TW202032847A - Electrolyte and electrochemical device - Google Patents

Abstract

One aspect of this invention is an electrolyte comprising a compound represented by formula (1) and a cyclic compound having a ring containing a sulfur atom. In formula (1), R1 to R3 independently represent an alkyl group or a fluorine atom, R4 represents an alkylene group, and R5 represents an organic group containing a nitrogen atom.

Description

Electrolyte and electrochemical device

The invention relates to an electrolyte and an electrochemical device.

In recent years, due to the popularization of portable electronic devices and electric vehicles, the following high-performance electrochemical devices are being required: non-aqueous electrolyte secondary batteries represented by lithium ion secondary batteries, capacitors, and the like. As a means for improving the performance of electrochemical devices, for example, the following method is being studied: adding predetermined additives to the electrolyte. Patent Document 1 discloses an electrolyte for a non-aqueous electrolyte battery, which contains a specific siloxane compound in order to improve cycle characteristics and internal resistance characteristics. [Prior Technical Literature] (Patent Document)

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

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

式(1)中，R¹ ～R³ 各自獨立地表示烷基或氟原子，R⁴ 表示伸烷基，R⁵ 表示包含硫原子之有機基團。One aspect of the present invention is an electrolyte solution, which contains: a compound represented by the following formula (1); and, a cyclic compound which does not have a silicon atom and has a ring containing a sulfur atom;

In formula (1), R ¹ to R ³ each independently represent an alkyl group or a fluorine atom, R ⁴ represents an alkylene group, and R ⁵ represents an organic group containing a sulfur atom.

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

At least one of R ¹ to R ³ may be a fluorine atom. The number of silicon atoms in one molecule of the compound represented by formula (1) may be one.

式(3)中，R⁸ 表示烷基，＊表示鍵結鍵(bond)；

式(4)中，R⁹ 表示烷基，＊表示鍵結鍵；

式(5)中，R¹⁰ 表示烷基，＊表示鍵結鍵。R ⁵ may be a group represented by any one of the following formula (3), formula (4), and formula (5):

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

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

In the formula (5), R ¹⁰ represents an alkyl group, and * represents a bonding bond.

式(X)中，A¹ 表示包含碳數為3～5的伸烷基或碳數為3～5的伸烯基之基團，該伸烷基和該伸烯基中的氫原子可被烷基、環烷基、芳基或氟基取代。The cyclic compound may include a cyclic sulfonate compound. The cyclic sulfonate compound may include a compound represented by the following formula (X):

In the formula (X), A ¹ represents a group containing an alkylene group having 3 to 5 carbons or an alkenylene group having 3 to 5 carbons, and the hydrogen atoms in the alkylene group and the alkenylene group may be Alkyl, cycloalkyl, aryl or fluoro substituted.

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

式(Y)中，A² 表示碳數為3～5的伸烷基或碳數為3～5的伸烯基，該伸烷基和該伸烯基中的氫原子可被烷基、環烷基或芳基所取代；

式(Z)中，A³ 表示碳數為3～5的伸烷基或碳數為3～5的伸烯基，該伸烷基和該伸烯基中的氫原子可被烷基、環烷基或芳基取代。The cyclic compound may include at least one selected from the group consisting of compounds represented by formula (Y) and compounds represented by formula (Z):

In the formula (Y), A ² represents an alkylene group having 3 to 5 carbons or an alkenylene group having 3 to 5 carbons, and the alkylene group and the hydrogen atom in the alkenylene group may be Alkyl or aryl substituted;

In the formula (Z), A ³ represents an alkylene group having 3 to 5 carbons or an alkenylene group having 3 to 5 carbons. The alkylene group and the hydrogen atom in the alkenylene group may be Alkyl or aryl substitution.

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

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

The negative electrode may contain carbon materials. The carbon material may contain graphite. The negative electrode may further contain the following material, which contains at least one element selected from the group consisting of silicon and tin.

