Nonaqueous electrolyte power storage element, nonaqueous electrolyte, and method for producing nonaqueous electrolyte power storage element

Abstract

A nonaqueous electrolyte power storage element according to an aspect of the present invention comprises: a positive electrode containing a lithium transition metal composite oxide; a negative electrode containing metallic lithium at least in a charged state; and a nonaqueous electrolyte containing an electrolyte salt and a fluorinated solvent, wherein the nonaqueous electrolyte contains or does not contain an ionic liquid, and the fluorinated solvent is at least one selected from the group consisting of fluorinated cyclic ethers and fluorinated chain diethers.

Description

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

[0001] The present invention relates to a nonaqueous electrolyte storage element, a nonaqueous electrolyte, and a method for producing a nonaqueous electrolyte 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] Metallic lithium is known as a negative electrode active material having a high energy density and used in nonaqueous electrolyte energy storage elements (see Patent Document 1). In recent years, nonaqueous electrolyte energy storage elements using an ionic liquid as the nonaqueous electrolyte have also been studied (see Patent Document 2).

[0004] JP 2016-100065 A JP 2001-319688 A

[0005] Ionic liquids have the advantage of being highly resistant to reduction and therefore highly stable against negative electrodes that use metallic lithium, etc. However, nonaqueous electrolyte storage elements that use metallic lithium in the negative electrode and an ionic liquid in the nonaqueous electrolyte do not have a sufficiently high capacity retention rate after charge-discharge cycles.

[0006] An object of the present invention is to provide a nonaqueous electrolyte storage element that uses metallic lithium in the negative electrode and has a high capacity retention rate after charge-discharge cycling, a method for manufacturing such a nonaqueous electrolyte storage element, and a nonaqueous electrolyte that can increase the capacity retention rate of a nonaqueous electrolyte storage element after charge-discharge cycling.

[0007] A nonaqueous electrolyte storage element according to one aspect of the present invention comprises a positive electrode containing a lithium transition metal composite oxide, a negative electrode containing metallic lithium at least in a charged state, and a nonaqueous electrolyte containing an electrolyte salt and a fluorinated solvent, wherein the nonaqueous electrolyte may or may not contain an ionic liquid, and the fluorinated solvent is at least one selected from the group consisting of fluorinated cyclic ethers and fluorinated chain diethers.

[0008] A non-aqueous electrolyte according to another aspect of the present invention includes an electrolyte salt, a fluorinated chain diether, and an ionic liquid.

[0009] A method for producing a nonaqueous electrolyte storage element according to another aspect of the present invention includes preparing a positive electrode containing a lithium transition metal composite oxide, preparing a negative electrode containing metallic lithium at least in a charged state, and preparing a nonaqueous electrolyte containing an electrolyte salt and a fluorinated solvent, wherein the nonaqueous electrolyte may or may not contain an ionic liquid, and the fluorinated solvent is at least one selected from the group consisting of fluorinated cyclic ethers and fluorinated chain diethers.

[0010] According to any one aspect of the present invention, it is possible to provide a nonaqueous electrolyte storage element that uses metallic lithium in the negative electrode and has a high capacity retention rate after charge-discharge cycling, a method for manufacturing such a nonaqueous electrolyte storage element, and a nonaqueous electrolyte that can increase the capacity retention rate of a nonaqueous electrolyte storage element after charge-discharge cycling.

[0011] Fig. 1 is a perspective view showing a nonaqueous electrolyte energy storage element according to one embodiment of the present invention. Fig. 2 is a schematic diagram showing an energy storage device including a plurality of nonaqueous electrolyte energy storage elements according to one embodiment of the present invention. Fig. 3 shows charge / discharge curves for the initial discharge and the charge / discharge after the initial discharge of the nonaqueous electrolyte energy storage element of Comparative Example 2.

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

[0013] [1] A nonaqueous electrolyte storage element according to one aspect of the present invention comprises a positive electrode containing a lithium transition metal composite oxide, a negative electrode containing metallic lithium at least in a charged state, and a nonaqueous electrolyte containing an electrolyte salt and a fluorinated solvent, wherein the nonaqueous electrolyte may or may not contain an ionic liquid, and the fluorinated solvent is at least one selected from the group consisting of fluorinated cyclic ethers and fluorinated chain diethers.

[0014] The nonaqueous electrolyte storage element described in [1] above is a nonaqueous electrolyte storage element using metallic lithium in the negative electrode, and exhibits a high capacity retention rate after charge / discharge cycling. While the reason for this is unclear, the following is presumed. For example, a nonaqueous electrolyte composed only of an ionic liquid and an electrolyte salt has high viscosity and low lithium ion diffusibility. Therefore, in a nonaqueous electrolyte storage element using such a nonaqueous electrolyte, the capacity may tend to decrease with repeated charge / discharge cycles. In contrast, fluorinated cyclic ethers and fluorinated chain diethers not only have sufficient reduction resistance but also have lower viscosity than ionic liquids. Therefore, by using a nonaqueous electrolyte containing at least one selected from the group consisting of fluorinated cyclic ethers and fluorinated chain diethers, the capacity decrease with repeated charge / discharge cycles can be suppressed. Furthermore, in the case of a nonaqueous electrolyte storage element using a sulfur-based active material as the positive electrode active material, for example, polysulfides formed on the positive electrode may dissolve in a specific fluorinated solvent, preventing sufficient charge / discharge. However, in the nonaqueous electrolyte storage element described in [1] above, which uses a lithium transition metal composite oxide as the positive electrode active material, such problems due to dissolution of polysulfides do not usually occur. For this reason, it is presumed that the nonaqueous electrolyte storage element described in [1] above, which uses metallic lithium in the negative electrode, has a high capacity retention rate after charge-discharge cycling.

[0015] The content of each component contained in the non-aqueous electrolyte is a value measured at 20°C under 1 atmosphere or a value converted to a value at 20°C under 1 atmosphere. 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), or the like. １The content of ionic compounds such as electrolyte salts and ionic liquids contained in the non-aqueous electrolyte is determined by IC. However, the content of cations in 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, １ Identification 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 ２The 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.

[0016] The type and content of nonionic compounds such as fluorinated solvents 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.

[0017] [2] In the nonaqueous electrolyte storage element according to [1] above, the nonaqueous electrolyte may contain the ionic liquid.

[0018] The nonaqueous electrolyte storage element described in [2] above has further advantages such as a high flash point and low volatility of the nonaqueous electrolyte due to the nonaqueous electrolyte containing an ionic liquid.

[0019] [3] In the nonaqueous electrolyte storage element according to [1] or [2] above, the total content of the fluorinated solvent and the ionic liquid relative to all components other than the electrolyte salt in the nonaqueous electrolyte may be 90% by volume or more.

[0020] The nonaqueous electrolyte storage element described in [3] above has a particularly sufficient total content of the fluorinated solvent and the ionic liquid in the nonaqueous electrolyte, and therefore has a higher capacity retention rate after charge-discharge cycles.

[0021] [4] In the nonaqueous electrolyte storage element according to any one of [1] to [3] above, the content of the fluorinated solvent relative to the total of the fluorinated solvent and the ionic liquid may be 25% by volume or more and 100% by volume or less.

