WO2023190335A1

WO2023190335A1 - Electrochemical device, and electrolyte solution for electrochemical device

Info

Publication number: WO2023190335A1
Application number: PCT/JP2023/012189
Authority: WO
Inventors: 馨今野; 洋介池田; 薫平山田; 恭章川口; 憲人西村
Original assignee: 株式会社レゾナック
Priority date: 2022-03-30
Filing date: 2023-03-27
Publication date: 2023-10-05
Also published as: JP2023147598A

Abstract

Disclosed is an electrochemical device. The electrochemical device comprises a positive electrode, a negative electrode, and an electrolyte. The electrolyte contains: a compound represented by formula (1); a first lithium salt compound; a second lithium salt compound having a different anion than the anion constituting the first lithium salt compound; and a nonaqueous solvent. [In formula (1), R1, R2, and R3 each independently represent a hydrogen atom or a methyl group, and X represents a divalent organic group.]

Description

Electrochemical devices and electrolytes for electrochemical devices

The present disclosure relates to an electrochemical device and an electrolyte for an electrochemical device.

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 for improving the performance of electrochemical devices, for example, a method of adding a predetermined additive to an electrolytic solution has been studied (for example, Patent Document 1).

International Publication No. 2012/147502

However, conventional electrochemical devices have a high rate of increase in resistance after cycle tests, and there is still room for improvement.

Therefore, the main purpose of the present disclosure is to sufficiently suppress the rate of increase in resistance of an electrochemical device after a cycle test.

According to studies by the present inventors, by using an electrolytic solution containing a specific isocyanate compound, two types of lithium salt compounds with different anions, and a nonaqueous solvent in an electrochemical device, it is possible to cycle the electrochemical device. It was found that the rate of increase in resistance after the test was sufficiently suppressed.

One aspect of the present disclosure relates to electrochemical devices. The electrochemical device includes a positive electrode, a negative electrode, and an electrolyte. The electrolytic solution contains a compound represented by the following formula (1), a first lithium salt compound, a second lithium salt compound having a different anion constituting the first lithium salt compound, and a nonaqueous solvent. do. According to such an electrochemical device, the rate of increase in resistance after a cycle test of the electrochemical device is sufficiently suppressed. In one embodiment, electrochemical devices tend to have excellent charge/discharge cycling characteristics. The electrochemical device may be a nonaqueous electrolyte secondary battery or a capacitor.

[In formula (1), R ¹ , R ² , and R ³ each independently represent a hydrogen atom or a methyl group, and X represents a divalent organic group. ]

Another aspect of the present disclosure relates to an electrolytic solution for electrochemical devices (hereinafter sometimes simply referred to as "electrolytic solution"). The electrolytic solution for an electrochemical device comprises a compound represented by the following formula (1), a first lithium salt compound, a second lithium salt compound in which the anion constituting the first lithium salt compound is different, and a non-containing lithium salt compound. Contains a water solvent. According to such an electrolytic solution for an electrochemical device, it is possible to sufficiently suppress the rate of increase in resistance of an electrochemical device after a cycle test. Further, in one embodiment, the electrolytic solution for an electrochemical device can improve the charge/discharge cycle characteristics of the electrochemical device.

Preferred embodiments (A) to (E) in each of the above aspects are shown below. A plurality of these preferred embodiments can be combined.
(A) R ¹ and R ² in formula (1) are hydrogen atoms.
(B) X in formula (1) is an alkylene group having 1 to 6 carbon atoms.
(C) The first lithium salt compound is lithium hexafluorophosphate.
(D) The second lithium salt compound is lithium difluorophosphate, lithium tetrafluoroborate, lithium fluorosulfonate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalate)boric acid. It is at least one selected from the group consisting of lithium, lithium difluorooxalate borate, lithium tetrafluorooxalate phosphate, and lithium difluorobis(oxalate) phosphate.
(E) The total content of the compound represented by formula (1) and the second lithium salt compound is 0.1 to 10% by mass based on the total amount of the electrolyte.

