WO2023008569A1

WO2023008569A1 - Electrochemical device, electrolyte solution, and additive used for electrolyte solution

Info

Publication number: WO2023008569A1
Application number: PCT/JP2022/029343
Authority: WO
Inventors: 馨今野; 薫平山田; 洋介池田; 晃士入江
Original assignee: 昭和電工マテリアルズ株式会社; 昭和電工株式会社
Priority date: 2021-07-29
Filing date: 2022-07-29
Publication date: 2023-02-02
Also published as: JPWO2023008569A1

Abstract

An electrochemical device which is provided with a positive electrode, a negative electrode and an electrolyte solution, wherein: the negative electrode contains a silicon-based active material; and the electrolyte solution contains a compound represented by formula (1).　In formula (1), each of R1 to R3 independently represents a hydrogen atom or a methyl group; and X represents a divalent organic group.

Description

Electrochemical devices, electrolytes, and additives used in electrolytes

The present invention relates to an electrochemical device, an electrolytic solution, and an additive used in the electrolytic solution.

In recent years, due to 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 means for improving the performance of electrochemical devices, for example, a method of adding a predetermined additive to the electrolytic solution has been investigated. For example, Patent Document 1 discloses a non-aqueous electrolytic solution containing a specific acrylate compound as an additive.

International Publication No. 2012/147502 Pamphlet

According to the studies of the present inventors, it was found that even if the additive is the same, if the type of the negative electrode (negative electrode active material, etc.) changes, the effect of the additive is different. More specifically, among the acrylate compounds described in Patent Document 1, when used in an electrochemical device having a negative electrode containing a silicon-based active material, the addition of the acrylate compound has a significantly different effect.

An object of the present invention is to improve the cycle characteristics of an electrochemical device having a negative electrode containing a silicon-based active material.

The present inventors have found that in an electrochemical device comprising a negative electrode containing a silicon-based active material, the use of an electrolytic solution containing a specific acrylate compound improves the cycle characteristics of the electrochemical device.

The present invention includes the following aspects.
[1] An electrochemical device comprising a positive electrode, a negative electrode, and an electrolytic solution, wherein the negative electrode contains a silicon-based active material, and the electrolytic solution contains a compound represented by the following formula (1): , electrochemical devices.

In formula (1), R ¹ to R ³ each independently represent a hydrogen atom or a methyl group, and X represents a divalent organic group.
[2] The electrochemical device according to [1], wherein R ¹ and R ² in formula (1) are hydrogen atoms.
[3] The electrochemical device according to [1] or [2], wherein X in formula (1) is an alkylene group having 1 to 6 carbon atoms.
[4] The electrochemical device according to [1] or [2], wherein X in formula (1) is an ethylene group.
[5] The electricity according to any one of [1] to [4], wherein the content of the compound represented by formula (1) is 0.001% by mass or more and 5% by mass or less based on the total amount of the electrolyte chemical device.
[6] The electrochemical device according to any one of [1] to [5], which is a non-aqueous electrolyte secondary battery or capacitor.

[7] An electrolytic solution used in an electrochemical device having a negative electrode containing a silicon-based active material, the electrolytic solution containing a compound represented by the following formula (1).

In formula (1), R ¹ to R ³ each independently represent a hydrogen atom or a methyl group, and X represents a divalent organic group.
[8] The electrolytic solution according to [7], wherein R ¹ and R ² in formula (1) are hydrogen atoms.
[9] The electrolytic solution according to [7] or [8], wherein X in formula (1) is an alkylene group having 1 to 6 carbon atoms.
[10] The electrolytic solution according to [7] or [8], wherein X in formula (1) is an ethylene group.
[11] The electrolysis according to any one of [7] to [10], wherein the content of the compound represented by formula (1) is 0.001% by mass or more and 5% by mass or less based on the total amount of the electrolytic solution. liquid.

[12] An additive used in an electrolytic solution of an electrochemical device having a negative electrode containing a silicon-based active material, the additive containing a compound represented by the following formula (1).

In formula (1), R ¹ to R ³ each independently represent a hydrogen atom or a methyl group, and X represents a divalent organic group.
[13] The additive according to [12], wherein R ¹ and R ² in formula (1) are hydrogen atoms.
[14] The additive according to [12] or [13], wherein X in formula (1) is an alkylene group having 1 to 6 carbon atoms.
[15] The additive according to [12] or [13], wherein X in formula (1) is an ethylene group.

