Nonaqueous electrolyte power storage element and method for using same

Abstract

A nonaqueous electrolyte power storage element according to one aspect of the present invention may be charged / discharged or left in an environment of 50°C or higher, and comprises: a positive electrode that has a positive electrode active material containing an iron element; and a nonaqueous electrolyte containing a compound having a fluorosulfonyl group. The content of the compound having a fluorosulfonyl group in the nonaqueous electrolyte is 0.8 mass% or more.

Description

Nonaqueous electrolyte storage element and method of using same

[0001] The present invention relates to a non-aqueous electrolyte electricity storage element and a method for using the same.

[0002] Due to their high energy density, non-aqueous electrolyte secondary batteries, such as lithium ion secondary batteries, are widely used in electronic devices such as personal computers and communication terminals, as well as in automobiles. Non-aqueous electrolyte secondary batteries generally have a pair of electrodes electrically isolated by a separator and a non-aqueous electrolyte interposed between the electrodes, and are configured to charge and discharge by transferring charge-transporting ions between the electrodes. In addition to non-aqueous electrolyte secondary batteries, capacitors such as lithium ion capacitors and electric double layer capacitors are also widely used as non-aqueous electrolyte energy storage elements.

[0003] Lithium iron phosphate is known as one of the positive electrode active materials used in non-aqueous electrolyte energy storage elements. Patent Document 1 describes a non-aqueous electrolyte secondary battery including a positive electrode containing lithium iron phosphate as the positive electrode active material and a negative electrode containing graphite as the negative electrode active material.

[0004] Japanese Patent Application Laid-Open No. 2007-213961

[0005] In nonaqueous electrolyte storage elements using a positive electrode active material containing iron, such as lithium iron phosphate, iron ions may leach out of the positive electrode active material into the nonaqueous electrolyte. In particular, when such nonaqueous electrolyte storage elements are charged / discharged or left standing for a long period of time in a high-temperature environment of 50° C. or higher, a large amount of iron ions leach out of the positive electrode active material into the nonaqueous electrolyte and precipitate on the negative electrode surface as metallic iron or iron compounds, which is likely to result in a decrease in discharge capacity.

[0006] An object of the present invention is to provide a nonaqueous electrolyte storage element that uses a positive electrode active material containing iron element and that has a high capacity retention rate after being charged / discharged or left standing for a long period of time in a high-temperature environment of 50°C or higher, and a method for using such a nonaqueous electrolyte storage element.

[0007] A nonaqueous electrolyte storage element according to one aspect of the present invention is capable of being charged / discharged or left standing in an environment of 50°C or higher, and comprises a positive electrode having a positive electrode active material containing elemental iron, and a nonaqueous electrolyte containing a compound having a fluorosulfonyl group, wherein the content of the compound having a fluorosulfonyl group in the nonaqueous electrolyte is 0.8 mass% or more.

[0008] A nonaqueous electrolyte storage element according to another aspect of the present invention is for in-vehicle or outdoor use, and comprises a positive electrode having a positive electrode active material containing elemental iron, and a nonaqueous electrolyte containing a compound having a fluorosulfonyl group, wherein the content of the compound having a fluorosulfonyl group in the nonaqueous electrolyte is 0.8 mass% or more.

[0009] A method of using a nonaqueous electrolyte storage element according to another aspect of the present invention comprises charging / discharging or leaving the nonaqueous electrolyte storage element in an environment of 50°C or higher, wherein the nonaqueous electrolyte storage element comprises a positive electrode having a positive electrode active material containing elemental iron, and a nonaqueous electrolyte containing a compound having a fluorosulfonyl group, and the content of the compound having a fluorosulfonyl group in the nonaqueous electrolyte is 0.8 mass% or more.

[0010] According to one aspect of the present invention, it is possible to provide a nonaqueous electrolyte storage element that uses a positive electrode active material containing elemental iron, and that has a high capacity retention rate after being charged / discharged or left standing for an extended period of time in a high-temperature environment of 50°C or higher, and a method for using such a nonaqueous electrolyte storage element.

[0011] Fig. 1 is a perspective view showing one embodiment of a nonaqueous electrolyte electricity storage element, and Fig. 2 is a schematic view showing one embodiment of an electricity storage device formed by assembling a plurality of nonaqueous electrolyte electricity storage elements.

[0012] First, an outline of the nonaqueous electrolyte electricity storage element and its use disclosed in this specification will be described.

[0013] [1] A nonaqueous electrolyte storage element according to one aspect of the present invention is capable of being charged / discharged or left standing in an environment of 50°C or higher, and comprises a positive electrode having a positive electrode active material containing elemental iron, and a nonaqueous electrolyte containing a compound having a fluorosulfonyl group, wherein the content of the compound having a fluorosulfonyl group in the nonaqueous electrolyte is 0.8 mass% or more.

[0014] The nonaqueous electrolyte storage element described in [1] above uses a positive electrode active material containing iron, and exhibits a high capacity retention rate after long-term charge / discharge or storage in a high-temperature environment of 50°C or higher. While the reason for this is unclear, the following is presumed. As described above, in conventional nonaqueous electrolyte storage elements using a positive electrode active material containing iron, a large amount of iron ions eluted from the positive electrode active material into the nonaqueous electrolyte during long-term charge / discharge or storage in a high-temperature environment of 50°C or higher are precipitated on the negative electrode surface as metallic iron or iron compounds, resulting in a decrease in capacity retention rate. In contrast, a compound having a fluorosulfonyl group is thought to capture iron ions in the nonaqueous electrolyte and to exist stably in the nonaqueous electrolyte in the form of, for example, a complex with iron as the central element. In the nonaqueous electrolyte storage element described in [1] above, the content of the compound having a fluorosulfonyl group in the nonaqueous electrolyte is 0.8% by mass or more, and a sufficient amount of the compound having a fluorosulfonyl group allows a sufficient amount of iron ions to exist stably and at a high concentration in the nonaqueous electrolyte. Therefore, in the nonaqueous electrolyte storage element described in [1] above, it is thought that iron ions eluted from the positive electrode active material into the nonaqueous electrolyte are inhibited from precipitating on the negative electrode surface as metallic iron or iron compounds, thereby increasing the capacity retention rate after long-term charge / discharge or storage in a high-temperature environment of 50°C or higher.

[0015] When a compound such as a compound having a fluorosulfonyl group contained in a nonaqueous electrolyte is a salt (ionic compound), qualitative and quantitative analysis is performed by ion chromatography (IC). The IC analysis equipment used is a "Dionex ICS-5000+" manufactured by Thermo Fisher Scientific. Water is used as the eluent. Specifically, the analysis is performed as follows. Note that a series of measurements are performed continuously under the same conditions. First, the nonaqueous electrolyte storage element is disassembled to remove the nonaqueous electrolyte or the electrode assembly containing the nonaqueous electrolyte. Salt is extracted from the removed nonaqueous electrolyte or the electrode assembly containing the nonaqueous electrolyte using an appropriate solvent (e.g., acetonitrile). Note that when extracting the salt, the nonaqueous electrolyte may be completely dissolved in an appropriate solvent (e.g., acetonitrile). (Qualitative Analysis) The measurement sample (salt) is subjected to IC analysis. The components contained in the measurement sample are predicted from the peak positions of each peak in the obtained ion chromatogram. A known sample of the predicted component (hereinafter referred to as "predicted component") is subjected to IC analysis. The retention time of the peak corresponding to the predicted component in each peak of the measured sample is compared with the retention time of the known sample, and if they match, the prediction is assumed to be correct. (Quantitative analysis) Quantitative analysis is performed using the calibration curve method. First, a known sample of the predicted component with a known concentration is subjected to IC measurement, and the peak area is determined to create a calibration curve. The calibration curve is calculated using the coefficient of determination (r ２ ) is created so that the ratio is 0.99 or more and 1 or less. The content of the predicted component in the measurement sample is determined from the calibration curve and the area of ​​the peak of the predicted component in the measurement sample. The above operation is performed for all peaks detected in the IC analysis of the measurement sample, and the content of each predicted component is determined. If the compound contained in the non-aqueous electrolyte is not a salt, that is, if it is a nonionic compound, qualitative and quantitative analysis is performed using liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-mass spectrometry (GC-MS) instead of IC analysis.

[0016] [2] A nonaqueous electrolyte storage element according to another aspect of the present invention is for in-vehicle or outdoor use, and includes a positive electrode having a positive electrode active material containing elemental iron, and a nonaqueous electrolyte containing a compound having a fluorosulfonyl group, wherein the content of the compound having a fluorosulfonyl group in the nonaqueous electrolyte is 0.8 mass% or more.

