Nonaqueous electrolyte storage element and method for manufacturing the same

Abstract

Provided are a nonaqueous electrolyte storage element that uses a positive electrode containing a sulfur-based active material and a nonaqueous electrolyte containing an ionic liquid, and that has excellent high-rate discharge performance, and a method for manufacturing such a nonaqueous electrolyte storage element. [Solution] A non-aqueous electrolyte storage element according to one aspect of the present invention comprises a positive electrode containing a sulfur-based active material and a non-aqueous electrolyte containing an electrolyte salt, an ionic liquid, and a non-aqueous solvent, and the non-aqueous solvent contains a specified fluorinated cyclic ether and another non-aqueous solvent.

Description

[Technical Field]

[0001] The present invention relates to a nonaqueous electrolyte electricity storage element and a method for manufacturing a nonaqueous 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, 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 non-aqueous electrolyte storage elements include lithium-sulfur batteries (Li-S batteries) and other non-aqueous electrolyte storage elements that use a sulfur-based active material as the positive electrode active material (see Patent Document 1). In recent years, research has also been progressing on non-aqueous electrolyte storage elements that use an ionic liquid as the non-aqueous electrolyte (see Patent Document 2). Ionic liquids, also known as room-temperature molten salts, have advantages such as being substantially non-volatile and highly flame-retardant, despite being liquid at room temperature. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-95390 [Patent Document 2] Japanese Patent Application Laid-Open No. 2001-319688 Summary of the Invention [Problem to be solved by the invention]

[0005] Sulfur-based active materials have a large theoretical capacity, and nonaqueous electrolyte energy storage elements using sulfur-based active materials as the positive electrode active material are expected to have high energy density. On the other hand, nonaqueous electrolyte energy storage elements using ionic liquids may not be able to exhibit sufficient performance in terms of high-rate discharge performance, etc., due to the high viscosity of the ionic liquid.

[0006] An object of the present invention is to provide a nonaqueous electrolyte storage element that uses a positive electrode containing a sulfur-based active material and a nonaqueous electrolyte containing an ionic liquid, and that has excellent high-rate discharge performance, and a method for manufacturing such a nonaqueous electrolyte storage element. [Means for solving the problem]

[0007] A nonaqueous electrolyte storage element according to one aspect of the present invention comprises a positive electrode containing a sulfur-based active material and a nonaqueous electrolyte containing an electrolyte salt, an ionic liquid, and a nonaqueous solvent, the nonaqueous solvent containing a fluorinated cyclic ether represented by the following formula (1) and another nonaqueous solvent: [ka] (In formula (1), R 1 are each independently a hydrogen atom, a fluorine atom, an alkyl group having 1 to 4 carbon atoms, or a fluorinated alkyl group having 1 to 4 carbon atoms. 1 At least one of the groups is a fluorine atom or a fluorinated alkyl group having 1 to 4 carbon atoms. n1 is an integer of 2 to 5.

[0008] A method for manufacturing a nonaqueous electrolyte storage element according to another aspect of the present invention includes preparing a positive electrode containing a sulfur-based active material, and preparing a nonaqueous electrolyte containing an electrolyte salt, an ionic liquid, and a nonaqueous solvent, wherein the nonaqueous solvent contains a fluorinated cyclic ether represented by the following formula (1) and another nonaqueous solvent: [ka] (In formula (1), R 1are each independently a hydrogen atom, a fluorine atom, an alkyl group having 1 to 4 carbon atoms, or a fluorinated alkyl group having 1 to 4 carbon atoms. 1 At least one of the groups is a fluorine atom or a fluorinated alkyl group having 1 to 4 carbon atoms. n1 is an integer of 2 to 5. [Effects of the Invention]

[0009] According to one aspect of the present invention, it is possible to provide a nonaqueous electrolyte storage element that uses a positive electrode containing a sulfur-based active material and a nonaqueous electrolyte containing an ionic liquid, and that has excellent high-rate discharge performance, and a method for manufacturing such a nonaqueous electrolyte storage element. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a perspective view showing a nonaqueous electrolyte electricity storage element according to one embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing an electricity storage device including a plurality of nonaqueous electrolyte electricity storage elements according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] 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.

[0012] [1] A nonaqueous electrolyte storage element according to one aspect of the present invention includes a positive electrode containing a sulfur-based active material and a nonaqueous electrolyte containing an electrolyte salt, an ionic liquid, and a nonaqueous solvent, wherein the nonaqueous solvent contains a fluorinated cyclic ether represented by the following formula (1) and another nonaqueous solvent: [ka] (In formula (1), R 1 are each independently a hydrogen atom, a fluorine atom, an alkyl group having 1 to 4 carbon atoms, or a fluorinated alkyl group having 1 to 4 carbon atoms. 1At least one of the groups is a fluorine atom or a fluorinated alkyl group having 1 to 4 carbon atoms. n1 is an integer of 2 to 5.

[0013] The nonaqueous electrolyte storage element described in [1] above is a nonaqueous electrolyte storage element that uses a positive electrode containing a sulfur-based active material and a nonaqueous electrolyte containing an ionic liquid, and exhibits high high-rate discharge performance. While the reason for this is unclear, the following is presumed. Nonaqueous electrolytes containing ionic liquids have high viscosity and low diffusivity of charge-transporting ions, so nonaqueous electrolyte storage elements using nonaqueous electrolytes containing ionic liquids may not exhibit sufficient charge-discharge performance. In response to this, the inventors discovered that adding a fluorinated cyclic ether represented by the above formula (1) to a nonaqueous electrolyte containing an ionic liquid can improve the charge-discharge performance (discharge capacity, capacity retention rate after charge-discharge cycles, etc.) of nonaqueous electrolyte storage elements. This is thought to be because the fluorinated cyclic ether has a lower viscosity than an ionic liquid and is a solvent with a relatively small number of donors. Therefore, a nonaqueous electrolyte containing such a fluorinated cyclic ether has a relatively low viscosity despite being a nonaqueous electrolyte containing an ionic liquid, and also suppresses the elution of polysulfides from the positive electrode into the nonaqueous electrolyte, which can affect charge-discharge performance. However, when the fluorinated cyclic ether is used alone as the nonaqueous solvent, the discharge capacity tends to decrease during high-current discharge (high-rate discharge performance is insufficient). In contrast, the nonaqueous electrolyte storage element described in [1] above contains a nonaqueous electrolyte that further contains another nonaqueous solvent in addition to the ionic liquid and the fluorinated cyclic ether. The presence of this other nonaqueous solvent is thought to further reduce the viscosity of the nonaqueous electrolyte and improve the diffusibility of charge-transporting ions in the nonaqueous electrolyte. Therefore, the nonaqueous electrolyte storage element described in [1] above is a nonaqueous electrolyte storage element that uses a positive electrode containing a sulfur-based active material and a nonaqueous electrolyte containing an ionic liquid, and is presumed to have excellent high-rate discharge performance.

[0014] The types of ionic compounds, such as electrolyte salts and ionic liquids, contained in non-aqueous electrolytes can be analyzed using ion chromatography (IC), liquid chromatography-mass spectrometry (LC-MS), 1 Identification is performed by combining the necessary analyses, such as H-NMR and multinuclear NMR. The content of ionic compounds such as electrolyte salts and ionic liquids contained in the non-aqueous electrolyte is determined by IC. However, the content of cations of ionic liquids contained in the non-aqueous electrolyte is determined by LC-MS. If it cannot be determined by LC-MS, 1 Identified by H-NMR internal standard method. Specifically, IC measurements are performed as follows: IC measurements are performed continuously under the same conditions. (A1) Collection of non-aqueous electrolyte First, the nonaqueous electrolyte storage element is disassembled to remove the nonaqueous electrolyte. If the nonaqueous electrolyte cannot be removed, the nonaqueous electrolyte storage element is centrifuged to remove the nonaqueous electrolyte. If the nonaqueous electrolyte cannot be removed even after centrifugation, an appropriate extraction solvent (e.g., acetonitrile) is poured into the nonaqueous electrolyte storage element, and the nonaqueous electrolyte diluted with the extraction solvent is removed. (A2)IC analysis The components of the collected non-aqueous electrolyte are analyzed by IC. The IC analysis is performed in the following order: qualitative analysis and quantitative analysis. (qualitative analysis) A measurement sample (non-aqueous electrolyte) is subjected to IC analysis. The components contained in the measurement sample are predicted from the peak positions of each peak in the obtained ion chromatogram. A known sample of the predicted components (hereinafter referred to as "predicted components") is subjected to IC analysis. The retention times of the peaks corresponding to each predicted component in the measurement sample are compared with the retention times of the peaks in known samples 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 predicted components with known concentrations is analyzed by IC analysis, and a calibration curve is created by calculating the peak area. The calibration curve is calculated using the coefficient of determination (r 2 ) is created so that it is between 0.999 and 1. The amount of the predicted component in the measurement sample is calculated from the calibration curve and the area of ​​the peak of the predicted component in the measurement sample. This process is performed for all peaks detected in the IC analysis of the measurement sample, and the amount of each predicted component is calculated.

[0015] The types and contents of nonionic compounds, such as nonaqueous solvents, contained in the nonaqueous electrolyte are identified by liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-mass spectrometry (GC-MS). Specifically, this is done as follows. Note that the LC-MS and GC-MS measurements are performed consecutively under the same conditions. (B1) Collection of non-aqueous electrolyte The non-aqueous electrolyte is extracted using the same procedure as in "(A1) Extraction of non-aqueous electrolyte" above. (B2) LC-MS The components of the collected non-aqueous electrolyte are analyzed by LC-MS. The LC-MS analysis is performed in the following order: qualitative analysis and quantitative analysis. The LC-MS analysis is performed using Waters' "Acquity H" and "Xevo G2-5QTof" instruments. Water is used as the eluent. Note that, regarding the measurement instrument, if it is not possible to perform the measurement using the above-mentioned model, other models that are considered to produce equivalent measurement results can be used. The same applies to other measurement instruments in this specification. (qualitative analysis) The measurement sample (non-aqueous electrolyte) is subjected to LC-MS analysis. If the peaks in the obtained liquid chromatogram cannot be separated, GC-MS analysis, described below, is performed instead of LC-MS analysis. If the peaks can be separated, the components contained in the measurement sample are predicted from the MS spectrum of each peak. A known sample of the predicted components is subjected to LC-MS analysis. The retention times and MS spectrum of the peaks corresponding to each predicted component in the measurement sample are compared with the retention times 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. Quantitative analysis by LC-MS is performed using the same procedure as the quantitative analysis by IC described above, and the content of each predicted component is determined. (B3) GC-MS The GC-MS analysis is performed in the following order: qualitative analysis and quantitative analysis. The GC-MS analysis equipment used is the Agilent 5975C. Argon is used as the carrier gas. (qualitative analysis) A 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 components is subjected to GC-MS analysis. The retention times and MS spectra of the peaks corresponding to the predicted components in the measurement sample are compared with the retention times and MS spectra of the peaks in known samples 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. Quantitative analysis by GC-MS is performed using the same procedure as the quantitative analysis by IC described above, and the content of each predicted component is determined.