The electrochemical device may be a non-aqueous electrolyte secondary battery or a capacitor. [effect]

According to the present invention, it is possible to provide an electrolyte solution which can improve the performance of an electrochemical device.

Hereinafter, embodiments of the present invention will be described while referring to the drawings as appropriate. However, the present invention is not limited to the following embodiments.

Fig. 1 is a perspective view showing an electrochemical device according to an embodiment. In this embodiment, the electrochemical device is a non-aqueous electrolyte secondary battery. As shown in Figure 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 case 3 for accommodating the electrode group 2. A positive current collecting terminal (tab) 4 and a negative current collecting terminal 5 are respectively provided on the positive electrode and the negative electrode. The positive electrode current collector terminal 4 and the negative electrode current collector terminal 5 respectively protrude from the inside to the outside of the battery case 3 so that the positive electrode and the negative electrode can be electrically connected to the outside of the non-aqueous electrolyte secondary battery 1. The battery case 3 is filled with electrolyte (not shown). The non-aqueous electrolyte secondary battery 1 may be a battery (coin type, cylindrical type, laminated type, etc.) other than the so-called "stack type" as described above.

The battery case 3 may be, for example, a container formed of a laminated film. The laminated film may be, for example, a laminated film, which is formed by sequentially laminating the following: resin films such as polyethylene terephthalate (PET) film; metal foils such as aluminum, copper, and stainless steel; and, Sealant layer of acrylic etc.

Fig. 2 is an exploded perspective view showing one embodiment of the electrode group 2 of the non-aqueous electrolyte secondary battery 1 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 so that the surfaces on the positive electrode mixture layer 10 side and the negative electrode mixture layer 12 side face the separator 7, respectively.

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

The positive electrode current collector 9 is formed of, for example, aluminum, titanium, stainless steel, nickel, baked carbon, conductive polymer, conductive glass, and the like. The positive electrode current collector 9 may be treated with carbon, nickel, titanium, silver, etc., on the surface of aluminum, copper, etc., for the purpose of improving adhesion, conductivity, and oxidation resistance. From the viewpoint of electrode strength and energy density, the thickness of the positive electrode current collector 9 is, for example, 1 to 50 μm.

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

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

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 may be 99% by mass or less based on the total amount of the positive electrode mixture layer.

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

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

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

The separator 7 is not particularly limited as long as it electrically insulates the positive electrode 6 and the negative electrode 8 and allows ions to penetrate, and has resistance to oxidation on the positive electrode 6 side and reduction on the negative electrode 8 side. As a material (material) of such a spacer 7, resin, an inorganic substance, etc. are mentioned, for example.

Examples of resins include olefin-based polymers, fluorine-based polymers, cellulose-based polymers, polyimides, nylon and the like. From the viewpoint of being stable to the electrolyte and excellent in liquid retention, the separator 7 is preferably a porous sheet or non-woven fabric formed of polyolefin such as polyethylene and polypropylene.

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 spacer 7 may be, for example, a spacer formed by attaching a fibrous or particulate inorganic substance to a film-shaped substrate such as a nonwoven fabric, a woven fabric, a microporous film, or the like.

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

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

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 can adsorb and release lithium ions. Examples of negative electrode active materials include carbon materials; metal composite oxides; oxides or nitrides of group IV elements such as tin, germanium, and silicon; lithium monomers; lithium alloys such as lithium aluminum alloys; Sn, Si Such as metals capable of forming 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 alone or a mixture of two or more. The shape of the negative electrode active material may be, for example, particulate.

Examples of carbon materials include amorphous carbon materials, natural graphite, composite carbon materials formed by forming an amorphous carbon material from natural graphite, artificial graphite (resin raw materials such as epoxy resin, phenol resin, or petroleum Graphite obtained by calcining pitch-based materials obtained from coal, etc.). 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 the negative electrode active materials, carbon materials have high conductivity and are particularly excellent in low-temperature characteristics and cycle stability. From the viewpoint of increasing the capacity, graphite is preferred among the carbon materials. Among graphite, it is preferable that the interlayer (d002) of the carbon mesh surface of the X-ray wide-angle diffraction method is less than 0.34 nm, and more preferably 0.3354 nm or more and 0.337 nm or less. Carbon materials satisfying such conditions are sometimes referred to as quasi-anisotropic carbon.