According to the present disclosure, it is possible to sufficiently suppress the rate of increase in resistance of an electrochemical device after a cycle test. Further, according to the present disclosure, there is provided an electrolytic solution for an electrochemical device that can improve the charge/discharge cycle characteristics of the electrochemical device.

FIG. 1 is a perspective view showing one embodiment of a non-aqueous electrolyte secondary battery as an electrochemical device. FIG. 2 is an exploded perspective view showing an electrode group of the non-aqueous electrolyte secondary battery shown in FIG. FIG. 3 is a graph showing the number of cycles at which the discharge capacity retention rate becomes less than 90% in cycle tests of lithium ion secondary batteries in Examples and Comparative Examples. FIG. 4 is a graph showing the measurement results of the resistance increase rate after cycle tests of lithium ion secondary batteries in Examples and Comparative Examples.

Hereinafter, embodiments of the present disclosure will be described with appropriate reference to the drawings. However, the present disclosure is not limited to the following embodiments.

The same applies to the numerical values and their ranges in the present disclosure, and they do not limit the present disclosure. In this specification, a numerical range indicated using "-" indicates a range that includes the numerical values written before and after "-" as the minimum and maximum values, respectively. In the numerical ranges described step by step in this specification, the upper limit value or lower limit value described in one numerical range may be replaced with the upper limit value or lower limit value of another numerical range described step by step. good. Further, in the numerical ranges described in this specification, the upper limit or lower limit of the numerical range may be replaced with the value shown in the Examples.

In this specification, the term "layer" includes a structure that is formed on the entire surface as well as a structure that is formed on a part of the layer when observed as a plan view. In addition, in this specification, the term "process" does not only refer to an independent process, but also refers to a process that cannot be clearly distinguished from other processes, as long as the intended effect of the process is achieved. included.

Unless otherwise specified, each component and material exemplified herein may be used alone or in combination of two or more.

FIG. 1 is a perspective view showing one embodiment of a non-aqueous electrolyte secondary battery as an electrochemical device. In this embodiment, the electrochemical device is a nonaqueous electrolyte secondary battery. As shown in FIG. 1, a nonaqueous 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 an electrode group of the non-aqueous electrolyte secondary battery shown in FIG. 1. 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 , 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 fluorine. Rubbers such as rubber, isoprene rubber, butadiene rubber, ethylene-propylene rubber; 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. Soft resins such as α-olefin copolymers; polyvinylidene fluoride (PVDF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, polytetrafluoroethylene/ethylene copolymer, polytetrafluoroethylene/vinylidene fluoride copolymer Examples include fluorine-containing resins such as; 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 in terms 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 14 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 such as energy density, the negative electrode mixture layer 12 preferably contains a carbon material, more preferably graphite, and still more preferably contains a carbon material as a negative electrode active material. It includes a mixture with a material containing at least one element selected from the group consisting of silicon and tin, 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.

The electrolytic solution (electrolytic solution for electrochemical devices) includes a compound represented by the following formula (1), a first lithium salt compound, and a second lithium salt compound having a different anion constituting the first lithium salt compound. and a non-aqueous solvent.

In formula (1), R ¹ , R ² , and R ³ each independently represent a hydrogen atom or a methyl group, and X represents a divalent organic group.

R ¹ and R ² are preferably hydrogen atoms. R ³ is preferably a hydrogen atom.

X may be, for example, a divalent hydrocarbon group, an alkylene group, or an alkylene group having 1 to 6 carbon atoms. The alkylene group may be linear or branched. The lower limit of the carbon number 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 a methylene group, an ethylene group, a propylene group, a butylene group, or a pentylene group, preferably an ethylene group.

X may be, for example, a divalent group in which a part of the divalent hydrocarbon group is substituted with a hetero atom. A heteroatom may be, for example, an oxygen atom. X may be, for example, a divalent group having an ether structure in which a part of the divalent hydrocarbon group is substituted with oxygen atoms. X may be, for example, a divalent group represented by the following formula (2).
-X ¹ -O-X 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 be 1 to 6, 1 to 5, 1 to 4, 1 to 3, or 1 to 2, respectively.

