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), a first lithium salt compound, a second lithium salt compound constituting the first lithium salt compound and having different anions, and a non-aqueous solvent. In formula (1), R1, R2, and R3 each independently represent a hydrogen atom or a methyl group, and X represents a divalent organic group. # 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] However, the resistance increase rate after the cycle test of conventional electrochemical devices is high and there is still room for improvement.

[0008] Therefore, a main object of the present invention is to sufficiently suppress the resistance increase rate after a cycle test of an electrochemical device.

[0009] Means for solving technical problems

[0010] According to the research conducted by the present inventors, it has been found that the resistance increase rate after the cycle test of the electrochemical device can be sufficiently suppressed by using an electrolyte solution containing a specific isocyanate compound, two lithium salt compounds having different anions, and a non-aqueous solvent in the 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), a first lithium salt compound, a second lithium salt compound having a different anion constituting the first lithium salt compound, and a non-aqueous solvent. According to this electrochemical device, the resistance increase rate after the cycle test of the electrochemical device is sufficiently suppressed. In one embodiment, the electrochemical device tends to be excellent in charge and discharge cycle characteristics. 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), a first lithium salt compound, a second lithium salt compound having a different anion constituting the first lithium salt compound, and a non-aqueous solvent. According to this electrolyte for an electrochemical device, the resistance increase rate after the cycle test of the electrochemical device can be fully suppressed. In addition, in one embodiment, the electrolyte for an electrochemical device can improve the charge and discharge cycle characteristics of the electrochemical device.

[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 first lithium salt compound is lithium hexafluorophosphate.

[0021] (D) The second lithium salt compound is at least one selected from the group consisting of lithium difluorophosphate, lithium tetrafluoroborate, lithium fluorosulfonate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalate)borate, lithium difluorooxalateborate, lithium tetrafluorooxalatephosphate and lithium difluorobis(oxalate)phosphate.

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

[0023] Effects of the Invention

[0024] According to the present invention, the resistance increase rate after the cycle test of the electrochemical device can be sufficiently suppressed. In addition, according to the present invention, an electrolyte solution for an electrochemical device is provided, which can improve the charge and discharge cycle characteristics of the electrochemical device. 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 This is a bar graph showing the number of cycles at which the discharge capacity retention rate is less than 90% in the cycle test of the lithium ion secondary batteries in Examples and Comparative Examples.

[0028] Figure 4 It is a bar graph showing the measurement results of the resistance increase rate after the cycle test of the lithium ion secondary batteries 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 represented by the following formula (1), a first lithium salt compound, a second lithium salt compound having a different anion constituting the first lithium salt compound, and a non-aqueous 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] R 1 and R 2 Preferably it is a hydrogen atom. 3 Preferred is a hydrogen atom.

[0063] 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.

[0064] 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).

[0065] -X 1 -OX 2 -(2)

[0066] 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 number of carbon atoms of the alkylene groups represented may be 1 to 6, 1 to 5, 1 to 4, 1 to 3 or 1 to 2, respectively, independently.

[0067] From the viewpoint of being able to more fully suppress the resistance increase rate after the cycle test of the electrochemical device, 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, 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.

[0068] The first lithium salt compound may be lithium hexafluorophosphate (LiPF6) because it has better solubility in solvents, charge and discharge characteristics, output characteristics, and charge and discharge cycle characteristics of the secondary battery.

[0069] From the viewpoint of excellent charge and discharge characteristics, the concentration of the first lithium salt compound is 0.5 mol / L or more, more preferably 0.7 mol / L or more, further preferably 0.8 mol / L or more, and 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.

[0070] The second lithium salt compound is not particularly limited as long as it is a compound with a different anion from that constituting the first lithium salt compound. For example, it can be at least one selected from the group consisting of lithium difluorophosphate (LiPO2F2), lithium tetrafluoroborate (LiB F4), lithium fluorosulfonate (LiSO3F), lithium bis(fluorosulfonyl)imide (LiN(SO2F)2, LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiN(SO2CF3)2, LiTFSI), lithium bis(oxalate)borate (LiB(C2O4)2, LiBOB), lithium difluorooxalate borate (LiBF2(C2O4, LiDFOB), lithium tetrafluorooxalate phosphate (LiPF4(C2O4, LiTFOP) and lithium difluorobis(oxalate)phosphate (LiPF2(C2O4)2, LiDFBOP). From the viewpoint of being able to more fully suppress the resistance increase rate after the cycle test of the electrochemical device, the second lithium salt compound may be lithium difluorophosphate (LiPO 2 F 2 ) or lithium bis(fluorosulfonyl)imide (LiN(SO 2 F) 2 , LiFSI).