[0016] [2] In the nonaqueous electrolyte electricity storage element according to the above [1], the fluorinated cyclic ether may be 3,3,4,4-tetrafluorotetrahydrofuran.

[0017] The nonaqueous electrolyte electricity storage element described in [2] above has higher high-rate discharge performance.

[0018] [3] In the nonaqueous electrolyte storage element according to the above [1] or [2], the other nonaqueous solvent may be at least one selected from the group consisting of non-fluorinated cyclic ethers and chain ethers.

[0019] The nonaqueous electrolyte storage element described in [3] above has higher high-rate discharge performance, presumably because the non-fluorinated cyclic ether and the chain ether have lower viscosities than the fluorinated cyclic ether, which allows the viscosity of the nonaqueous electrolyte to be lowered and the diffusibility of charge-transporting ions in the nonaqueous electrolyte to be increased.

[0020] [4] In the nonaqueous electrolyte storage element according to the above item [3], the non-fluorinated cyclic ether may be represented by the following formula (2), and the chain ether may be represented by the following formula (3). [ka] (In formula (2), R 2 are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and n2 is an integer of 2 to 5. [ka] (In formula (3), R 3 and R 4 are each independently an alkyl group having 1 to 3 carbon atoms or a fluorinated alkyl group having 1 to 3 carbon atoms. 5 is an alkanediyl group having 1 to 3 carbon atoms; and n3 is 0 or 1.

[0021] The nonaqueous electrolyte electricity storage element described in [4] above has higher high-rate discharge performance.

[0022] [5] In the nonaqueous electrolyte storage element according to any one of [1] to [4] above, the total content of the ionic liquid and the fluorinated cyclic ether relative to the total of the ionic liquid and the nonaqueous solvent may be 10% by volume or more.

[0023] The nonaqueous electrolyte energy storage element described in [5] above has a high high-rate discharge performance, a large discharge capacity, and a high capacity retention rate after charge-discharge cycles. The reason for this is presumably that the inclusion of an appropriate amount of other nonaqueous solvent further suppresses the elution of polysulfides from the positive electrode into the nonaqueous electrolyte.

[0024] [6] In the nonaqueous electrolyte storage element according to any one of [1] to [5] above, the viscosity of the nonaqueous electrolyte at 25° C. may be 19 mPa·s or less.

[0025] The nonaqueous electrolyte storage element described in [6] above has a sufficiently low viscosity nonaqueous electrolyte, and therefore has a higher high-rate discharge performance.

[0026] The viscosity of the non-aqueous electrolyte or the like is a value measured using a measuring device "LOVIS2000ME" manufactured by Anton Paar, with the temperature of the non-aqueous electrolyte to be measured set to 25°C.

[0027] [7] In the nonaqueous electrolyte storage element according to any one of [1] to [6] above, the ionic liquid may contain at least one cation selected from the group consisting of quaternary ammonium cations, imidazolium cations, pyrrolidinium cations, piperidinium cations, quaternary phosphonium cations, and sulfonium cations.

[0028] [8] In the nonaqueous electrolyte storage element according to any one of [1] to [7] above, the ionic liquid may have an imide anion.

[0029] [9] In the nonaqueous electrolyte storage element according to any one of [1] to [8] above, the electrolyte salt may be an imide salt.

[0030]

[10] In the nonaqueous electrolyte storage element according to any one of [1] to [9] above, the number of donors in the other nonaqueous solvent may be 14 or more and 30 or less.

[0031] The donor number is a parameter that represents the electron-pair donating ability of a solvent, and is defined as the negative value of the enthalpy of formation of a 1:1 adduct between antimony pentachloride in 1,2-dichloroethane and the target solvent. In this specification, the donor number is determined by the same method as that described in Viktor Gutmann, "The Donor-Acceptor Approach to Molecular Interactions," Springer, 1978 (ISBN-13:978-0306310645), except that boron trifluoride is selected as the Lewis acid.

[0032]

[11] In the nonaqueous electrolyte storage element according to any one of [1] to

[10] above, the viscosity of the other nonaqueous solvent at 25° C. may be less than 1.0 mPa·s.

[0033]

[12] In the nonaqueous electrolyte storage element according to any one of [1] to

[11] above, the total content of the ionic liquid and the fluorinated cyclic ether relative to the total content of the ionic liquid and the nonaqueous solvent may be 10% by volume or more and 95% by volume or less.

[0034]

[13] In the nonaqueous electrolyte storage element according to any one of [1] to

[12] above, the content of the ionic liquid relative to the total of the ionic liquid and the nonaqueous solvent may be 5% by volume or more and 90% by volume or less.

[0035]

[14] In the nonaqueous electrolyte storage element according to any one of [1] to

[13] above, the content of the fluorinated cyclic ether relative to the total of the ionic liquid and the nonaqueous solvent may be 5% by volume or more and 90% by volume or less.

[0036]

[15] In the nonaqueous electrolyte storage element according to any one of [3] to

[14] above, the total content of the non-fluorinated cyclic ether and the chain ether relative to the total of the ionic liquid and the nonaqueous solvent may be 5% by volume or more and 90% by volume or less.

[0037]

[16] In the nonaqueous electrolyte storage element according to any one of [1] to

[15] above, the molar concentration of the electrolyte salt in the nonaqueous electrolyte may be 0.3 mol / kg or more and 3.5 mol / kg or less.

[0038] Each of the nonaqueous electrolyte storage elements described in [7] to

[16] above is a preferred embodiment of the present invention, and has higher high-rate discharge performance.

[0039]

[17] The nonaqueous electrolyte storage element according to any one of [1] to

[16] above, wherein the positive electrode has a positive electrode active material layer containing the sulfur-based active material, and the mass per unit area of ​​the positive electrode active material layer is 5 mg / cm 2 It may be more than that.

[0040] In the nonaqueous electrolyte storage element described in

[17] above, the mass per unit area of ​​the positive electrode active material layer containing the sulfur-based active material is 5 mg / cm 2 As a result, the energy density of the nonaqueous electrolyte storage element can be increased. Furthermore, the nonaqueous electrolyte storage element described in

[17] above can achieve both high energy density and excellent high-rate discharge performance.

[0041] Mass per unit area of ​​the positive electrode active material layer (mg / cm 2 ) is the area of ​​the positive electrode active material layer (1 cm 2 ) is the mass (mg) of the positive electrode active material layer per 1000 μm of positive electrode active material layer. The area of ​​the positive electrode active material layer refers to the area of ​​one of the front and back surfaces (two surfaces other than the side surfaces) of one positive electrode active material layer. That is, for example, when the positive electrode active material layer is provided by coating, the area of ​​the positive electrode active material layer is equal to the area where the positive electrode active material layer is coated. When the positive electrode active material layer is provided on both surfaces of the positive electrode substrate, the area and mass of the positive electrode active material layer refer to the area and mass of one positive electrode active material layer. For example, when the positive electrode active material layer is provided on both surfaces of the positive electrode substrate with a thickness of 10 mg / cm, the area and mass of the positive electrode active material layer are equal to the area where the positive electrode active material layer is coated. 2 When the coating amount (solid content equivalent) is 10 mg / cm, the "mass per unit area of ​​the positive electrode active material layer" is 10 mg / cm. 2 The positive electrode active material layer is 10 mg / cm on one side of the positive electrode substrate.2 Even if the coating amount (solid content equivalent) is 10 mg / cm, the "mass per unit area of ​​the positive electrode active material layer" is 10 mg / cm. 2 is.

[0042]

[18] The nonaqueous electrolyte storage element according to any one of the above [1] to

[18] may further comprise a negative electrode containing metallic lithium at least in a charged state.

[0043] The nonaqueous electrolyte electricity storage element described in

[18] above has advantages such as a particularly high energy density due to the use of metallic lithium in the negative electrode.

[0044]

[19] A method for producing a nonaqueous electrolyte storage element according to another aspect of the present invention includes preparing a positive electrode containing a sulfur-based active material, and preparing a nonaqueous electrolyte containing an electrolyte salt, an ionic liquid, and a nonaqueous solvent, wherein the nonaqueous solvent contains a fluorinated cyclic ether represented by the following formula (1) and another nonaqueous solvent: [ka] (In formula (1), R 1 are each independently a hydrogen atom, a fluorine atom, an alkyl group having 1 to 4 carbon atoms, or a fluorinated alkyl group having 1 to 4 carbon atoms. 1 At least one of the groups is a fluorine atom or a fluorinated alkyl group having 1 to 4 carbon atoms. n1 is an integer of 2 to 5.

[0045] According to the method for producing a nonaqueous electrolyte storage element described in

[19] above, it is possible to produce a nonaqueous electrolyte storage element that uses a positive electrode containing a sulfur-based active material and a nonaqueous electrolyte containing an ionic liquid, and that has excellent high-rate discharge performance.

[0046] A nonaqueous electrolyte electricity storage element according to one embodiment of the present invention, a method for manufacturing a nonaqueous electrolyte electricity storage element, an electricity storage device, and other embodiments will be described in detail below.

[0047] <Non-aqueous electrolyte energy storage element> A nonaqueous electrolyte storage element according to one embodiment of the present invention comprises a positive electrode, a negative electrode, a nonaqueous electrolyte, and a container for accommodating these. The nonaqueous electrolyte storage element may further comprise a separator interposed between the positive electrode and the negative electrode to electrically insulate the positive electrode from the negative electrode. The positive electrode, the negative electrode, and any separator typically constitute an electrode assembly. At least a portion of the nonaqueous electrolyte typically exists in a state of being impregnated into the electrode assembly. The nonaqueous electrolyte storage element according to one embodiment of the present invention may further comprise other components.

[0048] For example, a nonaqueous electrolyte storage element 1 according to one embodiment of the present invention shown in FIG. 1 includes an electrode assembly 2, a nonaqueous electrolyte (not shown), and a rectangular parallelepiped container 3 that accommodates these. The nonaqueous electrolyte storage element 1 of FIG. 1 further includes a positive electrode lead 4, a positive electrode external terminal 5, a negative electrode lead 6, and a negative electrode external terminal 7. The positive electrode lead 4 and the negative electrode lead 6 are accommodated in the container 3 together with the electrode assembly 2 and the like. The positive electrode external terminal 5 and the negative electrode external terminal 7 are provided outside the container 3. The positive electrode constituting the electrode assembly 2 is electrically connected to the positive electrode external terminal 5 via the positive electrode lead 4. The negative electrode constituting the electrode assembly 2 is electrically connected to the negative electrode external terminal 7 via the negative electrode lead 6.

[0049] The nonaqueous electrolyte storage element of the present invention may be a nonaqueous electrolyte secondary battery. Below, the main components constituting the nonaqueous electrolyte storage element according to one embodiment of the present invention will be described in detail, mainly in the case where the nonaqueous electrolyte storage element is a nonaqueous electrolyte secondary battery (particularly a lithium ion secondary battery), but this is not intended to limit the application of the present invention.

[0050] The lower and upper limits of each numerical range described in the embodiments of the present invention can be combined in any manner.