[0017] The nonaqueous electrolyte storage element described in [2] above is a nonaqueous electrolyte storage element that uses a positive electrode active material containing iron element, and has a high capacity retention rate after long-term charge / discharge or storage in a high-temperature environment of 50° C. or higher. The reason for this is unclear, but it is presumed to be the same as that for the nonaqueous electrolyte storage element described in [1] above. Because the nonaqueous electrolyte storage element described in [2] above has such effects, it is useful as a nonaqueous electrolyte storage element for vehicle or outdoor use, which may be charged / discharged or stored for long periods in a high-temperature environment of 50° C. or higher.

[0018] [3] In the nonaqueous electrolyte storage element according to the above [1] or [2], the compound having a fluorosulfonyl group may be lithium difluorophosphonylfluorosulfonylimide.

[0019] Lithium difluorophosphonyl fluorosulfonylimide is thought to have particularly good iron ion trapping ability, and therefore the nonaqueous electrolyte energy storage element described in [3] above can further improve the capacity retention rate after long-term charge / discharge or storage in a high-temperature environment of 50°C or higher.

[0020] [4] In the nonaqueous electrolyte storage element according to the above [3], the nonaqueous electrolyte may further contain at least one selected from the group consisting of vinylene carbonate, lithium bis(oxalato)borate, and lithium bis(oxalato)difluorophosphate.

[0021] The nonaqueous electrolyte storage element described in [4] above can further increase the capacity retention rate after long-term charge / discharge or storage in a high-temperature environment of 50°C or higher. While the reason for this is unclear, it is presumed that vinylene carbonate, lithium bis(oxalate)borate, and lithium bis(oxalate)difluorophosphate are compounds that are more susceptible to reductive decomposition than lithium difluorophosphonylfluorosulfonylimide. That is, when these compounds are contained in the nonaqueous electrolyte, upon long-term charge / discharge or storage in a high-temperature environment, these compounds are preferentially reductively decomposed on the negative electrode surface, suppressing the reductive decomposition of lithium difluorophosphonylfluorosulfonylimide, and thus presumably making it easier to maintain the iron ion capture ability of lithium difluorophosphonylfluorosulfonylimide.

[0022] [5] In the nonaqueous electrolyte storage element according to any one of [1] to [4] above, the positive electrode active material may be lithium iron phosphate.

[0023] Lithium iron phosphate has advantages such as high thermal stability, and the nonaqueous electrolyte storage element described in [5] above is a preferred embodiment of the present invention.

[0024] [6] In the nonaqueous electrolyte storage element according to any one of [1] to [5] above, the nonaqueous electrolyte may further contain lithium hexafluorophosphate.

[0025] [7] In the nonaqueous electrolyte storage element according to any one of [1] to [6] above, the content of the compound having a fluorosulfonyl group in the nonaqueous electrolyte may be 0.8% by mass or more and 5.0% by mass or less.

[0026] [8] In the nonaqueous electrolyte storage element according to any one of [1] to [7] above, the nonaqueous electrolyte may further contain an unsaturated cyclic carbonate.

[0027] [9] In the non-aqueous electrolyte storage element according to any one of the above [1] to [8], the non-aqueous electrolyte may further contain a salt having an oxalate complex anion.

[0028]

[10] The nonaqueous electrolyte storage element according to any one of [1] to [9] above may further comprise a negative electrode on which a coating containing elemental fluorine, elemental sulfur, and elemental oxygen is formed.

[0029]

[11] The nonaqueous electrolyte storage element according to any one of [1] to [9] above may further include a negative electrode having a coating film formed thereon that contains a component derived from a compound having a fluorosulfonyl group.

[0030]

[12] The nonaqueous electrolyte storage element according to any one of [1] to [9] above may further include a negative electrode containing a carbon material.

[0031]

[13] In the nonaqueous electrolyte storage element according to the above

[10] or

[11] , the negative electrode may contain a carbon material.

[0032]

[14] The nonaqueous electrolyte storage element according to any one of [1] to [9] above may further include a negative electrode containing graphite.

[0033]

[15] In the nonaqueous electrolyte storage element according to the above

[10] or

[11] , the negative electrode may contain graphite.

[0034] The nonaqueous electrolyte storage elements described in the above items [6] to

[15] are also suitable embodiments of the present invention.

[0035]

[16] A method for using a nonaqueous electrolyte storage element according to another aspect of the present invention comprises charging / discharging or leaving the nonaqueous electrolyte storage element in an environment of 50°C or higher, wherein the nonaqueous electrolyte storage element comprises a positive electrode having a positive electrode active material containing elemental iron, and a nonaqueous electrolyte containing a compound having a fluorosulfonyl group, and the content of the compound having a fluorosulfonyl group in the nonaqueous electrolyte is 0.8 mass% or more.

[0036]

[17] A method for using a nonaqueous electrolyte storage element according to another aspect of the present invention comprises charging / discharging or leaving the nonaqueous electrolyte storage element according to any one of the above [1] to

[15] in an environment of 50°C or higher.

[0037] According to the method for using a nonaqueous electrolyte storage element described in

[16] or

[17] above, a nonaqueous electrolyte storage element using a positive electrode active material containing iron element can be used with a high capacity retention rate even after being charged / discharged or left standing for a long period of time in a high-temperature environment of 50°C or higher.

[0038] A nonaqueous electrolyte electricity storage element, a method for using a nonaqueous electrolyte electricity storage element, an electricity storage device, a method for manufacturing a nonaqueous electrolyte electricity storage element, and other embodiments according to one embodiment of the present invention will be described in detail below. Note that the names of the components (elementary components) used in each embodiment may differ from the names of the components (elementary components) used in the background art.

[0039] <Non-aqueous electrolyte storage element> A non-aqueous electrolyte storage element (hereinafter also simply referred to as "storage element") according to one embodiment of the present invention comprises an electrode assembly having a positive electrode, a negative electrode, and a separator, a non-aqueous electrolyte, and a container that accommodates the electrode assembly and the non-aqueous electrolyte. The electrode assembly is typically a stacked type in which a plurality of positive electrodes and a plurality of negative electrodes are stacked with separators interposed therebetween, or a wound type in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween and wound. At least a portion of the non-aqueous electrolyte exists in a state in which it permeates the voids between the positive electrode, the negative electrode, and the separator. As an example of a non-aqueous electrolyte storage element, a non-aqueous electrolyte secondary battery (hereinafter also simply referred to as "secondary battery") will be described.

[0040] (Positive Electrode) The positive electrode has a positive electrode substrate and a positive electrode active material layer disposed on the positive electrode substrate directly or via an intermediate layer.

[0041] The positive electrode substrate has electrical conductivity. Whether or not it has electrical conductivity is determined by whether or not the volume resistivity measured in accordance with JIS-H-0505 (1975) is 10 －２The resistance is determined using Ω cm as a threshold value. Metals such as aluminum, titanium, tantalum, and stainless steel, or alloys thereof, are used as the material for the positive electrode substrate. Among these, aluminum or aluminum alloys are preferred from the viewpoints of potential resistance, high conductivity, and cost. Examples of the positive electrode substrate include foil, vapor-deposited film, mesh, and porous material, with foil being preferred from the viewpoint of cost. Therefore, aluminum foil or aluminum alloy foil is preferred as the positive electrode substrate. Examples of aluminum or aluminum alloys include A1085, A3003, and A1N30, as specified in JIS-H-4000 (2014) or JIS-H-4160 (2006).

[0042] The average thickness of the positive electrode substrate is preferably 3 μm to 50 μm, more preferably 5 μm to 40 μm, even more preferably 8 μm to 30 μm, and particularly preferably 10 μm to 25 μm. By setting the average thickness of the positive electrode substrate within the above range, the strength of the positive electrode substrate can be increased while increasing the energy density of the nonaqueous electrolyte storage element.

[0043] The intermediate layer is a layer disposed between the positive electrode substrate and the positive electrode active material layer. The intermediate layer contains a conductive agent such as carbon particles to reduce the contact resistance between the positive electrode substrate and the positive electrode active material layer. The configuration of the intermediate layer is not particularly limited, and may contain, for example, a binder and a conductive agent.

[0044] The positive electrode active material layer contains a positive electrode active material containing elemental iron, and may contain optional components such as a conductive agent, a binder, a thickener, and a filler, as needed.

