WO2020027004A1

WO2020027004A1 - Electrolyte and electrochemical device

Info

Publication number: WO2020027004A1
Application number: PCT/JP2019/029544
Authority: WO
Inventors: 馨今野; 薫平山田
Original assignee: 日立化成株式会社
Priority date: 2018-07-31
Filing date: 2019-07-26
Publication date: 2020-02-06
Also published as: TWI812766B; TW202012420A; JPWO2020027004A1

Abstract

The present invention provides an electrolyte containing a compound indicated by formula (1) and a fluorine-containing cyclic carbonate. [In formula (1) R¹–R³ each independently indicate an alkyl group or a fluorine atom, R⁴ indicates an alkylene group, and R⁵ indicates an organic group including a nitrogen atom.]

Description

Electrolyte and electrochemical device

The present invention relates to an electrolytic solution and an electrochemical device.

In recent years, with the spread of portable electronic devices and electric vehicles, high-performance electrochemical devices such as non-aqueous electrolyte secondary batteries represented by lithium ion secondary batteries and capacitors have been required. As a means for improving the performance of an electrochemical device, for example, a method of adding a predetermined additive to an electrolytic solution has been studied. Patent Document 1 discloses an electrolyte for a non-aqueous electrolyte battery containing a specific siloxane compound in order to improve cycle characteristics and internal resistance characteristics.

JP-A-2005-005329

In order to apply electrochemical devices to in-vehicle applications, it is important to improve heat resistance at high temperatures. An index of the heat resistance of the electrochemical device includes, for example, suppression of expansion of the electrochemical device after storage at a high temperature. Alternatively, deterioration of various performances of the electrochemical device, such as a degree of capacity decrease after storage at a high temperature and a degree of increase in direct current (DCR) during discharge, is suppressed. If the electrochemical device expands and ruptures during storage at a high temperature, there is a problem in safety. Therefore, it is particularly important to suppress the expansion of the electrochemical device.

Therefore, an object of the present invention is to provide an electrolytic solution that can suppress the expansion of an electrochemical device even at a high temperature. Another object of the present invention is to provide an electrochemical device in which expansion is suppressed even at a high temperature.

The present inventors have found that expansion of an electrochemical device can be significantly suppressed by including a specific compound containing a silicon atom and a nitrogen atom and a fluorine-containing cyclic carbonate in an electrolytic solution. In particular, the present inventors have found that, when each compound is used alone, the electrochemical device expands easily, but the use of these compounds significantly suppresses the expansion of the electrochemical device. I found what I could do.

The present invention provides, as a first aspect, an electrolytic solution containing a compound represented by the following formula (1) and a fluorine-containing cyclic carbonate.

[In the 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 nitrogen atom. ]

R ⁵ is preferably a group represented by the following formula (2).

[In the formula (2), R ⁶ and R ⁷ each independently represent a hydrogen atom or an alkyl group, and * represents a bond. ]

At least one of R ¹ to R ³ is preferably a fluorine atom.

The fluorine-containing cyclic carbonate is preferably 4-fluoro-1,3-dioxolan-2-one.

合計 The total of the content of the compound represented by the formula (1) and the content of the fluorine-containing cyclic carbonate is preferably 10% by mass or less based on the total amount of the electrolytic solution.

The present invention provides, as a second aspect, an electrochemical device including a positive electrode, a negative electrode, and the above-mentioned electrolytic solution.

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

The electrochemical device is preferably a non-aqueous electrolyte secondary battery or a capacitor.

According to the present invention, it is possible to provide an electrolytic solution that can suppress the expansion of an electrochemical device even at a high temperature. Further, according to the present invention, it is possible to provide an electrochemical device in which expansion is suppressed even at a high temperature.

It is a perspective view showing the nonaqueous electrolyte secondary battery as an electrochemical device concerning one embodiment. FIG. 2 is an exploded perspective view illustrating an electrode group of the secondary battery illustrated in FIG. 1. It is a graph which shows the measurement result of the volume increase amount in an Example and a comparative example. It is a graph which shows the measurement result of discharge DCR in an example and a comparative example.

