Non-aqueous electrolyte energy storage element

Abstract

The nonaqueous-electrolyte electricity storage element according to one aspect of the present invention includes a positive electrode including sulfur and a nonaqueous electrolyte including a nonaqueous solvent comprising an unsaturated cyclic carbonate, wherein the nonaqueous electrolyte further includes at least one ester selected from the group consisting of chain esters and unsubstituted saturated cyclic esters.

Description

[Technical Field]

[0001] The present invention relates to a non-aqueous electrolyte electricity storage element. [Background technology]

[0002] Due to their high energy density, non-aqueous electrolyte secondary batteries, such as lithium ion secondary batteries, are widely used in electronic devices such as personal computers and communication terminals, automobiles, etc. The non-aqueous electrolyte secondary batteries generally have a pair of electrodes electrically isolated by a separator and a non-aqueous electrolyte interposed between the electrodes, and are configured to charge and discharge by transferring lithium ions between the electrodes. Furthermore, capacitors such as lithium ion capacitors and electric double layer capacitors are also widely used as non-aqueous electrolyte energy storage elements other than non-aqueous electrolyte secondary batteries.

[0003] Known nonaqueous electrolyte storage elements include lithium-sulfur batteries (Li-S batteries) and other nonaqueous electrolyte storage elements that use sulfur as the positive electrode active material (see Patent Document 1). Sulfur has a large theoretical capacity, and nonaqueous electrolyte storage elements that use sulfur as the positive electrode active material are expected to have high energy density. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-95390 Summary of the Invention [Problem to be solved by the invention]

[0005] The inventors have found that in nonaqueous electrolyte storage elements using sulfur as the positive electrode active material, adding an unsaturated cyclic carbonate such as vinylene carbonate to the nonaqueous solvent of the nonaqueous electrolyte can have the advantage of improving high-rate discharge performance. However, nonaqueous electrolyte storage elements equipped with a sulfur-containing positive electrode and a nonaqueous electrolyte containing an unsaturated cyclic carbonate have insufficient initial charge capacity.

[0006] The present invention has been made in light of the above circumstances, and an object of the present invention is to provide a nonaqueous electrolyte storage element that includes a sulfur-containing positive electrode and a nonaqueous electrolyte containing an unsaturated cyclic carbonate, and that has a large initial charge capacity. [Means for solving the problem]

[0007] A nonaqueous electrolyte storage element according to one aspect of the present invention includes a sulfur-containing positive electrode and a nonaqueous electrolyte containing a nonaqueous solvent including an unsaturated cyclic carbonate, wherein the nonaqueous electrolyte further contains at least one ester selected from the group consisting of a chain ester and an unsubstituted saturated cyclic ester. [Effects of the Invention]

[0008] According to one aspect of the present invention, there is provided a nonaqueous electrolyte storage element including a positive electrode containing sulfur and a nonaqueous electrolyte containing an unsaturated cyclic carbonate, the nonaqueous electrolyte storage element having a large initial charge capacity. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a perspective view showing one embodiment of a nonaqueous electrolyte electricity storage element. [Figure 2] FIG. 2 is a schematic diagram showing one embodiment of an electricity storage device configured by assembling a plurality of nonaqueous electrolyte electricity storage elements. DETAILED DESCRIPTION OF THE INVENTION

[0010] An embodiment of the present invention provides the following aspects.

[0011] Section 1. a cathode comprising sulfur, and Nonaqueous electrolyte containing a nonaqueous solvent containing an unsaturated cyclic carbonate Equipped with The nonaqueous electrolyte storage element further comprises at least one ester selected from the group consisting of chain esters and unsubstituted saturated cyclic esters.

[0012] Section 2. Item 2. The nonaqueous electrolyte storage element according to Item 1, wherein the ester comprises the chain ester.

[0013] Section 3. Item 3. The nonaqueous electrolyte storage element according to Item 2, wherein the chain ester is a fluorinated chain ester.

[0014] Section 4. Item 4. The nonaqueous electrolyte storage element according to item 1, 2, or 3, wherein the content of the ester relative to the nonaqueous solvent in the nonaqueous electrolyte is 3% by volume or more and 10% by volume or less.

[0015] Section 5. Item 5. The nonaqueous electrolyte storage element according to any one of items 1 to 4, wherein the content of the ester relative to the nonaqueous solvent in the nonaqueous electrolyte is 4% by volume or more and 9% by volume or less.

[0016] First, an outline of the nonaqueous electrolyte electricity storage element disclosed in this specification will be described.

[0017] A nonaqueous electrolyte storage element according to one aspect of the present invention includes a sulfur-containing positive electrode and a nonaqueous electrolyte containing a nonaqueous solvent including an unsaturated cyclic carbonate, wherein the nonaqueous electrolyte further contains at least one ester selected from the group consisting of a chain ester and an unsubstituted saturated cyclic ester.

[0018] The nonaqueous electrolyte storage element is a nonaqueous electrolyte storage element comprising a sulfur-containing positive electrode and a nonaqueous electrolyte containing an unsaturated cyclic carbonate, and has a large initial charge capacity. The reason for this is unclear, but it is thought that at least one ester selected from the group consisting of a chain ester and an unsubstituted saturated cyclic ester contained in the nonaqueous electrolyte contains sulfur or a sulfur-containing compound (Li2S n It is presumed that the reaction occurs with the cathode, forming a good coating on the surface of the cathode.

