Non-aqueous electrolyte energy storage element

Abstract

To provide a non-aqueous electrolyte power storage element that is excellent in life characteristics at high temperatures and capable of suppressing cross-sectional corrosion of a substrate containing aluminum.SOLUTION: A non-aqueous electrolyte power storage element includes a positive electrode 11 having a positive electrode substrate 21, a negative electrode 12 having a negative electrode substrate 22, and a non-aqueous electrolyte containing an electrolyte salt and a non-aqueous solvent, and the electrolyte salt contains an imide salt, the positive electrode base material 21, the negative electrode base material 22, or a combination thereof contains aluminum, and at least a portion of the cross section is covered with a coating layer.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a non-aqueous electrolyte energy storage element. [Background technology]

[0002] Non-aqueous electrolyte secondary batteries, typified by lithium-ion non-aqueous electrolyte secondary batteries, are widely used in electronic devices such as personal computers and communication terminals, automobiles, etc., due to their high energy density. The non-aqueous electrolyte secondary batteries generally include an electrode assembly having 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 ions between the electrodes. Furthermore, capacitors such as lithium-ion capacitors and electric double layer capacitors are also widely used as non-aqueous electrolyte energy storage elements other than non-aqueous electrolyte secondary batteries.

[0003] Imide salts such as lithium bis(fluorosulfonyl)imide (LiFSI) are known as electrolyte salts used in non-aqueous electrolytes. For example, in order to provide a non-aqueous electrolyte secondary battery with excellent high-temperature stability, a non-aqueous electrolyte secondary battery has been proposed in which the non-aqueous electrolyte contains a lithium imide salt represented by the general formula (R1SO2)(R2SO2)NLi (see JP 2004-031131 A). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-031131 Summary of the Invention [Problem to be solved by the invention]

[0005] The use of a nonaqueous electrolyte solution containing an electrolyte salt containing the imide salt improves the life performance of a nonaqueous electrolyte storage element at high temperatures, but if a substrate containing aluminum is used as the positive electrode substrate, negative electrode substrate, or a combination thereof, the substrate may corrode at high temperatures, which may lead to an increase in the resistance of the nonaqueous electrolyte storage element.

[0006] An object of the present invention is to provide a nonaqueous electrolyte electricity storage element that, when the substrate contains aluminum, has excellent life performance at high temperatures and can suppress corrosion of the cross section of the aluminum-containing substrate. [Means for solving the problem]

[0007] A nonaqueous electrolyte storage element according to one aspect of the present invention includes a positive electrode having a positive electrode substrate, a negative electrode having a negative electrode substrate, and a nonaqueous electrolyte containing an electrolyte salt and a nonaqueous solvent, wherein the electrolyte salt contains an imide salt, and the positive electrode substrate, the negative electrode substrate, or a combination thereof contains aluminum, and at least a portion of a cross section is covered with a coating layer. [Effects of the Invention]

[0008] According to one aspect of the present invention, when the substrate contains aluminum, the nonaqueous electrolyte storage element has excellent life performance at high temperatures and can suppress corrosion of the cross section of the aluminum-containing substrate. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a perspective view showing one embodiment of a nonaqueous electrolyte electricity storage element. [Figure 2] FIG. 2 is a schematic diagram illustrating an electrode assembly of a nonaqueous electrolyte electricity storage element as one example of one embodiment of the present invention. [Figure 3] FIG. 3 is a schematic cross-sectional view of a positive electrode of a nonaqueous electrolyte electricity storage element as one example of one embodiment of the present invention. [Figure 4] FIG. 4 is a schematic diagram showing one embodiment of an electricity storage device configured by assembling a plurality of nonaqueous electrolyte electricity storage elements. DETAILED DESCRIPTION OF THE INVENTION

[0010] First, an outline of the nonaqueous electrolyte electricity storage element disclosed in this specification will be described.

[0011] A nonaqueous electrolyte storage element according to one aspect of the present invention includes a positive electrode having a positive electrode substrate, a negative electrode having a negative electrode substrate, and a nonaqueous electrolyte containing an electrolyte salt and a nonaqueous solvent, wherein the electrolyte salt contains an imide salt, and the positive electrode substrate, the negative electrode substrate, or a combination thereof contains aluminum, and at least a portion of a cross section is covered with a coating layer.