Hereinafter, embodiments of the present invention will be described with reference 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 one embodiment. In this embodiment, the electrochemical device is a non-aqueous electrolyte secondary battery. As shown in FIG. 1, the nonaqueous electrolyte secondary battery 1 includes an electrode group 2 including a positive electrode, a negative electrode, and a separator, and a bag-shaped battery case 3 that houses the electrode group 2. The positive electrode and the negative electrode are provided with a positive electrode current collecting tab 4 and a negative electrode current collecting tab 5, respectively. The positive electrode current collecting tab 4 and the negative electrode current collecting tab 5 protrude from the inside of the battery package 3 to the outside such that the positive electrode and the negative electrode can be electrically connected to the outside of the nonaqueous electrolyte secondary battery 1 respectively. . The battery exterior 3 is filled with an electrolyte (not shown). The non-aqueous electrolyte secondary battery 1 may be a battery (a coin type, a cylindrical type, a stacked type, or the like) having a shape other than the so-called “laminated type” as described above.

The battery outer package 3 may be a container formed of, for example, a laminate film. The laminated film may be, for example, a laminated film in which a resin film such as a polyethylene terephthalate (PET) film, a metal foil such as aluminum, copper, and 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 nonaqueous 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, calcined carbon, conductive polymer, conductive glass, or the like. The positive electrode current collector 9 may be formed by processing a surface of aluminum, copper, or the like with carbon, nickel, titanium, silver, or the like for the purpose of improving adhesiveness, conductivity, and oxidation resistance. . The thickness of the positive electrode current collector 9 is, for example, 1 to 50 μm in terms of electrode strength and energy density.

(4) 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, a lithium oxide. Examples of the lithium oxide 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 , and 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, Na, Mg, Sc, Y , Mn, Fe, Co, Cu, Zn, Al , Cr, Pb, Sb, V and B represent at least one element selected from the group consisting of M and X (where M is an element different from the other elements in each formula). , 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 _{Mny 2} O _z (where x and z are the same as those described above, and y1 = 0 to 0.9, y2 = 0 to 0.9, and y1 + y2 = 0 to 0.9), for example, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , LiNi _0.6 Co _0.2 Mn _0.2 O _{2, and} LiNi _0.8 Co _0.1 Mn _0.1 O ₂ may be used. 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 those described above, and y3 = 0 to 0.9, y4 = 0 to 0.9, and y3 + y4 = 0 to 0.9), for example, LiNi _0.8 Co _0.15 Al _0.05 O ₂ . There may be.

The positive electrode active material may be, for example, a lithium phosphate. Examples of the lithium phosphate 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 ).

含有 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 may be carbon black such as acetylene black or Ketjen black, a carbon material such as graphite or graphene, or a carbon nanotube. 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, based on the total amount of the positive electrode mixture layer, and 50% by mass or less, 30% by mass or less. Or less, or 15% by mass or less.

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

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, based on the total amount of the positive electrode mixture layer, and 30% by mass or less, 20% by mass or less. % Or 10% by mass or less.

The separator 7 is not particularly limited as long as it electrically insulates the positive electrode 6 and the negative electrode 8 while allowing ions to permeate, and has resistance to oxidizing property on the positive electrode 6 side and reducing property on the negative electrode 8 side. Not done. Examples of the material (material) of such a separator 7 include a resin and an inorganic substance.

Examples of the resin include an olefin-based polymer, a fluorine-based polymer, a cellulose-based polymer, polyimide, and nylon. The separator 7 is preferably a porous sheet or a nonwoven fabric formed of a polyolefin such as polyethylene or polypropylene from the viewpoint of being stable with respect to the electrolytic solution and having excellent liquid retaining 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 adhered to a thin film substrate 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. The negative electrode current collector 11 is provided with a negative electrode current collection tab 5.

The negative electrode current collector 11 is formed of copper, stainless steel, nickel, aluminum, titanium, calcined carbon, conductive polymer, conductive glass, aluminum-cadmium alloy, or the like. The negative electrode current collector 11 may be formed of a material obtained by treating a surface of copper, aluminum, or the like with carbon, nickel, titanium, silver, or the like for the purpose of improving adhesion, conductivity, and reduction resistance. . The thickness of the negative electrode current collector 11 is, for example, 1 to 50 μm in terms of electrode strength and energy density.

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

The negative electrode active material is not particularly limited as long as it can absorb and release lithium ions. Examples of the negative electrode active material include carbon materials, metal composite oxides, oxides or nitrides of Group 4 elements such as tin, germanium, and silicon; simple substances of lithium; lithium alloys such as lithium aluminum alloys; and Sn and Si. And the like which can form an alloy with lithium. The negative electrode active material is preferably at least one selected from the group consisting of a carbon material and a metal composite oxide from the viewpoint of safety. The negative electrode active material may be one of these alone or a mixture of two or more thereof. The shape of the negative electrode active material may be, for example, a particle shape.

