Nonaqueous electrolyte power storage element and method for manufacturing 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 ether, and a cyclic sulfur-based compound. The cyclic sulfur-based compound is at least one selected from the group consisting of cyclic sulfonic acid esters and cyclic sulfuric acid esters. The content of the cyclic sulfur-based compound in the nonaqueous electrolyte is not less than 0.1 mass% to less than 10 mass%.

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 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, a decrease in capacity due to charge-discharge cycles may easily occur.

[0006] The objective of the present invention is to improve the capacity retention rate after charge-discharge cycles in 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.

[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 ether, and a cyclic sulfur compound, wherein the cyclic sulfur compound is at least one selected from the group consisting of cyclic sulfonic acid esters and cyclic sulfuric acid esters, and the content of the cyclic sulfur compound in the non-aqueous electrolyte is 0.1% by mass or more and less than 10% by mass.

[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 ether, and a cyclic sulfur compound, wherein the cyclic sulfur compound is at least one selected from the group consisting of cyclic sulfonic acid esters and cyclic sulfuric acid esters, and the content of the cyclic sulfur compound in the non-aqueous electrolyte is 0.1% by mass or more and less than 10% by mass.

[0009] According to one aspect of the present invention, a non-aqueous electrolyte energy storage element and a method for manufacturing a non-aqueous electrolyte energy storage element can be used in 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 the capacity retention rate after charge-discharge cycles can be increased.

[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.

[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 ether and a cyclic sulfur compound, wherein the cyclic sulfur compound is at least one selected from the group consisting of cyclic sulfonic acid esters and cyclic sulfuric acid esters, and the content of the cyclic sulfur compound in the non-aqueous electrolyte is 0.1% by mass or more and less than 10% by mass.

[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 can improve the capacity retention rate after charge-discharge cycles. The reason for this is not clear, but the following reasons are speculated. One reason why capacity decreases with charge-discharge cycles in conventional non-aqueous electrolyte energy storage elements that use a positive electrode containing a sulfur-based active material and a non-aqueous electrolyte containing ether is that polysulfides (Li) generated in the positive electrode ２ S ｘ One of the problems is that polysulfides may dissolve 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 predetermined amount of a cyclic sulfur compound, which is at least one selected from the group consisting of cyclic sulfonic acid esters and cyclic sulfuric acid esters. It is thought that such a cyclic sulfur compound forms an appropriate amount of film on the positive electrode surface, thereby suppressing the dissolution of polysulfides from the positive electrode into the non-aqueous electrolyte. Furthermore, it is thought that the fact that the non-aqueous electrolyte contains a fluorinated ether as a non-aqueous solvent also affects the suppression of the dissolution of polysulfides from the positive electrode into the non-aqueous electrolyte. For these reasons, it is presumed that, according to the non-aqueous electrolyte energy storage element described in [1] above, the capacity retention rate after charge-discharge cycles can be increased in 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.

[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,１ Identification is performed using the internal standard method by H-NMR. IC measurement is performed specifically as follows: (A1) Sampling 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 fluorine ethers and cyclic sulfur compounds 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 fluorinated ether may also contain a fluorinated cyclic ether.

[0017] The non-aqueous electrolyte energy storage element described in [2] above has a non-aqueous electrolyte that contains a fluorinated cyclic ether as a fluorinated ether, which further suppresses the elution of polysulfides from the positive electrode into the non-aqueous electrolyte and can further improve the capacity retention rate after charge-discharge cycles.

[0018] [3] In the non-aqueous electrolyte energy storage element described in [1] or [2] above, the fluorinated ether may contain a fluorinated chain ether.

[0019] The non-aqueous electrolyte energy storage element described in [3] above can increase the initial discharge capacity by increasing the solubility and diffusivity of the electrolyte salt in the non-aqueous electrolyte, as the non-aqueous electrolyte contains fluorinated chain ether as a fluorinated ether. In other words, the non-aqueous electrolyte energy storage element described in [3] above can increase the capacity retention rate after charge-discharge cycles and also increase the initial discharge capacity.

[0020] [4] In the non-aqueous electrolyte energy storage element described in any of [1] to [3] above, the fluorinated ether may contain a first fluorinated ether having a donor number of 8.0 or more and 15.0 or less.

[0021] The non-aqueous electrolyte energy storage element described in [4] above has a non-aqueous electrolyte that contains a first fluorinated ether with a relatively low donor number as a fluorinated ether, which further suppresses the elution of polysulfides from the positive electrode into the non-aqueous electrolyte and can further improve the capacity retention rate after charge-discharge cycles.

[0022] [5] In the non-aqueous electrolyte energy storage element described in any of [1] to [4] above, the fluorinated ether may contain a second fluorinated ether having more than 15.0 donors.

[0023] The non-aqueous electrolyte energy storage element described in [5] above can increase the initial discharge capacity by increasing the solubility and diffusivity of the electrolyte salt in the non-aqueous electrolyte, as the non-aqueous electrolyte contains a second fluorinated ether with a relatively high donor number. In other words, the non-aqueous electrolyte energy storage element described in [5] above can increase the capacity retention rate after charge-discharge cycles and also increase the initial discharge capacity.

[0024] [6] In the non-aqueous electrolyte energy storage element described in any of [1] to [5] above, the cyclic sulfur compound may be at least one selected from the group consisting of 1,3-propanesultone, 1,3-propensultone, 1,4-butanesultone, 2,4-butanesultone, ethylene sulfate, 2,3-propylene sulfate, 4,5-pentene sulfate, 1,3-propylene sulfate, 4,4'-bis(2,2-dioxo-1,3,2-dioxathiolane) and 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane.

[0025] The non-aqueous electrolyte energy storage element described in [6] above can further improve the capacity retention rate after charge-discharge cycles, etc.

[0026] [7] In the non-aqueous electrolyte energy storage element described in any of [1] to [6] above, the positive electrode further includes porous carbon that forms a composite with the sulfur-based active material, and the ratio of the volume of the charged sulfur-based active material to the pore volume of the porous carbon is 80% or less.

[0027] In the non-aqueous electrolyte storage element described in [7] above, when the ratio of the volume of the sulfur-based active material in the charged state to the pore volume of the porous carbon is 80% or less, the amount of the sulfur-based active material that bulges out of the pores of the porous carbon due to the expansion of the volume of the sulfur-based active material during discharge is small, and the contact between the bulged sulfur-based active material and the non-aqueous electrolyte is suppressed. Therefore, according to the non-aqueous electrolyte storage element described in [7] above, the elution of polysulfide from the positive electrode into the non-aqueous electrolyte is further suppressed, and the capacity retention rate after charge-discharge cycles can be increased, etc.

[0028] The measurement of the volume of the sulfur-based active material in the charged state and the pore volume of the porous carbon is performed according to the following procedure. First, a composite in a state containing no charge-transporting ions such as lithium ions before charge-discharge is prepared, or for the composite contained in the positive electrode of the non-aqueous electrolyte storage element, a composite in the charged state is prepared according to the following procedure. Note that a composite in a state containing no charge-transporting ions such as lithium ions before charge-discharge can be regarded as substantially equal to the composite in the charged state. The non-aqueous electrolyte storage element is charged at a constant current to the charge termination voltage during normal use at a current of 0.1 C. Then, the non-aqueous electrolyte storage element is disassembled to take out the composite, washed with 3,3,4,4-tetrafluorotetrahydrofuran (TFT-HF), and dried under reduced pressure at room temperature for 24 hours to obtain a composite in the charged state. When washing the composite, for the purpose of removing decomposition products adhering to the surface of the composite, etc., it may be further washed with an organic solvent other than TFT-HF, or washed with a mixed solvent of TFT-HF and an organic solvent other than TFT-HF, or ultrasonic treatment may be performed in an organic solvent. The obtained composite in the charged state is weighed, and the mass m １ of the composite in the charged state is obtained. The sulfur-based active material is removed by heat treatment of holding the composite in the charged state at 500 °C for a certain period of time in an inert atmosphere to obtain porous carbon. After the obtained porous carbon is cooled to room temperature, it is weighed, and the mass m ２ of the porous carbon is obtained. From the difference between the mass m １ and the mass m ２ , the mass m Ｓ of the sulfur-based active material in the charged state is obtained. The mass m ＳFrom the true density of the charged sulfur-based active material, the volume of the charged sulfur-based active material is determined. Next, the pore volume of the porous carbon treated above is measured using the nitrogen adsorption / desorption method, and the pore volume V per unit mass of the porous carbon is determined. ｐ We will find the above mass m. ２ and the above pore volume V ｐ The pore volume of porous carbon can be determined from the product of these two factors.

