Nonaqueous electrolyte power storage element and manufacturing method for nonaqueous electrolyte power storage element

Abstract

A nonaqueous electrolyte power 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, a fluorinated diether, and a nonionic compound containing a sulfur element.

Description

Non-aqueous electrolyte energy storage element and method for manufacturing a non-aqueous electrolyte energy storage element

[0001] The present invention relates to a non-aqueous electrolyte energy storage element and a method for manufacturing a non-aqueous electrolyte energy storage element.

[0002] 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 automobiles, due to their high energy density. Generally, non-aqueous electrolyte secondary batteries consist of a pair of electrodes electrically isolated by a separator, and a non-aqueous electrolyte interposed between these electrodes. They are configured to charge and discharge by transferring charge-transporting ions, such as lithium ions, between the two electrodes. Other non-aqueous electrolyte energy storage elements, such as lithium-ion capacitors and electric double-layer capacitors, are also widely used.

[0003] As non-aqueous electrolyte energy storage devices, lithium-sulfur batteries (Li-S batteries) and other non-aqueous electrolyte energy storage devices that use sulfur-based active materials as the positive electrode active material are known (see Patent Document 1). Sulfur-based active materials have a large theoretical capacity, and non-aqueous electrolyte energy storage devices that use sulfur-based active materials as the positive electrode active material are expected to be energy storage devices with high energy density.

[0004] Japanese Patent Publication No. 2010-95390

[0005] According to the inventors' findings, the high-rate discharge performance of a non-aqueous electrolyte energy storage element equipped with a positive electrode using a sulfur-based active material can be improved by incorporating a predetermined ether into the non-aqueous electrolyte. However, when an ether is incorporated into the non-aqueous electrolyte of a non-aqueous electrolyte energy storage element equipped with a positive electrode using a sulfur-based active material, the non-aqueous electrolyte energy storage element may not fully exhibit its initial discharge capacity even at a sufficiently low current density.

[0006] The object of the present invention is to provide a non-aqueous electrolyte energy storage element that uses a positive electrode containing a sulfur-based active material and a non-aqueous electrolyte containing an ether, and which has a large initial discharge capacity, and a method for manufacturing such a non-aqueous electrolyte energy storage element.

[0007] A non-aqueous electrolyte energy 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, a fluorinated diether, and a nonionic compound containing an element of sulfur.

[0008] A method for manufacturing a non-aqueous electrolyte energy storage element according to another aspect of the present invention comprises preparing a positive electrode containing a sulfur-based active material and preparing a non-aqueous electrolyte containing an electrolyte salt, a fluorinated diether, and a nonionic compound containing an element of sulfur.

[0009] According to any aspect of the present invention, it is possible to provide a non-aqueous electrolyte energy storage element using a positive electrode containing a sulfur-based active material and a non-aqueous electrolyte containing an ether, wherein the non-aqueous electrolyte energy storage element has a large initial discharge capacity, and a method for manufacturing such a non-aqueous electrolyte energy storage element.

[0010] Figure 1 is a perspective view showing a non-aqueous electrolyte energy storage element according to one embodiment of the present invention. Figure 2 is a schematic diagram showing an energy storage device comprising multiple non-aqueous electrolyte energy storage elements according to one embodiment of the present invention. Figure 3 shows the discharge curves at the initial stage of discharge in the first discharge of each non-aqueous electrolyte energy storage element in Examples 1 and 2 and Comparative Examples 1 to 4.

[0011] First, an overview of the non-aqueous electrolyte energy storage element and the method for manufacturing the non-aqueous electrolyte energy storage element disclosed herein will be described.

[0012] [1] A non-aqueous electrolyte energy 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, a fluorinated diether, and a nonionic compound containing an element of sulfur.

[0013] The non-aqueous electrolyte energy storage element described in [1] above is a non-aqueous electrolyte energy storage element that uses a positive electrode containing a sulfur-based active material and a non-aqueous electrolyte containing ether, and has a large initial discharge capacity. The reason for this is not clear, but the following reasons are speculated. One reason why the initial discharge capacity does not become sufficiently large in a non-aqueous electrolyte energy storage element that uses a non-aqueous electrolyte containing ether is that ether has a relatively large number of donors, and polysulfides (Li) produced at the positive electrode ２ S ｘIt is thought that the sulfur dioxide () is easily eluted into the non-aqueous electrolyte. In contrast, in the case of the non-aqueous electrolyte energy storage element described in [1] above, the non-aqueous electrolyte contains a nonionic compound containing sulfur along with a fluorinated diether as an ether. It is thought that the elution of polysulfides from the positive electrode into the non-aqueous electrolyte is suppressed by the formation of a film on the positive electrode surface by this nonionic compound containing sulfur. Furthermore, fluorinated diether is considered to be a solvent with high charge transport ion diffusivity compared to other ethers. For these reasons, the non-aqueous electrolyte energy storage element described in [1] above is a non-aqueous electrolyte energy storage element that uses a positive electrode containing sulfur-based active material and a non-aqueous electrolyte containing ether, and is presumed to have a large initial discharge capacity.

[0014] In this specification, the content of each component contained in the non-aqueous electrolyte shall be the value measured at 20°C and 1 atmosphere or the value converted to the value at 20°C and 1 atmosphere. The types of ionic compounds such as electrolyte salts and ionic liquids described later contained in the non-aqueous electrolyte shall be determined by ion chromatography (IC), liquid chromatography-mass spectrometry (LC-MS), etc. １ Identification is performed by combining necessary analyses from H-NMR and multinuclear NMR, etc. The content of ionic compounds such as electrolyte salts and ionic liquids contained in non-aqueous electrolytes is determined by IC. However, the cation content of ionic liquids contained in non-aqueous electrolytes is determined by LC-MS. If identification is not possible by LC-MS, １Identification is performed using the internal standard method by H-NMR. IC measurement is performed specifically as follows: (A1) Extraction of non-aqueous electrolyte First, the non-aqueous electrolyte energy storage element is charged with a constant current of 0.1C to the charging termination voltage for normal use, and is brought to a fully charged state. Here, "normal use" means using the non-aqueous electrolyte energy storage element under the charge and discharge conditions recommended or specified for the element, and if equipment for using the non-aqueous electrolyte energy storage element is available, it means using that equipment. "1C current" means the current that can discharge the theoretical capacity of the non-aqueous electrolyte energy storage element in one hour. The theoretical capacity of the non-aqueous electrolyte energy storage element is the theoretical capacity of the positive electrode if the theoretical capacity of the positive electrode is smaller than the theoretical capacity of the negative electrode, and the theoretical capacity of the negative electrode if the theoretical capacity of the negative electrode is smaller than the theoretical capacity of the positive electrode. The theoretical capacity of the positive electrode is calculated from the product of the capacity density per unit area of ​​the positive electrode active material layer laminated on one side of the positive electrode substrate and the area of ​​the positive electrode active material layer. The capacity density per unit area of ​​the positive electrode active material layer laminated on one side of the positive electrode substrate is calculated from the mass per unit area (g / cm³) of the positive electrode active material layer. ２) is calculated from the product of the content (mass%) of the positive electrode active material in the positive electrode active material layer and the theoretical capacity (mAh / g) of the positive electrode active material. The theoretical capacity of the negative electrode is calculated in accordance with the method for calculating the theoretical capacity of the positive electrode. Next, the fully charged non-aqueous electrolyte energy storage element is disassembled and the non-aqueous electrolyte is extracted. If it is not possible to extract it, the non-aqueous electrolyte is extracted by centrifugation of the non-aqueous electrolyte energy storage element. If it is not possible to extract it even after centrifugation, an appropriate extraction solvent (e.g., acetonitrile) is injected into the non-aqueous electrolyte energy storage element and the non-aqueous electrolyte diluted with the extraction solvent is extracted. (A2) IC analysis The components of the collected non-aqueous electrolyte are analyzed by IC. IC analysis is performed in the following order: qualitative analysis and quantitative analysis. (Qualitative analysis) The sample to be measured (non-aqueous electrolyte) is subjected to IC analysis. The components contained in the sample to be measured are predicted from the peak position 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 time of the peak corresponding to each predicted component in the measured sample is compared with the retention time of the peak of the known sample of each predicted component. If they match, the above prediction is presumed to be correct. (Quantitative analysis) Quantitative analysis is performed using the calibration curve method. First, IC analysis is performed on the known sample of the predicted component with known concentration, and the area of ​​the peak is determined to create a calibration curve. The calibration curve is calculated using the coefficient of determination (r ２ The calibration curve is prepared so that the result is between 0.999 and 1. The content of the predicted component in the sample is determined from the calibration curve and the area of ​​the peak of the predicted component in the sample. The above procedure is performed for all peaks detected by IC analysis of the sample to determine the content of each predicted component. In order to minimize the variation in measurement error between measurements, quantitative analysis shall be performed on the same day using the same equipment and under the same conditions, unless there are special circumstances, and consumables shall not be replaced or the equipment adjusted until all measurements are completed. The same applies to other quantitative analyses in this specification.

[0015] The types and content of nonionic compounds, such as fluorinated diethers and nonionic compounds containing sulfur elements, contained in nonaqueous electrolytes shall be identified by LC-MS and gas chromatography-mass spectrometry (GC-MS). However, in cases where it is difficult to identify the types of nonionic compounds by the above-mentioned analysis, １Identification is performed by combining necessary analyses from H-NMR, multinuclear NMR, and other analyses. Specifically, LC-MS and GC-MS measurements are performed as follows: (B1) Collection of non-aqueous electrolytes Non-aqueous electrolytes are collected using the same procedure as in "(A1) Collection of non-aqueous electrolytes" above. (B2) LC-MS The components of the collected non-aqueous electrolyte are analyzed by LC-MS. LC-MS analysis is performed in the following order: qualitative analysis and quantitative analysis. The LC-MS analyzer used is Waters' "Acquity H" and "Xevo G2-5QTof". Water or a non-aqueous solvent is used as the eluent. Examples of non-aqueous solvents include acetonitrile and tetrahydrofuran. If it is difficult to perform the measurement using the above-mentioned models, other models that are expected to produce equivalent measurement results may be used. The same applies to other measuring devices in this specification. (Qualitative analysis) The sample (non-aqueous electrolyte) is subjected to LC-MS analysis. If the peaks in the obtained liquid chromatogram are not separated, GC-MS analysis, as described below, is performed instead of LC-MS analysis. If the peaks obtained by LC-MS analysis are separated, the components contained in the sample are predicted from the MS spectrum of each peak. A sample of known predicted components is subjected to LC-MS analysis. The retention time and MS spectrum of the peaks corresponding to each predicted component in the sample are compared with the retention time and MS spectrum of the peaks of known samples of each predicted component. If they match, the above prediction is presumed to be correct. (Quantitative analysis) Quantitative analysis is performed using the calibration curve method. Quantitative analysis by LC-MS is performed in the same procedure as quantitative analysis by IC described above to determine the content of each predicted component. (B3) GC-MS Analysis by GC-MS is performed in the following order of qualitative analysis and quantitative analysis. The Agilent "5975C" is used as the GC-MS analyzer. Argon is used as the carrier gas. (Qualitative Analysis) The sample (non-aqueous electrolyte) is subjected to GC-MS analysis. The components contained in the sample are predicted from the MS spectra of each peak in the obtained gas chromatogram. Samples with known predicted components are subjected to GC-MS analysis.The retention time and MS spectrum of the peaks corresponding to the predicted components of the measured sample are compared with the retention time and MS spectrum of the peaks of known samples for each predicted component. If they match, the above prediction is presumed 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 to determine the content of each predicted component.