Examples of the carbon material include an amorphous carbon material, natural graphite, a composite carbon material in which a coating of an amorphous carbon material is formed on natural graphite, artificial graphite (a resin material such as an epoxy resin and a phenol resin, or oil, coal, etc.). Obtained by firing the pitch-based raw material obtained from the above). 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.

炭素 Among the negative electrode active materials, carbon materials have high conductivity, and are particularly excellent in low-temperature characteristics and cycle stability. Among carbon materials, graphite is preferable from the viewpoint of increasing the capacity. In graphite, the interlayer (d002) between carbon network planes in the X-ray wide angle diffraction method is preferably less than 0.34 nm, more preferably 0.3354 nm or more and 0.337 nm or less. A carbon material satisfying such conditions may be referred to as pseudo-anisotropic carbon.

The negative electrode active material may further include 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, silver , An alloy containing at least one selected from the group consisting of 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, a nitride, or a carbide, and specifically, for example, silicon oxide such as SiO, SiO ₂ , LiSiO, and the like. Material, silicon nitride such as Si ₃ N ₄ and Si ₂ N ₂ O, silicon carbide such as SiC, and tin oxide 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 contains graphite, more preferably contains a carbon material, silicon, and It contains a mixture with a material containing at least one element selected from the group consisting of tin, and particularly preferably contains a mixture of graphite and silicon oxide. The content of the carbon material (graphite) with respect to the material (silicon oxide) containing at least one element selected from the group consisting of silicon and tin in the mixture is 1% by mass or more, or 3% by mass, based on the total amount of the mixture. It may be at least 30% by mass.

含有 The content of the negative 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 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.

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

場合 When the negative electrode mixture layer 12 contains a thickener, its content is not particularly limited. From the viewpoint of applicability 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. The content of the thickener may be 5% by mass or less, preferably 3% by mass, based on the total amount of the positive electrode mixture layer, from the viewpoint of suppressing a decrease in battery capacity or an increase in resistance between the negative electrode active materials. %, More preferably 2% by mass or less.

In one embodiment, the electrolytic solution contains a compound represented by the following formula (1), a fluorine-containing cyclic carbonate, an electrolyte salt, and a non-aqueous solvent.

In the 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 nitrogen atom.

The alkyl group represented by R ¹ to R ³ may have one or more carbon atoms, and may have three or less carbon atoms. R ¹ to R ³ may be a methyl group, an ethyl group, or a propyl group, and may be linear or branched. At least one of R ¹ to R ³ is preferably a fluorine atom.

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

In one embodiment, R ⁵ may be a group represented by the following formula (2) from the viewpoint of further suppressing the expansion of the electrochemical device.

In the formula (2), R ⁶ and R ⁷ each independently represent a hydrogen atom or an alkyl group. The alkyl group represented by R ⁶ or R ⁷ may be the same as the alkyl group represented by R ¹ to R ³ described above. * Indicates a bond.

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

From the viewpoint of further suppressing the expansion of the electrochemical device, the content of the compound represented by the formula (1) is preferably 0.001% by mass or more, 0.005% by mass or more based on the total amount of the electrolytic solution. 0.01 mass% or more, 0.05 mass% or more, or 0.1 mass% or more, and 8 mass% or less, 5 mass% or less, 3 mass% or less, 2 mass% or less, or 1 mass% or less. is there.

Fluorine-containing cyclic carbonate is a cyclic carbonate containing a fluorine atom in the molecule. In one embodiment, the fluorine-containing cyclic carbonate is a cyclic carbonate containing a fluoro group. The fluorine-containing cyclic carbonate is not particularly limited as long as it is a cyclic carbonate ester containing a fluoro group. For example, 4-fluoro-1,3-dioxolan-2-one (fluoroethylene carbonate; FEC), 1,2 -Difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate and the like may be used. The fluorine-containing cyclic carbonate is preferably 4-fluoro-1,3-dioxolan-2-one (fluoroethylene carbonate; FEC) from the viewpoint of suppressing a side reaction when a stable film is formed on the negative electrode. is there.