[0019] "Unsaturated" in unsaturated cyclic carbonates and the like means that the molecule contains a carbon-carbon double bond or a carbon-carbon triple bond. "Saturated" in saturated cyclic esters and the like means that the molecule does not contain a carbon-carbon double bond or a carbon-carbon triple bond. "Unsubstituted" means that some or all of the hydrogen atoms in the molecule are not substituted with other atoms or groups other than hydrocarbon groups. Furthermore, "at least one ester selected from the group consisting of linear esters and unsubstituted saturated cyclic esters" is not included in the non-aqueous solvent. Esters include esters of various oxo acids, such as carboxylate esters, carbonate esters, sulfonate esters, sulfate esters, and sulfite esters.

[0020] The ester preferably includes the chain ester. The chain ester is more preferably a fluorinated chain ester. In this case, the initial charge capacity of the nonaqueous electrolyte storage element can be increased.

[0021] The content of the ester in the nonaqueous electrolyte relative to the nonaqueous solvent is preferably 3% by volume or more and 10% by volume or less, and more preferably 4% by volume or more and 9% by volume or less, which can increase the initial charge capacity of the nonaqueous electrolyte storage element.

[0022] A nonaqueous electrolyte electricity storage element, an electricity storage device, a method for manufacturing a nonaqueous electrolyte electricity storage element according to one embodiment of the present invention, and other embodiments will be described in detail below. Note that the names of the components (elementary components) used in each embodiment may differ from the names of the components (elementary components) used in the background art.

[0023] <Non-aqueous electrolyte energy storage element> A nonaqueous electrolyte storage element (hereinafter also simply referred to as "storage element") according to one embodiment of the present invention comprises an electrode assembly having a positive electrode, a negative electrode, and a separator, a nonaqueous electrolyte, and a container that accommodates the electrode assembly and the nonaqueous electrolyte. The electrode assembly is typically a stacked type in which a plurality of positive electrodes and a plurality of negative electrodes are stacked with separators interposed therebetween, or a wound type in which a positive electrode and a negative electrode are stacked with separators interposed therebetween and wound. The nonaqueous electrolyte is present in a state contained in the positive electrode, the negative electrode, and the separator. As an example of a nonaqueous electrolyte storage element, a nonaqueous electrolyte secondary battery (hereinafter also simply referred to as "secondary battery") will be described.

[0024] (positive electrode) The positive electrode has a positive electrode substrate and a positive electrode active material layer disposed on the positive electrode substrate directly or via an intermediate layer.

[0025] The positive electrode substrate is electrically conductive. Whether or not it has "electrical conductivity" is determined by whether the volume resistivity measured in accordance with JIS-H-0505 (1975) is 10 7 The threshold value is Ω·cm. The material of the positive electrode substrate is a metal such as aluminum, titanium, tantalum, or stainless steel, or an alloy of these. Among these, aluminum or an aluminum alloy is preferred from the viewpoints of potential resistance, high conductivity, and cost. Positive electrode substrates include foils, vapor-deposited films, meshes, and porous materials, with foil being preferred from the viewpoint of cost. Therefore, aluminum foil or aluminum alloy foil is preferred as the positive electrode substrate. Examples of aluminum or aluminum alloys include A1085, A3003, and A1N30, as specified in JIS-H-4000 (2014) or JIS-H-4160 (2006).

[0026] The average thickness of the positive electrode substrate is preferably 3 μm to 50 μm, more preferably 5 μm to 40 μm, even more preferably 8 μm to 30 μm, and particularly preferably 10 μm to 25 μm. By setting the average thickness of the positive electrode substrate within the above range, it is possible to increase the strength of the positive electrode substrate while increasing the energy density per volume of the secondary battery. The "average thickness" of the positive electrode substrate and the negative electrode substrate described below refers to the value obtained by dividing the punched mass when a substrate of a predetermined area is punched out by the true density and punched area of ​​the substrate.

[0027] The intermediate layer is a layer disposed between the positive electrode substrate and the positive electrode active material layer. The intermediate layer contains a conductive agent such as carbon particles to reduce the contact resistance between the positive electrode substrate and the positive electrode active material layer. The configuration of the intermediate layer is not particularly limited, and may contain, for example, a binder and a conductive agent.

[0028] The positive electrode active material layer contains sulfur. The positive electrode active material layer contains optional components such as a conductive agent, a binder, a thickener, and a filler, as needed. The positive electrode active material layer is usually formed from a positive electrode mixture containing sulfur and other optional components.

[0029] Sulfur is a component that functions as a positive electrode active material. The sulfur contained in the positive electrode or the positive electrode active material layer may be elemental sulfur or a sulfur compound. Examples of sulfur compounds include metal sulfides such as lithium sulfide, organic disulfide compounds, and organic sulfur compounds such as carbon sulfide compounds. Sulfur has advantages such as a high theoretical capacity and low cost.

[0030] Sulfur may be in the form of a composite with a conductive agent (a material with higher conductivity than sulfur). Examples of such composites include those in which sulfur is supported on a conductive agent or the like as a carrier, specifically a composite of sulfur and porous carbon (sulfur-porous carbon composite: SPC). The sulfur content in the SPC (the mass ratio of sulfur atoms to the mass of SPC) is preferably 50% by mass or more and 90% by mass or less, more preferably 60% by mass or more and 80% by mass or less. By setting the sulfur content in the SPC within the above range, it is possible to achieve both high electrical capacitance and good conductivity.

