Electrochemical device and electrolyte for electrochemical device

Abstract

The invention provides an electrochemical device. The electrochemical device includes a positive electrode, a negative electrode, and an electrolyte solution. The electrolyte solution contains a compound represented by formula (1) and a heterocyclic compound containing a sulfur atom. In formula (1), R1, R2, and R3 each independently represent a hydrogen atom or a methyl group, and X represents a divalent organic group. # imgabs0 #

Description

Technical Field

[0001] The invention relates to an electrochemical device and an electrolyte for the electrochemical device. Background Art

[0002] In recent years, with the popularity of portable electronic devices, electric vehicles, etc., high-performance electrochemical devices such as non-aqueous electrolyte secondary batteries and capacitors represented by lithium-ion secondary batteries are needed. As a method for improving the performance of electrochemical devices, for example, a method of adding a prescribed additive to the electrolyte is being studied (for example, Patent Document 1).

[0003] Previous technical literature

[0004] Patent Literature

[0005] Patent Document 1: International Publication No. 2012 / 147502 Summary of the invention

[0006] Technical issues to be solved by the invention

[0007] In order to apply electrochemical devices to vehicle-mounted applications, it is important to improve heat resistance at high temperatures (e.g., 60°C). As an indicator of the heat resistance of an electrochemical device, for example, the suppression of expansion of the electrochemical device after high-temperature storage can be cited. In addition, the degree of capacity reduction after high-temperature storage can also be cited to suppress the degradation of various properties of the electrochemical device. If the electrochemical device expands and ruptures during high-temperature storage, it becomes a problem in terms of safety, so it is particularly important to suppress the expansion of the electrochemical device.

[0008] Therefore, a main object of the present invention is to sufficiently suppress the expansion of an electrochemical device at high temperature.

[0009] Means for solving technical problems

[0010] According to the research conducted by the present inventors, it has been found that expansion at high temperature can be sufficiently suppressed by using an electrolyte solution containing a specific isocyanate compound and a heterocyclic compound containing a sulfur atom (hereinafter, sometimes simply referred to as a "heterocyclic compound") in an electrochemical device.

[0011] One aspect of the present invention relates to an electrochemical device. The electrochemical device comprises a positive electrode, a negative electrode and an electrolyte. The electrolyte contains a compound represented by the following formula (1) and a heterocyclic compound containing a sulfur atom. According to this electrochemical device, expansion at high temperature is sufficiently suppressed. In one embodiment, the electrochemical device tends to be excellent in capacity recovery rate after high temperature storage. The electrochemical device can be a non-aqueous electrolyte secondary battery or a capacitor.

[0012]

[0013] [In formula (1), R 1 , R 2 and R 3 Each independently represents a hydrogen atom or a methyl group, and X represents a divalent organic group.]

[0014] Another aspect of the present invention relates to an electrolyte for an electrochemical device (hereinafter, sometimes referred to as "electrolyte"). The electrolyte for an electrochemical device contains a compound represented by the following formula (1) and a heterocyclic compound containing a sulfur atom. According to this electrolyte for an electrochemical device, the expansion of the electrochemical device at high temperature can be fully suppressed. In addition, in one embodiment, the electrolyte for an electrochemical device can improve the capacity recovery rate of the electrochemical device after high-temperature storage.

[0015]

[0016] [In formula (1), R 1 , R 2 and R 3 Each independently represents a hydrogen atom or a methyl group, and X represents a divalent organic group.]

[0017] Preferred aspects (A) to (E) of the above-mentioned aspects are shown below. These preferred aspects may be combined in plural.

[0018] (A) R in formula (1) 1 and R 2 It's a hydrogen atom.

[0019] (B) In the formula (1), X is an alkylene group having 1 to 6 carbon atoms.

[0020] (C) The heterocyclic compound is a compound having an S═O bond.

[0021] (D) The heterocyclic compound is a cyclic sulfonate or a cyclic sulfate.

[0022] (E) The total content of the compound represented by the formula (1) and the heterocyclic compound is 0.1 to 10% by mass based on the total amount of the electrolyte.

[0023] Effects of the Invention

[0024] According to the present invention, it is possible to sufficiently suppress the expansion of an electrochemical device at a high temperature. In addition, according to the present invention, there is provided an electrolyte solution for an electrochemical device, which is able to sufficiently suppress the expansion of an electrochemical device at a high temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a perspective view showing one embodiment of a non-aqueous electrolyte secondary battery as an electrochemical device.

[0026] Figure 2 Yes means Figure 1 An exploded perspective view of an electrode assembly of a non-aqueous electrolyte secondary battery is shown.

[0027] Figure 3 It is a bar graph showing the measurement results of the volume change rate of the lithium ion secondary batteries after high-temperature storage in Examples and Comparative Examples.

[0028] Figure 4 It is a bar graph showing the measurement results of the capacity recovery rate of the lithium ion secondary batteries after high-temperature storage in Examples and Comparative Examples. DETAILED DESCRIPTION

[0029] 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.

[0030] The same is true for the numerical values ​​and their ranges in the present invention, and the present invention is not limited. In this specification, the numerical range represented by "~" represents the range of the numerical values ​​recorded before and after "~" as the minimum and maximum values, respectively. In the numerical ranges recorded in stages in this specification, the upper limit value or lower limit value recorded in one numerical range can also replace the upper limit value or lower limit value in the numerical range recorded in other stages. Moreover, in the numerical ranges recorded in this specification, the upper limit value or lower limit value of the numerical range can be replaced by the value shown in the embodiment.

