Non-aqueous electrolyte energy storage element

Abstract

A non-aqueous electrolyte storage element according to one aspect of the present invention includes: a negative electrode having a negative electrode active material layer; a separator; and a non-aqueous electrolyte including an electrolyte salt and a non-aqueous solvent, wherein the electrolyte salt in the non-aqueous electrolyte has a concentration of 0.7 mol / dm3 or more and 1.0 mol / dm3 or less, and a creep strain in the separator after maintaining a load of 2 MPa for 60 sec at a temperature of 65°C is 9% or more and 15% or less.

Description

Technical Field

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

Background Art

[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, and automobiles, etc. because of their high energy density. Generally, the above non-aqueous electrolyte secondary battery includes an electrode body having a pair of electrodes electrically separated by a separator, and a non-aqueous electrolyte interposed between the electrodes, and is configured to charge and discharge by transferring charge-transporting ions between both electrodes. In addition, as non-aqueous electrolyte storage elements other than non-aqueous electrolyte secondary batteries, capacitors such as lithium ion capacitors and electric double layer capacitors are also widely popular.

[0003] As the above non-aqueous electrolyte storage element, for example, there has been proposed a lithium ion secondary battery including an electrode body formed by winding a first electrode plate as a positive electrode plate, a second electrode plate as a negative electrode plate, and a separator, the electrode body having a power generation part where the active material coating part of the first electrode plate, the active material coating part of the second electrode plate, and the separator overlap, and a battery case for housing the same (see Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In recent years, non-aqueous electrolyte energy storage devices have been applied to the automotive sector, including hybrid vehicles, plug-in hybrid vehicles, and electric vehicles. When applying these devices to such vehicles, there is a need for improved output performance in low-temperature environments after repeated charging and discharging cycles. Further improvements in this regard are desired for non-aqueous electrolyte energy storage devices.

[0006] The objective of the present invention is to provide a non-aqueous electrolyte energy storage element that can increase output in low-temperature environments after charge-discharge cycles. [Means for solving the problem]

[0007] A non-aqueous electrolyte energy storage element according to one aspect of the present invention comprises a negative electrode having a negative electrode active material layer, a separator, and a non-aqueous electrolyte containing an electrolyte salt and a non-aqueous solvent, wherein the concentration of the electrolyte salt in the non-aqueous electrolyte is 0.7 mol / dm³. 3 More than 1.0mol / dm 3 The following conditions apply: the creep strain in the above separator after holding a 2 MPa load for 60 seconds at a temperature of 65°C is between 9% and 15%. [Effects of the Invention]

[0008] According to one aspect of the present invention, it is possible to provide a non-aqueous electrolyte energy storage element that can increase output in low-temperature environments after a charge-discharge cycle. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a perspective view showing one embodiment of a non-aqueous electrolyte energy storage element. [Figure 2] Figure 2 is a schematic diagram showing one embodiment of an energy storage device composed of multiple non-aqueous electrolyte energy storage elements. [Modes for carrying out the invention]

[0010] First, an overview of the non-aqueous electrolyte energy storage elements disclosed herein will be provided.

[0011] A non-aqueous electrolyte energy storage element according to one aspect of the present invention comprises a negative electrode having a negative electrode active material layer, a separator, and a non-aqueous electrolyte containing an electrolyte salt and a non-aqueous solvent, wherein the concentration of the electrolyte salt in the non-aqueous electrolyte is 0.7 mol / dm³. 3 More than 1.0mol / dm 3 The following conditions apply: the creep strain in the above separator after holding a 2 MPa load for 60 seconds at a temperature of 65°C is between 9% and 15%.

[0012] In a non-aqueous electrolyte energy storage element according to one aspect of the present invention, the concentration of the electrolyte salt in the non-aqueous electrolyte is 0.7 mol / dm³ 3 More than 1.0mol / dm 3 The following is true: The creep strain of the separator after holding a 2 MPa load at 65°C for 60 seconds is between 9% and 15%, which increases the output of the non-aqueous electrolyte energy storage element in low-temperature environments after charge-discharge cycles. The reason for this is not entirely clear, but it is speculated to be as follows: The negative electrode active material layer expands and contracts repeatedly with repeated charge-discharge cycles within the container of the non-aqueous electrolyte energy storage element, making the voids in the negative electrode active material layer more susceptible to collapse when the surface pressure inside the container increases. In this non-aqueous electrolyte energy storage element, the creep strain of the separator after holding a 2 MPa load at 65°C for 60 seconds is 9% or more, so when the surface pressure increases, the separator is compressed before the voids in the negative electrode active material layer, thus easing the surface pressure on the negative electrode active material layer and making the voids in the negative electrode active material layer less susceptible to collapse. Therefore, the degradation of the negative electrode active material layer due to repeated charge-discharge cycles is reduced, which increases the output of the non-aqueous electrolyte energy storage element in low-temperature environments after charge-discharge cycles. On the other hand, by keeping the creep strain in the separator below 15%, the increase in resistance due to excessive compression of the separator can be suppressed, thereby increasing the output in low-temperature environments after charge-discharge cycles. Furthermore, the concentration of the electrolyte salt in the non-aqueous electrolyte is 0.7 mol / dm³. 3 More than 1.0mol / dm 3By being as follows, good ion conductivity of the non-aqueous electrolyte is ensured, and the viscosity of the non-aqueous electrolyte can be lowered. As a result, the initial output in a low-temperature environment can be increased, and the output after charge-discharge cycles is also improved. Therefore, the non-aqueous electrolyte storage element can increase the output in a low-temperature environment after charge-discharge cycles.

[0013] In the non-aqueous electrolyte storage element according to one aspect of the present invention, it is preferable that the porosity of the negative electrode active material layer is 40% or more. In the non-aqueous electrolyte storage element, when the porosity of the negative electrode active material layer is 40% or more, the output in a low-temperature environment after charge-discharge cycles of the non-aqueous electrolyte storage element can be further increased.

