aluminum foil with a thickness of 20 μm as a positive electrode collector. Then, after the dispersion medium is volatilized, it is pressed by applying pressure to a density of 2.8 g/ ^cm3 to obtain a positive electrode.

[Preparation of negative electrode] A binder and carboxymethyl cellulose as a thickening agent are added to the negative electrode active material containing graphite and silicon oxide. The mass ratio is set to graphite:silicon oxide:binder:tackifier=92:5:1.5:1.5. Water as a dispersion medium is added to the obtained mixture and kneaded to prepare a slurry negative electrode mixture. A predetermined amount of this negative electrode mixture was evenly and uniformly applied to a 10 μm-thick rolled copper foil serving as a negative electrode current collector. Then, after the dispersion medium was volatilized, the dispersion medium was compressed by applying pressure 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 square of 13.5 ^cm2 was sandwiched with a separator, i.e., a polyethylene porous sheet (trade name: HIPORE (registered trademark), manufactured by Asahi Kasei Co., Ltd., thickness 30 μm), and the negative electrode cut into a square of 14.3 ^cm2 was further stacked to prepare an electrode group. This electrode group was placed in a container (battery casing) formed by an aluminum laminate film (trade name: aluminum laminate film, manufactured by Dai Nippon Printing Co., Ltd.). Then, 1 mL of electrolyte was added to the container, and the container was heat-fused to prepare a lithium-ion secondary battery for evaluation. As the electrolyte, an electrolyte was used, which was prepared by adding 1 mass % of vinyl carbonate (VC), 0.5 mass % of 4-fluoro- _1,3 -dioxacyclopentane-2-one (fluoroethyl carbonate; FEC), 0.5 mass % of compound A represented by the following formula (6), and 0.5 mass % (based on the total amount of the electrolyte) of 1,3-propane sultone to a 1 mol/L mixed solution of ethyl carbonate, dimethyl carbonate and ethyl methyl carbonate containing LiPF6, relative to the total amount of the mixed solution.

(Example 2) Regarding Example 1, except changing the addition amount of compound A to 2.0 mass %, it carried out similarly to Example 1, and produced the lithium ion secondary battery.

(Example 3) A lithium ion secondary battery was prepared in the same manner as in Example 1 except that 0.3 mass % of compound B represented by the following formula (7) was added instead of compound A.

(Example 4) A lithium ion secondary battery was produced in the same manner as in Example 1, except that 0.1 mass % of compound C represented by the following formula (8) was added instead of compound A.

(Example 5) Regarding Example 1, 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 6) Regarding Example 1, a lithium ion secondary battery was produced in the same manner as in Example 1, except that methylene methane disulfonate (MMDS) was used instead of 1,3-propane sultone.

(Example 7) In Example 1, a lithium ion secondary battery was produced in the same manner as in Example 1, except that ethylene sulfide was used instead of 1,3-propane sultone.

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

(Comparative example 2) Regarding Example 1, except not using compound A, it carried out similarly to Example 1, and produced the lithium ion secondary battery.

[Evaluation of high temperature storage characteristics] Each of the secondary batteries thus obtained was charged at a constant current at a current value of 0.1 C in an environment of 25°C until the upper limit voltage was 4.2 V, and then charged at a constant voltage at 4.2 V. The charging cutoff condition is set to a current value of 0.01 C. Then, the secondary batteries were stored in a constant temperature bath at 60° C. for 2 weeks. The volume (V1) of each secondary battery before the above-mentioned storage was measured using a hydrometer (electronic hydrometer MDS-300, manufactured by Alfa Mirage Co., Ltd.) according to the Archimedes method, and after the above-mentioned storage, it was left to stand still. The volume (V2) of each secondary battery after being exposed to an environment of 25°C. Using the measured V1 and V2, the volume change rate (%)=V2/V1×100 was calculated. The results are shown in Table 1.

