JP7380589B2 - Electrolytes and electrochemical devices - Google Patents

Description

The present invention relates to electrolytes and electrochemical devices.

In recent years, with the spread of portable electronic devices, electric vehicles, etc., there is a need for high-performance electrochemical devices such as non-aqueous electrolyte secondary batteries, typified by lithium ion secondary batteries, and capacitors. As a means to improve the performance of electrochemical devices, for example, a method of adding a predetermined additive to the electrolytic solution is being considered. Patent Document 1 discloses an electrolytic solution for a non-aqueous electrolyte battery that contains a specific siloxane compound in order to improve cycle characteristics and internal resistance characteristics.

Japanese Patent Application Publication No. 2015-005329

An object of the present invention is to provide an electrolytic solution that can improve the performance of electrochemical devices.

As a first aspect, the present invention provides an electrolytic solution that exhibits a peak within at least one chemical shift range of -180 ppm to -150 ppm and more than -150 ppm to -130 ppm when measured by ¹⁹ F-NMR. provide.

According to this electrolytic solution, in one aspect, the cycle characteristics of the electrochemical device can be improved as the performance of the electrochemical device.

In the first embodiment, the electrolytic solution may further exhibit a peak within a chemical shift range of more than -130 ppm and less than -110 ppm when measured by ¹⁹ F-NMR.

As a second aspect, the present invention provides an electrochemical device including a positive electrode, a negative electrode, and the above electrolyte.

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

In the second aspect, 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 that can improve the performance of an electrochemical device.

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 an electrode group of the secondary battery shown in FIG. 1. FIG. These are spectra obtained by ¹⁹ F-NMR measurement, in which (a) is a spectrum for the electrolytic solution of Example 1, and (b) is a spectrum for the electrolytic solution of Example 2. This is a spectrum obtained by ¹⁹ F-NMR measurement of the electrolytic solution of Comparative Example 2. These are spectra obtained by ¹⁹ F-NMR measurement, in which (a) is a spectrum for the electrolytic solution of Example 3, and (b) is a spectrum for the electrolytic solution of Example 4. These are spectra obtained by ¹⁹ F-NMR measurement, (a) is a spectrum for the electrolytic solution of Example 5, (b) is a spectrum for the electrolytic solution of Example 6, and (c) is a spectrum for the electrolytic solution of Example 6. FIG. 7 is a spectrum for the electrolyte of Example 7. It is a graph showing evaluation results of cycle characteristics.

Embodiments of the present invention will be described below with appropriate reference to the drawings. 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 nonaqueous electrolyte secondary battery. As shown in FIG. 1, the non-aqueous electrolyte secondary battery 1 includes an electrode group 2 composed of a positive electrode, a negative electrode, and a separator, and a bag-shaped battery exterior body 3 that houses the electrode group 2. A positive electrode current collector tab 4 and a negative electrode current collector tab 5 are provided on the positive electrode and the negative electrode, respectively. The positive electrode current collector tab 4 and the negative electrode current collector tab 5 protrude from the inside of the battery exterior body 3 to the outside so that the positive electrode and the negative electrode, respectively, can be electrically connected to the outside of the non-aqueous electrolyte secondary battery 1. . The battery exterior body 3 is filled with an electrolytic solution (not shown). The non-aqueous electrolyte secondary battery 1 may be a battery having a shape other than the so-called "laminate type" as described above (coin type, cylindrical type, laminated type, etc.).

The battery exterior body 3 may be, for example, a container formed of a laminate film. The laminate 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, or stainless steel, and a sealant layer such as polypropylene are laminated in this order.

FIG. 2 is an exploded perspective view showing one 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 a positive electrode current collector tab 4 .

The positive electrode current collector 9 is made of, for example, aluminum, titanium, stainless steel, nickel, fired carbon, conductive polymer, conductive glass, or the like. The positive electrode current collector 9 may be made of aluminum, copper, etc. whose surface is treated with carbon, nickel, titanium, silver, etc. for the purpose of improving adhesiveness, conductivity, and oxidation resistance. The thickness of the positive electrode current collector 9 is, for example, 1 to 50 μm in terms of electrode strength and energy density.

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

The positive electrode active material may be, for example, lithium oxide. Examples of lithium oxides 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 , 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 , 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 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 , It may be LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , LiNi _0.6 Co _0.2 Mn _0.2 O _{2 , or} 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 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 There may be.

The positive electrode active material may be, for example, lithium phosphate. Examples of lithium phosphates 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 a carbon black such as acetylene black or Ketjen black, or a carbon material such as graphite, graphene, or carbon nanotubes. The content of the conductive agent may be, for example, 0.01% by mass or more, 0.1% by mass or more, or 1% by mass or more, and 50% by mass or less, 30% by mass, based on the total amount of the positive electrode mixture layer. or 15% by mass or less.