[0045] The positive electrode active material containing iron is preferably a polyanionic compound containing iron. The positive electrode active material containing iron is also preferably a compound having an olivine-type crystal structure. The compound having the olivine-type crystal structure has a crystal structure that can be assigned to the space group Pnma. The crystal structure that can be assigned to the space group Pnma means that the compound has a peak that can be assigned to the space group Pnma in an X-ray diffraction diagram.

[0046] The positive electrode active material containing iron may be a compound containing lithium and iron. The positive electrode active material containing iron may be an oxoacid anion (PO ４ ３－ , S.O. ４ ２－ , SiO ４ ４－ , B.O. ３ ３－ , V.O. ４ ３－ Examples of suitable polyanion compounds include polyanion compounds containing lithium ions and iron ions, lithium ions, and iron ions. The polyanion compounds may further contain other elements (e.g., halogen elements). Examples of suitable oxoacid anions in polyanion compounds include phosphate anions (PO ４ ３－ ) is preferred.

[0047] The positive electrode active material containing iron element is preferably a polyanion compound represented by the following formula (1): Li ａ M ｂ (A.O. ｃ ) ｄ X ｅ ... (1) In formula (1), M is one or more transition metal elements including at least iron. A is at least one element selected from B, Al, Si, P, S, Cl, Ti, V, Cr, Mo, and W. X is at least one halogen element. a, b, c, d, and e are numbers satisfying 0<a≦3, 0<b≦2, 2≦c≦4, 1≦d≦3, and 0≦e≦1. a, b, c, d, and e may all be integers or decimals.

[0048] In formula (1), the Fe content in M ​​is preferably 50 mol% or more, more preferably 70 mol% or more, 90 mol% or more, or 99 mol% or more. A is preferably P. X is preferably F. In one embodiment, a = 1, b = 1, c = 4, d = 1, and e = 0 may be preferred.

[0049] Specific examples of the positive electrode active material containing iron include LiFePO ４ , LiFe ｘ Co １－ｘ P.O. ４ (0<x<1), LiFeｘ Mn １－ｘ P.O. ４ (0<x<1), LiFeVO ４ , Li ２ FeSiO ４ , Li ２ Fe ２ (SO ４ ) ３ , LiFeBO ３ , LiFePO ３．９ F ０．２ The atoms or polyanions in these compounds may be partially substituted with other atoms or anion species. Examples of positive electrode active materials containing iron include lithium iron phosphate (LiFePO ４ ) is preferable. The lithium iron phosphate may be one in which some of the atoms or polyanions constituting the lithium iron phosphate are substituted with other atoms or anion species. The positive electrode active material containing iron element may be used alone or in combination of two or more.

[0050] The iron-containing positive electrode active material may be present in the form of secondary particles. When the iron-containing positive electrode active material is a polyanionic compound, it is preferable that at least a portion of the surface of the polyanionic compound particles is coated with a carbon material. A portion of the carbon material may be present inside (between primary particles of) the secondary particles of the iron-containing polyanionic compound. By coating the surfaces of the iron-containing polyanionic compound particles with a carbon material, good electronic conductivity can be exhibited.

[0051] A carbon material refers to a material containing carbon as the main constituent element. A main constituent element refers to an element that is contained in the largest amount by mass. For example, the carbon content in the 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. The carbon material is preferably a carbon material other than an uncarbonized polymer compound. Examples of elements other than carbon that may be contained in the carbon material include oxygen, hydrogen, and nitrogen. Examples of carbon materials include graphite and non-graphitic carbon.

[0052] The average particle size of the iron-containing positive electrode active material is preferably, for example, 0.1 μm or more and 20 μm or less. By setting the average particle size of the iron-containing positive electrode active material to the above-mentioned lower limit or more, the production and handling of the iron-containing positive electrode active material becomes easier. By setting the average particle size of the iron-containing positive electrode active material to the above-mentioned upper limit or less, the electronic conductivity of the positive electrode active material layer is improved. When a composite of the cathode active material and another material is used, the average particle size of the composite is taken as the average particle size of the cathode active material. The term "average particle size" refers to the value at which the volume-based cumulative distribution calculated in accordance with JIS-Z-8819-2 (2001) is 50%, based on the particle size distribution measured by laser diffraction / scattering in a diluted solution obtained by diluting particles with a solvent in accordance with JIS-Z-8825 (2013).

[0053] To obtain powders with a predetermined particle size, grinders, classifiers, etc. are used. Grinding methods include, for example, methods using a mortar, ball mill, sand mill, vibration ball mill, planetary ball mill, jet mill, counter jet mill, swirling airflow jet mill, or sieves. Wet grinding in the presence of water or an organic solvent such as hexane can also be used during grinding. As classification methods, sieves, air classifiers, etc. are used as needed for both dry and wet methods.

[0054] The content of the iron-containing cathode active material in the cathode active material layer is preferably 50% by mass to 99% by mass, more preferably 70% by mass to 98% by mass, and even more preferably 80% by mass to 95% by mass. By setting the content of the iron-containing cathode active material in the above range, both high energy density and manufacturability of the cathode active material layer can be achieved.

[0055] The positive electrode active material layer may contain a positive electrode active material other than the positive electrode active material containing iron element. The other positive electrode active material may be appropriately selected from known positive electrode active materials. However, the content of the positive electrode active material containing iron element relative to all the positive electrode active materials contained in the positive electrode active material layer may be 90% by mass or more and 100% by mass or less, or may be 99% by mass or more and 100% by mass or less. The positive electrode active material layer may contain substantially only the positive electrode active material containing iron element as the positive electrode active material.

[0056] The conductive agent is not particularly limited as long as it is a material having electrical conductivity. Examples of such conductive agents include carbon materials, metals, and conductive ceramics. 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, and fullerenes. The conductive agent may be in the form of powder or fiber. As the conductive agent, one of these materials may be used alone, or two or more may be mixed. These materials may also be used in combination. For example, a composite of carbon black and carbon nanotubes may be used. Among these, carbon black is preferred from the viewpoints of electronic conductivity and coatability, and acetylene black is particularly preferred.

[0057] The content of the conductive agent in the positive electrode active material layer is preferably 1% by mass or more and 10% by mass or less, more preferably 3% by mass or more and 9% by mass or less. By setting the content of the conductive agent within the above range, the energy density of the nonaqueous electrolyte storage element can be increased. Note that the carbon material that coats the surfaces of the polyanion compound particles is not considered to be a conductive agent.

[0058] Examples of binders include thermoplastic resins such as fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), polyethylene, polypropylene, polyacrylic, and polyimide; elastomers such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber; and polysaccharide polymers.

[0059] The content of the binder in the positive electrode active material layer is preferably 1% by mass to 10% by mass, more preferably 2% by mass to 9% by mass, by which the positive electrode active material can be stably maintained.

[0060] Examples of thickeners include polysaccharide polymers such as carboxymethyl cellulose (CMC) and methyl cellulose. When the thickener has a functional group that reacts with lithium or the like, the functional group may be deactivated in advance by methylation or the like. In one embodiment of the present invention, the positive electrode active material layer may not contain a thickener.

[0061] The filler is not particularly limited. Examples of the filler include polyolefins such as polypropylene and polyethylene, inorganic oxides such as silicon dioxide, alumina, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates, hydroxides such as magnesium hydroxide, calcium hydroxide, and aluminum hydroxide, carbonates such as calcium carbonate, sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium sulfate, nitrides such as aluminum nitride and silicon nitride, mineral-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, and artificial products thereof. In one embodiment of the present invention, the positive electrode active material layer may not contain a filler.

[0062] The positive electrode active material layer may contain typical non-metallic elements such as B, N, P, F, Cl, Br, and I; typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba; and transition metallic elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, and W as components other than the positive electrode active material, conductive agent, binder, thickener, and filler.

[0063] The negative electrode has a negative electrode substrate and a negative electrode active material layer disposed on the negative electrode substrate directly or via an intermediate layer. The configuration of the intermediate layer is not particularly limited and can be selected from the configurations exemplified for the positive electrode above, for example.

[0064] The negative electrode substrate is conductive. Metals such as copper, nickel, stainless steel, nickel-plated steel, and aluminum, alloys thereof, and carbonaceous materials are used as the material for the negative electrode substrate. Among these, copper or copper alloys are preferred. Examples of the negative electrode substrate include foils, vapor-deposited films, meshes, and porous materials, with foils being preferred from the viewpoint of cost. Therefore, copper foil or copper alloy foil is preferred as the negative electrode substrate. Examples of copper foil include rolled copper foil and electrolytic copper foil.