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

From the viewpoint of further improving the performance of the electrochemical device such as low-temperature input characteristics, the negative electrode 8 preferably contains a carbon material as the negative electrode active material, more preferably contains graphite, and still more preferably contains the following mixture, which contains The carbon material and the material containing at least one element selected from the group consisting of silicon and tin, particularly preferably a mixture of graphite and silicon oxide. The content of the carbon material (graphite) in the mixture relative to the material (silicon oxide) of at least one element selected from the group consisting of silicon and tin, based on the total amount of the mixture, may be 1 Mass% or more or 3 mass% or more, and may be 30 mass% or less.

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

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

The negative electrode mixture layer 12 may contain a thickener in order to adjust the viscosity. The thickener is not particularly limited, and can be: carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and the like Wait. The thickener may be one of these alone or a mixture of two or more.

When the negative electrode mixture layer 12 contains a thickener, its content is not particularly limited. From the standpoint of the coatability of the negative electrode mixture layer, the content of the thickener may be 0.1% by mass based on the total amount of the negative electrode mixture layer. Above, 0.2% by mass or more is preferable, and 0.5% by mass or more is more preferable. From the viewpoint of suppressing the decrease in battery capacity or the increase in the resistance between the negative electrode active materials, the content of the thickening agent can be 5% by mass or less, preferably 3% by mass or less, based on the total amount of the negative electrode mixture layer. The mass% or less is preferable.

式(1)中，R¹ ～R³ 各自獨立地表示烷基或氟原子，R⁴ 表示伸烷基，R⁵ 表示包含硫原子之有機基團。In one embodiment, the electrolyte contains: a compound represented by the following formula (1), a cyclic compound having no silicon atom and a ring containing a sulfur atom (hereinafter also simply referred to as "cyclic compound"), and electrolyte salt And non-aqueous solvents.

In formula (1), R ¹ to R ³ each independently represent an alkyl group or a fluorine atom, R ⁴ represents an alkylene group, and R ⁵ represents an organic group containing a sulfur atom.

The carbon number of the alkyl group represented by R ¹ to R ³ may be 1 or more, and may be 3 or less. R ¹ to R ³ may be methyl, ethyl, or propyl, and may be linear or branched. At least one of R ¹ to R ³ is preferably a fluorine atom. R may be any one of a fluorine atom, any one among the R ¹ ~ R ³ 2 can be the fluorine atom, R ¹ ~ R ³ are both fluorine atoms may be all among ¹ ~ R ^3.

The carbon number of the alkylene group represented by R ⁴ may be 1 or more or 2 or more, and may be 5 or less or 4 or less. The alkylene group represented by R ⁴ may be methylene, ethylene, propylene, butylene, or pentylene, and may be linear or branched.

In one embodiment, the number of silicon atoms in one molecule of the compound represented by formula (1) is one. In other words, in one embodiment, the organic group represented by R ⁵ does not contain a silicon atom.

式(3)中，R⁸ 表示烷基，烷基可與上述的由R¹ ～R³ 表示的烷基相同，＊表示鍵結鍵；

式(4)中，R⁹ 表示烷基，烷基可與上述的由R¹ ～R³ 表示的烷基相同，＊表示鍵結鍵；

式(5)中，R¹⁰ 表示烷基，烷基可與上述的由R¹ ～R³ 表示的烷基相同，＊表示鍵結鍵。From the viewpoint of being able to further improve the performance of the electrochemical device, R ^{5 may} preferably be a group represented by any of the following formulas (3), (4), and (5):

In formula (3), R ⁸ represents an alkyl group, and the alkyl group may be the same as the alkyl group represented by R ¹ to R ³ above, and * represents a bonding bond;

In formula (4), R ⁹ represents an alkyl group, the alkyl group may be the same as the above-mentioned alkyl group represented by R ¹ to R ³ , and * represents a bonding bond;

In the formula (5), R ¹⁰ represents an alkyl group, the alkyl group may be the same as the alkyl group represented by R ¹ to R ³ described above, and * represents a bonding bond.

