Nonaqueous electrolyte energy storage device, nonaqueous electrolyte, and method for producing nonaqueous electrolyte energy storage device

Abstract

Provided are a nonaqueous electrolyte energy storage device in which a nonaqueous electrolyte containing an ionic liquid is used and which has a large discharge capacity even when the mass per unit area of a positive electrode active material layer is relatively large, a method for producing such a nonaqueous electrolyte energy storage device, and a nonaqueous electrolyte containing an ionic liquid, which can increase the discharge capacity of a nonaqueous electrolyte energy storage device even when the mass per unit area of a positive electrode active material layer is relatively large.SOLUTION: A nonaqueous electrolyte energy storage device according to an aspect of the present invention includes a positive electrode containing a sulfur-based active material, and a nonaqueous electrolyte containing an electrolyte salt, an ionic liquid, and a nonaqueous solvent represented by the following formula (1): R-O - (CH2) 2-O-Rf (1) (in the formula (1), R is an alkyl group having 1 or more and 3 or less carbon atoms). Rf is a fluorinated alkyl group having 1 or more and 3 or less carbon atoms. ) SELECTED DRAWING: Figure 1

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] Known non-aqueous electrolyte storage elements include lithium-sulfur batteries (Li-S batteries) and other non-aqueous electrolyte storage elements that use a sulfur-based active material as the positive electrode active material (see Patent Document 1). In recent years, research has also been progressing on non-aqueous electrolyte storage elements that use an ionic liquid 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. 2010-95390 [Patent Document 2] Japanese Patent Application Laid-Open No. 2001-319688 Summary of the Invention [Problem to be solved by the invention]

[0005] Sulfur-based active materials have a large theoretical capacity, and nonaqueous electrolyte storage elements using sulfur-based active materials as the positive electrode active material are expected to have high energy densities. Nonaqueous electrolyte storage elements including positive electrodes using sulfur-based active materials are also expected to have further improvements in discharge capacity, etc. In order to increase the energy density per volume of nonaqueous electrolyte storage elements, it is conceivable to increase the mass per unit area of ​​the active material layer, i.e., to thicken the active material layer. However, in nonaqueous electrolyte storage elements including a nonaqueous electrolyte containing an ionic liquid, increasing the mass per unit area of ​​the positive electrode active material layer tends to significantly decrease the discharge capacity.

[0006] An object of the present invention is to provide a nonaqueous electrolyte storage element that uses a nonaqueous electrolyte containing an ionic liquid and that has a large discharge capacity even when the mass per unit area of ​​the positive electrode active material layer is relatively large, a method for manufacturing such a nonaqueous electrolyte storage element, and a nonaqueous electrolyte that contains an ionic liquid and that can increase the discharge capacity of a nonaqueous electrolyte storage element even when the mass per unit area of ​​the positive electrode active material layer is relatively large. [Means for solving the problem]

[0007] A nonaqueous electrolyte storage element according to one aspect of the present invention includes a positive electrode containing a sulfur-based active material, and a nonaqueous electrolyte containing an electrolyte salt, an ionic liquid, and a nonaqueous solvent represented by the following formula (1). RO-(CH2)2-O-Rf (1) (In formula (1), R is an alkyl group having 1 to 3 carbon atoms. Rf is a fluorinated alkyl group having 1 to 3 carbon atoms.)

[0008] A nonaqueous electrolyte storage element according to another aspect of the present invention comprises a positive electrode containing a sulfur-based active material, and a nonaqueous electrolyte containing an electrolyte salt, an ionic liquid, and a nonaqueous solvent, the nonaqueous solvent being a mixture of 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide and the nonaqueous solvent in a molar ratio of 70:30, with 2.0 mol / dm lithium bis(fluorosulfonyl)imide added, as calculated based on classical molecular dynamics calculations. 3 The lithium ion diffusion coefficient at 300 K of the hypothetical electrolyte containing -8 cm 2 / s or more.

[0009] A non-aqueous electrolyte according to another aspect of the present invention includes an electrolyte salt, an ionic liquid, and a non-aqueous solvent represented by the following formula (1): RO-(CH2)2-O-Rf (1) (In formula (1), R is an alkyl group having 1 to 3 carbon atoms. Rf is a fluorinated alkyl group having 1 to 3 carbon atoms.)

[0010] A non-aqueous electrolyte according to another aspect of the present invention comprises an electrolyte salt, an ionic liquid, and a non-aqueous solvent, and the non-aqueous solvent is a mixture of 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide and the non-aqueous solvent in a molar ratio of 70:30, to which 2.0 mol / dm lithium bis(fluorosulfonyl)imide is added, as calculated based on classical molecular dynamics calculations. 3 The lithium ion diffusion coefficient at 300 K of the hypothetical electrolyte containing -8 cm 2 / s or more.

[0011] A method for manufacturing a nonaqueous electrolyte storage element according to one aspect of the present invention includes preparing a positive electrode containing a sulfur-based active material and preparing the nonaqueous electrolyte according to one aspect of the present invention. [Effects of the Invention]

[0012] According to any one aspect of the present invention, it is possible to provide a nonaqueous electrolyte storage element that uses a nonaqueous electrolyte containing an ionic liquid, and that has a large discharge capacity even when the mass per unit area of ​​the positive electrode active material layer is relatively large; a method for manufacturing such a nonaqueous electrolyte storage element; and a nonaqueous electrolyte that contains an ionic liquid and that can increase the discharge capacity of a nonaqueous electrolyte storage element even when the mass per unit area of ​​the positive electrode active material layer is relatively large. [Brief explanation of the drawings]

[0013] [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

[0014] 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.

[0015] [1] A nonaqueous electrolyte storage element according to one aspect of the present invention includes a positive electrode containing a sulfur-based active material, and a nonaqueous electrolyte containing an electrolyte salt, an ionic liquid, and a nonaqueous solvent represented by the following formula (1): RO-(CH2)2-O-Rf (1) (In formula (1), R is an alkyl group having 1 to 3 carbon atoms. Rf is a fluorinated alkyl group having 1 to 3 carbon atoms.)

[0016] The nonaqueous electrolyte storage element described in [1] above is a nonaqueous electrolyte storage element using a nonaqueous electrolyte containing an ionic liquid, and has a large discharge capacity even when the mass per unit area of ​​the positive electrode active material layer is relatively large. In other words, the nonaqueous electrolyte storage element described in [1] above is a nonaqueous electrolyte storage element using a nonaqueous electrolyte containing an ionic liquid, and has a positive electrode active material layer with a small mass per unit area (for example, a mass per unit area of ​​3 mg / cm2 When a positive electrode active material layer having a relatively large mass per unit area (for example, a mass per unit area of ​​10 mg / cm) is provided, 2 The discharge capacity is large regardless of whether or not a positive electrode active material layer (positive electrode active material layer) is provided. While the reason for this is unclear, the following is presumed. In a nonaqueous electrolyte storage element using a nonaqueous electrolyte containing an ionic liquid, when the mass per unit area of ​​the positive electrode active material layer is relatively large, one possible reason for the insufficient discharge capacity is that the nonaqueous electrolyte containing an ionic liquid has high viscosity and low diffusibility of charge-transporting ions. When the nonaqueous electrolyte has high viscosity, particularly when a positive electrode active material layer with a large mass per unit area, i.e., a thick positive electrode active material layer or a positive electrode active material layer with a high apparent density, is provided, the charge-transporting ions in the nonaqueous electrolyte are less likely to diffuse in the thickness direction of the positive electrode active material layer, and therefore sufficient discharge capacity is not achieved. In contrast, in the case of the nonaqueous electrolyte storage element described in [1] above, the nonaqueous electrolyte contains both an ionic liquid and a nonaqueous solvent represented by the above formula (1). The nonaqueous solvent represented by the formula (1) is thought to have a viscosity significantly lower than that of an ionic liquid and a high compatibility with the ionic liquid. A nonaqueous electrolyte containing such a nonaqueous solvent is thought to have a sufficiently low viscosity and high diffusibility of charge-transporting ions. Because the nonaqueous electrolyte described in [1] uses such a nonaqueous electrolyte, it is thought that even when a positive electrode active material layer with a relatively large mass per unit area is provided, charge-transporting ions in the nonaqueous electrolyte can be favorably diffused in the thickness direction of the positive electrode active material layer. For these reasons, the nonaqueous electrolyte storage element described in [1] is thought to have a large discharge capacity even when the positive electrode active material layer has a relatively large mass per unit area and uses a nonaqueous electrolyte containing an ionic liquid.

[0017] 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.

[0018] 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.

[0019] [2] A nonaqueous electrolyte storage element according to another aspect of the present invention includes a positive electrode containing a sulfur-based active material, and a nonaqueous electrolyte containing an electrolyte salt, an ionic liquid, and a nonaqueous solvent. The nonaqueous solvent is a mixture of 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide and the nonaqueous solvent in a molar ratio of 70:30, and lithium bis(fluorosulfonyl)imide at 2.0 mol / dm 3 The lithium ion diffusion coefficient at 300 K of the hypothetical electrolyte containing -8 cm 2 / s or more.

[0020] The nonaqueous electrolyte storage element described in [2] above is a nonaqueous electrolyte storage element that uses a nonaqueous electrolyte containing an ionic liquid, and exhibits a high discharge capacity even when the mass per unit area of ​​the positive electrode active material layer is relatively large. While the reason for this is unclear, the following is presumed. The nonaqueous solvent used in the nonaqueous electrolyte provided in the nonaqueous electrolyte storage element described in [2] above is a solvent calculated to produce a nonaqueous electrolyte with a high lithium ion diffusion coefficient when mixed with an ionic liquid. Therefore, the nonaqueous electrolyte provided in the nonaqueous electrolyte storage element described in [2] above is also presumed to have high charge-transport ion diffusivity. Because the nonaqueous electrolyte storage element described in [2] above uses such a nonaqueous electrolyte, it is presumed that, for the same reasons as the nonaqueous electrolyte storage element described in [1] above, a nonaqueous electrolyte storage element that uses a nonaqueous electrolyte containing an ionic liquid and exhibits a high discharge capacity even when the mass per unit area of ​​the positive electrode active material layer is relatively large. The calculation procedure based on classical molecular dynamics calculations will be described in detail later.