Examples of the binder include resins such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose; SBR (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), and fluororubber. , isoprene rubber, butadiene rubber, ethylene-propylene rubber, etc.; styrene-butadiene-styrene block copolymer or its hydrogenated product, EPDM (ethylene-propylene-diene terpolymer), styrene-ethylene-butadiene Thermoplastic elastomers such as ethylene copolymers, styrene/isoprene/styrene block copolymers or their hydrogenated products; syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene/vinyl acetate copolymers, propylene/α - Soft resins such as olefin copolymers; polyvinylidene fluoride (PVDF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, polytetrafluoroethylene/ethylene copolymer, polytetrafluoroethylene/vinylidene fluoride copolymer, etc. Examples include fluorine-containing resins; resins having a nitrile group-containing monomer as a monomer unit; and polymer compositions having ion conductivity for alkali metal ions (for example, lithium ions).

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

There are no particular restrictions on the separator 7 as long as it electronically insulates the positive electrode 6 and negative electrode 8 while allowing ions to pass therethrough, and has resistance to oxidation on the positive electrode 6 side and reducibility on the negative electrode 8 side. Not done. Examples of the material for such a separator 7 include resins, inorganic materials, and the like.

Examples of the resin include olefin polymers, fluorine polymers, cellulose polymers, polyimides, and nylon. The separator 7 is preferably a porous sheet or nonwoven fabric made of polyolefin, such as polyethylene or polypropylene, from the viewpoint of being stable to the electrolytic solution and having excellent liquid retention properties.

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

The negative electrode 8 includes a negative electrode current collector 11 and a negative electrode mixture layer 12 provided on the negative electrode current collector 11. A negative electrode current collector tab 5 is provided on the negative electrode current collector 11 .

The negative electrode current collector 11 is made of copper, stainless steel, nickel, aluminum, titanium, fired carbon, conductive polymer, conductive glass, aluminum-cadmium alloy, or the like. The negative electrode current collector 11 may be made of copper, aluminum, etc. whose surface is treated with carbon, nickel, titanium, silver, etc. for the purpose of improving adhesiveness, conductivity, and reduction resistance. The thickness of the negative electrode current collector 11 is, for example, 1 to 50 μm 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 is a material that can insert and release lithium ions. Examples of negative electrode active materials include carbon materials, metal composite oxides, oxides or nitrides of Group 4 elements such as tin, germanium, and silicon, elemental lithium, lithium alloys such as lithium aluminum alloys, Sn, Si, etc. Examples include metals that can form alloys with lithium. From the viewpoint of safety, the negative electrode active material is preferably at least one selected from the group consisting of carbon materials and metal composite oxides. The negative electrode active material may be one of these materials or a mixture of two or more thereof. The shape of the negative electrode active material may be, for example, particulate.

Carbon materials include amorphous carbon materials, natural graphite, composite carbon materials in which natural graphite is coated with an amorphous carbon material, and artificial graphite (resin raw materials such as epoxy resins and phenol resins, or petroleum, coal, etc.) (obtained by firing pitch-based raw materials obtained from). 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.

The negative electrode active material may further contain a material containing at least one element selected from the group consisting of silicon and tin. The material containing at least one element selected from the group consisting of silicon and tin may be a simple substance of silicon or tin, or a compound containing at least one element selected from the group consisting of silicon and tin. The compound may be an alloy containing at least one element selected from the group consisting of silicon and tin, for example, in addition to silicon and tin, nickel, copper, iron, cobalt, manganese, zinc, indium, and silver. , titanium, germanium, bismuth, antimony, and chromium. The compound containing at least one element selected from the group consisting of silicon and tin may be an oxide, nitride, or carbide, and specifically, for example, silicon oxide such as SiO, SiO ₂ , LiSiO, etc. silicon nitrides such as Si ₃ N ₄ and Si ₂ N ₂ O, silicon carbides such as SiC, and tin oxides such as SnO, SnO ₂ and LiSnO.

From the viewpoint of further improving the performance of the electrochemical device, the negative electrode mixture layer 12 preferably contains a carbon material, more preferably graphite, and still more preferably contains a carbon material, silicon, and tin as a negative electrode active material. It includes a mixture with a material containing at least one element selected from the group consisting of, and particularly preferably, a mixture of graphite and silicon oxide. The content of the material (silicon oxide) containing at least one element selected from the group consisting of silicon and tin in the mixture is 1% by mass or more, or 3% by mass or more, based on the total amount of the mixture. It may well be up to 30% by weight.

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

The negative electrode mixture layer 12 may further contain a thickener to adjust the viscosity. Thickeners are not particularly limited, and may include carboxymethylcellulose, methylcellulose, hydroxymethylcellulose, ethylcellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, salts thereof, and the like. The thickener may be one of these or a mixture of two or more thereof.

