Nonaqueous electrolyte power storage element and method for manufacturing same

Abstract

A nonaqueous electrolyte power storage element according to one aspect of the present invention comprises: a positive electrode that contains a composite body of a sulfur-based active material and porous carbon; and a nonaqueous electrolyte that contains a nonaqueous solvent. The nonaqueous solvent contains a fluorinated ether and at least one cyclic carbonate that is selected from the group consisting of a fluorinated cyclic carbonate and an unsaturated cyclic carbonate. The content of the cyclic carbonate in the nonaqueous solvent is more than 50% by volume. The fluorinated ether is represented by formula (1).　(1): R1-O-R2 (In formula (1), R1 represents a fluorinated alkyl group having 1 to 3 carbon atoms, and R2 represents an alkyl group having 1 or 2 carbon atoms.)

Description

Nonaqueous electrolyte storage element and method for manufacturing same

[0001] The present invention relates to a non-aqueous electrolyte electricity storage element and a method for producing the same.

[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, as well as in automobiles. 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 charge-transporting ions such as lithium ions between the electrodes. Other non-aqueous electrolyte energy storage elements besides non-aqueous electrolyte secondary batteries include capacitors such as lithium ion capacitors and electric double layer capacitors.

[0003] Known nonaqueous electrolyte storage elements include lithium-sulfur batteries (Li-S batteries) and other nonaqueous electrolyte storage elements that use a sulfur-based active material in the positive electrode (see Patent Document 1). Sulfur-based active materials have a large theoretical capacity, and nonaqueous electrolyte storage elements that use a sulfur-based active material in the positive electrode are expected to have high energy density. Furthermore, because sulfur-based active materials have low electronic conductivity, a composite of a sulfur-based active material and a conductive agent such as porous carbon is sometimes used in the positive electrode.

[0004] JP 2010-95390 A

[0005] In a nonaqueous electrolyte storage element using a sulfur-based active material in the positive electrode, when a nonaqueous electrolyte containing an ether-based nonaqueous solvent is used, charge-discharge reactions proceed through a shuttle reaction caused by the elution of polysulfides formed at the positive electrode into the nonaqueous electrolyte. In contrast, in a nonaqueous electrolyte storage element using a sulfur-based active material in the positive electrode, when a nonaqueous electrolyte containing a carbonate-based nonaqueous solvent is used, a coating is formed on the surface of the positive electrode composite by reaction between the positive electrode and the nonaqueous electrolyte (e.g., the cyclic carbonate) during initial discharge. Thereafter, charge-transport ions diffuse through this coating, resulting in the progress of charge-discharge reactions. Thus, in a nonaqueous electrolyte storage element using sulfur in the positive electrode, the reaction mechanisms at the positive electrode during charge-discharge are thought to be different when a nonaqueous electrolyte containing an ether-based nonaqueous solvent is used and when a nonaqueous electrolyte containing a carbonate-based nonaqueous solvent is used.

[0006] According to the findings of the inventors, among nonaqueous electrolyte energy storage elements having a positive electrode using a composite of a sulfur-based active material and porous carbon, those having a nonaqueous electrolyte using a cyclic carbonate such as fluoroethylene carbonate or vinylene carbonate are promising as energy storage elements having a high energy density per mass. However, nonaqueous electrolyte energy storage elements using such cyclic carbonates have a problem in that the discharge capacity per mass of the sulfur-based active material is not sufficiently large, and therefore improvement is desired.

[0007] An object of the present invention is to provide a nonaqueous electrolyte storage element including a positive electrode containing a composite of a sulfur-based active material and porous carbon, and a nonaqueous electrolyte containing a cyclic carbonate, the nonaqueous electrolyte storage element having a large discharge capacity per mass of the sulfur-based active material, and a method for manufacturing such a nonaqueous electrolyte storage element.

[0008] A nonaqueous electrolyte storage element according to one aspect of the present invention includes a positive electrode containing a composite of a sulfur-based active material and porous carbon, and a nonaqueous electrolyte containing a nonaqueous solvent, wherein the nonaqueous solvent contains at least one cyclic carbonate selected from the group consisting of fluorinated cyclic carbonates and unsaturated cyclic carbonates, and a fluorinated ether, the content of the cyclic carbonate in the nonaqueous solvent being greater than 50% by volume, and the fluorinated ether is represented by the following formula (1): １ -O-R ２ ...(1) (In formula (1), R １ is a fluorinated alkyl group having 1 to 3 carbon atoms. ２ is an alkyl group having 1 or 2 carbon atoms.

[0009] A method for producing a nonaqueous electrolyte storage element according to another aspect of the present invention includes preparing a positive electrode including a composite of a sulfur-based active material and porous carbon, and preparing a nonaqueous electrolyte including a nonaqueous solvent, wherein the nonaqueous solvent includes at least one cyclic carbonate selected from the group consisting of fluorinated cyclic carbonates and unsaturated cyclic carbonates, and a fluorinated ether, the content of the cyclic carbonate in the nonaqueous solvent being greater than 50% by volume, and the fluorinated ether is represented by the following formula (1): R １ -O-R ２ ...(1) (In formula (1), R １ is a fluorinated alkyl group having 1 to 3 carbon atoms. ２ is an alkyl group having 1 or 2 carbon atoms.

[0010] According to one aspect of the present invention, it is possible to provide a nonaqueous electrolyte storage element including a positive electrode containing a composite of a sulfur-based active material and porous carbon, and a nonaqueous electrolyte containing a cyclic carbonate, the nonaqueous electrolyte storage element having a large discharge capacity per mass of the sulfur-based active material, and a method for manufacturing such a nonaqueous electrolyte storage element.

[0011] Fig. 1 is a perspective view showing one embodiment of a nonaqueous electrolyte electricity storage element, and Fig. 2 is a schematic view showing one embodiment of an electricity storage device formed by assembling a plurality of nonaqueous electrolyte electricity storage elements.

[0012] First, an outline of the nonaqueous electrolyte storage element and the method for manufacturing the nonaqueous electrolyte storage element disclosed in this specification will be described.

[0013] [1] A nonaqueous electrolyte storage element according to one aspect of the present invention includes a positive electrode containing a composite of a sulfur-based active material and porous carbon, and a nonaqueous electrolyte containing a nonaqueous solvent, wherein the nonaqueous solvent contains at least one cyclic carbonate selected from the group consisting of fluorinated cyclic carbonates and unsaturated cyclic carbonates, and a fluorinated ether, the content of the cyclic carbonate in the nonaqueous solvent being greater than 50% by volume, and the fluorinated ether is represented by the following formula (1): R １ -O-R ２ ...(1) (In formula (1), R １ is a fluorinated alkyl group having 1 to 3 carbon atoms. ２ is an alkyl group having 1 or 2 carbon atoms.