[0021] In order to solve the problem of providing a nonaqueous electrolyte storage element using a nonaqueous electrolyte containing an ionic liquid, which has a large discharge capacity even when the mass per unit area of ​​the positive electrode active material layer is relatively large, it is possible to increase the diffusibility of charge-transporting ions by, for example, simply selecting a nonaqueous solvent or ionic liquid with a low viscosity or by reducing the viscosity of the nonaqueous electrolyte. However, for example, the viscosities of the nonaqueous electrolytes used in Examples 1, 4, and Comparative Example 1 described below are similar, and it is not possible to solve the problem simply by reducing the viscosity of the nonaqueous electrolyte. This is thought to be due to, for example, the complex interactions between the compatibility of the ionic liquid and the nonaqueous solvent. Therefore, various factors must be considered when selecting a suitable nonaqueous solvent to solve the problem. In this context, the present inventors have discovered that the value of the lithium ion diffusion coefficient calculated for a specific virtual electrolyte is a suitable parameter for selecting a nonaqueous solvent that can solve the problem, leading to the nonaqueous electrolyte storage element described in [2] above.

[0022] [3] In the nonaqueous electrolyte storage element according to [1], R is a methyl group or an ethyl group, and Rf is -CHCH n F 3-n (n is 0, 1 or 2).

[0023] The nonaqueous electrolyte storage element described in [3] above has a larger discharge capacity even when the mass per unit area of ​​the positive electrode active material layer is relatively large. Note that, hereinafter, when simply referring to a "larger discharge capacity," unless otherwise specified, this also means that the discharge capacity of the nonaqueous electrolyte storage element is large even when the mass per unit area of ​​the positive electrode active material layer is relatively large.

[0024] [4] In the nonaqueous electrolyte storage element according to the above item [2], the nonaqueous solvent may have 20 or less donors.

[0025] In non-aqueous electrolyte storage devices that use sulfur-based active materials in the positive electrode, polysulfides (Li2S x ) is difficult to dissolve in a nonaqueous solvent with a donor number of 20 or less. In the case of a nonaqueous electrolyte storage element including a nonaqueous electrolyte using such a nonaqueous solvent, the charge-discharge reaction does not proceed by a shuttle reaction caused by the elution of polysulfides formed in the positive electrode into the nonaqueous electrolyte, but rather by the solid-phase diffusion of charge-transporting ions within the sulfur-based active material. Therefore, in the case of a nonaqueous electrolyte storage element including a nonaqueous electrolyte using a nonaqueous solvent with a donor number of 20 or less, the shuttle reaction, i.e., the eluted LiS x It is believed that the capacity decrease due to the above (loss of active material and increase in viscosity of the non-aqueous electrolyte) is unlikely to occur, and that a large discharge capacity can be maintained even when the mass per unit area of ​​the positive electrode active material layer is large. Therefore, the non-aqueous electrolyte storage element described in [4] above has a large discharge capacity.

[0026] The donor number is a parameter that represents the electron-pair donating ability of a solvent, and is defined as the negative value of the enthalpy of formation of a 1:1 adduct between antimony pentachloride in 1,2-dichloroethane and the target solvent. In this specification, the donor number is the value determined by the method described in Viktor Gutmann, "The Donor-Acceptor Approach to Molecular Interactions," Springer, 1978 (ISBN-13:978-0306310645).

[0027] [5] In the nonaqueous electrolyte storage element according to the above [2] or [4], the nonaqueous solvent may be a fluorinated ether.

[0028] The nonaqueous electrolyte electricity storage element described in [5] above has a larger discharge capacity.

[0029] [6] In the nonaqueous electrolyte storage element according to the above [2], [4] or [5], the electrolyte salt is a lithium salt, and the nonaqueous electrolyte has a lithium ion diffusion coefficient of 2.0 × 10 at 300 K calculated based on classical molecular dynamics calculations. -8 cm 2 The electrolyte may be a non-aqueous electrolyte having a conductivity of 1 / s or more.

[0030] The nonaqueous electrolyte electricity storage element described in [6] above has a larger discharge capacity.

[0031] [7] In the nonaqueous electrolyte storage element according to any one of [1] to [6] above, the molar ratio of the ionic liquid to the nonaqueous solvent (ionic liquid / nonaqueous solvent) may be within a range of 5 / 95 to 95 / 5.

[0032] The nonaqueous electrolyte storage element described in [7] above has a larger discharge capacity because the molar ratio of the ionic liquid to the nonaqueous solvent is within a suitable range.

[0033] The number of moles of an ionic liquid is based on its composition formula. For example, if an ionic liquid contains a +1 cation (A + ) and a divalent anion (B2- When the formula is A2B, it means the number of moles of "A2B" and one cation (A + ) or anion (B 2- ) and the number of moles of cations (A + ) and the number of moles of anion (B 2- ) does not mean the total number of moles.

[0034] [8] In the nonaqueous electrolyte storage element according to any one of [1] to [7] above, the molar ratio of the ionic liquid to the nonaqueous solvent (ionic liquid / nonaqueous solvent) may be within a range of 5 / 95 to 60 / 40.

[0035] The nonaqueous electrolyte storage element described in [8] above has a larger discharge capacity due to the molar ratio of the ionic liquid to the nonaqueous solvent being within a suitable range. In particular, the nonaqueous electrolyte described in [8] above contains a sufficient amount of nonaqueous solvent in the nonaqueous electrolyte, which reduces the viscosity of the nonaqueous electrolyte, and therefore is highly effective in improving the discharge capacity when a positive electrode active material layer having a relatively large mass per unit area is provided.

[0036] [9] In the nonaqueous electrolyte storage element according to any one of [1] to [8] above, the total content of the ionic liquid and the nonaqueous solvent relative to all components other than the electrolyte salt in the nonaqueous electrolyte may be 80 mol % or more.

[0037]

[10] In the nonaqueous electrolyte storage element according to any one of [1] to [9] 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.

[0038]

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

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

[0039]

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

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

[0040] The nonaqueous electrolyte storage elements described in [9] to

[12] above are all suitable embodiments of the present invention, and have a larger discharge capacity.

[0041]

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

[12] above, the viscosity of the nonaqueous electrolyte at 25° C. may be 100 mPa·s or less.

[0042] The nonaqueous electrolyte storage element described in

[13] above has a large discharge capacity because the viscosity of the nonaqueous electrolyte is particularly sufficiently reduced.

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

[0044]

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

[13] above, wherein the electrolyte salt is a lithium salt, and the lithium ion conductivity of the nonaqueous electrolyte at 25°C is 4.5 × 10 -4 It may be S / cm or more.

[0045] The nonaqueous electrolyte storage element described in

[14] above has a larger discharge capacity because the nonaqueous electrolyte has particularly high lithium ion conductivity.

[0046] Lithium ion conductivity is calculated by multiplying the ionic conductivity of a nonaqueous electrolyte by the lithium ion transport number. The ionic conductivity of a nonaqueous electrolyte is determined based on AC impedance measurements performed using a Biologic VMP-300 measuring device. The temperature of the nonaqueous electrolyte to be measured is set to 25°C, and the nonaqueous electrolyte is sealed in an ionic conductivity measurement cell using a platinum blocking electrode as the target electrode. Specifically, the measurement is performed using the above measuring device, and the results are plotted as a Nyquist plot. The measurement conditions are an applied voltage amplitude of 5 mV, a frequency range of 1 MHz to 100 mHz, and a measurement temperature of 25°C. For nonaqueous electrolytes with no arc component in the Nyquist plot, if the values ​​on the imaginary axis are less than 0 at all measurement points, the value on the real axis at the highest frequency is taken as resistance R; otherwise, the value on the real axis at the intersection of the approximation line of the measurement points and the real axis is taken as resistance R. For non-aqueous electrolytes where an arc component is observed in the Nyquist plot, the value on the real axis at the end point of the arc on the low frequency side is taken as the resistance R. Lithium ion conductivity σ 25 (mScm -1 ) is the resistance R (Ω), the electrode distance L (cm), and the electrode area A (cm 2 ) and calculate it using the following formula (A). σ 25 =L / (RA) (A)

[0047] Lithium-ion (Li + The transference number of ) is calculated by the following formula: Lithium ion transport number =(Li + Diffusion coefficient of Li + (product of the diffusion coefficient of each ion contained in the non-aqueous electrolyte and its molar ratio) / (sum of the products of the diffusion coefficient of each ion contained in the non-aqueous electrolyte and its molar ratio) For example, in a non-aqueous electrolyte, Li ions are added. + and Py13 + (1-methyl-1-propylpyrrolidinium cation) and FSI - When the non-aqueous electrolyte contains bis(fluorosulfonyl)imide anion, the "sum of the products of the diffusion coefficients of each ion contained in the non-aqueous electrolyte and their molar ratios" is Li + Diffusion coefficient of Li+ and the product of the molar ratio of Py13 + Diffusion coefficient of Py13 + and the product of the molar ratio of FSI - Diffusion coefficient and FSI - The sum of the product of the molar ratios The molar ratio of each ion refers to the molar ratio of the content of each ion based on the total amount of all ions contained in the non-aqueous electrolyte.