From the viewpoint of further suppressing the expansion of the electrochemical device, the content of the fluorine-containing cyclic carbonate is preferably 0.001% by mass or more, 0.005% by mass or more, and 0.01% by mass based on the total amount of the electrolytic solution. As described above, the content is 0.05% by mass or more, or 0.1% by mass or more, and is 5% by mass or less, 3% by mass or less, 2% by mass or less, or 1% by mass or less.

The sum of the content of the compound represented by the formula (1) and the content of the fluorine-containing cyclic carbonate is preferably 0.001 mass based on the total amount of the electrolytic solution from the viewpoint of further suppressing the expansion of the electrochemical device. % Or more, 0.005% by mass or more, 0.01% by mass or more, 0.1% by mass or more, or 0.5% by mass or more, preferably 10% by mass or less, 7% by mass or less, 5% by mass Hereinafter, it is 3% by mass or less, 2% by mass or less, 1.5% by mass or less, or 1% by mass or less. From the same viewpoint, the total content of the compound represented by the formula (1) and the content of the fluorine-containing cyclic carbonate is preferably 0.001 to 10% by mass, 0.001 to 10% by mass based on the total amount of the electrolytic solution. 7% by mass, 0.001 to 5% by mass, 0.001 to 3% by mass, 0.001 to 2% by mass, 0.001 to 1.5% by mass, 0.001 to 1% by mass, 0.005% To 10% by mass, 0.005 to 7% by mass, 0.005 to 5% by mass, 0.005 to 3% by mass, 0.005 to 2% by mass, 0.005 to 1.5% by mass, 0.005% To 1% by mass, 0.01 to 10% by mass, 0.01 to 7% by mass, 0.01 to 5% by mass, 0.01 to 3% by mass, 0.01 to 2% by mass, 0.01 to 1% by mass 0.5 mass%, 0.01-1 mass%, 0.1-10 mass%, 0.1-7 mass%, 0.1-5 mass%, 0.1-3 mass %, 0.1 to 2% by mass, 0.1 to 1.5% by mass, 0.1 to 1% by mass, 0.5 to 10% by mass, 0.5 to 7% by mass, 0.5 to 5% by mass %, 0.5 to 3% by mass, 0.5 to 2% by mass, 0.5 to 1.5% by mass, or 0.5 to 1% by mass.

The mass ratio of the content of the compound represented by the formula (1) to the content of the fluorine-containing cyclic carbonate (content of the compound represented by the formula (1) / content of the fluorine-containing cyclic carbonate) is determined by the electrochemical device. From the viewpoint of further suppressing the expansion of, preferably 0.01 or more, 0.05 or more, 0.1 or more, 0.2 or more, or 0.25 or more, and preferably 100 or less, 50 or less Or 20 or less.

The electrolyte salt may be, for example, a lithium salt. Lithium salt, 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 selected from the group consisting of fluorosulfonylimide), LiN (SO ₂ CF ₃ ) ₂ (Li [TFSI], lithium bistrifluoromethanesulfonylimide), and LiN (SO ₂ CF ₂ CF ₃ ) ₂ Good. The lithium salt preferably contains LiPF ₆ from the viewpoint of further improving solubility in a solvent, charge / discharge characteristics of a secondary battery, output characteristics, cycle characteristics, and the like.

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

Non-aqueous solvents include, for example, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyl lactone, acetonitrile, 1,2-dimethoxyethane, dimethoxymethane, tetrahydrofuran, dioxolan, methylene chloride, methyl acetate, etc. It may be. The non-aqueous solvent may be a single type of these or a mixture of two or more types, and is preferably a mixture of two or more types.

The electrolytic solution may further contain other materials other than the compound represented by the formula (1), the fluorine-containing cyclic carbonate, the electrolyte salt, and the non-aqueous solvent. The other material may be, for example, a cyclic carbonate having a carbon-carbon double bond, and may be a nitrogen atom, a sulfur atom, or a heterocyclic compound containing a nitrogen atom and a sulfur atom other than the compounds described above, Acid esters and the like may be used. Other materials may be compounds having an unsaturated bond in the molecule other than these compounds.

環状 A cyclic carbonate having a carbon-carbon double bond is a cyclic carbonate having a carbon-carbon double bond. In one embodiment, in the cyclic carbonate, two carbons constituting the ring may form a double bond. The cyclic carbonate may be vinylene carbonate, vinylene carbonate, methyl vinylene carbonate, dimethyl vinylene carbonate (4,5-dimethyl vinylene carbonate), ethyl vinylene carbonate (4,5-diethyl vinylene carbonate), diethyl vinylene carbonate, or the like. From the viewpoint of improving the performance of the chemical device, vinylene carbonate is preferred.