[0031] The sulfur content in the positive electrode active material layer (mass ratio of sulfur atoms to the mass of the positive electrode active material layer) is preferably 40% by mass to 90% by mass, more preferably 50% by mass to 70% by mass. When SPC is used, the SPC content in the positive electrode active material layer is preferably 60% by mass to 95% by mass, more preferably 70% by mass to 90% by mass. By setting the sulfur or SPC content within the above range, it is possible to achieve both high electrical capacity and good conductivity, and to increase energy density, etc.

[0032] The positive electrode active material layer may contain a positive electrode active material other than sulfur, provided that the content of sulfur (elemental sulfur) in the total positive electrode active material is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, even more preferably 99% by mass or more, and particularly preferably 100% by mass.

[0033] The conductive agent is not particularly limited as long as it is a material having electrical conductivity. Note that this conductive agent does not include conductive agents that form a composite with sulfur. Examples of such conductive agents include carbonaceous materials, metals, and conductive ceramics. Examples of carbonaceous materials include graphite, non-graphitic carbon, and graphene-based carbon. Examples of non-graphitic carbon include carbon nanofibers, pitch-based carbon fibers, and carbon black. Examples of carbon black include furnace black, acetylene black, and ketjen black. Examples of graphene-based carbon include graphene, carbon nanotubes (CNTs), and fullerenes. The conductive agent may be in the form of powder or fiber. As the conductive agent, one of these materials may be used alone, or two or more may be mixed. These materials may also be used in combination. For example, a composite of carbon black and CNTs may be used. Among these, carbon black is preferred from the viewpoints of electronic conductivity and coatability, and acetylene black is particularly preferred.

[0034] The content of the conductive agent (excluding the conductive agent in the composite of sulfur and the conductive agent) in the positive electrode active material layer is preferably 1% by mass or more and 20% by mass or less, and more preferably 3% by mass or more and 15% by mass or less. By setting the content of the conductive agent in the above range, the energy density of the secondary battery can be increased.

[0035] Examples of binders include thermoplastic resins such as fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), polyethylene, polypropylene, polyacrylic, and polyimide; elastomers such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber; and polysaccharide polymers.

[0036] The binder content in the positive electrode active material layer is preferably 1% by mass to 10% by mass, more preferably 3% by mass to 9% by mass. By setting the binder content within the above range, the positive electrode active material, composite, etc. can be stably maintained.

[0037] Examples of thickeners include polysaccharide polymers such as carboxymethyl cellulose (CMC) and methyl cellulose. When the thickener has a functional group that reacts with lithium or the like, the functional group may be deactivated in advance by methylation or the like. The content of the thickener in the positive electrode active material layer is preferably 0.5% by mass or more and 10% by mass or less, and more preferably 2% by mass or more and 5% by mass or less.

[0038] The filler is not particularly limited. Examples of fillers include polyolefins such as polypropylene and polyethylene; inorganic oxides such as silicon dioxide, alumina, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates; hydroxides such as magnesium hydroxide, calcium hydroxide, and aluminum hydroxide; carbonates such as calcium carbonate; sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium sulfate; nitrides such as aluminum nitride and silicon nitride; mineral-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica; and artificial products thereof. The content of the filler in the positive electrode active material layer is preferably, for example, 0.1% by mass or more and 10% by mass or less. In one embodiment of the present invention, the positive electrode active material layer may not contain a filler.

[0039] The positive electrode active material layer may contain typical non-metallic elements such as B, N, P, F, Cl, Br, and I; typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba; and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, and W, as components other than sulfur, other positive electrode active materials, conductive agents, binders, thickeners, and fillers.

[0040] (Negative electrode) The negative electrode has a negative electrode substrate and a negative electrode active material layer disposed on the negative electrode substrate directly or via an intermediate layer. The configuration of the intermediate layer is not particularly limited and can be selected from the configurations exemplified for the positive electrode above, for example.

[0041] The negative electrode substrate is conductive. Metals such as copper, nickel, stainless steel, nickel-plated steel, and aluminum, alloys thereof, and carbonaceous materials are used as the material for the negative electrode substrate. Among these, copper or copper alloys are preferred. Examples of the negative electrode substrate include foils, vapor-deposited films, meshes, and porous materials, with foils being preferred from the viewpoint of cost. Therefore, copper foil or copper alloy foil is preferred as the negative electrode substrate. Examples of copper foil include rolled copper foil and electrolytic copper foil.

[0042] The average thickness of the negative electrode substrate is preferably 2 μm to 35 μm, more preferably 3 μm to 30 μm, even more preferably 4 μm to 25 μm, and particularly preferably 5 μm to 20 μm. By setting the average thickness of the negative electrode substrate within the above range, the strength of the negative electrode substrate can be increased while increasing the energy density per volume of the secondary battery.

[0043] The negative electrode active material layer contains a negative electrode active material. The negative electrode active material layer contains optional components such as a conductive agent, a binder, a thickener, and a filler as needed. The optional components such as the conductive agent, the binder, the thickener, and the filler can be selected from the materials exemplified for the positive electrode above. The negative electrode active material layer may be formed from a negative electrode mixture containing a negative electrode active material and other optional components. When the negative electrode active material is a metal such as metallic lithium, the layer may be formed from a foil or the like, and may not be formed from a negative electrode mixture.