[0029] [8] In the non-aqueous electrolyte energy storage element described in any of [1] to [7] above, the positive electrode further includes porous carbon that forms a composite with the sulfur-based active material, and the ratio of the volume of the sulfur-based active material in the discharged state to the pore volume of the porous carbon is 140% or less.

[0030] In the non-aqueous electrolyte energy storage element described in [8] above, the ratio of the volume of the sulfur-based active material in the discharge state to the pore volume of the porous carbon is 140% or less. This reduces the amount of sulfur-based active material that spills out of the pores of the porous carbon when it is in the most expanded discharge state, and suppresses contact between the spilled sulfur-based active material and the non-aqueous electrolyte. Therefore, the non-aqueous electrolyte energy storage element described in [8] above further suppresses the elution of polysulfides from the positive electrode into the non-aqueous electrolyte, and improves the capacity retention rate after charge-discharge cycles.

[0031] [9] In the non-aqueous electrolyte energy storage element described in any of [1] to [8] above, the content of the fluorinated ether in the non-aqueous solvent in the non-aqueous electrolyte may be 50% by volume or more.

[0032] The non-aqueous electrolyte energy storage element described in [9] above is a preferred embodiment of the present invention.

[0033] A "non-aqueous solvent" is a nonionic compound that dissolves electrolyte salts, and includes fluorinated ethers and any other non-aqueous solvents. However, cyclic sulfonic acid esters and cyclic sulfate esters are not included in non-aqueous solvents, regardless of whether they dissolve electrolyte salts or not.

[0034]

[10] In the non-aqueous electrolyte energy storage element described in any of [1] to [9] above, the non-aqueous electrolyte may further contain an ionic liquid.

[0035] Ionic liquids have advantages such as being liquid at room temperature, having virtually no volatility, and possessing high flame retardancy, making them promising for use in non-aqueous electrolytes. However, non-aqueous electrolytes containing ionic liquids have high viscosity, resulting in low diffusivity of charge transport ions. Consequently, 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 incorporating ether along with the ionic liquid into the non-aqueous electrolyte, the viscosity of the non-aqueous electrolyte can be reduced, thereby improving high-rate discharge performance and other aspects. However, as mentioned above, when ether is incorporated into a non-aqueous electrolyte, polysulfides generated at the positive electrode tend to dissolve into the non-aqueous electrolyte, leading to a decrease in the capacity retention rate after charge-discharge cycles of the non-aqueous electrolyte energy storage device. Therefore, by incorporating fluorinated ether as the ether into such a non-aqueous electrolyte, and further incorporating a predetermined amount of a specific cyclic sulfur compound, the capacity retention rate after charge-discharge cycles of the non-aqueous electrolyte energy storage device can be improved. In other words, the non-aqueous electrolyte energy storage element described in

[10] 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 an ionic liquid, which eliminates the disadvantage of using an ionic liquid, namely the high viscosity of the non-aqueous electrolyte, while increasing the capacity retention rate after charge-discharge cycles.

[0036]

[11] In the non-aqueous electrolyte energy storage element described in

[10] above, the ionic liquid may have 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.

[0037]

[12] In the non-aqueous electrolyte energy storage element described in

[10] or

[11] above, the ionic liquid may have an imide anion.

[0038]

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

[12] above, the electrolyte salt may be an imide salt.

[0039] Each of the non-aqueous electrolyte energy storage elements described in

[11] to

[13] above is a preferred embodiment of the present invention.

[0040]

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

[13] 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.

[0041] The non-aqueous electrolyte energy storage element described in

[14] 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

[14] above can achieve both high energy density and high capacity retention rate after charge-discharge cycles. Also, as mentioned above, non-aqueous electrolytes containing ionic liquids are usually highly viscous, so if the mass per unit area of ​​the positive electrode active material layer is increased in a non-aqueous electrolyte energy storage element using a non-aqueous electrolyte containing ionic liquids, 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

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

[14] above, especially when the non-aqueous electrolyte further contains an ionic liquid, can exhibit good charge and discharge performance even though an ionic liquid is used in the non-aqueous electrolyte and a thick positive electrode active material layer is provided, and can achieve both high energy density and high capacity retention rate after charge and discharge cycles.

[0042] 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). ２This 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 each side 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.

[0043]

[15] The non-aqueous electrolyte energy storage element described in any of [1] to

[14] above may further include a negative electrode containing metallic lithium, at least in the charged state.

[0044] The non-aqueous electrolyte energy storage element described in

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

[0045]

[16] In the non-aqueous electrolyte energy storage element described in any of [2] to

[15] above, the content of the fluorinated cyclic ether relative to the total content of the non-aqueous solvent and any ionic liquid in the non-aqueous electrolyte may be 30% by volume or more and 90% by volume or less.

[0046]

[17] In the non-aqueous electrolyte energy storage element described in any of [3] to

[16] above, the content of the fluorinated chain ether relative to the total content of the non-aqueous solvent and any ionic liquid in the non-aqueous electrolyte may be 5% by volume or more and 60% by volume or less.

[0047]

[18] In the non-aqueous electrolyte energy storage element described in any of [4] to

[15] above, the content of the first fluorinated ether relative to the total content of the non-aqueous solvent and any ionic liquid in the non-aqueous electrolyte may be 30% by volume or more and 90% by volume or less.

[0048]

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

[16] above, the content of the second fluorinated ether relative to the total content of the non-aqueous solvent and any ionic liquid in the non-aqueous electrolyte may be 5% by volume or more and 60% by volume or less.

[0049]

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

[19] above, the content of the fluorinated ether relative to the total content of the non-aqueous solvent and any ionic liquid in the non-aqueous electrolyte may be 20% by volume or more.

[0050]

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

[20] above, the total content of ether and the ionic liquid relative to the total content of the non-aqueous solvent and the arbitrary ionic liquid in the non-aqueous electrolyte may be 90% by volume or more.

[0051] The term "ether" refers to all ethers contained in non-aqueous electrolytes, including fluorinated ethers.

[0052]

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

[21] above, the total content of the fluorinated ether and the ionic liquid relative to the total content of the non-aqueous solvent and any ionic liquid in the non-aqueous electrolyte may be 90% by volume or more.

[0053]

[23] In the non-aqueous electrolyte energy storage element described in any of

[10] to

[22] above, the content of the ionic liquid relative to the total content of the non-aqueous solvent and the ionic liquid in the non-aqueous electrolyte may be 3% by volume or more and 80% by volume or less.

[0054]

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

[23] above, the average number of donors of the non-aqueous solvent and any ionic liquid in the non-aqueous electrolyte may be 16.0 or less.

[0055] "Average donor number" refers to the average volume-based number of donors for each component. For example, if a non-aqueous solvent and any ionic liquid have a donor number of D Ａ , content V Ａ (Volume %) of component A and the number of donors D Ｂ , content V Ｂ (Volume %) of component B and the number of donors D Ｃ , content V Ｃ If the C component is (volume %), the average number of donors is D Ａ ×V Ａ / 100+D Ｂ ×V Ｂ / 100+D Ｃ ×V Ｃ It is / 100.

[0056]

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

[24] above, the average number of donors of the non-aqueous solvent and any ionic liquid in the non-aqueous electrolyte may be 10.0 or more.

[0057]

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

[25] above, the molal concentration of the electrolyte salt in the non-aqueous electrolyte may be 0.5 mol / kg or more.

[0058] The "molality" of an electrolyte salt refers to the amount of substance (mol) of the electrolyte salt based on the total mass (kg) of the non-aqueous solvent and any ionic liquid contained in the non-aqueous electrolyte.

[0059] Any of the non-aqueous electrolyte energy storage elements described in

[16] to

[26] above is a preferred embodiment of the present invention.

[0060]

[27] 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 ether and a cyclic sulfur compound, wherein the cyclic sulfur compound is at least one selected from the group consisting of cyclic sulfonic acid esters and cyclic sulfuric acid esters, and the content of the cyclic sulfur compound in the non-aqueous electrolyte is 0.1% by mass or more and less than 10% by mass.

[0061] According to the method for manufacturing a non-aqueous electrolyte energy storage element described in

[27] above, it is possible to manufacture a non-aqueous electrolyte energy storage element in which a positive electrode containing a sulfur-based active material and a non-aqueous electrolyte containing an ether are used, and the capacity retention rate after the charge-discharge cycle is improved.

