Electrochemical devices and electrolytes for electrochemical devices

Abstract

To sufficiently restrain expansion of electrochemical device at high temperature.SOLUTION: An electrochemical device is disclosed. The electrochemical device includes a positive electrode, a negative electrode, and an electrolytic solution. The electrolytic solution contains a compound represented by the following 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.]SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to an electrochemical device and an electrolyte for an electrochemical device.

Background Art

[0002] In recent years, with the spread of portable electronic devices, electric vehicles, etc., high-performance electrochemical devices such as non-aqueous electrolyte secondary batteries represented by lithium-ion secondary batteries and capacitors have been in demand. As a means to improve the performance of electrochemical devices, for example, a method of adding a predetermined additive to an electrolyte has been studied (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In order to apply an electrochemical device to in-vehicle use, it is important to improve the heat resistance at high temperatures (for example, 60°C). As an index of the heat resistance of an electrochemical device, for example, it can be mentioned that the expansion of the electrochemical device after high-temperature storage is suppressed. Or, it can also be mentioned that deterioration of various performances of the electrochemical device, such as the degree of capacity decrease after high-temperature storage, is suppressed. Since it becomes a problem in terms of safety if the electrochemical device expands and ruptures during high-temperature storage, it is particularly important to suppress the expansion of the electrochemical device.

[0005] Therefore, the main object of the present disclosure is to sufficiently suppress the expansion of an electrochemical device at high temperatures.

Means for Solving the Problems

[0006] According to the inventors' studies, it has been found that in electrochemical devices, expansion at high temperatures can be sufficiently suppressed by using an electrolyte containing a specific isocyanate compound and a heterocyclic compound containing a sulfur atom (hereinafter sometimes simply referred to as "heterocyclic compound").

[0007] One aspect of this disclosure 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. Such an electrochemical device sufficiently suppresses expansion at high temperatures. In one embodiment, the electrochemical device tends to have excellent capacity recovery rate after high-temperature storage. The electrochemical device may be a non-aqueous electrolyte secondary battery or a capacitor. [ka] [In formula (1), R 1 , R 2 , and R 3 Each of these independently represents either a hydrogen atom or a methyl group, and X represents a divalent organic group.

[0008] Another aspect of this disclosure relates to an electrolyte for an electrochemical device (hereinafter sometimes simply referred to as "electrolyte"). This electrolyte for an electrochemical device contains a compound represented by the following formula (1) and a heterocyclic compound containing a sulfur atom. Such an electrolyte for an electrochemical device makes it possible to sufficiently suppress the expansion of the electrochemical device at high temperatures. In one embodiment, the electrolyte for an electrochemical device can also improve the capacity recovery rate of the electrochemical device after high-temperature storage. [ka] [In formula (1), R 1 , R 2 , and R 3 Each of these independently represents either a hydrogen atom or a methyl group, and X represents a divalent organic group.

[0009] Preferred embodiments (A) to (E) for each of the above aspects are shown below. Multiple combinations of these preferred embodiments are possible. (A) R in equation (1) 1 and R 2 This is a hydrogen atom. (B) In equation (1), X is an alkylene group having 1 to 6 carbon atoms. (C) Heterocyclic compounds are compounds that have an S=O bond. (D) The heterocyclic compound is a cyclic sulfonic acid ester or a cyclic sulfuric acid ester. (E) The total content of the compound represented by formula (1) and the heterocyclic compound is 0.1 to 10% by mass, based on the total volume of the electrolyte. [Effects of the Invention]

[0010] According to this disclosure, it is possible to sufficiently suppress the expansion of electrochemical devices at high temperatures. Furthermore, according to this disclosure, an electrolyte for electrochemical devices is provided that can sufficiently suppress the expansion of electrochemical devices at high temperatures. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a perspective view showing one embodiment of a non-aqueous electrolyte secondary battery as an electrochemical device. [Figure 2] Figure 2 is an exploded perspective view showing the electrode group of the non-aqueous electrolyte secondary battery shown in Figure 1. [Figure 3] Figure 3 is a graph showing the measurement results of the volume change rate of lithium-ion secondary batteries after high-temperature storage in the examples and comparative examples. [Figure 4] Figure 4 is a graph showing the measurement results of the capacity recovery rate of lithium-ion secondary batteries after high-temperature storage in the examples and comparative examples. [Modes for carrying out the invention]

[0012] The embodiments of this disclosure will be described below with reference to the drawings as appropriate. However, this disclosure is not limited to the embodiments described below.

[0013] The same applies to numerical values ​​and their ranges in this disclosure, and this disclosure is not limited. Numerical ranges indicated using "~" in this specification indicate a range that includes the numerical values ​​before and after "~" as the minimum and maximum values, respectively. In numerical ranges described in steps in this specification, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described in steps. Also, in numerical ranges described in this specification, the upper or lower limit of that numerical range may be replaced with the values ​​shown in the examples.