According to one aspect of the present invention, it is possible to improve the cycle characteristics of an electrochemical device provided with a negative electrode containing a silicon-based active material. According to another aspect of the present invention, the direct current resistance (discharge DCR) during discharge after storing the electrochemical device at high temperature can be reduced.

1 is a perspective view showing a non-aqueous electrolyte secondary battery as an electrochemical device according to one embodiment; FIG. FIG. 2 is an exploded perspective view showing an electrode group of the secondary battery shown in FIG. 1; 4 is a graph showing the results of cycle tests in Examples and Comparative Examples. 4 is a graph showing measurement results of resistance increase rates in Examples and Comparative Examples. It is a graph which shows the result of the CV measurement of the electrolyte solution in an evaluation example. It is a graph which shows the result of the pH measurement of the electrolyte solution in an evaluation example.

Hereinafter, embodiments of the present invention will be described 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 non-aqueous electrolyte secondary battery. As shown in FIG. 1 , the non-aqueous electrolyte secondary battery 1 includes an electrode group 2 composed of a positive electrode, a negative electrode, and a separator, and a bag-like battery casing 3 that accommodates the electrode group 2 . A positive electrode current collecting tab 4 and a negative electrode current collecting tab 5 are provided on the positive electrode and the negative electrode, respectively. The positive electrode current collecting tab 4 and the negative electrode current collecting tab 5 protrude from the inside of the battery exterior body 3 to the outside so that the positive electrode and the negative electrode can be electrically connected to the outside of the non-aqueous electrolyte secondary battery 1, respectively. . The battery outer casing 3 is filled with an electrolytic solution (not shown). The nonaqueous 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 outer package 3 may be a container made of, for example, a laminated film. The laminated film may be, for example, a laminated film in which a resin film such as a polyethylene terephthalate (PET) film, a metal foil such as aluminum, copper, 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 so 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 . A positive current collector tab 4 is provided on the positive current collector 9 .

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

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

The positive electrode active material may be, for example, 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- _{yM y} _O _z , Li _x Mn ₂ O ₄ and Li _x Mn _2- _{y My} O ₄ (wherein M is Na, Mg, Sc, Y, Mn, Fe, Co, Cu, Zn, Al , Cr, Pb, Sb, V and B (wherein 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). Lithium oxide represented by Li _x Ni _1-yM _y O _z is Li _x Ni _1-(y1+y2) Co _y1 Mn _y2 O _z (where x and z are the same as described above and y1= 0 to 0.9, y2=0 to 0.9, and y1+y2=0 to 0.9), for example LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , _{LiNi0.5Co0.2Mn0.3O2} _, _{LiNi0.6Co0.2Mn0.2O2} _, _{LiNi0.8Co0.1Mn0.1O2} _. _{_} _{_} _{_} _{_} _{_} _{_} Lithium oxide represented by Li _x Ni _1-yM _y O _z is Li _x Ni _1-(y3+y4) Co _y3 Al _y4 O _z (where x and z are the same as described above and y3= 0 to 0.9, y4=0 to 0.9, and y3+y4=0 to 0.9.), for example LiNi _0.8 Co _0.15 Al _0.05 O ₂ There may be.

The positive electrode active material may be, for example, lithium phosphate. Examples of lithium phosphates include lithium manganese phosphate ( _LiMnPO4 ), lithium iron phosphate ( _LiFePO4 ), lithium cobalt phosphate ( _LiCoPO4 ) and lithium vanadium phosphate ₍ _Li3V2 ₍ PO4). ₃ ).

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

The conductive agent may be carbon black such as acetylene black 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% by mass or more, 0.1% by mass or more, or 1% by mass or more, and 50% by mass or less, or 30% by mass, based on the total amount of the positive electrode mixture layer. or less, or 15% by mass or less.

Binders include resins such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose; SBR (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), fluororubber , isoprene rubber, butadiene rubber, ethylene-propylene rubber; Thermoplastic elastomers such as ethylene copolymers, styrene/isoprene/styrene block copolymers or hydrogenated products thereof; syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene/vinyl acetate copolymers, propylene/α - Soft resins such as olefin copolymers; polyvinylidene fluoride (PVDF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, polytetrafluoroethylene/ethylene copolymers, polytetrafluoroethylene/vinylidene fluoride copolymers, etc. a resin having a nitrile group-containing monomer as a monomer unit; and a polymer composition having ion conductivity for alkali metal ions (eg, lithium ions).