[0065] The average thickness of the negative electrode substrate is preferably 2 μm or more and 35 μm or less, more preferably 3 μm or more and 30 μm or less, even more preferably 4 μm or more and 25 μm or less, and particularly preferably 5 μm or more and 20 μm or less. By setting the average thickness of the negative electrode substrate within the above range, it is possible to increase the strength of the negative electrode substrate and to increase the energy density of the nonaqueous electrolyte storage element.

[0066] The negative electrode active material layer contains a negative electrode active material. The negative electrode active material layer contains optional components such as a conductive agent, a binder, a thickener, and a filler, as needed. The optional components such as the conductive agent, the binder, the thickener, and the filler can be selected from the materials exemplified for the positive electrode above.

[0067] The negative electrode active material layer may contain typical non-metallic elements such as B, N, P, F, Cl, Br, and I; typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba; and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, and W as components other than the negative electrode active material, conductive agent, binder, thickener, and filler.

[0068] The negative electrode active material can be appropriately selected from known negative electrode active materials. A material capable of absorbing and releasing lithium ions is usually used as the negative electrode active material for a lithium ion secondary battery. Examples of the negative electrode active material include metallic lithium; metals or semimetals such as Si and Sn; metal oxides or semimetal oxides such as Si oxide, Ti oxide, and Sn oxide; Li ４ Ti ５ O １２ , LiTiO ２、 TiNb ２ O ７Examples of the material include titanium-containing oxides such as titanium dioxide, polyphosphate compounds, silicon carbide, and carbon materials such as graphite and non-graphitic carbon (easily graphitizable carbon or non-graphitizable carbon). Among these materials, carbon materials are preferred, graphite or non-graphitic carbon is more preferred, and graphite is even more preferred. In the negative electrode active material layer, one of these materials may be used alone, or two or more may be used in combination.

[0069] "Graphite" refers to a graphite material that has an average lattice spacing (d ００２ ) is 0.33 nm or more and less than 0.34 nm. Examples of graphite include natural graphite and artificial graphite. Artificial graphite is preferred from the viewpoint of being able to obtain a material with stable physical properties.

[0070] "Non-graphitic carbon" refers to a carbon material that has an average lattice spacing (d ００２ ) is 0.34 nm or more and 0.42 nm or less. Examples of non-graphitizable carbon include non-graphitizable carbon and graphitizable carbon. Examples of non-graphitizable carbon include resin-derived materials, petroleum pitch or petroleum pitch-derived materials, petroleum coke or petroleum coke-derived materials, plant-derived materials, and alcohol-derived materials.

[0071] Here, the "discharged state" of the carbon material refers to a state in which the carbon material, which is the negative electrode active material, is discharged so that lithium ions that can be absorbed and released during charging and discharging are sufficiently released from the carbon material. For example, this refers to a state in which the open circuit voltage of a half cell using a negative electrode containing a carbon material as the negative electrode active material as the working electrode and metallic lithium as the counter electrode is 0.7 V or higher.

[0072] "Non-graphitizable carbon" refers to the above-mentioned d ００２ The carbon material has a particle size of 0.36 nm or more and 0.42 nm or less.

[0073] "Graphitizable carbon" refers to the above-mentioned d ００２ The term "carbon material" refers to a carbon material having a particle size of 0.34 nm or more and less than 0.36 nm.

[0074] The negative electrode active material is usually in the form of particles (powder). The average particle size of the negative electrode active material can be, for example, 1 nm or more and 100 μm or less. When the negative electrode active material is a carbon material, a titanium-containing oxide, or a polyphosphate compound, the average particle size may be 1 μm or more and 100 μm or less. When the negative electrode active material is Si, Sn, Si oxide, Sn oxide, or the like, the average particle size may be 1 nm or more and 1 μm or less. By setting the average particle size of the negative electrode active material to be equal to or greater than the above lower limit, the production or handling of the negative electrode active material becomes easier. By setting the average particle size of the negative electrode active material to be equal to or less than the above upper limit, the electronic conductivity of the negative electrode active material layer is improved. To obtain powder with a predetermined particle size, a pulverizer, a classifier, or the like is used. The pulverization method and classification method can be selected from, for example, the methods exemplified for the positive electrode. When the negative electrode active material is a metal such as metallic lithium, the negative electrode active material layer may be in the form of a foil.

[0075] The content of the negative electrode active material in the negative electrode active material layer is preferably 60% by mass to 99% by mass, more preferably 90% by mass to 98% by mass. By setting the content of the negative electrode active material within this range, both high energy density and manufacturability of the negative electrode active material layer can be achieved.

[0076] 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 may be 2% by mass or less. In one embodiment of the present invention, the negative electrode active material layer may not contain a conductive agent.

[0077] When the negative electrode active material layer contains a binder, the content of the binder in the negative electrode active material layer is preferably 1% by mass to 10% by mass, more preferably 2% by mass to 8% by mass.

[0078] When the negative electrode active material layer contains a thickener, the content of the thickener in the negative electrode active material layer is preferably 0.1% by mass to 10% by mass, more preferably 0.5% by mass to 8% by mass, and may be 5% by mass or less, or may be 2% by mass or less.

[0079] When the negative electrode active material layer contains a filler, the content of the filler in the negative electrode active material layer can be 0.1 mass % or more and 8 mass % or less, and usually 5 mass % or less is preferable, and 2 mass % or less is more preferable. In one embodiment of the present invention, the negative electrode active material layer does not necessarily contain a filler.

[0080] A coating containing elemental fluorine, elemental sulfur, and elemental oxygen may be formed on the negative electrode. Such a coating containing elemental fluorine, elemental sulfur, and elemental oxygen may be a coating derived from a compound having a fluorosulfonyl group contained in the non-aqueous electrolyte, which will be described in detail later. That is, a coating containing a component derived from a compound having a fluorosulfonyl group may be formed on the negative electrode. Such a coating may further contain a component derived from another compound contained in the non-aqueous electrolyte. Such a coating may be formed on the surface of the negative electrode active material layer, or on the surface of particles of the negative electrode active material. After assembly, the non-aqueous electrolyte storage element according to one embodiment of the present invention is usually subjected to initial charge / discharge for capacity confirmation, etc. During charging in this initial charge / discharge, a portion of the compound having a fluorosulfonyl group is reductively decomposed on the negative electrode surface, forming a coating on the negative electrode surface. That is, the formation of such a coating on the negative electrode surface means that the non-aqueous electrolyte storage element has been charged at least once.

[0081] (Separator) The separator can be appropriately selected from known separators. Examples of separators that can be used include separators consisting of only a substrate layer and separators in which a heat-resistant layer containing heat-resistant particles and a binder is formed on one or both surfaces of the substrate layer. Examples of the shape of the substrate layer of the separator include woven fabric, nonwoven fabric, and porous resin film. Among these shapes, porous resin films are preferred from the viewpoint of strength, and nonwoven fabrics are preferred from the viewpoint of non-aqueous electrolyte retention. Materials for the substrate layer of the separator are preferably polyolefins such as polyethylene and polypropylene from the viewpoint of shutdown function, and polyimide and aramid from the viewpoint of oxidative decomposition resistance. A composite material of these resins may also be used for the substrate layer of the separator.

[0082] The heat-resistant particles contained in the heat-resistant layer preferably exhibit a mass loss of 5% or less when heated from room temperature to 500°C under an air atmosphere at 1 atmosphere, and more preferably exhibit a mass loss of 5% or less when heated from room temperature to 800°C. Examples of materials exhibiting a mass loss of a predetermined value or less include inorganic compounds. Examples of inorganic compounds include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicate; nitrides such as aluminum nitride and silicon nitride; carbonates such as calcium carbonate; sulfates such as barium sulfate; sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium titanate; covalently bonded crystals such as silicon and diamond; mineral-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, as well as artificial products thereof. As the inorganic compound, these substances may be used alone or in the form of a complex, or two or more of them may be used in combination. Among these inorganic compounds, silicon oxide, aluminum oxide, or aluminosilicate is preferred from the viewpoint of safety of the nonaqueous electrolyte storage element.

[0083] The porosity of the separator is preferably 80% by volume or less from the viewpoint of strength, and is preferably 20% by volume or more from the viewpoint of discharge performance. Here, "porosity" refers to a volume-based value measured with a mercury porosimeter.

[0084] The separator may be a polymer gel composed of a polymer and a non-aqueous electrolyte. Examples of polymers include polyacrylonitrile, polyethylene oxide, polypropylene oxide, polymethyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, and polyvinylidene fluoride. The use of a polymer gel has the effect of suppressing leakage. The separator may be a combination of the porous resin film or nonwoven fabric described above and a polymer gel.

