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

Abstract

To provide a positive electrode for a nonaqueous electrolyte power storage element with increased energy density per mass of the positive electrode and the nonaqueous electrolyte power storage element including the same.SOLUTION: The positive electrode for a nonaqueous electrolyte power storage element has a positive electrode active material layer including a composite of a sulfur-based active material and a porous carbon. The average pore diameter of the porous carbon is 3 nm or less. The mass per unit area of the positive electrode active material layer is 5 mg / cm2 or more.SELECTED DRAWING: Figure 1

Description

Technical Field

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

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 because of their high energy density. Generally, the non-aqueous electrolyte secondary battery 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. In addition, as non-aqueous electrolyte storage elements other than non-aqueous electrolyte secondary batteries, capacitors such as lithium-ion capacitors and electric double layer capacitors are also widely spread.

[0003] As non-aqueous electrolyte storage elements, non-aqueous electrolyte storage elements 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 storage element using a sulfur-based active material as a positive electrode active material is expected as a storage element having a high energy density. In addition, 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] In order to further increase the energy density of a non-aqueous electrolyte storage element in which a sulfur-based active material is used as the positive electrode active material, it is desirable to increase the energy density per unit 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 non-aqueous electrolyte storage element having a high energy density per unit mass of the positive electrode, and a non-aqueous electrolyte storage element including such a positive electrode for a non-aqueous electrolyte storage element.

Means for Solving the Problems

[0007] The 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 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 2 or more.

[0008] The non-aqueous electrolyte storage element according to another aspect of the present invention includes the positive electrode for a non-aqueous electrolyte storage element according to one aspect of the present invention.

Effects of the Invention

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

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

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

[0012] (1) The 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 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 2 or more.

[0013] The positive electrode for a non-aqueous electrolyte storage element described in the above (1) (hereinafter, also simply referred to as "positive electrode") has a high energy density per unit mass of the positive electrode. The reason for this is not clear, but the following reasons are presumed. The mass per unit area of the positive electrode active material layer is 5 mg / cm 2By increasing it as described above, the mass ratio of the positive electrode active material layer in the positive electrode, and consequently the mass ratio of the sulfur-based active material as the positive electrode active material, increases. 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 instead decrease. The reason for this is not clear, but the following reasons are speculated. In the composite of the sulfur-based active material and porous carbon (hereinafter, also simply referred to as "composite"), it is common for the sulfur-based active material to be supported within the pores of the porous carbon. And usually, during the initial discharge, a film (also referred to as SEI, reaction layer, etc.) is formed on the surface of the composite due to the decomposition of the components contained in the non-aqueous electrolyte. Here, when the pore diameter of the porous carbon is large, it becomes easier for the non-aqueous electrolyte to penetrate into the pores. Therefore, it is considered that the contact area between the sulfur-based active material supported within 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 amount of film is formed on 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-transporting ions in the non-aqueous electrolyte to diffuse to the deep position of the positive electrode active material layer. Therefore, it is speculated that it is difficult for the energy density per unit mass of the positive electrode to increase. On the other hand, in the positive electrode described in the above (1) using porous carbon with a small pore diameter, the void volume in the positive electrode active material layer is sufficiently maintained, and even if the positive electrode active material layer is thick, the charge-transporting ions in the non-aqueous electrolyte can easily diffuse to the deep position of the positive electrode active material layer. From the above, it is speculated that the positive electrode described in the above (1) has a high energy density per unit mass of the positive electrode.

[0014] The "average pore diameter" of the porous carbon is the value measured by the following method. First, the pore size distribution measurement is performed using the nitrogen adsorption method. This measurement can be carried out by "autosorb iQ" manufactured by Quantachrome Corporation. 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 size 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 pore (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.

[0015] The "mass per unit area of the positive electrode active material layer (mg / cm 2 )" 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 side 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 , 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.

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

[0017] Since the non-aqueous electrolyte storage element described in (2) above includes the positive electrode described in (1) above, the energy density per unit mass of the positive electrode is high.

[0018] (3) In the non-aqueous electrolyte storage element described in (2) above, it may further include a non-aqueous electrolyte containing a non-aqueous solvent mainly composed of carbonate.

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

[0020] 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.

