Power storage element

Abstract

A power storage element according to one aspect of the present invention comprises an electrode body in which a positive electrode and a negative electrode are laminated with a separator interposed therebetween. The electrode body is in a state of being pressed in the lamination direction of the positive electrode and the negative electrode at a pressure of 1 MPa or more. The separator has a resin layer containing a resin having a melting point of 200°C or higher. The resin layer is positioned as the outermost layer on both sides of the separator in the lamination direction.

Description

Energy storage element

[0001] The present invention relates to an energy storage element.

[0002] Due to their high energy density, non-aqueous electrolyte secondary batteries, typified by lithium ion secondary batteries, are widely used in electronic devices such as personal computers and communication terminals, automobiles, etc. In addition, as electricity storage elements other than non-aqueous electrolyte secondary batteries, capacitors such as lithium ion capacitors and electric double layer capacitors, and electricity storage elements using electrolytes other than non-aqueous electrolytes, are also widely used.

[0003] A widely used energy storage device includes an electrode assembly in which a positive electrode having a positive electrode active material layer laminated on the surface of a positive electrode substrate and a negative electrode having a negative electrode active material layer laminated on the surface of a negative electrode substrate are stacked together via an insulating separator. In such energy storage devices, pressure may be applied to the electrode assembly in order to improve output performance, etc. (Patent Document 1).

[0004] JP 2016-189261 A

[0005] The separator may be made of a material primarily composed of a heat-resistant inorganic compound. Such a material is also useful for maintaining insulation in an electrode assembly subjected to pressure. However, in high-temperature environments, there is a concern that insulation may be reduced due to deformation of the separator, and from this perspective, further improvement in insulation may be desired.

[0006] The present invention has been made in light of the above circumstances, and has an object to provide an energy storage element that can suppress deterioration in the insulating properties of a separator in a high-temperature environment.

[0007] An energy storage element according to one aspect of the present invention comprises an electrode body in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween, the electrode body being pressed in the stacking direction of the positive electrode and the negative electrode at a pressure of 1 MPa or more, the separator having a resin layer containing a resin having a melting point of 200°C or more, and the resin layer being located as the outermost layer on both sides of the separator in the stacking direction.

[0008] An energy storage device according to one aspect of the present invention can suppress deterioration in the insulating properties of the separator in a high-temperature environment.

[0009] Fig. 1 is a see-through perspective view showing an energy storage element according to one embodiment of the present invention. Fig. 2 is a schematic diagram showing one embodiment of an energy storage device formed by assembling a plurality of energy storage elements according to one embodiment of the present invention. Fig. 3 is a diagram showing the relationship between pressure applied to an electrode assembly and the resistance of a separator. Fig. 4 is a diagram showing the relationship between the temperature of an energy storage element and the resistance of a separator.

[0010] First, an overview of the energy storage element disclosed in this specification will be described.

[0011] (1) An energy storage element according to one aspect of the present invention includes an electrode body in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween, the electrode body being pressed in a stacking direction of the positive electrode and the negative electrode with a pressure of 1 MPa or more, the separator having a resin layer containing a resin having a melting point of 200°C or more, and the resin layer being positioned as the outermost layer on both sides of the separator in the stacking direction.

[0012] The energy storage element described in (1) above can suppress a decrease in the insulating properties of the separator in a high-temperature environment. The reason for this effect is unclear, but the following reason is presumed. In the energy storage element, the electrode assembly is pressed in the stacking direction of the positive electrode and the negative electrode at a pressure of 1 MPa or more. In such an energy storage element, there may be a concern that the insulating properties of the separator will decrease due to deformation of the separator, particularly in a high-temperature environment. In this regard, in an energy storage element according to one aspect of the present invention, the separator has a resin layer containing a resin with a relatively high melting point, thereby suppressing melting of the resin layer in a high-temperature environment. Furthermore, since the resin layer is located on both outermost layers of the separator in the stacking direction, for example, if the separator has layers other than the resin layer, the resin layer is less likely to deform even if melting or the like occurs in the layers other than the resin layer in a high-temperature environment. Therefore, a decrease in the insulating properties of the separator can be suppressed in a high-temperature environment. The configuration in which the resin layers are "located as the outermost layers on both sides" of the separator also includes the case in which the separator has a single-layer structure consisting of one resin layer.

[0013] (2) In the energy storage element described in (1) above, the separator may further have a substrate layer, and the resin layer may be laminated on both sides of the substrate layer.

[0014] According to the energy storage element described in (2), the strength and ionic conductivity of the separator can be improved. In addition, since the resin layer is laminated on both sides of the base layer, deformation of the resin layer can be suppressed even if the base layer melts in a high-temperature environment.

[0015] (3) In the energy storage element according to (1) or (2), the resin layer may further contain inorganic particles.

[0016] According to the energy storage element described in (3) above, the insulating properties of the separator can be improved. In addition, the resin layer can easily form a porous structure, thereby improving the ionic conductivity of the separator.

[0017] (4) In the energy storage element according to any one of (1) to (3) above, the resin content in the resin layer may be 50% by mass or more.

[0018] According to the energy storage element described in (4) above, deformation of the resin layer in a high-temperature environment can be further suppressed.

[0019] Hereinafter, an energy storage element, an energy storage device, a method for manufacturing an energy storage element according to an embodiment of the present invention, and other embodiments will be described in detail. Note that the names of the components (elementary components) used in each embodiment may differ from the names of the components (elementary components) used in the background art.