[0014] In this specification, the term "layer" includes not only structures that are formed across the entire surface when observed in a plan view, but also structures that are formed in only a part of the surface. Furthermore, in this specification, the term "process" includes not only independent processes, but also processes that cannot be clearly distinguished from other processes, as long as their intended function is achieved.

[0015] Unless otherwise specified, each component and material exemplified herein may be used alone or in combination of two or more.

[0016] Figure 1 is a perspective view showing one 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. As shown in Figure 1, the non-aqueous electrolyte secondary battery 1 comprises an electrode group 2 consisting of a positive electrode, a negative electrode, and a separator, and a bag-shaped battery casing 3 that houses the electrode group 2. The positive electrode and negative electrode are provided with a positive electrode current collector tab 4 and a negative electrode current collector tab 5, respectively. The positive electrode current collector tab 4 and the negative electrode current collector tab 5 protrude from the inside to the outside of the battery casing 3 so that the positive electrode and the negative electrode can be electrically connected to the outside of the non-aqueous electrolyte secondary battery 1, respectively. The battery casing 3 is filled with an electrolyte (not shown). The non-aqueous electrolyte secondary battery 1 may be a battery of a shape other than the so-called "laminate type" described above (e.g., coin type, cylindrical type, stacked type).

[0017] The battery casing 3 may be, for example, a container formed from a laminate film. The laminate film may be, for example, a laminated film in which a resin film such as polyethylene terephthalate (PET) film, a metal foil such as aluminum, copper, or stainless steel, and a sealant layer such as polypropylene are laminated in this order.

[0018] Figure 2 is an exploded perspective view showing the electrode group of the non-aqueous electrolyte secondary battery shown in Figure 1. As shown in Figure 2, the electrode group 2 comprises a positive electrode 6, a separator 7, and a negative electrode 8 in that order. The positive electrode 6 and the negative electrode 8 are positioned so that their surfaces facing the positive electrode mixture layer 10 and the negative electrode mixture layer 12, respectively, face the separator 7.

[0019] The positive electrode 6 comprises a positive electrode current collector 9 and a positive electrode mixture layer 10 provided on the positive electrode current collector 9. The positive electrode current collector 9 is provided with a positive electrode current collector tab 4.

[0020] The positive electrode current collector 9 is formed of, for example, aluminum, titanium, stainless steel, nickel, fired carbon, a conductive polymer, conductive glass, or the like. The positive electrode current collector 9 may be one obtained by treating the surface of aluminum, copper, or the like with carbon, nickel, titanium, silver, or the like for the purpose of improving adhesion, conductivity, and oxidation resistance. The thickness of the positive electrode current collector 9 is, for example, 1 to 50 μm from the viewpoints of electrode strength and energy density.

[0021] 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.

[0022] The positive electrode active material may be, for example, a lithium oxide. Examples of the 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 、Li x 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 (where M is an element different from the other elements in each formula). x = 0 to 1.2, y = 0 to 0.9, and z = 2.0 to 2.3).) Examples include. Li x Ni 1-y M y [[ID=5...]] z The lithium oxide represented by O is Li x Ni 1-(y1+y2) Co y1 Mn y2 O z ​(However, x and z are the same as described above, y1 = 0 to 0.9, y2 = 0 to 0.9, and y1 + y2 = 0 to 0.9.) For example, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiLiLi 0.5 Co 0.2 Mn 0.3 O2, LiLiLi 0.6 Co 0.2 Mn 0.2 O2, or LiNi 0.8 Co 0.1 Mn 0.1 O2 is also acceptable. x Ni 1-y M y O z Lithium oxides, represented by Li x Ni 1-(y3+y4) Co y3 Al y4 O z (However, x and z are the same as described above, y3 = 0 to 0.9, y4 = 0 to 0.9, and y3 + y4 = 0 to 0.9.) For example, LiNi 0.8 Co 0.15 Al 0.05 O2 @.

[0023] The positive electrode active material may be, for example, a lithium phosphate. Examples of lithium phosphates include lithium manganese phosphate (LiMnPO4), lithium iron phosphate (LiFePO4), lithium cobalt phosphate (LiCoPO4), and lithium vanadium phosphate (Li3V2(PO4)3).

[0024] The content of the positive electrode active material may be 80% by mass or more, or 85% by mass or more, and 99% by mass or less, based on the total amount of the positive electrode mixture layer.

[0025] The conductive agent may be carbon black such as acetylene black or Ketjen black, graphite, graphene, or carbon nanotubes. The content of the conductive agent may be, for example, 0.01% by mass or more, 0.1% by mass or more, or 1% by mass or more, or 50% by mass or less, 30% by mass or less, or 15% by mass or less, based on the total amount of the positive electrode mixture layer.