[0031] In this specification, the term "layer" includes not only a shape structure formed on the entire surface but also a shape structure formed on a part when viewed as a plan view. Furthermore, in this specification, the term "process" is not limited to an independent process, but is also included in this term as long as the desired effect of the process is achieved even if it cannot be clearly distinguished from other processes.

[0032] Each component and material exemplified in the present specification may be used alone or in combination of two or more unless otherwise specified.

[0033] Figure 1 1 is a perspective view showing an embodiment of a non-aqueous electrolyte secondary battery as an electrochemical device. In this embodiment, the electrochemical device is a non-aqueous electrolyte secondary battery. Figure 1As shown, the non-aqueous electrolyte secondary battery 1 includes an electrode group 2 consisting of a positive electrode, a negative electrode and a separator, and a bag-shaped battery outer body 3 that accommodates the electrode group 2. A positive electrode collector lead 4 and a negative electrode collector lead 5 are provided on the positive electrode and the negative electrode, respectively. The positive electrode collector lead 4 and the negative electrode collector lead 5 protrude from the inside of the battery outer body 3 to the outside, respectively, 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 an electrolyte (not shown). The non-aqueous electrolyte secondary battery 1 can be a battery of a shape other than the so-called "laminated type" as described above (button type, cylindrical type, stacked type, etc.).

[0034] The battery case 3 may be a container formed of a laminate film, for example, in which a resin film such as polyethylene terephthalate (PET) film, a metal foil such as aluminum, copper, stainless steel, and a sealant layer such as polypropylene are sequentially laminated.

[0035] Figure 2 Yes means Figure 1 The exploded perspective view of the electrode group of the non-aqueous electrolyte secondary battery shown in FIG. Figure 2 As shown, 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.

[0036] The positive electrode 6 includes a positive electrode current collector 9 and a positive electrode mixture layer 10 provided on the positive electrode current collector 9. A positive electrode current collector tab 4 is provided on the positive electrode current collector 9.

[0037] The positive electrode current collector 9 is formed of, for example, aluminum, titanium, stainless steel, nickel, calcined carbon, conductive polymer, conductive glass, etc. The positive electrode current collector 9 may be a current collector treated with carbon, nickel, titanium, silver, etc. on the surface of aluminum, copper, etc., in order to improve 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.

[0038] 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.

[0039] The positive electrode active material may be, for example, lithium oxide. Examples of lithium oxide include Li x CoO2、Li x NiO2、Li x MnO2、Li x Co y Ni 1-y O2、Li x Co y M 1-y O z , Lix Ni 1-y M y O z , Li x Mn2O4、Li x Mn 2-y M y O4 (In each formula, M represents at least one element selected from the group consisting of Na, Mg, Sc, Y, Mn, Fe, Co, Cu, Zn, Al, Cr, Pb, Sb, V and B (wherein M is an element different from the other elements in each formula). x = 0 to 1.2, y = 0 to 0.9, z = 2.0 to 2.3.) Li x Ni 1-y M y O z The lithium oxide represented can be Li x Ni 1-(y1+y2) Co y1 Mn y2 O z (where x and z are the same as above, y1 = 0 to 0.9, y2 = 0 to 0.9, and y1 + y2 = 0 to 0.9.) For example, it can be LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2、LiNi 0.5 Co 0.2 Mn 0.3 O2、LiNi 0.6 Co 0.2 Mn 0.2 O2 or LiNi 0.8 Co 0.1 Mn 0.1 O2. By Li x Ni 1-y M y O z The lithium oxide represented can be Li x Ni 1-(y3+y4) Co y3 Al y4 O z (where x and z are the same as above, y3 = 0 to 0.9, y4 = 0 to 0.9, and y3 + y4 = 0 to 0.9.) For example, LiNi 0.8 C o 0.15 Al 0.05 O2.

[0040] The positive electrode active material may be, for example, a lithium phosphate, such as lithium manganese phosphate (LiMnPO4), lithium iron phosphate (LiFePO4), lithium cobalt phosphate (LiCoPO4), and lithium vanadium phosphate (Li3V2(PO4)3).

[0041] The content of the positive electrode active material may be 80% by mass or more, 85% by mass or more, or 99% by mass or less, based on the total amount of the positive electrode mixture layer.

[0042] The conductive agent may be carbon black such as acetylene black, Ketjen black, graphite, graphene, carbon nanotubes, etc. The content of the conductive agent may be, for example, 0.01 mass %, 0.1 mass %, or 1 mass %, or may be 50 mass %, 30 mass %, or 15 mass % or less, based on the total amount of the positive electrode mixture layer.

[0043] Examples of the binder include resins such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose; rubbers such as SBR (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), fluororubber, isoprene rubber, butadiene rubber, and ethylene-propylene rubber; styrene-butadiene-styrene block copolymers or hydrogenated products thereof, EPDM (ethylene-propylene-diene terpolymer), styrene-ethylene-butadiene-ethylene copolymers, styrene - Thermoplastic elastomers such as isoprene-styrene block copolymers or their hydrogenates; soft resins such as syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymers, and propylene-α-olefin copolymers; fluorine-containing resins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, polytetrafluoroethylene-ethylene copolymers, and polytetrafluoroethylene-vinylidene fluoride copolymers; resins having a nitrile-containing monomer as a monomer unit; polymer compositions having ion conductivity of alkali metal ions (e.g., lithium ions), etc.