[0014] The "porosity (%)" of the negative electrode active material layer is a value calculated by the following formula. Porosity = {1 - (apparent density of the negative electrode active material layer / true density of the negative electrode active material layer)} × 100 The "apparent density of the negative electrode active material layer" (g / cm 3 ) is a value calculated from the mass per unit area of the negative electrode active material layer and the average thickness of the negative electrode active material layer. The "average thickness" is defined as the average value of the thicknesses measured at any five locations as follows. The "true density of the negative electrode active material layer" (g / cm 3 ) is a value calculated from the true density of each constituent component contained in the negative electrode active material layer and the mass ratio of each constituent component.

[0015] The non-aqueous electrolyte storage element is preferably used as a power source for a hybrid vehicle. In a power source for a hybrid vehicle, output performance in a low-temperature environment is important. Therefore, the non-aqueous electrolyte storage element capable of increasing the output in a low-temperature environment after charge-discharge cycles is particularly useful as a power source for a hybrid vehicle.

[0016] A "hybrid vehicle" is a vehicle having two or more power sources (prime movers), and usually has an internal combustion engine (engine) and an electric motor (motor) as power sources.

[0017] The configuration of a non-aqueous electrolyte energy storage element, the configuration of an energy storage device, a method for manufacturing a non-aqueous electrolyte energy storage element, and other embodiments according to one embodiment of the present invention will be described in detail. Note that the names of the components (each element) used in each embodiment may differ from the names of the components (each element) used in the background art.

[0018] <Configuration of a non-aqueous electrolyte energy storage element> A non-aqueous electrolyte energy storage element (hereinafter also simply referred to as "energy storage element") according to one embodiment of the present invention comprises an electrode body having a negative electrode, a positive electrode, and a separator, a non-aqueous electrolyte, and a container for housing the electrode body and the non-aqueous electrolyte. The electrode body is usually a stacked type in which a plurality of negative electrodes and a plurality of positive electrodes are stacked with a separator in between, or a wound type in which the negative electrode and positive electrode are wound together with a separator in between. The non-aqueous electrolyte exists contained within the negative electrode, positive electrode, and separator. As an example of a non-aqueous electrolyte energy storage element, a non-aqueous electrolyte secondary battery (hereinafter also simply referred to as "secondary battery") will be described.

[0019] (Negative electrode) The negative electrode comprises a negative electrode substrate and a negative electrode active material layer disposed directly on the negative electrode substrate or via an intermediate layer.

[0020] The negative electrode substrate is conductive. Whether or not it is conductive is determined by the volume resistivity measured in accordance with JIS-H-0505 (1975), which is 10 7 The determination is made using Ω·cm as the threshold. The negative electrode substrate material can be metals such as copper, nickel, stainless steel, nickel-plated steel, and aluminum, or alloys thereof, or carbonaceous materials. Among these, copper or copper alloys are preferred. Examples of negative electrode substrates include foil, vapor-deposited film, mesh, and porous materials, with foil being preferred from a cost standpoint. 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. 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, it is possible to increase the strength of the negative electrode substrate while increasing the energy density per unit volume of the non-aqueous electrolyte energy storage element.

[0021] The intermediate layer is a layer placed between the negative electrode substrate and the negative electrode active material layer. The intermediate layer contains a conductive agent such as carbon particles to reduce the contact resistance between the negative electrode substrate and the negative electrode active material layer. The composition of the intermediate layer is not particularly limited and may include, for example, a binder and a conductive agent.

[0022] The negative electrode active material layer contains the negative electrode active material. The negative electrode active material layer may optionally contain conductive agents, binders, thickeners, fillers, and other optional components.

[0023] The negative electrode active material layer may contain typical nonmetallic elements such as B, N, P, F, Cl, Br, and I, typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba, and transition metallic elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, and W as components other than the negative electrode active material, conductive agent, binder, thickener, and filler.

[0024] The negative electrode active material can be appropriately selected from known negative electrode active materials. For lithium-ion secondary batteries, materials capable of intercalating and releasing lithium ions are typically used as negative electrode active materials. Examples of negative electrode active materials include: metallic Li; metals or metalloids such as Si and Sn; metal oxides or metalloid oxides such as Si oxide, Ti oxide, and Sn oxide; and Li4Ti5O 12 LiTiO 2、 Examples of materials include titanium-containing oxides such as TiNb2O7; polyphosphate compounds; silicon carbide; and carbon materials such as graphite and non-graphitizable carbon (easily graphitizable carbon or poorly graphitizable carbon). Among these materials, graphite and non-graphitizable 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 mixture form.

[0025] "Graphite" refers to the average lattice plane spacing (d) of the (002) plane, determined by X-ray diffraction before charging or discharging, or after discharge. 002 ) refers to carbon materials with a n-scale between 0.33 nm and less than 0.34 nm. Examples of graphite include natural graphite and artificial graphite. Artificial graphite is preferred from the standpoint of obtaining materials with stable physical properties.

[0026] "Non-graphite carbon" refers to the average lattice plane spacing (d) of the (002) plane, as determined by X-ray diffraction before charging / discharging or in the discharged state. 002 This refers to carbon materials with a nautical radius of 0.34 nm or more and 0.42 nm or less. Non-graphitized carbons include poorly graphitizable carbons and easily graphitizable carbons. Examples of non-graphitized carbons include resin-derived materials, petroleum pitch or materials derived from petroleum pitch, petroleum coke or materials derived from petroleum coke, plant-derived materials, and alcohol-derived materials.

[0027] Here, the "discharged state" of a carbon material such as graphite refers to a state in which sufficient ions such as lithium, which can be intercepted and released during charging and discharging, are released from the carbon material that serves as the negative electrode active material. For example, in a half-cell using a negative electrode containing a carbon material as the negative electrode active material as the working electrode and metallic lithium (Li) as the counter electrode, this refers to a state where the open-circuit voltage is 0.7V or higher.