[0020] [Electricity storage element] An electric storage element according to one embodiment of the present invention includes an electrode assembly having a positive electrode, a negative electrode, and a separator, a non-aqueous electrolyte, and a container for accommodating the electrode assembly and the non-aqueous electrolyte. The electrode assembly is typically a stacked type in which a plurality of positive electrodes and a plurality of negative electrodes are stacked with separators interposed therebetween, or a wound type in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween and wound. The non-aqueous electrolyte is present in a state contained in the positive electrode, the negative electrode, and the separator. As an example of an electric storage element, a non-aqueous electrolyte secondary battery (hereinafter also simply referred to as a "secondary battery") will be described.

[0021] <Positive Electrode> The positive electrode has a positive electrode substrate and a positive electrode active material layer laminated on the positive electrode substrate directly or via an intermediate layer.

[0022] The positive electrode substrate has electrical conductivity. Whether or not it has electrical conductivity is determined by whether or not the volume resistivity measured in accordance with JIS-H-0505 (1975) is 10 ７ The resistance is determined using Ω cm as a threshold value. Metals such as aluminum, titanium, tantalum, and stainless steel, or alloys thereof, are used as the material for the positive electrode substrate. Among these, aluminum or aluminum alloys are preferred from the viewpoints of potential resistance, high conductivity, and cost. Examples of the positive electrode substrate include foil, vapor-deposited film, mesh, and porous material, with foil being preferred from the viewpoint of cost. Therefore, aluminum foil or aluminum alloy foil is preferred as the positive electrode substrate. Examples of aluminum or aluminum alloys include A1085, A3003, and A1N30, as specified in JIS-H-4000 (2014) or JIS-H-4160 (2006).

[0023] 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 and also increase the energy density per volume of the energy storage element.

[0024] The intermediate layer is a layer disposed between the positive electrode substrate and the positive electrode active material layer. The intermediate layer contains a conductive agent such as carbon particles to reduce the contact resistance between the positive electrode substrate and the positive electrode active material layer. The configuration of the intermediate layer is not particularly limited, and may contain, for example, a binder and a conductive agent.

[0025] 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.

[0026] The positive electrode active material can be appropriately selected from known positive electrode active materials. As the positive electrode active material for a lithium ion secondary battery, a material capable of absorbing and releasing lithium ions is usually used. Examples of the positive electrode active material include α-NaFeO ２ Examples of suitable lithium transition metal composite oxides include those having a α-type crystal structure, those having a spinel type crystal structure, polyanion compounds, chalcogen compounds, and sulfur. ２ As the lithium transition metal composite oxide having a crystalline structure, for example, Li[Li ｘ Ni （１－ｘ） ]O ２ (0≦x<0.5), Li[Li ｘ Ni γ Co （１－ｘ－γ） ]O ２ (0≦x<0.5, 0<γ<1, 0<1-x-γ), Li[Li ｘ Co （１－ｘ） ]O ２ (0≦x<0.5), Li[Li ｘ Ni γ Mn （１－ｘ－γ） ]O ２ (0≦x<0.5, 0<γ<1, 0<1-x-γ), Li[Li ｘ Ni γ Mn β Co （１－ｘ－γ－β） ]O ２ (0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1, 0<1−x−γ−β), Li[Li ｘ Ni γ Co β Al （１－ｘ－γ－β） ]O ２(0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1, 0<1−x−γ−β), etc. Examples of lithium transition metal composite oxides having a spinel crystal structure include Li ｘ Mn ２ O ４ , Li ｘ Ni γ Mn （２－γ） O ４ Examples of polyanion compounds include LiFePO ４ , LiMnPO ４ , LiNiPO ４ , LiCoPO ４ , Li ３ V ２ (P.O. ４ ) ３ , Li ２ MnSiO ４ , Li ２ CoPO ４ Examples of the chalcogen compound 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 of them may be used in combination.

[0027] 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-mentioned lower limit or more, the positive electrode active material is easily manufactured or handled. By setting the average particle size of the positive electrode active material to the above-mentioned 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. "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).

[0028] 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.

[0029] 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 the above range, both high energy density and manufacturability of the positive electrode active material layer can be achieved.

[0030] 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 (CNT), 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 CNT may be used. Among these, carbon black is preferred from the viewpoints of electronic conductivity and coatability, and acetylene black is particularly preferred.

[0031] 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 in this range, the energy density of the energy storage element can be increased.

[0032] 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.

[0033] The content of the binder in the positive electrode active material layer is preferably 1% by mass to 10% by mass, more preferably 3% by mass to 9% by mass, by which the positive electrode active material can be stably maintained.

[0034] Examples of thickeners include polysaccharide polymers such as carboxymethyl cellulose (CMC) and methyl cellulose. When the thickener has a functional group that reacts with lithium or the like, the functional group may be deactivated in advance by methylation or the like. When a thickener is used, the content of the thickener in the positive electrode active material layer can be 0.1% by mass or more and 8% by mass or less, and typically 5% by mass or less is preferred, and 2% by mass or less is more preferred. The technology disclosed herein can be preferably implemented in an embodiment in which the positive electrode active material layer does not contain a thickener.

