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

Abstract

Provided are a nonaqueous electrolyte storage element in which an ionic liquid is used as the nonaqueous electrolyte, which has a small overvoltage and suppresses the occurrence of internal short circuits due to repeated charge and discharge, a method for manufacturing such a nonaqueous electrolyte storage element, and a nonaqueous electrolyte in which an ionic liquid is used, which can reduce the overvoltage of the nonaqueous electrolyte storage element and suppress the occurrence of internal short circuits due to repeated charge and discharge. [Solution] A nonaqueous electrolyte storage element according to one aspect of the present invention comprises a negative electrode containing metallic lithium at least in a charged state, and a nonaqueous electrolyte containing an electrolyte salt, an ionic liquid, and a nonaqueous solvent, wherein the nonaqueous solvent contains a fluorinated cyclic ether, and the molar concentration of the electrolyte salt in the nonaqueous electrolyte is 0.8 mol / kg or more and 3.5 mol / kg or less.

Description

[Technical Field]

[0001] The present invention relates to a nonaqueous electrolyte storage element, a nonaqueous electrolyte, and a method for producing a nonaqueous electrolyte storage element. [Background technology]

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

[0003] Metallic lithium is known as a negative electrode active material with high energy density that is used in non-aqueous electrolyte energy storage elements (see Patent Document 1). In recent years, research has also been progressing on non-aqueous electrolyte energy storage elements that use ionic liquids as the non-aqueous electrolyte (see Patent Document 2). Ionic liquids, also known as room-temperature molten salts, have advantages such as being substantially non-volatile and highly flame-retardant, despite being liquid at room temperature. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-100065 [Patent Document 2] Japanese Patent Application Laid-Open No. 2001-319688 Summary of the Invention [Problem to be solved by the invention]

[0005] Conventional non-aqueous electrolyte storage elements that use an ionic liquid as the non-aqueous electrolyte may not be able to perform satisfactory repeated charging and discharging due to factors such as a large overvoltage and the occurrence of internal short circuits with repeated charging and discharging.

[0006] An object of the present invention is to provide a nonaqueous electrolyte storage element in which an ionic liquid is used as the nonaqueous electrolyte, which has a low overvoltage and suppresses the occurrence of internal short circuits due to repeated charge and discharge, a method for manufacturing such a nonaqueous electrolyte storage element, and a nonaqueous electrolyte in which an ionic liquid is used, which can reduce the overvoltage of the nonaqueous electrolyte storage element and suppress the occurrence of internal short circuits due to repeated charge and discharge. [Means for solving the problem]

[0007] A nonaqueous electrolyte storage element according to one aspect of the present invention comprises a negative electrode containing metallic lithium at least in a charged state, and a nonaqueous electrolyte containing an electrolyte salt, an ionic liquid, and a nonaqueous solvent, wherein the nonaqueous solvent contains a fluorinated cyclic ether, and the molar concentration of the electrolyte salt in the nonaqueous electrolyte is 0.8 mol / kg or more and 3.5 mol / kg or less.

[0008] A non-aqueous electrolyte according to another aspect of the present invention includes an electrolyte salt, an ionic liquid, and a non-aqueous solvent, wherein the non-aqueous solvent includes a fluorinated cyclic ether, and the molar concentration of the electrolyte salt is 0.8 mol / kg or more and 3.5 mol / kg or less.

[0009] A method for manufacturing a nonaqueous electrolyte storage element according to another aspect of the present invention includes preparing a negative electrode that contains metallic lithium at least in a charged state, and preparing a nonaqueous electrolyte that contains an electrolyte salt, an ionic liquid, and a nonaqueous solvent, wherein the nonaqueous solvent contains a fluorinated cyclic ether, and the molar concentration of the electrolyte salt in the nonaqueous electrolyte is 0.8 mol / kg or more and 3.5 mol / kg or less. [Effects of the Invention]

[0010] According to any one aspect of the present invention, there can be provided a nonaqueous electrolyte storage element in which an ionic liquid is used as the nonaqueous electrolyte, which has a low overvoltage and is suppressed from occurring due to repeated charge and discharge, a method for manufacturing such a nonaqueous electrolyte storage element, and a nonaqueous electrolyte in which an ionic liquid is used, which can reduce the overvoltage of the nonaqueous electrolyte storage element and suppress the occurrence of internal short circuits due to repeated charge and discharge. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a perspective view showing a nonaqueous electrolyte electricity storage element according to one embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing an electricity storage device including a plurality of nonaqueous electrolyte electricity storage elements according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[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 negative electrode containing metallic lithium at least in a charged state, and a nonaqueous electrolyte containing an electrolyte salt, an ionic liquid, and a nonaqueous solvent, wherein the nonaqueous solvent contains a fluorinated cyclic ether, and the molar concentration of the electrolyte salt in the nonaqueous electrolyte is 0.8 mol / kg or more and 3.5 mol / kg or less.

[0014] The nonaqueous electrolyte storage element described in [1] above is a nonaqueous electrolyte storage element that uses an ionic liquid as the nonaqueous electrolyte. It exhibits low overvoltage and suppresses the occurrence of internal short circuits due to repeated charge and discharge. While the reason for this is unclear, the following is presumed. Nonaqueous electrolytes containing ionic liquids have high viscosity and low diffusivity of charge-transporting ions, resulting in high overvoltage in nonaqueous electrolyte storage elements using nonaqueous electrolytes containing ionic liquids. Therefore, adding an appropriate nonaqueous solvent to the nonaqueous electrolyte containing ionic liquid to reduce the viscosity of the nonaqueous electrolyte is considered. However, depending on the type of nonaqueous solvent added, the nonaqueous solvent itself may have low and unstable reduction resistance, or the coating derived from the nonaqueous solvent formed on the negative electrode surface may be highly resistant or unstable, resulting in insufficient reduction and increased susceptibility to internal short circuits. In contrast, fluorinated cyclic ethers are thought to have high reduction resistance and to form a good coating derived from the fluorinated cyclic ether on the negative electrode surface. Furthermore, since fluorinated cyclic ethers are less likely to interact with charge-transport ions, it is believed that they are less likely to inhibit the diffusibility of charge-transport ions. Furthermore, when the concentration of electrolyte salt in the nonaqueous electrolyte is low, the concentration of charge-transport ions in the nonaqueous electrolyte becomes low, while when the concentration of electrolyte salt is high, the viscosity of the nonaqueous electrolyte increases. In either case, the diffusibility of charge-transport ions decreases. Therefore, it is believed that the concentration of the electrolyte salt must be adjusted within an appropriate range to increase the diffusibility of charge-transport ions, reduce overvoltage, and suppress the occurrence of internal short circuits due to repeated charge and discharge. In the nonaqueous electrolyte storage element described in [1] above, the nonaqueous electrolyte contains a fluorinated cyclic ether together with an ionic liquid, and the molar concentration of the electrolyte salt is within a predetermined range. This results in high diffusibility of charge-transport ions in the nonaqueous electrolyte, and a good coating derived from the fluorinated cyclic ether is formed on the negative electrode surface. Therefore, it is believed that the nonaqueous electrolyte storage element described in [1] above has low overvoltage and suppresses the occurrence of internal short circuits due to repeated charge and discharge. Furthermore, the nonaqueous electrolyte electricity storage element described in [1] above is also suppressed from increasing in overvoltage due to repeated charge and discharge. Furthermore, the nonaqueous electrolyte storage element described in [1] above has an advantage of having a high energy density because it includes a negative electrode containing metallic lithium at least in a charged state. On the other hand, nonaqueous electrolyte storage elements that generally include a negative electrode containing metallic lithium are prone to the occurrence of internal short circuits due to repeated charge and discharge. Therefore, the nonaqueous electrolyte storage element described in [1] above has a particularly significant advantage of being able to suppress internal short circuits due to repeated charge and discharge and to perform satisfactory repeated charge and discharge. In other words, the nonaqueous electrolyte storage element described in [1] above can achieve both high energy density and suppression of internal short circuits.

