Nonaqueous electrolyte storage element, device, and method for producing the nonaqueous electrolyte storage element

Abstract

To provide a non-aqueous electrolyte storage element having a large discharge capacity per mass of sulfur, a device equipped with such a non-aqueous electrolyte storage element, and a method for manufacturing such a non-aqueous electrolyte storage element.SOLUTION: A non-aqueous electrolyte storage element includes a positive electrode including a composite of porous carbon and sulfur, and a non-aqueous electrolyte containing a non-aqueous solvent containing unsaturated cyclic carbonate and lithium salt, and a cumulative 70% pore diameter of the porous carbon is 2.0 nm or more and 7.0 nm or less, the content of the unsaturated cyclic carbonate in the non-aqueous solvent is 10 vol.% or more, and a positive electrode potential in a discharge cut-off voltage in normal use is 1.0 V vs. Li / Li+ or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] 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., due to their high energy density. 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 between the electrodes. In addition, capacitors such as lithium ion capacitors and electric double layer capacitors are also widely used as non-aqueous electrolyte 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 sulfur as a positive electrode active material. Although sulfur is a positive electrode active material with a large theoretical capacity, it has a high electrical resistivity. For this reason, attempts have been made to combine sulfur with a carbon material (see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2016 / 009936 Summary of the Invention [Problem to be solved by the invention]

[0005] Conventional nonaqueous electrolyte electricity storage elements using a carbon-sulfur composite in the positive electrode also do not have a sufficiently large discharge capacity due to low utilization rate of sulfur, which is the positive electrode active material.

[0006] An object of the present invention is to provide a nonaqueous electrolyte electricity storage element having a large discharge capacity per mass of sulfur, a device including such a nonaqueous electrolyte electricity storage element, and a method for manufacturing such a nonaqueous electrolyte electricity storage element. [Means for solving the problem]

[0007] A nonaqueous electrolyte storage element according to one aspect of the present invention comprises a positive electrode including a composite of porous carbon and sulfur, and a nonaqueous electrolyte including a nonaqueous solvent containing an unsaturated cyclic carbonate and a lithium salt, wherein the porous carbon has a cumulative 70% pore size of 2.0 nm or more and 7.0 nm or less, the nonaqueous solvent has a content of the unsaturated cyclic carbonate of 10 volume % or more, and the positive electrode potential at the end of discharge voltage during normal use is 1.0 V vs. Li / Li + The following is the result.

[0008] A device according to another aspect of the present invention includes the nonaqueous electrolyte electricity storage element according to the aspect of the present invention.

[0009] A method for producing a non-aqueous electrolyte electricity storage element according to another aspect of the present invention includes discharging an electricity storage element including a positive electrode containing a composite of porous carbon and sulfur, and a non-aqueous electrolyte containing a non-aqueous solvent containing an unsaturated cyclic carbonate and a lithium salt, wherein the porous carbon has a cumulative 70% pore size of 2.0 nm or more and 7.0 nm or less, the non-aqueous solvent has a content of the unsaturated cyclic carbonate of 10 vol % or more, and the discharging is performed at a positive electrode potential of 1.0 V vs. Li / Li + This continues until the following: Effect of the Invention

[0010] According to one aspect of the present invention, it is possible to provide a nonaqueous electrolyte electricity storage element having a large discharge capacity per mass of sulfur, a device including such a nonaqueous electrolyte electricity storage element, and a method for manufacturing such a nonaqueous electrolyte electricity storage element. [Brief description of the drawings]

[0011] [Figure 1]FIG. 1 is a perspective view showing one embodiment of a nonaqueous electrolyte electricity storage element. [Diagram 2] FIG. 2 is a schematic diagram showing one embodiment of an electricity storage device formed by assembling a plurality of nonaqueous electrolyte electricity storage elements. [Diagram 3] FIG. 3 is a diagram showing discharge curves in a charge / discharge test of each of the nonaqueous electrolyte storage elements of Example 2 and Comparative Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] First, an outline of the nonaqueous electrolyte storage element, the device, and the method for producing the nonaqueous electrolyte storage element disclosed in this specification will be described.

[0013] A nonaqueous electrolyte storage element according to one aspect of the present invention comprises a positive electrode including a composite of porous carbon and sulfur, and a nonaqueous electrolyte including a nonaqueous solvent containing an unsaturated cyclic carbonate and a lithium salt, wherein the porous carbon has a cumulative 70% pore size of 2.0 nm or more and 7.0 nm or less, the nonaqueous solvent has a content of the unsaturated cyclic carbonate of 10 volume % or more, and the positive electrode potential at the end of discharge voltage during normal use is 1.0 V vs. Li / Li + The following is the result.

[0014] The nonaqueous electrolyte storage element has a large discharge capacity per mass of sulfur. The reason for this is unclear, but the following reason is presumed. It is believed that the unsaturated cyclic carbonate contained in the nonaqueous solvent is polymerized and a coating is formed in the pores by mixing the nonaqueous electrolyte impregnated in the pores of the porous carbon with the lithium polysulfide soluble in the nonaqueous electrolyte formed during discharge. As the size of the pore diameter of the porous carbon increases, the amount of lithium polysulfide soluble in the nonaqueous electrolyte produced increases, so the mixing ratio of the nonaqueous electrolyte impregnated in the pores and the lithium polysulfide soluble in the nonaqueous electrolyte changes depending on the size of the pore diameter, and as a result, it is believed that the size of the pore diameter affects the ionic conductivity of the coating formed. It is believed that the size of the pore diameter of the porous carbon is within a predetermined range, and the mixing ratio of the nonaqueous electrolyte and the lithium polysulfide soluble in the nonaqueous electrolyte in the pores is optimized, so that a highly ionic conductive coating is formed in the pores, improving the utilization rate of sulfur. In addition, since the non-aqueous electrolyte contains a sufficient amount of unsaturated cyclic carbonate, a coating film having a high effect of suppressing sulfur elution is formed on the surface of the composite. Furthermore, since the non-aqueous electrolyte contains a sufficient amount of unsaturated cyclic carbonate and the positive electrode potential at the end of discharge during normal use is 1.0 V vs. Li / Li + The utilization rate of sulfur is increased by keeping the positive electrode potential at 1.0 V vs. Li / Li + When the battery is discharged to a potential of 1.0 V vs. Li / Li, not only does the discharge capacity increase due to deep discharge, but the sulfur utilization rate itself also increases. + The reason why the sulfur utilization rate increases by discharging the battery until the positive electrode potential reaches 1.0 V vs. Li / Li is presumed to be as follows. +When the battery is deeply discharged to below 1.0V, a coating is formed inside the composite, and the components of the coating (e.g., a polymer of an unsaturated cyclic carbonate such as polyvinylene carbonate) are lithiated, giving the coating good ionic conductivity. It is presumed that the sulfur utilization rate is increased in this nonaqueous electrolyte storage element due to the formation of a coating with good ionic conductivity inside the composite. From the above, it is presumed that the nonaqueous electrolyte storage element has a large discharge capacity per mass of sulfur. In addition, because the sulfur utilization rate itself is increased in this way, when the positive electrode potential reaches 1.0V vs. Li / Li + In the above potential range, the discharge capacity per mass of sulfur is large. Moreover, the nonaqueous electrolyte electricity storage element has a high energy density.