[0014] The nonaqueous electrolyte storage element described in [1] above is a nonaqueous electrolyte storage element comprising a positive electrode containing a composite of a sulfur-based active material and porous carbon, and a nonaqueous electrolyte containing a cyclic carbonate, and exhibits a large discharge capacity per mass of the sulfur-based active material. While the reason for this is unclear, the following is presumed. One of the reasons for the insufficient discharge capacity of conventional nonaqueous electrolyte storage elements comprising a positive electrode containing a composite of a sulfur-based active material and porous carbon (hereinafter simply referred to as the "composite") and a nonaqueous electrolyte containing a cyclic carbonate is thought to be the small contact area between the composite and the nonaqueous electrolyte due to the high viscosity of the nonaqueous electrolyte. The fluorinated ether represented by the above formula (1) has a relatively low molecular weight and low viscosity. Furthermore, the fluorinated ether represented by the above formula (1) has an alkyl group and a fluorinated alkyl group, and the alkyl group has a high affinity for the porous carbon of the composite. By incorporating such a fluorinated ether into the nonaqueous electrolyte, the viscosity of the nonaqueous electrolyte is reduced and the wettability of the nonaqueous electrolyte to the composite is improved. Therefore, it is presumed that in the nonaqueous electrolyte storage element described in [1] above, the contact area between the composite and the nonaqueous electrolyte is large, and the discharge capacity per mass of the sulfur-based active material is large.

[0015] The content of each component constituting the non-aqueous solvent is measured by liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-mass spectrometry (GC-MS). Specifically, the measurement is performed as follows. The LC-MS and GC-MS measurements are performed consecutively under the same conditions. 1. Collection of non-aqueous electrolyte First, the non-aqueous electrolyte storage element is disassembled to extract the non-aqueous electrolyte. If the non-aqueous electrolyte cannot be extracted, the non-aqueous electrolyte storage element is centrifuged to extract the non-aqueous electrolyte. If the non-aqueous electrolyte cannot be extracted even after centrifugation, an extraction solvent (e.g., acetonitrile) is injected into the non-aqueous electrolyte storage element, and the non-aqueous electrolyte diluted with the extraction solvent is extracted. 2. LC-MS The components of the extracted non-aqueous electrolyte are analyzed by LC-MS. LC-MS analysis is performed in the following order: qualitative analysis and quantitative analysis. Waters' "Acquity H" and "Xevo G2-5QTof" LC-MS analyzers are used. Water is used as the eluent. (Qualitative Analysis) The measurement sample (non-aqueous electrolyte) is subjected to LC-MS analysis. If the peaks in the obtained liquid chromatogram are not separated, GC-MS analysis, described below, is performed instead of LC-MS analysis. If the peaks are separated, the components contained in the measurement sample are predicted from the MS spectrum of each peak. A known sample of the predicted components (hereinafter referred to as "predicted components") is subjected to LC-MS analysis. The retention time and MS spectrum of the peaks corresponding to each predicted component in the measurement sample are compared with the retention time and MS spectrum of the peaks in a known sample of each predicted component, and if they match, the prediction is assumed to be correct. (Quantitative Analysis) Quantitative analysis is performed using the calibration curve method. First, a known sample of the predicted component with a known concentration is measured by LC-MS, and the peak area is calculated to create a calibration curve. ２) is created so that the difference is between 0.999 and 1. The content of the predicted component in the measurement sample is determined from the calibration curve and the area of ​​the peak of the predicted component in the measurement sample. The above process is performed for all peaks detected in the LC-MS analysis of the measurement sample to determine the content of each predicted component. 3. GC-MS GC-MS analysis is performed in the following order: qualitative analysis and quantitative analysis. The GC-MS analysis is performed using an Agilent 5975C. Argon is used as the carrier gas. (Qualitative Analysis) The measurement sample (non-aqueous electrolyte) is subjected to GC-MS analysis. The components contained in the sample are predicted from the MS spectrum of each peak in the obtained gas chromatogram. A known sample of the predicted component is subjected to GC-MS analysis. The retention time and MS spectrum of the peak corresponding to each predicted component in the measurement sample are compared with the retention time and MS spectrum of the peak of a known sample of each predicted component. If they match, the prediction is assumed to be correct. (Quantitative Analysis) Quantitative analysis is performed using a calibration curve method. Quantitative analysis by GC-MS is performed using the same procedure as the quantitative analysis by LC-MS described above, and the content of each predicted component is determined. 4. Calculation of the Content of Each Component The total content of each predicted component (i.e., each component) measured by LC-MS or GC-MS is taken as the content of the non-aqueous solvent, and the content of each component in the non-aqueous solvent is calculated. Note that, when calculating the content (volume %) of each component in the non-aqueous solvent, the mass-based content of each component measured by LC-MS or GC-MS is converted to a volume at 20°C, and the total volume-converted content of each component is taken as the content of the non-aqueous solvent. Furthermore, if an extraction solvent is used, the extraction solvent is excluded from the calculation.

[0016] [2] In the nonaqueous electrolyte storage element according to the above [1], the content of the fluorinated ether in the nonaqueous solvent may be 10% by volume or more and less than 50% by volume.

[0017] The nonaqueous electrolyte storage element described in the above [2] has a larger discharge capacity per mass of the sulfur-based active material due to an optimized composition of the nonaqueous solvent, etc.

[0018] [3] The nonaqueous electrolyte storage element according to the above [1] or [2] may further include a negative electrode containing metallic lithium.

[0019] The nonaqueous electrolyte storage element described in the above item [3] has a negative electrode containing metallic lithium, and thus has further advantages such as a high energy density.

[0020] [4] In the nonaqueous electrolyte storage element according to any one of [1] to [3] above, the fluorinated cyclic carbonate may contain fluoroethylene carbonate.

[0021] [5] In the nonaqueous electrolyte storage element according to any one of [1] to [4] above, the unsaturated cyclic carbonate may contain vinylene carbonate.

[0022] [6] In the nonaqueous electrolyte storage element according to any one of [1] to [5] above, the fluorinated ether may comprise at least one selected from the group consisting of methyl-1,1,2,2-tetrafluoroethyl ether, ethyl-1,1,2,2-tetrafluoroethyl ether, 1,1,2,3,3,3-hexafluoropropyl methyl ether, and 1,1,2,3,3,3-hexafluoropropyl ethyl ether.

[0023] [7] In the nonaqueous electrolyte storage element according to any one of [1] to [6] above, the total content of the cyclic carbonate and the fluorinated ether in the nonaqueous solvent may be 80% by volume or more.

[0024] [8] In the nonaqueous electrolyte storage element according to any one of [1] to [7] above, the nonaqueous electrolyte may contain an imide salt.

[0025] [9] In the nonaqueous electrolyte storage element according to any one of [1] to [8] above, the viscosity of the nonaqueous electrolyte at 25° C. may be 0.5 mPa·s or more and 6.5 mPa·s or less.

