Non-aqueous electrolyte power storage element and manufacturing method for non-aqueous electrolyte power storage element

Abstract

The present invention is provided with a positive electrode containing an organic sulfur-based compound and a non-aqueous electrolyte containing an electrolyte salt and a liquid component. The liquid component contains a fluorinated cyclic ether. The content of the fluorinated cyclic ether in the liquid component is more than 30% by volume.

Description

Nonaqueous electrolyte storage element and method for manufacturing the same

[0001] The present invention relates to a nonaqueous electrolyte electricity storage element and a method for manufacturing a nonaqueous electrolyte electricity storage element.

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

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

[0004] JP 2010-95390 A

[0005] Sulfur-based active materials are positive electrode active materials that operate at a lower potential than lithium transition metal composite oxides and the like. Therefore, nonaqueous electrolyte storage elements using sulfur-based active materials in the positive electrode have a low positive electrode potential during discharge, which can lead to reductive decomposition of the nonaqueous electrolyte. In response to this, the use of a nonaqueous electrolyte containing an ether as the nonaqueous solvent can improve reduction resistance. However, polysulfides tend to leach from the positive electrode into the nonaqueous electrolyte, and nonaqueous electrolyte storage elements using an ether as the nonaqueous electrolyte do not have sufficiently high initial discharge capacities or capacity retention rates after charge-discharge cycles. Therefore, there is a need for improvements in the initial discharge capacity and capacity retention rate after charge-discharge cycles of nonaqueous electrolyte storage elements using positive electrodes containing sulfur-based active materials.

[0006] An object of the present invention is to provide a nonaqueous electrolyte storage element that uses a positive electrode containing a sulfur-based active material, and that has a large initial discharge capacity and a high capacity retention rate after charge-discharge cycling, and a method for producing such a nonaqueous electrolyte storage element.

[0007] A nonaqueous electrolyte storage element according to one aspect of the present invention includes a positive electrode containing an organic sulfur-based compound and a nonaqueous electrolyte containing an electrolyte salt and a liquid component, wherein the liquid component contains a fluorinated cyclic ether, and the content of the fluorinated cyclic ether in the liquid component exceeds 30% by volume.

[0008] A nonaqueous electrolyte storage element according to one aspect of the present invention includes a positive electrode containing an organic sulfur-based compound and a nonaqueous electrolyte containing an electrolyte salt and a liquid component, wherein the liquid component contains an ether having a donor number of 15 or less, and the content of the ether having a donor number of 15 or less in the liquid component exceeds 30% by volume.

[0009] A method for manufacturing a nonaqueous electrolyte storage element according to another aspect of the present invention includes preparing a positive electrode containing an organic sulfur-based compound and preparing a nonaqueous electrolyte containing an electrolyte salt and a liquid component, wherein the liquid component contains a fluorinated cyclic ether and the content of the fluorinated cyclic ether in the liquid component exceeds 30% by volume.

[0010] A method for manufacturing a nonaqueous electrolyte storage element according to another aspect of the present invention includes preparing a positive electrode containing an organic sulfur-based compound, and preparing a nonaqueous electrolyte containing an electrolyte salt and a liquid component, wherein the liquid component contains an ether having a donor number of 15 or less, and the content of the ether having a donor number of 15 or less in the liquid component exceeds 30% by volume.

[0011] According to one aspect of the present invention, it is possible to provide a nonaqueous electrolyte storage element using a positive electrode containing a sulfur-based active material, which has a large initial discharge capacity and a high capacity retention rate after charge-discharge cycles, and a method for manufacturing such a nonaqueous electrolyte storage element.

[0012] Fig. 1 is a perspective view showing a nonaqueous electrolyte electricity storage element according to one embodiment of the present invention, and Fig. 2 is a schematic view showing an electricity storage device including a plurality of nonaqueous electrolyte electricity storage elements according to one embodiment of the present invention.

[0013] First, an outline of the nonaqueous electrolyte storage element and the method for manufacturing the nonaqueous electrolyte storage element disclosed in this specification will be described.

[0014] [1] A nonaqueous electrolyte storage element according to one aspect of the present invention includes a positive electrode containing an organic sulfur-based compound and a nonaqueous electrolyte containing an electrolyte salt and a liquid component, wherein the liquid component contains a fluorinated cyclic ether, and the content of the fluorinated cyclic ether in the liquid component exceeds 30% by volume.

[0015] The nonaqueous electrolyte storage element described in [1] above is a nonaqueous electrolyte storage element that uses a positive electrode containing a sulfur-based active material, and has a large initial discharge capacity and a high capacity retention rate after charge-discharge cycling. While the reasons for this are unclear, the following are presumed. First, the use of an organic sulfur-based compound as the sulfur-based active material suppresses the elution of polysulfides from the positive electrode into the nonaqueous electrolyte. Furthermore, fluorinated cyclic ethers are solvents that poorly dissolve polysulfides, and the inclusion of a sufficient amount of fluorinated cyclic ether in the nonaqueous electrolyte further suppresses the elution of polysulfides from the positive electrode into the nonaqueous electrolyte. Furthermore, fluorinated cyclic ethers are highly resistant to reduction, making it difficult for a high-resistance coating to form on the positive electrode surface. For these reasons, it is presumed that the nonaqueous electrolyte storage element described in [1] above has a large initial discharge capacity and a high capacity retention rate after charge-discharge cycling.

[0016] The liquid component refers to a component that is liquid at 20°C and 1 atmosphere. Examples of liquid components contained in the non-aqueous electrolyte include non-aqueous solvents, which are nonionic compounds, and ionic liquids, which are ionic compounds. The liquid component may be a non-aqueous solvent or any ionic liquid. The content of each component contained in the non-aqueous electrolyte is a value measured at 20°C and 1 atmosphere or a value converted to a numerical value at 20°C and 1 atmosphere.

[0017] The types of ionic compounds, such as electrolyte salts and ionic liquids, contained in the non-aqueous electrolyte can be determined by ion chromatography (IC), liquid chromatography mass spectrometry (LC-MS), １ The content of ionic compounds contained in the non-aqueous electrolyte is determined by IC. However, the content of cations of the ionic liquid contained in the non-aqueous electrolyte is determined by LC-MS. When it is difficult to determine the content by LC-MS, １Identification is performed using an internal standard method using H-NMR. IC measurement is specifically performed as follows. In order to minimize variation in measurement error for each component, quantitative analysis is performed on the same day using the same equipment and under the same conditions, unless there are special circumstances, and consumables are not replaced or the equipment is not adjusted until measurements of all components are completed, and the same applies below. (A1) Collection of Non-Aqueous Electrolyte: First, the non-aqueous electrolyte storage element is disassembled to extract the non-aqueous electrolyte. If the non-aqueous electrolyte cannot be extracted, the non-aqueous electrolyte storage element is centrifuged to extract the non-aqueous electrolyte. If the non-aqueous electrolyte cannot be extracted even after centrifugation, an appropriate extraction solvent (e.g., acetonitrile) is injected into the non-aqueous electrolyte storage element, and the non-aqueous electrolyte diluted with the extraction solvent is extracted. (A2) IC Analysis: The components of the extracted non-aqueous electrolyte are analyzed by IC. IC analysis is performed in the following order: qualitative analysis and quantitative analysis. The IC analysis equipment used was a "Dionex ICS-5000+" manufactured by Thermo Fisher Scientific. If it is difficult to perform measurements using the above-mentioned measuring equipment, another model that is believed to produce equivalent measurement results will be used, and the same applies below. Water is used as the eluent in IC measurements. (Qualitative Analysis) A measurement sample (non-aqueous electrolyte) is subjected to IC analysis. The components contained in the measurement sample are predicted from the peak positions of each peak in the obtained ion chromatogram. A known sample of the predicted component (hereinafter referred to as the "predicted component") is subjected to IC analysis. The retention times of the peaks corresponding to each predicted component in the measurement sample are compared with the retention times of the peaks in a known sample of each predicted component. If they match, the prediction is assumed to be correct. (Quantitative Analysis) Quantitative analysis is performed using the calibration curve method. First, a known sample of the predicted component with a known concentration is subjected to IC analysis, and the peak areas are determined to create a calibration curve. The calibration curve is based on the coefficient of determination (r ２ The calibration curve is created so that the difference (ratio) is between 0.999 and 1. The content of the predicted component in the measurement sample is determined from the calibration curve and the peak area of ​​the predicted component in the measurement sample. The above procedure is performed for all peaks detected in the IC analysis of the measurement sample, and the content of each predicted component is determined.

[0018] The type and content of nonionic compounds such as fluorinated cyclic ethers contained in the nonaqueous electrolyte are identified by liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-mass spectrometry (GC-MS). However, when it is difficult to identify the type of nonionic compound by the above-mentioned LC-MS and GC-MS, １The nonaqueous electrolyte is identified by combining necessary analyses such as H-NMR, multinuclear NMR, and other analyses. LC-MS and GC-MS measurements are specifically performed as follows: (B1) Collection of nonaqueous electrolyte: The nonaqueous electrolyte is extracted using the same procedure as in "(A1) Collection of nonaqueous electrolyte" above. (B2) LC-MS: The components of the extracted nonaqueous electrolyte are analyzed by LC-MS. LC-MS analysis is performed in the following order of qualitative and quantitative analysis. Water's "Acquity H" and "Xevo G2-5QTof" LC-MS analyzers are used. Water or a nonaqueous solvent is used as the eluent. Examples of nonaqueous solvents include acetonitrile and tetrahydrofuran. (Qualitative Analysis) The measurement sample (nonaqueous 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 successfully separated, the components contained in the measurement sample are predicted from the MS spectrum of each peak. A known sample of the predicted components is subjected to LC-MS analysis. The retention time and MS spectrum of the peak corresponding to each predicted component in the measurement sample are compared with the retention time and MS spectrum of the peak of a known sample of each predicted component. If they match, the prediction is assumed to be correct. (Quantitative Analysis) Quantitative analysis is performed using the calibration curve method. Quantitative analysis by LC-MS is performed using the same procedure as the quantitative analysis by IC described above, and the content of each predicted component is determined. (B3) GC-MS GC-MS analysis is performed in the following order: qualitative analysis and quantitative analysis. The GC-MS analyzer is an Agilent "5975C." Argon is used as the carrier gas. (Qualitative Analysis) The measurement sample (non-aqueous electrolyte) is subjected to GC-MS analysis. The components contained in the sample are predicted from the MS spectrum of each peak in the resulting gas chromatogram. A known sample of the predicted components is subjected to GC-MS analysis. The retention time and MS spectrum of the peak corresponding to the predicted component of the measured sample are compared with the retention time and MS spectrum of the peak of a known sample of each predicted component, and if they match, the prediction is assumed to be correct. (Quantitative Analysis) Quantitative analysis is performed using a calibration curve method.The quantitative analysis by GC-MS is carried out in the same manner as the quantitative analysis by IC described above, and the content of each predicted component is determined.

[0019] [2] A nonaqueous electrolyte storage element according to another aspect of the present invention includes a positive electrode containing an organic sulfur-based compound and a nonaqueous electrolyte containing an electrolyte salt and a liquid component, wherein the liquid component contains an ether having a donor number of 15 or less, and the content of the ether having a donor number of 15 or less in the liquid component exceeds 30% by volume.