[0044] The content of the binder based on the total amount of the positive electrode mixture layer may be, for example, 0.1 mass % or more, 1 mass % or more, or 30 mass % or less, 20 mass % or less, or 10 mass % or less.

[0045] The separator 7 is not particularly limited as long as it electronically insulates the positive electrode 6 and the negative electrode 8 while allowing ions to pass therethrough and is resistant to the oxidizing properties of the positive electrode 6 and the reducing properties of the negative electrode 8. Examples of the material of the separator 7 include resins and inorganic substances.

[0046] Examples of the resin include olefin polymers, fluorine polymers, cellulose polymers, polyimide, nylon, etc. The separator 7 is preferably a porous sheet or nonwoven fabric made of polyolefin such as polyethylene or polypropylene from the viewpoint of being stable to the electrolyte and having excellent liquid retention.

[0047] Examples of the inorganic substance include oxides such as aluminum oxide 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 a separator obtained by attaching a fibrous or granular inorganic substance to a thin film substrate such as nonwoven fabric, woven fabric, or microporous film.

[0048] 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. On the negative electrode current collector 11, a negative electrode current collector tab 5 is provided.

[0049] The negative electrode current collector 11 is formed of copper, stainless steel, nickel, aluminum, titanium, calcined carbon, conductive polymer, conductive glass, aluminum-cadmium alloy, etc. The negative electrode current collector 11 may be a current collector treated with carbon, nickel, titanium, silver, etc. on the surface of copper, aluminum, 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.

[0050] The negative electrode mixture layer 12 contains, for example, a negative electrode active material and a binder.

[0051] The negative electrode active material is not particularly limited as long as it is a material that can seal and release lithium ions. As the negative electrode active material, for example, carbon materials, metal composite oxides, oxides or nitrides of 14 group elements such as tin, germanium, and silicon, lithium monomers, lithium alloys such as lithium aluminum alloys, metals such as Sn and Si that can form alloys with lithium, etc. can be cited. 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 can be a single one of these or a mixture of two or more. The shape of the negative electrode active material can be, for example, granular.

[0052] As the carbon material, there can be mentioned an amorphous carbon material, natural graphite, a composite carbon material having a film of an amorphous carbon material formed on natural graphite, artificial graphite (a material obtained by burning a resin raw material such as an epoxy resin or a phenolic resin or a pitch-based raw material obtained from petroleum, coal, etc.), etc. From the viewpoint of high current density charge and discharge characteristics, the metal composite oxide preferably contains either or both of titanium and lithium, and more preferably contains lithium.

[0053] The negative electrode active material may also 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 monomer 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, an alloy containing at least one element selected from the group consisting of nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony and chromium in addition to silicon and tin. 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, specifically, for example, silicon oxides such as SiO, SiO2, LiSiO, silicon nitrides such as Si3N4, Si2N2O, silicon carbides such as SiC, tin oxides such as SnO, SnO2, and LiSnO.

[0054] From the viewpoint of further improving the performance of electrochemical devices such as energy density, the negative electrode mixture layer 12 preferably contains a carbon material as the negative electrode active material, more preferably graphite, and further preferably a mixture of a carbon material and a material of at least one element selected from the group consisting of silicon and tin, and particularly preferably a mixture of graphite and silicon oxide. Based on the total amount of the mixture, the content of the material (silicon oxide) containing at least one element selected from the group consisting of silicon and tin in the mixture can be 1% by mass or more, 3% by mass or more, or 30% by mass or less.

[0055] The content of the negative electrode active material may be 80% by mass or more, 85% by mass or more, or 99% by mass or less, based on the total amount of the negative electrode mixture layer.

[0056] The binder and its content may be the same as the binder and its content in the positive electrode mixture layer.

[0057] The negative electrode mixture layer 12 may further contain a thickener to adjust the viscosity. The thickener is not particularly limited, and may be carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, or salts thereof. The thickener may be a single one or a mixture of two or more of these.

[0058] In the case where the negative electrode mixture layer 12 contains a thickener, its content is not particularly limited. From the perspective of the coating property of the negative electrode mixture layer, the content of the thickener can be 0.1% by mass or more, preferably 0.2% by mass or more, and more preferably 0.5% by mass or more, based on the total amount of the negative electrode mixture layer. From the perspective of suppressing the reduction of battery capacity or the increase of resistance between negative electrode active materials, the content of the thickener can be 5% by mass or less, preferably 3% by mass or less, and more preferably 2% by mass or less, based on the total amount of the negative electrode mixture layer.

[0059] The electrolyte solution (electrochemical device electrolyte solution) contains a compound (isocyanate compound) represented by the following formula (1) and a heterocyclic compound containing a sulfur atom. In one embodiment, the electrolyte solution contains a compound represented by formula (1), a heterocyclic compound, an electrolyte salt, and a nonaqueous solvent.

[0060]

[0061] In formula (1), R 1 , R 2 and R 3 Each independently represents a hydrogen atom or a methyl group, and X represents a divalent organic group.

[0062] In other words, in one embodiment, the compound represented by formula (1) and the heterocyclic compound are additives for an electrolyte solution of an electrochemical device.

[0063] R 1 and R 2 Preferably it is a hydrogen atom. 3 Preferred is a hydrogen atom.

[0064] X may be, for example, a divalent hydrocarbon group, an alkylene group, or an alkylene group having 1 to 6 carbon atoms. The alkylene group may be linear or branched. The lower limit of the number of carbon atoms may be 2 or more. The upper limit of the number of carbon atoms may be 5 or less or 4 or less. The alkylene group represented by X may be a methylene group, an ethylene group, a propylene group, a butylene group, or a pentylene group, and is preferably an ethylene group.

