Non-aqueous electrolyte energy storage element, energy storage device, and method of using the non-aqueous electrolyte energy storage element

Abstract

This invention provides a non-aqueous electrolyte energy storage element and energy storage device equipped with a positive electrode containing a sulfur-based active material, which have a large discharge capacity during charge-discharge cycles, and a method for using a non-aqueous electrolyte energy storage element equipped with a positive electrode containing a sulfur-based active material that can increase the discharge capacity during charge-discharge cycles. [Solution] A non-aqueous electrolyte energy storage element according to one aspect of the present invention comprises a positive electrode containing a sulfur-based active material and a non-aqueous electrolyte containing a cyclic carbonate and a fluorinated carboxylic acid ester, wherein the upper limit charge potential of the positive electrode is 3.1V vs. Li / Li + More than 3.3V vs.Li / Li + The following applies:

Description

[Technical Field]

[0001] The present invention relates to a non-aqueous electrolyte energy storage element, an energy storage device, and a method for using a non-aqueous electrolyte energy 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, as well as automobiles, due to their high energy density. Generally, non-aqueous electrolyte secondary batteries consist of a pair of electrodes electrically isolated by a separator, and a non-aqueous electrolyte interposed between these electrodes. They are configured to charge and discharge by transferring charge-transporting ions, such as lithium ions, between the two electrodes. Other non-aqueous electrolyte energy storage elements, such as lithium-ion capacitors and electric double-layer capacitors, are also widely used.

[0003] As non-aqueous electrolyte energy storage devices, lithium-sulfur batteries (Li-S batteries) and other non-aqueous electrolyte energy storage devices that use an active material containing sulfur (sulfur-based active material) in the positive electrode are known (see Patent Document 1). Sulfur-based active materials have a large theoretical capacity, and non-aqueous electrolyte energy storage devices that use sulfur-based active materials in the positive electrode are expected to be energy storage devices with high energy density. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International Publication No. 2020 / 090986 [Overview of the project] [Problems that the invention aims to solve]

[0005] In non-aqueous electrolyte energy storage elements using sulfur-based active materials in the positive electrode, sufficient discharge capacity may not be obtained due to the leaching of polysulfides from the positive electrode into the non-aqueous electrolyte. Furthermore, while the formation of a film covering the sulfur-based active material through a reaction between the sulfur-based active material and the non-aqueous electrolyte can suppress the leaching of polysulfides from the positive electrode into the non-aqueous electrolyte, this can result in the disadvantage of reduced discharge capacity during charge-discharge cycles.

[0006] The object of the present invention is to provide a non-aqueous electrolyte energy storage element and energy storage device that have a positive electrode containing a sulfur-based active material and have a large discharge capacity during charge-discharge cycles, and a method for using a non-aqueous electrolyte energy storage element that has a positive electrode containing a sulfur-based active material and can increase the discharge capacity during charge-discharge cycles. [Means for solving the problem]

[0007] A non-aqueous electrolyte energy storage element according to one aspect of the present invention comprises a positive electrode containing a sulfur-based active material and a non-aqueous electrolyte containing a cyclic carbonate and a fluorinated carboxylic acid ester, wherein the upper limit charge potential of the positive electrode is 3.1V vs. Li / Li + More than 3.3V vs.Li / Li + The following applies:

[0008] Another aspect of the present invention relates to a non-aqueous electrolyte energy storage device comprising a positive electrode containing a sulfur-based active material and a non-aqueous electrolyte containing a cyclic carbonate and a fluorinated carboxylic acid ester, wherein the upper limit charge potential of the positive electrode is 3.1V vs. Li / Li + More than 3.3V vs.Li / Li + Control it as follows:

[0009] A method of using a non-aqueous electrolyte energy storage element according to another aspect of the present invention is to use a non-aqueous electrolyte energy storage element comprising a positive electrode containing a sulfur-based active material and a non-aqueous electrolyte containing a cyclic carbonate and a fluorinated carboxylic acid ester, wherein the potential of the positive electrode is 3.1V vs. Li / Li + More than 3.3V vs.Li / Li + It is equipped to charge up to the following point. [Effects of the Invention]

[0010] According to any aspect of the present invention, it is possible to provide a non-aqueous electrolyte energy storage element and energy storage device that have a positive electrode containing a sulfur-based active material and have a large discharge capacity during charge-discharge cycles, as well as a method for using a non-aqueous electrolyte energy storage element that has a positive electrode containing a sulfur-based active material and can increase the discharge capacity during charge-discharge cycles of the non-aqueous electrolyte energy storage element. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a perspective view showing a non-aqueous electrolyte energy storage element according to one embodiment of the present invention. [Figure 2] Figure 2 is a schematic diagram showing an energy storage device comprising a non-aqueous electrolyte energy storage element according to multiple embodiments of the present invention. [Modes for carrying out the invention]

[0012] First, an overview of the non-aqueous electrolyte energy storage elements, energy storage devices, and methods of using the non-aqueous electrolyte energy storage elements disclosed herein will be provided.

[0013] [1] A non-aqueous electrolyte energy storage element according to one aspect of the present invention comprises a positive electrode containing a sulfur-based active material and a non-aqueous electrolyte containing a cyclic carbonate and a fluorinated carboxylic acid ester, wherein the upper limit charge potential of the positive electrode is 3.1V vs. Li / Li + More than 3.3V vs.Li / Li + The following applies:

[0014] The non-aqueous electrolyte energy storage element described in [1] above has a positive electrode containing a sulfur-based active material and has a large discharge capacity during charge-discharge cycles. The reason for this is not clear, but the following reasons are speculated.

[0015] In a non-aqueous electrolyte storage device using a positive electrode containing a sulfur-based active material, there are cases where sufficient discharge capacity cannot be obtained due to the dissolution of polysulfides from the positive electrode into the non-aqueous electrolyte. On the other hand, in such a non-aqueous electrolyte storage device, for example, by using a non-aqueous electrolyte containing carbonate, a film covering the sulfur-based active material can be formed by the reaction of the sulfur-based active material and carbonate during the first discharge. As a result, the dissolution of polysulfides from the positive electrode into the non-aqueous electrolyte can be suppressed by the film derived from carbonate. However, also in this case, there may occur a disadvantage that the discharge capacity during charge-discharge cycles decreases due to the incorporation of sulfur element into the film derived from carbonate. In contrast, in the non-aqueous electrolyte storage device described in [1] above, since the non-aqueous electrolyte contains a cyclic carbonate, a film derived from the cyclic carbonate that can suppress the dissolution of polysulfides from the positive electrode into the non-aqueous electrolyte during the first discharge is formed on the surface of the sulfur-based active material. Further, since the non-aqueous electrolyte contains a fluorinated carboxylic acid ester, the above film becomes thin and good. Furthermore, since the upper charge limit potential of the positive electrode is 3.1V vs.Li / Li + or more and 3.3V vs.Li / Li + or less, the sulfur element incorporated into the above film can reversibly participate in charge-discharge as an active material, thereby increasing the discharge capacity during charge-discharge cycles. The relationship between the upper charge limit potential of the positive electrode and the sulfur element incorporated into the above film will be described in more detail below.

[0016] In a non-aqueous electrolyte storage device using a sulfur-based active material, it was common to set the upper charge potential of the positive electrode to 3.0V vs.Li / Li + or less. One of the reasons for this is that when the potential of the positive electrode becomes 4.0V vs.Li / Li + or more, the carbon material that can be used in combination with the sulfur-based active material is likely to deteriorate. Also, the sulfur element incorporated into the above film derived from carbonate formed during the first discharge was considered not to participate in charge-discharge and to be a factor increasing the irreversible capacity. In contrast, the present inventors deliberately set the potential of the positive electrode to 3.0V vs.Li / Li +We found that by increasing the value, the state of the sulfur elements incorporated into the above coating changes, and they can reversibly participate in charging and discharging again as an active material. In this case, the positive electrode potential is 3.0V vs. Li / Li + In addition to the charging capacity of the sulfur-based positive electrode up to that point, the positive electrode potential is 3.0V vs. Li / Li + In the range of the above, an additional charging capacity is obtained involving the sulfur element incorporated into the above coating. Based on these findings, in the non-aqueous electrolyte energy storage element described in [1] above, the upper limit charging potential of the positive electrode is 3.1V vs. Li / Li + More than 3.3V vs.Li / Li + The sulfur elements incorporated into the above-mentioned coating are adjusted to an appropriate range to obtain additional charging capacity.

[0017] From the above, a good film formed on the surface of the sulfur-based active material and a positive electrode potential of 3.0V vs. Li / Li + It is presumed that the non-aqueous electrolyte energy storage element described in [1] above has a large discharge capacity during charge-discharge cycles due to the synergistic effect of the sulfur elements incorporated into the above coating in the greater range, which reversibly participate in charging and discharging.

[0018] The "positive electrode charge limit potential" refers to the highest potential that the positive electrode of the non-aqueous electrolyte energy storage element reaches through charging during a charge-discharge cycle. The positive electrode charge limit potential may also be the positive electrode charge limit potential during normal use of the non-aqueous electrolyte energy storage element. Here, "normal use" refers to using the non-aqueous electrolyte energy storage element under the recommended or specified charge-discharge conditions, and, if a charger for the non-aqueous electrolyte energy storage element is available, using that charger. The positive electrode charge limit potential during normal use may be the positive electrode potential at the charge termination voltage during normal use. Positive electrode charging limit potential (V vs. Li / Li +If pure metallic lithium is used as the negative electrode active material of the non-aqueous electrolyte energy storage element, this value shall be considered to be the same as the charge termination voltage of the non-aqueous electrolyte energy storage element. If pure metallic lithium is not used as the negative electrode active material of the non-aqueous electrolyte energy storage element, the measurement shall be performed according to the following procedure. First, the non-aqueous electrolyte energy storage element, after initial charging and discharging, is discharged at a constant current of 0.1C until it reaches the discharge termination voltage for normal use, bringing it to a fully discharged state. Here, "0.1C current" refers to the current that can discharge the theoretical capacity of the non-aqueous electrolyte energy storage element in 10 hours. The theoretical capacity of the non-aqueous electrolyte energy storage element is calculated from the product of the capacity density per unit area of ​​one positive electrode active material layer and the area of ​​the positive electrode active material layer. The fully discharged non-aqueous electrolyte energy storage element is disassembled, and the positive and negative electrodes are removed. Then, the positive electrode is used as the working electrode, the negative electrode as the counter electrode, and metallic lithium as the reference electrode, and a trielectrode cell is fabricated using these electrodes and the non-aqueous electrolyte. As the non-aqueous electrolyte, a non-aqueous solvent was prepared by mixing fluoroethylene carbonate (FEC), vinylene carbonate (VC), and difluoroethyl acetate (EDFA) in a volume ratio of 25:25:50, to which lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was added at a concentration of 0.5 mol / dm³. 3 A product containing the specified amount of [substance] is used. The assembled three-electrode cell is charged with a constant current of 0.1C to the normal charging termination voltage of the non-aqueous electrolyte energy storage element, bringing it to a fully charged state. The potential difference between the working electrode and the reference electrode at this time is defined as the upper limit charging potential of the positive electrode. Both charging and discharging are performed in a constant temperature bath at 25°C.