[0062] 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.

[0063] <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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] (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.

[0068] 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, 3 μm or more and 1,000 μm or less. The lower limit of the average thickness of the positive electrode may be 5 μm, 10 μm, 20 μm, 30 μm, 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, 150 μm, 100 μm, or 50 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.

[0069] The positive electrode substrate is conductive. In this specification, "having conductivity" means that the volume resistivity is 10 －２This 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 ７ This means it is greater than or equal to Ω·cm.

[0070] 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.

[0071] 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.

[0072] The average thickness of the positive electrode substrate may be, for example, 1 μm or more and 50 μm or less. The lower limit of the average thickness of the positive electrode substrate may be 3 μm, 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, 15 μm, or 10 μm.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] As the sulfur-based active material, one that is elemental sulfur in the charged state is preferred. Note that a sulfur-based active material that is elemental sulfur in the charged state will be lithium sulfide (Li) in the discharged state. ２ It exists in the form of sulfur compounds such as S). However, even in sulfur-based active materials that are "elemental sulfur in the charged state," sulfur compounds such as lithium sulfide may remain in the charged state.

[0077] The lower limit of the sulfur element content in the charged sulfur-based active material is preferably 90% by mass, more preferably 95% by mass, and even more preferably 99% by mass. The upper limit of the sulfur element content in the charged sulfur-based active material may be 100% by mass.

[0078] The sulfur-based active material content in the positive electrode active material layer is preferably 50% by mass or more and 90% by mass or less, more preferably 55% by mass or more and 80% by mass or less, and even more preferably 60% by mass or more and 70% by mass or less.

[0079] 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.

[0080] The sulfur-based active material content in the complex may be 50% by mass or more and 90% by mass or less, or 60% by mass or more and 80% by mass or less.

[0081] 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.

[0082] The pore volume of porous carbon is, for example, 0.4 cm³. ３ / g or more 3.6cm ３ It may be less than or equal to 1.0 cm ３ / g or more 3.0cm ３ It may be less than / g.

[0083] The upper limit of the ratio of the volume of the charged sulfur-based active material to the pore volume of the porous carbon is preferably 80%, more preferably 75%, and may also be 70%, 65%, or 60%. By keeping the ratio of the volume of the charged sulfur-based active material to the pore volume of the porous carbon below the above upper limit, the capacity retention rate after charge-discharge cycles of the non-aqueous electrolyte energy storage element can be increased. The lower limit of the ratio of the volume of the charged sulfur-based active material to the pore volume of the porous carbon is preferably 40%, more preferably 45%, even more preferably 50%, and may also be 55%, 60%, 65%, or 70%. By keeping the ratio of the volume of the charged sulfur-based active material to the pore volume of the porous carbon above the above lower limit, the energy density of the non-aqueous electrolyte energy storage element can be increased. Furthermore, if the ratio of the volume of the charged sulfur-based active material to the pore volume of the porous carbon is above the lower limit mentioned above, the pores of the porous carbon are sufficiently filled with the sulfur-based active material to a certain extent, resulting in a relatively small specific surface area of ​​the composite. In such cases, when manufacturing the cathode by coating or other processes, the viscosity of the cathode mixture paste containing the composite is suppressed, thereby improving manufacturability.

[0084] The upper limit of the ratio of the volume of the sulfur-based active material in the discharged state to the pore volume of the porous carbon is preferably 140%, more preferably 130%, and may also be 120%, 110%, or 105%. By keeping the ratio of the volume of the sulfur-based active material in the discharged state to the pore volume of the porous carbon below the above upper limit, the capacity retention rate after charge-discharge cycles of the non-aqueous electrolyte energy storage element can be increased. The lower limit of the ratio of the volume of the sulfur-based active material in the discharged state to the pore volume of the porous carbon is preferably 70%, more preferably 80%, even more preferably 90%, and may also be 100%, 110%, or 120%. By keeping the ratio of the volume of the sulfur-based active material in the discharged state to the pore volume of the porous carbon above the above lower limit, the energy density of the non-aqueous electrolyte energy storage element can be increased. Furthermore, if the ratio of the volume of the sulfur-based active material in the discharge state to the pore volume of the porous carbon is above the above lower limit, the viscosity of the cathode mixture paste containing the composite can be suppressed when manufacturing the cathode by coating or the like, thereby improving manufacturability.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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. 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. 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. The lower limit of the content of the conductive agent may be 2% by mass, 3% by mass, 4% by mass, or 5% by mass.

[0090] Examples of binders include water-based binders and organic solvent-based binders.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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% to 8% by mass, and more preferably 0.1% to 6% by mass. Polyacrylic acid may also function as a binder.

[0097] 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.

[0098] 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.

[0099] 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, 6 mg / cm ２ More preferably, 7 mg / cm 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 or 7 mg / cm ２ That's fine.

[0100] (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.

[0101] (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.

[0102] 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, 3 μm or more and 1,000 μm or less. The lower limit of the average thickness of the negative electrode may be 4 μm, 5 μm, 10 μm, 20 μm, 30 μm, 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, 250 μm, 200 μm, 150 μm, 100 μm, or 50 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.

[0103] The negative electrode substrate is electrically conductive. Examples of materials for the negative electrode substrate include metals such as copper, nickel, titanium, iron, and their alloys (such as stainless steel), as well as carbon materials. Among these, nickel or nickel alloys are preferred.

[0104] 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.

[0105] The average thickness of the negative electrode substrate may be, for example, 1 μm or more and 35 μm or less. The lower limit of the average thickness of the negative electrode substrate may be 2 μm, 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, 10 μm, or 5 μm.

[0106] 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.

[0107] 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 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.

[0108] 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.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] 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.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] 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.

[0117] 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.

[0118] The negative electrode active material layer may be a non-porous layer (solid layer) or a porous layer, but a non-porous layer is preferred. 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).

[0119] 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, 1 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 2 μm, 3 μm, 5 μm, 10 μm, 20 μm, 30 μm, 40 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, 1,000 μm, 800 μm, 600 μm, 500 μm, 400 μm, 300 μm, 250 μm, 200 μm, 150 μm, 120 μm, 100 μm, 80 μm, 60 μm, or 40 μm.

[0120] (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 it (e.g., roll rolling).

[0121] (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.

[0122] 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.

[0123] 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.

[0124] Examples of binders used in the inorganic layer include those similar to those exemplified in the positive electrode active material layer.

[0125] 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.

[0126] 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.

[0127] 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.

[0128] (Electrode Body) As the electrode body, known structures such as wound electrode bodies and laminated electrode bodies can be used.

[0129] 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.

[0130] 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.

[0131] 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.

[0132] (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.

[0133] The non-aqueous electrolyte contains an electrolyte salt, a fluorinated ether, and a cyclic sulfur compound. The non-aqueous electrolyte may further contain an ionic liquid. In one embodiment of the present invention, the fluorinated ether 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 ether. The non-aqueous electrolyte may also be a non-aqueous electrolyte solution. That is, only a non-aqueous electrolyte solution may be used as the non-aqueous electrolyte. A non-aqueous electrolyte solution and a solid electrolyte may be used in combination. Furthermore, the non-aqueous electrolyte energy storage element may be a non-aqueous electrolyte energy storage element or a non-aqueous electrolyte secondary battery.

[0134] [Electrolyte Salt] 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.

[0135] 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 ４ F 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 ) ２２－ Examples of imide anions include PF. ６ － , PO 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.

[0136] 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, which can increase the initial discharge capacity of the non-aqueous electrolyte energy storage element and further increase the capacity retention rate after charge-discharge cycles. One or more types of anions can be used to constitute the electrolyte salt.

[0137] 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, even more preferably 1.0 mol / kg, and may be 1.1 mol / kg, 1.3 mol / kg, or 1.5 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 capacity retention rate after charge-discharge cycles of the non-aqueous electrolyte energy storage element can be further increased.

[0138] [Fluorinated Ethers] Fluorinated ethers are ethers containing the element fluorine. Fluorinated ethers may consist only of carbon, hydrogen, oxygen, and fluorine. Preferably, the oxygen elements in the fluorinated ether are only those that constitute the ether bond. That is, it is preferable that fluorinated ethers do not have oxygen-containing substituents such as hydroxyl groups and carboxyl groups. Fluorinated ethers may be monoethers (compounds with only one ether bond), diethers (compounds with two ether bonds), triethers (compounds with three ether bonds), etc. Fluorinated ethers are preferably saturated ethers. Saturated ethers are ethers that do not have unsaturated bonds between carbon atoms (carbon-carbon double bonds and carbon-carbon triple bonds). One or more types of fluorinated ethers can be used.