[0051] (positive electrode) The positive electrode has a positive electrode substrate and a positive electrode active material layer laminated on the positive electrode substrate directly or via an intermediate layer. Usually, the positive electrode has a portion where the positive electrode substrate is exposed. This exposed portion of the positive electrode substrate is usually connected to the above-mentioned positive electrode lead. The positive electrode may have a shape such as a sheet, plate, or strip.

[0052] The thickness of the positive electrode is appropriately set depending on the application of the nonaqueous electrolyte storage element. The average thickness of the positive electrode may be, for example, 30 μm or more and 1,000 μm or less. The lower limit of the average thickness of the positive electrode may be 50 μm, 100 μm, or 200 μm. The upper limit of the average thickness of the positive electrode may be 500 μm, 400 μm, 300 μm, 200 μm, or 100 μm. The average thickness of the positive electrode is the average thickness of the portion where the positive electrode active material layer is laminated on the positive electrode substrate directly or via an intermediate layer. When the positive electrode substrate has both a portion where the positive electrode active material layer is laminated on both sides and a portion where the positive electrode active material layer is laminated on only one side, the average thickness of the portion where the positive electrode active material layer is laminated on both sides of the positive electrode substrate is referred to. In addition, in this specification, "average thickness" means the average thickness of thicknesses measured at any five positions.

[0053] The positive electrode substrate has electrical conductivity. In this specification, "having electrical conductivity" means that the volume resistivity is 10 -2 The volume resistivity is a value measured in accordance with JIS-H-0505 (1975). On the other hand, in this specification, "not having electrical conductivity" or "having (electrical) insulation" means that the volume resistivity is 10 7 This means that the resistance is Ω·cm or more.

[0054] Examples of materials for the positive electrode substrate include metals such as aluminum, titanium, iron, and alloys thereof (stainless steel, etc.). Among these, aluminum or an aluminum alloy is preferred from the viewpoints of potential resistance, high electronic conductivity, and cost.

[0055] The positive electrode substrate has a shape such as a sheet, plate, or strip. Examples of the positive electrode substrate include foil, vapor-deposited film, mesh, and porous material, and foil is preferred. The positive electrode substrate may be, for example, aluminum foil or aluminum alloy foil.

[0056] The average thickness of the positive electrode substrate may be, for example, 3 μm or more and 50 μm or less. The lower limit of the average thickness of the positive electrode substrate may be 5 μm, 8 μm, 10 μm, or 15 μm. The upper limit of the average thickness of the positive electrode substrate may be 40 μm, 30 μm, 20 μm, or 15 μm.

[0057] The intermediate layer is a layer disposed between the positive electrode substrate and the positive electrode active material layer. The intermediate layer contains, for example, a conductive agent and a binder. When the intermediate layer contains a conductive agent, the contact resistance between the positive electrode substrate and the positive electrode active material layer can be reduced. Examples of the conductive agent and binder used in the intermediate layer include the same conductive agent and binder used in the positive electrode active material layer described below.

[0058] The positive electrode active material layer contains a sulfur-based active material. The positive electrode active material layer contains optional components such as a conductive agent, a binder, a dispersant, a thickener, and a filler, as necessary. The positive electrode active material layer may be formed from a positive electrode mixture containing a positive electrode active material and other optional components. The positive electrode active material layer may be provided on only one side or on both sides of a positive electrode substrate having a shape such as a sheet.

[0059] The sulfur-based active material 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. 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.

[0060] The content of the sulfur-based active material in the positive electrode active material layer is preferably 50% by mass to 90% by mass, more preferably 55% by mass to 80% by mass, and even more preferably 60% by mass to 70% by mass. By having the content of the sulfur-based active material in this range, it is possible to further improve the high-rate discharge performance and increase the discharge capacity of the nonaqueous electrolyte storage element.

[0061] The positive electrode active material layer preferably further includes porous carbon forming a composite with the sulfur-based active material. In other words, the sulfur-based active material is preferably contained in the positive electrode active material layer as a composite with porous carbon. Hereinafter, the composite of the sulfur-based active material and porous carbon will also be simply referred to as a "composite." In the composite, the 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 the sulfur-based active material and porous carbon, or may be substantially composed of only the sulfur-based active material and porous carbon. A composite substantially composed of only the 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.

[0062] 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 further improve the high-rate discharge performance and increase the discharge capacity of the nonaqueous electrolyte storage element.

[0063] 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 by mass. The lower limit of the carbon 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 content in porous carbon may be 100 mass% or 99.9 mass%. Porous carbon may contain elements other than carbon, such as oxygen and nitrogen.

[0064] 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.

[0065] 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 this range, it is possible to further improve the high-rate discharge performance and increase the discharge capacity of the nonaqueous electrolyte storage element.

[0066] 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.

[0067] The conductive agent is usually a component made of a material with electrical conductivity. Note that this conductive agent does not include the porous carbon that constitutes the composite. Even if the volume resistivity of the conductive agent cannot be measured directly, it is possible to estimate the volume resistivity by measuring the volume resistivity of the conductive agent. -2Conductive agents are materials known to have a resistivity of Ω·cm or less. Examples of conductive agents include carbon materials, metals, and conductive ceramics. Carbon materials are materials whose primary constituent element is carbon. The primary constituent element refers to the element with the highest content by mass. For example, the carbon content in a carbon material may be 80% by mass or more, 90% by mass or more, 95% by mass, 99% by mass, or 99.9% by mass or more. The carbon material is preferably a carbon material other than an uncarbonized polymer compound. Examples of carbon materials include graphite, non-graphitic carbon, and graphene-based carbon. Examples of non-graphitic carbon include carbon nanofiber, pitch-based carbon fiber, and carbon black. Examples of carbon black include furnace black, acetylene black, and ketjen black. Examples of graphene-based carbon include graphene, carbon nanotubes (CNT), and fullerene. Conductive agents may be in the form of powder, fiber, or the like. The conductive agent may be one or more types. The conductive agent may be a composite of these materials. For example, a composite material of carbon black and CNT may be used. The conductive agent is preferably carbon black or CNT, and acetylene black is more preferred as the carbon black. It is also preferred to use carbon black (preferably acetylene black) and CNT in combination.

[0068] The content of the conductive agent (excluding the porous carbon in the composite) in the positive electrode active material layer is preferably 0.1% by mass to 10% by mass, more preferably 1% by mass to 9% by mass. The upper limit of the content of the conductive agent may be 8%, 5%, 4%, 3%, or 2% by mass. By setting the content of the conductive agent within the above range, it is possible to increase the energy density of the nonaqueous electrolyte storage element.

[0069] Examples of the binder include a water-based binder and an organic solvent-based binder.

[0070] The aqueous binder is a binder that dissolves or disperses in water. The aqueous binder may be a binder that dissolves or disperses at 1 part by mass or more in 100 parts by mass of water at 20°C. When a positive electrode active material layer is formed using a positive electrode mixture paste whose dispersion medium is water or a mixed solvent mainly composed of water, an aqueous binder (a water-soluble or water-dispersible polymer material) can be used. Examples of aqueous binders include polyethylene oxide, polypropylene oxide, polyvinyl alcohol, polyacrylic acid, polymethacrylic acid, polytetrafluoroethylene, styrene-butadiene rubber, polyethylene, polypropylene, nitrile-butadiene rubber, and cellulose.

[0071] The organic solvent-based binder is a binder that dissolves or disperses in an organic solvent (e.g., N-methylpyrrolidone). The organic solvent-based binder may be a binder that dissolves or disperses at 1 part by mass or more in 100 parts by mass of an organic solvent (e.g., N-methylpyrrolidone) at 20°C. When a positive electrode active material layer is formed using a positive electrode mixture paste whose dispersion medium is an organic solvent or a mixed solvent mainly containing an organic solvent, an organic solvent-based binder (a polymer material that is soluble or dispersible in an organic solvent) can be used. Examples of organic solvent-based binders include polyvinylidene fluoride, copolymers of vinylidene fluoride and hexafluoropropylene, copolymers of ethylene and vinyl alcohol, polyacrylonitrile, polyphosphazene, polysiloxane, polyvinyl acetate, polymethyl methacrylate, polystyrene, polycarbonate, polyamide, polyimide, polyamideimide, crosslinked polymers of cellulose and chitosan pyrrolidone carboxylate, chitosan derivatives, and the like.

[0072] The binder may be a fluororesin (polytetrafluoroethylene, polyvinylidene fluoride, etc.), a polyolefin (polyethylene, polypropylene, etc.), an elastomer (ethylene propylene diene rubber, styrene butadiene rubber, fluororubber, etc.), a polysaccharide polymer (cellulose, chitosan derivatives, etc.), etc. One or more types of binders may be used.

[0073] The content of the binder in the positive electrode active material layer is preferably 0.1% by mass to 10% by mass, more preferably 1% by mass to 9% by mass, and even more preferably 2% by mass to 8% by mass. The upper limit of the binder content may be 5%, 4%, or 3% by mass. By setting the binder content within the above range, it is possible to stably hold the sulfur-based active material, etc. The technology disclosed herein can also be implemented in an embodiment in which the positive electrode active material layer does not contain a binder.

[0074] 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.

[0075] Examples of thickeners 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.

[0076] The filler is not particularly limited. The filler may be a component other than the positive electrode active material (sulfur-based active material and other positive electrode active materials), conductive agent, binder, dispersant, and thickener, and may be intentionally added. The filler may be added to fill gaps in the positive electrode active material layer, or may be added for other purposes. The filler may be an organic substance such as polyolefin, or an inorganic substance such as an inorganic oxide, hydroxide, or carbonate. One or more fillers may be used. When the positive electrode active material layer contains a filler, the content of the filler in the positive electrode active material layer may be 0.1% by mass or more and 8% by mass or less, usually preferably 5% by mass or less, and more preferably 2% by mass or less. The technology disclosed herein may also be implemented in an embodiment in which the positive electrode active material layer does not contain a filler.

[0077] The positive electrode active material layer may further contain other components in addition to the positive electrode active material (sulfur-based active material and other positive electrode active materials), conductive agent, binder, dispersant, thickener, and filler. The other components include those unintentionally generated in the positive electrode active material layer. The positive electrode active material layer may also contain unintentionally contained impurities as the other components, as long as the effects of the present invention are achieved. The upper limit of the content of the other components in the positive electrode active material layer may be 10% by mass, 5%, 2%, 1%, 0.1%, or 0.01% by mass. The upper limit of the content of the unintentionally generated components in the positive electrode active material layer may be 10% by mass, 5%, 2%, 1%, 0.1%, or 0.01% by mass. The upper limit of the content of impurities unintentionally contained in the positive electrode active material layer may be 10% by mass, 5% by mass, 2% by mass, 1% by mass, 0.1% by mass, or 0.01% by mass.