[0026] Examples of binders 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 copolymer or its hydrogenated derivatives, EPDM (ethylene-propylene-diene terpolymer), styrene-ethylene-butadiene-ethylene copolymer, and styrene-isoprene-styrene block copolymer. Examples include thermoplastic elastomers such as composites or hydrogenated thereof; soft resins such as syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymer, and propylene-α-olefin copolymer; fluorine-containing resins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, polytetrafluoroethylene-ethylene copolymer, and polytetrafluoroethylene-vinylidene fluoride copolymer; resins having nitrile group-containing monomers as monomer units; and polymer compositions having ionic conductivity for alkali metal ions (e.g., lithium ions).

[0027] The binder content may be, for example, 0.1% by mass or more, 1% by mass or more, or 1.5% by mass or more, based on the total amount of the positive electrode mixture layer, and may be 30% by mass or less, 20% by mass or less, or 10% by mass or less.

[0028] 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 through, and is resistant to oxidation on the positive electrode 6 side and reduction on the negative electrode 8 side. Examples of materials for such a separator 7 include resins and inorganic materials.

[0029] Examples of resins include olefin polymers, fluorine polymers, cellulose polymers, polyimides, and nylon. From the viewpoint of being stable to the electrolyte and having excellent liquid retention, the separator 7 is preferably a porous sheet or nonwoven fabric made of polyolefin such as polyethylene or polypropylene.

[0030] Examples of inorganic materials include oxides such as alumina and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates such as barium sulfate and calcium sulfate. The separator 7 may be, for example, a separator in which fibrous or particulate inorganic material is attached to a thin film substrate such as a nonwoven fabric, woven fabric, or microporous film.

[0031] The negative electrode 8 comprises a negative electrode current collector 11 and a negative electrode mixture layer 12 provided on the negative electrode current collector 11. The negative electrode current collector 11 is provided with a negative electrode current collector tab 5.

[0032] The negative electrode current collector 11 is made of copper, stainless steel, nickel, aluminum, titanium, calcined carbon, conductive polymer, conductive glass, aluminum-cadmium alloy, etc. The negative electrode current collector 11 may also be made of copper, aluminum, etc., with a surface treatment of carbon, nickel, titanium, silver, etc., for the purpose of improving adhesion, conductivity, and reduction resistance. The thickness of the negative electrode current collector 11 is, for example, 1 to 50 μm, from the viewpoint of electrode strength and energy density.

[0033] The negative electrode mixture layer 12 contains, for example, a negative electrode active material and a binder.

[0034] The negative electrode active material is not particularly limited as long as it is a material capable of intercalating and releasing lithium ions. Examples of negative electrode active materials include carbon materials, metal composite oxides, oxides or nitrides of Group 14 elements such as tin, germanium, and silicon, elemental lithium, lithium alloys such as lithium-aluminum alloys, and metals that can form alloys with lithium, such as Sn and Si. From a safety viewpoint, the negative electrode active material is preferably at least one selected from the group consisting of carbon materials and metal composite oxides. The negative electrode active material may be one of these alone or a mixture of two or more. The shape of the negative electrode active material may be, for example, particulate.

[0035] Examples of carbon materials include amorphous carbon materials, natural graphite, composite carbon materials obtained by forming an amorphous carbon material coating on natural graphite, and artificial graphite (obtained by calcining resin raw materials such as epoxy resin and phenolic resin, or pitch-based raw materials obtained from petroleum, coal, etc.). From the viewpoint of high current density charge-discharge characteristics, the metal composite oxide preferably contains either titanium or lithium, or both, and more preferably contains lithium.

[0036] The negative electrode active material may further include a material containing at least one element selected from the group consisting of silicon and tin. The material containing at least one element selected from the group consisting of silicon and tin may be elemental 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, nitride, or carbide, and specifically, for example, it may be a silicon oxide such as SiO, SiO2, LiSiO, a silicon nitride such as Si3N4, Si2N2O, a silicon carbide such as SiC, or a tin oxide such as SnO, SnO2, LiSnO.

[0037] The negative electrode mixture layer 12, from the viewpoint of further improving the performance of the electrochemical device, such as energy density, preferably contains a carbon material as the negative electrode active material, more preferably contains graphite, even more preferably contains a mixture of a carbon material and a material containing at least one element selected from the group consisting of silicon and tin, and particularly preferably contains a mixture of graphite and silicon oxide. The content of the material containing at least one element selected from the group consisting of silicon and tin (silicon oxide) in the mixture may be 1% by mass or more, or 3% by mass or more, and 30% by mass or less, based on the total amount of the mixture.

[0038] The content of the negative electrode active material may be 80% by mass or more, or 85% by mass or more, and 99% by mass or less, based on the total amount of the negative electrode mixture layer.

[0039] The binder and its content may be the same as the binder and its content in the positive electrode mixture layer described above.

[0040] The negative electrode mixture layer 12 may further contain a thickening agent to adjust the viscosity. The thickening agent is not particularly limited, but may be carboxymethylcellulose, methylcellulose, hydroxymethylcellulose, ethylcellulose, polyvinyl alcohol, starch oxide, starch phosphorylated, casein, or salts thereof. The thickening agent may be one of these alone or a mixture of two or more.