[0015] The types of ionic compounds, such as electrolyte salts and ionic liquids, contained in non-aqueous electrolytes can be analyzed using ion chromatography (IC), liquid chromatography-mass spectrometry (LC-MS), 1 Identification is performed by combining the necessary analyses, such as H-NMR and multinuclear NMR. The content of ionic compounds such as electrolyte salts and ionic liquids contained in the non-aqueous electrolyte is determined by IC. However, the content of cations of ionic liquids contained in the non-aqueous electrolyte is determined by LC-MS. If it cannot be determined by LC-MS, 1 Identified by H-NMR internal standard method. Specifically, IC measurements are performed as follows: IC measurements are performed continuously under the same conditions. (A1) Collection of non-aqueous electrolyte First, the nonaqueous electrolyte storage element is disassembled to remove the nonaqueous electrolyte. If the nonaqueous electrolyte cannot be removed, the nonaqueous electrolyte storage element is centrifuged to remove the nonaqueous electrolyte. If the nonaqueous electrolyte cannot be removed even after centrifugation, an appropriate extraction solvent (e.g., acetonitrile) is poured into the nonaqueous electrolyte storage element, and the nonaqueous electrolyte diluted with the extraction solvent is removed. (A2)IC analysis The components of the collected non-aqueous electrolyte are analyzed by IC. The IC analysis is performed in the following order: qualitative analysis and quantitative analysis. (qualitative analysis) A measurement sample (non-aqueous electrolyte) is subjected to IC analysis. The components contained in the measurement sample are predicted from the peak positions of each peak in the obtained ion chromatogram. A known sample of the predicted components (hereinafter referred to as "predicted components") is subjected to IC analysis. The retention times of the peaks corresponding to each predicted component in the measurement sample are compared with the retention times of the peaks in known samples of each predicted component, and if they match, the prediction is assumed to be correct. (Quantitative analysis) Quantitative analysis is performed using the calibration curve method. First, a known sample of predicted components with known concentrations is analyzed by IC analysis, and a calibration curve is created by calculating the peak area. The calibration curve is calculated using the coefficient of determination (r 2 ) is created so that it is between 0.999 and 1. The amount of the predicted component in the measurement sample is calculated from the calibration curve and the area of ​​the peak of the predicted component in the measurement sample. This process is performed for all peaks detected in the IC analysis of the measurement sample, and the amount of each predicted component is calculated.

[0016] The types and contents of nonionic compounds, such as nonaqueous solvents, contained in the nonaqueous electrolyte are identified by liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-mass spectrometry (GC-MS). Specifically, this is done as follows. Note that the LC-MS and GC-MS measurements are performed consecutively under the same conditions. (B1) Collection of non-aqueous electrolyte The non-aqueous electrolyte is extracted using the same procedure as in "(A1) Extraction of non-aqueous electrolyte" above. (B2) LC-MS The components of the collected non-aqueous electrolyte are analyzed by LC-MS. The LC-MS analysis is performed in the following order: qualitative analysis and quantitative analysis. The LC-MS analysis is performed using Waters' "Acquity H" and "Xevo G2-5QTof" instruments. Water is used as the eluent. Note that, regarding the measurement instrument, if it is not possible to perform the measurement using the above-mentioned model, other models that are considered to produce equivalent measurement results can be used. The same applies to other measurement instruments in this specification. (qualitative analysis) The measurement sample (non-aqueous electrolyte) is subjected to LC-MS analysis. If the peaks in the obtained liquid chromatogram cannot be separated, GC-MS analysis, described below, is performed instead of LC-MS analysis. If the peaks can be separated, the components contained in the measurement sample are predicted from the MS spectrum of each peak. A known sample of the predicted components is subjected to LC-MS analysis. The retention times and MS spectrum of the peaks corresponding to each predicted component in the measurement sample are compared with the retention times and MS spectrum of the peaks in a known sample of each predicted component, and if they match, the prediction is assumed to be correct. (Quantitative analysis) Quantitative analysis is performed using the calibration curve method. Quantitative analysis by LC-MS is performed using the same procedure as the quantitative analysis by IC described above, and the content of each predicted component is determined. (B3) GC-MS The GC-MS analysis is performed in the following order: qualitative analysis and quantitative analysis. The GC-MS analysis equipment used is the Agilent 5975C. Argon is used as the carrier gas. (qualitative analysis) A measurement sample (non-aqueous electrolyte) is subjected to GC-MS analysis. The components contained in the sample are predicted from the MS spectrum of each peak in the obtained gas chromatogram. A known sample of the predicted components is subjected to GC-MS analysis. The retention times and MS spectra of the peaks corresponding to the predicted components in the measurement sample are compared with the retention times and MS spectra of the peaks in known samples of each predicted component, and if they match, the prediction is assumed to be correct. (Quantitative analysis) Quantitative analysis is performed using the calibration curve method. Quantitative analysis by GC-MS is performed using the same procedure as the quantitative analysis by IC described above, and the content of each predicted component is determined.

[0017] "Mass molarity" refers to the amount of substance (mol) of the electrolyte salt based on the total mass (kg) of the ionic liquid and the non-aqueous solvent.

[0018] [2] In the nonaqueous electrolyte storage element according to [1] above, the content of the fluorinated cyclic ether relative to the total of the ionic liquid and the nonaqueous solvent may be 5% by volume or more and 95% by volume or less.

[0019] The nonaqueous electrolyte storage element described in [2] above has an appropriate content of fluorinated cyclic ether, has a smaller overvoltage, and is more effectively prevented from causing an internal short circuit.

[0020] [3] In the nonaqueous electrolyte storage element according to [1] or [2] above, the content of the fluorinated cyclic ether relative to the total of the ionic liquid and the nonaqueous solvent may be 5% by volume or more and 80% by volume or less.

[0021] The nonaqueous electrolyte storage element described in [3] above has a more appropriate content of fluorinated cyclic ether, has a smaller overvoltage, and is more inhibited from causing an internal short circuit.

[0022] [4] In the nonaqueous electrolyte storage element according to any one of [1] to [3] above, the molar ratio of the electrolyte salt to the ionic liquid may be 0.8 or more and 6.5 or less.

[0023] The nonaqueous electrolyte storage element described in [4] above has an appropriate molar ratio between the ionic liquid and the electrolyte salt, and therefore has a smaller overvoltage and is more effectively prevented from causing an internal short circuit.

[0024] [5] In the nonaqueous electrolyte storage element according to any one of [1] to [4] above, the nonaqueous solvent may further contain at least one selected from the group consisting of non-fluorinated cyclic ethers and chain ethers.

[0025] In the nonaqueous electrolyte storage element described in [5] above, the nonaqueous solvent further contains at least one selected from the group consisting of non-fluorinated cyclic ethers and chain ethers, thereby further reducing the viscosity of the nonaqueous electrolyte. As a result, the nonaqueous electrolyte storage element described in [5] above has low overvoltage, suppresses the occurrence of internal short circuits, and can exhibit further effects such as high high-rate discharge performance.

[0026] [6] In the nonaqueous electrolyte storage element according to [5] above, the total content of the non-fluorinated cyclic ether and the chain ether relative to the total of the ionic liquid and the nonaqueous solvent may be 5% by volume or more and 80% by volume or less.

[0027] The nonaqueous electrolyte storage element described in [6] above has an appropriate total content of non-fluorinated cyclic ether and chain ether, and the advantages of including at least one selected from the group consisting of non-fluorinated cyclic ethers and chain ethers are particularly fully obtained.

[0028] [7] In the nonaqueous electrolyte storage element according to any one of [1] to [6] above, the fluorinated cyclic ether may be represented by the following formula (1): [ka] (In formula (1), R 1 are each independently a hydrogen atom, a fluorine atom, an alkyl group having 1 to 4 carbon atoms, or a fluorinated alkyl group having 1 to 4 carbon atoms. 1 At least one of the groups is a fluorine atom or a fluorinated alkyl group having 1 to 4 carbon atoms. n1 is 4 or 5.

[0029] [8] In the nonaqueous electrolyte storage element according to any one of [5] to [7] above, the non-fluorinated cyclic ether may be represented by the following formula (2), and the chain ether may be represented by the following formula (3): [ka] (In formula (2), R 2 are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms; and n2 is 4 or 5. [ka] (In formula (3), R 3 and R 4 are each independently an alkyl group having 1 to 3 carbon atoms or a fluorinated alkyl group having 1 to 3 carbon atoms. 5 is an alkanediyl group having 1 to 3 carbon atoms; and n3 is 0 or 1.

[0030] [9] In the nonaqueous electrolyte storage element according to any one of [1] to [8] above, the ionic liquid may contain at least one cation selected from the group consisting of quaternary ammonium cations, imidazolium cations, pyrrolidinium cations, piperidinium cations, quaternary phosphonium cations, and sulfonium cations.

[0031]

[10] In the nonaqueous electrolyte storage element according to any one of [1] to [9] above, the ionic liquid may have an imide anion.

[0032]

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

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

[0033]

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

[11] above, the content of the ionic liquid relative to the total of the ionic liquid and the nonaqueous solvent may be 5% by volume or more and 95% by volume or less.