[0139] The fluorinated ether preferably contains a fluorinated cyclic ether. The inclusion of a fluorinated cyclic ether in the fluorinated ether can further improve the capacity retention rate after charge-discharge cycles of the non-aqueous electrolyte energy storage element. A fluorinated cyclic ether refers to a fluorinated ether having a ring structure. The fluorinated cyclic ether preferably has ether bonds in its ring structure. The fluorinated cyclic ether is preferably a saturated ether.

[0140] The lower limit of the number of ring members in the ring structure of the fluorinated cyclic ether is preferably 3, more preferably 4, and still more preferably 5. The upper limit of the number of ring members is preferably 8, more preferably 7, more preferably 6, and still more preferably 5. The lower limit of the number of carbon atoms in the fluorinated cyclic ether is preferably 2, more preferably 3, and still more preferably 4. The upper limit of the number of carbon atoms is preferably 7, more preferably 6, more preferably 5, and still more preferably 4. The lower limit of the number of fluorine atoms in the fluorinated cyclic ether is preferably 2, more preferably 3, and still more preferably 4. The upper limit of the number of fluorine atoms is preferably 10, more preferably 8, more preferably 6, and still more preferably 4.

[0141] The fluorinated cyclic ether is preferably represented by the following formula (1). (In formula (1), R １ Each of these is independently a hydrogen atom, a fluorine atom, an alkyl group having 1 to 4 carbon atoms, or a fluorinated alkyl group having 1 to 4 carbon atoms. However, multiple R １ At least one of these is a fluorine atom or a fluorinated alkyl group having 1 to 4 carbon atoms. n1 is an integer between 2 and 5.

[0142] R in equation (1) above １ When is an alkyl group or a fluorinated alkyl group, the number of carbon atoms is preferably 3 or less, and more preferably 2 or less. In formula (1) above, R １ The atom is preferably a hydrogen atom or a fluorine atom. n1 is preferably 4 or 5, and more preferably 4.

[0143] The number of donors for the fluorinated cyclic ether is not particularly limited, but it is preferably 8.0 to 15.0. That is, the fluorinated cyclic ether may be the first fluorinated ether described later.

[0144] Examples of fluorinated cyclic ethers include 3,3,4,4-tetrafluorotetrahydrofuran. One or more fluorinated cyclic ethers can be used.

[0145] The lower limit of the fluorinated cyclic ether content in the fluorinated ether is preferably 30% by volume, more preferably 40% by volume, even more preferably 50% by volume, even more preferably 60% by volume, and may also be 70% by volume. By setting the fluorinated cyclic ether content in the fluorinated ether to be above the above lower limit, the capacity retention rate after charge-discharge cycles of the non-aqueous electrolyte energy storage element can be further increased. The upper limit of the fluorinated cyclic ether content in the fluorinated ether may be 90% by volume, 85% by volume, or 80% by volume.

[0146] The lower limit of the fluorinated cyclic ether content relative to the total content of the non-aqueous solvent and any ionic liquid in a non-aqueous electrolyte is preferably 30% by volume, more preferably 40% by volume, even more preferably 50% by volume, even more preferably 60% by volume, and may also be 70% by volume. By setting the fluorinated cyclic ether content relative to the total content of the non-aqueous solvent and any ionic liquid to above the above lower limit, the capacity retention rate after charge-discharge cycles of the non-aqueous electrolyte energy storage element can be further increased. The upper limit of the fluorinated cyclic ether content relative to the total content of the non-aqueous solvent and any ionic liquid in a non-aqueous electrolyte may be 90% by volume, 85% by volume, 80% by volume, or 75% by volume.

[0147] The lower limit of the content of fluorinated cyclic ether relative to the total content of fluorinated ether and any ionic liquid in a non-aqueous electrolyte is preferably 30 vol%, more preferably 40 vol%, even more preferably 50 vol%, even more preferably 60 vol%, and may also be 70 vol%. By setting the content of fluorinated cyclic ether relative to the total content of fluorinated ether and any ionic liquid to be above the above lower limit, the capacity retention rate after charge-discharge cycles of the non-aqueous electrolyte energy storage element can be further increased. The upper limit of the content of fluorinated cyclic ether relative to the total content of fluorinated ether and any ionic liquid in a non-aqueous electrolyte may be 90 vol%, 85 vol%, 80 vol%, or 75 vol%.

[0148] The fluorinated ether may preferably contain a fluorinated linear ether, and more preferably contain both a fluorinated cyclic ether and a fluorinated linear ether. The inclusion of a fluorinated linear ether in the fluorinated ether can increase the initial discharge capacity of the non-aqueous electrolyte energy storage element. Furthermore, the inclusion of both a fluorinated cyclic ether and a fluorinated linear ether can increase the initial discharge capacity while further improving the capacity retention rate after charge-discharge cycles of the non-aqueous electrolyte energy storage element. A fluorinated linear ether refers to a fluorinated ether that does not have a cyclic structure. A fluorinated linear ether may consist only of carbon, hydrogen, oxygen, and fluorine. Preferably, the oxygen elements in the fluorinated linear ether are only those that constitute the ether bond. That is, it is preferable that the fluorinated linear ether does not have oxygen-containing substituents such as hydroxyl groups and carboxyl groups. The fluorinated linear ether is preferably a saturated ether. The fluorinated linear ether may be a monoether, diether, triether, etc., but it is preferably a diether. The fluorinated linear ether may be a fluorinated linear diether.

[0149] The lower limit of the number of carbon atoms in the fluorinated chain ether is preferably 3, more preferably 4, and still 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 chain ether is preferably 2, more preferably 3. The upper limit of the number of fluorine atoms may be 10, 9, preferably 8, and still more preferably 7, 6, 5, 4, or 3.

[0150] The fluorinated chain ether is preferably represented by the following formula (2). (In formula (2), R ２ R is an alkyl group having 1 to 3 carbon atoms or a fluorinated alkyl group having 1 to 3 carbon atoms. ３ R is a fluorinated alkyl group having 1 to 3 carbon atoms. ４ (This is an alkanediyl group with 1 to 3 carbon atoms. n2 is 0 or 1.)

[0151] R in equation (2) above ２ Alkyl groups are preferred, and methyl or ethyl groups are more preferred. ３ Preferably, the group is a fluorinated methyl group or a fluorinated ethyl group, more preferably a fluorinated ethyl group, and even more preferably a 2,2,2-trifluoroethyl group. ３ is, -CH ２ CH ｎ F ３－ｎ The group may be represented by (n is 0, 1, or 2). ４ As for, - (CH ２ ) ｍ - (where m is an integer between 1 and 3) is preferred, -CH ２ CH ２ - is more preferable. n2 is preferably 1.

[0152] The number of donors for the fluorinated chain ether is not particularly limited, but it is preferably greater than 15.0. That is, the fluorinated chain ether may be a second fluorinated ether as described later.

[0153] Examples of fluorinated chain ethers include 2-(2,2,2-trifluoroethoxy)ethyl methyl ether, 2-fluoroethoxymethoxyethane, ethoxy-2-fluoroethoxyethane, and ethyl-2-(2,2,2-trifluoroethoxy)ethyl ether. One or more types of fluorinated chain ethers can be used.

[0154] The lower limit of the fluorinated chain ether content in the fluorinated ether is preferably 10% by volume, more preferably 20% by volume, and may also be 30% by volume or 40% by volume. By setting the fluorinated chain ether content in the fluorinated ether to be above the above lower limit, the initial discharge capacity of the non-aqueous electrolyte energy storage element can be increased. The upper limit of the fluorinated chain ether content in the fluorinated ether may be 50% by volume, 40% by volume, 30% by volume or 25% by volume.

[0155] The lower limit of the fluorinated chain ether content relative to the total content of the non-aqueous solvent and any ionic liquid in a non-aqueous electrolyte is preferably 5 vol%, more preferably 10 vol%, even more preferably 15 vol%, and may also be 20 vol%, 25 vol%, 30 vol%, 35 vol%, or 40 vol%. By setting the fluorinated chain ether content relative to the total content of the non-aqueous solvent and any ionic liquid to above the above lower limit, the initial discharge capacity of the non-aqueous electrolyte energy storage element can be increased. The upper limit of the fluorinated chain ether content relative to the total content of the non-aqueous solvent and any ionic liquid in a non-aqueous electrolyte may be 60 vol%, and may also be 50 vol%, 40 vol%, or 30 vol%.