[0071] From the viewpoint of being able to more fully suppress the resistance increase rate after the cycle test of the electrochemical device, the content of the second lithium salt 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, based on the total amount of the electrolyte, or it can be less than 5 mass %, less than 4 mass %, less than 3 mass %, less than 2 mass %, less than 1 mass %, less than 0.8 mass %, less than 0.6 mass % or less than 0.5 mass %.

[0072] From the viewpoint of being able to more fully suppress the resistance increase rate after the cycle test of the electrochemical device, the total content of the compound represented by formula (1) and the second lithium salt compound can 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 second lithium salt compound can 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.

[0073] From the viewpoint of being able to more fully suppress the resistance increase rate after the cycle test of the electrochemical device, the ratio of the content of the compound represented by formula (1) to the total content of the compound represented by formula (1) and the second lithium salt compound (content of the compound represented by formula (1) / (total content of the compound represented by formula (1) and the second lithium salt compound)) can be, for example, 0.05 or more, 0.1 or more, 0.2 or more, 0.25 or more, 0.3 or more, 0.35 or more, or 0.4 or less, or 0.9 or less, 0.85 or less, 0.8 or less, 0.75 or less, 0.7 or less, 0.65 or less, or 0.6 or less.

[0074] The content of the second lithium salt compound may be 0.05% or more and 20% or less in molar ratio relative to the first lithium salt compound.

[0075] 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.

[0076] The electrolyte may also contain other components other than the compound represented by formula (1), the first lithium salt compound, the second lithium salt compound and the non-aqueous solvent. As other components, for example, unsaturated cyclic carbonates, fluorine-containing cyclic carbonates, compounds containing nitrogen atoms other than the compound represented by formula (1) etc. may be cited.

[0077] 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.

[0078] The inventors of the present invention have found that by using an electrolyte containing a compound represented by formula (1), a first lithium salt compound, a second lithium salt compound having different anions constituting the first lithium salt compound, and a non-aqueous solvent in an electrochemical device, the resistance increase rate after the cycle test is fully suppressed. The reason for exerting this effect is not clear, but the inventors 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 a reduction reaction on the negative electrode side before other additives or carbonate solvents. Then, it is speculated that the reduction and 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 first lithium salt compound, the second lithium salt compound, or compounds derived from these that are not reduced and decomposed on the positive electrode side form a film, and by suppressing the oxidative decomposition of other additives, non-aqueous solvents, electrolyte salts, etc., the ion conductivity on the surface of the positive electrode active material is reduced or the resistance increase caused by the stabilization of the crystal structure can be suppressed.

[0079] Furthermore, in one embodiment, by using an electrolyte containing a compound represented by formula (1), a first lithium salt compound, a second lithium salt compound, and a non-aqueous solvent in an electrochemical device, the electrochemical device tends to be excellent in charge and discharge cycle characteristics. 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) is used to reduce 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] Hereinafter, the present invention will be specifically described by way of Examples, but the present invention is not limited to these Examples.

[0087] (Example 1)

[0088] [Production of positive electrode]

[0089] 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.

[0090] [Production of negative electrode]

[0091] 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.

[0092] [Manufacturing of lithium-ion secondary batteries]

[0093] 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 2An electrode group was made by forming a quadrilateral negative electrode. The electrode group was housed in a container (battery outer body) formed of 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 as the first lithium salt compound, to which 0.5 mass % of compound A (R) represented by the following formula (1X) was added was used. 1 , R 2 and R 3 is a hydrogen atom, X is an ethylene compound represented by the formula (1)), 0.5 mass % of lithium difluorophosphate (LiPO2F2) as a second lithium salt compound, 1 mass % of vinylene carbonate and 1 mass % of fluoroethylene carbonate (all based on the total amount of the electrolyte).