[0019] The types and content of components (non-aqueous solvents) contained in the non-aqueous electrolyte are determined by liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-mass spectrometry (GC-MS). However, if the types of components (non-aqueous solvents) contained in the non-aqueous electrolyte cannot be determined by LC-MS and GC-MS, they may be determined by means other than LC-MS and GC-MS. LC-MS and GC-MS will be described in detail below. Note that LC-MS and GC-MS measurements will be performed consecutively under the same conditions. Furthermore, in this invention, the content of each component contained in the non-aqueous electrolyte is the value measured at 20°C and 1 atm, or the value converted to a value at 20°C and 1 atm. [1] Collection of non-aqueous electrolytes First, the non-aqueous electrolyte energy storage element is disassembled and the non-aqueous electrolyte is extracted. If extraction is not possible, the non-aqueous electrolyte is extracted by centrifuging the non-aqueous electrolyte energy storage element. If extraction is still not possible after centrifugation, a suitable extraction solvent (e.g., acetonitrile) is injected into the non-aqueous electrolyte energy storage element, and the non-aqueous electrolyte diluted with the extraction solvent is extracted. [2] LC-MS The components of the collected non-aqueous electrolyte are analyzed by LC-MS. The LC-MS analysis is performed in the following order: qualitative analysis followed by quantitative analysis. The LC-MS analyzers used are Waters' "Acquity H" and "Xevo G2-5QTof". Water is used as the eluent. In cases where it is not possible to measure using the above-mentioned instruments, other instruments that are expected to produce equivalent measurement results may be used. The same applies to other measuring instruments in this specification. (qualitative analysis) The sample (non-aqueous electrolyte) is subjected to LC-MS analysis. If the peaks in the resulting liquid chromatogram are not separated, GC-MS analysis, as described later, is performed instead of LC-MS analysis. If the peaks are separated, the components contained in the sample are predicted from the MS spectrum of each peak. A known sample of the predicted component (hereinafter referred to as "predicted component") is subjected to LC-MS analysis. The retention time and MS spectrum of the peak corresponding to each predicted component in the sample are compared with the retention time and MS spectrum of the peak in the known sample of each predicted component. If they match, the above prediction is presumed to be correct. (Quantitative analysis) Quantitative analysis is performed using the calibration curve method. First, known samples of predicted components with known concentrations are measured by LC-MS, and the area of ​​the peaks is determined to create a calibration curve. The calibration curve is then analyzed using the coefficient of determination (r 2 Prepare the calibration curve so that the result is between 0.999 and 1. Determine the content of the predicted component in the sample from the calibration curve and the area of ​​the peaks of the predicted component in the sample. Perform the above steps for all peaks detected by LC-MS analysis of the sample to determine the content of each predicted component. [3] GC-MS GC-MS analysis will be performed in the following order: qualitative analysis followed by quantitative analysis. An Agilent "5975C" GC-MS instrument will be used. Argon will be used as the carrier gas. (qualitative analysis) The 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. A sample of known components is subjected to GC-MS analysis. The retention time and MS spectrum of the peaks corresponding to each predicted component in the sample are compared with the retention time and MS spectrum of the peaks of known components in the sample. If they match, the above prediction is presumed to be correct. (Quantitative analysis) Quantitative analysis is performed using the calibration curve method. Quantitative analysis by GC-MS is performed using the same procedure as the quantitative analysis by LC-MS described above to determine the content of each predicted component. [4] Calculation of the content of each component The content of each non-aqueous solvent is calculated by summing the content of each non-aqueous solvent among the predicted components (i.e., each component) measured by LC-MS or GC-MS, and this is taken as the total amount of non-aqueous solvent. When calculating the content (volume %) of each non-aqueous solvent relative to the total amount of non-aqueous solvent, the mass-based content of each non-aqueous solvent measured by LC-MS or GC-MS is converted to volume at 20°C and 1 atm, and the sum of the volume-converted contents of each non-aqueous solvent is taken as the total amount of non-aqueous solvent. Furthermore, if an extraction solvent is used, the extraction solvent is excluded from consideration.

[0020] [2] In the non-aqueous electrolyte energy storage element described in [1] above, the cyclic carbonate may contain fluorinated saturated cyclic carbonate and unsaturated cyclic carbonate.

[0021] The non-aqueous electrolyte energy storage element described in [2] above has a better coating derived from cyclic carbonate, resulting in a larger discharge capacity during charge-discharge cycles.

[0022] [3] In the non-aqueous electrolyte energy storage element described in [1] or [2] above, the non-aqueous electrolyte may have a non-aqueous solvent containing the cyclic carbonate and the fluorinated carboxylic acid ester, and the content of the fluorinated carboxylic acid ester in the non-aqueous solvent may be 20% by volume or more.

[0023] The non-aqueous electrolyte energy storage element described in [3] above has a better coating derived from cyclic carbonate, resulting in a larger discharge capacity during charge-discharge cycles.

[0024] [4] In a non-aqueous electrolyte energy storage element according to any of [1] to [3] above, the positive electrode has a positive electrode active material layer containing the sulfur-based active material, and the capacity density per unit area of ​​one positive electrode active material layer is 10 mAh / cm². 2 That's fine too.

[0025] Generally, when the capacity density per unit area of ​​one positive electrode active material layer is high, the amount of polysulfide leached from the positive electrode into the non-aqueous electrolyte tends to increase. When the amount of polysulfide leached from the positive electrode into the non-aqueous electrolyte increases, the concentration of polysulfide in the non-aqueous electrolyte increases, and the viscosity of the non-aqueous electrolyte increases, which can degrade the performance of the non-aqueous electrolyte energy storage element. In contrast, the non-aqueous electrolyte energy storage element described in [4] above has a capacity density per unit area of ​​one positive electrode active material layer within the above range, thus significantly obtaining the advantages of the present invention, which include high discharge capacity during charge-discharge cycles while suppressing the leaching of polysulfide from the positive electrode into the non-aqueous electrolyte.

[0026] [5] In a non-aqueous electrolyte energy storage element according to any of [1] to [4] above, the positive electrode has a positive electrode active material layer containing the sulfur-based active material, and the mass per unit area of ​​one positive electrode active material layer is 5 mg / cm². 2 That's fine too.

[0027] The non-aqueous electrolyte energy storage element described in [5] above has a mass per unit area of ​​one positive electrode active material layer within the above range, thus significantly achieving the advantages of the present invention, which include a large discharge capacity during charge-discharge cycles while suppressing the elution of polysulfides from the positive electrode into the non-aqueous electrolyte.

[0028] "Capacitance density per unit area of ​​one positive electrode active material layer" refers to the mass per unit area of ​​one positive electrode active material layer (g / cm³). 3 This refers to the product of the content (mass%) of sulfur-based active material in the positive electrode active material layer and the theoretical capacity (mAh / g) of the sulfur-based active material.

[0029] [6] Another aspect of the present invention relates to a non-aqueous electrolyte energy storage device comprising a positive electrode containing a sulfur-based active material and a non-aqueous electrolyte containing a cyclic carbonate and a fluorinated carboxylic acid ester, wherein the upper limit charge potential of the positive electrode is 3.1V vs. Li / Li + More than 3.3V vs.Li / Li + Control it as follows:

[0030] In the energy storage device described in [6] above, the non-aqueous electrolyte contains a cyclic carbonate, which allows a cyclic carbonate-derived film to form on the surface of the sulfur-based active material during the first discharge, thereby suppressing the elution of polysulfides from the positive electrode to the non-aqueous electrolyte. Furthermore, the non-aqueous electrolyte contains a fluorinated carboxylic acid ester, resulting in a thin and effective film. In addition, the upper limit charge potential of the positive electrode is 3.1V vs. Li / Li + More than 3.3V vs.Li / Li + Therefore, the sulfur elements incorporated into the above coating reversibly participate in charging and discharging as active material, thereby increasing the discharge capacity during the charge-discharge cycle.

[0031] [7] Another aspect of the present invention relates to a method of using a non-aqueous electrolyte energy storage element comprising a positive electrode containing a sulfur-based active material and a non-aqueous electrolyte containing a cyclic carbonate and a fluorinated carboxylic acid ester, wherein the potential of the positive electrode is 3.1V vs. Li / Li + More than 3.3V vs.Li / Li + It is equipped to charge up to the following point.

[0032] The method of use described in [7] above applies to a non-aqueous electrolyte energy storage element in which a good coating derived from a sulfur-containing cyclic carbonate is formed on the surface of the sulfur-based active material, with a positive electrode potential of 3.1V vs. Li / Li + More than 3.3V vs.Li / Li + Because it is designed to charge down to the following point, the sulfur elements incorporated into the above coating reversibly participate in charging and discharging as active material, thereby increasing the discharge capacity during the charge-discharge cycle.

[0033] A non-aqueous electrolyte energy storage element, a method for manufacturing the non-aqueous electrolyte energy storage element, a method for using the non-aqueous electrolyte energy storage element, an energy storage device, and other embodiments according to one embodiment of the present invention will be described in detail below.

[0034] [Non-aqueous electrolyte energy storage element] A non-aqueous electrolyte energy storage element according to one embodiment of the present invention comprises a positive electrode, a negative electrode, a non-aqueous electrolyte, and a container housing them. The non-aqueous electrolyte energy storage element can increase the discharge capacity during charge-discharge cycles by having a configuration described later. The non-aqueous electrolyte energy storage element may further include a separator interposed between the positive electrode and the negative electrode to electrically insulate them. The positive electrode, the negative electrode, and any separator usually constitute an electrode body. At least a portion of the non-aqueous electrolyte usually exists in a state of permeating the electrode body. The non-aqueous electrolyte energy storage element according to one embodiment of the present invention may further include other members.