[0078] The lower limit of the mass per unit area of ​​the positive electrode active material layer is, for example, 1 mg / cm 2 3 mg / cm 2 may be 5 mg / cm 2 is preferred, and 7 mg / cm 2 More preferably, 9 mg / cm2 is more preferably 10 mg / cm 2 By setting the mass per unit area of ​​the positive electrode active material layer to the above lower limit or more, it is possible to increase the energy density of the nonaqueous electrolyte storage element. The upper limit of the mass per unit area of ​​the positive electrode active material layer is 30 mg / cm. 2 20 mg / cm 2 , 15 mg / cm 2 , 10 mg / cm 2 , 7 mg / cm 2 or 5 mg / cm 2 By setting the mass per unit area of ​​the positive electrode active material layer to the above upper limit or less, it is possible to further improve the high-rate discharge performance of the nonaqueous electrolyte storage element and increase the discharge capacity.

[0079] (Positive electrode manufacturing method) The positive electrode can be manufactured by a known method. The positive electrode can be manufactured, 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 then drying the paste to form a positive electrode active material layer. The positive electrode mixture paste typically contains a sulfur-based active material, other optional components, and a dispersion medium. After drying, the positive electrode active material layer may be pressed, etc.

[0080] (Negative electrode) The negative electrode has a negative electrode substrate and a negative electrode active material layer laminated on the negative electrode substrate directly or via an intermediate layer. Usually, the negative electrode has a portion where the negative electrode substrate is exposed. This exposed portion of the negative electrode substrate is usually connected to the above-mentioned negative electrode lead. The negative electrode may have a shape such as a sheet, plate, or strip.

[0081] The thickness of the negative electrode is appropriately set depending on the application of the nonaqueous electrolyte storage element, etc. The average thickness of the negative electrode may be, for example, 30 μm or more and 1,000 μm or less. The lower limit of the average thickness of the negative electrode may be 50 μm, 100 μm, or 200 μm. The upper limit of the average thickness of the negative electrode may be 500 μm, 400 μm, 300 μm, 200 μm, or 100 μm. The average thickness of the negative electrode is the average thickness of a portion where the negative electrode active material layer is laminated on the negative electrode substrate directly or via an intermediate layer. When the negative electrode substrate has both a portion where the negative electrode active material layer is laminated on both sides and a portion where the negative electrode active material layer is laminated on only one side, the average thickness of the portion where the negative electrode active material layer is laminated on both sides of the negative electrode substrate is taken as the average thickness.

[0082] The negative electrode substrate is conductive. Examples of materials for the negative electrode substrate include metals such as copper, nickel, iron, and alloys thereof (such as stainless steel), and carbon materials. Among these, nickel or a nickel alloy is preferred.

[0083] The negative electrode substrate has a shape such as a sheet, plate, or strip. Examples of the form of the negative electrode substrate include foil, vapor-deposited film, mesh, and porous material, and foil is preferred. The negative electrode substrate may be, for example, nickel foil or nickel alloy foil.

[0084] The average thickness of the negative electrode substrate may be, for example, 2 μm or more and 35 μm or less. The lower limit of the average thickness of the negative electrode substrate may be 3 μm, 4 μm, 5 μm, or 10 μm. The upper limit of the average thickness of the negative electrode substrate may be 30 μm, 20 μm, 15 μm, or 10 μm.

[0085] The structure of the intermediate layer of the negative electrode is not particularly limited, and can be selected from the structures exemplified for the intermediate layer of the positive electrode, for example.

[0086] 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 dispersant, a thickener, and a filler as needed. The optional components such as the conductive agent, the binder, the dispersant, 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. The negative electrode active material layer may be provided on only one side or on both sides of a negative electrode substrate having a shape such as a sheet.

[0087] The negative electrode active material can be a known negative electrode active material. A material capable of absorbing and releasing lithium ions is typically used as the negative electrode active material for lithium ion secondary batteries. Examples of the negative electrode active material include metallic lithium; metals or semimetals such as silicon and tin; metal oxides or semimetal oxides such as silicon oxide, titanium oxide, and tin oxide; and Li4Ti5O. 12 , LiTiO 2、 Examples of the negative electrode active material include titanium-containing oxides such as TiNb2O7; polyphosphate compounds; silicon carbide; and carbon materials such as graphite and non-graphitic carbon. Among these materials, carbon materials are preferred, and graphite or non-graphitic carbon may be more preferred. The surface of graphite may be coated with other materials such as non-graphitic carbon. One or more negative electrode active materials may be used. In the case of a negative electrode active material that does not contain charge transport ions such as lithium ions, a material doped with charge transport ions such as lithium ions may be used.

[0088] The negative electrode active material is preferably metallic lithium. In other words, the negative electrode or the negative electrode active material layer preferably contains metallic lithium at least in a charged state. It is more preferable that the negative electrode or the negative electrode active material layer contains metallic lithium in all states, including a charged state and a discharged state.

[0089] 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.

[0090] The negative electrode active material layer is preferably a layer substantially composed 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%. The upper limit of the lithium element content in the negative electrode active material layer may be 100 mass%.

[0091] When the negative electrode active material layer contains a conductive agent, the content of the conductive agent in the negative electrode active material layer is preferably 1% by mass or more and 10% by mass or less, and more preferably 3% by mass or more and 9% by mass or less. The content of the conductive agent in the negative electrode active material layer may be 5% by mass or less, or may be 2% by mass or less. The technology disclosed herein may also be implemented in an embodiment in which the negative electrode active material layer does not contain a conductive agent.

[0092] When the negative electrode active material layer contains a binder, the content of the binder in the negative electrode active material layer is preferably 0.1% by mass to 10% by mass, more preferably 0.5% by mass to 8% by mass. The content of the binder in the negative electrode active material layer may be 5% by mass or less, or may be 2% by mass or less. The technology disclosed herein may also be implemented in an embodiment in which the negative electrode active material layer does not contain a binder.

[0093] When the negative electrode active material layer contains a dispersant, the content of the dispersant in the negative 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 content of the dispersant in the negative electrode active material layer may be 1% by mass or less, or may be 0.1% by mass or less. The technology disclosed herein may also be implemented in an embodiment in which the negative electrode active material layer does not contain a dispersant.

[0094] When the negative electrode active material layer contains a thickener, the content of the thickener in the negative electrode active material layer is preferably 0.1% by mass or more and 10% by mass or less, and more preferably 0.5% by mass or more and 8% by mass or less. The content of the thickener in the negative electrode active material layer may be 5% by mass or less, or may be 2% by mass or less. The technology disclosed herein may also be implemented in an embodiment in which the negative electrode active material layer does not contain a thickener.

[0095] The filler in the negative electrode active material layer may be a component other than the negative electrode active material, conductive agent, binder, dispersant, and thickener, and may be an intentionally contained component. The filler may be contained as a component to fill gaps in the negative electrode active material layer, or may be contained for other purposes. When the negative electrode active material layer contains a filler, the content of the filler in the negative electrode active material layer can be 0.1% by mass or more and 8% by mass or less, and typically 5% by mass or less is preferred, and 2% by mass or less is more preferred. The technology disclosed herein may also be implemented in an embodiment in which the negative electrode active material layer does not contain a filler.

[0096] The negative electrode active material layer may further contain other components in addition to the negative electrode active material, conductive agent, binder, dispersant, thickener, and filler. The other components include those unintentionally present in the negative electrode active material layer. The negative electrode active material layer may also contain unintentionally contained impurities as the other components, as long as the effects of the present invention are achieved. The upper limit of the content of the other components in the negative electrode active material layer may be 10% by mass, 5%, 2%, 1%, 0.1%, or 0.01% by mass. The upper limit of the content of the unintentionally contained components in the negative electrode active material layer may be 10% by mass, 5%, 2%, 1%, 0.1%, or 0.01% by mass. The upper limit of the content of the unintentionally contained impurities in the negative electrode active material layer may be 10% by mass, 5%, 2%, 1%, 0.1%, or 0.01% by mass.

[0097] 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 may be, for example, 5 μm or more and 2,000 μm or less. The lower limit of the average thickness of one negative electrode active material layer in a charged state may be 10 μm, 20 μm, 30 μm, 50 μm, 100 μm, 200 μm, 300 μm, 400 μm, or 600 μm. The upper limit of the average thickness of one negative electrode active material layer in a charged state may be 1,500 μm, 1,200 μm, 800 μm, or 600 μm.

[0098] (Method of manufacturing negative electrode) The negative electrode can be manufactured by a known method. The negative electrode can be manufactured, for example, in the same manner as in the above-described method for manufacturing a positive electrode, by applying a paste-like negative electrode mixture (negative electrode mixture paste) to a negative electrode substrate directly or via an intermediate layer, and then drying the applied mixture to form a negative electrode active material layer. After drying, the negative electrode active material layer may be pressed, for example. When the negative electrode active material is a metal such as metallic lithium, the negative electrode can also be manufactured by laminating a metal foil on the negative electrode substrate directly or via an intermediate layer, and then pressing the metal foil.

[0099] (separator) The separator may be a known separator, such as a separator consisting of only a base layer, or a separator having an inorganic layer containing inorganic particles and a binder formed on one or both surfaces of a base layer.

[0100] Examples of the form of the substrate layer of the separator include woven fabric, nonwoven fabric, porous resin film, etc. Among these forms, porous resin film is preferred from the viewpoint of strength, etc., and nonwoven fabric is preferred from the viewpoint of non-aqueous electrolyte retention, etc. The material of the substrate layer of the separator is not particularly limited as long as it has insulating properties, but resins such as polyolefin (polyethylene, polypropylene, etc.), polyimide, aramid, etc. are preferred.

[0101] Examples of inorganic compounds constituting the inorganic particles include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, calcium oxide, and magnesium oxide; 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; mineral-derived substances such as talc, zeolite, kaolin, bentonite, and mica, or artificial products thereof. One or more types of inorganic particles can be used. The average particle size of the inorganic particles is preferably, for example, from 0.5 μm to 10 μm. The content of the inorganic particles in the inorganic layer is preferably from 50% to 99% by mass, and more preferably from 80% to 98% by mass.

[0102] Examples of binders used in the inorganic layer include the same binders as those exemplified for the positive electrode active material layer.

[0103] The porosity of the separator may be, for example, 20% or more and 80% or less. The lower limit of the porosity of the separator may be 30%, 40%, or 50% from the viewpoint of discharge performance, etc. The upper limit of the porosity of the separator may be 70%, 60%, or 50% from the viewpoint of strength, etc. In this specification, "porosity" refers to a volume-based value measured with a mercury porosimeter.

[0104] The average thickness of the separator may be, for example, 10 μm or more and 40 μm or less, or 15 μm or more and 30 μm or less.

[0105] The separator may be a polymer gel composed of a polymer and a non-aqueous electrolyte, or may be a combination of the porous resin film, nonwoven fabric, or the like described above and a polymer gel.

[0106] (electrode body) As the electrode body, for example, a wound type electrode body, a laminated type electrode body, or other electrode body having a known structure can be used.

[0107] A wound electrode body has a structure in which a positive electrode and a negative electrode are wound in an insulated state. The wound electrode body may be cylindrical (columnar) or flat. The electrode body 2 provided in the nonaqueous electrolyte storage element 1 of FIG. 1 is a flat wound electrode body. The wound electrode body can be produced, for example, by the following procedure. First, a positive electrode, a separator, and a negative electrode, each formed in a strip shape, are stacked together to obtain a laminate. This laminate is then wound to obtain a wound electrode body.