[0016] [2] In the non-aqueous electrolyte energy storage element described in [1] above, the content of the nonionic compound containing the sulfur element in the non-aqueous electrolyte may be 0.1% by mass or more and 20% by mass or less.

[0017] The non-aqueous electrolyte energy storage element described in [2] above has a larger initial discharge capacity due to factors such as an appropriate amount of coating formed on the positive electrode surface.

[0018] [3] In the non-aqueous electrolyte energy storage element described in [1] or [2] above, the nonionic compound containing the sulfur element may also contain a sulfonyl group.

[0019] The non-aqueous electrolyte energy storage element described in [3] above has a larger initial discharge capacity.

[0020] [4] In the non-aqueous electrolyte energy storage element described in any of [1] to [3] above, the nonionic compound containing the sulfur element may be a sultone.

[0021] The non-aqueous electrolyte energy storage element described in [4] above has a larger initial discharge capacity.

[0022] [5] In the non-aqueous electrolyte energy storage element described in any of [1] to [4] above, the non-aqueous electrolyte may further contain an ionic liquid.

[0023] Ionic liquids are expected to be used in non-aqueous electrolytes because they have advantages such as being liquid at room temperature, having substantially no volatility, and having high flame retardancy. However, since non-aqueous electrolytes containing ionic liquids have high viscosity, the diffusivity of charge-transporting ions is low, and non-aqueous electrolyte energy storage devices using non-aqueous electrolytes containing ionic liquids may not be able to fully exhibit charge-discharge performance such as high-rate discharge performance. Therefore, by including an ether together with the ionic liquid in the non-aqueous electrolyte, the viscosity of the non-aqueous electrolyte can be reduced, and the high-rate discharge performance and the like can be enhanced. However, when an ether is included in the non-aqueous electrolyte as described above, polysulfides generated at the positive electrode are likely to elute into the non-aqueous electrolyte, so the initial discharge capacity is likely to decrease. Therefore, by including a fluorinated diether as the ether in such a non-aqueous electrolyte and further including a non-ionic compound containing a sulfur element, the initial discharge capacity can be increased. That is, according to the non-aqueous electrolyte energy storage device described in [5] above, it is a non-aqueous electrolyte energy storage device in which a positive electrode containing a sulfur-based active material and a non-aqueous electrolyte containing an ionic liquid are used, and while eliminating the increase in viscosity of the non-aqueous electrolyte, which is a demerit of using an ionic liquid, the initial discharge capacity of the non-aqueous electrolyte energy storage device can also be increased.

[0024] [6] In the non-aqueous electrolyte energy storage device described in [5] above, the ionic liquid may have at least one 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.

[0025] [7] In the non-aqueous electrolyte energy storage device described in [5] or [6] above, the ionic liquid may have an imide anion. <00,00211>

[0026] [8] In the non-aqueous electrolyte energy storage device described in any one of [1] to [7] above, the electrolyte salt may be an imide salt.

[0027] [9] In the non-aqueous electrolyte energy storage device described in any one of [1] to [8] above, the fluorinated diether may be represented by the following formula (1). R−O−(CH ２ ) ２-O-Rf (1) (In formula (1), R is an alkyl group having 1 to 3 carbon atoms. Rf is a fluorinated alkyl group having 1 to 3 carbon atoms.)

[0028] Each of the non-aqueous electrolyte energy storage elements described in [6] to [9] above is a preferred embodiment of the present invention and has a larger initial discharge capacity.

[0029]

[10] In a non-aqueous electrolyte energy storage element according to any of [1] to [9] above, 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 / cm². ２ That's fine too.

[0030] The non-aqueous electrolyte energy storage element described in

[10] above has a positive electrode active material layer containing a sulfur-based active material with a mass per unit area of ​​5 mg / cm². ２ As a result of the above, the energy density of the non-aqueous electrolyte energy storage element can be increased. Furthermore, the non-aqueous electrolyte energy storage element described in

[10] above can achieve both high energy density and large initial discharge capacity. Also, as mentioned above, non-aqueous electrolytes containing ionic liquids are usually highly viscous. In particular, in non-aqueous electrolyte energy storage elements using non-aqueous electrolytes containing ionic liquids, if the mass per unit area of ​​the positive electrode active material layer is increased, that is, if the positive electrode active material layer is made thicker or the porosity is made lower, the charge transport ions in the non-aqueous electrolyte impregnated in the voids of the positive electrode active material layer cannot sufficiently diffuse in the thickness direction of the positive electrode active material layer, and good charge / discharge performance may not be achieved. In contrast, in the non-aqueous electrolyte energy storage element described in

[10] above, in particular, if the non-aqueous electrolyte further contains an ionic liquid, the viscosity of the non-aqueous electrolyte is sufficiently reduced by fluorinated diether, so the mass per unit area of ​​the positive electrode active material layer is 5 mg / cm². ２Even with the above, good charge and discharge performance can be achieved. In other words, the non-aqueous electrolyte energy storage element described in

[10] above, in particular when the non-aqueous electrolyte further contains an ionic liquid, can exhibit good charge and discharge performance even though an ionic liquid is used as the non-aqueous electrolyte and a thick positive electrode active material layer is provided, and can achieve both high energy density and large initial discharge capacity.

[0031] Mass per unit area of ​​the positive electrode active material layer (mg / cm²) ２ ) refers to the area of ​​the positive electrode active material layer (1 cm²). ２ This is the mass (mg) of the positive electrode active material layer per unit area. The area of ​​the positive electrode active material layer refers to the area of ​​one of the two surfaces (the front and back surfaces, excluding the sides) of a single positive electrode active material layer. That is, for example, if the positive electrode active material layer is provided by coating, the area of ​​the positive electrode active material layer is equal to the area to which the positive electrode active material layer is coated. If the positive electrode active material layer is provided on both sides of the positive electrode substrate, the area and mass of the positive electrode active material layer refer to the area and mass of one of the positive electrode active material layers. For example, if the positive electrode active material layer is 10 mg / cm² on both sides of the positive electrode substrate. ２ When the coating amount (in terms of solid content) is set to 10 mg / cm², the "mass per unit area of ​​the positive electrode active material layer" is 10 mg / cm². ２ The positive electrode active material layer is 10 mg / cm² on one side of the positive electrode substrate. ２ Even if the coating amount (based on solid content) is specified, the "mass per unit area of ​​the positive electrode active material layer" is 10 mg / cm². ２ Furthermore, the mass per unit area of ​​the positive electrode active material layer (mg / cm²) is also stated. ２ ) is the value in the charged state of a non-aqueous electrolyte energy storage element.

[0032]

[11] In the non-aqueous electrolyte energy storage element described in any of [1] to

[10] above, a negative electrode containing metallic lithium may be further provided, at least in the charged state.

[0033] The non-aqueous electrolyte energy storage element described in

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

[0034]

[12] In the non-aqueous electrolyte energy storage element described in any of [1] to

[11] above, the content of the fluorinated diether relative to the total content of the non-aqueous solvent (the sum of the fluorinated diether and any other non-aqueous solvent) and any ionic liquid contained in the non-aqueous electrolyte may be 10% by volume or more.

[0035] The non-aqueous electrolyte energy storage element described in

[12] above has a larger initial discharge capacity.

[0036]

[13] In the non-aqueous electrolyte energy storage element described in any of [5] to

[12] above, the content of the ionic liquid relative to the total content of the non-aqueous solvent (the sum of the fluorinated diether and any other non-aqueous solvent) and the ionic liquid contained in the non-aqueous electrolyte may be 30% by volume or more.

[0037] The non-aqueous electrolyte energy storage element described in

[13] above has advantages such as the non-aqueous electrolyte containing a sufficient amount of ionic liquid and having particularly high flame retardancy. On the other hand, non-aqueous electrolytes with a large ionic liquid content have high viscosity, and conventional non-aqueous electrolyte energy storage elements using such non-aqueous electrolytes tend not to have a large initial discharge capacity. In contrast, the non-aqueous electrolyte energy storage element described in

[13] above can have a large initial discharge capacity despite using such a non-aqueous electrolyte. In other words, the non-aqueous electrolyte energy storage element described in

[13] above can achieve both excellent flame retardancy of the non-aqueous electrolyte and a large initial discharge capacity.

[0038]

[14] In the non-aqueous electrolyte energy storage element described in any of [5] to

[13] above, the total content of the fluorinated diether and the ionic liquid relative to the total content of the non-aqueous solvent (the sum of the fluorinated diether and any other non-aqueous solvent) contained in the non-aqueous electrolyte and the ionic liquid may be 80% by volume or more.

[0039]

[15] In the non-aqueous electrolyte energy storage element described in any of [5] to

[14] above, the total content of the electrolyte salt, the fluorinated diether, the nonionic compound containing the sulfur element, and the ionic liquid in the non-aqueous electrolyte may be 80% by mass or more.

[0040] The non-aqueous electrolyte energy storage elements described in

[14] and

[15] above are also preferred embodiments of the present invention.

[0041]

[16] In the non-aqueous electrolyte energy storage element described in any of [1] to

[15] above, the viscosity of the non-aqueous electrolyte at 25°C may be 30 mPa·s or more.

[0042] As described above, conventional non-aqueous electrolyte energy storage elements that use non-aqueous electrolytes with relatively high viscosity tend not to have a large initial discharge capacity. In contrast, the non-aqueous electrolyte energy storage element described in

[16] above can have a large initial discharge capacity despite using such a non-aqueous electrolyte with relatively high viscosity.

[0043] The viscosity of non-aqueous electrolytes is defined as the value measured using the Anton Paar "LOVIS2000ME" measuring device, with the temperature of the non-aqueous electrolyte set to 25°C.

