JP2024021236A - Electrolyte, electrochemical device, and electrolyte additive - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: an electrolyte capable of improving the discharge capacity retention of an electrochemical device while inhibiting the resistance from increasing after initial charge-discharge and after a charge-discharge cycle test.

SOLUTION: An electrolyte comprises a compound represented by the formula (A) in the figure, and a lithium salt, where the amount of fluorine atoms in the compound is 0.160 mol or more per mole of lithium atoms in the lithium salt. [In the formula (A), each R independently represents a substituted or unsubstituted C_1-6 alkyl group, a substituted or unsubstituted phenyl group, or a substituted or unsubstituted benzyl group, provided that at least one R is the substituted or unsubstituted phenyl group or the substituted or unsubstituted benzyl group.]

SELECTED DRAWING: None

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present invention relates to an electrolyte, an electrochemical device, and an additive for an electrolyte.

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. In order to improve the performance of electrochemical devices, certain additives are sometimes added to the electrolytic solution along with lithium salt (Patent Documents 1 and 2).

JP2019-220415A JP2016-186910A

J. C. Burns et al, “Studies of the Effect of Varying Vinylene Carbonate (VC) Content in Lithium Ion Cells onCycling Performance and Cell Impedance”, Journal of The Electrochemical Society, 2013, 160(10), A1668-A1674.

When more additives for electrolyte solution are added to the electrolyte solution in order to further improve electrochemical device performance, the resistance of the electrochemical device may increase (Non-Patent Document 1, etc.).

One aspect of the present invention is an electrolytic solution that can improve the discharge capacity retention rate of an electrochemical device while suppressing an increase in resistance after initial charge/discharge and a charge/discharge cycle test, and an electrolysis method for obtaining the electrolytic solution. The purpose is to provide additives for liquids.

［式（Ａ）中、Ｒはそれぞれ独立して置換若しくは無置換のＣ_１－６アルキル基、置換若しくは無置換のフェニル基、又は、置換若しくは無置換のベンジル基を示し、Ｒの少なくとも一つが、前記置換若しくは無置換のフェニル基、又は、前記置換若しくは無置換のベンジル基である。］
［２］
前記化合物の含有量が、前記電解液全量を基準として、２．０質量％以上である、［１］に記載の電解液。
［３］
前記Ｃ_１－６アルキル基が、ハロゲン原子で置換されたＣ_１－６アルキル基又は無置換のＣ_１－６アルキル基である、［１］又は［２］に記載の電解液。
［４］
Ｒで表される置換基がフッ素原子を含まない、［１］～［３］のいずれかに記載の電解液。
［５］
前記化合物がフェニルジメチルフルオロシランである、［１］～［４］のいずれかに記載の電解液。
［６］
正極と、負極と、［１］～［５］のいずれかに記載の電解液と、を備える電気化学デバイス。
［７］
前記電気化学デバイスは、非水電解液二次電池又はキャパシタである、［６］に記載の電気化学デバイス。
［８］
下記式（Ａ）で表される化合物を含有する、電解液用添加剤。

［式（Ａ）中、Ｒはそれぞれ独立して置換若しくは無置換のＣ_１－６アルキル基、置換若しくは無置換のフェニル基、又は、置換若しくは無置換のベンジル基を示し、Ｒの少なくとも一つが、前記置換若しくは無置換のフェニル基、又は、前記置換若しくは無置換のベンジル基である。］
［９］
前記Ｃ_１－６アルキル基が、ハロゲン原子で置換されたＣ_１－６アルキル基又は無置換のＣ_１－６アルキル基である、［８］に記載の電解液用添加剤。
［１０］
前記化合物がフェニルジメチルフルオロシランである、［８］又は［９］に記載の電解液用添加剤。 In some aspects, the present invention provides the following [1] to [10].
[1]
An electrolytic solution containing a compound represented by the following formula (A) and a lithium salt, wherein the amount of fluorine atoms in the compound is 0.160 mol or more per 1 mol of lithium atoms in the lithium salt.

[In formula (A), R each independently represents a substituted or unsubstituted C _1-6 alkyl group, a substituted or unsubstituted phenyl group, or a substituted or unsubstituted benzyl group, and at least one of R is , the substituted or unsubstituted phenyl group, or the substituted or unsubstituted benzyl group. ]
[2]
The electrolyte solution according to [1], wherein the content of the compound is 2.0% by mass or more based on the total amount of the electrolyte solution.
[3]
The electrolytic solution according to [1] or [2], wherein the C _1-6 alkyl group is a halogen atom-substituted C _1-6 alkyl group or an unsubstituted C _1-6 alkyl group.
[4]
The electrolytic solution according to any one of [1] to [3], wherein the substituent represented by R does not contain a fluorine atom.
[5]
The electrolytic solution according to any one of [1] to [4], wherein the compound is phenyldimethylfluorosilane.
[6]
An electrochemical device comprising a positive electrode, a negative electrode, and the electrolyte according to any one of [1] to [5].
[7]
The electrochemical device according to [6], wherein the electrochemical device is a non-aqueous electrolyte secondary battery or a capacitor.
[8]
An additive for electrolyte solution containing a compound represented by the following formula (A).