[0022] The nonaqueous electrolyte storage element described in [4] above has a higher capacity retention rate after charge-discharge cycles because the nonaqueous electrolyte contains a particularly sufficient amount of a fluorinated solvent.

[0023] [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, and n is an integer of 2 to 7.

[0024] [6] In the nonaqueous electrolyte storage element according to any one of [1] to [5] above, the fluorinated chain diether may be represented by the following formula (2): (In formula (2), R ２ is a fluorinated alkyl group having 1 to 3 carbon atoms. ３ is 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.

[0025] [7] In the nonaqueous electrolyte storage element according to any one of [1] to [6] above, the ionic liquid may contain at least one cation selected from the group consisting of quaternary ammonium cations, imidazolium-based cations, pyrrolidinium-based cations, piperidinium-based cations, quaternary phosphonium cations, and sulfonium cations.

[0026] [8] In the nonaqueous electrolyte storage element according to any one of [1] to [7] above, the ionic liquid may have an imide anion.

[0027] [9] In the nonaqueous electrolyte storage element according to any one of [1] to [8] above, the electrolyte salt may be an imide salt.

[0028]

[10] In the nonaqueous electrolyte storage element according to any one of [1] to [9] above, the molar concentration of the electrolyte salt in the nonaqueous electrolyte may be 1.0 mol / kg or more and 4.0 mol / kg or less.

[0029] The term "molar concentration" refers to the amount of substance (mol) of the electrolyte salt based on the total mass (kg) of the nonaqueous solvent containing the fluorinated solvent and the ionic liquid.

[0030]

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

[10] above, the viscosity of the nonaqueous electrolyte at 25° C. may be 150 mPa·s or less.

[0031] The viscosity of the non-aqueous electrolyte is a value measured using a falling ball viscometer "LOVIS2000ME" manufactured by Anton Paar as a measuring device.

[0032] The nonaqueous electrolyte storage elements described in the above [5] to

[11] are all preferred embodiments of the present invention, and have a higher capacity retention rate after charge-discharge cycles.

[0033]

[12] A nonaqueous electrolyte according to another aspect of the present invention includes an electrolyte salt, a fluorinated chain diether, and an ionic liquid.

[0034] The non-aqueous electrolyte described in the above

[12] can increase the capacity retention rate of a non-aqueous electrolyte storage element after charge-discharge cycles.

[0035]

[13] In the nonaqueous electrolyte according to the above

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

[0036]

[14] In the nonaqueous electrolyte according to the above

[12] or

[13] , the ionic liquid may contain 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.

[0037]

[15] In the non-aqueous electrolyte according to any one of

[12] to

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

[0038]

[16] The nonaqueous electrolyte according to any one of

[12] to

[15] above may have a viscosity at 25°C of 150 mPa·s or less.

[0039]

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

[12] to

[16] above, the fluorinated chain diether may be represented by the following formula (2): (In formula (2), R ２ is a fluorinated alkyl group having 1 to 3 carbon atoms. ３ is 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.

[0040]

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

[12] to

[17] above, the fluorinated chain diether may comprise at least one selected from the group consisting of 2-(2,2,2-trifluoroethoxy)ethyl methyl ether, ethyl-2-(2,2,2-trifluoroethoxy)ethyl ether, 2-(2,2-difluoroethoxy)ethyl methyl ether, ethyl-2-(2,2-difluoroethoxy)ethyl ether, 2-(2-fluoroethoxy)ethyl methyl ether, and ethyl-2-(2-fluoroethoxy)ethyl ether.

[0041] Each of the nonaqueous electrolytes described in the above

[13] to

[18] is a preferred embodiment of the present invention, and can further increase the capacity retention rate of a nonaqueous electrolyte storage element after charge-discharge cycling.

[0042]

[19] A method for producing a nonaqueous electrolyte storage element according to another aspect of the present invention includes: preparing a positive electrode containing a lithium transition metal composite oxide; preparing a negative electrode containing metallic lithium at least in a charged state; and preparing a nonaqueous electrolyte containing an electrolyte salt and a fluorinated solvent, wherein the nonaqueous electrolyte may or may not contain an ionic liquid, and the fluorinated solvent is at least one selected from the group consisting of fluorinated cyclic ethers and fluorinated chain diethers.

[0043] According to the method for producing a nonaqueous electrolyte storage element described in

[19] above, it is possible to produce a nonaqueous electrolyte storage element that uses metallic lithium in the negative electrode and has a high capacity retention rate after charge-discharge cycles.

[0044] A nonaqueous electrolyte electricity storage element, a nonaqueous electrolyte, a method for manufacturing a nonaqueous electrolyte electricity storage element, an electricity storage device, and other embodiments according to one embodiment of the present invention will be described in detail below.

[0045] <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.

[0046] 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.

[0047] 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.

[0048] 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. In other words, a lower limit of A means that the range is equal to or greater than A. Similarly, an upper limit of B means that the range is equal to or less than B. Unless otherwise specified, the lower limit and upper limit of each numerical range are values ​​in the discharged state of the nonaqueous electrolyte storage element.

[0049] (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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] The positive electrode active material layer contains a positive electrode active material. The positive electrode active material layer contains optional components such as a conductive agent, a binder, a thickener, and a filler as needed. The positive electrode active material layer may be formed from a positive electrode mixture containing the positive electrode active material and other optional components. The positive electrode active material layer may be provided on only one side or on both sides of a positive electrode substrate having a shape such as a sheet.

[0057] The positive electrode active material is a lithium transition metal composite oxide. That is, the positive electrode or the positive electrode active material layer contains the lithium transition metal composite oxide. One or more types of the positive electrode active material can be used.

[0058] Examples of the transition metal element contained in the lithium transition metal composite oxide include nickel, cobalt, and manganese. The lithium transition metal composite oxide preferably contains one or more elements selected from the group consisting of nickel, cobalt, and manganese, and more preferably contains nickel, cobalt, and manganese. The lithium transition metal composite oxide may contain a typical metal element such as aluminum. Examples of the lithium transition metal composite oxide include α-NaFeO ２ lithium transition metal composite oxides having a crystalline structure, lithium transition metal composite oxides having a spinel crystalline structure, etc., and α-NaFeO ２ A lithium transition metal composite oxide having a type crystalline structure is preferred.

[0059] α-NaFeO ２ As the lithium transition metal composite oxide having a crystalline structure, Li α Ma β O ２ X γ (Ma is one or more elements selected from the group consisting of metal elements and metalloid elements excluding lithium, and includes at least one transition metal element. X is an element other than lithium, Ma, and oxygen. 0.9≦α≦1.5, 0≦γ≦1. β is a value determined depending on the valences of α, γ, Ma, and X, and is 0.5≦β≦1.5.) Ma preferably includes one or more elements selected from Ni, Co, and Mn, and more preferably includes Ni, Co, and Mn. The total content of Ni, Co, and Mn relative to Ma ((Ni+Co+Mn) / Ma) is preferably 90 mol% or more, more preferably 98 mol% or more. α may be 0.95 or more and 1.4 or less, 0.98 or more and 1.2 or less, or 1.0 or more and 1.1 or less.