[0034]

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

[12] above, the total content of the ionic liquid and the fluorinated cyclic ether relative to the total content of the ionic liquid and the nonaqueous solvent may be 20% by volume or more and 100% by volume or less.

[0035]

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

[13] above, the total content of the ionic liquid and the fluorinated cyclic ether relative to the total of the ionic liquid and the nonaqueous solvent may be 95% by volume or more and 100% by volume or less, and the content of the fluorinated cyclic ether may be 5% by volume or more and 35% by volume or less.

[0036]

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

[14] above, the total content of the ionic liquid and the ether (total of fluorinated cyclic ether, non-fluorinated cyclic ether, and chain ether) relative to the total of the ionic liquid and the nonaqueous solvent may be 90% by volume or more and 100% by volume or less.

[0037]

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

[15] above, the viscosity of the nonaqueous electrolyte at 25° C. may be 143 mPa·s or less.

[0038] The nonaqueous electrolyte storage elements described in the above [7] to

[16] are all suitable embodiments of the present invention, and have a lower overvoltage and are more inhibited from causing an internal short circuit.

[0039] The viscosity of the non-aqueous electrolyte is a value measured using a measuring device "LOVIS2000ME" manufactured by Anton Paar.

[0040]

[17] A non-aqueous electrolyte according to another aspect of the present invention includes an electrolyte salt, an ionic liquid, and a non-aqueous solvent, wherein the non-aqueous solvent includes a fluorinated cyclic ether, and the molar concentration of the electrolyte salt is 0.8 mol / kg or more and 3.5 mol / kg or less.

[0041] The nonaqueous electrolyte described in

[17] above is a nonaqueous electrolyte containing an ionic liquid, which can reduce the overvoltage of a nonaqueous electrolyte energy storage element and suppress the occurrence of internal short circuits that occur with repeated charge and discharge. Furthermore, the nonaqueous electrolyte described in

[17] above can also suppress an increase in overvoltage that occurs with repeated charge and discharge of a nonaqueous electrolyte energy storage element.

[0042]

[18] The nonaqueous electrolyte according to the above item

[17] may be used for a nonaqueous electrolyte storage element including a negative electrode containing metallic lithium at least in a charged state.

[0043] The non-aqueous electrolyte described in the above item

[18] can be particularly suitably used in a non-aqueous electrolyte storage element having a negative electrode containing metallic lithium at least in a charged state.

[0044]

[19] A method for manufacturing a nonaqueous electrolyte storage element according to another aspect of the present invention includes preparing a negative electrode that contains metallic lithium at least in a charged state, and preparing a nonaqueous electrolyte that contains an electrolyte salt, an ionic liquid, and a nonaqueous solvent, wherein the nonaqueous solvent contains a fluorinated cyclic ether, and the molar concentration of the electrolyte salt in the nonaqueous electrolyte is 0.8 mol / kg or more and 3.5 mol / kg or less.

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

[19] above, it is possible to produce a nonaqueous electrolyte storage element that uses an ionic liquid as the nonaqueous electrolyte, and that has a small overvoltage and is suppressed from causing an internal short circuit due to repeated charge and discharge. Furthermore, the nonaqueous electrolyte storage element obtained by the method for producing a nonaqueous electrolyte storage element described in

[19] above is also suppressed from increasing in overvoltage due to repeated charge and discharge.

[0046] 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.

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

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

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

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

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

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

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

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

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

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

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

[0058] The positive electrode active material layer contains a 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.

[0059] Known positive electrode active materials can be used for the positive electrode active material. Materials capable of absorbing and releasing lithium ions are typically used for the positive electrode active material of lithium ion secondary batteries. Examples of positive electrode active materials include lithium transition metal composite oxides, polyanion compounds, chalcogen compounds, sulfur-based active materials, and lithium oxide. One or more positive electrode active materials can be used.

[0060] Examples of the transition metal elements contained in the lithium transition metal composite oxide include nickel element, cobalt element, manganese element, etc. The lithium transition metal composite oxide may contain a typical metal element such as aluminum element. Examples of the lithium transition metal composite oxide include a lithium transition metal composite oxide having an α-NaFeO2-type crystal structure, a lithium transition metal composite oxide having a spinel-type crystal structure, etc.

[0061] Examples of the lithium transition metal composite oxide having an α-NaFeO2-type crystal structure include those represented by Li 1+α Ma 1-α O2 (Ma is a metal element other than lithium element, containing one or more kinds of transition metal elements. 0 ≦ α < 1.). Ma preferably contains one or more of Ni, Co, and Mn. The total content of Ni, Co, and Mn with respect to Ma ((Ni + Co + Mn) / Ma) is preferably 90 mol% or more, more preferably 98 mol% or more.

[0062] Examples of the lithium transition metal composite oxide having a spinel-type crystal structure include those represented by Li β Mb2O4 (Mb is a metal element other than lithium element, containing one or more kinds of transition metal elements. 0 < β ≦ 1.2.). Mb preferably contains Mn. The content of Mn with respect to Mb (Mn / Mb) is preferably 50 mol% or more, more preferably 80 mol% or more.

[0063] The polyanion compound is a compound composed of a polyanion (i.e., a polyvalent oxoacid anion) and a cation. The polyanion compound preferably contains a lithium cation and a transition metal cation as the cation. Examples of the polyanion compound include LiFePO4, LiMnPO4, LiMn x Fe 1-x PO4 (0 < x < 1), LiNiPO4, LiCoPO4, Li3V2(PO4)3, Li2MnSiO4, Li2CoPO4F, etc. The surface of the particles of the polyanion compound may be coated with another material (for example, a carbon material described later).

[0064] Examples of the chalcogen compound include titanium disulfide, molybdenum disulfide, and molybdenum dioxide.

[0065] In one embodiment of the present invention, the positive electrode active material may include a sulfur-based active material. The positive electrode active material may be a sulfur-based active material. The sulfur-based active material may be elemental sulfur, a sulfur compound, or a mixture thereof. Examples of sulfur compounds include metal sulfides such as lithium sulfide, organic disulfide compounds, and organic sulfur compounds such as carbon sulfide compounds. Sulfur-based active materials have advantages such as high theoretical capacity and low cost. In particular, nonaqueous electrolyte storage elements having a positive electrode containing a sulfur-based active material and a negative electrode containing metallic lithium at least in a charged state are prone to internal short-circuiting due to repeated charge and discharge, and are therefore less likely to be able to perform satisfactory charge and discharge cycles. Therefore, when the technology of the present invention is applied to such nonaqueous electrolyte storage elements, the advantages of reducing overvoltage and suppressing internal short-circuiting are particularly pronounced.

[0066] The sulfur-based active material may be in the form of a composite with a conductive agent (a material having higher conductivity than the sulfur-based active material), etc. This composite may be in the form in which the sulfur-based active material is supported on a conductive agent or the like as a carrier, and specifically may be a composite of sulfur and porous carbon (sulfur-porous carbon composite: SPC), etc.

[0067] The atoms or polyanions in these materials serving as the positive electrode active material may be partially substituted with atoms or anion species of other elements, and the surfaces of these materials may be coated with other materials.

[0068] The positive electrode active material is usually particulate. The average particle size of the positive electrode active material is preferably, for example, 0.1 μm to 20 μm. Setting the average particle size of the positive electrode active material above the lower limit facilitates the production and handling of the positive electrode active material. Setting the average particle size of the positive electrode active material below the upper limit improves the electronic conductivity of the positive electrode active material layer. When a composite of the positive electrode active material and another material is used, the average particle size of the composite is taken as the average particle size of the positive electrode active material. The term "average particle size" refers to the value at which the volume-based cumulative distribution (D50) reaches 50% as calculated in accordance with JIS-Z-8819-2 (2001) based on the particle size distribution measured by laser diffraction / scattering in a diluted solution of particles diluted with a solvent in accordance with JIS-Z-8825 (2013). Methods for obtaining particles of the positive electrode active material and the negative electrode active material described below with a predetermined particle size can be achieved by known methods, such as using a pulverizer or a classifier.

[0069] The content of the positive electrode active material in the positive electrode active material layer is preferably 50% by mass to 99% by mass, more preferably 70% by mass to 98% by mass, and may be 80% by mass to 95% by mass. By setting the content of the positive electrode active material within this range, both high energy density and manufacturability of the positive electrode active material layer can be achieved.