[0085] (Non-aqueous electrolyte) The non-aqueous electrolyte contains a compound having a fluorosulfonyl group (hereinafter also referred to as "compound X"). A non-aqueous electrolyte solution may be used as the non-aqueous electrolyte. The non-aqueous electrolyte solution contains, for example, a non-aqueous solvent, and compound X and an electrolyte salt dissolved or mixed in the non-aqueous solvent. When compound X is a salt, compound X may be used as the electrolyte salt. Furthermore, both compound X, which is a salt, and an electrolyte salt different from compound X may be contained in the non-aqueous electrolyte or non-aqueous electrolyte solution.

[0086] Compound X is a fluorosulfonyl group (—SO ２ F). Compound X may have only one fluorosulfonyl group per molecule, or may have two or more fluorosulfonyl groups per molecule. Compound X may be used alone or in combination of two or more.

[0087] Compound X may be a salt (ionic compound) or a compound other than a salt (non-ionic compound). When compound X is a salt, compound X preferably has an anion having a fluorosulfonyl group. Examples of an anion having a fluorosulfonyl group include difluorophosphonylfluorosulfonylimide anion (N － (POF ２ ) (SO ２ F)), bis(fluorosulfonyl)imide anion (N － (SO ２ F) ２ imide anions such as fluorosulfonate anions (O － (SO ２ Among these, imide anions are preferred, difluorophosphonylfluorosulfonylimide anions or bis(fluorosulfonyl)imide anions are more preferred, and difluorophosphonylfluorosulfonylimide anions are even more preferred.

[0088] Examples of the cation constituting the salt of compound X include alkali metal ions such as lithium ion, sodium ion, and potassium ion, with lithium ion being preferred, i.e., salt X is preferably a lithium salt.

[0089] Examples of the compound X that is not a salt include methanesulfonic acid fluoride.

[0090] Compound X is preferably a salt, more preferably an imide salt, and even more preferably a lithium imide salt, such as lithium difluorophosphonyl fluorosulfonylimide (LiN(POF ２ ) (SO ２ F)) and lithium bis(fluorosulfonyl)imide (LiN(SO ２ F) ２ The use of such a compound as compound X can further increase the capacity retention rate after long-term charge / discharge or storage in a high-temperature environment of 50° C. or higher.

[0091] The lower limit of the content of compound X in the non-aqueous electrolyte is 0.8% by mass, preferably 1.0% by mass, more preferably 1.2% by mass, and even more preferably 1.5% by mass. By setting the content of compound X at or above this lower limit, a sufficient amount of compound X can capture a sufficient amount of iron ions, thereby improving the capacity retention rate after long-term charge / discharge or storage in a high-temperature environment of 50°C or higher. The upper limit of the content of compound X in the non-aqueous electrolyte is preferably 5.0% by mass, more preferably 4.0% by mass, and even more preferably 3.0% by mass. By setting the content of compound X at or below this upper limit, excessive formation of a coating film on the negative electrode surface due to reductive decomposition of compound X is suppressed, and the capacity retention rate after long-term charge / discharge or storage in a high-temperature environment of 50°C or higher can be further improved. The content of compound X in the non-aqueous electrolyte can be within a range that combines any of the above-mentioned lower limits and any of the above-mentioned upper limits.

[0092] The electrolyte salt can be appropriately selected from known electrolyte salts, such as lithium salts, sodium salts, potassium salts, magnesium salts, and onium salts. Of these, lithium salts are preferred.

[0093] The lithium salt is LiPF６ , LiBF ４ , LiClO ４ Inorganic lithium salts such as LiSO ３ CF ３ , LiN(SO ２ CF ３ ) ２ , LiN(SO ２ C ２ F ５ ) ２ , LiN(SO ２ CF ３ ) (SO ２ C ４ F ９ ), LiC(SO ２ CF ３ ) ３ , LiC(SO ２ C ２ F ５ ) ３ Among these, inorganic lithium salts are preferred, and LiPF ６ (lithium hexafluorophosphate) is more preferred. ６ When the non-aqueous electrolyte is used, the effect of including 0.8 mass % or more of compound X in the non-aqueous electrolyte is significantly exhibited. As described above, compound X, which is a salt, can also be used as the electrolyte salt. One or more electrolyte salts can be used.

[0094] The content of the electrolyte salt in the non-aqueous electrolyte or non-aqueous electrolyte solution is 0.1 mol / dm ３ 2.5mol / dm or more ３ It is preferably 0.3 mol / dm or less. ３ 2.0mol / dm or more ３ It is more preferable that it is 0.5 mol / dm or less. ３ More than 1.7mol / dm ３ It is more preferable that it is 0.7 mol / dm or less. ３ 1.5mol / dm or more ３ By setting the content of the electrolyte salt within the above range, the ionic conductivity of the non-aqueous electrolyte or non-aqueous electrolytic solution can be increased.

[0095] The non-aqueous solvent can be appropriately selected from known non-aqueous solvents. Examples of non-aqueous solvents include cyclic carbonates, chain carbonates, carboxylic acid esters, phosphate esters, sulfonic acid esters, ethers, amides, and nitriles. Non-aqueous solvents in which some of the hydrogen atoms contained in these compounds have been substituted with halogens may also be used.

[0096] Examples of the cyclic carbonate include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), chloroethylene carbonate, fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), etc. The cyclic carbonate is preferably a saturated cyclic carbonate, and more preferably EC.

[0097] Examples of the chain carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diphenyl carbonate, trifluoroethyl methyl carbonate, bis(trifluoroethyl) carbonate, etc. Among these, DEC and EMC are preferred.

[0098] As the non-aqueous solvent, it is preferable to use at least one of a cyclic carbonate and a chain carbonate, and it is more preferable to use a combination of a cyclic carbonate and a chain carbonate. The use of a cyclic carbonate can promote dissociation of the electrolyte salt and improve the ionic conductivity of the non-aqueous electrolyte. The use of a chain carbonate can reduce the viscosity of the non-aqueous electrolyte. When a cyclic carbonate and a chain carbonate are used in combination, the volume ratio of the cyclic carbonate to the chain carbonate (cyclic carbonate:chain carbonate) is preferably in the range of, for example, 5:95 to 50:50.

[0099] The nonaqueous electrolyte or nonaqueous electrolytic solution may contain components other than Compound X, the electrolyte salt, and the nonaqueous solvent. Examples of such components include unsaturated cyclic carbonates such as vinylene carbonate (VC), methyl vinylene carbonate, ethyl vinylene carbonate, 1-phenyl vinylene carbonate, 1,2-diphenyl vinylene carbonate, and vinyl ethylene carbonate (VEC); salts having an oxalato complex anion such as lithium bis(oxalate)borate (LiBOB), lithium difluorooxalate borate (LiFOB), and lithium bis(oxalate)difluorophosphate (LiFOP); aromatic compounds such as phenyl, alkylbiphenyls, terphenyls, partially hydrogenated terphenyls, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran; partial halides of the above aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, and p-cyclohexylfluorobenzene; and halogenated anisoles such as 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, and 3,5-difluoroanisole. Compounds: succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, methyl methanesulfonate, busulfan, methyl toluenesulfonate, dimethyl sulfate, ethylene sulfate, sulfolane, dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, diethyl sulfoxide, tetramethylene sulfoxide, diphenyl sulfide, 4,4'-bis(2,2-dioxo-1, 3,2-dioxathiolane), 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane, thioanisole, diphenyl disulfide, dipyridinium disulfide, 1,3-propene sultone, 1,3-propane sultone, 1,4-butane sultone, 1,4-butene sultone, perfluorooctane, tristrimethylsilyl borate, tristrimethylsilyl phosphate, tetrakistrimethylsilyl titanate, lithium monofluorophosphate, and lithium difluorophosphate.These other components may be used alone or in combination of two or more.

[0100] The other components preferably include at least one of an unsaturated cyclic carbonate and a salt having an oxalato complex anion, and more preferably include both an unsaturated cyclic carbonate and a salt having an oxalato complex anion. In one embodiment of the present invention, the non-aqueous electrolyte preferably includes an unsaturated cyclic carbonate. As the unsaturated cyclic carbonate, VC is preferred. In one embodiment of the present invention, the non-aqueous electrolyte preferably includes a salt having an oxalato complex anion. As the salt having an oxalato complex anion, LiBOB and LiFOP are preferred.