[0015] The "cumulative 70% pore size of porous carbon" is measured by the following method. When porous carbon before assembly into a nonaqueous electrolyte storage element is available, the above measurement is performed on that porous carbon. For porous carbon incorporated in the positive electrode of a nonaqueous electrolyte storage element, the measurement is performed on porous carbon that has been treated according to the following procedure. First, the nonaqueous electrolyte storage element is discharged at a constant current of 0.05 C until it reaches the discharge end voltage during normal use, and is placed in a discharged state. After a 30-minute rest, it is charged at a constant current of 0.05 C until it reaches the upper limit voltage during normal use. The element is disassembled, the positive electrode is removed, and a test battery is assembled with a metallic lithium electrode as the counter electrode, and a current of 10 mA per 1 g of positive electrode mixture is applied until the positive electrode potential reaches 3.0 V vs. Li / Li. + The positive electrode is adjusted to a fully charged state by constant current charging until the positive electrode reaches a fully charged state. The positive electrode is disassembled again and removed. The non-aqueous electrolyte attached to the removed positive electrode is thoroughly washed using dimethyl carbonate. The washed positive electrode is dried at room temperature for one day and night, and then a composite of porous carbon and sulfur is collected and heat-treated for 5 hours at 800°C in an inert atmosphere to obtain the porous carbon to be measured. The work from disassembling the non-aqueous electrolyte storage element to collecting the composite is carried out in an argon atmosphere with a dew point of -60°C or less. The reason for performing heat treatment for 5 hours at 800°C in an inert atmosphere is to remove sulfur, sulfur reaction intermediates such as lithium polysulfide generated by charging and discharging, and coatings from the composite. The pore size distribution of the porous carbon before assembling the nonaqueous electrolyte storage element or the porous carbon after the above treatment is measured using a nitrogen adsorption / desorption method. This measurement can be performed using an "autosorb iQ" manufactured by Quantachrome. The pore volume with pore diameters up to 10 nm is defined as the total pore volume, and the pore diameter at which the cumulative pore volume is 70% of the total pore volume is defined as the cumulative 70% pore diameter.

[0016] The term "normal use" refers to a case where the nonaqueous electrolyte storage element is used under charge and discharge conditions recommended or specified for the nonaqueous electrolyte storage element. The discharge conditions are determined, for example, by the settings of the device in which the nonaqueous electrolyte storage element is used.

[0017] The content of oxygen in the composite relative to carbon, sulfur, oxygen and fluorine as measured by SEM-EDX analysis (scanning electron microscope-energy dispersive X-ray analysis) is preferably 20 mass% or more. + When the charge and discharge is performed to the range below 20%, as described above, a coating is formed even inside the composite, resulting in a large content of oxygen element in the composite. In other words, when the content of oxygen element is 20 mass% or more, this is considered to indicate that a coating is sufficiently formed even inside the composite, and the utilization rate of sulfur is increased, resulting in a larger discharge capacity per mass of sulfur.

[0018] The SEM-EDX analysis is performed on the composite taken from the positive electrode of a test battery that has been fully charged after dismantling the nonaqueous electrolyte storage element, using the same procedure as in the measurement of the "cumulative 70% pore size of porous carbon" described above. The acceleration voltage of the electron beam is set to 15 kV to detect characteristic X-rays that reflect the inside of the particles. Point analysis is performed at any four points on the particle surface of one composite. The average value of the oxygen element content calculated from the contents of carbon, sulfur, oxygen, and fluorine elements measured at each point is used.

[0019] The battery was constructed using two of the above positive electrodes, and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was added at 1.0 mol / dm 3 The capacitance of the positive electrode measured in a symmetric capacitor using a non-aqueous electrolyte solution containing vinylene carbonate (VC) as a non-aqueous solvent is preferably 2 F / g or more. The capacitance of the positive electrode affects the surface area of ​​the complex that can contribute to the reaction. In other words, when the capacitance of the positive electrode is 2 F / g or more, it can be said that a sufficient ion conduction path is formed even inside the complex, and the discharge capacity per mass of sulfur is larger.

[0020] To prepare the symmetric capacitor, two nonaqueous electrolyte storage elements of the same type were disassembled in the same manner as in the measurement of the "cumulative 70% pore size of porous carbon" described above, and a test battery was assembled to use two positive electrodes adjusted to a fully charged state. That is, one of the two positive electrodes removed from the nonaqueous electrolyte storage element was used as the positive electrode of the symmetric capacitor, and the other was used as the negative electrode of the symmetric capacitor. The capacitance was measured at a temperature of 25°C and a current of 0.02 mA / cm. 2 The capacitance is a value per mass of the porous carbon in the positive electrode composite.

[0021] A device according to another aspect of the present invention includes the nonaqueous electrolyte electricity storage element according to the aspect of the present invention.

[0022] The nonaqueous electrolyte electricity storage element included in the device has a large discharge capacity per mass of sulfur, which allows the device to be used, for example, with a reduced frequency of charging the nonaqueous electrolyte electricity storage element.

[0023] A method for producing a non-aqueous electrolyte electricity storage element according to another aspect of the present invention includes discharging an electricity storage element including a positive electrode containing a composite of porous carbon and sulfur, and a non-aqueous electrolyte containing a non-aqueous solvent containing an unsaturated cyclic carbonate and a lithium salt, wherein the porous carbon has a cumulative 70% pore size of 2.0 nm or more and 7.0 nm or less, the non-aqueous solvent has a content of the unsaturated cyclic carbonate of 10 vol % or more, and the discharging is performed at a positive electrode potential of 1.0 V vs. Li / Li + This continues until the following:

[0024] According to this production method, a nonaqueous electrolyte electricity storage element having a large discharge capacity per mass of sulfur can be produced.

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

[0026] <Non-aqueous electrolyte electricity storage element> A nonaqueous electrolyte storage element according to one embodiment of the present invention includes an electrode assembly having a positive electrode, a negative electrode, and a separator, a nonaqueous electrolyte, and a container for accommodating the electrode assembly and the nonaqueous electrolyte. The electrode assembly is usually a laminated type in which a plurality of positive electrodes and a plurality of negative electrodes are laminated with a separator interposed therebetween, or a wound type in which a positive electrode and a negative electrode are laminated with a separator interposed therebetween and wound. The nonaqueous electrolyte exists in a state in which it is contained in the positive electrode, the negative electrode, and the separator. A nonaqueous electrolyte secondary battery will be described as an example of a nonaqueous electrolyte storage element.