[0012] As described above, the use of a nonaqueous electrolyte solution containing an electrolyte salt containing an imide salt improves the life performance of nonaqueous electrolyte storage elements even at high temperatures exceeding 80°C. However, the use of an aluminum-containing substrate may result in corrosion of the substrate at high temperatures. This phenomenon is presumably caused by the imide anions of the imide salt destroying the Al2O3 film, a passive film formed by natural oxidation on the surface of the aluminum-containing substrate, when the nonaqueous electrolyte solution containing an electrolyte salt containing an imide salt comes into contact with the aluminum-containing substrate. In this nonaqueous electrolyte storage element, the positive electrode substrate, the negative electrode substrate, or a combination thereof contains aluminum, and at least a portion of the cross section is covered with a coating layer, thereby protecting the exposed aluminum surface of the aluminum-containing substrate. Therefore, contact between the nonaqueous electrolyte solution containing an electrolyte salt containing an imide salt and the Al2O3 film, a passive coating on the cross section of the aluminum-containing substrate, is physically inhibited, thereby suppressing corrosion of the cross section of the aluminum-containing substrate. Therefore, when the substrate of the nonaqueous electrolyte storage element contains aluminum, it has excellent life performance at high temperatures and can suppress corrosion of the cross section of the substrate containing aluminum.

[0013] The content of the imide salt in the electrolyte salt is preferably 50 mol % or more and 100 mol % or less, which can improve the life performance of the nonaqueous electrolyte storage element at high temperatures and the effect of inhibiting corrosion of the cross section of the aluminum-containing substrate.

[0014] The coating layer preferably contains a fluorine-containing resin, which promotes the substitution of oxygen for fluorine in the Al2O3 film, which is a passive coating on the cross section of the aluminum-containing substrate, and facilitates the formation of an AlF3 film, which is a passive coating, on the cross section of the aluminum-containing substrate, thereby suppressing corrosion of the cross section of the substrate by the imide salt.

[0015] The difference in SP value between the resin and the nonaqueous solvent is preferably 3 or more. A difference of 3 or more in SP value between the resin and the nonaqueous solvent makes it difficult for the resin to swell in the nonaqueous solvent and prevents the resin from dissolving in the nonaqueous solvent. Here, "SP value" refers to a solubility parameter. If the force acting between the solvent and the solute is assumed to be only an intermolecular force, this intermolecular force is regarded as the SP value. The SP values ​​of the resin and the nonaqueous solvent are values ​​specific to the resin composition and the nonaqueous solvent and serve as a guide for determining compatibility. Furthermore, when the coating layer contains two or more resins, the SP value of the resin is calculated by summing the values ​​obtained by multiplying the SP values ​​of each resin constituting the coating layer by the mass percentage of the content. When the nonaqueous electrolyte solution contains two or more nonaqueous solvents, the SP value of the nonaqueous solvent is calculated by summing the values ​​obtained by multiplying the SP values ​​of each nonaqueous solvent constituting the nonaqueous electrolyte solution by the volume percentage of the content.

[0016] The configuration of a nonaqueous electrolyte electricity storage element according to one embodiment of the present invention, the configuration of an electricity storage device, and a method for manufacturing a nonaqueous electrolyte electricity storage element, as well as other embodiments, will be described in detail below. Note that the names of the components used in each embodiment may differ from the names of the components used in the background art.

[0017] <Configuration of Nonaqueous Electrolyte Energy Storage Element> In the nonaqueous electrolyte storage element, the positive electrode substrate, the negative electrode substrate, or a combination thereof contains aluminum, and at least a portion of the cross section is coated with a coating layer. When an aluminum-containing substrate is used as the positive electrode substrate, the negative electrode substrate, or a combination thereof, the substrate may corrode at high temperatures, but at high potentials, corrosion of aluminum by imide salts is more likely to occur. Therefore, the effect of suppressing corrosion by imide salts by coating at least a portion of the cross section of the aluminum-containing substrate with a coating layer is more pronounced when the positive electrode substrate contains aluminum.