[0020] The nonaqueous electrolyte storage element described in [2] above is a nonaqueous electrolyte storage element that uses a positive electrode containing a sulfur-based active material, and has a large initial discharge capacity and a high capacity retention rate after charge-discharge cycling. While the reasons for this are unclear, the following reasons are presumed to be similar to those for the nonaqueous electrolyte storage element described in [1] above. First, the use of an organic sulfur-based compound as the sulfur-based active material suppresses the elution of polysulfides from the positive electrode into the nonaqueous electrolyte. Furthermore, ethers with a donor number of 15 or less are solvents in which polysulfides are poorly soluble. The inclusion of a sufficient amount of ether with a donor number of 15 or less in the nonaqueous electrolyte further suppresses the elution of polysulfides from the positive electrode into the nonaqueous electrolyte. Furthermore, ethers have high reduction resistance, making it difficult for a high-resistance coating to form on the positive electrode surface. For these reasons, it is presumed that the nonaqueous electrolyte storage element described in [2] above has a large initial discharge capacity and a high capacity retention rate after charge-discharge cycling.

[0021] The donor number is a parameter that represents the electron-pair donating ability of a solvent, and is defined as the negative value of the enthalpy of formation of a 1:1 addition compound between antimony pentachloride in 1,2-dichloroethane and the target solvent. In this specification, the donor number is a value determined by the same method as that described in Viktor Gutmann, "The Donor-Acceptor Approach to Molecular Interactions," Springer, 1978 (ISBN-13: 978-0306310645), except that boron trifluoride is selected as the Lewis acid.

[0022] [3] In the nonaqueous electrolyte storage element according to the above [1] or [2], the liquid component may further contain at least one of a chain ether and an ionic liquid.

[0023] The nonaqueous electrolyte storage element described in [3] above has a larger initial discharge capacity and a higher capacity retention rate after charge-discharge cycles due to the increased solubility of the electrolyte salt in the liquid component of the nonaqueous electrolyte.

[0024] [4] In the nonaqueous electrolyte storage element according to any one of [1] to [3] above, the total content of the ether and the optional ionic liquid in the liquid component may be 90% by volume or more.

[0025] The nonaqueous electrolyte storage element described in [4] above has a larger initial discharge capacity and a higher capacity retention rate after charge-discharge cycles.

[0026] The term "ether" refers to all ethers contained in the liquid component, including fluorinated cyclic ethers and ethers having 15 or less donors. The term "fluorinated ether" described below refers to all fluorinated ethers contained in the liquid component, including fluorinated cyclic ethers and ethers having 15 or less fluorine atom donors.

[0027] [5] In the nonaqueous electrolyte storage element according to any one of [1] to [4] above, the fluorinated cyclic ether may be represented by the following formula (1): (In formula (1), R １ are each independently a hydrogen atom, a fluorine atom, an alkyl group having 1 to 4 carbon atoms, or a fluorinated alkyl group having 1 to 4 carbon atoms. １ At least one of the groups is a fluorine atom or a fluorinated alkyl group having 1 to 4 carbon atoms. n1 is an integer of 2 to 5.

[0028] The nonaqueous electrolyte storage element described in [5] above has a larger initial discharge capacity and a higher capacity retention rate after charge-discharge cycles.

[0029] [6] In the nonaqueous electrolyte storage element according to any one of [3] to [5] above, the liquid component may contain the chain ether, and the chain ether may be represented by the following formula (2): (In formula (2), R ２ and R ３ are each independently an alkyl group having 1 to 3 carbon atoms or a fluorinated alkyl group having 1 to 3 carbon atoms. ４ is an alkanediyl group having 1 to 3 carbon atoms; and n2 is 0 or 1.

[0030] The nonaqueous electrolyte storage element described in [6] above has a larger initial discharge capacity and a higher capacity retention rate after charge-discharge cycles.

[0031] [7] In the nonaqueous electrolyte storage element according to any one of [3] to [6] above, the liquid component contains the ionic liquid, and the ionic liquid may have at least one cation selected from the group consisting of a quaternary ammonium cation, an imidazolium-based cation, a pyrrolidinium-based cation, a piperidinium-based cation, a quaternary phosphonium cation, and a sulfonium cation.

[0032] The nonaqueous electrolyte storage element described in [7] above has a larger initial discharge capacity and a higher capacity retention rate after charge-discharge cycles.

[0033] [8] In the nonaqueous electrolyte storage element according to any one of [1] to [7] above, the liquid component may contain carbonate in an amount of 10% by volume or less.

[0034] When a relatively large amount of carbonate is used as the non-aqueous solvent, a coating derived from the carbonate is formed on the surface of the positive electrode, which tends to increase the resistance. The non-aqueous electrolyte storage element described in [8] above, which does not use carbonate or uses a small amount of carbonate, has a larger initial discharge capacity and a higher capacity retention rate after charge-discharge cycling.

[0035] [9] In the nonaqueous electrolyte storage element according to any one of [1] to [8] above, the organic sulfur compound may be sulfur-modified polyacrylonitrile.

[0036] The nonaqueous electrolyte storage element described in [9] above has a larger initial discharge capacity and a higher capacity retention rate after charge-discharge cycles.

[0037]

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

[0038] The nonaqueous electrolyte storage element according to the above

[10] has a larger initial discharge capacity and a higher capacity retention rate after charge-discharge cycles.

[0039]

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

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

[0040] The nonaqueous electrolyte storage element described in

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

[0041]

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

[11] above, the liquid component may contain the chain ether, and the chain ether may have more than 15 donors.

[0042]

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

[12] above, the liquid component may contain the ionic liquid, and the ionic liquid may have an imide anion.

[0043]

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

[13] above, the liquid component may contain an ether in an amount of 80% by volume or more.

[0044]

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

[14] above, the liquid component may contain 80% by volume or more of the fluorinated ether.

[0045]

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

[15] above, the total content of the fluorinated ether and the ionic liquid in the liquid component may be 90% by volume or more.

[0046]

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

[16] above, the liquid component may have an average donor number of 16.0 or less.

[0047] "Average number of donors" refers to the volumetric average of the number of donors for each component. For example, if the liquid component has a donor count D Ａ , content V Ａ (volume %) of component A and the number of donors D Ｂ , content V Ｂ (volume %) of B component and the number of donors D Ｃ , content V Ｃ (vol %) of the C component, the average number of donors is D Ａ ×V Ａ / 100+D Ｂ ×V Ｂ / 100+D Ｃ ×V Ｃ / 100.

[0048]

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

[17] above, the liquid component may have an average donor number of 10.0 or more.

[0049]

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

[18] above, the molar concentration of the electrolyte salt in the nonaqueous electrolyte may be greater than 1.0 mol / kg.

[0050] "Mass molarity" refers to the amount of substance (mol) of the electrolyte salt based on the mass (kg) of the liquid component.

[0051] The nonaqueous electrolyte storage elements described in

[12] to

[19] above are all suitable embodiments of the present invention, and have a larger initial discharge capacity and a higher capacity retention rate after charge-discharge cycles.

[0052]

[20] A method for producing a nonaqueous electrolyte storage element according to another aspect of the present invention includes preparing a positive electrode containing an organic sulfur-based compound and preparing a nonaqueous electrolyte containing an electrolyte salt and a liquid component, wherein the liquid component contains a fluorinated cyclic ether, and the content of the fluorinated cyclic ether in the liquid component exceeds 30% by volume.

[0053]

[21] A method for producing a nonaqueous electrolyte storage element according to another aspect of the present invention includes preparing a positive electrode containing an organic sulfur-based compound, and preparing a nonaqueous electrolyte containing an electrolyte salt and a liquid component, wherein the liquid component contains an ether having a donor number of 15 or less, and the content of the ether having a donor number of 15 or less in the liquid component exceeds 30% by volume.

[0054] According to the method for producing a nonaqueous electrolyte storage element described in the above

[20] or

[21] , it is possible to produce a nonaqueous electrolyte storage element using a positive electrode containing a sulfur-based active material, which has a large initial discharge capacity and a high capacity retention rate after charge-discharge cycles.

[0055] A nonaqueous electrolyte electricity storage element according to one embodiment of the present invention, a method for manufacturing a nonaqueous electrolyte electricity storage element, an electricity storage device, and other embodiments will be described in detail below.

[0056] <Non-aqueous electrolyte storage element> A non-aqueous electrolyte storage element according to one embodiment of the present invention includes a positive electrode, a negative electrode, a non-aqueous electrolyte, and a container that accommodates these. The non-aqueous electrolyte storage element may further include a separator that is interposed between the positive electrode and the negative electrode to electrically insulate the positive electrode from the negative electrode. The positive electrode, the negative electrode, and any separator typically constitute an electrode assembly. At least a portion of the non-aqueous electrolyte typically exists in a state of being impregnated into the electrode assembly. The non-aqueous electrolyte storage element according to one embodiment of the present invention may further include other components.

[0057] For example, a nonaqueous electrolyte storage element 1 according to one embodiment of the present invention shown in Fig. 1 includes an electrode assembly 2, a nonaqueous electrolyte (not shown), and a rectangular parallelepiped container 3 that accommodates these. The nonaqueous electrolyte storage element 1 of Fig. 1 further includes a positive electrode lead 4, a positive electrode external terminal 5, a negative electrode lead 6, and a negative electrode external terminal 7. The positive electrode lead 4 and the negative electrode lead 6 are accommodated in the container 3 together with the electrode assembly 2 and the like. The positive electrode external terminal 5 and the negative electrode external terminal 7 are provided outside the container 3. The positive electrode constituting the electrode assembly 2 is electrically connected to the positive electrode external terminal 5 via the positive electrode lead 4. The negative electrode constituting the electrode assembly 2 is electrically connected to the negative electrode external terminal 7 via the negative electrode lead 6.

[0058] The nonaqueous electrolyte storage element of the present invention may be a nonaqueous electrolyte secondary battery. Below, the main components constituting the nonaqueous electrolyte storage element according to one embodiment of the present invention will be described in detail, focusing on the case where the nonaqueous electrolyte storage element is a nonaqueous electrolyte secondary battery (particularly a lithium ion secondary battery), but this is not intended to limit the scope of application of the present invention.

[0059] It should be noted that the lower limit and upper limit of each numerical range described in the embodiments of the present invention can be combined in any way (with the proviso that the upper limit is greater than the lower limit). Unless otherwise specified, the lower limit and upper limit of a numerical range include the lower limit and upper limit. That is, when the lower limit is A, it means that the range is equal to or greater than A. Similarly, when the upper limit is B, it means that the range is equal to or less than B. Furthermore, unless otherwise specified, the various numerical ranges for the nonaqueous electrolyte storage element are values ​​in a charged state.

[0060] (Positive electrode) The positive electrode has a positive electrode substrate and a positive electrode active material layer laminated on the positive electrode substrate directly or via an intermediate layer. Usually, the positive electrode has a portion where the positive electrode substrate is exposed. This exposed portion of the positive electrode substrate is usually connected to the above-mentioned positive electrode lead. The positive electrode may have a shape such as a sheet, plate, or strip.

[0061] The thickness of the positive electrode is appropriately set depending on the application of the nonaqueous electrolyte storage element. The average thickness of the positive electrode may be, for example, 30 μm or more and 1,000 μm or less. The lower limit of the average thickness of the positive electrode may be 50 μm, 100 μm, or 200 μm. The upper limit of the average thickness of the positive electrode may be 500 μm, 400 μm, 300 μm, 200 μm, or 100 μm. The average thickness of the positive electrode is the average thickness of the portion where the positive electrode active material layer is laminated directly on the positive electrode substrate or via an intermediate layer. In the case where both the portion where the positive electrode active material layer is laminated on both sides of the positive electrode substrate and the portion where the positive electrode active material layer is laminated on only one side of the positive electrode substrate are present, the average thickness of the portion where the positive electrode active material layer is laminated on both sides of the positive electrode substrate is taken as the average thickness. In addition, in this specification, "average thickness" means the average value of thicknesses measured at any five positions.