[0108] A laminated electrode body has a structure in which one or more positive electrodes and one or more negative electrodes are stacked in an insulated state. For example, a laminated electrode body can be obtained by stacking a positive electrode, a separator, and a negative electrode, each of which is formed in a rectangular shape.

[0109] As the electrode body, for example, one having a structure in which at least one of the positive electrode and the negative electrode is folded in an accordion-like manner and stacked can also be used.

[0110] (non-aqueous electrolyte) The nonaqueous electrolyte is a medium responsible for transporting charge-transporting ions (e.g., lithium ions) between a positive electrode and a negative electrode, and is substantially free of water. The water content in the nonaqueous electrolyte may be, for example, 10,000 ppm or less, or 5,000 ppm or less. The nonaqueous electrolyte includes an electrolyte salt, an ionic liquid, and a nonaqueous solvent. The nonaqueous solvent may be a nonionic compound. The nonaqueous electrolyte may be a nonaqueous electrolyte solution. In one embodiment of the present invention, the nonaqueous electrolyte storage element may be a nonaqueous electrolyte solution storage element.

[0111] The electrolyte salt refers to an ionic compound in which the cation is a charge-transporting ion and which is solid at room temperature (20°C) under 1 atmosphere. Known electrolyte salts can be used. Examples of the electrolyte salt include lithium salt, sodium salt, potassium salt, magnesium salt, and onium salt. Of these, lithium salt is preferred. One or more types of electrolyte salts can be used.

[0112] The anions that make up the electrolyte salt are N(CF3SO2)2 - (Bis(trifluoromethanesulfonyl)imide anion: TFSI - ), N(SO2F)2 - (Bis(fluorosulfonyl)imide anion: FSI - ), N(C2F5SO2)2 - (bis(pentafluoroethanesulfonyl)imide anion), N(C4F9SO2)2 - (bis(nonafluorobutanesulfonyl)imide anion), N(POF2)2 - (bis(difluorophosphonyl)imide anion), N(CF3SO2)(CF3CO) - ((Trifluoromethanesulfonyl)(trifluoromethanecarbonyl)imide anion), N(CN)2 - (dicyanoimide anion), CF3-SO2-N-SO2-N-SO2CF3 - , FSO2-N-SO2-C4F9 - , CF3-SO2-N-SO2-C4F9 - , CF3-SO2-N-SO2-CF2-SO2-N-SO2-CF3 2- , CF3-SO2-N-SO2-CF2-SO3 2- , CF3-SO2-N-SO2-CF2-SO2-C(-SO2CF3)2 2- Examples of the anions that make up the electrolyte salt include imide anions such as PF6 - , PO2F2 - , BF4 - , ClO4 - , NO2 - , NO3 - , I- , SO3CF3 - , C(SO2CF3)3 - , C(SO2C2F5)3 - Anions other than imide anions such as the above can also be used.

[0113] The anion constituting the electrolyte salt is preferably an imide anion, and more preferably a bis(trifluoromethanesulfonyl)imide anion (TFSI - ) and bis(fluorosulfonyl)imide anion (FSI - ), and bis(fluorosulfonyl)imide anion (FSI - ) is more preferred. That is, the electrolyte salt is preferably an imide salt, more preferably at least one selected from the group consisting of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium bis(fluorosulfonyl)imide (LiFSI), and even more preferably lithium bis(fluorosulfonyl)imide (LiFSI). In addition, the anion constituting the electrolyte salt preferably has a fluorine atom. When the anion constituting the electrolyte salt is such an anion, the ionic conductivity of the non-aqueous electrolyte is increased, and the high-rate discharge performance of the non-aqueous electrolyte storage element can be further improved and the discharge capacity can be increased. One or more types of electrolyte salts can be used.

[0114] The molar concentration of the electrolyte salt in the non-aqueous electrolyte may be, for example, 0.3 mol / kg or more and 3.5 mol / kg or less. The lower limit of the molar concentration of the electrolyte salt is preferably 0.5 mol / kg, more preferably 0.8 mol / kg, and may be 1.1 mol / kg, 1.3 mol / kg, 1.5 mol / kg, 1.8 mol / kg, or 2.0 mol / kg. The upper limit of the molar concentration of the electrolyte salt is preferably 3.0 mol / kg, and may be 2.8 mol / kg, 2.5 mol / kg, 2.2 mol / kg, 2.0 mol / kg, or 1.5 mol / kg. By setting the molar concentration of the electrolyte salt within the above range, the ionic conductivity of the non-aqueous electrolyte is optimized, and the high-rate discharge performance of the non-aqueous electrolyte storage element can be further improved and the discharge capacity can be increased. From the viewpoint of particularly sufficiently reducing the viscosity of the non-aqueous electrolyte, the upper limit of the molality of the electrolyte salt may be, for example, 2.5 mol / kg, 2.2 mol / kg, 2.0 mol / kg, or 1.5 mol / kg. In this specification, the molality refers to the amount of substance (mol) of the electrolyte salt based on the total mass (kg) of the ionic liquid and the non-aqueous solvent.

[0115] An ionic liquid is an ionic compound that is at least partially liquid at room temperature (20°C) under 1 atmosphere.

[0116] Examples of cations constituting the ionic liquid include quaternary ammonium cations, imidazolium-based cations, pyrrolidinium-based cations, piperidinium-based cations, pyridinium-based cations, pyrrolium-based cations, pyrazolium-based cations, pyrrolinium-based cations, quaternary phosphonium cations, and sulfonium cations.

[0117] Examples of the quaternary ammonium cation include tetraalkylammonium cations such as trimethylethylammonium cation, trimethylpropylammonium cation, trimethylbutylammonium cation, trimethylhexylammonium cation, and tetrapentylammonium cation.

[0118] Examples of imidazolium cations include 1,3-dimethylimidazolium cation, 1-ethyl-3-methylimidazolium cation, 1,3-diethylimidazolium cation, 1-butyl-3-methylimidazolium cation, 1,2,3-trimethylimidazolium cation, 1,2-dimethyl-3-ethylimidazolium cation, 1,2-dimethyl-3-propylimidazolium cation, and 1-butyl-2,3-dimethylimidazolium cation.

[0119] Examples of pyrrolidinium cations include 1,1-dimethylpyrrolidinium cation, 1-ethyl-1-methylpyrrolidinium cation, 1-methyl-1-propylpyrrolidinium cation, and 1-butyl-1-methylpyrrolidinium cation.

[0120] Examples of piperidinium cations include 1,1-dimethylpiperidinium cation, 1-ethyl-1-methylpiperidinium cation, 1-methyl-1-propylpiperidinium cation, and 1-butyl-1-methylpiperidinium cation.

[0121] Examples of pyridinium cations include 1-methylpyridinium cation, 1-ethylpyridinium cation, 1-propylpyridinium cation, 1-butylpyridinium cation, 1-ethyl-2-methylpyridinium cation, 1-butyl-4-methylpyridinium cation, and 1-butyl-2,4-dimethylpyridinium cation.

[0122] Examples of pyrrolium-based cations include 1,1-dimethylpyrrolium cation, 1-ethyl-1-methylpyrrolium cation, 1-methyl-1-propylpyrrolium cation, and 1-butyl-1-methylpyrrolium cation.

[0123] Examples of pyrazolium cations include 1,2-dimethylpyrazolium cation, 1-ethyl-2-methylpyrazolium cation, 1-propyl-2-methylpyrazolium cation, and 1-butyl-2-methylpyrazolium cation.

[0124] Examples of pyrrolinium-based cations include 1,2-dimethylpyrrolinium cation, 1-ethyl-2-methylpyrrolinium cation, 1-propyl-2-methylpyrrolinium cation, and 1-butyl-2-methylpyrrolinium cation.

[0125] Examples of the quaternary phosphonium cation include a tetramethylphosphonium cation, a tetraethylphosphonium cation, a trimethylethylphosphonium cation, a trimethylpropylphosphonium cation, a trimethylbutylphosphonium cation, a tetraphenylphosphonium cation, and a trimethylmethoxymethylphosphonium cation.

[0126] Examples of the sulfonium cation include a trimethylsulfonium cation, a triethylsulfonium cation, and a tributylsulfonium cation.

[0127] The cation constituting the ionic liquid is preferably at least one selected from the group consisting of quaternary ammonium cations, imidazolium cations, pyrrolidinium cations, piperidinium cations, quaternary phosphonium cations, and sulfonium cations, more preferably at least one selected from the group consisting of imidazolium cations, pyrrolidinium cations, and piperidinium cations, and even more preferably a pyrrolidinium cation. When the cation constituting the ionic liquid is such a cation, it is possible to further improve the high-rate discharge performance and increase the discharge capacity of the nonaqueous electrolyte storage element. One or more of these cations may be contained.

[0128] Examples of anions constituting the ionic liquid include the same anions as those constituting the electrolyte salt. As an anion constituting the ionic liquid, imide anions are preferred, and bis(trifluoromethanesulfonyl)imide anion (TFSI - ) and bis(fluorosulfonyl)imide anion (FSI - ), and bis(fluorosulfonyl)imide anion (FSI - ) is more preferable. Furthermore, the anion constituting the ionic liquid preferably has a fluorine atom. When the anion constituting the ionic liquid is such an anion, the high-rate discharge performance of the nonaqueous electrolyte energy storage element can be further improved, and the discharge capacity can be increased. One or more of these anions may be contained.

[0129] At least one of the electrolyte salt and the ionic liquid contains a bis(fluorosulfonyl)imide anion (FSI - It is preferable that the non-aqueous electrolyte contains a bis(fluorosulfonyl)imide anion (FSI) as an anion. - In this case, the high-rate discharge performance of the nonaqueous electrolyte electricity storage element can be further improved, and the discharge capacity can be increased.

[0130] In addition, it is preferable that the anions present in the non-aqueous electrolyte are substantially only imide anions, and the anions present in the non-aqueous electrolyte are substantially bis(trifluoromethanesulfonyl)imide anions (TFSI - ) and bis(fluorosulfonyl)imide anion (FSI - ) is more preferably at least one selected from the group consisting of. For example, the content of these anions relative to all anions in the non-aqueous electrolyte is preferably 90 mol % or more, more preferably 99 mol % or more, and even more preferably 99.9 mol % or more. By configuring the anions in the non-aqueous electrolyte in this way, the ionic conductivity of the non-aqueous electrolyte can be increased, and the high-rate discharge performance and discharge capacity of the non-aqueous electrolyte storage element can be further improved.

[0131] The lower limit of the content of the ionic liquid relative to the total of the ionic liquid and the non-aqueous solvent is preferably 5% by volume, more preferably 7% by volume, and may be 10%, 20%, or 30% by volume. The upper limit of the content is preferably 90% by volume, more preferably 80% by volume, and even more preferably 70% by volume, and may be 60%, 50%, 40%, 30%, 20%, or 10% by volume. By keeping the content of the ionic liquid within the above range, it is possible to further improve the high-rate discharge performance and increase the discharge capacity of the non-aqueous electrolyte storage element.

