Nonaqueous electrolyte power storage element

Abstract

To provide a nonaqueous electrolyte power storage element with the increased energy density per mass of the positive electrode active material when comparing nonaqueous electrolyte power storage elements with the same mass per unit area of the positive electrode active material layer.SOLUTION: The nonaqueous electrolyte power storage element includes a positive electrode having a positive electrode active material layer including a composite of a sulfur-based active material and porous carbon, and a non-aqueous electrolyte including a non-aqueous solvent containing a fluorinated cyclic carbonate. The average pore diameter of the porous carbon is 3 nm or less. The content of the fluorinated cyclic carbonate in the non-aqueous solvent is 5 volume% or more.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a non-aqueous electrolyte energy storage device.

Background Art

[0002] Non-aqueous electrolyte secondary batteries typified by lithium-ion secondary batteries are widely used in electronic devices such as personal computers and communication terminals, and automobiles, etc. because of their high energy density. The above non-aqueous electrolyte secondary battery generally has a pair of electrodes electrically isolated by a separator and a non-aqueous electrolyte interposed between the electrodes, and is configured to charge and discharge by transferring charge transport ions such as lithium ions between both electrodes. Further, as non-aqueous electrolyte energy storage devices other than non-aqueous electrolyte secondary batteries, capacitors such as lithium-ion capacitors and electric double layer capacitors are also widely popularized.

[0003] As non-aqueous electrolyte energy storage devices, non-aqueous electrolyte energy storage devices using a sulfur-based active material as a positive electrode active material, such as lithium-sulfur batteries (Li-S batteries), are known (see Patent Document 1). The sulfur-based active material has a large theoretical capacity, and a non-aqueous electrolyte energy storage device using a sulfur-based active material as a positive electrode active material is expected as an energy storage device having a high energy density. Further, since the sulfur-based active material has low electron conductivity, a composite of the sulfur-based active material and a conductive agent such as carbon may be used for the positive electrode.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Even in a conventional non-aqueous electrolyte storage device in which a sulfur-based active material is used as the positive electrode active material, the large theoretical capacity of the sulfur-based active material has not been fully utilized, and further increase in energy density is expected. On the other hand, generally in a non-aqueous electrolyte storage device, the mass per unit area of the positive electrode active material layer (typically, the coating amount per unit area) is designed according to the required performance (capacity, output performance, etc.), size, application, etc. In this regard, the inventors have found that differences may occur in the energy density per unit mass of the positive electrode active material depending on the mass per unit area of the positive electrode active material layer. From the viewpoint of fully utilizing the large theoretical capacity of the sulfur-based active material in each non-aqueous electrolyte storage device having a different mass per unit area of the positive electrode active material layer, among non-aqueous electrolyte storage devices having the same mass per unit area of the positive electrode active material layer, it is desirable that the energy density per unit mass of the positive electrode active material be high.

[0006] An object of the present invention is to provide a non-aqueous electrolyte storage device having a high energy density per unit mass of the positive electrode active material when compared among non-aqueous electrolyte storage devices having the same mass per unit area of the positive electrode active material layer.

Means for Solving the Problems

[0007] A non-aqueous electrolyte storage device according to one aspect of the present invention includes a positive electrode having a positive electrode active material layer containing a composite of a sulfur-based active material and porous carbon, and a non-aqueous electrolyte containing a non-aqueous solvent containing a fluorinated cyclic carbonate. The average pore diameter of the porous carbon is 3 nm or less, and the content of the fluorinated cyclic carbonate in the non-aqueous solvent is 5% by volume or more.

Effects of the Invention

[0008] According to one aspect of the present invention, it is possible to provide a non-aqueous electrolyte storage device having a high energy density per unit mass of the positive electrode active material when compared among non-aqueous electrolyte storage devices having the same mass per unit area of the positive electrode active material layer.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

DETAILED DESCRIPTION OF THE INVENTION

[0010] First, an overview of the non-aqueous electrolyte storage element disclosed by this specification will be described.

[0011] (1) The non-aqueous electrolyte storage element according to one aspect of the present invention includes a positive electrode having a positive electrode active material layer containing a composite of a sulfur-based active material and porous carbon, and a non-aqueous electrolyte containing a non-aqueous solvent containing a fluorinated cyclic carbonate. The average pore diameter of the porous carbon is 3 nm or less, and the content of the fluorinated cyclic carbonate in the non-aqueous solvent is 5% by volume or more.

[0012] When comparing non-aqueous electrolyte storage elements having the same mass per unit area of the positive electrode active material layer, the non-aqueous electrolyte storage element described in (1) above has a high energy density per mass of the positive electrode active material. The reason for this is not clear, but the following reasons are speculated. In a composite of a sulfur-based active material and porous carbon (hereinafter, also simply referred to as "composite"), it is common that the sulfur-based active material is supported in the pores of the porous carbon. In the non-aqueous electrolyte storage element described in (1) above, since the average pore diameter of the porous carbon is 3 nm or less and the pore diameter is small, the contact area per mass of the sulfur-based active material between the sulfur-based active material and the porous carbon is large, and thus the electron conductivity between the sulfur-based active material and the porous carbon is considered to be high. Also, usually, during the initial discharge, a film (also referred to as SEI, reaction layer, etc.) is formed on the composite surface due to the decomposition of carbonates or the like contained in the non-aqueous solvent of the non-aqueous electrolyte. When the pore diameter of the porous carbon is small, it is difficult for the non-aqueous electrolyte to penetrate into the pores. Therefore, in the non-aqueous electrolyte storage element described in (1) above in which porous carbon with a small pore diameter is used, the contact area between the sulfur-based active material supported in the pores of the porous carbon and the non-aqueous electrolyte is small, and the excessive formation of a film on the composite surface is suppressed. When an excessive film is formed on the composite surface, it is considered that the void volume in the positive electrode active material layer decreases and the diffusibility of charge-transporting ions decreases. Also, regarding the film formed, when the non-aqueous solvent of the non-aqueous electrolyte contains a fluorinated cyclic carbonate, a film with high ionic conductivity (a film containing LiF, etc.) is considered to be formed. In the non-aqueous electrolyte storage element described in (1) above, since the content of the fluorinated cyclic carbonate in the non-aqueous solvent is 5% by volume or more, a film having sufficient ionic conductivity is formed. For such reasons, in the non-aqueous electrolyte storage element described in (1) above, when comparing non-aqueous electrolyte storage elements having the same mass per unit area of the positive electrode active material layer, it is speculated that the energy density per mass of the positive electrode active material is high. Also, the non-aqueous electrolyte storage element described in (1) above also tends to have a high energy density per mass of the positive electrode when comparing non-aqueous electrolyte storage elements having the same mass per unit area of the positive electrode active material layer.

[0013] The "average pore diameter" of the porous carbon is the value measured by the following method. First, the pore diameter distribution measurement is performed using the nitrogen adsorption method. This measurement can be carried out by "autosorb iQ" manufactured by Quantachrome. Five points are extracted from the region of P / P0 = 0.06 to 0.3 of the obtained adsorption isotherm to perform a BET plot, and the BET specific surface area is calculated from the y-intercept and slope of the straight line. Also, the pore volume is calculated using the BJH method from the total adsorbed gas amount in the pore diameter distribution measurement. When assuming that the pores are cylindrical, the volume V of the pores and the surface area A of the pores are expressed as follows. V = π×(d / 2) 2 ×H A = π×d×H d: pore diameter, H: depth of the pores (corresponding to the height of the cylinder) In addition, in the calculation of the surface area, the area of the surface corresponding to the bottom surface of the cylinder can be ignored. From the above two equations, d = 4V / A is derived. Therefore, the average pore diameter d can be calculated from the equation d = 4V / A using the values of the BET specific surface area A and the pore volume V.