[0062] The positive electrode substrate has electrical conductivity. In this specification, "having electrical conductivity" means that the volume resistivity is 10 －２ The volume resistivity is a value measured in accordance with JIS-H-0505 (1975). On the other hand, in this specification, "not having electrical conductivity" or "having (electrical) insulation" means that the volume resistivity is 10 ７ It means that the resistance is Ω·cm or more.

[0063] Examples of materials for the positive electrode substrate include metals such as aluminum, titanium, iron, and alloys thereof (stainless steel, etc.). Among these, aluminum or an aluminum alloy is preferred from the viewpoints of potential resistance, high electronic conductivity, and cost.

[0064] The positive electrode substrate has a shape such as a sheet, plate, or strip. Examples of the positive electrode substrate include foil, vapor-deposited film, mesh, and porous material, and foil is preferred. The positive electrode substrate may be, for example, aluminum foil or aluminum alloy foil.

[0065] The average thickness of the positive electrode substrate may be, for example, 3 μm or more and 50 μm or less. The lower limit of the average thickness of the positive electrode substrate may be 5 μm, 8 μm, 10 μm, or 15 μm. The upper limit of the average thickness of the positive electrode substrate may be 40 μm, 30 μm, 20 μm, or 15 μm.

[0066] The intermediate layer is a layer disposed between the positive electrode substrate and the positive electrode active material layer. The intermediate layer contains, for example, a conductive agent and a binder. When the intermediate layer contains a conductive agent, the contact resistance between the positive electrode substrate and the positive electrode active material layer can be reduced. Examples of the conductive agent and binder used in the intermediate layer include the same conductive agent and binder used in the positive electrode active material layer described below.

[0067] The positive electrode active material layer contains an organic sulfur-based compound. The positive electrode active material layer contains optional components such as a conductive agent, a binder, a dispersant, a thickener, and a filler, as necessary. The positive electrode active material layer may be formed from a positive electrode mixture containing the organic sulfur-based compound and other optional components. The positive electrode active material layer may be provided on only one side or on both sides of a positive electrode substrate having a shape such as a sheet.

[0068] The organic sulfur compound is an organic compound that contains elemental sulfur and functions as a positive electrode active material. The organic sulfur compound is preferably an organic polymer. That is, the organic sulfur compound is preferably an organic polymer containing elemental sulfur. The organic sulfur compound may be an organic polymer into which elemental sulfur has been introduced by an addition reaction or a substitution reaction, or may be an organic polymer into which elemental sulfur or a sulfur compound (lithium polysulfide, lithium sulfide, etc.) has been introduced by interaction with a polymer skeleton. The organic sulfur compound preferably has a sulfur-bridged structure. Examples of organic polymers into which elemental sulfur or a sulfur compound has been introduced include polyacrylonitrile, acrylic resin, polyolefin, etc.

[0069] The organic sulfur-based compound is more preferably sulfur-modified polyacrylonitrile. Sulfur-modified polyacrylonitrile is a compound in which polyacrylonitrile, an organic polymer, is modified with elemental sulfur. The organic sulfur-based compound, sulfur-modified polyacrylonitrile, may be an organic sulfur-based compound in which elemental sulfur is introduced into polyacrylonitrile by an addition reaction or a substitution reaction, or an organic sulfur-based compound in which elemental sulfur or a sulfur compound is introduced by mutual coordination with the polymer skeleton. Sulfur-modified polyacrylonitrile can be obtained, for example, by heating a mixture of elemental sulfur and polyacrylonitrile. As sulfur-modified polyacrylonitrile, pre-manufactured products such as "SPAN" manufactured by ADEKA can also be procured and used.

[0070] Polyacrylonitrile is a polymer having structural units derived from (meth)acrylonitrile, and preferably a polymer having structural units derived from acrylonitrile. "(Meth)acrylonitrile" represents either acrylonitrile or methacrylonitrile. The same applies to other monomers with "(meth)". The content of structural units derived from (meth)acrylonitrile in all structural units of polyacrylonitrile is preferably 50% by mass or more, and may be 70% by mass or more, 90% by mass or more, or 95% by mass or more, or may be 100% by mass.

[0071] Polyacrylonitrile may have structural units other than those derived from (meth)acrylonitrile, such as acrylic monomers such as (meth)acrylic acid esters, (meth)acrylamide, ethylene glycol (meth)acrylate, 1,6-hexanediol (meth)acrylate, neopentyl glycol di(meth)acrylate, and glycerin di(meth)acrylate; and conjugated dienes such as butadiene and isoprene.

[0072] The content of the organic sulfur compound in the positive electrode active material layer is preferably 50% by mass to 100% by mass, more preferably 55% by mass to 99% by mass, and even more preferably 60% by mass to 98% by mass. By having the content of the organic sulfur compound in the above range, it is possible to further increase the energy density of the nonaqueous electrolyte storage element.

[0073] The positive electrode active material layer may contain a positive electrode active material other than the organic sulfur compound, provided that the content of the organic sulfur compound 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.

[0074] The conductive agent is usually a component made of a material having electrical conductivity. Even when the volume resistivity of the conductive agent cannot be measured directly, it is possible to measure the volume resistivity by measuring the volume resistivity of the conductive agent when the volume resistivity is 10 －２Conductive agents are materials known to have a resistivity of Ω·cm or less. Examples of conductive agents include carbon materials, metals, and conductive ceramics. Carbon materials are materials whose primary constituent element is carbon. The primary constituent element refers to the element with the highest content by mass. For example, the carbon content in the carbon material may be 80% by mass or more, 90% by mass or more, 95% by mass, 99% by mass, or 99.9% by mass or more. The carbon material is preferably a carbon material other than an uncarbonized polymer compound. Examples of carbon materials include graphite, non-graphitic carbon, and graphene-based carbon. Examples of non-graphitic carbon include carbon nanofibers, pitch-based carbon fibers, and carbon black. Examples of carbon black include furnace black, acetylene black, and ketjen black. Examples of graphene-based carbon include graphene, carbon nanotubes (CNTs), and fullerenes. The conductive agent may be in the form of a powder or fiber. The conductive agent may be one or more types. A composite of these materials may be used as the conductive agent. For example, a composite material of carbon black and CNT may be used. Carbon black or CNT is preferred as the conductive agent, and acetylene black is more preferred as the carbon black. It is also preferred to use carbon black (preferably acetylene black) and CNT in combination.

[0075] The content of the conductive agent in the positive electrode active material layer is preferably 0.1% by mass or more and 10% by mass or less, and more preferably 1% by mass or more and 9% by mass or less. The upper limit of the content of the conductive agent may be 8%, 5%, 4%, 3%, or 2% by mass. By setting the content of the conductive agent within the above range, it is possible to increase the energy density of the nonaqueous electrolyte storage element, etc.

[0076] Examples of the binder include a water-based binder and an organic solvent-based binder.

[0077] The aqueous binder is a binder that dissolves or disperses in water. The aqueous binder may be a binder that dissolves or disperses 1 part by mass or more in 100 parts by mass of water at 20°C. When a positive electrode active material layer is formed using a positive electrode mixture paste whose dispersion medium is water or a mixed solvent mainly composed of water, an aqueous binder (a water-soluble or water-dispersible polymer material) can be used. Examples of aqueous binders include polyethylene oxide, polypropylene oxide, polyvinyl alcohol, polyacrylic acid, polymethacrylic acid, polytetrafluoroethylene, styrene-butadiene rubber, polyethylene, polypropylene, nitrile-butadiene rubber, and cellulose.

[0078] The organic solvent-based binder is a binder that dissolves or disperses in an organic solvent (e.g., N-methylpyrrolidone). The organic solvent-based binder may be a binder that dissolves or disperses at 1 part by mass or more per 100 parts by mass of an organic solvent (e.g., N-methylpyrrolidone) at 20°C. When a positive electrode active material layer is formed using a positive electrode mixture paste whose dispersion medium is an organic solvent or a mixed solvent mainly composed of an organic solvent, an organic solvent-based binder (a polymer material that is soluble or dispersible in an organic solvent) can be used. Examples of organic solvent-based binders include polyvinylidene fluoride, copolymers of vinylidene fluoride and hexafluoropropylene, copolymers of ethylene and vinyl alcohol, polyacrylonitrile, polyphosphazene, polysiloxane, polyvinyl acetate, polymethyl methacrylate, polystyrene, polycarbonate, polyamide, polyimide, polyamideimide, crosslinked polymers of cellulose and chitosan pyrrolidone carboxylate, chitosan derivatives, and the like.

[0079] 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 can be used.

[0080] The content of the binder 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%, 4%, or 3% by mass. By setting the binder content within the above range, it is possible to stably retain the organic sulfur-based compound, etc. The technology disclosed herein can also be implemented in an embodiment in which the positive electrode active material layer does not contain a binder.

[0081] Examples of dispersants include polysaccharide polymers such as carboxymethyl cellulose (CMC) and methyl cellulose. When the dispersant has a functional group that reacts with lithium or the like, the functional group may be deactivated in advance by methylation or the like. The content of the dispersant in the positive electrode active material layer is preferably 0.05% by mass or more and 5% by mass or less, and more preferably 0.1% by mass or more and 2% by mass or less. The polysaccharide polymer may function as a thickener or a binder.

[0082] Examples of the thickener include polyacrylic acid (PAA). The content of the thickener in the positive electrode active material layer is preferably 0.05% by mass or more and 5% by mass or less, and more preferably 0.1% by mass or more and 4% by mass or less. Polyacrylic acid may function as a binder.

[0083] The filler is not particularly limited. The filler may be a component other than the positive electrode active material (organic sulfur-based compound and other positive electrode active materials), conductive agent, binder, dispersant, and thickener, and may be intentionally added. The filler may be added to fill gaps in the positive electrode active material layer, or may be added for other purposes. The filler may be an organic substance such as polyolefin, or an inorganic substance such as an inorganic oxide, hydroxide, or carbonate. One or more fillers may be used. When the positive electrode active material layer contains a filler, the content of the filler in the positive electrode active material layer may be 0.1% by mass or more and 8% by mass or less, typically 5% by mass or less is preferred, and 2% by mass or less is more preferred. The technology disclosed herein may also be implemented in an embodiment in which the positive electrode active material layer does not contain a filler.

[0084] The positive electrode active material layer may further contain other components in addition to the positive electrode active material (organic sulfur-based compound and other positive electrode active material), conductive agent, binder, dispersant, thickener, and filler. These other components include those unintentionally generated in the positive electrode active material layer. The positive electrode active material layer may also contain unintentionally contained impurities as the other components, as long as the effects of the present invention are achieved. The upper limit of the content of the other components in the positive electrode active material layer may be 10% by mass, 5%, 2%, 1%, 0.1%, or 0.01% by mass. The upper limit of the content of the unintentionally generated components in the positive electrode active material layer may be 10% by mass, 5%, 2%, 1%, 0.1%, or 0.01% by mass. The upper limit of the content of impurities unintentionally contained in the positive electrode active material layer may be 10% by mass, 5% by mass, 2% by mass, 1% by mass, 0.1% by mass, or 0.01% by mass.