[In formula (A), R each independently represents a substituted or unsubstituted C _1-6 alkyl group, a substituted or unsubstituted phenyl group, or a substituted or unsubstituted benzyl group, and at least one of R is , the substituted or unsubstituted phenyl group, or the substituted or unsubstituted benzyl group. ]
[9]
The additive for an electrolytic solution according to [8], wherein the C _1-6 alkyl group is a halogen atom-substituted C _1-6 alkyl group or an unsubstituted C _1-6 alkyl group.
[10]
The additive for electrolyte solution according to [8] or [9], wherein the compound is phenyldimethylfluorosilane.

According to the present invention, an electrolytic solution capable of improving the discharge capacity retention rate of an electrochemical device while suppressing an increase in resistance after initial charging/discharging and a charging/discharging cycle test, and an electrolytic solution for obtaining the electrolytic solution can provide additives for

FIG. 1 is a perspective view showing a non-aqueous electrolyte secondary battery as an electrochemical device according to an embodiment. FIG. 2 is an exploded perspective view showing an electrode group of the secondary battery shown in FIG. FIG. 3 is a graph showing the measurement results of AC impedance. FIG. 4 is a graph showing the measurement results of the discharge capacity retention rate (%) in each cycle.

Embodiments of the present disclosure will be described in detail below. However, the present disclosure is not limited to the following embodiments.

In this specification, the term "process" is used not only to refer to an independent process, but also to include any process that achieves the intended effect even if it cannot be clearly distinguished from other processes. It will be done. Furthermore, 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 present specification, if there are multiple substances corresponding to each component in the composition, the content of each component in the composition refers to the total amount of the multiple substances present in the composition, unless otherwise specified. means. Unless otherwise specified, the illustrated materials may be used alone or in combination of two or more.

In the numerical ranges described stepwise in this specification, the upper limit or lower limit of the numerical range of one step may be replaced with the upper limit or lower limit of the numerical range of another step. In the numerical ranges described in this specification, the upper limit or lower limit of the numerical range may be replaced with the values shown in the examples. "A or B" may include either A or B, or may include both.

In this specification, the term "layer" includes not only a structure formed on the entire surface but also a structure formed on a part of the layer when observed in a plan view.

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

The battery exterior body 3 may be, for example, a container formed of a laminate film. The laminate film may be, for example, a laminated film in which a resin film such as a polyethylene terephthalate (PET) film, a metal foil such as aluminum, copper, or stainless steel, and a sealant layer such as polypropylene are laminated in this order.

FIG. 2 is an exploded perspective view showing one embodiment of the electrode group 2 in the non-aqueous electrolyte secondary battery 1 shown in FIG. As shown in FIG. 2, the electrode group 2 includes a positive electrode 6, a separator 7, and a negative electrode 8 in this order. The positive electrode 6 and the negative electrode 8 are arranged such that the surfaces on the positive electrode mixture layer 10 side and the negative electrode mixture layer 12 side face the separator 7, respectively.

The positive electrode 6 includes a positive electrode current collector 9 and a positive electrode mixture layer 10 provided on the positive electrode current collector 9. The positive electrode current collector 9 is provided with a positive electrode current collector tab 4 .

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

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

The positive electrode active material may be, for example, lithium oxide. Examples of lithium oxides include Li _x CoO ₂ , Li _x NiO ₂ , Li _x MnO ₂ , Li _x Co _y Ni _1-y O ₂ , Li _x Co _y M _1-y O _z , Li _x Ni _{1- y} M _y O _z , Li _x Mn ₂ O ₄ and Li _x Mn _2-y M _y O ₄ (In each formula, M is Na, Mg, Sc, Y, Mn, Fe, Co, Cu, Zn, Al , Cr, Pb, Sb, V, and B (provided that M is an element different from the other elements in each formula). x = 0 to 1.2 , y=0 to 0.9, and z=2.0 to 2.3). The lithium oxide represented by Li _x Ni _1-y M _y O _z is Li _x Ni _1-(y1+y2) Co _y1 Mn _y2 O _z (where x and z are the same as above, and y1= 0 to 0.9, y2=0 to 0.9, and y1+y2=0 to 0.9), for example, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , It may be LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , LiNi _0.6 Co _0.2 Mn _0.2 O _{2 , or} LiNi _0.8 Co _0.1 Mn _0.1 O ₂ . The lithium oxide represented by Li _x Ni _1-y M _y O _z is Li _x Ni _1-(y3+y4) Co _y3 Al _y4 O _z (where x and z are the same as above, and y3= 0 to 0.9, y4=0 to 0.9, and y3+y4=0 to 0.9), for example, LiNi _0.8 Co _0.15 Al _0.05 O ₂ There may be.