The content of the compound represented by formula (1) is set at 0.001 mass based on the total amount of electrolyte solution, since this makes it possible to more fully suppress the rate of increase in resistance after a cycle test of an electrochemical device. % or more, 0.005 mass% or more, 0.01 mass% or more, 0.05 mass% or more, 0.1 mass% or more, 0.15 mass% or more, or 0.2 mass% or more, It may be 5% by mass or less, 4% by mass or less, 3% by mass or less, 2% by mass or less, 1% by mass or less, 0.8% by mass or less, 0.6% by mass or less, or 0.5% by mass or less. .

The first lithium salt compound may be lithium hexafluorophosphate (LiPF ₆ ) since it has better solubility in a solvent, charge and discharge characteristics of a secondary battery, output characteristics, charge and discharge cycle characteristics, and the like.

From the viewpoint of excellent charge/discharge characteristics, the concentration of the first lithium salt compound is 0.5 mol/L or more, more preferably 0.7 mol/L or more, and still more preferably 0.8 mol/L, based on the total amount of the nonaqueous solvent. L or more, preferably 1.5 mol/L or less, more preferably 1.3 mol/L or less, still more preferably 1.2 mol/L or less.

The second lithium salt compound is not particularly limited as long as the anion constituting the first lithium salt compound is different, but for example, lithium difluorophosphate (LiPO ₂ F ₂ ), lithium tetrafluoroborate (LiBF ₄ ), lithium fluorosulfonate (LiSO ₃ F), lithium bis(fluorosulfonyl)imide (LiN(SO ₂ F) ₂ , LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiN(SO ₂ CF ₃ ) ₂ , LiTFSI) ), lithium bis(oxalate)borate (LiB(C ₂ O ₄ ) ₂ , LiBOB), lithium difluorooxalate borate (LiBF ₂ (C ₂ O ₄ ), LiDFOB), lithium tetrafluorooxalate phosphate (LiPF) ₄ (C ₂ O ₄ ), LiTFOP), and lithium difluorobis(oxalate) phosphate (LiPF ₂ (C ₂ O ₄ ) ₂ , LiDFBOP). The second lithium salt compound is lithium difluorophosphate (LiPO ₂ F ₂ ) or bis(fluorosulfonyl)imide because it is possible to more fully suppress the rate of increase in resistance after a cycle test of an electrochemical device. It may also be lithium (LiN(SO ₂ F) ₂ , LiFSI).

The content of the second lithium salt compound is 0.001% by mass or more based on the total amount of the electrolytic solution, since this makes it possible to more fully suppress the rate of increase in resistance after the cycle test of the electrochemical device. It may be 0.005% by mass or more, 0.01% by mass or more, 0.05% by mass or more, 0.1% by mass or more, 0.15% by mass or more, or 0.2% by mass or more, and 5% by mass The content may be 4% by mass or less, 3% by mass or less, 2% by mass or less, 1% by mass or less, 0.8% by mass or less, 0.6% by mass or less, or 0.5% by mass or less.

The total content of the compound represented by formula (1) and the second lithium salt compound is determined by the total amount of the electrolyte because it is possible to more sufficiently suppress the resistance increase rate after the cycle test of the electrochemical device. It may be 0.1 to 10% by mass based on . The total content of the compound represented by formula (1) and the second lithium salt compound is 0.2% by mass or more, 0.3% by mass or more, or 0.4% by mass or more based on the total amount of the electrolyte solution. It may be 7% by mass or less, 5% by mass or less, 4% 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.

The ratio of the content of the compound represented by formula (1) to the total content of the compound represented by formula (1) and the second lithium salt compound (content of the compound represented by formula (1)/( The total content of the compound represented by formula (1) and the second lithium salt compound)) can more fully suppress the resistance increase rate after the cycle test of the electrochemical device. , 0.05 or more, 0.1 or more, 0.2 or more, 0.25 or more, 0.3 or more, 0.35 or more, or 0.4 or more, and 0.9 or less, 0.85 or less , 0.8 or less, 0.75 or less, 0.7 or less, 0.65 or less, or 0.6 or less.