[0132] The non-aqueous solvent contains a fluorinated cyclic ether represented by the following formula (1). [ka] (In formula (1), R 1 are each independently a hydrogen atom, a fluorine atom, an alkyl group having 1 to 4 carbon atoms, or a fluorinated alkyl group having 1 to 4 carbon atoms. 1 At least one of the groups is a fluorine atom or a fluorinated alkyl group having 1 to 4 carbon atoms. n1 is an integer of 2 to 5.

[0133] R in the above formula (1) 1 When R is an alkyl group or a fluorinated alkyl group, it preferably has 3 or less carbon atoms, more preferably 2 or less carbon atoms. 1 are each independently a hydrogen atom or a fluorine atom, and at least one is preferably a fluorine atom. n1 is preferably 4 or 5, and more preferably 4.

[0134] The lower limit of the number of fluorine atoms in the fluorinated cyclic ether is preferably 2, more preferably 3, and even more preferably 4. The upper limit of the number of fluorine atoms is preferably 10, more preferably 8, more preferably 6, and even more preferably 4.

[0135] The fluorinated cyclic ether is preferably 3,3,4,4-tetrafluorotetrahydrofuran. One or more of the fluorinated cyclic ethers can be used.

[0136] The lower limit of the total content of the ionic liquid and the fluorinated cyclic ether relative to the total of the ionic liquid and the non-aqueous solvent is preferably 10% by volume, more preferably 15% by volume, and even more preferably 20% by volume, and may be 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, or 80% by volume. By setting the total content at or above the lower limit, it is possible to increase the discharge capacity of the non-aqueous electrolyte storage element and improve the capacity retention rate after charge / discharge cycling. The upper limit of the total content is preferably 95% by volume, and may be 90%, 85%, 80%, 75%, 70%, 65%, 60%, 55%, 50%, 45%, 40%, 35%, or 30% by volume.

[0137] The lower limit of the content of the fluorinated cyclic ether relative to the total of the ionic liquid and the non-aqueous solvent is preferably 5% by volume, more preferably 10% by volume, even more preferably 20% by volume, and even more preferably 30% by volume. By setting the content at or above the lower limit, it is possible to increase the discharge capacity of the non-aqueous electrolyte storage element and improve the capacity retention rate after charge / discharge cycling. The lower limit of the content may be 40%, 50%, 60%, or 70% by volume. The upper limit of the content is preferably 90%, more preferably 80%, and even more preferably 70%, and may be 60%, 50%, 40%, or 30% by volume.

[0138] The nonaqueous solvent includes a nonaqueous solvent other than the fluorinated cyclic ether represented by the above formula (1). Examples of the other nonaqueous solvent include ethers other than the above fluorinated cyclic ethers, cyclic carbonates, chain carbonates, ethers, carboxylic acid esters, phosphate esters, amides, and nitriles.

[0139] The other nonaqueous solvent preferably has a donor number of 14 or more and 30 or less. The lower limit of the donor number is more preferably 15, even more preferably 16, and may be 17, 18, 19, 20, 21, or 22. Use of an other nonaqueous solvent having a donor number equal to or greater than the lower limit can enhance the dissociation of charge-transporting ions in the nonaqueous electrolyte, thereby further improving the high-rate discharge performance of the nonaqueous electrolyte storage element. The donor number of the other nonaqueous solvent is preferably greater than the donor number of the fluorinated cyclic ether represented by Formula (1). The upper limit of the donor number of the other nonaqueous solvent is more preferably 27, even more preferably 25, and may be 24, 23, 22, 21, 20, 19, 18, or 17. Use of an other nonaqueous solvent having a donor number equal to or less than the upper limit can particularly sufficiently suppress elution of polysulfides from the positive electrode to the nonaqueous electrolyte, thereby increasing the discharge capacity of the nonaqueous electrolyte storage element and improving the capacity retention rate after charge-discharge cycling.

[0140] The other nonaqueous solvent preferably has a viscosity of less than 1.0 mPa·s at 25°C. By using an other nonaqueous solvent with a viscosity below the above upper limit, the viscosity of the nonaqueous electrolyte can be particularly sufficiently reduced, and the high-rate discharge performance of the nonaqueous electrolyte storage element can be further improved. The viscosity is more preferably 0.9 mPa·s or less, and even more preferably 0.85 mPa·s or less. Furthermore, the viscosity of the other nonaqueous solvent at 25°C is preferably lower than the viscosity of the fluorinated cyclic ether represented by the above formula (1) at 25°C. The lower limit of the viscosity of the other nonaqueous solvent at 25°C may be, for example, 0.1 mPa·s, 0.3 mPa·s, 0.5 mPa·s, or 0.7 mPa·s.

[0141] The other nonaqueous solvent is preferably an ether other than the above-mentioned fluorinated cyclic ether. Such ethers include fluorinated cyclic ethers other than the fluorinated cyclic ether represented by the above formula (1), non-fluorinated cyclic ethers, and chain ethers. Among the other ethers, the other nonaqueous solvent is more preferably at least one selected from the group consisting of non-fluorinated cyclic ethers and chain ethers. When the other nonaqueous solvent is such a solvent, the high-rate discharge performance of the nonaqueous electrolyte storage element can be further improved.

[0142] The non-fluorinated cyclic ether may be a cyclic ether composed only of carbon, hydrogen, and oxygen. The oxygen element contained in the non-fluorinated cyclic ether is preferably only the oxygen element constituting the ether bond. In other words, the non-fluorinated cyclic ether preferably does not have an oxygen-containing substituent such as a hydroxy group or a carboxy group. The non-fluorinated cyclic ether may be any of a monoether (a compound having only one ether bond), a diether (a compound having two ether bonds), a triether (a compound having three ether bonds), etc., but is preferably a monoether. The non-fluorinated cyclic ether preferably has an ether bond in the ring structure. The non-fluorinated cyclic ether is preferably a saturated ether.

[0143] The lower limit of the number of ring members in the ring structure of the non-fluorinated cyclic ether is preferably 3, more preferably 4, and even more preferably 5. The upper limit of the number of ring members is preferably 8, more preferably 7, and even more preferably 6. The lower limit of the number of carbon atoms in the non-fluorinated cyclic ether is preferably 2, more preferably 3, and even more preferably 4. The upper limit of the number of carbon atoms is preferably 7, more preferably 6, and even more preferably 5.

[0144] The non-fluorinated cyclic ether is preferably represented by the following formula (2). [ka] (In formula (2), R 2are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and n2 is an integer of 2 to 5.

[0145] R in the above formula (2) 2 When R is an alkyl group, it preferably has 3 or less carbon atoms, more preferably 2 or less carbon atoms. 2 is preferably a hydrogen atom. n2 is preferably 4 or 5, and more preferably 4.

[0146] Examples of non-fluorinated cyclic ethers include tetrahydrofuran, tetrahydropyran, etc. One or more non-fluorinated cyclic ethers can be used.

[0147] The lower limit of the content of the non-fluorinated cyclic ether relative to the total of the ionic liquid and the non-aqueous solvent is preferably 5% by volume, more preferably 10% by volume, and even more preferably 20% by volume. By setting the content at or above the lower limit, it is possible to further improve the high-rate discharge performance of the non-aqueous electrolyte storage element. The lower limit of the content may be 30% by volume or 40% by volume. The upper limit of the content of the non-fluorinated cyclic ether relative to the total of the ionic liquid and the non-aqueous solvent is preferably 90% by volume, and may be 80%, 70%, 60%, 50%, 40%, 30%, 25%, or 20% by volume. By setting the content at or below the upper limit, it is possible to increase the discharge capacity of the non-aqueous electrolyte storage element and improve the capacity retention rate after charge / discharge cycling.

[0148] The chain ether may be a fluorinated chain ether or a non-fluorinated chain ether, but is preferably a fluorinated chain ether. The chain ether may be composed only of carbon, hydrogen, and oxygen elements, or may be composed only of carbon, hydrogen, oxygen, and fluorine elements. The oxygen element contained in the chain ether is preferably only the oxygen element constituting the ether bond. In other words, the chain ether preferably does not have an oxygen-containing substituent such as a hydroxy group or a carboxy group. The chain ether may be any of a monoether, diether, triether, etc., but is preferably a diether. The chain ether may be a fluorinated chain diether. The chain ether is preferably a saturated ether.

[0149] The lower limit of the number of carbon atoms in the chain ether is preferably 3, more preferably 4, and even more preferably 5. The upper limit of the number of carbon atoms is preferably 8, more preferably 7, and even more preferably 6. The lower limit of the number of fluorine atoms in the chain ether is preferably 2, and more preferably 3. The upper limit of the number of fluorine atoms is preferably 8, and even more preferably 7, 6, 5, 4, or 3.

[0150] The chain ether is preferably represented by the following formula (3). [ka] (In formula (3), R 3 and R 4 are each independently an alkyl group having 1 to 3 carbon atoms or a fluorinated alkyl group having 1 to 3 carbon atoms. 5 is an alkanediyl group having 1 to 3 carbon atoms; and n3 is 0 or 1.

[0151] R in the above formula (3) 3 R is preferably an alkyl group, more preferably a methyl group or an ethyl group. 4R is preferably a fluorinated alkyl group, more preferably a fluorinated methyl group or a fluorinated ethyl group, even more preferably a fluorinated ethyl group, and even more preferably a 2,2,2-trifluoroethyl group. 5 As -(CH2) m n3 is preferably - (m is an integer of 1 or more and 3 or less), and more preferably -CH2CH2-.

[0152] Examples of chain ethers include 2-(2,2,2-trifluoroethoxy)ethyl methyl ether, ethyl-2-(2,2,2-trifluoroethoxy)ethyl ether, 2-(2,2-difluoroethoxy)ethyl methyl ether, ethyl-2-(2,2-difluoroethoxy)ethyl ether, 2-(2-fluoroethoxy)ethyl methyl ether, ethyl-2-(2-fluoroethoxy)ethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, etc. One or more types of chain ethers can be used.

[0153] The lower limit of the content of the chain ether relative to the total of the ionic liquid and the non-aqueous solvent is preferably 5% by volume, more preferably 10% by volume, and even more preferably 20% by volume. By setting the content at or above the lower limit, it is possible to further improve the high-rate discharge performance of the non-aqueous electrolyte storage element. The lower limit of the content may be 30%, 40%, 50%, 60%, or 70% by volume. The upper limit of the content of the chain ether relative to the total of the ionic liquid and the non-aqueous solvent is preferably 90% by volume, and may be 80%, 70%, 60%, 50%, 40%, 30%, 25%, or 20% by volume. By setting the content at or below the upper limit, it is possible to increase the discharge capacity of the non-aqueous electrolyte storage element and improve the capacity retention rate after charge / discharge cycling.