[0035] For example, the non-aqueous electrolyte energy storage element 1 shown in Figure 1, according to one embodiment of the present invention, comprises an electrode body 2, a non-aqueous electrolyte (not shown), and a rectangular parallelepiped container 3 that houses them. The non-aqueous electrolyte energy storage element 1 in Figure 1 further comprises a positive electrode lead 4, a positive electrode external terminal 5, a negative electrode lead 6, and a negative electrode external terminal 7. The positive electrode lead 4 and the negative electrode lead 6 are housed together with the electrode body 2, etc., inside the container 3. The positive electrode external terminal 5 and the negative electrode external terminal 7 are provided outside the container 3. The positive electrode constituting the electrode body 2 is electrically connected to the positive electrode external terminal 5 via the positive electrode lead 4. The negative electrode constituting the electrode body 2 is electrically connected to the negative electrode external terminal 7 via the negative electrode lead 6.

[0036] The non-aqueous electrolyte energy storage element of the present invention may also be a non-aqueous electrolyte secondary battery. Below, the main components constituting the non-aqueous electrolyte energy storage element according to one embodiment of the present invention will be described in detail, focusing on the case where the non-aqueous electrolyte energy storage element is a non-aqueous electrolyte secondary battery (particularly a lithium-ion secondary battery), but this is not intended to limit the scope of application of the present invention.

[0037] Furthermore, the lower and upper limits of each numerical range described in the embodiments of the present invention can be combined in any way.

[0038] (positive electrode) The positive electrode comprises a positive electrode substrate and a positive electrode active material layer laminated directly to the positive electrode substrate or via an intermediate layer. Typically, the positive electrode has a portion where the positive electrode substrate is exposed. This exposed portion of the positive electrode substrate is usually connected to the positive electrode lead described above. The positive electrode may have a shape such as a sheet, plate, or strip.

[0039] The thickness of the positive electrode is set appropriately according to the application of the non-aqueous electrolyte energy storage element. The average thickness of the positive electrode may be, for example, 30 μm or more and 1,000 μm or less. The lower limit of the average thickness of the positive electrode may be 50 μm, 100 μm, or 200 μm. The upper limit of the average thickness of the positive electrode may be 500 μm, 400 μm, 300 μm, 200 μm, or 100 μm. The average thickness of the positive electrode is the average thickness of the portion in which the positive electrode active material layer is laminated directly onto the positive electrode substrate or via an intermediate layer. If both portions exist in which the positive electrode active material layer is laminated on both sides of the positive electrode substrate and portions in which the positive electrode active material layer is laminated on only one side of the positive electrode substrate, then the average thickness of the portion in which the positive electrode active material layer is laminated on both sides of the positive electrode substrate shall be used. Furthermore, in this specification, "average thickness" means the average value of the thickness measured at any five locations.

[0040] The positive electrode substrate is conductive. In this specification, "conductive" means that the volume resistivity is 10 -2 This means that the volume resistivity is Ω·cm or less. The volume resistivity shall be the value measured in accordance with JIS-H-0505 (1975). On the other hand, in this specification, "not conductive" or "having (electrical) insulating properties" means that the above volume resistivity is 10 7 This means it is greater than or equal to Ω·cm.

[0041] Examples of materials for the positive electrode substrate include metals such as aluminum, titanium, iron, and their alloys (stainless steel, etc.). Among these, aluminum or aluminum alloys are preferred from the viewpoint of high potential resistance, high electronic conductivity, and cost.

[0042] The positive electrode substrate has a shape such as a sheet, plate, or strip. Examples of positive electrode substrate forms include foil, vapor-deposited film, mesh, and porous material, with foil being preferred. The positive electrode substrate may also be, for example, aluminum foil or aluminum alloy foil.

[0043] The average thickness of the positive electrode substrate may be, for example, 3 μm or more and 50 μm or less. The lower limit of the average thickness of the positive electrode substrate may be 5 μm, 8 μm, 10 μm, or 15 μm. The upper limit of the average thickness of the positive electrode substrate may be 40 μm, 30 μm, 20 μm, or 15 μm.

[0044] The intermediate layer is a layer placed between the positive electrode substrate and the positive electrode active material layer. The intermediate layer includes, for example, a conductive agent and a binder. When the intermediate layer contains a conductive agent, the contact resistance between the positive electrode substrate and the positive electrode active material layer can be reduced. Examples of conductive agents and binders used in the intermediate layer are the same as those used in the positive electrode active material layer, which will be described later.

[0045] The positive electrode active material layer contains a sulfur-based active material. The positive electrode active material layer may optionally contain conductive agents, binders, dispersants, thickeners, fillers, and other optional components. The positive electrode active material layer may be formed from a positive electrode mixture containing a sulfur-based active material and other optional components. The positive electrode active material layer may be provided on only one side of a positive electrode substrate having a shape such as a sheet, or on both sides.

[0046] Sulfur-based active materials are components that function as positive electrode active materials. These sulfur-based active materials may be elemental sulfur (theoretical capacity 1675 mAh / g), sulfur compounds, or mixtures thereof. Examples of sulfur compounds include metal sulfides such as lithium sulfide (theoretical capacity 1170 mAh / g), organic disulfide compounds (theoretical capacity 500 to 700 mAh / g), and organic sulfur compounds such as carbon sulfide compounds. Sulfur-based active materials have advantages such as high theoretical capacity and low cost.

[0047] The sulfur-based active material content in the positive electrode active material layer is preferably 50% to 80% by mass, more preferably 55% to 75% by mass, and even more preferably 60% to 70% by mass. Furthermore, the sulfur element content in the positive electrode active material layer is preferably 50% to 80% by mass, more preferably 55% to 75% by mass, and even more preferably 60% to 70% by mass. By having the sulfur-based active material or sulfur element content in the positive electrode active material layer within the above ranges, it is possible to increase the initial discharge capacity, etc.

[0048] The positive electrode active material layer may contain positive electrode active materials other than sulfur-based active materials. Examples of such other positive electrode active materials include known materials such as lithium transition metal composite oxides, polyanion compounds, chalcogen compounds, and lithium oxide. However, the content of sulfur-based active materials in the total positive electrode active material is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, even more preferably 99% by mass or more, and particularly preferably 100% by mass.

[0049] In one embodiment of the present invention, the sulfur-based active material may exist in the positive electrode active material layer in the form of a composite with porous carbon. That is, the positive electrode active material layer may further contain porous carbon, and the sulfur-based active material and porous carbon may form a composite (sulfur-porous carbon composite). In the composite of sulfur-based active material and porous carbon (hereinafter also simply referred to as "composite"), the sulfur-based active material is usually supported within the pores of the porous carbon. Sufficient electronic conductivity is ensured by the composite being in this form. The composite may consist substantially only of sulfur-based active material and porous carbon, or it may consist only of sulfur-based active material and porous carbon. The composite consisting substantially only of sulfur-based active material and porous carbon means, for example, that the total content of sulfur-based active material (total of elemental sulfur and sulfur compounds) and porous carbon in the composite is 90% by mass or more, and may be 95% by mass or more, 98% by mass or more, or 99% by mass or more. The sulfur-based active material content (total of elemental sulfur and sulfur compounds) in the composite is preferably 50% to 90% by mass, and more preferably 60% to 80% by mass. By setting the sulfur-based active material content in the composite within the above range, it is possible to increase the initial discharge capacity, etc.

[0050] Porous carbon is electrically conductive. Porous carbon is generally a porous inorganic material whose main constituent element is carbon. The main constituent element refers to the element that is present in the largest quantity by mass. The lower limit of the carbon content in porous carbon is preferably 70% by mass, and more preferably 80%, 90%, 95%, or 97% by mass. The upper limit of the carbon content in porous carbon may be 100% by mass or 99.9% by mass. Porous carbon may also contain elements other than carbon, such as oxygen and nitrogen.

[0051] The composite can be manufactured by conventionally known methods. For example, it can be obtained by heating a mixture of a sulfur-based active material and porous carbon to a temperature above the melting point of the sulfur-based active material, and then cooling it.

[0052] The composite content in the positive electrode active material layer is preferably 60% to 97% by mass, more preferably 80% to 96% by mass, and even more preferably 90% to 95% by mass. By setting the composite content within the above range, it is possible to increase the initial discharge capacity, etc.

[0053] Conductive agents are typically components made of conductive materials. Note that these conductive agents do not contain porous carbon, which constitutes the composite. Even if the volume resistivity of the conductive agent cannot be directly measured, if the volume resistivity is 10 -2 Materials whose conductivity is known to be Ω·cm or less are classified as conductive agents. Examples of conductive agents include carbon materials, metals, and conductive ceramics. A carbon material is a material whose main constituent element is carbon. The main constituent element is the element that is present in the largest quantity by mass. For example, the carbon content in a carbon material may be 80% by mass or more, 90% by mass or more, 95% by mass, 99% by mass, or 99.9% by mass or more. It is preferable that the carbon material is a carbon material other than a non-carbonized polymer compound. Examples of carbon materials include graphite, non-graphitic carbon, and graphene-based carbon. Examples of non-graphitic carbon include carbon nanofibers, pitch-based carbon fibers, and carbon black. Examples of carbon black include furnace black, acetylene black, and Ketjen black. Examples of graphene-based carbon include graphene, carbon nanotubes (CNTs), and fullerenes. Conductive agents can take the form of powder or fibers. One or more conductive agents can be used. These materials may be used in combination as conductive agents. For example, a material made by combining carbon black and CNTs may be used. It is also preferable to use carbon black (preferably acetylene black) and CNTs in combination.

[0054] The content of the conductive agent in the positive electrode active material layer (excluding porous carbon in the composite) is preferably 0.1% by mass or more and 10% by mass or less, more preferably 1% by mass or more and 9% by mass or less, and even more preferably 3% by mass or more and 8% by mass or less. The upper limit of the conductive agent content may be 5% by mass, 4% by mass, or 3% by mass. By setting the conductive agent content within the above range, it is possible to increase the energy density of the non-aqueous electrolyte energy storage element.

[0055] Examples of binders include water-based binders and organic solvent-based binders.

[0056] A water-based binder is a binder that dissolves or disperses in water. A water-based binder may be one that dissolves or disperses in 100 parts by mass or more per 100 parts by mass of water at 20°C. When forming a positive electrode active material layer using a positive electrode mixture paste in which the dispersion medium is water or a mixed solvent mainly composed of water, a water-based binder (water-soluble or water-dispersible polymer material) can be used. Examples of water-based binders include polyethylene oxide, polypropylene oxide, polyvinyl alcohol, polyacrylic acid, polymethacrylic acid, polytetrafluoroethylene, styrene-butadiene rubber, polyethylene, polypropylene, nitrile-butadiene rubber, and cellulose.