[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, it is carried out as follows. The measurements of LC-MS and GC-MS are each carried out continuously under the same conditions. 1. Sampling of non-aqueous electrolyte First, disassemble the non-aqueous electrolyte storage element 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 even after centrifuging, an extraction solvent (for example, 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 The components of the non-aqueous electrolyte taken are analyzed by LC-MS. The LC-MS analysis is performed in the following order of qualitative analysis and quantitative analysis. For the LC-MS analysis apparatus, "Acquity H" and "Xevo G2-5QTof" manufactured by Waters 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 later is performed instead of LC-MS analysis. If the peaks are separated, the components contained in the measurement sample are predicted from the MS spectra of each peak. Known samples of the predicted components (hereinafter referred to as "predicted components") are subjected to LC-MS analysis. The retention time and MS spectrum of the peak corresponding to each predicted component in the measurement sample are compared with the retention time and MS spectrum of the peak of the known sample of each predicted component. If they match, it is presumed that the above prediction is correct. (Quantitative analysis) The quantitative analysis is performed by the calibration curve method. First, known samples of predicted components with known concentrations are measured by LC-MS, the areas of the peaks are determined, and a calibration curve is created. The calibration curve is created so that the coefficient of determination (r 2 ) is between 0.999 and 1. From the calibration curve and the area of the peak of the predicted component in the measurement sample, the content of the predicted component in the measurement sample is determined. The above operations are performed 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 following order of qualitative analysis and quantitative analysis. For the GC-MS analysis apparatus, "5975C" manufactured by Agilent is used. 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 spectra of each peak in the obtained gas chromatogram. Known samples of the predicted components are 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 the known sample of each predicted component. If they match, it is presumed 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 Using 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 of the contents of each component after volume conversion as the content of the non-aqueous solvent. Also, when an extraction solvent is used, the extraction solvent is considered excluded.

[0022] 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 shuttle reaction due to the dissolution of polysulfides formed on the positive electrode into the non-aqueous electrolyte causes the charge-discharge reaction to proceed. 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, and 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 of using a non-aqueous electrolyte containing a non-aqueous solvent mainly composed of ether and the case of using a non-aqueous electrolyte containing a non-aqueous solvent mainly composed of carbonate. However, even if the non-aqueous electrolyte does not mainly contain carbonate and a film is not formed on the surface of the composite, by increasing the mass per unit area of the positive electrode active material layer, the mass ratio of the positive electrode active material layer in the positive electrode, and thus the mass ratio of the sulfur-based active material as the positive electrode active material, relatively increases. Therefore, in the case of the positive electrode described in the above (1) and the non-aqueous electrolyte storage element described in the above (2), the effect of a high energy density per unit 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 storage element described in (4) above has a higher energy density per mass of the positive electrode. The reason for this is unclear, but the following reasons are presumed. When a fluorinated cyclic carbonate is contained, a coating containing a component with high ion conductivity (e.g., LiF, etc.) is formed, and it is believed that the average discharge voltage increases. On the other hand, when a non-fluorinated unsaturated cyclic carbonate is contained, a coating containing a polymer component (e.g., polyvinylene carbonate, etc.) is formed, and it is believed that the discharge capacity per mass of the positive electrode may be increased. It is presumed that the energy density per mass of the positive electrode is further increased by forming a coating containing both of these components. In addition, in the case of a non-aqueous electrolyte, when the content of the fluorinated cyclic carbonate is large, the viscosity tends to increase and the ionic conductivity tends to decrease. 2 That is, when the positive electrode active material layer is thick, the high viscosity of the non-aqueous electrolyte has a large effect on the decrease in the permeability and ion conductivity of the non-aqueous electrolyte in the thickness direction of the positive electrode active material layer. In contrast, it is presumed that the use of a non-fluorinated unsaturated cyclic carbonate together with a fluorinated cyclic carbonate as a non-aqueous solvent to suppress the increase in viscosity of the non-aqueous electrolyte increases the permeability and ion conductivity of the non-aqueous electrolyte in the thickness direction of the positive electrode active material layer, thereby further increasing the energy density per mass of the positive electrode. 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 coating film formed by increasing the content of the fluorinated cyclic carbonate in the nonaqueous solvent is significantly achieved.2 When it is less, if the non-aqueous solvent is only fluorinated cyclic carbonate, the energy density per unit mass of the positive electrode is high. Thus, due to the difference in the mass per unit area of the positive electrode active material layer, the suitable solvent composition for increasing the energy density per unit mass of the positive electrode is different.