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

The cyclic compound is a compound having a ring (heterocyclic ring) containing a sulfur atom. In addition, the cyclic compound is a compound other than the compound represented by the above formula (1). In other words, a cyclic compound is a compound that does not have a silicon atom.

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

式(X)中，A¹ 表示包含碳數為3～5的伸烷基或碳數為3～5的伸烯基之基團，該伸烷基和該伸烯基中的氫原子可被烷基、環烷基、芳基或氟基取代。The cyclic sulfonate compound having a ring containing one -OSO ₂ -group may be, for example, a compound represented by the following formula (X):

In the formula (X), A ¹ represents a group containing an alkylene group having 3 to 5 carbons or an alkenylene group having 3 to 5 carbons, and the hydrogen atoms in the alkylene group and the alkenylene group may be Alkyl, cycloalkyl, aryl or fluoro substituted.

The carbon number of the aforementioned alkyl group may be, for example, 1-12. The number of carbon atoms of the cycloalkyl group may be 3-6, for example. The carbon number of the aryl group may be, for example, 6-12.

A ^{1 is} preferably an alkylene group having 3 carbons or an alkenylene group having 3 carbons. In other words, the cyclic sulfonate compound is preferably a compound represented by the following formula (X-1) or (X-2).

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

As the cyclic sulfonate compound represented by the formula (X), for example, 1,3-propane sultone, 1,4-butane sultone, 2,4-butane sultone, 1, 3-propene sultone, 1,4-butene sultone, 1-methyl-1,3-propane sultone, 3-methyl-1,3-propane sultone, 1-fluoro-1 ,3-propane sultone, 3-fluoro-1,3-propane sultone and other monosulfonates. From the viewpoint of improving the performance of the electrochemical device, among these, 1,3-propane sultone (in formula (X-1), all of R ¹¹ to R ¹⁶ are compounds of hydrogen atoms) ) Or 1-propene-1,3-sultone (in formula (X-2), all of R ¹⁷ to R ²⁰ are hydrogen atoms).

式(X-3)中，B¹ 及B² 各自獨立地表示碳數為1～5的伸烷基或碳數為1～5的伸烯基，該伸烷基和該伸烯基中的氫原子可被烷基、環烷基、芳基或氟基取代。The cyclic sulfonate compound having a ring containing 2 -OSO ₂ -groups may be, for example, a compound represented by the following formula (X-3):

In formula (X-3), B ¹ and B ² each independently represent an alkylene group having 1 to 5 carbons or an alkenylene group having 1 to 5 carbons, the alkylene group and the alkenylene group The hydrogen atom may be substituted by an alkyl group, a cycloalkyl group, an aryl group, or a fluoro group.

B ¹ and B ^{2 are} preferably unsubstituted alkylene groups having 1 or 2 carbon atoms. Such cyclic sulfonic acid ester compounds may be disulfonic acid esters such as methylene methane disulfonate and ethylene methane disulfonate.

式(Y)、(Z)中，A² 及A³ 表示碳數為3～5的伸烷基或碳數為3～5的伸烯基，該伸烷基和該伸烯基中的氫原子可被烷基、環烷基或芳基取代。The cyclic compound may include, for example, at least one selected from the group consisting of compounds represented by formula (Y) and compounds represented by formula (Z):

In the formulas (Y) and (Z), A ² and A ³ represent an alkylene group having 3 to 5 carbons or an alkenylene group having 3 to 5 carbons, the alkylene group and the hydrogen in the alkenylene group Atoms may be substituted by alkyl, cycloalkyl or aryl groups.