[0060] Examples of lithium transition metal composite oxides having a spinel crystal structure include Li α Mb β O ４ X γ(Mb is one or more elements selected from the group consisting of metal elements and metalloid elements excluding lithium, and contains at least one transition metal element. X is an element other than lithium, Mb, and oxygen. 0.90≦α≦1.33, 0≦γ≦1. β is a value determined depending on the valences of α, γ, Mb, and X, and is 1.5≦β≦2.5.) Mb preferably contains Mn. The content of Mn relative to Mb (Mn / Mb) is preferably 50 mol % or more, and more preferably 80 mol % or more.

[0061] The lithium transition metal composite oxide is usually in the form of particles. The average particle size of the lithium transition metal composite oxide is preferably, for example, 0.1 μm or more and 20 μm or less. By setting the average particle size of the lithium transition metal composite oxide to the above-mentioned lower limit or more, the lithium transition metal composite oxide is easily produced or handled. By setting the average particle size of the lithium transition metal composite oxide to the above-mentioned upper limit or less, the electronic conductivity of the positive electrode active material layer is improved. The term "average particle size" refers to the value (D50) at which the volume-based cumulative distribution calculated in accordance with JIS-Z-8819-2 (2001) is 50% based on the particle size distribution measured by a laser diffraction / scattering method in accordance with JIS-Z-8825 (2013) for a diluted solution obtained by diluting particles with a solvent. For example, known methods using a pulverizer, a classifier, or the like can be used to obtain particles of the lithium transition metal composite oxide and the negative electrode active material described below with a predetermined particle size.

[0062] The content of the lithium transition metal composite oxide in the positive electrode active material layer is preferably 50% by mass or more and 99% by mass or less, more preferably 70% by mass or more and 98% by mass or less, and may be 80% by mass or more and 95% by mass or less. The lower limit of the content of the lithium transition metal composite oxide in the positive electrode active material layer may be 85% by mass, 90% by mass, or 93% by mass. By setting the content of the lithium transition metal composite oxide in the above range, both high energy density and manufacturability of the positive electrode active material layer can be achieved.

[0063] The positive electrode active material layer may contain a positive electrode active material other than the lithium transition metal composite oxide. Examples of the other positive electrode active material include a polyanion compound, a chalcogen compound, a sulfur-based active material, and lithium oxide. However, the content of the lithium transition metal composite oxide relative to all the positive electrode active materials contained in the positive electrode active material layer is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 99% by mass or more. The positive electrode active material layer may contain only the lithium transition metal composite oxide as the positive electrode active material.

[0064] The content of the positive electrode active material in the positive electrode active material layer is preferably 50% by mass or more and 99% by mass or less, more preferably 70% by mass or more and 98% by mass or less, and may be 80% by mass or more and 95% by mass or less. The lower limit of the content of the positive electrode active material in the positive electrode active material layer may be 85% by mass, 90% by mass, or 93% by mass. By setting the content of the positive electrode active material within the above range, both high energy density and manufacturability of the positive electrode active material layer can be achieved.

[0065] 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 kinds. The conductive agent may be a composite of these materials. For example, a composite material of carbon black and CNT may be used.

[0066] The content of the conductive agent in the positive electrode active material layer is preferably 0.1% by mass to 10% by mass, more preferably 1% by mass to 9% by mass, and even more preferably 3% by mass to 8% by mass. The upper limit of the content of the conductive agent may be 6%, 5%, or 4% 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.

[0067] Examples of the binder include a water-based binder and an organic solvent-based binder.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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 hold the positive electrode active material, etc. The technology disclosed herein can also be implemented in an embodiment in which the positive electrode active material layer does not contain a binder.

[0072] Examples of thickeners include polysaccharide polymers such as carboxymethyl cellulose and methyl cellulose. When the thickener 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 thickener may function as a binder. One or more types of thickeners may be used. When the positive electrode active material layer contains a thickener, the content of the thickener in the positive electrode active material layer is preferably 0.1% by mass or more and 8% by mass or less, more preferably 5% by mass or less, and even more preferably 2% by mass or less. The technology disclosed herein may also be implemented in an embodiment in which the positive electrode active material layer does not contain a thickener.

[0073] The filler is not particularly limited. The filler may be a component other than the positive electrode active material, conductive agent, binder, 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.

[0074] The positive electrode active material layer may further contain other components in addition to the positive electrode active material, conductive agent, binder, 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 the unintentionally contained impurities in the positive electrode active material layer may be 10% by mass, 5%, 2%, 1%, 0.1%, or 0.01% by mass.

[0075] 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, 5 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 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, or 40 μm. The mass per unit area of ​​the positive electrode active material layer is, for example, 4 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 6 mg / cm or less. ２ , 8 mg / cm ２ , 10 mg / cm ２ , 12 mg / cm ２ or 15 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 / cm ２ , 15 mg / cm ２ , 12 mg / cm ２ or 10 mg / cm ２ may be.

[0076] The porosity of the positive electrode active material layer may be, for example, 20% or more and 50% or less. The lower limit of the porosity of the positive electrode active material layer may be 25%, 30%, or 35%. The upper limit of the porosity of the positive electrode active material layer may be 45%, 40%, 35%, or 30%. The "porosity (%)" of the positive electrode active material layer and the negative electrode active material layer described later is calculated by dividing the apparent volume (volume including voids) of the positive (negative) electrode active material layer by V. １ The sum of the actual volumes of the materials constituting the positive (negative) electrode active material layer is V ２ In this case, (1-V ２ / V １ The sum of the actual volumes of the materials constituting the positive (negative) electrode active material layer, V ２ can be calculated from the content of each material in the positive (negative) electrode active material layer and the true density of each material.

[0077] (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 a positive electrode active material, other optional components, and a dispersion medium. After drying, the positive electrode active material layer may be pressed, etc.

[0078] (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.

[0079] The thickness of the negative electrode is appropriately set depending on the application of the nonaqueous electrolyte storage element, etc. The average thickness of the negative electrode may be, for example, 30 μm or more and 1,000 μm or less. The lower limit of the average thickness of the negative electrode may be 50 μm, 100 μm, or 200 μm. The upper limit of the average thickness of the negative electrode may be 500 μm, 400 μm, 300 μm, 200 μm, or 100 μm. The average thickness of the negative electrode is the average thickness of a portion where the negative electrode active material layer is laminated on the negative electrode substrate directly or via an intermediate layer. When 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.

[0080] The negative electrode substrate is conductive. Examples of materials for the negative electrode substrate include metals such as copper, nickel, iron, and alloys thereof (e.g., stainless steel), and carbon materials. Among these, nickel or a nickel alloy is preferred.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] The negative electrode active material layer contains a negative electrode active material. The negative electrode active material layer contains optional components such as a conductive agent, a binder, a thickener, and a filler as needed. The optional components such as the conductive agent, the binder, the thickener, and the filler can be selected from the materials exemplified for the positive electrode above. The negative electrode active material layer 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.

[0085] Metallic lithium is used as the negative electrode active material. In other words, the negative electrode or the negative electrode active material layer contains metallic lithium at least in a charged state. It is 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.