[0025] The positive electrode for a non-aqueous electrolyte storage element, non-aqueous electrolyte storage element, power storage device, method for manufacturing a non-aqueous electrolyte storage element, and other embodiments according to one 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.

[0026] <Positive Electrode for Non-Aqueous Electrolyte Storage Element> The positive electrode according to one embodiment of the present invention has a positive electrode substrate and a positive electrode active material layer disposed directly or via an intermediate layer on the positive electrode substrate. 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 including a non-aqueous electrolyte containing carbonate, and more preferably in a non-aqueous electrolyte storage element including a non-aqueous solvent containing carbonate as a main component.

[0027] 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 a 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 foil, vapor deposition film, mesh, porous material, etc., and 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).

[0028] 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 per volume of the positive electrode. The "average thickness" refers to the average value of the 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 for example, it contains 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 may contain optional components such as a conductive agent, a binder, a dispersant, a thickener, and a filler as necessary. 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, 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 the porous carbon, or may consist of only the sulfur-based active material and the porous carbon. That the composite consists essentially of only the sulfur-based active material and the porous carbon means, for example, that the total content of the sulfur-based active material (total of sulfur and sulfur compounds) and the 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, it is sufficient that the composite contains sulfur element together with 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.

[0033] 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, and 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, the energy density per mass of the positive electrode can be further increased.

[0034] The porous carbon has conductivity. Porous carbon is generally a porous inorganic material having carbon element as the main constituent element. The main constituent element means the element having 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, and 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.

[0035] 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 below the above upper limit, it is possible to increase the energy density per mass of the positive electrode and the like. The lower limit of the average pore diameter of the porous carbon is, for example, 0.5 nm, and it may be 1.0 nm. The average pore diameter of the porous carbon can be set to be not less than any of the above-mentioned lower limits and not more than any of the above-mentioned upper limits. The porous carbon can be selected and used from among conventionally known porous carbons such as activated carbon that have an average pore diameter of 3 nm or less.

[0036] 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.

[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, 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 further increase the energy density per mass of the positive electrode and the like.

[0038] 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.

[0039] 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, etc. Examples of carbonaceous materials include graphite, non-graphite carbon, graphene-based carbon, etc. Examples of non-graphite carbon include carbon nanofibers, pitch-based carbon fibers, 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), fullerenes, etc. Examples of the shape of the conductive agent include powder form, fibrous form, etc. As the conductive agent, one of these materials may be used alone, or two or more kinds may be mixed and used. Also, these materials may be used in a composite form. For example, a material in which carbon black and CNT are composite may be used. Among these, carbon black is preferable from the viewpoints of electron conductivity and coatability, and acetylene black is particularly preferable. Also, it is preferable to use carbon black (preferably acetylene black) and CNT in combination.

[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 mass% or more and 20 mass% or less, and more preferably 1 mass% or more and 15 mass% or less. By setting the content of the conductive agent within the above range, the energy density per mass of the positive electrode, etc. can be increased.

[0041] Examples of the binder include thermoplastic resins such as fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), polyethylene, polypropylene, polyacrylic, polyimide, etc.; elastomers such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, etc.; polysaccharide polymers, etc.

[0042] 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, complexes and the like can be stably retained.

[0043] 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 may function as a binder.

[0044] Examples of the thickener include polyacrylic acid (PAA) and the like. 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, and magnesium oxide, 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, and mineral resource-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, 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.

[0046] The positive electrode active material layer may contain typical non-metal elements such as B, N, P, F, Cl, Br, I, etc., typical metal elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, Ba, etc., and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, W, etc. 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 preferably 7 mg / cm 2 more preferably 8 mg / cm 2 , 10 mg / cm 2 or 12 mg / cm 2 is even more preferable. By setting the mass per unit area of the positive electrode active material layer to be equal to or higher than the above lower limit, the energy density per unit mass of the positive electrode can be increased. The upper limit of the mass per unit area of the positive electrode active material layer may be 30 mg / cm 2 or may be 20 mg / cm 2 or 10 mg / cm 2 The mass per unit area of the positive electrode active material layer can be set to be equal to or higher than any of the above lower limits and equal to or lower than any of the above upper limits (provided that the upper limit is greater than the lower limit).