[0014] The content of each component constituting the non-aqueous solvent is measured by liquid chromatography-mass spectrometry (Liquid Chromatography-Mass Spectrometry: LC-MS) and gas chromatography-mass spectrometry (Gas Chromatography-Mass Spectrometry: GC-MS). Specifically, it is carried out as follows. Note that the measurements of LC-MS and GC-MS are continuously carried out under the same conditions respectively. 1. Sampling of non-aqueous electrolyte First, the non-aqueous electrolyte storage element is disassembled to take out the non-aqueous electrolyte. If it cannot be taken out, the non-aqueous electrolyte is taken out by centrifuging the non-aqueous electrolyte storage element. If it still cannot be taken out after centrifuging, an extraction solvent (e.g., acetonitrile) is injected into the non-aqueous electrolyte storage element, and the non-aqueous electrolyte diluted with the extraction solvent is taken out. 2. LC-MS Analyze the components of the non-aqueous electrolyte taken by LC-MS. The LC-MS analysis is performed in the order of the following qualitative analysis and quantitative analysis. Use "Acquity H" and "Xevo G2-5QTof" manufactured by Waters for the LC-MS analysis equipment. Use water for the eluent. (Qualitative analysis) Subject the measurement sample (non-aqueous electrolyte) to LC-MS analysis. If the peaks in the obtained liquid chromatogram are not separated, perform GC-MS analysis described later instead of LC-MS analysis. If the peaks are separated, predict the components contained in the measurement sample from the MS spectra of each peak. Subject a known sample of the predicted component (hereinafter referred to as the "predicted component") to LC-MS analysis. Compare the retention time and MS spectrum of the peak corresponding to each predicted component in the measurement sample with the retention time and MS spectrum of the peak of the known sample of each predicted component. If they match, presume that the above prediction is correct. (Quantitative analysis) The quantitative analysis is performed by the calibration curve method. First, measure a known sample of the predicted component with a known concentration by LC-MS, obtain the peak area, and create a calibration curve. The calibration curve is created so that the coefficient of determination (r 2 ) is between 0.999 and 1. Determine the content of the predicted component in the measurement sample from the calibration curve and the peak area of the predicted component in the measurement sample. Perform the above operations for all the peaks detected in the LC-MS analysis of the measurement sample to determine the content of each predicted component. 3.GC-MS The analysis by GC-MS is performed in the order of the following qualitative analysis and quantitative analysis. Use "5975C" manufactured by Agilent for the GC-MS analysis equipment. Use argon as the carrier gas. (Qualitative analysis) Subject the measurement sample (non-aqueous electrolyte) to GC-MS analysis. Predict the components contained in the sample from the MS spectra of each peak in the obtained gas chromatogram. Subject a known sample of the predicted component to GC-MS analysis. Compare the retention time and MS spectrum of the peak corresponding to each predicted component in the measurement sample with the retention time and MS spectrum of the peak of the known sample of each predicted component. If they match, presume that the above prediction is correct. (Quantitative analysis) Quantitative analysis is performed by the calibration curve method. Quantitative analysis by GC-MS is carried out in the same procedure as the above-described quantitative analysis by LC-MS to determine the content of each predicted component. 4. Calculation of the content of each component Taking the total content of each predicted component (i.e., each component) measured by LC-MS or GC-MS as the content of the non-aqueous solvent, calculate the content of each component in the non-aqueous solvent. In calculating the content (volume %) of each component in the non-aqueous solvent, use the value obtained by converting the content on a mass basis of each component measured by LC-MS or GC-MS to the volume at 20°C, and take the total content of each volume-converted component as the content of the non-aqueous solvent. Also, when an extraction solvent is used, the extraction solvent is excluded from consideration.

[0015] (2) In the non-aqueous electrolyte storage element described in (1) above, the mass per unit area of the positive electrode active material layer is 5 mg / cm 2 or more may be acceptable.

[0016] The non-aqueous electrolyte storage element described in (2) above further exhibits the effect that the energy density per unit mass of the positive electrode is high, in addition to the effects of the non-aqueous electrolyte storage element described in (1) above. The reason for this is not clear, but the following reasons are speculated. When the mass per unit area of the positive electrode active material layer is 5 mg / cm 2By increasing it above, the mass ratio of the positive electrode active material layer in the positive electrode, and as a result, the mass ratio of the sulfur-based active material as the positive electrode active material increases, and as a result, the energy density per unit mass of the positive electrode increases. When porous carbon with an average pore diameter exceeding 3 nm is used, even if the mass per unit area of the positive electrode active material layer is increased, the energy density per unit mass of the positive electrode does not increase and may conversely decrease. This is presumably because when the pore diameter of the porous carbon is large, the non-aqueous electrolyte easily penetrates into the pores, so the contact area between the sulfur-based active material supported in the porous carbon and the non-aqueous electrolyte increases, and the amount of the film formed on the surface of the composite increases. That is, when the pore diameter of the porous carbon is large, an excessive film is formed on the surface of the composite, and the void volume in the positive electrode active material layer decreases. In such a state and when the mass per unit area of the positive electrode active material layer is large, that is, when the positive electrode active material layer is thick, it becomes difficult for the charge transport ions in the non-aqueous electrolyte to diffuse to a deep position in the positive electrode active material layer, so it is presumed that it is difficult for the energy density per unit mass of the positive electrode to increase.

[0017] "The mass (mg / cm 2 ) per unit area of the positive electrode active material layer" means the mass (mg) of the positive electrode active material layer per unit area (1 cm 2 ) of the positive electrode active material layer. The area of the positive electrode active material layer is the area of one surface of the positive electrode active material layer. 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. Also, for example, when the positive electrode active material layer is provided on both sides of the positive electrode substrate with a coating amount (in terms of solid content) of 10 mg / cm 2 each, the "mass per unit area of the positive electrode active material layer" is 10 mg / cm 2 . Even when the positive electrode active material layer is provided on one side of the positive electrode substrate with a coating amount (in terms of solid content) of 10 mg / cm 2 , the "mass per unit area of the positive electrode active material layer" is 10 mg / cm 2 . That is, in the positive electrode active material layer provided on one side or both sides of the positive electrode substrate, the "mass per unit area of the positive electrode active material layer" is the mass per unit area of the positive electrode active material layer per side.

[0018] (3) In the non-aqueous electrolyte storage element described in (2) above, the content of the fluorinated cyclic carbonate in the non-aqueous solvent may be 5% by volume or more and 95% by volume or less.

[0019] In addition to the effects of the non-aqueous electrolyte storage element described in (2) above, the non-aqueous electrolyte storage element described in (3) above has an additional effect that the energy density per mass of the positive electrode active material is higher when compared with non-aqueous electrolyte storage elements having the same mass per unit area of the positive electrode active material layer. The reason for this is not clear, but the following reasons are speculated. In the non-aqueous electrolyte, as the content of the fluorinated cyclic carbonate increases, the viscosity increases and the ionic conductivity tends to decrease. When the mass per unit area of the positive electrode active material layer is 5 mg / cm 2 or more, that is, when the positive electrode active material layer is thick, the influence of the decrease in the permeability and ionic conductivity of the non-aqueous electrolyte in the thickness direction in the positive electrode active material layer due to the high viscosity of the non-aqueous electrolyte is large. On the other hand, by suppressing the increase in the viscosity of the non-aqueous electrolyte by suppressing the content of the fluorinated cyclic carbonate in the non-aqueous solvent to 95% by volume or less, it is speculated that the permeability and ionic conductivity of the non-aqueous electrolyte in the thickness direction in the positive electrode active material layer increase, and the energy density per mass of the positive electrode active material increases.