[0018] FIG. 1 shows a nonaqueous electrolyte storage element 1 as an example of a prismatic battery. The figure is a see-through view of the inside of the container. An electrode 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.

[0019] FIG. 2 is a schematic diagram illustrating an electrode assembly 2 of a nonaqueous electrolyte storage element 1 according to one embodiment of the present invention. As shown in FIG. 2, the electrode assembly 2 is a wound electrode assembly in which a sheet including a positive electrode 11, a negative electrode 12, and a separator 25 is wound flat. The electrode assembly 2 is formed by winding a positive electrode 11 including a positive electrode active material layer 24 and a negative electrode 12 including a negative electrode active material layer 23, with the separator 25 interposed therebetween, flat. That is, in the electrode assembly 2, a strip-shaped separator 25 is formed on the outer periphery of the strip-shaped negative electrode 12, a strip-shaped positive electrode 11 is formed on the outer periphery of the separator 25, and another strip-shaped separator 25 is formed on the outer periphery of the positive electrode 11. An exposed region of the positive electrode substrate 21 on which the positive electrode active material layer 24 is not formed is formed at one end of the positive electrode 11. Furthermore, an exposed region of the negative electrode substrate 22 on which the negative electrode active material layer 23 is not formed is formed at one end of the negative electrode 12.

[0020] More specifically, in the electrode assembly 2 configured in this manner, the positive electrode 11 and the negative electrode 12 are wound with a separator 25 interposed therebetween, offset from each other in the direction of the winding axis. The positive electrode 11 has, at one end in the direction of the winding axis, an exposed region of the positive electrode substrate 21 that is not coated with a positive electrode active material. The negative electrode 12 has, at the other end in the direction of the winding axis, an exposed region of the negative electrode substrate 22 that is not coated with a negative electrode active material. As a result, the electrode assembly 2 has, at one end in the direction of the winding axis, a positive electrode side end on which the positive electrode substrate 21 of the positive electrode 11 is laminated, and at the other end in the direction of the winding axis, a negative electrode side end on which the negative electrode substrate 22 of the negative electrode 12 is laminated.

[0021] In this embodiment, the positive electrode substrate 21 contains aluminum, and at least a portion of its cross section is covered with a coating layer 10. Fig. 3 is a schematic cross-sectional view of a positive electrode of a nonaqueous electrolyte storage element as one example of one embodiment of the present invention. Specifically, as shown in Figs. 2 and 3, in this embodiment, at least a portion of four cross sections located at the ends of the positive electrode substrate 21 are covered with a coating layer 10.

[0022] (positive electrode) The positive electrode has a positive electrode substrate and a positive electrode active material layer disposed directly or indirectly on the positive electrode substrate.

[0023] The positive electrode substrate is electrically conductive. Whether or not it has "electrical conductivity" is determined by whether the volume resistivity measured in accordance with JIS-H-0505 (1975) is 10 7The threshold value is Ω·cm. The material of the positive electrode substrate is a metal such as aluminum, titanium, tantalum, or stainless steel, or an alloy thereof. In one example of this embodiment, the material of the positive electrode substrate is preferably aluminum or an aluminum alloy. The positive electrode substrate is made of aluminum or an aluminum alloy, which provides excellent 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 standpoint 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-H4160 (2006).

[0024] The average thickness of the positive electrode substrate is preferably 3 μm to 50 μm, more preferably 5 μm to 40 μm, even more preferably 8 μm to 30 μm, and particularly preferably 10 μm to 25 μm. By setting the average thickness of the positive electrode substrate within the above range, the strength of the positive electrode substrate can be increased while increasing the energy density per volume of the nonaqueous electrolyte storage element.

[0025] The coating layer preferably contains a fluorine-containing resin. The inclusion of a fluorine-containing resin in the coating layer promotes the substitution of oxygen with fluorine in the Al2O3 film, which is a passive coating on the cross section of the substrate, and facilitates the formation of an AlF3 film, which is a passive coating, on the cross section of the substrate, thereby suppressing corrosion of the cross section of the substrate due to imide salts. Examples of the fluorine-containing resin include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and modified polyvinylidene fluoride.