[0044] The negative electrode active material layer may contain typical non-metallic elements such as B, N, P, F, Cl, Br, and I; typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba; and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, and W as components other than the negative electrode active material, conductive agent, binder, thickener, and filler.

[0045] The negative electrode active material can be appropriately selected from known negative electrode active materials. Materials capable of absorbing and releasing lithium ions are typically used as negative electrode active materials for lithium ion secondary batteries. Examples of negative electrode active materials include metallic lithium; metals or semimetals such as Si and Sn; metal oxides or semimetal oxides such as Si oxide, Ti oxide, and Sn oxide; and Li4Ti5O 12 Examples of the material include titanium-containing oxides such as LiTiO2 and TiNb2O7; polyphosphate compounds; silicon carbide; and carbon materials such as graphite and non-graphitic carbon (easily graphitizable carbon or non-graphitizable carbon). In the negative electrode active material layer, one of these materials may be used alone, or two or more may be mixed and used. In lithium ion secondary batteries, if the positive electrode active material does not contain lithium element during production, a negative electrode active material containing lithium element is usually used.

[0046] "Graphite" refers to graphite that has an average lattice spacing (d 002 ) is 0.33 nm or more and less than 0.34 nm. Examples of graphite include natural graphite and artificial graphite. Artificial graphite is preferred from the viewpoint of being able to obtain a material with stable physical properties.

[0047] "Non-graphitic carbon" refers to the carbon that has an average lattice spacing (d 002 ) is 0.34 nm or more and 0.42 nm or less. Non-graphitic carbon includes non-graphitizable carbon and graphitizable carbon. Examples of non-graphitic carbon include resin-derived materials, petroleum pitch or petroleum pitch-derived materials, petroleum coke or petroleum coke-derived materials, plant-derived materials, and alcohol-derived materials.

[0048] Here, the "discharged state" refers to a state in which the negative electrode active material, a carbonaceous material, is discharged so that lithium ions capable of being absorbed and desorbed during charging and discharging are sufficiently released. For example, in a single-electrode battery using a negative electrode containing a carbonaceous material as a negative electrode active material as a working electrode and metallic Li as a counter electrode, this refers to a state in which the open circuit voltage is 0.7 V or higher.

[0049] "Non-graphitizable carbon" means the above d 002 This refers to carbon materials with a particle size of 0.36 nm or more and 0.42 nm or less.

[0050] "Graphitizable carbon" means the above d 002 This refers to carbon materials with a particle size of 0.34 nm or more and less than 0.36 nm.

[0051] The negative electrode active material is usually in the form of particles (powder). The average particle size of the negative electrode active material can be, for example, 1 nm or more and 100 μm or less. When the negative electrode active material is a carbon material, a titanium-containing oxide, or a polyphosphate compound, the average particle size may be 1 μm or more and 100 μm or less. When the negative electrode active material is Si, Sn, Si oxide, Sn oxide, or the like, the average particle size may be 1 nm or more and 1 μm or less. By setting the average particle size of the negative electrode active material to be equal to or greater than the above-mentioned lower limit, the negative electrode active material can be easily produced or handled. By setting the average particle size of the negative electrode active material to be equal to or less than the above-mentioned upper limit, the electronic conductivity of the active material layer is improved. A pulverizer, a classifier, or the like is used to obtain powder with a predetermined particle size. When the negative electrode active material is a metal such as metallic lithium, the negative electrode active material may be in the form of a foil.

[0052] In one embodiment of the present invention, the negative electrode active material preferably contains metallic lithium. That is, the negative electrode or the negative electrode active material layer preferably contains metallic lithium. The metallic lithium may be pure metallic lithium consisting essentially of lithium element alone, or may be a lithium alloy containing other metal elements. Examples of lithium alloys include lithium-silver alloys, lithium-zinc alloys, lithium-calcium alloys, lithium-aluminum alloys, lithium-magnesium alloys, and lithium-indium alloys. The lithium alloy may contain multiple metal elements other than lithium.

[0053] The negative electrode active material layer may be a non-porous layer (solid layer) or a porous layer. The average thickness of the negative electrode active material layer is preferably 5 μm to 1,000 μm, more preferably 10 μm to 500 μm, and even more preferably 30 μm to 300 μm. The "average thickness" of the negative electrode active material layer refers to the average value of thicknesses measured at any five positions in the negative electrode active material layer.

[0054] In one embodiment of the present invention, the content of the negative electrode active material in the negative electrode active material layer is preferably 60% by mass or more and 99% by mass or less, and more preferably 90% by mass or more and 98% by mass or less. By setting the content of the negative electrode active material within the above range, both high energy density and manufacturability of the negative electrode active material layer can be achieved. Furthermore, when the negative electrode active material contains metallic lithium, the content of lithium element in the negative electrode active material layer is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 99% by mass or more. The upper limit of the content of lithium element in the negative electrode active material layer may be 100% by mass.

[0055] (separator) The separator can be appropriately selected from known separators. Examples of separators that can be used include separators consisting of only a substrate layer and separators in which a heat-resistant layer containing heat-resistant particles and a binder is formed on one or both surfaces of the substrate layer. Examples of the shape of the substrate layer of the separator include woven fabric, nonwoven fabric, and porous resin film. Among these shapes, porous resin films are preferred from the viewpoint of strength, and nonwoven fabrics are preferred from the viewpoint of non-aqueous electrolyte retention. Materials for the substrate layer of the separator are preferably polyolefins such as polyethylene and polypropylene from the viewpoint of shutdown function, and polyimide and aramid from the viewpoint of oxidative decomposition resistance. A composite material of these resins may also be used for the substrate layer of the separator.