[0028] "Non-graphitizable carbon" refers to the above d 002 This refers to carbon materials with a wavelength between 0.36 nm and 0.42 nm.

[0029] "Easily graphitizable carbon" refers to the above d 002 This refers to carbon materials with a wavelength of 0.34 nm or more and less than 0.36 nm.

[0030] The negative electrode active material is usually in the form of particles (powder). To obtain the powder at a predetermined particle size, grinders and classifiers are used. Grinding methods include, for example, using a mortar and pestle, ball mill, sand mill, vibrating ball mill, planetary ball mill, jet mill, counter-jet mill, swirling airflow jet mill, or sieve. Wet grinding, using water or a non-aqueous solvent such as hexane, can also be used during grinding. For classification, sieves and air classifiers are used as needed, both dry and wet. If the negative electrode active material is a metal such as metallic lithium, the negative electrode active material may be in foil form.

[0031] The average particle size of the negative electrode active material can be, for example, between 1 nm and 100 μm. If the negative electrode active material is a carbon material, titanium-containing oxide, or polyphosphate compound, its average particle size may be between 1 μm and 100 μm. If the negative electrode active material is Si, Sn, Si oxide, or Sn oxide, its average particle size may be between 1 nm and 1 μm. Setting the average particle size of the negative electrode active material above the lower limit makes it easier to manufacture or handle the negative electrode active material. Setting the average particle size of the negative electrode active material below the upper limit improves the electronic conductivity of the negative electrode active material layer.

[0032] "Average particle size" refers to the value at which the volume-based integrated distribution, calculated in accordance with JIS-Z-8819-2 (2001), becomes 50%, based on the particle size distribution measured by laser diffraction / scattering on a diluted solution of particles diluted with a solvent, in accordance with JIS-Z-8825 (2013).

[0033] The content of the negative electrode active material in the negative electrode active material layer is preferably 60% by mass or more and 99% by mass or less, and more preferably 90% by mass or more and 98% by mass or less. By setting the content of the negative electrode active material within the above range, it is possible to achieve both high energy density and manufacturability in the negative electrode active material layer.

[0034] The conductive agent is not particularly limited as long as it is a conductive material. 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 can take the form of powder or fiber. One of these materials may be used alone as the conductive agent, or two or more may be used in mixture form. These materials may also be used in composite form. For example, a composite material of carbon black and CNTs may be used. Among these, carbon black is preferred from the viewpoint of electronic conductivity and coating properties, and acetylene black is particularly preferred.

[0035] 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. By setting the content of the conductive agent within the above range, the energy density of the secondary battery can be increased.

[0036] 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.

[0037] The binder content 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. By keeping the binder content within the above range, the negative electrode active material can be stably maintained.

[0038] Examples of thickening agents include polysaccharide polymers such as carboxymethylcellulose (CMC) and methylcellulose. If the thickening agent has a functional group that reacts with lithium or the like, this functional group may be deactivated beforehand by methylation or the like.

[0039] The filler is not particularly limited. Examples of fillers include polyolefins such as polypropylene and polyethylene; inorganic oxides such as silicon dioxide, aluminum oxide, 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 resource-derived materials such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or artificial products thereof.

[0040] The lower limit of the porosity of the negative electrode active material layer is preferably 40%, more preferably 42%, and even more preferably 44%. By setting the porosity to be above the lower limit, the output in a low-temperature environment after the charge-discharge cycle of the non-aqueous electrolyte energy storage element can be further increased. On the other hand, the upper limit of the porosity may be, for example, 55%, or 50% (for example, 48%). By setting the porosity to be below the upper limit, the above-mentioned effects are better realized. In addition, the energy density can be increased. The porosity of the negative electrode active material layer may be in the range of being above any of the lower limits and below any of the upper limits. The porosity of the negative electrode active material layer can be adjusted by pressing the negative electrode active material layer.

[0041] (positive electrode) The positive electrode comprises a positive electrode substrate and a positive electrode active material layer disposed directly on the positive electrode substrate or via an intermediate layer. The configuration of the intermediate layer is not particularly limited and can be selected from, for example, the configurations exemplified in the negative electrode.

[0042] The positive electrode substrate is electrically conductive. The positive electrode substrate can be made from metals such as aluminum, titanium, tantalum, or stainless steel, or alloys thereof. Among these, aluminum or aluminum alloys are preferred from the viewpoint of high potential resistance, high conductivity, and cost. Examples of positive electrode substrates include foil, vapor-deposited film, mesh, and porous materials, 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).

[0043] 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, it is possible to increase the strength of the positive electrode substrate while increasing the energy density per unit volume of the non-aqueous electrolyte energy storage element.

[0044] The positive electrode active material layer contains a positive electrode active material. The positive electrode active material layer may optionally contain components such as conductive agents, binders, thickeners, and fillers. These optional components can be selected from the materials exemplified above for the negative electrode.

[0045] The positive electrode active material can be appropriately selected from known positive electrode active materials. For lithium-ion secondary batteries, materials capable of intercalating and releasing lithium ions are typically used as positive electrode active materials. Examples of positive electrode active materials include lithium transition metal composite oxides having an α-NaFeO2 crystal structure, lithium transition metal composite oxides having a spinel crystal structure, polyanionic 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[Li x 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) Examples include ]O2 (0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1). As a lithium transition metal composite oxide having a spinel-type crystal structure, Li x Mn2O4, Li x Ni γ Mn (2-γ) Examples include O4. Examples of polyanion compounds include LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, Li3V2(PO4)3, Li2MnSiO4, Li2CoPO4F, etc. Examples of chalcogen compounds include titanium disulfide, molybdenum disulfide, molybdenum dioxide, etc. Some atoms or polyanions in these materials may be substituted with atoms or anions 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 mixture form.