[0026]

[10] A method for producing a nonaqueous electrolyte storage element according to another aspect of the present invention includes preparing a positive electrode including a composite of a sulfur-based active material and porous carbon, and preparing a nonaqueous electrolyte including a nonaqueous solvent, wherein the nonaqueous solvent includes at least one cyclic carbonate selected from the group consisting of fluorinated cyclic carbonates and unsaturated cyclic carbonates, and a fluorinated ether, the content of the cyclic carbonate in the nonaqueous solvent being greater than 50% by volume, and the fluorinated ether is represented by the following formula (1): R １ -O-R ２ ...(1) (In formula (1), R １ is a fluorinated alkyl group having 1 to 3 carbon atoms. ２ is an alkyl group having 1 or 2 carbon atoms.

[0027] According to the method for producing a nonaqueous electrolyte storage element described in

[10] above, it is possible to produce a nonaqueous electrolyte storage element that includes a positive electrode containing a composite of a sulfur-based active material and porous carbon, and a nonaqueous electrolyte containing a cyclic carbonate, and that has a large discharge capacity per mass of the sulfur-based active material.

[0028]

[11] In the method for producing a nonaqueous electrolyte storage element according to the above

[10] , the content of the fluorinated ether in the nonaqueous solvent may be 10% by volume or more and less than 50% by volume.

[0029]

[12] The method for producing a nonaqueous electrolyte storage element according to the above

[10] or

[11] may further comprise preparing a negative electrode containing metallic lithium.

[0030]

[13] In the method for producing a nonaqueous electrolyte storage element according to any one of

[10] to

[12] above, the fluorinated cyclic carbonate may contain fluoroethylene carbonate.

[0031]

[14] In the method for producing a nonaqueous electrolyte storage element according to any one of

[10] to

[13] above, the unsaturated cyclic carbonate may contain vinylene carbonate.

[0032]

[15] In the method for producing a nonaqueous electrolyte storage element according to any one of

[10] to

[14] above, the fluorinated ether may contain at least one selected from the group consisting of methyl-1,1,2,2-tetrafluoroethyl ether, ethyl-1,1,2,2-tetrafluoroethyl ether, 1,1,2,3,3,3-hexafluoropropyl methyl ether, and 1,1,2,3,3,3-hexafluoropropyl ethyl ether.

[0033]

[16] In the method for producing a nonaqueous electrolyte storage element according to any one of

[10] to

[15] above, the total content of the cyclic carbonate and the fluorinated ether in the nonaqueous solvent may be 80% by volume or more.

[0034]

[17] In the method for producing a non-aqueous electrolyte storage element according to any one of

[10] to

[16] above, the non-aqueous electrolyte may contain an imide salt.

[0035]

[18] In the method for producing a nonaqueous electrolyte storage element according to any one of

[10] to

[17] above, the viscosity of the nonaqueous electrolyte at 25°C may be 0.5 mPa·s or more and 6.5 mPa·s or less.

[0036] 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.

[0037] <Non-aqueous electrolyte storage element> A non-aqueous 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 non-aqueous electrolyte, and a container that accommodates the electrode assembly and the non-aqueous 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 a separator interposed therebetween and wound. The non-aqueous electrolyte exists in a state in which it is impregnated into the positive electrode, the negative electrode, and the separator. As an example of a non-aqueous electrolyte storage element, a non-aqueous electrolyte secondary battery (hereinafter also simply referred to as "secondary battery") will be described.

[0038] (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.

[0039] The positive electrode substrate has electrical conductivity. Whether or not it has electrical conductivity is determined by whether or not the volume resistivity measured in accordance with JIS-H-0505 (1975) is 10 －２ The resistance is determined using Ω cm as a threshold value. Metals such as aluminum, titanium, tantalum, and stainless steel, or alloys thereof, are used as the material for the positive electrode substrate. Among these, aluminum or aluminum alloys are preferred from the viewpoints of potential resistance, high conductivity, and cost. Examples of the positive electrode substrate include foil, vapor-deposited film, mesh, and porous material, 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).

[0040] 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, the strength of the positive electrode substrate can be increased while increasing the energy density per mass or volume of the positive electrode. "Average thickness" refers to the average value of thicknesses measured at any five locations.

[0041] 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.

[0042] The positive electrode active material layer contains a composite of a sulfur-based active material and porous carbon. The positive electrode active material layer contains optional components such as a conductive agent, a binder, a dispersant, a thickener, and a filler, as needed. The positive electrode active material layer is usually formed from a positive electrode mixture containing the composite and other optional components.

[0043] In the composite, a sulfur-based active material is usually supported in the pores of the porous carbon. This form of the composite ensures sufficient electronic conductivity. The composite may be substantially composed of only a sulfur-based active material and porous carbon, or may be substantially composed of only a sulfur-based active material and porous carbon. A composite substantially composed of only a sulfur-based active material and porous carbon means, for example, that the total content of the sulfur-based active material (sulfur elemental substance and sulfur compound) and porous carbon in the composite is 90% by mass or more, and may be 95% by mass or more, 98% by mass or more, or 99% by mass or more.

[0044] The sulfur-based active material contained in the composite is a component that functions as a positive electrode active material. The sulfur-based active material may be elemental sulfur, a sulfur compound, or a mixture thereof. That is, the composite may contain elemental sulfur together with porous carbon. Examples of sulfur compounds include metal sulfides such as lithium sulfide, organic disulfide compounds, and organic sulfur compounds such as carbon sulfide compounds. Sulfur-based active materials have advantages such as a large theoretical capacity and low cost.

[0045] The content of the sulfur-based active material in the composite is preferably 50% by mass to 90% by mass, more preferably 60% by mass to 80% by mass. By setting the content of the sulfur-based active material in the composite within this range, it is possible to increase the discharge capacity per mass of the sulfur-based active material.

[0046] Porous carbon has electrical conductivity. Porous carbon is generally a porous inorganic material whose main constituent element is carbon. The main constituent element refers to the element that is most abundant on a mass basis. The lower limit of the carbon element content in porous carbon is preferably 70 mass%, more preferably 80 mass%, 90 mass%, 95 mass%, or 97 mass%. The upper limit of the carbon element content in porous carbon may be 100 mass% or 99.9 mass%. The carbon element content in porous carbon can be within a range that combines any of the above-mentioned lower limits and the above-mentioned upper limit. Porous carbon may contain elements other than carbon, such as oxygen and nitrogen.

[0047] The composite can be produced by a conventional method, for example, by heating a mixture of a sulfur-based active material and porous carbon to a temperature equal to or higher than the melting point of the sulfur-based active material, and then cooling the mixture.

[0048] The content of the composite in the positive electrode active material layer is preferably 60% by mass to 97% by mass, more preferably 80% by mass to 96% by mass, and even more preferably 90% by mass to 95% by mass. By setting the content of the composite within the above range, it is possible to increase the discharge capacity per mass of the sulfur-based active material.

[0049] The positive electrode active material layer may contain a positive electrode active material other than the sulfur-based active material, provided that the content of the sulfur-based active material 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.