[0070] Conductive agents are usually components made of materials that have electrical conductivity. Even if the volume resistivity of a 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 a carbon material may be 80% by mass or more, 90% by mass or more, 95% by mass, 99% by mass, or 99.9% by mass or more. The carbon material is preferably a carbon material other than an uncarbonized polymer compound. Examples of carbon materials include graphite, non-graphitic carbon, and graphene-based carbon. Examples of non-graphitic carbon include carbon nanofiber, pitch-based carbon fiber, and carbon black. Examples of carbon black include furnace black, acetylene black, and ketjen black. Examples of graphene-based carbon include graphene, carbon nanotubes (CNT), and fullerene. Conductive agents may be in the form of powder, fiber, or the like. The conductive agent may be one or more types. The conductive agent may be a composite of these materials. For example, a composite material of carbon black and CNT may be used.

[0071] 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 5%, 4%, or 3% 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. Note that when a composite of a positive electrode active material and a conductive agent is used as the positive electrode active material, the content of the conductive agent in the composite is not included in the content of the conductive agent in the positive electrode active material layer.

[0072] Examples of the binder include a water-based binder and an organic solvent-based binder.

[0073] The aqueous binder is a binder that dissolves or disperses in water. The aqueous binder may be a binder that dissolves or disperses at 1 part by mass or more in 100 parts by mass of water at 20°C. When a positive electrode active material layer is formed using a positive electrode mixture paste whose dispersion medium is water or a mixed solvent mainly composed of water, an aqueous binder (a water-soluble or water-dispersible polymer material) can be used. Examples of aqueous binders include polyethylene oxide, polypropylene oxide, polyvinyl alcohol, polyacrylic acid, polymethacrylic acid, polytetrafluoroethylene, styrene-butadiene rubber, polyethylene, polypropylene, nitrile-butadiene rubber, and cellulose.

[0074] The organic solvent-based binder is a binder that dissolves or disperses in an organic solvent (e.g., N-methylpyrrolidone). The organic solvent-based binder may be a binder that dissolves or disperses at 1 part by mass or more in 100 parts by mass of an organic solvent (e.g., N-methylpyrrolidone) at 20°C. When a positive electrode active material layer is formed using a positive electrode mixture paste whose dispersion medium is an organic solvent or a mixed solvent mainly containing an organic solvent, an organic solvent-based binder (a polymer material that is soluble or dispersible in an organic solvent) can be used. Examples of organic solvent-based binders include polyvinylidene fluoride, copolymers of vinylidene fluoride and hexafluoropropylene, copolymers of ethylene and vinyl alcohol, polyacrylonitrile, polyphosphazene, polysiloxane, polyvinyl acetate, polymethyl methacrylate, polystyrene, polycarbonate, polyamide, polyimide, polyamideimide, crosslinked polymers of cellulose and chitosan pyrrolidone carboxylate, chitosan derivatives, and the like.

[0075] The binder may be a fluororesin (polytetrafluoroethylene, polyvinylidene fluoride, etc.), a polyolefin (polyethylene, polypropylene, etc.), an elastomer (ethylene propylene diene rubber, styrene butadiene rubber, fluororubber, etc.), a polysaccharide polymer (cellulose, chitosan derivatives, etc.), etc. One or more types of binders may be used.

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

[0077] 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 also 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.

[0078] 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 preferably 5% by mass or less, and more preferably 2% by mass or less. The technology disclosed herein may also be implemented in an embodiment in which the positive electrode active material layer does not contain a filler.

[0079] 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. The other components include those unintentionally present 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 contained 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.

[0080] 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 one positive electrode active material layer may be, for example, 5 μm or more and 1,000 μm or less. The lower limit of the average thickness of one 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 one 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 ​​one positive electrode active material layer is, for example, 4 mg / cm. 2 More than 100mg / cm 2 The lower limit of the mass per unit area of ​​one positive electrode active material layer may be 6 mg / cm or less. 2 , 8 mg / cm 2 or 10 mg / cm 2 The upper limit of the mass per unit area of ​​one positive electrode active material layer is 50 mg / cm. 2 , 20 mg / cm 2 , 15 mg / cm 2 , 12 mg / cm 2 or 10 mg / cm 2 may be.

[0081] 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%, or 35%. The "porosity (%)" of the positive electrode active material layer and the negative electrode active material layer described below is calculated by the formula (1-V2 / V1) × 100, where V1 is the apparent volume (volume including voids) of the positive (negative) electrode active material layer and V2 is the sum of the actual volumes of the materials constituting the positive (negative) electrode active material layer. The sum V2 of the actual volumes of the materials constituting the positive (negative) electrode active material layer can be calculated from the content of each material in the positive (negative) electrode active material layer and the true density of each material.

[0082] (Positive electrode manufacturing method) The positive electrode can be manufactured by a known method. The positive electrode can be manufactured, for example, by applying a paste-like positive electrode mixture (positive electrode mixture paste) to a positive electrode substrate directly or via an intermediate layer, and then drying the paste to form a positive electrode active material layer. The positive electrode mixture paste 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.

[0083] (Negative electrode) The negative electrode has a negative electrode substrate and a negative electrode active material layer laminated on the negative electrode substrate directly or via an intermediate layer. Usually, the negative electrode has a portion where the negative electrode substrate is exposed. This exposed portion of the negative electrode substrate is usually connected to the above-mentioned negative electrode lead. The negative electrode may have a shape such as a sheet, plate, or strip.

[0084] The thickness of the negative electrode is appropriately set depending on the application of the nonaqueous electrolyte storage element, etc. The average thickness of the negative electrode may be, for example, 30 μm or more and 1,000 μm or less. The lower limit of the average thickness of the negative electrode may be 50 μm, 100 μm, or 200 μm. The upper limit of the average thickness of the negative electrode may be 500 μm, 400 μm, 300 μm, 200 μm, or 100 μm. The average thickness of the negative electrode is the average thickness of a portion where the negative electrode active material layer is laminated on the negative electrode substrate directly or via an intermediate layer. When the negative electrode substrate has both a portion where the negative electrode active material layer is laminated on both sides and a portion where the negative electrode active material layer is laminated on only one side, the average thickness of the portion where the negative electrode active material layer is laminated on both sides of the negative electrode substrate is taken as the average thickness.

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

[0086] 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.

[0087] The average thickness of the negative electrode substrate may be, for example, 2 μm or more and 35 μm or less. The lower limit of the average thickness of the negative electrode substrate may be 3 μm, 4 μm, 5 μm, or 10 μm. The upper limit of the average thickness of the negative electrode substrate may be 30 μm, 20 μm, 15 μm, or 10 μm.

[0088] The 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.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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%.

[0094] 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%.

[0095] 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.

[0096] When the negative electrode active material layer contains a binder, the content of the binder in the negative electrode active material layer is preferably 0.1% by mass to 10% by mass, more preferably 0.5% by mass to 8% by mass. The content of the binder in the negative electrode active material layer may be 5% by mass or less, or may be 2% by mass or less. The technology disclosed herein may also be implemented in an embodiment in which the negative electrode active material layer does not contain a binder.

[0097] 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.

[0098] 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 other purposes. When the negative electrode active material layer contains a filler, the content of the filler in the negative electrode active material layer can be 0.1% by mass or more and 8% by mass or less, and typically 5% by mass or less is preferred, and 2% by mass or less is more preferred. The technology disclosed herein may also be implemented in an embodiment in which the negative electrode active material layer does not contain a filler.

[0099] 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. The other components include those unintentionally present in the negative electrode active material layer. The negative electrode active material layer may also contain unintentionally present 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 present 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 present impurities in the negative electrode active material layer may be 10% by mass, 5%, 2%, 1%, 0.1%, or 0.01% by mass.

[0100] The negative electrode active material layer may be a non-porous layer (solid layer) or a porous layer, but 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, and may be a layer made of metallic lithium foil (pure metallic lithium foil or lithium alloy foil). The average thickness of the negative electrode active material layer in the charged state may be, for example, 5 μm or more and 2,000 μm or less. The lower limit of the average thickness of one negative electrode active material layer in the charged state may be 10 μm, 20 μm, 30 μm, 50 μm, 100 μm, 200 μm, 300 μm, 400 μm, or 600 μm. The upper limit of the average thickness of one negative electrode active material layer in the charged state may be 1,500 μm, 1,200 μm, 800 μm, or 600 μm.

[0101] (Method of 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 then pressing the laminate. The negative electrode can also be manufactured, similarly to the above-described method for manufacturing a positive electrode, by applying a paste-like negative electrode mixture (negative electrode mixture paste) to the negative electrode substrate directly or via an intermediate layer, and then drying the paste to form a negative electrode active material layer.

[0102] 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.