[0027] (positive electrode) The positive electrode has a positive electrode substrate and a positive electrode active material layer disposed on the positive electrode substrate directly or via an intermediate layer.

[0028] The positive electrode substrate is conductive. Whether or not it has "conductivity" is determined by whether the volume resistivity measured in accordance with JIS-H-0505 (1975) is 10 7The threshold value is Ω·cm. The material of the positive electrode substrate is a metal such as aluminum, titanium, tantalum, stainless steel, or an alloy thereof. Among these, aluminum or an aluminum alloy is preferred from the viewpoints of potential resistance, high conductivity, and cost. The positive electrode substrate may be a foil, a vapor deposition film, a mesh, a porous material, etc., and a foil is preferred from the viewpoint of cost. Therefore, aluminum foil or an aluminum alloy foil is preferred as the positive electrode substrate. Examples of aluminum or an aluminum alloy include A1085, A3003, A1N30, etc., as specified in JIS-H-4000 (2014) or JIS-H4160 (2006).

[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 includes a composite of porous carbon and sulfur. The positive electrode active material layer includes optional components such as a conductive agent, a binder, a thickener, and a filler, as necessary. The positive electrode active material layer is usually formed from a positive electrode mixture including the composite and other optional components.

[0031] The composite of porous carbon and sulfur may have a form in which porous carbon and sulfur are contained in one particle. The composite may have a form in which at least a part of sulfur is disposed in the pores of the porous carbon. In other words, the composite may have a form in which at least a part of sulfur is impregnated into the porous carbon. In addition, the composite usually has a coating derived from the nonaqueous electrolyte formed on the surface. It is preferable that this coating is also formed in the pores of the composite.

[0032] Porous carbon is a porous body containing carbon as the main constituent element. The main constituent element refers to the element that is contained most abundantly by mass. The carbon content in the porous carbon is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more. The porous carbon may be substantially composed of carbon element only. The porous carbon may further contain other elements such as oxygen element in addition to carbon element.

[0033] The cumulative 70% pore size of the porous carbon is 2.0 nm to 7.0 nm, preferably 2.5 nm to 6.0 nm, more preferably 3.0 nm to 5.0 nm, and even more preferably 3.4 nm to 4.5 nm. When the cumulative 70% pore size of the porous carbon is within the above range, the discharge capacity per mass of sulfur of the nonaqueous electrolyte storage element is large.

[0034] The content of the porous carbon in the composite (the mass ratio of the porous carbon to the mass of the entire composite) is preferably 10% by mass to 50% by mass, more preferably 20% by mass to 45% by mass, and even more preferably 30% by mass to 40% by mass. By setting the content of the porous carbon in the composite within the above range, it is possible to increase the discharge capacity of the nonaqueous electrolyte storage element.

[0035] The sulfur in the composite functions as a positive electrode active material. The sulfur may be elemental sulfur or a sulfur compound. That is, the composite may contain elemental sulfur. Examples of the sulfur compound include metal sulfides such as lithium sulfide, organic disulfide compounds, and organic sulfur compounds such as carbon sulfide compounds. Sulfur has the advantages of high theoretical capacity and low cost.

[0036] The sulfur content in the composite (mass ratio of sulfur element to the mass of the entire composite) is preferably 50% by mass to 90% by mass, more preferably 55% by mass to 80% by mass, and even more preferably 60% by mass to 70% by mass. By setting the sulfur content in the composite within the above range, it is possible to increase the discharge capacity of the nonaqueous electrolyte storage element.

[0037] The main elements constituting the complex are carbon and sulfur. The complex preferably contains oxygen, and may further contain fluorine. The oxygen and fluorine elements may be elements constituting the coating derived from the non-aqueous electrolyte. The complex may also contain carbon, hydrogen, lithium, etc., and the carbon, hydrogen, lithium, etc. may be elements constituting the coating derived from the non-aqueous electrolyte.

[0038] The content of oxygen element relative to carbon element, sulfur element, oxygen element, and fluorine element in the composite measured by SEM-EDX analysis may be, for example, 15% by mass or more, preferably 20% by mass or more, more preferably 22% by mass or more. When the content of oxygen element is equal to or more than the above lower limit, the discharge capacity per mass of sulfur becomes larger. The content of oxygen element may be 40% by mass or less, 30% by mass or less, or 25% by mass or less. The content of oxygen element may be within a range equal to or more than any of the above lower limits and equal to or less than any of the above upper limits. The content of oxygen element tends to increase as the discharge is performed until the positive electrode potential becomes lower.

[0039] 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 the above range, it is possible to increase the discharge capacity and the energy density of the nonaqueous electrolyte storage element.

[0040] The positive electrode active material layer may contain a positive electrode active material other than the sulfur constituting the composite. However, the content of sulfur (sulfur element) in the total positive electrode active material is preferably 50 mass% or more, more preferably 70 mass% or more, even more preferably 90 mass% or more, even more preferably 99 mass% or more, and particularly preferably 100 mass%.

[0041] The conductive agent is not particularly limited as long as it is a material having electrical conductivity. The conductive agent does not include porous carbon constituting the composite. Examples of such conductive agents include carbonaceous materials, metals, conductive ceramics, and the like. Examples of carbonaceous materials include graphite, non-graphitic carbon, graphene-based carbon, and the like. Examples of non-graphitic carbon include carbon nanofibers, pitch-based carbon fibers, carbon black, and the like. Examples of carbon black include furnace black, acetylene black, ketjen black, and the like. Examples of graphene-based carbon include graphene, carbon nanotubes (CNT), fullerene, and the like. Examples of the conductive agent include powder and fiber. As the conductive agent, one of these materials may be used alone, or two or more of them may be mixed and used. These materials may also be used in a composite form. For example, a material in which carbon black and CNT are composited may be used. Among these, carbon black is preferable from the viewpoint of electronic conductivity and coatability, and acetylene black is preferable among them.

[0042] The content of the conductive agent in the positive electrode active material layer is preferably from 1 mass % to 20 mass %, more preferably from 3 mass % to 15 mass %. By setting the content of the conductive agent in the above range, the energy density of the nonaqueous electrolyte storage element can be increased.

[0043] Examples of binders 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.

[0044] The content of the binder in the positive electrode active material layer is preferably 1% by mass to 10% by mass, more preferably 3% by mass to 9% by mass. By setting the content of the binder in the above range, the composite and the like can be stably maintained.