[0020] (4) In the non-aqueous electrolyte storage element described in (2) or (3) above, the content of the fluorinated cyclic carbonate in the non-aqueous solvent may be 20% by volume or more.

[0021] In addition to the effects of the non-aqueous electrolyte storage element described in (2) or (3) above, the non-aqueous electrolyte storage element described in (4) above has an additional effect that the average discharge voltage is high.

[0022] (5) In the non-aqueous electrolyte storage element described in (1) above, the mass per unit area of the positive electrode active material layer is less than 5 mg / cm 2 and the content of the fluorinated cyclic carbonate in the non-aqueous solvent may be 40% by volume or more.

[0023] The non-aqueous electrolyte storage element described in (5) above further enhances the effects of the non-aqueous electrolyte storage element described in (1) above, and exhibits an additional effect that the discharge capacity per unit mass of the positive electrode active material is large when compared with non-aqueous electrolyte storage elements having the same mass per unit area of the positive electrode active material layer. The reason for this is not clear, but the following reasons are speculated. As described above, in the non-aqueous electrolyte, when the content of the fluorinated cyclic carbonate increases, the ionic conductivity decreases due to the increase in viscosity, and the permeability and ionic conductivity of the non-aqueous electrolyte in the thickness direction of the positive electrode active material layer tend to decrease. However, when the mass per unit area of the positive electrode active material layer is less than 5 mg / cm 2 and is small, that is, when the positive electrode active material layer is thin, the influence of the decrease in permeability due to the high viscosity of the above non-aqueous electrolyte is small. Therefore, when the mass per unit area of the positive electrode active material layer is less than 5 mg / cm 2 , the effect that the ionic conductivity of the formed film increases by increasing the content of the fluorinated cyclic carbonate in the non-aqueous solvent becomes remarkable. As a result, in the non-aqueous electrolyte storage element described in (5) above, when compared with non-aqueous electrolyte storage elements having the same mass per unit area of the positive electrode active material layer, it is speculated that the energy density per unit mass of the positive electrode active material becomes higher and the discharge capacity per unit mass of the positive electrode active material also increases.

[0024] (6) In the non-aqueous electrolyte storage element described in any one of (1) to (5) above, the non-aqueous solvent may contain carbonate as a main component.

[0025] The non-aqueous electrolyte storage element described in (6) above has a higher energy density per unit mass of the positive electrode active material when compared with non-aqueous electrolyte storage elements having the same mass per unit area of the positive electrode active material layer.

[0026] The "main component" in the non-aqueous solvent means a component having a content of 50% by volume or more in the non-aqueous solvent.

[0027] In a non-aqueous electrolyte storage element in which a sulfur-based active material is used for the positive electrode, when a non-aqueous electrolyte containing a non-aqueous solvent mainly composed of ether is used, the charge-discharge reaction proceeds due to the shuttle reaction caused by the dissolution of polysulfides formed on the positive electrode into the non-aqueous electrolyte. On the other hand, in a non-aqueous electrolyte storage element in which a sulfur-based active material is used for the positive electrode, when a non-aqueous electrolyte containing a non-aqueous solvent mainly composed of carbonate is used, a film is formed on the surface of the composite of the positive electrode by the reaction between the positive electrode and the non-aqueous electrolyte (such as carbonate) during the initial discharge. Thereafter, the charge-discharge reaction proceeds by the solid-phase diffusion of charge-transporting ions through this film. Thus, in a non-aqueous electrolyte storage element in which sulfur is used for the positive electrode, it is considered that the reaction mechanisms of the positive electrode during charge and discharge are different between the case where a non-aqueous electrolyte containing a non-aqueous solvent mainly composed of ether is used and the case where a non-aqueous electrolyte containing a non-aqueous solvent mainly composed of carbonate is used. However, even if the non-aqueous electrolyte does not mainly contain carbonate, as long as it contains carbonate, a film can be formed. Therefore, in the case of the non-aqueous electrolyte storage element described in (1) above, when comparing non-aqueous electrolyte storage elements having the same mass per unit area of the positive electrode active material layer, an effect that the energy density per mass of the positive electrode active material is high can be achieved.

[0028] A non-aqueous electrolyte storage element, a power storage device, a method for manufacturing a non-aqueous electrolyte storage element, and other embodiments according to an embodiment of the present invention will be described in detail. Note that the names of the respective constituent members (each constituent element) used in each embodiment may be different from the names of the respective constituent members (each constituent element) used in the background art.

[0029] <Non-aqueous electrolyte storage element> A non-aqueous electrolyte storage element according to an embodiment of the present invention (hereinafter, also simply referred to as a "storage element") includes an electrode body having a positive electrode, a negative electrode, and a separator, a non-aqueous electrolyte, and a container that houses the electrode body and the non-aqueous electrolyte. The electrode body is usually a laminated type in which a plurality of positive electrodes and a plurality of negative electrodes are laminated via a separator, or a wound type in which a positive electrode and a negative electrode are wound in a state of being laminated via a separator. The non-aqueous electrolyte exists in a state included in the positive electrode, the negative electrode, and the separator. As an example of the non-aqueous electrolyte storage element, a non-aqueous electrolyte secondary battery (hereinafter, also simply referred to as a "secondary battery") will be described.

[0030] (Positive electrode) The positive electrode has a positive electrode substrate and a positive electrode active material layer disposed directly or via an intermediate layer on the positive electrode substrate.

[0031] The positive electrode substrate has conductivity. Whether it has "conductivity" is determined with a volume resistivity measured in accordance with JIS-H-0505 (1975) of 10 -2 Ω·cm as the threshold value. As the material of the positive electrode substrate, metals such as aluminum, titanium, tantalum, and stainless steel, or alloys thereof are used. Among these, aluminum or an aluminum alloy is preferable from the viewpoints of potential resistance, high conductivity, and cost. Examples of the positive electrode substrate include a foil, a vapor deposition film, a mesh, and a porous material, and a foil is preferable from the viewpoint of cost. Therefore, an aluminum foil or an aluminum alloy foil is preferable as the positive electrode substrate. Examples of aluminum or an aluminum alloy include A1085, A3003, A1N30, etc. defined in JIS-H-4000 (2014) or JIS-H-4160 (2006).

[0032] The average thickness of the positive electrode substrate is preferably 3 μm or more and 50 μm or less, more preferably 5 μm or more and 40 μm or less, still more preferably 8 μm or more and 30 μm or less, and particularly preferably 10 μm or more and 25 μm or less. By setting the average thickness of the positive electrode substrate within the above range, it is possible to increase the strength of the positive electrode substrate while increasing the energy density per mass or volume of the positive electrode. The "average thickness" refers to the average value of the thicknesses measured at any five locations.

[0033] The intermediate layer is a layer disposed between the positive electrode substrate and the positive electrode active material layer. The intermediate layer contains a conductive agent such as carbon particles to reduce the contact resistance between the positive electrode substrate and the positive electrode active material layer. The configuration of the intermediate layer is not particularly limited, and for example, it contains a binder and a conductive agent.

[0034] The positive electrode active material layer contains a composite of a sulfur-based active material and porous carbon. The positive electrode active material layer optionally contains optional components such as a conductive agent, a binder, a dispersant, a thickener, and a filler. The positive electrode active material layer is usually formed from a positive electrode mixture containing the composite and other optional components.