When the negative electrode mixture layer 12 contains a thickener, the content is not particularly limited. From the viewpoint of coating properties of the negative electrode mixture layer, the content of the thickener may be 0.1% by mass or more, preferably 0.2% by mass or more, based on the total amount of the negative electrode mixture layer. , more preferably 0.5% by mass or more. 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% by mass or less, preferably 3% by mass, based on the total amount of the negative electrode mixture layer. % or less, more preferably 2% by mass or less.

In order to improve the performance of the electrochemical device, the electrolytic solution has at least one chemical shift of -180 ppm to -150 ppm and more than -150 ppm to -130 ppm in ¹⁹ F-NMR (Fluorine-19 Nuclear Magnetic Resonance) measurement. A peak is shown within the range of .

The electrolytic solution may exhibit a peak within any of the chemical shift ranges of -180 ppm to -150 ppm, and more than -150 ppm to -130 ppm. The electrolytic solution may exhibit peaks within two chemical shift ranges of -180 ppm to -150 ppm and more than -150 ppm to -130 ppm.

In this specification, ¹⁹ F-NMR measurement of an electrolytic solution is performed under the following conditions.
Measuring device: Avance neo manufactured by Bruker Japan
Measurement method: Single pulse method Observation nucleus: ¹⁹ F
Spectrum width: 90kHz
Pulse width: 15μs (90° pulse)
Pulse repetition time: 1s
Reference substance: C ₆ H ₅ CF ₃ (external standard: -63.9ppm)
Temperature: 23℃
Sample rotation speed: 20Hz

In one embodiment, the electrolyte exhibits a peak (peak A) within a chemical shift range of -180 ppm to -150 ppm. The chemical shift range in which peak A exists is -175 ppm to -155 ppm, -170 ppm to -158 ppm, -168 ppm to -160 ppm, -165 ppm to -160 ppm, or -163 ppm to -161 ppm. good. The peak A may be a peak group consisting of a plurality of peaks existing within a chemical shift range of -180 ppm or more and -150 ppm or less.

In another embodiment, the electrolyte exhibits a peak (Peak B) within a chemical shift range of greater than -150 ppm and less than or equal to -130 ppm. The chemical shift range in which peak B exists is -145 ppm or more -130 ppm or less, -143 ppm or more -133 ppm or less, -140 ppm or more -130 ppm or less, -140 ppm or more -133 ppm or less, -140 ppm or more and -135 ppm or less, or -138 ppm or more It may be -133 ppm or less. The peak B may be a peak group consisting of a plurality of peaks existing within a chemical shift range of more than -150 ppm and less than -130 ppm.

式中、Ｒ^１～Ｒ^３は、それぞれ独立に、アルキル基又はフッ素原子を示し、Ｒ^４はアルキレン基を示し、Ｒ^５は、硫黄原子又は窒素原子を含む有機基を示し、Ｒ^１～Ｒ^３の少なくとも１つはフッ素原子である。In one embodiment, each of the peaks described above (peaks A and B) originates from a compound represented by the following formula (1) contained in the electrolytic solution. That is, in one embodiment, the electrolytic solution contains a compound represented by the following formula (1).

In the formula, R ¹ to R ³ each independently represent an alkyl group or a fluorine atom, R ⁴ represents an alkylene group, R ⁵ represents an organic group containing a sulfur atom or a nitrogen atom, and R ¹ to R At least one of ³ is a fluorine atom.

When R ¹ to R ³ are alkyl groups, the number of carbon atoms in the alkyl group may be 1 or more and 3 or less. R ¹ to R ³ may be a methyl group, an ethyl group, or a propyl group, and may be linear or branched.

式中、Ｒ^２及びＲ^３は、それぞれ独立にアルキル基を示し、Ｒ^４はアルキレン基を示し、Ｒ^５は、硫黄原子又は窒素原子を含む有機基を示す。At least one of R ¹ to R ³ is a fluorine atom. When any one of R ¹ to R ³ is a fluorine atom, that is, when the electrolytic solution contains a compound represented by the following formula (2), the electrolytic solution has the above-mentioned peak A in ¹⁹ F-NMR measurement. shows.

In the formula, R ² and R ³ each independently represent an alkyl group, R ⁴ represents an alkylene group, and R ⁵ represents an organic group containing a sulfur atom or a nitrogen atom.

式中、Ｒ^３はアルキル基を示し、Ｒ^４はアルキレン基を示し、Ｒ^５は、硫黄原子又は窒素原子を含む有機基を示す。

式中、Ｒ^４はアルキレン基を示し、Ｒ^５は、硫黄原子又は窒素原子を含む有機基を示す。When two of R ¹ to R ³ are fluorine atoms, or when all of R ¹ to R ³ are fluorine atoms, that is, the electrolytic solution contains a compound represented by the following formula (3) or (4). In this case, the electrolyte exhibits the above-mentioned peak B in ¹⁹ F-NMR measurement.