The positive electrode active material may be, for example, lithium phosphate. Examples of lithium phosphates include lithium manganese phosphate (LiMnPO ₄ ), lithium iron phosphate (LiFePO 4 ), lithium cobalt phosphate (LiCoPO ₄ ), and lithium vanadium phosphate (Li _{3 V 2 (} PO ₄ )). ₃ ).

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

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

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

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

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

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

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

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

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

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

The negative electrode active material is not particularly limited as long as it is a material that can insert and release lithium ions. Examples of negative electrode active materials include carbon materials, metal composite oxides, oxides or nitrides of Group 4 elements such as tin, germanium, and silicon, elemental lithium, lithium alloys such as lithium aluminum alloys, Sn, Si, etc. Examples include metals that can form alloys with lithium. From the viewpoint of safety, the negative electrode active material is preferably at least one selected from the group consisting of carbon materials and metal composite oxides. The negative electrode active material may be one of these materials or a mixture of two or more thereof. The shape of the negative electrode active material may be, for example, particulate.

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

Among negative electrode active materials, carbon materials have high electrical conductivity and are particularly excellent in low-temperature characteristics and cycle stability. Among carbon materials, graphite is preferred from the viewpoint of increasing capacity. In graphite, the carbon network interlayer (d002) measured by X-ray wide-angle diffraction is preferably less than 0.34 nm, more preferably 0.3354 nm or more and 0.337 nm or less. A carbon material that satisfies such conditions is sometimes referred to as pseudo-anisotropic carbon.

The negative electrode active material may further contain a material containing at least one element selected from the group consisting of silicon and tin. The material containing at least one element selected from the group consisting of silicon and tin may be a simple substance of silicon or tin, or a compound containing at least one element selected from the group consisting of silicon and tin. The compound may be an alloy containing at least one element selected from the group consisting of silicon and tin, for example, in addition to silicon and tin, nickel, copper, iron, cobalt, manganese, zinc, indium, 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 low-temperature input characteristics, the negative electrode 8 preferably contains a carbon material, more preferably graphite, as a negative electrode active material.

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 contain a thickener to adjust the viscosity. Thickeners may include, but are not limited to, carboxymethylcellulose (CMC), methylcellulose, hydroxymethylcellulose, ethylcellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, salts thereof, and the like. The thickener may be one of these or a mixture of two or more thereof.

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

In one embodiment, the electrolytic solution contains a compound represented by the following formula (A) (hereinafter also referred to as "compound A"), a lithium salt, and a nonaqueous solvent. In one embodiment, an electrolyte additive containing Compound A is provided.

In formula (A), R each independently represents a substituted or unsubstituted C _1-6 alkyl group, a substituted or unsubstituted phenyl group, or a substituted or unsubstituted benzyl group, and at least one of R is , a substituted or unsubstituted phenyl group, or a substituted or unsubstituted benzyl group. A plurality of R's may be the same or different.

As used herein, "C _1-6 alkyl group" means an alkyl group having 1 to 6 carbon atoms. Each R may independently be an alkyl group having 1 to 4, 1 to 3, or 1 to 2 carbon atoms. The C _1-6 alkyl group represented by R may be linear or branched. R may be a methyl group, an ethyl group, a propyl group (n-propyl group or isopropyl group), or a butyl group (n-butyl group, sec-butyl group, isobutyl group, or tert-butyl group).

Examples of the substituent for the C _1-6 alkyl group represented by R include a halogen atom. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. The substituted C _1-6 alkyl group may be a group in which some or all of the hydrogen atoms of the above-mentioned C _1-6 alkyl group are substituted with halogen atoms. Examples of the substituted C _1-6 alkyl group include trifluoromethyl group.

The substituted or unsubstituted C _1-6 alkyl group represented by R is preferably a C _1-6 alkyl group substituted with a halogen atom or an unsubstituted C 1-6 alkyl group, and is preferably a C _1-6 alkyl group substituted with a fluorine atom. More preferably, it is a substituted C _1-6 alkyl group or an unsubstituted C _1-6 alkyl group.

Examples of substituents for the phenyl group and benzyl group represented by R include an alkyl group, a halogen atom, a sulfo group, a ketone group, a carboxy group, a hydroxy group, a nitro group, an amino group, and an aldehyde group.