The carbon numbers of the alkyl group, cycloalkyl group, and aryl group in A ² and A ³ are the same as the carbon numbers of the alkyl group, cycloalkyl group, and aryl group described in formula (X), respectively.

The compound represented by the formula (Y) includes, for example, cyclobutane, 2-methylcyclobutane, 3-methylcyclobutane, 2-ethylcyclobutane, 3-ethylcyclobutane, 2,4-Dimethylcyclobutene, 2-phenylcyclobutene, 3-phenylcyclobutene, cyclobutene (sulfolene), 3-methylcyclobutene, etc. From the viewpoint that the performance of the electrochemical device can be further improved, the compound represented by the formula (Y) is preferably cyclobutane.

Examples of the compound represented by the formula (Z) include ethylene sulfide, propane sulfide, butane sulfide, ethylene sulfide, and phenyl ethylene sulfide. From the viewpoint that the performance of the electrochemical device can be further improved, the compound represented by formula (Z) is preferably ethylene sulfide.

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

From the viewpoint of improving the performance of the electrochemical device, the content of the cyclic compound based on the total amount of electrolyte is preferably: 0.001 mass% or more, 0.005 mass% or more, 0.01 mass% or more, 0.05 mass% Or more, or 0.1% by mass or more, and 5% by mass or less, 3% by mass or less, 2% by mass or less, or 1% by mass or less.

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

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

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

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

The non-aqueous solvent may be, for example: ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, acetonitrile, 1,2-dimethoxyethane , Dimethoxymethane, tetrahydrofuran, dioxolane (dioxolane), dichloromethane, methyl acetate, etc. The non-aqueous solvent may be one of these alone or a mixture of two or more, preferably a mixture of two or more.

The electrolyte solution may further contain other materials other than the compound represented by formula (1), cyclic compound, electrolyte salt, and non-aqueous solvent. As other materials, for example, cyclic carbonates such as fluorine-containing cyclic carbonates and cyclic carbonates having carbon-carbon double bonds; compounds having nitrogen atoms; compounds represented by formula (1) and cyclic compounds Other compounds with sulfur atoms; cyclic carboxylic acid esters, etc.

The fluorine-containing cyclic carbonate may be, for example, 4-fluoro-1,3-dioxolane-2-one (fluoroethylene carbonate; FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, etc., with 4-fluoro-1,3-bis Oxololane-2-one (fluoroethylene carbonate; FEC) is preferred. The cyclic carbonate having a carbon-carbon double bond may be, for example, vinylene carbonate. The compound containing a nitrogen atom may be a nitrile compound such as succinonitrile.

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

Specifically, according to the electrolytic solution of one embodiment, the performance as an electrochemical device can suppress the increase in volume after the electrochemical device is stored at a high temperature. In addition, with the electrolytic solution of one embodiment, the cycle characteristics of the electrochemical device can be improved (in particular, the capacity retention rate after the cycle test is improved, and the discharge DCR increase after the cycle test is suppressed). In addition, according to the electrolytic solution of one embodiment, the discharge DCR after the electrochemical device is stored at a high temperature can be reduced.

Next, a method of manufacturing the non-aqueous electrolyte secondary battery 1 will be described. The manufacturing method of the non-aqueous electrolyte secondary battery 1 includes: a first step, which obtains a positive electrode 6; a second step, which obtains a negative electrode 8; and a third step, which houses the electrode group 2 in a battery outer case 3; and , The fourth step, which injects the electrolyte into the battery casing 3.

In the first step, the materials used in the positive electrode mixture layer 10 are dispersed in a dispersion medium using a kneader, disperser, etc. to obtain a slurry positive electrode mixture, and then a doctor blade method, dipping method, This positive electrode mixture is applied to the positive electrode current collector 9 by a spray method or the like, and then the dispersion medium is volatilized, thereby obtaining the positive electrode 6. After volatilizing the dispersion medium, a compression molding step by roll pressing can be set as needed. The positive electrode mixture layer 10 can be formed into a positive electrode mixture layer of a multilayer structure by performing the steps from the application of the positive electrode mixture to the volatilization of 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 of forming the negative electrode mixture layer 12 on the negative electrode current collector 11 may be the same method as the first step described above.