[0094]

[0095] (Example 2)

[0096] 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.

[0097] (Example 3)

[0098] A lithium ion secondary battery was produced in the same manner as in Example 2, except that an electrolyte to which 0.2 mass % of lithium difluorophosphate (LiPO 2 F 2 ) was added based on the total amount of the electrolyte was used.

[0099] (Example 4)

[0100] 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.

[0101] (Example 5)

[0102] 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.

[0103]

[0104] (Example 6)

[0105] A lithium ion secondary battery was produced in the same manner as in Example 1 except that an electrolyte containing 0.5 mass % of lithium bis(fluorosulfonyl)imide (LiN(SO2F)2, LiFSI) was added based on the total amount of the electrolyte instead of lithium difluorophosphate (LiPO2F2).

[0106] (Comparative Example 1)

[0107] A lithium ion secondary battery was produced in the same manner as in Example 1 except that compound A and lithium difluorophosphate (LiPO 2 F 2 ) were not added to the electrolyte solution.

[0108] (Comparative Example 2)

[0109] A lithium ion secondary battery was produced in the same manner as in Comparative Example 1, except that 0.5% by mass of hexamethylene diisocyanate (HDI) was added based on the total amount of the electrolyte.

[0110] (Comparative Example 3)

[0111] A lithium ion secondary battery was produced in the same manner as in Example 1 except that an electrolyte solution to which hexamethylene diisocyanate (HDI) was added in an amount of 0.5 mass % based on the total amount of the electrolyte solution instead of the compound A was used.

[0112] [Evaluation of charge and discharge cycle characteristics]

[0113] (Initial charge and discharge)

[0114] 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 in 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, 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)".).

[0115] (Evaluation of charge and discharge cycle characteristics)

[0116] After the initial charge and discharge, each lithium-ion battery was subjected to a high-temperature cycle test, and the charge and discharge cycle characteristics were evaluated. As a charging pattern, constant current charging was performed at a current value of 0.5C until the upper limit voltage was 4.2V, and then constant voltage charging was performed at 4.2V in an environment of 45°C. The charge termination condition was set to a current value of 0.05C. Regarding discharge, constant current discharge was performed at 1.0C until 2.7V, and the discharge capacity was calculated. This series of charge and discharge was repeated for 500 cycles, and the discharge capacity was measured during each charge and discharge. The relative value of the discharge capacity (Q2) in each cycle relative to the discharge capacity (Q1) of the first cycle of charge and discharge was calculated (discharge capacity retention rate (%) = Q2 / Q1×100), and the number of cycles (times) at which the discharge capacity retention rate was less than 90% was calculated. Figure 3 Table 1 shows the number of cycles in which the discharge capacity retention rate was less than 90% in the cycle test of the lithium ion secondary battery.

[0117] [Calculation of resistance increase rate]

[0118] (Determination of discharge DCR)

[0119] The DC resistance (discharge DCR) of each lithium ion secondary battery produced during discharge was measured as follows. First, a constant current charge of 0.2C was performed to an upper limit voltage of 4.2V, and then a constant voltage charge was performed at 4.2V. The charge termination condition was set to a current value of 0.02C. Then, a constant current discharge with a termination voltage of 2.7V was performed at a current value of 0.2C, and the current value at this time was set to I 0.2C , the voltage change 10 seconds after the discharge starts is defined as ΔV 0.2C Next, the battery was charged at a constant current of 0.2C until the upper limit voltage was 4.2V, and then charged at a constant voltage of 4.2V (the charging termination condition was set to a current value of 0.02C). Then, a constant current discharge was performed at a current value of 0.5C with a termination voltage of 2.7V, and the current value at this time was set to I 0.5C , the voltage change 10 seconds after the discharge starts is defined as ΔV 0.5C According to the same charge and discharge, the current value I 1C , Voltage change ΔV 10 seconds after discharge starts 1C The least square method was used to plot the three points of the current value-voltage change (I 0.2C , ΔV 0.2C )、(I 0.5C , ΔV 0.5C )、(I 1C , ΔV 1C ) draw an approximate straight line and set its slope to the value of discharge DCR.