At least one of R may be a substituted or unsubstituted phenyl group or a substituted or unsubstituted benzyl group, and at least one of R may be a substituted or unsubstituted C _1-6 alkyl group. One or two of R may be a substituted or unsubstituted phenyl group or a substituted or unsubstituted benzyl group, and the remaining R may be a substituted or unsubstituted C _1-6 alkyl group. It is preferable that one of R is a substituted or unsubstituted phenyl group, and the remaining R is a substituted or unsubstituted C _1-6 alkyl group. R does not need to contain a fluorine atom.

Compound A may include a compound represented by the following formula (A1).

In formula (A1), R ¹ each independently represents a substituted or unsubstituted C _1-6 alkyl group, and R ² represents a substituted or unsubstituted phenyl group or a substituted or unsubstituted benzyl group. A plurality of R ^1s may be the same group or different groups.

The substituted or unsubstituted C _1-6 alkyl group represented by R ¹ may be the same substituent as the substituted or unsubstituted C _1-6 alkyl group represented by R. The substituted or unsubstituted phenyl group represented by R ² may be the same substituent as the substituted or unsubstituted phenyl group represented by R. The substituted or unsubstituted benzyl group represented by R ² may be the same substituent as the substituted or unsubstituted benzyl group represented by R.

Compound A is, for example, phenyldimethylfluorosilane, phenyldiethylfluorosilane, phenyldipropylfluorosilane, diphenylmethylfluorosilane, triphenylfluorosilane, fluorophenyldimethylfluorosilane, difluorophenyldimethylfluorosilane, trifluorophenyldimethylfluorosilane. , pentafluorophenyldimethylfluorosilane, phenylditrifluoromethylfluorosilane, pentafluorophenylditrifluoromethylfluorosilane, benzyldimethylfluorosilane, and pentafluorobenzylditrifluoromethylfluorosilane. It's okay to be there. Compound A is preferably phenyldimethylfluorosilane.

Even when the content of Compound A is increased, the increase in resistance after initial charging and discharging and after the charging and discharging cycle test is suppressed. Therefore, by using Compound A as an additive for electrolytic solution, the discharge capacity retention rate of electrochemical devices can be improved while suppressing the resistance increase after initial charge/discharge and after charge/discharge cycle test due to increasing the content. be able to.

Compound A has an excellent overcharge prevention effect because it contains a substituted or unsubstituted phenyl group or a substituted or unsubstituted benzyl group. The reason why such an effect is obtained is not particularly limited, but in Compound A, the substituted or unsubstituted phenyl group or the substituted or unsubstituted benzyl group decomposes and polymerizes at a predetermined voltage and forms the surface of the positive electrode. It is presumed that this is achieved by coating, clogging separator holes, generating hydrogen gas during decomposition and polymerization, and activating a CID (current interrupt device).

Since Compound A contains a substituted or unsubstituted phenyl group or a substituted or unsubstituted benzyl group, it also has excellent permeability into electrodes, especially graphite negative electrodes.

The content of compound A is 1.5% by mass or more, 2.0% by mass or more, 2.5% by mass or more, 3.0% by mass, based on the total amount of electrolyte solution, since the discharge capacity retention rate is further improved. % or more, 3.5 mass% or more, 4.0 mass% or more, 4.5 mass% or more, 5.0 mass% or more, 6.0 mass% or more, 7.0 mass% or more, 8.0 mass% 9.0% by mass or more, 10.0% by mass or more, 12.0% by mass or more, 14.0% by mass or more, 16.0% by mass or more, 18.0% by mass or more, 20.0% by mass or more , 22.0% by mass or more, 24.0% by mass or more, 26.0% by mass or more, or 28.0% by mass or more. The content of compound A is 30.0% by mass or less, 28.0% by mass or less, 26.0% by mass or less, 24.0% by mass or less, 22.0% by mass or less, 20% by mass or less, based on the total amount of electrolyte solution. .0 mass% or less, 18.0 mass% or less, 16.0 mass% or less, 14.0 mass% or less, 12.0 mass% or less, 10.0 mass% or less, 9.0 mass% or less, 8. It may be 0% by mass or less, 7.0% by mass or less, 6.0% by mass or less, 5.0% by mass or less, 4.0% by mass or less, or 3.0% by mass or less.

Lithium salts include, for example, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiB(C ₆ H ₅ ) ₄ , LiCH ₃ SO ₃ , CF ₃ SO ₂ OLi, LiN(SO ₂ F) ₂ (Li[FSI], lithium bis at least one member selected from the group consisting of LiN(SO ₂ CF ₃ ) ₂ (Li[TFSI], lithium bistrifluoromethanesulfonylimide), and LiN(SO ₂ CF ₂ CF _{3 )} good. The lithium salt may be a compound containing a lithium atom and a fluorine atom, and preferably contains LiPF ₆ from the viewpoint of further excellent solubility in a solvent, charge/discharge characteristics of a secondary battery, output characteristics, cycle characteristics, etc.