[0086] In the case of a nonaqueous electrolyte storage element configured so that metallic lithium is deposited on at least a portion of the negative electrode surface during charging and substantially all of the metallic lithium on the negative electrode surface is eluted into the nonaqueous electrolyte during discharging, the negative electrode may not have a negative electrode active material layer in a discharged state.

[0087] 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.

[0088] 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%.

[0089] As the negative electrode active material, other negative electrode active materials may be used together with metallic lithium. Examples of other negative electrode active materials include conventionally known materials. However, it is preferable to use substantially only metallic lithium as the negative electrode active material. The lower limit of the content of lithium element relative to all negative electrode active materials contained 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 content of lithium element relative to all negative electrode active materials contained in the negative electrode active material layer may be 100 mass%.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] The filler in the negative electrode active material layer may be a component other than the negative electrode active material, conductive agent, binder, 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.

[0094] The negative electrode active material layer may further contain other components in addition to the negative electrode active material, conductive agent, binder, 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.

[0095] 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 in the form of a foil, or may be a layer made of metallic lithium foil (pure metallic lithium foil or lithium alloy foil).

[0096] 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, 5 μm or more and 2,000 μm or less. The lower limit of the average thickness of the negative electrode active material layer in a charged state may be 10 μm, 20 μm, 30 μm, 50 μm, 100 μm, 200 μm, 300 μm, 400 μm, or 600 μm. The upper limit of the average thickness of the negative electrode active material layer in a charged state may be 1,500 μm, 1,200 μm, 800 μm, or 600 μm.

[0097] The average thickness of the negative electrode active material layer in a discharged state may be, for example, 0 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 discharged state may be 5 μm, 10 μm, 20 μm, 30 μm, 50 μm, 100 μm, 200 μm, 300 μm, 400 μm, or 600 μm. The upper limit of the average thickness of the negative electrode active material layer in a discharged state may be 1,500 μm, 1,200 μm, 800 μm, or 600 μm.

[0098] (Method for manufacturing negative electrode) The negative electrode can be manufactured by a known method. The negative electrode can be manufactured, for example, by laminating a metallic lithium foil directly or via an intermediate layer on a negative electrode substrate, and pressing the laminate. Similarly to the method for manufacturing the positive electrode described above, the negative electrode can also be manufactured by applying a paste-like negative electrode mixture (negative electrode mixture paste) to the negative electrode substrate directly or via an intermediate layer, and drying the mixture to form a negative electrode active material layer.

[0099] In the case of a nonaqueous electrolyte storage element configured such that metallic lithium is deposited on at least a portion of the negative electrode surface during charge and substantially all of the metallic lithium on the negative electrode surface is eluted into the nonaqueous electrolyte during discharge, the negative electrode to be manufactured does not need to be provided with a negative electrode active material layer, i.e., the negative electrode to be manufactured may be a negative electrode having a surface region on which metallic lithium can be deposited during charge.

[0100] (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.

[0101] 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.

[0102] 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.

[0103] Examples of binders used in the inorganic layer include the same binders as those exemplified for the positive electrode active material layer.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] (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.

[0108] 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.

[0109] 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.

[0110] 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.

[0111] (Non-aqueous electrolyte) The non-aqueous electrolyte is a medium responsible for transporting charge-transporting ions (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.

[0112] The nonaqueous electrolyte contains an electrolyte salt and a fluorinated solvent. The nonaqueous electrolyte may or may not contain an ionic liquid. In the nonaqueous electrolyte, the electrolyte salt and the fluorinated solvent are essential components, and the ionic liquid is an optional component. That is, the nonaqueous electrolyte may or may not contain an ionic liquid. The nonaqueous electrolyte may be a nonaqueous electrolyte solution. In one embodiment of the present invention, the nonaqueous electrolyte storage element may be a nonaqueous electrolyte solution storage element.

[0113] The electrolyte salt refers to an ionic compound whose cation is a charge-transporting ion and which is solid at room temperature (20°C) under 1 atmosphere. Known electrolyte salts can be used as the electrolyte salt. Typically, lithium salts are used as the electrolyte salt. One or more types of electrolyte salts can be used.

[0114] 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(SO２ C ２ F ５ ) ３ － Anions other than imide anions such as the above can also be used.

[0115] The anion constituting the electrolyte salt is preferably an imide anion, and more preferably a bis(trifluoromethanesulfonyl)imide anion (TFSI － ) and bis(fluorosulfonyl)imide anion (FSI － ), and bis(fluorosulfonyl)imide anion (FSI － ) is more preferred. That is, the electrolyte salt is preferably an imide salt, more preferably at least one selected from the group consisting of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium bis(fluorosulfonyl)imide (LiFSI), and even more preferably lithium bis(fluorosulfonyl)imide (LiFSI). In addition, the anion constituting the electrolyte salt preferably has a fluorine atom. When the anion constituting the electrolyte salt is such an anion, the ionic conductivity of the non-aqueous electrolyte is increased, and the capacity retention rate of the non-aqueous electrolyte storage element after charge-discharge cycling can be further increased. One or more types of anions can be used as the anion constituting the electrolyte salt.

[0116] The molar mass concentration of the electrolyte salt in the non-aqueous electrolyte is preferably 1.0 mol / kg or more and 4.0 mol / kg or less. By having the molar mass concentration of the electrolyte salt within the above range, the ionic conductivity of the non-aqueous electrolyte can be optimized, and the capacity retention rate of the non-aqueous electrolyte storage element after charge-discharge cycling can be further increased. The lower limit of the molar mass concentration of the electrolyte salt in the non-aqueous electrolyte is more preferably 1.2 mol / kg, even more preferably 1.5 mol / kg, and may be 2.0 mol / kg or 2.5 mol / kg. Increasing the molar mass concentration of the electrolyte salt tends to increase the flash point of the non-aqueous electrolyte. The upper limit of the molar mass concentration of the electrolyte salt is more preferably 3.5 mol / kg, even more preferably 3.0 mol / kg, and may be 2.5 mol / kg, 2.0 mol / kg, or 1.5 mol / kg. Within the above range, by relatively lowering the molar mass concentration of the electrolyte salt, the capacity retention rate of the non-aqueous electrolyte storage element after charge-discharge cycling tends to be further increased.

[0117] The fluorinated solvent is at least one selected from the group consisting of fluorinated cyclic ethers and fluorinated chain diethers. The fluorinated solvent may be a fluorinated cyclic ether or a fluorinated chain diether.

[0118] The fluorinated solvent is preferably a fluorinated chain diether. Use of the fluorinated chain diether tends to further increase the capacity retention rate of the nonaqueous electrolyte storage element after charge-discharge cycling and also tends to increase the flash point of the nonaqueous electrolyte. One or more fluorinated solvents can be used.

[0119] The term "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. The saturated ether refers to an ether that does not have unsaturated bonds between carbon atoms (carbon-carbon double bonds and carbon-carbon triple bonds).

[0120] The lower limit of the number of 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.

[0121] 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. １At least one of the groups is a fluorine atom or a fluorinated alkyl group having 1 to 4 carbon atoms, and n is an integer of 2 to 7.