[0035] The filler is not particularly limited. Examples of fillers include polyolefins such as polypropylene and polyethylene, inorganic oxides such as silicon dioxide, alumina, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates, hydroxides such as magnesium hydroxide, calcium hydroxide, and aluminum hydroxide, carbonates such as calcium carbonate, sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium sulfate, nitrides such as aluminum nitride and silicon nitride, mineral-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, and artificial products thereof. When a filler is used, the content of the filler in the positive electrode active material layer can be 0.1% by mass or more and 8% by mass or less, and typically 5% by mass or less is preferred, and 2% by mass or less is more preferred. The technology disclosed herein can be preferably implemented in an embodiment in which the positive electrode active material layer does not contain a filler.

[0036] The positive electrode active material layer may contain typical non-metallic elements such as B, N, P, F, Cl, Br, and I; typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba; and transition metallic elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, and W as components other than the positive electrode active material, conductive agent, binder, thickener, and filler.

[0037] The negative electrode has a negative electrode substrate and a negative electrode active material layer disposed on the negative electrode substrate directly or via an intermediate layer. The configuration of the intermediate layer is not particularly limited and can be selected from the configurations exemplified for the positive electrode above, for example.

[0038] The negative electrode substrate is conductive. Metals such as copper, nickel, stainless steel, nickel-plated steel, and aluminum, alloys thereof, and carbonaceous materials are used as the material for the negative electrode substrate. Among these, copper or copper alloys are preferred. Examples of the negative electrode substrate include foils, vapor-deposited films, meshes, and porous materials, with foils being preferred from the viewpoint of cost. Therefore, copper foil or copper alloy foil is preferred as the negative electrode substrate. Examples of copper foil include rolled copper foil and electrolytic copper foil.

[0039] 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 and also increase the energy density per volume of the energy storage element.

[0040] 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.

[0041] 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.

[0042] The negative electrode active material can be appropriately selected from known negative electrode active materials. A material capable of absorbing and releasing lithium ions is usually used as the negative electrode active material for a lithium ion secondary battery. Examples of the negative electrode active material include metal Li; metals or semimetals such as Si and Sn; metal oxides or semimetal oxides such as Si oxide, Ti oxide, and Sn oxide; Li ４ Ti ５ O １２ , LiTiO ２、 TiNb ２ O ７ Examples of the material include titanium-containing oxides such as titanium dioxide, polyphosphate compounds, silicon carbide, and carbon materials such as graphite and non-graphitic carbon (easily graphitizable carbon or non-graphitizable carbon). Among these materials, 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.

[0043] "Graphite" refers to a graphite material that has an average lattice spacing (d００２ ) 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 availability of a material with stable physical properties.

[0044] "Non-graphitic carbon" refers to a carbon having an average lattice spacing (d ００２ ) is 0.34 nm or more and 0.42 nm or less. Examples of non-graphitizable carbon include non-graphitizable carbon and graphitizable carbon. Examples of non-graphitizable carbon include resin-derived materials, petroleum pitch or petroleum pitch-derived materials, petroleum coke or petroleum coke-derived materials, plant-derived materials, and alcohol-derived materials.

[0045] Here, the "discharged state" refers to a state in which the battery is discharged so that lithium ions capable of being absorbed and desorbed during charging and discharging are sufficiently released from the carbon material serving as the negative electrode active material. For example, in a single-electrode battery using a negative electrode containing a carbon material as the negative electrode active material as the working electrode and metallic Li as the counter electrode, the state refers to a state in which the open circuit voltage is 0.7 V or higher.

[0046] "Non-graphitizable carbon" refers to the above-mentioned d ００２ The term "carbon material" refers to a carbon material having a particle size of 0.36 nm or more and 0.42 nm or less.

[0047] "Graphitizable carbon" refers to the above-mentioned d ００２ The term "carbon material" refers to a carbon material having a particle size of 0.34 nm or more and less than 0.36 nm.

[0048] The negative electrode active material is usually in the form of particles (powder). The average particle size of the negative electrode active material can be, for example, 1 nm or more and 100 μm or less. When the negative electrode active material is a carbon material, a titanium-containing oxide, or a polyphosphate compound, the average particle size may be 1 μm or more and 100 μm or less. When the negative electrode active material is Si, Sn, Si oxide, Sn oxide, or the like, the average particle size may be 1 nm or more and 1 μm or less. By setting the average particle size of the negative electrode active material to be equal to or greater than the above lower limit, the production or handling of the negative electrode active material becomes easier. By setting the average particle size of the negative electrode active material to be equal to or less than the above upper limit, the electronic conductivity of the negative electrode active material layer is improved. To obtain powder with a predetermined particle size, a pulverizer, a classifier, or the like is used. The pulverization method and classification method can be selected from, for example, the methods exemplified for the positive electrode. When the negative electrode active material is a metal such as metallic Li, the negative electrode active material may be in the form of a foil.

[0049] 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, both high energy density and manufacturability of the negative electrode active material layer can be achieved. When the negative electrode active material is metallic Li, the content of the negative electrode active material in the negative electrode active material layer may be 99% by mass or more, or may be 100% by mass.

[0050] <Separator> A separator according to one embodiment of the present invention includes a substrate layer and a resin layer laminated on the substrate layer and containing a resin having a melting point of 200°C or higher (hereinafter also referred to as a "heat-resistant resin"). The resin layer is laminated on both sides of the substrate layer. By including a substrate layer and a resin layer in the separator, the substrate layer can ensure the strength and ionic conductivity of the separator while the resin layer can improve the insulating properties. For example, when the substrate layer melts in a high-temperature environment, the resin layer containing the heat-resistant resin tends to maintain its shape without melting. Therefore, the separator can suppress a decrease in insulating properties in a high-temperature environment. Furthermore, by laminating the resin layers on both sides of the substrate layer, the resin layer is less susceptible to the influence of the substrate layer when the substrate layer deforms, shrinks, melts, or the like in a high-temperature environment, compared to when the resin layer is laminated on one side of the substrate layer. In other words, deformation of the resin layer in accordance with the substrate layer and exposure of the substrate layer can be suppressed. Therefore, the separator can easily suppress a decrease in insulating properties in a high-temperature environment.