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

The separator 7 is particularly limited as long as it electronically insulates between the positive electrode 6 and the negative electrode 8, allows ions to pass therethrough, and has resistance to oxidation on the positive electrode 6 side and reducibility on the negative electrode 8 side. not. Examples of materials (materials) for such a separator 7 include resins and inorganic substances.

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

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 material is adhered to a thin-film base material such as non-woven fabric, woven fabric, or 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 collector tab 5 is provided on the negative electrode collector 11 .

The negative electrode current collector 11 is made of copper, stainless steel, nickel, aluminum, titanium, baked carbon, conductive polymer, conductive glass, aluminum-cadmium alloy, or the like. The negative electrode current collector 11 may be one in which the surface of copper, aluminum, or the like is treated with carbon, nickel, titanium, silver, or the like for the purpose of improving adhesiveness, conductivity, and resistance to reduction. The thickness of the negative electrode current collector 11 is, for example, 1 to 50 μm in terms of electrode strength and energy density.

The negative electrode mixture layer 12 contains a negative electrode active material. The shape of the negative electrode active material may be, for example, particulate. The negative electrode active material contains a silicon-based active material. The silicon-based active material contains at least silicon (Si) as a constituent element. The silicon-based active material may be a simple substance of silicon or a compound containing silicon and other elements. The compound may be an alloy containing silicon and at least one selected from the group consisting of nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony and chromium. The compound may be an oxide, nitride or carbide of silicon. Silicon oxides include, for example, SiOx (SiO, _SiO2 , etc.) and LiSiO. _Nitrides of silicon include, for example, _Si3N4 _and _Si2N2O . Examples of carbides of silicon include SiC.

The negative electrode active material may further contain a negative electrode active material other than the silicon-based active material. Examples of negative electrode active materials other than silicon-based active materials include carbon-based active materials. Examples of carbon materials that make up the carbon-based active material include amorphous carbon materials, natural graphite, composite carbon materials in which a film of an amorphous carbon material is formed on natural graphite, and artificial graphite (resin raw materials such as epoxy resin and phenol resin). , or those obtained by firing pitch-based raw materials obtained from petroleum, coal, etc.).

From the viewpoint of increasing the capacity of electrochemical devices, the carbon-based active material is preferably a graphite-based active material composed of graphite. Graphite preferably has a carbon network interlayer (d002) of less than 0.34 nm, more preferably 0.3354 nm or more and 0.337 nm or less, as determined by wide-angle X-ray diffraction. A carbon material (graphite) that satisfies such conditions is sometimes referred to as quasi-anisotropic carbon.

In addition to the above negative electrode active materials, the negative electrode active material is composed of metal composite oxides, oxides or nitrides of group 4 elements such as tin and germanium, elemental lithium, lithium alloys such as lithium aluminum alloys, and the like. may further include a negative electrode active material.

The negative electrode active material preferably contains a silicon-based active material and a carbon-based active material, and more preferably contains a silicon-based active material and a graphite-based active material, from the viewpoint of further improving the performance of the electrochemical device such as low-temperature input characteristics. . In this case, the content of the silicon-based active material may be 1 part by mass or more, 2 parts by mass or more, or 3 parts by mass or more with respect to the total amount of 100 parts by mass of the silicon-based active material and the carbon-based active material. , 30 parts by mass or less, 20 parts by mass or less, or 10 parts by mass or less.

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

The negative electrode mixture layer 12 may further contain a binder. 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. The thickener is not particularly limited, but may be carboxymethylcellulose, methylcellulose, hydroxymethylcellulose, ethylcellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, salts thereof, and the like. The thickener may be one of these alone or a mixture of two or more thereof.

When the negative electrode mixture layer 12 contains a thickener, its 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 mass % or less.

The electrolytic solution, in one embodiment, contains a compound represented by the following formula (1), an electrolyte salt, and a non-aqueous solvent.

In formula (1), R ¹ to R ³ each independently represent a hydrogen atom or a methyl group, and X represents a divalent organic group.

In other words, in one embodiment, the compound represented by formula (1) is an additive used in the electrolytic solution of the electrochemical device 1.