The present inventors have studied compounds having various structures and functional groups. As a result, by applying the compound represented by the above formula (1) and the fluorine-containing cyclic carbonate to the electrolytic solution, the high temperature of the electrochemical device can be improved. It revealed that the expansion underneath can be suppressed. In particular, the present inventors cannot suppress the expansion of the electrochemical device when any one of the compound represented by the formula (1) and the fluorine-containing cyclic carbonate is applied to the electrolytic solution, but rather accelerate the expansion. Nevertheless, it has been clarified that when both compounds are applied to the electrolytic solution, the expansion of the electrochemical device can be significantly suppressed. The present inventors presume the effects of using the compound represented by the formula (1) and the fluorine-containing cyclic carbonate in the electrolytic solution as follows. That is, when the compound and the fluorine-containing cyclic carbonate act on the places where the effects are most likely to be expressed in the lithium ion secondary battery, for example, contribute to the stable film formation of the positive electrode or the negative electrode, or the stabilization of the electrolytic solution. Conceivable. Alternatively, it is considered that the interaction between the compound represented by the formula (1) and the fluorine-containing cyclic carbonate stabilizes the electrolytic solution and suppresses gas generation due to decomposition of the electrolyte salt. As a result, expansion of an electrochemical device such as the non-aqueous electrolyte secondary battery 1 at a high temperature is suppressed.

Furthermore, as a characteristic other than the heat resistance required for an electrochemical device, it is also required to suppress an increase in DCR during discharging. By including the compound represented by the formula (1) in the electrolytic solution, it is also possible to suppress an increase in DCR during discharging of the electrochemical device. The compound represented by the formula (1) forms a stable film on the positive electrode or the negative electrode. This is presumed to suppress a decrease in DCR caused by the decomposition product of the electrolytic solution deposited on the positive electrode or the negative electrode.

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

In the first step, the material used for the positive electrode mixture layer 10 is dispersed in a dispersion medium using a kneader, a disperser, or the like to obtain a positive electrode mixture in a slurry form. 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 by a roll press may be provided as necessary. The positive electrode mixture layer 10 may be formed as a positive electrode mixture layer having a multilayer structure by performing the above-described steps from application of the positive electrode mixture to volatilization of the dispersion medium a plurality of times. The dispersion medium may be water, 1-methyl-2-pyrrolidone (hereinafter, also referred to as NMP) or the like.

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

{Circle around (3)} In the third step, the electrode group 2 is formed by sandwiching the separator 7 between the produced positive electrode 6 and negative electrode 8. Next, the electrode group 2 is housed in the battery exterior body 3.

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

In another embodiment, the electrochemical device may be a capacitor. The capacitor may include an electrode group composed of a positive electrode, a negative electrode, and a separator, and a bag-shaped battery case housing the electrode group, similarly to the nonaqueous electrolyte secondary battery 1 described above. Details of each component of the capacitor may be the same as those of the nonaqueous electrolyte secondary battery 1.

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

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

[Preparation of negative electrode]
A binder and carboxymethyl cellulose as a thickener were added to graphite as a negative electrode active material. The mass ratio of the negative electrode active material: the binder: the thickener was 98: 1: 1. Water as a dispersion medium was added to the obtained mixture, and the mixture was kneaded to prepare a slurry negative electrode mixture. This negative electrode mixture was uniformly and uniformly applied in a predetermined amount to a rolled copper foil having a thickness of 10 μm as a negative electrode current collector. Thereafter, the dispersion medium was volatilized, and then pressed to a density of 1.6 g / cm ³ by pressing to obtain a negative electrode.

[Production of lithium ion secondary battery]
The positive electrode cut into a square of 13.5 cm ² is sandwiched between porous polyethylene sheets (trade name: Hypore (registered trademark), manufactured by Asahi Kasei Corporation, 30 μm in thickness) as a separator, and further a square of 14.3 cm ² . The electrode group was prepared by overlapping the cut negative electrodes. This electrode group was housed in a container (battery exterior) formed of an aluminum laminate film (trade name: aluminum laminate film, manufactured by Dai Nippon Printing Co., Ltd.). Next, 1 mL of an electrolytic solution was added into the container, and the container was heat-sealed to produce a lithium ion secondary battery for evaluation. As an electrolytic solution, a mixture solution of ethylene carbonate, dimethyl carbonate, and diethyl carbonate containing 1 mol / L of LiPF ₆ was added with 1 mass% of vinylene carbonate (VC) based on the total amount of the mixed solution, and expressed by the following formula (3). The compound A added was 0.5% by mass and 4-fluoro-1,3-dioxolan-2-one (fluoroethylene carbonate; FEC) was added in an amount of 0.5% by mass (based on the total amount of the electrolytic solution).