[0103] (separator) The separator may be a known separator, such as a separator consisting of only a base layer, or a separator having an inorganic layer containing inorganic particles and a binder formed on one or both surfaces of a base layer.

[0104] Examples of the form of the substrate layer of the separator include woven fabric, nonwoven fabric, porous resin film, etc. Among these forms, porous resin film is preferred from the viewpoint of strength, etc., and nonwoven fabric is preferred from the viewpoint of non-aqueous electrolyte retention, etc. The material of the substrate layer of the separator is not particularly limited as long as it has insulating properties, but resins such as polyolefin (polyethylene, polypropylene, etc.), polyimide, aramid, etc. are preferred.

[0105] Examples of inorganic compounds constituting the inorganic particles include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, calcium oxide, and magnesium oxide; nitrides such as aluminum nitride and silicon nitride; carbonates such as calcium carbonate; sulfates such as barium sulfate; sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium titanate; covalently bonded crystals such as silicon; mineral-derived substances such as talc, zeolite, kaolin, bentonite, and mica, or artificial products thereof. One or more types of inorganic particles can be used. The average particle size of the inorganic particles is preferably, for example, from 0.5 μm to 10 μm. The content of the inorganic particles in the inorganic layer is preferably from 50% to 99% by mass, and more preferably from 80% to 98% by mass.

[0106] Examples of binders used in the inorganic layer include the same binders as those exemplified for the positive electrode active material layer.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] (electrode body) As the electrode body, for example, a wound type electrode body, a laminated type electrode body, or other electrode body having a known structure can be used.

[0111] A wound electrode body has a structure in which a positive electrode and a negative electrode are wound in an insulated state. The wound electrode body may be cylindrical (columnar) or flat. The electrode body 2 provided in the nonaqueous electrolyte storage element 1 of FIG. 1 is a flat wound electrode body. The wound electrode body can be produced, for example, by the following procedure. First, a positive electrode, a separator, and a negative electrode, each formed in a strip shape, are stacked together to obtain a laminate. This laminate is then wound to obtain a wound electrode body.

[0112] A laminated electrode body has a structure in which one or more positive electrodes and one or more negative electrodes are stacked in an insulated state. For example, a laminated electrode body can be obtained by stacking a positive electrode, a separator, and a negative electrode, each of which is formed in a rectangular shape.

[0113] 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.

[0114] (non-aqueous electrolyte) The nonaqueous electrolyte is a medium responsible for transporting charge-transporting ions (e.g., lithium ions) between a positive electrode and a negative electrode, and is substantially free of water. The water content in the nonaqueous electrolyte may be, for example, 10,000 ppm or less, or 5,000 ppm or less. The nonaqueous electrolyte includes an electrolyte salt, an ionic liquid, and a nonaqueous solvent. The nonaqueous solvent may be a nonionic compound. The nonaqueous electrolyte may be a nonaqueous electrolyte solution. In one embodiment of the present invention, the nonaqueous electrolyte storage element may be a nonaqueous electrolyte solution storage element.

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

[0116] The anions that make up the electrolyte salt are N(CF3SO2)2 - (Bis(trifluoromethanesulfonyl)imide anion: TFSI - ), N(SO2F)2 - (Bis(fluorosulfonyl)imide anion: FSI - ), N(C2F5SO2)2 - (bis(pentafluoroethanesulfonyl)imide anion), N(C4F9SO2)2 - (bis(nonafluorobutanesulfonyl)imide anion), N(POF2)2 - (bis(difluorophosphonyl)imide anion), N(CF3SO2)(CF3CO) - ((Trifluoromethanesulfonyl)(trifluoromethanecarbonyl)imide anion), N(CN)2 - (dicyanoimide anion), CF3-SO2-N-SO2-N-SO2CF3 - , FSO2-N-SO2-C4F9 - , CF3-SO2-N-SO2-C4F9 - , CF3-SO2-N-SO2-CF2-SO2-N-SO2-CF3 2- , CF3-SO2-N-SO2-CF2-SO3 2- , CF3-SO2-N-SO2-CF2-SO2-C(-SO2CF3)2 2- Examples of the anions that make up the electrolyte salt include imide anions such as PF6 - , PO2F2 - , BF4 - , ClO4 - , NO2 - , NO3 - , I- , SO3CF3 - , C(SO2CF3)3 - , C(SO2C2F5)3 - Anions other than imide anions such as the above can also be used.

[0117] 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, the overvoltage of the non-aqueous electrolyte storage element can be further reduced, and the occurrence of internal short circuits due to repeated charge and discharge can be further suppressed. One or more types of anions can be used to constitute the electrolyte salt.

[0118] The molar concentration of the electrolyte salt in the non-aqueous electrolyte is 0.8 mol / kg or more and 3.5 mol / kg or less. By having the molar concentration of the electrolyte salt within this range, the ionic conductivity of the non-aqueous electrolyte can be optimized, the overvoltage of the non-aqueous electrolyte storage element can be reduced, and the occurrence of internal short circuits due to repeated charge and discharge can be suppressed. The lower limit of the molar concentration of the electrolyte salt is preferably 1.0 mol / kg, more preferably 1.2 mol / kg, and even more preferably 1.5 mol / kg, and may be 2.0 mol / kg, 2.5 mol / kg, or 3.0 mol / kg. The upper limit of the molar concentration of the electrolyte salt is preferably 3.2 mol / kg, more preferably 3.0 mol / kg, and may be 2.5 mol / kg, 2.0 mol / kg, 1.5 mol / kg, or 1.0 mol / kg.

[0119] The molar ratio of the electrolyte salt to the ionic liquid (electrolyte salt / ionic liquid) is preferably 0.8 or more and 6.5 or less. By having the molar ratio (electrolyte salt / ionic liquid) within this range, the ionic conductivity of the non-aqueous electrolyte is optimized, which makes it possible to reduce the overvoltage of the non-aqueous electrolyte storage element and suppress the occurrence of internal short circuits due to repeated charge and discharge. The lower limit of the molar ratio (electrolyte salt / ionic liquid) is more preferably 0.80, and may be 0.82, 0.98, 1.04, 1.05, 1.36, 1.43, 1.46, 1.53, 1.63, 1.64, 1.93, 1.96, 2.15, 2.25, 3.00, 4.00, 5.00, 6.00, or 6.21. The upper limit of the molar ratio (electrolyte salt / ionic liquid) is more preferably 6.21, and may be 5.00, 4.00, 3.00, 2.25, 2.15, 1.96, 1.93, 1.64, 1.63, 1.53, 1.46, 1.43, 1.36, 1.05, 1.04, 0.98, or 0.82.

[0120] An ionic liquid is an ionic compound that is at least partially liquid at room temperature (20°C) under 1 atmosphere.

[0121] 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.

[0122] Examples of the quaternary ammonium cation include tetraalkylammonium cations such as trimethylethylammonium cation, trimethylpropylammonium cation, trimethylbutylammonium cation, trimethylhexylammonium cation, and tetrapentylammonium cation.

[0123] 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.

[0124] 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.

[0125] 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.

[0126] 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.

[0127] 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.

[0128] 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.

[0129] Examples of pyrrolinium-based cations include 1,2-dimethylpyrrolinium cation, 1-ethyl-2-methylpyrrolinium cation, 1-propyl-2-methylpyrrolinium cation, and 1-butyl-2-methylpyrrolinium cation.

[0130] 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.

[0131] Examples of the sulfonium cation include a trimethylsulfonium cation, a triethylsulfonium cation, and a tributylsulfonium cation.

[0132] 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 imidazolium cations. When the cations constituting the ionic liquid are such cations, the overvoltage of the nonaqueous electrolyte energy storage element can be further reduced, and the occurrence of internal short circuits due to repeated charge and discharge can be further suppressed. One or more of these cations may be contained.

[0133] Examples of anions constituting the ionic liquid include the same anions as those constituting the electrolyte salt. As an anion constituting the ionic liquid, imide anions are preferred, and bis(trifluoromethanesulfonyl)imide anion (TFSI - ) and bis(fluorosulfonyl)imide anion (FSI - ), and bis(fluorosulfonyl)imide anion (FSI - ) is more preferable. Furthermore, the anion constituting the ionic liquid preferably contains a fluorine atom. When the anion constituting the ionic liquid is such an anion, the overvoltage of the nonaqueous electrolyte storage element can be further reduced, and the occurrence of internal short circuits due to repeated charge and discharge can be further suppressed. One or more of these anions may be contained.