[0056] The heat-resistant particles contained in the heat-resistant layer preferably exhibit a mass loss of 5% or less when heated from room temperature to 500°C in an air atmosphere at 1 atmosphere pressure, and more preferably exhibit a mass loss of 5% or less when heated from room temperature to 800°C. Examples of materials exhibiting a mass loss of a predetermined value or less include inorganic compounds. Examples of inorganic compounds include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicate; nitrides such as aluminum nitride and silicon nitride; carbonates such as calcium carbonate; sulfates such as barium sulfate; sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium titanate; covalently bonded crystals such as silicon and diamond; mineral-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, as well as artificial products thereof. As the inorganic compound, these substances may be used alone or in the form of a complex, or two or more of them may be used in combination. Among these inorganic compounds, silicon oxide, aluminum oxide, or aluminosilicate is preferred from the viewpoint of the safety of the secondary battery.

[0057] The porosity of the separator is preferably 80% by volume or less from the viewpoint of strength, and is preferably 20% by volume or more from the viewpoint of discharge performance. Here, "porosity" refers to a volume-based value measured with a mercury porosimeter.

[0058] The separator may be a polymer gel composed of a polymer and a non-aqueous electrolyte. Examples of polymers include polyacrylonitrile, polyethylene oxide, polypropylene oxide, polymethyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, and polyvinylidene fluoride. The use of a polymer gel has the effect of suppressing leakage. The separator may be a combination of the porous resin film or nonwoven fabric described above and a polymer gel.

[0059] (non-aqueous electrolyte) The nonaqueous electrolyte is preferably a nonaqueous electrolyte solution containing a nonaqueous solvent and an electrolyte salt dissolved in the nonaqueous solvent. The nonaqueous electrolyte solution further contains at least one ester X selected from the group consisting of a chain ester and an unsubstituted saturated cyclic ester.

[0060] [Non-aqueous solvent] The non-aqueous solvent contains an unsaturated cyclic carbonate. The inclusion of the unsaturated cyclic carbonate in the non-aqueous solvent can improve the high-rate discharge performance, etc., of the secondary battery. The non-aqueous solvent does not contain at least one ester X selected from the group consisting of chain esters and unsubstituted saturated cyclic esters. The unsaturated cyclic carbonate has a carbon-carbon double bond or a carbon-carbon triple bond in its molecule, preferably a carbon-carbon double bond in its molecule. In the unsaturated cyclic carbonate, the carbon-carbon double bond or the carbon-carbon triple bond may be present within the ring structure or outside the ring structure, but is preferably present within the ring structure. The unsaturated cyclic carbonate may have some or all of its hydrogen atoms substituted with halogen.

[0061] Examples of unsaturated cyclic carbonates include vinylene carbonate (VC), fluorovinylene carbonate, methylvinylene carbonate, fluoromethylvinylene carbonate, ethylvinylene carbonate, propylvinylene carbonate, butylvinylene carbonate, dimethylvinylene carbonate, diethylvinylene carbonate, dipropylvinylene carbonate, trifluoromethylvinylene carbonate, and vinylethylene carbonate, and among these, VC is preferred. One or more unsaturated cyclic carbonates can be used.

[0062] The content of the unsaturated cyclic carbonate in the non-aqueous solvent is preferably 20% by volume or more and 80% by volume or less, more preferably 35% by volume or more and 65% by volume or less, and even more preferably 40% by volume or more and 60% by volume or less. By setting the content of the unsaturated cyclic carbonate to the above lower limit or more, high-rate discharge performance can be improved. By setting the content of the unsaturated cyclic carbonate to the above upper limit or less, initial charge capacity can be further increased.

[0063] The non-aqueous solvent may further contain another non-aqueous solvent other than the unsaturated cyclic carbonate. Examples of the other non-aqueous solvent include halogenated saturated cyclic carbonates, ethers, amides, nitriles, etc. The halogenated saturated cyclic carbonate refers to a saturated cyclic carbonate in which some or all of the hydrogen atoms have been substituted with halogen. The ethers, amides, nitriles, etc. may be saturated cyclic carbonates in which some or all of the hydrogen atoms have been substituted with halogen. One or more of the other non-aqueous solvents can be used.

[0064] As the other non-aqueous solvent, a halogenated saturated cyclic carbonate is preferred, and a fluorinated saturated cyclic carbonate is more preferred. By containing a halogenated saturated cyclic carbonate, the oxidation resistance of the non-aqueous electrolyte can be improved. Examples of the halogenated saturated cyclic carbonate include chloroethylene carbonate, fluoroethylene carbonate (FEC), and difluoroethylene carbonate (DFEC). Among these, the fluorinated saturated cyclic carbonates FEC and DFEC are preferred.

[0065] The content of the halogenated saturated cyclic carbonate in the non-aqueous solvent is preferably 20% by volume to 80% by volume, more preferably 35% by volume to 65% by volume, and even more preferably 40% by volume to 60% by volume.