[0026] The lower limit of the weight-average molecular weight of the resin is preferably 100,000, more preferably 200,000. When the weight-average molecular weight of the resin is equal to or greater than the lower limit, the resin can be prevented from dissolving in a non-aqueous solvent. On the other hand, the upper limit of the weight-average molecular weight of the resin is not particularly limited, but may be, for example, 1,000,000. Here, "weight-average molecular weight" refers to the average molecular weight measured using gel permeation chromatography (GPC) in accordance with JIS-K7252-1 (2008) "Plastics - Determination of average molecular weight and molecular weight distribution of polymers by size exclusion chromatography - Part 1: General rules."

[0027] The lower limit of the difference in SP value between the resin and the non-aqueous solvent is preferably 2.5, more preferably 3. When the difference in SP value between the resin and the non-aqueous solvent is equal to or greater than the lower limit, the resin is less likely to swell in the non-aqueous solvent and the resin can be prevented from dissolving in the non-aqueous solvent. Note that there is no particular upper limit to the difference in SP value between the resin and the non-aqueous solvent.

[0028] The positive electrode active material layer contains a positive electrode active material and, if necessary, optional components such as a conductive agent, a binder, a thickener, and a filler.

[0029] The positive electrode active material can be appropriately selected from known positive electrode active materials. A material capable of absorbing and releasing lithium ions is usually used as the positive electrode active material for a lithium ion secondary battery. Examples of the positive electrode active material include lithium transition metal composite oxides having an α-NaFeO2 crystal structure, lithium transition metal composite oxides having a spinel crystal structure, polyanion compounds, chalcogen compounds, and sulfur. Examples of lithium transition metal composite oxides having an α-NaFeO2 crystal structure include Li[Li x Ni (1-x) ]O2(0≦x<0.5), Li[Li x Ni γ Co (1-x-γ) ]O2(0≦x<0.5, 0<γ<1), Li[Li x Co (1-x) ]O2(0≦x<0.5), Li[Lix Ni γ Mn (1-x-γ) ]O2(0≦x<0.5, 0<γ<1), Li[Li x Ni γ Mn β Co (1-x-γ-β) ]O2(0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1), Li[Li x Ni γ Co β Al (1-x-γ-β) ]O2 (0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1). Lithium transition metal composite oxides with spinel crystal structure include Li x Mn2O4, Li x Ni γ Mn (2-γ) Examples of polyanion compounds include LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, Li3V2(PO4)3, Li2MnSiO4, and Li2CoPO4F. Examples of chalcogen compounds include titanium disulfide, molybdenum disulfide, and molybdenum dioxide. Atoms or polyanions in these materials may be partially substituted with atoms or anion species of other elements. The surfaces of these materials may be coated with other materials. In the positive electrode active material layer, one of these materials may be used alone, or two or more may be used in combination.

[0030] The positive electrode active material is usually in the form of particles (powder). The average particle size of the 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 positive electrode active material to the above lower limit or more, the positive electrode active material becomes easier to manufacture and handle. By setting the average particle size of the positive electrode active material to the above upper limit or less, the electronic conductivity of the positive electrode active material layer is improved. Note that when a composite of the positive electrode active material and another material is used, the average particle size of the composite is taken as the average particle size of the positive electrode active material. The "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).

[0031] 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.

[0032] The content of the positive electrode active material in the positive electrode 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 positive electrode active material within this range, both high energy density and manufacturability of the positive electrode active material layer can be achieved.

[0033] The conductive agent is not particularly limited as long as it is a material having electrical conductivity. Examples of such conductive agents include carbonaceous materials, metals, and conductive ceramics. Examples of carbonaceous 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. 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 CNTs may be used. Among these, carbon black is preferred from the viewpoints of electronic conductivity and coatability, and acetylene black is particularly preferred.

[0034] The content of the conductive agent in the positive electrode active material layer is preferably 1% by mass to 10% by mass, more preferably 3% by mass to 9% by mass. By setting the content of the conductive agent within this range, the energy density of the nonaqueous electrolyte storage element can be increased.