[0050] 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 the porous carbon that constitutes the composite. Examples of such conductive agents include carbonaceous materials, metals, conductive ceramics, etc. Examples of carbonaceous materials include graphite, non-graphitic carbon, graphene-based carbon, etc. Examples of non-graphitic carbon include carbon nanofiber, pitch-based carbon fiber, carbon black, etc. Examples of carbon black include furnace black, acetylene black, ketjen black, etc. Examples of graphene-based carbon include graphene, carbon nanotubes (CNT), fullerene, etc. The conductive agent may be in the form of powder, fiber, etc. 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 CNT may be used. Among these, carbon black is preferred from the viewpoints of electronic conductivity and coatability, and acetylene black is particularly preferred. It is also preferable to use carbon black (preferably acetylene black) in combination with CNT.

[0051] The content of the conductive agent (excluding the porous carbon in the composite) in the positive electrode active material layer is preferably 0.5% by mass or more and 15% by mass or less, and more preferably 1% by mass or more and 10% by mass or less. The upper limit of the content of the conductive agent in the positive electrode active material layer may be 5% by mass or 3% by mass. By setting the content of the conductive agent in the above range, the energy density per mass of the positive electrode can be increased.

[0052] 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.

[0053] The content of the binder in the positive electrode active material layer is preferably 1% by mass or more and 10% by mass or less, more preferably 2% by mass or more and 9% by mass or less. The upper limit of the content of the binder in the positive electrode active material layer may be 6% by mass or 4% by mass. By setting the content of the binder in the above range, the composite and the like can be stably maintained.

[0054] Examples of dispersants include polysaccharide polymers such as carboxymethyl cellulose (CMC) and methyl cellulose. When the dispersant 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 dispersant in the positive electrode active material layer is preferably 0.05% by mass or more and 5% by mass or less, and more preferably 0.1% by mass or more and 2% by mass or less. The polysaccharide polymer may function as a thickener or a binder.

[0055] Examples of the thickener include polyacrylic acid (PAA). The content of the thickener in the positive electrode active material layer is preferably 0.05% by mass or more and 5% by mass or less, and more preferably 0.1% by mass or more and 4% by mass or less. Polyacrylic acid may function as a binder.

[0056] The filler is not particularly limited. Examples of the filler 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. When the positive electrode active material layer contains a filler, 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.

[0057] 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 the composite, other positive electrode active materials, conductive agents, binders, dispersants, thickeners, and fillers.

[0058] The mass per unit area of ​​the positive electrode active material layer is not particularly limited, but is preferably 1 mg / cm ２ 30mg / cm or more ２ Preferably, less than 5 mg / cm ２ 25mg / cm or more ２ More preferably, 10 mg / cm or less ２ 20mg / cm or more ２ The following is even more preferable: When the mass per unit area of ​​the positive electrode active material layer is within the above range, the discharge capacity per mass of the sulfur-based active material can be increased.

[0059] The porosity of the positive electrode active material layer is not particularly limited, but is preferably 15% to 50%, more preferably 20% to 40%, and even more preferably 25% to 35%. When the porosity of the positive electrode active material layer is in the above range, the discharge capacity per mass of the sulfur-based active material can be increased.

[0060] The "porosity (%)" of the positive electrode active material layer is the apparent volume (volume including voids) of the positive electrode active material layer, expressed as V １ The sum of the actual volumes of the materials constituting the positive electrode active material layer is V ２ In this case, (1-V ２ / V １ The sum of the actual volumes of the materials constituting the positive electrode active material layer, V ２ can be calculated from the content of each material in the positive electrode active material layer and the true density of each material.

[0061] 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.

[0062] The negative electrode substrate is conductive. Metals such as copper, nickel, stainless steel, and nickel-plated steel, alloys thereof, and carbonaceous materials are used as the material for the negative electrode substrate. Among these, nickel or nickel alloys are preferred. Examples of the negative electrode substrate include foil, vapor-deposited film, mesh, and porous material, with foil being preferred from the viewpoint of cost. Therefore, nickel foil or nickel alloy foil is preferred as the negative electrode substrate. Examples of copper foil include rolled copper foil and electrolytic copper foil.

[0063] 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 nonaqueous electrolyte storage element.

[0064] 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 does not necessarily contain optional components such as the conductive agent, the binder, the thickener, and the filler.

[0065] 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.

[0066] The negative electrode active material can be appropriately selected from known negative electrode active materials. A material capable of absorbing and releasing lithium ions is usually used as the negative electrode active material for a lithium ion secondary battery. Examples of the negative electrode active material 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; Li ４ Ti ５ O １２ , LiTiO ２、 TiNb ２ O ７ Examples of the negative electrode active material include titanium-containing oxides such as those mentioned above, polyphosphate compounds, silicon carbide, and carbon materials such as graphite and non-graphitizable carbon (easily graphitizable carbon or non-graphitizable carbon). In the case of a negative electrode active material that does not contain charge transport ions such as lithium ions, a material doped with lithium ions or the like can be used.

[0067] Metallic lithium is preferred as the negative electrode active material. 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 the lithium alloy include a lithium-silver alloy, a lithium-zinc alloy, a lithium-calcium alloy, a lithium-aluminum alloy, a lithium-magnesium alloy, and a lithium-indium alloy. The lithium alloy may contain multiple metal elements other than lithium element.

[0068] The negative electrode active material layer may contain a negative electrode active material other than metallic lithium. However, the negative electrode active material layer is preferably a layer consisting essentially of metallic lithium (pure metallic lithium or a lithium alloy). The lower limit of the lithium element content in the negative electrode active material layer is preferably 80 mass%, more preferably 90 mass%, and even more preferably 99 mass% or more. The upper limit of the lithium element content in the negative electrode active material layer may be 100 mass%. The lithium element content in the negative electrode active material layer can be within a range that combines any of the above-mentioned lower limits and the above-mentioned upper limit.

[0069] The negative electrode active material layer may be a non-porous layer (solid layer) or a porous layer, but is preferably a non-porous layer. The negative electrode active material layer may be a layer of metallic lithium. The negative electrode active material layer may be a layer made of metallic lithium foil (pure metallic lithium foil or lithium alloy foil). The average thickness of the negative electrode active material layer in a charged state is preferably 5 μm or more and 2,000 μm or less, more preferably 30 μm or more and 1,200 μm or less, and even more preferably 100 μm or more and 800 μm or less.

[0070] (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.

[0071] The heat-resistant particles contained in the heat-resistant layer preferably have a mass loss of 5% or less when heated from room temperature to 500°C in an air atmosphere at 1 atmosphere, and more preferably have a mass loss of 5% or less when heated from room temperature to 800°C. Examples of materials that have a mass loss of a predetermined amount or less include inorganic compounds. That is, the heat-resistant layer may be an inorganic particle layer containing inorganic particles and a binder. 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 aluminosilicates; 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 resource-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, as well as artificial products thereof. As inorganic compounds, these substances may be used alone or in the form of a complex, or two or more may be mixed and used. Among these inorganic compounds, silicon oxide, aluminum oxide, or aluminosilicates are preferred from the viewpoint of the safety of nonaqueous electrolyte storage elements.