[0066] The nonaqueous solvent may consist essentially of an unsaturated cyclic carbonate and a halogenated saturated cyclic carbonate. In this case, the high-rate discharge performance of the secondary battery can be further improved. The total content of the unsaturated cyclic carbonate and the halogenated saturated cyclic carbonate in the nonaqueous solvent is preferably 70% by volume or more, more preferably 90% by volume or more, even more preferably 99% by volume or more, and particularly preferably 100% by volume.

[0067] [Electrolyte salt] The electrolyte salt can be appropriately selected from known electrolyte salts, such as lithium salts, sodium salts, potassium salts, magnesium salts, and onium salts. Of these, lithium salts are preferred.

[0068] Examples of lithium salts include inorganic lithium salts such as LiPF, LiPOF, LiBF, LiClO, and LiN(SOF); lithium oxalate salts such as lithium bis(oxalato)borate (LiBOB), lithium difluorooxalatoborate (LiFOB), and lithium bis(oxalato)difluorophosphate (LiFOP); and lithium salts having halogenated hydrocarbon groups such as LiSOCF, LiN(SOCF), LiN(SOCF), LiN(SOCF), LiN(SOCF)(SOCF), and LiC(SOCF). Among these, inorganic lithium salts are preferred, with LiPF and LiN(SOF) being more preferred. Also preferred are imide salts such as LiN(SOF), LiN(SOCF), LiN(SOCF), and LiN(SOCF)(SOCF).

[0069] The content of electrolyte salt in the non-aqueous electrolyte is 0.1 mol / dm at 20°C and 1 atmosphere. 3 More than 2.5mol / dm 3 It is preferable that the value is 0.3 mol / dm or less. 3 More than 2.0mol / dm 3 It is more preferable that it is 0.5 mol / dm or less. 3 More than 1.7mol / dm 3It is more preferable that it is 0.7 mol / dm or less. 3 More than 1.5mol / dm 3 By setting the content of the electrolyte salt within the above range, the ionic conductivity of the non-aqueous electrolyte can be increased.

[0070] [Ester X] The ester X is at least one selected from the group consisting of a chain ester and an unsubstituted saturated cyclic ester.

[0071] Examples of the chain ester include a chain carboxylic acid ester, a chain carbonate (a chain carbonate ester), a chain sulfonic acid ester, a chain sulfate ester, a chain sulfite ester, etc., and chain carboxylic acid esters and chain carbonates are preferred, and chain carbonates are more preferred. Furthermore, the chain ester may be a saturated chain ester or an unsaturated chain ester, but is preferably a saturated chain ester.

[0072] The chain ester may be one in which some or all of the hydrogen atoms are substituted with halogen (halogenated chain ester), and is preferably a fluorinated chain ester. Among the fluorinated chain esters, fluorinated chain carboxylic acid esters and fluorinated chain carbonates are more preferred, and fluorinated chain carbonates are even more preferred.

[0073] Examples of the chain carboxylic acid ester include methyl acetate, ethyl acetate, propyl acetate, 2,2,2-trifluoroethyl acetate, 2,2,2-trifluoroethyl trifluoroacetate, methyl propionate, ethyl propionate, ethyl 2-fluoropropionate, propyl propionate, etc. Among these, the fluorinated chain carboxylic acid esters 2,2,2-trifluoroethyl acetate, 2,2,2-trifluoroethyl trifluoroacetate, and ethyl 2-fluoropropionate are preferred.

[0074] Examples of the chain carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diphenyl carbonate, 2,2,2-trifluoroethyl methyl carbonate (TFEMC), bis(2,2,2-trifluoroethyl) carbonate (BTFEC), etc. Among these, the fluorinated chain carbonates TFEMC and BTFEC are preferred, and TFEMC is more preferred.

[0075] Examples of the chain sulfonate ester include methyl methanesulfonate, busulfan, and methyl trifluoromethanesulfonate.

[0076] Examples of chain sulfate esters include dimethyl sulfate.

[0077] Examples of the chain sulfite ester include dimethyl sulfite.

[0078] Examples of unsubstituted saturated cyclic esters include unsubstituted saturated cyclic carboxylic acid esters, unsubstituted saturated cyclic carbonates (unsubstituted saturated cyclic carbonates), unsubstituted saturated cyclic sulfonic acid esters, unsubstituted saturated cyclic sulfates, and unsubstituted saturated cyclic sulfites. Unsubstituted saturated cyclic carboxylic acid esters and unsubstituted saturated cyclic carbonates are preferred, and unsubstituted saturated cyclic carbonates are more preferred.

[0079] Examples of the unsubstituted saturated cyclic carboxylic acid ester include γ-butyrolactone and δ-valerolactone.

[0080] Examples of unsubstituted saturated cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. Among these, EC is preferred.

[0081] Examples of unsubstituted saturated cyclic sulfonic acid esters include propane sultone and butane sultone.

[0082] Examples of unsubstituted saturated cyclic sulfates include ethylene sulfate and propylene sulfate.

[0083] Examples of unsubstituted saturated cyclic sulfites include ethylene sulfite and propylene sulfite.

[0084] The content of ester X may be, for example, 1% by volume or more and 20% by volume or less, preferably 3% by volume or more and 10% by volume or less, more preferably 4% by volume or more and 9% by volume or less, and more preferably 7% by volume or less, when the content of the non-aqueous solvent is taken as 100% by volume. By setting the content of ester X within the above range, the initial charge capacity of the secondary battery can be increased.