[0035] In the composite, usually, the sulfur-based active material is supported in the pores of the porous carbon. By having such a form of the composite, sufficient electron conductivity is ensured. The composite may consist essentially of only the sulfur-based active material and porous carbon, or may consist of only the sulfur-based active material and porous carbon. That the composite consists essentially of only the sulfur-based active material and porous carbon means, for example, that the total content of the sulfur-based active material (total of sulfur and sulfur compounds) and porous carbon in the composite is 90% by mass or more, and may be 95% by mass or more, 98% by mass or more, or 99% by mass or more.

[0036] The sulfur-based active material contained in the composite is a component that functions as a positive electrode active material. The sulfur-based active material may be sulfur, a sulfur compound, or a mixture thereof. That is, it suffices that the composite contains sulfur elements together with the porous carbon. Examples of the sulfur compound include metal sulfides such as lithium sulfide, organic disulfide compounds, and organic sulfur compounds such as carbon sulfide compounds. The sulfur-based active material has advantages such as a large theoretical capacity and low cost.

[0037] The content of sulfur element in the composite (mass ratio of sulfur element to the mass of the composite) is preferably 50% by mass or more and 90% by mass or less, more preferably 55% by mass or more and 80% by mass or less. By setting the content of sulfur element in the composite within the above range, it is possible to increase the energy density per mass of the positive electrode active material when comparing non-aqueous electrolyte storage elements with the same mass per unit area of the positive electrode active material layer, etc.

[0038] The porous carbon has conductivity. Porous carbon is generally a porous inorganic material mainly composed of carbon element. The main constituent element refers to the element with the highest content on a mass basis. The lower limit of the content of carbon element in the porous carbon is preferably 70% by mass, more preferably 80% by mass, 90% by mass, 95% by mass or 97% by mass. The upper limit of the content of carbon element in the porous carbon may be 100% by mass or 99.9% by mass. The content of carbon element in the porous carbon can be set to be not less than any of the above lower limits and not more than any of the above upper limits. The porous carbon may contain elements other than carbon element such as oxygen element and nitrogen element.

[0039] The upper limit of the average pore diameter of the porous carbon is 3 nm, preferably 3.0 nm, more preferably 2.5 nm. By the average pore diameter of the porous carbon being not more than the above upper limit, it is possible to increase the energy density per mass of the positive electrode active material when comparing non-aqueous electrolyte storage elements with the same mass per unit area of the positive electrode active material layer, etc. The lower limit of the average pore diameter of the porous carbon is, for example, 0.5 nm, and it may also be 1.0 nm. The average pore diameter of the porous carbon can be set to be not less than any of the above lower limits and not more than any of the above upper limits. The porous carbon can be selected and used from conventionally known porous carbons such as activated carbon, those having an average pore diameter of 3 nm or less.

[0040] The composite can be produced by a conventionally known method. For example, it can be obtained 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 it, etc.

[0041] The content of the composite in the positive electrode active material layer is preferably 60% by mass or more and 95% by mass or less, more preferably 70% by mass or more and 90% by mass or less. By setting the content of the composite within the above range, it is possible to increase the energy density per mass of the positive electrode active material when comparing non-aqueous electrolyte storage elements having the same mass per unit area of the positive electrode active material layer, and so on.

[0042] The positive electrode active material layer may contain other positive electrode active materials in addition to the sulfur-based active material. However, the content of the sulfur-based active material (total of sulfur and sulfur compounds) in all the positive electrode active materials is preferably 50% by mass or more, more preferably 70% by mass or more, further preferably 90% by mass or more, even more preferably 99% by mass or more, and particularly preferably 100% by mass.

[0043] The conductive agent is not particularly limited as long as it is a material having conductivity. Note that the conductive agent does not include the porous carbon constituting the composite. Examples of such a conductive agent include carbonaceous materials, metals, conductive ceramics, and the like. Examples of the carbonaceous material include graphite, non-graphitic carbon, graphene-based carbon, and the like. Examples of the non-graphitic carbon include carbon nanofibers, pitch-based carbon fibers, carbon black, and the like. Examples of the carbon black include furnace black, acetylene black, ketjen black, and the like. Examples of the graphene-based carbon include graphene, carbon nanotubes (CNT), fullerenes, and the like. Examples of the shape of the conductive agent include powder form, fibrous form, and the like. As the conductive agent, one of these materials may be used alone, or two or more of them may be mixed and used. Further, these materials may be used in a composite form. For example, a material obtained by compositeizing carbon black and CNT may be used. Among these, carbon black is preferable from the viewpoints of electron conductivity and coatability, and acetylene black is particularly preferable. Further, it is also preferable to use carbon black (preferably acetylene black) and CNT in combination.

[0044] The content of the conductive agent (excluding the porous carbon in the composite) in the positive electrode active material layer is preferably 0.5% by mass or more and 20% by mass or less, and more preferably 1% by mass or more and 15% by mass or less. By setting the content of the conductive agent within the above range, the energy density per mass of the positive electrode can be increased.

[0045] Examples of the binder include thermoplastic resins such as fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), polyethylene, polypropylene, polyacrylic, and polyimide; elastomers such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber; and polysaccharide polymers.

[0046] The content of the binder in the positive electrode active material layer is preferably 1% by mass or more and 10% by mass or less, and more preferably 2% by mass or more and 9% by mass or less. By setting the content of the binder within the above range, the composite or the like can be stably held.

[0047] Examples of the dispersant 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, this 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 as a binder.

[0048] Examples of the thickener include polyacrylic acid (PAA). The content of the thickener in the positive electrode active material layer is preferably 0.05% by mass or more and 5% by mass or less, and more preferably 0.1% by mass or more and 4% by mass or less. Polyacrylic acid may function as a binder.

[0049] The filler is not particularly limited. Examples of the filler include polyolefins such as polypropylene and polyethylene, inorganic oxides such as silicon dioxide, alumina, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicate, hydroxides such as magnesium hydroxide, calcium hydroxide, and aluminum hydroxide, carbonates such as calcium carbonate, sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium sulfate, nitrides such as aluminum nitride and silicon nitride, mineral resource-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or artificial products thereof. When the positive electrode active material layer contains a filler, the content of the filler in the positive electrode active material layer is preferably, for example, 0.1% by mass or more and 10% by mass or less. In one embodiment of the present invention, the positive electrode active material layer may not contain a filler.

[0050] The positive electrode active material layer may contain typical non-metal elements such as B, N, P, F, Cl, Br, and I, typical metal elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba, and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, and Nb as components other than the composite, other positive electrode active materials, conductive agents, binders, dispersants, thickeners, and fillers.

[0051] The mass per unit area of the positive electrode active material layer is not particularly limited, and can be, for example, 0.5 mg / cm 2 or more and 30 mg / cm 2 or less, and can also be 1 mg / cm 2 or more and 20 mg / cm 2 or less. In one embodiment, the mass per unit area of the positive electrode active material layer can be 5 mg / cm 2 or more, 7 mg / cm 2 or more, 8 mg / cm 2 or more, 10 mg / cm 2 or more, or 12 mg / cm 2It can also be set as above. By setting the mass per unit area of the positive electrode active material layer to be equal to or greater than the above lower limit, the energy density per unit mass of the positive electrode can be increased. In other embodiments, the mass per unit area of the positive electrode active material layer can be less than 5 mg / cm 2 and can be less than 4 mg / cm 2 or less than 3 mg / cm 2 as well. By setting the mass per unit area of the positive electrode active material layer to be less than the above upper limit and increasing the content of fluorinated cyclic carbonate in the non-aqueous solvent as described later, the energy density per unit mass of the positive electrode active material can be further increased and the discharge capacity per unit mass of the positive electrode active material can be increased when comparing non-aqueous electrolyte storage elements with the same mass per unit area of the positive electrode active material layer. The mass per unit area of the positive electrode active material layer can be equal to or greater than any of the above lower limits and equal to or less than (but the upper limit is greater than the lower limit) any of the above upper limits or less.