[0035] Examples of binders include thermoplastic resins such as the above-mentioned fluororesins (polytetrafluoroethylene, polyvinylidene fluoride, 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. Among these, preferred binders are fluorine-containing materials, with fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) being more preferred. By including fluorine in the binder, corrosion of the positive electrode substrate at the interface with the positive electrode active material layer due to imide salts can be further suppressed.

[0036] The binder content in the positive electrode active material layer is preferably 1% by mass to 10% by mass, more preferably 3% by mass to 9% by mass. By setting the binder content within this range, the active material can be stably held.

[0037] Examples of thickeners include polysaccharide polymers such as carboxymethyl cellulose (CMC), methyl cellulose, etc. When the thickener has a functional group that reacts with lithium or the like, this functional group may be deactivated in advance by methylation or the like.

[0038] The filler is not particularly limited, and 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, substances derived from mineral resources such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, and artificial products thereof.

[0039] The positive electrode active material layer may contain typical non-metallic elements such as B, N, P, F, Cl, Br, and I; typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba; and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, and W as components other than the positive electrode active material, conductive agent, binder, thickener, and filler.

[0040] The nonaqueous electrolyte storage element preferably includes a conductive barrier layer between the positive electrode substrate and the positive electrode active material layer. The barrier layer prevents direct contact between the nonaqueous electrolyte and the positive electrode substrate, thereby further enhancing the effect of inhibiting corrosion of the positive electrode substrate by the imide salt. The configuration of the barrier layer is not particularly limited, and may include, for example, a binder and a conductive agent.

[0041] The lower limit of the average thickness of the barrier layer is preferably 0.1 μm, more preferably 0.2 μm. When the average thickness of the barrier layer is equal to or greater than the lower limit, the adhesion between the positive electrode substrate and the positive electrode active material layer via the barrier layer can be sufficiently increased. On the other hand, the upper limit of the average thickness of the barrier layer is preferably 2 μm, more preferably 1 μm. When the average thickness of the barrier layer is equal to or less than the upper limit, the battery capacity can be sufficiently increased. The average thickness of the barrier layer is the average value of thickness measurements taken at 10 arbitrary locations.

[0042] (non-aqueous electrolyte) The non-aqueous electrolyte includes a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent.

[0043] The electrolyte salt contains an imide salt. By containing the imide salt, the life performance of the nonaqueous electrolyte storage element at high temperatures can be improved. In the present invention, the imide salt includes not only an imide salt having a structure in which two carbonyl groups are bonded to a nitrogen atom, but also an imide salt having a structure in which two sulfonyl groups are bonded to a nitrogen atom, an imide salt having a structure in which two phosphonyl groups are bonded to a nitrogen atom, an imide salt having a structure in which two groups selected from a carbonyl group, a sulfonyl group, and a phosphonyl group are bonded to a nitrogen atom, and the like.

[0044] Examples of the imide salt include lithium salt, sodium salt, potassium salt, magnesium salt, onium salt, etc. Among these, lithium salt is preferred. Examples of the imide salt include: lithium sulfonylimide salts such as LiN(SO2F)2 (lithium bis(fluorosulfonyl)imide: LiFSI), LiN(SO2CF3)2 (lithium bis(trifluoromethanesulfonyl)imide: LiTFSI), LiN(SO2C2F5)2 (lithium bis(pentafluoroethanesulfonyl)imide: LiBETI), LiN(SO2C4F9)2 (lithium bis(nonafluorobutanesulfonyl)imide), CF3-SO2-N-SO2-N-SO2CF3Li2, FSO2-N-SO2-C4F9Li, CF3-SO2-N-SO2-CF2-SO2-N-SO2-CF3Li2, CF3-SO2-N-SO2-CF2-SO3Li2, CF3-SO2-N-SO2-CF2-SO3Li2, CF3-SO2-N-SO2-CF2-SO2-C(-SO2CF3)2Li2; Examples include lithium phosphonylimide salts such as LiN(POF2)2 (lithium bis(difluorophosphonyl)imide: LiDFPI).