[0122] R in the above formula (1) １ When R is an alkyl group or a fluorinated alkyl group, the number of carbon atoms in the group is preferably 3 or less, and more preferably 2 or less. １ are each independently a hydrogen atom or a fluorine atom, and at least one is preferably a fluorine atom. n is preferably 4 or 5, and more preferably 4.

[0123] The fluorinated cyclic ether may be, for example, 3,3,4,4-tetrafluorotetrahydrofuran, 2,2,3,4,5,5-hexafluorotetrahydrofuran, 2,2,3,3,4,5,5-heptafluorotetrahydrofuran, 2,2,3,3,4,4,5-heptafluorotetrahydrofuran, octafluorooxolane, perfluoro-(2-butyltetrahydrofuran), perfluorotetrahydropyran, or perfluoropropyltetrahydropyran.

[0124] The fluorinated chain diether refers to an ether having a fluorine atom and two ether bonds but no ring structure. The fluorinated chain diether may be composed only of a carbon atom, a hydrogen atom, an oxygen atom, and a fluorine atom. The oxygen element contained in the fluorinated chain diether is preferably only the oxygen element constituting the ether bond. In other words, the fluorinated chain diether preferably does not have an oxygen-containing substituent such as a hydroxy group or a carboxy group. The fluorinated chain diether is preferably a saturated ether.

[0125] The lower limit of the number of carbon atoms in the fluorinated chain diether 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, more preferably 6, and even more preferably 5. The lower limit of the number of fluorine atoms in the fluorinated chain diether may be 1, preferably 2, and more preferably 3. The upper limit of the number of fluorine atoms is preferably 10, and may be 9, 8, 7, 6, 5, 4, or 3.

[0126] The fluorinated chain diether is preferably one represented by the following formula (2). (In formula (2), R ２ is a fluorinated alkyl group having 1 to 3 carbon atoms. ３ is 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.

[0127] R in the above formula (2) ２ R is preferably a fluorinated alkyl group having 1 or 2 carbon atoms, more preferably a fluorinated alkyl group having 2 carbon atoms. ３ As R, an alkyl group having 1 or 2 carbon atoms is preferred, and a methyl group is more preferred. 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 - is more preferable.

[0128] Examples of chain ethers include 2-(2,2,2-trifluoroethoxy)ethyl methyl ether, ethyl-2-(2,2,2-trifluoroethoxy)ethyl ether, 2-(2,2-difluoroethoxy)ethyl methyl ether, ethyl-2-(2,2-difluoroethoxy)ethyl ether, 2-(2-fluoroethoxy)ethyl methyl ether, and ethyl-2-(2-fluoroethoxy)ethyl ether.

[0129] The lower limit of the content of the fluorinated solvent relative to the total of the fluorinated solvent (fluorinated cyclic ether and fluorinated chain diether) and the ionic liquid is preferably 25% by volume, more preferably 30% by volume, and may be 40%, 50%, 60%, 70%, 80%, 90%, 95%, or 99% by volume. By setting the content of the fluorinated solvent at or above the lower limit, it is possible to further increase the capacity retention rate of the non-aqueous electrolyte storage element after charge / discharge cycling. The upper limit of the content of the fluorinated solvent relative to the total of the fluorinated solvent (fluorinated cyclic ether and fluorinated chain diether) and the ionic liquid may be 100% by volume, or may be 90%, 80%, 70%, 60%, 50%, 40%, or 30% by volume. By setting the content of the fluorinated solvent at or below the upper limit, it is possible to increase the flash point of the non-aqueous electrolyte, reduce its volatility, and the like.

[0130] The lower limit of the content of the fluorinated solvent (fluorinated cyclic ether and fluorinated chain diether) relative to all components other than the electrolyte salt in the non-aqueous electrolyte is preferably 25% by volume, more preferably 30% by volume, and may be 40%, 50%, 60%, 70%, 80%, 90%, 95%, or 99% by volume. By setting the content of the fluorinated solvent at or above the lower limit, it is possible to further increase the capacity retention rate of the non-aqueous electrolyte storage element after charge / discharge cycling. The upper limit of the content of the fluorinated solvent relative to all components other than the electrolyte salt in the non-aqueous electrolyte may be 100% by volume, or may be 90%, 80%, 70%, 60%, 50%, 40%, or 30% by volume. By setting the content of the fluorinated solvent at or below the upper limit, it is possible to increase the flash point and reduce the volatility of the non-aqueous electrolyte.

[0131] The non-aqueous electrolyte may further contain a non-aqueous solvent other than the above-mentioned fluorinated solvents (fluorinated cyclic ethers and fluorinated chain diethers). Examples of the other non-aqueous solvent include ethers other than fluorinated cyclic ethers and fluorinated chain diethers, carbonates, esters, amides, nitriles, etc. The non-aqueous solvent may be a non-ionic compound.

[0132] The lower limit of the content of the fluorinated solvent (fluorinated cyclic ether and fluorinated chain diether) relative to all nonaqueous solvents contained in the nonaqueous electrolyte is preferably 80% by volume, more preferably 90% by volume, even more preferably 95% by volume, and even more preferably 99% by volume. By using essentially at least one selected from the group consisting of fluorinated cyclic ethers and fluorinated chain diethers as the nonaqueous solvent, it is possible to further increase the capacity retention rate of the nonaqueous electrolyte storage element after charge-discharge cycling.

[0133] The lower limit of the content of the fluorinated solvent (fluorinated cyclic ether and fluorinated chain diether) relative to the total of all nonaqueous solvents and ionic liquid contained in the nonaqueous electrolyte is preferably 25% by volume, more preferably 30% by volume, and may be 40% by volume, 50% by volume, 60% by volume, 70% by volume, 80% by volume, 90% by volume, 95% by volume, or 99% by volume. By setting the content of the fluorinated solvent at or above the lower limit, it is possible to further increase the capacity retention rate of the nonaqueous electrolyte storage element after charge / discharge cycles. The upper limit of the content of the fluorinated solvent relative to the total of all nonaqueous solvents and ionic liquid contained in the nonaqueous electrolyte may be 100% by volume, or may be 90% by volume, 80% by volume, 70% by volume, 60% by volume, 50% by volume, 40% by volume, or 30% by volume. By setting the content of the fluorinated solvent at or below the upper limit, it is possible to increase the flash point of the nonaqueous electrolyte, reduce volatility, etc.

[0134] The lower limit of the content of all fluorinated solvents (the total of fluorinated cyclic ethers, fluorinated chain diethers, and other fluorinated solvents) relative to all nonaqueous solvents contained in the nonaqueous electrolyte is preferably 80% by volume, more preferably 90% by volume, even more preferably 95% by volume, and even more preferably 99% by volume. In this way, by using substantially only fluorinated solvents as the nonaqueous solvent, it is possible to further increase the capacity retention rate of the nonaqueous electrolyte storage element after charge-discharge cycling.

[0135] The non-aqueous electrolyte preferably contains an ionic liquid. By including an ionic liquid in the non-aqueous electrolyte, further effects such as a high flash point and reduced volatility of the non-aqueous electrolyte can be achieved. An ionic liquid refers to an ionic compound that is at least partially liquid at room temperature (20°C) under 1 atmosphere.