[0045] Examples of the thickener include polysaccharide polymers such as carboxymethyl cellulose (CMC) and methyl cellulose. When the thickener has a functional group that reacts with lithium or the like, the functional group may be deactivated in advance by methylation or the like. The content of the thickener in the positive electrode active material layer is preferably 0.5% by mass or more and 10% by mass or less, and more preferably 2% by mass or more and 5% by mass or less. In one embodiment of the present invention, the positive electrode active material layer may not contain a thickener.

[0046] The filler is not particularly limited. Examples of the filler include polyolefins such as polypropylene and polyethylene, inorganic oxides such as silicon dioxide, alumina, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicate, hydroxides such as magnesium hydroxide, calcium hydroxide, and aluminum hydroxide, carbonates such as calcium carbonate, poorly soluble ion crystals such as calcium fluoride, barium fluoride, and barium sulfate, nitrides such as aluminum nitride and silicon nitride, mineral resource-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, and artificial products thereof. 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.

[0047] The positive electrode active material layer may contain a typical nonmetallic element such as B, N, P, F, Cl, Br, or I, a typical metallic element such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, or Ba, or a transition metal element such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, or W, as a composite, a positive electrode active material other than sulfur, a conductive agent, a binder, a thickener, or a component other than a filler.

[0048] The nonaqueous electrolyte storage element was fabricated using two positive electrodes, and LiTFSI was added at 1.0 mol / dm 3 The capacitance of the positive electrode measured in a symmetrical capacitor using a non-aqueous electrolyte solution containing VC as a non-aqueous solvent is preferably 2 F / g or more, more preferably 2.2 F / g or more, and even more preferably 2.4 F / g or more. When the capacitance is equal to or more than the lower limit, the discharge capacity per mass of sulfur is larger. The capacitance may be 4 F / g or less, or may be 3 F / g or less. The capacitance may be within a range between any of the lower limits and any of the upper limits. The capacitance tends to increase as the discharge is performed until the positive electrode potential becomes lower.

[0049] (Negative electrode) 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.

[0050] The negative electrode substrate has electrical conductivity. Metals such as copper, nickel, stainless steel, nickel-plated steel, and aluminum, or alloys thereof, carbonaceous materials, etc. are used as the material of the negative electrode substrate. Among these, copper or copper alloys are preferred. Examples of the negative electrode substrate include foils, vapor deposition films, meshes, and porous materials, and foils are preferred from the viewpoint of cost. Therefore, copper foil or copper alloy foil is preferred as the negative electrode substrate. Examples of copper foil include rolled copper foil and electrolytic copper foil.

[0051] The average thickness of the negative electrode substrate is preferably 2 μm to 35 μm, more preferably 3 μm to 30 μm, further 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, it is possible to increase the strength of the negative electrode substrate and to increase the energy density per volume of the nonaqueous electrolyte storage element.

[0052] 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, a filler, etc., as necessary. The optional components such as a conductive agent, a binder, a thickener, a filler, etc. can be selected from the materials exemplified for the positive electrode above.

[0053] The negative electrode active material in the nonaqueous electrolyte storage element is usually a negative electrode active material containing lithium, such as metallic lithium or a lithium compound. Among these, metallic lithium is preferable as the negative electrode active material. The metallic lithium may be pure metallic lithium consisting essentially of lithium element, 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 a plurality of metal elements other than the lithium element. Examples of the lithium compound include Li4Ti5O 12 , LiTiO2, etc.

[0054] 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 further preferably 99% by mass or more.

[0055] The negative electrode active material layer may be a non-porous layer (solid layer) containing lithium element. The negative electrode active material layer may be a porous layer having particles containing lithium element. The negative electrode active material layer may be a layer consisting essentially of lithium element. The negative electrode active material layer may be a pure metal lithium foil or a lithium alloy foil. The average thickness of the negative electrode active material layer 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. The "average thickness" of the negative electrode active material layer refers to the average value of thicknesses measured at any five points in the negative electrode active material layer.

[0056] The negative electrode active material layer may further contain a negative electrode active material other than the negative electrode active material containing lithium element, however, the content of the negative electrode active material containing lithium element relative to all the negative electrode active materials contained in the negative electrode active material layer is preferably 90 mass% or more, more preferably 99 mass% or more, and even more preferably 100 mass%.

[0057] The negative electrode active material layer may contain typical nonmetallic 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 metallic 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.

[0058] (Separator) The separator can be appropriately selected from known separators. For example, a separator consisting of only a substrate layer, a separator in which a heat-resistant layer containing heat-resistant particles and a binder is formed on one or both surfaces of the substrate layer, etc. can be used as the separator. Examples of the shape of the substrate layer of the separator include woven fabric, nonwoven fabric, and porous resin film. Among these shapes, a porous resin film is preferred from the viewpoint of strength, and a nonwoven fabric is preferred from the viewpoint of non-aqueous electrolyte retention. As the material of the substrate layer of the separator, polyolefins such as polyethylene and polypropylene are preferred from the viewpoint of shutdown function, and polyimide and aramid are preferred from the viewpoint of oxidation decomposition resistance. A material obtained by combining these resins may be used as the substrate layer of the separator.

[0059] 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 under an air atmosphere at 1 atmosphere, 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 ion crystals such as calcium fluoride, barium fluoride, and barium titanate; covalent crystals such as silicon and diamond; mineral resource-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or artificial products thereof. 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 mixed and used. Among these inorganic compounds, silicon oxide, aluminum oxide, or aluminosilicate is preferred from the viewpoint of the safety of the nonaqueous electrolyte storage element.

[0060] 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.

[0061] 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, polyvinylpyrrolidone, and polyvinylidene fluoride. The use of the polymer gel has an effect of suppressing leakage. As the separator, the above-mentioned porous resin film or nonwoven fabric may be used in combination with the polymer gel.

[0062] (Non-aqueous electrolyte) The non-aqueous electrolyte contains a non-aqueous solvent and a lithium salt, and is usually a non-aqueous electrolyte solution.

[0063] The non-aqueous solvent contains an unsaturated cyclic carbonate. The unsaturated cyclic carbonate is a cyclic carbonate having an unsaturated bond between carbon atoms. It is considered that the unsaturated cyclic carbonate in the non-aqueous electrolyte provided in the non-aqueous electrolyte storage element polymerizes with discharge, and a coating having a high sulfur elution effect can be formed on the surface of the composite in the positive electrode. Therefore, by using a non-aqueous solvent containing an unsaturated cyclic carbonate, the discharge capacity per mass of sulfur is increased, and the capacity decrease with charge and discharge cycles can be suppressed. The unsaturated bond between the carbon atoms in the unsaturated cyclic carbonate may be present in the cyclic portion or in other portions, but is preferably present in the cyclic portion. The unsaturated cyclic carbonate may be one in which some or all of the hydrogen atoms are replaced with halogen atoms such as fluorine atoms. One or more types of unsaturated cyclic carbonates can be used.