[0156] The lower limit of the content of fluorinated chain ether relative to the total content of fluorinated ether and any ionic liquid in a non-aqueous electrolyte is preferably 5 vol%, more preferably 10 vol%, even more preferably 15 vol%, and may also be 20 vol%, 25 vol%, 30 vol%, 35 vol%, or 40 vol%. By setting the content of fluorinated chain ether relative to the total content of fluorinated ether and any ionic liquid to be above the above lower limit, the initial discharge capacity of the non-aqueous electrolyte energy storage element can be increased. The upper limit of the content of fluorinated chain ether relative to the total content of fluorinated ether and any ionic liquid in a non-aqueous electrolyte may be 60 vol%, and may also be 50 vol%, 40 vol%, or 30 vol%.

[0157] The fluorinated ether may also preferably contain a first fluorinated ether with a donor number of 8.0 or more and 15.0 or less. By including a first fluorinated ether with a relatively low donor number as the fluorinated ether in the non-aqueous electrolyte, the capacity retention rate after charge-discharge cycles of the non-aqueous electrolyte energy storage element can be further increased. The upper limit of the donor number of the first fluorinated ether is preferably 14.5, more preferably 14.0, and even more preferably 13.5. By keeping the donor number of the first fluorinated ether below the above upper limit, the capacity retention rate after charge-discharge cycles can be further increased. The lower limit of the donor number of the first fluorinated ether is preferably 9.0, more preferably 10.0, and may be 11.0, 12.0, or 13.0.

[0158] The first fluorinated ether may be a linear ether or a cyclic ether, but it is preferably a cyclic ether (fluorinated cyclic ether).

[0159] Examples of the first fluorinated ether include ethyl-2-(2,2,2-trifluoroethoxy)ethyl ether (number of donors: 9.6), ethyl-2-(2,2-difluoroethoxy)ethyl ether (number of donors: 9.9), ethyl-2-(2-fluoroethoxy)ethyl ether (number of donors: 12.3), bis(2,2,2-trifluoroethyl) ether (number of donors: 10.3), and 3,3,4,4-tetrafluorotetrahydrofuran (number of donors: 13.2). One or more of the first fluorinated ethers can be used.

[0160] The lower limit of the content of the first fluorinated ether in the fluorinated ether is preferably 30% by volume, more preferably 40% by volume, even more preferably 50% by volume, even more preferably 60% by volume, and may also be 70% by volume. By setting the content of the first fluorinated ether in the fluorinated ether to be above the above lower limit, the capacity retention rate after charge-discharge cycles of the non-aqueous electrolyte energy storage element can be further increased. The upper limit of the content of the first fluorinated ether in the fluorinated ether may be 90% by volume, 85% by volume, or 80% by volume.

[0161] The lower limit of the content of the first fluorinated ether relative to the total content of the non-aqueous solvent and any ionic liquid in the non-aqueous electrolyte is preferably 30 vol%, more preferably 40 vol%, even more preferably 50 vol%, even more preferably 60 vol%, and may also be 70 vol%. By setting the content of the first fluorinated ether relative to the total content of the non-aqueous solvent and any ionic liquid to above the above lower limit, the capacity retention rate after charge-discharge cycles of the non-aqueous electrolyte energy storage element can be further increased. The upper limit of the content of the first fluorinated ether relative to the total content of the non-aqueous solvent and any ionic liquid in the non-aqueous electrolyte may be 98 vol%, and may also be 95 vol%, 90 vol%, 85 vol%, 80 vol%, or 75 vol%.

[0162] The lower limit of the content of the first fluorinated ether relative to the total content of the fluorinated ether and any ionic liquid in the non-aqueous electrolyte is preferably 30 vol%, more preferably 40 vol%, even more preferably 50 vol%, even more preferably 60 vol%, and may also be 70 vol%. By setting the content of the first fluorinated ether relative to the total content of the fluorinated ether and any ionic liquid to be above the above lower limit, the capacity retention rate after charge-discharge cycles of the non-aqueous electrolyte energy storage element can be further increased. The upper limit of the content of the first fluorinated ether relative to the total content of the fluorinated ether and any ionic liquid in the non-aqueous electrolyte may be 98 vol%, and may also be 95 vol%, 90 vol%, 85 vol%, 80 vol%, or 75 vol%.

[0163] The fluorinated ether may preferably include a second fluorinated ether with a donor number greater than 15.0, and more preferably include both a first fluorinated ether and a second fluorinated ether. By including a second fluorinated ether with a relatively high donor number as the fluorinated ether in the non-aqueous electrolyte, the initial discharge capacity of the non-aqueous electrolyte energy storage element can be increased. Furthermore, by including both a first and a second fluorinated ether in the fluorinated ether, the initial discharge capacity can be increased while further improving the capacity retention rate after charge-discharge cycles of the non-aqueous electrolyte energy storage element. The lower limit of the donor number of the second fluorinated ether is preferably 15.5, more preferably 16.0, even more preferably 16.5, and even more preferably 17.0, 17.5, 18.0, or 18.5. The upper limit of the donor number of the second fluorinated ether may be, for example, 25.0, or 24.0, 23.0, 22.0, 21.0, 20.0, or 19.0.

[0164] The second fluorinated ether may be a linear ether or a cyclic ether, but it is preferably a linear ether (fluorinated linear ether), and more preferably a fluorinated linear diether.

[0165] Examples of secondary fluorinated ethers include 2-(2,2,2-trifluoroethoxy)ethyl methyl ether (18.7 donors), 2-fluoroethoxymethoxyethane (19.4 donors), ethoxy-2-fluoroethoxyethane (20.1 donors), and ethyl-2-(2,2,2-trifluoroethoxy)ethyl ether (17.2 donors). One or more secondary fluorinated ethers can be used.

[0166] The lower limit of the content of the second fluorinated ether in the fluorinated ether is preferably 10% by volume, more preferably 20% by volume, and may also be 30% by volume or 40% by volume. By setting the content of the second fluorinated ether in the fluorinated ether to be above the above lower limit, the initial discharge capacity of the non-aqueous electrolyte energy storage element can be increased. The upper limit of the content of the second fluorinated ether in the fluorinated ether may be 50% by volume, and may also be 40% by volume, 30% by volume or 25% by volume.

[0167] The lower limit of the content of the second fluorinated ether relative to the total content of the non-aqueous solvent and any ionic liquid in the non-aqueous electrolyte is preferably 5 vol%, more preferably 10 vol%, even more preferably 15 vol%, and may also be 20 vol%, 25 vol%, 30 vol%, 35 vol%, or 40 vol%. By setting the content of the second fluorinated ether relative to the total content of the non-aqueous solvent and any ionic liquid to be above the above lower limit, the initial discharge capacity of the non-aqueous electrolyte energy storage element can be increased. The upper limit of the content of the second fluorinated ether relative to the total content of the non-aqueous solvent and any ionic liquid in the non-aqueous electrolyte may be 60 vol%, and may also be 50 vol%, 40 vol%, or 30 vol%.

[0168] The lower limit of the content of the second fluorinated ether relative to the total content of the fluorinated ether and any ionic liquid in the non-aqueous electrolyte is preferably 5 vol%, more preferably 10 vol%, even more preferably 15 vol%, and may also be 20 vol%, 25 vol%, 30 vol%, 35 vol%, or 40 vol%. By setting the content of the second fluorinated ether relative to the total content of the fluorinated ether and any ionic liquid to be above the above lower limit, the initial discharge capacity of the non-aqueous electrolyte energy storage element can be increased. The upper limit of the content of the second fluorinated ether relative to the total content of the fluorinated ether and any ionic liquid in the non-aqueous electrolyte may be 60 vol%, and may also be 50 vol%, 40 vol%, or 30 vol%.

[0169] The lower limit of the fluorinated ether content in the non-aqueous solvent of a non-aqueous electrolyte is preferably 50% by volume, more preferably 60% by volume, even more preferably 70% by volume, and may be 80%, 85%, 90%, 95%, 97%, 99%, or 100% by volume. The upper limit of the fluorinated ether content in the non-aqueous solvent of a non-aqueous electrolyte may be 100% by volume.

[0170] The lower limit of the fluorinated ether content relative to the total content of the nonaqueous solvent and any ionic liquid in a nonaqueous electrolyte is preferably 20% by volume, more preferably 30% by volume, even more preferably 40% by volume, even more preferably 50% by volume, and may also be 60%, 70%, 80%, 85%, or 90% by volume. The upper limit of the fluorinated ether content relative to the total content of the nonaqueous solvent and any ionic liquid may be 100% by volume, 95%, or 90% by volume.