[0044]

[17] In the non-aqueous electrolyte energy storage element described in any of [5] to

[16] above, the content of the fluorinated diether relative to the total of the fluorinated diether and the ionic liquid may be 10% by volume or more and 60% by volume or less.

[0045]

[18] In the non-aqueous electrolyte energy storage element described in any of [1] to

[17] above, the molal concentration of the electrolyte salt in the non-aqueous electrolyte may be 0.3 mol / kg or more and 3.5 mol / kg or less.

[0046]

[19] In the non-aqueous electrolyte energy storage element described in any of [1] to

[18] above, the positive electrode further contains porous carbon, and the sulfur-based active material and the porous carbon may form a composite.

[0047]

[20] A method for manufacturing a non-aqueous electrolyte energy storage element according to another aspect of the present invention comprises preparing a positive electrode containing a sulfur-based active material and preparing a non-aqueous electrolyte containing an electrolyte salt, a fluorinated diether, and a nonionic compound containing an element of sulfur.

[0048] According to the method for manufacturing a non-aqueous electrolyte energy storage element described in

[20] above, it is possible to manufacture a non-aqueous electrolyte energy storage element that uses a positive electrode containing a sulfur-based active material and a non-aqueous electrolyte containing an ether, and which has a large initial discharge capacity.

[0049] A non-aqueous electrolyte energy storage element, a method for manufacturing a non-aqueous electrolyte energy storage element, an energy storage device, and other embodiments according to one embodiment of the present invention will be described in detail below.

[0050] <Non-aqueous electrolyte energy storage element> A non-aqueous electrolyte energy storage element according to one embodiment of the present invention comprises a positive electrode, a negative electrode, a non-aqueous electrolyte, and a container for housing them. The non-aqueous electrolyte energy storage element may further include a separator interposed between the positive electrode and the negative electrode to electrically insulate them. The positive electrode, the negative electrode, and any separator typically constitute an electrode body. At least a portion of the non-aqueous electrolyte is usually present in a state of being impregnated into the electrode body. The non-aqueous electrolyte energy storage element according to one embodiment of the present invention may further include other components.

[0051] For example, the non-aqueous electrolyte energy storage element 1 shown in Figure 1, according to one embodiment of the present invention, comprises an electrode body 2, a non-aqueous electrolyte (not shown), and a rectangular parallelepiped container 3 that houses them. The non-aqueous electrolyte energy storage element 1 in Figure 1 further comprises 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 housed together with the electrode body 2, etc., inside the container 3. 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 body 2 is electrically connected to the positive electrode external terminal 5 via the positive electrode lead 4. The negative electrode constituting the electrode body 2 is electrically connected to the negative electrode external terminal 7 via the negative electrode lead 6.

[0052] The non-aqueous electrolyte energy storage element of the present invention may also be a non-aqueous electrolyte secondary battery. The following will describe in detail the main components constituting the non-aqueous electrolyte energy storage element according to one embodiment of the present invention, focusing on the case where the non-aqueous electrolyte energy storage element is a non-aqueous electrolyte secondary battery (particularly a lithium-ion secondary battery), but this is not intended to limit the scope of application of the present invention.

[0053] In the embodiments of the present invention, the lower and upper limits of each numerical range can be combined in any way (however, the upper limit is greater than the lower limit). Unless otherwise specified, the lower and upper limits of each numerical range are included within that range. That is, a lower limit of A means that it is greater than or equal to A. Similarly, an upper limit of B means that it is less than or equal to B. Unless otherwise specified, the lower and upper limits of each numerical range are the values ​​in the charged state of the non-aqueous electrolyte energy storage element.

[0054] (Positive electrode) The positive electrode comprises a positive electrode substrate and a positive electrode active material layer laminated directly to the positive electrode substrate or via an intermediate layer. Typically, 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 positive electrode lead described above. The positive electrode may have a shape such as a sheet, plate, or strip.

[0055] The thickness of the positive electrode is set appropriately according to the application of the non-aqueous electrolyte energy 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 in which the positive electrode active material layer is laminated directly onto the positive electrode substrate or via an intermediate layer. If both portions exist in which the positive electrode active material layer is laminated on both sides of the positive electrode substrate and portions in which the positive electrode active material layer is laminated on only one side of the positive electrode substrate, then the average thickness of the portion in which the positive electrode active material layer is laminated on both sides of the positive electrode substrate shall be used. Furthermore, in this specification, "average thickness" means the average value of the thickness measured at any five locations.

[0056] The positive electrode substrate is conductive. In this specification, "having conductivity" means that the volume resistivity is 10 －２ This means that the volume resistivity is Ω·cm or less. The volume resistivity shall be the value measured in accordance with JIS-H-0505 (1975). On the other hand, in this specification, "not conductive" or "having (electrical) insulating properties" means that the above volume resistivity is 10 ７This means it is greater than or equal to Ω·cm.

[0057] Examples of materials for the positive electrode substrate include metals such as aluminum, titanium, iron, and their alloys (stainless steel, etc.). Among these, aluminum or aluminum alloys are preferred from the viewpoint of high potential resistance, high electronic conductivity, and cost.

[0058] The positive electrode substrate has a shape such as a sheet, plate, or strip. Examples of positive electrode substrate forms include foil, vapor-deposited film, mesh, and porous material, with foil being preferred. The positive electrode substrate may also be, for example, aluminum foil or aluminum alloy foil.

[0059] 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.

[0060] The intermediate layer is a layer placed between the positive electrode substrate and the positive electrode active material layer. The intermediate layer includes, 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 conductive agents and binders used in the intermediate layer are the same as those used in the positive electrode active material layer, which will be described later.

[0061] The positive electrode active material layer contains a sulfur-based active material. The positive electrode active material layer may optionally contain optional components such as a conductive agent, binder, dispersant, thickener, and filler. The positive electrode active material layer may be formed from a positive electrode mixture containing the positive electrode active material and other optional components. The positive electrode active material layer may be provided on only one side of a positive electrode substrate having a shape such as a sheet, or on both sides.

[0062] Sulfur-based active materials are components that function as positive electrode active materials. Sulfur-based active materials may be elemental sulfur, sulfur compounds, or mixtures 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 high theoretical capacity and low cost.

[0063] The sulfur-based active material content in the positive electrode active material layer is preferably 50% to 90% by mass, more preferably 55% to 80% by mass, and even more preferably 60% to 70% by mass. Having the sulfur-based active material content within the above range allows for a larger initial discharge capacity of the non-aqueous electrolyte energy storage element.

[0064] The positive electrode active material layer preferably further contains porous carbon that forms a composite with a sulfur-based active material. In other words, it is preferable that the sulfur-based active material is contained in the positive electrode active material layer as a composite with porous carbon. Hereinafter, the composite of sulfur-based active material and porous carbon will also be simply referred to as the "composite." In the composite, the sulfur-based active material is usually supported within the pores of the porous carbon. Sufficient electronic conductivity is ensured by the composite being in this form. The composite may consist substantially only of sulfur-based active material and porous carbon, or it may consist only of sulfur-based active material and porous carbon. When the composite consists substantially only of sulfur-based active material and porous carbon, for example, the total content of sulfur-based active material (total of elemental sulfur and sulfur compounds) 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.

[0065] The sulfur-based active material content in the composite is preferably 50% to 90% by mass, and more preferably 60% to 80% by mass. By setting the sulfur-based active material content in the composite within the above range, it is possible to increase the initial discharge capacity of the non-aqueous electrolyte energy storage element.

[0066] Porous carbon is electrically conductive. Porous carbon is generally a porous inorganic material whose main constituent element is carbon. The main constituent element refers to the element that is present in the largest quantity by mass. The lower limit of the carbon content in porous carbon is preferably 70% by mass, and more preferably 80%, 90%, 95%, or 97% by mass. The upper limit of the carbon content in porous carbon may be 100% by mass or 99.9% by mass. Porous carbon may also contain elements other than carbon, such as oxygen and nitrogen.

[0067] The composite can be manufactured by conventionally known methods. For example, it can be obtained by heating a mixture of a sulfur-based active material and porous carbon to a temperature above the melting point of the sulfur-based active material, and then cooling it.

[0068] The composite content in the positive electrode active material layer is preferably 60% to 97% by mass, more preferably 80% to 96% by mass, and even more preferably 90% to 95% by mass. By setting the composite content within the above range, it is possible to increase the initial discharge capacity of the non-aqueous electrolyte energy storage element.

[0069] The positive electrode active material layer may contain positive electrode active materials other than sulfur-based active materials. However, the content of sulfur-based active materials 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.

[0070] Conductive agents are typically components made of conductive materials. Note that these conductive agents do not contain porous carbon, which constitutes the composite. Even if the volume resistivity of the conductive agent cannot be directly measured, the volume resistivity is 10 －２Materials whose conductivity is known to be Ω·cm or less are classified as conductive agents. Examples of conductive agents include carbon materials, metals, and conductive ceramics. A carbon material is a material whose main constituent element is carbon. The main constituent element is the element with the highest mass content. 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. It is preferable that the carbon material is a carbon material other than a non-carbonized polymer compound. Examples of carbon materials include graphite, non-graphitic carbon, and graphene-based carbon. Examples of non-graphitic carbon include carbon nanofibers, pitch-based carbon fibers, and carbon black. Examples of carbon black include furnace black, acetylene black, and Ketjen black. Examples of graphene-based carbon include graphene, carbon nanotubes (CNT), and fullerene. Conductive agents can take the form of powder or fibers. One or more conductive agents can be used. These materials may be used in combination as conductive agents. For example, a material made by combining carbon black and CNTs may be used. Carbon black or CNTs are preferred as conductive agents, and acetylene black is more preferred as carbon black. It is also preferable to use carbon black (preferably acetylene black) and CNTs in combination.

[0071] The content of the conductive agent (excluding porous carbon in the composite) in the positive electrode active material layer is preferably 0.1% by mass or more and 10% by mass or less, and more preferably 1% by mass or more and 9% by mass or less. The upper limit of the content of the conductive agent may be 8% by mass, 5% by mass, 4% by mass, 3% by mass, 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 non-aqueous electrolyte energy storage element.

[0072] Examples of binders include water-based binders and organic solvent-based binders.

[0073] A water-based binder is a binder that dissolves or disperses in water. A water-based binder may be one in mass or more that dissolves or disperses in 100 parts by mass of water at 20°C. When forming a positive electrode active material layer using a positive electrode mixture paste in which the dispersion medium is water or a mixed solvent mainly composed of water, a water-based binder (a water-soluble or water-dispersible polymer material) can be used. Examples of water-based binders include polyethylene oxide, polypropylene oxide, polyvinyl alcohol, polyacrylic acid, polymethacrylic acid, polytetrafluoroethylene, styrene-butadiene rubber, polyethylene, polypropylene, nitrile-butadiene rubber, and cellulose.