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

In the electrolytic solution, the amount of fluorine atoms in compound A per mole of lithium atoms in the lithium salt is 0.160 mole or more. The amount of fluorine atoms in compound A may be the amount of fluorine atoms in compound A that are directly bonded to silicon atoms (fluorine atoms in Si—F bonds). By increasing the amount of fluorine atoms in compound A per mole of lithium atoms in the lithium salt, the discharge capacity retention rate of the electrochemical device tends to improve. On the other hand, in conventional electrolytic solutions, when the amount of additives added per mole of lithium atoms of the lithium salt is increased, the resistance after initial charging/discharging and after a charging/discharging cycle test tends to increase. By containing Compound A, the electrolytic solution according to the present embodiment can improve the discharge capacity retention rate of the electrochemical device while suppressing an increase in resistance after initial charge/discharge and after a charge/discharge cycle test.

The amount of fluorine atoms in compound A per mole of lithium atom of the lithium salt is 0.165 mol or more, 0.170 mol or more, 0.180 mol or more, 0.190 mol or more, since the discharge capacity retention rate is further improved. mol or more, 0.200 mol or more, 0.240 mol or more, 0.280 mol or more, 0.320 mol or more, 0.360 mol or more, 0.400 mol or more, 0.500 mol or more, 0.600 mol or more , 0.700 mol or more, 0.800 mol or more, 0.900 mol or more, 1.000 mol or more, 1.200 mol or more, 1.400 mol or more, 1.600 mol or more, 1.800 mol or more, 2 It may be .000 mol or more or 2.400 mol or more. From the viewpoint of further improving the cost-effectiveness of the electrolyte, the amount of fluorine atoms in compound A per mole of lithium atom of the lithium salt is 3.000 mol or less, 2.600 mol or less, 2.200 mol or less, 1 .800 mol or less, 1.400 mol or less, 1.000 mol or less, 0.600 mol or less, 0.500 mol or less, 0.400 mol or less, 0.300 mol or less, 0.200 mol or less, or 0. It may be 180 moles or less.

The amount of fluorine atoms in Compound A per mole of lithium atoms of the lithium salt can be measured using ¹⁹ F NMR. When the electrolytic solution is an electrolytic solution containing Compound A and a compound containing a lithium atom and a fluorine atom (for example, LiPF ₆ ) as a lithium salt, the amount of fluorine atoms in Compound A with respect to 1 mole of lithium atoms of the lithium salt. can be measured, for example, by the following method. First, a calibration curve is created using an electrolytic solution containing Compound A and a lithium salt. A plurality of electrolytic solutions for preparing a calibration curve are prepared in which the content of compound A is a specific amount based on the total amount of the electrolytic solution. For example, the content of compound A in the electrolytic solution for creating a calibration curve is 1% by mass, 3% by mass, or 5% by mass, respectively, based on the total amount of the electrolytic solution. The content of lithium salt is constant in each electrolytic solution for creating a calibration curve. 10 μL of an electrolytic solution for creating a calibration curve is diluted with 700 μL of deuterated acetonitrile containing 1% by volume of tetramethylsilane (TMS) and placed in an NMR tube to prepare a sample for NMR measurement for the calibration curve. Using a sample for NMR measurement for a calibration curve, the area of the peak derived from the fluorine atom in compound A and the area of the peak derived from the fluorine atom of the lithium salt are calculated in ¹⁹ F NMR. When the lithium salt contains multiple fluorine atoms, the area of the peak derived from the fluorine atoms of the lithium salt is the total area of the peaks derived from the multiple fluorine atoms of the lithium salt. The horizontal axis shows the amount of fluorine atoms in compound A relative to 1 mole of fluorine atoms in the lithium salt (amount charged), and the vertical axis shows the amount of fluorine atoms in compound A relative to the area of the peak derived from the fluorine atoms in the lithium salt. Create a calibration curve that plots the ratio of the areas of the derived peaks. Next, ¹⁹ F NMR measurement is performed in the same manner as when creating a calibration curve, except that the electrolyte to be measured is used. Calculate the "ratio of the peak area derived from the fluorine atom in Compound A to the area of the peak derived from the fluorine atom in the lithium salt" in the electrolytic solution to be measured, and calculate the lithium atom 1 of the lithium salt in the electrolytic solution from the calibration curve. The amount of fluorine atoms in Compound A in terms of moles can be calculated.