[0171] The lower limit of the fluorinated ether content relative to the total content of fluorinated ether and any ionic liquid in a non-aqueous electrolyte is preferably 20% by volume, more preferably 30% by volume, even more preferably 40% by volume, even more preferably 50% by volume, and may also be 60%, 70%, 80%, 85%, or 90% by volume. The upper limit of the fluorinated ether content relative to the total content of fluorinated ether and any ionic liquid may be 100% by volume, 95%, or 90% by volume.

[0172] [Other Non-Aqueous Solvents, etc.] The non-aqueous electrolyte may contain other non-aqueous solvents besides fluorinated ethers. Examples of other non-aqueous solvents include ethers other than fluorinated ethers, cyclic carbonates, linear carbonates, carboxylic acid esters, phosphate esters, amides, nitriles, and the like.

[0173] The lower limit of the total content of ether (the sum of fluorinated ether and non-fluorinated ether) and any ionic liquid in the non-aqueous electrolyte, relative to the total content of the non-aqueous solvent and any ionic liquid, is preferably 90% by volume, more preferably 95% by volume, even more preferably 97% by volume, and even more preferably 99% by volume. By having the non-aqueous solvent and any ionic liquid mainly composed of ether and any ionic liquid, the capacity retention rate after charge-discharge cycles of the non-aqueous electrolyte energy storage element can be further increased. The upper limit of the above total content may be 100% by volume.

[0174] The lower limit of the total content of fluorinated ether and any ionic liquid relative to the total content of the nonaqueous solvent and any ionic liquid in the nonaqueous electrolyte is preferably 90% by volume, more preferably 95% by volume, even more preferably 97% by volume, and even more preferably 99% by volume. By having the nonaqueous solvent and any ionic liquid mainly composed of fluorinated ether and any ionic liquid, the capacity retention rate after charge-discharge cycles of the nonaqueous electrolyte energy storage element can be further increased. The upper limit of the above total content may be 100% by volume.

[0175] The upper limit for the carbonate content (total of cyclic carbonates and linear carbonates) relative to the total content of the nonaqueous solvent and any ionic liquid in a nonaqueous electrolyte is preferably 10% by volume, more preferably 5% by volume, even more preferably 3% by volume, and still more preferably 1% by volume. Similarly, the upper limit for the carbonate content in the nonaqueous solvent is preferably 10% by volume, more preferably 5% by volume, even more preferably 3% by volume, and still more preferably 1% by volume. The nonaqueous solvent does not need to contain carbonates.

[0176] [Ionic Liquids] Ionic liquids are ionic compounds that are at least partially liquid at room temperature (20°C) at 1 atmosphere. The inclusion of ionic liquids in non-aqueous electrolytes can enhance their flame retardancy, among other properties.

[0177] 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.

[0178] Examples of quaternary ammonium cations include tetraalkylammonium cations such as trimethylethylammonium cation, trimethylpropylammonium cation, trimethylbutylammonium cation, trimethylhexylammonium cation, and tetrapentylammonium cation.

[0179] 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.

[0180] 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.

[0181] 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.

[0182] 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.

[0183] 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.

[0184] 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.

[0185] 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.

[0186] Examples of quaternary phosphonium cations include tetramethylphosphonium cation, tetraethylphosphonium cation, trimethylethylphosphonium cation, trimethylpropylphosphonium cation, trimethylbutylphosphonium cation, tetraphenylphosphonium cation, and trimethylmethoxymethylphosphonium cation.

[0187] Examples of sulfonium cations include trimethylsulfonium cation, triethylsulfonium cation, and tributylsulfonium cation.

[0188] 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 capacity retention rate after charge-discharge cycles of the non-aqueous electrolyte energy storage element can be further increased. These cations may be present in one or more forms.

[0189] The anions that make up the ionic liquid are the same as those listed for the anions that make up the electrolyte salt. Idone anions are preferred as the anions that make up the ionic liquid, and bis(trifluoromethanesulfonyl)imid 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 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 capacity retention rate after charge-discharge cycles of the non-aqueous electrolyte energy storage element can be further increased. These anions may be present in one or more forms.

[0190] 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 capacity retention rate after charge-discharge cycles of the non-aqueous electrolyte energy storage element can be further increased.

[0191] 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 configuring the anions in the non-aqueous electrolyte in this way, the ionic conductivity of the non-aqueous electrolyte is increased, and the capacity retention rate after charge-discharge cycles of the non-aqueous electrolyte energy storage element can be further increased.

[0192] The lower limit of the ionic liquid content relative to the total content of the nonaqueous solvent and ionic liquid in a nonaqueous electrolyte is preferably 3 vol%; more preferably 5 vol%; even more preferably 7 vol%; and may also be 10 vol%. By setting the ionic liquid content above the above lower limit, the flame retardancy of the nonaqueous electrolyte can be increased. The upper limit of the ionic liquid content relative to the total content of the nonaqueous solvent and ionic liquid in a nonaqueous electrolyte is preferably 80 vol%; it may also be 70 vol%, 60 vol%, 50 vol%, 40 vol%, 30 vol%, 20 vol%, 15 vol%, or 10 vol%. By setting the ionic liquid content below the above upper limit, the viscosity of the nonaqueous electrolyte can be reduced.

[0193] The lower limit of the ionic liquid content relative to the total content of fluorinated ether and ionic liquid in a non-aqueous electrolyte is preferably 3 vol%; more preferably 5 vol%; even more preferably 7 vol%; and may also be 10 vol%. By setting the ionic liquid content above the above lower limit, the flame retardancy of the non-aqueous electrolyte can be increased. The upper limit of the ionic liquid content relative to the total content of fluorinated ether and ionic liquid is preferably 80 vol%; it may also be 70 vol%, 60 vol%, 50 vol%, 40 vol%, 30 vol%, 20 vol%, 15 vol%, or 10 vol%. By setting the ionic liquid content below the above upper limit, the viscosity of the non-aqueous electrolyte can be reduced.

[0194] The upper limit of the average number of donors for the non-aqueous solvent and any ionic liquid in the non-aqueous electrolyte is preferably 16.0, more preferably 15.5, even more preferably 15.0, and even more preferably 14.5. The lower limit of the average number of donors is preferably 10.0, more preferably 11.0, even more preferably 12.0, even more preferably 13.0, and even more preferably 14.0. Having the average number of donors within the above range makes it possible to increase the initial discharge capacity of the non-aqueous electrolyte energy storage element and to further improve the capacity retention rate after charge-discharge cycles.

[0195] [Cyclic Sulfur Compounds] A cyclic sulfur compound is at least one selected from the group consisting of cyclic sulfonic acid esters and cyclic sulfuric acid esters. By including such a cyclic sulfur compound in the non-aqueous electrolyte, the capacity retention rate after charge-discharge cycles of the non-aqueous electrolyte energy storage element can be increased. Cyclic sulfonic acid esters and cyclic sulfuric acid esters are usually nonionic compounds. One or more cyclic sulfur compounds can be used.

[0196] A cyclic sulfonic acid ester is a cyclic sulfonic acid ester in which two carbon atoms each form a sulfonyloxy group (-S (=O)). ２This refers to a compound having a ring structure, including a structure bonded to an O-). Cyclic sulfonic acid esters preferably have a sulfonyloxy group in their ring structure. A cyclic sulfonic acid ester may have one sulfonyloxy group in a single ring structure, or two or more sulfonyloxy groups, but it is preferable to have one sulfonyloxy group in a single ring structure. A cyclic sulfonic acid ester having one sulfonyloxy group in a single ring structure is also called a sultone. The ring structure of a cyclic sulfonic acid ester is preferably a five-membered or six-membered ring. A cyclic sulfonic acid ester may have only one ring structure in a single molecule, or it may have two or more ring structures.

[0197] Specific examples of cyclic sulfonic acid esters include 1,3-propanesultone, 1,3-propensultone, 1,4-butanesultone, 2,4-butanesultone, 1-methyl-1,3-propensultone, 2-methyl-1,3-propensultone, 3-methyl-1,3-propensultone, methylene-methanedisulfonic acid ester, ethylene-methanedisulfonic acid ester, and the like.

[0198] As the cyclic sulfonic acid ester, sultones are preferred, more preferably 1,3-propanesultone, 1,3-propensultone, 1,4-butanesultone, or 2,4-butanesultone, and even more preferably 1,3-propensultone or 1,4-butanesultone.