[0136] 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.

[0137] Examples of the quaternary ammonium cation include tetraalkylammonium cations such as trimethylethylammonium cation, trimethylpropylammonium cation, trimethylbutylammonium cation, trimethylhexylammonium cation, and tetrapentylammonium cation.

[0138] 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.

[0139] 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.

[0140] 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.

[0141] 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.

[0142] 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.

[0143] 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.

[0144] 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.

[0145] 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.

[0146] Examples of the sulfonium cation include a trimethylsulfonium cation, a triethylsulfonium cation, and a tributylsulfonium cation.

[0147] The cations constituting the ionic liquid are 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, even more preferably at least one selected from the group consisting of imidazolium cations and pyrrolidinium cations, and even more preferably pyrrolidinium cations. When the cations constituting the ionic liquid are such cations, the capacity retention rate of the nonaqueous electrolyte storage element after charge-discharge cycling can be further improved. One or more of these cations may be contained.

[0148] 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 preferable. 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 capacity retention rate after charge-discharge cycles of the nonaqueous electrolyte storage element. One or more of these anions may be contained.

[0149] 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 further increase the capacity retention rate of the nonaqueous electrolyte storage element after charge-discharge cycles.

[0150] In addition, it is preferable that the anions present in the non-aqueous electrolyte are substantially only imide anions, and the anions present in the non-aqueous electrolyte are substantially bis(trifluoromethanesulfonyl)imide anions (TFSI － ) and bis(fluorosulfonyl)imide anion (FSI － ) is more preferably at least one selected from the group consisting of. For example, the content of these anions relative to all anions in the non-aqueous electrolyte is preferably 90 mol % or more, more preferably 99 mol % or more, and even more preferably 99.9 mol % or more. By configuring the anions in the non-aqueous electrolyte in this way, the ionic conductivity of the non-aqueous electrolyte can be increased, and the capacity retention rate of the non-aqueous electrolyte storage element after charge-discharge cycles can be further increased.

[0151] The lower limit of the content of the ionic liquid relative to all components other than the electrolyte salt in the non-aqueous electrolyte may be 0% by volume, or may be 10%, 20%, 30%, 40%, 50%, 60%, or 70% by volume. By setting the content of the ionic liquid at or above the lower limit, it is possible to increase the flash point of the non-aqueous electrolyte, reduce volatility, etc. The upper limit of the content of the ionic liquid relative to all components other than the electrolyte salt in the non-aqueous electrolyte is preferably 75% by volume, more preferably 70% by volume, and may be 60%, 50%, 40%, 30%, 20%, 10%, 5%, or 1% by volume. By setting the content of the ionic liquid at or below the upper limit, it is possible to further increase the capacity retention rate of the non-aqueous electrolyte storage element after charge / discharge cycling.

[0152] The lower limit of the content of the ionic liquid relative to the total of all nonaqueous solvents and ionic liquid contained in the nonaqueous electrolyte may be 0% by volume, 10% by volume, 20% by volume, 30% by volume, 40% by volume, 50% by volume, 60% by volume, or 70% by volume. By setting the content of the ionic liquid at or above the lower limit, it is possible to increase the flash point of the nonaqueous electrolyte, reduce volatility, etc. The upper limit of the content of the ionic liquid relative to the total of all nonaqueous solvents and ionic liquid contained in the nonaqueous electrolyte is preferably 75% by volume, more preferably 70% by volume, and may be 60% by volume, 50% by volume, 40% by volume, 30% by volume, 20% by volume, 10% by volume, 5% by volume, or 1% by volume. By setting the content of the ionic liquid at or below the upper limit, it is possible to further increase the capacity retention rate of the nonaqueous electrolyte storage element after charge / discharge cycling.

[0153] The lower limit of the total content of the fluorinated solvent (fluorinated cyclic ether and fluorinated chain diether) and ionic liquid relative to all components other than the electrolyte salt in the nonaqueous electrolyte is preferably 90% by volume, more preferably 95% by volume, and may be 97%, 98%, or 99% by volume. Thus, by having the nonaqueous electrolyte primarily comprised of the electrolyte salt, the fluorinated solvent, and the optional ionic liquid, the capacity retention rate of the nonaqueous electrolyte storage element after charge-discharge cycling can be further increased. The upper limit of the total content may be 100% by volume.

[0154] The lower limit of the total content of the fluorinated solvent (fluorinated cyclic ether and fluorinated chain diether) and the ionic liquid relative to the total of all nonaqueous solvents and the ionic liquid contained in the nonaqueous electrolyte is preferably 90% by volume, more preferably 95% by volume, and may be 97%, 98%, or 99% by volume. The upper limit of the total content may be 100% by volume.

[0155] The non-aqueous electrolyte may contain other components in addition to the electrolyte salt, the non-aqueous solvent, and the ionic liquid. Examples of other components include additives.

[0156] 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.

[0157] The upper limit of the viscosity of the non-aqueous electrolyte at 25°C is preferably 150 mPa·s, more preferably 120 mPa·s. When the viscosity of the non-aqueous electrolyte is equal to or less than the upper limit, the capacity retention rate of the non-aqueous electrolyte storage element after charge-discharge cycles tends to be higher. The upper limit of the viscosity may be 100 mPa·s, 80 mPa·s, 60 mPa·s, 40 mPa·s, or 30 mPa·s. The lower limit of the viscosity may be, for example, 5 mPa·s, or may be 10 mPa·s, 15 mPa·s, 20 mPa·s, 30 mPa·s, 40 mPa·s, 50 mPa·s, or 60 mPa·s.

[0158] The lower limit of the flash point of the non-aqueous electrolyte may be, for example, 10° C., or may be 20° C., 30° C., 40° C., 50° C., 60° C., or 70° C. The upper limit of the flash point may be, for example, 200° C., or may be 170° C., 150° C., 120° C., 100° C., 80° C., 70° C., 60° C., 50° C., or 40° C. The non-aqueous electrolyte according to one embodiment of the present invention may be one whose flash point cannot be measured by the flash point measurement method described below, for example, when the content of ionic liquid relative to the total of all non-aqueous solvents and ionic liquid contained in the non-aqueous electrolyte is large.

[0159] The flash point of a non-aqueous electrolyte is a value measured using the following lamp method and rapid equilibrium method. (Lamp method) First, while raising the temperature of the non-aqueous electrolyte at a constant rate, a test flame is brought close to the non-aqueous electrolyte at approximately 1°C intervals to check for ignition. The flash point is determined approximately using this lamp method. If the flash point is roughly determined, determining the flash point using this lamp method may be omitted. (Rapid equilibrium method) Next, a test flame is brought close to the non-aqueous electrolyte maintained at a set temperature to check for ignition. The temperature of the non-aqueous electrolyte is set near the temperature at which ignition is confirmed using the lamp method, and the temperature at which ignition is confirmed using the rapid equilibrium method is taken as the flash point. A Setaflash series 8 flash point measuring device is used as the measuring device.

