Positive electrode for nonaqueous electrolyte power storage elements, and nonaqueous electrolyte power storage element

Abstract

A positive electrode for nonaqueous electrolyte power storage elements according to one aspect of the present invention has a positive electrode active material layer that contains a complex of a sulfur-based active material and porous carbon. The average pore diameter of the porous carbon is 3 nm or less, and the mass per unit area of the positive electrode active material layer is 5 mg / cm2 or more.

Description

Positive electrode for non-aqueous electrolyte storage element and non-aqueous electrolyte storage element

[0001] The present invention relates to a positive electrode for a nonaqueous electrolyte storage element and a nonaqueous electrolyte storage element.

[0002] Due to their high energy density, non-aqueous electrolyte secondary batteries, such as lithium ion secondary batteries, are widely used in electronic devices such as personal computers and communication terminals, automobiles, etc. The 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. Furthermore, capacitors such as lithium ion capacitors and electric double layer capacitors are also widely used as non-aqueous electrolyte energy storage elements other than non-aqueous electrolyte secondary batteries.

[0003] Known nonaqueous electrolyte storage elements include lithium-sulfur batteries (Li-S batteries) and other nonaqueous electrolyte storage elements that use a sulfur-based active material as the positive electrode active material (see Patent Document 1). Sulfur-based active materials have a large theoretical capacity, and nonaqueous electrolyte storage elements that use a sulfur-based active material as the positive electrode active material are expected to have high energy density. Furthermore, because sulfur-based active materials have low electronic conductivity, a composite of a sulfur-based active material and a conductive agent such as carbon is sometimes used in the positive electrode.

[0004] JP 2010-95390 A

[0005] To further increase the energy density of a nonaqueous electrolyte storage element using a sulfur-based active material as the positive electrode active material, it is desirable to increase the energy density per mass of the entire positive electrode, including components other than the positive electrode active material.

[0006] An object of the present invention is to provide a positive electrode for a nonaqueous electrolyte storage element having a high energy density per mass of the positive electrode, and a nonaqueous electrolyte storage element including such a positive electrode for a nonaqueous electrolyte storage element.

[0007] A positive electrode for a non-aqueous electrolyte storage element according to one aspect of the present invention has a positive electrode active material layer containing a composite of a sulfur-based active material and porous carbon, the porous carbon having an average pore diameter of 3 nm or less, and a mass per unit area of ​​the positive electrode active material layer of 5 mg / cm.２ That's all.

[0008] A nonaqueous electrolyte storage element according to another aspect of the present invention includes the positive electrode for a nonaqueous electrolyte storage element according to the aspect of the present invention.

[0009] According to any one aspect of the present invention, it is possible to provide a positive electrode for a nonaqueous electrolyte electricity storage element having a high energy density per mass of the positive electrode, and a nonaqueous electrolyte electricity storage element including such a positive electrode for a nonaqueous electrolyte electricity storage element.

[0010] Fig. 1 is a perspective view showing one embodiment of a nonaqueous electrolyte electricity storage element, and Fig. 2 is a schematic view showing one embodiment of an electricity storage device formed by assembling a plurality of nonaqueous electrolyte electricity storage elements.

[0011] First, an outline of the positive electrode for a nonaqueous electrolyte storage element and the nonaqueous electrolyte storage element disclosed in this specification will be described.

[0012] (1) A positive electrode for a nonaqueous electrolyte storage element according to one aspect of the present invention has a positive electrode active material layer containing a composite of a sulfur-based active material and porous carbon, the porous carbon having an average pore diameter of 3 nm or less, and a mass per unit area of ​​the positive electrode active material layer of 5 mg / cm. ２ That's all.

[0013] The positive electrode for a nonaqueous electrolyte storage element (hereinafter simply referred to as "positive electrode") described in (1) above has a high energy density per mass of the positive electrode. The reason for this is unclear, but the following reason is presumed. When the mass per unit area of ​​the positive electrode active material layer is 5 mg / cm ２By increasing the mass ratio of the positive electrode active material layer to the above range, the mass ratio of the sulfur-based active material, which is the positive electrode active material, in the positive electrode is relatively increased, and as a result, the energy density per mass of the positive electrode is increased. Note that when porous carbon having an average pore diameter of more than 3 nm is used, even if the mass per unit area of ​​the positive electrode active material layer is increased, the energy density per mass of the positive electrode does not increase, and may even decrease. The reason for this is unclear, but the following reason is presumed. A composite of a sulfur-based active material and porous carbon (hereinafter simply referred to as a "composite") generally has a form in which the sulfur-based active material is supported in the pores of the porous carbon. Then, usually, during initial discharge, a coating (also referred to as an SEI, reaction layer, etc.) is formed on the surface of the composite due to decomposition of components contained in the non-aqueous electrolyte. Here, when the pore diameter of the porous carbon is large, the non-aqueous electrolyte easily penetrates into the pores, increasing the contact area between the sulfur-based active material supported in the porous carbon and the non-aqueous electrolyte, which is thought to result in a larger amount of coating formed on the surface of the composite. That is, when the pore diameter of the porous carbon is large, an excessive coating is formed on the composite, reducing the void volume in the positive electrode active material layer. In this state, if the mass per unit area of ​​the positive electrode active material layer is large, i.e., the positive electrode active material layer is thick, it is thought that charge-transporting ions in the non-aqueous electrolyte are less likely to diffuse deep into the positive electrode active material layer, making it difficult to increase the energy density per mass of the positive electrode. In contrast, in the positive electrode described in (1) above, in which porous carbon with a small pore diameter is used, the void volume in the positive electrode active material layer is sufficiently maintained, and charge-transporting ions in the non-aqueous electrolyte are more likely to diffuse deep into the positive electrode active material layer, even if the positive electrode active material layer is thick. From the above, it is presumed that the positive electrode described in (1) above has a high energy density per mass of the positive electrode.