R ¹ and R ² are preferably hydrogen atoms. R ³ is preferably a hydrogen atom from the viewpoint of further improving cycle characteristics.

X may be, for example, a divalent hydrocarbon group or an alkylene group. The alkylene group may be linear or branched. The number of carbon atoms in the divalent hydrocarbon group and alkylene group may be, for example, 1-6. The lower limit of the number of carbon atoms may be 2 or more. The upper limit of the carbon number may be 5 or less or 4 or less. The alkylene group represented by X may be methylene, ethylene, propylene, butylene or pentylene, preferably ethylene.

X may be, for example, a divalent group in which part of the divalent hydrocarbon group is substituted with a heteroatom. A heteroatom may be, for example, an oxygen atom. X may be, for example, a divalent group having an ether structure in which a portion of a divalent hydrocarbon group is substituted with oxygen atoms. X may be, for example, a divalent group represented by the following formula (2).
-X ¹ -OX ² - (2)
In formula (2), X ¹ and X ² each independently represent an alkylene group. The alkylene group may be linear or branched. The number of carbon atoms in the alkylene groups represented by X ¹ and X ² may each independently be 1-6, 1-5, 1-4, 1-3, or 1-2.

The content of the compound represented by formula (1) is preferably 0.001% by mass or more, based on the total amount of the electrolyte, from the viewpoint of further improving the performance (especially cycle characteristics) of the electrochemical device. More preferably 0.005% by mass or more, still more preferably 0.01% by mass or more, particularly preferably 0.05% by mass or more, even more preferably 0.1% by mass or more, preferably 8% by mass or less, More preferably 5% by mass or less, still more preferably 3% by mass or less, particularly preferably 2% by mass or less, and even more preferably 1% by mass or less.

The electrolyte salt may be, for example, a lithium salt. Lithium salts are, for example, _LiPF6 , LiBF4, LiClO4, LiB( _C6H5 ) ₄ , _LiCH3SO3 _, _CF3SO2OLi _, LiN ₍ _SO2F ) ₂ ₍ Li[FSI], lithium _bis fluorosulfonylimide), LiN(SO ₂ CF ₃ ) ₂ (Li[TFSI], lithium bistrifluoromethanesulfonylimide), and LiN(SO ₂ CF ₂ CF ₃ ) ₂ at least one selected from the group consisting of good. The lithium salt preferably contains LiPF ₆ from the viewpoint of further improving solubility in solvents, charge/discharge characteristics, output characteristics, cycle characteristics, etc. of the secondary battery.

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

Non-aqueous solvents are, for example, chain carbonate compounds such as dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, and methyl butyl carbonate. Alternatively, cyclic carbonate compounds such as ethylene carbonate, propylene carbonate and butylene carbonate. Alternatively, chain carboxylic acid ester compounds such as methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, and propyl propionate. cyclic carboxylic acid ester compounds such as γ-butyl lactone; Alternatively, chain ether compounds such as dimethoxymethane, dimethoxyethane and diethoxyethane. Alternatively, cyclic ether compounds such as tetrahydrofuran, tetrahydropyran, and dioxolane. Alternatively, it may be a nitrile compound such as acetonitrile, or a sulfur compound such as sulfolane. The non-aqueous solvent may be one of these alone or a mixture of two or more, preferably a mixture of two or more.

The electrolytic solution may further contain materials other than the compound represented by Formula (1), the electrolyte salt, and the non-aqueous solvent. Other materials include, for example, unsaturated cyclic carbonates, fluorine-containing cyclic carbonates, compounds containing nitrogen atoms, sulfur atoms, or nitrogen and sulfur atoms other than compounds represented by formula (1), cyclic carboxylic acid esters, and the like. can be

Examples of unsaturated cyclic carbonates include vinylene carbonate, methylvinylene carbonate, dimethylvinylene carbonate (4,5-dimethylvinylene carbonate), ethylvinylene carbonate (4,5-diethylvinylene carbonate), diethylvinylene carbonate, vinylethylene carbonate, and the like. and preferably vinylene carbonate from the viewpoint of further improving the performance of the electrochemical device. Fluorine-containing cyclic carbonates include, for example, 4-fluoro-1,3-dioxolan-2-one (fluoroethylene carbonate; FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2 -trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, etc., preferably 4-fluoro-1,3-dioxolan-2-one (fluoroethylene carbonate; FEC). The compound containing a nitrogen atom other than the compound represented by formula (1) may be, for example, a nitrile compound such as succinonitrile. Compounds containing a sulfur atom other than the compound represented by formula (1) may be, for example, cyclic sulfonate compounds such as 1,3-propanesultone and 1-propene-1,3-sultone.