[0085] The thickness of the positive electrode active material layer is appropriately set depending on the type of positive electrode active material, the application of the nonaqueous electrolyte storage element, and the like. The average thickness of the positive electrode active material layer laminated on one surface of the positive electrode substrate may be, for example, 1 μm or more and 1,000 μm or less. The lower limit of the average thickness of the positive electrode active material layer may be 2 μm, 3 μm, 5 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, or 100 μm. The upper limit of the average thickness of the positive electrode active material layer may be 800 μm, 500 μm, 200 μm, 100 μm, 80 μm, 60 μm, 40 μm, 20 μm, 15 μm, or 10 μm. The mass per unit area of ​​the positive electrode active material layer is, for example, 1 mg / cm. ２ 100mg / cm or more ２ The lower limit of the mass per unit area of ​​the positive electrode active material layer may be 2 mg / cm or less. ２ , 3 mg / cm ２ , 4 mg / cm ２ , 6 mg / cm ２ , 8 mg / cm ２ or 10 mg / cm ２ The upper limit of the mass per unit area of ​​the positive electrode active material layer may be 50 mg / cm ２ , 20 mg / cm２ , 15 mg / cm ２ , 12 mg / cm ２ , 10 mg / cm ２ or 8 mg / cm ２ may be.

[0086] (Method for manufacturing positive electrode) The positive electrode can be manufactured by a known method. The positive electrode can be manufactured, for example, by applying a paste-like positive electrode mixture (positive electrode mixture paste) to a positive electrode substrate directly or via an intermediate layer, and drying the paste to form a positive electrode active material layer. The positive electrode mixture paste usually contains an organic sulfur-based compound, other optional components, and a dispersion medium. After drying, the positive electrode active material layer may be pressed, etc.

[0087] (Negative electrode) The negative electrode has a negative electrode substrate and a negative electrode active material layer laminated on the negative electrode substrate directly or via an intermediate layer. Usually, the negative electrode has a portion where the negative electrode substrate is exposed. This portion where the negative electrode substrate is exposed is usually connected to the above-mentioned negative electrode lead. The negative electrode may have a shape such as a sheet, plate, or strip.

[0088] The thickness of the negative electrode is appropriately set depending on the application of the nonaqueous electrolyte 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 a portion where the negative electrode active material layer is laminated on the negative electrode substrate directly or via an intermediate layer. When there are both a portion where the negative electrode active material layer is laminated on both sides of the negative electrode substrate and a portion where the negative electrode active material layer is laminated on only one side of the negative electrode substrate, the average thickness of the portion where the negative electrode active material layer is laminated on both sides of the negative electrode substrate is taken as the average thickness.

[0089] The negative electrode substrate is conductive. Examples of materials for the negative electrode substrate include metals such as copper, nickel, titanium, iron, and alloys thereof (e.g., stainless steel), and carbon materials. Among these, nickel or a nickel alloy is preferred.

[0090] The negative electrode substrate has a shape such as a sheet, plate, or strip. Examples of the form of the negative electrode substrate include foil, vapor-deposited film, mesh, and porous material, and foil is preferred. The negative electrode substrate may be, for example, nickel foil or nickel alloy foil.

[0091] The average thickness of the negative electrode substrate may be, for example, 2 μm or more and 35 μm or less. The lower limit of the average thickness of the negative electrode substrate may be 3 μm, 4 μm, 5 μm, or 10 μm. The upper limit of the average thickness of the negative electrode substrate may be 30 μm, 20 μm, 15 μm, or 10 μm.

[0092] The structure of the intermediate layer of the negative electrode is not particularly limited, and can be selected from the structures exemplified for the intermediate layer of the positive electrode, for example.

[0093] The negative electrode active material layer contains a negative electrode active material. The negative electrode active material layer contains optional components such as a conductive agent, a binder, a dispersant, a thickener, and a filler as needed. The optional components such as the conductive agent, the binder, the dispersant, the thickener, and the filler can be selected from the materials exemplified for the positive electrode above. The negative electrode active material layer may be formed from a negative electrode mixture containing a negative electrode active material and other optional components. The negative electrode active material layer may be provided on only one side or on both sides of a negative electrode substrate having a shape such as a sheet.

[0094] As the negative electrode active material, a known negative electrode active material can be used. A material capable of absorbing and releasing lithium ions is usually used as the negative electrode active material for a lithium ion secondary battery. Examples of the negative electrode active material include metallic lithium; metals or semimetals such as silicon and tin; metal oxides or semimetal oxides such as silicon oxide, titanium oxide, and tin oxide; Li ４ Ti ５ O １２ , LiTiO ２、 TiNb ２ O ７Examples of the negative electrode active material include titanium-containing oxides such as titanium dioxide, polyphosphate compounds, silicon carbide, and carbon materials such as graphite and non-graphitic carbon. Among these materials, carbon materials are preferred, and graphite or non-graphitic carbon may be more preferred. The surface of graphite may be coated with another material such as non-graphitic carbon. One or more negative electrode active materials may be used. In the case of a negative electrode active material that does not contain charge transport ions such as lithium ions, a material doped with charge transport ions such as lithium ions may be used.

[0095] The negative electrode active material is preferably metallic lithium. In other words, the negative electrode or the negative electrode active material layer preferably contains metallic lithium at least in a charged state. It is more preferable that the negative electrode or the negative electrode active material layer contains metallic lithium in all states, including a charged state and a discharged state.

[0096] The metallic lithium may be pure metallic lithium consisting essentially of lithium element alone, or may be a lithium alloy containing other metal elements. Examples of the lithium alloy include a lithium-silver alloy, a lithium-zinc alloy, a lithium-calcium alloy, a lithium-aluminum alloy, a lithium-magnesium alloy, and a lithium-indium alloy. The lithium alloy may contain multiple metal elements other than lithium element.

[0097] The negative electrode active material layer is preferably a layer substantially composed of metallic lithium (pure metallic lithium or a lithium alloy). The lower limit of the lithium element content in the negative electrode active material layer is preferably 80 mass%, more preferably 90 mass%, and even more preferably 99 mass%. The upper limit of the lithium element content in the negative electrode active material layer may be 100 mass%.

[0098] When the negative electrode active material layer contains a conductive agent, the content of the conductive agent in the negative electrode active material layer is preferably 1% by mass or more and 10% by mass or less, and more preferably 3% by mass or more and 9% by mass or less. The content of the conductive agent in the negative electrode active material layer may be 5% by mass or less, or may be 2% by mass or less. The technology disclosed herein may also be implemented in an embodiment in which the negative electrode active material layer does not contain a conductive agent.

[0099] When the negative electrode active material layer contains a binder, the content of the binder in the negative electrode active material layer is preferably 0.1 mass% to 10 mass%, more preferably 0.5 mass% to 8 mass%. The content of the binder in the negative electrode active material layer may be 5 mass% or less, or may be 2 mass% or less. The technology disclosed herein may also be implemented in an embodiment in which the negative electrode active material layer does not contain a binder.

[0100] When the negative electrode active material layer contains a dispersant, the content of the dispersant in the negative electrode active material layer is preferably 0.05% by mass or more and 5% by mass or less, and more preferably 0.1% by mass or more and 2% by mass or less. The content of the dispersant in the negative electrode active material layer may be 1% by mass or less, or may be 0.1% by mass or less. The technology disclosed herein may also be implemented in an embodiment in which the negative electrode active material layer does not contain a dispersant.

[0101] When the negative electrode active material layer contains a thickener, the content of the thickener in the negative electrode active material layer is preferably 0.1% by mass or more and 10% by mass or less, and more preferably 0.5% by mass or more and 8% by mass or less. The content of the thickener in the negative electrode active material layer may be 5% by mass or less, or may be 2% by mass or less. The technology disclosed herein may also be implemented in an embodiment in which the negative electrode active material layer does not contain a thickener.

[0102] The filler in the negative electrode active material layer may be a component other than the negative electrode active material, conductive agent, binder, dispersant, and thickener, and may be an intentionally contained component. The filler may be contained as a component to fill gaps in the negative electrode active material layer, or may be contained for another purpose. When the negative electrode active material layer contains a filler, the content of the filler in the negative electrode active material layer may be 0.1% by mass or more and 8% by mass or less, and typically 5% by mass or less is preferred, and 2% by mass or less is more preferred. The technology disclosed herein may also be implemented in an embodiment in which the negative electrode active material layer does not contain a filler.

[0103] The negative electrode active material layer may further contain other components in addition to the negative electrode active material, conductive agent, binder, dispersant, thickener, and filler. These other components include those unintentionally generated in the negative electrode active material layer. The negative electrode active material layer may also contain unintentionally contained impurities as the other components, as long as the effects of the present invention are achieved. The upper limit of the content of the other components in the negative electrode active material layer may be 10% by mass, 5%, 2%, 1%, 0.1%, or 0.01% by mass. The upper limit of the content of the unintentionally generated components in the negative electrode active material layer may be 10% by mass, 5%, 2%, 1%, 0.1%, or 0.01% by mass. The upper limit of the content of the unintentionally contained impurities in the negative electrode active material layer may be 10% by mass, 5%, 2%, 1%, 0.1%, or 0.01% by mass.

[0104] The negative electrode active material layer may be a non-porous layer (solid layer) or a porous layer, but is preferably a non-porous layer. The negative electrode active material layer may be a layer of metallic lithium. The negative electrode active material layer may be a layer made of metallic lithium foil (pure metallic lithium foil or lithium alloy foil).

[0105] The average thickness of the negative electrode active material layer laminated on one surface of the negative electrode substrate in a 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 a 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 a charged state may be 1,500 μm, 1,200 μm, 1,000 μm, 800 μm, 700 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.

[0106] (Method for manufacturing a negative electrode) The negative electrode can be manufactured by a known method. The negative electrode can be manufactured, for example, in the same manner as in the method for manufacturing a positive electrode described above, by applying a paste-like negative electrode mixture (negative electrode mixture paste) to a negative electrode substrate directly or via an intermediate layer, and drying the applied mixture to form a negative electrode active material layer. After drying, the negative electrode active material layer may be pressed, for example. When the negative electrode active material is a metal such as metallic lithium, the negative electrode can also be manufactured by laminating a metal foil on the negative electrode substrate directly or via an intermediate layer, and then pressing the metal foil (for example, rolling).

[0107] (Separator) A known separator can be used as the separator, for example, a separator consisting of only a base layer, or a separator in which an inorganic layer containing inorganic particles and a binder is formed on one or both surfaces of a base layer.

[0108] Examples of the form of the separator substrate layer 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 nonaqueous electrolyte retention. The material of the separator substrate layer is not particularly limited as long as it has insulating properties, but resins such as polyolefin (polyethylene, polypropylene, etc.), polyimide, and aramid are preferred.

[0109] Examples of inorganic compounds constituting the inorganic particles include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, calcium oxide, and magnesium oxide; nitrides such as aluminum nitride and silicon nitride; carbonates such as calcium carbonate; sulfates such as barium sulfate; sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium titanate; covalently bonded crystals such as silicon; mineral resource-derived substances such as talc, zeolite, kaolin, bentonite, and mica, or artificial products thereof. One or more types of inorganic particles can be used. The average particle size of the inorganic particles is preferably, for example, 0.5 μm to 10 μm. The content of the inorganic particles in the inorganic layer is preferably 50% by mass to 99% by mass, more preferably 80% by mass to 98% by mass.

[0110] Examples of binders used in the inorganic layer include the same binders as those exemplified for the positive electrode active material layer.