[0072] 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.

[0073] 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.

[0074] (Non-aqueous electrolyte) The non-aqueous electrolyte contains a non-aqueous solvent. As the non-aqueous electrolyte, a non-aqueous electrolytic solution containing a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent is usually used. In one embodiment of the present invention, the non-aqueous electrolyte storage element may be a non-aqueous electrolyte storage element.

[0075] The non-aqueous solvent contains at least one cyclic carbonate selected from the group consisting of fluorinated cyclic carbonates and unsaturated cyclic carbonates (hereinafter also referred to as "cyclic carbonate (A)"). When the non-aqueous solvent contains such a cyclic carbonate (A), it is possible to increase the energy density per mass, etc. The cyclic carbonate (A) may contain a fluorinated unsaturated cyclic carbonate that is both a fluorinated cyclic carbonate and an unsaturated cyclic carbonate.

[0076] A fluorinated cyclic carbonate refers to a compound in which some or all of the hydrogen atoms of a cyclic carbonate have been substituted with fluorine atoms. A cyclic carbonate refers to a carbonate having a ring structure containing a carbonate group (—O—C(═O)—O—). The fluorinated cyclic carbonate is preferably a fluorinated saturated cyclic carbonate. A fluorinated saturated cyclic carbonate refers to a fluorinated cyclic carbonate that does not have a carbon-carbon double bond or a carbon-carbon triple bond in the molecule.

[0077] Examples of the fluorinated cyclic carbonate include fluorinated ethylene carbonates such as fluoroethylene carbonate (FEC) and difluoroethylene carbonate (DFEC), fluorinated propylene carbonate, fluorinated butylene carbonate, and fluorinated vinylene carbonate. Among these, fluorinated ethylene carbonate is preferred, and FEC is more preferred. One or more types of fluorinated cyclic carbonates can be used.

[0078] The lower limit of the content of the fluorinated cyclic carbonate in the non-aqueous solvent may be 0% by volume, preferably 30% by volume, more preferably 40% by volume, and even more preferably 50% by volume, and may be 60%, 70%, or 80% by volume. The upper limit of the content of the fluorinated cyclic carbonate in the non-aqueous solvent may be 95% by volume, or may be 90%, 80%, 70%, 60%, or 50% by volume. The content of the fluorinated cyclic carbonate in the non-aqueous solvent may be within a range combining any of the above-mentioned lower limits and any of the above-mentioned upper limits (however, the upper limit is greater than the lower limit). When the non-aqueous solvent contains an unsaturated cyclic carbonate, the non-aqueous solvent may not contain a fluorinated cyclic carbonate.

[0079] The unsaturated cyclic carbonate refers to a cyclic carbonate having a carbon-carbon double bond or a carbon-carbon triple bond in the molecule. The unsaturated cyclic carbonate preferably has a carbon-carbon double bond in the molecule. The unsaturated cyclic carbonate may have a carbon-carbon double bond or a carbon-carbon triple bond in the ring structure or in a portion other than the ring structure, but preferably has the bond in the ring structure. The unsaturated cyclic carbonate may be fluorinated or non-fluorinated, but is preferably non-fluorinated.

[0080] Examples of unsaturated cyclic carbonates include vinylene carbonate (VC), methyl vinylene carbonate, ethyl vinylene carbonate, propyl vinylene carbonate, butyl vinylene carbonate, dimethyl vinylene carbonate, diethyl vinylene carbonate, dipropyl vinylene carbonate, and vinyl ethylene carbonate, with VC being preferred. One or more unsaturated cyclic carbonates can be used.

[0081] The lower limit of the content of the unsaturated cyclic carbonate in the non-aqueous solvent may be 0 vol%, 5 vol%, 10 vol%, 20 vol%, or 30 vol%. The upper limit of the content of the unsaturated cyclic carbonate in the non-aqueous solvent may be 95 vol%, 90 vol%, 80 vol%, 60 vol%, 40 vol%, 20 vol%, or 10 vol%. The content of the unsaturated cyclic carbonate in the non-aqueous solvent may be within a range combining any of the above-mentioned lower limits and any of the above-mentioned upper limits (however, the upper limit is greater than the lower limit). When the non-aqueous solvent contains a fluorinated cyclic carbonate, the non-aqueous solvent does not need to contain an unsaturated cyclic carbonate.

[0082] The content of the cyclic carbonate (A) in the non-aqueous solvent is more than 50% by volume. The lower limit of the content of the cyclic carbonate (A) in the non-aqueous solvent may be 55% by volume, 60% by volume, 65% by volume, 70% by volume, 75% by volume, 80% by volume, 85% by volume, or 90% by volume. The upper limit of the content of the cyclic carbonate (A) in the non-aqueous solvent may be 95% by volume, or may be 90% by volume, 85% by volume, 80% by volume, 75% by volume, 70% by volume, 65% by volume, 60% by volume, or 55% by volume. The content of the cyclic carbonate (A) in the non-aqueous solvent may be within a range combining any of the above-mentioned lower limits and any of the above-mentioned upper limits (however, the upper limit is greater than the lower limit). In the nonaqueous electrolyte storage element according to one embodiment of the present invention, the content of the cyclic carbonate (A) in the nonaqueous solvent is more than 50% by volume, and therefore it is believed that a charge-discharge reaction occurs in the positive electrode due to solid-phase diffusion of charge-transporting ions through the above-described coating. That is, since the content of the cyclic carbonate (A) in the nonaqueous solvent is more than 50% by volume, a satisfactory coating is sufficiently formed on the surface of the composite, and the energy density per mass of the nonaqueous electrolyte storage element can be increased.

[0083] The non-aqueous solvent contains a fluorinated ether represented by the following formula (1) (hereinafter also referred to as "fluorinated ether (B)"). When the non-aqueous solvent contains such a fluorinated ether (B), the discharge capacity per mass of the sulfur-based active material can be increased. １-O-R ２ ...(1) (In formula (1), R １ is a fluorinated alkyl group having 1 to 3 carbon atoms. ２ is an alkyl group having 1 or 2 carbon atoms.

[0084] R １ Examples of R include groups in which some or all of the hydrogen atoms in a methyl group, an ethyl group, a propyl group, or a 1-methylethyl group have been substituted with fluorine atoms. １ The number of carbon atoms in R is preferably 2 or 3. １ The number of fluorine atoms is preferably 2 or more and 6 or less, and more preferably 4 or more and 6 or less.

[0085] R １ Examples of the group represented by the formula (I) include a 1,1,2,2-tetrafluoroethyl group and a 1,1,2,3,3,3-hexafluoropropyl group.

[0086] R ２ The group represented by the formula: is a methyl group or an ethyl group, and an ethyl group is preferred.