[0101] Suitable other components include at least one selected from the group consisting of VC, LiBOB, and LiFOP. In one embodiment of the present invention, it is preferred that the compound X contained in the non-aqueous electrolyte is lithium difluorophosphonylfluorosulfonylimide, and that the non-aqueous electrolyte further contains at least one selected from the group consisting of VC, LiBOB, and LiFOP. In such a case, the other components (VC, LiBOB, LiFOP) are preferentially reductively decomposed on the negative electrode surface over compound X. Therefore, even when the non-aqueous electrolyte storage element is charged / discharged or left standing for a long period of time in a temperature environment of 50°C or higher, compound X is likely to remain in the non-aqueous electrolyte, and the capacity retention rate of the non-aqueous electrolyte storage element is further improved.

[0102] The content of other components contained in the non-aqueous electrolyte or non-aqueous electrolytic solution is preferably 0.01% by mass or more and 10% by mass or less, more preferably 0.1% by mass or more and 5% by mass or less, even more preferably 0.2% by mass or more and 3% by mass or less, and particularly preferably 0.3% by mass or more and 2% by mass or less, relative to the total mass of the non-aqueous electrolyte or non-aqueous electrolytic solution. By setting the content of other components within the above range, it is possible to improve capacity retention or cycle performance after high-temperature storage, and to further improve safety. When the other component is at least one selected from the group consisting of VC, LiBOB, and LiFOP, by setting the content of other components within the above range, it is possible to further improve the capacity retention rate after long-term charge / discharge or storage in a high-temperature environment of 50°C or more.

[0103] The non-aqueous electrolyte may be a combination of a non-aqueous electrolytic solution and a solid electrolyte.

[0104] The solid electrolyte can be selected from any material that has ionic conductivity of lithium, sodium, calcium, etc. and is solid at room temperature (e.g., 15° C. to 25° C.) Examples of the solid electrolyte include sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, and polymer solid electrolytes.

[0105] Examples of sulfide solid electrolytes include Li ２ S-P ２ S ５ , LiI-Li ２ S-P ２ S ５ , Li １０ Ge-P ２ S １２ etc.

[0106] (Usage Form, etc.) A nonaqueous electrolyte storage element according to one embodiment of the present invention is one that is charged / discharged or left in an environment of 50°C or higher. The nonaqueous electrolyte storage element exhibits suppressed capacity reduction even after being charged / discharged or left in an environment of 50°C or higher. A nonaqueous electrolyte storage element that is charged / discharged or left in an environment of 50°C or higher may also be charged / discharged or left in an environment below 50°C. A nonaqueous electrolyte storage element that is charged / discharged or left in an environment of 50°C or higher may be one that is intended to be charged / discharged or left in an environment of 50°C or higher. The lower limit of the temperature when the nonaqueous electrolyte storage element is charged / discharged or left in an environment of 50°C or higher may be 55°C, 60°C, or 65°C. The upper limit of the temperature may be 150°C, 110°C, 100°C, or 90°C. The temperature when the nonaqueous electrolyte storage element is charged / discharged or left in an environment of 50°C or higher may be within a range that combines any of the above-mentioned lower limits and any of the above-mentioned upper limits.

[0107] A nonaqueous electrolyte storage element according to another embodiment of the present invention is a nonaqueous electrolyte storage element for vehicle or outdoor use. Examples of nonaqueous electrolyte storage elements for vehicle use include those disposed in engine compartments. Such nonaqueous electrolyte storage elements may be used in electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and the like. Examples of nonaqueous electrolyte storage elements for outdoor use include those disposed outdoors as storage batteries for storing power generated by solar power generation or the like. Nonaqueous electrolyte storage elements for vehicle or outdoor use may be charged / discharged or left unused in an environment of 50°C or higher. A nonaqueous electrolyte storage element having a high capacity retention rate after long-term charge / discharge or storage in a high-temperature environment of 50°C or higher is useful as a nonaqueous electrolyte storage element for vehicle or outdoor use.

[0108] The shape of the nonaqueous electrolyte storage element of this embodiment is not particularly limited, and examples thereof include cylindrical batteries, prismatic batteries, flat batteries, coin batteries, and button batteries.

[0109] Figure 1 shows a nonaqueous electrolyte storage element 1 as an example of a prismatic battery. The figure is a see-through view of the inside of the container. An electrode assembly 2 having a positive electrode and a negative electrode wound with a separator sandwiched between them is housed in a prismatic container 3. The positive electrode is electrically connected to a positive electrode terminal 4 via a positive electrode lead 41. The negative electrode is electrically connected to a negative electrode terminal 5 via a negative electrode lead 51.

[0110] <Method of Using the Non-Aqueous Electrolyte Storage Element> The non-aqueous electrolyte storage element according to one embodiment of the present invention can be used in a conventionally known manner. The non-aqueous electrolyte storage element can be used satisfactorily even after being charged / discharged or left standing for a long period of time in a high-temperature environment of 50°C or higher.

[0111] A method for using a nonaqueous electrolyte storage element according to one embodiment of the present invention includes charging / discharging or leaving the nonaqueous electrolyte storage element in an environment of 50°C or higher. The nonaqueous electrolyte storage element includes a positive electrode having a positive electrode active material containing iron and a nonaqueous electrolyte containing a compound having a fluorosulfonyl group, and the content of the compound having a fluorosulfonyl group in the nonaqueous electrolyte is 0.8% by mass or higher. Specific and preferred embodiments of the nonaqueous electrolyte storage element used in this method are the same as those of the nonaqueous electrolyte storage element according to one embodiment of the present invention. According to this method, a nonaqueous electrolyte storage element using a positive electrode active material containing iron can be used with a high capacity retention rate even after being charged / discharged or left standing for an extended period of time in a high-temperature environment of 50°C or higher. The lower limit of the temperature for charging / discharging or leaving the nonaqueous electrolyte storage element may be 55°C, 60°C, or 65°C. The upper limit of the temperature may be 150°C, 110°C, 100°C, or 90°C. The temperature at which the nonaqueous electrolyte storage element is charged / discharged or left standing may be within a range that combines any of the above-mentioned lower limits with any of the above-mentioned upper limits.

[0112] <Electricity storage device> The nonaqueous electrolyte energy storage element of the present embodiment can be mounted as an energy storage unit (battery module) comprising a plurality of nonaqueous electrolyte energy storage elements in a power source for an automobile such as an EV, HEV, or PHEV, a power source for electronic devices such as a personal computer or a communication terminal, or a power source for power storage, etc. In this case, the technology of the present invention may be applied to at least one nonaqueous electrolyte energy storage element included in the energy storage unit.

[0113] 2 shows an example of an energy storage device 30 in which energy storage units 20, each of which is an assembly of two or more electrically connected nonaqueous electrolyte energy storage elements 1, are further assembled. The energy storage device 30 may include a bus bar (not shown) that electrically connects two or more nonaqueous electrolyte energy storage elements 1, a bus bar (not shown) that electrically connects two or more energy storage units 20, etc. The energy storage unit 20 or the energy storage device 30 may include a status monitoring device (not shown) that monitors the status of one or more nonaqueous electrolyte energy storage elements.

[0114] <Method for Manufacturing Nonaqueous Electrolyte Storage Element> The method for manufacturing the nonaqueous electrolyte storage element of this embodiment can be appropriately selected from known methods, but the following method is preferred. That is, the method for manufacturing a nonaqueous electrolyte storage element according to one embodiment of the present invention includes preparing a positive electrode having a positive electrode active material containing elemental iron, and preparing a nonaqueous electrolyte containing a compound having a fluorosulfonyl group. The content of the compound having a fluorosulfonyl group (compound X) in the nonaqueous electrolyte is, for example, preferably 1.2 mass% or more and 6.0 mass% or less, and more preferably 1.5 mass% or more and 3.0 mass% or less. Note that a nonaqueous electrolyte storage element according to one embodiment of the present invention is typically completed through initial charge / discharge after assembly, and a portion of compound X, etc. is reductively decomposed on the surface of the negative electrode during charging in the initial charge / discharge. Therefore, the content of compound X in the prepared nonaqueous electrolyte is typically different from the content of compound X in the nonaqueous electrolyte provided in the nonaqueous electrolyte storage element according to one embodiment of the present invention.

[0115] Preparing a positive electrode may also mean fabricating a positive electrode. The fabrication of a positive electrode can be performed, for example, by applying a positive electrode mixture paste to a positive electrode substrate directly or via an intermediate layer, and drying the paste. The positive electrode mixture paste contains components constituting a positive electrode active material layer, such as a positive electrode active material containing iron, and a dispersion medium. After drying the applied positive electrode mixture paste, pressing or the like may be performed.