[0041] If the negative electrode mixture layer 12 contains a thickening agent, its content is not particularly limited. From the viewpoint of the coatability of the negative electrode mixture layer, the content of the thickening agent may 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 viewpoint of suppressing a decrease in battery capacity or an increase in resistance between negative electrode active materials, the content of the thickening agent may 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.

[0042] The electrolyte (electrolyte for electrochemical devices) contains a compound represented by the following formula (1) (isocyanate compound) and a heterocyclic compound containing a sulfur atom. In one embodiment, the electrolyte contains the compound represented by formula (1), the heterocyclic compound, an electrolyte salt, and a non-aqueous solvent.

[0043] [ka]

[0044] In formula (1), R 1 , R 2 , and R 3 Each of these independently represents either a hydrogen atom or a methyl group, and X represents a divalent organic group.

[0045] In other words, in one embodiment, the compound represented by formula (1) and the heterocyclic compound are additives used in the electrolyte of an electrochemical device.

[0046] R 1 and R 2 R is preferably a hydrogen atom. 3 Preferably, it is a hydrogen atom.

[0047] 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.

[0048] X may be, for example, a divalent group in which part 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 part 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). -X1 -OX 2 - (2)

[0049] In formula (2), X 1 and X 2 Each of these independently represents an alkylene group. This alkylene group may be linear or branched. 1 and X 2 The number of carbon atoms in the alkylene group shown may be independently 1-6, 1-5, 1-4, 1-3, or 1-2.

[0050] The content of the compound represented by formula (1) can be 0.001% by mass or more, 0.005% by mass or more, 0.01% by mass or more, 0.05% by mass or more, 0.1% by mass or more, 0.15% by mass or more, or 0.2% by mass or more, based on the total amount of electrolyte, and may be 5% by mass or less, 4% by mass or less, 3% by mass or less, 2% by mass or less, 1% by mass or less, 0.8% by mass or less, 0.6% by mass or less, or 0.5% by mass or less, as it is possible to more sufficiently suppress the expansion of the electrochemical device at high temperatures.

[0051] Heterocyclic compounds contain a sulfur atom. Heterocyclic compounds containing a sulfur atom may be, for example, compounds having an S=O bond. Examples of compounds having an S=O bond include cyclic sulfonic acid esters, cyclic sulfuric acid esters, cyclic sulfite esters, and cyclic sulfones. Among these, the heterocyclic compound or the compound having an S=O bond may be a cyclic sulfonic acid ester or a cyclic sulfuric acid ester.

[0052] Examples of cyclic sulfonic acid esters include 1,3-propanesultone, 1-fluoro-1,3-propanesultone, 2-fluoro-1,3-propanesultone, 3-fluoro-1,3-propanesultone, 1-methyl-1,3-propanesultone, 2-methyl-1,3-propanesultone, 3-methyl-1,3-propanesultone, 1-propene-1,3-sultone, 2-propene-1,3-sultone, 1-fluoro-1-propene-1,3-sultone, 2-fluoro-1-propene-1,3-sultone, 3-fluoro-1-propene-1,3-sultone, and 1-fluoro-2-propene-1,3 Examples include sultone compounds such as -sultone, 2-fluoro-2-propene-1,3-sultone, 3-fluoro-2-propene-1,3-sultone, 1-methyl-1-propene-1,3-sultone, 2-methyl-1-propene-1,3-sultone, 3-methyl-1-propene-1,3-sultone, 1-methyl-2-propene-1,3-sultone, 2-methyl-2-propene-1,3-sultone, 3-methyl-2-propene-1,3-sultone, 1,4-butanesultone, and 1,5-pentanesultone; and disulfonate compounds such as methylenemethanedisulfonate and ethylenemethanedisulfonate. The cyclic sulfonic acid ester may be at least one selected from the group consisting of 1,3-propanesultone, 1-propene-1,3-sultone, and methylenemethanedisulfonate.

[0053] Examples of cyclic sulfuric acid esters include alkylene sulfate compounds such as 1,2-ethylene sulfate (1,3,2-dioxathiolane-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 sulfuric acid ester may be 1,2-ethylene sulfate (1,3,2-dioxathiolane-2,2-dioxide).

[0054] Examples of cyclic sulfite esters 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.

[0055] Examples of cyclic sulfones include alkylene sulfone compounds such as sulfolane, methylsulfolane, and 4,5-dimethylsulfolane; and alkylylene sulfone compounds such as sulfolene.

[0056] The heterocyclic compound content can more effectively suppress the expansion of electrochemical devices at high temperatures. Therefore, based on the total amount of electrolyte, the heterocyclic compound content may be 0.001% by mass or more, 0.005% by mass or more, 0.01% by mass or more, 0.05% by mass or more, 0.1% by mass or more, 0.15% by mass or more, or 0.2% by mass or more, and may be 5% by mass or less, 4% by mass or less, 3% by mass or less, 2% by mass or less, 1% by mass or less, 0.8% by mass or less, 0.6% by mass or less, or 0.5% by mass or less.