[0045] From the viewpoint of improving the life performance at high temperatures, the imide salt preferably contains a fluorine atom, and specifically, for example, preferably contains a fluorosulfonyl group, a difluorophosphonyl group, a fluoroalkyl group, etc. Among imide salts, lithium sulfonylimide salts are preferred, LiFSI, LiTFSI, and LiBETI are more preferred, and LiFSI is even more preferred.

[0046] The lower limit of the content of the imide salt in the electrolyte salt is preferably 50 mol%, more preferably 65 mol%, and even more preferably 70 mol%. By setting the concentration of the electrolyte salt to the lower limit or higher, the life performance of the nonaqueous electrolyte storage element at high temperatures can be improved. On the other hand, the upper limit of the content of the imide salt may be 100 mol%.

[0047] The electrolyte salt may contain other electrolyte salts besides the imide salt. The other electrolyte salts can be appropriately selected from known electrolyte salts. Examples of the other electrolyte salts include lithium salts, sodium salts, potassium salts, magnesium salts, and onium salts. Among these, lithium salts are preferred.

[0048] Examples of the lithium salt that is the other electrolyte salt include inorganic lithium salts such as LiPF6, LiPO2F2, LiBF4, and LiClO4, lithium oxalate salts such as lithium bis(oxalate)borate (LiBOB), lithium difluorooxalateborate (LiFOB), and lithium bis(oxalate)difluorophosphate (LiFOP), and lithium salts having a halogenated hydrocarbon group such as LiSO3CF3, LiC(SO2CF3)3, and LiC(SO2C2F5)3. Among these, inorganic lithium salts are preferred, and LiPF6 is more preferred.

[0049] The content of electrolyte salt in the non-aqueous electrolyte is 0.1 mol / dm at 20°C and 1 atmosphere. 3 More than 2.5mol / dm 3 It is preferable that the value is 0.3 mol / dm or less. 3 More than 2.0mol / dm 3 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 More than 1.5mol / dm 3By setting the content of the electrolyte salt within the above range, the ionic conductivity of the non-aqueous electrolyte can be increased.

[0050] 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.

[0051] Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinylethylene carbonate (VEC), chloroethylene carbonate, fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), styrene carbonate, 1-phenylvinylene carbonate, 1,2-diphenylvinylene carbonate, etc. Among these, EC is preferred.

[0052] 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, EMC is preferred.

[0053] It is preferable to use a cyclic carbonate or a chain carbonate as the non-aqueous solvent, 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.

[0054] (Negative electrode) The negative electrode has a negative electrode substrate and a negative electrode active material layer disposed directly or indirectly on the negative electrode substrate.

[0055] 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. In one example of this embodiment, aluminum or an aluminum alloy is used as the material for the negative electrode substrate. However, from the viewpoints of potential resistance and high conductivity, the negative electrode substrate is preferably copper or a copper alloy. That is, in the nonaqueous electrolyte storage element according to this embodiment, the positive electrode substrate preferably contains aluminum. Examples of the negative electrode substrate include foil, vapor-deposited film, mesh, and porous material, with foil being preferred from the viewpoint of cost. Therefore, 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.

[0056] The average thickness of the negative electrode substrate is preferably 2 μm to 35 μm, more preferably 3 μm to 30 μm, even more preferably 4 μm to 25 μm, and particularly preferably 5 μm to 20 μm. By setting the average thickness of the negative electrode substrate within the above range, the strength of the negative electrode substrate can be increased while also increasing the energy density per volume of the nonaqueous electrolyte storage element.

[0057] 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.

[0058] 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.

[0059] 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 lithium ion secondary batteries. Examples of the negative electrode active material include metallic Li; metals or semimetals such as Si and Sn; metal oxides or semimetal oxides such as Si oxide, Ti oxide, and Sn oxide; and Li4Ti5O 12 , LiTiO 2、 Examples of the material include titanium-containing oxides such as TiNbO; polyphosphate compounds; silicon carbide; and carbon materials such as graphite and non-graphitic carbon (easily graphitizable carbon or non-graphitizable carbon). Among these materials, graphite and non-graphitic carbon are 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.

[0060] "Graphite" refers to graphite 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.