[Evaluation of cycle characteristics] (Initial charge and discharge) The first charge and discharge were performed on each of the secondary batteries produced as follows. First, constant current charging was performed at a current value of 0.1 C in an environment of 25°C until the upper limit voltage was 4.2 V, and then constant voltage charging was performed at 4.2 V. The charge cutoff condition was set to a current value of 0.01 C. Then, constant current discharge was performed at a current value of 0.1 C with a cutoff voltage of 2.7 V. This charge and discharge cycle was repeated three times. In addition, "C" used as a unit of current value means "current value (A)/battery capacity (Ah)" (the same applies below).

(Measurement of discharge DCR) For each secondary battery after initial charge and discharge, the DC resistance during discharge (discharge DCR) was measured in the following manner. First, constant current charging of 0.2 C is performed until the upper limit voltage is 4.2 V, and then constant voltage charging is performed at 4.2 V. The charging cutoff condition is set to a current value of 0.02 C. Then, after performing constant current discharge with a cut-off voltage of 2.7 V at a current value of 0.2 C, the current value at this time is set to I _0.2C , and the voltage change 10 seconds after the start of discharge is set to ΔV _0.2C . Then, charge with a constant current of 0.2 C until the upper limit voltage is 4.2 V, and then charge with a constant voltage of 4.2 V (charge cutoff condition is set to a current value of 0.02 C), then charge with a current value of 0.5 C to a cutoff voltage of 2.7 After discharge with a constant current of V, let the current value at this time be I _0.5C , and let the voltage change 10 seconds after the start of discharge be ΔV _0.5C . From the same charge and discharge, the current value I _1C of 1 C and the voltage change ΔV _1C 10 seconds after the start of discharge were evaluated. Use the least squares method to draw a linear approximation straight line at the three plot points of the current value-voltage change (I _0.2C , ΔV _0.2C ), (I _0.5C , ΔV _0.5C ), (I _1C , ΔV _1C ), And its slope is set to the value R1 of the discharge DCR.

(Cycle test) The following charge and discharge cycle test was repeated for each secondary battery after the initial charge and discharge. The charging mode is to charge the secondary battery at a current value of 0.5 C in an environment of 45°C until the upper limit voltage is 4.2 V, and then charge it at a constant voltage of 4.2 V. The charge cut-off condition is set to a current of 0.05 C. The discharge is performed at a constant current of 1 C until 2.7 V, and the discharge capacity is calculated. This series of charge and discharge is repeated for 630 cycles. The discharge capacity Q1 after the first cycle of charge and discharge and the discharge capacity Q2 after the 630th cycle of charge and discharge are used to calculate the discharge capacity maintenance rate (%) = Q1/Q2×100. The results are shown in Table 1. In addition, for the secondary battery after 500 cycles, the discharge DCR value R2 was obtained in the same manner as above. Using the discharge DCR value R1 after the first charge and discharge and the discharge DCR value R2 after the 630th charge and discharge cycle, the discharge DCR increase rate (%) = R2/R1×100 was obtained. The results are shown in Table 1.

[Table 1]

As can be seen from Table 1, the electrolyte solutions of Examples 1 to 7 contain the compound represented by formula (1) and the cyclic compound, and the lithium ion secondary batteries of Comparative Examples 1 to 2 do not contain the compound represented by formula (1). and the electrolyte solution of either or both of the cyclic compounds, and compared with the lithium ion secondary batteries of Comparative Examples 1 to 2, the high-temperature storage of the lithium ion secondary battery using the electrolyte solution of Examples 1 to 7 The characteristics are better (the volume change rate after high-temperature storage is small), and the cycle characteristics are also better (the capacity retention rate after cycle testing is high and the increase in discharge DCR can be suppressed). We believe that the reason for this is that in addition to the cyclic compound forming a stable film on the positive electrode or the negative electrode, the compound represented by formula (1) also contributes to stabilizing the electrolyte.