[0057] 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 electrolyte, in order to more sufficiently suppress the expansion of the electrochemical device at high temperatures. 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 more, and may be 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 electrolyte.

[0058] 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, 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 more, and may be 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, as this makes it possible to more sufficiently suppress the expansion of the electrochemical device at high temperatures.

[0059] The electrolyte salt may be, for example, a lithium salt. The lithium salt may be at least one selected from the group consisting of, for example, LiPF6, LiBF4, LiClO4, LiB(C6H5)4, LiCH3SO3, CF3SO2OLi, LiN(SO2F)2(Li[FSI], lithium bisfluorosulfonylimide), LiN(SO2CF3)2(Li[TFSI], lithium bistrifluoromethanesulfonylimide), and LiN(SO2CF2CF3)2. The lithium salt preferably contains LiPF6 because it is even better in terms of solubility in the solvent, charge / discharge characteristics of the secondary battery, output characteristics, cycle characteristics, etc.

[0060] From the viewpoint of excellent charge-discharge characteristics, the concentration of the electrolyte salt is 0.5 mol / L or more, more preferably 0.7 mol / L or more, even more preferably 0.8 mol / L or more, preferably 1.5 mol / L or less, more preferably 1.3 mol / L or less, and even more preferably 1.2 mol / L or less, based on the total amount of non-aqueous solvent.

[0061] Examples of non-aqueous solvents include linear carbonate compounds such as dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, and methyl butyl carbonate; cyclic carbonate compounds such as ethylene carbonate, propylene carbonate, and butylene carbonate; linear carboxylic acid ester compounds such as methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, and propyl propionate; cyclic carboxylic acid ester compounds such as γ-butyl lactone; linear ether compounds such as dimethoxymethane, dimethoxyethane, and diethoxyethane; cyclic ether compounds such as tetrahydrofuran, tetrahydropyran, and dioxolane; and nitrile compounds such as acetonitrile. The non-aqueous solvent may be used alone or as a mixture of two or more. Preferably, the non-aqueous solvent is a mixture of two or more.

[0062] The electrolyte may further contain other components besides the compound represented by formula (1), heterocyclic compounds, electrolyte salts, and non-aqueous solvents. Examples of other components include unsaturated cyclic carbonates, fluorine-containing cyclic carbonates, and compounds containing nitrogen atoms other than the compound represented by formula (1).

[0063] Examples of unsaturated cyclic carbonates include vinylene carbonate, methyl vinylene carbonate, dimethyl vinylene carbonate (4,5-dimethyl vinylene carbonate), ethyl vinylene carbonate (4,5-diethyl vinylene carbonate), diethyl vinylene carbonate, and vinylethylene carbonate. From the viewpoint of further improving the performance of electrochemical devices, vinylene carbonate is preferred as the unsaturated cyclic carbonate. Examples of fluorine-containing cyclic carbonates include 4-fluoro-1,3-dioxolan-2-one (fluoroethylene carbonate; FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, and 1,1,2,2-tetrafluoroethylene carbonate. The fluorine-containing cyclic carbonate is preferably 4-fluoro-1,3-dioxolan-2-one (fluoroethylene carbonate; FEC). The nitrogen atom-containing compound other than the compound represented by formula (1) may be, for example, a nitrile compound such as succinonitrile.

[0064] The inventors have found that by using an electrolyte containing the compound represented by formula (1) and a heterocyclic compound in an electrochemical device, expansion at high temperatures is sufficiently suppressed. The reason for this effect is not entirely clear, but the inventors speculate as follows: During the initial charge, the unsaturated carbon bond structure of the compound represented by formula (1) undergoes a reduction reaction on the negative electrode side before other additives or carbonate solvents, forming a film. Subsequently, the isocyanate moiety reacts to form a stable film, which suppresses the reductive decomposition of other additives, non-aqueous solvents, electrolyte salts, etc. on the negative electrode side. Furthermore, on the positive electrode side, the heterocyclic compound that remains without reductive decomposition forms a film, or the compound represented by formula (1) and the heterocyclic compound react to form a stable film, thus suppressing the oxidative decomposition of other additives, non-aqueous solvents, electrolyte salts, etc. on the positive electrode side as well.

[0065] Furthermore, in one embodiment, by using an electrolyte containing the compound represented by formula (1) and a heterocyclic compound in an electrochemical device, the electrochemical device tends to exhibit superior capacity recovery after high-temperature storage. Although the reason for this effect is not entirely clear, the inventors surmise that, in addition to the formation of stable films on the positive and negative electrodes, the reduction of hydrofluoric acid (HF) in the electrolyte by the compound represented by formula (1) suppresses side reactions such as the dissolution of the positive electrode active material and the formation of films such as LiF on the negative electrode.

[0066] Next, a method for manufacturing a non-aqueous electrolyte secondary battery 1 will be described. The method for manufacturing a non-aqueous electrolyte secondary battery 1 comprises 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 casing 3, and a fourth step of pouring the electrolyte into the battery casing 3. The order of the first to fourth steps is arbitrary.