In the formula, R ³ represents an alkyl group, R ⁴ represents an alkylene group, and R ⁵ represents an organic group containing a sulfur atom or a nitrogen atom.

In the formula, R ⁴ represents an alkylene group, and R ⁵ represents an organic group containing a sulfur atom or a nitrogen atom.

The number of carbon atoms in the alkylene group represented by R ⁴ in the above formulas (1) to (4) may be 1 or more or 2 or more, and may be 5 or less or 4 or less. The alkylene group represented by R ⁴ may be a methylene group, an ethylene group, a propylene group, a butylene group, or a pentylene group, and may be linear or branched.

In one embodiment, R ⁵ in the above formulas (1) to (4) may be an organic group containing a sulfur atom.

式中、Ｒ^６はアルキル基を示す。アルキル基は、上述したＲ^１～Ｒ^３で表されるアルキル基と同様であってよい。＊は結合手を示す（以下同様）。When R ⁵ is an organic group containing a sulfur atom, R ⁵ may be a group represented by the following formula (5) in one embodiment.

In the formula, R ⁶ represents an alkyl group. The alkyl group may be the same as the alkyl groups represented by R ¹ to R ³ described above. * indicates a bond (the same applies below).

式中、Ｒ^７はアルキル基を示す。アルキル基は、上述したＲ^１～Ｒ^３で表されるアルキル基と同様であってよい。When R ⁵ is an organic group containing a sulfur atom, R ⁵ may be a group represented by the following formula (6) in another embodiment.

In the formula, R ⁷ represents an alkyl group. The alkyl group may be the same as the alkyl groups represented by R ¹ to R ³ described above.

式中、Ｒ^８はアルキル基を示す。アルキル基は、上述したＲ^１～Ｒ^３で表されるアルキル基と同様であってよい。When R ⁵ is an organic group containing a sulfur atom, R ⁵ may be a group represented by the following formula (7) in another embodiment.

In the formula, R ⁸ represents an alkyl group. The alkyl group may be the same as the alkyl groups represented by R ¹ to R ³ described above.

In another embodiment, R ⁵ may be an organic group containing a nitrogen atom.

式中、Ｒ^９及びＲ^１０は、それぞれ独立に、水素原子又はアルキル基を示す。アルキル基は、上述したＲ^１～Ｒ^３で表されるアルキル基と同様であってよい。When R ⁵ is an organic group containing a nitrogen atom, R ⁵ may be a group represented by the following formula (8) in one embodiment.

In the formula, R ⁹ and R ¹⁰ each independently represent a hydrogen atom or an alkyl group. The alkyl group may be the same as the alkyl groups represented by R ¹ to R ³ described above.

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 contain a silicon atom.

From the viewpoint of further improving the performance of the electrochemical device, the content of the compound represented by formula (1) is preferably 0.001% by mass or more, 0.005% by mass or more, based on the total amount of the electrolyte solution. 0.01% by mass or more, 0.05% by mass or more, 0.1% by mass or more, 0.3% by mass or more, or 0.5% by mass or more, and preferably 10% by mass or less, 7% by mass % or less, 5% by mass or less, 3% by mass or less, 2% by mass or less, 1.5% by mass or less, or 1% by mass or less.

In addition to the above-mentioned peaks A and B, the electrolytic solution may further exhibit a peak (peak C) within a chemical shift range of more than -130 ppm and less than -110 ppm when measured by ¹⁹ F-NMR.

The chemical shift range in which peak C exists may be -128 ppm to -115 ppm, -126 ppm to -120 ppm, -125 ppm to -122 ppm, or -123 ppm to -120 ppm. The peak C may be a peak group consisting of a plurality of peaks existing within a chemical shift range of more than -130 ppm and less than -110 ppm.

In one embodiment, peak C originates from fluorine-containing cyclic carbonates that may be included in the electrolyte. That is, in one embodiment, the electrolyte may contain a fluorine-containing cyclic carbonate.

A fluorine-containing cyclic carbonate is a cyclic carbonate ester containing a fluorine atom in its molecule. In one embodiment, the fluorine-containing cyclic carbonate is a cyclic carbonate containing a fluoro group. The fluorine-containing cyclic carbonate is not particularly limited as long as it is a cyclic carbonate containing a fluoro group, but examples include 4-fluoro-1,3-dioxolan-2-one (fluoroethylene carbonate; FEC), 1,2 -difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, etc. The fluorine-containing cyclic carbonate is preferably 4-fluoro-1,3-dioxolan-2-one (fluoroethylene carbonate; FEC) from the viewpoint of suppressing side reactions on the negative electrode.

From the viewpoint of further improving the performance of the electrochemical device, the content of the fluorine-containing cyclic carbonate is preferably 0.001% by mass or more, 0.005% by mass or more, or 0.01% by mass, based on the total amount of the electrolyte. The content is 0.05% by mass or more, or 0.1% by mass or more, and 5% by mass or less, 3% by mass or less, 2% by mass or less, or 1% by mass or less.