[0048] The diffusion coefficient of ions such as lithium ions is a value measured under the following conditions using a pulsed field gradient nuclear magnetic resonance (PFG-NMR) method. (Measurement conditions) Equipment: JEOL JNM-ECA400WB Sample tube: 5mm Shigemi symmetrical micro sample tube Observation kernel: 7 Li, 1 H, 19 F (For example, in a non-aqueous electrolyte, Li ions are + and Py13 + and FSI - If it contains 7 Li is Li + is the observation kernel of 1 H is for Py13 + is the observation kernel of 19 F is for FSI - The observation nucleus is set appropriately depending on the type of element that constitutes each ion contained in the non-aqueous electrolyte that is the observation target. Measurement sequence: Bipolar Gradient Stimulated Echo with LED Measurement temperature: 25℃ The attenuation of the signal intensity of the PFG-NMR spectrum assigned to each ion of each observed nucleus with changes in the magnetic field gradient strength (g) of the sample is plotted according to the following formula, and each plot is approximated by a linear function using the least squares method, and the diffusion coefficient D is calculated from the slope of the approximate line.

[0049]

number

[0050]

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

[14] above, wherein the positive electrode has a positive electrode active material layer containing the sulfur-based active material, and the mass per unit area of ​​the positive electrode active material layer is 5 mg / cm 2 It may be more than that.

[0051] The nonaqueous electrolyte storage element according to the above

[15] has a positive electrode active material layer having a mass per unit area of ​​5 mg / cm 2 As a result, the energy density per unit volume of the nonaqueous electrolyte energy storage element can be increased. Furthermore, the nonaqueous electrolyte energy storage element described in

[15] above can achieve both a high energy density per unit volume and a large discharge capacity.

[0052] Mass per unit area of ​​the positive electrode active material layer (mg / cm 2 ) is the area of ​​the positive electrode active material layer (1 cm 2 ) is the mass (mg) of the positive electrode active material layer per 1000 μm of positive electrode active material layer. The area of ​​the positive electrode active material layer refers to the area of ​​one of the front and back surfaces (two surfaces other than the side surfaces) of one positive electrode active material layer. That is, for example, when the positive electrode active material layer is provided by coating, the area of ​​the positive electrode active material layer is equal to the area where the positive electrode active material layer is coated. When the positive electrode active material layer is provided on both surfaces of the positive electrode substrate, the area and mass of the positive electrode active material layer refer to the area and mass of one positive electrode active material layer. For example, when the positive electrode active material layer is provided on both surfaces of the positive electrode substrate with a thickness of 10 mg / cm, the area and mass of the positive electrode active material layer are equal to the area where the positive electrode active material layer is coated. 2 When the coating amount (solid content equivalent) is 10 mg / cm, the "mass per unit area of ​​the positive electrode active material layer" is 10 mg / cm. 2 The positive electrode active material layer is 10 mg / cm on one side of the positive electrode substrate. 2 Even if the coating amount (solid content equivalent) is 10 mg / cm, the "mass per unit area of ​​the positive electrode active material layer" is 10 mg / cm. 2 is.

[0053]

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

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

[0054] The nonaqueous electrolyte electricity storage element described in

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

[0055]

[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 represented by the following formula (1): RO-(CH2)2-O-Rf (1) (In formula (1), R is an alkyl group having 1 to 3 carbon atoms. Rf is a fluorinated alkyl group having 1 to 3 carbon atoms.)

[0056] The nonaqueous electrolyte described in

[17] above is a nonaqueous electrolyte containing an ionic liquid, and can increase the discharge capacity of a nonaqueous electrolyte storage element even when the mass per unit area of ​​the positive electrode active material layer is relatively large.

[0057]

[18] A nonaqueous electrolyte according to another aspect of the present invention includes an electrolyte salt, an ionic liquid, and a nonaqueous solvent, and the nonaqueous solvent is a mixture of 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide and the nonaqueous solvent in a molar ratio of 70:30, with 2.0 mol / dm lithium bis(fluorosulfonyl)imide added, as calculated based on classical molecular dynamics calculations. 3 The lithium ion diffusion coefficient at 300 K of the hypothetical electrolyte containing -8 cm 2 / s or more.

[0058] The nonaqueous electrolyte described in

[18] above is a nonaqueous electrolyte containing an ionic liquid, and can increase the discharge capacity of a nonaqueous electrolyte storage element even when the mass per unit area of ​​the positive electrode active material layer is relatively large.

[0059]

[19] The nonaqueous electrolyte according to either

[17] or

[18] above may be used for a nonaqueous electrolyte storage element having a positive electrode containing a sulfur-based active material.

[0060]

[20] A method for manufacturing a nonaqueous electrolyte storage element according to another aspect of the present invention includes preparing a positive electrode containing a sulfur-based active material and preparing the nonaqueous electrolyte according to any one of

[17] to

[19] above.

[0061] According to the method for producing a nonaqueous electrolyte storage element described in

[20] above, it is possible to produce a nonaqueous electrolyte storage element that uses a nonaqueous electrolyte containing an ionic liquid and has a large discharge capacity even when the mass per unit area of ​​the positive electrode active material layer is relatively large.

[0062] 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.

[0063] <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.

[0064] 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.

[0065] 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.

[0066] The lower and upper limits of each numerical range described in the embodiments of the present invention can be combined in any manner.

[0067] (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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] The positive electrode active material layer contains a sulfur-based active material. The positive electrode active material layer contains optional components such as a conductive agent, a binder, a dispersant, a thickener, and a filler, as necessary. The positive electrode active material layer may be formed from a positive electrode mixture containing a 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.

[0075] The sulfur-based active material is a component that functions as a positive electrode 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 a large theoretical capacity and low cost.

[0076] The content of the sulfur-based active material in the positive electrode active material layer is preferably 50% by mass to 90% by mass, more preferably 55% by mass to 80% by mass, and even more preferably 60% by mass to 70% by mass. By having the content of the sulfur-based active material in the above range, it is possible to further increase the discharge capacity, etc.

[0077] The positive electrode active material layer preferably further includes porous carbon forming a composite with the sulfur-based active material. In other words, the sulfur-based active material is preferably contained in the positive electrode active material layer as a composite with porous carbon. Hereinafter, the composite of the sulfur-based active material and porous carbon will also be simply referred to as a "composite." In the composite, the sulfur-based active material is usually supported in the pores of the porous carbon. This form of the composite ensures sufficient electronic conductivity. The composite may be substantially composed of only the sulfur-based active material and porous carbon, or may be substantially composed of only the sulfur-based active material and porous carbon. A composite substantially composed of only the sulfur-based active material and porous carbon means, for example, that the total content of the sulfur-based active material (sulfur elemental substance and sulfur compound) and porous carbon in the composite is 90% by mass or more, and may be 95% by mass or more, 98% by mass or more, or 99% by mass or more.

[0078] The content of the sulfur-based active material in the composite is preferably 50% by mass to 90% by mass, more preferably 60% by mass to 80% by mass. By setting the content of the sulfur-based active material in the composite within this range, it is possible to further increase the discharge capacity, etc.

[0079] Porous carbon has electrical conductivity. Porous carbon is generally a porous inorganic material whose main constituent element is carbon. The main constituent element refers to the element that is most abundant by mass. The lower limit of the carbon content in porous carbon is preferably 70 mass%, more preferably 80 mass%, 90 mass%, 95 mass%, or 97 mass%. The upper limit of the carbon content in porous carbon may be 100 mass% or 99.9 mass%. The carbon content in porous carbon may be within a range that combines any of the above-mentioned lower limits and any of the above-mentioned upper limits. Porous carbon may also contain elements other than carbon, such as oxygen and nitrogen.

[0080] The composite can be produced by a conventional method, for example, by heating a mixture of a sulfur-based active material and porous carbon to a temperature equal to or higher than the melting point of the sulfur-based active material, and then cooling the mixture.

[0081] The content of the composite in the positive electrode active material layer is preferably 60% by mass to 97% by mass, more preferably 80% by mass to 96% by mass, and even more preferably 90% by mass to 95% by mass. By setting the content of the composite within the above range, it is possible to further increase the discharge capacity, etc.

[0082] The positive electrode active material layer may contain a positive electrode active material other than the sulfur-based active material, provided that the content of the sulfur-based active material in the total positive electrode active material is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, even more preferably 99% by mass or more, and particularly preferably 100% by mass.

[0083] The conductive agent is usually a component made of a material with electrical conductivity. Note that this conductive agent does not include the porous carbon that constitutes the composite. Even if the volume resistivity of the conductive agent cannot be measured directly, it is possible to estimate the volume resistivity by measuring the volume resistivity of the conductive agent. -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. The conductive agent is preferably carbon black or CNT, and acetylene black is more preferred as the carbon black. It is also preferred to use carbon black (preferably acetylene black) and CNT in combination.

[0084] The content of the conductive agent (excluding the porous carbon in the composite) 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. The upper limit of the content of the conductive agent may be 8%, 5%, 4%, 3%, or 2% by mass. By setting the content of the conductive agent within the above range, it is possible to increase the energy density of the nonaqueous electrolyte storage element.

[0085] Examples of the binder include a water-based binder and an organic solvent-based binder.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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 sulfur-based active material, etc. The technology disclosed herein can also be implemented in an embodiment in which the positive electrode active material layer does not contain a binder.

[0090] Examples of dispersants include polysaccharide polymers such as carboxymethyl cellulose (CMC) and methyl cellulose. When the dispersant has a functional group that reacts with lithium or the like, the functional group may be deactivated in advance by methylation or the like. The content of the dispersant in the positive electrode active material layer is preferably 0.05% by mass or more and 5% by mass or less, and more preferably 0.1% by mass or more and 2% by mass or less. The polysaccharide polymer may function as a thickener or a binder.

[0091] Examples of thickeners include polyacrylic acid (PAA). The content of the thickener in the positive electrode active material layer is preferably 0.05% by mass or more and 5% by mass or less, and more preferably 0.1% by mass or more and 4% by mass or less. Polyacrylic acid may function as a binder.