[0154] The lower limit of the total content of the non-fluorinated cyclic ether and the chain ether relative to the total of the ionic liquid and the non-aqueous solvent is preferably 5% by volume, more preferably 10% by volume, and even more preferably 20% by volume. By setting the total content at or above the lower limit, it is possible to further improve the high-rate discharge performance of the non-aqueous electrolyte storage element. The lower limit of the total content may be 30%, 40%, 50%, 60%, or 70% by volume. The upper limit of the total content of the non-fluorinated cyclic ether and the chain ether relative to the total of the ionic liquid and the non-aqueous solvent is preferably 90% by volume, and may be 80%, 70%, 60%, 50%, 40%, 30%, 25%, or 20% by volume. By setting the total content at or below the upper limit, it is possible to increase the discharge capacity of the non-aqueous electrolyte storage element and improve the capacity retention rate after charge / discharge cycling.

[0155] The lower limit of the content of the other nonaqueous solvent (a nonaqueous solvent other than the fluorinated cyclic ether represented by Formula (1)) relative to the total of the ionic liquid and the nonaqueous solvent is preferably 5% by volume, more preferably 10% by volume, and even more preferably 20% by volume. By setting the content at or above the lower limit, it is possible to further improve the high-rate discharge performance of the nonaqueous electrolyte storage element. The lower limit of the content may be 30%, 40%, 50%, 60%, or 70% by volume. The upper limit of the content of the other nonaqueous solvent relative to the total of the ionic liquid and the nonaqueous solvent is preferably 90% by volume, or may be 80%, 70%, 60%, 50%, 40%, 30%, 25%, or 20% by volume. By setting the content at or below the upper limit, it is possible to increase the discharge capacity of the nonaqueous electrolyte storage element and improve the capacity retention rate after charge-discharge cycling.

[0156] The non-aqueous solvent is preferably composed mainly of ether. The content of ether (the above-mentioned fluorinated cyclic ether and other ether) in the non-aqueous solvent may be 90% by volume or more, 95% by volume or more, or 99% by volume or more. When the non-aqueous solvent is composed mainly of ether, the discharge capacity of the non-aqueous electrolyte storage element tends to be large. The upper limit of the content of ether in the non-aqueous solvent may be 100% by volume. In one embodiment of the present invention, the non-aqueous solvent may be composed essentially of ether only, or the non-aqueous solvent may consist solely of ether.

[0157] The total content of the ionic liquid and the ether (the fluorinated cyclic ether and other ethers) relative to the total of the ionic liquid and the non-aqueous solvent may be 90% by volume or more, 95% by volume or more, or 99% by volume or more, and the upper limit of the total content may be 100% by volume.

[0158] The total content of the ionic liquid and the ether (the fluorinated cyclic ether and other ethers) relative to all components other than the electrolyte salt in the non-aqueous electrolyte may be 90% by volume or more, 95% by volume or more, or 99% by volume or more. When the non-aqueous electrolyte is thus primarily composed of the electrolyte salt, the ionic liquid, and the ether as the non-aqueous solvent, the discharge capacity of the non-aqueous electrolyte storage element tends to be large. The upper limit of the total content may be 100% by volume.

[0159] The non-aqueous electrolyte may contain other components in addition to the electrolyte salt, ionic liquid, and non-aqueous solvent. Examples of other components include additives.

[0160] One or more additives can be used. When an additive is used in the non-aqueous electrolyte, the content of the additive 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.

[0161] The upper limit of the viscosity of the non-aqueous electrolyte at 25°C is preferably 19 mPa·s, more preferably 18 mPa·s, even more preferably 17 mPa·s, and even more preferably 16 mPa·s, and may be 15 mPa·s, 14 mPa·s, 13 mPa·s, 12 mPa·s, 11 mPa·s, or 10 mPa·s. When the viscosity of the non-aqueous electrolyte is equal to or less than the upper limit, the high-rate discharge performance of the non-aqueous electrolyte storage element tends to be further improved. The lower limit of the viscosity may be, for example, 1 mPa·s, or may be 3 mPa·s, 5 mPa·s, 7 mPa·s, 9 mPa·s, or 10 mPa·s.

[0162] (container) The container accommodates the electrode assembly and the non-aqueous electrolyte in its internal space. The container may be made of a metal material such as aluminum or stainless steel, or a resin material. Metal materials are preferred from the viewpoint of strength, etc. Composite materials of metal and resin may also be used.

[0163] The shape of the container is not particularly limited, and may be cylindrical, rectangular (square), disk-like, etc. The container may also be in the shape of a sheet formed from a metal resin composite film.

[0164] (shape, use, etc. of non-aqueous electrolyte storage element) The shape of the nonaqueous electrolyte storage element according to one embodiment of the present invention is not particularly limited, and may be, for example, a cylindrical battery, a prismatic battery, a flat battery, a coin battery, a button battery, or the like.

[0165] The use of the nonaqueous electrolyte electricity storage element according to one embodiment of the present invention is not particularly limited, and the nonaqueous electrolyte electricity storage element can be used, for example, as a power source for automobiles such as electric vehicles, hybrid vehicles, and plug-in hybrid vehicles, a power source for electronic devices such as personal computers and communication terminals, a power source for power storage, etc.

[0166] The nonaqueous electrolyte electricity storage element of the present invention may be used singly or in plural. When the required output and required voltage are small, the nonaqueous electrolyte electricity storage element may be used singly. On the other hand, when at least one of the required output and required voltage is large, the nonaqueous electrolyte electricity storage element may be used as an electricity storage device in combination with other nonaqueous electrolyte electricity storage elements. In an electricity storage device in which a plurality of nonaqueous electrolyte electricity storage elements are combined, at least one nonaqueous electrolyte electricity storage element included in the electricity storage device may be the nonaqueous electrolyte electricity storage element according to one embodiment of the present invention. The electricity storage device will be described in detail later.

[0167] In a nonaqueous electrolyte energy storage element according to one embodiment of the present invention, for example, the container may be constrained so as to maintain a constant thickness, or may not be constrained in this manner. Alternatively, the container may be constrained so as to apply a constant load to it. When the container is constrained, expansion of the container due to charge / discharge cycles, etc., may be suppressed, and deterioration of charge / discharge performance may be suppressed. When the container is constrained, a load may or may not be applied to the electrode assembly within the container. For example, a constraining member that performs such constraining may be provided in the nonaqueous electrolyte energy storage element or the energy storage device.

[0168] <Method of manufacturing nonaqueous electrolyte energy storage element> A nonaqueous electrolyte storage element according to one embodiment of the present invention can be manufactured by a known method. The manufacturing method of the nonaqueous electrolyte storage element includes, for example, preparing a positive electrode containing a sulfur-based active material, preparing a negative electrode, preparing a nonaqueous electrolyte containing an electrolyte salt, an ionic liquid, and a nonaqueous solvent, and housing the positive electrode, negative electrode, and nonaqueous electrolyte in a container. The manufacturing method may also include preparing a separator, and manufacturing an electrode assembly using the positive electrode, negative electrode, and separator. The nonaqueous solvent of the prepared nonaqueous electrolyte includes the fluorinated cyclic ether represented by the above formula (1) and another nonaqueous solvent. Housing the positive electrode, negative electrode, and nonaqueous electrolyte in a container may also mean housing the electrode assembly and nonaqueous electrolyte in a container.

[0169] Preparing a positive electrode may mean manufacturing a positive electrode. Manufacturing a positive electrode can be performed by the method described above. Preparing a negative electrode may mean manufacturing a negative electrode. Manufacturing a negative electrode can be performed by the method described above. Preparing a non-aqueous electrolyte may mean preparing a non-aqueous electrolyte. Specific and preferred forms of the prepared positive electrode, negative electrode, non-aqueous electrolyte, etc. are the same as the specific and preferred forms of the positive electrode, negative electrode, non-aqueous electrolyte, etc. provided in the non-aqueous electrolyte storage element according to one embodiment of the present invention described above. The positive electrode, negative electrode, separator, non-aqueous electrolyte, etc. may be prepared by purchasing, etc.

[0170] The electrode assembly (or the positive electrode and negative electrode) and the non-aqueous electrolyte can be housed in a container by a known method. When the non-aqueous electrolyte is a non-aqueous electrolyte solution, for example, the electrode assembly (or the positive electrode and negative electrode) is first housed in a container, and then the non-aqueous electrolyte solution is poured into the container through an inlet provided in the container. The inlet is sealed after the non-aqueous electrolyte solution is poured into the container. The method for producing the non-aqueous electrolyte storage element may further include initially charging and discharging the assembled uncharged / discharged storage element. In this production method, the initial charging and discharging usually starts with discharging. The number of charging and discharging cycles in the initial charging and discharging is not particularly limited.

[0171] The nonaqueous electrolyte electricity storage element according to one embodiment of the present invention may be manufactured by other methods.

[0172] <Electricity storage device> 2 includes a plurality of energy storage units 20. Each energy storage unit 20 includes a plurality of electrically connected nonaqueous electrolyte energy storage elements 1. The energy storage device 30 may include a bus bar (not shown) that electrically connects the plurality of nonaqueous electrolyte energy storage elements 1, a bus bar (not shown) that electrically connects the plurality of energy storage units 20, and the like. The energy storage unit 20 or the energy storage device 30 may include a state monitoring device (not shown) that monitors the state of one or more nonaqueous electrolyte energy storage elements 1.

[0173] <Other embodiments> The nonaqueous electrolyte storage element and the method for manufacturing a nonaqueous electrolyte storage element of the present invention are 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.

[0174] In the above embodiment, the nonaqueous electrolyte storage element is used as a chargeable and dischargeable nonaqueous electrolyte secondary battery, but the nonaqueous electrolyte storage element may be of any type, shape, size, capacity, etc. The present invention can also be applied to various secondary batteries, electric double layer capacitors, lithium ion capacitors, and other capacitors.

[0175] In the above embodiment, the electrode assembly is described in which a separator is interposed between the positive electrode and the negative electrode. However, 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, with a non-conductive layer formed on the active material layer of the positive electrode or the negative electrode. In this way, the positive electrode and the negative electrode may further include layers other than the substrate, the intermediate layer, and the active material layer. Furthermore, the positive electrode and the negative electrode may not have a layer structure. [Example]

[0176] 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.

[0177] The components used in preparing the non-aqueous electrolytes of the Examples and Comparative Examples are shown below. The donor numbers and viscosities at 25° C. of the ionic liquid and non-aqueous solvent, determined by the above-mentioned methods, are also shown. (electrolyte salt) LiFSI: Lithium bis(fluorosulfonyl)imide (ionic liquid) Py13FSI: 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide (donor number 13.0, viscosity 41.1 mPa s) (non-aqueous solvent) TFTHF: 3,3,4,4-tetrafluorotetrahydrofuran (donor number 13.2, viscosity 1.01 mPa s) THF: tetrahydrofuran (donor number 23.8, viscosity 0.82 mPa·s) THP: tetrahydropyran (donor number 22.5, viscosity 0.84 mPa s) TFEME: 2-(2,2,2-trifluoroethoxy)ethyl methyl ether (donor number 18.7, viscosity 0.82 mPa·s) ETFEEE: Ethyl 2-(2,2,2-trifluoroethoxy)ethyl ether (donor number 17.2, viscosity not measured)

[0178] [Example 1] (Preparation of positive electrode) Elemental sulfur and porous carbon, which are sulfur-based active materials, 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 mixture was heated to 150°C at a rate of 5°C / min and held for 5 hours. After cooling to 80°C, the temperature at which elemental sulfur solidifies, the mixture was again heated to 300°C at a rate of 5°C / min and held for 2 hours to produce a composite (sulfur-porous carbon composite: SPC). A positive electrode mixture paste containing the composite obtained above, acetylene black and carbon nanotubes as conductive agents, carboxymethyl cellulose as a dispersant, polyacrylic acid as a thickener, and styrene-butadiene rubber as a binder, was applied to an aluminum positive electrode substrate (average thickness 15 μm) and dried. Note that the mass per unit area of ​​the positive electrode active material layer after drying of the dispersion medium was 10 mg / cm. 2 The amount of the positive electrode mixture paste applied was adjusted so that the following was achieved: By the above steps, a positive electrode in which a positive electrode active material layer was laminated on a positive electrode substrate was obtained.