[0048] <Non-aqueous electrolyte energy storage device> The non-aqueous electrolyte energy storage device (hereinafter, also simply referred to as "energy storage device") according to an embodiment of the present invention includes an electrode body having a positive electrode, a negative electrode, and a separator, a non-aqueous electrolyte, and a container for housing 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 the positive electrode and the negative electrode are wound in a state of being laminated via a separator. The non-aqueous electrolyte exists in a state contained in the positive electrode, the negative electrode, and the separator. As an example of the non-aqueous electrolyte energy storage device, a non-aqueous electrolyte secondary battery (hereinafter, also simply referred to as "secondary battery") will be described.

[0049] (Positive electrode) The positive electrode uses the one described above as the positive electrode for a non-aqueous electrolyte storage element according to an embodiment of the present invention.

[0050] (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 for example, it can be selected from the configurations exemplified for the positive electrode above.

[0051] 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.

[0052] 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, further 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, the strength of the negative electrode substrate can be increased while increasing the energy density per unit volume of the non-aqueous 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 necessary. The optional components such as a conductive agent, a binder, a thickener, and a filler can be selected from the materials exemplified for the positive electrode above. The negative electrode active material layer may not contain optional components such as a conductive agent, a binder, a thickener, and a filler.

[0054] The negative electrode active material layer may contain, as components other than the negative electrode active material, conductive agent, binder, thickener, and filler, typical non-metal elements such as B, N, P, F, Cl, Br, I, etc., typical metal elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, Ba, etc., and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, W, etc.

[0055] 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, a material doped with lithium ions or the like can be used.

[0056] As the negative electrode active material, metallic lithium is preferred. The metallic lithium may be pure metallic lithium consisting essentially of only lithium element, or a lithium alloy containing other metal 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 metal elements other than the lithium element.

[0057] 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 essentially of only 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 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 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 limit.

[0058] 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.

[0059] (Separator) The separator can be appropriately selected from known separators. As the separator, for example, a separator consisting of only 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 preferred from the viewpoint of strength, and a non-woven fabric is preferred 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 preferred from the viewpoint of the shut-down function, and polyimides and aramids are preferred from the viewpoint of oxidation decomposition resistance. A composite material of these resins may be used as the base material layer of the separator.

[0060] The heat-resistant particles contained in the heat-resistant layer preferably have a mass loss of 5% or less when heated from room temperature to 500 °C in an air atmosphere at 1 atm, and more preferably have a mass loss of 5% or less when heated from room temperature to 800 °C. Examples of materials with a mass loss of a predetermined amount 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; and substances derived from mineral resources such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or artificial products thereof. As the inorganic compound, these substances may be used alone or in combination, or two or more of them may be mixed and used. Among these inorganic compounds, from the viewpoint of the safety of non-aqueous electrolyte storage elements, silicon oxide, aluminum oxide, or aluminosilicate is preferred.

[0061] From the viewpoint of strength, the porosity of the separator is preferably 80% by volume or less, and from the viewpoint of discharge performance, it is preferably 20% by volume or more. Here, the "porosity" is a value based on volume and means the measured value by a mercury porosimeter.

[0062] 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, and polyvinylidene fluoride. 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 may be used in combination with a polymer gel.

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

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

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

[0066] As the carbonate, it is preferably 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, it is possible to further increase the energy density per mass of the positive electrode, etc. 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 above 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 more than any of the above lower limits and equal to or less than or less than the above upper limits.

[0067] 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.