[0057] An organic solvent-based binder is a binder that dissolves or disperses in an organic solvent (e.g., N-methylpyrrolidone). An organic solvent-based binder may be a binder that dissolves or disperses at 1 part by mass or more per 100 parts by mass of an organic solvent (e.g., N-methylpyrrolidone) at 20°C. When forming a positive electrode active material layer using a positive electrode mixture paste in which the dispersion medium is an organic solvent or a mixed solvent mainly composed of an organic solvent, an organic solvent-based binder (a polymer material having solubility or dispersibility in an organic solvent) can be used. Examples of organic solvent-based binders include polyvinylidene fluoride, copolymers of vinylidene fluoride and hexafluoropropylene, copolymers of ethylene and vinyl alcohol, polyacrylonitrile, polyphosphazene, polysiloxane, polyvinyl acetate, polymethyl methacrylate, polystyrene, polycarbonate, polyamide, polyimide, polyamideimide, crosslinked polymers of cellulose and chitosan pyrrolidone carboxylate, and derivatives of chitosan.

[0058] The binder may be a fluororesin (polytetrafluoroethylene, polyvinylidene fluoride, etc.), a polyolefin (polyethylene, polypropylene, etc.), an elastomer (ethylene propylene diene rubber, styrene butadiene rubber, fluororubber, etc.), a polysaccharide polymer (cellulose, chitosan derivatives, etc.), etc. Fluororesins and elastomers are preferred as binders, elastomers are more preferred, and styrene butadiene rubber is even more preferred. One or more types of binders can be used.

[0059] The binder content in the positive electrode active material layer is preferably 0.1% by mass or more and 10% by mass or less, more preferably 1% by mass or more and 9% by mass or less, and even more preferably 3% by mass or more and 8% by mass or less. The upper limit of the binder content may be 5% by mass, 4% by mass, or 3% by mass. By setting the binder content within the above range, it is possible to stably retain sulfur-based active materials, etc. The technology disclosed herein can also be implemented in a form in which the positive electrode active material layer does not contain a binder.

[0060] Examples of dispersants include polysaccharide polymers such as carboxymethylcellulose (CMC) and methylcellulose. If the dispersant has functional groups that react with lithium, these functional groups may be deactivated beforehand by methylation or the like. The dispersant content in the positive electrode active material layer is preferably 0.05% to 5% by mass, and more preferably 0.1% to 2% by mass. The polysaccharide polymer may function as a thickener or as a binder.

[0061] Examples of thickening agents include polyacrylic acid (PAA). The content of the thickening agent in the positive electrode active material layer is preferably 0.05% to 5% by mass, and more preferably 0.1% to 4% by mass. Polyacrylic acid may also function as a binder.

[0062] The filler is not particularly limited. The filler may be any component other than sulfur-based active materials, other positive electrode active materials, porous carbon, conductive agents, binders, dispersants, and thickeners, and may be a component that is intentionally included. The filler may be included as a component that fills gaps in the positive electrode active material layer, or it may be included for other purposes. The filler may be an organic substance such as a polyolefin, or an inorganic substance such as an inorganic oxide, hydroxide, or carbonate. One or more types of fillers may be used. When the positive electrode active material layer contains a filler, the filler content in the positive electrode active material layer can be 0.1% by mass or more and 8% by mass or less, usually preferably 5% by mass or less, and more preferably 2% by mass or less. The technology disclosed herein can also be carried out in a form in which the positive electrode active material layer does not contain a filler.

[0063] The positive electrode active material layer may further contain other components besides sulfur-based active material, other positive electrode active material, porous carbon, conductive agent, binder, dispersant, thickener, and filler. These other components may include those unintentionally present in the positive electrode active material layer. Furthermore, the positive electrode active material layer may contain impurities unintentionally present as these other components, insofar as they achieve the effects of the present invention. The upper limit of the content of these other components in the positive electrode active material layer may be 10% by mass, 5% by mass, 2% by mass, 1% by mass, 0.1% by mass, or 0.01% by mass. The upper limit of the content of unintentionally present components in the positive electrode active material layer may be 10% by mass, 5% by mass, 2% by mass, 1% by mass, 0.1% by mass, or 0.01% by mass. The upper limit for the amount of unintentionally included impurities in the positive electrode active material layer may be 10% by mass, or it may be 5% by mass, 2% by mass, 1% by mass, 0.1% by mass, or 0.01% by mass.

[0064] The lower limit of the capacity density per unit area of ​​one positive electrode active material layer is 5 mAh / cm². 2 Preferably, 9mAh / cm² 2 More preferably, 10mAh / cm² 2 A more preferable option is 11mAh / cm². 2 Even more preferable is 13mAh / cm². 2 Or 16mAh / cm² 2 This may also be the case. By having a capacity density per unit area of ​​one positive electrode active material layer within the above range, the advantages of the present invention, which allow for increased discharge capacity during charge-discharge cycles while suppressing the elution of polysulfides from the positive electrode into the non-aqueous electrolyte, can be significantly obtained. On the other hand, the upper limit of the capacity density per unit area of ​​one positive electrode active material layer is set at 31 mAh / cm² from the viewpoint of suppressing the elution of polysulfides from the positive electrode into the non-aqueous electrolyte. 2 Preferably, 26mAh / cm² 2 More preferably, 21mAh / cm² 2 A more preferable option is 18mAh / cm². 2 Or 16mAh / cm² 2 That's fine.

[0065] The lower limit of the mass per unit area of ​​one positive electrode active material layer is 5 mg / cm². 2 Preferably, 8 mg / cm³ 2 More preferably, 10 mg / cm³ 2 More preferably, 12 mg / cm³ 2 or 15 mg / cm³ 2 This may also be the case. By having the mass per unit area of ​​one positive electrode active material layer within the above range, the advantages of the present invention, which are that the discharge capacity after the initial discharge can be increased while suppressing the elution of polysulfides from the positive electrode to the non-aqueous electrolyte, can be significantly obtained. The upper limit of the mass per unit area of ​​one positive electrode active material layer is 30 mg / cm³ from the viewpoint of suppressing the elution of polysulfides from the positive electrode to the non-aqueous electrolyte. 2 Preferably, 25 mg / cm³ 2 More preferably, 20 mg / cm³ 2 More preferably, 15 mg / cm³ 2 That's fine.

[0066] The porosity of the positive electrode active material layer may be, for example, 20% or more and 50% or less. The lower limit of the porosity of the positive electrode active material layer may be 25%, 30%, or 35%. The upper limit of the porosity of the positive electrode active material layer may be 45%, 40%, or 35%. The "porosity (%)" of the positive electrode active material layer and the negative electrode active material layer described later is calculated using the formula (1-V2 / V1)×100, where V1 is the apparent volume (volume including voids) of the positive (negative) electrode active material layer and V2 is the sum of the actual volumes of each material constituting the positive (negative) electrode active material layer. The sum of the actual volumes V2 of each material constituting the positive (negative) electrode active material layer can be calculated from the content of each material in the positive (negative) electrode active material layer and the true density of each material.

[0067] (Method of manufacturing the positive electrode) The positive electrode can be manufactured by known methods. For example, the positive electrode can be manufactured by applying a paste-like positive electrode mixture (positive electrode mixture paste) directly to a positive electrode substrate or via an intermediate layer, and then drying it to form a positive electrode active material layer. The positive electrode mixture paste typically contains a sulfur-based active material, other optional components, and a dispersion medium. After drying, the positive electrode active material layer may be subjected to pressing or other similar processes.

[0068] (Negative electrode) The negative electrode comprises a negative electrode substrate and a negative electrode active material layer laminated directly to the negative electrode substrate or via an intermediate layer. Typically, the negative electrode has a portion where the negative electrode substrate is exposed. This exposed portion of the negative electrode substrate is usually connected to the negative electrode lead described above. The negative electrode may have a shape such as a sheet, plate, or strip.

[0069] The thickness of the negative electrode is set appropriately according to the application of the non-aqueous electrolyte energy storage element. The average thickness of the negative electrode may be, for example, 30 μm or more and 1,000 μm or less. The lower limit of the average thickness of the negative electrode may be 50 μm, 100 μm, or 200 μm. The upper limit of the average thickness of the negative electrode may be 500 μm, 400 μm, 300 μm, 200 μm, or 100 μm. The average thickness of the negative electrode is the average thickness of the portion in which the negative electrode active material layer is laminated directly to the negative electrode substrate or via an intermediate layer. If there are portions in which the negative electrode active material layer is laminated on both sides of the negative electrode substrate and portions in which the negative electrode active material layer is laminated on only one side of the negative electrode substrate, then the average thickness of the portion in which the negative electrode active material layer is laminated on both sides of the negative electrode substrate shall be used.

[0070] The negative electrode substrate is electrically conductive. Examples of materials for the negative electrode substrate include metals such as copper, nickel, iron, and their alloys (such as stainless steel), as well as carbon materials. Among these, nickel or nickel alloys are preferred.

[0071] The negative electrode substrate has a shape such as a sheet, plate, or strip. Examples of negative electrode substrate forms include foil, vapor-deposited film, mesh, and porous material, with foil being preferred. The negative electrode substrate may also be, for example, nickel foil or nickel alloy foil.

[0072] The average thickness of the negative electrode substrate may be, for example, 2 μm or more and 35 μm or less. The lower limit of the average thickness of the negative electrode substrate may be 3 μm, 4 μm, 5 μm, or 10 μm. The upper limit of the average thickness of the negative electrode substrate may be 30 μm, 20 μm, 15 μm, or 10 μm.

[0073] The configuration of the negative electrode intermediate layer is not particularly limited; for example, it can be selected from the configurations exemplified for the positive electrode intermediate layer.

[0074] The negative electrode active material layer contains a negative electrode active material. The negative electrode active material layer optionally contains optional components such as a conductive agent, binder, thickener, and filler. The optional components such as the conductive agent, binder, thickener, and filler can be selected from the materials exemplified above for the positive electrode. The negative electrode active material layer may be formed from a negative electrode mixture containing the negative electrode active material and other optional components. The negative electrode active material layer may be provided on only one side of a negative electrode substrate having a shape such as a sheet, or on both sides.