[0051] (Substrate Layer) Examples of the shape of the separator substrate layer include woven fabric, nonwoven fabric, and porous resin film. Among these shapes, porous resin film is preferred from the viewpoint of strength, and nonwoven fabric is preferred from the viewpoint of nonaqueous electrolyte retention. As the material for the separator substrate layer, polyolefins such as polyethylene and polypropylene are preferred from the viewpoint of shutdown effect during heat generation, and polyimides are preferred from the viewpoint of resistance to oxidative decomposition. A composite material of the above-mentioned resins may also be used for the separator substrate layer. Among these, it is more preferred to adopt a porous resin film as the shape of the substrate layer and a polyolefin as the material for the substrate layer. This makes it possible to easily suppress deterioration of the separator's insulating properties in high-temperature environments.

[0052] The lower limit of the porosity of the substrate layer is preferably 20% by volume, more preferably 25% by volume, and even more preferably 30% by volume. On the other hand, the upper limit of the porosity of the substrate layer is preferably 80% by volume, more preferably 70% by volume, and even more preferably 60% by volume. When the porosity of the substrate layer is equal to or higher than the lower limit, the ionic conductivity of the substrate layer is easily ensured. Furthermore, when the porosity of the substrate layer is equal to or lower than the upper limit, the strength of the substrate layer is easily improved. The porosity of the substrate layer is preferably 20% by volume or more and 80% by volume or less, more preferably 25% by volume or more and 70% by volume or less, and even more preferably 30% by volume or more and 60% by volume or less. Note that "porosity" refers to the mass m [g] and volume V [cm] of the object to be measured. ３ ] and true density ρ [g / cm ３ ] by the following formula 1: Porosity [vol %] = {1 - (m / V) / ρ} × 100 ... 1 The porosity of the base layer can be controlled by appropriately selecting the material of the base layer, appropriately selecting the method and conditions for producing the base layer, applying pressure to the base layer, etc.

[0053] The lower limit of the average thickness of the substrate layer is preferably 2 μm, more preferably 4 μm. The upper limit of the average thickness of the substrate layer is preferably 30 μm, more preferably 20 μm. When the average thickness is equal to or greater than the lower limit, the strength of the separator can be easily ensured. Furthermore, when the average thickness is equal to or less than the upper limit, a decrease in the energy density of the electrode body can be suppressed. The average thickness of the substrate layer is preferably 2 μm or more and 30 μm or less, more preferably 4 μm or more and 20 μm or less. Note that "average thickness" refers to the arithmetic mean value of the thickness measured at at least three points.

[0054] (Resin Layer) The resin layer is preferably porous. By making the resin layer porous, it is easy to ensure the ionic conductivity of the resin layer. The lower limit of the porosity of the resin layer is preferably 20 vol%, more preferably 25 vol%, and even more preferably 30 vol%. On the other hand, the upper limit of the porosity of the resin layer is preferably 80 vol%, more preferably 70 vol%, and even more preferably 60 vol%. When the porosity of the resin layer is equal to or higher than the lower limit, it is easy to ensure the ionic conductivity of the resin layer. Furthermore, when the porosity of the resin layer is equal to or lower than the upper limit, it is easy to improve the insulating properties of the resin layer. The porosity of the resin layer is preferably 20 vol% to 80 vol%, more preferably 25 vol% to 70 vol%, and even more preferably 30 vol% to 60 vol%. The porosity of the resin layer can be controlled by appropriately selecting the heat-resistant resin contained in the resin layer, appropriately selecting the lamination method and lamination conditions of the resin layer, applying pressure to the resin layer, etc.

[0055] As described above, the lower limit of the melting point of the heat-resistant resin contained in the resin layer is 200°C, preferably 250°C, more preferably 300°C, and even more preferably 350°C. When the melting point of the heat-resistant resin is equal to or higher than the lower limit, deterioration of insulating properties in high-temperature environments can be suppressed. On the other hand, from the viewpoint of suppressing an increase in the cost of introducing the heat-resistant resin, the upper limit of the melting point of the heat-resistant resin is preferably 500°C, more preferably 450°C, and even more preferably 400°C. The melting point of the heat-resistant resin is preferably 200°C or higher and 500°C or lower, more preferably 250°C or higher and 500°C or lower, even more preferably 300°C or higher and 450°C or lower, and even more preferably 350°C or higher and 400°C or lower.

[0056] Examples of the heat-resistant resin include aramid and polyimide. Aramid refers to an aromatic polyamide, more specifically, a polymer containing an amide bond linking an aromatic ring to the main chain. Polyimide refers to a polymer containing an imide bond in the repeating unit, and is typically an aromatic polyimide in which aromatic rings are linked by imide bonds. Among these, aramid is preferred. Furthermore, the proportion of amide bonds linked to aromatic rings among all amide bonds in aramid is preferably 60% or more, more preferably 70% or more, even more preferably 80% or more, and even more preferably 90% or more, on a molar basis. These heat-resistant resins may be used alone or in combination of two or more.