[0116] The preparation of the non-aqueous electrolyte may be performed by mixing components of the non-aqueous electrolyte, such as a compound having a fluorosulfonyl group.

[0117] The manufacturing method may further include preparing a negative electrode, preparing an electrode assembly, and housing the electrode assembly and the non-aqueous electrolyte in a container.

[0118] Preparing a negative electrode may mean fabricating a negative electrode. The negative electrode can be fabricated, for example, by applying a negative electrode mixture paste to a negative electrode substrate directly or via an intermediate layer, and then drying. The negative electrode mixture paste contains components constituting a negative electrode active material layer, such as a negative electrode active material, and a dispersion medium. After drying, the applied negative electrode mixture paste may be pressed or the like. Instead of applying the negative electrode mixture paste, a negative electrode active material layer may also be provided by laminating metal foil.

[0119] Preparing the electrode body may mean fabricating the electrode body. The electrode body can be fabricated, for example, by stacking or winding a positive electrode and a negative electrode with a separator interposed therebetween. The method for housing the non-aqueous electrolyte in the container can be appropriately selected from known methods. For example, when a non-aqueous electrolyte solution is used as the non-aqueous electrolyte, the non-aqueous electrolyte solution may be injected through an injection port formed in the container, and then the injection port may be sealed.

[0120] The method for manufacturing the nonaqueous electrolyte storage element may further include initially charging and discharging an uncharged / discharged storage element assembled using a positive electrode, a negative electrode, and a nonaqueous electrolyte. The number of charge / discharge cycles in the initial charge / discharge may be one or two, or may be three or more. The initial charge / discharge cycle may be one or more. Charging in the initial charge / discharge cycle reduces and decomposes a portion of the compound X contained in the nonaqueous electrolyte on the surface of the negative electrode, forming a coating on the surface of the negative electrode.

[0121] <Other Embodiments> The nonaqueous electrolyte storage element and its method of use of the present invention are not limited to the above-described embodiments, and various modifications may be made without departing from the spirit of the present invention. For example, the configuration of one embodiment can be added to the configuration of another embodiment, or part of the configuration of one embodiment can be replaced with the configuration of another embodiment or well-known technology. Furthermore, part of the configuration of one embodiment can be deleted. Also, well-known technology can be added to the configuration of one embodiment.

[0122] In the above embodiment, the nonaqueous electrolyte storage element is used as a chargeable and dischargeable nonaqueous electrolyte secondary battery (e.g., a lithium ion secondary battery), but the type, shape, size, capacity, etc. of the nonaqueous electrolyte storage element are arbitrary. The present invention can also be applied to various secondary batteries.

[0123] In the above embodiment, the electrode assembly in which the positive electrode and the negative electrode are stacked with a separator interposed therebetween has been described, but the electrode assembly may not include a separator. For example, the positive electrode and the negative electrode may be in direct contact with each other in a state in which a non-conductive layer is formed on the active material layer of the positive electrode or the negative electrode.

[0124] 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.

[0125] [Example 1] (Preparation of Positive Electrode) A positive electrode mixture paste was prepared using lithium iron phosphate (LFP) as a positive electrode active material, acetylene black (AB) as a conductive agent, polyvinylidene fluoride (PVDF) as a binder, and N-methylpyrrolidone (NMP) as a dispersion medium. The mass ratio of LFP, AB, and PVDF was 90:5:5 in terms of solid content. Furthermore, secondary particles whose surfaces were coated with a carbon material were used for the LFP. This positive electrode mixture paste was applied to aluminum foil as a positive electrode substrate, dried, and roll-pressed to form a positive electrode active material layer, thereby obtaining a positive electrode.

[0126] (Preparation of Negative Electrode) A negative electrode mixture paste was prepared by mixing graphite as a negative electrode active material, styrene-butadiene rubber (SBR) as a binder, carboxymethyl cellulose (CMC) as a thickener, and water as a dispersion medium. The mass ratio of graphite to SBR to CMC was 98.0:1.0:1.0 in terms of solid content. This negative electrode mixture paste was applied to copper foil as a negative electrode substrate, dried, and roll-pressed to form a negative electrode active material layer, thereby obtaining a negative electrode.

[0127] (Preparation of non-aqueous electrolyte) LiPF 6 as an electrolyte salt was added to a non-aqueous solvent obtained by mixing ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate in a volume ratio of 20:35:45. ６ to 0.9 mol / dm ３ To this solution, 1.5 mass% of lithium difluorophosphonylfluorosulfonylimide (Compound X), 0.5 mass% of vinylene carbonate (VC), 0.5 mass% of lithium bis(oxalate)difluorophosphate (LiFOP), and 0.2 mass% of lithium bis(oxalate)borate (LiBOB) were mixed to obtain a nonaqueous electrolyte.

[0128] (Separator) A polyethylene microporous film was used as the separator.

[0129] (Assembly of Uncharged and Discharged Non-Aqueous Electrolyte Storage Element) The positive electrode, the negative electrode, and the separator were stacked to prepare an electrode assembly. The resulting electrode assembly was placed in a container, and the non-aqueous electrolyte was then poured into the container and sealed to obtain an uncharged and discharged non-aqueous electrolyte storage element.

[0130] (Initial Charge / Discharge) The assembled non-charged / discharged non-aqueous electrolyte storage element was subjected to initial charge / discharge under the following conditions. In a thermostatic chamber at 25°C, constant current charging was performed with a charging current of 0.2 C and a charge cut-off voltage of 3.5 V, followed by constant voltage charging at 3.5 V. The charge was terminated when the current decayed to 0.01 C. A 10-minute rest period was then provided. Constant current discharge was performed with a discharge current of 0.2 C and a discharge cut-off voltage of 2.0 V. A 10-minute rest period was then provided. The above charge / discharge was repeated twice, and the quantity of electricity discharged in the second cycle was defined as the initial discharge capacity. After the above initial charge / discharge, a non-aqueous electrolyte storage element of Example 1 was obtained. The content of Compound X in the non-aqueous electrolyte of the non-aqueous electrolyte storage element of Example 1 obtained after the initial charge / discharge was 1.1% by mass.

[0131] [Examples 2 and 3, Comparative Example 1] The nonaqueous electrolyte storage elements of Examples 2 and 3 and Comparative Example 1 were obtained in the same manner as in Example 1, except that the content of compound X in the nonaqueous electrolyte of each nonaqueous electrolyte storage element obtained after initial charge and discharge was set to the value shown in Table 1. Table 1 also shows the content of compound X in the nonaqueous electrolyte of each nonaqueous electrolyte storage element obtained after initial charge and discharge.

[0132] [Reference Example 1] (Preparation of Positive Electrode) LiNi was used as the positive electrode active material. １／３ Mn １／３ Co １／３ O ２ A positive electrode was obtained in the same manner as in Example 1 except that (NCM) was used.

[0133] (Preparation of non-aqueous electrolyte) LiPF 6 as an electrolyte salt was added to a non-aqueous solvent obtained by mixing ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate in a volume ratio of 30:35:35. ６ to 1.2 mol / dm ３ To this solution, 1.0 mass % of lithium difluorophosphonylfluorosulfonylimide (Compound X), 0.5 mass % of vinylene carbonate (VC), and 0.2 mass % of lithium bis(oxalate)borate (LiBOB) were mixed to obtain a nonaqueous electrolyte.

[0134] (Assembly of Uncharged and Discharged Non-Aqueous Electrolyte Storage Element) An uncharged and discharged non-aqueous electrolyte storage element was obtained in the same manner as in Example 1, except that the above positive electrode and the above non-aqueous electrolyte were used.

[0135] (Initial Charge / Discharge) The assembled non-charged / discharged non-aqueous electrolyte storage element was initially charged / discharged under the following conditions. In a thermostatic chamber at 25°C, constant current charging was performed with a charging current of 1.0 C and a charge cut-off voltage of 4.10 V, followed by constant voltage charging at 4.10 V. The charge was terminated when the current decayed to 0.01 C. A 10-minute rest period was then provided. Constant current discharge was performed with a discharge current of 1.0 C and a discharge cut-off voltage of 2.75 V. A 10-minute rest period was then provided. The above charge / discharge cycle was repeated twice, and the quantity of electricity discharged in the second cycle was taken as the initial discharge capacity. Through the above initial charge / discharge cycle, a non-aqueous electrolyte storage element of Reference Example 1 was obtained.