[0085] The non-aqueous electrolyte may contain, as a component other than the non-aqueous solvent and the electrolyte salt, additives other than ester X. Examples of such additives include aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran; partial halides of the aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, and p-cyclohexylfluorobenzene; and halogenated anisoles such as 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, and 3,5-difluoroanisole. succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic anhydride; propene sultone, sulfolane, dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, diethyl sulfoxide, tetramethylene sulfoxide, diphenyl sulfide, thioanisole, diphenyl disulfide, dipyridinium disulfide, perfluorooctane, tristrimethylsilyl borate, tristrimethylsilyl phosphate, tetrakistrimethylsilyl titanate, etc. These other additives may be used alone or in combination of two or more.

[0086] The content of other additives contained in the non-aqueous electrolyte is preferably 0.01% by mass to 10% by mass, more preferably 0.1% by mass to 7% by mass, even more preferably 0.2% by mass to 5% by mass, and particularly preferably 0.3% by mass to 3% by mass, based on the total mass of the non-aqueous electrolyte. By setting the content of other additives within the above ranges, it is possible to improve capacity retention or cycle performance after high-temperature storage, and further improve safety.

[0087] The nonaqueous electrolyte may be a combination of a nonaqueous electrolytic solution and a solid electrolyte. The solid electrolyte may be selected from any material that has lithium ion conductivity and is solid at room temperature (e.g., 15°C to 25°C). Examples of the solid electrolyte include sulfide solid electrolytes, oxide solid electrolytes, oxynitride solid electrolytes, and polymer solid electrolytes.

[0088] The shape of the nonaqueous electrolyte storage element of this embodiment is not particularly limited, and examples thereof include cylindrical batteries, prismatic batteries, flat batteries, coin batteries, and button batteries.

[0089] FIG. 1 shows a nonaqueous electrolyte storage element 1 as an example of a prismatic battery. The figure is a see-through view of the inside of the container. An electrode assembly 2 having a positive electrode and a negative electrode wound with a separator sandwiched between them is housed in a prismatic container 3. The positive electrode is electrically connected to a positive electrode terminal 4 via a positive electrode lead 41. The negative electrode is electrically connected to a negative electrode terminal 5 via a negative electrode lead 51.

[0090] <Electricity storage device> The nonaqueous electrolyte energy storage element of this embodiment can be mounted as an energy storage unit (battery module) comprising a plurality of nonaqueous electrolyte energy storage elements 1 in an automobile power source such as an electric vehicle (EV), a hybrid electric vehicle (HEV), or a plug-in hybrid electric vehicle (PHEV), a power source for electronic devices such as a personal computer or a communication terminal, or a power storage power source, etc. In this case, the technology of the present invention may be applied to at least one nonaqueous electrolyte energy storage element included in the energy storage unit.

[0091] 2 shows an example of an electricity storage device 30 in which electricity storage units 20, each of which is an assembly of two or more electrically connected nonaqueous electrolyte electricity storage elements 1, are further assembled. The electricity storage device 30 may include a bus bar (not shown) that electrically connects two or more nonaqueous electrolyte electricity storage elements 1, a bus bar (not shown) that electrically connects two or more electricity storage units 20, etc. The electricity storage unit 20 or the electricity storage device 30 may include a status monitoring device (not shown) that monitors the status of one or more nonaqueous electrolyte electricity storage elements.

[0092] <Method of manufacturing nonaqueous electrolyte energy storage element> The method for manufacturing the nonaqueous electrolyte storage element of this embodiment can be appropriately selected from known methods. The manufacturing method includes, for example, preparing an electrode assembly, preparing a nonaqueous electrolyte, and housing the electrode assembly and the nonaqueous electrolyte in a container. Preparing the electrode assembly includes preparing a positive electrode and a negative electrode, and forming the electrode assembly by stacking or winding the positive electrode and the negative electrode with a separator interposed therebetween.

[0093] <Other embodiments> The nonaqueous electrolyte storage element of the present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the spirit of the present invention. For example, the configuration of one embodiment may be added to the configuration of another embodiment, or part of the configuration of one embodiment may be replaced with the configuration of another embodiment or well-known technology. Furthermore, part of the configuration of one embodiment may be deleted. Also, well-known technology may be added to the configuration of one embodiment.

[0094] In the above embodiment, the nonaqueous electrolyte storage element is used as a chargeable and dischargeable nonaqueous electrolyte secondary battery (e.g., a lithium ion secondary battery), but the type, shape, size, capacity, etc. of the nonaqueous electrolyte storage element are arbitrary. The present invention can also be applied to various secondary batteries, electric double layer capacitors, lithium ion capacitors, and other capacitors.

[0095] In the above embodiment, the electrode assembly in which the positive electrode and the negative electrode are stacked with a separator interposed therebetween has been described, but the electrode assembly may not include a separator. For example, the positive electrode and the negative electrode may be in direct contact with each other in a state in which a non-conductive layer is formed on the active material layer of the positive electrode or the negative electrode. [Example]

[0096] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0097] [Example 1]

[0098] (Preparation of positive electrode) Sulfur and porous carbon (CNovel) (manufactured by Toyo Tanso Co., Ltd.) were mixed in a mass ratio of 72:28. This mixture was placed in a sealed electric furnace. After argon flow for 1 hour, the mixture was heated to 150°C at a rate of 5°C / min and held for 5 hours. It was then allowed to cool to 80°C, the temperature at which sulfur solidifies. Thereafter, the mixture was heated again to 300°C at a rate of 5°C / min and held for 2 hours, producing a composite (sulfur-porous carbon composite: SPC). A positive electrode mixture paste containing the composite obtained above, acetylene black as a conductive agent, CMC as a thickener, and SBR as a binder in a mass ratio of 80:10:3.6:6.4, using water as a dispersion medium, was applied to an aluminum positive electrode substrate and dried to prepare a positive electrode.