[0111] The separator may have an inorganic layer containing aramid as a binder. The separator may have a layer containing aramid on its surface. Such a separator has good wettability even when the non-aqueous electrolyte has a high viscosity. Therefore, the use of such a separator is particularly useful when the concentration of the non-aqueous electrolyte is high (for example, when the molar concentration of the non-aqueous electrolyte salt exceeds 1.0 mol / kg) or when the non-aqueous electrolyte contains an ionic liquid.

[0112] The porosity of the separator may be, for example, 20% or more and 80% or less. The lower limit of the porosity of the separator may be 30%, 40%, or 50% from the viewpoint of discharge performance, etc. The upper limit of the porosity of the separator may be 70%, 60%, or 50% from the viewpoint of strength, etc. In this specification, "porosity" refers to a volume-based value measured with a mercury porosimeter.

[0113] 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.

[0114] The separator may be a polymer gel composed of a polymer and a non-aqueous electrolyte, or may be a combination of the porous resin film, nonwoven fabric, or the like described above and a polymer gel.

[0115] (Electrode Body) As the electrode body, for example, a wound type electrode body, a laminated type electrode body, or the like having a known structure can be used.

[0116] A wound electrode body has a structure in which a positive electrode and a negative electrode are wound in an insulated state. The wound electrode body may be cylindrical (columnar) or flat. The electrode body 2 provided in the nonaqueous electrolyte storage element 1 of FIG. 1 is a flat wound electrode body. The wound electrode body can be produced, for example, by the following procedure. First, a positive electrode, a separator, and a negative electrode, each formed in a strip shape, are stacked together to obtain a laminate. The wound electrode body is obtained by rolling this laminate.

[0117] The stacked electrode assembly 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 stacked electrode assembly can be obtained by stacking a positive electrode, a separator, and a negative electrode, each of which is formed in a rectangular shape.

[0118] As the electrode body, for example, one having a structure in which at least one of the positive electrode and the negative electrode is folded in an accordion-like manner and stacked can also be used.

[0119] (Non-aqueous electrolyte) The non-aqueous electrolyte is a medium responsible for transporting charge-transporting ions (e.g., lithium ions) between the positive electrode and the negative electrode, and is substantially free of water. The water content in the 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, or 100 ppm or less, preferably 50 ppm or less, and more preferably 20 ppm or less.

[0120] The non-aqueous electrolyte includes an electrolyte salt and a liquid component. The liquid component includes a non-aqueous solvent and, optionally, a non-ionic liquid. The non-aqueous electrolyte may be a non-aqueous electrolyte solution. In one embodiment of the present invention, the non-aqueous electrolyte storage element may be a non-aqueous electrolyte solution storage element.

[0121] [Electrolyte Salt] The electrolyte salt refers to an ionic compound in which the cation is a charge-transporting ion and which is solid at 20°C and 1 atmosphere. Known electrolyte salts can be used. Examples of the electrolyte salt include lithium salt, sodium salt, potassium salt, magnesium salt, and onium salt. Among these, lithium salt is preferred. One or more types of electrolyte salts can be used.

[0122] The anions constituting 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 － , C.F. ３ -SO ２ -N-SO ２ -C ４ F ９ － , C.F. ３ -SO ２ -N-SO ２ -CF ２ -SO ２ -N-SO ２ -CF ３ ２－ , C.F. ３ -SO ２ -N-SO ２ -CF ２ -SO ３ ２－ , C.F. ３ -SO ２ -N-SO ２-CF ２ -SO ２ -C(-SO ２ CF ３ ) ２ ２－ Examples of anions constituting the electrolyte salt include imide anions such as PF ６ － , P.O. ２ F ２ － , B.F. ４ － , ClO ４ － , NO ２ － , NO ３ － , I － , S.O. ３ CF ３ － , C(SO ２ CF ３ ) ３ － , C(SO ２ C ２ F ５ ) ３ － Anions other than imide anions such as the above can also be used.

[0123] The anion constituting the electrolyte salt is preferably an imide anion, and more preferably a bis(trifluoromethanesulfonyl)imide anion (TFSI － ) and bis(fluorosulfonyl)imide anion (FSI － ), and bis(fluorosulfonyl)imide anion (FSI －) is more preferred. That is, the electrolyte salt is preferably an imide salt, more preferably at least one selected from the group consisting of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium bis(fluorosulfonyl)imide (LiFSI), and even more preferably lithium bis(fluorosulfonyl)imide (LiFSI). In addition, the anion constituting the electrolyte salt preferably has a fluorine atom. When the anion constituting the electrolyte salt is such an anion, the ionic conductivity of the nonaqueous electrolyte is increased, and the initial discharge capacity of the nonaqueous electrolyte storage element can be increased, and the capacity retention rate after charge / discharge cycles can be further increased. One or more electrolyte salts can be used.

[0124] The molar concentration of the electrolyte salt in the non-aqueous electrolyte can be, for example, 0.5 mol / kg or more, but is preferably greater than 1.0 mol / kg. The lower limit of the molar concentration may be 1.1 mol / kg, 1.3 mol / kg, or 1.5 mol / kg. The upper limit of the molar concentration of the electrolyte salt is preferably 3.0 mol / kg, or may be 2.5 mol / kg, 2.0 mol / kg, or 1.5 mol / kg. By setting the molar concentration of the electrolyte salt within the above range, the ionic conductivity of the non-aqueous electrolyte can be optimized, and the initial discharge capacity of the non-aqueous electrolyte storage element can be increased and the capacity retention rate after charge / discharge cycles can be improved.

[0125] [Fluorinated Cyclic Ether] In one embodiment of the present invention, the liquid component includes a fluorinated cyclic ether. The fluorinated cyclic ether is a non-aqueous solvent. The fluorinated cyclic ether refers to an ether having a fluorine atom and a ring structure. The fluorinated cyclic ether may be composed only of carbon, hydrogen, oxygen, and fluorine. The oxygen atoms contained in the fluorinated cyclic ether are preferably only oxygen atoms constituting ether bonds. In other words, the fluorinated cyclic ether preferably does not have an oxygen-containing substituent such as a hydroxy group or a carboxy group. The fluorinated cyclic ether may be a monoether (a compound having only one ether bond), a diether (a compound having two ether bonds), a triether (a compound having three ether bonds), or the like, but is preferably a monoether. The fluorinated cyclic ether preferably has an ether bond in the ring structure. The fluorinated cyclic ether is preferably a saturated ether. A saturated ether refers to an ether that does not have unsaturated bonds between carbon atoms (carbon-carbon double bonds and carbon-carbon triple bonds).

[0126] 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 even more preferably 5. The upper limit of the number of ring members is preferably 8, more preferably 7, more preferably 6, and even more preferably 5. The lower limit of the number of carbon atoms in the fluorinated cyclic ether is preferably 2, more preferably 3, and even more preferably 4. The upper limit of the number of carbon atoms is preferably 7, more preferably 6, more preferably 5, and even more preferably 4. The lower limit of the number of fluorine atoms in the fluorinated cyclic ether is preferably 2, more preferably 3, and even more preferably 4. The upper limit of the number of fluorine atoms is preferably 10, more preferably 8, more preferably 6, and even more preferably 4.

[0127] The upper limit of the number of donors in the fluorinated cyclic ether is preferably 15, more preferably 14.5, even more preferably 14, and still more preferably 13.5. The lower limit of the number of donors in the fluorinated cyclic ether may be 8, 9, 10, 11, 12, or 13.

[0128] The fluorinated cyclic ether is preferably represented by the following formula (1): (In formula (1), R １ are each independently a hydrogen atom, a fluorine atom, an alkyl group having 1 to 4 carbon atoms, or a fluorinated alkyl group having 1 to 4 carbon atoms. １ At least one of the groups is a fluorine atom or a fluorinated alkyl group having 1 to 4 carbon atoms. n1 is an integer of 2 to 5.

[0129] R in the above formula (1) １ When R is an alkyl group or a fluorinated alkyl group, it preferably has 3 or less carbon atoms, more preferably 2 or less carbon atoms. １ is preferably a hydrogen atom or a fluorine atom. n1 is preferably 4 or 5, and more preferably 4.

[0130] The fluorinated cyclic ether may be, for example, 3,3,4,4-tetrafluorotetrahydrofuran. One or more kinds of fluorinated cyclic ethers can be used.

[0131] The content of the fluorinated cyclic ether in the liquid component is greater than 30% by volume. When the content of the fluorinated cyclic ether in the liquid component is greater than 30% by volume, elution of polysulfides from the positive electrode into the non-aqueous electrolyte is suppressed, the initial discharge capacity of the non-aqueous electrolyte storage element is increased, and the capacity retention rate after charge-discharge cycling is improved. The lower limit of the content is preferably 35% by volume, more preferably 40% by volume, even more preferably 45% by volume, even more preferably 50% by volume, and may be 55% by volume, 60% by volume, 65% by volume, 70% by volume, 75% by volume, or 80% by volume. The upper limit of the content is preferably 95% by volume, more preferably 90% by volume, even more preferably 85% by volume, even more preferably 80% by volume, and may be 75% by volume, 70% by volume, 65% by volume, 60% by volume, 55% by volume, or 50% by volume.

[0132] [Ether with a donor number of 15 or less] In one embodiment of the present invention, the liquid component includes an ether with a donor number of 15 or less. The ether with a donor number of 15 or less is a non-aqueous solvent. Use of such an ether with a small donor number suppresses elution of polysulfides from the positive electrode into the non-aqueous electrolyte, increases the initial discharge capacity of the non-aqueous electrolyte storage element, and improves the capacity retention rate after charge-discharge cycling. The upper limit of the donor number of this ether is preferably 14.5, more preferably 14, and even more preferably 13.5. The lower limit of the donor number of this ether may be 8, 9, 10, 11, 12, or 13.

[0133] An ether having 15 or fewer donors may be a linear ether or a cyclic ether. A linear ether refers to an ether without a ring structure. A cyclic ether refers to an ether with a ring structure. An ether having 15 or fewer donors may be a fluorinated ether or a non-fluorinated ether. An ether having 15 or fewer donors may be composed only of carbon, hydrogen, and oxygen, or may be composed only of carbon, hydrogen, oxygen, and fluorine. The oxygen elements contained in an ether having 15 or fewer donors are preferably only oxygen elements constituting ether bonds. In other words, an ether having 15 or fewer donors preferably does not have an oxygen-containing substituent such as a hydroxy group or a carboxy group. An ether having 15 or fewer donors may be any of a monoether, diether, triether, etc. An ether having 15 or fewer donors is preferably a saturated ether. An ether having 15 or fewer donors is preferably a fluorinated ether, more preferably a fluorinated cyclic ether.

[0134] Examples of ethers having a donor number of 15 or less include ethyl-2-(2,2,2-trifluoroethoxy)ethyl ether (donor number 9.6), 2-(2,2-difluoroethoxy)ethyl methyl ether (donor number 15.0), ethyl-2-(2,2-difluoroethoxy)ethyl ether (donor number 9.9), ethyl-2-(2-fluoroethoxy)ethyl ether (donor number 12.3), bis(2,2,2-trifluoroethyl)ether (donor number 10.3), 3,3,4,4-tetrafluorotetrahydrofuran (donor number 13.2), etc. One or more types of ethers having a donor number of 15 or less can be used.