[0092] The filler is not particularly limited. The filler may be a component other than the positive electrode active material (sulfur-based active material and other positive electrode active materials), conductive agent, binder, dispersant, and thickener, and may be 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, usually 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.

[0093] The positive electrode active material layer may further contain other components in addition to the positive electrode active material, conductive agent, binder, dispersant, 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.

[0094] The lower limit of the mass per unit area of ​​the positive electrode active material layer is, for example, 1 mg / cm 2 3 mg / cm 2 may be 5 mg / cm 2 is preferred, and 7 mg / cm 2 More preferably, 9 mg / cm 2is more preferably 10 mg / cm 2 By setting the mass per unit area of ​​the positive electrode active material layer to the above lower limit or more, it is possible to increase the energy density per volume of the nonaqueous electrolyte storage element. The upper limit of the mass per unit area of ​​the positive electrode active material layer is 30 mg / cm. 2 20 mg / cm 2 , 15 mg / cm 2 , 10 mg / cm 2 , 7 mg / cm 2 or 5 mg / cm 2 By setting the mass per unit area of ​​the positive electrode active material layer to the above upper limit or less, it is possible to further increase the discharge capacity, etc. The mass per unit area of ​​the positive electrode active material layer can be set within a range that combines any of the above upper limits and any of the above lower limits (however, the upper limit is greater than the lower limit).

[0095] (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 typically contains a sulfur-based active material, other optional components, and a dispersion medium. After drying, the positive electrode active material layer may be pressed, etc.

[0096] (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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] The negative electrode active material layer contains a negative electrode active material. The negative electrode active material layer contains optional components such as a conductive agent, a binder, a dispersant, a thickener, and a filler as needed. The optional components such as the conductive agent, the binder, the dispersant, the thickener, and the filler can be selected from the materials exemplified for the positive electrode above. The negative electrode active material layer may be formed from a negative electrode mixture containing a negative electrode active material and other optional components. The negative electrode active material layer may be provided on only one side or on both sides of a negative electrode substrate having a shape such as a sheet.

[0103] The negative electrode active material can be a known negative electrode active material. A material capable of absorbing and releasing lithium ions is typically used as the negative electrode active material for lithium ion secondary batteries. Examples of the negative electrode active material include metallic lithium; metals or semimetals such as silicon and tin; metal oxides or semimetal oxides such as silicon oxide, titanium oxide, and tin oxide; and Li4Ti5O. 12 , LiTiO 2、 Examples of the negative electrode active material include titanium-containing oxides such as TiNb2O7; polyphosphate compounds; silicon carbide; and carbon materials such as graphite and non-graphitic carbon. Among these materials, carbon materials are preferred, and graphite or non-graphitic carbon may be more preferred. The surface of graphite may be coated with other materials such as non-graphitic carbon. One or more negative electrode active materials may be used. In the case of a negative electrode active material that does not contain charge transport ions such as lithium ions, a material doped with charge transport ions such as lithium ions may be used.

[0104] The negative electrode active material is preferably metallic lithium. In other words, the negative electrode or the negative electrode active material layer preferably contains metallic lithium at least in a charged state. It is more preferable that the negative electrode or the negative electrode active material layer contains metallic lithium in all states, including a charged state and a discharged state.

[0105] 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.

[0106] The negative electrode active material layer is preferably a layer consisting essentially 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%. The lithium element content in the negative electrode active material layer may be within a range that combines any of the above-mentioned lower limits with the above-mentioned upper limit.

[0107] 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.

[0108] 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.

[0109] When the negative electrode active material layer contains a dispersant, the content of the dispersant in the negative electrode active material layer is preferably 0.05% by mass or more and 5% by mass or less, and more preferably 0.1% by mass or more and 2% by mass or less. The content of the dispersant in the negative electrode active material layer may be 1% by mass or less, or may be 0.1% by mass or less. The technology disclosed herein may also be implemented in an embodiment in which the negative electrode active material layer does not contain a dispersant.

[0110] 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.

[0111] The filler in the negative electrode active material layer may be a component other than the negative electrode active material, conductive agent, binder, dispersant, and thickener, and may be an intentionally contained component. The filler may be contained as a component to fill gaps in the negative electrode active material layer, or may be contained for 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.

[0112] The negative electrode active material layer may further contain other components in addition to the negative electrode active material, conductive agent, binder, dispersant, thickener, and filler. The other components include those unintentionally present in the negative electrode active material layer. The negative electrode active material layer may also contain unintentionally contained impurities as the other components, as long as the effects of the present invention are achieved. The upper limit of the content of the other components in the negative electrode active material layer may be 10% by mass, 5%, 2%, 1%, 0.1%, or 0.01% by mass. The upper limit of the content of the unintentionally contained components in the negative electrode active material layer may be 10% by mass, 5%, 2%, 1%, 0.1%, or 0.01% by mass. The upper limit of the content of the unintentionally contained impurities in the negative electrode active material layer may be 10% by mass, 5%, 2%, 1%, 0.1%, or 0.01% by mass.

[0113] The negative electrode active material layer may be a non-porous layer (solid layer) or a porous layer, but is preferably a non-porous layer. The negative electrode active material layer may be a layer of metallic lithium. The negative electrode active material layer may be a layer made of metallic lithium foil (pure metallic lithium foil or lithium alloy foil). The average thickness of the negative electrode active material layer in a charged state may be, for example, 5 μm or more and 2,000 μm or less. The lower limit of the average thickness of one negative electrode active material layer in a charged state may be 10 μm, 20 μm, 30 μm, 50 μm, 100 μm, 200 μm, 300 μm, 400 μm, or 600 μm. The upper limit of the average thickness of one negative electrode active material layer in a charged state may be 1,500 μm, 1,200 μm, 800 μm, or 600 μm. The average thickness of one negative electrode active material layer in a charged state can be set within a range that is a combination of any of the above-mentioned lower limits and any of the above-mentioned upper limits.

[0114] (Method of manufacturing negative electrode) The negative electrode can be manufactured by a known method. The negative electrode can be manufactured, for example, in the same manner as in the above-described method for manufacturing a positive electrode, by applying a paste-like negative electrode mixture (negative electrode mixture paste) to a negative electrode substrate directly or via an intermediate layer, and then drying the applied mixture to form a negative electrode active material layer. After drying, the negative electrode active material layer may be pressed, for example. When the negative electrode active material is a metal such as metallic lithium, the negative electrode can also be manufactured by laminating a metal foil on the negative electrode substrate directly or via an intermediate layer, and then pressing the metal foil.

[0115] (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.

[0116] 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.

[0117] 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.

[0118] Examples of binders used in the inorganic layer include the same binders as those exemplified for the positive electrode active material layer.

[0119] 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.

[0120] 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.

[0121] 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.

[0122] (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.

[0123] 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.

[0124] 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.

[0125] 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.

[0126] (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 contains an electrolyte salt, an ionic liquid, and a nonaqueous solvent. 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.

[0127] 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.

[0128] 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.

[0129] The anion constituting the electrolyte salt is preferably an imide anion, and more preferably a bis(trifluoromethanesulfonyl)imide anion (TFSI -) and bis(fluorosulfonyl)imide anion (FSI - ), and bis(fluorosulfonyl)imide anion (FSI - ) is more preferred. That is, the electrolyte salt is preferably an imide salt, more preferably at least one selected from the group consisting of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium bis(fluorosulfonyl)imide (LiFSI), and even more preferably lithium bis(fluorosulfonyl)imide (LiFSI). In addition, the anion constituting the electrolyte salt preferably has a fluorine atom. When the anion constituting the electrolyte salt is such an anion, the ionic conductivity of the non-aqueous electrolyte is increased, and the discharge capacity of the non-aqueous electrolyte storage element can be further increased. One or more types of anions can be used as the anion constituting the electrolyte salt.

[0130] The content of the electrolyte salt in the non-aqueous electrolyte is 0.3 mol / dm at 20°C and 1 atmosphere. 3 More than 3.0mol / dm 3 The lower limit of the content of the electrolyte salt is preferably 0.5 mol / dm 3 is preferred, and 0.8 mol / dm 3 More preferably, 1.2 mol / dm 3 , 1.6 mol / dm 3 , 1.8 mol / dm 3 or 2.0 mol / dm 3 The upper limit of the content of the electrolyte salt is 2.8 mol / dm 3 More preferably, 2.5 mol / dm 3 , 2.2 mol / dm 3 or 2.0 mol / dm 3 By setting the content of the electrolyte salt within the above range, the ionic conductivity of the non-aqueous electrolyte can be optimized, and the discharge capacity of the non-aqueous electrolyte storage element can be increased.

[0131] An ionic liquid is an ionic compound that is at least partially liquid at room temperature (20°C) under 1 atmosphere.

[0132] 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.

[0133] Examples of the quaternary ammonium cation include tetraalkylammonium cations such as trimethylethylammonium cation, trimethylpropylammonium cation, trimethylbutylammonium cation, trimethylhexylammonium cation, and tetrapentylammonium cation.

[0134] 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.

[0135] 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.

[0136] 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.

[0137] 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.

[0138] 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.

[0139] 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.

[0140] 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.

[0141] 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.

[0142] Examples of the sulfonium cation include a trimethylsulfonium cation, a triethylsulfonium cation, and a tributylsulfonium cation.

[0143] The cation constituting the ionic liquid is preferably at least one selected from the group consisting of quaternary ammonium cations, imidazolium cations, pyrrolidinium cations, piperidinium cations, quaternary phosphonium cations, and sulfonium cations, more preferably at least one selected from the group consisting of imidazolium cations, pyrrolidinium cations, and piperidinium cations, and even more preferably a pyrrolidinium cation. When the cation constituting the ionic liquid is such a cation, the discharge capacity of the nonaqueous electrolyte storage element can be further increased. One or more of these cations may be contained.