[0199] A cyclic sulfate ester is a cyclic sulfate ester in which two carbon atoms each form an oxysulfonyloxy group (-O-S (=O)). ２This refers to a compound having a ring structure, including a structure bonded to an O-(-) ring. Cyclic sulfate esters are also called cyclic sulfates. Cyclic sulfate esters preferably have an oxysulfonyloxy group in their ring structure. A cyclic sulfate ester may have one oxysulfonyloxy group in one ring structure, or it may have two or more oxysulfonyloxy groups, but it is preferable to have one oxysulfonyloxy group in one ring structure. The ring structure of a cyclic sulfate ester is preferably a five-membered ring or a six-membered ring, and more preferably a five-membered ring. A cyclic sulfate ester may have only one ring structure in a single molecule, or it may have two or more ring structures.

[0200] Specific examples of cyclic sulfate esters include ethylene sulfate, 2,3-propylene sulfate, 4,5-pentene sulfate, 1,3-propylene sulfate, 4,4'-bis(2,2-dioxo-1,3,2-dioxathiolane), and 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane. 4,4'-bis(2,2-dioxo-1,3,2-dioxathiolane) is preferred as the cyclic sulfate ester.

[0201] The cyclic sulfur compound is preferably at least one selected from the group consisting of 1,3-propanesultone, 1,3-propensultone, 1,4-butanesultone, 2,4-butanesultone, ethylene sulfate, 2,3-propylene sulfate, 4,5-pentene sulfate, 1,3-propylene sulfate, 4,4'-bis(2,2-dioxo-1,3,2-dioxathiolane) and 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane, and more preferably at least one selected from the group consisting of 1,3-propensultone, 1,4-butanesultone and 4,4'-bis(2,2-dioxo-1,3,2-dioxathiolane).

[0202] The cyclic sulfur compound may also preferably have a five-membered or six-membered ring structure. Furthermore, the cyclic sulfur compound may also preferably consist only of hydrogen, carbon, oxygen, and sulfur.

[0203] The content of cyclic sulfur compounds in the non-aqueous electrolyte is 0.1% by mass or more and less than 10% by mass. Having the cyclic sulfur compounds within this range allows for the formation of an appropriate amount of film on the positive electrode surface, thereby increasing the capacity retention rate after charge-discharge cycles of the non-aqueous electrolyte energy storage element. Furthermore, if the content of cyclic sulfur compounds in the non-aqueous electrolyte is 10% by mass or more, short circuits in the non-aqueous electrolyte energy storage element become more likely to occur during charge-discharge cycles. The lower limit of the content of cyclic sulfur compounds in the non-aqueous electrolyte is preferably 0.3% by mass, more preferably 0.5% by mass, and may also be 0.7% by mass, 1% by mass, 2% by mass, 3% by mass, 4% by mass, or 5% by mass. By setting the content of cyclic sulfur compounds above the lower limit, a particularly sufficient film is formed on the positive electrode surface, further increasing the capacity retention rate after charge-discharge cycles of the non-aqueous electrolyte energy storage element. The upper limit of the content of cyclic sulfur compounds is preferably 8% by mass, more preferably 7% by mass, and even more preferably 5% by mass. By keeping the content of the above-mentioned cyclic sulfur compound below the above upper limit, the formation of an excessive film on the positive electrode surface is suppressed, and the capacity retention rate after charge-discharge cycles of the non-aqueous electrolyte energy storage element can be further improved. The upper limit of the content of the above-mentioned cyclic sulfur compound may be 4% by mass, 3% by mass, 2% by mass, or 1% by mass.

[0204] The lower limit of the total content of the electrolyte salt, fluorinated ether, any ionic liquid, and cyclic sulfur compound 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 be 97% or 99% by mass. The upper limit of the total content of the electrolyte salt, fluorinated ether, any ionic liquid, and cyclic sulfur compound may be 100% by mass.

[0205] Non-aqueous electrolytes may contain other components besides the electrolyte salt, non-aqueous solvent (fluorinated ether and other non-aqueous solvents), ionic liquid, and cyclic sulfur compounds. Other components include additives other than the cyclic sulfur compounds mentioned above (at least one selected from the group consisting of cyclic sulfonic acid esters and cyclic sulfuric acid esters).

[0206] Other additives may be ionic compounds or nonionic compounds. If the other additive is an ionic compound, the additive may also function as an electrolyte salt or an ionic liquid. One or more types of other additives may be used. When other additives are used in a nonaqueous electrolyte, the content of the other additive 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.

[0207] (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.

[0208] 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.

[0209] (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.

[0210] 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.

[0211] 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.

[0212] 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.

[0213] <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 ether, and a cyclic sulfur compound, wherein the cyclic sulfur compound is at least one selected from the group consisting of cyclic sulfonic acid esters and cyclic sulfuric acid esters, and the content of the cyclic sulfur compound in the non-aqueous electrolyte is 0.1% by mass or more and less than 10% by mass. 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 mean housing the electrode body and non-aqueous electrolyte in a container.

[0214] 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.

[0215] 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.

[0216] A non-aqueous electrolyte energy storage element according to one embodiment of the present invention may be manufactured by other methods.

[0217] <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.

[0218] <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.

[0219] 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.

[0220] 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.

[0221] 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.

[0222] The components used in the preparation of the non-aqueous electrolytes in the examples and comparative examples are shown below. The donor numbers obtained by the above-described method for both the ionic liquid and the non-aqueous solvent are also shown. (Electrolyte salt) LiFSI: Lithium bis(fluorosulfonyl)imide (Ionic liquid) Py13FSI: 1-Methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide (Donor number 13.0) (Non-aqueous solvent) TFTHF: 3,3,4,4-Tetrafluorotetrahydrofuran (Donor number 13.2) TFEME: 2-(2,2,2-trifluoroethoxy)ethyl methyl ether (Donor number 18.7) (Cyclic sulfur compounds and other components (additives)) Compound (A): 1,3-propensultone compound (B): 1,4-butanesultone compound (C): 4,4'-bis(2,2-dioxo-1,3,2-dioxathiolane) Compound (a): Dimethyl sulfoxide compound (b): Tetrahydrothiophene 1,1-dioxide compound (c): Ethylene sulfite compound (d): 1,3,2-dioxathiolane 2-oxide compound (e): Dipropyl sulfite

[0223]

[0224] [Example 1] (Preparation of positive electrode) A mixture of elemental sulfur, a sulfur-based active material, and porous carbon was prepared. 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 prepare a composite (sulfur-porous carbon composite: SPC). In the obtained composite, the ratio of the volume of elemental sulfur to the pore volume of porous carbon (hereinafter also referred to as "S packing rate") was 72%. It should be noted that this S packing rate is considered to be substantially equal to the ratio of the volume of the charged sulfur-based active material to the pore volume of porous carbon. Furthermore, all of the elemental sulfur in this composite reacted with lithium to form lithium sulfide (Li ２ Assuming that S is the case, the Li ratio to the pore volume of this porous carbon ２ Volume ratio of S (hereinafter referred to as "Li ２Also called "S filling rate".) The rate was 127%. Note that this Li ２ The sulfur content is considered to be substantially equal to the ratio of the volume of the sulfur-based active material in the discharge state to the pore volume of the porous carbon. A cathode mixture paste containing the composite obtained above, acetylene black and carbon nanotubes as conductive agents, carboxymethylcellulose as a dispersant, polyacrylic acid as a thickener, and styrene-butadiene rubber as a binder was applied to an aluminum cathode substrate (average thickness 15 μm) using water as the dispersion medium and dried. The mass per unit area of ​​the cathode active material layer after drying the dispersion medium was 7 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.

[0225] (Preparation of the negative electrode) A pure metallic lithium foil (average thickness 600 μm) was prepared as the negative electrode.

[0226] (Preparation of non-aqueous electrolyte) A mixture was prepared by mixing the ionic liquid Py13FSI, the fluorinated cyclic ether TFTHF, and the fluorinated linear ether TFEME in a volume ratio of 10:70:20. LiFSI, an electrolyte salt, was added to this mixture at a molality of 1.5 mol / kg. Compound (A), a cyclic sulfur compound, was further added to the resulting liquid as an additive at a content of 0.5% by mass to prepare a non-aqueous electrolyte.

[0227] (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.