[0065] X may be, for example, a divalent group in which a portion of a divalent hydrocarbon group is substituted with a heteroatom. The heteroatom may be, for example, an oxygen atom. X may be, for example, a divalent group having an ether structure in which a portion of a divalent hydrocarbon group is substituted with an oxygen atom. X may be, for example, a divalent group represented by the following formula (2).

[0066] -X 1 -OX 2 -(2)

[0067] In formula (2), X 1 and X 2 Each independently represents an alkylene group. The alkylene group may be linear or branched. 1 and X 2 The alkylene groups represented may each independently have 1 to 6, 1 to 5, 1 to 4, 1 to 3 or 1 to 2 carbon atoms.

[0068] From the viewpoint of being able to more fully suppress the expansion of the electrochemical device at high temperature, the content of the compound represented by formula (1) can be 0.001 mass %, 0.005 mass %, 0.01 mass %, 0.05 mass %, 0.1 mass %, 0.15 mass % or 0.2 mass % or more, based on the total amount of the electrolyte, or it can be 5 mass %, 4 mass %, 3 mass %, 2 mass %, 1 mass %, 0.8 mass %, 0.6 mass % or 0.5 mass % or less.

[0069] The heterocyclic compound contains a sulfur atom. The heterocyclic compound containing a sulfur atom may be, for example, a compound having an S=O bond. Examples of the compound having an S=O bond include cyclic sulfonates, cyclic sulfates, cyclic sulfites, and cyclic sulfones. Among these, the heterocyclic compound or the compound having an S=O bond may be a cyclic sulfonate or a cyclic sulfate.

[0070] Examples of the cyclic sulfonic acid ester include 1,3-propane sultone, 1-fluoro-1,3-propane sultone, 2-fluoro-1,3-propane sultone, 3-fluoro-1,3-propane sultone, 1-methyl-1,3-propane sultone, 2-methyl-1,3-propane sultone, 3-methyl-1,3-propane sultone, 1-propylene-1,3-sultone, 2-propylene-1,3-sultone, 1-fluoro-1-propylene-1,3-sultone, 2-fluoro-1-propylene-1,3-sultone, 3-fluoro-1-propylene-1,3-sultone, 1-fluoro-2 ...3-fluoro-1-propylene-1,3-sultone, 1-fluoro-2-propylene-1,3-sultone, 2-fluoro-1-propylene-1,3-sultone, 3-fluoro-1-propylene-1,3-sultone, 1-fluoro-2-propylene-1,3-sultone, 1-fluoro-2-propylene Sultone compounds such as sultone, 2-fluoro-2-propylene-1,3-sultone, 3-fluoro-2-propylene-1,3-sultone, 1-methyl-1-propylene-1,3-sultone, 2-methyl-1-propylene-1,3-sultone, 3-methyl-1-propylene-1,3-sultone, 1-methyl-2-propylene-1,3-sultone, 2-methyl-2-propylene-1,3-sultone, 3-methyl-2-propylene-1,3-sultone, 1,4-butane sultone, and 1,5-pentane sultone; disulfonate compounds such as methylene methane disulfonate and ethylene methane disulfonate, etc. The cyclic sulfonate ester may be at least one selected from the group consisting of 1,3-propane sultone, 1-propylene-1,3-sultone, and methylene methane disulfonate.

[0071] Examples of the cyclic sulfate include alkylene sulfate compounds such as 1,2-vinyl sulfate (1,3,2-dioxolane-2,2-dioxide), 1,2-propylene sulfate, 1,3-propylene sulfate, 1,2-butylene sulfate, 1,3-butylene sulfate, 1,4-butylene sulfate, 1,2-pentylene sulfate, 1,3-pentylene sulfate, 1,4-pentylene sulfate, and 1,5-pentylene sulfate. Among these, the cyclic sulfate may be 1,2-vinyl sulfate (1,3,2-dioxolane-2,2-dioxide).

[0072] Examples of the cyclic sulfite include alkylene sulfite compounds such as 1,2-ethylene sulfite, 1,2-propylene sulfite, 1,3-propylene sulfite, 1,2-butylene sulfite, 1,3-butylene sulfite, 1,4-butylene sulfite, 1,2-pentylene sulfite, 1,3-pentylene sulfite, 1,4-pentylene sulfite and 1,5-pentylene sulfite.

[0073] Examples of the cyclic sulfone include alkylene sulfone compounds such as sulfolane, methyl sulfolane, and 4,5-dimethyl sulfolane; and alkynylene sulfone compounds such as sulfolene.

[0074] From the viewpoint of being able to more fully suppress the expansion of electrochemical devices at high temperatures, the content of the heterocyclic compound can be 0.001 mass %, 0.005 mass %, 0.01 mass %, 0.05 mass %, 0.1 mass %, 0.15 mass % or 0.2 mass % or more, or it can be 5 mass %, 4 mass %, 3 mass %, 2 mass %, 1 mass %, 0.8 mass %, 0.6 mass % or 0.5 mass % or less, based on the total amount of the electrolyte.