[0135] The content of the ether having a donor number of 15 or less in the liquid component is greater than 30% by volume. When the content of the ether having a donor number of 15 or less in the liquid component is greater than 30% by volume, elution of polysulfides from the positive electrode into the nonaqueous electrolyte is suppressed, the initial discharge capacity of the nonaqueous electrolyte storage element is increased, and the capacity retention rate after charge-discharge cycles is improved. The lower limit of the content is preferably 35% by volume, more preferably 40% by volume, even more preferably 45% by volume, even more preferably 50% by volume, and may be 55% by volume, 60% by volume, 65% by volume, 70% by volume, 75% by volume, or 80% by volume. The upper limit of the content is preferably 95% by volume, more preferably 90% by volume, even more preferably 85% by volume, even more preferably 80% by volume, and may be 75% by volume, 70% by volume, 65% by volume, 60% by volume, 55% by volume, or 50% by volume.

[0136] [Chain Ether, etc.] The liquid component preferably further includes at least one of a chain ether and an ionic liquid. The inclusion of these components in the non-aqueous electrolyte increases the solubility of the electrolyte salt, thereby enabling the non-aqueous electrolyte storage element to have a larger initial discharge capacity and a higher capacity retention rate after charge-discharge cycles.

[0137] The inclusion of a chain ether in the liquid component can increase the solubility of the electrolyte salt in the non-aqueous electrolyte while reducing the viscosity of the non-aqueous electrolyte, thereby increasing the initial discharge capacity of the non-aqueous electrolyte storage element and improving the capacity retention rate after charge-discharge cycling. The chain ether may be a fluorinated chain ether or a non-fluorinated chain ether, but is preferably a fluorinated chain ether. The chain ether may be composed only of carbon, hydrogen, and oxygen, or may be composed only of carbon, hydrogen, oxygen, and fluorine. The oxygen element contained in the chain ether is preferably only the oxygen element constituting the ether bond. In other words, the chain ether preferably does not have an oxygen-containing substituent such as a hydroxy group or a carboxy group. The chain ether may be a monoether, diether, triether, etc., but is preferably a diether. The chain ether may be a fluorinated chain diether. The chain ether is preferably a saturated ether.

[0138] The lower limit of the number of carbon atoms in the chain ether is preferably 3, more preferably 4, and even more preferably 5. The upper limit of the number of carbon atoms is preferably 8, more preferably 7, and even more preferably 6. The lower limit of the number of fluorine atoms in the chain ether is preferably 2, and more preferably 3. The upper limit of the number of fluorine atoms is preferably 8, and even more preferably 7, 6, 5, 4, or 3.

[0139] The chain ether is preferably represented by the following formula (2). (In formula (2), R ２ and R ３ are each independently an alkyl group having 1 to 3 carbon atoms or a fluorinated alkyl group having 1 to 3 carbon atoms. ４ is an alkanediyl group having 1 to 3 carbon atoms; and n2 is 0 or 1.

[0140] R in the above formula (2) ２ R is preferably an alkyl group, more preferably a methyl group or an ethyl group. ３R is preferably a fluorinated alkyl group, more preferably a fluorinated methyl group or a fluorinated ethyl group, even more preferably a fluorinated ethyl group, and even more preferably a 2,2,2-trifluoroethyl group. ４ As for -(CH ２ ) ｍ - (m is an integer of 1 or more and 3 or less) is preferred, and -CH ２ CH ２ n2 is preferably 1.

[0141] The number of donors in the chain ether is preferably more than 15. The lower limit of the number of donors in the chain ether is preferably 15.5, more preferably 16.0, even more preferably 16.5, and still more preferably 17.0, 17.5, 18.0, or 18.5. The upper limit of the number of donors in the chain ether may be, for example, 25, or may be 24, 23, 22, 21, 20, or 19.

[0142] Examples of the chain ether include 2-(2,2,2-trifluoroethoxy)ethyl methyl ether, 2-(2-fluoroethoxy)ethyl methyl ether, ethyl-2-(2,2,2-trifluoroethoxy)ethyl ether, etc. One or more types of chain ethers can be used.

[0143] The lower limit of the content of the chain ether in the liquid component is preferably 5% by volume, more preferably 10% by volume, and even more preferably 15% by volume, and may be 20%, 25%, 30%, 35%, 40%, 45%, or 50% by volume. The upper limit of the content is preferably 60% by volume, more preferably 50% by volume, and may be 40%, 30%, or 20% by volume.

[0144] [Ionic Liquid] An ionic liquid refers to an ionic compound that is liquid at 20° C. and 1 atmosphere. By including an ionic liquid in the liquid component, it is possible to increase the solubility of an electrolyte salt in the non-aqueous electrolyte while also increasing the flame retardancy of the non-aqueous electrolyte.

[0145] The number of donors in the ionic liquid is not particularly limited. For example, the number of donors in the ionic liquid may be 8 to 18, or 10 to 16. The number of donors in the ionic liquid may be 15 or less.

[0146] Examples of cations constituting the ionic liquid include quaternary ammonium cations, imidazolium-based cations, pyrrolidinium-based cations, piperidinium-based cations, pyridinium-based cations, pyrrolium-based cations, pyrazolium-based cations, pyrrolinium-based cations, quaternary phosphonium cations, and sulfonium cations.

[0147] Examples of the quaternary ammonium cation include tetraalkylammonium cations such as trimethylethylammonium cation, trimethylpropylammonium cation, trimethylbutylammonium cation, trimethylhexylammonium cation, and tetrapentylammonium cation.

[0148] Examples of imidazolium cations include 1,3-dimethylimidazolium cation, 1-ethyl-3-methylimidazolium cation, 1,3-diethylimidazolium cation, 1-butyl-3-methylimidazolium cation, 1,2,3-trimethylimidazolium cation, 1,2-dimethyl-3-ethylimidazolium cation, 1,2-dimethyl-3-propylimidazolium cation, and 1-butyl-2,3-dimethylimidazolium cation.

[0149] Examples of pyrrolidinium cations include 1,1-dimethylpyrrolidinium cation, 1-ethyl-1-methylpyrrolidinium cation, 1-methyl-1-propylpyrrolidinium cation, and 1-butyl-1-methylpyrrolidinium cation.

[0150] Examples of piperidinium cations include 1,1-dimethylpiperidinium cation, 1-ethyl-1-methylpiperidinium cation, 1-methyl-1-propylpiperidinium cation, and 1-butyl-1-methylpiperidinium cation.

[0151] Examples of pyridinium cations include 1-methylpyridinium cation, 1-ethylpyridinium cation, 1-propylpyridinium cation, 1-butylpyridinium cation, 1-ethyl-2-methylpyridinium cation, 1-butyl-4-methylpyridinium cation, and 1-butyl-2,4-dimethylpyridinium cation.

[0152] 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.

[0153] Examples of pyrazolium cations include 1,2-dimethylpyrazolium cation, 1-ethyl-2-methylpyrazolium cation, 1-propyl-2-methylpyrazolium cation, and 1-butyl-2-methylpyrazolium cation.

[0154] Examples of pyrrolinium cations include 1,2-dimethylpyrrolinium cation, 1-ethyl-2-methylpyrrolinium cation, 1-propyl-2-methylpyrrolinium cation, and 1-butyl-2-methylpyrrolinium cation.

[0155] Examples of the quaternary phosphonium cation include a tetramethylphosphonium cation, a tetraethylphosphonium cation, a trimethylethylphosphonium cation, a trimethylpropylphosphonium cation, a trimethylbutylphosphonium cation, a tetraphenylphosphonium cation, and a trimethylmethoxymethylphosphonium cation.

[0156] Examples of the sulfonium cation include a trimethylsulfonium cation, a triethylsulfonium cation, and a tributylsulfonium cation.

[0157] The cation constituting the ionic liquid is preferably at least one selected from the group consisting of quaternary ammonium cations, imidazolium cations, pyrrolidinium cations, piperidinium cations, quaternary phosphonium cations, and sulfonium cations, more preferably at least one selected from the group consisting of imidazolium cations, pyrrolidinium cations, and piperidinium cations, and even more preferably a pyrrolidinium cation. When the cation constituting the ionic liquid is such a cation, it is possible to further increase the initial discharge capacity of the nonaqueous electrolyte energy storage element and further increase the capacity retention rate after charge-discharge cycling. One or more of these cations may be contained.

[0158] Examples of anions constituting the ionic liquid include the same anions as those constituting the electrolyte salt. As an anion constituting the ionic liquid, imide anions are preferred, and bis(trifluoromethanesulfonyl)imide anion (TFSI) is preferred. － ) and bis(fluorosulfonyl)imide anion (FSI － ), and bis(fluorosulfonyl)imide anion (FSI － ) is more preferred. Furthermore, the anion constituting the ionic liquid preferably has a fluorine atom. When the anion constituting the ionic liquid is such an anion, it is possible to further increase the initial discharge capacity of the nonaqueous electrolyte energy storage element and further increase the capacity retention rate after charge / discharge cycles. One or more of these anions may be contained.

[0159] At least one of the electrolyte salt and the ionic liquid contains a bis(fluorosulfonyl)imide anion (FSI) as an anion. － It is preferable that the non-aqueous electrolyte contains a bis(fluorosulfonyl)imide anion (FSI) as an anion. － In this case, it is possible to increase the initial discharge capacity of the nonaqueous electrolyte storage element and to improve the capacity retention rate after charge-discharge cycles.

[0160] In addition, it is preferable that the anions present in the non-aqueous electrolyte are substantially only imide anions, and the anions present in the non-aqueous electrolyte are substantially bis(trifluoromethanesulfonyl)imide anions (TFSI － ) and bis(fluorosulfonyl)imide anion (FSI － ) is more preferably at least one selected from the group consisting of. For example, the content of these anions relative to all anions in the non-aqueous electrolyte is preferably 90 mol % or more, more preferably 99 mol % or more, and even more preferably 99.9 mol % or more. By configuring the anions in the non-aqueous electrolyte in this way, the ionic conductivity of the non-aqueous electrolyte is increased, and the initial discharge capacity of the non-aqueous electrolyte storage element can be increased, and the capacity retention rate after charge-discharge cycles can be improved.

[0161] The lower limit of the ionic liquid content in the liquid component is preferably 5% by volume, more preferably 7% by volume, and even more preferably 10% by volume. The upper limit of the content is preferably 50% by volume, more preferably 40% by volume, and may be 30%, 20%, 15%, or 10% by volume. By setting the content of the ionic liquid at or below the upper limit, the viscosity of the non-aqueous electrolyte can be reduced, thereby improving the output performance of the non-aqueous electrolyte storage element.

[0162] The lower limit of the total content of at least one of a fluorinated cyclic ether, an ether having a donor number of 15 or less, and a chain ether, and an ionic liquid in the liquid component is preferably 90% by volume, more preferably 95% by volume, even more preferably 97% by volume, and even more preferably 99% by volume. Having the liquid component primarily comprise these components can increase the initial discharge capacity of the nonaqueous electrolyte storage element and improve the capacity retention rate after charge / discharge cycles. The upper limit of the total content may be 100% by volume.

[0163] [Other Components in the Liquid Component] The liquid component may contain an ether corresponding to at least one of a fluorinated cyclic ether, an ether having a donor number of 15 or less, and a chain ether, and other components other than the ionic liquid. Examples of other components include fluorinated cyclic ethers, other ethers that do not correspond to either an ether having a donor number of 15 or less or a chain ether, carbonates (cyclic carbonates and chain carbonates), carboxylic acid esters, phosphate esters, amides, nitriles, etc. Examples of other ethers include non-fluorinated cyclic ethers having a donor number of more than 15 (e.g., tetrahydrofuran, tetrahydropyran, etc.). Note that ethers, carbonates, carboxylic acid esters, phosphate esters, amides, nitriles, etc. all fall under the category of non-aqueous solvents.