[0067] In the first step, the materials to be used for the positive electrode mixture layer 10 are dispersed in a dispersion medium using a kneader, disperser, etc. to obtain a slurry-like positive electrode mixture. This positive electrode mixture is then applied onto the positive electrode current collector 9 by a doctor blade method, dipping method, spray method, etc., and the positive electrode 6 is obtained by volatilizing the dispersion medium. After volatilizing the dispersion medium, a compression molding step using a roll press may be provided as needed. The positive electrode mixture layer 10 may be formed as a multilayer positive electrode mixture layer by performing the above-described steps from application of the positive electrode mixture to volatilization of the dispersion medium multiple times. The dispersion medium may be water, 1-methyl-2-pyrrolidone (hereinafter sometimes referred to as "NMP"), etc.

[0068] In the second step, the negative electrode 8 is obtained in the same manner as in the first step described above for obtaining the positive electrode 6. The method for forming the negative electrode mixture layer 12 on the negative electrode current collector 11 may be the same as in the first step described above, except that the positive electrode current collector 9 and the positive electrode mixture layer 10 are replaced with the negative electrode current collector 11 and the negative electrode mixture layer 12.

[0069] In the third step, a separator 7 is placed between the fabricated positive electrode 6 and negative electrode 8 to form an electrode group 2. Next, this electrode group 2 is housed in the battery casing 3.

[0070] In the fourth step, the electrolyte is injected into the battery casing 3. The electrolyte can be prepared, for example, by first dissolving the electrolyte salt in a solvent, and then dissolving the other materials.

[0071] In another embodiment, the electrochemical device may be a capacitor. The capacitor may comprise an electrode group consisting of a positive electrode, a negative electrode, and a separator, and a bag-shaped battery casing that houses the electrode group, similar to the non-aqueous electrolyte secondary battery 1 described above. The details of each component in the capacitor may be the same as those in the non-aqueous electrolyte secondary battery 1. [Examples]

[0072] The present disclosure will be specifically described below with reference to examples, but the present disclosure is not limited to these examples.

[0073] (Example 1) [Fabrication of the positive electrode] Lithium nickel-cobalt-manganate (92% by mass) was used as the positive electrode active material, to which acetylene black (AB) (4% by mass) was added as a conductive agent and polyvinylidene fluoride (PVDF) (4% by mass) was added as a binder, and the mixture was mixed. NMP was added to the resulting mixture as a dispersion medium and kneaded to prepare a slurry-like positive electrode mixture. A predetermined amount of this positive electrode mixture was evenly and homogeneously coated onto a 20 μm thick aluminum foil, which served as the positive electrode current collector. After the dispersion medium was evaporated, the mixture was pressed to obtain a density of 2.8 g / cm³. 3 The material was compacted to obtain the positive electrode.

[0074] [Fabrication of the negative electrode] As negative electrode active materials, graphite-based active material (artificial graphite, average particle size (D50); approximately 23 μm) and silicon-based active material (SiOx, average particle size (D50); approximately 10 μm) were used. Styrene-butadiene rubber (SBR) as a binder and carboxymethylcellulose as a thickener were added to these active materials. The mass ratio of these was graphite active material:silicon-based active material:binder:thickener = 92:5:1.5:1.5. Water was added to the resulting mixture as a dispersion medium and kneaded to prepare a slurry-like negative electrode mixture. A predetermined amount of this negative electrode mixture was evenly and homogeneously coated onto a 10 μm thick rolled copper foil to be used as a negative electrode current collector. After that, the dispersion medium was volatilized and then pressed to obtain a density of 1.6 g / cm³. 3 The material was compacted to this extent to obtain the negative electrode.

[0075] [Manufacturing of lithium-ion secondary batteries] 13.5cm 2 The positive electrode, cut into a rectangle, is sandwiched between a porous polyethylene sheet (30 μm thick) acting as a separator, and then further sandwiched between 14.3 cm 2 An electrode group was fabricated by stacking negative electrodes cut into rectangular shapes. This electrode group was placed in a container (battery casing) made of 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-sealed to fabricate a lithium-ion secondary battery for evaluation. The electrolyte was a mixed solution of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate = 1 / 1 / 1 (volume ratio) containing 1 mol / L LiPF6, to which compound A(R) represented by the following formula (1X) was added. 1 , R 2 , and R 3 A solution was used which contained 0.5% by mass of a compound represented by formula (1), in which x is a hydrogen atom and x is an ethylene group, 0.5% by mass of 1,3-propanesultone (heterocyclic compound 1), 1% by mass of vinylene carbonate, and 1% by mass of fluoroethylene carbonate (all based on the total amount of electrolyte).

[0076] [ka]

[0077] (Example 2) A lithium-ion secondary battery was prepared in the same manner as in Example 1, except that an electrolyte containing 0.2% by mass of compound A based on the total amount of the electrolyte was used.