[0074] An organic solvent-based binder is a binder that dissolves or disperses in an organic solvent (e.g., N-methylpyrrolidone). An organic solvent-based binder may be a binder that dissolves or disperses at 1 part by mass or more per 100 parts by mass of an organic solvent (e.g., N-methylpyrrolidone) at 20°C. When forming a positive electrode active material layer using a positive electrode mixture paste in which the dispersion medium is an organic solvent or a mixed solvent mainly composed of an organic solvent, an organic solvent-based binder (a polymer material having solubility or dispersibility 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, and derivatives of chitosan.

[0075] 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.

[0076] The binder content in the positive electrode active material layer is preferably 0.1% by mass or more and 10% by mass or less, more preferably 1% by mass or more and 9% by mass or less, and even more preferably 2% by mass or more and 8% by mass or less. The upper limit of the binder content may be 5% by mass, 4% by mass, or 3% by mass. By setting the binder content within the above range, it is possible to stably retain sulfur-based active materials, etc. The technology disclosed herein can also be implemented in a form in which the positive electrode active material layer does not contain a binder.

[0077] Examples of dispersants include polysaccharide polymers such as carboxymethylcellulose (CMC) and methylcellulose. If the dispersant has functional groups that react with lithium, these functional groups may be deactivated beforehand by methylation or the like. The dispersant content 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 as a binder.

[0078] Examples of thickening agents include polyacrylic acid (PAA). The content of the thickening agent 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 also function as a binder.

[0079] 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 a component that is intentionally included. The filler may be included as a component that fills gaps in the positive electrode active material layer, or it may be included for other purposes. The filler may be an organic substance such as a polyolefin, or an inorganic substance such as an inorganic oxide, hydroxide, or carbonate. One or more types of fillers may be used. When the positive electrode active material layer contains a filler, the filler content in the positive electrode active material layer can 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 can also be carried out in a form in which the positive electrode active material layer does not contain a filler.

[0080] The positive electrode active material layer may further contain other components besides the positive electrode active material (sulfur-based active material and other positive electrode active materials), conductive agent, binder, dispersant, thickener, and filler. These other components may include those unintentionally present in the positive electrode active material layer. Furthermore, the positive electrode active material layer may contain impurities unintentionally present as these other components, insofar as they achieve the effects of the present invention. The upper limit of the content of these other components 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. The upper limit of the content of unintentionally present components 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. The upper limit for the amount of impurities unintentionally included in the positive electrode active material layer may be 10% by mass, or it may be 5% by mass, 2% by mass, 1% by mass, 0.1% by mass, or 0.01% by mass.

[0081] For example, the lower limit of the mass per unit area of ​​the positive electrode active material layer is 1 mg / cm². ２ It may also be 3 mg / cm³ ２ It may be 5 mg / cm³. ２ Preferably, 7 mg / cm ２ More preferably, 9 mg / cm ２ More preferably, 10 mg / cm³ ２ This is even more preferable. By setting the mass per unit area of ​​the positive electrode active material layer to above the lower limit mentioned above, the energy density of the non-aqueous electrolyte energy storage element can be increased. The upper limit for the mass per unit area of ​​the positive electrode active material layer is 30 mg / cm³. ２ It may also be 20 mg / cm³ ２ , 15 mg / cm ２ , 10 mg / cm ２ 7 mg / cm³ ２ or 5 mg / cm ２ This is also acceptable. By keeping the mass per unit area of ​​the positive electrode active material layer below the above upper limit, the initial discharge capacity of the non-aqueous electrolyte energy storage element can be increased.

[0082] (Method for Manufacturing a Positive Electrode) A positive electrode can be manufactured by known methods. A positive electrode can be manufactured, for example, by applying a paste-like positive electrode mixture (positive electrode mixture paste) directly to a positive electrode substrate or via an intermediate layer, and then drying it to form a positive electrode active material layer. The positive electrode mixture paste usually contains a sulfur-based active material, other optional components, and a dispersion medium. After drying, the positive electrode active material layer may be pressed or otherwise subjected to other processes.

[0083] (Negative electrode) The negative electrode comprises a negative electrode substrate and a negative electrode active material layer laminated directly to the negative electrode substrate or via an intermediate layer. Typically, 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 negative electrode lead described above. The negative electrode may have a shape such as a sheet, plate, or strip.

[0084] The thickness of the negative electrode is set appropriately according to the application of the non-aqueous electrolyte energy storage element. 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 the portion in which the negative electrode active material layer is laminated directly to the negative electrode substrate or via an intermediate layer. If there are portions in which the negative electrode active material layer is laminated on both sides of the negative electrode substrate and portions in which the negative electrode active material layer is laminated on only one side of the negative electrode substrate, then the average thickness of the portion in which the negative electrode active material layer is laminated on both sides of the negative electrode substrate shall be used.

[0085] The negative electrode substrate is electrically conductive. Examples of materials for the negative electrode substrate include metals such as copper, nickel, iron, and their alloys (such as stainless steel), as well as carbon materials. Among these, nickel or nickel alloys are preferred.

[0086] The negative electrode substrate has a shape such as a sheet, plate, or strip. Examples of negative electrode substrate forms include foil, vapor-deposited film, mesh, and porous material, with foil being preferred. The negative electrode substrate may also be, for example, nickel foil or nickel alloy foil.

[0087] 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.

[0088] The configuration of the negative electrode intermediate layer is not particularly limited; for example, it can be selected from the configurations exemplified for the positive electrode intermediate layer.

[0089] The negative electrode active material layer contains a negative electrode active material. The negative electrode active material layer optionally contains optional components such as a conductive agent, binder, dispersant, thickener, and filler. The optional components such as the conductive agent, binder, dispersant, thickener, and filler can be selected from the materials exemplified above for the positive electrode. The negative electrode active material layer may be formed from a negative electrode mixture containing the negative electrode active material and other optional components. The negative electrode active material layer may be provided on only one side of a negative electrode substrate having a shape such as a sheet, or on both sides.

[0090] For the negative electrode active material, known negative electrode active materials can be used. For lithium-ion secondary batteries, materials that can intercept and release lithium ions are usually used as negative electrode active materials. Examples of negative electrode active materials include metallic lithium; metals or metalloids such as silicon and tin; metal oxides or metalloid oxides such as silicon oxide, titanium oxide, and tin oxide; Li ４ Ti ５ O １２ LiTio ２、 TiNb ２ O ７ Examples include titanium-containing oxides; 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 even more preferred. Graphite may have its surface coated with other materials such as non-graphitic carbon. One or more types of negative electrode active materials can 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 can be used.

[0091] As the negative electrode active material, metallic lithium is preferred. In other words, it is preferable that the negative electrode or negative electrode active material layer contains metallic lithium at least in the charged state. It is more preferable that the negative electrode or negative electrode active material layer contains metallic lithium in all states, including the charged and discharged states.

[0092] Lithium metal may be pure lithium, consisting substantially of only lithium, or it may be a lithium alloy containing other metallic elements. Examples of lithium alloys include lithium silver alloy, lithium zinc alloy, lithium calcium alloy, lithium aluminum alloy, lithium magnesium alloy, and lithium indium alloy. Lithium alloys may also contain multiple metallic elements other than lithium.

[0093] The negative electrode active material layer is preferably a layer consisting substantially only of metallic lithium (pure metallic lithium or lithium alloy). The lower limit of the lithium element content in the negative electrode active material layer is preferably 80% by mass, more preferably 90% by mass, and even more preferably 99% by mass. The upper limit of the lithium element content in the negative electrode active material layer may be 100% by mass.

[0094] 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 2% by mass or less. The technology disclosed herein can also be carried out in a form in which the negative electrode active material layer does not contain a conductive agent.

[0095] When the negative electrode active material layer contains a binder, the binder content 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 binder content in the negative electrode active material layer may be 5% by mass or less, or 2% by mass or less. The technology disclosed herein can also be carried out in a form in which the negative electrode active material layer does not contain a binder.

[0096] When the negative electrode active material layer contains a dispersant, the dispersant content 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 dispersant content in the negative electrode active material layer may be 1% by mass or less, or 0.1% by mass or less. The technology disclosed herein can also be carried out in a form in which the negative electrode active material layer does not contain a dispersant.

[0097] When the negative electrode active material layer contains a thickening agent, the content of the thickening agent 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 thickening agent in the negative electrode active material layer may be 5% by mass or less, or 2% by mass or less. The technology disclosed herein can also be carried out in a form in which the negative electrode active material layer does not contain a thickening agent.

[0098] The filler in the negative electrode active material layer is a component other than the negative electrode active material, conductive agent, binder, dispersant, and thickener, and may be a component that is intentionally included. The filler may be included as a component that fills gaps in the negative electrode active material layer, or it may be included for other purposes. When the negative electrode active material layer contains a filler, the filler content in the negative electrode active material layer can 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 can also be carried out in a form in which the negative electrode active material layer does not contain a filler.

[0099] The negative electrode active material layer may further contain other components besides the negative electrode active material, conductive agent, binder, dispersant, thickener, and filler. These other components may include those unintentionally present in the negative electrode active material layer. Furthermore, the negative electrode active material layer may contain impurities unintentionally present as these other components, insofar as they achieve the effects of the present invention. The upper limit of the content of these other components in the negative electrode active material layer may be 10% by mass, or 5%, 2%, 1%, 0.1%, or 0.01% by mass. The upper limit of the content of unintentionally present components in the negative electrode active material layer may be 10% by mass, or 5%, 2%, 1%, 0.1%, or 0.01% by mass. The upper limit of the content of unintentionally present impurities in the negative electrode active material layer may be 10% by mass, or 5%, 2%, 1%, 0.1%, or 0.01% by mass.

[0100] The negative electrode active material layer may be a non-porous layer (solid layer) or a porous layer, but it is preferable that it be 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 laminated on one side of the negative electrode substrate in the charged state may be, for example, 5 μm or more and 2,000 μm or less. The lower limit of the average thickness of the negative electrode active material layer in the 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 the negative electrode active material layer in the charged state may be 1,500 μm, 1,200 μm, 800 μm, or 600 μm.