[0164] The lower limit of the total content of the ether and the ionic liquid in the liquid component is preferably 90% by volume, more preferably 95% by volume, even more preferably 97% by volume, and even more preferably 99% by volume. When the liquid component is primarily composed of the ether and the ionic liquid, the initial discharge capacity of the nonaqueous electrolyte storage element can be increased, and the capacity retention rate after charge / discharge cycles can be improved. The upper limit of the total content may be 100% by volume.

[0165] The lower limit of the total content of the fluorinated ether and ionic liquid in the liquid component is preferably 90% by volume, more preferably 95% by volume, even more preferably 97% by volume, and even more preferably 99% by volume. When the liquid component is mainly composed of a fluorinated ether and an ionic liquid, it is possible to increase the initial discharge capacity of the nonaqueous electrolyte storage element and further improve the capacity retention rate after charge / discharge cycles. The upper limit of the total content may be 100% by volume. Fluorinated ethers include all ethers that are fluorinated, i.e., contain a fluorine element, regardless of the number of donors and the structure (cyclic or chain).

[0166] The lower limit of the ether content in the liquid component is preferably 80 vol%, more preferably 85 vol%, even more preferably 90 vol%, and may be 95 vol% or 99 vol%. Having a liquid component mainly composed of ether can increase the initial discharge capacity of the nonaqueous electrolyte storage element and further improve the capacity retention rate after charge / discharge cycles. The upper limit of the content may be 100 vol%, or may be 99 vol%, 95 vol%, or 90 vol%.

[0167] The lower limit of the fluorinated ether content in the liquid component is preferably 80 vol%, more preferably 85 vol%, even more preferably 90 vol%, and may be 95 vol% or 99 vol%. When the liquid component is mainly composed of a fluorinated ether, the initial discharge capacity of the nonaqueous electrolyte storage element can be increased, and the capacity retention rate after charge / discharge cycles can be improved. The upper limit of the content may be 100 vol%, or may be 99 vol%, 95 vol%, or 90 vol%.

[0168] The lower limit of the total content of at least one of fluorinated cyclic ethers, ethers having a donor number of 15 or less, and chain ethers in the nonaqueous solvent is preferably 90% by volume, more preferably 95% by volume, even more preferably 97% by volume, and even more preferably 99% by volume. The lower limit of the content of the ether in the nonaqueous solvent is preferably 90% by volume, more preferably 95% by volume, even more preferably 97% by volume, and even more preferably 99% by volume. The lower limit of the content of the fluorinated ether in the nonaqueous solvent is preferably 90% by volume, more preferably 95% by volume, even more preferably 97% by volume, and even more preferably 99% by volume. When the nonaqueous solvent is composed of such components, it is possible to increase the initial discharge capacity of the nonaqueous electrolyte storage element and to increase the capacity retention rate after charge-discharge cycling.

[0169] The upper limit of the carbonate content in the liquid component is preferably 10% by volume, more preferably 5% by volume, even more preferably 3% by volume, and even more preferably 1% by volume. The upper limit of the carbonate content in the non-aqueous solvent is preferably 10% by volume, more preferably 5% by volume, even more preferably 3% by volume, and even more preferably 1% by volume. A low carbonate content in the liquid component or non-aqueous solvent can increase the initial discharge capacity of the non-aqueous electrolyte storage element and improve the capacity retention rate after charge-discharge cycles. The liquid component or non-aqueous solvent does not need to contain carbonate.

[0170] The upper limit of the average donor number in the liquid component is preferably 16.0, more preferably 15.5, and even more preferably 15.0. The lower limit of the average donor number is preferably 10.0, more preferably 11.0, even more preferably 12.0, even more preferably 13.0, and particularly preferably 14.0. When the average donor number is within the above range, it is possible to increase the initial discharge capacity of the nonaqueous electrolyte storage element and to increase the capacity retention rate after charge-discharge cycles.

[0171] The non-aqueous electrolyte may contain other components in addition to the electrolyte salt and liquid components (non-aqueous solvent and ionic liquid). Examples of other components include additives.

[0172] When an additive is used in the non-aqueous electrolyte, the content of the additive in the non-aqueous electrolyte is preferably 0.01% by mass to 10% by mass, more preferably 0.1% by mass to 7% by mass, even more preferably 0.2% by mass to 5% by mass, and particularly preferably 0.3% by mass to 3% by mass.

[0173] (Container) The container accommodates the electrode assembly and the non-aqueous electrolyte in its internal space. Materials for the container include metal materials such as aluminum and stainless steel, and resin materials, with metal materials being preferred from the standpoint of strength, etc. Composite materials of metal and resin materials can also be used.

[0174] The shape of the container is not particularly limited, and may be cylindrical, rectangular (square), disk-like, etc. The container may also be in the shape of a sheet formed from a metal-resin composite film.

[0175] (Shape, Use, etc. of Nonaqueous Electrolyte Storage Element) The shape of the nonaqueous electrolyte storage element according to one embodiment of the present invention is not particularly limited. The nonaqueous electrolyte storage element may be, for example, a cylindrical battery, a prismatic battery, a flat battery, a coin battery, a button battery, etc.

[0176] The use of the nonaqueous electrolyte electricity storage element according to one embodiment of the present invention is not particularly limited, and the nonaqueous electrolyte electricity storage element can be used, for example, as a power source for automobiles such as electric vehicles, hybrid vehicles, and plug-in hybrid vehicles, a power source for electronic devices such as personal computers and communication terminals, a power source for power storage, etc.

[0177] The nonaqueous electrolyte electricity storage element of the present invention may be used singly or in plural. When the required output and required voltage are small, the nonaqueous electrolyte electricity storage element may be used singly. On the other hand, when at least one of the required output and required voltage is large, the nonaqueous electrolyte electricity storage element may be used as an electricity storage device in combination with other nonaqueous electrolyte electricity storage elements. In an electricity storage device in which a plurality of nonaqueous electrolyte electricity storage elements are combined, at least one nonaqueous electrolyte electricity storage element included in the electricity storage device may be the nonaqueous electrolyte electricity storage element according to one embodiment of the present invention. The electricity storage device will be described in detail later.

[0178] In a nonaqueous electrolyte energy storage element according to one embodiment of the present invention, for example, the container may be constrained so as to maintain a constant thickness, or may not be constrained in this manner. Alternatively, the container may be constrained so as to apply a constant load to it. When the container is constrained, expansion of the container due to charge / discharge cycles, etc., may be suppressed, and deterioration of charge / discharge performance may be suppressed. When the container is constrained, a load may or may not be applied to the electrode assembly within the container. For example, a constraining member that performs such constraining may be provided in the nonaqueous electrolyte energy storage element or the energy storage device.

[0179] <Method for Manufacturing Nonaqueous Electrolyte Storage Element> A nonaqueous electrolyte storage element according to one embodiment of the present invention can be manufactured by a known method. The method for manufacturing the nonaqueous electrolyte storage element includes, for example, preparing a positive electrode containing an organic sulfur-based compound, preparing a negative electrode, preparing a nonaqueous electrolyte containing an electrolyte salt and a liquid component, and housing the positive electrode, the negative electrode, and the nonaqueous electrolyte in a container. In one embodiment of the present invention, the liquid component of the prepared nonaqueous electrolyte includes a fluorinated cyclic ether, and the content of the fluorinated cyclic ether in the liquid component is greater than 30% by volume. In another embodiment of the present invention, the liquid component of the prepared nonaqueous electrolyte includes an ether having a donor number of 15 or less, and the content of the ether having a donor number of 15 or less in the liquid component is greater than 30% by volume. The manufacturing method may also include preparing a separator, and manufacturing an electrode assembly using the positive electrode, the negative electrode, and the separator. Housing the positive electrode, the negative electrode, and the nonaqueous electrolyte in a container may mean housing the electrode assembly and the nonaqueous electrolyte in the container.

[0180] Preparing a positive electrode may mean manufacturing a positive electrode. Manufacturing a positive electrode can be performed by the method described above. Preparing a negative electrode may mean manufacturing a negative electrode. Manufacturing a negative electrode can be performed by the method described above. Preparing a non-aqueous electrolyte may mean preparing a non-aqueous electrolyte. Specific and preferred forms of the prepared positive electrode, negative electrode, non-aqueous electrolyte, etc. are the same as the specific and preferred forms of the positive electrode, negative electrode, non-aqueous electrolyte, etc. provided in the non-aqueous electrolyte storage element according to one embodiment of the present invention described above. The positive electrode, negative electrode, separator, non-aqueous electrolyte, etc. may be prepared by purchasing, etc.

[0181] The electrode assembly (or the positive electrode and negative electrode) and the nonaqueous electrolyte can be housed in a container by a known method. When the nonaqueous electrolyte is a nonaqueous electrolyte solution, for example, the electrode assembly (or the positive electrode and negative electrode) is first housed in a container, and then the nonaqueous electrolyte solution is poured into the container through an inlet provided in the container. The inlet is sealed after the nonaqueous electrolyte solution is poured into the container. The method for manufacturing the nonaqueous electrolyte storage element may further include initially charging and discharging the assembled uncharged / discharged 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.

[0182] The nonaqueous electrolyte electricity storage element according to one embodiment of the present invention may be manufactured by other methods.

[0183] 2 includes a plurality of energy storage units 20. Each energy storage unit 20 includes a plurality of electrically connected nonaqueous electrolyte energy storage elements 1. The energy storage device 30 may include a bus bar (not shown) that electrically connects the plurality of nonaqueous electrolyte energy storage elements 1, a bus bar (not shown) that electrically connects the plurality of energy storage units 20, and the like. The energy storage unit 20 or the energy storage device 30 may include a state monitoring device (not shown) that monitors the state of one or more nonaqueous electrolyte energy storage elements 1.

[0184] <Other Embodiments> The nonaqueous electrolyte storage element and the method for manufacturing a nonaqueous electrolyte storage element of the present invention are not limited to the above-described embodiments, and various modifications may be made without departing from the spirit of the present invention. For example, the configuration of one embodiment can be added to the configuration of another embodiment, or part of the configuration of one embodiment can be replaced with the configuration of another embodiment or well-known technology. Furthermore, part of the configuration of one embodiment can be deleted. Also, well-known technology can be added to the configuration of one embodiment.

[0185] In the above embodiment, the nonaqueous electrolyte storage element is used as a chargeable and dischargeable nonaqueous electrolyte secondary battery, but the nonaqueous electrolyte storage element may be of any type, shape, size, capacity, etc. The present invention can also be applied to various secondary batteries, electric double layer capacitors, lithium ion capacitors, and other capacitors.

[0186] In the above embodiment, the electrode assembly is described in which a separator is interposed between the positive electrode and the negative electrode. However, the electrode assembly may not include a separator. For example, the positive electrode and the negative electrode may be in direct contact with each other, with a non-conductive layer formed on the active material layer of the positive electrode or the negative electrode. In this way, the positive electrode and the negative electrode may further include layers other than the substrate, the intermediate layer, and the active material layer. Furthermore, the positive electrode and the negative electrode may not have a layer structure.

[0187] 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.