[0078] (Example 3) A lithium-ion secondary battery was prepared in the same manner as in Example 2, except that an electrolyte containing 0.2% by mass of 1,3-propanesultone (based on the total amount of the electrolyte) was used.

[0079] (Example 4) A lithium-ion secondary battery was prepared in the same manner as in Example 3, except that an electrolyte containing 1% by mass of compound A based on the total amount of the electrolyte was used.

[0080] (Example 5) Compound B (R) is represented by the following formula (1Y) instead of compound A. 1 and R 2 is a hydrogen atom, and R 3 A lithium-ion secondary battery was prepared in the same manner as in Example 1, except that an electrolyte containing 0.5% by mass of a compound represented by formula (1), in which (x) is a methyl group and (x) is an ethylene group, based on the total amount of the electrolyte, was used.

[0081] [ka]

[0082] (Example 6) A lithium-ion secondary battery was prepared in the same manner as in Example 1, except that an electrolyte containing 1-propene-1,3-sultone (heterocyclic compound 2) at a concentration of 0.5% by mass relative to the total amount of the electrolyte was used instead of 1,3-propanesultone.

[0083] (Example 7) A lithium-ion secondary battery was prepared in the same manner as in Example 1, except that an electrolyte containing 1,3,2-dioxathiolane-2,2-dioxide (DTD, heterocyclic compound 3) at a concentration of 0.5% by mass relative to the total volume of the electrolyte was used instead of 1,3-propanesultone.

[0084] (Example 8) A lithium-ion secondary battery was prepared in the same manner as in Example 1, except that methylene methane disulfonate (MMDS, heterocyclic compound 4) was added to the electrolyte at a concentration of 0.5% by mass relative to the total amount of the electrolyte, instead of 1,3-propanesultone.

[0085] (Comparative Example 1) A lithium-ion secondary battery was prepared in the same manner as in Example 1, except that compound A and 1,3-propanesultone were not added to the electrolyte.

[0086] (Comparative Example 2) A lithium-ion secondary battery was prepared 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.

[0087] (Comparative Example 3) A lithium-ion secondary battery was prepared in the same manner as in Example 1, except that p-toluenesulfonyl isocyanate (PTSI) was added to the electrolyte at a concentration of 0.5% by mass relative to the total amount of the electrolyte, instead of compound A.

[0088] [Initial charge / discharge] For each lithium-ion secondary battery produced, the initial charge and discharge cycle was performed using the method described below. First, constant current charging was performed at a current of 0.1C up to a maximum voltage of 4.2V in an environment of 25°C, followed by constant voltage charging at 4.2V. The charging termination condition was a current of 0.01C. Subsequently, constant current discharge was performed at a current of 0.1C with a termination voltage of 2.7V. This charge and discharge cycle was repeated three times (the unit "C" used for the current value means "current value (A) / battery capacity (Ah)"). The discharge capacity after the third cycle was defined as the capacity of the lithium-ion secondary battery (Q1).

[0089] [High-temperature storage test] For each lithium-ion secondary battery in Examples 1-8 and Comparative Examples 1-3, after the initial charge-discharge procedure described above, constant current charging was performed at a current value of 0.1C up to a maximum voltage of 4.2V in an environment of 25°C, followed by constant voltage charging at 4.2V. The charging termination condition was a current value of 0.01C. Subsequently, these lithium-ion secondary batteries were stored in a constant temperature bath at 60°C for 4 weeks. After storage, the volume change rate and capacity recovery rate of the lithium-ion secondary batteries were measured according to the procedure shown below. Subsequently, the measured batteries were charged at a constant current value of 0.1C up to a maximum voltage of 4.2V in an environment of 25°C, followed by constant voltage charging at 4.2V. The charging termination condition was a current value of 0.01C. Subsequently, the lithium-ion secondary batteries were stored in a constant temperature bath at 60°C, and the volume change rate and capacity recovery rate of the lithium-ion secondary batteries were measured 8 weeks and 12 weeks after storage, respectively. Figure 3 shows the measurement results of the volume change rate of lithium-ion secondary batteries after 12 weeks of storage at 60°C. Figure 4 shows the measurement results of the capacity recovery rate of lithium-ion secondary batteries after 12 weeks of storage at 60°C.