When the electrolytic solution contains both the compound represented by formula (1) and the fluorine-containing cyclic carbonate, the total content of the compound represented by formula (1) and the content of the fluorine-containing cyclic carbonate is: From the viewpoint of further improving the performance of the electrochemical device, based on the total amount of the electrolyte, preferably 0.001% by mass or more, 0.005% by mass or more, 0.01% by mass or more, 0.1% by mass or more, or 0.5% by mass or more, preferably 10% by mass or less, 7% by mass or less, 5% by mass or less, 3% by mass or less, 2% by mass or less, 1.5% by mass or less, or 1% by mass or less It is.

In addition to the compound represented by formula (1) and the fluorine-containing cyclic carbonate, the electrolytic solution may further contain an electrolyte salt, a nonaqueous solvent, and an additive.

The electrolyte salt may be, for example, a lithium salt. Lithium salts include, for example, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiB(C ₆ H ₅ ) ₄ , LiCH ₃ SO ₃ , CF ₃ SO ₂ OLi, LiN(SO ₂ F) ₂ (Li[FSI], lithium bis at least one member selected from the group consisting of LiN(SO ₂ CF ₃ ) ₂ (Li[TFSI], lithium bistrifluoromethanesulfonylimide), and LiN(SO ₂ CF ₂ CF _{3 )} good. The lithium salt preferably contains LiPF ₆ from the viewpoint of solubility in a non-aqueous solvent, which will be described later, and better performance of the electrochemical device.

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 the nonaqueous solvent, from the viewpoint of excellent charge/discharge characteristics. It is also preferably 1.5 mol/L or less, more preferably 1.3 mol/L or less, even more preferably 1.2 mol/L or less.

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

The additive is a compound other than the compound represented by the above formula (1) and a fluorine-containing cyclic carbonate, such as a cyclic carbonate having a carbon-carbon double bond, a nitrile compound, a cyclic sulfonic acid ester compound, etc. It's good. The content of the additive may be, for example, 0.001% by mass or more and 5% by mass or less based on the total amount of the electrolytic solution.

A cyclic carbonate having a carbon-carbon double bond is a cyclic carbonate ester having a carbon-carbon double bond. In one embodiment, in the cyclic carbonate, two carbon atoms constituting the ring may form a double bond. The cyclic carbonate may be vinylene carbonate, vinylene carbonate, methylvinylene carbonate, dimethylvinylene carbonate (4,5-dimethylvinylene carbonate), ethylvinylene carbonate (4,5-diethylvinylene carbonate), diethylvinylene carbonate, etc. Vinylene carbonate is preferred from the viewpoint of further improving the performance of chemical devices.

A nitrile compound is a compound having at least one cyano group (nitrile group). The nitrile compound may have, for example, one, two or three 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, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, or the like. The nitrile compound having three cyano groups may be, for example, 1,2,3-propanetricarbonitrile, 1,3,5-pentanetricarbonitrile, or the like. As a nitrile compound, from the viewpoint of forming a stable film on the positive electrode or negative electrode and suppressing battery expansion caused by decomposition of the electrolyte, it is recommended to use a nitrile compound that has two or more cyano groups and excludes carbon atoms in the cyano group. Compounds having two or more carbon atoms are preferred. The nitrile compound is more preferably a compound having two or three cyano groups and having two or more carbon atoms excluding carbon atoms in the cyano group. The nitrile compound is more preferably succinonitrile, glutaronitrile, adiponitrile, pimeronitrile, suberonitrile, 1,2,3-propanetricarbonitrile, or 1,3,5-pentanetricarbonitrile, and is suitable for use in electrochemical devices. Particularly preferred is succinonitrile from the viewpoint of further improving performance.

The cyclic sulfonic acid ester compound is a compound having a ring containing one or two -OSO ₂ - groups. Examples of the cyclic sulfonic acid ester compound include 1,3-propane sultone, 1-propene-1,3-sultone, 1,3-propane sultone, 1,4-butane sultone, 2,4-butane sultone, 1,3-propene Sulton, 1,4-butenesultone, 1-methyl-1,3-propane sultone, 3-methyl-1,3-propane sultone, 1-fluoro-1,3-propane sultone, 3-fluoro-1,3-propane It may be a monosulfonic acid ester such as sultone, a disulfonic acid ester such as methylenemethane disulfonic acid ester, ethylenemethane disulfonic acid ester, etc., and from the viewpoint of further improving the performance of the electrochemical device, preferably 1, 3-propane sultone or 1-propene-1,3-sultone.