[0101] (Method for Manufacturing the Negative Electrode) The negative electrode can be manufactured by known methods. The negative electrode can be manufactured, for example, in the same way as the method for manufacturing the positive electrode described above, by applying a paste-like negative electrode mixture (negative electrode mixture paste) directly to the negative electrode substrate or via an intermediate layer, and drying it to form a negative electrode active material layer. After drying, the negative electrode active material layer may be pressed or otherwise subjected to the process. If the negative electrode active material is a metal such as metallic lithium, it can also be manufactured by laminating metal foil directly to the negative electrode substrate or via an intermediate layer, and then pressing or otherwise performing the process.

[0102] (Separator) A known separator can be used. Examples of separators include a separator consisting only of a substrate layer, or a separator in which an inorganic layer containing inorganic particles and a binder is formed on one or both sides of the substrate layer.

[0103] Examples of the substrate layer form of the separator include woven fabric, nonwoven fabric, and porous resin film. Among these forms, porous resin film is preferred from the viewpoint of strength, and nonwoven fabric is preferred from the viewpoint of liquid retention of non-aqueous electrolytes. The material of the substrate layer of the separator is not particularly limited as long as it has insulating properties, but resins such as polyolefins (polyethylene, polypropylene, etc.), polyimide, and aramid are preferred.

[0104] 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; covalent crystals such as silicon; mineral resource-derived materials such as talc, zeolite, kaolin, bentonite, and mica, or their artificial counterparts. One or more types of inorganic particles can be used. The average particle size of the inorganic particles is preferably, for example, 0.5 μm to 10 μm. The inorganic particle content in the inorganic layer is preferably 50% to 99% by mass, and more preferably 80% to 98% by mass.

[0105] Examples of binders used in the inorganic layer include those similar to those exemplified in the positive electrode active material layer.

[0106] The porosity of the separator may be, for example, 20% or more and 80% or less. The lower limit of the separator's porosity may be 30%, 40%, or 50% from the viewpoint of discharge performance, etc. The upper limit of the separator's porosity may be 70%, 60%, or 50% from the viewpoint of strength, etc. In this specification, "porosity" refers to a volume-based value and means a measurement value obtained using a mercury porosimeter.

[0107] 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.

[0108] A polymer gel composed of a polymer and a non-aqueous electrolyte may be used as a separator. A polymer gel may also be used in combination with a porous resin film, nonwoven fabric, etc., as described above, as a separator.

[0109] (Electrode Body) As the electrode body, known structures such as wound electrode bodies and laminated electrode bodies can be used.

[0110] A wound electrode has a structure in which the positive electrode and negative electrode are wound together while being insulated. The wound electrode may be cylindrical or flattened. The electrode 2 of the non-aqueous electrolyte energy storage element 1 in Figure 1 is a flattened wound electrode. A wound electrode can be manufactured, for example, by the following procedure. First, a laminate is obtained by stacking a positive electrode, a separator, and a negative electrode, each formed in a strip shape. A wound electrode is obtained by winding this laminate.

[0111] 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 formed in a rectangular shape.

[0112] Other electrode structures can also be used, such as those in which at least one of the positive and negative electrodes is folded in a bellows-like manner and stacked.

[0113] (Non-aqueous electrolyte) A non-aqueous electrolyte is a medium that carries charge transport ions (e.g., lithium ions) between the positive and negative electrodes and substantially does not contain water. The water content in a non-aqueous electrolyte may be, for example, 10,000 ppm or less, 5,000 ppm or less, 1,000 ppm or less, 500 ppm or less, 100 ppm or less, preferably 50 ppm or less, and more preferably 20 ppm or less.

[0114] The non-aqueous electrolyte contains an electrolyte salt, a fluorinated diether, and a nonionic compound containing an element of sulfur. The non-aqueous electrolyte may further contain an ionic liquid. In one embodiment of the present invention, the fluorinated diether is a non-aqueous solvent that dissolves the electrolyte salt. The non-aqueous electrolyte may further contain other non-aqueous solvents other than the fluorinated diether. The non-aqueous electrolyte may also be a non-aqueous electrolyte solution. In one embodiment of the present invention, the non-aqueous electrolyte energy storage element may also be a non-aqueous electrolyte solution energy storage element.

[0115] An electrolyte salt is an ionic compound in which the cation is a charge transport ion and which is solid at room temperature (20°C) at 1 atmosphere. Known electrolyte salts can be used. Examples of electrolyte salts include lithium salts, sodium salts, potassium salts, magnesium salts, and onium salts. Among these, lithium salts are preferred. One or more electrolyte salts can be used.

[0116] The anions that make up the electrolyte salt include N(CF) ３ SO ２ ) ２ － (Bis(trifluoromethanesulfonyl)imide anion: TFSI － ), N (SO ２ F) ２ － (Bis(fluorosulfonyl)imide anion: FSI － ), N (C ２ F ５ SO ２ ) ２ － (Bis(pentafluoroethanesulfonyl)imide anion), N(C ４F ９ SO ２ ) ２ － (bis(nonafluorobutanesulfonyl)imide anion), N(POF ２ ) ２ － (bis(difluorophosphonyl)imide anion), N(CF ３ SO ２ )(CF ３ (CO)) － ((trifluoromethanesulfonyl)(trifluoromethanecarbonyl)imide anion), N(CN) ２ － (dicyanoimide anion), CF ３ -SO ２ -N-SO ２ -N-SO ２ CF ３ － , FSO ２ -N-SO ２ -C ４ F ９ － , CF ３ -SO ２ -N-SO ２ -C ４ F ９ － , CF ３ -SO ２ -N-SO ２ -CF ２ -SO ２ -N-SO ２ -CF ３ ２－ , CF ３ -SO ２ -N-SO ２ -CF ２ -SO ３ ２－ , CF ３ -SO ２ -N-SO ２ )-CF ２ -SO ２ -C(-SO ２ CF ３ ) ２ ) ２－ ６ － , PO ２ ２ － ４ － ４ － ２ － ３ － － [[ID=Y]] ３ ３ － ２ ３ ３ － ]>[[]END]] ２ ２ ５ ３ >< － － － － ２ ２ <00\00140> ｎ ３－ｎ － － － [[ID=1)]] － － － － ２ ２ ２ ２ ２ ３ ３ ６ ２ ２ ２

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[0036] <２ F ２ － BF ４ － , ClO ４ － NO ２ － NO ３ － , I － SO ３ CF ３ － , C (SO ２ CF ３ ) ３ － , C (SO ２ C ２ F ５ ) ３ － Other anions besides imidone anions can also be used.

[0117] The anion that constitutes the electrolyte salt is preferably an imide anion, and is bis(trifluoromethanesulfonyl)imide anion (TFSI － ) and bis(fluorosulfonyl)imide anion (FSI － At least one selected from the group consisting of ) is more preferably a bis(fluorosulfonyl)imide anion (FSI － ) is even more preferred. That is, as the electrolyte salt, an imide salt is preferred, at least one selected from the group consisting of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium bis(fluorosulfonyl)imide (LiFSI) is more preferred, and lithium bis(fluorosulfonyl)imide (LiFSI) is even more preferred. Furthermore, it is preferable that the anion constituting the electrolyte salt 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 initial discharge capacity of the non-aqueous electrolyte energy storage element can be made larger. One or more types of anions can be used to constitute the electrolyte salt.

[0118] The molal 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 molal 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 molal 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 molal concentration of the electrolyte salt within the above range, the ionic conductivity of the non-aqueous electrolyte is optimized, and the initial discharge capacity of the non-aqueous electrolyte energy storage element can be increased. In this specification, molality refers to the amount of substance (mol) of the electrolyte salt based on the total mass (kg) of the non-aqueous solvent (the sum of fluorinated diethers and other non-aqueous solvents) and the ionic liquid contained in the non-aqueous electrolyte.

[0119] Fluorinated diethers are diethers containing the element fluorine. A diether is a compound having two ether bonds. Fluorinated diethers may be cyclic or linear, but linear fluorinated diethers are preferred. "Linear" means not having a cyclic structure. Fluorinated diethers may be composed only of carbon, hydrogen, oxygen, and fluorine. Preferably, the oxygen elements in a fluorinated diether are only those that constitute the ether bonds. That is, it is preferable that fluorinated diethers do not have oxygen-containing substituents such as hydroxyl groups and carboxyl groups. Fluorinated diethers are preferably saturated ethers. A saturated ether is an ether that does not have unsaturated bonds between carbon atoms (carbon-carbon double bonds and carbon-carbon triple bonds).

[0120] The lower limit of the number of carbon atoms in the fluorinated diether is 3, preferably 4, and more preferably 5. The upper limit of the number of carbon atoms is preferably 8, more preferably 7, and still more preferably 6. The lower limit of the number of fluorine atoms in the fluorinated diether is preferably 2, more preferably 3. The upper limit of the number of fluorine atoms may be 10, may be 9, preferably 8, and still more preferably 7, 6, 5, 4, or 3.

[0121] Fluorinated diethers are preferably represented by the following formula (1): R-O-(CH ２ ) ２ -O-Rf (1) (In formula (1), R is an alkyl group having 1 to 3 carbon atoms. Rf is a fluorinated alkyl group having 1 to 3 carbon atoms.)

[0122] Examples of alkyl groups with 1 to 3 carbon atoms represented by R in formula (1) include methyl group, ethyl group, propyl group, and 1-methylethyl group, with methyl group or ethyl group being preferred, and methyl group being more preferred.

[0123] A fluorinated alkyl group is a group in which at least one of the hydrogen atoms of an alkyl group is replaced by a fluorine atom. Examples of fluorinated alkyl groups represented by Rf of formula (1) with 1 to 3 carbon atoms include groups in which at least one hydrogen atom of an alkyl group represented by R with 1 to 3 carbon atoms is replaced by a fluorine atom. The lower limit of the number of fluorine atoms in Rf is 1, preferably 2, and more preferably 3. The upper limit of the number of fluorine atoms is, for example, 7, but may be 6, 5, 4, or 3. The number of carbon atoms in Rf is preferably 2.

[0124] Rf is -CH ２ CH ｎ F ３－ｎ It is preferable that the group is represented by (where n is 0, 1, or 2). It is preferable that n is 0.

[0125] Examples of fluorinated diethers 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, and ethyl-2-(2-fluoroethoxy)ethyl ether. One or more types of fluorinated diethers can be used.

[0126] The lower limit of the fluorinated diether content relative to the total content of the non-aqueous solvent (total of fluorinated diether and other non-aqueous solvents) and ionic liquid in the non-aqueous electrolyte is preferably 10% by volume, more preferably 20% by volume, even more preferably 25% by volume, and may also be 30% by volume. The upper limit of the fluorinated diether content is preferably 60% by volume, more preferably 50% by volume, even more preferably 40% by volume, even more preferably 35% by volume, and may also be 30% by volume. By having the fluorinated diether content within the above range, it is possible to increase the initial discharge capacity of the non-aqueous electrolyte energy storage element.