[0052] (Negative electrode) The negative electrode has a negative electrode substrate and a negative electrode active material layer disposed directly or via an intermediate layer on the negative electrode substrate. The configuration of the intermediate layer is not particularly limited and can be selected, for example, from the configurations exemplified for the above positive electrode.

[0053] The negative electrode substrate has conductivity. As the material of the negative electrode substrate, metals such as copper, nickel, stainless steel, nickel-plated steel, or alloys thereof, carbonaceous materials, etc. are used. Among these, nickel or a nickel alloy is preferable. Examples of the negative electrode substrate include foil, vapor deposition film, mesh, porous material, etc., and foil is preferable from the viewpoint of cost. Therefore, a nickel foil or a nickel alloy foil is preferable as the negative electrode substrate. Examples of copper foil include rolled copper foil, electrolytic copper foil, etc.

[0054] The average thickness of the negative electrode substrate is preferably 2 μm or more and 35 μm or less, more preferably 3 μm or more and 30 μm or less, still more preferably 4 μm or more and 25 μm or less, and particularly preferably 5 μm or more and 20 μm or less. By setting the average thickness of the negative electrode substrate within the above range, it is possible to increase the strength of the negative electrode substrate while increasing the energy density per volume of the non-aqueous electrolyte storage element.

[0055] The negative electrode active material layer contains a negative electrode active material. The negative electrode active material layer may contain optional components such as a conductive agent, a binder, a thickener, and a filler as required. The optional components such as a conductive agent, a binder, a thickener, and a filler can be selected from the materials exemplified in the above positive electrode. The negative electrode active material layer may not contain optional components such as a conductive agent, a binder, a thickener, and a filler.

[0056] The negative electrode active material layer may contain typical non-metal elements such as B, N, P, F, Cl, Br, and I, typical metal elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba, and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, and Nb as components other than the negative electrode active material, the conductive agent, the binder, the thickener, and the filler.

[0057] The negative electrode active material can be appropriately selected from known negative electrode active materials. As the negative electrode active material for a lithium-ion secondary battery, a material that can occlude and release lithium ions is usually used. Examples of the negative electrode active material include metallic lithium; metals or semi-metals such as Si and Sn; metal oxides or semi-metal oxides such as silicon oxide, titanium oxide, and tin oxide; Li 4 Ti 5 O 12 , LiTiO 2、 TiNb 2 O 7 and other titanium-containing oxides; polyphosphoric acid compounds; silicon carbide; carbon materials such as graphite (graphite), non-graphitic carbon (easily graphitizable carbon or hardly graphitizable carbon), etc. In the case of a negative electrode active material that does not contain charge transport ions such as lithium ions, those doped with lithium ions or the like can be used.

[0058] As the negative electrode active material, metallic lithium is preferred. The metallic lithium may be pure metallic lithium consisting substantially only of lithium element, or may be a lithium alloy containing other metallic elements. Examples of the lithium alloy include lithium-silver alloy, lithium-zinc alloy, lithium-calcium alloy, lithium-aluminum alloy, lithium-magnesium alloy, lithium-indium alloy, etc. The lithium alloy may contain a plurality of metallic elements other than the lithium element.

[0059] The negative electrode active material layer may contain other negative electrode active materials other than metallic lithium. However, the negative electrode active material layer is preferably a layer consisting substantially only of metallic lithium (pure metallic lithium or lithium alloy). The content of lithium element in the negative electrode active material layer is preferably 80% by mass or more, more preferably 90% by mass or more, and still more preferably 99% by mass or more. The upper limit of the content of lithium element in the negative electrode active material layer may be 100% by mass. The content of lithium element in the negative electrode active material layer can be set to be equal to or more than any of the above-described lower limits and equal to or less than or less than the above-described upper limit.

[0060] The negative electrode active material layer may be a non-porous layer (solid layer) or a porous layer, but a non-porous layer is preferred. The negative electrode active material layer may be a layer of metallic lithium. The negative electrode active material layer may be a layer made of a metallic lithium foil (pure metallic lithium foil or lithium alloy foil). The average thickness of the negative electrode active material layer in the charged state is preferably 5 μm or more and 1,000 μm or less, more preferably 10 μm or more and 500 μm or less, and still more preferably 30 μm or more and 300 μm or less.

[0061] (Separator) The separator can be appropriately selected from known separators. As the separator, for example, a separator composed only of a base material layer, a separator having a heat-resistant layer containing heat-resistant particles and a binder formed on one or both surfaces of the base material layer, etc. can be used. Examples of the shape of the base material layer of the separator include woven fabric, non-woven fabric, porous resin film, etc. Among these shapes, a porous resin film is preferable from the viewpoint of strength, and a non-woven fabric is preferable from the viewpoint of the liquid retention property of the non-aqueous electrolyte. As the material of the base material layer of the separator, polyolefins such as polyethylene and polypropylene are preferable from the viewpoint of the shutdown function, and polyimides, aramids, etc. are preferable from the viewpoint of oxidation decomposition resistance. As the base material layer of the separator, a material obtained by compounding these resins may be used.

[0062] The heat-resistant particles contained in the heat-resistant layer preferably have a mass reduction of 5% or less when the temperature is raised from room temperature to 500 °C in an air atmosphere at 1 atm, and more preferably have a mass reduction of 5% or less when the temperature is raised from room temperature to 800 °C. Examples of materials with a mass reduction of a predetermined value or less include inorganic compounds. Examples of inorganic compounds include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicate; nitrides such as aluminum nitride and silicon nitride; carbonates such as calcium carbonate; sulfates such as barium sulfate; sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium titanate; covalent crystals such as silicon and diamond; mineral resource-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or artificial products thereof, etc. As the inorganic compound, these substances may be used alone as a single substance or a composite, or two or more kinds may be mixed and used. Among these inorganic compounds, silicon oxide, aluminum oxide, or aluminosilicate is preferable from the viewpoint of the safety of the non-aqueous electrolyte storage element.

[0063] The porosity of the separator is preferably 80% by volume or less from the viewpoint of strength, and preferably 20% by volume or more from the viewpoint of discharge performance. Here, the "porosity" is a volume-based value and means the measured value by a mercury porosimeter.

[0064] As the separator, a polymer gel composed of a polymer and a non-aqueous electrolyte may be used. Examples of the polymer include polyacrylonitrile, polyethylene oxide, polypropylene oxide, polymethyl methacrylate, polyvinyl acetate, polyvinyl pyrrolidone, polyvinylidene fluoride, and the like. Using a polymer gel has the effect of suppressing liquid leakage. As the separator, a porous resin film or non-woven fabric as described above and a polymer gel may be used in combination.

[0065] (Non-aqueous electrolyte) The non-aqueous electrolyte contains a non-aqueous solvent. As the non-aqueous electrolyte, a non-aqueous electrolyte solution usually containing a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent is preferably used. In one embodiment of the present invention, the non-aqueous electrolyte storage element may be a non-aqueous electrolyte solution storage element.