Next, a method for manufacturing the non-aqueous electrolyte secondary battery 1 will be explained. The method for manufacturing the non-aqueous electrolyte secondary battery 1 includes a first step of obtaining a positive electrode 6, a second step of obtaining a negative electrode 8, a third step of housing the electrode group 2 in a battery exterior body 3, and a fourth step of injecting the electrolyte 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 dispersion machine, etc. to obtain a slurry-like positive electrode mixture, and then this positive electrode mixture is processed by a doctor blade method. The positive electrode 6 is obtained by coating the positive electrode current collector 9 by dipping, spraying, or the like, and then volatilizing the dispersion medium. After volatilizing the dispersion medium, a compression molding step using a roll press may be provided as necessary. The positive electrode mixture layer 10 may be formed as a positive electrode mixture layer with a multilayer structure by performing the steps described above from applying the positive electrode mixture to volatilizing the dispersion medium multiple times. The dispersion medium may be water, 1-methyl-2-pyrrolidone (hereinafter also referred to as NMP), or the like.

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

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

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

In other embodiments, the electrochemical device may be a capacitor. Like the non-aqueous electrolyte secondary battery 1 described above, the capacitor may include an electrode group composed of a positive electrode, a negative electrode, and a separator, and a bag-shaped battery exterior body that houses the electrode group. The details of each component in the capacitor may be the same as those of the non-aqueous electrolyte secondary battery 1.

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

(Example 1)
[Preparation of electrolyte]
In a mixed solution of ethylene carbonate, dimethyl carbonate and diethyl carbonate containing 1 mol/L of LiPF ₆ , 1% by mass of vinylene carbonate (VC) and compound A represented by the following formula (9) were added to the total amount of the mixed solution. An electrolyte solution was prepared by adding 1% by mass (based on the total amount of electrolyte solution).

[ ^19F -NMR measurement]
¹⁹ F-NMR measurement was performed on the prepared electrolyte according to the measurement conditions described above. As a result, a peak derived from PF ₆ ^- and its reactants is shown within the chemical shift range of -100 ppm to -70 ppm, and a peak derived from compound A is shown within the chemical shift range of -180 ppm to -150 ppm. A spectrum was obtained. A spectrum showing a peak derived from compound A is shown in FIG. 3(a).
¹⁹ F-NMR: -73.68ppm, -75.56ppm, -82.74ppm, -85.34ppm, -86.80ppm, -89.65ppm, -162.07ppm

(Example 2)
[Preparation of electrolyte]
An electrolyte solution was prepared in the same manner as in Example 1, except that 1% by mass (based on the total amount of electrolyte solution) of compound B represented by the following formula (10) was added in place of compound A.

[ ^19F -NMR measurement]
¹⁹ F-NMR measurement was performed on the prepared electrolyte. As a result, a peak derived from PF ₆ ^- and its reactants is shown within the chemical shift range of -100 ppm to -70 ppm, and a peak derived from compound B is shown within the chemical shift range of -180 ppm to -150 ppm. A spectrum was obtained. A spectrum showing a peak derived from compound B is shown in FIG. 3(b).
¹⁹ F-NMR: -73.26ppm, -75.14ppm, -82.65ppm, -85.26ppm, -86.79ppm, -89.64ppm, -162.02ppm

(Comparative example 1)
[Preparation of electrolyte]
An electrolytic solution was prepared in the same manner as in Example 1 except that Compound A was not used.

[ ^19F -NMR measurement]
¹⁹ F-NMR measurement was performed on the prepared electrolyte. As a result, a spectrum showing peaks derived from PF ₆ ^- and its reactants within a chemical shift range of -100 ppm to -70 ppm was obtained.
¹⁹ F-NMR: -75.03ppm, -75.28ppm, -76.91ppm, -77.16ppm, -88.07ppm, -90.92ppm

(Comparative example 2)
[Preparation of electrolyte]
Example 1 except that Compound A was not used and 1% by mass (based on the total amount of electrolyte solution) of 4-fluoro-1,3-dioxolan-2-one (fluoroethylene carbonate; FEC) was added. An electrolytic solution was prepared in the same manner as above.

[ ^19F -NMR measurement]
¹⁹ F-NMR measurement was performed on the prepared electrolyte. As a result, peaks derived from PF ₆ ^- and its reactants are shown within the chemical shift range of -100 ppm to -70 ppm, and peaks derived from FEC are shown within the chemical shift range of -130 ppm to -110 ppm. A spectrum was obtained. FIG. 4 shows a spectrum showing peaks derived from FEC.
¹⁹ F-NMR: -73.69ppm, -75.57ppm, -82.62ppm, -85.22ppm, -86.82ppm, -89.67ppm, -121.30ppm

(Example 3)
[Preparation of electrolyte]
An electrolyte solution was prepared in the same manner as in Example 1, except that 1% by mass (based on the total amount of electrolyte solution) of compound C represented by the following formula (11) was added in place of compound A.