[0057] The lower limit of the content of the heat-resistant resin in the resin layer is preferably 50% by mass, more preferably 60% by mass, even more preferably 70% by mass, even more preferably 80% by mass, and even more preferably 90% by mass. When the content of the heat-resistant resin is equal to or greater than the lower limit, the shape of the resin layer is easily maintained in a high-temperature environment. On the other hand, the upper limit of the content of the heat-resistant resin can be, for example, 95% by mass. The content of the heat-resistant resin in the resin layer is preferably 50% by mass or more and 95% by mass or less, more preferably 60% by mass or more and 95% by mass or less, even more preferably 70% by mass or more and 95% by mass or less, even more preferably 80% by mass or more and 95% by mass or less, and even more preferably 90% by mass or more and 95% by mass or less. Note that, when two or more types of heat-resistant resins are used in combination, the content of the heat-resistant resin refers to the total content of the heat-resistant resins.

[0058] The resin layer preferably further contains inorganic particles in addition to the heat-resistant resin. When the resin layer contains inorganic particles, for example, the spaces between the inorganic particles can be filled with the heat-resistant resin as a binder. By further containing inorganic particles in the resin layer in this way, the resin layer is easily made porous. Furthermore, by further containing inorganic particles in the resin layer, the insulating properties of the resin layer can be improved.

[0059] The inorganic particle material contained in the resin layer preferably exhibits a mass loss of 5% or less when heated from room temperature to 500° C. in an air atmosphere at 1 atmosphere pressure, and more preferably exhibits 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 amount or less include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, barium titanate, 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 and barium fluoride; covalently bonded crystals such as silicon and diamond; mineral resource-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, as well as artificial products thereof. As the material for the inorganic particles, these substances may be used alone or in combination of two or more thereof. Among these inorganic particle materials, silicon oxide, aluminum oxide, or aluminosilicate is preferred from the viewpoint of the safety of the energy storage device.

[0060] The lower limit of the average particle size of the inorganic particles is preferably 0.1 μm, more preferably 0.3 μm. On the other hand, the upper limit of the average particle size of the inorganic particles is preferably 1.0 μm, more preferably 0.8 μm. When the average particle size of the inorganic particles is equal to or greater than the lower limit, the cost of introducing the inorganic particles can be reduced. Furthermore, when the average particle size of the inorganic particles is equal to or less than the upper limit, the shape of the resin layer can be easily maintained in a high-temperature environment. The average particle size of the inorganic particles is preferably 0.1 μm or more and 1.0 μm or less, more preferably 0.3 μm or more and 0.8 μm or less. In order to obtain the inorganic particles with a predetermined particle size, for example, a pulverizer or a classifier is used.

[0061] The lower limit of the content of the inorganic particles in the resin layer is preferably 1% by mass, more preferably 3% by mass, and even more preferably 5% by mass. On the other hand, the upper limit of the content of the inorganic particles is preferably 30% by mass, more preferably 20% by mass, and even more preferably 10% by mass. When the content of the inorganic particles is equal to or greater than the lower limit, the insulating properties of the resin layer can be easily improved. When the content of the inorganic particles is equal to or less than the upper limit, the shape of the resin layer can be easily maintained in a high-temperature environment. The content of the inorganic particles in the resin layer is preferably 1% by mass or more and 30% by mass or less, more preferably 3% by mass or more and 20% by mass or less, and even more preferably 5% by mass or more and 10% by mass or less. Note that, when two or more types of inorganic particles are used in combination, the content of the inorganic particles refers to the total content of the inorganic particles.

[0062] The resin layer may further contain optional components other than the heat-resistant resin and the inorganic particles, such as resins other than the heat-resistant resin.

[0063] The lower limit of the average thickness of one surface of the resin layer is preferably 1 μm, more preferably 2 μm. On the other hand, the upper limit of the average thickness of one surface of the resin layer is preferably 10 μm, more preferably 8 μm. When the average thickness is equal to or greater than the lower limit, it becomes easier to maintain the shape of the resin layer in a high-temperature environment. Furthermore, when the average thickness is equal to or less than the upper limit, it is possible to suppress a decrease in the energy density of the electrode body. The average thickness of one surface of the resin layer is preferably 1 μm or more and 10 μm or less, more preferably 2 μm or more and 8 μm or less.

[0064] <Non-aqueous Electrolyte> A non-aqueous electrolyte solution may be used as the non-aqueous electrolyte. The non-aqueous electrolyte solution includes a non-aqueous solvent, an electrolyte salt dissolved in the non-aqueous solvent, and an additive.

[0065] 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.

[0066] 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. Of these, EC is preferred.

[0067] 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.

[0068] 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 cyclic carbonate and a chain carbonate in combination. 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.

[0069] The electrolyte salt can be appropriately selected from known electrolyte salts, such as lithium salts, sodium salts, potassium salts, magnesium salts, and onium salts. Of these, lithium salts are preferred.

[0070] The lithium salt is LiPF ６ , LiBF ４ , LiClO ４ , LiN(SO ２ F) ２inorganic lithium salts such as lithium oxalate salts, lithium bis(oxalate)borate (LiBOB), lithium difluorooxalateborate (LiFOB), and lithium bis(oxalate)difluorophosphate (LiFOP); ３ CF ３ , LiN(SO ２ CF ３ ) ２ , LiN(SO ２ C ２ F ５ ) ２ , LiN(SO ２ CF ３ ) (SO ２ C ４ F ９ ), LiC(SO ２ CF ３ ) ３ , LiC(SO ２ C ２ F ５ ) ３ Among these, inorganic lithium salts are preferred, and LiPF ６ is more preferred.