[0066] The non-aqueous solvent contains a fluorinated cyclic carbonate. By containing a fluorinated cyclic carbonate in the non-aqueous solvent, it is possible to increase the energy density per mass of the positive electrode active material when comparing non-aqueous electrolyte storage elements with the same mass per unit area of the positive electrode active material layer. The fluorinated cyclic carbonate refers to a compound in which some or all of the hydrogen atoms of the cyclic carbonate are substituted with fluorine atoms. The cyclic carbonate refers to a carbonate having a ring structure containing a carbonate group (-O-C(=O)-O-). Examples of the fluorinated cyclic carbonate include fluorinated ethylene carbonates such as fluoroethylene carbonate (FEC) and difluoroethylene carbonate (DFEC), fluorinated propylene carbonate, fluorinated butylene carbonate, and fluorinated vinylene carbonate. Among these, fluorinated ethylene carbonate is preferred, and FEC is more preferred. The fluorinated cyclic carbonate is preferably a fluorinated saturated cyclic carbonate. The fluorinated saturated cyclic carbonate is a fluorinated cyclic carbonate that does not have a carbon-carbon double bond and a carbon-carbon triple bond in the molecule. One or more kinds of fluorinated cyclic carbonates can be used.

[0067] The lower limit of the content of the fluorinated cyclic carbonate in the non-aqueous solvent is 5% by volume, preferably 10% by volume, and may be more preferably 20% by volume, 30% by volume, 40% by volume, 50% by volume or 60% by volume. By increasing the content of the fluorinated cyclic carbonate, advantages such as an increase in the ionic conductivity of the formed film are more easily obtained, and the energy density per unit mass of the positive electrode active material tends to be higher, the average discharge voltage tends to be higher, etc., when comparing non-aqueous electrolyte storage elements having the same mass per unit area of the positive electrode active material layer. The lower limit of the content of the fluorinated cyclic carbonate in the non-aqueous solvent may be more preferably 70% by volume, 80% by volume or 90% by volume. The upper limit of the content of the fluorinated cyclic carbonate in the non-aqueous solvent may be 100% by volume, and may be preferably 95% by volume, 90% by volume, 80% by volume, 70% by volume, 60% by volume, 50% by volume, 40% by volume, 30% by volume or 20% by volume. By decreasing the content of the fluorinated cyclic carbonate, advantages such as a decrease in the viscosity of the non-aqueous electrolyte are more easily obtained. The content of the fluorinated cyclic carbonate in the non-aqueous solvent can be set to be not less than any of the above lower limits and not more than any of the above upper limits (however, the upper limit is greater than the lower limit).

[0068] When the mass per unit area of the positive electrode active material layer is relatively large (for example, 5 mg / cm 2When the above is the case), the content of the fluorinated cyclic carbonate in the non-aqueous solvent is preferably 5% by volume or more and 95% by volume or less, more preferably 10% by volume or more and 90% by volume or less, and still more preferably 20% by volume or more and 80% by volume or less from the viewpoint of energy density. In such a case, the energy density per mass of the positive electrode active material is increased when comparing non-aqueous electrolyte storage elements having the same mass per unit area of the positive electrode active material layer. Further, when the mass per unit area of the positive electrode active material layer is relatively large, by setting the content of the fluorinated cyclic carbonate in the non-aqueous solvent to 20% by volume or more, and further 30% by volume or more, the average discharge voltage of the non-aqueous electrolyte storage element can be increased. Further, when the mass per unit area of the positive electrode active material layer is relatively large, by reducing the content of the fluorinated cyclic carbonate in the non-aqueous solvent, the discharge capacity per mass of the positive electrode active material tends to increase.

[0069] When the mass per unit area of the positive electrode active material layer is relatively small (for example, less than 5 mg / cm 2 When less than), the lower limit of the content of the fluorinated cyclic carbonate in the non-aqueous solvent is preferably 40% by volume, and more preferably 60% by volume, 70% by volume, 80% by volume or 90% by volume. At this time, the upper limit of the content of the fluorinated cyclic carbonate in the non-aqueous solvent may be 100% by volume. In such a case, the energy density per mass of the positive electrode active material is increased when comparing non-aqueous electrolyte storage elements having the same mass per unit area of the positive electrode active material layer, and the energy density per mass of the positive electrode active material itself is also increased. Further, in such a case, the discharge capacity per mass of the positive electrode active material also tends to increase when comparing non-aqueous electrolyte storage elements having the same mass per unit area of the positive electrode active material layer.

[0070] The non-aqueous solvent preferably contains carbonate as the main component. The lower limit of the carbonate content in the non-aqueous solvent is preferably 60% by volume, more preferably 70% by volume, and still more preferably 80% by volume, 90% by volume, 95% by volume or 99% by volume. The upper limit of the carbonate content in the non-aqueous solvent may be 100% by volume. The non-aqueous solvent may consist only of carbonate. The carbonate content in the non-aqueous solvent can be equal to or greater than any of the above-mentioned lower limits and equal to or less than or less than the above-mentioned upper limits.

[0071] The non-aqueous solvent may contain other carbonates other than fluorinated cyclic carbonates. Examples of other carbonates include chain carbonates and non-fluorinated cyclic carbonates (non-fluorinated cyclic carbonates). One or more of other carbonates can be used.

[0072] The chain carbonate refers to a carbonate that does not have a ring structure containing a carbonate group among carbonates. Examples of the chain carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diphenyl carbonate, 2,2,2-trifluoroethyl methyl carbonate (TFEMC), bis(2,2,2-trifluoroethyl) carbonate (TFEC), and the like.

[0073] Examples of non-fluorinated cyclic carbonates include saturated cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and chloroethylene carbonate, and unsaturated cyclic carbonates such as vinylene carbonate (VC), methylvinylene carbonate, ethylvinylene carbonate, propylvinylene carbonate, butylvinylene carbonate, dimethylvinylene carbonate, diethylvinylene carbonate, dipropylvinylene carbonate, and vinyl ethylene carbonate. A saturated cyclic carbonate is a cyclic carbonate that does not have a carbon-carbon double bond and a carbon-carbon triple bond in the molecule. An unsaturated cyclic carbonate is a cyclic carbonate that has a carbon-carbon double bond or a carbon-carbon triple bond in the molecule, and preferably has a carbon-carbon double bond in the molecule.

[0074] As other carbonates other than fluorinated cyclic carbonates, non-fluorinated cyclic carbonates are preferred, non-fluorinated unsaturated cyclic carbonates are more preferred, and VC is even more preferred. When the non-aqueous solvent further contains such a carbonate, the formed film may be better. For example, from non-fluorinated unsaturated cyclic carbonates, a film containing a polymer component (for example, polyvinylenecarbonate, etc.) can be formed.

[0075] When the non-aqueous solvent contains a non-fluorinated cyclic carbonate (particularly, a non-fluorinated unsaturated cyclic carbonate), the lower limit of the content of the non-fluorinated cyclic carbonate in the non-aqueous solvent may be 5% by volume, or may be 10% by volume, 20% by volume, 30% by volume, 40% by volume, 50% by volume, 60% by volume, 70% by volume, 80% by volume, or 90% by volume. The upper limit of the content of the non-fluorinated cyclic carbonate in the non-aqueous solvent may be 95% by volume, or may be 90% by volume, 80% by volume, 70% by volume, 60% by volume, 50% by volume, 40% by volume, 30% by volume, 20% by volume, or 10% by volume. The content of the non-fluorinated cyclic carbonate in the non-aqueous solvent can be any of the above lower limits or more and any of the above upper limits or less (however, the upper limit is greater than the lower limit).

[0076] The lower limit of the total content of the fluorinated cyclic carbonate and the non-fluorinated cyclic carbonate (particularly, the non-fluorinated unsaturated cyclic carbonate) in the non-aqueous solvent is preferably 60% by volume, more preferably 70% by volume, and even more preferably 80% by volume, 90% by volume, 95% by volume or 99% by volume. The upper limit of the total content may be 100% by volume. When the total content of the fluorinated cyclic carbonate and the non-fluorinated cyclic carbonate in the non-aqueous solvent is equal to or greater than the lower limit, the effect of the positive electrode active material having a high energy density per mass is particularly remarkable when compared between non-aqueous electrolyte storage elements having the same mass per unit area of ​​the positive electrode active material layer. The total content of the fluorinated cyclic carbonate and the non-fluorinated cyclic carbonate in the non-aqueous solvent can be equal to or greater than any of the lower limits and equal to or less than the upper limit.