[ ^19F -NMR measurement]
¹⁹ F-NMR measurement was performed on the prepared electrolyte. As a result, a peak derived from PF ₆ ^- and its reactants was found within the chemical shift range of -100 ppm to -70 ppm, and a peak derived from compound C was found within the chemical shift range of more than -150 ppm to -110 ppm. The spectrum shown was obtained. A spectrum showing a peak derived from compound C is shown in FIG. 5(a).
¹⁹ F-NMR: -73.66ppm, -75.54ppm, -82.65ppm, -85.25ppm, -86.81ppm, -89.66ppm, -135.13ppm

(Example 4)
[Preparation of electrolyte]
An electrolyte solution was prepared in the same manner as in Example 1, except that 1% by mass (based on the total amount of electrolyte solution) of compound D represented by the following formula (12) was added in place of compound A.

[ ^19F -NMR measurement]
¹⁹ F-NMR measurement was performed on the prepared electrolyte. As a result, a peak derived from PF ₆ ^- and its reactants was found within the chemical shift range of -100 ppm to -70 ppm, and a peak derived from Compound D was found within the chemical shift range of more than -150 ppm to -110 ppm. The spectrum shown was obtained. A spectrum showing a peak derived from Compound D is shown in FIG. 5(b).
¹⁹ F-NMR: -73.62ppm, -75.49ppm, -82.76ppm, -85.37ppm, -86.78ppm, -89.63ppm, -136.60ppm

(Example 5)
[Preparation of electrolyte]
In Example 1, the electrolyte solution was prepared in the same manner as in Example 1, except that the content of Compound A was changed to 0.5% by mass and 0.5% by mass of FEC was added (both based on the total amount of electrolyte solution). Prepared.

[ ^19F -NMR measurement]
¹⁹ F-NMR measurement was performed on the prepared electrolyte. As a result, a peak derived from PF ₆ ^- and its reactants was found within the chemical shift range of -100 ppm to -70 ppm, a peak derived from compound A was found within the chemical shift range of -180 ppm to -150 ppm, and A spectrum showing a peak derived from FEC within a chemical shift range of more than -130 ppm and less than -110 ppm was obtained. A spectrum showing a peak derived from Compound A and a peak derived from FEC is shown in FIG. 6(a).
¹⁹ F-NMR: -73.69ppm, -75.58ppm, -82.73ppm, -85.25ppm, -86.85ppm, -89.70ppm, -121.45ppm, -162.10ppm

(Example 6)
[Preparation of electrolyte]
In Example 3, the electrolyte solution was prepared in the same manner as in Example 3, except that the content of compound C was changed to 0.5% by mass, and 0.5% by mass of FEC was added (both based on the total amount of electrolyte solution). Prepared.

[ ^19F -NMR measurement]
¹⁹ F-NMR measurement was performed on the prepared electrolyte. As a result, a peak derived from PF ₆ ^- and its reactants was found within the chemical shift range of -100 ppm to -70 ppm, a peak derived from compound C was found within the chemical shift range of more than -150 ppm to -130 ppm, and , a spectrum showing a peak derived from FEC within a chemical shift range of more than -130 ppm and less than -110 ppm was obtained. A spectrum showing a peak derived from Compound C and a peak derived from FEC is shown in FIG. 6(b).
¹⁹ F-NMR: -73.67ppm, -75.55ppm, -82.68ppm, -85.25ppm, -86.80ppm, -89.65ppm, -121.23ppm, -135.14ppm

(Example 7)
[Preparation of electrolyte]
In Example 4, the electrolyte solution was prepared in the same manner as in Example 4, except that the content of Compound D was changed to 0.5% by mass and 0.5% by mass of FEC was added (all based on the total amount of electrolyte solution). Prepared.

[ ^19F -NMR measurement]
¹⁹ F-NMR measurement was performed on the prepared electrolyte. As a result, a peak derived from PF ₆ ^- and its reactants was found within the chemical shift range of -100 ppm to -70 ppm, a peak derived from compound D was found within the chemical shift range of more than -150 ppm to -130 ppm, and , a spectrum showing a peak derived from FEC within a chemical shift range of more than -130 ppm and less than -110 ppm was obtained. A spectrum showing a peak derived from Compound D and a peak derived from FEC is shown in FIG. 7(c).
¹⁹ F-NMR: -73.68ppm, -75.57ppm, -82.57ppm, -85.17ppm, -86.83ppm, -89.68ppm, -121.35ppm, -136.69ppm

[Preparation of positive electrode]
Lithium cobalt oxide (95% by mass) as a positive electrode active material, fibrous graphite (1% by mass) and acetylene black (AB) (1% by mass) as a conductive agent, and a binder (3% by mass). were added sequentially and mixed. NMP as a dispersion medium was added to the obtained mixture and kneaded to prepare a slurry-like positive electrode mixture. A predetermined amount of this positive electrode mixture was applied evenly and homogeneously onto an aluminum foil having a thickness of 20 μm as a positive electrode current collector. Thereafter, the dispersion medium was volatilized, and the material was compacted by pressing to a density of 3.6 g/cm ³ to obtain a positive electrode.