[0014] The "average pore diameter" of porous carbon is a value measured by the following method. First, pore size distribution is measured using a nitrogen adsorption method. This measurement can be performed using an "autosorb iQ" manufactured by Quantachrome. Five points are extracted from the region of P / P0 = 0.06 to 0.3 of the resulting adsorption isotherm, and a BET plot is performed. The BET specific surface area is calculated from the y-intercept and slope of the line. In addition, the pore volume is calculated using the BJH method from the total amount of adsorbed gas in the pore size distribution measurement. Assuming that the pores are cylindrical, the pore volume V and the pore surface area A are expressed as follows: V = π × (d / 2) ２ × H A = π × d × H d: pore diameter, H: pore depth (corresponding to the height of the cylinder) Note that in calculating the surface area, the area of ​​the surface corresponding to the bottom 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.

[0015] "Mass per unit area of ​​the positive electrode active material layer (mg / cm ２ ")" is the unit area (1 cm ２ 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 surfaces of the positive electrode substrate at a density of 10 mg / cm, the area of ​​the positive electrode active material layer is equal to the area where the positive electrode active material layer is coated. ２ When the positive electrode active material layer is formed with a coating amount (solid content equivalent) of 10 mg / cm ２ The positive electrode active material layer is formed on one side of the positive electrode substrate in an amount of 10 mg / cm ２ Even when the coating amount (solid content equivalent) of the positive electrode active material layer is 10 mg / cm, the "mass per unit area of ​​the positive electrode active material layer" is 10 mg / cm. ２ That is, in the case of a positive electrode active material layer provided on one or both sides of a 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 on one side.

[0016] (2) A nonaqueous electrolyte storage element according to another aspect of the present invention includes the positive electrode described in (1) above.

[0017] The nonaqueous electrolyte storage element described in (2) above includes the positive electrode described in (1) above, and therefore has a high energy density per mass of the positive electrode.

[0018] (3) The nonaqueous electrolyte storage element according to (2) above may further include a nonaqueous electrolyte containing a nonaqueous solvent containing carbonate as a main component.

[0019] The nonaqueous electrolyte electricity storage element described in (3) above has a higher energy density per mass of the positive electrode.

[0020] The "main component" in the non-aqueous solvent means a component whose content in the non-aqueous solvent is 50% by volume or more.

[0021] The content of each component constituting the non-aqueous solvent is measured by liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-mass spectrometry (GC-MS). Specifically, this is performed as follows. The LC-MS and GC-MS measurements are performed consecutively under the same conditions. 1. Collection of non-aqueous electrolyte First, the non-aqueous electrolyte storage element is disassembled to extract the non-aqueous electrolyte. If the non-aqueous electrolyte cannot be extracted, the non-aqueous electrolyte storage element is centrifuged to extract the non-aqueous electrolyte. If the non-aqueous electrolyte cannot be extracted even after centrifugation, an extraction solvent (e.g., acetonitrile) is injected into the non-aqueous electrolyte storage element, and the non-aqueous electrolyte diluted with the extraction solvent is extracted. 2. LC-MS The components of the extracted non-aqueous electrolyte are analyzed by LC-MS. LC-MS analysis is performed in the following order: qualitative analysis and quantitative analysis. Waters' "Acquity H" and "Xevo G2-5QTof" LC-MS analyzers are used. Water is used as the eluent. (Qualitative Analysis) The measurement sample (non-aqueous electrolyte) is subjected to LC-MS analysis. If the peaks in the obtained liquid chromatogram are not separated, GC-MS analysis, described below, is performed instead of LC-MS analysis. If the peaks are separated, the components contained in the measurement sample are predicted from the MS spectrum of each peak. A known sample of the predicted components (hereinafter referred to as "predicted components") is subjected to LC-MS analysis. The retention time and MS spectrum of the peaks corresponding to each predicted component in the measurement sample are compared with the retention time 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. First, a known sample of the predicted component with a known concentration is measured by LC-MS, and the peak area is calculated to create a calibration curve. ２) is created so that the difference is between 0.999 and 1. The content of the predicted component in the measurement sample is determined from the calibration curve and the area of ​​the peak of the predicted component in the measurement sample. The above process is performed for all peaks detected in the LC-MS analysis of the measurement sample to determine the content of each predicted component. 3. GC-MS GC-MS analysis is performed in the following order: qualitative analysis and quantitative analysis. The GC-MS analysis is performed using an Agilent 5975C. Argon is used as the carrier gas. (Qualitative Analysis) The measurement sample (non-aqueous electrolyte) is subjected to GC-MS analysis. The components contained in the sample are predicted from the MS spectrum of each peak in the obtained gas chromatogram. A known sample of the predicted component is subjected to GC-MS analysis. The retention time and MS spectrum of the peak corresponding to each predicted component in the measurement sample are compared with the retention time and MS spectrum of the peak of a known sample of each predicted component. If they match, the prediction is assumed to be correct. (Quantitative Analysis) Quantitative analysis is performed using a calibration curve method. Quantitative analysis by GC-MS is performed using the same procedure as the quantitative analysis by LC-MS described above, and the content of each predicted component is determined. 4. Calculation of the Content of Each Component The total content of each predicted component (i.e., each component) measured by LC-MS or GC-MS is taken as the content of the non-aqueous solvent, and the content of each component in the non-aqueous solvent is calculated. Note that, when calculating the content (volume %) of each component in the non-aqueous solvent, the mass-based content of each component measured by LC-MS or GC-MS is converted to a volume at 20°C, and the total volume-converted content of each component is taken as the content of the non-aqueous solvent. Furthermore, if an extraction solvent is used, the extraction solvent is excluded from the calculation.