[0120] (Determination of resistance increase rate)

[0121] The discharge DCR (R1) of each lithium ion battery before the above cycle test and the discharge DCR (R2) measured after standing at 25°C for 30 minutes after the above cycle test (45°C, 500 cycles) were measured. Using the measured R1 and R2, the resistance increase rate was calculated according to the following formula. Figure 4 Table 1 shows the measurement results of the resistance increase rate after the cycle test of the lithium ion secondary battery.

[0122] Resistance increase rate (%) = R2 / R1×100

[0123] [Table 1]

[0124]

[0125] from Figure 3 and Figure 4 As shown in Table 1, the lithium ion secondary batteries of Examples 1 to 6 using an electrolyte containing a compound represented by formula (1), a first lithium salt compound, a second lithium salt compound having a different anion constituting the first lithium salt compound, and a non-aqueous solvent have a lower resistance increase rate and a larger number of cycles at which the discharge capacity retention rate is less than 90% than the lithium ion secondary battery of Comparative Example 1 using an electrolyte not containing these compounds. On the other hand, the lithium ion secondary battery of Comparative Example 2 using an electrolyte containing a compound having an isocyanate group that does not satisfy the requirements of formula (1), i.e., HDI, and the lithium ion secondary battery of Comparative Example 3 using an electrolyte containing HDI and LiPO2F2 (a second lithium salt compound) have a lower resistance increase rate than the lithium ion secondary battery of Comparative Example 1, but the lithium ion secondary batteries of Examples 1 to 6 have a greater resistance increase rate suppression effect. Furthermore, it was found that the lithium ion secondary batteries of Examples 1 to 6 had a greater number of cycles at which the discharge capacity retention rate was less than 90% than the lithium ion secondary batteries of Comparative Examples 2 and 3. From the above, it was confirmed that the resistance increase rate after the cycle test of the electrochemical device can be sufficiently suppressed.

[0126] The inventors of the present invention speculate that the effect of fully suppressing the resistance increase rate after the cycle test by using an electrolyte containing a compound represented by formula (1), a first lithium salt compound, a second lithium salt compound with different anions constituting the first lithium salt compound, and a non-aqueous solvent for 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 the reduction and 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 first lithium salt compound, the second lithium salt compound, or compounds derived from these that are not reduced and decomposed on the positive electrode side form a film, and by suppressing the oxidative decomposition of other additives, non-aqueous solvents, electrolyte salts, etc., the ion conductivity on the surface of the positive electrode active material is reduced or the resistance increase caused by the stabilization of the crystal structure can be suppressed.

[0127] Furthermore, in one embodiment, by using an electrolyte containing a compound represented by formula (1), a first lithium salt compound, a second lithium salt compound, and a non-aqueous solvent in an electrochemical device, the electrochemical device tends to be excellent in charge and discharge cycle characteristics. 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) is used to reduce 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.

[0128] Explanation of symbols

[0129] 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), a first lithium salt compound, a second lithium salt compound having a different anion constituting the first lithium salt compound, and a non-aqueous solvent. In formula (1), R 1 , R 2 and R 3 Each independently 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 first lithium salt compound is lithium hexafluorophosphate.

5. The electrochemical device according to any one of claims 1 to 4, wherein: The second lithium salt compound is at least one selected from the group consisting of lithium difluorophosphate, lithium tetrafluoroborate, lithium fluorosulfonate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalate)borate, lithium difluorooxalate borate, lithium tetrafluorooxalate phosphate and lithium difluorobis(oxalate)phosphate.

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 second lithium salt 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), a first lithium salt compound, a second lithium salt compound having a different anion from that of the first lithium salt compound, and a non-aqueous solvent, 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 first lithium salt compound is lithium hexafluorophosphate.

12. The electrolyte for an electrochemical device according to any one of claims 8 to 11, wherein The second lithium salt compound is at least one selected from the group consisting of lithium difluorophosphate, lithium tetrafluoroborate, lithium fluorosulfonate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalate)borate, lithium difluorooxalate borate, lithium tetrafluorooxalate phosphate and lithium difluorobis(oxalate)phosphate.

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 second lithium salt compound is 0.1 to 10% by mass based on the total amount of the electrolyte.

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