[0075] From the viewpoint of being able to more fully suppress the expansion of the electrochemical device at high temperature, the total content of the compound represented by formula (1) and the heterocyclic compound may be 0.1 to 10% by mass based on the total amount of the electrolyte. The total content of the compound represented by formula (1) and the heterocyclic compound may be 0.2% by mass or more, 0.3% by mass or more, or 0.4% by mass or less, or 7% by mass or less, 5% by mass or less, 4% by mass or less, 3% by mass or less, 2% by mass or less, 1.5% by mass or less, or 1% by mass or less, based on the total amount of the electrolyte.

[0076] From the viewpoint of being able to more fully suppress the expansion of the electrochemical device at high temperature, the ratio of the content of the compound represented by formula (1) to the total content of the compound represented by formula (1) and the heterocyclic compound (content of the compound represented by formula (1) / (total content of the compound represented by formula (1) and the heterocyclic compound)) can be, for example, greater than 0.05, greater than 0.1, greater than 0.2, greater than 0.25, greater than 0.3, greater than 0.35 or greater than 0.4, or less than 0.9, less than 0.85, less than 0.8, less than 0.75, less than 0.7, less than 0.65 or less than 0.6.

[0077] The electrolyte salt may be, for example, a lithium salt. The lithium salt may be, for example, at least one selected from the group consisting of LiPF6, LiBF4, LiClO4, LiB(C6H5)4, LiCH3SO3, CF3SO2OLi, LiN(SO2F)2 (Li[FSI], lithium bis(trifluoromethanesulfonyl)imide), LiN(SO2CF3)2 (Li[TFSI], lithium bis(trifluoromethanesulfonyl)imide) and LiN(SO2CF2CF3)2. The lithium salt preferably includes LiPF6 because it is more excellent in solubility in solvents, charge and discharge characteristics, output characteristics, cycle characteristics, etc. of secondary batteries.

[0078] From the viewpoint of excellent charge and discharge characteristics, the concentration of the electrolyte salt is 0.5 mol / L or more, more preferably 0.7 mol / L or more, further preferably 0.8 mol / L or more, and is preferably 1.5 mol / L or less, more preferably 1.3 mol / L or less, further preferably 1.2 mol / L or less, based on the total amount of the non-aqueous solvent.

[0079] As the non-aqueous solvent, for example, it can be a chain carbonate compound such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl butyl carbonate, etc.; a cyclic carbonate compound such as ethylene carbonate, propylene carbonate, butylene carbonate, etc.; a chain carboxylate compound such as methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, etc.; a cyclic carboxylate compound such as γ-butyrolactone; a chain ether compound such as dimethoxymethane, dimethoxyethane, diethoxyethane, etc.; a cyclic ether compound such as tetrahydrofuran, tetrahydropyran, dioxolane, etc.; a nitrile compound such as acetonitrile. The non-aqueous solvent can be used alone or in combination of two or more. The non-aqueous solvent is preferably a mixture of two or more.

[0080] The electrolyte may also contain other components other than the compound represented by formula (1), heterocyclic compound, electrolyte salt and nonaqueous solvent. As other components, for example, unsaturated cyclic carbonate, fluorine-containing cyclic carbonate, compounds containing nitrogen atoms other than the compound represented by formula (1) etc. may be cited.

[0081] As unsaturated cyclic carbonate, for example, vinylene carbonate, methyl vinylene carbonate, dimethyl vinylene carbonate (4,5-dimethyl vinylene carbonate), ethyl vinylene carbonate (4,5-diethyl vinylene carbonate), diethyl vinylene carbonate, vinyl ethylene carbonate, etc. can be cited. From the viewpoint of being able to further improve the performance of the electrochemical device, the unsaturated cyclic carbonate is preferably vinylene carbonate. As fluorine-containing cyclic carbonate, 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. can be cited. Fluorine-containing cyclic carbonate is preferably 4-fluoro-1,3-dioxolane-2-one (fluoroethylene carbonate; FEC). Compounds containing nitrogen atoms other than the compounds represented by formula (1) can be, for example, nitrile compounds such as succinonitrile.

[0082] The inventors of the present invention have found that by using an electrolyte containing a compound represented by formula (1) and a heterocyclic compound in an electrochemical device, expansion at high temperature is fully suppressed. The reason for exerting this effect is not clear, but the inventors and others speculate as follows. That is, during the initial charge, the unsaturated carbon bond structure of the compound represented by formula (1) forms a film by reduction reaction on the negative electrode side before other additives or carbonate solvents. Then, it is speculated that a stable film is formed by reacting through the isocyanate site, and the reduction decomposition of other additives, non-aqueous solvents, electrolyte salts, etc. can be suppressed on the negative electrode side. In addition, it is speculated that the heterocyclic compound that is not reduced and decomposed and remains on the positive electrode side forms a film, or the compound represented by formula (1) reacts with the heterocyclic compound to form a stable film, so the oxidative decomposition of other additives, non-aqueous solvents, electrolyte salts, etc. can also be suppressed on the positive electrode side.

[0083] Furthermore, in one embodiment, by using an electrolyte containing a compound represented by formula (1) and a heterocyclic compound in an electrochemical device, the electrochemical device tends to have an excellent capacity recovery rate after high temperature storage. The reason for exerting this effect is not clear, but the inventors of the present invention speculate that this is because, in addition to the formation of a stable film on the positive and negative electrodes, the compound represented by formula (1) reduces fluoric acid (HF) in the electrolyte, which can inhibit the dissolution of the positive electrode active material and the side reaction caused by the formation of a film such as LiF on the negative electrode.