The present inventors improved the cycle characteristics of an electrochemical device by using the electrolytic solution containing the compound represented by the above formula (1) in an electrochemical device provided with a negative electrode containing a silicon-based active material. I found that it can be done. The present inventors presume the effects of using the compound represented by formula (1) in the electrolytic solution as follows. That is, the compound represented by the formula (1) forms a stable and dense film on the negative electrode containing the silicon-based active material, and this film suppresses the decomposition of the electrolyte, so that the cycle of the secondary battery is improved. It is considered that the improvement of the characteristics has been achieved. Further, in one embodiment, by using the electrolytic solution containing the compound represented by the above formula (1) in an electrochemical device having a negative electrode containing a silicon-based active material, The compound forms a stable coating on the negative electrode containing a silicon-based active material, and this coating suppresses the decomposition of the electrolyte solution. DCR) can be reduced.

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

In the first step, the material used for the positive electrode mixture layer 10 is dispersed in a dispersion medium using a kneader, a disperser, or the like to obtain a slurry-like positive electrode mixture. The positive electrode 6 is obtained by coating the positive electrode current collector 9 by a dipping method, a spray method, or the like, and then volatilizing the dispersion medium. After volatilizing the dispersion medium, if necessary, a compression molding step using a roll press may be provided. The positive electrode mixture layer 10 may be formed as a positive electrode mixture layer having a multi-layer structure by performing the steps from applying the positive electrode mixture to volatilizing the dispersion medium a plurality of times. The dispersion medium may be water, 1-methyl-2-pyrrolidone (hereinafter also referred to as NMP), or the like.

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

In the third step, the electrode group 2 is formed by sandwiching the separator 7 between the produced positive electrode 6 and negative electrode 8 . Next, this electrode group 2 is accommodated in the battery outer package 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.

As another embodiment, 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-like battery outer body that accommodates 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 .

The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

(Example 1)
[Preparation of positive electrode]
Acetylene black (AB) (4% by mass) as a conductive agent and PVDF (4% by mass) as a binder were successively added to nickel cobalt lithium manganate (92% by mass) as a positive electrode active material and mixed. . NMP as a dispersion medium was added to the resulting mixture, and the mixture was kneaded to prepare a slurry positive electrode mixture. A predetermined amount of this positive electrode mixture was evenly and homogeneously applied to an aluminum foil having a thickness of 20 μm as a positive electrode current collector. Then, after volatilizing the dispersion medium, it was compressed to a density of 2.8 g/cm ³ by pressing to obtain a positive electrode.

[Preparation of negative electrode]
As the negative electrode active material, a silicon-based active material (SiOx (0<x<2.0), average particle size (50% particle size of volume cumulative particle size distribution); about 10 μm) and a graphite-based active material (artificial graphite, average particle size diameter (D50); about 23 μm). SBR as a binder and carboxymethyl cellulose as a thickener were added to these active materials. The mass ratio of these materials was graphite active material:silicon-based active material: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 evenly and homogeneously applied to a rolled copper foil having a thickness of 10 μm as a negative electrode current collector. Thereafter, after volatilizing the dispersion medium, the mixture was compressed to a density of 1.6 g/cm ³ by pressing to obtain a negative electrode.

[Production of lithium ion secondary battery]
A positive electrode cut into a square of 13.5 cm ² was sandwiched between polyethylene porous sheets (thickness 30 μm) as a separator, and a negative electrode cut into a square of 14.3 cm ² was overlaid to prepare an electrode group. This electrode group was accommodated in a container (battery outer package) formed of an aluminum laminate film (trade name: aluminum laminate film, manufactured by Dai Nippon Printing Co., Ltd.). Next, 1 mL of the electrolytic solution was added into the container, and the container was thermally welded to produce a lithium ion secondary battery for evaluation. As the electrolytic solution, a mixed solution of ethylene carbonate/dimethyl carbonate/ethyl methyl carbonate = 1/1/1 (volume ratio) containing 1 mol/L of LiPF ₆ was mixed with a compound X represented by the following formula (X) to 0. 0.5% by mass, 1% by mass of vinylene carbonate, and 1% by mass of fluoroethylene carbonate (all based on the total amount of the electrolytic solution) were added.