[0022] In a nonaqueous electrolyte storage element using a sulfur-based active material in the positive electrode, when a nonaqueous electrolyte containing an ether-based nonaqueous solvent is used, charge / discharge reactions proceed through a shuttle reaction caused by polysulfides formed at the positive electrode dissolving into the nonaqueous electrolyte. In contrast, in a nonaqueous electrolyte storage element using a sulfur-based active material in the positive electrode, when a nonaqueous electrolyte containing a carbonate-based nonaqueous solvent is used, a coating is formed on the surface of the positive electrode composite by reaction between the positive electrode and the nonaqueous electrolyte (carbonate, etc.), and then charge / discharge reactions proceed through solid-phase diffusion of charge-transporting ions through this coating. Thus, in a nonaqueous electrolyte storage element using sulfur in the positive electrode, the reaction mechanisms at the positive electrode during charge / discharge are thought to be different when a nonaqueous electrolyte containing an ether-based nonaqueous solvent is used and when a nonaqueous electrolyte containing a carbonate-based nonaqueous solvent is used. However, even if the non-aqueous electrolyte does not contain carbonate as a main component and no coating is formed on the surface of the composite, increasing the mass per unit area of ​​the positive electrode active material layer will relatively increase the mass ratio of the positive electrode active material layer in the positive electrode, and ultimately the mass ratio of the sulfur-based active material that is the positive electrode active material. Therefore, with the positive electrode described in (1) above and the non-aqueous electrolyte storage element described in (2) above, the effect of high energy density per mass of the positive electrode can be achieved.

[0023] (4) In the nonaqueous electrolyte storage element described in (3) above, the carbonate may include a fluorinated cyclic carbonate and a non-fluorinated unsaturated cyclic carbonate.

[0024] The nonaqueous electrolyte energy storage element described in (4) above has a higher energy density per mass of the positive electrode. While the reason for this is unclear, the following reasons are presumed. It is believed that the inclusion of a fluorinated cyclic carbonate results in the formation of a coating containing a component with high ionic conductivity (e.g., LiF, etc.), which increases the average discharge voltage. On the other hand, the inclusion of a non-fluorinated unsaturated cyclic carbonate results in the formation of a coating containing a polymer component (e.g., polyvinylene carbonate, etc.), which may increase the discharge capacity per mass of the positive electrode. It is presumed that the formation of a coating containing both of these components further increases the energy density per mass of the positive electrode. Furthermore, in nonaqueous electrolytes, as the content of the fluorinated cyclic carbonate increases, the viscosity tends to increase and the ionic conductivity tends to decrease. When the mass per unit area of ​​the positive electrode active material layer is 5 mg / cm or less, the average discharge voltage is presumed to be 5 mg / cm or less. ２ In other words, when the positive electrode active material layer is thick, the high viscosity of the non-aqueous electrolyte significantly reduces the permeability and ionic conductivity of the non-aqueous electrolyte in the thickness direction of the positive electrode active material layer. In contrast, by using a non-fluorinated unsaturated cyclic carbonate together with a fluorinated cyclic carbonate as the non-aqueous solvent to prevent the non-aqueous electrolyte from becoming too viscous, the permeability and ionic conductivity of the non-aqueous electrolyte in the thickness direction of the positive electrode active material layer are enhanced, and the energy density per mass of the positive electrode is presumably further increased. On the other hand, when the mass per unit area of ​​the positive electrode active material layer is 5 mg / cm, ２ In other words, when the positive electrode active material layer is thin, the influence of the high viscosity of the nonaqueous electrolyte, such as a decrease in permeability, is small. ２ When the mass per unit area of ​​the positive electrode active material layer is less than 5 mg / cm, the effect of increasing the ionic conductivity of the formed coating film by increasing the content of the fluorinated cyclic carbonate in the nonaqueous solvent is significantly achieved. ２ When the nonaqueous solvent is a fluorinated cyclic carbonate alone, the energy density per unit mass of the positive electrode is high. Thus, the suitable solvent composition for increasing the energy density per unit mass of the positive electrode varies depending on the mass per unit area of ​​the positive electrode active material layer.

[0025] A positive electrode for a nonaqueous electrolyte energy storage element, a nonaqueous electrolyte energy storage element, an energy storage device, a method for manufacturing a nonaqueous electrolyte energy storage element, and other embodiments according to one embodiment of the present invention will be described in detail below. Note that the names of the components (elements) used in each embodiment may differ from the names of the components (elements) used in the background art.

[0026] <Positive electrode for non-aqueous electrolyte storage element> A positive electrode according to one embodiment of the present invention includes a positive electrode substrate and a positive electrode active material layer disposed on the positive electrode substrate directly or via an intermediate layer. The positive electrode is used in a non-aqueous electrolyte storage element, and is preferably used in a lithium-sulfur battery. The positive electrode can be suitably used in a non-aqueous electrolyte storage element having a non-aqueous electrolyte containing a carbonate, and is more suitably used in a non-aqueous electrolyte storage element having a non-aqueous solvent containing a carbonate as a main component.

[0027] The positive electrode substrate has electrical conductivity. Whether or not it has electrical conductivity is determined by whether or not the volume resistivity measured in accordance with JIS-H-0505 (1975) is 10 －２ The resistance is determined using Ω cm as a threshold value. Metals such as aluminum, titanium, tantalum, and stainless steel, or alloys thereof, are used as the material for the positive electrode substrate. Among these, aluminum or aluminum alloys are preferred from the viewpoints of potential resistance, high conductivity, and cost. Examples of the positive electrode substrate include foil, vapor-deposited film, mesh, and porous material, with foil being preferred from the viewpoint of cost. Therefore, aluminum foil or aluminum alloy foil is preferred as the positive electrode substrate. Examples of aluminum or aluminum alloys include A1085, A3003, and A1N30, as specified in JIS-H-4000 (2014) or JIS-H-4160 (2006).