[0134] At least one of the electrolyte salt and the ionic liquid contains a bis(fluorosulfonyl)imide anion (FSI - It is preferable that the non-aqueous electrolyte contains a bis(fluorosulfonyl)imide anion (FSI) as an anion. -In this case, the overvoltage of the nonaqueous electrolyte storage element can be further reduced, and the occurrence of internal short circuits due to repeated charge and discharge can be further suppressed.

[0135] 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, the overvoltage of the non-aqueous electrolyte storage element can be further reduced, and the occurrence of internal short circuits due to repeated charge and discharge can be further suppressed.

[0136] The lower limit of the ionic liquid content relative to the total of the ionic liquid and the non-aqueous solvent is preferably 5% by volume, more preferably 10% by volume, and may be 20%, 24%, 30%, 36%, 40%, 50%, 59%, 60%, 70%, 80%, or 90% by volume. The upper limit of the content is preferably 90% by volume, and may be 80%, 70%, 60%, 59%, 50%, 40%, 36%, 30%, 24%, 20%, or 10% by volume. The higher the ionic liquid content, the more likely it is that internal short circuits caused by repeated charge and discharge of the non-aqueous electrolyte storage element will be suppressed.

[0137] The non-aqueous solvent contains a fluorinated cyclic ether. The fluorinated cyclic ether refers to an ether having a fluorine atom and a ring structure. The fluorinated cyclic ether may be composed only of carbon, hydrogen, oxygen, and fluorine. The oxygen atoms contained in the fluorinated cyclic ether are preferably only oxygen atoms constituting ether bonds. In other words, the fluorinated cyclic ether preferably does not have an oxygen-containing substituent such as a hydroxy group or a carboxy group. The fluorinated cyclic ether may be a monoether (a compound having only one ether bond), a diether (a compound having two ether bonds), a triether (a compound having three ether bonds), or the like, but is preferably a monoether. The fluorinated cyclic ether preferably has an ether bond in the ring structure. The fluorinated cyclic ether is preferably a saturated ether. 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).

[0138] The lower limit of the number of ring members in the ring structure of the fluorinated cyclic ether is preferably 4, 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 3, 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.

[0139] The fluorinated cyclic ether is preferably represented by the following formula (1). [ka] (In formula (1), R 1are each independently a hydrogen atom, a fluorine atom, an alkyl group having 1 to 4 carbon atoms, or a fluorinated alkyl group having 1 to 4 carbon atoms. 1 At least one of the groups is a fluorine atom or a fluorinated alkyl group having 1 to 4 carbon atoms. n1 is 4 or 5.

[0140] R in the above formula (1) 1 When R is an alkyl group or a fluorinated alkyl group, it preferably has 3 or less carbon atoms, more preferably 2 or less carbon atoms. 1 are each independently a hydrogen atom or a fluorine atom, and at least one is preferably a fluorine atom.

[0141] 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. One or more types of fluorinated cyclic ethers can be used.

[0142] The lower limit of the content of the fluorinated cyclic ether relative to the total of the ionic liquid and the non-aqueous solvent is preferably 5% by volume, more preferably 10% by volume. By setting the content at or above the lower limit, it is possible to further reduce overvoltage and further suppress the occurrence of internal short circuits due to repeated charge and discharge. The lower limit of the content may be 20%, 30%, 40%, 41%, 50%, 60%, 64%, 70%, or 76% by volume. The upper limit of the content is preferably 95%, more preferably 80%, and even more preferably 76% by volume. By setting the content at or below the upper limit, it is possible to further reduce overvoltage and further suppress the occurrence of internal short circuits due to repeated charge and discharge. The upper limit of the content may be 70%, 64%, 60%, 50%, 41%, 40%, 35%, 30%, 20%, or 10% by volume.

[0143] The lower limit of the total content of the ionic liquid and the fluorinated cyclic ether relative to the total of the ionic liquid and the non-aqueous solvent is preferably 20% by volume, more preferably 30% by volume, and even more preferably 40% by volume. By setting the total content at or above the lower limit, it is possible to further reduce the overvoltage of the non-aqueous electrolyte storage element and further suppress the occurrence of internal short circuits due to repeated charge and discharge. The lower limit of the total content may be 50%, 60%, 70%, 80%, 90%, or 95% by volume. The upper limit of the total content may be 100%, 95%, 90%, 80%, 70%, 60%, 50%, or 40% by volume.

[0144] In one embodiment of the present invention, the total content of the ionic liquid and the fluorinated cyclic ether relative to the total of the ionic liquid and the non-aqueous solvent may be 95% by volume or more and 100% by volume or less, and the content of the fluorinated cyclic ether may be 5% by volume or more and 35% by volume or less. When the non-aqueous electrolyte has such a composition, the occurrence of internal short circuits due to repeated charge and discharge of the non-aqueous electrolyte storage element can be particularly sufficiently suppressed.

[0145] The non-aqueous solvent may contain a solvent other than the fluorinated cyclic ether. The other solvent is preferably an ether other than the fluorinated cyclic ether. In one embodiment of the present invention, the non-aqueous solvent may further contain at least one solvent selected from the group consisting of a non-fluorinated cyclic ether and a chain ether.

[0146] The non-fluorinated cyclic ether may be a cyclic ether composed only of carbon, hydrogen, and oxygen. The oxygen element contained in the non-fluorinated cyclic ether is preferably only the oxygen element constituting the ether bond. In other words, the non-fluorinated cyclic ether preferably does not have an oxygen-containing substituent such as a hydroxy group or a carboxy group. The non-fluorinated cyclic ether may be any of a monoether, diether, triether, etc., but is preferably a monoether. The non-fluorinated cyclic ether preferably has an ether bond in the ring structure. The non-fluorinated cyclic ether is preferably a saturated ether.

[0147] The lower limit of the number of ring members in the ring structure of the non-fluorinated cyclic ether is preferably 4, more preferably 5. The upper limit of the number of ring members is preferably 8, more preferably 7, and even more preferably 6. The lower limit of the number of carbon atoms in the non-fluorinated cyclic ether is preferably 3, more preferably 4. The upper limit of the number of carbon atoms is preferably 7, more preferably 6, and even more preferably 5.

[0148] The non-fluorinated cyclic ether is preferably represented by the following formula (2). [ka] (In formula (2), R 2 are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms; and n2 is 4 or 5.

[0149] R in the above formula (2) 2When R is an alkyl group, it preferably has 3 or less carbon atoms, more preferably 2 or less carbon atoms. 2 is preferably a hydrogen atom.

[0150] Examples of non-fluorinated cyclic ethers include tetrahydrofuran, tetrahydropyran, etc. One or more non-fluorinated cyclic ethers can be used.

[0151] The lower limit of the content of the non-fluorinated cyclic ether relative to the total of the ionic liquid and the non-aqueous solvent may be 5 vol%, 10 vol%, 20 vol%, 30 vol%, 40 vol%, 50 vol%, or 60 vol%, and the upper limit of the content may be 80 vol%, 70 vol%, 60 vol%, 50 vol%, 40 vol%, 30 vol%, 20 vol%, or 10 vol%.

[0152] The chain ether may be a fluorinated chain ether or a non-fluorinated chain ether. The chain ether may be composed only of carbon, hydrogen, and oxygen, or may be composed only of carbon, hydrogen, oxygen, and fluorine. The oxygen element contained in the chain ether is preferably only the oxygen element constituting the ether bond. In other words, the chain ether preferably does not have an oxygen-containing substituent such as a hydroxy group or a carboxy group. The chain ether may be any of a monoether, diether, triether, etc., but is preferably a monoether or diether. The chain ether may be a fluorinated chain diether. The chain ether is preferably a saturated ether.

[0153] The lower limit of the number of carbon atoms in the chain ether is preferably 3, more preferably 4, and even more preferably 5. The upper limit of the number of carbon atoms is preferably 8, more preferably 7, and even more preferably 6. The lower limit of the number of fluorine atoms in the chain ether may be 0, or may be 1, 2, 3, 4, 5, or 6. The upper limit of the number of fluorine atoms is preferably 10, and may be 9, 8, 7, 6, 5, 4, or 3.

[0154] The chain ether is preferably represented by the following formula (3). [ka] (In formula (3), R 3 and R 4 are each independently an alkyl group having 1 to 3 carbon atoms or a fluorinated alkyl group having 1 to 3 carbon atoms. 5 is an alkanediyl group having 1 to 3 carbon atoms; and n3 is 0 or 1.

[0155] R in the above formula (3) 5 As -(CH2) m - (m is an integer of 1 or more and 3 or less) is preferred, and -CH2CH2- is more preferred.