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

(Example 3)
Lithium ion secondary was produced in the same manner as in Example 1 except that an electrolyte solution in which 0.5% by mass based on the total amount of the electrolyte solution was added with compound Y represented by the following formula (Y) instead of compound X was used. A battery was produced.

(Comparative example 1)
A lithium ion secondary battery was produced in the same manner as in Example 1, except that the compound X was not added to the electrolytic solution.

(Comparative example 2)
Lithium ion secondary was produced in the same manner as in Example 1, except that an electrolyte solution in which 0.5% by mass of a compound Z represented by the following formula (Z) was added based on the total amount of the electrolyte solution was used instead of the compound X. A battery was produced.

(Comparative Example 3)
A lithium ion secondary battery was produced in the same manner as in Example 1, except that an electrolytic solution containing 0.2% by mass of hexamethylene diisocyanate (HDI) based on the total amount of the electrolytic solution was used instead of compound X.

[Initial charge/discharge]
Each lithium ion battery produced was subjected to initial charge/discharge by the method described below. First, under an environment of 25° C., constant current charging was performed with a current value of 0.1 C up to an upper limit voltage of 4.2V, and then constant voltage charging was performed at 4.2V. A charge 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 2.7V. This charging/discharging cycle was repeated three times (“C” used as a unit of current value means “current value (A)/battery capacity (Ah)”).

[Evaluation of cycle characteristics]
After the initial charge/discharge, the cycle characteristics of each secondary battery were evaluated by a cycle test in which charge/discharge was repeated. As a charging pattern, in an environment of 45° C., the secondary batteries of Examples 1 to 3 and Comparative Examples 1 and 2 were subjected to constant current charging at a current value of 0.5 C up to an upper limit voltage of 4.2 V. Constant voltage charging was performed at 4.2V. A charge termination condition was a current value of 0.05C. As for the discharge, constant current discharge was performed at 1.0 C to 2.7 V, and the discharge capacity was obtained. This series of charging/discharging was repeated 500 cycles, and the discharge capacity was measured each time charging/discharging was performed. A relative value of the discharge capacity in each cycle (discharge capacity retention rate (%)) with respect to the discharge capacity after the first cycle of charge and discharge was determined. The results of the cycle test are shown in FIG.

The discharge capacity retention rates at the 500th cycle of Examples 1 to 3 using the electrolyte solution containing compound X or compound Y are 84.2%, 83.2%, and 83.7%, respectively. It was clarified that the cycle characteristics were improved more than the discharge capacity retention rate (81.5%) at the 100th cycle of Comparative Example 1, which did not contain. The reason for this is thought to be that compound X or compound Y forms a stable and dense film on the negative electrode, and this film suppresses the decomposition of the electrolytic solution, thereby improving the cycle characteristics of the secondary battery. In addition, the discharge capacity retention rates of Comparative Example 2 using the electrolytic solution containing compound Z and Comparative Example 3 using the electrolytic solution containing HDI were 82.2% and 82.3%, respectively. Although the cycle characteristics are improved as compared with Comparative Example 1 which does not contain, the cycle characteristics improvement effect of Examples 1 to 3 was superior. Although the reason for this is not clear, compared to compound Z and HDI, compound X and compound Y can form a stable and dense coating on the negative electrode even when added in small amounts. It is considered that the characteristics have improved.

[High temperature storage test]
For each of the secondary batteries of Examples 1 to 3 and Comparative Examples 1 and 3, after performing the above-described initial charge and discharge, constant current charging was performed at a current value of 0.1 C in an environment of 25 ° C. with an upper limit voltage of 4.2 V. After that, constant voltage charging was performed at 4.2V. A charge termination condition was a current value of 0.01C. After that, those secondary batteries were stored in a constant temperature bath at 60° C. for 4 weeks.