[0179] (Preparing the negative electrode) A pure metallic lithium foil (average thickness 600 μm) was prepared as the negative electrode.

[0180] (Preparation of non-aqueous electrolyte) A non-aqueous electrolyte was prepared by mixing an ionic liquid, Py13FSI, a fluorinated cyclic ether represented by the above formula (1), TFTHF, and another non-aqueous solvent, THF, in a volume ratio of 10:70:20, and adding an electrolyte salt, LiFSI, at a molar concentration of 1.5 mol / kg to the mixture.

[0181] (Assembly of non-aqueous electrolyte energy storage element) The separator was prepared by laminating inorganic particle layers on both sides of a polyethylene microporous membrane, and had such high wettability that the nonaqueous electrolyte could penetrate into the pores. The nonaqueous electrolyte storage element of Example 1 was obtained using the positive electrode, negative electrode, separator, and nonaqueous electrolyte.

[0182] [Examples 2 to 9, Comparative Example 1, Reference Examples 1 to 3] Non-aqueous electrolyte storage elements of Examples 2 to 9, Comparative Example 1 and Reference Examples 1 to 3 were obtained in the same manner as in Example 1, except that the compositions of the non-aqueous electrolytes were as shown in Table 1.

[0183] The viscosity of the nonaqueous electrolyte at 25° C. in each of the nonaqueous electrolyte storage elements of Examples 4 and 6 and Comparative Example 1 was measured by the method described above. The measurement results are shown in Table 1.

[0184] [evaluation] (Initial charge / discharge) The obtained nonaqueous electrolyte storage elements of Examples, Comparative Examples, and Reference Examples were subjected to the following initial charge / discharge in a constant temperature bath at 25°C. First, a constant current (CC) discharge was performed as the initial discharge under conditions of a discharge current of 0.05C and a discharge cut-off voltage of 1.0V. Then, a constant current / constant voltage (CCCV) charge was performed as the initial charge under conditions of a charge current of 0.05C and a charge cut-off voltage of 3.0V for a total charge time of 30 hours. Next, a constant current (CCCV) discharge was performed as the second discharge under conditions of a discharge current of 0.05C and a discharge cut-off voltage of 1.0V. Note that 1C was 1675mAh / g. A 10-minute pause was provided after the initial discharge and the initial charge. The quantity of electricity (discharge capacity) in each of the two discharges was divided by the mass of the sulfur-based active material (sulfur elemental substance) to obtain the discharge capacity. Each discharge capacity is shown in Table 1.

[0185] (Charge-discharge cycle test) The nonaqueous electrolyte storage elements of Examples, Comparative Examples, and Reference Examples, which had undergone initial charge and discharge, were subjected to the following charge and discharge cycle test in a thermostatic chamber at 25°C. The nonaqueous electrolyte storage elements of Reference Examples 1 and 2 were not subjected to a charge and discharge cycle test because a short circuit occurred during the initial charge and discharge. The nonaqueous electrolyte storage element of Example 5 was also not subjected to a charge and discharge cycle test. Constant-current, constant-voltage (CCCV) charging was performed under conditions of a charge current of 0.05 C and a charge cut-off voltage of 3.0 V for a total charge time of 30 hours. Next, constant-current (CC) discharging was performed under conditions of a discharge current of 0.1 C and a discharge cut-off voltage of 1.0 V. A 10-minute pause was provided after each charge and discharge. The above charge and discharge cycles were repeated 10 times. The capacity retention rate after charge-discharge cycling was calculated as the percentage of the discharge capacity at the 10th cycle to the discharge capacity at the 1st cycle in the "charge-discharge cycle test." The results are shown in Table 1.

[0186] (High rate discharge test) For each of the nonaqueous electrolyte storage elements of the Examples and Comparative Examples that had undergone initial charging and discharging, a discharge test was first conducted at 0.05 C in a thermostatic chamber at 25°C as follows: Constant current / constant voltage (CCCV) charging was performed for a total charge time of 30 hours under conditions of a charging current of 0.05 C and a charge cut-off voltage of 3.0 V. Next, constant current (CC) discharging was performed at a discharge current of 0.05 C and a discharge cut-off voltage of 1.0 V. Next, a discharge test was conducted at 0.5 C in a thermostatic chamber at 25°C as follows: Constant current / constant voltage (CCCV) charging was performed for a total charge time of 30 hours under conditions of a charging current of 0.05 C and a charge cut-off voltage of 3.0 V. Next, constant current (CC) discharging was performed at a discharge current of 0.5 C and a discharge cut-off voltage of 1.0 V. A 10-minute pause was provided after each charge and discharge. As the high-rate discharge performance, the percentage of the discharge capacity at a discharge current of 0.5 C relative to the discharge capacity at a discharge current of 0.05 C was calculated. The results are shown in Table 1.

[0187] [Table 1]

[0188] As shown in Table 1, each of the nonaqueous electrolyte storage elements of the Examples, in which the nonaqueous solvent contained the fluorinated cyclic ether represented by the above formula (1) and another nonaqueous solvent, had higher high-rate discharge performance than the nonaqueous electrolyte storage element of Comparative Example 1, in which the nonaqueous solvent did not contain another nonaqueous solvent. Furthermore, by comparing the nonaqueous electrolyte storage element of Comparative Example 1 with the nonaqueous electrolyte storage elements of Reference Examples 1 to 3, it was confirmed that when the nonaqueous solvent contains a fluorinated cyclic ether represented by the above formula (1), the performance of the nonaqueous electrolyte storage element, such as the discharge capacity and the capacity retention rate after charge / discharge cycling, tends to improve. Furthermore, by comparing the nonaqueous electrolyte storage elements of the Examples, it was confirmed that increasing the total content of the ionic liquid and the fluorinated cyclic ether represented by the above formula (1) relative to the total of the ionic liquid and the nonaqueous solvent tends to increase the discharge capacity of the nonaqueous electrolyte storage element and also increase the capacity retention rate. In other words, it was confirmed that by adjusting the total content of the ionic liquid and the fluorinated cyclic ether represented by the above formula (1) relative to the total of the ionic liquid and the nonaqueous solvent within an appropriate range, the high-rate discharge performance, discharge capacity, and capacity retention rate of the nonaqueous electrolyte storage element can be optimized in a balanced manner. [Industrial Applicability]

[0189] The present invention can be applied to nonaqueous electrolyte storage elements used as power sources for electronic devices such as personal computers and communication terminals, automobiles, industrial equipment, and the like. [Explanation of symbols]

[0190] 1. Non-aqueous electrolyte energy storage element 2 Electrode body 3 containers 4 Positive lead 5 Positive external terminal 6 Negative lead 7 Negative external terminal 20 Energy storage unit 30 Electricity storage device

Claims

1. a positive electrode containing a sulfur-based active material; a non-aqueous electrolyte containing an electrolyte salt, an ionic liquid, and a non-aqueous solvent; Equipped with The nonaqueous electrolyte storage element includes the nonaqueous solvent containing a fluorinated cyclic ether represented by the following formula (1) and another nonaqueous solvent: 【Chemistry 1】 (In formula (1), R １ are each independently a hydrogen atom, a fluorine atom, an alkyl group having 1 to 4 carbon atoms, or a fluorinated alkyl group having 1 to 4 carbon atoms. １ At least one of the groups is a fluorine atom or a fluorinated alkyl group having 1 to 4 carbon atoms. n1 is an integer of 2 to 5.

2. 2. The nonaqueous electrolyte electricity storage element according to claim 1, wherein the fluorinated cyclic ether is 3,3,4,4-tetrafluorotetrahydrofuran.

3. 3. The nonaqueous electrolyte storage element according to claim 1, wherein the other nonaqueous solvent is at least one selected from the group consisting of non-fluorinated cyclic ethers and chain ethers.

4. 4. The nonaqueous electrolyte storage element according to claim 3, wherein the non-fluorinated cyclic ether is represented by the following formula (2), and the chain ether is represented by the following formula (3): 【Chemistry 2】 (In formula (2), R ２ are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms; and n2 is an integer of 2 to 5. 【Transformation 3】 (In formula (3), R ３ and R ４ are each independently an alkyl group having 1 to 3 carbon atoms or a fluorinated alkyl group having 1 to 3 carbon atoms. ５ is an alkanediyl group having 1 to 3 carbon atoms; and n3 is 0 or 1.

5. 3. The nonaqueous electrolyte storage element according to claim 1, wherein a total content of the ionic liquid and the fluorinated cyclic ether relative to the total of the ionic liquid and the nonaqueous solvent is 10% by volume or more.

6. 3. The nonaqueous electrolyte storage element according to claim 1, wherein the viscosity of the nonaqueous electrolyte at 25°C is 19 mPa·s or less.

7. 3. The nonaqueous electrolyte storage element according to claim 1, wherein the ionic liquid contains at least one cation selected from the group consisting of a quaternary ammonium cation, an imidazolium-based cation, a pyrrolidinium-based cation, a piperidinium-based cation, a quaternary phosphonium cation, and a sulfonium cation.

8. 3. The nonaqueous electrolyte storage element according to claim 1, wherein the ionic liquid has an imide anion.

9. 3. The nonaqueous electrolyte storage element according to claim 1, wherein the electrolyte salt is an imide salt.

10. 3. The nonaqueous electrolyte storage element according to claim 1, further comprising a negative electrode containing metallic lithium at least in a charged state.

11. providing a positive electrode including a sulfur-based active material; preparing a non-aqueous electrolyte containing an electrolyte salt, an ionic liquid, and a non-aqueous solvent; Equipped with The method for producing a nonaqueous electrolyte storage element includes the nonaqueous solvent containing a fluorinated cyclic ether represented by the following formula (1) and another nonaqueous solvent: 【Chemistry 4】 (In formula (1), R １ are each independently a hydrogen atom, a fluorine atom, an alkyl group having 1 to 4 carbon atoms, or a fluorinated alkyl group having 1 to 4 carbon atoms. １ At least one of the groups is a fluorine atom or a fluorinated alkyl group having 1 to 4 carbon atoms. n1 is an integer of 2 to 5.

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