Non-aqueous solvents include, for example, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propionate, ethyl propionate, propyl propionate, γ-butyllactone, acetonitrile, 1,2-dimethoxyethane, dimethoxy It may be methane, tetrahydrofuran, dioxolane, methylene chloride, methyl acetate, and the like. The non-aqueous solvent may be a single type of these or a mixture of two or more types, preferably a mixture of two or more types.

The content of the non-aqueous solvent is 40% by mass or more, 45% by mass or more, 50% by mass or more, 55% by mass or more, 60% by mass or more, 65% by mass or more, 70% by mass or more, based on the total amount of the electrolyte. It may be 75% by weight or more, 80% by weight or more, or 85% by weight or more, and may be 95% by weight or less, 90% by weight or less, 85% by weight or less, 80% by weight or less, or 75% by weight or less.

The electrolytic solution may further contain materials other than Compound A, lithium salt, and nonaqueous solvent. Other materials may be, for example, cyclic carbonates, cyclic sulfone compounds, or nitrile compounds.

Examples of the cyclic carbonate include vinylene carbonate, fluoroethylene carbonate, methylvinylene carbonate, dimethylvinylene carbonate (4,5-dimethylvinylene carbonate), ethylvinylene carbonate (4,5-diethylvinylene carbonate), and diethylvinylene carbonate. , 2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, and 1,1,2,2-tetrafluoroethylene carbonate.

Examples of the cyclic sulfone compound include 1,3-propanesultone, 1,4-butanesultone, 2,4-butanesultone, 1,3-propenesultone, 1,4-butenesultone, 1-methyl-1,3-propanesultone , 3-methyl-1,3-propane sultone, 1-fluoro-1,3-propane sultone, 3-fluoro-1,3-propane sultone, methylenemethane disulfonic acid ester, ethylenemethane disulfonic acid ester, sulfolane, 2- Methylsulfolane, 3-methylsulfolane, 2-ethylsulfolane, 3-ethylsulfolane, 2,4-dimethylsulfolane, 2-phenylsulfolane, 3-phenylsulfolane, sulfolene, and 3-methylsulfolane, ethylene sulfite, propylene sulfolane phyto, butylene sulfite, vinylene sulfite, and phenylethylene sulfite.

Examples of the nitrile compound include butyronitrile, valeronitrile, n-heptanenitrile, succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, 1,2,3-propanetricarbonitrile, and 1,3,5-pentanetrile. Carbonitrile is mentioned.

The content of other materials is based on the total amount of the electrolyte, 0.1% by mass or more, 0.3% by mass or more, 0.5% by mass or more, 0.7% by mass or more, 0.9% by mass or more, It may be 1.1% by mass or more, 1.3% by mass or more, 1.5% by mass or more, or 1.7% by mass or more, and 20.0% by mass or less, 15.0% by mass or less, 10.0 It may be less than or equal to 5.0% by mass, or less than or equal to 2.0% by mass. The content of the cyclic carbonate may be within the range described above for the content of other materials.

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

In the first step, the material used for the positive electrode mixture layer 10 is dispersed in a dispersion medium using a kneader, a dispersion machine, etc. to obtain a slurry-like positive electrode mixture, and then this positive electrode mixture is processed by a doctor blade method. The positive electrode 6 is obtained by coating the positive electrode current collector 9 by dipping, spraying, or the like, and then volatilizing the dispersion medium. After volatilizing the dispersion medium, a compression molding step using a roll press may be provided as necessary. The positive electrode mixture layer 10 may be formed as a positive electrode mixture layer with a multilayer structure by performing the steps described above from applying the positive electrode mixture to volatilizing the dispersion medium multiple times. The dispersion medium may be water, 1-methyl-2-pyrrolidone (hereinafter also referred to as NMP), or the like.

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

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

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

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

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

Phenyldimethylfluorosilane (PDFS) was synthesized by the following method and used as additive X1. A stirring bar and 25.7 g of phenyldimethylchlorosilane (manufactured by Tokyo Kasei Kogyo Co., Ltd.) were placed in a PFA (perfluoroalkoxyalkane polymer) flask whose interior was purged with nitrogen gas, and ammonium hydrogen fluoride (Fujifilm Wako Pure) was placed there. 9.5 g of powder (manufactured by Yakuhin Co., Ltd.) was added. After stirring for 1 hour with a stirrer under a nitrogen atmosphere, 2.5 g of ammonium hydrogen fluoride was added, and the mixture was further stirred for 1 hour. The solution after the reaction was filtered to remove ammonium hydrogen fluoride. Additive X1 was obtained by adding 2.5 g of dried molecular sieve to the obtained solution and distilling it at normal pressure in an oil bath at 190°C. The purity calculated by GC-FID was 99.3%.