[0075] For the negative electrode active material, known negative electrode active materials can be used. For lithium-ion secondary batteries, materials capable of intercalating and releasing lithium ions are typically used as negative electrode active materials. Examples of negative electrode active materials include: metallic lithium; metals or metalloids such as silicon and tin; metal oxides or metalloids such as silicon oxide, titanium oxide, and tin oxide; and Li4Ti5O 12 LiTiO 2、 Examples include titanium-containing oxides such as TiNb2O7; polyphosphate compounds; silicon carbide; and carbon materials such as graphite and non-graphitic carbon. In the case of a negative electrode active material that does not contain charge transport ions such as lithium ions, a material doped with charge transport ions such as lithium ions can be used. One or more types of negative electrode active materials can be used.

[0076] As the negative electrode active material, metallic lithium is preferred. In other words, it is preferable that the negative electrode or negative electrode active material layer contains metallic lithium at least in the charged state. It is more preferable that the negative electrode or negative electrode active material layer contains metallic lithium in all states, including the charged and discharged states. The metallic lithium may be pure metallic lithium consisting substantially only of the element lithium, or it may be a lithium alloy containing other metallic elements. Examples of lithium alloys include lithium silver alloy, lithium zinc alloy, lithium calcium alloy, lithium aluminum alloy, lithium magnesium alloy, and lithium indium alloy. The lithium alloy may contain multiple metallic elements other than the element lithium.

[0077] The negative electrode active material layer may contain other negative electrode active materials besides metallic lithium. However, it is preferable that the negative electrode active material layer is substantially composed solely of metallic lithium (pure metallic lithium or lithium alloy). In this case, the negative electrode active material layer may be in the form of a foil substantially composed solely of metallic lithium. The lower limit of the lithium element content in the negative electrode active material layer is preferably 80% by mass, more preferably 90% by mass, and even more preferably 99% by mass or more. The upper limit of the lithium element content in the negative electrode active material layer may be 100% by mass.

[0078] When the negative electrode active material layer contains a conductive agent, the content of the conductive agent in the negative electrode active material layer is preferably 1% by mass or more and 10% by mass or less, and more preferably 3% by mass or more and 9% by mass or less. The content of the conductive agent in the negative electrode active material layer may be 5% by mass or less, or 2% by mass or less. The technology disclosed herein can also be carried out in a form in which the negative electrode active material layer does not contain a conductive agent.

[0079] When the negative electrode active material layer contains a binder, the binder content in the negative electrode active material layer is preferably 0.1% by mass or more and 10% by mass or less, and more preferably 0.5% by mass or more and 8% by mass or less. The binder content in the negative electrode active material layer may be 5% by mass or less, or 2% by mass or less. The technology disclosed herein can also be carried out in a form in which the negative electrode active material layer does not contain a binder.

[0080] When the negative electrode active material layer contains a thickening agent, the content of the thickening agent in the negative electrode active material layer is preferably 0.1% by mass or more and 10% by mass or less, and more preferably 0.5% by mass or more and 8% by mass or less. The content of the thickening agent in the negative electrode active material layer may be 5% by mass or less, or 2% by mass or less. The technology disclosed herein can also be carried out in a form in which the negative electrode active material layer does not contain a thickening agent.

[0081] The filler in the negative electrode active material layer is a component other than the negative electrode active material, conductive agent, binder, and thickener, and may be a component that is intentionally included. The filler may be included as a component that fills gaps in the negative electrode active material layer, or it may be included for other purposes. When the negative electrode active material layer contains a filler, the filler content in the negative electrode active material layer can be 0.1% by mass or more and 8% by mass or less, usually preferably 5% by mass or less, and more preferably 2% by mass or less. The technology disclosed herein can also be carried out in a form in which the negative electrode active material layer does not contain a filler.

[0082] The negative electrode active material layer may further contain other components besides the negative electrode active material, conductive agent, binder, thickener, and filler. These other components may include those unintentionally present in the negative electrode active material layer. Furthermore, the negative electrode active material layer may contain impurities unintentionally present as these other components, insofar as they achieve the effects of the present invention. The upper limit of the content of these other components in the negative electrode active material layer may be 10% by mass, 5% by mass, 2% by mass, 1% by mass, 0.1% by mass, or 0.01% by mass. The upper limit of the content of unintentionally present components in the negative electrode active material layer may be 10% by mass, 5% by mass, 2% by mass, 1% by mass, 0.1% by mass, or 0.01% by mass. The upper limit of the content of unintentionally present impurities in the negative electrode active material layer may be 10% by mass, 5% by mass, 2% by mass, 1% by mass, 0.1% by mass, or 0.01% by mass.

[0083] 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 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 may be, for example, 5 μm or more and 1,000 μm or less. The lower limit of the average thickness of the negative electrode active material layer in the charged state may be 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, or 100 μm. The upper limit of the average thickness of the negative electrode active material layer in the charged state may be 800 μm, 500 μm, 200 μm, 100 μm, 80 μm, 60 μm, or 40 μm.

[0084] (Method of manufacturing the negative electrode) The negative electrode can be manufactured by known methods. For example, the negative electrode can be manufactured by applying a paste-like negative electrode mixture (negative electrode mixture paste) directly to the negative electrode substrate or via an intermediate layer, and then drying it to form a negative electrode active material layer, similar to the manufacturing method of the positive electrode described above. The negative electrode mixture paste typically contains a negative electrode active material, other optional components, and a dispersion medium. After drying, the negative electrode active material layer may be pressed or otherwise subjected to other processes. If the negative electrode active material is a metal such as metallic lithium, it can also be manufactured by laminating metal foil directly to the negative electrode substrate or via an intermediate layer, and then pressing or otherwise performing other processes.

[0085] (Separator) A known separator can be used. Examples of separators include a separator consisting only of a substrate layer, or a separator in which an inorganic layer containing inorganic particles and a binder is formed on one or both sides of the substrate layer.

[0086] Examples of the substrate layer form of the separator include woven fabric, nonwoven fabric, and porous resin film. Among these forms, porous resin film is preferred from the viewpoint of strength, and nonwoven fabric is preferred from the viewpoint of liquid retention of non-aqueous electrolytes. The material of the substrate layer of the separator is not particularly limited as long as it has insulating properties, but resins such as polyolefins (polyethylene, polypropylene, etc.), polyimide, and aramid are preferred.

[0087] Examples of inorganic compounds constituting inorganic particles include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, calcium oxide, and magnesium oxide; nitrides such as aluminum nitride and silicon nitride; carbonates such as calcium carbonate; sulfates such as barium sulfate; sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium titanate; covalent crystals such as silicon; mineral resource-derived materials such as talc, zeolite, kaolin, bentonite, and mica, or their artificial counterparts. One or more types of inorganic particles can be used. The average particle size of the inorganic particles is preferably, for example, 0.5 μm to 10 μm. The inorganic particle content in the inorganic layer is preferably 50% to 99% by mass, and more preferably 80% to 98% by mass.

[0088] Examples of binders used in the inorganic layer include those similar to those exemplified in the positive electrode active material layer.

[0089] The porosity of the separator may be, for example, 20% or more and 80% or less. The lower limit of the separator's porosity may be 30%, 40%, or 50% from the viewpoint of discharge performance, etc. The upper limit of the separator's porosity may be 70%, 60%, or 50% from the viewpoint of strength, etc. In this specification, "porosity" refers to a volume-based value and means a measurement value obtained with a mercury porosimeter.

[0090] The average thickness of the separator may be, for example, 10 μm to 40 μm, or 15 μm to 30 μm.

[0091] A polymer gel composed of a polymer and a non-aqueous electrolyte may be used as a separator. A polymer gel may also be used in combination with a porous resin film, nonwoven fabric, etc., as described above, as a separator.

[0092] (electrode body) As the electrode body, known structures such as wound electrode bodies and laminated electrode bodies can be used.

[0093] A wound electrode has a structure in which the positive electrode and negative electrode are wound together while being insulated. The wound electrode may be cylindrical or flattened. The electrode 2 of the non-aqueous electrolyte energy storage element 1 in Figure 1 is a flattened wound electrode. A wound electrode can be manufactured, for example, by the following procedure. First, a laminate is obtained by stacking a positive electrode, a separator, and a negative electrode, each formed in a strip shape. A wound electrode is obtained by winding this laminate.

[0094] A laminated electrode body has a structure in which one or more positive electrodes and one or more negative electrodes are stacked in an insulated state. For example, a laminated electrode body can be obtained by stacking a positive electrode, a separator, and a negative electrode, each formed in a rectangular shape.

[0095] Other electrode structures can also be used, such as those in which at least one of the positive and negative electrodes is folded in a bellows-like manner and stacked.

[0096] (Non-aqueous electrolytes) A non-aqueous electrolyte is a medium that carries charge transport ions (e.g., lithium ions) between the positive and negative electrodes and contains substantially no water. The water content in a non-aqueous electrolyte may be, for example, 10,000 ppm or less, or 5,000 ppm or less.

[0097] A non-aqueous electrolyte contains a non-aqueous solvent. Typically, a non-aqueous electrolyte solution containing a non-aqueous solvent and an electrolyte salt dissolved in this non-aqueous solvent is preferred as the non-aqueous electrolyte. In one embodiment of the present invention, the non-aqueous electrolyte energy storage element may be a non-aqueous electrolyte energy storage element.

[0098] Non-aqueous solvents include cyclic carbonates and fluorinated carboxylic acid esters.

[0099] Cyclic carbonates are carbonates that have a ring structure containing a carbonate group (-OC(=O)-O-). Examples of cyclic carbonates include fluorinated cyclic carbonates and unfluorinated cyclic carbonates.

[0100] A fluorinated cyclic carbonate is a compound in which some or all of the hydrogen atoms in a cyclic carbonate are replaced with fluorine atoms. A fluorinated cyclic carbonate may be a fluorinated saturated cyclic carbonate or a fluorinated unsaturated cyclic carbonate, but a fluorinated saturated cyclic carbonate is preferred. A saturated cyclic carbonate is a cyclic carbonate that does not contain either a carbon-carbon double bond or a carbon-carbon triple bond in its molecule. Examples of fluorinated saturated cyclic carbonates include fluorinated ethylene carbonates such as fluoroethylene carbonate (FEC) and difluoroethylene carbonate (DFEC), fluorinated propylene carbonate, and fluorinated butylene carbonate. Among these, fluorinated ethylene carbonate is preferred, and FEC is more preferred. One or more types of fluorinated cyclic carbonates can be used.

[0101] The unfluorinated cyclic carbonate is preferably an unfluorinated unsaturated cyclic carbonate. An unsaturated cyclic carbonate is a cyclic carbonate having a carbon-carbon double bond or a carbon-carbon triple bond in its molecule. It is preferable that the unsaturated cyclic carbonate has a carbon-carbon double bond in its molecule. The unsaturated cyclic carbonate may have the carbon-carbon double bond or carbon-carbon triple bond in the ring structure or in a part other than the ring structure, but it is preferable that it is in the ring structure. Examples of unfluorinated unsaturated cyclic carbonates 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., with VC being preferred. One or more types of unfluorinated cyclic carbonates can be used.