[0228] [Examples 2 to 11, Comparative Examples 1 to 9] S filling ratio and Li of the composite ２Examples 2 to 11 and Comparative Examples 1 to 9 were obtained in the same manner as in Example 1, except that the S filling rate and the composition of the non-aqueous electrolyte were as shown in Tables 1 to 3. Note that the non-aqueous electrolyte energy storage elements in Table 1 differ only in the type and content of the additive. The two non-aqueous electrolyte energy storage elements in Table 2 differ only in the presence or absence of an additive. The two non-aqueous electrolyte energy storage elements in Table 3 also differ only in the presence or absence of an additive.

[0229] [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 0.02C 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 0.02C and a charge termination voltage of 3.0V until the total charging time reached 60 hours. Next, as the second discharge, constant current (CC) discharge was performed under the conditions of a discharge current of 0.02C 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) ２ The product of ( ) was used. In addition, a 10-minute rest period was provided after the first discharge and after the first charge. The amount of discharged electricity (discharge capacity) in the second discharge described above was defined as the initial discharge capacity.

[0230] (Charge-Discharge Cycle Test) Next, the following charge-discharge cycle test was performed on each non-aqueous electrolyte energy storage element in a constant temperature bath at 25°C. Constant current charging was performed under the conditions of a charging current of 0.2C and a charging termination voltage of 3.0V. Subsequently, constant current discharge was performed under the conditions of a discharge current of 0.2C and a discharge termination voltage of 1.0V. A 10-minute rest period was provided after charging and after discharging. The above charging and discharging was performed 100 times. After the above charge-discharge cycle test, the following capacity verification test was performed in a constant temperature bath at 25°C. Constant current constant voltage (CCCV) charging was performed under the conditions of a charging current of 0.02C and a charging termination voltage of 3.0V until the total charging time reached 60 hours. After a 10-minute rest period, constant current (CC) discharge was performed under the conditions of a discharge current of 0.02C and a discharge termination voltage of 1.0V. The amount of discharged electricity (discharge capacity) in the discharge during the capacity verification test after the above charge-discharge cycle test was defined as the discharge capacity after the charge-discharge cycle test. The capacity retention rate after the charge-discharge cycle test was calculated as the percentage of the initial discharge capacity relative to the discharge capacity. The results are shown in Tables 1 to 3.

[0231]

[0232]

[0233]

[0234] As shown in Tables 1 to 3, by including at least one compound (compound (A), compound (B), or compound (C)) selected from the group consisting of cyclic sulfonic acid esters and cyclic sulfate esters in the non-aqueous electrolyte in a content range of 0.1% by mass or more and less than 10% by mass, the capacity retention rate after charge-discharge cycles was improved compared to cases where no additive was included. Furthermore, as shown in Table 1, when a sulfur-based compound other than at least one selected from the group consisting of cyclic sulfonic acid esters and cyclic sulfate esters was included as an additive, or when the additive content was 10% by mass or more, the capacity retention rate after charge-discharge cycles could not be improved. In a non-aqueous electrolyte energy storage element, if the capacity retention rate after charge-discharge cycles was improved by including an additive in the non-aqueous electrolyte of the non-aqueous electrolyte energy storage element, it was determined that the problem to be solved had been resolved. In other words, for each non-aqueous electrolyte energy storage element in Table 1, the problem is solved if the capacity retention rate after the charge-discharge cycle is higher than that of the non-aqueous electrolyte energy storage element in Comparative Example 1; for the non-aqueous electrolyte energy storage elements in Table 2, the problem is solved if the capacity retention rate after the charge-discharge cycle is higher than that of the non-aqueous electrolyte energy storage element in Comparative Example 8; and for the non-aqueous electrolyte energy storage elements in Table 3, the problem is solved if the capacity retention rate after the charge-discharge cycle is higher than that of the non-aqueous electrolyte energy storage element in Comparative Example 9. Furthermore, the discharge capacity after the charge-discharge cycle test of each non-aqueous electrolyte energy storage element in Examples 1 to 9 shown in Table 1 was greater than that of the non-aqueous electrolyte energy storage element in Comparative Example 1, while the discharge capacity after the charge-discharge cycle test of each non-aqueous electrolyte energy storage element in Comparative Examples 3 and 4 was smaller than that of the non-aqueous electrolyte energy storage element in Comparative Example 1. Furthermore, the discharge capacity of the non-aqueous electrolyte energy storage element of Example 10 shown in Table 2 after the charge-discharge cycle test was greater than that of the non-aqueous electrolyte energy storage element of Comparative Example 8, and the discharge capacity of the non-aqueous electrolyte energy storage element of Example 11 shown in Table 3 after the charge-discharge cycle test was greater than that of the non-aqueous electrolyte energy storage element of Comparative Example 9.Thus, by including at least one cyclic sulfur compound selected from the group consisting of cyclic sulfonic acid esters and cyclic sulfuric acid esters in an amount of 0.1% by mass or more and less than 10% by mass, the discharge capacity of the non-aqueous electrolyte energy storage element after charge-discharge cycles tended to increase.

[0235] 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.

[0236] 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

A positive electrode containing a sulfur-based active material, Non-aqueous electrolytes containing electrolyte salts, fluorinated ethers, and cyclic sulfur compounds Equipped with, The above-mentioned cyclic sulfur compound is at least one selected from the group consisting of cyclic sulfonic acid esters and cyclic sulfuric acid esters. A non-aqueous electrolyte energy storage element wherein the content of the cyclic sulfur compound in the non-aqueous electrolyte is 0.1% by mass or more and less than 10% by mass. 　 The non-aqueous electrolyte energy storage element according to claim 1, wherein the fluorinated ether includes a fluorinated cyclic ether. 　 The non-aqueous electrolyte energy storage element according to claim 1 or claim 2, wherein the fluorinated ether includes a fluorinated chain ether. 　 The non-aqueous electrolyte energy storage element according to claim 1, wherein the fluorinated ether comprises a first fluorinated ether having a donor number of 8.0 or more and 15.0 or less. 　 The non-aqueous electrolyte energy storage element according to claim 1 or claim 4, wherein the fluorinated ether includes a second fluorinated ether with a donor number of more than 15.

0. The non-aqueous electrolyte energy storage element according to claim 1 or claim 2, wherein the above-mentioned cyclic sulfur compound is at least one selected from the group consisting of 1,3-propanesultone, 1,3-propensultone, 1,4-butanesultone, 2,4-butanesultone, ethylene sulfate, 2,3-propylene sulfate, 4,5-pentene sulfate, 1,3-propylene sulfate, 4,4'-bis(2,2-dioxo-1,3,2-dioxathiolane) and 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane. 　 The above positive electrode further contains porous carbon that forms a complex with the above sulfur-based active material, The non-aqueous electrolyte energy storage element according to claim 1 or claim 2, wherein the ratio of the volume of the sulfur-based active material in the charged state to the pore volume of the porous carbon is 80% or less. 　 The above positive electrode further contains porous carbon that forms a complex with the above sulfur-based active material, The non-aqueous electrolyte energy storage element according to claim 1 or claim 2, wherein the ratio of the volume of the sulfur-based active material in the discharged state to the pore volume of the porous carbon is 140% or less. 　 The non-aqueous electrolyte energy storage element according to claim 1 or claim 2, wherein the content of the fluorinated ether in the non-aqueous solvent in the non-aqueous electrolyte is 50% by volume or more. 　 The non-aqueous electrolyte energy storage element according to claim 1 or claim 2, wherein the non-aqueous electrolyte further contains an ionic liquid. 　 The non-aqueous electrolyte energy storage element according to claim 10, 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. 　 The non-aqueous electrolyte energy storage element according to claim 10, wherein the ionic liquid has an imide anion. 　 The non-aqueous electrolyte energy storage element according to claim 1 or claim 2, wherein the electrolyte salt is an imide salt. 　 The above positive electrode has a positive electrode active material layer containing the above sulfur-based active material, The mass per unit area of ​​the above positive electrode active material layer is 5 mg / cm². ２ The non-aqueous electrolyte energy storage element according to claim 1 or claim 2. 　 A 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. 　 Prepare a positive electrode containing a sulfur-based active material, Prepare a non-aqueous electrolyte containing an electrolyte salt, a fluorinated ether, and a cyclic sulfur compound. Equipped with, The above-mentioned cyclic sulfur compound is at least one selected from the group consisting of cyclic sulfonic acid esters and cyclic sulfuric acid esters. A method for manufacturing a non-aqueous electrolyte energy storage element, wherein the content of the cyclic sulfur compound in the non-aqueous electrolyte is 0.1% by mass or more and less than 10% by mass.

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