[0077] The non-aqueous solvent may further contain other non-aqueous solvents other than carbonates, such as ethers, amides, and nitriles.

[0078] The electrolyte salt can be appropriately selected from known electrolyte salts. Examples of the electrolyte salt include lithium salts, sodium salts, potassium salts, magnesium salts, onium salts, etc. Among these, lithium salts are preferred.

[0079] The lithium salt is LiPF 6 , LiPO 2 F 2 , LiBF 4 , LiClO 4 , LiN(SO 2 F) 2 inorganic lithium salts such as lithium oxalate (LiBOB), lithium difluorooxalate (LiFOB), lithium bis(oxalate) difluorophosphate (LiFOP), and other lithium oxalates; LiSO 3 CF 3 , LiN(SO 2 CF 3 ) 2, LiN(SO 2 C 2 F 5 ) 2 , LiN(SO 2 CF 3 )(SO 2 C 4 F 9 ), LiC(SO 2 CF 3 ) 3 , LiC(SO 2 C 2 F 5 ) 3 and the like, such as lithium salts having a halogenated hydrocarbon group. Among these, inorganic lithium salts are preferred, LiPF 6 and LiN(SO 2 F) 2 are more preferred, and LiN(SO 2 F) 2 is even more preferred. Also, LiN(SO 2 F) 2 , LiN(SO 2 CF 3 ) 2 , LiN(SO 2 C 2 F 5 ) 2 , LiN(SO 2 CF 3 )(SO 2 C 4 F 9 ) and the like are also preferably imide salts, and LiN(SO 2 CF 3 ) 2 is more preferred.

[0080] The content of the electrolyte salt in the non-aqueous electrolyte is preferably 0.1 mol / dm 3 or more and 2.5 mol / dm 3 or less at 20°C and 1 atm, more preferably 0.3 mol / dm 3 or more and 2.0 mol / dm 3 or less, even more preferably 0.5 mol / dm 3 or more and 1.7 mol / dm 3 or less, and most preferably 0.7 mol / dm 3 or more and 1.5 mol / dm 3It is particularly preferable that the content of the electrolyte salt is within the above range, as it can increase the ionic conductivity of the non-aqueous electrolyte solution.

[0081] In addition to the non-aqueous solvent and the electrolyte salt, the non-aqueous electrolyte solution may contain an additive. Examples of the additive include oxalates such as lithium bis(oxalato)borate (LiBOB), lithium difluorooxalate borate (LiFOB), and lithium bis(oxalato)difluorophosphate (LiFOP); imide salts such as lithium bis(fluorosulfonyl)imide (LiFSI); aromatic compounds such as biphenyl, alkyl biphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran; partially halogenated compounds of the above aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, and p-cyclohexylfluorobenzene; halogenated anisole compounds such as 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, and 3,5-difluoroanisole; succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, methyl methanesulfonate, busulfan, methyl toluenesulfonate, dimethyl sulfate, ethylene sulfate, sulfolane, dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, diethyl sulfoxide, tetramethylene sulfoxide, diphenyl sulfide, 4,4'-bis(2,2-dioxo-1,3,2-dioxathiolane), 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane, thioanisole, diphenyl disulfide, dipyridinium disulfide, 1,3-propenesultone, 1,3-propanesultone, 1,4-butanesultone, 1,4-butene sultone, perfluorooctane, tris(trimethylsilyl) borate, tris(trimethylsilyl) phosphate, tetrakis(trimethylsilyl) titanate, lithium monofluorophosphate, lithium difluorophosphate, etc. These additives may be used alone or in combination of two or more.

[0082] The content of the additive contained in the non-aqueous electrolyte is preferably 0.01% by mass or more and 10% by mass or less, more preferably 0.1% by mass or more and 7% by mass or less, still more preferably 0.2% by mass or more and 5% by mass or less, and particularly preferably 0.3% by mass or more and 3% by mass or less with respect to the mass of the entire non-aqueous electrolyte. By setting the content of the additive within the above range, it is possible to improve the capacity retention performance or cycle performance after high-temperature storage, or to further improve the safety.

[0083] For the non-aqueous electrolyte, a non-aqueous electrolyte and a solid electrolyte may be used in combination. As the solid electrolyte, for example, any material having lithium ion conductivity and being solid at room temperature (for example, from 15°C to 25°C) can be selected. Examples of the solid electrolyte include sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, halide solid electrolytes, polymer solid electrolytes, and the like.

[0084] The shape of the non-aqueous electrolyte storage element of the present embodiment is not particularly limited, and examples thereof include a cylindrical battery, a prismatic battery, a flat battery, a coin-type battery, a button-type battery, and the like.

[0085] FIG. 1 shows a non-aqueous electrolyte storage element 1 as an example of a prismatic battery. The figure is a perspective view of the inside of the container. An electrode body 2 having a positive electrode and a negative electrode wound with a separator interposed therebetween is housed in a prismatic container 3. The positive electrode is electrically connected to a positive electrode terminal 4 via a positive electrode lead 41. The negative electrode is electrically connected to a negative electrode terminal 5 via a negative electrode lead 51.

[0086] <Power storage device> The non-aqueous electrolyte storage element of this embodiment can be mounted as a power storage unit (battery module) configured by aggregating a plurality of non-aqueous electrolyte storage elements in a power source for automobiles such as electric vehicles (EVs), hybrid vehicles (HEVs), plug-in hybrid vehicles (PHEVs), a power source for electronic devices such as personal computers and communication terminals, or a power source for power storage. In this case, the technology of the present invention may be applied to at least one non-aqueous electrolyte storage element included in the power storage unit.

[0087] FIG. 2 shows an example of a power storage device 30 formed by further aggregating power storage units 20 in which two or more non-aqueous electrolyte storage elements 1 electrically connected are aggregated. The power storage device 30 may include a bus bar (not shown) for electrically connecting two or more non-aqueous electrolyte storage elements 1, a bus bar (not shown) for electrically connecting two or more power storage units 20, and the like. The power storage unit 20 or the power storage device 30 may include a state monitoring device (not shown) for monitoring the state of one or more non-aqueous electrolyte storage elements.

[0088] <Method for manufacturing non-aqueous electrolyte storage element> The method for manufacturing the non-aqueous electrolyte storage element of this embodiment can be appropriately selected from known methods. The manufacturing method includes, for example, preparing an electrode body, preparing a non-aqueous electrolyte, and accommodating the electrode body and the non-aqueous electrolyte in a container. Preparing the electrode body includes preparing a positive electrode and a negative electrode, and forming the electrode body by laminating or winding the positive electrode and the negative electrode with a separator interposed therebetween.

[0089] Accommodating the non-aqueous electrolyte in the container can be appropriately selected from known methods. For example, when a non-aqueous electrolyte solution is used as the non-aqueous electrolyte, after injecting the non-aqueous electrolyte solution from an injection port formed in the container, the injection port may be sealed.

[0090] The manufacturing method may include performing initial charge and discharge on the undischarged non-aqueous electrolyte storage element. Note that the initial charge and discharge usually start with discharge. The first discharge or the like may be referred to as a formation process. The number of charge and discharge cycles in the initial charge and discharge is not particularly limited. By undergoing the initial charge and discharge or the formation process, a good film is formed on the surface of the composite of the positive electrode due to the decomposition of a part of the non-aqueous electrolyte.