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

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

As another embodiment, the electrochemical device may be a capacitor. The capacitor may be provided with the same as the non-aqueous electrolyte secondary battery 1 described above: an electrode group consisting of a positive electrode, a negative electrode, and a separator; and a pouch-shaped battery case for accommodating the electrode group. The details of each component in the capacitor are the same as those of the non-aqueous electrolyte secondary battery 1. [Example]

Hereinafter, the present invention will be described in detail through examples, but the present invention is not limited by these examples.

(Example 1) [Preparation of positive electrode] Acetylene black (AB) (4% by mass) and binder (4% by mass) as a conductive agent were sequentially added to lithium nickel cobalt manganate (92% by mass) as the positive electrode active material %) and mix. By adding NMP as a dispersion medium to the obtained mixture and kneading, a slurry-like positive electrode mixture is prepared. A predetermined amount of this positive electrode mixture was uniformly and homogeneously applied to an aluminum foil having a thickness of 20 μm as a positive electrode current collector. Then, after volatilizing the dispersion medium, it was pressed to a density of 2.8 g/cm ³ by pressing to obtain a positive electrode.

[Preparation of negative electrode] A binder and carboxymethyl cellulose as a thickener are added to the negative electrode active material containing graphite and silicon oxide. These mass ratios are set as graphite: silicon oxide: binder: tackifier = 92:5:1.5:1.5. The slurry-like negative electrode mixture is prepared by adding water as a dispersion medium to the obtained mixture and kneading it. A predetermined amount of this negative electrode mixture was uniformly and homogeneously applied to a rolled copper foil having a thickness of 10 μm as a negative electrode current collector. Then, after volatilizing the dispersion medium, it was pressed to a density of 1.6 g/cm ³ by pressing to obtain a negative electrode.

[Production of Lithium Ion Secondary Battery] A porous sheet made of polyethylene (trade name: HIPORE (registered trademark), manufactured by Asahi Kasei Co., Ltd., thickness 30 μm), which is a spacer, is cut into 13.5 cm ² squares Clamp the positive electrode and further stack the negative electrode cut into 14.3 cm ² squares to make an electrode group. This electrode group was housed in a container (battery case) formed of a laminated film made of aluminum (trade name: aluminum laminated film, manufactured by Dainippon Printing Co., Ltd.). Then, 1 mL of the electrolyte solution was added to the container, and the container was thermally welded to produce a lithium ion secondary battery for evaluation. As the electrolyte, an electrolyte is used, which is a 1 mol/L mixed solution containing LiPF ₆ of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate, with respect to the total amount of the mixed solution, adding 1 Mass% of vinylene carbonate (VC), 0.5% by mass of 4-fluoro-1,3-dioxolane-2-one (fluoroethylene carbonate; FEC), 0.5% by mass of the following It is composed of compound A represented by formula (6) and 0.5% by mass (based on the total amount of electrolyte) of 1,3-propane sultone.

(Example 2) Regarding Example 1, except that the addition amount of the compound A was changed to 2.0% by mass, the same procedure as in Example 1 was carried out to produce a lithium ion secondary battery.

(Example 3) About Example 1, except having added 0.3 mass% of compound B represented by following formula (7) instead of compound A, it carried out similarly to Example 1, and produced the lithium ion secondary battery.

(Example 4) About Example 1, except having added 0.1 mass% of compound C represented by following formula (8) instead of compound A, it carried out similarly to Example 1, and produced a lithium ion secondary battery.

(Example 5) Regarding Example 1, except that 1,3-propene sultone was used instead of 1,3-propane sultone, the same procedure as in Example 1 was carried out to produce a lithium ion secondary battery.