[0087] Examples of the fluorinated ether (B) include methyl-1,1,2,2-tetrafluoroethyl ether, ethyl-1,1,2,2-tetrafluoroethyl ether, 1,1,2,3,3,3-hexafluoropropyl methyl ether, 1,1,2,3,3,3-hexafluoropropyl ethyl ether, etc. The fluorinated ether (B) can be used alone or in combination of two or more.

[0088] The lower limit of the content of the fluorinated ether (B) in the non-aqueous solvent is preferably 5% by volume, more preferably 10% by volume, and may be 15%, 20%, or 25% by volume. The content of the fluorinated ether (B) in the non-aqueous solvent is less than 50% by volume. The upper limit of the content of the fluorinated ether (B) in the non-aqueous solvent may be 45%, 40%, 35%, 30%, 25%, 20%, 15%, or 10% by volume. The content of the fluorinated ether (B) in the non-aqueous solvent may be within a range combining any of the above-mentioned lower limits and any of the above-mentioned upper limits (however, the upper limit is greater than the lower limit). When the content of the fluorinated ether in the non-aqueous solvent is within the above range, the discharge capacity per mass of the sulfur-based active material of the non-aqueous electrolyte storage element can be increased.

[0089] The lower limit of the total content of the cyclic carbonate (A) and the fluorinated ether (B) in the non-aqueous solvent is preferably 70% by volume, preferably 75% by volume, more preferably 80% by volume, more preferably 85% by volume, even more preferably 90% by volume, and may be 95% by volume, 96% by volume, 97% by volume, or 98% by volume. The upper limit of the total content of the cyclic carbonate (A) and the fluorinated ether (B) in the non-aqueous solvent may be 100% by volume, and the non-aqueous solvent may be substantially composed of only the cyclic carbonate (A) and the fluorinated ether (B). When the non-aqueous solvent is substantially composed of only the cyclic carbonate (A) and the fluorinated ether (B), the effect of increasing the discharge capacity per mass of the sulfur-based active material can be particularly well achieved. The total content of the cyclic carbonate (A) and the fluorinated ether (B) in the non-aqueous solvent can be within a range that combines the above-mentioned lower limit and any of the above-mentioned upper limits.

[0090] The non-aqueous solvent may further contain a solvent other than the cyclic carbonate (A) and the fluorinated ether (B). Examples of the other solvent include a cyclic carbonate other than the cyclic carbonate (A), a chain carbonate, an ether other than the fluorinated ether (B), an ester, an amide, a nitrile, and the like. Examples of the other cyclic carbonate include non-fluorinated saturated cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and chloroethylene carbonate. Examples of the chain carbonate include diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, diphenyl carbonate, 2,2,2-trifluoroethyl methyl carbonate, and bis(2,2,2-trifluoroethyl)carbonate.

[0091] 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.

[0092] The lithium salt is LiPF ６ , LiPO ２ F ２ , LiBF ４ , LiClO ４ , LiN(SO ２ F) ２ inorganic lithium salts such as lithium oxalate salts, lithium bis(oxalate)borate (LiBOB), lithium difluorooxalateborate (LiFOB), and lithium bis(oxalate)difluorophosphate (LiFOP); ３ CF ３ , LiN(SO ２ CF ３ ) ２ , LiN(SO ２ C ２ F ５ ) ２ , LiN(SO ２ CF ３ ) (SO ２ C ４ F ９ ), LiC(SO ２ CF ３ )３ , LiC(SO ２ C ２ F ５ ) ３ Among these, inorganic lithium salts are preferred, and LiPF ６ and LiN(SO ２ F) ２ is more preferred, and LiN(SO ２ F) ２ is more preferable. ２ F) ２ , LiN(SO ２ CF ３ ) ２ , LiN(SO ２ C ２ F ５ ) ２ , LiN(SO ２ CF ３ ) (SO ２ C ４ F ９ ) and other imide salts are also preferred. ２ CF ３ ) ２ is more preferred.

[0093] The content of the electrolyte salt in the non-aqueous electrolytic solution or non-aqueous electrolyte is 0.1 mol / dm ３ 2.5mol / dm or more ３ It is preferably 0.3 mol / dm or less. ３ 2.0mol / dm or more ３ It is more preferable that it is 0.5 mol / dm or less. ３ More than 1.7mol / dm ３ It is more preferable that it is 0.7 mol / dm or less. ３ 1.5mol / dm or more ３ By setting the content of the electrolyte salt within the above range, the ionic conductivity of the non-aqueous electrolytic solution or non-aqueous electrolyte can be increased.

[0094] The non-aqueous electrolyte may contain additives in addition to the non-aqueous solvent and the electrolyte salt. Examples of the 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; halogenated anisole compounds 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, and cyclohexanedicarboxylic anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, methyl methanesulfonate, and butyl benzene. Examples of the additive include sulfane, methyl toluenesulfonate, dimethyl sulfate, ethylene sulfate, sulfolane, dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, diethyl sulfoxide, tetramethylene sulfoxide, diphenyl sulfide, 4,4'-bis(2,2-dioxo-1,3,2-dioxathiolane), 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane, thioanisole, diphenyl disulfide, dipyridinium disulfide, 1,3-propene sultone, 1,3-propane sultone, 1,4-butane sultone, 1,4-butene sultone, perfluorooctane, tristrimethylsilyl borate, tristrimethylsilyl phosphate, tetrakistrimethylsilyl titanate, lithium monofluorophosphate, and lithium difluorophosphate. These additives may be used alone or in combination of two or more.

[0095] The content of the additive 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 the additive within the above range, it is possible to improve the capacity retention performance or cycle performance after high-temperature storage, and further improve safety.

[0096] The upper limit of the viscosity of the non-aqueous electrolyte or non-aqueous electrolyte at 25°C is preferably 6.5 mPa·s, more preferably 6.0 mPa·s, and may be 5.5 mPa·s, 5.0 mPa·s, 4.5 mPa·s, or 4.0 mPa·s. The lower limit of the viscosity may be 0.5 mPa·s, or may be 1.0 mPa·s, 1.2 mPa·s, 1.4 mPa·s, 1.6 mPa·s, 1.8 mPa·s, 2.0 mPa·s, 2.4 mPa·s, or 2.8 mPa·s. The viscosity may be within a range combining any of the lower limits and any of the upper limits. The viscosity was measured using a LOVIS2000ME manufactured by Anton Paar as a measuring device, with the ambient temperature of the room in which the measuring device was placed set to 25°C.

[0097] 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, nitride solid electrolytes, halide solid electrolytes, and polymer solid electrolytes.

[0098] 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.

[0099] Figure 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.

[0100] <Electricity Storage Device> The nonaqueous electrolyte energy storage element of the present embodiment can be mounted as an energy storage unit (battery module) comprising a plurality of nonaqueous electrolyte energy storage elements in an automobile power source such as an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), etc., a power source for electronic devices such as a personal computer or a communication terminal, or a power source for power storage, 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.