[0028] The average thickness of the positive electrode substrate is preferably 3 μm to 50 μm, more preferably 5 μm to 40 μm, even more preferably 8 μm to 30 μm, and particularly preferably 10 μm to 25 μm. By setting the average thickness of the positive electrode substrate within the above range, the strength of the positive electrode substrate can be increased while increasing the energy density per mass or volume of the positive electrode. "Average thickness" refers to the average value of thicknesses measured at any five locations.

[0029] 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 may contain, for example, a binder and a conductive agent.

[0030] The positive electrode active material layer contains a composite of a sulfur-based active material and porous carbon. The positive electrode active material layer contains optional components such as a conductive agent, a binder, a dispersant, a thickener, and a filler, as needed. The positive electrode active material layer is usually formed from a positive electrode mixture containing the composite and other optional components.

[0031] In the composite, a 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 a sulfur-based active material and porous carbon, or may be substantially composed of only a sulfur-based active material and porous carbon. A composite substantially composed of only a 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.

[0032] 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 elemental sulfur, a sulfur compound, or a mixture thereof. That is, the composite may contain elemental sulfur together with porous carbon. 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.

[0033] The sulfur content in the composite (mass ratio of sulfur to the mass of the composite) is preferably 50% by mass or more and 90% by mass or less, and more preferably 55% by mass or more and 80% by mass or less. By setting the sulfur content in the composite within the above range, it is possible to further increase the energy density per mass of the positive electrode.

[0034] 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 on a mass basis. The lower limit of the carbon element 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 element content in porous carbon may be 100 mass% or 99.9 mass%. The carbon element content in porous carbon may be equal to or greater than any of the above-mentioned lower limits and equal to or less than any of the above-mentioned upper limits. Porous carbon may contain elements other than carbon, such as oxygen and nitrogen.

[0035] The upper limit of the average pore diameter of the porous carbon is 3 nm, preferably 3.0 nm, and more preferably 2.5 nm. By having the average pore diameter of the porous carbon be equal to or less than the above upper limit, it is possible to increase the energy density per mass of the positive electrode. The lower limit of the average pore diameter of the porous carbon is, for example, 0.5 nm, or may be 1.0 nm. The average pore diameter of the porous carbon can be equal to or greater than any of the above lower limits and equal to or less than any of the above upper limits. The porous carbon can be selected from conventionally known porous carbons such as activated carbon and have an average pore diameter of 3 nm or less.

[0036] 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.

[0037] 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, and more preferably 70% by mass or more and 90% by mass or less. By setting the content of the composite in this range, it is possible to further increase the energy density per mass of the positive electrode.

[0038] 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 (total of elemental sulfur and sulfur compounds) 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.

[0039] The conductive agent is not particularly limited as long as it is a material having electrical conductivity. Note that this conductive agent does not include the porous carbon that constitutes the composite. Examples of such conductive agents include carbonaceous materials, metals, conductive ceramics, etc. Examples of carbonaceous materials include graphite, non-graphitic carbon, graphene-based carbon, etc. Examples of non-graphitic carbon include carbon nanofiber, pitch-based carbon fiber, carbon black, etc. Examples of carbon black include furnace black, acetylene black, ketjen black, etc. Examples of graphene-based carbon include graphene, carbon nanotubes (CNT), fullerene, etc. The conductive agent may be in the form of powder, fiber, etc. As the conductive agent, one of these materials may be used alone, or two or more may be mixed. These materials may also be used in combination. For example, a composite of carbon black and CNT may be used. Among these, carbon black is preferred from the viewpoints of electronic conductivity and coatability, and acetylene black is particularly preferred. It is also preferable to use carbon black (preferably acetylene black) in combination with CNT.

[0040] 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.

[0041] Examples of binders 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.

[0042] The content of the binder in the positive electrode active material layer is preferably 1% by mass to 10% by mass, more preferably 2% by mass to 9% by mass. By setting the binder content within this range, the composite and the like can be stably maintained.

[0043] 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.

[0044] 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.

[0045] 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 aluminosilicates, 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-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, and 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.

[0046] The positive electrode active material layer may contain typical non-metallic elements such as B, N, P, F, Cl, Br, and I; typical metallic 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, Nb, and W as components other than the composite, other positive electrode active materials, conductive agents, binders, dispersants, thickeners, and fillers.

[0047] The lower limit of the mass per unit area of ​​the positive electrode active material layer is 5 mg / cm ２ and 7 mg / cm ２ is preferred, and 8 mg / cm ２ , 10 mg / cm ２ or 12 mg / cm ２ By setting the mass per unit area of ​​the positive electrode active material layer to the above lower limit or more, the energy density per mass of the positive electrode can be increased. The upper limit of the mass per unit area of ​​the positive electrode active material layer is 30 mg / cm. ２ and 20 mg / cm ２ or 10 mg / cm ２The mass per unit area of ​​the positive electrode active material layer may be equal to or greater than any of the lower limits described above and equal to or less than any of the upper limits described above (however, the upper limit is greater than the lower limit).

[0048] <Non-aqueous electrolyte storage element> A non-aqueous electrolyte storage element (hereinafter also simply referred to as "storage element") according to one embodiment of the present invention comprises an electrode assembly having a positive electrode, a negative electrode, and a separator, a non-aqueous electrolyte, and a container that accommodates the electrode assembly and the non-aqueous electrolyte. The electrode assembly is typically a stacked type in which a plurality of positive electrodes and a plurality of negative electrodes are stacked with separators interposed therebetween, or a wound type in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween and wound. The non-aqueous electrolyte is present in a state contained in the positive electrode, the negative electrode, and the separator. As an example of a non-aqueous electrolyte storage element, a non-aqueous electrolyte secondary battery (hereinafter also simply referred to as "secondary battery") will be described.