The content of the second lithium salt compound may be 0.05% or more and 20% or less in molar ratio with respect to the first lithium salt compound.

Examples of non-aqueous solvents include linear carbonate compounds such as dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, and methyl butyl carbonate; cyclic carbonate compounds such as ethylene carbonate, propylene carbonate, and butylene carbonate; Chain carboxylic acid ester compounds such as methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate; cyclic carboxylic acid ester compounds such as γ-butyllactone; chains such as dimethoxymethane, dimethoxyethane, diethoxyethane, etc. cyclic ether compounds such as tetrahydrofuran, tetrahydropyran, and dioxolane; and nitrile compounds such as acetonitrile. The non-aqueous solvents may be used alone or in combination of two or more. The non-aqueous solvent is preferably a mixture of two or more.

The electrolytic solution may further contain components other than the compound represented by formula (1), the first lithium salt compound, the second lithium salt compound, and the nonaqueous solvent. Examples of other components include unsaturated cyclic carbonates, fluorine-containing cyclic carbonates, and compounds containing nitrogen atoms other than the compound represented by formula (1).

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, etc. can be mentioned. The unsaturated cyclic carbonate is preferably vinylene carbonate from the viewpoint of further improving the performance of the electrochemical device. Examples of the fluorine-containing cyclic carbonate include 4-fluoro-1,3-dioxolan-2-one (fluoroethylene carbonate; FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1, Examples include 2-trifluoroethylene carbonate and 1,1,2,2-tetrafluoroethylene carbonate. The fluorine-containing cyclic carbonate is 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.

The present inventors prepared a compound represented by formula (1), a first lithium salt compound, a second lithium salt compound having a different anion constituting the first lithium salt compound, and a nonaqueous solvent. It has been found that by using the electrolytic solution contained in the electrolyte in an electrochemical device, the rate of increase in resistance after a cycle test can be sufficiently suppressed. Although the reason for such an effect is not necessarily clear, the present inventors speculate as follows. That is, at the time of initial charging, the unsaturated carbon bond structure of the compound represented by formula (1) undergoes a reduction reaction on the negative electrode side before other additives or carbonate solvents, forming a film. It is speculated that this is because a stable film is formed by the subsequent reaction of the isocyanate sites, and the reductive decomposition of other additives, non-aqueous solvents, electrolyte salts, etc. can be suppressed on the negative electrode side. In addition, on the positive electrode side, the first lithium salt compound, the second lithium salt compound, or a compound derived therefrom that remains without being reductively decomposed forms a film, and other additives, nonaqueous solvents, electrolyte salts, etc. It is presumed that this is because by suppressing the oxidative decomposition of the positive electrode active material, it is possible to suppress the decrease in ionic conductivity on the surface of the positive electrode active material or the increase in resistance due to the stabilization of the crystal structure.

In one embodiment, an electrolytic solution containing a compound represented by formula (1), a first lithium salt compound, a second lithium salt compound, and a nonaqueous solvent is used in an electrochemical device. As a result, electrochemical devices tend to have excellent charge/discharge cycle characteristics. Although the reason for such an effect is not necessarily clear, the present inventors have found that in addition to forming stable films on the positive and negative electrodes, the compound represented by formula (1) can reduce fluorine in the electrolyte. It is speculated that this is because by reducing the amount of acid (HF), side reactions due to elution of the positive electrode active material and formation of a film such as LiF on the negative electrode can be suppressed.

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 sometimes referred to as "NMP"), or the like.

In the second step, the negative electrode 8 is obtained in the same manner as the step of obtaining the positive electrode 6 in the first step described above. The method for forming the negative electrode mixture layer 12 on the negative electrode current collector 11 is the same as the first method described above, except that the positive electrode current collector 9 and the positive electrode mixture layer 10 are changed to the negative electrode current collector 11 and the negative electrode mixture layer 12. The method may be similar to the process described in .

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 made up of a positive electrode, a negative electrode, and a separator, and a bag-shaped battery exterior housing 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.