(Example 2)
A lithium ion secondary battery was produced in the same manner as in Example 1, except that 0.8% by mass of compound A and 0.2% by mass of FEC (based on the total amount of the electrolytic solution) were added.

(Example 3)
A lithium ion secondary battery was fabricated in the same manner as in Example 1, except that 0.2% by mass of Compound A and 0.8% by mass of FEC (based on the total amount of the electrolytic solution) were added.

(Comparative Example 1)
A lithium ion secondary battery was produced in the same manner as in Example 1, except that Compound A and FEC were not used.

(Comparative Example 2)
A lithium ion secondary battery was fabricated in the same manner as in Example 1 except that Compound A was not used and FEC was added in an amount of 1.0% by mass.

(Reference Example 1)
A lithium ion secondary battery was produced in the same manner as in Example 1 except that Compound A was added in an amount of 1.0% by mass without using FEC.

[Initial charge / discharge]
Initial charge / discharge was performed on the produced lithium ion battery by the following method. First, under an environment of 25 ° C., constant-current charging was performed at a current value of 0.1 C up to an upper limit voltage of 4.45 V, and subsequently, constant-voltage charging was performed at 4.45 V. The charge termination condition was a current value of 0.01C. Thereafter, constant current discharge at a cutoff voltage of 2.5 V was performed at a current value of 0.1 C. This charge / discharge cycle was repeated three times ("C" used as a unit of the current value means "current value (A) / battery capacity (Ah)").

[High temperature storage test]
Each of the secondary batteries of Examples 1 to 3, Comparative Examples 1 and 2, and Reference Example 1 was subjected to constant current charging at a current value of 0.1 C to an upper limit voltage of 4.45 V in an environment of 25 ° C. Constant voltage charging was performed at .45V. The charge termination condition was a current value of 0.01C. Thereafter, the secondary batteries were stored in a constant temperature bath at 80 ° C. for 4 hours.

[Measurement of volume increase]
The volume of each of the secondary batteries of Examples 1 to 3, Comparative Examples 1 and 2, and Reference Example 1 was measured by a hydrometer (electronic hydrometer MDS-300, manufactured by Alpha Mirage) based on the Archimedes method. The difference between the volume of the secondary battery before the high-temperature storage test and the volume of the secondary battery held at 25 ° C. for 30 minutes after the high-temperature storage test was determined, and the degree of expansion of the secondary battery was evaluated. The results are shown in FIG.

As shown in FIG. 3, a lithium ion secondary battery of Comparative Example 2 including a fluorine-containing cyclic carbonate and using an electrolyte containing no compound A, and an electrolyte containing compound A and containing no fluorine-containing cyclic carbonate were used. The volume increase of the applied lithium ion secondary battery of Reference Example 1 was larger than the volume increase of the lithium ion secondary battery of Comparative Example 1 to which the electrolyte containing neither Compound A nor the fluorine-containing cyclic carbonate was applied. Was. This is because fluorine-containing cyclic carbonate or compound A undergoes oxidative decomposition under high voltage (about 4.45 V) and high temperature (80 ° C.) environment to generate gas, or the decomposition product reacts with the electrolyte solution component. This is probably because gas was generated. On the other hand, the lithium ion secondary batteries of Examples 1 to 3 to which the electrolytic solution containing both the compound A and the fluorine-containing cyclic carbonate were applied were compared with the lithium ion secondary batteries of Comparative Examples 1 and 2 and Reference Example 1 in volume. The increase was dramatically reduced, confirming the effect of suppressing the expansion of the lithium ion secondary battery due to gas generation. Although the mechanism of this volume increase reduction is not necessarily clear, it is considered that the decomposition of the electrolytic solution or LiPF ₆ could be suppressed because a stable film was formed on the positive electrode or the negative electrode by the interaction of the compound A and the fluorine-containing cyclic carbonate. Can be Or, compounds according to the interaction of the compound A and the fluorine-containing cyclic carbonate electrolyte or to stabilize LiPF _6, since that suppresses decomposition of the electrolyte or LiPF _6, is considered.