[0046] 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. Setting the average particle size of the positive electrode active material above the lower limit facilitates the manufacturing and handling of the positive electrode active material. Setting the average particle size of the positive electrode active material below the upper limit improves the electronic conductivity of the positive electrode active material layer. When a composite material of the positive electrode active material and other materials is used, the average particle size of the composite material is used as the average particle size of the positive electrode active material. To obtain powder with a predetermined particle size, a pulverizer or classifier is used. The pulverization and classification methods can be selected from, for example, the methods exemplified above for the negative electrode.

[0047] The content of the positive electrode active material in the positive electrode active material layer is preferably 50% to 99% by mass, more preferably 70% to 98% by mass, and even more preferably 80% to 95% by mass. By setting the content of the positive electrode active material within the above range, it is possible to achieve both high energy density and manufacturability in the positive electrode active material layer.

[0048] The positive electrode active material layer may contain typical nonmetallic elements such as B, N, P, F, Cl, Br, and I, typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba, and transition 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.

[0049] (Separator) The separator has a base layer. The separator may also have an inorganic layer. The lower limit of the creep strain of the separator after holding a load of 2 MPa for 60 seconds at a temperature of 65°C is 9%, preferably 10%. When the creep strain of the separator is above the lower limit, when the surface pressure inside the container increases due to the expansion and contraction associated with repeated charging and discharging of the negative electrode active material layer, the separator is compressed before the voids in the negative electrode active material layer. As a result, the surface pressure on the negative electrode active material layer is relieved, and the voids in the negative electrode active material layer are less likely to collapse. Therefore, the deterioration of the negative electrode active material layer due to repeated charging and discharging is reduced, and the output in the low-temperature environment after the charge-discharge cycle can be increased. On the other hand, the upper limit of the creep strain of the separator is 15%, preferably 14%, and more preferably 13%. By keeping the creep strain in the separator below the upper limit, the increase in resistance due to excessive compression of the separator can be suppressed, thereby increasing the output in low-temperature environments after charge-discharge cycles. Note that "a load of 2 MPa at a temperature of 65°C" is a relatively severe condition among the loads that the negative electrode active material layer and separator are expected to be exposed to in the container of a non-aqueous electrolyte energy storage element used in automotive power supplies such as electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs). Under such conditions, if the creep strain of the separator is within the above range, the voids in the negative electrode active material layer and the separator will not be excessively compressed even after repeated charge-discharge cycles, and the effects of the present invention will be fully realized. The creep strain of the separator may also be within the range of either the lower limit or higher and either the upper limit or lower. The creep strain of the above-mentioned separator can be adjusted by changing the material, manufacturing method, porosity, pore size, pore distribution, pore shape, and thickness of the base layer, as well as the material, porosity, pore shape, and thickness of the inorganic layer if the separator has an inorganic layer.

[0050] The creep strain of the above separator after being subjected to a 2 MPa load for 60 seconds at a temperature of 65°C is the ratio of the change in the separator's thickness after being subjected to a 2 MPa load for 60 seconds at a temperature of 65°C to the initial separator thickness, and is specifically measured by the following method. First, a sample consisting of 200 stacked separators is prepared, and the thickness of the sample (A) in an unloaded state at a temperature of 65°C is measured. Next, at a temperature of 65°C, a 50 mm diameter cylindrical indenter is pressed against the sample in the thickness direction using a load cell type creep tester (manufactured by MIZ Testing Machine Co., Ltd.) to compress the sample. After the compressive stress reaches 2 MPa, it is held in that state for 60 seconds. The thickness of the sample (B) after being subjected to stress for 60 seconds is measured while maintaining that stressed state. The creep strain [%] after holding a 2 MPa load at 65°C for 60 seconds is calculated using the following formula 1, based on the sample thickness in an unloaded state (A) and the sample thickness after holding a 2 MPa load at 65°C for 60 seconds (B). Creep strain [%] = {(AB) / A} × 100 ... 1

[0051] The separator can be appropriately selected from known separators that have a suitable range of creep strain. Examples of separators that can be used include a separator consisting only of a resin base layer, or a separator in which an inorganic layer containing inorganic particles and a binder is formed on one or both sides of a resin base layer. Examples of the form of the separator base layer include woven fabric, nonwoven fabric, and porous resin film. Among these forms, a porous resin film is preferred from the viewpoint of strength.

[0052] From the viewpoint of ensuring that the creep strain of the separator is within an appropriate range, examples of materials for the substrate layer of the separator include polyethylene, polyolefins such as polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacrylonitrile, polyphenylene sulfide, polyimide, and fluororesin, among which polyolefins are preferred.

[0053] As the substrate layer of the separator, a uniaxially oriented or biaxially oriented porous resin film can be used. Among these, a biaxially oriented porous resin film can be preferably used. Here, "uniaxial orientation" refers to the process of stretching a resin film at a temperature above the glass transition temperature to orient the molecules, in only one direction (for example, the longitudinal direction), while "biaxial orientation" refers to stretching in two orthogonal directions (for example, the longitudinal direction and the width direction). The width direction is parallel to the transport surface of the resin film and is perpendicular to the longitudinal direction.

[0054] As a means of creating porosity in the manufacturing process of the separator base layer, a dry base layer can be produced by dry stretching, in which stretching (e.g., uniaxial stretching) is performed after drying, or a wet base layer can be produced by wet stretching, in which stretching (e.g., biaxial stretching) is performed in a wet state (e.g., a state in which the raw material resin and solvent are mixed). Among these, it is preferable that the separator base layer is stretched by a wet method. By stretching by a wet method, a separator with a creep strain of 9% to 15% can be produced relatively easily.