[Measurement of discharge DCR]
The discharge DCR (R1) of each secondary battery before high temperature storage and the discharge DCR (R2) measured after standing in an environment of 25 ° C. for 30 minutes after high temperature storage were measured, and the measured R1 and Using R2, resistance increase rate (%)=R2/R1×100 was calculated. The results are shown in FIG.
Discharge DCR (direct current resistance during discharge) was measured as follows.
First, constant current charging at 0.2C was performed up to an upper limit voltage of 4.2V, and then constant voltage charging was performed at 4.2V. A charge termination condition was a current value of 0.02C. Thereafter, constant current discharge was performed at a current value of 0.2 C and a final voltage of 2.7 V. The current value at this time was I _{0.2 C} , and the voltage change 10 seconds after the start of discharge was ΔV _{0.2 C.} Next, constant-current charging at 0.2 C was performed up to an upper limit voltage of 4.2 V, followed by constant-voltage charging at 4.2 V (the charging termination condition was a current value of 0.02 C). Thereafter, constant current discharge was performed at a current value of 0.5 C and a final voltage of 2.7 V. The current value at this time was I _{0.5 C} , and the voltage change 10 seconds after the start of discharge was ΔV _{0.5 C.} From the same charge/discharge, the current value at 1C was evaluated as I _1C , and the voltage change ΔV _1C after 10 seconds from the start of discharge was evaluated. _Using the _least _- _squares _method , _linear An approximate straight line was drawn, and the slope thereof was taken as the discharge DCR value.

Examples 1 to 3 show resistance increase rates of 128%, 144%, and 138%, respectively, and suppress the resistance increase due to high-temperature storage more than Comparative Examples 1 and 3 (resistance increase rates of 153% and 158%, respectively). It became clear that it was possible. The reason for this is thought to be that compound X and compound Y formed a stable coating on the negative electrode, and this coating suppressed the decomposition of the electrolyte solution, thereby suppressing the increase in resistance of the secondary battery due to high-temperature storage.

As described above, the lithium ion secondary batteries of Examples 1 to 3 to which the electrolytic solution containing the compound X or the compound Y is applied are the lithium ion secondary batteries of Comparative Example 1 that do not contain the above compound, and the compound Z. Compared to the lithium ion secondary batteries of Comparative Example 2, in which the electrolyte solution containing HDI was applied, and Comparative Example 3, in which the electrolyte solution containing HDI was applied, the lithium ion secondary battery exhibited excellent life characteristics and high-temperature storage characteristics.

(Evaluation examples 1-1 to 1-4)
[Measurement of electrolyte reduction stability]
Cyclic voltammetry (CV) was measured to evaluate the reduction stability of the electrolytic solution. As a cell for CV evaluation, a 2016 type coin cell was prepared using SUS as a working electrode, metallic lithium as a counter electrode, a polyethylene microporous membrane having a thickness of 30 μm as a separator, and an electrolytic solution. As the electrolytic solution, a mixed solution of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate = 1/1/1 (volume ratio) containing 1 mol / L LiPF ₆ was mixed with the additives shown in Table 1 based on the total amount of the electrolytic solution. Each electrolytic solution of Evaluation Examples 1-1 to 1-4, which was added in the amount shown in Table 1, was used. As for the CV measurement conditions, the reduction stability of the electrolytic solution was evaluated by scanning the voltage range of 2.0 V to 0 V at 0.2 mV/s for 3 cycles in an environment of 25°C. FIG. 5 shows the results of CV measurement in the third cycle.

As a result of CV measurement, the electrolytic solution of Evaluation Example 1-1 containing compound X and the electrolytic solution of Evaluation Example 1-2 containing compound Y were compared with the electrolytic solution of Evaluation Example 1-3 containing no additive. , the current between 2.0 V and 0 V is small, and the reductive decomposition of the electrolyte is suppressed. In addition, the electrolytic solution of Evaluation Example 1-4 containing compound Z has a slightly smaller current than the electrolytic solution of Evaluation Example 1-3 containing no additive, but the electrolytic solutions of Evaluation Examples 1-1 and 1-2 No significant effect was observed. From these results, it is considered that the addition of a compound having a unique structure found in compound X and compound Y suppressed the reductive decomposition of the electrolytic solution, and thus the effect of improving the life and suppressing the increase in resistance was obtained.

(Evaluation examples 2-1 to 2-5)
[pH measurement of electrolytic solution]
The pH of the electrolytic solution was measured under the following conditions. The electrolytic solution is a mixed solution of ethylene carbonate/dimethyl carbonate/ethyl methyl carbonate = 1/1/1 (volume ratio) containing 1 mol/L of _LiPF6 , and 1% by mass of vinylene carbonate is added based on the total amount of the electrolytic solution. , an electrolytic solution in which the additive shown in Table 2 was further added in the amount shown in Table 2 based on the total amount of the electrolytic solution. 3 ml of the above electrolytic solution was added to 50 ml of pure water, and the pH of the electrolytic solution was measured. The pH measurement was carried out at 25° C. using an automatic titrator (trade name: COM-A19S, manufactured by Hiranuma Sangyo). As electrodes, a glass electrode (GE-101B) and a reference electrode (RE-201) were used. The pH measurement results are shown in FIG.