[0049] (Positive Electrode) The positive electrode used is the same as that described above as the positive electrode for a nonaqueous electrolyte storage element according to one embodiment of the present invention.

[0050] The negative electrode has a negative electrode substrate and a negative electrode active material layer disposed on the negative electrode substrate directly or via an intermediate layer. The configuration of the intermediate layer is not particularly limited and can be selected from the configurations exemplified for the positive electrode above, for example.

[0051] The negative electrode substrate is conductive. Metals such as copper, nickel, stainless steel, and nickel-plated steel, alloys thereof, and carbonaceous materials are used as the material for the negative electrode substrate. Among these, nickel or nickel alloys are preferred. Examples of the negative electrode substrate include foil, vapor-deposited film, mesh, and porous material, with foil being preferred from the viewpoint of cost. Therefore, nickel foil or nickel alloy foil is preferred as the negative electrode substrate. Examples of copper foil include rolled copper foil and electrolytic copper foil.

[0052] The average thickness of the negative electrode substrate is preferably 2 μm to 35 μm, more preferably 3 μm to 30 μm, even more preferably 4 μm to 25 μm, and particularly preferably 5 μm to 20 μm. By setting the average thickness of the negative electrode substrate within the above range, the strength of the negative electrode substrate can be increased while increasing the energy density per volume of the nonaqueous electrolyte storage element.

[0053] The negative electrode active material layer contains a negative electrode active material. The negative electrode active material layer contains optional components such as a conductive agent, a binder, a thickener, and a filler, as needed. The optional components such as the conductive agent, the binder, the thickener, and the filler can be selected from the materials exemplified for the positive electrode above. The negative electrode active material layer does not necessarily contain optional components such as the conductive agent, the binder, the thickener, and the filler.

[0054] The negative electrode active material layer may contain typical non-metallic elements such as B, N, P, F, Cl, Br, and I; typical metallic 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, Nb, and W as components other than the negative electrode active material, conductive agent, binder, thickener, and filler.

[0055] The negative electrode active material can be appropriately selected from known negative electrode active materials. A material capable of absorbing and releasing lithium ions is usually used as the negative electrode active material for a lithium ion secondary battery. Examples of the negative electrode active material include metallic lithium; metals or semimetals such as Si and Sn; metal oxides or semimetal oxides such as Si oxide, Ti oxide, and Sn oxide; Li ４ Ti ５ O １２ , LiTiO ２、 TiNb ２ O ７ Examples of the negative electrode active material include titanium-containing oxides such as those mentioned above, polyphosphate compounds, silicon carbide, and carbon materials such as graphite and non-graphitizable carbon (easily graphitizable carbon or non-graphitizable carbon). In the case of a negative electrode active material that does not contain charge transport ions such as lithium ions, a material doped with lithium ions or the like can be used.

[0056] Metallic lithium is preferred as the negative electrode active material. 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.

[0057] The negative electrode active material layer may contain a negative electrode active material other than metallic lithium. However, the negative electrode active material layer is preferably a layer consisting essentially of metallic lithium (pure metallic lithium or a 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 even 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 may be equal to or greater than any of the above-mentioned lower limits and equal to or less than the above-mentioned upper limit.

[0058] 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 is preferably 5 μm or more and 1,000 μm or less, more preferably 10 μm or more and 500 μm or less, and even more preferably 30 μm or more and 300 μm or less.

[0059] (Separator) The separator can be appropriately selected from known separators. Examples of separators that can be used include separators consisting of only a substrate layer and separators in which a heat-resistant layer containing heat-resistant particles and a binder is formed on one or both surfaces of the substrate layer. Examples of the shape of the substrate layer of the separator include woven fabric, nonwoven fabric, and porous resin film. Among these shapes, porous resin films are preferred from the viewpoint of strength, and nonwoven fabrics are preferred from the viewpoint of non-aqueous electrolyte retention. Materials for the substrate layer of the separator are preferably polyolefins such as polyethylene and polypropylene from the viewpoint of shutdown function, and polyimide and aramid from the viewpoint of oxidative decomposition resistance. A composite material of these resins may also be used for the substrate layer of the separator.

[0060] The heat-resistant particles contained in the heat-resistant layer preferably exhibit a mass loss of 5% or less when heated from room temperature to 500°C under an air atmosphere at 1 atmosphere, and more preferably exhibit a mass loss of 5% or less when heated from room temperature to 800°C. Examples of materials exhibiting a mass loss 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; covalently bonded crystals such as silicon and diamond; mineral-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, as well as artificial products thereof. As the inorganic compound, these substances may be used alone or in the form of a complex, or two or more of them may be used in combination. Among these inorganic compounds, silicon oxide, aluminum oxide, or aluminosilicate is preferred from the viewpoint of safety of the nonaqueous electrolyte storage element.

[0061] The porosity of the separator is preferably 80% by volume or less from the viewpoint of strength, and is preferably 20% by volume or more from the viewpoint of discharge performance. Here, "porosity" refers to a volume-based value measured with a mercury porosimeter.

[0062] The separator may be a polymer gel composed of a polymer and a non-aqueous electrolyte. Examples of polymers include polyacrylonitrile, polyethylene oxide, polypropylene oxide, polymethyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, and polyvinylidene fluoride. The use of a polymer gel has the effect of suppressing leakage. The separator may be a combination of the porous resin film or nonwoven fabric described above and a polymer gel.

[0063] (Non-aqueous electrolyte) The non-aqueous electrolyte contains a non-aqueous solvent. As the non-aqueous electrolyte, a non-aqueous electrolytic solution containing a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent is usually used. In one embodiment of the present invention, the non-aqueous electrolyte storage element may be a non-aqueous electrolyte storage element.

[0064] The non-aqueous solvent can be appropriately selected from known non-aqueous solvents. Examples of non-aqueous solvents include carbonates, carboxylic acid esters, phosphate esters, sulfonic acid esters, ethers, amides, and nitriles. Non-aqueous solvents in which some of the hydrogen atoms contained in these compounds have been substituted with halogens may also be used.