[0101] 2 shows an example of an energy storage device 30 in which energy storage units 20, each of which is an assembly of two or more electrically connected nonaqueous electrolyte energy storage elements 1, are further assembled. The energy storage device 30 may include a bus bar (not shown) that electrically connects two or more nonaqueous electrolyte energy storage elements 1, a bus bar (not shown) that electrically connects two or more energy storage units 20, etc. The energy storage unit 20 or the energy storage device 30 may include a status monitoring device (not shown) that monitors the status of one or more nonaqueous electrolyte energy storage elements.

[0102] <Method for Manufacturing Nonaqueous Electrolyte 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 a positive electrode, preparing a negative electrode, preparing a separator, preparing a nonaqueous electrolyte, fabricating an electrode assembly using the positive electrode, the negative electrode, and the separator, and housing the electrode assembly and the nonaqueous electrolyte in a container.

[0103] The prepared positive electrode includes a composite of a sulfur-based active material and porous carbon. Specific and preferred embodiments of the prepared positive electrode are the same as those of the positive electrode included in the nonaqueous electrolyte storage element according to one embodiment of the present invention described above. Preparing a positive electrode may also mean fabricating a positive electrode. The positive electrode can be fabricated, for example, by applying a paste-like positive electrode mixture (positive electrode mixture paste) to a positive electrode substrate directly or via an intermediate layer, and drying the mixture to form a positive electrode active material layer. The positive electrode mixture paste includes a composite of a sulfur-based active material and porous carbon, other components constituting the positive electrode active material layer, and a dispersion medium.

[0104] Preparing a negative electrode may also mean fabricating a negative electrode. Specific and preferred embodiments of the prepared negative electrode are the same as those of the negative electrode included in the nonaqueous electrolyte storage element according to one embodiment of the present invention described above. A negative electrode containing metallic lithium can be fabricated by laminating a negative electrode active material layer containing metallic lithium directly or via an intermediate layer on a negative electrode substrate, and then pressing the layer. The negative electrode active material layer containing metallic lithium may be a pure metallic lithium foil or a lithium alloy foil. Fabrication of the negative electrode can also be performed by the same method as fabrication of the positive electrode.

[0105] The prepared non-aqueous electrolyte includes a non-aqueous solvent, and the non-aqueous solvent includes a cyclic carbonate (A) and a fluorinated ether (B), and the content of the cyclic carbonate (A) in the non-aqueous solvent is more than 50% by volume. Specific and preferred embodiments of the prepared non-aqueous electrolyte are the same as those of the non-aqueous electrolyte included in the non-aqueous electrolyte storage element according to one embodiment of the present invention described above. Preparing the non-aqueous electrolyte may mean preparing a non-aqueous electrolyte. The preparation of the non-aqueous electrolyte can be performed, for example, by mixing an electrolyte salt and a non-aqueous solvent.

[0106] The electrode assembly can be produced by stacking or winding a positive electrode and a negative electrode with a separator interposed therebetween.

[0107] The method for placing the non-aqueous electrolyte in the container can be appropriately selected from known methods. For example, when a non-aqueous electrolyte solution is used as the non-aqueous electrolyte, the non-aqueous electrolyte solution may be poured into the container through an inlet formed in the container, and then the inlet may be sealed.

[0108] The manufacturing method may include performing initial charging and discharging on an undischarged nonaqueous electrolyte storage element. The initial charging and discharging usually starts with discharging. The first discharging may be referred to as a chemical conversion treatment. The number of times of charging and discharging in the initial charging and discharging is not particularly limited. By undergoing the initial charging and discharging or chemical conversion treatment, a good coating is formed on the surface of the positive electrode composite due to a reaction between a portion of the positive electrode and the nonaqueous electrolyte.

[0109] <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 can be added to the configuration of another embodiment, or part of the configuration of one embodiment can be replaced with the configuration of another embodiment or well-known technology. Furthermore, part of the configuration of one embodiment can be deleted. Also, well-known technology can be added to the configuration of one embodiment.

[0110] In the above embodiment, the nonaqueous electrolyte storage element is used as a chargeable and dischargeable nonaqueous electrolyte secondary battery (e.g., a lithium-sulfur 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, capacitors, etc.

[0111] 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.

[0112] 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.

[0113] [Example 1] (Preparation of Positive Electrode) Elemental sulfur, which is a sulfur-based active material, and porous carbon ("CNovel" manufactured by Toyo Tanso Co., Ltd.) were mixed in a mass ratio of 70:30. This mixture was placed in a sealed electric furnace. After argon flow for 1 hour, the temperature was increased to 150°C at a heating rate of 5°C / min and held for 5 hours, and then allowed to cool to 80°C, the temperature at which elemental sulfur solidifies. Thereafter, the temperature was again increased to 300°C at a heating rate of 5°C / min and held for 2 hours. A composite (sulfur-porous carbon composite: SPC) was prepared. A positive electrode mixture paste containing the composite obtained above, acetylene black and CNT as a conductive agent, CMC as a dispersant, PAA as a thickener, and SBR as a binder, was applied to an aluminum positive electrode substrate (average thickness 15 μm) and dried. After drying the dispersion medium, the mass per unit area of ​​the positive electrode active material layer was 15 mg / cm ２ The amount of the positive electrode mixture paste applied was adjusted so that the positive electrode active material layer was formed on the positive electrode substrate by the above steps. The porosity of the positive electrode active material layer in the resulting positive electrode was 30%.

[0114] (Preparation of Negative Electrode) A pure metallic lithium foil (average thickness: 600 μm) was prepared as a negative electrode.

[0115] (Preparation of non-aqueous electrolyte) A non-aqueous solvent was prepared by mixing fluoroethylene carbonate (FEC) as a fluorinated cyclic carbonate, vinylene carbonate (VC) as an unsaturated cyclic carbonate, and ethyl-1,1,2,2-tetrafluoroethyl ether (ETFEE) as a fluorinated ether (B) in a volume ratio of 43:43:13. LiN(SO 4 ) was added as an electrolyte salt to the non-aqueous solvent. ２ CF ３ ) ２ to 1.0 mol / dm ３ The viscosity of the obtained non-aqueous electrolyte at 25° C. was measured by the above-mentioned method and was found to be 4.1 mPa·s.

[0116] (Assembly of non-aqueous electrolyte storage element) A separator was prepared in which inorganic particle layers were laminated on both sides of a polyethylene microporous membrane. The non-aqueous electrolyte storage element of Example 1 was obtained using the positive electrode, negative electrode, separator, and non-aqueous electrolyte.