[0084] Next, the method for manufacturing the nonaqueous electrolyte secondary battery 1 is described. The method for manufacturing the nonaqueous electrolyte secondary battery 1 includes: a first step of obtaining a positive electrode 6; a second step of obtaining a negative electrode 8; a third step of housing the electrode group 2 in a battery outer casing 3; and a fourth step of injecting an electrolyte into the battery outer casing 3. The order of the first step to the fourth step is arbitrary.

[0085] In the first step, after the materials used in the positive electrode mixture layer 10 are dispersed in the dispersion medium using a mixer, a disperser, etc. to obtain a slurry-like positive electrode mixture, the positive electrode mixture is applied to the positive electrode collector 9 by a scraper method, an immersion method, a spraying method, etc., and then the dispersion medium is volatilized to obtain the positive electrode 6. After the dispersion medium is volatilized, a compression molding step by rolling can be provided as needed. The positive electrode mixture layer 10 can be formed into a multilayer structure by performing multiple steps from the application of the above-mentioned positive electrode mixture to the volatilization of the dispersion medium. The dispersion medium can be water, 1-methyl-2-pyrrolidone (hereinafter, sometimes referred to as "NMP"), etc.

[0086] In the second step, the negative electrode 8 is obtained in the same manner as the step of obtaining the positive electrode 6 in the first step. Regarding the method of forming the negative electrode mixture layer 12 on the negative electrode collector 11, the positive electrode collector 9 and the positive electrode mixture layer 10 are replaced with the negative electrode collector 11 and the negative electrode mixture layer 12, and the method can be the same as the first step.

[0087] In the third step, the separator 7 is sandwiched between the produced positive electrode 6 and negative electrode 8 to form the electrode group 2. Next, the electrode group 2 is housed in the battery exterior body 3.

[0088] In the fourth step, the electrolyte solution is injected into the battery exterior body 3. For example, the electrolyte solution can be prepared by first dissolving an electrolyte salt in a solvent and then dissolving other materials.

[0089] As another embodiment, the electrochemical device may be a capacitor. Like the above-mentioned non-aqueous electrolyte secondary battery 1, the capacitor may include an electrode group consisting of a positive electrode, a negative electrode and a separator, and a bag-shaped battery outer body for accommodating the electrode group. The details of each component in the capacitor may be the same as those of the non-aqueous electrolyte secondary battery 1.

[0090] Hereinafter, the present invention will be specifically described by way of Examples, but the present invention is not limited to these Examples.

[0091] (Example 1)

[0092] [Production of positive electrode]

[0093] Acetylene black (AB) (4% by mass) as a conductive agent and polyvinylidene fluoride (PVDF) (4% by mass) as a binder were added to lithium nickel cobalt manganese oxide (92% by mass) as a positive electrode active material and mixed. NMP as a dispersion medium was added to the obtained mixture, and a slurry-like positive electrode mixture was prepared by kneading. The positive electrode mixture was uniformly and homogeneously applied to an aluminum foil with a thickness of 20 μm as a positive electrode collector in a specified amount. Then, after the dispersion medium was volatilized, it was compacted to a density of 2.8 g / cm by punching. 3 , thus obtaining the positive electrode.

[0094] [Production of negative electrode]

[0095] As negative electrode active materials, graphite-based active materials (artificial graphite, average particle size (D50); about 23 μm) and silicon-based active materials (SiOx, average particle size (D50); about 10 μm) were used. Styrene-butadiene rubber (SBR) as a binder and carboxymethyl cellulose as a thickener were added to these active materials. The mass ratio of these is set to graphite active material: silicon-based active material: binder: thickener = 92:5:1.5:1.5. Water as a dispersion medium is added to the obtained mixture, and a slurry-like negative electrode mixture is prepared by kneading. The negative electrode mixture is evenly and homogeneously applied in a specified amount on a rolled copper foil with a thickness of 10 μm as a negative electrode collector. Then, after the dispersion medium is volatilized, it is compacted to a density of 1.6 g / cm by punching. 3 , thus obtaining the negative electrode.

[0096] [Manufacturing of lithium-ion secondary batteries]

[0097] The 13.5 cm thick polyethylene porous sheet (thickness 30 μm) was used as a separator to cut the 2 The quadrilateral positive electrode is further overlapped and cut into 14.3cm 2 An electrode group was made by forming a quadrilateral negative electrode. The electrode group was housed in a container (battery outer body) formed by an aluminum laminate film (product name: aluminum laminate film, manufactured by Dai Nippon Printing Co., Ltd.). Next, 0.25 mL of electrolyte was added to the container, and the container was heat-welded to make a lithium-ion secondary battery for evaluation. As the electrolyte, a mixed solution of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate = 1 / 1 / 1 (volume ratio) containing 1 mol / L of LiPF6 was used, in which 0.5% by mass of compound A (R) represented by the following formula (1X) was added. 1 , R 2 and R 3is a hydrogen atom, X is an ethylene compound represented by the formula (1)), 0.5 mass% of 1,3-propane sultone (heterocyclic compound 1), 1 mass% of vinylene carbonate and 1 mass% of fluoroethylene carbonate (all based on the total amount of the electrolyte).

[0098]

[0099] (Example 2)

[0100] A lithium ion secondary battery was produced in the same manner as in Example 1, except that an electrolyte solution to which the compound A was added in an amount of 0.2 mass % based on the total amount of the electrolyte solution was used.

[0101] (Example 3)

[0102] A lithium ion secondary battery was produced in the same manner as in Example 2, except that an electrolyte solution to which 0.2 mass % of 1,3-propane sultone was added based on the total amount of the electrolyte solution was used.