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

(Example 1)
[Preparation of positive electrode]
Nickel cobalt lithium manganate (92% by mass) as a positive electrode active material, acetylene black (AB) (4% by mass) as a conductive agent, and polyvinylidene fluoride (PVDF) (4% by mass) as a binder are sequentially added. Added 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 2.8 g/cm ³ to obtain a positive electrode.

[Preparation of negative electrode]
As negative electrode active materials, a graphite-based active material (artificial graphite, average particle diameter (D50); approximately 23 μm) and a silicon-based active material (SiOx, average particle diameter (D50); approximately 10 μm) were used. Styrene-butadiene rubber (SBR) as a binder and carboxymethyl cellulose as a thickener were added to these active materials. Regarding these mass ratios, 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 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 square of 13.5 cm ² was sandwiched between polyethylene porous sheets (thickness 30 μm) serving as separators, and a negative electrode cut into a square of 14.3 cm ² was further stacked to form an electrode group. 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, 0.25 mL of electrolyte solution was added into the container, and the container was thermally welded to produce a lithium ion secondary battery for evaluation. As an _electrolytic solution, the following formula (1 0.5% by mass of the compound A represented by formula (1) in which R ¹ , R ² , and R ³ are hydrogen atoms and X is an ethylene group, and the second 0.5% by mass of lithium difluorophosphate (LiPO ₂ F ₂ ) as a lithium salt compound, 1% by mass of vinylene carbonate, and 1% by mass of fluoroethylene carbonate (all based on the total amount of electrolyte solution) were added. I used something.

(Example 2)
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 Compound A, based on the total amount of the electrolytic solution, was used.

(Example 3)
A lithium ion secondary battery was produced in the same manner as in Example 2, except that an electrolytic solution containing 0.2% by mass of lithium difluorophosphate (LiPO ₂ F ₂ ) based on the total amount of the electrolytic solution was used.

(Example 4)
A lithium ion secondary battery was produced in the same manner as in Example 3, except that an electrolytic solution containing 1% by mass of Compound A based on the total amount of the electrolytic solution was used.

(Example 5)
Compound B represented by the following formula (1Y) instead of compound A (represented by formula (1), where R ¹ and R ² are hydrogen atoms, R ³ is a methyl group, and X is an ethylene group) A lithium ion secondary battery was produced in the same manner as in Example 1, except that an electrolytic solution containing 0.5% by mass of 0.5% by mass, based on the total amount of the electrolytic solution, was added.

(Example 6)
An electrolytic solution was used in which lithium bis(fluorosulfonyl)imide (LiN(SO ₂ F) ₂ , LiFSI) was added in an amount of 0.5% by mass based on the total amount of the electrolyte instead of lithium difluorophosphate (LiPO ₂ F ₂ ). A lithium ion secondary battery was produced in the same manner as in Example 1 except for the above.

(Comparative example 1)
A lithium ion secondary battery was produced in the same manner as in Example 1, except that Compound A and lithium difluorophosphate (LiPO ₂ F ₂ ) were not added to the electrolyte.

(Comparative example 2)
A lithium ion secondary battery was produced in the same manner as Comparative Example 1, except that 0.5% by mass of hexamethylene diisocyanate (HDI) was added based on the total amount of the electrolyte.

(Comparative example 3)
A lithium ion secondary battery was produced in the same manner as in Example 1, except that an electrolytic solution containing 0.5% by mass of hexamethylene diisocyanate (HDI) based on the total amount of the electrolytic solution was used instead of Compound A.

[Evaluation of charge/discharge cycle characteristics]
(Initial charge/discharge)
Each of the produced lithium ion secondary batteries 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 2.7V. 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 charge/discharge cycle characteristics)
After the initial charge and discharge, each lithium ion battery was subjected to a high temperature cycle test to evaluate its charge and discharge cycle characteristics. As a charging pattern, constant current charging was performed at a current value of 0.5 C to an upper limit voltage of 4.2 V in an environment of 45° C., and then constant voltage charging was performed at 4.2 V. The charging termination condition was a current value of 0.05C. Regarding discharge, constant current discharge was performed at 1.0 C to 2.7 V, and the discharge capacity was determined. This series of charging and discharging was repeated for 500 cycles, and the discharge capacity was measured every time the charging and discharging was performed. The relative value of the discharge capacity (Q2) in each cycle with respect to the discharge capacity (Q1) of the first cycle of charging and discharging (discharge capacity retention rate (%) = Q2/Q1 × 100) is calculated, and the discharge capacity retention rate is 90 The number of cycles (times) at which the value was less than % was determined. FIG. 3 and Table 1 show the number of cycles at which the discharge capacity retention rate becomes less than 90% in a cycle test of a lithium ion secondary battery.