[0064] Examples of unsaturated cyclic carbonates include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), 1-phenylvinylene carbonate, 1,2-diphenylvinylene carbonate, etc. Among these, VC is preferred.

[0065] The lower limit of the content of the unsaturated cyclic carbonate in the non-aqueous solvent is 10% by volume, preferably 20% by volume, more preferably 30% by volume, and even more preferably 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 having the content of the unsaturated cyclic carbonate in the non-aqueous solvent be equal to or more than the lower limit, the discharge capacity per mass of sulfur of the non-aqueous electrolyte storage element can be increased. The non-aqueous solvent may be substantially composed of the unsaturated cyclic carbonate, or may be composed of the unsaturated cyclic carbonate alone.

[0066] The non-aqueous solvent may further contain other non-aqueous solvents other than the unsaturated cyclic carbonate. Examples of the other non-aqueous solvents include saturated cyclic carbonates, chain carbonates, carboxylates, phosphates, sulfonates, ethers, amides, nitriles, etc. Among these, saturated cyclic carbonates are preferred.

[0067] The saturated cyclic carbonate is a cyclic carbonate that does not have an unsaturated bond between carbon atoms. Examples of the saturated cyclic carbonate include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), chloroethylene carbonate, fluoroethylene carbonate (FEC), and difluoroethylene carbonate (DFEC).

[0068] The lower limit of the content of the cyclic carbonate (unsaturated cyclic carbonate and saturated cyclic carbonate) in the non-aqueous solvent is preferably 50% by volume, more preferably 70% by volume, and even more preferably 80% by volume, 90% by volume, 95% by volume, or 99% by volume. By having the content of the cyclic carbonate in the non-aqueous solvent be equal to or greater than the lower limit, the discharge capacity per mass of sulfur of the non-aqueous electrolyte storage element can be increased. The non-aqueous solvent may be substantially composed of the cyclic carbonate, or may be composed of the cyclic carbonate only.

[0069] The lithium salt can be appropriately selected from known lithium salts. Examples of the lithium salt include LiPF6, LiPO2F2, LiClO4, lithium imide salts, etc. One or more types of lithium salts can be used.

[0070] The lithium salt is preferably a lithium imide salt. The lithium imide salt includes not only a lithium imide salt having a structure in which two carbonyl groups are bonded to a nitrogen atom, but also a lithium imide salt having a structure in which two sulfonyl groups are bonded to a nitrogen atom, a lithium imide salt having a structure in which two phosphonyl groups are bonded to a nitrogen atom, and the like.

[0071] Lithium imide salts include LiN(SO2F)2 (lithium bis(fluorosulfonyl)imide: LiFSI), LiN(SO2CF3)2 (lithium bis(trifluoromethanesulfonyl)imide: LiTFSI), LiN(SO2C2F5)2 (lithium bis(pentafluoroethanesulfonyl)imide: LiBETI), LiN(SO2C4F9)2 (lithium bis(nonafluorobutanesulfonyl)imide), CF3-SO2-N-SO2-N-S Examples include lithium sulfonylimide salts such as O2CF3Li2, FSO2-N-SO2-C4F9Li, CF3-SO2-N-SO2-CF2-SO2-N-SO2-CF3Li2, CF3-SO2-N-SO2-CF2-SO3Li2, CF3-SO2-N-SO2-CF2-SO2-C(-SO2CF3)2Li2; and lithium phosphonylimide salts such as LiN(POF2)2 (lithium bis(difluorophosphonyl)imide: LiDFPI).

[0072] The lithium imide salt preferably has a fluorine atom, specifically, for example, a fluorosulfonyl group, a difluorophosphonyl group, a fluoroalkyl group, etc. Among the lithium imide salts, lithium sulfonylimide salts are preferred, LiTFSI and LiFSI are more preferred, and LiTFSI is even more preferred.

[0073] The lithium salt content in the non-aqueous electrolyte is 0.1 mol / dm at 20°C and 1 atm. 3 More than 2.5mol / dm 3 It is preferable that the value is 0.3 mol / dm or less. 3 More than 2.0mol / dm 3 More preferably, it is 0.5 mol / dm or less. 3 More than 1.7mol / dm 3 More preferably, it is 0.7 mol / dm or less. 3 More than 1.5mol / dm 3 By setting the content of the lithium salt within the above range, the ionic conductivity of the non-aqueous electrolyte can be increased.

[0074] The non-aqueous electrolyte may contain additives in addition to the non-aqueous solvent and the lithium salt. Examples of additives include 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, glutaconic anhydride, itaconic anhydride, and cyclohexanedicarboxylic anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, Examples of the additives include 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, and tetrakistrimethylsilyl titanate. These additives may be used alone or in combination of two or more.

[0075] 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. 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 to further improve safety.

[0076] The nonaqueous electrolyte may be a combination of a nonaqueous electrolyte 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 a sulfide solid electrolyte, an oxide solid electrolyte, an oxynitride solid electrolyte, and a polymer solid electrolyte.

[0077] (Positive electrode potential at the end of discharge voltage during normal use, etc.) In the nonaqueous electrolyte storage element according to one embodiment of the present invention, the upper limit of the positive electrode potential at the discharge end voltage during normal use is 1.0 V vs. Li / Li + 0.9V vs. Li / Li + is preferable, and 0.8V vs. Li / Li + is more preferable, 0.7V vs. Li / Li + , 0.6V vs. Li / Li + , 0.5V vs. Li / Li + , 0.4V vs. Li / Li + Or 0.3V vs. Li / Li + By setting the positive electrode potential at the discharge end voltage during normal use to the above upper limit or less, the utilization rate of sulfur is increased and the discharge capacity per mass of sulfur is increased. In addition, by setting the positive electrode potential at the discharge end voltage during normal use to the above upper limit or less, the positive electrode potential is 1.0 V vs. Li / Li + In the above potential range, the discharge capacity per mass of sulfur also increases, and the energy density also tends to increase. On the other hand, the lower limit of the positive electrode potential at the discharge end voltage during normal use is, for example, 0.1 V vs. Li / Li + 0.2V vs. Li / Li + 0.3V vs. Li / Li + The positive electrode potential may be within a range not less than any of the lower limits described above and not more than any of the upper limits described above.

[0078] For the non-aqueous electrolyte storage element, the positive electrode potential is 1.0 V vs. Li / Li +According to the method of use, the utilization rate of sulfur is increased, and the discharge capacity per mass of sulfur in the nonaqueous electrolyte storage element is increased. + In the above potential range, the discharge capacity per mass of sulfur of the nonaqueous electrolyte storage element also tends to be large, and the energy density of the nonaqueous electrolyte storage element also tends to be high. In this usage method, it is preferable to discharge the nonaqueous electrolyte storage element until the positive electrode potential falls within the suitable range at the discharge end voltage during normal use.