[0102] The unfluorinated cyclic carbonate may also be an unfluorinated saturated cyclic carbonate. Examples of unfluorinated saturated cyclic carbonates include ethylene carbonate, propylene carbonate, butylene carbonate, and chloroethylene carbonate.

[0103] The cyclic carbonate preferably contains fluorinated cyclic carbonates and unsaturated cyclic carbonates, more preferably contains fluorinated saturated cyclic carbonates and unsaturated cyclic carbonates, and even more preferably contains fluorinated saturated cyclic carbonates and unfluorinated unsaturated cyclic carbonates.

[0104] The lower limit of the cyclic carbonate content in the non-aqueous solvent is preferably 10% by volume, more preferably 20% by volume, even more preferably 30% by volume, even more preferably 40% by volume, and particularly preferably 45% or 50% by volume. A cyclic carbonate content above the above lower limit allows for a larger discharge capacity during charge-discharge cycles. The upper limit of the cyclic carbonate content in the non-aqueous solvent is preferably 90% by volume, more preferably 80% by volume, and even more preferably 70%, 60%, or 50% by volume. A cyclic carbonate content below the above upper limit allows for a larger discharge capacity during charge-discharge cycles.

[0105] The lower limit of the fluorinated cyclic carbonate content in the non-aqueous solvent is preferably 5% by volume, more preferably 10% by volume, even more preferably 15% by volume, even more preferably 20% by volume, and particularly preferably 25% by volume. A fluorinated cyclic carbonate content above the above lower limit allows for a larger discharge capacity during charge-discharge cycles. The upper limit of the fluorinated cyclic carbonate content in the non-aqueous solvent is preferably 70% by volume, more preferably 60% by volume, and even more preferably 50%, 40%, 30%, or 25% by volume. A fluorinated cyclic carbonate content below the above upper limit allows for a larger discharge capacity during charge-discharge cycles.

[0106] The lower limit of the unsaturated cyclic carbonate content in the non-aqueous solvent is preferably 5% by volume, more preferably 10% by volume, even more preferably 15% by volume, even more preferably 20% by volume, and particularly preferably 25% by volume. A content of unsaturated cyclic carbonate above the above lower limit allows for a larger discharge capacity during charge-discharge cycles. The upper limit of the unsaturated cyclic carbonate content in the non-aqueous solvent is preferably 70% by volume, more preferably 60% by volume, and even more preferably 50%, 40%, 30%, or 25% by volume. A content of unsaturated cyclic carbonate below the above upper limit allows for a larger discharge capacity during charge-discharge cycles.

[0107] The lower limit of the total content of fluorinated cyclic carbonates and unsaturated cyclic carbonates in a non-aqueous solvent is preferably 10% by volume, more preferably 20% by volume, even more preferably 30% by volume, even more preferably 40% by volume, and particularly preferably 45% or 50% by volume. A total content of fluorinated cyclic carbonates and unsaturated cyclic carbonates in a non-aqueous solvent that is above the above lower limit allows for a larger discharge capacity during charge-discharge cycles. The upper limit of the total content of fluorinated cyclic carbonates and unsaturated cyclic carbonates in a non-aqueous solvent is preferably 90% by volume, more preferably 80% by volume, and even more preferably 70%, 60%, or 50% by volume. A total content of fluorinated cyclic carbonates and unsaturated cyclic carbonates in a non-aqueous solvent that is below the above upper limit allows for a larger discharge capacity during charge-discharge cycles.

[0108] The volume ratio of fluorinated cyclic carbonate to unsaturated cyclic carbonate in a non-aqueous solvent (fluorinated cyclic carbonate:unsaturated cyclic carbonate) is preferably 10:90 to 90:10, more preferably 20:80 to 80:20, even more preferably 30:70 to 70:30, even more preferably 40:60 to 60:40, and particularly preferably 50:50. By having the volume ratio of fluorinated cyclic carbonate to unsaturated cyclic carbonate within the above range, the discharge capacity during charge-discharge cycles can be increased.

[0109] Fluorinated carboxylic acid esters are compounds in which some or all of the hydrogen atoms in the hydrocarbon group constituting the carboxylic acid ester are replaced with fluorine atoms. Fluorinated carboxylic acid esters can be used individually or in mixtures of two or more types.

[0110] Fluorinated carboxylic acid esters are preferably linear fluorinated carboxylic acid esters. By using linear fluorinated carboxylic acid esters, the initial discharge capacity can be increased. The fluorinated carboxylic acid ester may also be a compound represented by the following formula (1). R 1 -COO-R2 ...(1) In formula (1), R 1 and R 2 Each of these is independently a hydrocarbon group or a fluorinated hydrocarbon group. However, R 1 and R 2 At least one of them is a fluorinated hydrocarbon group.

[0111] The hydrocarbon group may be either an aliphatic hydrocarbon group or an aromatic hydrocarbon group, but an aliphatic hydrocarbon group is preferred, and an alkyl group is more preferred. The number of carbon atoms in the hydrocarbon group is preferably 1 to 10, more preferably 1 to 5, and even more preferably 1 to 3. Examples of alkyl groups include methyl, ethyl, propyl, and butyl groups, with alkyl groups having 1 to 3 carbon atoms being preferred.

[0112] Examples of the above-mentioned fluorinated hydrocarbon group include groups in which some or all of the hydrogen atoms of the hydrocarbon group are replaced with fluorine atoms. The number of carbon atoms in the above-mentioned fluorinated hydrocarbon group is preferably 1 to 10, more preferably 1 to 5, and even more preferably 1 to 3. The number of fluorine atoms in the above-mentioned fluorinated hydrocarbon group is preferably 1 to 5, and more preferably 2 to 3. As for the above-mentioned fluorinated hydrocarbon group, fluorinated alkyl groups are preferred. Specific examples of fluorinated alkyl groups include difluoromethyl group, trifluoromethyl group, 2,2-difluoroethyl group, 2,2,2-trifluoroethyl group, 1,1,2,2,2-pentafluoroethyl group, 3,3,3-trifluoropropyl group, 2,2,3,3,3-pentafluoropropyl group, 4,4,4-trifluorobutyl group, and the like.

[0113] The above R 1 The preferred groups are the hydrocarbon groups and fluorinated hydrocarbon groups mentioned above, but among them, the methyl group or fluorinated methyl group is preferred, the fluorinated methyl group is more preferred, and the difluoromethyl group is even more preferred. Also, the above R 1 When R is a fluorinated hydrocarbon group, the initial discharge capacity and the discharge capacity during the charge-discharge cycle tend to be larger. From this point of view, the above R1 A fluorinated hydrocarbon group may be preferable in some cases.

[0114] The above R 2 The preferred groups are the hydrocarbon groups and fluorinated hydrocarbon groups mentioned above, but among them, the ethyl group or the fluorinated ethyl group is preferred, and the ethyl group is more preferred. Also, the above R 2 When R is a hydrocarbon group, the initial discharge capacity and the discharge capacity during the charge-discharge cycle tend to be larger. From this point of view, the above R 2 A hydrocarbon group may be preferable in some cases.

[0115] The above R 1 and the above R 2 It is also preferable that one of them is a fluorinated hydrocarbon group and the other is a hydrocarbon group. For example, the above R 1 is a fluorinated hydrocarbon group, and the above R 2 It may be a hydrocarbon group.

[0116] Specific examples of fluorinated carboxylic acid esters include methyl difluoroacetate, ethyl difluoroacetate, methyl trifluoroacetate, ethyl trifluoroacetate, methyl 3,3,3-trifluoropropionate, ethyl 3,3,3-trifluoropropionate, trifluoromethyl acetate, 2,2-difluoroethyl acetate, 2,2,2-trifluoroethyl acetate, trifluoromethyl propionate, and 2,2,2-trifluoroethyl propionate.

[0117] As the fluorinated carboxylic acid ester, fluorinated acetate is preferred, difluoroethyl acetate (EDFA) and 2,2,2-trifluoroethyl acetate (TFEA) are more preferred, and EDFA is even more preferred.

[0118] The lower limit of the fluorinated carboxylic acid ester content in the non-aqueous solvent may be 10% by volume, but 20% by volume is preferred, 30% by volume is more preferred, 40% by volume is even more preferred, and 50% by volume is even more preferred. By setting the fluorinated carboxylic acid ester content to be above the lower limit, the discharge capacity during charge-discharge cycles can be increased. The upper limit of the fluorinated carboxylic acid ester content in the non-aqueous solvent is preferably 90% by volume, more preferably 80% by volume, and even more preferably 70%, 60%, or 50% by volume. By setting the fluorinated carboxylic acid ester content to be below the upper limit, the discharge capacity during charge-discharge cycles can be increased.

[0119] The lower limit of the total content of cyclic carbonate and fluorinated carboxylic acid ester in the non-aqueous solvent is preferably 80% by volume, more preferably 90% by volume, and may be 95%, 98%, or 99% by volume. The upper limit of the total content of cyclic carbonate and fluorinated carboxylic acid ester in the non-aqueous solvent may be 100% by volume, and the non-aqueous solvent may consist substantially only of cyclic carbonate and fluorinated carboxylic acid ester. When the non-aqueous solvent consists substantially only of cyclic carbonate and fluorinated carboxylic acid ester, the effect of increasing the discharge capacity during charge-discharge cycles can be particularly well achieved.

[0120] The volume ratio of cyclic carbonate to fluorinated carboxylic acid ester in a non-aqueous solvent (cyclic carbonate:fluorinated carboxylic acid ester) is preferably 10:90 to 90:10, more preferably 20:80 to 80:20, even more preferably 30:70 to 70:30, even more preferably 40:60 to 60:40, and particularly preferably 50:50. By having the volume ratio of cyclic carbonate to fluorinated carboxylic acid ester within the above range, the discharge capacity during charge-discharge cycles can be increased.

[0121] The non-aqueous solvent may further contain other solvents other than cyclic carbonates and fluorinated carboxylic acid esters. Examples of other solvents include chain carbonates, ethers, esters other than fluorinated carboxylic acid esters, amides, nitriles, and the like.

[0122] The electrolyte salt can be appropriately selected from known electrolyte salts. Examples of the electrolyte salt include lithium salts, sodium salts, potassium salts, magnesium salts, onium salts, and the like. Among these, lithium salts are preferred. One or more electrolyte salts can be used.