[0144] 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 has a fluorine atom. When the anion constituting the ionic liquid is such an anion, the discharge capacity of the nonaqueous electrolyte storage element can be further increased. One or more of these anions may be contained.

[0145] 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 discharge capacity of the nonaqueous electrolyte storage element can be increased.

[0146] 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 80 mol % or more, more preferably 90 mol % or more, even more preferably 99 mol % or more, and even more preferably 99.9 mol % or more. By configuring the anions in the non-aqueous electrolyte in this way, the ionic conductivity of the non-aqueous electrolyte can be increased, and the discharge capacity of the non-aqueous electrolyte storage element can be increased, for example.

[0147] In one embodiment of the present invention, the non-aqueous solvent is a non-aqueous solvent (X1) represented by the following formula (1). RO-(CH2)2-O-Rf (1) (In formula (1), R is an alkyl group having 1 to 3 carbon atoms. Rf is a fluorinated alkyl group having 1 to 3 carbon atoms.)

[0148] The nonaqueous solvent (X1) is considered to be a solvent that has a viscosity sufficiently lower than that of an ionic liquid and is highly compatible with the ionic liquid. The nonaqueous solvent (X1) also has the advantage of being less likely to dissolve polysulfides. Use of such a nonaqueous solvent (X1) can increase the discharge capacity of the nonaqueous electrolyte storage element. One or more types of nonaqueous solvent (X1) can be used.

[0149] Examples of the alkyl group having 1 to 3 carbon atoms represented by R in formula (1) include a methyl group, an ethyl group, a propyl group, and a 1-methylethyl group, with a methyl group or an ethyl group being preferred.

[0150] The fluorinated alkyl group refers to a group in which at least one hydrogen atom of an alkyl group is substituted with a fluorine atom. Examples of the fluorinated alkyl group having 1 to 3 carbon atoms and represented by Rf in formula (1) include a group in which at least one hydrogen atom of an alkyl group having 1 to 3 carbon atoms and represented by R is substituted with a fluorine atom. The lower limit of the number of fluorine atoms in Rf is 1, preferably 2, and more preferably 3. The upper limit of the number of fluorine atoms is, for example, 6, and may be 5, 4, or 3. The number of carbon atoms in Rf is preferably 2.

[0151] Rf is -CH2CH n F 3-n (n is 0, 1 or 2). Preferably, n is 0.

[0152] In one embodiment of the present invention, the non-aqueous solvent is a mixture of 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide (Py13FSI) and the non-aqueous solvent in a molar ratio of 70:30, to which lithium bis(fluorosulfonyl)imide (LiFSI) is added at 2.0 mol / dm 3 The lithium ion diffusion coefficient (calculated value) at 300 K of the hypothetical electrolyte containing -8 cm 2 / s or more.

[0153] The nonaqueous solvent (X2) is a solvent calculated to obtain a nonaqueous electrolyte having sufficient ionic conductivity when mixed with an ionic liquid. By using such a nonaqueous solvent (X2), it is possible to increase the discharge capacity of the nonaqueous electrolyte energy storage element. The lower limit of the lithium ion diffusion coefficient (calculated value) of the above hypothetical electrolyte at 300 K is 2.3 × 10 -8 cm 2 / s is preferred, 2.4 × 10 -8 cm 2 / s is more preferable, 2.6 × 10 -8 cm 2 / s, 2.9 × 10 -8 cm 2 / s or 3.0 × 10 -8 cm 2 The upper limit of the lithium ion diffusion coefficient (calculated value) of the above virtual electrolyte at 300 K is 5.0 × 10 -8 cm 2 / s, 4.0 x 10 -8 cm 2 / s, 3.5 × 10 -8 cm 2 / s, 3.2 × 10 -8 cm 2 / s, 3.1 × 10 -8 cm 2 / s, 3.0 × 10 -8 cm 2 / s or 2.9 × 10 -8 cm 2 / s. The lithium ion diffusion coefficient (calculated value) of the virtual electrolyte at 300 K can be within a range that combines any of the above-mentioned lower limits and any of the above-mentioned upper limits (however, the upper limit is greater than the lower limit). One or more types of non-aqueous solvent (X2) can be used.

[0154] The calculation procedure based on the classical molecular dynamics calculations is described in detail below. The calculations are performed in the order of equilibration calculations and main calculations. The Large-scale Atomic / Molecular Massively Parallel Simulator (LAMMPS) software is used for the following calculations. GAFF2 is applied as the force field parameters for molecules and ions, and the parameters for lithium ions are those from Aqvist et al. (Aqvist, J. Ion-Water Interaction Potentials Derived from Free Energy Perturbation Simulations. The Journal of Physical Chemistry 1990, 94(21), 8021-8024.) are used as is. The charges for molecules and ions are calculated using the RESP method and assigned using the Antechamber program. The RESP charges are calculated using the General Atomic and Molecular Electronic Structure System (GAMESS) program at the B3LYP / 6-31G(d,p) level, and then scaled by a factor of 0.7. The time step in the molecular dynamics calculation is set to 1.0 fs, and the temperature and pressure are controlled by the Nose-Hoover method.

[0155] (Equilibrium calculation) For the initial structure, a cubic cell is used in which the constituent molecules and ions are randomly arranged and filled using the Packmol program. 200 molecules of Py13FSI are used as the base, and LiFSI is added at 2.0 mol / dm to a mixed liquid with the non-aqueous solvent of the calculation target at a molar ratio of 70:30. 3 The density of the virtual electrolyte is 0.8 g / cm 3 Create it so that it becomes: For the above model, the atomic coordinates are optimized to minimize the energy, and then calculations are performed in the following order for the (a) NVT, (b) NPT, and (c) NVT ensemble to determine the thermodynamically equilibrium structure (density, distribution). (a) NVT calculation: temperature 300K, calculation time 10ps (b) NPT calculation: (1) Temperature 300K, pressure 1atm, calculation time 50ps, (2) Temperature 300K to 700K at a constant rate, pressure 1atm, calculation time 500ps, (3) Temperature 700K, pressure 1atm, calculation time 250ps, (4) Temperature 700K to 300K at a constant rate, pressure 1atm, calculation time 500ps, (5) Temperature 300K, pressure 1atm, calculation time 1ns (c) NVT calculation: temperature 300K, calculation time 500ps

[0156] (Main calculation) Based on the structure equilibrated by the above equilibration calculation, the diffusion coefficients of lithium ions and cations and anions of Py13FSI at 300 K are calculated by (d) NVT calculation under the following conditions: (d) NVT calculation: temperature 300K, calculation time 3000ps Specifically, the mean square displacement is calculated from the time-dependent changes in the coordinates of the lithium ions and the cations and anions of Py13FSI. At this time, only the central nitrogen atom is considered for the cations and anions of Py13FSI, and the diffusion coefficient of each ion is calculated from the slope of the mean square displacement versus time for each ion. The diffusion coefficient is calculated by creating multiple structures with different initial structures for one composition (3 structures), calculating the diffusion coefficient for each, and then taking the average to obtain the final value. In addition, the lithium ion transport number t Li+ is calculated using the following formula from the diffusion coefficients of lithium ions and the cations and anions of Py13FSI.

[0157]

number

[0158] The mixture of Py13FSI and non-aqueous solvent (X2) in a molar ratio of 70:30 was calculated by the above method. LiFSI was added at 2.0 mol / dm 3 The lithium ion (Li +) diffusion coefficient (calculated value) and lithium ion (Li + The transference numbers (calculated values) of Py13FSI and the non-aqueous solvent (X2) were actually measured by adding 2.0 mol / dm LiFSI to a mixed liquid of Py13FSI and a non-aqueous solvent (X2) in a molar ratio of 70:30. 3 The lithium ion (Li + ) diffusion coefficient (experimental value) and lithium ion (Li + ) and the transference number (experimental value) are also shown.

[0159] [Table 1]

[0160] In Table 1, TFEME is 2-(2,2,2-trifluoroethoxy)ethyl methyl ether (a compound represented by formula (1) in which R is a methyl group and Rf is —CH2CF3), ETFEEE is ethyl-2-(2,2,2-trifluoroethoxy)ethyl ether (a compound represented by formula (1) in which R is an ethyl group and Rf is —CH2CF3); DFEME is 2-(2,2-difluoroethoxy)ethyl methyl ether (a compound represented by formula (1) in which R is a methyl group and Rf is -CH2CHF2), EDFEE is ethyl-2-(2,2-difluoroethoxy)ethyl ether (a compound represented by formula (1) in which R is an ethyl group and Rf is -CH2CHF2), TFETFPE stands for 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether. The lithium ion diffusion coefficient (calculated value) of TFETFPE obtained by the above method is 2.0 × 10 -8 cm 2 / s, so it does not fall under the category of non-aqueous solvent (X2).

[0161] As shown in Table 1, the calculated lithium ion diffusion coefficients obtained by the above calculations have a high correlation with the experimental values. Furthermore, as will be shown in the examples described later, the calculated lithium ion diffusion coefficients obtained by the above calculations are 2.0 × 10 -8 cm 2 When a nonaqueous solvent (X2) having a solubility of 1 / s or more is used, the discharge capacity of the nonaqueous electrolyte electricity storage element can be increased.

[0162] In addition, the non-aqueous solvent (X2) has a high calculated and experimental value of the transference number of lithium ions obtained by the above calculation. 3 The lower limit of the lithium ion transport number (calculated value) at 300 K of the virtual electrolyte containing the above content is preferably 0.110, more preferably 0.115, still more preferably 0.120, or may be 0.126. The upper limit of the lithium ion transport number (calculated value) of the virtual electrolyte at 300 K may be 0.150, or may be 0.140, 0.130, 0.126, or 0.120. The lithium ion transport number (calculated value) of the virtual electrolyte at 300 K may be within a range that combines any of the above lower limits and any of the above upper limits (however, the upper limit is greater than the lower limit).