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

[0080] Fig. 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 body 2 having a positive electrode and a negative electrode wound with a separator sandwiched therebetween is housed in a prismatic container 3. The positive electrode is electrically connected to a positive electrode terminal 4 via a positive electrode lead 41. The negative electrode is electrically connected to a negative electrode terminal 5 via a negative electrode lead 51.

[0081] <Equipment> An apparatus according to an embodiment of the present invention includes the nonaqueous electrolyte electricity storage element according to the embodiment of the present invention described above. The apparatus may be, but is not limited to, a personal computer, an electronic device such as a communication terminal, a home appliance, an automobile (EV, HEV, PHEV, etc.), or other industrial equipment.

[0082] For example, the device is configured such that the positive electrode potential of the non-aqueous electrolyte storage element is 1.0 V vs. Li / Li + The charge / discharge control device is configured to discharge the battery until the battery reaches a voltage lower than the threshold voltage (discharge end voltage) of 1.0 V vs. Li / Li. For example, in the charge / discharge control device, a discharge end voltage (discharge end voltage) is set for discharging the nonaqueous electrolyte storage element when the device is used, and the positive electrode potential at the discharge end voltage is set to 1.0 V vs. Li / Li.+ In other words, in the device, the nonaqueous electrolyte storage element has a positive electrode potential of 1.0 V vs. Li / Li + The device is designed to be discharged until the positive electrode potential reaches 1.0 V vs. Li / Li when using the device. + Do not discharge until the positive electrode potential is 1.0 V vs. Li / Li + The device is preferably configured to discharge the nonaqueous electrolyte storage element up to a suitable range of the positive electrode potential at the discharge cut-off voltage during normal use of the nonaqueous electrolyte storage element according to one embodiment of the present invention.

[0083] The nonaqueous electrolyte storage element provided in the device has a large discharge capacity per mass of sulfur, and therefore can be used with reduced charging frequency, etc. Furthermore, the device can use the nonaqueous electrolyte storage element at a high energy density.

[0084] <Electricity storage device> The nonaqueous electrolyte storage element of the present embodiment can be mounted as an electricity storage unit (battery module) comprising a plurality of nonaqueous electrolyte storage elements 1 assembled together in a power source for an automobile such as an EV, HEV, or PHEV, a power source for electronic devices such as a personal computer or a communication terminal, or a power storage power source, etc. In this case, the technology of the present invention may be applied to at least one nonaqueous electrolyte storage element included in the electricity storage unit.

[0085] 2 shows an example of an electricity storage device 30 in which electricity storage units 20, each of which is an assembly of two or more electrically connected nonaqueous electrolyte electricity storage elements 1, are further assembled. The electricity storage device 30 may include a bus bar (not shown) that electrically connects two or more nonaqueous electrolyte electricity storage elements 1, a bus bar (not shown) that electrically connects two or more electricity storage units 20, and the like. The electricity storage unit 20 or the electricity storage device 30 may include a status monitoring device (not shown) that monitors the status of one or more nonaqueous electrolyte electricity storage elements.

[0086] <Method of Manufacturing Nonaqueous Electrolyte Storage Element> A method for producing a non-aqueous electrolyte storage element according to one embodiment of the present invention includes discharging an electricity storage element including a positive electrode containing a composite of porous carbon and sulfur, and a non-aqueous electrolyte containing a non-aqueous solvent containing an unsaturated cyclic carbonate and a lithium salt, the porous carbon having a cumulative 70% pore size of 2.0 nm or more and 7.0 nm or less, the non-aqueous solvent having a content of the unsaturated cyclic carbonate of 10 volume % or more, and the discharge is performed at a positive electrode potential of 1.0 V vs. Li / Li + This continues until the following:

[0087] In this manufacturing method, a nonaqueous electrolyte storage element (B) is obtained by performing a predetermined discharge on a nonaqueous electrolyte storage element (A) including a positive electrode containing a composite of porous carbon and sulfur, and a nonaqueous electrolyte containing a nonaqueous solvent containing an unsaturated cyclic carbonate and a lithium salt. A specific form of the nonaqueous electrolyte storage element (A) is the nonaqueous electrolyte storage element according to one embodiment of the present invention described above, in which no coating is formed on the composite in the positive electrode. The nonaqueous electrolyte storage element (A) may be, for example, a nonaqueous electrolyte storage element in an undischarged state assembled using a positive electrode, a negative electrode, and a nonaqueous electrolyte. The nonaqueous electrolyte storage element (A) is also a nonaqueous electrolyte storage element in an undischarged state assembled using a positive electrode, a negative electrode, and a nonaqueous electrolyte. + The discharge may not reach the above level. In such a case, a coating may be present on the surface of the composite in the positive electrode of the nonaqueous electrolyte storage element (A). When the positive electrode potential of such a nonaqueous electrolyte storage element (A) is 1.0 V vs. Li / Li + It is presumed that by discharging the battery until the discharge capacity reaches the range below 1000 V, a good ion conduction path is formed even inside the composite. As a result, the production method provides a nonaqueous electrolyte storage element (B) with a large discharge capacity.

[0088] In the nonaqueous electrolyte storage element (B) obtained by this production method, the positive electrode potential is 1.0 V vs. Li / Li + The utilization rate of sulfur is increased by discharging the nonaqueous electrolyte storage element (B) obtained by the manufacturing method at least once until the positive electrode potential reaches 1.0 V vs. Li / Li during use.+ Even without discharging to the below level, the discharge capacity per mass of sulfur is large and the energy density is also high.

[0089] The production method may include, for example, preparing a positive electrode, preparing a negative electrode, preparing a nonaqueous electrolyte, assembling a nonaqueous electrolyte storage element (A) using the positive electrode, the negative electrode, and the nonaqueous electrolyte, and discharging the nonaqueous electrolyte storage element (A) by a predetermined amount.

[0090] The preparation of a positive electrode may be the fabrication of a positive electrode. The fabrication of a positive electrode can be performed, for example, by applying a positive electrode mixture paste directly or via an intermediate layer to a positive electrode substrate, and drying the paste. The positive electrode mixture paste contains each component constituting a positive electrode mixture (positive electrode active material layer), such as a composite of porous carbon and sulfur, and an optional conductive agent, binder, etc. The positive electrode mixture paste may further contain a dispersion medium.

[0091] The composite of porous carbon and sulfur can be produced, for example, by the following procedure. Porous carbon and sulfur are mixed. This mixture is heated to the melting point of sulfur (115°C) or higher in an inert gas atmosphere (e.g., an argon atmosphere) to allow the molten sulfur to penetrate into the pores of the porous carbon. Thereafter, the mixture is cooled to the melting point of sulfur or lower. The above heating and cooling may be repeated multiple times.