[0156] Examples of chain ethers include 2-(2,2,2-trifluoroethoxy)ethyl methyl ether, ethyl-2-(2,2,2-trifluoroethoxy)ethyl ether, 2-(2,2-difluoroethoxy)ethyl methyl ether, ethyl-2-(2,2-difluoroethoxy)ethyl ether, 2-(2-fluoroethoxy)ethyl methyl ether, ethyl-2-(2-fluoroethoxy)ethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, bis(2,2,2-trifluoroethyl)ether, ethyl propyl ether, etc. One or more types of chain ethers can be used.

[0157] The lower limit of the amount of the chain ether relative to the total amount of the ionic liquid and the non-aqueous solvent may be 5, 10, or 20% by volume, and the upper limit of the amount may be 80, 70, 60, 50, 40, 30, 20, or 10% by volume.

[0158] The lower limit of the total content of the non-fluorinated cyclic ether and chain ether relative to the total of the ionic liquid and the non-aqueous solvent may be 5 vol%, 10 vol%, 20 vol%, 30 vol%, 40 vol%, 50 vol%, or 60 vol%, and the upper limit of the total content may be 80 vol%, 70 vol%, 60 vol%, 50 vol%, 40 vol%, 30 vol%, 20 vol%, or 10 vol%.

[0159] The nonaqueous solvent may further contain a nonaqueous solvent other than the fluorinated cyclic ether, the nonfluorinated cyclic ether, and the chain ether (i.e., ether). Examples of the other nonaqueous solvent include cyclic carbonates, chain carbonates, ethers, carboxylic acid esters, phosphate esters, amides, and nitriles. However, it is preferable that the nonaqueous solvent is composed essentially of ethers. The content of ethers (the total of the fluorinated cyclic ethers, the nonfluorinated cyclic ethers, and the chain ethers) in the nonaqueous solvent may be 90% by volume or more, 95% by volume or more, or 99% by volume or more. In this way, when the nonaqueous solvent is composed mainly of ethers, the overvoltage of the nonaqueous electrolyte storage element tends to be smaller, and the occurrence of internal short circuits tends to be further suppressed.

[0160] The total content of the ionic liquid and the ether (the total of the fluorinated cyclic ether, the non-fluorinated cyclic ether, and the chain ether) relative to the total of the ionic liquid and the non-aqueous solvent may be 90% by volume or more, 95% by volume or more, or 99% by volume or more, and the upper limit of the total content may be 100% by volume.

[0161] The total content of the ionic liquid and the ether (the sum of the fluorinated cyclic ether, the non-fluorinated cyclic ether, and the chain ether) relative to all components other than the electrolyte salt in the non-aqueous electrolyte may be 90% by volume or more, 95% by volume or more, or 99% by volume or more. Thus, when the non-aqueous electrolyte is primarily composed of the electrolyte salt, the ionic liquid, and the ether as the non-aqueous solvent, the overvoltage of the non-aqueous electrolyte storage element tends to be smaller and the occurrence of internal short circuits tends to be more suppressed. The upper limit of the total content may be 100% by volume.

[0162] The non-aqueous electrolyte may contain other components in addition to the electrolyte salt, ionic liquid, and non-aqueous solvent. Examples of other components include additives.

[0163] One or more additives can be used. When an additive is used in the non-aqueous electrolyte, the content of the additive in the non-aqueous electrolyte is preferably 0.01% by mass to 10% by mass, more preferably 0.1% by mass to 7% by mass, even more preferably 0.2% by mass to 5% by mass, and particularly preferably 0.3% by mass to 3% by mass.

[0164] The upper limit of the viscosity of the non-aqueous electrolyte at 25°C is preferably 143 mPa·s, more preferably 141.6 mPa·s. When the viscosity of the non-aqueous electrolyte is equal to or less than the upper limit, the overvoltage of the non-aqueous electrolyte storage element tends to be smaller, and the occurrence of internal short circuits tends to be further suppressed. The upper limit of the viscosity may be 139.4 mPa·s, 119.7 mPa·s, 65.9 mPa·s, 57.2 mPa·s, or 48.0 mPa·s. The lower limit of the viscosity may be, for example, 10 mPa·s, 20 mPa·s, 30 mPa·s, 40 mPa·s, or 48.0 mPa·s.

[0165] The lower limit of the ionic conductivity of the nonaqueous electrolyte at 25°C is preferably 1.0 mS / cm, more preferably 1.5 mS / cm, and may be 1.7 mS / cm, 1.9 mS / cm, or 2.0 mS / cm. When the ionic conductivity of the nonaqueous electrolyte is equal to or greater than the lower limit, the overvoltage of the nonaqueous electrolyte storage element tends to be smaller and the occurrence of internal short circuits tends to be more suppressed. The upper limit of the ionic conductivity may be, for example, 10 mS / cm, 8 mS / cm, 6 mS / cm, or 5 mS / cm.

[0166] The ionic conductivity is a value measured using a measuring device "VMP-300" manufactured by Biologic.

[0167] (container) The container accommodates the electrode assembly and the non-aqueous electrolyte in its internal space. The container may be made of a metal material such as aluminum or stainless steel, or a resin material. Metal materials are preferred from the viewpoint of strength, etc. Composite materials of metal and resin may also be used.

[0168] 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.

[0169] (shape, use, etc. of non-aqueous electrolyte storage element) The shape of the nonaqueous electrolyte storage element according to one embodiment of the present invention is not particularly limited, and may be, for example, a cylindrical battery, a prismatic battery, a flat battery, a coin battery, a button battery, or the like.

[0170] 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.

[0171] 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.

[0172] 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.

[0173] <Non-aqueous electrolyte> A non-aqueous electrolyte according to one embodiment of the present invention includes an electrolyte salt, an ionic liquid, and a non-aqueous solvent, wherein the non-aqueous solvent includes a fluorinated cyclic ether, and the molar concentration of the electrolyte salt is 0.8 mol / kg or more and 3.5 mol / kg or less.

[0174] A nonaqueous electrolyte according to one embodiment of the present invention is a nonaqueous electrolyte that uses an ionic liquid, and is capable of reducing the overvoltage of a nonaqueous electrolyte storage element and suppressing the occurrence of internal short circuits associated with repeated charge and discharge. Specific and preferred embodiments of the nonaqueous electrolyte according to one embodiment of the present invention are the same as those of the nonaqueous electrolyte used in the nonaqueous electrolyte storage element according to an embodiment of the present invention. However, 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, and more preferably in a nonaqueous electrolyte storage element having a negative electrode that contains metallic lithium at least in a charged state.

[0175] The non-aqueous electrolyte according to one embodiment of the present invention can be prepared by mixing the components.

[0176] <Method of manufacturing nonaqueous electrolyte energy storage element> A nonaqueous electrolyte storage element according to one embodiment of the present invention can be manufactured by a known method. A method for manufacturing a nonaqueous electrolyte storage element according to one embodiment of the present invention includes preparing a negative electrode containing metallic lithium at least in a charged state, and preparing a nonaqueous electrolyte containing an electrolyte salt, an ionic liquid, and a nonaqueous solvent, wherein the nonaqueous solvent contains a fluorinated cyclic ether, and the molar concentration of the electrolyte salt in the nonaqueous electrolyte is 0.8 mol / kg or more and 3.5 mol / kg or less. The manufacturing method may further include preparing a positive electrode, 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 nonaqueous electrolyte in a container. Housing the positive electrode, the negative electrode, and the nonaqueous electrolyte in a container may mean housing the electrode assembly and the nonaqueous electrolyte in the container.

[0177] 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. When preparing a negative electrode having a surface region on which metallic lithium can be deposited during charging, a positive electrode having a positive electrode active material containing lithium ions is prepared in advance. Preparing a nonaqueous electrolyte may mean preparing a nonaqueous electrolyte. Specific and preferred embodiments of the prepared positive electrode, negative electrode, nonaqueous electrolyte, etc. are the same as the specific and preferred embodiments of the positive electrode, negative electrode, nonaqueous electrolyte, etc. provided in the nonaqueous electrolyte storage element according to one embodiment of the present invention described above. The positive electrode, negative electrode, separator, nonaqueous electrolyte, etc. may be prepared by purchasing, etc.

[0178] 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.

[0179] The nonaqueous electrolyte electricity storage element according to one embodiment of the present invention may be manufactured by other methods.