In addition, the discharge DCR of the secondary batteries of Example 1 and Comparative Examples 1 and 2 after the above-mentioned high-temperature storage was also measured. As a result, the discharge DCR of Example 1 was 1.70 Ω, the discharge DCR of Comparative Example 1 was 1.98 Ω, and the discharge DCR of Comparative Example 2 was 1.79 Ω. The lithium-ion secondary battery of Comparative Example 2 used an electrolyte containing 1,3-propane sultone and not containing compound A, and the lithium-ion secondary battery of Comparative Example 1 used an electrolyte containing neither compound A nor 1,3-propane sultone. Compared with the lithium-ion secondary battery of Comparative Example 1, the discharge DCR of the lithium-ion secondary battery of Comparative Example 2 after high-temperature storage was further reduced. We believe that the reason is that 1,3-propane sultone has formed a stable film on the positive electrode or the negative electrode. In addition, the lithium ion secondary battery of Example 1 uses an electrolyte containing both compound A and 1,3-propane sultone, and the discharge DCR of the lithium ion secondary battery of Example 1 after high temperature storage is better by about 15% and about 5% respectively compared with the lithium ion secondary batteries of Comparative Examples 1 and Comparative Examples 2. We believe that the reason is that in addition to 1,3-propane sultone having formed a stable film on the positive electrode or the negative electrode, compound A also helps to stabilize the electrolyte.

1: Non-aqueous electrolyte secondary battery (electrochemical device) 2: Electrode group 3: Battery casing 4: Positive electrode collector terminal 5: Negative electrode collector terminal 6: Positive electrode 7: Spacer 8: Negative electrode 9: Positive electrode collector 10: Positive electrode compound layer 11: Negative electrode collector 12: Negative electrode compound layer

FIG. 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 the electrode group of the secondary battery shown in FIG. 1 .

Domestic storage information (please note in order of storage institution, date and number) without

Overseas storage information (please note the storage country, institution, date, and number in order) None

Claims (14)

An electrolyte solution comprising: a compound represented by the following formula (1); and a cyclic compound having no silicon atom and 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 sulfur atom. The electrolyte solution as described in claim 1, wherein at least one of the above R ¹ to R ³ is a fluorine atom. The electrolyte solution as described in claim 1 or 2, wherein the number of silicon atoms in one molecule of the compound represented by formula (1) is 1. The electrolyte solution as claimed in claim 1 or 2, wherein the aforementioned R ⁵ is a group represented by any one of the following formulas (3), (4) and (5):

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

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

In formula (5), R ¹⁰ represents an alkyl group, and * represents a bond. The electrolyte solution as described in claim 1 or 2, wherein the cyclic compound comprises a cyclic sulfonate compound. The electrolyte 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 with 3 to 5 carbon atoms or an alkenylene group with 3 to 5 carbon atoms. The hydrogen atoms in the alkylene group and the alkenylene group can be Alkyl, cycloalkyl, aryl or fluoro substitution. The electrolyte solution according to claim 6, wherein the compound represented by formula (X) is selected from the group consisting of 1,3-propane sultone and 1-propene-1,3-sultone. of at least 1 species. The electrolyte solution according to claim 1 or 2, wherein the aforementioned cyclic compound includes at least one selected from the group consisting of a compound represented by formula (Y) and a compound represented by formula (Z):

In the formula (Y), A ² represents an alkylene group with 3 to 5 carbon atoms or an alkenylene group with 3 to 5 carbon atoms. The hydrogen atoms in the alkylene group and the alkenylene group can be alkyl groups or cycloalkanes. base or aryl substitution;

In the formula (Z), A ³ represents an alkylene group with 3 to 5 carbon atoms or an alkenylene group with 3 to 5 carbon atoms. The hydrogen atoms in the alkylene group and the alkenylene group can be alkyl groups, rings Alkyl or aryl substitution. The electrolyte solution according to claim 1 or 2, wherein the total amount of the 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 electrolyte solution. . An electrochemical device, which is provided with: a positive electrode, a negative electrode, and the electrolyte solution described in any one of claims 1 to 9. An electrochemical device as described in claim 10, wherein the negative electrode contains a carbon material. The electrochemical device according to claim 11, wherein the carbon material contains graphite. An electrochemical device as described in claim 11 or 12, wherein the negative electrode further contains the following material, which contains at least one element selected from the group consisting of silicon and tin. The electrochemical device according to any one of claims 10 to 12, wherein the electrochemical device is a non-aqueous electrolyte secondary battery or a capacitor.