Allyldimethylfluorosilane (ADFS) was synthesized by the following method and used as additive X2. A stirring bar and 20 g of allyldimethylchlorosilane (Tokyo Kasei Kogyo Co., Ltd.) were placed in a PFA flask whose interior was purged with nitrogen gas, and 9. 3g was added. After stirring for 1 hour with a stirrer under a nitrogen atmosphere, 2.5 g of ammonium hydrogen fluoride was added, and the mixture was further stirred for 1 hour. The solution after the reaction was filtered to remove ammonium hydrogen fluoride. Additive X2 was obtained by adding 2.5 g of dried molecular sieve to the obtained solution and distilling it at normal pressure in an oil bath at 70°C. The purity calculated by GC-FID was 99.0%.

<Production of secondary battery 1 for evaluation>
[Preparation of positive electrode mixture layer (positive electrode active material layer)]
Li (Co _0.2 Ni _0.6 Mn _0.2 ) O ₂ (positive electrode active material) 92 parts by mass, carbon black (conductive agent, trade name: Li400, average particle size 48 nm (manufacturer catalog value), Denka Corporation ) 4 parts by mass, polyvinylidene fluoride solution (binder, trade name: Kureha KF Polymer #1120, solid content: 12% by mass, Kureha Co., Ltd.) 33.3 parts by mass (including 4 parts by mass solid content) , and 15 parts by mass of N-methyl-2-pyrrolidone (dispersion medium, NMP) were mixed to prepare a slurry. This slurry was applied onto a positive electrode current collector (aluminum foil with a thickness of 15 μm), dried at 120°C, and then rolled to form a positive electrode with a coating amount of 200 g/m ² on one side and a mixture density of 2.8 g/cm ³ . A coating layer was formed. Thereby, a rectangular positive electrode laminate in which a positive electrode mixture layer was formed on one surface of the positive electrode current collector was obtained.

[Preparation of negative electrode mixture layer (negative electrode active material layer)]
A slurry was prepared by mixing 98 parts by mass of graphite (negative electrode active material) and 2 parts by mass of CMC (carboxymethylcellulose)-SBR (styrene-butadiene rubber) with pure water so that they were uniformly dispersed. This slurry was applied onto a negative electrode current collector (copper foil with a thickness of 10 μm), dried at 80°C, and then rolled to form a negative electrode mixture with a coating amount of 102 g/m ² on one side and a mixture density of 1.6 g/cm ³ . formed a layer. Thereby, a rectangular negative electrode laminate in which a negative electrode mixture layer was formed on one surface of the negative electrode current collector was obtained.

[Preparation of electrolyte]
A mixed solution of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) (EC/DMC/EMC=1:1:1 (volume ratio)) containing 1 mol/L of LiPF ₆ was electrolyzed. An electrolytic solution was prepared by adding 1% by mass of vinylene carbonate (VC) and 3.8% by mass of additive X1 based on the total amount of the solution. The amount of fluorine atoms directly bonded to the silicon atoms of additive X1 per mole of lithium atoms in the lithium salt was 0.317 moles.

[Battery assembly]
A positive electrode cut into a 13.5 cm ² square was sandwiched between polyethylene porous sheets (product name: Hipore (registered trademark), manufactured by Asahi Kasei Corporation, thickness 30 μm) as separators, and then cut into a 14.3 cm ² square. An electrode group was fabricated by overlapping the negative electrodes cut into two. This electrode group was housed in a container (battery exterior body) formed of an aluminum laminate film (trade name: aluminum laminate film, manufactured by Dainippon Printing Co., Ltd.). Next, 1 mL of electrolyte solution was added into the container, and the container was thermally welded to produce a secondary battery 1 for evaluation.

<Production of secondary battery 2 for evaluation>
A secondary battery for evaluation was prepared in the same manner as the secondary battery for evaluation 1, except that 0.38 mass% of the additive X1 was added instead of 3.8 mass% of the additive X1 in preparing the electrolyte. Battery 2 was produced. The amount of fluorine atoms directly bonded to the silicon atoms of additive X1 was 0.032 mol per mol of lithium atom of the lithium salt.

<Production of secondary battery 3 for evaluation>
A secondary battery for evaluation was prepared in the same manner as secondary battery for evaluation 1, except that 0.29 mass% of the additive X2 was added in place of 3.8 mass% of the additive X1 in preparing the electrolyte. Battery 3 was produced. The amount of fluorine atoms directly bonded to the silicon atoms of additive X2 was 0.032 moles per mole of lithium atoms in the lithium salt.

<Production of secondary battery 4 for evaluation>
A secondary battery for evaluation was prepared in the same manner as the secondary battery for evaluation 1, except that 2.9% by mass of the additive X2 was added in place of the 3.8% by mass of the additive X1 in preparing the electrolyte. Battery 4 was produced. The amount of fluorine atoms directly bonded to the silicon atoms of additive X2 was 0.316 moles per mole of lithium atoms in the lithium salt.