[0136] Reference Example 2 A nonaqueous electrolyte storage element of Reference Example 2 was obtained in the same manner as in Reference Example 1, except that the content of Compound X in the preparation of the nonaqueous electrolyte was set to the value shown in Table 1.

[0137] The content of Compound X in the nonaqueous electrolyte of each of the nonaqueous electrolyte storage elements obtained in Reference Examples 1 and 2 was not measured.

[0138] [Evaluation] (1) Measurement of Capacity Retention Rate After Storage in a 65°C Environment Each nonaqueous electrolyte storage element of the Examples and Comparative Examples was subjected to constant-current charging in a 25°C thermostatic chamber with a charging current of 0.2 C and a charge cut-off voltage of 3.5 V to achieve an SOC of 100%. Each nonaqueous electrolyte storage element was left in the 65°C thermostatic chamber for 120 days in this 100% SOC state. It was then stored in the 25°C thermostatic chamber for 3 hours. Subsequently, a constant-current discharge was performed with a discharge current of 1.0 C and a discharge cut-off voltage of 2.0 V. A 10-minute rest period was then allowed. Thereafter, charge and discharge were performed once under the same conditions as the initial charge and discharge described above, and the discharge capacity after storage was determined. The percentage of the discharge capacity after storage relative to the initial discharge capacity was calculated as the capacity retention rate after 120 days at 65°C. The results are shown in Table 1. Each nonaqueous electrolyte storage element of the Reference Example was subjected to constant current charging at a charging current of 1.0 C in a thermostatic chamber at 25°C until the SOC reached 80%. Each nonaqueous electrolyte storage element was left in this 80% SOC state in a thermostatic chamber at 65°C for 120 days. It was then stored in the thermostatic chamber at 25°C for 3 hours. Subsequently, a constant current discharge was performed with a discharge current of 1.0 C and a discharge cut-off voltage of 2.75 V. A 10-minute rest period was then provided. Then, a single charge / discharge cycle was performed under the same conditions as the initial charge / discharge cycle, and the discharge capacity after storage was determined. The percentage of the discharge capacity after storage relative to the initial discharge capacity was calculated as the capacity retention rate after 120 days at 65°C. The results are shown in Table 1.

[0139] (2) Measurement of Capacity Retention Rate After Storage at 45°C Each of the nonaqueous electrolyte storage elements of the Examples and Comparative Examples was subjected to constant-current charging in a thermostatic chamber at 25°C with a charging current of 0.2 C and a cut-off voltage of 3.5 V to achieve an SOC of 100%. Each nonaqueous electrolyte storage element was left in the thermostatic chamber at 45°C for 120 days in this 100% SOC state. It was then stored in the thermostatic chamber at 25°C for 3 hours. Subsequently, a constant-current discharge was performed with a discharge current of 1.0 C and a cut-off voltage of 2.0 V. A 10-minute rest period was then allowed. Thereafter, charge and discharge were performed once under the same conditions as the initial charge and discharge described above, and the discharge capacity after storage was determined. The percentage of the discharge capacity after storage relative to the initial discharge capacity was calculated as the capacity retention rate after 120 days at 45°C. The results are shown in Table 1.

[0140] (3) Measurement of Capacity Retention Rate After Charge-Discharge Cycles in a 45°C Environment A charge-discharge cycle test was performed on each of the nonaqueous electrolyte storage elements of the Examples and Comparative Examples as follows. A constant-current, constant-voltage charge was performed in a thermostatic chamber at 45°C, with a charge current of 1.0 C and a charge cut-off voltage of 3.5 V. The charge cut-off condition was when the current decayed to 0.01 C. Subsequently, a constant-current discharge was performed with a discharge current of 1.0 C and a discharge cut-off voltage of 2.0 V. A 10-minute rest period was provided after each charge and discharge. This charge-discharge cycle was repeated 1,500 times. After the charge-discharge cycle test, the element was stored in a thermostatic chamber at 25°C for 3 hours. Subsequently, charge-discharge was performed under the same conditions as the initial charge-discharge cycle, and the discharge capacity after the charge-discharge cycle was determined. The percentage of the discharge capacity after the charge-discharge cycle relative to the initial discharge capacity was calculated as the capacity retention rate after the 45°C charge-discharge cycle. The results are shown in Table 1.

[0141]

[0142] As shown in Table 1, the nonaqueous electrolyte storage element of Comparative Example 1, in which the content of Compound X in the nonaqueous electrolyte was 0.5% by mass, had a low capacity retention rate of 71.6% after storage in a 65°C environment. In contrast, the nonaqueous electrolyte storage elements of Examples 1 to 3, in which the content of Compound X in the nonaqueous electrolyte was 0.8% by mass or more, had high capacity retention rates of 73% or more after storage in a 65°C environment. Furthermore, the capacity retention rate after storage in a 45°C environment and the capacity retention rate after charge-discharge cycling in a 45°C environment decreased with increasing content of Compound X in the nonaqueous electrolyte. This is thought to be because, in environments below 50°C, large amounts of iron ions do not leach from the positive electrode active material into the nonaqueous electrolyte, and instead, the impact of capacity reduction due to the reductive decomposition reaction of Compound X on the negative electrode surface is significant. In other words, the improvement in capacity retention rate due to the inclusion of a predetermined amount or more of Compound X is thought to be a unique effect that occurs when the element is charged / discharged or stored for an extended period of time in an environment above 50°C. Furthermore, in the case of the nonaqueous electrolyte storage elements of Reference Examples 1 and 2, in which the positive electrode active material was an NCM containing no iron, the capacity retention rate after storage in a 65°C environment was high regardless of the content of Compound X in the nonaqueous electrolyte. It was confirmed that the problem of low capacity retention rate after long-term storage in a high-temperature environment of 50°C or higher is a problem specific to nonaqueous electrolyte storage elements using a positive electrode active material containing iron. In the above examples, the effects of storing a nonaqueous electrolyte storage element in a high-temperature environment of 50°C or higher for a long period of time were confirmed. It is believed that phenomena such as the elution of iron ions from the positive electrode active material into the nonaqueous electrolyte occur not only when the nonaqueous electrolyte storage element is stored in a high-temperature environment of 50°C or higher for a long period of time, but also when the nonaqueous electrolyte storage element is charged and discharged in a high-temperature environment of 50°C or higher for a long period of time. Therefore, it is estimated that the same effects as those of the above examples will be obtained even when the nonaqueous electrolyte storage element is charged and discharged in a high-temperature environment of 50°C or higher for a long period of time.

[0143] The present invention can be applied to nonaqueous electrolyte electricity storage elements used as power sources for electronic devices such as personal computers and communication terminals, and automobiles.

[0144] REFERENCE SIGNS LIST 1 nonaqueous electrolyte energy storage element 2 electrode body 3 container 4 positive electrode terminal 41 positive electrode lead 5 negative electrode terminal 51 negative electrode lead 20 energy storage unit 30 energy storage device

Claims

1. A non-aqueous electrolyte storage element that is charged / discharged or left standing in an environment of 50°C or higher, and that comprises: a positive electrode having a positive electrode active material containing iron; and a non-aqueous electrolyte containing a compound having a fluorosulfonyl group, wherein the content of the compound having a fluorosulfonyl group in the non-aqueous electrolyte is 0.8 mass% or more.

2. A non-aqueous electrolyte storage element for vehicle or outdoor use, comprising: a positive electrode having a positive electrode active material containing iron; and a non-aqueous electrolyte containing a compound having a fluorosulfonyl group, wherein the content of the compound having a fluorosulfonyl group in the non-aqueous electrolyte is 0.8 mass% or more.

3. The nonaqueous electrolyte storage element according to claim 1 or 2, wherein the compound having a fluorosulfonyl group is lithium difluorophosphonylfluorosulfonylimide.

4. The non-aqueous electrolyte storage element according to claim 3, wherein the non-aqueous electrolyte further contains at least one selected from the group consisting of vinylene carbonate, lithium bis(oxalato)borate, and lithium bis(oxalato)difluorophosphate.

5. The nonaqueous electrolyte storage element according to claim 1 or 2, wherein the positive electrode active material is lithium iron phosphate.

6. A method for using a non-aqueous electrolyte storage element, comprising charging / discharging or leaving the non-aqueous electrolyte storage element in an environment of 50°C or higher, wherein the non-aqueous electrolyte storage element comprises: a positive electrode having a positive electrode active material containing iron; and a non-aqueous electrolyte containing a compound having a fluorosulfonyl group, and the content of the compound having a fluorosulfonyl group in the non-aqueous electrolyte is 0.8 mass% or more.

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