[Preparation of negative electrode]
A binder and carboxymethyl cellulose as a thickener were added to graphite and silicon oxide as negative electrode active materials. Regarding these mass ratios, graphite: silicon oxide: binder: thickener = 92:5:1.5:1.5. Water as a dispersion medium was added to the obtained mixture, and the mixture was kneaded to prepare a slurry-like negative electrode mixture. A predetermined amount of this negative electrode mixture was applied evenly and homogeneously 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 the material was compacted by pressing to a density of 1.6 g/cm ³ to obtain a negative electrode.

[Fabrication of lithium ion secondary battery]
A positive electrode cut into a 13.5 cm ² square was sandwiched between polyethylene porous sheets (product name: Hipore (registered trademark), manufactured by Asahi Kasei Corporation, thickness 30 μm) as separators, and further cut into a 14.3 cm ² square. An electrode group was created by overlapping the cut negative electrodes. This electrode group was housed in a container (battery exterior body) formed of an aluminum laminate film (trade name: aluminum laminate film, manufactured by Dainippon Printing Co., Ltd.). Next, 1 mL of each of the electrolytic solutions of Example 1, Example 2, Comparative Example 1, or Comparative Example 2 prepared in Example 1, Example 2, Comparative Example 1, or Comparative Example 2 was added into the container, and the container was thermally welded to produce a lithium ion secondary battery for evaluation. .

[Initial charge/discharge]
The produced lithium ion battery was charged and discharged for the first time using the method shown below. First, constant current charging was performed at a current value of 0.1 C in an environment of 25° C. to an upper limit voltage of 4.2 V, and then constant voltage charging was performed at 4.2 V. The charging termination condition was a current value of 0.01C. Thereafter, constant current discharge was performed at a current value of 0.1C and a final voltage of 2.5V. This charge/discharge cycle was repeated three times ("C" used as the unit of current value means "current value (A)/battery capacity (Ah)").

[Evaluation of cycle characteristics]
After the initial charging and discharging, the cycle characteristics of each secondary battery using the electrolyte solutions of Examples 1 and 2 and Comparative Examples 1 and 2 were evaluated by a cycle test in which charging and discharging were repeated. As a charging pattern, in an environment of 45° C., the secondary battery was charged with a constant current at a current value of 0.5 C to an upper limit voltage of 4.2 V, and then charged with a constant voltage at 4.2 V. The charging termination condition was a current value of 0.05C. Regarding discharge, constant current discharge was performed at 1C to 2.5V, and the discharge capacity was determined. This series of charging and discharging was repeated for 200 cycles, and the discharge capacity was measured each time the charging and discharging was performed. Assuming that the discharge capacity after the first charge/discharge cycle in Comparative Example 1 was 1, the relative value of the discharge capacity (discharge capacity ratio) in each cycle was determined. FIG. 7 shows the relationship between the number of cycles and the relative value of discharge capacity.

As shown in FIG. 7, in the lithium ion secondary batteries of Examples 1 and 2, in which the electrolyte solution exhibiting a peak within the chemical shift range of -180 ppm or more and -150 ppm or less in measurement by ¹⁹ F-NMR, the The discharge capacity ratio at the 200th cycle was larger than that of the lithium ion secondary batteries of Comparative Examples 1 and 2 in which an electrolyte solution that did not show a peak in the range was applied. Therefore, the lithium ion secondary batteries of Examples 1 and 2 exhibit excellent performance (cycle characteristics).

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

Claims (7)

The following formula (1):
[In the formula, R ¹ to R ³ each independently represent an alkyl group or a fluorine atom, R ⁴ represents an alkylene group, R ⁵ represents an organic group containing a sulfur atom or a nitrogen atom, and R ¹ to At least one of R ³ is a fluorine atom. ]
An electrolytic solution containing a compound represented by
An electrolytic solution that exhibits a peak within at least one chemical shift range of -180 ppm or more and -150 ppm or less and more than -150 ppm and -130 ppm or less when measured by ¹⁹ F-NMR. The electrolytic solution according to claim 1, which further exhibits a peak within a chemical shift range of more than -130 ppm and less than -110 ppm when measured by ¹⁹ F-NMR. An electrochemical device comprising a positive electrode, a negative electrode, and the electrolytic solution according to claim 1 or 2. The electrochemical device according to claim 3, wherein the negative electrode contains a carbon material. The electrochemical device according to claim 4, wherein the carbon material contains graphite. The electrochemical device according to claim 4 or 5, 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 4 to 6, wherein the electrochemical device is a non-aqueous electrolyte secondary battery or a capacitor.

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