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

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

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

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

[Evaluation of high temperature storage characteristics] Each secondary battery produced was charged with a constant current at a current value of 0.1 C in an environment at 25°C until the upper limit voltage was 4.2 V, and then charged with a constant voltage at 4.2 V. The charge cutoff condition is set to a current value of 0.01C. Then, the secondary battery was stored in a thermostat at 60°C for 2 weeks. A hydrometer (electronic hydrometer MDS-300, manufactured by Alfa Mirage) according to the Archimedes method was used to measure the volume (V1) of each secondary battery before the storage, and to stand still after storage The volume (V2) of each secondary battery after in an environment of 25°C. Using the measured V1 and V2, calculate the volume change rate (%)=V2/V1×100. The results are shown in Table 1.

[Evaluation of cycle characteristics] (First charge and discharge) For each of the manufactured secondary batteries, initial charge and discharge were performed in the following manner. First, perform constant current charging at a current value of 0.1 C in an environment of 25°C until the upper limit voltage is 4.2 V, and then perform constant voltage charging at 4.2 V. The charge cutoff condition is set to a current value of 0.01C. Then, a constant current discharge with a cut-off voltage of 2.7 V was performed at a current value of 0.1 C. Repeat this charge and discharge cycle 3 times. In addition, "C" used as a unit of the current value means "current value (A)/battery capacity (Ah)" (the same applies hereinafter).

(Measurement of Discharge DCR) For each secondary battery after the initial charge and discharge, the DC resistance during discharge (discharge DCR) was measured in the following manner. First, charge with a constant current of 0.2 C to the upper limit voltage of 4.2 V, and then charge with a constant voltage of 4.2 V. The charge cutoff condition is set to a current value of 0.02C. Then, after performing a constant current discharge with a cut-off voltage of 2.7 V at a current value of _{0.2 C} , the current value at this time is set to I _0.2C and the voltage change 10 seconds after the start of discharge is set to ΔV _0.2C . Then, charge with a constant current of 0.2 C to the upper limit voltage of 4.2 V, and then charge with a constant voltage of 4.2 V (the charging cut-off condition is set to a current value of 0.02 C), and then conduct a cut-off voltage of 2.7 with a current value of 0.5 C. After the constant current discharge of V, the current value at this time is set to I _0.5C , and the voltage change 10 seconds after the start of discharge is set to ΔV _0.5C . From the same charge and discharge, evaluate the current value I _{1C of} 1 C and the voltage change ΔV _1C 10 seconds after the start of discharge. Use the least square method to draw a linear approximate straight line at the 3 drawing points (I _0.2C ,ΔV _0.2C ), (I _0.5C ,ΔV _0.5C ), (I _1C ,ΔV _1C ) of the current value-voltage change, And its slope is set to discharge DCR value R1.

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

[Table 1]

It can be seen from Table 1 that the electrolyte solutions of Examples 1 to 7 contain the compound represented by the formula (1) and the cyclic compound, and the lithium ion secondary batteries of Comparative Examples 1 to 2 do not contain the compound represented by the formula (1) Compared with the lithium ion secondary batteries of Comparative Examples 1 to 2, the high temperature storage of lithium ion secondary batteries using the electrolytes of Examples 1 to 7 The characteristics are more excellent (the volume change rate after high-temperature storage is small), and the cycle characteristics are also more excellent (the capacity retention rate after the cycle test is high and the increase in discharge DCR can be suppressed). We think the reason is that in addition to the cyclic compound having formed a stable coating on the positive electrode or negative electrode, the compound represented by formula (1) also contributes to stabilizing the electrolyte.