[0127] When the non-aqueous electrolyte contains an ionic liquid, the lower limit of the fluorinated diether content relative to the total of the fluorinated diether and the ionic liquid is preferably 10% by volume, more preferably 20% by volume, even more preferably 25% by volume, and may also be 30% by volume. The upper limit of the fluorinated diether content is preferably 60% by volume, more preferably 50% by volume, even more preferably 40% by volume, even more preferably 35% by volume, and may also be 30% by volume. By having the fluorinated diether content within the above range, it is possible to increase the initial discharge capacity of the non-aqueous electrolyte energy storage element.

[0128] An ionic liquid is an ionic compound that, at least partially, exhibits a liquid state at room temperature (20°C) and one atmosphere of pressure.

[0129] Examples of cations that constitute ionic liquids include quaternary ammonium cations, imidazolium cations, pyrrolidinium cations, piperidinium cations, pyridinium cations, pyrrolium cations, pyrazolium cations, pyrrolium cations, quaternary phosphonium cations, sulfonium cations, and the like.

[0130] Examples of quaternary ammonium cations include tetraalkylammonium cations such as trimethylethylammonium cation, trimethylpropylammonium cation, trimethylbutylammonium cation, trimethylhexylammonium cation, and tetrapentylammonium cation.

[0131] Examples of imidazolium-based 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.

[0132] Examples of pyrrolidinium-based cations include 1,1-dimethylpyrrolidinium cation, 1-ethyl-1-methylpyrrolidinium cation, 1-methyl-1-propylpyrrolidinium cation, and 1-butyl-1-methylpyrrolidinium cation.

[0133] Examples of piperidinium-based cations include 1,1-dimethylpiperidinium cation, 1-ethyl-1-methylpiperidinium cation, 1-methyl-1-propylpiperidinium cation, and 1-butyl-1-methylpiperidinium cation.

[0134] Examples of pyridinium-based 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.

[0135] 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.

[0136] Examples of pyrazolium-based cations include 1,2-dimethylpyrazolium cation, 1-ethyl-2-methylpyrazolium cation, 1-propyl-2-methylpyrazolium cation, and 1-butyl-2-methylpyrazolium cation.

[0137] 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.

[0138] Examples of quaternary phosphonium cations include tetramethylphosphonium cation, tetraethylphosphonium cation, trimethylethylphosphonium cation, trimethylpropylphosphonium cation, trimethylbutylphosphonium cation, tetraphenylphosphonium cation, and trimethylmethoxymethylphosphonium cation.

[0139] Examples of sulfonium cations include trimethylsulfonium cation, triethylsulfonium cation, and tributylsulfonium cation.

[0140] The cation constituting the ionic liquid is preferably at least one selected from the group consisting of quaternary ammonium cations, imidazolium-based cations, pyrrolidinium-based cations, piperidinium-based cations, quaternary phosphonium cations, and sulfonium cations, more preferably at least one selected from the group consisting of imidazolium-based cations, pyrrolidinium-based cations, and piperidinium-based cations, and even more preferably pyrrolidinium-based cations. When the cation constituting the ionic liquid is such a cation, the initial discharge capacity of the non-aqueous electrolyte energy storage element can be increased. These cations may be present in one or more forms.

[0141] The anions that make up the ionic liquid are the same as those listed for the anions that make up the electrolyte salt. Idide anions are preferred as the anions that make up the ionic liquid, and bis(trifluoromethanesulfonyl)imide anions (TFSI) － ) and bis(fluorosulfonyl)imide anion (FSI － At least one selected from the group consisting of ) is more preferably a bis(fluorosulfonyl)imide anion (FSI － ) is even more preferable. Furthermore, it is preferable that the anions constituting the ionic liquid have a fluorine atom. When the anions constituting the ionic liquid are such anions, the initial discharge capacity of the non-aqueous electrolyte energy storage element can be made larger, etc. One or more of these anions may be included.

[0142] The anions constituting the electrolyte salt and the ionic liquid may be the same or different, but at least one of the electrolyte salt and the ionic liquid may contain a bis(fluorosulfonyl)imide anion (FSI － It is preferable that the non-aqueous electrolyte contains a bis(fluorosulfonyl)imide anion (FSI － It is preferable that the following are included. In such cases, the initial discharge capacity of the non-aqueous electrolyte energy storage element can be increased, etc.

[0143] Furthermore, it is preferable that the anions present in the non-aqueous electrolyte are substantially only imide anions, and substantially bis(trifluoromethanesulfonyl)imide anions (TFSI － ) and bis(fluorosulfonyl)imide anion (FSI － It is more preferable that the anions consist of at least one selected from the group consisting of the above. For example, the content ratio of these anions to the total 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 having the anions in the non-aqueous electrolyte in this configuration, the ionic conductivity of the non-aqueous electrolyte is increased, and the initial discharge capacity of the non-aqueous electrolyte energy storage element can be increased.

[0144] The lower limit of the ionic liquid content relative to the total content of the non-aqueous solvent (total of fluorinated diether and other non-aqueous solvents) and ionic liquid in the non-aqueous electrolyte may be, for example, 10 vol% or 20 vol%, but 30 vol% is preferred, 40 vol% is more preferred, 50 vol% is even more preferred, 60 vol% is even more preferred, and it may also be 65 vol% or 70 vol%. By setting the ionic liquid content above the lower limit, it is possible to increase the initial discharge capacity of the non-aqueous electrolyte energy storage element while improving the flame retardancy of the non-aqueous electrolyte. The upper limit of the ionic liquid content is preferred, 80 vol% is more preferred, 75 vol% is even more preferred, and it may also be 70 vol%. By setting the ionic liquid content below the upper limit, it is possible to increase the initial discharge capacity of the non-aqueous electrolyte energy storage element.

[0145] Other non-aqueous solvents that may be included in the non-aqueous electrolyte include ethers other than fluorinated diethers, cyclic carbonates, linear carbonates, carboxylic acid esters, phosphate esters, amides, nitriles, etc. However, the lower limit of the total content of fluorinated diether and ionic liquid relative to the total content of non-aqueous solvents (total of fluorinated diether and other non-aqueous solvents) and ionic liquid in the non-aqueous electrolyte is preferably 80% by volume, more preferably 85% by volume, even more preferably 90% by volume, even more preferably 95% by volume, and may also be 97% or 99% by volume. In this way, because the total of non-aqueous solvents and ionic liquids in the non-aqueous electrolyte is mainly composed of fluorinated diether and ionic liquid, the initial discharge capacity of the non-aqueous electrolyte energy storage element tends to be larger. The upper limit of the total content of fluorinated diether and ionic liquid may be 100% by volume.

[0146] Nonionic compounds containing sulfur are typically organic compounds containing sulfur. Examples of nonionic compounds containing sulfur include sulfates, sulfonic acid esters, sulfones, sulfites, sulfoxides, sulfides, and disulfides. One or more nonionic compounds containing sulfur can be used.

[0147] Sulfates are compounds in which two carbon atoms each form an oxysulfonyloxy group (-O-S (=O)). ２ This refers to compounds that contain a structure bonded to an O-). Examples of sulfates include cyclic sulfates and linear sulfates. Specific examples of cyclic sulfates include ethylene sulfate, 1,3-propylene sulfate, 2,3-propylene sulfate, 4,5-pentene sulfate, 4,4'-bis(2,2-dioxo-1,3,2-dioxathiolane), and 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane. Specific examples of linear sulfates include dimethyl sulfate and diethyl sulfate.

[0148] Sulfonic acid esters are compounds in which two carbon atoms each form a sulfonyloxy group (-S (=O)).２ This refers to compounds containing a structure bonded to an O-). Examples of sulfonic acid esters include cyclic sulfonic acid esters and linear sulfonic acid esters. Cyclic sulfonic acid esters having one sulfonyloxy group in one ring structure are also called sultones. Specific examples of cyclic sulfonic acid esters include 1,3-propanesultone, 1,4-butanesultone, 1,3-propensultone, 1-methyl-1,3-propensultone, 2-methyl-1,3-propensultone, 3-methyl-1,3-propensultone, methylene-methanedisulfonic acid ester, ethylene-methanedisulfonic acid ester, etc. Cyclic sulfonic acid esters may have one sulfonyloxy group in one ring structure, or they may have two or three or more sulfonyloxy groups. Specific examples of linear sulfonic acid esters include methyl methanesulfonate and ethyl methanesulfonate.

[0149] Sulfones are compounds in which two carbon atoms each form a sulfonyl group (-S (=O)). ２ This refers to compounds that contain a structure bonded to a ligature (-). Examples of sulfones include cyclic sulfones and linear sulfones. Specific examples of cyclic sulfones include sulfolane, 3-methylsulfolane, 3-sulfolene, 1,1-dioxothiophene, 3-methyl-2,5-dihydrothiophene-1,1-dioxide, and methyl 3-sulfolene-3-carboxylate. Specific examples of linear sulfones include dimethyl sulfone, diethyl sulfone, ethylmethyl sulfone, and divinyl sulfone.

[0150] Sulfites are compounds that contain a structure in which two carbon atoms are each bonded to an oxysulfinyloxy group (-O-S(=O)-O-). Examples of sulfites include cyclic sulfites and linear sulfites. Specific examples of cyclic sulfites include ethylene sulfite, 1,2-propylene glycol sulfite, trimethylene sulfite, and 1,3-butylene glycol sulfite. Specific examples of linear sulfites include dimethyl sulfite.

[0151] Sulfoxides are compounds that contain a structure in which two carbon atoms are each bonded to a sulfinyl group (-S (=O)-). Examples of sulfoxides include cyclic sulfoxides and linear sulfoxides. Specific examples of cyclic sulfoxides include tetramethylene sulfoxide. Specific examples of linear sulfoxides include dimethyl sulfoxide and diethyl sulfoxide.

[0152] Sulfides are compounds that contain a structure in which two carbon atoms are each bonded to a divalent sulfur (-S-). Examples of sulfides include cyclic sulfides and linear sulfides. Specific examples of cyclic sulfides include tetrahydrothiophene, thiophene, thiane, 1,3-dithiane, 5,6-dihydro-1,4-dithiyne-2,3-dicarboxylic anhydride, and 3,4-thiophenedicarboxylic anhydride. Specific examples of linear sulfides include diallyl sulfide, diphenyl sulfide, and thioanisole.

[0153] Disulfides are compounds that contain a structure in which two carbon atoms are each bonded to a disulfide group (-S-S-). Examples of disulfides include cyclic disulfides and linear disulfides. Specific examples of disulfides include diphenyl disulfide, dipyridinium disulfide, and diallyl disulfide.