[0061] "Non-graphitic carbon" refers to the carbon that has an average lattice spacing (d 002 ) is 0.34 nm or more and 0.42 nm or less. Non-graphitic carbon includes non-graphitizable carbon and graphitizable carbon. Examples of non-graphitic 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.

[0062] Here, the "discharged state" refers to a state in which the negative electrode active material, a carbonaceous material, is discharged so that lithium ions capable of being absorbed and desorbed during charging and discharging are sufficiently released. For example, this refers to a state in which the open circuit voltage of a half cell using a negative electrode containing a carbonaceous material as a negative electrode active material as a working electrode and metallic Li as a counter electrode is 0.7 V or higher.

[0063] "Non-graphitizable carbon" means the above d 002 This refers to carbon materials with a particle size of 0.36 nm or more and 0.42 nm or less.

[0064] "Graphitizable carbon" means the above d 002 This refers to carbon materials with a particle size of 0.34 nm or more and less than 0.36 nm.

[0065] 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 negative electrode active material can be easily produced or handled. 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 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 the powder 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 Li, the negative electrode active material may be in the form of a foil.

[0066] 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.

[0067] (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 form of the substrate layer of the separator include woven fabric, nonwoven fabric, and porous resin film. Among these forms, 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.

[0068] 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 pressure, 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 the safety of the energy storage device.

[0069] The porosity of the separator is preferably 80% by volume or less from the viewpoint of strength, and 20% by volume or more from the viewpoint of discharge performance. Here, "porosity" refers to a volume-based value measured with a mercury porosimeter.

[0070] 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.

[0071] <Configuration of the power storage device> 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.

[0072] The nonaqueous electrolyte energy storage element of this embodiment can be mounted as an energy storage unit (battery module) comprising a plurality of nonaqueous electrolyte energy storage elements in automotive power sources such as electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs), power sources for electronic devices such as personal computers and communication terminals, or power storage power sources. In this case, the technology of the present invention may be applied to at least one of the nonaqueous electrolyte energy storage elements included in the energy storage unit. The nonaqueous electrolyte energy storage element of this embodiment has excellent life performance even at high temperatures exceeding 80°C and can inhibit corrosion of the cross section of the aluminum-containing substrate. Therefore, it can be mounted in the engine compartment of an automobile or the like, which may be exposed to high-temperature environments, and can be suitably used as a power source for starting the engine of an automobile or the like. 4 shows an example of an electricity storage device 30 in which electricity storage units 20, each of which is an assembly of two or more electrically connected nonaqueous electrolyte electricity storage elements 1, are further assembled. The electricity storage device 30 may include a bus bar (not shown) that electrically connects two or more nonaqueous electrolyte electricity storage elements 1, a bus bar (not shown) that electrically connects two or more electricity storage units 20, etc. The electricity storage unit 20 or the electricity storage device 30 may include a status monitoring device (not shown) that monitors the status of one or more nonaqueous electrolyte electricity storage elements 1.

[0073] <Method of manufacturing nonaqueous electrolyte energy storage element> The method for manufacturing the nonaqueous electrolyte storage element of this embodiment can be appropriately selected from known methods. The manufacturing method includes, for example, preparing an electrode assembly, preparing a nonaqueous electrolyte, and housing the electrode assembly and the nonaqueous electrolyte in a container. Preparing the electrode assembly includes forming a coating layer on at least a portion of a cross section of an aluminum-containing substrate, preparing a positive electrode and a negative electrode, and stacking or winding the positive electrode and the negative electrode with a separator interposed therebetween to form the electrode assembly.

[0074] The positive electrode can be prepared by, for example, applying a positive electrode mixture paste to the positive electrode substrate directly or via the barrier layer, followed by drying. The positive electrode mixture paste contains positive electrode active material particles and optional components such as a conductive agent and a binder, which constitute the positive electrode active material layer. The positive electrode mixture paste typically further contains a dispersion medium. Examples of the dispersion medium include N-methylpyrrolidone (NMP) and toluene. The negative electrode can be prepared in the same manner as the positive electrode.