[0092] The preparation of the negative electrode may be the fabrication of the negative electrode. For example, when the negative electrode active material layer is substantially made of a pure metal lithium metal foil or a lithium alloy foil, the negative electrode may be fabricated by laminating the pure metal lithium foil or the lithium alloy foil directly or through an intermediate layer on the negative electrode substrate. The negative electrode may also be fabricated by applying a negative electrode mixture paste containing a negative electrode active material directly or through an intermediate layer to the negative electrode substrate and drying the paste. The negative electrode mixture paste contains each component constituting the negative electrode mixture (negative electrode active material layer), such as the negative electrode active material, and optional components such as a conductive agent and a binder. The negative electrode mixture paste may further contain a dispersion medium.

[0093] The provision of the non-aqueous electrolyte may be the preparation of the non-aqueous electrolyte. The preparation of the non-aqueous electrolyte can be performed by mixing components such as an unsaturated cyclic carbonate and a lithium salt.

[0094] The nonaqueous electrolyte storage element (A) can be assembled using a positive electrode, a negative electrode, and a nonaqueous electrolyte by a conventionally known procedure, for example, by forming an electrode assembly in which the positive electrode and the negative electrode are alternately stacked by stacking or winding the electrodes with a separator interposed therebetween, housing the electrode assembly in a container, and injecting the nonaqueous electrolyte into the container.

[0095] When the nonaqueous electrolyte storage element (A) is discharged as specified, the positive electrode potential is 1.0 V vs. Li / Li + Discharging is performed until the positive electrode potential at the discharge end voltage during normal use of the nonaqueous electrolyte storage element according to one embodiment of the present invention falls within a suitable range. After such discharging, the nonaqueous electrolyte may be replaced with another nonaqueous electrolyte, for example.

[0096] <Other embodiments> The nonaqueous electrolyte storage element of the present invention is not limited to the above-described embodiment, and various modifications may be made without departing from the scope of the present invention. For example, the configuration of one embodiment may be added to the configuration of another embodiment, and part of the configuration of one embodiment may be replaced with the configuration of another embodiment or a well-known technique. Furthermore, part of the configuration of one embodiment may be deleted. Also, a well-known technique may be added to the configuration of one embodiment.

[0097] In the above embodiment, the nonaqueous electrolyte storage element is mainly used as a chargeable and dischargeable nonaqueous electrolyte secondary battery (lithium-sulfur battery), but the nonaqueous electrolyte storage element may be of any type, shape, size, capacity, etc. The present invention can also be applied to various secondary batteries, electric double layer capacitors, lithium ion capacitors, and other capacitors.

[0098] 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. EXAMPLES

[0099] 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.

[0100] [Example 1] (Preparation of positive electrode) Porous carbon and sulfur were mixed in a mass ratio of 35:65. This mixture was placed in an electric furnace. The temperature was raised to 155°C in air, and after being held for 6 hours, it was allowed to cool to room temperature to produce a composite. The cumulative 70% pore diameter of the porous carbon used was measured based on the pore size distribution measurement using the nitrogen adsorption / desorption method described above, and was found to be 3.8 nm. The cumulative 70% pore diameter of the other porous carbons used was also measured in the same manner. A positive electrode mixture paste was prepared using water as a dispersion medium and containing the composite obtained above, acetylene black as a conductive agent, CMC as a thickener, and SBR as a binder in a mass ratio of 90:5:3:2. This positive electrode mixture paste was applied to an aluminum positive electrode substrate and dried to produce a positive electrode.

[0101] (Preparation of the negative electrode) As the negative electrode, a sheet of pure metallic lithium was prepared.

[0102] (Preparation of non-aqueous electrolyte) Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was added at 1.0 mol / dm in vinylene carbonate (VC), a non-aqueous solvent. 3 A non-aqueous electrolyte was prepared by dissolving the aqueous solution in the above-mentioned solution at a concentration of 1:1.

[0103] (Assembly of non-aqueous electrolyte storage element and initial discharge) A polyethylene microporous film was prepared as a separator. The above positive electrode, negative electrode, separator and nonaqueous electrolyte were used to assemble a nonaqueous electrolyte storage element in an undischarged state. This nonaqueous electrolyte storage element in an undischarged state was initially (first) discharged at 25° C. with a discharge cut-off voltage of 0.3 V and a discharge current of 0.1 C to obtain a nonaqueous electrolyte storage element of Example 1. The voltage between the positive and negative electrodes in the obtained nonaqueous electrolyte storage element in an undischarged state and the nonaqueous electrolyte storage element obtained through the initial discharge can be considered to be approximately equal to the positive electrode potential relative to the oxidation-reduction potential of metallic lithium.

[0104] [Examples 2 to 8, Comparative Examples 1 to 13] Each of the nonaqueous electrolyte storage elements of Examples 2 to 8 and Comparative Examples 1 to 13 was obtained in the same manner as in Example 1, except that a porous carbon having a cumulative 70% pore size shown in Table 1, a nonaqueous solvent having a composition shown in Table 1, and an initial discharge was performed at the discharge cut-off voltage shown in Table 1 were used.

[0105] [Example 9] A non-discharged non-aqueous electrolyte storage element was assembled in the same manner as in Example 2, and after initial discharge, the non-aqueous electrolyte was replaced with a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 50:50, to which LiTFSI was added at 1.0 mol / dm 3 The nonaqueous electrolyte electricity storage element of Example 9 was obtained by replacing the aqueous solution with one in which the aqueous solution had been dissolved at a concentration of 1:1.

[0106] [Evaluation] (Charge / discharge test) For each of the obtained nonaqueous electrolyte storage elements of Examples 1 to 3 and Comparative Examples 1 to 11, a constant current charge of 0.1C was performed at 25°C to 3.0V as the initial charge. Thereafter, a constant current discharge of 0.1C was performed at 25°C to the discharge end voltage listed in Table 1 as the second discharge. In addition, for each of the obtained nonaqueous electrolyte storage elements of Examples 4 to 9 and Comparative Examples 12 and 13, a constant current charge of 0.1C was performed at 25°C to 3.0V as the initial charge, and then a constant voltage charge was performed at 3.0V until the charging current became 0.01C. Thereafter, a constant current discharge of 0.1C was performed at 25°C to the discharge end voltage listed in Table 1 as the second discharge. The discharge capacity per mass of sulfur was calculated from the discharged electricity amount of these second discharges. The results are shown in Table 1. In addition, the discharge curves in the charge and discharge tests of each of the nonaqueous electrolyte storage elements of Example 2 and Comparative Example 1 are shown in FIG. 3. Based on the second discharge, the discharge capacity per mass of sulfur in the voltage range of 1.0 V or more and the sulfur utilization rate in the voltage range of 1.0 V or more were calculated. In calculating the sulfur utilization rate, the theoretical capacity of sulfur was set to 1674 mAh / g. These results are shown in Table 1.