As a result of pH measurement, the pH of the electrolytic solutions of Evaluation Example 2-1, Evaluation Example 2-2, and Evaluation Example 2-3 containing compound X or compound Y were 7.1, 6.0, and 6.4, respectively. It was found that the pH was higher than the pH 3.9 of the electrolytic solution of Evaluation Example 2-4 containing no additive and was close to neutral. Further, the pH of the electrolytic solution of Evaluation Example 2-5 containing compound Z was 4.0, which was found to be substantially the same as the pH of the electrolytic solution of Evaluation Example 2-4 containing no additive. From these measurement results, in the electrolytic solutions of Evaluation Examples 2-1, 2-2, and 2-3 containing compound X or compound Y, hydrofluoric acid (HF) derived from lithium salt (LiPF ₆ ) was added. assumed to be decreasing. As a result, deterioration such as elution of the silicon-based active material due to hydrofluoric acid could be suppressed, so it is considered that the effect of suppressing the deterioration of the life of the battery containing the silicon-based active material was obtained.

DESCRIPTION OF SYMBOLS 1... Non-aqueous electrolyte secondary battery (electrochemical device), 2... Electrode group, 3... Battery outer body, 4... Positive electrode collector tab, 5... Negative electrode collector tab, 6... Positive electrode, 7... Separator, 8... Negative electrode 9... Positive electrode current collector 10... Positive electrode mixture layer 11... Negative electrode current collector 12... Negative electrode mixture layer.

Claims

An electrochemical device comprising a positive electrode, a negative electrode, and an electrolytic solution,
The negative electrode contains a silicon-based active material,
The electrochemical device, wherein the electrolytic solution contains a compound represented by the following formula (1).

[In Formula (1), R 1 to R 3 each independently represent a hydrogen atom or a methyl group, and X represents a divalent organic group. ]
The electrochemical device according to claim 1, wherein R1 and R2 in formula (1) are hydrogen atoms.
The electrochemical device according to claim 1 or 2, wherein X in said formula (1) is an alkylene group having 1 to 6 carbon atoms.
The electrochemical device according to claim 1 or 2, wherein X in said formula (1) is an ethylene group.
The electrochemistry according to any one of claims 1 to 4, wherein the content of the compound represented by the formula (1) is 0.001% by mass or more and 5% by mass or less based on the total amount of the electrolytic solution. device.
The electrochemical device according to any one of claims 1 to 5, wherein the electrochemical device is a non-aqueous electrolyte secondary battery or a capacitor.
An electrolytic solution for use in an electrochemical device having a negative electrode containing a silicon-based active material,
An electrolytic solution containing a compound represented by the following formula (1).

[In Formula (1), R 1 to R 3 each independently represent a hydrogen atom or a methyl group, and X represents a divalent organic group. ]
The electrolytic solution according to claim 7, wherein R1 and R2 in formula (1) are hydrogen atoms.
The electrolytic solution according to claim 7 or 8, wherein X in the formula (1) is an alkylene group having 1 to 6 carbon atoms.
The electrolytic solution according to claim 7 or 8, wherein X in the formula (1) is an ethylene group.
The electrolyte solution according to any one of claims 7 to 10, wherein the content of the compound represented by the formula (1) is 0.001% by mass or more and 5% by mass or less based on the total amount of the electrolyte solution. .
An additive used in an electrolyte solution of an electrochemical device having a negative electrode containing a silicon-based active material,
An additive containing a compound represented by the following formula (1).

[In Formula (1), R 1 to R 3 each independently represent a hydrogen atom or a methyl group, and X represents a divalent organic group. ]
13. The additive according to claim 12, wherein R1 and R2 in formula (1) are hydrogen atoms.
The additive according to claim 12 or 13, wherein X in formula (1) is an alkylene group having 1 to 6 carbon atoms.
The additive according to claim 12 or 13, wherein X in formula (1) is an ethylene group.