[0090] (Measurement of volume change rate) The volume (V1) of each lithium-ion secondary battery before high-temperature storage, and the volume (V2) of each lithium-ion secondary battery after being left undisturbed at 25°C for 30 minutes, were measured using an Archimedes hydrometer (electronic hydrometer MDS-300, manufactured by Alpha Mirage Co., Ltd.). Using the measured V1 and V2, the volume change rate was calculated from 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. Volume change rate (%) = V2 / V1 × 100

[0091] (Measurement of capacity recovery rate) After high-temperature storage, each lithium-ion secondary battery was left to stand at 25°C for 30 minutes, followed by constant-current discharge at a current of 0.1C with a cutoff voltage of 2.7V. Next, constant-current charging was performed at a current of 0.1C up to an upper voltage limit of 4.2V, followed by constant-voltage charging at 4.2V. The charging cutoff condition was a current of 0.01C. Subsequently, constant-current discharge was performed at a current of 0.1C with a cutoff voltage of 2.7V. The discharge capacity at this time was defined as the capacity after the high-temperature storage test (Q2). Using Q1 and Q2 above, the capacity recovery rate was calculated from the following formula. Tables 1 and 2 show the measurement results of the capacity recovery rate of lithium-ion secondary batteries after 12 weeks of storage at 60°C. Capacity recovery rate (%)=Q2 / Q1×100

[0092] [Table 1]

[0093] [Table 2]

[0094] From Figures 3 and 4 and Tables 1 and 2, the lithium-ion secondary batteries of Examples 1 to 8, which used an electrolyte containing the compound represented by formula (1) and a heterocyclic compound, showed a lower volume change rate and a higher capacity recovery rate compared to the lithium-ion secondary battery of Comparative Example 1, which used an electrolyte not containing these compounds. On the other hand, the lithium-ion secondary battery of Comparative Example 2, which used an electrolyte containing PTSI, a compound having both an isocyanate group and a sulfonyl group containing a sulfur atom within the same molecule, and the lithium-ion secondary battery of Comparative Example 3, which used an electrolyte containing PTSI and 1,3-propanesultone (heterocyclic compound 1), showed 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 showed a greater suppression effect on volume expansion. From these results, it was confirmed that the electrochemical device of this disclosure is capable of sufficiently suppressing expansion at high temperatures. Furthermore, while the lithium-ion secondary batteries of Comparative Examples 2 and 3 showed a lower capacity recovery rate than the lithium-ion secondary battery of Comparative Example 1, the lithium-ion batteries of Examples 1 to 8 were found to have a higher capacity recovery rate than the lithium-ion secondary batteries of Comparative Examples 1 to 3. From these results, it was confirmed that the electrochemical device of this disclosure also exhibits excellent capacity recovery rate after high-temperature storage.

[0095] The present inventors speculate that the effect of using an electrolyte containing the compound represented by formula (1) and a heterocyclic compound in an electrochemical device, which sufficiently suppresses expansion at high temperatures, is as follows: During the initial charge, the unsaturated carbon bond structure of the compound represented by formula (1) undergoes a reduction reaction on the negative electrode side before other additives or carbonate solvents, forming a film. Subsequently, the isocyanate moiety reacts to form a stable film, which suppresses the reductive decomposition of other additives, non-aqueous solvents, electrolyte salts, etc. on the negative electrode side. Furthermore, on the positive electrode side, the heterocyclic compound that remains without reductive decomposition forms a film, or the compound represented by formula (1) and the heterocyclic compound react to form a stable film, thus suppressing the oxidative decomposition of other additives, non-aqueous solvents, electrolyte salts, etc. on the positive electrode side as well. [Explanation of Symbols]

[0096] 1...Non-aqueous electrolyte secondary battery (electrochemical device), 2...Electrode group, 3...Battery casing, 4...Positive electrode current collector tab, 5...Negative electrode current collector tab, 6...Positive electrode, 7...Separator, 8...Negative electrode, 9...Positive electrode current collector, 10...Positive electrode mixture layer, 11...Negative electrode current collector, 12...Negative electrode mixture layer.

Claims

1. It comprises a positive electrode, a negative electrode, and an electrolyte. The electrolyte contains a compound represented by the following formula (1) and a cyclic sulfate ester. Electrochemical devices. 【Chemistry 1】 [In formula (1), R １ , R ２ , and R ３ Each of these independently represents either a hydrogen atom or a methyl group, and X represents a divalent organic group.

2. R in formula (1) １ and R ２ That is a hydrogen atom. The electrochemical device according to claim 1.

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

4. The total content of the compound represented by formula (1) and the cyclic sulfate ester is 0.1 to 10% by mass, based on the total amount of the electrolyte. The electrochemical device according to any one of claims 1 to 3.

5. The electrochemical device is a non-aqueous electrolyte secondary battery or a capacitor. The electrochemical device according to any one of claims 1 to 4.

6. A compound represented by the following formula (1), and a cyclic sulfate ester are included. Electrolyte for electrochemical devices. 【Chemistry 2】 [In formula (1), R １ , R ２ , and R ３ Each of these independently represents either a hydrogen atom or a methyl group, and X represents a divalent organic group.

7. R in the formula (1) １ and R ２ are hydrogen atoms The electrolyte for an electrochemical device according to claim 6.

8. In formula (1) above, X is an alkylene group having 1 to 6 carbon atoms. The electrolyte for an electrochemical device according to claim 6 or 7.

9. The total content of the compound represented by formula (1) and the cyclic sulfate ester is 0.1 to 10% by mass, based on the total amount of the electrolyte. The electrolyte for an electrochemical device according to any one of claims 6 to 8.

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