[0163] The number of donors in the nonaqueous solvent (X2) is preferably 20 or less. Use of a nonaqueous solvent (X2) having a donor number of 20 or less can increase the discharge capacity. For example, the donor number of TFEME is 14.4, the donor number of ETFEEE is 9.6, the donor number of DFEME is 15.0, and the donor number of EDFEE is 9.9. The upper limit of the donor number is preferably 18, more preferably 16, and may be 15, 14, 13, 12, 11, or 10. The lower limit of the donor number is preferably 1, and may be 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, or 14. The donor number can be within a range that combines any of the above-mentioned lower limits and any of the above-mentioned upper limits (however, the upper limit is greater than the lower limit).

[0164] The nonaqueous solvent (X2) is preferably a fluorinated solvent, more preferably a fluorinated ether. A fluorinated solvent is a solvent containing a fluorine element, and a fluorinated ether is an ether containing a fluorine element. The nonaqueous solvent (X2) is also preferably a chain solvent. A chain solvent is a solvent (molecule) having a molecular structure without a ring structure. A particularly suitable embodiment of the nonaqueous solvent (X2) is the above-mentioned nonaqueous solvent (X1). Use of such a nonaqueous solvent (X2) can further increase the discharge capacity of the nonaqueous electrolyte storage element. Hereinafter, the nonaqueous solvent (X1) and the nonaqueous solvent (X2) will be collectively referred to as the nonaqueous solvent (X).

[0165] The molar ratio of the ionic liquid to the nonaqueous solvent (X) (ionic liquid / nonaqueous solvent (X)) is preferably within a range of 5 / 95 to 99 / 5. By setting the molar ratio of the ionic liquid to the nonaqueous solvent (X) within this range, the ratio of the ionic liquid to the nonaqueous solvent becomes a suitable range, and the discharge capacity can be further increased. The threshold A of the range of the molar ratio (ionic liquid / nonaqueous solvent (X)) may be 90 / 10, 80 / 20, 70 / 30, 60 / 40, 50 / 50, 40 / 60, 35 / 65, or 30 / 70. By setting the molar ratio (ionic liquid / nonaqueous solvent (X)) to be lower than the threshold A of the range, i.e., by increasing the molar ratio of the nonaqueous solvent (X), the viscosity of the nonaqueous electrolyte can be further reduced, and the discharge capacity of a nonaqueous electrolyte storage element having a positive electrode active material layer with a large mass per unit area can be further increased. The threshold B of the range of the above molar ratio (ionic liquid / non-aqueous solvent (X)) may be 10 / 90, 20 / 80, 30 / 70, 40 / 60, 50 / 50, 60 / 40, or 70 / 30. The above molar ratio (ionic liquid / non-aqueous solvent (X)) can be set within a range that combines any of the above thresholds A and any of the above thresholds B (however, threshold A is a larger molar ratio of the ionic liquid than threshold B).

[0166] The lower limit of the total content of the ionic liquid and nonaqueous solvent (X) relative to all components other than the electrolyte salt in the nonaqueous electrolyte is preferably 80 mol%, more preferably 90 mol%, even more preferably 95 mol%, and even more preferably 99 mol%. Thus, when the nonaqueous electrolyte is primarily composed of the electrolyte salt, the ionic liquid, and the nonaqueous solvent (X), the discharge capacity of the nonaqueous electrolyte storage element tends to be greater. The upper limit of the total content may be 100 mol%.

[0167] The non-aqueous electrolyte may contain other components in addition to the electrolyte salt, the ionic liquid, and the non-aqueous solvent (X). Examples of other components include a non-aqueous solvent other than the non-aqueous solvent (X), an additive, and the like.

[0168] The other non-aqueous solvents are non-aqueous solvents that do not fall under the category of the non-aqueous solvent (X), and examples thereof include cyclic carbonates, chain carbonates, ethers, carboxylic acid esters, phosphate esters, amides, and nitriles.

[0169] 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.

[0170] The upper limit of the viscosity of the non-aqueous electrolyte at 25°C may be, for example, 500 mPa·s, 400 mPa·s, 300 mPa·s, or 200 mPa·s, but is preferably 100 mPa·s, more preferably 80 mPa·s, and even more preferably 70 mPa·s, and may be 60 mPa·s, 50 mPa·s, 40 mPa·s, or 30 mPa·s. Having a viscosity of the non-aqueous electrolyte equal to or less than the upper limit allows the discharge capacity of the non-aqueous electrolyte storage element to be increased. The lower limit of the viscosity may be 1 mPa·s, or may be 3 mPa·s, 5 mPa·s, 10 mPa·s, 20 mPa·s, or 30 mPa·s. The viscosity may be within a range that combines any of the upper and lower limits described above.

[0171] The viscosity of the non-aqueous electrolyte tends to decrease, for example, by increasing the content of the non-aqueous solvent (X), decreasing the content of the electrolyte salt, etc. The viscosity of the non-aqueous electrolyte can also be adjusted by the types of the electrolyte salt, ionic liquid, and non-aqueous solvent (X), etc.

[0172] When the non-aqueous electrolyte contains a lithium salt as an electrolyte salt, the lower limit of the lithium ion conductivity of the non-aqueous electrolyte at 25°C is 4.5 × 10 -4 S / cm is preferred, 5.0×10 -4 S / cm is more preferable, 5.5 × 10 -4 S / cm is more preferable, and 6.0×10 -4 S / cm, 7.0 x 10 -4 S / cm, 8.0 x 10 -4 S / cm or 9.0 x 10 -4 S / cm. When the lithium ion conductivity of the nonaqueous electrolyte is equal to or higher than the lower limit, the discharge capacity of the nonaqueous electrolyte energy storage element can be increased. The upper limit of the ion conductivity is, for example, 15.0 × 10 -4 S / cm, and 12.0 × 10 -4 S / cm, 10.0 x 10 -4 S / cm, 8.0 x 10 -4 S / cm, 7.0 x 10 -4 S / cm or 6.0 x 10 -4It may be S / cm.

[0173] When the non-aqueous electrolyte contains a lithium salt as an electrolyte salt, the lower limit of the lithium ion diffusion coefficient (calculated value) of the non-aqueous electrolyte at 300 K is 2.0 × 10 -8 cm 2 / s is preferred, 2.3 × 10 -8 cm 2 / s is more preferable, 2.4 × 10 -8 cm 2 / s is more preferable, and 2.6 × 10 -8 cm 2 / s, 2.9 × 10 -8 cm 2 / s or 3.0 × 10 -8 cm 2 / s. When the lithium diffusion coefficient (calculated value) of the nonaqueous electrolyte is equal to or greater than the lower limit, the discharge capacity of the nonaqueous electrolyte energy storage element can be increased. The upper limit of the lithium ion diffusion coefficient (calculated value) is 5.0 × 10 -8 cm 2 / s, 4.0 x 10 -8 cm 2 / s, 3.5 × 10 -8 cm 2 / s, 3.2 × 10 -8 cm 2 / s, 3.1 × 10 -8 cm 2 / s, 3.0 × 10 -8 cm 2 / s or 2.9 × 10 -8 cm 2 / s is also acceptable.

[0174] The lithium ion diffusion coefficient (calculated value) of the non-aqueous electrolyte at 300 K is a value calculated based on classical molecular dynamics calculations. This calculation is performed using the same procedure as for the lithium ion diffusion coefficient (calculated value) of the virtual electrolyte described above. That is, the lithium ion diffusion coefficient (calculated value) of the non-aqueous electrolyte at 300 K is a value calculated by applying the calculation procedure based on the classical molecular dynamics calculations described above to the composition of an actual non-aqueous electrolyte.

[0175] When the non-aqueous electrolyte contains a lithium salt as an electrolyte salt, the lower limit of the lithium ion diffusion coefficient (experimental value) of the non-aqueous electrolyte at 25°C is 0.5 × 10 -7 cm 2 / s is preferred, 1.0 × 10 -7 cm 2 / s is more preferable, 1.4 × 10 -7 cm 2 / s is more preferable. When the lithium diffusion coefficient (experimental value) of the nonaqueous electrolyte is equal to or greater than the lower limit, the discharge capacity of the nonaqueous electrolyte energy storage element can be increased. The upper limit of the lithium ion diffusion coefficient (experimental value) is 5.0 × 10 -7 cm 2 / s, 4.0 x 10 -7 cm 2 / s, 3.0 × 10 -7 cm 2 / s or 2.4 × 10 -7 cm 2 / s is also acceptable.

[0176] When the non-aqueous electrolyte contains a lithium salt as the electrolyte salt, the lower limit of the lithium ion transport number (experimental value) of the non-aqueous electrolyte at 25°C is preferably 0.10, more preferably 0.12, and even more preferably 0.14. When the lithium ion transport number (experimental value) of the non-aqueous electrolyte is equal to or greater than the lower limit, the discharge capacity of the non-aqueous electrolyte storage element can be increased. The upper limit of the lithium ion transport number (experimental value) may be 0.30, 0.25, or 0.20.

[0177] (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.

[0178] 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.

[0179] (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.

[0180] 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.

[0181] 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.

[0182] 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.

[0183] <Non-aqueous electrolyte> A non-aqueous electrolyte according to one embodiment of the present invention contains an electrolyte salt, an ionic liquid, and a non-aqueous solvent (X1) represented by the following formula (1). RO-(CH2)2-O-Rf (1) (In formula (1), R is an alkyl group having 1 to 3 carbon atoms. Rf is a fluorinated alkyl group having 1 to 3 carbon atoms.)