[0103] (Example 4)

[0104] A lithium ion secondary battery was produced in the same manner as in Example 3, except that an electrolyte solution to which the compound A was added in an amount of 1 mass % based on the total amount of the electrolyte solution was used.

[0105] (Example 5)

[0106] The compound B (R) represented by the following formula (1Y) was added in an amount of 0.5% by mass based on the total amount of the electrolyte. 1 and R 2 is a hydrogen atom, R 3 A lithium ion secondary battery was produced in the same manner as in Example 1, except that the electrolyte solution of Compound A was replaced with a compound represented by the formula (1) in which Compound A is a methyl group and X is an ethylene group.

[0107]

[0108] (Example 6)

[0109] A lithium ion secondary battery was produced in the same manner as in Example 1 except that an electrolyte solution to which 0.5 mass % of 1-propylene-1,3-sultone (heterocyclic compound 2) was added instead of 1,3-propane sultone was used based on the total amount of the electrolyte solution.

[0110] (Example 7)

[0111] A lithium ion secondary battery was produced in the same manner as in Example 1 except that an electrolyte solution containing 0.5 mass % of 1,3,2-dioxolane-2,2-dioxide (DTD, heterocyclic compound 3) added instead of 1,3-propane sultone was used based on the total amount of the electrolyte solution.

[0112] (Example 8)

[0113] A lithium ion secondary battery was produced in the same manner as in Example 1 except that an electrolyte solution to which 0.5 mass % of methylene methane disulfonate (MM DS, heterocyclic compound 4) was added instead of 1,3-propane sultone based on the total amount of the electrolyte solution was used.

[0114] (Comparative Example 1)

[0115] A lithium ion secondary battery was produced in the same manner as in Example 1, except that the compound A and 1,3-propane sultone were not added to the electrolytic solution.

[0116] (Comparative Example 2)

[0117] A lithium ion secondary battery was produced in the same manner as in Comparative Example 1 except that 0.5% by mass of p-toluenesulfonyl isocyanate (PTSI) was added based on the total amount of the electrolyte solution.

[0118] (Comparative Example 3)

[0119] A lithium ion secondary battery was produced in the same manner as in Example 1 except that an electrolyte solution to which 0.5 mass % of p-toluenesulfonyl isocyanate (PTSI) was added instead of Compound A based on the total amount of the electrolyte solution was used.

[0120] [First charge and discharge]

[0121] For each lithium-ion secondary battery produced, the initial charge and discharge were implemented by the method shown below. First, constant current charging was performed at a current value of 0.1C at 25°C until the upper limit voltage was 4.2V, and then constant voltage charging was performed at 4.2V. The charging termination condition was set to a current value of 0.01C. Then, constant current discharge with a termination voltage of 2.7V was performed at a current value of 0.1C. This charge and discharge cycle was repeated 3 times (the "C" used as the unit of current value refers to "current value (A) / battery capacity (Ah)".). The discharge capacity of the third cycle is set to the capacity (Q1) of the lithium-ion secondary battery.

[0122] [High temperature storage test]

[0123] For each lithium-ion secondary battery of Examples 1 to 8 and Comparative Examples 1 to 3, after the above-mentioned initial charge and discharge, constant current charging was performed at a current value of 0.1C until the upper limit voltage was 4.2V in an environment of 25°C, and then constant voltage charging was performed at 4.2V. The charging termination condition was set to a current value of 0.01C. Then, these lithium-ion secondary batteries were stored in a constant temperature chamber at 60°C for 4 weeks. After storage, the volume change rate and capacity recovery rate of the lithium-ion secondary battery were measured in the order shown below. Then, the measured battery was charged at a constant current value of 0.1C at an environment of 25°C until the upper limit voltage was 4.2V, and then constant voltage charging was performed at 4.2V. The charging termination condition was set to a current value of 0.01C. Then, the lithium-ion secondary battery was stored in a constant temperature chamber at 60°C, and the volume change rate and capacity recovery rate of the lithium-ion secondary battery were measured 8 weeks and 12 weeks after the storage.

[0124] Figure 3 The figures show the measurement results of the volume change rate of the lithium ion secondary battery after storage at 60° C. for 12 weeks.

[0125] Figure 4 The figures show the measurement results of the capacity recovery rate of lithium ion secondary batteries after storage at 60° C. for 12 weeks.

[0126] (Determination of volume change rate)

[0127] The volume (V1) of each lithium-ion secondary battery before high-temperature storage and the volume (V2) of each lithium-ion secondary battery after standing at 25°C for 30 minutes after high-temperature storage were measured by a densimeter based on the Archimedean method (electronic densimeter MDS-300, manufactured by Alfa Mirage Co., Ltd.). The measured V1 and V2 were used to calculate the volume change rate according to the following formula. Tables 1 and 2 show the measurement results of the volume change rate of lithium-ion secondary batteries after storage at 60°C for 12 weeks.

[0128] Volume change rate (%) = V2 / V1×100

[0129] (Determination of Capacity Recovery Rate)

[0130] After each lithium-ion secondary battery after high-temperature storage was left to stand at 25°C for 30 minutes, a constant current discharge with a termination voltage of 2.7V was performed at a current value of 0.1C. Next, constant current charging was performed at a current value of 0.1C until the upper limit voltage was 4.2V, and then constant voltage charging was performed at 4.2V. The charge termination condition was set to a current value of 0.01C. Then, a constant current discharge with a termination voltage of 2.7V was performed at a current value of 0.1C. The discharge capacity at this time was set to the capacity after the high-temperature storage test (Q2). Using the above Q1 and Q2, the capacity recovery rate was calculated according to the following formula. Tables 1 and 2 show the measurement results of the capacity recovery rate of lithium-ion secondary batteries after storage at 60°C for 12 weeks.