[0160] The non-aqueous electrolyte can be prepared by mixing the components, for example.

[0161] (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.

[0162] 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.

[0163] (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.

[0164] 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.

[0165] 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.

[0166] 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.

[0167] <Non-aqueous Electrolyte> A non-aqueous electrolyte according to one embodiment of the present invention contains an electrolyte salt, a fluorinated chain diether, and an ionic liquid.

[0168] A nonaqueous electrolyte according to one embodiment of the present invention can improve the capacity retention rate of a nonaqueous electrolyte storage element after charge-discharge cycling. Furthermore, because the nonaqueous electrolyte contains an ionic liquid, it has advantages such as a high flash point and low volatility. Specific and preferred embodiments of the nonaqueous electrolyte are the same as those of the nonaqueous electrolyte described above as a nonaqueous electrolyte used in a nonaqueous electrolyte storage element according to an embodiment of the present invention, in which the fluorinated solvent is a fluorinated chain diether and an ionic liquid is an essential component. The use of the nonaqueous electrolyte according to one embodiment of the present invention is not particularly limited. The nonaqueous electrolyte is preferably used in a nonaqueous electrolyte storage element, more preferably in a nonaqueous electrolyte storage element having a negative electrode containing metallic lithium at least in a charged state, and even more preferably in a nonaqueous electrolyte storage element having a positive electrode containing a lithium transition metal composite oxide and a negative electrode containing metallic lithium at least in a charged state.

[0169] The non-aqueous electrolyte according to one embodiment of the present invention can be prepared by mixing the components.

[0170] <Method for Manufacturing Non-Aqueous Electrolyte Storage Element> A non-aqueous electrolyte storage element according to one embodiment of the present invention can be manufactured by a known method. A method for manufacturing a non-aqueous electrolyte storage element according to one embodiment of the present invention includes: preparing a positive electrode containing a lithium transition metal composite oxide; preparing a negative electrode containing metallic lithium at least in a charged state; and preparing a non-aqueous electrolyte containing an electrolyte salt and a fluorinated solvent, wherein the non-aqueous electrolyte may or may not contain an ionic liquid, and the fluorinated solvent is at least one selected from the group consisting of fluorinated cyclic ethers and fluorinated chain diethers. The manufacturing method may further include preparing a separator, manufacturing an electrode assembly using the positive electrode, the negative electrode, and the separator, and housing the positive electrode, the negative electrode, and the non-aqueous electrolyte in a container. Housing the positive electrode, the negative electrode, and the non-aqueous electrolyte in a container may also mean housing the electrode assembly and the non-aqueous electrolyte in a container.

[0171] Preparing a positive electrode may mean manufacturing a positive electrode. The manufacturing of a positive electrode can be performed by the method described above. Preparing a negative electrode may mean manufacturing a negative electrode. The manufacturing of a negative electrode can be performed by the method described above. The prepared negative electrode may be a negative electrode having metallic lithium or a negative electrode having a surface region on which metallic lithium can be deposited during charging. The negative electrode having a surface region on which metallic lithium can be deposited during charging may be, for example, a negative electrode consisting only of a negative electrode substrate. 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.

[0172] 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 producing the nonaqueous electrolyte storage element may further include initially charging and discharging the assembled, uncharged storage element.

[0173] The nonaqueous electrolyte electricity storage element according to one embodiment of the present invention may be manufactured by other methods.

[0174] 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.

[0175] <Other Embodiments> The nonaqueous electrolyte storage element, nonaqueous electrolyte, and 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.

[0176] 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.

[0177] 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.

[0178] 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.

[0179] The components used in preparing the non-aqueous electrolytes of the Examples and Comparative Examples are as follows: (Electrolyte salt) LiFSI: lithium bis(fluorosulfonyl)imide (Non-aqueous solvent) TFTHF: 3,3,4,4-tetrafluorotetrahydrofuran TFEME: 2-(2,2,2-trifluoroethoxy)ethyl methyl ether TFETFPE: 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (Ionic liquid) Py13FSI: 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide

[0180] Example 1 Preparation of Non-Aqueous Electrolyte A non-aqueous electrolyte was prepared by mixing an ionic liquid, Py13FSI, and a fluorinated solvent, TFTHF, in a volume ratio of 70:30, and adding an electrolyte salt, LiFSI, at a molar concentration of 2.5 mol / kg to the mixture.

[0181] (Preparation of Positive Electrode) Lithium transition metal composite oxide LiNi ０．６ Co ０．２ Mn ０．２ O ２ A positive electrode mixture paste containing lithium transition metal composite oxide (NCM), acetylene black as a conductive agent, and styrene-butadiene rubber as a binder was prepared. The mass ratio of the lithium transition metal composite oxide, the conductive agent, and the binder was 94.5:4.0:1.5 in terms of solid content. The positive electrode mixture paste was applied to an aluminum positive electrode substrate and dried. Note that the mass per unit area of ​​the positive electrode active material layer after drying was 18 mg / cm. ２ The amount of the positive electrode mixture paste applied was adjusted so that the positive electrode active material layer was 27%. Through the above steps, a positive electrode was obtained in which a positive electrode active material layer was laminated on a positive electrode substrate. The porosity of the formed positive electrode active material layer was 27%.

[0182] (Preparation of Negative Electrode) A pure metallic lithium foil (average thickness: 600 μm) was prepared as a negative electrode.

[0183] (Assembly of non-aqueous electrolyte storage element) A separator was prepared in which inorganic particle layers were laminated on both sides of a polyethylene microporous membrane. The non-aqueous electrolyte storage element of Example 1 was obtained using the positive electrode, negative electrode, separator, and non-aqueous electrolyte.

[0184] [Examples 2 to 8, Comparative Examples 1, 3 to 5] The nonaqueous electrolyte storage elements of Examples 2 to 8 and Comparative Examples 1 and 3 to 5 were obtained in the same manner as in Example 1, except that the compositions of the nonaqueous electrolytes were as shown in Table 1. The contents of the ionic liquid and the fluorinated solvent in Table 1 are the contents relative to the total of the ionic liquid and the fluorinated solvent.

[0185] Comparative Example 2: Elemental sulfur (S), a sulfur-based active material, 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 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. It was then heated again to 300°C at a rate of 5°C / min and held for 2 hours to produce a composite. A positive electrode mixture paste was prepared containing the composite obtained above, acetylene black and carbon nanotubes as conductive agents, carboxymethyl cellulose as a dispersant, polyacrylic acid as a thickener, and styrene-butadiene rubber as a binder. The positive electrode mixture paste 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 a positive electrode substrate. A nonaqueous electrolyte storage element of Comparative Example 2 was obtained in the same manner as in Example 1, except that the positive electrode obtained above was used and the composition of the nonaqueous electrolyte was as shown in Table 1.

[0186] (Measurement of Viscosity) The viscosity at 25° C. of each of the nonaqueous electrolytes of Examples 1 to 4, and 7 and Comparative Example 1 was measured by the method described above. The measurement results are shown in Table 1.

[0187] (Measurement of Flash Point) The flash point of each of the nonaqueous electrolytes of Examples 1 to 8 was measured by the above-described method. The measurement results are shown in Table 1.