[0107] [SEM-EDX analysis] For each of the nonaqueous electrolyte storage elements of Example 2 and Comparative Example 1, a positive electrode composite was collected by the above-mentioned method and subjected to SEM-EDX analysis to determine the oxygen content relative to the carbon, sulfur, oxygen and fluorine elements. The oxygen element content was 17% by mass in the composite of the nonaqueous electrolyte storage element of Comparative Example 1, in which the discharge end voltage was set to 1.3 V. In contrast, the oxygen element content was 23% by mass in the composite of the nonaqueous electrolyte storage element of Example 2, in which the discharge end voltage was set to 0.5 V.

[0108] [Capacitance measurement] Two nonaqueous electrolyte storage elements were separately produced for each of Examples 2 and 3 and Comparative Example 1. Using two nonaqueous electrolyte storage elements for each, positive electrodes were prepared by the above-mentioned method, symmetrical capacitors were produced, and the electrostatic capacitance of the positive electrodes was measured. The positive electrode capacitance of the nonaqueous electrolyte storage element of Comparative Example 1, in which the end-of-discharge voltage was set to 1.3 V, was 0.99 F / g. In contrast, the positive electrode capacitance of the nonaqueous electrolyte storage element of Example 3, in which the end-of-discharge voltage was set to 0.8 V, was 2.3 F / g, and the positive electrode capacitance of the nonaqueous electrolyte storage element of Example 2, in which the end-of-discharge voltage was set to 0.5 V, was 2.5 F / g.

[0109] [Table 1]

[0110] As shown in Table 1, each of the nonaqueous electrolyte storage elements of Examples 1 to 9 had a large discharge capacity per mass of sulfur of 900 mAh / g or more. In each of these nonaqueous electrolyte storage elements, the discharge capacity per mass of sulfur in the voltage range of 1.0 V or more was also large, and the utilization rate of sulfur was high. Therefore, it can be seen that in each of the nonaqueous electrolyte storage elements of Examples 1 to 9, the discharge capacity is larger than the amount of electricity discharged in the range of 1.0 V or less. In addition, from the discharge curves in the charge / discharge test of each of the nonaqueous electrolyte storage elements of Example 2 and Comparative Example 1 in FIG. 3, it can be confirmed that the discharge capacity in the same voltage range (voltage range of 1.3 V or more) is large in the nonaqueous electrolyte storage element of Example 2, and the utilization rate of sulfur is high.

[0111] In addition, the nonaqueous electrolyte storage element of Example 9 had a sufficiently large discharge capacity per mass of sulfur calculated from the second discharged amount of electricity, but it was confirmed that the discharge capacity was significantly reduced when the charge-discharge cycle was repeated, compared with the nonaqueous electrolyte storage elements of other Examples. It can be seen that the use of a nonaqueous solvent containing 10% by volume or more of unsaturated cyclic carbonate can also suppress the capacity reduction accompanying the charge-discharge cycle of the nonaqueous electrolyte storage element.

[0112] In addition, the energy density per mass of sulfur in each of the nonaqueous electrolyte storage elements of Example 2 and Comparative Example 1 was determined from the second discharged electricity quantity in the charge / discharge test. The energy density per mass of sulfur in the nonaqueous electrolyte storage element of Example 2 was 1830 Wh / kg, and the energy density per mass of sulfur in the nonaqueous electrolyte storage element of Comparative Example 1 was 1403 Wh / kg. As a result, the energy density increased even when the discharge cut-off voltage was lowered. [Industrial Applicability]

[0113] 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. [Explanation of symbols]

[0114] 1. Non-aqueous electrolyte storage element 2 Electrode body 3 containers 4 Positive terminal 41 Positive lead 5 Negative terminal 51 Negative lead 20 Energy Storage Unit 30 Energy storage device

Claims

1. A positive electrode comprising a composite of porous carbon and sulfur; and Non-aqueous electrolyte comprising a non-aqueous solvent containing an unsaturated cyclic carbonate and a lithium salt Equipped with the non-aqueous solvent further contains ethylene carbonate, propylene carbonate, or butylene carbonate; The porous carbon has a cumulative 70% pore diameter of 2.0 nm or more and 7.0 nm or less, The content of the unsaturated cyclic carbonate in the non-aqueous solvent is 10% by volume or more; The positive electrode potential at the end of discharge during normal use is 1.0 V vs. Li / Li ＋ The nonaqueous electrolyte storage element is as follows:

2. A positive electrode comprising a composite of porous carbon and sulfur; and Non-aqueous electrolyte comprising a non-aqueous solvent containing an unsaturated cyclic carbonate and a lithium salt Equipped with The porous carbon has a cumulative 70% pore diameter of 2.0 nm or more and 7.0 nm or less, The content of the unsaturated cyclic carbonate in the non-aqueous solvent is 10% by volume or more; A nonaqueous electrolyte electricity storage element having a positive electrode potential of 0.9 V vs. Li / Li + or less at a discharge cut-off voltage during normal use.

3. 3. The nonaqueous electrolyte storage element according to claim 1, wherein the content of oxygen in the composite relative to the carbon, sulfur, oxygen and fluorine elements as measured by SEM-EDX analysis is 20 mass % or more.

4. The battery was constructed using two of the above positive electrodes, and lithium bis(trifluoromethanesulfonyl)imide was added at 1.0 mol / dm ３ and a capacitance of the positive electrode measured in a symmetrical capacitor using a nonaqueous electrolyte solution containing vinylene carbonate as a nonaqueous solvent is 2 F / g or more.

5. An apparatus comprising the nonaqueous electrolyte electricity storage element according to any one of claims 1 to 4.

6. Discharging an electric storage element including a positive electrode including a composite of porous carbon and sulfur and a non-aqueous electrolyte including a non-aqueous solvent containing an unsaturated cyclic carbonate and a lithium salt; the non-aqueous solvent further contains ethylene carbonate, propylene carbonate, or butylene carbonate; The porous carbon has a cumulative 70% pore diameter of 2.0 nm or more and 7.0 nm or less, The content of the unsaturated cyclic carbonate in the non-aqueous solvent is 10% by volume or more; The above discharge was performed at a positive electrode potential of 1.0 V vs. Li / Li ＋ A method for producing a nonaqueous electrolyte electricity storage element, comprising the steps of:

7. A method for producing a battery comprising discharging a storage element including a positive electrode including a composite of porous carbon and sulfur, and a non-aqueous electrolyte including a non-aqueous solvent containing an unsaturated cyclic carbonate and a lithium salt; The porous carbon has a cumulative 70% pore diameter of 2.0 nm or more and 7.0 nm or less, The content of the unsaturated cyclic carbonate in the non-aqueous solvent is 10% by volume or more; The method for producing a nonaqueous electrolyte electricity storage element includes performing the above-mentioned discharge until the positive electrode potential becomes 0.9 V vs. Li / Li + or less.

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