[0071] The content of the electrolyte salt in the non-aqueous electrolyte solution is 0.1 mol / dm at 20°C and 1 atmosphere. ３ 2.5mol / dm or more ３ It is preferably 0.3 mol / dm or less. ３ 2.0mol / dm or more ３ It is more preferable that it is 0.5 mol / dm or less. ３ More than 1.7mol / dm ３ It is more preferable that it is 0.7 mol / dm or less. ３ 1.5mol / dm or more ３ By setting the content of the electrolyte salt within the above range, the ionic conductivity of the non-aqueous electrolyte can be increased.

[0072] The non-aqueous electrolyte may contain additives in addition to the non-aqueous solvent and the electrolyte salt. Examples of the additives include halogenated carbonates such as fluoroethylene carbonate (FEC) and difluoroethylene carbonate (DFEC); oxalates such as lithium bis(oxalate)borate (LiBOB), lithium difluorooxalateborate (LiFOB), and lithium bis(oxalate)difluorophosphate (LiFOP); imide salts such as lithium bis(fluorosulfonyl)imide (LiFSI); biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, and silyl. Aromatic compounds such as cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran; partial halides of the above aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, and p-cyclohexylfluorobenzene; halogenated anisole compounds such as 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, and 3,5-difluoroanisole; vinylene carbonate, methylvinylene carbonate, ethylvinylene carbonate, and the like. Carbonate, succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, methyl methanesulfonate, busulfan, methyl toluenesulfonate, dimethyl sulfate, ethylene sulfate, sulfolane, dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, diethyl sulfoxide, tetramethylene sulfoxide, diphenyl sulfide, 4,4'-bis(2,2-dioxo-1 ,3,2-dioxathiolane), 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane, thioanisole, diphenyl disulfide, dipyridinium disulfide, 1,3-propene sultone, 1,3-propane sultone, 1,4-butane sultone, 1,4-butene sultone, perfluorooctane, tristrimethylsilyl borate, tristrimethylsilyl phosphate, tetrakistrimethylsilyl titanate, lithium monofluorophosphate, lithium difluorophosphate, etc. These additives may be used alone or in combination of two or more.

[0073] The content of the additive contained in the non-aqueous electrolyte is preferably 0.01% by mass to 10% by mass, more preferably 0.1% by mass to 7% by mass, even more preferably 0.2% by mass to 5% by mass, and particularly preferably 0.3% by mass to 3% by mass, based on the total mass of the non-aqueous electrolyte. By setting the content of the additive within the above range, it is possible to improve the capacity retention performance or charge / discharge cycle performance after high-temperature storage, and further improve safety.

[0074] The non-aqueous electrolyte may be a solid electrolyte, or a non-aqueous electrolytic solution and a solid electrolyte may be used in combination.

[0075] The solid electrolyte can be selected from any material that has ionic conductivity of lithium, sodium, calcium, etc. and is solid at room temperature (e.g., 15° C. to 25° C.) Examples of the solid electrolyte include sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, and polymer solid electrolytes.

[0076] As the sulfide solid electrolyte, in the case of a lithium ion secondary battery, for example, Li ２ S-P ２ S ５ , LiI-Li ２ S-P ２ S ５ , Li １０ Ge-P ２ S １２ etc.

[0077] The shape of the energy storage element of this embodiment is not particularly limited, and examples thereof include cylindrical batteries, prismatic batteries, flat batteries, coin batteries, and button batteries. FIG. 1 shows an energy storage element 1 as an example of a prismatic battery. Note that this figure is a see-through view of the inside of the container. An electrode body 2 having a positive electrode and a negative electrode wound with a separator sandwiched 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.

[0078] The electrode assembly 2 is pressed in the stacking direction of the positive and negative electrodes. The lower limit of the pressure pressing the electrode assembly 2 in the stacking direction is 1.0 MPa, preferably 1.5 MPa, and more preferably 2.0 MPa. On the other hand, the upper limit of the pressure pressing the electrode assembly 2 in the stacking direction is preferably 5.0 MPa, and more preferably 4.0 MPa. When the pressure is equal to or greater than the lower limit, the effect of the present invention of suppressing deterioration of the insulating properties of the separator in a high-temperature environment is particularly remarkable. Furthermore, when the pressure is equal to or less than the upper limit, the pressure applied to the electrode assembly 2 is too great, and damage to the electrode assembly 2 can be suppressed. The pressure pressing the electrode assembly 2 in the stacking direction is preferably 1.0 MPa to 5.0 MPa, more preferably 1.5 MPa to 5.0 MPa, and even more preferably 2.0 MPa to 4.0 MPa.

[0079] One possible method for placing the electrode body 2 in a pressed state is to use a conventionally known restraining member (not shown) to restrain the energy storage element 1 in a state where it is pressed in the stacking direction of the positive and negative electrodes. The restraining member is not particularly limited as long as it is capable of pressing the energy storage element 1. Examples of a method for pressing the electrode body 2 using a restraining member or the like include pressing the energy storage element 1 with the restraining member so that the pressing force applied to the energy storage element 1 is constant (constant pressure restraint). The area and shape of the region (pressed region) on the outer surface of the energy storage element 1 that is pressed by the restraining member or the like (pressed region) are not particularly limited and can be set appropriately taking into account the performance required of the energy storage element 1, etc. The container 3 is preferably thin and flexible. Furthermore, it is preferable to place a known buffer member between the restraining member and the container 3, as this allows the pressure applied to the electrode body 2 to be constant from the beginning.