[0184] Furthermore, a non-aqueous electrolyte according to another embodiment of the present invention includes an electrolyte salt, an ionic liquid, and a non-aqueous solvent (X2). The non-aqueous solvent (X2) is a mixture of 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide and the non-aqueous solvent (X2) in a molar ratio of 70:30, to which 2.0 mol / dm lithium bis(fluorosulfonyl)imide is added, as calculated based on classical molecular dynamics calculations. 3 The lithium ion diffusion coefficient at 300 K of the hypothetical electrolyte containing -8 cm 2 / s or more.

[0185] The nonaqueous electrolyte according to the embodiment of the present invention is a nonaqueous electrolyte containing an ionic liquid, and can increase the discharge capacity of a nonaqueous electrolyte storage element even when the mass per unit area of ​​the positive electrode active material layer is relatively large. Specific and preferred embodiments of the nonaqueous electrolyte according to the embodiment of the present invention are the same as those described above as the nonaqueous electrolyte used in the nonaqueous electrolyte storage element according to the embodiment of the present invention. However, the use of the nonaqueous electrolyte according to the 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 positive electrode containing a sulfur-based active material.

[0186] The non-aqueous electrolyte according to the embodiment of the present invention can be prepared by, for example, mixing the components.

[0187] <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. The manufacturing method of the nonaqueous electrolyte storage element includes, for example, preparing a positive electrode containing a sulfur-based active material, preparing a negative electrode, preparing a nonaqueous electrolyte, and housing the positive electrode, negative electrode, and nonaqueous electrolyte in a container. The manufacturing method may also include preparing a separator, and manufacturing an electrode assembly using the positive electrode, negative electrode, and separator. Housing the positive electrode, negative electrode, and nonaqueous electrolyte in a container may include housing the electrode assembly and nonaqueous electrolyte in the container.

[0188] Preparing a positive electrode containing a sulfur-based active material may mean manufacturing a positive electrode containing a sulfur-based active material. Manufacturing a positive electrode containing a sulfur-based active material may be performed by the method described above. Preparing a negative electrode may mean manufacturing a negative electrode. Manufacturing a negative electrode may be performed by the method described above. The nonaqueous electrolyte prepared by preparing a nonaqueous electrolyte is the nonaqueous electrolyte according to the embodiment of the present invention described above. Preparing a nonaqueous electrolyte may mean preparing a nonaqueous electrolyte. The positive electrode, negative electrode, separator, nonaqueous electrolyte, etc. may be prepared by purchasing, etc.

[0189] The electrode assembly (or the positive electrode and negative electrode) and the non-aqueous electrolyte can be housed in a container by a known method. When the non-aqueous electrolyte is a non-aqueous electrolyte solution, for example, the electrode assembly (or the positive electrode and negative electrode) is first housed in a container, and then the non-aqueous electrolyte solution is poured into the container through an inlet provided in the container. The inlet is sealed after the non-aqueous electrolyte solution is poured into the container. The method for manufacturing the non-aqueous electrolyte storage element may further comprise initially charging and discharging the assembled uncharged and discharged storage element. In the non-aqueous electrolyte storage element according to one embodiment of the present invention, the initial charging and discharging usually begins with discharging, i.e., chemical conversion treatment. The number of charging and discharging cycles in the initial charging and discharging is not particularly limited.

[0190] The nonaqueous electrolyte electricity storage element according to one embodiment of the present invention may be manufactured by other methods.

[0191] <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.

[0192] <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.

[0193] 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.

[0194] 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]

[0195] 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.

[0196] 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 LiTFSI: Lithium bis(trifluoromethanesulfonyl)imide (ionic liquid) Py13FSI: 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide (non-aqueous solvent) TFEME: 2-(2,2,2-trifluoroethoxy)ethyl methyl ether (a compound represented by formula (1) where R is a methyl group and Rf is -CH2CF3: donor number 14.4) ETFEEE: Ethyl-2-(2,2,2-trifluoroethoxy)ethyl ether (a compound in which R is an ethyl group and Rf is -CH2CF3 in formula (1): donor number 9.6) DFEME: 2-(2,2-difluoroethoxy)ethyl methyl ether (a compound in formula (1) where R is a methyl group and Rf is -CH2CHF2: donor number 15.0) EDFEE: Ethyl-2-(2,2-difluoroethoxy)ethyl ether (a compound in formula (1) where R is an ethyl group and Rf is -CH2CHF2: donor number 9.9) FEME: 2-(2-fluoroethoxy)ethyl methyl ether (a compound in which R is a methyl group and Rf is -CH2CH2F in formula (1): donor number 17.1) EFEE: Ethyl 2-(2-fluoroethoxy)ethyl ether (a compound in which R is an ethyl group and Rf is -CH2CH2F in formula (1): donor number 12.3) TFETFPE: 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether FEC: Fluoroethylene carbonate VC: vinylene carbonate

[0197] [Example 1] (Preparation of positive electrode) Elemental sulfur and porous carbon, which are sulfur-based active materials, were mixed in a mass ratio of 70:30. This mixture was placed in a sealed electric furnace. After argon flow for 1 hour, the mixture was heated to 150°C at a rate of 5°C / min and held for 5 hours. After cooling to 80°C, the temperature at which elemental sulfur solidifies, the mixture was again heated to 300°C at a rate of 5°C / min and held for 2 hours to produce a composite (sulfur-porous carbon composite: SPC). A positive electrode mixture paste containing the composite obtained above, acetylene black and carbon nanotubes as conductive agents, carboxymethyl cellulose as a dispersant, polyacrylic acid as a thickener, and styrene-butadiene rubber as a binder, was applied to an aluminum positive electrode substrate (average thickness 15 μm) and dried. Note that the mass per unit area of ​​the positive electrode active material layer after drying of the dispersion medium was 10 mg / cm. 2 or 3 mg / cm 2 The amount of the positive electrode mixture paste applied was adjusted so that the following was achieved: By the above steps, a positive electrode in which a positive electrode active material layer was laminated on a positive electrode substrate was obtained.

[0198] (Preparing the negative electrode) A pure metallic lithium foil (average thickness 600 μm) was prepared as the negative electrode.

[0199] (Preparation of non-aqueous electrolyte) The ionic liquid Py13FSI and the non-aqueous solvent TFEME were mixed in a molar ratio of 70:30, and the electrolyte salt LiFSI was added at a concentration of 2.0 mol / dm 3 The non-aqueous electrolyte was prepared by adding the above-mentioned components in an amount of 1:1.

[0200] (Assembly of non-aqueous electrolyte energy storage element) The separator was prepared by laminating inorganic particle layers on both sides of a polyethylene microporous membrane, and had such high wettability that the nonaqueous electrolyte could penetrate into the pores. The nonaqueous electrolyte storage element of Example 1 was obtained using the positive electrode, negative electrode, separator, and nonaqueous electrolyte.

[0201] [Examples 2 to 5, Comparative Examples 1 to 3, Reference Example 1] Non-aqueous electrolyte storage elements of Examples 2 to 5, Comparative Examples 1 to 3 and Reference Example 1 were obtained in the same manner as in Example 1, except that the compositions of the non-aqueous electrolytes were as shown in Table 2. In Table 1, "M" in the composition of the nonaqueous electrolyte is expressed as "mol / dm 3 " represents.

[0202] (viscosity measurement) The viscosity (experimental value) at 25° C. was measured by the above-described method for the nonaqueous electrolyte in each of the nonaqueous electrolyte storage elements of Examples 1, 3, and 4, Comparative Examples 1 to 3, and Reference Example 1. The results are shown in Table 2.

[0203] (Lithium ion (Li + ) Measurement of diffusion coefficient) The lithium ion diffusion coefficient (experimental value) at 25° C. was measured by the above-described method for the nonaqueous electrolyte in each of the nonaqueous electrolyte storage elements of Examples 1, 4, and 5, Comparative Examples 1 to 3, and Reference Example 1. The results are shown in Table 2.

[0204] (Lithium ion (Li + )Calculation of transference number) The lithium ion transport number (experimental value) at 25° C. was determined by the above-described method for the nonaqueous electrolyte in each of the nonaqueous electrolyte storage elements of Examples 1, 4, and 5, Comparative Examples 1 to 3, and Reference Example 1. The results are shown in Table 2.

[0205] (Lithium ion (Li + ) Conductivity measurement) The lithium ion conductivity (experimental value) at 25° C. was measured by the above-described method for the nonaqueous electrolyte in each of the nonaqueous electrolyte storage elements of Examples 1, 4, and 5, Comparative Examples 1 to 3, and Reference Example 1. The results are shown in Table 2.

[0206] (Lithium ion (Li + ) Calculation of diffusion coefficient and transport number) The lithium ion diffusion coefficient (calculated value) and lithium ion transport number (calculated value) at 300 K were determined for the nonaqueous electrolytes of each of the nonaqueous electrolyte storage elements of Examples 1 and 4, Comparative Example 1, and Reference Example 1, as well as for the nonaqueous electrolytes of Calculation Examples 1 to 8, by calculations based on the classical molecular dynamics calculations described above. In calculating the lithium ion diffusion coefficient and lithium ion transport number for each nonaqueous electrolyte, the molar ratio of the ionic liquid to the nonaqueous solvent was set to the molar ratio (70:30 or 50:50) shown in Table 2. The results are shown in Table 2.