[0154] Nonionic compounds containing the element sulfur include sulfonyl groups (-S (=O) ２ Compounds containing (-) are preferred. Examples of such compounds include the sulfates, sulfonic acid esters, and sulfones mentioned above, with sulfonic acid esters being preferred. Furthermore, nonionic compounds containing sulfur are preferably cyclic compounds, more preferably cyclic sulfonic acid esters, and even more preferably sultones. Nonionic compounds containing sulfur are also preferably composed only of sulfur, oxygen, carbon, and hydrogen as constituent elements.

[0155] Among cyclic sulfonic acid ers, sultones having one sulfonyloxy group in one ring structure are preferred, and sultones having one sulfonyloxy group in one molecule are also preferred. Furthermore, sultones with a five-membered ring or a six-membered ring are preferred, sultones with a five-membered ring are more preferred, and 1,3-propanesultone or 1,3-propenesultone are even more preferred.

[0156] The lower limit of the content of nonionic compounds containing sulfur in the nonaqueous electrolyte is preferably 0.1% by mass, more preferably 0.3% by mass, even more preferably 0.5% by mass, and even more preferably 0.7% by mass, 1% by mass, 2% by mass, or 3% by mass. By setting the content of the nonionic compounds containing sulfur above the lower limit, a particularly sufficient film is formed on the positive electrode surface, which can increase the initial discharge capacity of the nonaqueous electrolyte energy storage element. The lower limit of the content of the nonionic compounds containing sulfur may be 4% by mass, 5% by mass, 6% by mass, 7% by mass, 8% by mass, 9% by mass, or 10% by mass. The upper limit of the content of the nonionic compounds containing sulfur is preferably 20% by mass, more preferably 15% by mass, even more preferably 10% by mass, and even more preferably 7% by mass, 5% by mass, 4% by mass, or 3% by mass. By keeping the content of the nonionic compound containing the above-mentioned sulfur element below the above upper limit, the formation of an excessive film on the positive electrode surface is suppressed, and the initial discharge capacity of the non-aqueous electrolyte energy storage element can be increased. The upper limit of the content of the nonionic compound containing the above-mentioned sulfur element may be 2% by mass or 1% by mass.

[0157] The lower limit of the total content of electrolyte salts, fluorinated diethers, ionic liquids, and nonionic compounds containing sulfur elements in the nonaqueous electrolyte is preferably 80% by mass, more preferably 85% by mass, even more preferably 90% by mass, even more preferably 95% by mass, and may also be 97% by mass or 99% by mass. Thus, because the nonaqueous electrolyte is mainly composed of electrolyte salts, fluorinated diethers, ionic liquids, and nonionic compounds containing sulfur elements, the initial discharge capacity of the nonaqueous electrolyte energy storage element tends to be larger. The upper limit of the total content of the above-mentioned electrolyte salts, fluorinated diethers, ionic liquids, and nonionic compounds containing sulfur elements may be 100% by mass.

[0158] Non-aqueous electrolytes may contain other components besides electrolyte salts, non-aqueous solvents (fluorinated diethers and other non-aqueous solvents), ionic liquids, and nonionic compounds containing sulfur elements. Examples of other components include additives other than nonionic compounds containing sulfur elements.

[0159] The additive may be an ionic compound or a nonionic compound. If the additive is an ionic compound, it may also function as an electrolyte salt or an ionic liquid. One or more additives may be used. When an additive is used in a nonaqueous electrolyte, the content of the additive (excluding nonionic compounds containing sulfur) in the nonaqueous electrolyte is preferably 0.01% by mass or more and 10% by mass or less, more preferably 0.1% by mass or more and 7% by mass or less, even more preferably 0.2% by mass or more and 5% by mass or less, and particularly preferably 0.3% by mass or more and 3% by mass or less.

[0160] The lower limit of the viscosity of the non-aqueous electrolyte at 25°C may be, for example, 10 mPa·s or 20 mPa·s, but 30 mPa·s is preferred, and 40 mPa·s or 50 mPa·s is more preferred. The non-aqueous electrolyte energy storage element according to one embodiment of the present invention can increase the initial discharge capacity even when a non-aqueous electrolyte with such relatively high viscosity is used. The upper limit of the viscosity of the non-aqueous electrolyte at 25°C is, for example, 100 mPa·s is preferred, 90 mPa·s is more preferred, and 80 mPa·s, 70 mPa·s, or 60 mPa·s is even more preferred. By setting the viscosity of the non-aqueous electrolyte to be below the above upper limit, the initial discharge capacity of the non-aqueous electrolyte energy storage element can be increased.

[0161] (Container) The container houses the electrode body and non-aqueous electrolyte in its internal space. The container material can be a metal material such as aluminum or stainless steel, or a resin material, with metal materials being preferred from the viewpoint of strength, etc. A composite material of metal and resin materials can also be used.

[0162] The shape of the container is not particularly limited, but it can be cylindrical, rectangular (square), disc-shaped, etc. The container may also be in the form of a sheet or other shape formed from a metal-resin composite film.

[0163] (Shape and application of non-aqueous electrolyte energy storage element) The shape of the non-aqueous electrolyte energy storage element according to one embodiment of the present invention is not particularly limited. The non-aqueous electrolyte energy storage element may be, for example, a cylindrical battery, a prismatic battery, a flat battery, a coin cell battery, a button cell battery, etc.

[0164] The applications of the non-aqueous electrolyte energy storage element according to one embodiment of the present invention are not particularly limited. The non-aqueous electrolyte energy storage element can be used, for example, as a power source for automobiles such as electric vehicles, hybrid vehicles, and plug-in hybrid vehicles, as a power source for electronic devices such as personal computers and communication terminals, and as a power storage power source.

[0165] The non-aqueous electrolyte energy storage element of the present invention can be used individually or in combination. The non-aqueous electrolyte energy storage element may be used individually when the required output and voltage are small. On the other hand, when at least one of the required output and voltage is large, the non-aqueous electrolyte energy storage element may be used as part of an energy storage device combined with other non-aqueous electrolyte energy storage elements. In an energy storage device composed of multiple non-aqueous electrolyte energy storage elements, at least one of the non-aqueous electrolyte energy storage elements included in the energy storage device may be a non-aqueous electrolyte energy storage element according to one embodiment of the present invention. The energy storage device will be described in detail later.

[0166] In the non-aqueous electrolyte energy storage element according to one embodiment of the present invention, the container may be restrained to maintain a certain thickness, or it may not be restrained in such a way. Alternatively, the container may be restrained to have a certain load applied to it. When the container is restrained, expansion of the container due to charge-discharge cycles, etc., may be suppressed, and a decrease in charge-discharge performance may be suppressed. When the container is restrained, the electrode body inside the container may or may not have a load applied to it. For example, the non-aqueous electrolyte energy storage element or energy storage device may be provided with a restraining member that performs such restraint.

[0167] <Method for Manufacturing a Non-Aqueous Electrolyte Energy Storage Element> A non-aqueous electrolyte energy storage element according to one embodiment of the present invention can be manufactured by a known method. The method for manufacturing the non-aqueous electrolyte energy storage element comprises preparing a positive electrode containing a sulfur-based active material and preparing a non-aqueous electrolyte containing an electrolyte salt, a fluorinated diether, and a nonionic compound containing an element of sulfur. The manufacturing method may also include preparing a negative electrode, preparing a separator, manufacturing an electrode body using the positive electrode, negative electrode, and separator, and housing the positive electrode, negative electrode, and non-aqueous electrolyte in a container. Housing the positive electrode, negative electrode, and non-aqueous electrolyte in a container may also mean housing the electrode body and non-aqueous electrolyte in a container.

[0168] Preparing the positive electrode may also mean manufacturing the positive electrode. The positive electrode can be manufactured by the method described above. Preparing the negative electrode may also mean manufacturing the negative electrode. The negative electrode can be manufactured by the method described above. Preparing the non-aqueous electrolyte may also mean preparing the non-aqueous electrolyte. The specific forms and preferred forms of the prepared positive electrode, negative electrode, non-aqueous electrolyte, etc. are the same as the specific forms and preferred forms of the positive electrode, negative electrode, non-aqueous electrolyte, etc. provided in the non-aqueous electrolyte energy storage element according to the embodiment of the present invention described above. The positive electrode, negative electrode, separator, non-aqueous electrolyte, etc. may be prepared by purchase or other means.

[0169] The electrode body (or positive and negative electrode) and the non-aqueous electrolyte can be housed in a container by known methods. If the non-aqueous electrolyte is a non-aqueous electrolyte solution, for example, the electrode body (or positive and negative electrode) can be housed in the container first, and then the non-aqueous electrolyte solution can be injected through an inlet provided in the container. The inlet is sealed after the non-aqueous electrolyte solution is injected. The method for manufacturing the non-aqueous electrolyte energy storage element may further include initial charging and discharging of the assembled uncharged energy storage element. In this manufacturing 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.

[0170] A non-aqueous electrolyte energy storage element according to one embodiment of the present invention may be manufactured by other methods.

[0171] <Energy Storage Device> The energy storage device 30 in Figure 2 comprises a plurality of energy storage units 20. Each energy storage unit 20 comprises a plurality of electrically connected non-aqueous electrolyte energy storage elements 1. The energy storage device 30 may also include busbars (not shown) for electrically connecting the plurality of non-aqueous electrolyte energy storage elements 1, busbars (not shown) for electrically connecting the plurality of energy storage units 20, etc. The energy storage unit 20 or the energy storage device 30 may also include a condition monitoring device (not shown) for monitoring the state of one or more non-aqueous electrolyte energy storage elements 1.

[0172] <Other Embodiments> The non-aqueous electrolyte energy storage element and the method for manufacturing the non-aqueous electrolyte energy storage element of the present invention are not limited to the embodiments described above, and various modifications may be made without departing from the spirit of the present invention. For example, the configuration of one embodiment may be added to the configuration of another embodiment, and a part of the configuration of one embodiment may be replaced with the configuration of another embodiment or with well-known technology. Furthermore, a part of the configuration of one embodiment may be deleted. Also, well-known technology may be added to the configuration of one embodiment.

[0173] In the above embodiment, a case in which a non-aqueous electrolyte energy storage element is used as a rechargeable non-aqueous electrolyte secondary battery was described, but the type, shape, dimensions, capacity, etc. of the non-aqueous electrolyte energy storage element are arbitrary. The present invention can also be applied to various secondary batteries, electric double-layer capacitors, lithium-ion capacitors, and other capacitors.