[0055] Examples of inorganic particles contained in the inorganic layer include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates; nitrides such as aluminum nitride and silicon nitride; carbonates such as calcium carbonate; sulfates such as barium sulfate; sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium titanate; covalent crystals such as silicon and diamond; mineral resource-derived materials or artificial products thereof such as talc, montmorillonite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica. These materials may be used individually or in composites as inorganic particles, or two or more may be used as a mixture. Among these inorganic compounds, silicon oxide, aluminum oxide, or aluminosilicates are preferred from the viewpoint of safety for non-aqueous electrolyte energy storage elements. The inorganic particles are preferably those whose mass loss is 5% or less when heated from room temperature to 500°C in an air atmosphere of 1 atmosphere, and more preferably those whose mass loss is 5% or less when heated from room temperature to 800°C.

[0056] Specific types of binders for the inorganic layer mentioned above include, in addition to those exemplified as binders for the negative electrode active material layer, polyvinyl alcohol, polyvinyl ester, and the like.

[0057] The lower limit of the porosity of the separator is preferably 40 vol% and more preferably 45 vol%. On the other hand, the upper limit of the porosity is preferably 60 vol% and more preferably 55 vol% (e.g., 50 vol%, typically 48 vol%). The porosity of the separator may be in the range of either the lower limit or less than or equal to either of the upper limits. "Porosity" is a volume-based value and refers to the measurement value obtained using a mercury porosimeter.

[0058] The average thickness of the separator (or the total thickness of the substrate layer and the inorganic layer if an inorganic layer is included) is not particularly limited, but the lower limit of the average thickness of the separator is preferably 5 μm, and more preferably 10 μm. The upper limit of the average thickness of the separator is preferably 40 μm, and more preferably 30 μm (e.g., 20 μm, typically 15 μm). The average thickness of the separator may be in the range of either the lower limit or more and either the upper limit or less than or equal to either of the above limits.

[0059] When the separator has a resin base layer and an inorganic layer, the lower limit of the average thickness of the inorganic layer (or the total average thickness if there are two or more inorganic layers in one separator) is preferably 1 μm, and more preferably 3 μm. By setting the average thickness of the inorganic layer to be above the above lower limit, it becomes easier to adjust the creep strain of the separator to a range of 9% to 15%. The upper limit of the average thickness of the inorganic layer is preferably 8 μm, and more preferably 6 μm (for example, 5 μm). The average thickness of the inorganic layer may be within the range of above the lower limit and below the upper limit.

[0060] The air permeability of the above separator is not particularly limited, but its upper limit is approximately 180 seconds / 100 cm. 3 And, 170 seconds / 100cm 3 Preferably, 160 seconds / 100cm 3 This is more preferable. In some embodiments, the air permeability of the separator is 150 seconds / 100 cm. 3 The following are also acceptable: 140 seconds / 100cm 3 The following is also acceptable. The above-mentioned effects can be better achieved when the air permeability of the separator is below the above upper limit. On the other hand, the lower limit for the air permeability of the separator is 80 seconds / 100cm. 3 And, 90 seconds / 100cm 3 This is more preferable. In some embodiments, the air permeability of the separator is 100 seconds / 100 cm. 3 It may be greater than or equal to 110 seconds / 100cm 3 It may be greater than or equal to 120 seconds / 100cm 3 It may be greater than or equal to 130 seconds / 100cm3 The above values ​​may also be used. The above effects can be better achieved when the air permeability of the separator is above the lower limit. The air permeability of the separator may be within the range of above the lower limit and below the upper limit. "Air permeability" is a value measured by the "Gurley testing machine method" in accordance with JIS-P-8117 (2009).

[0061] (Non-aqueous electrolytes) As the non-aqueous electrolyte, it can be appropriately selected from known non-aqueous electrolytes. A non-aqueous electrolyte solution may be used as the non-aqueous electrolyte. The non-aqueous electrolyte solution contains a non-aqueous solvent and an electrolyte salt dissolved in this non-aqueous solvent.

[0062] As the non-aqueous solvent, it can be appropriately selected from known non-aqueous solvents. Examples of non-aqueous solvents include cyclic carbonates, linear carbonates, carboxylic acid esters, phosphate esters, sulfonic acid esters, ethers, amides, and nitriles. As the non-aqueous solvent, compounds in which some of the hydrogen atoms contained in these compounds are substituted with halogens may also be used.

[0063] 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, and 1,2-diphenylvinylene carbonate. Among these, EC is preferred.

[0064] Examples of linear carbonates include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diphenyl carbonate, trifluoroethyl methyl carbonate, and bis(trifluoroethyl) carbonate. Among these, EMC is preferred.

[0065] It is preferable to use a cyclic carbonate or a linear carbonate as the non-aqueous solvent, and it is more preferable to use a cyclic carbonate and a linear carbonate in combination. Using a cyclic carbonate can promote the dissociation of the electrolyte salt and improve the ionic conductivity of the non-aqueous electrolyte. Using a linear carbonate can keep the viscosity of the non-aqueous electrolyte low. When using a cyclic carbonate and a linear carbonate in combination, the volume ratio of the cyclic carbonate to the linear carbonate (cyclic carbonate:linear carbonate) is preferably in the range of 5:95 to 50:50.

[0066] The electrolyte salt can be appropriately selected from known electrolyte salts. Examples of electrolyte salts include lithium salts, sodium salts, potassium salts, magnesium salts, and onium salts. Among these, lithium salts are preferred.

[0067] Examples of lithium salts include inorganic lithium salts such as LiPF6, LiPO2F2, LiBF4, LiClO4, and LiN(SO2F)2; lithium oxalate salts such as lithium bis(oxalate)borate (LiBOB), lithium difluorooxalate borate (LiFOB), and lithium bis(oxalate)difluorophosphate (LiFOP); and lithium salts having halogenated hydrocarbon groups such as LiSO3CF3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), LiC(SO2CF3)3, and LiC(SO2C2F5)3. Among these, inorganic lithium salts are preferred, and LiPF6 is more preferred.