[0207] [evaluation] (Initial charge / discharge) The obtained nonaqueous electrolyte storage elements of Examples 1 to 5, Comparative Examples 1 and 2, and Reference Examples 1 and 2 were subjected to the following initial charge and discharge in a thermostatic chamber at 25°C. First, as a chemical conversion treatment, constant current discharge was performed under conditions of a discharge current of 0.1 C and a discharge cut-off voltage of 1.0 V. Then, as an initial charge, a charge current of 0.05 C (when the mass per unit area of ​​the positive electrode active material layer was 10 mg / cm) was used. 2 ) or 0.1C (when the mass per unit area of ​​the positive electrode active material layer is 3 mg / cm 2 (In the case of a positive electrode active material layer with a mass per unit area of ​​10 mg / cm) 2 ) or 30 hours (when the mass per unit area of ​​the positive electrode active material layer is 3 mg / cm 2 The battery was charged at constant current and constant voltage (CCCV) until the battery reached a constant voltage of 0.1 C. Then, the first discharge was performed at a constant current of 0.1 C and a discharge cut-off voltage of 1.0 V. A 10-minute pause was provided after the chemical conversion treatment and the first charge. The quantity of electricity (discharge capacity) in the first discharge was calculated as the quantity of electricity per mass of the sulfur-based active material (sulfur element). 2 The discharge capacity of the non-aqueous electrolyte storage element is Q1, and the mass per unit area of ​​the positive electrode active material layer is 3 mg / cm. 2 The discharge capacity of the nonaqueous electrolyte storage element is shown as Q2 in Table 2. Table 2 also shows the discharge capacity of the positive electrode active material layer when the mass per unit area is 3 mg / cm 2The mass per unit area of ​​the positive electrode active material layer relative to the discharge capacity (Q2) of the non-aqueous electrolyte storage element is 10 mg / cm 2 The ratio (Q1 / Q2) of the discharge capacity (Q1) of the nonaqueous electrolyte storage element is expressed as a percentage (%).

[0208] [Table 2]

[0209] As shown in Table 2, in each of the nonaqueous electrolyte storage elements of the Examples in which a nonaqueous electrolyte containing TFEME or ETFEEE corresponding to the nonaqueous solvent (X) together with an electrolyte salt and an ionic liquid was used, the mass per unit area of ​​the positive electrode active material layer was 10 mg / cm. 2 The discharge capacity (Q1) of the non-aqueous electrolyte storage element and the mass per unit area of ​​the positive electrode active material layer are 3 mg / cm 2 The discharge capacities (Q2) of the nonaqueous electrolyte storage elements were all large, and the ratios (Q1 / Q2) were 90% or more.

[0210] In contrast, in each of the nonaqueous electrolyte storage elements of Comparative Examples 1 and 2, in which a nonaqueous electrolyte containing TFETFPE was used instead of the nonaqueous solvent (X), and Comparative Example 3, in which a nonaqueous electrolyte not containing the nonaqueous solvent (X) was used, the mass per unit area of ​​the positive electrode active material layer was 10 mg / cm 2 In this case, the discharge capacity (Q1) was small, and the ratio (Q1 / Q2) was below 90%. The nonaqueous electrolyte storage element of Reference Example 1, in which the nonaqueous electrolyte did not contain an ionic liquid or a nonaqueous solvent (X), did not have a sufficiently large discharge capacity regardless of the mass per unit area of ​​the positive electrode active material layer.

[0211] Furthermore, from the calculated values ​​of the lithium ion diffusion coefficients of the nonaqueous electrolytes of Examples 1 and 4 and Comparative Example 1, it was found that in the calculation results based on classical molecular dynamics calculations, LiFSI was added at 2.0 mol / dm to a mixed liquid in which the molar ratio of Py13FSI to the nonaqueous solvent to be calculated was 70:30. 3 The lithium ion diffusion coefficient at 300 K of the hypothetical electrolyte containing -8 cm 2By using TFEME or ETFEEE, which is a non-aqueous solvent (X2) with a mass per unit area of ​​the positive electrode active material layer of 10 mg / cm or more, 2 The discharge capacity (Q1) of the non-aqueous electrolyte storage element and the mass per unit area of ​​the positive electrode active material layer are 3 mg / cm 2 It was confirmed that both the discharge capacity (Q2) and the discharge capacity (Q3) of the nonaqueous electrolyte energy storage element of Examples 1 and 4, Comparative Example 1, and Reference Example 1 increased. Furthermore, from the calculated and experimental values ​​of the lithium ion diffusion coefficients of the nonaqueous electrolytes of Examples 1 and 4, Comparative Example 1, and Reference Example 1, it is considered that there is a high correlation between the calculated lithium ion diffusion coefficients based on the classical molecular dynamics calculations and the actually measured lithium ion diffusion coefficients, and that the calculated results are valid as indicators of the height of the actual lithium ion diffusion coefficients.

[0212] Regarding the non-aqueous solvent (X2), the results of Calculation Examples 1 and 2 show that DFEME and EDFEE also correspond to the non-aqueous solvent (X2). In addition, the composition of the non-aqueous electrolyte in Calculation Examples 3 to 8 is similar to "a mixed liquid of Py13FSI and the non-aqueous solvent of the calculation target in a molar ratio of 70:30, in which LiFSI is added at 2.0 mol / dm 3 However, the calculated lithium ion diffusion coefficients of Calculation Examples 3 and 4, in which FEME and EFEE were used, are higher than the calculated lithium ion diffusion coefficients of Calculation Examples 5 to 8, in which DFEME, EDFEE, TFEME, and ETFEEE were used, which have been confirmed to correspond to non-aqueous solvents (X2). Therefore, it is considered that the calculated lithium ion diffusion coefficients of the virtual electrolytes in which the non-aqueous solvent to be calculated is FEME or EFEE are also higher than the calculated lithium ion diffusion coefficients of the virtual electrolytes in which the non-aqueous solvent to be calculated is DFEME, EDFEE, TFEME, or ETFEEE, i.e., the calculated lithium ion diffusion coefficients of Examples 1 and 4 and Calculation Examples 1 and 2. Therefore, it is considered that FEME and EFEE also correspond to non-aqueous solvents (X2). [Industrial Applicability]

[0213] 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]

[0214] 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 Energy storage device

Claims

1. a positive electrode containing a sulfur-based active material; a non-aqueous electrolyte containing an electrolyte salt, an ionic liquid, and a non-aqueous solvent represented by the following formula (1); A non-aqueous electrolyte electricity storage element comprising: R-O-(CH ２ ) ２ -O-Rf (1) (In formula (1), R is an alkyl group having 1 to 3 carbon atoms. Rf is a fluorinated alkyl group having 1 to 3 carbon atoms.)

2. a positive electrode containing a sulfur-based active material; a non-aqueous electrolyte containing an electrolyte salt, an ionic liquid, and a non-aqueous solvent; Equipped with The non-aqueous solvent was prepared by adding lithium bis(fluorosulfonyl)imide to a mixed liquid of 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide at a molar ratio of 70:30 based on classical molecular dynamics calculations. ３ The lithium ion diffusion coefficient at 300 K of the virtual electrolyte containing －８ cm ２ A non-aqueous electrolyte storage element in which the solvent is a solvent having a viscosity of 1 / s or more.

3. The R is a methyl group or an ethyl group, and the Rf is —CH ２ CH ｎ F ３－ｎ 2. The nonaqueous electrolyte storage element according to claim 1, wherein n is a group represented by the formula: (n is 0, 1 or 2).

4. 3. The nonaqueous electrolyte electricity storage element according to claim 2, wherein the number of donors in the nonaqueous solvent is 20 or less.

5. 5. The nonaqueous electrolyte storage element according to claim 2, wherein the nonaqueous solvent is a fluorinated ether.

6. the electrolyte salt is a lithium salt, The non-aqueous electrolyte has a lithium ion diffusion coefficient of 2.0×10 at 300 K, as calculated based on classical molecular dynamics. －８ cm ２ The nonaqueous electrolyte storage element according to claim 2 or 4, wherein the nonaqueous electrolyte has a capacitance of 1 / s or more.

7. 3. The nonaqueous electrolyte storage element according to claim 1, wherein the molar ratio of the ionic liquid to the nonaqueous solvent (ionic liquid / nonaqueous solvent) is within a range of 5 / 95 to 95 / 5.

8. 3. The nonaqueous electrolyte storage element according to claim 1, wherein the molar ratio of the ionic liquid to the nonaqueous solvent (ionic liquid / nonaqueous solvent) is within a range of 5 / 95 to 60 / 40.

9. 3. The nonaqueous electrolyte storage element according to claim 1, wherein a total content of the ionic liquid and the nonaqueous solvent relative to all components other than the electrolyte salt in the nonaqueous electrolyte is 80 mol % or more.

10. 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.

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

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

13. 3. The nonaqueous electrolyte storage element according to claim 1, wherein the viscosity of the nonaqueous electrolyte at 25°C is 100 mPa·s or less.

14. the electrolyte salt is a lithium salt, The lithium ion conductivity of the non-aqueous electrolyte at 25°C is 4.5 × 10 －４ 3. The nonaqueous electrolyte storage element according to claim 1, wherein the electrical conductivity is 1.5 S / cm or more.

15. the positive electrode has a positive electrode active material layer containing the sulfur-based active material, The mass per unit area of ​​the positive electrode active material layer is 5 mg / cm ２ The nonaqueous electrolyte storage element according to claim 1 or 2, wherein

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

17. A non-aqueous electrolyte comprising an electrolyte salt, an ionic liquid, and a non-aqueous solvent represented by the following formula (1): R-O-(CH ２ ) ２ -O-Rf (1) (In formula (1), R is an alkyl group having 1 to 3 carbon atoms. Rf is a fluorinated alkyl group having 1 to 3 carbon atoms.)

18. The electrolytic solution includes an electrolyte salt, an ionic liquid, and a non-aqueous solvent. The non-aqueous solvent was prepared by adding lithium bis(fluorosulfonyl)imide to a mixed liquid of 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide at a molar ratio of 70:30 based on classical molecular dynamics calculations. ３ The lithium ion diffusion coefficient at 300 K of the virtual electrolyte containing －８ cm ２ / s or more.

19. The non-aqueous electrolyte according to claim 17 or 18, which is for a non-aqueous electrolyte storage element having a positive electrode containing a sulfur-based active material.

20. providing a positive electrode including a sulfur-based active material; Preparing the nonaqueous electrolyte according to claim 17 or 18; A method for manufacturing a nonaqueous electrolyte electricity storage element, comprising:

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