[0065] The non-aqueous solvent preferably contains a carbonate, and more preferably contains a carbonate as a main component. By containing a carbonate in the non-aqueous solvent, preferably as a main component, the energy density per mass of the positive electrode can be further increased. The lower limit of the carbonate content 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 carbonate content in the non-aqueous solvent may be 100% by volume. The non-aqueous solvent may consist solely 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 the above-mentioned upper limit.

[0066] The carbonate preferably contains at least one of a fluorinated cyclic carbonate and a non-fluorinated unsaturated cyclic carbonate, and more preferably contains both of them. In such a case, the energy density per mass of the positive electrode can be further increased. The lower limit of the total content of the fluorinated cyclic carbonate and 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. The total content of the fluorinated cyclic carbonate and the non-fluorinated unsaturated cyclic carbonate in the non-aqueous solvent can be equal to or greater than any of the above lower limits and equal to or less than the above upper limit.

[0067] A fluorinated cyclic carbonate refers to a compound in which some or all of the hydrogen atoms of a cyclic carbonate have been substituted with fluorine atoms. A cyclic carbonate refers to a carbonate having a ring structure containing a carbonate group (—O—C(═O)—O—). Examples of fluorinated cyclic carbonates 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. A fluorinated saturated cyclic carbonate is a fluorinated cyclic carbonate that does not have a carbon-carbon double bond or a carbon-carbon triple bond in the molecule. One or more fluorinated cyclic carbonates can be used.

[0068] When the non-aqueous solvent contains a fluorinated cyclic carbonate, the lower limit of the content of the fluorinated cyclic carbonate in the non-aqueous solvent is preferably 5% by volume, more preferably 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95% or 99% by volume. By increasing the content of the fluorinated cyclic carbonate, it becomes easier to obtain advantages such as increased ionic conductivity of the formed coating, and for example, the average discharge voltage tends to increase. The upper limit of the content of the fluorinated cyclic carbonate in the non-aqueous solvent may be 100% by mass, and may be preferably 95%, 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20% or 10% by volume. By reducing the content of the fluorinated cyclic carbonate, it becomes easier to obtain advantages such as a lower viscosity of the non-aqueous electrolyte, and for example, the discharge capacity per mass of the positive electrode tends to be increased. The content of the fluorinated cyclic carbonate in the non-aqueous solvent can be equal to or greater than any of the lower limits described above and equal to or less than any of the upper limits described above (however, the upper limit is greater than the lower limit).

[0069] The non-fluorinated unsaturated cyclic carbonate refers to a compound in which the hydrogen atoms of the unsaturated cyclic carbonate are not substituted with fluorine atoms. The unsaturated cyclic carbonate is a cyclic carbonate having a carbon-carbon double bond or a carbon-carbon triple bond in the molecule, and is preferably a cyclic carbonate having a carbon-carbon double bond in the molecule. Examples of the non-fluorinated unsaturated cyclic carbonate include vinylene carbonate (VC), methyl vinylene carbonate, ethyl vinylene carbonate, propyl vinylene carbonate, butyl vinylene carbonate, dimethyl vinylene carbonate, diethyl vinylene carbonate, dipropyl vinylene carbonate, and vinyl ethylene carbonate, with VC being preferred. One or more types of non-fluorinated unsaturated cyclic carbonates can be used.

[0070] When the non-aqueous solvent contains a non-fluorinated unsaturated cyclic carbonate, the lower limit of the content of the non-fluorinated unsaturated cyclic carbonate in the non-aqueous solvent is preferably 5% by volume, more preferably 10% by volume, 20% by volume, 30% by volume, 40% by volume, 50% by volume, 60% by volume, 70% by volume, 80% by volume, 90% by volume, 95% by volume or 99% by volume may be more preferred. By increasing the content of the non-fluorinated unsaturated cyclic carbonate, the discharge capacity per mass of the positive electrode tends to increase. The upper limit of the content of the non-fluorinated unsaturated cyclic carbonate in the non-aqueous solvent may be 100% by volume, and may be 95% by volume, 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 may be preferred. The content of the non-fluorinated unsaturated cyclic carbonate 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 any of the above-mentioned upper limits (however, the upper limit is greater than the lower limit).

[0071] The volume ratio of the fluorinated cyclic carbonate to the non-fluorinated unsaturated cyclic carbonate in the non-aqueous solvent (fluorinated cyclic carbonate:non-fluorinated unsaturated cyclic carbonate) is preferably in the range of 5:95 to 95:5, more preferably in the range of 10:90 to 90:10, even more preferably in the range of 40:60 to 80:20, and even more preferably in the range of 60:40 to 75:25. By having the volume ratio of the fluorinated cyclic carbonate to the non-fluorinated unsaturated cyclic carbonate in the above range, the balance between the fluorinated cyclic carbonate and the non-fluorinated unsaturated cyclic carbonate is optimized, and the energy density per mass of the positive electrode can be further increased.

[0072] The non-aqueous solvent may use a carbonate other than a fluorinated cyclic carbonate or a non-fluorinated unsaturated cyclic carbonate. Examples of other carbonates include chain carbonates and non-fluorinated saturated cyclic carbonates. Chain carbonates refer to carbonates that do not have a ring structure containing a carbonate group. Examples of chain carbonates 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), etc. Examples of non-fluorinated saturated cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), chloroethylene carbonate, etc. These other carbonates may be used in conjunction with or in place of the fluorinated cyclic carbonates and non-fluorinated unsaturated cyclic carbonates.

[0073] The electrolyte salt can be appropriately selected from known electrolyte salts, such as lithium salts, sodium salts, potassium salts, magnesium salts, and onium salts. Of these, lithium salts are preferred.