[0188] The components used in preparing the non-aqueous electrolytes of the examples and comparative examples are listed below. The donor numbers determined by the above-mentioned methods for the ionic liquid and fluorinated ether are also shown. (Electrolyte salt) LiFSI: lithium bis(fluorosulfonyl)imide (Liquid component: ionic liquid) Py13FSI: 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide (donor number 13.0) (Liquid component: 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) FEC: fluoroethylene carbonate DMC: dimethyl carbonate DMSF: dimethylamidosulfuric fluoride TFEA: 2,2,2-trifluoroethyl acetate

[0189] [Example 1] (Fabrication of Positive Electrode) A positive electrode mixture paste containing water as a dispersion medium, sulfur-modified polyacrylonitrile ("SPAN" manufactured by ADEKA) as an organic sulfur-based compound, acetylene black and carbon nanotubes as conductive agents, carboxymethyl cellulose as a dispersant, polyacrylic acid as a thickener, and styrene-butadiene rubber as a binder, was applied to an aluminum positive electrode substrate and dried. Through the above process, a positive electrode was obtained in which a positive electrode active material layer was laminated on the positive electrode substrate.

[0190] (Preparation of Negative Electrode) A pure metallic lithium foil (average thickness: 600 μm) was prepared as a negative electrode.

[0191] (Preparation of Non-Aqueous Electrolyte) A liquid component obtained by mixing Py13FSI, TFTHF, and TFEME in a volume ratio of 10:70:20 was mixed with LiFSI, an electrolyte salt, at a molar concentration of 1.5 mol / kg to prepare a non-aqueous electrolyte.

[0192] (Assembly of non-aqueous electrolyte storage element) A separator was prepared, which was a polyethylene microporous membrane with composite layers of inorganic particles and aramid laminated on both sides, and had such high wettability that the non-aqueous electrolyte could penetrate into the pores. The non-aqueous electrolyte storage element of Example 1 was obtained using the above positive electrode, negative electrode, separator, and non-aqueous electrolyte.

[0193] [Examples 2 to 4, Comparative Examples 1 to 5] Non-aqueous electrolyte storage elements of Examples 2 to 4 and Comparative Examples 1 to 5 were obtained in the same manner as in Example 1, except that the compositions of the non-aqueous electrolytes were as shown in Table 1.

[0194] Comparative Example 6 A nonaqueous electrolyte storage element of Comparative Example 6 was obtained in the same manner as in Example 1, except that the composition of the nonaqueous electrolyte was as shown in Table 2.

[0195] Comparative Example 7: Elemental sulfur and porous carbon were mixed in a mass ratio of 70:30. This mixture was placed in a sealed electric furnace. After argon flow for 1 hour, the mixture was heated to 150°C at a heating rate of 5°C / min and held for 5 hours. It was then allowed to cool to 80°C, the temperature at which elemental sulfur solidifies. The mixture was then heated again to 300°C at a heating rate of 5°C / min and held for 2 hours, producing a composite (sulfur-carbon composite: SC). A nonaqueous electrolyte storage element of Comparative Example 7 was obtained in the same manner as in Example 1, except that the composite (SC) was used instead of sulfur-modified polyacrylonitrile (SPAN) as the positive electrode active material.

[0196] Comparative Example 8 A nonaqueous electrolyte storage element of Comparative Example 8 was obtained in the same manner as in Comparative Example 7, except that the composition of the nonaqueous electrolyte was as shown in Table 2.

[0197] [Evaluation] (Initial Charge / Discharge) The nonaqueous electrolyte storage elements of the Examples and Comparative Examples were subjected to the following initial charge / discharge cycles in a constant temperature bath at 30°C. First, as discharge (1), constant current discharge was performed under conditions of a discharge current of 0.1 C and a discharge cut-off voltage of 1.0 V. Then, as charge (1), constant current charging was performed under conditions of a charge current of 0.1 C and a charge cut-off voltage of 3.0 V, followed by constant voltage charging at 3.0 V. The charge termination condition was the point when the current decayed to 0.05 C. Next, as discharge (2), constant current discharge was performed under conditions of a discharge current of 0.1 C and a discharge cut-off voltage of 1.0 V. Nine cycles of the above charge (1) and discharge (2) were performed. Note that a 10-minute pause was provided after each discharge and charge.

[0198] (Initial Capacity Confirmation Test) The following initial capacity confirmation test was performed on each nonaqueous electrolyte storage element that had undergone initial charging and discharging in a constant temperature bath at 30°C. Constant current charging was performed under conditions of a charging current of 0.1 C and a charge cut-off voltage of 3.0 V, followed by constant voltage charging at 3.0 V. The charge was terminated when the current decayed to 0.05 C. After a 10-minute pause, constant current discharge was performed under conditions of a discharge current of 0.1 C and a discharge cut-off voltage of 1.0 V. The quantity of electricity discharged at this time was taken as the initial discharge capacity. The results are shown in Tables 1 and 2. The initial discharge capacity was calculated by dividing the value by the mass of sulfur element contained in the positive electrode.

[0199] (Charge-Discharge Cycle Test) Next, the following charge-discharge cycle test was performed on each nonaqueous electrolyte storage element in a thermostatic chamber at 30°C. Constant-current charging was performed under conditions of a charging current of 0.1 C and a charge cut-off voltage of 3.0 V, followed by constant-voltage charging at 3.0 V. The charge was terminated when the current decayed to 0.05 C. Subsequently, constant-current discharging was performed under conditions of a discharge current of 0.3 C and a discharge cut-off voltage of 1.0 V. A 10-minute pause was provided after each charge and discharge. For each of the nonaqueous electrolyte storage elements of the Examples and Comparative Examples listed in Table 1, the above charge and discharge cycles were performed 100 times. The capacity retention rate (after 100 cycles) was calculated as the percentage of the discharge capacity at the 100th cycle relative to the discharge capacity at the first cycle. The results are shown in Table 1. Furthermore, for each of the nonaqueous electrolyte storage elements of the Examples and Comparative Examples listed in Table 2, the above charge and discharge cycles were performed 50 times. The capacity retention rate (after 50 cycles) was calculated as a percentage of the discharge capacity at the 50th cycle relative to the discharge capacity at the 1st cycle. The results are shown in Table 2.

[0200]

[0201]

[0202] As shown in Table 1, each of the nonaqueous electrolyte storage elements of Examples 1 to 4, which contained more than 30% by volume of TFTHF, a fluorinated cyclic ether with a donor number of 15 or less, in the liquid component, had high initial discharge capacity and high capacity retention (after 100 cycles). Furthermore, as can be seen from a comparison between Comparative Examples 7 and 8 in Table 2, when the positive electrode active material was a sulfur-carbon composite (SC), the capacity retention (after 50 cycles) decreased when TFTHF, a fluorinated cyclic ether with a donor number of 15 or less, was used in the nonaqueous electrolyte. This is thought to be due to the fact that polysulfides are easily eluted from the positive electrode into the nonaqueous electrolyte when the positive electrode active material was a sulfur-carbon composite (SC). That is, when carbonate is used for the non-aqueous electrolyte as in Comparative Example 8, the coating formed on the positive electrode surface by the carbonate can suppress the elution of polysulfides from the positive electrode into the non-aqueous electrolyte. However, when ether is used for the non-aqueous electrolyte as in Comparative Example 7, no coating is formed on the positive electrode surface, and polysulfides are likely to elute from the positive electrode into the non-aqueous electrolyte. The non-aqueous electrolyte storage element of Comparative Example 8 also had a small initial discharge capacity, which is thought to be due to an increase in resistance caused by the coating formed on the positive electrode surface. Furthermore, as can be seen from the comparison between Example 1 and Comparative Example 6 in Table 2, when the positive electrode active material was sulfur-modified polyacrylonitrile (SPAN), which is an organic sulfur-based compound, and TFTHF, which is a fluorinated cyclic ether and an ether with a donor number of 15 or less, was used for the non-aqueous electrolyte, both the initial discharge capacity and the capacity retention rate (after 50 cycles) were improved. This is thought to be because, when the positive electrode active material is an organic sulfur-based compound and a specific ether is used for the non-aqueous electrolyte, the elution of polysulfides from the positive electrode into the non-aqueous electrolyte is suppressed even if a coating is not substantially formed on the positive electrode surface. That is, in Comparative Example 6, the formation of a carbonate-derived coating on the positive electrode surface increases the resistance, and the initial discharge capacity and capacity retention rate (after 50 cycles) are thought to be lower than those of Example 1.

[0203] The present invention can be applied to nonaqueous electrolyte storage elements used as power sources for electronic devices such as personal computers and communication terminals, automobiles, industrial equipment, and the like.

[0204] REFERENCE SIGNS LIST 1 nonaqueous electrolyte energy storage element 2 electrode body 3 container 4 positive electrode lead 5 positive electrode external terminal 6 negative electrode lead 7 negative electrode external terminal 20 energy storage unit 30 energy storage device

Claims

1. A non-aqueous electrolyte storage element comprising: a positive electrode containing an organic sulfur-based compound; and a non-aqueous electrolyte containing an electrolyte salt and a liquid component, wherein the liquid component contains a fluorinated cyclic ether, and the content of the fluorinated cyclic ether in the liquid component is greater than 30% by volume.

2. A non-aqueous electrolyte storage element comprising: a positive electrode containing an organic sulfur-based compound; and a non-aqueous electrolyte containing an electrolyte salt and a liquid component, wherein the liquid component contains an ether having a donor number of 15 or less, and the content of the ether having a donor number of 15 or less in the liquid component exceeds 30% by volume.

3. The nonaqueous electrolyte storage element according to claim 1 or 2, wherein the liquid component further contains at least one of a chain ether and an ionic liquid.

4. The nonaqueous electrolyte storage element according to claim 1 or 2, wherein the total content of the ether and the optional ionic liquid in the liquid component is 90% by volume or more.

5. The nonaqueous electrolyte storage element according to claim 1, wherein the fluorinated cyclic ether is represented by the following formula (1): (In formula (1), R １ are each independently a hydrogen atom, a fluorine atom, an alkyl group having 1 to 4 carbon atoms, or a fluorinated alkyl group having 1 to 4 carbon atoms. １ At least one of the groups is a fluorine atom or a fluorinated alkyl group having 1 to 4 carbon atoms. n1 is an integer of 2 to 5.

6. The nonaqueous electrolyte storage element according to claim 3, wherein the liquid component contains the chain ether, and the chain ether is represented by the following formula (2): (In formula (2), R ２ and R ３ are each independently an alkyl group having 1 to 3 carbon atoms or a fluorinated alkyl group having 1 to 3 carbon atoms. ４ is an alkanediyl group having 1 to 3 carbon atoms; and n2 is 0 or 1.

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

8. The nonaqueous electrolyte storage element according to claim 1 or 2, wherein the content of carbonate in the liquid component is 10% by volume or less.

9. The nonaqueous electrolyte storage element according to claim 1 or 2, wherein the organic sulfur compound is sulfur-modified polyacrylonitrile.

10. The nonaqueous electrolyte storage element according to claim 1 or 2, wherein the electrolyte salt is an imide salt.

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

12. A method for manufacturing a non-aqueous electrolyte storage element, comprising: preparing a positive electrode containing an organic sulfur-based compound; and preparing a non-aqueous electrolyte containing an electrolyte salt and a liquid component, wherein the liquid component contains a fluorinated cyclic ether, and the content of the fluorinated cyclic ether in the liquid component is more than 30% by volume.

13. A method for manufacturing a non-aqueous electrolyte storage element, comprising: preparing a positive electrode containing an organic sulfur-based compound; and preparing a non-aqueous electrolyte containing an electrolyte salt and a liquid component, wherein the liquid component contains an ether having a donor number of 15 or less, and the content of the ether having a donor number of 15 or less in the liquid component exceeds 30% by volume.

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