[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, and may be 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. By increasing the content of the fluorinated cyclic carbonate, advantages such as an increase in the ionic conductivity of the formed film are easily obtained. 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% 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. By decreasing the content of the fluorinated cyclic carbonate, advantages such as a decrease in the viscosity of the non-aqueous electrolyte are easily obtained. For example, the discharge capacity per unit mass of the positive electrode tends to increase. The content of the fluorinated cyclic carbonate in the non-aqueous solvent can be set to be equal to or higher than any of the above lower limits and equal to or lower than any of the above upper limits (provided that 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 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, vinyl ethylene carbonate, etc., and VC is preferred. One or more 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, and may be 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. By increasing the content of the non-fluorinated unsaturated cyclic carbonate, the discharge capacity per unit 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 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, 20% by volume or 10% by volume. The content of the non-fluorinated unsaturated 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 (provided that 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, still more preferably in the range of 40:60 to 80:20, and even more preferably in the range of 60:40 to 75:25. When the volume ratio of the fluorinated cyclic carbonate to the non-fluorinated unsaturated cyclic carbonate is within the above range, the balance between the fluorinated cyclic carbonate and the non-fluorinated unsaturated cyclic carbonate is optimized, and the energy density per unit mass of the positive electrode can be further increased, etc.

[0072] As the non-aqueous solvent, carbonates other than fluorinated cyclic carbonates and non-fluorinated unsaturated cyclic carbonates may be used. Examples of other carbonates include chain carbonates, non-fluorinated saturated cyclic carbonates, and the like. A chain carbonate refers to a carbonate that does not have a ring structure containing a carbonate group among carbonates. 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), and the like. Examples of non-fluorinated saturated cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), chloroethylene carbonate, and the like. These other carbonates may be used together with fluorinated cyclic carbonates and non-fluorinated unsaturated cyclic carbonates, or may be used in place of fluorinated cyclic carbonates and non-fluorinated unsaturated cyclic carbonates.

[0073] As the electrolyte salt, it can be appropriately selected from known electrolyte salts. Examples of electrolyte salts include lithium salts, sodium salts, potassium salts, magnesium salts, onium salts, and the like. Among these, lithium salts are preferred.

[0074] Examples of lithium salts include inorganic lithium salts such as LiPF 6 , LiPO 2 F 2 , LiBF 4 , LiClO 4 , LiN(SO 2 F) 2 , lithium oxalate salts such as lithium bis(oxalate) borate (LiBOB), lithium difluorooxalate borate (LiFOB), lithium bis(oxalate) difluorophosphate (LiFOP), LiSO 3 CF 3 , LiN(SO 2 CF 3 ) 2 , LiN(SO 2 C2 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 Examples of the lithium salt include those having a halogenated hydrocarbon group such as these. Among these, inorganic lithium salts are preferred, and LiPF 6 and LiN(SO 2 F) 2 are more preferred, and LiN(SO 2 F) 2 is even more preferred. Also, it is preferable that they are imide salts such as 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 ), etc., and LiN(SO 2 CF 3 ) 2 is more preferred.

[0075] 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 still more 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. By setting the content of the electrolyte salt within the above range, the ionic conductivity of the non-aqueous electrolyte can be increased.

[0076] In addition to the non-aqueous solvent and the electrolyte salt, the non-aqueous electrolyte 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; partial halides 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, 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 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, based on 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.

[0078] 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.

[0079] The shape of the non-aqueous electrolyte storage element of this embodiment is not particularly limited, and examples include cylindrical batteries, rectangular batteries, flat batteries, coin-type batteries, button-type batteries, and the like.

[0080] FIG. 1 shows a non-aqueous electrolyte storage element 1 as an example of a rectangular battery. Note that 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 rectangular container 3. The positive electrode is electrically connected to the positive electrode terminal 4 via the positive electrode lead 41. The negative electrode is electrically connected to the negative electrode terminal 5 via the negative electrode lead 51.

[0081] <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 electric vehicles (HEVs), plug-in hybrid electric 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.

[0082] 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.

[0083] <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.

[0084] The method of 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 the injection port formed in the container, the injection port may be sealed.

[0085] 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 treatment. 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 treatment, a good film formed by the decomposition of a part of the non-aqueous electrolyte can be formed on the composite of the positive electrode.

[0086] <Other Embodiments> In addition, the non-aqueous electrolyte storage element of the present invention is not limited to the above embodiments, and various changes 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.

[0087] In the above embodiments, the case where the non-aqueous electrolyte storage element is used as a chargeable and dischargeable 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.