[0123] Examples of the anion constituting the electrolyte salt include N(CF3SO2)2 - (bis(trifluoromethanesulfonyl)imide anion: TFSI - ), N(SO2F)2 - (bis(fluorosulfonyl)imide anion: FSI - ), N(C2F5SO2)2 - (bis(pentafluoroethanesulfonyl)imide anion), N(C4F9SO2)2 - (bis(nonafluorobutanesulfonyl)imide anion), N(POF2)2 - (bis(difluorophosphonyl)imide anion), N(CF3SO2)(CF3CO) - ((trifluoromethanesulfonyl)(trifluoromethanecarbonyl)imide anion), N(CN)2 - (dicyanoimide anion), CF3-SO2-N-SO2-N-SO2CF3 - , FSO2-N-SO2-C4F9 - , CF3-SO2-N-SO2-C4F9 - , CF3-SO2-N-SO2-CF2-SO2-N-SO2-CF3 2- , CF3-SO2-N-SO2-CF2-SO3 2- , CF3-SO2-N-SO2-CF2-SO2-C(-SO2CF3)2 2- and other imide anions. Examples of the anion constituting the electrolyte salt include PF6 - , PO2F2 -, BF4 - , ClO4 - , NO2 - , NO3 - , I - , SO3CF3 - , C(SO2CF3)3 - , C(SO2C2F5)3 - Anions other than imide anions such as these can also be used.

[0124] As the anion constituting the electrolyte salt, from the viewpoint of enhancing the ionic conductivity and charge-discharge performance of the non-aqueous electrolyte, those having a fluorine atom are preferable. Also, from the same viewpoint, imide anions are preferable. Specifically, as the anion constituting the electrolyte salt, at least one selected from the group consisting of bis(trifluoromethanesulfonyl)imide anion (TFSI - ) and bis(fluorosulfonyl)imide anion (FSI - ) is preferable, and bis(fluorosulfonyl)imide anion (FSI - ) is more preferable. That is, as the electrolyte salt, imide salts are preferable, and at least one selected from the group consisting of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium bis(fluorosulfonyl)imide (LiFSI) is more preferable, and lithium bis(fluorosulfonyl)imide (LiFSI) is even more preferable. The electrolyte salt can be used singly or in combination of two or more.

[0125] As the lower limit of the content of the electrolyte salt in the non-aqueous electrolyte, at 20°C and 1 atm, 0.1 mol / dm 3 is preferable, 0.3 mol / dm 3 is more preferable, and 0.5 mol / dm 3 is even more preferable. The upper limit of the content of the electrolyte salt is, at 20°C and 1 atm, 3.0 mol / dm 3 is preferable, 2.5 mol / dm 3 is more preferable, 2.0 mol / dm 3 , 1.5 mol / dm 3 or 1.0 mol / dm 3This may also be the case. By setting the electrolyte salt content within the above range, the ionic conductivity of the non-aqueous electrolyte can be optimized, thereby improving the charge and discharge performance of the non-aqueous electrolyte energy storage element. The electrolyte salt content can be within a range that combines any of the lower limits and any of the upper limits mentioned above.

[0126] The non-aqueous electrolyte may contain additives in addition to the non-aqueous solvent and electrolyte salt. One or more types of additives may be used. When additives are used in the non-aqueous electrolyte, the additive content 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, even 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.

[0127] (container) The container houses the electrode body and non-aqueous electrolyte within its internal space. The container material can be a metal material such as aluminum or stainless steel, or a resin material; metal materials are preferred from the viewpoint of strength, etc. Composite materials of metal and resin materials can also be used.

[0128] The shape of the container is not particularly limited, but it can be cylindrical, rectangular (square), disc-shaped, etc. The container may also be in the form of a sheet or other shape formed from a metal-resin composite film.

[0129] (Usage conditions, shape, and applications of non-aqueous electrolyte energy storage elements, etc.) In the non-aqueous electrolyte energy storage element, the lower limit of the positive electrode's charge limit potential is 3.1V vs. Li / Li + Therefore, 3.2V vs. Li / Li + This is more preferable. By having the positive electrode's upper charge potential limit be above the lower limit, the discharge capacity during the charge-discharge cycle can be increased. From the viewpoint of increasing the discharge capacity during the charge-discharge cycle, the upper limit of the positive electrode's upper charge potential is 3.3V vs. Li / Li + Therefore, 3.2V vs. Li / Li +In some cases, this is preferable. Also, the upper limit of the positive electrode's charging potential should be set to 3.2V vs. Li / Li, from the viewpoint of suppressing the decrease in discharge capacity during charge-discharge cycles while increasing the initial discharge capacity. + In some cases, it is preferable to set it to be greater than the limit. The upper limit potential of the positive electrode charge can be adjusted, for example, by adjusting the charge termination voltage of the non-aqueous electrolyte energy storage element.

[0130] The shape of the non-aqueous electrolyte energy storage element is not particularly limited. The non-aqueous electrolyte energy storage element may be, for example, a cylindrical battery, a prismatic battery, a flat battery, a coin cell battery, a button cell battery, etc.

[0131] The applications of the non-aqueous electrolyte energy storage element are not particularly limited. For example, it can be used as a power source for automobiles such as electric vehicles, hybrid vehicles, and plug-in hybrid vehicles, as well as a power source for electronic devices such as personal computers and communication terminals, and as a power storage power source.

[0132] The non-aqueous electrolyte energy storage elements of the above embodiment can be used individually or in combination. When the required output and voltage are small, the non-aqueous electrolyte energy storage elements may be used individually. On the other hand, when at least one of the required output and voltage is large, the non-aqueous electrolyte energy storage elements may be used in a combined energy storage device with other non-aqueous electrolyte energy storage elements. In an energy storage device composed of multiple non-aqueous electrolyte energy storage elements, at least one of the non-aqueous electrolyte energy storage elements included in the energy storage device may be a non-aqueous electrolyte energy storage element according to one embodiment of the present invention. The energy storage device will be described in detail later.

[0133] The non-aqueous electrolyte energy storage element may be constrained, for example, so that the container maintains a certain thickness, or it may not be constrained in such a way. Alternatively, it may be constrained so that a certain load is applied to the container. When the container is constrained, expansion of the container due to charge-discharge cycles, etc., may be suppressed, and a decrease in charge-discharge performance may be suppressed. When the container is constrained, a load may or may not be applied to the electrode body inside the container. For example, the non-aqueous electrolyte energy storage element or energy storage device may be provided with a constraining member that performs such constraint.

[0134] [Manufacturing method for non-aqueous electrolyte energy storage elements] The non-aqueous electrolyte energy storage element of the above embodiment can be manufactured by known methods. The manufacturing method of the non-aqueous electrolyte energy storage element includes, for example, preparing a positive electrode, preparing a negative electrode, preparing a non-aqueous electrolyte, and housing the positive electrode, negative electrode, and non-aqueous electrolyte in a container. The manufacturing method may also include preparing a separator, and manufacturing an electrode body using the positive electrode, negative electrode, and separator. Housing the positive electrode, negative electrode, and non-aqueous electrolyte in a container may be equivalent to housing the electrode body and non-aqueous electrolyte in a container.

[0135] Preparing the positive electrode may also mean manufacturing the positive electrode. The positive electrode can be manufactured by the method described above. Preparing the negative electrode may also mean manufacturing the negative electrode. The negative electrode can be manufactured by the method described above. Preparing the non-aqueous electrolyte may also mean preparing the non-aqueous electrolyte. The non-aqueous electrolyte can be prepared, for example, by dissolving an electrolyte salt in a non-aqueous solvent. The positive electrode, negative electrode, separator, non-aqueous electrolyte, etc., may be prepared by purchase or other means.

[0136] The electrode body (or positive and negative electrode) and the non-aqueous electrolyte can be housed in a container by known methods. If the non-aqueous electrolyte is a non-aqueous electrolyte solution, for example, the electrode body (or positive and negative electrode) can be housed in the container first, and then the non-aqueous electrolyte solution can be injected through an inlet provided in the container. The inlet is sealed after the non-aqueous electrolyte solution is injected. The method for manufacturing the non-aqueous electrolyte energy storage element may further include initial charging and discharging of the assembled uncharged energy storage element. In the non-aqueous electrolyte energy storage element according to one embodiment of the present invention, initial charging and discharging usually starts with discharging. The number of charging and discharging cycles in initial charging and discharging is not particularly limited. Through initial charging and discharging, a good film is formed on the surface of the sulfur-based active material by the reaction of the positive electrode and a portion of the non-aqueous electrolyte.

[0137] [How to use non-aqueous electrolyte energy storage elements] A method for using a non-aqueous electrolyte energy storage element according to one embodiment of the present invention is a method for using a non-aqueous electrolyte energy storage element comprising a positive electrode containing a sulfur-based active material and a non-aqueous electrolyte containing a cyclic carbonate and a fluorinated carboxylic acid ester. In this method of use, the positive electrode potential of the non-aqueous electrolyte energy storage element is 3.1V vs. Li / Li + More than 3.3V vs.Li / Li + The device is equipped with the ability to charge to the following extent. The configuration of the positive electrode, non-aqueous electrolyte, etc., of the non-aqueous electrolyte energy storage element used in this method of use, as well as the usage conditions, shape, application, etc., can be the same as those of the non-aqueous electrolyte energy storage element according to the embodiment of the present invention described above.

[0138] [Energy storage device] The energy storage device 30 in Figure 2 comprises a plurality of energy storage units 20. Each energy storage unit 20 comprises a plurality of electrically connected non-aqueous electrolyte energy storage elements 1. The non-aqueous electrolyte energy storage element 1 comprises a positive electrode containing a sulfur-based active material and a non-aqueous electrolyte containing a cyclic carbonate and a fluorinated carboxylic acid ester. The energy storage device 30 sets the upper limit charge potential of the positive electrode of the non-aqueous electrolyte energy storage element 1 to 3.1V vs. Li / Li + More than 3.3V vs.Li / Li +The following controls are applied. The configuration of the positive electrode, non-aqueous electrolyte, etc., of the non-aqueous electrolyte energy storage element 1, as well as its operating conditions, shape, and applications, can be the same as those of the non-aqueous electrolyte energy storage element according to the embodiment of the present invention described above.