<Preparation of reference secondary battery>
A reference secondary battery was produced in the same manner as evaluation secondary battery 1 except that 3.8% by mass of the additive X1 was not added in preparing the electrolytic solution.

<Measurement of AC impedance>
AC impedance of evaluation secondary batteries 1 to 4 and reference secondary battery was measured by the following method. AC impedance was measured by connecting a potentiogalvanostat type 1287 and a frequency response analyzer type 1260 (manufactured by Solartron) in a constant temperature bath at 25° C., an applied voltage of 10 mV, and a frequency range of 0.05 Hz to 200 kHz. All cells were measured at SOC 100 (fully charged state). FIG. 3 shows the measurement results of AC impedance. In Figure 3, "Ref" is the reference secondary battery, "PDFS3.8" is the evaluation secondary battery 1, "PDFS0.38" is the evaluation secondary battery 2, and "ADFS0.29" is the evaluation secondary battery. Battery 3, "PDFS3.8" shows the measurement results when secondary battery 4 for evaluation was used.

As shown in FIG. 3, the resistance of additive X2 (ADFS) increased significantly as the amount added was increased. On the other hand, even when the additive amount of Additive X1 (PDFS) was increased, no increase in resistance was observed after the initial charge/discharge and after the charge/discharge cycle test.

<Evaluation of discharge capacity maintenance rate>
For the evaluation secondary batteries 1 and 2 and the reference secondary battery, initial charging and discharging was carried out by 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)"). Subsequently, the same charge/discharge cycle was performed once in an environment of 50°C.

After the initial charging and discharging, the discharge capacity retention rate of each secondary battery was evaluated by a cycle test in which charging and discharging were repeated. The charging pattern was to perform constant current charging at a current value of 0.5C to an upper limit voltage of 4.2V for evaluation secondary batteries 1 and 2 and reference secondary batteries in an environment of 45°C, and then Constant voltage charging was performed at .2V. The charging termination condition was a current value of 0.05C. Regarding discharge, constant current discharge was performed at 1C to 2.7V, 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. Note that at the 100th cycle and the 300th cycle, charging and discharging were performed to confirm the capacity. That is, constant current charging at 0.2C was performed to the 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. Regarding discharge, constant current discharge was performed at 0.2C to 2.7V. The 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 are shown in Figure 4. In FIG. 4, "F0_2" indicates the measurement results using the reference secondary battery, "PDFS3.8_1" indicates the evaluation secondary battery 1, and "PDFS0.38_2" indicates the measurement results using the evaluation secondary battery 2. Table 1 shows the discharge capacity retention rate after 500 cycles.

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

Claims (11)

Comprising a compound represented by the following formula (A) and a lithium salt,
An electrolytic solution wherein the amount of fluorine atoms in the compound is 0.160 mol or more per 1 mol of lithium atoms of the lithium salt.

[In formula (A), R each independently represents a substituted or unsubstituted C _1-6 alkyl group, a substituted or unsubstituted phenyl group, or a substituted or unsubstituted benzyl group,
At least one of R is the substituted or unsubstituted phenyl group or the substituted or unsubstituted benzyl group. ] The electrolytic solution according to claim 1, wherein the content of the compound is 2.0% by mass or more based on the total amount of the electrolytic solution. The electrolytic solution according to claim 1 or 2, wherein the C _1-6 alkyl group is a halogen atom-substituted C _1-6 alkyl group or an unsubstituted C _1-6 alkyl group. The electrolytic solution according to claim 1 or 2, wherein R does not contain a fluorine atom. The electrolytic solution according to claim 1 or 2, wherein the compound is phenyldimethylfluorosilane. An electrochemical device comprising a positive electrode, a negative electrode, and the electrolytic solution according to claim 1 or 2. The electrochemical device according to claim 6, wherein the electrochemical device is a non-aqueous electrolyte secondary battery or a capacitor. An additive for electrolyte solution containing a compound represented by the following formula (A).

[In formula (A), R each independently represents a substituted or unsubstituted C _1-6 alkyl group, a substituted or unsubstituted phenyl group, or a substituted or unsubstituted benzyl group,
At least one of R is the substituted or unsubstituted phenyl group or the substituted or unsubstituted benzyl group. ] The additive for electrolytic solution according to claim 8, wherein the C _1-6 alkyl group is a halogen atom-substituted C _1-6 alkyl group or an unsubstituted C _1-6 alkyl group. The additive for electrolyte solution according to claim 8 or 9, wherein R does not contain a fluorine atom. The additive for an electrolytic solution according to claim 8 or 9, wherein the compound is phenyldimethylfluorosilane.

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