[0080] [Electricity Storage Device] The energy storage element of the present embodiment can be mounted as an energy storage unit (battery module) configured by assembling a plurality of energy storage elements in an automobile power source such as an electric vehicle (EV), a hybrid electric vehicle (HEV), or a plug-in hybrid electric vehicle (PHEV), a power source for electronic devices such as a personal computer or a communication terminal, or a power storage power source. In this case, the technology of the present invention may be applied to at least one energy storage element included in the energy storage unit. FIG. 2 shows an example of an energy storage device 30 in which energy storage units 20, each of which is an assembly of two or more electrically connected energy storage elements 1, are further assembled. The energy storage device 30 may include a bus bar (not shown) that electrically connects the two or more energy storage elements 1, a bus bar (not shown) that electrically connects the two or more energy storage units 20, or the like. The energy storage unit 20 or the energy storage device 30 may include a status monitoring device (not shown) that monitors the status of one or more energy storage elements.

[0081] [Method for Manufacturing Energy Storage Element] The method for manufacturing the energy storage element of this embodiment can be appropriately selected from known methods. The manufacturing method includes, for example, preparing an electrode assembly, preparing a non-aqueous electrolyte, and housing the electrode assembly and the non-aqueous electrolyte in a container. Preparing the electrode assembly includes preparing a positive electrode and a negative electrode, and forming the electrode assembly by stacking or winding the positive electrode and the negative electrode with a separator interposed therebetween.

[0082] 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.

[0083] [Other Embodiments] The energy storage device 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 can be added to the configuration of another embodiment, and part of the configuration of one embodiment can be replaced with the configuration of another embodiment or well-known technology. Furthermore, part of the configuration of one embodiment can be deleted. Also, well-known technology can be added to the configuration of one embodiment.

[0084] In the above embodiment, the case where the energy storage element is used as a chargeable and dischargeable non-aqueous electrolyte secondary battery (e.g., a lithium ion secondary battery) has been described, but the energy storage element may be of any type, shape, size, capacity, etc. The present invention can also be applied to various secondary batteries, electric double layer capacitors, lithium ion capacitors, and other capacitors.

[0085] In the above embodiment, the separator is described as having resin layers laminated on both sides of the substrate layer, but the separator may have a single-layer structure consisting of one resin layer. Also, the separator may have multiple layers between the outermost resin layers.

[0086] In the above embodiment, the resin layer is porous, but the resin layer may be fibrous. For example, the resin layer may contain a fibrous heat-resistant resin. In this case, the resin layer may not contain inorganic particles.

[0087] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0088] [Example 1] (Preparation of Positive Electrode) α-NaFeO ２ It has a Li-type crystal structure. １＋α Me １－α O ２ (Me is a transition metal) was used. Here, the molar ratio of Li to Me, Li / Me, was 1.33, and Me was composed of Ni and Mn, and contained in a molar ratio of Ni:Mn=1:2.

[0089] Next, a positive electrode mixture paste containing the positive electrode active material, acetylene black (AB) as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder in a mass ratio of 90:5:5 in terms of solid content was prepared using N-methylpyrrolidone (NMP) as a dispersion medium. The positive electrode mixture paste was directly applied to both sides of an aluminum foil positive electrode substrate, dried, and then pressed. This resulted in a positive electrode in which positive electrode active material layers were laminated on both sides of the positive electrode substrate.

[0090] (Preparation of Negative Electrode) A negative electrode mixture paste was prepared by mixing graphite (Gr) as a negative electrode active material, styrene-butadiene rubber (SBR) as a binder, carboxymethyl cellulose (CMC) as a thickener, and water as a dispersion medium. The mass ratio of Gr, SBR, and CMC was 96:2:2 in terms of solid content. The negative electrode mixture paste was applied to both sides of copper foil as a negative electrode substrate, dried, and then pressed. This resulted in a negative electrode in which negative electrode active material layers were laminated on both sides of the negative electrode substrate.

[0091] (Preparation of non-aqueous electrolyte) A non-aqueous solvent containing EC, DMC, and EMC mixed in a volume ratio of 30:35:35 was added to the non-aqueous solvent. ６ to 1.2 mol / dm ３ The above solution was used as a non-aqueous electrolyte.

[0092] (Separator Preparation) A polyolefin substrate and a mixture containing alumina particles and aramid resin were prepared. The alumina particle content in this mixture was less than 10% by mass, and the aramid resin content was greater than 90% by mass. The melting point of the aramid resin was 350°C. A solvent was then added to the mixture to form a paste, which was then applied to both sides of the substrate layer by roll transfer using a gravure coating method and dried to prepare a separator in which resin coating layers were laminated on both sides of the substrate layer. Table 1 shows the thicknesses of the substrate layer and coating layer (one side), the lamination method for the coating layer, the type of resin in the coating layer, and the resin content in the coating layer.

[0093] (Fabrication of Energy Storage Element) The positive electrode and the negative electrode were stacked with a separator interposed therebetween to fabricate an electrode body of Example 1. This electrode body was housed in a container made of a metal resin composite film, and the nonaqueous electrolyte was poured into the container, which was then sealed by thermal welding to obtain an energy storage element of Example 1.