[0075] The coating layer can be formed, for example, by applying or spraying a coating material prepared by dissolving a resin in an appropriate amount of a solvent (e.g., N-methyl-2-pyrrolidone) onto at least a portion of the cross section of the aluminum-containing substrate, followed by drying. The coating layer can be formed on the cross section of the positive electrode substrate only before the positive electrode is fabricated, or after a barrier layer is provided on the positive electrode substrate, or after a positive electrode active material layer is provided on the positive electrode substrate directly or via a barrier layer. The coating layer can be formed on the cross section of the negative electrode substrate in the same manner as the coating layer on the cross section of the positive electrode substrate.

[0076] The method for placing the non-aqueous electrolyte in the container can be appropriately selected from known methods. For example, when a non-aqueous electrolyte solution is used as the non-aqueous electrolyte, the non-aqueous electrolyte solution may be poured into the container through an inlet formed in the container, and then the inlet may be sealed.

[0077] <Other embodiments> The nonaqueous electrolyte storage element of the present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the spirit of the present invention. For example, the configuration of one embodiment may be added to the configuration of another embodiment, or part of the configuration of one embodiment may be replaced with the configuration of another embodiment or well-known technology. Furthermore, part of the configuration of one embodiment may be deleted. Also, well-known technology may be added to the configuration of one embodiment.

[0078] In the above embodiment, the positive electrode substrate contains aluminum, and at least a portion of the cross section of the positive electrode substrate is covered with a coating layer. However, the negative electrode substrate may contain aluminum, and at least a portion of the cross section of the negative electrode substrate may be covered with a coating layer. Alternatively, the positive electrode substrate and the negative electrode substrate may contain aluminum, and at least a portion of the cross section of the positive electrode substrate and the negative electrode substrate may be covered with a coating layer. This protects the exposed aluminum surface of the cross section of the aluminum-containing substrate, and suppresses corrosion of the cross section of the aluminum-containing substrate. Therefore, the life performance of the nonaqueous electrolyte storage element at high temperatures can be improved, and corrosion of the cross section of the aluminum-containing substrate can be suppressed.

[0079] When the negative electrode substrate contains aluminum, it is preferable to use, for example, titanium oxide, titanium-containing oxide, non-graphitic carbon, etc. as the negative electrode active material. As in the case when the positive electrode substrate contains aluminum, the binder for the negative electrode active material layer is preferably a fluorine-containing material, and more preferably a fluororesin such as polytetrafluoroethylene or polyvinylidene fluoride. Furthermore, like the positive electrode substrate, the nonaqueous electrolyte storage element preferably includes a conductive barrier layer between the negative electrode substrate and the negative electrode active material layer.

[0080] When the positive electrode substrate does not contain aluminum, the material of the positive electrode substrate is a metal such as titanium, tantalum, stainless steel, or an alloy thereof.

[0081] 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, electric double layer capacitors, lithium ion capacitors, and other capacitors.

[0082] 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. [Explanation of symbols]

[0083] 1. Non-aqueous electrolyte energy storage element 2 Electrode body 3 containers 4 Positive terminal 41 Positive lead 5 Negative terminal 51 Negative lead 10 Covering layer 11 Positive electrode 12 Negative electrode 20 Energy storage unit 21 Positive electrode substrate 22 Negative electrode substrate 23 Negative electrode active material layer 24 Cathode active material layer 25 Separator 30 Energy storage device

Claims

1. a positive electrode having a positive electrode substrate and a positive electrode active material layer; a negative electrode having a negative electrode substrate and a negative electrode active material layer; a non-aqueous electrolyte containing an electrolyte salt and a non-aqueous solvent; Equipped with the electrolyte salt contains an imide salt, a substrate that is at least one of the positive electrode substrate and the negative electrode substrate contains aluminum, At least a part of a cross section of the substrate is coated with a coating layer containing a fluorine-containing resin, The nonaqueous electrolyte storage element has a surface of the substrate facing the positive electrode active material layer or the negative electrode active material layer that is not covered with the covering layer.

2. 2. The nonaqueous electrolyte storage element according to claim 1, wherein the content of the imide salt in the electrolyte salt is 50 mol % or more and 100 mol % or less.

3. 3. The nonaqueous electrolyte storage element according to claim 1, wherein the difference in SP value between the resin and the nonaqueous solvent is 3 or more.

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