[0131] Capacity recovery rate (%) = Q2 / Q1×100

[0132] [Table 1]

[0133]

[0134] [Table 2]

[0135]

[0136] from Figure 3 and Figure 4 As shown in Tables 1 and 2, the lithium ion secondary batteries of Examples 1 to 8 using electrolytes containing the compound represented by formula (1) and heterocyclic compounds have a lower volume change rate and a higher capacity recovery rate than the lithium ion secondary battery of Comparative Example 1 using electrolytes not containing these compounds. On the other hand, the lithium ion secondary battery of Comparative Example 2 using electrolytes containing PTSI, a compound having an isocyanate group and a functional group (sulfonyl group) containing a sulfur atom in the same molecule, and the lithium ion secondary battery of Comparative Example 3 using electrolytes containing PTSI and 1,3-propane sultone (heterocyclic compound 1) have a lower volume change rate than the lithium ion secondary battery of Comparative Example 1, but the lithium ion secondary batteries of Examples 1 to 8 have a greater effect of suppressing volume expansion. Based on the above results, it is confirmed that the electrochemical device of the present invention can fully suppress expansion at high temperatures. Furthermore, it was found that the capacity recovery rates of the lithium ion secondary batteries of Comparative Examples 2 and 3 were lower than that of the lithium ion secondary battery of Comparative Example 1, but the capacity recovery rates of the lithium ion secondary batteries of Examples 1 to 8 were higher than those of Comparative Examples 1 to 3. Based on the above results, it was confirmed that the electrochemical device of the present invention was also excellent in capacity recovery rate after high temperature storage.

[0137] The inventors of the present invention speculate that the effect of fully suppressing expansion at high temperature by using an electrolyte containing a compound represented by formula (1) and a heterocyclic compound in an electrochemical device is as follows. That is, during the initial charge, the unsaturated carbon bond structure of the compound represented by formula (1) forms a film by a reduction reaction on the negative electrode side before other additives or carbonate solvents. Then, it is speculated that a stable film is formed by reacting through the isocyanate site, and the reduction decomposition of other additives, non-aqueous solvents, electrolyte salts, etc. can be suppressed on the negative electrode side. In addition, it is speculated that the heterocyclic compound that is not reduced and decomposed on the positive electrode side forms a film, or the compound represented by formula (1) reacts with the heterocyclic compound to form a stable film, so the oxidative decomposition of other additives, non-aqueous solvents, electrolyte salts, etc. can also be suppressed on the positive electrode side.

[0138] Explanation of symbols

[0139] 1- non-aqueous electrolyte secondary battery (electrochemical device), 2- electrode group, 3- battery outer casing, 4- positive electrode current collector lead, 5- negative electrode current collector lead, 6- positive electrode, 7- separator, 8- negative electrode, 9- positive electrode collector, 10- positive electrode mixture layer, 11- negative electrode collector, 12- negative electrode mixture layer.

Claims

1. An electrochemical device comprising a positive electrode, a negative electrode and an electrolyte, The electrolyte solution contains a compound represented by the following formula (1) and a heterocyclic compound containing a sulfur atom, In formula (1), R 1 , R 2 and R 3 Each independently represents a hydrogen atom or a methyl group, and X represents a divalent organic group.

2. The electrochemical device according to claim 1, wherein In the formula (1), R 1 and R 2 It's a hydrogen atom.

3. The electrochemical device according to claim 1 or 2, wherein: In the above formula (1), X is an alkylene group having 1 to 6 carbon atoms.

4. The electrochemical device according to any one of claims 1 to 3, wherein: The heterocyclic compound is a compound having an S═O bond.

5. The electrochemical device according to any one of claims 1 to 4, wherein: The heterocyclic compound is a cyclic sulfonate or a cyclic sulfate.

6. The electrochemical device according to any one of claims 1 to 5, wherein: The total content of the compound represented by the formula (1) and the heterocyclic compound is 0.1 to 10% by mass based on the total amount of the electrolyte.

7. The electrochemical device according to any one of claims 1 to 6, wherein: The electrochemical device is a non-aqueous electrolyte secondary battery or a capacitor.

8. An electrolyte for an electrochemical device, comprising a compound represented by the following formula (1) and a heterocyclic compound containing a sulfur atom, In formula (1), R 1 , R 2 and R 3 Each independently represents a hydrogen atom or a methyl group, and X represents a divalent organic group.

9. The electrolyte solution for an electrochemical device according to claim 8, wherein In the formula (1), R 1 and R 2 It's a hydrogen atom.

10. The electrolyte solution for an electrochemical device according to claim 8 or 9, wherein In the above formula (1), X is an alkylene group having 1 to 6 carbon atoms.

11. The electrolyte for an electrochemical device according to any one of claims 8 to 10, wherein The heterocyclic compound is a compound having an S═O bond.

12. The electrolyte for an electrochemical device according to any one of claims 8 to 11, wherein The heterocyclic compound is a cyclic sulfonate or a cyclic sulfate.

13. The electrolyte for an electrochemical device according to any one of claims 8 to 12, wherein The total content of the compound represented by the formula (1) and the heterocyclic compound is 0.1 to 10% by mass based on the total amount of the electrolyte.

Images