[0068] The lower limit of the concentration of electrolyte salts in non-aqueous electrolytes is 0.7 mol / dm³. 3 Therefore, 0.8 mol / dm 3 It is preferable that the concentration of the electrolyte salt is above the lower limit. By setting the concentration of the electrolyte salt above the lower limit, the ionic conductivity of the non-aqueous electrolyte can be increased, thereby increasing the initial output in low-temperature environments and further increasing the output after the charge-discharge cycle. On the other hand, the upper limit of the concentration of the electrolyte salt is 1.0 mol / dm³. 3 Therefore, 0.9 mol / dm3 It is preferable that the above electrolyte salt concentration is below the above upper limit, thereby lowering the viscosity of the non-aqueous electrolyte, which increases the initial output in low-temperature environments and also increases the output after charge-discharge cycles. The above electrolyte salt concentration may be within the range of either the lower limit or higher and either the upper limit or lower. The above electrolyte salt concentration is the concentration at 20°C and 1 atmosphere.

[0069] Non-aqueous electrolytes may contain additives in addition to the non-aqueous solvent and electrolyte salt. Examples of additives include: aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran; partially halides of the above aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, and p-cyclohexylfluorobenzene; halogenated anisole compounds such as 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, and 3,5-difluoroanisole; vinylene carbonate, methylvinylene carbonate, ethylvinylene carbonate, succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic acid anhydride; and ethyl sulfite. Examples include propylene sulfite, dimethyl sulfite, methyl methanesulfonate, busulfan, methyl toluenesulfonate, dimethyl sulfate, ethylene sulfate, sulfolane, dimethyl sulfone, diethylsulfone, dimethyl sulfoxide, diethylsulfoxide, 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-propensultone, 1,3-propanesultone, 1,4-butanesultone, 1,4-butensultone, perfluorooctane, tristrimethylsilyl borate, tristrimethylsilyl phosphate, tetrakithrimethylsilyl titanate, etc. These additives may be used individually or in combination of two or more.

[0070] The additive content in the non-aqueous electrolyte is preferably 0.01% to 10% by mass relative to the total mass of the non-aqueous electrolyte, more preferably 0.1% to 7% by mass, even more preferably 0.2% to 5% by mass, and particularly preferably 0.3% to 3% by mass. By setting the additive content within the above range, it is possible to improve the capacity retention performance or cycle performance after high-temperature storage, and to further improve safety.

[0071] <Configuration of the energy storage device> The shape of the non-aqueous electrolyte energy storage element in this embodiment is not particularly limited, and examples include cylindrical batteries, prismatic batteries, flat batteries, coin-type batteries, button-type batteries, and the like.

[0072] Figure 1 shows a non-aqueous electrolyte energy storage element 1 as an example of a rectangular battery. Note that the figure is a transparent view of the inside of the container. An electrode body 2 having a positive electrode and a negative electrode wound around a separator is housed in a rectangular container 3. The positive electrode is electrically connected to the positive electrode terminal 4 via a positive electrode lead 41. The negative electrode is electrically connected to the negative electrode terminal 5 via a negative electrode lead 51.

[0073] The non-aqueous electrolyte energy storage element of this embodiment can increase output in low-temperature environments after charge-discharge cycles. For this reason, the non-aqueous electrolyte energy storage element of this embodiment is suitably used as a power source for automobiles such as electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs), and is particularly suitably used as a power source for HEVs. Furthermore, the non-aqueous electrolyte energy storage element of this embodiment has an output of 6 mA / cm². 2 Furthermore, 7 mA / cm 2 This device is suitably used in applications where charging and discharging occur at the above current densities. For example, the upper limit of the current density when charging and discharging the non-aqueous electrolyte energy storage element of this embodiment is 20 mA / cm². 2 It may also be 10mA / cm 2 That's fine.

[0074] Figure 2 shows an example of an energy storage device 30 which is formed by further assembling energy storage units 20, each of which is an assembly of two or more electrically connected non-aqueous electrolyte energy storage elements 1. The energy storage device 30 may include busbars (not shown) that electrically connect two or more non-aqueous electrolyte energy storage elements 1, busbars (not shown) that electrically connect two or more energy storage units 20, etc. The energy storage unit 20 or the energy storage device 30 may include a condition monitoring device (not shown) that monitors the state of one or more non-aqueous electrolyte energy storage elements 1.

[0075] <Method for manufacturing a non-aqueous electrolyte energy storage element> The method for manufacturing the non-aqueous electrolyte energy storage element of this embodiment can be appropriately selected from known methods. This manufacturing method, for example, involves preparing an electrode body and ensuring that the electrolyte salt concentration is 0.7 mol / dm³. 3 More than 1.0mol / dm 3 The method comprises preparing a non-aqueous electrolyte and housing the electrode body and the non-aqueous electrolyte in a container. Preparing the electrode body comprises preparing a positive electrode and a negative electrode and forming the electrode body by stacking or winding the positive electrode and the negative electrode via a separator whose creep strain after holding a load of 2 MPa at a temperature of 65°C for 60 seconds is 9% or more and 15% or less.

[0076] The method for housing the non-aqueous electrolyte in a container can be appropriately selected from known methods. For example, when using a non-aqueous electrolyte solution, the non-aqueous electrolyte solution can be injected through an inlet formed in the container, and then the inlet can be sealed.

[0077] <Other Embodiments> Furthermore, the non-aqueous electrolyte energy storage element of the present invention is not limited to the above 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, and a part of the configuration of one embodiment may be replaced with the configuration of another embodiment or known technology. In addition, a part of the configuration of one embodiment may be deleted. Also, known technology may be added to the configuration of one embodiment.