[0174] In the above embodiment, an electrode body in which a separator is interposed between the positive electrode and the negative electrode was described, but the electrode body does not need to have 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 either the positive electrode or the negative electrode. Thus, the positive electrode and the negative electrode may further have layers other than the base material, intermediate layer, and active material layer. Furthermore, the positive electrode and the negative electrode do not need to have a layered structure.

[0175] 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.

[0176] The components used in the preparation of the non-aqueous electrolytes in the examples and comparative examples are shown below. (Electrolyte salt) LiFSI: Lithium bis(fluorosulfonyl)imide (Ionic liquid) Py13FSI: 1-Methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide (Fluorinated diethers and other ethers) TFEME: 2-(2,2,2-trifluoroethoxy)ethyl methyl ether (where R is a methyl group and Rf is -CH in formula (1)) ２ CF ３Compounds represented by ) TFETFPE: 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (nonionic compounds containing sulfur and other components (additives)) PS: 1,3-propanesultone PRS: 1,3-propensultone LiDFOB: lithium difluorooxalate borate LiNO ３ Lithium nitrate (LiPF) ６ : Lithium hexafluorophosphate

[0177] [Example 1] (Preparation of positive electrode) A mixture of elemental sulfur, a sulfur-based active material, and porous carbon was mixed in a mass ratio of 70:30. This mixture was placed in a sealed electric furnace. After 1 hour of argon flow, the temperature was raised to 150°C at a heating rate of 5°C / min and held for 5 hours. Then, it was allowed to cool to 80°C, the temperature at which elemental sulfur solidifies. After that, the temperature was raised again to 300°C at a heating rate of 5°C / min and held for 2 hours to produce a composite (sulfur-porous carbon composite: SPC). Using water as a dispersion medium, a positive electrode mixture paste containing the above-mentioned composite, conductive agents acetylene black and carbon nanotubes, dispersant carboxymethylcellulose, thickener polyacrylic acid, and binder styrene-butadiene rubber was applied to an aluminum positive electrode substrate (average thickness 15 μm) and dried. The mass per unit area of ​​the positive electrode active material layer after drying the dispersion medium was 10 mg / cm². ２ The amount of positive electrode mixture paste applied was adjusted accordingly. Through the above steps, a positive electrode was obtained in which a positive electrode active material layer was laminated on a positive electrode substrate.

[0178] (Preparation of the negative electrode) A pure metallic lithium foil (average thickness 600 μm) was prepared as the negative electrode.

[0179] (Preparation of Non-Aqueous Electrolyte) A non-aqueous electrolyte was prepared by mixing the ionic liquid Py13FSI and the fluorinated diether TFEME in a volume ratio of 70:30, and then adding the electrolyte salt LiFSI at a molality of 1.5 mol / kg to the mixture. Further adding PS, a nonionic compound containing sulfur, at a content of 1% by mass to the resulting liquid. The viscosity of the above liquid obtained by adding LiFSI at a molality of 1.5 mol / kg to the mixture of Py13FSI and TFEME in a volume ratio of 70:30 was 56.3 mPa·s at 25°C.

[0180] (Assembly of Non-Aqueous Electrolyte Energy Storage Element) As a separator, a separator was prepared in which inorganic particle layers were laminated on both sides of a polyethylene microporous membrane, and which had high wettability to the extent that the non-aqueous electrolyte could seep into the pores. Using the above positive electrode, negative electrode, separator and non-aqueous electrolyte, the non-aqueous electrolyte energy storage element of Example 1 was obtained.

[0181] [Examples 2 to 5, Comparative Examples 1 to 6] Non-aqueous electrolyte energy storage elements for Examples 2 to 5 and Comparative Examples 1 to 6 were obtained in the same manner as in Example 1, except that the composition of the non-aqueous electrolyte was as shown in Table 1.

[0182] [Evaluation] (Initial Charge / Discharge) The following initial charge / discharge procedures were performed on each of the obtained non-aqueous electrolyte energy storage elements in a constant temperature bath at 25°C. First, as the initial discharge, constant current (CC) discharge was performed under the conditions of a discharge current of 0.1C and a discharge termination voltage of 1.0V. Then, as the initial charge, constant current constant voltage (CCCV) charging was performed under the conditions of a charging current of 0.05C and a charge termination voltage of 3.0V until the total charging time reached 30 hours. Next, as the second discharge, constant current (CC) discharge was performed under the conditions of a discharge current of 0.1C and a discharge termination voltage of 1.0V. Note that 1C was defined as the current that can charge the theoretical capacity based on the design of the non-aqueous electrolyte energy storage element in one hour. The theoretical capacity (mAh) based on the design of the non-aqueous electrolyte energy storage element is defined as the capacity density per unit area of ​​the positive electrode active material layer (mAh / cm³). ２ ) and the area of ​​the positive electrode active material layer (cm²) ２The product of the two values ​​was calculated. In addition, a 10-minute rest period was provided after the first discharge and after the first charge. The discharge amount (discharge capacity) in the second discharge was divided by the mass of the sulfur-based active material (sulfur element) to obtain the discharge capacity. Also, in the second discharge, the discharge amount until the discharge curve reached a plateau (flat region) of 1.8V was divided by the mass of the sulfur-based active material (sulfur element) to obtain the amount of electricity. The results are shown in Table 1. Furthermore, Figure 3 shows the discharge curves for each non-aqueous electrolyte energy storage element in Examples 1 and 2 and Comparative Examples 1 to 4 during the initial stage of the second discharge (from 0 mAh / g to 100 mAh / g of discharge amount divided by the mass of the sulfur-based active material (sulfur element)).

[0183]

[0184] As shown in Table 1, the non-aqueous electrolyte energy storage elements in Examples 1 to 5, each containing PS or PRS, a nonionic compound containing sulfur, along with TFEME, a fluorinated diether, as the non-aqueous electrolyte, had a discharge capacity of 1600 mAh / g or more, indicating a large initial discharge capacity. On the other hand, the non-aqueous electrolyte energy storage elements in Comparative Examples 1 to 4, each containing a non-aqueous electrolyte that does not contain a nonionic compound containing sulfur, or that contains other components (additives) instead of a nonionic compound containing sulfur, had a small initial discharge capacity. Furthermore, the non-aqueous electrolyte energy storage elements in Comparative Examples 5 and 6, each containing TFETFPE, which is not a fluorinated diether, had a small initial discharge capacity regardless of whether the non-aqueous electrolyte contained a nonionic compound containing sulfur. Furthermore, as shown in Table 1 and Figure 3, it was confirmed that by including a nonionic compound containing sulfur in the nonaqueous electrolyte, the amount of discharge electricity required to reach the 1.8V plateau in the second discharge was reduced, and the higher the content of the nonionic compound containing sulfur, the lower the amount of discharge electricity required to reach the 1.8V plateau. These results suggest that including a nonionic compound containing sulfur in the nonaqueous electrolyte suppresses the elution of polysulfides from the positive electrode.

[0185] This invention can be applied to non-aqueous electrolyte energy storage elements used as power sources for electronic devices such as personal computers and communication terminals, as well as for automobiles and industrial applications.

[0186] 1. Non-aqueous electrolyte energy storage element 2. Electrode body 3. Container 4. Positive electrode lead 5. Positive electrode external terminal 6. Negative electrode lead 7. Negative electrode external terminal 20. Energy storage unit 30. Energy storage device

Claims

1. A non-aqueous electrolyte energy storage element comprising a positive electrode containing a sulfur-based active material and a non-aqueous electrolyte containing an electrolyte salt, a fluorinated diether, and a nonionic compound containing an element of sulfur.

2. The non-aqueous electrolyte energy storage element according to claim 1, wherein the content of the nonionic compound containing the sulfur element in the non-aqueous electrolyte is 0.1% by mass or more and 20% by mass or less.

3. The non-aqueous electrolyte energy storage element according to claim 1 or claim 2, wherein the non-ionic compound containing the above-mentioned sulfur element contains a sulfonyl group.

4. The non-aqueous electrolyte energy storage element according to claim 1 or claim 2, wherein the non-ionic compound containing the above-mentioned sulfur element is a sultone.

5. The non-aqueous electrolyte energy storage element according to claim 1, wherein the non-aqueous electrolyte further contains an ionic liquid.

6. The non-aqueous electrolyte energy storage element according to claim 5, wherein the ionic liquid has at least one selected from the group consisting of quaternary ammonium cations, imidazolium-based cations, pyrrolidinium-based cations, piperidinium-based cations, quaternary phosphonium cations, and sulfonium cations.

7. The non-aqueous electrolyte energy storage element according to claim 5, wherein the ionic liquid has an imide anion.

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

9. The non-aqueous electrolyte energy storage element according to claim 1 or claim 2, wherein the fluorinated diether is represented by the following formula (1): R-O-(CH ２ ) ２ -O-Rf (1) (In formula (1), R is an alkyl group having 1 to 3 carbon atoms. Rf is a fluorinated alkyl group having 1 to 3 carbon atoms.) 10. 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 / cm². ２ The non-aqueous electrolyte energy storage element according to claim 1 or claim 5.

11. The non-aqueous electrolyte energy storage element according to claim 1 or 2, further comprising a negative electrode containing metallic lithium in at least the charged state.

12. The non-aqueous electrolyte energy storage element according to claim 1 or 2, wherein the content of the fluorinated diether relative to the total content of the non-aqueous solvent and any ionic liquid contained in the non-aqueous electrolyte is 10% by volume or more.

13. The non-aqueous electrolyte energy storage element according to claim 5 or claim 6, wherein the content of the ionic liquid relative to the total content of the non-aqueous solvent and the ionic liquid contained in the non-aqueous electrolyte is 30% by volume or more.

14. The non-aqueous electrolyte energy storage element according to claim 5 or claim 6, wherein the total content of the fluorinated diether and the ionic liquid relative to the total content of the non-aqueous solvent and the ionic liquid contained in the non-aqueous electrolyte is 80% by volume or more.

15. The non-aqueous electrolyte energy storage element according to claim 5 or claim 6, wherein the total content of the electrolyte salt, the fluorinated diether, the nonionic compound containing the sulfur element, and the ionic liquid in the non-aqueous electrolyte is 80% by mass or more.

16. The non-aqueous electrolyte energy storage element according to claim 1 or claim 5, wherein the viscosity of the non-aqueous electrolyte at 25°C is 30 mPa·s or more.

17. A method for manufacturing a non-aqueous electrolyte energy storage element, comprising: preparing a positive electrode containing a sulfur-based active material; and preparing a non-aqueous electrolyte containing an electrolyte salt, a fluorinated diether, and a nonionic compound containing an element of sulfur.

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