[0139] The energy storage device 30 may include a charge control device (not shown) for controlling the upper limit charge potential of the positive electrode of one or more non-aqueous electrolyte energy storage elements 1, a busbar (not shown) for electrically connecting a plurality of non-aqueous electrolyte energy storage elements 1, a busbar (not shown) for electrically connecting a plurality of energy storage units 20, and the like. The energy storage unit 20 or the energy storage device 30 may include a condition monitoring device (not shown) for monitoring the state of one or more non-aqueous electrolyte energy storage elements 1.

[0140] [Other embodiments] The non-aqueous electrolyte energy storage element and energy storage device of the present invention are not limited to the embodiments described above, and various modifications may be made without departing from the spirit of the invention. For example, the configuration of one embodiment may be added to the configuration of another embodiment, and a part of the configuration of one embodiment may be replaced with the configuration of another embodiment or with well-known technology. Furthermore, a part of the configuration of one embodiment may be deleted. Also, well-known technology may be added to the configuration of one embodiment.

[0141] In the above embodiment, a case in which a non-aqueous electrolyte energy storage element is used as a rechargeable non-aqueous electrolyte secondary battery was described, but the type, shape, dimensions, capacity, etc. of the non-aqueous electrolyte energy storage element are arbitrary. The present invention can also be applied to various secondary batteries, electric double-layer capacitors, lithium-ion capacitors, and other capacitors.

[0142] In the above embodiment, an electrode body in which a separator is interposed between the positive electrode and the negative electrode was described, but the electrode body does not need to have a separator. For example, the positive electrode and the negative electrode may be in direct contact with each other, with a non-conductive layer formed on the active material layer of either the positive electrode or the negative electrode. Thus, the positive electrode and the negative electrode may further have layers other than the base material, intermediate layer, and active material layer. Furthermore, the positive electrode and the negative electrode do not need to have a layered structure. [Examples]

[0143] 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.

[0144] [Example 1] (Fabrication of the positive electrode) A mixture of elemental sulfur, a sulfur-based active material, and porous carbon was mixed in a mass ratio of 70:30. This mixture was placed in a sealed electric furnace. After 1 hour of argon flow, the temperature was increased to 150°C at a rate of 5°C / min and held for 5 hours. Then, it was allowed to cool to 80°C, the temperature at which elemental sulfur solidifies. Subsequently, the temperature was increased again to 300°C at a rate of 5°C / min and held for 2 hours to produce a composite (sulfur-porous carbon composite: SPC). A cathode mixture paste containing the composite obtained above, acetylene black and carbon nanotubes (CNTs) as conductive agents, carboxymethylcellulose (CMC) as a dispersant, polyacrylic acid (PAA) as a thickener, and styrene-butadiene rubber (SBR) as a binder was applied to one side of an aluminum cathode substrate (average thickness 15 μm) and dried. The mass per unit area of ​​one cathode active material layer after drying the dispersion medium was 15 mg / cm². 2 The capacity density per unit area is 17.6 mAh / cm³. 2 The amount of positive electrode mixture paste applied was adjusted accordingly. Through the above steps, a positive electrode was obtained in which a positive electrode active material layer was laminated on a positive electrode substrate.

[0145] (Preparing the negative electrode) A pure metallic lithium foil (average thickness 600 μm) was prepared as the negative electrode.

[0146] (Preparation of non-aqueous electrolytes) A non-aqueous solvent was prepared by mixing fluoroethylene carbonate (FEC), vinylene carbonate (VC), and difluoroethyl acetate (EDFA) in a volume ratio of 25:25:50, to which lithium bis(fluorosulfonyl)imide (LiFSI) was added as the electrolyte salt at a concentration of 0.5 mol / dm³. 3A non-aqueous electrolyte was prepared by incorporating the specified content.

[0147] (Assembly of non-aqueous electrolyte energy storage elements) As a separator, a separator was prepared in which inorganic particle layers were laminated on both sides of a polyethylene microporous membrane. Using the above positive electrode, negative electrode, separator and non-aqueous electrolyte, the non-aqueous electrolyte energy storage element of Example 1 was obtained.

[0148] [Examples 2 to 5, Comparative Examples 1 to 7] Non-aqueous electrolyte energy storage elements for Examples 2 to 5 and Comparative Examples 1 to 7 were obtained in the same manner as in Example 1, except that the composition of the non-aqueous solvent was as shown in Table 1. The non-aqueous solvents used are as follows: FEC: Fluoroethylene carbonate VC: Vinylen carbonate EDFA: Difluoroethyl acetate TFEA: 2,2,2-trifluoroethyl acetate

[0149] [evaluation] (Measurement of initial discharge capacity) For each non-aqueous electrolyte energy storage element, a constant current discharge was first performed as the initial discharge, with a discharge current of 0.02C and a discharge termination voltage of 1.0V. This was followed by a 10-minute rest period. Subsequently, constant current and constant voltage charging was performed with a charging current of 0.1C and a charging limit voltage as shown in Table 1. In this embodiment, this charging limit voltage was considered to be the charging limit potential of the positive electrode. The charging termination condition was set to a total charging time of 30 hours. Next, after a 10-minute pause, constant current discharge was performed with a discharge current of 0.1C and a discharge termination voltage of 1.0V. Discharge, charging, and pause were all performed in a constant temperature bath at 25°C. The amount of electricity per unit mass of the sulfur-based active material (elemental sulfur) during the discharge after the above charging is shown in Table 1 as the "initial discharge capacity".

[0150] (Charge-discharge cycle test) For each non-aqueous electrolyte energy storage element that underwent the "initial discharge capacity measurement" described above, charge-discharge cycle tests were performed according to the following procedure. Constant current and constant voltage charging was performed with a charging current of 0.1C and a maximum charging voltage as shown in Table 1. The charging termination condition was when the total charging time reached 15 hours. Next, constant current discharge was performed with a discharge current of 0.1C and a discharge termination voltage of 1.0V. A 10-minute rest period was provided after both discharge and charging. Discharge, charging, and rest were all performed in a constant temperature bath at 25°C. 1.0C was set as the current that could charge the initial discharge capacity in 1 hour. The above charging and discharging cycles were performed 10 times. The amount of electricity per unit mass of sulfur-based active material (elementary sulfur) during the discharge of the 10th cycle in the charge-discharge cycle test is shown in Table 1 as the "discharge capacity of the 10th cycle".

[0151] [Table 1]

[0152] As shown in Table 1, the device is equipped with a non-aqueous electrolyte containing cyclic carbonate and fluorinated carboxylic acid ester, with a maximum charging voltage of 3.1V to 3.3V (maximum charging potential of the positive electrode is 3.1V vs. Li / Li + More than 3.3V vs.Li / Li + Examples 1 and 2 (described below) have similar non-aqueous electrolyte compositions and have a charging limit voltage of less than 3.1V or greater than 3.3V (positive electrode charging limit potential of 3.1V vs. Li / Li + Less than 3.3V vs. Li / Li + Compared to Comparative Examples 1 and 2, which are (ultra), the discharge capacity at the 10th cycle (discharge capacity during charge-discharge cycles) was larger. Similarly, it is equipped with a non-aqueous electrolyte containing a cyclic carbonate and a fluorinated carboxylic acid ester, and the upper limit charge voltage is 3.1V to 3.3V (the upper limit charge potential of the positive electrode is 3.1V vs. Li / Li + More than 3.3V vs.Li / Li + Examples 3 to 5 (described below) have similar non-aqueous electrolyte compositions and a maximum charging voltage of less than 3.1V (maximum charging potential of the positive electrode is 3.1V vs. Li / Li +Compared to Comparative Example 3, which was less than , the discharge capacity at the 10th cycle (discharge capacity during charge-discharge cycles) was larger. On the other hand, in Comparative Examples 4 to 7, in which the non-aqueous electrolyte did not contain either a cyclic carbonate or a fluorinated carboxylic acid ester, the upper limit charge voltage was 3.1V or more and 3.3V or less (the upper limit charge potential of the positive electrode was 3.1V vs. Li / Li + More than 3.3V vs.Li / Li + Even with the following, no effect was obtained in increasing the discharge capacity at the 10th cycle. From this result, it was shown that the effect of the present invention, which is to increase the discharge capacity during charge-discharge cycles, can only be obtained by combining a non-aqueous electrolyte containing a cyclic carbonate and a fluorinated carboxylic acid ester with a predetermined upper charge potential of the positive electrode. [Industrial applicability]

[0153] This invention can be applied to non-aqueous electrolyte energy storage elements used as power sources for electronic devices such as personal computers and communication terminals, as well as for automobiles and industrial applications. [Explanation of Symbols]

[0154] 1. Non-aqueous electrolyte energy storage element 2 Electrode body 3 containers 4 Positive lead 5. Positive external terminal 6 Negative lead 7. Negative external terminal 20 Energy storage units 30 Energy storage devices

Claims

1. A positive electrode containing a sulfur-based active material, Non-aqueous electrolytes containing cyclic carbonates and fluorinated carboxylic acid esters Equipped with, The above positive electrode's upper charge limit potential is 3.1V vs. Li / Li ＋ Above 3.3V vs. Li / Li ＋ The following are non-aqueous electrolyte energy storage elements.

2. The non-aqueous electrolyte energy storage element according to claim 1, wherein the above-mentioned cyclic carbonate contains a fluorinated saturated cyclic carbonate and an unsaturated cyclic carbonate.

3. The above non-aqueous electrolyte has a non-aqueous solvent containing the above cyclic carbonate and the above fluorinated carboxylic acid ester. The non-aqueous electrolyte energy storage element according to claim 1 or claim 2, wherein the content of the fluorinated carboxylic acid ester in the non-aqueous solvent is 20% by volume or more.

4. The above positive electrode has a positive electrode active material layer containing the above sulfur-based active material, The capacity density per unit area of ​​one positive electrode active material layer is 10 mAh / cm³. ２ The non-aqueous electrolyte energy storage element according to claim 1 or claim 2.

5. The non-aqueous electrolyte energy storage element comprises a positive electrode containing a sulfur-based active material and a non-aqueous electrolyte containing a cyclic carbonate and a fluorinated carboxylic acid ester, with the upper limit charge potential of the positive electrode set to 3.1V vs. Li / Li ＋ Above 3.3V vs. Li / Li ＋ The following are the energy storage devices to be controlled.

6. For a non-aqueous electrolyte energy storage element comprising a positive electrode containing a sulfur-based active material and a non-aqueous electrolyte containing a cyclic carbonate and a fluorinated carboxylic acid ester, the potential of the positive electrode is 3.1V vs. Li / Li ＋ Above 3.3V vs. Li / Li ＋ A method for using a non-aqueous electrolyte energy storage element that can be charged to the following extent.

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