[0180] <Electricity storage device> 2 includes a plurality of energy storage units 20. Each energy storage unit 20 includes a plurality of electrically connected nonaqueous electrolyte energy storage elements 1. The energy storage device 30 may include a bus bar (not shown) that electrically connects the plurality of nonaqueous electrolyte energy storage elements 1, a bus bar (not shown) that electrically connects the plurality of energy storage units 20, and the like. The energy storage unit 20 or the energy storage device 30 may include a state monitoring device (not shown) that monitors the state of one or more nonaqueous electrolyte energy storage elements 1.

[0181] <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.

[0182] 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.

[0183] In the above embodiment, the electrode assembly is described in which a separator is interposed between the positive electrode and the negative electrode. However, the electrode assembly may not include a separator. For example, the positive electrode and the negative electrode may be in direct contact with each other, with a non-conductive layer formed on the active material layer of the positive electrode or the negative electrode. In this way, the positive electrode and the negative electrode may further include layers other than the substrate, the intermediate layer, and the active material layer. Furthermore, the positive electrode and the negative electrode may not have a layer structure. [Example]

[0184] 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.

[0185] The components used in preparing the non-aqueous electrolytes of the Examples and Comparative Examples are shown below. (electrolyte salt) LiFSI: Lithium bis(fluorosulfonyl)imide (ionic liquid) Py13FSI: 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide EMIFSI: 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (non-aqueous solvent) TFTHF: 3,3,4,4-tetrafluorotetrahydrofuran THF: tetrahydrofuran THP: tetrahydropyran EPE: Ethyl propyl ether TFETFPE: 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether BTFEE: Bis(2,2,2-trifluoroethyl) ether TFEME: 2-(2,2,2-trifluoroethoxy)ethyl methyl ether EA: Ethyl acetate TFEA: 2,2,2-trifluoroethyl acetate

[0186] [Example 1] (Preparation of non-aqueous electrolyte) A non-aqueous electrolyte was prepared by mixing the ionic liquid Py13FSI and the non-aqueous solvent TFTHF in a volume ratio of 24:76, and adding the electrolyte salt LiFSI at a molar concentration of 1.00 mol / kg.

[0187] (Preparation of test cell) Two pure metal lithium foils were prepared as a pair of electrodes. A separator was prepared, in which inorganic particle layers were laminated on both sides of a polyethylene microporous membrane. A test cell (Li symmetric cell) of Example 1 was fabricated using the prepared nonaqueous electrolyte and the prepared pair of electrodes and separator.

[0188] [Examples 2 to 18, Comparative Examples 1 to 10] Test cells of Examples 2 to 18 and Comparative Examples 1 to 10 were obtained in the same manner as in Example 1, except that the composition of the non-aqueous electrolyte was as shown in Table 1. The contents of the ionic liquid, fluorinated cyclic ether, and other non-aqueous solvent in Table 1 are the contents relative to the total of the ionic liquid and non-aqueous solvent (fluorinated cyclic ether and other non-aqueous solvent). Table 1 also shows the molar ratio of electrolyte salt to ionic liquid (electrolyte salt / ionic liquid) in the non-aqueous electrolyte used in the test cells of the Examples and some Comparative Examples.

[0189] The viscosity and ionic conductivity of the nonaqueous electrolyte at 25° C. or 50° C. were measured by the above-described methods in each of the test cells of Examples 4, 5, 7, 8, 9, and 11 and Comparative Examples 1 and 7. The measurement results are shown in Table 2.

[0190] [evaluation] (Lithium dissolution and precipitation test) A lithium dissolution and deposition test was carried out on each test cell under the following conditions: 50°C, current density 5.0 mA / cm 2 and a capacity density of 10.0 mAh / cm 2 After applying the current for 10 minutes, the direction of the current was reversed and the same conditions were applied. After each application, a 10-minute rest period was provided. The above current application was repeated, and the number of cycles leading to an internal short circuit was determined. The overvoltage at the second cycle and the increase in the overvoltage at the ninth cycle relative to the overvoltage at the second cycle (overvoltage increase = overvoltage at the ninth cycle - overvoltage at the second cycle) were also determined. The results are shown in Table 1.

[0191] [Table 1]

[0192] [Table 2]

[0193] In the test cell of Comparative Example 1, which used a nonaqueous electrolyte consisting only of electrolyte salt and ionic liquid, the number of cycles leading to an internal short circuit was high, but the overvoltage was also high. In contrast, the test cells of Comparative Examples 2 to 8, in which only a chain ether, a non-fluorinated cyclic ether, or an ester was further added to the nonaqueous electrolyte, and the test cell of Comparative Example 9, in which the nonaqueous electrolyte did not contain an ionic liquid, were unable to achieve both a low overvoltage and a high number of cycles leading to an internal short circuit. Furthermore, the test cell of Comparative Example 10, in which the nonaqueous electrolyte further contained a fluorinated cyclic ether but the electrolyte salt concentration was low, showed a high overvoltage and a low number of cycles leading to an internal short circuit. In contrast, in the test cells of Examples 1 to 18, in which a fluorinated cyclic ether was further added to the nonaqueous electrolyte containing an electrolyte salt and an ionic liquid, and the electrolyte salt concentration was adjusted within a predetermined range, the overvoltage was small and the number of cycles leading to an internal short circuit was large. Note that when the overvoltage in the second cycle was 105 mV or less, the overvoltage was evaluated as small, and when the number of cycles leading to an internal short circuit was 22 or more, the number of cycles leading to an internal short circuit was evaluated as large, and the occurrence of an internal short circuit due to repeated charge and discharge was evaluated as being suppressed. Furthermore, among the Examples, in the test cells of Examples 4, 5, 7, 8, 9, and 11, in which the total content of the ionic liquid and the fluorinated cyclic ether relative to the total of the ionic liquid and the non-aqueous solvent was 95% by volume or more and 100% by volume or less, and the content of the fluorinated cyclic ether was 5% by volume or more and 35% by volume or less, the number of cycles leading to an internal short circuit was 34 or more, and the occurrence of an internal short circuit due to repeated charging and discharging was particularly suppressed. [Industrial Applicability]

[0194] The present invention can be applied to nonaqueous electrolyte storage elements used as power sources for electronic devices such as personal computers and communication terminals, automobiles, industrial equipment, and the like. [Explanation of symbols]

[0195] 1. Non-aqueous electrolyte energy storage element 2 Electrode body 3 containers 4 Positive lead 5 Positive external terminal 6 Negative lead 7 Negative external terminal 20 Energy storage unit 30 Electricity storage device

Claims

1. a negative electrode containing metallic lithium at least in a charged state; a non-aqueous electrolyte containing an electrolyte salt, an ionic liquid, and a non-aqueous solvent; Equipped with the non-aqueous solvent contains a fluorinated cyclic ether, The nonaqueous electrolyte storage element has a molar concentration of the electrolyte salt in the nonaqueous electrolyte of 0.8 mol / kg or more and 3.5 mol / kg or less.

2. 2. The nonaqueous electrolyte storage element according to claim 1, wherein the content of the fluorinated cyclic ether relative to the total of the ionic liquid and the nonaqueous solvent is 5% by volume or more and 95% by volume or less.

3. 2. The nonaqueous electrolyte storage element according to claim 1, wherein the content of the fluorinated cyclic ether relative to the total of the ionic liquid and the nonaqueous solvent is 5% by volume or more and 80% by volume or less.

4. 3. The nonaqueous electrolyte storage element according to claim 1, wherein a molar ratio of the electrolyte salt to the ionic liquid is 0.8 or more and 6.5 or less.

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

6. 6. The nonaqueous electrolyte storage element according to claim 5, wherein the total content of the non-fluorinated cyclic ether and the chain ether relative to the total of the ionic liquid and the nonaqueous solvent is 5% by volume or more and 80% by volume or less.

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

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

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

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

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

12. The electrolytic solution includes an electrolyte salt, an ionic liquid, and a non-aqueous solvent. the non-aqueous solvent contains a fluorinated cyclic ether, The non-aqueous electrolyte has a molar concentration of the electrolyte salt of 0.8 mol / kg or more and 3.5 mol / kg or less.

13. The non-aqueous electrolyte according to claim 12, which is for use in a non-aqueous electrolyte storage element having a negative electrode containing metallic lithium at least in a charged state.

14. providing a negative electrode comprising metallic lithium at least in a charged state; preparing a non-aqueous electrolyte containing an electrolyte salt, an ionic liquid, and a non-aqueous solvent; Equipped with the non-aqueous solvent contains a fluorinated cyclic ether, a method for producing a nonaqueous electrolyte storage element, wherein the nonaqueous electrolyte has a molar concentration of the electrolyte salt of 0.8 mol / kg or more and 3.5 mol / kg or less;

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