[0094] [Comparative Example 1] An electrode body and a storage element of Comparative Example 1 were obtained in the same manner as in Example 1, except that a coating layer was laminated on one side of the base layer and the thickness of the coating layer was changed as shown in Table 1.

[0095] [Comparative Examples 2 to 4] Electrode bodies and energy storage elements of Comparative Examples 2 to 4 were obtained by the same procedure as in Example 1, except that the thicknesses of the substrate layer and coating layer, the lamination method of the coating layer, the type of resin in the coating layer, and the content of the resin in the coating layer were changed as shown in Table 1. The melting points of the acrylic resins in Comparative Examples 2 and 3 were around 90°C.

[0096]

[0097] (Initial Charge / Discharge) Each of the obtained energy storage elements was pressed from both sides in the stacking direction of the positive and negative electrodes using two stainless steel plates. The two stainless steel plates were fixed with bolts and nuts, and a torque wrench was used to adjust the pressure applied by the two stainless steel plates to 1.0 MPa. Initial charge / discharge was performed at 25°C as follows: constant current / constant voltage charging was performed with a charging current of 0.1 C and a charge cut-off voltage of 3.6 V. The charge was terminated until the charging current reached 0.02 C. A 10-minute rest period was then provided. Subsequently, constant current discharge was performed with a discharge current of 0.1 C and a discharge cut-off voltage of 2.0 V. Each energy storage element was capable of being charged and discharged.

[0098] (Measurement of Separator Electrical Resistance) Electrode bodies identical to those in Example 1 and Comparative Examples 1 to 4 were prepared. Each electrode body was pressed from both sides in the stacking direction of the positive and negative electrodes by two stainless steel plates. The two stainless steel plates were fixed with bolts and nuts, and the pressure with which the two stainless steel plates pressed the electrode body was adjusted using a torque wrench. Next, each electrode body pressed by the two stainless steel plates was placed in a thermostatic chamber, and the temperature inside the thermostatic chamber was adjusted to a predetermined temperature of 200°C or less. After maintaining this state for 30 minutes, the electrode body was removed from the thermostatic chamber and left for 4 hours or more to return the electrode body to room temperature. The electrode body was then connected to a resistance meter to measure the electrical resistance [Ω] of the separator.

[0099] FIG. 3 shows the electrical resistance [Ω] of the separators of Example 1, Comparative Example 1, and Comparative Example 2 when the temperature inside the thermostatic chamber was adjusted to 180° C. and the pressure pressing the electrode assembly was changed stepwise from 0.5 MPa to 10 MPa.

[0100] FIG. 4 shows the electrical resistance [Ω] of the separators of Comparative Examples 2 to 4 when the temperature in the thermostatic chamber was changed stepwise from 25° C. to 200° C. and the pressure pressing the electrode assembly was adjusted to 1.0 MPa.

[0101] 3 , in a high-temperature environment in which the electrode body is pressed at a pressure of 1.0 MPa or more, the separator of Example 1, which has coating layers containing an aramid resin on both sides of the substrate layer, has a higher electrical resistance than the separator of Comparative Example 1, which has a coating layer containing an aramid resin on one side of the substrate layer. That is, in Example 1, the coating layers are laminated on both sides of the substrate layer, thereby improving the insulation properties in a high-temperature environment.

[0102] 3, in Comparative Example 1, in which the aramid resin content in the coating layer is 90% by mass or more, the electrical resistance is less likely to decrease when the electrode body is pressed with a pressure of 1.0 MPa or more, compared to Comparative Example 2, in which the acrylic resin content in the coating layer is 5% by mass or less. In other words, it was shown that the electrical resistance is less likely to decrease in a high-temperature environment when the electrode body is pressed with a pressure of 1.0 MPa or more due to the high content of resin having a melting point of 200°C or more in the coating layer.

[0103] 4, Comparative Example 4, in which the aramid resin content in the coating layer is 90% by mass or more, is less likely to experience a decrease in electrical resistance than Comparative Examples 2 and 3, in which the acrylic resin content in the coating layer is 5% by mass or less, under conditions where the temperature exceeds 160° C. In other words, it was shown that the high content of resin with a melting point of 200° C. or higher in the coating layer makes it less likely for the electrical resistance to decrease in a high-temperature environment in which the electrode body is pressed with a pressure of 1.0 MPa or more.

[0104] The present invention can be applied to electric storage elements used as power sources for electronic devices such as personal computers and communication terminals, and automobiles.

[0105] REFERENCE SIGNS LIST 1 Energy storage element 2 Electrode body 3 Container 4 Positive electrode terminal 41 Positive electrode lead 5 Negative electrode terminal 51 Negative electrode lead 20 Energy storage unit 30 Energy storage device

Claims

1. An energy storage element comprising an electrode body in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween, the electrode body being pressed in the stacking direction of the positive electrode and the negative electrode with a pressure of 1 MPa or more, the separator having a resin layer containing a resin having a melting point of 200°C or more, and the resin layer being located as the outermost layer on both sides of the separator in the stacking direction.

2. The energy storage element according to claim 1, wherein the separator further comprises a substrate layer, and the resin layer is laminated on both sides of the substrate layer.

3. The energy storage element according to claim 1 or 2, wherein the resin layer further contains inorganic particles.

4. The energy storage element according to claim 1 or 2, wherein the resin content in the resin layer is 50% by mass or more.

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