[0099] (Preparing the negative electrode) As the negative electrode, a sheet of metallic lithium was prepared.

[0100] (Preparation of non-aqueous electrolyte) A non-aqueous solvent consisting of a 50:50 mixture of vinylene carbonate (VC) and fluoroethylene carbonate (FEC) was added as an electrolyte salt at a concentration of 1.0 mol / dm 3 and ethylene carbonate (EC) as ester X was added in an amount of 3% by volume relative to 100% by volume of the non-aqueous solvent, to prepare a non-aqueous electrolyte.

[0101] (Assembly of non-aqueous electrolyte energy storage element) A microporous polyethylene film was prepared as the separator. The positive electrode, negative electrode, separator, and non-aqueous electrolyte were used to obtain a non-aqueous electrolyte storage element (secondary battery) of Example 1.

[0102] [Examples 2 to 9, Comparative Example 1] The nonaqueous electrolyte storage elements of Examples 2 to 9 and Comparative Example 1 were obtained in the same manner as Example 1, except that the type and content of Ester X used in preparing the nonaqueous electrolyte were as shown in Table 1. In Table 1, TFEMC represents 2,2,2-trifluoroethyl methyl carbonate, EA represents ethyl acetate, and FEA represents 2,2,2-trifluoroethyl acetate. In Comparative Example 1, the nonaqueous electrolyte did not contain Ester X.

[0103] [evaluation] (First charge capacity measurement) For each of the obtained nonaqueous electrolyte storage elements, a constant current discharge of 0.1 C was performed at 25°C to 1.0 V as the initial discharge. After the discharge, a constant current charge of 0.2 C was performed at 25°C to 3.0 V as the initial charge. The measured initial charge capacity (charged electricity amount) is shown in Table 1. The initial charge capacity is shown as the capacity per mass of sulfur contained in the positive electrode.

[0104] [Table 1]

[0105] As shown in Table 1, in each of the nonaqueous electrolyte storage elements of Examples 1 to 9, the nonaqueous electrolyte contains at least one ester X selected from the group consisting of a chain ester and an unsubstituted saturated cyclic ester, which results in a large initial charge capacity. A comparison of Examples 2, 5, 7, and 8, in which the content of ester X is 5% by volume, reveals that the initial charge capacity is larger when ester X is a fluorinated chain ester. Furthermore, it can be seen that the initial charge capacity is larger when the content of ester X is 4% by volume or more and 9% by volume or less.

[0106] [Reference example 1] A nonaqueous electrolyte storage element of Reference Example 1 was obtained in the same manner as in Comparative Example 1, except that the VC in the nonaqueous solvent was replaced with TFEMC, and the initial charge capacity was measured in the same manner. The initial charge capacity of the nonaqueous electrolyte storage element of Reference Example 1 was 862 mAh / g. A comparison of Comparative Example 1 (852 mAh / g) and Reference Example 1 (862 mAh / g) shows that when the nonaqueous solvent contains an unsaturated cyclic carbonate, the initial charge capacity tends to be smaller. However, as in the nonaqueous electrolyte storage elements of Examples 1 to 9, when the nonaqueous electrolyte in which the nonaqueous solvent contains an unsaturated cyclic carbonate further contains a specific ester X, the initial charge capacity was larger than that of the nonaqueous electrolyte storage elements of Comparative Example 1 and Reference Example 1, which did not contain either the unsaturated cyclic carbonate or the ester X. [Industrial Applicability]

[0107] The present invention can be applied to nonaqueous electrolyte electricity storage elements used as power sources for electronic devices such as personal computers and communication terminals, and automobiles. [Explanation of symbols]

[0108] 1. Non-aqueous electrolyte energy storage element 2 Electrode body 3 containers 4 Positive terminal 41 Positive lead 5 Negative terminal 51 Negative lead 20 Energy storage unit 30 Energy storage device

Claims

1. a cathode comprising sulfur, and Nonaqueous electrolyte containing a nonaqueous solvent containing an unsaturated cyclic carbonate Equipped with The nonaqueous electrolyte storage element further comprises at least one ester selected from the group consisting of chain esters and unsubstituted saturated cyclic esters.

2. 2. The nonaqueous electrolyte storage element according to claim 1, wherein the ester comprises the chain ester.

3. 3. The nonaqueous electrolyte storage element according to claim 2, wherein the chain ester is a fluorinated chain ester.

4. 4. The nonaqueous electrolyte storage element according to claim 1, wherein the content of the ester relative to the nonaqueous solvent in the nonaqueous electrolyte is 3% by volume or more and 10% by volume or less.

5. 5. The nonaqueous electrolyte storage element according to claim 1, wherein the content of the ester relative to the nonaqueous solvent in the nonaqueous electrolyte is 4% by volume or more and 9% by volume or less.

Images