[0188] (Initial Charge / Discharge) The nonaqueous electrolyte storage elements of Examples 1 to 8 and Comparative Examples 1 and 3 to 5 were subjected to the following initial charge / discharge in a constant temperature bath at 25°C. Constant current / constant voltage charging was performed under conditions of a charging current of 0.1 C and a charge cut-off voltage of 4.3 V. The charge cut-off condition was the point when the charging current decayed to 0.05 C. Subsequently, constant current discharging was performed under conditions of a discharge current of 0.1 C and a discharge cut-off voltage of 3.0 V. The above charge / discharge cycles were repeated for two cycles. A 10-minute pause was provided after each charge and discharge. At 1 C, the current per unit mass of the positive electrode active material was 174 mA / g.

[0189] For the nonaqueous electrolyte storage element of Comparative Example 2, the following initial discharge and subsequent charge / discharge were performed in a thermostatic chamber at 25°C as initial charge / discharge. First, constant current discharge (initial discharge) was performed under conditions of a discharge current of 0.1 C and a discharge cut-off voltage of 1.0 V. Then, constant current / constant voltage charge was performed under conditions of a charge current of 0.1 C and a charge cut-off voltage of 3.0 V. The charge cut-off condition was set when the charge time reached 30 hours. Then, 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. Note that a 10-minute pause was provided after each discharge and charge. 1 C was defined as the current at which the theoretical capacity based on the design of the nonaqueous electrolyte storage element could be charged in 1 hour. The theoretical capacity (mAh) based on the design of the nonaqueous electrolyte storage element was calculated based on the capacity density per unit area of ​​the positive electrode active material layer (mAh / cm ２ ) and the area of ​​the positive electrode active material layer (cm ２ ) and multiplied it.

[0190] (Charge-Discharge Cycle Test) The nonaqueous electrolyte storage elements of Examples 1 to 8 and Comparative Examples 1, 3, and 4 that had undergone the initial charge-discharge cycle test were subjected to the following charge-discharge cycle test in a thermostatic chamber at 25°C. Constant-current, constant-voltage charging was performed with a charging current of 0.33 C and a charge cut-off voltage of 4.3 V. The charge cut-off condition was the point at which the charging current decayed to 0.05 C. Subsequently, constant-current discharging was performed with a discharge current of 0.33 C and a discharge cut-off voltage of 3.0 V. The above charge and discharge cycles were repeated 100 times. A 10-minute rest period was provided after each charge and discharge. The discharge quantity of electricity at the 100th cycle relative to the discharge quantity of electricity at the first cycle was calculated as the capacity retention ratio. The results are shown in Table 1.

[0191]

[0192] As shown in Table 1, the nonaqueous electrolyte storage elements of Examples 1 to 8, which used a lithium transition metal composite oxide (NCM) as the positive electrode active material and a fluorinated cyclic carbonate (TFTHF) or a fluorinated chain diether (TFEME) as the fluorinated solvent for the nonaqueous electrolyte, exhibited high capacity retention rates of 99.0% or higher after the charge-discharge cycle test. On the other hand, the nonaqueous electrolyte storage elements of Comparative Example 1, in which the nonaqueous electrolyte did not contain a fluorinated solvent, and Comparative Examples 3 and 4, in which a fluorinated chain monoether (TFETFPE) was used as the fluorinated solvent for the nonaqueous electrolyte, exhibited low capacity retention rates after the charge-discharge cycle test. The nonaqueous electrolyte storage element of Comparative Example 2, which used elemental sulfur as the positive electrode active material, exhibited voltage disturbances during initial charge-discharge. Figure 3 shows the charge-discharge curves for the initial discharge and subsequent charge-discharge of the nonaqueous electrolyte storage element of Comparative Example 2. It is believed that the unstable behavior, such as voltage disturbances, occurred as a result of polysulfides formed in the positive electrode dissolving in the nonaqueous electrolyte. Furthermore, in the nonaqueous electrolyte storage element of Comparative Example 5, in which the nonaqueous electrolyte did not contain an ionic liquid and a fluorinated chain monoether (TFETFPE) was used as the fluorinated solvent, the open circuit voltage (OCV) after initial charge and discharge was low, at not more than 1 V. Thus, the nonaqueous electrolyte storage elements of Comparative Examples 2 and 5 were both determined to have insufficient charge and discharge performance, and therefore were not subjected to charge and discharge cycle tests.

[0193] 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.

[0194] 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 energy storage element comprising: a positive electrode containing a lithium transition metal composite oxide; a negative electrode containing metallic lithium at least in a charged state; and a non-aqueous electrolyte containing an electrolyte salt and a fluorinated solvent, wherein the non-aqueous electrolyte may or may not contain an ionic liquid, and the fluorinated solvent is at least one selected from the group consisting of fluorinated cyclic ethers and fluorinated chain diethers.

2. The nonaqueous electrolyte energy storage element according to claim 1, wherein the nonaqueous electrolyte contains the ionic liquid.

3. The nonaqueous electrolyte storage element according to claim 1 or 2, wherein the total content of the fluorinated solvent and the ionic liquid relative to all components other than the electrolyte salt in the nonaqueous electrolyte is 90% by volume or more.

4. The nonaqueous electrolyte storage element according to claim 1 or 2, wherein the content of the fluorinated solvent relative to the total of the fluorinated solvent and the ionic liquid is 25% by volume or more and 100% by volume or less.

5. The nonaqueous electrolyte storage element according to claim 1 or 2, 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, and n is an integer of 2 to 7.

6. The nonaqueous electrolyte storage element according to claim 1 or 2, wherein the fluorinated chain diether is represented by the following formula (2): (In formula (2), R ２ is a fluorinated alkyl group having 1 to 3 carbon atoms. ３ is 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.

7. The nonaqueous electrolyte storage element according to claim 1 or 2, wherein the ionic liquid contains at least one cation selected from the group consisting of quaternary ammonium cations, imidazolium cations, pyrrolidinium cations, piperidinium cations, quaternary phosphonium cations, and sulfonium cations.

8. The nonaqueous electrolyte storage element according to claim 1 or 2, wherein the ionic liquid has an imide anion.

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

10. The nonaqueous electrolyte storage element according to claim 1 or 2, wherein the molar concentration of the electrolyte salt in the nonaqueous electrolyte is 1.0 mol / kg or more and 4.0 mol / kg or less.

11. The nonaqueous electrolyte storage element according to claim 1 or 2, wherein the viscosity of the nonaqueous electrolyte at 25° C. is 150 mPa·s or less.

12. A non-aqueous electrolyte comprising an electrolyte salt, a fluorinated linear diether, and an ionic liquid.

13. A method for producing a non-aqueous electrolyte storage element, comprising: preparing a positive electrode containing a lithium transition metal composite oxide; preparing a negative electrode containing metallic lithium at least in a charged state; and preparing a non-aqueous electrolyte containing an electrolyte salt and a fluorinated solvent, wherein the non-aqueous electrolyte may or may not contain an ionic liquid, and the fluorinated solvent is at least one selected from the group consisting of fluorinated cyclic ethers and fluorinated chain diethers.

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