[Calculation of resistance increase rate]
(Measurement of discharge DCR)
For each of the manufactured lithium ion secondary batteries, the direct current resistance during discharge (discharge DCR) was measured as follows. First, constant current charging at 0.2C was performed to an upper limit voltage of 4.2V, and then constant voltage charging was performed at 4.2V. The charging termination condition was a current value of 0.02C. Thereafter, constant current discharge was performed at a current value of 0.2C and a final voltage of 2.7V, and the current value at this time was defined as I _0.2C and the voltage change 10 seconds after the start of discharge was defined as ΔV _0.2C . Next, constant current charging at 0.2C was performed to an upper limit voltage of 4.2V, followed by constant voltage charging at 4.2V (the charging termination condition was a current value of 0.02C). Thereafter, constant current discharge was performed at a current value of 0.5C and a final voltage of 2.7V, and the current value at this time was defined as I _0.5C and the voltage change 10 seconds after the start of discharge was defined as ΔV _0.5C . From similar charging and discharging, the current value of 1C was evaluated as I _1C , and the voltage change ΔV _1C 10 seconds after the start of discharge was evaluated. The three-point plot of the current value vs. voltage change (I _0.2C , ΔV _0.2C ), (I _0.5C , ΔV _0.5C ), (I _1C , ΔV _1C ) is plotted using the least squares method. An approximate straight line was drawn, and its slope was taken as the value of discharge DCR.

(Measurement of resistance increase rate)
The discharge DCR (R1) of each lithium ion battery before the above cycle test, and the discharge DCR (R2) measured after the above cycle test (45 °C, 500 cycles) after leaving it for 30 minutes in a 25 °C environment. ) was measured. Using the measured R1 and R2, the resistance increase rate was calculated from the following formula. FIG. 4 and Table 1 show the measurement results of the resistance increase rate after the cycle test of the lithium ion secondary battery.
Resistance increase rate (%) = R2/R1 x 100

From FIGS. 3 and 4 and Table 1, it can be seen that the compound represented by formula (1), the first lithium salt compound, the second lithium salt compound in which the anion constituting the first lithium salt compound is different, and the non- The lithium ion secondary batteries of Examples 1 to 6, in which electrolytes containing water solvents were applied, had increased resistance compared to the lithium ion secondary batteries of Comparative Example 1, in which electrolytes not containing these compounds were applied. The rate was low, and the number of cycles at which the discharge capacity retention rate became less than 90% was large. On the other hand, the lithium ion secondary battery of Comparative Example 2 to which an electrolytic solution containing HDI, which is a compound having an isocyanate group, which does not satisfy the requirements of formula (1), and HDI and LiPO ₂ F ₂ (second The lithium ion secondary battery of Comparative Example 3 in which an electrolyte containing a lithium salt compound) was applied had a lower resistance increase rate than the lithium ion secondary battery of Comparative Example 1, but the lithium ion secondary battery of Examples 1 to 6 The secondary battery had a greater effect of suppressing the rate of increase in resistance. Furthermore, it was found that the lithium ion secondary batteries of Examples 1 to 6 had a greater number of cycles at which the discharge capacity retention rate became less than 90% than the lithium ion secondary batteries of Comparative Examples 2 and 3. From the above, it was confirmed that it is possible to sufficiently suppress the rate of increase in resistance of an electrochemical device after a cycle test.