[0074] 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 salts, lithium bis(oxalate)borate (LiBOB), lithium difluorooxalateborate (LiFOB), and lithium bis(oxalate)difluorophosphate (LiFOP); 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 Among these, inorganic lithium salts are preferred, and LiPF ６ and LiN(SO ２ F) ２ is more preferred, and LiN(SO ２ F) ２ is more preferable. 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 other imide salts are also preferred. ２ CF ３ ) ２ is more preferred.

[0075] The content of the electrolyte salt in the non-aqueous electrolyte solution is 0.1 mol / dm at 20°C and 1 atmosphere. ３ 2.5mol / dm or more ３ It is preferably 0.3 mol / dm or less. ３ 2.0mol / dm or more ３ It is more preferable that it is 0.5 mol / dm or less. ３ More than 1.7mol / dm ３ It is more preferable that it is 0.7 mol / dm or less. ３ 1.5mol / dm or more ３ By setting the content of the electrolyte salt within the above range, the ionic conductivity of the non-aqueous electrolyte can be increased.

[0076] The non-aqueous electrolyte may contain additives in addition to the non-aqueous solvent and the electrolyte salt. Examples of the additives include oxalates such as lithium bis(oxalate)borate (LiBOB), lithium difluorooxalateborate (LiFOB), and lithium bis(oxalate)difluorophosphate (LiFOP); imide salts such as lithium bis(fluorosulfonyl)imide (LiFSI); aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran; partial halides of the 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, and glutaconic anhydride. Examples of the alkyl acrylate include 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-propene sultone, 1,3-propane sultone, 1,4-butane sultone, 1,4-butene sultone, perfluorooctane, tristrimethylsilyl borate, tristrimethylsilyl phosphate, tetrakistrimethylsilyl titanate, lithium monofluorophosphate, and lithium difluorophosphate. These additives may be used alone or in combination of two or more.

[0077] The content of the additive contained 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, based on the total mass of the 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, and further improve safety.

[0078] The nonaqueous electrolyte may be a combination of a nonaqueous electrolytic solution and a solid electrolyte. The solid electrolyte may be selected from any material that has lithium ion conductivity and is solid at room temperature (e.g., 15°C to 25°C). Examples of the solid electrolyte include sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, halide solid electrolytes, and polymer solid electrolytes.

[0079] The shape of the nonaqueous electrolyte storage element of this embodiment is not particularly limited, and examples thereof include cylindrical batteries, prismatic batteries, flat batteries, coin batteries, and button batteries.

[0080] Figure 1 shows a nonaqueous electrolyte storage element 1 as an example of a prismatic battery. The figure is a see-through view of the inside of the container. An electrode assembly 2 having a positive electrode and a negative electrode wound with a separator sandwiched between them 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.

[0081] <Electricity Storage Device> The nonaqueous electrolyte energy storage element of the present embodiment can be mounted as an energy storage unit (battery module) comprising a plurality of nonaqueous electrolyte energy storage elements in an automobile power source such as an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), etc., a power source for electronic devices such as a personal computer or a communication terminal, or a power source for power storage, etc. In this case, the technology of the present invention may be applied to at least one nonaqueous electrolyte energy storage element included in the energy storage unit.

[0082] 2 shows an example of an energy storage device 30 in which energy storage units 20, each of which is an assembly of two or more electrically connected nonaqueous electrolyte energy storage elements 1, are further assembled. The energy storage device 30 may include a bus bar (not shown) that electrically connects two or more nonaqueous electrolyte energy storage elements 1, a bus bar (not shown) that electrically connects two or more energy storage units 20, etc. The energy storage unit 20 or the energy storage device 30 may include a status monitoring device (not shown) that monitors the status of one or more nonaqueous electrolyte energy storage elements.

[0083] <Method for manufacturing nonaqueous electrolyte storage element> The method for manufacturing the nonaqueous electrolyte storage element of this embodiment can be appropriately selected from known methods. The manufacturing method includes, for example, preparing an electrode assembly, preparing a nonaqueous electrolyte, and housing the electrode assembly and the nonaqueous electrolyte in a container. Preparing the electrode assembly includes preparing a positive electrode and a negative electrode, and forming the electrode assembly by stacking or winding the positive electrode and the negative electrode with a separator interposed therebetween.

[0084] The method for placing 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, the non-aqueous electrolyte solution may be poured into the container through an inlet formed in the container, and then the inlet may be sealed.

[0085] The manufacturing method may include performing initial charging and discharging on an undischarged nonaqueous electrolyte storage element. The initial charging and discharging usually starts with discharging. The first discharge may be referred to as a chemical conversion treatment. The number of times of charging and discharging in the initial charging and discharging is not particularly limited. By undergoing the initial charging and discharging or chemical conversion treatment, a good coating can be formed on the positive electrode composite due to partial decomposition of the nonaqueous electrolyte.

[0086] <Other Embodiments> The nonaqueous electrolyte storage element of the present invention is 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.

[0087] In the above embodiment, the nonaqueous electrolyte storage element is used as a chargeable and dischargeable nonaqueous electrolyte secondary battery (e.g., a lithium-sulfur battery), but the type, shape, size, capacity, etc. of the nonaqueous electrolyte storage element are arbitrary. The present invention can also be applied to various secondary batteries, capacitors, etc.

[0088] In the above embodiment, the electrode assembly in which the positive electrode and the negative electrode are stacked with a separator interposed therebetween has been described, but 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 in a state in which a non-conductive layer is formed on the active material layer of the positive electrode or the negative electrode.

[0089] 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.