[0078] In the above embodiment, the case in which the non-aqueous electrolyte energy storage element is used as a rechargeable non-aqueous electrolyte secondary battery (e.g., a lithium-ion secondary battery) was described, but the type, shape, dimensions, capacity, etc. of the non-aqueous electrolyte energy storage element are arbitrary. The present invention can also be applied to various secondary batteries, electric double-layer capacitors, or capacitors such as lithium-ion capacitors. [Examples]

[0079] The present invention will be described in more detail below with reference to examples. The present invention is not limited to the following examples.

[0080] [Example 1] (Fabrication of the negative electrode) A negative electrode mixture paste was prepared containing graphite as the negative electrode active material, styrene-butadiene rubber (SBR) as a binder, and carboxymethylcellulose (CMC) as a thickener, with water as the dispersion medium. The ratio of the negative electrode active material to the binder and thickener was 98:1:1 by mass (on a solid content basis). The negative electrode mixture paste was coated onto both sides of a copper foil used as the negative electrode substrate and dried. Subsequently, it was pressed to form a negative electrode active material layer and obtain a negative electrode. The porosity of the negative electrode active material layer in the obtained negative electrode was 45%.

[0081] (Fabrication of the positive electrode) LiNi as a positive electrode active material 1 / 3 Co 1 / 3 Mn 1 / 3 A positive electrode mixture paste was prepared containing O2, polyvinylidene fluoride (PVDF) as a binder, and acetylene black (AB) as a conductive agent, with N-methylpyrrolidone (NMP) as the dispersion medium. The ratio of positive electrode active material to binder to conductive agent was 90:5:5 by mass (on a solid content basis). The positive electrode mixture paste was coated onto both sides of an aluminum foil used as the positive electrode substrate and dried. Subsequently, a positive electrode active material layer was formed by pressing. This resulted in a positive electrode in which positive electrode active material layers were laminated on both sides of the positive electrode substrate.

[0082] (Preparation of non-aqueous electrolytes) A non-aqueous solvent prepared by mixing ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 30:35:35 is mixed with lithium hexafluorophosphate (LiPF6) at a concentration of 0.9 mol / dm³ as the electrolyte salt. 3 A non-aqueous electrolyte was prepared by dissolving it at the specified concentration.

[0083] (Separator) As a separator, an inorganic layer containing aluminum oxide as inorganic particles and polyvinyl alcohol as a binder was formed on one side of a substrate layer made of wet-biaxially oriented porous polyolefin resin film. The porosity of the separator was 46 volume%, and the air permeability was 140 seconds / 100 cm. 3 The average thickness of the substrate layer was 10 μm, and the average thickness of the inorganic layer was 4 μm. The creep strain of the separator of Example 1, measured by the method described above, after holding a load of 2 MPa for 60 seconds at a temperature of 65°C, was 10%.

[0084] (Fabrication of non-aqueous electrolyte energy storage elements) Next, the positive electrode and the negative electrode were stacked and wound together via the separator to produce a wound electrode body. The inorganic layer was positioned on the surface facing the positive electrode. This electrode body was placed in a rectangular aluminum container, and the positive and negative electrode terminals were attached. After the non-aqueous electrolyte was injected into the container, it was sealed to obtain the non-aqueous electrolyte energy storage element of Example 1.

[0085] [Example 2, Comparative Example 1, and Comparative Example 2] Non-aqueous electrolyte energy storage elements for Example 2, Comparative Example 1, and Comparative Example 2 were obtained in the same manner as in Example 1, except that the concentration of lithium hexafluorophosphate, which is the electrolyte salt in the non-aqueous electrolyte, was changed to the concentration shown in Table 1.

[0086] [Comparative Example 4] A separator having a base layer made of a dry-uniaxially stretched porous polyolefin resin film is used, and the air permeability of the separator is set to 225 seconds / 100 cm. 3A non-aqueous electrolyte energy storage element of Comparative Example 4 was obtained in the same manner as in Example 1, except that the creep strain after holding a load of 2 MPa at a temperature of 65°C for 60 seconds in the separator, the average thickness of the substrate layer and the inorganic layer, and the porosity were as shown in Table 1.

[0087] [Comparative Examples 3, 5, 7, 8] Non-aqueous electrolyte energy storage elements of Comparative Examples 3, 5, 7, and 8 were obtained in the same manner as Comparative Example 4, except that the concentration of lithium hexafluorophosphate, which is the electrolyte salt in the non-aqueous electrolyte, and the porosity of the negative electrode active material layer were as shown in Table 1.

[0088] [Comparative Example 6] The air permeability of the separator is 100 seconds / 100 cm. 3 A non-aqueous electrolyte energy storage element of Comparative Example 6 was obtained in the same manner as in Example 2, except that the creep strain and porosity after holding a load of 2 MPa for 60 seconds at a temperature of 65°C in the separator were as shown in Table 1.

[0089] [evaluation] (Initial charge / discharge) Each obtained non-aqueous electrolyte energy storage element was subjected to constant current charging at a charging current of 0.2C to 4.1V under 25°C conditions, followed by constant voltage charging at 4.1V. The charging termination condition was set to 7 hours from the start of charging. After a 10-minute rest period, constant current discharge was performed at a discharge current of 1.0C to 3.0V, followed by another 10-minute rest period. These charging and discharging cycles constituted one cycle, and two initial charge-discharge cycles were performed.