[0091] <Other Embodiments> In addition, the non-aqueous electrolyte storage element of the present invention is not limited to the above embodiments, and various modifications may be made without departing from the gist of the present invention. For example, the configuration of another embodiment can be added to the configuration of a certain embodiment, and a part of the configuration of a certain embodiment can be replaced with the configuration of another embodiment or well-known technology. Furthermore, a part of the configuration of a certain embodiment can be deleted. Also, well-known technology can be added to the configuration of a certain embodiment.

[0092] In the above embodiments, the case where the non-aqueous electrolyte storage element is used as a rechargeable non-aqueous electrolyte secondary battery (for example, a lithium-sulfur battery) has been described. However, the type, shape, dimensions, capacity, etc. of the non-aqueous electrolyte storage element are arbitrary. The present invention can also be applied to various secondary batteries, capacitors, etc.

[0093] In the above embodiments, the electrode body in which the positive electrode and the negative electrode are laminated via a separator has been described. However, the electrode body may not include a separator. For example, the positive electrode and the negative electrode may be in direct contact with each other in a state where a non-conductive layer is formed on the active material layer of the positive electrode or the negative electrode.

Examples

[0094] Hereinafter, the present invention will be described more specifically by way of examples. However, the present invention is not limited to the following examples.

[0095] [Example 1] (Fabrication of Positive Electrode) As the porous carbon, micro-porous carbon with an average pore diameter of 2 nm was prepared. Sulfur, which is a sulfur-based active material, and the above porous carbon were mixed at a mass ratio of 70:30. This mixture was placed in a sealed electric furnace. After flowing argon for 1 hour, the temperature was raised to 150 °C at a rate of 5 °C / min, held for 5 hours, then cooled to 80 °C, which is the temperature at which sulfur solidifies, and then the temperature was raised again to 300 °C at a rate of 5 °C / min and held for 2 hours for heat treatment to produce a composite (sulfur-porous carbon composite: SPC). Using water as a dispersion medium, a positive electrode active material paste containing the composite obtained above, acetylene black and CNT as conductive agents, PPA as a thickener, CMC as a dispersant, and SBR as a binder in an appropriate mass ratio was applied to an aluminum positive electrode substrate (average thickness 15 μm) and dried. Note that the coating amount of the positive electrode active material paste was adjusted so that the mass per unit area of the positive electrode active material layer after drying the dispersion medium was 15 mg / cm 2 . Through the above steps, a positive electrode with a positive electrode active material layer laminated on the positive electrode substrate was obtained. The content of the composite in the positive electrode active material layer was 93% by mass.

[0096] (Preparation of negative electrode) As the negative electrode, a pure metal lithium foil was prepared.

[0097] (Preparation of non-aqueous electrolyte) LiN(SO 2 CF 3 ) 2 was added to fluororoethylene carbonate (FEC), which is a non-aqueous solvent, at a content of 1.0 mol / dm 3 to prepare a non-aqueous electrolyte.

[0098] (Assembly of non-aqueous electrolyte storage element) As the separator, a polyethylene microporous membrane was prepared. Using the above positive electrode, negative electrode, separator and non-aqueous electrolyte, a non-aqueous electrolyte storage element of Example 1 was obtained.

[0099] [Examples 2 to 13, Comparative Examples 1 to 9] Except for using the porous carbon having the average pore diameter described in Table 1 and setting the mass per unit area of the positive electrode active material layer and the composition of the non-aqueous solvent as described in Table 1, non-aqueous electrolyte storage elements of Examples 2 to 13 and Comparative Examples 1 to 9 were obtained in the same manner as in Example 1. A part of the examples and comparative examples was extracted and described in Table 2. The non-aqueous solvents used are as follows. FEC: Fluoroethylene carbonate VC: Vinylene carbonate

[0100] [Evaluation] (Initial charge-discharge test) For each of the obtained non-aqueous electrolyte storage elements, first, constant current discharge was performed at a current of 0.1C up to 1.0V as a formation treatment. Thereafter, constant current charging was performed at a current of 0.1C up to 3.0V. Next, constant current discharge was performed at a current of 0.1C up to 1.0V. A rest of 10 minutes was provided after discharge and after charging. Discharge, charging, and rest were all performed in a thermostatic bath at 25°C. The discharge capacity per mass of the positive electrode active material (sulfur monomer) (discharge capacity per mass of the positive electrode active material), average discharge voltage, energy density per mass of the positive electrode active material, and energy density per mass of the positive electrode were determined during the discharge after the above charging. The results are shown in Table 1 and Table 2.

[0101] [Table 1]

[0102] [Table 2]

[0103] As shown in Table 1, each non-aqueous electrolyte storage element of the examples had a higher energy density per mass of the positive electrode active material and a higher energy density per mass of the positive electrode when compared with non-aqueous electrolyte storage elements having the same mass per unit area of the positive electrode active material layer. Further, as is particularly clear from Table 2, in each non-aqueous electrolyte storage element of the examples, the energy density per mass of the positive electrode tended to increase as the mass per unit area of the positive electrode active material layer increased. Furthermore, from the comparison of each non-aqueous electrolyte storage element of the examples in Table 1, the following tendencies can be confirmed. When the mass per unit area of the positive electrode active material layer is large and the content of the fluorinated cyclic carbonate in the non-aqueous solvent is 5% by volume or more and 95% by volume or less, the energy density per mass of the positive electrode active material is higher when compared with non-aqueous electrolyte storage elements having the same mass per unit area of the positive electrode active material layer. On the other hand, when the mass per unit area of the positive electrode active material layer is small, the energy density per mass of the positive electrode active material increases more as the content of the fluorinated cyclic carbonate in the non-aqueous solvent increases, and the discharge capacity per mass of the positive electrode active material also tends to increase. Furthermore, the average discharge voltage tended to increase as the content of the fluorinated cyclic carbonate in the non-aqueous solvent increased.

Industrial Applicability

[0104] The present invention can be applied to non-aqueous electrolyte storage elements used as power sources for electronic devices such as personal computers and communication terminals, automobiles, and the like.

Explanation of Symbols

[0105] 1 Non-aqueous electrolyte storage element 2 Electrode body 3 Container 4 Positive electrode terminal 41 Positive electrode lead 5 Negative electrode terminal 51 Negative electrode lead 20 Power storage unit 30 Power storage device

Claims

1. A positive electrode having a positive electrode active material layer containing a composite of a sulfur-based active material and porous carbon, and a non-aqueous electrolyte containing a non-aqueous solvent containing a fluorinated cyclic carbonate are provided, wherein the average pore diameter of the porous carbon is 3 nm or less, and the content of the fluorinated cyclic carbonate in the non-aqueous solvent is 5% by volume or more. A non-aqueous electrolyte storage element.

2. The mass per unit area of the above positive electrode active material layer is 5 mg / cm ２ or more, the non-aqueous electrolyte storage element according to claim 1.

3. The non-aqueous electrolyte storage element according to claim 2, wherein the content of the fluorinated cyclic carbonate in the non-aqueous solvent is 5% by volume or more and 95% by volume or less.

4. The non-aqueous electrolyte storage element according to claim 2, wherein the content of the fluorinated cyclic carbonate in the non-aqueous solvent is 20% by volume or more.

5. The mass per unit area of the above-mentioned positive electrode active material layer is less than 5 mg / cm ２ and The non-aqueous electrolyte storage element according to claim 1, wherein the content of the fluorinated cyclic carbonate in the non-aqueous solvent is 40% by volume or more.

6. The non-aqueous electrolyte storage element according to any one of claims 1 to 5, wherein the non-aqueous solvent is mainly composed of carbonate.

Images