[0088] 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

[0089] Hereinafter, the present invention will be described more specifically by way of examples, but the present invention is not limited to the following examples.

[0090] [Example 1] (Fabrication of Positive Electrode) As the porous carbon, micro-porous carbon with an average pore diameter of 2 nm was prepared. Sulfur as a sulfur-based active material and the above-mentioned porous carbon were mixed at a mass ratio of 70:30. This mixture was placed in a sealed electric furnace. After performing an argon flow 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 heat-treated for 2 hours 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, PAA as a thickener, CMC as a dispersant, and SBR as a binder in appropriate mass ratios 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 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.

[0091] (Preparation of negative electrode) As the negative electrode, a pure metal lithium foil was prepared.

[0092] (Preparation of non-aqueous electrolyte) LiN(SO 2 CF 3 ) 2 was added to a non-aqueous solvent in which fluoroethylene carbonate (FEC) and vinylene carbonate (VC) were mixed at a volume ratio of 50:50 at a content of 1.0 mol / dm 3 to prepare a non-aqueous electrolyte.

[0093] (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.

[0094] [Examples 2 to 8, Comparative Examples 1 to 10] Examples 2 to 8 and Comparative Examples 1 to 10 of non-aqueous electrolyte storage elements were obtained in the same manner as in Example 1, except that the porous carbon having the average pore diameter described in Tables 1 and 2 was used, and the mass per unit area of the positive electrode active material layer and the composition of the non-aqueous solvent were as described in Tables 1 and 2. Note that Example 1 and Comparative Example 1 are described in both Tables 1 and 2.

[0095] [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 0.1 C up to 1.0 V as a formation treatment. Thereafter, constant current charging was performed at a current of 0.1 C up to 3.0 V. Next, constant current discharge was performed at a current of 0.1 C up to 1.0 V. Note that a 10-minute rest 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, the average discharge voltage, the energy density per mass of the positive electrode active material (sulfur simple substance) (energy density per mass of the positive electrode active material), and the energy density per mass of the positive electrode were determined during the discharge after the above charging. The results are shown in Tables 1 and 2.

[0096]

Table 1

[0097]

Table 2

[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 2Each of the non-aqueous electrolyte storage elements of Examples 1 to 8 described above had an energy density per mass of the positive electrode exceeding 500 Wh / kg, which was a high value. On the other hand, when the average pore diameter of the porous carbon was 3 nm or more, as in the non-aqueous electrolyte storage elements of Comparative Examples 2 and 3 shown in Table 1, even if the mass per unit area of the positive electrode active material layer was increased, the energy density per mass of the positive electrode did not reach a high value. Also, 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 non-aqueous electrolyte storage elements of the Examples described above, the average discharge voltage increased because the non-aqueous solvent contained a fluorinated cyclic carbonate, and the discharge capacity per mass of the positive electrode increased because it contained a non-fluorinated unsaturated cyclic carbonate. As a result, when both a fluorinated cyclic carbonate and a non-fluorinated unsaturated cyclic carbonate were included, the energy density per mass of the positive electrode tended to increase. This is different from the tendency of the non-aqueous electrolyte storage elements in Comparative Examples 5 to 10 where the mass per unit area of the positive electrode active material layer was less than 5 mg / cm 2 in that the greater the content of the fluorinated cyclic carbonate in the non-aqueous solvent, the greater the discharge capacity per mass of the positive electrode and the higher the energy density per mass of the positive electrode.

Industrial Applicability

[0099] 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, and automobiles.

Explanation of Symbols

[0100] 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. having a positive electrode active material layer containing a composite of a sulfur-based active material and porous carbon, wherein the average pore diameter of the porous carbon is 3 nm or less, The mass per unit area of the above positive electrode active material layer is 5 mg / cm ２ or more, a positive electrode for a non-aqueous 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 non-aqueous electrolyte storage element according to Claim 2, further comprising a non-aqueous electrolyte containing a non-aqueous solvent mainly composed of carbonate.

4. The non-aqueous electrolyte storage element according to Claim 3, wherein the carbonate contains a fluorinated cyclic carbonate and a non-fluorinated unsaturated cyclic carbonate.

Images