[0117] [Examples 2 to 11, Comparative Examples 1 to 5] Non-aqueous electrolyte storage elements of Examples 2 to 11 and Comparative Examples 1 to 5 were obtained in the same manner as in Example 1, except that the compositions of the non-aqueous solvents were as shown in Table 1. The non-aqueous solvents used were as follows. Table 1 also shows the viscosity at 25°C of the non-aqueous electrolyte in each non-aqueous electrolyte storage element. FEC: fluoroethylene carbonate VC: vinylene carbonate ETFEE: ethyl-1,1,2,2-tetrafluoroethyl ether HFPEE: 1,1,2,3,3,3-hexafluoropropyl ethyl ether TFETFPE: 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether

[0118] [Evaluation] (Charge-Discharge Cycle Test) Each of the obtained nonaqueous electrolyte storage elements was first subjected to a chemical conversion treatment, whereby constant-current discharge was performed at a current of 0.1 C down to 1.0 V. Thereafter, constant-current charging was performed at a current of 0.1 C down to 3.0 V. Next, constant-current discharge was performed at a current of 0.1 C down to 1.0 V. A 10-minute pause was provided after discharge and after charge. Discharge, charge, and pause were all performed in a thermostatic chamber at 25°C. The quantity of electricity per mass of the sulfur-based active material (elemental sulfur) during discharge after the above charge was calculated as discharge capacity (discharge capacity per mass of the sulfur-based active material). The results are shown in Table 1.

[0119]

[0120] As shown in Table 1, each nonaqueous electrolyte storage element of the Examples had a discharge capacity per mass of sulfur-based active material of 1,190 mAh / g or more, indicating a large discharge capacity per mass of sulfur-based active material. Furthermore, for example, by comparing Comparative Example 1 with Examples 1 to 4 and 11, it was confirmed that the viscosity of the nonaqueous electrolyte was reduced by including a fluorinated ether (B) in the nonaqueous electrolyte. On the other hand, in Comparative Examples 2 and 3, in which a TFETFPE having two fluorinated alkyl groups bonded to an oxygen atom was included in the nonaqueous electrolyte, the viscosity of the nonaqueous electrolyte was reduced, but the discharge capacity per mass of the sulfur-based active material was not sufficiently increased. The fluorinated ether (B) represented by the above formula (1) not only reduces the viscosity of the nonaqueous electrolyte, but also improves the wettability of the nonaqueous electrolyte to the composite due to its molecular structure, which is believed to result in a sufficiently large discharge capacity.

[0121] 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.

[0122] REFERENCE SIGNS LIST 1 nonaqueous electrolyte energy storage element 2 electrode body 3 container 4 positive electrode terminal 41 positive electrode lead 5 negative electrode terminal 51 negative electrode lead 20 energy storage unit 30 energy storage device

Claims

1. A non-aqueous electrolyte storage element comprising: a positive electrode including a composite of a sulfur-based active material and porous carbon; and a non-aqueous electrolyte including a non-aqueous solvent, wherein the non-aqueous solvent includes at least one cyclic carbonate selected from the group consisting of fluorinated cyclic carbonates and unsaturated cyclic carbonates, and a fluorinated ether, the content of the cyclic carbonate in the non-aqueous solvent being more than 50% by volume, and the fluorinated ether being represented by the following formula (1). １ -O-R ２ ...(1) (In formula (1), R １ R is a fluorinated alkyl group having 1 to 3 carbon atoms. ２ is an alkyl group having 1 or 2 carbon atoms.

2. The nonaqueous electrolyte storage element according to claim 1, wherein the content of the fluorinated ether in the nonaqueous solvent is 10% by volume or more and less than 50% by volume.

3. The nonaqueous electrolyte storage element according to claim 1 or 2, further comprising a negative electrode containing metallic lithium.

4. The nonaqueous electrolyte storage element according to claim 1 or 2, wherein the fluorinated cyclic carbonate includes fluoroethylene carbonate.

5. The nonaqueous electrolyte storage element according to claim 1 or 2, wherein the unsaturated cyclic carbonate includes vinylene carbonate.

6. The nonaqueous electrolyte storage element according to claim 1 or 2, wherein the fluorinated ether comprises at least one selected from the group consisting of methyl-1,1,2,2-tetrafluoroethyl ether, ethyl-1,1,2,2-tetrafluoroethyl ether, 1,1,2,3,3,3-hexafluoropropyl methyl ether and 1,1,2,3,3,3-hexafluoropropyl ethyl ether.

7. The nonaqueous electrolyte storage element according to claim 1 or 2, wherein the total content of said cyclic carbonate and said fluorinated ether in said nonaqueous solvent is 80% by volume or more.

8. The non-aqueous electrolyte storage element according to claim 1 or 2, wherein the non-aqueous electrolyte contains an imide salt.

9. The nonaqueous electrolyte storage element according to claim 1 or 2, wherein the viscosity of the nonaqueous electrolyte at 25° C. is from 0.5 mPa·s to 6.5 mPa·s.

10. A method for producing a nonaqueous electrolyte storage element, comprising: preparing a positive electrode including a composite of a sulfur-based active material and porous carbon; and preparing a nonaqueous electrolyte including a nonaqueous solvent, wherein the nonaqueous solvent includes at least one cyclic carbonate selected from the group consisting of fluorinated cyclic carbonates and unsaturated cyclic carbonates, and a fluorinated ether, the content of the cyclic carbonate in the nonaqueous solvent being more than 50% by volume, and the fluorinated ether being represented by the following formula (1). １ -O-R ２ ...(1) (In formula (1), R １ R is a fluorinated alkyl group having 1 to 3 carbon atoms. ２ is an alkyl group having 1 or 2 carbon atoms.

11. The method for producing a nonaqueous electrolyte storage element according to claim 10, wherein the content of the fluorinated ether in the nonaqueous solvent is 10% by volume or more and less than 50% by volume.

12. The method for producing a nonaqueous electrolyte storage element according to claim 10 or 11, further comprising preparing a negative electrode containing metallic lithium.

13. The method for producing a nonaqueous electrolyte storage element according to claim 10 or 11, wherein the fluorinated cyclic carbonate includes fluoroethylene carbonate.

14. The method for producing a nonaqueous electrolyte storage element according to claim 10 or 11, wherein the unsaturated cyclic carbonate includes vinylene carbonate.

15. The method for producing a nonaqueous electrolyte storage element according to claim 10 or 11, wherein the fluorinated ether includes at least one selected from the group consisting of methyl-1,1,2,2-tetrafluoroethyl ether, ethyl-1,1,2,2-tetrafluoroethyl ether, 1,1,2,3,3,3-hexafluoropropyl methyl ether and 1,1,2,3,3,3-hexafluoropropyl ethyl ether.

16. The method for producing a nonaqueous electrolyte storage element according to claim 10 or 11, wherein the total content of the cyclic carbonate and the fluorinated ether in the nonaqueous solvent is 80 volume % or more.

17. The method for producing a nonaqueous electrolyte storage element according to claim 10 or 11, wherein the nonaqueous electrolyte contains an imide salt.

18. The method for producing a nonaqueous electrolyte storage element according to claim 10 or 11, wherein the viscosity of the nonaqueous electrolyte at 25° C. is from 0.5 mPa·s to 6.5 mPa·s.

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