In addition, for the secondary batteries of Example 1 and Comparative Examples 1 and 2, the discharge DCR after the above-mentioned high-temperature storage was also measured. As a result, the discharge DCR of Example 1 was 1.70 Ω, the discharge DCR of Comparative Example 1 was 1.98 Ω, and the discharge DCR of Comparative Example 2 was 1.79 Ω. The lithium ion secondary battery of Comparative Example 2 uses an electrolyte containing 1,3-propane sultone and does not contain compound A, and the lithium ion secondary battery of Comparative Example 1 uses an electrolyte that does not contain compound A and 1,3-propane Compared with the lithium ion secondary battery of Comparative Example 1, the lithium ion secondary battery of Comparative Example 2 has an even lower discharge DCR after high-temperature storage. We believe that the reason is that 1,3-propane sultone has formed a stable film on the positive or negative electrode. In addition, the lithium ion secondary battery of Example 1 uses an electrolyte solution containing both compound A and 1,3-propane sultone. Compared with the lithium ion secondary batteries of Comparative Examples 1 and 2, the Examples The discharge DCR after high-temperature storage of the lithium ion secondary battery of 1 was better by about 15% and about 5%, respectively. We believe that the reason is that in addition to 1,3-propane sultone has formed a stable film on the positive or negative electrode, compound A also contributes to stabilizing the electrolyte.

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

Fig. 1 is a perspective view showing a non-aqueous electrolyte secondary battery as an electrochemical device according to an embodiment. Fig. 2 is an exploded perspective view showing the electrode group of the secondary battery shown in Fig. 1.

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Claims (14)

An electrolyte solution containing: a compound represented by the following formula (1); and, a cyclic compound having no silicon atom and a ring containing a sulfur atom;

In formula (1), R ¹ to R ³ each independently represent an alkyl group or a fluorine atom, R ⁴ represents an alkylene group, and R ⁵ represents an organic group containing a sulfur atom. The electrolytic solution according to claim 1, wherein at least one of R ¹ to R ³ is a fluorine atom. The electrolyte according to claim 1 or 2, wherein the number of silicon atoms in one molecule of the compound represented by formula (1) is one. The electrolyte solution according to any one of claims 1 to 3, wherein the aforementioned R ⁵ is a group represented by any one of the following formulas (3), (4), and (5):

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

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

In the formula (5), R ¹⁰ represents an alkyl group, and * represents a bonding bond. The electrolytic solution according to any one of claims 1 to 4, wherein the cyclic compound includes a cyclic sulfonate compound. The electrolytic solution according to claim 5, wherein the cyclic sulfonate compound contains a compound represented by the following formula (X):

In the formula (X), A ¹ represents a group containing an alkylene group having 3 to 5 carbons or an alkenylene group having 3 to 5 carbons, and the hydrogen atoms in the alkylene group and the alkenylene group may be Alkyl, cycloalkyl, aryl or fluoro substituted. The electrolyte according to claim 6, wherein the compound represented by the formula (X) is selected from the group consisting of 1,3-propane sultone and 1-propene-1,3-sultone At least one of them. The electrolytic solution according to any one of claims 1 to 7, wherein the cyclic compound includes at least 1 selected from the group consisting of a compound represented by formula (Y) and a compound represented by formula (Z) Species:

In the formula (Y), A ² represents an alkylene group having 3 to 5 carbons or an alkenylene group having 3 to 5 carbons. The alkylene group and the hydrogen atom in the alkenylene group may be substituted by an alkyl group or a cycloalkane group. Group or aryl substitution;

In the formula (Z), A ³ represents an alkylene group having 3 to 5 carbons or an alkenylene group having 3 to 5 carbons. The alkylene group and the hydrogen atom in the alkenylene group may be Alkyl or aryl substitution. The electrolytic solution according to any one of claims 1 to 8, wherein the total amount of the content of the compound represented by the formula (1) and the content of the cyclic compound is calculated on the basis of the total amount of the electrolytic solution 10% by mass or less. An electrochemical device comprising: a positive electrode, a negative electrode, and the electrolyte according to any one of claims 1 to 9. The electrochemical device according to claim 10, wherein the negative electrode contains a carbon material. The electrochemical device according to claim 11, wherein the carbon material contains graphite. The electrochemical device according to claim 11 or 12, wherein the negative electrode further contains a material including at least one element selected from the group consisting of silicon and tin. The electrochemical device according to any one of claims 10 to 13, wherein the electrochemical device is a non-aqueous electrolyte secondary battery or a capacitor.

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