The present inventors prepared a compound represented by formula (1), a first lithium salt compound, a second lithium salt compound having a different anion constituting the first lithium salt compound, and a nonaqueous solvent. The effects of using the contained electrolytic solution in an electrochemical device to sufficiently suppress the rate of increase in resistance after a cycle test are speculated as follows. That is, at the time of initial charging, the unsaturated carbon bond structure of the compound represented by formula (1) undergoes a reduction reaction on the negative electrode side before other additives or carbonate solvents, forming a film. It is speculated that this is because a stable film is formed by the subsequent reaction of the isocyanate sites, and the reductive decomposition of other additives, non-aqueous solvents, electrolyte salts, etc. can be suppressed on the negative electrode side. In addition, on the positive electrode side, the first lithium salt compound, the second lithium salt compound, or a compound derived therefrom that remains without being reductively decomposed forms a film, and other additives, nonaqueous solvents, electrolyte salts, etc. It is presumed that this is because by suppressing the oxidative decomposition of the positive electrode active material, it is possible to suppress the decrease in ionic conductivity on the surface of the positive electrode active material or the increase in resistance due to the stabilization of the crystal structure.

DESCRIPTION OF SYMBOLS 1... Non-aqueous electrolyte secondary battery (electrochemical device), 2... Electrode group, 3... Battery exterior body, 4... Positive electrode current collector tab, 5... Negative electrode current 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

Comprising a positive electrode, a negative electrode, and an electrolyte,
The electrolytic solution includes a compound represented by the following formula (1), a first lithium salt compound, a second lithium salt compound having a different anion constituting the first lithium salt compound, and a nonaqueous solvent. containing,
Electrochemical device.

[In formula (1), R 1 , R 2 , and R 3 each independently represent a hydrogen atom or a methyl group, and X represents a divalent organic group. ]
R 1 and R 2 in the formula (1) are hydrogen atoms,
The electrochemical device according to claim 1.
X in the formula (1) is an alkylene group having 1 to 6 carbon atoms,
The electrochemical device according to claim 1 or 2.
the first lithium salt compound is lithium hexafluorophosphate;
The electrochemical device according to any one of claims 1 to 3.
The second lithium salt compound is lithium difluorophosphate, lithium tetrafluoroborate, lithium fluorosulfonate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalate)borate, At least one member selected from the group consisting of lithium difluorooxalate borate, lithium tetrafluorooxalate phosphate, and lithium difluorobis(oxalate) phosphate,
The electrochemical device according to any one of claims 1 to 4.
The total content of the compound represented by the formula (1) and the second lithium salt compound is 0.1 to 10% by mass based on the total amount of the electrolyte,
The electrochemical device according to any one of claims 1 to 5.
the electrochemical device is a non-aqueous electrolyte secondary battery or a capacitor;
The electrochemical device according to any one of claims 1 to 6.
A compound represented by the following formula (1), a first lithium salt compound, a second lithium salt compound having a different anion constituting the first lithium salt compound, and a nonaqueous solvent.
Electrolyte for electrochemical devices.

[In formula (1), R 1 , R 2 , and R 3 each independently represent a hydrogen atom or a methyl group, and X represents a divalent organic group. ]
R 1 and R 2 in the formula (1) are hydrogen atoms,
The electrolytic solution for electrochemical devices according to claim 8.
X in the formula (1) is an alkylene group having 1 to 6 carbon atoms,
The electrolytic solution for electrochemical devices according to claim 8 or 9.
the first lithium salt compound is lithium hexafluorophosphate;
The electrolytic solution for electrochemical devices according to any one of claims 8 to 10.
The second lithium salt compound is lithium difluorophosphate, lithium tetrafluoroborate, lithium fluorosulfonate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalate)borate, At least one member selected from the group consisting of lithium difluorooxalate borate, lithium tetrafluorooxalate phosphate, and lithium difluorobis(oxalate) phosphate,
The electrolytic solution for electrochemical devices according to any one of claims 8 to 11.
The total content of the compound represented by the formula (1) and the second lithium salt compound is 0.1 to 10% by mass based on the total amount of the electrolyte,
The electrolytic solution for electrochemical devices according to any one of claims 8 to 12.