[0090] (Initial power output performance test in a low-temperature environment) The initial power output performance [W] in a low-temperature environment was evaluated using the following procedure. Each of the above non-aqueous electrolyte energy storage elements was charged with a constant current of 1C at a charging current to 4.1V in a 25°C environment, and then charged with a constant voltage at 4.1V. The charging termination condition was when the charging current reached 0.05C. After a 10-minute rest period following charging, a constant current discharge was performed with a discharge current of 1C to 3.0V in a 25°C environment, and the "1C discharge capacity at 25°C" was measured. Next, a state of charge of half the amount of electricity measured for this "1C discharge capacity at 25°C" was defined as SOC 50%, and constant current charging was performed with a charging current of 0.1C from the fully discharged state until SOC 50% was reached. After that, the elements were stored in a -10°C environment for 2 hours, discharged with a discharge current of 1C for 30 seconds, a 10-minute rest period was observed, and then supplemental charging was performed with a charging current of 0.5C until SOC 50% was reached. Similarly, the discharge current was adjusted to 2C and 3C, and each was discharged for 30 seconds. After a 10-minute rest period, supplemental charging was performed with a charging current of 0.5C until the SOC reached 50%. The "-10°C initial output" was calculated from the current and the voltage 10 seconds after the start of discharge in each discharge. The ratio of the "-10°C initial output" of each non-aqueous electrolyte energy storage element to the "-10°C initial output" of Comparative Example 1 (set to 100) was then determined. The results of the initial output performance test in a low-temperature environment (-10°C) are shown in Table 1.

[0091] (Power output performance test in a low-temperature environment after charge-discharge cycles) For each non-aqueous electrolyte energy storage element after measuring the "initial output at -10°C," constant current (CC) charging was performed in a 25°C constant temperature bath with a charging current of 10C and a charging termination voltage of 4.0V. Subsequently, without a rest period, constant current (CC) discharge was performed with a discharge current of 10C and a discharge termination voltage of 3.5V. This charge-discharge cycle was performed 5000 times. After 5000 cycles, the output at -10°C was measured under the same conditions as the initial output performance test in a low-temperature environment, and this output was defined as the "-10°C charge-discharge cycle output." The ratio of the "-10°C charge-discharge cycle output" for each non-aqueous electrolyte energy storage element to the "-10°C initial output" of Comparative Example 1 (set as 100) was then calculated. The output performance test results in a low-temperature environment (-10°C) after the charge-discharge cycle are shown in Table 1.

[0092] [Table 1]

[0093] As shown in Table 1, the concentration of the electrolyte salt is 0.7 mol / dm³ 3 More than 1.0mol / dm 3 Examples 1 and 2, in which the creep strain after holding a 2 MPa load at 65°C for 60 seconds in the separator was between 9% and 15%, showed high output in the low-temperature environment after the charge-discharge cycle.

[0094] On the other hand, Comparative Examples 4 and 5, in which the creep strain after holding a 2 MPa load at 65°C for 60 seconds in the separator was less than 9%, and Comparative Example 6, in which the creep strain exceeded 15%, showed a significant decrease in output in the low-temperature environment after the charge-discharge cycle compared to the Examples. Furthermore, the electrolyte salt concentration was 0.7 mol / dm³. 3 Comparative Example 2, which is less than 1.0 mol / dm³, and the electrolyte salt concentration is 1.0 mol / dm³. 3 Comparative Example 1, which exceeds the above, and the creep strain in the separator is less than 9% and the electrolyte salt concentration is 1.0 mol / dm 3 Comparative Examples 3, 7, and 8, which exceeded the specified limit, showed lower output in the low-temperature environment after the charge-discharge cycle compared to the Examples. In Comparative Examples 3 to 5, the creep strain after holding a 2 MPa load at 65°C for 60 seconds in the separator was less than 9%. In this case, the output in the low-temperature environment after the charge-discharge cycle tended to decrease as the electrolyte salt concentration decreased. In contrast, Examples 1 and 2 and Comparative Examples 1 and 2 all showed creep strain of 9% to 15% after holding a 2 MPa load at 65°C for 60 seconds in the separator. In this case, the electrolyte salt concentration was 0.7 mol / dm³. 3 More than 1.0mol / dm 3 Examples 1 and 2, as described below, used an electrolyte salt concentration of 1.2 mol / dm³. 3 Comparative Example 1 and the concentration of the electrolyte salt were set to 0.6 mol / dm³. 3Compared to Comparative Example 2, the output in the low-temperature environment after the charge-discharge cycle was higher. Based on these results, the creep strain in the separator after holding a 2 MPa load for 60 seconds at a temperature of 65°C should be between 9% and 15%, and the electrolyte salt concentration should be 0.7 mol / dm³. 3 More than 1.0mol / dm 3 It was confirmed that the output in a low-temperature environment after a charge-discharge cycle becomes particularly high when the following conditions are met. In other words, a separator with a creep strain of 9% to 15% after holding a 2 MPa load for 60 seconds at a temperature of 65°C, and an electrolyte salt concentration of 0.7 mol / dm³ 3 More than 1.0mol / dm 3 By combining it with the following non-aqueous electrolyte, it is believed that a non-aqueous electrolyte energy storage element with high output in low-temperature environments after charge-discharge cycles was obtained as a synergistic effect of this combination.

[0095] The results above demonstrate that the non-aqueous electrolyte energy storage element can increase output in low-temperature environments after charge-discharge cycles. [Explanation of symbols]

[0096] 1. Non-aqueous electrolyte energy storage element 2 Electrode body 3 containers 4 Positive terminal 41 Positive lead 5 Negative terminal 51 Negative lead 20 Energy storage units 30 Energy storage devices

Claims

1. A negative electrode having a negative electrode active material layer, Separator and, Non-aqueous electrolyte containing an electrolyte salt and a non-aqueous solvent Equipped with, The concentration of the electrolyte salt in the above non-aqueous electrolyte is 0.7 mol / dm³ ３ 1.0mol / dm or more ３ The following: A non-aqueous electrolyte energy storage element in which the creep strain of the separator described above is 9% to 15% after holding a load of 2 MPa for 60 seconds at a temperature of 65°C.

2. The non-aqueous electrolyte energy storage element according to claim 1, wherein the porosity of the negative electrode active material layer is 40% or more.

3. A non-aqueous electrolyte energy storage element according to claim 1 or claim 2, for use as a power source for a hybrid vehicle.

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