[Measurement of discharge DCR]
With respect to the secondary battery after the first charge / discharge, the direct current resistance (discharge DCR) at the time of discharge was measured as follows.
First, constant current charging at 0.2 C was performed up to an upper limit voltage of 4.45 V, and then constant voltage charging was performed at 4.45 V. The charge termination condition was a current value of 0.02C. Thereafter, a constant current discharge with a final voltage of 2.5 V was performed at a current value of 0.2 C. The current value at this time was I _{0.2 C} , and the voltage change 10 seconds after the start of discharge was ΔV _{0.2 C.} Next, 0.2 C constant current charging was performed up to an upper limit voltage of 4.45 V, and then constant voltage charging was performed at 4.45 V (the charging termination condition was a current value of 0.02 C). At a current value of 5 C, a constant current discharge with a final voltage of 2.5 V was performed. The current value at this time was I _{0.5 C} , and the voltage change 10 seconds after the start of discharge was ΔV _{0.5 C.} A current value of 1 _C from the same charge and discharge was evaluated as I _1C , and a voltage change ΔV _1C after 10 seconds from the start of discharge was evaluated. Using the least squares method on the plot (I _0.2C , ΔV _0.2C ), (I _0.5C , ΔV _0.5C ), (I _1C , ΔV _1C ) of the three points of the current value-voltage change An approximate straight line was drawn, and the slope was used as the value of the discharge DCR.
FIG. 4 shows the results.

As shown in FIG. 4, the lithium ion secondary battery of Comparative Example 2 including a fluorine-containing cyclic carbonate and using an electrolyte solution containing no compound A was prepared using an electrolyte solution containing neither the compound A nor the fluorine-containing cyclic carbonate. The discharge DCR was better (decreased) as compared to the applied lithium ion secondary battery of Comparative Example 1. It is considered that the discharge DCR of Comparative Example 2 was lowered because the film formed by the fluorine-containing cyclic carbonate mainly formed a stable film on the negative electrode, and suppressed excessive decomposition of the electrolytic solution. On the other hand, in the lithium ion secondary batteries of Examples 1 to 3 to which the electrolytic solution containing both the compound A and the fluorine-containing cyclic carbonate was applied, the discharge DCR was very low as compared with the lithium ion secondary batteries of Comparative Examples 1 and 2. It was good. Although the mechanism by which the discharge DCR is favorable in the lithium ion secondary batteries of Examples 1 to 3 is not always clear, it is stable and stable at the positive electrode or the negative electrode as in the lithium ion secondary battery of Reference Example 1 containing only Compound A. It is considered that a film having good ionic conductivity was formed.

# 1: Non-aqueous electrolyte secondary battery (electrochemical device), 6: positive electrode, 7: separator, 8: negative electrode.

Claims

An electrolytic solution containing a compound represented by the following formula (1) and a fluorine-containing cyclic carbonate.

[In the 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 nitrogen atom. ]
Wherein R 5 is a group represented by the following formula (2), the electrolyte solution according to claim 1.

[In the formula (2), R 6 and R 7 each independently represent a hydrogen atom or an alkyl group, and * represents a bond. ]
3. The electrolytic solution according to claim 1, wherein at least one of R 1 to R 3 is a fluorine atom.
The electrolytic solution according to any one of claims 1 to 3, wherein the fluorine-containing cyclic carbonate is 4-fluoro-1,3-dioxolan-2-one.
The method according to any one of claims 1 to 4, wherein a total of the content of the compound represented by the formula (1) and the content of the fluorine-containing cyclic carbonate is 10% by mass or less based on the total amount of the electrolytic solution. An electrolytic solution according to item 1.
電気 An electrochemical device comprising a positive electrode, a negative electrode, and the electrolytic solution according to any one of claims 1 to 5.
7. The electrochemical device according to claim 6, wherein the negative electrode contains a carbon material.
The electrochemical device according to claim 7, wherein the carbon material contains graphite.
The electrochemical device according to claim 7, wherein the negative electrode further contains a material containing at least one element selected from the group consisting of silicon and tin.
The electrochemical device according to any one of claims 6 to 9, wherein the electrochemical device is a non-aqueous electrolyte secondary battery or a capacitor.