[0090] [Example 1] (Preparation of Positive Electrode) Microporous carbon with an average pore diameter of 2 nm was prepared as the porous carbon. Elemental sulfur, a sulfur-based active material, and the porous carbon were mixed in a mass ratio of 70:30. This mixture was placed in a sealed electric furnace. After argon flow for 1 hour, the temperature was increased to 150 ° C at a rate of 5 ° C / min and held for 5 hours. After that, the mixture was allowed to cool to 80 ° C, the temperature at which elemental sulfur solidifies. The temperature was then increased again to 300 ° C at a rate of 5 ° C / min and held for 2 hours to prepare a composite (sulfur-porous carbon composite: SPC). A positive electrode mixture paste containing the composite obtained above, acetylene black and CNT as a conductive agent, PAA 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. After drying the dispersion medium, the mass per unit area of ​​the positive electrode active material layer was 15 mg / cm ２ The amount of the positive electrode mixture paste applied was adjusted so that the positive electrode active material layer was formed on the positive electrode substrate. The positive electrode active material layer contained 93% by mass of the composite.

[0091] (Preparation of Negative Electrode) A pure metallic lithium foil was prepared as the negative electrode.

[0092] (Preparation of non-aqueous electrolyte) A non-aqueous solvent was prepared by mixing fluoroethylene carbonate (FEC) and vinylene carbonate (VC) in a volume ratio of 50:50, and LiN(SO 4 ) was added as an electrolyte salt. ２ CF ３ ) ２ to 1.0 mol / dm ３ The non-aqueous electrolyte was prepared by adding the above-mentioned components in an amount of 1:1.

[0093] (Assembly of Nonaqueous Electrolyte Storage Element) A polyethylene microporous film was prepared as a separator. The positive electrode, negative electrode, separator, and nonaqueous electrolyte were used to obtain a nonaqueous electrolyte storage element of Example 1.

[0094] [Examples 2 to 8, Comparative Examples 1 to 10] Nonaqueous electrolyte storage elements of Examples 2 to 8 and Comparative Examples 1 to 10 were obtained in the same manner as in Example 1, except that porous carbons having average pore diameters shown in Tables 1 and 2 were used and that the mass per unit area of ​​the positive electrode active material layer and the composition of the nonaqueous solvent were as shown in Tables 1 and 2. Example 1 and Comparative Example 1 are shown in both Tables 1 and 2.

[0095] [Evaluation] (Initial Charge / Discharge Test) Each of the obtained nonaqueous electrolyte storage elements was first subjected to a chemical conversion treatment, whereby constant-current discharge was performed at a current of 0.1 C down to 1.0 V. Thereafter, constant-current charging was performed at a current of 0.1 C down to 3.0 V. Next, constant-current discharging was performed at a current of 0.1 C down to 1.0 V. A 10-minute pause was provided after discharge and charge. Discharge, charge, and pause were all performed in a thermostatic chamber at 25°C. The discharge capacity per mass of the positive electrode, average discharge voltage, energy density per mass of the positive electrode active material (sulfur element) (energy density per mass of the positive electrode active material), and energy density per mass of the positive electrode during discharge after the above charge were determined. The results are shown in Tables 1 and 2.

[0096]

[0097]

[0098] As shown in Tables 1 and 2, the average pore diameter of the porous carbon is 3 nm or less, and the mass per unit area of ​​the positive electrode active material layer is 5 mg / cm ２The nonaqueous electrolyte storage elements of Examples 1 to 8 each had a high energy density per mass of the positive electrode exceeding 500 Wh / kg. In contrast, when the average pore diameter of the porous carbon was 3 nm or more, as in the nonaqueous electrolyte storage elements of Comparative Examples 2 and 3 shown in Table 1, the energy density per mass of the positive electrode did not become high even when the mass per unit area of ​​the positive electrode active material layer was increased. Furthermore, as shown in Table 2, when the average pore diameter of the porous carbon was 3 nm or less and the mass per unit area of ​​the positive electrode active material layer was 5 mg / cm ２ In each of the nonaqueous electrolyte storage elements of the above Examples, the inclusion of a fluorinated cyclic carbonate in the nonaqueous solvent increased the average discharge voltage, and the inclusion of a non-fluorinated unsaturated cyclic carbonate increased the discharge capacity per mass of the positive electrode. As a result, the inclusion of both a fluorinated cyclic carbonate and a non-fluorinated unsaturated cyclic carbonate tended to increase the energy density per mass of the positive electrode. This is because the greater the content of fluorinated cyclic carbonate in the nonaqueous solvent, the greater the discharge capacity per mass of the positive electrode and the higher the energy density per mass of the positive electrode. In Comparative Examples 5 to 10, the mass per unit area of ​​the positive electrode active material layer was 5 mg / cm. ２ This was a different tendency from that of the nonaqueous electrolyte storage element having a capacitance of less than 100 kJ / cm.

[0099] The present invention can be applied to nonaqueous electrolyte electricity storage elements used as power sources for electronic devices such as personal computers and communication terminals, and automobiles.

[0100] REFERENCE SIGNS LIST 1 nonaqueous electrolyte energy storage element 2 electrode body 3 container 4 positive electrode terminal 41 positive electrode lead 5 negative electrode terminal 51 negative electrode lead 20 energy storage unit 30 energy storage device

Claims

1. A positive electrode active material layer including a composite of a sulfur-based active material and porous carbon, the average pore diameter of the porous carbon being 3 nm or less, and the mass per unit area of ​​the positive electrode active material layer being 5 mg / cm ２ The above is the positive electrode for a nonaqueous electrolyte storage element.

2. A non-aqueous electrolyte storage element comprising the positive electrode for a non-aqueous electrolyte storage element according to claim 1.

3. The nonaqueous electrolyte storage element according to claim 2, further comprising a nonaqueous electrolyte containing a nonaqueous solvent mainly composed of carbonate.

4. The nonaqueous electrolyte storage element according to claim 3, wherein the carbonate comprises a fluorinated cyclic carbonate and a non-fluorinated unsaturated cyclic carbonate.

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